Erbium(III) complexes with fluoroquinolones: Structure and biological properties

Four erbium(III) complexes with the fluoroquinolones enrofloxacin, levofloxacin, flumequine and sparfloxacin as ligands were synthesized and characterized by a wide range of physicochemical and spectroscopic techniques as well as single–crystal X–ray crystallography. The compounds were evaluated for their activity against the bacterial strains Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Xanthomonas campestris, which was higher than that of the corresponding free quinolones. The interaction mode of the complexes with calf–thymus DNA is via intercalation, as suggested by diverse studies such as UV–vis spectroscopy, DNA–viscosity measurements and competitive studies with ethidium bromide. Fluorescence emission spectroscopy revealed the high affinity of the complexes for bovine and human serum albumin and the determined binding constants suggested a tight and reversible binding of the compounds with both albumins. Four erbium(III) complexes with fluoroquinolones as ligands were synthesized and characterized. The compounds have shown noteworthy antimicrobial activity, can interact with calf-thymus DNA via intercalation and bind tightly and reversibly to serum albumins. [Display omitted] •Erbium(III) complexes with four fluoroquinolones were characterized.•Neutral or cationic mononuclear Er(III) complexes were isolated.•The compounds show noteworthy antimicrobial activity.•The interaction of the complexes with calf-thymus DNA is tight.•The complexes may bind reversibly to serum albumins.