WorldWideScience

Sample records for optimizes electron transfer

  1. Electron transfer in proteins

    DEFF Research Database (Denmark)

    Farver, O; Pecht, I

    1991-01-01

    Electron migration between and within proteins is one of the most prevalent forms of biological energy conversion processes. Electron transfer reactions take place between active centers such as transition metal ions or organic cofactors over considerable distances at fast rates and with remarkable...... specificity. The electron transfer is attained through weak electronic interaction between the active sites, so that considerable research efforts are centered on resolving the factors that control the rates of long-distance electron transfer reactions in proteins. These factors include (in addition......-containing proteins. These proteins serve almost exclusively in electron transfer reactions, and as it turns out, their metal coordination sites are endowed with properties uniquely optimized for their function....

  2. Electron transfer reactions

    CERN Document Server

    Cannon, R D

    2013-01-01

    Electron Transfer Reactions deals with the mechanisms of electron transfer reactions between metal ions in solution, as well as the electron exchange between atoms or molecules in either the gaseous or solid state. The book is divided into three parts. Part 1 covers the electron transfer between atoms and molecules in the gas state. Part 2 tackles the reaction paths of oxidation states and binuclear intermediates, as well as the mechanisms of electron transfer. Part 3 discusses the theories and models of the electron transfer process; theories and experiments involving bridged electron transfe

  3. Electron transfer in peptides.

    Science.gov (United States)

    Shah, Afzal; Adhikari, Bimalendu; Martic, Sanela; Munir, Azeema; Shahzad, Suniya; Ahmad, Khurshid; Kraatz, Heinz-Bernhard

    2015-02-21

    In this review, we discuss the factors that influence electron transfer in peptides. We summarize experimental results from solution and surface studies and highlight the ongoing debate on the mechanistic aspects of this fundamental reaction. Here, we provide a balanced approach that remains unbiased and does not favor one mechanistic view over another. Support for a putative hopping mechanism in which an electron transfers in a stepwise manner is contrasted with experimental results that support electron tunneling or even some form of ballistic transfer or a pathway transfer for an electron between donor and acceptor sites. In some cases, experimental evidence suggests that a change in the electron transfer mechanism occurs as a result of donor-acceptor separation. However, this common understanding of the switch between tunneling and hopping as a function of chain length is not sufficient for explaining electron transfer in peptides. Apart from chain length, several other factors such as the extent of the secondary structure, backbone conformation, dipole orientation, the presence of special amino acids, hydrogen bonding, and the dynamic properties of a peptide also influence the rate and mode of electron transfer in peptides. Electron transfer plays a key role in physical, chemical and biological systems, so its control is a fundamental task in bioelectrochemical systems, the design of peptide based sensors and molecular junctions. Therefore, this topic is at the heart of a number of biological and technological processes and thus remains of vital interest.

  4. Electron Transfer Chain Catalysis

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    @@ Electron-transfer chain (ETC) catalysis belongs to the family of chain reactions where the electron is the catalyst. The ETC mechanism could be initiated by chemical activation, electrochemistry, or photolysis. If this pathway is applied to the preparation of organometallic complexes, it utilizes the greatly enhanced reactivity of organometallic 17e and 19e radicals. The chemical propagation is followed by the cross electron-transfer while the electron-transfer step is also followed by the chemical propagation, creating a loop in which reactants are facilely transformed into products. Interestingly the overall reaction is without any net redox change.

  5. Electron Transfer Chain Catalysis

    Institute of Scientific and Technical Information of China (English)

    LIU; LingKang

    2001-01-01

    Electron-transfer chain (ETC) catalysis belongs to the family of chain reactions where the electron is the catalyst. The ETC mechanism could be initiated by chemical activation, electrochemistry, or photolysis. If this pathway is applied to the preparation of organometallic complexes, it utilizes the greatly enhanced reactivity of organometallic 17e and 19e radicals. The chemical propagation is followed by the cross electron-transfer while the electron-transfer step is also followed by the chemical propagation, creating a loop in which reactants are facilely transformed into products. Interestingly the overall reaction is without any net redox change.  ……

  6. Electron Transfer Pathways in Cell

    OpenAIRE

    Yan Liu

    2012-01-01

    Analysis of the electron salvation process data indicates that the electron transfer between the electron donor and acceptor is hindered by the electron salvation process. It is proposed that the electron transfer in the cell environment must be assisted by intermediate messenger called the “transport protein”.

  7. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S

    1993-01-01

    Advances in Electron Transfer Chemistry, Volume 3 presents studies that discuss findings in the various aspects of electron chemistry. The book is comprised of four chapters; each chapter reviews a work that tackles an issue in electron transfer chemistry. Chapter 1 discusses the photoinduced electron transfer in flexible biaryl donor-acceptor molecules. Chapter 2 tackles light-induced electron transfer in inorganic systems in homogeneous and heterogeneous phases. The book also covers internal geometry relaxation effects on electron transfer rates of amino-centered systems. The sequential elec

  8. Electronic Correlations in Electron Transfer Systems

    Science.gov (United States)

    Bulla, Ralf; Tornow, Sabine; Anders, Frithjof

    Electron transfer processes play a central role in many chemical and biological systems. Already the transfer of a single electron from the donor to the acceptor can be viewed as a complicated many-body problem, due to the coupling of the electron to the infinitely many environmental degrees of freedom, realized by density fluctuations of the solvent or molecular vibrations of the protein matrix. We focus on the quantum mechanical modelling of two-electron transfer processes whose dynamics is governed by the Coulomb interaction between the electrons as well as the environmental degrees of freedoms represented by a bosonic bath. We identify the regime of parameters in which concerted transfer of the two electrons occurs and discuss the influence of the Coulomb repulsion and the coupling strength to the environment on the electron transfer rate. Calculations are performed using the non-perturbative numerical renormalization group approach for both equilibrium and non-equilibrium properties.

  9. Electron Transfer Reactivity Patterns at Chemically Modified Electrodes: Fundamentals and Application to the Optimization of Redox Recycling Amplification Systems

    Energy Technology Data Exchange (ETDEWEB)

    Bergren, Adam Johan [Iowa State Univ., Ames, IA (United States)

    2006-01-01

    Electroanalytical chemistry is often utilized in chemical analysis and Fundamental studies. Important advances have been made in these areas since the advent of chemically modified electrodes: the coating of an electrode with a chemical film in order to impart desirable, and ideally, predictable properties. These procedures enable the exploitation of unique reactivity patterns. This dissertation presents studies that investigate novel reaction mechanisms at self-assembled monolayers on gold. In particular, a unique electrochemical current amplification scheme is detailed that relies on a selective electrode to enable a reactivity pattern that results in regeneration of the analyte (redox recycling). This regenerating reaction can occur up to 250 times for each analyte molecule, leading to a notable enhancement in the observed current. The requirements of electrode selectivity and the resulting amplification and detection limit improvements are described with respect to the heterogeneous and homogeneous electron transfer rates that characterize the system. These studies revealed that the heterogeneous electrolysis of the analyte should ideally be electrochemically reversible, while that for the regenerating agent should be held to a low level. Moreover, the homogeneous reaction that recycles the analyte should occur at a rapid rate. The physical selectivity mechanism is also detailed with respect to the properties of the electrode and redox probes utilized. It is shown that partitioning of the analyte into/onto the adlayer leads to the extraordinary selectivity of the alkanethiolate monolayer modified electrode. Collectively, these studies enable a thorough understanding of the complex electrode mechanism required for successful redox recycling amplification systems, Finally, in a separate (but related) study, the effect of the akyl chain length on the heterogeneous electron transfer behavior of solution-based redox probes is reported, where an odd-even oscillation

  10. Heat Transfer Augmentation for Electronic Cooling

    Directory of Open Access Journals (Sweden)

    Suabsakul Gururatana

    2012-01-01

    Full Text Available Problem statement: The performance of electronic devices has been improving along with the rapid technology development. Cooling of electronic systems is consequently essential in controlling the component temperature and avoiding any hot spot. The study aims to review the present electronic cooling methods which are widely used in electronic devices. Approach: There are several methods to cool down the electronics components such as the pin-fin heat sink, confined jet impingement, heat pipe, micro heat sink and so on. Results: The cooling techniques can obviously increase heat transfer rate. Nonetheless, for active and passive cooling methods the pressure drop could extremely rise, when the heat transfer rate is increased. Conclusion: When the cooling techniques are used, it is clearly seen that the heat transfer increases with pressure drop. To avoid excessive expense due to high pressure drop, optimization method is required to obtain optimum cost and cooling rate.

  11. Advances in electron transfer chemistry

    CERN Document Server

    Mariano, Patrick S

    1995-01-01

    Advances in Electron Transfer Chemistry, Volume 4 presents the reaction mechanisms involving the movement of single electrons. This book discusses the electron transfer reactions in organic, biochemical, organometallic, and excited state systems. Organized into four chapters, this volume begins with an overview of the photochemical behavior of two classes of sulfonium salt derivatives. This text then examines the parameters that control the efficiencies for radical ion pair formation. Other chapters consider the progress in the development of parameters that control the dynamics and reaction p

  12. Two-Electron Transfer Pathways.

    Science.gov (United States)

    Lin, Jiaxing; Balamurugan, D; Zhang, Peng; Skourtis, Spiros S; Beratan, David N

    2015-06-18

    The frontiers of electron-transfer chemistry demand that we develop theoretical frameworks to describe the delivery of multiple electrons, atoms, and ions in molecular systems. When electrons move over long distances through high barriers, where the probability for thermal population of oxidized or reduced bridge-localized states is very small, the electrons will tunnel from the donor (D) to acceptor (A), facilitated by bridge-mediated superexchange interactions. If the stable donor and acceptor redox states on D and A differ by two electrons, it is possible that the electrons will propagate coherently from D to A. While structure-function relations for single-electron superexchange in molecules are well established, strategies to manipulate the coherent flow of multiple electrons are largely unknown. In contrast to one-electron superexchange, two-electron superexchange involves both one- and two-electron virtual intermediate states, the number of virtual intermediates increases very rapidly with system size, and multiple classes of pathways interfere with one another. In the study described here, we developed simple superexchange models for two-electron transfer. We explored how the bridge structure and energetics influence multielectron superexchange, and we compared two-electron superexchange interactions to single-electron superexchange. Multielectron superexchange introduces interference between singly and doubly oxidized (or reduced) bridge virtual states, so that even simple linear donor-bridge-acceptor systems have pathway topologies that resemble those seen for one-electron superexchange through bridges with multiple parallel pathways. The simple model systems studied here exhibit a richness that is amenable to experimental exploration by manipulating the multiple pathways, pathway crosstalk, and changes in the number of donor and acceptor species. The features that emerge from these studies may assist in developing new strategies to deliver multiple

  13. Orbital-optimized coupled-electron pair theory and its analytic gradients: accurate equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions.

    Science.gov (United States)

    Bozkaya, Uğur; Sherrill, C David

    2013-08-07

    Orbital-optimized coupled-electron pair theory [or simply "optimized CEPA(0)," OCEPA(0), for short] and its analytic energy gradients are presented. For variational optimization of the molecular orbitals for the OCEPA(0) method, a Lagrangian-based approach is used along with an orbital direct inversion of the iterative subspace algorithm. The cost of the method is comparable to that of CCSD [O(N(6)) scaling] for energy computations. However, for analytic gradient computations the OCEPA(0) method is only half as expensive as CCSD since there is no need to solve the λ2-amplitude equation for OCEPA(0). The performance of the OCEPA(0) method is compared with that of the canonical MP2, CEPA(0), CCSD, and CCSD(T) methods, for equilibrium geometries, harmonic vibrational frequencies, and hydrogen transfer reactions between radicals. For bond lengths of both closed and open-shell molecules, the OCEPA(0) method improves upon CEPA(0) and CCSD by 25%-43% and 38%-53%, respectively, with Dunning's cc-pCVQZ basis set. Especially for the open-shell test set, the performance of OCEPA(0) is comparable with that of CCSD(T) (ΔR is 0.0003 Å on average). For harmonic vibrational frequencies of closed-shell molecules, the OCEPA(0) method again outperforms CEPA(0) and CCSD by 33%-79% and 53%-79%, respectively. For harmonic vibrational frequencies of open-shell molecules, the mean absolute error (MAE) of the OCEPA(0) method (39 cm(-1)) is fortuitously even better than that of CCSD(T) (50 cm(-1)), while the MAEs of CEPA(0) (184 cm(-1)) and CCSD (84 cm(-1)) are considerably higher. For complete basis set estimates of hydrogen transfer reaction energies, the OCEPA(0) method again exhibits a substantially better performance than CEPA(0), providing a mean absolute error of 0.7 kcal mol(-1), which is more than 6 times lower than that of CEPA(0) (4.6 kcal mol(-1)), and comparing to MP2 (7.7 kcal mol(-1)) there is a more than 10-fold reduction in errors. Whereas the MAE for the CCSD method is

  14. Experimental Approaches to Studying Biological Electron Transfer.

    Science.gov (United States)

    Scott, Robert A.; And Others

    1985-01-01

    Provides an overview on biological electron-transfer reactions, summarizing what is known about how distance, spatial organization, medium, and other factors affect electron transfer. Experimental approaches, including studies of bimolecular electron transfer reactions (electrostatic effects and precursor complexes), are considered. (JN)

  15. Heterostructure Intervalley Transferred Electron Effects

    Institute of Scientific and Technical Information of China (English)

    XUE Fang-Shi

    2001-01-01

    A Gunn active layer is used as an X electron probe to detect the X tunnelling current in the GaAs-AlAs heterostructure, from which a new heterostructure intervalley transferred electron (HITE) device is obtained. In the 8 mm band, the highest pulse output power of these diodes is 2.65 W and the highest conversion efficiency is 18%. The dc and rf performance of the HITE devices was simulated by the band mixing resonant tunnelling theory and Monte Carlo transport simulation. The HITE effect has transformed the transit-time dipole-layer mode in the Gunn diode into a relaxation oscillation mode in the HITE device. From the comparison of simulated results to the measured data, the HITE effect is demonstrated straightforwardly

  16. Exocellular electron transfer in anaerobic microbial communities

    NARCIS (Netherlands)

    Stams, A.J.M.; Bok, de F.A.M.; Plugge, C.M.; Eekert, van M.H.A.; Dolfing, J.; Schraa, G.

    2006-01-01

    Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory

  17. Exocellular electron transfer in anaerobic microbial communities

    NARCIS (Netherlands)

    Stams, A.J.M.; Bok, de F.A.M.; Plugge, C.M.; Eekert, van M.H.A.; Dolfing, J.; Schraa, G.

    2006-01-01

    Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory

  18. Supramolecular electron transfer by anion binding.

    Science.gov (United States)

    Fukuzumi, Shunichi; Ohkubo, Kei; D'Souza, Francis; Sessler, Jonathan L

    2012-10-11

    Anion binding has emerged as an attractive strategy to construct supramolecular electron donor-acceptor complexes. In recent years, the level of sophistication in the design of these systems has advanced to the point where it is possible to create ensembles that mimic key aspects of the photoinduced electron-transfer events operative in the photosynthetic reaction centre. Although anion binding is a reversible process, kinetic studies on anion binding and dissociation processes, as well as photoinduced electron-transfer and back electron-transfer reactions in supramolecular electron donor-acceptor complexes formed by anion binding, have revealed that photoinduced electron transfer and back electron transfer occur at time scales much faster than those associated with anion binding and dissociation. This difference in rates ensures that the linkage between electron donor and acceptor moieties is maintained over the course of most forward and back electron-transfer processes. A particular example of this principle is illustrated by electron-transfer ensembles based on tetrathiafulvalene calix[4]pyrroles (TTF-C4Ps). In these ensembles, the TTF-C4Ps act as donors, transferring electrons to various electron acceptors after anion binding. Competition with non-redox active substrates is also observed. Anion binding to the pyrrole amine groups of an oxoporphyrinogen unit within various supramolecular complexes formed with fullerenes also results in acceleration of the photoinduced electron-transfer process but deceleration of the back electron transfer; again, this is ascribed to favourable structural and electronic changes. Anion binding also plays a role in stabilizing supramolecular complexes between sulphonated tetraphenylporphyrin anions ([MTPPS](4-): M = H(2) and Zn) and a lithium ion encapsulated C(60) (Li(+)@C(60)); the resulting ensemble produces long-lived charge-separated states upon photoexcitation of the porphyrins.

  19. Hierarchical control of electron-transfer

    DEFF Research Database (Denmark)

    Westerhoff, Hans V.; Jensen, Peter Ruhdal; Egger, Louis;

    1997-01-01

    In this chapter the role of electron transfer in determining the behaviour of the ATP synthesising enzyme in E. coli is analysed. It is concluded that the latter enzyme lacks control because of special properties of the electron transfer components. These properties range from absence of a strong...... back pressure by the protonmotive force on the rate of electron transfer to hierarchical regulation of the expression of the gens that encode the electron transfer proteins as a response to changes in the bioenergetic properties of the cell.The discussion uses Hierarchical Control Analysis...

  20. Optimal Current Transfer in Dendrites

    Science.gov (United States)

    Bird, Alex D.

    2016-01-01

    Integration of synaptic currents across an extensive dendritic tree is a prerequisite for computation in the brain. Dendritic tapering away from the soma has been suggested to both equalise contributions from synapses at different locations and maximise the current transfer to the soma. To find out how this is achieved precisely, an analytical solution for the current transfer in dendrites with arbitrary taper is required. We derive here an asymptotic approximation that accurately matches results from numerical simulations. From this we then determine the diameter profile that maximises the current transfer to the soma. We find a simple quadratic form that matches diameters obtained experimentally, indicating a fundamental architectural principle of the brain that links dendritic diameters to signal transmission. PMID:27145441

  1. Essentially Optimal Universally Composable Oblivious Transfer

    DEFF Research Database (Denmark)

    Damgård, Ivan Bjerre; Nielsen, Jesper Buus; Orlandi, Claudio

    2009-01-01

    Oblivious transfer is one of the most important cryptographic primitives, both for theoretical and practical reasons and several protocols were proposed during the years. We provide the first oblivious transfer protocol which is simultaneously optimal on the following list of parameters: Security...

  2. Optimizing Reduced-Order Transfer Functions

    Science.gov (United States)

    Spanos, John T.; Milman, Mark H.; Mingori, D. Lewis

    1992-01-01

    Transfer-function approximations made optimal in special least-squares sense. Algorithm computes reduced-order rational-fraction approximates to single-input/single-output transfer functions. Reduces amount of computation needed for such purposes as numerical simulation of dynamics and design of control subsystems.

  3. Recent Developments in Electron Transfer Reactions

    OpenAIRE

    Marcus, Rudolph A.

    1987-01-01

    Earlier results and more recent developments in electron transfer reactions are reviewed. The more recent results include inverted behavior, electronic orientation effects on reaction rates, solvent dynamics, early steps in photosynthesis, and light emission from metal electrodes.

  4. Optimal Low Energy Earth-Moon Transfers

    Science.gov (United States)

    Griesemer, Paul Ricord; Ocampo, Cesar; Cooley, D. S.

    2010-01-01

    The optimality of a low-energy Earth-Moon transfer is examined for the first time using primer vector theory. An optimal control problem is formed with the following free variables: the location, time, and magnitude of the transfer insertion burn, and the transfer time. A constraint is placed on the initial state of the spacecraft to bind it to a given initial orbit around a first body, and on the final state of the spacecraft to limit its Keplerian energy with respect to a second body. Optimal transfers in the system are shown to meet certain conditions placed on the primer vector and its time derivative. A two point boundary value problem containing these necessary conditions is created for use in targeting optimal transfers. The two point boundary value problem is then applied to the ballistic lunar capture problem, and an optimal trajectory is shown. Additionally, the ballistic lunar capture trajectory is examined to determine whether one or more additional impulses may improve on the cost of the transfer.

  5. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    OpenAIRE

    2007-01-01

    This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH−-containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH−, upon photo-excitation of FADH− with 350–450 nm light...

  6. Alternative ground states enable pathway switching in biological electron transfer

    Science.gov (United States)

    Abriata, Luciano A.; Álvarez-Paggi, Damián; Ledesma, Gabriela N.; Blackburn, Ninian J.; Vila, Alejandro J.; Murgida, Daniel H.

    2012-01-01

    Electron transfer is the simplest chemical reaction and constitutes the basis of a large variety of biological processes, such as photosynthesis and cellular respiration. Nature has evolved specific proteins and cofactors for these functions. The mechanisms optimizing biological electron transfer have been matter of intense debate, such as the role of the protein milieu between donor and acceptor sites. Here we propose a mechanism regulating long-range electron transfer in proteins. Specifically, we report a spectroscopic, electrochemical, and theoretical study on WT and single-mutant CuA redox centers from Thermus thermophilus, which shows that thermal fluctuations may populate two alternative ground-state electronic wave functions optimized for electron entry and exit, respectively, through two different and nearly perpendicular pathways. These findings suggest a unique role for alternative or “invisible” electronic ground states in directional electron transfer. Moreover, it is shown that this energy gap and, therefore, the equilibrium between ground states can be fine-tuned by minor perturbations, suggesting alternative ways through which protein–protein interactions and membrane potential may optimize and regulate electron–proton energy transduction. PMID:23054836

  7. Photoinduced electron transfer across molecular bridges: electron- and hole-transfer superexchange pathways.

    Science.gov (United States)

    Natali, Mirco; Campagna, Sebastiano; Scandola, Franco

    2014-06-21

    Photoinduced electron transfer plays key roles in many areas of chemistry. Superexchange is an effective model to rationalize photoinduced electron transfer, particularly when molecular bridges between donor and acceptor subunits are present. In this tutorial review we discuss, within a superexchange framework, the complex role played by the bridge, with an emphasis on differences between thermal and photoinduced electron transfer, oxidative and reductive photoinduced processes, charge separation and charge recombination. Modular bridges are also considered, with specific attention to the distance dependence of donor-acceptor electronic coupling and electron transfer rate constants. The possibility of transition, depending on the bridge energetics, from coherent donor-acceptor electron transfer to incoherent charge injection and hopping through the bridge is also discussed. Finally, conceptual analogies between bridge effects in photoinduced electron transfer and optical intervalence transfer are outlined. Selected experimental examples, instrumental to illustration of the principles, are discussed.

  8. Topology optimization for transient heat transfer problems

    DEFF Research Database (Denmark)

    Zeidan, Said; Sigmund, Ole; Lazarov, Boyan Stefanov

    The focus of this work is on passive control of transient heat transfer problems using the topology optimization (TopOpt) method [1]. The goal is to find distributions of a limited amount of phase change material (PCM), within a given design domain, which optimizes the heat energy storage [2]. Our......, TopOpt has later been extended to transient problems in mechanics and photonics (e.g. [5], [6] and [7]). In the presented approach, the optimization is gradient-based, where in each iteration the non-steady heat conduction equation is solved,using the finite element method and an appropriate time...

  9. Hot-Electron Transfer from Semiconductor Nanocrystals

    National Research Council Canada - National Science Library

    William A. Tisdale; Kenrick J. Williams; Brooke A. Timp; David J. Norris; Eray S. Aydil; X.-Y. Zhu

    2010-01-01

    ... that limits device efficiency. Although fabricating the semiconductor in a nanocrystalline morphology can slow this cooling, the transfer of hot carriers to electron and hole acceptors has not yet been thoroughly demonstrated...

  10. Improved thermally conducting electron transfer polymers

    Science.gov (United States)

    Jenkins, R. K.; Byrd, N. R.; Lister, J. L.

    1972-01-01

    Development of polymers with improved heat transfer coefficients for use in encapsulating electronic modules is discussed. Chemical reactions for synthesizing the polymers are described and thermodynamic and physical properties are analyzed.

  11. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    Science.gov (United States)

    Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

    2007-12-01

    This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH--containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH-, upon photo-excitation of FADH- with 350-450 nm light. We compute the lowest singlet excited states of FADH- in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH- that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron-acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH--thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green's function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH- causes a π→π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH--to-dimer electronic coupling, thus inducing rapid electron transfer.

  12. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    Science.gov (United States)

    Skourtis, Spiros S.; Prytkova, Tatiana; Beratan, David N.

    2012-01-01

    This contribution describes molecular dynamics, semi-empirical and ab-initio studies of the primary photo-induced electron transfer reaction in DNA photolyase. DNA photolyases are FADH−-containing proteins that repair UV-damaged DNA by photo-induced electron transfer. A DNA photolyase recognizes and binds to cyclobutatne pyrimidine dimer lesions of DNA. The protein repairs a bound lesion by transferring an electron to the lesion from FADH−, upon photo-excitation of FADH− with 350–450 nm light. We compute the lowest singlet excited states of FADH− in DNA photolyase using INDO/S configuration interaction, time-dependent density-functional, and time-dependent Hartree-Fock methods. The calculations identify the lowest singlet excited state of FADH− that is populated after photo-excitation and that acts as the electron donor. For this donor state we compute conformationally-averaged tunneling matrix elements to empty electron- acceptor states of a thymine dimer bound to photolyase. The conformational averaging involves different FADH− - thymine dimer confromations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. The tunneling matrix element computations use INDO/S-level Green’s function, energy splitting, and Generalized Mulliken-Hush methods. These calculations indicate that photo-excitation of FADH− causes a π → π* charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH− - to - dimer electronic coupling, thus inducing rapid electron transfer. PMID:23226907

  13. Electron Transfer for Large Molecules through Delocalization

    Energy Technology Data Exchange (ETDEWEB)

    Neuhauser, D.; Reslan, R.; Hernandez, S.; Arnsen, C.; Lopata, K.; Govind, N.; Gao, Y.; Tolbert, S.; Schwartz, B.; Rubin, Y.; Nardes, A.; Kopidakis, N.

    2012-01-01

    Electron transfer for large molecules lies in between a Marcus-Theory two-state transfer and a Landauer description. We discuss a delocalization formalism which,through the introduction of artificial electric fields which emulate bulk dipole fields, allows calculation between a pair of identical molecules (A+A- (R)A-+A) with several open states. Dynamical electron polarization effects can be inserted with TDDFT and are crucial for large separations.

  14. Advances in electron transfer chemistry, v.6

    CERN Document Server

    Mariano, PS

    1999-01-01

    It is clear that electron transfer chemisty is now one of the most active areas of chemical study. Advances in Electron Transfer Chemistry has been designed to allow scientists who are developing new knowledge in this rapidly expanding area to describe their most recent research findings. This volume will serve those interested in learning about current breakthroughs in this rapidly expanding area of chemical research.

  15. Thermally conducting electron transfer polymers

    Science.gov (United States)

    Byrd, N. R.; Jenkins, R. K.; Lister, J. L.

    1969-01-01

    New polymeric material exhibits excellent physical shock protection, high electrical resistance, and thermal conductivity. It is especially useful for electronic circuitry, such as subminiaturization of components and modular construction of circuits.

  16. Photoselected electron transfer pathways in DNA photolyase.

    Science.gov (United States)

    Prytkova, Tatiana R; Beratan, David N; Skourtis, Spiros S

    2007-01-16

    Cyclobutane dimer photolyases are proteins that bind to UV-damaged DNA containing cyclobutane pyrimidine dimer lesions. They repair these lesions by photo-induced electron transfer. The electron donor cofactor of a photolyase is a two-electron-reduced flavin adenine dinucleotide (FADH(-)). When FADH(-) is photo-excited, it transfers an electron from an excited pi --> pi* singlet state to the pyrimidine dimer lesion of DNA. We compute the lowest excited singlet states of FADH(-) using ab initio (time-dependent density functional theory and time-dependent Hartree-Fock), and semiempirical (INDO/S configuration interaction) methods. The calculations show that the two lowest pi --> pi* singlet states of FADH(-) are localized on the side of the flavin ring that is proximal to the dimer lesion of DNA. For the lowest-energy donor excited state of FADH(-), we compute the conformationally averaged electronic coupling to acceptor states of the thymine dimer. The coupling calculations are performed at the INDO/S level, on donor-acceptor cofactor conformations obtained from molecular dynamics simulations of the solvated protein with a thymine dimer docked in its active site. These calculations demonstrate that the localization of the (1)FADH(-)* donor state on the flavin ring enhances the electronic coupling between the flavin and the dimer by permitting shorter electron-transfer pathways to the dimer that have single through-space jumps. Therefore, in photolyase, the photo-excitation itself enhances the electron transfer rate by moving the electron towards the dimer.

  17. Electron transfer across a thermal gradient.

    Science.gov (United States)

    Craven, Galen T; Nitzan, Abraham

    2016-08-23

    Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor-acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures.

  18. Ultrafast Photoinduced Electron Transfer from Peroxide Dianion.

    Science.gov (United States)

    Anderson, Bryce L; Maher, Andrew G; Nava, Matthew; Lopez, Nazario; Cummins, Christopher C; Nocera, Daniel G

    2015-06-18

    The encapsulation of peroxide dianion by hexacarboxamide cryptand provides a platform for the study of electron transfer of isolated peroxide anion. Photoinitiated electron transfer (ET) between freely diffusing Ru(bpy)3(2+) and the peroxide dianion occurs with a rate constant of 2.0 × 10(10) M(-1) s(-1). A competing electron transfer quenching pathway is observed within an ion pair. Picosecond transient spectroscopy furnishes a rate constant of 1.1 × 10(10) s(-1) for this first-order process. A driving force dependence for the ET rate within the ion pair using a series of Ru(bpy)3(2+) derivatives allows for the electronic coupling and reorganization energies to be assessed. The ET reaction is nonadiabatic and dominated by a large inner-sphere reorganization energy, in accordance with that expected for the change in bond distance accompanying the conversion of peroxide dianion to superoxide anion.

  19. Engineered electron-transfer chain in photosystem 1 based photocathodes outperforms electron-transfer rates in natural photosynthesis.

    Science.gov (United States)

    Kothe, Tim; Pöller, Sascha; Zhao, Fangyuan; Fortgang, Philippe; Rögner, Matthias; Schuhmann, Wolfgang; Plumeré, Nicolas

    2014-08-25

    Photosystem 1 (PS1) triggers the most energetic light-induced charge-separation step in nature and the in vivo electron-transfer rates approach 50 e(-)  s(-1)  PS1(-1). Photoelectrochemical devices based on this building block have to date underperformed with respect to their semiconductor counterparts or to natural photosynthesis in terms of electron-transfer rates. We present a rational design of a redox hydrogel film to contact PS1 to an electrode for photocurrent generation. We exploit the pH-dependent properties of a poly(vinyl)imidazole Os(bispyridine)2Cl polymer to tune the redox hydrogel film for maximum electron-transfer rates under optimal conditions for PS1 activity. The PS1-containing redox hydrogel film displays electron-transfer rates of up to 335±14 e(-)  s(-1)  PS1(-1), which considerably exceeds the rates observed in natural photosynthesis or in other semiartificial systems. Under O2 supersaturation, photocurrents of 322±19 μA cm(-2) were achieved. The photocurrents are only limited by mass transport of the terminal electron acceptor (O2). This implies that even higher electron-transfer rates may be achieved with PS1-based systems in general. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  20. Unusual distance dependences of electron transfer rates.

    Science.gov (United States)

    Kuss-Petermann, Martin; Wenger, Oliver S

    2016-07-28

    Usually the rates for electron transfer (kET) decrease with increasing donor-acceptor distance, but Marcus theory predicts a regime in which kET is expected to increase when the transfer distance gets longer. Until recently, experimental evidence for such counter-intuitive behavior had been very limited, and consequently this effect is much less well-known than the Gaussian free energy dependence of electron transfer rates leading to the so-called inverted driving-force effect. This article presents the theoretical concepts that lead to the prediction of electron transfer rate maxima at large donor-acceptor distances, and it discusses conditions that are expected to favor experimental observations of such behavior. It continues with a consideration of specific recent examples in which electron transfer rates were observed to increase with increasing donor-acceptor distance, and it closes with a discussion of the importance of this effect in the context of light-to-chemical energy conversion.

  1. Electron transfer in ion-atom collisions

    Energy Technology Data Exchange (ETDEWEB)

    Lin, C D

    1979-01-01

    Recent theoretical development in the understanding of electron transfer processes is reviewed. K-K electron transfer processes are studied for projectiles (nuclear charge Z/sub B/) and targets (nuclear charge Z/sub A/) in which Z/sub A/ and Z/sub B/ range from Z/sub A/ much greater than Z/sub B/ to Z/sub A/ approx. = Z/sub B/, over the energy range 0.1 < v/v/sub e/ < 2. (GHT)

  2. Quantifying electron transfer reactions in biological systems

    DEFF Research Database (Denmark)

    Sjulstok, Emil Sjulstok; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling...... which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between...... quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment...

  3. Facile Interfacial Electron Transfer of Hemoglobin

    Directory of Open Access Journals (Sweden)

    Chunhai Fan

    2005-12-01

    Full Text Available Abstract: We herein describe a method of depositing hemoglobin (Hb and sulfonated polyaniline (SPAN on GC electrodes that facilitate interfacial protein electron transfer. Well-defined, reproducible, chemically reversible peaks of Hb and SPAN can be obtained in our experiments. We also observed enhanced peroxidase activity of Hb in SPAN films. These results clearly showed that SPAN worked as molecular wires and effectively exchanged electrons between Hb and electrodes.Mediated by Conjugated Polymers

  4. Optimal Energy Transfer in Light-Harvesting Systems

    Directory of Open Access Journals (Sweden)

    Lipeng Chen

    2015-08-01

    Full Text Available Photosynthesis is one of the most essential biological processes in which specialized pigment-protein complexes absorb solar photons, and with a remarkably high efficiency, guide the photo-induced excitation energy toward the reaction center to subsequently trigger its conversion to chemical energy. In this work, we review the principles of optimal energy transfer in various natural and artificial light harvesting systems. We begin by presenting the guiding principles for optimizing the energy transfer efficiency in systems connected to dissipative environments, with particular attention paid to the potential role of quantum coherence in light harvesting systems. We will comment briefly on photo-protective mechanisms in natural systems that ensure optimal functionality under varying ambient conditions. For completeness, we will also present an overview of the charge separation and electron transfer pathways in reaction centers. Finally, recent theoretical and experimental progress on excitation energy transfer, charge separation, and charge transport in artificial light harvesting systems is delineated, with organic solar cells taken as prime examples.

  5. Optimal Energy Transfer in Light-Harvesting Systems.

    Science.gov (United States)

    Chen, Lipeng; Shenai, Prathamesh; Zheng, Fulu; Somoza, Alejandro; Zhao, Yang

    2015-08-20

    Photosynthesis is one of the most essential biological processes in which specialized pigment-protein complexes absorb solar photons, and with a remarkably high efficiency, guide the photo-induced excitation energy toward the reaction center to subsequently trigger its conversion to chemical energy. In this work, we review the principles of optimal energy transfer in various natural and artificial light harvesting systems. We begin by presenting the guiding principles for optimizing the energy transfer efficiency in systems connected to dissipative environments, with particular attention paid to the potential role of quantum coherence in light harvesting systems. We will comment briefly on photo-protective mechanisms in natural systems that ensure optimal functionality under varying ambient conditions. For completeness, we will also present an overview of the charge separation and electron transfer pathways in reaction centers. Finally, recent theoretical and experimental progress on excitation energy transfer, charge separation, and charge transport in artificial light harvesting systems is delineated, with organic solar cells taken as prime examples.

  6. Electron transfer statistics and thermal fluctuations in molecular junctions.

    Science.gov (United States)

    Goswami, Himangshu Prabal; Harbola, Upendra

    2015-02-28

    We derive analytical expressions for probability distribution function (PDF) for electron transport in a simple model of quantum junction in presence of thermal fluctuations. Our approach is based on the large deviation theory combined with the generating function method. For large number of electrons transferred, the PDF is found to decay exponentially in the tails with different rates due to applied bias. This asymmetry in the PDF is related to the fluctuation theorem. Statistics of fluctuations are analyzed in terms of the Fano factor. Thermal fluctuations play a quantitative role in determining the statistics of electron transfer; they tend to suppress the average current while enhancing the fluctuations in particle transfer. This gives rise to both bunching and antibunching phenomena as determined by the Fano factor. The thermal fluctuations and shot noise compete with each other and determine the net (effective) statistics of particle transfer. Exact analytical expression is obtained for delay time distribution. The optimal values of the delay time between successive electron transfers can be lowered below the corresponding shot noise values by tuning the thermal effects.

  7. 75 FR 16579 - Electronic Fund Transfers

    Science.gov (United States)

    2010-04-01

    ... From the Federal Register Online via the Government Publishing Office ] Part II Federal Reserve System 12 CFR Part 205 Electronic Fund Transfers; Final Rule #0;#0;Federal Register / Vol. 75 , No. 62... Consumers from Hidden Gift Card Fees Secretly Draining Shoppers' Pockets'', Press Release, Mar. 27,...

  8. Electronic Energy Transfer in Polarizable Heterogeneous Environments

    DEFF Research Database (Denmark)

    Svendsen, Casper Steinmann; Kongsted, Jacob

    2015-01-01

    Theoretical prediction of transport and optical properties of protein-pigment complexes is of significant importance when aiming at understanding the structure versus function relationship in such systems. Electronic energy transfer (EET) couplings represent a key property in this respect since...

  9. Nonlocal bacterial electron transfer to hematite surfaces

    Science.gov (United States)

    Rosso, Kevin M.; Zachara, John M.; Fredrickson, Jim K.; Gorby, Yuri A.; Smith, Steven C.

    2003-03-01

    Mechanisms by which dissimilatory iron-reducing bacteria utilize iron and manganese oxide minerals as terminal electron acceptors for respiration are poorly understood. In the absence of exogenous electron shuttle compounds, extracellular electron transfer is generally thought to occur through the interfacial contact area between mineral surfaces and attached cells. Possible alternative reduction pathways have been proposed based on the discovery of a link between an excreted quinone and dissimilatory reduction. In this study, we utilize a novel experimental approach to demonstrate that Shewanella putrefaciens reduces the surface of crystalline iron oxides at spatial locations that are distinct from points of attachment.

  10. Algorithmic Aspects of Several Data Transfer Service Optimization Problems

    CERN Document Server

    Andreica, Mugurel Ionut; Ionescu, Florin; Andreica, Cristina Teodora

    2009-01-01

    Optimized data transfer services are highly demanded nowadays, due to the large amounts of data which are frequently being produced and accessed. In this paper we consider several data transfer service optimization problems (optimal server location in path networks, optimal packet sequencing and minimum makespan packet scheduling), for which we provide novel algorithmic solutions.

  11. Biotechnological Aspects of Microbial Extracellular Electron Transfer

    Science.gov (United States)

    Kato, Souichiro

    2015-01-01

    Extracellular electron transfer (EET) is a type of microbial respiration that enables electron transfer between microbial cells and extracellular solid materials, including naturally-occurring metal compounds and artificial electrodes. Microorganisms harboring EET abilities have received considerable attention for their various biotechnological applications, in addition to their contribution to global energy and material cycles. In this review, current knowledge on microbial EET and its application to diverse biotechnologies, including the bioremediation of toxic metals, recovery of useful metals, biocorrosion, and microbial electrochemical systems (microbial fuel cells and microbial electrosynthesis), were introduced. Two potential biotechnologies based on microbial EET, namely the electrochemical control of microbial metabolism and electrochemical stimulation of microbial symbiotic reactions (electric syntrophy), were also discussed. PMID:26004795

  12. Vibrational control of electron-transfer reactions: a feasibility study for the fast coherent transfer regime.

    Science.gov (United States)

    Antoniou, P; Ma, Z; Zhang, P; Beratan, D N; Skourtis, S S

    2015-12-14

    Molecular vibrations and electron-vibrational interactions are central to the control of biomolecular electron and energy-transfer rates. The vibrational control of molecular electron-transfer reactions by infrared pulses may enable the precise probing of electronic-vibrational interactions and of their roles in determining electron-transfer mechanisms. This type of electron-transfer rate control is advantageous because it does not alter the electronic state of the molecular electron-transfer system or irreversibly change its molecular structure. For bridge-mediated electron-transfer reactions, infrared (vibrational) excitation of the bridge linking the electron donor to the electron acceptor was suggested as being capable of influencing the electron-transfer rate by modulating the bridge-mediated donor-to-acceptor electronic coupling. This kind of electron-transfer experiment has been realized, demonstrating that bridge-mediated electron-transfer rates can be changed by exciting vibrational modes of the bridge. Here, we use simple models and ab initio computations to explore the physical constraints on one's ability to vibrationally perturb electron-transfer rates using infrared excitation. These constraints stem from the nature of molecular vibrational spectra, the strengths of the electron-vibrational coupling, and the interaction between molecular vibrations and infrared radiation. With these constraints in mind, we suggest parameter regimes and molecular architectures that may enhance the vibrational control of electron transfer for fast coherent electron-transfer reactions.

  13. Promoting Interspecies Electron Transfer with Biochar

    Science.gov (United States)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Malvankar, Nikhil S.; Liu, Fanghua; Fan, Wei; Nevin, Kelly P.; Lovley, Derek R.

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why biochar may enhance methane production from organic wastes under anaerobic conditions. PMID:24846283

  14. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar...... to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were...... attached to the biochar, yet not in close contact, suggesting that electrons were likely conducted through the biochar, rather than biological electrical connections. The finding that biochar can stimulate DIET may be an important consideration when amending soils with biochar and can help explain why...

  15. Education and solar conversion. Demonstrating electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Smestad, Greg P. [Institute of Physical Chemistry, ICP-2, Swiss Federal Institute of Technology, EPFL, CH-1015 Lausanne (Switzerland)

    1998-07-23

    A simplified solar cell fabrication procedure is presented that uses natural anthocyanin or chlorophyll dyes extracted from plants. This procedure illustrates how interdisciplinary science can be taught at lower division university and upper division high school levels for an understanding of renewable energy as well as basic science concepts. Electron transfer occurs on the Earth in the mitochondrial membranes found in living cells, and in the thylakoid membranes found in the photosynthetic cells of green plants. Since we depend on the results of this electron and energy transfer, e.g. in our use of petroleum and agricultural products, it is desirable to understand and communicate how the electron transfer works. The simplified solar cell fabrication procedure, based on nanocrystalline dye-sensitized solar cells, has therefore been developed so that it can be inexpensively reproduced and utilized in the teaching of basic principles in biology, chemistry, physics, and environmental science. A water-based solution of commercial nanocrystalline titanium dioxide (TiO{sub 2}) powder is used to deposit a highly porous semiconductor electron acceptor. This acceptor couples the light-driven processes occurring at an organic dye to the macroscopic world and an external electrical circuit. Materials science and semiconductor physics are emphasized during the deposition of the sintered TiO{sub 2} nanocrystalline ceramic film. Chelation, complexation and molecular self-assembly are demonstrated during the attachment of the dye molecule to the surface of the TiO{sub 2} semiconductor particles. Environmental chemistry and energy conversion can be linked to these concepts via the regenerative oxidation and reduction cycle found in the cell. The resulting device, made in under 3 h, can be used as a light detector or power generator that produces 0.4-0.5 V at open circuit, and 1-2 mA per square cm under solar illumination

  16. Heat transfer in high density electronics packaging

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    In order to get an insight into the thermal characteristic and to evaluate the thermal reliability of the "System in Packaging"(SIP), a new solution of electronics packaging, a heat transfer model of SIP was developed to predict the heat dissipation capacity and to investigate the effect of different factors on the temperature distribution in the electronics. The affecting parameters under consideration include the thermophysical properties of the substrates, the coefficient of convection heat transfer, the thickness of the chip, and the density of power dissipation. ALGOR, a kind of finite element analysis software,was used to do the model simulation. Based on the sinulation and analysis of the heat conduction and convection resistance, criteria for the thermal design were established and possible measurement for enhancing power dissipation was provided, The results show that the heat transfer model provides a new and effective way to the thermal design and thermal analysis of SIP and to the mechanical analysis for the further investigation of SIP.

  17. Topology Optimization of Spacecraft Transfer Compartment

    Directory of Open Access Journals (Sweden)

    A. A. Borovikov

    2016-01-01

    Full Text Available IntroductionThe subject of this research is topology optimization of the adapter of a spacecraft transfer compartment. The finite element topology optimization [1] is widely used for simple structure elements [6, 7]. It is argued that using this method in conjunction with additive technology (3D - printing it is possible to create construction designs with the best weight characteristics. However, the paper shows that when applying this method to a complex construction design the optimization results are highly sensitive to optimization algorithm parameters. The goal of this research is to study parameters of the topology optimization algorithm and the influence of their variations on results.1.      Problem formulation   A commercial software Altair HyperWorks/OptiStruct (student’s license performed numerical calculations. The paper presents a detailed description of the finite element model.The main features of the proposed model are as follows:-          Simplicity with non-complicated geometry;-          Building a finite element model in terms of computing time minimization;-          Using the lumped mass elements to simulate the impacts of the conjugates on the adapter;-          A limit of material strength, decreased by an order of magnitude, to eliminate stress concentrators;-          The gravitational load applied corresponds to the loads for the Angara-A5 launcher [8]. 2.      Method of solutionA brief description of the SIMP-method realized in the Altair HyperWorks/OptiStruct software is given.3.      ResultsPerformed numerical calculations, and shown the influence of variations of algorithm parameters (DISCRETE, MATINIT, MINDIM, MAXDIM on construction design as well as the parameters SINGLE and SPLIT used to reveal restrictions on manufacturing.Shown that, depending on variations of parameters, an adapter construction strives to «truss» or «shell» type. Described

  18. Mechanisms for control of biological electron transfer reactions.

    Science.gov (United States)

    Williamson, Heather R; Dow, Brian A; Davidson, Victor L

    2014-12-01

    Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions. Copyright © 2014 Elsevier Inc. All rights reserved.

  19. Electron transfer pathways in microbial oxygen biocathodes

    Energy Technology Data Exchange (ETDEWEB)

    Freguia, Stefano, E-mail: stefano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Tsujimura, Seiya, E-mail: seiya@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Kano, Kenji, E-mail: kkano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan)

    2010-01-01

    The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O{sub 2} reduction by heme compounds. Here we showed that 1 muM of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O{sub 2} reduction to H{sub 2}O{sub 2} with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

  20. Mediated Electron Transfer at Redox Active Monolayers

    Directory of Open Access Journals (Sweden)

    Michael E.G. Lyons

    2001-12-01

    Full Text Available A theoretical model describing the transport and kinetic processes involved in heterogeneous redox catalysis of solution phase reactants at electrode surfaces coated with redox active monolayers is presented. Although the analysis presented has quite general applicability, a specific focus of the paper is concerned with the idea that redox active monolayers can be used to model an ensemble of individual molecular nanoelectrodes. Three possible rate determining steps are considered: heterogeneous electron transfer between immobilized mediator and support electrode ; bimolecular chemical reaction between redox mediator and reactant species in the solution phase, and diffusional mass transport of reactant in solution. A general expression for the steady state reaction flux is derived which is valid for any degree of reversibility of both the heterogeneous electron transfer reaction involving immobilized mediator species and of the bimolecular cross exchange reaction between immobilized mediator and solution phase reactant. The influence of reactant transport in solution is also specifically considered. Simplified analytical expressions for the net reaction flux are derived for experimentally reasonable situations and a kinetic case diagram is constructed outlining the relationships between the various approximate solutions. The theory enables simple diagnostic plots to be constructed which can be used to analyse experimental data.

  1. INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS

    NARCIS (Netherlands)

    Bartoloni, Fernando Heering; Monteiro Leite Ciscato, Luiz Francisco; Augusto, Felipe Alberto; Baader, Wilhelm Josef

    2010-01-01

    INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS. Chemiluminescence properties of the peroxyoxalate reaction in the presence of activators bearing electron withdrawing substituents were studied, to evaluate the possible occurrence of an inverse electron tr

  2. INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS

    NARCIS (Netherlands)

    Bartoloni, Fernando Heering; Monteiro Leite Ciscato, Luiz Francisco; Augusto, Felipe Alberto; Baader, Wilhelm Josef

    2010-01-01

    INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS. Chemiluminescence properties of the peroxyoxalate reaction in the presence of activators bearing electron withdrawing substituents were studied, to evaluate the possible occurrence of an inverse electron tr

  3. INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS

    NARCIS (Netherlands)

    Bartoloni, Fernando Heering; Monteiro Leite Ciscato, Luiz Francisco; Augusto, Felipe Alberto; Baader, Wilhelm Josef

    2010-01-01

    INVERSE ELECTRON TRANSFER IN PEROXYOXALATE CHEMIEXCITATION USING EASILY REDUCIBLE ACTIVATORS. Chemiluminescence properties of the peroxyoxalate reaction in the presence of activators bearing electron withdrawing substituents were studied, to evaluate the possible occurrence of an inverse electron

  4. Particle swarm optimization applied to impulsive orbital transfers

    Science.gov (United States)

    Pontani, Mauro; Conway, Bruce A.

    2012-05-01

    The particle swarm optimization (PSO) technique is a population-based stochastic method developed in recent years and successfully applied in several fields of research. It mimics the unpredictable motion of bird flocks while searching for food, with the intent of determining the optimal values of the unknown parameters of the problem under consideration. At the end of the process, the best particle (i.e. the best solution with reference to the objective function) is expected to contain the globally optimal values of the unknown parameters. The central idea underlying the method is contained in the formula for velocity updating. This formula includes three terms with stochastic weights. This research applies the particle swarm optimization algorithm to the problem of optimizing impulsive orbital transfers. More specifically, the following problems are considered and solved with the PSO algorithm: (i) determination of the globally optimal two- and three-impulse transfer trajectories between two coplanar circular orbits; (ii) determination of the optimal transfer between two coplanar, elliptic orbits with arbitrary orientation; (iii) determination of the optimal two-impulse transfer between two circular, non-coplanar orbits; (iv) determination of the globally optimal two-impulse transfer between two non-coplanar elliptic orbits. Despite its intuitiveness and simplicity, the particle swarm optimization method proves to be capable of effectively solving the orbital transfer problems of interest with great numerical accuracy.

  5. Solar sail time-optimal interplanetary transfer trajectory design

    Institute of Scientific and Technical Information of China (English)

    Sheng-Ping Gong; Yun-Feng Gao; Jun-Feng Li

    2011-01-01

    The fuel consumption associated with some interplanetary transfer trajectories using chemical propulsion is not affordable.A solar sail is a method of propulsion that does not consume fuel.Transfer time is one of the most pressing problems of solar sail transfer trajectory design.This paper investigates the time-optimal interplanetary transfer trajectories to a circular orbit of given inclination and radius.The optimal control law is derived from the principle of maximization.An indirect method is used to solve the optimal control problem by selecting values for the initial adjoint variables,which are normalized within a unit sphere.The conditions for the existence of the time-optimal transfer are dependent on the lightness number of the sail and the inclination and radius of the target orbit.A numerical method is used to obtain the boundary values for the time-optimal transfer trajectories.For the cases where no time-optimal transfer trajectories exist,first-order necessary conditions of the optimal control are proposed to obtain feasible solutions.The results show that the transfer time decreases as the minimum distance from the Sun decreases during the transfer duration.For a solar sail with a small lightness number,the transfer time may be evaluated analytically for a three-phase transfer trajectory.The analytical results are compared with previous results and the associated numerical results.The transfer time of the numerical result here is smaller than the transfer time from previous results and is larger than the analytical result.

  6. Electron transfer at sensitized semiconductor electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Spitler, M.T.

    1977-03-01

    Electron transfer from the excited state of sensitizing dyes to the conduction band of semiconductors has been studied through photoelectrochemical techniques. Two systems were analyzed in detail: rhodamine B on ZnO and rose bengal on TiO/sub 2/. Prior to electrochemical experimentation, the adsorption characteristics of these dyes were investigated using ZnO, ZnS, and TiO/sub 2/ single crystals as substrates. Absorbance measurements of the adsorbed dye were taken as a function of the solution concentration of the dye. Adsorption isotherms heats of adsorption were also established; they were similar to literature data reported for adsorption of these dyes on powdered substrates. Using the absorbance data, the quantum efficiency for photoinjection of electrons from rhodamine B into a ZnO electrode was determined to be 2.7 x 10/sup -2/. This value was independent of the dye surface concentration down to 50% coverage of the electrode. With the assumption that not all of the rhodamine B adsorbed on the electrode has the same rate of electron injection, a kinetic model for the time decay of the photocurrent was developed; data were analyzed according to this theory. A rate constant for photoreduction of the adsorbed dye was determined for the reducing agents. 86 references.

  7. Visual prosthesis wireless energy transfer system optimal modeling.

    Science.gov (United States)

    Li, Xueping; Yang, Yuan; Gao, Yong

    2014-01-16

    Wireless energy transfer system is an effective way to solve the visual prosthesis energy supply problems, theoretical modeling of the system is the prerequisite to do optimal energy transfer system design. On the basis of the ideal model of the wireless energy transfer system, according to visual prosthesis application condition, the system modeling is optimized. During the optimal modeling, taking planar spiral coils as the coupling devices between energy transmitter and receiver, the effect of the parasitic capacitance of the transfer coil is considered, and especially the concept of biological capacitance is proposed to consider the influence of biological tissue on the energy transfer efficiency, resulting in the optimal modeling's more accuracy for the actual application. The simulation data of the optimal model in this paper is compared with that of the previous ideal model, the results show that under high frequency condition, the parasitic capacitance of inductance and biological capacitance considered in the optimal model could have great impact on the wireless energy transfer system. The further comparison with the experimental data verifies the validity and accuracy of the optimal model proposed in this paper. The optimal model proposed in this paper has a higher theoretical guiding significance for the wireless energy transfer system's further research, and provide a more precise model reference for solving the power supply problem in visual prosthesis clinical application.

  8. Transfer line TT70 (electrons from PS to SPS)

    CERN Multimedia

    CERN PhotoLab

    1981-01-01

    As injectors for LEP, PS and SPS had to be converted to the acceleration of electrons and positrons. So far, only positively charged particles had been transferred from the PS to the SPS, for the negatively charged electrons a new transfer line, TT70, had to be built. Due to the difference in level of the two machines, the transfer line slopes and tilts.

  9. GPU-accelerated computation of electron transfer.

    Science.gov (United States)

    Höfinger, Siegfried; Acocella, Angela; Pop, Sergiu C; Narumi, Tetsu; Yasuoka, Kenji; Beu, Titus; Zerbetto, Francesco

    2012-11-05

    Electron transfer is a fundamental process that can be studied with the help of computer simulation. The underlying quantum mechanical description renders the problem a computationally intensive application. In this study, we probe the graphics processing unit (GPU) for suitability to this type of problem. Time-critical components are identified via profiling of an existing implementation and several different variants are tested involving the GPU at increasing levels of abstraction. A publicly available library supporting basic linear algebra operations on the GPU turns out to accelerate the computation approximately 50-fold with minor dependence on actual problem size. The performance gain does not compromise numerical accuracy and is of significant value for practical purposes. Copyright © 2012 Wiley Periodicals, Inc.

  10. Respiratory electron transfer in Escherichia coli : components, energetics and regulation

    NARCIS (Netherlands)

    Bekker, M.

    2009-01-01

    The respiratory chain that is housed in the bacterial cytoplasmic membrane, generally transfers electrons from NADH to oxygen; in the absence of oxygen it can use several alternative electron acceptors, such as nitrate and fumarate. Transfer of electrons through this chain is usually coupled to the

  11. Soliton-like Solutions and Electron Transfer in DNA.

    Science.gov (United States)

    Lakhno, V D

    2000-06-01

    We consider various mechanisms of long-range electron transfer in DNAwhich enable us to explain recent controversial experiments. We show thatcontinuous super-exchange theory can explain the values of electron rateconstants in short fragments of DNA. The soliton-type electron transfer inlong segments of DNA is also dealt with.

  12. Soliton-like Solutions and Electron Transfer in DNA

    OpenAIRE

    Lakhno, V.D.

    2000-01-01

    We consider various mechanisms of long-range electron transfer in DNAwhich enable us to explain recent controversial experiments. We show thatcontinuous super-exchange theory can explain the values of electron rateconstants in short fragments of DNA. The soliton-type electron transfer inlong segments of DNA is also dealt with.

