Thermotropic and lyotropic liquid crystalline phases of Guerbet branched-chain -D-glucosides

Abstract

The effect of chain branching on glycolipid thermotropic and lyotropic phases was investigated for a series of synthetic β-D-glucosides derived from Guerbet alcohols, whose total hydrocarbon chain length ranged from C 8 to C 24 . The compounds, which can be viewed as isosteric mimics for glycoglycerolipids, were synthesised in high purity and their liquid crystalline phases were studied using optical polarising microscopy (OPM), and small-angle X-ray diffraction. When dry, the shortest compound (total C 8 ) exhibits a monotropic L α phase while longer ones (C 16 and C 20 ) adopt inverse hexagonal H II phases. The C 24 compound forms an ordered lamellar phase at room temperature, but exhibits a metastable H II phase upon cooling. Curiously the intermediate chain length homologue (C 12 ) adopts an isotropic inverse micellar (L 2 ) phase in the dry state over the range of temperatures studied. Upon hydration, the C 8 compound dissolves, and the C 12 compound forms a fluid lamellar L α phase. The C 16 Guerbet glucoside (i.e. β-Glc-C 10 C 6 ) exhibits an inverse bicontinuous cubic phase of space group Ia3d in excess water, never previously observed in branched-chain lipids, and very seldom observed in excess water. The C 20 compound remains in the H II phase upon hydrating, with the lattice parameter swelling substantially.

Hexagonal phase with ordered acyl chains formed by a short chain asymmetric ceramide

“…In order to further inspect the ceramide arrangements we carried out polarized light microscopy at room temperature of C10:0 ceramide films that were hydrated in glass slides at temperatures above the transition. Pictures in Figure 4 indicate that C10:0 ceramide films under crossed polarizers illumination display a fan-like texture, typical of hexagonal phases [27,28], supporting the idea of a hexagonal type of arrangement of the short-chain ceramide in tubular micelles at temperatures below that of the main transition.…”

New insights into the transitional behaviour of methyl-6-O-(n-dodecanoyl)-α-D-glucopyranoside using variable temperature FTIR spectroscopy and X-ray diffraction

“…[2,3,5,6] The molecular architecture of a carbohydrate-based mesogen typically consists of a hydrophilic (polar) head group attached to one or more lipophilic (nonpolar) chains. [2] This amphiphilic character promotes the formation of microphase-separated hydrophilic and hydrophobic phases, and consequently these materials have a great tendency to self-assemble and exhibit lyotropic liquid crystalline behaviour.…”

Dry Thermotropic Glycolipid Self-Assembly:A Review

“…The estimated v/l values are adequate to compare these two chain designs, although they may vary with phase structure, temperature, hydration level and molecular structure. As shown in Table 5, the effect of chain length on T C for branched-chain glycosides series is not as obvious as the straight chain glycoside series 18,74,75 . This is probably because the short chain Guerbet glycosides give usually the lamellar phase but the longer chain ones give a hexagonal phase.…”