Backbone-Constrained Tripeptides Enable Sequence Control of Solid-State Dynamics

Understanding how peptide sequence relates to supramolecular dynamics and consequent solid-state material properties remains a central challenge for rational peptide materials design. Here, we use N-terminal proline as a strategic conformational constraint in minimalist tripeptides (PXX; P = proline, X = phenylalanine (F) or tryptophan (W)) to isolate side-chain contributions from backbone and show that simple aromatic exchange dictates crystallization pathways and solid-state dynamics. In this design, proline rigidifies the backbone, the central residue supports assembly, and the C-terminal aromatic residue dictates conformational adaptability. Combining molecular dynamics simulations with NMR and fluorescence spectroscopy, we show that peptides with W at the C-terminus, with a diverse interaction space, display shallow energy landscapes with multiple accessible states, whereas a C-terminal F, with a stringent hydrophobic nature and limited interaction space, restricts the peptide into fewer conformations. As a result, PXF peptides form soluble supramolecular aggregates, while PXW peptides access more adaptable conformations that promote crystallization. Solid-state characterization reveals that these sequence-encoded supramolecular dynamics directly influence bulk properties: W-containing peptides form stiff crystals with dynamic, wettable surfaces, whereas F analogues yield static, hydrophobic materials. Together, these results establish how aromatic-residues dictate supramolecular assembly and crystallization, offering a straightforward approach to engineering dynamic properties in solid-state peptide materials.