  13. Electronic and Nuclear Factors in Charge and Excitation Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Piotr Piotrowiak

    2004-09-28

    We report the and/or state of several subprojects of our DOE sponsored research on Electronic and Nuclear Factors in Electron and Excitation Transfer: (1) Construction of an ultrafast Ti:sapphire amplifier. (2) Mediation of electronic interactions in host-guest molecules. (3) Theoretical models of electrolytes in weakly polar media. (4) Symmetry effects in intramolecular excitation transfer.

  14. Respiratory electron transfer in Escherichia coli : components, energetics and regulation

    NARCIS (Netherlands)

    Bekker, M.

    2009-01-01

    The respiratory chain that is housed in the bacterial cytoplasmic membrane, generally transfers electrons from NADH to oxygen; in the absence of oxygen it can use several alternative electron acceptors, such as nitrate and fumarate. Transfer of electrons through this chain is usually coupled to the

  15. Theory of interrelated electron and proton transfer processes

    DEFF Research Database (Denmark)

    Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    A simple theory of elementary act of interrelated reactions of electron and proton transfer is developed. Mechanisms of synchronous and multistage transfer and coherent transitions via a dynamically populated intermediate state are discussed. Formulas for rate constants of adiabatic and nonadiaba......A simple theory of elementary act of interrelated reactions of electron and proton transfer is developed. Mechanisms of synchronous and multistage transfer and coherent transitions via a dynamically populated intermediate state are discussed. Formulas for rate constants of adiabatic...

  16. Teaching basic science to optimize transfer.

    Science.gov (United States)

    Norman, Geoff

    2009-09-01

    Basic science teachers share the concern that much of what they teach is soon forgotten. Although some evidence suggests that relatively little basic science is forgotten, it may not appear so, as students commonly have difficulty using these concepts to solve or explain clinical problems: This phenomenon, using a concept learned in one context to solve a problem in a different context, is known to cognitive psychologists as transfer. The psychology literature shows that transfer is difficult; typically, even though students may know a concept, fewer than 30% will be able to use it to solve new problems. However a number of strategies to improve transfer can be adopted at the time of initial teaching of the concept, in the use of exemplars to illustrate the concept, and in practice with additional problems. In this article, we review the literature in psychology to identify practical strategies to improve transfer. Critical review of psychology literature to identify factors that enhance or impede transfer. There are a number of strategies available to teachers to facilitate transfer. These include active problem-solving at the time of initial learning, imbedding the concept in a problem context, using everyday analogies, and critically, practice with multiple dissimilar problems. Further, mixed practice, where problems illustrating different concepts are mixed together, and distributed practice, spread out over time, can result in significant and large gains. Transfer is difficult, but specific teaching strategies can enhance this skill by factors of two or three.

  17. [Electron transfer between globular proteins. Evaluation of a matrix element].

    Science.gov (United States)

    Lakhno, V D; Chuev, G N; Ustinin, M N

    1998-01-01

    The dependence of the matrix element of the probability of interprotein electron transfer on the mutual orientation of the donor and acceptor centers and the distance between them was calculated. The calculations were made under the assumption that electron transfer proceeds mainly by a collective excitation of polaron nature, like a solvated electron state. The results obtained are consistent with experimental data and indicate the nonexponential behavior of this dependence in the case when the distance transfer is less than 20 A.

  18. Electron transfer and interfacial behavior of redox proteins

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    This paper reviews the recent progress in the electron transfer and interfacial behavior of redox proteins. Significant achievements in the relevant fields are summarized including the direct electron transfer between proteins and electrodes, the thermodynamic and kinetic properties, catalytic activities and activity regulation of the redox proteins. It has been demonstrated that the electrochemical technique is an effective tool for protein studies, especially for probing into the electron transfer and interfacial behavior of redox proteins.

  19. Transcriptomic and genetic analysis of direct interspecies electron transfer

    DEFF Research Database (Denmark)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Summers, Zarath M

    2013-01-01

    The possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in which Geobacter sulfurreducens was the elect......The possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in which Geobacter sulfurreducens....... These results demonstrate that there are unique gene expression patterns that distinguish DIET from HIT and suggest that metatranscriptomics may be a promising route to investigate interspecies electron transfer pathways in more-complex environments....

  20. Single-element Electron-transfer Optical Detector System

    Science.gov (United States)

    Jordan, Jeffrey D. (Inventor)

    2004-01-01

    An optical detector system includes an electrically resistive screen that is substantially transparent to radiation energy having a wavelength of interest. An electron transfer element (e.g., a low work function photoactive material or a carbon nanotube (CNT)-based element) has a first end and a second end with its first end spaced apart from the screen by an evacuated gap. When radiation energy passes through the screen with a bias voltage being applied thereto, transfer of electrons through the electron transfer element is induced from its first to its second end such that a quantity indicative of the electrons transferred can be detected.

  1. Cation-modulated electron-transfer channel: H-atom transfer vs proton-coupled electron transfer with a variable electron-transfer channel in acylamide units.

    Science.gov (United States)

    Chen, Xiaohua; Bu, Yuxiang

    2007-08-08

    The mechanism of proton transfer (PT)/electron transfer (ET) in acylamide units was explored theoretically using density functional theory in a representative model (a cyclic coupling mode between formamide and the N-dehydrogenated formamidic radical, FF). In FF, PT/ET normally occurs via a seven-center cyclic proton-coupled electron transfer (PCET) mechanism with a N-->N PT and an O-->O ET. However, when different hydrated metal ions are bound to the two oxygen sites of FF, the PT/ET mechanism may significantly change. In addition to their inhibition of PT/ET rate, the hydrated metal ions can effectively regulate the FF PT/ET cooperative mechanism to produce a single pathway hydrogen atom transfer (HAT) or a flexible proton coupled electron transfer (PCET) mechanism by changing the ET channel. The regulation essentially originates from the change in the O...O bond strength in the transition state, subject to the binding ability of the hydrated metal ions. In general, the high valent metal ions and those with large binding energies can promote HAT, and the low valent metal ions and those with small binding energies favor PCET. Hydration may reduce the Lewis acidity of cations, and thus favor PCET. Good correlations among the binding energies, barrier heights, spin density distributions, O...O contacts, and hydrated metal ion properties have been found, which can be used to interpret the transition in the PT/ET mechanism. These findings regarding the modulation of the PT/ET pathway via hydrated metal ions may provide useful information for a greater understanding of PT/ET cooperative mechanisms, and a possible method for switching conductance in nanoelectronic devices.

  2. Vibrationally Resolved Electron Transfer Rates in Solution

    Science.gov (United States)

    Spears, Kenneth G.

    2002-03-01

    We have re-examined our earlier report of electron transfer in the [Co(Cp)_2|V(CO)_6] radical-pair using ultrafast infrared transient absorption spectroscopy in room temperature solutions. The radical-pair is created from the [Co(Cp)_2^+|V(CO)_6^-] ion-pair by ultrafast visible charge-transfer excitation. Transient absorption experiments with ps time constants. A small ET component with a 75 ps time constant is due to some separation and reformation of the radical-pairs. Transient absorption experiments monitoring the recovery of the ion-pair state shows that both fast components are due to ET rather than some other vibrational relaxation (VR) process in the radical state. We analyze the visible charge-transfer band and assign the two fast ET decay times to two ion-pair contact geometries with absorption origins different by about 1250 ± 350 cm-1. For excitation at 800 and 700 nm the 700 fs ET lifetime depends on the vibrational quantum state of the nontotally symmetric CO stretch in the V(CO)6 radical, where the lifetime decreases by 10% for the first vibrational quantum and 45% for the second quantum. There is no quantum effect for the second ion-pair geometry with a 5 ps ET lifetime. Standard ET rate models cannot explain the rate dependence upon vibrational quantum state for a nontotally symmetric vibration, and it may arise from a breakdown of the Condon approximation. We also report rates for IVR of CO stretching modes and for VR of low frequency vibrations. At excitation wavelengths of 620 and 555 nm there is sufficient internal vibrational energy in low-frequency vibrations to cause geometric inter-conversion between energetically similar Jahn-Teller geometries in the V(CO)6 radical. This process creates a 200 fs rise time for the V(CO)6 radical species to assume a stable geometry, which requires VR of low frequency vibrations to the solvent. These results demonstrate that earlier ET measurements from our group on the same molecule had insufficient time

  3. Kinetics of electron transfer from photoexcited superlattice electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Nozik, A.J.; Turner, J.A.; Peterson, M.W.

    1988-05-05

    A kinetic model has been developed that quantitatively describes electron transfer from photoexcited superlattice electrodes into liquid solutions. The model permits electron transfer from all quantum levels as well as from surface states; it also takes into account recombination in the bulk, space charge layer, and surfaces states, and band-edge movement. The model calculations define the values of the rate constants for heterogeneous electron transfer and hot electron thermalization among the various energy levels in the supperlattice quantum wells that are necessary to achieve hot electron transfer from excited quantum states. The question of whether hot electron transfer is manifested by a dependence of the photocurrent action spectra on acceptor redox potential is examined in detail.

  4. Electronic transfer of sensitive patient data.

    Science.gov (United States)

    Detterbeck, A M W; Kaiser, J; Hirschfelder, U

    2015-01-01

    The purpose of this study was to develop decision-making aids and recommendations for dental practitioners regarding the utilization and sharing of sensitive digital patient data. In the current environment of growing digitization, healthcare professionals need detailed knowledge of secure data management to maximize confidentiality and minimize the risks involved in both archiving patient data and sharing it through electronic channels. Despite well-defined legal requirements, an all-inclusive technological solution does not currently exist. The need for a preliminary review and critical appraisal of common practices of data transfer prompted a search of the literature and the Web to identify viable methods of secure data exchange and to develop a flowchart. A strong focus was placed on the transmission of datasets both smaller than and larger than 10 MB, and on secure communication by smartphone. Although encryption of patient-related data should be routine, it is often difficult to implement. Pretty Good Privacy (PGP) and Secure/Multipurpose Internet Mail Extensions (S/MIME) are viable standards for secure e-mail encryption. Sharing of high-volume data should be accomplished with the help of file encryption. Careful handling of sensitive patient data is mandatory, and it is the end-user's responsibility to meet any requirements for encryption, preferably by using free, open-source (and hence transparent) software.

  5. Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1993-03-01

    This project involves the design, synthesis and study of molecules which mimic some of the important aspects of photosynthetic electron and energy transfer. This research project is leading to a better understanding of the energy conserving steps of photosynthesis via the study of synthetic model systems which abstract features of the natural photosynthetic apparatus. The knowledge gained from these studies will aid in the design of artificial photosynthetic reaction centers which employ the basic chemistry and physics of photosynthesis to help meet mankind`s energy needs. The approach to artificial photosynthesis employed in this project is to use synthetic pigments, electron donors, and electron acceptors similar to those found in biological reaction centers, but to replace the protein component with covalent bonds. These chemical linkages determine the electronic coupling between the various moieties by controlling separation, relative orientation, and overlap of electronic orbitals. The model systems are designed to mimic the following aspects of natural photosynthetic electron transfer: electron donation from a tetrapyrrole excited single state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they mimic carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

  6. 78 FR 66251 - Electronic Fund Transfers(Regulation E)

    Science.gov (United States)

    2013-11-05

    ... PROTECTION 12 CFR Part 1005 RIN 3170-AA33 Electronic Fund Transfers (Regulation E) AGENCY: Bureau of Consumer... countries that qualify for an exception in subpart B of Regulation E, which implements the Electronic Fund....consumerfinance.gov/remittances-transfer-rule-amendment-to-regulation-e/ . SUPPLEMENTARY INFORMATION: The...

  7. 14 CFR 1260.69 - Electronic funds transfer payment methods.

    Science.gov (United States)

    2010-01-01

    .... Electronic Funds Transfer Payment Methods October 2000 (a) Payments under this grant will be made by the Government by electronic funds transfer through the Treasury Fedline Payment System (FEDLINE) or the Automated Clearing House (ACH), at the option of the Government. After award, but no later than 14 days...

  8. 14 CFR 1274.931 - Electronic funds transfer payment methods.

    Science.gov (United States)

    2010-01-01

    ... cooperative agreement will be made by the Government by electronic funds transfer through the Treasury Fedline Payment System (FEDLINE) or the Automated Clearing House (ACH), at the option of the Government. After... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Electronic funds transfer payment methods...

  9. Time-resolved EPR identifies unexpected electron transfer in cryptochrome**

    Science.gov (United States)

    Biskup, Till; Hitomi, Kenichi; Getzoff, Elizabeth D.; Krapf, Sebastian; Koslowski, Thorsten; Schleicher, Erik

    2012-01-01

    Tuning photoinduced electron transfer: Subtle differences in local sequence and conformation can produce diversity and specificity in electron transfer (ET) in proteins, despite high structural conservation of redox partners. For individual ET steps, distance is not necessarily the decisive parameter; orientation and solvent accessibility of ET partners, and therefore, stabilization of charge-separated states contribute substantially. PMID:22086606

  10. 77 FR 6310 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-02-07

    ... PROTECTION 12 CFR Part 1005 RIN 3170-AA15 Electronic Fund Transfers (Regulation E) AGENCY: Bureau of Consumer... Financial Protection (Bureau) is proposing to amend Regulation E, which implements the Electronic Fund... phrase ``normal course of business'' in the definition of ``remittance transfer provider.''...

  11. 76 FR 708 - Electronic Funds Transfer of Depository Taxes; Correction

    Science.gov (United States)

    2011-01-06

    ... Internal Revenue Service 26 CFR Parts 1, 31, 40, and 301 RIN 1545-BJ13 Electronic Funds Transfer of...) providing guidance relating to Federal tax deposits (FTDs) by Electronic Funds Transfer (EFT). The temporary... Days and Legal Holidays'', line 8 from the bottom of the page, the language ``section 7503, the term...

  12. 76 FR 709 - Electronic Funds Transfer of Depository Taxes; Correction

    Science.gov (United States)

    2011-01-06

    ... Internal Revenue Service 26 CFR Parts 40 and 301 RIN 1545-BJ13 Electronic Funds Transfer of Depository... deposits (FTDs) by Electronic Funds Transfer (EFT). The temporary and final regulations provide rules under...)-3 0 Par. 2. Section 40.6302(c)-3, paragraph (c) is amended by removing the language in the third...

  13. THE ELECTRONIC COURSE OF HEAT AND MASS TRANSFER

    Directory of Open Access Journals (Sweden)

    Alexander P. Solodov

    2013-01-01

    Full Text Available The Electronic course of heat and mass transfer in power engineering is presented containing the full Electronic book as the structured hypertext document, the full set of Mathcad-documents with the whole set of educative computer models of heat and mass transfer, the computer labs, and selected educational presentations. 

  14. Electron and hole transfer from indium phosphide quantum dots.

    Science.gov (United States)

    Blackburn, J L; Selmarten, D C; Ellingson, R J; Jones, M; Micic, O; Nozik, A J

    2005-02-24

    Electron- and hole-transfer reactions are studied in colloidal InP quantum dots (QDs). Photoluminescence quenching and time-resolved transient absorption (TA) measurements are utilized to examine hole transfer from photoexcited InP QDs to the hole acceptor N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and electron transfer to nanocrystalline titanium dioxide (TiO2) films. Core-confined holes are effectively quenched by TMPD, resulting in a new approximately 4-ps component in the TA decay. It is found that electron transfer to TiO2 is primarily mediated through surface-localized states on the InP QDs.

  15. Heme electron transfer in peroxidases: the propionate e-pathway.

    Science.gov (United States)

    Guallar, Victor

    2008-10-23

    Computational modeling offers a new insight about the electron transfer pathway in heme peroxidases. Available crystal structures have revealed an intriguing arrangement of the heme propionate side chains in heme-heme and heme-substrate complexes. By means of mixed quantum mechanical/molecular mechanics calculations, we study the involvement of these propionate groups into the substrate oxidation in ascorbate peroxidase and into the heme to heme electron transfer in bacterial cytochrome c peroxidase. By selectively turning on/off different quantum regions, we obtain the electron transfer pathway which directly involves the porphyrin ring and the heme propionates. Furthermore, in ascorbate peroxidase the presence of the substrate appears to be crucial for the activation of the electron transfer channel. The results might represent a general motif for electron transfer from/to the heme group and change our view for the propionate side chains as simple electrostatic binding anchors. We name the new mechanism "the propionate e-pathway".

  16. Density matrix theory for reductive electron transfer in DNA

    Energy Technology Data Exchange (ETDEWEB)

    Kleinekathoefer, Ulrich [Institut fuer Physik, Technische Universitaet Chemnitz, 09107 Chemnitz (Germany)]. E-mail: kleinekathoefer@physik.tu-chemnitz.de; Li Guangqi [Institut fuer Physik, Technische Universitaet Chemnitz, 09107 Chemnitz (Germany); Schreiber, Michael [Institut fuer Physik, Technische Universitaet Chemnitz, 09107 Chemnitz (Germany)

    2006-07-15

    Reductive electron transfer in DNA is investigated using the reduced density matrix formalism. For reductive electron transfer in DNA an electron donor is attached to the DNA. The photo-excitation of this donor by ultrashort laser pulses is described explicitly in the current investigation, as well as the transfer of the electron from the donor to the acceptor. In addition, the effect of an additional bridge molecule is studied. All these studies are performed using three different quantum master equations: a Markovian one and two non-Markovian ones derived from either a time-local or a time-nonlocal formalism. The deviations caused by these three different approaches are discussed.

  17. Variable Electron Transfer Pathways in an Amphibian Cryptochrome

    Science.gov (United States)

    Biskup, Till; Paulus, Bernd; Okafuji, Asako; Hitomi, Kenichi; Getzoff, Elizabeth D.; Weber, Stefan; Schleicher, Erik

    2013-01-01

    Electron transfer reactions play vital roles in many biological processes. Very often the transfer of charge(s) proceeds stepwise over large distances involving several amino acid residues. By using time-resolved electron paramagnetic resonance and optical spectroscopy, we have studied the mechanism of light-induced reduction of the FAD cofactor of cryptochrome/photolyase family proteins. In this study, we demonstrate that electron abstraction from a nearby amino acid by the excited FAD triggers further electron transfer steps even if the conserved chain of three tryptophans, known to be an effective electron transfer pathway in these proteins, is blocked. Furthermore, we were able to characterize this secondary electron transfer pathway and identify the amino acid partner of the resulting flavin-amino acid radical pair as a tyrosine located at the protein surface. This alternative electron transfer pathway could explain why interrupting the conserved tryptophan triad does not necessarily alter photoreactions of cryptochromes in vivo. Taken together, our results demonstrate that light-induced electron transfer is a robust property of cryptochromes and more intricate than commonly anticipated. PMID:23430261

  18. Carboxylate shifts steer interquinone electron transfer in photosynthesis.

    Science.gov (United States)

    Chernev, Petko; Zaharieva, Ivelina; Dau, Holger; Haumann, Michael

    2011-02-18

    Understanding the mechanisms of electron transfer (ET) in photosynthetic reaction centers (RCs) may inspire novel catalysts for sunlight-driven fuel production. The electron exit pathway of type II RCs comprises two quinone molecules working in series and in between a non-heme iron atom with a carboxyl ligand (bicarbonate in photosystem II (PSII), glutamate in bacterial RCs). For decades, the functional role of the iron has remained enigmatic. We tracked the iron site using microsecond-resolution x-ray absorption spectroscopy after laser-flash excitation of PSII. After formation of the reduced primary quinone, Q(A)(-), the x-ray spectral changes revealed a transition (t½ ≈ 150 μs) from a bidentate to a monodentate coordination of the bicarbonate at the Fe(II) (carboxylate shift), which reverted concomitantly with the slower ET to the secondary quinone Q(B). A redox change of the iron during the ET was excluded. Density-functional theory calculations corroborated the carboxylate shift both in PSII and bacterial RCs and disclosed underlying changes in electronic configuration. We propose that the iron-carboxyl complex facilitates the first interquinone ET by optimizing charge distribution and hydrogen bonding within the Q(A)FeQ(B) triad for high yield Q(B) reduction. Formation of a specific priming intermediate by nuclear rearrangements, setting the stage for subsequent ET, may be a common motif in reactions of biological redox cofactors.

  19. NASA Electronic Library System (NELS) optimization

    Science.gov (United States)

    Pribyl, William L.

    1993-01-01

    This is a compilation of NELS (NASA Electronic Library System) Optimization progress/problem, interim, and final reports for all phases. The NELS database was examined, particularly in the memory, disk contention, and CPU, to discover bottlenecks. Methods to increase the speed of NELS code were investigated. The tasks included restructuring the existing code to interact with others more effectively. An error reporting code to help detect and remove bugs in the NELS was added. Report writing tools were recommended to integrate with the ASV3 system. The Oracle database management system and tools were to be installed on a Sun workstation, intended for demonstration purposes.

  20. Laboratory Transferability of Optimally Shaped Laser Pulses for Quantum Control

    CERN Document Server

    Tibbetts, Katharine Moore; Rabitz, Herschel

    2013-01-01

    Optimal control experiments can readily identify effective shaped laser pulses, or "photonic reagents", that achieve a wide variety of objectives. For many practical applications, an important criterion is that a particular photonic reagent prescription still produce a good, if not optimal, target objective yield when transferred to a different system or laboratory, {even if the same shaped pulse profile cannot be reproduced exactly. As a specific example, we assess the potential for transferring optimal photonic reagents for the objective of optimizing a ratio of photoproduct ions from a family of halomethanes through three related experiments.} First, applying the same set of photonic reagents with systematically varying second- and third-order chirp on both laser systems generated similar shapes of the associated control landscape (i.e., relation between the objective yield and the variables describing the photonic reagents). Second, optimal photonic reagents obtained from the first laser system were found...

  1. Dissipative two-electron transfer: A numerical renormalization group study

    Science.gov (United States)

    Tornow, Sabine; Bulla, Ralf; Anders, Frithjof B.; Nitzan, Abraham

    2008-07-01

    We investigate nonequilibrium two-electron transfer in a model redox system represented by a two-site extended Hubbard model and embedded in a dissipative environment. The influence of the electron-electron interactions and the coupling to a dissipative bosonic bath on the electron transfer is studied in different temperature regimes. At high temperatures, Marcus transfer rates are evaluated, and at low temperatures, we calculate equilibrium and nonequilibrium population probabilities of the donor and acceptor with the nonperturbative numerical renormalization group approach. We obtain the nonequilibrium dynamics of the system prepared in an initial state of two electrons at the donor site and identify conditions under which the electron transfer involves one concerted two-electron step or two sequential single-electron steps. The rates of the sequential transfer depend nonmonotonically on the difference between the intersite and on-site Coulomb interaction, which become renormalized in the presence of the bosonic bath. If this difference is much larger than the hopping matrix element, the temperature as well as the reorganization energy, simultaneous transfer of both electrons between donor and acceptor can be observed.

  2. K-shell Analysis Reveals Distinct Functional Parts in an Electron Transfer Network and Its Implications for Extracellular Electron Transfer

    Science.gov (United States)

    Ding, Dewu; Li, Ling; Shu, Chuanjun; Sun, Xiao

    2016-01-01

    Shewanella oneidensis MR-1 is capable of extracellular electron transfer (EET) and hence has attracted considerable attention. The EET pathways mainly consist of c-type cytochromes, along with some other proteins involved in electron transfer processes. By whole genome study and protein interactions inquisition, we constructed a large-scale electron transfer network containing 2276 interactions among 454 electron transfer related proteins in S. oneidensis MR-1. Using the k-shell decomposition method, we identified and analyzed distinct parts of the electron transfer network. We found that there was a negative correlation between the ks (k-shell values) and the average DR_100 (disordered regions per 100 amino acids) in every shell, which suggested that disordered regions of proteins played an important role during the formation and extension of the electron transfer network. Furthermore, proteins in the top three shells of the network are mainly located in the cytoplasm and inner membrane; these proteins can be responsible for transfer of electrons into the quinone pool in a wide variety of environmental conditions. In most of the other shells, proteins are broadly located throughout the five cellular compartments (cytoplasm, inner membrane, periplasm, outer membrane, and extracellular), which ensures the important EET ability of S. oneidensis MR-1. Specifically, the fourth shell was responsible for EET and the c-type cytochromes in the remaining shells of the electron transfer network were involved in aiding EET. Taken together, these results show that there are distinct functional parts in the electron transfer network of S. oneidensis MR-1, and the EET processes could achieve high efficiency through cooperation through such an electron transfer network. PMID:27148219

  3. A molecular shift register based on electron transfer

    Science.gov (United States)

    Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

    1988-01-01

    An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

  4. Photoinduced electron transfer between benzyloxy dendrimer phthalocyanine and benzoquinone

    Science.gov (United States)

    Zhang, Tiantian; Ma, Dongdong; Pan, Sujuan; Wu, Shijun; Jiang, Yufeng; Zeng, Di; Yang, Hongqin; Peng, Yiru

    2016-10-01

    Photo-induced electron transfer (PET) is an important and fundamental process in natural photosynthesis. To mimic such interesting PET process, a suitable donor and acceptor couple were properly chosen. Dendrimer phthalocyanines and their derivatives have emerged as promising materials for artificial photosynthesis systems. In this paper, the electron transfer between the light harvest dendrimer phthalocyanine (donor) and the 1,4-benzoquinone (acceptor) was studied by UV/Vis and fluorescence spectroscopic methods. It was found that fluorescence of phthalocyanine was quenched by benzoquinone (BQ) via excited state electron transfer, from the phthalocyanine to the BQ upon excitation at 610 nm. The Stern-Volmer constant (KSV) of electron transfer was calculated. Our study suggests that this dendritic phthalocyanine is an effective new electron donor and transmission complex and could be used as a potential artificial photosynthesis system.

  5. Kinetic pathway for interfacial electron transfer from a semiconductor to a molecule

    Science.gov (United States)

    Hu, Ke; Blair, Amber D.; Piechota, Eric J.; Schauer, Phil A.; Sampaio, Renato N.; Parlane, Fraser G. L.; Meyer, Gerald J.; Berlinguette, Curtis P.

    2016-09-01

    Molecular approaches to solar-energy conversion require a kinetic optimization of light-induced electron-transfer reactions. At molecular-semiconductor interfaces, this optimization has previously been accomplished through control of the distance between the semiconductor donor and the molecular acceptor and/or the free energy that accompanies electron transfer. Here we show that a kinetic pathway for electron transfer from a semiconductor to a molecular acceptor also exists and provides an alternative method for the control of interfacial kinetics. The pathway was identified by the rational design of molecules in which the distance and the driving force were held near parity and only the geometric torsion about a xylyl- or phenylthiophene bridge was varied. Electronic coupling through the phenyl bridge was a factor of ten greater than that through the xylyl bridge. Comparative studies revealed a significant bridge dependence for electron transfer that could not be rationalized by a change in distance or driving force. Instead, the data indicate an interfacial electron-transfer pathway that utilizes the aromatic bridge orbitals.

  6. Intermolecular and intramolecular electron transfer from eosin ester to viologen

    Institute of Scientific and Technical Information of China (English)

    张丰雷; 张曼华; 沈涛

    1996-01-01

    The covalently -(CH2)10- linked eosin-butylviologen compound has been synthesized. The photoinduced electron transfer of eosin ester and butylviologen as well as the influence of addition of cyclodextrin or amylose into the solution of linked compound on the system have been studied by the absorption spectra, fluorescence spectra and fluorescence lifetime. The results indicated that the intramolecular electron transfer is much more efficient than the intermolecular one. Due to the formation of inclusion complex, the process of intramolecular electron transfer was changed after adding cydodextrin or amylose.

  7. Intermodal Energy Transfer in a Tapered Optical Fiber: Optimizing Transmission

    CERN Document Server

    Ravets, S; Kordell, P R; Wong-Campos, J D; Rolston, S L; Orozco, L A

    2013-01-01

    We present an experimental and theoretical study of the energy transfer between modes during the tapering process of an optical nanofiber through spectrogram analysis. The results allow optimization of the tapering process, and we measure transmission in excess of 99.95% for the fundamental mode. We quantify the adiabaticity condition through calculations and place an upper bound on the amount of energy transferred to other modes at each step of the tapering, giving practical limits to the tapering angle.

  8. REFLECTIONS ON THE TWO-STATE ELECTRON TRANSFER MODEL.

    Energy Technology Data Exchange (ETDEWEB)

    Brunschwig, B.S.

    2000-01-12

    There is general agreement that the two most important factors determining electron transfer rates in solution are the degree of electronic interaction between the donor and acceptor sites, and the changes in the nuclear configurations of the donor, acceptor, and surrounding medium that occur upon the gain or loss of an electron Ll-51. The electronic interaction of the sites will be very weak, and the electron transfer slow, when the sites are far apart or their interaction is symmetry or spin forbidden. Since electron motion is much faster than nuclear motion, energy conservation requires that, prior to the actual electron transfer, the nuclear configurations of the reactants and the surrounding medium adjust from their equilibrium values to a configuration (generally) intermediate between that of the reactants and products. In the case of electron transfer between , two metal complexes in a polar solvent, the nuclear configuration changes involve adjustments in the metal-ligand and intraligand bond lengths and angles, and changes in the orientations of the surrounding solvent molecules. In common with ordinary chemical reactions, an electron transfer reaction can then be described in terms of the motion of the system on an energy surface from the reactant equilibrium configuration (initial state) to the product equilibrium configuration (final state) via the activated complex (transition state) configuration.

  9. [Electron transfer between globular proteins. Dependence of the rate of transfer on distance].

    Science.gov (United States)

    Lakhno, V D; Chuev, G N; Ustinin, M N; Komarov, V M

    1998-01-01

    Based on the assumption that electron transfer between globular proteins occurs by a collective excitation of polaron type, the dependence of the rate of this process on the distance between the donor and acceptor centers with regard to their detailed electron structure was calculated. The electron structure of the heme was calculated by the quantum-chemical MNDO-PM3 method. The results were compared with experimental data on interprotein and intraglobular electron transfer. It is shown that, in the framework of this model, the electron transfer is not exponential and does not require a particular transfer pathway since the whole protein macromolecule is involved in the formation of the electron excited state.

  10. Extracellular electron transfer mechanisms between microorganisms and minerals

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Liang; Dong, Hailiang; Reguera, Gemma; Beyenal, Haluk; Lu, Anhuai; Liu, Juan; Yu, Han-Qing; Fredrickson, James K.

    2016-08-30

    Electrons can be transferred from microorganisms to multivalent metal ions that are associated with minerals and vice versa. As the microbial cell envelope is neither physically permeable to minerals nor electrically conductive, microorganisms have evolved strategies to exchange electrons with extracellular minerals. In this Review, we discuss the molecular mechanisms that underlie the ability of microorganisms to exchange electrons, such as c-type cytochromes and microbial nanowires, with extracellular minerals and with microorganisms of the same or different species. Microorganisms that have extracellular electron transfer capability can be used for biotechnological applications, including bioremediation, biomining and the production of biofuels and nanomaterials.

  11. Combining UV photodissociation with electron transfer for peptide structure analysis.

    Science.gov (United States)

    Shaffer, Christopher J; Marek, Ales; Pepin, Robert; Slovakova, Kristina; Turecek, Frantisek

    2015-03-01

    The combination of near-UV photodissociation with electron transfer and collisional activation provides a new tool for structure investigation of isolated peptide ions and reactive intermediates. Two new types of pulse experiments are reported. In the first one called UV/Vis photodissociation-electron transfer dissociation (UVPD-ETD), diazirine-labeled peptide ions are shown to undergo photodissociation in the gas phase to form new covalent bonds, guided by the ion conformation, and the products are analyzed by electron transfer dissociation. In the second experiment, called ETD-UVPD wherein synthetic labels are not necessary, electron transfer forms new cation-peptide radical chromophores that absorb at 355 nm and undergo specific backbone photodissociation reactions. The new method is applied to distinguish isomeric ions produced by ETD of arginine containing peptides. Copyright © 2015 John Wiley & Sons, Ltd.

  12. Blocking layer modeling for temperature analysis of electron transfer ...

    African Journals Online (AJOL)

    Blocking layer modeling for temperature analysis of electron transfer rate in quantum dot sensitized solar cells. ... Journal of Fundamental and Applied Sciences ... of the quantum dots and free energy of system and finally the Marcus equation.

  13. Supramolecular networks with electron transfer in two dimensions

    Energy Technology Data Exchange (ETDEWEB)

    Stupp, Samuel I.; Stoddart, J. Fraser; Shveyd, Alexander K.; Tayi, Alok S.; Sue, Chi-Hau; Narayanan, Ashwin

    2016-09-13

    Organic charge-transfer (CT) co-crystals in a crossed stack system are disclosed. The co-crystals exhibit bidirectional charge transfer interactions where one donor molecule shares electrons with two different acceptors, one acceptor face-to-face and the other edge-to-face. The assembly and charge transfer interaction results in a pleochroic material whereby the optical absorption continuously changes depending on the polarization angle of incident light.

  14. Analysis of transmission efficiency of SSRF electron beam transfer lines

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this article, the main factors which influence transmission efficiency of the SSRF electron beam transfer lines are described, including physical requirements for magnet system, vacuum system, beam diagnostic system,trajectory correction system, etc. The dynamic simulation calculation and transmission efficiency analysis of the SSRF electron beam transfer lines are presented, and the studies show that the design purpose of efficient beam transmission and injection will be achieved.

  15. 75 FR 9120 - Electronic Fund Transfers

    Science.gov (United States)

    2010-03-01

    ... assess overdraft fees for paying automated teller machine (ATM) and one-time debit card transactions that... Transfer Act, limiting a financial institution's ability to assess fees for paying ATM and one- time debit... secured by margin securities in brokerage accounts extended by Securities and Exchange Commission or...

  16. 76 FR 29901 - Electronic Fund Transfers

    Science.gov (United States)

    2011-05-23

    ... protections for consumers who send remittance transfers to consumers or entities in a foreign country, by providing consumers with disclosures and error resolution rights. The proposed amendments implement statutory requirements set forth in the Dodd-Frank Wall Street Reform and Consumer Protection Act. DATES...

  17. Promoting Knowledge Transfer with Electronic Note Taking

    Science.gov (United States)

    Katayama, Andrew D.; Shambaugh, R. Neal; Doctor, Tasneem

    2005-01-01

    We investigated the differences between (a) copying and pasting text versus typed note-taking methods of constructing study notes simultaneously with (b) vertically scaffolded versus horizontally scaffold notes on knowledge transfer. Forty-seven undergraduate educational psychology students participated. Materials included 2 electronic…

  18. Theoretical aspects of electron transfer reactions of complex molecules

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    2001-01-01

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive ...... vibrational frequency changes, local mode anharmonicity, and rotational reorganization, in both diabatic and adiabatic limits. Systems for which this formalism is appropriate are discussed....

  19. 78 FR 30661 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2013-05-22

    ... Transfers (Regulation E); Final Rule #0;#0;Federal Register / Vol. 78 , No. 99 / Wednesday, May 22, 2013... Electronic Fund Transfers (Regulation E) AGENCY: Bureau of Consumer Financial Protection. ACTION: Final rule.../regulations/final-remittance-rule-amendment-regulation-e/ . SUPPLEMENTARY INFORMATION: I. Summary of the...

  20. Real-time electron dynamics simulation of two-electron transfer reactions induced by nuclear motion

    Science.gov (United States)

    Suzuki, Yasumitsu; Yamashita, Koichi

    2012-04-01

    Real-time electron dynamics of two-electron transfer reactions induced by nuclear motion is calculated by three methods: the numerically exact propagation method, the time-dependent Hartree (TDH) method and the Ehrenfest method. We find that, as long as the nuclei move as localized wave packets, the TDH and Ehrenfest methods can reproduce the exact electron dynamics of a simple charge transfer reaction model containing two electrons qualitatively well, even when nonadiabatic transitions between adiabatic states occur. In particular, both methods can reproduce the cases where a complete two-electron transfer reaction occurs and those where it does not occur.

  1. Electron Donor-Acceptor Quenching and Photoinduced Electron Transfer for Coumarin Dyes.

    Science.gov (United States)

    1983-10-31

    Mechanism of cousarin photodegradation . Ithe behavior of eoiuma dyes is water ad In aqueous detergent media,. and the effsects of medism aud, additives on...D-i36 345 ELECTRON DONOR-ACCEPTOR UENCHING AND PHOTOINDUCED i/i Ai ELECTRON TRANSFER FOR COUMARIN DYES (U) BOSTON UNIY MR DEPT OF CHEMISTRY G JONES...TYPE OF REPORT & PEIOD COVERED Electron Donor-acceptor Quenching and Photo- Technical, 1/1/82-10/31/82 induced Electron Transfer for Coumarin Dyes S

  2. Direct interspecies electron transfer between Geobacter metallireducens and Methanosarcina barkeri

    DEFF Research Database (Denmark)

    Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Liu, Fanghua

    2014-01-01

    Direct interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability of Methanosarcina barkeri, to participate in DIET was evaluated in co-culture with Geobacter...... metallireducens. Co-cultures formed aggregates that shared electrons via DIET during the stoichiometric conversion of ethanol to methane. Co-cultures could not be initiated with a pilin-deficient G. metallireducens, suggesting that long-range electron transfer along pili was important for DIET. Amendments...... physical contact was not necessary for interspecies H2 transfer. M. barkeri is the second methanogen found to accept electrons via DIET and the first methanogen known to be capable of using either H2 or electrons derived from DIET for CO2 reduction. Furthermore, M. barkeri is genetically tractable, making...

  3. Potential Energy Diagrams: A Conceptual Tool in the Study of Electron Transfer Reactions.

    Science.gov (United States)

    Lewis, Nita A.

    1980-01-01

    Describes how the potential energy diagram may be used to theoretically describe the processes involved in a system undergoing electron transfer. Examines factors important in electron transfer reactions and discusses several classes of electron transfer reactions. (CS)

  4. Shape Optimization of Inclined Ribs as Heat Transfer Augmentation Device

    Institute of Scientific and Technical Information of China (English)

    Kwang-Yong Kim; Hong-Min Kim

    2006-01-01

    This work presents numerical optimization techniques for the design of a rectangular channel with inclined ribs to enhance turbulent heat transfer.The response surface method with Reynolds-averaged Navier-Stokes analysis is used for optimization.Shear stress transport turbulence model is used as a turbulence closure.Computational results for local heat transfer rate show a reasonable agreement with the experimental data.Width-to-rib height ratio and attack angle of the rib are chosen as design variables.The objective function is defined as a linear combination of heat-transfer and friction-loss related terms with the weighting factor.Full-factorial experimental design method is used to determine the data points.Optimum shapes of the channel have been obtained in a range of the weighting factor.

  5. OPTIMIZING OUTCOME IN THE UNIVERSITY-INDUSTRY TECHNOLOGY TRANSFER PROJECTS

    Directory of Open Access Journals (Sweden)

    Hamed ALAVI

    2016-04-01

    Full Text Available Transferring inventions of academic scientists to private enterprises for the purpose of commercialization is long known as University-Industry (firm Technology Transfer While the importance of this phenomenon is simultaneously raising in public and private sector, only a part of patented academic inventions succeed in passing the process of commercialization. Despite the fact that formal Technology Transfer process and licencing of patented innovations to third party is the main legal tool for safeguarding rights of academic inventors in commercialization of their inventions, it is not sufficient for transmitting tacit knowledge which is necessary in exploitation of transferred technology. Existence of reciprocal and complementary relations between formal and informal technology transfer process has resulted in formation of different models for university-industry organizational collaboration or even integration where licensee firms keep contact with academic inventors after gaining legal right for commercialization of their patented invention. Current paper argues that despite necessity for patents to legally pass the right of commercialization of an invention, they are not sufficient for complete knowledge transmission in the process of technology transfer. Lack of efficiency of formal mechanism to end the Technology Transfer loop makes an opportunity to create innovative interpersonal and organizational connections among patentee and licensee company. With emphasize on need for further elaboration of informal mechanisms as critical and underappreciated aspect of technology transfer process, article will try to answer the questions of how to optimize knowledge transmission process in the framework of University-Industry Technology Transfer Projects? What is the theoretical basis for university-industry technology transfer process? What are organization collaborative models which can enhance overall performance by improving transmission of

  6. Evolutionary Optimization of Electronic Circuitry Cooling Using Nanofluid

    Directory of Open Access Journals (Sweden)

    Manu Mital

    2012-01-01

    Full Text Available Liquid cooling electronics using microchannels integrated in the chips is an attractive alternative to bulky aluminum heat sinks. Cooling can be further enhanced using nanofluids. The goals of this study are to evaluate heat transfer in a nanofluid heat sink with developing laminar flow forced convection, taking into account the pumping power penalty. The proposed model uses semi-empirical correlations to calculate effective nanofluid thermophysical properties, which are then incorporated into heat transfer and friction factor correlations in literature for single-phase flows. The model predicts the thermal resistance and pumping power as a function of four design variables that include the channel diameter, velocity, number of channels, and nanoparticle fraction. The parameters are optimized with minimum thermal resistance as the objective function and fixed specified value of pumping power as the constraint. For a given value of pumping power, the benefit of nanoparticle addition is evaluated by independently optimizing the heat sink, first with nanofluid and then with water. Comparing the minimized thermal resistances revealed only a small benefit since nanoparticle addition increases the pumping power that can alternately be diverted towards an increased velocity in a pure water heat sink. The benefit further diminishes with increase in available pumping power.

  7. Optical transfer function optimization based on linear expansions

    Science.gov (United States)

    Schwiegerling, Jim

    2015-09-01

    The Optical Transfer Function (OTF) and its modulus the Modulation Transfer Function (MTF) are metrics of optical system performance. However in system optimization, calculation times for the OTF are often substantially longer than more traditional optimization targets such as wavefront error or transverse ray error. The OTF is typically calculated as either the autocorrelation of the complex pupil function or as the Fourier transform of the Point Spread Function. We recently demonstrated that the on-axis OTF can be represented as a linear combination of analytical functions where the weighting terms are directly related to the wavefront error coefficients and apodization of the complex pupil function. Here, we extend this technique to the off-axis case. The expansion technique offers a potential for accelerating OTF optimization in lens design, as well as insight into the interaction of aberrations with components of the OTF.

  8. 77 FR 30923 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-05-24

    ... (ACH) transactions, telephone bill-payment plans, and remote banking service. Regulation E defines an... Part 1005 [Docket No. CFPB-2012-0019] RIN 3170-AA22 Electronic Fund Transfers (Regulation E) AGENCY... methods: Electronic: http://www.regulations.gov . Follow the instructions for submitting comments. Mail...

  9. Numerical Simulation of Transient Moisture Transfer into an Electronic Enclosure

    DEFF Research Database (Denmark)

    Shojaee Nasirabadi, Parizad; Jabbaribehnam, Mirmasoud; Hattel, Jesper Henri

    2016-01-01

    inside the enclosures to be able to protect the electronic systems.In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce theCPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which...

  10. Numerical Simulation of Transient Moisture Transfer into an Electronic Enclosure

    DEFF Research Database (Denmark)

    Shojaee Nasirabadi, Parizad; Jabbaribehnam, Mirmasoud; Hattel, Jesper Henri

    2016-01-01

    inside the enclosures to be able to protect the electronic systems.In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce theCPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which...

  11. Electron transfer through rigid organic molecular wires enhanced by electronic and electron-vibration coupling.

    Science.gov (United States)

    Sukegawa, Junpei; Schubert, Christina; Zhu, Xiaozhang; Tsuji, Hayato; Guldi, Dirk M; Nakamura, Eiichi

    2014-10-01

    Electron transfer (ET) is a fundamental process in a wide range of biological systems, photovoltaics and molecular electronics. Therefore to understand the relationship between molecular structure and ET properties is of prime importance. For this purpose, photoinduced ET has been studied extensively using donor-bridge-acceptor molecules, in which π-conjugated molecular wires are employed as bridges. Here, we demonstrate that carbon-bridged oligo-p-phenylenevinylene (COPV), which is both rigid and flat, shows an 840-fold increase in the ET rate compared with the equivalent flexible molecular bridges. A 120-fold rate enhancement is explained in terms of enhanced electronic coupling between the electron donor and the electron acceptor because of effective conjugation through the COPVs. The remainder of the rate enhancement is explained by inelastic electron tunnelling through COPV caused by electron-vibration coupling, unprecedented for organic molecular wires in solution at room temperature. This type of nonlinear effect demonstrates the versatility and potential practical utility of COPVs in molecular device applications.

  12. Electron Transfer Dissociation of Doubly Sodiated Glycerophosphocholine Lipids

    Science.gov (United States)

    Liang, Xiaorong; Liu, Jian; LeBlanc, Yves; Covey, Tom; Ptak, A. Celeste; Brenna, J. Thomas; McLuckey, Scott A.

    2009-01-01

    The ability to generate gaseous doubly charged cations of glycerophosphocholine (GPC) lipids via electrospray ionization has made possible the evaluation of electron transfer dissociation (ETD) for their structural characterization. Doubly sodiated GPC cations have been reacted with azobenzene radical anions in a linear ion trap mass spectrometer. The ion/ion reactions proceed through sodium transfer, electron transfer, and complex formation. Electron transfer reactions are shown to give rise to cleavage at each ester linkage with the subsequent loss of a neutral quaternary nitrogen moiety. Electron transfer without dissociation produces [M+2Na]+• radical cations, which undergo collision-induced dissociation (CID) to give products that arise from bond cleavage of each fatty acid chain. The CID of the complex ions yields products similar to those produced directly from the electron transfer reactions of doubly sodiated GPC, although with different relative abundances. These findings indicate that the analysis of GPC lipids by ETD in conjunction with CID can provide some structural information, such as the number of carbons, degree of unsaturation for each fatty acid substituent, and the positions of the fatty acid substituents; some information about the location of the double bonds may be present in low intensity CID product ions. PMID:17719238

  13. Toddlers' word learning and transfer from electronic and print books.

    Science.gov (United States)

    Strouse, Gabrielle A; Ganea, Patricia A

    2017-04-01

    Transfer from symbolic media to the real world can be difficult for young children. A sample of 73 toddlers aged 17 to 23months were read either an electronic book displayed on a touchscreen device or a traditional print book in which a novel object was paired with a novel label. Toddlers in both conditions learned the label within the context of the book. However, only those who read the traditional format book generalized and transferred the label to other contexts. An older group of 28 toddlers aged 24 to 30months did generalize and transfer from the electronic book. Across ages, those children who primarily used screens to watch prerecorded video at home transferred less from the electronic book than those with more diverse home media experiences. Copyright © 2016 Elsevier Inc. All rights reserved.

  14. Bacterial Electron Transfer Chains Primed by Proteomics

    NARCIS (Netherlands)

    Wessels, H.; Almeida, N.M. de; Kartal, B.; Keltjens, J.T.

    2016-01-01

    Electron transport phosphorylation is the central mechanism for most prokaryotic species to harvest energy released in the respiration of their substrates as ATP. Microorganisms have evolved incredible variations on this principle, most of these we perhaps do not know, considering that only a fracti

  15. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena; Shrestha, Pravin Malla;

    2014-01-01

    to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with Geobacter sulfurreducens or Methanosarcina barkeri in which ethanol was the electron donor. Cells were...

  16. 75 FR 31665 - Electronic Fund Transfers

    Science.gov (United States)

    2010-06-04

    ... purposes of this rulemaking. List of Subjects in 12 CFR Part 205 Consumer protection, Electronic fund... the consumer of the right to revoke the opt-in at any time. See Sec. 205.17(d)(6), which permits... a consumer's account, unless the consumer affirmatively consents, or opts in, to the institution's...

  17. Lewis Acid Coupled Electron Transfer of Metal-Oxygen Intermediates.

    Science.gov (United States)

    Fukuzumi, Shunichi; Ohkubo, Kei; Lee, Yong-Min; Nam, Wonwoo

    2015-12-01

    Redox-inactive metal ions and Brønsted acids that function as Lewis acids play pivotal roles in modulating the redox reactivity of metal-oxygen intermediates, such as metal-oxo and metal-peroxo complexes. The mechanisms of the oxidative CH bond cleavage of toluene derivatives, sulfoxidation of thioanisole derivatives, and epoxidation of styrene derivatives by mononuclear nonheme iron(IV)-oxo complexes in the presence of triflic acid (HOTf) and Sc(OTf)3 have been unified as rate-determining electron transfer coupled with binding of Lewis acids (HOTf and Sc(OTf)3 ) by iron(III)-oxo complexes. All logarithms of the observed second-order rate constants of Lewis acid-promoted oxidative CH bond cleavage, sulfoxidation, and epoxidation reactions of iron(IV)-oxo complexes exhibit remarkably unified correlations with the driving forces of proton-coupled electron transfer (PCET) and metal ion-coupled electron transfer (MCET) in light of the Marcus theory of electron transfer when the differences in the formation constants of precursor complexes were taken into account. The binding of HOTf and Sc(OTf)3 to the metal-oxo moiety has been confirmed for Mn(IV) -oxo complexes. The enhancement of the electron-transfer reactivity of metal-oxo complexes by binding of Lewis acids increases with increasing the Lewis acidity of redox-inactive metal ions. Metal ions can also bind to mononuclear nonheme iron(III)-peroxo complexes, resulting in acceleration of the electron-transfer reduction but deceleration of the electron-transfer oxidation. Such a control on the reactivity of metal-oxygen intermediates by binding of Lewis acids provides valuable insight into the role of Ca(2+) in the oxidation of water to dioxygen by the oxygen-evolving complex in photosystem II. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  18. Improving Data Transfer Throughput with Direct Search Optimization

    Energy Technology Data Exchange (ETDEWEB)

    Balaprakash, Prasanna; Morozov, Vitali; Kettimuthu, Rajkumar; Kumaran, Kalyan; Foster, Ian

    2016-01-01

    Improving data transfer throughput over high-speed long-distance networks has become increasingly difficult. Numerous factors such as nondeterministic congestion, dynamics of the transfer protocol, and multiuser and multitask source and destination endpoints, as well as interactions among these factors, contribute to this difficulty. A promising approach to improving throughput consists in using parallel streams at the application layer.We formulate and solve the problem of choosing the number of such streams from a mathematical optimization perspective. We propose the use of direct search methods, a class of easy-to-implement and light-weight mathematical optimization algorithms, to improve the performance of data transfers by dynamically adapting the number of parallel streams in a manner that does not require domain expertise, instrumentation, analytical models, or historic data. We apply our method to transfers performed with the GridFTP protocol, and illustrate the effectiveness of the proposed algorithm when used within Globus, a state-of-the-art data transfer tool, on productionWAN links and servers. We show that when compared to user default settings our direct search methods can achieve up to 10x performance improvement under certain conditions. We also show that our method can overcome performance degradation due to external compute and network load on source end points, a common scenario at high performance computing facilities.

  19. A Novel Optimization Means of Transfer Efficiency for Resonance Coupled Wireless Power Transfer

    Directory of Open Access Journals (Sweden)

    Tan Linlin

    2013-05-01

    Full Text Available When the transmitting and receiving coils are equivalent with or not significantly smaller than their separation distance between the two coils, the results of numerical simulations for transfer efficiency of system show that the maximum coupling of two coils or maximum transfer efficiency occur with a certain tilt angle between two coils, which means the two coils with parallel on the same axis is not able to obtain the maximum transmission efficiency. In view of this feature of the wireless power transfer system, we propose a novel means to optimize the transfer efficiency by designing rotatable transmitting coils to achieve the appropriate tile angle. The experimental results show that the presented means is efficient and greatly improves the transfer efficiency.

  20. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    -molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken...... in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems...... to show general (or expected) properties. Properties such as in the physical and (semi-)chemical interface between classical and quantum systems and the effects of molecular bond length constraints on the temperature during simulations. As a second step the methodology is applied to the symmetric...

  1. On frequency optimization of assymetric resonant inductive coupling wireless power transfer links

    OpenAIRE

    2014-01-01

    Resonant Inductive Coupling Wireless Power Transfer (RIC-WPT) is a leading field of research due to the growing number of applications that can benefit from this technology: from biomedical implants to consumer electronics, fractionated spacecraft and electric vehicles amongst others. However, current applications are limited to symetric point-to-point-links. New challenges and applications of RIC-WPT emphasize the necessity to explore, predict and optimize the behavior of these links for dif...

  2. [Electron transfer, ionization, and excitation in atomic collisions]. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    1992-12-31

    Fundamental processes of electron transfer, ionization, and excitation in ion-atom and ion-ion collisions are studied. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-ion core can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. At intermediate collision energies (e.g., proton energies for p-He{sup +} collisions on the order of 100 kilo-electron volts), many electronic states are strongly coupled during the collision, a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. At higher collision energies (million electron-volt energies) the coupling is weaker with, however, many more states being coupled together, so that high-order perturbation theory is essential.

  3. Plugging in or going wireless: strategies for interspecies electron transfer

    Science.gov (United States)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena

    2014-01-01

    Interspecies exchange of electrons enables a diversity of microbial communities to gain energy from reactions that no one microbe can catalyze. The first recognized strategies for interspecies electron transfer were those that relied on chemical intermediates that are recycled through oxidized and reduced forms. Well-studied examples are interspecies H2 transfer and the cycling of sulfur intermediates in anaerobic photosynthetic communities. Direct interspecies electron transfer (DIET) in which two species establish electrical contact is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions. PMID:24904551

  4. Plugging in or Going Wireless: Strategies for Interspecies Electron Transfer

    Directory of Open Access Journals (Sweden)

    Pravin Malla Shrestha

    2014-05-01

    Full Text Available Interspecies exchange of electrons enables a diversity of microbial communities to gain energy from reactions that no one microbe can catalyze. The first recognized strategies for interspecies electron transfer were those that relied on chemical intermediates that are recycled through oxidized and reduced forms. Well-studied examples are interspecies H2 transfer and the cycling of sulfur intermediates in anaerobic photosynthetic communities. Direct interspecies electron transfer (DIET in which two species establish electrical contacts is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. It seems likely that there are additional alternative strategies for interspecies electrical connections that have yet to be discovered. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions.

  5. Ultrafast electron and hole transfer in bulk heterojunctions of low-bandgap polymers

    Science.gov (United States)

    Kozlov, Oleg V.; Pavelyev, Vlad G.; de Gier, Hilde D.; Havenith, Remco W. A.; van Loosdrecht, Paul H. M.; Hummelen, Jan C.; Pshenichnikov, Maxim S.

    2016-12-01

    In modern bulk heterojunction (BHJ) organic solar cells, blends of low-bandgap polymer and [70]PCBM acceptor are used in the active layer. In this combination, the polymer absorbs photons from the red and near-IR parts of the solar spectrum, while the blue and near-UV photons are harvested by [70]PCBM. As a result, both electron transfer from polymer to [70]PCBM and hole transfer from [70]PCBM to polymer are of utmost importance in free charge generation and have to be optimized simultaneously. Here we study electron and hole transfer processes in BHJ blends of two low-bandgap polymers, BTT-DPP and PCPDTBT, by ultrafast photoinduced spectroscopy (PIA). By tracking the PIA dynamics, we observed substantially different charge separation pathways in BHJs of the two polymers with [70]PCBM. From the photoinduced anisotropy dynamics, we demonstrated that in the PCPDTBT:[70]PCBM system both electron and hole transfer processes are highly efficient, while in the BTTBPP:[ 70]PCBM electron transfer is blocked due to the unfortunate energy level alignment leaving hole transfer the only pathway to free charge generation. Calculations at the density functional theory level are used to gain more insight into our findings. The presented results highlight the importance of the energy level alignment on the charge separation process.

