Theoretical Study on Glycosyl Group Effect on Antioxidant Ability of Chrysin Bioflavonoid

Antioxidants are compounds which can prevent biological and chemical substances from oxidative damage by reactive oxygen species. Flavonoids are the most important class of polyphenolic compounds that because of their antioxidant characters possess biological activities and pharmacological effects. Chrysin-6-C-fucopyranoside and chrysin-3-malonyl-6-C-fucopyranoside are mono C-glycosyl derivatives of chrysin and flavonoid metabolites in leaves of Cyclanthera pedata. In order to study the effect of glycoside group on the antioxidant ability of chrysin, theoretical parameters including bond dissociation enthalpy (BDE), energy gap (∆E) and spin density for three above mentioned flavonoids are calculated using DFT method at the B3LYP/6-311** level in gas phase. In order to consider the various environments, solvent effects in water and DMSO using self-consistent reaction field (SCRF) and the polarizable continuum model (PCM) at B3LYP/6-311** level are performed. Obtained results show that solvent is able to cause significant change in the reaction enthalpies but no significant change on energy gap (∆E) and spin density. Our results indicate that BDE values due to its space prevention and presence of intra hydrogen bond between O atom of glycoside group (O-C1gg) in chrysin derivatives and 7OH have a low inverse effect on the BDE and so on antioxidant ability. We use Bader’s atoms in molecules (AIM) theory to perform a topological study on chrysin and its derivatives to emphasize the presence of intra hydrogen bonds. Base on AIM analyses, these hydrogen bonds have covalent nature. Energy gap (∆E) and spin density of flavonoid radicals almost do not change in the presence of glycoside group in gas phase, as well as in water and DMSO solvents. So, linked glycoside agent to chrysin does not improve its antioxidant ability.