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Author (up) Burtscher, D.; Grela, K. file  url
doi  openurl
  Title Aqueous olefin metathesis Type Journal Article
  Year 2009 Publication Angewandte Chemie (International ed. in English) Abbreviated Journal Angew Chem Int Ed Engl  
  Volume 48 Issue 3 Pages 442-454  
  Keywords aqueous media; homogeneous catalysis; olefin metathesis; ruthenium; sustainable chemistry  
  Abstract According to popular belief, oxygen and water are the natural enemies of organometallic reactions and therefore must be excluded rigorously from the reaction vessel. This belief is founded in the case of the highly reactive nucleophilic metal alkylidene complexes that were used in early catalytic olefin metathesis. However, owing to the high stability of the ruthenium carbene complexes introduced by Grubbs, metathesis in water has become reality.  
  Call Number Serial 247  
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Author (up) Czerlinski, G.; Ypma, T. file  url
doi  openurl
  Title Mechanisms of telomerase-dimer catalysis Type Journal Article
  Year 2008 Publication Journal of Theoretical Biology Abbreviated Journal J Theor Biol  
  Volume 250 Issue 3 Pages 512-523  
  Keywords Allosteric Regulation/physiology; Catalysis; HIV/genetics; Humans; *Models, Genetic; RNA/metabolism/*physiology; Telomerase/metabolism/*physiology; Telomere/metabolism; Templates, Genetic  
  Abstract There is evidence that human telomerase acts as a dimer [Wenz, C., Enenkel, B., Amacker, M., Kelleher, C., Damm, K., Lingner, J., 2001. Human telomerase contains two cooperating telomerase RNA molecules. EMBO J. 20, 3526-3534]. Three possible mechanisms have been proposed. We translate those proposals into three detailed mechanistic models for telomerase action, also introducing optional isomerizations with equilibrium constants inversely related to the number of bound nucleotides. To distinguish between these models by in situ experiments we propose a microscopic system which uses two-photon excitation of fluorescence in a volume of about 0.5 microm(3). A variety of detection strategies and experimental designs are considered; we focus on those best suited to observation of a small volume under limitations imposed by diffusion to and from the reacting micro-volume, and consequently restrict ourselves to constant flow. Numerical simulation is used to help identify an optimal experimental design. The detection of mechanistic changes hinges on linking fluorescence reporters to selected reaction components, either directly (chemically) or indirectly (via an indicator reaction). We show that rapid mixing experiments are better than chemical relaxation experiments, as the statistics of single molecule kinetics affects the latter more than the former. However, some fast reaction steps can only be revealed by chemical relaxation coupled with mixing experiments. We explore connections between our methods and studies of HIV and other systems with RNA to DNA transcription.  
  Call Number Serial 129  
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Author (up) Ge, L.; Ran, R.; Shao, Z.; Zhu, Z.H.; Liu, S. file  url
  Title Low-temperature synthesis of La0.6Sr0.4Co0.2Fe0.8O3-δ perovskite powder via asymmetric sol-gel process and catalytic auto-combustion Type Journal Article
  Year 2009 Publication Ceramics International Abbreviated Journal Ceramics International  
  Volume 35 Issue 7 Pages 2809-2815  
  Keywords Ceramic powder; Auto-combustion synthesis; Asymmetry; Catalysis  
  Abstract La0.6Sr0.4Co0.2Fe0.8O3−δ powder was synthesized by a combined EDTA-citrate complexing process via low-temperature auto-combustion synthesis with NH4NO3 as an oxidizer and a combustion trigger. Two novel methods were explored to improve this auto-combustion technology with reduced NH4NO3 addition: the use of La0.6Sr0.4Co0.2Fe0.8O3−δ as the combustion catalyst and the application of asymmetric sol–gel process to provide the precursor with different NH4NO3 concentrations. The prepared perovskite powder was characterized by BET, SEM, XRD and iodometric titration techniques. The catalytic performance of the powder was also examined in the decomposition of peroxide hydrogen. Experimental results indicate that powders from catalytic combustion and asymmetric precursor routes have more advantages in terms of better crystallites, higher specific surface area, higher B-site valence state, improved sintering capability and better catalytic performance in peroxide hydrogen decomposition than that from the synthesis with uniform NH4NO3 distribution.  
