Synthesis and supramolecular self-assembly of glutamic acid-based squaramides

Juan V. Alegre-Requena, Marleen Häring, Isaac G. Sonsona, Alex Abramov, Eugenia Marqués-López, Raquel P. Herrera and David Díaz Díaz

Beilstein J. Org. Chem. 2018, 14, 2065–2073.

Abstract: We describe the preparation and characterization of two new unsymmetrical squaramide-based organogelators. The synthesis of the compounds was carried out by subsequent amine condensations starting from dimethyl squarate. The design of the gelators involved a squaramide core connected on one side to a long aliphatic chain and on the other side to a glutamic acid residue. The gelator bearing the free carboxylic groups showed a lower gelation capacity than its precursor diester derivative. Some selected gels were further studied by infrared spectroscopy, rheology and electron microscopy. Critical gelation concentrations and gel-to-sol transition temperatures were also determined for each case. In addition, the superior squaramide diester gelator was compared with an analogue triazole-based gelator in terms of critical gelation concentration, gelation kinetics and thermal phase transition.

Keywords: glutamic acid derivative; organogel; self-assembly; squaramide; supramolecular gel