Photocurrent generation through peptide-based self-assembled monolayers on a gold surface: antenna and junction effects (original) (raw)
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The journal of physical chemistry. A, 2014
Photoinduced electron transfer (PET) experiments have been carried out on peptide self-assembled monolayers (SAM) chemisorbed on a gold substrate. The oligopeptide building block was exclusively formed by C(α)-tetrasubstituted α-aminoisobutyric residues to attain a helical conformation despite the shortness of the peptide chain. Furthermore, it was functionalized at the C-terminus by a pyrene choromophore to enhance the UV photon capture cross-section of the compound and by a lipoic group at the N-terminus for linking to gold substrates. Electron transfer across the peptide SAM has been studied by photocurrent generation experiments in an electrochemical cell employing a gold substrate modified by chemisorption of a peptide SAM as a working electrode and by steady-state and time-resolved fluorescence experiments in solution and on a gold-coated glass. The results show that the electronic flow through the peptide bridge is strongly asymmetric; i.e., PET from the C-terminus to gold is...
Spectroscopy and Electrochemistry of Peptide-Based Self-Assembled Monolayers
Lecture Notes in Electrical Engineering, 2011
Mono and bi-component peptide-based self-assembled monolayers (SAMs) immobilized on a gold surface were studied by electrochemical and spectroscopic techniques. The peptides investigated were exclusively formed by C a-tetrasubstituted amino acids. These residues, due to their peculiar conformational properties, constrain the peptide in a helical conformation, as confirmed by X-ray diffraction structure determinations, and Circular Dichroism and NMR experiments in solution. Both mono-and bi-component peptide SAMs were functionalized with electroactive, fluorescent chromophores strongly absorbing in the UV region. While electrochemical experiments indicated the formation of densely-packed films on the gold surface, fluorescence spectroscopy revealed the occurrence of aromatic-aromatic interactions between the pyrene units functionalizing the peptide chains, obtaining important information on the structural and dynamical properties of the peptide SAMs investigated.
Electron Transfer Across α-Helical Peptide Monolayers: Importance of Interchain Coupling
Langmuir, 2012
Four helical peptides with the general formula (Boc)-Cys-(S-Acm)-(Ala-Leu) n-NH-(CH 2) 2-SH (n = 4−7) were synthesized and further used for the preparation of self-assembled monolayers (SAMs) on gold substrates. The electron-transfer behavior of these systems was probed using current-sensing atomic force microscopy (CS-AFM). It was found that the electron transmission through SAMs of helical peptides trapped between an AFM conductive tip and a gold substrate occurs very efficiently and that the distance dependence obeys the exponential trend with a decay constant of 4.6 nm −1. This result indicates that the tunneling mechanism is operative in this case. Conductance measurements under mechanical stress show that peptide-mediated electron transmission occurs with the possible contribution of intermolecular electron tunneling between adjacent helices. It was also demonstrated that an external electric field applied between metallic contacts can affect the structure of the peptide SAM by changing its thickness. This explains the asymmetry of the current−voltage response of metal−monolayer−metal junction.
Langmuir, 2011
Electron transfer through R-helices has attracted much attention from the viewpoints of their contributions to efficient long-range electron transfer occurring in biological systems and their utility as molecular-electronics elements. In this study, we synthesized a long 80mer helical peptide carrying a redox-active ferrocene unit at the terminal and immobilized the helical peptide on a gold surface. The molecular length is calculated to be 134 Å , in which the helix accounts for 120 Å . The preparation conditions of the self-assembled monolayers were intentionally changed to obtain monolayers with different physical states to study the correlation between molecular motions and electron transfer. Ellipsometry and infrared spectroscopy showed that the helical peptide forms a self-assembled monolayer with vertical orientation. Electrochemical measurements revealed that an electron is transferred from the ferrocene unit to gold through the monolayer composed of this long helical peptide, and the experimental data are well explained by theoretical results calculated under the assumption that electron transfer occurs by a unique hopping mechanism with the amide groups as hopping sites. Furthermore, we have observed a unique dependence of electron transfer on the monolayer packing, suggesting the importance of structural fluctuations of peptides on the electron transfer controlled by the hopping mechanism.
Biosensors and Bioelectronics, 2004
We fabricated a self-assembled monolayer (SAM) of a chimeric protein created as a novel model protein for an artificial light-harvesting complex (LHC) composed of two proteins, cytochrome b 562 (cytb 562 ) mutated for SAM fabrication (cytb 562 , N22C, G82C) and enhanced green fluorescent protein (EGFP). The SAM formation of chimeric protein on a single-crystalline Au(1 1 1) substrate was confirmed by atomic force microscopy (AFM) measurement. The rectified photocurrent of the chimeric protein SAM on a gold substrate was detected by light-illumination scanning tunneling microscopy (LI-STM) co-operated with a lock-in technique. The photocurrent generation of the chimeric protein SAM was wavelength-specific to the light-illumination (488 nm), which indicated that the EGFP part of the chimera plays a role as a sensitizer in the photo-induced electron transfer process.
