Sequence dependent proton conduction in self-assembled peptide nanostructures

Abstract

The advancement of diverse electrochemistry technologies depends on the development of novel proton conducting polymers. Inspired by the efficacy of proton transport through proteins, we show in this work that self-assembling peptide nanostructures may be a promising alternative for such organic proton conducting materials. We demonstrate that aromatic amino acids, which participate in charge transport in nature, unprecedentedly promote proton conduction under both high and low relative humidity conditions for d,l α-cyclic peptide nanotubes. For dehydrated networks long-range order of the assemblies, induced by the aromatic side chains, is shown to be a dominating factor for promoting conductivity. However, for hydrated networks this order of effect is less significant and conductivity can be improved by the introduction of proton donating carboxylic acid peptide side chains in addition to the aromatic side chains despite the lower order of the assemblies. Based on these observations, a novel cyclic peptide that incorporates non-natural naphthyl side chains was designed. Self-assembled nanotubes of this peptide show greatly improved dehydrated conductivity, while maintaining high conductivity under hydrated conditions. We envision that the demonstrated modularity and versatility of these bio inspired nanostructures will make them extremely attractive building blocks for the fabrication of devices for energy conversion and storage applications, as well as other applications that involve proton transport, whether dry or wet conductivity is desired.

Significant Enhancement of Proton Transport in Bioinspired Peptide Fibrils by Single Acidic or Basic Amino Acid Mutation

“…Accordingly, noncanonical aromatic amino acids have been used to enhance electron conductivity of peptide fibrils . We have further demonstrated the possibility of inducing proton and mixed proton–electron transport in such fibrils . In particular, we have shown that the introduction of four redox‐active aromatic side chains can improve proton conductivity of self‐assembled octapeptide nanotubes, in particular under dry conditions .…”

“…Proton conduction in protein films relies greatly on the relationships between proteins' structure and the underlying fundamental proton transfer processes . Revealing these links can aid in developing and optimizing protein‐based biomaterials for future bioelectronics applications.…”

Macroscale Biomolecular Electronics and Ionics

“…In this review, we mainly focused on protonic conductivity, and we believe that macroscopic protein‐ or peptide‐based structures can vastly contribute to our understanding of natural proton conduction. For instance, and as discussed above, films of the reflectin protein as well as self‐assembled structure of amyloid‐like peptides were used to decipher the role of a certain amino acid in the proton conduction mechanism …”

Genetically encoded conductive protein nanofibers secreted by engineered cells

“…Conductive self-assembled peptide systems are of considerable interest because of the well-recognized ability of the selfassembly process to enhance the conductivity of polymers, 69,70 and the promising applications of conductive self-assembled peptides for a range of disciplines. 56,57,71 In this work, we report the rst demonstration of a curli-based self-assembling system that is secreted directly by E. coli cells and exhibits higher conductivity compared to native biolms. Sequence optimization of the PilA-inspired peptide molecule revealed that aromatic amino acids were responsible for conductivity, possibly due to p-p stacks and electron hopping.…”