Probing Charge Transport through Peptide Bonds

Abstract

We measure the conductance of unmodified peptides at the single-molecule level using the scanning tunneling microscope-based break-junction method, utilizing the N-terminal amine group and the C-terminal carboxyl group as gold metal-binding linkers. Our conductance measurements of oligoglycine and oligoalanine backbones do not rely on peptide side-chain linkers. We compare our results with alkanes terminated asymmetrically with an amine group on one end and a carboxyl group on the other to show that peptide bonds decrease the conductance of an otherwise saturated carbon chain. Using a newly developed first-principles approach, we attribute the decrease in conductance to charge localization at the peptide bond, which reduces the energy of the frontier orbitals relative to the Fermi energy and the electronic coupling to the leads, lowering the tunneling probability. Crucially, this manifests as an increase in conductance decay of peptide backbones with increasing length when compared with alkanes.

Charge Transport through Peptides in Single‐Molecule Electrical Measurements

“…Recently, Brisendine et al . studied the charge transport properties of unmodified peptides in aqueous solution, utilizing the carboxyl and amine group as gold metal‐binding linkers (as shown in Figure c) . They measured a serious of oligoglycine…”

“…Reproduced with permission from Brisendine et al . Copyright 2018, The Journal of Physical Chemistry Letters …”

“…Brisendine et al . carried out the conductance measurements using STM‐BJ technique to investigate the charge transport properties through natural peptides in aqueous solutions . It was found that the conductance of the single‐peptide junctions decreased with the increasing number of peptide bonds and the charge transport of the peptides showed a distinct tunneling mechanism.…”

Doping hepta-alanine with tryptophan: A theoretical study of its effect on the electrical conductance of peptide-based single-molecule junctions

“…2,3,18 For this reason, the study of the conduction properties of individual peptides and polypeptides, which are their building blocks, is essential and sparking interest recently. 1,[19][20][21][22][23][24][25][26][27][28][29][30][31] It is well known that peptides can act as bridges for long-range electron transfer and that this process depends on details of the amino acid sequence as well as on their secondary structure. 32,33 The situation is not so clear in the case of electron transport through peptide-based molecular junctions, where it has been reported that homopeptide monolayers can be more conductive than, for instance, alkane chains.…”

“…29 However, it has also been shown that peptide bonds actually reduce the conductance of single-molecule junctions below those of saturated carbon chains. 31 This work is motivated by the experimental results of Ref. 34.…”