Sani, Faramarz Aliasghari (2012) Synthesis and self-assembly studies of glycoside surfactants and chromonics / Faramarz Aliasghari Sani. PhD thesis, University of Malaya.
Abstract
This thesis focused on the synthesis and self assembly studies of compounds involving carbohydrates. Two different types of materials were studied, i.e. surfactants and chromonics. Physical investigations of the compounds were conducted by TGA, DSC, OPM, UV-Vis spectroscopy, 1H NMR and surface tension measurements. Sugar-based surfactants are interesting compounds for pharmaceutical and personal care products. Current commercially available surfactants such as alkyl poly glucoside surfactants (APGs) are prepared from low miscibility of sugars and fatty alcohols. In order to solve the miscibility problems of the starting materials, homogenizers are required. This, however, leads to impurities in products, which affects the use of the surfactant for life science applications. Therefore, this work focused on an economic preparation of pure glycoside surfactants. The synthesis approach applied a separation of glycosides and a coupling of sugar and fatty alcohols with different length and chain branching by click chemistry. Twenty one alkyl triazole glycoside surfactants (ATGs) were prepared with more than 80% yield. Twelve of these were anomeric pure products (>95% purity) and nine were technical products of α/ anomeric mixtures. The materials were characterized for their liquid crystal behaviours. Contact penetration studies showed a whole range of lyotropic phases from lamellar to cubic and hexagonal. ATGs’ CMCs were found to be lower than those of APG surfactants. An increase in their chain length meant a decrease in CMC values. Hence these materials could be identified for oil-based surfactants applications. Chromonics or lyotropic chromonic liquid crystals (LCLCs) are formed by the selfassociation of aromatic disk-shaped molecules with hydrophilic groups at the periphery in aqueous solutions. The chromonics are assembled from π-π interactions of the aromatic cores. This leads to aggregates based on stacking of the molecules. Most chromonic molecules are based on ionic structures. The research embraced the synthesis and assembly studies of non ionic chromonics consisting of triphenylenebased units surrounded by glycosides. The key point for the synthesis of triphenylene core was oxidative trimerization of veratrole and guaiacol under anhydrous conditions in the presence of ferric chloride. A symmetric compound with six sugars and an asymmetric one with three sugar units were synthesized. The materials were of purity over 95% and more than 75% yield. Due to the anisotropic effect on the aromatic ring on 1H NMR, the chemical shift on the aromatic ring changed when the concentration was increased. This means the materials formed aggregation and enabled the determination of critical aggregation concentrations (CAC). Moreover, this property also showed temperature dependency. At higher concentrations and under examination by polarizing light microscopy, the chromonic exhibited liquid crystalline properties (Col phase).
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