Betulin is a naturally occurring pentacyclic triterpenoid abundant in birch bark and characterized by a rigid hydrophobic backbone with polar functionalities at terminal positions. These structural features make betulin a promising molecular building block for supramolecular assembly and soft material formation. Despite its abundance and well-documented biological activity, the supramolecular behaviour of betulin and its potential to form structured soft materials remain to be elucidated. This thesis investigates betulin through two complementary studies: (1) the solvent-directed self-assembly of betulin molecules and (2) the formation of betulin-based organogels. In the first study, crude betulin extracted from birch bark was purified through two successive recrystallization steps, yielding highly ordered crystals with an overall recovery of 67.15%. The spontaneous self-assembly of betulin was then examined in a range of organic solvents at concentrations defined relative to their solubility limits. Scanning electron microscopy revealed diverse supramolecular morphologies, including spherical, flower-like, and fibrillar assemblies, demonstrating that solvent properties and saturation levels strongly influence the resulting structures. In the second study, betulin organogels were prepared in isopropyl myristate through a heating-cooling process. Rheological analyses confirmed the formation of viscoelastic networks, with storage modulus increasing with gelator concentration. Structural characterization via polarized optical microscopy, Fourier transform infrared spectroscopy, powder X-ray diffraction, and differential scanning calorimetry indicated that gelation arises from crystalline needle-like morphologies of betulin. This work establishes betulin as a versatile supramolecular building block capable of forming solvent-directed assemblies and functional organogels, providing new insight into triterpenoid self-assembly and expanding the potential of bio-derived molecules for soft material applications.
Matthew Cao (Thu,) studied this question.