A smart supramolecular hydrogel of N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine exhibiting pH-modulated properties.

Six L-histidine-based amphiphiles, N(alpha)-(4-n-alkyloxybenzoyl)-L-histidine of different hydrocarbon chain lengths, were designed, synthesized, and examined for their ability to gelate water. Four of members of this family of amphiphiles were observed to form thermoreversible hydrogels in a wide range of pH at room temperature. The structural variations were characterized by critical gelation concentration, gelation time, gel melting temperature (T(gs)), rheology, and electron microscopy. Among the amphiphiles, the n-octyl derivative showed better gelation ability in the studied pH range. The amphiphiles were found to have T(gs) higher than body temperature (37 degrees C) showing their stability. Also, relatively higher yield stress (>1000 Pa) values of the hydrogels show their higher strength. The effective gelator molecules self-assemble into fibrous structures. Scanning electron microscopic picture of the hydrogels revealed large ribbons with right-handed twist. Small-angle XRD and circular dichroism spectroscopy were also employed to characterize the hydrogels. It was observed that pi-pi stacking, hydrophobic interaction, amide hydrogen bonding, and solubility factor contribute to the stability and strength of the hydrogels.