  Call Number Serial 1407  
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Author (up) Huang, Y.; Lu, Z.; Liu, N.; Chen, Y. file  url
  Title Identification of important residues in diketoreductase from Acinetobacter baylyi by molecular modeling and site-directed mutagenesis Type Journal Article
  Year 2012 Publication Biochimie Abbreviated Journal Biochimie  
  Volume 94 Issue 2 Pages 471-478  
  Keywords 3-Hydroxyacyl CoA Dehydrogenases/chemistry/genetics/metabolism; Acinetobacter/*enzymology/genetics; Amino Acid Motifs; Amino Acid Substitution; Bacterial Proteins/*chemistry/genetics/metabolism; Binding Sites; Biocatalysis; Esters/*metabolism; Humans; Hydrogen-Ion Concentration; Hydroxymethylglutaryl-CoA Reductase Inhibitors/metabolism; Kinetics; Molecular Dynamics Simulation; Molecular Sequence Data; Mutagenesis, Site-Directed; NAD/metabolism; Oxidation-Reduction; Oxidoreductases/*chemistry/genetics/metabolism; Protein Structure, Tertiary; Recombinant Proteins/chemistry/genetics/metabolism; Sequence Homology, Amino Acid; Stereoisomerism  
  Abstract Diketoreductase (DKR) from Acinetobacter baylyi exhibits a unique property of double reduction of a beta, delta-diketo ester with excellent stereoselectivity, which can serve as an efficient biocatalyst for the preparation of an important chiral intermediate for cholesterol lowering statin drugs. Taken the advantage of high homology between DKR and human heart 3-hydroxyacyl-CoA dehydrogenase (HAD), a molecular model was created to compare the tertiary structures of DKR and HAD. In addition to the possible participation of His-143 in the enzyme catalysis by pH profile, three key amino acid residues, Ser-122, His-143 and Glu-155, were identified and mutated to explore the possibility of involving in the catalytic process. The catalytic activities for mutants S122A/C, H143A/K and E155Q were below detectable level, while their binding affinities to the diketo ester substrate and cofactor NADH did not change obviously. The experimental results were further supported by molecular docking, suggesting that Ser-122 and His-143 were essential for the proton transfer to the carbonyl functional groups of the substrate. Moreover, Glu-155 was crucial for maintaining the proper orientation and protonation of the imidazole ring of His-143 for efficient catalysis.  
  Call Number Serial 1415  
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Author (up) Höfle, G.; Steglich, W.; Vorbrüggen, H. file  url
  Title 4-Dialkylaminopyridines as Highly Active Acylation Catalysts. [New synthetic method (25)] Type Journal Article
  Year 1978 Publication Angewandte Chemie International Edition in English Abbreviated Journal Angew. Chem. Int. Ed. Engl.  
  Volume 17 Issue 8 Pages 569-583  
  Keywords 4-Dialkylaminopyridines; Amino pyridines; Acylation; Catalysis; Synthetic methods; Pyridines  
  Abstract The synthesis of 4-dialkylaminopyridines can be accomplished in two steps starting from pyridine. Compared to pyridine, these derivatives are approximately 104 times more active when used as acylation catalysts. Dialkylaminopyridines are being used with ever-increasing frequency for acylation reactions which proceed either incompletely or not at all in pyridine. This article reviews the various possible applications of 4-dialkylaminopyridines in terpene, steroid, carbohydrate and nucleoside chemistry as well as in the transformation of amino acids into α-acyl aminoketones and polymerization of isocyanates. In addition, N-substituted 4-dialkylaminopyridinium salts can be used for the transfer of sensitive groups to nucleophiles in aqueous medium. The exceptional catalytic effect of these derivatives, even in non-polar solvents, is due, in part, to the formation of high concentrations of N-acylpyridinium salts which are present in solution as loosely-bound, highly reactive ion pairs.  
