Zinc complexes of flufenamic acid: Characterization and biological evaluation

The reaction of ZnCl₂ with the non-steroidal anti-inflammatory drug flufenamic acid (Hfluf) led to the formation of complex [Zn(fluf-O)₂(MeOH)₄], 1. When the reaction takes places in the presence of a N,N'-donor heterocyclic ligand such as 2.2'-bipyridylamine (bipyam), 2.2'-bipyridine (bipy), 1.10-phenanthroline (phen) and 2.2'-dipyridylketone oxime (Hpko), the complexes [Zn(fluf)₂(bipyam)], 2, [Zn(fluf)₂(bipy)], 3, [Zn(fluf)(phen)₂(H₂O)](fluf)·0.2MeOH, 4·0.2MeOH and [Zn(fluf)₂(Hpko)₂], 5 were isolated, respectively. The complexes were characterized by physicochemical and spectroscopic techniques and the crystal structures of complexes 2 and 4 were determined by X-ray crystallography. The ability of the complexes to scavenge 1.1-diphenyl-picrylhydrazyl, 2.2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) and hydroxyl radicals and to inhibit soybean lipoxygenase was evaluated; the complexes were more active than free Hfluf. The interaction of the complexes with serum albumins was investigated by fluorescence emission spectroscopy and the corresponding binding constants were calculated. UV-vis spectroscopy, viscosity measurements and fluorescence emission spectroscopy for the competitive studies of the complexes with ethidium bromide were the techniques employed to monitor the interaction of the complexes with calf-thymus DNA and revealed intercalation as the most possible mode of binding.