Functional Gels Based On Betulin

Triterpenoids,an abundant class of natural products,have been playing significant role in supramolecular gels owing to their unique rigid hydrophobic skeleton,multiple chiral centers and functional groups.However,reported triterpenoid-based gels focus on oleanolic acid and glycyrrhetinic acid and payed less attention on betulin with lupane skeleton.And most of triterpenoid-based gels are short of abundant properties and functions,preventing triterpenoid from realizing their full potential in soft materials.Therefore,it is of vital importance to develop supramolecular gels based on betulin,a natural triterpenoid with outstanding assembly property,and to take advantage of the hydrophobic,chiral and sustainable nature of triterpenoid,which will not only exploit natural resources,but al so expand the application of triterpenoid-based materials。In this dissertation,a series of amphiphiles have been synthesized from betulin conjugated with pyridyl groups by urethane bonds.Through bottom-up assembly strategy,we have fabricated supramolecular gels with Cu²⁺-triggered shrinkage,regulable supramolecular chirality and supramolecular eutectogel in deep eutectic solvents,and have explored their functions and applications:The balance of hydrophobic and hydrophobic fragments of amphiphiles was achieved by introducing pyridine groups to different positions of the hydrophobic skeleton.Pyridine-conjugated betulin could assemble into supramolecular gel with fibrous nanostructures.Cu²⁺triggered the cross-linking of nanofibrous network and the hydrophobic nature of betulin skeleton expelled solvents out of gel phase,resulting a macroscopic shrinkage in triterpenoid-based gels for the first time.Shrunken gel could self-demold spontaneously and exhibited improved mechanical performance,overcoming mechanical defects of traditional supramolecular gels and providing a facile approach to fabricate self-supporting supramolecular gels at low LMWG concentration.A series of betulin-based gelators were synthesized with isomerism in the N atom positions of pyridine groups,and the effect of isomerism on supramolecular chirality was investigated,realizing the chiral regulation of gels.Meanwhile,the chirality of supramolecular gels could be further modulated by the Ag⁺-induced conformational change through coordination.The mechanism of chiral regulation was explored,and chiral gels were capable of templates for in situ synthesis of chiral silver nanoparticles,which promoted the application of triterpenoid-based gels in chiral materials.Supramolecular eutectogels were fabricated by bio-based betulin amphiphiles and green sustainable deep eutectic solvents for the first time.,greatly expanded the types of triterpenoid-based gels.Eutectogels possessed better mechanical performance,wider temperatu re range when compared to traditional supramolecular gels,and could be applied to more practical fields.The excellent ionic conductivity and thixotropy of eutectogels made them green solid electrolyte and afforded potentials for application as electrodes and strain sensors,providing a basis for the development of new triterpenoid-based functional materials.