WorldWideScience

Sample records for intermolecular electron transfer

  1. Frontier orbital symmetry control of intermolecular electron transfer. Final report, September 15, 1988--December 31, 1994

    Energy Technology Data Exchange (ETDEWEB)

    Stevens, B.

    1997-07-01

    This report discusses the following topics: the recovery of intermolecular transfer parameters from fluorescence quenching in liquids; photoinduced intramolecular electron transfer in flexible donor/space/acceptor systems containing an extended unsaturated spacer; electron transfer sensitized reaction; the recovery of solute and fractal dimensions from electron transfer quenching data; and frontier orbital symmetry control of back electron transfer.

  2. Electrochemical study of the intermolecular electron transfer to Pseudomonas aeruginosa cytochrome cd1 nitrite reductase

    International Nuclear Information System (INIS)

    The kinetics of electron transfer reaction between cytochrome cd1 nitrite reductase (NiR) from Pseudomonas aeruginosa and various physiological/non physiological redox partners was investigated using cyclic voltammetry at the pyrolytic graphite electrode. While NiR did not exchange electron with the electrode, cytochrome c551 and azurin, both from Ps. aeruginosa, behaved as fast electrochemical systems. The intermolecular electron transfers between NiR and cytochrome c551 or azurin as electron shuttles, in the presence of nitrite, were studied. Second order rate constants of 2x106 and 1.4x105 M-1 s-1 are calculated for cytochrome c551 and azurin, respectively. The dependence of the second-order rate constant on ionic strength and pH is discussed. Finally, the effect of the global charge of the electron shuttles was explored using differently charged species (proteins or small ions). The experimental results suggest involvement of polar interactions as well as of hydrophobic contacts in the protein recognition prior to the intermolecular electron transfer. As the cross-reaction between Ps. nautica cytochrome c552 and Ps. aeruginosa NiR was shown to be as efficient as the catalytic reaction involving the physiological partners, it is concluded to a 'pseudo-specificity' in the recognition between NiR and the electron donor

  3. Protein Phosphorylation and Intermolecular Electron Transfer: A Joint Experimental and Computational Study of a Hormone Biosynthesis Pathway

    OpenAIRE

    Zöllner, Andy; Pasquinelli, Melissa A.; Bernhardt, Rita; Beratan, David N.

    2007-01-01

    Protein phosphorylation is a common regulator of enzyme activity. Chemical modification of a protein surface, including phosphorylation, could alter the function of biological electron-transfer reactions. However, the sensitivity of intermolecular electron-transfer kinetics to post-translational protein modifications has not been widely investigated. We have therefore combined experimental and computational studies to assess the potential role of phosphorylation in electron-transfer reactions...

  4. Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies.

    Science.gov (United States)

    Lemmetyinen, Helge; Tkachenko, Nikolai V; Efimov, Alexander; Niemi, Marja

    2011-01-14

    The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications. PMID:21031207

  5. Photoinduced intermolecular electron transfer and off-resonance Raman characteristics of Rhodamine 101/N,N-diethylaniline

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, Li-lin [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); School of Mechanical and Electronic Engineering, Hezhou University, Hezhou 542800 (China); Liu, Wei-long; Song, Yun-fei; He, Xing; Wang, Yang; Wang, Chang; Wu, Hong-lin [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); Yang, Fang [National Key Laboratory of Science and Technology on Tunable Laser, Department of Optoelectronics Information Science Technology, Harbin Institute of Technology, Harbin 150001 (China); Yang, Yan-qiang, E-mail: yqyang@hit.edu.cn [Department of Physics, Harbin Institute of Technology, Harbin 150001 (China); National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, China Academy of Engineering Physics, Mianyang 621900, Sichuan (China)

    2014-01-31

    Highlights: • Mechanism of PIET reaction process for the Rh101{sup +}/DEA system is investigated. • The significant geometrical changes of the charge–transfer complex are explained. • Forward Electron transfer from DEA to Rh101{sup +?} occurs with lifetime of 425–560 fs. • Backward electron transfer occurs with a time constant of 46.16–51.40 ps. • Intramolecular vibrational relaxation occurs with lifetime of 2.77–5.39 ps. - Abstract: The ultrafast photoinduced intermolecular electron transfer (PIET) reaction of Rhodamine 101 (Rh101{sup +}) in N,N-diethylaniline (DEA) was investigated using off-resonance Raman, femtosecond time-resolved multiplex transient grating (TG) and transient absorption (TA) spectroscopies. The Raman spectra indicate that the C=C stretching vibration of the chromophore aromatic ring is more sensitive to ET compared with the C-C stretching mode. The ultrafast photoinduced intermolecular forward ET (FET) from DEA to Rh101{sup +?} occurs on a time scale of ?{sub FET} = 425–560 fs. The backward ET (BET) occurs in the inverted region with a time constant of ?{sub BET} = 46.16–51.40 ps. The intramolecular vibrational relaxation (IVR) process occurs on the excited state potential energy surface with the time constant of ?{sub IVR} = 2.77–5.39 ps.

  6. Electronic transitions and intermolecular forces

    International Nuclear Information System (INIS)

    This thesis describes two different subjects - electronic transitions and intermolecular forces - that are related mainly by the following observation: The wavenumber at which an electronic transition in an atom or molecule occurs, depends on the environment of that atom or molecule. This implies, for instance, that when a molecule becomes solvated its absorption spectrum may be shifted either to the blue or to the red side of the original gasphase spectrum. In part I attention is paid to the experimental aspects of VUV spectroscopy, both in the gasphase and in the condensed phase. In part II a series of papers are presented, dealing with the calculation of intermolecular forces (and some related topics) both for the ground state and for the excited state interactions, using different non-empirical methods. The calculations provide, among other results, a semiquantitative interpretation of the spectral blue shifts encountered in our experiments. (Auth.)

  7. Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(1S) + H2(B 1?/sub u/+)

    International Nuclear Information System (INIS)

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H2(B 1?/sub u/+) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H2(B 1?/sub u/+). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H2(E,F 1?/sub g/+) and with He + H2(X 1?/sub g/+) and cause a local maximum and a deep minimum in the He + H2(B 1?/sub u/+) PES, respectively. The crossing with He + H2(X 1?/sub g/+) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H2(B 1?/sub u/+) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs

  8. Inter-molecular electronic transfer.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Warrendale, PA : Materials Research Society, 2010 - (Steckel, J.; Kotov, N.; Norris, D.; Bawendi, M.; Kuno, M.), 1207N0905-1-7 ISBN 9781617387623. - (MRS Symposium Proceedings. 1207). [MRS Fall Meeting 2009. Boston (US), 30.11.2009-04.12.2009] R&D Projects: GA MŠk ME 866; GA ?R GA202/07/0643 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40500505 Keywords : zero-dimensional nanostructures * quantum dots * DNA molecule * electric conduction Subject RIV: BM - Solid Matter Physics ; Magnetism http://dx.doi.org/10.1557/PROC-1207-N09-05

  9. Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions

    Energy Technology Data Exchange (ETDEWEB)

    Huddleston, R.K.; Miller, J.R.

    1982-04-15

    A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 77/sup 0/K. Good agreement between the model and the experimental kinetic results was obtained.

  10. Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions

    International Nuclear Information System (INIS)

    A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 770K. Good agreement between the model and the experimental kinetic results was obtained

  11. Nanophotonic boost of intermolecular energy transfer

    CERN Document Server

    de Roque, P M; Sapienza, R

    2015-01-01

    We propose a scheme for efficient long-range energy transfer between two distant light emitters separated by more than one wavelength of light, i.e. much beyond the classical Forster radius. A hybrid nanoantenna-waveguide system mediates the transmission of energy, showing enhancements up to 10^8 as compared to vacuum. Our model shows how energy transfer in nanostructured media can be boosted, beyond the simple donor Purcell enhancement, and in particular for large donor-acceptor separations. The scheme we propose connects realistic emitters and could lead to practical on-chip implementations.

  12. Intermolecular Hydrogen Transfer in Isobutane Hydrate

    Directory of Open Access Journals (Sweden)

    Takeshi Sugahara

    2012-05-01

    Full Text Available Electron spin resonance (ESR spectra of butyl radicals induced with ?-ray irradiation in the simple isobutane (2-methylpropane hydrate (prepared with deuterated water were investigated. Isothermal annealing results of the ?-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a hydrogen atom from the isobutane molecule through shared hexagonal-faces of adjacent large cages. During this “hydrogen picking” process, the isobutyl radical is apparently transformed into a tert-butyl radical, while the sum of isobutyl and tert-butyl radicals remains constant. The apparent transformation from isobutyl to tert-butyl radicals is an irreversible first-order reaction and the activation energy was estimated to be 35 ± 3 kJ/mol, which was in agreement with the activation energy (39 ± 5 kJ/mol of hydrogen picking in the ?-ray-irradiated propane hydrate with deuterated water.

  13. Intra- and intermolecular energy transfer in highly excited ozone complexes.

    Science.gov (United States)

    Ivanov, Mikhail V; Grebenshchikov, Sergy Yu; Schinke, Reinhard

    2004-06-01

    The energy transfer of highly excited ozone molecules is investigated by means of classical trajectories. Both intramolecular energy redistribution and the intermolecular energy transfer in collisions with argon atoms are considered. The sign and magnitude of the intramolecular energy flow between the vibrational and the rotational degrees of freedom crucially depend on the projection K(a) of the total angular momentum of ozone on the body-fixed a axis. The intermolecular energy transfer in single collisions between O(3) and Ar is dominated by transfer of the rotational energy. In accordance with previous theoretical predictions, the direct vibrational de-excitation is exceedingly small. Vibration-rotation relaxation in multiple Ar+O(3) collisions is also studied. It is found that the relaxation proceeds in two clearly distinguishable steps: (1) During the time between collisions, the vibrational degrees of freedom are "cooled" by transfer of energy to rotation; even at low pressure equilibration of the internal energy is slow compared to the time between collisions. (2) In collisions, mainly the rotational modes are "cool" by energy transfer to argon. PMID:15268022

  14. Intermolecular electronic and vibrational energy transfer from the single vibronic levels of p-difluorobenzene (1B2/sub u/) to cyclobutanone

    International Nuclear Information System (INIS)

    An attempt has been made to measure the singlet--singlet electronic energy transfer rates from 17 single vibronic levels (SVL) of p-C6H4F2(1B2/sub u/) to cyclobutanone. No variation in the energy transfer cross sections have been found for the 17 SVL transitions, and an average value of 103 A2 (?sigma/sub c/2) is obtained. This value is nearly identical to the value obtained for the vibrationally relaxed, thermal levels. The reason for the lack of variation is suggested to be the consequence of rapid, intramolecular vibrational energy redistribution induced by collisional perturbation

  15. Determination of stepsize parameters for intermolecular vibrational energy transfer

    International Nuclear Information System (INIS)

    The understanding of intermolecular vibrational energy transfer (IVET) is important since it is involved in any mechanism in which internal energy is added or removed from molecules. The database for the details of IVET for highly excited polyatomic molecules is inadequate and must be expanded. The overall objectives of this project are: (1) to determine the dependence of energy relaxation on excitation energy and on the molecular complexity of substrate and deactivator, (2) to assess the importance of intermolecular attractions on IVET, (3) to obtain more detailed information on the energy distribution after collision, and (4) to evaluate the importance of IVET on high temperature unimolecular reactions. The first three objectives are being met by experimentally measuring the time evolution of the average energy of the vibrationally excited species (hydro- and fluoro- carbons excited by a pulsed CO2 laser) and the average energy transferred into relative translation via time resolved IR spectrometry, interferometry and optoacoustic techniques. Trajectory calculations simulating IVET are being performed for model substrate/deactivator pairs to provide additional details and insight on the critical parameters. Our calculations for high temperature unimolecular reactions indicate that IVET effects are significant and must be correctly taken into account. 9 refs., 3 figs., 6 tabs

  16. Determination of stepsize parameters for intermolecular vibrational energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Tardy, D.C.

    1992-03-01

    Intermolecular energy transfer of highly excited polyatomic molecules plays an important role in many complex chemical systems: combustion, high temperature and atmospheric chemistry. By monitoring the relaxation of internal energy we have observed trends in the collisional efficiency ({beta}) for energy transfer as a function of the substrate's excitation energy and the complexities of substrate and deactivator. For a given substrate {beta} increases as the deactivator's mass increase to {approximately}30 amu and then exhibits a nearly constant value; this is due to a mass mismatch between the atoms of the colliders. In a homologous series of substrate molecules (C{sub 3}{minus}C{sub 8}) {beta} decreases as the number of atoms in the substrate increases; replacing F with H increases {beta}. All substrates, except for CF{sub 2}Cl{sub 2} and CF{sub 2}HCl below 10,000 cm{sup {minus}1}, exhibited that {beta} is independent of energy, i.e. <{Delta}E>{sub all} is linear with energy. The results are interpreted with a simple model which considers that {beta} is a function of the ocillators energy and its vibrational frequency. Limitations of current approximations used in high temperature unimolecular reactions were evaluated and better approximations were developed. The importance of energy transfer in product yields was observed for the photoactivation of perfluorocyclopropene and the photoproduction of difluoroethyne. 3 refs., 18 figs., 4 tabs.

  17. Intermolecular proton transfer induced by excess electron attachment to adenine(formic acid)n (n = 2, 3) hydrogen-bonded complexes

    Energy Technology Data Exchange (ETDEWEB)

    Mazurkiewicz, Kamil; Haranczyk, Maciej; Storoniak, Piotr; Gutowski, Maciej S.; Rak, Janusz; Radisic, Dunja; Eustis, Soren; Wang, Di; Bowen, Kit H.

    2007-12-06

    The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA)2,3 complexes span a range of 0.8–1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A–FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed.

  18. Intermolecular proton transfer induced by excess electron attachment to adenine(formic acid) n ( n = 2, 3) hydrogen-bonded complexes

    Science.gov (United States)

    Mazurkiewicz, Kamil; Haranczyk, Maciej; Storoniak, Piotr; Gutowski, Maciej; Rak, Janusz; Radisic, Dunja; Eustis, Soren N.; Wang, Di; Bowen, Kit H.

    2007-12-01

    The propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA) 2,3 complexes span a range of 0.8-1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A-FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed.

  19. Intermolecular proton transfer induced by excess electron attachment to adenine(formic acid)n (n = 2, 3) hydrogen-bonded complexes

    International Nuclear Information System (INIS)

    The propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA)2,3 complexes span a range of 0.8-1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A-FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed

  20. Intermolecular Coulombic Decay in Biology: The Initial Electron Detachment from FADH(-) in DNA Photolyases.

    Science.gov (United States)

    Harbach, Philipp H P; Schneider, Matthias; Faraji, Shirin; Dreuw, Andreas

    2013-03-21

    Intermolecular coulombic decay (ICD) is an efficient mechanism of low-energy electron generation in condensed phases and is discussed as their potential source in living cells, tissues, and materials. The first example of ICD as an operating mechanism in real biological systems, that is, in the DNA repair enzymes photolyases, is presented. Photolyase function involves light-induced electron detachment from a reduced flavin adenine dinucleotide (FADH(-)), followed by its transfer to the DNA-lesion triggering repair of covalently bound nucleobase dimers. Modern quantum chemical methods are employed to demonstrate that the transferred electron is efficiently generated via a resonant ICD process between the antenna pigment and the FADH(-) cofactors. PMID:26291360

  1. Theoretical study on the effect of solvent and intermolecular fluctuations in proton transfer reactions: General theory

    International Nuclear Information System (INIS)

    We present a theory of proton transfer reactions which incorporate the modulation of the proton's potential surface by intermolecular vibrations and the effect of coupling to solvent degree of freedom. The proton tunnels between states corresponding to it being localized in the wells of a double minimum potential. The resulting tunnel splitting depends on the intermolecular separation. The solvent response to the proton's charge is modeled as that of a continuous distribution of harmonic oscillators and the intermolecular stretching mode is also damped because of the interaction with solvent degree of freedom. The transition rate is given by the Fermi Gorlden Rule expression

  2. Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane

    DEFF Research Database (Denmark)

    Medjanik, K.; Perkert, S.

    2010-01-01

    Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP -TCNQ ) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d =0.894nm and d =0.677nm). A softening of the CN stretching vibration (redshift by 7 cm?-1) of TCNQ is visible in the IR spectra, being indicative of a CT on the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts in the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of density-functional theory (DFT) calculations (GAUSSIAN03 with hybrid functional B3LYP). STS reveals a highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods. © 2010 The American Physical Society.

  3. Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane

    DEFF Research Database (Denmark)

    Medjanik, K.; Perkert, S.; Naghavi, S.; Rudloff, Milan; Solovyeva, Vita; Chercka, D.; Huth, M.; Nepijko, S.A.; Methfessel, T.; Felser, C.; Baumgarten, M.; Müllen, K.; Elmers, H.J.; Schönhense, G.

    2010-01-01

    Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP -TCNQ ) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d =0.894nm and d =0.677nm). A softening of the CN stretching vibration (redshift by ...

  4. Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials

    OpenAIRE

    Zang, Huidong; Yan, Liang; Li, Mingxing; HE, LEI; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

    2013-01-01

    Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experime...

  5. 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

  6. Vibronic spectra of perylene bisimide oligomers: effects of intermolecular charge-transfer excitation and conformational flexibility.

    Science.gov (United States)

    Gao, Fang; Zhao, Yi; Liang, WanZhen

    2011-03-31

    We have recently presented a theoretical study on the temperature-dependent absorption and photoluminescence spectroscopy of rubrene multichromophores by combining the time-dependent long-range-corrected density functional theory with the Frenkel exciton model (Gao; et al. J. Phys. Chem. A2009, 113, 12847). The spectra of rubrene multichromophores up to heptamers have been calculated and the effects of exciton-phonon coupling and temperature on the photophysical properties of both H- and J-aggregated oligomers were addressed. However, in that work the contribution of intermolecular charge-transfer excitons (CTEs) to vibronic spectra was not addressed. Here we take into account the effect of CTEs for the absorption and emission spectra of the aggregated perylene bisimide (PBI) oligomers in order to have a quantitative explanation to the experimental absorption and emission spectra of the PBI dyes. The role of intermolecular CTEs is discussed for different intermolecular orientations and distances. The simulations demonstrate that the contribution of CTEs becomes significant when the intermolecular distance is less than 4.5 Å for the ?-? stacked PBI aggregates, and the mixed exciton model is prerequisite to explain the experimentally observed red-shift of the absorption spectra in this case. The large Stokes shift of the emission spectra can be reproduced by our model, and it is induced by the asymmetric nature of the lowest excitonic state of the H-aggregated oligomers. The experimentally observed broad emission bands come from two species with different conformations. As for J-aggregated PBI oligomers, the interactions of FEs induce the red-shift and the increase of the relative intensity of 0-0 peak of the absorption spectra with more aggregated units. PMID:21384839

  7. TDDFT study of twisted intramolecular charge transfer and intermolecular double proton transfer in the excited state of 4'-dimethylaminoflavonol in ethanol solvent.

    Science.gov (United States)

    Wang, Ye; Shi, Ying; Cong, Lin; Li, Hui

    2015-02-25

    Time-dependent density functional theory method at the def-TZVP/B3LYP level was employed to investigate the intramolecular and intermolecular hydrogen bonding dynamics in the first excited (S1) state of 4'-dimethylaminoflavonol (DMAF) monomer and in ethanol solution. In the DMAF monomer, we demonstrated that the intramolecular charge transfer (ICT) takes place in the S1 state. This excited state ICT process was followed by intramolecular proton transfer. Our calculated results are in good agreement with the mechanism proposed in experimental work. For the hydrogen-bonded DMAF-EtOH complex, it was demonstrated that the intermolecular hydrogen bonds can induce the formation of the twisted intramolecular charge transfer (TICT) state and the conformational twisting is along the C3-C4 bond. Moreover, the intermolecular hydrogen bonds can also facilitate the intermolecular double proton transfer in the TICT state. A stepwise intermolecular double proton transfer process was revealed. Therefore, the intermolecular hydrogen bonds can alter the mechanism of intramolecular charge transfer and proton transfer in the excited state for the DMAF molecule. PMID:25282020

  8. 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 th...

  9. Ground state of ?-conjugated polymer chains forming an intermolecular charge-transfer complex as probed by Raman spectroscopy

    International Nuclear Information System (INIS)

    The intermolecular charge-transfer complex (CTC) between the conjugated polymer MEH-PPV and the low-molecular organic acceptor trinitrofluorenone (TNF) has been studied by Raman and optical absorption spectroscopy. On mixing MEH-PPV with TNF, an absorption band due to the CTC appeared in the optical gap of the polymer, whereas, in the Raman spectra, characteristic bands of the polymer are shifted and their widths and intensities change. The low-frequency shift of the strongest band at 1580 cm-1 in the Raman spectrum of the polymer, assigned to the symmetric stretching vibration of the phenyl group, is shown to be due to electron density transfer from the ?-conjugated system of the polymer to the acceptor and is as large as 5 cm-1, which corresponds to a charge transfer on the order of 0.1e-1. Even at a low acceptor concentration (one TNF molecule per 10 monomer units of the polymer), most Raman-active conjugated chains are involved in the CTC. It is suggested that conjugated segments of the polymer can form a CTC of variable composition MEH-PPV: TNF = 1: X, where 0.1 ? X ? 0.5 (for each monomer unit of the polymer), and one TNF molecule can thereby interact with two conjugated segments of MEH-PPV. The conjugated polymer chains involved in the CTC can become more planar, and their interaction with the local environment can noticeably change; however, their conjugation length, most likely, remains unaltered

  10. Magneto-dielectric effects induced by optically-generated intermolecular charge-transfer states in organic semiconducting materials.

    Science.gov (United States)

    Zang, Huidong; Yan, Liang; Li, Mingxing; He, Lei; Gai, Zheng; Ivanov, Ilia; Wang, Min; Chiang, Long; Urbas, Augustine; Hu, Bin

    2013-01-01

    Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experimental evidence indicate that the singlets and triplets in charge-transfer states have stronger and weaker electrical polarizations, respectively. Therefore, the observed magneto-dielectric effect can be attributed to magnetically-dependent singlet/triplet ratio in intermolecular charge-transfer states. In principle, a magneto-dielectric effect can be generated through two different channels based on magneto-polarization and magneto-current effects when the singlet/triplet ratio in intermolecular charge-transfer states is changed by a magnetic field. We find, from the simulation of dielectric effects, that magneto-polarization and magneto-current effects play primary and secondary roles in the generation of magneto-dielectric effect. PMID:24084983

  11. On the reaction mechanism of the complete intermolecular O2 transfer between mononuclear nickel and manganese complexes with macrocyclic ligands.

    Science.gov (United States)

    Zapata-Rivera, Jhon; Caballol, Rosa; Calzado, Carmen J; Liakos, Dimitrios G; Neese, Frank

    2014-10-01

    The recently described intermolecular O2 transfer between the side-on Ni-O2 complex [(12-TMC)Ni-O2](+) and the manganese complex [(14-TMC)Mn](2+), where 12-TMC and 14-TMC are 12- and 14-membered macrocyclic ligands, 12-TMC=1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane and 14-TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, is studied by means of DFT methods. B3LYP calculations including long-range corrections and solvent effects are performed to elucidate the mechanism. The potential energy surfaces (PESs) compatible with different electronic states of the reactants have been analyzed. The calculations confirm a two-step reaction, with a first rate-determining bimolecular step and predict the exothermic character of the global process. The relative stability of the products and the reverse barrier are in line with the fact that no reverse reaction is experimentally observed. An intermediate with a ?-?(1):?(1)-O2 coordination and two transition states are identified on the triplet PES, slightly below the corresponding stationary points of the quintet PES, suggesting an intersystem crossing before the first transition state. The calculated activation parameters and the relative energies of the two transition sates and the products are in very good agreement with the experimental data. The calculations suggest that a superoxide anion is transferred during the reaction. PMID:25179780

  12. Intermolecular hydrogen bonds: From temperature-driven proton transfer in molecular crystals to denaturation of DNA

    Indian Academy of Sciences (India)

    Mark Johnson

    2008-11-01

    We have combined neutron scattering and a range of numerical simulations to study hydrogen bonds in condensed matter. Two examples from a recent thesis will be presented. The first concerns proton transfer with increasing temperature in short inter-molecular hydrogen bonds [1,2]. These bonds have unique physical and chemical properties and are thought to play a fundamental role in processes like enzymatic catalysis. By combining elastic and inelastic neutron scattering results with ab initio, lattice dynamics and molecular dynamics simulations, low frequency lattice modes are identified which modulate the potential energy surface of the hydrogen bond proton and drive proton transfer. The second example concerns base-pair opening in DNA which is the fundamental physical process underlying biological processes like denaturation and transcription. We have used an emprical force field and a large scale, all-atom phonon calculation to gain insight into the base-pair opening modes and the apparent `energy gap' between the accepted frequencies for these modes ($\\sim 100$ cm-1 or $\\sim 140$ K) and the temperature of the biological processes (room temperature to 100° C) [3]. Inelastic neutron scattering spectra on aligned, highly crystalline DNA samples, produced at the ILL, provide the reference data for evaluating the precision of these simulation results.

  13. Reversible electron-induced cis-trans isomerization mediated by intermolecular interactions

    International Nuclear Information System (INIS)

    Reversible isomerization processes are rarely found when organic molecular switches are adsorbed on metal surfaces. One obstacle is the large energy difference of the isomeric forms, since usually the most planar conformer has the largest adsorption energy. In the example of an imine derivative, we show a strategy for also stabilizing the non-planar isomer by intermolecular bonding to its neighbors. Tunneling electrons from the tip of a scanning tunneling microscope can then be used to induce reversible switching between the trans and cis-like state. Supported by model force-field calculations, we illustrate that the most probable cause of the enhanced stability of the three-dimensional cis state at specific adsorption sites is the electrostatic interaction with N sites of the neighboring molecule.

  14. Electron transfer in biology

    Science.gov (United States)

    Williams, R. J. P.

    Electron transfer is one of the key reactions of biology not just in catalysis of oxidation/reduction reactions but in the conversion of sources of energy such as light to usable form for chemical transformations. There are then two intriguing problems. What is the nature of the matrix in which electrons flow in a biological cell after the initial charge separation due for example to the absorption of light. Here we are examining biological structures similar to man's electronic wires and the construction must be of low resistance in what are apparently insulators - organic polymers. It has been found that the electronic conduction system is largely made from metallo-proteins associated with lipid membranes. We understand much about these biological wires today. The second problem concerns the conversion of the energy captured from the light into usable chemical form. The major synthetic step in the production of biological polymers, including proteins, DNA, RNA, polysaccharides and fats, is condensation, i.e. the removal of water in the formation of amides, esters and so on. Now these condensation reactions are driven in biology by using a drying agent in water, namely the anhydride, pyrophosphate, in a special compound ATP, adenosine triphosphate. The central problem is to discover exactly how the flow of electrons can be related to the synthesis of (bound) pyrophosphate. (In a thermodynamic sense pyrophosphate is a water soluble kinetically stable drying agent comparable with solid P2O5.) In the biological systems the connection between these different classes of reaction, electron transfer and condensation, is known to be via the production of an energized gradient of protons across the biological membrane which arises from the flow of electrons across the same membrane in the electron transport wires of biology. However we do not understand thoroughly the steps which lead from electron flow in a membrane to proton gradients in that membrane, i.e. electron/proton coupling. Again we do not understand thoroughly how subsequently the proton gradient across a membrane makes ATP, pyrophosphate. Today there is good experimental evidence as to the likely answers in principle. These analyse the coupling devices in mechanical terms. In this article I describe at first the 'wires' of biology, uncoupled simple electron flow, and then go on to the ways in which electron flow could be transduced by mechanical devices, also proteins, into proton gradients and then ATP. This will be termed coupled electron flow. The objective of the article is to stimulate participation by physical chemists in the further description of biological energy capture from light or the oxidation of hydrocarbons to a form suitable for driving chemical syntheses in a controlled manner.

  15. Determination of stepsize parameters for intermolecular vibrational energy transfer: Progress report, May 1, 1987-April 30, 1988

    International Nuclear Information System (INIS)

    Intermolecular vibrational energy transfer for highly excited polyatomic molecules is involved in any mechanism in which excitation energy is required (pyrolysis) or in which energy must be removed from a hot source (cooling). The average energy removed per collision, , is a useful quantity to compare efficiency for energy transfer. The objectives of this work are: to determine the dependence of on excitation energy and on the molecular complexity (number of vibrational modes) of substrate and deactivator; to assess the importance of intermolecular attractions (complex formation) on vibrational energy transfer; to obtain detailed information on the energy distribution after collision and to evaluate the importance of on high-temperature unimolecular reactions. This information will be obtained by monitoring the time dependence of the infrared emission, ultraviolet absorption, refractive index and pressure. The results from these complementary techniques will be benchmarked with values from previous studies on the relaxation of chemically activated alkyl and fluoroalkyl radicals. Trajectory calculations simulating energy transfer are being performed for ''generic'' substrate/deactivator pairs to provide additional details and insight on the important parameters. Model calculations are also being performed to determine the feasibility of obtaining information from experimental data for high-temperature unimolecular reactions

  16. 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

  17. Intramolecular electron transfer rates

    Science.gov (United States)

    Hupp, Joseph T.

    The initial goals of this project were: (1) to construct pulsed-accelerated-flow and pulsed-laser (transient absorbance) instruments for intramolecular electron-transfer rate measurements, (2) to design and synthesize appropriate molecules and perform such measurements, (3) to develop further an electrochemical method for gauging site-to-site electronic coupling, and (4) to apply time-dependent Raman scattering theory to the problem of inner-shell reorganization in charge-transfer reactions. Although all four goals were met, we also found it necessary to pursue studies in some unforeseen directions. For example, early on we discovered that medium effects (aggregation and ion pairing) could play a very large, and previously unrecognized, role in some optical intervalence reactions. Given the importance of the effects to the areas above, we chose to map them in a fairly complete fashion. Also, in anticipation of possible renewal we initiated studies in a new area: bimolecular photoredox kinetics in supercritical media. Finally, in a small project carried out largely by undergraduates we examined solvent tuning effects upon lifetimes of photo-excited ruthenium am(m)ine bipyridine complexes. The key new findings and other highlights of these studies are outlined.

  18. Electron transfer at nickel electrode

    International Nuclear Information System (INIS)

    There is considerable contemporary interest in the electron transfer reaction. at active (transition) metal electrodes. this work reports the electrochemical behavior of potassium ferrocyanide at nickel electrode in aqueous potassium nitrate solution. Potassium ferrocyanide is frequently employed to probe one-electron transfer reactions at solid, electrodes. It was found that the voltammetric oxidation of ferrocyanide at nickel is a simple electron transfer reaction. Normal pulse voltammetry revealed similar behavior. (author)

  19. Proton-Coupled Electron Transfer

    Energy Technology Data Exchange (ETDEWEB)

    Weinberg, Dave; Gagliardi, Christopher J.; Hull, Jonathan F; Murphy, Christine Fecenko; Kent, Caleb A.; Westlake, Brittany C.; Paul, Amit; Ess, Daniel H; McCafferty, Dewey Granville; Meyer, Thomas J

    2012-07-11

    Proton-Coupled Electron Transfer (PCET) describes reactions in which there is a change in both electron and proton content between reactants and products. It originates from the influence of changes in electron content on acid-base properties and provides a molecular-level basis for energy transduction between proton transfer and electron transfer. Coupled electron-proton transfer or EPT is defined as an elementary step in which electrons and protons transfer from different orbitals on the donor to different orbitals on the acceptor. There is (usually) a clear distinction between EPT and H-atom transfer (HAT) or hydride transfer, in which the transferring electrons and proton come from the same bond. Hybrid mechanisms exist in which the elementary steps are different for the reaction partners. EPT pathways such as PhO•/PhOH exchange have much in common with HAT pathways in that electronic coupling is significant, comparable to the reorganization energy with H{sub DA} ~ ?. Multiple-Site Electron-Proton Transfer (MS-EPT) is an elementary step in which an electron-proton donor transfers electrons and protons to different acceptors, or an electron-proton acceptor accepts electrons and protons from different donors. It exploits the long-range nature of electron transfer while providing for the short-range nature of proton transfer. A variety of EPT pathways exist, creating a taxonomy based on what is transferred, e.g., 1e-/2H+ MS-EPT. PCET achieves “redox potential leveling” between sequential couples and the buildup of multiple redox equivalents, which is of importance in multielectron catalysis. There are many examples of PCET and pH-dependent redox behavior in metal complexes, in organic and biological molecules, in excited states, and on surfaces. Changes in pH can be used to induce electron transfer through films and over long distances in molecules. Changes in pH, induced by local electron transfer, create pH gradients and a driving force for long-range proton transfer in Photosysem II and through other biological membranes. In EPT, simultaneous transfer of electrons and protons occurs on time scales short compared to the periods of coupled vibrations and solvent modes. A theory for EPT has been developed which rationalizes rate constants and activation barriers, includes temperature- and driving force (?G)-dependences implicitly, and explains kinetic isotope effects. The distance-dependence of EPT is dominated by the short-range nature of proton transfer, with electron transfer being far less demanding.Changes in external pH do not affect an EPT elementary step. Solvent molecules or buffer components can act as proton donor acceptors, but individual H2O molecules are neither good bases (pKa(H3O+) = -1.74) nor good acids (pKa(H2O) = 15.7). There are many examples of mechanisms in chemistry, in biology, on surfaces, and in the gas phase which utilize EPT. PCET and EPT play critical roles in the oxygen evolving complex (OEC) of Photosystem II and other biological reactions by decreasing driving force and avoiding high-energy intermediates.

  20. Determination of stepsize parameters for intermolecular vibrational energy transfer. Final report, May 1, 1987--December 31, 1991

    Energy Technology Data Exchange (ETDEWEB)

    Tardy, D.C.

    1992-03-01

    Intermolecular energy transfer of highly excited polyatomic molecules plays an important role in many complex chemical systems: combustion, high temperature and atmospheric chemistry. By monitoring the relaxation of internal energy we have observed trends in the collisional efficiency ({beta}) for energy transfer as a function of the substrate`s excitation energy and the complexities of substrate and deactivator. For a given substrate {beta} increases as the deactivator`s mass increase to {approximately}30 amu and then exhibits a nearly constant value; this is due to a mass mismatch between the atoms of the colliders. In a homologous series of substrate molecules (C{sub 3}{minus}C{sub 8}) {beta} decreases as the number of atoms in the substrate increases; replacing F with H increases {beta}. All substrates, except for CF{sub 2}Cl{sub 2} and CF{sub 2}HCl below 10,000 cm{sup {minus}1}, exhibited that {beta} is independent of energy, i.e. <{Delta}E>{sub all} is linear with energy. The results are interpreted with a simple model which considers that {beta} is a function of the ocillators energy and its vibrational frequency. Limitations of current approximations used in high temperature unimolecular reactions were evaluated and better approximations were developed. The importance of energy transfer in product yields was observed for the photoactivation of perfluorocyclopropene and the photoproduction of difluoroethyne. 3 refs., 18 figs., 4 tabs.

  1. Chemistry of binuclear bridge complexes of platinum metals. 5. Intermolecular electron transfer in mixed-valent complexes [(NH3)5Ru-py-(C2H2)n-py-Ru(NH3)5]5+ with extended bridge ligands

    International Nuclear Information System (INIS)

    Energies and intensities of spectral transitions in [(NH3)5Ru-py-(C2H2)n-py-Ru(NH3)5]5+ complexes are calculated in the framework of quantum-chemical procedure developed and approved earlier. Structure-dynamic approach is suggested for considering the process of intramolecular electron transfer; which is based on the solution of nonstationary Shroedinger equation in the basis of multi-electron functions describing different structural nodes of Ru(2) -> pyridyl -> (C2H2)n -> pyridyl -> Ru(3) electron-transport chain

  2. Intermolecular Atom Transfer Radical Addition to Olefins Mediated by Oxidative Quenching of Photoredox Catalysts

    OpenAIRE

    Nguyen, John D.; Tucker, Joseph W.; Konieczynska, Marlena D.; Corey R. J. Stephenson

    2011-01-01

    Atom transfer radical addition of haloalkanes and ?-halocarbonyls to olefins is efficiently performed with the photocatalyst Ir[(dF(CF3)ppy)2(dtbbpy)]PF6. This protocol is characterized by excellent yields, mild conditions, low catalyst loading, and broad scope. In addition, the atom transfer protocol can be used to quickly and efficiently introduce vinyl trifluoromethyl groups to olefins and access 1,1-cyclopropane diesters.

  3. Solvation study of the non-specific lipid transfer protein from wheat by intermolecular NOEs with water and small organic molecules

    Energy Technology Data Exchange (ETDEWEB)

    Liepinsh, Edvards [Karolinska Institutet, Department of Molecular Biochemistry and Biophysics (Sweden); Sodano, Patrick; Tassin, Severine [Rue Charles Sadron, Centre de Biophysique Moleculaire (France); Marion, Didier [INRA, Laboratoire de Biochimie et Technologie des Proteines (France); Vovelle, Francoise [Rue Charles Sadron, Centre de Biophysique Moleculaire (France); Otting, Gottfried [Karolinska Institutet, Department of Molecular Biochemistry and Biophysics (Sweden)

    1999-11-15

    Intermolecular nuclear Overhauser effects (NOEs) were measured between the protons of various small solvent or gas molecules and the non-specific lipid transfer protein (ns-LTP) from wheat. Intermolecular NOEs were observed with the hydrophobic pocket in the interior of wheat ns-LTP, which grew in intensity in the order cyclopropane (saturated solution) < methane (140 bar) < ethane (40 bar) < acetonitrile (5% in water) < cyclohexane (saturated solution) < benzene (saturated solution). No intermolecular NOEs were observed with dioxane (5% in water). The intermolecular NOEs were negative for all of the organic molecules tested. Intermolecular NOEs between wheat ns-LTP and water were weak or could not be distinguished from exchange-relayed NOEs. As illustrated by the NOEs with cyclohexane versus dioxane, the hydrophobic pocket in wheat ns-LTP preferably binds non-polar molecules. Yet, polar molecules like acetonitrile can also be accommodated. The pressure dependence of the NOEs between methane and wheat ns-LTP indicated incomplete occupancy, even at 190 bar methane pressure. In general, NOE intensities increased with the size of the ligand molecule and its vapor pressure. NMR of the vapor phase showed excellent resolution between the signals from the gas phase and those from the liquid phase. The vapor concentration of cyclohexane was fivefold higher than that of the dioxane solution, supporting the binding of cyclohexane versus uptake of dioxane.

  4. Analytical model for rates of electron attachment and intramolecular electron transfer in electron transfer dissociation mass spectrometry.

    Science.gov (United States)

    Simons, Jack

    2010-05-26

    A new physical model is put forth to allow the prediction of electron transfer rates and distances for (i) intramolecular transfer from an n > or = 3 Rydberg orbital on a positive site to a disulfide or amide bond site and (ii) intermolecular transfer from an anion donor to an n > or = 3 Rydberg orbital of a positively charged polypeptide. Although ab initio methods have proven capable of handling such electron transfer events when the Rydberg orbital has principal quantum number n = 3, they have proven to be incapable of handling Rydberg states having quantum number n > 3, so having a new tool capable of handling n > 3 Rydberg states is important. The model (i) focuses on each Rydberg orbital's large peak of high amplitude, (ii) approximates the electron density within this peak as constant within a radial shell characterized by a radius and thickness T both of which depend on the quantum number n, and (iii) assumes that strong coupling (either with an orbital of an anion donor or to a disulfide sigma* or a backbone amide pi* orbital) occurs when the valence orbital penetrates fully within the radial shell of the Rydberg orbital. These assumptions permit a derivation of the ratios of rates of electron transfer for n > 3 to those for n = 3. Combining these ratios with ab initio rates for n = 3 allows one to make rate predictions for inter- and intramolecular electron transfer involving Rydberg orbitals appropriate to the electron transfer dissociation process. One important prediction of this model is that the combination of large-penetration and Landau-Zener surface-crossing conditions places very severe limitations on which Rydberg levels can initially be populated in electron transfer dissociation. Another prediction is that a Rydberg orbital of a given principal quantum number n has a limited range of distances over which it can transfer an electron; sigma* or pi* orbitals either too far from or too close to a given Rydberg orbital cannot accept an electron from that orbital. PMID:20438123

  5. Experimental and theoretical electron-density study of three isoindole derivatives: topological and Hirshfeld surface analysis of weak intermolecular interactions.

