Mono- and bi-nuclear ruthenium(II) complexes containing a new asymmetric ligand 3-(pyrazin-2-yl)-as-triazino[5,6-f]1,10-phenanthroline:: synthesis, characterization and DNA-binding properties

A novel asymmetric ligand 3-(pyrazin-2-yl)-as-triazino[5,6-f]1,10-phenanthroline (pztp) and its mono- and bi-nuclear complexes [Ru(bpy)(2)(pztp)](2+) 1 and [(bpy)(2)Ru(pztp)Ru(bpy)(2)](4+) 2 (bpy = 2,2'-bipyridine) have been synthesized and characterized by UV/VIS, IR, H-1 NMR and mass spectra. The electrochemical behaviours of complexes 1 and 2 were observed and displayed oxidation potentials at 1.37 and 1.39 and 1.60 V vs. saturated calomel electrode, respectively. The binding of the two complexes with calf thymus DNA has also been investigated by a spectrophotometric method and viscosity measurements. The results indicated that the two complexes interact with DNA in sharply different ways. The mononuclear complex 1 intercalates into DNA base pairs despite its small hypochromicity value, while the binuclear complex 2 binds to DNA via electrostatic interaction. The circular dichroism signals of the dialysates of the racemic complexes against calf thymus DNA are discussed.