  Call Number Serial 1812  
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Author (up) Jiang, D.; Peng, J.; Chen, Y. file  url
doi  openurl
  Title Pd-catalyzed carboetherification of beta,gamma-unsaturated oximes: a novel approach to Delta2-isoxazolines Type Journal Article
  Year 2008 Publication Organic Letters Abbreviated Journal Org Lett  
  Volume 10 Issue 9 Pages 1695-1698  
  Keywords Catalysis; Isoxazoles/*chemical synthesis/chemistry; Molecular Structure; Oximes/*chemistry; Palladium/chemistry  
  Abstract A novel route to the synthesis of Delta2-isoxazoline derivatives is described. Reaction of beta,gamma-unsaturated oximes with aryl bromides via palladium-catalyzed carboetherification affords 3,5-disubstituted Delta2-isoxazolines in good yields. The use of Xantphos as ligand is crucial for the transformation. The carboetherification products can be further converted to beta-hydroxy ketones in the presence of Fe powder and NH4Cl.  
  Call Number Serial 206  
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Author (up) Jow, T.R.; Xu, K.; Ding, M.S.; Zhang, S.S.; Allen, J.L.; Amine, K. file  url
doi  openurl
  Title LiBOB-Based Electrolytes for Li-Ion Batteries for Transportation Applications Type Journal Article
  Year 2004 Publication Journal of The Electrochemical Society Abbreviated Journal J. Electrochem. Soc.  
  Volume 151 Issue 10 Pages A1702  
  Keywords lithium compounds; nickel compounds; secondary cells; electrolytes; electrochemical; electrodes; electrical conductivity; blending; electrochemistry; oxidation; thermal stability; catalysis  
  Abstract The low-temperature performance and the stability of LiBOB-based electrolytes were studied in Li-ion cells and on various cathode materials, respectively. It was found that the conductivity of LiBOB in carbonate solvents can be improved by blending with ester solvents. It was also found that the capacity delivered using such electrolytes at subzero temperatures can be improved by adding ester solvents into electrolyte compositions, although at the expense of the stability against high-temperature cycling. The BOB− anion remains electrochemically stable on strongly oxidizing electrode material such as LiNi1­y­zMyM′zO2 as shown by high-temperature cycling and storage. Nonetheless, the BOB− stability may vary with different cathode materials depending on the reactivity among BOB− anion, solvent, and lithiated metal oxide cathode materials. To maximize the advantages of LiBOB over the industry standard LiPF6, further work in electrolyte formulation is desired. © 2004 The Electrochemical Society. All rights reserved.  
  Call Number Serial 816  
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Author (up) Kohli, R.M.; Walsh, C.T.; Burkart, M.D. file  url
  Title Biomimetic synthesis and optimization of cyclic peptide antibiotics Type Journal Article
  Year 2002 Publication Nature Abbreviated Journal Nature  
  Volume 418 Issue 6898 Pages 658-661  
  Keywords Amino Acid Sequence; Anti-Bacterial Agents/*biosynthesis/*chemical synthesis/pharmacology; Bacteria/drug effects; Biological Products/biosynthesis/chemical synthesis/pharmacology; Catalysis; Cyclization; Erythrocytes/drug effects; Humans; Hydrolysis; Microbial Sensitivity Tests; Molecular Mimicry; Molecular Sequence Data; Peptides, Cyclic/*biosynthesis/*chemical synthesis/pharmacology; Substrate Specificity; Thiolester Hydrolases/metabolism; Tyrocidine/analogs & derivatives/biosynthesis/chemical synthesis/pharmacology  
  Abstract Molecules in nature are often brought to a bioactive conformation by ring formation (macrocyclization). A recurrent theme in the enzymatic synthesis of macrocyclic compounds by non-ribosomal and polyketide synthetases is the tethering of activated linear intermediates through thioester linkages to carrier proteins, in a natural analogy to solid-phase synthesis. A terminal thioesterase domain of the synthetase catalyses release from the tether and cyclization. Here we show that an isolated thioesterase can catalyse the cyclization of linear peptides immobilized on a solid-phase support modified with a biomimetic linker, offering the possibility of merging natural-product biosynthesis with combinatorial solid-phase chemistry. Starting from the cyclic decapeptide antibiotic tyrocidine A, this chemoenzymatic approach allows us to diversify the linear peptide both to probe the enzymology of the macrocyclizing enzyme, TycC thioesterase, and to create a library of cyclic peptide antibiotic products. We have used this method to reveal natural-product analogues of potential therapeutic utility; these compounds have an increased preference for bacterial over eukaryotic membranes and an improved spectrum of activity against some common bacterial pathogens.  
