Abstract
The <TEX>$[Ru(tpy)_2]Cl_2$</TEX> (tpy:2,2':6',2"-terpyridine) complex was synthesized and its structure was confirmed by <TEX>$^1H$</TEX>-NMR and elemental analysis. Its binding mode toward DNA was compared with the well-known <TEX>$[Ru(bpy)_3]Cl_2$</TEX> (bpy:2,2-bipyridyl), using isotropic absorption, linear dichroism(LD) spectroscopy, and an energy minimization study. Compared to <TEX>$[Ru(bpy)_3]^{2+}$</TEX>, the <TEX>$[Ru(tpy)_2]^{2+}$</TEX> 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 <TEX>$[Ru(tpy)_2]^{2+}$</TEX> complex produced a strong positive LD signal in the ligand absorption region, which is in contrast with the <TEX>$[Ru(bpy)_3]^{2+}$</TEX> complex. Observed spectral properties led to the conclusion that the interaction between the ligands and DNA bases is negligible for the <TEX>$[Ru(tpy)_2]^{2+}$</TEX> 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.
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