Computational study on the antioxidant activity of five plant food benzoic acid derivatives: dearomatization and stability of H abstraction radicals

In this study, we report a computational investigation of the antioxidant activity of five plant food benzoic acid derivatives, namely gallic acid (GA), para-hydroxybenzoic acid (PHBA), protocatechuic acid (PCA), syringic acid (SA), and vanillic acid (VA). Based on a series of computed thermodynamics parameters, we have developed a comparative debate regarding their free radical scavenging activity in the gas phase and polar solutions (considering water and methanol solvents). This discussion expands to the elucidation of both the most preferred mechanism and the order of antioxidant activity in each environment. Paradoxically, calculations using the harmonic oscillator model of aromaticity (HOMA) suggest that H abstraction radicals gain stability as the central benzene ring loses structural aromaticity. Finally, spin densities and Fukui function f0 appear to be good indicators of the local reactivity of the five antioxidants toward free radicals.