  Call Number Serial 1894  
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Author (up) Leão, R.; de F. de Moraes, P.; Pedro, M.; Costa, P. file  url
doi  openurl
  Title Synthesis of Coumarins and Neoflavones through Zinc Chloride Catalyzed Hydroarylation of Acetylenic Esters with Phenols Type Journal Article
  Year 2011 Publication Synthesis Abbreviated Journal Synthesis  
  Volume 2011 Issue 22 Pages 3692-3696  
  Keywords Lactone; Oxygen heterocycle; Alkyne; Catalysis; Phenols; Ester; Acetylenic compound; Arylation; Catalytic reaction; Zinc II Chlorides; Coumarine derivatives; Chemical synthesis  
  Abstract Acetylenic esters react with oxygenated phenols under solvent-free conditions in the presence of only 5 mol% of zinc chloride as a catalyst to give coumarins and neoflavones in reasonable-to-good yields.  
  Call Number Serial 776  
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Author (up) Lin, Y.-G.; Hsu, Y.-K.; Chen, Y.-C.; Lee, B.-W.; Hwang, J.-S.; Chen, L.-C.; Chen, K.-H. file  url
  Title Cobalt-phosphate-assisted photoelectrochemical water oxidation by arrays of molybdenum-doped zinc oxide nanorods Type Journal Article
  Year 2014 Publication ChemSusChem Abbreviated Journal ChemSusChem  
  Volume 7 Issue 9 Pages 2748-2754  
  Keywords Catalysis; Electrochemistry; Electrodes; Molybdenum/*chemistry; Nanotubes/*chemistry; Oxidation-Reduction; Phosphates/*chemistry; *Photochemical Processes; Water/*chemistry; Zinc Compounds/*chemistry; Zinc Oxide/*chemistry; doping; molybdenum; photocatalysis; water splitting; zinc oxides  
  Abstract We report the first demonstration of cobalt phosphate (Co-Pi)-assisted molybdenum-doped zinc oxide nanorods (Zn(1-x)Mo(x)O NRs) as visible-light-sensitive photofunctional electrodes to fundamentally improve the performance of ZnO NRs for photoelectrochemical (PEC) water splitting. A maximum photoconversion efficiency as high as 1.05% was achieved, at a photocurrent density of 1.4 mA cm(-2). More importantly, in addition to achieve the maximum incident photon to current conversion efficiency (IPCE) value of 86%, it could be noted that the IPCE of Zn(1-x)Mo(x)O photoanodes under monochromatic illumination (450 nm) is up to 12%. Our PEC performances are comparable to those of many oxide-based photoanodes in recent reports. The improvement in photoactivity of PEC water splitting may be attributed to the enhanced visible-light absorption, increased charge-carrier densities, and improved interfacial charge-transfer kinetics due to the combined effect of molybdenum incorporation and Co-Pi modification, contributing to photocatalysis. The new design of constructing highly photoactive Co-Pi-assisted Zn(1-x)Mo(x)O photoanodes enriches knowledge on doping and advances the development of high-efficiency photoelectrodes in the solar-hydrogen field.  
  Call Number Serial 1428  
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