A new class of homologous gelators, LG12-(CH2)n-BSA, composed of bipyridinyl groups, L-glutamic moieties having double dodecyl chains, and linked alkyl spacers with different lengths were synthesized. It was found that these gelators could immobilize medium-polarity solvents readily and the behaviors of these gels showed a dependence on the spacer length. Of all the gels, the LG12-(CH2)11-BSA gels exhibited self-healing property and multiple-stimulus responsibility, such as heating, shaking, and sonication. The investigation of CD spectra indicated that the supramolecular chirality, which was attributed to the chiral transfer from the chiral center to the assemblies, was also closely related to the length of methylene spacers. The longer the alkyl spacers, the weaker the transmitted supramolecular chirality. Only LG12-(CH2)1-BSA gelators, which had the shortest spacers, formed right-handed nanoscale chiral twists owing to crowded hydrogen bonding interactions. Moreover, the high-polarity solvent DMF was found to be able to regulate the chiral twist as well as its pitch length readily.
A new class of L-glutamic gelators, LG12(CH2)nCOOH, containing different lengths of methylene spacer were synthesized. It was found that the gelation ability of these compounds themselves was very weak. However, when another compound, p-xylylenediamine (XEA), was introduced, the gelation ability was improved greatly. In particular, LG12(CH2)10COOH showed super-gelation ability in the presence of XEA, which could immobilize almost all of the solvents except methanol. Moreover, the formed supramolecular gels even could be molded. Interestingly, some supramolecular gels of LG12(CH2)nCOOH and XEA could respond to multiple stimuli, such as heating, shaking, sonication, and acid/base. The studies of CD spectra suggested that the supramolecular chirality induced by self-assembled chiral gelator molecules in gels could be tuned by the length of methylene spacer. In addition, the supramolecular chirality could be regulated as on/off by heating–cooling or external NH3/HCl. This would facilitate the development of dual chiroptical switches by temperature and acid/base.
