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.