Study of the effect of polymorphism on the self-assembly and catalytic performance of an l-proline based molecular hydrogelator

Abstract

An exhaustive study of the polymorphism found for aggregates and hydrogels of an L-proline based hydrogelator under different preparation conditions is undertaken. The effect of heating temperature, aging time, ultrasound and pH switching on the self-assembly in water has been studied. WAXD analysis of the freeze-dried materials revealed the presence of four polymorphs, three of which could be isolated under specific conditions. Polymorphic differences have been studied by DSC, FTIR, circular dichroism and electron microscopy. Furthermore, the catalytic activity of each polymorph has been tested for the direct aldol reaction between cyclohexanone and 4-nitrobenzaldehyde revealing differences in the reaction rates that could be attributed to differences in molecular packing and aggregate morphology among them. The current study highlights the role that polymorphism plays in the application of functional supramolecular soft materials.