NMR evidence for specific intercalation of .DELTA.-rh(phen)2.phi.3+ in [d(GTCGAC)2]

The anchoring of metal complexes in the major groove of DNA through intercalation has been increasingly useful in the shape-selective design of novel metal complexes which bind DNA with high sequence-selectivity. Toward that goal, direct structural information regarding this intercalative interaction is essential. Phenanthrenequinone diimine (phi) complexes of Rh(III) bind avidly (K_b 1 ≥ 10^7) to DNA by intercalation in the major groove. Here we report the first ^1H-NMR studies of Δ-rh(phen)_2phi^(3+) bound to an oligonucleotide. These studies provide direct structural evidence for specific intercalation by this octahedral complex in the major groove of DNA.