Electron Transfer In Solution Research Articles

Host-Guest-Induced Electron Transfer Triggers Radical-Cation Catalysis.

Modifying the reactivity of substrates by encapsulation is a fundamental principle of capsule catalysis. Here we show an alternative strategy, wherein catalytic activation of otherwise inactive quinone "co-factors" by a simple Pd2L4 capsule promotes a range of bulk-phase, radical-cation cycloadditions. Solution electron-transfer experiments and cyclic voltammetry show that the cage anodically shifts the redox potential of the encapsulated quinone by a significant 1 V. Moreover, the capsule also protects the reduced semiquinone from protonation, thus transforming the role of quinones from stoichiometric oxidants into catalytic single-electron acceptors. We envisage that the host-guest-induced release of an "electron hole" will translate to various forms of non-encapsulated catalysis that involve other difficult-to-handle, highly reactive species.

Verdazyls as Possible Building Blocks for Multifunctional Molecular Materials: A Case Study on 1,5-Diphenyl-3-(p-iodophenyl)-verdazyl Focusing on Magnetism, Electron Transfer and the Applicability of the Sonogashira-Hagihara Reaction.

This work explores the use of Kuhn verdazyl radicals as building blocks in multifunctional molecular materials in an exemplary study, focusing on the magnetic and the electron transfer (ET) characteristics, but also addressing the question whether chemical modification by cross-coupling is possible. The ET in solution is studied spectroscopically, whereas solid state measurements afford information about the magnetic susceptibility or the conductivity of the given samples. The observed results are rationalized based on the chemical structures of the molecules, which have been obtained by X-ray crystallography. The crystallographically observed molecular structures as well as the interpretation based on the spectroscopic and physical measurements are backed up by DFT calculations. The measurements indicate that only weak, antiferromagnetic (AF) coupling is observed in Kuhn verdazyls owed to the low tendency to form face-to-face stacks, but also that steric reasons alone are not sufficient to explain this behavior. Furthermore, it is also demonstrated that ET reactions proceed rapidly in verdazyl/verdazylium redox couples and that Kuhn verdazyls are suited as donor molecules in ET reactions.

Electron transfer in an acidophilic bacterium: interaction between a diheme cytochrome and a cupredoxin.

Acidithiobacillus ferrooxidans, a chemolithoautotrophic Gram-negative bacterium, has a remarkable ability to obtain energy from ferrous iron oxidation at pH 2. Several metalloproteins have been described as being involved in this respiratory chain coupling iron oxidation with oxygen reduction. However, their properties and physiological functions remain largely unknown, preventing a clear understanding of the global mechanism. In this work, we focus on two metalloproteins of this respiratory pathway, a diheme cytochrome c4 (Cyt c4) and a green copper protein (AcoP) of unknown function. We first demonstrate the formation of a complex between these two purified proteins, which allows homogeneous intermolecular electron-transfer in solution. We then mimic the physiological interaction between the two partners by replacing one at a time with electrodes displaying different chemical functionalities. From the electrochemical behavior of individual proteins, we show that, while electron transfer on AcoP requires weak electrostatic interaction, electron transfer on Cyt c4 tolerates different charge and hydrophobicity conditions, suggesting a pivotal role of this protein in the metabolic chain. The electrochemical study of the proteins incubated together demonstrates an intermolecular electron transfer involving the protein complex, in which AcoP is reduced through the high potential heme of Cyt c4. Modelling of the electrochemical signals at different scan rates allows us to estimate the rate constant of this intermolecular electron transfer in the range of a few s-1. Possible routes for electron transfer in the acidophilic bacterium are deduced.

Effects of tunnelling and asymmetry for system-bath models of electron transfer.

