Figure 5.

Hydration and MPD binding within the minor groove of 2′-O-Me(CGCGCG)₂ in its P3₂12 form. A single row of seven water molecules spans both duplex strands: each water bridges, by donating a pair of hydrogen bonds, either to two self-parallel cytosines or two self-parallel guanines. Two MPD molecules intrude into the minor groove. For each MPD molecule the oxygen of its secondary hydroxyl group is the hydrogen bond acceptor from the exo-NH₂ group of the G2A (MPD1) or G2B (MPD2) guanine residue (A). ‘Omit’ (F_o – F_c) maps, contoured at the 3 r.m.s. level, are shown for the two MPD molecules (B and C). The maps were calculated after omitting MPD from the model and 10 cycles of least squares minimisation.