  6. Direct interspecies electron transfer between Geobacter metallireducens and Methanosarcina barkeri.

    Science.gov (United States)

    Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Liu, Fanghua; Markovaite, Beatrice; Chen, Shanshan; Nevin, Kelly P; Lovley, Derek R

    2014-08-01

    Direct interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability of Methanosarcina barkeri to participate in DIET was evaluated in coculture with Geobacter metallireducens. Cocultures formed aggregates that shared electrons via DIET during the stoichiometric conversion of ethanol to methane. Cocultures could not be initiated with a pilin-deficient G. metallireducens strain, suggesting that long-range electron transfer along pili was important for DIET. Amendments of granular activated carbon permitted the pilin-deficient G. metallireducens isolates to share electrons with M. barkeri, demonstrating that this conductive material could substitute for pili in promoting DIET. When M. barkeri was grown in coculture with the H2-producing Pelobacter carbinolicus, incapable of DIET, M. barkeri utilized H2 as an electron donor but metabolized little of the acetate that P.carbinolicus produced. This suggested that H2, but not electrons derived from DIET, inhibited acetate metabolism. P. carbinolicus-M. barkeri cocultures did not aggregate, demonstrating that, unlike DIET, close physical contact was not necessary for interspecies H2 transfer. M. barkeri is the second methanogen found to accept electrons via DIET and the first methanogen known to be capable of using either H2 or electrons derived from DIET for CO2 reduction. Furthermore, M. barkeri is genetically tractable,making it a model organism for elucidating mechanisms by which methanogens make biological electrical connections with other cells.

  7. Optimal trajectories for LEO-to-LEO aeroassisted orbital transfer

    Science.gov (United States)

    Miele, A.; Lee, W. Y.; Mease, K. D.

    This paper considers both classical and minimax problems of optimal control arising in the study of noncoplanar, aeroassisted orbital transfer. The maneuver considered involves the transfer from one planetary orbit to another having different orbital inclination, but the same radius. An example is the LEO-to-LEO transfer of a spacecraft with a prescribed plane change, where LEO denotes low Earth orbit. The basic idea is to employ the hybrid combination of propulsive maneuvers in space and aerodynamic maneuvers in the sensible atmosphere. Hence, this type of flight is also called synergetic space flight. With reference to the atmospheric part of the maneuver, trajectory control is achieved by modulating the lift coefficient (hence, the angle of attack) and the angle of bank. The presence of upper and lower bounds on the lift coefficient is considered. Three different transfer maneuvers are studied. Type 1 involves four impulses and four space plane changes; Type 2 involves three impulses and three space plane changes; and Type 3 involves three impulses and no space plane change. In Type 1, the initial impulse directs the spacecraft away from Earth, and then is followed by an apogee impulse propelling the spacecraft toward Earth; in Types 2 and 3, the initial impulse directs the spacecraft toward Earth. A common element of these maneuvers is that they all include an atmospheric pass, with velocity depletion coupled with plane change. Within the framework of classical optimal control, the following problems are studied: (P1) minimize the energy required for orbital transfer; (P4) maximize the time of flight during the atmospheric portion of the trajectory; (P5) minimize the time integral of the square of the path inclination. Within the framework of minimax optimal control, the following problem is studied: (Q1) minimize the peak heating rate. Numerical solutions for Problems (P1), (P4), (P5), (Q1) are obtained by means of the sequential gradient-restoration algorithm

  8. Electron transfer NO2++NO→NO2+NO+ in aromatic nitration

    Institute of Scientific and Technical Information of China (English)

    李象远; 何福城

    1997-01-01

    A simple model for computing the electron transfer rate constant of a cross-reaction has been proposed in the framework of semiclassical theory and employed to investigate the electron transfer system NO2+/NO.The encounter complex of electron transfer NO2++NO→NO2+NO+has been optimized at the level of UHF/6-31G.In the construction of diabatic potential energy surfaces the linear coordinate was used and the kinetic quantities,such as the activation energies and the electron transfer matrix elements,have been obtained.For comparison,the related self-exchange reation systems NO2+/NO2 and NO+/NO were kinetically investigated.The calculated activation energies for the electron transfer reactions of systems NO2+/NO,NO2+/NO2,and NO+/NO are 81 4,128.8,and 39.8kJ mol-1,respectively With the solvent effect taken into account,the contribution of solvent reorganization to the activation energy has been estimated according to the geometric parameters of the transition states.The obtained rate constants show that the

  9. Nanoantioxidant-driven plasmon enhanced proton-coupled electron transfer

    Science.gov (United States)

    Sotiriou, Georgios A.; Blattmann, Christoph O.; Deligiannakis, Yiannis

    2015-12-01

    Proton-coupled electron transfer (PCET) reactions involve the transfer of a proton and an electron and play an important role in a number of chemical and biological processes. Here, we describe a novel phenomenon, plasmon-enhanced PCET, which is manifested using SiO2-coated Ag nanoparticles functionalized with gallic acid (GA), a natural antioxidant molecule that can perform PCET. These GA-functionalized nanoparticles show enhanced plasmonic response at near-IR wavelengths, due to particle agglomeration caused by the GA molecules. Near-IR laser irradiation induces strong local hot-spots on the SiO2-coated Ag nanoparticles, as evidenced by surface enhanced Raman scattering (SERS). This leads to plasmon energy transfer to the grafted GA molecules that lowers the GA-OH bond dissociation enthalpy by at least 2 kcal mol-1 and therefore facilitates PCET. The nanoparticle-driven plasmon-enhancement of PCET brings together the so far unrelated research domains of nanoplasmonics and electron/proton translocation with significant impact on applications based on interfacial electron/proton transfer.Proton-coupled electron transfer (PCET) reactions involve the transfer of a proton and an electron and play an important role in a number of chemical and biological processes. Here, we describe a novel phenomenon, plasmon-enhanced PCET, which is manifested using SiO2-coated Ag nanoparticles functionalized with gallic acid (GA), a natural antioxidant molecule that can perform PCET. These GA-functionalized nanoparticles show enhanced plasmonic response at near-IR wavelengths, due to particle agglomeration caused by the GA molecules. Near-IR laser irradiation induces strong local hot-spots on the SiO2-coated Ag nanoparticles, as evidenced by surface enhanced Raman scattering (SERS). This leads to plasmon energy transfer to the grafted GA molecules that lowers the GA-OH bond dissociation enthalpy by at least 2 kcal mol-1 and therefore facilitates PCET. The nanoparticle-driven plasmon

  10. Multi-Element Electron-Transfer Optical Detector System

    Science.gov (United States)

    Jordan, Jeffrey D. (Inventor)

    2004-01-01

    A multi-element optical detector system includes an electrically resistive screen that is substantially transparent to radiation energy having a wavelength of interest. A plurality of electron transfer elements (e.g., a low work function photoactive material or a carbon nanotube (CNT)-based element) are provided with each having a first end and a second end. The first end of each element is spaced apart from the screen by an evacuated gap. When the radiation energy passes through the screen with a bias voltage applied thereto, transfer of electrons through each element is induced from the first end to the second end such that a quantity indicative of the electrons transferred through each element can be detected.

  11. Vibrationally Assisted Electron Transfer Mechanism of Olfaction: Myth or Reality?

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Chang, Po-Yao; Schulten, Klaus

    2012-01-01

    to this suggestion an olfactory receptor is activated by electron transfer assisted through odorant vibrational excitation. The hundreds to thousands of different olfactory receptors in an animal recognize odorants over a discriminant landscape with surface properties and vibrational frequencies as the two major......, thereby, recent experiments performed on Drosophila melanogaster. Our demonstration is based on known physical properties of biological electron transfer and on ab initio calculations on odorants carried out for the purpose of the present study. We identify a range of physical characteristics which...... olfactory receptors and odorants must obey for the vibrationally assisted electron transfer mechanism to function. We argue that the stated characteristics are feasible for realistic olfactory receptors, noting, though, that the receptor structure presently is still unknown, but can be studied through...

  12. Electron transfer in proteins: theory, applications and future perspectives.

    Science.gov (United States)

    Saen-Oon, Suwipa; Lucas, Maria Fatima; Guallar, Victor

    2013-10-07

    The study of electron transfer (ET) by means of computational techniques has experienced a great development in the last few decades. In particular, understanding the atomic details of its mechanism in complex biological systems is currently possible with a large range of different in silico modelling tools. We review here some theories and representative major contributions to this development. We also underline some of our group's main inputs, focusing on long range and protein-protein electron transfer, and analyse future perspectives. At the end of the article, we emphasize the importance of the basic electron transfer knowledge in the frame of medical and bioengineering applications: mitochondrial therapeutic targets, bioengineering for clean energy, and biosensors.

  13. Engine Optimization for a Solar Thermal Powered Orbit Transfer Vehicle

    Science.gov (United States)

    1998-06-01

    Recent technological advancements in solar thermal rocket propulsion and solar orbit transfer vehicles make it critical to perform additional engine performance analyses. Several system level flight demonstrations are imminent. Space flight hardware component testing is being conducted at the Air Force Research Laboratory, Edwards AFB, California. The focus of current research is engine and nozzle configurations for a solar orbit transfer vehicle. The optimal design must produce 1-10 pounds thrust, perform at high lsp and be compatible in a hybrid of spiral, perigee, and apogee (multi-burn) configurations. The nozzle material must not ablate when subjected to extreme thermal loading, yet be durable enough to withstand widely varying temperature differentials during frequent thermal cycling. This paper addresses propulsive needs in the orbit transfer arena and defines governing upper stage vehicle engine equations. These equations are modified versions of rocket engine equations used for chemical systems. The correction factors and modifications are for Solar Thermal Propulsion specific hardware.

  14. PHOTOINDUCED CHARGE TRANSFER POLYMERIZATION OF STYRENE INITIATED BY ELECTRON ACCEPTOR

    Institute of Scientific and Technical Information of China (English)

    CAO Weixiao; ZHANG Peng; FENG Xinde

    1995-01-01

    Photoinduced charge transfer polymerization of styrene(St) with electron acceptor as initiator was investigated. In case of fumaronitrile (FN) or maleic anhydride (MA) as initiator the polymerization takes place regularly, whereas the tetrachloro-1, 4-benzenequinone (TCQ), 2, 3-dichloro-5, 6-dicyano-1, 4-benzenequinone (DDQ) . or tetracyano ethylene (TCNE) as initiator the polymerization proceeds reluctantly only after the photoaddition reaction. A mechanism was proposed that free radicals would be formed following the charge and proton transfer in the exciplex formed between St and electron acceptors.

  15. Marcus Electron Transfer Reactions with Bulk Metallic Catalysis

    CERN Document Server

    Widom, A; Srivastava, Y N

    2015-01-01

    Electron transfer organic reaction rates are considered employing the classic physical picture of Marcus wherein the heats of reaction are deposited as the energy of low frequency mechanical oscillations of reconfigured molecular positions. If such electron transfer chemical reaction events occur in the neighborhood of metallic plates, then electrodynamic interface fields must also be considered in addition to mechanical oscillations. Such electrodynamic interfacial electric fields in principle strongly effect the chemical reaction rates. The thermodynamic states of the metal are unchanged by the reaction which implies that metallic plates are purely catalytic chemical agents.

  16. Promoting direct interspecies electron transfer with activated carbon

    DEFF Research Database (Denmark)

    Liu, Fanghua; Rotaru, Amelia-Elena; Shrestha, Pravin M.

    2012-01-01

    of methanogenesis might be to facilitate direct interspecies electron transfer (DIET) between bacteria and methanogens. Metabolism was substantially accelerated when GAC was added to co-cultures of Geobacter metallireducens and Geobacter sulfurreducens grown under conditions previously shown to require DIET. Cells...... were attached to GAC, but did not aggregate as they do when making biological electrical connections between cells. Studies with a series of gene deletion mutants eliminated the possibility that GAC promoted electron exchange via interspecies hydrogen or formate transfer and demonstrated that DIET...

  17. High-pressure effects on intramolecular electron transfer compounds

    CERN Document Server

    He Li Ming; Li Hong; Zhang Bao Wen; Li Yi; Yang Guo Qiang

    2002-01-01

    We explore the effect of pressure on the fluorescence spectra of the intramolecular electron transfer compound N-(1-pyrenylmethyl), N-methyl-4-methoxyaniline (Py-Am) and its model version, with poly(methyl methacrylate) blended in, at high pressure up to 7 GPa. The emission properties of Py-Am and pyrene show distinct difference with the increase of pressure. This difference indicates the strength of the charge transfer interaction resulting from the adjusting of the conformation of Py-Am with increase of pressure. The relationship between the electronic state of the molecule and pressure is discussed.

  18. Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives

    DEFF Research Database (Denmark)

    Borovok, N; Kotlyar, A B; Pecht, I;

    1999-01-01

    efficiency. TUPS derivatives of azurin, singly labeled at specific lysine residues, were prepared and purified to homogeneity by ion exchange HPLC. Transient absorption spectroscopy was used to directly monitor the rates of the electron transfer reaction from the photoexcited triplet state of TUPS to Cu...... of the crystal structure of Pseudomonas aeruginosa azurin and molecular structure calculation of the TUPS modified proteins, electron transfer pathways were calculated. Analysis of the results revealed a good correlation between separation distance from donor to Cu ligating atom (His-N or Cys-S) and the observed...

  19. Investigation of transferred-electron oscillations in diamond

    Science.gov (United States)

    Suntornwipat, N.; Majdi, S.; Gabrysch, M.; Isberg, J.

    2016-05-01

    The recent discovery of Negative Differential Mobility (NDM) in intrinsic single-crystalline diamond enables the development of devices for high frequency applications. The Transferred-Electron Oscillator (TEO) is one example of such devices that uses the benefit of NDM to generate continuous oscillations. This paper presents theoretical investigations of a diamond TEO in the temperature range of 110 to 140 K where NDM has been observed. Our simulations map out the parameter space in which transferred-electron oscillations are expected to occur for a specific device geometry. The results are promising and indicate that it is possible to fabricate diamond based TEO devices.

  20. Reactant-Product Quantum Coherence in Electron Transfer Reactions

    CERN Document Server

    Kominis, I K

    2012-01-01

    We investigate the physical meaning of quantum superposition states between reactants and products in electron transfer reactions. We show that such superpositions are strongly suppressed and to leading orders of perturbation theory do not pertain in electron transfer reactions. This is because of the intermediate manifold of states separating the reactants from the products. We provide an intuitive description of these considerations with Feynman diagrams. We also discuss the relation of such quantum coherences to understanding the fundamental quantum dynamics of spin-selective radical-ion-pair reactions.

  1. Protein electron transfer: is biology (thermo)dynamic?

    Science.gov (United States)

    Matyushov, Dmitry V.

    2015-12-01

    Simple physical mechanisms are behind the flow of energy in all forms of life. Energy comes to living systems through electrons occupying high-energy states, either from food (respiratory chains) or from light (photosynthesis). This energy is transformed into the cross-membrane proton-motive force that eventually drives all biochemistry of the cell. Life’s ability to transfer electrons over large distances with nearly zero loss of free energy is puzzling and has not been accomplished in synthetic systems. The focus of this review is on how this energetic efficiency is realized. General physical mechanisms and interactions that allow proteins to fold into compact water-soluble structures are also responsible for a rugged landscape of energy states and a broad distribution of relaxation times. Specific to a protein as a fluctuating thermal bath is the protein-water interface, which is heterogeneous both dynamically and structurally. The spectrum of interfacial fluctuations is a consequence of protein’s elastic flexibility combined with a high density of surface charges polarizing water dipoles into surface nanodomains. Electrostatics is critical to the protein function and the relevant questions are: (i) What is the spectrum of interfacial electrostatic fluctuations? (ii) Does the interfacial biological water produce electrostatic signatures specific to proteins? (iii) How is protein-mediated chemistry affected by electrostatics? These questions connect the fluctuation spectrum to the dynamical control of chemical reactivity, i.e. the dependence of the activation free energy of the reaction on the dynamics of the bath. Ergodicity is often broken in protein-driven reactions and thermodynamic free energies become irrelevant. Continuous ergodicity breaking in a dense spectrum of relaxation times requires using dynamically restricted ensembles to calculate statistical averages. When applied to the calculation of the rates, this formalism leads to the nonergodic

  2. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    Science.gov (United States)

    2010-01-01

    ... 12 Banks and Banking 2 2010-01-01 2010-01-01 false Electronic fund transfer of government benefits... RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of government... consumer for use in initiating an electronic fund transfer of government benefits from an account,...

  3. Multiswarm Particle Swarm Optimization with Transfer of the Best Particle

    Directory of Open Access Journals (Sweden)

    Xiao-peng Wei

    2015-01-01

    Full Text Available We propose an improved algorithm, for a multiswarm particle swarm optimization with transfer of the best particle called BMPSO. In the proposed algorithm, we introduce parasitism into the standard particle swarm algorithm (PSO in order to balance exploration and exploitation, as well as enhancing the capacity for global search to solve nonlinear optimization problems. First, the best particle guides other particles to prevent them from being trapped by local optima. We provide a detailed description of BMPSO. We also present a diversity analysis of the proposed BMPSO, which is explained based on the Sphere function. Finally, we tested the performance of the proposed algorithm with six standard test functions and an engineering problem. Compared with some other algorithms, the results showed that the proposed BMPSO performed better when applied to the test functions and the engineering problem. Furthermore, the proposed BMPSO can be applied to other nonlinear optimization problems.

  4. Conduction mechanism studies on electron transfer of disordered system

    Institute of Scientific and Technical Information of China (English)

    徐慧; 宋祎璞; 李新梅

    2002-01-01

    Using the negative eigenvalue theory and the infinite order perturbation theory, a new method was developed to solve the eigenvectors of disordered systems. The result shows that eigenvectors change from the extended state to the localized state with the increase of the site points and the disordered degree of the system. When electric field is exerted, the electrons transfer from one localized state to another one. The conductivity is induced by the electron transfer. The authors derive the formula of electron conductivity and find the electron hops between localized states whose energies are close to each other, whereas localized positions differ from each other greatly. At low temperature the disordered system has the character of the negative differential dependence of resistivity and temperature.

  5. Charge transfer to ground-state ions produces free electrons

    Science.gov (United States)

    You, D.; Fukuzawa, H.; Sakakibara, Y.; Takanashi, T.; Ito, Y.; Maliyar, G. G.; Motomura, K.; Nagaya, K.; Nishiyama, T.; Asa, K.; Sato, Y.; Saito, N.; Oura, M.; Schöffler, M.; Kastirke, G.; Hergenhahn, U.; Stumpf, V.; Gokhberg, K.; Kuleff, A. I.; Cederbaum, L. S.; Ueda, K.

    2017-01-01

    Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne-Kr mixed clusters.

  6. Charge transfer to ground-state ions produces free electrons

    Science.gov (United States)

    You, D.; Fukuzawa, H.; Sakakibara, Y.; Takanashi, T.; Ito, Y.; Maliyar, G. G.; Motomura, K.; Nagaya, K.; Nishiyama, T.; Asa, K.; Sato, Y.; Saito, N.; Oura, M.; Schöffler, M.; Kastirke, G.; Hergenhahn, U.; Stumpf, V.; Gokhberg, K.; Kuleff, A. I.; Cederbaum, L. S.; Ueda, K

    2017-01-01

    Inner-shell ionization of an isolated atom typically leads to Auger decay. In an environment, for example, a liquid or a van der Waals bonded system, this process will be modified, and becomes part of a complex cascade of relaxation steps. Understanding these steps is important, as they determine the production of slow electrons and singly charged radicals, the most abundant products in radiation chemistry. In this communication, we present experimental evidence for a so-far unobserved, but potentially very important step in such relaxation cascades: Multiply charged ionic states after Auger decay may partially be neutralized by electron transfer, simultaneously evoking the creation of a low-energy free electron (electron transfer-mediated decay). This process is effective even after Auger decay into the dicationic ground state. In our experiment, we observe the decay of Ne2+ produced after Ne 1s photoionization in Ne–Kr mixed clusters. PMID:28134238

  7. Photoinduced Reductive Electron Transfer in LNA:DNA Hybrids

    DEFF Research Database (Denmark)

    Wenge, Ulrike; Wengel, Jesper; Wagenknecht, Hans-Achim

    2012-01-01

    Lock it, but not too much: LNA units (locked or bridging nucleic acids) in LNA:DNA hybrids lead to a negative effect on electron transfer (ET), but they also force the nucleic acid structure in the A-type double helix, which allows a better base stacking than the normal B-type and thus positively...... influences the ET. This result is significant for the design of nucleic acids of molecular electronics....

  8. Nanoscale and single-molecule interfacial electron transfer

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Wackerbarth, Hainer; Nielsen, Jens Ulrik

    2003-01-01

    Electrochemical science and technology in the 21st century have reached high levels of sophistication. A fundamental quantum mechanical theoretical frame for interfacial electrochemical electron transfer (ET) was introduced by Revaz Dogonadze. This frame has remained for four decades as a basis...... scanning tunneling microscopy (STM) and single-electron tunneling (SET, or Coulomb blockade) in electrochemical. systems directly in aqueous electrolyte solution and at room temperature. We illustrate the new theoretical formalism and its perspectives by recent cases of electrochemical SET, negative...

  9. Quantum Mechanical Hysteresis and the Electron Transfer Problem

    CERN Document Server

    Etchegoin, P G

    2004-01-01

    We study a simple quantum mechanical symmetric donor-acceptor model for electron transfer (ET) with coupling to internal deformations. The model contains several basic properties found in biological ET in enzymes and photosynthetic centers; it produces tunnelling with hysteresis thus providing a simple explanation for the slowness of the reversed rate and the near 100% efficiency of ET in many biological systems. The model also provides a conceptual framework for the development of molecular electronics memory elements based on electrostatic architectures.

  10. Electronic Coupling Dependence of Ultrafast Interfacial Electron Transfer on Nanocrystalline Thin Films and Single Crystal

    Energy Technology Data Exchange (ETDEWEB)

    Lian, Tianquan

    2014-04-22

    The long-term goal of the proposed research is to understand electron transfer dynamics in nanoparticle/liquid interface. This knowledge is essential to many semiconductor nanoparticle based devices, including photocatalytic waste degradation and dye sensitized solar cells.

  11. Photochemistry between a ruthenium(II) pyridylimidazole complex and benzoquinone: simple electron transfer versus proton-coupled electron transfer.

    Science.gov (United States)

    Hönes, Roland; Kuss-Petermann, Martin; Wenger, Oliver S

    2013-02-01

    A ruthenium(II) complex with two 4,4'-bis(trifluoromethyl)-2,2'-bipyridine chelates and a 2-(2'-pyridyl)imidazole ligand was synthesized and characterized by electrochemical and optical spectroscopic means. The respective complex has the potential to act as a combined electron-proton donor when promoted to its long-lived (3)MLCT excited state with visible light. The possibility of proton-coupled electron transfer (PCET) between the ruthenium(II) complex and 1,4-benzoquinone as an electron/proton acceptor was explored by steady-state and time-resolved luminescence spectroscopy, as well as by transient absorption spectroscopy in the nanosecond time regime. Excited-state deactivation is found to occur predominantly via simple oxidative quenching involving no proton motion, but a minor fraction of the photoexcited complex appears to react via PCET since there is spectral evidence for semiquinone as a photoproduct. Presumably, PCET is not kinetically competitive with simple electron transfer because the latter process is sufficiently exergonic and because there is little thermodynamic benefit from coupling proton transfer to the photoinduced electron transfer.

  12. Electron transfer in pH-sensitive nitroxide radicals

    Science.gov (United States)

    Barbon, Antonio; Bortolus, Marco; Isse, Abdirisak A.; Reznikov, Vladimir A.; Weiner, Lev

    2016-11-01

    Two pH-sensitive stable nitroxide radicals are characterized by EPR spectroscopy and cyclic voltammetry in aqueous solution at different pH values. The rates of the photochemically-induced electron transfer reactions from the protonated and deprotonated forms of the radicals to a ruthenium complex are determined.

  13. Correlating electronic and vibrational motions in charge transfer systems

    Energy Technology Data Exchange (ETDEWEB)

    Khalil, Munira [Univ. of Washington, Seattle, WA (United States)

    2014-06-27

    The goal of this research program was to measure coupled electronic and nuclear motions during photoinduced charge transfer processes in transition metal complexes by developing and using novel femtosecond spectroscopies. The scientific highlights and the resulting scientific publications from the DOE supported work are outlined in the technical report.

  14. A molecularly based theory for electron transfer reorganization energy

    Energy Technology Data Exchange (ETDEWEB)

    Zhuang, Bilin; Wang, Zhen-Gang, E-mail: zgw@cheme.caltech.edu [Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (United States)

    2015-12-14

    Using field-theoretic techniques, we develop a molecularly based dipolar self-consistent-field theory (DSCFT) for charge solvation in pure solvents under equilibrium and nonequilibrium conditions and apply it to the reorganization energy of electron transfer reactions. The DSCFT uses a set of molecular parameters, such as the solvent molecule’s permanent dipole moment and polarizability, thus avoiding approximations that are inherent in treating the solvent as a linear dielectric medium. A simple, analytical expression for the free energy is obtained in terms of the equilibrium and nonequilibrium electrostatic potential profiles and electric susceptibilities, which are obtained by solving a set of self-consistent equations. With no adjustable parameters, the DSCFT predicts activation energies and reorganization energies in good agreement with previous experiments and calculations for the electron transfer between metallic ions. Because the DSCFT is able to describe the properties of the solvent in the immediate vicinity of the charges, it is unnecessary to distinguish between the inner-sphere and outer-sphere solvent molecules in the calculation of the reorganization energy as in previous work. Furthermore, examining the nonequilibrium free energy surfaces of electron transfer, we find that the nonequilibrium free energy is well approximated by a double parabola for self-exchange reactions, but the curvature of the nonequilibrium free energy surface depends on the charges of the electron-transferring species, contrary to the prediction by the linear dielectric theory.

  15. Polymer glass transitions switch electron transfer in individual molecules

    NARCIS (Netherlands)

    Siekierzycka, J.R.; Hippius, C.; Würthner, F.; Williams, R.M.; Brouwer, A.M.

    2010-01-01

    Essentially complete photoinduced electron transfer quenching of the fluorescence of a perylene−calixarene compound occurs in poly(methyl acrylate) and poly(vinyl acetate) above their glass transition temperatures (T-g), but the fluorescence is completely recovered upon cooling the polymer matrix to

  16. Electron transfer flavoprotein deficiency: Functional and molecular aspects

    DEFF Research Database (Denmark)

    Schiff, M; Froissart, R; Olsen, Rikke Katrine Jentoft

    2006-01-01

    Multiple acyl-CoA dehydrogenase deficiency (MADD) is a recessively inherited metabolic disorder that can be due to a deficiency of electron transfer flavoprotein (ETF) or its dehydrogenase (ETF-ubiquinone oxidoreductase). ETF is a mitochondrial matrix protein consisting of alpha- (30kDa) and beta...

  17. Direct interspecies electron transfer between Geobacter metallireducens and Methanosarcina barkeri

    DEFF Research Database (Denmark)

    Rotaru, Amelia-Elena; Shrestha, Pravin Malla; Liu, Fanghua;

    2014-01-01

    Direct interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability of Methanosarcina barkeri, to participate in DIET was evaluated in co-culture with Geobacter...

  18. Adsorption and Interfacial Electron Transfer of Saccharomyces Cerevisiae

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Boisen, Anja; Nielsen, Jens Ulrik

    2003-01-01

    We have studied the adsorption and electron-transfer dynamics of Saccharomyces cerevisiae (yeast) iso-l-cytochrome c adsorbed on Au(lll) electrodes in aqueous phosphate buffer media. This cytochrome possesses a thiol group dos e to the protein surface (Cysl02) suitable for linking the protein...

  19. Nanoantioxidant-driven plasmon enhanced proton-coupled electron transfer.

    Science.gov (United States)

    Sotiriou, Georgios A; Blattmann, Christoph O; Deligiannakis, Yiannis

    2016-01-14

    Proton-coupled electron transfer (PCET) reactions involve the transfer of a proton and an electron and play an important role in a number of chemical and biological processes. Here, we describe a novel phenomenon, plasmon-enhanced PCET, which is manifested using SiO2-coated Ag nanoparticles functionalized with gallic acid (GA), a natural antioxidant molecule that can perform PCET. These GA-functionalized nanoparticles show enhanced plasmonic response at near-IR wavelengths, due to particle agglomeration caused by the GA molecules. Near-IR laser irradiation induces strong local hot-spots on the SiO2-coated Ag nanoparticles, as evidenced by surface enhanced Raman scattering (SERS). This leads to plasmon energy transfer to the grafted GA molecules that lowers the GA-OH bond dissociation enthalpy by at least 2 kcal mol(-1) and therefore facilitates PCET. The nanoparticle-driven plasmon-enhancement of PCET brings together the so far unrelated research domains of nanoplasmonics and electron/proton translocation with significant impact on applications based on interfacial electron/proton transfer.

  20. Solvent-Controlled Acceleration of Electron Transfer in Binary Mixtures

    NARCIS (Netherlands)

    Pugžlys, Audrius; Hartog, Harald P. den; Baltuška, Andrius; Pshenichnikov, Maxim S.; Umapathy, Siva; Wiersma, Douwe A.

    2001-01-01

    We report a 5-fold acceleration of the backward intermolecular electron transfer between a rhodamine 800 dye molecule and N,N-dimethylaniline (DMA). This effect results from the controlled variation of the solvent dynamical properties in binary mixtures of DMA and acetonitrile. The observed

  1. Dimers of Azurin as model systems for electron transfer

    NARCIS (Netherlands)

    Jongh, Thyra Estrid de

    2006-01-01

    This thesis describes the investigation of crosslinked complexes of the blue copper protein azurin by means of spectroscopic techniques such as Uv-Vis and NMR as well as by X-ray crystallography. These non-physiological dimers serve as model systems for interprotein electron transfer (ET) and allow

  2. Electron transfer in syntrophic communities of anaerobic bacteria and archaea

    NARCIS (Netherlands)

    Stams, A.J.M.; Plugge, C.M.

    2009-01-01

    Interspecies electron transfer is a key process in methanogenic and sulphate-reducing environments. Bacteria and archaea that live in syntrophic communities take advantage of the metabolic abilities of their syntrophic partner to overcome energy barriers and break down compounds that they cannot dig

  3. The intramolecular electron transfer between copper sites of nitrite reductase

    DEFF Research Database (Denmark)

    Farver, O; Eady, R R; Abraham, Z H

    1998-01-01

    The intramolecular electron transfer (ET) between the type 1 Cu(I) and the type 2 Cu(II) sites of Alcaligenes xylosoxidans dissimilatory nitrite reductase (AxNiR) has been studied in order to compare it with the analogous process taking place in ascorbate oxidase (AO). This internal process...

  4. Fundamental Research on Convective Heat Transfer in Electronic Cooling Technology

    Institute of Scientific and Technical Information of China (English)

    C.F.Ma; Y.P.Gan; 等

    1992-01-01

    During the past six years comprehensive research programs have been conducted at the Beijing Polytechnic University to provide a better understanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microelestanding of heat transfer characteristics of existing and condidate cooling techniques for electronic and microleectronic devices.This paper provides a review and summary of the programs with emphasis on direct liquid cooling.Included in this review are the heat transfer investigations related to the following cooling modes:liquid free,mixed and forced convection.liquid jet impingement,flowing liquid film cooling,pool boiling,spray cooling,foreign gas jet impingement in liquid pool,and forced convection air-cooling.

  5. Photoinduced electron transfer of chlorophyll in lipid bilayer system

    Indian Academy of Sciences (India)

    D K Lee; K W Seo; Y S Kang

    2002-12-01

    Photoinduced electron transfer from chlorophyll- through the interface of dipalmitoylphosphatidylcholine (DPPC) headgroup of the lipid bilayers was studied with electron magnetic resonance (EMR). The photoproduced radicals were identified with electron spin resonance (ESR) and radical yields of chlorophyll- were determined by double integration ESR spectra. The formation of vesicles was identified by changes in measured max values from diethyl ether solutions to vesicles solutions indirectly, and observed directly with SEM and TEM images. The efficiency of photosynthesis in model system was determined by measuring the amount of chlorophyll-a radical yields which were obtained from integration of ESR spectra.

  6. Ion and electron velocity distributions within flux transfer events

    Science.gov (United States)

    Thomsen, M. F.; Stansberry, J. A.; Bame, S. J.; Fuselier, S. A.; Gosling, J. T.

    1987-01-01

    The detailed nature of the thermal and suprathermal ion and electron distributions within magnetic flux transfer events (FTEs) is examined. Examples of both magnetosheath FTEs and magnetospheric FTEs are discussed. The detailed distributions confirm that FTEs contain a mixture of magnetosheath and magnetospheric plasmas. To lowest order, the distributions are consistent with a simple superposition of the two interpenetrating populations, with no strong interactions between them. To first order, some interesting differences appear, especially in the electron distributions, suggesting that considerable pitch angle scattering and some electron energy diffusion are also occurring. These observations should provide a useful test of analytical and numerical studies of interpenetrating plasmas.

  7. Electron transfer in donor-acceptor systems: Many-particle effects and influence of electronic correlations

    Science.gov (United States)

    Tornow, S.; Tong, N.-H.; Bulla, R.

    2006-03-01

    We investigate electron transfer processes in donor-acceptor systems with a coupling of the electronic degrees of freedom to a common bosonic bath. The model allows to study many-particle effects and the influence of the local Coulomb interaction U between electrons on donor and acceptor sites. Using the non-perturbative numerical renormalization group approach we find distinct differences between the electron transfer characteristics in the single- and two-particle subspaces. We calculate the critical electron-boson coupling αc as a function of U and show results for density-density correlation functions in the whole parameter space. The possibility of many-particle (bipolaronic) and Coulomb-assisted transfer is discussed.

  8. Activation of Electron-Deficient Quinones through Hydrogen-Bond-Donor-Coupled Electron Transfer.

    Science.gov (United States)

    Turek, Amanda K; Hardee, David J; Ullman, Andrew M; Nocera, Daniel G; Jacobsen, Eric N

    2016-01-11

    Quinones are important organic oxidants in a variety of synthetic and biological contexts, and they are susceptible to activation towards electron transfer through hydrogen bonding. Whereas this effect of hydrogen bond donors (HBDs) has been observed for Lewis basic, weakly oxidizing quinones, comparable activation is not readily achieved when more reactive and synthetically useful electron-deficient quinones are used. We have successfully employed HBD-coupled electron transfer as a strategy to activate electron-deficient quinones. A systematic investigation of HBDs has led to the discovery that certain dicationic HBDs have an exceptionally large effect on the rate and thermodynamics of electron transfer. We further demonstrate that these HBDs can be used as catalysts in a quinone-mediated model synthetic transformation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Ultrafast proton coupled electron transfer (PCET dynamics in 9-anthranol-aliphatic amine system

    Directory of Open Access Journals (Sweden)

    Nibbering Erik T. J.

    2013-03-01

    Full Text Available Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part in an ultrafast electron transfer (ET reaction in electron-donating triethylamine solvent, but that ultrafast proton coupled electron transfer (PCET occurs in diethylamine solvent.

  10. Protein dynamics modulated electron transfer kinetics in early stage photosynthesis.

    Science.gov (United States)

    Kundu, Prasanta; Dua, Arti

    2013-01-28

    A recent experiment has probed the electron transfer kinetics in the early stage of photosynthesis in Rhodobacter sphaeroides for the reaction center of wild type and different mutants [Science 316, 747 (2007)]. By monitoring the changes in the transient absorption of the donor-acceptor pair at 280 and 930 nm, both of which show non-exponential temporal decay, the experiment has provided a strong evidence that the initial electron transfer kinetics is modulated by the dynamics of protein backbone. In this work, we present a model where the electron transfer kinetics of the donor-acceptor pair is described along the reaction coordinate associated with the distance fluctuations in a protein backbone. The stochastic evolution of the reaction coordinate is described in terms of a non-Markovian generalized Langevin equation with a memory kernel and Gaussian colored noise, both of which are completely described in terms of the microscopics of the protein normal modes. This model provides excellent fits to the transient absorption signals at 280 and 930 nm associated with protein distance fluctuations and protein dynamics modulated electron transfer reaction, respectively. In contrast to previous models, the present work explains the microscopic origins of the non-exponential decay of the transient absorption curve at 280 nm in terms of multiple time scales of relaxation of the protein normal modes. Dynamic disorder in the reaction pathway due to protein conformational fluctuations which occur on time scales slower than or comparable to the electron transfer kinetics explains the microscopic origin of the non-exponential nature of the transient absorption decay at 930 nm. The theoretical estimates for the relative driving force for five different mutants are in close agreement with the experimental estimates obtained using electrochemical measurements.

  11. A unified diabatic description for electron transfer reactions, isomerization reactions, proton transfer reactions, and aromaticity.

    Science.gov (United States)

    Reimers, Jeffrey R; McKemmish, Laura K; McKenzie, Ross H; Hush, Noel S

    2015-10-14

    While diabatic approaches are ubiquitous for the understanding of electron-transfer reactions and have been mooted as being of general relevance, alternate applications have not been able to unify the same wide range of observed spectroscopic and kinetic properties. The cause of this is identified as the fundamentally different orbital configurations involved: charge-transfer phenomena involve typically either 1 or 3 electrons in two orbitals whereas most reactions are typically closed shell. As a result, two vibrationally coupled electronic states depict charge-transfer scenarios whereas three coupled states arise for closed-shell reactions of non-degenerate molecules and seven states for the reactions implicated in the aromaticity of benzene. Previous diabatic treatments of closed-shell processes have considered only two arbitrarily chosen states as being critical, mapping these states to those for electron transfer. We show that such effective two-state diabatic models are feasible but involve renormalized electronic coupling and vibrational coupling parameters, with this renormalization being property dependent. With this caveat, diabatic models are shown to provide excellent descriptions of the spectroscopy and kinetics of the ammonia inversion reaction, proton transfer in N2H7(+), and aromaticity in benzene. This allows for the development of a single simple theory that can semi-quantitatively describe all of these chemical phenomena, as well as of course electron-transfer reactions. It forms a basis for understanding many technologically relevant aspects of chemical reactions, condensed-matter physics, chemical quantum entanglement, nanotechnology, and natural or artificial solar energy capture and conversion.

  12. Electromicrobiology: Electron Transfer via Biowires in Nature and Practical Applications

    Directory of Open Access Journals (Sweden)

    Lovley Derek

    2016-01-01

    Full Text Available One of the most exciting developments in the field of electromicrobiology has been the discovery of electrically conductive pili (e-pili in Geobacter species that transport electrons with a metallic-like mechanism. The e-pili are essential for extracellular electron transport to Fe(III oxides and longrange electron transport through the conductive biofilms that form on the anodes of microbial fuel cells. The e-pili also facilitate direct interspecies electron transfer between Geobacter and Methanosaeta or Methanosarcina species. Metatranscriptomic studies have demonstrated that Geobacter/Methanosaeta DIET is an important process in anaerobic digesters converting brewery wastes to methane. Increasing e-pili expression through genetic modification of regulatory systems or adaptive evolution yields strains with enhanced rates of extracellular electron transfer. Measurement of the conductivity of individual e-pili has demonstrated that they have conductivities higher than those of a number of synthetic conducting organic polymers. Multiple lines of evidence have demonstrated that aromatic amino acids play an important role in the electron transport along e-pili, suggesting opportunities to tune e-pili conductivity via genetic manipulation of the amino acid composition of e-pili. It is expected that e-pili will be harnessed to improve microbe-electrode processes such as microbial electrosynthesis and for the development of novel biosensors. Also, e-pili show promise as a sustainable ‘green’ replacement for electronic materials that contain toxic components and/or are produced with harsh chemicals.

  13. Transfer Printed Crystalline Nanomembrane for Versatile Electronic Applications

    Science.gov (United States)

    Seo, Jung-Hun

    Flexible electronics have traditionally been addressed low-frequency applications, since the materials for the traditional flexible electronics, such as polymer and non-crystalline inorganic semiconductors, have poor electronic properties. Fast flexible electronics that operate at radio frequencies (RF), particularly at microwave frequencies, could lead to a number of novel RF applications where rigid chip-based solid-state electronics cannot easily fulfill. Single-crystal semiconductor nanomembranes (NM) that can be released from a number of wafer sources are mechanically very flexible yet exhibit outstanding electronic properties that are equivalent to their bulky counterparts. These thin flexible single-crystal materials can furthermore be placed, via transfer printing techniques, to nearly any substrate, including flexible polymers, thus creating the opportunity to realize RF flexible electronics. In this thesis, various RF transistors made of semiconductor NMs on plastic substrates will be discussed. In addition, as a photonic application, the demonstration of large-area Si NM surface normal ultra-compact photonic crystal reflectors fabricated using the laser interference lithography technique (LIL) will be discussed. Particularly, the mechanism of LIL and NM transfer without using an adhesive layer will be introduced and their optical performance will be addressed. Lastly, the realization of selective substitutional boron doping, using heavily doped Si NM as a doping source, will be discussed. A detailed mechanism using computational modeling and experimental analyses will be provided. The fabrication of high voltage diamond p-i diodes and their performance will be discussed.

  14. Profiling optimization for big data transfer over dedicated channels

    Energy Technology Data Exchange (ETDEWEB)

    Yun, D. [New Jersey Institute of Technology; Wu, Qishi [University of Memphis; Rao, Nageswara S [ORNL; Kettimuthu, R. [Argonne National Laboratory (ANL); Jung, E. S. [Argonne National Laboratory (ANL)

    2016-01-01

    The transfer of big data is increasingly supported by dedicated channels in high-performance networks, where transport protocols play an important role in maximizing applicationlevel throughput and link utilization. The performance of transport protocols largely depend on their control parameter settings, but it is prohibitively time consuming to conduct an exhaustive search in a large parameter space to find the best set of parameter values. We propose FastProf, a stochastic approximation-based transport profiler, to quickly determine the optimal operational zone of a given data transfer protocol/method over dedicated channels. We implement and test the proposed method using both emulations based on real-life performance measurements and experiments over physical connections with short (2 ms) and long (380 ms) delays. Both the emulation and experimental results show that FastProf significantly reduces the profiling overhead while achieving a comparable level of end-to-end throughput performance with the exhaustive search-based approach.

  15. Optimization of a transferred arc reactor for metal nanoparticle synthesis

    Science.gov (United States)

    Stein, Matthias; Kruis, Frank Einar

    2016-09-01

    The demand for metal nanoparticles is increasing strongly. Transferred arc synthesis is a promising process in this respect, as it shows high production rates, good quality particles and the ability of up-scaling. The influence of several process parameters on the performance of the process in terms of production rate and particle size is investigated. These parameters are the electrode design and adjustment, the gas flow rate and power input. A novel feeding mechanism allows process operation over an extended time period. It is shown that the process is capable of producing pure metal nanoparticles with variable primary particle sizes and comparatively high production rates. Optimal process conditions for a single transferred arc electrode pair are found, which allow further scale-up by numbering up.

  16. Syntrophic Growth via Quinone-Mediated Interspecies Electron Transfer

    Directory of Open Access Journals (Sweden)

    Jessica A Smith

    2015-02-01

    Full Text Available The mechanisms by which microbial species exchange electrons are of interest because interspecies electron transfer can expand the metabolic capabilities of microbial communities. Previous studies with the humic substance analog anthraquinone-2,6-disulfonate (AQDS suggested that quinone-mediated interspecies electron transfer (QUIET is feasible, but it was not determined if sufficient energy is available from QUIET to support the growth of both species. Furthermore, there have been no previous studies on the mechanisms for the oxidation of anthrahydroquinone-2,6-disulfonate (AHQDS. A co-culture of Geobacter metallireducens and Geobacter sulfurreducens metabolized ethanol with the reduction of fumarate much faster in the presence of AQDS, and there was an increase in cell protein. G. sulfurreducens was more abundant, consistent with G. sulfurreducens obtaining electrons from acetate that G. metallireducens produced from ethanol, as well as from AHQDS. Cocultures initiated with a citrate synthase-deficient strain of G. sulfurreducens that was unable to use acetate as an electron donor also metabolized ethanol with the reduction of fumarate and cell growth, but acetate accumulated over time. G. sulfurreducens and G. metallireducens were equally abundant in these co-cultures reflecting the inability of the citrate synthase-deficient strain of G. sulfurreducens to metabolize acetate. Evaluation of the mechanisms by which G. sulfurreducens accepts electrons from AHQDS demonstrated that a strain deficient in outer-surface c-type cytochromes that are required for AQDS reduction was as effective at QUIET as the wild-type strain. Deletion of additional genes previously implicated in extracellular electron transfer also had no impact on QUIET. These results demonstrate that QUIET can yield sufficient energy to support the growth of both syntrophic partners, but that the mechanisms by which electrons are derived from extracellular hydroquinones require

  17. Optimizing energy transfer efficiency in highly branched nanoplasmonic waveguides

    Science.gov (United States)

    Voronine, Dmitri; Traverso, Andrew; Wang, Kai; Yi, Zhenhuan; Sokolov, Alexei

    2011-03-01

    Energy transfer in highly branched nanoplasmonic particle waveguides is simulated and optimized by varying the waveguide branching geometry and composition. The periodically branched nanostructures provide a new route towards efficient nanoscale light concentration and local field enhancement. On the one hand, they mimick the analogous randomly branched plasmonic nanostructures which have been previously used for surface-enhanced optical spectroscopy such as SERS. On the other hand, the design is inspired by branched molecular aggregates used for energy funneling. The proposed nanostructures may find applications in sensing, light harvesting and nanophotonics.

  18. Electron transfer by excited benzoquinone anions: slow rates for two-electron transitions.

    Science.gov (United States)

    Zamadar, Matibur; Cook, Andrew R; Lewandowska-Andralojc, Anna; Holroyd, Richard; Jiang, Yan; Bikalis, Jin; Miller, John R

    2013-09-05

    Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ΔG°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -ΔG° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-ΔG°) can restore fast rates of electron transfer.

  19. Electronic Commerce Logistics Network Optimization Based on Swarm Intelligent Algorithm

    Directory of Open Access Journals (Sweden)

    Yabing Jiao

    2013-09-01

    Full Text Available This article establish an efficient electronic commerce logistics operation system to reduce distribution costs and build a logistics network operation model based on around the B2C electronic commerce enterprise logistics network operation system. B2C electronic commerce transactions features in the enterprise network platform. To solve the NP-hard problem this article use hybrid ant colony algorithm, particle swarm algorithm and group swarm intelligence algorithm to get a best solution. According to the intelligent algorithm, design of electronic commerce logistics network optimization system, enter the national 22 electronic commerce logistics network for validation. Through the experiment to verify the optimized logistics cost greatly decreased. This research can help B2C electronic commerce enterprise logistics network to optimize decision-making under the premise of ensuring the interests of consumers and service levels also can be an effective way for enterprises to improve the efficiency of logistics services and reduce operation costs

  20. Optimized Negative-Staining Electron Microscopy for Lipoprotein Studies

    Science.gov (United States)

    Zhang, Lei; Tong, Huimin; Garewal, Mark; Ren, Gang

    2012-01-01

    Background Negative-staining (NS), a rapid, simple and conventional technique of electron microscopy (EM), has been commonly used to initially study the morphology and structure of proteins for half a century. Certain NS protocols however can cause artifacts, especially for structurally flexible or lipid-related proteins, such as lipoproteins. Lipoproteins were often observed in the form of rouleau as lipoprotein particles appeared to be stacked together by conventional NS protocols. The flexible components of lipoproteins, i.e. lipids and amphipathic apolipoproteins, resulted in the lipoprotein structure being sensitive to the NS sample preparation parameters, such as operational procedures, salt concentrations, and the staining reagents. Scope of review The most popular NS protocols that have been used to examine lipoprotein morphology and structure were reviewed. Major conclusions The comparisons show that an optimized NS (OpNS) protocol can eliminate the rouleau artifacts of lipoproteins, and that the lipoproteins are similar in size and shape as statistically measured from two EM methods, OpNS and cryo-electron microscopy (cryo-EM). OpNS is a high-throughput, high-contrast and high-resolution (near 1 nm, but rarely better than 1 nm) method which has been used to discover the mechanics of a small protein, 53 kDa cholesterol ester transfer protein (CETP), and the structure of an individual particle of a single protein by individual-particle electron tomography (IPET), i.e. a 14 Å-resolution IgG antibody three-dimensional map. General significance It is suggested that OpNS can be used as a general protocol to study the structure of proteins, especially highly dynamic proteins with equilibrium-fluctuating structures. PMID:23032862

  1. Electron Transfer and Solvent-Mediated Electronic Localization in Molecular Photocatalysis

    DEFF Research Database (Denmark)

    Dohn, Asmus Ougaard; Kjær, Kasper Skov; Harlang, Tobias B.

    2016-01-01

    This work provides a detailed mechanism for electron transfer in a heterodinuclear complex designed as a model system in which to study homogeneous molecular photocatalysis. With efficient Born–Oppenheimer molecular dynamics simulations, we show how intermediate, charge-separated states can mediate...... the electron transfer. We observe how Jahn–Teller distortion effects play out in solution, when the molecule has energetically close-lying states, and how this distortion is averaged out in the thermal sampling. Finally, we demonstrate how the solvent helps stabilize and localize the separated charge....... The information on the electronic configuration and separate states is of key importance for designing next-generation photocatalysts....

  2. Hardwiring microbes via direct interspecies electron transfer: mechanisms and applications.

    Science.gov (United States)

    Cheng, Qiwen; Call, Douglas F

    2016-08-10

    Multicellular microbial communities are important catalysts in engineered systems designed to treat wastewater, remediate contaminated sediments, and produce energy from biomass. Understanding the interspecies interactions within them is therefore essential to design effective processes. The flow of electrons within these communities is especially important in the determination of reaction possibilities (thermodynamics) and rates (kinetics). Conventional models of electron transfer incorporate the diffusion of metabolites generated by one organism and consumed by a second, frequently referred to as mediated interspecies electron transfer (MIET). Evidence has emerged in the last decade that another method, called direct interspecies electron transfer (DIET), may occur between organisms or in conjunction with electrically conductive materials. Recent research has suggested that DIET can be stimulated in engineered systems to improve desired treatment goals and energy recovery in systems such as anaerobic digesters and microbial electrochemical technologies. In this review, we summarize the latest understanding of DIET mechanisms, the associated microorganisms, and the underlying thermodynamics. We also critically examine approaches to stimulate DIET in engineered systems and assess their effectiveness. We find that in most cases attempts to promote DIET in mixed culture systems do not yield the improvements expected based on defined culture studies. Uncertainties of other processes that may be co-occurring in real systems, such as contaminant sorption and biofilm promotion, need to be further investigated. We conclude by identifying areas of future research related to DIET and its application in biological treatment processes.

  3. Alternating electron and proton transfer steps in photosynthetic water oxidation.

    Science.gov (United States)

    Klauss, André; Haumann, Michael; Dau, Holger

    2012-10-02

    Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel-production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese-calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S(2) → S(3) transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (Y Z OX). The rate-determining elementary step (τ, approximately 30 µs at 20 °C) in the long-distance proton relocation toward the protein-water interface is characterized by a high activation energy (E(a) = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S(0) → S(1) transition are similar (τ, approximately 100 µs; E(a) = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established.

  4. Optimal control for perfect state transfer in linear quantum memory

    Science.gov (United States)

    Nakao, Hideaki; Yamamoto, Naoki

    2017-03-01

    A quantum memory is a system that enables transfer, storage, and retrieval of optical quantum states by ON/OFF switching of the control signal in each stage of the memory. In particular, it is known that, for perfect transfer of a single-photon state, appropriate shaping of the input pulse is required. However, in general, such a desirable pulse shape has a complicated form, which would be hard to generate in practice. In this paper, for a wide class of linear quantum memory systems, we develop a method that reduces the complexity of the input pulse shape of a single photon while maintaining the perfect state transfer. The key idea is twofold; (i) the control signal is allowed to vary continuously in time to introduce an additional degree of freedom, and then (ii) an optimal control problem is formulated to design a simple-formed input pulse and the corresponding control signal. Numerical simulations are conducted for Λ-type atomic media and networked atomic ensembles, to show the effectiveness of the proposed method.

  5. Electron-Nuclear Spin Transfer in Triple Quantum Dot Networks

    Science.gov (United States)

    Prada, Marta; Toonen, Ryan; Harrison, Paul

    2005-03-01

    We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of delta- and y-junction networks and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalised to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in presence of nuclear spin relaxation. We find that the gradual depolarisation of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.

  6. Electron nuclear spin transfer in quantum-dot networks

    Science.gov (United States)

    Prada, M.; Toonen, R. C.; Blick, R. H.; Harrison, P.

    2005-05-01

    We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of different geometries of a two-dimensional network of quantum dots and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalized to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in the presence of nuclear spin relaxation. We find that the gradual depolarization of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.

  7. A polaron model for electron transfer in globular proteins.

    Science.gov (United States)

    Chuev, G N; Lakhno, V D

    1993-07-07

    Polaron models have been considered for the electron states in protein globules existing in a solvent. These models account for two fundamental effects, viz, polarization interaction of an electron with the conformational vibrations and the heterogeneity of the medium. Equations have been derived to determine the electron state in a protein globule. The parameters of this state show that it is an extended state with an energy of 2 eV. The electron transfer rate for cyt C self-exchange reaction has been calculated in the polaron model. Reorganization energy, tunneling matrix element and the rate constant have also been estimated. The results are compared with experimental data. The influence of model parameters on the significance of the data obtained has been studied. The potentialities of the model are discussed.

  8. pH-dependent electron transfer reaction and direct bioelectrocatalysis of the quinohemoprotein pyranose dehydrogenase

    Energy Technology Data Exchange (ETDEWEB)

    Takeda, Kouta [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Matsumura, Hirotoshi; Ishida, Takuya [Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657 (Japan); Yoshida, Makoto [Department of Environmental and Natural Resource Science, Tokyo University of Agriculture and Technology, Fuchu, Tokyo 183-8509 (Japan); Igarashi, Kiyohiko; Samejima, Masahiro [Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657 (Japan); Ohno, Hiroyuki [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan); Nakamura, Nobuhumi, E-mail: nobu1@cc.tuat.ac.jp [Department of Biotechnology and Life Science, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588 (Japan)

    2016-08-26

    A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of L-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. - Highlights: • pH dependencies of activity were different for the reduction of cyt c and DCPIP. • DET-based bioelectrocatalysis of CcPDH was observed. • The similar pH-dependent profile was found with cyt c and electrode. • The present results suggested that IET reaction of CcPDH shows pH dependence.

  9. The Electron Transfer Reaction between p-Nitrobenzoates and β-N, N-Dimethylaminonaphthalene

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    A few of p-nitrobenzoates were synthesized, and the electron transfer of them with β-N, N-dimethylaminonaphthalene (DMAN) in methanol solution was studied. Steady-state fluore-scence results showed the cyclodextrin moiety in p-nitrobenzoyl-β-cyclodextrin would block the electron transfer pathway from DMAN compared with other electron acceptors, thus, reduced the electron transfer efficiency.

  10. Dynamics of Electron Transfer for a Nonsuperexchange Coherent Mechanism. I

    Science.gov (United States)

    1989-10-13

    numerically. One rough but simple analytical result for the latter is also given. tPresent address: Departmento de Quimica , Facultad de Ciencias...With the change of coordinates from (q,, q21, q3) to (x, y, z) it is seen from eqs. (2.9) - (2.11) that the x-motion is identical for all H,’s and so...the geometrical changes . The calculation of the dynamics of the electron transfer starting from electronic configuration 1, i.e., from D*BA, now

  11. Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration

    DEFF Research Database (Denmark)

    Farver, O; Bendahl, L; Skov, L K

    1999-01-01

    Pulse radiolytic reduction of disulfide bridges in ceruloplasmin yielding RSSR(-) radicals induces a cascade of intramolecular electron transfer (ET) processes. Based on the three-dimensional structure of ceruloplasmin identification of individual kinetically active disulfide groups and type 1 (T1...... and indeed electron equilibration between T1A and the trinuclear copper center in the domain 1-6 interface takes place with a rate constant of 2.9 +/- 0.6 s(-1). The equilibrium constant is 0.17. Following reduction of T1A Cu(II), another ET process takes place between RSSR(-) and T1B copper(II) of domain 4...

