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Arsenic trioxide (ATO) is highly effective for treating acute promyelocytic leukemia. It also holds the promise for treating solid tumors, including gastric carcinoma. However, the molecular mechanism of the effectiveness of ATO to solid tumor is still poorly understood. In this study, we chosed gastric carcinoma as an example and tried to reveal the antitumor mechanism through metabolomics. Gastric carcinoma cell line SGC7901 was treated with ATO for 6, 12, and 24 h. The global metabolite profiles were monitored by metabolomics analysis using gas chromatography (GC)/mass spectrometry (MS) and liquid chromatography/MS/MS. A total of 281 certified metabolites were reliably detected. Bioinformatics analysis showed that glycerophospholipid synthesis, one-carbon synthesis, and glutathione synthesis were affected dramatically. Other cellular functions/pathways that had been affected included inflammatory response, nicotinamide adenine dinucleotide (NAD(+)), and polyamine biosynthesis pathway. The metabolomics data from this study, in combination with previous transcriptomics and proteomics data, could serve as valuable resources for the understanding of the specific antitumor mechanism of ATO treatment.
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The S-phase kinase associated protein 2 (Skp2), a member of the F-box protein family, regulates cell cycle progression and is highly expressed in pancreatic cancer (PC). Recently, we reported that arsenic trioxide (ATO) inhibited cell growth and invasion via downregulation of Skp2 in PC cells. Emerging evidence has revealed that Skp2 plays a crucial role in drug resistance in several kinds of cancers. Here, we determined whether ATO enhanced the sensitivity of PC cell lines to gemcitabine (GEM). We found that the combined treatment of ATO and GEM demonstrated strong antitumor effects in Patu8988 and Panc-1 PC cells. In addition, ATO potentiated the effects of GEM via downregulation of the Skp2 pathway in PC cells. Together, these findings suggested that Skp2 may be a promising therapeutic target to overcome resistance to GEM in PC.
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Our ability to tailor the electronic properties of surfaces by nanomodification is paramount for various applications, including development of sensing, fuel cell, and solar technologies. Moreover, in order to improve the rational design of conducting surfaces, an improved understanding of structure/function relationships of nanomodifications and effect they have on the underlying electronic properties is required. Herein, we report on the tuning and optimization of the electrochemical properties of indium tin oxide (ITO) functionalized with single-walled carbon nanotubes (SWCNTs). This was achieved by controlling in situ grafting of aryl amine diazonium films on the nanoscale which were used to covalently tether SWCNTs. The structure/function relationship of these nanomodifications on the electronic properties of ITO was elucidated via time-of-flight secondary ion mass spectrometry and electrochemical and physical characterization techniques which has led to new mechanistic insights into the in situ grafting of diazonium. We discovered that the connecting bond is a nitro group which is covalently linked to a carbon on the aryl amine. The increased understanding of the surface chemistry gained through these studies enabled us to fabricate surfaces with optimized electron transfer kinetics. The knowledge gained from these studies allows for the rational design and tuning of the electronic properties of ITO-based conducting surfaces important for development of various electronic applications.
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eng_Latn
| 31,100 |
Methanol dehydrogenation to CO and H on Pd(111) is systematically investigated using self-consistent periodic density functional theory (DFT). All possible intermediates involved are calculated. Methanol and formaldehyde adsorb weakly on the Pd(111) surface because they are saturated molecules. CO and H prefer 3-fold sites with the adsorption energies of 41.6 and 64.4 kcal/mol. CH3O binds stably at 3-fold and bridge sites. Most of the other intermediates are inclined to adsorb to the surface with the sp3 configuration of the carbon atom and a hydroxyl-like configuration for O, i.e., top (η1-C) for CH2OH, bridge (η2-C) for CHOH, 3-fold (η3-C) for COH, bridge (η1-C−η1-O) for CH2O, and 3-fold (η2-C−η1-O) for CHO. All possible dehydrogenation pathways are calculated and four different routes via initial O−H and C−H bond scissions are found. The theoretical calculations indicate the initial C−H bond scission is more favorable for methanol decomposition, while O−H bond scission is preferable to C−H bond scissio...
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We present a model of the surface kinetics of the dehydrogenation reaction of methanol on the Pd(111), Pt(111), and Ni(111) metal surfaces. The mechanism consists of 10 reversible dehydrogenation reactions that lead to the final products of CO and H2. The rate coefficients for each step are calculated using ab initio transition state theory that employs a new approach to obtain the symmetry factors. The potential energies and frequencies of the reagents and transition states are computed using plane wave DFT with the PW91 exchange correlation functional. The mechanism is investigated for low coverages using a global sensitivity analysis that monitors the response of a target function of the kinetics to the value of the rate coefficients. On Pd(111) and Ni(111), the reaction COH → CO + H is found to be rate limiting, and overall rates are highly dependent upon the decomposition time of the COH intermediate. Reactions at branches in the reaction network are also particularly important in the kinetics. A sto...
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Starch that escapes digestion in the small intestine increases the elimination of chenodeoxycholate and its metabolites in the faeces of both mice and hamsters. In contrast, the elimination of cholate and its metabolites is not increased. In vitro, the affinity of starch for chenodeoxycholate is about 90-fold greater than for cholate. beta-Cyclodextrin, which approximates to one turn of the helical structures formed by the 1,4-linked glucose units of starch, shares these properties. It is proposed that these helical structures in starch act as binding sites for bile salts.
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eng_Latn
| 31,101 |
Although broad-spectrum antibacterial agents have been developed for antibacterial treatment, the balance of microbial flora may break and this usually results in increasing resistance. To this end, developing simple and effective strain-selective bactericidal strategies are demanding. Herein we designed an intelligent Gram-selective antimicrobial system based on MoS2 and a photoacid molecule. This system can be modulated by light for surface charge conversion from negative to positive and simultaneously activation of the enzymatic activity of MoS2 by changing pH. In consideration of the different cell wall composition and structures of bacterial strains, Gram-selective antibacterial has been accomplished simply by controlling the light irradiation time. Taken together, we provided a simple and efficient photoregulated method to realize strain-selective antibacterial.
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The marked augment of drug-resistance to traditional antibiotics underlines the crying need for novel replaceable antibacterials. Research advances have revealed the considerable sterilization potential of two-dimension graphene-based nanomaterials. Subsequently, two-dimensional nanomaterials beyond graphene (2D NBG) as novel antibacterials have also demonstrated their power for disinfection due to their unique physicochemical properties and good biocompatibility. Therefore, the exploration of antibacterial mechanisms of 2D NBG is vital to manipulate antibacterials for future applications. Herein, we summarize the recent research progress of 2D NBG-based antibacterial agents, starting with a detailed introduction of the relevant antibacterial mechanisms, including direct contact destruction, oxidative stress, photo-induced antibacterial, control drug/metallic ions releasing, and the multi-mode synergistic antibacterial. Then, the effect of the physicochemical properties of 2D NBG on their antibacterial activities is also discussed. Additionally, a summary of the different kinds of 2D NBG is given, such as transition-metal dichalcogenides/oxides, metal-based compounds, nitride-based nanomaterials, black phosphorus, transition metal carbides, and nitrides. Finally, we rationally analyze the current challenges and new perspectives for future study of more effective antibacterial agents. This review not only can help researchers grasp the current status of 2D NBG antibacterials, but also may catalyze breakthroughs in this fast-growing field.
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We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.
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eng_Latn
| 31,102 |
Two new ruthenium(II) polypyridyl complexes [Ru(dmb) 2 (Fpp)](ClO 4 ) 2 1 (Fpp = 2-(3′,3′-difluoro-3,4-methylenedioxyphenyl)imidazo[4,5- f ][1,10]phenanthroline, dmb = 4,4′-dimethyl-2,2′-bipyridine) and [Ru(bpy) 2 (Fpp)](ClO 4 ) 2 2 (bpy = 2,2′-bipyridine) have been synthesized and characterized by elemental analysis, FAB-MS, ES-MS, IR, 1 H NMR and 13 C NMR. The DNA-binding behaviors of these complexes were investigated by absorption spectroscopic titration, viscosity measurements, thermal denaturation and photocleavage. The mechanism studies of photocleavage reveal that singlet oxygen ( 1 O 2 ) and superoxide anion radical (O 2 − ) may play an important role in the photocleavage. The cytotoxicity of complexes 1 and 2 have been evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method.
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The mixed ligand surfactant-cobalt(III)-phendione complexes of the type cis-[Co(phendione) 2 (DA)Cl](ClO 4 ) 2 and cis-[Co(phendione) 2 (DA) 2 ](ClO 4 ) 3 (Phendione = 1,10-Phenanthroline-5,6-dione, DA = Dodecylamine) were synthesized and characterized. The interaction between surfactant-cobalt(III)-phendione complexes and calf thymus DNA in aqueous solution was investigated by spectroscopic methods, viscosity, and electrophoresis measurements. Results suggest that the complexes bind to DNA via intercalation binding. The cytotoxicity of the surfactant-cobalt(III)-phendione complexes has been evaluated by MTT assay. Surfactant-cobalt(III)-phendione complexes were tested for antibacterial and antifungal activities having good activities.
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The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.).
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eng_Latn
| 31,103 |
Dipyridamole is a well-known inhibitor of nucleoside transport by various cell membranes and is frequently used in in vitro studies that characterize nucleoside transport properties. Because interactions between the renal transport of organic cations and nucleosides have previously been suggested, we studied the effect of dipyridamole on the renal transport of the typical organic cations cimetidine and N1-methylnicotinamide by LLCPK1 monolayer cells grown on a permeable support. [14C]Mannitol was used to correct for extracellular flux. Basolateral to apical transcellular flux (transepithelial flux-extracellular flux) of [3H]cimetidine was significantly reduced by the monolayer cells (90%) in the presence of 50 microM dipyridamole. In addition, the effect of dipyridamole on cimetidine renal transport was dose dependent (IC50 = 7.7 microM). The dipyridamole inhibitory effect was nearly comparable with the effect of 1 mM quinine (a typical organic cation transport inhibitor), which led to 95% inhibition of cimetidine renal transport over time. The dipyridamole effect on N1-methylnicotinamide renal transport was less potent. The effect of 1 mM of typical probes of the nucleoside transporters (i.e., thymidine, adenosine, uridine) and the effect of 100 nM of another nucleoside transport inhibitor, dilazep, were also studied on cimetidine transport by LLCPK1 monolayer cells. These compounds did not exert any significant effect. These results suggest that dipyridamole, a widely used nucleoside transport inhibitor, is also an inhibitor of organic cation renal transport and they alert us to possible interactions between the renal transport of nucleosides and organic cations. This finding also has relevance to the interpretation of in vitro studies using this agent as a nucleoside membrane transport inhibitor.
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Inhibition of adenosine reuptake by nucleoside transport inhibitors, such as dipyridamole and dilazep, is proposed to increase extracellular levels of adenosine and thereby potentiate adenosine receptor-dependent pathways that promote cardiovascular health. Thus adenosine can act as a paracrine and/or autocrine hormone, which has been shown to regulate glucose uptake in some cell types. However, the role of adenosine in modulating glucose transport in cardiomyocytes is not clear. Therefore, we investigated whether exogenously applied adenosine or inhibition of adenosine transport by S-(4-nitrobenzyl)-6-thioinosine (NBTI), dipyridamole, or dilazep modulated basal and insulin-stimulated glucose uptake in the murine cardiomyocyte cell line HL-1. HL-1 cell lysates were subjected to SDS-PAGE and immunoblotting to determine which GLUT isoforms are present. Glucose uptake was measured in the presence of dipyridamole (3–300 μM), dilazep (1–100 μM), NBTI (10–500 nM), and adenosine (50–250 μM) or the nonmetabolizab...
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Nickel oxide loaded on zirconia (NiO/ZrO2) as an expedient catalyst is reported for the synthesis of 18 unsymmetrical 1,4-dihydropyridine derivatives. The Lewis acidic nature of the catalyst proved an excellent choice for the one-pot, four-component fusion reaction with excellent yields of 89–98% and a completion time of 20–45 min. Mechanistic studies show that enamine and imine functionalities are the two possible pathways for the formation of 1,4-dihydropyridines with high selectivity. Crystal structures of two novel compounds (5a, 5c) were reported. The catalyst demonstrated reusability up to six cycles. The reaction at room temperature and ethanol as a solvent make this protocol green and economical.
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eng_Latn
| 31,104 |
The metal complexation reactions of bis(hexafluoroacetylacetonato)copper(II) (Cu(hfac)2) with alkoxyamines (diethyl(2,2-dimethyl-1-(tert-butyl-(1-(pyridine-4-yl)ethoxy)amino)propyl)phosphonate and diethyl (2,2-dimethyl-1-(tert-butyl-(1-(pyridine-2-yl)ethoxy)amino)propyl)phosphonate) were studied. According to X-ray analysis, the molecular and crystal structures of 1:1 complexes depend on the configuration of the free alkoxyamines, that is dimeric (RSSR) and chain-polymeric (RR/SS) structures for para-pyridyl-substituted alkoxyamines, and cyclic unimeric (RS/SR) structure for ortho-pyridyl derivative. The complex (2:1 ratio Cu(hfac)2/alkoxyamine) for ortho-pyridyl-substituted alkoxyamine is not resolved. Upon warming, ortho complexes decomposed into free alkoxyamines and only a weak activation was observed. Upon warming, para complexes decomposed into their corresponding unimers, and then, a 21-fold increase in the rate constant of the C–ON bond homolysis was observed compared to the corresponding free alkoxyamines. Tuning of the homolysis rate constant of the C–ON bond via addition of pyridine is also reported.
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Because alkoxyamines are employed in a number of important applications, such as nitroxide-mediated polymerization, radical chemistry, redox chemistry, and catalysis, research into their reactivity is especially important. Typically, the rate of alkoxyamine homolysis is strongly dependent on temperature. Nonetheless, thermal regulation of such reactions is not always optimal. This review describes various ways to reversibly change the rate of C–ON bond homolysis of alkoxyamines at constant temperature. The major methods influencing C–ON bond homolysis without alteration of temperature are protonation of functional groups in an alkoxyamine, formation of metal–alkoxyamine complexes, and chemical transformation of alkoxyamines. Depending on the structure of an alkoxyamine, these approaches can have a significant effect on the homolysis rate constant, by a factor of up to 30, and can shorten the half-lifetime from days to seconds. These methods open new prospects for the application of alkoxyamines in biology and increase the safety of (and control over) the nitroxide-mediated polymerization method.
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The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.).
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eng_Latn
| 31,105 |
In this work we apply state-of-the-art electronic-structure-based computational methods based on hybrid-exchange density functional theory to study the mechanism of the aerobic oxidation of hydrocarbons catalysed by Mn-doped nanoporous aluminophosphates (Mn-AlPOs). We compare our results with available experimental data. We show that the catalytic efficiency of Mn-AlPOs in oxidation reactions is intrinsically linked to 1) the Mn redox activity, in particular between 2+ and 3+ oxidation states, and 2) the coordinative insaturation of tetrahedral Mn embedded in AlPO frameworks, which facilitates the reaction by stabilising oxo-type radicals through the formation of Mn complexes. Our mechanism demonstrates the crucial role of both Mn(III) and Mn(II) in the reaction mechanism: Mn(III) sites undergo an initial reaction cycle that leads to the production of the alkyl hydroperoxide intermediate, which can only be transformed into the oxidative products (alcohol, aldehyde and acid) by Mn(II). A preactivation step is required to yield the reduced Mn(II) sites able to decompose the hydroperoxide intermediates; this step takes place through a transformation of the hydrocarbon into the corresponding peroxo-derivative, stabilised by forming a complex with Mn(III) and yielding at the same time reduced Mn(II) sites. Both species enter a subsequent propagation cycle in which Mn(II) catalyses the dissociation of the hydroperoxide that proceeds until the formation of the oxidative products by two parallel pathways, through alkoxy- or hydroxy-radical-like intermediates, whilst the Mn(III)-peroxo complex enables further production of the hydroperoxide intermediate.
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We discuss the mechanism and energetics for the aerobic oxidation of hydrocarbons catalysed by Mn-doped nanoporous aluminophosphates with the AFI structure (Mn-APO-5), obtained computationally using electronic structure techniques. Calculations have been performed employing hybrid exchange density functional theory methods under periodic boundary conditions. The active sites of the catalyst are tetrahedral Mn ions isomorphously replacing Al in the microporous crystalline framework of the AlPO host. Since all Al sites in AFI are symmetry equivalent, all Mn dopants are in an identical chemical and structural environment, and hence satisfy the definition of a single-site heterogeneous catalyst. We focus in particular on the atomic-level origin of selectivity in this catalytic reaction.
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The concentrations of potential organic (e.g., proteins, polysaccharides, uronic acids, hydroquinones, hydroxamate- and catechol-type siderophores) and inorganic (Fe, Mn, Si, and CaCO 3 ) carrier phases for radionuclides ( 234 Th, 233 Pa, 210 Po, 210 Pb and 7 Be) and their particle–water partition coefficients (K d ) were determined for particles collected by sediment traps deployed at the Oceanic Flux Program (OFP) site off Bermuda (500, 1500 and 3200 m). The purpose was to better understand the mechanisms that control the chemical composition of sinking particles as well as the scavenging and fractionation behavior of those five radionuclides. Different components contributed differently to the scavenging of different radionuclides at the three depths. Chemical considerations (e.g., ionic potential, ionization energy, multifunctional group structures), as well as factor analysis (FA) and correlations of logK d values with chemical parameters, indicate that hydroxamate siderophores are major classes of biopolymers that have a role in binding Po and Pa. MnO 2 and FeO 2 , whose presence is closely related to that of hydroxamate siderophores (HS), are also involved in binding of Pa and Po. The carbonate and biogenic silica phases are identified to be important in predicting removal and fractionation of Th and Be in the ocean.
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eng_Latn
| 31,106 |
Stable dark red (M = Al) or dark green (M = Ga) neutral radicals {[PhB(μ-NtBu)2]2M}˙ are obtained by the oxidation of their corresponding anions with iodine, and EPR spectra supported by DFT calculations show that the spin density is equally delocalized over all four nitrogen atoms in these spiroconjugated systems.
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In this work, the nature of the chemical interactions between the metalloid atom (M = Si, Ge, As, Sb, Te, Po) and the nitrogen atoms in the bora-amidinate (bam) complexes (ClnM[PhB(NtBu)2]) are investigated, mainly via density-based indices. The descriptors used are derived using the quantum theory of atoms in molecules and natural orbitals for chemical valence approaches. It is shown that the strongest interaction is achieved with silicon. Indeed, it is generally the lightest metalloid in a particular group of the periodic table (i.e., Si, As, and Te for groups 14–16, respectively) that exhibits the strongest bond in the bam complex. This suggests that the atomic radius of the metalloid is a useful parameter for predicting the bonding strength. Extended transition state (ETS) decomposition results indicate that the interactions are more electrostatic than due to orbital interactions.
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The anticancer activity of acridone derivatives has attracted increasing interest, therefore, a variety of substituted analogs belonging to this family have been developed and evaluated for their anti-cancer properties. A series of N-alkyl-acridones 1–6 and N,N′-dialkyl-9,9′-biacridylidenes 7–12 with variable alkyl chains were examined for their topoisomerase I activity at neutral and acidic conditions as well as for their binding capacity to calf thymus and possible radical trapping antioxidant activity. It was found that at a neutral pH, topoisomerase I activity of both classes of compounds was similar, while under acidic conditions, enhanced intercalation was observed. N-alkyl-acridone derivatives 1–6 exhibited stronger, dose-dependent, cytotoxic activity against MCF-7 human breast epithelial cancer cells than N,N′-dialkyl-9,9′-biacridylidenes 7–12, revealing that conjugation of the heteroaromatic system plays a significant role on the effective distribution of the compound in the intracellular environment. Cellular investigation of long alkyl derivatives against cell migration exhibited 40–50% wound healing effects and cytoplasm diffusion, while compounds with shorter alkyl chains were accumulated both in the nucleus and cytoplasm. All N,N′-dialkyl-9,9′-biacridylidenes showed unexpected high scavenging activity towards DPPH or ABTS radicals which may be explained by higher stabilization of radical cations by the extended conjugation of heteroaromatic ring system.
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eng_Latn
| 31,107 |
Aerobic alcohol oxidation catalyzed by the newly synthesized dimeric [(neocuproine)Pd(μ-OAc)]2(OTf)2 (1; neocuproine = 2,9-dimethyl-1,10-phenanthroline) proceeds under exceptionally mild conditions (room temperature, ambient air) compared to those required for the previously reported monomeric diacetate analogue (neocuproine)Pd(OAc)2 (2) and the monomeric ditriflate analogue (neocuproine)Pd(MeCN)2(OTf)2 (3). An unprecedented initial turnover frequency (TOFi) for such mild conditions (78 (Pd atom)-1 h-1) is observed with catalyst 1; however, competitive oxidation of a methyl group on the ligand to a carboxylate group results in catalyst inactivation. During the study of 1, we isolated for the first time [(neocuproine)Pd(μ-OH)]2(OTf)2 (4), a possible intermediate in the catalytic cycle, and we report its crystal structure and catalytic activity herein.
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The behavior of a Pd(OAc)2/P4VP catalyst submitted to different pretreatments (prereduced, preoxidized, and untreated) during the aerobic oxidation of 2-propanol to acetone in the gas phase has been investigated. Synchronous, time-resolved, SAXS/XAS/MS techniques coupled with operando DRIFT spectroscopy (which gave information on the destiny of the acetate ligands) and ex situ HR-TEM (to detect the formation of Pd nanoparticles and to obtain their size distribution) were employed to accomplish a dynamical picture of the changes occurring to the Pd phase under transient reaction conditions. In addition, the catalytic performances were qualitatively explored by means of a CATLAB microreactor, with the final aim to establish structure–activity relationships. Our approach clearly demonstrates that highly isolated Pd2+ cationic species, either atomically dispersed or in the form of ultrasmall Pd2+–oxo clusters, are efficient and very stable active sites for the gas-phase aerobic oxidation of 2-propanol to acet...
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Background ::: Serum calcium (Ca) and inorganic phosphate (Pi) concentrations and calcium-phosphate product (CPP) levels are positively associated with worse outcomes in patients with chronic kidney disease, but there are few data for Pi or Ca and none for CPP in patients with chronic heart failure (CHF).
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eng_Latn
| 31,108 |
Aryl/alkyl-sulfonylamido, arylsulfenylamido, arylcarboxamido and ureido/thioureido derivatives of 2-aminophenoxathiin were prepared by reaction of the title compound with sulfonyl/sulfenyl halides, sulfonic acid anhydrides, acyl chlorides, tosyl isocyanate, aryl/allyl isocyanates or isothiocyanates. Some of these derivatives, containing free amino groups, have been further derivatized by reaction with 2,4,6-trisubstituted-pyrylium salts, aryl/allyl isocyanate/isothiocyanates or tosyl isocyanate. Several of the newly synthesized compounds act as effective antifungal agents against Aspergillus and Candida spp. , some of them showing activities comparable to ketoconazole or itraconazole (against the aspergilli) but being much less effective against Candida . The mechanism of action of these compounds involves inhibition of ergosterol biosynthesis, and probably interaction with lanosterol-14-α-demethylase (CYP51A1), since reduced amounts of ergosterol were evidenced by means of HPLC in cultures of the sensitive strain A. niger treated with some of these inhibitors. Thus, the two classes of antifungal compounds, i.e. the azoles and the new derivatives reported here, might possess a similar mechanism of action at molecular level.
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The reactions of phenoxathiin radical cations with diverse organic compounds in ambient conditions were realized by using fused-droplet electrospray ionization mass spectrometry. In the investigation, the phenoxathiin radical cation was prepared by electrospray ionization. The reactants included aliphatic alcohols, phenol and phenyl halides and the reaction studies showed the unique reactivity the of phenoxathiin radical cation towards neutral organic compounds in ambient conditions, which has not been revealed in previous studies.
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Our ability to tailor the electronic properties of surfaces by nanomodification is paramount for various applications, including development of sensing, fuel cell, and solar technologies. Moreover, in order to improve the rational design of conducting surfaces, an improved understanding of structure/function relationships of nanomodifications and effect they have on the underlying electronic properties is required. Herein, we report on the tuning and optimization of the electrochemical properties of indium tin oxide (ITO) functionalized with single-walled carbon nanotubes (SWCNTs). This was achieved by controlling in situ grafting of aryl amine diazonium films on the nanoscale which were used to covalently tether SWCNTs. The structure/function relationship of these nanomodifications on the electronic properties of ITO was elucidated via time-of-flight secondary ion mass spectrometry and electrochemical and physical characterization techniques which has led to new mechanistic insights into the in situ grafting of diazonium. We discovered that the connecting bond is a nitro group which is covalently linked to a carbon on the aryl amine. The increased understanding of the surface chemistry gained through these studies enabled us to fabricate surfaces with optimized electron transfer kinetics. The knowledge gained from these studies allows for the rational design and tuning of the electronic properties of ITO-based conducting surfaces important for development of various electronic applications.
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eng_Latn
| 31,109 |
Tandem mass spectrometry was evaluated as a reliable sequencing methodology to read codes encrypted in monodisperse sequence-coded oligo(triazole amide)s. The studied oligomers were composed of monomers containing a triazole ring, a short ethylene oxide segment, and an amide group as well as a short alkyl chain (propyl or isobutyl) which defined the 0/1 molecular binary code. Using electrospray ionization, oligo(triazole amide)s were best ionized as protonated molecules and were observed to adopt a single charge state, suggesting that adducted protons were located on every other monomer unit. Upon collisional activation, cleavages of the amide bond and of one ether bond were observed to proceed in each monomer, yielding two sets of complementary product ions. Distribution of protons over the precursor structure was found to remain unchanged upon activation, allowing charge state to be anticipated for product ions in the four series and hence facilitating their assignment for a straightforward characterization of any encoded oligo(triazole amide)s.
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In order to improve their MS/MS sequencing, structure of sequence-controlled synthetic polymers can be optimized based on considerations regarding their fragmentation behavior in collision-induced dissociation conditions, as demonstrated here for two digitally encoded polymer families. In poly(triazole amide)s, the main dissociation route proceeded via cleavage of the amide bond in each monomer, hence allowing the chains to be safely sequenced. However, a competitive cleavage of an ether bond in a tri(ethylene glycol) spacer placed between each coding moiety complicated MS/MS spectra while not bringing new structural information. Changing the tri(ethylene glycol) spacer to an alkyl group of the same size allowed this unwanted fragmentation pathway to be avoided, hence greatly simplifying the MS/MS reading step for such undecyl-based poly(triazole amide)s. In poly(alkoxyamine phosphodiester)s, a single dissociation pathway was achieved with repeating units containing an alkoxyamine linkage, which, by very low dissociation energy, made any other chemical bonds MS/MS-silent. Structure of these polymers was further tailored to enhance the stability of those precursor ions with a negatively charged phosphate group per monomer in order to improve their MS/MS readability. Increasing the size of both the alkyl coding moiety and the nitroxide spacer allowed sufficient distance between phosphate groups for all of them to be deprotonated simultaneously. Because the charge state of product ions increased with their polymerization degree, MS/MS spectra typically exhibited groups of fragments at one or the other side of the precursor ion depending on the original α or ω end-group they contain, allowing sequence reconstruction in a straightforward manner. Graphical ᅟ ᅟ
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MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity.
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eng_Latn
| 31,110 |
Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-reduction method is developed and evaluated for the decomposition of perfluorooctanoic acid (PFOA) in aqueous phase with potassium iodide (KI) as a mediator. The experiment was conducted under 254 nm irradiation at room temperature and pH 9 under anaerobic conditions. Ultraviolet photolysis of iodide solutions led to the generation of hydrated electrons (e(aq)(-), E(aq/e) degrees = -2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic analysis indicated that the PFOA decomposition fit the first-order model with a rate constant of 7.3 x 10(-3) min(-1). Besides fluoride ions, additional intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amounts of CF(3)H and C(2)F(6) were also detected as reaction products by using GC/MS. With observation of the degradation products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF(2) by UV irradiation and hydrolysis. This method was applied to the decomposition of PFOA in wastewater issued from a fluorochemical plant and proved to be effective.
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Perfluorinated chemicals (PFCs) are anthropogenic contaminants which have prompted much concern regarding their environment persistence and bioaccumulation. The main sources of PFCs are from wastewater of fluorine chemical. Decomposition and defluorination of PFCs in wastewater by photo-induced hydrated electrons was well and firstly investigated in this paper. In this work the proposed method was tested to deal with PFCs containing wastewaters from a Teflon-manufacturing plant in Jiangsu Province, China. 95.5% of perfluorooctanoic acid (PFOA) was decomposed after 12 hours treatment and defluorination rate of PFCs could reach about 60%. PFCs were transformed into harmless fluoride, acetic acid and formic acid. It was suggested this system can efficiently decompose PFCs from fluorine chemical plant. In brief, this study demonstrates that the photo-reduction is a high efficient, energy-saving method which produced less-toxic products for PFCs removal, compared with activated carbon absorption and combustion.
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Chemically reinforced essential fatty acids (FAs) promise to fight numerous age-related diseases including Alzheimer’s, Friedreich’s ataxia and other neurological conditions. The reinforcement is achieved by substituting the atoms of hydrogen at the bis-allylic methylene of these essential FAs with the isotope deuterium. This substitution leads to a significantly slower oxidation due to the kinetic isotope effect, inhibiting membrane damage. The approach has the advantage of preventing the harmful accumulation of reactive oxygen species (ROS) by inhibiting the propagation of lipid peroxidation while antioxidants potentially neutralize beneficial oxidative species. Here, we developed a model system to mimic the human dietary requirement of omega-3 in Caenorhabditis elegans to study the role of deuterated polyunsaturated fatty acids (D-PUFAs). Deuterated trilinolenin [D-TG(54:9)] was sufficient to prevent the accumulation of lipid peroxides and to reduce the accumulation or ROS. Moreover, D-TG(54:9) significantly extended the lifespan of worms under normal and oxidative stress conditions. These findings demonstrate that D-PUFAs can be used as a food supplement to decelerate the aging process, resulting in extended lifespan.
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eng_Latn
| 31,111 |
In this communication, we report the first synthesis of Pt NPs stabilized with NHC ligands and their investigation as catalysts in the chemoselective hydrogenation of nitroarenes. The results in catalysis show that by a proper choice of the NHC stabilizer and the adjustment of the NHC/metal ratio, these NHC-capped Pt NPs exhibit high levels of activity and selectivity in the hydrogenation reactions. In particular, Pt NPs stabilized with 2 equiv. of IPr carbene (PtIPr0.2) catalyze the chemoselective reduction of a series of functionalized nitroarenes under mild conditions (1 bar H2, 30 °C). This catalyst tolerates the presence of a range of functional groups including hydroxyl, benzyloxy, carbonyl and olefinic moeities as well as halogens.
