Experimental and theoretical study on DNA-binding and photocleavage properties of chiral complexes delta- and lambdal-[Ru(bpy)2L](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 - and -[Ru(bpy)2L](L =o-hpip, m-hpip and p-hpip) on the basis of reported - and [Ru(bpy)2(o-hpip)](-1 and -1), a series of novel enantiomerically pure polypyridyl ruthenium(II) complexes, - and -[Ru(bpy)2(m-hpip)](PF6)2(-2 and -2; bpy = 2,2-bipyridine, m-hpip = 2-(3-hydroxyphenyl)imidazo[4,5-f][1,10] phenanthroline), and - and -[Ru(bpy)2(p-hpip)](PF6)2(-3 and -3, p-hpip = 2-(4-hydroxyphenyl)imidazo[4,5-f][1,10] phenanthroline), have been synthesized and characterized by elemental analysis, 1H 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 isomer is stronger than that of -isomer, whereas that of -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 (× 10–4M) for -2, -2, -3 and -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 1MLCT transitions of [Ru(bpy)2L]2+ are presented, and applied to reasonably explain the obtained experimental regularities or trends in the DNAbinding strength or binding constants (Kb) and some spectral properties of the complexes.