    Science.gov (United States)

    Ch?ci?ska, Lilianna; Grabowsky, Simon; Ma?ecka, Magdalena; Rybarczyk-Pirek, Agnieszka J; Jó?wiak, Andrzej; Paulmann, Carsten; Luger, Peter

    2011-12-01

    A combined experimental and theoretical study of three isoindole derivatives was made on the basis of a topological analysis of their electron-density distributions. Experimental electron densities were determined from high-resolution X-ray diffraction data sets measured with synchrotron radiation at 100 K, whereas theoretical calculations were performed using DFT methods at the B3LYP\\6-311++G(3df,3pd) level of approximation. Both experimental and theoretical models are in good agreement with each other. Since the analysed structures possess a variety of hydrogen-bonding interactions, weak intermolecular contacts of C-H···C(?), C,N(?)···C,N(?) and H···H types were subject to our special interest and are discussed in detail. They were characterized quantitatively and qualitatively by topological properties using Bader's Atoms in Molecules theory and by mapping the electron-density distribution, electrostatic potential and a geometric function on the Hirshfeld surface. This way the forces and directions of intermolecular interactions as present on the molecular surfaces were depicted and described. These interactions not only guide crystal packing, but are likewise important for recognition processes involving (aza)isoindole fragments in a biological environment. PMID:22101546

  6. Dynamical aspects of intermolecular proton transfer in liquid water and low-density amorphous ices

    Science.gov (United States)

    Tahat, Amani; Martí, Jordi

    2014-05-01

    The microscopic dynamics of an excess proton in water and in low-density amorphous ices has been studied by means of a series of molecular dynamics simulations. Interaction of water with the proton species was modelled using a multistate empirical valence bond Hamiltonian model. The analysis of the effects of low temperatures on proton diffusion and transfer rates has been considered for a temperature range between 100 and 298 K at the constant density of 1 g cm-3. We observed a marked slowdown of proton transfer rates at low temperatures, but some episodes are still seen at 100 K. In a similar fashion, mobility of the lone proton gets significantly reduced when temperature decreases below 273 K. The proton transfer in low-density amorphous ice is an activated process with energy barriers between 1-10 kJ/mol depending of the temperature range considered and eventually showing Arrhenius-like behavior. Spectroscopic data indicated the survival of both Zundel and Eigen structures along the whole temperature range, revealed by significant spectral frequency shifts.

  7. 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

  8. Dynamical aspects of intermolecular proton transfer in liquid water and low-density amorphous ices

    OpenAIRE

    Tahat, Amani; Martí Rabassa, Jordi

    2014-01-01

    The microscopic dynamics of an excess proton in water and in low-density amorphous ices has been studied by means of a series of molecular dynamics simulations. Interaction of water with the proton species was modelled using a multistate empirical valence bond Hamiltonian model. The analysis of the effects of low temperatures on proton diffusion and transfer rates has been considered for a temperature range between 100 and 298 K at the constant density of 1 g cm -3 . We observed a marked slo...

  9. Intermolecular energy transfer from UO22+ to Eu3+ in solutions

    International Nuclear Information System (INIS)

    The quenching constants for the UO22+ ion fluorescence by the Eu3+ ion in H2O, D2O, potassium formate and acetic acid media were determined by measuring the decrease in intensity of the 5050 A fluorescence peak and the lifetime of the UO22+ ion fluorescence. The energy transferred to the Eu3+ ion was found to be a small fraction of the energy lost by the UO22+ ion by the non-radiative processes. The variations of the quenching constants of the UO22+ ion and the fluorescence lifetimes were determined for different concentrations of potassium formate and acetic acid. These results indicate that the UO22+ ion forms inner sphere complexes with the two ligands mentioned

  10. Probing intermolecular protein-protein interactions in the calcium-sensing receptor homodimer using bioluminescence resonance energy transfer (BRET)

    DEFF Research Database (Denmark)

    Jensen, Anders A.; Hansen, Jakob L

    2002-01-01

    The calcium-sensing receptor (CaR) belongs to family C of the G-protein coupled receptor superfamily. The receptor is believed to exist as a homodimer due to covalent and non-covalent interactions between the two amino terminal domains (ATDs). It is well established that agonist binding to family C receptors takes place at the ATD and that this causes the ATD dimer to twist. However, very little is known about the translation of the ATD dimer twist into G-protein coupling to the 7 transmembrane moieties (7TMs) of these receptor dimers. In this study we have attempted to delineate the agonist-induced intermolecular movements in the CaR homodimer using the new bioluminescence resonance energy transfer technique, BRET2, which is based on the transference of energy from Renilla luciferase (Rluc) to the green fluorescent protein mutant GFP2. We tagged CaR with Rluc and GFP2 at different intracellular locations. Stable and highly receptor-specific BRET signals were obtained in tsA cells transfected with Rluc- and GFP2-tagged CaRs under basal conditions, indicating that CaR is constitutively dimerized. However, the signals were not enhanced by the presence of agonist. These results could indicate that at least parts of the two 7TMs of the CaR homodimer are in close proximity in the inactivated state of the receptor and do not move much relative to one another upon agonist activation. However, we cannot exclude the possibility that the BRET technology is unable to register putative conformational changes in the CaR homodimer induced by agonist binding because of the bulk sizes of the Rluc and GFP2 molecules.

  11. Intermolecular charge transfer and vibrational analysis of hydrogen bonding in acetazolamide

    Science.gov (United States)

    Chaturvedi, Deepika; Gupta, Vineet; Tandon, Poonam; Sharma, Anamika; Baraldi, C.; Gamberini, M. C.

    2012-12-01

    In the present work the structural and spectral characteristics of acetazolamide have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. Based on these results, we have discussed the correlation between the vibrational modes and the structure of the dimers of acetazolamide. The calculated vibrational spectra of three dimers of acetazolamide have been compared with observed spectra, and the assignment of observed bands was carried out using potential energy distribution. The observed spectra agree well with the values computed from the DFT. A comparison of observed and calculated vibrational spectra clearly shows the effect of hydrogen bonding. The frequency shifts observed for the different dimers are in accord with the hydrogen bonding in acetazolamide. Natural bond orbital (NBO) analyses reflect the charge transfer interaction in the individual hydrogen bond units and the stability of different dimers of acetazolamide.

  12. Intermolecular interactions of proton transfer compounds: synthesis, crystal structure and Hirshfeld surface analysis.

    Science.gov (United States)

    Direm, Amani; Altomare, Angela; Moliterni, Anna; Benali-Cherif, Nourredine

    2015-08-01

    Three new proton transfer compounds, [2-ammonio-5-methylcarboxybenzene perchlorate (1), (C8H10NO2(+)·ClO4(-)), 4-(ammoniomethyl)carboxybenzene nitrate (2), (C8H10NO2(+)·NO3(-)), and 4-(ammoniomethyl)carboxybenzene perchlorate (3), (C8H10NO2(+)·ClO4(-))], have been synthesized, their IR modes of vibrations have been assigned and their crystal structures studied by means of single-crystal X-ray diffraction. Their asymmetric units consist of one cation and one anion for both compounds (1) and (2). However, the crystal structure of compound (3) is based on a pair of cations and a pair of anions in its asymmetric unit. The three-dimensional Hirshfeld surface analysis and the two-dimensional fingerprint maps revealed that the three structures are dominated by H...O/O...H and H...H contacts. The strongest hydrogen-bonding interactions are associated with O-H...O and N-H...O constituting the highest fraction of approximately 50%, followed by those of the H...H type contributing 20%. Other close contacts are also present, including weak C...H/H...C contacts (with about 10%). PMID:26208623

  13. Spectroscopic study on the intermolecular double proton transfer in 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine with acid

    International Nuclear Information System (INIS)

    With 2,4,6-trichloro-1,3,5-triazine as starting material, a functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated by UV–vis absorption and fluorescence emission. It is found that both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer, resulting in amino–imino tautomerization emission in excited state. - Highlights: ? A functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. ? Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated. ? Both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer. ? Amino–imino tautomerization emission in excited state are proposed.

  14. Spectroscopic study on the intermolecular double proton transfer in 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine with acid

    Energy Technology Data Exchange (ETDEWEB)

    Li Zongyao [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Research Institute of Henan Coal and Chemical Industry Group, Zhengzhou 450046 (China); Li Chunli [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Zhao Chunmei [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Institute for Functional Nanomaterials, Huanghe Science and Technology College, Zhengzhou 450000 (China); Wu Wei [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Wang Hua, E-mail: hwang@henu.edu.cn [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China)

    2012-10-15

    With 2,4,6-trichloro-1,3,5-triazine as starting material, a functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated by UV-vis absorption and fluorescence emission. It is found that both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer, resulting in amino-imino tautomerization emission in excited state. - Highlights: Black-Right-Pointing-Pointer A functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Black-Right-Pointing-Pointer Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated. Black-Right-Pointing-Pointer Both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer. Black-Right-Pointing-Pointer Amino-imino tautomerization emission in excited state are proposed.

  15. Electrostatic orientation during electron transfer between flavodoxin and cytochrome c.

    Science.gov (United States)

    Matthew, J B; Weber, P C; Salemme, F R; Richards, F M

    1983-01-13

    Various studies have shown that reaction rates between reversibly binding electron transfer proteins depend strongly on solution ionic strength. These observations suggest that intermolecular electrostatic interactions are important in facilitating the formation of a productive reaction complex. A recently examined system involves the reduction of vertebrate cytochrome c by bacterial flavodoxin. Although this is a nonphysiological reaction, it proceeds with rates typical for natural partners and is similarly inhibited at high ionic strengths. Here we describe computational studies which examine the role of electrostatics in the formation of a putative reaction complex between flavodoxin and cytochrome c. The results suggest that electrostatic interactions preorient the molecules before they make physical contact, facilitating the formation of an optimal reaction complex. PMID:6296691

  16. Observation of proton transfer in 2-aminopyridine dimer by electron and mass spectroscopy.

    Science.gov (United States)

    Samoylova, Elena; Radloff, Wolfgang; Ritze, Hans-Hermann; Schultz, Thomas

    2009-07-23

    A photoinitiated intermolecular electron-proton transfer reaction in 2-aminopyridine dimer was investigated by femtosecond pump-probe electron-ion coincidence spectroscopy and accompanying theory. Excited-state population dynamics were observed in real time by time-resolved mass spectroscopy, and the respective excited-state character of locally excited and proton/hydrogen transfer states was identified in coincident electron spectra. Two reaction channels for an ultrafast (sub-50 fs) and a slower (approximately 75 ps) proton/hydrogen transfer were observed and indicate that vibrational energy redistribution may lead to efficient population trapping in the excited state. Spectroscopic evidence of an unexpected hydrogen-transfer reaction in photoexcited aminopyridine monomer is also presented. PMID:19569694

  17. Ground and excited state electron transfer dynamics

    OpenAIRE

    Brennan, Jennifer L.

    2002-01-01

    The focus of this work is the investigation of the factors controlling electron transfer in molecular electronic systems, in particular those affecting electron transfer to and from electronically excited states. To achieve this, a number of mono- and trimetallic osmium and ruthenium complexes were synthesised and characterised. Monolayers of an osmium polypyridyl complex bound to a platinum microelectrode via a ¿rara-l,2-bis-(4-pyridyl)ethylene bridge were formed to probe ground state electr...

  18. Anisotropy of intermolecular forces

    Energy Technology Data Exchange (ETDEWEB)

    Leonas, V.B.

    1979-01-01

    The paper reviews the recent literature on anisotropic intermolecular interactions. Attention is given to: (1) the theory of intermolecular potentials, (2) theoretical and semiempirical determinations of short-duration intermolecular forces, and (3) experimental data on anisotropic intermolecular interactions. Prospects for future studies in this field are discussed.

  19. Valence anions in complexes of adenine and 9-methyladenine with formic acid - stabilization by intermolecular proton transfer

    Energy Technology Data Exchange (ETDEWEB)

    Mazurkiewicz, Kamil; Haranczyk, Maciej; Gutowski, Maciej S.; Rak, Janusz; Radisic, Dunja; Eustis, Soren; Wang, Di; Bowen, Kit H.

    2007-02-07

    The photoelectron spectra of the adenine-formic acid (AFA)- and 9-methyladenine-formic acid (MAFA)- anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9- methyladenine and formic acid were also studied computationally at the B3LYP, second order Møller-Plesset and coupled clusters levels of theory, with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both (AFA)- and (MAFA)- occupies a p* orbital localized on adenine/9-methyladenine and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA- and MAFA-, respectively. The excess electron attachment to the complexes induces a barrierfree proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-mathyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine(9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low energy electrons. The calculations were performed at the Academic Computer Center in Gda?sk (TASK) and at the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory, which is operated by Battelle for the US Department of Energy. The MSCF resources were available through a Computational Grand Challenge Application grant.

  20. Density matrix based microscopic theory of molecule metal-nanoparticle interactions: Linear absorbance and plasmon enhancement of intermolecular excitation energy transfer

    Science.gov (United States)

    Kyas, Gerold; May, Volkhard

    2011-01-01

    A microscopic theory of interacting molecule metal-nanoparticle (MNP) systems is presented and used to compute absorption spectra and the plasmon enhancement of intermolecular excitation energy transfer (EET). The approach is based on a nonperturbative consideration of the Coulomb coupling matrix elements responsible for EET between the molecules and the MNP. In this way, the need to determine the local fields induced by surface plasmon excitations of the MNP is removed, but the whole description is restricted to distances among the interacting species less than the wavelength of absorbed photons. Based on a density matrix theory, the approach accounts for the vibrational level structure of the molecules, intramolecular vibrational energy redistribution (IVR), and plasmon damping. Numerical results for linear absorbance spectra and EET dynamics are offered. In this respect the importance of energy dissipation in the MNP due to rapid surface plasmon decay is emphasized.

  1. Computer simulation of electron transfer in molecular electronic devices

    OpenAIRE

    Correia, Helena M. G.; Ramos, Marta M. D.

    2005-01-01

    The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-Bis((2???-para-mercaptophen...

  2. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

    CERN Document Server

    Haverkate, Lucas; Johnson, Mark; Carter, Elisabeth; Kotlewski, Arek; Picken, Stephen; Mulder, Fokko; Kearley, Gordon

    2013-01-01

    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics within the CT complex, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the groundstate of the complex: a charge delocalization of about 10-2 electron from the HAT6 core to TNF is deduced from both Raman and NMR measurements, implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visi...

  3. 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.

  4. Rates and Routes of Electron Transfer of [NiFe]-Hydrogenase in an Enzymatic Fuel Cell.

    Science.gov (United States)

    Petrenko, Alexander; Stein, Matthias

    2015-10-29

    Hydrogenase enzymes are being used in enzymatic fuel cells immobilized on a graphite or carbon electrode surface, for example. The enzyme is used for the anodic oxidation of molecular hydrogen (H2) to produce protons and electrons. The association and orientation of the enzyme at the anode electrode for a direct electron transfer is not completely resolved. The distal FeS-cluster in [NiFe]-hydrogenases contains a histidine residue which is known to play a critical role in the intermolecular electron transfer between the enzyme and the electrode surface. The [NiFe]-hydrogenase graphite electrode association was investigated using Brownian Dynamics simulations. Residues that were shown to be in proximity to the electrode surface were identified (His184, Ser196, Glu461, Glu464), and electron transfer routes connecting the distal FeS-cluster with the surface residues were investigated. Several possible pathways for electron transfer between the distal FeS-cluster and the terminal amino acid residues were probed in terms of their rates of electron transfer using DFT methods. The reorganization energies ? of the distal iron-sulfur cluster and coronene as a molecular model for graphite were calculated. The reorganization energy of the distal (His)(Cys)3 cluster was found to be not very different from that of a standard cubane clusters with a (Cys)4 coordination. Electronic coupling matrix elements and rates of electron transfer for the different pathways were calculated according to the Marcus equation. The rates for glutamate-mediated electrode binding were found to be incompatible with experimental data. A direct electron transfer from the histidine ligand of the distal FeS-cluster to the electrode yielded rates of electron transfer in excellent agreement with experiment. A second pathway, however, from the distal FeS-cluster to the Ser196 residue was found to be equally efficient and feasible. PMID:26218232

  5. Application of multistep deactivation processes in the interpretation of intermolecular energy transfer following chemical activation by kinetic techniques

    International Nuclear Information System (INIS)

    Interpretation of vibrational energy transfer following kinetically controlled chemical activation is refined by incorporating multistep deactivation processes into the RRKM treatment of the excited molecule. The functional form of the initial primary product energy distribution used is based on that suggested by Bunker. This model is applied in interpreting collisional energy transfer from cyclobutane-t, chemically activated by nuclear recoil reaction. New low pressure experimental data are used to estimate the average energy of the nascent cyclobutane-t and the average step sizes for energy transfer to He, N2, CO2, and parent on collision based on a stepladder deactivation model. Step sizes found for cyclobutane, He, N2, and CO2 are 10.0, 0.5, 2.0, and 5.0 kcal, respectively. 4 figures, 3 tables

  6. Intermolecular Adhesion in Conjugated Polymers

    CERN Document Server

    Schmit, J D; Schmit, Jeremy D.; Levine, Alex J.

    2006-01-01

    Conjugated polymers are observed to aggregate in solution. To account for this observation we propose a inter-chain binding mechanism based on the intermolecular tunneling of the delocalized $\\pi$-electrons occurring at points where the polymers cross. This tunneling mechanism predicts specific bound structures of chain that depend on whether they are semiconducting or metallic. Semiconducting chains should form polyacene-like states exhibiting binding at every other site, while (doped) metallic chains can bind at each site. We also show that solitons co-localize with the intermolecular binding sites thereby strengthening the binding effect and investigate the conformational statistics of the resulting bimolecular aggregates.

  7. Medium effects in photoinduced electron transfer reactions

    International Nuclear Information System (INIS)

    The transfer of an electron between two molecules is a fundamental chemical process of great significance in biochemistry as well as in general chemistry. Electron transfer reactions can be induced by the absorption of light - as in photosynthesis - so that one of the molecules reacts through an electronically excited state; a net storage of chemical energy may then take place. When electron transfer involves molecules in condensed phase, the role of the liquid or solid medium must be considered. In the first place, a polar solvent may promote electron transfer through the stabilization of ion pairs and the separation of ions; but if the polar solvent must reorganize prior to the reaction, then an activation barrier will exist against electron transfer in polar solvents. This article gives a citical review of this field, with some novel ideas concerning the role of the medium (liquid solvent or solid matrix) in the overall energy balance of electron transfer, in the kinetics of the reaction, and in the further process of charge separation. It is suggested in particular that no dielectric screening by a polar solvent can exist when ions are formed in direct contact; and that the extensive reorganization of the solvent prior to electron transfer is so unlikely as to be discounted. In these respects the model presented in this article diverges from the commonly accepted model of Weller and of Marcus and Hush. In the Conclusion section some areas of particular importance for further research in this field are outlined. (author) 28 refs., 20 figs., 2 tabs

  8. Single Molecule Spectroscopy of Electron Transfer

    International Nuclear Information System (INIS)

    The objectives of this research are threefold: (1) to develop methods for the study electron transfer processes at the single molecule level, (2) to develop a series of modifiable and structurally well defined molecular and nanoparticle systems suitable for detailed single molecule/particle and bulk spectroscopic investigation, (3) to relate experiment to theory in order to elucidate the dependence of electron transfer processes on molecular and electronic structure, coupling and reorganization energies. We have begun the systematic development of single molecule spectroscopy (SMS) of electron transfer and summaries of recent studies are shown. There is a tremendous need for experiments designed to probe the discrete electronic and molecular dynamic fluctuations of single molecules near electrodes and at nanoparticle surfaces. Single molecule spectroscopy (SMS) has emerged as a powerful method to measure properties of individual molecules which would normally be obscured in ensemble-averaged measurement. Fluctuations in the fluorescence time trajectories contain detailed molecular level statistical and dynamical information of the system. The full distribution of a molecular property is revealed in the stochastic fluctuations, giving information about the range of possible behaviors that lead to the ensemble average. In the case of electron transfer, this level of understanding is particularly important to the field of molecular and nanoscale electronics: from a device-design standpoint, understanding and controlling this picture of the overall range of possible behaviors will likely prove to be as important as designing ia the ideal behavior of any given molecule.

  9. Ultra-fast charge transfer in organic electronic materials and at hybrid interfaces studied using the core-hole clock technique

    Energy Technology Data Exchange (ETDEWEB)

    Friedlein, R. [School of Materials Science and Research Center for Integrated Science, Japan Advanced Institute of Science and Technology, Nomi, Ishikawa 923-1292 (Japan); Braun, S. [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, S-581 83 Linkoeping (Sweden); Jong, M.P. de [University of Twente, 7500 AE, Enschede (Netherlands); Osikowicz, W. [SAPA Industries, 61281 Finspang (Sweden); Fahlman, M. [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, S-581 83 Linkoeping (Sweden); Salaneck, W.R., E-mail: wrs@ifm.liu.s [Department of Physics, Chemistry and Biology (IFM), Linkoeping University, S-581 83 Linkoeping (Sweden)

    2011-01-15

    Research highlights: {yields} The use of resonant photoemission in its 'core-hole clock' expression for the study of the dynamical charge transfer across hybrid organic-inorganic interfaces and for the intermolecular charge transfer in the bulk of organic thin films is reviewed. {yields} The electronic coupling to the substrate and the efficiency of charge transport across hybrid interfaces is different for individual electronic subsystems of the molecular adsorbate. {yields} The intermolecular charge transfer in the bulk of discotic liquid crystals occurs on the order of a few femtoseconds and is faster than expected from the macroscopic charge transport characteristics of the material. -- Abstract: The focus of this brief review is the use of resonant photoemission in its 'core-hole clock' expression for the study of two important problems relevant for the field of organic electronics: the dynamical charge transfer across hybrid organic-inorganic interfaces, and the intermolecular charge transfer in the bulk of organic thin films. Following an outline of the technique, a discussion of its applicability and a short overview of experimental results obtained thus far, two examples are used to illustrate particular results relevant for the understanding of the charge transport in organic electronic devices. First, for Fe(II)-tetraphenylporphyrin molecules on semi-metallic molybdenum disulfide substrates, the electronic coupling to the substrate and the efficiency of charge transport across the interface different for the individual molecular electronic subsystems is discussed. And second, a discotic liquid crystalline material forming columnar assemblies is used to illustrate ultra-fast intermolecular charge transfer on the order of a few femtoseconds indicating an electronic coupling between the phthalocyanine units stronger than expected from the macroscopic charge transport characteristics of the material.

  10. Mechanism of the hydrogen transfer from the OH group to oxygen-centered radicals: proton-coupled electron-transfer versus radical hydrogen abstraction.

    Science.gov (United States)

    Olivella, Santiago; Anglada, Josep M; Solé, Albert; Bofill, Josep M

    2004-07-19

    High-level ab initio electronic structure calculations have been carried out with respect to the intermolecular hydrogen-transfer reaction HCOOH+.OH-->HCOO.+H(2)O and the intramolecular hydrogen-transfer reaction .OOCH2OH-->HOOCH(2)O.. In both cases we found that the hydrogen atom transfer can take place via two different transition structures. The lowest energy transition structure involves a proton transfer coupled to an electron transfer from the ROH species to the radical, whereas the higher energy transition structure corresponds to the conventional radical hydrogen atom abstraction. An analysis of the atomic spin population, computed within the framework of the topological theory of atoms in molecules, suggests that the triplet repulsion between the unpaired electrons located on the oxygen atoms that undergo hydrogen exchange must be much higher in the transition structure for the radical hydrogen abstraction than that for the proton-coupled electron-transfer mechanism. It is suggested that, in the gas phase, hydrogen atom transfer from the OH group to oxygen-centered radicals occurs by the proton-coupled electron-transfer mechanism when this pathway is accessible. PMID:15252786

  11. Site-selective photoinduced electron transfer from alcoholic solvents to the chromophore facilitated by hydrogen bonding: a new fluorescence quenching mechanism.

    Science.gov (United States)

    Zhao, Guang-Jiu; Liu, Jian-Yong; Zhou, Li-Chuan; Han, Ke-Li

    2007-08-01

    Solute-solvent intermolecular photoinduced electron transfer (ET) reaction was proposed to account for the drastic fluorescence quenching behaviors of oxazine 750 (OX750) chromophore in protic alcoholic solvents. According to our theoretical calculations for the hydrogen-bonded OX750-(alcohol)(n) complexes using the time-dependent density functional theory (TDDFT) method, we demonstrated that the ET reaction takes place from the alcoholic solvents to the chromophore and the intermolecular ET passing through the site-specific intermolecular hydrogen bonds exhibits an unambiguous site selectivity. In our motivated experiments of femtosecond time-resolved stimulated emission pumping fluorescence depletion spectroscopy (FS TR SEP FD), it could be noted that the ultrafast ET reaction takes place as fast as 200 fs. This ultrafast intermolecular photoinduced ET is much faster than the diffusive solvation process, and even significantly faster than the intramolecular vibrational redistribution (IVR) process of the OX750 chromophore. Therefore, the ultrafast intermolecular ET should be coupled with the hydrogen-bonding dynamics occurring in the sub-picosecond time domain. We theoretically demonstrated for the first time that the selected hydrogen bonds are transiently strengthened in the excited states for facilitating the ultrafast solute-solvent intermolecular ET reaction. PMID:17616225

  12. Intermolecular hydrogen transfer between guest species in small and large cages of methane + propane mixed gas hydrates.

    Science.gov (United States)

    Sugahara, Takeshi; Kobayashi, Yusuke; Tani, Atsushi; Inoue, Tatsuya; Ohgaki, Kazunari

    2012-03-15

    To investigate the molecular interaction between guest species inside of the small and large cages of methane + propane mixed gas hydrates, thermal stabilities of the methyl radical (possibly induced in small cages) and the normal propyl and isopropyl radicals (induced in large cages) were investigated by means of electron spin resonance measurements. The increase of the total amount of the normal propyl and isopropyl radicals reveals that the methyl radical in the small cage withdraws one hydrogen atom from the propane molecule enclathrated in the adjacent large cage of the structure-II hydrate. A guest species in a hydrate cage has the ability to interact closely with the other one in the adjacent cages. The clathrate hydrate may be utilized as a possible nanoscale reaction field. PMID:22352402

  13. 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

  14. Quantum effects in biological electron transfer.

    Czech Academy of Sciences Publication Activity Database

    de la Lande, A.; Babcock, N. S.; ?ezá?, Jan; Levy, B.; Sanders, B. C.; Salahub, D.

    2012-01-01

    Ro?. 14, ?. 17 (2012), s. 5902-5918. ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron transfer * tunnelling * decoherence * semi-classical molecular dynamics * density functional theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012

  15. 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

    2015-11-18

    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. PMID:25909507

  16. Photoinduced charge accumulation by metal ion-coupled electron transfer.

    Science.gov (United States)

    Bonn, Annabell G; Wenger, Oliver S

    2015-10-01

    An oligotriarylamine (OTA) unit, a Ru(bpy)3(2+) photosensitizer moiety (Ru), and an anthraquinone (AQ) entity were combined to a molecular dyad (Ru-OTA) and a molecular triad (AQ-Ru-OTA). Pulsed laser excitation at 532 nm led to the formation of charge-separated states of the type Ru(-)-OTA(+) and AQ(-)-Ru-OTA(+) with lifetimes of ?10 ns and 2.4 ?s, respectively, in de-aerated CH3CN at 25 °C. Upon addition of Sc(OTf)3, very long-lived photoproducts were observed. Under steady-state irradiation conditions using a flux of (6.74 ± 0.21) × 10(15) photons per second at 450 nm, the formation of twofold oxidized oligotriarylamine (OTA(2+)) was detected in aerated CH3CN containing 0.02 M Sc(3+), as demonstrated unambiguously by comparison with UV-Vis absorption spectra obtained in the course of chemical oxidation with Cu(2+). Photodriven charge accumulation on the OTA unit of Ru-OTA and AQ-Ru-OTA is possible due to the lowering of the O2 reduction potential caused by the interaction of superoxide with the strong Lewis acid Sc(3+). The presence of the anthraquinone unit in AQ-Ru-OTA accelerates the rate-determining reaction step for charge accumulation by a factor of 10 compared to the Ru-OTA dyad. This is attributed to the formation of Sc(3+)-stabilized anthraquinone radical anion intermediates in the triad. Possible mechanistic pathways leading to charge accumulation are discussed. Photodriven charge accumulation is of key importance for solar fuels because their production will have to rely on multi-electron chemistry rather than single-electron reaction steps. Our study is the first to demonstrate that metal ion-coupled electron transfer (MCET) can be exploited to accumulate charges on a given molecular unit using visible light as an energy input. The approach of using a combination of intra- and intermolecular electron transfer reactions which are enabled by MCET is conceptually novel, and the fundamental insights gained from our study are relevant in the greater context of solar energy conversion. PMID:26312416

  17. Electronic transfer between low-dimensional nanosystems.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel

    Hoboken : Wiley, 2011 - (Nair, K.; Priya, S.; Jia, Q.), s. 33-40 ISBN 9781118059999. - (Ceramic Transactions. vol. 226). [Materials Science and Technology meeting 2010 (MS&T'10). Dielectric Ceramic Materials and Electronic Devices .. Houston (US), 17.10.2010-21.10.2010] R&D Projects: GA MŠk(CZ) OC10007 Institutional research plan: CEZ:AV0Z10100520 Keywords : electron transfer * nanostructures quantum dots Subject RIV: BM - Solid Matter Physics ; Magnetism http://eu.wiley.com/WileyCDA/WileyTitle/productCd-1118059999,descCd-tableOfContents.html

  18. Theory of intermolecular forces

    CERN Document Server

    Margenau, H; Ter Haar, D

    1971-01-01

    Theory of Intermolecular Forces deals with the exposition of the principles and techniques of the theory of intermolecular forces. The text focuses on the basic theory and surveys other aspects, with particular attention to relevant experiments. The initial chapters introduce the reader to the history of intermolecular forces. Succeeding chapters present topics on short, intermediate, and long range atomic interactions; properties of Coulomb interactions; shape-dependent forces between molecules; and physical adsorption. The book will be of good use to experts and students of quantum mechanics

  19. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    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 Ge...

  20. Resonant electron transfer between quantum dots

    OpenAIRE

    Openov, Leonid A.

    1999-01-01

    An interaction of electromagnetic field with a nanostructure composed of two quantum dots is studied theoretically. An effect of a resonant electron transfer between the localized low-lying states of quantum dots is predicted. A necessary condition for such an effect is the existence of an excited bound state whose energy lies close to the top of the barrier separating the quantum dots. This effect may be used to realize the reversible quantum logic gate NOT if the superposi...

  1. Electron transfer in branched expanded pyridinium molecules.

    Czech Academy of Sciences Publication Activity Database

    Hromadová, Magdaléna; Lachmanová, Št?pánka; Pospíšil, Lubomír; Fortage, J.; Dupeyre, G.; Perruchot, Ch.; Lainé, P. P.

    Aveiro : DEMAC - Universidade de Aveiro, 2014. s. 99-99. [Meeting of the Portuguese Electrochemical Society /19./. Iberian Meeting of Electrochemistry /16./. 30.06.2014-02.07.2014, Aveiro] R&D Projects: GA ?R(CZ) GA14-05180S Grant ostatní: Rada Programu interní porpory projekt? mezinárodní spolupráce AV ?R M200401202 Institutional support: RVO:61388955 Keywords : electron transfer * electrochemistry * pyridinium Subject RIV: CG - Electrochemistry

  2. Quantum coherent contributions in biological electron transfer

    OpenAIRE

    Dorner, Ross; Goold, John; Heaney, Libby; Farrow, Tristan; Roberts, Philippa G.; Hirst, Judy; Vedral, Vlatko

    2011-01-01

    Many biological electron transfer (ET) reactions are mediated by metal centres in proteins. NADH:ubiquinone oxidoreductase (complex I) contains an intramolecular chain of seven iron-sulphur (FeS) clusters, one of the longest chains of metal centres in biology and a test case for physical models of intramolecular ET. In biology, intramolecular ET is commonly described as a diffusive hopping process, according to the semi-classical theories of Marcus and Hopfield. However, rec...

  3. Promoting Interspecies Electron Transfer with Biochar

    OpenAIRE

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

    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...

  4. Electron transfer and reaction mechanism of laccases.

    Science.gov (United States)

    Jones, Stephen M; Solomon, Edward I

    2015-03-01

    Laccases are part of the family of multicopper oxidases (MCOs), which couple the oxidation of substrates to the four electron reduction of O2 to H2O. MCOs contain a minimum of four Cu's divided into Type 1 (T1), Type 2 (T2), and binuclear Type 3 (T3) Cu sites that are distinguished based on unique spectroscopic features. Substrate oxidation occurs near the T1, and electrons are transferred approximately 13 Å through the protein via the Cys-His pathway to the T2/T3 trinuclear copper cluster (TNC), where dioxygen reduction occurs. This review outlines the electron transfer (ET) process in laccases, and the mechanism of O2 reduction as elucidated through spectroscopic, kinetic, and computational data. Marcus theory is used to describe the relevant factors which impact ET rates including the driving force, reorganization energy, and electronic coupling matrix element. Then, the mechanism of O2 reaction is detailed with particular focus on the intermediates formed during the two 2e(-) reduction steps. The first 2e(-) step forms the peroxide intermediate, followed by the second 2e(-) step to form the native intermediate, which has been shown to be the catalytically relevant fully oxidized form of the enzyme. PMID:25572295

  5. Promoting interspecies electron transfer with biochar

    DEFF Research Database (Denmark)

    Chen, Shanshan; Rotaru, Amelia-Elena

    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.

  6. 77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...

    Science.gov (United States)

    2012-06-08

    ...Collection of Information: Electronic Transfer Account...on a continuing information collection. By...FMS-111, ``Electronic Transfer Account...collection of information described below: Title: Electronic Transfer...

  7. Enhanced Electron Lifetimes in Dye-Sensitized Solar Cells Using a Dichromophoric Porphyrin: The Utility of Intermolecular Forces.

    Science.gov (United States)

    Zhao, Long; Wagner, Pawel; van der Salm, Holly; Gordon, Keith C; Mori, Shogo; Mozer, Attila J

    2015-10-01

    Electron lifetimes in dye-sensitized solar cells employing a porphyrin dye, an organic dye, a 1:1 mixture of the two dyes, and a dichromophoric dye design consisting of the two dyes using a nonconjugated linker were measured, suggesting that the dispersion force of the organic dyes has a significant detrimental effect on the electron lifetime and that the dichromophoric design can be utilized to control the effect of the dispersion force. PMID:26375165

  8. Electron transfer pathways in mixed-valence paracyclophane-bridged bis-triarylamine radical cations.

    Science.gov (United States)

    Kaupp, Martin; Gückel, Simon; Renz, Manuel; Klawohn, Sascha; Theilacker, Kolja; Parthey, Matthias; Lambert, Christoph

    2016-01-01

    A series of paracyclophane (PC) bridged mixed-valence (MV) bis-triarylamine radical cations with different ([2.2], [3.3], [4.4]) linkers, with and without additional ethynyl spacers, have been studied by quantum-chemical calculations (BLYP35-D3/TZVP/COSMO) of ground-state structures, thermal electron-transfer barriers, hyperfine couplings, and lowest-lying excited states. Such PC-bridged MV systems are important intra-molecular model systems for inter-molecular electron transfer (ET) via ?-stacked aromatics, since they allow enforcement of a more or less well-defined geometrical arrangement. Closely comparable ET barriers and electronic couplings for all [2.2] and [3.3] bridges are found for these class-II MV systems, irrespective of the use of pseudo-para and pseudo-meta connections. While the latter observation contradicts notions of quantum interference for off-resonant conduction through molecular wires, it agrees with the less intricate nodal structures of the highest occupied molecular orbitals. The ET in such MV systems may be more closely connected with hole conduction in the resonant regime. Computations on model cations, in which the [2.2] linkers have been truncated, confirm predominant through-space ?-? electronic coupling. Systems with [4.4] PC bridges exhibit far more structural flexibility and concomitantly weaker electronic interactions between the redox centers. © 2015 Wiley Periodicals, Inc. PMID:26265245

  9. Direct heterogeneous electron transfer of theophylline oxidase

    OpenAIRE

    Christenson, Andreas; Dock, Eva; Gorton, Lo; Ruzgas, Tautgirdas

    2004-01-01

    Direct electron transfer (DET) was shown between the heme containing enzyme theophylline oxidase (ThO) and the surface of both graphite and gold electrodes. As proof on graphite a steady state current for theophylline was recorded using the electrode modified with adsorbed ThO. The electrode showed a Michaelis–Menten-like response to theophylline with a detection limit of 0.2 mM and a Michaelis–Menten constant equal to 3.2 mM. These initial results open up a possibility for the development of...

  10. Quantum tunneling resonant electron transfer process in Lorentzian plasmas

    International Nuclear Information System (INIS)

    The quantum tunneling resonant electron transfer process between a positive ion and a neutral atom collision is investigated in nonthermal generalized Lorentzian plasmas. The result shows that the nonthermal effect enhances the resonant electron transfer cross section in Lorentzian plasmas. It is found that the nonthermal effect on the classical resonant electron transfer cross section is more significant than that on the quantum tunneling resonant charge transfer cross section. It is shown that the nonthermal effect on the resonant electron transfer cross section decreases with an increase of the Debye length. In addition, the nonthermal effect on the quantum tunneling resonant electron transfer cross section decreases with increasing collision energy. The variation of nonthermal and plasma shielding effects on the quantum tunneling resonant electron transfer process is also discussed

  11. 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.

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

    CERN Multimedia

    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.

  13. Electron transfer patterns of the di-heme protein cytochrome c(4) from Pseudomonas stutzeri

    DEFF Research Database (Denmark)

    Raffalt, Anders Christer; Schmidt, L.

    2009-01-01

    We report kinetic data for the two-step electron transfer (ET) oxidation and reduction of the two-domain di-heme redox protein Pseudomonas stutzeri cytochrome (cyt) c(4) by [Co(bipy)(3)](2- 3-) (bipy = 2,2'-bipyridine). Following earlier reports, the data accord with both bi- and tri-exponential kinetics. A complete kinetic scheme includes both "cooperative" intermolecular ET between each heme group and the external reaction partner, and intramolecular ET between the two heme groups. A now data analysis scheme shows unequivocally that two-ET oxidation and reduction of P. stutzeri cyt c(4) is entirely dominated by intermolecular ET between the heme groups and the external reaction partner in the ms time range, with virtually no contribution from intramolecular interheme ET in this time range. This is in striking contrast to two-ET electrochemical oxidation or reduction of P. stutzeri cyt c(4) for which fast, ms to sub-ms intramolecular interheme ET is a crucial step. The rate constant dependence on the solventviscosity has disclosed strong coupling to both a (set of) frictionally damped solvent/protein nuclear modes and intramolecular friction-less "ballistic" modes, indicative of notable protein structural mobility in the overall two-ET process. We suggest that conformational protein mobility blocks intramolecular interheme ET in bulk homogeneous solution but triggers opening of this gated ET channel in the electrochemical environment or in the membrane environment of natural respiratory cyt c(4) function.

  14. Intermolecular and surface forces

    CERN Document Server

    Israelachvili, Jacob N

    2011-01-01

    This reference describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition.· starts fr

  15. 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.

  16. The effects of energy and charge transfer on the electronic structure and optical properties of molecular aggregates

    Science.gov (United States)

    Manas, Eric S.

    The effects of energy and charge transfer on the electronic structure and optical properties of molecular aggregates are studied theoretically, with focus on the influence of intermolecular interactions. The effects of inter-macrocycle interactions on the second hyperpolarizabilities intermolecular excitation energy transfer. Using a simplified analysis in the static and near-resonant regimes, two mechanisms are identified that lead to dramatic enhancements in the aggregate value of intermolecular charge transfer are considered. Applications to other systems are discussed as well. Collective excitations in ordered aggregates of ?- conjugated oligomers are also studied. Each oligomer is modeled using a Pariser-Parr-Pople Hamiltonian, which accounts for charge transfer along each oligomer, as well as intra-oligomer Coulombic interactions. Charge transfer between oligomers is neglected, but Coulombic interactions between oligomers are treated to first order. Aggregate spontaneous emission and linear absorption are both considered. Intermolecular interactions are shown to cause an energy shift of the optically allowed (K = 0, B/sp- symmetry) exciton states due to first order inter-chain excitation energy transfer. This results in an absorption blue shift that initially increases with oligomer size N, peaks, and then tends to a small value when the oligomer dimensions greatly exceed the inter-oligomer separation. The exciton radiative decay rates ?B/sp- in an aggregate of M aligned oligomers are shown to be superradiant, being M times faster than the decay rates of isolated oligomer exciton states. When N is large, ?B/sp- also scales linearly with N, so ?B/sp-/propto MN (two-dimensional superradiance). However, for N/ ~

  17. Intermolecular spectroscopy of gases

    International Nuclear Information System (INIS)

    Spectroscopic techniques have been very successfully applied to the study of individual molecules. The same techniques can also be used to investigate intermolecular interactions. Collision-induced absorption (CIA) and collision-induced light scattering (CILS) are important examples of intermolecular interactions. These effects can be described by the dynamical information contained in the general intermolecular correlation functions. One of the aims of this review is to stress the central role of these correlation functions in the field of intermolecular spectroscopy. Because they have a well-defined physical meaning, they are very suitable for the purpose of introducing new physical approximations, particularly in the case of liquids. Some aspects of the theory of CIA will be discussed, mainly as applied to gases. References to similar situations in CILS will occasionally be made, but no comprehensive review will be attempted. One of the basic quantities in CIA is the absorption coefficient. The question is investigated wether it can be expanded in powers of the density. Finally, the moments of the spectrum, interference effects and line shapes are discussed. (KBE)

  18. Direct electron transfer based enzymatic fuel cells

    International Nuclear Information System (INIS)

    In this mini-review we briefly describe some historical developments made in the field of enzymatic fuel cells (FCs), discussing important design considerations taken when constructing mediator-, cofactor-, and membrane-less biological FCs (BFCs). Since the topic is rather extensive, only BFCs utilizing direct electron transfer (DET) reactions on both the anodic and cathodic sides are considered. Moreover, the performance of mostly glucose/oxygen biodevices is analyzed and compared. We also present some unpublished results on mediator-, cofactor-, and membrane-less glucose/oxygen BFCs recently designed in our group and tested in different human physiological fluids, such as blood, plasma, saliva, and tears. Finally, further perspectives for BFC applications are highlighted.

