HPLC, fluorescence spectroscopy, UV spectroscopy and DFT calculations on the mechanism of scavenging •OH radicals by Hypericin

In this article, the scavenging ability of hypericin on hydroxyl radicals was evaluated by UV spectra, HPLC and fluorescence spectra. The reaction mechanism of the scavenging of free radicals by hypericin was also investigated. The Gaussian calculations obtained for the spatial structure and electrostatic potential of hypericin revealed that the active site for the reaction of hypericin with hydroxyl radicals is on the phenolic hydroxyl group of hypericin. The dissociation energy, spin density and frontline orbitals of the dehydrogenated hypericin radicals yielded that hypericin 7-OH and 7′ -OH are most likely to react with hydroxyl radicals. the transition state structure, enthalpy change and Gibbs free energy change and energy change of the reaction between hypericin and hydroxyl radicals,and the results of the above calculations indicate that hypericin 7-OH and 7′ -OH have the highest activity, can be directly involved in the scavenging process of radicals, followed by 5-OH and 5′ -OH, and finally 4-OH (4′ - OH).In-depth study of the antioxidant mechanism of hypericin molecules can help to design and synthesize new antioxidants in a more rational way.