Cobalt(ii) complexes with the quinolone antimicrobial drug oxolinic acid: structure and biological perspectives

Abstract

The interaction of cobalt(II) with the quinolone antimicrobial agent oxolinic acid (Hoxo) in the absence or presence of the Lewis bases 2,2′-bipyridine (bipy), 2,2′-bipyridylamine (bipyam), 1,10-phenanthroline (phen), pyridine (py) or 4-benzylpyridine (4bzpy) resulted in the formation of a series of mononuclear complexes which were characterized with physicochemical and spectroscopic techniques. The crystal structure of [Co(oxo)₂(bipy)]·3MeOH was determined by X-ray crystallography. The interaction of the complexes with calf-thymus DNA (CT DNA) was investigated by UV spectroscopy, viscosity measurements and cyclic voltammetry in order to evaluate the possible DNA-binding mode and to calculate the corresponding DNA-binding constants. The binding of the complexes to human or bovine serum albumin was monitored by fluorescence emission spectroscopy and relatively high binding constant values were determined. The antimicrobial activity of the complexes was tested against four different microorganisms (Escherichia coli, Xanthomonas campestris, Staphylococcus aureus and Bacillus subtilis) and was found to be similar to that of free Hoxo. Molecular docking simulations on the crystal structure of CT DNA, HSA and BSA were employed in order to study in silico the ability of the resultant complexes to bind biomacromolecules. This is the first report for metal–quinolone complexes combining experimental data and molecular docking simulations of their interaction with DNA and serum albumins.