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Chemoselectivity is a cornerstone of catalysis, permitting the targeted modification of specific functional groups within complex starting materials. Here we elucidate key structural and electronic factors controlling the liquid phase hydrogenation of cinnamaldehyde and related benzylic aldehydes over Pt nanoparticles. Mechanistic insight from kinetic mapping reveals cinnamaldehyde hydrogenation is structure-insensitive over metallic platinum, proceeding with a common Turnover Frequency independent of precursor, particle size or support architecture. In contrast, selectivity to the desired cinnamyl alcohol product is highly structure sensitive, with large nanoparticles and high hydrogen pressures favoring C=O over C=C hydrogenation, attributed to molecular surface crowding and suppression of sterically-demanding adsorption modes. In situ vibrational spectroscopies highlight the role of support polarity in enhancing C=O hydrogenation (through cinnamaldehyde reorientation), a general phenomenon extending to alkyl-substituted benzaldehydes. Tuning nanoparticle size and support polarity affords a flexible means to control the chemoselective hydrogenation of aromatic aldehydes.
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Channel Hot Carrier (CHC) degradation on uniaxially strained pMOS and nMOS samples with different S/D materials has been analyzed. The results show that the CHC damage is larger in the strained samples in comparison with the unstrained devices, and increases with the temperature.
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eng_Latn
| 31,112 |
Zinc phthalocyanine (ZnPc) derivatives with asymmetric (Zn-tri-PcNc-2) or symmetric (Zn-tetrad-Nc) structure, which possess wide spectral response in the visible/near-IR light region, are synthesized and utilized as a sensitizer of graphitic carbon nitride (g-C3N4) with 0.5 wt% Pt-loading for photocatalytic H2 production. The experimental results indicate that Zn-tri-PcNc-2 exhibits much better photosensitization on g-C3N4 than Zn-tetrad-Nc under visible/near-IR light although Zn-tetrad-Nc possesses wider and stronger optical absorption property than Zn-tri-PcNc-2. Zn-tri-PcNc-2-Pt/g-C3N4 exhibits an average H2 production rate of 132 μmol h(-1), which is much better than that (26.1 μmol h(-1)) of Zn-tetrad-Nc-Pt/g-C3N4 under visible-light (λ ≥ 500 nm) irradiation. Moreover, Zn-tri-PcNc-2-Pt/g-C3N4 also shows much higher apparent quantum yield (AQY) than Zn-tetrad-Nc-Pt/g-C3N4 under red/near-IR light irradiation. Especially, Zn-tri-PcNc-2-Pt/g-C3N4 exhibits impressively higher AQY (1.07%) than that (0.22%) of the Zn-tetrad-Nc-Pt/g-C3N4 under 700 nm monochromatic light irradiation. The much better photoactivity of Zn-tri-PcNc-2-Pt/g-C3N4 than Zn-tetrad-Nc-Pt/g-C3N4 is caused by the asymmetric structure of Zn-tri-PcNc-2, which can result in the electronic orbital directionality of its excited state, much faster photogenerated electron transfer to g-C3N4, and higher red/near-IR light utilization efficiency as compared to Zn-tetrad-Nc-Pt/g-C3N4. The present results provide an important insight into the effects of molecular structure and optical absorption property of phthalocyanine derivatives on the photoactivity of the dye-sensitized semiconductor, and also guide us to further improve the solar energy conversion efficiency by optimizing the molecular structure and effectively utilizing the visible/near-IR light of sunlight.
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Graphitic carbon nitride (g-C3N4) is a photocatalyst with wide application in removal of organic pollutants. In this study, we designed a porous g-C3N4 (p-g-C3N4)/8-quinolinolato iron(III) (Q3Fe)/H2O2 system to enhance the organic pollutant removal efficiency by combining photocatalysis and Fenton interaction under neutral condition. The p-g-C3N4 was prepared through a two-step thermal oxidation reaction. Afterwards, Q3Fe-coupled p-g-C3N4 was prepared by an impregnating method. The 2,4-dichlorophenol (2,4-DCP) photodegradation ratio and decomposition rate of the p-g-C3N4/Q3Fe/H2O2 system are approximately 5 and 18 times as high as those of individual p-g-C3N4 system, respectively. Besides, its degradation rate is 4.3 times as high as that in the p-g-C3N4/H2O2 system. Meanwhile, Q3Fe/g-C3N4 also exhibits higher activity than individual p-g-C3N4 in 2,4-DCP photo-decomposing. On the basis of the results of the radical trapping experiments and the Fe(II) concentration in different systems, the synergistic effect between photocatalysis and Fenton reaction is vital for the efficient pollutant degradation. The coupled system combining p-g-C3N4 with Q3Fe and H2O2 shows potential for efficient treatment of recalcitrant organic pollutants. The combined system in this work indicated a new idea for the decomposition of organic pollutants.
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ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system...
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eng_Latn
| 31,113 |
Sodium- and potassium-coupled transporters clear the excitatory neurotransmitter glutamate from the synaptic cleft. Their function is essential for effective glutamatergic neurotransmission. Glutamate transporters have an unusual topology, containing eight membrane-spanning domains and two reentrant loops of opposite orientation. We have introduced pairwise cysteine substitutions in several structural elements of the GLT-1 transporter. A complete inhibition of transport by Cu(II)(1,10-phenanthroline)(3) is observed in the double mutants A412C/V427C and A364C/S440C, but not in the corresponding single mutants. No inhibition is observed in more then 20 other double cysteine mutants. The Cu(II)(1,10-phenanthroline)(3) inhibition can be partly prevented by the nontransportable glutamate analogue dihydrokainate. Treatment with dithiothreitol restores much of the transport activity. Moreover, micromolar concentrations of cadmium ions reversibly inhibit transport catalyzed by A412C/V427C and A364C/S440C double mutants, but not by the corresponding single mutants. Inhibition by Cu(II)(1,10-phenanthroline)(3) and by cadmium is only observed when the cysteine pairs are introduced in the same polypeptide. Therefore, in both cases the proximity appears to be intra- rather than intermolecular. Positions 364 and 440 are located on reentrant loop I and II, respectively. Our results suggest that these two loops, previously shown to be essential for glutamate transport, come in close proximity.
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The human reduced folate carrier (RFC) is the major membrane transport system for both reduced folates and chemotherapeutic antifolate drugs, such as methotrexate (MTX). Although the RFC protein has been subjected to intensive study in order to identify critical structural and functional determinants of transport, it is impossible to assess the significance of these studies without characterizing the essential domain structure and membrane topology. The primary amino acid sequence from the cloned cDNAs predicts that the human RFC protein has 12 transmembrane domains (TMDs) with a large cytosolic loop between TMDs 6 and 7, and cytosolic-facing N- and C-termini. To establish the RFC membrane topology, a hemagglutinin (HA) epitope was inserted into the individual predicted intracellular and extracellular loops. HA insertions into putative TMD interconnecting loops 3/4, 6/7, 7/8, and 8/9, and the N- and C-termini all preserved MTX transport activity upon expression in transport-impaired K562 cells. Immunofluorescence detection with HA-specific antibody under both permeabilized and non-permeabilized conditions confirmed extracellular orientations for loops 3/4 and 7/8, and cytosolic orientations for loops 6/7 and 8/9, and the N- and C-termini. Insertion of a consensus N-glycosylation site [NX(S/T)] into putative loops 5/6, 8/9, and 9/10 of deglycosylated RFC-Gln(58) had minimal effects on MTX transport. Analysis of glycosylation status on Western blots suggested an extracellular orientation for loop 5/6, and intracellular orientations for loops 8/9 and 9/10. Our findings strongly support the predicted topology model for TMDs 1-8 and the C-terminus of human RFC. However, our results raise the possibility of an alternative membrane topology for TMDs 9-12.
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Graphitic carbon nitride (g-C3N4) is a photocatalyst with wide application in removal of organic pollutants. In this study, we designed a porous g-C3N4 (p-g-C3N4)/8-quinolinolato iron(III) (Q3Fe)/H2O2 system to enhance the organic pollutant removal efficiency by combining photocatalysis and Fenton interaction under neutral condition. The p-g-C3N4 was prepared through a two-step thermal oxidation reaction. Afterwards, Q3Fe-coupled p-g-C3N4 was prepared by an impregnating method. The 2,4-dichlorophenol (2,4-DCP) photodegradation ratio and decomposition rate of the p-g-C3N4/Q3Fe/H2O2 system are approximately 5 and 18 times as high as those of individual p-g-C3N4 system, respectively. Besides, its degradation rate is 4.3 times as high as that in the p-g-C3N4/H2O2 system. Meanwhile, Q3Fe/g-C3N4 also exhibits higher activity than individual p-g-C3N4 in 2,4-DCP photo-decomposing. On the basis of the results of the radical trapping experiments and the Fe(II) concentration in different systems, the synergistic effect between photocatalysis and Fenton reaction is vital for the efficient pollutant degradation. The coupled system combining p-g-C3N4 with Q3Fe and H2O2 shows potential for efficient treatment of recalcitrant organic pollutants. The combined system in this work indicated a new idea for the decomposition of organic pollutants.
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eng_Latn
| 31,114 |
The synthesis, molecular structure, spectroscopic properties and bonding in a complex of dinitrogen with trivalent uranium are described. The molecule has a side-on U–N2–U core which is supported by U N2 donation with no significant N2U bonding. Steric compression between the spectator triamidoamine ligands prevents the uranium atoms from approaching the N2 ligand at the optimum distance for overlap, and thus the N–N distance is not displaced significantly from that in gaseous dinitrogen. © 2001 Elsevier Science B.V. All rights reserved.
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This review covers the activation of molecular pnictogens (group 15 elements) by homogeneous rare earth and actinide complexes. All examples of molecular pnictogen activation (dinitrogen, white phosphorus, yellow arsenic) by both rare earths and actinides, to date (2015), are discussed, focusing on synthetic methodology and the structure and bonding of the resulting complexes.
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This study carried out the direct-bonding between titanium and polyamide using nanosecond laser, investigated the effect of the textured micro-groove depth on the strength of the joint and obtained the optimal joint strength.
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eng_Latn
| 31,115 |
The TFA-catalyzed condensation of 5-(thienyl)dipyrromethane with thiophene carboxaldehyde allows for the formation of the thienyl meso-substituted 5,10,15-tris(2-thienyl)corrole H3(T2TC) (1) and the 5,10,15-tris(3-thienyl)corrole H3(T3TC) (2). These ligands undergo metalation with copper and cobalt acetate to yield the four respective metallocorroles. Single-crystal X-ray crystallographic solutions for Cu(T2TC) (3), Co(T2TC)(Py)2 (5) and Co(T3TC)(Py)2 (6) have been obtained, confirming the direct pyrrole–pyrrole link and axial pyridine groups in the case of the cobalt structures. Cyclic voltammetry data indicated the 2-thienyl derivatives are more difficult to oxidize when compared to trispentafluorophenyl corroles (TPFC). Both metal complex isomers are comparably stable towards the formation of dinuclear products resulting from intermolecular C–C coupling. Soret bands for both ligands and complexes have been obtained and variable temperature 1H NMR studies (−50–60 °C) for 3 and 4 reveal a fluxional rotational behavior for the three thienyl substituents believed to impart a less electron withdrawing effect on the corrole core, opposed to the TPFC’s.
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Two sets of complexes of Co–triarylcorrole–bispyridine complexes, Co[TpXPC](py)2 and Co[Br8TpXPC](py)2 have been synthesized, where TpXPC refers to a meso-tris(para-X-phenyl)corrole ligand with X = CF3, H, Me, and OMe and Br8TpXPC to the corresponding β-octabrominated ligand. The axial pyridines in these complexes were found to be labile and, in dilute solutions in dichloromethane, the complexes dissociate almost completely to the five-coordinate monopyridine complexes. Upon addition of a small quantity of pyridine, the complexes revert back to the six-coordinate forms. These transformations are accompanied by dramatic changes in color and optical spectra. 1H NMR spectroscopy and X-ray crystallography have confirmed that the bispyridine complexes are authentic low-spin Co(III) species. Strong substituent effects on the Soret maxima and broken-symmetry DFT calculations, however, indicate a CoII–corrole•2– formulation for the five-coordinate Co[TpXPC](py) series. The calculations implicate a Co(dz2)–corrole...
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Following the introduction of hydrochlorofluorocarbon (HCFCs) and hydrofluorocarbon (HFCs) gases as replacements for the ozone-destroying chlorofluorocarbons (CFCs), it has been discovered that HCFCs/HFCs can degrade in the atmosphere to produce trifluoroacetic acid, a compound with no known loss mechanisms in the environment, and higher concentrations in natural waters have been shown to be mildly phytotoxic. Present environmental levels of trifluooracetic acid are not accounted by HCFC/HFC degradation alone. Here we report that thermolysis of fluorinated polymers, such as the commercial polymers Teflon and Kel-F, can also produce trifluoroacetate and the similar compound chlorodifluoroacetate. This can occur either directly, or indirectly via products that are known to degrade to these haloacetates in the atmosphere. The environmental significance of these findings is confirmed by modelling, which indicates that the thermolysis of fluoropolymers in industrial and consumer high-temperature applications (ovens, non-stick cooking utensils and combustion engines) is likely to be a significant source of trifluoroacetate in urban rain water ( approximately 25 ng l-1, as estimated for Toronto). Thermolysis also leads to longer chain polyfluoro- and/or polychlorofluoro- (C3-C14) carboxylic acids which may be equally persistent. Some of these products have recently been linked with possible adverse health and environmental impacts and are being phased out of the US market. Furthermore, we detected CFCs and fluorocarbons-groups that can destroy ozone and act as greenhouse gases, respectively-among the other thermal degradation products, suggesting that continued use of fluoropolymers may also exacerbate stratospheric ozone-depletion and global warming.
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eng_Latn
| 31,116 |
Publisher Summary The structural diversity of Uranium-containing coordination polymers is rather extensive. This can be attributed to two synergistic factors: a rich local geometry of the uranyl cation and a diverse pool of organic linker molecules. Developments within transition metal and lanthanide based metal-organic framework materials are making their way into the actinide materials. Much of the original interest in uranium structural chemistry stemmed from its role in the nuclear fuel cycle, yet promising new compounds reviewed in the chapter suggest that an extension of their utility is on the horizon. New and exciting applications for these materials are currently being explored with considerable intensity. Catalytic and fluorescent behaviors hold particular promise as coordination polymers offer unique opportunities for tunable fluorescence as well as heterogeneous catalysis. The latter of these properties results from the photocatalytic ability of excited state uranyl cations.
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Typical fission product formation experiments utilize metal or oxide target materials that must be dissolved prior to product separation. We report here a novel study using metal–organic frameworks for recovery of fission products into acidic media. We further show that the frameworks are largely preserved, such that this bulk target material could be retained for additional irradiations or characterizations. Through this approach, fission products can be separated from the actinide-based metal–organic framework using 0.01 M HNO3 without the need to dissolve the framework itself, reducing the amount of acidic waste. Extraction yields of four frameworks with varying pore sizes are compared. The results suggest that it may be possible to use porous frameworks as target materials for the extraction of select fission products.
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Background ::: Serum calcium (Ca) and inorganic phosphate (Pi) concentrations and calcium-phosphate product (CPP) levels are positively associated with worse outcomes in patients with chronic kidney disease, but there are few data for Pi or Ca and none for CPP in patients with chronic heart failure (CHF).
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eng_Latn
| 31,117 |
In an effort to develop new ruthenium(II) complexes, this work describes the design, synthesis and characterization of a ruthenium(II) functionalized phenanthroline complex with extended π-conjugation. The ligand were L1 (4,7-bis(2,3-dimethylacrylic acid)-1,10-phenanthroline), synthesized by a direct aromatic substitution reaction, and L2 (4,7-bis(trianthracenyl-2,3-dimethylacrylic acid)-1,10-phenanthroline), which was synthesized by the dehalogenation of halogenated aromatic compounds using a zero-valent palladium cross-catalyzed reaction in the absence of magnesium-diene complexes and/or cyclooctadienyl nickel (0) catalysts to generate a new carbon-carbon bond (C-C bond) polymerized hydrocarbon units. The ruthenium complex [RuL1L2(NCS)2] showed improved photophysical properties (red-shifted metal-to-ligand charge-transfer transition absorptions and enhanced molar extinction coefficients), luminescence and interesting electrochemical properties. Cyclic and square wave voltammetry revealed five major redox processes. The number of electron(s) transferred by the ruthenium complex was determined by chronocoulometry in each case. The results show that processes I, II and III are multi-electron transfer reactions while processes IV and V involved one-electron transfer reaction. The photophysical property of the complex makes it a promising candidate in the design of chemosensors and photosensitizers, while its redox-active nature makes the complex a potential mediator of electron transfer in photochemical processes.
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Dye sensitized solar cell (DSSC) is the only solar cell that can offer both the flexibility and transparency. Its efficiency is comparable to amorphous silicon solar cells but with a much lower cost. This review not only covers the fundamentals of DSSC but also the related cutting-edge research and its development for industrial applications. Most recent research topics on DSSC, for example, applications of nanostructured TiO(2), ZnO electrodes, ionic liquid electrolytes, carbon nanotubes, graphene and solid state DSSC have all been included and discussed.
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The goal of this study is to establish the effect of [(H2O)(NH3)5Ru(II)]2+ reaction of nuclei on their RNA transcription levels. This question is important because ammineruthenium compounds share chemical and biological properties with the chemotherapeutic agent cis-dichlorodiammineplatinum(II) or cisplatin. First we demonstrate that mouse liver nuclei are active in RNA transcription in vitro and characterize the optimum conditions for in vitro transcription. Synthetic rates in the presence of inhibitors actinomycin D and α-Amanitin and measurements of oligo(dT)-cellulose RNA binding levels suggest that all three RNA Polymerases are active in synthesis at about the following percentages-RNA Polymerase I(30%), II(50%) and III(20%). Mouse liver nuclei reacted with [(H2O)(NH3)5Ru(II)]2+ and then oxidized had (NH3)5 Ru(III)3+-DNA adduct levels inversely related to total RNA synthetic rates. Oligo(dT) cellulose RNA binding levels did not vary with DNA adduct density. These data suggest that direct DNA lesions rather than [(NH3)5Ru(III)]3+ effects on other aspects of the transcription system are responsible for the diminished RNA synthesis levels. Ammineruthenium complexes remain desirable candidates for chemotherapeutic agents that may be safely administered in the unreactive ruthenium(III) state and be activated toward DNA binding by reduction in the hypoxic environment of many tumour cells.
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eng_Latn
| 31,118 |
The structural stability of aniline, 2,4,6-trichloroaniline and 2,3,5,6-tetrachloroaniline was investigated by DFT-B3LYP and ab initio MP2 and MP4(SDQ) calculations with the 6-311G∗∗ basis set. From the calculations the three molecules were predicted to exist predominantly in a symmetric near-planar structure. The NH 2 inversion barrier was estimated from the MP2/6-311G∗∗ level of theory to be about 9.6 kJ/mol for aniline, 5.9 kJ/mol for the trichloro and 4.6 kJ/mol for the tetrachloro derivatives. The line intensities of the ring breathing and the C Cl stretching modes were shown to have a great dependence on the number of chlorine atoms on the benzene ring. The relative change in Raman line intensity of the C Cl stretching mode was explained on the basis of the inductive effect of the chlorine atoms on the benzene ring. The vibrational frequencies were computed at the DFT-B3LYP level and the infrared and Raman spectra for each molecule were calculated. Complete vibrational assignments were made on the basis of normal coordinate analyses and potential energy distributions for the two chloroanilines.
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In this paper, the reaction of aniline with ammonium persulphate and concentrated HCl was studied. As a result of our experimental studies, 2,4,6-trichlorophenylamine was identified as the main product. This shows that a high concentration of HCl does not favour oxidative polymerisation of phenylamine, even though the ammonium persulphate/HCl system is widely used in polyaniline synthesis. On the basis of the experimental data and density functional theory for reaction path modelling, we proposed a mechanism for oxidative chlorination of aniline. We assumed that this reaction proceeded in three cyclically repeated steps; protonation of aniline, formation of singlet ground state phenylnitrenium cation, and nucleophilic substitution. In order to confirm this mechanism, kinetic, thermochemical, and natural bond orbital population analyses were performed.
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The reduction of proline by Clostridium sporogenes NCIB8053 is coupled to transmembrane proton translocation in an uncoupler-sensitive fashion (and might therefore conserve free energy). This finding serves to explain the increase in the growth yield of this organism when proline is added to a defined growth medium containing glucose as the catabolic substrate.
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eng_Latn
| 31,119 |
The biochemical effect of N-acylethanolamines on trout erythrocytes from Salmo irideus was studied by following their susceptibility to hemolysis and measuring steady-state fluorescence anisotropy of the fluorescent probe, 1,6diphenyl-1,3,5-hexatriene (DPH) on isolated membranes. The hemolytic process was strongly affected by different ethanolamine derivatives. However, only slight changes in fluorescence anisotropy were detected in these models, therefore, it appears that acylethanolamine derivatives do not produce significant variations in the physico-chemical characteristics of the membrane. The localization of these molecules in particular microdomains is hypothesized, thus locally modifying physiological membrane activities.
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The proapoptotic and antineoplastic properties of cannabinoids with emphasis on effects of N-acylethanolamines were analyzed. Cannabinoids enhanced apoptotic and necrotic processes in many types of tumour cells and tissues. Involvement of different types of receptors and signaling pathways in mediating the proapoptotic effects of cannabinoids are discussed. The evidences in favour of both proapoptotic, pronecrotic and protective, antiapoptotic effects of cannabinoids and, especially N-acylethanolamines, are evaluated. The hypothesis is suggested that N-acylethanolamines, formed in some tissues under strong stress conditions, can be not a consequence of tissue damage but cause such damage. The conclusion is made on promising of cannabinoids as potential anticancer agents.
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2-Ethylhexanoic acid has been applied as a dual solvent-catalyst for the one-pot, four-component synthesis of 1,2,4,5-tetrasubstituted imidazoles. This naturally occurring and widely produced fatty acid exhibited remarkable catalytic activity and was easily separated by extraction. The reusability of this catalytic media was examined up to four times and no significant drop in catalytic activity was observed. Utilizing ecofriendly, low cost and commercially available reagent, short reaction times (30-90 min), very good to excellent yields (88-93) and straightforward workup procedure are the salient properties offered by this methodology.
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eng_Latn
| 31,120 |
A series of flower-like Bi2WO6 with oxygen vacancies were produced through an etching process at room temperature using NaBH4 as reducing agent. The structure and morphology were further confirmed by XRD, SEM, HRTEM and XPS. The performance of photoelectrochemical (PEC) water splitting for all samples was investigated by evaluating the charge-transfer resistance, electrons lifetime and photoinduced carrier density. The results demonstrated that the Bi2WO6 with appropriate concentration of oxygen vacancies exhibited higher PEC properties than pure Bi2WO6 and the enhanced PEC performance of the Bi2WO6-x was ascribed to the presence of oxygen vacancies. The oxygen vacancies can introduce impurity levels under the conduction band which can act as electron trapping centers in Bi2WO6-x resulted in the band gap narrowing, which accelerates the separation and transfer of charges and reduced the recombination of photogenerated electron-hole.
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Bi2O3 nanomaterials were synthesized via a facile solvothermal routine both in the absence and presence of reducing agent of ascorbic acid. XRD measurements were applied to confirm the phase formation and structure. The morphological, optical absorbance, photocatalytic activities, and photoluminescence of the final samples showed a strict dependence on the presence of reductant used in the synthesis. Solvothermal synthesis without ascorbic acid produced α-Bi2O3 nanoplates, which aggregated together forming the flowerlike balls. Due to the in situ reduction of bismuth ions by ascorbic acid, the ball-like Bi/Bi2O2.75 nanocomposites (100 nm) were obtained in the presence of reducing agent via introducing the metallic Bi0 on the surface. The photocatalytic and photoluminescence activities of the samples were investigated. Bi/Bi2O2.75 nanocomposites showed a good photocatalytic behavior on the degradation of organic dye solutions. The photocatalysis was discussed on the luminescence, decay lifetime, and multivalent ions. Grapichal Grapichal
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REACCTING (Research on Emissions Air Quality, Climate, and Cooking Technologies in Northern Ghana) was a 200-home cookstove intervention study from 2013 to 2015. Study households were divided into four groups: a control group, a group given two locally made rocket stoves, a group given two Philips forced draft stoves, and a group given a locally made rocket stove and a Philips stove. In a subset of study households, 48-hour PM2.5 exposure samples were collected for adults and children, as well as in the primary cooking area. Further, weekly ambient background PM2.5 samples were collected for the first nine months of the study. All PM2.5 samples were analyzed for elemental and organic carbon (EC/OC), and a subset was also analyzed for organics. Mixed effects modeling was applied to quantify differences in PM exposures between the groups and to assess relationships between exposures and cooking area measurements. Results showed that personal OC exposure for the intervention groups was 56.6% lower than the control group (p≤0.01). Both intervention groups given Philips stoves had significantly lower EC exposure than the control group (60.6% reduction, p≤0.02). Only weak relationships were found between personal and cooking area EC or OC. Source apportionment modeling was performed on both the personal/microenvironment and the ambient organics PM2.5 data sets to assess the sources of the observed PM. We identified six PM sources. The identified source factors were similar among the data sets, as well as with previous work in Navrongo. Two sources, one characterized by the presence of methoxyphenols, and one by the presence of polyaromatic hydrocarbons and EC, were associated with biomass burning, and accounted for a median of 9.2% of OC and 15.3% of EC personal exposure. Here, we demonstrate the utility of using the cooking-related source apportionment factors within a mixed effects model for more precise estimation of exposures due to cooking, rather than other combustion sources unrelated to the intervention.
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| 31,121 |
In this paper we show that cultured chorionic villous fibroblasts efficiently catalyse the peroxisomal β-oxidation of hexacosanoic acid (cerotic acid), a saturated very long chain fatty acid containing 26 carbon atoms. Hexacosanoic β-oxidation was found to be strongly impaired in cultured chorionic villous fibroblasts from a Zellweger foetus. This finding indicates that measurement of peroxisomal β-oxidation can be used (in addition to measurement of acyl-CoA : dihydroxyacetone phosphate acyltransferase, de novo plasmalogen biosynthesis, the amount of particle-bound catalase and phytanic acid oxidase) for prenatal diagnosis in the first trimester of Zellweger syndrome, infantile Refsum disease and neonatal adrenoleukodystrophy. The method should be equally applicable to the early prenatal diagnosis of disorders in which there is a deficiency of a single peroxisomal β-oxidation enzyme. Such diseases include X-linked adrenoleukodystrophy (peroxisomal very long chain fatty acyl CoA ligase deficiency), ‘ pseudo-Zellweger syndrome’ (peroxisomal 3-oxoacyl-CoA thiolase deficiency) and ‘pseudo-neonatal adrenoleukodystrophy’ (acyl-CoA oxidase deficiency).
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Goldfischer and coworkers (1973) were the first to describe the absence of morphologically distinguishable peroxisomes in liver and kidney tubule cells of patients with the cerebro-hepato-renal (Zellweger) syndrome (McKusick 21410). In recent years it has become clear that peroxisomes are also (virtually) absent in patients with neonatal adrenoleukodystrophy (McKusick 20237), infantile Refsum disease and hyperpipecolic acidaemia (McKusick 23940), at least in the four patients described in the literature (see Wanders et al., 1988, for discussion). The (virtual) absence of peroxisomes in these patients is associated with a generalized loss of peroxisomal functions as reflected in the accumulation of very long-chain fatty acids, bile acid intermediates, pipecolic acid and phytanic acid in plasma from the patients.
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A novel hyperbranched zinc phthalocyanine dye, i.e. HBZnPc-COOH, was synthesized, characterized, and applied into ::: dye-sensitized solar cells (DSSCs) as TiO 2 sensitizer. UV-visible absorption, steady-state fluorescence, femtosecond ::: time-resolved fluorescence, cyclic voltammetry, current–voltage characteristics, and photoelectrical properties of the ::: active material/device were investigated. The utilization of hyperbranched structure was proved to be able to solve the ::: aggregation issue of phthalocyanine dyes on TiO 2 surface which has been widely considered as one of the key limiting ::: issues that severely lower the efficiencies of phthalocyanine dye sensitized solar cells. With appropriate highest occupied ::: molecular orbital and lowest unoccupied molecular orbital energy levels, HBZnPc-COOH exhibited efficient and ::: ultrafast multi-phasic electron injection from both the Soret band and Q band to the conduction band of TiO 2 , leading to ::: a solar cell power conversion efficiency of 1.15% and a high incident photon to current conversion efficiency of 66.7% ::: at 670 nm.
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eng_Latn
| 31,122 |
Presented here are authoritative and up-to-date assessments of the homogenous and heterogenous chemical and physical processes occuring in the troposphere and stratosphere, especially during the "ozone hole" event. The book begins with an overview of atmospheric chemistry, followed by reviews of relevant homogenous reactions in the gas phase and the microphysics and physical chemistry of heterogenous processes that occur on, or in aerosols, rain and ice. Low temperature laboratory studies are compared with related fieldwork measurements, particularly in relation to the formation and composition of polar stratospheric clouds. Also discussed are measurements in glacial ice. Finally chemical modelling of the troposphere and stratosphere, including heterogenous processes, is reviewed.
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We demonstrate time-resolved frequency comb spectroscopy (TRFCS), a new broadband absorption spectroscopy technique for the study of trace free radicals on the microsecond timescale. We apply TRFCS to study the time-resolved, mid-infrared absorption of the deuterated hydroxyformyl radical trans-DOCO, an important short-lived intermediate along the OD + CO reaction path. Directly after photolysis of the chemical precursor acrylic acid-d1, we measure absolute trans-DOCO product concentrations with a sensitivity of 5 × 10(10) cm(-3) and observe its subsequent loss with a time resolution of 25 μs. The multiplexed nature of TRFCS allows us to detect simultaneously the time-dependent concentration of several other photoproducts and thus unravel primary and secondary chemical reaction pathways.
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Catalysts which comprise silica are rendered less susceptible to physical damage during processing with aqueous liquids by pre-steaming them.
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| 31,123 |
Thymine analogs with saturated 5-6 bonds are important types of DNA damage that are recognized by the DNA N-glycosylase activity of E. coli endonuclease III. Seeking agents which could preferentially form 5,6-hydrated thymine residues in duplex DNA both in vivo and in vitro, we exposed purified duplex DNA to 325- or 313-nm light; however, after such exposure pyrimidine dimers greatly predominated over 5,6-hydrated thymine. Hydrogen peroxide, on the other hand, formed significant numbers of endonuclease III-sensitive sites in vitro which were not apurinic/apyrimidinic lesions and thus were likely to be 5,6-hydrated thymines.