We apply the newly derived nonadiabatic golden-rule instanton theory to asymmetric models describing electron-transfer in solution. The models go beyond the usual spin-boson description and have anharmonic free-energy surfaces with different values for the reactant and product reorganization energies. The instanton method gives an excellent description of the behaviour of the rate constant with respect to asymmetry for the whole range studied. We derive a general formula for an asymmetric version of the Marcus theory based on the classical limit of the instanton and find that this gives significant corrections to the standard Marcus theory. A scheme is given to compute this rate based only on equilibrium simulations. We also compare the rate constants obtained by the instanton method with its classical limit to study the effect of tunnelling and other quantum nuclear effects. These quantum effects can increase the rate constant by orders of magnitude.

Integrating Enzymes into Cytochrome c –Based Multilayer Architectures – General Considerations and Example with Fructose Dehydrogenase

The creation of artificial electron transfer (ET) chains based on the defined arrangement of enzymes and redox proteins on electrode surfaces represents an interesting field in bioelectronics1. One approach exploits the self exchange properties of cytochrome c (cyt c) to build up new sensing electrodes2. In this study we have investigated the ET reaction of the flavin-dependent enzyme fructose dehydrogenase (FDH) with the redox protein cyt c. Two different pH optima are detected for the reaction of both proteins in solution - at acidic and neutral pH. When one reaction partner - cyt c - is immobilized on a thiol-modified gold electrode and FDH is in solution ET proceeds efficiently at neutral pH which can be concluded from well-shaped catalytic currents obtained in cyclic voltammetry. In addition, a defined dependence on the substrate concentration has been found. In acidic media the reaction can also be verified but appears to be less efficient. Furthermore, it can be demonstrated that both partners can be assembled in a stable multilayer architecture, using the biopolymer DNA as a negatively charged polyelectrolyte building block. The defined layered deposition of DNA and a mixture of FDH and cyt c is confirmed by surface plasmon resonance (SPR) measurements. Prepared on electrodes, substantial catalytic currents are recorded upon addition of fructose. The response can be enhanced by the number of layers deposited on the surface. This shows that an artificial signal chain can be constructed through multiple protein layers. FDH is not the only enzyme which can be immobilized and connected to the electrode by means of the redox protein cyt c. Cellobiose dehydrogenase, sulfite oxidase or billirubin oxidase are other examples3,4. This may indicate that cyt c based multilayers can have some general applicability when some preconditions are fullfilled. 1. Feifel et al , in Biosensors Based on Aptamers and Enzymes, Springer 2014, 140, 253-298 2. Lisdat et al., Chemical Communications 3 2009, 274-283. 3. Feifel et al., Angew. Chemie 126(22) 2014 5782-86 4 Dronov et al. JACS 2008 130(4) 1122.

Nitroxyl Radicals for Studying Electron Transfer

Electron-transfer (ET) rates are measured by use of time-resolved EPR spectroscopy, involving photooxidation of nitroxyl radicals by a ruthenium bipyridyl complex. This permits acquisition of the fundamental characteristics of ET in solution. The method was used on two spin-labeled derivatives of bacteriorhodopsin, and is applicable to proteins, nucleic acids, and biological membranes. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Surface Composition and Electrical and Electrochemical Properties of Freshly Deposited and Acid-Etched Indium Tin Oxide Electrodes

