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Rhodium(III)-Catalyzed Redox-Neutral C–H Activation/Annulation of N-Aryloxyacetamides with Alkynyloxiranes: Synthesis of Highly Functionalized 2,3-Dihydrobenzofurans
|
Rh(III)-Catalyzed C–H Bond Activation for the Construction of Heterocycles with sp3-Carbon Centers
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Meyrier ) 2 , 8-Dihydroxyadeninuria-induced progressive renal failure
|
eng_Latn
| 31,000 |
Amine-flavin electron transfer photochemistry. Potential models for monoamine oxidase catalysis and inhibition.
|
Synthesis and Structure–Activity Relationship Studies of N-Benzyl-2-phenylpyrimidin-4-amine Derivatives as Potent USP1/UAF1 Deubiquitinase Inhibitors with Anticancer Activity against Nonsmall Cell Lung Cancer
|
Absence of CCR8 does not impair the response to ovalbumin-induced allergic airway disease.
|
eng_Latn
| 31,001 |
Diradical Character Based Design for Singlet Fission of Condensed-Ring Systems with 4nπ Electrons
|
Antiaromatic character of cycloheptatriene-bis-annelated indenofluorene framework mainly originated from heptafulvene segment
|
Cardiac sympathetic denervation is not related to nigrostriatal degeneration in Parkinson’s disease
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eng_Latn
| 31,002 |
Hirshfeld surface analysis of new phosphoramidates.
|
Evaluation of N–H···O hydrogen bond interactions in two new phosphoric triamides with a P(O)[NHCH(CH3)2]2 segment by means of topological (AIM) calculations, Hirshfeld surface analysis and 3D energy framework approach
|
Oral insulin does not alter gut microbiota composition of NOD mice
|
eng_Latn
| 31,003 |
Metal-Free Broensted Acid Catalyzed Formal [3 + 3] Annulation. Straightforward Synthesis of Dihydro-2H-chromenones, Pyranones, and Tetrahydroquinolinones.
|
SO 4 2-/ SnO 2-Catalyzed efficient one-pot synthesis of 7 , 8-Dihydro-2 H-Chromen-5-ones by formal [ 3 + 3 ] cycloaddition and 1 , 8-Dioxo-octahydroxanthenes via a Knoevenagel condensation
|
Meyrier ) 2 , 8-Dihydroxyadeninuria-induced progressive renal failure
|
eng_Latn
| 31,004 |
Molecular Structure, Quadrupole Coupling Tensor and Dipole Moment of Ethyl Cyanide
|
Chirped-pulse Fourier transform millimeter-wave spectroscopy of ten vibrationally excited states of i-propyl cyanide: exploring the far-infrared region
|
Microtubule capture by CENP-E silences BubR1-dependent mitotic checkpoint signaling
|
eng_Latn
| 31,005 |
Inhibitory activity of vitamin E and α-naphthoflavone on β-carotene-enhanced transformation of BALB/c 3T3 cells by benzo(a)pyrene and cigarette-smoke condensate.
|
Cigarettes, cancer, and carotenoids: a continuing, unresolved antioxidant paradox
|
Excellent photocatalytic activity of titania–graphene nanocomposites prepared by a facile route
|
eng_Latn
| 31,006 |
Synthesis, spectroscopy and excited-state redox properties of novel luminescent trinuclear three-co-ordinate gold(I) phosphine complexes
|
Crystalline-Amorphous-Crystalline Transformation in a Highly Brilliant Luminescent System with Trigonal-Planar Gold(I) Centers
|
Oral spray wintertime vitamin D3 supplementation has no impact on inflammation in Gaelic footballers
|
eng_Latn
| 31,007 |
Fischer-Tropsch catalyst deactivation in commercial microchannel reactor operation
|
Effect of Co-Feeding Inorganic and Organic Molecules in the Fe and Co Catalyzed Fischer–Tropsch Synthesis: A Review
|
The Origin of the Molecular Diversity and Functional Anchoring of Cholinesterases
|
eng_Latn
| 31,008 |
Proton Transfer of Guanine Radical Cations Studied by Time-Resolved Resonance Raman Spectroscopy Combined with Pulse Radiolysis
|
Hole Trapping of G-Quartets in a G-Quadruplex
|
Genomic evidence for the absence of a functional cholesteryl ester transfer protein gene in mice and rats.
|
eng_Latn
| 31,009 |
Transient structural response to photoexcitation in polyacetylene
|
Coherent Electron Transfer in Polyacetylene
|
Transcriptional activation of HIF-1 by a ROS-ERK axis underlies the resistance to photodynamic therapy
|
eng_Latn
| 31,010 |
Gold Nanoparticles Stabilized with Aromatic Thiols: Interaction at the Molecule–Metal Interface and Ligand Arrangement in the Molecular Shell Investigated by SR-XPS and NEXAFS
|
Photo-induced transformation process at gold clusters-semiconductor interface: Implications for the complexity of gold clusters-based photocatalysis
|
Ligand-free nickel-catalyzed CS bond formation : synthesis of 2-aminobenzothiazoles
|
eng_Latn
| 31,011 |
Remote Multiproton Storage within a Pyrrolide-Pincer-Type Ligand.
|
Catalytic transformation of dinitrogen into ammonia and hydrazine by iron-dinitrogen complexes bearing pincer ligand
|
Plasma cell labeling index and beta 2-microglobulin predict survival independent of thymidine kinase and C-reactive protein in multiple myeloma.
|
eng_Latn
| 31,012 |
Double role of the hydroxy group of phosphoryl in palladium(II)-catalyzed ortho-olefination: a combined experimental and theoretical investigation.
|
Probing the Origin of Challenge of Realizing Metallaphosphabenzenes: Unfavorable 1,2-Migration in Metallapyridines Becomes Feasible in Metallaphosphabenzenes
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Oral spray wintertime vitamin D3 supplementation has no impact on inflammation in Gaelic footballers
|
eng_Latn
| 31,013 |
A novel photosubstitution of dicyanobenzenes by allylic and benzylic silanes
|
A strategy for the preparation of cyclic polyarenes based on single electron transfer-promoted photocyclization reactions
|
Oral spray wintertime vitamin D3 supplementation has no impact on inflammation in Gaelic footballers
|
eng_Latn
| 31,014 |
Photochemical transformation of aqueous C60 clusters in sunlight.
|
Beyond nC60: strategies for identification of transformation products of fullerene oxidation in aquatic and biological samples
|
Transcriptional activation of HIF-1 by a ROS-ERK axis underlies the resistance to photodynamic therapy
|
eng_Latn
| 31,015 |
The Sommelet Reaction in the Synthesis of Aromatic Dialdehydes1
|
SYNTHESIS OF SOME 2-R-5-FORMIL-1,3,4- THIADIAZOLE DERIVATIVES BY SOMMELET REACTION
|
Evidence against a role for platelet-derived molecules in liver regeneration after partial hepatectomy in humans
|
eng_Latn
| 31,016 |
Isolation and identification of 6-desmethylnaproxen sulfate as a new metabolite of naproxen in human plasma.
|
Involvement of multiple cytochrome P450 isoforms in naproxen O-demethylation
|
Involvement of multiple cytochrome P450 isoforms in naproxen O-demethylation
|
eng_Latn
| 31,017 |
Photoaquation of methylated cis-dichlorobis(1,10-phenanthroline)rhodium(III)chloride compounds by direct population of a photoactive triplet excited state.
|
Interaction with calf-thymus DNA and photoinduced cleavage of pBR322 by rhodium(III) and iridium(III) complexes containing crown thioether ligands
|
Transcriptional activation of HIF-1 by a ROS-ERK axis underlies the resistance to photodynamic therapy
|
eng_Latn
| 31,018 |
Recent Advances in the Chemistry of Benzo[b]furan and Its Derivatives. Part I: Occurrence and Synthesis
|
Theoretical study of the regioselective cyclization of enaminones in the construction of benzofurans and indoles
|
Nanoparticles of barium induce apoptosis in human phagocytes
|
eng_Latn
| 31,019 |
Photosensitization of single-strand breaks in pBR322 DNA by rose bengal.
|
UVA photoirradiation of benzo[a]pyrene metabolites: induction of cytotoxicity, reactive oxygen species, and lipid peroxidation
|
Porin channels in intact cells of Escherichia coli are not affected by Donnan potentials across the outer membrane.
|
eng_Latn
| 31,020 |
Herein, carbazole derivatized non-peripheral (1,(4)-tetra(carbazol-2-yloxy)phthalocyaninatozinc(II), 3-TCbZnPc) and peripheral (2,(3)-tetra(carbazol-2-yloxy)phthalocyaninato zinc(II), 4-TCbZnPc) are conjugated to silver nanoparticles and their photochemical and photophysical behavior are reported. The presence of silver nanoparticles resulted in reduced fluorescence, and increased triplet and singlet oxygen quantum yields. The conjugates were further electrospun into polystyrene fibers, and employed for the photodegradation of methyl orange. The photodegradation of methyl orange using all functionalized fibers followed first order kinetics, and was faster when the conjugates with silver nanoparticles were used. The non-peripherally substituted 3-TCbZnPc gave better photocatalytic activity compared to its peripherally substituted counterpart (4-TCbZnPc). The hybrid electrospun fibers provide great potential as active photocatalysts for degrading organic pollutants.
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Activated carbon fiber-supported cobalt phthalocyanine photocatalyst (Co-TDTAPc-F) was prepared in this study, and its performance for dye wastewater decoloration was investigated, and Acid Orange II (AO7) was selected as the target pollutant. The morphology analysis of Co-TDTAPc-F was conducted, and the effects of catalyst loading, H2O2 addition, solution pH, and catalyst reuse on AO7 decoloration efficiency were evaluated. The results showed that AO7 decoloration efficiency increased by 23.2% during the Co-TDTAPc-F photocatalytic process as compared with solely Co-TDTAPc-F adsorption, and the decoloration process was fitted by pseudo first-order reaction. The increase of catalyst loading and H2O2 content both benefitted AO7 decoloration. Strong photocatalytic activities were observed at both acidic and alkaline conditions; however, total organic carbon (TOC) removal efficiency decreased with the increase of solution pH. Strong photocatalytic activity was still observed after four times reuse. The mechanisms of AO7 photocatalytic decomposition by Co-TDTAPc-F were proposed.
|
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).
|
eng_Latn
| 31,021 |
Novel curcumin analogs were synthesized using Knoevenagel condensation to convert enolic diketones of curcumin into non-enolizable ones and Schiff bases were prepared using a bioactive thiosemicarbazide pharmacophore. Copper(II) conjugates of all synthesized ligands were prepared and structurally characterized as well as evaluated for their potential of inhibiting TNF-induced NF-κB activation and proliferation in human leukemic KBM-5 cells wherein compound 13 was found to be more potent than curcumin. Compounds were further examined on other tumor cell lines such as Jurkat, H1299, and MM1, respectively.
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Novel complexes of Cu(II), Ni(II), Co(II), Zn(II) and VO(II) have been prepared using a Schiff base derived from 1-phenyl-2,3-dimethyl-4-imino-benzylidene-pyrazol-5-one and dimethylglyoxime. The structural features of the chelates have been confirmed by microanalytical data, IR, UV-Vis., 1 H NMR and ESR spectral techniques. Electronic absorption and IR spectra of the complexes indicate an octahedral geometry around the central metal ion except VO(II) complex which shows square pyramidal geometry. The monomeric nature of the complexes is confirmed from their magnetic susceptibility. Low conductance data of the chelates support their non-electrolytic nature except vanadyl complex which shows electrolytic in nature due to the presence of sulphate ion outside the coordination sphere. The cyclic voltammogram of the copper and vanadyl complexes in MeCN at 300 K were well studied. The ESR spectra of copper and vanadyl complexes in DMSO solution at 300 and 77 K were recorded and their salient features are reported. The molecular orbital coefficients were calculated for the complexes. The antimicrobial activity of the ligand and its complexes has been extensively studied on microorganisms such as Staphylococcus aureus, Klebsiela pneumoniae, Bacillus subtilis, Escherichia coli and Salmonella typhi . Most of the complexes have higher activity than that of the free ligand.
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Berzelius failed to make use of Faraday's electrochemical laws in his laborious determination of equivalent weights.
