Synthesis, DNA-binding and photocleavage studies of ruthenium(II) complexes [Ru(btz)(3)](2+) and [Ru(btz)(dppz)(2)](2+)

Two new ruthenium(II) complexes, [Ru(btz)(3)](ClO4)(2) (1) and [Ru(btz)(dppz)(2)](ClO4)(2) (2) (btz = 4,4'-bithiazole, dppz = dipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized by elemental analysis, H-1 NMR, ES-MS and X-ray crystallography. The DNA binding behaviors of two complexes have been studied by spectroscopic and viscosity measurements. The results suggest that complex 1 binds to CT-DNA via an electrostatic mode, while complex 2 via an intercalative mode. Under irradiation at 365 nm, both complexes were found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II. The mechanism studies reveal that singlet oxygen O-1(2) and hydroxyl radical (OH.) play a significant role in the photocleavage process.