A new class of selective low-molecular-weight gelators based on salts of diaminotriazinecarboxylic acids

New low-molecular-weight gelators can be discovered by an approach that integrates classical methods for identifying potential gelators with strategies recently developed by crystal engineers to build porous molecular networks. This hybrid approach has yielded a potent new class of selective gelators based on salts of 4,6-bis(arylamino)-1,3,5-triazine-2-carboxylic acids. These compounds lack the high degree of conformational flexibility and long alkyl chains typical of classical gelators, and Na+ and DMSO play specific roles in the mechanism of gelation. Scanning electron microscopy and atomic force microscopy showed that the resulting gels consist of elemental nanofibers that are approximately 30-100 nm in width, and X-ray diffraction yielded the structure of needle-shaped crystals of a gelator obtained directly from its gel. The crystals are constructed from bilayers, with the hydrophobic aryl groups of the gelators interacting intermolecularly to form the core of the bilayers and polar triazinecarboxylate headgroups aligned on the surface. The polar surfaces then stack in a process directed by the formation by multiple intermolecular hydrogen bonds and chelation of Na+. The hybrid approach that led to the discovery of these gels promises to yield other new molecular materials at the boundary between gels and crystalline solids.