|
eng_Latn
| 31,022 |
Preface Volume One INTRODUCTION Some Historical Remarks on Supramolecular Chemistry The Noncovalent Bond: a Brief Overview Basic Concepts in Supramolecular Chemistry Conclusions: Diverse Methods for a Diverse Research Area QUANTITATIVE ANALYSIS OF BINDING PROPERTIES Theoretical Principles A Practical Course of Binding Constant Determination by UV/Vis Spectroscopy Practical Course of Action for NMR Spectroscopic Binding Constant Determination Other Important Examples with Practical Actions of Data Treatment Conclusion ISOTHERMAL TITRATION CALORIMETRY IN SUPRAMOLECULAR CHEMISTRY Introduction The Thermodynamic Platform Acquiring Experimental Calorimetric Data Extending the Measurement Range Perspectives EXTRACTION METHODS Introduction The Extraction Technique The Technical Process The Extraction Equilibrium Principles of Supramolecular Extraction Examples of Supramolecular Extraction Conclusions and Future Perspectives MASS SPECTROMETRY AND GAS PHASE CHEMISTRY OF SUPRAMOLECULES Introduction Instrumentation Particularities and Limitations of Mass Spectrometry Beyond Analytical Characterization: Tandem MS Experiments for the Examination of the Gas-Phase Chemistry of Supramolecules Selected Examples Conclusions DIFFUSION NMR IN SUPRAMOLECULAR CHEMISTRY AND COMPLEXED SYSTEMS Introduction Concepts of Molecular Diffusion Measuring Diffusion with NMR Applications of Diffusion NMR in Supramolecular Chemistry: Selected Examples Advantages and Limitations of High Resolution Diffusion NMR Diffusion NMR and Chemical Exchange Diffusion Modes and Signal Decay in Diffusion MR Experiments Applications of Diffusion NMR in Complex Systems Summary and Outlook PHOTOPHYSICS AND PHOTOCHEMISTRY OF SUPRAMOLECULAR SYSTEMS Introduction Spectrophotometry and Spectrofluorometry Time-Resolved Fluorescence Techniques Fluorescence Anisotropy Transient Absorption Spectroscopy Concluding Remarks CIRCULAR DICHROISM SPECTROSCOPY Basic Considerations Measurement Techniques (Methodology of CD Measurement) Processing of Circular Dichroism Spectra Theory Examples of Vibrational Circular Dichroism Applications Concluding Remarks Volume Two ELECTROCHEMICAL METHODS Introduction Basic Principles of Electrochemistry Overview of Electrochemical Techniques Electrochemical Analysis of Supramolecular Systems Selected Examples Concluding Remarks CRYSTALLOGRAPHY AND CRYSTAL ENGINEERING Introduction Crystallography Crystal Engineering Methyl-Resorcinarene as a Crystal Engineering Target Concluding Remarks SCANNING PROBE MICROSCOPY Introduction: What Is the Strength of Scanning Probe Techniques? How Do Scanning Probe Microscopes Work? Which Molecules Can Be Studied? What Results Have Been Obtained in the Field of Supramolecular Chemistry? SINGLE-MOLECULE FORCE SPECTROSCOPY OF SUPRAMOLECULAR COMPLEXES Introduction and Motivation Functionally Immobilizing Supramolecules Supramolecular Interactions Investigated by AFM-SMFS Summary and Outlook CONFOCAL LASER SCANNING MICROSCOPY: A VERSATILE SPECTROSCOPIC TOOL FOR THE INVESTIGATION OF MOLECULAR GELS Introduction: Molecular Gels Methods Classically Used for the Characterization of Molecular Gels Confocal Laser Scanning Microscopy (CLSM) Conclusion TRANSMISSION ELECTRON MICROSCOPY (TEM) OF RADIATION SENSITIVE SUPRAMOLECULAR ARCHITECTURES - STRATEGIES FOR A COMPREHENSIVE STRUCTURE CHARACTERIZATION Introduction Instrumentation Contrast in TEM Sample Preparation Strategies and Examples to Characterize Supramolecular Structures by Complementary TEM Methods THE CHARACTERIZATION OF SYNTHETIC ION CHANNELS AND PORES Introduction Methods Characteristics Structural Studies Concluding Remarks THEORETICAL METHODS FOR SUPRAMOLECULAR CHEMISTRY Introduction A Survey of Theoretical Methods Standard Classification of Intermolecular Interactions Qualitative Understanding and Decomposition Schemes General Mechanism for a Static, Step-Wise View on Host-Guest Recognition Conclusions and Perspective Index
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Advances in supramolecular chemistry and crystal engineering reported from India within the last decade are highlighted in the categories of new intermolecular interactions, designed supramolecular architectures, network structures, multi-component host-guest systems, cocrystals, and polymorphs. Understanding self-assembly and crystallization through X-ray crystal structures is illustrated by two important prototypes — the large unit cell of elusive saccharin hydrate, Na16(sac)16 · 30H2O, which contains regular and irregular domains in the same structure, and by the Aufbau build up of zinc phosphate framework structures, e.g. ladder motif in [C3N2H12][Zn(HPO4)2] to layer structure in [C3N2H12][Zn2(HPO4)3] upon prolonged hydrothermal conditions. The pivotal role of accurate X-ray diffraction in supramolecular and structural studies is evident in many examples. Application of the bottomup approach to make powerful NLO and magnetic materials, design of efficient organogelators, and crystallization of novel pharmaceutical polymorphs and cocrystals show possible future directions for interdisciplinary research in chemistry with materials and pharmaceutical scientists. This article traces the evolution of supramolecular chemistry and crystal engineering starting from the early nineties and projects a center stage for chemistry in the natural sciences.
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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.
|
yue_Hant
| 31,023 |
Three new Copper(II) polymers coordinated by both rigid and flexible ligands, [Cu(bpy)(C5H6O4)]n (1), [Cu(bpy)(C6H8O4)]n (2), and [Cu2(bpy)2(C6H8O4)2]n (3) (bpy = 4,4′-bipyridine), have been hydrothermally synthesized and structurally characterized. Complex 1 features a box-like bilayer motif of (4, 4) net. It crystallizes in triclinic space group with cell parameters: a = 8.1395(6) A, b = 9.43 12(8) A, c = 10.5473(8) A, α = 112.1830(1)°, β = 92.423(2)°, γ = 104.752(2)°, V = 716.31(1) A3, Z = 2. Complex 2 crystallizes in triclinic space group with a = 8.8652(4) A, b = 8.9429(4) A, c = 10.6390(4) A, α = 89.520(2)°, β = 69.123(2)°, γ = 75.2440(1)°, V = 758.92(6) A3, Z = 2. Complex 3 crystallizes in monoclinic space group Cc with a = 11.1521(1) A, b = 15.3961(1) A, c = 17.7419(1) A, β = 105.715(3)°, V = 2932.4(5) A3, Z = 4. Complexes 2 and 3 are isomeric with different coordination modes of adipato ligand. Both of them possess the two-fold interpenetrated 3-D pcu topological net.
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The average and commensurate superstructures of the one-dimensional coordination polymer {Cu(NO3)(H2O)}(HTae)(Bpy) (H2Tae = 1,1,2,2-tetraacetylethane, Bpy = 4,4′-bipyridine) were determined by single-crystal X-ray diffraction, and the possible symmetry relations between the space group of the average structure and the superstructure were checked. The crystal structure consists in parallel and oblique {Cu(HTae)(Bpy)} zigzag metal–organic chains stacked along the [100] crystallographic direction. The origin of the fivefold c axis in the commensurate superstructure is ascribed to a commensurate modulation of the coordination environment of the copper atoms. The commensurately ordered nitrate groups and coordinated water molecules establish a two-dimensional hydrogen-bonding network. Moreover, the crystal structure shows a commensurate to incommensurate transition at room temperature. The release of the coordination water molecules destabilizes the crystal framework, and the compound shows an irreversible str...
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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.).
|
eng_Latn
| 31,024 |
In this study, a novel approach for constructing different very sensitive and efficient photoelectrochemical biosensors called as P(SNS-NH2)/ChOx/[Ru(bpy)3]2+ and ChOx/[Ru(bpy)3]2+, were fabricated by bonding ChOx covalently to P(SNS-NH2) modified electrode and bare thioaniline modififed gold slide, respectively, using gluteraldehyde and tethering the N-hydroxysuccinimidyl ester functionalized Ru(II)-trisbipryridine to the ChOx enzyme. In the presence of different concentrations of cholesterol, the photocurrents were obtained by irradiating of the photoelectrochemical cell containing P(SNS-NH2)/ChOx/[Ru(bpy)3]2+ or ChOx/[Ru(bpy)3]2+ electrode as the anode under air. The bipyridine complex [Ru(bpy)3]2+ was used to activate photoinduced electron-transfer reaction and it acted as a redox mediator to activate the bioelectrocatalytic functions of ChOx. Therefore, it was shown the photonic electron-transfer wiring of ChOx with the electrode. ChOx/[Ru(bpy)3]2+ and P(SNS-NH2)/ChOx/[Ru(bpy)3)2+ biosensors showed a...
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We report the preparation of poly (propylene imine) dendrimer (PPI) and CdTe/CdSe/ZnSe quantum dots (QDs) as a suitable platform for the development of an enzyme-based electrochemical cholesterol biosensor with enhanced analytical performance. The mercaptopropionic acid (MPA)-capped CdTe/CdSe/ZnSe QDs was synthesized in an aqueous phase and characterized using photoluminescence (PL) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, transmission electron microscopy (TEM), X-ray power diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy. The absorption and emission maxima of the QDs red shifted as the reaction time and shell growth increased, indicating the formation of CdTe/CdSe/ZnSe QDs. PPI was electrodeposited on a glassy carbon electrode followed by the deposition (by deep coating) attachment of the QDs onto the PPI dendrimer modified electrode using 1-Ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC), and N-hydroxysuccinimide (NHS) as a coupling agent. The biosensor was prepared by incubating the PPI/QDs modified electrode into a solution of cholesterol oxidase (ChOx) for 6 h. The modified electrodes were characterized by voltammetry and impedance spectroscopy. Since efficient electron transfer process between the enzyme cholesterol oxidase (ChOx) and the PPI/QDs-modified electrode was achieved, the cholesterol biosensor (GCE/PPI/QDs/ChOx) was able to detect cholesterol in the range 0.1⁻10 mM with a detection limit (LOD) of 0.075 mM and sensitivity of 111.16 μA mM-1 cm-2. The biosensor was stable for over a month and had greater selectivity towards the cholesterol molecule.
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ABSTRACT Let A be a nilpotent matrix of index three and consider the Yang–Baxter-like matrix equation AXA=XAX. We first obtain a simplified matrix equation of the same type with A replaced by its Jordan form, whose Jordan blocks are at most . Then we obtain a system of matrix equations of smaller sizes to find all the commuting solutions of the original matrix equation.
|
eng_Latn
| 31,025 |
An efficient process for the conversion of glucose into 5-hydroxymethylfurfural (HMF) with environmentally friendly and cheap catalysts was studied in the ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). Among the catalysts employed, the combination of 12-tungstophosphoric acid (12-TPA)/boric acid (B(OH) 3 ) in the experiments resulted in the highest yield of HMF. The effects of various reaction parameters on HMF yields were also investigated. An HMF yield of 51.9% was achieved at 140 °C for 40 min. In addition, a small amount of water in this reaction system had little effect on the HMF yields. After the extraction of HMF, [BMIM]Cl and 12-TPA/B(OH) 3 could be reused and exhibited stable activities after five successive runs. More interestingly, like [BMIM]Cl, tetraethyl ammonium chloride (TEAC) could be favorable to HMF formation and was also used as an effective solvent for the conversion of glucose into HMF.
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This review highlighted the developments of safe, effective, economic, and environmental friendly catalytic technologies to transform lignocellulosic biomass into the activated carbon (AC). In the photocatalysis applications, this AC can further be used as a support material. The limits of AC productions raised by energy assumption and product selectivity have been uplifted to develop sustainable carbon of the synthesis process, where catalytic conversion is accounted. The catalytic treatment corresponding to mild condition provided a bulk, mesoporous, and nanostructure AC materials. These characteristics of AC materials are necessary for the low energy and efficient photocatalytic system. Due to the excellent oxidizing characteristics, cheapness, and long-term stability, semiconductor materials have been used immensely in photocatalytic reactors. However, in practical, such conductors lead to problems with the separation steps and loss of photocatalytic activity. Therefore, proper attention has been given to develop supported semiconductor catalysts and certain matrixes of carbon materials such as carbon nanotubes, carbon microspheres, carbon nanofibers, carbon black, and activated carbons have been recently considered and reported. AC has been reported as a potential support in photocatalytic systems because it improves the transfer rate of the interface charge and lowers the recombination rate of holes and electrons.
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Hydroxymethyl furfural (HMF) is one of important intermediates formed in Maillard reaction and caramelization. It was found that HMF existed in many Chinese herbal medicines (CHMs) and accumulated during CHM processing. In recent years, increasing attention has been paid to its safety and actions in CHMs, which has led to many reports about different aspects of HMF. In this paper, previous and recent studies on HMF formation, its presence in CHMs, its metabolism and bioactivities, together with its implications for CHMs were summarized, with the purpose of contributing to a better understanding of CHMs.
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eng_Latn
| 31,026 |
Cytochrome oxidase o has been isolated from the obligately aerobic, methylotrophic bacterium Methylophilus methylotrophus in the form of a cytochrome c L - o complex. The latter is comprised of cytochrome c L ( M r 21 000) and cytochrome o ( M r 29 000) in a 1–2:1 ratio, possibly in association with one or more minor polypeptides; the complex exhibits a high ascorbate-TMPD oxidase activity which is inhibited non-competitively by cyanide ( K i ≈ 2 μM). In contrast, the oxidation of methanol by whole cells is inhibited uncompetitively by cyanide ( K i ≈4 μM), thus indicating the involvement in methanol oxidation of cytochrome oxidase aa 3 rather than o .
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Membranes of the acidophilic methylotroph Acetobacter methanolicus contained only b- and c-type cytochrome and a CO-binding b-type cytochrome. An azide-sensitive oxidase that oxidizes cytochrome c and ascorbate/TMPD was solubilized from the membrane with a mixture of CHAPS and Zwittergent3-12 (1.7 fold increase in specific activity with 32% yield). The solubilized oxidase is unusually stable with respect to high ionic strength (200 mM-NaCl) and stable between pH 4.0 and 6.8. Of the two soluble c-type cytochromes from A. methanolicus only the typical class I cytochrome (cytochrome c ::: H) was a good substrate, as was equine cytochrome c. The oxidase was partially purified by anion-exchange chromatography but further purification proved impossible. The yield with respect to equine cytochrome c oxidation was 18%, with a 22-fold purification, but during purification most of the activity with respect to cytochrome c ::: H and TMPD was lost. Neutral phospholipids had little effect on activity of the oxidase but the charged phospholipids phosphatidylglycerol and phosphatidylserine stimulated activity up to about fourfold. It proved impossible to incorporate the oxidase into active lipoprotein vesicles. During the purification process the pH optimum for oxidation of cytochrome c ::: H was unchanged (pH 5.6) whereas that for oxidation of equine cytochrome changed from pH 9.5 to 7.5 and the sensitivity of the oxidase to azide changed from non-competitive to competitive during the purification process. The partially-purified oxidase contained only b-type cytochrome, some of which was CO-reactive. It is proposed that the oxidase is a cytochrome co type of oxidase that loses its cytochrome c component during the purification process and is only able to oxidize c-type cytochromes if these can be formed into a ‘reconstituted’ cytochrome co with the partially-purified oxidase.
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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
| 31,027 |
We have developed a novel method to synthesise artificial ligand-bearing DNAs utilising a template-independent DNA polymerase. Hydroxypyridone ligand-bearing nucleotides (H) were successively appended to DNA primers by the enzyme. The resulting strands, tailed with H nucleotides, formed CuII-mediated metallo-DNA duplexes through the formation of metal-mediated artificial base pairs (H–CuII–H).
