Cobalt(II) complexes with the antimicrobial drug enrofloxacin: Structure, antimicrobial activity, DNA- and albumin-binding

•Five cobalt(II) complexes with the quinolone enrofloxacin were synthesized.•Two structures of co-enrofloxacinato complexes were determined by X-ray crystallography.•The complexes show enhanced antimicrobial activity in comparison to free drug.•The co-enrofloxacinato complexes can bind to human or bovine serum albumin proteins.•Intercalation is the most possible binding mode of the complexes to DNA.

The cobalt(II) complexes with the quinolone antimicrobial agent enrofloxacin (Herx) in the presence of the nitrogen-donor heterocyclic ligands pyridine (py), 2,2′-bipyridylamine (bipyam), 1,10-phenanthroline (phen), 2,2′-bipyridine (bipy) or the oxygen-donor ligand N,N-dimethylformamide (DMF) were synthesized and characterized. The crystal structures of complexes [Co(erx)2(py)2]·MeOH·6H2O and [Co(erx)2(bipyam)]·4.5MeOH·1.25H2O were determined by X-ray crystallography. The deprotonated enrofloxacinato ligands are bidentately bound to cobalt(II) ion through the pyridone oxygen and a carboxylato oxygen. The antimicrobial activity of the complexes was tested against five different microorganisms (Escherichia coli XL1, Xanthomonas campestris ATCC 33013, Staphylococcus aureus ATCC 29213, Bacillus cereus ATCC 11778 and Bacillus subtilis ATCC 6633) and the complexes were more active than free Herx. The binding of the complexes to calf-thymus DNA (CT DNA) was monitored by spectroscopic techniques, viscosity measurements, cyclic voltammetry and by mobility shift experiments in agarose gel electrophoresis with CT DNA and plasmid DNA (pDNA). All complexes exhibited a preference for binding to the supercoiled structure of the pDNA. The ability of the complexes to displace ethidium bromide (EB) from the EB–DNA complex was also investigated. The experiments indicated intercalation as the most possible mode and the DNA-binding strength of the complexes were also calculated. The complexes bind to human or bovine serum albumin protein exhibiting relatively high binding constant values.

Graphical abstractThe interaction of CoCl2 with the deprotonated quinolone enrofloxacin in the presence of O- or N-donor ligands results in the formation of complexes which exhibit pronounced antimicrobial activity and present significant binding to calf-thymus and plasmid DNA.Figure optionsDownload full-size imageDownload as PowerPoint slide