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

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 (13)C 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 degrees C. The powder X-ray diffraction data of the room-temperature conformer has been utilized to unambiguously determine the structure at room temperature.