Antioxidant Activity and Electrochemical Properties of Tetradentate Schiff Bases and Their Cd(II) Complexes

This study describes the effects of the substituents on electrochemical behavior and antioxidant activity of the three tetradentate Schiff bases, containing ethane-1,2- diamine, propane-1,3- diamine and butan-1,4- diamine as the amine part and salicylaldehyde, and corresponding Cd(II) complexes. Cyclic voltammograms of these compounds were recorded in dimethylsulfoxide and 0.1 M sodium perchlorate as supporting electrolyte with glassy carbon as working electrode at different scan rates. The voltammograms of Schiff bases alone showed only one irreversible peak. Voltammograms recorded for complexes showed the presence of quasi-reversible processes taking place at the metal center and reversible process at the ligand part. Both steric and inductive effects of substituents and structure of imine bridge of Schiff base ligands as well as complexes were discussed. These effects appear relevant for the antioxidant activity. Antioxidant activity of the investigated compounds expressed as Trolox equivalent antioxidant capacity is also discussed. The electrochemical behavior showed a high correlation with the antioxidant activity for investigated compounds.