pH‐Dependent Packing Mode Variations and Chirality Inversion in Short Peptide Self‐Assembly

Abstract Precise control of structures and morphologies in peptide self‐assembly has been challenging. We report the self‐assembly of amphiphilic peptides I 3 H, designed with a modular structure featuring three consecutive isoleucine residues as a hydrophobic tail and a C‐terminal histidine‐based hydrophilic headgroup. Microscopic, neutron scattering, and spectroscopic techniques demonstrate that the designed peptides self‐assemble into β‐sheet nanofibrils, with their helix handedness exhibiting subtle pH‐dependent inversion. pH titration, NMR, and molecular dynamics simulations reveal the underlying mechanism correlates with the protonation state of histidine and the molecular packing modes in β‐sheet assemblies. The protonated histidine promotes antiparallel β‐sheet packing at lower pH while its deprotonated state favors parallel packing when pH is increased. Strong π‐π stacking interactions between deprotonated histidine side chains in parallel β‐sheet arrangements drive chiral flipping of β‐strands, ultimately inducing supramolecular helix inversion. Furthermore, such a pH‐dependent helix inversion can be engineered by inserting the achiral and flexible glycine at the hydrophobic/hydrophilic interface, with I 3 GH assembly maintaining this effect while I 3 GGH assembly abolishing it. This work not only advances our mechanistic understanding of peptide chirality inversion at the level of individual β‐sheets but also provides a blueprint for designing hierarchical chirality through precise modulation of molecular packing modes and side‐chain interactions.