Designing Stimuli-Responsive Supramolecular Gels by Tuning the Non-Covalent Interactions of the Functional Groups

The physical characteristics of a supramolecular gel are greatly influenced by the nature and arrangement of functional groups in the gelator. This work focuses on the impact of the functional groups, specifically the hydroxyl group, on the stimuli-responsive properties of a gel. We used a <i>C</i>₃-symmetric benzene-1,3,5-tricarboxamide (BTA) platform, which was attached to the methyl ester of phenylalanine (MPBTA) and tyrosine (MTBTA). The gelation studies revealed that MPBTA gelled in alcohols, non-polar aromatic solvents, and aqueous mixtures (1:1, <i>v</i>/<i>v</i>) of high-polar solvents, whereas MTBTA gelled only in an aqueous mixture of DMF (1:1, <i>v</i>/<i>v</i>). The mechanical and thermal strength of the gels were evaluated by rheological and <i>T_gel</i> studies, and the results indicated that MPBTA gels were stronger than MTBTA gels. The gels were characterized by powder X-ray diffraction and scanning electron microscopy (SEM). The analysis of stimuli-responsive properties revealed that MPBTA gels were intact in the presence of sodium/potassium salts, but the MTBTA gel network was disrupted. These results indicate that the elegant choice of functional groups could be used to tune the constructive or destructive stimuli-responsive behavior of gels. This study highlights the significant role of functional groups in modulating the stimuli-responsive properties of supramolecular gels.