The Correlation of Electrochemical Measurements and Molecular Junction Conductance Simulations in β‐Strand Peptides

Abstract

Understanding the electronic properties of single peptides is not only of fundamental importance, but it is also paramount to the realization of peptide-based molecular electronic components. Electrochemical and theoretical studies are reported on two β-strand-based peptides, one with its backbone constrained with a triazole-containing tether introduced by Huisgen cycloaddition (peptide 1) and the other a direct linear analogue (peptide 2). Density functional theory (DFT) and non-equilibrium Green's function were used to investigate conductance in molecular junctions containing peptides 3 and 4 (analogues of 1 and 2). Although the peptides share a common β-strand conformation, they display vastly different electronic transport properties due to the presence (or absence) of the side-bridge constraint and the associated effect on backbone rigidity. These studies reveal that the electron transfer rate constants of 1 and 2, and the conductance calculated for 3 and 4, differ by approximately one order of magnitude, thus providing two distinctly different conductance states and what is essentially a molecular switch. A definitive correlation of electrochemical measurements and molecular junction conductance simulations is demonstrated using two different charge transfer techniques. This study furthers our understanding of the electronic properties of peptides at the molecular level, which provides an opportunity to fine-tune their molecular orbital energies through suitable structural manipulation.

Exploiting the interplay of quantum interference and backbone rigidity on electronic transport in peptides: a step towards bio-inspired quantum interferometers

“…A similar correlation was previously found for β-strand linear/cyclic peptides attached to electrode(s) comprising a triazole linker. 27 Destructive quantum interference is always accompanied by a reduction in the rate of electron transfer, 41,42 which was observed with the cyclic peptide 9. Despite peptides 9 and 10 sharing a common β-strand conformation, the effects of destructive quantum interference were found to occur essentially in the cyclic peptide, through the heterogenous backbone and the additional tunneling pathway provided by the side-bridge constraint.…”

“…Our earlier studies 4,5 suggest that this may be the result of the additional backbone rigidity imparted by the sidebridge constraint, which restricts the precise backbone torsional motion required by a hopping mechanism to facilitate intramolecular electron transfer through the peptide. 16,27 However, it is also possible that the side-chain tether can provide an additional electron transport pathway.…”

“…This design was formulated as electrochemical measurements for peptides bearing a ferrocene moiety and STM conductance of peptides terminated with two thiol groups both reveal crucial insights into electronic transport properties. 27,31,32 The transmission spectra of molecular junctions containing individual peptides were computed at different bias voltages, ranging from -2 V to 2 V, in order to calculate the current, and ultimately conductance, through the respective molecular junctions.…”

“…Peptides 9 and 10 ( Fig. 4a) were separately bound between two gold electrodes via thiol groups that contribute efficient electronic coupling at the peptide/electrode interface, 27,33 to form a molecular junction with an S-S distance of 18 Å (Table S8). The transmission function for the molecular junction containing peptide 9 was found to be significantly lower than that of peptide 10 at a bias voltage of 0 V (Fig.…”

“…between 0.1 V and 1.1 V vs Ag/AgCl. 27 The conductance values for the cyclic and linear peptides, 9 and 10, were Please do not adjust margins…”