Supramolecular amino acid based hydrogels: Probing the contribution of additive molecules using NMR spectroscopy

Supramolecular hydrogels are composed of self-assembled solid networks that restrict the flow of water. L-phenylalanine is the smallest molecule reported to date to form gel networks in water, and it is of particular interest due to its crystalline gel state. Single and multi-component hydrogels of L-phenylalanine are used herein as model materials to develop an NMR-based analytical approach to gain insight into the mechanisms of supramolecular gelation. Structure and composition of the gel fibres were probed using PXRD, solid-state NMR experiments and microscopic techniques. Solution-state NMR studies probed the properties of free gelator molecules in an equilibrium with bound molecules. The dynamics of exchange at the gel/solution interfaces was investigated further using HR-MAS and saturation transfer difference (STD) NMR experiments. This approach allowed us to identify which additive molecules contributed in modifying the material properties.