Intrinsically Charged Peptide Nanomembranes as Self-Organized Electrostatic Interfaces in Confined Ionic Liquids

Abstract Self-assembled biomolecular materials provide a promising route for designing soft, sustainable, and molecularly tunable electrostatic interfaces that are relevant to energy storage, iontronics, and bioinspired electrochemical systems. However, the molecular mechanisms by which charged peptide assemblies organize confined ionic environments and generate interfacial electrostatic gradients remain poorly understood. Here, we use fully atomistic molecular dynamics simulations to investigate self-assembled peptide nanomembranes composed of the bolaamphiphilic sequences EFL4FE and RFL4FR immersed in the ionic liquid [PYR][TFSI]. We examine these nanosheets as intrinsically charged supramolecular interfaces, whose surface charges arise from peptide composition, predefined protonation states, and supramolecular organization. The distinct charge characteristics of the two peptide sequences produce sequence-dependent ionic organization with preferential recruitment of cations or anions according to the local sign of the peptide charge. In both systems, localized peptide charges induce compact counterion accumulation, co-ion depletion, charge density oscillations, and electrical double-layer (EDL)-like organization. Consequently, the confined ionic liquid exhibits pronounced interfacial structuring and electrostatic potential gradients governed by the spatial distribution of charges within the peptide nanomembranes. Moreover, the electrostatic potential profiles indicate that the interfacial perturbation extends into the supramolecular membrane rather than being restricted to the electrolyte-facing surface. Within the limitations of the nonreactive classical fixed-charge model, these results provide molecular-level evidence that intrinsically charged peptide nanomembranes can organize confined ionic liquids and sustain electrostatic gradients across supramolecular interfaces. Their potential use as electrostatic transduction elements or components of iontronic and electrochemical devices requires further investigation, explicitly addressing electronic transport, external electrical coupling, and device-level operation.