Deprotonation of flavonoids severely alters the thermodynamics of the hydrogen atom transfer

Deprotonated polyphenolics exhibit different free radical scavenging activity than parent molecules. Therefore, this study is focused on the hydrogen atom transfer (HAT) from mono-deprotonated forms (phenoxide anions) of 16 flavonoids in terms of O-H bond dissociation enthalpies, BDE(A), using B3LYP/6-311++G** approach. Solvent (benzene and water) contribution is computed using integral equation formalism polarized continuum model, IEF-PCM. Obtained BDE(A) values are usually lower than BDEs of the parent species. In general, from the thermodynamic point of view, HAT from a phenoxide anion is favored to the electron transfer, i.e. formation of the phenoxy radical. For the studied environments, preferred radical anions are identified. Obtained results can contribute to the explanation of experimentally observed pH dependent antioxidant effect of polyphenolics. (C) 2016 Elsevier B.V. All rights reserved.