Nickel(II) coordination compounds of 4'-chloro-fenamic acid: characterization and biological activity.

With the aim of investigating whether the coordination of fenamates to Ni(II) affects the biological profile, a chloro-derivative of fenamic acid (4'-chloro-fenamic acid) was synthesized and used as a ligand for the synthesis of seven nickel(II) complexes in the absence or presence of the nitrogen-donors pyridine, β-picoline, 1H-imidazole, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,2'-bipyridylamine. The characterization of the resultant Ni(II) complexes was performed with diverse techniques (elemental analysis, molar conductivity measurements, mass spectrometry, IR and UV-vis spectroscopy, and single-crystal X-ray crystallography). The compounds were evaluated for their in vitro biological activity in terms of the antioxidant activity via free radical scavenging and H2O2 reduction, the antimicrobial activity against two Gram-positive and two Gram-negative bacterial strains, the interaction with calf-thymus DNA, the cleavage of supercoiled pBR322 plasmid DNA (pDNA) in the dark or under UVB/UVA/visible light irradiation, and the binding affinity toward bovine and human serum albumins. The antioxidant activity of the compounds is noteworthy against 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radicals and H2O2, and comparable with that of the reference compounds. The complexes exhibit notable antimicrobial activity against the strains tested. The compounds interact with calf-thymus DNA via intercalation with binding constants of 105-106 M-1 magnitude. The pDNA-cleavage ability of the compounds is significantly enhanced under irradiation. All the compounds can bind tightly and reversibly to both albumins tested.