DNA binding, photocleavage behavior, and topoisomerase I inhibitory activity of Ru(II) complexes incorporating an asymmetric phenazine-type ligand

Two ruthenium complexes incorporating an asymmetric ligand, [Ru(L)₂pipz]²⁺ (L = bpy (2,2′-bipyridine), phen (1,10-phenanthroline), pipz = 2-pyridine-1H-imidazo[4,5-b]phenazine), have been synthesized and characterized. The interactions of the two complexes with DNA have been investigated by UV–visible spectroscopy, fluorescence spectroscopy, and viscosity measurements. Both complexes bind to DNA by intercalation and efficiently cleave pBR322 DNA under irradiation. Singlet oxygen () was the main reactive oxygen species involved in DNA photocleavage. Topoisomerase inhibition and DNA strand passage assay demonstrated that both complexes can act as efficient catalytic inhibitors of DNA topoisomerase I.