A mononuclear cadmium(II) complex of formula [Cd(5,5'-dmbipy)2(OAc)2]·2H2O (5,5'-dmbipy = 5,5'-dimethyl-2,2'-bipyridine and OAc = acetato ligand) has been synthesized and characterized by FT-IR, UV-Vis, 1H-NMR, elemental analysis and single-crystal X-ray structure analysis. The molecular structure of the complex shows a distorted tetragonal antiprism CdN4O4 coordination geometry around the cadmium atom, resulting in coordination by four nitrogen atoms from two 5,5'-dmbipy ligands and four oxygen atoms from two acetate anions. The interaction of this complex to FS-DNA (fish sperm DNA) has also been studied by electronic absorption, fluorescence and gel electrophoresis techniques. Binding constant (Kb), Stern-Volmer constant (Ksv), number of binding sites (n) and bimolecular quenching rate constant (kq) have been calculated from these spectroscopic data. These results have revealed that the metal complex can bind effectively to FS-DNA via groove binding. The calculated thermodynamic parameters (ΔH°, ΔS° and ΔG°) show that hydrogen bonding and van der Waals forces have an important function in the Cd(II) complex-DNA interaction. The antibacterial effects of the synthesized cadmium complex have also been examined in vitro against standard bacterial strains: one Gram-positive (Staphylococcus aureus, ATCC 25923) and one Gram-negative (Escherichia coli, ATCC 25922) bacteria, using disk diffusion and macro-dilution broth methods. The obtained results show that the Cd(II) complex exhibits a marked antibacterial activity which is significantly better than those observed for its free ligand and metal salt for both Gram-positive and Gram-negative bacteria. However, this metal complex is a more potent antibacterial agent against the Gram-positive than that of the Gram-negative bacteria.Communicated by Ramaswamy H. Sarma.
Keywords: 55′-dimethyl-22′-bipyridine; Cd(II) complex; DNA binding; X-ray crystallography; antibacterial activity.