  12. Resolution of two distinct electron transfer sites on azurin

    DEFF Research Database (Denmark)

    Farver, O; Blatt, Y; Pecht, I

    1982-01-01

    reaction rates of the Cr(III)-modified protein are attenuated. This decreased reactivity of Cr(III)-labeled azurin toward one of its physiological partners suggests the involvement of the labeled region in the electron transfer reaction with cytochrome c551. Furthermore, the presence of a second active...... in the redox system of the bacterium. The Pseudomonas cytochrome oxidase catalyzed oxidation of reduced native and Cr(III)-labeled azurin by O2 was found to be unaffected by the modification. The kinetics of the electron exchange reaction between native or Cr(III)-labeled azurin and cytochrome c551 were...

  13. Aza-heterocyclic Receptors for Direct Electron Transfer Hemoglobin Biosensor

    Science.gov (United States)

    Kumar, Vinay; Kashyap, D. M. Nikhila; Hebbar, Suraj; Swetha, R.; Prasad, Sujay; Kamala, T.; Srikanta, S. S.; Krishnaswamy, P. R.; Bhat, Navakanta

    2017-01-01

    Direct Electron Transfer biosensors, facilitating direct communication between the biomolecule of interest and electrode surface, are preferable compared to enzymatic and mediator based sensors. Although hemoglobin (Hb) contains four redox active iron centres, direct detection is not possible due to inaccessibility of iron centres and formation of dimers, blocking electron transfer. Through the coordination of iron with aza-heterocyclic receptors - pyridine and imidazole - we report a cost effective, highly sensitive and simple electrochemical Hb sensor using cyclic voltammetry and chronoamperometry. The receptor can be either in the form of liquid micro-droplet mixed with blood or dry chemistry embedded in paper membrane on top of screen printed carbon electrodes. We demonstrate excellent linearity and robustness against interference using clinical samples. A truly point of care technology is demonstrated by integrating disposable test strips with handheld reader, enabling finger prick to result in less than a minute. PMID:28169325

  14. Aza-heterocyclic Receptors for Direct Electron Transfer Hemoglobin Biosensor

    Science.gov (United States)

    Kumar, Vinay; Kashyap, D. M. Nikhila; Hebbar, Suraj; Swetha, R.; Prasad, Sujay; Kamala, T.; Srikanta, S. S.; Krishnaswamy, P. R.; Bhat, Navakanta

    2017-02-01

    Direct Electron Transfer biosensors, facilitating direct communication between the biomolecule of interest and electrode surface, are preferable compared to enzymatic and mediator based sensors. Although hemoglobin (Hb) contains four redox active iron centres, direct detection is not possible due to inaccessibility of iron centres and formation of dimers, blocking electron transfer. Through the coordination of iron with aza-heterocyclic receptors - pyridine and imidazole - we report a cost effective, highly sensitive and simple electrochemical Hb sensor using cyclic voltammetry and chronoamperometry. The receptor can be either in the form of liquid micro-droplet mixed with blood or dry chemistry embedded in paper membrane on top of screen printed carbon electrodes. We demonstrate excellent linearity and robustness against interference using clinical samples. A truly point of care technology is demonstrated by integrating disposable test strips with handheld reader, enabling finger prick to result in less than a minute.

  15. Catalytic Olefin Hydroamidation Enabled by Proton-Coupled Electron Transfer.

    Science.gov (United States)

    Miller, David C; Choi, Gilbert J; Orbe, Hudson S; Knowles, Robert R

    2015-10-28

    Here we report a ternary catalyst system for the intramolecular hydroamidation of unactivated olefins using simple N-aryl amide derivatives. Amide activation in these reactions occurs via concerted proton-coupled electron transfer (PCET) mediated by an excited state iridium complex and weak phosphate base to furnish a reactive amidyl radical that readily adds to pendant alkenes. A series of H-atom, electron, and proton transfer events with a thiophenol cocatalyst furnish the product and regenerate the active forms of the photocatalyst and base. Mechanistic studies indicate that the amide substrate can be selectively homolyzed via PCET in the presence of the thiophenol, despite a large difference in bond dissociation free energies between these functional groups.

  16. Status of the proton and electron transfer lines for the AWAKE Experiment at CERN

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, J.S., E-mail: janet.schmidt@cern.ch [CERN, Geneva (Switzerland); Bauche, J. [CERN, Geneva (Switzerland); Biskup, B. [CERN, Geneva (Switzerland); Czech Technical University, Prague (Czech Republic); Bracco, C.; Doebert, S.; Goddard, B.; Gschwendtner, E.; Jensen, L.K.; Jones, O.R.; Mazzoni, S.; Meddahi, M.; Pepitone, K.; Petrenko, A.; Velotti, F.M.; Vorozhtsov, A. [CERN, Geneva (Switzerland)

    2016-09-01

    The AWAKE project at CERN is planned to study proton driven plasma wakefield acceleration with an externally injected electron beam. Therefore two transfer lines are being designed in order to provide the proton beam from the SPS and the electron beam from an RF gun to the plasma cell. The commissioning of the proton line will take place in 2016 for the first phase of the experiment, which is focused on the self-modulation of a 12 cm long proton bunch in the plasma. The electron line will be added for the second phase of AWAKE in 2017, when the wakefield will be probed with an electron beam of 10–20 MeV/c. The challenge for these transfer lines lies in the parallel operation of the proton, electron and laser beam used to ionize the plasma and seed the self-modulation. These beams, of different characteristics, need to be synchronized and positioned for optimized injection conditions into the wakefield. This task requires great flexibility in the transfer line optics. The status of these designs will be presented in this paper.

  17. Status of the proton and electron transfer lines for the AWAKE Experiment at CERN

    Science.gov (United States)

    Schmidt, J. S.; Bauche, J.; Biskup, B.; Bracco, C.; Doebert, S.; Goddard, B.; Gschwendtner, E.; Jensen, L. K.; Jones, O. R.; Mazzoni, S.; Meddahi, M.; Pepitone, K.; Petrenko, A.; Velotti, F. M.; Vorozhtsov, A.

    2016-09-01

    The AWAKE project at CERN is planned to study proton driven plasma wakefield acceleration with an externally injected electron beam. Therefore two transfer lines are being designed in order to provide the proton beam from the SPS and the electron beam from an RF gun to the plasma cell. The commissioning of the proton line will take place in 2016 for the first phase of the experiment, which is focused on the self-modulation of a 12 cm long proton bunch in the plasma. The electron line will be added for the second phase of AWAKE in 2017, when the wakefield will be probed with an electron beam of 10-20 MeV/c. The challenge for these transfer lines lies in the parallel operation of the proton, electron and laser beam used to ionize the plasma and seed the self-modulation. These beams, of different characteristics, need to be synchronized and positioned for optimized injection conditions into the wakefield. This task requires great flexibility in the transfer line optics. The status of these designs will be presented in this paper.

  18. Marcus wins nobel prize in chemistry for electron transfer theory

    Energy Technology Data Exchange (ETDEWEB)

    Levi, B.G.

    1993-01-01

    This article describes the work of Rudolf Marcus of Caltech leading to his receipt of the 1992 Nobel Prize in Chemistry [open quotes]for his contributions to the theory of electron transfer reactions in chemical systems.[close quotes] Applications of Marcus' theory include such diverse phenomena as photosynthesis, electrically conducting polymers, chemiluminescence, and corrosion. Historical aspects of his career are given. 10 refs., 1 fig.

  19. Hetero-cycloreversions Mediated by Photoinduced Electron Transfer

    OpenAIRE

    Pérez Ruiz, Raul; Jiménez Molero, María Consuelo; Miranda Alonso, Miguel Ángel

    2014-01-01

    Discovered more than eight decades ago, the Diels-Alder (DA) cycloaddition (CA) remains one of the most versatile tools in synthetic organic chemistry. Hetero-DA processes are powerful methods for the synthesis of densely functionalized six-membered heterocycles, ubiquitous substructures found in natural products and bioactive compounds. These reactions frequently employ azadienes and oxadienes, but only a few groups have reported DA processes with thiadienes. The electron transfer (ET) versi...

  20. Real-time simulations of photoinduced coherent charge transfer and proton-coupled electron transfer.

    Science.gov (United States)

    Eisenmayer, Thomas J; Buda, Francesco

    2014-10-20

    Photoinduced electron transfer (ET) and proton-coupled electron transfer (PCET) are fundamental processes in natural phenomena, most noticeably in photosynthesis. Time-resolved spectroscopic evidence of coherent oscillatory behavior associated with these processes has been reported both in complex biological environments, as well as in biomimetic models for artificial photosynthesis. Here, we consider a few biomimetic models to investigate these processes in real-time simulations based on ab initio molecular dynamics and Ehrenfest dynamics. This allows for a detailed analysis on how photon-to-charge conversion is promoted by a coupling of the electronic excitation with specific vibrational modes and with proton displacements. The ET process shows a characteristic coherence that is linked to the nuclear motion at the interface between donor and acceptor. We also show real-time evidence of PCET in a benzimidazole-phenol redox relay. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Ultrafast Photoinduced Electron Transfer in Bimolecular Donor-Acceptor Systems

    KAUST Repository

    Alsulami, Qana A.

    2016-11-30

    The efficiency of photoconversion systems, such as organic photovoltaic (OPV) cells, is largely controlled by a series of fundamental photophysical processes occurring at the interface before carrier collection. A profound understanding of ultrafast interfacial charge transfer (CT), charge separation (CS), and charge recombination (CR) is the key determinant to improving the overall performances of photovoltaic devices. The discussion in this dissertation primarily focuses on the relevant parameters that are involved in photon absorption, exciton separation, carrier transport, carrier recombination and carrier collection in organic photovoltaic devices. A combination of steady-state and femtosecond broadband transient spectroscopies was used to investigate the photoinduced charge carrier dynamics in various donor-acceptor systems. Furthermore, this study was extended to investigate some important factors that influence charge transfer in donor-acceptor systems, such as the morphology, energy band alignment, electronic properties and chemical structure. Interestingly, clear correlations among the steady-state measurements, time-resolved spectroscopy results, grain alignment of the electron transporting layer (ETL), carrier mobility, and device performance are found. In this thesis, we explored the significant impacts of ultrafast charge separation and charge recombination at donor/acceptor (D/A) interfaces on the performance of a conjugated polymer PTB7-Th device with three fullerene acceptors: PC71BM, PC61BM and IC60BA. Time-resolved laser spectroscopy and high-resolution electron microscopy can illustrate the basis for fabricating solar cell devices with improved performances. In addition, we studied the effects of the incorporation of heavy metals into π-conjugated chromophores on electron transfer by monitoring the triplet state lifetime of the oligomer using transient absorption spectroscopy, as understanding the mechanisms controlling intersystem crossing and

  2. Insights into Proton-Coupled Electron Transfer from Computation

    Science.gov (United States)

    Provorse, Makenzie R.

    Proton-coupled electron transfer (PCET) is utilized throughout Nature to facilitate essential biological processes, such as photosynthesis, cellular respiration, and DNA replication and repair. The general approach to studying PCET processes is based on a two-dimensional More O'Ferrall-Jencks diagram in which electron transfer (ET) and proton transfer (PT) occur in a sequential or concerted fashion. Experimentally, it is difficult to discern the contributing factors of concerted PCET mechanisms. Several theoretical approaches have arisen to qualitatively and quantitatively investigate these reactions. Here, we present a multistate density functional theory (MSDFT) method to efficiently and accurately model PCET mechanisms. The MSDFT method is validated against experimental and computational data previously reported on an isoelectronic series of small molecule self-exchange hydrogen atom transfer reactions and a model complex specifically designed to study long-range ET through a hydrogen-bonded salt-bridge interface. Further application of this method to the hydrogen atom abstraction of ascorbate by a nitroxyl radical demonstrates the sensitivity of the thermodynamic and kinetic properties to solvent effects. In particular, the origin of the unusual kinetic isotope effect is investigated. Lastly, the MSDFT is employed in a combined quantum mechanical/molecular mechanical (QM/MM) approach to explicitly model PCET in condensed phases.

  3. Optimization Model for Environmental Stress Screening of Electronic Components

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Environmental stress screening (ESS) is a technological process to reduce the costly early field failure ofelectronic components. This paper builds an optimization model for ESS of electronic components to obtain the optimalESS duration. The failure phenomena of ESS are modeled by mix ed distribution, and optimal ESS duration is definedby maximizing life-cycle cost savings under the condition of meeting reliability requirement.

  4. The electron transfer system of syntrophically grown Desulfovibrio vulgaris

    Energy Technology Data Exchange (ETDEWEB)

    Walker, C.B.; He, Z.; Yang, Z.K.; Ringbauer, Jr., J.A.; He, Q.; Zhou, J.; Voordouw, G.; Wall, J.D.; Arkin, A.P.; Hazen, T.C.; Stolyar, S.; Stahl, D.A.

    2009-05-01

    Interspecies hydrogen transfer between organisms producing and consuming hydrogen promotes the decomposition of organic matter in most anoxic environments. Although syntrophic couplings between hydrogen producers and consumers are a major feature of the carbon cycle, mechanisms for energy recovery at the extremely low free energies of reactions typical of these anaerobic communities have not been established. In this study, comparative transcriptional analysis of a model sulfate-reducing microbe, Desulfovibrio vulgaris Hildenborough, suggested the use of alternative electron transfer systems dependent upon growth modality. During syntrophic growth on lactate with a hydrogenotrophic methanogen, D. vulgaris up-regulated numerous genes involved in electron transfer and energy generation when compared with sulfate-limited monocultures. In particular, genes coding for the putative membrane-bound Coo hydrogenase, two periplasmic hydrogenases (Hyd and Hyn) and the well-characterized high-molecular weight cytochrome (Hmc) were among the most highly expressed and up-regulated. Additionally, a predicted operon coding for genes involved in lactate transport and oxidation exhibited up-regulation, further suggesting an alternative pathway for electrons derived from lactate oxidation during syntrophic growth. Mutations in a subset of genes coding for Coo, Hmc, Hyd and Hyn impaired or severely limited syntrophic growth but had little affect on growth via sulfate-respiration. These results demonstrate that syntrophic growth and sulfate-respiration use largely independent energy generation pathways and imply that understanding of microbial processes sustaining nutrient cycling must consider lifestyles not captured in pure culture.

  5. The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris

    Energy Technology Data Exchange (ETDEWEB)

    PBD; ENIGMA; GTL; VIMSS; Walker, Christopher B.; He, Zhili; Yang, Zamin K.; Ringbauer Jr., Joseph A.; He, Qiang; Zhou, Jizhong; Voordouw, Gerrit; Wall, Judy D.; Arkin, Adam P.; Hazen, Terry C.; Stolyar, Sergey; Stahl, David A.

    2009-06-22

    Interspecies hydrogen transfer between organisms producing and consuming hydrogen promotes the decomposition of organic matter in most anoxic environments. Although syntrophic couplings between hydrogen producers and consumers are a major feature of the carbon cycle, mechanisms for energy recovery at the extremely low free energies of reactions typical of these anaerobic communities have not been established. In this study, comparative transcriptional analysis of a model sulfate-reducing microbe, Desulfovibrio vulgaris Hildenborough, suggested the use of alternative electron transfer systems dependent upon growth modality. During syntrophic growth on lactate with a hydrogenotrophic methanogen, D. vulgaris up-regulated numerous genes involved in electron transfer and energy generation when compared with sulfate-limited monocultures. In particular, genes coding for the putative membrane-bound Coo hydrogenase, two periplasmic hydrogenases (Hyd and Hyn) and the well-characterized high-molecular weight cytochrome (Hmc) were among the most highly expressed and up-regulated. Additionally, a predicted operon coding for genes involved in lactate transport and oxidation exhibited up-regulation, further suggesting an alternative pathway for electrons derived from lactate oxidation during syntrophic growth. Mutations in a subset of genes coding for Coo, Hmc, Hyd and Hyn impaired or severely limited syntrophic growth but had little affect on growth via sulfate-respiration. These results demonstrate that syntrophic growth and sulfate-respiration use largely independent energy generation pathways and imply that understanding of microbial processes sustaining nutrient cycling must consider lifestyles not captured in pure culture.

  6. Theoretical study on electron transfer in biological systems (Ⅲ)——Intramolecular electron transfer in metal-containing spiro π-electron system

    Institute of Scientific and Technical Information of China (English)

    翟宇峰; 蒋华良; 朱维良; 顾健德; 陈建忠; 陈凯先; 嵇汝运

    1999-01-01

    Intramolecular electron transfer of metal-containing spiro π-electron system was studied by AM1 method in the MOPAC-ET program developed by the present group. The results indicated that with the increasing of the outer electric field F, the activation energy of the reaction decreased. When F reaches a certain threshold value, the activation energy barrier becomes zero and the rate of reaction achieves the largest value. The results also indicated that electron transfer matrix elements VAB and reorganization energy λ were not obviously affected by outer electric field while the exothermicity ΔE was directly proportional to it.

  7. First-Principles Calculations of Electron Transfer in Organic Molecules

    Science.gov (United States)

    Pati, Ranjit; Karna, Shashi P.

    2000-03-01

    Suitably tailored organic structures are considered potential candidates as components in molecular electronic devices. A common molecular architecture for electronics consists of an electron donor (D) and an electron acceptor (A) moiety bonded together by a chemically inert bridging moiety, called spacer (S). The D-S-A combination constitutes the basic component equivalent of a solid state capacitor. A useful physical property that determines the applicability of molecular structures in moletronics is the electron transfer (ET) rate, which is related, in a two-state approximation, to the coupling matrix between the two electronic states representing the localization of electrons. In an effort to model potential organic structures, we have calculated the ET coupling matrix elements in a number of D-, S-, and A-type organic molecules with the use of ab initio Hartree-Fock method and two different basis sets, namely an STO-3G and a double zeta plus polarization (DZP). A number of important findings have emerged from this study: (i) The ET coupling matrix strongly depends upon the geometrical arrangement of the molecular fragment(s) in the architecture. (ii) In an oligomeric chain, the ET matrix decreases exponentially with molecular length (number of monomer units). (iii) In cyclic alkanes, the magnitude of the ET coupling matrix decreases with increasing size of fused rings.

  8. Charge-Transfer Emitting Triarylborane π-Electron Systems.

    Science.gov (United States)

    Li, Sheng-Yong; Sun, Zuo-Bang; Zhao, Cui-Hua

    2017-08-07

    Triarylboranes have attracted significantly increasing research interest as a remarkable class of photoelectronic π-electron materials. Because of the presence of vacant p orbital on the B center, the boryl group is a very unique electron acceptor that exhibits not only electron-accepting ability through p-π* conjugation but also high Lewis acidity to coordinate with Lewis bases and steric bulk arising from the aryl substituent on the B center to get enough kinetic stability. Thus, the incorporation of a trivalent B element into π-conjugated systems is an efficient strategy to tune the electronic and stereo structures and thus the photoelectronic properties of π-electron systems. When an electron-donating group, such as amino, is present, triarylboranes would likely display intramolecular charge-transfer transitions. These kinds of molecules are often highly emissive. In addition, the geometry of the molecules has a great impact on the emission properties. In this Forum Article, we herein describe our recent progress on the charge-transfer emitting triarylborane π-electron systems with novel geometries, which include the lateral boryl-substituted π-system with amino groups at the terminal positions, the o,o'-substituted biaryl π-system with boryl and amino groups at the o,o'-positions, a triarylborane-based BODIPY system, and a B,N/S-bridged ladder-type π-system. We mainly put the emphasis on the molecular design concept, structure-property relationships, intriguing emission properties and great applications of the corresponding triarylborane π-systems.

  9. Syntrophic anaerobic photosynthesis via direct interspecies electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Ha, Phuc T.; Lindemann, Stephen R.; Shi, Liang; Dohnalkova, Alice C.; Fredrickson, James K.; Madigan, Michael T.; Beyenal, Haluk

    2017-01-09

    Microbial phototrophs are key primary producers on Earth. Currently known electron donors for microbial photosynthesis include H2O, H2, H2S and other reduced inorganic compounds. We describe a new form of metabolism linking anoxygenic photosynthesis to anaerobic respiration, or “syntrophic anoxygenic photosynthesis.” We show that photoautotrophy in green sulfur bacterium Prosthecochloris aestaurii can be driven not only by electrons from a graphite electrode, but also by acetate oxidation via interspecies electron transfer from heterotrophic partner bacterium Geobacter sulfurreducens. P. aestuarii photosynthetic growth using reductant provided by either an electrode or syntrophy was robust and light-dependent. By contrast, P. aestuarii did not grow in co-culture with a G. sulfurreducens mutant lacking a trans-outer membrane porin-cytochrome protein complex required for direct intercellular electron transfer,. This syntrophic interaction suggests revisitation of global carbon cycling in anoxic environments and lays a foundation for further engineering of phototrophic microbial communities for biotechnological applications, such as waste treatment and bioenergy production.

  10. Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization

    Directory of Open Access Journals (Sweden)

    Veliko Donchev

    2013-10-01

    Full Text Available Computational modeling offers an opportunity for a better understanding and investigation of thermal transfer mechanisms. It can be used for the optimization of the electron beam melting process and for obtaining new materials with improved characteristics that have many applications in the power industry, medicine, instrument engineering, electronics, etc. A time-dependent 3D axis-symmetrical heat model for simulation of thermal transfer in metal ingots solidified in a water-cooled crucible at electron beam melting and refining (EBMR is developed. The model predicts the change in the temperature field in the casting ingot during the interaction of the beam with the material. A modified Pismen-Rekford numerical scheme to discretize the analytical model is developed. These equation systems, describing the thermal processes and main characteristics of the developed numerical method, are presented. In order to optimize the technological regimes, different criteria for better refinement and obtaining dendrite crystal structures are proposed. Analytical problems of mathematical optimization are formulated, discretized and heuristically solved by cluster methods. Using important for the practice simulation results, suggestions can be made for EBMR technology optimization. The proposed tool is important and useful for studying, control, optimization of EBMR process parameters and improving of the quality of the newly produced materials.

  11. Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization.

    Science.gov (United States)

    Vutova, Katia; Donchev, Veliko

    2013-10-18

    Computational modeling offers an opportunity for a better understanding and investigation of thermal transfer mechanisms. It can be used for the optimization of the electron beam melting process and for obtaining new materials with improved characteristics that have many applications in the power industry, medicine, instrument engineering, electronics, etc. A time-dependent 3D axis-symmetrical heat model for simulation of thermal transfer in metal ingots solidified in a water-cooled crucible at electron beam melting and refining (EBMR) is developed. The model predicts the change in the temperature field in the casting ingot during the interaction of the beam with the material. A modified Pismen-Rekford numerical scheme to discretize the analytical model is developed. These equation systems, describing the thermal processes and main characteristics of the developed numerical method, are presented. In order to optimize the technological regimes, different criteria for better refinement and obtaining dendrite crystal structures are proposed. Analytical problems of mathematical optimization are formulated, discretized and heuristically solved by cluster methods. Using important for the practice simulation results, suggestions can be made for EBMR technology optimization. The proposed tool is important and useful for studying, control, optimization of EBMR process parameters and improving of the quality of the newly produced materials.

  12. Optimization method for electron beam melting and refining of metals

    Science.gov (United States)

    Donchev, Veliko; Vutova, Katia

    2014-03-01

    Pure metals and special alloys obtained by electron beam melting and refining (EBMR) in vacuum, using electron beams as a heating source, have a lot of applications in nuclear and airspace industries, electronics, medicine, etc. An analytical optimization problem for the EBMR process based on mathematical heat model is proposed. The used criterion is integral functional minimization of a partial derivative of the temperature in the metal sample. The investigated technological parameters are the electron beam power, beam radius, the metal casting velocity, etc. The optimization problem is discretized using a non-stationary heat model and corresponding adapted Pismen-Rekford numerical scheme, developed by us and multidimensional trapezional rule. Thus a discrete optimization problem is built where the criterion is a function of technological process parameters. The discrete optimization problem is heuristically solved by cluster optimization method. Corresponding software for the optimization task is developed. The proposed optimization scheme can be applied for quality improvement of the pure metals (Ta, Ti, Cu, etc.) produced by the modern and ecological-friendly EBMR process.

  13. Electron transfer reactions of osmium(II) complexes with phenols and phenolic acids

    Science.gov (United States)

    Rajeswari, Angusamy; Ramdass, Arumugam; Muthu Mareeswaran, Paulpandian; Velayudham, Murugesan; Rajagopal, Seenivasan

    2016-07-01

    Three [Os(NN)3]2+ complexes (NN = polypyridine) with ligands of varying hydrophobicity were synthesized and characterized by NMR spectral techniques. The geometry of the molecules are optimized by DFT calculations. The interaction between [Os(NN)3]2+ complexes and phenolate ion in ground state is confirmed by absorption spectral study and the binding constant values are in the range of 3-740 M-1. The photoinduced electron transfer reaction of these [Os(NN)3]2+ complexes with phenols and phenolic acids at pH 12.5 leads to the formation of phenoxyl radical confirmed through transient absorption spectral study. Binding constants and electron transfer rate constants within the [Os(NN)3]2+-phenolate ion adduct account for the change for the overall quenching constant with the change of structure of reactants.

  14. Electron Transfer and Solvent-Mediated Electronic Localization in Molecular Photocatalysis

    DEFF Research Database (Denmark)

    Dohn, Asmus Ougaard; Kjær, Kasper Skov; Harlang, Tobias B.

    2016-01-01

    This work provides a detailed mechanism for electron transfer in a heterodinuclear complex designed as a model system in which to study homogeneous molecular photocatalysis. With efficient Born–Oppenheimer molecular dynamics simulations, we show how intermediate, charge-separated states can mediate...... the electron transfer. We observe how Jahn–Teller distortion effects play out in solution, when the molecule has energetically close-lying states, and how this distortion is averaged out in the thermal sampling. Finally, we demonstrate how the solvent helps stabilize and localize the separated charge...

  15. Noise-assisted quantum electron transfer in photosynthetic complexes

    CERN Document Server

    Nesterov, Alexander I; Martínez, José Manuel Sánchez; Sayre, Richard T

    2013-01-01

    Electron transfer (ET) between primary electron donors and acceptors is modeled in the photosystem II reaction center (RC). Our model includes (i) two discrete energy levels associated with donor and acceptor, interacting through a dipole-type matrix element and (ii) two continuum manifolds of electron energy levels ("sinks"), which interact directly with the donor and acceptor. Namely, two discrete energy levels of the donor and acceptor are embedded in their independent sinks through the corresponding interaction matrix elements. We also introduce classical (external) noise which acts simultaneously on the donor and acceptor (collective interaction). We derive a closed system of integro-differential equations which describes the non-Markovian quantum dynamics of the ET. A region of parameters is found in which the ET dynamics can be simplified, and described by coupled ordinary differential equations. Using these simplified equations, both sharp and flat redox potentials are analyzed. We analytically and nu...

  16. Electron transfer, ionization, and excitation in atomic collisions

    Energy Technology Data Exchange (ETDEWEB)

    Winter, T.G.; Alston, S.G.

    1992-01-01

    The research being carried out at Penn State by Winter and Alston addresses the fundamental processes of electron transfer, ionization, and excitation in ion-atom (and ion-ion) collisions. The focus is on intermediate- and higher-energy collisions, corresponding to proton energies of about 25 kilo-electron-volts (keV) or larger. At intermediate energies, where the transition probabilities are not small, many states must be coupled in a large calculation, while at higher energies, perturbative approaches may be used. Several studies have been carried out in the current three-year period; most of these treat systems with only one or two electrons, so that fewer approximations need be made and the basic collisional mechanisms can be more clearly described.

  17. Electron transfer rates and equilibrium within cytochrome c oxidase

    DEFF Research Database (Denmark)

    Farver, O; Einarsdóttir, O; Pecht, I

    2000-01-01

    identical within experimental error and independent of the enzyme concentration. This demonstrates that a fast intramolecular electron equilibration is taking place between CuA and heme a. The rate constants for CuA --> heme a ET and the reverse (heme a --> CuA) process were found to be 13 000 s-1 and 3700......Intramolecular electron transfer (ET) between the CuA center and heme a in bovine cytochrome c oxidase was investigated by pulse radiolysis. CuA, the initial electron acceptor, was reduced by 1-methyl nicotinamide radicals in a diffusion-controlled reaction, as monitored by absorption changes...... at 830 nm. After the initial reduction phase, the 830 nm absorption was partially restored, corresponding to reoxidation of the CuA center. Concomitantly, the absorption at 445 nm and 605 nm increased, indicating reduction of heme a. The rate constants for heme a reduction and CuA reoxidation were...

  18. ELECTRON TRANSFER MECHANISM AT THE SOLID-LIQUID INTERFACE OF PHYLLOSILICATES

    Science.gov (United States)

    Interfacial electron transfer processes on clay minerals have significant impact in natural environments and geochemical systems. Nitrobenzene was used as molecular probes to study the electron transfer mechanism at the solid-water interfaces of Fe-containing phyllosicates. For...

  19. Application of Electron-Transfer Theory to Several Systems of Biological Interest

    Science.gov (United States)

    Marcus, R. A.; Sutin, N.

    1985-03-23

    Electron-transfer reaction rates are compared with theoretically calculated values for several reactions in the bacterial photosynthetic reaction center. A second aspect of the theory, the cross-relation, is illustrated using protein-protein electron transfers.

  20. Direct observation of the ultrafast electron transfer process in a polymer/fullerene blend

    NARCIS (Netherlands)

    Cerullo, G.; Lanzani, G.; Silvestri, S. De; Brabec, Ch.J.; Zerza, G.; Sariciftci, N.S.; Hummelen, J.C.

    2000-01-01

    Photoinduced electron transfer in organic molecules is an extensively investigated topic both because of fundamental interest in the photophysics and for applications to artificial photosynthesis. Highly efficient ultrafast electron transfer from photoexcited conjugated polymers to C60 has been

  1. Mechanisms for the Direct Electron Transfer of Cytochrome c Induced by Multi-Walled Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Qin-Zheng Yang

    2012-08-01

    Full Text Available Multi-walled carbon nanotube (MWCNT-modified electrodes can promote the direct electron transfer (DET of cytochrome c (Cyt c. There are several possible mechanisms that explain the DET of Cyt c. In this study, several experimental methods, including Fourier transform infrared spectroscopy, circular dichroism, ultraviolet-visible absorption spectroscopy, and electron paramagnetic resonance spectroscopy were utilized to investigate the conformational changes of Cyt c induced by MWCNTs. The DET mechanism was demonstrated at various nano-levels: secondary structure, spatial orientation, and spin state. In the presence of MWCNTs, the secondary structure of Cyt c changes, which exposes the active site, then, the orientation of the heme is optimized, revolving the exposed active center to the optimum spatial orientation for DET; and finally, a transition of spin states is induced, providing relatively high energy and a more open microenvironment for electron transfer. These changes at different nano-levels are closely connected and form a complex process that promotes the electron transfer of Cyt c.

  2. Reduced density matrix hybrid approach: application to electronic energy transfer.

    Science.gov (United States)

    Berkelbach, Timothy C; Markland, Thomas E; Reichman, David R

    2012-02-28

    Electronic energy transfer in the condensed phase, such as that occurring in photosynthetic complexes, frequently occurs in regimes where the energy scales of the system and environment are similar. This situation provides a challenge to theoretical investigation since most approaches are accurate only when a certain energetic parameter is small compared to others in the problem. Here we show that in these difficult regimes, the Ehrenfest approach provides a good starting point for a dynamical description of the energy transfer process due to its ability to accurately treat coupling to slow environmental modes. To further improve on the accuracy of the Ehrenfest approach, we use our reduced density matrix hybrid framework to treat the faster environmental modes quantum mechanically, at the level of a perturbative master equation. This combined approach is shown to provide an efficient and quantitative description of electronic energy transfer in a model dimer and the Fenna-Matthews-Olson complex and is used to investigate the effect of environmental preparation on the resulting dynamics.

  3. Overpotential-induced lability of the electronic overlap factor in long-range electrochemical electron transfer: charge and distance dependence

    DEFF Research Database (Denmark)

    Kornyshev, A. A.; Kuznetsov, A. M.; Nielsen, Jens Ulrik;

    2000-01-01

    Long-distance electrochemical electron transfer exhibits approximately exponential dependence on the electron transfer distance. On the basis of a jellium model of the metal surface we show that the slope of the logarithm of the current vs. the transfer distance also depends strongly...

  4. Transfer Pricing – Between Optimization and International Tax Evasion

    Directory of Open Access Journals (Sweden)

    Valentin SAVA

    2017-04-01

    Full Text Available Each enterprise in the private sector aims to increase financial return, which is achieved by obtaining the higher net profit by increasing revenue and reducing expenditure. In this endeavor, compliance with tax obligations occupy a very important role because handling taxes may lead to an increase in revenue and / or a reduction of spending, and this action is called tax optimization. In the case of multinational companies, the main tool that can be used to lower the tax burden and increasing, sometimes in sizeable benefits in net, is the transfer prices or the prices they registered entities in the group transactions between them, along with another instrument with great impact, ie tax havens. Tax evasion, designating evading payment obligations of a company according to the national tax system, may be legal in the sense that tax optimization does not violate the rules, but exploiting loopholes that are in them. But when legal tax rules are violated, we deal with tax fraud, which will be subject to punitive measures by public authorities as it affects the whole population.

  5. Hetero-cycloreversions mediated by photoinduced electron transfer.

    Science.gov (United States)

    Pérez-Ruiz, Raúl; Jiménez, M Consuelo; Miranda, Miguel A

    2014-04-15

    Discovered more than eight decades ago, the Diels-Alder (DA) cycloaddition (CA) remains one of the most versatile tools in synthetic organic chemistry. Hetero-DA processes are powerful methods for the synthesis of densely functionalized six-membered heterocycles, ubiquitous substructures found in natural products and bioactive compounds. These reactions frequently employ azadienes and oxadienes, but only a few groups have reported DA processes with thiadienes. The electron transfer (ET) version of the DA reaction, though less investigated, has emerged as a subject of increasing interest. In the last two decades, researchers have paid closer attention to radical ionic hetero-cycloreversions, mainly in connection with their possible involvement in the repair of pyrimidine(6-4)pyrimidone photolesions in DNA by photolyases. In biological systems, these reactions likely occur through a reductive photosensitization mechanism. In addition, photooxidation can lead to cycloreversion (CR) reactions, and researchers can exploit this strategy for DNA repair therapies. In this Account, we discuss electron-transfer (ET) mediated hetero-CR reactions. We focus on the oxidative and reductive ET splitting of oxetanes, azetidines, and thietanes. Photoinduced electron transfer facilitates the splitting of a variety of four-membered heterocycles. In this context, researchers have commonly examined oxetanes, both experimentally and theoretically. Although a few studies have reported the cycloreversion of azetidines and thietanes carried out under electron transfer conditions, the number of examples remains limited. In general, the cleavage of the ionized four-membered rings appears to occur via a nonconcerted two-step mechanism. The trapping of the intermediate 1,4-radical ions and transient absorption spectroscopy data support this hypothesis, and it explains the observed loss of stereochemistry in the products. In the initial step, either C-C or C-X bond breaking may occur, and the

  6. Polyoxometalate-mediated electron transfer-oxygen transfer oxidation of cellulose and hemicellulose to synthesis gas.

    Science.gov (United States)

    Sarma, Bidyut Bikash; Neumann, Ronny

    2014-08-01

    Terrestrial plants contain ~70% hemicellulose and cellulose that are a significant renewable bioresource with potential as an alternative to petroleum feedstock for carbon-based fuels. The efficient and selective deconstruction of carbohydrates to their basic components, carbon monoxide and hydrogen, so called synthesis gas, is an important key step towards the realization of this potential, because the formation of liquid hydrocarbon fuels from synthesis gas are known technologies. Here we show that by using a polyoxometalate as an electron transfer-oxygen transfer catalyst, carbon monoxide is formed by cleavage of all the carbon-carbon bonds through dehydration of initially formed formic acid. In this oxidation-reduction reaction, the hydrogen atoms are stored on the polyoxometalate as protons and electrons, and can be electrochemically released from the polyoxometalate as hydrogen. Together, synthesis gas is formed. In a hydrogen economy scenario, this method can also be used to convert carbon monoxide to hydrogen.

  7. Local operator partitioning of electronic energy for electronic energy transfer: An efficient algorithm

    CERN Document Server

    Nagesh, Jayashree; Brumer, Paul

    2013-01-01

    An efficient computational algorithm to implement a local operator approach to partitioning electronic energy in general molecular systems is presented. This approach, which rigorously defines the electronic energy on any subsystem within a molecule, gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. We apply the technique to the $9-$(($1-$naphthyl)$-$methyl)-anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH$_2-$naphthyl groups as subsystems, and examine their electronic energies and populations for several excited states using Configuration Interaction Singles method. The implemented approach shows a wide variety of different behaviors amongst these excited electronic states.

  8. Gunn effect and transferred electron devices. Citations from the NTIS data base

    Science.gov (United States)

    Reed, W. E.

    1980-06-01

    A bibliography containing 99 abstracts addressing the Gunn effect and transferred electron devices is presented. The application of Gunn effect and transferred electron devices to microwave generation, amplification, and control is included. The Gunn effect in semiconductors is dicussed along with the design, fabrication, and properties of Gunn diodes and transferred electron devices.

  9. Mechanisms of bridge-mediated electron transfer: a TDDFT electronic dynamics study.

    Science.gov (United States)

    Ding, Feizhi; Chapman, Craig T; Liang, Wenkel; Li, Xiaosong

    2012-12-14

    We present a time-dependent density functional theory approach for probing the dynamics of electron transfer on a donor-bridge-acceptor polyene dye scaffold. Two kinds of mechanisms, namely, the superexchange mechanism and the sequential mechanism, may be involved in the electron transfer process. In this work, we have focused on the crossover between these two charge transfer mechanisms on a series of donor-bridge-acceptor polyene dye systems with varying lengths of conjugated bridges. A number of methods and quantities are used to assist in the analysis, including the phase relationship of charge evolution and frequency domain spectra of the time-dependent dipole. Our simulations show that the superexchange mechanism plays a dominant role in the electron transfer from donor to acceptor when the bridge length is small, and the sequential mechanism becomes more important as the polyene bridge is lengthened. Full Ehrenfest dynamics with nuclear motion show that molecular vibrations play a very small role in such ultrafast charge transfer processes.

  10. MATHEMATICAL MODELING OF EXTRACELLULAR ELECTRON TRANSFER IN BIOFILMS

    Energy Technology Data Exchange (ETDEWEB)

    Renslow, Ryan S.; Babauta, Jerome T.; Kuprat, Andrew P.; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim K.; Beyenal, Haluk

    2015-09-12

    Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as terminal electron acceptors for their metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce the requisite components for both mechanisms. In this study, a generic model is presented that incorporates the diffusion- and the conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to S. oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found in the literature. Our simulation results show that 1) biofilms having both mechanisms available, especially if they can interact, may have a metabolic advantage over biofilms that can use only a single mechanism; 2) the thickness of G. sulfurreducens biofilms is likely not limited by conductivity; 3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and 4) the local biofilm potential and redox potential are two distinct parameters and cannot be assumed to have identical values. Finally, we determined that simulated cyclic and squarewave voltammetry based on our model are currently not capable of determining the specific percentages of extracellular electron transfer mechanisms in a biofilm. The developed model will be a critical tool for designing experiments to explain EET mechanisms.

  11. Controlling time scales for electron transfer through proteins

    Directory of Open Access Journals (Sweden)

    Scot Wherland

    2015-12-01

    Full Text Available Electron transfer processes within proteins constitute key elements in biological energy conversion processes as well as in a wide variety of biochemical transformations. Pursuit of the parameters that control the rates of these processes is driven by the great interest in the latter reactions. Here, we review a considerable body of results emerging from investigation of intramolecular electron transfer (ET reactions in two types of proteins, all done by the use of the pulse-radiolysis method: first are described results of extensive studies of a model system, the bacterial electron mediating protein azurin, where an internal ET between the disulfide radical ion and the Cu(II is induced. Impact of specific structural changes introduced into azurin on the reaction rates and the parameters controlling it are discussed. Then, the presentation is extended to results of investigations of intra-protein ET reactions that are part of catalytic cycles of multi-copper containing enzymes. Again, the rates and the parameters controlling them are presented and discussed in the context of their efficacy and possible constraints set on their evolution.

  12. Modeling biofilms with dual extracellular electron transfer mechanisms

    Science.gov (United States)

    Renslow, Ryan; Babauta, Jerome; Kuprat, Andrew; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim; Beyenal, Haluk

    2013-01-01

    Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as terminal electron acceptors for their metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce the requisite components for both mechanisms. In this study, a generic model is presented that incorporates the diffusion- and the conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to S. oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found in the literature. Our simulation results show that 1) biofilms having both mechanisms available, especially if they can interact, may have a metabolic advantage over biofilms that can use only a single mechanism; 2) the thickness of G. sulfurreducens biofilms is likely not limited by conductivity; 3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and 4) the local biofilm potential and redox potential are two distinct parameters and cannot be assumed to have identical values. Finally, we determined that simulated cyclic and squarewave voltammetry based on our model are currently not capable of determining the specific percentages of extracellular electron transfer mechanisms in a biofilm. The developed model will be a critical tool for designing experiments to explain EET mechanisms. PMID:24113651

  13. Microbial extracellular electron transfer and its relevance to iron corrosion.

    Science.gov (United States)

    Kato, Souichiro

    2016-03-01

    Extracellular electron transfer (EET) is a microbial metabolism that enables efficient electron transfer between microbial cells and extracellular solid materials. Microorganisms harbouring EET abilities have received considerable attention for their various biotechnological applications, including bioleaching and bioelectrochemical systems. On the other hand, recent research revealed that microbial EET potentially induces corrosion of iron structures. It has been well known that corrosion of iron occurring under anoxic conditions is mostly caused by microbial activities, which is termed as microbiologically influenced corrosion (MIC). Among diverse MIC mechanisms, microbial EET activity that enhances corrosion via direct uptake of electrons from metallic iron, specifically termed as electrical MIC (EMIC), has been regarded as one of the major causative factors. The EMIC-inducing microorganisms initially identified were certain sulfate-reducing bacteria and methanogenic archaea isolated from marine environments. Subsequently, abilities to induce EMIC were also demonstrated in diverse anaerobic microorganisms in freshwater environments and oil fields, including acetogenic bacteria and nitrate-reducing bacteria. Abilities of EET and EMIC are now regarded as microbial traits more widespread among diverse microbial clades than was thought previously. In this review, basic understandings of microbial EET and recent progresses in the EMIC research are introduced.

  14. Application of entransy dissipation extremum principle in radiative heat transfer optimization

    Institute of Scientific and Technical Information of China (English)

    WU Jing; LIANG XinGang

    2008-01-01

    The concepts of entransy flux and entransy dissipation in radiative heat transfer were introduced based on the analogy with heat conduction and heat convection processes. Entransy will be partially dissipated during the radiative heat transfer processes due to the irreversibility. The extremum principle of entransy dissipation was developed for optimizing radiative heat transfer processes. This principle states that for a fixed boundary temperature the radiative heat transfer is optimized when the entransy dissipation is maximized, while for a fixed boundary heat flux the radiative heat transfer process is optimized when the entransy dissipation is minimized. Finally, examples for the application of the entransy dissipation extre-mum principle are presented.

  15. Application of entransy dissipation extremum principle in radiative heat transfer optimization

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The concepts of entransy flux and entransy dissipation in radiative heat transfer were introduced based on the analogy with heat conduction and heat convection processes. Entransy will be partially dissipated during the radiative heat transfer processes due to the irreversibility. The extremum principle of entransy dissipation was developed for optimizing radiative heat transfer processes. This principle states that for a fixed boundary temperature the radiative heat transfer is optimized when the entransy dissipation is maximized, while for a fixed boundary heat flux the radiative heat transfer process is optimized when the entransy dissipation is minimized. Finally, examples for the application of the entransy dissipation extre- mum principle are presented.

  16. Adsorption and Interfacial Electron Transfer of Saccharomyces Cerevisiae

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thanulov

    2003-01-01

    We have studied the adsorption and electron-transfer dynamics of Saccharomyces cerevisiae (yeast) iso-l-cytochrome c adsorbed on Au(lll) electrodes in aqueous phosphate buffer media. This cytochrome possesses a thiol group dos e to the protein surface (Cysl02) suitable for linking the protein...... negative ofthe equilibrium potential of YCC, where the protein is electrochemically functional. The MCS data show tensile differential stress signals when YCC is adsorbed on a gold-coate d MCS, with distinguishable adsorption phases in the time range from

  17. The electronic transfer of information and aerospace knowledge diffusion

    Science.gov (United States)

    Pinelli, Thomas E.; Bishop, Ann P.; Barclay, Rebecca O.; Kennedy, John M.

    1992-01-01

    Increasing reliance on and investment in information technology and electronic networking systems presupposes that computing and information technology will play a motor role in the diffusion of aerospace knowledge. Little is known, however, about actual information technology needs, uses, and problems within the aerospace knowledge diffusion process. The authors state that the potential contributions of information technology to increased productivity and competitiveness will be diminished unless empirically derived knowledge regarding the information-seeking behavior of the members of the social system - those who are producing, transferring, and using scientific and technical information - is incorporated into a new technology policy framework. Research into the use of information technology and electronic networks by U.S. aerospace engineers and scientists, collected as part of a research project designed to study aerospace knowledge diffusion, is presented in support of this assertion.

  18. Electron transfer pathway analysis in bacterial photosynthetic reaction center

    CERN Document Server

    Kitoh-Nishioka, Hirotaka

    2016-01-01

    A new computational scheme to analyze electron transfer (ET) pathways in large biomolecules is presented with applications to ETs in bacterial photosynthetic reaction center. It consists of a linear combination of fragment molecular orbitals and an electron tunneling current analysis, which enables an efficient first-principles analysis of ET pathways in large biomolecules. The scheme has been applied to the ET from menaquinone to ubiquinone via nonheme iron complex in bacterial photosynthetic reaction center. It has revealed that not only the central Fe$^{2+}$ ion but also particular histidine ligands are involved in the ET pathways in such a way to mitigate perturbations that can be caused by metal ion substitution and depletion, which elucidates the experimentally observed insensitivity of the ET rate to these perturbations.

  19. Molecular Models for Conductance in Junctions and Electrochemical Electron Transfer

    Science.gov (United States)

    Mazinani, Shobeir Khezr Seddigh

    This thesis develops molecular models for electron transport in molecular junctions and intra-molecular electron transfer. The goal is to identify molecular descriptors that afford a substantial simplification of these electronic processes. First, the connection between static molecular polarizability and the molecular conductance is examined. A correlation emerges whereby the measured conductance of a tunneling junction decreases as a function of the calculated molecular polarizability for several systems, a result consistent with the idea of a molecule as a polarizable dielectric. A model based on a macroscopic extension of the Clausius-Mossotti equation to the molecular domain and Simmon's tunneling model is developed to explain this correlation. Despite the simplicity of the theory, it paves the way for further experimental, conceptual and theoretical developments in the use of molecular descriptors to describe both conductance and electron transfer. Second, the conductance of several biologically relevant, weakly bonded, hydrogen-bonded systems is systematically investigated. While there is no correlation between hydrogen bond strength and conductance, the results indicate a relation between the conductance and atomic polarizability of the hydrogen bond acceptor atom. The relevance of these results to electron transfer in biological systems is discussed. Hydrogen production and oxidation using catalysts inspired by hydrogenases provides a more sustainable alternative to the use of precious metals. To understand electrochemical and spectroscopic properties of a collection of Fe and Ni mimics of hydrogenases, high-level density functional theory calculations are described. The results, based on a detailed analysis of the energies, charges and molecular orbitals of these metal complexes, indicate the importance of geometric constraints imposed by the ligand on molecular properties such as acidity and electrocatalytic activity. Based on model calculations of

  20. Electromagnetic field generation by ATP-induced reverse electron transfer.

    Science.gov (United States)

    Steele, Richard H

    2003-03-01

    This paper describes a mechanism to explain low-level light emission in biology. A biological analog of the electrical circuitry, modeled on the parallel plate capacitor, traversed by a helical structure, required to generate electromagnetic radiation in the optical spectral range, is described. The charge carrier required for the emissions is determined to be an accelerating electron driven by an ATP-induced reverse electron transfer. The radial velocity component, the emission trajectory, of the moving charges traversing helical protein structures in a cyclotron-type mechanism is proposed to be imposed by the ferromagnetic field components of the iron in the iron-sulfur proteins. The redox systems NADH, riboflavin, and chlorophyll were examined with their long-wavelength absorption maxima determining the energetic parameters for the calculations. Potentials calculated from the axial velocity components for the riboflavin and NADH systems were found to equal the standard redox potentials of these systems as measured electrochemically and enzymatically. The mechanics for the three systems determined the magnetic moments, the angular momenta, and the orbital magnetic fluxes to be adiabatic invariant parameters. The De Broglie dual wave-particle equation, the fundamental equation of wave mechanics, and the key idea of quantum mechanics, establishes the wavelengths for accelerating electrons which, divided into a given radial velocity, gives its respective emission frequency. Electrons propelled through helical structures, traversed by biologically available electric and magnetic fields, make accessible to the internal environment the optical spectral frequency range that the solar spectrum provides to the external environment.

  1. Enzymatic cellulose oxidation is linked to lignin by long-range electron transfer

    DEFF Research Database (Denmark)

    Westereng, Bjorge; Cannella, David; Wittrup Agger, Jane;

    2015-01-01

    cell walls. Electron transfer was confirmed by electron paramagnetic resonance spectroscopy showing that LPMO activity on cellulose changes the level of unpaired electrons in the lignin. The discovery of a long-range electron transfer mechanism links the biodegradation of cellulose and lignin and sheds...... new light on how oxidative enzymes present in plant degraders may act in concert....

  2. Enzymatic cellulose oxidation is linked to lignin by long-range electron transfer

    DEFF Research Database (Denmark)

    Westereng, Bjorge; Cannella, David; Wittrup Agger, Jane;

    2015-01-01

    cell walls. Electron transfer was confirmed by electron paramagnetic resonance spectroscopy showing that LPMO activity on cellulose changes the level of unpaired electrons in the lignin. The discovery of a long-range electron transfer mechanism links the biodegradation of cellulose and lignin and sheds...

  3. Activity-stability relationships revisited in blue oxidases catalyzing electron transfer at extreme temperatures.

    Science.gov (United States)

    Roulling, Frédéric; Godin, Amandine; Cipolla, Alexandre; Collins, Tony; Miyazaki, Kentaro; Feller, Georges

    2016-09-01

    Cuproxidases are a subset of the blue multicopper oxidases that catalyze the oxidation of toxic Cu(I) ions into less harmful Cu(II) in the bacterial periplasm. Cuproxidases from psychrophilic, mesophilic, and thermophilic bacteria display the canonical features of temperature adaptation, such as increases in structural stability and apparent optimal temperature for activity with environmental temperature as well as increases in the binding affinity for catalytic and substrate copper ions. In contrast, the oxidative activities at 25 °C for both the psychrophilic and thermophilic enzymes are similar, suggesting that the nearly temperature-independent electron transfer rate does not require peculiar adjustments. Furthermore, the structural flexibilities of both the psychrophilic and thermophilic enzymes are also similar, indicating that the firm and precise bindings of the four catalytic copper ions are essential for the oxidase function. These results show that the requirements for enzymatic electron transfer, in the absence of the selective pressure of temperature on electron transfer rates, produce a specific adaptive pattern, which is distinct from that observed in enzymes possessing a well-defined active site and relying on conformational changes such as for the induced fit mechanism.

  4. Effect of a Physical Phase Plate on Contrast Transfer in an Aberration-Corrected Transmission Electron Microscope

    OpenAIRE

    Gamm, B.; Schultheiß, K.; Schröder, R. R.; Gerthsen, D.

    2010-01-01

    In this theoretical study we analyze contrast transfer of weak-phase objects in a transmission electron microscope, which is equipped with an aberration corrector (Cs-corrector) in the imaging lens system and a physical phase plate in the back focal plane of the objective lens. For a phase shift of pi/2 between scattered and unscattered electrons induced by a physical phase plate, the sine-type phase contrast transfer function is converted into a cosine-type function. Optimal imaging conditio...

  5. Determination of the electronics transfer function for current transient measurements

    CERN Document Server

    Scharf, Christian

    2014-01-01

    We describe a straight-forward method for determining the transfer function of the readout of a sensor for the situation in which the current transient of the sensor can be precisely simulated. The method relies on the convolution theorem of Fourier transforms. The specific example is a planar silicon pad diode connected with a 50 $\\Omega $ cable to an amplifier followed by a 5 GS/s sampling oscilloscope. The charge carriers in the sensor were produced by picosecond lasers with light of wavelengths of 675 and 1060 nm. The transfer function is determined from the 1060 nm data with the pad diode biased at 1000 V. It is shown that the simulated sensor response convoluted with this transfer function provides an excellent description of the measured transients for the laser light of both wavelengths, at voltages 50 V above the depletion voltage of about 90 V up to the maximum applied voltage of 1000 V. The method has been developed for the precise measurement of the dependence of the drift velocity of electrons an...

  6. MD studies of electron transfer at ambient and elevated pressures

    Science.gov (United States)

    Giles, Alex; Spooner, Jacob; Weinberg, Noham

    2013-06-01

    The effect of pressure on the rate constants of outer-sphere electron transfer reactions has often been described using the Marcus-Hush theory. This theory agrees well with experiment when internal reorganization of the ionic system is negligible, however it does not offer a recipe for calculation of the effects that result from significant solute restructuring. We have recently developed a molecular dynamics technique that accurately describes structural dependence of molecular volumes in non-polar and weakly polar systems. We are now extending this approach to the case of highly polar ionic systems where both solvent and solute restructuring components are important. For this purpose we construct pressure-dependent two-dimensional surfaces for electron transfer reactions in coordinate system composed of interionic distance and Marcus-type solvent polarization coordinate, and use these surfaces to describe pressure effects on reaction kinetics. R.A. Marcus. J. Chem. Phys. 24, 966 (1956); 24, 979 (1956); 26, 867 (1957). Discuss. Faraday Soc. 29, 21 (1960). Faraday Discuss. Chem. Soc. 74, 7 (1982); N.S. Hush. Trans. Faraday Soc. 57, 557 (1961).

  7. Promoting direct interspecies electron transfer with activated carbon

    DEFF Research Database (Denmark)

    Liu, Fanghua; Rotaru, Amelia-Elena; Shrestha, Pravin M.

    2012-01-01

    Granular activated carbon (GAC) is added to methanogenic digesters to enhance conversion of wastes to methane, but the mechanism(s) for GAC’s stimulatory effect are poorly understood. GAC has high electrical conductivity and thus it was hypothesized that one mechanism for GAC stimulation of metha......Granular activated carbon (GAC) is added to methanogenic digesters to enhance conversion of wastes to methane, but the mechanism(s) for GAC’s stimulatory effect are poorly understood. GAC has high electrical conductivity and thus it was hypothesized that one mechanism for GAC stimulation...... of methanogenesis might be to facilitate direct interspecies electron transfer (DIET) between bacteria and methanogens. Metabolism was substantially accelerated when GAC was added to co-cultures of Geobacter metallireducens and Geobacter sulfurreducens grown under conditions previously shown to require DIET. Cells...... were attached to GAC, but did not aggregate as they do when making biological electrical connections between cells. Studies with a series of gene deletion mutants eliminated the possibility that GAC promoted electron exchange via interspecies hydrogen or formate transfer and demonstrated that DIET...

  8. Efficient Hybrid Optimal Design Method for Power Electronics Converters

    CERN Document Server

    AUTHOR|(SzGeCERN)697719; Aguglia, Davide; Viarouge, Philippe; Cros, Jérôme

    2015-01-01

    This paper presents a novel design methodology for dimensioning optimal power-electronic converters, which is able to achieve the precision of numerical simulation-based optimization procedures, however minimizing the overall computation time. The approach is based on the utilization of analytical and frequency-domain design models for a numerical optimization process, a validation with numerical simulations of the intermediate optimal solutions, and the correction of the analytical design models precision from the numerical simulation results. This method allows using the numerical simulation in an efficient way, where typically less than ten correction iterations are required. In order to demonstrate the performances of the proposed methodology, the calculation of the control parameters for an H-bridge DC-DC converter and the optimal dimensioning of a damped output filter for a buck converter using the proposed approach is presented.

