Crystal specific interactions

To understand how chirality is expressed, it is important to first describe the different thermotropic mesophase assemblies which can be formed by chiral discotics. Even though expression of chirality has been observed in thermotropic mesophases, the chiral expression occurs in a rather uncontrolled manner, and systems which are suitable for applications, for example, easily switchable columns/ferroelectric discotic liquid crystals, consequently have not yet been developed. Hence, the assembly of discotics in solution has received considerable attention. Supramolecular assemblies of discotic molecules in solution are still in their infancy and have not yet found commercial application, but they are of fundamental importance since they allow a detailed and focused investigation of the specific interactions that are required to express chirality at higher levels of organization. As such, the fundamental knowledge acquired from supramolecular assemblies in solution might formulate the design criteria for thermotropic chiral discotic mesophases and provide the necessary tools for the creation of functional systems. 

Note 1 The essential feature of a lyotropic liquid crystal is the formation of molecular aggregates or micelles as a result of specific interactions involving the molecules of the amphiphilic mesogen and those of the solvent. 

Anils. A large number of anils have been reported to be photo-chromic in the solid state as typified by salicylidene-2-chloroaniline shown in Figure 4 (21). Early explanations for the mechanism of photo-chromism in the anils involved aggregation and crystal lattice interactions (22-26). However, recent investigations by Cohen et al. (21,27,28) show that isolated molecules in glassy solutions also exhibit photochromic activity, thus ruling out such specific solid-state interactions as prerequisite to photochromism. 

It is interesting that the PEMA-PVdF blends are amorphous up to at least 50 wt % PVdF even though the Tg of the latter is 24°C. The crystallization of PVdF observed in the analogous PMMA blend does not occur under the same conditions with PEMA—PVdF. This suggests that there is a specific interaction between the fluoropolymer and the methacrylate polymer which is sufficient to "dissolve PVdF in the PMMA and PEMA, and that this specific interaction is superimposed on the conventional diluent-crystalline polymer interactions. The complexity of the rate processes involved with high molecular weight systems arising from molecular mobility makes it impossible to elucidate the nature of... 

Since the discovery of crown ethers, cryptands, and other macrocyclic ligands by Cram, Lehn, and Pedersen, who were awarded the 1987 Nobel Prize in chemistry for their development and use of molecules with structure-specific interactions of high selectivity [1], a completely new research field was opened supramolecular chemistry [2-4-]. Since then, this research field has been extended in many fields such as molecular recognition, organic sensing, and liquid crystals. 

The cholesterol-lowering properties of dietary plant sterols have been known for decades (Best et al., 1954 Peterson, 1951 Poliak, 1953), due specifically to reductions in cholesterol absorption. Inverse correlations between plant sterol intake and cholesterol absorption have been reported in animals (Carr et al., 2002 Ntanios and Jones, 1999) and humans (Ellegard et al., 2000). The exact mechanism by which plant sterols inhibit cholesterol absorption is unclear, and several mechanisms of action have been proposed, including (1) competition with cholesterol for solubilization in micelles within the intestinal lumen, (2) cocrystallization with cholesterol to form insoluble crystals, (3) interaction with digestive enzymes, and (4) regulation of intestinal transporters of cholesterol. 

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