Ruthenium(II) complexes containing asymmetric ligands: synthesis, characterization, crystal structure and DNA-binding

Two new asymmetric ligands, 3-(pyrazin-2-yl)-as-triazino[5,6-f]acenaphthylene (dta) and 3-(pyrazin-2-yl)-astriazino[5,6-f]phenanthrene (dpt) and three novel ruthenium(II) complexes [Ru(bpy)(2)(L)][ClO4](2) (bpy = 2,2'-bipyridine, L = ddt (1), dta (2) and dpt (3), ddt = 3-(pyrazin-2-yl)-5,6-diphenyl-as-triazine) have been synthesized and characterized by mass spectroscopy, H-1 NMR and cyclic voltammetry. The crystal structures of dta and [Ru(bpy)(2)(ddt)][ClO4](2) (1) were also determined. Interactions of the complexes with calf thymus DNA have also been investigated by spectrophotometric and viscosity measurements. The planar extension of the intercalative ligand increases the interaction of the complex with DNA, indicating that the size and shape of the intercalated ligand have a marked effect on the strength of interaction. The circular dichroism signals of the dialysates of the racemic complexes against calf thymus DNA suggest that complexes 2 and 3 interact enantioselectively with calf thymus DNA, but not complex 1. Complexes 2 and 3 have been found to promote the cleavage of plasmid pBR 322 DNA, from the supercoiled form I to the open circular form II upon irradiation.