Abstract

The antioxidant activities of flavonoids have been found to occur through different mechanisms. In this study, the Density Functional Theory (DFT) method was employed to investigate the mechanisms for the antioxidant activities of a polyphenolic flavonoid, Quercetin and its three metal complex derivatives at the level B3LYP/6-31G (d) and B3LYP/LanL2DZ level of theories respectively. The bond dissociation enthalpies (BDEs), ionization potentials (IPs), proton dissociation enthalpies (PDEs), proton affinities (PAs), and electron transfer enthalpies (ETEs) connected to the H-atom transfer (HAT), single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET) mechanisms respectively were determined for quercetin, quercetin-cadmium complex1[Cd (Q) (Bpy) (CH3COO)2] , quercetin-cadmium complex2 [Cd (Q) (Phen) (CH3COO)2] and quercetin-vanadium complex [VO(Que)2]. The IP values for most phenolic -OH positions of the three metal complex derivatives studied are lower in magnitude when compared with their corresponding BDE values but the natural flavonoid, quercetin shows a considerable higher IP values for the phenolic-OH positions. The results suggest that quercetin uses the HAT mechanism for its antioxidant activity, while its three metal complexes preferred the SET-PT mechanism. The Molecular docking experiment showed successful binding of studied compounds to the standard drug’s binding pocket on the receptor with binding affinities -35.6 kJmol-1, -38.5 kJmol-1, -39.3 kJmol-1 and -39.7 kJmol-1 for quercetin, quercetin-Cd complex1, quercetin-V complex and quercetin-Cd complex2 respectively.