Mixed-ligand complexes of ruthenium(II) containing new photoactive or electroactive ligands: synthesis, spectral characterization and DNA interactions |
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| Authors: | Tamal Ghosh Bhaskar G Maiya Anunay Samanta Atindra D Shukla D Amilan Jose D Krishna Kumar Amitava Das |
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| Institution: | (1) School of Chemistry, University of Hyderabad, Hyderabad, 500 046, India;(2) Central Salt and Marine Chemicals Research Institute, Bhavnagar, 364002, India |
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| Abstract: | 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, 1H 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→π*sq) transitions. The other three ruthenium(II) complexes containing three photoactive ligands, mppne, mppae and mpppe, exhibit MLCT (d
Ru→π*bpy ) bands in the 454–461-nm region and are diamagnetic. These can be characterized by the 1H NMR method. Ru(bpy)2(mppne)]2+, Ru(bpy)2(mppae)]2+ and Ru(bpy)2(mpppe)]2+ exhibit redox waves corresponding to the RuIII/RuII couple along with the expected ligand (bpy and substituted bpy) based ones in their cyclic and differential pulse voltammograms (CH3CN, 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 105 to 106 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.Electronic Supplementary Material Supplementary material is available for this article at . |
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| Keywords: | Ru(II) complexes DNA binding DNA photocleavage Oxidation of sugar unit in DNA Semiquinone |
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