pH-Regulated supramolecular chirality of phenylalanine-based hydrogels

To achieve desired physicochemical and biochemical activities of optically active molecules at targetted sites in biological systems, tuning of chiral sense by varying internal conditions (e.g., pH) is of utmost importance. However, it has been a challenge to gain the balance of non-covalent interactions required for chiral transformations merely by deviations in biochemical environment. Herein, pH-controlled chirality of supramolecular nanostructures obtained from coassembly of phenylalanine-derived gelator and achiral cationic polyacrylamide has successfully been achieved. Specifically, any changes in the pH remarkably influence the chirality of these nanostructures. For instance, coassembled hydrogels possessing l-enantiomer provide right-handed nanostructures at pH < 7; whereas at pH ≥ 7, handedness of nanostructures switches to the left-handed nanostructures. Moreover, viscoelastic properties and twist pitch were also regulated under the influence of pH change. This study may provide a methodology to control chirality by simply varying biochemical conditions, which points toward its potential to be used in biological systems as a key to gain preferential chiral sense in different sites of living systems.