Computational Insights into the Radical Scavenging Activity and Xanthine Oxidase Inhibition of the Five Anthocyanins Derived from Grape Skin

Anthocyanins, typical polyphenol compounds in grape skin, have attracted increasing interest due to their health-promoting properties. In this body of work, five representative anthocyanins (Cy-3-<i>O</i>-glc, Dp-3-<i>O</i>-glc, Pn-3-<i>O</i>-glc, Mv-3-<i>O</i>-glc, and Pt-3-<i>O</i>-glc) were studied using the density functional theory (DFT) to elucidate structure-radical scavenging activity in the relationship and the reaction path underlying the radical-trapping process. Based on thermodynamic parameters involved in HAT, SET-PT, and SPLET mechanisms, along with the structural attributes, it was found that the C4' hydroxyl group mainly contributes to the radical scavenging activities of the investigated compounds. Pt-3-<i>O</i>-glc exhibits a good antioxidant capacity among the five compounds. The preferred radical scavenging mechanisms vary in different phases. For the Pt-3-<i>O</i>-glc compound, the calculations indicate the thermodynamically favoured product is benzodioxole, rather than <i>o</i>-quinone, displaying considerably reduced energy in double HAT mechanisms. Additionally, the thermodynamic and kinetic calculations indicate that the reaction of ^•OH into the 4'-OH site of Pt-3-<i>O</i>-glc has a lower energy barrier (7.6 kcal/mol), a higher rate constant (5.72 × 10⁹ M^-1 s^-1), and exhibits potent ^•OH radical scavenging properties. Molecular docking results have shown the strong affinity of the studied anthocyanins with the pro-oxidant enzyme xanthine oxidase, displaying their significant role in inhibiting ROS formation.