Novel Dimeric Cholesteryl Derivatives and Their Smart Thixotropic Gels

Three novel LS(2)-type dimeric-cholesteryl derivatives (1-3), where S is a steroidal residue and L stands for a linker connecting the two S residues and contains three benzene rings and two amide and two carbamate groups, were designed and prepared. The compounds can gel a wide variety of organic solvents via three different ways, including mixing at room temperature, a heating-cooling cycle, and ultrasound treatment. SEM measurements revealed that the structures and the concentrations of the gelators, the nature of the solvent, and the preparation method employed have a great effect on the morphologies of the gel networks. It was revealed that 1 is a supergelator for DMSO (cgc = 0.04% w/v) and that the 1/DMSO gel can be prepared via any of the three methods mentioned above. Furthermore, the gel possesses excellent mechanical strength and a very smart thixotropic property. FT-IR and temperature- and concentration-dependent (1)H NMR spectroscopy studies revealed that hydrogen bonding and pi-pi stacking among the molecules of 1 are two important driving forces for the physical gelation of DMSO. In addition, XRD analysis confirmed the layered packing structure of 1 in its DMSO gel.