  9. Vibrational dynamics in photoinduced electron transfer. Progress report, December 1, 1992--November 30, 1993

    Energy Technology Data Exchange (ETDEWEB)

    Spears, K.G.

    1993-09-08

    Objective is to perform a new type of measurement for optically excited electron transfer processes that can provide unique experimental insight into the molecular mechanism of electron transfer. Measurements of optically excited electron transfer are done with picosecond infrared (IR) absorption spectroscopy to monitor the vibrational motions of the molecules immediately after electron transfer. Theory and experiment suggest that molecular vibrations and distortions are important controlling elements for electron transfer, and direct information has yet to be obtained on these elements of electron transfer mechanisms. The second period of funding has been dedicated to finishing technique development and performing studies of electron transfer in ion pair systems to identify if vibrational dependent electron transfer rates are present in this system. We have succeeded in measuring, for the first time, electron transfer rates as a function of vibrational state in an ion pair complex in solution. In a different area of electron transfer research we have proposed a new mechanism of solvent gated electron transfer.

  10. Linear energy relationships in ground state proton transfer and excited state proton-coupled electron transfer.

    Science.gov (United States)

    Gamiz-Hernandez, Ana P; Magomedov, Artiom; Hummer, Gerhard; Kaila, Ville R I

    2015-02-12

    Proton-coupled electron transfer (PCET) processes are elementary chemical reactions involved in a broad range of radical and redox reactions. Elucidating fundamental PCET reaction mechanisms are thus of central importance for chemical and biochemical research. Here we use quantum chemical density functional theory (DFT), time-dependent density functional theory (TDDFT), and the algebraic diagrammatic-construction through second-order (ADC(2)) to study the mechanism, thermodynamic driving force effects, and reaction barriers of both ground state proton transfer (pT) and photoinduced proton-coupled electron transfer (PCET) between nitrosylated phenyl-phenol compounds and hydrogen-bonded t-butylamine as an external base. We show that the obtained reaction barriers for the ground state pT reactions depend linearly on the thermodynamic driving force, with a Brønsted slope of 1 or 0. Photoexcitation leads to a PCET reaction, for which we find that the excited state reaction barrier depends on the thermodynamic driving force with a Brønsted slope of 1/2. To support the mechanistic picture arising from the static potential energy surfaces, we perform additional molecular dynamics simulations on the excited state energy surface, in which we observe a spontaneous PCET between the donor and the acceptor groups. Our findings suggest that a Brønsted analysis may distinguish the ground state pT and excited state PCET processes.

  11. Martian Radiative Transfer Modeling Using the Optimal Spectral Sampling Method

    Science.gov (United States)

    Eluszkiewicz, J.; Cady-Pereira, K.; Uymin, G.; Moncet, J.-L.

    2005-01-01

    The large volume of existing and planned infrared observations of Mars have prompted the development of a new martian radiative transfer model that could be used in the retrievals of atmospheric and surface properties. The model is based on the Optimal Spectral Sampling (OSS) method [1]. The method is a fast and accurate monochromatic technique applicable to a wide range of remote sensing platforms (from microwave to UV) and was originally developed for the real-time processing of infrared and microwave data acquired by instruments aboard the satellites forming part of the next-generation global weather satellite system NPOESS (National Polarorbiting Operational Satellite System) [2]. As part of our on-going research related to the radiative properties of the martian polar caps, we have begun the development of a martian OSS model with the goal of using it to perform self-consistent atmospheric corrections necessary to retrieve caps emissivity from the Thermal Emission Spectrometer (TES) spectra. While the caps will provide the initial focus area for applying the new model, it is hoped that the model will be of interest to the wider Mars remote sensing community.

  12. Computational characterization of competing energy and electron transfer states in bimetallic donor-acceptor systems for photocatalytic conversion

    Science.gov (United States)

    Fredin, Lisa A.; Persson, Petter

    2016-09-01

    The rapidly growing interest in photocatalytic systems for direct solar fuel production such as hydrogen generation from water splitting is grounded in the unique opportunity to achieve charge separation in molecular systems provided by electron transfer processes. In general, both photoinduced and catalytic processes involve complicated dynamics that depend on both structural and electronic effects. Here the excited state landscape of metal centered light harvester-catalyst pairs is explored using density functional theory calculations. In weakly bound systems, the interplay between structural and electronic factors involved can be constructed from the various mononuclear relaxed excited states. For this study, supramolecular states of electron transfer and excitation energy transfer character have been constructed from constituent full optimizations of multiple charge/spin states for a set of three Ru-based light harvesters and nine transition metal catalysts (based on Ru, Rh, Re, Pd, and Co) in terms of energy, structure, and electronic properties. The complete set of combined charge-spin states for each donor-acceptor system provides information about the competition of excited state energy transfer states with the catalytically active electron transfer states, enabling the identification of the most promising candidates for photocatalytic applications from this perspective.

  13. Computational characterization of competing energy and electron transfer states in bimetallic donor-acceptor systems for photocatalytic conversion.

    Science.gov (United States)

    Fredin, Lisa A; Persson, Petter

    2016-09-14

    The rapidly growing interest in photocatalytic systems for direct solar fuel production such as hydrogen generation from water splitting is grounded in the unique opportunity to achieve charge separation in molecular systems provided by electron transfer processes. In general, both photoinduced and catalytic processes involve complicated dynamics that depend on both structural and electronic effects. Here the excited state landscape of metal centered light harvester-catalyst pairs is explored using density functional theory calculations. In weakly bound systems, the interplay between structural and electronic factors involved can be constructed from the various mononuclear relaxed excited states. For this study, supramolecular states of electron transfer and excitation energy transfer character have been constructed from constituent full optimizations of multiple charge/spin states for a set of three Ru-based light harvesters and nine transition metal catalysts (based on Ru, Rh, Re, Pd, and Co) in terms of energy, structure, and electronic properties. The complete set of combined charge-spin states for each donor-acceptor system provides information about the competition of excited state energy transfer states with the catalytically active electron transfer states, enabling the identification of the most promising candidates for photocatalytic applications from this perspective.

  14. ATP-induced electron transfer by redox-selective partner recognition.

    Science.gov (United States)

    Hennig, Sandra E; Goetzl, Sebastian; Jeoung, Jae-Hun; Bommer, Martin; Lendzian, Friedhelm; Hildebrandt, Peter; Dobbek, Holger

    2014-08-11

    Thermodynamically unfavourable electron transfers are enabled by coupling to an energy-supplying reaction. How the energy is transduced from the exergonic to the endergonic process is largely unknown. Here we provide the structural basis for an energy transduction process in the reductive activation of B12-dependent methyltransferases. The transfer of one electron from an activating enzyme to the cobalamin cofactor is energetically uphill and relies on coupling to an ATPase reaction. Our results demonstrate that the key to coupling is, besides the oxidation state-dependent complex formation, the conformational gating of the electron transfer. Complex formation induces a substitution of the ligand at the electron-accepting Co ion. Addition of ATP initiates electron transfer by provoking conformational changes that destabilize the complex. We show how remodelling of the electron-accepting Co(2+) promotes ATP-dependent electron transfer; an efficient strategy not seen in other electron-transferring ATPases.

  15. Mitochondrial nitric oxide production supported by reverse electron transfer.

    Science.gov (United States)

    Bombicino, Silvina S; Iglesias, Darío E; Zaobornyj, Tamara; Boveris, Alberto; Valdez, Laura B

    2016-10-01

    Heart phosphorylating electron transfer particles (ETPH) produced NO at 1.2 ± 0.1 nmol NO. min(-1) mg protein(-1) by the mtNOS catalyzed reaction. These particles showed a NAD(+) reductase activity of 64 ± 3 nmol min(-1) mg protein(-1) sustained by reverse electron transfer (RET) at expenses of ATP and succinate. The same particles, without NADPH and in conditions of RET produced 0.97 ± 0.07 nmol NO. min(-1) mg protein(-1). Rotenone inhibited NO production supported by RET measured in ETPH and in coupled mitochondria, but did not reduce the activity of recombinant nNOS, indicating that the inhibitory effect of rotenone on NO production is due to an electron flow inhibition and not to a direct action on mtNOS structure. NO production sustained by RET corresponds to 20% of the total amount of NO released from heart coupled mitochondria. A mitochondrial fraction enriched in complex I produced 1.7 ± 0.2 nmol NO. min(-1) mg protein(-1) and reacted with anti-75 kDa complex I subunit and anti-nNOS antibodies, suggesting that complex I and mtNOS are located contiguously. These data show that mitochondrial NO production can be supported by RET, and suggest that mtNOS is next to complex I, reaffirming the idea of a functional association between these proteins.

  16. Optimal configuration for a finite low-temperature source refrigerator cycle with heat transfer law

    Directory of Open Access Journals (Sweden)

    Jun Li, Lingen Chen, Yanlin Ge, Fengrui Sun

    2016-01-01

    Full Text Available The optimal configuration of a refrigeration cycle operating between a finite low-temperature source and an infinite high-temperature sink are derived by using finite time thermodynamics based on a complex heat transfer law, including Newtonian heat transfer law, linear phenomenological heat transfer law, radiative heat transfer law, Dulong-Petit heat transfer law, generalized convective heat transfer law and generalized radiative heat transfer law. In the refrigeration cycle model the only irreversibility of finite rate heat transfer is considered. The optimal relation between cooling load and coefficient of performance (COP of the refrigeration cycle is also derived by using an equivalent temperature of low-temperature source. The obtained results include those with various heat transfer laws and infinite low-temperature source, and can provide some theoretical guidelines for the designs of practical refrigerators.

  17. Fabrication and single-electron-transfer operation of a triple-dot single-electron transistor

    Energy Technology Data Exchange (ETDEWEB)

    Jo, Mingyu, E-mail: mingyujo@eis.hokudai.ac.jp; Uchida, Takafumi; Tsurumaki-Fukuchi, Atsushi; Arita, Masashi; Takahashi, Yasuo [Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814 (Japan); Fujiwara, Akira; Nishiguchi, Katsuhiko [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi 243-0198 (Japan); Ono, Yukinori [Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555 (Japan); Inokawa, Hiroshi [Research Institute of Electronics, Shizuoka University, 3-5-1, Johoku, Hamamatsu 432-8011 (Japan)

    2015-12-07

    A triple-dot single-electron transistor was fabricated on silicon-on-insulator wafer using pattern-dependent oxidation. A specially designed one-dimensional silicon wire having small constrictions at both ends was converted to a triple-dot single-electron transistor by means of pattern-dependent oxidation. The fabrication of the center dot involved quantum size effects and stress-induced band gap reduction, whereas that of the two side dots involved thickness modulation because of the complex edge structure of two-dimensional silicon. Single-electron turnstile operation was confirmed at 8 K when a 100-mV, 1-MHz square wave was applied. Monte Carlo simulations indicated that such a device with inhomogeneous tunnel and gate capacitances can exhibit single-electron transfer.

  18. Optimization of electron-beam pumped excimer laser

    Science.gov (United States)

    Lowum, T. F.; Swecker, J. L.

    The output energy of an electron-beam pumped xenon flouride laser has been enhanced by optimizing certain electron-gun and gas-mix parameters. The optimized e-gun parameters include anode-cathode spacing, magnetic field strength, and cathode voltage. The optimized laser gas parameters include NF3 concentration, Xe concentration, and total pressure. The shortest anode-cathode spacing (9 cm), the strongest magnetic guide field (1600 Gauss), and the highest cathode voltage (375 kV) gave the highest laser output. The optimum gas concentrations were 0.05 percent NF3, 0.3 percent Xe, with Ne added to bring the total gas pressure to 60 psia. The energy degraded by 2 percent per shot with this gas mix.

  19. Photoinduced Bimolecular Electron Transfer from Cyano Anions in Ionic Liquids.

    Science.gov (United States)

    Wu, Boning; Liang, Min; Maroncelli, Mark; Castner, Edward W

    2015-11-19

    Ionic liquids with electron-donating anions are used to investigate rates and mechanisms of photoinduced bimolecular electron transfer to the photoexcited acceptor 9,10-dicyanoanthracene (9,10-DCNA). The set of five cyano anion ILs studied comprises the 1-ethyl-3-methylimidazolium cation paired with each of these five anions: selenocyanate, thiocyanate, dicyanamide, tricyanomethanide, and tetracyanoborate. Measurements with these anions dilute in acetonitrile and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide show that the selenocyanate and tricyanomethanide anions are strong quenchers of the 9,10-DCNA fluorescence, thiocyanate is a moderately strong quencher, dicyanamide is a weak quencher, and no quenching is observed for tetracyanoborate. Quenching rates are obtained from both time-resolved fluorescence transients and time-integrated spectra. Application of a Smoluchowski diffusion-and-reaction model showed that the complex kinetics observed can be fit using only two adjustable parameters, D and V0, where D is the relative diffusion coefficient between donor and acceptor and V0 is the value of the electronic coupling at donor-acceptor contact.

  20. Intramolecular electron transfer in Pseudomonas aeruginosa cd(1) nitrite reductase

    DEFF Research Database (Denmark)

    Farver, Ole; Brunori, Maurizio; Cutruzzolà, Francesca

    2009-01-01

    nitrite reductase has been determined in both fully oxidized and reduced states. Intramolecular electron transfer (ET), between c and d(1) hemes is an essential step in the catalytic cycle. In earlier studies of the Pseudomonas stutzeri enzyme, we observed that a marked negative cooperativity......The cd(1) nitrite reductases, which catalyze the reduction of nitrite to nitric oxide, are homodimers of 60 kDa subunits, each containing one heme-c and one heme-d(1). Heme-c is the electron entry site, whereas heme-d(1) constitutes the catalytic center. The 3D structure of Pseudomonas aeruginosa......-controlled bimolecular process, followed by unimolecular electron equilibration between the c and d(1) hemes (k(ET) = 4.3 s(-1) and K = 1.4 at 298 K, pH 7.0). In the case of the mutant, the latter ET rate was faster by almost one order of magnitude. Moreover, the internal ET rate dropped (by approximately 30-fold...

  1. Mechanically Controlled Electron Transfer in a Single-Polypeptide Transistor

    Science.gov (United States)

    Sheu, Sheh-Yi; Yang, Dah-Yen

    2017-01-01

    Proteins are of interest in nano-bio electronic devices due to their versatile structures, exquisite functionality and specificity. However, quantum transport measurements produce conflicting results due to technical limitations whereby it is difficult to precisely determine molecular orientation, the nature of the moieties, the presence of the surroundings and the temperature; in such circumstances a better understanding of the protein electron transfer (ET) pathway and the mechanism remains a considerable challenge. Here, we report an approach to mechanically drive polypeptide flip-flop motion to achieve a logic gate with ON and OFF states during protein ET. We have calculated the transmission spectra of the peptide-based molecular junctions and observed the hallmarks of electrical current and conductance. The results indicate that peptide ET follows an NC asymmetric process and depends on the amino acid chirality and α-helical handedness. Electron transmission decreases as the number of water molecules increases, and the ET efficiency and its pathway depend on the type of water-bridged H-bonds. Our results provide a rational mechanism for peptide ET and new perspectives on polypeptides as potential candidates in logic nano devices.

  2. Generic Mechanism of Optimal Energy Transfer Efficiency: A Scaling Theory of the Mean First Passage Time in Exciton Systems

    CERN Document Server

    Wu, Jianlan; Silbey, Robert J

    2013-01-01

    An asymptotic scaling theory is presented using the conceptual basis of trapping-free subspace (i.e., orthogonal subspace) to establish the generic mechanism of optimal efficiency of excitation energy transfer (EET) in light-harvesting systems. Analogous to Kramers' turnover in classical rate theory, the enhanced efficiency in the weak damping limit and the suppressed efficiency in the strong damping limit define two asymptotic scaling regimes, which are interpolated to predict the functional form of optimal efficiency of the trapping-free subspace. In the presence of static disorder, the scaling law of transfer time with respect to dephasing rate changes from linear to square root, suggesting a weaker dependence on the environment. Though formulated in the context of EET, the analysis and conclusions apply in general to open quantum processes, including electron transfer, fluorescence emission, and heat conduction.

  3. Exogenous electron shuttle-mediated extracellular electron transfer of Shewanella putrefaciens 200: electrochemical parameters and thermodynamics.

    Science.gov (United States)

    Wu, Yundang; Liu, Tongxu; Li, Xiaomin; Li, Fangbai

    2014-08-19

    Despite the importance of exogenous electron shuttles (ESs) in extracellular electron transfer (EET), a lack of understanding of the key properties of ESs is a concern given their different influences on EET processes. Here, the ES-mediated EET capacity of Shewanella putrefaciens 200 (SP200) was evaluated by examining the electricity generated in a microbial fuel cell. The results indicated that all the ESs substantially accelerated the current generation compared to only SP200. The current and polarization parameters were linearly correlated with both the standard redox potential (E(ES)(0)) and the electron accepting capacity (EAC) of the ESs. A thermodynamic analysis of the electron transfer from the electron donor to the electrode suggested that the EET from c-type cytochromes (c-Cyts) to ESs is a crucial step causing the differences in EET capacities among various ESs. Based on the derived equations, both E(ES)(0) and EAC can quantitatively determine potential losses (ΔE) that reflect the potential loss of the ES-mediated EET. In situ spectral kinetic analysis of ES reduction by c-Cyts in a living SP200 suspension was first investigated with the E(ES), E(c-Cyt), and ΔE values being calculated. This study can provide a comprehensive understanding of the role of ESs in EET.

  4. Studies on photooxidation (VIII)——Electron transfer photooxygenation mechanism of acenaphthenone as electron donor

    Institute of Scientific and Technical Information of China (English)

    吴树屏; 刘继峰; 江致勤

    1996-01-01

    The photooxidation and its electron transfer (ET) mechanism of acenaphthenone (ANO) sensitized by 9,10-dicyanoanthracence (DCA) are investigated. It has been found that the reaction with a stepwise manner led to the formation of 1,8- (3’-hydroxy)-β-naphthalene lactone and 1,8-naphthalenedicarboxylic anhydride. By cyclic voltammetry, fluorescence quenching, exciplex emission, co-sensitbation of biphenyl/DCA as well as CIDNP studies, it is verified that ANO can behave as an electron donor to undergo ET reaction with singlet DCA which is a thermodynamically-favored process.

  5. Electronic shift register memory based on molecular electron-transfer reactions

    Science.gov (United States)

    Hopfield, J. J.; Onuchic, Jose Nelson; Beratan, David N.

    1989-01-01

    The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip.

  6. Electronic Nose Based on an Optimized Competition Neural Network

    Directory of Open Access Journals (Sweden)

    Haiping Zhang

    2011-05-01

    Full Text Available In view of the fact that there are disadvantages in that the class number must be determined in advance, the value of learning rates are hard to fix, etc., when using traditional competitive neural networks (CNNs in electronic noses (E-noses, an optimized CNN method was presented. The optimized CNN was established on the basis of the optimum class number of samples according to the changes of the Davies and Bouldin (DB value and it could increase, divide, or delete neurons in order to adjust the number of neurons automatically. Moreover, the learning rate changes according to the variety of training times of each sample. The traditional CNN and the optimized CNN were applied to five kinds of sorted vinegars with an E-nose. The results showed that optimized network structures could adjust the number of clusters dynamically and resulted in good classifications.

  7. Electrochemical Electron Transfer and Proton-Coupled Electron Transfer: Effects of Double Layer and Ionic Environment on Solvent Reorganization Energies

    Energy Technology Data Exchange (ETDEWEB)

    Ghosh, Soumya; Soudackov, Alexander; Hammes-Schiffer, Sharon

    2016-06-14

    Electron transfer and proton coupled electron transfer (PCET) reactions at electrochemical interfaces play an essential role in a broad range of energy conversion processes. The reorganization energy, which is a measure of the free energy change associated with solute and solvent rearrangements, is a key quantity for calculating rate constants for these reactions. We present a computational method for including the effects of the double layer and ionic environment of the diffuse layer in calculations of electrochemical solvent reorganization energies. This approach incorporates an accurate electronic charge distribution of the solute within a molecular-shaped cavity in conjunction with a dielectric continuum treatment of the solvent, ions, and electrode using the integral equations formalism polarizable continuum model. The molecule-solvent boundary is treated explicitly, but the effects of the electrode-double layer and double layer-diffuse layer boundaries, as well as the effects of the ionic strength of the solvent, are included through an external Green’s function. The calculated total reorganization energies agree well with experimentally measured values for a series of electrochemical systems, and the effects of including both the double layer and ionic environment are found to be very small. This general approach was also extended to electrochemical PCET and produced total reorganization energies in close agreement with experimental values for two experimentally studied PCET systems. This research was supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center, funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  8. Transfer of optical orbital angular momentum to a bound electron

    Science.gov (United States)

    Schmiegelow, Christian T.; Schulz, Jonas; Kaufmann, Henning; Ruster, Thomas; Poschinger, Ulrich G.; Schmidt-Kaler, Ferdinand

    2016-10-01

    Photons can carry angular momentum, not only due to their spin, but also due to their spatial structure. This extra twist has been used, for example, to drive circular motion of microscopic particles in optical tweezers as well as to create vortices in quantum gases. Here we excite an atomic transition with a vortex laser beam and demonstrate the transfer of optical orbital angular momentum to the valence electron of a single trapped ion. We observe strongly modified selection rules showing that an atom can absorb two quanta of angular momentum from a single photon: one from the spin and another from the spatial structure of the beam. Furthermore, we show that parasitic ac-Stark shifts from off-resonant transitions are suppressed in the dark centre of vortex beams. These results show how light's spatial structure can determine the characteristics of light-matter interaction and pave the way for its application and observation in other systems.

  9. Electron Transfer Reactions: Generalized Spin-Boson Approach

    CERN Document Server

    Merkli, Marco

    2012-01-01

    We introduce a mathematically rigorous analysis of a generalized spin-boson system for the treatment of a donor-acceptor (reactant-product) quantum system coupled to a thermal quantum noise. The donor/acceptor probability dynamics describes transport reactions in chemical processes in presence of a noisy environment -- such as the electron transfer in a photosynthetic reaction center. Besides being rigorous, our analysis has the advantages over previous ones that (1) we include a general, non energy-conserving system-environment interaction, and that (2) we allow for the donor or acceptor to consist of multiple energy levels lying closely together. We establish explicit expressions for the rates and the efficiency (final donor-acceptor population difference) of the reaction. In particular, we show that the rate increases for a multi-level acceptor, but the efficiency does not.

  10. Optimal information transfer in enzymatic networks: A field theoretic formulation

    Science.gov (United States)

    Samanta, Himadri S.; Hinczewski, Michael; Thirumalai, D.

    2017-07-01

    Signaling in enzymatic networks is typically triggered by environmental fluctuations, resulting in a series of stochastic chemical reactions, leading to corruption of the signal by noise. For example, information flow is initiated by binding of extracellular ligands to receptors, which is transmitted through a cascade involving kinase-phosphatase stochastic chemical reactions. For a class of such networks, we develop a general field-theoretic approach to calculate the error in signal transmission as a function of an appropriate control variable. Application of the theory to a simple push-pull network, a module in the kinase-phosphatase cascade, recovers the exact results for error in signal transmission previously obtained using umbral calculus [Hinczewski and Thirumalai, Phys. Rev. X 4, 041017 (2014), 10.1103/PhysRevX.4.041017]. We illustrate the generality of the theory by studying the minimal errors in noise reduction in a reaction cascade with two connected push-pull modules. Such a cascade behaves as an effective three-species network with a pseudointermediate. In this case, optimal information transfer, resulting in the smallest square of the error between the input and output, occurs with a time delay, which is given by the inverse of the decay rate of the pseudointermediate. Surprisingly, in these examples the minimum error computed using simulations that take nonlinearities and discrete nature of molecules into account coincides with the predictions of a linear theory. In contrast, there are substantial deviations between simulations and predictions of the linear theory in error in signal propagation in an enzymatic push-pull network for a certain range of parameters. Inclusion of second-order perturbative corrections shows that differences between simulations and theoretical predictions are minimized. Our study establishes that a field theoretic formulation of stochastic biological signaling offers a systematic way to understand error propagation in

  11. Optically monitoring voltage in neurons by photo-induced electron transfer through molecular wires.

    Science.gov (United States)

    Miller, Evan W; Lin, John Y; Frady, E Paxon; Steinbach, Paul A; Kristan, William B; Tsien, Roger Y

    2012-02-07

    Fluorescence imaging is an attractive method for monitoring neuronal activity. A key challenge for optically monitoring voltage is development of sensors that can give large and fast responses to changes in transmembrane potential. We now present fluorescent sensors that detect voltage changes in neurons by modulation of photo-induced electron transfer (PeT) from an electron donor through a synthetic molecular wire to a fluorophore. These dyes give bigger responses to voltage than electrochromic dyes, yet have much faster kinetics and much less added capacitance than existing sensors based on hydrophobic anions or voltage-sensitive ion channels. These features enable single-trial detection of synaptic and action potentials in cultured hippocampal neurons and intact leech ganglia. Voltage-dependent PeT should be amenable to much further optimization, but the existing probes are already valuable indicators of neuronal activity.

  12. Redox induced electron transfer in doublet azo-anion diradical rhenium(II) complexes. Characterization of complete electron transfer series.

    Science.gov (United States)

    Paul, Nandadulal; Samanta, Subhas; Goswami, Sreebrata

    2010-03-15

    Reactions of dirhenium decacarbonyl with the two azoaromatic ligands, L(a) = (2-phenylazo)pyridine and L(b) = (4-chloro-2-phenylazo)pyridine (general abbreviation of the ligands is L) afford paramagnetic rhenium(II) complexes, [Re(II)(L(*-))(2)(CO)(2)] (1) (S = 1/2 ground state) with two one-electron reduced azo-anion radical ligands in an octahedral geometrical arrangement. At room temperature (300 K) the complexes 1a-b, showed magnetic moments (mu(eff)) close to 1.94 mu(B), which is suggestive of the existence of strong antiferromagnetic interactions in the complexes. The results of magnetic measurements on one of the complexes, 1b, in the temperature range 2-300 K are reported. The above complexes showed two cathodic and two anodic responses in cyclic voltammetry where one-electron oxidation leads to an unusual redox event involving simultaneous reduction of the rhenium(II) and oxidation of the second ligand via intramolecular electron transfer. The oxidized complexes 1a(+) and 1b(+) are air stable and were isolated as crystalline solids as their tri-iodide (I(3)(-)) salts. The structures of the two representative complexes, 1b and [1b]I(3), as determined by X-ray crystallography, are compared. The anionic complexes, [1](-) and [1](2-) were characterized in solution by their spectral properties.

  13. Photocathode Optimization for a Dynamic Transmission Electron Microscope: Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Ellis, P; Flom, Z; Heinselman, K; Nguyen, T; Tung, S; Haskell, R; Reed, B W; LaGrange, T

    2011-08-04

    The Dynamic Transmission Electron Microscope (DTEM) team at Harvey Mudd College has been sponsored by LLNL to design and build a test setup for optimizing the performance of the DTEM's electron source. Unlike a traditional TEM, the DTEM achieves much faster exposure times by using photoemission from a photocathode to produce electrons for imaging. The DTEM team's work is motivated by the need to improve the coherence and current density of the electron cloud produced by the electron gun in order to increase the image resolution and contrast achievable by DTEM. The photoemission test setup is nearly complete and the team will soon complete baseline tests of electron gun performance. The photoemission laser and high voltage power supply have been repaired; the optics path for relaying the laser to the photocathode has been finalized, assembled, and aligned; the internal setup of the vacuum chamber has been finalized and mostly implemented; and system control, synchronization, and data acquisition has been implemented in LabVIEW. Immediate future work includes determining a consistent alignment procedure to place the laser waist on the photocathode, and taking baseline performance measurements of the tantalum photocathode. Future research will examine the performance of the electron gun as a function of the photoemission laser profile, the photocathode material, and the geometry and voltages of the accelerating and focusing components in the electron gun. This report presents the team's progress and outlines the work that remains.

  14. ELECTRON TRANSFER COLLISION OF NEON IONS WITH Ne IN A RF ION TRAP

    Institute of Scientific and Technical Information of China (English)

    满宝元; 王象泰; 等

    1995-01-01

    The pulsed electron beam rf ion stroage system is used to study neon ions electron transfer,The rate coefficients for electron transfer of the neon ions with the neon gas are measured.the results are better than those in other ion storage system.

  15. Machine Learning for Silver Nanoparticle Electron Transfer Property Prediction.

    Science.gov (United States)

    Sun, Baichuan; Fernandez, Michael; Barnard, Amanda S

    2017-09-22

    Nanoparticles exhibit diverse structural and morphological features that are often inter-connected, making the correlation of structure/property relationships challenging. In this study a multi-structure/single-property relationship of silver nanoparticles is developed for the energy of Fermi level, which can be tuned to improve the transfer of electrons in a variety of applications. By combining different machine learning analytical algorithms, including k-mean, logistic regression and random forest with electronic structure simulations, we find that the degree of twinning (characterised by the fraction of hexagonal closed packed atoms) and the population of {111} facet (characterized by a surface coordination number of 9) are strongly correlated to the Fermi energy of silver nanoparticles. A concise 3 layer artificial neural network together with principal component analysis is built to predict this property, with reduced geometrical, structural and topological features, making the method ideal for efficient and accurate high-throughput screening of large-scale virtual nanoparticles libraries, and the creation of single-structure/single-property, multi-structure/single-property and single-structure/multi-property relationships in the near future.

  16. Enhanced electron transfer dissociation through fixed charge derivatization of cysteines.

    Science.gov (United States)

    Vasicek, Lisa; Brodbelt, Jennifer S

    2009-10-01

    Electron transfer dissociation (ETD) has proven to be a promising new ion activation method for proteomics applications due to its ability to generate c- and z-type fragment ions in comparison to the y- and b-type ions produced upon the more conventional collisional activation of peptides. However, low precursor charge states hinder the success of electron-based activation methods due to competition from nondissociative charge reduction and incomplete sequence coverage. In the present report, the reduction and alkylation of disulfide bonds prior to ETD analysis is evaluated by comparison of three derivatization reagents: iodoacetamide (IAM), N,N-dimethyl-2-chloro-ethylamine (DML), and (3-acrylamidopropyl)-trimethyl ammonium chloride (APTA). While both the DML and APTA modifications lead to an increase in the charge states of peptides, the APTA-peptides provided the most significant improvement in percent fragmentation and sequence coverage for all peptides upon ETD, including formation of diagnostic ions that allow characterization of both the C- and N-termini. In addition, the formation of product ions in multiple charge states upon ETD is minimized for the APTA-modified peptides.

  17. Enhanced rate of intramolecular electron transfer in an engineered purple CuA azurin.

    Science.gov (United States)

    Farver, O; Lu, Y; Ang, M C; Pecht, I

    1999-02-02

    The recent expression of an azurin mutant where the blue type 1 copper site is replaced by the purple CuA site of Paracoccus denitrificans cytochrome c oxidase has yielded an optimal system for examining the unique electron mediation properties of the binuclear CuA center, because both type 1 and CuA centers are placed in the same location in the protein while all other structural elements remain the same. Long-range electron transfer is induced between the disulfide radical anion, produced pulse radiolytically, and the oxidized binuclear CuA center in the purple azurin mutant. The rate constant of this intramolecular process, kET = 650 +/- 60 s-1 at 298 K and pH 5.1, is almost 3-fold faster than for the same process in the wild-type single blue copper azurin from Pseudomonas aeruginosa (250 +/- 20 s-1), in spite of a smaller driving force (0.69 eV for purple CuA azurin vs. 0.76 eV for blue copper azurin). The reorganization energy of the CuA center is calculated to be 0.4 eV, which is only 50% of that found for the wild-type azurin. These results represent a direct comparison of electron transfer properties of the blue and purple CuA sites in the same protein framework and provide support for the notion that the binuclear purple CuA center is a more efficient electron transfer agent than the blue single copper center because reactivity of the former involves a lower reorganization energy.

  18. Objective evaluation of the relative modulation transfer function of densitometers for digitisation of electron micrographs

    Energy Technology Data Exchange (ETDEWEB)

    Roseman, A.M.; Neumann, K

    2003-08-15

    Digitisation of images recorded on film is a crucial part of data acquisition in electron microscopy, particularly for electron cryo-microscopy of biological specimens where the contrast and signal-to-noise ratio are low. A quantitative method to evaluate and compare the quality of densitometers, as measured by the modulation transfer function (MTF), is described here. The densitometer is modelled as a linear system, the output being the convolution of the input image and a point spread function. The MTF is the magnitude of the Fourier transform of the point spread function. The relative MTF describes the quality of signal transfer with spatial frequency. It is important that fine structural details in the micrograph are digitised with a high value for the MTF which does not vary with direction. A test pattern has been generated by projecting an electron image of a grid pattern onto film. The film is scanned and a computer program measures the intensities of the diffraction orders of the repeating pattern. Three different scanners are compared, one is a point scanner and the other two are line scanners. The test can be used to check if a scanner is set up optimally, and how it compares with another scanner.

  19. A new model for electron flow during anaerobic digestion: direct interspecies electron transfer to Methanosaeta for the reduction of carbon dioxide to methane

    DEFF Research Database (Denmark)

    Rotaru, Amelia-Elena; Shrestha, Pravin M.; Liu, Fanghua

    2013-01-01

    , the most abundant bacteria in the aggregates, highly expressed genes for ethanol metabolism and for extracellular electron transfer via electrically conductive pili, suggesting that Geobacter and Methanosaeta species were exchanging electrons via direct interspecies electron transfer (DIET...

  20. Phase II Final Report Computer Optimization of Electron Guns

    Energy Technology Data Exchange (ETDEWEB)

    R. Lawrence Ives; Thuc Bui; Hien Tran; Michael Read; Adam Attarian; William Tallis

    2011-04-15

    This program implemented advanced computer optimization into an adaptive mesh, finite element, 3D, charged particle code. The routines can optimize electron gun performance to achieve a specified current, beam size, and perveance. It can also minimize beam ripple and electric field gradients. The magnetics optimization capability allows design of coil geometries and magnetic material configurations to achieve a specified axial magnetic field profile. The optimization control program, built into the charged particle code Beam Optics Analyzer (BOA) utilizes a 3D solid modeling package to modify geometry using design tables. Parameters within the graphical user interface (currents, voltages, etc.) can be directly modified within BOA. The program implemented advanced post processing capability for the optimization routines as well as the user. A Graphical User Interface allows the user to set up goal functions, select variables, establish ranges of variation, and define performance criteria. The optimization capability allowed development of a doubly convergent multiple beam gun that could not be designed using previous techniques.

  1. Optimizing Geothermal Drilling: Oil and Gas Technology Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Denninger, Kate; Eustes, Alfred; Visser, Charles; Baker, Walt; Bolton, Dan; Bell, Jason; Bell, Sean; Jacobs, Amelia; Nagandran, Uneshddarann; Tilley, Mitch; Quick, Ralph

    2015-09-02

    There is a significant amount of financial risk associated with geothermal drilling. This study of drilling operations seeks opportunities to improve upon current practices and technologies. The scope of this study included analyzing 21 geothermal wells and 21 oil and gas wells. The goal was to determine a 'Perfect Well' using historical data to compare the best oil and gas well to the best geothermal well. Unfortunately, limitations encountered in the study included missing data (bit records, mud information, etc.) and poor data collection practices An online software database was used to format drilling data to IADC coded daily drilling reports and generate figures for analysis. Six major issues have been found in geothermal drilling operations. These problems include lost circulation, rig/ equipment selection, cementing, penetration rate, drilling program, and time management. As a result of these issues, geothermal drilling averaged 56.4 days longer than drilling comparable oil and gas wells in the wells in this study. Roughly $13.9 million was spent on non-productive time in the 21 geothermal wells, compared with only $1.3 million in the oil and gas wells, assuming a cost of $50,000 per day. Comparable events such as drilling the same sized hole, tripping in/out, cementing, and running the same size casing took substantially less time in the oil and gas wells. Geothermal wells were drilled using older and/or less advanced technology to depths less than 10,000 feet, while oil and gas wells reached 12,500 feet faster with purpose built rigs. A new approach is now underway that will optimize drilling programs throughout the drilling industry using Mechanical Specific Energy (MSE) as a tool to realize efficient drilling processes. Potential improvements for current geothermal operations are: the use of electronic records, real time services, and official glossary terms to describe rig operations, and advanced drilling rigs/technology.

  2. Modular electron transfer circuits for synthetic biology: Insulation of an engineered biohydrogen pathway

    OpenAIRE

    Agapakis, Christina M; Silver, Pamela A

    2010-01-01

    Electron transfer is central to a wide range of essential metabolic pathways, from photosynthesis to fermentation. The evolutionary diversity and conservation of proteins that transfer electrons makes these pathways a valuable platform for engineered metabolic circuits in synthetic biology. Rational engineering of electron transfer pathways containing hydrogenases has the potential to lead to industrial scale production of hydrogen as an alternative source of clean fuel and experimental assay...

  3. TAX OPTIMIZATION THROUGH TRANSFER PRICING, COMMON AND MANIPULATIVE PRACTICE

    Directory of Open Access Journals (Sweden)

    Jurcau Anca Sabina

    2009-05-01

    Full Text Available This paper is about how multinational enterprises choose transfer prices in the presence of differential corporate income tax rates. A transfer prince is a value placed on the goods which are traded between divisions of an organization. We review and exte

  4. Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy

    Science.gov (United States)

    Milot, Rebecca Lee

    Terahertz spectroscopy is distinguished from other far infrared and millimeter wave spectroscopies by its inherent phase sensitivity and sub-picosecond time resolution making it a versatile technique to study a wide range of physical phenomena. As THz spectroscopy is still a relatively new field, many aspects of THz generation mechanisms have not been fully examined. Using terahertz emission spectroscopy (TES), THz emission from ZnTe(110) was analyzed and found to be limited by two-photon absorption and free-carrier generation at high excitation fluences. Due to concerns about the continued use of fossil fuels, solar energy has been widely investigated as a promising source of renewable energy. Dye-sensitized solar cells (DSSCs) have been developed as a low-cost alternative to conventional photovoltaic solar cells. To solve the issues of the intermittency and inefficient transport associated with solar energy, researchers are attempting to adapt DSSCs for water oxidation and chemical fuel production. Both device designs incorporate sensitizer molecules covalently bound to metal oxide nanoparticles. The sensitizer, which is comprised of a chromophore and anchoring group, absorbs light and transfers an electron from its excited state to the conduction band of the metal oxide, producing an electric current. Using time-resolved THz spectroscopy (TRTS), an optical pump/THz probe technique, the efficiency and dynamics of electron injection from sensitizers to metal oxides was evaluated as a function of the chromophore, its anchoring group, and the metal oxide identity. Experiments for studying fully functioning DSSCs and water oxidation devices are also described. Bio-inspired pentafluorophenyl porphyrin chromophores have been designed and synthesized for use in photoelectrochemical water oxidation cells. Influences on the efficiency and dynamics of electron injection from the chromophores into TiO2 and SnO2 nanoparticles due to changes in both the central substituent to

  5. Syntrophic growth with direct interspecies electron transfer as the primary mechanism for energy exchange

    DEFF Research Database (Denmark)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Aklujkar, Muktak

    2013-01-01

    Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy...... dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration....... to support cell growth. In order to investigate this, co-cultures of Geobacter metallireducens, which can transfer electrons to wild-type G. sulfurreducens via DIET, were established with a citrate synthase-deficient G. sulfurreducens strain that can receive electrons for respiration through DIET only...

  6. Control of Electron Transfer from Lead-Salt Nanocrystals to TiO 2

    KAUST Repository

    Hyun, Byung-Ryool

    2011-05-11

    The roles of solvent reorganization energy and electronic coupling strength on the transfer of photoexcited electrons from PbS nanocrystals to TiO 2 nanoparticles are investigated. We find that the electron transfer depends only weakly on the solvent, in contrast to the strong dependence in the nanocrystal-molecule system. This is ascribed to the larger size of the acceptor in this system, and is accounted for by Marcus theory. The electronic coupling of the PbS and TiO 2 is varied by changing the length, aliphatic and aromatic structure, and anchor groups of the linker molecules. Shorter linker molecules consistently lead to faster electron transfer. Surprisingly, linker molecules of the same length but distinct chemical structures yield similar electron transfer rates. In contrast, the electron transfer rate can vary dramatically with different anchor groups. © 2011 American Chemical Society.

  7. Adaptive surrogate model based multi-objective transfer trajectory optimization between different libration points

    Science.gov (United States)

    Peng, Haijun; Wang, Wei

    2016-10-01

    An adaptive surrogate model-based multi-objective optimization strategy that combines the benefits of invariant manifolds and low-thrust control toward developing a low-computational-cost transfer trajectory between libration orbits around the L1 and L2 libration points in the Sun-Earth system has been proposed in this paper. A new structure for a multi-objective transfer trajectory optimization model that divides the transfer trajectory into several segments and gives the dominations for invariant manifolds and low-thrust control in different segments has been established. To reduce the computational cost of multi-objective transfer trajectory optimization, a mixed sampling strategy-based adaptive surrogate model has been proposed. Numerical simulations show that the results obtained from the adaptive surrogate-based multi-objective optimization are in agreement with the results obtained using direct multi-objective optimization methods, and the computational workload of the adaptive surrogate-based multi-objective optimization is only approximately 10% of that of direct multi-objective optimization. Furthermore, the generating efficiency of the Pareto points of the adaptive surrogate-based multi-objective optimization is approximately 8 times that of the direct multi-objective optimization. Therefore, the proposed adaptive surrogate-based multi-objective optimization provides obvious advantages over direct multi-objective optimization methods.

  8. Optimizing sparse sampling for 2D electronic spectroscopy

    Science.gov (United States)

    Roeding, Sebastian; Klimovich, Nikita; Brixner, Tobias

    2017-02-01

    We present a new data acquisition concept using optimized non-uniform sampling and compressed sensing reconstruction in order to substantially decrease the acquisition times in action-based multidimensional electronic spectroscopy. For this we acquire a regularly sampled reference data set at a fixed population time and use a genetic algorithm to optimize a reduced non-uniform sampling pattern. We then apply the optimal sampling for data acquisition at all other population times. Furthermore, we show how to transform two-dimensional (2D) spectra into a joint 4D time-frequency von Neumann representation. This leads to increased sparsity compared to the Fourier domain and to improved reconstruction. We demonstrate this approach by recovering transient dynamics in the 2D spectrum of a cresyl violet sample using just 25% of the originally sampled data points.

  9. Hydrated Electron Transfer to Nucleobases in Aqueous Solutions Revealed by Ab Initio Molecular Dynamics Simulations.

    Science.gov (United States)

    Zhao, Jing; Wang, Mei; Fu, Aiyun; Yang, Hongfang; Bu, Yuxiang

    2015-08-03

    We present an ab initio molecular dynamics (AIMD) simulation study into the transfer dynamics of an excess electron from its cavity-shaped hydrated electron state to a hydrated nucleobase (NB)-bound state. In contrast to the traditional view that electron localization at NBs (G/A/C/T), which is the first step for electron-induced DNA damage, is related only to dry or prehydrated electrons, and a fully hydrated electron no longer transfers to NBs, our AIMD simulations indicate that a fully hydrated electron can still transfer to NBs. We monitored the transfer dynamics of fully hydrated electrons towards hydrated NBs in aqueous solutions by using AIMD simulations and found that due to solution-structure fluctuation and attraction of NBs, a fully hydrated electron can transfer to a NB gradually over time. Concurrently, the hydrated electron cavity gradually reorganizes, distorts, and even breaks. The transfer could be completed in about 120-200 fs in four aqueous NB solutions, depending on the electron-binding ability of hydrated NBs and the structural fluctuation of the solution. The transferring electron resides in the π*-type lowest unoccupied molecular orbital of the NB, which leads to a hydrated NB anion. Clearly, the observed transfer of hydrated electrons can be attributed to the strong electron-binding ability of hydrated NBs over the hydrated electron cavity, which is the driving force, and the transfer dynamics is structure-fluctuation controlled. This work provides new insights into the evolution dynamics of hydrated electrons and provides some helpful information for understanding the DNA-damage mechanism in solution. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Microbial electron transport and energy conservation – the foundation for optimizing bioelectrochemical systems

    Directory of Open Access Journals (Sweden)

    Frauke eKracke

    2015-06-01

    Full Text Available Microbial electrochemical techniques describe a variety of emerging technologies that use electrode-bacteria-interactions for biotechnology applications including the production of electricity, waste and wastewater treatment, bioremediation and production of valuable products. Central in each application is the ability of the microbial catalyst to interact with external electron acceptors and/or donors and its metabolic properties that enable the combination of electron transport and carbon metabolism. And here also lies the key challenge. A wide range of microbes has been discovered to be able to exchange electrons with solid surfaces or mediators but only a few have been studied in depth. Especially electron transfer mechanisms from cathodes towards the microbial organism are poorly understood but are essential for many applications such as microbial electrosynthesis. We analyse the different electron transport chains that nature offers for organisms such as metal respiring bacteria and acetogens, but also standard biotechnological organisms currently used in bio-production. Special focus lies on the essential connection of redox and energy metabolism, which is often ignored when studying bio-electrochemical systems. The possibility of extracellular electron exchange at different points in each organism is discussed regarding required redox potentials and effect on cellular redox and energy levels. Key compounds such as electron carriers (e.g. cytochromes, ferredoxin, quinones, flavins are identified and analysed regarding their possible role in electrode-microbe-interactions. This work summarizes our current knowledge on electron transport processes and uses a theoretical approach to predict the impact of different modes of transfer on the energy metabolism. As such it adds an important piece of fundamental understanding of microbial electron transport possibilities to the research community and will help to optimize and advance bio

  11. Microbial electron transport and energy conservation - the foundation for optimizing bioelectrochemical systems.

    Science.gov (United States)

    Kracke, Frauke; Vassilev, Igor; Krömer, Jens O

    2015-01-01

    Microbial electrochemical techniques describe a variety of emerging technologies that use electrode-bacteria interactions for biotechnology applications including the production of electricity, waste and wastewater treatment, bioremediation and the production of valuable products. Central in each application is the ability of the microbial catalyst to interact with external electron acceptors and/or donors and its metabolic properties that enable the combination of electron transport and carbon metabolism. And here also lies the key challenge. A wide range of microbes has been discovered to be able to exchange electrons with solid surfaces or mediators but only a few have been studied in depth. Especially electron transfer mechanisms from cathodes towards the microbial organism are poorly understood but are essential for many applications such as microbial electrosynthesis. We analyze the different electron transport chains that nature offers for organisms such as metal respiring bacteria and acetogens, but also standard biotechnological organisms currently used in bio-production. Special focus lies on the essential connection of redox and energy metabolism, which is often ignored when studying bioelectrochemical systems. The possibility of extracellular electron exchange at different points in each organism is discussed regarding required redox potentials and effect on cellular redox and energy levels. Key compounds such as electron carriers (e.g., cytochromes, ferredoxin, quinones, flavins) are identified and analyzed regarding their possible role in electrode-microbe interactions. This work summarizes our current knowledge on electron transport processes and uses a theoretical approach to predict the impact of different modes of transfer on the energy metabolism. As such it adds an important piece of fundamental understanding of microbial electron transport possibilities to the research community and will help to optimize and advance bioelectrochemical

  12. Thermodynamic, kinetic and electronic structure aspects of a charge-transfer active bichromophoric organofullerene

    Indian Academy of Sciences (India)

    K Senthil Kumar; Archita Patnaik

    2013-03-01

    Our recent work on charge transfer in the electronically push-pull dimethylaminoazobenzene-fullerene C60 donor-bridge-acceptor dyad through orbital picture revealed charge displacement from the n(N=N) (non-bonding) and (N=N) type orbitals centred on the donor part to the purely fullerene centred LUMOs and (LUMO+n) orbitals, delocalized over the entire molecule. Consequently, this investigation centres around the kinetic and thermodynamic parameters involved in the solvent polarity dependent intramolecular photo-induced electron transfer processes in the dyad, indispensable for artificial photosynthetic systems. A quasi-reversible electron transfer pathway was elucidated with electrode-specific heterogeneous electron transfer rate constants.

  13. Type IV pili of Acidithiobacillus ferrooxidans can transfer electrons from extracellular electron donors.

    Science.gov (United States)

    Li, Yongquan; Li, Hongyu

    2014-03-01

    Studies on Acidithiobacillus ferrooxidans accepting electrons from Fe(II) have previously focused on cytochrome c. However, we have discovered that, besides cytochrome c, type IV pili (Tfp) can transfer electrons. Here, we report conduction by Tfp of A. ferrooxidans analyzed with a conducting-probe atomic force microscope (AFM). The results indicate that the Tfp of A. ferrooxidans are highly conductive. The genome sequence of A. ferrooxidans ATCC 23270 contains two genes, pilV and pilW, which code for pilin domain proteins with the conserved amino acids characteristic of Tfp. Multiple alignment analysis of the PilV and PilW (pilin) proteins indicated that pilV is the adhesin gene while pilW codes for the major protein element of Tfp. The likely function of Tfp is to complete the circuit between the cell surface and Fe(II) oxides. These results indicate that Tfp of A. ferrooxidans might serve as biological nanowires transferring electrons from the surface of Fe(II) oxides to the cell surface. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Vibrational and Electronic Energy Transfer and Dissociation of Diatomic Molecules by Electron Collisions

    Science.gov (United States)

    Huo, Winifred M.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also

  15. Lyapunov-based Low-thrust Optimal Orbit Transfer: An approach in Cartesian coordinates

    CERN Document Server

    Zhang, Hantian; Cao, Qingjie

    2014-01-01

    This paper presents a simple approach to low-thrust optimal-fuel and optimal-time transfer problems between two elliptic orbits using the Cartesian coordinates system. In this case, an orbit is described by its specific angular momentum and Laplace vectors with a free injection point. Trajectory optimization with the pseudospectral method and nonlinear programming are supported by the initial guess generated from the Chang-Chichka-Marsden Lyapunov-based transfer controller. This approach successfully solves several low-thrust optimal problems. Numerical results show that the Lyapunov-based initial guess overcomes the difficulty in optimization caused by the strong oscillation of variables in the Cartesian coordinates system. Furthermore, a comparison of the results shows that obtaining the optimal transfer solution through the polynomial approximation by utilizing Cartesian coordinates is easier than using orbital elements, which normally produce strongly nonlinear equations of motion. In this paper, the Eart...

  16. Modeling and multidimensional optimization of a tapered free electron laser

    Directory of Open Access Journals (Sweden)

    Y. Jiao

    2012-05-01

    Full Text Available Energy extraction efficiency of a free electron laser (FEL can be greatly increased using a tapered undulator and self-seeding. However, the extraction rate is limited by various effects that eventually lead to saturation of the peak intensity and power. To better understand these effects, we develop a model extending the Kroll-Morton-Rosenbluth, one-dimensional theory to include the physics of diffraction, optical guiding, and radially resolved particle trapping. The predictions of the model agree well with that of the GENESIS single-frequency numerical simulations. In particular, we discuss the evolution of the electron-radiation interaction along the tapered undulator and show that the decreasing of refractive guiding is the major cause of the efficiency reduction, particle detrapping, and then saturation of the radiation power. With this understanding, we develop a multidimensional optimization scheme based on GENESIS simulations to increase the energy extraction efficiency via an improved taper profile and variation in electron beam radius. We present optimization results for hard x-ray tapered FELs, and the dependence of the maximum extractable radiation power on various parameters of the initial electron beam, radiation field, and the undulator system. We also study the effect of the sideband growth in a tapered FEL. Such growth induces increased particle detrapping and thus decreased refractive guiding that together strongly limit the overall energy extraction efficiency.

  17. Electron transfer reactions of macrocyclic compounds of cobalt

    Energy Technology Data Exchange (ETDEWEB)

    Heckman, R.A.

    1978-08-01

    The kinetics and mechanisms of reduction of H/sub 2/O/sub 2/, Br/sub 2/, and I/sub 2/ by various macrocyclic tetraaza complexes of cobalt(II), including Vitamin B/sub 12r/, were studied. The synthetic macrocycles studied were all 14-membered rings which varied in the degree of unsaturation,substitution of methyl groups on the periphery of the ring, and substitution within the ring itself. Scavenging experiments demonstrated that the reductions of H/sub 2/O/sub 2/ produce free hydroxyl radicals only in the case of Co((14)ane)/sup 2 +/ but with none of the others. In the latter instances apparently H/sub 2/O/sub 2/ simultaneously oxidizes the metal center and the ligand. The reductions of Br/sub 2/ and I/sub 2/ produce an aquohalocobalt(III) product for all reductants (except B/sub 12r/ + Br/sub 2/, which was complicated by bromination of the corrin ring). The mechanism of halogen reduction was found to involve rate-limiting inner-sphere electron transfer from cobalt to halogen to produce a dihalide anion coordinated to the cobalt center. This intermediate subsequently decomposes in rapid reactions to halocobalt(III) and halogen atom species or reacts with another cobalt(II) center to give two molecules of halocobalt(III). The reductions of halomethylcobaloximes and related compounds and diamminecobaloxime by Cr/sup 2 +/ were also studied. The reaction was found to be biphasic in all cases with the reaction products being halomethane (for the halomethylcobaloximes), Co/sup 2 +/ (in less than 100 percent yield), a Cr(III)-dimethylglyoxime species, a small amount of free dmgH/sub 2/, and a highly-charged species containing both cobalt and chromium. The first-stage reaction occurs with a stoichiometry of 1:1 producing an intermediate with an absorption maximum at 460 nm for all starting reagents. The results were interpreted in terms of inner-sphere coordination of the cobaloxime to the Cr(II) and electron transfer through the oxime N-O bond.

  18. Thermal transfer structures coupling electronics card(s) to coolant-cooled structure(s)

    Science.gov (United States)

    David, Milnes P; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Parida, Pritish R; Schmidt, Roger R

    2014-12-16

    Cooling apparatuses and coolant-cooled electronic systems are provided which include thermal transfer structures configured to engage with a spring force one or more electronics cards with docking of the electronics card(s) within a respective socket(s) of the electronic system. A thermal transfer structure of the cooling apparatus includes a thermal spreader having a first thermal conduction surface, and a thermally conductive spring assembly coupled to the conduction surface of the thermal spreader and positioned and configured to reside between and physically couple a first surface of an electronics card to the first surface of the thermal spreader with docking of the electronics card within a socket of the electronic system. The thermal transfer structure is, in one embodiment, metallurgically bonded to a coolant-cooled structure and facilitates transfer of heat from the electronics card to coolant flowing through the coolant-cooled structure.

  19. DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)

    Science.gov (United States)

    There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

  20. [Theory of long-distance electron transfer in nanoscale biological structures].

    Science.gov (United States)

    Krasil'nikov, P M

    2011-01-01

    Macromolecular biological systems accomplishing the directed electron transfer are nano-sized structures. The distance between carrier molecules (cofactors), which represent practically isolated electron localization centers, reaches tens of angstroms. The electron transfer theory based on the concept of delocalized electron states, which is conventionally used in biophysics, is unable to adequately interpret the results of concrete observations in many cases. On the basis of the theory of electronic transitions in the case of localized states, developed in the physics of disorder matter, a mechanism of long distance electron transfer in biological systems is suggested. The molecular relaxation of the microenvironment of electron localization centers that accompanies the electron transfer process is also considered.

  1. DETERMINATION OF HETEROGENEOUS ELECTRON TRANSFER RATE CONSTANTS AT MICROFABRICATED IRIDIUM ELECTRODES. (R825511C022)

    Science.gov (United States)

    There has been an increasing use of both solid metal and microfabricated iridium electrodes as substrates for various types of electroanalysis. However, investigations to determine heterogeneous electron transfer rate constants on iridium, especially at an electron beam evapor...

