Kinetic study of the electron-transfer oxidation of the phenolate anion of a vitamin E model by molecular oxygen generating superoxide anion in an aprotic medium

摘要

Electron-transfer reduction of molecular oxygen (O_2) by the phenolate anion (1~-) of a vitamin E model, 2,2,5,7,8-pentamethylchroman-6-ol(1H), occurred to produce superoxide anion, which could be directly detected by a low-temperature EPR measurement. The rate of electron transfer from 1~- to O_2 was relatively slow, since this process is energetically unfavourable. The one-electron oxidation potential of 1~- determined by cyclic voltammetric measurements is sufficiently negative to reduce 2,2-bis(4-tert-octylphenyl)-1-picrylhydrazyl radical (DOPPH') to the corresponding one-electron reduced anion, DOPPH~-, suggesting that 1~- can also act as an efficient radical scavenger.