Liquid Crystalline Copolymers Containing Sulfonic and Light-Responsive Groups: From Molecular Design to Conductivity.

In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). By using a cascade of reversible addition-fragmentation chain polymerisations, RAFT, we have tailored different side-chain polymeric structures by controlling monomer composition (MeOAzB/AMPS/MMA) and configuration. We have yielded simultaneous liquid crystalline behaviour and appreciable conductivity in polymers with low concentrations of polar acid groups, by the formation of smectic phases in narrow aggregates. The light-responsiveness of the polymers, via reversible trans-to-cis photoisomerization of azobenzene groups, and the local activation of conductivity at relatively low temperatures, opens the possibility to prepare polymer electrolytes for energy conversion and storage, whose conductivity could be controlled and optimised by external stimuli, including light irradiation.

Dry Thermotropic Glycolipid Self-Assembly:A Review.

Also recognized as carbohydrate liquid crystals, glycolipids are amphiphiles whose basic unit comprises of a sugar group attached to an alkyl chain. Glycolipids are amphitropic, which means these materials form liquid crystal self-assemblies when dry (thermotropic) as well as when dissolved in solvents (lyotropic/surfactants) such as water. Many glycolipids are also naturally derived since these can be found in cell membranes. Their membrane and surfactant functions are largely understood through their lyotropic properties. While glycolipids are expected to play major roles as eco-friendly surfactants in the global surfactant market, their usefulness as thermotropic liquid crystal material is, to date, unknown, due to relatively lack of research performed and data reported in the literature. Understandably since glycolipids are hygroscopic with many hydroxy groups, removing the last trace water is very challenging. In recent time, with careful lyophilization and more consistent characterization technique, some researchers have attempted serious studies into "dry" or anhydrous glycolipids. Motivated by possible developments of novel thermotropic applications, some results from these studies also provide surprising new understanding to support conventional wisdom of the lyotropic systems. Here we review the dry state of glycosides, a family of glycolipids whose sugar headgroup is linked to the lipid chain via a glycosidic oxygen linker. The structure property relationship of both linear and anhydrous Guerbet glycosides will be examined. In particular, how the variation of sugar stereochemistry (e.g. anomer vs. epimer), the chain length and chain branching affect the formation of thermotropic liquid crystals phases, which not only located under equilibrium but also far from equilibrium conditions (glassy phase) are scrutinized. The dry glycolipid assembly has been subjected to electric and magnetic fields and the results show interesting behaviors including a possible transient current generation.

Effect of vesicle's membrane packing behaviour on skin penetration of model lipophilic drug.

Disaccharide glycosides synthesised from food grade resources consist of the hydrophilic head group of maltose or lactose and provide better hydrophilic-lipophilic balance (HLB = 12) to the long alkyl chain derived from palm oil (PO) and palm kernel oil (PKO). Maltoside provides more flexibility in the vesicle's membrane because of its low packing density in the bilayer membrane compared to lactoside. The bending of the molecular structure in maltose form a less compact assembly for maltoside, whereas lactose is more linear in shape. Apart from hydrophilic moieties, packing behaviour was also governed by the hydrophobic moieties. PO has higher degree of unsaturation compared to PKO, thus providing higher fluidity in the bilayer membrane. Vesicle with high membrane flexibility is easier to disintegrate and deform to enhance drug penetration into the skin. Results showed that the glycosides delivered vitamin E (VE) into deeper skin layer at least two-fold higher than free VE.

Preparation of vesicle drug carrier from palm oil- and palm kernel oil-based glycosides.

A new mixture of alkyl glycosides derived from palm oil (PO) or palm kernel oil (PKO) was synthesised. This mixture contains glycosylated disaccharide of either maltose or lactose with aliphatic chain that varies according to the PO or PKO fatty acids composition. The synthesis method produced no polymerised sugar unlike the production of the commercial glycosides (APG). The mixture only contains various glycosides differing by the alkyl chain and stereoisomers. Three anomeric mixtures can be produced depending on the reaction time and catalyst: α-dominant mixture, ß-dominant mixture and equal mixture. The PO and PKO derived glycosides were able to form a stable vesicle with a small amount of dicetyl phosphate (DCP) and showed high vitamin E encapsulation efficiency. Low packing density of the membrane bilayer enabled more vitamin E to participate in the membrane formation. The anomeric mixtures of the maltosides provide no difference in membrane packing behaviour as it was governed by the hydrophilic region. Significant difference in membrane packing density was observed for lactosides anomeric mixtures because the packing behaviour was influenced by the hydrophobic region. Inclusion of cholesterol led to decrease in vitamin E encapsulation as well as reducing the stability of the vesicle system. The vesicular formulations of the glycosides were stable for 3 months when stored at refrigeration temperature.