			Home About us Contact

Reduction Mechanism (reduction + mechanism)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

A Theoretical Study of Surface Reduction Mechanisms of CeO2(111) and (110) by H2

CHEMPHYSCHEM, Issue 6 2007
Hsin-Tsung Chen Dr.
Abstract Reaction mechanisms for the interactions between CeO2(111) and (110) surfaces are investigated using periodic density functional theory (DFT) calculations. Both standard DFT and DFT+U calculations to examine the effect of the localization of Ce 4f states on the redox chemistry of H2,CeO2 interactions are described. For mechanistic studies, molecular and dissociative local minima are initially located by placing an H2 molecule at various active sites of the CeO2 surfaces. The binding energies of physisorbed species optimized using the DFT and DFT+U methods are very weak. The dissociative adsorption reactions producing hydroxylated surfaces are all exothermic; exothermicities at the DFT level range from 4.1 kcal,mol,1 for the (111) to 26.5 kcal,mol,1 for the (110) surface, while those at the DFT+U level are between 65.0 kcal,mol,1 for the (111) and 81.8 kcal,mol,1 for the (110) surface. Predicted vibrational frequencies of adsorbed OH and H2O species on the surfaces are in line with available experimental and theoretical results. Potential energy profiles are constructed by connecting molecularly adsorbed and dissociatively adsorbed intermediates on each CeO2 surface with tight transition states using the nudged elastic band (NEB) method. It is found that the U correction method plays a significant role in energetics, especially for the intermediates of the exit channels and products that are partially reduced. The surface reduction reaction on CeO2(110) is energetically much more favorable. Accordingly, oxygen vacancies are more easily formed on the (110) surface than on the (111) surface. [source]

Crystallization and preliminary X-ray studies of azoreductases from Bacillus sp.

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 5 2010

Azoreductases from Bacillus sp. B29 are NADH-dependent flavoenzymes which contain a flavin mononucleotide (FMN) as a prosthetic group and exist as homodimers composed of 23,kDa subunits. These enzymes catalyze the reductive degradation of various azo compounds by a ping-pong mechanism. In order to determine the structure,function relationship of the azo-dye reduction mechanism, an X-ray crystallographic study of azoreductases was performed. Selenomethionine-labelled AzrA (SeMet-AzrA) and AzrC were crystallized by the hanging-drop vapour-diffusion method. A crystal of SeMet-AzrA diffracted to 2.0,Å resolution and was determined to belong to space group P212121, with unit-cell parameters a = 56.9, b = 69.0, c = 105.4,Å. The native crystals of AzrC belonged to space group C2, with unit-cell parameters a = 192.0, b = 56.6, c = 105.5,Å, , = 115.7°, and diffracted to 2.21,Å resolution. [source]

A Radical-Anion Chain Mechanism Initiated by Dissociative Electron Transfer to a Bicyclic Endoperoxide: Insight into the Fragmentation Chemistry of Neutral Biradicals and Distonic Radical Anions

CHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2008
David
Abstract The electron-transfer (ET) reduction of two diphenyl-substituted bicyclic endoperoxides was studied in N,N -dimethylformamide by heterogeneous electrochemical techniques. The study provides insight into the structural parameters that affect the reduction mechanism of the OO bond and dictate the reactivity of distonic radical anions, in addition to evaluating previously unknown thermochemical parameters. Notably, the standard reduction potentials and the bond dissociation energies (BDEs) were evaluated to be ,0.55±0.15,V and 20±3,kcal,mol,1, respectively, the last representing some of the lowest BDEs ever reported. The endoperoxides react by concerted dissociative electron transfer (DET) reduction of the OO bond yielding a distonic radical-anion intermediate. The reduction of 1,4-diphenyl-2,3-dioxabicyclo[2.2.2]oct-5-ene (1) results in the quantitative formation of 1,4-diphenylcyclohex-2-ene- cis -1,4-diol by an overall two-electron mechanism. In contrast, ET to 1,4-diphenyl-2,3-dioxabicyclo[2.2.2]octane (2) yields 1,4-diphenylcyclohexane- cis -1,4-diol as the major product; however, in competition with the second ET from the electrode, the distonic radical anion undergoes a ,-scission fragmentation yielding 1,4-diphenyl-1,4-butanedione radical anion and ethylene in a mechanism involving less than one electron. These observations are rationalized by an unprecedented catalytic radical-anion chain mechanism, the first ever reported for a bicyclic endoperoxide. The product ratios and the efficiency of the catalytic mechanism are dependent on the electrode potential and the concentration of weak non-nucleophilic acid. A thermochemical cycle for calculating the driving force for ,-scission fragmentation is presented, and provides insight into why the fragmentation chemistry of distonic radical anions is different from analogous neutral biradicals. [source]

Redox Properties of Mixed Lutetium/Yttrium Nitride Clusterfullerenes: Endohedral LuxY3,xN@C80(I) (x=0,3) Compounds

CHEMPHYSCHEM, Issue 7 2009
Ján Tarábek Dr.
Abstract The complex redox behavior of mixed lutetium/yttrium nitride clusterfullerenes of the series LuxY3,xN§C80(Ih, x=0,3) (see figure) results in up to three irreversible reduction steps. A reduction mechanism is proposed based on fast-scan and square-wave voltammetry experiments combined with simulations of the voltammograms. The redox behavior of mixed lutetium/yttrium nitride clusterfullerenes of the series LuxY3,xN@C80(Ih, x=0,3) is studied for the first time by means of cyclic voltammetry, fast-scan cyclic voltammetry, square-wave voltammetry, and electron paramagnetic resonance (EPR) spectroelectrochemistry. A reversible single-electron-transfer process, which does not result in an EPR signal, is detected during the anodic oxidation sweep of cyclic voltammetry experiments performed at different temperatures (296 and 360 K). The cathodic reduction sweep reveals a rather complex response for all the four clusterfullerenes,with up to three irreversible reduction steps. By correlating the results of fast-scan and square-wave voltammetry and combining them with simulations of the voltammograms, we are able to propose a reduction mechanism for the LuxY3,xN@C80(I) (x=0,3) fullerenes. [source]