Free radical scavenging behavior of folic acid: Evidence for possible antioxidant activity

The free radical scavenging properties and possible antioxidant activity of folic acid are reported. Pulse radiolysis technique is employed to study t he one-electron oxidation of folic acid in homogeneous aqueous solution. Th e radicals used for this study are CCl3O2., N-3(.), SO4.-, Br-2(.-), (OH)-O -., and O-.(-). All these radicals react with folic acid under ambient cond ition at an almost diffusion-controlled rate producing two types of transie nts. The first transient absorption maximum is around 430 nm, which decays, and a simultaneous growth at around 390 nm is observed. Considering the ch emical structure of folic acid, the absorption maximum at 430 nm has been a ssigned to a phenoxyl radical. The latter one is proposed to be a delocaliz ed molecular radical. A permanent product has been observed in the oxidatio n of folic acid with CCl3O2. and N-2(.) radicals, with a broad absorption b and around 370-400 nm. The bimolecular rate constants for all the radical-i nduced oxidation reactions of folic acid have been measured. Folic acid is seen to scavenge these radicals very efficiently. In the reaction of thiyl radicals with folic acid, it has been observed that folic acid can not only scavenge thiyl radicals but can also repair these thiols at physiological pH. While carrying out the lipid peroxidation study, in spite of the fact t hat folic acid is considerably soluble in water, we observed a significant inhibition property in microsomal Lipid peroxidation. A suitable mechanism for oxidation of folic acid and repair of thiyl radicals by folic acid has been proposed. (C) 2001 Elsevier Science Inc.