Surface Science, 2006
A novel hexapeptide was functionalized at the N-terminus by a lipoyl group for binding to gold substrates. Owing to the high content of a-aminoisobutyric acid residues, the peptide adopts a rigid helical conformation despite the shortness of its main chain. Binding of the peptide to gold was investigated by quartz crystal microbalance, cyclic voltammetry, X-ray photoelectron spectroscopy, and scanning tunneling microscopy under ultra-high vacuum conditions. Scanning tunneling microscopy experiments revealed that the peculiar self-assembly properties of this short helical peptide determine the complex morphology of the monolayer, showing 'stripes', i.e. peptide aggregates horizontally layered on the gold surface, and 'holes', i.e. Au vacancy islands coated by the peptide monolayer.
Langmuir, 2006
Amphiphilic R-helices were formed from designed synthetic peptides comprising alanine, phenylalanine, and lysine residues. The insertion of the R-helical peptides into hybrid bilayers assembled on gold was studied by a variety of methods to assess the resulting structural characteristics, such as electrical resistance and molecular orientation. Self-assembled monolayers (SAMs) of dodecanethiol (DDT); octadecanethiol (ODT); and 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol (DPPTE) were formed on gold substrates with and without incorporated peptide. Supported hybrid bilayers and multilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) were formed on SAMs by the "paint-freeze" method of bilayer formation. Modeling of electrochemical impedance spectroscopy data using equivalent electrochemical circuits revealed that the addition of peptide decreased dramatically the resistive element of the bilayer films while maintaining the value of the capacitive element, indicating successful incorporation of peptide into a well-formed bilayer. Near-edge X-ray absorption fine structure spectroscopy data provided evidence that the molecules in the SAMs and hybrid multilayers were ordered even in the presence of peptide. The peptide insertion into the SAM was confirmed by observing the π* resonance peak correlating with phenylalanine and a peak in the nitrogen K-edge regime attributable to the peptide bond.
Chemistry – A European Journal, 2021
External stimuli are potent tools that Nature uses to control protein function and activity. For instance, during viral entry and exit, pH variations are known to trigger large protein conformational changes. In Nature, also the electron transfer (ET) properties of ET proteins are influenced by pH-induced conformational changes. In this work, a pH-controlled, reversible 3 10helix to α-helix conversion (from acidic to highly basic pH values and vice versa) of a peptide supramolecular system built on a gold surface is described. The effect of pH on the ability of the peptide SAM to generate a photocurrent was investigated, with particular focus on the effect of the pH-induced conformational change on photocurrent efficiency. The films were characterized by electrochemical and spectroscopic techniques, and were found to be very stable over time, also in contact with a solution. They were also able to generate current under illumination, with an efficiency that is the highest recorded so far with biomolecular systems.
Biomacromolecules, 2007
Light-harvesting antenna core (LH1-RC) complexes isolated from Rhodoseudomonas palustris were self-assembled on a gold electrode modified with self-assembled monolayers (SAMs) of the alkanethiols NH 2 (CH 2) n SH, n) 2, 6, 8, 11; HOOC(CH 2) 7 SH; and CH 3 (CH 2) 7 SH, respectively. Adsorption of the LH1-RC complexes on the SAMs depended on the terminating group of the alkanethiols, where the adsoption increased in the following order for the terminating groups: amino groups > carboxylic acid groups > methyl groups. Further, the adsorption on a gold electrode modified with SAMs of NH 2 (CH 2) n SH, n) 2, 6, 8, 11, depended on the methylene chain length, where the adsorption increased with increasing the methylene chain length. The presence of the well-known light-harvesting and reaction center peaks of the near infrared (NIR) absorption spectra of the LH1-RC complexes indicated that these complexes were only fully stable on the SAM gold electrodes modified with the amino group. In the case of modification with the carboxyl group, the complexes were partially stable, while in the presence of the terminal methyl group the complexes were extensively denatured. An efficient photocurrent response of these complexes on the SAMs of NH 2 (CH 2) n SH, n) 2, 6, 8, 11, was observed upon illumination at 880 nm. The photocurrent depended on the methylene chain length (n), where the maximum photocurrent response was observed at n) 6, which corresponds to a distance between the amino terminal group in NH 2 (CH 2) 6 SH and the gold surface of 1.0 nm.