Theoretical investigation on antioxidant activity of vitamins and phenolic acids for designing a novel antioxidant

Theoretical calculations have been performed to predict antioxidant property for two interesting classes of compounds including phenolic acids and vitamins. important characteristics of antioxidants such as O-H bond dissociation enthalpy (BDE) and ionization potential (IP) were calculated in the gas-phase to analyze the effect of heterocyclic ring, intramolecular hydrogen bonding and presence of electron donating group near the O-H on the antioxidant activity. The results reveal that the presence of intramolecular hydrogen bonding through ortho-hydroxy group lowers BIDE, IP and spin density. In general, phenolic acids were found to be more effective antioxiclant than vitamins. The H-atom transfer (HAT) mechanism was selected to study the hydrogen abstraction from phenolic compounds by hydroperoxyl radical. It is found that the antioxiclant with lower BDE undergoes hydrogen abstraction with low barrier and considerable exothermicity. On the basis of these results we were able to design a novel antioxiclant with enhanced activity. (C) 2009 Elsevier B.V. All rights reserved.