Synthesis and organogelation properties of bis-carbamate compounds bearing spacers with a stereogenic center

A series of bis-carbamates with a stereogenic center were prepared as low-molecular-weight organic gelators. The gelating propensity of racemates and pure enantiomers was examined in a range of organic solvents to explore the effects of chirality and the para-alkyl chain length on self-assembly. It was found that the gelation abilities in vegetable oils and esters were mainly affected by the para-alkyl chain length and the number of carbons in the spacer between the carbamate groups. In addition, molecular chirality was found to have a significant effect on the gelation properties of bis-carbamate derivatives with three-carbon spacer. Furthermore, morphology of the bis-carbamate gels was investigated by optical microscopy and scanning electron microscopy. Birefringent helix-like structures between birefringent spherulites were observed by polarized optical microscopy in the gel structures of chiral bis-carbamate derivatives with three-carbon spacer. The bulk properties of the gels were evaluated through rheological studies. The results can be used for developing novel chiral gels and relevant applications such as enantiomeric separation.