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Bioconjugation, biosensing, bioimaging, bionanomaterials, etc., are only a few examples of application of functionalized DNA. Since base-modified nucleic acids contribute not only to a broad range of biotechnological fields but also to the understanding of various cellular processes, it is crucial to design novel modifications with unique properties. Here, we demonstrate the utilization of N4-cytidine modified oligonucleotides, which contain reactive acetophenone (AP) or benzophenone (BP) groups, for the UV-induced cross-linking. We find that terminal deoxynucleotidyl transferase-mediated 3'-tailing using AP/BP-containing modified nucleotides generates photoactive DNA, suitable for a straightforward covalent cross-linking with both interacting proteins and a variety of well-known solid polymeric supports. Moreover, we show that AP/BP-functionalization of nucleic acid molecules induces an efficient cross-linking upon exposure to UVA light. Our findings reveal that 3'-tailed single-stranded DNA bearing AP/BP-moieties is easily photoimmobilized onto untreated polystyrene, polypropylene, polylactate, polydimethylsiloxane, sol-gel and borosilicate glass substrates. Furthermore, we demonstrate that such immobilized DNA probes can be further used for successful hybridization of complementary DNA targets. Our results establish novel N4-cytosine nucleobase modifications as photoreactive labels and suggest an effortless approach for photoimmobilization of nucleic acids.
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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.).
|
eng_Latn
| 31,028 |
A new class of chiral N,P-ligands for the Ir-catalyzed asymmetric hydrogenation of aryl alkenes has been developed. These new ligands proved to be highly efficient and tolerates a broad range of substrates. The enantiomeric excesses are in the range of the best ever reported. The results can be rationalized with the proposed selectivity model.
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In the present study, iron oxide magnetic nanoparticles (Fe3O4 MNPs) were synthesized in a green biosynthetic manner using aqueous extract of clover leaves. Fe3O4 MNPs were applied as a magnetically separable nanocatalyst for the green syntheses of functionalized [1,3]-oxazoles 1(a–e) and 1H-pyrrolo-[1,3]-oxazoles 4(a–i) as promising antioxidant compounds in excellent yields at 50 °C and room temperature, respectively. The antioxidant activities of the most stable compounds (1a, 1b, 4a, and 4b) were evaluated by both 2,2-diphenyl-1-picrylhydrazyl radical scavenging and ferric reduction activity potential assays. Compound 1b was shown a remarkable radical scavenging activity, and 4a was shown very good reducing activity relative to standards (BHT and TBHQ).
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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
| 31,029 |
Fast spreading drug resistance to commonly used antimalarial drugs like chloroquine and pyrimethamine has posed urgent requirement for newer drugs. Identification of critical biochemical processes necessary for parasite survival and their characterization is necessary for targeted drug design. Despite prolonged research, biochemistry of malaria parasite is poorly understood. Many common biochemical pathways, well characterized in other organisms, are yet to be looked at in malaria parasite. Polymerization of heme to form hemozoin pigment is a process unique to Plasmodia. This has attracted much attention in the recent years as a potential target for antimalarial chemotherapy, as specific inhibitors designed against such a process have the chance of high selectivity in interaction with metabolism of the host harbouring the parasite. Although the last word has yet to be said on mechanism of heme polymerization by malaria parasite, a consensus is evolving between various research groups working in this area, about its potential as a target for antimalarial design. In this review we have discussed the problem of heme polymerization and its possible use as a target for drug design as well as provide an account of the work being done in this direction by us as well as other research groups.
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The haem detoxification pathway of the malaria parasite Plasmodium falciparum is a potential biochemical target for drug development. Free haem, released after haemoglobin degradation, is polymerized by the parasite to form haemozoin pigment. Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2) has been implicated as the catalytic scaffold for detoxification of haem in the malaria parasite. Previously we have shown that a hexapeptide repeat sequence (Ala-His-His-Ala-Ala-Asp), which appears 33 times in Pfhrp-2, may be the major haem binding site in this protein. The haem binding studies carried out by ourselves indicate that up to 18 equivalents of haem could be bound by this protein with an observed K(d) of 0.94 microM. Absorbance spectroscopy provides evidence that chloroquine is capable of extracting haem bound to Pfhrp-2. This was supported by the K(d) value, of 37 nM, observed for the haem-chloroquine complex. The native PAGE studies reveal that the formation of the haem-Pfhrp-2 complex is disrupted by chloroquine. These results indicate that chloroquine may be acting by inhibiting haem detoxification/binding to Pfhrp-2. Moreover, the higher affinity of chloroquine for haem than Pfhrp-2 suggests a possible mechanism of action for chloroquine; it may remove the haem bound to Pfhrp-2 and form a complex that is toxic to the parasite.
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We report enhancement of the mechanical stability of graphene through a one-step method to disperse gold nanoparticles on the pristine graphene without any added agent.
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eng_Latn
| 31,030 |
The case of a 54-year-old man with delirium secondary to phenytoin and disulfiram administration is presented. The pharmacology, interaction, and resulting toxicity of these two drugs are explored. The patient made an uneventful recovery when the medications were withheld.
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Drug interactions are one of the most common causes of side effects in polypharmacy. Alcoholics are a category of patients at high risk of pharmacological interactions, due to the presence of comorbidities, the concomitant intake of several medications and the pharmacokinetic and pharmacodynamic interferences of ethanol. However, the data available on this issue are limited. These reasons often frighten clinicians when prescribing appropriate pharmacological therapies for alcohol use disorder (AUD), where less than 15% of patients receive an appropriate treatment in the most severe forms. The data available in literature regarding the relevant drug-drug interactions of the medications currently approved in United States and in some European countries for the treatment of AUD (benzodiazepines, acamprosate, baclofen, disulfiram, nalmefene, naltrexone and sodium oxybate) are reviewed here. The class of benzodiazepines and disulfiram are involved in numerous pharmacological interactions, while they are not conspicuous for acamprosate. The other drugs are relatively safe for pharmacological interactions, excluding the opioid withdrawal syndrome caused by the combination of nalmefene or naltrexone with an opiate medication. The information obtained is designed to help clinicians in understanding and managing the pharmacological interactions in AUDs, especially in patients under multi-drug treatment, in order to reduce the risk of a negative interaction and to improve the treatment outcomes.
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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
| 31,031 |
Firefly bioluminescence attracts people by its glaring beauty and fascinating applications, but what is the light emitter of a firefly? The answer to this question has been explored since before the 1960s. The unanimously accepted answer is that excited-state oxyluciferin is the light emitter. The complexity of this question arises from the existence of six chemical forms (keto, enol, keto-1, enol-1, enol-1′, and enol-2) of oxyluciferin. After decades of experimental and theoretical efforts, a consistent conclusion was almost reached in 2011: excited-state keto-1 is the only light emitter in fireflies. However, the debate is raised again by the latest in vitro experimental results. This study will solve this contradiction via hybrid quantum mechanics and molecular mechanics (QM/MM) calculations combined with molecular dynamics (MD). The calculations were performed in the real protein for the six chemical forms of oxyluciferin and their corresponding analogues employed in the latest experiments. By considering the real environment, the pH value, and a possible equilibrium of the chemical forms of oxyluciferin in vivo, the calculated results indicate that the main emitter is still the excited-state keto-1 form.
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How the unique luciferase of Phrixothrix hirtus (PxRE) railroad worm catalyzes the emission of red bioluminescence using the same luciferin of fireflies, remains a mystery. Although PxRE luciferase is a very attractive tool for bioanalysis and bioimaging in hemoglobin rich tissues, it displays lower quantum yield (15%) when compared to green emitting luciferases (>40%). To identify which parts of PxRE luciferin binding site (LBS) determine bioluminescence color, and to develop brighter and more red-shifted emitting luciferases, we compared the effects of site-directed mutagenesis and of larger 6′-substituted aminoluciferin analogues (6′-morpholino- and 6′-pyrrolidinyl-LH) on the bioluminescence properties of PxRE and green-yellow emitting beetle luciferases. The effects of mutations in the benzothiazolyl and thiazolyl parts of PxRE LBS on the KM and catalytic efficiencies, indicated their importance for luciferin binding and catalysis. However, the absence of effects on the bioluminescence spectrum indicated a less interactive LBS in PxRE during light emission. Mutations at the bottom of LBS of PxRE blue-shifted the spectra and increased catalytic efficiency, suggesting that lack of interactions of this part of LBS with excited oxyluciferin phenolate underlie red light emission. The much higher bioluminescence activity and red-shifted spectra of PxRE luciferase with 6′-morpholino- (634 nm) and 6′-pyrrolidinyl-luciferins (644 nm), when compared to other beetle luciferases, revealed a larger luciferin phenolate binding pocket. The size and orientation of the side-chains of L/I/H348 are critical for amino-analogues accommodation and modulate bioluminescence color, affecting the interactions and mobility of excited oxyluciferin phenolate. The PxRE luciferase and 6′-aminoluciferins provide potential far-red combinations for bioimaging applications.
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This study has used proton transfer reaction-mass spectrometry (PTR-MS) for direct air analyses of volatile products resulting from the reactions of ozone with human skin lipids. An initial series of small-scale in vitro and in vivo experiments were followed by experiments conducted with human subjects in a simulated office. The latter were conducted using realistic ozone mixing ratios (≈15 ppb with occupants present). Detected products included mono- and bifunctional compounds that contain carbonyl, carboxyl, or α-hydroxy ketone groups. Among these, three previously unreported dicarbonyls have been identified, and two previously unreported α-hydroxy ketones have been tentatively identified. The compounds detected in this study (excepting acetone) have been overlooked in surveys of indoor pollutants, reflecting the limitations of the analytical methods routinely used to monitor indoor air. The results are fully consistent with the Criegee mechanism for ozone reacting with squalene, the single most abundant unsaturated constituent of skin lipids, and several unsaturated fatty acid moieties in their free or esterified forms. Quantitative product analysis confirms that squalene is the major scavenger of ozone at the interface between room air and the human envelope. Reactions between ozone and human skin lipids reduce the mixing ratio of ozone in indoor air, but concomitantly increase the mixing ratios of volatile products and, presumably, skin surface concentrations of less volatile products. Some of the volatile products, especially the dicarbonyls, may be respiratory irritants. Some of the less volatile products may be skin irritants.
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eng_Latn
| 31,032 |
The development of a general, mild, and chemoselective catalytic aerobic oxidation of amines to imines is described. The combination of a less sterically demanding and electron-deficient new N-oxyl radical (ketoABNO: 5) and copper(I) salt is key for the high catalytic activity and allows for the use of molecular oxygen as the stoichiometric oxidant producing H2O as the sole side-product. The novel method is extendable to a direct α-derivatization of secondary amines via sequential aerobic oxidation of amines to imines followed by C–C bond-formation to the resulting imines, including the novel catalytic asymmetric aerobic cross-dehydrogenative coupling reaction. Mechanistic insight into the novel catalytic system is also discussed.
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The ketones was successfully prepared from secondary alcohols using 9-azabicyclo[3.3.1]nonane-N-oxyl (ABNO) as the catalyst and 2,6-lutidine as the base in acetonitrile solution. The electrochemical activity of ABNO for oxidation of 1-phenylethanol was investigated by cyclic voltammetry, in situ Fourier transform infrared spectroscopy (FTIR) and constant current electrolysis experiments. The resulting cyclic voltammetry indicated that ABNO exhibited much higher electrochemical activity when compared with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) under the similar conditions. A reasonable reaction mechanism of the electrocatalytic oxidation of 1-phenylethanol to acetophenone was proposed. In addition, a series of secondary alcohols could be converted to the corresponding ketones at room temperature in 80–95% isolated yields.
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Aromatic amines are mammary carcinogens in rodents and exposure to aromatic amines may be associated with increased risk of breast cancer in women. Peroxidases present in milk can oxidize aromatic amines to reactive electrophiles which bind to DNA and induce mutations. Hydrogen peroxide, required for peroxidase-dependent oxidations, is supplied by milk xanthine oxidase and by the respiratory burst of neutrophils, cells which are present in milk and activated by exposure to it. In this paper, I propose that lactoperoxidase and myeloperoxidase activate aromatic amines, within the breast ducts, and that these enzymes play a crucial role in the chemical induction of breast cancer.
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eng_Latn
| 31,033 |
We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor–acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki–Miyaura and Sonogashira coupling reactions, respectively. In UV–vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600–650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.
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The photochemical activity of electron donor-acceptor (EDA) complexes provides a way to generate radicals under mild conditions. This strategy has found application in chemical synthesis and recently in enantioselective catalysis. Reported methods classically relied on the formation of intermolecular EDA complexes, generated upon aggregation of two suitable reagents. Herein, we further expand the synthetic utility of this strategy demonstrating that an intramolecular EDA complex can trigger a photochemical catalytic enantioselective radical process. This approach enables radical conjugate additions to β-substituted cyclic enones to form quaternary carbon stereocenters with high stereocontrol using visible light irradiation. Crucial for success is the use of an amine catalyst, adorned with a carbazole moiety, which generates, upon condensation with enones, chiral iminium ions that show a broad absorption band in the visible region. This optical property originates from an intramolecular charge transfer π-π interaction between the electron-rich carbazole nucleus and the electron-deficient iminium double bond.
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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
| 31,034 |
The effects of two nearly isoenergetic C–H stretching motions on the gas-phase reaction of atomic chlorine with methane are examined. First, a 1:4:9 mixture of Cl2, CH4, and He is coexpanded into a vacuum chamber. Then, either the antisymmetric stretch (ν3=3019 cm−1) of CH4 is prepared by direct infrared absorption or the infrared-inactive symmetric stretch (ν1=2917 cm−1) of CH4 is prepared by stimulated Raman pumping. Photolysis of Cl2 at 355 nm generates fast Cl atoms that initiate the reaction with a collision energy of 1290±175 cm−1 (0.16±0.02 eV). Finally, the nascent HCl or CH3 products are detected state-specifically via resonance enhanced multiphoton ionization and separated by mass in a time-of-flight spectrometer. We find that the rovibrational distributions and state-selected differential cross sections of the HCl and CH3 products from the two vibrationally excited reactions are nearly indistinguishable. Although Yoon et al. [J. Chem. Phys. 119, 9568 (2003)] report that the reactivities of thes...
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The dynamics of a combustion reaction, namely, O(P-3) + CH4 -> OH + CH3, is investigated with an eight-dimensional quantum model that includes representatives of all vibrational modes of CH4 and with a full-dimensional quasi-classical trajectory (QCT) method. The calculated excitation functions for the ground vibrational state CH4 agree well with experiment. Both quantum and QCT results suggest that excitation of the stretching modes of CH4 enhances the reaction, while the bending and umbrella modes have a smaller impact on reactivity, again consistent with experimental findings. However, none of the vibrational excitations has comparable efficiency in promoting the reaction as translational energy.
