Calix [4] Arene Derivatives Of Cholesterol Synthesis And Supramolecular Chemistry Design

Supramolecular host with peculiar molecular recognition ability not only can be used to construct ordered microstructures, novel morphologies and stimuli-responsive materials, but also can be used extensively in separation, catalysis, pharmaceutics, etc. Supramolecular gels containing supramolecular host show unusual functional properties such as reversible thixotropy and multiple stimuli-responsive properties including pH, temperature, etc. According to the host-guest interaction between crown ether and secondary ammonium, the compound appended crown ether or secondary ammonium could physically interlink together and form high strength and stimuli-responsive supramolecular gels. Supramolecular hydrogels based on the inclusion complexation of cyclodextrin and cucurbituril with various guest molecules also show abilities of multiple stimuli response and self-healing property.Calixarenes, as the third generation supramolecuar host, possessing a flexibly hydrophobic cavity and hydrophilic bonding sites, have attracted considerable attention. However, the related research is rarely reported on the low molecular mass gelators containing calixarene. Cholesterol possesses rigid skeleton, multiple chiral centers and a strong tendency to form aggregates via van der Waals interaction, so supramolecular gels based on cholesteryl derivatives have been considerably favored. Our group has designed and synthesized many kinds of low molecular mass gelators containing cholesterol group. Based on the previous work, a series of gelators containing both calixarene and cholesterol are synthesized through varying the structure of the spacer and the number of cholesteryl units, respectively. These gelators displayed diverse gelation properties in a variety of polar/nonpolar organic solvents. The properties and formation mechanism of these gels have been investigated through rheology, SEM, AFM, XRD,1H NMR, FTIR etc. This thesis is mainly composed of the following four parts:1. A novel calix[4]arene-based dimeric-cholesteryl derivative was synthesized, and its gelation behaviour in thirty organic solvents was investigated. It has been shown that the compound cannot gel any of the pure solvents tested. However, it gels a mixture of solvents n-decane and acetonitrile efficiently, provided the volume ratio of the two solvents in a mixture is within9:1and3:2. AFM and SEM measurements revealed that the molecules of the compound aggregate into micro-/nano-rods first, then fine fibers, and then thick fibers, and finally networked structures in the mixture solvents. Interestingly, the gel with a composition of1to1(vn-Decane:v Acetonitrile) and2.5%(w/v) of the compound exhibits super-smart and fully reversible thixotropic properties, a phenomenon never reported before. Furthermore, the mechanical strength of the gel could be easily adjusted by altering the concentration of the gelator and the composition of the mixture solvents. Further interrogation of the gel revealed that structurally the gel is a gel-emulsion with acetonitrile dispersed in n-decane, a rarely found O/O (oil in oil) gel-emulsion which may find uses in the templated preparation of low-density materials with complicated internal structures.2. Two novel cholesteryl derivatives of calix[4]arene with L-or D-phenylalanine residue in the linkers (II and III) were designed and synthesized. The gelation behaviors of the compounds in30organic solvents were tested. It was demonstrated that II gels butanol and pentanol at room temperature, but III gels isopropanol only under the treatment of heating-cooling cycle or energy supplement via sonication, vortex or agitation at room temperature. AFM and SEM measurements revealed that the structures of the gel networks are greatly affected by the spatial configurations of the linkers contained in the calix[4]arene derivatives. Furthermore, mechanical treatment not only promotes the gelation of the system of III/isopropanol, but also enhances the strength of the gel. Specifically,18min of agitation at room temperature makes the storage modulus and the yield stress of the gel (3.5%, w/v) exceed1×106Pa and6×103Pa, respectively, which are only second to the mechanically strongest low-molecular mass compound-based molecular gel reported till now. XRD analysis revealed the hexagonal packing structure of II in its pentanol gel.3. Dimeric and tetra cholesteryl derivatives of calix[4]arene with hexamethylenedianine in the linkers (IV and V) were designed and synthesized. Gelation behaviors of IV and V revealed a dramatic difference in the gelation behaviors. IV can dissolve in30organic solvents and V can gel13kinf of30solvents. SEM measurement revealed the nature of solvent and the temperature significantly affects the microstructure of the aggregation the gel of V/kerosene. Further intensive study was in progress.4. Dimeric cholesteryl derivatives of calix[4]arene with triazole and L-or D-phenylalanine residue in the linkers (VI and VII) were prepared. Gelation test demonstrated that VI and VII cann’t gelate any kind of solvents of30solvent, but the system of Ⅶ/n-butanol become viscious solution. This work was also in progress.