Chiral fiber

J.-M. Lehn et al. designed helical architectures via the pre-programming of molecular self-assembly through specific non-bonding interactions [116, 117]. The formation of chiral fiber-like architectures had been also observed from non-chiral monomers such as in the gels of bis-urea building blocks [118]. 

Chiral substituents, e.g., open-chain carbohydrates, induce the formation of chiral fibers, and strong CD effects become observable. Similar to the salts of hydroxy-stearic acids (see Sec. 2.5.3), one finds a reversal of sign with a change... 

Chiral Fibers as Templates for Helical Crystallization of Proteins. 207... 

Chiral Fibers as Templates for the Growth of Inorganic Replicas. 209... 

One of the reasons why gels and self-assembled fibers affracf so much attention is their very high potential for applications. The last section of this chapter addresses applications which specifically make use of chirality, such as those based on enantioselective molecular recognition, or those based on the use of chiral fibers as templates for the generation of helical arrays of proteins or of chiral inorganic materials. 

Optical microscopy can provide information about the morphology of chiral fibers if their dimensions exceed a few hundred nanometers (0.2 p.m is the lower theoretical limit in the wavelength range of visible light). Numerous examples of chiral fibers observed through this technique can be found, as illustrated in Figs. 9 and 14, which show optical micrographs of both helical and twisted ribbons [88,92,98,99,101,109]. 

Scheme 6 Enantioselective reaction induced by chiral fibers...

The groups of Ihara and Sagawa have prepared fibrous assemblies of porphyrin 9 and pyrene 10 substituted by L-glutamic acid (Fig. 8) [30]. By amide hydrogen bonding, both chromophores self-assemble cofacially into chiral fibers several micrometers in length which can be controlled by temperature. The porphyrins form a physical gel and optical studies confirmed the... 

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