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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
| 31,035 |
Genetically transferred resistance to the antischistosomal drug hycanthone has been observed in several strains of Schistosoma mansoni: 1) in the progeny of worms to whose hosts hycanthone had been administered 54 to 70 days after exposure to cercariae (Type I); 2) in the progeny of worms to whose hosts hycanthone had been administered when the worms were still in an immature stage (27 to 29 days after percutaneous cercarial exposure) (Type II); and 3) in the progeny of worms from hosts that had been infected with cercariae of one sex followed by infection with the opposite sex 2 to 58 weeks later (Type III). In types I and II, drug resistance was transferred maternally. Hycanthone-resistant schistosomes were cross-resistant to antischistosomal drugs structurally related to hycanthone, such as oxamniquine and two chloro-indazole analogs of hycanthone, but not to niridazole and to another nitroheterocyclic compound.
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In this work, an attempt was made to induceng resistance to 3 schistosomicidal drugs in a Brazilian strain of S. mansoni, according to the Type II resistance induction scheme proposed by JANSMA et al. in 1977. Three attempts were unsuccessful. The parental generation treated with the drug during the immature stage of the worm was less susceptible to the chemotherapeutic agents than generations F1 and F2. A hypothesis is suggested as an explanation.
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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
| 31,036 |
In situ infrared spectroscopy has been used to show that aqueous cadmium sulfide photocorrosion leads to solution sulfate via an adsorbed thiosulfate intermediate. Infrared spectra were recorded from thin films of colloidal cadmium sulfide deposited on zinc selenide internal reflection elements and in contact with aqueous solutions. Infrared absorptions at 1005 and 1152 cm-1 have been ascribed to adsorbed thiosulfate by comparisons with the corresponding absorptions in solution. Simultaneous in situ photolysis and infrared spectroscopy showed that adsorbed thiosulfate was initially formed but gradually converted to sulfate. Adsorption isotherm data, derived from absorbances in the infrared spectra, showed that thiosulfate is strongly adsorbed and that sulfate is weakly adsorbed to cadmium sulfide. This accounts for the lack of detection of thiosulfate in solution when photocorrosion occurs.
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The step-wise oxidation of the disulfide group during pyrite oxidation by ferric iron was investigated using in situ attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy. Pyrite oxidation by ferric iron was investigated at pH 2.0, in the dark, and with both ultraviolet and visible wavelength illumination. We concluded that the spectra collected during pyrite oxidation are consistent with the existence of more than a single sulfur species at the pyrite surface. Exact assignment of all of the sulfur species was not realistic. However, the assignment of sulfate in an outer-sphere complex and thiosulfate in a monodentate complex was possible. The presence of multiple sulfur species at the pyrite surface directly confirms the step-wise oxidation of the disulfide group, and the presence of sulfate suggests that this species is the surface release group. Photochemical experiments verify an increase in the rate of pyrite oxidation with illumination and suggest that either the mechanism or the rate of sulfur oxidation is affected by illumination.
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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
| 31,037 |
ALowPressureImpactor(LPI) wasusedto collect aerosolgeneratedby the reactions of ozone with a -cedrene, a -copaene, b -caryophyllene, and a -humulene. Theaerosolwasgeneratedinanenvironmentalchamberandthechemicalcomposition of the aerosol was examined using Fourier Transform Infrared Spectroscopy (FTIR). The relative molar concentrations of functional groups in the aerosol were estimated based on the infrared spectra and model compound calibrations. Ketones and alde- hydes were the dominant functional groups in the aerosol-phase reaction products. Two to four carbonyl groups were present in average aerosol molecules. Hydroxyl groups were present in both carboxylic acid (0.2- 0.7 groups per average molecule) and alcohol (0.5- 1.3 groups per average molecule) structures. These structural char- acterizations of aerosol phase products were used to postulate chemical pathways for aerosol formation.
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Secondary organic aerosol (SOA) was formed in an environmental reaction chamber from the ozonolysis of β-caryophyllene (β-C) at low concentrations (5 ppb or 20 ppb). Experimental parameters were varied to characterize the effects of hydroxyl radicals, light and the presence of lower molecular weight terpene precursor (isoprene) for β-C SOA formation and cloud condensation nuclei (CCN) characteristics. Changes in β-C SOA chemicophysical properties (e.g., density, volatility, oxidation state) were explored with online techniques to improve our predictive understanding of β-C CCN activity. In the absence of OH scavenger, light intensity had negligible impacts on SOA oxidation state and CCN activity. In contrast, when OH reaction was effectively suppressed (> 11 ppm scavenger), SOA showed a much lower CCN activity and slightly less oxygenated state consistent with previously reported values. Though there is significant oxidized material present (O / C > 0.25), no linear correlation existed between the mass ratio ion fragment 44 in the bulk organic mass ( f 44 ) and O / C for the β-C-O 3 system. No direct correlations were observed with other aerosol bulk ion fragment fraction ( f x ) and κ as well. A mixture of β-C and lower molecular weight terpenes (isoprene) consumed more ozone and formed SOA with distinct characteristics dependent on isoprene amounts. The addition of isoprene also improved the CCN predictive capabilities with bulk aerosol chemical information. The β-C SOA CCN activity reported here is much higher than previous studies (κ
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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
| 31,038 |
Two‐color time‐of‐flight mass spectra of 3‐ and 4‐dimethylaminobenzonitrile (3‐ and 4‐DMABN) bare molecules and clusters with methane, water, acetone, dichloromethane, and acetonitrile are reported and discussed. The clusters and molecules are isolated and cooled in a supersonic expansion. Both 3‐ and 4‐DMABN bare molecules display significant changes in geometry, associated with rotation–inversion coordinates of the dimethylamino group, upon excitation from the ground electronic state S0 to the first excited singlet state S1. Cluster spectra for the monosolvates [CH4, H2O, (CH3)2CO, CH2Cl2, CH3CN] of 3‐ and 4‐DMABN evidence two general types of behavior. (1) Cluster spectra have both red and blue shifts from their respective bare molecule origins which are relatively small (in general less than 200 cm−1). These cluster spectra are nearly identical with the bare molecule spectra; the solvation process seems to have little effect on the DMABN molecule, especially the –N(CH3)2 moiety, for these clusters or ...
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Absorption as well as fluorescence emission studies of p-dimethylaminobenzaldehyde (DMABA) in solvents with different polarity have been reported by varying the concentration of the solute. Dual fluorescence corresponding to the non-polar (NP) and twisted intramolecular charge transfer (TICT) states has been observed. The optimized geometry of DMABA was evaluated using ab-initio theory at various levels. The optimized geometries of the hydrogen bonded complexes with the solvent molecules were also calculated with the theory Hartree Fock at the basis set 6-31+G (HF/6-31+G). The results have been used to understand the structure of the molecule and the spectral changes in terms of hydrogen bonding and solute-solvent interaction.
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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
| 31,039 |
The single-molecular conductance of a redox active molecular bridge has been studied in an electrochemical single-molecule transistor configuration in a room-temperature ionic liquid (RTIL). The redox active pyrrolo-tetrathiafulvalene (pTTF) moiety was attached to gold contacts at both ends through −(CH2)6S– groups, and gating of the redox state was achieved with the electrochemical potential. The water-free, room-temperature, ionic liquid environment enabled both the monocationic and the previously inaccessible dicationic redox states of the pTTF moiety to be studied in the in situ scanning tunneling microscopy (STM) molecular break junction configuration. As the electrode potential is swept to positive potentials through both redox transitions, an ideal switching behavior is observed in which the conductance increases and then decreases as the first redox wave is passed, and then increases and decreases again as the second redox process is passed. This is described as an “off–on–off–on–off” conductance ...
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Controlling the electrical conductance and in particular the occurrence of quantum interference in single-molecule junctions through gating effects has potential for the realization of high-performance functional molecular devices. In this work we used an electrochemically gated, mechanically controllable break junction technique to tune the electronic behaviour of thiophene-based molecular junctions that show destructive quantum interference features. By varying the voltage applied to the electrochemical gate at room temperature, we reached a conductance minimum that provides direct evidence of charge transport controlled by an anti-resonance arising from destructive quantum interference. Our molecular system enables conductance tuning close to two orders of magnitude within the non-faradaic potential region, which is significantly higher than that achieved with molecules not showing destructive quantum interference. Our experimental results, interpreted using quantum transport theory, demonstrate that electrochemical gating is a promising strategy for obtaining improved in situ control over the electrical performance of interference-based molecular devices. Electrochemical gating of single-molecule junctions shows signatures of anti-resonance typical of destructive quantum interference effects and conductance tuning by two orders of magnitude in thiophene molecules.
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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
| 31,040 |
Polythiophenes are the most widely utilized semiconducting polymers in organic electronics, but they are scarcely exploited in photonics due to their high photo-induced absorption caused by interchain polaron pairs, which prevents the establishment of a window of net optical gain. Here we study the photophysics of poly(3-hexylthiophene) configured with different degrees of supramolecular ordering, spin-coated thin films and templated nanowires, and find marked differences in their optical properties. Transient absorption measurements evidence a partially-polarized stimulated emission band in the nanowire samples, in contrast with the photo-induced absorption band observed in spin-coated thin films. In combination with theoretical modeling, our experimental results reveal the origin of the primary photoexcitations dominating the dynamics for different supramolecular ordering, with singlet excitons in the nanostructured samples superseding the presence of polaron pairs, which are present in the disordered films. Our approach demonstrates a viable strategy to direct optical properties through structural control, and the observation of optical gain opens the possibility to the use of polythiophene nanostructures as building blocks of organic optical amplifiers and active photonic devices.
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A combination of wavelength-, time-, and polarization-resolved photoluminescence imaging on isolated P3HT nanofibers of varying molecular weight (from 10 to 65 kDa) has revealed a transition in dominant exciton coupling from primarily interchain (H-aggregation) for low molecular weight nanofibers, to predominantly intrachain (J-aggregation) coupling for high molecular weight nanofibers. Based on nanofiber width measurement from TEM imaging, the driving force for this transition appears to be folding of individual polymer chains within the lamellae, resulting in enhanced chain planarity and reduced torsional disorder.
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OBJECTIVE ::: To evaluate the association between inhalation exposure to jet propulsion fuel 8 (JP-8) and urinary metabolites among US Air Force (USAF) personnel, and investigate the role of glutathione S-transferase polymorphisms. ::: ::: ::: METHODS ::: Personal air samples were collected from 37 full-time USAF personnel during 4 consecutive workdays and analyzed for JP-8 constituents and total hydrocarbons. Pre- and postshift urine samples were collected each day and analyzed for polycyclic aromatic hydrocarbon urinary metabolites. ::: ::: ::: RESULTS ::: Work shift exposure to total hydrocarbons was significantly associated with postshift urinary 1-naphthol (β = 0.17; P = <0.0001), 2-naphthol (β = 0.09; P = 0.005), and 2-hydroxyfluorene concentrations (β = 0.08; P = 0.006), and a significant gene-environment interaction was observed with glutathione S-transferase mu-1. ::: ::: ::: CONCLUSIONS ::: USAF personnel experience inhalation exposure to JP-8, which is associated with absorption of JP-8 constituents while performing typical job-related tasks, and in our data the glutathione S-transferase mu-1 polymorphism was associated with differential metabolism of naphthalene.
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eng_Latn
| 31,041 |
Band gap-tunable potassium doped graphitic carbon nitride with enhanced mineralization ability was prepared using dicyandiamide monomer and potassium hydrate as precursors. X-ray diffraction (XRD), N2 adsorption, UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The CB and VB potentials of graphitic carbon nitride could be tuned from -1.09 and +1.56 eV to -0.31 and +2.21 eV by controlling the K concentration. Besides, the addition of potassium inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area and increased the separation rate for photogenerated electrons and holes. The visible-light-driven Rhodamine B (RhB) photodegradation and mineralization performances were significantly improved after potassium doping. A possible influence mechanism of the potassium concentration on the photocatalytic performance was proposed.
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Covalent triazine-based frameworks (CTFs) are a subclass of conjugated microporous polymers (CMPs) that can be used as organic photocatalysts for photocatalytic hydrogen evolution from water. Seven materials with varied spacer units from phenylene to quarterphenylene were synthesized, either by trifluoromethanesulfonic acid (TfOH) catalysis from nitriles or by Suzuki-Miyaura polycondensation. The photocatalytic performance under visible light of all materials was systematically studied in the presence of a hole-scavenger, showing that both synthesis routes produce CTFs with similar hydrogen evolution rates (HER), but different optical properties. The highest hydrogen evolution rate in the cyclotrimerized series was found for CTF-2 with an apparent quantum yield of 1.6% at 420 nm in a mixture of water and triethanolamine with a platinum co-catalyst. Based on (TD-)DFT calculations, the highest performance was expected for CTF-1 and this discrepancy is explained by a trade-off between increased light absorption and decreased thermodynamic driving force.
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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
| 31,042 |
::: The thermal dissociation of tri-n-octylamine hydrochloride (TOAHCl) was investigated using both the quantum chemical simulation and experimental methods. The pathway through which a mixture of tri-n-octylamine (TOA) and hydrogen chloride (HCl), rather than di-n-octylamine (DOA) and 1-chlorooctane, are produced has been determined through transition state (TS) search with Intrinsic Reaction Coordinate (IRC) calculations. Particularly, strong agreement between the experimental FTIR spectra and that of TOA demonstrates the same result for the first time. Moreover, the thermal dissociation of TOAHCl proceeds in two continuous steps, which is different from the low molecular mass amine hydrochlorides. The experimental enthalpy of the dissociation was 70.793 \(\hbox {kJ mol}^{-1}\) with DSC measurement which is very close to the density functional theory (DFT) calculation result 69.395 \(\hbox {kJ mol}^{-1}\). Furthermore, with the aid of DFT calculations, some other important thermochemical characteristics such as crystal lattice energy with the value of 510.597 \(\hbox {kJ mol}^{-1}\) were evaluated by means of Born–Fajans–Haber cycle.
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The proton affinities, gas phase basicities and adiabatic ionization energies and electron affinities of some important hydroxylamines and alkanolamines were calculated using B3LYP, CBS-Q and G4MP2 methods. Also, the B3LYP method was used to calculate vertical ionization energies and electron affinities of the molecules. The calculated ionization energies are in the range of 8-10.5 eV and they decrease as the number of carbon atoms increases. Computational results and ion mobility spectrometry study confirm that some alkanolamines lose a water molecule due to protonation at oxygen site and form cationic cyclic compounds. Effect of different substitutions on the cyclization of ethanolamine was studied theoretically.
