Section 22.4.5.6. Intermolecular motif formation in small-molecule crystal structures

Desiraju (1995) has stressed that the design process in crystal engineering depends crucially on the high probabilities of formation of certain well known intermolecular motifs, e.g. the hydrogen-bonded dimer frequently formed by pairs of carboxylate groups. By analogy with molecular synthesis, he describes these general non-covalent motifs (which often contain strong hydrogen bonds) as supramolecular synthons , and points to their importance in supramolecular chemistry as a whole (see e.g. Lehn, 1988; Whitesides et al., 1995). Since protein–protein and protein–ligand interactions are also supramolecular phenomena, it follows that information about common interaction motifs is also of importance in structural biology. A computer program is now being written at the CCDC to establish the topologies, chemical constitutions and probabilities of formation of intermolecular motifs directly from the CSD. Initial results (Allen, Raithby et al., 1998; Allen et al., 1999) provide statistics for the most common cyclic hydrogen-bonded motifs, and it is likely that motif information will be included in the developing IsoStar knowledge-based library described in Section 22.4.5.8.