Figure 4.

Anomalous difference map (contoured at 6.0 σ above mean level) showing inner-sphere binding of a cobalt tetrammine cation to N7 of a guanine and to the phosphate of a bulged-out adenine in the subtype-A DIS duplex. Distances between the cation and RNA ligands lie within 1.9–2.4 Å. This implies that two amines from the hexammine shell were displaced.