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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
| 31,043 |
Highly stable, hydrophilic carbon quantum dots (CQDs) with a fluorescence quantum yield of 43% were prepared by dehydration/condensation and aromatization/carbonization of a mixture of diethylenetriamine and trisodium citrate. The CQDs possess a mixed crystalline and polycrystalline structure in the basic and acidic medium respectively. The fluorescence of the CQDs (with excitation/emission peaks at 390/450 nm) arises from both the CQDs and from molecular fluorophores incorporated in the CQDs and is highly pH dependent in the range between pH 2.0 and 9.0. Fluorescence is strongly quenched by vitamin B12 (VitB12). This finding is exploited in a quenchometric method for the quantification of VitB12 that works in the VitB12 concentration range between 1 nM to 20 μM, and the lower limit of detection is 210 pM.
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We report on a single-step thermolysis strategy to prepare highly luminescent nitrogen-doped and amino acid-functionalized graphene quantum dots (NA-GQDs) by using glycine as both carbon and nitrogen source. The NA-GQDs display an excitation wavelength-dependent fluorescence with maximum excitation and emission wavelengths of 380 and 450 nm, respectively, and a quantum yield of ~16 %. Fluorescence is quenched by Fe(III) and Hg(II), and the effect was used to develop a method for the determination of Fe(III). Quenching by Fe(III) is attributed to its higher thermodynamic affinity (compared to other transition-metal ions) for the ligands on the GQDs in which nitrogen atoms mainly act as the chelating atoms. A linear relationship was observed between fluorescence intensity and the concentration of Fe(III) over the 0.5 μM to 0.5 mM range. The detection limit is 0.1 μM.
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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
| 31,044 |
A novel fluorescent bis-calix[4]arene macrocycle 9 incorporating metal-binding pockets was successfully prepared. The structure of macrocycle 9 and its precursors were characterized via EI-MS, MALDI-TOF-MS, ESI-MS, (1)H NMR, (13)CNMR, 2D NMR, and X-ray crystallography. The macrocycle 9 displayed selective fluorescence quenching after interacting with Cu(2+) in the presence competing metal cations including Mg(2+), Ca(2+), Ba(2+), Ag(+), Zn(2+), Ti(4+),Cd(2+), Hg(2+), Pb(2+), In(3+), La(3+), Cr(3+), Ni(2+), Sb(3+), V(5+), Fe(3+), Co(2+), Sn(2+), Sn(2+), and Tl(+). The Cu(2+) limit of detection was found to be 40 nM much lower than its threshold level (∼ 20 μM) in drinking water permitted by the U.S Environmental Protection Agency (EPA). Furthermore, drinking water samples from Karachi University (Pakistan) spiked with Cu(2+) were analysed with the sensing system and the results showed an excellent agreement with the fluorescence quenching phenomenon of macrocycle 9 examined in deionized water. Importantly, the chemosensor 9 could be used to detect Cu(2+) in living cells.
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A new highly selective and sensitive fluorescent probe for Cu2+, N-n-butyl-4-(1′-cyclooctene-1′,3′,6′-triazole)-1,8-naphthalimide (L), was synthesized and evaluated. The structure of compound L was characterized via IR, 1H-NMR, 13C-NMR and HRMS. The fluorescent probe was quenched by Cu2+ with a 1:1 binding ratio and behaved as a “turn-off” sensor. An efficient and sensitive spectrofluorometric method was developed for detecting and estimating trace levels of Cu2+ in EtOH/H2O. The ligand exhibited excitation and emission maxima at 447 and 518 nm, respectively. The equilibrium binding constant of the ligand with Cu2+ was 1.57 × 104 M−1, as calculated using the Stern
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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
| 31,045 |
The hydrogenation of 2-ethylanthraquinone (eAQ) was performed over alumina, silica and carbon supported palladium catalysts. Present research is concentrated on the process of eAQ degradation and especially a role of the type of catalyst is examined. Degradation of eAQ in the catalytic experiments has been discussed on the basis of reaction pattern reported for the reduction of carbonyl groups in anthraquinone by standard procedures (Zn, Sn, NaBH4). Various by-products formed by degradation of hydroquinone (eAQH2) have been identified by GC–MS. They are the product of CO hydrogenolysis such as 2-ethylanthrone (eAN, two isomers), 2-ethylanthracene (eANT) and the products of eAN hydrogenation (H4eAN, two isomers). Tautomerization of partially and fully saturated hydroquinones produces OXO-isomers [two isomers OXO-H4(1,2) and OXO-H8(1,2)]. Reduction of eAQ with NaBH4 gives 2-ethyl-9,10-dihydroxy-9,10-dihydroanthraquinone, intermediate product in the consecutive reactions occurring during the hydrogenolysis of CO and resulting in eAN. A difference in performance of 0.5% Pd/C, 0.5% Pd/SiO2 and 0.5% Pd/Al2O3 catalysts is related with their reactivity in degradation of eAQH2. Much higher reactivity in the whole degradation process and especially in the formation of intermediate product exhibits alumina-supported catalyst.
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The hydrogenation of 2-ethylanthraquinone (eAQ), 2-tert-amylanthraquinone (taAQ) and their mixtures with molar ratios of 1:1 and 1:2 to the corresponding hydroquinones (eAQH2 and taAQH2) were studied over a Pd/Al2O3 catalyst in a semi-batch slurry reactor at 60 °C and at 0.3 MPa. Compared to eAQ, TaAQ exhibited a significantly slower hydrogenation rate (about half) but had a higher maximum yield of H2O2 and a smaller amount of degradation products. This can be ascribed to the longer and branched side chain in taAQ, which limits its accessibility to the Pd surface and its diffusion through the pores of the catalyst. Density functional theory calculations showed that it is more difficult for taAQ to adsorb onto a Pd (111) surface than for eAQ. The hydrogenation of the eAQ/taAQ mixtures had the slowest rates, lowest H2O2 yields and the highest amounts of degradation products.
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The experimental oral carcinogenesis induced by the chemical 4-nitroquinoline 1-oxide (4NQO) is one of the most frequent in the study of squamous cell carcinoma of the oral cavity (CCEC). The clear advantage is that the model is very similar to the physiological process of malignancy. The model has clear benefits by and is suitable for applications in therapeutic research.
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eng_Latn
| 31,046 |
For the first time, the synthesis of organosilicon derivatives of dialkyl[1]benzothieno[3,2-b][1]-benzothiophene (BTBT) capable of forming a semiconducting monolayer at the water-air interface is reported. Self-assembled monolayer organic field-effect transistors prepared from these materials using the Langmuir-Blodgett technique showed high hole mobilities and excellent air stability.
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Synthesis of novel organosilicon derivatives of [1]benzothieno[3,2-b][1]-benzothiophene (BTBT) linked though flexible aliphatic spacers to a disiloxane anchor group is reported. They were successfully used in monolayer OFETs with the charge carrier mobilities up to 0.02 cm 2 /Vs, threshold voltage close to 0 V and On/Off ratio up to 10,000. Influence of the chemical structure of the molecules synthesized on the morphology, molecular 2D ordering in the monolayers and their semiconducting properties is considered. The effect of different methods of the ultrathin semiconducting layer preparation, such as Langmuir-Blodgett, Langmuir-Schaefer, spin coating or doctor blade, on the OFET performance is discussed.
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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.).
|
eng_Latn
| 31,047 |
We have studied the oxidative addition of the methane C–H and chloromethane C–Cl bonds to a number of main group (Be, Mg and Ca) and transition metals (Pd, Zn and Cd), using relativistic density functional theory (DFT) at ZORA-BLYP/TZ2P. The purpose is to better understand what causes the characteristic differences in reactivity between main group and transition metals towards oxidative addition. Thus, we have analyzed our model reactions using the Activation Strain model in which the activation energy Δ E ≠ is decomposed into the activation strain Δ E strain ≠ of and the stabilizing TS interaction Δ E int ≠ between the reactants in the activated complex: Δ E ≠ = Δ E strain ≠ + Δ E int ≠ . Activation of the C–H bond goes with higher barriers than activation of the C–Cl bond because the higher bond strength of the former translates into a higher activation strain Δ E strain ≠ . The barriers for bond activation increase along Pd Δ E int ≠ , that is, in terms of the bonding capabilities of the metals. Pd yields the lowest barriers because it achieves the most stabilizing Δ E int ≠ . This is the result of the small HOMO–LUMO gap between its occupied 4d and unfilled 5s AOs, which makes Pd both a good electron donor and acceptor. Zn and Cd yield the highest barriers because the large HOMO–LUMO gap between the occupied valence n s and unfilled valence n p AOs makes them both poor donors and poor acceptors of electronic charge.
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Tetrafluoroethylene and butadiene form the 2+2 cycloadduct under kinetic control, but the Diels-Alder cycloadduct is formed under thermodynamic control. Borden and Getty showed that the preference for 2+2 cycloaddition is due to the necessity for syn-pyramidalization of the two CF2 groups in the 4+2 transition state. We have explored the full potential energy surface for the concerted and stepwise reactions of tetrafluoroethylene and butadiene with DFT (B3LYP and M06-2X), DLPNO-UCCSD(T), and CASSCF-NEVPT2 methods and with the distortion/interaction-activation strain model to explain the energetics of different pathways. The 2+2 cycloadduct occurs by an anti-transition state followed by two rotations and a final bond formation transition state. Energetics are compared to the reaction of maleic anhydride and ethylene.
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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
| 31,048 |
Novel therapies to prevent bacterial infections are of utmost importance in biomedical research due to the emergence of multidrug-resistant strains of bacteria. Herein, we report the preparation, characterization and antibacterial evaluation of sulfonated polystyrene nanoparticles simultaneously releasing two antibacterial species, nitric oxide (NO) and singlet oxygen (O2(1Δg)), upon irradiation with visible light. The nanoparticles were prepared by simple and scalable processes from nanofiber membranes with an encapsulated NO photodonor and/or ionically entangled tetracationic porphyrin/phthalocyanine photosensitizers. The release of NO and O2(1Δg) from the polystyrene nanoparticles is controlled by light wavelength and dose, as well as by temperature, which influences the diffusion coefficient and solubility of both species in the polystyrene matrix. The concentrations of NO and O2(1Δg) were measured by amperometric and time-resolved spectroscopic techniques and by chemical analysis. Due to the efficient photogeneration of both species at physiological temperature and resultant strong antibacterial action observed on Escherichia coli, the nanoparticles are a promising material for antibacterial applications triggered/modulated by light and temperature.
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An expanded and revised compilation on the reactivity of singlet oxygen, the lowest electronically excited singlet state of molecular oxygen, 1O2*(1Δg), in fluid solution is presented, which supersedes the publication of Wilkinson and Brummer, J. Phys. Chem. Ref. Data 10, 809 (1981). Rate constants for the chemical reaction and physical deactivation of singlet oxygen available through 1993 have been critically compiled. Solvent deactivation rates (kd) are tabulated for 145 solvents or solvent mixtures and second‐order rate constants for interaction of singlet oxygen with 1915 compounds are reported.
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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
| 31,049 |
An efficient synthesis has been developed for the preparation in high configurational purity of dopamines (3,4-di-hydroxyphenethylamines) stereospecifically labelled at C-2 with isotopes of hydrogen. By incubating (2R)-, and (2S)-[2-2H1]dopamines with dopamine β-hydroxylase (E.C. 1.14.17.1) it has been shown that the pro-R-hydrogen atom is lost in the formation of noradrenaline; thus the hydroxylation of the benzylic methylene group occurs with retention of configuration.
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Many bioactive peptides must be amidated at their carboxy terminus to exhibit full activity. Surprisingly, the amides are not generated by a transamidation reaction. Instead, the hormones are synthesized from glycine-extended intermediates that are transformed into active amidated hormones by oxidative cleavage of the glycine N-C alpha bond. In higher organisms, this reaction is catalyzed by a single bifunctional enzyme, peptidylglycine alpha-amidating monooxygenase (PAM). The PAM gene encodes one polypeptide with two enzymes that catalyze the two sequential reactions required for amidation. Peptidylglycine alpha-hydroxylating monooxygenase (PHM; EC 1.14.17.3) catalyzes the stereospecific hydroxylation of the glycine alpha-carbon of all the peptidylglycine substrates. The second enzyme, peptidyl-alpha-hydroxyglycine alpha-amidating lyase (PAL; EC 4.3.2.5), generates alpha-amidated peptide product and glyoxylate. PHM contains two redox-active copper atoms that, after reduction by ascorbate, catalyze the reduction of molecular oxygen for the hydroxylation of glycine-extended substrates. The structure of the catalytic core of rat PHM at atomic resolution provides a framework for understanding the broad substrate specificity of PHM, identifying residues critical for PHM activity, and proposing mechanisms for the chemical and electron-transfer steps in catalysis. Since PHM is homologous in sequence and mechanism to dopamine beta-monooxygenase (DBM; EC 1.14.17.1), the enzyme that converts dopamine to norepinephrine during catecholamine biosynthesis, these structural and mechanistic insights are extended to DBM.
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The formation, stereostructure, and cellular reactions of the 7,8-diol-9,10-epoxide metabolites of the carcinogen benzo[a]pyrene have been examined after topical application of benzo[a]pyrene to the skin of mice. In this known target tissue, polymer adducts from diastereomeric diol epoxides, (+)-(7S, 8R, 9R, 10R) and (+)-(7R, 8S, 9R, 10R), were formed stereospecifically from their corresponding 7,8-dihydrodiols. Both diol epoxides bind with proteins, RNA, and DNA in vivo. For the nucleic acids, binding occurs preferentially at the 2-amino group of guanine in cellular RNA and DNA in vivo. Methods for establishing the structure of the cellular adducts as well as the possible biological implications of their formation are discussed.
