Molecular assembly, aggregate structure

Recently, Okuyama et al. succeeded to prepare single crystals of some azobenzene amphiphiles and decided molecular and aggregation structure of single crystals [14-19], The spectral prediction of the chromophore orientation in the bilayer assemblies were very consistent with the X-ray structural analyses of the single crystals. 

In biological systems molecular assemblies connected by non-covalent interactions are as common as biopolymers. Examples arc protein and DNA helices, enzyme-substrate and multienzyme complexes, bilayer lipid membranes (BLMs), and aggregates of biopolymers forming various aqueous gels, e.g, the eye lens. About 50% of the organic substances in humans are accounted for by the membrane structures of cells, which constitute the medium for the vast majority of biochemical reactions. Evidently organic synthesis should also develop tools to mimic the Structure and propertiesof biopolymer, biomembrane, and gel structures in aqueous media. 

Irrespective of the experiment to be done, sample preparation contains a number of necessary conditions. First, aggregation must be prevented if one wants to investigate structure and conformation of single molecules. Second, the adsorption process must be reversible, or at least, very slow in order to approach the equilibrium state and allow statistical analysis of the molecular assembly. Third, adhesion of the molecules to the substrate must be strong enough to sustain the mechanical and adhesive interactions with the tip. However, it should be relatively low to prevent the native structure from deformation. 

Nanoscale assembly Self-assembling micellar structures [113,114] Bio-self-assembly and aggregation [115,116] Nanomanipulation [117,118] Soft lithography [119,120] Molecular imprinting [121,122] Layer-by-layer electrostatic deposition [123,124] Chemical vapor deposition [125]... 

Aqueous molecular assemblies such as micelles and bilayer membranes are formed by the self-assembly of amphiphihc compounds (Figure 11.la, b) [10]. Aqueous micelles have been utihzed for a variety of apphcations in surfactant industry, including emulsification, washing, and extraction processes [11]. BUayer membranes are basic structural components of biomembranes, and their structures are maintained even in dilute aqueous media. This is in contrast to micelles that show dynamic equihbrium between aggregates and monomeric species. Thus bilayers are more stable and sophisticated self-assemblies, and they require suitable molecular design of the constituent amphiphiles. BUayer membranes and vesicles have wide-ranging applications, as exemphfied by drug dehvery [12], sensors [13], and bilayer-templated material synthesis [14]. 

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