Page 98 - Science at the nanoscale

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June 12, 2009
From Atoms and Molecules to Nanoscale Materials
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and the rigidity needed of the complex structures. This brings
us to the fascinating research field of supramolecules and self-
assembly processes.
Supramolecules
4.4.2
Historically, chemists started off by developing synthetic method-
ologies that form strong bonding such as the C–C, C–O, etc.
covalent bonds. In supramolecular synthesis, attention is focused
on the weaker and reversible non-covalent interactions such as hy-
drogen bonding, van der Waals forces, π–π interaction, metal co-
ordination, etc. These syntheses require careful design of the mo-
tif (molecules or segments of a molecule) such that it contains the
necessary functionalities that will allow it to integrate to form a
more complex structure. A simple illustration is given in Fig. 4.27.
Here, the –NHC=O motif is incorporated in the molecule A to
act as both hydrogen-bond donor and acceptor. Two A molecules
form a cyclic aggregate spontaneously. On the other hand, an in-
correctly “coded” molecule B will not lead to the ring formation.
One of the key concepts in supramolecular chemistry is self-
assembly, whereby molecules or segments of molecules integrate
C
C
N
N
O
H
O
H
A
C C O N H C B C H N O ch04
N
N
O
H O H
H
H O
O
N N
C C
Figure 4.27. Illustration of the –NHC=O motif encoded in molecule A to
form a cyclic assembly, whereas wrongly coded molecule B will not. 11
11 Y. Ducharme and J. D. Wuest, J. Org. Chem. 53, 5787–5789 (1988).