Bile acid–amino acid ester conjugates: gelation, structural properties, and thermoreversible solid to solid phase transition

Abstract

Design, synthesis, and gelation properties of three novel biocompatible bile acid–L-methionine methyl ester conjugates are presented. Two of the conjugates have been shown to undergo self-assembly leading to organogelation in certain aromatic solvents. The properties of these gels have been investigated by conventional methods typical for molecular gel studies along with ¹³C CPMAS NMR spectroscopic studies of the native gel. In addition, properties in solid and solution states for all three compounds have been investigated, and single crystal X-ray structures of all compounds determined. Furthermore, powder X-ray diffraction studies have revealed that compound 1 undergoes a dynamic and reversible conformational change in the solid state when cooling from ambient temperature to −150 °C. The powder X-ray diffraction data of the room-temperature conformer has been utilized to unambiguously determine the structure at room temperature.