title: A [4+2] mixed ligand approach to ruthenium DNA metallointercalators [Ru(tpa)(N-N)](PF(6))(2) using a tris(2-pyridylmethyl)amine (tpa) capping ligand.
abstract: A series of five tris(2-pyridylmethyl)amine (tpa) ruthenium complexes [Ru(tpa)(N-N)](PF(6))(2) with N-N=bpy (2,2'-bipyridine), phen (1,10-phenanthroline), dpq (dipyrido[3,2-d:2',3'-f]quinoxaline), dppz (dipyrido[3,2-a;2',3'-c]phenazine), and dppn (4,5,9,16-tetraazadibenzo[a,c]naphthacene) was prepared and characterized by NMR, UV-Visible (UV/Vis), and fluorescence spectroscopy as well as cyclic voltammetry. Structures optimized with density functional theory methods (DFT, BP86, TZVP) without constraints show C(1) symmetry while in solution, the (1)H and (13)C NMR spectra are in accordance with an average C(s) symmetry. This is thought to be due to a low energy barrier for flipping of the equatorial pyridine ring from one side of the N-N plane to the other. The electronic structure of the compounds was studied with DFT and a change in the highest occupied molecular orbital (HOMO) character from Ru t(2g) for the bpy, phen, and dpq to N-N ligand-based for the dppz and dppn complexes was found. TDDFT calculations showed dominant N-N-based intra-ligand charge transfer (ILCT) transitions in the latter two complexes mixed with metal-to-ligand charge transfer (MLCT) bands found for all five compounds. DNA binding of the complexes was studied with UV/Vis titrations, the fluorescent ethidium bromide displacement assay, and CD spectroscopy. The affinity increases with the aromatic surface area of of the bidentate N-N ligand in the order bpy<<phen<dpq<dppz approximately dppn. Viscosity measurements support an intercalative binding mode for the latter three compounds, while the others did not show a pronounced effect of the hydrodynamic properties of calf thymus (CT) DNA.
authors.affiliation: Institut für Pharmazie und Molekulare Biotechnologie, Ruprecht-Karls-Universität Heidelberg, Germany.
authors.forename: Sabine Seeberg née
authors.initials: SS
authors.lastname: Kraft
authors.forename: Caroline
authors.initials: C
authors.lastname: Bischof
authors.forename: Annette
authors.initials: A
authors.lastname: Loos
authors.forename: Sebastian
authors.initials: S
authors.lastname: Braun
authors.forename: Nigar
authors.initials: N
authors.lastname: Jafarova
authors.forename: Ulrich
authors.initials: U
authors.lastname: Schatzschneider
mesh_terms: D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D055664:Electrochemical Techniques; D004996:Ethidium; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D017975:Ruthenium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D013053:Spectrophotometry; D014783:Viscosity
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D011725:Pyridines; D017975:Ruthenium Compounds; C431843:tris(2-pyridylmethyl)amine; D004247:DNA; D004996:Ethidium