We compare the near-surface composition and electroactivity of commercial indium tin oxide (ITO) thin films, activated by plasma cleaning or etching with strong haloacids, with ITO films that have been freshly deposited in high vacuum, before and after exposure to the atmosphere or water vapor. Conductive-tip AFM, X-ray photoelectron spectroscopy (XPS), and the electrochemistry of probe molecules in solution were used to compare the relative degrees of electroactivity and the near-surface composition of these materials. Brief etching of commercial ITO samples with concentrated HCl or HI significantly enhances the electrical activity of these oxides as revealed by C-AFM. XPS was used to compare the composition of these activated surfaces, focusing on the intrinsically asymmetric O 1s line shape. Energy-loss processes associated with photoemission from the tin-doped, oxygen-deficient oxides complicate the interpretation of the O 1s spectra. O 1s spectra from the stoichiometric indium oxide lattice are accompanied by higher-binding-energy peaks associated with hydroxylated forms of the oxide (and in some cases carbonaceous impurities) and overlapping photoemission associated with energy-loss processes. Characterization of freshly sputter-deposited indium oxide (IO) and ITO films, transferred under high vacuum to the surface analysis environment, allowed us to differentiate the contributions of tin doping and oxygen-vacancy doping to the O 1s line shape, relative to higher-binding-energy O 1s components associated with hydroxyl species and carbonaceous impurities. Using these approaches, we determined that acid activation and O2 plasma etching create an ITO surface that is still covered with an average of one to two monolayers of hydroxide. Both of these activation treatments lead to significantly higher rates of electron transfer to solution probe molecules, such as dimethyferrocene in acetonitrile. Solution electron-transfer events appear to occur at no more than 4x10(7) electroactive sites per cm2 (each with diameters of ca. 50-200 nm) (i.e., a small fraction of the geometric area of the electrode). Electron-transfer rates correlate with the near-surface tin dopant concentration, suggesting that these electroactive sites arise from near-surface tin enrichment.

Charge Transfer on the Nanoscale: Current Status

This is the report of a DOE-sponsored workshop organized to discuss the status of our understanding of charge-transfer processes on the nanoscale and to identify research and other needs for progress in nanoscience and nanotechnology. The current status of basic electron-transfer research, both theoretical and experimental, is addressed, with emphasis on the distance-dependent measurements, and we have attempted to integrate terminology and notation of solution electron-transfer kinetics with that of conductance analysis. The interface between molecules or nanoparticles and bulk metals is examined, and new research tools that advance description and understanding of the interface are presented. The present state-of-the-art in molecular electronics efforts is summarized along with future research needs. Finally, novel strategies that exploit nanoscale architectures are presented for enhancing the efficiences of energy conversion based on photochemistry, catalysis, and electrocatalysis principles.

Electronic decoherence in condensed phases

The impact of electronic decoherence on electronic dynamics, and electron transfer (ET) reactions in particular, in condensed phase environments is discussed. Analytical expressions are considered for a common model system in which ET occurs between relatively displaced harmonic surfaces. We identify a relationship in the semi-classical Marcus limit between electronic decoherence and the Wigner distribution of nuclear configurations. Generalization to more complex surfaces is discussed. Additionally, we discuss electronic decoherence for ET via so-called bridge sites in materials, for both direct (superexchange) mechanisms and sequential mechanisms of ET. Quantitative simulation studies of factors affecting characteristic decoherence times for ET in solution are also presented and discussed.

Ab initio study of long-range electron transfer between biphenyl anion radical and naphthalene

After the separation of the donor, the acceptor, and the σ-type bridge from the π-σ-π system, the geometries of biphenyl, biphenyl anion radical, naphthalene, and naphthalene anion radical are optimized, and then the reorganization energy for the intermolecular electron transfer (ET) at the levels of HF/4-31G and HF/DZP is calculated. The ET matrix elements of the self-exchange reactions of theπ-σ-π systems have been calculated by means of both the direct calculation based on the variational principle, and the transition energy between the molecular orbitals at the linear coordinateR = 0.5. For the cross reactions, the ET matrix element and the geometry of the transition state are determined by searching the minimum energy splitting Δmin along the reaction coordinate. In the evaluation of the solvent reorganization energy of the ET in solution, the Marcus’ two- sphere model has been invoked. A few of ET rate constants for the intramolecular ET reactions for the π-σ-π systems, which contain the biphenylyl as the donor and both biphenylyl and naphthyl as the acceptor, have been obtained.