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eng_Latn
| 31,050 |
The electrochemical behavior of riboflavin at a carbon paste electrode and electrodes modified with aza crown ethers have been studied using voltammetric techniques. The macrocycles used as modifiers were 1,4,8,11-tetraazacyclooctadecane; 7,16-dibenzyl-1,4,10,13-tetraoxa-7,16-diazacyclooctadecane; 1,4,7,10-tetraoxa-13-azacyclopentadecane and 1,4,7,10-tetratosyl-1,4,7,10-tetraazacyclooctadecane, out of which 1,4,8,11-tetraazacyclooctadecane showed better response for riboflavin. The interaction of riboflavin with 1,4,8,11-tetraazacyclooctadecane was confirmed by complexation study in 20% DMSO + water (log K 5.58) using differential pulse polarography. The kinetic parameters viz. electron transfer coefficient and rate constant of electron transfer across the modified electrode were found to be 0.708 and 5.5 s −1 , respectively. The surface coverage of the 1,4,8,11-tetraazacyclooctadecane modified electrode was calculated to be 5 × 10 −10 mol cm −2 by cyclic voltammetry and chronocoulometry. A linear working range of 0.5 ng cm −3 to 70 μg cm −3 with a detection limit of 0.2 ng cm −3 has been obtained using 1,4,8,11-tetraazacyclooctadecane modified electrode by square wave anodic stripping voltammetry. It was possible to determine riboflavin in presence of some organic molecules like thiamine hydrochloride, nicotinamide, pyridoxine hydrochloride, ascorbic acid, para -aminobenzoic acid and l -tryptophan. Also simultaneous and quantitative determinations were achieved for combination of some of these. The electrode could be used for estimation of riboflavin in pharmaceutical and food samples.
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Compared to other voltammetric techniques a square wave voltammetry (SWV), which is presented in this minireview, has a several advantages such as high speed, increased analytical sensitivity and relative insensitivity to the presence of dissolved oxygen. Also it is an electrochemical technique used in analytical applications and fundamental studies of electrode mechanism. This paper delivers both the underlying theory and the practical guidance needed to apply square wave techniques and also provides a wide collection of data for the description of diverse tendencies that characterize several electrochemical reactions analyzed by SWV. This review summarizes some of the recent developments and application of direct and stripping SWV for drug compounds in their dosage forms and biological samples as reported in the period from 1997 till 2010 year.
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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
| 31,051 |
Effective biodegradation of 1,3-dichlorobenzene by a mutant of Bacillus cereus PF-11
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Isolation, Identification and Degradation Characterization of 1,2-Dichlorobenzene Degrading Strain
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Isolation, Identification and Degradation Characterization of 1,2-Dichlorobenzene Degrading Strain
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eng_Latn
| 31,052 |
A High-Level Theoretical Study on the Gas-Phase Identity Methyl Transfer Reactions
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Benchmark Study on the Smallest Bimolecular Nucleophilic Substitution Reaction: H−+CH4 → CH4+H−
|
Microtubule capture by CENP-E silences BubR1-dependent mitotic checkpoint signaling
|
eng_Latn
| 31,053 |
Dehydrogenation of 1,3-butanediol over Cu-based catalyst
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Engineering of glycerol dehydrogenase for improved activity towards 1, 3-butanediol
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Inhibition of 1,4-butanediol metabolism in human liver in vitro
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eng_Latn
| 31,054 |
Synthesis and use of α-aminophosphine oxides and N,N-bis(phosphinoylmethyl)amines - A study on the related ring platinum complexes
|
Application of the Microwave Technique in Continuous Flow Processing of Organophosphorus Chemical Reactions
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High-affinity glucose uptake in Saccharomyces cerevisiae is not dependent on the presence of glucose-phosphorylating enzymes
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eng_Latn
| 31,055 |
Basicities of methyl-, methylphenyl-, and phenylphosphines in the gas phase
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Metal-based biologically active compounds: design, synthesis, medicinal, toxicity and DNA interaction assay
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S phase block following MEC1ATR inactivation occurs without severe dNTP depletion
|
eng_Latn
| 31,056 |
Organocatalyzed Tsuji–Trost reaction: a new method for the closure of five- and six-membered rings
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Enamine/Transition Metal Combined Catalysis: Catalytic Transformations Involving Organometallic Electrophilic Intermediates
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5-HT3 receptor ligands lack modulatory influence on acetycholine release in rat entorhinal cortex
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eng_Latn
| 31,057 |
A Common Polymorphism in HIBCH Influences Methylmalonic Acid Concentrations in Blood Independently of Cobalamin.
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HIBCH mutations can cause Leigh-like disease with combined deficiency of multiple mitochondrial respiratory chain enzymes and pyruvate dehydrogenase
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Synthesis and aggregation of a porphyrin cored hyperbranched polyglycidol and its application as a macromolecular photosensitizer for photodynamic therapy
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eng_Latn
| 31,058 |
Ligand effects in chromium diphosphine catalysed olefin co-trimerisation and diene trimerisation
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The novel [Ni{(Ph2P)2N(CH2)3Si(OCH3)3-P,P´}I2] complex: Structural features and catalytic reactivity in the oligomerization of ethylene
|
Oral spray wintertime vitamin D3 supplementation has no impact on inflammation in Gaelic footballers
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eng_Latn
| 31,059 |
Adsorption of lanthanides(III), uranium(VI) and thorium(IV) from nitric acid solutions by carbon inverse opals modified with tetraphenylmethylenediphospine dioxide.
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Preparation of chemically oxidized porous carbon and its adsorption of uranium(VI) from aqueous solution
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Kynurenic acid blocks nicotinic synaptic transmission to hippocampal interneurons in young rats.
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eng_Latn
| 31,060 |
Cucurbit[n]urils as a potential fine-tuned instrument for modifying photophysical properties of D–π–A+–π–D “push–pull” chromophores
|
Tunable Fluorescence-Responsive Double Hydrophilic Block Polymers Induced by the Formation of Pseudopolyrotaxanes with Cucurbit[7]Uril
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Absence of CCR8 does not impair the response to ovalbumin-induced allergic airway disease.
|
eng_Latn
| 31,061 |
Highly efficient electrochemical recognition and quantification of amine enantiomers based on a guest-free homochiral MOF
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Metal-Organic Frameworks for the Development of Biosensors: A Current Overview
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Diclofenac Distinguishes among Homomeric and Heteromeric Potassium Channels Composed of KCNQ4 and KCNQ5 Subunits
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eng_Latn
| 31,062 |
Bisdemethoxycurcumin inhibits PDGF-induced vascular smooth muscle cell motility and proliferation.
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Phytochemical Compounds and Protection from Cardiovascular Diseases: A State of the Art
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Solvent-free synthesis of 6-unsubstituted dihydropyrimidinones using 2-pyrrolidonium bisulphate as efficient catalyst
|
eng_Latn
| 31,063 |
A quantum chemical view of enthalpy–entropy compensation
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The Molecular Origin of Enthalpy/Entropy Compensation in Biomolecular Recognition
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Using Weighted Entropy to Rank Chemicals in Quantitative High-Throughput Screening Experiments
|
eng_Latn
| 31,064 |
Synthesis of olive-green few-layered BiOI for efficient photoreduction of CO2 into solar fuels under visible/near-infrared light
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Construction of BiOBrxI1−x/MXene Ti3C2Tx composite for improved photocatalytic degradability
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Oral spray wintertime vitamin D3 supplementation has no impact on inflammation in Gaelic footballers
|
eng_Latn
| 31,065 |
Photochemical Behavior of a New Long-chain UV Absorber†, Derived from 4-tert-Butyl-4′-Methoxydibenzoylmethane¶
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PHOTODECOMPOSITION OF SEVERAL COMPOUNDS COMMONLY USED AS SUNSCREEN AGENTS
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Physical and electrochemical properties of ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide
|
eng_Latn
| 31,066 |
Degradation of Dyes Using Zinc Oxide as the Photocatalyst
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Preparation, Characterization of Mn/Cr2O3 and Investigation of The Photocatalytic Degradability by UV light
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Recent Advances in the Catalytic Asymmetric Reactions of Oxaziridines
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eng_Latn
| 31,067 |
Effects of catechol, sodium chloride and ethanol either alone or in combination on gastric carcinogenesis in rats pretreated with N-methyl-N'-nitro-N-nitrosoguanidine.
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Mechanisms of induction of chromosomal aberrations by hydroquinone in V79 cells.
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Facile synthesis of PtCo nanowires with enhanced electrocatalytic performance for ethanol oxidation reaction
|
eng_Latn
| 31,068 |
Sulfur Compounds in Hydrocarbon Pyrolysis
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Kinetics and modelling of heptane steam-cracking
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Hydrogen sulfide inhibits macrophage-derived foam cell formation
|
eng_Latn
| 31,069 |
Inorganic pyrophosphatases of Family II-two decades after their discovery.
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X-ray Crystallography and Electron Paramagnetic Resonance Spectroscopy Reveal Active Site Rearrangement of Cold-Adapted Inorganic Pyrophosphatase
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X-ray Crystallography and Electron Paramagnetic Resonance Spectroscopy Reveal Active Site Rearrangement of Cold-Adapted Inorganic Pyrophosphatase
|
eng_Latn
| 31,070 |
Synthesis, spectroscopic, and theoretical studies of tin(II) complexes with biologically active Schiff bases derived from amino acids
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Synthesis, spectral characterization of Schiff base transition metal complexes: DNA cleavage and antimicrobial activity studies
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Brain Injury Does Not Alter the Intrinsic Differentiation Potential of Adult Neuroblasts
|
eng_Latn
| 31,071 |
Chemistry of aliphatic unconjugated nitramines. Part 4.—Photophysical processes of secondary nitramines
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Deep-Ultraviolet Resonance Raman Excitation Profiles of NH4NO3, PETN, TNT, HMX, and RDX
|
Constant delay enumeration with FPT-preprocessing for conjunctive queries of bounded submodular width
|
eng_Latn
| 31,072 |
Photophysical Properties of Novel PDT Photosensitizer Radachlorin in Different Media
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In Vitro Models for Cutaneous Phototoxicity
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Altered thyroxin and retinoid metabolic response to 2,3,7,8-tetrachlorodibenzo-p-dioxin in aryl hydrocarbon receptor-null mice
|
kor_Hang
| 31,073 |
Picard Groups of Hypersurfaces in Toric Varieties
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Dual polyhedra and mirror symmetry for Calabi–Yau hypersurfaces in toric varieties
|
Transcriptional activation of HIF-1 by a ROS-ERK axis underlies the resistance to photodynamic therapy
|
eng_Latn
| 31,074 |
Solid-State 67Zn NMR spectroscopic studies and ab initio molecular orbital calculations on a synthetic analogue of carbonic anhydrase.
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Biomimetic Applications of Metal Systems Supported by Scorpionates
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Trace copper levels in the drinking water, but not zinc or aluminum influence CNS Alzheimer-like pathology.
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eng_Latn
| 31,075 |
Catalytic Generation of Cesium Acetylide by CsF: Synthesis of 1,3-Benzothiazines from Cyclic Sulfenamides
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An improved and scalable synthesis of zolpidem via a CuI/BINOL-mediated tandem reaction of imine and alkyne
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Due to symbiotic N2 fixation, five years of elevated atmospheric pCO2 had no effect on the N concentration of plant litter in fertile, mixed grassland
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eng_Latn
| 31,076 |
Choline and betaine aldehyde oxidation by rat liver mitochondria
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Betaine Aldehyde Oxidation by Spinach Chloroplasts 1
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Betaine Aldehyde Oxidation by Spinach Chloroplasts 1
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eng_Latn
| 31,077 |
Applications of immobilized biocatalysts in chemical analysis
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Study on a pyruvate oxidase biosensor based on ß-cyclodextrin included ferrocene as electron-transfer mediator
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Brain Injury Does Not Alter the Intrinsic Differentiation Potential of Adult Neuroblasts
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eng_Latn
| 31,078 |
Calculations on the electronic excited states of ureas and oligoureas.
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DichroCalc: Improvements in computing protein circular dichroism spectroscopy in the near-ultraviolet
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Absence of CCR8 does not impair the response to ovalbumin-induced allergic airway disease.
|
eng_Latn
| 31,079 |
Nickel nanoparticles modified CdS – A potential photocatalyst for hydrogen production through water splitting under visible light irradiation
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Synthesis and Characterization of Metal-Doped (Ni, Co, Ce, Sb) CdS Catalysts and Their Use in Methylene Blue Degradation under Visible Light Irradiation
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Oral insulin does not alter gut microbiota composition of NOD mice
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eng_Latn
| 31,080 |
Reductive transformation and dechlorination of chloronitrobenzenes in UASB reactor enhanced with zero-valent iron addition
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Recent electrochemical methods in electrochemical degradation of halogenated organics: a review
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Human health risk of chlorobenzenes associated with seafood consumption in Korea
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eng_Latn
| 31,081 |
Comparative Design, In Silico Dockingand Predictive ADME/ TOX Properties of Some Novel 2, 4-hydroxy Derivatives of Thiazolidine-2, 4-diones as PPARγ Modulator
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Preparation and biological evaluation of quinoline amines as anticancer agents and its molecular docking
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Altered thyroxin and retinoid metabolic response to 2,3,7,8-tetrachlorodibenzo-p-dioxin in aryl hydrocarbon receptor-null mice
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eng_Latn
| 31,082 |
Activation energies for reactions of hydroxyl radicals with hydrogen and carbon monoxide
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Transition from Branching‐Chain Kinetics to Partial Equilibrium in the Combustion of Lean Hydrogen‐Oxygen Mixtures in Shock Waves
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A new CYP21A2 nonsense mutation causing severe 21-hydroxylase deficiency
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eng_Latn
| 31,083 |
5-Methylcytosine Selective Photoligation Using Photoresponsive Oligonucleotides Containing Various 5-Vinyl-2′-deoxyuridines Having an Aromatic Group
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Methods for detection of cytosine and thymine modifications in DNA
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Deficient Activity of Mitochondrial Flavine Adenine Dinucleotide-Linked Glycerophosphate Dehydrogenase in Pancreatic Islet Beta Cells as a Determinant of Non-Insulin-Dependent Diabetes Mellitus
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eng_Latn
| 31,084 |
One-pot Reductive Amination of Carbonyl Compounds with NaBH4-B(OSO3H)3/SiO2 in Acetonitrile and in Solvent-free Condition
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Nano silica boron sulfuric acid as a dual Brønsted/Lewis acid and a heterogeneous catalyst in Baeyer–Villiger oxidation of ketones with hydrogen peroxide
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Increased plasminogen activator inhibitor-1 concentrations in bronchoalveolar lavage fluids are associated with increased mortality in a cohort of patients with Pseudomonas aeruginosa.
