Figure 1.

(a) Left, side-by-side, head-to-tail co-operative interaction between distamycin molecules in the 2:1 complex; right, co-operative head-to-head interaction between H33258 molecules in the minor groove of the 2:1 complex described here. (b) Selection of NOEs observed from non-exchangeable protons that define the position of H33258 within the minor groove. (c) Direct and solvent-mediated hydrogen bonding interactions with the floor of the minor groove (adenine N₃ and thymine O₂; w, water). Mean distances and standard deviations are given in Table 1.