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Sperm DNA integrity is of paramount importance for the accurate conveyance of genetic material. DNA damage may be a major contributory factor in male infertility as DNA from sperm of infertile men has been found to be more susceptible to induced DNA damage in vitro than DNA from fertile men. Reactive oxygen species (ROS) are a significant source of DNA damage and human sperm are extremely sensitive to ROS attack due to their high content of polyunsaturated fatty acids and lack of capacity for DNA repair. Seminal plasma, which contains a wealth of antioxidants, provides sperm with crucial protection against oxidative insult. However, during preparation for use in assisted conception techniques, sperm are separated from seminal plasma and deprived of that essential protection. The aim of this study was to determine the effects of supplementation with glutathione and hypotaurine during sperm preparation on subsequent sperm motility, DNA integrity, induced DNA damage and ROS generation. Semen samples (n = 45) were divided into aliquots and prepared by Percoll density centrifugation (95.0-47.5%) using medium which had been supplemented with these antioxidants to a number of different concentrations all within physiological levels. Control aliquots were included which had no glutathione or hypotaurine added. Sperm motility was determined using computer-assisted semen analysis. DNA damage was induced using H(2)O(2) and DNA integrity was determined using a modified alkaline single cell gel electrophoresis (Comet) assay, while ROS generation was measured using chemiluminescence. Addition of glutathione and hypotaurine, either singly or in combination, to sperm preparation medium had no significant effect on sperm progressive motility or baseline DNA integrity. Despite this, sperm were still afforded significant protection against H(2)O(2)-induced damage and ROS generation.
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Hydrogen bond geometries in the proton-bound homodimers of ortho-unsubstituted and ortho-methylsubstituted pyridine derivatives in aprotic polar solution were estimated using experimental NMR data. Within the series of homodimers studied the hydrogen bond lengths depend on the proton affinity of pyridines and--at least for the ortho-methylsubstituted pyridines--on the pKa of the conjugate acids in an approximately quadratic manner. The shortest possible hydrogen bond in the homodimers of ortho-unsubstituted pyridines is characterized by the N···N distance of 2.613 Å. Steric repulsion between the methyl groups of the ortho-methylsubstituted pyridines becomes operative at an N···N distance of ∼2.7 Å and limits the closest approach to 2.665 Å.
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eng_Latn
| 31,124 |
The positron-emission tomography (PET) probe 2-(1-[6-[(2-fluoroethyl)(methyl)amino]-2-naphthyl]ethylidene) (FDDNP) is used for the noninvasive brain imaging of amyloid-β (Aβ) and other amyloid aggregates present in Alzheimer’s disease and other neurodegenerative diseases. A series of FDDNP analogs has been synthesized and characterized using spectroscopic and computational methods. The binding affinities of these molecules have been measured experimentally and explained through the use of a computational model. The analogs were created by systematically modifying the donor and the acceptor sides of FDDNP to learn the structural requirements for optimal binding to Aβ aggregates. FDDNP and its analogs are neutral, environmentally sensitive, fluorescent molecules with high dipole moments, as evidenced by their spectroscopic properties and dipole moment calculations. The preferred solution-state conformation of these compounds is directly related to the binding affinities. The extreme cases were a nonplanar analog t-butyl-FDDNP, which shows low binding affinity for Aβ aggregates (520 nM Ki) in vitro and a nearly planar tricyclic analog cDDNP, which displayed the highest binding affinity (10 pM Ki). Using a previously published X-ray crystallographic model of 1,1-dicyano-2-[6-(dimethylamino)naphthalen-2-yl]propene (DDNP) bound to an amyloidogenic Aβ peptide model, we show that the binding affinity is inversely related to the distortion energy necessary to avoid steric clashes along the internal surface of the binding channel.
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Naphthalene derivatives bearing electron-accepting and electron-donating groups at the 2,6-positions belong to the family of D-π-A push-pull dyes. It has been found that these compounds, e.g., 2-(1-(6-((2-(fluoro)ethyl)(methyl)amino)naphthalen-2-yl)ethylidene)malononitrile (FDDNP), show not only interesting optical properties, such as solvatochromism, but they have the potential to label protein aggregates of different compositions formed in the brain of patients suffering from neurodegenerative diseases like Alzheimer’s (AD). In continuation of our research we set our goal to find new FDDNP analogs, which would inherit optical and binding properties but hopefully show better specificity for tau protein aggregates, which are characteristic for neurodegeneration caused by repetitive mild trauma. In this work we report on the synthesis of new FDDNP analogs in which the acceptor group has been formally replaced with an aromatic five- or six-membered heterocycle. The heterocyclic moiety was annealed to the central naphthalene ring either by classical ring closure reactions or by modern transition metal-catalyzed coupling reactions. The chemical characterization, NMR spectra, and UV/vis properties of all new compounds are reported.
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The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.).
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eng_Latn
| 31,125 |
The circular dichroism spectrum of protocatechuate 3,4-dioxygenase from Pseudomonas aeruginosa has been examined in the absence of the substrates, protocatechuic acid and O-2 and in the presence of the competitive inhibitors, protocatechualdehyde and p-hydroxybenzoic acid. The native enzyme has a low alpha-helical content (less than 1%) and exhibits several positive ellipticity bands between 250 and 300 nm (255,269,275 and 292 nm) and two, low intensity, negative bands at 330 and 480 nm. In the presence of protocatechuic acid and the absence of O-2, spectral changes are evident in the side chain and visible regions. There is a shift in the aromatic-region maximum from 275 to 267 and in the visible region from 330 to 348 and from 480 to 555 nm. No spectral changes are observed upon the removal or addition of only O-2. Different spectral changes in both the side chain and visible regions are observed in the enzyme with the two competitive inhibitors under either aerobic or anaerobic conditions. The spectral changes observed in the side chain region suggest the possible participation of aromatic residues in the binding process, but it is not yet established as to whether these residues play an active or passive role in binding and/or catalysis.
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The isofunctional enzymes of catechol 1,2-dioxygenase from species of Acinetobacter, Pseudomonas, Nocardia, Alcaligenes, and Corynebacterium oxidize 3-methylcatechol according to both the intradiol and extradiol cleavage patterns. However, the enzyme preparations from Brevibacterium and Arthrobacter have only the intradiol cleavage activity. Comparison of substrate specificity among these isofunctional dioxygenases shows striking differences in the oxidation of 3-methylcatechol, 4-methylcatechol and pyrogallol.
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Continuous optical excitation of excitons in quantum wells driven by intense, monochromatic terahertz fields leads to high-order sideband generation. With optical and terahertz fields perpendicular, sideband generation is enhanced, leading to 60th-order and higher processes.
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eng_Latn
| 31,126 |
Novel visible light-induced g-C3N4/Bi2WO6 composite photocatalysts were synthesized by introducing polymeric g-C3N4. The obtained g-C3N4/Bi2WO6 products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, ultraviolet–visible diffuse reflection spectroscopy (DRS), and photoluminescence spectroscopy. The DRS results revealed that the g-C3N4/Bi2WO6 samples had a red shift and strong absorption in the visible light region. The photocatalytic oxidation ability of the novel photocatalyst was evaluated using methyl orange as a target pollutant. The photocatalysts exhibited a significantly enhanced photocatalytic performance in degrading methyl orange. The optimal g-C3N4 content for the photocatalytic activity of the heterojunction structures was determined. The synergic effect between g-C3N4 and Bi2WO6 was found to lead to an improved photo-generated carrier separation. Consequently, the photocatalytic performance of the g-C3N4/Bi2WO6 composites under visible light irradiation (λ > 420 nm) was enhanced. The possible photocatalytic mechanism of the composites was proposed to guide the further improvement of their photocatalytic activity.
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A template-assisted synthetic method including the thermal polycondensation of guanidine hydrochloride (GndCl) was utilized to synthesize highly-organized mesoporous graphitic carbon nitride (mpg-C3N4) photocatalysts. Comprehensive structural analysis of the mpg-C3N4 materials were performed by XPS, XRD, FT-IR, BET and solid-state NMR spectroscopy. Photocatalytic performance of the mpg-C3N4 materials was studied for the photodegradation of several dyes under visible and UV light illumination as a function of catalyst loading and the structure of mpg-C3N4 depending on the polycondensation temperature. Among all of the formerly reported performances in the literature (including the ones for Degussa P25 commercial benchmark), currently synthesized mpg-C3N4 photocatalysts exhibit a significantly superior visible light-induced photocatalytic activity towards rhodamine B (RhB) dye. Enhanced catalytic efficiency could be mainly attributed to the terminated polycondensation process, high specific surface area, and mesoporous structure with a wide pore size distribution.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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eng_Latn
| 31,127 |
Low concentrations of the antibacterial agent hexachlorophene (HCP) inhibited a number of pyridine nucleotide-linked dehydrogenase enzymes, including bovine liver glutamate dehydrogenase (GDH), beef heart malate dehydrogenase (MDH), torula yeast glucose 6-phosphate dehydrogenase (G-6-P-D), horse liver alcohol dehydrogenase (ADH), pig heart isocitrate dehydrogenase (ICD), and beef heart lactate dehydrogenase (LDH). Initial velocity studies at appropriate enzyme concentrations gave I 50 values for the dehydrogenases which ranged between 1.6 μM for GDH and 105 μM for ICD and LDH. More detailed kinetic analyses of G-6-P-D, ICD and GDH showed that inhibition by HCP in most cases was of the noncompetitive type. Calculations made from the kinetic data gave apparent K i values with G-6-P-D, of 59 μM for NADP + and of 38 μM for glucose 6-phosphate; with ICD, of 1.0 μM for NADP + and of 25 μM for isocitrate; and, with GDH, of 2.0 μM for NADH, of 7.4 μM for α-ketoglutarate, and of 2.3 μM for ammonium acetate.
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Type II fatty acid biosynthesis represents an attractive target for the discovery of new antimalarial drugs. Previous studies have identified malarial ENR (enoyl acyl-carrier-protein reductase, or FabI) as the target for the antiseptic triclosan. In the present paper, we report the biochemical properties and 1.5 A (1 A = 0.1 nm) crystal structure of OAR (3-oxoacyl acyl-carrier-protein reductase, or FabG), the second reductive step in fatty acid biosynthesis and its inhibition by hexachlorophene. Under optimal conditions of pH and ionic strength, Plasmodiumfalciparum OAR displays kinetic properties similar to those of OAR from bacteria or plants. Activity with NADH is < 3 % of that with NADPH. Fluorescence enhancement studies indicate that NADPH can bind to the free enzyme, consistent with kinetic and product inhibition studies suggesting a steady-state ordered mechanism. The crystal structure reveals a tetramer with a sulphate ion bound in the cofactor-binding site such that the side chains of the catalytic triad of serine, tyrosine and lysine are aligned in an active conformation, as previously observed in the Escherichia coli OAR-NADP + complex. A cluster of positively charged residues is positioned at the entrance to the active site, consistent with the proposed recognition site for the physiological substrate (3-oxo-acyl-acyl-carrier protein) in E. coli OAR. The antibacterial and anthelminthic agent hexachlorophene is a potent inhibitor of OAR (IC 5 0 2.05 μM) displaying non-linear competitive inhibition with respect to NADPH. Hexachlorophene (EC 5 0 6.2 μM) and analogues such as bithionol also have antimalarial activity in vitro, suggesting they might be useful leads for further development.
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The concatenated Greenberger-Horne-Zeiglinger (C-GHZ) state which is a new type of logic-qubit entanglement has attracted a lot of attentions recently. We present a feasible entanglement concentration protocol (ECP) for logic-qubit entanglement. This ECP is based on the linear optics, and it does not know the initial coefficients of the less-entangled C-GHZ state. This protocol can be extended to arbitrary C-GHZ state. This protocol may be useful in future quantum information processing tasks.
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eng_Latn
| 31,128 |
Modeling and simulation techniques are presented, which are both physically accurate and computationally efficient for treating complex organic structures that have relevance to sensing and characterization, including structures with covalent bonding to biological (i.e., DNA) molecules. The theoretical study of large and complex biological molecular systems is very challenging because ab initio quantum mechanical methods are usually too computationally demanding and alternative empirical approaches are often insufficient for describing the internal interactions and dynamics. The goal of this research is to provide detailed insight into the molecular interaction mechanisms (e.g., terahertz (THz) frequency spectral absorption), which can be used to define novel types of bioelectronic-sensing devices. Therefore, a mixed ab initio/molecular mechanical-modeling approach is implemented and applied to the study of stilbene-DNA conjugates that offer switchable spectral characteristics that may be useful for detection and identification purposes. In particular, results are generated for two conformations of a TGCGCA-DNA duplex with trimethoxystilbene carboxamide (TMS) end capping that are confirmed by experimental data. The model is also used to derive the influences of DNA sequence and/or TMS orientation on the conformation, electronic states, and atomic vibrations of single- and doubled-stranded variants of the TGCGCA-DNA duplex. These results, which include very distinct absorption spectra in the THz to UV range, demonstrate that hybrid methodologies can bridge the gap in understanding electronic and atomic structure, and light-induced interactions in complex bioorganic systems.
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The experimental and computational study of bacterial thioredoxin, an E. coli protein, at THz frequencies is presented. The absorption spectrum of the entire protein in water was studied numerically in the terahertz range (0.1 – 2 THz). In our work, the initial X-ray molecular structure of thioredoxin was optimized using the molecular dynamical (MD) simulations at room temperature and atmospheric pressure. The effect of a liquid content of a bacterial cell was taken into account explicitly via the simulation of water molecules using the TIP3P water model. Using atomic trajectories from the room-temperature MD simulations, thioredoxin's THz vibrational spectrum and the absorption coefficient were calculated in a quasi harmonic approximation. For our terahertz transmission measurements, we used solutions of thioredoxin in distilled water obtained from Sigma. The experimental and simulated signatures are correlated and dominant peaks are close in frequencies. The results of this study demonstrate that terahertz spectroscopy is a promising tool in generating spectral data for cellular components of bio agents such as bacterial cells and spores.
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ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system...
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eng_Latn
| 31,129 |
Randomized slices of bacon were cooked at home by 25 consumers by their usual method of preparation and the edible portions were analyzed for nitrosamines. N-nitrosodimethylamine (DMNA) and N-nitrosopyrrolidine (NPyr) were found in all samples. Of the 25 preparations, five contained DMNA and five contained NPyr in concentrations greater than 10 μg/kg; only one sample contained both nitrosamines in concentrations greater than 10 μg/kg. Although the association between nitrosamine concentration, time and amount of heat is not strong, it appears that frying bacon at low or medium heat for less than 10 min can result in less than 10 μg/kg DMNA or NPyr.
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Since certain N-nitrosamines are highly carcinogenic, formation and isolation of these compounds from food systems has received much attention in the past decade. This paper reviews the N-nitrosamine literature of the past 3 years, especially as it relates to cured meat products. This review examines occurrence of nitrites and amines in food systems, presence of N-nitrosamines in bacon, and also means of minimizing formation of these compounds. In addition, regulatory changes pertaining to nitrite usage in curing procedures as well as some areas of future research are discussed.
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Two new model systems for use within the rapidly develop- ing ultrafast time resolved x-ray scattering techniques have been prepared. Their photoisomerisation from norbornadiene to quadricyclane was found to be a suitable reaction to fol- low. Simulations of scattering patterns (not included in this report) showed that if heavy atoms are included in these molecular structures, then the transformation can be followed by transient X-ray scattering techniques. Two new bromosub- stituted norbornadienes were synthesised and characterised. Absorption spectroscopy showed that the norbornadienes are converted quantitatively to quadricyclanes under ultra- violet irradiation. Nuclear magnetic resonance (NMR) studies showed that the process was fully reversible and that the norbornadienes could be completely recovered even without addition of catalysts. Furthermore, it was shown that the formation of quadricyclane from norbornadiene was unaf- fected by triplet sensitisers. The two new model systems synthesised thus are strong candidates for use in time- resolved X-ray scattering studies in both gas and condensed phases.
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eng_Latn
| 31,130 |
Boron trifluoride and indium(III) trifluoromethanesulfonate were found to efficiently catalyse the isomerisation of thionolactones to thiolactones in good yields. When applied to an optically active γ-thionolactone, the isomerisation reaction proceeded with a complete inversion of configuration by using BF 3 ·Et 2 O.
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A modular platform based on free-radical xanthate addition to alkenes enables access to a large series of functional γ-thiolactones. This methodology includes two different pathways based on xanthate chemistry involving radical addition and Chugaev elimination steps. The first method uses the addition of an ester-functionalized xanthate to various commercially functional alkenes, whereas the second one is based on the addition of functional xanthates to an ester-functionalized alkene. In both cases, a series of xanthate/alkene monoadducts was obtained, and their thermolysis and subsequent cyclization led to a library of functional γ-thiolactones in moderate to good yield. For a few cases where it may not be possible to directly incorporate some targeted functional groups via the proposed process involving free radicals and high temperature, a bromo-functionalized thiolactone was used as a starting material for chemical transformations.
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Alkylaminium sulfates originate from the neutralisation reaction between short-chained amines and sulfuric acid and have been detected in atmospheric aerosol particles. Their physicochemical behaviour is less well characterised than their inorganic equivalent, ammonium sulfate, even though they play a role in atmospheric processes such as the nucleation and growth of new particles and cloud droplet formation. In this work, a comparative evaporation kinetics experimental technique using a cylindrical electrodynamic balance is applied to determine the hygroscopic properties of six short-chained alkylaminium sulfates, specifically mono-, di-, and tri-methylaminium sulfate and mono-, di-, and tri-ethyl aminium sulfate. This approach allows for the retrieval of a water-activity-dependent growth curve in less than 10 s, avoiding the uncertainties that can arise from the volatilisation of semi-volatile components. Measurements are made on particles > 5 µm in radius, avoiding the need to correct equilibrium measurements for droplet-surface curvature with assumed values of the droplet-surface tension. Variations in equilibrium solution droplet composition with varying water activity are reported over the range 0.5 to > 0.98, along with accurate parameterisations of solution density and refractive index. The uncertainties in water activities associated with the hygroscopicity measurements are typically 0.9 and ∼ ±1 % below 0.9, with maximum uncertainties in diameter growth factors of ±0.7 %. Comparison with previously reported measurements show deviation across the entire water activity range.
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eng_Latn
| 31,131 |
The effect of chlorophyllin (CHLN) on the mutagenicity of four monofunctional alkylating agents (MFAAs) was evaluated in the wing spot test in Drosophila. Three of the compounds are direct-acting (ethylnitrosamine (ENU), methylnitrosourea (MNU), and methylmethanesulfonate (MMS)) and one indirect-acting (diethylnitrosamine, DEN). Results indicate that the mutagenicity of all four compounds is strongly inhibited by CHLN. The findings are not in agreement with the conclusion of Romert et al. (1992) that CHLN has no effect on the mutagenicity of direct acting MFFAs inferred from their work with MNU and ethylmethanesulfonate (EMS) in the V79 and Salmonella in vitro test systems. The results suggest the possibility that the action of CHLN need not include an inhibiting effect on metabolic activation.
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Food-borne heterocyclic aromatic amines (HCAs) are known mutagens and carcinogens present especially in Western population diet, which contains large amount of meat and its products. HCAs are capable of interacting with DNA directly through the formation of covalent adducts, however this process requires biological activation in liver, mainly by cytochrome P450 enzymes. This process may produce mutations and in consequence may contribute to the development of cancer. However, there are many studies showing that several biologically active aromatic compounds (BACs) may protect against genotoxic effects of HCAs. Direct interactions and noncovalent heterocomplexes formation may be one of the most important mechanisms of such protection. This work describes several BACs present in human diet, which are capable of molecular complexes formation with HCAs and protect cells as well as whole organisms against HCAs action.
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Asymmetric transmission (AT) holds significant applications in controlling polarization and propagation directions of electromagnetic waves. In this paper, tilted rectangular nanohole (TRNH) arrays in a square lattice are proposed to realize an AT effect. Numerical results show two AT modes in the transmission spectrum, and they are ascribed to the localized surface plasmon resonances around the two ends of TRNH and surface plasmon polaritons on the golden film. AT properties of the TRNH strongly depend on structural parameters, such as width, length, thickness, and tilted angle of TRNH. Results provide a novel mechanism for generating AT effect and offer potential plasmonic device applications, such as asymmetric wave splitters and optical isolators.
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eng_Latn
| 31,132 |
Four new compounds of reduced polyoxomolybdenum phosphate (V) with the formula (H2enMe)4(MnH2O)2{Mn[Mo6O12(OH)3(HPO4)2(PO4)2]2}·5H2O (1) (enMe = 1,2-diaminopropane), (H3N(CH2)4NH3)4(MnH2O)2{Mn[Mo6O12(OH)3(HPO4)2 (PO4)2]2}·2H2O (2), (H3dien)4{Mn[Mo6O12(OH)3(HPO4)2(PO4)2]2}·8H2O (3) (dien = diethylenetriamine) and (H2en)5{Cu2[Mo6O12(OH)3(HPO4)3(PO4)]2}·3H2O (4) (en = ethylenediamine) have been successfully synthesized under similar reactive condition and characterized by single-crystal X-ray diffraction. For compounds 1–3, despite slight distinction of amine, the organic amine template effect lead them to have different topological structures. The transition metal ion Mn2+ was replaced by Cu+, resulting in compound 4 with infinite chains since Cu+ exhibits a two-coordination mode. To the best of our knowledge, compound 4 is the first zigzag chain-like structure reduced polyoxomolybdenum phosphates containing Cu+. Other characterizations of these compounds by elemental, IR, thermal analysis and catalytic properties are also performed. The formation of these four compounds reveals that the organoamine and transition metal play important roles during the synthesis.
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Solutions of the quaternary ammonium salts of a set of classic polyoxometalates (POMs) (Keggin [XM12O40](n-), Dawson [P2W18O62](6-), and Lindqvist [M6O19](2-) (X = P, Si; M = W, Mo) were characterized by electrospray mass spectrometry. The gas-phase fragmentations of a series of quaternary ammonium-associated clusters were investigated by their collision-induced dissociations to elucidate their fragmentation mechanisms. It was found that the quaternary ammonium-associated clusters had distinctive dissociation characteristics. Moreover, the mono-quaternary ammonium-associated clusters, {NR4[POMs]}((n-1)-), shared a common fragmentation feature, that is, they decomposed exclusively into their respective alkyl cation-bound clusters irrespective of the different cation sizes and the different natures of the polyoxoanions. The optimized geometries and the binding energies of the mono cation-bound Lindqvist POM-based clusters were obtained by calculations. To the best of our knowledge, this is the first investigation of the gas-phase fragmentations of these noncovalent complexes between organic amines and inorganic POM anions by a combination of theory and mass spectrometry.
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The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.).
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eng_Latn
| 31,133 |
Phytocannabinoids have well-known cardiovascular implications. For instance, Δ9-tetrahydrocannabinol (Δ9-THC), the principal component of cannabis, induces tachycardia in humans. In order to understand the impact of phytocannabinoids on human cardiovascular health, there is a need to study the metabolism of phytocannabinoids by cardiac cytochromes p450 (CYPs). CYP2J2, the primary CYP of cardiomyocytes, is responsible for the metabolism of the endocannabinoid, anandamide (AEA), into cardioprotective epoxides (EET-EAs). Herein, we have investigated the kinetics of the direct metabolism of six phytocannabinoids (Δ9-THC, Δ8-tetrahydrocannabinol, cannabinol, cannabidiol, cannabigerol, and cannabichromene) by CYP2J2. CYP2J2 mainly produces 1′/1″-OH metabolites of these phytocannabinoids. These phytocannabinoids are metabolized with greater catalytic efficiency compared to the metabolism of AEA by CYP2J2. We have also determined that the phytocannabinoids are potent inhibitors of CYP2J2-mediated AEA metabolism, with Δ9-THC being the strongest inhibitor. Most of the inhibition of CYP2J2 by the phytocannabinoids follow a noncompetitive inhibition model, and therefore dramatically reduce the formation of EET-EAs by CYP2J2. Taken together, these data demonstrate that phytocannabinoids are directly metabolized by CYP2J2 and inhibit human cardiac CYP2J2, leading to a reduction in the formation of cardioprotective EET-EAs.
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The influence of Arginine 117 of human cytochrome P450 2J2 in the recognition of ebastine and a series of terfenadone derivatives was studied by site-directed mutagenesis. R117K, R117E, and R117L mutants were produced, and the behavior of these mutants in the hydroxylation of ebastine and terfenadone derivatives was compared to that of wild-type CYP2J2. The data clearly showed the importance of the formation of a hydrogen bond between R117 and the keto group of these substrates. The data were interpreted on the basis of 3D homology models of the mutants and of dynamic docking of the substrates in their active site. These modeling studies also suggested the existence of a R117-E222 salt bridge between helices B' and F that would be important for maintaining the overall folding of CYP2J2.
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Purpose ::: This study was undertaken to examine the MetaSite algorithm by comparing its predictions with experimentally characterized metabolites of statins produced by cytochromes P450 (CYPs).
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eng_Latn
| 31,134 |
Fluorescence spectra, ultraviolet spectra and protonation of Ofloxacin (OFL) at different pH values have been studied. In strong acidic solutions, OFL molecule might accept two protons to exist as ternary acid H3L2+ with a maximum emission wavelength (lambdamax) at 505 nm. Along with the increase in pH value, fluorescence spectrum of OFL changed, an iso-fluorescence point at 352 nm was found in the fluorescence excitation spectra, and at the same time, isosbestic points were found in its UV absorption spectra. This spectral feature reveals that H3L2+ gradually lost hydrogen ion combined on C-4 keto oxygen. In the range of pH 2.5 to pH 4, OFL exists as H2L+ with lambdamax at 499 nm. When pH>4, the fluorescence emission peak at 499 nm gradually blue-shifted to 455 nm as pH was increasing, and an iso-fluorescence emission point was formed at 484 nm, indicating the dissociation of hydrogen ion of carboxylic acid at C-3. At about pH 7.0, OFL exists in the dipole ion form HL with lambdamax at 455 nm, which is the strongest fluorescence form. When pH>8, lambdamax red-shift from 455 to 475 nm as pH increases, meanwhile, fluorescence intensity decreases, indicating that HL lost hydrogen ion combined on N-4 of piperazinyl group. When pH>10, OFL exists in anion ion form L-, and fluorescence intensity decreases with pH increasing, but lambdamax remains essentially constant, indicating that medium environment influences the fluorescence property of OFL.
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Fluorescence spectra of hymecromone (4MU) aqueous solutions are investigated at different pHs. Two fluorescent species of 4MU, neutral molecular form and anion form, are considered to be the main fluorescent forms. Quantum yields of the two forms are measured to be 0.74 at pH 5.98 and 0.95 at pH 9.75, respectively. The ionization constant of 7-hydroxyl proton of 4MU is determined to be by a pH-fluorescence method. Addition of methanol into 4MU aqueous solution leads to a blue shift of maximum emission wavelength from 445 nm to 380 nm, and a decrease in fluorescence intensity. 3D fluorescence spectra of Chinese patent drug Compound Dantong Capsule (CDC) and its four component herbal drugs are also investigated. Based on their fluorescent properties, a novel fluorimetric method is proposed for the selective determination of 4MU in CDC without preseparation. The new method is suitable for the routine quality evaluation of CDC.
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We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.
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eng_Latn
| 31,135 |
A simple and efficient synthesis of 1,4-bis(furo[2,3- d ]pyrimidine-2,4(1 H ,3 H )-dione-5-yl)benzene derivatives was achieved via a one-pot three-component reaction of isocyanides, N , N ′-dimethylbarbituric acid, and terephthaldialdehyde in DMF at room temperature for 30 min. These improved reaction conditions allow the preparation of highly substituted furopyrimidinones in high yields and purity under mild reaction conditions.
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The aim of this review is to provide an overview of the contributions and recent advances made by Iranian scientists in the field of isocyanide-based reactions between 1999 and 2009. With over 100 publications during this period, Iranians are responsible for approximately 10% of all publications in the world involving isocyanide-based multicomponent reactions (IMCRs). Some important aspects of these IMCRs include the execution of reactions in green reaction mediums like water or ethanol, high atom economies, mild reaction conditions, high yields, and catalyst-free processes. On the other hand, in most of these reactions, new classes of heterocyclic compounds with potential biological and medicinal activities have been reported.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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eng_Latn
| 31,136 |
We have obtained high‐resolution (∼1.5 cm−1) photoionization spectra of supersonically cooled (Trot∼50 K) H2O and D2O in the 1000–900 A range. The light source, which used the technique of frequency tripling in a pulsed free jet of gas, is described briefly. Spectra are rotationally resolved. Vibrationally excited autoionizing Rydberg series converging to the ground electronic [X; (1b1)−1] state of the molecular ion are detected. This may well be the first example of a highly resolved Rydberg spectrum of a stable polyatomic molecule. From the convergence limit, the ionization potential H2O is determined to be 101 777±7 cm−1. Intensities of the Rydberg state autoionization signals are smaller than predicted with known Franck–Condon factors, indicating that predissociation is a competitive decay channel. Rydberg state lifetimes are ∼1 ps, deduced from homogeneous linewidths. Autoionizing features from Rydberg states associated with the ion’s quasilinear A (3a1)−1 state are observed with linewidths above 1...
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Benzene cluster cations were revisited as a sensitive and selective reagent ion for the chemical ionization of dimethyl sulfide (DMS) and a select group of volatile organic compounds (VOCs). Laboratory characterization was performed using both a new set of compounds (i.e., DMS, β-caryophyllene) as well as previously studied VOCs (i.e., isoprene, α-pinene). Using a field deployable chemical-ionization time-of-flight mass spectrometer (CI-ToFMS), benzene cluster cations demonstrated high sensitivity (> 1 ncps ppt^(−1)) to DMS, isoprene, and α-pinene standards. Parallel measurements conducted using a chemical-ionization quadrupole mass spectrometer, with a much weaker electric field, demonstrated that ion–molecule reactions likely proceed through a combination of ligand-switching and direct charge transfer mechanisms. Laboratory tests suggest that benzene cluster cations may be suitable for the selective ionization of sesquiterpenes, where minimal fragmentation ( 0.95, 10 s averages) over a wide range of sampling conditions.
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In this short note we prove that if X is a separably rationally connected variety over an algebraically closed field of positive characteristic, then H^1(X, O_X)=0.
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eng_Latn
| 31,137 |
..beta..-cyclodextrin (CD) crystallizes from water in monoclinic space group P2/sub 1/. The crystal structure was initially determined from x-ray data. Neutron diffraction studies were carried out to determine the hydrogen-bonding schemes of ..beta..-CD, which are broken down into a few clearly defined motifs. This study again demonstrates that hydrogen-bonding schemes cannot be assigned with confidence if only oxygen atoms are located from x-ray diffraction data.
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The aim of the presented work is the comparison of aqueous and 1-octanol solubilities of different acyclovir derivatives and their hydroxypropyl-β-cyclodextrin inclusion complexes. The solubility measurements were carried out at different temperatures over the range 25–45 °C using water, 1-octanol, water saturated with 1-octanol, 1-octanol saturated with water, buffered aqueous solutions (pH = 5.5 and 7.0) and buffered aqueous solutions containing cyclodextrin as solvents. The aqueous solubilities of the compounds are very low but may be enhanced by complexation with hydroxypropyl-β-cyclodextrin, especially if the acyclovir derivatives have aromatic groups which may be included in the cyclodextrin cavity. The values of 1-octanol–water partition coefficients of acyclovir derivatives, obtained using extraction experiments, showed a similar sequence as the solubility results in 1-octanol. Additionally, some molecular mechanics and molecular dynamic calculations were performed to determine optimized structures of acyclovir derivative complexes with β-cyclodextrin treated as a model.
