Electron transfer chemical mechanism

CE (chemical-electron-transfer) mechanism] the shape of the resulting peak depends on the chemical reaction rate. If the chemical reaction is very slow,... 

At present, new developments challenge previous ideas concerning the role of nitric oxide in oxidative processes. The capacity of nitric oxide to oxidize substrates by a one-electron transfer mechanism was supported by the suggestion that its reduction potential is positive and relatively high. However, recent determinations based on the combination of quantum mechanical calculations, cyclic voltammetry, and chemical experiments suggest that °(NO/ NO-) = —0.8 0.2 V [56]. This new value of the NO reduction potential apparently denies the possibility for NO to react as a one-electron oxidant with biomolecules. However, it should be noted that such reactions are described in several studies. Thus, Sharpe and Cooper [57] showed that nitric oxide oxidized ferrocytochrome c to ferricytochrome c to form nitroxyl anion. These authors also proposed that the nitroxyl anion formed subsequently reacted with dioxygen, yielding peroxynitrite. If it is true, then Reactions (24) and (25) may represent a new pathway of peroxynitrite formation in mitochondria without the participation of superoxide. 

The competition between antioxidant and prooxidant activity of flavonoids depends firstly on their chemical structure. If we suppose that the oxidation of flavonoids (Reaction (17)) takes place by one-electron transfer mechanism, then it must depend on the capacity of flavonoids to donate an electron, i.e., on their one-electron oxidation potentials. 

Some of the materials highlighted in this review offer novel redox-active cavities, which are candidates for studies on chemistry within cavities, especially processes which involve molecular recognition by donor-acceptor ii-Jt interactions, or by electron transfer mechanisms, e.g. coordination of a lone pair to a metal center, or formation of radical cation/radical anion pairs by charge transfer. The attachment of redox-active dendrimers to electrode surfaces (by chemical bonding, physical deposition, or screen printing) to form modified electrodes should provide interesting novel electron relay systems. 

If in indirect electrolyses the homogeneous chemical step is a pure electron transfer (mechanism A), the following advantages can be used as compared with direct electrolysis ... 

Two types of redox catalysts are used in indirect electrolyses [3] (1) pure, outer-sphere, or non-bonded electron transfer agents, and (2) redox reagents that undergo a homogeneous chemical reaction that is intimately combined with a redox step. This may be called inner-sphere electron transfer or bonded electron transfer mechanism. 

Electron transfer, Chemical step, Electron transfer) mechanism in acetonitrile was proposed the reduction products have been characterized.13... 

From Fig. 6.14, it can be deduced that for A Ef = —142.4 mV, the two mechanisms show distinctly different voltammograms for small values of %cw(= (k 1 + ki) ja), whereas the responses become more similar as the chemical kinetics is faster. Thus, for// v >100 the voltammetric signal of the ECE mechanism is equivalent to that of an EE mechanism where the half-wave potentials correspond to those of the EC (first electron transfer) and CE (second electron transfer) mechanisms under fully labile conditions (Eqs. (3.201c) and (3.221b) for <5, > 0, respectively). 

Finally, it should be stressed that organic electron transfers only rarely occur as isolated steps because of the high chemical reactivity of odd-electron species. Normally, they are part of multi-step mechanisms together with other types of elementary reaction, such as bond forming and breaking. In organic electrochemistry a useful shorthand nomenclature for electrode mechanisms denotes electrochemical (= electron transfer) steps by E and chemical ones by C, and it is appropriate to use the same notation for homogeneous electron-transfer mechanisms too. Thus, an example of a very common mechanism would be the ECEC sequence illustrated below by the Ce(IV) oxidation of an alkylaromatic compound (14-17) (Baciocchi et al., 1976,... 

A state-of-the-art description of broadband ultrafast infrared pulse generation and multichannel CCD and IR focal plane detection methods has been given in this chapter. A few poignant examples of how these techniques can be used to extract molecular vibrational energy transfer rates, photochemical reaction and electron transfer mechanisms, and to control vibrational excitation in complex systems were also described. The author hopes that more advanced measurements of chemical, material, and biochemical systems will be made with higher time and spectral resolution using multichannel infrared detectors as they become available to the scientific research community. 

The electron transfer mechanism of azurin, a well known example for this type of proteins, has been systematically studied using the chemical relaxation method and a well defined inorganic outer sphere redox couple. In parallel, the investigations of the reaction with its presumed physiological partner, cytochrome c, were pursued (7). The specificity of the interaction between azurin and cytochrome c P-551 is expressed in higher specific rates and in the control of the electron transfer equilibrium by conformational transitions of both proteins. 

Mechanistic studies of the chemical oxidation of aliphatic amines have been reviewed extensively by Chow et al. [22]. Many studies of the mechanism of oxidation of amines have been performed with chlorine dioxide or ferricyanide as oxidants, because they have absorption bands with maxima at 357 and 420 nm, respectively. Changes in the absorbance at these wavelengths for the respective oxidants can be conveniently used to follow the kinetics of the reactions. On the basis of these studies, the electron-transfer mechanism shown in Scheme 1 has been proposed for amine oxidation. 

To clarify the mechanism of reaction of P-450, it is crucial to characterize the reactive intermediates in the rate-determining step. Definitive evidence for an electron-transfer mechanism (C in Scheme 2) for the 7V-demethylation of N,N-dimethylanilines has been obtained by direct observation of the reduction of the high-valent species responsible for P-450 catalysis [96]. For peroxidase, an oxoferryl porphyrin 7r-radical cation, compound I ([(P)Fe =0] "), has been well characterized as the species equivalent to the proposed active intermediate of P-450 [97-103]. Compound I of horseradish peroxidase (HRP) can be readily generated by chemical oxidation of HRP [100-103]. The involvement of the electron-transfer process of compound I in the oxidation of several amines catalyzed by HRP was... 

Obviously, when the mass transfer rate is much larger than that of the chemical steps, the transfer of P from the electrode surface to the bulk solution is not affected by the presence of kinetics. Thus the electrochemical behavior of the EC sequence in Eqs. (120) and (121) is identical to that of a simple electron transfer mechanism. The R/P electron... 

Voltammetry is widely used by analytical, inorganic, physical, and biological chemists for fundamental studies of( 1) o.xidation and reduction processes in various media, (2) adsorption processes on surfaces, and (3) electron transfer mechanisms at chemically modified electrode surfaces. For analytical purposes, several fonns of... 

Beratan, D.N. and Skourtis, S.S. (1998) Electron transfer mechanisms. Current Opinion in Chemical Biology, 2 (2), 235-243. 

The tris(diimine)Ru(II) complexes are potential mediators in the conversion of solar energy to chemical energy via electron-transfer mechanisms (see 13.4). Their spectra display intense visible-range absorption bands and the relative long lifetimes of the lowest-energy ES, MLCT in character, allow efficient bimolecular energy and electron-transfer processes in solution. The photolability of certain bis(diimine)Ru(II) complexes is of synthetic utility ... 

In acetonitrile HOOH is oxidized to O2 via an electron-transfer/chemical/ electron-transfer (ECE) mechanism... 

We have recently found that this free radical oxidation of the methyl groups is in fact not a major pathway in the photooxidation of poly(phenylene oxide). Instead, the oxidation apparently occurs through an electron-transfer mechanism on the backbone of the polymer not chemically involving the methyl groups at all. In this paper, we present evidence inconsistent with the free radical mechanism and supporting this novel pathway for polymer photooxidation. 

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