Two tridentate polypyridyl complexes of cobalt(II) [DMPhTPY＝6,6 -dimethyl-4 -phenyl-2,2 :6 ,2 -terpyridine] (A) and [Co(H₂Bzimpy)₂]Cl₂ [H₂Bzimpy]₂＝2,6-bis(benz- imidazol-2-yl)pyridine] (B) were synthesized and characterized by elemental analysis and IR. The crystal structure of complex A was determined. The interactions of the complexes with calf thymus DNA (CTDNA) have been investigated by absorption spectroscopy, fluorescence spectroscopy, cyclic voltammetry and agarose gel electrophoresis. The studies suggested that complexes A and B bind to CTDNA by partial intercalation and electrostatic interaction. The agarose gel electrophoresis showed that complex A converted supercoiled pBR322 DNA to nicked and linear DNA when it was irradiated at 310 nm for 15 min.

Key words: tridentate polypyridyl ligand, cobalt(II) complex, crystal structure, DNA, photocleavage