Role of Alpha‐Tocopherol, Ascorbic Acid, Citric Acidand EDTA as Oxidants in Model Systems

The effects of four widely employed “antioxidants” on iron-mediated hydroxyl radical formation and lipid peroxidation were studied in aqueous model systems. Iron and copper served as catalysts for the reactions which oxidized ascorbic acid and alpha-tocopherol and reduced oxygen. Ferrous ion spontaneously reduced oxygen to O−2 (su-peroxide anion radical) which led to OH (hydroxyl radical) and H2O2 generation and lipid peroxidation. Precipitation or sequestration of iron greatly depressed these oxidative events. Complexation by EDTA and citric acid, however, formed catalytically active iron chelates. The concomitant increase in iron solubility explained the substantial enhancement of iron-driven redox reactions by EDTA and citric acid.