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Mesophase Formation (mesophase + formation)

Distribution by Scientific Domains

Chemistry	50%

Selected Abstracts

Synthesis and Liquid Crystalline Properties of Mono-, Di- and Tri- O -alkyl Pentaerythritol Derivatives Bearing Tri-, Di- or Monogalactosyl Heads: The Effects of Curvature of Molecular Packing on Mesophase Formation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2007
Fabienne Dumoulin Dr.
Abstract Self-organisation and self-assembly are critical to the stability of synthetic and biological membranes. Of particular importance is consideration of the packing arrangements of the various molecular species. Both phospho- and glycolipids can pack in ways in which curvature can be introduced into self-organised or self-assembled systems. For instance, it is known that the degree of curvature can affect the structures of any condensed phases that are formed. In this article we report on a systematic study in which we have varied the shapes of glycolipids and examined the condensed phases that they form. In doing so, we have also unified the shape dependency of lyotropic liquid crystals with those of thermotropic liquid crystals. In order to undertake this systematic study a range of different pentaerythritol derivatives was synthesized, which covers combinations of one to three alkyl chains of different lengths (6,7,9,10,11,12,14,16 carbon atoms) and three to one galactosyl heads. Mono- and di- O -galactosyl derivatives were prepared directly by glycosylation of the corresponding alcohols using 2,3,4,6-tetra- O -benzoyl or acetyl - ,- D - galactopyranosyl trichloroacetimidate or bromide as the donors; the tri- O -galactosyl derivatives were synthesized from O -alkyl- O -benzyl di- O -galactosyl pentaerythritol intermediates, followed by de- O -benzylation and glycosylation steps. All of the fully deprotected products were obtained by standard methods, and their self-organising and self-assembling properties examined. [source]

Columnar Mesophase Formation of Cyclohexa- m -phenylene-Based Macrocycles

CHEMISTRY - AN ASIAN JOURNAL, Issue 1 2007
Wojciech Pisula Dr.
Abstract Two novel discotic macrocycles, substituted cyclohexa- m -phenylene (CHP) and cyclo-3,6-trisphenanthrylene (CTP), and the linear oligomer 3,3,:6,,3,,-terphenanthrene (TP) as a model substance have been synthesized by repetitive cross-coupling reactions. To correlate the molecular design with the supramolecular architecture and the established macroscopic order, 2D wide-angle X-ray scattering experiments were performed on mechanically extruded filaments. At room temperature in their crystalline phases, all three compounds revealed columnar assemblies in which the macrocycles self-organized by ,-stacking interactions. The degree of macroscopic order was found to depend upon the planarity and stiffness of the aromatic core. The flexible CHP ring showed a poor macroscopic order of the columnar structures and a low isotropization temperature, whereas the more-planar, less-flexible CTP self-assembled into well-defined superstructures. The larger ,-stacking area and the more-pronounced intermolecular interactions for CTP led to the formation of a mesophase over a very large temperature range. The surprising columnar organization of the "open" TP system was explained by back-folding of the molecule into a ringlike structure. [source]

Measurement of critical concentration for mesophase formation of chitosan derivatives in both aqueous and organic solutions

POLYMER INTERNATIONAL, Issue 12 2006
Yan-ming Dong
Abstract A novel chitosan derivative, acryloyl chitosan (AcCs), and two N -maleoyl chitosans, MaCs-1 and MaCs-2, with different degrees of substitution were synthesized using completely deacetylated chitosan as raw material under different reaction conditions. AcCs is an amphiphilic chitosan derivative, but MaCs-1 and MaCs-2 are soluble in water and organic solvents respectively. The concentrated solutions of AcCs, MaCs-1 and MaCs-2 all demonstrated mesophases and were investigated using polarizing optical microscopy (POM). Circular dichroism (CD) was also employed for determining the critical concentration for mesophase formation. A broad peak in the visible light region of CD spectra had its origin in the appearance of the mesophase, and arose from the selective reflection of cholesteric helix pitches. The results of CD measurements agreed with those of POM. The critical concentration values for aqueous solutions were much lower than those for organic solutions, which was explained by the strong interactions between the chitosan derivatives and water. Copyright © 2006 Society of Chemical Industry [source]