Surface-hopping modeling of photoinduced relaxation dynamics on coupled potential-energy surfaces

A mixed quantum-classical description of nonadiabatic photoreactions such as internal conversion and electron transfer is outlined. In particular the validity and limitations of Tully’s surface-hopping (SH) model [J. Chem. Phys. 93, 1061 (1990)] is investigated in the case of photoinduced relaxation processes which are triggered by a multidimensional conical intersection (or avoided crossing) of two potential-energy surfaces. Detailed numerical studies are presented, adopting (i) a three-mode model of the S2→S1 internal-conversion process in pyrazine, (ii) a multimode model of ultrafast intramolecular electron-transfer, (iii) a model exhibiting nonadiabatic photoisomerization dynamics, and (iv) various spin-boson-type models with an Ohmic bath for the description of electron-transfer in solution. The SH simulations are compared to exact quantum-mechanical calculations as well as to results obtained by an alternative mixed quantum-classical description, that is, the self-consistent classical-path method. In all cases, the SH data are shown to reproduce the quantum results at least qualitatively; in some cases the SH results are in quantitative agreement with the complex electronic and vibrational relaxation dynamics exhibited by the quantum calculations. Depending on the physical situation under consideration, either the SH or the self-consistent classical-path method was found to be superior. The characteristic features of a mixed quantum-classical description of photoinduced bound-state dynamics (e.g., the start of the trajectories on a diabatic electronic potential-energy surface, high chance of a trajectory undergoing multiple electronic transitions) as well as the specific problems of the SH approach are discussed in some detail. In particular, the focus is on the ability of a method to account for the branching of trajectories, to correctly describe the electronic phase coherence and the vibrational motion on coupled potential-energy surfaces, and to obey the principle of microreversibility. Furthermore, an alternative way to handle classically forbidden electronic transitions is proposed, which is shown to lead to significantly better results than the usual procedure.

Rate constants for the solution and electrode electron-transfer to substituted bromobenzenes in DMF

The rate constants k set for the solution electron-transfer between radical anions of chrysene and a series of substituted bromobenzenes have been obtained using homogeneous redox catalysis. Linear correlation of log k set versus the Hammett substituent constants has been found and used to estimate formal potentials. The heterogeneous standard rate constant, calculated from voltammetric peak potentials, is independent of the substituent in agreement with the Marcus-Hush model.

Effects of the Solvent Dynamics and Vibrational Motions in Electron Transfer

Abstract Recent theoretical and experimental progress concerning electron transfer (ET) in solution is reviewed by focusing on the mechanism of ET, which occurs much faster than solvation dynamics. Theories of ET in solution are briefly reviewed with particular emphasis placed on the relation to solvent dynamics. Experimental methods to investigate solvent polarization relaxation are described. Ultrafast intramolecular ET, which is found in back ET from the photo-induced charge-transfer state to the ground state, is described concerning highly polar betaines and mixed-valence compounds. Ultrafast intermolecular ET has been observed for the systems of various dyes in electron-donating solvents. A non-exponential process with a significant temperature dependence was observed in aniline. A faster ET with a single exponential decay as fast as 1013 s−1 was observed with no temperature dependence in a system of oxazine 1 in N,N-dimethylaniline. The ET rate constants of excited coumarins in electron-donating solvents drastically depend on the substituent groups of the coumarin. Relatively small Stokes shifts in steady-state fluorescence spectra of ultrafast reacting molecules in solution are evidence of a “chemical timing” effect; namely, the reaction occurs in a non-equilibrium configuration of the solvent. These experimental observations are explained in terms of the extended Sumi–Marcus theory, in which the effect of solvation dynamics and low- and high-frequency vibrational modes are taken into account.

