The effect of structure on the gel formation ability and the properties of bile acid based supramolecular organogels

Abstract

The thread behind this thesis has been fascinating. The study has focused on how changes in the alkyl side chain structure of the bile acid derivatives effects on the self-assembly properties of the compounds. Side chain structures were chosen not to contain any functional groups because of the novelty of the compounds in the field of steroidal supramolecular gels. In addition, the work could provide important insights on how to design supramolecular gelator molecules with divergent properties. The 19 compounds presented in this thesis work were prepared by mixed anhydride synthesis method. All the compounds were characterized with NMR-spectroscopy and mass spectrometry. Single crystal structures were obtained from majority of the compounds studied. Additionally, some of the compounds were investigated by solid state NMR. The gelation abilities of the compounds were observed by utilizing conventional test-tube inversion method in divergent solvents and, in a few cases, aqueous solvent mixtures. Morphology of the dried gel systems were studied by scanning electron microscopy. In this thesis, the structure of the side chain and the nature of the bile acid backbone were observed to affect the self-assembly properties of the compounds. For example, the side chain had a major impact on the stability of the gels when the gels were exposed to physical stimuli (disturbed with a spatula). SEM-images revealed that the bile acid backbone impacted on the morphology of the gel system as fibrous or spherical structures were seen depending on the amount of hydroxyl groups in the bile acid backbone. As a conclusion, this work provides a perspective on how the gelator structure effects on the self-assembly ability of the compound and properties of the formed gel systems. In addition to this thesis, a review article of steroidal supramolecular metallogels was published (Chem. Soc. Rev., 2020, 49, 1977–1998) during the making of the current thesis work.