One of the important challenges in the development of protein-mimetic materials is understanding the sequence-specific assembly behavior and dynamic folding change. Conventional strategies for constructing two-dimensional (2D) nanostructures from peptides have been limited to using β-sheet forming sequences as building blocks due to their natural tendency to form sheet-like aggregations. We have identified a peptide sequence (YFCFY) that can form dimers via a disulfide bridge, fold into a helix, and assemble into macroscopic flat sheets at the air/water interface. Due to the large driving force for 2D assembly and high elastic modulus of the resulting sheet, the peptide assembly induces flattening of the initially round water droplet. Additionally, we found that stabilization of the helix by dimerization is a key determinant for maintaining macroscopic flatness over a few tens of centimeters even with a uniform thickness of <10 nm. Furthermore, the ability to transfer the sheets from a water droplet to another substrate allows for multiple stacking of 2D peptide nanostructures, suggesting possible applications in biomimetic catalysis, biosensors, and 2D related electronic devices.

Proton conduction is an essential process that regulates an integral part of several enzymatic catalyses and bioenergetics. Proton flows in biological entities are sensitively controlled by several mechanisms. To understand and manipulate proton conduction in biosystems, several studies have investigated bulk proton conduction in biomaterials such as polyaspartic acid, collagen, reflectin, serum albumin mats, and eumelanin. However, little is known about the bulk proton conductivity of short peptides and their sequence‐dependent behavior. Here, this paper focuses on a short tyrosine‐rich peptide that has redox‐active and cross‐linkable phenol groups. The spin‐coated peptide nanofilm is immersed in potassium permanganate solution to induce cross‐linking and oxidation, simultaneously leading to hybridization with manganese oxide (MnOx). The peptide/MnOx hybrid nanofilm can efficiently transport protons, and its proton conductivity is ≈18.6 mS cm−1 at room temperature. This value is much higher than that of biomaterials and comparable to those of other synthetic proton‐conducting materials. These results suggest that peptide‐based hybrid materials can be a promising new class of proton conductor.

Mobile protons affect dielectric properties of peptides by forming an electrical double layer.