Figure 4.

Hydration of the 2′-O-Me(CGCGCG)₂ duplex in the P3₂12 form within the major groove. Atoms lying in the further perspective are omitted for clarity (A). The pattern of fused 5- and 6-membered rings seen in the P6₁22 crystal (33) is observed. The (3F_o – 2F_c) electron density is shown for magnesium ions MG4 (B) and MG5 (of a second strand) (B), together with their three coordinating ordered water molecules; two of them are hydrogen bonded to N⁷ and O⁶ of guanine and the third to N⁴ of cytosine. The hydration pattern is disrupted near the 5′-ends by electron density [blue contours, (3F_o – 2F_c) map at 1 r.m.s. level], probably corresponding to partially disordered MPD.