Tweaking of supramolecular hydrogel property of single and two-component gel systems by a bifunctional molecule

Abstract The properties of the supramolecular hydrogel built from the self-assembly of low molecular weight (LMW) compound play a crucial role in selecting the hydrogel for specific or targeted applications. Instead of developing new hydrogels, tweaking the properties of existing, well-known hydrogels using guest compounds may provide a way to design new hydrogel materials with desired properties. In this context, the influence of a bifunctional molecule (guest), namely 4,4′-Azopyridine (APy), on the thermal stability and viscoelastic properties of the supramolecular hydrogels built from a single (Fluorenylmethoxycarbonyl-L-Phenylalanine, FmF / Fluorenylmethoxycarbonyl-L-Tyrosine, FmY) and two-component (FmF+FmY) systems were analyzed. APy can connect the gelators through hydrogen bonding, and thereby it can tweak the property of the hydrogel. Various biophysical studies indicated that APy increased the gelation time of single and two-component systems while significantly improving the viscoelastic nature of both systems. Unlike FmF hydrogel, the regelation (thixotropy) efficiency of a two-component FmF+FmY gel system with APy showed complete recovery, suggesting that tweaking of thixotropic efficiency depends on the type of component gel systems. The Tgel of FmF gel was unaltered, while the two-component gel system had decreased stability in the presence of APy, suggesting that guest molecule can modulate the thermal stability of the two-component gel system. Gel characterization using various spectroscopic and microscopic techniques suggested that supramolecular self-assembly of gelators in a single and two-component systems with APy leads to fibrillar morphology, which is stabilized through intermolecular aromatic π-π stacking and hydrogen bonding interactions. NMR and FTIR analysis confirmed the interaction of APy with gelators in the self-assembled structure. Thus, the contemporary study demonstrated that the mechanical and thermal stability of the existing and/or new supramolecular gel systems could be modulated by co-assembly with guest molecules.