  2. Optimal Tax-Transfer Policies, Life-Cycle Labour Supply and Present-Biased Preferences

    DEFF Research Database (Denmark)

    Gunnersen, Lasse Frisgaard; Rasmussen, Bo Sandemann

    Using a two-period model with two types of agents that are characterized by present-biased preferences second-best optimal tax-transfer policies are considered. The paternalistic optimal tax-transfer policy has two main concerns: Income redistribution from high to low ability households...... consequences not only for optimal subsidies to savings but also for optimal marginal income taxes....... and correction of undersaving due to present-biasedness. Policies must comply with incentive-compatibility constraints that restricts both how much income redistribution that can take place and how much savings should be subsidized. A main result is that the degree of present-biasedness has important...

  3. Direct electron transfer from glucose oxidase immobilized on a nano-porous glassy carbon electrode

    Energy Technology Data Exchange (ETDEWEB)

    Haghighi, Behzad, E-mail: haghighi@iasbs.ac.ir [Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Gava Zang, Zanjan (Iran, Islamic Republic of); Tabrizi, Mahmoud Amouzadeh [Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Gava Zang, Zanjan (Iran, Islamic Republic of)

    2011-11-30

    Highlights: > A direct electron transfer reaction of glucose oxidase was observed on the surface of a nano-porous glassy carbon electrode. > A pair of well-defined and reversible redox peaks was observed at the formal potential of approximately -0.439 V. > The apparent electron transfer rate constant was measured to be 5.27 s{sup -1}. > A mechanism for the observed direct electron transfer reaction was proposed, which consists of a two-electron and a two-proton transfer. - Abstract: A pair of well-defined and reversible redox peaks was observed for the direct electron transfer (DET) reaction of an immobilized glucose oxidase (GOx) on the surface of a nano-porous glassy carbon electrode at the formal potential (E{sup o}') of -0.439 V versus Ag/AgCl/saturated KCl. The electron transfer rate constant (k{sub s}) was calculated to be 5.27 s{sup -1}. The dependence of E{sup o}' on pH indicated that the direct electron transfer of the GOx was a two-electron transfer process, coupled with two-proton transfer. The results clearly demonstrate that the nano-porous glassy carbon electrode is a cost-effective and ready-to-use scaffold for the fabrication of a glucose biosensor.

  4. [Mechanisms of electron transfer to insoluble terminal acceptors in chemoorganotrophic bacteria].

    Science.gov (United States)

    Samarukha, I A

    2014-01-01

    The mechanisms of electron transfer of association of chemoorganotrophic bacteria to the anode in microbial fuel cells are summarized in the survey. These mechanisms are not mutually exclusive and are divided into the mechanisms of mediator electron transfer, mechanisms of electron transfer with intermediate products of bacterial metabolism and mechanism of direct transfer of electrons from the cell surface. Thus, electron transfer mediators are artificial or synthesized by bacteria riboflavins and phenazine derivatives, which also determine the ability of bacteria to antagonism. The microorganisms with hydrolytic and exoelectrogenic activity are involved in electron transfer mechanisms that are mediated by intermediate metabolic products, which are low molecular carboxylic acids, alcohols, hydrogen etc. The direct transfer of electrons to insoluble anode is possible due to membrane structures (cytochromes, pili, etc.). Association of microorganisms, and thus the biochemical mechanisms of electron transfer depend on the origin of the inoculum, substrate composition, mass transfer, conditions of aeration, potentials and location of electrodes and others, that are defined by technological and design parameters.

  5. Optimizing Geothermal Drilling: Oil and Gas Technology Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Tilley, Mitch; Eustes, Alfred; Visser, Charles; Baker, Walt; Bolton, Dan; Bell, Jason; Nagandran, Uneshddarann; Quick, Ralph

    2015-01-26

    There is a significant amount of financial risk associated with geothermal drilling; however, there are opportunities to improve upon current practices and technologies used. The scope of this drilling operational study included 21 geothermal wells and 21 oil and gas wells. The goal was to determine a 'perfect well' using historical data to compare the best oil and gas well to the best geothermal well. Unfortunately, limitations encountered in the study included missing data (bit records, mud information, etc.), poor data collection, and difficult to ascertain handwriting. An online software database was used to format drilling data to IADC coded daily drilling reports and generate analysis figures. Six major issues have been found in geothermal drilling operations. These problems include lost circulation, rig/equipment selection, cementing, penetration rate, drilling program, and time management. As a result of these issues, geothermal drilling averages 56.4 days longer than drilling comparable oil and gas wells in the wells in this study. Roughly $13.9 million would be lost due to non-productive time in the 21 geothermal wells and only $1.3 million in the oil and gas wells, assuming a cost of $50,000 per day. Comparable events such as drilling the same sized hole, tripping in/out, cementing, and running the same size casing took substantially less time in the oil and gas wells. Geothermal wells were drilled using older and/or less advanced technology to depths less than 10,000 feet, while oil and gas wells reached 12,500 feet faster with purpose built rigs. A new approach is now underway that will optimize drilling programs throughout the drilling industry. It is the use of Mechanical Specific Energy (MSE) as a tool to realize efficient drilling processes. However, a work-flow must also be established in order for there to be an efficient drilling program. Potential improvements for current geothermal operations are: the use of electronic records, real

  6. Topology optimization for nano-scale heat transfer

    DEFF Research Database (Denmark)

    Evgrafov, Anton; Maute, Kurt; Yang, Ronggui

    2009-01-01

    We consider the problem of optimal design of nano-scale heat conducting systems using topology optimization techniques. At such small scales the empirical Fourier's law of heat conduction no longer captures the underlying physical phenomena because the mean-free path of the heat carriers, phonons...

  7. On the ultrafast kinetics of the energy and electron transfer reactions in photosystem I

    Energy Technology Data Exchange (ETDEWEB)

    Slavov, Chavdar Lyubomirov

    2009-07-09

    The subject of the current work is one of the main participants in the light-dependent phase of oxygenic photosynthesis, Photosystem I (PS I). This complex carries an immense number of cofactors: chlorophylls (Chl), carotenoids, quinones, etc, which together with the protein entity exhibit several exceptional properties. First, PS I has an ultrafast light energy trapping kinetics with a nearly 100% quantum efficiency. Secondly, both of the electron transfer branches in the reaction center are suggested to be active. Thirdly, there are some so called 'red' Chls in the antenna system of PS I, absorbing light with longer wavelengths than the reaction center. These 'red' Chls significantly modify the trapping kinetics of PS I. The purpose of this thesis is to obtain better understanding of the above-mentioned, specific features of PS I. This will not merely cast more light on the mechanisms of energy and electron transfer in the complex, but also will contribute to the future developments of optimized artificial light-harvesting systems. In the current work, a number of PS I complexes isolated from different organisms (Thermosynechococcus elongatus, Chlamydomonas reinhardtii, Arabidopsis thaliana) and possessing distinctive features (different macroorganisation, monomers, trimers, monomers with a semibelt of peripheral antenna attached; presence of 'red' Chls) is investigated. The studies are primarily focused on the electron transfer kinetics in each of the cofactor branches in the PS I reaction center, as well as on the effect of the antenna size and the presence of 'red' Chls on the trapping kinetics of PS I. These aspects are explored with the help of several ultrafast optical spectroscopy methods: (i) time-resolved fluorescence ? single photon counting and synchroscan streak camera; and (ii) ultrafast transient absorption. Physically meaningful information about the molecular mechanisms of the energy trapping in PS I is

  8. Stereoselectivity in electron-transfer reactions in chiral media.

    Science.gov (United States)

    Olmstead, Deborah; Hua, Xaio; Osvath, Peter; Lappin, A Graham

    2010-02-07

    The oxidation of [Co(edta)](2-) by [IrCl(6)](2-) proceeds by both inner-sphere and outer-sphere electron-transfer pathways. In the presence of added [Co(en)(3)](3+), the outer-sphere pathway is enhanced. When optically active [Co(en)(3)](3+) is used, the [Co(edta)](-) formed is optically active, reflecting a 1.5% DeltaLambda selectivity. It is proposed that the selectivity arises from preferential formation and reactivity of the DeltaLambda ion pair, {[Co(edta)](2-),[Co(en)(3)](3+)}. Direct reaction of [Co(edta)](-) with [Co(en)(3)](2+) has also been investigated in the optically active solvent, (S)-(-)-1,2-propylene carbonate. The induction is small, forming 0.75% Delta-[Co(en)(3)](3+), consistent with the important role for hydrogen bonding in determining the precursor stereoselectivity to the exclusion of solvent.

  9. Proton-Coupled Electron Transfer: Moving Together and Charging Forward

    Energy Technology Data Exchange (ETDEWEB)

    Hammes-Schiffer, Sharon

    2015-07-22

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pKa’s for molecular electrocatalysts, as well as methods for simulating the nonadiabatic dynamics of photoinduced processes, are also described. Representative applications to PCET in solution, proteins, electrochemistry, and photoinduced processes are presented, highlighting the interplay between theoretical and experimental studies. The current challenges and suggested future directions are outlined for each type of application, concluding with an overall view to the future. The work described herein was supported by National Science Foundation Grant CHE-13-61293 (theory development), National Institutes of Health Grant GM056207 (soybean lipoxygenase), Center for Chemical Innovation of the National Science Foundation Solar Fuels Grant CHE-1305124 (cobalt catalysts), Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (nickel catalysts), and Air Force Office of Scientific Research Award No. FA9550-14-1-0295 (photoinduced PCET).

  10. Revisiting direct electron transfer in nanostructured carbon laccase oxygen cathodes.

    Science.gov (United States)

    Adam, Catherine; Scodeller, Pablo; Grattieri, Matteo; Villalba, Matías; Calvo, Ernesto J

    2016-06-01

    The biocatalytic electroreduction of oxygen has been studied on large surface area graphite and Vulcan® carbon electrodes with adsorbed Trametes trogii laccase. The electrokinetics of the O2 reduction reaction (ORR) was studied at different electrode potentials, O2 partial pressures and concentrations of hydrogen peroxide. Even though the overpotential at 0.25 mA·cm(-2) for the ORR at T1Cu of the adsorbed laccase on carbon is 0.8 V lower than for Pt of similar geometric area, the rate of the reaction and thus the operative current density is limited by the enzyme reaction rate at the T2/T3 cluster site for the adsorbed enzyme. The transition potential for the rate determining step from the direct electron transfer (DET) to the enzyme reaction shifts to higher potentials at higher oxygen partial pressure. Hydrogen peroxide produced by the ORR on bare carbon support participates in an inhibition mechanism, with uncompetitive predominance at high H2O2 concentration, non-competitive contribution can be detected at low inhibitor concentration.

  11. Electron transfer precedes ATP hydrolysis during nitrogenase catalysis

    Science.gov (United States)

    Duval, Simon; Danyal, Karamatullah; Shaw, Sudipta; Lytle, Anna K.; Dean, Dennis R.; Hoffman, Brian M.; Antony, Edwin; Seefeldt, Lance C.

    2013-01-01

    The biological reduction of N2 to NH3 catalyzed by Mo-dependent nitrogenase requires at least eight rounds of a complex cycle of events associated with ATP-driven electron transfer (ET) from the Fe protein to the catalytic MoFe protein, with each ET coupled to the hydrolysis of two ATP molecules. Although steps within this cycle have been studied for decades, the nature of the coupling between ATP hydrolysis and ET, in particular the order of ET and ATP hydrolysis, has been elusive. Here, we have measured first-order rate constants for each key step in the reaction sequence, including direct measurement of the ATP hydrolysis rate constant: kATP = 70 s−1, 25 °C. Comparison of the rate constants establishes that the reaction sequence involves four sequential steps: (i) conformationally gated ET (kET = 140 s−1, 25 °C), (ii) ATP hydrolysis (kATP = 70 s−1, 25 °C), (iii) Phosphate release (kPi = 16 s−1, 25 °C), and (iv) Fe protein dissociation from the MoFe protein (kdiss = 6 s−1, 25 °C). These findings allow completion of the thermodynamic cycle undergone by the Fe protein, showing that the energy of ATP binding and protein–protein association drive ET, with subsequent ATP hydrolysis and Pi release causing dissociation of the complex between the Feox(ADP)2 protein and the reduced MoFe protein. PMID:24062462

  12. Effects of quantum coherence in metalloprotein electron transfer

    Science.gov (United States)

    Dorner, Ross; Goold, John; Heaney, Libby; Farrow, Tristan; Vedral, Vlatko

    2012-09-01

    Many intramolecular electron transfer (ET) reactions in biology are mediated by metal centers in proteins. This process is commonly described by a model of diffusive hopping according to the semiclassical theories of Marcus and Hopfield. However, recent studies have raised the possibility that nontrivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we investigate the potential effects of quantum coherence in biological ET by extending the semiclassical model to allow for the possibility of quantum coherent phenomena using a quantum master equation based on the Holstein Hamiltonian. We test the model on the structurally defined chain of seven iron-sulfur clusters in nicotinamide adenine dinucleotide plus hydrogen:ubiquinone oxidoreductase (complex I), a crucial respiratory enzyme and one of the longest chains of metal centers in biology. Using experimental parameters where possible, we find that, in limited circumstances, a small quantum mechanical contribution can provide a marked increase in the ET rate above the semiclassical diffusive-hopping rate. Under typical biological conditions, our model reduces to well-known diffusive behavior.

  13. Synthetic Applications of Proton-Coupled Electron Transfer.

    Science.gov (United States)

    Gentry, Emily C; Knowles, Robert R

    2016-08-16

    Redox events in which an electron and proton are exchanged in a concerted elementary step are commonly referred to as proton-coupled electron transfers (PCETs). PCETs are known to operate in numerous important biological redox processes, as well as recent inorganic technologies for small molecule activation. These studies suggest that PCET catalysis might also function as a general mode of substrate activation in organic synthesis. Over the past three years, our group has worked to advance this hypothesis and to demonstrate the synthetic utility of PCET through the development of novel catalytic radical chemistries. The central aim of these efforts has been to demonstrate the ability of PCET to homolytically activate a wide variety of common organic functional groups that are energetically inaccessible using known molecular H atom transfer catalysts. To do so, we made use of a simple formalism first introduced by Mayer and co-workers that allowed us to predict the thermodynamic capacity of any oxidant/base or reductant/acid pair to formally add or remove H· from a given substrate. With this insight, we were able to rationally select catalyst combinations thermodynamically competent to homolyze the extraordinarily strong E-H σ-bonds found in many common protic functional groups (BDFEs > 100 kcal/mol) or to form unusually weak bonds to hydrogen via the reductive action of common organic π-systems (BDFEs < 35 kcal/mol). These ideas were reduced to practice through the development of new catalyst systems for reductive PCET activations of ketones and oxidative PCET activation of amide N-H bonds to directly furnish reactive ketyl and amidyl radicals, respectively. In both systems, the reaction outcomes were found to be successfully predicted using the effective bond strength formalism, suggesting that these simple thermochemical considerations can provide useful and actionable insights into PCET reaction design. The ability of PCET catalysis to control

  14. Tailoring Macroscale Response of Mechanical and Heat Transfer Systems by Topology Optimization of Microstructural Details

    DEFF Research Database (Denmark)

    Alexandersen, Joe; Lazarov, Boyan Stefanov

    2015-01-01

    -contrast material parameters is proposed to alleviate the high computational cost associated with solving the discrete systems arising during the topology optimization process. Problems within important engineering areas, heat transfer and linear elasticity, are considered for exemplifying the approach...

  15. Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators

    Science.gov (United States)

    Badalyan, Artavazd; Stahl, Shannon S.

    2016-07-01

    electron-proton-transfer mediators, such as TEMPO, may be used in combination with first-row transition metals, such as copper, to achieve efficient two-electron electrochemical processes, thereby introducing a new concept for the development of non-precious-metal electrocatalysts.

  16. Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators.

    Science.gov (United States)

    Badalyan, Artavazd; Stahl, Shannon S

    2016-07-21

    electron-proton-transfer mediators, such as TEMPO, may be used in combination with first-row transition metals, such as copper, to achieve efficient two-electron electrochemical processes, thereby introducing a new concept for the development of non-precious-metal electrocatalysts.

  17. Ab initio quantum mechanical/molecular mechanical simulation of electron transfer process: fractional electron approach.

    Science.gov (United States)

    Zeng, Xiancheng; Hu, Hao; Hu, Xiangqian; Cohen, Aron J; Yang, Weitao

    2008-03-28

    Electron transfer (ET) reactions are one of the most important processes in chemistry and biology. Because of the quantum nature of the processes and the complicated roles of the solvent, theoretical study of ET processes is challenging. To simulate ET processes at the electronic level, we have developed an efficient density functional theory (DFT) quantum mechanical (QM)/molecular mechanical (MM) approach that uses the fractional number of electrons as the order parameter to calculate the redox free energy of ET reactions in solution. We applied this method to study the ET reactions of the aqueous metal complexes Fe(H(2)O)(6)(2+/3+) and Ru(H(2)O)(6)(2+/3+). The calculated oxidation potentials, 5.82 eV for Fe(II/III) and 5.14 eV for Ru(II/III), agree well with the experimental data, 5.50 and 4.96 eV, for iron and ruthenium, respectively. Furthermore, we have constructed the diabatic free energy surfaces from histogram analysis based on the molecular dynamics trajectories. The resulting reorganization energy and the diabatic activation energy also show good agreement with experimental data. Our calculations show that using the fractional number of electrons (FNE) as the order parameter in the thermodynamic integration process leads to efficient sampling and validate the ab initio QM/MM approach in the calculation of redox free energies.

  18. Electron-transfer acceleration investigated by time resolved infrared spectroscopy.

    Science.gov (United States)

    Vlček, Antonín; Kvapilová, Hana; Towrie, Michael; Záliš, Stanislav

    2015-03-17

    Ultrafast electron transfer (ET) processes are important primary steps in natural and artificial photosynthesis, as well as in molecular electronic/photonic devices. In biological systems, ET often occurs surprisingly fast over long distances of several tens of angströms. Laser-pulse irradiation is conveniently used to generate strongly oxidizing (or reducing) excited states whose reactions are then studied by time-resolved spectroscopic techniques. While photoluminescence decay and UV-vis absorption supply precise kinetics data, time-resolved infrared absorption (TRIR) and Raman-based spectroscopies have the advantage of providing additional structural information and monitoring vibrational energy flows and dissipation, as well as medium relaxation, that accompany ultrafast ET. We will discuss three cases of photoinduced ET involving the Re(I)(CO)3(N,N) moiety (N,N = polypyridine) that occur much faster than would be expected from ET theories. [Re(4-N-methylpyridinium-pyridine)(CO)3(N,N)](2+) represents a case of excited-state picosecond ET between two different ligands that remains ultrafast even in slow-relaxing solvents, beating the adiabatic limit. This is caused by vibrational/solvational excitation of the precursor state and participation of high-frequency quantum modes in barrier crossing. The case of Re-tryptophan assemblies demonstrates that excited-state Trp → *Re(II) ET is accelerated from nanoseconds to picoseconds when the Re(I)(CO)3(N,N) chromophore is appended to a protein, close to a tryptophan residue. TRIR in combination with DFT calculations and structural studies reveals an interaction between the N,N ligand and the tryptophan indole. It results in partial electronic delocalization in the precursor excited state and likely contributes to the ultrafast ET rate. Long-lived vibrational/solvational excitation of the protein Re(I)(CO)3(N,N)···Trp moiety, documented by dynamic IR band shifts, could be another accelerating factor. The last

  19. Generic mechanism of optimal energy transfer efficiency: a scaling theory of the mean first-passage time in exciton systems.

    Science.gov (United States)

    Wu, Jianlan; Silbey, Robert J; Cao, Jianshu

    2013-05-17

    An asymptotic scaling theory is presented using the conceptual basis of trapping-free subspace (i.e., orthogonal subspace) to establish the generic mechanism of optimal efficiency of excitation energy transfer in light-harvesting systems. A quantum state orthogonal to the trap will exhibit noise-assisted transfer, clarifying the significance of initial preparation. For such an initial state, the efficiency is enhanced in the weak damping limit (⟨t⟩ ∼ 1/Γ), and suppressed in the strong damping limit (⟨t⟩ ∼ Γ), analogous to Kramers turnover in classical rate theory. An interpolating expression ⟨t⟩ = A/Γ + B + CΓ quantitatively describes the trapping time over the entire range of the dissipation strength, and predicts the optimal efficiency at Γ(opt) ∼ J for homogenous systems. In the presence of static disorder, the scaling law of transfer time with respect to dephasing rate changes from linear to square root, suggesting a weaker dependence on the environment. The prediction of the scaling theory is verified in a symmetric dendrimer system by numerically exact quantum calculations. Though formulated in the context of excitation energy transfer, the analysis and conclusions apply in general to open quantum processes, including electron transfer, fluorescence emission, and heat conduction.

  20. Electron dynamics and intermolecular energy transfer in aqueous solutions studied by X-ray electron spectroscopy

    Science.gov (United States)

    Winter, Bernd

    2009-03-01

    X-ray photoelectron spectroscopy measurements from a vacuum liquid microjet are performed to investigate the electronic structure of aqueous solutions. Here, focus is on the excited-state dynamics of chloride and hydroxide anions in water, following core-level excitation. A series of Cl^-(aq) charge-transfer-to-solvent (CTTS) states, and their ultrafast relaxation, on the time scale of the core hole, is identified from the occurrence of spectator Auger decay. Resonant oxygen 1s excitation of aqueous hydroxide, in contrast, leads to non-local decay, involving energy transfer into a neighboring water molecule. This channel is argued to arise from the weak hydrogen donor bond of OH^-(aq), and thus identifies a special transient hydration configuration, which can explain hydroxide's unusual and fast transport in water. Analogous measurements from pure water point to a similar relaxation channel, which is concluded from a strong isotope effect. The characteristic resonance spectral features are considerably stronger for H2O(aq) than for D2O(aq). As for OH^-(aq) the results can be understood in terms of energy transfer from the excited water molecule to a neighbor water molecule.

  1. Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles.

    Science.gov (United States)

    Tvrdy, Kevin; Frantsuzov, Pavel A; Kamat, Prashant V

    2011-01-04

    Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO(2), TiO(2), and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO(2)) were not the same as those which showed the highest photocurrent (TiO(2)). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency.

  2. Monitoring Chemical and Biological Electron Transfer Reactions with a Fluorogenic Vitamin K Analogue Probe.

    Science.gov (United States)

    Belzile, Mei-Ni; Godin, Robert; Durantini, Andrés M; Cosa, Gonzalo

    2016-12-21

    We report herein the design, synthesis, and characterization of a two-segment fluorogenic analogue of vitamin K, B-VKQ, prepared by coupling vitamin K3, also known as menadione (a quinone redox center), to a boron-dipyrromethene (BODIPY) fluorophore (a lipophilic reporter segment). Oxidation-reduction reactions, spectroelectrochemical studies, and enzymatic assays conducted in the presence of DT-diaphorase illustrate that the new probe shows reversible redox behavior on par with that of vitamin K, provides a high-sensitivity fluorescence signal, and is compatible with biological conditions, opening the door to monitor remotely (i.e., via imaging) redox processes in real time. In its oxidized form, B-VKQ is non-emissive, while upon reduction to the hydroquinone form, B-VKQH2, BODIPY fluorescence is restored, with emission quantum yield values of ca. 0.54 in toluene. Density functional theory studies validate a photoinduced electron transfer intramolecular switching mechanism, active in the non-emissive quinone form and deactivated upon reduction to the emissive dihydroquinone form. Our results highlight the potential of B-VKQ as a fluorogenic probe to study electron transfer and transport in model systems and biological structures with optimal sensitivity and desirable chemical specificity. Use of such a probe may enable a better understanding of the role that vitamin K plays in biological redox reactions ubiquitous in key cellular processes, and help elucidate the mechanism and pathological significance of these reactions in biological systems.

  3. Solvent Reorganization Energy of Intramolecular Electron Transfer in Peptides Involving Tryptophan and Tyrosine

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ying-Yi; MA Jian-Yi; ZHAO Xiao-Jun; LI Xiang-Yuan

    2008-01-01

    Intramolecular electron transfer(ET)from tyrosine to tryptophan within peptide Trp-(Pro),-Tyr(n=1,2)has been investigated by ab initio calculation associated with a proper consideration of solvent effect by a continuum model.After geometry optimizations of the charge-localized reactant and product,double-well potentials have been constructed by adopting the linear reaction coordinate.The transition state has been determined by finding the crossing point of the potential energy curves.The realistic ET reaction was found complicated in polar solvent,hence the solvent reorganization energy of the electron transfer has received especial attention in this work.Apply-ing the nonequilibrium solvation procedure implemented based on the polarizable continuum model by the authors,the solvent reorganization energy was estimated to be 87.36 kJ/mol for the ET in Trp-Pro-Tyr system and 105.80 kJ/mol for Trp-(Pro)2-Tyr.

  4. Enzymatic cellulose oxidation is linked to lignin by long-range electron transfer.

    Science.gov (United States)

    Westereng, Bjørge; Cannella, David; Wittrup Agger, Jane; Jørgensen, Henning; Larsen Andersen, Mogens; Eijsink, Vincent G H; Felby, Claus

    2015-12-21

    Enzymatic oxidation of cell wall polysaccharides by lytic polysaccharide monooxygenases (LPMOs) plays a pivotal role in the degradation of plant biomass. While experiments have shown that LPMOs are copper dependent enzymes requiring an electron donor, the mechanism and origin of the electron supply in biological systems are only partly understood. We show here that insoluble high molecular weight lignin functions as a reservoir of electrons facilitating LPMO activity. The electrons are donated to the enzyme by long-range electron transfer involving soluble low molecular weight lignins present in plant cell walls. Electron transfer was confirmed by electron paramagnetic resonance spectroscopy showing that LPMO activity on cellulose changes the level of unpaired electrons in the lignin. The discovery of a long-range electron transfer mechanism links the biodegradation of cellulose and lignin and sheds new light on how oxidative enzymes present in plant degraders may act in concert.

  5. 27 CFR 41.115a - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ... electronic fund transfer. 41.115a Section 41.115a Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO..., CIGARETTE PAPERS AND TUBES, AND PROCESSED TOBACCO Puerto Rican Tobacco Products and Cigarette Papers and....115a Payment of tax by electronic fund transfer. (a) General. (1) Each taxpayer who was liable, during...

  6. 27 CFR 40.357 - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ... electronic fund transfer. 40.357 Section 40.357 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO..., CIGARETTE PAPERS AND TUBES, AND PROCESSED TOBACCO Manufacture of Cigarette Papers and Tubes Taxes § 40.357 Payment of tax by electronic fund transfer. (a) General. (1) Each taxpayer who was liable, during a...

  7. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ... electronic fund transfer. 41.63 Section 41.63 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX..., CIGARETTE PAPERS AND TUBES, AND PROCESSED TOBACCO Taxes Customs' Collection of Taxes § 41.63 Payment of tax by electronic fund transfer. (a) Each importer who was liable, during a calendar year, for a gross...

  8. 27 CFR 40.165a - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ... making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and... electronic fund transfer. 40.165a Section 40.165a Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO..., CIGARETTE PAPERS AND TUBES, AND PROCESSED TOBACCO Operations by Manufacturers of Tobacco Products...

  9. 76 FR 67153 - Federal Acquisition Regulation; Submission for OMB Review; Payment by Electronic Fund Transfer

    Science.gov (United States)

    2011-10-31

    ... would enable the Government to make payments under the contract by electronic fund transfer (EFT). The... From the Federal Register Online via the Government Publishing Office ] DEPARTMENT OF DEFENSE... Regulation; Submission for OMB Review; Payment by Electronic Fund Transfer AGENCY: Department of Defense (DOD...

  10. 41 CFR 102-118.70 - Must my agency make all payments via electronic funds transfer?

    Science.gov (United States)

    2010-07-01

    ... payments via electronic funds transfer? 102-118.70 Section 102-118.70 Public Contracts and Property... Services § 102-118.70 Must my agency make all payments via electronic funds transfer? Yes, under 31 U.S.C. 3332, et seq., your agency must make all payments for goods and services via EFT (this includes...

  11. Superexchange coupling and electron transfer in globular proteins via polaron excitations.

    Science.gov (United States)

    Chuev, G N; Lakhno, V D; Ustitnin, M N

    2000-06-01

    The polaron approach is used to treat long-range electron transfersbetween globular proteins. A rate expression for the polaron transfer model is given along with a description of appropriate conditions forits use. Assuming that electrons transfer via a superexchange couplingdue to a polaron excitation, we have estimated the distance dependenceof the rate constant for the self-exchange reactions between globularproteins in solutions. The distance dependence of the polaron coupling andsolvent reorganization energy are provided as a basis forunderstanding and interpreting a long-range electron transfer experiment.The difficulties and problems of the polaron treatment of long-rangeelectron transfers are discussed, and suggestions for new experimentsare made.

  12. Photoinduced energy and electron transfer in rubrene-benzoquinone and rubrene-porphyrin systems

    KAUST Repository

    Khan, Jafar Iqbal

    2014-11-01

    Excited-state electron and energy transfer from singlet excited rubrene (Ru) to benzoquinone (BQ) and tetra-(4-aminophenyl) porphyrin (TAPP) were investigated by steady-state absorption and emission, time-resolved transient absorption, and femtosecond (fs)-nanosecond (ns) fluorescence spectroscopy. The low reduction potential of BQ provides the high probability of electron transfer from the excited Ru to BQ. Steady-state and time-resolved results confirm such an excited electron transfer scenario. On the other hand, strong spectral overlap between the emission of Ru and absorption of TAPP suggests that energy transfer is a possible deactivation pathway of the Ru excited state.

  13. Light harvesting, electron transfer and electron cycling of a native photosynthetic membrane adsorbed onto a gold surface

    NARCIS (Netherlands)

    Magis, G.J; Hollander, den M. -J.; Onderwaater, W. G.; Olsen, J.D.; Hunter, C.N.; Aartsma, T.J.; Frese, R.N.

    2010-01-01

    Photosynthetic membranes comprise a network of light harvesting and reaction center pigment–protein complexes responsible for the primary photoconversion reactions: light absorption, energy transfer and electron cycling. The structural organization of membranes of the purple bacterial species Rb. sp

  14. Ultrafast Photoinduced Electron Transfer in a π-Conjugated Oligomer/Porphyrin Complex

    KAUST Repository

    Aly, Shawkat Mohammede

    2014-10-02

    Controlling charge transfer (CT), charge separation (CS), and charge recombination (CR) at the donor-acceptor interface is extremely important to optimize the conversion efficiency in solar cell devices. In general, ultrafast CT and slow CR are desirable for optimal device performance. In this Letter, the ultrafast excited-state CT between platinum oligomer (DPP-Pt(acac)) as a new electron donor and porphyrin as an electron acceptor is monitored for the first time using femtosecond (fs) transient absorption (TA) spectroscopy with broad-band capability and 120 fs temporal resolution. Turning the CT on/off has been shown to be possible either by switching from an organometallic oligomer to a metal-free oligomer or by controlling the charge density on the nitrogen atom of the porphyrin meso unit. Our time-resolved data show that the CT and CS between DPP-Pt(acac) and cationic porphyrin are ultrafast (approximately 1.5 ps), and the CR is slow (ns time scale), as inferred from the formation and the decay of the cationic and anionic species. We also found that the metallic center in the DPP-Pt(acac) oligomer and the positive charge on the porphyrin are the keys to switching on/off the ultrafast CT process.

  15. Visualizing the non-equilibrium dynamics of photoinduced intramolecular electron transfer with femtosecond X-ray pulses

    DEFF Research Database (Denmark)

    Canton, Sophie E.; Kjær, Kasper S.; Vankó, György;

    2015-01-01

    Ultrafast photoinduced electron transfer preceding energy equilibration still poses many experimental and conceptual challenges to the optimization of photoconversion since an atomic-scale description has so far been beyond reach. Here we combine femtosecond transient optical absorption...... spectroscopy with ultrafast X-ray emission spectroscopy and diffuse X-ray scattering at the SACLA facility to track the non-equilibrated electronic and structural dynamics within a bimetallic donor–acceptor complex that contains an optically dark centre. Exploiting the 100-fold increase in temporal resolution...

  16. Bio-batteries and bio-fuel cells: leveraging on electronic charge transfer proteins.

    Science.gov (United States)

    Kannan, A M; Renugopalakrishnan, V; Filipek, S; Li, P; Audette, G F; Munukutla, L

    2009-03-01

    Bio-fuel cells are alternative energy devises based on bio-electrocatalysis of natural substrates by enzymes or microorganisms. Here we review bio-fuel cells and bio-batteries based on the recent literature. In general, the bio-fuel cells are classified based on the type of electron transfer; mediated electron transfer and direct electron transfer or electronic charge transfer (ECT). The ECT of the bio-fuel cells is critically reviewed and a variety of possible applications are considered. The technical challenges of the bio-fuel cells, like bioelectrocatalysis, immobilization of bioelectrocatalysts, protein denaturation etc. are highlighted and future research directions are discussed leveraging on the use of electron charge transfer proteins. In addition, the packaging aspects of the bio-fuel cells are also analyzed and the found that relatively little work has been done in the engineering development of bio-fuel cells.

  17. Ultrafast electron and energy transfer in dye-sensitized iron oxide and oxyhydroxide nanoparticles

    DEFF Research Database (Denmark)

    Gilbert, Benjamin; Katz, Jordan E.; Huse, Nils

    2013-01-01

    –310 fs were found for all samples. Comparison between TA dynamics on uncoated and dye-sensitized hematite nanoparticles revealed the dye de-excitation pathway to consist of a competition between electron and energy transfer to the nanoparticles. We analyzed the TA data for hematite nanoparticles using...... a four-state model of the dye-sensitized system, finding electron and energy transfer to occur on the same ultrafast timescale. The interfacial electron transfer rates for iron oxides are very close to those previously reported for DCF-sensitized titanium dioxide (for which dye–oxide energy transfer...... photo-initiated interfacial electron transfer. This approach enables time-resolved study of the fate and mobility of electrons within the solid phase. However, complete analysis of the ultrafast processes following dye photoexcitation of the sensitized iron(iii) oxide nanoparticles has not been reported...

  18. Optimal Truncation in Ionization of hydrogen by Electron Impact

    Institute of Scientific and Technical Information of China (English)

    张程华; 牛英煜; 吴炜; 邱卫; 辛君丽; 王晓伟; 王京阳

    2003-01-01

    An analytic expression for the ionization amplitude of hydrogen by electron impact is found to contain a polynomial by an optimal truncation in an asymptotic series and a convergent series. The ionization amplitude, i.e., the transition matrix element on the energy shell, is decomposed into two parts: the structure-scattering factor and correlation factor, based on an approximation of the projectile plane wave in coplanar asymmetric geometries.The contribution of these factors to the triple differential cross section is evaluated using the method of optional truncation of asymptotic and convergent series.

  19. Interfacial electron transfer of Shewanella putrefaciens enhanced by nanoflaky nickel oxide array in microbial fuel cells

    Science.gov (United States)

    Qiao, Yan; Wu, Xiao-Shuai; Li, Chang Ming

    2014-11-01

    A uniform nanoflaky nickel oxide (NiO) array is constructed on carbon cloth via optimized conditions, and further employed as an anode in Shewanella putrefaciens (S. putrefaciens) microbial fuel cells (MFCs). Results indicate that the NiO nanoflakes/carbon cloth anode significantly improves the MFC performance in comparison to the unmodified carbon cloth, delivering about three times higher power density. This attributes to an enhanced interfacial electron transfer rate between bacteria cell and nanoflaky NiO array-modified carbon fiber and improved adhesion of bacteria cells on the modified carbon fiber for more active reaction centers. Considering the facile synthesis process, low cost and long discharging lifetime, this NiO/carbon cloth anode could be very promising to be applied for high performance, large scale MFCs.

  20. Electron transfer catalysis with monolayer protected Au25 clusters

    Science.gov (United States)

    Antonello, Sabrina; Hesari, Mahdi; Polo, Federico; Maran, Flavio

    2012-08-01

    Au25L18 (L = S(CH2)2Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au25L18+ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au25L18+ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au25L18/Au25L18- and the Au25L18+/Au25L18 redox couples as redox mediators. Simulation of the CV curves led to determination of the ET rate constant (kET) values for concerted dissociative ET to the peroxides. The ET free energy ΔG° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log kETvs. ΔG°) relationship. Comparison with the kET obtained using a ferrocene-type donor with a formal potential similar to that of Au25L18/Au25L18- showed that the presence of the capping monolayer affects the ET rate rather significantly, which is attributed to the intrinsic nonadiabaticity of peroxide acceptors.Au25L18 (L = S(CH2)2Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au25L18+ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au25L18+ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au25L18/Au25L18- and

  1. Research on Layout Optimization of Urban Circle Solid Waste Transfer and Disposal Stations

    Directory of Open Access Journals (Sweden)

    Xuhui Li

    2013-08-01

    Full Text Available Based on the Systematic Layout Planning theory and the analysis of transfer stations’ technological processes, a layout optimization model for solid waste transfer and disposal stations was made. The operating units’ layout of the solid waste transfer and disposal stations was simulated and optimized using the genetic algorithm, which could achieve reasonable technological processes, the smallest floor space and the lowest construction cost. The simulation result can also direct the initial engineering design and can also provide reference for similar engineering design methods.

  2. Optimization of radiative heat transfer in hyperbolic metamaterials for thermophotovoltaic applications.

    Science.gov (United States)

    Simovski, Constantin; Maslovski, Stanislav; Nefedov, Igor; Tretyakov, Sergei

    2013-06-17

    Using our recently developed method we analyze the radiative heat transfer in micron-thick multilayer stacks of metamaterials with hyperbolic dispersion. The metamaterials are especially designed for prospective thermophotovoltaic systems. We show that the huge transfer of near-infrared thermal radiation across micron layers of metamaterials is achievable and can be optimized. We suggest an approach to the optimal design of such metamaterials taking into account high temperatures of the emitting medium and the heating of the photovoltaic medium by the low-frequency part of the radiation spectrum. We show that both huge values and frequency selectivity are achievable for the radiative heat transfer in hyperbolic multilayer stacks.

  3. Heat and mass transfer intensification and shape optimization a multi-scale approach

    CERN Document Server

    2013-01-01

    Is the heat and mass transfer intensification defined as a new paradigm of process engineering, or is it just a common and old idea, renamed and given the current taste? Where might intensification occur? How to achieve intensification? How the shape optimization of thermal and fluidic devices leads to intensified heat and mass transfers? To answer these questions, Heat & Mass Transfer Intensification and Shape Optimization: A Multi-scale Approach clarifies  the definition of the intensification by highlighting the potential role of the multi-scale structures, the specific interfacial area, the distribution of driving force, the modes of energy supply and the temporal aspects of processes.   A reflection on the methods of process intensification or heat and mass transfer enhancement in multi-scale structures is provided, including porous media, heat exchangers, fluid distributors, mixers and reactors. A multi-scale approach to achieve intensification and shape optimization is developed and clearly expla...

  4. Communication: Charge transfer dominates over proton transfer in the reaction of nitric acid with gas-phase hydrated electrons

    Science.gov (United States)

    Lengyel, Jozef; Med, Jakub; Slavíček, Petr; Beyer, Martin K.

    2017-09-01

    The reaction of HNO3 with hydrated electrons (H2O)n- (n = 35-65) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and ab initio molecular dynamics simulations. Kinetic analysis of the experimental data shows that OH-(H2O)m is formed primarily via a reaction of the hydrated electron with HNO3 inside the cluster, while proton transfer is not observed and NO3-(H2O)m is just a secondary product. The reaction enthalpy was determined using nanocalorimetry, revealing a quite exothermic charge transfer with -241 ± 69 kJ mol-1. Ab initio molecular dynamics simulations indicate that proton transfer is an allowed reaction pathway, but the overall thermochemistry favors charge transfer.

  5. Industrial Application of Topology Optimization for Combined Conductive and Convective Heat Transfer Problems

    DEFF Research Database (Denmark)

    Zhou, Mingdong; Alexandersen, Joe; Sigmund, Ole

    2016-01-01

    This paper presents an industrial application of topology optimization for combined conductive and convective heat transfer problems. The solution is based on a synergy of computer aided design and engineering software tools from Dassault Systemes. The considered physical problem of steady......-state heat transfer under convection is simulated using SIMULIA-Abaqus. A corresponding topology optimization feature is provided by SIMULIA-Tosca. By following a standard workflow of design optimization, the proposed solution is able to accommodate practical design scenarios and results in efficient...

  6. A Comparison of Electron-Transfer Dynamics inIonic Liquids and Neutral Solvents

    Energy Technology Data Exchange (ETDEWEB)

    Wishart J. F.; Lee, H.Y.; Issa, J.B.; Isied, S.S.; Castner, Jr., E.W.; Pan, Y.; Hussey, C.L.; Lee, K.S.

    2012-03-01

    The effect of ionic liquids on photoinduced electron-transfer reactions in a donor-bridge-acceptor system is examined for two ionic liquid solvents, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide and tributylmethylammonium bis(trifluoromethylsulfonyl)amide. The results are compared with those for the same system in methanol and acetonitrile solution. Electron-transfer rates were measured using time-resolved fluorescence quenching for the donor-bridge-acceptor system comprising a 1-N,1-N-dimethylbenzene-1,4-diamine donor, a proline bridge, and a coumarin 343 acceptor. The photoinduced electron-transfer processes are in the inverted regime (-{Delta}G > {lambda}) in all four solvents, with driving forces of -1.6 to -1.9 eV and estimated reorganization energies of about 1.0 eV. The observed electron-transfer kinetics have broadly distributed rates that are generally slower in the ionic liquids compared to the neutral solvents, which also have narrower rate distributions. To describe the broad distributions of electron-transfer kinetics, we use two different models: a distribution of exponential lifetimes and a discrete sum of exponential lifetimes. Analysis of the donor-acceptor electronic coupling shows that for ionic liquids this intramolecular electron-transfer reaction should be treated using a solvent-controlled electron-transfer model.

  7. Redox potential of the terminal quinone electron acceptor QB in photosystem II reveals the mechanism of electron transfer regulation.

    Science.gov (United States)

    Kato, Yuki; Nagao, Ryo; Noguchi, Takumi

    2016-01-19

    Photosystem II (PSII) extracts electrons from water at a Mn4CaO5 cluster using light energy and then transfers them to two plastoquinones, the primary quinone electron acceptor QA and the secondary quinone electron acceptor QB. This forward electron transfer is an essential process in light energy conversion. Meanwhile, backward electron transfer is also significant in photoprotection of PSII proteins. Modulation of the redox potential (Em) gap of QA and QB mainly regulates the forward and backward electron transfers in PSII. However, the full scheme of electron transfer regulation remains unresolved due to the unknown Em value of QB. Here, for the first time (to our knowledge), the Em value of QB reduction was measured directly using spectroelectrochemistry in combination with light-induced Fourier transform infrared difference spectroscopy. The Em(QB (-)/QB) was determined to be approximately +90 mV and was virtually unaffected by depletion of the Mn4CaO5 cluster. This insensitivity of Em(QB (-)/QB), in combination with the known large upshift of Em(QA (-)/QA), explains the mechanism of PSII photoprotection with an impaired Mn4CaO5 cluster, in which a large decrease in the Em gap between QA and QB promotes rapid charge recombination via QA (-).

  8. Redox potential of the terminal quinone electron acceptor QB in photosystem II reveals the mechanism of electron transfer regulation

    Science.gov (United States)

    Kato, Yuki; Nagao, Ryo; Noguchi, Takumi

    2016-01-01

    Photosystem II (PSII) extracts electrons from water at a Mn4CaO5 cluster using light energy and then transfers them to two plastoquinones, the primary quinone electron acceptor QA and the secondary quinone electron acceptor QB. This forward electron transfer is an essential process in light energy conversion. Meanwhile, backward electron transfer is also significant in photoprotection of PSII proteins. Modulation of the redox potential (Em) gap of QA and QB mainly regulates the forward and backward electron transfers in PSII. However, the full scheme of electron transfer regulation remains unresolved due to the unknown Em value of QB. Here, for the first time (to our knowledge), the Em value of QB reduction was measured directly using spectroelectrochemistry in combination with light-induced Fourier transform infrared difference spectroscopy. The Em(QB−/QB) was determined to be approximately +90 mV and was virtually unaffected by depletion of the Mn4CaO5 cluster. This insensitivity of Em(QB−/QB), in combination with the known large upshift of Em(QA−/QA), explains the mechanism of PSII photoprotection with an impaired Mn4CaO5 cluster, in which a large decrease in the Em gap between QA and QB promotes rapid charge recombination via QA−. PMID:26715751

  9. LADS: Optimizing Data Transfers using Layout-Aware Data Scheduling

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Youngjae [ORNL; Atchley, Scott [ORNL; Vallee, Geoffroy R [ORNL; Shipman, Galen M [ORNL

    2015-01-01

    While future terabit networks hold the promise of signifi- cantly improving big-data motion among geographically distributed data centers, significant challenges must be overcome even on today s 100 gigabit networks to real- ize end-to-end performance. Multiple bottlenecks exist along the end-to-end path from source to sink. Data stor- age infrastructure at both the source and sink and its in- terplay with the wide-area network are increasingly the bottleneck to achieving high performance. In this paper, we identify the issues that lead to congestion on the path of an end-to-end data transfer in the terabit network en- vironment, and we present a new bulk data movement framework called LADS for terabit networks. LADS ex- ploits the underlying storage layout at each endpoint to maximize throughput without negatively impacting the performance of shared storage resources for other users. LADS also uses the Common Communication Interface (CCI) in lieu of the sockets interface to use zero-copy, OS-bypass hardware when available. It can further im- prove data transfer performance under congestion on the end systems using buffering at the source using flash storage. With our evaluations, we show that LADS can avoid congested storage elements within the shared stor- age resource, improving I/O bandwidth, and data transfer rates across the high speed networks.

  10. 77 FR 50243 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-08-20

    ... From the Federal Register Online via the Government Publishing Office ] Vol. 77 Monday, No. 161... that many senders scheduling preauthorized remittance transfers are more concerned with the convenience... than with comparison shopping with pre-payment disclosures for each transfer. Thus, these commenters...

  11. Terawatt x-ray free-electron-laser optimization by transverse electron distribution shaping

    Directory of Open Access Journals (Sweden)

    C. Emma

    2014-11-01

    Full Text Available We study the dependence of the peak power of a 1.5 Å Terawatt (TW, tapered x-ray free-electron laser (FEL on the transverse electron density distribution. Multidimensional optimization schemes for TW hard x-ray free-electron lasers are applied to the cases of transversely uniform and parabolic electron beam distributions and compared to a Gaussian distribution. The optimizations are performed for a 200 m undulator and a resonant wavelength of λ_{r}=1.5  Å using the fully three-dimensional FEL particle code genesis. The study shows that the flatter transverse electron distributions enhance optical guiding in the tapered section of the undulator and increase the maximum radiation power from a maximum of 1.56 TW for a transversely Gaussian beam to 2.26 TW for the parabolic case and 2.63 TW for the uniform case. Spectral data also shows a 30%–70% reduction in energy deposited in the sidebands for the uniform and parabolic beams compared with a Gaussian. An analysis of the transverse coherence of the radiation shows the coherence area to be much larger than the beam spotsize for all three distributions, making coherent diffraction imaging experiments possible.

  12. Investigating the electronic structure of the Atox1 copper(I) transfer mechanism with density functional theory.

    Science.gov (United States)

    Pitts, Amanda L; Hall, Michael B

    2013-09-16

    To maintain correct copper homeostasis, the body relies on ion binding metallochaperones, cuprophilic ligands, and proteins to move copper around as a complexed metal. The most common binding site for Cu(I) proteins is the CX1X2C motif, where X1 and X2 are nonconserved residues. Although this binding site motif is well established, the mechanistic and electronic details for the transfer of Cu(I) between two binding sites have not been fully established, in particular, whether the transfer is dissociative or associative or if the electron-rich Cu(I)-Cys interactions influence the transfer. In this work, we investigated the electronic structure of the Cu(I)-S interactions during the copper transfer between Atox1 and a metal binding domain on the ATP7A or ATP7B protein. Initially, three Cu(I) methylthiolate complexes, [Cu(SCH3)2](-1), [Cu(SCH3)3](-2), [Cu(SCH3)4](-3), were investigated with density functional theory (DFT) to fully elucidate the electronic structure and bonding between Cu(I) and thiolate species. The two-coordinate, linear species with a C-S-S-C dihedral angle of ∼90° is the lowest energy conformation because the filled π antibonding orbitals are stabilized in this geometry. The importance of π-overlap is also seen with the trigonal planar, three-coordinate Cu(I) complex, which is similarly stabilized. A corresponding four-coordinate species could not be consistently optimized, so it was concluded that tetrahedral coordination was not likely to be stable. The transfer of Cu(I) from the Atox1 metallochaperone to a metal binding domain of the ATP7A or ATP7B protein was then modeled by using the CGGC Atox1 binding site for the donor model and the dithiotreitol ligand (DTT) for the acceptor model. The two- and three-coordinate intermediates calculated along the five-step transfer mechanism converged to near optimal Cu-S π-overlap for the respective geometries, which demonstrates that the electronic structure in this electron-rich environment

  13. Excess-Electron Transfer in DNA by a Fluctuation-Assisted Hopping Mechanism.

    Science.gov (United States)

    Lin, Shih-Hsun; Fujitsuka, Mamoru; Majima, Tetsuro

    2016-02-04

    The dynamics of excess-electron transfer in DNA has attracted the attention of scientists from all kinds of research fields because of its importance in biological processes. To date, several studies on excess-electron transfer in consecutive adenine (A):thymine (T) sequences in donor-DNA-acceptor systems have been published. However, the reported excess-electron transfer rate constants for consecutive T's are in the range of 10(10)-10(11) s(-1) depending on the photosensitizing electron donor, which provides various driving forces for excess-electron injection into DNA. In this study, we employed a strongly electron-donating photosensitizer, a dimer of 3,4-ethylenedioxythiophene (2E), and an electron acceptor, diphenylacetylene (DPA), to synthesize a series of modified DNA oligomers (2-Tn, n = 3-6) in order to investigate the excess-electron transfer dynamics in these donor-DNA-acceptor systems using femtosecond laser flash photolysis. The relation between the free energy change for charge injection and the excess-electron transfer rate among consecutive T's provided an intrinsic excess-electron hopping rate constant of (3.8 ± 1.5) × 10(10) s(-1) in the DNA, which is consistent with the fluctuation frequency of the DNA sugar backbone and bases (3.3 × 10(10) s(-1)). Thus, we discuss the effect of structural fluctuations on the excess-electron hopping in DNA.

  14. Where Does the Electron Go? Stable and Metastable Peptide Cation Radicals Formed by Electron Transfer

    Science.gov (United States)

    Pepin, Robert; Layton, Erik D.; Liu, Yang; Afonso, Carlos; Tureček, František

    2017-01-01

    Electron transfer to doubly and triply charged heptapeptide ions containing polar residues Arg, Lys, and Asp in combination with nonpolar Gly, Ala, and Pro or Leu generates stable and metastable charge-reduced ions, (M + 2H)+●, in addition to standard electron-transfer dissociation (ETD) fragment ions. The metastable (M + 2H)+● ions spontaneously dissociate upon resonant ejection from the linear ion trap, giving irregularly shaped peaks with offset m/ z values. The fractions of stable and metastable (M + 2H)+● ions and their mass shifts depend on the presence of Pro-4 and Leu-4 residues in the peptides, with the Pro-4 sequences giving larger fractions of the stable ions while showing smaller mass shifts for the metastables. Conversion of the Asp and C-terminal carboxyl groups to methyl esters further lowers the charge-reduced ion stability. Collisional activation and photodissociation at 355 nm of mass-selected (M + 2H)+● results in different dissociations that give sequence specific MS3 spectra. With a single exception of charge-reduced (LKGLADR + 2H)+●, the MS3 spectra do not produce ETD sequence fragments of the c and z type. Hence, these (M + 2H)+● ions are covalent radicals, not ion-molecule complexes, undergoing dramatically different dissociations in the ground and excited electronic states. The increased stability of the Pro-4 containing (M + 2H)+● ions is attributed to radicals formed by opening of the Pro ring and undergoing further stabilization by hydrogen atom migrations. UV-VIS photodissociation action spectroscopy and time-dependent density functional theory calculations are used in a case in point study of the stable (LKGPADR + 2H)+● ion produced by ETD. In contrast to singly-reduced peptide ions, doubly reduced (M + 3H)+ ions are stable only when formed from the Pro-4 precursors and show all characteristics of even electron ions regarding no photon absorption at 355 nm or ion-molecule reactions, and exhibiting proton driven

  15. Model-based optimization of tapered free-electron lasers

    Directory of Open Access Journals (Sweden)

    Alan Mak

    2015-04-01

    Full Text Available The energy extraction efficiency is a figure of merit for a free-electron laser (FEL. It can be enhanced by the technique of undulator tapering, which enables the sustained growth of radiation power beyond the initial saturation point. In the development of a single-pass x-ray FEL, it is important to exploit the full potential of this technique and optimize the taper profile a_{w}(z. Our approach to the optimization is based on the theoretical model by Kroll, Morton, and Rosenbluth, whereby the taper profile a_{w}(z is not a predetermined function (such as linear or exponential but is determined by the physics of a resonant particle. For further enhancement of the energy extraction efficiency, we propose a modification to the model, which involves manipulations of the resonant particle’s phase. Using the numerical simulation code GENESIS, we apply our model-based optimization methods to a case of the future FEL at the MAX IV Laboratory (Lund, Sweden, as well as a case of the LCLS-II facility (Stanford, USA.

  16. Studies on electron transfer reactions of Keggin-type mixed addenda heteropolytungstovanadophosphates with NADH

    Indian Academy of Sciences (India)

    Ponnusamy Sami; Kasi Rajasekaran

    2009-03-01

    The coenzyme nicotinamide adenine dinucleotide (NADH) undergoes facile electron transfer reaction with vanadium (V) substituted Keggin-type heteropolyanions (HPA) [PVVW11O40]4- (PV1) and [PV$^{V}_{2}$W10O40]5- (PV2) in aqueous phosphate buffer of pH 6 at ambient temperature. Electrochemical and optical studies show that the stoichiometry of the reaction is 1 : 2 (NADH : HPA). EPR and optical studies show that HPA act as one electron acceptor and the products of electron transfer reactions are one electron reduced heteropoly blues (HPB), viz. [PVIVW11O40]5- and [PVIVVVW10O40]6-. Oxygraph measurements show that there is no uptake of molecular oxygen during the course of reaction. The reaction proceeds through multi-step electron-proton-electron transfer mechanism, with rate limiting initial one electron transfer from NADH to HPA by outer sphere electron transfer process. Bimolecular rate constant for electron transfer reaction between NADH and PV2 in phosphate buffer of pH = 6 has been determined spectrophotometrically.

  17. Electron transfer and catalysis with high-valent metal-oxo complexes.

    Science.gov (United States)

    Fukuzumi, Shunichi

    2015-04-21

    High-valent metal-oxo complexes are produced by reductive activation of dioxygen via reduction of metal complexes with reductants and dioxygen. Photoinduced electron transfer from substrates to metal complexes with dioxygen also leads to the generation of high-valent metal-oxo complexes that can oxygenate substrates. In such a case metal complexes act as a photocatalyst to oxygenate substrates with dioxygen. High-valent metal-oxo complexes are also produced by proton-coupled electron-transfer oxidation of metal complexes by one-electron oxidants with water, oxygenating substrates to regenerate metal complexes. In such a case metal complexes act as a catalyst for electron-transfer oxygenation of substrates by one-electron oxidants with water that acts as an oxygen source. The one-electron oxidants which can oxidize metal complexes can be replaced by much weaker oxidants by a combination of redox photocatalysts and metal complexes. Thus, photocatalytic oxygenation of substrates proceeds via photoinduced electron transfer from a photocatalyst to reductants followed by proton-coupled electron transfer oxidation of metal complexes with the oxidized photocatalyst to produce high-valent metal-oxo complexes that oxygenate substrates. Thermal and photoinduced electron-transfer catalytic reactions of high-valent metal-oxo complexes for oxygenation of substrates using water or dioxygen as an oxygen source are summarized in this perspective.

