Quantum Chemical Investigation on the Antioxidant Activity of Neutral and Anionic Forms of Juglone: Metal Chelation and Its Effect on Radical Scavenging Activity

Abstract

The chelation ability of divalent Mg, Ca, Fe, Co, Ni, Cu, Zn, and monovalent Cu ions by neutral and anionic forms of juglone has been investigated at DFT/B3LYP/6-31+G(d,p) level of theory in gas and aqueous phases. It is noteworthy that only the 1 : 1 stoichiometry was considered herein. The effects of these metals on the radical scavenging activity of neutral juglone were evaluated via the usual descriptors of hydrogen atom transfer. According to our results, metal chelation by the two forms of juglone was spontaneous and exothermic in both media. Based on the binding energies, Cu(II) ion showed the highest affinity for the ligands. QTAIM analyses identified the metal-ligand bonds as intermediate type interactions in all the chelates, except those of Ca and Mg. It was also found that the chelates were better radical scavengers than the ligands. In the gas phase, the scavenging activity of the compounds was found to be governed by direct hydrogen atom transfer, the Co(II) chelate being the most reactive. In the aqueous phase also, the sequential proton loss electron transfer was preferred by all the molecules, while the Cu(II) chelates were the most reactive.

Ability ofB12N12fullerene like nano‐cage for sensing and improving the antioxidant activity of juglone and its derivative: Density functional theory investigation

“…One of the most popular naphtoquinones is juglone (5-hydroxy-1,4-naphthoquinone) which is a phenolic allelochemical responsible for walnut allelopathy and the inhibitory effect of black walnut (Juglans nigra) in associated plant species [27]. In our previous works, the antioxidant activity (AOA) of juglone (Jug) based on hydrogen transfer mechanisms as well as the metal chelation ability have been substantially studied [27][28][29]. Our findings revealed a huge improvement in the AOA of (Jug) through the substitution of the H-atom ortho to its hydroxyl group by another OH group [29].…”