Computational study of the interaction of metal ions (Na+, K+, Mg2+, Ca2+, and Al3+) with Quercetin and its antioxidant properties

In recent years, the chelation between quercetin and transition metals has attracted much attention because the complexes formed have higher antioxidant and medicinal activities. However, the theoretical investigation of the mechanisms of flavonoid functioning along with the structures of quercetin–metal complexes is still not sufficiently studied. In this research work, quercetin–complexes with Na + , K + , Mg 2+ , Ca 2+ , and Al 3+ are studied theoretically by using density functional theory (DFT) method in order to investigate the stability, reactivity, nature of interaction, and the application of the quercetin-metal complexes as potential antioxidants. From the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) results, the K-quercetin salt was observed to be more stable as compared to the other metals while Ca seemed to be the most reactive with the least values in the neutral form of the metal - quercetin interaction. The results of the antioxidant activity in the neutral state present Ca and Mg to have the higher values of ionization potential (IP) indicating that the antioxidant activity of Ca/Mg complexes with quercetin are less pronounced, while K-complex with the least value indicating the higher the electron donating reactivity. In comparison, it is worth to note that Mg-Q and Ca-Q in the deprotonated state of quercetin showcase lower IP, higher ability of H-atom transfer and electron transfer reactivity, therefore, better antioxidant candidates of the quercetin complexes than their other counterparts.