Self small molecule-based

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

In a system based largely on self-assembly through mesogenic interactions such as the above example by Percec, it can also be beneficial to incorporate hydrogen bonding as well for an added element of organizational control. For instance, Frechet and coworkers demonstrated sequential, hierarchical self-assembly of various levels of order in a small molecule-based system which ultimately resulted in a hydrogen-bonded liquid crystalline network (Fig. 7.9) [53]. 

Yang Z, Xu B. Supramolecular hydrogels based on biofunctional nanofibers of self-assembled small molecules. J Mater Chem 2007 17 2385-2393. 

Surfactants at Interfaces. Somewhat surprisingly, the successes described above in the in-situ studies of protein adsorption have not inspired extensive applications to the study of the adsorption of surfactants. The common materials used in the fabrication of IREs, thalliumbromoiodide, zinc selenide, germanium and silicon do, in fact, offer quite a range in adsorption substrate properties, and the potential of employing a thin layer of a substance as a modifier of the IRE surface which is presented to a surfactant solution has also been examined in the studies of proteins. Based on the appearance of the studies described below, and recent concerns about the kinetics of formation of self-assembled layers, (108) it seems likely that in-situ ATR studies of small molecules at solid - liquid interfaces ("wet" solids), will continue to expand in scope. 

While technically simpler than the covalent approach, the self-assembly approach creates more heterogeneous sites and also requires templates with specific functional groups.8 Since sol-gel chemistry is aqueous based, H-bonding interactions are significantly weaker compared to the conventional organic polymerization methods. Often, hydrophobic effects and ionic interactions are utilized. A number of other examples of the noncovalent approach to imprinting in sol-gel-derived materials are provided in recent reviews.5 17 In the sections below, the focus will be on some of the newer aspects of small molecule imprinting in silica that involve the use of chiral templates... 

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-... 

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],... 

The independent, noninteracting behaviors of these two modes of self-assembly allowed for the creation of a self-assembled, multifunctional, reversible, cross-linked material in one self-assembly step. This simultaneous self-assembly strategy, based on the results outlined above, allows the creation of a fully functionalized, cross-linked systems. Simultaneous addition of a small metal-complexing molecule such as pyridine, along with a hydrogen-bonding cross-linker such as... 

The diffusion of small molecules in rubbers is of both theoretical and practical importance. The theories of diffusion based on consideration of free volume can be tested by measurement of self-diffusion using methods such as pulsed field gradient NMR. Selfdiffusion of small molecules must be understood for applications of rubbers as seals in contact with solvents, and for example for diffusion of plasticisers and other small molecules. 

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