Abstract
<jats:p>Peptide self-assembly in aqueous media is dominated by hydrophobic collapse and backbone hydrogen bonding, further stabilized by side-chain-specific interactions such as cation-π, aromatic stacking, and electrostatics. However, under non-aqueous and low-water conditions, reduced contributions from the hydrophobic effect allow a rebalancing of intermolecular interactions. This opens up alternative assembly configurations, including ones suited to dry-state and solvent-responsive peptide materials. Here, we investigate how solvent environment (methanol vs water) and peptide sequence collectively impact supramolecular organization. We use a series of amphiphilic octapeptides with the general sequence (XEXK)2 where X represents hydrophobic amino acids with distinct side-chain properties (Phe, Trp, Ile, or Leu). In water, (FEFK)2, (IEIK)2 and (WEWK)2 formed the expected β-sheet-rich bilayer nanofiber assemblies, whereas (LELK)2 remained largely disordered. In methanol (MeOH), while (FEFK)2, and (IEIK)2 retained similar structures, solvent-dependent structural reconfiguration was observed for (WEWK)2 with a shift toward side-chain directed assembly, resulting in morphological transitions from one-dimensional nanofibers in water to extended two-dimensional nanosheets in MeOH. Comparison of molecular dynamics simulations in water and MeOH suggests significant reorganization of intermolecular interactions stabilized by H-bonding and electrostatic interactions, and presenting Trp residues toward solvent interface. In the dry state, these MeOH- assembled (WEWK)2 nanosheets could be transformed into nanofibers in the solid state, upon exposure to high relative humidity (RH) (or upon solvation in liquid water). These findings establish the internal conformational entropy and steric of amino acid side chains regulate the dynamicity, structural adaptability, and solvent-driven reconfiguration of peptide bilayer assemblies. This provides a framework for engineering adaptive, reconfigurable solid state peptide materials beyond aqueous self-assembly.</jats:p>