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

    OpenAIRE

    PravinMallaShrestha; Amelia-ElenaRotaru

    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 whi...

  20. Theory of plasmon enhanced interfacial electron transfer

    Science.gov (United States)

    Wang, Luxia; May, Volkhard

    2015-04-01

    A particular attempt to improve the efficiency of a dye sensitized solar cell is it's decoration with metal nano-particles (MNP). The MNP-plasmon induced enhancement of the local field enlarges the photoexcitation of the dyes and a subsequent improvement of the charge separation efficiency may result. In a recent work (2014 J. Phys. Chem. C 118 2812) we presented a theory of plasmon enhanced interfacial electron transfer for perylene attached to a TiO2 surface and placed in the proximity of a spherical MNP. These earlier studies are generalized here to the coupling of to up to four MNPs and to the use of somewhat altered molecular parameters. If the MNPs are placed close to each other strong hybridization of plasmon excitations appears and a broad resonance to which molecular excitations are coupled is formed. To investigate this situation the whole charge injection dynamics is described in the framework of the density matrix theory. The approach accounts for optical excitation of the dye coupled to the MNPs and considers subsequent electron injection into the rutile TiO2-cluster. Using a tight-binding model for the TiO2-system with about 105 atoms the electron motion in the cluster is described. We again consider short optical excitation which causes an intermediate steady state with a time-independent overall probability to have the electron injected into the cluster. This probability is used to introduce an enhancement factor which rates the influence of the MNP. Values larger than 500 are obtained.

  1. Electron transfer reactions of metal complexes in solution

    International Nuclear Information System (INIS)

    A few representative electron-transfer reactions are selected and their kinetic parameters compared with the predictions of activated complex models. Since Taube has presented an elegant treatment of intramolecular electron-transfer reactions, emphasis is on bimolecular reactions. The latter electron-transfer reactions are more complicated to treat theoretically since the geometries of their activated complexes are not as well known as for the intramolecular case. In addition in biomolecular reactions, the work required to bring the two reactants together needs to be calculated. Since both reactants generally carry charges this presents a non-trivial problem at the ionic strengths usually used to study bimolecular electron transfer

  2. Intramolecular electron transfer on the vibrational timescale in mixed valence ruthenium clusters

    International Nuclear Information System (INIS)

    The thermodynamic stability of the mixed valence (one electron reduced) state between linked Ru3 units was studied by means of electrochemical methods for the series of the ligand-bridged triruthenium cluster dimer, [Ru3(?3-O)(?-CH3CO2)6(CO)(L)(?-BL)Ru3(?3-O)(?-CH3CO2)6(CO)(L)] (BL = 1,4 pyrazine: L = 4-dimethylaminopyridine (dmap) (1a), pyridine (py) (1b), 4-cyanopyridine (cpy) (1c), 1-azabicyclo[2.2.2]octane (1d); BL = 4,4'-bipyridine: L= dmap (2a), py(2b), cpy (2c); BL 2,7-diazapyrene; L = dmap (3a); BL = 1,4-diazabicyclo[2.2.2]octane: L = dmap (4a), py(4b), cpy (4c). The mixed valence states undergoing rapid intermolecular electron transfers were observed by IR spectro-electrochemistry. By simulating dynamical effects on the observed ?(CO) absorption band shapes, the rate constants ke for electron transfer in the mixed valence states of 1a, 1b, 1c and 1d were estimated to be 9x1011 s-1 (at room temperature (rt)), 5x1011 s-1 (at rt), ca. 1x1011 s-1 (at rt), and 1x1012 s-1 (at -18 oC), respectively. Possible applications of this approach to asymmetric mixed valence systems were discussed. (author)

  3. Adrenodoxin reductase-adrenodoxin complex structure suggests electron transfer path in steroid biosynthesis.

    Science.gov (United States)

    Müller, J J; Lapko, A; Bourenkov, G; Ruckpaul, K; Heinemann, U

    2001-01-26

    The steroid hydroxylating system of adrenal cortex mitochondria consists of the membrane-attached NADPH-dependent adrenodoxin reductase (AR), the soluble one-electron transport protein adrenodoxin (Adx), and a membrane-integrated cytochrome P450 of the CYP11 family. In the 2.3-A resolution crystal structure of the Adx.AR complex, 580 A(2) of partly polar surface are buried. Main interaction sites are centered around Asp(79), Asp(76), Asp(72), and Asp(39) of Adx and around Arg(211), Arg(240), Arg(244), and Lys(27) of AR, respectively. In particular, the region around Asp(39) defines a new protein interaction site for Adx, similar to those found in plant and bacterial ferredoxins. Additional contacts involve the electron transfer region between the redox centers of AR and Adx and C-terminal residues of Adx. The Adx residues Asp(113) to Arg(115) adopt 3(10)-helical conformation and engage in loose intermolecular contacts within a deep cleft of AR. Complex formation is accompanied by a slight domain rearrangement in AR. The [2Fe-2S] cluster of Adx and the isoalloxazine rings of FAD of AR are 10 A apart suggesting a possible electron transfer route between these redox centers. The AR.Adx complex represents the first structure of a biologically relevant complex between a ferredoxin and its reductase. PMID:11053423

  4. 77 FR 71035 - Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT...

    Science.gov (United States)

    2012-11-28

    ...Collection of Information: Electronic Funds Transfer...on a continuing information collection. By...concerning the ``Electronic Funds Transfer...collection of information described below: Title: Electronic Funds...

  5. 77 FR 22066 - Proposed Collection of Information: “Notice of Reclamation Electronic Funds Transfer, Federal...

    Science.gov (United States)

    2012-04-12

    ...Collection of Information: ``Notice of Reclamation Electronic Funds Transfer...continuing information collection...Reclamation. Electronic Funds Transfer...collection of information described...Reclamation, Electronic Funds...

  6. Electromagnetically induced electron transfer between quantum dots via conduction band

    International Nuclear Information System (INIS)

    The Stark-like mechanism of electron transfer between quantum dots under the influence of electromagnetic field is considered. Analytical estimations and numerical simulation results clarifying the special role of conduction band are adduced. Two-photon mechanism of electron transfer between quantum dots via conduction band is suggested

  7. Photoinduced Electron-transfer Reaction of Pentafluoroiodobenzene with Alkenes

    Directory of Open Access Journals (Sweden)

    Qing-Yun Chen

    1997-01-01

    Full Text Available Irradiation of pentafluoroiodobenzene and alkenes gave the corresponding adducts. The presence of single electron-transfer scavengers, (p-dinitrobenzene and t-Bu2NO and the free radical inhibitor (hydroquinone suppressed the reaction. A photoinduced electron-transfer mechanism is proposed.

  8. Computer Simulation of Electron Transfer at Hematite Surfaces

    International Nuclear Information System (INIS)

    Molecular dynamics simulations in combination with ab initio calculations were carried out to determine the rate of electron transfer in bulk hematite (?-Fe2O3) and at two low-index surfaces, namely the (012) and (001) surfaces. The electron transfer reactions considered here involve the II/III valence interchange between nearest-neighbor iron atoms. Two electron transfer directions were investigated namely the basal plane and c direction charge transfers. Electron transfer rates obtained in bulk hematite were in good agreement with ab initio electronic structure calculations thus validating the potential model. The surfaces were considered both in vacuum and in contact with an equilibrated aqueous solution. The reorganization energy is found to increase significantly at the first surface layer and this value is little affected by the presence of water. In addition, in the case of the (012) surface, the electronic coupling matrix element for the topmost basal plane transfer was calculated at the Hartree-Fock level and was found to be weak compared to the corresponding charge transfer in the bulk. Therefore, most surfaces show a decrease in the rate of charge transfer at the surface. However, where iron atoms involved in the charge transfer reaction are directly coordinated to water molecules, water lowers the free energy of activation to a great extent and provides a large driving force for electrons to diffuse toward the bulk thus opposing the intrinsic surface effect. The surfaces considered in this work show different charge transfer properties. Hematite has been shown to exhibit anisotropic conductivity and thus different surfaces will show different intra- and inter-layer rates depending on their orientation. Moreover, the calculations of charge transfers at the hydroxyl- and iron-terminated (001) surfaces revealed that surface termination has a significant effect on the charge transfer parameters in the vicinity of the surface. Finally, our findings indicate that undercoordinated terminal iron atoms could act as electron traps at the surface

  9. 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. PMID:25911828

  10. Quantum coherent contributions in biological electron transfer

    CERN Document Server

    Dorner, Ross; Heaney, Libby; Farrow, Tristan; Roberts, Philippa G; Hirst, Judy; Vedral, Vlatko

    2011-01-01

    Many biological electron transfer (ET) reactions are mediated by metal centres in proteins. NADH:ubiquinone oxidoreductase (complex I) contains an intramolecular chain of seven iron-sulphur (FeS) clusters, one of the longest chains of metal centres in biology and a test case for physical models of intramolecular ET. In biology, intramolecular ET is commonly described as a diffusive hopping process, according to the semi-classical theories of Marcus and Hopfield. However, recent studies have raised the possibility that non-trivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we extend the semi-classical model for biological ET to incorporate both semi-classical and coherent quantum phenomena using a quantum master equation based on the Holstein Hamiltonian. We test our model on the structurally-defined chain of FeS clusters in complex I. By exploring a wide range of realistic parameters we and that, when the energy profile for ET along the chain is relatively at, ...

  11. Electron Transfer Dissociation of Milk Oligosaccharides

    Science.gov (United States)

    Han, Liang; Costello, Catherine E.

    2011-06-01

    For structural identification of glycans, the classic collision-induced dissociation (CID) spectra are dominated by product ions that derived from glycosidic cleavages, which provide only sequence information. The peaks from cross-ring fragmentation are often absent or have very low abundances in such spectra. Electron transfer dissociation (ETD) is being applied to structural identification of carbohydrates for the first time, and results in some new and detailed information for glycan structural studies. A series of linear milk sugars was analyzed by a variety of fragmentation techniques such as MS/MS by CID and ETD, and MS3 by sequential CID/CID, CID/ETD, and ETD/CID. In CID spectra, the detected peaks were mainly generated via glycosidic cleavages. By comparison, ETD generated various types of abundant cross-ring cleavage ions. These complementary cross-ring cleavages clarified the different linkage types and branching patterns of the representative milk sugar samples. The utilization of different MS3 techniques made it possible to verify initial assignments and to detect the presence of multiple components in isobaric peaks. Fragment ion structures and pathways could be proposed to facilitate the interpretation of carbohydrate ETD spectra, and the main mechanisms were investigated. ETD should contribute substantially to confident structural analysis of a wide variety of oligosaccharides.

  12. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    2013-01-01

    The step from ab initio atomic and molecular properties to thermodynamic - or macroscopic - properties requires the combination of several theoretical tools. This dissertation presents constant temperature molecular dynamics with bond length constraints, a hybrid quantum mechanics-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 and asymmetric charge transfer reactions between several first-row transition metals in water. The results are compared to experiments and rationalised with classical analytic expressions. Shortcomings of the methods are accounted for with clear steps towards improved accuracy. Later the analysis is extended to more complex systems composed of a larger osmium complex in solution and at the solute-substrate interfaces, where in particular the redox state of the complex is controlled through chemical means. The efficiency of the hybrid-classical and quantum mechanics method is used to generate adequate statistics and a simple post-sampling scheme used to generate free energy surfaces - which compare to full ab initio calculations. In the last part both the molecular dynamics and hybrid classical and quantum mechanics method are used to generate a vast data set for the accurate analysis of dynamical structure modes. This is for a large iridium-iridium dimer complex which shows a dramatic structural (and vibrational) change upon electronic excitation.

  13. Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

    Science.gov (United States)

    Basilevsky, M. V.; Odinokov, A. V.; Titov, S. V.; Mitina, E. A.

    2013-12-01

    The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ?0 = ??0/kBT where ?0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (?0 kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T ? 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.

  14. Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices

    International Nuclear Information System (INIS)

    The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ?0=??0/kBT where ?0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (?0 0? 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T? 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems

  15. Proton-transfer mediated enhancement of nonlocal electronic relaxation processes in X-ray irradiated liquid water.

    Science.gov (United States)

    Slaví?ek, Petr; Winter, Bernd; Cederbaum, Lorenz S; Kryzhevoi, Nikolai V

    2014-12-31

    We have simulated the oxygen 1s Auger-electron spectra of normal and heavy liquid water using ab initio and quantum dynamical methods. The computed spectra are analyzed and compared to recently reported experimental data. The electronic relaxation in liquid water exposed to ionizing X-ray radiation is shown to be far more diverse and complex than anticipated and extremely different than for an isolated water molecule. A core-level ionized water molecule in the liquid phase, in addition to a local Auger process, relaxes through nonlocal energy and charge transfer, such as intermolecular Coulombic decay and electron-transfer mediated decay (ETMD). We evaluate the relative efficiencies for these three classes of relaxation processes. The quantitative estimates for the relative efficiencies of different electronic decay modes help determine yields of various reactive species produced by ionizing X-rays. The ETMD processes which are considered here for the first time in the core-level regime are found to have a surprisingly high efficiency. Importantly, we find that all nonlocal electronic relaxation processes are significantly enhanced by ultrafast proton transfer between the core-ionized water and neighboring molecules. PMID:25493917

  16. A Simple Marcus-Theory Type Model for Hydrogen Atom Transfer/Proton-Coupled Electron Transfer

    OpenAIRE

    MAYER, JAMES M.

    2011-01-01

    Hydrogen atom transfer reactions are the simplest class of proton-coupled electron transfer (PCET) processes. These reactions involve transfer of one electron and one proton from one reagent to another, in the same kinetic step: XH + Y ? X + HY. A predictive model for these reactions based on the Marcus cross relation is described. The model predicts rate constants within one or two orders of magnitude in most cases, over a very wide range of reactants and solvents. This remarkable result imp...

  17. A molecular shift register based on electron transfer.

    Science.gov (United States)

    Hopfield, J J; Onuchic, J N; Beratan, D N

    1988-08-12

    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. PMID:17829175

  18. Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

    Energy Technology Data Exchange (ETDEWEB)

    Haverkate, Lucas A.; Mulder, Fokko M. [Reactor Institute Delft, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Zbiri, Mohamed, E-mail: zbiri@ill.fr; Johnson, Mark R. [Institut Laue Langevin, 38042 Grenoble Cedex 9 (France); Carter, Elizabeth [Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, NSW 2008 (Australia); Kotlewski, Arek; Picken, S. [ChemE-NSM, Faculty of Chemistry, Delft University of Technology, 2628BL/136 Delft (Netherlands); Kearley, Gordon J. [Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 (Australia)

    2014-01-07

    Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10{sup ?2} electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

  19. Electron transfer in SmHfCo alloys

    International Nuclear Information System (INIS)

    The rare-earth electron-transfer concept in the rare-earth--transition-metal compounds was evaluated for the binary compounds Sm2Co17 and Sm1Co5 from published data. The cobalt moment was found to be consistent with a two-transferred-electron rigid-band model. These results were verified by saturation magnetization measurements on the mixed-valence pseudobinary Sm/sub 2(1-x)/Hf/sub 2x/Co17 alloys where the moment per cobalt atom was consistent with a tetravalent-hafnium divalent-samarium electron-transfer mechanism

  20. 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...previously approved information collection...payment by electronic fund transfer...contract by electronic fund transfer (EFT). The information necessary...

  1. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    Science.gov (United States)

    2010-10-01

    ...false Submission of Electronic Funds Transfer Information with Offer. 52...232-38 Submission of Electronic Funds Transfer Information with Offer. As... Submission of Electronic Funds Transfer Information With Offer...

  2. 76 FR 709 - Electronic Funds Transfer of Depository Taxes; Correction

    Science.gov (United States)

    2011-01-06

    ...Funds Transfer of Depository Taxes; Correction AGENCY: Internal...guidance relating to Federal tax deposits (FTDs) by Electronic...202) 622-4910 (not a toll-free number). SUPPLEMENTARY...Subjects 26 CFR Part 40 Excise taxes, Reporting and...

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

    Czech Academy of Sciences Publication Activity Database

    Shaffer, C. J.; Marek, Aleš; Pepin, R.; Slováková, K.; Ture?ek, F.

    2015-01-01

    Ro?. 50, ?. 3 (2015), s. 470-475. ISSN 1076-5174 Institutional support: RVO:61388963 Keywords : electron transfer dissociation * laser photodissociation * peptide ions * cation radical * chromophores * isomer distinction Subject RIV: CE - Biochemistry Impact factor: 2.379, year: 2014

  4. Electron-Transfer Acceleration Investigated by Time Resolved Infrared Spectroscopy.

    Czech Academy of Sciences Publication Activity Database

    Vl?ek Jr., Antonín; Kvapilová, Hana; Towrie, M.; Záliš, Stanislav

    2015-01-01

    Ro?. 48, ?. 3 (2015), s. 868-876. ISSN 0001-4842 Institutional support: RVO:61388955 Keywords : electron transfer * infrared spectroscopy Subject RIV: CG - Electrochemistry Impact factor: 22.323, year: 2014

  5. 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 theory of charge transfer in polar media offers convenient tools for the treatment of experimental data for such systems, with due account of large-amplitude strongly anharmonic intramolecular reorganiza...

  6. 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 nonadiabatic reactions are derived.

  7. Transcriptomic and genetic analysis of direct interspecies electron transfer

    DEFF Research Database (Denmark)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Summers, Zarath M; Shrestha, Minita; Liu, Fanghua; Lovley, Derek R

    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 electron-accepting partner for either Geobacter metallireducens, which performs DIET, or Pelobacter carbinolicus, which relies on HIT. Transcript abundance for G. sulfurreducens uptake hydrogenase genes was 7...

  8. Desensitization of metastable intermolecular composites

    Science.gov (United States)

    Busse, James R. (South Fork, CO); Dye, Robert C. (Los Alamos, NM); Foley, Timothy J. (Los Alamos, NM); Higa, Kelvin T. (Ridgecrest, CA); Jorgensen, Betty S. (Jemez Springs, NM); Sanders, Victor E. (White Rock, NM); Son, Steven F. (Los Alamos, NM)

    2011-04-26

    A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

  9. Electronic reorganization triggered by electron transfer: the intervalence charge transfer of a Fe³?/Fe²? bimetallic complex.

    Science.gov (United States)

    Domingo, Alex; Angeli, Celestino; de Graaf, Coen; Robert, Vincent

    2015-04-30

    The key role of the molecular orbitals in describing electron transfer processes is put in evidence for the intervalence charge transfer (IVCT) of a synthetic nonheme binuclear mixed-valence Fe(3+)/Fe(2+) compound. The electronic reorganization induced by the IVCT can be quantified by controlling the adaptation of the molecular orbitals to the charge transfer process. We evaluate the transition energy and its polarization effects on the molecular orbitals by means of ab initio calculations. The resulting energetic profile of the IVCT shows strong similarities to the Marcus' model, suggesting a response behaviour of the ensemble of electrons analogue to that of the solvent. We quantify the extent of the electronic reorganization induced by the IVCT process to be 11.74 eV, a very large effect that induces the crossing of states reducing the total energy of the transfer to 0.89 eV. PMID:25739890

  10. Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides

    OpenAIRE

    Liu, Jian; McLuckey, Scott A.

    2012-01-01

    The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentati...

  11. Electron and proton transfer in chemistry and biology

    International Nuclear Information System (INIS)

    This book constitutes the proceedings of an international meeting held in September 19-21, 1990, at Zentrum fuer Interdisziplinaere Forschung, Universitaet Bielefeld, Germany. It describes various aspects of electron and proton transfer in chemistry and biology. The book starts with a survey of physiochemical principles of electron transfer in the gas and the solid phase, with thermodynamic and photochemical driving force. Inner and outer sphere mechanisms and the coupling of electron transfer to nuclear rearrangements are reviewed. These principles are applied to construct artificial photosynthesis. This leads to biological electron transfer involving proteins with transition metal and/or organic redox centres. The tuning of the free energy profile on the reaction trajectory through the protein by single amino acids or by the larger ensemble that determines the electrostatic properties of the reaction path is one major issue. Another one is the transformation of one-electron to paired-electron steps with protection against hazardous radical intermediates. The diversity of electron transport systems is represented in some chapters with emphasis on photosynthesis, respiration and nitrogenases. In photosynthesis of green plants light driven vectorial electron transfer is coupled to protolytic reactions, with about one quarter of the useful work derived from light quanta utilized for proton pumping across a coupling membrane. That is where the interchange of electrochemical (Dm) and chemical (ATP) forms of free energy storage and transfer in cellular energetics starts. The proton is distinguished from other reactants by an extremely small diameter and the ability of tunneling at reasonable rates. This is the basis for particular polarization, solvent and isotope effects as well as for hydrogen-bonded networks that are suited to long-range proton-transfer. (author). refs.; figs.; tabs

  12. Direct simulation of electron transfer reactions in DNA radical cations.

    Science.gov (United States)

    Steinbrecher, Thomas; Koslowski, Thorsten; Case, David A

    2008-12-25

    The electron transfer properties of DNA radical cations are important in DNA damage and repair processes. Fast long-range charge transfer has been demonstrated experimentally, but the subtle influences that experimental conditions as well as DNA sequences and geometries have on the details of electron transfer parameters are still poorly understood. In this work, we employ an atomistic QM/MM approach, based on a one-electron tight binding Hamiltonian and a classical molecular mechanics forcefield, to conduct nanosecond length MD simulations of electron holes in DNA oligomers. Multiple spontaneous electron transfer events were observed in 100 ns simulations with neighboring adenine or guanine bases. Marcus parameters of charge transfer could be extracted directly from the simulations. The reorganization energy lambda for hopping between neighboring bases was found to be ca. 25 kcal/mol and charge transfer rates of 4.1 x 10(9) s(-1) for AA hopping and 1.3 x 10(9) s(-1) for GG hopping were obtained. PMID:19049302

  13. Electron transfer in the Hf1Co6 magnetic alloy

    International Nuclear Information System (INIS)

    The cobalt atomic magnetic moment in Hf1Co6 was determined from the measured saturation magnetization and compared with predictions of an electron transfer model. Good agreement was found when hafnium contributes only two of its four valence electrons to the empty states in the minority spin band of cobalt

  14. The effect of intermolecular hydrogen bonding on the fluorescence of a bimetallic platinum complex.

    Science.gov (United States)

    Zhao, Guang-Jiu; Northrop, Brian H; Han, Ke-Li; Stang, Peter J

    2010-09-01

    The bimetallic platinum complexes are known as unique building blocks and arewidely utilized in the coordination-driven self-assembly of functionalized supramolecular metallacycles. Hence, photophysical study of the bimetallic platinum complexes will be very helpful for the understanding on the optical properties and further applications of coordination-driven self-assembled supramolecular metallacycles. Herein, we report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the significant intermolecular hydrogen bonding effects on the intramolecular charge transfer (ICT) fluorescence of a bimetallic platinum compound 4,4'-bis(trans-Pt(PEt(3))(2)OTf)benzophenone 3 in solution. We demonstrated that the fluorescent state of compound 3 can be assigned as a metal-to-ligand charge transfer (MLCT) state. Moreover, it was observed that the formation of intermolecular hydrogen bonds can effectively lengthen the fluorescence lifetime of 3 in alcoholic solvents compared with that in hexane solvent. At the same time, the electronically excited states of 3 in solution are definitely changed by intermolecular hydrogen bonding interactions. As a consequence, we propose a new fluorescence modulation mechanism by hydrogen bonding to explain different fluorescence emissions of 3 in hydrogen-bonding solvents and nonhydrogen-bonding solvents. PMID:20698713

  15. Conformational analysis of a Chlamydia-specific disaccharide ?-Kdo-(2?8)-?-Kdo-(2?O)-allyl in aqueous solution and bound to a monoclonal antibody: Observation of intermolecular transfer NOEs

    International Nuclear Information System (INIS)

    The disaccharide ?-Kdo-(2?8)-?-Kdo (Kdo: 3-deoxy-d-manno-oct-2-ulosonic acid) represents a genus-specific epitope of the lipopolysaccharide of the obligate intracellular human pathogen Chlamydia. The conformation of the synthetically derived disaccharide ?-Kdo-(2?8)-?-Kdo-(2?O)-allyl was studied in aqueous solution, and complexed to a monoclonal antibody S25-2. Various NMR experiments based on the detection of NOEs (or transfer NOEs) and ROEs (or transfer ROEs) were performed. A major problem was the extensive overlap of almost all 1H NMR signals of ?-Kdo-(2?8)-?-Kdo-(2?O)-allyl. To overcome this difficulty, HMQC-NOESY and HMQC-trNOESY experiments were employed. Spin diffusion effects were identified using trROESY experiments, QUIET-trNOESY experiments and MINSY experiments. It was found that protein protons contribute to the observed spin diffusion effects. At 800 MHz, intermolecular trNOEs were observed between ligand protons and aromatic protons in the antibody binding site. From NMR experiments and Metropolis Monte Carlo simulations, it was concluded that ?-Kdo-(2?8)-?-Kdo-(2?O)-allyl in aqueous solution exists as a complex conformational mixture. Upon binding to the monoclonal antibody S25-2, only a limited range of conformations is available to ?-Kdo-(2?8)-?-Kdo-(2?O)-allyl. These possible bound conformations were derived from a distance geometry analysis using transfer NOEs as experimental constraints. It is clear that a conformation is selected which lies within a part of the conformational space that is highly populated in solution. This conformational space also includes the conformation found in the crystal structure. Our results provide a basis for modeling studies of the antibody-disaccharide complex

  16. Conformational analysis of a Chlamydia-specific disaccharide {alpha}-Kdo-(2{sup {yields}}8)-{alpha}-Kdo-(2{sup {yields}}O)-allyl in aqueous solution and bound to a monoclonal antibody: Observation of intermolecular transfer NOEs

    Energy Technology Data Exchange (ETDEWEB)

    Sokolowski, Tobias; Haselhorst, Thomas; Scheffler, Karoline [Medizinische Universitaet, Institut fuer Chemie (Germany); Weisemann, Ruediger [Bruker Analytik GmbH, Silberstreifen (Germany); Kosma, Paul [Institut fuer Chemie der Universitaet fuer Bodenkultur Wien (Austria); Brade, Helmut; Brade, Lore [Forschungszentrum Borstel, Zentrum fuer Medizin und Biowissenschaften Parkallee 22 (Germany); Peters, Thomas [Medizinische Universitaet, Institut fuer Chemie (Germany)

    1998-07-15

    The disaccharide {alpha}-Kdo-(2{sup {yields}}8)-{alpha}-Kdo (Kdo: 3-deoxy-d-manno-oct-2-ulosonic acid) represents a genus-specific epitope of the lipopolysaccharide of the obligate intracellular human pathogen Chlamydia. The conformation of the synthetically derived disaccharide {alpha}-Kdo-(2{sup {yields}}8)-{alpha}-Kdo-(2{sup {yields}}O)-allyl was studied in aqueous solution, and complexed to a monoclonal antibody S25-2. Various NMR experiments based on the detection of NOEs (or transfer NOEs) and ROEs (or transfer ROEs) were performed. A major problem was the extensive overlap of almost all {sup 1}H NMR signals of {alpha}-Kdo-(2{sup {yields}}8)-{alpha}-Kdo-(2{sup {yields}}O)-allyl. To overcome this difficulty, HMQC-NOESY and HMQC-trNOESY experiments were employed. Spin diffusion effects were identified using trROESY experiments, QUIET-trNOESY experiments and MINSY experiments. It was found that protein protons contribute to the observed spin diffusion effects. At 800 MHz, intermolecular trNOEs were observed between ligand protons and aromatic protons in the antibody binding site. From NMR experiments and Metropolis Monte Carlo simulations, it was concluded that {alpha}-Kdo-(2{sup {yields}}8)-{alpha}-Kdo-(2{sup {yields}}O)-allyl in aqueous solution exists as a complex conformational mixture. Upon binding to the monoclonal antibody S25-2, only a limited range of conformations is available to {alpha}-Kdo-(2{sup {yields}}8)-{alpha}-Kdo-(2{sup {yields}}O)-allyl. These possible bound conformations were derived from a distance geometry analysis using transfer NOEs as experimental constraints. It is clear that a conformation is selected which lies within a part of the conformational space that is highly populated in solution. This conformational space also includes the conformation found in the crystal structure. Our results provide a basis for modeling studies of the antibody-disaccharide complex.

  17. Catching the role of anisotropic electronic distribution and charge transfer in halogen bonded complexes of noble gases

    Science.gov (United States)

    Bartocci, Alessio; Belpassi, Leonardo; Cappelletti, David; Falcinelli, Stefano; Grandinetti, Felice; Tarantelli, Francesco; Pirani, Fernando

    2015-05-01

    The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl4 and CF4. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypical Ng-CCl4 and Ng-CF4 and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF4, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl4, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential suggested by the analysis of the experiments actually reflect two chemically meaningful contributions, namely, a stabilizing interaction arising from the anisotropy of the charge distribution around the Cl atom in CCl4 and a stereospecific electron transfer that occurs at the intermolecular distances mainly probed by the experiments. Our model calculations suggest that the largest effect is for the vertex geometry of CCl4 while other geometries appear to play a minor to negligible role.

  18. 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. PMID:26404482

  19. Effect of electronic and nuclear factors on the dynamics of dye-to-semiconductor electron transfer

    OpenAIRE

    Wenger, Bernard

    2006-01-01

    Dye-to-semiconductor electron transfer is the initial step in many processes where light is used for the storage of information (e. g. color photography) or converted into electricity as in dye-sensitized solar cells. In the latter, interfacial charge injection occurs on a timescale spanning from tens of femtoseconds (10-15 s) to several picoseconds (10-12 s), with an efficiency approaching 100 %. In standard electron transfer theory, the parameters controlling charge transfer dynamics are di...

  20. Computational Approach to Electron Charge Transfer Reactions

    DEFF Research Database (Denmark)

    Jónsson, Elvar Örn

    2013-01-01

    The step from ab initio atomic and molecular properties to thermodynamic - or macroscopic - properties requires the combination of several theoretical tools. This dissertation presents constant temperature molecular dynamics with bond length constraints, a hybrid quantum mechanics-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 en...

  1. Electron transfer from nucleobase electron adducts to 5-bromouracil: a radiation chemical study

    International Nuclear Information System (INIS)

    Electron transfer to 5-bromouracil from their nucleobase electron adducts and their protonated forms has been studied by product analysis. When an electron is transferred to 5-bromouracil, the ensuing 5-bromouracil radical anion rapidly loses a bromide ion. The uracilyl radical thus formed reacts with added t-butanol, yielding uracil. From the uracil yields measured as a function of (N)/(5-BrU) after ?-radiolysis of Ar-saturated solutions it is concluded that the hetero atom protonated forms transfer electron quantitatively to 5-bromouracil. (author). 3 refs., 1 fig

  2. Electron transfer reactions in microporous solids

    Energy Technology Data Exchange (ETDEWEB)

    Mallouk, T.E.

    1993-01-01

    Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H[sub 2] and I[sub 3][sup [minus

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

    Directory of Open Access Journals (Sweden)

    PravinMallaShrestha

    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.

  4. 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

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

    DEFF Research Database (Denmark)

    Shrestha, Pravin; 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.

  6. Improved Formulas for the Calculation of the Electrostatic Contribution to the Intermolecular Interaction Energy from Multipolar Expansion of the Electronic Distribution.

    Science.gov (United States)

    Piquemal, Jean-Philip; Gresh, Nohad; Giessner-Prettre, Claude

    2003-12-01

    We have, within the framework of the molecular mechanics method SIBFA, improved the formulation of the Coulomb (electrostatic) energy contribution to the intermolecular interaction energy. This was done by integrating "overlap-like" terms into two components of the multipolar development used to calculate this contribution in SIBFA. The calibration of the new component is done on five water dimers by fitting this augmented electrostatic contribution to the corresponding Ec term. Several tests are done on (i) representative neutral and ionic hydrogen-bonded complexes; (ii) the complexes of metal cations (Cu(I) and Cu(II)) with a neutral or an anionic ligand; and (iii) a representative stacked complex. The improvement brought by the new formulation reduces the difference between the ab initio (Ec) and molecular mechanics (EMTP*) values by almost an order of magnitude when compared to the values of EMTP calculated using the standard method. PMID:26313624

  7. Photocurrent generation by direct electron transfer using photosynthetic reaction centres

    International Nuclear Information System (INIS)

    Photosynthetic reaction centres (RCs) convert light into separated charges with nearly perfect quantum efficiency, and have been used to generate photocurrent. Previous work has shown that electron tunnelling rates between redox centres in proteins depend exponentially on the tunnelling distance. In this work the RC from Rhodobacter sphaeroides was genetically modified with the aim of achieving the shortest tunnelling distances yet demonstrated between the RC's electron-accepting P site and underlying graphite and gold electrodes, and between the electron donor Q site and graphite electrodes. Opposite charges are carried to counter electrodes using mobile mediators, as in dye-sensitised solar cells. Native RCs are bound to graphite surfaces through N-(1-pyrene)iodoacetamide. Although the linker's length is only 4 Å, the electron transfer pathway between the Q electron donor site on the RC and the electrode surface is still too large for current to be significant. A mutant version with the electron acceptor P side close to the graphite surface produced currents of 15 nA cm?2 upon illumination. Direct binding of RCs to a gold surface is shown, resulting in currents of 5 nA cm?2. In both cases the current was unaffected by mediator concentration but increased with illumination, suggesting that direct electron transfer was achieved. The engineering of an RC to achieve direct electron transfer will help with long term efforts to demonstrate RC-based photovoltaic devices

  8. Heavy particle interference and diffraction in fast electron transfer collisions

    OpenAIRE

    Gudmundsson, Magnus

    2011-01-01

    This thesis presents experimental results from the synchrotron cooler and storage ring CRYRING on charge transfer processes in fast electron transfer collisions using high-resolution cold target recoil-ion momentum spectroscopy. The main focus of these studies was to investigate a key concept of quantum mechanics: the wave-particle duality. One series of experiments has been dedicated to the study of heavy particle de Broglie wave interference due to scattering on a molecular ’double slit’. T...

  9. Electron transfer, ionization, and excitation atomic collisions

    International Nuclear Information System (INIS)

    Basic atomic-collision processes at intermediate and high energies are being studied theoretically at Penn State by Alston and Winter. In the high velocity regime, single-electron capture is treated using a high order multiple-scattering approach; extensive comparison with experiment and analysis of mechanisms have been made. Fitting the calculated amplitude with a simple analytic form, the asymptotic velocity dependence of the cross section is obtained. The effect on the capture amplitude of altering the inner part of the internuclear potential has also been explored. In the intermediate velocity regime, earlier work on collisions between protons and hydrogenic-ion targets using a coupled-state approach is being extended to the two-electron helium target. 29 refs

  10. Numerical modeling of fast electron energy transfer

    International Nuclear Information System (INIS)

    In this paper methods of calculating energy transport by fast electrons that are currently used in the ''Diana'' program are described; this program is intended to address issues in laser thermonuclear fusion. A method is proposed for solving a kinetic equation which has the following properties: conservativeness, the absence of constraints on the grid spacing relation, monitonicity, and second order approximation. The applicability of a ''front-back'' approximation is analyzed

  11. Electronic structure aspects of the complete O2 transfer reaction between Ni(II) and Mn(II) complexes with cyclam ligands.

    Science.gov (United States)

    Zapata-Rivera, Jhon; Caballol, Rosa; Calzado, Carmen J

    2015-01-28

    This work explores the electronic structure aspects involving the complete intermolecular O2 transfer between Ni(ii) and Mn(ii) complexes, both containing N-tetramethylated cyclams (TMC). The energy of the low-lying states of reactants, intermediates and products is established at the CASSCF level and also the DDCI level when possible. The orthogonal valence bond analysis of the wave functions obtained from CASSCF and DDCI calculations indicates the dominant superoxide nature of all the adducts participating in the reaction, and consequently that the whole reaction can be described as the transfer of the superoxide O2(-) between Ni(ii) and Mn(ii) complexes, without any additional change in the electronic structure of the fragments. PMID:25502350

  12. Intra- and intermolecular vibrational energy transfer in tungsten carbonyl complexes W(CO)5(X) (X=CO, CS, CH3CN, and CD3CN).

    Science.gov (United States)

    Banno, Motohiro; Iwata, Koichi; Hamaguchi, Hiro-o

    2007-05-28

    Vibrational energy relaxation of degenerate CO stretches of four tungsten carbonyl complexes, W(CO)6, W(CO)5(CS), W(CO)5(CH3CN), and W(CO)5(CD3CN), is observed in nine alkane solutions by subpicosecond time-resolved infrared (IR) pump-probe spectroscopy. Between 0 and 10 ps after the vibrational excitation, the bleaching signal of the ground-state IR absorption band shows anisotropy. Decay of the anisotropic component corresponds either to the rotational diffusion of the molecule or to the intramolecular vibrational energy transfer among the degenerate CO stretch modes. The time constant of the anisotropy decay, tauaniso, shows distinct solvent dependence. By comparing the results for the T1u CO stretch of W(CO)6 and the A1 CO stretch of W(CO)5(CS), the time constant of the rotational diffusion, taur, and the time constant of the intramolecular energy transfer among the three degenerate vibrational modes, taue, are determined as 12 and 8 ps, respectively. The tauaniso value increases as the number of carbon atoms in the alkane solvent increases. After 10 ps, the recovery of the bleaching becomes isotropic. The isotropic decay represents the vibrational population relaxation, from v=1 to v=0. In heptane, the time constant for the isotropic decay, tau1, for W(CO)5(CS) and W(CO)6 was 140 ps. The tau1 for the two acetonitrile-substituted complexes, however, shows a smaller value of 80 ps. The vibrational energy relaxation of W(CO)5(CH3CN) and W(CO)5(CD3CN) is accelerated by the intramolecular energy redistribution from the CO ligand to the acetonitrile ligand. In the nine alkane solutions, the tau1 value of W(CO)6 ranges between 124 and 158 ps, showing the apparent V-shaped solvent dependence with its minimum in decane, while the tau1 value shows little solvent dependence for W(CO)5(CH3CN) and W(CO)5(CD3CN). PMID:17552772

  13. Electron transfer statistics and thermal fluctuations in molecular junctions

    International Nuclear Information System (INIS)

    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

  14. 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.

  15. Electron Transfer Dissociation Mass Spectrometry of Hemoglobin on Clinical Samples

    Science.gov (United States)

    Coelho Graça, Didia; Lescuyer, Pierre; Clerici, Lorella; Tsybin, Yury O.; Hartmer, Ralf; Meyer, Markus; Samii, Kaveh; Hochstrasser, Denis F.; Scherl, Alexander

    2012-10-01

    A mass spectrometry-based assay combining the specificity of selected reaction monitoring and the protein ion activation capabilities of electron transfer dissociation was developed and employed for the rapid identification of hemoglobin variants from whole blood without previous proteolytic cleavage. The analysis was performed in a robust ion trap mass spectrometer operating at nominal mass accuracy and resolution. Subtle differences in globin sequences, resulting with mass shifts of about one Da, can be unambiguously identified. These results suggest that mass spectrometry analysis of entire proteins using electron transfer dissociation can be employed on clinical samples in a workflow compatible with diagnostic applications.

