Zinc(ii) complexes of 3-bromo-5-chloro-salicylaldehyde: characterization and biological activity

Abstract

Five neutral zinc(II) complexes of 3-bromo-5-chloro-salicylaldehyde (3-Br-5-Cl-saloH) were synthesized in the absence or presence of the nitrogen-donor co-ligands 2,2′-bipyridine (bipy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (neoc), or 2,2′-bipyridylamine (bipyam) and were characterized by various techniques. The obtained complexes were [Zn(3-Br-5-Cl-salo)₂(H₂O)₂] (1), [Zn(3-Br-5-Cl-salo)₂(bipy)] (2), [Zn(3-Br-5-Cl-salo)₂(phen)] (3), [Zn(3-Br-5-Cl-salo)₂(neoc)] (4) and [Zn(3-Br-5-Cl-salo)₂(bipyam)] (5). The crystal structures of complexes 1 and 3 were determined by single-crystal X-ray crystallography. The interaction of the compounds with calf-thymus DNA takes place via intercalation. The compounds may moderately cleave pBR322 plasmid DNA at a concentration of 500 μM. The compounds may bind tightly and reversibly to serum albumins. The antioxidant activity of the compounds was examined towards 1,1-diphenyl-picrylhydrazyl and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radicals and H₂O₂. The antimicrobial potency of the compounds was investigated against Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633, Escherichia coli NCTC 29212 and Xanthomonas campestris ATCC 1395.