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

Supramolecular Synthons and Pattern Recognition 75
cular structures result from the information stored in the components and the
interactions between them. The supramolecular aggregates generated by selfassembly
principles are good examples of nanostructures. The goal of nanochemistry
is to evolve design strategies to express a desired property or function
in a material of a given structure [43, 44].
In this context, the zigzag array of DAD:ADA hydrogen bonds in the solid
state was examined by Lehn and co-workers in the 1:1 complex 39 of 3-butyl-
2,4,6-triaminopyrimidine and 5,5-diethylbarbituric acid [45]. Each component
forms six hydrogen bonds with its two complementary neighbours as illustrated
in Scheme 9. The consequence of such a pattern of hydrogen bonds is that all
pyrimidines are located on one side of the strand and all the barbituric acids on
the other. Such an ordered and oriented arrangement of molecules in the crystal
offers the opportunity for inducing specific NLO, electronic, ionic and magnetic
properties (For more examples of H-bonded tapes and similar motifs, see the
article by R.E. Meléndez and A.D. Hamilton in this volume).
The triply hydrogen bonded motifs discussed in the context of biomacromolecules
and materials have been constructed purely with N-H◊◊◊O and
N-H◊◊◊N hydrogen bonds. Notwithstanding the pivotal role of strong hydrogen
bonds in biological systems and supramolecular structures, the contribution of
weak hydrogen bonds and interactions should not be underestimated [46–48].
This is because weak interactions have more gradual distance fall-off characteristics
and are operative at much longer intermolecular distances. Early recognition
events between molecules could be influenced by the soft and polarisable
weak interactions at long distances. Although much weaker (