Proton Conduction in a Tyrosine-Rich Peptide/Manganese Oxide Hybrid Nanofilm

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 (MnO_x). The peptide/MnO_x 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.