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ConspectusProviding energy for a population projected to reach 9 billion people within the middle of this century is one of the most pressing societal issues. Burning fossil fuels at a rate and scale that satisfy our near-term demand will irreversibly damage the living environment. Among the various sources of alternative and CO2-emission-free energies, the sun is the only source that is capable of providing enough energy for the whole world. Sunlight energy, however, is intermittent and requires an efficient storage mechanism. Sunlight-driven water splitting to make hydrogen is widely considered as one of the most attractive methods for solar energy storage. Water splitting needs a hydrogen evolution catalyst to accelerate the rate of hydrogen production and to lower the energy loss in this process. Precious metals such as Pt are superior catalysts, but they are too expensive and scarce for large-scale applications.In this Account, we summarize our recent research on the preparation, characterization, an...
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eng_Latn
| 31,138 |
Studies of unmasked and masked extractions of the uranyl bis(dibenzoylmethane) dibenzoylmethane chelate from aqueous solutions into chloroform containing dibenzoylmethane have been made. Aqueous media containing the following were studied: perchlorate, fluoride, acetate, oxalate, citrate, tartrate, nitrilotriacetate, ethylenediaminetetraacetate. A number of fundamental constants have been determined, these values allowing theoretical interpretations of several of the systems to be made.
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A novel and reversible optical sensor based on immobilization of 2,2′-(1,8-dihydroxy-3,6-disulfonaphthalene-2,7-bisazo) bisbenzenearsonic acid [arsenazo(III)] on a porous cellulosic polymer film as solid membrane support was developed and its application was considered in the determination of uranium(VI) in aqueous solutions. The procedure of immobilizing arsenazo on the membrane is useful for the fabrication of sensors using dye molecules that are unstable in ethylenediamine alkaline solution as the main solvent in preparation of optical sensors. The calibration curve was linear in the range of 0.01–4.00 μg mL−1 (3.70 × 10−8–1.48 × 10−5 mol L−1) of uranium in the sample solution, with a regression coefficient (r) of 0.9995. The detection limit (SNR = 3) was 0.006 μg mL−1 (2.20 × 10−8 mol L−1) and precision experiments resulted in good RSDs for both intra-day and inter-day precision. The proposed optical sensor can be successfully applied in the evaluation of this metal in different environmental water samples with satisfactory results.
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AcOH as the solvent……enables extraordinarily fast and effective palladium(II)-catalyzed direct intramolecularallylic aminations by assisting the benzoquinone-mediated palladium reoxidation andionization of the intermediate palladium complexes. For details see the Communicationby Poli et al. on page 11078 ff.
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eng_Latn
| 31,139 |
The photochemistry of thymidylyl-(3' leads to 5')- deoxycytidine (dTpdC) was studied as a model system of adjacent thymine and cytosine bases in DNA. Acetophenonesensitized irradiation causes the cytosine moiety in dTpdC to react with the thymine moiety intramolecularly. Three unstable photoproducts are formed initially which are converted into three isomeric dinucleoside phosphates of thymine-uracil cyclobutane photodimer in a ratio of 4.2:2.2:1. Under the same irradiation condition thymidylyl-(3' leads to 5')-thymidine (dTpdT) yields two products in a ratio of 6:1. The structures of these products are established by chemical and spectroscopic methods. The major product in these reactions has been identified as the stereoisomer which has the same anti,anti relationship between the pyrimidine rings and the deoxyribose group as in the parent dinucleoside phosphates. The efficiency of the intramolecular dimerization of dTpdC is about one-third that of dTpdT. The results suggest that the cytosine base in DNA may be converted to a uracil base via photodimerization with an adjacent pyrimidine base, hydrolysis, and photoreactivation.
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We reconstituted two biochemical processes that may contribute to UV-induced mutagenesis in vitro and analysed the mutational profiles in the products. One process is translesion synthesis (TLS) by DNA polymerases (Pol) δ, η and ζ, which creates C>T transitions at pyrimidine dimers by incorporating two dAMPs opposite of the dimers. The other process involves spontaneous deamination of cytosine, producing uracil in pyrimidine dimers, followed by monomerization of the dimers by secondary UV irradiation, and DNA synthesis by Pol δ. The mutational spectrum resulting from deamination without translesion synthesis is similar to a mutational signature found in melanomas, suggesting that cytosine deamination encountered by the replicative polymerase has a prominent role in melanoma development. However, CC>TT dinucleotide substitution, which is also commonly observed in melanomas, was produced almost exclusively by TLS. We propose that both TLS-dependent and deamination-dependent mutational processes are likely involved in UV-induced melanoma development.
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MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity.
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eng_Latn
| 31,140 |
Metals and metalloids are priority contaminants due to their non-degradable and bioaccumulative nature, and their ability to regulate and perturb diverse physiological processes in various species. Metal(loid)s are known to cause oxidative stress through production of reactive oxygen species (ROS), thus related endpoints like lipid peroxidation (LPO) have received considerable attention as biomarkers of exposure. However, the implications of metal(loid) toxicity including LPO on actual lipid profiles of species inhabiting contaminated systems are poorly understood. Here we applied Nuclear Magnetic Resonance (NMR) spectroscopy for untargeted lipidomics of mosquitofish (Gambusia holbrooki) collected from reference and metal(loid)-contaminated wetlands. We measured a range of trace elements in water and fish using inductively coupled plasma – mass spectrometry (ICP-MS), and interpreted site differences in the lipid profiles of mosquitofish in the context of known physiological responses to sub-lethal metal(loid) exposure. Results indicate deregulation of cellular membrane lipids (i.e., glycerophospholipids, cholesterol and sphingolipids) and increased energy storage molecules (i.e., triacylglycerols and fatty acids) in fish from the contaminated wetland. These responses are consistent with the recognised induction of oxidative stress pathways in organisms exposed to metal(loid)s and could also be symptomatic of mitochondrial dysfunction and endocrine disruption. It is difficult to attribute metal(loid)s as the sole factor causing differences between wetlands, and a more controlled experimental approach is therefore warranted to further explore mechanistic pathways. Nevertheless, our study highlights the benefits of untargeted 1H NMR-based lipidomics as a relatively fast and simple approach for field-scale assessment and monitoring of organisms inhabiting metal(loid) contaminated environments.
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Lipids are key molecules in various biological processes, thus their quantification is a crucial point in a lot of studies and should be taken into account in lipidomics development. This family is complex and presents a very large diversity of structures, so analyzing and quantifying all this diversity is a real challenge. In this review, the different techniques to analyze lipids will be presented: from nuclear magnetic resonance (NMR) to mass spectrometry (with and without chromatography) including universal detectors. First of all, the state of the art of quantification, with the definitions of terms and protocol standardization, will be presented with quantitative lipidomics in mind, and then technical considerations and limitations of analytical chemistry’s tools, such as NMR, mass spectrometry and universal detectors, will be discussed, particularly in terms of absolute quantification.
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Chemical looping combustion (CLC) and chemical looping reforming (CLR) are innovative technologies for clean and efficient hydrocarbon conversion into power, fuels, and chemicals through cyclic redox reactions. Metal oxide materials play an essential role in the chemical looping redox processes. During reduction, the oxygen carriers donate the required amount of oxygen ions for hydrocarbon conversion and product synthesis. In the oxidation step, the depleted metal oxide oxygen carriers are replenished with molecular oxygen from the air while heat is released. In recent years, there have been significant advances in oxygen carrier materials for various chemical looping applications. Among these metal oxide materials, iron-based oxygen carriers are attractive due to their high oxygen-carrying capacity, cost benefits, and versatility in applications for chemical looping reactions. Their reactivity can also be enhanced via structural design and modification. This review discusses recent advances in the development of oxygen carrier materials and the mechanisms of hydrocarbon conversion over these materials. These advances will facilitate the development of oxygen carrier materials for more efficient chemical looping technology applications.
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eng_Latn
| 31,141 |
Circular dichroism is known to be a very sensitive probe of the molecular conformation and implementation of this technique in a pump-probe experiment is very appealing to access information on the dynamics of conformational changes occurring in photochemical or photobiological processes. In the past years, we have developed such techniques in various ways and applied them to several chemical or biological studies which are presented in this article. Applications concern spectroscopic studies of the excited state in ruthenium tris(bipyridyl) or tris(phenanthroline), dynamics of conformational changes in photoexcited binaphthol and study of the conformational changes occurring in photolyzed carboxy-myoglobin. Extension of these techniques towards biological issues such as protein folding is discussed.
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Remembrance of Things Past: A Career in Chiroptical Research (J.T. Yang). Theory of Circular Dichroism of Proteins (R.W. Woody). Determination of Protein Secondary Structure (S.Y. Venyaminov, J.T. Yang). Aromatic and Cystine Sidechain Circular Dichroism in Proteins (R.W. Woody, A.K. Dunker). Stoppedflow Circular Dichroism (K. Kuwajima). Circular Dichroism of Collagen and Related Polypeptides (R.S. Bhatnagar, C.A. Gough). CD Spectroscopy and the Helixcoil Transition in Peptides and Polypeptides (N.R. Kallenbach et al.). The GBPIiGBP Sheet=Coil Transition of Polypeptides: As Determined by Circular Dichroism (L. Tilstra, W.L. Mattice). Turns (A. Perczel, M. Hollosi). Differentiation between Transmembrane Helices and Peripheral Helices by the Deconvolution of Circular Dichroism Spectra of Membrane Proteins (G.D. Fasman). Theories of Circular Dichroism for Nucleic Acids (D. Keller). Determination of the Conformation of Nucleic Acids by Electronic CD (W.C. Johnson, Jr.). Circular Dichroism of Proteinnucleic Acid Interactions (D.M. Gray). Carbohydrates (E.S. Stevens). Chaperones (G.D. Fasman). Vibrational Circular Dichroism: Applications to Conformational Analysis of Biomolecules (T.A. Keiderling). Circular Dichroism Using Synchrotron Radiation: From Ultraviolet to Xrays (J.C. Sutherland). Circular Dichroism Instrumentation (W.C. Johnson, Jr.). Vibrational Raman Optical Activity of Biomolecules (L.D. Barron et al.). 252 illustrations. Index.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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eng_Latn
| 31,142 |
In an attempt to shed light on how the addition of a benzothiadiazole (BTD) moiety influences the properties of dyes, a series of newly designed triphenylamine-based sensitizers incorporating a BTD unit as an additional electron-withdrawing group in a specific donor-acceptor-π-acceptor architecture has been investigated. We found that different positions of the BTD unit provided significantly different responses for light absorption. Among these, it was established that the further the BTD unit is away from the donor part, the broader the absorption spectra, which is an observation that can be applied to improve light-harvesting ability. However, when the BTD unit is connected to the anchoring group a faster, unfavorable charge recombination takes place; therefore, a thiophene unit was inserted between these two acceptors, providing redshifted absorption spectra as well as blocking unfavorable charge recombination. The results of our calculations provide valuable information and illustrate the potential benefits of using computation-aided sensitizer design prior to further experimental synthesis.
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The geometrical, conformational, and electronic properties of a series of D-π-A metal-free dyes designed for use as sensitizers in DSSCs were studied using DFT and TD-DFT methods. A substituted triphenylamine moiety was used as the donor group and 2-cyanoacrylic acid as the acceptor group in these dyes. They also contained conjugated bridging π-linker groups containing two or more thiophene rings to enhance the intramolecular charge transfer. The B3LYP, M06-HF, ωB97XD and CAM-B3LYP functionals were utilized in combination with the 6-31G(d,p) basis set for the calculations. The dye solvation process was taken into account via the polarizable continuum model. To rationalize the relationships between dye structure and the photochemical properties of the dyes when used as sensitizers in DSSCs, the vertical excitation energies, the light-harvesting efficiencies, the free-energy changes during the process of injecting an electron into the surface of a TiO2 nanocrystalline semiconductor, and the open-circuit potentials were calculated for all of the dyes in the solvent THF using the above methods. The results of these computations are discussed and compared with the available corresponding experimental data.
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ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system...
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eng_Latn
| 31,143 |
DDA3 regulates spindle microtubule (MT) dynamics and chromosome movement in mitosis through its interaction with and subsequent recruitment of Kif2a, a minus end-MT depolymerase. Depletion of DDA3 causes a hyper-stabilization of spindle MT, a loss of inter-kinetochore tension, and a defect in chromosome congression, leading to unaligned chromosomes at metaphase. We report here that DDA3 is also localized at kinetochores and interacts with MCAK. Furthermore, CENP-E, a plus end-motor protein, accumulates at kinetochores in unaligned chromosomes in mitotic cells depleted of DDA3. On the other hand, the localization of chromosomal passenger complex (CPC) and the kinase activity of Aurora B are normal in DDA3-depleted cells. We conclude that MCAK and CENP-E are involved in DDA3-mediated chromosome congression.
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Until recently, the knowledge of Aurora A kinase functions during mitosis was limited to pre-metaphase events, particularly centrosome maturation, G2/M transition, and mitotic spindle assembly. However, an involvement of Aurora A in post-metaphase events was also suspected, but not clearly demonstrated due to the technical difficulty to perform the appropriate experiments. Recent developments of both an analog specific version of Aurora A, and of small molecule inhibitors have led to the first demonstration that Aurora A is required for the early steps of cytokinesis. As in pre-metaphase, Aurora A plays diverse functions during anaphase, essentially participating in astral microtubules dynamics and central spindle assembly and functioning. The present review describes the experimental systems used to decipher new functions of Aurora A during late mitosis and situate these functions into the context of cytokinesis mechanisms.
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Graphitic carbon nitride (g-C3N4) is a photocatalyst with wide application in removal of organic pollutants. In this study, we designed a porous g-C3N4 (p-g-C3N4)/8-quinolinolato iron(III) (Q3Fe)/H2O2 system to enhance the organic pollutant removal efficiency by combining photocatalysis and Fenton interaction under neutral condition. The p-g-C3N4 was prepared through a two-step thermal oxidation reaction. Afterwards, Q3Fe-coupled p-g-C3N4 was prepared by an impregnating method. The 2,4-dichlorophenol (2,4-DCP) photodegradation ratio and decomposition rate of the p-g-C3N4/Q3Fe/H2O2 system are approximately 5 and 18 times as high as those of individual p-g-C3N4 system, respectively. Besides, its degradation rate is 4.3 times as high as that in the p-g-C3N4/H2O2 system. Meanwhile, Q3Fe/g-C3N4 also exhibits higher activity than individual p-g-C3N4 in 2,4-DCP photo-decomposing. On the basis of the results of the radical trapping experiments and the Fe(II) concentration in different systems, the synergistic effect between photocatalysis and Fenton reaction is vital for the efficient pollutant degradation. The coupled system combining p-g-C3N4 with Q3Fe and H2O2 shows potential for efficient treatment of recalcitrant organic pollutants. The combined system in this work indicated a new idea for the decomposition of organic pollutants.
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eng_Latn
| 31,144 |
The diffusion dynamics and enantiomeric structure of the alkyl-substituted isophthalic acid adlayer physisorbed on highly oriented pyrolytic graphite (HOPG) have been investigated in the vicinity of defect by scanning tunneling microscopy (STM). Through molecular motion and reorientation, the defect in the monolayer is filled and an ordered two-dimensional (2D) packing appears. Moreover, an enantiomeric structure is also observed. These findings can be explained by the role of molecular mobility and the cooperation of molecule/molecule and molecule/substrate interactions. The result provides experimental evidences for molecular diffusion and chirality in two dimensions.
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Since the invention of scanning tunneling microscopy (STM), 2D supramolecular architectures have been observed under various experimental conditions. The construction of these architectures arises from the balance between interactions at the medium-solid interface. This review summarizes molecular motion observed in 2D-supramolecular structures on surfaces using nanospace resolution STM. The observation of molecular motion on surfaces provides a visual understanding of intermolecular interactions, which are the major driving force behind supramolecular arrangement.
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There has been a renaissance of interest in the significance of enantiomeric composition in biological systems. Three chiral monoterpene alcohol aggregation pheromone components (ipsenol, ipsdienol, andcis-verbenol) commonly isolated from engraver beetles (Ips spp.) provide a paradigm for this theme as it relates to olfactory-guided insect behavior. The literature pertaining to this system is reviewed and the effects of the enantiomeric composition of these semiochemicals on theIps spp. community is explored on two trophic levels. Hypotheses generated from the well-studied aggregation pheromone production and response patterns forI. paraconfusus Lanier andI. pini (Say) are generalized to the North American species in the genus. Despite the progress withI. paraconfusus andI. pini, substantial deficiencies exist in our understanding of the role of enantiomeric composition in pheromonal/allomonal effects in different subgeneric groups, in the regulation and mechanisms of stereoselective biosynthesis of the monoterpene alcohols, and in the benefits derived by individual insects that produce relatively large proportions of inactive or interruptive enantiomers with attractive enantiomers.
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eng_Latn
| 31,145 |
In this study it was investigated the application of different potentials range and distinct light sources in the formation of Prussian blue (PB) on single walled carbon nanotubes (SWCNT) thin films. The carbonaceous films were deposited through liquid-liquid interface method, with posterior voltammetric cyclic technique been employed for PB deposition and consequent formation of the SWCNT/Prussian blue nanocomposite. The range of applied potential has a great influence on the amount of electrosynthesized PB nanocubes, with the potential window of −0.3 to 1.4 V leading to the maximum formation of product. The process of Prussian blue film formation is accelerated by both UVA, UVC and white light radiation. UVA radiation provided the best condition for hexacyanoferrate dissociation, with consequent increase in current and PB deposition. The Prussian Blue/SWCNT films were characterized by different spectroscopic, microscopic, and electrochemical techniques and exhibit high electrochemical stability.
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Microbial electrosynthesis (MES) is a promising bioelectrochemical approach to produce biochemicals. A previous study showed that Rhodopseudomonas palustris TIE-1 can directly use poised electrodes as electron donors for photoautotrophic growth at cathodic potentials that avoid electrolytic H2 production (photoelectroautotrophy). To make TIE-1 an effective biocatalyst for MES, we need to improve its electron uptake ability and growth under photoelectroautotrophic conditions. Because TIE-1 interacts with various forms of iron while using it as a source of electrons for photoautotrophy (photoferrotrophy), we tested the ability of iron-based redox mediators to enhance direct electron uptake. Our data show that soluble iron cannot act as a redox mediator for electron uptake by TIE-1 from a cathode poised at +100mV vs. Standard Hydrogen electrode. We then tested whether an immobilized iron-based redox mediator Prussian Blue (PB) can enhance electron uptake by TIE-1. Chronoamperometry indicates that cathodic current uptake by TIE-1 increased from 1.47 ± 0.04 to 5.6 ± 0.09 µA/cm2 (3.8 times) and the production of the bioplastic, polyhydroxybutyrate (PHB) improved from 13.5 ± 0.2 g/L to 18.8 ± 0.5 g/L (1.4 times) on electrodes coated with PB. Overall, our data show that immobilized PB can increase direct electron uptake by TIE-1 and enhances PHB production.
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ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system...
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eng_Latn
| 31,146 |
Surface-enhanced Raman scattering (SERS) spectra of a metal-complexing ligand, immobilized to a silver electrode surface, exhibits significant structural changes upon application of modest potentials. A detailed spectroscopic investigation shows that the potential applied to the electrode surface governs the tautomerization equilibrium of the immobilized ligand, p-((8-hydroxyquinoline)azo)benzenethiol (SHQ). Potential-dependent SERS spectra reveal that SHQ exists predominantly in a keto−hydrazone tautomeric form at applied potentials that are negative of −300 mV (vs Ag/AgCl), while the enol−azo tautomer is strongly favored at potentials positive of this value. The observed switching of the tautomer population occurs within a narrow range of applied potentials, ∼200 mV (Ag/AgCl). Electrical control over the tautomerization equilibrium of immobilized SHQ governs the reactivity of the ligand toward metal ion complexation, where the enol−azo tautomer exhibits much greater affinity for metal ion binding compar...
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In order to obtain an optimum scheme for separating the proton-transfer tautomer, a dynamic investigation into the effect of the external electric field on the proton-transfer tautomeric conversion in imidazole 3-oxide and 1-hydroxyimidazole was carried out at the M06-2X/6-311++G** and CCSD(T)/6-311++G(2d,p) level, accompanied by the analysis of the surface electrostatic potentials. The results show that, for both the forward reaction “imidazole 3-oxide → N-hydroxyimidazole free radical → 1-hydroxyimidazole” and its reverse reaction processes, the fields parallel to the N→O or N−OH bond axis affect the barrier heights and rate constants considerably more than those parallel to the other orientations. As the field strength is increased along the orientation from the O to N atom, the chemical equilibrium moves toward the direction for the formation of 1-hydroxyimidazole, while the amount of imidazole 3-oxide is increased with the increased field strength along the opposite orientation. In the fields along the orientation consistent with the dipole moment, the electrostatic potentials and their variances “abnormally” increase for the transition states with the N→O bond in comparison with those in no field (they decrease generally), which enhances the nucleophilicity of the coordination O atom and the electrophilicity of the activated H atom. The analyses of the AIM (atoms in molecules) and NICS (nucleus-independent chemical shift) were used to explain the above anomaly.
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We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.
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eng_Latn
| 31,147 |
Atmospheric particles are notorious for their effects on human health and visibility and are known to influence climate. Though sulfuric acid and ammonia/amines are recognized as main contributors to new particle formation (NPF), models and observations have indicated that other species may be involved. It has been shown that nucleation from methanesulfonic acid (MSA) and amines, which is enhanced with added water, can also contribute to NPF. While organics are ubiquitous in air and likely to be involved in NPF by stabilizing small clusters for further growth, their effects on the MSA-amine system are not known. This work investigates the effect of oxalic acid (OxA) on NPF from the reaction of MSA and methylamine (MA) at 1 atm and 294 K in the presence and absence of water vapor using an aerosol flow reactor. OxA and MA do not efficiently form particles even in the presence of water, but NPF is enhanced when adding MSA to OxA-MA with and without water. The addition of OxA to MSA-MA mixtures yields a modest NPF enhancement, whereas the addition of OxA to MSA-MA-H2O has no effect. Possible reasons for these effects are discussed.
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Ammonia and amines are important common trace atmospheric species that can enhance new particle formation (NPF) in the Earth's atmosphere. However, the synergistic effect of these two bases involving nucleation is still lacking. We studied the most stable geometric structures and thermodynamics of quaternary (NH3)(CH3NH2)(H2SO4) m(H2O) n ( m = 1-3, n = 0-4) clusters at the PW91PW91/6-311++G(3df,3pd) level of theory for the first time. We find that the proton transfer from H2SO4 molecule to CH3NH2 molecule is easier than to NH3 molecule in the free or hydrated H2SO4-base clusters, and thus leads to the stability. The energetically favorable formation of the (NH3)(CH3NH2)(H2SO4) m(H2O) n ( n = 0-4) clusters, by hydration or attachment of base or substitution of ammonia by methylamine at 298.15 K, indicate that ammonia and methylamine together could enhance the stabilization of small binary clusters. At low RH and an ambient temperature of 298.15 K, the concentration of total hydrated (NH3)(CH3NH2)(H2SO4)2 clusters could reach that of total hydrated (NH3)(H2SO4)2 clusters, which is the most stable ammonia-containing cluster. These results indicate that the synergistic effect of NH3 and CH3NH2 might be important in forming the initial cluster with sulfuric acid and subsequently growth process. In addition, the evaporation rates of (NH3)(CH3NH2)(H2SO4)(H2O), (NH3)(CH3NH2)(H2SO4)2 and (NH3)(CH3NH2)(H2SO4)3 clusters, three relative abundant clusters in (NH3)(CH3NH2)(H2SO4) m(H2O) n system, were calculated. We find the stability increases with the increasing number of H2SO4 molecules.
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Human immunodeficiency virus type 1 (HIV-1) is rapidly inactivated by exposure to a naturally occurring antimicrobial system consisting of peroxidase, H2O2, and a halide. Among the potential sources of H2O2 is the amine oxidase system in which mono-, di-, and polyamines are oxidatively deaminated with the formation of H2O2. The polyamine spermine is present at exceptionally high concentrations in semen. We report here that spermine, spermidine, and, to a lesser degree, the synthetic polyamine 15-deoxyspergualin are viricidal to HIV-1 when combined with amine oxidase and myeloperoxidase. Antiviral activity required each component of the spermine-amine oxidase-peroxidase system and was inhibited by azide (a peroxidase inhibitor) and by catalase but not by superoxide dismutase. Heat treatment of catalase largely abolished its inhibitory effect. These findings implicate H2O2 formed by the amine oxidase system in the antiviral effect and raise the possibility that the polyamine-amine oxidase-peroxidase system influences the survival of HIV-1 in semen and in the vaginal canal.
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eng_Latn
| 31,148 |
We have demonstrated that the simplest steady-state random sequential Bi Bi mechanism is sufficient to explain the previously reported non-hyperbolic kinetics of glutathione S-transferase 3-3 [Pabst MJ et al., J Biol Chem 249: 7140-7150, 1974; Jakobson I et al., Biochem J 177: 861-868, 1979]. The metabolism of 1-chloro-2,4-dinitrobenzene by rat liver glutathione S-transferase isoenzymes 2-2 and 3-3 and of 1,2-dichloro-4-nitrobenzene by isoenzyme 3-4 was shown to exhibit non-hyperbolic kinetics, which are best fit by the simplest steady-state random sequential Bi Bi mechanism. Neither more complex steady-state mechanisms nor the superimposition of product inhibition or enzyme memory on the simplest steady-state mechanism was necessary to generate non-hyperbolic kinetics for the glutathione S-transferases.
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PDZ domains function in nature as protein-binding domains within scaffold and membrane-associated proteins. They comprise approximately 90 residues and undergo specific, high-affinity interactions with complementary C-terminal peptide sequences, other PDZ domains, and/or phospholipids. We have previously shown that the specific, strong interactions of PDZ domains with their ligands make them well suited for use in affinity chromatography. This unit provides protocols for the PDZ affinity chromatography procedure that are applicable for the purification of proteins that contain PDZ domains or PDZ domain-binding ligands, either naturally or introduced by genetic engineering. We detail the preparation of affinity resins composed of PDZ domains or PDZ domain peptide ligands coupled to solid supports. These resins can be used to purify proteins containing endogenous or genetically introduced PDZ domains or ligands, eluting the proteins with free PDZ domain peptide ligands.
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The aim of this work was to characterize the methyl isocyanate hydrolysis reaction and to identify its operational criteria. The parametric sensitivity and dynamic stability methodologies were performed at the Bhopal disaster circumstances, over the relevant operating parameter space. Stable and unstable conditions, bifurcations points, turning points and oscillatory behavior were determined. The combined methodology give useful guidance on the operative conditions selection and the appropriate strategy to overcome hazardous situations. The obtained results demonstrated high sensitivity to small perturbations (thermal runaway) and prevalent oscillatory behavior. Moreover, the following critical parameters for the studied dynamic system were defined: the inverse residence time of 1.5700103 and the heat transfer coefficient of 752.394.
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eng_Latn
| 31,149 |
Deep eutectic solvent (DES)/lipase catalyzed efficient synthesis of N-aryl amines from electron deficient aryl chlorides and amines at ambient temperature is reported. Its significant features include excellent yields of products, use of biodegradable, non-toxic and recyclable catalysts, thereby avoiding toxic metal catalyst/solvents making these protocols environmentally benign.
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Biocatalysis is a green and sustainable technology for which the ideal solvent should be nontoxic, biocompatible, biodegradable, and sustainable, in addition to supporting high enzyme activity and stability. Deep eutectic solvents (DESs), a novel class of green solvents, have recently emerged as excellent alternatives for use in various biocatalytic reactions and, in particular, in lipase-catalyzed reactions with enzymes. This review discusses the achievements that have been made so far in the use of DESs as reaction media for lipase-catalyzed reactions. In addition, the application of DESs in esterification, transesterification, and amidation reactions with isolated or immobilized biocatalysts, toward enabling the synthesis of biodiesels, sugar esters, phenolipids, and fatty acyl ethanolamides, is summarized, while advances in lipase-catalyzed chemoenzymatic epoxidation reactions, C–C bond-forming Aldol reactions, and hydrolysis reactions in DESs are also discussed. This review also summarize some remaining questions concerning the use of DESs, including the intriguing role of water as a cosolvent in biocatalytic reactions carried out in DESs, and the relationship between the nature of the DESs and their influence on the enzyme stability and activity at the molecular level.
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Oxidative stress (OS) is thought to play an important role in the pharmacological and toxic effects of various drugs of abuse. Herein we review the literature on the mechanisms responsible for the cardiovascular and hepatic toxicity of cocaine with special focus on OS-related mechanisms. We also review the preclinical and clinical literature concerning the putative therapeutic effects of OS modulators (such as N-acetylcysteine, superoxide dismutase mimetics, nitroxides and nitrones, NADPH oxidase inhibitors, xanthine oxidase inhibitors, and mitochondriotropic antioxidants) for the treatment of cocaine toxicity. We conclude that available OS modulators do not appear to have clinical efficacy.
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eng_Latn
| 31,150 |
Nonthermal plasma-induced decomposition of ortho, meta, and para isomers of hydroxy-, chloro-, and nitrophenols in water was investigated using the hybrid series gas−liquid electrical discharge reactor that generates gas-phase discharge above the water surface simultaneously with the electrical discharge directly in the liquid. Degradation of substituted phenols was evaluated for two gas-phase compositions, pure argon and pure oxygen, above the aqueous solution. Removal of all phenols was found to follow first-order kinetics. Hydroquinone was the most reactive among substituted phenols under an oxygen atmosphere, whereas in argon the most reactive were 4-chlorophenol and 2-nitrophenol. Electrophilic attack by hydroxyl radicals and ozone were determined to be the main oxidation pathways for degradation of phenols in the hybrid series reactor under argon and oxygen atmospheres, respectively. Hydroxylated aromatic byproducts were identified during degradation of all substituted phenols under both gas-phase c...
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This study uses density functional theory (DFT) simulations to predict the main pathways by which hydroxyl (OH) radicals oxidize phenol into monohydroxylated products during an electrical discharge directly in or contacting water. The calculated activation energies and reaction rate constants indicate that phenol ring H abstraction is less likely to occur than OH addition, which will be the fastest in the ortho and para positions. The chain propagation with molecular oxygen of such formed ortho and para radicals will result in the production of hydroquinone and catechol, which are, concurrently, the most likely products of phenol degradation by OH radicals. Electron transfer reactions between dihydroxycyclohexadienyl radicals and plasma oxidative species are another important reaction mechanism which may be contributing significantly to the formation of products. Good agreement between computed kinetic and experimental data demonstrates the feasibility of applying DFT to investigate chemical reaction mechanisms.
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Nitro substituted picolinonitriles, in particular 3-nitro-picolinonitrile, have been found to be useful as anti-bacterial and anti-fungal agents.
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eng_Latn
| 31,151 |
A series of bone-targeting prodrugs, dendritic L-Asp and L-Glu peptides Naproxen conjugates have been synthesized in a convergent approach and well characterized by NMR and MS techniques. Their solubility in water and hydroxyapatite affinity were evaluated in in vitro conditions. All the prodrugs were water soluble and exhibited high affinity to HAP. Compound NAP-G(2)-Asp was found more potent in HAP binding. The efficient release of the active drug moiety (naproxen) occurred by the cleavage of an amide bond in physiological conditions. These results indicated that the dendritic peptides might become a delivery system for bone tissues and provided an effective entry to the development of new bone-targeting molecules.
