DNA photocleavage activity of cobalt(III) polypyridyl complexes containing dpq ligand

Four cobalt(III) polypyridyl complexes, Co(phen)_3−n(dpq)_n]³⁺ (phen = 1,10-phenanthroline, dpq = dipyrido3,2-f:2′,3′-h]-quinoxaline) (n = 0, 1, 2, and 3) were synthesized and the influences of the dpq ligand on the photophysical properties, electrochemical properties, DNA binding affinities, as well as photonuclease activities of the complexes, were examined in detail. The presence of dpq ligand increases the DNA binding affinities of the corresponding complexes remarkably with respect to Co(phen)₃]³⁺. With the sequential substitution of phen ligand by dpq ligand, the ¹O₂ quantum yields of the corresponding complexes are enhanced greatly. As a result, the photonuclease activities follow the order of Co(dpq)₃]³⁺ > Co(phen)(dpq)₂]³⁺ > Co(phen)₂(dpq)]³⁺ ? Co(phen)₃]³⁺. It was found all the examined complexes can generate OH upon UV irradiation, and OH is also involved in DNA photocleavage as reactive oxygen species.