Mononuclear metal complexes with ciprofloxacin: Synthesis, characterization and DNA-binding properties.

Five novel metal complexes of the quinolone antibacterial agent ciprofloxacin with Mn(2+), Fe(3+), Co(2+), Ni(2+) and MoO(2)(2+) have been prepared and characterized with physicochemical, spectroscopic and electrochemical techniques. In all these complexes, ciprofloxacin acts as a bidentate deprotonated ligand bound to the metal through the pyridone oxygen and one carboxylate oxygen. The central metal in each complex is six-coordinate and a slightly distorted octahedral geometry is proposed. The lowest energy model structures of the Mn(2+), Fe(3+) and MoO(2)(2+) complexes have been determined with molecular modeling calculations. The cyclic voltammograms of the complexes have been recorded in dmso solution and in 1/2 dmso/buffer (containing 150mM NaCl and 15mM trisodium citrate at pH 7.0) solution and the corresponding redox potentials have been estimated. The biological activity of the complexes has been evaluated by examining their ability to bind to calf-thymus DNA (CT DNA) with UV and fluorescence spectroscopies and cyclic voltammetry. UV studies of the interaction of the complexes with DNA have shown that these compounds can bind to CT DNA. The binding constants of the complexes with CT DNA have also been calculated. The cyclic voltammograms of the complexes in the presence of CT DNA have shown that the complexes can bind to CT DNA by both the intercalative and the electrostatic binding mode. Competitive studies with ethidium bromide (EB) have shown that the complexes exhibit the ability to displace the DNA-bound EB indicating that the complexes bind to DNA probably via intercalation in strong competition with EB for the intercalative binding site.