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Prodrug design is a widely known molecular modification strategy that aims to optimize the physicochemical and pharmacological properties of drugs to improve their solubility and pharmacokinetic features and decrease their toxicity. A lack of solubility is one of the main obstacles to drug development. This review aims to describe recent advances in the improvement of solubility via the prodrug approach. The main chemical carriers and examples of successful strategies will be discussed, highlighting the advances of this field in the last ten years.
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Leakage of jet fuel from an oil skimmer has resulted in soil and groundwater contamination at the fire fighting training site of the Oslo international airport. The site is located on an unconfined sandy aquifer formed by the Gardermoen ice contact delta. A strong relationship between hydrogeological settings and spatial distribution of the hydrocarbons has been observed. Leaching hydrocarbons constitute a source of dissolved BTEX and naphthalene. Concentration of the dissolved hydrocarbons, electron acceptors and metabolic by-products has revealed concomitant changes in space and in time, in response to groundwater fluctuations. Correlation between high concentrations of hydrocarbons, elevated alkalinity and depleted electron acceptors supports the hypothesis that intrinsic bioremediation has been taking place at the site. Naphthalene, however, has been found persistent under anoxic conditions. Calculations of biodegradation potential indicates that Fe(III) reduction, methanogenesis, nitrate and sulphate reduction are the main factors controlling biodegradation.
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eng_Latn
| 31,152 |
The cysteine proteinase cathepsin B (EC 3.4.22.1) has been proposed to play an important role in the proteolytic mechanism of the ability of breast cancer cells to invade into and through normal tissues during metastasis. In this study, activity of cathepsin B was measured with a fluorometric microtiter plate assay in human breast tumors as well as in mammary gland dysplasias and in four human breast cancer cell lines (BT-20, MDA-MB-231, PMC42 and T47D). It was found that primary breast carcinomas and cystosarcomas phyllodes contain significantly higher levels of cathepsin B activity than mammary dysplasias; the activity of cathepsin B in cystosarcomas phyllodes was comparable with that in breast carcinomas. The enzyme from breast carcinoma tissue exhibited properties of a mature form of cathepsin B. All investigated breast cancer cell lines display positive cytochemical staining for cathepsin B activity with granular pattern of distribution of the final reaction product. Biochemically, the breast cancer cell lines differed significantly from each other in the level of cathepsin B activity decreasing in the following order: T47D, PMC42, MDA-MB-231 and BT-20.
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In the present work, we report the synthesis and systematic evaluation of differently substituted semicarbazones and thiosemicarbazones on lysosomal cysteine protease, cathepsin B [3.4.22.1]. Thiosemicarbazones have been found to inhibit cathepsin B activity to a greater extent than semicarbazones. Among the differently functionalized semicarbazones (1a–1j) and thiosemicarbazones (2a–2j), chloro-substituted compounds have been found to inhibit cathepsin B most effectively with the K i value of 1.16 × 10−4 and 1.48 × 10−5 M, respectively. The designed derivatives have been found to be competitive inhibitors to cathepsin B. The results of docking experiments also show a decrease in energy after ligand–enzyme active site interaction supporting the designed compounds as inhibitors to cathepsin B.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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eng_Latn
| 31,153 |
α-Chymotrypsin was lyophilized in the presence of 2,3,6-tri-O-methyl β-cyclodextrin, and it displayed activity 40 fold higher than free α-chymotrypsin for transesterification in acetonitrile. α-Chymotrypsin which was co-lyophilized with hydroxypropylated β- or γ-cyclodextrins retained more than 98% of its initial activity after 6 h incubation in acetonitrile.
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This article discusses the application of thermodynamic and related analysis to reaction systems for enzymic or whole cell catalysis, in which there are high proportions of organic liquid, gas, or supercritical fluid. A variety of predictions may be made, especially based on the partitioning of components between the different phases normally present. In many cases, observed behavior can be explained without invoking any direct molecular effects on the biocatalyst. The predictable changes should always be allowed for before seeking explanations for the residual effects, which are often very different from the crude observations. A summary of the general thermodynamics of multiphase systems is presented, and then the main classes of component that distribute between the phases are discussed in turn. Thermodynamic water activity (aw) determines the mass action effects of water on hydrolytic equilibria. It also describes the distribution of water between the various phases that can compete in binding water. Because catalytic activity is very sensitive to the hydration of the enzyme molecules, aw often predicts an unchanging optimum as other aspects of the system are changed. Hence the aw should be measured and/or controlled in these systems, whether the primary aim is to study the effects of water or of other changes. The methods available for measurement and control of aw are discussed. Adverse effects of organic solvents or similar nonpolar species partly reflect their tendency to partition into the relatively polar phase around the biocatalyst, especially when this is dilute aqueous. The well-established log P parameter is a measure of this. But other mechanisms of inactivation can occur: directly through contact of the biocatalyst with the phase interface, or indirectly via hydration changes. In these cases the molecular property log P is probably not the best solvent parameter. In low-water systems the biocatalyst remains in a separate phase even when water-miscible solvents are used. Hence, the categorization of solvents in terms of miscibility becomes less relevant. This accounts for the "two peak" dependence of catalytic activity on water content in some miscible systems. Differential solvation of reactants and products, as the bulk phase is altered, causes changes in concentration-based equilibrium constants and yields. These changes in solvation may be monitored through partition coefficient or solubility measurements. Reactant solvation can also account for differences in biocatalyst kinetics, whether or not partitioning into a dilute aqueous phase is involved. These predictable effects should be allowed for when studying effects of solvent or similar changes on activity or specificity.(ABSTRACT TRUNCATED AT 400 WORDS)
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MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity.
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eng_Latn
| 31,154 |
We report six tetrameric compounds synthesized via direct (hetero)arylation methods based on phthalimide, naphthalimide, and perylene diimide end groups with fused thiophene cores. Substitution at both the 2 and 3 positions of the thiophene building blocks is achieved using a standard set of reaction conditions. Each tetramer is fully characterized and analyzed using 1H and 13C NMR spectroscopy, elemental analysis, cyclic voltammetry, and optical absorption and emission spectroscopy. This work demonstrates an efficient method for synthesizing complex tetrameric materials for organic electronic applications.
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Major Symbols. Standard Abbreviations. Introduction and Overview of Electrode Processes. Potentials and Thermodynamics of Cells. Kinetics of Electrode Reactions. Mass Transfer by Migration and Diffusion. Basic Potential Step Methods. Potential Sweep Methods. Polarography and Pulse Voltammetry. Controlled--Current Techniques. Method Involving Forced Convention--Hydrodynamic Methods. Techniques Based on Concepts of Impedance. Bulk Electrolysis Methods. Electrode Reactions with Coupled Homogeneous Chemical Reactions. Double--Layer Structure and Adsorption. Electroactive Layers and Modified Electrodes. Electrochemical Instrumentation. Scanning Probe Techniques. Spectroelectrochemistry and Other Coupled Characterization Methods. Photoelectrochemistry and Electrogenerated Chemiluminescence. Appendix A: Mathematical Methods. Appendix B: Digital Simulations of Electrochemical Problems. Appendix C: Reference Tables. Index.
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MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity.
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eng_Latn
| 31,155 |
Singlet oxygen, created in photosensitization, peroxidizes unsaturated fatty acids of the membrane's lipids. This generates alcoholic or aldehyde groups at double bonds' breakage points. In a previous study, we examined the leakage of a K(+) -induced cross-membrane electric potential of liposomes that undergo photosensitization. The question remains to what extent peroxidized lipids can compromise the stability of the membrane. In this study, we studied the effect of the oxidatively modified lipids PGPC and ALDOPC in the membrane on its stability, by monitoring the membrane electric potential with the potentiometric dye DiSC(2)(5). As the content of the modified lipids increases the membrane becomes less stable, and even at just 2% of the modified lipids the membrane's integrity is affected, in respect to the leakage of ions through it. When the liposomes that contain the modified lipids undergo photosensitization by hematoporphyrin, the lipid bilayer becomes even more unstable and passage of ions is accelerated. We conclude that the existence of lipids with a shortened fatty acid that is terminated by a carboxylic acid or an aldehyde and more so when photosensitized damage occurs to unsaturated fatty acids in lecithin, add up to a critical alteration of the membrane, which becomes leaky to ions.
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Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.
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We characterize stability under composition, inversion, and solution of ordinary differential equations for ultradifferentiable classes, and prove that all these stability properties are equivalent.
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eng_Latn
| 31,156 |
New photolabile protecting groups have been found in the 2-(2-nitrophenyl)ethoxycarbonyl and the 2-(2-nitrophenyl)ethylsulfonyl group, respectively. The influence of substituents at the phenyl ring as well as the side-chain has been investigated regarding the photolysis rates on irradiation at 365 mn. β-Branching in the side-chain leads to highly increased rates of photodeprotection. A new type of photocleavage mechanism consisting of a photoinduced β-elimination process is proposed.
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BACKGROUND ::: DNA microarrays are a core element of modern genomics research and medical diagnostics, allowing the simple and simultaneous determination of the relative abundances of hundreds of thousands to millions of genomic DNA or RNA sequences in a sample. Photolithographic in situ synthesis, using light projection from a digitally-controlled array of micromirrors, has been successful at both commercial and laboratory scales. The advantages of this synthesis method are its ability to reliably produce high-quality custom microarrays with a very high spatial density of DNA features using a compact device with few moving parts. The phosphoramidite chemistry used in photolithographic synthesis is similar to that used in conventional solid-phase synthesis of oligonucleotides, but some unique differences require an independent optimization of the synthesis chemistry to achieve fast and low-cost synthesis without compromising microarray quality. ::: ::: ::: RESULTS ::: High microarray quality could be maintained while reducing coupling time to a few seconds using DCI activator. Five coupling activators were compared, which resulted in microarray hybridization signals following the order ETT > Activator 42 > DCI ≫ BTT ≫ pyridinium chloride, but only the use of DCI led to both high signal and highly uniform feature intensities. The photodeprotection time was also reduced to a few seconds by replacing the NPPOC photolabile group with the new thiophenyl-NPPOC group. Other chemical parameters, such as oxidation and washing steps were also optimized. ::: ::: ::: CONCLUSIONS ::: Highly optimized and microarray-specific phosphoramidite chemistry, along with the use of the very photosensitive thiophenyl-NPPOC protecting group allow for the synthesis of high-complexity DNA arrays using coupling times of 15 s and deprotection times of 9 s. The resulting overall cycle time (coupling to coupling) of about 50 s, results in a three-fold reduction in synthesis time.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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eng_Latn
| 31,157 |
Hypoxia is a feature of some regions of many tumours, ischaemic events, and arthritis. Drugs activated in hypoxia have wide potential application, particularly in overcoming the resistance of hypoxic tumour cells to radiotherapy. Key features of such drugs include redox properties appropriate for activation by reductase enzymes (typically flavoproteins), and oxygen-sensitive reduction chemistry such that normal levels of oxygen inhibit or reverse reduction. In many cases this selectivity is achieved by a fast, free-radical reaction in which the drug radical (often an obligate intermediate in drug reduction) reduces oxygen to form superoxide radicals and thus 'futile cycles' the drug in normoxic tissues. However, this enhances cellular oxidative stress, which may be linked to normal tissue toxicity. Appropriate redox properties are found with nitroarene, quinone, or aromatic N-oxide moieties. A particularly promising and versatile exploitation of bioreductive activation is for reduction of such triggers' to activate release of an 'effector', an agent that can obviously be active against diverse conditions associated with hypoxia. The same approach can also be used in diagnosis of hypoxia. Much information concerning the reactions of intermediates in drug action and the quantitative prediction of redox properties of analogues has been accrued. Drug design can be mechanism-led, with the wealth of literature quantifying redox properties of drug candidates a rich source of potential new leads. There is a clear appreciation of the kinetic factors that limit drug efficacy or selectivity. Thus the potential for rapid expansion of these concepts to diverse diseases is considerable.
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A potential approach for activating prodrugs in hypoxic regions of tumors is to use ionizing radiation, rather than bioreductive enzymes, to effect reduction. This study investigates radiolytic release of 8-hydroxyquinoline (8-HQ), as a model for hydroxyaza-chloromethylbenzindoline DNA minor groove alkylators, from Co(III) complexes under hypoxia. 8-HQ release, measured by HPLC, showed higher efficiency (one-electron stoichiometry) when the auxiliary ligand was a tetraazamacrocycle [e.g. 1,4,7,10-tetraazacyclododecane (cyclen)] rather than a triazamacrocycle [1,4,7-triazacyclononane (TACN)]. These complexes differ from the bioreductive cobalt complex SN 24771 in that their reduction provides stable cobalt-containing products rather than free (aquated) Co(2+). Radiolytic release of 8-HQ from Co(cyclen)(8-HQ) and Co(TACN)(CN)(8-HQ) was also demonstrated in deoxygenated human plasma, selectively in the absence of oxygen, again with higher efficiency for the cyclen system. The cobalt complexes were >1000-fold less potent than free 8-HQ as inhibitors of cell proliferation and were metabolically stable in aerobic and hypoxic cell cultures. Investigation of cell uptake of total cobalt, by inductively coupled plasma mass spectrometry, showed that these complexes enter cells but do not accumulate to the high concentrations seen with SN 24771. The results demonstrate the feasibility of masking the cytotoxicity of hydroxyquinoline-based cytotoxins as Co(III) complexes and demonstrate the utility of cyclen-based auxiliary ligands for optimizing radiolytic activation of these novel prodrugs under hypoxia.
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Impaired gastric motility ascribable to a defective nitric oxide (NO) production has been reported in dystrophic (mdx) mice. Since relaxin upregulates NO biosynthesis, its effects on the motor resp...
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eng_Latn
| 31,158 |
Novel mononuclear Zn(ii) 4, Co(ii) 5 and Cu(ii) 6 metallophthalocyanines have been synthesized from 4,4'(ethane-1,1-p-phenol-2,2-p-phenoxy)phthalonitrile 3, which can be obtained by the reaction of 4-nitrophthalonitrile 1 with 1,1,2,2-tetrakis(p-hydroxy-phenyl)-ethane 2. The target water-soluble derivatives of 7-9 were acquired from a boiling suspension of the compounds in aqueous 20% KOH solution. The synthesized complexes have been characterized by UV-vis, IR, (1)H NMR and MALDI-TOF-mass spectroscopies. In addition, the geometric and electronic structures of 2-6 were investigated by ab initio/DFT quantum mechanical calculations using the Gaussian 03 program with HF theory at the B3LYP/3-21G level. The redox properties of the complexes 4-6 were examined by cyclic voltammetry on platinum in DMSO/TBAP. These complexes displayed one-electron metallophthalocyanine-based and multi-electron hydroxyphenyl-based redox processes. The effect of temperature on the d.c. conductivity and impedance spectra of spin coated films of compounds were investigated at the temperatures between 300-452 K and in the frequency range of 40-105 Hz. Thermally activated conductivity dependence on temperature was observed for all compounds. A.c. results indicated that conduction mechanism can be explained by classical hopping barriers mechanism for all films.
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Partial table of contents: Synthesis and Chromatographic Separation of Tetrasubstituted and Unsymmetrically Substituted Phthalocyaniens Nonlinear Optical Properties and Applications of Phthalocyanines Chemical Fixation and Photoreduction of Carbon Dioxide Catalyzed by Metal Phthalocyanine Derivatives Zeolite Encapsulated Metallophthalocyanines Molecular Orbituals and Electronic Spectra of Phthalocyanine Analogues Radiolabelled Phthalocyanines for Imaging and Therapy Recent Developments in Photobiology of Phthalocyanines.
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Physicochemical properties of banana flour (BF) were studied in two varieties (Cavendish and Dream) and two stages of ripeness (green and ripe). BF's were analyzed for pH, total soluble solids (TSS), water holding capacity (WHC) and oil holding capacity (OHC) at 40 ℃, 60 ℃ and 80 ℃, color values L * , a * and b * , back extrusion force and viscosity. Physicochemical data were analyzed by Multivariate Analysis of Variance, discriminant analysis and cluster analysis. All statistical analyses showed that physicochemical properties of BF prepared from different variety and stage of ripeness were different from each other. Viscosity, WHC40, WHC60 and TSS were recommended methods for discrimination between banana flour prepared from the two varieties, whilst viscosity, WHC60 and WHC80 were suggested for differentiation of banana flour prepared using green and ripe banana.
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eng_Latn
| 31,159 |
In the replica-permutation method (RPM), temperatures are not only exchanged between two replicas but also permutated among more than two replicas using the Suwa–Todo algorithm, which minimizes the rejection ratio in Monte Carlo trials. We verify the sampling efficiency of RPM that adopts Suwa–Todo algorithms with and without a detailed balance condition (DBC). To compare these techniques, molecular dynamics simulations of RPM with and without the DBC and the replica-exchange method (REM) were carried out for a chignolin molecule in explicit water. Although no difference in the numbers of folding and unfolding events was observed, the numbers of tunneling events of the two RPM simulations were larger than that of REM. This indicates that the minimization of the rejection ratio by the Suwa–Todo algorithm in RPM realizes efficient sampling. Furthermore, the sampling efficiency was slightly higher in the RPM without the DBC than in that with the DBC. The reason for this difference is also discussed.
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The structure, topology and orientation of membrane-bound antibiotic alamethicin were studied using solid state nuclear magnetic resonance (NMR) spectroscopy. (13)C chemical shift interaction was observed in [1-(13)C]-labeled alamethicin. The isotropic chemical shift values indicated that alamethicin forms a helical structure in the entire region. The chemical shift anisotropy of the carbonyl carbon of isotopically labeled alamethicin was also analyzed with the assumption that alamethicin molecules rotate rapidly about the bilayer normal of the phospholipid bilayers. It is considered that the adjacent peptide planes form an angle of 100° or 120° when it forms α-helix or 310-helix, respectively. These properties lead to an oscillation of the chemical shift anisotropy with respect to the phase angle of the peptide plane. Anisotropic data were acquired for the 4 and 7 sites of the N- and C-termini, respectively. The results indicated that the helical axes for the N- and C-termini were tilted 17° and 32° to the bilayer normal, respectively. The chemical shift oscillation curves indicate that the N- and C-termini form the α-helix and 310-helix, respectively. The C-terminal 310-helix of alamethicin in the bilayer was experimentally observed and the unique bending structure of alamethicin was further confirmed by measuring the internuclear distances of [1-(13)C] and [(15)N] doubly-labeled alamethicin. Molecular dynamics simulation of alamethicin embedded into dimyristoyl phophatidylcholine (DMPC) bilayers indicates that the helical axes for α-helical N- and 310-helical C-termini are tilted 12° and 32° to the bilayer normal, respectively, which is in good agreement with the solid state NMR results.
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Ultrawideband radar with high-range resolution is a promising technology for use in short-range 3-D imaging applications, in which optical cameras are not applicable. One of the most efficient 3-D imaging methods is the range-point migration (RPM) method, which has a definite advantage for the synthetic aperture radar approach in terms of computational burden, high accuracy, and high spatial resolution. However, if an insufficient aperture size or angle is provided, these kinds of methods cannot reconstruct the whole target structure due to the absence of reflection signals from large part of target surface. To expand the 3-D image obtained by RPM, this paper proposes an image expansion method by incorporating the RPM feature and fully polarimetric data-based machine learning approach. Following ellipsoid-based scattering analysis and learning with a neural network, this method expresses the target image as an aggregation of parts of ellipsoids, which significantly expands the original image by the RPM method without sacrificing the reconstruction accuracy. The results of numerical simulation based on 3-D finite-difference time-domain analysis verify the effectiveness of our proposed method, in terms of image-expansion criteria.
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eng_Latn
| 31,160 |
A selection of bolaamphiphilic perylene bisimides (PBI) were prepared from the reaction of perylenetetracarboxylic dianhydride with α-amino acids. These molecules were obtained in good yield using a simple synthetic protocol and avoiding the need for complex purification methods, a major advantage for future applications. Carbon nanotubes (CNT) were dispersed in an aqueous solution of the PBI, buffered at pH 7, and the suspension was studied by absorption and emission spectroscopy. PBI functionalized with Boc-lysine and phenylalanine led to an excellent suspension of CNT in water, stable for at least 24 h at room temperature. Theoretical calculations were used to support and explain the experimental observations.
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Perylene bisimides (PBIs) are one example of useful π-conjugated molecules that can be used in optoelectronic devices as n-type materials with strong visible light absorption. PBIs can self-assemble into a range of structures, but it is rare to be able to control the packing such that the same PBI can form either H-type or J-type aggregates. This is important because the conductivity pathways and optoelectronic properties are directly affected by this packing. Here, we show that we can control the packing of a single PBI functionalized with an amino acid by a subtle change in pH. Under one set of conditions, H-type aggregates form a gel when the pH is decreased. At a slightly different set of starting conditions, J-type aggregates are formed, but they cannot form a gel when the pH is lowered. We show that films formed from the self-assembled structures have very different photoconductive properties.
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Pyrus pyrifolia (Asian pear) cell cultures respond to yeast extract (YE) treatment by accumulating benzoate-derived biphenyl phytoalexins, namely, noraucuparin and aucuparin. Biphenyl phytoalexins are defense-marker metabolites of the sub-tribe Malinae of the family Rosaceae. The substrates for biphenyl biosynthesis are benzoyl-CoA and malonyl-CoA, which combine in the presence of biphenyl synthase (BIS) to produce 3,5-dihydroxybiphneyl. In the non-β-oxidative pathway, benzoyl-CoA is directly derived from benzoic acid in a reaction catalyzed by benzoate-CoA ligase (BZL). Although the core β-oxidative pathway of benzoic acid biosynthesis is well-understood, the complete cascade of enzymes and genes involved in the non-β-oxidative pathway at the molecular level is poorly understood. In this study, we report the detection of benzaldehyde dehydrogenase (BD) activity in YE-treated cell cultures of P. pyrifolia. BD catalyzes the conversion of benzaldehyde to benzoic acid. BD and BIS activities were coordinately induced by elicitor treatment, suggesting their involvement in biphenyl metabolism. Changes in phenylalanine ammonia-lyase (PAL) activity preceded the increases in BD and BIS activities. Benzaldehyde was the preferred substrate for BD (Km=52.0μM), with NAD+ being the preferred co-factor (Km=64μM). Our observations indicate the contribution of BD towards biphenyl phytoalexin biosynthesis in the Asian pear.
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eng_Latn
| 31,161 |
An ultrasound-assisted synthesis of functionalized vinylic chlorides is described by palladium-catalyzed cross-coupling reaction of potassium aryltrifluoroborate salts and (Z)-2-chloro vinylic tellurides. This procedure offers easy access to vinylic chlorides architecture that contains sterically demanding groups in good yields.
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This chapter highlights the utility of electrophilic achiral and chiral organoselenium reagents in organic synthesis. A range of reactions from alkene functionalizations, the functionalization of aliphatic and aromatic C–H bonds using stoichiometric and catalytic approaches as well as rearrangement reactions are described. In addition, the utility of organotellurium reagents in organic synthesis is covered in this chapter.
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Accurate classification of gases/odors is a classical challenge. Gas sensor arrays are generally used to enhance classification accuracy as they generate unique signature patterns for each individual gas/odor sample. However, instead of using these raw signatures directly, analyzing these signatures in certain hyperspaces also improves classification results. Most of the clusters created using existing transformations and normalization techniques are usually non-spherical and overlapping, leading to ambiguous classification results. In this paper, a new transformation called normalized difference sensor response transformation has been proposed. Here, virtual multi-sensor responses are generated from raw signature responses. These virtual responses show unambiguous association between data belonging to respective gases/odors. In addition, the signatures generated from virtual responses are grossly concentration independent, which further enhances the accuracy of classification. Experiments were conducted by using a thick-film four-element gas sensor array for four hazardous gases viz., acetone, carbon tetrachloride (CCl4), ethyl methyl ketone, and xylene. The results show cluster compaction by an average of 94.38% in terms of intra-cluster distance with respect to raw sensor responses. In addition, when compared with existing techniques, only the proposed transformation could generate non-overlapping clusters. Furthermore, minimum inter-cluster separation was 0.80 units.
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eng_Latn
| 31,162 |
In the last decade and a half, numerous bioorthogonal reactions have been developed with a goal to study biological processes in their native environment, i.e., in living cells and animals. Among them, the photo-triggered reactions offer several unique advantages including operational simplicity with the use of light rather than toxic metal catalysts and ligands, and exceptional spatiotemporal control through the application of an appropriate light source with pre-selected wavelength, light intensity and exposure time. While the photoinduced reactions have been studied extensively in materials research, e.g., on macromolecular surface, the adaptation of these reactions for chemical biology applications is still in its infancy. In this chapter, we review the recent efforts in the discovery and optimization the photo-triggered bioorthogonal reactions, with a focus on those that have shown broad utility in biological systems. We discuss in each cases the chemical and mechanistic background, the kinetics of the reactions and the biological applicability together with the limiting factors.
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Labeling of a protein with a specific dye or tag at defined positions is a critical step in tracing the subtle behavior of the protein and assessing its cellular function. Over the last decade, many strategies have been developed to achieve selective labeling of proteins in living cells. In particular, the site-specific unnatural amino acid (UAA) incorporation technique has gained increasing attention since it enables attachment of various organic probes to a specific position of a protein in a more precise way. In this review, we describe how the UAA incorporation technique has expanded our ability to achieve site-specific labeling and visualization of target proteins for functional analyses in live cells.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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eng_Latn
| 31,163 |
A fluorimetric method for the determination of low levels of theophylline based on the inhibition of the enzyme activity of alkaline phosphatase is proposed. The approach used is a flow-injection configuration where bovine alkaline phosphatase is immobilized on controlled pore glass. The enzymatic reaction is based on the hydrolysis of 4-methylumbelliferone phosphate with fluorimetric monitoring of the 4-methylumbelliferone formed at λ ex = 365 nm and λ em = 445 nm. The presence of theophylline in the samples inhibits the catalytic effect of alkaline phosphatase. The linear determination range was found to be between 0.1 and 200 μmol l −1 , with a relative standard deviation
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A single-step end point method is presented for determination of the activity of the enzyme alkaline phosphatase (ALP) using the effect of enhancement of fluorescence of the easily accessible europium(III)-tetracycline 3:1 complex (Eu 3 TC). Its luminescence, peaking at 616 nm if excited at 405 nm, is enhanced by a factor of 2.5 in the presence of phosphate. Phenyl phosphate was used as a substrate that is enzymatically hydrolyzed to form phenol and phosphate. The latter coordinates to Eu 3 TC and enhances its luminescence intensity as a result of the displacement of water from the inner coordination sphere of the central metal. The assay is performed in a time-resolved (gated) mode, which is shown to yield larger signal changes than steady-state measurement of fluorescence. The limit of detection for ALP is 4 μmol L –1 . Based on this scheme, a model assay for theophylline as inhibitor for ALP was developed with a linear range from 14 to 68 μmol L –1 of theophylline. (Journal of Biomolecular Screening 2008:9-16)
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Alcohols and alkenes are the most abundant and commonly used organic building blocks in the large-scale chemical synthesis. Herein, this is the first time to report a novel and operationally simple coupling reaction of vinylarenes and aliphatic alcohols catalyzed by manganese in the presence of TBHP (tert-butyl hydroperoxide). This coupling reaction provides the oxyalkylated products of vinylarenes with good regioselectivity and accomplishes with the principles of step-economies. A possible reaction mechanism has also been proposed.
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| 31,164 |
The chemoselective formation of trialkyl(benzylidene) ylides in water and their Wittig reaction with aromatic and aliphatic aldehydes provides a practical, stereoselective and environmentally benign route to valuable (E)-stilbenes and alkenes. The synthesis of the phytoalexin resveratrol is described. In addition, the method allows for a gram-scale synthesis of the anticancer agent DMU-212 utilizing no organic solvent at any stage. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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Control of positional selectivity in C–H activation reactions remains a challenge for synthetic chemists. Noncovalent catalysis has the potential to be a powerful strategy to address this challenge. As a part of our ongoing investigations into the use of ion-pairing interactions in site-selective catalysis, we demonstrate that several classes of aromatic phosphonium salts undergo iridium-catalyzed C–H borylation with a high selectivity for the arene meta position. This is achieved using a bifunctional bipyridine ligand bearing a pendant sulfonate group, which had previously been successful for borylation of aromatic ammonium salts. In this case, the phosphonium salts give a higher meta selectivity than the corresponding ammonium salts. We propose that the high selectivity occurs due to an attractive electrostatic interaction between the substrate and the ligand in the transition state for borylation.
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Beta-amyloid peptide is considered to be responsible for the formation of senile plaques that accumulate in the brains of patients with Alzheimer’s disease. There has been compelling evidence supporting the idea that β-amyloid-induced cytotoxicity is mediated through the generation of reactive oxygen intermediates (ROIs). Considerable attention has been focused on identifying phytochemicals that are able to scavenge excess ROIs, thereby protecting against oxidative stress and cell death. Resveratrol (3,5,4′-trihydroxy-trans-stilbene), a phytoalexin found in the skin of grapes, has strong antioxidative properties that have been associated with the protective effects of red wine consumption against coronary heart disease (“the French paradox”). In this study, we have investigated the effects of resveratrol on β-amyloid-induced oxidative cell death in cultured rat pheochromocytoma (PC12) cells. PC12 cells treated with β-amyloid exhibited increased accumulation of intracellular ROI and underwent apoptotic death as determined by characteristic morphological alterations and positive in situ terminal end-labeling (TUNEL staining). Beta-amyloid treatment also led to the decreased mitochondrial membrane potential, the cleavage of poly(ADP-ribose)polymerase, an increase in the Bax/Bcl-XL ratio, and activation of c-Jun N-terminal kinase. Resveratrol attenuated β-amyloid-induced cytotoxicity, apoptotic features, and intracellular ROI accumulation. Beta-amyloid transiently induced activation of NF-κB in PC12 cells, which was suppressed by resveratrol pretreatment.
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| 31,165 |
A simple, robust and high-yielding process for the preparation of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium tetrafluoroborate (DMTMM BF 4 ) and hexafluorophosphate (DMTMM PF 6 ) has been developed, which avoids the use of expensive or unusual reagents.
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The activation of carboxyl groups with N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide (EDC/NHS) for amide formation is the standard method for amine ligation to hyaluronan (HA), and a very well established wide-ranging bioconjugation method. In this paper we compare 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM) to EDC/NHS activation chemistry for HA ligation using an array of substrates including small, large and functional molecules. For all the substrates tested DMTMM yields were superior at parity of feed ratio. DMTMM chemistry resulted effective also in absence of pH control, which is essential for EDC/NHS conjugation. Overall our results demonstrate that DMTMM is more efficient than EDC/NHS for ligation of amines to HA and does not require accurate pH control or pH shift during the reaction to be effective. DMTMM-mediated ligation is a new promising chemical tool to synthesize HA derivatives for biomedical and pharmaceutical applications.
