Conductance of α-Helical Peptides Trapped within Molecular Junctions

Abstract

Self-assembled monolayers of alpha-helical peptides on a gold surface were employed as model systems for the investigation of mediated electron transfer. The peptides contained 14, 15, 16, and 17 amino acid residues. The measurements of electron transmission through single molecules of helical peptides were performed using scanning tunneling spectroscopy (STS). The molecules were trapped between the gold tip and the substrate. Electrical contact between the molecule and the gold probe was achieved by the use of peptides containing thiol groups present at each end of the helix. The conductance behavior of the peptides was examined as a function of tip-substrate distance at fixed bias voltage. Measurements performed with peptides containing different numbers of amino acid residues indicate that the distance dependence of electron transmission through an alpha-helix is weaker than that through simple n-alkyl bridges.

Solid-state electron transport via cytochrome c depends on electronic coupling to electrodes and across the protein

“…Thus, it is very likely that the Hg drop contacts in each case only the most exposed amino acids. The lack of correlation between the measured current densities and the calculated electrode separation distances (protein monolayer widths) is in contrast to results obtained from ETp studies via peptides (35)(36)(37) and peptide nucleic acids (38). However, none of the latter molecules contain an internal cofactor, like CytC and Az do.…”

Distance dependence of long‐range electron transfer through helical peptides

“…Especially, electron transfer through helices has attracted much attention because it is believed that α-helical segments play an essential role in mediating an electron and determining its direction in biological systems [6]. To study the nature of electron transfer, radiolysis [7,8] and photoinduced electron-transfer [9] studies in solution (donor-peptide-acceptor), electrochemical studies on self-assembled monolayer (SAM) systems (donor-peptide-metal) [10][11][12][13][14][15], and recently, single molecule measurements by scanning probe microscopy (metal-peptide-metal) [16][17][18], have been conducted intensively. Most of the researchers agree that a helical peptide is a good electron mediator and enables electron transfer over a long distance.…”

“…tunneling behavior for Ala-rich 14mer to 17mer peptides with β of 0.50Å −1 [18]. Their peptides were long but they were substantially tilted on the gold surface, where the shortcut distance along the surface normal was 18-21Å, implying to be in the distance range of tunneling.…”

Tuning electronic transport via hepta-alanine peptides junction by tryptophan doping

“…oligopeptide | electron transport | self-assembled monolayer | inelastic electron tunneling spectroscopy | doping E lectron transfer (ET) processes taking place between prosthetic groups across the polypeptide matrices of proteins (1-3) have been extensively explored by, e.g., time-resolved photolysis (4,5), pulse radiolysis (6, 7), scanning tunneling microscopy (8,9), electrochemical methods (10)(11)(12), and by theoretical studies (13)(14)(15)(16). The surprisingly fast and efficient ET over considerable distances (up to ∼25 Å) (17) via peptide matrices in proteins suggests possible development of peptide-and protein-based bioelectronics with diverse functionality and relative ease of modification (18,19).…”