Manganese(II) complexes of the quinolone family member flumequine: Structure, antimicrobial activity and affinity for albumins and calf-thymus DNA

Abstract

In the present contribution, the synthesis and the characterization of the manganese(II) complexes with the quinolone antimicrobial agent flumequine (Hflmq) in the absence or presence of the N,N′-donor heterocyclic ligands 1,10-phenanthroline (phen) and 2,2′-bipyridylamine (bipyam) are reported. The structure of complex [Mn(flmq)2(phen)]·2MeOH was also determined by X-ray crystallography. In the novel complexes, the quinolone ligands are bound to manganese(II) in a bidentate manner through a carboxylato oxygen and the pyridone oxygen. The affinity of the complexes to human or bovine serum albumin proteins was investigated by fluorescence emission spectroscopy and the corresponding binding constants exhibit relatively high values. The binding of the complexes to calf-thymus (CT) DNA was studied by UV–Vis spectroscopy and DNA-viscosity measurements. The DNA-binding constants of the complexes were calculated. Intercalation is the most possible DNA-binding mode, and this was verified through the ability of the complexes to displace ethidium bromide (EB) from the EB–DNA conjugate. The antimicrobial activity of the complexes was tested against four different microorganisms (Escherichia coli, Xanthomonas campestris, Staphylococcus aureus and Bacillus subtilis) and was found similar or higher than free Hflmq.