Interaction of Λ- and Δ-[Ru(bpy)2(pbmz)](PF6)2 with the oligonucleotide duplex d(CGCGAATTCGCG)2

The interaction of the enantiomeric complexes Λ- and Δ-[Ru(bpy)2(pbmz)](PF6)2 (bpy = 2,2′-bipyridine, pbmz = 2-(2′-pyridyl)benzimidazole) with the DNA duplex d(CGCGAATTCGCG)2 was investigated by means of 2D NMR techniques. The synthesis of the enantiomers was based on the optically pure complexes Λ- and Δ-[Ru(bpy)2(py)2]2+ and were characterized by CD and NMR spectroscopy. NMR data indicate that both enantiomers bind weakly to the oligonucleotide, approaching from the minor groove at the centre of the helix. The perturbation of the B-DNA conformation is minor with an apparent absence of enantioselectivity. Molecular modelling calculations in conjunction with the NOE data support the suggestion that more than one binding modes are present. The imidazole amine group of the pbmz ligand is probably hydrogen bonded to the DNA phosphodiesteric backbone at the AATT step, and this may provide an explanation for the diminished enantioselectivity observed.