A theoretical study of the antioxidant properties of phenolic acid amides investigated through the radical-scavenging and metal chelation mechanisms

Abstract

Phenolic amides have been investigated extensively as efficient antioxidant compounds by means of experimental techniques. However, their mode of action has not been determined through the use of theoretical approaches. In this study, theoretical studies on the conformational and antioxidant properties of phenolic acid amides were performed to investigate factors that contribute to their conformational preferences and to elucidate their antioxidant properties and mechanisms. The antioxidant activity of selected phenolic acid amides has been considered through the ability of the compounds to scavenge free radical species and chelate metal ions. The antiradical mechanisms were investigated using the B3LYP/6-311+G(d,p) method, and the metal chelation mechanism was investigated using the B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) method. The results show that the preferred conformers for the neutral and anionic conformers are stabilised by the presence of intramolecular hydrogen bonds (IHBs). The neutral and cationic radical species are stabilised by both IHBs and the spin density delocalisation of the unpaired electron. The preferred Cu complex is one in which the Cu ion interacts simultaneously with the carbonyl group and the benzene ring of the aromatic amine moiety. An estimated metal ion affinity is influenced by the nature of the ligand and the media. In comparison with the isolated Cu(II) ion, the charge on the coordinated metal ion decreases from 2 to ~1 suggesting that the Cu ion is reduced on interaction with the ligand molecule undergoes oxidation.