The roles of O2-, HO(.), and secondarily derived radicals in oxidation reactions catalyzed by vanadium salts

Abstract

V(IV) decomposed H2O2, with evolution of O2, in a free radical chain process involving O2- and HO(.). When V(IV) was limiting, the presence of V(V) augmented O2 evolution because it allowed production of additional V(IV) from the reduction of V(V) by O2-. Gradual addition of V(IV) increased the yield of O2 evolved, per V(IV) added, to greater than 1--a clear indication of a free radical chain reaction. Reductants such as ethanol, Hepes, and NADH imposed a phase of O2 consumption because of HO.-initiated oxidation reactions. The radical produced from the reaction of HO. with ethanol was unable to directly oxidize NADH, whereas that produced from Hepes was able to do so. Ethanol consequently inhibited the oxidation of NADH by anaerobic V(IV) + H2O2, whereas Hepes did not. These results, and others reported herein, are explained on the basis of a coherent set of reactions. Data already in the literature are also clarified on the basis of these reactions.