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The photochemical reactivity of three ionic liquids (1-ethylpyridinium tetrafluoroborate, 1-butyl-4-methylpyridinium tetrafluoroborate, and 1-(3-cyanopropyl)pyridinium chloride) was studied by combining laboratory experiments and photochemical modeling, to get insight into the possible behavior in surface-water environments. Among the studied compounds, phototransformation in sunlit surface waters could be an important attenuation pathway for 1-butyl-4-methylpyridinium tetrafluoroborate (BMPOTFB). In this case the reaction with the carbonate radicals (CO3-) would prevail at low values of the dissolved organic carbon (DOC), while the direct photolysis would be important at intermediate to high DOC values. The sensitization by the triplet states of chromophoric dissolved organic matter could play a significant role at high DOC, especially in the presence of a considerable fraction of highly photoreactive pedogenic organic matter derived from soil runoff. The main processes that account for the phototransformation of BMPOTFB and produce the main detected transformation products (TPs) are hydroxylation, detachment/shortening of the butyl chain and double bond formation. Interestingly, there is a considerable overlap between the TPs formed by direct photolysis and those produced by indirect photochemistry. Some of the TPs formed from BMPOTFB are more toxic than the parent compound towards Vibrio fischeri bacteria, and account for the increase in toxicity of the irradiated mixtures. Differently from BMPOTFB, in the case of the other two studied ionic liquids the photodegradation would play a negligible role in environmental attenuation, with the possible exception of very shallow waters with low DOC.
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| 31,166 |
Bi nanoparticles are grown on BiOCl nanosheets via an in situ chemical reduction in a KBH4 aqueous solution. Bi/BiOCl nanosheets with different contents of Bi nanoparticles can be achieved by changing the concentration of the KBH4 solution. The structure, morphology, elemental composition and optical absorption performance are characterized using an X-ray diffraction diffractometer, a scanning electron microscope, a high resolution transmission electron microscope, an X-ray photoelectron spectrometer and a UV-Vis diffuse reflection spectrometer. The photocatalytic activities of the as-prepared photocatalysts are tested using the degradation of methyl orange under both UV light and visible light irradiation. Bi nanoparticles modified on BiOCl nanosheets not only enhance the photocatalytic activity under UV light irradiation, but also achieve visible light photocatalytic activity. The mechanism of the photocatalytic processes, such as optical absorption, charge transfer and surface reactions, for the Bi/BiOCl nanosheets are discussed in detail.
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In this work, a series of flower-like Bi/BiOClxBr(1−x) heterojunction photocatalysts have been developed. Bi nanoparticles were grown on the BiOClxBr(1−x) nanosheets via an in situ chemical reduction with the assistance of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide aqueous solution. The in situ growth of Bi nanoparticles on the BiOClxBr(1−x) nanosheets could not only give rise to the optical absorption in the visible region, but also promote the photocatalytic performance of BiOClxBr(1−x). Bi/BiOCl0.8Br0.2 exhibited the highest photocatalytic performance, which could completely degrade RhB in 12 min under the UV light irradiation and 6 min under visible light irradiation, respectively. Moreover, holes and superoxide radicals were verified to be the primarily active species in the photocatalytic process.
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In this work, a series of flower-like Bi/BiOClxBr(1−x) heterojunction photocatalysts have been developed. Bi nanoparticles were grown on the BiOClxBr(1−x) nanosheets via an in situ chemical reduction with the assistance of cetyltrimethylammonium chloride and cetyltrimethylammonium bromide aqueous solution. The in situ growth of Bi nanoparticles on the BiOClxBr(1−x) nanosheets could not only give rise to the optical absorption in the visible region, but also promote the photocatalytic performance of BiOClxBr(1−x). Bi/BiOCl0.8Br0.2 exhibited the highest photocatalytic performance, which could completely degrade RhB in 12 min under the UV light irradiation and 6 min under visible light irradiation, respectively. Moreover, holes and superoxide radicals were verified to be the primarily active species in the photocatalytic process.
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| 31,167 |
The anticonvulsant drug mephenytoin is available as a racemic mixture of the S and R enantiomers. The S enantiomer is selectively 4'-hydroxylated in the liver by the cytochrome P450 enzyme, CYP2C19. This reaction has a polymorphic distribution in human populations. Racemic mephenytoin has been extensively used as a probe drug to assign metabolic phenotypes for this genetically-determined polymorphism. Specific base substitution mutations in the CYP2C19 gene are responsible for the poor metabolism (PM) phenotype which is inherited as a recessive autosomal trait. The poor metabolizers (PMs) of S-mephenytoin are homozygous for these mutations. In contrast, extensive metabolizers (EMs) are either heterozygous or homozygous for the wild-type allele(s). Poor metabolizers have the inactive enzyme and therefore have reduced ability to metabolize substrates of CYP2C19, many of which are psychotropic drugs. Genotyping an individual before treatment with substrates of CYP2C19 will reduce the risk of side effects and improve compliance in PMs. The prevalence of PMs is relatively low in African-Americans and Caucasians and is as high as 20 percent in Asian populations.
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Objective ::: To investigate whether urinary proguanil (chlorguanide) metabolite ratios incorporating its minor metabolite, 4-chlorophenylbiguanide, define individuals as extensive metabolisers (EMs) or poor metabolisers (PMs) of CYP2C19 more reliably than the standard phenotyping ratio [proguanil/cycloguanil (PG/CG)].
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A new generation of porous polymer networks has been obtained in quantitative yield by reacting two rigid trifunctional aromatic monomers (1,3,5-triphenylbenzene and triptycene) with two ketones having electron-withdrawing groups (trifluoroacetophenone and isatin) in superacidic media. The resulting amorphous networks are microporous materials, with moderate Brunauer-Emmett-Teller surface areas (from 580 to 790 m2 g-1), and have high thermal stability. In particular, isatin yields networks with a very high narrow microporosity contribution, 82% for triptycene and 64% for 1,3,5-triphenylbenzene. The existence of favorable interactions between lactams and CO2 molecules has been stated. The materials show excellent CO2 uptakes (up to 207 mg g-1 at 0 °C/1 bar) and can be regenerated by vacuum, without heating. Under postcombustion conditions, their CO2/N2 selectivities are comparable to those of other organic porous networks. Because of the easily scalable synthetic method and their favorable characteristics, these materials are very promising as industrial adsorbents.
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| 31,168 |
he fluorescence yield of chlorophyll a in dark adapted Anacystis nidulans undergoes a slow change with continuous illumination. After the completion of the initial fast transient, the fluorescence yield rises from the level S to a plateau M within a minute, declining only after prolonged illumination. Both normal and 1,1-dimethyl-3(3'4'-dichloro)-phenylurea (DCMU)-poisoned Anacystis are capable of these changes. In normal Anacystis, the slow increase in the fluorescence yield (S --> M) requires light absorbed in system II while light absorbed in system I is ineffective. In DCMU-poisoned Anacystis, however, these changes are also promoted by light absorbed in system I. Addition of carbonyl cyanide p-trifluoromethoxy phenylhydrazone (FCCP), a photophosphorylation uncoupler acting near the photosynthetic electron transport chain, abolishes the rise from S to M in normal but has no effect in the DCMU-poisoned system. Phlorizin, a phosphorylase inhibitor, has very little effect. These results suggest that the light-induced variation in the fluorescence yield is related to the conformational changes which accompany photophosphorylation. The fluorescence yield of the auxiliary pigment phycocyanin remains constant throughout the interval of the light-induced changes in the fluorescence yield of chlorophyll a. Consequently, the fluorescence spectrum of the alga is variable on continuous illumination.
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This review is dedicated to David Walker (1928–2012), a pioneer in the field of photosynthesis and chlorophyll fluorescence. We begin this review by presenting the history of light emission studies, from the ancient times. Light emission from plants is of several kinds: prompt fluorescence (PF), delayed fluorescence (DF), thermoluminescence, and phosphorescence. In this article, we focus on PF and DF. Chlorophyll a fluorescence measurements have been used for more than 80 years to study photosynthesis, particularly photosystem II (PSII) since 1961. This technique has become a regular trusted probe in agricultural and biological research. Many measured and calculated parameters are good biomarkers or indicators of plant tolerance to different abiotic and biotic stressors. This would never have been possible without the rapid development of new fluorometers. To date, most of these instruments are based mainly on two different operational principles for measuring variable chlorophyll a fluorescence: (1) a PF signal produced following a pulse-amplitude-modulated excitation and (2) a PF signal emitted during a strong continuous actinic excitation. In addition to fluorometers, other instruments have been developed to measure additional signals, such as DF, originating from PSII, and light-induced absorbance changes due to the photooxidation of P700, from PSI, measured as the absorption decrease (photobleaching) at about 705 nm, or increase at 820 nm. In this review, the technical and theoretical basis of newly developed instruments, allowing for simultaneous measurement of the PF and the DF as well as other parameters is discussed. Special emphasis has been given to a description of comparative measurements on PF and DF. However, DF has been discussed in greater details, since it is much less used and less known than PF, but has a great potential to provide useful qualitative new information on the back reactions of PSII electron transfer. A review concerning the history of fluorometers is also presented.
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The emergence of superbugs that are resistant to last-resort antibiotics poses a serious threat to human health, and we are in a “race against time to develop new antibiotics.” New approaches are urgently needed to control drug-resistant pathogens, and to reduce the emergence of new drug-resistant microbes. Targeting bacterial virulence has emerged as an important strategy for combating drug-resistant pathogens. It has been shown that pyocyanin, which is produced by the phenazine biosynthesis pathway, plays a key role in the virulence of Pseudomonas aeruginosa infection, making it an attractive target for anti-infective drug discovery. In order to discover efficient therapeutics that inhibit the phenazine biosynthesis in a timely fashion, we screen 2004 clinical and pre-clinical drugs to target multiple enzymes in the phenazine biosynthesis pathway, using a novel procedure of protein–ligand docking. Our detailed analysis suggests that kinase inhibitors, notably Lifirafenib, are promising lead compounds for inhibiting aroQ, phzG, and phzS enzymes that are involved in the phenazine biosynthesis, and merit further experimental validations. In principle, inhibiting multiple targets in a pathway will be more effective and have less chance of the emergence of drug resistance than targeting a single protein. Our multi-target structure-based drug design strategy can be applied to other pathways, as well as provide a systematic approach to polypharmacological drug repositioning.
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| 31,169 |
Highly hindered magnesium and metal-free green 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecaneopentoxyphthalocyanine and 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadeca(cyclohexylmethyloxy)phthalocyanine were prepared via magnesium 1-octanolate and 3,4,5,6-tetraneopentoxyphthalonitrile or 3,4,5,6-tetra(cyclohexylmethyloxy)phthalonitrile. Treatment of the metal-free phthalocyanine with Mn(OAc)2 yielded deep red manganese(III) hexadecaalkoxy phthalocyanines. Electrochemical and spectroelectrochemical studies led to the characterization, in solution, of a series of species in a range of different manganese and phthalocyanine oxidation states.
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Photophysical and photochemical measurements have been made on a series of novel alpha octa(alkyl-substituted) silicon, zinc and palladium phthalocyanines for which the synthesis is outlined. Fluorescence quantum yields and lifetimes, triplet quantum yields and lifetimes and singlet delta oxygen quantum yields were measured in 1% v/v pyridine in toluene. The effects of varying central atom and addition of alkyl substituents relative to unsubstituted parent molecules, zinc phthalocyanine (ZnPc) and silicon phthalocyanine (SiPc), are discussed. All phthalocyanines studied exhibit absorption and emission maxima in the region of 680–750 nm with molar absorptivity of the Q-band ∼105 M−1 cm−1. The series of compounds also exhibited triplet quantum yields of 0.65–0.95 and singlet oxygen quantum yields of 0.49–0.93.
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ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system...
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| 31,170 |
This study focuses on the understanding of the interaction of phenothiazinium dyes methylene blue (MB), new methylene blue (NMB), azure A (AZA) and azure B (AZB) with tRNAPhe with particular emphasis on deciphering the mode and energetics of the binding. Strong intercalative binding to tRNAPhe was observed for MB, NMB and AZB, bound by a partial intercalative mode. AZA has shown groove binding characteristics. From spectroscopic studies binding affinity values of the order of 105 M-1 were deduced for these dyes; the trend varied as MB > NMB > AZB > AZA. The binding was characterized by an increase of thermal melting temperatures and perturbation in the circular dichroism spectrum of tRNA. All the dyes acquired optical activity upon binding to tRNA. The binding was predominantly entropy driven with a favorable enthalpy term that increased with temperature in all the cases. Dissection of the Gibbs energy to polyelectrolytic and non-polyelectrolytic terms revealed a major role of the non-electrostatic forces in the binding. The small but significant heat capacity changes and the observed enthalpy-entropy compensation phenomenon confirmed the involvement of multiple weak non-covalent forces driving the interaction. The mode of binding was confirmed from quenching, viscosity and cyclic voltammetric results. Using density functional theory, ground state optimized structures of the dyes were calculated to provide insight into theoretical docking studies to correlate the experimental approaches. The modeling results verified the binding location as well as the binding energy of complexation. The results may provide new insights into the structure-activity relationship useful in the design of effective RNA targeted therapeutic agents.
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In the present study, we have investigated the effect of nature of surfactant, chain length and counter-ion on the mixed micellization behaviour ofvarious cationic surfactants, tetradecyltrimethylammonium bromide (TTAB), dodecyltrimethylammonium chloride (DTAC) and cationic gemini surfactant, bis(tetradecyldimethylammonium)hexane dibromide(C14-6-C14,2Br) with surface active ionic liquid (SAIL) tetradecylisoquinolinium bromide [C14iQuin][Br]. The interactions and mixed micellar behaviour of cationic surfactants and SAIL in aqueous medium have been studied by employing conductometry measurements and 1H NMR technique. The critical micelle concentration (cmc) and various thermodynamic parameters like standard Gibbs free energy of micellization (ΔGm0), change in standard enthalpy (ΔHm0) and entropy of micellization (ΔSm0) have been calculated from conductometry measurements. Mixed micellar parameters such as ideal cmc (cmc*), micellar mole fraction (X1m), micellar interaction parameter (βm) and activity coefficients, (f1 and f2) have been evaluated by applying Clint, Rubingh and Motomura theoretical models. Synergistic and non-ideal interactions have been found between SAIL and surfactants.
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Blunt trauma abdomen rarely leads to gastrointestinal injury in children and isolated gastric rupture is even rarer presentation. We are reporting a case of isolated gastric rupture after fall from height in a three year old male child.
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| 31,171 |
For the first time, spironaphthopyrano[1,2-b]indeno-7,3′-indolines were prepared by cyclo-condensation of 1,3-indandione, isatin, and 2-naphthol under solvent-free and catalyst-free conditions. This procedure is not only environmentally benign but is also a simple, one-pot, three-component procedure with the advantages of easy work-up and mild reaction conditions. The same reaction was investigated with other β-diketones instead of 1,3-indandione, and the results are reported. The compounds synthesized were screened for antimicrobial activity.
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Indandione is an important starting material that has drawn great attention in various organic transformations because of its attributes, such as low cost, easy to handle and eco-friendliness generally affording the corresponding products in excellent yields. In this review, we summarize recent data describing the most important MCRs reactions in which one of the starting materials is indandione. This review will also present two-, three-, four-, and five-component and one-pot reactions for the functionalization of indandione with the to increase awareness on the versatility of using this compound among organic chemists.
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Our ability to tailor the electronic properties of surfaces by nanomodification is paramount for various applications, including development of sensing, fuel cell, and solar technologies. Moreover, in order to improve the rational design of conducting surfaces, an improved understanding of structure/function relationships of nanomodifications and effect they have on the underlying electronic properties is required. Herein, we report on the tuning and optimization of the electrochemical properties of indium tin oxide (ITO) functionalized with single-walled carbon nanotubes (SWCNTs). This was achieved by controlling in situ grafting of aryl amine diazonium films on the nanoscale which were used to covalently tether SWCNTs. The structure/function relationship of these nanomodifications on the electronic properties of ITO was elucidated via time-of-flight secondary ion mass spectrometry and electrochemical and physical characterization techniques which has led to new mechanistic insights into the in situ grafting of diazonium. We discovered that the connecting bond is a nitro group which is covalently linked to a carbon on the aryl amine. The increased understanding of the surface chemistry gained through these studies enabled us to fabricate surfaces with optimized electron transfer kinetics. The knowledge gained from these studies allows for the rational design and tuning of the electronic properties of ITO-based conducting surfaces important for development of various electronic applications.
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| 31,172 |
A systematic investigation of the kinetics of the electrochemical reduction of a series of 11 arylmethyl halides in acetonitrile and N,N' dimethylformamide reveals a striking change in the reductive cleavage mechanism as a function of the energy of the π* orbital liable to accept the incoming electron. With ring-substituted nitrobenzyl chlorides and bromides, a stepwise mechanism involving the intermediacy of the anion radical takes place. When slightly less electron-withdrawing substituents, such as nitrile or ester groups, are involved, the reaction occurs via a concerted electron transfer-bond breaking mechanism
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Low-energy electrons (LEEs) are produced in large quantities in any type of material irradiated by high-energy particles. In biological media, these electrons can fragment molecules and lead to the formation of highly reactive radicals and ions. The results of recent experiments performed on biomolecular films bombarded with LEEs under ultra-high vacuum conditions are reviewed in the present article. The major type of experiments, which measure fragments produced in such films as a function of incident electron energy (0.1-45 eV), are briefly described. Examples of the results obtained from DNA films are summarized along with those obtained from the fragmentation of elementary components of the DNA molecule (i.e., thin solid films of H(2)O, DNA bases, sugar analogs, and oligonucleotides) and proteins. By comparing the results of these different experiments, it is possible to determine fundamental mechanisms that are involved in the dissociation of biomolecules and the production of single- and double-strand breaks in DNA, and to show that base damage is dependent on the nature of the bases and on their sequence context. Below 15 eV, electron resonances (i.e., the formation of transient anions) play a dominant role in the fragmentation of all biomolecules investigated. These transient anions fragment molecules by decaying into dissociative electronically excited states or by dissociating into a stable anion and a neutral radical. These fragments usually initiate other reactions with nearby molecules, causing further chemical damage. The damage caused by transient anions is dependent on the molecular environment.
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This Account describes our achievements toward the development of a new class of platinum(II) complexes with interesting photophysical properties. The general motif of a strongly donating N-heterocyclic carbene with a cyclometalating phenyl group attached to the nitrogen atom together with β-diketonate based counterligands enabled us to synthesize a new class of phosphorescent emitters for use in organic light-emitting diodes (OLEDs). This Account is divided into sections and introduces imidazolium based as well as triazolium based structures and discusses the effects of structural changes on the photophysical properties. Starting from the basic methylated (substituted) phenylimidalium presursors, we initially extended the π-system of the phenyl ring to the dibenzofuran ligand, its regioisomer, and thio-derivative. As the substituents of the β-diketonate ligands turned out to have a strong influence on the photophysical properties (higher quantum yields as well as shorter decay times) a series of dibenzofuranyl-3-methylimidazol as well as diphenylbenzimidazol platinum complexes were synthesized to investigate the different steric and electronic effects, which are described in a separate section. The next section of the Account then describes other extensions of the π-system. Exchange of the methyl group against a phenyl ring, as well as the extension of the π-system in the backbone of the NHC-ligand lead to a significant improvement of the photophysical properties, which reached a maximum for the diphenylbenzimidazole (DPBIC) system. Further extension of the π-system to the diphenylnaphthylimidazol then lead to a unfavorable long decay time. The effect of substitution is discussed for cyano groups, which change the electronic situation and lead to highly emissive complexes. We are currently working on studying the effect of other substituents on the photophysical properties, as well as the introduction of additional heteroatoms into the general motif. Our initial work in that area had been on 1,2,4-triazole complexes. For the basic phenyl/methyl substituted system, two different isomers are accessible, the 4-phenyl-4H-1,2,4-triazoles as well as the 1-phenyl-1H-1,2,4 triazoles. It was interesting to note that the photophysical properties of the corresponding complexes are strongly dependent on the substituent R of the β-diketonate ligand. For R = methyl, the properties are significantly different, while we found almost identical photophysical results for R = mesityl for both 1,2,4-triazole isomers. The last section describes the synthesis of bimetallic complexes. To investigate whether it is possible to cyclometalate twice into the same phenyl ring, we synthesized dicationic NHC precursors from para- and meta-disubstituted bis(imidazole)benzenes. The bimetallic complexes show interesting photophysical properties with quantum yields of up to 93%. All experimental work was accompanied by quantum chemical calculations, which turned out to be very useful for the prediction of the emission wavelengths as well as the interpretation of the emissive states of the platinum complexes.
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| 31,173 |
Classification methods based on linear discriminant analysis, recursive partitioning, and hierarchical agglomerative clustering are examined for their ability to separate active and inactive compounds in a diverse chemical database. Topology-based descriptions of chemical structure from the Molconn-X and ISIS programs are used in conjunction with these classification techniques to identify ACE inhibitors, beta-adrenergic antagonists, and H2 receptor antagonists. Overall, discriminant analysis misclassifies the smallest number of active compounds, while recursive partitioning yields the lowest rate of misclassification among inactives. Binary structural keys from the ISIS package are found to generally outperform the whole-molecule Molconn-X descriptors, especially for identification of inactive compounds. For all targets and classification methods, sensitivity toward active compounds is increased by making repetitive classification using training sets that contain equal numbers of actives and inactives. These balanced training sets provide an average numerical class membership score which may be used to select subsets of compounds that are enriched in actives.
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Benzil has been identified as a potent selective inhibitor of carboxylesterases (CEs). Essential components of the molecule required for inhibitory activity include the dione moiety and the benzene rings, and substitution within the rings affords increased selectivity toward CEs from different species. Replacement of the benzene rings with heterocyclic substituents increased the Ki values for the compounds toward three mammalian CEs when using o-nitrophenyl acetate as a substrate. Logarithmic plots of the Ki values versus the empirical resonance energy, the heat of union of formation energy, or the aromatic stabilization energy determined from molecular orbital calculations for the ring structures yielded linear relationships that allowed prediction of the efficacy of the diones toward CE inhibition. Using these data, we predicted that 2,2‘-naphthil would be an excellent inhibitor of mammalian CEs. This was demonstrated to be correct with a Ki value of 1 nM being observed for a rabbit liver CE. In additio...
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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| 31,174 |
This brief review recapitulates the main kinetic models of the oxygen reduction reaction at platinum-based catalysts. Two major flavors of models are being discussed: the first corresponds to a single Tafel equation with phenomenological treatment of various effects of chemisorbed oxygen intermediates and the second encompasses mechanistic models on the basis of the microkinetic treatment of reaction steps and using fundamental parameters from first principles calculations. The importance of a consistent description of the electrical double layer is highlighted, and a perspective on future developments needed in theory and computation is provided.
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Noble metal nanoclusters (M NCs), defined as an aggregation of a few to tens of atoms, are considered a borderline between atoms and metal nanoparticles (M NPs), which tends to exhibit molecule-like behaviours such as discrete electronic state and size-dependent fluorescence. In the past decades, gold and silver nanoclusters (Au NCs and Ag NCs) have been massively explored and utilized in the field of industrial catalysis, optoelectronic devices, biological imaging, environmental detection, clinical diagnoses, and treatment. The analogue of Au and Ag NCs and platinum nanoclusters (Pt NCs), especially their biological applications, is relatively and rarely discussed. This review firstly investigates the synthetic methodology of Pt NCs including template-assisted and template-free approaches and then introduces their unique optical, catalytic, and thermal properties. Particular importance here is the biological applications of Pt NCs such as the bioimaging of various cells as a preferred fluorophore in contrast to traditional fluorescent markers (e.g., organic dye, semiconductor quantum dots, and fluorescent proteins), the usage of Pt NCs-based antitumour drugs as a new class chemotherapeutics for malignant tumour therapy, and the utilization of antibacteria as an alternative of Ag-based antibacterial agent. On the whole, the development of Pt NCs has already gained delectable progress; however, the study of ultrafine Pt NCs is at the beginning stage and there are still plenty of challenges like synthesis of near-infrared (NIR) fluorescent Pt NCs, the explicit signal pathway of cell apoptosis, and attempt in diverse biological applications that need to be urgently tackled in future.
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We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.
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| 31,175 |
Difficulties associated with computer-aided molecular design (CAMD) of carborane containing molecules have hampered drug development in boron neutron capture therapy (BNCT). A new approach of modeling and docking of carborane containing molecules with the readily available software packages hyperchem , sybyl and flexx is described. This new method is intended as a guide for boron chemists interested in using CAMD of carborane containing agents for medical applications such as BNCT.
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Molecularly imprinted polymer (MIP) was synthesized to selectively detect estrogen-like chemicals depending on their shapes and binding characteristics to Estrogen Receptor (ER) active site. MIP was synthesized on self-assembled monolayer (SAM) formed by thiol-acrylate photopolymerization on Surface Plasmon Resonance (SPR) chip. The imprinting factor was calculated based on the shift of SPR angle at which the excitation of surface plasmons by light was minimum level. The imprinting factor, 4.3, was calculated by angle shift by SPR, which showed higher imprinting factor than the previous studies. We also validated the specificity of molecularly imprinted polymer loaded gold chip and compared the binding ability to estrogenicity known by in-vivo and in-vitro biological test. Molecular imprinting reflected the whole surface characteristics including three dimensional shape, types and location of functional groups, and distribution of interaction forces such as hydrogen bonding and van der Waals interaction. Therefore, MIP binding response could provide more insight on structure and estrogenic activity. Another purpose was to provide the basic data for future development of EDC screening array chip to find out various hormone activities at once.
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ABSTRACTUNC-45A is an ubiquitously expressed protein highly conserved throughout evolution. Most of what we currently know about UNC-45A pertains to its role as a regulator of the actomyosin system...
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| 31,176 |
Li-Na ternary amidoborane, Na[Li(NH(2)BH(3))(2)], was recently synthesized by reacting LiH and NaH with NH(3)BH(3). This mixed-cation amidoborane shows improved dehydrogenation performance compared to that of single-cation amidoboranes, i.e., LiNH(2)BH(3) and NaNH(2)BH(3). In this paper, we synthesized the Li-Na ternary amidoborane by blending and re-crystallizing equivalent LiNH(2)BH(3) and NaNH(2)BH(3) in tetrahydrofuran (THF), and employed first-principles calculations and the special quasirandom structure (SQS) method to theoretically explore the likelihood for the existence of Li(1-x)Na(x)(NH(2)BH(3)) for various Li/Na ratios. The thermodynamic, electronic and phononic properties were investigated to understand the possible dehydrogenation mechanisms of Na[Li(NH(2)BH(3))(2)].
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Double metal amidoborans are considered to the most promising candidates for metal amidoborans. In this paper, the crystal structures, electronic properties, chemical bonds, hydrogen removal energies, and HOMO-LUMO of NaAB, NaLiAB, and NaMgAB have been studied. The GGA corrected density functional theory have been employed in the first principles calculations. Due to the alkali and alkali earth metals coexisting, the crystal structures of these compounds change significantly and the B–H, N–H and B-N bond lengths shorten. Moreover, the band structures and density of states of NaAB, NaLiAB, and NaMgAB were calculated. The charge density distributions and bond populations are used to understand the nature of bonding. The hydrogen removal energy states removing H(B) and H(N) from NaLiAB more easily than NaAB and NaMgAB. In addition, the frontier molecular orbital reveals that the intermolecular and intramolecular dehydrogenation of NaLiAB and NaMgAB may concur. The calculated HOMO-LUMO energy gaps suggest that the chemical reactivity is: NaLiAB> NaAB> NaMgAB.
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In Pseudomonas putida strain G7, a LysR-type positive transcriptional activator protein encoded by nahR is necessary for activation of two operons involved in naphthalene catabolism [Schell, M. A. & Poser, E. F. (1989) ::: R33 ::: . J Bacteriol 171, 837–846]. The role of an nahR homologue, NCIB-nahR, in another naphthalene-metabolizing bacterium, P. putida NCIB 9816-4 was verified. Targeted disruption of NCIB-nahR by homologous recombination resulted in a growth defect in the presence of naphthalene or salicylate as sole carbon and energy source. The nahR homologues and intergenic regions between nahR-like and nahG-like genes from P. putida NCIB 9816-4 and seven bacteria native to a naphthalene-rich coal tar contaminated site were amplified by PCR using degenerate primers. The amplified nahR homologues and the intergenic regions were cloned and sequenced. Alignment of the deduced amino acid sequences from NahR homologues revealed that NahR-like proteins showed only minor variations in all investigated naphthalene-degrading isolates. The intergenic regions, together with known NahR-binding sites showed the consensus NahR-protein-binding sites (5′-ATTCACGCTN2TGAT-3′). Surprisingly, amplified intergenic regions from naphthalene-degrading micro-organisms native to this study site were 100% identical to that of the pDTG1 plasmid (an archetypal naphthalene-catabolic plasmid from Pseudomonas putida NCIB 9816-4), but the nahR coding regions were not. DNA representing the uncultured microbial community was extracted from six sediment samples with varying coal tar exposure histories. PCR amplification of nahR from sediment DNA was observed in contaminated samples, but in uncontaminated samples only following laboratory incubation with naphthalene. The sediment-derived PCR products were sequenced and also found to be almost identical to known nahR genes. Thus, the structure and function of nahR-nahG regulatory genes appear to be highly conserved.
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| 31,177 |
Mass spectral studies of some chlorinated aromatic pesticidal compounds are reported. The compounds studied include substituted diphenyl derivatives of methane, ethene and methanol. ::: ::: ::: ::: The diphenylmethanes are characterized by a relatively intense peak at m/e 165. Comparison of their low voltage spectra with 9-dichloromethylfluorene indicates that this ion has a fluorenyl ion structure. ::: ::: ::: ::: The structure of the base peak (m/e 246) of the diphenylethenes was investigated by comparing competitive metastable transitions with 9-dichloromethylenefluorene and utilizing defocusing metastables. Additional studies of model compounds suggest that the m/e 246 ion is very complex and is probably comprised of a number of structures. ::: ::: ::: ::: The mass spectra of the diphenylmethanols are significantly different from the other two groups. The hydroxyl group markedly affects the fragmentation process for these compounds; the characteristic peak is presumably the chlorobenzoyl ion and is probably precursor for other fragment ions. ::: ::: ::: ::: Mass spectral correlations of pesticidal compounds of similar structure are needed to obtain enough background to facilitate interpretation of the mass spectra of their metabolites. Furthermore, such studies make feasible the identification of characteristic product ions formed by rearrangement processes during ionization of organic molecules in the gas phase. This information can be a nucleus for correlating the other significant mass spectral data of an unknown compound. Intensive studies of carbamates,1 organophosphorus2 and bridged polycyclic chlorinated pesticidal3 compounds were invaluable in identifying metabolites of the aforementioned pesticides.4,5,6 The compounds in this ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: Work are chlorinated aromatic pesticidal compounds which consist of a diphenylemthane, a diphenylethylene, or a diphenylmethanol structure. The compounds p,ṕ-DDE were briefly discussed by Jorg, Houriet and Spiteller.7 The compounds examined are listed in Table 1. ::: ::: ::: ::: Treatment of data. The mass spectra of the pesticides are presented as bar graphs in Figs 1 to 12 ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: ::: It a metastable peak is observed, the metastable transition is indicated by m* on the figures and also by (m*) when confirmed or identified using the defocusing technique.8 Since the relative abundances of the metastable peaks for these compounds are very small (<0.1%) on special effort was made to establish their presence unless they wre pertinent.
