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

Abstract

In this article, the antoxidative mechanisms HAT, SPLET, and SET-PT of the ortho-, meta-, and para-hydroxybenzoic acids and corresponding carboxylate anions with different radicals (·OO-, ·OH, ·OOH, and CH3OO ·) were investigated. For this reason, the ΔH BDE, ΔH IP, and ΔH PA 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 -·O2, whereas meta- and para-hydroxybenzoic acids react with -·O2 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. Graphical Abstract: [Figure not available: see fulltext.] © 2014 Springer-Verlag Wien.