198 Topics in Current Chemistry Editorial Board: A. de Meijere KN ...

Directional Aspects of Intermolecular Interactions 39
searching for metal-binding sites in proteins. The method was used successfully
to locate two metal sites in the enzyme xylose isomerase from Streptomyces
rubiginosus [81]. One metal-binding site involves three carboxylates (aspartate
and glutamate), one histidine, and water, and the other involves four carboxylate
groups and water. This test is complementary to that suggested by David Eisenberg
and co-workers [82], in which the existence of hydrophilic areas in the protein
(negatively-charged oxygen atoms) with a hydrophobic area immediately
behind them (carbon atoms of the carboxylate group) are identified.
7
Networks of Interactions
When large molecules interact they recognize motifs containing appropriate
functional groups. These motifs may lie in one molecule or may be formed as
two or more aggregates. Therefore networks of interacting groups are of interest
in studies of binding of large molecules to each other. As a result the types of
interactions on a multimolecular scale are now being studied, having been
characterized as “supramolecular synthons”by Desiraju [83] (see also the article
by A. Nangia and G.R. Desiraju in this volume). Such synthons are structural
units that can be assembled by intermolecular interactions. Each of the types of
interactions described here can take part in such synthons. Some examples are
shown in Fig. 32. Major participants in supramolecular synthons are hydrogen
bonds and therefore they are discussed here. But any other types of intermolecular
interactions, such as metal coordination or C-S-C interactions, could be
involved.
Fig. 32. Descriptions of hydrogen-bonding networks [30, 84]. Shown are some examples with
their graph-set designations (R=ring, C=chain, S=intramolecular)