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Between 1945 and 1965, 1.82 million hectares, or about 17 percent of the total commercial forestland in Oregon, were treated with 2.02 million kg DDT. Detectable residues of this insecticide might be present in forest soils, even those which have never received a direct application of insecticide. Forest floor and mineral soil samples were collected along four east-west transects across the Coast and Cascade Ranges. DDT residues were found in all samples, even though all but one site had never received a direct application of insecticide. In the Coast Ranges, mean concentrations of sigma DDT in forest floor samples were 0.049 ppm at the coast and 0.047, 0.064, 0.075, and 0.119 ppm at 16, 32, 48, and 64 km inland, respectively. Mean residue levels in the surface layers of mineral soil were much lower, 0.009 ppm and 0.006 ppm in the 0 to 7.5-cm and 7.5 to 15-cm depths, respectively. Sampling sites along the Cascade Range transects were selected on the basis of elevation except that the eastern site of each transect was located 16 km east of the crest of the Cascades. Residue concentrations in forest floor samples were three to four times higher than in the Coast Ranges, but were still below 0.50 ppm. In general, sigma DDT levels increased with increasing elevation up to 1,372 meters and then decreased quite sharply east of the crest. Variations can be explained on the basis of total rainfall distribution and by transect location relative to agricultural and metropolitan centers.
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This Account describes our achievements toward the development of a new class of platinum(II) complexes with interesting photophysical properties. The general motif of a strongly donating N-heterocyclic carbene with a cyclometalating phenyl group attached to the nitrogen atom together with β-diketonate based counterligands enabled us to synthesize a new class of phosphorescent emitters for use in organic light-emitting diodes (OLEDs). This Account is divided into sections and introduces imidazolium based as well as triazolium based structures and discusses the effects of structural changes on the photophysical properties. Starting from the basic methylated (substituted) phenylimidalium presursors, we initially extended the π-system of the phenyl ring to the dibenzofuran ligand, its regioisomer, and thio-derivative. As the substituents of the β-diketonate ligands turned out to have a strong influence on the photophysical properties (higher quantum yields as well as shorter decay times) a series of dibenzofuranyl-3-methylimidazol as well as diphenylbenzimidazol platinum complexes were synthesized to investigate the different steric and electronic effects, which are described in a separate section. The next section of the Account then describes other extensions of the π-system. Exchange of the methyl group against a phenyl ring, as well as the extension of the π-system in the backbone of the NHC-ligand lead to a significant improvement of the photophysical properties, which reached a maximum for the diphenylbenzimidazole (DPBIC) system. Further extension of the π-system to the diphenylnaphthylimidazol then lead to a unfavorable long decay time. The effect of substitution is discussed for cyano groups, which change the electronic situation and lead to highly emissive complexes. We are currently working on studying the effect of other substituents on the photophysical properties, as well as the introduction of additional heteroatoms into the general motif. Our initial work in that area had been on 1,2,4-triazole complexes. For the basic phenyl/methyl substituted system, two different isomers are accessible, the 4-phenyl-4H-1,2,4-triazoles as well as the 1-phenyl-1H-1,2,4 triazoles. It was interesting to note that the photophysical properties of the corresponding complexes are strongly dependent on the substituent R of the β-diketonate ligand. For R = methyl, the properties are significantly different, while we found almost identical photophysical results for R = mesityl for both 1,2,4-triazole isomers. The last section describes the synthesis of bimetallic complexes. To investigate whether it is possible to cyclometalate twice into the same phenyl ring, we synthesized dicationic NHC precursors from para- and meta-disubstituted bis(imidazole)benzenes. The bimetallic complexes show interesting photophysical properties with quantum yields of up to 93%. All experimental work was accompanied by quantum chemical calculations, which turned out to be very useful for the prediction of the emission wavelengths as well as the interpretation of the emissive states of the platinum complexes.
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Interaction between the normal cucurbit[n]urils (n = 6,7,8; Q[6], Q[7], Q[8]) and a sym-tetramethyl-substituted cucurbit[6]uril derivative (TMeQ[6]) with the hydrochloride salts of some imidazole derivatives N-(4-hydroxylphenyl)imidazole (g1), N-(4-aminophenyl)imidazole (g2), 2-phenylimidazole (g3) in aqueous solution was investigated by using 1H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by using a single crystal X-ray diffraction determination. The 1H NMR spectra analysis established a basic interaction model in which inclusion complexes with a host:guest ratio of 1:1 forms for the Q[6]s and Q[7] cases, while with a host:guest ratio of 1:2 form for the Q[8] cases. It was common that the hosts selectively bound the phenyl moiety of the guests. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes at pH 5.8 with a host:guest ratio of 1:1 form quantitatively as logK values between 4 and 5 for the smaller hosts Q[6 or 7]s, while with a host:guest ratio of 1:2 form quantitatively as logK values between 11 and 12 for the host Q[8]. Two single crystal X-ray structures of the inclusion complexes TMeQ[6]-g2 · HCl and TMeQ[6]-g3 · HCl showed the phenyl moiety of these two guests inserted into the host cavity, which supported particularly the 1H NMR spectroscopic study in solution.
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The interaction of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene is studied using fluorescence technique. The quenching of fluorescence intensity explains the efficiency of binding via binding constant and quenching constant. The excited state lifetime of n-(4-hydroxyphenyl)-imidazole is decreased upon interaction with p-sulfonatocalix[4]arene. The cyclic voltametric studies emphasized the interaction of n-(4-hydroxyphenyl)-imidazole with p-sulfonatocalix[4]arene. Quantum chemical calculations are carried out to study the interactions as well as charge transfer between the host and the guest upon complexation. The simulations revealed that the n-(4-hydroxyphenyl)-imidazole interacts with p-sulfonatocalix[4]arene with horizontal orientation with in the p-sulfonatocalix[4]arene cavity.
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We prove that groups acting geometrically on delta-quasiconvex spaces contain no essential Baumslag-Solitar quotients as subgroups. This implies that they are translation discrete, meaning that the translation numbers of their nontorsion elements are bounded away from zero.
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| 31,179 |
The native carbon oxidation and PolyChloroDibenzo-p-Dioxins and PolyChloroDibenzoFurans, PCDD/F, formation were simultaneously studied at different temperatures (230–350 C) and times (0– 1440 min) in order to establish a direct correlation between the disappearance of the reagent and the formation of the products. The kinetic runs were conducted in an experimental set up where conditions were chosen to gain information on the role of fly ash deposits in cold zones of municipal solid waste incinerators in PCDD/F formation reaction. The carbon oxidation measured as the decrease of total organic carbon of fly ash was in agreement with the carbon evolved as sum of CO and CO2. The carbon mass balance indicated an increase in the efficiency of carbon conversion in CO and CO2 with temperature. The CO and CO2 formation was the result of two parallel pseudo first order reactions thus giving significant information about the reaction mechanism. PCDD/F formation as a function of temperature showed that the maximum formation was achieved in a narrow range around 280 C; the time effect at 280 C was a progressive formation increase at least up to 900 min. The PCDF:PCDD molar ratio increased with temperature and time, and the most abundant homologues were HxCDD, HpCDD, OCDD for PCDD, and HxCDF, HpCDF within PCDF. These experimental results supported the hypothesis that the formation mechanism was the de novo synthesis.
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The inhibitory effects of four amino compounds on the formation of chlorobenzenes (CBzs)--dioxin precursors and indicators, and the inhibitory mechanisms were explored. The results show NH4H2PO4 can decrease the total yields of CBzs (1,2di-CBz, 1,3di-CBz, 1,4di-CBz, penta-CBz and hexa-CBz) by 98.1%±1.6% and 96.1%±0.7% under air and nitrogen flow. The inhibitory effects indicated by the total yields of CBzs follow the order NH4H2PO4 > NH4HF2 > (NH4)2SO4 > NH4Br under air flow and NH4H2PO4 ≈ (NH4)2SO4 ≈ NH4HF2 >NH4Br under nitrogen flow. The inhibition mechanism revealed by thermal analysis that CuCl2 was converted to CuPO3 by reacting with NH4H2PO4 below 200 °C, which can block the transfer of chlorine and formation of C-Cl bonds at 350 °C. The effects of the other three inhibitors were weaker because their reactions with CuCl2, which form other copper compounds, and the reaction of CuCl2 with carbon, which forms C-Cl bonds, were almost simultaneous and competitive. Oxygen influenced the yield of CBzs obviously, and the total yield of five CBzs sharply increased with oxygen. Because of their high efficiency, low environmental impact, low cost, and availability, amino compounds--especially NH4H2PO4--can be utilized as inhibitors of CBzs during incineration.
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The oxygen and carbon dioxide transporting properties of the haemolymph from an amphibious Australian crab,Holthuisana transversa were investigated. Within the temperature range 15 to 35°C increasing temperature markedly decreased oxygen affinity (ΔH=−54 kJ·mol−1). The Bohr effect was small at all temperatures with a mean value of −0.13. Over the temperature range 15–35°C there was a significant increase in the cooperativity of oxygen binding. Changing the concentration of Ca,l-lactate or haemocyanin in the haemolymph could elicit no significant change in either O2 affinity or cooperativity of O2 binding. There was no evidence in support of a specific effect of CO2 on oxygen affinity of either non-dialysed or dialysed haemolymph.
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| 31,180 |
Methylation of position-specific lysine residues in histone N termini is a central modification for regulating epigenetic transitions in chromatin. Each methylatable lysine residue can exist in a mono-, di-, or trimethylated state, thereby extending the indexing potential of this particular modification. Here, we examine all possible methylation states for histone H3 lysine 9 (H3-K9) and lysine 27 (H3-K27) in mammalian chromatin. Using highly specific antibodies together with quantitative mass spectrometry, we demonstrate that pericentric heterochromatin is selectively enriched for H3-K27 monomethylation and H3-K9 trimethylation. This heterochromatic methylation profile is dependent on the Suv39h histone methyltransferases (HMTases) but independent of the euchromatic G9a HMTase. In Suv39h double null cells, pericentric heterochromatin is converted to alternative methylation imprints and accumulates H3-K27 trimethylation and H3-K9 monomethylation. Our data underscore the selective presence of distinct histone lysine methylation states in partitioning chromosomal subdomains but also reveal a surprising plasticity in propagating methylation patterns in eukaryotic chromatin.
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Transcriptional repression mechanisms are important during differentiation of multipotential hematopoietic progenitors, where they are thought to regulate lineage commitment and to extinguish alternative differentiation programs. PU.1 and GATA-1 are two critical hematopoietic transcription factors that physically interact and mutually antagonize each other's transcriptional activity and ability to promote myeloid and erythroid differentiation, respectively. We find that PU.1 inhibits the erythroid program by binding to GATA-1 on its target genes and organizing a complex of proteins that creates a repressive chromatin structure containing lysine-9 methylated H3 histones and heterochromatin protein 1. Although these features are thought to be stable aspects of repressed chromatin, we find that silencing of PU.1 expression leads to removal of the repression complex, loss of the repressive chromatin marks and reactivation of the erythroid program. This process involves incorporation of the replacement histone variant H3.3 into nucleosomes. Repression of one transcription factor bound to DNA by another transcription factor not on the DNA represents a new mechanism for downregulating an alternative gene expression program during lineage commitment of multipotential hematopoietic progenitors.
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Alkylaminium sulfates originate from the neutralisation reaction between short-chained amines and sulfuric acid and have been detected in atmospheric aerosol particles. Their physicochemical behaviour is less well characterised than their inorganic equivalent, ammonium sulfate, even though they play a role in atmospheric processes such as the nucleation and growth of new particles and cloud droplet formation. In this work, a comparative evaporation kinetics experimental technique using a cylindrical electrodynamic balance is applied to determine the hygroscopic properties of six short-chained alkylaminium sulfates, specifically mono-, di-, and tri-methylaminium sulfate and mono-, di-, and tri-ethyl aminium sulfate. This approach allows for the retrieval of a water-activity-dependent growth curve in less than 10 s, avoiding the uncertainties that can arise from the volatilisation of semi-volatile components. Measurements are made on particles > 5 µm in radius, avoiding the need to correct equilibrium measurements for droplet-surface curvature with assumed values of the droplet-surface tension. Variations in equilibrium solution droplet composition with varying water activity are reported over the range 0.5 to > 0.98, along with accurate parameterisations of solution density and refractive index. The uncertainties in water activities associated with the hygroscopicity measurements are typically 0.9 and ∼ ±1 % below 0.9, with maximum uncertainties in diameter growth factors of ±0.7 %. Comparison with previously reported measurements show deviation across the entire water activity range.
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| 31,181 |
A specific series of dumbbell-shaped bis-carbazoles or bis-phenothiazines dyes (1, 2, 3 and 4) constructed with styrene or biphenylethyne as the π-bridge have been synthesized and characterized. Detailed spectral properties including linear absorption, one and two-photon fluorescence properties were investigated. The results show that extending conjugated chain and introducing donors have substantial effect on their photophysical properties. Among them, two-photon absorption cross sections (σ) of the four dyes in DMF determined by the Z-scan technique are successively increased from 1 to 4 with enhancing electron-donating ability and extending conjugated chain, but electron-donating ability has larger contribution to the σ values than extending conjugated chain based on the comparison of small molecules (D-π-D). Two-photon initiation polymerization (TPIP) microfabrication experiments have been carried out using compound 4 as an initiator under irradiation of 200 fs, 76 MHz femtosecond laser at 760 nm. The results confirm that the four dyes can be effectively used as organic two-photon photopolymerization initiators.
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During recent years there have been notorious advances in the development of organic molecules and π-conjugated polymers with two-photon activity, i.e., emission of fluorescence promoted by the molecular absorption of two photons. Novel organic materials have reached very large two-photon activity, and many of them have been processed successfully into nanostructured platforms. In contrast to their inorganic counterpart, organic nanoparticles with photonic properties is a topic that so far has not been well explored, although deserves big potential in biomedical applications. This chapter presents recent advances in this field, particularly, in the use of organic nanoparticles as contrast agents to obtain bioimages.
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The emergence of superbugs that are resistant to last-resort antibiotics poses a serious threat to human health, and we are in a “race against time to develop new antibiotics.” New approaches are urgently needed to control drug-resistant pathogens, and to reduce the emergence of new drug-resistant microbes. Targeting bacterial virulence has emerged as an important strategy for combating drug-resistant pathogens. It has been shown that pyocyanin, which is produced by the phenazine biosynthesis pathway, plays a key role in the virulence of Pseudomonas aeruginosa infection, making it an attractive target for anti-infective drug discovery. In order to discover efficient therapeutics that inhibit the phenazine biosynthesis in a timely fashion, we screen 2004 clinical and pre-clinical drugs to target multiple enzymes in the phenazine biosynthesis pathway, using a novel procedure of protein–ligand docking. Our detailed analysis suggests that kinase inhibitors, notably Lifirafenib, are promising lead compounds for inhibiting aroQ, phzG, and phzS enzymes that are involved in the phenazine biosynthesis, and merit further experimental validations. In principle, inhibiting multiple targets in a pathway will be more effective and have less chance of the emergence of drug resistance than targeting a single protein. Our multi-target structure-based drug design strategy can be applied to other pathways, as well as provide a systematic approach to polypharmacological drug repositioning.
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| 31,182 |
How do ribonucleotide reductases functionalize CH bonds? Theoretical studies of small model systems for the C−H bond activation step in ribonucleotide reductases predict that carboxylates are efficient catalysts. The catalytic efficiency is due to the formation of a short strong hydrogen bond, which is strongest in the transition state (illustrated here) for hydrogen-atom transfer to the electrophilic thiyl radical.
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Ribonucleotide reductases (RNRs) catalyze the production of deoxyribonucleotides, which are essential for DNA synthesis and repair in all organisms. The three currently known classes of RNRs are postulated to utilize a similar mechanism for ribonucleotide reduction via a transient thiyl radical, but they differ in the way this radical is generated. Class I RNR, found in all eukaryotic organisms and in some eubacteria and viruses, employs a diferric iron center and a stable tyrosyl radical in a second protein subunit, R2, to drive thiyl radical generation near the substrate binding site in subunit R1. From extensive experimental and theoretical research during the last decades, a general mechanistic model for class I RNR has emerged, showing three major mechanistic steps: generation of the tyrosyl radical by the diiron center in subunit R2, radical transfer to generate the proposed thiyl radical near the substrate bound in subunit R1, and finally catalytic reduction of the bound ribonucleotide. Amino acid- or substrate-derived radicals are involved in all three major reactions. This article summarizes the present mechanistic picture of class I RNR and highlights experimental and theoretical approaches that have contributed to our current understanding of this important class of radical enzymes.
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Iron and iron compounds may facilitate hydroxyl-radical generation from activated oxygen species. Earlier work on the generation of this radical has been focused on simple, low-molecular-weight iron compounds. We hypothesized that free hemoglobin, like other iron-rich substances, might also mediate hydroxyl-radical generation. We find: 1) In the presence of a superoxide anion-generating system (hypoxanthine and xanthine oxidase), hemoglobin promotes hydroxyl-radical formation in a dose-dependent fashion. 2) This generation of hydroxyl radical is greatly decreased by prior oxidation of the hemoglobin, equilibration of hemoglobin with carbon monoxide, or addition of catalase, while added superoxide dismutase has little effect. Therefore, hydroxyl radical probably arises primarily via reaction between the ferrous heme iron and H2O2. 3) In further support of this, hydroxyl radical forms as readily upon the addition of H2O2 to hemoglobin. 4) Hemoglobin also increases hypoxanthine/xanthine oxidase-driven peroxidation of poly-unsaturated fatty acids such as arachidonic acid and human red cell membrane lipids. 5) The addition of sufficient haptoglobin (the plasma hemoglobin-binding protein) suppresses both hemoglobin-driven hydroxyl radical and malondialdehyde generation. Thus, free hemoglobin may be biologically hazardous, in part because it acts as a "Fenton" reagent, having the potential to catalyze hydroxyl-radical generation in areas of inflammation. Haptoglobin, which binds hemoglobin very tightly, blocks this through a presently unknown mechanism. An important physiologic function of haptoglobin may be prevention of such hemoglobin-mediated oxidation.
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The antibiotic colistin (polymyxin E) inhibited the lytic cycle of the mycobacteriophage D29 in the tubercle bacilli, but not the D29 adsorption. The protein and nucleic acid synthesis in D29-infected bacteria were not affected significantly. The inhibitory activity was reversed by washing off the antibiotic, and by addition of Ca++, but not in media made iso-osmotic by addition of NaCl or sucrose. Transmission electron microscopy revealed an asymmetric to symmetric transition in the staining profile of the cytoplasmic membrane. Though no mature phage particles were ever observed in colistin-treated, D29-infected tubercle bacilli, loosely arranged aggregates resembling phage proheads were occasionally found. Judging from the above data, it was concluded that colistin inhibited D29 lytic cycle by causing molecular displacements in the inner leaflet of the cytoplasmic membrane, and consequently, the binding sites for D29 structural proteins were not available.
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Phage production in response to antibiotics varied among four isolates of a Pseudomonas aeruginosa cystic fibrosis (CF) epidemic strain. Whereas ciprofloxacin induced higher levels of phage production, other CF-relevant antibiotics led to reduced production. We detected free phages directly in CF patient sputum samples by both plaque (40% positive) and PCR (76% positive) assays. Our observations suggest that the choice of antibiotics could influence the number of free phages within the CF lung environment.
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This Account describes our achievements toward the development of a new class of platinum(II) complexes with interesting photophysical properties. The general motif of a strongly donating N-heterocyclic carbene with a cyclometalating phenyl group attached to the nitrogen atom together with β-diketonate based counterligands enabled us to synthesize a new class of phosphorescent emitters for use in organic light-emitting diodes (OLEDs). This Account is divided into sections and introduces imidazolium based as well as triazolium based structures and discusses the effects of structural changes on the photophysical properties. Starting from the basic methylated (substituted) phenylimidalium presursors, we initially extended the π-system of the phenyl ring to the dibenzofuran ligand, its regioisomer, and thio-derivative. As the substituents of the β-diketonate ligands turned out to have a strong influence on the photophysical properties (higher quantum yields as well as shorter decay times) a series of dibenzofuranyl-3-methylimidazol as well as diphenylbenzimidazol platinum complexes were synthesized to investigate the different steric and electronic effects, which are described in a separate section. The next section of the Account then describes other extensions of the π-system. Exchange of the methyl group against a phenyl ring, as well as the extension of the π-system in the backbone of the NHC-ligand lead to a significant improvement of the photophysical properties, which reached a maximum for the diphenylbenzimidazole (DPBIC) system. Further extension of the π-system to the diphenylnaphthylimidazol then lead to a unfavorable long decay time. The effect of substitution is discussed for cyano groups, which change the electronic situation and lead to highly emissive complexes. We are currently working on studying the effect of other substituents on the photophysical properties, as well as the introduction of additional heteroatoms into the general motif. Our initial work in that area had been on 1,2,4-triazole complexes. For the basic phenyl/methyl substituted system, two different isomers are accessible, the 4-phenyl-4H-1,2,4-triazoles as well as the 1-phenyl-1H-1,2,4 triazoles. It was interesting to note that the photophysical properties of the corresponding complexes are strongly dependent on the substituent R of the β-diketonate ligand. For R = methyl, the properties are significantly different, while we found almost identical photophysical results for R = mesityl for both 1,2,4-triazole isomers. The last section describes the synthesis of bimetallic complexes. To investigate whether it is possible to cyclometalate twice into the same phenyl ring, we synthesized dicationic NHC precursors from para- and meta-disubstituted bis(imidazole)benzenes. The bimetallic complexes show interesting photophysical properties with quantum yields of up to 93%. All experimental work was accompanied by quantum chemical calculations, which turned out to be very useful for the prediction of the emission wavelengths as well as the interpretation of the emissive states of the platinum complexes.
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Uroporphyrinogen oxidation by hepatic microsomes from chick embryos or mice pretreated with methylcholanthrene was increased by addition of iron-EDTA. This increase was partially prevented by catalase, mannitol, ketoconazole and piperonyl butoxide, whereas only ketoconazole and piperonyl butoxide inhibited the oxidation in the presence and absence of iron-EDTA. These data suggest that the oxidations of uroporphyrinogen in the presence and absence of added iron occur by different mechanisms.
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The coexistence of factors considered to contribute to development of porphyria cutanea tarda was studied in 39 consecutive patients. Highly prevalent factors were alcohol intake in 79%, smoking in 86%, hepatitis C virus infection in 74%, estrogen use in 73% of 11 females, and at least one mutation in the HFE (hereditary hemochromatosis) gene in 65%. The C282Y mutation was found in 29%, H63D in 47%, and S65C in 0%. HFE genotypes included C282Y/C282Y in 9%, H63D/H63D in 9%, C282Y/H63D in 12%, C282Y/wild type in 9%, and H63D/wild type in 26%. Less prevalent were HIV infection in 15% (or 25% of those tested, N = 24) and erythrocyte uroporphyrinogen decarboxylase deficiency, which distinguishes familial (type 2) from “sporadic” (type 1) porphyria cutanea tarda, in 19%. Multiple contributing factors coexisted in both types 1 and 2, with 92% of all patients having three or more factors. These observations indicate that this porphyria is multifactorial in the individual patient, and therefore is seldom attributable to a single identifiable cause. Profiling for all potentially contributing factors is important for individualizing management.
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Alcohols and alkenes are the most abundant and commonly used organic building blocks in the large-scale chemical synthesis. Herein, this is the first time to report a novel and operationally simple coupling reaction of vinylarenes and aliphatic alcohols catalyzed by manganese in the presence of TBHP (tert-butyl hydroperoxide). This coupling reaction provides the oxyalkylated products of vinylarenes with good regioselectivity and accomplishes with the principles of step-economies. A possible reaction mechanism has also been proposed.
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| 31,185 |
Bromine-mediated intramolecular cyclization of 1,4-diaryl buta-1,3-diynes has been developed for the construction of naphthalene motifs. A number of 1,2,3-tribromo-4-aryl naphthalenes are synthesized under mild reaction condition by the 6-endo-dig electrophilic cyclization of the corresponding 1,4-diaryl buta-1,3-diynes by Br2 in moderate to excellent yields. This methodology has been successfully extended to the synthesis of 1,2,3,4-tetraphenyl naphthalene derivatives.
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Cycloaddition reactions of alkynes are elegant, atom-efficient transformations for the synthesis of carbo- and heterocycles, mostly aromatic, involving the construction of challenging skeletons of complex molecules. Therefore significant efforts have recently been devoted to the development of novel methodologies, efficient strategies and different catalytic systems to broaden the scope of these reactions. We summarize in this review the recent advances in the cycloaddition reactions of 1,3-butadiynes to provide facile and reliable approaches to various functionalized carbo- and heterocycles.
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MLL1 regulates circadian promoters by depositing H3K4 trimethyl marks, whose levels are also modulated by the NAD+-dependent deacetylase SIRT1. SIRT1 is now shown to promote circadian deacetylation of MLL1, thus affecting MLL1's methyltransferase activity.
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| 31,186 |
To clarify the roles of superoxide anion (O2.-) and methylene blue in the reductive activation of the heme protein indoleamine 2,3-dioxygenase, effects of xanthine oxidase-hypoxanthine used at various oxidase concentration levels as an O2.- source and an electron donor on the catalytic activity of the dioxygenase have been examined in the presence and absence of either methylene blue or superoxide dismutase using L- and D-tryptophan as substrates. In the absence of methylene blue, initial rates of the product N-formylkynurenine formation are enhanced in parallel with the xanthine oxidase level up to approximately 100 and approximately 50% of the apparent maximal activity (approximately 2 s-1) for L- and D-Trp, respectively. Superoxide dismutase effectively inhibits the reactions by 80-98% for both isomers. Additions of methylene blue (25 microM) help to maintain the linearity of the product formation that would be rapidly lost a few minutes after the start of the reaction without the dye, especially for L-Trp. Additions of methylene blue also enhance the activity to the maximal level for D-Trp. In the presence of methylene blue, the inhibitory effects of superoxide dismutase are considerably decreased with the increase in xanthine oxidase concentration, and at near maximal dioxygenase activity levels superoxide dismutase is totally without effect. In separate anaerobic experiments leuco-methylene blue, generated either by photoreduction or by ascorbate reduction, is shown to be able to reduce the ferric dioxygenase up to 25-40%. Substrate Trp and heme ligands (CO, n-butyl isocyanide) help to shift a ferric form----ferrous form equilibrium to the right. Thus, under aerobic conditions leuco-methylene blue might similarly be able to reduce the dioxygenase in the presence of an electron donor with the aid of substrate and O2. These results strongly suggest that indoleamine 2,3-dioxygenase can be activated through different pathways either by O2.- or by an electron donor-methylene blue system. For the latter case, the dye is acting as an electron mediator from the donor to the ferric dioxygenase.
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The first step in the kynurenine pathway of tryptophan catabolism is the cleavage of the 2,3-double bond of the indole ring of tryptophan. In mammals, this reaction is performed independently by indoleamine 2,3-dioxygenase-1 (IDO1), tryptophan 2,3-dioxygenase (TDO) and the recently discovered indoleamine 2,3-dioxygenase-2 (IDO2). Here we describe characteristics of a purified recombinant mouse IDO2 enzyme, including its pH stability, thermal stability and structural features. An improved assay system for future studies of recombinant/isolated IDO2 has been developed using cytochrome b 5 as an electron donor. This, the first description of the interaction between IDO2 and cytochrome b 5, provides further evidence of the presence of a physiological electron carrier necessary for activity of enzymes in the “IDO family”. Using this assay, the kinetic activity and substrate range of IDO2 were shown to be different to those of IDO1. 1-Methyl-d-tryptophan, a current lead IDO inhibitor used in clinical trials, was a poor inhibitor of both IDO1 and IDO2 activity. This suggests that its immunosuppressive effect may be independent of pharmacological inhibition of IDO enzymes, in the mouse at least. The different biochemical characteristics of the mouse IDO proteins suggest that they have evolved to have distinct biological roles.
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Methylene Blue (MB) and Xanthene (XE) dyes sensitized polyvinyl alcohol have been employed for application of correlation peak detection. Bleaching of the MB and XE sensitized films has been studied in detail. The effect of various amines on the bleaching efficiency has been presented. The dark reversibility of these systems has also been evaluated.
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| 31,187 |
The conformer model of tryptophan photophysics ascribes the multiple fluorescence lifetimes to ground-state heterogeneity. It is usually assumed that the different conformers do not interconvert in the excited state. Previous studies of two constrained tryptophan derivatives supported this assumption (Colucci, W. J.; Tilstra, L.; Sattler, M. C.; Fronczek, F. R.; Barkley, M. D. J. Am. Chem. Soc. 1990, 112, 9182-9190; Yu, H.-T.; Vela, M. A.; Fronczek, F. R.; McLaughlin, M. L.; Barkley, M. D. J. Am. Chem. Soc. 1995, 117, 348-357). Five constrained derivatives have been synthesized and shown to undergo conformer inversion during the lifetime of the excited state. All derivatives have two ground-state conformations as determined by X-ray crystallography, molecular mechanics calculations, and 1H-NMR. Fluorescence lifetime data were fit to singleand double-exponential models and to a reversible two-state excited-state reaction model. 2-Amino-1,2dihydrocyclopenta[b]indole-2-carboxylic acid has a single-exponential decay consistent with conformer inversion much faster than fluorescence decay. 1,2,3,4-Tetrahydrocarbazole-3-carboxylic acid, ethyl 1,2,3,4tetrahydrocarbazole-3-carboxylate, and their 9-methyl derivatives have double-exponential decays with a minor second component of small positive or negative amplitude. Conformer inversion rates of ∼107 s-1 were determined by analyzing the fluorescence decay data using the excited-state reaction model. Temperature dependence of the fluorescence lifetimes was measured in H2O and D2O, and solvent quenching rates were calculated from the Arrhenius parameters. The carboxylate and carbonyl functional groups appear to have little effect on solvent quenching of indole fluorescence. Model calculations examining the effect of conformer inversion rate on the decay parameters of a biexponential model indicate that the presence of a small amplitude, short lifetime component may be a good predictor of excited-state conformer interconversion of tryptophans in peptides and proteins.
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Fluorescence spectroscopy and its multiple applications to the life sciences have undergone rapid development. This is due to numerous technical advances in both instrumentation and methods of data analysis as well as to a vast proliferation of basic techniques. Applications of fluorescence spectroscopy to protein and peptide analysis are governed by three principal factors: the dynamic nature of the signal, its localized nature, and its redundancy. Although these features can complicate interpretation of the experimental result, they also can be exploited to obtain unique structural and dynamic information. The availability and simplicity of basic data acquisition and analysis are important practical features behind the popularity of fluorescence as compared to other spectroscopic techniques. Yet this simplicity does not appear to compromise its advantages. This article is intended first to provide an overview of the fluorescence phenomenon in proteins, and second to illustrate applications of fluorescence spectroscopy in advanced (but not necessarily high-tech) studies. Three areas of protein studies, namely protein–ligand interactions, protein folding and studies of membrane proteins, have been chosen to demonstrate key advantages of fluorescence spectroscopy: it is sensitive, versatile, and it lends itself readily to fast data acquisition.
