Chiral gelators constructed from 11-aminoundecanoic (AUDA), lauric and amino acid units.: Synthesis, gelling properties and preferred gelation of racemates vs. the pure enantiomers

A new class of efficient low molecular weight gelator molecules has been designed by combining 11-aminoundecanoic acid (AUDA), lauric acid and aromatic and aliphatic amino acid units in the same molecule. This yields a special class of fatty acid amphiphiles with core chiral centres and hydrogen bonding sites. Some of the compounds with terminal carboxylic acid and sodium carboxylate functions exhibited ambidextrous gelation properties, being able to form gels both with highly polar solvents (water, DMSO) and also with highly lipophilic solvents, including two hydrocarbon fuels. At variance with several recent observations that the enantiomers are generally more efficient gelators than the corresponding racemates, some of the racemic gelators prepared in this work were found to be capable of gelling up to 16 times larger volumes of certain solvents than the pure enantiomers. Temperature-dependent FTIR and H-1 NMR studies of the gels formed by derivatives with terminal carboxylic acid groups and lipophilic solvents revealed that intermolecular hydrogen bonding between amidic and carboxylic acid units was involved in the self-assembly of gel aggregates. Additional strong stabilization of the aggregates was observed in the gelators possessing terminal sodium carboxylate groups, and this was attributed to the electrostatic and ion-dipole interactions between the sodium carboxylate groups. This additional stabilization appears to be responsible for considerably higher thermal stability of the latter gels in relation to those formed by gelators with terminal carboxylic acid groups.