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

12 J.P. Glusker
lographic structure determinations in order to derive analytical expressions (in
the same manner that analytical expressions were derived for PAHs), and these
types of studies are still underway [12, 13]. The force fields so derived are used
to predict how, for example, drugs bind to biological macromolecules [13,
15–17].
4.2
Nucleophile and Electrophile Interactions with Sulfur and Halogen Atoms
Surroundings of covalently bound sulfur atoms in crystal structures provide an
excellent example of the directionality of intermolecular interactions. Directional
preferences of binding around divalent sulfur bonded to two other atoms
(XSY where X and Y are commonly carbon) were studied in a wide variety of
crystal structures. This was one of the early analyses of intermolecular interactions
in crystal structures, before the CSD was generally available [18]. The
analysis was made on nonbonded contacts, up to 4.2 Å from the sulfur atoms; it
showed, as indicated in Fig. 5, that the locations of functional groups around the
CSC group depend on their (partial) charges.
a
b
Fig. 5 a – c. Directional preferences of binding of X-S-Y groups: a diagram of the directions in
which charged groups approach the sulfur atom; b chemical formula of mesolanthionine
dihydrochloride