A controllable mechanistic transition of charge transfer in helical peptides: from hopping to superexchange

Abstract

Understanding the electronic properties inherent to peptides is crucial for controlling charge transfer, and precursory to the design and fabrication of bio-inspired next generation electronic components. However, to achieve this objective one must first be able to predict and control the associated charge transfer mechanisms. Here we demonstrate for the first time a controllable mechanistic transition in peptides resulting directly from the introduction of a side-bridge. High level computational studies on two similar 3₁₀-helical hexapeptides, one further constrained into this geometry by linking the i to i + 3 residues with a lactam side-bridge, highlight the effects of the bridge on electron transfer parameters, i.e. thermodynamic driving forces, reorganization energies, and electronic coupling factors. The additional backbone rigidity imparted by the bridge significantly alters the molecular dynamics of the peptide to such an extent as to induce a mechanistic transition from hopping in the linear peptide, to superexchange in the constrained peptide. This exciting finding not only advances our fundamental knowledge of the mechanisms governing charge transfer in peptides, but also reveals novel approaches to design and develop new functional devices that are tailored for applications in molecular electronics.