Cyclodextrins (CDs) are a group of cyclic oligosaccharides consisting of 6-8 glucose units which are linked together via -(1,4)-glycosidic linkages. These molecules are interesting because they are shaped like a truncated cone with a central cavity that can be used to form inclusion complexes with organic molecules. Chemical modifications have generated amphiphilic CD derivatives that exhibit thermotropic liquid crystalline properties.
Based on previous observations, a series of novel amphiphilic -CD derivatives capable of forming hydrogen bonding networks of different strength have been designed and synthesized. These compounds have been used to probe the role of the hydrogen bonding network in the formation of liquid crystals (LCs) of amphiphilic CDs. Using differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM) and X-ray diffractometry, one compound was found to exhibit liquid crystalline properties
An efficient and versatile synthetic methodology has been developed for the selective modification of the wider face of -CD using the Huisgen 1,3-dipolar cycloaddition. The novel strategy has proved to be highly effective to introduce a wide range of functional groups to -CD.
Using the newly established synthetic methodology, another two series of -CD derivatives capable of establishing hydrogen bond networks of different strength either at the wider end via flexible linkers or at narrower end of -CD have been synthesized. All these compounds were found to self-assemble into liquid crystalline phases. The obtained results also show that the clearing and melting temperatures of these amphiphilic molecules can be tuned independently either by modifying the depth of hydrophobic region or by modifying the strength of the hydrogen bonding network. Additionally, a novel oligoethoxy group-functionalized -CD derivative was found to exhibit liquid crystalline properties without relying on a hydrogen bonding network. This unprecedented discovery should stimulate new approaches to design CD-based liquid crystalline materials in the future.
Finally, the liquid crystalline properties of inclusion complexes formed by an amphiphilic -CD were investigated for the first time using DSC, FT-IR, and solid state 13CNMR. It was found that the complexes displayed altered thermotropic liquid crystalline properties compared to the host.