Chiral polypeptide liquid crystals

Other apphcations of covariance NMR include natural abundance deuterium NMR spectroscopy in chiral polypeptide liquid crystals [78] and three-dimensional experiments of combined homonuclear spin-exchange and separated-local-field spectroscopies [79]. These works also presented new sampling schemes and will be introduced in the next section. 

The idea of NUS has found considerable interest and applications in the context of the conventional 2D-FT schemes. NUS is also compatible with the covariance spectroscopy. Lafon et al. reported on natural abundance deuterium NMR spectroscopy of 2-ethyloxirane (C4H8O) and methyl vemoleate (C19H34O3) dissolved in chiral polypeptide liquid crystals... 

Lesot E, Sarfati M, and Courtieu J (2003) Natural abundance deuterium NMR spectroscopy in polypeptide liquid crystals as a new and incisive means for the enatiodifferentiation of chiral hydrocarbons. Chemistry -A European Journal 9 1724—1745. 

D. Merlet, B. Ancian, J. Courtieu, P. Lesot, Two-dimensional deuterium NMR spectroscopy of chiral molecules oriented in a polypeptide liquid crystal appHcations for the enantiomeric analysis through natural abundance deuterium NMR, J. Am. Chem. Soc. 121 (1999) 5249. 

Shiau, C.C. Labes, M.M. Control of the pitch of synthetic polypeptide lyotropic phases utilizing a chiral solvent. Molec. Crystals Liquid Crystals... 

Samulski et al2D suggested that an asymetric helical molecular conformation may provide an explanation for the cholesteric structure, and very small oscillations of helices relative to their neighbors in the liquid crystal would be biased to one side of the parallel position because of the chirality of the van der Waals surface of the polypeptide molecules. Further, they found a linear relationship between the pitch and the reciprocal of temperature. This relation holds quite well for a number of thermotropic liquid crystal systems and was explained theoretically by Keating ), who treated the macroscopic twist as a rotational analogue of thermal expansion with the dominant anharmonic forces coming from nearest neigh-... 

Although instances of lyotropic PLCs predate studies of thermotropic PLCs, as they involved solutions of comparatively esoteric species — virus particles and helical polypeptides — studies of these liquid crystals were isolated to a few laboratories. Nevertheless, observations on these lyotropic PLCs did stimulate the first convincing theoretical rationalizations of spontaneously ordered fluid phases (see below). Much of the early experimental work was devoted to characterizing the texture of polypeptide solutions. (23) The chiral polypeptides (helical rods) generate a cholesteric structure in the solution the cholesteric pitch is strongly dependent on polymer concentration, dielectric properties of the solvent, and polymer molecular weight. Variable pitch (<1 - 100 pm) may be stabilized and locked into the solid state by (for example) evaporating the solvent in the presence of a nonvolatile plasticizer.(24)... 

In the pioneer paper published by Thierry and Skoulios [20], it was advanced that polypeptides with sufficient long polymethylene side chains could display liquid-crystalline phases upon melting of the side chain. They in fact reported a high temperature nematic phase that reversed upon cooling into a lower temperature phase, whose structure was not elucidated. Since then, a good amount of research has been made on comblike polyglutamates, with the focus mainly toward the development of thin films with thermochromic properties. The liquid-crystal structure anticipated for these systems should be cholesteric according to the chiral nature of the main chain a-helix. However other mesomorphs have been described under certain conditions and for certain side chain compositions. 

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