One-electron oxidation mechanism

Oxidants that operate according to this one-electron oxidation mechanism include potassium ferricyanide in alkaline solution, cobalt, copper complexes with dioxygen, and some enzymes. 

Figure 24 The mechanism of oxidation of heteroatom-containing compounds by P450 enzymes (a) The one-electron oxidation mechanism of heteroatom oxygenation (b) The one-electron and hydrogen atom abstraction mechanisms of heteroatom dealkylation...

One-electron oxidation mechanism of methionine methyl ester (MME), N-acetylmethionine (NAM), N-acetylmethionine amide (NAMA), and N-acetylmethionine methyl ester (NAMME) employing OH radicals were studied by means of pulse radiolysis in aqueous solutions. 

In a neutral amide -C(=0)-NH2, the carbonyl oxygen atom represents the better nucleophile compared to nitrogen atom. This fact is corroborated by pulse radiolysis studies of N-acetylmethionine methyl ester (NAMME) (Chart 7) showing similar kinetic and spectral features to NAMA. The theoretical parameters calculated by DPT (including TD-DFT) methods support to a large extent the experimentally identified one-electron oxidation mechanism of NAMA. ... 

E Srebotnik, KAJ Jensen, S Kawai, KE Hammel. Evidence that Ceriporiopsis subvermispora degrades nonphenolic lignin structures by a one-electron-oxidation mechanism. Appl Environ Microbiol 63(ll) 4435-4440, 1997. 

Figure 8. Possible one-electron oxidation mechanisms of phenol to the phenoxyl radical...

Hence, our calculations emphasized a step-wise mechanism over most oxides H-abstraction leads to a surface hydroxyl, in conjunction with the alkyl radical formation, which rapidly rebounds to a nearby oxygen to form a surface alkoxy. This step-wise one-electron oxidation mechanism not only offers an energetically more favorable route than the one-step two-electron oxidation mechanism such as (5+2), but also provides a plausible solution to the puzzle as contrasting the EPR results [50] to the IR results [49] (cf. Fig. 6). We propose that EPR with higher time resolution (10 -10 s) detected the radical formation, whose stability was enhanced by the higher acidity of the tungstated zirconia catalyst which retarded the rebound process. On the contrary, IR with lower time resolution (10 -10 s) was unable to capture the active alkyl intermediates, showing the peaks related to the existence of both surface hydroxy and alkoxy after rebound. 

As we know, the first step in the metabolization of phenothiazines is a one electron oxidation mechanism giving a cation radical. This structure is supposed to be responsible for the psychotic properties but also for the toxic side effects of phenothiaizines. Cyclic voltammetric studies of a recent phenothiazine, quisultidine (Fig.l, structure I) possessing little psychotic activity have permitted to point out in a rapid and easy manner its unusual behaviour. Phenothiazines are readily electrooxidized giving a cation radical which is rather stable in nonaqueous or high acidic aqueous media. 

Subsequent studies (63,64) suggested that the nature of the chemical activation process was a one-electron oxidation of the fluorescer by (27) followed by decomposition of the dioxetanedione radical anion to a carbon dioxide radical anion. Back electron transfer to the radical cation of the fluorescer produced the excited state which emitted the luminescence characteristic of the fluorescent state of the emitter. The chemical activation mechanism was patterned after the CIEEL mechanism proposed for dioxetanones and dioxetanes discussed earher (65). Additional support for the CIEEL mechanism, was furnished by demonstration (66) that a linear correlation existed between the singlet excitation energy of the fluorescer and the chemiluminescence intensity which had been shown earher with dimethyl dioxetanone (67). 

Ce4+ is a versatile one-electron oxidizing agent (E° = - 1.71 eV in HC10466 capable of oxidizing sulfoxides. Rao and coworkers66 have described the oxidation of dimethyl sulfoxide to dimethyl sulfone by Ce4+ cation in perchloric acid and proposed a SET mechanism. In the first step DMSO rapidly replaces a molecule of water in the coordination sphere of the metal (Ce v has a coordination number of 8). An intramolecular electron transfer leads to the production of a cation which is subsequently converted into sulfone by reaction with water. The formation of radicals was confirmed by polymerization of acrylonitrile added to the medium. We have written a plausible mechanism for the process (Scheme 8), but there is no compelling experimental data concerning the inner versus outer sphere character of the reaction between HzO and the radical cation of DMSO. 

Interestingly, the nucleophilic addition of water in the sequence of events giving rise to 41 represents a relevant model system for investigating the mechanism of the generation of DNA-protein cross-links under radical-mediated oxidative conditions [80, 81]. Thus, it was shown that lysine tethered to dGuo via the 5 -hydroxyl group is able to participate in an intramolecular cyclization reaction with the purine base at C-8, subsequent to one electron oxidation [81]. 

A relatively low potential, one-electron oxidation is observed (Equation (72)), followed above pH 2.2 by a two-electron oxidation, two-proton step (Equation (73)) and a one-electron oxidation (Equation (74)). In more acidic solutions a direct three-electron oxidation occurs leading also to the [Ruv O Ruv]4+ species. In various studies the Rulv O Rulv, RuIV-0 Ruv, and Ruv O Ruv species have been considered as the catalytically active form. Although these species have been characterized by resonance Raman and EPR spectroscopies,475,476,480 no definitive conclusion about the mechanism involved in the catalysis can be drawn and the question remains largely open. 

At present a variety of studies with PAH, as well as other chemicals, suggest that metabolic activation in target tissues can occur by one-electron oxidation (6,7). The electrophilic intermediate radical cations generated by thTs mechanism can react directly with various cellular nucleophiles. In this paper, we will discuss chemical, biochemical and biological evidence which indicates that one-electron oxidation plays an important role in the metabolic activation of PAH. 

The first line of evidence derives from the predominant formation of quinones when metabolism of BP is conducted under peroxi-datic conditions, namely by prostaglandin H synthase (21) or by cytochrome P-450 with cumene hydroperoxide as cofactor T22). Under these metabolic conditions one-electron oxidation is the preponderant mechanism of activation. 

The carcinogenicity of a series of PAH in the mammary gland has been examined in 50-day-old female Sprague-Dawley rats using direct application of the compound to the mammary tissue (1 , 17, 18). The results of these experiments, presented in Table III, are compared to the carcinogenicity results in mouse skin from repeated application obtained in our laboratory and others. PAH were selected because they were or were not expected to be activated by one-electron oxidation, based on the hypothesis that compounds with relatively high IP cannot be activated by this mechanism. Furthermore, some... 

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. 

Furthermore, Laranjinha and Cadenas [58] have recently showed that nitric oxide oxidizes 3,4-dihydroxyphenylacetic acid (DOPAC) to form nitrosyl anion and the DOPAC semiqui-none supposedly by one-electron transfer mechanism. 

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