Experimental and theoretical study on DNA-binding and photocleavage properties of chiral complexes Delta- and Lambda-[Ru(bpy)(2)L] (L = o-hpip, m-hpip and p-hpip)

In order to systematically perform an experimental and theoretical study on DNA-binding and photocleavage properties of chiral complexes Delta- and Lambda-[Ru(bpy)(2)L] (L = o-hpip, m-hpip and p-hpip) on the basis of reported Delta- and Lambda-[Ru(bpy)(2)(o-hpip)] (Delta-1 and Lambda-1), a series of novel enantiomerically pure polypyridyl ruthenium(II) complexes, Delta- and Lambda-[Ru(bpy)(2)(m-hpip)](PF6)(2) ( Delta-2 and Lambda-2; bpy = 2,2'-bipyridine, m-hpip = 2-(3-hydroxyphenyl)imidazo[ 4,5-f][1,10] phenanthroline), and Delta- and Lambda-[Ru(bpy)(2)(p-hpip)](PF6)(2) (Delta-3 and Lambda-3, p-hpip = 2-(4-hydroxyphenyl)imidazo[ 4,5-f][1,10] phenanthroline), have been synthesized and characterized by elemental analysis, H-1 NMR, ESI-MS and CD spectra. The DNA-binding properties of these complexes have been investigated with UV-Vis, emission spectra, CD spectra and viscosity measurements. It is experimentally found that ( 1) both complexes [Ru(bpy)(2)(m-hpip)](2+) 2 and [Ru(bpy)(2)(p-hpip)](2+) 3 can bind to DNA with intercalation; (2) for complexes 2 and 3, a subtle but detectable difference was observed in the interaction of these isomers with CT-DNA. The DNA-binding of the Delta-isomer is stronger than that of Lambda-isomer, whereas that of Lambda-isomer is swifter. (3) Under irradiation with UV light, Ru(II) complexes 2 and 3 can promote almost complete conversion of pBR322 DNA from form I to form II at concentrations of 0.5, 1.0, 0.5, 1.0 ( x 10(-4)M) for Delta-2, Lambda-2, Lambda-3 and Lambda-3, respectively. On the other hand, theoretical calculations for these three isomer complexes have been carried out applying the density functional theory (DFT) method on the level of the B3LYP/LanL2DZ basis set. Some frontier molecular orbital energies and stereographs, as well as a schematic diagram of the energies and related (MLCT)-M-1 transitions of [Ru(bpy)(2)L](2+) are presented, and applied to reasonably explain the obtained experimental regularities or trends in the DNA-binding strength or binding constants (K-b) and some spectral properties of the complexes.