  18. Standardless quantification by parameter optimization in electron probe microanalysis

    Energy Technology Data Exchange (ETDEWEB)

    Limandri, Silvina P. [Instituto de Fisica Enrique Gaviola (IFEG), CONICET (Argentina); Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, Medina Allende s/n, (5016) Cordoba (Argentina); Bonetto, Rita D. [Centro de Investigacion y Desarrollo en Ciencias Aplicadas Dr. Jorge Ronco (CINDECA), CONICET, 47 Street 257, (1900) La Plata (Argentina); Facultad de Ciencias Exactas, Universidad Nacional de La Plata, 1 and 47 Streets (1900) La Plata (Argentina); Josa, Victor Galvan; Carreras, Alejo C. [Instituto de Fisica Enrique Gaviola (IFEG), CONICET (Argentina); Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, Medina Allende s/n, (5016) Cordoba (Argentina); Trincavelli, Jorge C., E-mail: trincavelli@famaf.unc.edu.ar [Instituto de Fisica Enrique Gaviola (IFEG), CONICET (Argentina); Facultad de Matematica, Astronomia y Fisica, Universidad Nacional de Cordoba, Medina Allende s/n, (5016) Cordoba (Argentina)

    2012-11-15

    A method for standardless quantification by parameter optimization in electron probe microanalysis is presented. The method consists in minimizing the quadratic differences between an experimental spectrum and an analytical function proposed to describe it, by optimizing the parameters involved in the analytical prediction. This algorithm, implemented in the software POEMA (Parameter Optimization in Electron Probe Microanalysis), allows the determination of the elemental concentrations, along with their uncertainties. The method was tested in a set of 159 elemental constituents corresponding to 36 spectra of standards (mostly minerals) that include trace elements. The results were compared with those obtained with the commercial software GENESIS Spectrum Registered-Sign for standardless quantification. The quantifications performed with the method proposed here are better in the 74% of the cases studied. In addition, the performance of the method proposed is compared with the first principles standardless analysis procedure DTSA for a different data set, which excludes trace elements. The relative deviations with respect to the nominal concentrations are lower than 0.04, 0.08 and 0.35 for the 66% of the cases for POEMA, GENESIS and DTSA, respectively. - Highlights: Black-Right-Pointing-Pointer A method for standardless quantification in EPMA is presented. Black-Right-Pointing-Pointer It gives better results than the commercial software GENESIS Spectrum. Black-Right-Pointing-Pointer It gives better results than the software DTSA. Black-Right-Pointing-Pointer It allows the determination of the conductive coating thickness. Black-Right-Pointing-Pointer It gives an estimation for the concentration uncertainties.

  19. Optimization adn Guidance of Very Low-Thrust Transfers to Geostatoinary Orbit

    Science.gov (United States)

    Gil-Fernandez, J.; Tarabini, L.; Graziano, M.; Gomez-Tierno, M. A.

    A new hybrid direct-indirect optimization algorithm is presented to compute the minimum-time transfer between two orbits, including the phasing with a desired spacecraft. Very-low thrust means several hundred revolutions to perform the large change in orbital elements. The optimal control solution of the fast-evolution problem combined with a direct method for the secular trajectory avoids the numerical instability arising in very long propagations, decreases the computational time, reduces the sensitivity to the initial guess and provides a feasible transfer at every optimization step. Optimization of transfers from GTO to GEO is presented and two types of trajectories are analysed, sub-synchronous (apogee constrained below GEO altitude) and super-synchronous (free apogee altitude). The optimization of a transfer from LEO to a very high orbit (11 x 23 RE) is presented, showing the applicability of the method to different problems. A guidance algorithm is presented to compensate the deviations of the real trajectory from the optimal one due to off-nominal conditions. The results in closed-loop simulation of the guidance scheme to compensate deterministic perturbations not considered in the optimization show good performances in both analysed missions.

  20. Concerted proton-coupled electron transfer from a metal-hydride complex.

    Science.gov (United States)

    Bourrez, Marc; Steinmetz, Romain; Ott, Sascha; Gloaguen, Frederic; Hammarström, Leif

    2014-02-01

    Metal hydrides are key intermediates in the catalytic reduction of protons and CO2 as well as in the oxidation of H2. In these reactions, electrons and protons are transferred to or from separate acceptors or donors in bidirectional protoncoupled electron transfer (PCET) steps. The mechanistic interpretation of PCET reactions of metal hydrides has focused on the stepwise transfer of electrons and protons. A concerted transfer may, however, occur with a lower reaction barrier and therefore proceed at higher catalytic rates. Here we investigate the feasibility of such a reaction by studying the oxidation–deprotonation reactions of a tungsten hydride complex. The rate dependence on the driving force for both electron transfer and proton transfer—employing different combinations of oxidants and bases—was used to establish experimentally the concerted, bidirectional PCET of a metal-hydride species. Consideration of the findings presented here in future catalyst designs may lead to more-efficient catalysts.

  1. A Thesis on Design Optimization of Heat Sink in Power Electronics

    Directory of Open Access Journals (Sweden)

    P.Chennakesavarao

    2014-10-01

    Full Text Available The heat sinks are used in electronic systems to remove heat from the chip and effectively transfer it to the ambient. The heat sink geometry is designed by the mechanical engineers with the primary aim of reducing the thermal resistance of the heat sink for better cooling in the electronic systems. Due to the proximity of the heat sink with the ICs, the RF fields created by RF currents in the ICs/PCBs gets coupled to heat sinks. Hence, the coupled RF current can cause radiated emission. This radiated noise from the device can couple and disturb the functioning of the nearby electronic systems. Also this radiated emission from the device poses a problem to the system compliance with respect to EMI/EMC regulations. The international EMI/EMC standards require the radiated emission from the electronic devices to be kept below the specified limits. As a result the design of Heat Sink is very important factor for the efficient operation of the electronic equipment. In this project design optimization of a Heat sink in a Power amplifier is performed to reduce the weight and size .Power amplifier is electronic equipment mounted in an army vehicle. The power modules inside the amplifier generates a heat of 1440 Watts and a temperature of 140 0c.Two Heat sinks are used to dissipate the heat generated inside the equipment and maintain a temperature of less than 850c. The existing heat sink which is being used is weighing around 10.3kgs and height of 51mm; as a result the unit is very robust. The objective of my project is To design & optimize the heat sink to reduce the weight and size. The optimized heat sink should also dissipate heat generated by power modules and maintain a temperature of less than 850c inside. To achieve the design a steady state thermal analysis will be performed on the heat sink and plot the Temperature distribution on the fins. Based on the above analysis results we will increase/decrease the number of fins, thickness of fins, and

  2. High throughput electron transfer from carbon dots to chloroplast: a rationale of enhanced photosynthesis

    Science.gov (United States)

    Chandra, Sourov; Pradhan, Saheli; Mitra, Shouvik; Patra, Prasun; Bhattacharya, Ankita; Pramanik, Panchanan; Goswami, Arunava

    2014-03-01

    A biocompatible amine functionalized fluorescent carbon dots were developed and isolated for gram scale applications. Such carbogenic quantum dots can strongly conjugate over the surface of the chloroplast and due to that strong interaction the former can easily transfer electrons towards the latter by assistance of absorbed light or photons. An exceptionally high electron transfer from carbon dots to the chloroplast can directly effect the whole chain electron transfer pathway in a light reaction of photosynthesis, where electron carriers play an important role in modulating the system. As a result, carbon dots can promote photosynthesis by modulating the electron transfer process as they are capable of fastening the conversion of light energy to the electrical energy and finally to the chemical energy as assimilatory power (ATP and NADPH).A biocompatible amine functionalized fluorescent carbon dots were developed and isolated for gram scale applications. Such carbogenic quantum dots can strongly conjugate over the surface of the chloroplast and due to that strong interaction the former can easily transfer electrons towards the latter by assistance of absorbed light or photons. An exceptionally high electron transfer from carbon dots to the chloroplast can directly effect the whole chain electron transfer pathway in a light reaction of photosynthesis, where electron carriers play an important role in modulating the system. As a result, carbon dots can promote photosynthesis by modulating the electron transfer process as they are capable of fastening the conversion of light energy to the electrical energy and finally to the chemical energy as assimilatory power (ATP and NADPH). Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06079a

  3. Enhanced Performance of Dye-Sensitized Solar Cells with Nanostructure Graphene Electron Transfer Layer

    Directory of Open Access Journals (Sweden)

    Chih-Hung Hsu

    2014-01-01

    Full Text Available The utilization of nanostructure graphene thin films as electron transfer layer in dye-sensitized solar cells (DSSCs was demonstrated. The effect of a nanostructure graphene thin film in DSSC structure was examined. The nanostructure graphene thin films provides a great electron transfer channel for the photogenerated electrons from TiO2 to indium tin oxide (ITO glass. Obvious improvements in short-circuit current density of the DSSCs were observed by using the graphene electron transport layer modified photoelectrode. The graphene electron transport layer reduces effectively the back reaction in the interface between the ITO transparent conductive film and the electrolyte in the DSSC.

  4. Sequential energy and electron transfer in a three-component system aligned on a clay nanosheet.

    Science.gov (United States)

    Fujimura, Takuya; Ramasamy, Elamparuthi; Ishida, Yohei; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, Vaidhyanathan

    2016-02-21

    To achieve the goal of energy transfer and subsequent electron transfer across three molecules, a phenomenon often utilized in artificial light harvesting systems, we have assembled a light absorber (that also serves as an energy donor), an energy acceptor (that also serves as an electron donor) and an electron acceptor on the surface of an anionic clay nanosheet. Since neutral organic molecules have no tendency to adsorb onto the anionic surface of clay, a positively charged water-soluble organic capsule was used to hold neutral light absorbers on the above surface. A three-component assembly was prepared by the co-adsorption of a cationic bipyridinium derivative, cationic zinc porphyrin and cationic octaamine encapsulated 2-acetylanthracene on an exfoliated anionic clay surface in water. Energy and electron transfer phenomena were monitored by steady state fluorescence and picosecond time resolved fluorescence decay. The excitation of 2-acetylanthracene in the three-component system resulted in energy transfer from 2-acetylanthracene to zinc porphyrin with 71% efficiency. Very little loss due to electron transfer from 2-acetylanthracene in the cavitand to the bipyridinium derivative was noticed. Energy transfer was followed by electron transfer from the zinc porphyrin to the cationic bipyridinium derivative with 81% efficiency. Analyses of fluorescence decay profiles confirmed the occurrence of energy transfer and subsequent electron transfer. Merging the concepts of supramolecular chemistry and surface chemistry we realized sequential energy and electron transfer between three hydrophobic molecules in water. Exfoliated transparent saponite clay served as a matrix to align the three photoactive molecules at a close distance in aqueous solutions.

  5. Allosteric control of internal electron transfer in cytochrome cd1 nitrite reductase

    DEFF Research Database (Denmark)

    Farver, Ole; Kroneck, Peter M H; Zumft, Walter G

    2003-01-01

    Cytochrome cd1 nitrite reductase is a bifunctional multiheme enzyme catalyzing the one-electron reduction of nitrite to nitric oxide and the four-electron reduction of dioxygen to water. Kinetics and thermodynamics of the internal electron transfer process in the Pseudomonas stutzeri enzyme have...

  6. Photoinduced electron transfer processes in oligothiophene/C60 composite films

    NARCIS (Netherlands)

    Janssen, R.A.J.; Christiaans, M.P.T.; Pakbaz, K.; Moses, D.; Hummelen, Jan C.; Sariciftci, N.S.

    1995-01-01

    We present near steady-state photoinduced absorption (PIA) spectroscopy and steady-state light-induced electron spin resonance (LESR) studies on photoinduced electron transfer reactions in composite films of well defined α-oligothiophenes (Tn, n=6, 7, 9, and 11) as electron donor with

  7. Photoinduced electron transfer processes in oligothiophene/C60 composite films

    NARCIS (Netherlands)

    Janssen, R.A.J.; Christiaans, M.P.T.; Pakbaz, K.; Moses, D.; Hummelen, Jan C.; Sariciftci, N.S.

    1995-01-01

    We present near steady-state photoinduced absorption (PIA) spectroscopy and steady-state light-induced electron spin resonance (LESR) studies on photoinduced electron transfer reactions in composite films of well defined α-oligothiophenes (Tn, n=6, 7, 9, and 11) as electron donor with buckminsterful

  8. High throughput electron transfer from carbon dots to chloroplast: a rationale of enhanced photosynthesis.

    Science.gov (United States)

    Chandra, Sourov; Pradhan, Saheli; Mitra, Shouvik; Patra, Prasun; Bhattacharya, Ankita; Pramanik, Panchanan; Goswami, Arunava

    2014-04-07

    A biocompatible amine functionalized fluorescent carbon dots were developed and isolated for gram scale applications. Such carbogenic quantum dots can strongly conjugate over the surface of the chloroplast and due to that strong interaction the former can easily transfer electrons towards the latter by assistance of absorbed light or photons. An exceptionally high electron transfer from carbon dots to the chloroplast can directly effect the whole chain electron transfer pathway in a light reaction of photosynthesis, where electron carriers play an important role in modulating the system. As a result, carbon dots can promote photosynthesis by modulating the electron transfer process as they are capable of fastening the conversion of light energy to the electrical energy and finally to the chemical energy as assimilatory power (ATP and NADPH).

  9. Optimal aeroassisted orbital transfer with plane change using collocation and nonlinear programming

    Science.gov (United States)

    Shi, Yun. Y.; Nelson, R. L.; Young, D. H.

    1990-01-01

    The fuel optimal control problem arising in the non-planar orbital transfer employing aeroassisted technology is addressed. The mission involves the transfer from high energy orbit (HEO) to low energy orbit (LEO) with orbital plane change. The basic strategy here is to employ a combination of propulsive maneuvers in space and aerodynamic maneuvers in the atmosphere. The basic sequence of events for the aeroassisted HEO to LEO transfer consists of three phases. In the first phase, the orbital transfer begins with a deorbit impulse at HEO which injects the vehicle into an elliptic transfer orbit with perigee inside the atmosphere. In the second phase, the vehicle is optimally controlled by lift and bank angle modulations to perform the desired orbital plane change and to satisfy heating constraints. Because of the energy loss during the turn, an impulse is required to initiate the third phase to boost the vehicle back to the desired LEO orbital altitude. The third impulse is then used to circularize the orbit at LEO. The problem is solved by a direct optimization technique which uses piecewise polynomial representation for the state and control variables and collocation to satisfy the differential equations. This technique converts the optimal control problem into a nonlinear programming problem which is solved numerically. Solutions were obtained for cases with and without heat constraints and for cases of different orbital inclination changes. The method appears to be more powerful and robust than other optimization methods. In addition, the method can handle complex dynamical constraints.

  10. Conceptual modeling to optimize the haul and transfer of municipal solid waste.

    Science.gov (United States)

    Komilis, D P

    2008-11-01

    Two conceptual mixed integer linear optimization models were developed to optimize the haul and transfer of municipal solid waste (MSW) prior to landfilling. One model is based on minimizing time (h/d), whilst the second model is based on minimizing total cost (euro/d). Both models aim to calculate the optimum pathway to haul MSW from source nodes (waste production nodes, such as urban centers or municipalities) to sink nodes (landfills) via intermediate nodes (waste transfer stations). The models are applicable provided that the locations of the source, intermediate and sink nodes are fixed. The basic input data are distances among nodes, average vehicle speeds, haul cost coefficients (in euro/ton km), equipment and facilities' operating and investment cost, labor cost and tipping fees. The time based optimization model is easier to develop, since it is based on readily available data (distances among nodes). It can be used in cases in which no transfer stations are included in the system. The cost optimization model is more reliable compared to the time model provided that accurate cost data are available. The cost optimization model can be a useful tool to optimally allocate waste transfer stations in a region and can aid a community to investigate the threshold distance to a landfill above which the construction of a transfer station becomes financially beneficial. A sensitivity analysis reveals that queue times at the landfill or at the waste transfer station are key input variables. In addition, the waste transfer station ownership and the initial cost data affect the optimum path. A case study at the Municipality of Athens is used to illustrate the presented models.

  11. From charge transfer to electron transfer in halogen-bonded complexes of electrophilic bromocarbons with halide anions.

    Science.gov (United States)

    Rosokha, Sergiy V; Traversa, Alfredo

    2015-02-21

    Experimental and computational studies of the halogen-bonded complexes, [R-Br, X(-)], of bromosubstituted electrophiles, R-Br, and halide anions, X(-), revealed that decrease of a gap between the frontier orbitals of interacting species led to reduction of the energy of the optical charge-transfer transition and to increase in the ground-state charge transfer (X(-) → R-Br) in their associates. These variations were accompanied by weakening of the intramolecular, C-Br, and strengthening of the intermolecular, BrX(-), bonds. In the limit of the strongest electron donor-acceptor pairs, formation of the halogen-bonded complexes was followed by the oxidation of iodide to triiodide, which took place despite the fact that the I(-) → R-Br electron-transfer step was highly endergonic and the calculated outer-sphere rate constant was negligibly small. However, the calculated barrier for the inner-sphere electron transfer accompanied by the halogen transfer, R-BrI(-) → R˙Br-I(-)˙, was nearly 24 kcal mol(-1) lower as compared to that calculated for the outer-sphere process and the rate constant of such reaction was consistent with the experimental kinetics. A dramatic decrease of the electron-transfer barriers (leading to 18-orders of magnitude increase of the rate constant) was related to the strong electronic coupling of the donor and acceptor within the halogen-bonded precursor complex, as well as to the lower solvent reorganization energy and the successor-complex stabilization.

  12. Robust method optimization strategy-a useful tool for method transfer: the case of SFC.

    Science.gov (United States)

    Dispas, Amandine; Lebrun, Pierre; Andri, Bertyl; Rozet, Eric; Hubert, Philippe

    2014-01-01

    The concept of Quality by Design (QbD) is now well established in pharmaceutical industry and should be applied to the development of any analytical methods. In this context, the key concept of Design Space (DS) was introduced in the field of analytical method optimization. In chromatographic words, the DS is the space of chromatographic conditions that will ensure the quality of peaks separation, thus DS is a zone of robustness. In the present study, the interest of robust method optimization strategy was investigated in the context of direct method transfer from sending to receiving laboratory. The benefit of this approach is to speed up the method life cycle by performing only one quantitative validation step in the final environment of method use. A Supercritical Fluid Chromatography (SFC) method previously developed was used as a case study in this work. Moreover, the interest of geometric transfer was investigated simultaneously in order to stress a little bit more the transfer exercise and, by the way, emphasize the additional benefit of DS strategy in this particular context. Three successful transfers were performed on two column geometries. In order to compare original and transferred methods, the observed relative retention times (RT) were modelled as a function of the predicted relative RT and of the method type (original or transferred). The observed relative RT of the original and transferred methods are not statistically different and thus the method transfer is successfully achieved thanks to the robust optimization strategy. Furthermore, the analytical method was improved considering analysis time (reduced five times) and peak capacity (increased three times). To conclude, the advantage of using a DS strategy implemented for the optimization and transfer of SFC method was successfully demonstrated in this work.

  13. Intramolecular electron transfer in cytochrome cd(1) nitrite reductase from Pseudomonas stutzeri; kinetics and thermodynamics

    DEFF Research Database (Denmark)

    Farver, Ole; Kroneck, Peter M H; Zumft, Walter G

    2002-01-01

    , internal electron transfer between these sites is an inherent element in the catalytic cycle of this enzyme. We have investigated the internal electron transfer reaction employing pulse radiolytically produced N-methyl nicotinamide radicals as reductant which reacts solely with the heme-c in an essentially...... diffusion controlled process. Following this initial step, the reduction equivalent is equilibrating between the c and d(1) heme sites in a unimolecular process (k=23 s(-1), 298 K, pH 7.0) and an equilibrium constant of 1.0. The temperature dependence of this internal electron transfer process has been...

  14. Theoretical Study of Electron Transfer in Bimolecular System of NH3 and H2O

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Mulliken, NPA, MK and CHelpG population analyses have been accomplished at the level of MP2/6-31G(d,p) for the title system. The variations of four kinds of charges on NH3 with intermolecular distance infer that electron transfers from NH3 to H2O. MK and CHelpG population analyses indicate more electron transfer than Mulliken and NPA ones. The atomic charges resulted from MK and CHelpG schemes infer that electron transfers from N in NH3 to H in H2O, which confirms that this bimolecular complex possesses linear structure as H3N…HOH.

  15. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid

    Science.gov (United States)

    Rury, Aaron S.; Sorenson, Shayne; Dawlaty, Jahan M.

    2016-03-01

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm-1 oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology.

  16. Design and optimization of pulsed Chemical Exchange Saturation Transfer MRI using a multiobjective genetic algorithm.

    Science.gov (United States)

    Yoshimaru, Eriko S; Randtke, Edward A; Pagel, Mark D; Cárdenas-Rodríguez, Julio

    2016-02-01

    Pulsed Chemical Exchange Saturation Transfer (CEST) MRI experimental parameters and RF saturation pulse shapes were optimized using a multiobjective genetic algorithm. The optimization was carried out for RF saturation duty cycles of 50% and 90%, and results were compared to continuous wave saturation and Gaussian waveform. In both simulation and phantom experiments, continuous wave saturation performed the best, followed by parameters and shapes optimized by the genetic algorithm and then followed by Gaussian waveform. We have successfully demonstrated that the genetic algorithm is able to optimize pulse CEST parameters and that the results are translatable to clinical scanners.

  17. Heat transfer optimization of SCO2 porous flow based on Brinkman model

    Directory of Open Access Journals (Sweden)

    Lin David T.W.

    2016-01-01

    Full Text Available The purpose of this study is to obtain the optimal operating condition in order to find the maximum supercritical CO2 heat extraction in the enhanced geothermal system (EGS. In this study, the heat transfer model conjugated with the Brinkman model is used to evaluate the thermal behavior in the reservoir of the EGS. This numerical model is validated by experiment. Optimization is processed based on the Nelder-Mead approach. The optimal operating conditions are proposed with different pressure, porosity. This study will build the optimal platform of heat source of geothermal power plant.

  18. Syntrophic growth with direct interspecies electron transfer as the primary mechanism for energy exchange.

    Science.gov (United States)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Aklujkar, Muktak; Liu, Fanghua; Shrestha, Minita; Summers, Zarath M; Malvankar, Nikhil; Flores, Dan Carlo; Lovley, Derek R

    2013-12-01

    Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy to support cell growth. In order to investigate this, co-cultures of Geobacter metallireducens, which can transfer electrons to wild-type G. sulfurreducens via DIET, were established with a citrate synthase-deficient G. sulfurreducens strain that can receive electrons for respiration through DIET only. In a medium with ethanol as the electron donor and fumarate as the electron acceptor, co-cultures with the citrate synthase-deficient G. sulfurreducens strain metabolized ethanol as fast as co-cultures with wild-type, but the acetate that G. metallireducens generated from ethanol oxidation accumulated. The lack of acetate metabolism resulted in less fumarate reduction and lower cell abundance of G. sulfurreducens. RNAseq analysis of transcript abundance was consistent with a lack of acetate metabolism in G. sulfurreducens and revealed gene expression levels for the uptake hydrogenase, formate dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration. © 2013 John Wiley & Sons Ltd and Society for Applied Microbiology.

  19. Gradient type optimization methods for electronic structure calculations

    CERN Document Server

    Zhang, Xin; Wen, Zaiwen; Zhou, Aihui

    2013-01-01

    The density functional theory (DFT) in electronic structure calculations can be formulated as either a nonlinear eigenvalue or direct minimization problem. The most widely used approach for solving the former is the so-called self-consistent field (SCF) iteration. A common observation is that the convergence of SCF is not clear theoretically while approaches with convergence guarantee for solving the latter are often not competitive to SCF numerically. In this paper, we study gradient type methods for solving the direct minimization problem by constructing new iterations along the gradient on the Stiefel manifold. Global convergence (i.e., convergence to a stationary point from any initial solution) as well as local convergence rate follows from the standard theory for optimization on manifold directly. A major computational advantage is that the computation of linear eigenvalue problems is no longer needed. The main costs of our approaches arise from the assembling of the total energy functional and its grad...

  20. Role of coherence and delocalization in photo-induced electron transfer at organic interfaces

    Science.gov (United States)

    Abramavicius, V.; Pranculis, V.; Melianas, A.; Inganäs, O.; Gulbinas, V.; Abramavicius, D.

    2016-09-01

    Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces.

  1. Role of protein fluctuation correlations in electron transfer in photosynthetic complexes.

    Science.gov (United States)

    Nesterov, Alexander I; Berman, Gennady P

    2015-04-01

    We consider the dependence of the electron transfer in photosynthetic complexes on correlation properties of random fluctuations of the protein environment. The electron subsystem is modeled by a finite network of connected electron (exciton) sites. The fluctuations of the protein environment are modeled by random telegraph processes, which act either collectively (correlated) or independently (uncorrelated) on the electron sites. We derived an exact closed system of first-order linear differential equations with constant coefficients, for the average density matrix elements and for their first moments. Under some conditions, we obtained analytic expressions for the electron transfer rates and found the range of parameters for their applicability by comparing with the exact numerical simulations. We also compared the correlated and uncorrelated regimes and demonstrated numerically that the uncorrelated fluctuations of the protein environment can, under some conditions, either increase or decrease the electron transfer rates.

  2. The Role of Protein Fluctuation Correlations in Electron Transfer in Photosynthetic Complexes

    CERN Document Server

    Nesterov, Alexander I

    2014-01-01

    We consider the dependence of the electron transfer in photosynthetic complexes on correlation properties of random fluctuations of the protein environment. The electron subsystem is modeled by a finite network of connected electron (exciton) sites. The fluctuations of the protein environment are modeled by random telegraph processes, which act either collectively (correlated) or independently (uncorrelated) on the electron sites. We derived an exact closed system of first-order linear differential equations with constant coefficients, for the average density matrix elements and for their first moments. Under some conditions, we obtain analytic expressions for the electron transfer rates. We compare the correlated and uncorrelated regimes, and demonstrated numerically that the uncorrelated fluctuations of the protein environment can, under some conditions, either increase or decrease the electron transfer rates.

  3. Effect of a physical phase plate on contrast transfer in an aberration-corrected transmission electron microscope.

    Science.gov (United States)

    Gamm, B; Schultheiss, K; Gerthsen, D; Schröder, R R

    2008-08-01

    In this theoretical study we analyze contrast transfer of weak-phase objects in a transmission electron microscope, which is equipped with an aberration corrector (C(s)-corrector) in the imaging lens system and a physical phase plate in the back focal plane of the objective lens. For a phase shift of pi/2 between scattered and unscattered electrons induced by a physical phase plate, the sine-type phase contrast transfer function is converted into a cosine-type function. Optimal imaging conditions could theoretically be achieved if the phase shifts caused by the objective lens defocus and lens aberrations would be equal to zero. In reality this situation is difficult to realize because of residual aberrations and varying, non-zero local defocus values, which in general result from an uneven sample surface topography. We explore the conditions--i.e. range of C(s)-values and defocus--for most favourable contrast transfer as a function of the information limit, which is only limited by the effect of partial coherence of the electron wave in C(s)-corrected transmission electron microscopes. Under high-resolution operation conditions we find that a physical phase plate improves strongly low- and medium-resolution object contrast, while improving tolerance to defocus and C(s)-variations, compared to a microscope without a phase plate.

  4. Optimized Data Transfers Based on the OpenCL Event Management Mechanism

    Directory of Open Access Journals (Sweden)

    Hiroyuki Takizawa

    2015-01-01

    Full Text Available In standard OpenCL programming, hosts are supposed to control their compute devices. Since compute devices are dedicated to kernel computation, only hosts can execute several kinds of data transfers such as internode communication and file access. These data transfers require one host to simultaneously play two or more roles due to the need for collaboration between the host and devices. The codes for such data transfers are likely to be system-specific, resulting in low portability. This paper proposes an OpenCL extension that incorporates such data transfers into the OpenCL event management mechanism. Unlike the current OpenCL standard, the main thread running on the host is not blocked to serialize dependent operations. Hence, an application can easily use the opportunities to overlap parallel activities of hosts and compute devices. In addition, the implementation details of data transfers are hidden behind the extension, and application programmers can use the optimized data transfers without any tricky programming techniques. The evaluation results show that the proposed extension can use the optimized data transfer implementation and thereby increase the sustained data transfer performance by about 18% for a real application accessing a big data file.

  5. Electron Beam Melting and Refining of Metals: Computational Modeling and Optimization

    National Research Council Canada - National Science Library

    Katia Vutova; Veliko Donchev

    2013-01-01

    ..., instrument engineering, electronics, etc. A time-dependent 3D axis-symmetrical heat model for simulation of thermal transfer in metal ingots solidified in a water-cooled crucible at electron beam melting and refining (EBMR) is developed...

  6. Optimal paths for a light-driven engine with a linear phenomenological heat transfer law

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    An irreversible light-driven engine is described in this paper, in which the heat transfer between the working fluid and the environment obeys a linear phenomenological heat transfer law [ q ∝Δ(T -1)], with a working fluid composed of the bimolecular reacting system 2SO 3 F■S 2 O 6 F2. Piston trajectories maximizing work output and minimizing entropy generation are determined for such an engine with rate-dependent loss mechanisms of friction and heat leakage. The optimal control theory is applied to determine the optimal configurations of the piston motion trajectory and the fluid temperature. Numerical examples for the optimal configuration are provided, and the obtained results are compared with those derived with Newtonian heat transfer law [ q ∝Δ(T )].

  7. Optimal state transfer of a single dissipative two-level system

    Science.gov (United States)

    Jirari, Hamza; Wu, Ning

    2016-04-01

    Optimal state transfer of a single two-level system (TLS) coupled to an Ohmic boson bath via off-diagonal TLS-bath coupling is studied by using optimal control theory. In the weak system-bath coupling regime where the time-dependent Bloch-Redfield formalism is applicable, we obtain the Bloch equation to probe the evolution of the dissipative TLS in the presence of a time-dependent external control field. By using the automatic differentiation technique to compute the gradient for the cost functional, we calculate the optimal transfer integral profile that can achieve an ideal transfer within a dimer system in the Fenna-Matthews-Olson (FMO) model. The robustness of the control profile against temperature variation is also analyzed.

  8. Optimal Design and Analysis of the Stepped Core for Wireless Power Transfer Systems

    Directory of Open Access Journals (Sweden)

    Xiu Zhang

    2016-01-01

    Full Text Available The key of wireless power transfer technology rests on finding the most suitable means to improve the efficiency of the system. The wireless power transfer system applied in implantable medical devices can reduce the patients’ physical and economic burden because it will achieve charging in vitro. For a deep brain stimulator, in this paper, the transmitter coil is designed and optimized. According to the previous research results, the coils with ferrite core can improve the performance of the wireless power transfer system. Compared with the normal ferrite core, the stepped core can produce more uniform magnetic flux density. In this paper, the finite element method (FEM is used to analyze the system. The simulation results indicate that the core loss generated in the optimal stepped ferrite core can reduce about 10% compared with the normal ferrite core, and the efficiency of the wireless power transfer system can be increased significantly.

  9. Optimal Control of Population Transfer in Three-Level A System with Genetic Algorithms

    Institute of Scientific and Technical Information of China (English)

    ZHANG Xiang-Yun; SUN Zhen-Rong; CHEN Guo-Liang; WANG Zu-Geng; XU Zhi-Zhan; LI Ru-Xin

    2004-01-01

    Population transfer in a three-level A system is simulated numerically and optimized. Almost complete population transfer from |1〉 to |3〉 is achieved by a genetic algorithm while the population in state |2〉 reached minimum over the entire evolution at the same time. The result shows that the optimal pulse sequence is the well-known stimulated Raman adiabatic passage (STIRAP) scheme. The detuning of pump pulse and Stokes pulse △p and △s with the opposite sign and the chirps χp and χs with the same sign are in favour of the complete and robust population transfer for few-cycle laser pulse. Rabi frequencies Ωp and Ωs have insensitive effects on the complete population transfer during a large scope of their ratio when they are large enough.

  10. Theoretical Analysis for Heat Transfer Optimization in Subcritical Electrothermal Energy Storage Systems

    Directory of Open Access Journals (Sweden)

    Peng Hu

    2017-02-01

    Full Text Available Electrothermal energy storage (ETES provides bulk electricity storage based on heat pump and heat engine technologies. A subcritical ETES is described in this paper. Based on the extremum principle of entransy dissipation, a geometry model is developed for heat transfer optimization for subcritical ETES. The exergy during the heat transfer process is deduced in terms of entropy production. The geometry model is validated by the extremum principle of entropy production. The theoretical analysis results show that the extremum principle of entransy dissipation is an effective criterion for the optimization, and the optimum heat transfer for different cases with the same mass flux or pressure has been discussed. The optimum heat transfer can be achieved by adjusting the mass flux and pressure of the working fluid. It also reveals that with the increase of mass flux, there is a minimum exergy in the range under consideration, and the exergy decreases with the increase of the pressure.

  11. On the connection of semiclassical instanton theory with Marcus theory for electron transfer in solution.

    Science.gov (United States)

    Shushkov, Philip

    2013-06-14

    We present a derivation of Marcus theory of electron transfer in solution starting from semiclassical instanton theory. The conventional semiclassical instanton theory provides an inadequate description of the electron transfer process in the inverted Marcus regime. This has been attributed to the lack of backscattering in the product region, which is represented as a semi-infinite continuum of states. For electron transfer processes in condensed phase, the electronic states in the acceptor well are bound, which violates the continuum assumption. We show by detailed analysis of the minimum action path of a model system for electron transfer that the proper tunneling coordinate is a delocalized, "bead-count" mode. The tunneling mode is analytically continued in the complex plane as in the traditional derivation. Unlike the traditional analysis where the method of steepest descent is used, the tunneling coordinate is treated as a quasi-zero mode. This feature allows including the influence of backscattering in the acceptor well and leads to the recovery of the Marcus formula for the rate of electron transfer. The results have implications on the performance of ring polymer molecular dynamics for the study of electron transfer dynamics.

  12. Pulse radiolytic studies of electron transfer processes and applications to solar photochemistry. Progress report

    Energy Technology Data Exchange (ETDEWEB)

    Neta, P.

    1995-02-01

    The pulse radiolysis technique is applied to the study of electron transfer processes in a variety of chemical systems. Reactive intermediates are produced in solution by electron pulse irradiation and the kinetics of their reactions are followed by time resolved absorption spectrophotometry. Complementary experiments are carried out with excimer laser flash photolysis. These studies are concerned with mechanisms, kinetics, and thermodynamics of reactions of organic and inorganic radicals and unstable oxidation states of metal ions. Reactions are studied in both aqueous and non-aqueous solutions. The studies focus on the unique ability of pulse radiolysis to provide absolute rate constants for reactions of many inorganic radicals and organic peroxyl radicals, species that are key intermediates in many chemical processes. A special concern of this work is the study of electron transfer reactions of metalloporphyrins, which permits evaluation of these molecules as intermediates in solar energy conversion. Metalloporphyrins react with free radicals via electron transfer, involving the ligand or the metal center, or via bonding to the metal, leading to a variety of chemical species whose behavior is also investigated. The highlights of the results during the past three years are summarized below under the following sections: (a) electron transfer reactions of peroxyl radicals, concentrating on the characterization of new peroxyl radicals derived from vinyl, phenyl, other aryl, and pyridyl; (b) solvent effects on electron transfer reactions of inorganic and organic peroxyl radicals, including reactions with porphyrins, and (c) electron transfer and alkylation reactions of metalloporphyrins and other complexes.

  13. The optimal path of piston motion for Otto cycle with linear phenomenological heat transfer law

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    An Otto cycle engine with internal and external irreversibilities of friction and heat leakage, in which the heat transfer between the working fluid and the environment obeys linear phenomenological heat transfer law [q ∝△(T -1)], is studied in this paper. The optimal piston motion trajectory for maximizing the work output per cycle is derived for the fixed total cycle time and fuel consumed per cycle. Optimal control theory is applied to determine the optimal piston trajectories for the cases of with and without piston acceleration constraint on each stroke and the optimal distribution of the total cycle time among the strokes. The optimal piston motion with acceleration constraint for each stroke consists of three segments, including initial maximum acceleration and final maximum deceleration boundary segments, respectively. Numerical examples for optimal configuration are provided, and the obtained results are compared with those obtained with Newton’s heat transfer law [q ∝△(T )]. The results also show that optimizing the piston motion can improve power and efficiency of the engine by more than 9%. This is primarily due to the decrease in heat leakage loss on the initial portion of the power stroke.

  14. Optimization of multi-revolution low-thrust transfer based on modified direct method

    Institute of Scientific and Technical Information of China (English)

    CUI Ping-yuan; SHANG Hai-bin; REN Yuan; LUAN En-jie

    2008-01-01

    A modified direct optimization method is proposed to solve the optimal muhi-revolution transfer with low-thrust between Earth-orbits. First, through parametefizing the control steering angles by costate variables, the search space of free parameters has been decreased. Then, in order to obtain the global optimal solution ef-fectively and robustly, the simulated annealing and penalty function strategies were used to handle the con-straints, and a GA/SQP hybrid optimization algorithm was utilized to solve the parameter optimization problem, in which, a feasible suboptimal solution obtained by GA was submitted as an initial parameter set to SQP for re-finement. Comparing to the classical direct method, this novel method has fewer free parameters, needs not ini-tial guesses, and has higher computation precision. An optimal-fuel transfer problem from LEO to GEO was taken as an example to validate the proposed approach. The results of simulation indicate that our approach is a-vailable to solve the problem of optimal multi-revolution transfer between Earth-orbits.

  15. The optimal path of piston motion for Otto cycle with linear phenomenological heat transfer law

    Institute of Scientific and Technical Information of China (English)

    XIA ShaoJun; CHEN LinGen; SUN FengRui

    2009-01-01

    An Otto cycle engine with internal and external irreversibilities of friction and heat leakage, in which the heat transfer between the working fluid and the environment obeys linear phenomenological heat transfer law [q∝△(T-1)], is studied in this paper. The optimal piston motion trajectory for maximizing the work output per cycle is derived for the fixed total cycle time and fuel consumed per cycle. Optimal control theory is applied to determine the optimal piston trajectories for the cases of with and without piston acceleration constraint on each stroke and the optimal distribution of the total cycle time among the strokes. The optimal piston motion with acceleration constraint for each stroke consists of three segments, including initial maximum acceleration and final maximum deceleration boundary segments,respectively. Numerical examples for optimal configuration are provided, and the obtained results are compared with those obtained with Newton's heat transfer law [q∝△(T)]. The results also show that optimizing the piston motion can improve power and efficiency of the engine by more than 9%. This is primarily due to the decrease in heat leakage loss on the initial portion of the power stroke.

  16. Electron Transfer in Flavodoxin-based Redox Maquettes

    NARCIS (Netherlands)

    Alagaratnam, S.

    2005-01-01

    Small redox proteins play the role of electron taxis in the cell, picking electrons up at one location and delivering them at another. While it is known that these reactions are the basis for the processes of energy generation by respiration and photosynthesis, the means by which these 'taxis' recog

  17. An Electronic Structure Approach to Charge Transfer and Transport in Molecular Building Blocks for Organic Optoelectronics

    Science.gov (United States)

    Hendrickson, Heidi Phillips

    A fundamental understanding of charge separation in organic materials is necessary for the rational design of optoelectronic devices suited for renewable energy applications and requires a combination of theoretical, computational, and experimental methods. Density functional theory (DFT) and time-dependent (TD)DFT are cost effective ab-initio approaches for calculating fundamental properties of large molecular systems, however conventional DFT methods have been known to fail in accurately characterizing frontier orbital gaps and charge transfer states in molecular systems. In this dissertation, these shortcomings are addressed by implementing an optimally-tuned range-separated hybrid (OT-RSH) functional approach within DFT and TDDFT. The first part of this thesis presents the way in which RSH-DFT addresses the shortcomings in conventional DFT. Environmentally-corrected RSH-DFT frontier orbital energies are shown to correspond to thin film measurements for a set of organic semiconducting molecules. Likewise, the improved RSH-TDDFT description of charge transfer excitations is benchmarked using a model ethene dimer and silsesquioxane molecules. In the second part of this thesis, RSH-DFT is applied to chromophore-functionalized silsesquioxanes, which are currently investigated as candidates for building blocks in optoelectronic applications. RSH-DFT provides insight into the nature of absorptive and emissive states in silsesquioxanes. While absorption primarily involves transitions localized on one chromophore, charge transfer between chromophores and between chromophore and silsesquioxane cage have been identified. The RSH-DFT approach, including a protocol accounting for complex environmental effects on charge transfer energies, was tested and validated against experimental measurements. The third part of this thesis addresses quantum transport through nano-scale junctions. The ability to quantify a molecular junction via spectroscopic methods is crucial to their

  18. Electron impact excitation of SO2 - Differential, integral, and momentum transfer cross sections

    Science.gov (United States)

    Vuskovic, L.; Trajmar, S.

    1982-01-01

    Electron impact excitation of the electronic states of SO2 was investigated. Differential, integral, and inelastic momentum transfer cross sections were obtained by normalizing the relative measurements to the elastic cross sections. The cross sections are given for seven spectral ranges of the energy-loss spectra extending from the lowest electronic state to near the first ionization limit. Most of the regions represent the overlap of several electronic transitions. No measurements for these cross sections have been reported previously.

  19. [Long-range electron transfer in globular proteins by polaron excitation].

    Science.gov (United States)

    Lakhno, V L; Chuev, G N

    1997-01-01

    Considering polaron model, we have calculated an electron state localized in the protein heme. Using these calculations: the electron density and electron energy, we estimated the self-exchange rate constant for cyt c (horse heart), its reorganization energy, matrix element, and dependence of this rate on the distance between hemes. The results are compared with the experimental data and other theoretical estimations. We discuss the role of polaron excitations in the long-range electron transfer in globular proteins.

  20. Study on Synergistic Mechanism of Inhibitor Mixture Based on Electron Transfer Behavior

    Science.gov (United States)

    Han, Peng; He, Yang; Chen, Changfeng; Yu, Haobo; Liu, Feng; Yang, Hong; Ma, Yue; Zheng, Yanjun

    2016-01-01

    Mixing is an important method to improve the performance of surfactants due to their synergistic effect. The changes in bonding interaction and adsorption structure of IM and OP molecules before and after co-adsorbed on Fe(001) surface is calculated by DFTB+ method. It is found that mixture enable the inhibitor molecules with higher EHOMO donate more electrons while the inhibitor molecules with lower ELUMO accept more electrons, which strengthens the bonding interaction of both inhibitor agent and inhibitor additive with metal surface. Meanwhile, water molecules in the compact layer of double electric layer are repulsed and the charge transfer resistance during the corrosion process increases. Accordingly, the correlation between the frontier orbital (EHOMO and ELUMO of inhibitor molecules and the Fermi level of metal) and inhibition efficiency is determined. Finally, we propose a frontier orbital matching principle for the synergistic effect of inhibitors, which is verified by electrochemical experiments. This frontier orbital matching principle provides an effective quantum chemistry calculation method for the optimal selection of inhibitor mixture. PMID:27671332

  1. Study on Synergistic Mechanism of Inhibitor Mixture Based on Electron Transfer Behavior

    Science.gov (United States)

    Han, Peng; He, Yang; Chen, Changfeng; Yu, Haobo; Liu, Feng; Yang, Hong; Ma, Yue; Zheng, Yanjun

    2016-09-01

    Mixing is an important method to improve the performance of surfactants due to their synergistic effect. The changes in bonding interaction and adsorption structure of IM and OP molecules before and after co-adsorbed on Fe(001) surface is calculated by DFTB+ method. It is found that mixture enable the inhibitor molecules with higher EHOMO donate more electrons while the inhibitor molecules with lower ELUMO accept more electrons, which strengthens the bonding interaction of both inhibitor agent and inhibitor additive with metal surface. Meanwhile, water molecules in the compact layer of double electric layer are repulsed and the charge transfer resistance during the corrosion process increases. Accordingly, the correlation between the frontier orbital (EHOMO and ELUMO of inhibitor molecules and the Fermi level of metal) and inhibition efficiency is determined. Finally, we propose a frontier orbital matching principle for the synergistic effect of inhibitors, which is verified by electrochemical experiments. This frontier orbital matching principle provides an effective quantum chemistry calculation method for the optimal selection of inhibitor mixture.

  2. An optimized surface plasmon photovoltaic structure using energy transfer between discrete nano-particles.

    Science.gov (United States)

    Lin, Albert; Fu, Sze-Ming; Chung, Yen-Kai; Lai, Shih-Yun; Tseng, Chi-Wei

    2013-01-14

    Surface plasmon enhancement has been proposed as a way to achieve higher absorption for thin-film photovoltaics, where surface plasmon polariton(SPP) and localized surface plasmon (LSP) are shown to provide dense near field and far field light scattering. Here it is shown that controlled far-field light scattering can be achieved using successive coupling between surface plasmonic (SP) nano-particles. Through genetic algorithm (GA) optimization, energy transfer between discrete nano-particles (ETDNP) is identified, which enhances solar cell efficiency. The optimized energy transfer structure acts like lumped-element transmission line and can properly alter the direction of photon flow. Increased in-plane component of wavevector is thus achieved and photon path length is extended. In addition, Wood-Rayleigh anomaly, at which transmission minimum occurs, is avoided through GA optimization. Optimized energy transfer structure provides 46.95% improvement over baseline planar cell. It achieves larger angular scattering capability compared to conventional surface plasmon polariton back reflector structure and index-guided structure due to SP energy transfer through mode coupling. Via SP mediated energy transfer, an alternative way to control the light flow inside thin-film is proposed, which can be more efficient than conventional index-guided mode using total internal reflection (TIR).

  3. An electron-transfer photochromic crystalline MOF accompanying photoswitchable luminescence in a host-guest system.

    Science.gov (United States)

    Liu, Yu-Shuang; Luo, Yu-Hui; Li, Li; Zhang, Hong

    2017-03-23

    A new electron transfer type photoactive host-guest supramolecule was constructed by introducing (CH3)2NH2(+) cations to the MOF framework. The resulting compound 1 exhibits reversible photochromic property without using photochromic components, resulting from photoinduced electron-transfer between the electron-rich anionic framework and the electron-deficient guest ions. In addition, a photoluminescence "on/off switch" occurs during the coloration-decoloration process. The raw materials are non-poisonous and harmless, hence compound 1 may be more cost-effective, clean, and harmless to the heath than existing photochromic materials.

  4. 77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...

    Science.gov (United States)

    2012-06-08

    ... Fiscal Service Financial Management Service; Proposed Collection of Information: Electronic Transfer Account (ETA) Financial Agency Agreement AGENCY: Financial Management Service, Fiscal Service, Treasury. ACTION: Notice and Request for comments. SUMMARY: The Financial Management Service, as part of its...

  5. 77 FR 71035 - Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT...

    Science.gov (United States)

    2012-11-28

    ... Fiscal Service Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT) Market Research Study AGENCY: Financial Management Service, Fiscal Service, Treasury. ACTION: Notice and Request for comments. SUMMARY: The Financial Management Service, as part of its continuing...

  6. 77 FR 10373 - Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid...

    Science.gov (United States)

    2012-02-22

    ... AGENCY 40 CFR Part 98 RIN 2060-AR09 Greenhouse Gas Reporting Program: Electronics Manufacturing... category of the Greenhouse Gas Reporting Rule related to fluorinated heat transfer fluids. More... INFORMATION CONTACT: Carole Cook, Climate Change Division, Office of Atmospheric Programs...

  7. Photoinduced electron transfer reactions of ruthenium(II)-complexes containing amino acid with quinones.

    Science.gov (United States)

    Eswaran, Rajkumar; Kalayar, Swarnalatha; Paulpandian, Muthu Mareeswaran; Seenivasan, Rajagopal

    2014-05-01

    With the aim of mimicking, at basic level the photoinduced electron transfer process in the reaction center of photosystem II, ruthenium(II)-polypyridyl complexes, carrying amino acids were synthesized and studied their photoinduced electron transfer reactions with quinones by steady state and time resolved measurements. The reaction of quinones with excited state of ruthenium(II)-complexes, I-V in acetonitrile has been studied by luminescence quenching technique and the rate constant, k(q), values are close to the diffusion controlled rate. The detection of the semiquinone anion radical in this system using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. The semiclassical theory of electron transfer has been successfully applied to the photoluminescence quenching of Ru(II)-complexes with quinones.

  8. Design of a Molecular Memory Device: The Electron Transfer Shift Register Memory

    Science.gov (United States)

    Beratan, D.

    1993-01-01

    A molecular shift register memory at the molecular level is described. The memory elements consist of molecules can exit in either an oxidized or reduced state and the bits are shifted between the cells with photoinduced electron transfer reactions.

  9. Controlling an electron-transfer reaction at a metal surface by manipulating reactant motion and orientation.

    Science.gov (United States)

    Bartels, Nils; Krüger, Bastian C; Auerbach, Daniel J; Wodtke, Alec M; Schäfer, Tim

    2014-12-08

    The loss or gain of vibrational energy in collisions of an NO molecule with the surface of a gold single crystal proceeds by electron transfer. With the advent of new optical pumping and orientation methods, we can now control all molecular degrees of freedom important to this electron-transfer-mediated process, providing the most detailed look yet into the inner workings of an electron-transfer reaction and showing how to control its outcome. We find the probability of electron transfer increases with increasing translational and vibrational energy as well as with proper orientation of the reactant. However, as the vibrational energy increases, translational excitation becomes unimportant and proper orientation becomes less critical. One can understand the interplay of all three control parameters from simple model potentials. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. ElectronTransfer Induced Ring Opening of α-Epoxyketones: Spirodioxolane Formation

    Directory of Open Access Journals (Sweden)

    Farzad Nikpour

    2002-01-01

    Full Text Available Stereospecific formation of spirodioxolanes has been observed on electron transfer induced ring opening of α-epoxyketones by 2,4,6-triphenylpyrylium tetrafluoroborate in the presence of cyclohexanone

  11. Heterogeneous electron transfer kinetics and electrocatalytic behaviour of mixed self-assembled ferrocenes and SWCNT layers

    CSIR Research Space (South Africa)

    Nkosi, D

    2010-01-01

    Full Text Available The electron transfer dynamics and electrocatalytic behaviour of ferrocene-terminated self-assembled monolayers (SAMs), co-adsorbed with single-walled carbon nanotubes (SWCNTs) on a gold electrode, have been interrogated for the first time...

  12. 36 CFR 1235.48 - What documentation must agencies transfer with electronic records?

    Science.gov (United States)

    2010-07-01

    ... NARA Form 14097, Technical Description for Transfer of Electronic Records, for magnetic tape media, and... layouts, data element definitions, and code translation tables (codebooks) for coded data. Data element...

  13. Performance Analysis and Optimization of a Solar Powered Stirling Engine with Heat Transfer Considerations

    Directory of Open Access Journals (Sweden)

    Chia-En Ho

    2012-09-01

    Full Text Available This paper investigates the optimization of the performance of a solar powered Stirling engine based on finite-time thermodynamics. Heat transference in the heat exchangers between a concentrating solar collector and the Stirling engine is studied. The irreversibility of a Stirling engine is considered with the heat transfer following Newton's law. The power generated by a Stirling engine is used as an objective function for maximum power output design with the concentrating solar collector temperature and the engine thermal efficiency as the optimization parameters. The maximum output power of engine and its corresponding system parameters are determined using a genetic algorithm.

  14. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'yov, Ilia A

    2015-12-22

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  15. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

    Science.gov (United States)

    Sjulstok, Emil; Olsen, Jógvan Magnus Haugaard; Solov'Yov, Ilia A.

    2015-12-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  16. Bi-Level Optimization for Available Transfer Capability Evaluation in Deregulated Electricity Market

    Directory of Open Access Journals (Sweden)

    Beibei Wang

    2015-11-01

    Full Text Available Available transfer capability (ATC is the transfer capability remaining in the physical transmission network for further commercial activity over and above already committed uses which needs to be posted in the electricity market to facilitate competition. ATC evaluation is a complicated task including the determination of total transfer capability (TTC and existing transfer capability (ETC. In the deregulated electricity market, ETC is decided by the independent system operator’s (ISO’s economic dispatch (ED. TTC can then be obtained by a continuation power flow (CPF method or by an optimal power flow (OPF method, based on the given ED solutions as well as the ETC. In this paper, a bi-level optimization framework for the ATC evaluation is proposed in which ATC results can be obtained simultaneously with the ED and ETC results in the deregulated electricity market. In this bi-level optimization model, ATC evaluation is formulated as the upper level problem and the ISO’s ED is the lower level problem. The bi-level model is first converted to a mathematic program with equilibrium constraints (MPEC by recasting the lower level problem as its Karush-Kuhn-Tucher (KKT optimality condition. Then, the MPEC is transformed into a mixed-integer linear programming (MILP problem, which can be solved with the help of available optimization software. In addition, case studies on PJM 5-bus, IEEE 30-bus, and IEEE 118-bus systems are presented to demonstrate the proposed methodology.

  17. Characterization and modelling of interspecies electron transfer mechanisms and microbial community dynamics of a syntrophic association

    DEFF Research Database (Denmark)

    Nagarajan, Harish; Embree, Mallory; Rotaru, Amelia-Elena

    2013-01-01

    Syntrophic associations are central to microbial communities and thus have a fundamental role in the global carbon cycle. Despite biochemical approaches describing the physiological activity of these communities, there has been a lack of a mechanistic understanding of the relationship between...... metallireducens and Geobacter sulfurreducens. Genome-scale modelling of direct interspecies electron transfer reveals insights into the energetics of electron transfer mechanisms. While G. sulfurreducens adapts to rapid syntrophic growth by changes at the genomic and transcriptomic level, G. metallireducens...

  18. Electron Transfer Studies of Ruthenium(II) Complexes with Biologically Important Phenolic Acids and Tyrosine.

    Science.gov (United States)

    Rajeswari, Angusamy; Ramdass, Arumugam; Muthu Mareeswaran, Paulpandian; Rajagopal, Seenivasan

    2016-03-01

    The ruthenium(II) complexes having 2,2'-bipyridine and phenanthroline derivatives are synthesized and characterized. The photophysical properties of these complexes at pH 12.5 are studied. The electron transfer reaction of biologically important phenolic acids and tyrosine are studied using absorption, emission and transient absorption spectral techniques. Semiclassical theory is applied to calculate the rate of electron transfer between ruthenium(II) complexes and biologically important phenolic acids.

  19. Enhanced ionization of embedded clusters by Electron Transfer Mediated Decay in helium nanodroplets

    CERN Document Server

    LaForge, A C; Gokhberg, K; von Vangerow, J; Kryzhevoi, N; O'Keeffe, P; Ciavardini, A; Krishnan, S R; Coreno, M; Prince, K C; Richter, R; Moshammer, R; Pfeifer, T; Cederbaum, L; Stienkemeier, F; Mudrich, M

    2015-01-01

    Here, we report the observation of electron transfer mediated decay For Mg clusters embedded in He nanodroplets. The process is mediated by the initial ionization of helium followed by an autoionization process by electron transfer in the Mg clusters. The photoelectron spectrum (PES) reveal a low energy ETMD peak. For Mg clusters larger than 7 atoms, we observe the formation of stable doubly ionized clusters. The process is shown to be the primamry ionization mechanism for embedded clusters.

  20. Single-sphere model for solvent reorganization energy and its application to electron transfer

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In this work, the authors give detailed deductions and develop the single-sphere model of solvent reorganization energy in electron transfer with point dipole approximation. At the level of DFT/6- 31++G**, the electron transfer between 7,7,8,8-tetracyanoquinodimethane and its anion has been investigated. Using the novel single-sphere model, the authors evaluate the solvent reorganization energy of this system, and the computational result proves rational in comparison with the experimental estimations.

