Small Molecule-based Multi-step Self-assembly

Small Molecule-based Multi-step Self-assembly 

The self-assembly of small molecules into complex material based on a multitude of different noncovalent interactions, such as hydrogen bonding, ionic interactions, hydrophobicity and metal coordination, has been established over the last century [2, 30, 38, 44-49]. In this context, the real power of self-assembly becomes evident when not only multiple noncovalent interactions but also multiple levels of self-assembly occur within the same small molecule system. These multiple tiers of self-organizational hierarchy can yield highly complex structures with sec- 

In this case, the authors started their material development with small hydro-gen-bonding units based on DNA base pairs that have been reported previously to self-assemble into cyclic structures [51]. By functionalizing these hydrogenbonding units with an amino acid moiety, they imparted to the self-assembled cyclic structure (a) chirality and (b) a highly polar outer portion. 

There are a great many methods by which small molecules can be assembled to form nanotubes and other similar columnar aggregates [50]. Unlike the stacked disc methodology employed by Fenniri s group, Russell and co-workers took a completely different approach, which consisted of nanotubes made by way of rolled-up bilayers [48], Their study of biocidal nanotubes from a self-assembled diacetylene salt employed a hydrophobically driven bilayer type of self-assembly step. This bilayer formation was based on the alignment of the hydrophobic chains, including aligned Ji-systems of the acetylenes on the interior of the bilayer and the polar hydrobromide salts of an amine on the exterior of the bilayer (Fig. 7.6). 

Small molecules can undergo self-organization into a wide variety of orientations besides nanotubes. For example, in 2003, Percec designed a system of self-assembled dendritic benzamides based on methyl gallate and trimethoxyben-zene that exhibited a liquid crystalline phase both as monomers and as polymers (Fig. 7.7) [52], 

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Small Molecule-based Multi-step Self-assembly I 265... 

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