Biological Liquid Crystals

The widespread interest in transport across membranes of living cells has led to studies of diffusion in lyotropic liquid crystals. Biological membranes are generally thought to contain single bimolecular leaflets of phospholipid material, leaflets which are like the large, flat micelles of lamellar liquid crystals. No effort is made here to review the literature on transport either across actual cell membranes or across single bimolecular leaflets (black lipid films) which have often been used recently as model systems for membrane studies. Instead, experiments where lamellar liquid crystals have been used as model systems are discussed. 

Hydrated bilayers containing one or more lipid components are commonly employed as models for biological membranes. These model systems exhibit a multiplicity of structural phases that are not observed in biological membranes. In the state that is analogous to fluid biological membranes, the liquid crystal or La bilayer phase present above the main bilayer phase transition temperature, Ta, the lipid hydrocarbon chains are conforma-tionally disordered and fluid ( melted ), and the lipids diffuse in the plane of the bilayer. At temperatures well below Ta, hydrated bilayers exist in the gel, or Lp, state in which the mostly all-trans chains are collectively tilted and pack in a regular two-dimensional... 

Caffrey, M. Structural, Mesomorphic and Time-Resolved Studies of Biological Liquid Crystals and Lipid Membranes Using Synchrotron X-Radiation. 151, 75-109 (1989). 

Liquid crystal sounds like a contradiction. Liquids are fluid, their molecules continually changing places in a manner that is not particularly well organized. Crystals are immobile, their molecules locked into fixed positions that form regular patterns. Yet, not only does this unusual combination of fluidity and regular patterns exist, it plays important roles in biological organisms. 

Liquid crystals were discovered by an Austrian biologist, Frederich Reinitzer, in 1888. Reinitzer found that cholesteryl benzoate, a biological chemical, melts to form a hazy liquid. At a higher temperature, the haziness disappears. This clear state is what we know now as a liquid crystal. 

Enzymes are proteins catalyzing all in vivo biological reactions. Enzymatic catalysis can also be utilized for in vitro reactions of not only natural substrates but some unnatural ones. Typical characteristics of enzyme catalysis are high catalytic activity, large rate acceleration of reactions under mild reaction conditions, high selectivities of substrates and reaction modes, and no formation of byproducts, in comparison with those of chemical catalysts. In the field of organic synthetic chemistry, enzymes have been powerful catalysts for stereo- and regioselective reactions to produce useful intermediates and end-products such as medicines and liquid crystals. ... 

Aromatic fluorination certainly is one of the best candidate reactions for micro reactors. Fluorinated compounds are of high industrial interest. For instance, they find wide application as pharmaceuticals, dyes, liquid crystals and crop-protection agents [3,13,16, 38] about every third drug contains a fluorine moiety. The introduction of fluorine moieties in molecules has unique effects on biological activity (see original citations in [16]). 

Similar behavior can occur when a crystalline network is disassembled by adding a solvent rather than by heating. These mesogens are called lyotropic liquid crystals and the mesophase formation shows temperature and concentration dependence. They are very important in biological systems, but have been much less studied in materials science. 

The thickness of the membrane phase can be either macroscopic ( thick )—membranes with a thickness greater than micrometres—or microscopic ( thin ), i.e. with thicknesses comparable to molecular dimensions (biological membranes and their models, bilayer lipid films). Thick membranes are crystalline, glassy or liquid, while thin membranes possess the properties of liquid crystals (fluid) or gels (crystalline). 

FBAs are used to brighten not only textile materials but also paper, leather and plastics. They are important constituents of household detergent formulations. More specialised areas of application include lasers, liquid crystals and biological stains. By far the most important uses for FBAs, however, are in applications to textiles and paper. Much of what follows will be concerned with these two categories. 

Knight, D. P., and Vollrath, F. (2002). Biological liquid crystal elastomers. Philos. Trans. R Soc. Lond. B Biol. Sci. 357, 155-163. 

Liquid crystal display technology, 15 113 Liquid crystalline cellulose, 5 384-386 cellulose esters, 5 418 Liquid crystalline conducting polymers (LCCPs), 7 523-524 Liquid crystalline compounds, 15 118 central linkages found in, 15 103 Liquid crystalline materials, 15 81-120 applications of, 15 113-117 availability and safety of, 15 118 in biological systems, 15 111-113 blue phases of, 15 96 bond orientational order of, 15 85 columnar phase of, 15 96 lyotropic liquid crystals, 15 98-101 orientational distribution function and order parameter of, 15 82-85 polymer liquid crystals, 15 107-111 polymorphism in, 15 101-102 positional distribution function and order parameter of, 15 85 structure-property relations in,... 

Confocal fluorescence microscopy has been extensively used in cell biology. Single living cells can indeed be studied by this technique visualization of organelles, distribution of electrical potential, pH imaging, Ca2+ imaging, etc. (Lemasters, 1996). Interesting applications in chemistry have also been reported in the fields of colloids, liquid crystals and polymer blends. 

D. Eden and C. Sunshine, in Dynamic Behavior of Macromolecules, Colloids, Liquid Crystals and Biological Systems by Optical and Electro-Optical Methods (H. Watanabe, ed.), pp. 000-000, Hirokawa, Tokyo (1989). 

The basic modem data describing the atomic stmcture of matter have been obtained by the using of diffraction methods - X-ray, neutron and electron diffraction. All three radiations are used not only for the stmcture analysis of various natural and synthetic crystals - inorganic, metallic, organic, biological crystals but also for the analysis of other condensed states of matter - quasicrystals, incommensurate phases, and partly disordered system, namely, for high-molecular polymers, liquid crystals, amorphous substances and liquids, and isolated molecules in vapours or gases. This tremendous... 

The therapy of a chronic disease requires repeated drug dosing. In the case of a short biological half-life, the drug has to be administered up to several times daily within short intervals. To reduce the application frequency, sustained formulations have been developed. For this purpose liquid crystalline excipients are appropriate candidates, because in a liquid crystalline vehicle the drug diffusion is reduced by a factor of 10 to 1000 in comparison with a liquid vehicle such as a solution [35-37]. The factor depends on liquid crystal. 

Imidazo[2,l-fe]thiazoles have been known since 1936 (36CB1650), but only recently has there been much interest in this class of compounds. These substances not only exhibit biological activity, but also seem to be interesting starting materials fo the preparation of compounds with unique physical properties [(e.g., liquid crystals (96UPl)i. In the following articles, both the synthesis and the reactions and properties of these compounds are delineated. 

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