Study of the interaction of Co(III) polypyridyl complexes with DNA: an experimental and computational approach

Three new cobalt(III) polypyridyl complexes, [Co(L - L)₂IIP]³⁺ where IIP = 2-(2H-isoindol-1-yl)-2H-imidazo[4,5-f][1, 10]phenanthroline, L = 1) phen (1,10-phenanthroline), 2) bpy (2,2'bipyridyl), 3) dmb (4, 4-dimethyl 2, 2'-bipyridine) have been synthesized, characterized (UV -VIS, IR, ¹HNMR and ¹³C NMR spectroscopy) and screened for their in vitro antibacterial activity against E.coli, Staphylococcus aureus and Bacillus subtilis. The binding of these complexes with calf-thymus DNA (CT-DNA) has been investigated by absorption and fluorescence spectroscopy, viscosity measurements. The experimental studies indicate that complexes bind to CT-DNA by means of intercalation, but with different binding affinities due to differences in the planarity of the ancillary ligand. The complexes promote photocleavage of plasmid DNA from super coiled form I to the open circular form II. The antibacterial activities suggest that the metal complexes are more active as compared to the prepared un-complexed IIP ligand. In addition, a conformational search was carried out by Molecular Dynamics Simulations, and docking revealed that complexes intercalate between base pairs of DNA. The experimental and computational approaches reveal that the length of the intercalator and the nature of ancillary ligand are highly important factors for DNA binding.