SPECTROSCOPIC INVESTIGATION OF DIFFERENTIAL BINDING MODES OF DELTA-RU(BPY)2(PPZ)2+ AND LAMBDA-RU(BPY)2(PPZ)2+ WITH CALF THYMUS DNA

The binding of enantiomers of Ru(bpy)2(ppz)2+ (bpy = 2,2'-bipyridine; ppz = 4,7-phenanthrolino[6,5-b]-pyrazine) to calf thymus DNA is investigated using absorption, fluorescence and resonance enhanced Raman spectroscopies. Both isomers show absorption hypochromicity, steady-state fluorescence increase, reduced accessibility to an anionic quencher, and fluorescence lifetime increase associated with binding to B-form DNA, though the effect for the LAMBDA isomer is always less. However, the maximal fluorescence polarization for both isomers is the same, indicating a similarly rigid binding to DNA. These findings are consistent with a major groove binding in which the ppz ligand is partially intercalated for both enantiomers. The bpy ligands are relatively small and not competent for inducing intercalative binding, but enantioselectivity is maintained by the differential interactions of these bpy ligands with the surface of the major groove as the ppz ligand partially intercalates.