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Direct Reduction (direct + reduction)
Selected AbstractsChemInform Abstract: Direct Reduction of Alcohols: Highly Chemoselective Reducing System for Secondary or Tertiary Alcohols Using Chlorodiphenylsilane with a Catalytic Amount of Indium Trichloride.CHEMINFORM, Issue 18 2002Makoto Yasuda Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Facile Synthesis of Gold Octahedra by Direct Reduction of HAuCl4 in an Aqueous SolutionCHEMISTRY - AN ASIAN JOURNAL, Issue 6 2010Weiyang Li Abstract This paper describes a water-based protocol that provides a simple, convenient, and environmentally benign route to the synthesis of Au octahedra. Specifically, we obtained single-crystal Au octahedra (ca.,85,% of the product) with an edge length of 32.4±2.3,nm and singly twinned, truncated bipyramids (ca.,15,%) by reducing HAuCl4 with N -vinyl pyrrolidone in an aqueous solution in the presence of a proper amount of cetyltrimethylammonium chloride (CTAC). Our mechanistic study indicates that the formation of Au octahedra could be explained by oxidative etching, a pathway that has already been validated for the synthesis of nanocrystals for a number of different noble metals. [source] Electroreduction of Oxygen by Cytochrome,c Oxidase Immobilized in Electrode-Supported Lipid Bilayer MembranesCHEMISTRY & BIODIVERSITY, Issue 9 2004Lianyong Su Cytochrome c oxidase is the terminal enzyme in mammalian respiration, and one of its main functions is to catalyze the reduction of oxygen under physiological conditions. Direct reduction of oxygen at electrodes requires application of substantial overpotentials. In this work, bovine cytochrome c oxidase has been immobilized in electrode-supported lipid bilayer membranes to investigate the electroreduction of oxygen under flow conditions. The effect that temperature, solution pH, and solution composition have on the reduction of oxygen by this novel enzyme-modified electrode is reported. Results indicate that the electroreduction of oxygen is most pronounced at low pH (6.4) and elevated temperature (38°). At an applied potential of ,350,mV vs. Ag/AgCl (1M KCl), a current density of ca. 7,,A/cm2 was obtained. The current responses obtained at these electrodes are stable over a period of ca. 10,14 days (10,15% decrease in response). The cytochrome c oxidase-modified electrodes described here could potentially be used for the direct electroreduction of oxygen to water in a biofuel cell. [source] The Role of Amine,B(C6F5)3 Adducts in the Catalytic Reduction of Imines with H2: A Computational StudyEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 15 2009Timofei Privalov Abstract This study thoroughly examines the potential energy surfaces (PESs) of two possible mechanisms for reduction of imines by B(C6F5)3 and H2. The key reaction steps of the first catalytic mechanism, which is the focus of our study, are: (i) the uptake of H2 by a thermally activated amine,B(C6F5)3 species; (ii) proton transfer from the NH2+ moiety of [RNH2CH2R,]+[HB(C6F5)3], to the imine; (iii) nucleophillic attack of the C-center of the iminium ion by the BH, group. The potential energy barriers of the latter, as determined by calculating the evolution of the H-bonded complex of an imine and [RNH2CH2R,]+[HB(C6F5)3], in toluene, are around 10 kcal,mol,1 each. In the second mechanism, only imines serve as basic partners of B(C6F5)3 in the H2 activation, which affords an [RN(H)CHR,]+[HB(C6F5)3], ion pair; direct reduction then proceeds via nucleophilic attack of the C-center by the BH, in [RN(H)CHR,]+[HB(C6F5)3],. This route becomes catalytic when the product amine is released into the solvent and B(C6F5)3 is re-used for H2 activation. Upon taking into account the association energy of an amine,B(C6F5)3 adduct [,9.5 kcal,mol,1 for tBuN(H)CH2Ph and B(C6F5)3 in toluene], the potential energy barrier for H2 uptake by an imine and B(C6F5)3 increases to 14.5 kcal,mol,1. We report a somewhat lower potential energy barrier for H2 uptake by thermally activated amine,B(C6F5)3 adducts [12.7 kcal,mol,1 for the B-N adduct of tBuN(H)CH2Ph and B(C6F5)3 in toluene], although the difference between the two H2 activationbarriers is within the expected error of the computational method. Two catalytic routes are compared based on B3LYP-computed PESs in solvent (toluene).