Synthesis, Antioxidant, and Antibacterial Studies of Zn(II), Cd(II), and Hg(II) Complexes with 3-Formylpyridinethiosemicar bazone and Its N4-Methyl Analogue

Abstract

Evaluation of stability constants of the complexes formed in solution by the biologically important ligands and metal ions can aid in understanding the application of metal complexes in chelation therapy. Hence, complexation equilibrium studies of the ligands (L), 3-formylpyridinethiosemicarbazone (H3FPT) and 3-formylpyridine-N⁴-methylthiosemicarbazone (H3FP4MT) with Zn(II) and Cd(II) metal ions (M) are carried out in 70% v/v DMF-water medium at 0.1M KNO₃ ionic strength and the stability constants are determined pH-metrically at 303 K. The binary complexes are formed in 1: 1 (M: L) ratio and are fairly stable. The binary complexes of H3FPT and H3FP4MT (L) with Zn(II), Cd(II) and Hg(II) ions are synthesized and characterized by various analytical and spectral techniques including elemental analysis, molar conductance, LC-MS, TGA, IR and ¹H NMR spectroscopy. According to the accumulated information, the complexes are polymeric (ML)n with n > 2, except that of Hg(II)-H3FP4MT, which is ML₂. The antioxidant activity of the ligands and their Zn(II) and Hg(II) complexes demonstrate higher activity than their corresponding ligands Cd(II) complexes. Antibacterial activity of the ligands and the complexes is tested against gram positive: Staphylococcus aureus, Bacillus subtilis and gram negative: Escherichia coli and Klebsiella pneumonia bacterial strains. Activity of complexes is determined to be higher than that of the corresponding free ligands.