Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions.
Mixed-ligand ruthenium(II) complexes of three photoactive ligands, viz., (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-naphthyl)-1-ethene (mppne), (E)-1-(9-anthryl)-2-[2-(4-methyl-2-pyridyl)-4-pyridyl]-1-ethene (mppae) and (E)-1-[2-(4-methyl-2-pyridyl)-4-pyridyl]-2-(1-pyrenyl)-1-ethene (mpppe), in which a 2,2'-bipyridyl unit is linked via an ethylinic linkage to either a naphthalene, an anthracene or a pyrene chromophore and three electroactive ligands, viz., 4-(4-pyridyl)-1,2-benzenediol (catpy), 5,6-dihydroxy-1,10-phenanthroline (catphen) and 1,2-benzenediol (cat), were synthesized in good to moderate yields. Complexes [Ru(bpy)(2)(mppne)](2+) (bpy is 2, 2'-bipyridyl), [Ru(bpy)(2)(mppae)](2+), [Ru(bpy)(2)(mpppe)](2+), [Ru(bpy)(2)(sq-py)](+), [Ru(bpy)(2)(sq-phen)](+) and [Ru(phen)(2)(bsq)](+) (phen is 1,10-phenanthroline) were fully characterized by elemental analysis, IR, (1)H NMR, fast-atom bombardment or electron-impact mass, UV-vis and cyclic voltammetric methods. In the latter three complexes, the ligands catpy, catphen and cat are actually bound to the metal center as the corresponding semiquinone species, viz., 4-(4-pyridyl)-1,2-benzenedioleto(+I) (sq-py), 1,10-phenanthroline-5,6-dioleto(+I) (sq-phen) and 1,2-benzenedioleto(+I) (bsq), thus making the overall charge of the complexes formally equal to + 1 in each case. These three complexes are electron paramagnetic resonance active and exhibit an intense absorption band between 941 and 958 nm owing to metal-to-ligand charge transfer (MLCT, d (Ru)-->pi*(sq)) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d (Ru)-->pi*(bpy) ) bands in the 454-461-nm region and are diamagnetic. These can be characterized by the (1)H NMR method. [Ru(bpy)(2)(mppne)](2+), [Ru(bpy)(2)(mppae)](2+) and [Ru(bpy)(2)(mpppe)](2+) exhibit redox waves corresponding to the Ru(III)/Ru(II) couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH(3)CN, 0.1 M tetrabutylammonium hexafluorophosphate)-corresponding voltammograms of [Ru(bpy)(2)(sq-py)](+), [Ru(bpy)(2)(sq-phen)](+) and [Ru(phen)(2)(bsq)](+) are mainly characterized by waves corresponding to the quinone/semiquinone (q/sq) and semiquinone/1,2-diol (sq/cat) redox processes. The results of absorption and fluorescence titration as well as thermal denaturation studies reveal that [Ru(bpy)(2)(mppne)](2+) and [Ru(bpy)(2)(mppae)](2+) are moderate-to-strong binders of calf thymus DNA with binding constants ranging from 10(5) to 10(6) M(-1). Under the identical conditions of drug and light dose, the DNA (supercoiled pBR 322) photocleavage activities of these two complexes follow the order:[Ru(bpy)(2)(mppne)](2+)>[Ru(bpy)(2)(mppae)](2+), although the emission quantum yields follow the reverse order. The other ruthenium(II) complexes containing the semiquinone-based ligands are found to be nonluminescent and inefficient photocleavage agents of DNA. However, experiments shows that [Ru(bpy)(2)(sq)](+)-based complexes oxidize the sugar unit and could be used as mild oxidants for the sugar moiety of DNA. Possible explanations for these observations are presented.
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
Tamal
T
Ghosh
Bhaskar G
BG
Maiya
Anunay
A
Samanta
Atindra D
AD
Shukla
D Amilan
DA
Jose
D Krishna
DK
Kumar
Amitava
A
Das
D004247:DNA / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D017975:Ruthenium Compounds / Q000737:chemistry*
D017975:Ruthenium Compounds; D004247:DNA