Antioxidative activity of chlorogenic acid relative to trolox in aqueous solution - DFT study.

Chlorogenic acid (5CQA) is a dietary polyphenol known for its high biological activity. Antioxidative behavior of 5CQA relative to trolox (Tx) toward the HO and CHOO radicals in aqueous solution at pH = 7.4 was simulated using density functional theory. This is the first study where behavior of monoanion and dianion of 5CQA at physiological conditions is described. Both anionic forms undergo only hydrogen atom transfer (HAT) mechanism with CHOO. With HO, anionic forms of 5CQA conform to the HAT, radical adduct formation, sequential proton loss electron transfer, and single electron transfer - proton transfer mechanisms. Contribution of dianion to scavenging HO is comparable to that of more abundant monoanion. The calculated rate constant for overall reaction of 5CQA with HO is in perfect agreement with the corresponding experimental value. In comparison to Tx, 5CQA is more reactive toward HO, but less reactive toward CHOO.