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eng_Latn
| 31,085 |
Oxidation of Cycloalkanes by Hydrogen Peroxide in a Biomimetic Iron Porphyrin System
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Vanadium Catalyzed Partial Oxidation of Some Saturated Hydrocarbons to Functionalized Products Under Mild Conditions
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No iron fertilization in the equatorial Pacific Ocean during the last ice age
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eng_Latn
| 31,086 |
The major reaction path for oxidation of di-tert-butyl peroxide (DTBP) is generally considered to occur via fission of the weak peroxide ROOR bond at temperatures above 393 K. The initial stable intermediates in the thermal decomposition or combustion of DTBP are acetone and ethane, and the overall reaction is accompanied by an important heat release which when mixed with air (oxygen) may exceed the self-ignition temperatures. A kinetic study on plausible DTBP reaction paths was initiated in this work, and a detailed study of the thermochemistry of new intermediates, transition state structures, and products is reported. The density functional theory (DFT; B3LYP/6-311g(d,p)), which is practical for large compounds along with the composite ab initio G3MP2B3 and G3 calculations, (when possible), are used. Computational chemistry results from DFT and ab initio calculations are coupled with isodesmic reaction analysis which, as demonstrated in previous studies, results in good accuracy. Over 10 unimolecular decomposition pathways are identified and reported.
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An overview in the field of chemical kinetics on the thermal decomposition of dicumyl peroxide (DCPO) is implemented in this study. Thermal data are detected by heat flow or adiabatic calorimeters. Chemical kinetics on the thermal decomposition of DCPO obeys nth-order reaction and the type of Arrhenius equation. In the neat state of DCPO, activation energy and logA behave with good precision in an averaged value of (131.4 ± 4.3) and (13.5 ± 0.6) kJ mol−1 are determined by DSC. The averaged activation energy and logA are determined to be (129.3 ± 4.7) and (13.6 ± 0.3) kJ mol−1 by the accelerating rate calorimeter. DCPO diluted in cumene or gray paste, activation energy and logA (A in s−1) have an averaged value of (132.7 ± 6.5) and (13.6 ± 0.5) kJ mol−1 determined by DSC. However, DCPO diluted in cumene, activation energy and logA (A in s−1) have an averaged value of (144.5 ± 9.1) and (15.6 ± 2.0) kJ mol−1 determined by Phi-TEC calorimeter. logA (A in s−1) has the distribution from 10.1 to 16.6 in neat DCPO and from 10.96 to 17.6 in diluted DCPO, respectively. Activation energy distributes, respectively, from 117 to 173 kJ mol−1 in neat DCPO and from 112.8 to 156.6 kJ mol−1 in diluted DCPO. Published data in relation to the kinetics and mechanism on thermal decomposition of DCPO are summarized and discussed.
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Pneumoperitoneum was observed in five patients with acute perforative appendicitis (APA). In each case this radiographic observation led to an incorrect diagnosis. Free intraperitoneal gas is found in a small number of patients with APA and has no apparent effect on the course or prognosis of the disease.
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eng_Latn
| 31,087 |
A nanocomposite of poly(m-phenylenediamine)/palygorskite (PmPD–PG) is facilely synthesized via in situ oxidative polymerization of m-phenylenediamine (mPD) on palygorskite (PG) and its reactive adsorbability to Cr(VI) is examined. PG in the nanocomposite plays important roles in the improvement of adsorptivity of Cr(VI). The pH value of the solution is increased after adsorption, which is quite different from Pb(II) adsorption with aromatic diamine polymers. This unusual removal behavior of Cr(VI) with PmPD–PG is due to the redox reaction between Cr(VI) and amino/imino groups on the PmPD chains.
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In this study, ranitidine (RT), a cationic drug was tested for its removal by palygorskite (PA) under different physico-chemical conditions, such as initial RT concentrations, contact time, equilibrium solution pH, ionic strength, and temperature. FTIR, SEM, and XRD analyses were conducted to determine the mechanisms of RT uptake on PA. The results showed that cation exchange or electrostatic interactions between the negatively charged PA surfaces and positively charge dimethylamine of RT was the major mechanism of RT uptake when solution pH was less than the p K a value of RT. Under high pH conditions, the 2,5-disubstituted furan group interacted with the PA surface via a delocalized π-bond, suggesting that the RT molecules were parallel to PA surface. The larger values for the RT distribution coefficient between PA and solution via electrostatic or cation exchange interactions and delocalized π-bonds in a multi-regression analysis confirmed these mechanisms. The XRD results showed no expansion of the (1 1 0) reflection of PA while the SEM observation showed no changes in crystal size and morphology, indicating that the sites for RT uptake were limited to the external surfaces of PA.
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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
| 31,088 |
Alkaline phosphatase of intestinal origin hydrolyzed the S-substituted monoesters of phosphorothioic acid of the type RSPO3Na2 (R = —CH2CH2NH2, —CH2CH2NHCOCH3, —CH2COO, or —CH2CH2COOC2H5) at the S—P bond to yield orthophosphate and the corresponding thioalcohols. The rate of enzymic hydrolysis of cysteamine S-phosphate was measured at pH 9.0 in 0.1 n sodium barbital buffer at different concentrations of substrate and MgCl2. The Km and Vmax values obtained, as well as the amount of MgCl2 required for complete activation of the enzyme, were similar to the corresponding values obtained when p-nitrophenyl phosphate was used as the substrate. In marked contrast, however, O-substituted monoesters of phosphorothioic acid of the type ROPO2SKH (R = —CH3, —CH2CH3, or [See PDF for structure]NO2) were completely resistant to hydrolysis by alkaline phosphatases from Escherichia coli and from intestine. The O-substituted monoesters of thiophosphoric acid (10-7 m) inhibited the enzymic hydrolysis of both cysteamine S-phosphate and p-nitrophenyl phosphate (10-3 m) at a 10-fold concentration of the enzyme. Acid phosphatases from wheat germ, potato, and prostate gland did not hydrolyze S-substituted monoesters of phosphorothioic acid at detectable rates, but did hydrolyze O-substituted monoesters of phosphorothioic acid at rates comparable with those obtained when p-nitrophenyl phosphate served as the substrate for these enzymes. These findings suggest that acid and alkaline phosphatases act by two different mechanisms.
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In this study we evaluated phosphatase activity in members of the family Enterobacteriaceae by conventional methods and by a novel method. The novel method is based on the formation of bright-green-strained colonies by phosphatase-positive, but not phosphatase-negative, strains in the presence of a phosphate substrate, such as phenolphthalein monophosphate or 6-benzoylnaphthyl phosphate (6-BNP), and methyl green. A total of 1,055 strains belonging to 65 different species of Enterobacteriaceae were tested for green staining of the colonies in the presence of methyl green and either phenolphthalein monophosphate or 6-BNP and for phosphatase activity by three different conventional methods. With the sole exception of one Leminorella richardii type strain, all isolates of all of the species formed green-stained colonies in the presence of the substrate 6-BNP. All strains were phosphatase positive by all of the conventional methods.
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Electrospray ionization mass spectrometry (ESI-MS) has been utilized to investigate the self-assembly processes occurring during the formation of the microporous metal–organic framework CPO-27-M (M = Co, Ni). The mono- and dinuclear building units {M(Hxdhtp)} and {M2(Hxdhtp)}, where Hxdhtp is the organic linker HxC8O6 and fragments thereof, were identified as key species present in the reaction mixture during the product formation. Time-resolved powder X-ray diffraction analysis was used to follow the synthesis and confirmed that no other crystalline products occur in the reaction mixture prior to the crystallization of CPO-27-Ni. When equimolar reactions were performed at room temperature, compounds [(M(H2dhtp)(H2O)4·2H2O] (M = Co, Ni) crystallized instead of CPO-27 obtained at the higher temperature of the solvothermal procedure. It was confirmed that mono- and dinuclear species are key building blocks not only in the formation of CPO-27-M but also in the formation of the 1D chain structure (M(H2dhtp)(H...
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eng_Latn
| 31,089 |
A novel bis-pyrazolyl-carboxyl ligand, 2,6-bis(5-methyl-3-carboxypyrazol-1-ylmethyl)pyridine ( L ), was designed and synthesized and its several lanthanide(III) complexes Eu(III), Tb(III), Sm(III) and Gd(III) were successfully prepared and characterized in detail based on elemental analysis, infrared, mass, proton nuclear magnetic resonance spectroscopy and TG–DTA studies. Analysis of the IR spectra suggested that each of the lanthanide metal ions coordinated to the ligand via the carbonyl oxygen atoms and the nitrogen atom of the pyridine ring and pyrazole rings. The fluorescence spectra exhibits that the Tb(III) complex and the Eu(III) complex display characteristic metal-centered fluorescence in solid state while ligand fluorescence is completely quenched. However, the Tb(III) complex displays more effective fluorescence than the other complexes, which is attributed to especial effectivity in transferring energy from the lowest triplet energy level of the ligand ( L ) onto the excited state ( 5 D 4 ) of Tb(III).
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Synthesis of pyrazole derivative ligand 2-(1,5-diphenyl-4,5-dihydro-1H-pyrazole-3-yl) pyridine (L) has been successfully carried out by the Claisen-Schmidt condensation followed by the excess addition of phenyl hydrazine in ethanol solution. Reddish yellow solid with a 28.85% yield then characterized using FTIR , UV-Visible, and H1-NMR spectroscopy. UV-Visible spectroscopy was conducted to determine the complex formation between lanthanide ions with ligands. Fluorescent experiment with spectrofluorometer has conducted in compound emission intensity change upon addition of La3+ and the Eu3+. UV-Visible result show complex formation in molar ratio Eu3+ : L (1:2) which occurred at a absorption wavelength of 366 nm, while the complex with the ratio La3+ : L (1:3) exhibited at 342 nm in acetonitrile. Fluorescence analysis showed ligands have two excitation λ at 257 nm 365 nm with a noticeable molar absorptivity at concentration 2x10-5 M. The addition of La3+ ions lead to the fluorescence enhancement effect on the λem at 355 nm. While the addition of the Eu3+ demonstrates the effect of fluorescence quenching at the λem 340 nm.
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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
| 31,090 |
A high-yield one-pot two-step synthesis of 2-aminoimidazoles (2-AI), exploiting an under-air heterocyclodehydration process between α-chloroketones and guanidine derivatives, and using deep eutectic solvents (DESs) as nonconventional, “green” and “innocent” reaction media, has been accomplished successfully. The combination of either glycerol or urea with choline chloride (ChCl) proved to be effective for decreasing the reaction time to about 4–6 h in contrast to the 10–12 h usually required for the same reaction run in toxic and volatile organic solvents and under an argon atmosphere. In addition, the use of the ChCl–urea as a DES also enables the direct isolation of triaryl-substituted 2-AI derivatives by means of a simple work-up procedure consisting in filtration and crystallization, and allows the recycle of the DES mixture. A plausible mechanism highlighting the potential role played by hydrogen bonding catalysis has also been illustrated.
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Deep eutectic solvents, as green and environmentally friendly media, were utilized in the synthesis of novel coumarinyl Schiff bases. Novel derivatives were synthesized from 2-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)acetohydrazide and corresponding aldehyde in choline chloride:malonic acid (1:1) based deep eutectic solvent. In these reactions, deep eutectic solvent acted as a solvent and catalyst as well. Novel Schiff bases were synthesized in high yields (65–75%) with no need for further purification, and their structures were confirmed by mass spectra, 1H and 13C NMR. Furthermore, their antioxidant activity was determined and compared to antioxidant activity of previously synthesized derivatives, thus investigating their structure–activity relationship utilizing quantitative structure-activity relationship QSAR studies. Calculation of molecular descriptors has been performed by DRAGON software. The best QSAR model (Rtr = 0.636; Rext = 0.709) obtained with three descriptors (MATS3m, Mor22u, Hy) implies that the pairs of atoms higher mass at the path length 3, three-dimensional arrangement of atoms at scattering parameter s = 21 A−1, and higher number of hydrophilic groups (-OH, -NH) enhanced antioxidant activity. Electrostatic potential surface of the most active compounds showed possible regions for donation of electrons to 1,1-diphenyl-2-picryhydrazyl (DPPH) radicals.
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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
| 31,091 |
Chromium is a metal which has both biological and environmental interest. It occurs in nature mostly in two stable oxidation states Cr(III) and Cr(VI). Cr(III) is non-toxic and plays a significant role in carbohydrate and fat metabolism, whereas Cr(VI) is highly toxic (MAC value 50 μg L−1 only). Being a major industrial pollutant, it has a hazardous effect on man, animal and plant life. In the present investigation, an attempt has been made to develop a highly selective and sensitive method for the spectrophotometric determination of Cr(III), Cr(VI) and total Cr in various water samples. Cr(VI) is extracted with N-hydroxy-N, N'-diphenylbenzamidine in chloroform over 0.2–0.8 M HCI and for total Cr the sample is oxidised before extraction. The extracts are separately reacted with 1,5-diphenylcarbazide in strong hydrochloric acid media to give a red-violet coloured compound having a molar absorptivity of (9.10) x 104 L mor−1cm−1 at λmax 540 nm. The difference between the two gives the value for Cr(II...
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Chromium (Cr +6 ) tolerant acidophilic bacteria were isolated from tanneries' effluents, optimized for growth conditions and biochemically characterized. Two of the isolates were assessed for their Cr +6 reduction potential. It was found that the isolates No. 22 and 25 efficiently reduced 750 µg Cr +6 /ml of the medium within 4 days of incubation. These bacteria can be considered important for bioremediation of metal rich acidic environments or industrial effluents. These microbes may play role for developing new strategies for remediation of heavy metals' polluted wastewaters characterized by low pH.
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Chromium is a non-essential and well-known toxic metal for microorganisms and plants. The widespread industrial use of this heavy metal has caused it to be considered as a serious environmental pollutant. Chromium exists in nature as two main species, the trivalent form, Cr(III), which is relatively innocuous, and the hexavalent form, Cr(VI), considered a more toxic species. At the intracellular level, however, Cr(III) seems to be responsible for most toxic effects of chromium. Cr(VI) is usually present as the oxyanion chromate. Inhibition of sulfate membrane transport and oxidative damage to biomolecules are associated with the toxic effects of chromate in bacteria. Several bacterial mechanisms of resistance to chromate have been reported. The best characterized mechanisms comprise efflux of chromate ions from the cell cytoplasm and reduction of Cr(VI) to Cr(III). Chromate efflux by the ChrA transporter has been established in Pseudomonas aeruginosa and Cupriavidus metallidurans (formerly Alcaligenes eutrophus) and consists of an energy-dependent process driven by the membrane potential. The CHR protein family, which includes putative ChrA orthologs, currently contains about 135 sequences from all three domains of life. Chromate reduction is carried out by chromate reductases from diverse bacterial species generating Cr(III) that may be detoxified by other mechanisms. Most characterized enzymes belong to the widespread NAD(P)H-dependent flavoprotein family of reductases. Several examples of bacterial systems protecting from the oxidative stress caused by chromate have been described. Other mechanisms of bacterial resistance to chromate involve the expression of components of the machinery for repair of DNA damage, and systems related to the homeostasis of iron and sulfur.