  1. Pathways of electron transfer in Escherichia coli DNA photolyase: Trp306 to FADH.

    OpenAIRE

    1999-01-01

    We describe the results of a series of theoretical calculations of electron transfer pathways between Trp306 and *FADH. in the Escherichia coli DNA photolyase molecule, using the method of interatomic tunneling currents. It is found that there are two conformationally orthogonal tryptophans, Trp359 and Trp382, between donor and acceptor that play a crucial role in the pathways of the electron transfer process. The pathways depend vitally on the aromaticity of tryptophans and the flavin molecu...

  2. Optimization of energy transfer in microwave electrothermal thrusters

    Science.gov (United States)

    Sullivan, D. J.; Micci, M. M.

    1993-01-01

    Results are presented from preliminary tests conducted to evaluate the performance of a prototype microwave electrothermal thruster. The primary component of the device is a microwave resonant cavity. The device produces stable axial plasmas within a pressurized section of the cavity with the plasma positioned in the inlet region of the nozzle. Plasma stability is enhanced by axial power coupling, an optimal distribution of electric power density within the cavity, and a propellant gas flow which has a large vortical velocity component. The thruster has been operated with a number of propellant gases: helium, nitrogen, ammonia, and hydrogen. Plasmas can be formed in a reliable manner at cavity pressures of 1 kPa and incident power levels ranging from 50 W to 350 W, depending on the gas used, and can be operated at pressures up to 300 kPa at power levels up to 2200 W. Ideal performance results of vacuum Isp and thermal efficiency vs. specific power are presented for each gas. Representative results of this preliminary work are: He - Isp = 625 s, eta-thermal = 90 percent; N2 - Isp = 270 s, eta-thermal = 41 percent; NH3 - Isp = 475 s, eta-thermal= 55 percent; H2 - Isp = 1040 s, eta-thermal = 53 percent.

  3. Transferred metal electrode films for large-area electronic devices

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Jin-Guo [Department of Physics, National University of Singapore, Lower Kent Ridge Road, Singapore S117543 (Singapore); NUS Graduate School for Integrative Sciences and Engineering (NGS), National University of Singapore, Medical Drive, Singapore S117456 (Singapore); Kam, Fong-Yu [Department of Chemistry, National University of Singapore, Lower Kent Ridge Road, Singapore S117543 (Singapore); Chua, Lay-Lay [Department of Chemistry, National University of Singapore, Lower Kent Ridge Road, Singapore S117543 (Singapore); Department of Physics, National University of Singapore, Lower Kent Ridge Road, Singapore S117543 (Singapore)

    2014-11-10

    The evaporation of metal-film gate electrodes for top-gate organic field-effect transistors (OFETs) limits the minimum thickness of the polymer gate dielectric to typically more than 300 nm due to deep hot metal atom penetration and damage of the dielectric. We show here that the self-release layer transfer method recently developed for high-quality graphene transfer is also capable of giving high-quality metal thin-film transfers to produce high-performance capacitors and OFETs with superior dielectric breakdown strength even for ultrathin polymer dielectric films. Dielectric breakdown strengths up to 5–6 MV cm{sup −1} have been obtained for 50-nm thin films of polystyrene and a cyclic olefin copolymer TOPAS{sup ®} (Zeon). High-quality OFETs with sub-10 V operational voltages have been obtained this way using conventional polymer dielectrics and a high-mobility polymer semiconductor poly[2,5-bis(3-tetradecylthiophene-2-yl)thieno[3,2-b]thiophene-2,5-diyl]. The transferred metal films can make reliable contacts without damaging ultrathin polymer films, self-assembled monolayers and graphene, which is not otherwise possible from evaporated or sputtered metal films.

  4. 76 FR 35219 - Federal Acquisition Regulation; Information Collection; Payment by Electronic Fund Transfer

    Science.gov (United States)

    2011-06-16

    ... Regulation; Information Collection; Payment by Electronic Fund Transfer AGENCY: Department of Defense (DOD... transfer. Public comments are particularly invited on: Whether this collection of information is necessary... those who are to respond, through the use of appropriate technological collection techniques or...

  5. 48 CFR 52.232-33 - Payment by Electronic Funds Transfer-Central Contractor Registration.

    Science.gov (United States)

    2010-10-01

    ... Government under this contract shall be made by electronic funds transfer (EFT), except as provided in... also include the payment information transfer. (2) In the event the Government is unable to release one... mutually agreeable method of payment; or (ii) Request the Government to extend the payment due date until...

  6. New Oxime Ligand with Potential for Proton-Coupled Electron-Transfer Reactions

    DEFF Research Database (Denmark)

    Deville, Claire; Sundberg, Jonas; McKenzie, Christine Joy

    Proton-coupled electron-transfer (PCET) is found in a range of oxidation-reduction reactions in biology.1 This mechanism is of interest for applications in energy conversion processes. The PCET reaction has been shown to be facilitated when the proton is transferred to an intramolecular basic sit...

  7. 9,10-Diphenylanthracene as a matrix for MALDI-MS electron transfer secondary reactions.

    Science.gov (United States)

    Boutaghou, M Nazim; Cole, Richard B

    2012-08-01

    The most common secondary-ionization mechanism in positive ion matrix-assisted laser desorption/ionization (MALDI) involves a proton transfer reaction to ionize the analyte. Peptides and proteins are molecules that have basic (and acidic) sites that make them susceptible to proton transfer. However, non-polar, aprotic compounds that lack basic sites are more difficult to protonate, and creating charged forms of this type of analyte can pose a problem when conventional MALDI matrices are employed. In this case, forming a radical molecular ion through electron transfer is a viable alternative, and certain matrices may facilitate the process. In this work, we investigate the performance of a newly developed electron-transfer secondary reaction matrix: 9,10-diphenylanthracene (9,10-DPA). The use of 9,10-DPA as matrix for MALDI analysis has been tested using several model compounds. It appears to promote ionization through electron transfer in a highly efficient manner as compared to other potential matrices. Thermodynamic aspects of the observed electron transfers in secondary-ionization reactions were also considered, as was the possibility for kinetically controlled/endothermic, electron-transfer reactions in the MALDI plume.

  8. Infrared Laser Driven Double Proton Transfer. An Optimal Control Theory Study

    CERN Document Server

    Abdel-Latif, Mahmoud

    2009-01-01

    Laser control of ultrafast double proton transfer is investigated for a two-dimensional model system describing stepwise and concerted transfer pathways. The pulse design has been done by employing optimal control theory in combination with the multiconfiguration time-dependent Hartree wave packet propagation. The obtained laser fields correspond to multiple pump-dump pulse sequences. Special emphasis is paid to the relative importance of stepwise and concerted transfer pathways for the driven wave packet and its dependence on the parameters of the model Hamiltonian as well as on the propagation time. While stepwise transfer is dominating in all cases considered, for high barrier systems concerted transfer proceeding via tunneling can make a contribution.

  9. Infrared laser driven double proton transfer. An optimal control theory study

    Energy Technology Data Exchange (ETDEWEB)

    Abdel-Latif, Mahmoud K. [Chemistry Department, Faculty of Science, Beni-Suef University, Beni-Suef (Egypt); Institut fuer Physik, Universitaet Rostock, D-18051 Rostock (Germany); Kuehn, Oliver, E-mail: oliver.kuehn@uni-rostock.de [Institut fuer Physik, Universitaet Rostock, D-18051 Rostock (Germany)

    2010-02-18

    Laser control of ultrafast double proton transfer is investigated for a two-dimensional model system describing stepwise and concerted transfer pathways. The pulse design has been done by employing optimal control theory in combination with the multiconfiguration time-dependent Hartree wave packet propagation. The obtained laser fields correspond to multiple pump-dump pulse sequences. Special emphasis is paid to the relative importance of stepwise and concerted transfer pathways for the driven wave packet and its dependence on the parameters of the model Hamiltonian as well as on the propagation time. While stepwise transfer is dominating in all cases considered, for high barrier systems concerted transfer proceeding via tunneling can make a contribution.

  10. MDTM: Optimizing Data Transfer using Multicore-Aware I/O Scheduling

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Liang [Fermilab; Demar, Phil [Fermilab; Wu, Wenji [Fermilab; Kim, Bockjoo [Florida U.

    2017-05-09

    Bulk data transfer is facing significant challenges in the coming era of big data. There are multiple performance bottlenecks along the end-to-end path from the source to destination storage system. The limitations of current generation data transfer tools themselves can have a significant impact on end-to-end data transfer rates. In this paper, we identify the issues that lead to underperformance of these tools, and present a new data transfer tool with an innovative I/O scheduler called MDTM. The MDTM scheduler exploits underlying multicore layouts to optimize throughput by reducing delay and contention for I/O reading and writing operations. With our evaluations, we show how MDTM successfully avoids NUMA-based congestion and significantly improves end-to-end data transfer rates across high-speed wide area networks.

  11. Electrostatic effect on electron transfer between cytochrome b5 and cytochrome c

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The binding and electron transfer between wild type, E44A, E56A, E44/56A, E44/48/56A/D60Aand F35Y variants of cytochrome b5 and cytochrome c were studied. When mixed with cytochrome c, the cytochrome b5E44/48/56A/D60A did not show the typical UV-vis difference spectrum of absorption, indicating that the alteration ofthe surface electrostatic potential obviously influenced the spectrum. The electron transfer rates of wild type cytochromeb5, its variants and cytochrome e at different temperature and ionic strength exhibited an order of F35Y > wild type >E56A > E44A > E44/48/56A/D60A. The enthalpy and entropy of the reaction did not change obviously, suggestingthat the mutation did not significantly disturb the electron transfer conformation. The investigation of electron transfer rateconstants at different ionic strength demonstrated that electrostatic interaction obviously affected the electron transfer pro-cess. The significant difference of Cyt b5 F35Y and E44/48/56A/D60A from the wild type protein further confirmed thegreat importance of the electrostatic interaction in the protein electron transfer.

  12. Transfer calibration of the transmission of electron-energy spectrometers

    Science.gov (United States)

    Gardner, J. L.; Samson, J. A. R.

    1975-01-01

    Relative intensities of strong peaks in the Hel photoelectron spectra of N2, CO2, CO, and O2 are tabulated. These data were measured with an electron energy analyzer whose relative transmission was calibrated to an accuracy of + or - 5%. The tables are useful for calibrating the transmission of other analyzers for electron energies below 9 eV. Correction for angular distribution effects is discussed.

  13. Solvent-mediated electron hopping: long-range charge transfer in IBr-(CO2) photodissociation.

    Science.gov (United States)

    Sheps, Leonid; Miller, Elisa M; Horvath, Samantha; Thompson, Matthew A; Parson, Robert; McCoy, Anne B; Lineberger, W Carl

    2010-04-09

    Chemical bond breaking involves coupled electronic and nuclear dynamics that can take place on multiple electronic surfaces. Here we report a time-resolved experimental and theoretical investigation of nonadiabatic dynamics during photodissociation of a complex of iodine monobromide anion with carbon dioxide [IBr-(CO2)] on the second excited (A') electronic state. Previous experimental work showed that the dissociation of bare IBr- yields only I- + Br products. However, in IBr-(CO2), time-resolved photoelectron spectroscopy reveals that a subset of the dissociating molecules undergoes an electron transfer from iodine to bromine 350 femtoseconds after the initial excitation. Ab initio calculations and molecular dynamics simulations elucidate the mechanism for this charge hop and highlight the crucial role of the carbon dioxide molecule. The charge transfer between two recoiling atoms, assisted by a single solvent-like molecule, provides a notable limiting case of solvent-driven electron transfer over a distance of 7 angstroms.

  14. Rapid electron transfer by the carbon matrix in natural pyrogenic carbon

    Science.gov (United States)

    Sun, Tianran; Levin, Barnaby D. A.; Guzman, Juan J. L.; Enders, Akio; Muller, David A.; Angenent, Largus T.; Lehmann, Johannes

    2017-01-01

    Surface functional groups constitute major electroactive components in pyrogenic carbon. However, the electrochemical properties of pyrogenic carbon matrices and the kinetic preference of functional groups or carbon matrices for electron transfer remain unknown. Here we show that environmentally relevant pyrogenic carbon with average H/C and O/C ratios of less than 0.35 and 0.09 can directly transfer electrons more than three times faster than the charging and discharging cycles of surface functional groups and have a 1.5 V potential range for biogeochemical reactions that invoke electron transfer processes. Surface functional groups contribute to the overall electron flux of pyrogenic carbon to a lesser extent with greater pyrolysis temperature due to lower charging and discharging capacities, although the charging and discharging kinetics remain unchanged. This study could spur the development of a new generation of biogeochemical electron flux models that focus on the bacteria–carbon–mineral conductive network. PMID:28361882

  15. Intramolecular electron transfer in cytochrome cd(1) nitrite reductase from Pseudomonas stutzeri; kinetics and thermodynamics

    DEFF Research Database (Denmark)

    Farver, Ole; Kroneck, Peter M H; Zumft, Walter G

    2002-01-01

    , internal electron transfer between these sites is an inherent element in the catalytic cycle of this enzyme. We have investigated the internal electron transfer reaction employing pulse radiolytically produced N-methyl nicotinamide radicals as reductant which reacts solely with the heme-c in an essentially...... diffusion controlled process. Following this initial step, the reduction equivalent is equilibrating between the c and d(1) heme sites in a unimolecular process (k=23 s(-1), 298 K, pH 7.0) and an equilibrium constant of 1.0. The temperature dependence of this internal electron transfer process has been......Cytochrome cd(1) nitrite reductase from Pseudomonas stutzeri catalyzes the one electron reduction of nitrite to nitric oxide. It is a homodimer, each monomer containing one heme-c and one heme-d(1), the former being the electron uptake site while the latter is the nitrite reduction site. Hence...

  16. Full-electron ligand-to-ligand charge transfer in a compact Re(I) complex.

    Science.gov (United States)

    Yue, Yuankai; Grusenmeyer, Tod; Ma, Zheng; Zhang, Peng; Schmehl, Russell H; Beratan, David N; Rubtsov, Igor V

    2014-11-13

    Ligand-to-ligand charge transfer (LLCT) states in transition metal complexes are often characterized by fractional electron transfer due to coupling of the LLCT state with many other states via the metal. We designed and characterized a compact Re(I) complex that displays essentially full-electron charge transfer in the LLCT excited state. The complex, [Re(DCEB)(CO)3(L)](+) (DCEB = 4,4'-dicarboxyethyl-2,2'-bipyridine), referred to as ReEBA, features two redox active ligands with strong electron accepting (DCEB) and electron donating (L is 3-dimethylaminobenzonitrile (3DMABN)) properties. The lowest energy excited state formed with a ca. 10 ps time constant and was characterized as the full-electron 3DMABN → DCEB LLCT state using time-resolved infrared spectroscopy (TRIR), transient absorption spectroscopy, and DFT computations. Analysis of a range of vibrational modes helped to assign the charge transfer characteristics of the complex. The LLCT state lifetime in ReEBA shows a strong dependence on the solvent polarity and features solvent dependent frequency shifts for several vibrational reporters. The formation of a full-electron LLCT state (∼92%) was enabled by tuning the redox properties of the electron accepting ligand (DCEB) and simultaneously decoupling the redox active group of the electron donating ligand (3DMABN) from the metal center. This strategy is generally applicable for designing compact transition metal complexes that have full-electron LLCT states.

  17. Beyond frontier molecular orbital theory: a systematic electron transfer model (ETM) for polar bimolecular organic reactions.

    Science.gov (United States)

    Cahill, Katharine J; Johnson, Richard P

    2013-03-01

    Polar bimolecular reactions often begin as charge-transfer complexes and may proceed with a high degree of electron transfer character. Frontier molecular orbital (FMO) theory is predicated in part on this concept. We have developed an electron transfer model (ETM) in which we systematically transfer one electron between reactants and then use density functional methods to model the resultant radical or radical ion intermediates. Sites of higher reactivity are revealed by a composite spin density map (SDM) of odd electron character on the electron density surface, assuming that a new two-electron bond would occur preferentially at these sites. ETM correctly predicts regio- and stereoselectivity for a broad array of reactions, including Diels-Alder, dipolar and ketene cycloadditions, Birch reduction, many types of nucleophilic additions, and electrophilic addition to aromatic rings and polyenes. Conformational analysis of radical ions is often necessary to predict reaction stereochemistry. The electronic and geometric changes due to one-electron oxidation or reduction parallel the reaction coordinate for electrophilic or nucleophilic addition, respectively. The effect is more dramatic for one-electron reduction.

  18. A new semiclassical decoupling scheme for electronic transitions in molecular collisions - Application to vibrational-to-electronic energy transfer

    Science.gov (United States)

    Lee, H.-W.; Lam, K. S.; Devries, P. L.; George, T. F.

    1980-01-01

    A new semiclassical decoupling scheme (the trajectory-based decoupling scheme) is introduced in a computational study of vibrational-to-electronic energy transfer for a simple model system that simulates collinear atom-diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic-energy separation (lambda), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate-based decoupling scheme) failed. Interference effects are not exhibited in P vs lambda results.

  19. The dipole moment of the electron carrier adrenodoxin is not critical for redox partner interaction and electron transfer.

    Science.gov (United States)

    Hannemann, Frank; Guyot, Arnaud; Zöllner, Andy; Müller, Jürgen J; Heinemann, Udo; Bernhardt, Rita

    2009-07-01

    Dipole moments of proteins arise from helical dipoles, hydrogen bond networks and charged groups at the protein surface. High protein dipole moments were suggested to contribute to the electrostatic steering between redox partners in electron transport chains of respiration, photosynthesis and steroid biosynthesis, although so far experimental evidence for this hypothesis was missing. In order to probe this assumption, we changed the dipole moment of the electron transfer protein adrenodoxin and investigated the influence of this on protein-protein interactions and electron transfer. In bovine adrenodoxin, the [2Fe-2S] ferredoxin of the adrenal glands, a dipole moment of 803 Debye was calculated for a full-length adrenodoxin model based on the Adx(4-108) and the wild type adrenodoxin crystal structures. Large distances and asymmetric distribution of the charged residues in the molecule mainly determine the observed high value. In order to analyse the influence of the resulting inhomogeneous electric field on the biological function of this electron carrier the molecular dipole moment was systematically changed. Five recombinant adrenodoxin mutants with successively reduced dipole moment (from 600 to 200 Debye) were analysed for their redox properties, their binding affinities to the redox partner proteins and for their function during electron transfer-dependent steroid hydroxylation. None of the mutants, not even the quadruple mutant K6E/K22Q/K24Q/K98E with a dipole moment reduced by about 70% showed significant changes in the protein function as compared with the unmodified adrenodoxin demonstrating that neither the formation of the transient complex nor the biological activity of the electron transfer chain of the endocrine glands was affected. This is the first experimental evidence that the high dipole moment observed in electron transfer proteins is not involved in electrostatic steering among the proteins in the redox chain.

  20. Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems.

    Science.gov (United States)

    Barry, Bridgette A

    2015-01-01

    In bioenergetic reactions, electrons are transferred long distances via a hopping mechanism. In photosynthesis and DNA synthesis, the aromatic amino acid residue, tyrosine, functions as an intermediate that is transiently oxidized and reduced during long distance electron transfer. At physiological pH values, oxidation of tyrosine is associated with a deprotonation of the phenolic oxygen, giving rise to a proton coupled electron transfer (PCET) reaction. Tyrosine-based PCET reactions are important in photosystem II, which carries out the light-induced oxidation of water, and in ribonucleotide reductase, which reduces ribonucleotides to form deoxynucleotides. Photosystem II contains two redox-active tyrosines, YD (Y160 in the D2 polypeptide) and YZ (Y161 in the D1 polypeptide). YD forms a light-induced stable radical, while YZ functions as an essential charge relay, oxidizing the catalytic Mn₄CaO₅ cluster on each of four photo-oxidation reactions. In Escherichia coli class 1a RNR, the β2 subunit contains the radical initiator, Y122O•, which is reversibly reduced and oxidized in long range electron transfer with the α2 subunit. In the isolated E. coli β2 subunit, Y122O• is a stable radical, but Y122O• is activated for rapid PCET in an α2β2 substrate/effector complex. Recent results concerning the structure and function of YD, YZ, and Y122 are reviewed here. Comparison is made to recent results derived from bioengineered proteins and biomimetic compounds, in which tyrosine-based charge transfer mechanisms have been investigated. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. Copyright © 2014 Elsevier B.V. All rights reserved.

  1. Identification of a new electron-transfer relaxation pathway in photoexcited pyrrole dimers.

    Science.gov (United States)

    Neville, Simon P; Kirkby, Oliver M; Kaltsoyannis, Nikolas; Worth, Graham A; Fielding, Helen H

    2016-04-21

    Photoinduced electron transfer is central to many biological processes and technological applications, such as the harvesting of solar energy and molecular electronics. The electron donor and acceptor units involved in electron transfer are often held in place by covalent bonds, π-π interactions or hydrogen bonds. Here, using time-resolved photoelectron spectroscopy and ab initio calculations, we reveal the existence of a new, low-energy, photoinduced electron-transfer mechanism in molecules held together by an NH⋯π bond. Specifically, we capture the electron-transfer process in a pyrrole dimer, from the excited π-system of the donor pyrrole to a Rydberg orbital localized on the N-atom of the acceptor pyrrole, mediated by an N-H stretch on the acceptor molecule. The resulting charge-transfer state is surprisingly long lived and leads to efficient electronic relaxation. We propose that this relaxation pathway plays an important role in biological and technological systems containing the pyrrole building block.

  2. Identification of a new electron-transfer relaxation pathway in photoexcited pyrrole dimers

    Science.gov (United States)

    Neville, Simon P.; Kirkby, Oliver M.; Kaltsoyannis, Nikolas; Worth, Graham A.; Fielding, Helen H.

    2016-04-01

    Photoinduced electron transfer is central to many biological processes and technological applications, such as the harvesting of solar energy and molecular electronics. The electron donor and acceptor units involved in electron transfer are often held in place by covalent bonds, π-π interactions or hydrogen bonds. Here, using time-resolved photoelectron spectroscopy and ab initio calculations, we reveal the existence of a new, low-energy, photoinduced electron-transfer mechanism in molecules held together by an NH⋯π bond. Specifically, we capture the electron-transfer process in a pyrrole dimer, from the excited π-system of the donor pyrrole to a Rydberg orbital localized on the N-atom of the acceptor pyrrole, mediated by an N-H stretch on the acceptor molecule. The resulting charge-transfer state is surprisingly long lived and leads to efficient electronic relaxation. We propose that this relaxation pathway plays an important role in biological and technological systems containing the pyrrole building block.

  3. Transfer printing of thermoreversible ion gels for flexible electronics.

    Science.gov (United States)

    Lee, Keun Hyung; Zhang, Sipei; Gu, Yuanyan; Lodge, Timothy P; Frisbie, C Daniel

    2013-10-09

    Thermally assisted transfer printing was employed to pattern thin films of high capacitance ion gels on polyimide, poly(ethylene terephthalate), and SiO2 substrates. The ion gels consisted of 20 wt % block copolymer poly(styrene-b-ethylene oxide-b-styrene and 80 wt % ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)amide. Patterning resolution was on the order of 10 μm. Importantly, ion gels containing the block polymer with short PS end blocks (3.4 kg/mol) could be transfer-printed because of thermoreversible gelation that enabled intimate gel-substrate contact at 100 °C, while gels with long PS blocks (11 kg/mol) were not printable at the same temperature due to poor wetting contact between the gel and substrates. By using printed ion gels as high-capacitance gate insulators, electrolyte-gated thin-film transistors were fabricated that operated at low voltages (<1 V) with high on/off current ratios (∼10(5)). Statistical analysis of carrier mobility, turn-on voltage, and on/off ratio for an array of printed transistors demonstrated the excellent reproducibility of the printing technique. The results show that transfer printing is an attractive route to pattern high-capacitance ion gels for flexible thin-film devices.

  4. 2-Dimensional CFD Simulation and Correlation Development for Optimization of Fin Heatsinks in Electronic Cooling

    Institute of Scientific and Technical Information of China (English)

    Jing YANG; Li WANG; Huazhi LI

    2001-01-01

    CFD has penetrated into the field of electronic cooling for some time. Both parallel and staggered plate fin heatsinks are widely used in modern computers. This paper presents the ways to make most use of CFD in optimization design of those heatsinks: the flow and heat transfer of staggered and parallel plate fm heatsinks of various geometry were simulated by using Fluent 5.0 commercial CFD code. Based on 60 different simulation solutions, two correlations, concerning Nusselt number and friction factor as the functions of geometrical and operational parameters of the heatsinks were developed. The presentation parameter examination was also performed by comparing the numerical solutions with the analytical solutions of parallel plate arrays, showing that the correct parameters are used in the correlations.

  5. Ion atmosphere relaxation controlled electron transfers in cobaltocenium polyether molten salts.

    Science.gov (United States)

    Harper, Amanda S; Leone, Anthony M; Lee, Dongil; Wang, Wei; Ranganathan, Srikanth; Williams, Mary Elizabeth; Murray, Royce W

    2005-10-13

    A room-temperature redox molten salt for the study of electron transfers in semisolid media, based on combining bis(cyclopentadienyl)cobalt with oligomeric polyether counterions, [Cp2Co](MePEG350SO3), is reported. The transport properties of the new molten salt can be varied (plasticized) by varying the polyether content. The charge transport rate during voltammetric reduction of the ionically conductive [Cp2Co](MePEG350SO3) molten salt exceeds the actual physical diffusivity of [Cp2Co]+ because of rapid [Cp2Co](+/0) electron self-exchanges. The measured [Cp2Co](+/0) electron self-exchange rate constants (k(EX)) are proportional to the diffusion coefficients (D(CION)) of the counterions in the melt. The electron-transfer activation barrier energies are also close to those of ionic diffusion but are larger than those derived from optical intervalent charge-transfer results. Additionally, the [Cp2Co](+/0) rate constant results are close to those of dissimilar redox moieties in molten salts where D(CION) values are similar. All of these characteristics are consistent with the rates of electron transfers of [Cp2Co](+/0) (and the other donor-acceptor pairs) being controlled not by the intrinsic electron-transfer rates but by the rate of relaxation of the ion atmosphere around the reacting pair. In the low driving force regime of mixed-valent concentration gradients, the ion atmosphere relaxation is competitive with electron transfer. The results support the generality of the recently proposed model of ionic atmosphere relaxation control of electron transfers in ionically conductive, semisolid materials.

  6. Research on Optimization of Bearing Span of Main Reducer Gear System Based on the Transfer Matrix

    Directory of Open Access Journals (Sweden)

    Huang Feng Yun

    2016-01-01

    Full Text Available The research object is the bearing span of the main reducer gear of the crossover vehicle for improving the performance of the Noise-Vibration-Harshness (NVH on the rear axle. It could get the optimal bearing span by modal analysis of the driving gear shaft and the vibration test of the main reducer, based on the transfer matrix. It is verified that the vibration and transmission stability are greatly improved with this optimal bearing span by the dynamic simulations of different bearing spans in ADAMS. And it can provide reference for the structural optimization design of the main reducer and the research on the vibration and noise reduction.

  7. Adjoint analyses of enhanced solidification for shape optimization in conjugate heat transfer problem

    Science.gov (United States)

    Morimoto, Kenichi; Kinoshita, Hidenori; Suzuki, Yuji

    2016-11-01

    In the present study, an adjoint-based shape-optimization method has been developed for designing extended heat transfer surfaces in conjugate heat transfer problems. Here we specifically consider heat conduction-dominated solidification problem under different thermal boundary conditions: (i) the isothermal condition, and (ii) the conjugate condition with thermal coupling between the solidified liquid and the solid wall inside the domain bounded by the extended heat transfer surface. In the present shape-optimization scheme, extended heat transfer surfaces are successively refined in a local way based on the variational information of a cost functional with respect to the shape modification. In the computation of the developed scheme, a meshless method is employed for dealing with the complex boundary shape. For high-resolution analyses with boundary-fitted node arrangement, we have introduced a bubble-mesh method combined with a high-efficiency algorithm for searching neighboring bubbles within a cut-off distance. The present technique can be easily applied to convection problems including high Reynolds number flow. We demonstrate, for the isothermal boundary condition, that the present optimization leads to tree-like fin shapes, which achieve the temperature field with global similarity for different initial fin shapes. We will also show the computational results for the conjugate condition, which would regularize the present optimization due to the fin-efficiency effect.

  8. Optimization of Low-Thrust Earth-Moon Transfers Using Evolutionary Neurocontrol

    NARCIS (Netherlands)

    Ohndorf, A.; Dachwald, B.; Gill, E.K.A.

    2009-01-01

    Although low-thrust propulsion is an interesting option for scientific and reconnaissance missions to targets in planetary space, like the Moon, associated transfer strategies pose challenging requirements in terms of optimal control. The method of Evolutionary Neurocontrol (ENC), which has been app

  9. Optimization of Low-Thrust Earth-Moon Transfers Using Evolutionary Neurocontrol

    NARCIS (Netherlands)

    Ohndorf, A.; Dachwald, B.; Gill, E.K.A.

    2009-01-01

    Although low-thrust propulsion is an interesting option for scientific and reconnaissance missions to targets in planetary space, like the Moon, associated transfer strategies pose challenging requirements in terms of optimal control. The method of Evolutionary Neurocontrol (ENC), which has been

  10. Industrial Application of Topology Optimization for Combined Conductive and Convective Heat Transfer Problems

    DEFF Research Database (Denmark)

    Zhou, Mingdong; Alexandersen, Joe; Sigmund, Ole;

    2016-01-01

    This paper presents an industrial application of topology optimization for combined conductive and convective heat transfer problems. The solution is based on a synergy of computer aided design and engineering software tools from Dassault Systemes. The considered physical problem of steady...

  11. The thermodynamics of charge transfer in DNA photolyase: using thermodynamic integration calculations to analyse the kinetics of electron transfer reactions.

    Science.gov (United States)

    Krapf, Sebastian; Koslowski, Thorsten; Steinbrecher, Thomas

    2010-08-28

    DNA Photolyases are light sensitive oxidoreductases present in many organisms that participate in the repair of photodamaged DNA. They are capable of electron transfer between a bound cofactor and a chain of tryptophan amino acid residues. Due to their unique mechanism and important function, photolyases have been subject to intense study in recent times, with both experimental and computational efforts. In this work, we present a novel application of classical molecular dynamics based free energy calculations, combined with quantum mechanical computations, to biomolecular charge transfer. Our approach allows for the determination of all reaction parameters in Marcus' theory of charge transport. We were able to calculate the free energy profile for the movement of a positive charge along protein sidechains involved in the biomolecule's function as well as charge-transfer rates that are in good agreement with experimental results. Our approach to simulate charge-transfer reactions explicitly includes the influence of protein flexibility and solvent dynamics on charge-transfer energetics. As applied here to a biomolecular system of considerable scientific interest, we believe the method to be easily adaptable to the study of charge-transfer phenomena in biochemistry and other fields.

  12. A semiclassical theory of electron transfer reactions in Condon approximation and beyond

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Sokolov, V. V.; Ulstrup, Jens

    2001-01-01

    The effect of the modulation of the electronic wave functions by configurational fluctuations of the molecular environment on the kinetic parameters of electron transfer reactions is discussed. A self-consistent algorithm for the calculation of the potential profile along the reaction coordinate...

  13. "Super-Reducing" Photocatalysis: Consecutive Energy and Electron Transfers with Polycyclic Aromatic Hydrocarbons.

    Science.gov (United States)

    Brasholz, Malte

    2017-08-21

    Donation welcome: Recent developments in visible-light photocatalysis allow the utilization of increasingly negative reduction potentials. Successive energy and electron transfer with polycyclic aromatic hydrocarbons enables the catalytic formation of strongly reducing arene radical anions, classical stoichiometric reagents for one-electron reduction in organic synthesis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Electronic properties of the charge transfer material MnPc/F4TCNQ

    Science.gov (United States)

    Rückerl, Florian; Mahns, Benjamin; Dodbiba, Eni; Nikolis, Vasileios; Herzig, Melanie; Büchner, Bernd; Knupfer, Martin; Hahn, Torsten; Kortus, Jens

    2016-09-01

    We present electronic properties of a charge transfer material consisting of Manganese(ii)Phthalocyanine (MnPc) and 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), investigated by means of photoemission spectroscopy and electron energy-loss spectroscopy, as well as supporting density functional theory calculations. We report the successful formation of a bulk material characterized by a strong interaction of the molecular compounds which affects the optical properties significantly. Our investigations reveal a significant charge transfer, whereas the MnPc molecule is oxidized and F4TCNQ is reduced. The valence band data indicate a full charge transfer between the two partners. The electronic excitation spectrum reveals a relatively small energy gap of MnPc/F4TCNQ of about 0.7 eV, which is related to a charge transfer excitation.

  15. Experimental exploration of the Mulliken-Hush relationship for intramolecular electron transfer reactions.

    Science.gov (United States)

    Mukherjee, Tamal; Ito, Naoki; Gould, Ian R

    2011-03-17

    The Mulliken-Hush (M-H) relationship provides the critical link between optical and thermal electron transfer processes, and yet very little direct experimental support for its applicability has been provided. Dicyanovinylazaadamantane (DCVA) represents a simple two-state (neutral/charge-transfer) intramolecular electron transfer system that exhibits charge-transfer absorption and emission spectra that are readily measurable in solvents with a wide range of polarities. In this regard it represents an ideal model system for studying the factors that control both optical charge separation (absorption) and recombination (emission) processes in solution. Here we explore the applicability of the M-H relation to quantitative descriptions of the optical charge-transfer processes in DCVA. For DCVA, the measured radiative rate constants exhibit a linear dependence on transition energy, and transition dipole moments exhibit an inverse dependence on transition energy, consistent with the M-H relationship.

  16. Conformal Electronics Wrapped Around Daily Life Objects Using an Original Method: Water Transfer Printing.

    Science.gov (United States)

    Le Borgne, Brice; De Sagazan, Olivier; Crand, Samuel; Jacques, Emmanuel; Harnois, Maxime

    2017-09-06

    The water transfer printing method is used to transfer patterned films on random three-dimensional objects. This industrially viable technology has been demonstrated to intimately wrap metallic and polymeric films around different materials. This method avoids the use of rigid substrate during the transfer step. Patterns can be transferred to objects without folds even when holed, addressing a challenging issue in the field of conformal electronics. This technique allows high film bending properties to be reached. This promising method enables us to integrate large-area films onto daily life objects. A bent capacitive touchpad is fabricated showing the potential applications of this technology.

  17. Fabrication of nanowire electronics on nonconventional substrates by water-assisted transfer printing method

    Science.gov (United States)

    Lee, Chi Hwan; Kim, Dong Rip; Zheng, Xiaolin

    2015-06-01

    We report a simple, versatile, and wafer-scale water-assisted transfer printing method (WTP) that enables the transfer of nanowire devices onto diverse nonconventional substrates that were not easily accessible before, such as paper, plastics, tapes, glass, polydimethylsiloxane (PDMS), aluminum foil, and ultrathin polymer substrates. The WTP method relies on the phenomenon of water penetrating into the interface between Ni and SiO2. The transfer yield is nearly 100%, and the transferred devices, including NW resistors, diodes, and field effect transistors, maintain their original geometries and electronic properties with high fidelity.

  18. Nanoparticle Facilitated Extracellular Electron Transfer in Microbial Fuel Cells

    Science.gov (United States)

    2014-10-13

    tances.19 Nanoscale materials and devices, such as metal /semi- conductor nanoparticles, nanowires, and carbon nanotubes, have been widely exploited...redox centers. In addition, dissimilatory intermembrane and intramembrane reduction of metals into nanoparticles has been well-documented29,30...different length scales. Biomineralized iron sulfide was employed for the current studies because of the importance of sulfur-mediated electron

  19. Electron transfer from alpha-keggin anions to dioxygen

    Science.gov (United States)

    Yurii V. Geletii; Rajai H. Atalla; Craig L. Hill; Ira A. Weinstock

    2004-01-01

    Polyoxometalates (POMs), of which alpha-Keggin anions are representative, are a diverse and rapidly growing class of water-soluble cluster-anion structures with applications ranging from molecular catalysis to materials. [1] POMs are inexpensive, minimally or non-toxic, negatively charged clusters comprised of early transition-metals, usually in their do electronic...

  20. Multistep photoinduced electron transfer in a photoacceptor terminated molecular triode

    NARCIS (Netherlands)

    Bakker, N.A.C.; Wiering, P.G.; Brouwer, A.M.; Warman, J.M.; Verhoeven, J.W.

    1990-01-01

    A mol.ecular triode (I) containing a nonconjugatively interconnected array (D2-D1-Pa) of 2 potential 1-electron donor (D) moieties and a powerful photoacceptor (Pa), is described. In a related diode (II) consisting of the array D1-Pa excitation of the photoacceptor, Pa, induces charge-separation as

  1. Photoinduced Electron Transfer within Supramolecular Donor-Acceptor Peptide Nanostructures under Aqueous Conditions.

    Science.gov (United States)

    Sanders, Allix M; Magnanelli, Timothy J; Bragg, Arthur E; Tovar, John D

    2016-03-16

    We report the synthesis, self-assembly, and electron transfer capabilities of peptide-based electron donor-acceptor molecules and supramolecular nanostructures. These modified peptides contain π-conjugated oligothiophene electron donor cores that are peripherally substituted with naphthalene diimide electron acceptors installed via imidation of site-specific lysine residues. These molecules self-assemble into one-dimensional nanostructures in aqueous media, as shown through steady-state absorption, photoluminescence, and circular dichroism spectra, as well as transmission electron microscopy. Excitation of the oligothiophene donor moieties results in electron transfer to the acceptor units, ultimately creating polar, charge-separated states that persist for over a nanosecond as observed with transient absorption spectroscopy. This study demonstrates how transient electric fields can be engineered into aqueous nanomaterials of biomedical relevance through external, temporally controlled photonic inputs.

  2. Generalization of the Mulliken-Hush treatment for the calculation of electron transfer matrix elements

    Science.gov (United States)

    Cave, Robert J.; Newton, Marshall D.

    1996-01-01

    A new method for the calculation of the electronic coupling matrix element for electron transfer processes is introduced and results for several systems are presented. The method can be applied to ground and excited state systems and can be used in cases where several states interact strongly. Within the set of states chosen it is a non-perturbative treatment, and can be implemented using quantities obtained solely in terms of the adiabatic states. Several applications based on quantum chemical calculations are briefly presented. Finally, since quantities for adiabatic states are the only input to the method, it can also be used with purely experimental data to estimate electron transfer matrix elements.

  3. Riboflavin-shuttled extracellular electron transfer from Enterococcus faecalis to electrodes in microbial fuel cells.

    Science.gov (United States)

    Zhang, Enren; Cai, Yamin; Luo, Yue; Piao, Zhe

    2014-11-01

    Great attention has been focused on Gram-negative bacteria in the application of microbial fuel cells. In this study, the Gram-positive bacterium Enterococcus faecalis was employed in microbial fuel cells. Bacterial biofilms formed by E. faecalis ZER6 were investigated with respect to electricity production through the riboflavin-shuttled extracellular electron transfer. Trace riboflavin was shown to be essential for transferring electrons derived from the oxidation of glucose outside the peptidoglycan layer in the cell wall of E. faecalis biofilms formed on the surface of electrodes, in the absence of other potential electron mediators (e.g., yeast extract).

  4. On the use of topology optimization for improving heat transfer in molding process

    Science.gov (United States)

    Agazzi, A.; LeGoff, R.; Truc-Vu, C.

    2016-10-01

    In the plastic industry, one of the key factor is to control heat transfer. One way to achieve that goal is to design an effective cooling system. But in some area of the mold, where it is not possible to design cooling system, the use of a highly conductive material, such as copper pin, is often used. Most of the time, the location, the size and the quantity of the copper pin are made by empirical considerations, without using optimization procedures. In this article, it is proposed to use topology optimization, in order to improve transient conductive heat transfer in an injection/blowing mold. Two methodologies are applied and compared. Finally, the optimal distribution of cooper pin in the mold is given.

  5. Direct electron transfer from electrode to electrochemically active bacteria in a bioelectrochemical dechlorination system.

    Science.gov (United States)

    Liu, Ding; Lei, Lecheng; Yang, Bin; Yu, Qingni; Li, Zhongjian

    2013-11-01

    Pentachlorophenol (PCP) was dechlorinated by electrochemically active bacteria using an electrode as the direct electron donor. Dechlorination efficiency and coulombic efficiency (CE) were investigated. When hydrogen evolution reaction was eliminated by controlling the potential, both dechlorination efficiency and CE increase as the potential decreases, which implied the dechlorination was stimulated by electric current rather than hydrogen gas. Further investigation of the cyclic voltammetry characterization of the medium revealed nearly no redox mediator secreted by the bacteria. Moreover, the comparison of dechlorination experiments carried out with filtered and unfiltered medium provided convincible evidence that the dominating electron transfer mechanism for the dechlorination is direct electron transfer. Additionally, 454 pyrosequencing technique was employed to gain a comprehensive understanding of the biocathodic microbial community. The results showed Proteobacteria, Bacteroidetes and Firmicutes were the three predominant groups. This paper demonstrated the direct electron transfer mechanism could be involved in PCP dechlorination with a biocathode. Copyright © 2013 Elsevier Ltd. All rights reserved.

  6. Direct observation of electron-to-hole energy transfer in CdSe quantum dots.

    Science.gov (United States)

    Hendry, E; Koeberg, M; Wang, F; Zhang, H; de Mello Donegá, C; Vanmaekelbergh, D; Bonn, M

    2006-02-10

    We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots. Time-resolved luminescence and terahertz spectroscopy reveal that the rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This constitutes the first direct, quantitative measurement of electron-to-hole energy transfer, the hypothesis behind the Auger cooling mechanism proposed in quantum dots, which is found to occur on a 1 +/- 0.15 ps time scale.

  7. Enzymatic cellulose oxidation is linked to lignin by long-range electron transfer

    DEFF Research Database (Denmark)

    Westereng, Bjorge; Cannella, David; Wittrup Agger, Jane

    2015-01-01

    Enzymatic oxidation of cell wall polysaccharides by lytic polysaccharide monooxygenases (LPMOs) plays a pivotal role in the degradation of plant biomass. While experiments have shown that LPMOs are copper dependent enzymes requiring an electron donor, the mechanism and origin of the electron supply...... in biological systems are only partly understood. We show here that insoluble high molecular weight lignin functions as a reservoir of electrons facilitating LPMO activity. The electrons are donated to the enzyme by long-range electron transfer involving soluble low molecular weight lignins present in plant...... new light on how oxidative enzymes present in plant degraders may act in concert....

  8. Turbulent heat transfer in liquid iron during electron beam evaporation

    Energy Technology Data Exchange (ETDEWEB)

    Karcher, Ch.; Schaller, R. [Dresden University of Technology, Dresden (Germany). Institute for Aerospace Engineering; Boeck, Th.; Thess, A. [Ilmenau University of Technology, Ilmenau (Germany). Department of Mechanical Engineering; Metzner, Ch [Fraunhofer Institute for Electron Beam and Plasma Technologies, Dresden (Germany)

    2000-05-01

    Electron beam evaporation of high-purity liquid metals is characterized by vigorous (turbulent) convection in the melt pool resulting in unwelcome heat losses. This convective motion is exclusively driven by thermocapillary forces. We exploit this unique feature to measure the Nusselt number in liquid iron for Marangoni numbers up to 10{sup 8}. The experiments are carried out in a real-to-life test facility for electron beam evaporation. We compare the results of our investigations with findings of a recent scaling analysis. Moreover, we perform direct numerical simulations employing a 2D model. The numerical results demonstrate the turbulent character of the flow as well as the dominance of thermocapillarity over buoyancy. (author)

  9. Electronic Structure of the Perylene / Zinc Oxide Interface: A Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

    KAUST Repository

    Li, Jingrui

    2015-07-29

    The electronic properties of dye-sensitized semiconductor surfaces consisting of pery- lene chromophores chemisorbed on zinc oxide via different spacer-anchor groups, have been studied at the density-functional-theory level. The energy distributions of the donor states and the rates of photoinduced electron transfer from dye to surface are predicted. We evaluate in particular the impact of saturated versus unsaturated aliphatic spacer groups inserted between the perylene chromophore and the semiconductor as well as the influence of surface defects on the electron-injection rates.

  10. Bound Flavin-Cytochrome Model of Extracellular Electron Transfer in Shewanella oneidensis: Analysis by Free Energy Molecular (Postprint)

    Science.gov (United States)

    2016-06-06

    AFRL-RX-WP-JA-2017-0192 BOUND FLAVIN−CYTOCHROME MODEL OF EXTRACELLULAR ELECTRON TRANSFER IN SHEWANELLA ONEIDENSIS: ANALYSIS BY FREE...23 June 2016 Interim 11 January 2013- 10 October 2015 4. TITLE AND SUBTITLE BOUND FLAVIN−CYTOCHROME MODEL OF EXTRACELLULAR ELECTRON TRANSFER IN...Flavins are known to enhance extracellular electron transfer (EET) in Shewanella oneidensis MR-1 bacteria, which reduce electron acceptors through outer

  11. Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches

    Energy Technology Data Exchange (ETDEWEB)

    Ramakrishnan, Raghunathan, E-mail: r.ramakrishnan@unibas.ch [Institute of Physical Chemistry, National Center for Computational Design and Discovery of Novel Materials (MARVEL), Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel (Switzerland); Nest, Mathias [Theoretische Chemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching (Germany)

    2015-01-13

    Highlights: • We model electron dynamics across cyano alkanethiolates attached to gold cluster. • We present electron transfer time scales from TD-DFT and TD-CI based simulations. • Both DFT and CI methods qualitatively predict the trend in time scales. • TD-CI predicts the experimental relative time scale very accurately. - Abstract: We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual π{sup ∗} molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

  12. Ab Initio Study of the Electron Transfer in an Ionized Stacked Complex of Guanines

    Science.gov (United States)

    Cauët, Emilie; Liévin, Jacques

    2009-08-01

    The charge transfer process in an ionized stacking of two consecutive guanines (G5'G3')+ has been studied by means of state-averaged CASSCF/MRCI and RASSCF/RASPT2 calculations. The ground and two first excited states of the radical cation have been characterized, and the topology of the corresponding potential energy surfaces (PESs) has been studied as a function of all intermolecular geometrical parameters. The results demonstrate that the charge transfer process in (G5'G3')+ is governed by the avoiding crossing between the ground and first excited states of the complex. Relative translation motions of both guanines in their molecular planes are shown to lead to the charge migration between G5' and G3'. Five stationary points (three minima and two saddle points) have been characterized along the reaction path describing the passage of the positive charge from G5' to G3'. The global minimum on the PES is found to correspond to the charge configuration G5'+G3'. The existence of an intermediate minimum along the reaction path has been established, characterizing a structure where the positive charge is equally distributed between the two guanines. The calculated energy profile allowed us to determine the height of the potential energy barrier (7.33 kcal/mol) and to evaluate the electronic coupling at a geometry close to the avoiding crossing (3.6 kcal/mol). Test calculations showed that the topology of the ground state PES of the complex GG+ is qualitatively conserved upon optimization of the intramolecular geometrical parameters of the stationary points.

  13. Scaling Relations and Optimization of Excitonic Energy Transfer Rates between One-Dimensional Molecular Aggregates

    NARCIS (Netherlands)

    Chuang, Chern; Knoester, Jasper; Cao, Jianshu

    2014-01-01

    We theoretically study the distance, chain length, and temperature dependence of the electronic couplings as well as the excitonic energy transfer rates between one-dimensional (1D) chromophore aggregates. In addition to the well-known geometry dependent factor that leads to the deviation from Forst

  14. Expanding the Diet for DIET: Electron Donors Supporting Direct Interspecies Electron Transfer (DIET in Defined Co-Cultures

    Directory of Open Access Journals (Sweden)

    Li-YIng eWang

    2016-03-01

    Full Text Available Direct interspecies electron transfer (DIET has been recognized as an alternative to interspecies H2 transfer as a mechanism for syntrophic growth, but previous studies on DIET with defined co-cultures have only documented DIET with ethanol as the electron donor in the absence of conductive materials. Co-cultures of Geobacter metallireducens and Geobacter sulfurreducens metabolized propanol, butanol, propionate, and butyrate with the reduction of fumarate to succinate. G. metallireducens utilized each of these substrates whereas only electrons available from DIET supported G. sulfurreducens respiration. A co-culture of G. metallireducens and a strain of G. sulfurreducens that could not metabolize acetate oxidized acetate with fumarate as the electron acceptor, demonstrating that acetate can also be syntrophically metabolized via DIET. A co-culture of G. metallireducens and Methanosaeta harundinacea previously shown to syntrophically convert ethanol to methane via DIET metabolized propanol or butanol as the sole electron donor, but not propionate or butyrate. The stoichiometric accumulation of propionate or butyrate in the propanol- or butanol-fed cultures demonstrated that M. harundinaceae could conserve energy to support growth solely from electrons derived from DIET. Co-cultures of G. metallireducens and Methanosarcina barkeri could also incompletely metabolize propanol and butanol and did not metabolize propionate or butyrate as sole electron donors. These results expand the range of substrates that are known to be syntrophically metabolized through DIET, but suggest that claims of propionate and butyrate metabolism via DIET in mixed microbial communities warrant further validation.

  15. Electron-transfer and acid-base properties of a two-electron oxidized form of quaterpyrrole that acts as both an electron donor and an acceptor.

    Science.gov (United States)

    Zhang, Min; E, Wenbo; Ohkubo, Kei; Sanchez-Garcia, David; Yoon, Dae-Wi; Sessler, Jonathan L; Fukuzumi, Shunichi; Kadish, Karl M

    2008-02-21

    Electron-transfer interconversion between the four-electron oxidized form of a quaterpyrrole (abbreviated as P4 for four pyrroles) and the two-electron oxidized form (P4H2) as well as between P4H2 and its fully reduced form (P4H4) bearing analogous substituents in the alpha- and beta-pyrrolic positions was studied by means of cyclic voltammetry and UV-visible spectroelectrochemistry combined with ESR and laser flash photolysis measurements. The two-electron oxidized form, P4H2, acts as both an electron donor and an electron acceptor. The radical cation (P4H2*+) and radical anion (P4H2*-) are both produced by photoinduced electron transfer from dimeric 1-benzyl-1,4-dihydronicotinamide to P4H2, whereas the cation radical form of the compound is also produced by electron-transfer oxidation of P4H2 with [Ru(bpy)3]3+. The ESR spectra of P4H2*+ and P4H2*- were recorded at low temperature and exhibit spin delocalization over all four pyrrole units. Thus, the two-electron oxidized form of the quaterpyrrole (P4H2) displays redox and electronic features analogous to those seen in the case of porphyrins and may be considered as a simple, open-chain model of this well-studied tetrapyrrolic macrocycle. The dynamics of deprotonation from P4H2*+ and disproportionation of P4H2 were examined by laser flash photolysis measurements of photoinduced electron-transfer oxidation and reduction of P4H2, respectively.

  16. Optimization of on-resonant magnetization transfer contrast in coronary vein MRI.

    Science.gov (United States)

    Stoeck, Christian T; Hu, Peng; Peters, Dana C; Kissinger, Kraig V; Goddu, Beth; Goepfert, Lois; Ngo, Long; Manning, Warren J; Kozerke, Sebastian; Nezafat, Reza

    2010-12-01

    Magnetization transfer contrast has been used commonly for endogenous tissue contrast improvements in angiography, brain, body, and cardiac imaging. Both off-resonant and on-resonant RF pulses can be used to generate magnetization transfer based contrast. In this study, on-resonant magnetization transfer preparation using binomial pulses were optimized and compared with off-resonant magnetization transfer for imaging of coronary veins. Three parameters were studied with simulations and in vivo measurements: flip angle, pulse repetitions, and binomial pulse order. Subsequently, first or second order binomial on-resonant magnetization transfer pulses with eight repetitions of 720° and 240° flip angle were used for coronary vein MRI. Flip angles of 720° yielded contrast enhancement of 115% (P < 0.0006) for first order on-resonant and 95% (P < 0.0006) for off-resonant magnetization transfer. There was no statistically significance difference between off-resonant and on-resonant first order binomial Magnetization transfer at 720°. However, for off-resonance pulses, much more preparation time is needed when compared with the binomials but with considerably reduced specific absorption rate.

  17. [Electron transfer, ionization, and excitation in atomic collisions]. [Pennsylvania State Univ

    Energy Technology Data Exchange (ETDEWEB)

    1992-01-01

    Fundamental processes of electron transfer, ionization, and excitation in ion-atom and ion-ion collisions are studied. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-ion core can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. At intermediate collision energies (e.g., proton energies for p-He[sup +] collisions on the order of 100 kilo-electron volts), many electronic states are strongly coupled during the collision, a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. At higher collision energies (million electron-volt energies) the coupling is weaker with, however, many more states being coupled together, so that high-order perturbation theory is essential.

  18. Excitation dependent bidirectional electron transfer in phthalocyanine-functionalised MoS2 nanosheets.

    Science.gov (United States)

    Nguyen, Emily P; Carey, Benjamin J; Harrison, Christopher J; Atkin, Paul; Berean, Kyle J; Della Gaspera, Enrico; Ou, Jian Zhen; Kaner, Richard B; Kalantar-Zadeh, Kourosh; Daeneke, Torben

    2016-09-15

    Two-dimensional (2D) transition metal chalcogenides such as 2D MoS2 are considered prime candidate materials for the design of next generation optoelectronics. Functionalisation of these materials is considered to be a key step in tailoring their properties towards specific applications and unlocking their full potential. Here we present a van der Waals functionalisation strategy for creating MoS2 nanosheets decorated with free base phthalocyanine chromophores. The semiconducting sheets are found to intimately interact with these optoelectronically active chromophores, resulting in an electronic heterostructure that exhibits enhanced optoelectronic properties and exploitable charge transfer. We show that by utilising laterally confined MoS2 nanosheets, the conduction band of the semiconductor could be positioned between the chromophore's S1 and S2 states. Consequently, bidirectional photoinduced electron transfer processes are observed, with excitation of the functionalised nanosheet's semiconductor transition resulting in electron transfer to the phthalocyanine's LUMO, and excitation of the chromophore's S2 state leading to electron injection into the MoS2 conduction band. However, charge transfer from the dye's S1 transition to the MoS2 nanosheet is found to be thermodynamically unfavourable, resulting in intense radiative recombination. These findings may enable controlling and tuning the charge carrier density of semiconducting nanosheets via optical means through the exploitation of photoinduced electron transfer. Furthermore this work provides access to 2D semiconductor-hybrids with tailored absorption profiles and photoluminescence.

  19. Redox-linked conformation change and electron transfer between monoheme c-type cytochromes and oxides

    Energy Technology Data Exchange (ETDEWEB)

    Khare, Nidhi; Lovelace, David M.; Eggleston, Carrick M.; Swenson, Michael; Magnuson, Timothy S.

    2006-06-15

    Electron transfer between redox active proteins and mineral oxides is important in a variety of natural as well as technological processes, including electron transfer from dissimilatory metal-reducing bacteria to minerals. One of the pathways that could trigger electron transfer between proteins and minerals is redox-linked conformation change. We present electrochemical evidence that mitochondrial cytochrome c (Mcc) undergoes significant conformation change upon interaction with hematite and indium-tin oxide (ITO) surfaces. The apparent adsorption-induced conformation change causes the protein to become more reducing, which makes it able to transfer electrons to the hematite conduction band. Although Mcc is not a protein thought to be involved in interaction with mineral surfaces, it shares (or can be conformed so as to share) some characteristics with multiheme outer-membrane cytochromes thought to be involved in the transfer of electrons from dissimilatory iron-reducing bacteria to ferric minerals during respiration. We present evidence that a 10.1 kDa monohoeme cytochrome isolated and purified from Acidiphilium cryptum, with properties similar to those of Mcc, also undergoes conformation change as a result of interaction with hematite surfaces.

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

    Institute of Scientific and Technical Information of China (English)

    李象远; 肖顺清; 何福城

    1999-01-01

    After the separation of the donor, the aeceptor, 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 the π-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 coordinate R=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 △min 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