  16. Electron transfer and fragmentation in fullerene collisions

    OpenAIRE

    Zettergren, Henning

    2005-01-01

    In this thesis, we present results from detailed gas phase studies of intrinsic properties of fullerenes (C60) and clusters of fullerenes as probed by slow multiply charged (atomic or cluster) ions in combination with coincidence time-of-flight mass spectrometry. We have investigated the structures, stabilities, and the electron mobilities of multiply charged clusters of fullerenes, (C60)nr+ (r=2-5). We found that the (C60)nr+ cluster ions are weakly bound by van der Waals forces and the elec...

  17. Evaluation of the influence of intermolecular electron-nucleus couplings and intrinsic metal binding sites on the measurement of 15N longitudinal paramagnetic relaxation enhancements in proteins by solid-state NMR.

    Science.gov (United States)

    Nadaud, Philippe S; Sengupta, Ishita; Helmus, Jonathan J; Jaroniec, Christopher P

    2011-11-01

    Magic-angle spinning solid-state NMR measurements of (15)N longitudinal paramagnetic relaxation enhancements (PREs) in (13)C,(15)N-labeled proteins modified with Cu(2+)-chelating tags can yield multiple long-range electron-nucleus distance restraints up to ~20 Å (Nadaud et al. in J Am Chem Soc 131:8108-8120, 2009). Using the EDTA-Cu(2+) K28C mutant of B1 immunoglobulin binding domain of protein G (GB1) as a model, we investigate the effects on such measurements of intermolecular electron-nucleus couplings and intrinsic metal binding sites, both of which may potentially complicate the interpretation of PRE data in terms of the intramolecular protein fold. To quantitatively assess the influence of intermolecular (15)N-Cu(2+) interactions we have determined a nearly complete set of longitudinal (15)N PREs for a series of microcrystalline samples containing ~10, 15 and 25 mol percent of the (13)C,(15)N-labeled EDTA-Cu(2+)-tagged protein diluted in a matrix of diamagnetic natural abundance GB1. The residual intermolecular interactions were found to be minor on the whole and account for only a fraction of the relatively small but systematic deviations observed between the experimental (15)N PREs and corresponding values calculated using protein structural models for residues furthest removed from the EDTA-Cu(2+) tag. This suggests that these deviations are also caused in part by other factors not related to the protein structure, such as the presence in the protein of intrinsic secondary sites capable of binding Cu(2+) ions. To probe this issue we performed a Cu(2+) titration study for K28C-EDTA GB1 monitored by 2D (15)N-(1)H solution-state NMR, which revealed that while for Cu(2+):protein molar ratios of ? 1.0 Cu(2+) binds primarily to the high-affinity EDTA tag, as anticipated, at even slightly super-stoichiometric ratios the Cu(2+) ions can also associate with side-chains of aspartate and glutamate residues. This in turn is expected to lead to enhanced PREs for residues located in the vicinity of the secondary Cu(2+) binding sites, and indeed many of these residues were ones found to display the elevated longitudinal (15)N PREs in the solid phase. PMID:21826518

  18. 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.

  19. Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis*

    OpenAIRE

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

    2010-01-01

    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-resolu...

  20. 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.

  1. 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

    2015-09-23

    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. PMID:26193994

  2. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Khalil, Munira

    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.

  3. Heterogeneous electron transfer of pesticides. Current trends and applications.

    Czech Academy of Sciences Publication Activity Database

    Sokolová, Romana; Hromadová, Magdaléna; Pospíšil, Lubomír

    Kerala : Transworld Research Network, 2008 - (Colombini, M.; Tassi, L.), s. 43-76 ISBN 978-81-7895-343-4 R&D Projects: GA AV ?R IAA400400505; GA MŠk LC510; GA MŠk OC 140 Institutional research plan: CEZ:AV0Z40400503 Keywords : heterogeneous electron transfer * pesticides * redox reactions Subject RIV: CF - Physical ; Theoretical Chemistry

  4. Electron transfer reactions involving porphyrins and chlorophyll a

    International Nuclear Information System (INIS)

    Electron transfer reactions involving porphyrins (P) and quinones (Q) have been studied by pulse radiolysis. The porphyrins used were tetraphenylporphyrin (H2TPP), its tetracarboxy derivative (H2TCPP), the sodium and zinc compounds (Na2TPP and ZnTPP), and chlorophyll a (Chl a). These compounds were found to be rapidly reduced by electron transfer from (CH3)2CO-. Reduction by (CH3)2COH was rapid in aqueous solutions but relatively slow in i-PrOH solutions. Transient spectra of the anion radicals were determined and, in the case of H2TCPP-., a pK = 9.7 was derived for its protonation. Electron-transfer reactions from the anion radical of H2TCPP to benzoquinone, duroquinone, 9,10-anthraquinone 2-sulfonate, and methylviologen occur in aqueous solutions with rate constants approx. 107-109 M-1 s-1 which depend on the pH and the quinone reduction potential. Reactions of Na2TPP-., ZnTPP-., and Chl a-. with anthraquinone in basic i-PrOH solutions occur with rate constants approx. 109 M-1 s-1. The spectral changes associated with these electron-transfer reactions as observed over a period of approx. 1 ms indicated, in some cases, the formation of an intermediate complex [P...Q-.]. 8 figures, 2 tables

  5. Electronic excitation energy transfer between quasi-zero-dimensional systems.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Ostrava : Tanger, 2013. ISBN 978-80-87294-44-4. [International Conference NANOCON 2013 /5./. Brno (CZ), 16.10.2013-18.10.2013] R&D Pro jects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

  6. 77 FR 6310 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-02-07

    ... would complete the rulemaking process. 76 FR 29902 (May 23, 2011). This proposal has two parts. First... information on whether it should revise these threshold numbers in Regulation Z. See 76 FR 75825 (Dec. 5, 2011... PROTECTION 12 CFR Part 1005 RIN 3170-AA15 Electronic Fund Transfers (Regulation E) AGENCY: Bureau of...

  7. 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 $\\lambda_{\\max}$ 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.

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

    Science.gov (United States)

    Kundu, Prasanta; Dua, Arti

    2013-01-01

    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.

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

    International Nuclear Information System (INIS)

    The fundamental processes of electron transfer, ionization, and excitation in ion-atom collisions are being studied. These collision processes are treated in the context of simple one- or two-electron systems in order to provide unambiguous results and reveal more clearly the collisional mechanisms. As outlined in the original proposal, three coupled-state calculations are being carried out over the present three-year period: a Sturmian-pseudostate study of ionization in collisions between protons and the hydrogenic ions He+, Li2+, Be3+, ...; a triple-center, atomic-state study of ionization in collisions between ? particles and H(ls) atoms and between protons and He+(ls) ions; and an atomic-state study of electron transfer and excitation in collisions between protons and neutral He atoms. 12 refs

  10. Simulations of charge transfer in Electron Multiplying Charge Coupled Devices

    Science.gov (United States)

    Bush, N.; Stefanov, K.; Hall, D.; Jordan, D.; Holland, A.

    2014-12-01

    Electron Multiplying Charge Coupled Devices (EMCCDs) are a variant of traditional CCD technology well suited to applications that demand high speed operation in low light conditions. On-chip signal amplification allows the sensor to effectively suppress the noise introduced by readout electronics, permitting sub-electron read noise at MHz pixel rates. The devices have been the subject of many detailed studies concerning their operation, however there has not been a study into the transfer and multiplication process within the EMCCD gain register. Such an investigation has the potential to explain certain observed performance characteristics, as well as inform further optimisations to their operation. In this study, the results from simulation of charge transfer within an EMCCD gain register element are discussed with a specific focus on the implications for serial charge transfer efficiency (CTE). The effects of operating voltage and readout speed are explored in context with typical operating conditions. It is shown that during transfer, a small portion of signal charge may become trapped at the semiconductor-insulator interface that could act to degrade the serial CTE in certain operating conditions.

  11. Hydrogen-bond relays in concerted proton-electron transfers.

    Science.gov (United States)

    Bonin, Julien; Costentin, Cyrille; Robert, Marc; Savéant, Jean-Michel; Tard, Cédric

    2012-03-20

    Reaction mechanisms in which electron and proton transfers are coupled are central to a huge number of processes, both natural and synthetic. Moreover, most of the new approaches to address modern energy challenges involve proton-coupled electron transfer (PCET). Recent research has focused on the possibility that the two steps are concerted, that is, concerted proton-electron transfer (CPET) reactions, rather than stepwise pathways in which proton transfer precedes (PET) or follows (EPT) electron transfer. CPET pathways have the advantage of bypassing the high-energy intermediates of stepwise pathways, although this thermodynamic benefit may have a kinetic cost. Concerted processes require short distances between the group being oxidized and the proton acceptor (and vice versa for a reduction process), which usually involves the formation of a hydrogen bond. Unlike the electron in outer-sphere electron-transfer reactions, the distance a proton may travel in a CPET is therefore rather limited. The idea has recently emerged, however, that this distance may be substantially increased via a H-bond relay located between the electron-transfer-triggered proton source and the proton acceptor. Generally speaking, the relay is a group bearing a H atom able to accept a H-bond from the moiety being oxidized and, at the same time, to form a H-bond with the proton-accepting group without going through a protonated intermediate. Although these molecules do not retain all the properties of chains of water molecules engaged in Grotthuss-type transport of a proton, the OH group in these molecules does possess a fundamental property of water molecules: namely, it is both a hydrogen-bond acceptor and a hydrogen-bond donor. Despite centuries of study, the mechanisms of proton movement in water remain active experimental and theoretical research areas, but so far with no connection to CPET reactions. In this Account, we bring together recent results concerning (i) the oxidative response of molecules containing a H-bond relay and (ii) the oxidation of phenol with water (in water) as the proton acceptor. In the first case, a nondestructive electrochemical method (cyclic voltammetry) was used to investigate the oxidation of phenol molecules containing one H-bond relay and an amine proton acceptor compared with a similar amino phenol deprived of relay. In the second, the kinetics of phenol oxidation with water (in water) as proton acceptor is contrasted with that of conventional proton acceptors (such as hydrogen phosphate and pyridine) to afford evidence of the concerted nature of Grotthuss-type proton displacement with electron transfer. First indications were provided by the same electrochemical method, whereas a more complete kinetic characterization was obtained from laser flash photolysis. Older electrochemical results concerning the reduction of superoxide ion in the presence of water are also examined. The result is a timely picture of current insight into concerted mechanisms involving electron transfer coupled with proton transport over simple H-bond relays and over H-bond networks. PMID:22029773

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

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Chang, Po-Yao

    2012-01-01

    Smell is a vital sense for animals. The mainstream explanation of smell is based on recognition of the odorant molecules through characteristics of their surface, e.g., shape, but certain experiments suggest that such recognition is complemented by recognition of vibrational modes. According 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 dimensions. In the present paper we introduce the vibrationally assisted mechanism of olfaction and demonstrate for several odorants that, indeed, a strong enhancement of an electron tunneling rate due to odorant vibrations can arise. We discuss in this regard the influence of odorant deuteration and explain, 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 homology modeling.

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

    Science.gov (United States)

    Klauss, André; Haumann, Michael; Dau, Holger

    2012-10-01

    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 (?, 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 (?, 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. PMID:22988080

  14. A Dynamical Theory of Electron Transfer: Crossover from Weak to Strong Electronic Coupling

    OpenAIRE

    Stockburger, Juergen T.; Mak, C H

    1996-01-01

    We present a real-time path integral theory for the rate of electron transfer reactions. Using graph theoretic techniques, the dynamics is expressed in a formally exact way as a set of integral equations. With a simple approximation for the self-energy, the rate can then be computed analytically to all orders in the electronic coupling matrix element. We present results for the crossover region between weak (nonadiabatic) and strong (adiabatic) electronic coupling and show t...

  15. Neutral histidine and photoinduced electron transfer in DNA photolyases.

    Science.gov (United States)

    Domratcheva, Tatiana

    2011-11-16

    The two major UV-induced DNA lesions, the cyclobutane pyrimidine dimers (CPD) and (6-4) pyrimidine-pyrimidone photoproducts, can be repaired by the light-activated enzymes CPD and (6-4) photolyases, respectively. It is a long-standing question how the two classes of photolyases with alike molecular structure are capable of reversing the two chemically different DNA photoproducts. In both photolyases the repair reaction is initiated by photoinduced electron transfer from the hydroquinone-anion part of the flavin adenine dinucleotide (FADH(-)) cofactor to the photoproduct. Here, the state-of-the-art XMCQDPT2-CASSCF approach was employed to compute the excitation spectra of the respective active site models. It is found that protonation of His365 in the presence of the hydroquinone-anion electron donor causes spontaneous, as opposed to photoinduced, coupled proton and electron transfer to the (6-4) photoproduct. The resulting neutralized biradical, containing the neutral semiquinone and the N3'-protonated (6-4) photoproduct neutral radical, corresponds to the lowest energy electronic ground-state minimum. The high electron affinity of the N3'-protonated (6-4) photoproduct underlines this finding. Thus, it is anticipated that the (6-4) photoproduct repair is assisted by His365 in its neutral form, which is in contrast to the repair mechanisms proposed in the literature. The repair via hydroxyl group transfer assisted by neutral His365 is considered. The repair involves the 5'base radical anion of the (6-4) photoproduct which in terms of electronic structure is similar to the CPD radical anion. A unified model of the CPD and (6-4) photoproduct repair is proposed. PMID:21970417

  16. 77 FR 10373 - Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid...

    Science.gov (United States)

    2012-02-22

    ...Electronics Manufacturing: Revisions to Heat Transfer Fluid Provisions AGENCY: Environmental...Reporting Rule related to fluorinated heat transfer fluids. More specifically, EPA...the definition of fluorinated heat transfer fluids and to the provisions...

  17. Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

    International Nuclear Information System (INIS)

    The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact

  18. Ligand reorganization and activation energies in nonadiabatic electron transfer reactions

    Science.gov (United States)

    Zhu, Jianjun; Wang, Jianji; Stell, George

    2006-10-01

    The activation energy and ligand reorganization energy for nonadiabatic electron transfer reactions in chemical and biological systems are investigated in this paper. The free energy surfaces and the activation energy are derived exactly in the general case in which the ligand vibration frequencies are not equal. The activation energy is derived by free energy minimization at the transition state. Our formulation leads to the Marcus-Hush [J. Chem. Phys. 24, 979 (1956); 98, 7170 (1994); 28, 962 (1958)] results in the equal-frequency limit and also generalizes the Marcus-Sumi [J. Chem. Phys. 84, 4894 (1986)] model in the context of studying the solvent dynamic effect on electron transfer reactions. It is found that when the ligand vibration frequencies are different, the activation energy derived from the Marcus-Hush formula deviates by 5%-10% from the exact value. If the reduced reorganization energy approximation is introduced in the Marcus-Hush formula, the result is almost exact.

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

    DEFF Research Database (Denmark)

    Farver, Ole; Brunori, Maurizio; Cutruzzolà, Francesca; Rinaldo, Serena; Wherland, Scot; Pecht, Israel

    2009-01-01

    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 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 s...

  20. Two-photon electron transfer between quantum dots

    International Nuclear Information System (INIS)

    The effective Hamiltonian of a system describing electrons of two quantum dots in a two-frequency electromagnetic field upon Raman resonance of the field with a pair of the electronic levels of different dots is obtained by the method of equivalent transformation. The states of the continuous spectrum (conduction bands) are correctly taken into account. The role of the terms describing the dynamic Stark effect in a two-body system is analysed. A new mechanism of particle transfer between quantum wells in a non-resonance electromagnetic field is proposed, which is free from disadvantages of previous models. (fourth seminar to the memory of d.n. klyshko)

  1. Electron transfer between quasi-zero-dimensional nanostructures.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav

    Munich : IEEE, 2010, s. 1-5. ISBN 978-1-4244-7799-9. [International Conference on Transparent Optical Networks /12./. Mnichov (DE), 27.06.2010-01.07.2010] R&D Projects: GA MŠk(CZ) OC10007; GA MŠk ME 866 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40500505 Keywords : electron transfer * quantum dots * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism http://dx.doi.org/10.1109/ICTON.2010.5548991

  2. 76 FR 35219 - Federal Acquisition Regulation; Information Collection; Payment by Electronic Fund Transfer

    Science.gov (United States)

    2011-06-16

    ... From the Federal Register Online via the Government Printing Office DEPARTMENT OF DEFENSE GENERAL...; Information Collection; Payment by Electronic Fund Transfer AGENCY: Department of Defense (DOD), General... previously approved information collection requirement concerning payment by electronic fund transfer....

  3. 77 FR 22067 - Proposed Collection of Information: Trace Request for Electronic Funds Transfer (EFT) Payment...

    Science.gov (United States)

    2012-04-12

    ...Proposed Collection of Information: Trace Request for Electronic Funds Transfer...on a continuing information collection. By...Trace Request for Electronic Funds Transfer...Highway, Records and Information Management...

  4. 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 to gold without drastic protein unfolding. A comprehensive approach, based on linear sweep and differential pulse voltammetry, capacitance measurements, X-ray photoelectron spectroscopy (XPS) , in situscann...

  5. Crossed Andreev reflection versus electron transfer in graphene nanoribbons

    OpenAIRE

    Haugen, Håvard; Huertas-Hernando, Daniel; Brataas, Arne; Waintal, Xavier

    2009-01-01

    We investigate the transport properties of three-terminal graphene devices, where one terminal is superconducting and two are normal metals. The terminals are connected by nanoribbons. Electron transfer (ET) and crossed Andreev reflection (CAR) are identified via the non-local signal between the two normal terminals. Analytical expressions for ET and CAR in symmetric devices are found. We compute ET and CAR numerically for asymmetric devices. ET dominates CAR in symmetric de...

  6. Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives

    DEFF Research Database (Denmark)

    Borovok, N; Kotlyar, A B; Pecht, I; Skov, L K; Farver, O

    1999-01-01

    A novel method for the initiation of intramolecular electron transfer reactions in azurin is reported. The method is based on laser photoexcitation of covalently attached thiouredopyrenetrisulfonate (TUPS), the reaction that generates the low potential triplet state of the dye with high quantum 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 m...

  7. Diffusion, spin and reaction control in geminate reverse electron transfer

    OpenAIRE

    Anatoly I. Burshtein; Krissinel, Evgenii B.; Steiner, Ulrich

    2001-01-01

    Kinetic analyses of geminate radical escape yields in terms of a simple (exponential) reaction scheme with first-order rate constants of separation and geminate recombination have been widely used in the literature, e.g. to evaluate rate constants of reverse electron transfer (k et). Here we demonstrate the limited value of such rate constants by formally analysing, in terms of the exponential model, the diffusion coefficient (?iz. viscosity) dependence of the radical escape yield as theoreti...

  8. Promoting direct interspecies electron transfer with activated carbon

    DEFF Research Database (Denmark)

    Liu, Fanghua; Rotaru, Amelia-Elena; Shrestha, Pravin M.; Malvankar, Nikhil S.; Nevin, Kelly P.; Lovley, Derek R.

    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 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 met...

  9. Nanoscale and single-molecule interfacial electron transfer

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Wackerbarth, Hainer; Nielsen, Jens Ulrik; Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    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 for comprehensive later theoretical work and data interpretation in many areas of chemistry, electrochemistry, and biology. We discuss here some new areas of theoretical electrochemical ET science, with f...

  10. Electrochemical studies on small electron transfer proteins using membrane electrodes

    OpenAIRE

    Moura, José J G; Santos, M.M. Correia dos; Sousa, P. M. Paes de; Gonçalves, M.L. Simões; Krippahl, L.; Lojou, É.; Bianco, P

    2003-01-01

    Membrane electrodes (ME) were constructed using gold, glassy carbon and pyrolytic graphite supports and a dialysis membrane, and used to study the electrochemical behavior of small size electron transfer proteins: monohemic cytochrome c522 from Pseudomonas nautica and cytochrome c533 as well as rubredoxin from Desulfovibrio vulgaris . Different electrochemical techniques were used including cyclic voltammetry (CV), square wave voltammetry (SW) and differential pulse voltammetry (DP). A ...

  11. Low activation barriers characterize intramolecular electron transfer in ascorbate oxidase

    DEFF Research Database (Denmark)

    Farver, O; Pecht, I

    1992-01-01

    Anaerobic reduction kinetics of the zucchini squash ascorbate oxidase (AO; L-ascorbate:oxygen oxidoreductase, EC 1.10.3.3) by pulse radiolytically produced CO2- radical ions were investigated. Changes in the absorption bands of type 1 [Cu(II)] (610 nm) and type 3 [Cu(II)] (330 nm) were monitored over a range of reactant concentrations, pH, and temperature. The direct bimolecular reduction of type 1 [Cu(II)] [(1.2 +/- 0.2) x 10(9) M-1.s-1] was followed by its subsequent reoxidation in three distinct phases, all found to be unimolecular processes with the respective specific rates of 201 +/- 8, 20 +/- 4, and 2.3 +/- 0.2 s-1 at pH 5.5 and 298 K. While at this pH no direct bimolecular reduction was resolved in the 330-nm band, at pH 7.0 such a direct process was observed [(6.5 +/- 1.2) x 10(8) M-1.s-1]. In the same slower time domains where type 1 [Cu(I)] reoxidation was monitored, reduction of type 3 [Cu(II)] was observed, which was also concentration independent and with identical rate constants and amplitudes commensurate with those of type 1 [Cu(II)] reoxidation. These results show that after electron uptake by type 1 [Cu(II)], its reoxidation takes place by intramolecular electron transfer to type 3 [Cu(II)]. The observed specific rates are similar to values reported for the limiting-rate constants of AO reduction by excess substrate, suggesting that internal electron transfer is the rate-determining step of AO activity. The temperature dependence of the intramolecular electron transfer rate constants was measured from 275 to 308 K at pH 5.5 and, from the Eyring plots, low activation enthalpies were calculated--namely, 9.1 +/- 1.1 and 6.8 +/- 1.0 kJ.mol-1 for the fastest and slowest phases, respectively. The activation entropies observed for these respective phases were -170 +/- 9 and -215 +/- 16 J.K-1.mol-1. The exceptionally low enthalpy barriers imply the involvement of highly optimized electron transfer pathways for internal electron transfer.

  12. Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives.

    Science.gov (United States)

    Borovok, N; Kotlyar, A B; Pecht, I; Skov, L K; Farver, O

    1999-08-27

    A novel method for the initiation of intramolecular electron transfer reactions in azurin is reported. The method is based on laser photoexcitation of covalently attached thiouredopyrenetrisulfonate (TUPS), the reaction that generates the low potential triplet state of the dye with high quantum 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(II) and the back reaction from Cu(I) to the oxidized dye. For all singly labeled derivatives, the rate constants of copper ion reduction were one or two orders of magnitude larger than for its reoxidation, consistent with the larger thermodynamic driving force for the former process. Using 3-D coordinates 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 rate constants of Cu(II) reduction. PMID:10471793

  13. Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives

    DEFF Research Database (Denmark)

    Borovok, N; Kotlyar, A B

    1999-01-01

    A novel method for the initiation of intramolecular electron transfer reactions in azurin is reported. The method is based on laser photoexcitation of covalently attached thiouredopyrenetrisulfonate (TUPS), the reaction that generates the low potential triplet state of the dye with high quantum 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(II) and the back reaction from Cu(I) to the oxidized dye. For all singly labeled derivatives, the rate constants of copper ion reduction were one or two orders of magnitude larger than for its reoxidation, consistent with the larger thermodynamic driving force for the former process. Using 3-D coordinates 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 rate constants of Cu(II) reduction.

  14. 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.

  15. 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.

  16. Intercellular wiring enables electron transfer between methanotrophic archaea and bacteria.

    Science.gov (United States)

    Wegener, Gunter; Krukenberg, Viola; Riedel, Dietmar; Tegetmeyer, Halina E; Boetius, Antje

    2015-10-22

    The anaerobic oxidation of methane (AOM) with sulfate controls the emission of the greenhouse gas methane from the ocean floor. In marine sediments, AOM is performed by dual-species consortia of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB) inhabiting the methane-sulfate transition zone. The biochemical pathways and biological adaptations enabling this globally relevant process are not fully understood. Here we study the syntrophic interaction in thermophilic AOM (TAOM) between ANME-1 archaea and their consortium partner SRB HotSeep-1 (ref. 6) at 60 °C to test the hypothesis of a direct interspecies exchange of electrons. The activity of TAOM consortia was compared to the first ANME-free culture of an AOM partner bacterium that grows using hydrogen as the sole electron donor. The thermophilic ANME-1 do not produce sufficient hydrogen to sustain the observed growth of the HotSeep-1 partner. Enhancing the growth of the HotSeep-1 partner by hydrogen addition represses methane oxidation and the metabolic activity of ANME-1. Further supporting the hypothesis of direct electron transfer between the partners, we observe that under TAOM conditions, both ANME and the HotSeep-1 bacteria overexpress genes for extracellular cytochrome production and form cell-to-cell connections that resemble the nanowire structures responsible for interspecies electron transfer between syntrophic consortia of Geobacter. HotSeep-1 highly expresses genes for pili production only during consortial growth using methane, and the nanowire-like structures are absent in HotSeep-1 cells isolated with hydrogen. These observations suggest that direct electron transfer is a principal mechanism in TAOM, which may also explain the enigmatic functioning and specificity of other methanotrophic ANME-SRB consortia. PMID:26490622

  17. Coherent wavepacket motion in an ultrafast electron transfer system monitored by femtosecond degenerate four-wave-mixing and pump-probe spectroscopy

    Science.gov (United States)

    Nagasawa, Yutaka; Yoneda, Yusuke; Nambu, Shohei; Muramatsu, Masayasu; Takeuchi, Eisuke; Tsumori, Hiroki; Morikawa, Soichiro; Katayama, Tetsuro; Miyasaka, Hiroshi

    2014-10-01

    Coherent nuclear wavepacket motions were monitored by three types of femtosecond time-resolved spectroscopy, namely, transient absorption measurement utilizing white-light supercontinuum (WC-TA), degenerate four-wave-mixing (DFWM), and pump-probe (PP) measurements, for an ultrafast intermolecular electron transfer (ET) system with a dye molecule, oxazine 1 (Ox1), dissolved in an electron donating solvent, N,N-dimethylaniline (DMA). Vibrational frequencies of the wavepacket motion in the excited and in the ground states were 560-562 and 567-569 cm-1, respectively, with only a few frequency difference of 5-9 cm-1, which were clearly distinguishable by the highly accurate measurements. In DMA, the excited state wavepacket motion declined with time constant of 160-240 fs which is somewhat longer than that of the ultrafast ET; 60-80 fs.

  18. 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; Ulstrup, Jens

    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 on the electrode charge. The slope is smaller the more negative the charge density due to enhanced extension of the surface electronic density profile on the solution side, and thereby better electronic overlap with...

  19. Electron Transfer Dissociation (ETD) of Peptides Containing Intrachain Disulfide Bonds

    Science.gov (United States)

    Cole, Scott R.; Ma, Xiaoxiao; Zhang, Xinrong; Xia, Yu

    2012-02-01

    The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z + 33 Da, c + 32 Da, and z-32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N-C? backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N-C? bond was cleaved first, and radical-driven reactions caused cleavage at either an S-S bond or an S-C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%-100% of possible backbone fragmentation.

  20. Coherence Transfer by Passage Pulses in Electron Paramagnetic Resonance Spectroscopy.

    Science.gov (United States)

    Jeschke, Gunnar; Pribitzer, Stephan; Doll, Andrin

    2015-10-29

    Linear passage pulses provide a simple approach to ultra-wideband electron paramagnetic resonance (EPR) spectroscopy. We show by numerical simulations that the efficiency of inversion of polarization or coherence order on a single transition by idealized passage pulses is an exponential function of critical adiabaticity during passage, which allows for defining an effective flip angle for fast passage. This result is confirmed by experiments on E' centers in Herasil glass. Deviations from the exponential law arise due to relaxation and a distribution of the adiabaticity parameter that comes from inhomogeneity of the irradiation field. Such inhomogeneity effects as well as edge effects in finite sweep bands cause a distribution of dynamic phase shifts, which can be partially refocused in echo experiments. In multilevel systems, passage of several transitions leads to generation of coherence on formally forbidden transitions that can also be described by the concept of an effective flip angle. On the one hand, such transfer to coherence on forbidden transitions is a significant magnetization loss mechanism for dipole-dipole coupled electron spin pairs at distances below about 2 nm. On the other hand, it can potentially be harnessed for electron spin echo envelope modulation (ESEEM) experiments, where matching of the irradiation field strength to the nuclear Zeeman frequency leads to efficient generation of nuclear coherence and efficient back transfer to electron coherence on allowed transitions at high adiabaticity. PMID:25941897

  1. 48 CFR 52.232-35 - Designation of Office for Government Receipt of Electronic Funds Transfer Information.

    Science.gov (United States)

    2010-10-01

    ...Government Receipt of Electronic Funds Transfer Information. 52.232-35...Government Receipt of Electronic Funds Transfer Information. As prescribed...Government Receipt of Electronic Funds Transfer Information (MAY 1999)...

  2. Electron transfer. 88. Cobalt(III)-bound phosphite and hypophosphite

    International Nuclear Information System (INIS)

    Phosphite and hypophosphite coordinate to cobalt(III) in (NH3)5Co/sup III/ through oxygen, rather than through phosphorus. The resulting complexes undergo electron-transfer reactions with Ru(NH3)62+ much more slowly than with Eu2+ or V2+, indicating that the latter two reactants preferentially utilize ligand bridging. Reductions with Cr2+ are shown to accompanied by transfer of the phosphorus-containing ligands, and reaction of the protonated phosphito (biphosphito) derivative (pK/sub A/ = 3.06 at 230C) proceeds through a combination of acid-independent and inverse-acid paths, both routes yielding the same phosphito-bound Cr(III) product. The hypophosphito, but not the biphosphito, complex reacts with Ce(IV), producing Co2+ in an induced electron-transfer process. The yield of Co2+ falls off progressively as [Ce/sup IV/] is increased, pointing to a sequence in which a Co(III)-bound P(II) radical is formed in initial attack by Ce(IV) but subsequently undergoes partition between competing reaction paths, i.e. internal electron transfer to Co(III) vs external oxidation by a second Ce(IV) center. The hypophosphito complex, but not the biphosphito complex, smoothly decomposes in basic media via an internal redox reaction, yielding Co(II) quantitatively, along with a 1:1 mixture of phosphite, and hypophosphite. This transformation, which fails with mixtures of (NH3)5Co(H2O)3+ and H2PO2- appears to be catalyzed specifically by OH-. Deuterium-labeling experiments disclose a solvent isotope effect. Reaction mechanisms are suggested for all the observed results. 54 references, 5 tables

  3. 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...

  4. Effects of electrostatic interactions on electron transfer reactions

    International Nuclear Information System (INIS)

    The fast reactions of electron transfer are studied by pulse radiolysis. This technique allows the creation in about 10-8 second radicals and radical ions with high redox potentials. For solvated electrons electrostatic interaction on the kinetics of reactions limited by diffusion is described by Debye's equation when ion mobility is known. Deviation from theory can occur in ion pairs formation. This is evidenced experimentally for anions by cation complexation with a cryptate. Relatively slow reactions are more sensitive to electrostatic interactions than limited by diffusion. If ion pairs are not formed kinetics constant depends on dielectric constant of solvent and reaction radius. Experimentally is studied the effect of electrostatic interaction on the rate constants of solvated electrons with anions and cations in water-ethanol mixtures where the dielectric constant change from 80 to 25 at room temperature. 17 refs

  5. Electron-transfer reactions of tryptophan and tyrosine derivatives

    International Nuclear Information System (INIS)

    Oxidation of tryptophan, tyrosine, and derivatives by oxidizing radicals was studied by pulse radiolysis in aqueous solutions at 20 0C. Rate constants for the oxidation of tryptophan derivatives with .N3 and Br2-. radicals vary from 8 x 108 to 4.8 and 109 M-1 s-1 and oxidation goes to completion; no pH dependence was observed. Oxidation rate constants for tyrosine derivatives increase upon deprotonation of the phenolic residue at higher pH. Redox potentials for the indolyl and phenoxyl radicals were derived from the measured equilibrium constants by using p-methoxyphenol (E/sub 7.5/ = 0.6 and E13 = 0.4 V), bisulfite (E3 = 0.84 V), and guanosine (E7 = 0.91 V) redox couples as reference systems. Redox potentials of tryptophan derivatives were found to be in dependent on the nature of the side chain and higher than the redox potentials of tryptophan derivatives. Electron transfer from tyrosine to tryptophyl radical was found to be slow in neutral media and is suggested to proceed via multiple steps, one of which is proton transfer from tyrosine to tryptophyl radical followed by electron transfer. 26 references, 2 figures, 4 tables

  6. Modeling biofilms with dual extracellular electron transfer mechanisms

    Energy Technology Data Exchange (ETDEWEB)

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

    2013-11-28

    Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as their terminal electron acceptor for 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 components requisite for both mechanisms. In this study, a generic model is presented that incorporates both diffusion- and conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to Shewanella oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found the literature. Our simulation results showed that 1) biofilms having both mechanisms available, especially if they can interact, may have metabolic advantage over biofilms that can use only a single mechanism; 2) the thickness of Geobacter 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 measurements and cannot be assumed to have identical values. Finally, we determined that cyclic and squarewave voltammetry are currently not good tools to determine the specific percentage of extracellular electron transfer mechanisms used by biofilms. The developed model will be a critical tool in designing experiments to explain EET mechanisms.

  7. 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.

  8. Single Electron Transfer Living Radical Polymerization via a New Initiator

    Science.gov (United States)

    Bai, Xiongxiong; Hu, Ying; Zhang, Xu; Ai, Lingling; Cheng, Chuanjie

    2014-08-01

    Research and development of novel initiating system such as single electron transfer living radical polymerization (SET-LRP) is of high importance in polymer chemistry. A new SET-LRP initiator was synthesized and applied to prepare end-functionalized poly(methyl methacrylate) (PMMA) in this study. ?-Trichloromethyl benzyl alcohol was firstly synthesized, followed by preparation of PMMA under SET-LRP conditions. Conversion of MMA was 81.9%, and the molecular weight of PMMA was about 2.5 kDa at 60 °C for 1 h. Consistency of the number-average molecular weight of PMMA from NMR, GPC and theoretical calculation indicated that the polymerization featured controllable property. Broad molecular weight distribution (MWD) may be ascribed to branched polymers formed by initiation and chain transfer.

  9. A stochastic reorganizational bath model for electronic energy transfer

    CERN Document Server

    Fujita, Takatoshi; Aspuru-Guzik, Alan

    2014-01-01

    The fluctuations of optical gap induced by the environment play crucial roles in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker model, in which the energy-gap fluctuation is approximated as a white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to take the thermal fluctuation of excitation energies into account. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equ...

  10. 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.

  11. Electronic excitation energy transfer between quasi-zero-dimensional systems.

    Czech Academy of Sciences Publication Activity Database

    Král, Karel; Menšík, Miroslav; Mao, H.

    Tokyo : The Surface Science Society of Japan, 2014, s. 11-17. ISSN 1348-0391. [International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures /12/ - International Colloquium on Scanning Probe Microscopy /21./. Tsukuba (JP), 04.11.2013-08.11.2013] R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism https://www.jstage.jst.go.jp/result?item1=4&word1=Atomically+Controlled+Surfaces+AND+kral

  12. Photoinduced electron transfer from phycoerythrin to colloidal metal semiconductor nanoparticles

    Science.gov (United States)

    Kathiravan, A.; Chandramohan, M.; Renganathan, R.; Sekar, S.

    2009-04-01

    Phycoerythrin is a water soluble pigment which absorbs in the visible region at 563 nm. The interaction of phycoerythrin with colloidal metal semiconductors was studied by absorption, FT-IR and fluorescence spectroscopy. Phycoerythrin adsorbed strongly on the surface of TiO 2 nanoparticles, the apparent association constant for the association between colloidal metal-TiO 2 nanoparticles and phycoerythrin was determined from fluorescence quenching data. The free energy change (? Get) for electron transfer process has been calculated by applying Rehm-Weller equation.

  13. Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber

    Directory of Open Access Journals (Sweden)

    Tanya M. Monro

    2011-10-01

    Full Text Available We combine suspended-core microstructured optical fibers with the photoinduced electron transfer (PET effect to demonstrate a new type of fluorescent optical fiber-dip sensing platform for small volume ion detection. A sensor design based on a simple model PET-fluoroionophore system and small core microstructured optical fiber capable of detecting sodium ions is demonstrated. The performance of the dip sensor operating in a high sodium concentration regime (925 ppm Na+ and for lower sodium concentration environments (18.4 ppm Na+ is explored and future approaches to improving the sensor’s signal stability, sensitivity and selectivity are discussed.

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

    DEFF Research Database (Denmark)

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

    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 is induced following reduction of the type 1 Cu(II) by radicals produced by pulse radiolysis. The reversible ET reaction proceeds with a rate constant kET = k(1-->2) + k(2-->1) of 450 +/- 30 s(-1) at pH 7.0 a...

  15. Computer simulation studies of electron transfer in methanol

    Science.gov (United States)

    Fonseca, Teresa; Ladanyi, Branka M.

    1994-02-01

    We describe the results of our molecular dynamics (MD) simulation studies of intramolecular electron transfer reactions in methanol. We consider the reactions of the type DA?D+A- in which the reactant state is nonpolar and the product state polar. Equilibrium MD is used to construct the solvent-dependent reaction free energy profiles and nonequilibrium MD simulations are used to calculate the reaction dynamics for barrierless and low barrier photochemical reactions. The roles of solute size, hydrogen-bonding, solvation dynamics for solutes of different polarity, and reaction driving force are investigated.

  16. Light induced electron transfer reactions of metal complexes

    International Nuclear Information System (INIS)

    Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed

  17. Effect of electrostatic interactions on electron-transfer reactions

    International Nuclear Information System (INIS)

    Fast reactions of electron transfer are studied by pulsed radiolysis. By this technique radicals and ionic radicals with high redox potentials are created homogeneously in the solution in about 10-8 second. For solvated electron effect of electrostatic interaction on kinetics of reactions limited by diffusion is obtained with a good approximation by the Debye equation when ion mobility is known. Deviation from the theory occurs in ion pair formation, which is evidenced experimentally in reactions between anions when cations are complexed by a cryptate. Slow reactions k 8 M-1 s-1 are more sensitive to electrostatic interactions than reactions limited by diffusion. When there is no ion pair formation the velocity constant depends upon dielectric constant of the solvent and reaction distance. 17 refs

  18. 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.

  19. Nanoscale and single-molecule interfacial electron transfer

    DEFF Research Database (Denmark)

    Hansen, Allan Glargaard; Wackerbarth, Hainer

    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 for comprehensive later theoretical work and data interpretation in many areas of chemistry, electrochemistry, and biology. We discuss here some new areas of theoretical electrochemical ET science, with focus on nanoscale electrochemical and bioelectrochemical sciences. Particular attention is given to in situ 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 differential resistance patterns, and by ET dynamics of organized assemblies of biological macromolecules, such as redox metalloproteins and oligonucleotides on single-crystal Au(III)-electrode surfaces.

  20. Generalized Holstein model for spin-dependent electron transfer reaction

    CERN Document Server

    Yang, Li-Ping; Sun, C P

    2011-01-01

    Some chemical reactions are described by electron transfer (ET) processes. The underlying mechanism could be modeled as a polaron motion in the molecular crystal-the Holstein model. By taking spin degrees of freedom into consideration, we generalize the Holstein model (molecular crystal model) to microscopically describe an ET chemical reaction. In our model, the electron spins in the radical pair simultaneously interact with a magnetic field and their nuclear-spin environments. By virtue of the perturbation approach, we obtain the chemical reaction rates for different initial states. It is discovered that the chemical reaction rate of the triplet state demonstrates its dependence on the direction of the magnetic field while the counterpart of the singlet state does not. This difference is attributed to the explicit dependence of the triplet state on the direction when the axis is rotated. Our model may provide a possible candidate for the microscopic origin of avian compass.

  1. 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 of adiabatic electron transfer reactions is elaborated. A new formula for the transition probability of non-adiabatic electron transfer reactions is obtained in an improved Condon approximation A regular...

