DNA binding of Lambda- and Delta-cis-beta-[Ru(RR-picchxn)(phen)](2+) studied by NMR and flow linear dichroism spectroscopy

Two novel substitutionally-inert diastereomeric ruthenium(II) cations of th e form Lambda- and Delta-cis-beta-[Ru(RR-picchxn)(phen)](2+), where RR-picc hxn is N,N'-dimethyl-N,N'-di(2-picolyl)-IR,2R-diaminocyclohexane and phen i s 1,10-phenanthroline, have been studied with respect to their interactions with duplex DNA. NMR investigations show that both diastereomers bind to t he oligonucleotide [d(CGCGATCGCG)](2) in the fast exchange regime and that binding predominantly takes place in the minor groove of the oligonucleotid e, but that the governing interactions are significantly different for the two Delta and Lambda forms. Linear dichroism data support the latter interp retation, in that the relative orientations of cis-beta-[Ru(RR-picchxn)(phe n)](2+) to calf thymus DNA also are observed to differ for the Delta and La mbda diastereomers. Interpretation of these data indicates the Lambda form to be bound with the planar phen ligand closely parallel to the DNA base-pa irs, but the average orientation of the phen ligand in the Delta form devia tes significantly from a parallel alignment.