Electrical Behavior of Molecular Junctions Incorporating α-Helical Peptide

Abstract

We synthesized an alpha-helical peptide containing two terminal thiol groups and demonstrated the method of preparation of a self-assembled monolayer (SAM) on gold with uniform orientation of the molecules on the surface. The monolayers were employed as model systems for the investigations of mediated electron transfer. The measurements of electron transfer efficiency through the peptide were performed using scanning tunneling spectroscopy (STS). The molecules were trapped between the gold tip and the substrate using a Au-S linkage. The electron transfer behavior of the peptide was examined as a function of the tip-substrate distance at fixed bias voltage and as a function of bias voltage at a fixed distance between the tip and the substrate. The data obtained from these experiments indicated that the electron transfer through alpha-helical peptide is very efficient, and its conductivity is comparable to those observed for dodecanedithiol. There is also a directional dependence of electron transmission through the peptide, which is connected with the electric field generated by the molecular dipole of the helix.

Distal Charge Transport in Peptides

“…In fact, such structures could even lead to an interesting new class of electronic devices. [63,[104][105][106] We suggest that one of the principal motions for peptides reacting and transferring charge on a subpicosecond ultrafast time scale are the dihedral motions between neighboring amino acid sites. These unique motions could be of fundamental importance for the very early processes in protein dynamics.…”

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.…”

Bioinspired approach toward molecular electrets: synthetic proteome for materials

“…of CT across a junction between liquid and a solid conductor. A junction between solid conductors interfaced with assemblies of polypeptide helices extends the studies of such dipole effects onto charge-transport currents [129][130][131]. The use of polypeptides composed of residues with chargeable side chains such as lysine, however, raises question about the effect of the counterions in the SAMs on the measured rectification, which may depend on the state of protonation of the polypeptides.…”

“…When the structures with opposing dipole direction are not completely symmetrical, the differences in the electronic coupling can prevail over the dipole-induced effect for relatively large −ΔG CT (0) [125]. Since the beginning of the 21 st century, studies of dipole effects on CT have focused on systems comprising polypeptide helices [12,95,99,[126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141]. Donor-bridge-acceptor (DBA) constructs, where the bridge is a helix, allow for testing dipole-induced charge-transfer rectification, i.e.…”