Probing the DNA-binding behavior of tryptophan incorporating mixed-ligand complexes

Mixed-ligand Cu(II), Ni(II), Co(II), and Zn(II) complexes using a tryptophan-derived Schiff base (obtained by the condensation of tryptophan and benzaldehyde) as the primary ligand and 1,10-phenanthroline as the co-ligand were synthesized and characterized analytically and spectroscopically by performing elemental analyses, magnetic susceptibility and molar conductance measurements, UV-Vis, IR, NMR, and FAB-MS. The binding properties of metal complexes with DNA were investigated by electronic absorption spectroscopy, cyclic voltammetry, and by performing viscosity measurements, and the results showed that these complexes have the ability to interact with DNA via an intercalative mode. The DNA cleavage efficiencies of these complexes with pUC19 DNA were investigated by gel electrophoresis. The complexes were found to promote the cleavage of pUC19 DNA from the supercoiled form I to the open circular form II and the linear form III in the presence of ascorbic acid. Finally, the in vitro antibacterial activities of the Schiff base and its mixed-ligand metal complexes were screened against the bacteria Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Salmonella typhi. The antibacterial screening data revealed that the complexes show growth inhibitory activity against bacteria.