Oxidation‐Responsive Supramolecular Hydrogel Based on a Simple Fmoc‐Cysteine Derivative Capable of Showing Autonomous Gel–Sol–Gel Transitions

Abstract

AbstractAqueous soft matter, including supramolecular hydrogels capable of exhibiting stimuli–responsive macroscopic phase transitions, has attracted increasing attention for the exploration of functional soft materials. However, the investigation of supramolecular hydrogels that undergo autonomous and multiple macroscopic phase transitions (e.g., gel–sol–gel, sol–gel–sol) in response to the surrounding environment without repeated additions of stimuli has remained largely unexplored. In this study, the oxidation‐responsive autonomous gel–sol–gel transitions of supramolecular hydrogels fabricated via the self‐assembly of a simple fluorenylmethyloxycarbonyl (Fmoc)‐protected, benzylated cysteine (Fmoc‐CBzl) is presented. During the evaluation of the oxidation process of Fmoc‐CBzl, it is revealed that the oxidized products, two diastereomeric sulfoxides (Fmoc‐CBzl‐(R)‐O and Fmoc‐CBzl‐(S)‐O), exhibit significantly different self‐assembly propensities under aqueous conditions. It may be noteworthy that the chirality of sulfoxide is largely overlooked and not effectively used to modulate supramolecular, self‐assembled nanostructures. The difference in the self‐assembly propensities and kinetics of self‐assembly/disassembly as well as co‐assembly will contribute to oxidation‐responsive autonomous gel–sol–gel transitions.