Proton dissociation is important to understanding structure–activity relationships of gallic acid antioxidants

Gallic acid derivatives (GADs) can efficiently scavenge free radicals, which is partially responsible for their neuroprotective effects. As GADs tend to deprotonate to give birth to GAD anions, which has big influence on the radical-scavenging behaviors of GADs, to understand the structure–activity relationships (SARs) of GAD antioxidants, the anions should be taken into consideration. In this paper, a combined density functional theory method, labeled as (RO)B3LYP/6-311 + G(2d,2p)//AM1/AM1, was employed to calculate homolytic O–H bond dissociation enthalpies and adiabatic ionization potentials for GADs and derived anions in solvent (ethanol), by which the experimentally observed SARs of GADs were better elucidated.