The generation of hydroxyl and alkoxyl radicals from the interaction of ferrous bi pyridyl with per oxides differential oxidation of typical hydroxyl radical scavengers
Winston, G.W.; Harvey, W.; Berl, L.; Cederbaum, A.I.
Biochemical Journal 216(2): 415-422
ISSN/ISBN: 0264-6021 Accession: 006681704
Reaction conditions by which the Fe-chelate ferrous bipyridyl can be used as a Fenton reagent to generate specifically alkoxyl radical (.OR) from its corresponding alkyl hydroperoxide (ROOH) without producing hydroxyl radical (.OH) as a result of autoxidation are described. In this manner, the relative ability of common .OH-scavenging agents to react with .OH and various .OR species could be assessed. When .OH was generated from H2O2, 4-methylmercapto-2-oxobutyrate, ethanol and benzoate all were oxidized. When .OR (cumoxyl radical, tert-butoxyl radical or ethoxyl radical) was generated specifically, each was found oxidize 4-methylmercapto-2-oxobutyrate and ethanol. In contrast with .OH, however, none of the .cntdot.OR radicals mediated the decarboxylation of benzoate. Cross-competition studies with the scavengers showed that, in contrast with the .OH-dependent reaction, the .OR-dependent oxidation of 4-methylmercapto-2-oxobutyrate and ethanol was not inhibited by benzoate. Rate constants for ferrous bipyridyl oxidation by ROOH and by H2O2 were essentially the same, and therefore the differential oxidation of the various scavengers was not a reflection of Fe-peroxide interaction, but rather an interaction between generated oxy radicals and the scavengers. In contrast with the H2O2 system, catalase did not inhibit the oxidation of 4-methylmercapto-2-oxobutyrate or ethanol by either the cumene hydroperoxide or the tert-butyl hydroperoxide system, suggesting that the oxidizing species was not derived from H2O2. Benzoate decarboxylation might serve as a more specific probe to detect the presence of .OH than either 4-methylmercapto-2-oxobutyrate or ethanol, which react readily with .OR.