title: Synthesis, characterization and DNA-binding properties of rac-[Ru(5,6-dmp)2(dppz)]2+--enantiopreferential DNA binding and co-ligand promoted exciton coupling.
abstract: The new mixed ligand complex [Ru(5,6-dmp)2(dppz)]Cl2 [5,6-dmp = 5,6-dimethyl-1,10-phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine] has been isolated and its DNA-binding properties studied by employing UV-visible (UV-Vis), steady-state and time-resolved emission and circular dichroism spectral methods, viscometry, thermal denaturation and cyclic/differential pulse voltammetric techniques. The complex acts as a 'molecular light-switch' on binding to DNA, but the enhancement in emission intensity is only 75% of that of the parent complex [Ru(phen)2(dppz)]2+ (phen = 1,10-phenanthroline). The emission decay curves and quenching studies suggest two different DNA-binding modes both involving intercalation of the dppz ligand of [Ru(5,6-dmp)2(dppz)]Cl2. The characteristic red-shift of the induced CD signal, which is not observed for the phen analogue, arises from exciton coupling. The hydrophobicity and polarizability of 5,6-dmp co-ligand strongly favour the formation of a stable structural and electronic scaffold on the DNA surface for the unbound molecules to couple with the DNA-bound complexes facilitating spontaneous assembly of novel extended molecular aggregates using DNA as a helical nanotemplate. This observation is consistent with the shift in Ru(II)/Ru(III) redox potential to more positive values with a dramatic drop in peak current on binding of the 5,6-dmp complex to calf thymus (CT) DNA. Equilibrium dialysis experiments monitored by CD spectroscopy unambiguously reveal the preferential binding of the delta-enantiomer to the right-handed calf thymus (CT) DNA. The 5,6-dmp complex exhibits preferential binding to [d(AT)6]2 over [d(GC)6]2 and the complex aggregates formed consist of six [Ru(5,6-dmp)2(dppz)]2+ cations per base pair of [d(AT)6]2; however, only one [Ru(phen)2(dppz)]2+ cation per base pair is involved in DNA binding.
authors.affiliation: School of Chemistry, Bharathidasan University, Palkalaiperur, Tiruchirappalli 620 024, Tamilnadu, India.
authors.forename: Palanisamy Uma
authors.initials: PU
authors.lastname: Maheswari
authors.forename: Venugopal
authors.initials: V
authors.lastname: Rajendiran
authors.forename: Mallayan
authors.initials: M
authors.lastname: Palaniandavar
authors.forename: Ramalingam
authors.initials: R
authors.lastname: Parthasarathi
authors.forename: Venkatesan
authors.initials: V
authors.lastname: Subramanian
mesh_terms: D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D008024:Ligands; D008163:Luminescent Measurements; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011119:Polynucleotides / Q000737:chemistry / Q000378:metabolism; D021281:Quantitative Structure-Activity Relationship; D017975:Ruthenium Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013056:Spectrophotometry, Ultraviolet
chemical_list: D008024:Ligands; D009930:Organic Chemicals; D009942:Organometallic Compounds; D011119:Polynucleotides; D017975:Ruthenium Compounds; C057718:6-(Dimethylamino)-2-((1E,3E)-4-(4-(dimethylamino)phenyl)-1,3-butadien-1-yl)-1-ethylquinolinium perchlorate; D004247:DNA