Electron Transfer across Helical Peptides

Abstract

Electron transfer (ET) across proteins is one of the fundamental processes in nature. While trying to decipher and understand natural ET, much scientific effort has been employed in scaling down the process to the role of the elementary secondary‐structure units of proteins, that is, β sheets and α helices. Among these two motifs, the vast majority of studies have focused on α‐helical peptides because they require fewer amino acids for formation, they can be easily assembled on surfaces, and they can be easily functionalized. Herein, the focus is only on ET across α‐helical peptides, not only because of the reasons discussed, but also because they are one of the most promising biological molecules for integration into ET‐based bioelectronic devices. The different methodologies used to follow ET across the peptides, namely, photoinduced ET, electrochemistry, and solid‐state conductivity measurements (referred to as electron transport, ETp), are reviewed and discussed. In this context, the fundamental differences between the different methodologies, the appropriate interpretation of the results, and possible mechanisms to describe the ET(p) process in each methodology are discussed. Furthermore, possible functionalization of the helical peptides to modify and control their (opto‐)electronic properties is reviewed.

Macroscale Biomolecular Electronics and Ionics

“…The spatial organization of the redox centers is directed by proteins, where the redox center is usually a protein's cofactor, hence the medium between the donor and acceptor redox sites is the protein structure. The observation that electron flows can be mediated within proteins led to the emergence of a subfield in bioelectronics in the early 2000s, where proteins and peptides were examined for their electrical conductance in a molecular junction configuration . Likewise, DNA has been proposed as a candidate for low‐cost sequence programmable nanometer‐scale molecular devices .…”

Electron Hopping Across Hemin‐Doped Serum Albumin Mats on Centimeter‐Length Scales

“…Proteins are the main mediators of biological electron transport (ET), the best‐known processes being the mitochondrial respiratory ET chain reaction and the photosynthetic light reaction in plants, algae, and cyanobacteria . With inspiration from nature, the new field of “bioelectronics”—biologically based and/or biologically targeted electronics—has emerged.…”

Insights into the Distance Dependence of Electron Transfer through Conformationally Constrained Peptides

“…Understanding how peptide chains enable electron tunneling over long distances is the key to rationalize charge transfer processes in proteins and possibly control them in related synthetic systems. Many factors influence the actual electron transfer (ET) reaction in proteins, such as the nature of the peptide backbones involved, the presence of hydrogen bonds, the distance between neighbor peptide chains, the effect of the surrounding medium, and conformational fluctuation . The dynamics and mechanisms by which ET takes place in peptides have been the subject of active research and debate, especially regarding the possibility of triggering a superexchange or a sequential hopping mechanism as a function of the length and the primary and secondary structures of the given peptide .…”

“…Many factors influence the actual electron transfer (ET) reaction in proteins, such as the nature of the peptide backbones involved, the presence of hydrogen bonds, the distance between neighbor peptide chains, the effect of the surrounding medium, and conformational fluctuation. [1][2][3][4][5][6][7][8][9] The dynamics and mechanisms by which ET takes place in peptides have been the subject of active research and debate, especially regarding the possibility of triggering a superexchange [10][11][12] or a sequential hopping mechanism [12,13] as a function of the length and the primary and secondary structures of the given peptide. [2][3][4][5][6][7][8][9][10] These two mechanisms differ for the effective role of the molecular bridge (B) separating the donor (D) and the acceptor (A).…”