Cobalt(II) Complexes of 4′–Nitro–Fenamic Acid: Characterization and Biological Evaluation

A nitro-derivative of fenamic acid (4'-nitro-fenamic acid) was synthesized and used as ligand for the synthesis of four Co(II) complexes in the absence or presence of the <i>N</i>,<i>N</i>'-donors 2,2'-bipyridylamine, 1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline. The characterization of the resultant complexes was performed with diverse techniques (elemental analysis, molar conductivity measurements, IR and UV-vis spectroscopy, single-crystal X-ray crystallography). The biological evaluation of the compounds encompassed (i) antioxidant activity via hydrogen peroxide (H₂O₂) reduction and free radical scavenging; (ii) antimicrobial screening against two Gram-positive and two Gram-negative bacterial strains; (iii) interactions with calf-thymus (CT) DNA; (iv) cleavage of supercoiled pBR322 plasmid DNA (pDNA), in the dark or under UVA/UVB/visible light irradiation; and (v) binding affinity towards bovine and human serum albumins. The antioxidant activity of the compounds against 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radicals and H₂O₂ is significant, especially in the case of H₂O₂. The complexes exhibit adequate antimicrobial activity against the strains tested. The complexes interact with CT DNA through intercalation with binding constants reaching a magnitude of 10⁶ M^-1. The compounds have a significantly enhanced pDNA-cleavage ability under irradiation, showing promising potential as photodynamic therapeutic agents. All compounds can bind tightly and reversibly to both albumins tested.