An Easy Access to Organic Salt-Based Stimuli-Responsive and Multifunctional Supramolecular Hydrogels

By exploiting orthogonal hydrogen bonding involving supramolecular synthons and hydrophobic/hydrophilic interactions, a new series of simple organic salt based hydrogelators derived from pyrene butyric acid and its beta-alanine amide derivative, and various primary amines has been achieved. The hydrogels were characterised by microscopy, table-top rheology and dynamic rheology. FTIR, variable-temperature H-1 NMR and emission spectroscopy established the role of various supramolecular interactions such as hydrogen bonding and p-p stacking in hydrogelation. Single-crystal X-ray diffraction (SXRD) studies supported the conclusion that orthogonal hydrogen bonding involving amide-amide and primary ammonium monocarboxylate (PAM) synthons indeed played a crucial role in hydrogelation. The hydrogels were found to be stimuli-responsive and were capable of sensing ammonia and adsorbing water-soluble dye (methylene blue). All the hydrogelators were biocompatible (MTT assay in RAW 264.7 cells), indicating their suitability for use in drug delivery.