THEORETICAL PARAMETERS TO CHARACTERIZE ANTIOXIDANTS .1. THE CASE OF VITAMIN-E AND ANALOGS

The objectives of this work were a) to evaluate parameters obtained by quantum-mechanical calculations as predictors of antioxidant activiti es, and b) to obtain information on the molecular mechanism(s) underly ing the antioxidant effects of vitamin E and analogs. To this effect, we selected a large series of tocopherol analogs for which some experi mental antioxidant activities were available in the literature (i.e., peak of oxidation potential, E-p, and rate constant of the reaction wi th a free radical log k(s)). AMI Semi-empirical calculations were perf ormed, the results of which were validated by ab initio calculations o n a subset of compounds. The quantum chemical descriptors considered h ere (HOMO, Delta H-ox and Delta H-abs) were fairly well correlated wit h the experimental antioxidant activities (E-p and k(s)). Moreover, th ese theoretical parameters were intercorrelated, suggesting that vitam in E analogs may act by a dual mechanism of single-electron transfer ( SET) and direct H-atom abstraction.