Free Radical Scavenging Potency of Dihydroxybenzoic Acids

In order to evaluate the free radical scavenging potency of dihydroxybenzoic acids (DHBAs) the Density FunctionalTheory (DFT) was used. The M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d, p) theoretical models were applied. Three possible antioxidant mechanisms were examined: hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton loss electron transfer (SPLET) mechanisms. All of these mechanisms have been studied in nonpolar (benzene and pentylethanoate) and polar solvents (water) using an implicit solvationmodel (SMD). Thefollowing thermodynamic quantities related to these mechanisms were calculated: bond dissociation enthalpy (BDE), ionization potential (IP), and proton affinity (PA). The obtained results indicated the HAT mechanism as the most favourable reaction pathway for antioxidative action of DHBAs in benzene. On the other hand, SPLET is indicated as predominant reaction mechanism in polar solvent. The SET-PT mechanism was not favourable reaction path for antioxidative action in any of the solvents under investigation.