Zinc complexes of salicylaldehydes: synthesis, characterization and DNA-binding properties.

The neutral mononuclear zinc complexes with substituted salicylaldehydes, in the absence or presence of a nitrogen donor heterocyclic ligand 2,2'-bipyridine or 1,10-phenanthroline or 2,2'-dipyridylamine, have been synthesized and characterized by IR, UV and NMR spectroscopies. The experimental data suggest that salicylaldehyde is on deprotonated mode acting as a bidentate ligand coordinated to the metal ion through the phenolato and one aldehydo oxygen atoms. The crystal structures of bis(5-nitro-salicyladehydato)(2,2'-dipyridylamine)zinc(II), bis(5-chloro-salicylaldehydato)(2,2'-bipyridine)zinc(II) monohydrate and bis(5-bromo-salicyladehydato)bis(methanol)zinc(II) have been determined with X-ray crystallography. The ability of the complexes to bind to calf-thymus DNA (CT DNA) has been studied by UV and fluorescence spectroscopy and viscosity measurements. UV studies of the interaction of the complexes with DNA have shown that they can bind to CT DNA. The calculated binding constants of the complexes to DNA reveal tight binding to DNA. The complexes can probably bind to CT DNA via intercalation as concluded by studying the viscosity of a DNA solution in the presence of the complexes. Competitive studies with ethidium bromide (EB) have shown that the complexes can displace the DNA-bound EB suggesting strong competition with EB for the intercalation site of DNA.