Synthesis, characterization, DNA-binding and photocleavage of complexes [Ru(phen)2(6-OH-dppz)]2+ and [Ru(phen)2(6-NO2-dppz)]2+

Two new complexes, ([Ru(phen)2(6-OH-dppz)]2+) (1) and ([Ru(phen)2(6-NO2-dppz)]2+) (2) (phen = 1,10-phenanthroline; 6-OH-dppz = 6-hydroxyl-dipyrido[3,2-a:2′,3′-c]phenazine; 6-NO2-dppz = 6-nitro-dipyrido[3,2-a:2′,3′-c]phenazine), have been synthesized and characterized by elemental analysis, ES-MS (electrospray mass spectra), 1H NMR, UV–Vis (UV–visible) and CV (cyclic voltammetry). The DNA-binding behaviors of both complexes have been studied by spectroscopic methods and viscosity measurements. The results indicate that the two complexes all bind to calf thymus DNA (CT-DNA) in an intercalative mode, and the DNA-binding affinity of complex 2 is greater than that of complex 1. In addition, complex 1 can promote photocleavage of pBR322 DNA upon irradiation, whereas complex 2 can promote cleavage of pBR322 DNA both upon irradiation and in the dark, with more efficient cleavage occurring upon irradiation. Theoretical studies for these complexes have been also carried out with the density functional theory (DFT) method. The difference in the DNA-binding behaviors of the two complexes can be reasonably explained by the DFT calculations.