  2. Photoinduced electron transfer in rhenium(I)-oligotriarylamine molecules.

    Science.gov (United States)

    Bonn, Annabell G; Neuburger, Markus; Wenger, Oliver S

    2014-10-20

    Two molecular triads with an oligotriarylamine multielectron donor were synthesized and investigated with a view to obtaining charge-separated states in which the oligotriarylamine is oxidized 2-fold. Such photoinduced accumulation of multiple redox equivalents is of interest for artificial photosynthesis. The first triad was comprised of the oligotriarylamine and two rhenium(I) tricarbonyl diimine photosensitizers each of which can potentially accept one electron. In the second triad the oligotriarylamine was connected to anthraquinone, in principle an acceptor of two electrons, via a rhenium(I) tricarbonyl diimine unit. With nanosecond transient absorption spectroscopy (using an ordinary pump-probe technique) no evidence for the generation of 2-fold oxidized oligotriarylamine or 2-fold reduced anthraquinone was found. The key factors limiting the photochemistry of the new triads to simple charge separation of one electron and one hole are discussed, and the insights gained from this study are useful for further research in the area of charge accumulation in purely molecular (nanoparticle-free) systems. An important problem of the rhenium-based systems considered here is the short wavelength required for photoexcitation. In the second triad, photogenerated anthraquinone monoanion is protonated by organic acids, and the resulting semiquinone species leads to an increase in lifetime of the charge-separated state by about an order of magnitude. This shows that the proton-coupled electron transfer chemistry of quinones could be beneficial for photoinduced charge accumulation. PMID:25271567

  3. Electron emission and electron transfer processes in proton-naphthalene collisions at intermediate velocities

    Science.gov (United States)

    Mishra, P. M.; Rajput, J.; Safvan, C. P.; Vig, S.; Kadhane, U.

    2013-11-01

    We investigate the fragmentation and ionization of naphthalene by protons at intermediate velocities (between 1.41 and 2.68 a.u.). Relative cross sections for electron capture (EC), electron emission (EE), and capture ionization are measured. The EC cross sections decrease rapidly over the energy range under consideration (50-150 keV) and are lower than EE cross sections. The EE cross sections, on the other hand, change very slowly in this energy range. The energetics of interactions is quantified by comparing the mass spectra with the photodissociation breakdown curves from literature. In the case of single capture, resonant electron transfer to n = 1 state in H+ is seen to dominate the interaction but is shown to be accompanied by a small amount of electronic energy loss. In the EE mode, two mechanisms are shown to be active in the collision process: large impact parameter plasmon excitation mode, and closer encounters with higher amounts of electronic energy loss.

  4. 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...

  5. Electron-transfer functionality of synthetic coiled-coil metalloproteins

    Scientific Electronic Library Online (English)

    Michael Y., Ogawa; Jiufeng, Fan; Anna, Fedorova; Jing, Hong; Olesya A., Kharenko; Anna Y., Kornilova; Robin C., Lasey; Fei, Xie.

    2006-12-01

    Full Text Available O campo emergente da engenharia molecular de metaloproteínas visa preparar proteínas artificiais, cujas propriedades podem imitar e talvez até mesmo melhorar várias características encontradas nas metaloenzimas naturais. Este artigo de revisão resume nossos esforços recentes na preparação de metalop [...] roteínas sintéticas, construídas a partir de "coiled-coils" alfa-hélices, e na incorporação de grupos de transferência de elétrons nesses sistemas. Recentemente, concebemos uma cisteína contendo um peptídeo com hélice randômica, o qual forma uma estrutura "coiled-coil" alfa-helicoidal ao se ligar a vários metais. O aduto de CuI pode atuar como agente fotoindutor de transferência de elétrons para receptores exógenos, e transfere elétrons por colisão na região invertida de Marcus para várias aminas de rutênio, as quais atuam como receptores. Especula-se que este resultado inesperado advenha do posicionamento do cofator de CuI no interior da porção hidrofóbica da proteína, o qual proíbe a aproximação entre o doador e o receptor, diminuindo a velocidade de transferência eletrônica daquelas reações termodinamicamente muito favorecidas, para velocidades inferiores à do limite difusional. Abstract in english The emerging field of metalloprotein design seeks to prepare artificial proteins whose properties can mimic, enhance, and perhaps improve upon many features found in natural metalloenzymes. This review summarizes our recent efforts to prepare synthetic metalloproteins built from alpha-helical coiled [...] -coils and to incorporate electron-transfer functionality within these systems. We have recently designed a cysteine-containing random-coil peptide which forms a alpha-helical coiled-coil upon binding various metals. The CuI adduct can serve as photoinduced electron-transfer agent to exogenous acceptors and undergoes collisional electron-transfer in the inverted Marcus region to various ruthenium ammine acceptors. It is speculated that this unexpected result might be due to the positioning of the CuI cofactor within the hydrophobic core of the protein which prohibits close approach between the donor and acceptor to slow the high driving force reaction rates below the diffusion limit.

  6. Concerted Proton-Electron Transfers: Fundamentals and Recent Developments

    Science.gov (United States)

    Savéant, Jean-Michel

    2014-06-01

    Proton-coupled electron transfers (PCET) are ubiquitous in natural and synthetic processes. This review focuses on reactions where the two events are concerted. Semiclassical models of such reactions allow their kinetic characterization through activation versus driving force relationships, estimates of reorganization energies, effects of the nature of the proton acceptor, and H/D kinetic isotope effect as well as their discrimination from stepwise pathways. Several homogeneous reactions (through stopped-flow and laser flash-quench techniques) and electrochemical processes are discussed in this framework. Once the way has been rid of the improper notion of pH-dependent driving force, water appears as a remarkable proton acceptor in terms of reorganization energy and pre-exponential factor, thanks to its H-bonded and H-bonding properties, similarly to purposely synthesized “H-bond train” molecules. The most recent developments are in modeling and description of emblematic concerted proton-electron transfer (CPET) reactions associated with the breaking of a heavy-atom bond in an all-concerted process.

  7. ELECTRONIC FUNDS TRANSFER: EXPLORING THE DIFFICULTIES OF SECURITY

    Directory of Open Access Journals (Sweden)

    MPAKWANA ANNASTACIA MTHEMBU

    2010-10-01

    Full Text Available Generally the banking laws, regulations and supervision were designed primarily to address the fundamental principle relating to safe and sound business practices by financial institutions. In order to maintain safe and sound business practice it is of outmost importance that customers are protected against losses resulting from inadequate remedies available to them. Banking by its very nature is a high risk business. However, the major risks associated with banking are legal risks, credit interest rates and liquidity. Internet banking has increased some of these risks by creating new ones. Electronic funds transfers are based on technology which by its nature is designed to extend the geographical reach of banks and customers. This kind of a market expansion extend beyond borders, therefore there will be problems which banks will try to avoid like regulation and supervision. Other regulatory and legal risks include, the uncertainty about legal requirements in some countries and jurisdiction ambiguities regarding the responsibilities of different national authorities. Customers and banks may be exposed to legal risks associated with non-compliance with different national laws and regulations including consumer protection laws, record keeping and report requirements. Due to insecurity created by electronic funds transfer, it of importance to analyse measures under South African Law and whether these measures can effectively prevent insecurity and what lessons can be learned from abroad.

  8. Frustrated Solvation Structures Can Enhance Electron Transfer Rates.

    Science.gov (United States)

    Remsing, Richard C; McKendry, Ian G; Strongin, Daniel R; Klein, Michael L; Zdilla, Michael J

    2015-12-01

    Polar surfaces can interact strongly with nearby water molecules, leading to the formation of highly ordered interfacial hydration structures. This ordering can lead to frustration in the hydrogen bond network, and, in the presence of solutes, frustrated hydration structures. We study frustration in the hydration of cations when confined between sheets of the water oxidation catalyst manganese dioxide. Frustrated hydration structures are shown to have profound effects on ion-surface electron transfer through the enhancement of energy gap fluctuations beyond those expected from Marcus theory. These fluctuations are accompanied by a concomitant increase in the electron transfer rate in Marcus's normal regime. We demonstrate the generality of this phenomenon-enhancement of energy gap fluctuations due to frustration-by introducing a charge frustrated XY model, likening the hydration structure of confined cations to topological defects. Our findings shed light on recent experiments suggesting that water oxidation rates depend on the cation charge and Mn-oxidation state in these layered transition metal oxide materials. PMID:26573339

  9. Promoting direct interspecies electron transfer with activated carbon

    DEFF Research Database (Denmark)

    Liu, Fanghua; Rotaru, Amelia-Elena

    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 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 in the presence of GAC did not require the electrically conductive pili and associated c-type cytochrome involved in biological interspecies electrical connections. GAC also greatly stimulated ethanol metabolism and methane production in co-cultures of G. metallireducens and Methanosarcina barkeri. Cells were attached to GAC, but not closely aggregated, suggesting little opportunity for biological electrical contacts between the species. GAC also enhanced methane production in samples from a methanogenic digester in which Methanosaeta were the predominant methanogens. The results demonstrate that GAC can promote DIET and suggest that stimulation of metabolism in methanogenic digesters can be attributed, at least in part, to the high conductivity of GAC providing better interspecies electrical connections than those that can be forged biologically.

  10. 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).

  11. Hydrogen transfer between sulfuric acid and hydroxyl radical in the gas phase: competition among hydrogen atom transfer, proton-coupled electron-transfer, and double proton transfer.

    Science.gov (United States)

    Anglada, Josep M; Olivella, Santiago; Solé, Albert

    2006-02-01

    In an attempt to assess the potential role of the hydroxyl radical in the atmospheric degradation of sulfuric acid, the hydrogen transfer between H2SO4 and HO* in the gas phase has been investigated by means of DFT and quantum-mechanical electronic-structure calculations, as well as classical transition state theory computations. The first step of the H2SO4 + HO* reaction is the barrierless formation of a prereactive hydrogen-bonded complex (Cr1) lying 8.1 kcal mol(-1) below the sum of the (298 K) enthalpies of the reactants. After forming Cr1, a single hydrogen transfer from H2SO4 to HO* and a degenerate double hydrogen-exchange between H2SO4 and HO* may occur. The single hydrogen transfer, yielding HSO4* and H2O, can take place through three different transition structures, the two lowest energy ones (TS1 and TS2) corresponding to a proton-coupled electron-transfer mechanism, whereas the higher energy one (TS3) is associated with a hydrogen atom transfer mechanism. The double hydrogen-exchange, affording products identical to reactants, takes place through a transition structure (TS4) involving a double proton-transfer mechanism and is predicted to be the dominant pathway. A rate constant of 1.50 x 10(-14) cm(3) molecule(-1) s(-1) at 298 K is obtained for the overall reaction H2SO4 + HO*. The single hydrogen transfer through TS1, TS2, and TS3 contributes to the overall rate constant at 298 K with a 43.4%. It is concluded that the single hydrogen transfer from H2SO4 to HO* yielding HSO4* and H2O might well be a significant sink for gaseous sulfuric acid in the atmosphere. PMID:16451034

  12. Impact of electron delocalization on the nature of the charge-transfer states in model pentacene/C60 Interfaces: A density functional theory study

    KAUST Repository

    Yang, Bing

    2014-12-04

    Electronic delocalization effects have been proposed to play a key role in photocurrent generation in organic photovoltaic devices. Here, we study the role of charge delocalization on the nature of the charge-transfer (CT) states in the case of model complexes consisting of several pentacene molecules and one fullerene (C60) molecule, which are representative of donor/acceptor heterojunctions. The energies of the CT states are examined by means of time-dependent density functional theory (TD-DFT) using the long-range-corrected functional, ?B97X, with an optimized range-separation parameter, ?. We provide a general description of how the nature of the CT states is impacted by molecular packing (i.e., interfacial donor/acceptor orientations), system size, and intermolecular interactions, features of importance in the understanding of the charge-separation mechanism.

  13. Electron transfer collision of neon ions with Ne in a RF ion trap

    International Nuclear Information System (INIS)

    The pulsed electron beam rf ion storage 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

  14. A note on the standard electron transfer potential at the interface between two immiscible electrolyte solutions.

    Czech Academy of Sciences Publication Activity Database

    Samec, Zden?k

    2009-01-01

    Ro?. 55, ?. 2 (2009), s. 75-81. ISSN 0034-6691 R&D Projects: GA ?R(CZ) GA203/07/1257 Institutional research plan: CEZ:AV0Z40400503 Keywords : interface between two immiscible electrolyte solutions * interfacial electron transfer * standard electron trasfer potential * homogeneous electron transfer Subject RIV: CG - Electrochemistry

  15. Correlation properties of surface and percolation transfer of electrons

    International Nuclear Information System (INIS)

    In this work was received equation, connecting correlatively properties of surface with electrons distribution function. Usually for equilibrium is necessary a large number of collisions. Collisions are 'destroying' correlations. In case rare collisions large importance have correlations and 'memory' effects. Non-Markov's character of emitting particles by surface lead to strongly nonequilibrium condition of 'gas'. Here kinetic equation of diffusive form does not apply. Classical kinetic equation are described only conditions near to equilibrium. This work offers to use ideas anomal diffusion in phase-space. The correlation properties of surface describe by correlations of velocities of emitting electrons: B(t). We offer to use functional equation for probability collision instead of kinetic equation: ?0?0WnoncollF(?) dv = 1 - B(t). This functional allow to consider 'memory' effects. It is important for consideration of electrons and clusters near surfaces. Distribution function become direct connected with correlations. In classical Kubo-Mory theory of transfer is necessary to get nondivergences integral: D ? ?0?B(t). In considering case we can use even 'power function'. It was used 'slow' correlation function as Kohlraush in calculations. The information about kinetics and correlations properties are containing in one functional equation. It was received solution of this equation in form Levy function: F(?) ? 1/?? exp(-1/?). The solution of this form can not be get with help asymptotic methods of kinetic theory. Asymptotics of solution have scale-invariant character F(V) ? 1/V?. This indicate on fractal properties phase-space. (author)

  16. Photoinduced tautomerism of 2,6-dicarbomethoxyphenol in DMF–water mixtures: Perturbation from intermolecular processes

    Energy Technology Data Exchange (ETDEWEB)

    Mandal, Abhijit, E-mail: pcam2008@gmail.com [Department of Chemistry and Environment, Heritage Institute of Technology, Chowbaga Road, Anandapur, Kolkata 700107 (India); Misra, Ramprasad [Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032 (India)

    2014-06-01

    In this paper, we report the spectral signatures of photoinduced tautomerism of 4-methyl-2,6-dicarbomethoxyphenol (CMOH) in DMF–water mixtures with varying compositions. Excited state intramolecular proton transfer (ESIPT) reaction of CMOH has been observed in bulk DMF, indicated by dual fluorescence from its normal and tautomeric forms while only a single emission peak is observed in water from its anionic species. Binary mixture of a polar aprotic (DMF) and a polar protic (water) solvent gives rise to a competition between intramolecular and intermolecular hydrogen bonding (with media) processes of the probe. This competition is found to be largely dependent on the proton affinity of the media and also on the excitation energy. Solvent separated ion pair and intermolecularly H-bonded CMOH–Solvent complex have been detected in the excited state at specific solvent compositions that are converted to the anionic form due to the change in excitation wavelengths. The formation of hydrogen bonded 1:1 molecular clusters of different rotamers of CMOH with DMF and water in the ground state has been investigated using quantum chemical calculations. A combined experimental and theoretical analysis indicates that the HOMO to LUMO transitions dictate the electronic absorption profiles of the CMOH–DMF and CMOH–water clusters. These findings are expected to shed light on the mechanism of acid–base reactions of several hydrogen bonded systems that are part of many biologically relevant processes. -- Highlights: •Photoinduced tautomerization of CMOH has been studied in DMF–water mixture. •CMOH forms 1:1 molecular clusters with DMF and water. •The competition between intra- and intermolecular hydrogen bonding is revealed. •HOMO to LUMO transition dictates the absorption spectra of CMOH in DMF and water.

  17. 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.

  18. Facile direct electron transfer in glucose oxidase modified electrodes

    Energy Technology Data Exchange (ETDEWEB)

    Wang Dan [Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701 (United States); Chen Liwei [Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701 (United States); Suzhou Institute of Nano Tech and Nano Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou Industrial Park, Suzhou, Jiangsu 215125 (China)], E-mail: lwchen2008@sinano.ac.cn

    2009-07-15

    Glucose oxidase (GOx) is widely used in the glucose biosensor industry. However, mediatorless direct electron transfer (DET) from GOx to electrode surfaces is very slow. Recently, mediatorless DET has been reported via the incorporation of nanomaterials such as carbon nanotubes and nanoparticles in the modification of electrodes. Here we report GOx electrodes showing DET without the need for any nanomaterials. The enzyme after immobilization with poly-L-lysine (PLL) and Nafion retains the biocatalytic activities and oxidizes glucose efficiently. The amperometric response of Nafion-PLL-GOx modified electrode is linearly proportional to the concentration of glucose up to 10 mM with a sensitivity of 0.75 {mu}A/mM at a low detection potential (-0.460 V vs. Ag/AgCl). The methodology developed in this study will have impact on glucose biosensors and biofuel cells and may potentially simplify enzyme immobilization in other biosensing systems.

  19. Electron transfer of rare earth impurities in liquid tin

    International Nuclear Information System (INIS)

    The electric transfer of the admixtures of rare earths in liquid tin has been investigated. Tin - r.e.e. alloys were prepared at the temperature of 400 deg C in the vacuum of about 1O-5 to 10-6 mm Hg, the proportion of each rare earth being equal to about 0.01 to 1 wt.%. The effective charges of the admixtures of rare earths were determined in liquid tin at the temperature of about 400 deg C. Presented is a dependence of the effective charge of the admixtures of rare earths on the serial number of an element of the periodic chart. The data testify to a considerable part played by the atomic 4 f-states in the scattering of the conduction electrons

  20. Electron-proton scattering at very small momentum transfer

    International Nuclear Information System (INIS)

    An electron scattering experiment is described to determine the ratio ?Gsub(E)/Gsub(M) of the form factors of the proton at small momentum transfer. In the region 0.09 2 -2, an average value of four measured points was found to be ?Gsub(E)/Gsub(M) = 1.01 +- 0.02. An analysis of all available data at present of Gsub(E) for q2 -2 gave a rms radius of the charge distribution of the proton of Rsub(m)(E) = 0.85 +- 0.02 fm. Deviations from the proportionality rule of ?Gsub(E)/Gsub(m) = 1 in the region q2 -2 were not found for the ratio ?Gsub(E)/Gsub(M). (orig./LH)

  1. Photoinduced Electron Transfer Between Conjugated Polymers and a Homologous Series of TCNQ Derivatives

    OpenAIRE

    Heeger, Alan; Wudl, Fred; Serdar Sariciftci, N.; Janssen, Rene A. J.; Martin, Nazario

    1996-01-01

    The results of photoinduced absorption (PIA) and photoluminescence studies of the photoinduced electron transfer reactions from conjugated polymer donors onto a series of acceptors based on TCNQ and benzoquinone derivatives containing fused aromatic rings are summarized. The results are compared to the well-defined photoinduced electron transfer demonstrated from conjugated polymer donors onto buckminsterfullerene, C60. For the TCNQ derivatives, the efficiency of the electron transfer process...

  2. Coherent wavepacket motion in an ultrafast electron transfer system monitored by femtosecond degenerate four-wave-mixing and pump–probe spectroscopy

    International Nuclear Information System (INIS)

    Highlights: • Coherent wavepacket motion was investigated for ultrafast electron transfer (ET) system. • Vibrations originating from ground and excited states were extracted with high accuracy. • The dephasing of the excited state vibration was accelerated by the ultrafast ET. - Abstract: Coherent nuclear wavepacket motions were monitored by three types of femtosecond time-resolved spectroscopy, namely, transient absorption measurement utilizing white-light supercontinuum (WC-TA), degenerate four-wave-mixing (DFWM), and pump–probe (PP) measurements, for an ultrafast intermolecular electron transfer (ET) system with a dye molecule, oxazine 1 (Ox1), dissolved in an electron donating solvent, N,N-dimethylaniline (DMA). Vibrational frequencies of the wavepacket motion in the excited and in the ground states were 560–562 and 567–569 cm?1, respectively, with only a few frequency difference of 5–9 cm?1, which were clearly distinguishable by the highly accurate measurements. In DMA, the excited state wavepacket motion declined with time constant of 160–240 fs which is somewhat longer than that of the ultrafast ET; 60–80 fs

  3. Ab initio study on electron excitation and electron transfer in tryptophan-tyrosine system

    International Nuclear Information System (INIS)

    In this article, ab initio calculation has been performed to evaluate the transition energy of electronic excitation in tryptophan and tyrosine by using semiempirical molecular orbital method AM1 and complete active space self-consistent field method. The solvent effect has been considered by means of the conductor-like screening model. After geometric optimizations of isolated tryptophan and tyrosine, and their corresponding radicals and cations, reaction heat of these electron transfer reactions have been obtained by the means of complete active space self-consistent field method. The transition energies from the ground state, respectively, to the lowest excited state and to the lowest triplet state of these two amino acids are also calculated and compared with the experimentally observed values. The ionization potential and electron affinity are also calculated for tryptophan and tyrosine employing Koopmans' theorem and ab initio calculation. Compared with the experimental measurements, the theoretical results are found satisfactory. Theoretical results give good explanations on the experimental phenomena that N3· can preferably oxide the side chain of tryptophan residue and then the electron transfer from tyrosine residue to tryptophan residue follows in peptides involving tryptophan and tyrosine

  4. Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration

    DEFF Research Database (Denmark)

    Farver, O; Bendahl, L

    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) copper centers, the following is proposed. The first T1 copper(II) ion to be reduced in ceruloplasmin is the blue copper center of domain 6 (T1A) by ET from RSSR(-) of domain 5. The rate constant is 28 +/- 2 s(-1) at 279 K and pH 7.0. T1A is in close covalent contact with the type 3 copper pair 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 with a rate constant of 3.9 +/- 0.8. No reoxidation of T1B Cu(I) could be resolved. It appears that the third T1 center(T1C of domain 2) is not participating in intramolecular ET, as it seems to be in a reduced state in the resting enzyme.

  5. Theory of Electron-Transfer Reactions and of Related Phenomena

    International Nuclear Information System (INIS)

    Data on electronexchange reactions have provided insight into factors influencing rates of electron-transfer reactions in solution. The present paper has the twofold purpose of discussing some of these factors and of describing applications of these exchange data and theory to other phenomena. The reaction rate depends upon the extent of reorganization of bond lengths (angles) in the reactants and of solvent reorientation outside them. The reorganization is facilitated or hindered in a comparatively simple way by a favorable or unfavorable standard free energy of reaction. The rate depends, too, on coulombic and other interactions, as evidenced perhaps by certain salt effects, though probably only by a few orders of magni - tude typically. The observed variation of rates of some 15 orders of magnitude is best attributed primarily to differences in the vibrational reorganization term, a factor calculable from bond lengths and force constants when known. A remaining factor, non-adiabaticity, is at present of uncertain importance. Arrhenius frequency factors in chemical and electrochemical exchange rate constants would provide the most direct information, but can be complicated or even dwarfed by solvent reordering effects in the coulombic interaction. Available data are few. They provide examples where a non-adiabatic effect is minor. There appear to be no known examples where it is major (Fe2+ - Fe3+, could be a candidate but its mechanism is apparently uncertain). Reorganization in reactants and in solvent occurs in a variety of related phenomena, and related concepts will be applied to treat them. In turn, chemical exchange data have useful applications to the latter. These areas include electrochemical exchange reactions, chemiluminescent electron-transfer reactions (between positive and negative aromatic ions, for example), and redox reactions of the solvated electron. An explanation for the chemiluminescent reactions will be based on the possible ''inverse ?F°'' effect, discussed several years ago by the author. A related phenomenon involving solvent 'orientation strain' occurs in light absorption or emission by polar solutes in polar solvents, and the theoretical approach used by the author for treating it is closely related to that used for the exchange reactions. (author)

  6. 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.

  7. Desensitization and recovery of metastable intermolecular composites

    Science.gov (United States)

    Busse, James R. (South Fork, CO); Dye, Robert C. (Los Alamos, NM); Foley, Timothy J. (Los Alamos, NM); Higa, Kelvin T. (Ridgecrest, CA); Jorgensen, Betty S. (Jemez Springs, NM); Sanders, Victor E. (White Rock, NM); Son, Steven F. (Los Alamos, NM)

    2010-09-07

    A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

  8. Highly Stereoselective Intermolecular Haloetherification and Haloesterification of Allyl Amides.

    Science.gov (United States)

    Soltanzadeh, Bardia; Jaganathan, Arvind; Staples, Richard J; Borhan, Babak

    2015-08-10

    An organocatalytic and highly regio-, diastereo-, and enantioselective intermolecular haloetherification and haloesterification reaction of allyl amides is reported. A variety of alkene substituents and substitution patterns are compatible with this chemistry. Notably, electronically unbiased alkene substrates exhibit exquisite regio- and diastereoselectivity for the title transformation. We also demonstrate that the same catalytic system can be used in both chlorination and bromination reactions of allyl amides with a variety of nucleophiles with little or no modification. PMID:26110812

  9. 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; Pecht, Israel

    2002-01-01

    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, 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 pro...

  10. Modeling of ultrafast electron-transfer processes: Validity of multilevel Redfield theory

    International Nuclear Information System (INIS)

    The capability of multilevel Redfield theory to describe ultrafast photoinduced electron-transfer reactions is investigated. Adopting a standard model of photoinduced electron transfer in a condensed-phase environment, we consider electron-transfer reactions in the normal and inverted regimes, as well as for different values of the electron-transfer parameters, such as reorganization energy, electronic coupling, and temperature. Based on the comparison with numerically exact reference results, obtained using the self-consistent hybrid method, we discuss in some detail the advantages and shortcomings of two different versions of Redfield theory, which employ the time-dependent and stationary Redfield tensor, respectively. The results of the study demonstrate that multilevel Redfield theory, if applied in the appropriate parameter regime, is well suited to describe the ultrafast coherent dynamics of photoinduced electron-transfer reactions

  11. A bifurcated molecular pentad capable of sequential electronic energy transfer and intramolecular charge transfer.

    Science.gov (United States)

    Harriman, Anthony; Stachelek, Patrycja; Sutter, Alexandra; Ziessel, Raymond

    2015-10-21

    An extended molecular array, comprising three distinct types of chromophores and two additional redox-active subunits, that harvests photons over most of the visible spectral range has been synthesized and characterised. The array exhibits a rich variety of electrochemical waves when examined by cyclic voltammetry but assignment can be made on the basis of control compounds and molecular orbital calculations. Stepwise electronic energy transfer occurs along the molecular axis, corresponding to a gradient of excitation energies, to populate the lowest-energy excited state of the ultimate acceptor. The latter species, which absorbs and emits in the far-red region, enters into light-induced charge transfer with a terminal amine group. The array is relatively stable under illumination with white light but degrades slowly via a series of well-defined steps, the first of which is autocatalytic. One of the main attributes of this system is the capability to harvest an unusually high fraction of sunlight while providing protection against exposure to UV light. PMID:26381219

  12. Light-induced electron transfer vs. energy transfer in molecular thin-film systems

    International Nuclear Information System (INIS)

    Quenching of fluoranthene (FA) singlets by tetrabromo-o-benzoquinone (TBBQ) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was studied both in xylene solutions and in spin-cast polystyrene (PS) films. Emphasis was placed on time-resolved fluorescence transients resulting from pulsed excitation. Linear Stern-Volmer plots were obtained for quenching in solution and gave diffusion-controlled rate constants, of 1.45 x 1010 M-1 sec-1 and 1.53 x 1010 M-1 sec-1 for TBBQ and TMPD, respectively. TBBQ was found to quench FA singlets in PS over the studied concentration range 12 mM 0 was experimentally determined to be 24.3 A, which is in good agreement with the theoretical value of 23 A calculated from spectral data. Quenching of FA singlets in PS films was found to be independent of FA concentration over a 300 mM to 1200 mM FA concentration range for a constant TBBQ concentration of 24.0 mM. TMPD was only slightly effective as a quencher of FA singlets in PS because it apparently behaves strictly as a contact quencher based on reversible charge transfer. The implications of these results for the design of systems intended to exploit light-induced electron transfer are discussed

  13. 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.

  14. ELECTRONIC FUNDS TRANSFER: EXPLORING THE DIFFICULTIES OF SECURITY

    Directory of Open Access Journals (Sweden)

    MPAKWANA ANNASTACIA MTHEMBU

    2010-09-01

    Full Text Available 800x600 Normal 0 false false false EN-GB X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Calibri","sans-serif"; mso-bidi-font-family:"Times New Roman";} Generally the banking laws, regulations and supervision were designed primarily to address the fundamental principle relating to safe and sound business practices by financial institutions. In order to maintain safe and sound business practice it is of outmost importance that customers are protected against losses resulting from inadequate remedies available to them. Banking by its very nature is a high risk business. However, the major risks associated with banking are legal risks, credit interest rates and liquidity. Internet banking has increased some of these risks by creating new ones. Electronic funds transfers are based on technology which by its nature is designed to extend the geographical reach of banks and customers. This kind of a market expansion extend beyond borders, therefore there will be problems which banks will try to avoid like regulation and supervision. Other regulatory and legal risks include, the uncertainty about legal requirements in some countries and jurisdiction ambiguities regarding the responsibilities of different national authorities. Customers and banks may be exposed to legal risks associated with non-compliance with different national laws and regulations including consumer protection laws, record keeping and report requirements. Due to insecurity created by electronic funds transfer, it of importance to analyse measures under South African Law and whether these measures can effectively prevent insecurity and what lessons can be learned from abroad.

  15. 77 FR 10373 - Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid...

    Science.gov (United States)

    2012-02-22

    ...The EPA is finalizing technical revisions to the electronics manufacturing source category of the Greenhouse Gas Reporting Rule related to fluorinated heat transfer fluids. More specifically, EPA is finalizing amendments to the definition of fluorinated heat transfer fluids and to the provisions to estimate and report emissions from fluorinated heat transfer fluids. This final rule is narrow......

  16. Double strand interaction is the predominant pathway for intermolecular recombination of adeno-associated viral genomes

    International Nuclear Information System (INIS)

    Intermolecular recombination is the foundation for dual vector mediated larger gene transfer by recombinant adeno-associated virus (rAAV). To identify precursors for intermolecular recombination, we sequentially infected skeletal muscle with AAV LacZ trans-splicing viruses. At 1 month postinfection, nearly all inputting single-strand (ss) AAV genomes were cleared out in muscle. If ss-ss interaction is absolutely required for intermolecular recombination, LacZ expression from sequential infection will be negligible to that from coinfection. Interestingly, expression from sequential infection reached ?50% of that from coinfection at the 1-month time-point in BL6 mice. In immune deficient SCID mice, expression from sequential infection was comparable to that from coinfection at the 4- and 13-month time points. Our results suggest that ds interaction represents the predominant pathway for AAV intermolecular recombination

  17. 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.

  18. Coherent phonons in CdSe quantum dots triggered by ultrafast electron transfer

    Directory of Open Access Journals (Sweden)

    Wachtveitl J.

    2013-03-01

    Full Text Available The origin of coherent oscillations in CdSe quantum dots and in the CdSe/methylviologen electron transfer system is studied. In CdSe/methylviologen coherent phonons are triggered by the electron transfer from the quantum dot to methylviologen.

  19. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ...IMPORTATION OF TOBACCO PRODUCTS, CIGARETTE PAPERS AND TUBES, AND PROCESSED...Taxes § 41.63 Payment of tax by electronic fund transfer. (a) Each importer...in taxes on cigars, cigarettes, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of...

  20. The microwave-look into the photo electrode: What can we learn about interfacial electron transfer?

    International Nuclear Information System (INIS)

    By combining photo-electrochemical and photo-induced microwave conductivity measurements, information on potential dependent minority charge carrier accumulation, on interfacial minority carrier concentration and on interfacial charge transfer rates can be obtained. It suggests a correlation between electron transfer processes and accumulated charge carriers dominated by non-equilibrium conditions. This is inconsistent with the general assumptions leading to the classical Marcus-Gerischer electron transfer at electrodes, conceived for weak interaction, quasi-equilibrium and absence of polarisability effects. It is considered only to be applicable in special situations. A non-linear interfacial electron transfer theory, the properties of which are outlined, will on the other hand open the potential for new phenomena. They include faster (stimulated), and cooperative electron transfer. The latter, which is excluded by the classical theory, requires non linear dynamic feedback polarisability, which will have to be developed on the basis of structural-electronic considerations for semiconductor interfaces to become highly catalytic

  1. Selective electron transfer between the quantum dots under the resonant pulse

    OpenAIRE

    Tsukanov, A. V.; Openov, L. A.

    2004-01-01

    The coherent quantum dynamics of an electron in the quantum-dot ring structure under the resonant electromagnetic pulse is studied theoretically. A possibility of the selective electron transfer between any two dots is demonstrated. The transfer probability as a function of the pulse and dot parameters is calculated. It is shown that this probability can be close to unity. The factors lowering the transfer probability in real systems are discussed. The results obtained may b...

  2. A short comparison of electron and proton transfer processes in biological systems

    Energy Technology Data Exchange (ETDEWEB)

    Bertrand, Patrick [Laboratoire de Bioenergetique et Ingenierie des Proteines, CNRS-IBSM, 31, chemin Joseph-Aiguier, 13402 Marseille Cedex 20 (France); Universite de Provence, 3, place Victor Hugo, 13331 Marseille Cedex 3 (France)]. E-mail: bertrand@ibsm.cnrs-mrs.fr

    2005-02-01

    The main differences between electron and proton transfers that take place in biological systems are examined. The relation between the distance dependence of the rate constant and the mass of the transferred particle is analyzed in detail. Differences between the two processes have important consequences at the experimental level, which are discussed. The various mechanisms that ensure the coupling between electron and proton transfers are briefly described.

  3. Combined influences of electronic structure, solvent energetics and solvent dynamics on electron transfer kinetics

    International Nuclear Information System (INIS)

    The mechanisms of electron transfer reactions are analyzed theoretically, with particular emphasis on the role of electronic structure and the manner in which its influence may be affected by energetic and dynamical properties of the medium in which the reaction occurs. Theoretical techniques are developed both for calculating and interpreting the extent of donor/acceptor coupling in terms of superexchange models. The role of solvent is studied in a variety of ways, including the use of (1) supermolecule clusters containing inner-shell solvent, (2) continuum reaction field models, and (3) classical molecular dynamics simulation of solvated ions. Electronic structure computations based on ab initio or semi-empirical (INDO) orbital models have been applied to redox processes involving metal ions complexed to various ligends, including the porphyrin macrocyle. Studies of metallocene/metallocinium (Cp2M/Cp2M+) redox pairs have identified an interesting mechanistic contrast for the cases of M = Fe and M = Co, which are found to be controlled, respectively, by superxchange mechanisms of the electron and hole type. The electronic coupling was demonstrated to conform quantiatively (to within 95%) to a 1-electron model. The electronic coupling is also strongly-dependent on relative orientation of reactants, and the relative energetics of these oreintations are in turn, strongly influenced by the nature of the medium. Analysis of the properties of aqueous ferrous and ferric ions in terms of equilibrium H/D isotope effects have been carried out by exploiting classical molecular dynamics techniques, in conjunction with the MFE supercomputing facilities

  4. Single cell activity reveals direct electron transfer in methanotrophic consortia.

    Science.gov (United States)

    McGlynn, Shawn E; Chadwick, Grayson L; Kempes, Christopher P; Orphan, Victoria J

    2015-10-22

    Multicellular assemblages of microorganisms are ubiquitous in nature, and the proximity afforded by aggregation is thought to permit intercellular metabolic coupling that can accommodate otherwise unfavourable reactions. Consortia of methane-oxidizing archaea and sulphate-reducing bacteria are a well-known environmental example of microbial co-aggregation; however, the coupling mechanisms between these paired organisms is not well understood, despite the attention given them because of the global significance of anaerobic methane oxidation. Here we examined the influence of interspecies spatial positioning as it relates to biosynthetic activity within structurally diverse uncultured methane-oxidizing consortia by measuring stable isotope incorporation for individual archaeal and bacterial cells to constrain their potential metabolic interactions. In contrast to conventional models of syntrophy based on the passage of molecular intermediates, cellular activities were found to be independent of both species intermixing and distance between syntrophic partners within consortia. A generalized model of electric conductivity between co-associated archaea and bacteria best fit the empirical data. Combined with the detection of large multi-haem cytochromes in the genomes of methanotrophic archaea and the demonstration of redox-dependent staining of the matrix between cells in consortia, these results provide evidence for syntrophic coupling through direct electron transfer. PMID:26375009

  5. Electron transfer of peroxidase assemblies at tailored nanocarbon electrodes

    International Nuclear Information System (INIS)

    In bioelectrochemistry, the catalytic function of redox enzymes depends largely upon the nature of the working electrode material. One major example of this phenomenon is the improvement of biogenic analyte detection at graphitic carbon with increased edge plane character in the graphene lattice. In our laboratories, we have found that the edge plane character of carbon nanotubes (CNTs) prepared using chemical vapor deposition (CVD) can be tuned via selective doping with nitrogen, termed N-CNTs. In this report, we extend these studies to investigate the influence of N-doping of nanocarbons on the electron transfer of horseradish peroxidase (HRP) using spectrophotometric enzyme activity assays and electrochemical measurements. Our findings demonstrate that HRP adsorption at N-CNTs increases by a factor of two relative to that of nondoped CNTs, with surface coverages, ?m, of 75 ± 4 and 33 ± 5 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) U/mg, respectively. Surprisingly, however, only ?40% of the HRP adsorbed at N-CNTs is electroactive, as assessed by voltammetry of the HRP Fe2+/3+ redox response. By contrast, HRP adsorbed at nondoped CNTs is nearly 100% electroactive, suggesting that the nature of the HRP adsorption (e.g., electrostatic, van der Waals) and geometric factors of heme orientation affect the biocatalytic performance. We also describe studies that utilize the properties of both nondoped CNTs and N-CNTs with adsorbed HRP for unmediated, quantitative H2O2 sensing

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

    Science.gov (United States)

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

    2010-02-01

    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. PMID:20104365

  7. Multiple electron transfer in slow collisions of very high-charged Xe-ions and atoms

    International Nuclear Information System (INIS)

    We have measured absolute cross sections for processes of one and multi-electron capture in slow (0.1--0.2 a.u.) Xeq+-Xe collisions in the charge state regime 15?q?37. The transfer of two to six electrons from the target to the projectile, where two electrons stay on the projectile after deexcitation is studied. We find that the probability for keeping two electrons on the projectile (i.e. radiative stabilization of two electrons) increases rapidly with q and with the number of electrons initially transferred

  8. Multiple electron transfer in slow collisions of very high-charged Xe-ions and atoms

    Energy Technology Data Exchange (ETDEWEB)

    Biedermann, C.; Cederquist, H.; Selberg, N. (Manne Siegbahn Institute of Physics, S-10405 Stockholm (Sweden)); Hutton, R. (Manne Siegbahn Institute of Physics, S-10405 Stockholm (Sweden) University of Lund, S-22362 Lund (Sweden)); Levin, J.C. (Manne Siegbahn Institute of Physics, S-10405 Stockholm (Sweden) The University of Tennessee, Knoxville, Tennessee 37996-1200 (United States)); Beebe, E.; Liljeby, L.; Engestroem, A. (Manne Siegbahn Institute of Physics, S-10405 Stockholm (Sweden))

    1993-06-05

    We have measured absolute cross sections for processes of one and multi-electron capture in slow (0.1--0.2 a.u.) Xe[sup q+]-Xe collisions in the charge state regime 15[le]q[le]37. The transfer of two to six electrons from the target to the projectile, where two electrons stay on the projectile after deexcitation is studied. We find that the probability for keeping two electrons on the projectile (i.e. radiative stabilization of two electrons) increases rapidly with q and with the number of electrons initially transferred.

  9. Role of Information Technologies in Electronic Information Transfer and in Providing Value-Added Information Services

    Directory of Open Access Journals (Sweden)

    V. Sreenivasulu

    1999-09-01

    Full Text Available information technology plays an important role in electronic. message transfer, electronic data interchange (EDI, electronic files transfer protocols, transfer of voice, text and images through ISDN, remote electronic information access and retrieval, and the enforcement of research, education and distance learning through 'virtual global university'. In future, these information technologies can engage in interactive TV, picture phones and TV/PCs purchase. Findings of a survey, conducted to determine the potential. use, non-use and non-availability of IT service in different libraries/documentation centres are also given.

  10. Harvesting and Electron-Exchange Energy Transfer by d0 Metallocene-Based Organized Systems

    Directory of Open Access Journals (Sweden)

    Loukova G.V.

    2013-09-01

    Full Text Available The present contribution will provide an up-to-date overview of novel experimental and theoretical (derived quantum-chemically knowledge on photonics of group IV metallocene-based systems, also with respect to their prominent use in catalysis and photoluminescent sensor activity. We have developed photophysical approach to study measurable properties of the frontier MOs of the complexes, estimate orbital nature of rare long-lived ligand-to-metal charge transfer (LMCT excited states and also supramolecular interactions between basic components of catalytic systems for polymerization: d0-metal complexes and unsaturated hydrocarbon substrates in fluid systems. In the similar way, the photophysical approach is highlighted to enable studying fine intermolecular interactions in homogeneous systems with low (catalytic concentrations of metal complexes that cannot be achieved by other conventional methods.

