Synthesis, characterization and DNA-binding studies of cobalt(III) polypyridyl complexes

[Co(bpy)(2)(HNOIP)](3+) and [Co(phen)(2)(HNOIP)](3+) (HNOIP=2-(2-hydroxy-5-nitrophenyl)imidazo[4,5-f][1,10]phenanthroline) have been synthesized and characterized by UV-Vis, EA and mass spectra. The binding of the two complexes with calf thymus DNA has been investigated by absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and viscosity measurements. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that both complexes bind to CT DNA by intercalation via HNOIP into the base pairs of DNA. The NO, and OH substitute groups have no significant effect on the spectral properties and DNA-binding behavior of both complexes. Both complexes have also been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation. The cleaving mechanism for the two complexes has been proposed. (C) 2001 Elsevier Science Ltd. All rights reserved.