Understanding the expression of molecular chirality in the self-assembly of a peptidomimetic organogelator

The expression of molecular chirality during the self-assembly of an amino-acid-based macrocyclic organogelator (1) has been studied. The gelation behaviour of enantiopure samples, as well as mixtures of both enantiomers, of this compound have been studied and important differences have been found between them. For example, the enantiopure samples form gels whereas the racemates does not. Electron microscopy reveals the formation of helicoidal fibers of opposite handedness in the gels formed by pure enantiomers, whereas only straight ribbons are found in the racemate and most of the nonenantiopure mixtures, X-ray powder diffraction shows an enantiospecific self-assembly in the mixtures that indicates the formation of enantiopure aggregates in all cases. These results are rationalized by considering the influence of the aggregates size on the gelation ability as well as the chirality expression at the supramolecular level. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).