Comparison of the Binding Modes of [Ru(2,2′-bipyridine)3]2+ and [Ru(2,2′:6′,2"-terpyridine)2]2+ to Native DNA

The [Ru(tpy)(2)]Cl-2 (tpy:2,2':6',2 ''-terpyridine) complex was synthesized and its structure was confirmed by H-1-NMR and elemental analysis. Its binding mode toward DNA was compared with the well-known [Ru(bpy)(3)]Cl-2 (bpy:2,2-bipyridyl), using isotropic absorption, linear dichroism(LD) spectroscopy, and an energy minimization study. Compared to [Ru (bpy)(3)](2+), the [Ru(tpy)(2)](2+) complex exhibited very little change in its absorption pattern, especially in the MLCT band, upon binding to DNA. Furthermore, upon DNA binding, both Ru(II) complexes induced a decrease in the LD magnitude in the DNA absorption region. The [Ru(tpy)(2)](2+) complex produced a strong positive LD signal in the ligand absorption region, which is in contrast with the [Ru(bpy)(3)](2+) complex. Observed spectral properties led to the conclusion that the interaction between the ligands and DNA bases is negligible for the [Ru(tpy)(3)](2+) complex, although it formed an adduct with DNA. This conclusion implies that both complexes bind to the surface of DNA, most likely to negatively charged phosphate groups via a simple electrostatic interaction, thereby orienting to exhibit the LD signal. The energy minimization calculation also supported this conclusion.