Autooxidation-reduction reactions

Sometimes, a single reactant can act as both oxidizing agent and redncing agent in the same reaction. Such a reactant is said to undergo autooxidation-reduction, or disproportionation. 

Another method for photodegrading polyethylene is to include metal salts, which catalyze photooxidation reactions, in the solid polymer. The compounds most generally used for that purpose are divalent transition-metal salts of higher aliphatic acids, such as stearic acid or dithiocarbonates or acetoacetic acid. The photochemical reaction is an oxidation-reduction reaction that forms free radicals capable of reacting with polyethylene, RH, to initiate an autooxidation chain reaction, as follows ... 

Witkop and Goodwyn reported (288) that ozonolysis of yohimbine (74) and its derivatives led to the corresponding quinolone derivatives. This reaction has been thoroughly investigated by Winterfeldt (289). For example, autooxidation of lactam 347 resulted in quinolone 599, which upon treatment with phosphoryl chloride, followed by catalytic reduction, gave pyrrolo[3,4-h]quioline derivative 600 (290). This transformation was also used as a key step in the biomimetic synthesis of camptothecin (601), performed by Winterfeldt et al. (291, 292). 

From a practical point of view the study of the chemistry of dioxygen complexes has considerable interest. Complexation of molecular oxygen by a transition metal has been widely adopted by biological systems as a means of reducing the considerable kinetic barrier to the reduction of O2. Quite apart from the inherent interest of the biological systems, the transition metal complexes offer the possibility of efficient catalysis of autooxidation reactions, and have recently attracted interest as possible catalysts for the reduction of O2 in fuel cells ... 

Each aromatic amine molecule, InH, terminates many free radical chains in autooxidation of alcohols and amines due to the ability of oxyperoxy and aminoperoxy radicals to oxidize InH as well as to reduce In to InH (JO. However, the coefficient of inhibition, f > 2, can be very often observed in oxidizing hydrocarbons too (2 ). Therefore, some reduction of aminyl radicals to InH proceeds in oxidizing hydrocarbons. To ellucidate the ways of such reduction we have studied the products and kinetics of the reactions of diphenylaminyl radical In. ... 

Brunmark and Cadenas (27A15) reviewed the major mechanisms that are involved in quinone-induced cytotoxicity in 1989. The redox chemistry of quinoid compounds was surveyed in terms of (1) reactions involving only electron transfers, such as those accomplished during the enzymatic reduction of quinones and nonenzymatic interaction with redox couples generating semiquinones, and (2) nucleophilic addition reactions. In their explanation of the mechanisms involved, quinone is reduced to the hydroquinone or semiqui-none radical by cellular reductase. The semiquinone radical then undergoes rapid autooxidation with the generation of the parent quinone and concomitant formation of superoxide. The hydroquinone reacts rapidly with superoxide to form H2O2 and the semiquinone. 

Pulich (4) had observed the autooxidation of low potential cytochrome c in extracts of Nostoc when supplied with NADPH under aerobic conditions and he suggested that cytochrome reduction was catalysed by ferredoxin-NADP oxidoreductase in his preparation. We could easily repeat Pulich s observation using purified proteins but found the rate of cytochrome reduction was very low. The addition of crude ferredoxin to the reaction mixture greatly stimulated the rate of electron transfer. When extracts of the soluble proteins of cyanobacteria are chromatographed on DEAE cellulose ion exchange columns, two forms of ferredoxin are occasionally observed. When cells are grown with sufficient iron, one finds a ferredoxin which elutes from the column al 0.4 to 0.5 M NaCl and which is usually identified with electron transfer from Photosystem I to FNR. This is called ferredoxin I. 

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