Voltammetric studies on the α-tocopherol anion and α-tocopheroxyl (Vitamin E) radical in acetonitrile

Abstract

The α-tocopheroxyl radical was generated voltammetrically by one-electron oxidation of the α-tocopherol anion ( E r 1/2=−0.73 V versus Ag|Ag +) that was prepared by reacting α-tocopherol with Et 4NOH in acetonitrile (with Bu 4NPF 6 as the supporting electrolyte). Cyclic voltammograms recorded at variable scan rates (0.05–10 V s −1), temperatures (−20 to 20°C) and concentrations (0.5–10 mM) were modelled using digital simulation techniques to determine the rate of bimolecular self-reaction of α-tocopheroxyl radicals. The k values were calculated to be 3×10 3 l mol −1 s −1 at 20°C, 2×10 3 l mol −1 s −1 at 0°C and 1.2×10 3 l mol −1 s −1 at −20°C. In situ electrochemical-EPR experiments performed at a channel electrode confirmed the existence of the α-tocopheroxyl radical.