Structure-activity relationship in the quenching reaction of singlet oxygen by tocopherol (vitamin E) derivatives and related phenols. Finding of linear correlation between the rates of quenching of singlet oxygen and scavenging of peroxyl and phenoxyl radicals in solution

Abstract

The rate of quenching of 1 O 2 by 17 kinds of tocopherol derivatives, including α, β-, γ-, and δ-tocopherols, and five structurally related phenols has been measured spectrophotometrically in ethanol at 35 o C. The result indicates that the overall rate constants, k Q (k Q =k q +k r , physical quenching+chemical reaction), increase as the total electron-donating capacity of the alkyl substituents on the aromatic ring increases. The log of the rate constants, k Q , was found to correlate with their half-peak oxidation potentials, E P/2 ; the tocopherols that have smaller E P/2 values show higher reactivities