Investigation of the radical scavenging potency of hydroxybenzoic acids and their carboxylate anions

In this article, the antoxidative mechanisms HAT, SPLET, and SET-PT of the ortho-, meta-, and parahydroxybenzoic acids and corresponding carboxylate anions with different radicals ((OO-)-O-center dot, (OH)-O-center dot, (OOH)-O-center dot, and CH3OO center dot) were investigated. For this reason, the Delta H-BDE, DHIP, and DHPA values of the corresponding reactions in different solvents (water, DMSO, pentylethanoate, and benzene) were examined. For this purpose, the M05-2X/6-311++G(d,p) and B3LYP-D2/6-311++G(d, p) theoretical models were applied. Although the B3LYP-D2 method produced lower reaction enthalpy values, both theoretical models exhibited the same trend. It was found that SET-PT is not a favorable reaction path for any hydroxybenzoic acids and their anions with any radicals in any solvents. No anion reacts with O--center dot(2), whereas meta-and para-hydroxybenzoic acids react with O--center dot(2) only in nonpolar solvents. In all other cases, the HAT and SPLET mechanisms are competitive. Which of them is dominant depends on the properties of the acids, anions, radicals, and solvents.