Evaluation of Radical Scavenging activity of Br-Substituted Schiff Base metal complexes: Investigating the Inhibitory Role of Inductive Electron Withdrawal
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Abstract
The persistent search in medicinal chemistry for active synthetic antioxidants has the goal of relieving oxidative stress-related diseases. In this study, Schiff base ligands and their corresponding metal complexes using copper, nickel, and cobalt were synthesized, with the ligands substituted with bromine (INHBrS) or unsubstituted (INH-5H). The compounds were identified using FTIR, NMR, elemental analysis and AAS (for metal complexes only). In determining the antioxidant capacity of the ligands and their corresponding metal complexes, the compounds were subjected to the DPPH, FRAP, Nitric Oxide Radical Scavenging Assay, and Total Antioxidant Capacity tests using ascorbic acid as the standard control. The study demonstrated the critical role of the nature of the substituent in the scavenging capacity of the compounds. In INH-5BrS compound, the bromine is an electron-withdrawing group due to the inductive effect (-I), resulting in a decrease in the electron density on the aromatic ring, thereby showing less antioxidant potential compared to 1NH-5H. In the 1NH-5H series, the nickel complex 1NH-5HNi has the best antioxidant capacity in the DPPH Inhibition Assay (92.345%) and the Total Antioxidant Capacity (97.4%) tests, surpassing ascorbic acid. This study provides critical insights into the structure-activity relationship (SAR) regarding inductive effects in phenolic antioxidant systems.
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