Synthesis, DNA-binding and photocleavage studies of ruthenium complexes [Ru(bpy)(2)(mitatp)](2+) and [Ru(bpy)(2)(nitatp)](2+)

Two new ruthenium complexes [Ru(bpy)(2)(mitatp)](ClO4)(2) 1 and [Ru(bpy)(2)(nitatp)](ClO4)(2) 2 (bpy = 2,2'-bipyridine, mitatp = 5-methoxy-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene, nitatp = 5-nitro-isatino[1,2-b]-1,4,8,9-tetraazatriphenylene) have been synthesized and characterized by elemental analysis, H-1 NMR, mass spectrometry and cyclic voltammetry. Spectroscopic and viscosity measurements proved that the two Ru(II) complexes intercalate DNA with larger binding constants than that of [Ru(bpy)(2)(dppz)](2+) (dppz = dipyrido[3,2-a:2',3'-c]phenazine) and possess the excited lifetime of microsecond scale upon binding to DNA. Both complexes can efficiently photocleave pBR322 DNA in vitro under irradiation. Singlet oxygen (O-1(2)) was proved to contribute to the DNA photocleavage process, the O-1(2) quantum yields was determined to be 0.43 and 0.36 for 1 and 2, respectively. Moreover, a photoinduced electron transfer mechanism was also found to be involved in the DNA cleavage process. (C) 2009 Elsevier Inc. All rights reserved.