Squaramides are four-membered, vinylogously conjugated diamides derived from squaric acid and show a high synthetic versatility. The field of squaramide chemistry has undergone exceptional growth in the wake of the pioneering studies of Rawal et al. who used these compounds as organocatalysts. One important feature of these scaffolds is their ability to bind selectively to different hydrogen bond acceptors through their acidic NH groups. Remarkably, squaramides play a dual role as they are also able to act as good hydrogen bond acceptors, making them suitable receptors for cation recognition. The N,N’-disubstituted squaramide 1 has been found to form nanostructured supramolecular alcogels in a range of alcoholic solvents via a self-assembly process. These gels show the ability to respond to thermal, mechanical, optical, and chemical stimuli. Gelation ability tests, solubility studies, PXRD studies, and computer modeling of a variety of structurally related squaramides demonstrated the existence of a unique combination of non-covalent molecular interactions and a favorable hydrophobic/hydrophilic balance in 1, which promotes the anisotropic growth of physical gel networks. The application of ultrasound revealed a remarkable effect on both the gelation kinetics and the properties of the alcogels. For instance, a decrease of the critical gelation concentration and gelation times were observed in comparison to the classical heating-cooling protocol. Moreover, the morphology of the gel aggregates (e.g., straight laths, entangled fibers) was found to be influenced by the nature of the solvent. Overall, these gels exemplify the strong competition between gelation and macroscopic crystallization typically observed in weak physical gels.

Resumen del póster presentado al 6th EuCheMS Chemistry Congress, celebrado en Sevilla (España) del 11 al 15 de septiembre de 2016.

Peer Reviewed