Computer simulation of large-scale controlled-potential electrolysis. Father—son and grandfather—grandson self-protonation systems

In some electrochemical systems, transfer of an electron from the electrode to the starting material is followed by a reaction in which the electrogenerated intermediate (radical anion) abstracts a proton from unreduced starting material. Products of this self-protonation or father—son proton transfer are a neutral radical, thought to be more easily reduced than the starting material, and the conjugate base of the parent. Linear scan voltammetry fails to discriminate between two mechanistic scenarios, one where transfer of a second electron to the neutral radical occurs at the electrode surface (EC/kE irr) and the other where the second electron is transferred to the neutral radical in solution by the radical anion (DISP1). Reduction of the neutral radical results in an anion that is thought to be more basic than the radical anion; thus this anion should be more reactive toward unreduced starting material than the radical anion. We have utilized computer simulations of controlled-potential electrolyses to investigate systematically the competition between (i) unreduced starting material and the neutral radical for the radical anion in father—son proton-transfer systems, (ii) father—son and grandfather—grandson self-protonation reactions, and (iii) protonation of the son and grandson species by the medium. Under typical experimental conditions for controlled-potential electrolyses, the maximum yield of two-electron reduction product formed via the heterogeneous electron transfer is 64%. In addition, we have found that, when the second-order rate constant for the father—son proton-transfer reaction is less than 2.5 × 10 8 M −1 s −1, more than 95% of the two-electron reduction product is formed via the solution electron-transfer reaction. For a mechanistic scheme where father—son and grandfather—grandson proton-transfer reactions both play a role, product distributions vary, as a function of three parameters, from quantitative formation of the two-electron reduction product to a 1:2 mixture of the two-electron reduction product and the conjugate base of the starting material.

ChemInform Abstract: Solution Electron‐Transfer Reactions in Organic and Organometallic Electrochemistry

ChemInformVolume 21, Issue 48 Reviews ChemInform Abstract: Solution Electron-Transfer Reactions in Organic and Organometallic Electrochemistry D. H. EVANS, D. H. EVANS Dep. Chem. Biochem., Univ. Del., Newark, DE 19716, USASearch for more papers by this author D. H. EVANS, D. H. EVANS Dep. Chem. Biochem., Univ. Del., Newark, DE 19716, USASearch for more papers by this author First published: November 27, 1990 https://doi.org/10.1002/chin.199048329Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume21, Issue48November 27, 1990 RelatedInformation

Solution electron-transfer reactions in organic and organometallic electrochemistry

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolution electron-transfer reactions in organic and organometallic electrochemistryDennis H. EvansCite this: Chem. Rev. 1990, 90, 5, 739–751Publication Date (Print):July 1, 1990Publication History Published online1 May 2002Published inissue 1 July 1990https://doi.org/10.1021/cr00103a004RIGHTS & PERMISSIONSArticle Views1307Altmetric-Citations161LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

ChemInform Abstract: THE ROLE OF DISTANCE IN ELECTRON TRANSFER IN SOLUTION. EXPERIMENTAL VERIFICATION OF THE HUSH‐MARCUS THEORY USING MIXED‐VALENCE COMPLEXES

Chemischer InformationsdienstVolume 8, Issue 1 Organoelement Compounds ChemInform Abstract: THE ROLE OF DISTANCE IN ELECTRON TRANSFER IN SOLUTION. EXPERIMENTAL VERIFICATION OF THE HUSH-MARCUS THEORY USING MIXED-VALENCE COMPLEXES M. J. POWERS, M. J. POWERSSearch for more papers by this authorD. J. SALMON, D. J. SALMONSearch for more papers by this authorR. W. CALLAHAN, R. W. CALLAHANSearch for more papers by this authorT. J. MEYER, T. J. MEYERSearch for more papers by this author M. J. POWERS, M. J. POWERSSearch for more papers by this authorD. J. SALMON, D. J. SALMONSearch for more papers by this authorR. W. CALLAHAN, R. W. CALLAHANSearch for more papers by this authorT. J. MEYER, T. J. MEYERSearch for more papers by this author First published: January 4, 1977 https://doi.org/10.1002/chin.197701368Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume8, Issue1January 4, 1977 RelatedInformation