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We characterize stability under composition, inversion, and solution of ordinary differential equations for ultradifferentiable classes, and prove that all these stability properties are equivalent.
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eng_Latn
| 31,188 |
The density functional theory (DFT) is currently predominating theoretical approach in quantum chemistry. It is suitable for investigating structures up to several hundreds of atoms, studying of reaction pathways and calculating precisely reaction energy values. The usage of the DFT approach for studying enzyme–substrate interactions could be a prospective way for elaborating new efficient enzyme inhibitors. This is a direct way to discovery of new drugs and modification of the existing drugs. While enzymes are still too large for the computational analysis using DFT, numerous efforts have been exerted in the last years in this field using simplified enzyme models or calculating for the substrate some valuable properties, important in the enzyme–substrate interactions. These examples have been analyzed in the current review. A rapid development of new efficient calculation routines makes it possible to increase the role of the DFT methods in medicinal chemistry in the nearest future.
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Both DHPS (dihydropteroate synthase) and DHFR (dihydrofolate reductase) play important physiological roles in the survivability of Mycobacterium tuberculosis (MTB). Sulfonamides are the potent drugs to monitor growth and proliferation of MTBs by inhibiting the activity of DHPS and DHFR which could explain the mechanism of action of these molecules. In this work, 102 heterocyclic sulfonamides (HSF) have been screened by discovery studio molecular docking programme to search the best suitable molecule for the treatment of MTBs. Lipinski’s rule of five protocols is followed to screen drug likeness of these molecules and ADMET (absorption, distribution, metabolism, excretion and toxicity) filtration has been used to value their toxicity. Only fourteen molecules are found to obey the Lipinski’s rule and able to cross the ADMET filter. A small difference between HOMO and LUMO energy signifies the electronic excitation energy which is essential to calculate molecular reactivity and stability of the best docked compound and easy activation of drug in the protein environment. Both 4-amino-N-(6-hydroxypyridin-2-yl)benzenesulfonamide (M1) and 4-amino-N-(9H-carbazol-2-yl)benzenesulfonamide (M2) show the best theoretical efficiency with DHPS and DHFR, respectively. These compounds are also found to bind to the adenine–thymine region of tuberculosis DNA.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
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| 31,189 |
QuickFF is a software package to derive accurate force fields for isolated and complex molecular systems in a quick and easy manner. Apart from its general applicability, the program has been designed to generate force fields for metal-organic frameworks in an automated fashion. The force field parameters for the covalent interaction are derived from ab initio data. The mathematical expression of the covalent energy is kept simple to ensure robustness and to avoid fitting deficiencies as much as possible. The user needs to produce an equilibrium structure and a Hessian matrix for one or more building units. Afterward, a force field is generated for the system using a three-step method implemented in QuickFF. The first two steps of the methodology are designed to minimize correlations among the force field parameters. In the last step, the parameters are refined by imposing the force field parameters to reproduce the ab initio Hessian matrix in Cartesian coordinate space as accurate as possible. The method is applied on a set of 1000 organic molecules to show the easiness of the software protocol. To illustrate its application to metal-organic frameworks (MOFs), QuickFF is used to determine force fields for MIL-53(Al) and MOF-5. For both materials, accurate force fields were already generated in literature but they requested a lot of manual interventions. QuickFF is a tool that can easily be used by anyone with a basic knowledge of performing ab initio calculations. As a result, accurate force fields are generated with minimal effort. © 2015 Wiley Periodicals, Inc.
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Molecular sieving can lead to ultrahigh selectivity and low regeneration energy because it completely excludes all larger molecules via a size restriction mechanism. However, it allows adsorption of all molecules smaller than the pore aperture and so separations of complicated mixtures can be hindered. Here, we report an intermediate-sized molecular sieving (iSMS) effect in a metal–organic framework (MAF-41) designed with restricted flexibility, which also exhibits superhydrophobicity and ultrahigh thermal/chemical stabilities. Single-component isotherms and computational simulations show adsorption of styrene but complete exclusion of the larger analogue ethylbenzene (because it exceeds the maximal aperture size) and smaller toluene/benzene molecules that have insufficient adsorption energy to open the cavity. Mixture adsorption experiments show a high styrene selectivity of 1,250 for an ethylbenzene/styrene mixture and 3,300 for an ethylbenzene/styrene/toluene/benzene mixture (orders of magnitude higher than previous reports). This produces styrene with a purity of 99.9%+ in a single adsorption–desorption cycle. Controlling/restricting flexibility is the key for iSMS and can be a promising strategy for discovering other exceptional properties. Molecular sieving separates larger from smaller molecules, but all molecules smaller than the pore adsorb, hindering selectivity. Here, a MOF is reported with both molecular sieving and gate-opening, separating intermediate-sized molecules from larger and smaller analogues.
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The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.).
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eng_Latn
| 31,190 |
Two novel nanosized hybrid inorganic–organic frameworks, VO(C14H9COO)2, and VO(C10H7COO)2 have been solvothermally synthesized and their structures elucidated using a combination of powder XRD and DFT geometry optimization. They contain one-dimensional chains of corner-sharing tetrahedra in the case of VO(C10H7COO)2, and corner-sharing octahedra for VO(C14H9COO)2 oriented along orthorhombic/monoclinic c-axis, respectively. While VO(C14H9COO)2 exhibits bidentate bridging binding of organic moiety to the metal center, VO(C10H7COO)2 shows a monodentate mode as evidenced from DFT and infrared spectroscopy. Both hybrids exhibit fiber-like morphology, consisting of smaller individual single crystals aligned in parallel to the growth direction along the c-axis. They are thermally stable up to 350 °C having even more stable impurities containing vanadium in its highest oxidation state. The magnetic properties have also been investigated and indicate antiferromagnetic ordering along the chains characterized by rather low spin exchange parameters.
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Aluminium tris(ethyl acetoacetate), Al(C6H9O3)3 has been prepared and characterized by means of 1H and 13C nuclear magnetic resonance spectroscopy, scanning electron microscopy and X-ray powder diffraction (XRPD). It was determined that two stereoisomeric complexes can be distinguished in the solution: meridional and facial. The crystal structure of Al(C6H9O3)3 has been determined from XRPD data. The compound crystallizes in the monoclinic space group P21/n.
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The oxidative polymorphism of debrisoquine (DBQ) has been determined in 89 patients with colo-rectal cancer and in 556 normal control subjects. Four patients and 34 controls, with a metabolic ratio >12.6, were classified as poor metabolisers of DBQ (n.s.).
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eng_Latn
| 31,191 |
Substitution reactions of binuclear niobium cluster anion [Nb2S4(NCS)8]4– with different types of pyridine-based diimine ligands have been carried out. In the case of 2,2′-bipyridine (bipy) and its derivatives, only monosubstituted complexes [Nb2S4(NCS)6L]2– have been isolated. In the case of 1,10-phenanthroline and 2-(2-pyridyl)benzimidazole (Hpbz), both mono- and disubstituted complexes, [Nb2S4(NCS)6L]2– and [Nb2S4(NCS)4L2], respectively, have been obtained. Crystal structures of (Et4N)2[Nb2S4(NCS)6(bipy)]·0.5bipy·0.7CH3CN and [Nb2S4(pbmz)2(NCS)4]·5DMF·0.8H2O have been determined. All compounds have been characterized by NMR, ESI mass spectrometry, IR, UV/Vis spectroscopy, and CV. TiO2 nanoparticles modified with (Et4N)2[Nb2S4(NCS)6(bipy)] show moderate photocatalytic activity in the reaction of H2 generation from water in the presence of Na2S/Na2SO3 as a sacrificial electron donor system. The linear and nonlinear optical properties of the complexes with bipyridine ligands have been studied; the complexes function as broad-band optical limiters.
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Syntheses and structural elucidations of a series of chalcogen stabilized binuclear complexes of group 5 and 6 transition metals have been described. Room temperature reaction of [Cp*CrCl]2 (Cp* = η5-C5Me5) with Li[BH3(SePh)] afforded a Se inserted binuclear chromium complex, [(Cp*Cr)2(µ-Se2SePh)2], 1. In an attempt to make the analogous complexes with heavier group 6 metals, reactions of [Cp*MCl4] (M = Mo and W) with Li[BH3(SePh)] were carried out that yielded Se inserted binuclear complexes [(Cp*M)2(µ-Se)2(µ-SePh)2], 2 and 3 (2: M = Mo and 3: M = W) along with known [(Cp*M)2B5H9], 4a–b (4a: M = Mo and 4b: M = W). Similarly, the reactions of [Cp*NbCl4] with Li[BH3(EPh)] (E = S or Se) followed by thermolysis led to the formation of binuclear chalcogen complexes [(Cp*Nb)2(µ-E2)2], 5 and 6 (5: E = S and 6: E = Se) and known [(Cp*Nb)2(B2H6)2], 7. All these complexes have been characterized by 1H and 13C NMR spectroscopy and mass spectrometry. The structural integrity of complexes 1, 3, 5 and 6 was established by the X-ray diffraction studies. The DFT studies further exemplify the bonding interactions present in these complexes, especially the multiple bond character between the metals in 1–3. The syntheses and structural characterizations of three chalcogen-bridged bimetallic complexes of group 5 and 6 metals, such as [(Cp*Nb)2(µ-E2)2] (E = S and Se) (right), [(Cp*Cr)2(µ-Se2SePh)2] (centre) and [(Cp*M)2(µ-Se)2(µ-SePh)2], (M = Mo and W) (left) are reported.
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Pyrus pyrifolia (Asian pear) cell cultures respond to yeast extract (YE) treatment by accumulating benzoate-derived biphenyl phytoalexins, namely, noraucuparin and aucuparin. Biphenyl phytoalexins are defense-marker metabolites of the sub-tribe Malinae of the family Rosaceae. The substrates for biphenyl biosynthesis are benzoyl-CoA and malonyl-CoA, which combine in the presence of biphenyl synthase (BIS) to produce 3,5-dihydroxybiphneyl. In the non-β-oxidative pathway, benzoyl-CoA is directly derived from benzoic acid in a reaction catalyzed by benzoate-CoA ligase (BZL). Although the core β-oxidative pathway of benzoic acid biosynthesis is well-understood, the complete cascade of enzymes and genes involved in the non-β-oxidative pathway at the molecular level is poorly understood. In this study, we report the detection of benzaldehyde dehydrogenase (BD) activity in YE-treated cell cultures of P. pyrifolia. BD catalyzes the conversion of benzaldehyde to benzoic acid. BD and BIS activities were coordinately induced by elicitor treatment, suggesting their involvement in biphenyl metabolism. Changes in phenylalanine ammonia-lyase (PAL) activity preceded the increases in BD and BIS activities. Benzaldehyde was the preferred substrate for BD (Km=52.0μM), with NAD+ being the preferred co-factor (Km=64μM). Our observations indicate the contribution of BD towards biphenyl phytoalexin biosynthesis in the Asian pear.
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eng_Latn
| 31,192 |
Recently, single-walled carbon nanotubes as well as graphene functionalized with azobenzene chromophores have drawn attention for applications in optoelectronics due to their ability to undergo cis-trans isomerization when exposed to light. The electronic properties of the nanocarbon materials at these unconventional interfaces can be tailored by gaining structural insight into the organic monolayers at the molecular level. In this work, we use polarization-dependent X-ray absorption spectroscopy to probe the orientation of three chromophores on graphene, all identical except for their terminal groups. All three terminal groups (methyl, nitro, and nitrile) are well-oriented, with a tilt angle of about 30° from the substrate for the shared azobenzene group. Density functional theory calculations are in good agreement with experimental results and give two similar, stable configurations for the orientation of these molecules on graphene.
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X-rays from synchrotron radiation enable incisive spectroscopic techniques which speed up the discovery of new materials for photovoltaics and photoelectrochemistry. A particularly useful method is X-ray absorption spectroscopy (XAS), which probes empty electronic states. XAS is element- and bond-specific, with the additional capability of determining the bond orientation. Close feedback from density functional calculations makes it possible to discover and exploit systematic trends in the electronic properties. Case studies are presented, such as solar cells that combine an absorber with an electron donor and an acceptor in one molecular complex and nanowire arrays serving as photoanodes for water splitting. In addition to the energy levels the lifetimes of the charge carriers play an essential role in device performance. A new generation of laser-like X-ray sources will make it possible to follow the fate of excited charge carriers traveling across a molecular complex or through a device structure in real time.
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Nymphs ofTriatoma infestans andTriatoma mazzottii are weakly attracted to their feces and to extracts of feces in polar solvents, but not to nonpolar solvent extracts. The major volatile compounds identified in feces by solvent extraction and thermal desorption wereo-aminoacetophenone, 4-methylquinazoline, and 2,4-dimethylquinazoline, but these showed no attractant activity at a range of concentrations. Choice tests with a moving current of air gave no positive reaction to feces, extracts, or pure compounds.
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| 31,193 |
The photosensitized decomposition of the main steroids used in oral contraceptives was studied. Under the circumstances applied, ethinyl estradiol and norethynodrel decomposed rapidly (t 1/2 = 11.0 + or - 0.2 minutes for ethinyl estradiol and 5.7 + or - 0.4 minutes for norethynodrel). The decomposition product of ethinyl estradiol has been identified as 17 alpha-ethynyl-10 beta-hydroperoxy-17 beta-hydroxyestra-1,4-dien-3-one. The decomposition products of ethinyl estradiol and norethnodrel were previously found in experiments in which the irreversible binding of these steroids to protein was studied. Photosensitized decomposition of the steroids may be the cause of photoallergic side effects of "the pill."
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Introduction Keratinocyte carcinoma (KC) is the most common malignancy in the United States. The two most common forms of KC are basal cell carcinoma and squamous cell carcinoma (SCC), which account for 80% and 20% of cases, respectively. Objective There are many well-established risk factors for KC, but a more controversial risk factor for KC development is menopausal hormone therapy (MHT). This review synthesizes existing information on this topic and identifies knowledge gaps for future study. Methods A systematic review of the literature using the Medical Subject Headings terms “menopausal hormone therapy; skin neoplasms” was conducted in the PubMed database from March 19, 2018 to April 1, 2018. This yielded 168 articles, case reports, and reviews, which were further refined for inclusion during the development of this manuscript. Additional articles were identified from cited references. Results Four studies pertaining to this topic were identified. The results were evaluated in the context of these studies’ strengths and weaknesses. MHT contributes to an increased risk of basal cell carcinoma in Caucasian subjects and may make these tumors histologically more aggressive. There is not enough evidence to make a conclusion with regard to a potential relationship between MHT and SCC. However, one study suggested an increased risk of SCC with MHT use and another demonstrated a temporal association with prolonged MHT use and increased risk of SCC development. Conclusion Ever users of MHT should be screened more frequently for KC. This issue is of importance to dermatologists because patients who receive earlier diagnoses of KC will have a better opportunity to pursue treatment.
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Two new model systems for use within the rapidly develop- ing ultrafast time resolved x-ray scattering techniques have been prepared. Their photoisomerisation from norbornadiene to quadricyclane was found to be a suitable reaction to fol- low. Simulations of scattering patterns (not included in this report) showed that if heavy atoms are included in these molecular structures, then the transformation can be followed by transient X-ray scattering techniques. Two new bromosub- stituted norbornadienes were synthesised and characterised. Absorption spectroscopy showed that the norbornadienes are converted quantitatively to quadricyclanes under ultra- violet irradiation. Nuclear magnetic resonance (NMR) studies showed that the process was fully reversible and that the norbornadienes could be completely recovered even without addition of catalysts. Furthermore, it was shown that the formation of quadricyclane from norbornadiene was unaf- fected by triplet sensitisers. The two new model systems synthesised thus are strong candidates for use in time- resolved X-ray scattering studies in both gas and condensed phases.
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| 31,194 |
The role of electron- and proton-transfer processes in the photophysics of hydrogen-bonded molecular systems has been investigated with ab initio electronic-structure calculations. Adopting indole, pyridine, and ammonia as molecular building blocks, we discuss generic mechanisms of the photophysics of isolated aromatic chromophores (indole), complexes of pi systems with solvent molecules (indole-ammonia, pyridine-ammonia), hydrogen-bonded aromatic pairs (indole-pyridine), and intramolecularly hydrogen-bonded pi systems (7-(2'-pyridyl)indole). The reaction mechanisms are discussed in terms of excited-state minimum-energy paths, conical intersections, and the properties of frontier orbitals. A common feature of the photochemistry of the various systems is the electron-driven proton-transfer (EDPT) mechanism: highly polar charge-transfer states of 1pipi*, 1npi*, or 1pisigma* character drive the proton transfer, which leads, in most cases, to a conical intersection of the S1 and S0 surfaces and thus ultrafast internal conversion. In intramolecularly hydrogen-bonded aromatic systems, out-of-plane torsion is additionally needed for barrierless access to the S1-S0 conical intersection. The EDPT process plays an essential role in diverse photophysical phenomena, such as fluorescence quenching in protic solvents, the function of organic photostabilizers, and the photostability of biological molecules.
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Electron-induced proton transfer depicts the proton motion coupled with the attachment of a low-energy electron to a molecule, which helps to understand copious fundamental chemical processes. Intramolecular electron-induced proton transfer is a similar process that occurs within a single molecule. To date, there is only one known intramolecular example, to the best of our knowledge. By studying the 10-hydroxybenzo[h]quinoline and 8-hydroxyquinoline molecules using anion photoelectron spectroscopy and density functional theory, and by theoretical screening of six other molecules, here we show the intramolecular electron-induced proton transfer capability of a long list of molecules that meanwhile have the excited-state intramolecular proton transfer property. Careful examination of the intrinsic electronic signatures of these molecules reveals that these two distinct processes should occur to the same category of molecules. Intramolecular electron-induced proton transfer could have potential applications such as molecular devices that are responsive to electrons or current.Intramolecular electron-induced proton transfer (iEIPT) describes proton motion coupled with the attachment of an electron within a molecule. Here, the authors build a “search engine” for iEIPT-capable molecules that also have the excited-state intramolecular proton transfer property.
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Electric vehicles (EVs) are quickly gaining widespread interest as attractive alternatives to conventional petrol driven vehicles. If EVs derive some or all of their power from renewable sources, then they can help reduce global dependence on fossil fuels for transportation. Inductive power transfer (IPT) is a method that can transfer power to EVs over an air gap without physical contact. If IPT systems are incorporated into highways, then EVs can be charged dynamically as they travel. This will dramatically increase the range, convenience and safety of EV charging as well as reduce range anxiety and battery bank capacities. One of the major difficulties involves detecting an EV as it travels along the highway. By detecting the approaching EV, the primary power supply can energize the primary IPT coupler buried in the roadway to enable contactless power transfer to the EV. A three coil detection system, which focuses on these sensor coils and which is independent of the specific IPT coupler used, is presented to allow the power supply to detect the approaching EV mounted secondary IPT coupler. The proposed detection method was tested on a laboratory scale prototype and can detect EVs approaching at different speeds, ground clearances, and horizontal misalignments.
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| 31,195 |
Components within synthetic chemical and natural product extract libraries often interfere with fluorescence-based assays. Fluorescence interference can result when the intrinsic spectral properties of colored compounds overlap with the fluorescent probes. Typically, fluorescence-based protease assays use peptide amidomethylcoumarin derivatives as substrates. However, because many organic compounds absorb in the ultraviolet region, they can interfere with coumarin-based fluorescence assays. Red-shifted fluorescent dyes such as peptidyl rhodamine derivatives are useful because there is generally less interference from organic compounds outside the ultraviolet wavelengths. In this report, rhodamine-based fluorogenic substrates, such as bis-(Leu)2-Rhod110 and bis-(Ala-Pro)2-Rhod110, were developed for leucine aminopeptidase and dipeptidyl aminopeptidase. Novel, tandem rhodamine substrates such as Ala-Pro-Rhod110-Leu were designed with 2 protease cleavage sites and used to assay 2 proteases in a multiplex for...
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SARS-coronavirus (SARS-CoV) encodes a main prote- ase, 3CLpro, which plays an essential role in the viral life cycle and is currently the prime target for discovering new anti-coronavirus agents. In this article, we report our success in developing a novel red-shifted (RS) fluores- cence-based assay for 3CLpro and its application for identifying small-molecule anti-SARS agents from marine organisms. We have synthesised and characterised the first generation of a red-shifted internally quenched fluo- rogenic substrate (RS-IQFS) for 3CL pro based on reso- nance energy transfer between the donor and acceptor pair CAL Fluor Red 610 and Black Hole Quencher-1 (Km and kcat values of 14 mM and 0.65 min-1). The RS-IQFS primary sequence was selected based on the results of our screening analysis of 3CLpro performed using a series of blue-shifted (BS)-IQFSs corresponding to the 3CL pro - mediated cleavage junctions of the SARS-CoV polypro- teins. In contrast to BS-IQFSs, the RS-IQFS was not susceptible to fluorescence interference from coloured samples and allowed for successful screening of marine natural products and identification of a coumarin deriv- ative, esculetin-4-carboxylic acid ethyl ester, a novel 3CL pro inhibitor (IC50s46 mM) and anti-SARS agent (EC50s112 mM; median toxic concentration )800 mM) from the tropical marine sponge Axinella corrugata.
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By using a superluminescent diode as the light source and a depolariser inside the fibre coil, a constant scale factor is achieved without using polarisation control elements. For long-term behaviour an RMS-bias drift of 10 degrees/h is obtained.
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| 31,196 |
The product of reaction between the carcinogen, 7-bromomethyl-12-methylbenz[a]anthracene, and 2'-deoxyadenosine, i.e., N6-(12-methylbenz[a]anthracenyl-7-methyl)deoxyadenosine, has been prepared and characterized, and its structure has been determined by X-ray crystallographic techniques. The major structural features are: (a) the adenine and polycyclic aromatic hydrocarbon residues lie nearly perpendicular to one another; (b) the conformation about the glycosidic bond is syn, rather than anti, and an internal hydrogen bond between the deoxyribose 5'-hydroxyl group and N(3) of the adenine residue is present; and (c) the more planar anthracene portion of the hydrocarbon is stacked between adenine residues of other molecules throughout the crystal.
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We have previously shown that butadiene monoxide (BM), the primary metaholite of 1,3-butadiene, reacted with nucleosides to form alkylation products that exhibited different rates of formation and different stabilities under in vitro physiological conditions. In the present study, BM was reacted with single-stranded (ss) and double-stranded (ds) calf thymus DNA and the alkylation products were characterized after enzymatic hydrolysis of the DNA. The primary products were regioisomeric N-7-guanine adducts. N-3-(2-hydroxy-3-buten.1-yl)adenine and N-3-(1-hydroxy-3-buten-2-yl)adenine, which were depurinated from the DNA more rapidly than the N-7-guanine adducts, were also formed. In addition,N 6 -(2-hydroxy-3-buten-1-yl)deoxy-adenosine and N 6 -(1-hydroxy-3-buten-2-yl)deoxyadenosine were detected and evidence was obtained that these adducts were formed by Dimroth rearrangement of the corresponding N-1-deoxyadenosine adducts, not while in the DNA, but following the release of the N-1-alkylated nucleosides by enzymatic hydrolysis. N-3-(2-hydroxy-3-buten-1-yl)d-eoxyuridine adducts, which were apparently formed subsequent to deamination reactions of the corresponding deoxycytidine adducts, were also detected and were stable in the DNA. Adduct formation was linearly dependent upon BM concentration (10-1000 mM), with adduct ratios being similar at the various BM concentrations. At a high BM concentration (750 mM), the adducts were formed in a linear fashion for up to 8 h in both ssDNA and dsDNA. However, the rates of formation of the N-3-deoxyuridine and N 6 -deoxyadenosine adducts increased 10- to 20-fold in ssDNA versus dsDNA, whereas the N-7-guanine adducts increased only slightly, presumably due to differences in hydrogen bonding in ssDNA versus dsDNA. These results may contribute to a better understanding of the molecular mechanisms of mutagenesis and carcinogenesis of both BM and its parent compound, 1,3-butadiene.
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The interactions of water with polycyclic aromatic hydrocarbons, from benzene to graphene, are investigated using various exchange-correlation functionals selected across the hierarchy of density functional theory (DFT) approximations. The accuracy of the different functionals is assessed through comparisons with random phase approximation (RPA) and coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] calculations. Diffusion Monte Carlo (DMC) data reported in the literature are also used for comparison. Relatively large variations are found in interaction energies predicted by different DFT models, with GGA functionals underestimating the interaction strength for configurations with the water oxygen pointing toward the aromatic molecules. The meta-GGA B97M-rV and range-separated hybrid, meta-GGA ωB97M-V functionals provide nearly quantitative agreement with CCSD(T) values for the water–benzene, water–coronene, and water–circumcoronene dimers, while RPA and DMC predict interac...
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eng_Latn
| 31,197 |
Rationally designed assembly structures are of high scientific and technological importance for the development of multifunctional materials and devices. Among various types of nanobuilding blocks, polyoxometalates (POMs) are a class of metal oxide nanoclusters that offer rich structural versatility and enormous applications. The recent progresses in the synthesis of POM-based amphiphilic units have revolutionized POM chemistry, and consequently a variety of robust and well-defined assembly architectures with tunable properties have been developed, including one-dimensional wires and fibers, two-dimensional thin-films and disks, and threedimensional vesicles, spheres, tubes, and flowers. Although, these assembly structures hold great promise for the design of new functional materials, in reality they have been less explored for their potential use in various scientific fields. POMs have been extensively applied as catalysts for the oxidation of a variety of compounds such as alkenes, alcohols, and sulfides. Particularly, the oxidation of sulfides to sulfones, which is environmentally highly important, yet brings up a key challenge. To meet this challenge, many strategies in both homogeneous and heterogeneous catalytic reaction systems have been developed. The homogeneous approaches utilize the POM catalyst in bare form or in combination with a phase-transfer reagent, which generally have drawbacks associated with difficult catalyst separation and recovery. The heterogeneous approaches involve encapsulation with specific cations, immobilization of POM into silica or polymer matrices, or microemulsion formation. Although, heterogeneous systems provide easier catalyst recovery, generally it is based on filtration, which may be highly cumbersome on an industrial scale. In addition, the immobilization of POMs in supporting matrices involves complicated and lengthy catalyst preparation processes. Therefore, alternative multifunctional and superior approaches are needed. Recently, we reported well-defined, robust Keggin ion based nanocones, obtained by a simple and fast synthesis technique at room temperature. Herein, we report the functionalization of nanocones with magnetite nanocrystals and their controlled manipulation in the reaction system. For example, we applied these nanocones for the catalytic oxidation of sulfides in which they act as nanoreactors to provide enhanced efficiency, selectivity, and easier recovery under an external magnetic field. Figure 1 illustrates the concept of the nanocone nanoreactors. According to the accepted mechanism for the increased efficiency of the POM hybrid building block (DODA)3PW12O40 (DODA= dimethyldioctadecylammo-
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A self-assembled mesoporous polyoxometalate-based ionic hybrid catalyst [TMGHA]2.4H0.6PW was prepared by combination of alcohol amino-tethered guanidinium ionic liquid [TMGHA]Cl with Keggin phosphotungstic acid H3PW12O40 (PW). Nitrogen sorption experiment validated the formation of mesostructure with moderate BET surface area, and scanning and transmission electron microscopy (SEM and TEM) showed a fluffy coral-shaped morphology for the hybrid. The contact angle test displayed that the hybrid owned hydrophilic-hydrophobic balanced surface that exhibited well wettability for both water and organic substrate like benzyl alcohol. Therefore, the hybrid can efficiently catalyze the water-mediated triphasic oxidation of benzyl alcohol with H2O2. During the reaction, the triphase catalytic system showed a special "on water" effect mainly due to the suitable mesostructure and surface wettability, thus providing some clues for the preparation of green heterogeneous catalyst.
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Solutions of the quaternary ammonium salts of a set of classic polyoxometalates (POMs) (Keggin [XM12O40](n-), Dawson [P2W18O62](6-), and Lindqvist [M6O19](2-) (X = P, Si; M = W, Mo) were characterized by electrospray mass spectrometry. The gas-phase fragmentations of a series of quaternary ammonium-associated clusters were investigated by their collision-induced dissociations to elucidate their fragmentation mechanisms. It was found that the quaternary ammonium-associated clusters had distinctive dissociation characteristics. Moreover, the mono-quaternary ammonium-associated clusters, {NR4[POMs]}((n-1)-), shared a common fragmentation feature, that is, they decomposed exclusively into their respective alkyl cation-bound clusters irrespective of the different cation sizes and the different natures of the polyoxoanions. The optimized geometries and the binding energies of the mono cation-bound Lindqvist POM-based clusters were obtained by calculations. To the best of our knowledge, this is the first investigation of the gas-phase fragmentations of these noncovalent complexes between organic amines and inorganic POM anions by a combination of theory and mass spectrometry.
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eng_Latn
| 31,198 |
Introduction ::: Progesterone receptors (PRs) are present in many breast tumors, and their levels are increased by certain endocrine therapies. They can be used as targets for diagnostic imaging and radiotherapy.
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The halogens bromine and iodine have similar chemical properties and undergo similar reactions due to their closeness in Group 17 of the periodic chart. There are a number of bromine and iodine radionuclides that have properties useful for diagnosis and therapy of human diseases. The emission properties of radiobromine and radioiodine nuclides with half-lives longer than 1 h are summarized along with properties that make radionuclides useful in PET/SPECT imaging and β/Auger therapy, such that the reader can assess which of the radionuclides might be useful for medical applications. An overview of chemical approaches that have been used to radiolabel molecules with radiobromine and radioiodine nuclides is provided with examples. Further, references to a large variety of different organ/cancer-targeting agents utilizing the radiolabeling approaches described are provided.
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Abiotic stresses arising from climate change negates crop growth and yield, leading to food insecurity. Drought causes oxidative stress on plants, arising from excessive production of reactive oxygen species (ROS) due to inadequate CO2, which disrupts the photosynthetic machinery of plants. The use of conventional methods for the development of drought-tolerant crops is time-consuming, and the full adoption of modern biotechnology for crop enhancement is still regarded with prudence. Plant growth-promoting rhizobacteria (PGPR) could be used as an inexpensive and environmentally friendly approach for enhancing crop growth under environmental stress. The various direct and indirect mechanisms used for plant growth enhancement by PGPR were discussed. Synthesis of 1-aminocyclopropane−1-carboxylate (ACC) deaminase enhances plant nutrient uptake by breaking down plant ACC, thereby preventing ethylene accumulation, and enable plants to tolerate water stress. The exopolysaccharides produced also improves the ability of the soil to withhold water. PGPR enhances osmolyte production, which is effective in reducing the detrimental effects of ROS. Multifaceted PGPRs are potential candidates for biofertilizer production to lessen the detrimental effects of drought stress on crops cultivated in arid regions. This review proffered ways of augmenting their efficacy as bio-inoculants under field conditions and highlighted future prospects for sustainable agricultural productivity.
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eng_Latn
| 31,199 |
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