Preparation of dicholesteryl-derivatives: The effect of spatial configuration upon gelation

To investigate the effect of spatial configuration on the gelation properties of low molecular mass gelators(LMMGs),four novel di-cholesteryl derivatives have been specially designed and synthesized by introducing the cis-/trans-isomers of butene diacid and the optical isomers of D/L-phenylalanine into the linker between two cholesteryl moieties.These isomers have been denoted as MaDC,FaDC,MaLC and FaLC,respectively.The gelation properties of the compounds were examined in 26 organic solvents,and it was found that the trans-configuration is more favorable for the gelation,but the chirality of the linker shows little effect to the gelation.FaDC has the strongest gelation ability among the four isomers.Interestingly,FaDC and FaLC display phase-selective gelation of benzene,toluene and xylene from their mixtures with water at room temperature,which establishes a foundation for the purification of water contaminated by oil or aromatic solvents.SEM and CD spectroscopy studies revealed that the spatial configuration of the linkers of the gelators affects significantly the aggregation mode,the morphologies and the chirality of the network of the gels.Moreover,the different aggregation behaviors also have an impact on mechanical properties of the gels,which are consistent with the results from rheological studies.Furthermore,temperature-and concentration-dependent 1 H NMR and FTIR measurements demonstrated that intermolecular hydrogen bonding and-stacking are the main driving forces for the formation of the gels.