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eng_Latn
| 31,092 |
Cobalt(III) complexes of 2-acetyl- and 2-formylpyridine 4 N -methylthiosemicarbazone, [Co(L4M) 2 ]BF 4 and [Co(4M) 2 ]BF 4 , respectively, have been synthesized, their crystal structures solved and their spectral properties measured. The crystal structures show that each complex has its two ligands coordinated in a mer configuration, but that the stereochemistry of the thiosemicarbazone moiety's 4 N position of coordinated L4M and 4M is different. The complexes' bond lengths and bond angles are compared with other thiosemicarbazone complexes. The 1 H and 13 C NMR spectra show uncomplexed HL4M and H4M to be in the E and Z configurations, respectively, and that the two ligands within each complex are nearly identical.
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New complexes of dioxovanadium(V), zinc(II), ruthenium(II), palladium(II), and platinum(II) with 6-methylpyridine-2-carbaldehyde-N(4)-ethylthiosemicarbazone (HmpETSC) have been synthesized. The composition of these complexes is discussed on the basis of elemental analyses, IR, Raman, NMR (1H, 13C, and 31P), and electronic spectral data. The X-ray crystal structures of [VO2(mpETSC)] and [Pt(mpETSC)Cl] are also reported. The HmpETSC and its [Zn(HmpETSC)Cl2] and [Pd(mpETSC)Cl] complexes exhibit antineoplastic activity against colon cancer human cell lines (HCT 116).
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During and after the application of currently used pesticides (CUPs) a significant fraction of applied pesticides can be lost to the air. A confirmatory and rapid procedure has been developed for the determination of four fungicides (carbendazim, thiabendazol, imazalil and bitertanol), three insecticides (imidacloprid, methidathion and pyriproxyfen), one helicide (methiocarb) and one acaricide (hexythiazox) in fine airborne particulate matter (PM 2.5) at trace level. The proposed method includes extraction of PM 2.5-bound pesticides by pressurized liquid extraction (PLE) followed by a direct injection into LC-MS/MS. The main parameters affecting the performance of the electrospray ionization source and PLE parameters were optimised using statistical design of experiments (DoE). The matrix effect was also evaluated. Recoveries ranged from 86 to 106% and the limit of quantification (LoQ) was 6.5 pg m(-3) for eight out of nine pesticides, when air volumes of 760 m(3) were collected. The method was applied to 60 samples collected from four stations of the monitoring network of the Regional Valencia Government (Spain) during August-October 2007. The measured concentrations ranged from not detected to 1,371 pg m(-3).
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eng_Latn
| 31,093 |
In recent years, visible-light-driven organic reactions have been experiencing a significant renaissance in response to topical interest in environmentally friendly green chemical synthesis. The transformations using inexpensive, readily available visible-light sources have come to the forefront in organic chemistry as a powerful strategy for the activation of small molecules. In this review, we focus on recent advances in the development of visible-light-driven organic reactions, including aerobic oxidation, hydrogen-evolution reactions, energy-transfer reactions and asymmetric reactions. These key research topics represent a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.
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Tuning electron transfer (ET) rates from catalysts to substrates is important for modulating photocatalytic organic reactions. In this work, we have taken pyrene-based photocatalysts (Py) for photocatalytic hydrodefluorination of polyfluoroarenes (FA) as model systems, and conducted a first-principle study on modulating ET rates from Py to FA via chemical modification of Py with different electron donating/withdrawing groups (EDGs/EWGs). The computed spatial distributions of frontier Kohn-Sham orbitals suggest that ET is energetically more favorable for Py-EDGs than for Py-EWGs. The estimated ET rates by a simplified Marcus model show that they are appreciably enhanced by EDGs substitution and weakened by EWGs substitution. Noticeably, the associated Gibbs free energy change plays a dominant role. Our findings of tuning ET rates for Py-FA complexes via chemical group modifications cast new insight into the rational design of metal-free photocatalysts for organic transformations.
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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
| 31,094 |
Three component equilibria between H+, silicic acid, and the catecholamines dopamine and L-DOPA were studied by means of potentiometric (glass electrode) measurements in 0.6 M Na(Cl) medium at 25°C. Experimental data cover the ranges 2≤ −log[H+]≤9.5, 0.002≤0.005 M; 0.005 ≤ C ≤ 0.016 M, and 1 ≤ C/B ≤ 6 (B and C stand for the total concentration of Si and catecholamine, respectively). In acidic and near-neutral solutions no interactions were registered while, in slightly alkaline solutions, both systems are characterized by a formation of mononuclear tris-complexes SiL3 containing pyrocatechol-type bonds. The species forming at −log[H+] ≈ 7.5 have fully protonated amine side-chains which, at somewhat higher −log[H+] values, start to deprotonate. Simultaneously, a decomposition of the octahedrally coordinated complex is occurring and the hydrolytic species SiO(OH)3− becomes increasingly important. With dopamine, the equilibrium constants characterizing the system are log K (Si(OH)4 + 3H3L+ α Si(HL)3+ + 2H+ + 4H2O) − 9.70 ± 0.03 and log K (Si(OH)4 + 3H3L+ α SiL(HL)2 + 3H+ + 4H2O) − 19.33 ± 0.03. The corresponding equilibrium reactions with L-DOPA are log K (Si(OH)4 + 3H3L α Si(HL)32− + 2H+ + 4H2O) − 10.08 ± 0.05 and log K (Si(OH)4 + 3H3L α SiL(HL)23− + 3H+ + 4H2O) −19.35 ± 0.07. Data were analyzed using the least-squares computer program LETAGROPVRID. ::: ::: The octahedral oxygen coordination around the silicon atom in these complexes has been verified by using the 29Si NMR method. Via model calculations it is shown that a minimum of ∼ 0.004 M catecholamine is needed to double the aqueous solubility of quartz.
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Dopamine and 4 related compounds were studied by 1H NMR-pH titrations and a case-tailored evaluation method. The resulting acid-base properties of dopamine are quantified in terms of 3 macroscopic and 12 microscopic protonation constants and the concomitant 3 interactivity parameters. The species- and site-specific basicities are interpreted by means of inductive and shielding effects through various intra- and intermolecular comparisons. The site-specific basicities determined this way are key parameters for the prediction of pharmacokinetic behavior and receptor-binding at the molecular level.
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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
| 31,095 |
The H-bonded complexes of pyridine N-oxide (PyO) with H2O, acetic, cyanoacetic, propiolic, tribromoacetic, trichloroacetic, trifluoroacetic, hydrochloric, and methanesulfonic acids have been studied by FTIR and NMR spectroscopy, X-ray diffraction, and quantum chemical DFT calculations. Correlations between vibrational frequencies of the NO stretching and PyO ring modes and geometric parameters of the H-bond have been established. FTIR experiments show and DFT calculations confirm that definite discontinuity is present in the vicinity of the midpoint in the proton transfer pathway. The established correlations significantly aid in the understanding of fine effects such as the isotope (deuteration) effect, crystal-to-solution transition, or criticality of aqueous solutions induced by ionic pairs. Geometric isotope effect in the ionic H-bond aggregate of PyO·H(D)Cl was found to be extraordinary large. Measured FTIR, CP/MAS, and high-resolution 13C NMR spectra indicate that H-bond in the PyO·HCl complex in po...
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We study a series of intermolecular hydrogen-bonded 1 : 1 complexes formed by chloroacetic acid with 19 substituted pyridines and one aliphatic amine dissolved in CD2Cl2 at low temperature by 1H and 13C NMR and FTIR spectroscopy. The hydrogen bond geometries in these complexes vary from molecular (O-HN) to zwitterionic (O-H-N+) ones, while NMR spectra show the formation of short strong hydrogen bonds in intermediate cases. Analysis of C[double bond, length as m-dash]O stretching and asymmetric CO2- stretching bands in FTIR spectra reveal the presence of proton tautomerism. On the basis of these data, we construct the overall proton transfer pathway. In addition to that, we also study by use of ab initio molecular dynamics the complex formed by chloroacetic acid with 2-methylpyridine, surrounded by 71 CD2Cl2 molecules, revealing a dual-maximum distribution of hydrogen bond geometries in solution. The analysis of the calculated trajectory shows that the proton jumps between molecular and zwitterionic forms are indeed driven by dipole-dipole solvent-solute interactions, but the primary cause of the jumps is the formation/breaking of weak CHO bonds from solvent molecules to oxygen atoms of the carboxylate group.
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A unique synthetic approach to 3-hydroxy-4-substituted picolinonitriles is achieved via gold(I)-catalyzed cyclization of 4-propargylaminoisoxazoles and subsequent N-O bond cleavage of isoxazolopyridines under mild reaction conditions in a stepwise and one-pot fashion.
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eng_Latn
| 31,096 |
The photochemistry and molecular structure of 1-phenyl-4-allyl-tetrazolone (PAT) was studied by FT-IR matrix isolation spectroscopy and DFT(B3LYP)/6-311++G(d,p) calculations. The spectrum of matrix-isolated PAT monomers agrees well with the sum spectrum of three conformers predicted theoretically. UV irradiation (λ > 235 nm) of matrix-isolated PAT induces three types of photofragmentation: (1) production of phenylazide and allyl-isocyanate, with phenylazide then losing N2 to yield 1-aza-1,2,4,6-cycloheptatetraene; (2) formation of phenyl-isocyanate and allylazide; (3) N2 elimination leading to formation of 1-allyl-2-phenyldiaziridin-3-one; this compound partially reacts further to form 1-allyl-1H-benzoimidazol-2(3H)-one. The observed photochemistry of the matrix-isolated PAT is distinct from the preferred photochemical fragmentation in solution, where 3,4-dihydro-3-phenylpyrimidin-2(1H)-one is produced as the primary photoproduct.
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Photolysis (193 nm) of propiolic acid (HCCCOOH) was studied with Fourier transform infrared spectroscopy in noble-gas (Ar, Kr, and Xe) solid matrixes. The photolysis products were assigned using ab initio quantum chemistry calculations. The novel higher-energy conformer of propiolic acid was efficiently formed upon UV irradiation, and it decayed back to the ground-state conformer on a time scale of approximately 10 min by tunneling of the hydrogen atom through the torsional energy barrier. In addition, the photolysis produced a number of matrix-isolated 1:1 molecular complexes such as HCCH...CO2, HCCOH...CO, and H2O...C3O. The HCCH...CO2 complex dominated among the photolysis products, and the computations suggested a parallel geometry of this complex characterized by an interaction energy of -9.6 kJ/mol. The HCCOH...CO complex also formed efficiently, but its concentration was strongly limited by its light-induced decomposition. In this complex, the most probable geometry was found to feature the interaction of carbon monoxide with the OH group via the carbon atom, and the computational interaction energy was determined to be -18.3 kJ/mol. The formation of the strong H2O...C3O complex (interaction energy -21 kJ/mol) was less efficient, which might be due to the inefficiency of the involved radical reaction.
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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
| 31,097 |
Indoleamine 2,3-dioxygenase catalyzes the O2-dependent oxidation of l-tryptophan (l-Trp) to N-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high l-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with l-tryptophan (l-Trp) can be accounted for by the sequential, ordered binding of O2 and l-Trp. Analysis of the data shows that at low concentrations of l-Trp, O2 binds first followed by the binding of l-Trp; at higher concentrations of l-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (Em0) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable co...
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The kynurenine pathway is the major route of L-tryptophan (L-Trp) catabolism in biology, leading ultimately to the formation of NAD(+). The initial and rate-limiting step of the kynurenine pathway involves oxidation of L-Trp to N-formylkynurenine. This is an O2-dependent process and catalyzed by indoleamine 2,3-dioxygenase and tryptophan 2,3-dioxygenase. More than 60 years after these dioxygenase enzymes were first isolated (Kotake, Y., and Masayama, I. (1936) Z. Physiol. Chem. 243, 237-244), the mechanism of the reaction is not established. We examined the mechanism of substrate oxidation for a series of substituted tryptophan analogues by indoleamine 2,3-dioxygenase. We observed formation of a transient intermediate, assigned as a Compound II (ferryl) species, during oxidation of L-Trp, 1-methyl-L-Trp, and a number of other substrate analogues. The data are consistent with a common reaction mechanism for indoleamine 2,3-dioxygenase-catalyzed oxidation of tryptophan and other tryptophan analogues.
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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
| 31,098 |
2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ) and 5,8-dihydroxy-[1,4]-naphthoquinone (DHNQ) are two key chromophores which are almost ubiquitous in cellulosic materials. Their fate under conditions of alkaline peroxide bleaching (P stage) has been established previously, but the intermediacy of cyclic peroxides, which so far had only been postulated, remained an open issue. By means of 17O NMR spectroscopy, additionally supported by other NMR techniques, it was demonstrated that both DHBQ and DHNQ form cyclic peroxides as primary intermediates in the reaction with hydrogen peroxide under alkaline conditions. These intermediates are subsequently further degraded to products already known. The experimental confirmation of the cyclic peroxides is an important step in the understanding of reaction mechanisms in pulp bleaching chemistry.
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5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores in cellulosic materials. Its almost ubiquitous presence in cellulosic materials makes it a target molecule of the pulp and paper industry’s bleaching efforts. In the presented study, DHNQ was treated with hydrogen peroxide under alkaline conditions at pH 10, resembling the conditions of industrial hydrogen peroxide bleaching (P stage). The reaction mechanism, reaction intermediates, and final degradation products were analyzed by UV/vis, NMR, GC–MS, and EPR. The degradation reaction yielded C1–C4 carboxylic acids as the final products. Highly relevant for pulp bleaching are the findings on intermediates of the reaction, as two of them, 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) and 1,4,5,8-naphthalenetetrone, are potent chromophores themselves. While DHBQ is one of the three key cellulosic chromophores and its degradation by H2O2 is well-established, the second intermediate, 1,4,5,8-naphthalenetetrone, is reported for the first time in ...
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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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