Interaction of rac-[Ru(5,6-dmp)₃]²⁺ with DNA:  Enantiospecific DNA Binding and Ligand-Promoted Exciton Coupling

Abstract

The X-ray crystal structure of the complex rac-[Ru(5,6-dmp)(3)]Cl(2) (5,6-dmp = 5,6-dimethyl-1,10-phenanthroline) reveals a distorted octahedral coordination geometry with the Ru-N bond distances shorter than in its phen analogue. Absorption spectral titrations with CT DNA reveal that rac-[Ru(5,6-dmp)(3)](2+) interacts (K(b), (8.0 +/- 0.2) x 10(4) M(-1)) much more strongly than its phen analogue. The emission intensity of the 5,6-dmp complex is dramatically enhanced on binding to DNA, which is higher than that of the phen analogue. Also, interestingly, time-resolved emission measurements on the DNA-bound complex shows biexponential decay of the excited states with the lifetimes of short- and long-lived components being higher than those for the phen analogue. The CD spectral studies of rac-[Ru(5,6-dmp)(3)](2+) bound to CT DNA provide a definite and elegant evidence for the enantiospecific interaction of the complex with B-form DNA. Competitive DNA binding studies using rac-[Ru(phen)(3)](2+) provide support for the strong binding of the complex with DNA. The Delta-enantiomer of rac-[Ru(5,6-dmp)(3)](2+) binds specifically to the right-handed B-form of poly d(GC)(12) at lower ionic strength (0.05 M NaCl), and the Lambda-enantiomer binds specifically to the left-handed Z-form of poly d(GC)(12) generated by treating the B-form with 5 M NaCl. The strong electronic coupling of the DNA-bound complex with the unbound complex facilitates the change in its enantiospecificity upon changing the conformation of DNA. The (1)H NMR spectra of rac-[Ru(5,6-dmp)(3)](2+) bound to poly d(GC)(12) reveal that the complex closely interacts most possibly in the major grooves of DNA. Electrochemical studies using ITO electrode show that the 5,6-dmp complex stabilizes CT DNA from electrocatalytic oxidation of its guanine base more than the phen analogue does.

DNA binding and cleavage properties of certain tetrammine ruthenium(II) complexes of modified 1,10-phenanthrolines – effect of hydrogen-bonding on DNA-binding affinity

“…The values of the binding constants (K b ) obtained ( [43]. Interestingly, it is much higher than that reported for [Ru(phen) 3 ] 2þ (K b , 5.5 Â 10 3 M À1 ) [44] and particularly, [Ru(NH 3 ) 4 (phen)] 2þ (K b , 2.0 Â 10 3 M À1 ) [31]. It appears that, as in the DNA binding model proposed for [Ru(dip) 3 ] 2þ [45], one of the skewed phenyl groups on the non-planar dip ligand in [Ru(NH 3 ) 4 (dip)] 2þ is completely inserted and stacked between the DNA base pairs effectively, which is supported by the non-intercalating phenyl group involved in hydrophobic nonstacking interaction, leading to a stronger DNA binding of the complex.…”

“…The dip complex shows a binding site size of 0.48 base pairs, which is higher than that of the phen complex (0.20) [31], indicating the non-classical docking of the dip ligand on the double stranded DNA. The ip, pip and hpip complexes also show similar binding site sizes ($0.41 base pairs), suggesting their involvement in a similar intercalative mode of DNA binding.…”

“…The lower intensity of the MLCT bands for this family of complexes is expected of the interactions of coordinated NH 3 ligands with solvent molecules [38]. The energies of the MLCT transitions exhibit decreased solvatochromism compared to the methyl substituted phenanthroline complexes [30,31]. The electron withdrawing character of the extended aromatic diimine ligands pull electrons from the N-H bond of NH 3 and render the complexes less susceptible to solvents, as in the case of [Ru(NH 3 ) 4 (dppz)] 2þ [30].…”

DNA-binding studies of complex of Pt(bpy)(pip)]2+ and [Pt(bpy)(hpip)]2+ by electrochemical methods: development of an electrochemical DNA biosensor

“…Over the last two decades, there have been growing interest in synthesizing the transition metal complexes [7], like ruthenium(II) [8,9], rhodium(II), copper(II) [1,10,11] or cobalt(III) [12], Os(II) [13,14], Ni(II) [5,15], Mg(II) [10] and Fe(II) [16] in order to investigate binding properties of above-mentioned metal complexes to DNA and for the Electronic supplementary material The online version of this article (doi:10.1007/s10008-015-2859-y) contains supplementary material, which is available to authorized users. construction of spectroscopic or electrochemical DNA biosensors, based on the immobilization of oligonucleotide on an electrode surface.…”

A novel DNA light switch [Ru(bpy)2pzip]2+ activated by cobalt(II) ion

“…[1][2][3]. In particular, Ru(II) complexes with polypyridine ligands, due to a combination of easily constructed rigid chiral structures spanning all three dimensions and a rich photophysical repertoire, have attracted considerable attention [2][3][4][5][6][7][8][9][10][11]. As is well known, [Ru(bpy) 2 -(dppz)] 2+ (dppz = dipyrido-[3,2-a:2 0 ,3 0 -c]phenazine) is the most extensively investigated complex as molecular ''light switch" for DNA, because the complex shows no photoluminescence in aqueous solution at ambient temperature but displays strong photoluminescence in DNA solution [12].…”