Kinetics and mechanism of the reactions of superoxide ion in solution. Part 5. Kinetics and mechanism of the interaction of superoxide ion with vitamin E and ascorbic acid

Abstract

The reactions of electrochemically generated O₂ ^–˙ with α-tocopherol and α-tocopheryl acetate have been studied in acetonitrile and with ascorbic acid in acetonitrile and mixed acetonitrile–water solvents. It was found that both α-tocopherol and ascorbic acid react with superoxide ion via a deprotonation mechanism to form the corresponding anions. On subsequent steps of the process these anions are oxidized by O₂ to form O₂ ^–˙ The mechanism of the oxidation of ascorbate anion depended on the solvent composition: in aqueous solution the reaction proceeded only in the presence of Fe³⁺ ion, but in acetonitrile a direct one-electron transfer from the ascorbate anion to dioxygen was observed. Both mechanisms were suppressed to a considerable extent in mixed solvents.