  11. Photoinduced bimolecular electron transfer kinetics in small unilamellar vesicles

    International Nuclear Information System (INIS)

    Photoinduced electron transfer (ET) from N,N-dimethylaniline to some coumarin derivatives has been studied in small unilamellar vesicles (SUVs) of the phospholipid, DL-?-dimyristoyl-phosphatidylcholine, using steady-state and time-resolved fluorescence quenching, both below and above the phase transition temperature of the vesicles. The primary interest was to examine whether Marcus inversion [H. Sumi and R. A. Marcus, J. Chem. Phys. 84, 4894 (1986)] could be observed for the present ET systems in these organized assemblies. The influence of the topology of SUVs on the photophysical properties of the reactants and consequently on their ET kinetics has also been investigated. Absorption and fluorescence spectral data of the coumarins in SUVs and the variation of their fluorescence decays with temperature indicate that the dyes are localized in the bilayer of the SUVs. Time-resolved area normalized emission spectra analysis, however, reveals that the dyes are distributed in two different microenvironments in the SUVs, which we attribute to the two leaflets of the bilayer, one toward bulk water and the other toward the inner water pool. The microenvironments in the two leaflets are, however, not indicated to be that significantly different. Time-resolved anisotropy decays were biexponential for all the dyes in SUVs, and this has been interpreted in terms of the compound motion model according to which the dye molecules can experience a fast wobbling-in-cone type of motion as well as a slow overall rotating motion of the cone containing the molecule. The expected bimolecular diffusion-controlled rates in SUVs, as estimated by comparing the microviscosities in SUVs (determined from rotational correlation times) and that in acetonitrile solution, are much slower than the observed fluorescence quenching rates, suggesting that reactant diffusion (translational) does not play any role in the quenching kinetics in the present systems. Accordingly, clear inversions are observed in the correlation of the fluorescence quenching rate constants kq with the free energy change, ?G0 of the reactions. However, the coumarin dyes, C152 and C481 (cf. Scheme 1), show unusually high kq values and high activation barriers, which is not expected from Marcus ET theory. This unusual behavior is explained on the basis of participation of the twisted intramolecular charge transfer states of these two dyes in the ET kinetics

  12. Photoinduced bimolecular electron transfer kinetics in small unilamellar vesicles

    Science.gov (United States)

    Choudhury, Sharmistha Dutta; Kumbhakar, Manoj; Nath, Sukhendu; Pal, Haridas

    2007-11-01

    Photoinduced electron transfer (ET) from N,N-dimethylaniline to some coumarin derivatives has been studied in small unilamellar vesicles (SUVs) of the phospholipid, DL-?-dimyristoyl-phosphatidylcholine, using steady-state and time-resolved fluorescence quenching, both below and above the phase transition temperature of the vesicles. The primary interest was to examine whether Marcus inversion [H. Sumi and R. A. Marcus, J. Chem. Phys. 84, 4894 (1986)] could be observed for the present ET systems in these organized assemblies. The influence of the topology of SUVs on the photophysical properties of the reactants and consequently on their ET kinetics has also been investigated. Absorption and fluorescence spectral data of the coumarins in SUVs and the variation of their fluorescence decays with temperature indicate that the dyes are localized in the bilayer of the SUVs. Time-resolved area normalized emission spectra analysis, however, reveals that the dyes are distributed in two different microenvironments in the SUVs, which we attribute to the two leaflets of the bilayer, one toward bulk water and the other toward the inner water pool. The microenvironments in the two leaflets are, however, not indicated to be that significantly different. Time-resolved anisotropy decays were biexponential for all the dyes in SUVs, and this has been interpreted in terms of the compound motion model according to which the dye molecules can experience a fast wobbling-in-cone type of motion as well as a slow overall rotating motion of the cone containing the molecule. The expected bimolecular diffusion-controlled rates in SUVs, as estimated by comparing the microviscosities in SUVs (determined from rotational correlation times) and that in acetonitrile solution, are much slower than the observed fluorescence quenching rates, suggesting that reactant diffusion (translational) does not play any role in the quenching kinetics in the present systems. Accordingly, clear inversions are observed in the correlation of the fluorescence quenching rate constants kq with the free energy change, ?G0 of the reactions. However, the coumarin dyes, C152 and C481 (cf. Scheme 1), show unusually high kq values and high activation barriers, which is not expected from Marcus ET theory. This unusual behavior is explained on the basis of participation of the twisted intramolecular charge transfer states of these two dyes in the ET kinetics.

  13. Structural, dynamic, and energetic aspects of long-range electron transfer in photosynthetic reaction centers

    OpenAIRE

    Kriegl, Jan M.; Nienhaus, G. Ulrich

    2003-01-01

    Intramolecular electron transfer within proteins plays an essential role in biological energy transduction. Electron donor and acceptor cofactors are bound in the protein matrix at specific locations, and protein–cofactor interactions as well as protein conformational changes can markedly influence the electron transfer rates. To assess these effects, we have investigated charge recombination from the primary quinone acceptor to the special pair bacteriochlorophyll dimer in wild-type reaction...

  14. Preferred sites and pathways for electron transfer in blue copper proteins

    DEFF Research Database (Denmark)

    Farver, O; Pecht, I

    1988-01-01

    Long-range electron transfer reactions proceed within and between metalloproteins at relatively fast rates and with marked specificities. The blue single copper proteins are well known electron carriers with their redox center being of limited accessibility to solvent and solutes. The question of where and how electrons are transferred to and from the copper-ion have been investigated. One experimental approach developed in order to pursue these problems is that of reductively labeling several r...

  15. Photoinduced electron and proton transfer in the hydrogen-bonded pyridine-pyrrole system.

    Science.gov (United States)

    Frutos, Luis Manuel; Markmann, Andreas; Sobolewski, Andrzej L; Domcke, Wolfgang

    2007-06-01

    We present here a detailed analysis of the mechanism of photoinduced electron and proton transfer in the planar pyrrole-pyridine hydrogen-bonded system, a model for the photochemistry of hydrogen bonds in DNA base pairs. Two different crossings, an avoided crossing and a conical intersection, are the key steps for forward and backward electron and proton transfer providing to the system photostability against UV radiation by restoring the system in its initial electronic and geometric structure. PMID:17503807

  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. Influence of intermolecular order at the interfaces

    OpenAIRE

    Sehati, Parisa

    2012-01-01

    The work presented in this thesis covers a range of different surfaces and interfaces of organic molecules/polymers and metallic materials. It is of vita importance to understand how charge transfer processes and other electrical interactions existing at physisorped contacts can influence the electronic structure at an interface. Hence our mission in these studies was to understand the physics happening at the aforementioned surfaces and interfaces of relevance to electronic devices, mainly s...

  18. Quantitative analysis of intermolecular interactions in orthorhombic rubrene

    Directory of Open Access Journals (Sweden)

    Venkatesha R. Hathwar

    2015-09-01

    Full Text Available Rubrene is one of the most studied organic semiconductors to date due to its high charge carrier mobility which makes it a potentially applicable compound in modern electronic devices. Previous electronic device characterizations and first principles theoretical calculations assigned the semiconducting properties of rubrene to the presence of a large overlap of the extended ?-conjugated core between molecules. We present here the electron density distribution in rubrene at 20?K and at 100?K obtained using a combination of high-resolution X-ray and neutron diffraction data. The topology of the electron density and energies of intermolecular interactions are studied quantitatively. Specifically, the presence of C?...C? interactions between neighbouring tetracene backbones of the rubrene molecules is experimentally confirmed from a topological analysis of the electron density, Non-Covalent Interaction (NCI analysis and the calculated interaction energy of molecular dimers. A significant contribution to the lattice energy of the crystal is provided by H—H interactions. The electron density features of H—H bonding, and the interaction energy of molecular dimers connected by H—H interaction clearly demonstrate an importance of these weak interactions in the stabilization of the crystal structure. The quantitative nature of the intermolecular interactions is virtually unchanged between 20?K and 100?K suggesting that any changes in carrier transport at these low temperatures would have a different origin. The obtained experimental results are further supported by theoretical calculations.

  19. Quantitative analysis of intermolecular interactions in orthorhombic rubrene.

    Science.gov (United States)

    Hathwar, Venkatesha R; Sist, Mattia; Jørgensen, Mads R V; Mamakhel, Aref H; Wang, Xiaoping; Hoffmann, Christina M; Sugimoto, Kunihisa; Overgaard, Jacob; Iversen, Bo Brummerstedt

    2015-09-01

    Rubrene is one of the most studied organic semiconductors to date due to its high charge carrier mobility which makes it a potentially applicable compound in modern electronic devices. Previous electronic device characterizations and first principles theoretical calculations assigned the semiconducting properties of rubrene to the presence of a large overlap of the extended ?-conjugated core between molecules. We present here the electron density distribution in rubrene at 20?K and at 100?K obtained using a combination of high-resolution X-ray and neutron diffraction data. The topology of the electron density and energies of intermolecular interactions are studied quantitatively. Specifically, the presence of C??C? interactions between neighbouring tetracene backbones of the rubrene molecules is experimentally confirmed from a topological analysis of the electron density, Non-Covalent Interaction (NCI) analysis and the calculated interaction energy of molecular dimers. A significant contribution to the lattice energy of the crystal is provided by H-H interactions. The electron density features of H-H bonding, and the interaction energy of molecular dimers connected by H-H interaction clearly demonstrate an importance of these weak interactions in the stabilization of the crystal structure. The quantitative nature of the intermolecular interactions is virtually unchanged between 20?K and 100?K suggesting that any changes in carrier transport at these low temperatures would have a different origin. The obtained experimental results are further supported by theoretical calculations. PMID:26306198

  20. 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 activated kinetics, which extends the transition-state theory to dynamically dispersive media. Releasing the grip of thermodynamics in kinetic calculations through nonergodicity provides the mechanism for an efficient optimization between reaction rates and the spectrum of relaxation times of the protein-water thermal bath. Bath dynamics, it appears, play as important role as the free energy in optimizing biology's performance. PMID:26558324

  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 activated kinetics, which extends the transition-state theory to dynamically dispersive media. Releasing the grip of thermodynamics in kinetic calculations through nonergodicity provides the mechanism for an efficient optimization between reaction rates and the spectrum of relaxation times of the protein-water thermal bath. Bath dynamics, it appears, play as important role as the free energy in optimizing biology’s performance.

  2. Specific intermolecular interactions of organic compounds

    CERN Document Server

    Baev, Alexei K

    2012-01-01

    This volume sets out the development of the thermodynamic theory of specific intermolecular interactions for a wide spectrum of organic compounds, laying down the framework of an unconventional approach to H-bonding based on a pentacoordinate carbon atom.

  3. Vibrational coherence in electron transfer: an exactly solvable model

    International Nuclear Information System (INIS)

    The exact solution for a transition probability in vibrationally modulated electron transfer is found by employing three independent methods based on: (a) a path integral technique, (b) direct diagonalization of the Hamiltonian by a unitary transformation, and (c) Keldysh-Green's function techniques. We also consider a solution in the noninteracting blip approximation (NIBA). The comparative analysis reveals that the NIBA is valid at longer times, small reorganization energy, high temperatures, and for small transition matrix elements, ?0, while at large ?0 the NIBA provides relaxation rates as much as twice greater. When ?0=0, the NIBA transition probability difference oscillates in time with the frequency ??(ErkT/(h/2?)) exhibiting incorrect behavior. At low temperatures, the exact solution yields power-law evolution. The NIBA solution exhibits incorrect behavior at small values of ?0. At larger transition matrix elements, the NIBA practically yields a correct description, i.e. the decay in accordance with the exact solution while the coherent oscillations reveal some phase shift at longer times. An important case of several mode modulation is also studied. The Fourier analysis of the transition probability provides useful information of the vibrational couplings and frequencies. In general, the Fourier spectrum of the transition probability is the sum of the contributions from the harmonics with the frequencies vertical bar ?0+?i=0n(±)ki?i vertical bar (ki=0,1,2,3,...), where ?i is a modulating frequency. Thus, a generally used assumption about coincidence of coherence and vibrational frequencies appears to be incorrect

  4. Demonstration of Lignin-to-Peroxidase Direct Electron Transfer

    Science.gov (United States)

    Sáez-Jiménez, Verónica; Baratto, Maria Camilla; Pogni, Rebecca; Rencoret, Jorge; Gutiérrez, Ana; Santos, José Ignacio; Martínez, Angel T.; Ruiz-Dueñas, Francisco Javier

    2015-01-01

    Versatile peroxidase (VP) is a high redox-potential peroxidase of biotechnological interest that is able to oxidize phenolic and non-phenolic aromatics, Mn2+, and different dyes. The ability of VP from Pleurotus eryngii to oxidize water-soluble lignins (softwood and hardwood lignosulfonates) is demonstrated here by a combination of directed mutagenesis and spectroscopic techniques, among others. In addition, direct electron transfer between the peroxidase and the lignin macromolecule was kinetically characterized using stopped-flow spectrophotometry. VP variants were used to show that this reaction strongly depends on the presence of a solvent-exposed tryptophan residue (Trp-164). Moreover, the tryptophanyl radical detected by EPR spectroscopy of H2O2-activated VP (being absent from the W164S variant) was identified as catalytically active because it was reduced during lignosulfonate oxidation, resulting in the appearance of a lignin radical. The decrease of lignin fluorescence (excitation at 355 nm/emission at 400 nm) during VP treatment under steady-state conditions was accompanied by a decrease of the lignin (aromatic nuclei and side chains) signals in one-dimensional and two-dimensional NMR spectra, confirming the ligninolytic capabilities of the enzyme. Simultaneously, size-exclusion chromatography showed an increase of the molecular mass of the modified residual lignin, especially for the (low molecular mass) hardwood lignosulfonate, revealing that the oxidation products tend to recondense during the VP treatment. Finally, mutagenesis of selected residues neighboring Trp-164 resulted in improved apparent second-order rate constants for lignosulfonate reactions, revealing that changes in its protein environment (modifying the net negative charge and/or substrate accessibility/binding) can modulate the reactivity of the catalytic tryptophan. PMID:26240145

  5. 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

  6. Role of ligand substitution on long-range electron transfer in azurins

    DEFF Research Database (Denmark)

    Farver, O; Jeuken, L J

    2000-01-01

    Azurin contains two potential redox sites, a copper centre and, at the opposite end of the molecule, a cystine disulfide (RSSR). Intramolecular electron transfer between a pulse radiolytically produced RSSR- radical anion and the blue Cu(II) ion was studied in a series of azurins in which single-site mutations were introduced into the copper ligand sphere. In the Met121His mutant, the rate constant for intramolecular electron transfer is half that of the corresponding wild-type azurin. In the His46Gly and His117Gly mutants, a water molecule is co-ordinated to the copper ion when no external ligands are added. Both these mutants also exhibit slower intramolecular electron transfer than the corresponding wild-type azurin. However, for the His117Gly mutant in the presence of excess imidazole, an azurin-imidazole complex is formed and the intramolecular electron-transfer rate increases considerably, becoming threefold faster than that observed in the native protein. Activation parameters for all these electron-transfer processes were determined and combined with data from earlier studies on intramolecular electron transfer in wild-type and single-site-mutated azurins. A linear relationship between activation enthalpy and activation entropy was observed. These results are discussed in terms of reorganization energies, driving force and possible electron-transfer pathways.

  7. Modulation transfer function and detective quantum efficiency of electron bombarded charge coupled device detector for low energy electrons.

    Czech Academy of Sciences Publication Activity Database

    Horá?ek, Miroslav

    2005-01-01

    Ro?. 76, ?. 9 (2005), 093704:1-6. ISSN 0034-6748 R&D Projects: GA ?R(CZ) GA202/03/1575 Keywords : electron bombarded CCD * modulation transfer function * detective quantum efficiency Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 1.235, year: 2005

  8. 78 FR 66251 - Electronic Fund Transfers(Regulation E)

    Science.gov (United States)

    2013-11-05

    ...date of availability for a transfer involving a currency exchange. The Final Rule explains that a remittance...the list when the sender funds a transfer in a currency other than the local currency (i.e., not the Aruban florin and the...

  9. Single-molecule interfacial electron transfer dynamics manipulated by external electric current

    CERN Document Server

    Zhang, Guofeng; Chen, Ruiyun; Gao, Yan; Wang, Xiaobo; Jia, Suotang

    2011-01-01

    Interfacial electron transfer (IET) dynamics in 1,1'-dioctadecyl-3, 3, 3', 3'-tetramethylindodicarbocyanine (DiD) dye molecules / indium tin oxide (ITO) film system have been probed at the ensemble and single-molecule level by recording the change of fluorescence emission intensity. By comparing the difference of the external electric current (EEC) dependence of lifetime and intensity for enambles and single molecules, it is shown that the single-molecule probe can effcienly demonstrate the IET dynamics. The backward electron transfer and electron transfer of ground state induce the single molecules fluorescence quenching when an EEC is applied to ITO film.

  10. Effects of anharmonicity on diffusive-controlled symmetric electron transfer rates: From the weak to the strong electronic coupling regions

    Science.gov (United States)

    Zhu, Wenjuan; Zhao, Yi

    2008-11-01

    The approach for the diffusive-controlled electron transfer rates [W. Zhu and Y. Zhao, J. Chem. Phys. 126, 184105 (2007)], which is modeled after the Sumi-Marcus theory, is applied to symmetric electron-transfer reactions in a solvent environment with anharmonic potential functions. The electron-transfer rates are evaluated using the quantum R-matrix theory for dealing with the intramolecular vibrational motions and imaginary-time split operator technique for solving the diffusive equations, thereby taking explicit account of the weak-to-strong electronic couplings. The effect of anharmonicity for both the solvent and intramolecular vibrational degrees of freedom are investigated. It is found that the anharmonicity of the intramolecular modes always enhances the rate while the solvent anharmonicity decreases the rate, compared with the harmonic modes. The possible mechanisms have been clarified.

  11. Covalent intermolecular interaction of the nitric oxide dimer (NO)2

    Science.gov (United States)

    Zhang, Hui; Zheng, Gui-Li; Lv, Gang; Geng, Yi-Zhao; Ji, Qing

    2015-09-01

    Covalent bonds arise from the overlap of the electronic clouds in the internucleus region, which is a pure quantum effect and cannot be obtained in any classical way. If the intermolecular interaction is of covalent character, the result from direct applications of classical simulation methods to the molecular system would be questionable. Here, we analyze the special intermolecular interaction between two NO molecules based on quantum chemical calculation. This weak intermolecular interaction, which is of covalent character, is responsible for the formation of the NO dimer, (NO)2, in its most stable conformation, a cis conformation. The natural bond orbital (NBO) analysis gives an intuitive illustration of the formation of the dimer bonding and antibonding orbitals concomitant with the breaking of the ? bonds with bond order 0.5 of the monomers. The dimer bonding is counteracted by partially filling the antibonding dimer orbital and the repulsion between those fully or nearly fully occupied nonbonding dimer orbitals that make the dimer binding rather weak. The direct molecular mechanics (MM) calculation with the UFF force fields predicts a trans conformation as the most stable state, which contradicts the result of quantum mechanics (QM). The lesson from the investigation of this special system is that for the case where intermolecular interaction is of covalent character, a specific modification of the force fields of the molecular simulation method is necessary. Project supported by the National Natural Science Foundation of China (Grant Nos. 90403007 and 10975044), the Key Subject Construction Project of Hebei Provincial Universities, China, the Research Project of Hebei Education Department, China (Grant Nos. Z2012067 and Z2011133), the National Natural Science Foundation of China (Grant No. 11147103), and the Open Project Program of State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, China (Grant No. Y5KF211CJ1).

  12. Experimental insights on the electron transfer and energy transfer processes between Ce3+-Yb3+ and Ce3+-Tb3+ in borate glass

    International Nuclear Information System (INIS)

    A facile method to describe the electron transfer and energy transfer processes among lanthanide ions is presented based on the temperature dependent donor luminescence decay kinetics. The electron transfer process in Ce3+-Yb3+ exhibits a steady rise with temperature, whereas the Ce3+-Tb3+ energy transfer remains nearly unaffected. This feature has been investigated using the rate equation modeling and a methodology for the quantitative estimation of interaction parameters is presented. Moreover, the overall consequences of electron transfer and energy transfer process on donor-acceptor luminescence behavior, quantum efficiency, and donor luminescence decay kinetics are discussed in borate glass host. The results in this study propose a straight forward approach to distinguish the electron transfer and energy transfer processes between lanthanide ions in dielectric hosts, which is highly advantageous in view of the recent developments on lanthanide doped materials for spectral conversion, persistent luminescence, and related applications

  13. Two-Dimensional Electronic Spectroscopy Using Incoherent Light: Theoretical Analysis

    OpenAIRE

    Turner, Daniel B.; Howey, Dylan J.; Sutor, Erika J.; Hendrickson, Rebecca A.; Gealy, M. W.; Ulness, Darin J.

    2012-01-01

    Electronic energy transfer in photosynthesis occurs over a range of time scales and under a variety of intermolecular coupling conditions. Recent work has shown that electronic coupling between chromophores can lead to coherent oscillations in two-dimensional electronic spectroscopy measurements of pigment-protein complexes measured with femtosecond laser pulses. A persistent issue in the field is to reconcile the results of measurements performed using femtosecond laser pul...

  14. 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.

  15. 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.

  16. Ultrafast tryptophan-to-heme electron transfer in myoglobins revealed by UV 2D spectroscopy.

    Science.gov (United States)

    Consani, Cristina; Auböck, Gerald; van Mourik, Frank; Chergui, Majed

    2013-03-29

    Tryptophan is commonly used to study protein structure and dynamics, such as protein folding, as a donor in fluorescence resonant energy transfer (FRET) studies. By using ultra-broadband ultrafast two-dimensional (2D) spectroscopy in the ultraviolet (UV) and transient absorption in the visible range, we have disentangled the excited state decay pathways of the tryptophan amino acid residues in ferric myoglobins (MbCN and metMb). Whereas the more distant tryptophan (Trp(7)) relaxes by energy transfer to the heme, Trp(14) excitation predominantly decays by electron transfer to the heme. The excited Trp(14)?heme electron transfer occurs in edge-to-edge distance below ~10 angstroms, outcompeting the FRET process. Our results raise the question of whether such electron transfer pathways occur in a larger class of proteins. PMID:23393092

  17. Toward transferable interatomic van der Waals potentials: The role of multipole electrostatics and many-body dispersion without electrons

    CERN Document Server

    Bereau, Tristan

    2014-01-01

    We estimate polarizabilities of atoms in molecules without electron density, using a Voronoi partitioning approach instead. The resulting atomic dispersion coefficients are calculated, as well as many-body dispersion effects on intermolecular potential energies. We also estimate contributions from multipole electrostatics and compare them to dispersion. We assess the performance of the resulting intermolecular potential from dispersion and electrostatics for more than 1,300 neutral and charged, small organic molecular dimers. Applications to water clusters, the benzene crystal, the anti-cancer drug ellipticine---intercalated between two Watson-Crick DNA base pairs, as well as six macro-molecular host-guest complexes highlight the potential of this method and help to identify points of future improvement. Overall, the method achieves an accuracy well within sophisticated empirical force fields, such as OPLS and Amber FF03, while exhibiting a simple parametrization protocol without the need for experimental inp...

  18. Bi-directional magnetic resonance based wireless power transfer for electronic devices

    Science.gov (United States)

    Kar, Durga P.; Nayak, Praveen P.; Bhuyan, Satyanarayan; Mishra, Debasish

    2015-09-01

    In order to power or charge electronic devices wirelessly, a bi-directional wireless power transfer method has been proposed and experimentally investigated. In the proposed design, two receiving coils are used on both sides of a transmitting coil along its central axis to receive the power wirelessly from the generated magnetic fields through strongly coupled magnetic resonance. It has been observed experimentally that the maximum power transfer occurs at the operating resonant frequency for optimum electric load connected across the receiving coils on both side. The optimum wireless power transfer efficiency is 88% for the bi-directional power transfer technique compared 84% in the one side receiver system. By adopting the developed bi-directional power transfer method, two electronic devices can be powered up or charged simultaneously instead of a single device through usual one side receiver system without affecting the optimum power transfer efficiency.

  19. Application of Degenerately Doped Metal Oxides in the Study of Photoinduced Interfacial Electron Transfer.

    Science.gov (United States)

    Farnum, Byron H; Morseth, Zachary A; Brennaman, M Kyle; Papanikolas, John M; Meyer, Thomas J

    2015-06-18

    Degenerately doped In2O3:Sn semiconductor nanoparticles (nanoITO) have been used to study the photoinduced interfacial electron-transfer reactivity of surface-bound [Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+) (RuP(2+)) molecules as a function of driving force over a range of 1.8 eV. The metallic properties of the ITO nanoparticles, present within an interconnected mesoporous film, allowed for the driving force to be tuned by controlling their Fermi level with an external bias while their optical transparency allowed for transient absorption spectroscopy to be used to monitor electron-transfer kinetics. Photoinduced electron transfer from excited-state -RuP(2+*) molecules to nanoITO was found to be dependent on applied bias and competitive with nonradiative energy transfer to nanoITO. Back electron transfer from nanoITO to oxidized -RuP(3+) was also dependent on the applied bias but without complication from inter- or intraparticle electron diffusion in the oxide nanoparticles. Analysis of the electron injection kinetics as a function of driving force using Marcus-Gerischer theory resulted in an experimental estimate of the reorganization energy for the excited-state -RuP(3+/2+*) redox couple of ?* = 0.83 eV and an electronic coupling matrix element, arising from electronic wave function overlap between the donor orbital in the molecule and the acceptor orbital(s) in the nanoITO electrode, of Hab = 20-45 cm(-1). Similar analysis of the back electron-transfer kinetics yielded ? = 0.56 eV for the ground-state -RuP(3+/2+) redox couple and Hab = 2-4 cm(-1). The use of these wide band gap, degenerately doped materials provides a unique experimental approach for investigating single-site electron transfer at the surface of oxide nanoparticles. PMID:25668488

  20. 78 FR 30661 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2013-05-22

    ...specifically related to a remittance transfer. For organizational purposes, the December Proposal divided comment...Similarly, there are limited data on consumer behavior, which would be essential for quantifying the benefits or costs to...

  1. Model-free Investigation of Ultrafast Bimolecular Chemical Reactions: Bimolecular Photo Induced Electron Transfer

    OpenAIRE

    Rosspeintner Arnulf; Lang Bernhard; Vauthey Eric

    2013-01-01

    Using photoinduced bimolecular electron transfer reactions as example we demonstrate how diffusion controlled bimolecular chemical reactions can be studied in a model-free manner by quantitatively combining different ultrafast spectroscopical tools.

  2. Facilitation of Electron Transfer in the Presence of Mitochondria-Targeting Molecule SS31

    Science.gov (United States)

    Nosach, Tetiana; Ebrahim, Mark; Ren, Yuhang; Darrah, Shaun; Szeto, Hazel

    2010-03-01

    Electron transfer (ET) processes in mitochondria are very important for the production of adenosine triphosphate (ATP), the common source of the chemical energy. The inability to transfer electrons efficiently in mitochondrial ET chain plays a major role in age associated diseases, including diabetes and cancer. In this work, we used the time dependent absorption and photoluminescence spectroscopy to study the electron transfer kinetics along the ET chain of mitochondria. Our spectroscopic results suggest that SS31, a small peptide molecule targeting to the mitochondrial inner membrane, can facilitate electron transfer and increase ATP production. We show that SS31 targets cytochrome c to both increase the availability of state and also potentially reduce the energy barrier required to reduce cytochrome c.

  3. Electrode assemblies composed of redox cascades from microbial respiratory electron transfer chains

    Energy Technology Data Exchange (ETDEWEB)

    Gates, Andrew J.; Marritt, Sophie; Bradley, Justin; Shi, Liang; McMillan, Duncan G.; Jeuken, Lars J.; Richardson, David; Butt, Julea N.

    2013-10-01

    Respiratory and photosynthetic electron transfer chains are dependent on vectorial electron transfer through a series of redox proteins. Examples include electron transfer from NapC to NapAB nitrate reductase in Paracoccus denitrificans and from CymA to Fcc3 (flavocytochrome c3) fumarate reductase in Shewanella oneidensis MR-1. In the present article, we demonstrate that graphite electrodes can serve as surfaces for the stepwise adsorption of NapC and NapAB, and the stepwise adsorption of CymA and Fcc3. Aspects of the catalytic properties of these assemblies are different from those of NapAB and Fcc3 adsorbed in isolation. We propose that this is due to the formation of NapC-NapAB and of CymA-Fcc3 complexes that are capable of supporting vectorial electron transfer.

  4. 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$_{\\text{(N=N)}}$ (non-bonding) and $\\pi_{\\text{(N=N)}}$ 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.

  5. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    Science.gov (United States)

    2010-01-01

    ...15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION...as through automated teller machines or point-of-sale terminals, but does not include an...

  6. Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions

    Directory of Open Access Journals (Sweden)

    Patrice Vanelle

    2002-12-01

    Full Text Available A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

  7. Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions

    OpenAIRE

    Patrice Vanelle; Vincent Rémusat; Pascal Rathelot

    2002-01-01

    A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

  8. Time-bin state transfer to electron spin coherence in solids

    International Nuclear Information System (INIS)

    We demonstrate that a coherent superposition state of two temporally separated optical pulses, called a time-bin state, can be transferred to that of up/down electron spins in a semiconductor by synchronizing the time separation to the precession period of either electrons or holes. The time-bin transfer scheme does not require polarization mode degeneracy and can map the time-bin state to the electron spin state that is not accessible directly using only polarization. The scheme offers a new approach for quantum interfaces between photons and electron spins

  9. Quantized orbital angular momentum transfer and magnetic dichroism in the interaction of electron vortices with matter.

    Science.gov (United States)

    Lloyd, Sophia; Babiker, Mohamed; Yuan, Jun

    2012-02-17

    Following the very recent experimental realization of electron vortices, we consider their interaction with matter, in particular, the transfer of orbital angular momentum in the context of electron energy-loss spectroscopy, and the recently observed dichroism in thin film magnetized iron samples. We show here that orbital angular momentum exchange does indeed occur between electron vortices and the internal electronic-type motion, as well as center-of-mass motion of atoms in the electric dipole approximation. This contrasts with the case of optical vortices where such transfer only occurs in transitions involving multipoles higher than the dipole. The physical basis of the observed dichroism is explained. PMID:22401214

  10. Time-bin state transfer to electron spin coherence in solids

    Energy Technology Data Exchange (ETDEWEB)

    Kosaka, Hideo; Inagaki, Takahiro; Hitomi, Ryuta; Izawa, Fumishige; Mitsumori, Yasuyoshi; Edamatsu, Keiichi [Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Rikitake, Yoshiaki [Sendai National College of Technology, Sendai 989-3128 (Japan); Imamura, Hiroshi [Nanosystem Research Institute, AIST, Tsukuba 305-8568 (Japan)

    2014-12-04

    We demonstrate that a coherent superposition state of two temporally separated optical pulses, called a time-bin state, can be transferred to that of up/down electron spins in a semiconductor by synchronizing the time separation to the precession period of either electrons or holes. The time-bin transfer scheme does not require polarization mode degeneracy and can map the time-bin state to the electron spin state that is not accessible directly using only polarization. The scheme offers a new approach for quantum interfaces between photons and electron spins.

  11. Electron excitation and energy transfer rates for H2O in the upper atmosphere

    OpenAIRE

    Brunger Michael; Campbell Laurence; Thorn Penny

    2009-01-01

    Abstract Recent measurements of the cross sections for electronic state excitations in H2O have made it possible to calculate rates applicable to these excitation processes. We thus present here calculations of electron energy transfer rates for electronic and vibrational state excitations in H2O, as well as rates for excitation of some of these states by atmospheric thermal and auroral secondary electrons. The calculation of these latter rates is an important first step towards our aim of in...

  12. Deterministic quantum state transfer from an electronic charge qubit to a photonic polarization qubit

    CERN Document Server

    Ament, L J P

    2006-01-01

    Building on an earlier proposal for the production of polarization-entangled microwaves by means of intraband transitions in a pair of quantum dots, we show how this device can be used to transfer an unknown single-qubit state from electronic charge to photonic polarization degrees of freedom. No postselection is required, meaning that the quantum state transfer happens deterministically. Decoherence of the charge qubit causes a non-monotonic decay of the fidelity of the transferred state with increasing decoherence rate.

  13. 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.

    2015-01-01

    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 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. PMID:26689792

  14. Modelling the effect of contact formation on electron transfer in single-molecule device

    OpenAIRE

    Ramos, Marta M. D.; Correia, Helena M. G.

    2010-01-01

    The electric properties of single-molecule devices are very sensitive to details of contact formation between the molecule and the metallic electrodes. However the factors that control the electron transfer through the molecule in these devices, corresponding to slightly different molecule-metal attachments, are not well understood. In this work, we used a self-consistent molecular dynamics method to study the effect of symmetric and asymmetric contact realizations on electron transfer betwee...

  15. Charge transfer in quasi-one-electron systems at 'high' energy

    International Nuclear Information System (INIS)

    We have made absolute and relative measurements of differential cross sections for single-electron transfer in collisions between Mg+ (30-150 keV) and Be+ (56.25 keV) ions and He atoms. The behaviour of transfer probability as a function of impact parameter can be understood qualitatively from recent molecular orbital calculations of quasi-one-electron systems. (author)

  16. 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.

  17. Observation of orientation-dependent electron transfer in molecule–surface collisions

    OpenAIRE

    Bartels, Nils; Golibrzuch, Kai; Bartels, Christof; Chen, Li; Auerbach, Daniel J.; Wodtke, Alec M.; Schäfer, Tim

    2013-01-01

    How molecules point in space—that is, their spatial orientation—determines how they interact with their environment. Exchange of energy, photons, and particles as well as chemical reactions are all elementary processes that depend on orientation. Electron transfer reactions are of particular interest because of their importance in a remarkably wide range of phenomena. In this work, we examine electron transfer reactions at surfaces, which control the change of oxidation state in surface chemi...

  18. Precursor charge state prediction for electron transfer dissociation tandem mass spectra

    OpenAIRE

    Sharma, Vagisha; Eng, Jimmy K.; Feldman, Sergey; Von Haller, Priska D.; MacCoss, Michael J; Noble, William S.

    2010-01-01

    Electron-transfer dissociation (ETD) induces fragmentation along the peptide backbone by transferring an electron from a radical anion to a protonated peptide. In contrast with collision induced dissociation, side chains and modifications such as phosphorylation are left intact through the ETD process. Because the precursor charge state is an important input to MS/MS sequence database search tools, the ability to accurately determine the precursor charge is helpful for the identification proc...

  19. Experimental and Theoretical Demonstrations for the Mechanism behind Enhanced Microbial Electron Transfer by CNT Network

    OpenAIRE

    Xian-Wei Liu; Jie-Jie Chen; Yu-Xi Huang; Xue-Fei Sun; Guo-Ping Sheng; Dao-Bo Li; Lu Xiong; Yuan-Yuan Zhang; Feng Zhao; Han-Qing Yu

    2014-01-01

    Bioelectrochemical systems (BESs) share the principle of the microbially catalyzed anodic substrate oxidation. Creating an electrode interface to promote extracellular electron transfer from microbes to electrode and understanding such mechanisms are crucial for engineering BESs. In this study, significantly promoted electron transfer and a 10-times increase in current generation in a BES were achieved by the utilization of carbon nanotube (CNT) network, compared with carbon paper. The mechan...

  20. Amplified electron transfer at poly-ethylene-glycol (PEG) grafted electrodes.

    Science.gov (United States)

    Hotchen, Christopher E; Maybury, Ian J; Nelson, Geoffrey W; Foord, John S; Holdway, Philip; Marken, Frank

    2015-05-01

    "Amplified" electron transfer is observed purely based on electron transfer kinetic effects at modified carbon surfaces. An anodic attachment methodology is employed to modify the surface of glassy carbon or boron doped diamond electrodes with poly-ethylene glycols (PEGs) for polymerisation degrees of n = 4.5 to 9.1 (PEG200 to PEG400). Voltammetry and impedance data for aqueous Fe(CN)6(3-/4-) suggest systematic PEG structure-dependent effects on the standard rate constant for heterogeneous electron transfer as a function of PEG deposition conditions and average polymer chain length. Tunnel distance coefficients are polymerisation degree dependent and estimated for shorter PEG chains, ? = 0.17 Å(-1) for aqueous Fe(CN)6(3-/4-), consistent with a diffuse water-PEG interface. In contrast, electron transfer to 1,1'-ferrocene-dimethanol (at 1 mM concentration) appears un-impeded by PEG grafts. Mediated or "amplified" electron transfer to Fe(CN)6(3-/4-) based on the 1,1'-ferrocene-dimethanol redox shuttle is observed for both oxidation and reduction with estimated bimolecular rate constants for homogeneous electron transfer of kforward = 4 × 10(5) mol dm(3) s(-1) and kbackward = 1 × 10(5) mol dm(3) s(-1). Digital simulation analysis suggests an additional resistive component within the PEG graft double layer. PMID:25836325

  1. Molecular Computational Investigation of Electron Transfer Kinetics across Cytochrome-Iron Oxide Interfaces

    International Nuclear Information System (INIS)

    The interface between electron transfer proteins such as cytochromes and solid phase mineral oxides is central to the activity of dissimilatory-metal reducing bacteria. A combination of potential-based molecular dynamics simulations and ab initio electronic structure calculations are used in the framework of Marcus' electron transfer theory to compute elementary electron transfer rates from a well-defined cytochrome model, namely the small tetraheme cytochrome (STC) from Shewanella oneidensis, to surfaces of the iron oxide mineral hematite (a-Fe2O3). Room temperature molecular dynamics simulations show that an isolated STC molecule favors surface attachment via direct contact of hemes I and IV at the poles of the elongated axis, with electron transfer distances as small as 9 Angstroms. The cytochrome remains attached to the mineral surface in the presence of water and shows limited surface diffusion at the interface. Ab initio electronic coupling matrix element (VAB) calculations of configurations excised from the molecular dynamics simulations reveal VAB values ranging from 1 to 20 cm-1, consistent with nonadiabaticity. Using these results, together with experimental data on the redox potential of hematite and hemes in relevant cytochromes and calculations of the reorganization energy from cluster models, we estimate the rate of electron transfer across this model interface to range from 1 to 1000 s-1 for the most exothermic driving force considered in this work, and from 0.01 to 20 s-1 for the most endothermic. This fairly large range of electron transfer rates highlights the sensitivity of the rate upon the electronic coupling matrix element, which is in turn dependent on the fluctuations of the heme configuration at the interface. We characterize this dependence using an idealized bis-imidazole heme to compute from first principles the VAB variation due to porphyrin ring orientation, electron transfer distance, and mineral surface termination. The electronic matrix element and consequently the rate of electron transfer are found to be sensitive to all parameters considered. This work indicates that biomolecularly similar solvent-exposed bis-histidine hemes in outer-membrane cytochromes such as MtrC or OmcA are likely to have an affinity for the oxide surface in water governing the approach and interfacial conformation and, if allowed sufficient conformational freedom, will achieve distances and configurations required for direct interfacial electron transfer.

  2. Dependence of Vibronic Coupling on Molecular Geometry and Environment: Bridging Hydrogen Atom Transfer and Electron-Proton Transfer.

    Science.gov (United States)

    Harshan, Aparna Karippara; Yu, Tao; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2015-10-28

    The rate constants for typical concerted proton-coupled electron transfer (PCET) reactions depend on the vibronic coupling between the diabatic reactant and product states. The form of the vibronic coupling is different for electronically adiabatic and nonadiabatic reactions, which are associated with hydrogen atom transfer (HAT) and electron-proton transfer (EPT) mechanisms, respectively. Most PCET rate constant expressions rely on the Condon approximation, which assumes that the vibronic coupling is independent of the nuclear coordinates of the solute and the solvent or protein. Herein we test the Condon approximation for PCET vibronic couplings. The dependence of the vibronic coupling on molecular geometry is investigated for an open and a stacked transition state geometry of the phenoxyl-phenol self-exchange reaction. The calculations indicate that the open geometry is electronically nonadiabatic, corresponding to an EPT mechanism that involves significant electronic charge redistribution, while the stacked geometry is predominantly electronically adiabatic, corresponding primarily to an HAT mechanism. Consequently, a single molecular system can exhibit both HAT and EPT character. The dependence of the vibronic coupling on the solvent or protein configuration is examined for the soybean lipoxygenase enzyme. The calculations indicate that this PCET reaction is electronically nonadiabatic with a vibronic coupling that does not depend significantly on the protein environment. Thus, the Condon approximation is shown to be valid for the solvent and protein nuclear coordinates but invalid for the solute nuclear coordinates in certain PCET systems. These results have significant implications for the calculation of rate constants, as well as mechanistic interpretations, of PCET reactions. PMID:26412613

  3. What are the benefits of bound (protonation) states for the electron-transfer kinetics?

    OpenAIRE

    Matyushov, Dmitry V.

