From Amorphous Bundles to Nanoporous Peptide Frameworks: Solvent-driven Self-assembly of Pro-Val-Pro-Val

Peptides are ubiquitous and functionally diverse biomolecules with a strong propensity to self-assemble into a wide range of non-covalent nanostructures. Remarkably, even short-chain sequences can give rise to molecular architectures with unexpected complexity. In this study, we utilise Nuclear Magnetic Resonance (NMR), X-ray diffraction, and computational materials modelling to investigate the solvent-directed self-assembly of an amphiphilic L-Prolyl-L-Valyl-L-Prolyl-L-Valine (PVPV) tetrapeptide, resulting in two distinct crystal architectures. Crystallization from a water–methanol mixture yields a symmetric, nanoporous tetragonal framework incorporating a highly disordered water network. In contrast, nucleation from pure water results in either a minimally hydrated amorphous phase or a dense, conformationally disordered triclinic structure. In both cases, crystallographic analysis reveals a helical secondary structure primarily stabilized by charge-assisted hydrogen bonding. Theoretical calculations indicate that the porous tetragonal framework is energetically unfavourable, highlighting the importance of water disorder and conformational flexibility in the formation of metastable, non-covalent frameworks. These features pose challenges for first-principles modelling, exposing limitations of static semi-local density functional theory. The low-hydration phase exhibits intrinsic conformational disorder, calling for in-depth investigation via NMRcrystallography. Advanced solid-state NMR on isotopically labelled samples provides spectral assignments, revealing subtle, off-symmetric molecular distortions that affect local molecular ordering.