Helicity Inversion of Supramolecular Hydrogels Induced by Achiral Substituents

Probing
the supramolecular chirality of assemblies and controlling
their handedness are closely related to the origin of chirality at
the supramolecular level and the development of smart materials with
desired handedness. However, it remains unclear how achiral residues
covalently bonded to chiral amino acids can function in the chirality
inversion of supramolecular assemblies. Herein, we report macroscopic
chirality and dynamic manipulation of chiroptical activity of hydrogels
self-assembled from phenylalanine derivatives, together with the inversion
of their handedness achieved solely by exchanging achiral substituents
between oligo­(ethylene glycol) and carboxylic acid groups. This helicity
inversion is mainly induced by distinct stacking mode of the self-assembled
building blocks, as collectively confirmed by scanning electron microscopy,
circular dichroism, crystallography, and molecular dynamics calculations.
Through this straightforward approach, we were able to invert the
handedness of helical assemblies by merely exchanging achiral substituents
at the terminal of chiral gelators. This work not only presents a
feasible strategy to achieve the handedness inversion of helical nanostructures
for better understanding of chiral self-assembly process in supramolecular
chemistry but also facilities the development of smart materials with
controllable handedness in materials science.