    2007-01-01

    We describe a model of electron transfer reactions affected by local binding to the donor or acceptor sites of a particle in equilibrium with the solution. The statistics of fluctuations of the donor-acceptor energy gap caused by binding/unbinding events are non-Gaussian, and the resulting free energy surfaces of electron transfer are non-parabolic. The band-width of the charge-transfer optical transition is predicted to pass through a maximum as a function of the concentrat...

  4. Excess Electron Trapping in Duplex DNA: Long Range Transfer via Stacked Adenines

    OpenAIRE

    Black, Paul J.; Bernhard, William A.

    2012-01-01

    An understanding of charge transfer (CT) in DNA lies at the root of assessing the risks and benefits of exposure to ionizing radiation. Energy deposition by high-energy photons and fast charged particles creates holes and excess electrons (EE) in DNA and the subsequent reactions determine the complexity of DNA damage and ultimately the risk of disease. Further interest in CT comes from the possibility that hole transfer and/or excess electron transfer (EET) in DNA might be used to develop nan...

  5. Effect of the excitation pulse frequency on the ultrafast photoinduced electron transfer dynamics

    International Nuclear Information System (INIS)

    The dependence of the ultrafast photoinduced electron transfer dynamics in donor-acceptor complexes on the excitation pulse carrier frequency (spectral effect) has been investigated in the framework of a model involving three electronic state. The spectral effect has been shown to strongly depend on the angle ? between the reaction coordinate directions corresponding to optical and charge transfer transitions. Describing the solvent as a linear homogenous polar medium and accounting for Coulombic interaction of the transferred charge with the medium polarization fluctuations, the angle ? has been found out to be typically in the area 40 deg. -85 deg. Exactly in this area of ? the spectral effect is predicted to be most pronounced

  6. Study on electron transfer mechanism in surface enhanced Raman scattering

    International Nuclear Information System (INIS)

    The Raman intensity from the pyridine on the silver electrode is measured as the function of electrode potential. The charge transfer mechanism can be confirmed by measuring the potential dependence of peak value of Raman intensity as varying the incident photon energy. In order to find the potential dependence of resonent Raman Scattering intensity through the charge transfer process, the Herzberg-Teller terms of polarization tensor is in the theoritical study and this is compared with experimental value. During the potential range of constant surface complex concentration, the experimental result of Raman intensity profile is coincide quite well with theoritical calculation.(Author)

  7. Importance of the Donor:Fullerene intermolecular arrangement for high-efficiency organic photovoltaics

    KAUST Repository

    Graham, Kenneth

    2014-07-09

    The performance of organic photovoltaic (OPV) material systems are hypothesized to depend strongly on the intermolecular arrangements at the donor:fullerene interfaces. A review of some of the most efficient polymers utilized in polymer:fullerene PV devices, combined with an analysis of reported polymer donor materials wherein the same conjugated backbone was used with varying alkyl substituents, supports this hypothesis. Specifically, the literature shows that higher-performing donor-acceptor type polymers generally have acceptor moieties that are sterically accessible for interactions with the fullerene derivative, whereas the corresponding donor moieties tend to have branched alkyl substituents that sterically hinder interactions with the fullerene. To further explore the idea that the most beneficial polymer:fullerene arrangement involves the fullerene docking with the acceptor moiety, a family of benzo[1,2-b:4,5-b]dithiophene-thieno[3,4-c]pyrrole-4,6-dione polymers (PBDTTPD derivatives) was synthesized and tested in a variety of PV device types with vastly different aggregation states of the polymer. In agreement with our hypothesis, the PBDTTPD derivative with a more sterically accessible acceptor moiety and a more sterically hindered donor moiety shows the highest performance in bulk-heterojunction, bilayer, and low-polymer concentration PV devices where fullerene derivatives serve as the electron-accepting materials. Furthermore, external quantum efficiency measurements of the charge-transfer state and solid-state two-dimensional (2D) 13C{1H} heteronuclear correlation (HETCOR) NMR analyses support that a specific polymer:fullerene arrangement is present for the highest performing PBDTTPD derivative, in which the fullerene is in closer proximity to the acceptor moiety of the polymer. This work demonstrates that the polymer:fullerene arrangement and resulting intermolecular interactions may be key factors in determining the performance of OPV material systems. © 2014 American Chemical Society.

  8. Concerted electron-proton transfer in the optical excitation of hydrogen-bonded dyes

    Energy Technology Data Exchange (ETDEWEB)

    Westlake, Brittany C.; Brennaman, Kyle M; Concepcion, Javier J; Paul, Jared J.; Bettis, Stephanie E; Hampton, Shaun D; Miller, Stephen A.; Lebedeva, Natalia V.; Forbes, Malcolm D. E.; Moran, Andrew M.; Meyer, Thomas J.; Papanikolas, John M.

    2011-05-24

    The simultaneous, concerted transfer of electrons and protons—electron-proton transfer (EPT)—is an important mechanism utilized in chemistry and biology to avoid high energy intermediates. There are many examples of thermally activated EPT in ground-state reactions and in excited states following photoexcitation and thermal relaxation. Here we report application of ultrafast excitation with absorption and Raman monitoring to detect a photochemically driven EPT process (photo-EPT). In this process, both electrons and protons are transferred during the absorption of a photon. Photo-EPT is induced by intramolecular charge-transfer (ICT) excitation of hydrogen-bonded-base adducts with either a coumarin dye or 4-nitro-4'-biphenylphenol. Femtosecond transient absorption spectral measurements following ICT excitation reveal the appearance of two spectroscopically distinct states having different dynamical signatures. One of these states corresponds to a conventional ICT excited state in which the transferring H? is initially associated with the proton donor. Proton transfer to the base (B) then occurs on the picosecond time scale. The other state is an ICT-EPT photoproduct. Upon excitation it forms initially in the nuclear configuration of the ground state by application of the Franck–Condon principle. However, due to the change in electronic configuration induced by the transition, excitation is accompanied by proton transfer with the protonated base formed with a highly elongated ?H–B bond. Coherent Raman spectroscopy confirms the presence of a vibrational mode corresponding to the protonated base in the optically prepared state.

  9. 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.

  10. Transferred metal electrode films for large-area electronic devices

    International Nuclear Information System (INIS)

    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?1 have been obtained for 50-nm thin films of polystyrene and a cyclic olefin copolymer TOPAS® (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

  11. 77 FR 50243 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-08-20

    ...1005.31 to add new paragraphs (a...regarding the content and format of the disclosures...transfer provider sets a retail exchange rate. Thus...estimation methodology. New comment 32(d...must give senders new pre-payment disclosures before accepting payment if...

  12. 77 FR 77187 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-12-31

    ..., originating providers (whether depository or non-depository) using open networks or other systems that deposit... published February 7, 2012 (77 FR 6194) and August 20, 2012 (77 FR 50244) must be received by January 15... transfer; (ii) cancellation and refund rights; (iii) the investigation and remedy of errors by...

  13. 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.

  14. What are the benefits of bound (protonation) states for the electron-transfer kinetics?

    CERN Document Server

    Matyushov, Dmitry V

    2007-01-01

    We describe a model of electron transfer reactions affected by local binding to the donor or acceptor sites of a particle in equilibrium with the solution. The statistics of fluctuations of the donor-acceptor energy gap caused by binding/unbinding events are non-Gaussian, and the resulting free energy surfaces of electron transfer are non-parabolic. The band-width of the charge-transfer optical transition is predicted to pass through a maximum as a function of the concentration of binding particles in the solution. The model is used to rationalize recent observations of pH-dependence of electron transfer rates involving changes in the protonation state of the donor-acceptor complex.

  15. ESR studies of radiation induced electron transfer between myosin and caffeic acid

    International Nuclear Information System (INIS)

    The mechanism of radiation induced electron transfer within a series of binary molecular aggregates, which were composed of myosin and caffeic acid with varied molar ratios (r) of amino acid residues in myosin to caffeic acid, has been studied by resolution of composite ESR spectra recorded at 77 K. A series of spin transfer ratios (RST) defined as the spin concentration ratios of caffeic acid anion radical arising from transfer of captured electron by peptide chain of myosin to that from directly trapping of secondary electrons by caffeic acid were obtained. A series of RST were plotted against r varied from 1:1 to 100:1. A linear relationship between RSt and r demonstrates that RSt increase linearly with decrease of caffeic acid content. The capture of radiation induced secondary electrons depend on the electron affinities of components including electron affinitive amino acid residues and peptide carbonyl of myosin and caffeic acid. The process of electron transfer along peptide chain and trapping on caffeic acid finally has been elucidated based on the comparison of the energies of lowest empty molecular orbital (ELUMO) of the electron affinitive components and reaction rate constants of eaq- with these components respectively using pulse radiolysis techniques

  16. Modeling time-coincident ultrafast electron transfer and solvation processes at molecule-semiconductor interfaces

    International Nuclear Information System (INIS)

    Kinetic models based on Fermi's Golden Rule are commonly employed to understand photoinduced electron transfer dynamics at molecule-semiconductor interfaces. Implicit in such second-order perturbative descriptions is the assumption that nuclear relaxation of the photoexcited electron donor is fast compared to electron injection into the semiconductor. This approximation breaks down in systems where electron transfer transitions occur on 100-fs time scale. Here, we present a fourth-order perturbative model that captures the interplay between time-coincident electron transfer and nuclear relaxation processes initiated by light absorption. The model consists of a fairly small number of parameters, which can be derived from standard spectroscopic measurements (e.g., linear absorbance, fluorescence) and/or first-principles electronic structure calculations. Insights provided by the model are illustrated for a two-level donor molecule coupled to both (i) a single acceptor level and (ii) a density of states (DOS) calculated for TiO2 using a first-principles electronic structure theory. These numerical calculations show that second-order kinetic theories fail to capture basic physical effects when the DOS exhibits narrow maxima near the energy of the molecular excited state. Overall, we conclude that the present fourth-order rate formula constitutes a rigorous and intuitive framework for understanding photoinduced electron transfer dynamics that occur on the 100-fs time scale

  17. A systematic study of electron or hole transfer along DNA dimers, trimers and polymers

    International Nuclear Information System (INIS)

    Highlights: • We systematically study carrier transfer along DNA dimers, trimers and polymers. • We define max transfer percentage, pure max transfer rate, pure mean transfer rate. • For exponential (power-law) fit, the inverse decay length ? (exponent ?) is computed. • The results are compared with theoretical and experimental works. • The method assesses the extent a specific DNA segment can serve for charge transfer. - Abstract: A systematic study of carrier transfer along DNA dimers, trimers and polymers including poly(dG)–poly(dC), poly(dA)–poly(dT), GCGCGC…, ATATAT… is presented allowing to determine the spatiotemporal evolution of electrons or holes along a N base-pair DNA segment. Physical quantities are defined including maximum transfer percentage p and pure maximum transfer rate p/T when a period T is defined; pure mean transfer rate k and speed u=kd, where d is the charge transfer distance. The inverse decay length ? for the exponential fit k=k0exp(-?d) and the exponent ? for the power-law fit k=k0?N-? are computed. ?? 0.2–2 ??1, k0 is usually 10?2–10?1 PHz, generally ?10?4–10 PHz. ??1.7–17, k0? is usually 10?2–10?1 PHz, generally ?10?4–103 PHz. The results are compared with theoretical and experimental works. This method allows to assess the extent at which a specific DNA segment can serve for charge transfer

  18. Excitation of the ligand-to-metal charge transfer band induces electron tunnelling in azurin

    Energy Technology Data Exchange (ETDEWEB)

    Baldacchini, Chiara [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy); Institute of Agro-environmental and Forest Biology, National Research Council, I-05010 Porano (Italy); Bizzarri, Anna Rita; Cannistraro, Salvatore, E-mail: cannistr@unitus.it [Biophysics and Nanoscience Centre, DEB-CNISM, Università della Tuscia, I-01100 Viterbo (Italy)

    2014-03-03

    Optical excitation of azurin blue copper protein immobilized on indium-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light-induced current tunnelling within the protein milieu. The related electron transport rate is estimated to be about 10{sup 5}?s{sup ?1}. A model based on resonant tunnelling through an azurin excited molecular state is proposed. The capability of controlling electron transfer processes through light pulses opens interesting perspectives for implementation of azurin in bio-nano-opto-electronic devices.

  19. Electron transfer and ionization from the K shell of neon by proton impact

    International Nuclear Information System (INIS)

    Cross sections are being calculate or electron transfer and ionization from the K shell of neutral neon atoms by 250-1500 keV proton impact. As an extension of work recently published for carbon targets, a coupled-Sturmian-pseudostate approach is taken using a central potentials to represent the interaction of the active electron with the ion core. After a binding energy correction is made, preliminary results show excellent agreement with experimental results for ionization, as for carbon targets. The smaller electron-transfer cross section is more sensitive to basis size, particularly so for neon targets, but agreement with experimental results is satisfactory

  20. Metal Bridging for Directing and Accelerating Electron Transfer as Exemplified by Harnessing the Reactivity of AIBN.

    Science.gov (United States)

    Xie, Yinjun; Guo, Shengmei; Wu, Longmin; Xia, Chungu; Huang, Hanmin

    2015-05-11

    A new strategy for tuning the electron transfer between radicals and enolates has been developed. This method elicits the innate reactivity of AIBN with a copper catalyst and enables a cascade reaction with cinnamic acids. Electron paramagnetic resonance studies and control experiments indicate that the redox-active copper species not only activates the radical by coordination, but also serves as a bridge to bring the radical and nucleophile within close proximity to facilitate electron transfer. By exploiting possible combinations of redox-active metals and radical entities with suitable coordinating functional groups, this strategy should contribute to the development of a broad range of radical-based reactions. PMID:25809686

  1. Long range transfer of positive charge between dopant molecules in a rigid glassy matrix

    International Nuclear Information System (INIS)

    Pulse radiolysis has been used to observe and measure the kinetics for intermolecular positive charge (hole) transfer from biphenyl+ or pyrene+ ions to TMPD molecules in rigid 2-chlorobutane glass at 77 K. These hole transfers occur over distances of about 17 A at 10-6 s, increasing to about 34 A at 102 s. The kinetic data are interpreted in terms of current theories which treat electron transfer processes as radiationless transitions. Estimates of the required electron exchange interactions based on the usual electron tunneling models can not explain the fast reactions observed, even when Coulombic effects on the ''barrier'' are considered. A superexchange model is proposed which involves interactions propagated by both negative and positive ion states of the solvent. This model adequately interprets the data in terms of a dominant role of the solvent positive ion states, and is also applicable to negative charge transfer in the condensed phase. In samples containing only one solute (biphenyl or pyrene), ion recombination with Cl- removed about one third of the positive ions of the solute between 10-6 and 102 s. The data on intermolecular hole transfer between two solutes must be corrected for the effects of ion recombination. The correction is simple and quantitative only when it is possible to observe decay of the reactants without substantial spectral overlap from the products. Because the effects of ion recombination on product growths are complex, it is not presently possible to use the growths to measure reliably the kinetics intermolecular positive charge transfer

  2. Electron transfer from sulfate-reducing becteria biofilm promoted by reduced graphene sheets

    Science.gov (United States)

    Wan, Yi; Zhang, Dun; Wang, Yi; Wu, Jiajia

    2012-01-01

    Reduced graphene sheets (RGSs) mediate electron transfer between sulfate-reducing bacteria (SRB) and solid electrodes, and promote the development of microbial fuel cells (MFC). We have investigated RSG-promoted electron transfer between SRB and a glassy carbon (GC) electrode. The RGSs were produced at high yield by a chemical sequence involving graphite oxidation, ultrasonic exfoliation of nanosheets, and N2H4 reduction. Cyclic voltammetric testing showed that the characteristic anodic peaks (around 0.3 V) might arise from the combination of bacterial membrane surface cytochrome c3 and the metabolic products of SRB. After 6 d, another anodic wave gradually increased to a maximum current peak and a third anodic signal became visible at around 0 V. The enhancements of two characteristic anodic peaks suggest that RSGs mediate electron-transfer kinetics between bacteria and the solid electrode. Manipulation of these recently-discovered electron-transport mechanisms will lead to significant advances in MFC engineering.

  3. Double K-shell-to-K-shell electron transfer in ion-atom collisions

    International Nuclear Information System (INIS)

    In this paper we present the first study of the role of double K-shell-to-K-shell electron transfer in heavy-ion--atom collisions. Consistent analysis procedures for obtaining total cross sections for both single and double K-shell-to-K-shell electron transfer are outlined based on the charge-state dependence of the total x-ray-production cross sections for K-shell satellite and hypersatellite x rays, respectively. Theoretical calculations for the single and double electron-transfer cross sections based on the two-state atomic expansion model and the independent-electron approximation are presented and are found to be in excellent agreement with experiment

  4. Modulating the electronic structure of chromophores by chemical substituents for efficient energy transfer: application to fluorone.

    Science.gov (United States)

    Sand, Andrew M; Liu, Claire; Valentine, Andrew J S; Mazziotti, David A

    2014-08-01

    Strong electron correlation within a quasi-spin model of chromophores was recently shown to enhance exciton energy transfer significantly. Here we investigate how the modulation of the electronic structure of the chromophores by chemical substitution can enhance energy-transfer efficiency. Unlike previous work that does not consider the direct effect of the electronic structure on exciton dynamics, we add chemical substituents to the fluorone dimer to study the effect of electron-donating and electron-withdrawing substituents on exciton energy transfer. The exciton dynamics are studied from the solution of a quantum Liouville equation for an open system whose model Hamiltonian is derived from excited-state electronic structure calculations. Both van der Waals energies and coupling energies, arising from the Hellmann-Feynman force generated upon transferring the dimers from infinity to a finite separation, are built into the model Hamiltonian. Though these two effects are implicitly treated in dipole-based models, their explicit and separate treatment as discussed here is critical to forging the correct connection with the electronic structure calculations. We find that the addition of electron-donating substituents to the fluorone system results in an increase in exciton-transfer rates by factors ranging from 1.3-1.9. The computed oscillator strength is consistent with the recent experimental results on a larger heterodimer system containing fluorone. The oscillator strength increases with the addition of electron-donating substituents. Our results indicate that the study of chromophore networks via electronic structure will help in the future design of efficient synthetic light-harvesting systems. PMID:25062094

  5. The effect of intramolecular quantum modes on free energy relationships for electron transfer reactions

    DEFF Research Database (Denmark)

    Ulstrup, Jens; Jortner, Joshua

    1975-01-01

    A general quantum mechanical description of exothermic electron transfer reactions is formulated by treating such reactions as the nonradiative decay of a ''supermolecule'' consisting of the electron donor, the electron acceptor, and the polar solvent. In particular, the role of the high-frequency intramolecular degrees of feedom on the free energy relationship for series of closely related reactions was investigated for various model systems involving displacement of potential energy surfaces, ...

  6. Properties of the transfer matrices of deflecting magnet systems for free electron laser

    International Nuclear Information System (INIS)

    The oscillation of the free electron laser (FEL) requires the high current and low emittance electron beam. The beam transport system should be achromatic and isochronous to preserve the brightness and the emittance of the electron beam. In this paper we clarify the algebraic properties of the transfer matrices of the magnetic deflection system, which is a key component in the beam transport line. (author)

  7. ELECTRON TRANSFER IN Hg1-xCdxTe-CdTe HETEROSTRUCTURES

    OpenAIRE

    Boebinger, G.; Vieren, J.; Guldner, Y.; Voos, M.; Faurie, J.

    1987-01-01

    Far infrared magneto-absorption experiments performed at 1.6K in HgCdTe-CdTe heterojunctions show that a two-dimensional electron gas is formed in the HgCdTe layer at the HgCdTe-CdTe interface. The electron effective masses of the two populated subbands is obtained and compared to previous theoretical calculations. The electron transfer across the interface involves deep traps in the CdTe layers.

  8. Direct observation of ultrafast-electron-transfer reactions unravels high effectiveness of reductive DNA damage

    OpenAIRE

    Nguyen, Jenny; Ma, Yuhan; LUO, TING; Bristow, Robert G.; Jaffray, David A.; Lu, Qing-Bin

    2011-01-01

    Both water and electron-transfer reactions play important roles in chemistry, physics, biology, and the environment. Oxidative DNA damage is a well-known mechanism, whereas the relative role of reductive DNA damage is unknown. The prehydrated electron (), a novel species of electrons in water, is a fascinating species due to its fundamental importance in chemistry, biology, and the environment. is an ideal agent to observe reductive DNA damage. Here, we report both the first in situ femtosec...

  9. Potential for direct interspecies electron transfer in methanogenic wastewater digester aggregates

    DEFF Research Database (Denmark)

    Morita, Masahiko; Malvankar, Nikhil S; Franks, Ashley E; Summers, Zarath M; Giloteaux, Ludovic; Rotaru, Amelia E; Rotaru, Camelia; Lovley, Derek R; Rotaru, Amelia-Elena

    2011-01-01

    Mechanisms for electron transfer within microbial aggregates derived from an upflow anaerobic sludge blanket reactor converting brewery waste to methane were investigated in order to better understand the function of methanogenic consortia. The aggregates were electrically conductive, with conductivities 3-fold higher than the conductivities previously reported for dual-species aggregates of Geobacter species in which the two species appeared to exchange electrons via interspecies electron trans...

  10. Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes

    DEFF Research Database (Denmark)

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    Intramolecular electron transfer (ET) over distances up to about 10 Å between states in which the electron is localized on donor and acceptor groups by interaction with molecular or external solvent nuclear motion occurs, in particular, in two classes of systems. The excess electron in anionic radicals containing two aromatic end groups connected by a flexible polymethylene chain or a rigid cyclohexane frame is thus trapped on either aromatic end group, and ET between these groups can be detecte...

  11. Probing intermolecular couplings in liquid water with two-dimensional infrared photon echo spectroscopy

    Science.gov (United States)

    Paarmann, A.; Hayashi, T.; Mukamel, S.; Miller, R. J. D.

    2008-05-01

    Two-dimensional infrared photon echo and pump probe studies of the OH stretch vibration provide a sensitive probe of the correlations and couplings in the hydrogen bond network of liquid water. The nonlinear response is simulated using numerical integration of the Schrödinger equation with a Hamiltonian constructed to explicitly treat intermolecular coupling and nonadiabatic effects in the highly disordered singly and doubly excited vibrational exciton manifolds. The simulated two-dimensional spectra are in close agreement with our recent experimental results. The high sensitivity of the OH stretch vibration to the bath dynamics is found to arise from intramolecular mixing between states in the two-dimensional anharmonic OH stretch potential. Surprisingly small intermolecular couplings reproduce the experimentally observed intermolecular energy transfer times.

  12. A new intermolecular mechanism to selectively drive photoinduced damages

    CERN Document Server

    Gokhberg, Kirill; Kuleff, Alexander I; Cederbaum, Lorenz S

    2014-01-01

    Low-energy electrons (LEEs) are known to be effective in causing strand breaks in DNA. Recent experiments show that an important direct source of LEEs is the intermolecular Coulombic decay (ICD) process. Here we propose a new cascade mechanism initiated by core excitation and terminated by ICD and demonstrate its properties. Explicit calculations show that the energies of the emitted ICD-electrons can be controlled by selecting the initial atomic excitation. The properties of the cascade may have interesting applications in the fields of electron spectroscopy and radiation damage. Initiating such a cascade by resonant X-ray absorption from a high-Z element embedded in a cancerous cell nucleus, ICD will deliver genotoxic particles \\textit{locally} at the absorption site, increasing in that way the controllability of the induced damage.

  13. Designed Surface Residue Substitutions in [NiFe] Hydrogenase that Improve Electron Transfer Characteristics

    Directory of Open Access Journals (Sweden)

    Isaac T. Yonemoto

    2015-01-01

    Full Text Available Photobiological hydrogen production is an attractive, carbon-neutral means to convert solar energy to hydrogen. We build on previous research improving the Alteromonas macleodii “Deep Ecotype” [NiFe] hydrogenase, and report progress towards creating an artificial electron transfer pathway to supply the hydrogenase with electrons necessary for hydrogen production. Ferredoxin is the first soluble electron transfer mediator to receive high-energy electrons from photosystem I, and bears an electron with sufficient potential to efficiently reduce protons. Thus, we engineered a hydrogenase-ferredoxin fusion that also contained several other modifications. In addition to the C-terminal ferredoxin fusion, we truncated the C-terminus of the hydrogenase small subunit, identified as the available terminus closer to the electron transfer region. We also neutralized an anionic patch surrounding the interface Fe-S cluster to improve transfer kinetics with the negatively charged ferredoxin. Initial screening showed the enzyme tolerated both truncation and charge neutralization on the small subunit ferredoxin-binding face. While the enzyme activity was relatively unchanged using the substrate methyl viologen, we observed a marked improvement from both the ferredoxin fusion and surface modification using only dithionite as an electron donor. Combining ferredoxin fusion and surface charge modification showed progressively improved activity in an in vitro assay with purified enzyme.

  14. Charge transfer dynamics from adsorbates to surfaces with single active electron and configuration interaction based approaches

    International Nuclear Information System (INIS)

    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 ?? 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

  15. Proton-coupled electron transfer cleavage of heavy-atom bonds in electrocatalytic processes. Cleavage of a C-O bond in the catalyzed electrochemical reduction of CO2.

    Science.gov (United States)

    Costentin, Cyrille; Drouet, Samuel; Passard, Guillaume; Robert, Marc; Savéant, Jean-Michel

    2013-06-19

    Most of the electrocatalytic processes of interest in the resolution of modern energy challenges are associated with proton transfer. In the cases where heavy atom bond cleavage occurs concomitantly, the question arises of the exact nature of its coupling with proton-electron transfer within the catalytic cycle. The cleavage of a C-O bond in the catalyzed electrochemical conversion of CO2 to CO offers the opportunity to address this question. Electrochemically generated iron(0) porphyrins are efficient, specific, and durable catalysts provided they are coupled with Lewis or Brönsted acids. The cocatalyst properties of four Brönsted acids of increasing strength, water, trifluoroethanol, phenol, and acetic acid, have been systematically investigated. Preparative-scale electrolyses showed that carbon monoxide is the only product of the catalytic reaction. Methodic application of a nondestructive technique, cyclic voltammetry, with catalyst and CO2 concentrations, as well as H/D isotope effect, as diagnostic parameters allowed the dissection of the reaction mechanism. It appears that the key step of the reaction sequence consists of an electron transfer from the catalyst concerted with the cleavage of a C-O bond and the transfer of one proton. This is the second example, and an intermolecular version of such a concerted proton-electron bond-breaking reaction after a similar electrochemical process involving the cleavage of O-O bonds has been identified. It is the first time that a proton-electron transfer concerted with bond breaking has been uncovered as the crucial step in a catalytic multistep reaction. PMID:23692448

  16. An unprecedented self-assembled porous framework constructed by intermolecular S···S contacts

    International Nuclear Information System (INIS)

    An unprecedented self-assembled porous framework is constructed with a multi-sulfur donor molecule with ferrocenyl group (FcVET). The solvent-specific framework maintained by intermolecular S···S contacts forms one-dimensional hexagonal channels (? ? 7.5 A) filled with the solvated molecules. A careful evacuation of the solvated FcVET crystals leaves solvent-free FcVET crystals in which the identical framework structure with the same intermolecular S···S contacts is maintained. In contrast to the polar hydrogen bond donor-acceptor pairs, thiol-containing moieties are not regarded as good hydrogen bond tectons due to their insufficient polarity. On the other hand, although it is not directional, the intermolecular S···S interaction can be used in forming functional molecular assemblies as exemplified in the sulfur-rich molecular complexes of 4,5-bis(ethylenedithio)tetrathiafulvalene (ET) and metal-bisdithiolene complexes. These intermolecular charge transfer complexes need close contacts in solid states to exhibit electrical conductivity or magnetic properties, and the S···S interactions provide favorable interactions among the molecular components. The significant strength of this intermolecular interaction originates from a complementary electrophile-nucleophile interaction, or can be explained by a polar flattening model

  17. Fast electron transfer through a single molecule natively structured redox protein

    DEFF Research Database (Denmark)

    Della Pia, Eduardo Antonio; Chi, Qijin

    2012-01-01

    The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b562 in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum–iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be ‘gated’ through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b562 molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent.

  18. Correlation between biological activity and electron transferring of bovine liver catalase: Osmolytes effects

    International Nuclear Information System (INIS)

    Highlights: • Proline increases ET in Bovine Liver Catalase (BLC) whereas histidine decreases it. • Proline also increased the biological activity, whereas histidine decreased it. • Electron transferring and biological activity for BLC are directly correlated. • Proline causes favorable ET for BLC shown by positive E1/2 (E°?) and negative ?G. • Histidine makes ET unfavorable for BLC, manifested by E1/2 (E°?) 0. -- Abstract: Catalase is a crucial antioxidant enzyme that protects life against detrimental effects of H2O2 by disproportionating it into water and molecular oxygen. Effect of proline as a compatible and histidine as a non compatible osmolyte on the electron transferring and midpoint potential of catalase has been investigated. Proline increases the midpoint potential (?Em > 0), therefore causing the ?GET to be less positive and making the electron transfer reaction more facile whereas histidine decreases the Em (?Em ET, thereby rendering the electron transfer reaction less efficient. These results indicate the inhibitory effect of histidine evident by a ?37% decrease in the cathodic peak current compared to 16% increase in the case of proline indicative of activation. The insight paves the tedious way towards our ultimate goal of elucidating a correlation between biological activity and electron transferring

  19. Influence of Solvent, Electron Acceptors and Arenes on Photochemical Decarboxylation of Free Carboxylic Acids via Single Electron Transfer (SET

    Directory of Open Access Journals (Sweden)

    Yasuharu Yoshimi

    2010-04-01

    Full Text Available Single electron transfer (SET-photochemical decarboxylation of free carboxylic acids was performed in a polar solvent using several arenes such as phenanthrene, naphthalene, 1-methylnaphthalene, biphenyl, triphenylene, and chrysene in the presence of various electron acceptors such as 1,2-, 1,3-, and 1,4-dicyanobenzenes, methyl 4-cyanobenzoate, and 1,4-dicyanonaphthalene. The decarboxylation reaction was influenced by the arenes, electron acceptors, and solvent. The best result was achieved by the photoreaction using biphenyl and 1,4-dicyanonaphthalene in aqueous acetonitrile.

  20. 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.

  1. 75 FR 75897 - Electronic Funds Transfer of Depository Taxes

    Science.gov (United States)

    2010-12-07

    ...the Electronic Federal Tax Payment System (EFTPS...abatement. According to IRS research, however, employers...depositor of Form 943 taxes is determined according...deposit of employment taxes attributable to payments...be considered to be in compliance with Sec. Sec....

  2. 77 FR 6310 - Electronic Fund Transfers (Regulation E)

    Science.gov (United States)

    2012-02-07

    ...following methods: Electronic...official business days between...Division of Research, Markets...data, and research results on...course of business in the proposed...and the quantitative and qualitative...provide data, research results...types of businesses through which...and the quantitative and...

  3. Activators generated by electron transfer for atom transfer radical polymerization of styrene in the presence of mesoporous silica nanoparticles

    International Nuclear Information System (INIS)

    Graphical abstract: Effect of mesoporous silica nanoparticles (MCM-41) on the activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP) is investigated. Decrement of conversion and number average molecular weight and also increment of polydispersity index (PDI) values are three main results of addition of MCM-41 nanoparticles. Incorporation of MCM-41 nanoparticles in the polystyrene matrix can clearly increase thermal stability and decrease glass transition temperature of the nanocomposites. - Highlights: • Spherical morphology, hexagonal structure, and high surface area with regular pore diameters of the synthesized MCM-41 nanoparticles are examined. • AGET ATRP of styrene in the presence of MCM-41 nanoparticles is performed. • Effect of MCM-41 nanoparticles addition on the polymerization rate, conversion and molecular weights of the products are discussed. • Improvement in thermal stability of the nanocomposites and decreasing Tg values was also observed by incorporation of MCM-41 nanoparticles. - Abstract: Activator generated by electron transfer for atom transfer radical polymerization was employed to synthesize well-defined mesoporous silica nanoparticles/polystyrene composites. Inherent features of spherical mesoporous silica nanoparticles were evaluated by nitrogen adsorption/desorption isotherm, X-ray diffraction and scanning electron microscopy analysis techniques. Conversion and molecular weight evaluations were carried out using gas and size exclusion chromatography respectively. By the addition of only 3 wt% mesoporous silica nanoparticles, conversion decreases from 81 to 58%. Similarly, number average molecular weight decreases from 17,116 to 12,798 g mol?1. However, polydispersity index (PDI) values increases from 1.24 to 1.58. A peak around 4.1–4.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric analysis shows that thermal stability of the nanocomposites increases by adding nanoparticles content. Decrease of glass transition temperature is also demonstrated by the addition of 3 wt% of silica nanoparticles according to the differential scanning calorimetry results

  4. Coherent state transfer between an electron- and nuclear spin in 15N@C60

    CERN Document Server

    Brown, Richard M; Porfyrakis, Kyriakos; Gauger, Erik M; Lovett, Brendon W; Ardavan, Arzhang; Lyon, S A; Briggs, G Andrew D; Morton, John J L

    2010-01-01

    Electron spin qubits in molecular systems offer high reproducibility and the ability to self assemble into larger architectures. However, interactions between neighbouring qubits are 'always-on' and although the electron spin coherence times can be several hundred microseconds, these are still much shorter than typical times for nuclear spins. Here we implement an electron-nuclear hybrid scheme which uses coherent transfer between electron and nuclear spin degrees of freedom in order to both controllably turn on/off dipolar interactions between neighbouring spins and benefit from the long nuclear spin decoherence times (T2n). We transfer qubit states between the electron and 15N nuclear spin in 15N@C60 with a two-way process fidelity of 88%, using a series of tuned microwave and radiofrequency pulses and measure a nuclear spin coherence lifetime of over 100 ms.

  5. Bidirectional microbial electron transfer: Switching an acetate oxidizing biofilm to nitrate reducing conditions.

    Science.gov (United States)

    Pous, Narcís; Carmona-Martínez, Alessandro A; Vilajeliu-Pons, Anna; Fiset, Erika; Bañeras, Lluis; Trably, Eric; Balaguer, M Dolors; Colprim, Jesús; Bernet, Nicolas; Puig, Sebastià

    2016-01-15

    Up to date a few electroactive bacteria embedded in biofilms are described to catalyze both anodic and cathodic reactions in bioelectrochemical systems (i.e. bidirectional electron transfer). How these bacteria transfer electrons to or from the electrode is still uncertain. In this study the extracellular electron transfer mechanism of bacteria within an electroactive biofilm was investigated by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). First, a mature anodic electroactive biofilm was developed from an activated sludge sample (inoculum), acetate as electron donor and a poised electrode (+397mV vs. SHE). Later, this biofilm was "switched" to biocathodic conditions by feeding it with a medium containing nitrates and poising the electrode at -303mV vs. SHE. The electrochemical characterization indicated that both, acetate oxidation and nitrate reduction took place at a similar formal potential of -175±05 and -175±34mV vs. SHE, respectively. The biofilm was predominantly composed by Geobacter sp. at both experimental conditions. Taken together, the results indicated that both processes could be catalyzed by using the same electron conduit, and most likely by the same bacterial consortium. Hence, this study suggests that electroactive bacteria within biofilms could use the same electron transfer conduit for catalyzing anodic and cathodic reactions. PMID:26339932

  6. Electronic system for the automatic transfer of data from multichannel analyzer memory to computer

    International Nuclear Information System (INIS)

    An electronic system has been build for the automatic transfer of data from Intertechnique Multichannel analyzer Memory to HP 2116 C computer. By using a balanced twisted-pair transmission line, transfer can be made from devices separated up to 300 meters. A logic interface is associated to each apparatus. Computer manages the transmission process and indicates the errors that could happen. 4096 channels are transmitted into 17 sec

  7. Deterministic quantum state transfer from an electronic charge qubit to a photonic polarization qubit

    OpenAIRE

    Ament, L.J.P.; Beenakker, C. W. J.

    2006-01-01

    Building on an earlier proposal for the production of polarization-entangled microwaves by means of intraband transitions in a pair of quantum dots, we show how this device can be used to transfer an unknown single-qubit state from electronic charge to photonic polarization degrees of freedom. No postselection is required, meaning that the quantum state transfer happens deterministically. Decoherence of the charge qubit causes a non-monotonic decay of the fidelity of the tra...

  8. Breakdown of the Born-Oppenheimer-Condon-Marcus approximation in long distance electron transfer

    International Nuclear Information System (INIS)

    We consider the issue of how the breakdown of the Born-Oppenheimer-Condon-Marcus approximation affects the dependence of the electron-transfer rate k upon distance, as well as the dependences upon the driving force and temperature. For large distances, ca. r>10 A, it is predicted that: (i) the slope of lnk vs r dependence decreases down to zero; (ii) the bell-shaped Marcus dependence upon the driving force is distorted, with the maximum shifting toward ?G>0; and (iii) the apparent activation energy increases and the temperature dependence more and more declines from the Arrhenius form. These effects can be experimentally distinguished from similar effects due to other mechanisms, such as thermal activation of the electron transferred and temperature dependence of the reorganization parameters and driving force. Experimental data by Isied et al. [J. Phys. Chem. 97 (1993) 11456] on electron transfer between metal ions across rigid oligoproline bridges are well fitted using the present theory

  9. Nobel Prize 1992: Rudolph A. Marcus: theory of electron transfer reactions in chemical systems

    International Nuclear Information System (INIS)

    A review of the theory developed by Rudolph A. Marcus is presented, who for his rating to the theory of electron transfer in chemical systems was awarded the Nobel Prize in Chemistry in 1992. Marcus theory has constituted not only a good extension of the use of a spectroscopic principle, but also has provided an energy balance and the application of energy conservation for electron transfer reactions. A better understanding of the reaction coordinate is exposed in terms energetic and establishing the principles that govern the transfer of electrons, protons and some labile small molecular groups as studied at present. Also, the postulates and equations described have established predictive models of reaction time, very useful for industrial environments, biological, metabolic, and others that involve redox processes. Marcus theory itself has also constituted a large contribution to the theory of complex transition

  10. Transfer function restoration in 3D electron microscopy via iterative data refinement

    International Nuclear Information System (INIS)

    Three-dimensional electron microscopy (3D-EM) is a powerful tool for visualizing complex biological systems. As with any other imaging device, the electron microscope introduces a transfer function (called in this field the contrast transfer function, CTF) into the image acquisition process that modulates the various frequencies of the signal. Thus, the 3D reconstructions performed with these CTF-affected projections are also affected by an implicit 3D transfer function. For high-resolution electron microscopy, the effect of the CTF is quite dramatic and limits severely the achievable resolution. In this work we make use of the iterative data refinement (IDR) technique to ameliorate the effect of the CTF. It is demonstrated that the approach can be successfully applied to noisy data

  11. Synthesis of nickel oxides nanoparticles on glassy carbon as an electron transfer facilitator for horseradish peroxidase: Direct electron transfer and H2O2 determination

    International Nuclear Information System (INIS)

    In this study, horseradish peroxidase/nickel oxides nanoparticles/glassy carbon (HRP/NiO NPs/GC) electrode was prepared by first applying nickel oxides nanoparticles on glassy carbon surface and then horseradish peroxidase immobilized on the NiO NPs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) have been used as a diagnostic tools to identify the synthesized NiO NPs. Immobilized HRP showed an electrochemical redox behavior pertained to HRP(Fe(III)-Fe(II)) by direct electron transfer between protein and nanoparticles with a formal potential (E0') of - 55.5 mV (vs. Ag/AgCl and 141.5 mV vs. NHE) in 50 mM phosphate buffer solution (PBS). The anodic charge transfer coefficient (?) and heterogeneous electron transfer rate constant (ks) were 0.42 and 0.75 s-1, respectively. Biocatalytic activity of HRP/NiO NPs/GC electrode for reduction of hydrogen peroxide and application to hydrogen peroxide determination was exemplified.

  12. A systematic study of electron or hole transfer along DNA dimers, trimers and polymers

    CERN Document Server

    Simserides, Constantinos

    2014-01-01

    A systematic study of electron or hole transfer along DNA dimers, trimers and polymers is presented with a tight-binding approach at the base-pair level, using the relevant on-site energies of the base-pairs and the hopping parameters between successive base-pairs. A system of $N$ coupled differential equations is solved numerically with the eigenvalue method, allowing the temporal and spatial evolution of electrons or holes along a $N$ base-pair DNA segment to be determined. Useful physical quantities are defined and calculated including the maximum transfer percentage $p$ and the pure maximum transfer rate $\\frac{p}{T}$ for cases where a period $T$ can be defined, as well as the pure mean carrier transfer rate $k$ and the speed of charge transfer $u=kd$, where $d = N \\times$ 3.4 {\\AA} is the charge transfer distance. The inverse decay length $\\beta$ used for the exponential fit $k = k_0 \\exp(-\\beta d)$ and the exponent $\\eta$ used for the power law fit $k = k_0' N^{-\\eta}$ are computed. The electron and hol...

