Effect of intramolecular hydrogen-bond on the DNA-binding and photocleavage properties of polypyridyl cobalt(III) complexes

Two polypyridyl cobalt(III) complexes containing intramolecular hydrogen-bond [Co(phen)2HPIP]3+ (HPIP=2-(2-hydroxyphenyl)imidazo[4,5-f][1,10]phenanthroline) and [Co(phen)2HNAIP]3+ (HNAIP=2-(2-hydroxy-l-naphthyl)imidazo[4,5-f][1,10]phenanthroline) have been synthesized and characterized by UV–Vis, EA and MS spectra. Binding of both complexes with calf thymus DNA has been investigated by cyclic voltammetry, absorption spectroscopy, luminescence titration, viscosity measurements and DNA cleavage assay. The results suggested that the complex [Co(phen)2HPIP]3+ bound to CT DNA by intercalation via HPIP into the base pairs of DNA, while [Co(phen)2HNAIP]3+ bound with DNA by partial intercalating the ligand HNAIP. In addition, both complexes have been found to promote the single-stranded cleavage of plasmid pBR 322 DNA upon irradiation, and [Co(phen)2HPIP]3+ exhibited the higher cleaving efficiency.