Orbital overlap effects in electron transfer reactions across a metal nanowire/electrolyte solution interface

In this paper, we report on calculations of the orbital overlap between Fe(III) and Cr(III) aquacomplexes and different electrode surfaces: Cu(111), Ag (111), Au(111), Pt(111), and corresponding monatomic wires. The electronic structure of the monocrystalline surfaces and nanowires are described in terms of the electronic spillover and density of electronic states at the Fermi level obtained from periodic density functional theory (DFT) calculations. The transmission coefficients (κ) characterizing the first stage of outer-sphere electron transfer for the reduction of aquacomplexes are calculated on the basis of Landau–Zener theory as a function of electrode–reactant separation; the electronic transmission coefficients for the [Cr(H2O)6]3+/2+ redox couple were found to be smaller than those for [Fe(H2O)6]3+/2+. Two different intervals can be clearly distinguished for Cu, Au and Pt: “a catalytic region”, where κ(wire) > κ(Me slab) and “an inhibition region”, where κ(wire) < κ(Me slab). A similar behavior exhibits the coupling constant estimated for a hydrogen atom adsorbed at the Au(111) surface and the Au monatomic wire. These effects originate from some specific features of electronic density profile for metal nanowires: at short distances the electronic density of nanowires is higher compared with the (111) metal surfaces, while at larger separations it decreases more sharply.Fil: Nazmutdinov, Renat R.. Kazan National Research Technological University; RusiaFil: Berezin, Alexander S.. Kazan National Research Technological University; RusiaFil: Soldano, Germán. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Schmickler, Wolfgang. Universitat Ulm; Alemani

Kinetic data for the hexacyanoferrate (II)/(III) couple on platinum electrode in various chlorides of monovalent cations

An experimental study of the hexacyanoferrate (II)/(III) couple at a platinum disc electrode in hydrochloric acid, in alkali metal, ammonium and tetraalkylammonium chlorides solutions is carried out. Diffusion coefficients, equilibrium potentials and transfer rate constants are determined. Our results complete those previously published and clearly show a correlation between the magnitude of the apparent charge transfer rate constant and the extent of cation association with both hexacyanoferrate (II) and (III) anions

Impact of Self-Assembly Composition on the Alternate Interfacial Electron Transfer for Electrostatically Immobilized Cytochrome C

We report on the effects of self-assembled monolayer (SAM) dilution and thickness on the electron transfer (ET) event for cytochrome c (CytC) electrostatically immobilized on carboxyl terminated groups. We observed biphasic kinetic behavior for a logarithmic dependence of the rate constant on the SAM carbon number (ET distance) within the series of mixed SAMs of C5COOH/ C2OH, C10COOH/C6OH, and C15COOH/C11OH that is in overall similar to that found earlier for the undiluted SAM assemblies. However, in the case of C15COOH/C11OH and C10COOH/C6OH mixed SAMs a notable increase of the ET standard rate constant was observed, in comparison with the corresponding unicomponent (x–COOH) SAMs. In the case of the C5COOH/C2OH composite SAM a decrease of the rate constant versus the unicomponent analogue was observed. The value of the reorganization free energy deduced through the Marcuslike data analysis did not change throughout the series;this fact along with the other observations indicates uncomplicated rate-determining unimolecular ET in all cases. Our results are consistent with a model that considers a changeover between the alternate, tunneling and adiabatic intrinsic ET mechanisms. The physical mechanism behind the observed fine kinetic effects in terms of the protein-rigidifying x–COOH/CytC interactions arising in the case of mixed SAMs are also discussed

Electron transfer with self-assembled copper ions at Au-deposited biomimetic films : mechanistic "anomalies" disclosed by temperature- and pressure-assisted fast-scan voltammetry

It has been suggested that electron transfer (ET) processes occurring in complex environments capable of glass transitions, specifically in biomolecules, under certain conditions may experience the medium ’ s nonlinear response and nonergodic kinetic patterns. The interiors of self-assembled organic films (SAMs) deposited on solid conducting platforms (electrodes) are known to undergo glassy dynamics as well, hence they may also exhibit the abovementioned ‘ irregularities ’ . We took advantage of Cu 2+ ions as redox-active probes trapped in the Au-deposited − COOH-terminated SAMs, either L-cysteine, or 3-mercaptopropionic acid diluted by the inert 2-mercaptoethanol, to systematically study the impact of glassy dynamics on ET using the fast-scan voltammetry technique and its temperature and high-pressure extensions. We found that respective kinetic data can be rationalized within the extended Marcus theory, taking into account the frictionally controlled (adiabatic) mechanism for short-range ET, and complications due to the medium ’ s nonlinear response and broken ergodicity. This combination shows up in essential deviations from the conventional energy gap (overpotential) dependence and in essentially nonlinear temperature (Arrhenius) and high-pressure patterns, respectively. Biomimetic aspects for these systems are also discussed in the context of recently published results for interfacial ET involving self-assembled blue copper protein (azurin) placed in contact with a glassy environment

Electron transfer with myoglobin in free and strongly confined regimes: disclosing diverse mechanistic role of the Fe-coordinated water by temperature- and pressure-assisted voltammetric studies

<div><p>The naturally occurring electron-transfer (ET) event for myoglobin (Mb) can be mimicked through its functionalization at diversely modified metal platforms to allow for the electron exchange either in freely diffusing or immobilized regimes. In this work, horse muscle Mb was involved in the electron exchange with Au electrodes modified by dissimilar, thin or thick alkanethiol SAMs, terminated either by unicomponent (–OH) or 1 : 1 mixed (–OH/–COOH) functional (externally exposed) entities, respectively. The systematic, temperature- and pressure-supported cyclic voltammetry studies perfectly confirmed certainty of two kinds of ET patterns for Mb, embodying: (a) different operational kinetic regimes (including protein’s freely diffusing and strongly confined motifs) and (b) different intrinsic physical mechanisms (including dynamically controlled and non-adiabatic modes). Our analysis of obtained and published data for Mb and the reference redox-active protein, cytochrome <i>c</i>, specified further the central mechanistic role of the Fe-(heme-)coordinated water whose displacement is directly coupled to ET, and can be, in turn, controlled by the conformational organization and intrinsic fluctuational mobility of the Mb macromolecule.</p></div