Dimeric 2,2′-bipyridylruthenium(II) complexes containing 2,2′-bis(1,2,4-triazin-3-yl)-4,4′-bipyridine-like bridging ligands: Syntheses, characterization and DNA-binding

Article abstract of DOI:10.1002/ejic.200300710

Three new bridging ligands 2,2′-bis(1,2,4-triazin-3-yl)-4,4′- bipyridine (btb), 2,2′-bis(1,2,4-triazino[5,6-f] acenaphthylen-3-yl)-4, 4′-bipyridine (btapb), 2,2′-bis(5,6-diphenyl-1,2,4-triazin-3-yl)-4, 4′-bipyridine (bdptb) and their dimeric 2,2′-bipyridylruthenium(II) complexes [Ru(bpy)₂(btb)Ru(bpy)₂]⁴⁺ (1), [Ru(bpy)₂(btapb)Ru(bpy)₂]⁴⁺ (2), [Ru(bpy) ₂(bdptb)Ru(bpy)₂]⁴⁺ (3) have been synthesized and characterized by elemental analysis, fast atom bombardment (FAB) mass spectrometry or electrospray mass spectrometry (ES-MS), ¹H NMR and UV/Visible spectroscopy. The binding behavior of these dimeric complexes with calf thymus DNA (CT-DNA) was investigated by electronic absorption spectroscopy, viscosity measurements, and equilibrium dialysis experiments. The hypochromism of the metal-ligand charge transfer (MLCT) band in the electronic absorption spectra of the dinuclear complexes 1, 2, and 3 is 8.7%, 19% and 33%, respectively, with bathochromic shifts of 5, 5 and 14 nm, respectively. The binding constants are 7.5±10⁴ M^-1, 4.8±10⁵ M^-1 and 7.6±10⁵ M ^-1, respectively. Increasing the size of the plane of the bridging ligand increases the hydrophobicity of their complexes, leading to stronger binding by the complexes to calf thymus DNA. The effect of increasing concentrations of these novel dimeric ruthenium(II) complexes on the relative viscosities of CT-DNA is less notable than that of well-known intercalators such as [Ru(bpy)₂(dppz)]²⁺. The equilibrium experiments showed that ΛΛ-3 binding is stronger than ΛΛ-3 binding to CT-DNA. This is the first example of a dinuclear complex binding enantioselectively to CT-DNA measured by equilibrium dialysis. The experiments suggest that the three complexes may be DNA groove binders. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.