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] The importance of rapid, disturbance-induced losses in carbon management and sequestrationGLOBAL ECOLOGY, Issue 1 2002David D. Breshears Abstract Management of terrestrial carbon fluxes is being proposed as a means of increasing the amount of carbon sequestered in the terrestrial biosphere. This approach is generally viewed only as an interim strategy for the coming decades while other longer-term strategies are developed and implemented , the most important being the direct reduction of carbon emissions. We are concerned that the potential for rapid, disturbance-induced losses may be much greater than is currently appreciated, especially by the decision-making community. Here we wish to: (1) highlight the complex and threshold-like nature of disturbances , such as fire and drought, as well as the erosion associated with each , that could lead to carbon losses; (2) note the global extent of ecosystems that are at risk of such disturbance-induced carbon losses; and (3) call for increased consideration of and research on the mechanisms by which large, rapid disturbance-induced losses of terrestrial carbon could occur. Our lack of ability as a scientific community to predict such ecosystem dynamics is precluding the effective consideration of these processes into strategies and policies related to carbon management and sequestration. Consequently, scientists need to do more to improve quantification of these potential losses and to integrate them into sound, sustainable policy options. [source] Biological evaluation and comparison of three different procedures for labelling of amino acids tyrosine and lysine with technetium-99mJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 3 2007D. Djoki Abstract The 99mTc-labelling of the amino acids tyrosine (Tyr) and lysine (Lys), fundamental building blocks of proteins and peptides, as well as biological properties of the labelled compounds are investigated. Three different approaches for the labelling with 99mTc have been investigated: direct reduction with stannous tin in the presence of the amino acids, the preformed chelate approach through polydentate chelates DTPA and GH, and the ,organometallic approach' using [99m Tc(CO)3(H2O)3]+ precursor. The direct labelling approach was not successful and the yield was poor. In the presence of DTPA and GH, the labelling efficiency was between 43.6 and 97.8%, depending on the amino acid and the polydentate chelate. The use of [99mTc(CO)3(H2O)3]+ precursor point at the formation of 99m Tc(I) co-ordinated complexes with high yield. In this approach, pH and heating influenced the yields. The results of organ distribution study for [99mTc(Tyr)(H2O)(CO)3] and [99mTc(Lys)(H2O)(CO)3] show accumulation in liver, kidneys and intestine. Copyright © 2007 John Wiley & Sons, Ltd. [source] Transplasma membrane electron transport comes in two flavorsBIOFACTORS, Issue 3 2008Darius J. R. Lane Abstract All tested cells possess transplasma membrane electron transfer (tPMET) systems that are capable of reducing extracellular electron acceptors at the cost of cytosolic electron donors. In mammals, classically NAD(P)H- and NADH-dependent systems have been distinguished. The NADH-dependent system has been suggested to be involved in non-transferrin-bound iron (NTBI) reduction and uptake. Recently we reported that transplasma membrane ascorbate/dehydroascorbate cycling can promote NTBI reduction and uptake by human erythroleukemia (K562) cells (D.J.R. Lane and A. Lawen, J Biol Chem 283 (2008), 12701-12708). This system, involves i) cellular import of dehydroascorbate, ii) intracellular reduction of dehydroascorbate to ascorbate using metabolically-derived reducing equivalents, iii) export of ascorbate down its concentration gradient, iv) direct reduction of low molecular weight iron chelates by ascorbate, and v) uptake of iron (II) into the cell. We here propose the consideration of this system as a novel form of tPMET which shares with classical enzyme-mediated tPMET systems the net transfer of reducing equivalents from the cytoplasmic compartment to the extracellular space, but lacks the involvement of the plasma membrane oxidoreductases responsible for the latter. Thus, transplasma membrane electron transfer can and does occur at two mechanistically distinct levels: i) enzyme-mediated transmembrane electron transfer and ii) transmembrane metabolite shuttling/cycling. [source] | |||||||||||||