Publications

Electron transfer (ET) between redox proteins is an essential process in the respiratory and photosynthetic transport chains. While intra-protein ET is well characterized, the experimental methods to investigate inter-protein ET are limited by the presence of the solvent and by the transient nature of the protein-protein interaction and ET event, which are averaged in protein ensembles. Wiring precisely oriented redox protein partners to the nanoscale electrodes of an electrochemical scanning tunneling microscope allows recording the time- and distance-dependence of the current flowing between them. These methods have revealed that the current flowing between individual protein pairs extends beyond tunneling distances and that it is electrochemically gated. However, the corresponding mechanism and the identity of the charge carriers in aqueous solution remain to be elucidated. To determine the species involved in long-distance charge transport between the redox partner proteins Cc and Cc 1 of the respiratory chain, recordings are performed as a function of pH, in heavy water solutions, and in degassed solutions. It is observed that the spatial span and electrochemical gating of long-distance currents are reduced at high pH, in heavy water, and at low oxygen concentration, showing that the currents are assisted by superoxide anions and by protons.

JTD Keywords: Catalysis, Coupled electron-transfer, Dynamics, Electrochemical stm, Gouy-chapman conduit, Grotthuss (grothuss) proton hopping conduction, Interface, Kinetic isotope effect kie, Mechanism, Mitochondria, Pathways, Ph, Proteins, Proton coupled electron transfer pcet, Reactive oxygen species ros, Reductase, Superoxide radical anion sox, Tyrosine phosphorylation

The electrochemical response of alpha/beta-peptides with (L-Ala-beta-Fpg)n sequence, where beta-Fpg refers to syn 3-amino-2-(2-fluorophenyl)-3-phenylpropanoic acid, has been investigated examining the effects of the peptide length (n = 1-3), the stereochemistry of the beta 2,3-diaryl-amino acid and their self-assembly. alpha/beta-Peptides have been deposited by drop-casting on a conducting polymer (CP) film, which is previously electropolymerized on a stainless steel conducting substrate. The current-potential response of the CP coated by the different studied peptides suggests that, for alpha/beta-peptides, the role played by the electron transport through intermolecular stacking of aromatic side groups prevails over peptide length and stereochemistry. In order to prove such a hypothesis, the experimental conditions used to achieve an ordered self-assembly are optimized for one of the alpha/beta-peptides. The achieved self-assembled structures, which consist of well-defined long microfibers, considerably improve the electrochemical response of the CP. Finally, the prepared alpha/beta-peptide-based electrodes are used to electrochemically detect the oxidation of nicotinamide adenine dinucleotide (NADH). The analytical parameters are better for electrodes with well-defined peptide microfibers than for uncoated CP, corroborating the importance of pi-pi stacking interactions in the response of alpha/beta-peptides.

JTD Keywords: Acid, Alpha/beta-peptides, Beta-peptides, Bioelectronics, Design, Electron-transfer, Foldamers, Nadh, Nadh detection, Nanomaterials, Self-assembly, Stacking interactions

Charge separation and transport through the reaction center of photosystem I (PSI) is an essential part of the photosynthetic electron transport chain. A strategy is developed to immobilize and orient PSI complexes on gold electrodes allowing to probe the complex's electron acceptor side, the chlorophyll special pair P700. Electrochemical scanning tunneling microscopy (ECSTM) imaging and current-distance spectroscopy of single protein complex shows lateral size in agreement with its known dimensions, and a PSI apparent height that depends on the probe potential revealing a gating effect in protein conductance. In current-distance spectroscopy, it is observed that the distance-decay constant of the current between PSI and the ECSTM probe depends on the sample and probe electrode potentials. The longest charge exchange distance (lowest distance-decay constant ?) is observed at sample potential 0 mV/SSC (SSC: reference electrode silver/silver chloride) and probe potential 400 mV/SSC. These potentials correspond to hole injection into an electronic state that is available in the absence of illumination. It is proposed that a pair of tryptophan residues located at the interface between P700 and the solution and known to support the hydrophobic recognition of the PSI redox partner plastocyanin, may have an additional role as hole exchange mediator in charge transport through PSI.© 2021 Wiley-VCH GmbH.

JTD Keywords: azurin, current distance decay spectroscopy, cytochrome c(6), electrochemical scanning tunneling microscopy (ecstm), electrochemistry, photosystem i, photosystem-i, plastocyanin, protein electron transfer, recognition, single metalloprotein, single molecules, structural basis, tunneling spectroscopy, 'current, Amino acids, Charge transfer, Chlorine compounds, Chlorophyll, Current distance decay spectroscopy, Decay spectroscopies, Distance decay, Electrochemical scanning tunneling microscopy, Electrochemical scanning tunneling microscopy (ecstm), Electrodes, Electron transfer, Electron transport, Electron transport properties, Gold compounds, Kinetics, Oxidation-reduction, Photosynthesis, Photosystem i, Photosystem i protein complex, Photosystems, Protein electron transfer, Protein electron-transfer, Proteins, Scanning tunneling microscopy, Silver halides, Single molecule, Single molecules

Bistable molecules that behave as switches in solution have long been known. Systems that can be reversibly converted between two stable states that differ in their physical properties are particularly attractive in the development of memory devices when immobilized in substrates. Here, we report a highly robust surface-confined switch based on an electroactive, persistent organic radical immobilized on indium tin oxide substrates that can be electrochemically and reversibly converted to the anion form. This molecular bistable system behaves as an extremely robust redox switch in which an electrical input is transduced into optical as well as magnetic outputs under ambient conditions. The fact that this molecular surface switch, operating at very low voltages, can be patterned and addressed locally, and also has exceptionally high long-term stability and excellent reversibility and reproducibility, makes it a very promising platform for non-volatile memory devices.

JTD Keywords: Self-assembled monolayers, Chromophore-based monolayers, Ultrathin platinum films, Carbon free-radicals, Per-million levels, Polychlorotriphenylmethyl radicals, Electron-transfer, Surface, Logic, Quantification