Interaction of Zn(II) with quinolone drugs: Structure and biological evaluation

Zinc complexes with the third-generation quinolone antibacterial drugs levofloxacin and sparfloxacin have been synthesized and characterized. The deprotonated quinolones act as bidentate ligands coordinated to zinc ion through the pyridone and a carboxylato oxygen atom. The crystal structures of [bis(aqua)bis(levofloxacinato)zinc(II)], 1, and [bis(sparfloxacinato)(1,10-phenanthroline) zinc(II)], 3, have been determined by X-ray crystallography. The biological activity of the complexes has been evaluated by examining their ability to bind to calf-thymus DNA (CT DNA) by UV spectroscopy and viscosity measurements. UV studies of the interaction of the complexes with DNA have revealed that they can bind to CT DNA probably by the intercalative binding mode which has also been verified by DNA solution viscosity measurements. The DNA binding constants have been also calculated. A competitive study with ethidium bromide (EB) showed that the complexes exhibit the ability to displace the DNA-bound EB indicating that they bind to DNA in strong competition with EB for the intercalative binding site. The interaction of the complexes with human and bovine serum albumin proteins has been studied by fluorescence spectroscopy showing that the complexes exhibit good binding propensity to these proteins having relatively high binding constant values. The biological properties of the complexes have been evaluated in comparison to the previously reported Zn(II) complexes with the first- and second-generation quinolones oxolinic acid and enrofloxacin.