Two-electron redox processes

A model of a flavin-based redox enzyme was prepared.[15] Redox enzymes are often flavoproteins containing flavin cofactors flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). They mediate one- or two-electron redox processes at potentials which vary in a range of more than 500 mV. The redox properties of the flavin part must be therefore tuned by the apoenzyme to ensure the specific function of the enzyme. Influence by hydrogen bonding, aromatic stacking, dipole interactions and steric effects have been so far observed in biological systems, but coordination to metal site has never been found before. Nevertheless, the importance of such interactions for functions and structure of other biological molecules make this a conceivable scenario. 

Mn catalysts are useful in one- and two-electron redox processes. Reactions of immobilized Mn porphyrins and phthalocyanines are discussed later with the corresponding Fe complexes. 

Figure 5.13 reproduces the results of Bleda-Martinez et al. [210], based on which these authors argued that carboxylic anhydride groups (A) exhibit a two-electron redox process and thus have a capacitance-enhancing effect, similar to that of the CO-yielding quinone groups ... 

The conversion of L-lactate to pyruvate is a two-electron redox process. One could consider this occurring as two one-electron steps (a radical mechanism) or as one two-electron step. There are two options for a single two-electron step, and these are hydride transfer (H ) or proton (H+) abstraction followed by a two-electron transfer from a carbanion intermediate. These two alternatives for lactate are shown formally in Eqs. (1) and (2) for hydride transfer and the carbanion mechanism, respectively. 

Two-electron redox processes are facile in metal sulfide surfaces, and thus M-S bond breaking and re-making in such extended arrays may provide an energetically favorable pathway to modify the electron count at a particular metal center. Although Tl -bonded thiophenes have not been invoked in heterogeneous HDS mechanisms, T T transformations such as the ones defined in organometallic complexes could be envisaged to take place at the active sites of HDS catalysts, as possible routes for... 

The electrochemical reactions (limited in the battery to a two-electron redox process on iron) can be represented by... 

It is well known that the oxidative carbonylation of aniline and the reductive carbonylation of nitrocompounds to give DPU or MPC occur according to the stoichiometry of reactions (1-2) and (4-5). Alkoxycarbonyl complexes (M-COOR 1) and carbamoyl complexes (M-CONHR 2) which then evolve into the final products, are believed to be key intermediates for these reactions. The two accepted different mechanisms for the formation of 1 and 2 along with their catalytic cycles are illustrated in the schemes 1 and 2 for the oxidative carbonylation of amines catalyzed by noble metals. Both the cycles involve a two electron redox process. 

In this case the reaction is a two-electron redox process, since the product is nickel(ii). E.s.r. studies of the reaction suggest that it occurs... 

Molybdenum has a number of accessible oxidation states under physiological conditions and is often involved in two-electron redox processes involving oxygen atom transfer. Typically, the metal cycles between the dioxo molybdenum +6 oxidation state ([Mo02 ] and the mono-oxo molybdenum +4 oxidation state ([MoO ]). There have been a number of studies of oxo and/or hydroxo transfer for model systems of xanthine oxidase [38, 91-95], DMSO reductase [96] and sulfite oxidase [97] but the DFT methods and protocols applied are relatively standard and have been covered elsewhere in this article. 

The anti-cancer drug ds,cis,traw5-[Pt(IV)(NH2Pr )2Cl2(OH2)2] has been postulated to react through the reduced Pt(II) species. The rate of reduction by ascorbic acid has been measured and equilibrium kinetics observed with kf = 0.103 and kb = 0.78 X 10" Ms" at 25 °C. From the data, a two-electron redox process has been proposed. ... 

Comparing the activation mode of iminium and enamine catalysis, iminium catalysis is based on a LUMO-activation mode of the electrophile whereas enamine catalysis is based on a HOMO-activation of the nucleophile. Keeping in mind the fact that enamine and iminium species are rapidly interconverted via a two-electron redox process (proton abstraction of an iminium species results in an enamine), MacMillan and co-workers reasoned that it should be possible to interrupt this equilibrium chemically by carrying out just a one-electron oxidation of an enamine. This would then generate a three-7i-electron radical cation with a singly occupied molecular orbital (SOMO) that should be activated towards catalytic transfomiatirHis (racemic or asymmetric) not possible using classical enamine or iminium activation (Scheme 80) 316). 

The milestone discovery by Cotton and coworkers opened a new horizon not only for fundamental palladium organometallic chemistry but also for palladium catalysis. As the cornerstone of modern organic synthesis, palladium cattilysis was widely accepted to be based on Pd(II)/Pd(IV) monosite two-electron redox process. The two-electron oxidation of dipaUadium(II) 146 into diptJladium(III)... 

The one or two electron redox process (the ith atom is oxidized) are represented by and > where corresponds to the number... 

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