Proton‐Conductive Melanin‐Like Fibers through Enzymatic Oxidation of a Self‐Assembling Peptide

Abstract

Melanin pigments have various properties that are of technological interest including photo‐ and radiation protection, rich coloration, and electronic functions. Nevertheless, laboratory‐based synthesis of melanin and melanin‐like materials with morphologies and chemical structures that are specifically optimized for these applications, is currently not possible. Here, melanin‐like materials that are produced by enzymatic oxidation of a supramolecular tripeptide structures that are rich in tyrosine and have a 1D morphology are demonstrated, that are retained during the oxidation process while conducting tracks form through oxidative tyrosine crosslinking. Specifically, a minimalistic self‐assembling peptide, Lys–Tyr–Tyr (KYY) with strong propensity to form supramolecular fibers, is utilized. Analysis by Raman spectroscopy shows that the tyrosines are pre‐organized inside these fibers and, upon enzymatic oxidation, result in connected catechols. These form 1D conducting tracks along the length of the fiber, which gives rise to a level of internal disorder, but retention of the fiber morphology. This results in highly conductive structures demonstrated to be dominated by proton conduction. This work demonstrates the ability to control oxidation but retain a well‐defined fibrous morphology that does not have a known equivalent in biology, and demonstrate exceptional conductivity that is enhanced by enzymatic oxidation.

Elucidation of the structure of supramolecular polymorphs in peptide nanofibres using Raman spectroscopy

“…The previously reported point-based Raman analysis of KYY nanofibres assigned the spectrum to a supramolecular system in a β-sheet confirmation. [18] However, a fuller elucidation of the nanofibre was achieved in this study by providing more detailed spectroscopic interpretation on the system using Raman mapping analysis. First, the Raman spectra of the tripeptide KYY powder, structure shown in Figure 1a, tyrosine and lysine were collected and are shown in Figure S1 (supporting information).…”

“…They furthered this work by designing a tripeptide, lysine-tyrosine-tyrosine (KYY) precursor that selfassembles into supramolecular nanofibres, that retained their fibrillar morphology and present melanin-like properties after enzymatic oxidation. [18] In order to fully characterise the self-assembled nanofibres before oxidation, averaged point-based Raman spectroscopy was included in the analysis. Overall, the results suggested the nanofibres were in a β-sheet confirmation, however the Raman data was complex and variations in intensity were noted.…”

Anisotropic Synthetic Allomelanin Materials via Solid‐State Polymerization of Self‐Assembled 1,8‐Dihydroxynaphthalene Dimers

“…Synthetic melanins are polymeric materials formed by oxidative polymerization. [18] Therefore,t or ealize synthetic allomelanins,t he pre-organized DHN dimers self-assembled…”

Diketopiperazine Gels: New Horizons from the Self-Assembly of Cyclic Dipeptides

“…In particular, self-assembling short-peptides represent cheap building blocks for large-scale production, and with overall promising properties in terms of bioactivity [ 2 ] and biocompatibility to achieve functional materials [ 3 , 4 ]. The large chemical diversity they provide ensures continuous advancements, and even considering just the publications in the last couple of years, numerous regard self-assembling tripeptides [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ] and dipeptides [ 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Furthermore, the study of such simple systems could advance the understanding of prebiotic chemistry, relative to the potential role of peptide-based organized structures in the emergence of catalytic activity [ 26 ].…”