Influence of intrinsic and extrinsic factors on the antiradical activity of Gallic acid: a theoretical study

The factors responsible for the potent antioxidant activity of gallic acid (GA) are explored by employing density functional theory (DFT). It is found that the intrinsic characteristic features of the molecule play a significant role in its overall effectiveness as an antioxidant. The arrangement of the three hydroxyl groups with respect to each other imparts efficient antioxidant and antiradical property to GA. The external factors, such as polarity and pH of the reaction medium, also have a significant role to play. The polarity of the medium substantially affects the electron donating ability of GA, whereas the hydrogen atom donating ability is only marginally influenced. GA is a poor electron donor, but it can efficiently donate the hydrogen atom from its para hydroxyl group and effectively quench free radicals. It proves to be a better antiradical agent at the physiological pH, wherein it exists in the monoanionic form. Further, a comparison with other phenolic acids substantiates the importance of the carboxyl and hydroxyl groups in the antiradical activity of GA.