Backbone-Constrained Peptides: Temperature and Secondary Structure Affect Solid-State Electron Transport

Abstract

The primary sequence and secondary structure of a peptide is crucial to peptide charge migration, not only in solution (electron transfer, ET), but also in the solid-state (electron transport, ETp). Hence, understanding the charge migration mechanisms is fundamental to develop biomolecular devices and sensors. We report studies on four Aib-containing helical peptide analogues: two acyclic linear peptides with one and two electron-rich alkene-based side chains, respectively, and two peptides that are further rigidified into a macrocycle by a side bridge constraint, containing one or no alkene. ETp was investigated across Au/peptide/Au junctions, between 80 and 340 K in combination with the molecular dynamic (MD) simulations. The results reveal that the helical structure of peptide and electron-rich side chain both facilitate the ETp. With increasing temperature, the loss of helical structure, change of monolayer tilt angle and the increase of thermally activated fluctuations affect the conductance of peptides. Specifically, room temperature conductance across the peptide monolayers correlates well with previously observed ET rate constants, where combined actions between backbone rigidity and electron-rich side chains were revealed. Our findings provide new means to manipulate electronic transport across solid-state peptide junctions.