Synthesis, characterization, DNA interaction and antimicrobial screening of isatin-based polypyridyl mixed-ligand Cu(II) and Zn(II) complexes

Several mixed ligand Cu(II)/Zn(II) complexes using 3-(phenylimino)-1,3-dihydro-2H-indol-2-one (obtained by the condensation of isatin and aniline) as the primary ligand and 1,10-phenanthroline (phen)/2,2'-bipyridine (bpy) as an additional ligand were synthesized and characterized analytically and spectroscopically by elemental analyses, magnetic susceptibility and molar conductance measurements, as well as by UV-Vis, IR, NMR and FAB mass spectroscopy. The interaction of the complexes with calf thymus (CT) DNA was studied using absorption spectra, cyclic voltammetric and viscosity measurements. They exhibit absorption hypochromicity, and the specific viscosity increased during the binding of the complexes to calf thymus DNA. The shifts in the oxidation-reduction potential and changes in peak current on addition of DNA were shown by CV measurements. The Cu(II)/Zn(II) complexes were found to promote cleavage of pUC19 DNA from the supercoiled form I to the open circular form II and linear form III. The complexes show enhanced antifungal and antibacterial activities compared with the free ligand.