Synthesis and Mesomorphic Properties of Geometric and Conformation-Modulated Amphiphilic β-Cyclodextrin Liquid Crystals

This study explores the liquid crystalline properties of novel amphiphilic β-cyclodextrin derivatives functionalized with seven oligoethylene glycol chains at the primary face, terminated with either an O-methyl or an O-cyanoethyl group, and fourteen hydrophobic aliphatic chains (elaidic or oleic acids) at the secondary face. These derivatives were designed to study the impact of chain conformation and terminal group polarity on their mesomorphic behavior. Thermal, microscopic, and X-ray diffraction studies revealed that the elaidic derivatives form columnar hexagonal mesophases, with the O-cyanoethyl derivative undergoing a slow, temperature-dependent transition to a bicontinuous cubic phase. The oleic derivatives, although less stable, also exhibit columnar hexagonal phases, but clear differences were observed in the clearing temperatures between these two groups of molecules, and they are also different from analogous derivatives containing no alkene functionalities. This work provides direct insights into the structure-mesomorphic property relationships of amphiphilic cyclodextrins in terms of the geometry and conformation flexibility of the hydrophobic regions, as well as the functional group attached to the end of the polar region.