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Supramolecular assemblies from other cases

A particular point of interest included in these hehcal complexes concerns the chirality. The heUcates obtained from the achiral strands are a racemic mixture of left- and right-handed double heUces (Fig. 34) (202). This special mode of recognition where homochiral supramolecular entities, as a consequence of homochiral self-recognition, result from racemic components is known as optical self-resolution (203). It appears in certain cases from racemic solutions or melts (spontaneous resolution) and is often quoted as one of the possible sources of optical resolution in the biological world. On the other hand, the more commonly found process of heterochiral self-recognition gives rise to a racemic supramolecular assembly of enantio pairs (204). [Pg.194]

The third section describes the hierarchy and supramolecular chirality of molecular assemblies in the crystalline state. The steroidal molecules construct hierarchical assemblies on the basis of sequential information, as in the case of proteins. The notable feature is that each hierarchical assembly exhibits supramolecular chirality, such as three-axial, tilt, helical, and bundle chirality. On the other hand, the primary ammonium salts construct hierarchical hydrogen bonding networks which, in some cases, create supramolecular chirality from achiral components. The creation of chirality can be interpreted from a topological viewpoint, leading us to define the handedness of the supramolecular chirality. At the end of this section we present the general concept that molecular-level information on organic substances can be expressed by their assemblies through non-covalent interactions. [Pg.224]

In the Languimir-Blodgett assemblies described by Shimomura (this volume, Chapter 11) the recognition between the substrate and the first layer, and between subsequently transferred layers, represents the supramolecular component. A chemical reaction can in some cases occur between the monolayer and the substrate. In other cases a phase change from a two-dimensional liquid crystalline phase on the water surface to a crystalline phase over the substrate may occur [160,161]. The engineered growth is instead controlled by the applied deposition pressure, the type of deposition (Y-, Z-, and X-type), and by the number of transferred layers [160]. Variations in the orientation of consecutive layers may also be obtained [162]. [Pg.52]

Models with increasing sophistication for the analysis of dynamic processes in supramolecular systems, notably micelles, as well as for the determination of other parameters have been developed over the past two decades. The basic conceptual framework has been described early on [59,60,95,96] and has been classifred into different cases which take into account the extent of quencher mobility and the mechanism of quenching [95]. Two of those cases lead to information about mobility and will be discussed. It is important to emphasize that this analysis is only applicable to self-assembled system such as micelles and vesicles it cannot be applied to host-guest complexes. This model assumes that the probe is exclusively bound to the supramolecular system and that no probe migration occurs during its excited state lifetime. The distribution of probe and quencher has been modeled by different statistical distributions, but in most cases, data are consistent with a Poisson distribution. The Poisson distribution implies that the quencher association/dissociation rate constants to/from the supramolecular system does not depend on how many... [Pg.405]


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Other cases

Supramolecular assemblies from

Supramolecular assembling

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