Electronic structure of dipeptides in the gas-phase and as an adsorbed monolayer

The electronic properties of peptide molecules can change considerably with their structure, allowing for diverse design possibilities of peptide-based molecular electronic devices. We explore the effect of the side-chain on the peptide’s electronic properties, by using both experimental and computational tools to detect the energy levels of the electronic structure of two model peptides - 2Ala and 2Trp - as well as these peptides with a 3-mercaptopropionic acid linker which allows them to form monolayers on Au surface. Specifically, we compare experimental gas phase ultraviolet photoemission spectroscopy measurements with density functional theory-based computational results, using the optimally-tuned range-separated hybrid functional formalism. By analyzing differences in frontier energy levels and molecular orbitals between peptides in gas-phase and in a monolayer, we find that the electronic properties of the peptide side-chain are maintained during binding of the peptide to the gold substrate. This indicates that the energy barrier for the peptide electron transport can be tuned by the amino acid compositions, which suggests a route for structural design of peptide-based electronic devices.