  13. Transient kinetics of electron transfer from a variety of c-type cytochromes to plastocyanin.

    Science.gov (United States)

    Meyer, T E; Zhao, Z G; Cusanovich, M A; Tollin, G

    1993-05-01

    Plastocyanin (PC) and its physiological reaction partner cytochrome (cyt) f form a complex which is electrostatically stabilized by interactions between complementary localized charges. We have measured the kinetics of intracomplex electron transfer between several reduced cytochromes and PC using laser flash photolysis. With spinach cyt f and spinach PC, we obtain first-order rate constants, kforward = 2780 s-1 and kreverse = 1050 s-1, for the reversible reaction and a complex dissociation constant of about 23 microM at an ionic strength (I) of 5 mM. The observed rate constant increases by a factor of 2 between I = 5 and 40 mM and then decreases monotonically at higher ionic strengths. This indicates that the complex is not completely dissociated until I = 150 mM and that the proteins within the electrostatically most stable complex are not optimally oriented for electron transfer. Similar results were obtained with turnip cyt f and spinach PC, although in this case intracomplex electron transfer is about 4 times as fast. Horse cyt c also forms an electrostatically stabilized complex with PC, and yields a limiting rate constant for intracomplex electron transfer (1750 s-1) and a dissociation constant (10 microM) comparable to those for spinach cyt f. The ionic strength dependence shows that the complex is more readily dissociated (complete at I = 25 mM) than is that of cyt f and that rearrangement is not required for optimal electron transfer. Addition of polylysine results in 10-fold inhibition of the rate of electron transfer. Pseudomonas cyt c-551 is an acidic cytochrome which does not form a complex with PC.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8387337

  14. Mimicking the electron transfer chain in photosystem II with a molecular triad thermodynamically capable of water oxidation

    OpenAIRE

    Megiatto, Jackson D.; Antoniuk-Pablant, Antaeres; Sherman, Benjamin D.; Kodis, Gerdenis; Gervaldo, Miguel; Moore, Thomas A.; Moore, Ana L.; Gust, Devens

    2012-01-01

    In the photosynthetic photosystem II, electrons are transferred from the manganese-containing oxygen evolving complex (OEC) to the oxidized primary electron-donor chlorophyll P680•+ by a proton-coupled electron transfer process involving a tyrosine-histidine pair. Proton transfer from the tyrosine phenolic group to a histidine nitrogen positions the redox potential of the tyrosine between those of P680•+ and the OEC. We report the synthesis and time-resolved spectroscopic study of a molecular...

  15. Electron excitation and energy transfer rates for H2O in the upper atmosphere

    Directory of Open Access Journals (Sweden)

    Brunger Michael

    2009-01-01

    Full Text Available Abstract Recent measurements of the cross sections for electronic state excitations in H2O have made it possible to calculate rates applicable to these excitation processes. We thus present here calculations of electron energy transfer rates for electronic and vibrational state excitations in H2O, as well as rates for excitation of some of these states by atmospheric thermal and auroral secondary electrons. The calculation of these latter rates is an important first step towards our aim of including water into a statistical equilibrium model of the atmosphere under auroral conditions. PACS Codes: 34.50.Gb 34.50.Ez

  16. Electron transfer across anodic films formed on tin in carbonate-bicarbonate buffer solution

    International Nuclear Information System (INIS)

    Impedance and steady-state data were recorded in order to study the kinetics of electron transfer between passive tin electrodes and an electrolytic solution containing the K3Fe(CN)6-K4Fe(CN)6 redox couple. Film thickness plays a key role in determining the type of electronic conduction of these oxide covered electrodes. Electron exchange with the oxide takes place with participation of the conduction band in the semiconducting film. A mechanism involving direct electron tunneling through the space charge barrier is the most suitable to interpret the experimental evidence

  17. Evidence of low intermolecular coupling in rubrene single crystals by Raman scattering

    Energy Technology Data Exchange (ETDEWEB)

    Weinberg-Wolf, J R [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27713 (United States); McNeil, L E [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27713 (United States); Liu Shubin [Division of Research Computing, Information Technology Services, University of North Carolina, Chapel Hill, NC 27713 (United States); Kloc, Christian [Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, NJ 07974 (United States)

    2007-07-11

    The observed Raman spectra for single crystals of rubrene and tetracene are compared with the calculated spectra for the isolated molecules. The Raman measurements presented are of the bulk properties of the material, and they confirmed that the vapour growth process yields very pure, unstrained rubrene crystals. Finally, Raman measurements indicate that rubrene, unlike many other oligoacenes, has very weak intermolecular coupling and no observable intermolecular Raman vibrational modes. We discuss the apparent conflict between the high mobility and the weak {pi}-electron overlap in this material.

  18. Evidence of low intermolecular coupling in rubrene single crystals by Raman scattering

    International Nuclear Information System (INIS)

    The observed Raman spectra for single crystals of rubrene and tetracene are compared with the calculated spectra for the isolated molecules. The Raman measurements presented are of the bulk properties of the material, and they confirmed that the vapour growth process yields very pure, unstrained rubrene crystals. Finally, Raman measurements indicate that rubrene, unlike many other oligoacenes, has very weak intermolecular coupling and no observable intermolecular Raman vibrational modes. We discuss the apparent conflict between the high mobility and the weak ?-electron overlap in this material

  19. Ultrafast electron transfer in type II GaAs/AlAs superlattices by femtosecond luminescence

    International Nuclear Information System (INIS)

    Electron transfer from GaAs wells (? wavefunctions) to AlAs barriers (X wavefunctions) in GaAs/AlAs type II superlattices has been studied by time resolved luminescence with femtosecond resolution. Transfer times can be as short as 140 fs for narrow wells and as long as 25 ps for the widest wells. They do not depend appreciably on the barrier thickness. We discuss the possible contribution to the transfer mechanism of state mixing, intervalley scattering and Froelich interaction. Our measurement favors phonon assisted, intervalley type scattering, modified by the overlap of the different wavefunctions. (orig.)

  20. Controllable Quantum State Transfer Between a Josephson Charge Qubit and an Electronic Spin Ensemble

    Science.gov (United States)

    Yan, Run-Ying; Wang, Hong-Ling; Feng, Zhi-Bo

    2015-05-01

    We propose a theoretical scheme to implement controllable quantum state transfer between a superconducting charge qubit and an electronic spin ensemble of nitrogen-vacancy centers. By an electro-mechanical resonator acting as a quantum data bus, an effective interaction between the charge qubit and the spin ensemble can be achieved in the dispersive regime, by which state transfers are switchable due to the adjustable electrical coupling. With the accessible experimental parameters, we further numerically analyze the feasibility and robustness. The present scheme could provide a potential approach for transferring quantum states controllably with the hybrid system.

  1. Near-contact adiabatic suppression of electron transfer in the inverted region

    International Nuclear Information System (INIS)

    A few theories of activated electron transfer in inverted Marcus region are used for bridging the non-adiabatic, solvent controlled and deeply adiabatic transfer. The simple analytical interpolation between dynamic and stochastic theories provides a continuous description of the electron transfer rate at any non-adiabatic coupling between the diabatic states. When coupling increases with shortening of inter-particle distance the pre-exponent of the Arrhenius transfer rate first increases being quadratic in coupling, then levels off approaching the 'dynamic solvent effect' (DSE) region and finally is cut off exponentially due to adiabaticity of the transfer. These changes affect significantly the spatial dependence of the transfer rate near the contact provided the coupling there is strong. The rate tends to zero at contact distance being strongly suppressed nearby adiabatically. It is much smaller then the perturbation (golden rule) and even DSE results. The latter is actually unattainable anywhere if contact tunneling is really strong. The transfer rate is a bell-shaped curve adiabatic and non-adiabatic on the opposite sides and sensitive to the friction (DSE damping) only in between, near the maximum

  2. An efficient implementation of the localized operator partitioning method for electronic energy transfer

    International Nuclear Information System (INIS)

    The localized operator partitioning method [Y. Khan and P. Brumer, J. Chem. Phys. 137, 194112 (2012)] rigorously defines the electronic energy on any subsystem within a molecule and gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. However, an efficient implementation of this approach has been hindered by complicated one- and two-electron integrals arising in its formulation. Using a resolution of the identity in the definition of partitioning, we reformulate the method in a computationally efficient manner that involves standard one- and two-electron integrals. We apply the developed algorithm to the 9 ? ((1 ? naphthyl) ? methyl) ? anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH2 ? 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 the excited electronic states

  3. Subshell resolved L-K electron transfer and ionization of Yb with Si ion impact

    International Nuclear Information System (INIS)

    We have measured subshell resolved L-K electron transfer cross sections from the L subshell of the Yb target to the vacant K-shell of the Si projectile at energies varying between 2-4.5 MeV/A. In addition, the L subshell ionization cross sections are also obtained for Yb. It is observed that contrary to expectations, the L2 subshell electron transfer as well as ionization cross sections are substantially lower than the corresponding cross sections for the L1 subshell. (orig.)

  4. Electronic memory switching in a new charge transfer-complex thin film

    Science.gov (United States)

    Wang, K. Z.; Xue, Z. Q.; Ouyang, M.; Zhang, H. X.; Huang, C. H.

    1995-11-01

    Charge transfer-complex thin films of 1,4-bis(2,2-dicyanovinyl)benzene(BDCB) with silver, sandwiched between two silver elctrodes, show current-controlled bistable electronic switching and memory behavior. The switching from a high to low impedance is believed to be associated with chemical phase change similar to that for charge transfer-complex thin films of TCNQ with either copper or silver. The films are analyzed by infrared, ultraviolet-visible spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction.

  5. Nonlinear response of metal nanoparticles: Double plasmon excitation and electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Shiwu [Beijing Computational Science Research Center, Zhongguancun Software Park II, 100094, Beijing (China)

    2015-06-21

    We investigate the dynamical response of a metal nanoparticle and the electron transfer to a molecule near its surface using time-dependent density functional theory. In addition to the linear response of the Mie resonance, double plasmon excitations and a low-frequency charge transfer band emerge and become prominent at high laser intensities. Both modes are nonlinear processes, which are derived from the re-excitation and decay of the primary plasmon mode, respectively. Our results shed light on the localised characters of the plasmon-molecule coupling and hot electron distributions. These findings have general implications to photoinduced phenomena in nanosystems.

  6. Direct electron transfer: an approach for electrochemical biosensors with higher selectivity and sensitivity

    Directory of Open Access Journals (Sweden)

    Freire Renato S.

    2003-01-01

    Full Text Available The most promising approach for the development of electrochemical biosensors is to establish a direct electrical communication between the biomolecules and the electrode surface. This review focuses on advances, directions and strategies in the development of third generation electrochemical biosensors. Subjects covered include a brief description of the fundamentals of the electron transfer phenomenon and amperometric biosensor development (different types and new oriented enzyme immobilization techniques. Special attention is given to different redox enzymes and proteins capable of electrocatalyzing reactions via direct electron transfer. The analytical applications and future trends for third generation biosensors are also presented and discussed.

  7. Photo-induced regeneration of hormones by electron transfer processes: Potential biological and medical consequences

    Energy Technology Data Exchange (ETDEWEB)

    Getoff, Nikola, E-mail: nikola.getoff@univie.ac.a [Section of Radiation Biology, Faculty of Life Sciences, University of Vienna, A-1090 Vienna (Austria); Hartmann, Johannes [Department of Gynecologic Endocrinology and Reproduction, Medical University of Vienna, A-1090 Vienna (Austria); Schittl, Heike [Section of Radiation Biology, Faculty of Life Sciences, University of Vienna, A-1090 Vienna (Austria); Gerschpacher, Marion [Department of Gynecologic Endocrinology and Reproduction, Medical University of Vienna, A-1090 Vienna (Austria); Quint, Ruth Maria [Section of Radiation Biology, Faculty of Life Sciences, University of Vienna, A-1090 Vienna (Austria)

    2011-08-15

    Based on the previous results concerning electron transfer processes in biological substances, it was of interest to investigate if hormone transients resulting by e.g. electron emission can be regenerated. The presented results prove for the first time that the hormone transients originating by the electron emission process can be successfully regenerated by the transfer of electrons from a potent electron donor, such as vitamin C (VitC). Investigations were performed using progesterone (PRG), testosterone (TES) and estrone (E1) as representatives of hormones. By irradiation with monochromatic UV light ({lambda}=254 nm) in a media of 40% water and 60% ethanol, the degradation as well as the regeneration of the hormones was studied with each hormone individually and in the mixture with VitC as a function of the absorbed UV dose, using HPLC. Calculated from the obtained initial yields, the determined regeneration of PRG amounted to 52.7%, for TES to 58.6% and for E1 to 90.9%. The consumption of VitC was determined in the same way. The reported results concerning the regeneration of hormones by the transfer of electrons from an electron donor offer a new, promising method for the therapy with hormones. As a consequence of the regeneration of hormones, a decreased formation of carcinogenic metabolites is expected.

  8. Experimental studies of fundamental issues in electron transfer through nanometer scale devices

    Science.gov (United States)

    Yamamoto, Hiromichi

    Electron transfer reactions constitute many of the primary events in materials science, chemistry, physics, and biochemistry, e.g. the electron transport properties and photoexcited processes in solids and molecules, chemical reactions, corrosion, photosynthesis, respiration, and so forth. A self-assembled monolayer (SAM) film provides us with a unique environment not only to understand and manipulate the surface electronic properties of a solid, but also to control electron transfer processes at the interface. The first topic in this thesis describes the structure and electron tunneling characterization of alkanethiol SAMs on InP(100). Angle-resolved X-ray photoelectron spectroscopy was used to characterize the bonding of alkanethiols to n-InP surfaces and to measure the monolayer thickness. The results showed that the sulfur binds to In atoms on the surface, and provided film thicknesses of 6.4 A for C8H17SH, 11.1 A for C12H25SH, and 14.9 A for C16H 33SH, resulting in an average tilt angle of 55°. The analysis indicated that super-exchange coupling between the alkane chains plays an important role in defining electron tunneling barriers, especially for highly tilted chains. The second topic describes studies of cytochrome c bound to pure and mixed SAMs of o-terminated alkanethiol (terminated with pyridine, imidazole or nitrile groups) and alkanethiol on gold. Electrochemical methods are used to determine electron transfer rate constants of cytochrome c, and scanning tunneling microscopy to observe the cytochrome c on the SAM. Detailed analysis revealed direct association of the heme of cytochrome c with the terminal groups of the SAMs and a 'turning-over' of the electron transfer of cytochrome c from adiabatic to non-adiabatic regime. The third topic describes studies of oxidation and reduction of cytochrome c in solution through eleven different self-assembled monolayers (SAMs) on gold electrodes by cyclic voltammetry. Electron transfer rate constants of cytochrome c through the eleven SAMs ranged from ?10-4 to ˜10-1 cm/sec. A strong correlation between the electron transfer rate constants and the hydrogen bonding ability of the SAM is identified. This correlation is discussed in terms of the dependence of the rate constant on the outer-sphere reorganization energy and the electronic coupling between the cytochrome and the differently terminated monolayer films.

  9. DFT and time-resolved IR investigation of electron transfer between photogenerated 17- and 19-electron organometallic radicals

    Energy Technology Data Exchange (ETDEWEB)

    Cahoon, James B.; Kling, Matthias F.; Sawyer, Karma R.; Andersen, Lars K.; Harris, Charles B.

    2008-04-30

    The photochemical disproportionation mechanism of [CpW(CO){sub 3}]{sub 2} in the presence of Lewis bases PR{sub 3} was investigated on the nano- and microsecond time-scales with Step-Scan FTIR time-resolved infrared spectroscopy. 532 nm laser excitation was used to homolytically cleave the W-W bond, forming the 17-electron radicals CpW(CO){sub 3} and initiating the reaction. With the Lewis base PPh{sub 3}, disproportionation to form the ionic products CpW(CO){sub 3}PPh{sub 3}{sup +} and CpW(CO){sub 3}{sup -} was directly monitored on the microsecond time-scale. Detailed examination of the kinetics and concentration dependence of this reaction indicates that disproportionation proceeds by electron transfer from the 19-electron species CpW(CO){sub 3}PPh{sub 3} to the 17-electron species CpW(CO){sub 3}. This result is contrary to the currently accepted disproportionation mechanism which predicts electron transfer from the 19-electron species to the dimer [CpW(CO){sub 3}]{sub 2}. With the Lewis base P(OMe){sub 3} on the other hand, ligand substitution to form the product [CpW(CO){sub 2}P(OMe){sub 3}]{sub 2} is the primary reaction on the microsecond time-scale. Density Functional Theory (DFT) calculations support the experimental results and suggest that the differences in the reactivity between P(OMe){sub 3} and PPh{sub 3} are due to steric effects. The results indicate that radical-to-radical electron transfer is a previously unknown but important process for the formation of ionic products with the organometallic dimer [CpW(CO){sub 3}]{sub 2} and may also be applicable to the entire class of organometallic dimers containing a single metal-metal bond.

  10. A de novo designed 2[4Fe-4S] ferredoxin mimic mediates electron transfer.

    Science.gov (United States)

    Roy, Anindya; Sommer, Dayn Joseph; Schmitz, Robert Arthur; Brown, Chelsea Lynn; Gust, Devens; Astashkin, Andrei; Ghirlanda, Giovanna

    2014-12-10

    [Fe-S] clusters, nature's modular electron transfer units, are often arranged in chains that support long-range electron transfer. Despite considerable interest, the design of biomimetic artificial systems emulating multicluster-binding proteins, with the final goal of integrating them in man-made oxidoreductases, remains elusive. Here, we report a novel bis-[4Fe-4S] cluster binding protein, DSD-Fdm, in which the two clusters are positioned within a distance of 12 Å, compatible with the electronic coupling necessary for efficient electron transfer. The design exploits the structural repeat of coiled coils as well as the symmetry of the starting scaffold, a homodimeric helical protein (DSD). In total, eight hydrophobic residues in the core of DSD were replaced by eight cysteine residues that serve as ligands to the [4Fe-4S] clusters. Incorporation of two [4Fe-4S] clusters proceeds with high yield. The two [4Fe-4S] clusters are located in the hydrophobic core of the helical bundle as characterized by various biophysical techniques. The secondary structure of the apo and holo proteins is conserved; further, the incorporation of clusters results in stabilization of the protein with respect to chemical denaturation. Most importantly, this de novo designed protein can mimic the function of natural ferredoxins: we show here that reduced DSD-Fdm transfers electrons to cytochrome c, thus generating the reduced cyt c stoichiometrically. PMID:25437708

  11. Linker effects on monolayer formation and long-range electron transfer in helical peptide monolayers.

    Science.gov (United States)

    Arikuma, Yoko; Takeda, Kazuki; Morita, Tomoyuki; Ohmae, Masashi; Kimura, Shunsaku

    2009-05-01

    Helical peptides carrying a ferrocene unit at the C-terminus were immobilized on gold at the N-terminus via three different linkers to form self-assembled monolayers, and the long-range electron transfer from the ferrocene unit to gold was electrochemically studied. The linkers are 4-thiobenzoic acid, 3-fluoro-4-thiobenzoic acid, and 2-methoxy-4-thiobenzoic acid. All the peptides formed a monolayer with vertical orientation but some differences in monolayer packing and ferrocene surface density as they formed. However, the treatment with dodecanethiol in a gas phase uniformed to show similar monolayer physical parameters, and the electron-transfer rate constants were reproducibly obtained as well. These three peptide monolayers exhibited the same electron-transfer rate constants despite three linkers with different oxidation potentials. On the other hand, the electron transfer was decelerated seemingly by reducing the ferrocene surface density. Theoretical calculations with simple models demonstrated that the experimental result supports a hopping mechanism rather than electron tunneling though it cannot be fully excluded. PMID:19361180

  12. 36 CFR 1235.46 - What electronic media may be used for transferring records to the National Archives of the United...

    Science.gov (United States)

    2010-07-01

    ...Agencies may transfer electronic records to the National Archives of the United...transfer permanent electronic records to the National Archives of the United...or the National Archives and Records Administration, Electronic/Special...

  13. Electronic parameters for the hole transfer in DNA duplex oligomers

    CERN Document Server

    Berashevich, D J A; Berashevich, Dr. Julia A.; Chakraborty, Tapash

    2007-01-01

    We report on our calculations of the inner-sphere reorganization energy and the interaction of the pi orbitals within DNA oligomers. The exponential decrease of the electronic coupling between the highest and second highest occupied base orbitals of the intrastrand nucleobases in the (A-T)n and (G-C)n oligomers have been found with an increase of the sequence number n in the DNA structure. We conclude that for realistic estimation of the electronic coupling values between the nucleobases within the DNA molecule, a DNA chain containing at least four base pairs is required. We estimate the geometry relaxation of the base pairs within the (A-T)n and (G-C)n oligomers (n=1-6) due to their oxidation. The decrease of the inner-sphere reorganization energy with elongation of the oligomer structure participating in the oxidation process have been observed. The maximum degree of geometry relaxation of the nucleobase structures and correspondingly the higher charge density in the oxidized state are found to be located c...

  14. Electrostatic models of electron-driven proton transfer across a lipid membrane

    CERN Document Server

    Smirnov, Anatoly Yu; Nori, Franco

    2010-01-01

    We present two models for electron-driven uphill proton transport across lipid membranes, with the electron energy converted to the proton gradient via the electrostatic interaction. In the first model, associated with the cytochrome c oxidase complex in the inner mitochondria membranes, the electrostatic coupling to the site occupied by an electron lowers the energy level of the proton-binding site, making the proton transfer possible. In the second model, roughly describing the redox loop in a nitrate respiration of E. coli bacteria, an electron displaces a proton from the negative side of the membrane to a shuttle, which subsequently diffuses across the membrane and unloads the proton to its positive side. We show that both models can be described by the same approach, which can be significantly simplified if the system is separated into several clusters, with strong Coulomb interaction inside each cluster and weak transfer couplings between them. We derive and solve the equations of motion for the electro...

  15. Photoinduced electron transfer in donor-acceptor complexes of ethylene with molecular and atomic iodine.

    Science.gov (United States)

    Kalume, Aimable; George, Lisa; Powell, Andrew D; Dawes, Richard; Reid, Scott A

    2014-08-28

    Building upon our recent studies of radical addition pathways following excitation of the I2 chromophore in the donor-acceptor complex of ethylene and I2 (C2H4···I2), in this article, we extend our studies to examine photoinduced electron transfer. Thus, irradiation into the intense charge-transfer band of the complex (?max = 247 nm) gave rise to a band at 366 nm that is assigned to the bridged ethylene-I radical complex on the basis of our prior work. The formation of the radical complex is explained by a mechanism that involves rapid back electron transfer leading to I-I bond fission. Excitation into the charge-transfer band of the radical complex led to regeneration of the parent complex and the formation of the final photoproduct, anti- and gauche-1,2-diiodoethane, which confirms that the reaction proceeds ultimately by a radical addition mechanism. This finding is contrasted with our previous study of the C2H4···Br2 complex, where CT excitation led to only one product, anti-1,2-dibromoethane, a result explained by a single electron-transfer mechanism proceeding via a bridged bromonium ion intermediate. For the I2 complex, the breakup of the photolytically generated I2(-•) anion radical is apparently sufficiently slow to render it uncompetitive with back electron transfer. Finally, we report a detailed computational examination of the parent and radical complexes of both bromine and iodine, using high-level single- and multireference methods, which provide insight into the different behaviors of the charge-transfer states of the two radicals and the role of spin-orbit coupling. PMID:25075444

  16. Electron transfer kinetics in water-splitting dye-sensitized photoelectrochemical cells

    Science.gov (United States)

    Swierk, John R.

    Water-splitting dye-sensitized photoelectrochemical (WS-DSPECs) cells utilize molecular sensitizers absorbed on mesoporous TiO2 electrodes to harvest visible light, inject photoexcited electrons into the conduction band of TiO2, and finally transfer holes across the TiO2 surface to water oxidation catalysts, which in turn oxidize water to give molecular oxygen and four protons. Within the TiO2 layer photoinjected electrons are transported to a transparent conductor back contact and from there to a dark cathode to reduce protons to molecular hydrogen. WS-DSPECs offer several advantages for alternative solar fuels systems: the use of low-cost materials, tunable molecular sensitizers, and relaxed catalytic turnover requirements to name a few. Despite these advantageous features, power conversion efficiencies in WS-DSPECs are generally low. Broadly, this thesis explores the fundamental electron transfer processes that control the efficiency of these cells. Chapter 1 presents a survey of the previous literature and individually considers each component of a WS-DSPEC (water oxidation catalyst, sensitizers, electrode materials, redox mediators, and overall system design). Chapter 2 presents a novel method of preparing a WS-DSPEC that utilizes crystalline IrO2 nanoparticles directly sintered to TiO2 as a water oxidation catalyst and describes a previously unknown electron-scavenging pathway by IrO2. Chapter 3 explores how electron trapping by and proton intercalation into TiO2 controls the photoelectrochemical performance of WS-DSPECs. Chapter 4 characterizes how electron recombination with the oxidized sensitizer and electron scavenging by the IrO 2 catalyst combine to limit the concentration of conduction band electrons and by extension photocurrent in WS-DSPECs. Chapter 5 demonstrates the use of the first totally organic sensitizers for light driven water-splitting and explores how the molecular and electronic structure of a sensitizer affects the electron transfer steps of injection, recombination, and hole transfer among others. Finally, in Chapter 6 a model system that describes electron transfer between an oxidized sensitizer and water oxidation catalyst is demonstrated and provides insight into sensitizer regeneration in WS-DSPECs. Together the results in these chapters present a detailed picture of how electron scavenging, recombination, and transport combine to generate photocurrent in a fully characterized WS-DSPEC and serve as starting point for the further development of WS-DSPECs.

  17. Two-photon Induced Hot Electron Transfer to a Single Molecule in a Scanning Tunneling Microscope

    OpenAIRE

    Wu, Shiwei; Ho, Wilson

    2010-01-01

    The junction of a scanning tunneling microscope (STM) operating in the tunneling regime was irradiated with femtosecond laser pulses. A photo-excited hot electron in the STM tip resonantly tunnels into an excited state of a single molecule on the surface, converting it from the neutral to the anion. The electron transfer rate depends quadratically on the incident laser power, suggesting a two-photon excitation process. This nonlinear optical process is further confirmed by t...

  18. Investigations of bimolecular photoinduced electron transfer reactions in polar solvents using ultrafast spectroscopy

    OpenAIRE

    Vauthey, Eric

    2006-01-01

    Several controversial questions in the field of bimolecular photoinduced electron transfer reactions in polar solvents are first briefly reviewed. Results obtained in our group using ultrafast spectroscopy and giving a new insight into these problems will then be described. They concern the driving force dependence of the charge separation distance, the formation of the reaction product in an electronic excited state, the absence of normal region for weakly exergonic charge recombination proc...

  19. Photoinduced Reductive Electron Transfer in LNA:DNA Hybrids : A Compromise between Conformation and Base Stacking

    DEFF Research Database (Denmark)

    Wenge, Ulrike; Wengel, Jesper

    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.

  20. Reorganization energy of the initial electron-transfer step in photosynthetic bacterial reaction centers.

    OpenAIRE

    Parson, W. W.; Chu, Z. T.; Warshel, A (Arieh)

    1998-01-01

    The reorganization energy (lambda) for electron transfer from the primary electron donor (P*) to the adjacent bacteriochlorophyll (B) in photosynthetic bacterial reaction centers is explored by molecular-dynamics simulations. Relatively long (40 ps) molecular-dynamics trajectories are used, rather than free energy perturbation techniques. When the surroundings of the reaction center are modeled as a membrane, lambda for P* B --> P+ B- is found to be approximately 1.6 kcal/mol. The results are...

  1. Dynamics and mechanisms of interfacial photoinduced electron transfer processes of third generation photovoltaics and photocatalysis.

    OpenAIRE

    Bauer, C.; Teuscher, J.; Brauer, JC; Punzi, A; Marchioro, A.; Ghadiri, E.; De Jonghe, J; Wielopolski, M.; Banerji, N; Moser, JE

    2011-01-01

    Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic syste...

  2. Influence of Complex Stabilities on Electron-Transfer Reactions

    International Nuclear Information System (INIS)

    The rate of exchange in solutions containing sulphate ions was measured in the system FeII/FeIII at different temperatures with 5'9Fe as a tracer. At 25°C and an ionic strength of 1 the rate constants are: k1[FeSO+4/Fe2+] =295 litres mole-1 sec-1, k2[Fe(SO4)2-/Fe2+] =17 500 litres mole-1 sec-1. The activation energies are E1 =13.8 kcal/mole, E2 = 15kcal/mole. For the rate constants of the electron exchange between different complexes of FeIII and Fe2+ ions the following relation was found: log10k = 1.1 + 0. 5 |?log10K|, where ? log10K is the difference between the logarithms of the stability constants of the FeIII and FeII complexes with the same ligands. All rate constants for electron exchange between FeIII complexes and Fe2+ ions follow this relation (as far as stability constants are known). In the system CeIII/ CeIV a first-order reaction with respect to CeIII contributes to the exchange reaction. This is explained by the formation of excited CeIII ions. The rate constant is k5 = 4.45 x 10-4 sec-1 (0°C). At 0°C the rate constants for the second-order reactions are: k1[CeSO+24/Ce3+] = 0.10 litres mole-1 sec-1, k2[Ce(SO4)2/Ce3+] = 0.11 litres mole-1 sec-1; k3[Ce(SO4)2-3/Ce3+] = 0.17 litres mole-1 sec-1, k4 [Ce4+/Ce3+] = 5.05 x 10-3 litres mole-1 sec-1. The electron exchange is accelerated by sulphate ions, but not to the same extent as in the system FeII/FeIII. The fact that the rate constants k, k2 and k3 are nearly equal shows that the charge of the complexes has no influence. The rate constants in the system CeIII/CeIV also follow a relation of the form log k = a + b?log K. The constants a and b were found to be: a = -2.3, b = 0.4. In the system UIV/UVI - in the absence of light - the rate of the electron exchange in solutions containing sulphate ions is proportional to the concentrations of UIV and UVI and inversely proportional to the third power of the H+ concentration. The rate determining step is the disproportionation of UV which is present in small quantities in equilibrium with UIV and UVI. The rate constant was found to be 1.2 x 10-4 mole2 litre-2sec-1 (25°C, ionic strength 2). This value is by a factor of about 600 higher than the rate constant in a solution containing Perchlorate ions instead of sulphate ions. The activation energy was found to be 10.2 kcal/mole. (author)

  3. Charge transfer and electronic doping in nitrogen-doped graphene

    Science.gov (United States)

    Joucken, Frédéric; Tison, Yann; Le Fèvre, Patrick; Tejeda, Antonio; Taleb-Ibrahimi, Amina; Conrad, Edward; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Ghijsen, Jacques; Sporken, Robert; Amara, Hakim; Ducastelle, François; Lagoute, Jérôme

    2015-01-01

    Understanding the modification of the graphene’s electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants’ concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors. PMID:26411651

  4. Charge transfer and electronic doping in nitrogen-doped graphene

    Science.gov (United States)

    Joucken, Frédéric; Tison, Yann; Le Fèvre, Patrick; Tejeda, Antonio; Taleb-Ibrahimi, Amina; Conrad, Edward; Repain, Vincent; Chacon, Cyril; Bellec, Amandine; Girard, Yann; Rousset, Sylvie; Ghijsen, Jacques; Sporken, Robert; Amara, Hakim; Ducastelle, François; Lagoute, Jérôme

    2015-09-01

    Understanding the modification of the graphene’s electronic structure upon doping is crucial for enlarging its potential applications. We present a study of nitrogen-doped graphene samples on SiC(000) combining angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy and X-ray photoelectron spectroscopy (XPS). The comparison between tunneling and angle-resolved photoelectron spectra reveals the spatial inhomogeneity of the Dirac energy shift and that a phonon correction has to be applied to the tunneling measurements. XPS data demonstrate the dependence of the N 1s binding energy of graphitic nitrogen on the nitrogen concentration. The measure of the Dirac energy for different nitrogen concentrations reveals that the ratio usually computed between the excess charge brought by the dopants and the dopants’ concentration depends on the latter. This is supported by a tight-binding model considering different values for the potentials on the nitrogen site and on its first neighbors.

  5. Are the orientation and bond strength of the RCO2(-)M link key factors for ultrafast electron transfers?

    Science.gov (United States)

    Luo, Peng; Karsenti, Paul-Ludovic; Brisard, Gessie; Marsan, Benoit; Harvey, Pierre D

    2015-11-24

    The photo-induced electron transfers in the "straight up" ionic assemblies [] and [][] ([]* ? or ) are ultrafast (bent geometry to obtain fast electron injection in porphyrin-containing DSSCs. PMID:26463512

  6. Technology transfer present and futures in the electronic arts

    Directory of Open Access Journals (Sweden)

    Brian Degger

    2008-01-01

    Full Text Available We are entering an era where creating the fantastical is possible in the arts. In the areas of mixed reality and biological arts, responsive works are created based on advances in basic science and technology. This is enabling scientists and artists to pose new questions. As the time between discovery and application is so short, artists need imaginative ways of accessing new technology in order to critique and use it.These are the new paints that the majority of artists cannot afford or access, technology to enable cloning of DNA, to print channels on a chip, to access proprietary 3G networks. Currently, partnerships or residencies are used to facilitate artist’s access to these technologies. What would they do if technology was available that enabled them to make any art work they so desire? Are the limitations in current technology an advantage rather than a disadvantage in some of their works? Does interaction with technologists make their work more robust? Are there disadvantages? How do they get access to the technology they require? Open source or proprietary? Or have they encountered the situation where their vision is greater than technology allows. When their work breaks because of this fact, is their art broken? Blast Theory (Brighton,UK, FoAM(Brussels, Belgium and Amsterdam, Netherlands, SymbioticA (Perth, Australia are organisations pushing technological boundaries in the service of art. This paper addresses some questions of technology transfer in relation to recent artworks, particularly I like Frank in Adelaide (Blast Theory, transient reality generators (trg (FoAM and Multi electrode array artist (MeART (SymbioticA.

  7. Single-molecule magnets ``without'' intermolecular interactions

    Science.gov (United States)

    Wernsdorfer, W.; Vergnani, L.; Rodriguez-Douton, M. J.; Cornia, A.; Neugebauer, P.; Barra, A. L.; Sorace, L.; Sessoli, R.

    2012-02-01

    Intermolecular magnetic interactions (dipole-dipole and exchange) affect strongly the magnetic relaxation of crystals of single-molecule magnets (SMMs), especially at low temperature, where quantum tunneling of the magnetization (QTM) dominates. This leads to complex many-body problems [l]. Measurements on magnetically diluted samples are desirable to clearly sort out the behaviour of magnetically-isolated SMMs and to reveal, by comparison, the effect of intermolecular interactions. Here, we diluted a Fe4 SMM into a diamagnetic crystal lattice, affording arrays of independent and iso-oriented magnetic units. We found that the resonant tunnel transitions are much sharper, the tunneling efficiency changes significantly, and two-body QTM transitions disappear. These changes have been rationalized on the basis of a dipolar shuffling mechanism and of transverse dipolar fields, whose effect has been analyzed using a multispin model. Our findings directly prove the impact of intermolecular magnetic couplings on the SMM behaviour and disclose the magnetic response of truly-isolated giant spins in a diamagnetic crystalline environment.[4pt] [1] W. Wernsdorfer, at al, PRL 82, 3903 (1999); PRL 89, 197201 (2002); Nature 416, 406 (2002); IS Tupitsyn, PCE Stamp, NV Prokof'ev, PRB 69, 132406 (2004).

  8. (Comparison of group transfer, inner sphere and outer sphere electron transfer mechanisms of organometallic complexes)

    Energy Technology Data Exchange (ETDEWEB)

    Atwood, J.

    1990-01-01

    During the course of Grant ER13775 we have constructed an infrared stopped-flow spectrophotometer and initiated a study of the mechanisms of reactions that involve a change in the oxidation state of organometallic complexes. The spectrometer combined conventional stopped-flow techniques with an infrared optical system comprised of a carbon monoxide laser, an IRTRAN flow-through cell and a mercury-cadium-telluride detector. In this summary we will highlight our results on reactions: (1) that formally involve exchange of a charged species between two metal carbonyl anions, (2) that involve additional of an electron to, or removal of an electron from organometallic complexes that contain a metal-metal bond, and (3) between coordination complexes and metal carbonyl anions. 12 refs.

  9. An efficient implementation of the localized operator partitioning method for electronic energy transfer

    CERN Document Server

    Nagesh, Jayashree; Brumer, Paul

    2014-01-01

    The localized operator partitioning method [Y. Khan and P. Brumer, J. Chem. Phys. 137, 194112 (2012)] rigorously defines the electronic energy on any subsystem within a molecule and gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. However, an efficient implementation of this approach has been hindered by complicated one- and two-electron integrals arising in its formulation. Using a resolution of the identity in the definition of partitioning we reformulate the method in a computationally e?cient manner that involves standard one- and two-electron integrals. We apply the developed algorithm to the 9-((1-naphthyl)-methyl)-anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH2-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 o...

  10. The ‘porin–cytochrome’ model for microbe-to-mineral electron transfer

    Energy Technology Data Exchange (ETDEWEB)

    Richardson, David J.; Butt, Julea N.; Fredrickson, Jim K.; Zachara, John M.; Shi, Liang; Edwards, Marcus J.; White, Gaye F.; Baiden, Nanakow; Gates, Andrew J.; Marritt, Sophie; Clarke, Thomas A.

    2012-05-30

    Many species of bacteria can couple anaerobic growth to the respiratory reduction of insoluble minerals containing Fe(III) or Mn(III/IV). It has been suggested that in Shewanella species electrons cross the outer membrane to extracellular substrates via 'porin-cytochrome' electron transport modules. The molecular structure of an outer-membrane extracellular-facing deca-haem terminus for such a module has recently been resolved. It is debated how, once outside the cells, electrons are transferred from outer-membrane cytochromes to insoluble electron sinks. This may occur directly or by assemblies of cytochromes, perhaps functioning as 'nanowires', or via electron shuttles. Here we review recent work in this field and explore whether it allows for unification of the electron transport mechanisms supporting extracellular mineral respiration in Shewanella that may extend into other genera of Gram-negative bacteria.

  11. Fast electron transfer through a single molecule natively structured redox protein

    Science.gov (United States)

    Della Pia, Eduardo Antonio; Chi, Qijin; MacDonald, J. Emyr; Ulstrup, Jens; Jones, D. Dafydd; Elliott, Martin

    2012-10-01

    The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b562 in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum-iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be `gated' through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b562 molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent.The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b562 in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum-iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be `gated' through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b562 molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent. Electronic supplementary information (ESI) available: Experimental methods, DNA and protein sequences, additional STM statistical analysis and images, electrochemical data and It-z data analysis. See DOI: 10.1039/c2nr32131a

  12. Transfer and reconstruction of the density matrix in off-axis electron holography

    International Nuclear Information System (INIS)

    The reduced density matrix completely describes the quantum state of an electron scattered by an object in transmission electron microscopy. However, the detection process restricts access to the diagonal elements only. The off-diagonal elements, determining the coherence of the scattered electron, may be obtained from electron holography. In order to extract the influence of the object from the off-diagonals, however, a rigorous consideration of the electron microscope influences like aberrations of the objective lens and the Möllenstedt biprism in the presence of partial coherence is required. Here, we derive a holographic transfer theory based on the generalization of the transmission cross-coefficient including all known holographic phenomena. We furthermore apply a particular simplification of the theory to the experimental analysis of aloof beam electrons scattered by plane silicon surfaces. - Highlights: • Density matrix transfer theory for off-axis electron holography is derived. • Generalizing the concept of the transmission-cross coefficient. • Conditions for direct density matrix reconstruction are found. • 2D-density matrix reconstruction for aloof beam electrons is conducted

  13. Rates, distances, and energy control of electron tunneling reactions in rigid media

    International Nuclear Information System (INIS)

    Electron tunneling leads to transfer of trapped positive, or negative charge tens of angstroms in rigid matrices. Franck-Condon effects give energy specificity to charge transfer and ion recombination, and adds sensitivity to molecular structure, solvation and H/D isotope effects. The specificity is important in photosynthesis and solar energy storage as well as in radiation chemistry. We feel that the question of hopping vs. tunneling is definitely settled in favor of tunneling for intermolecular electron transfer at low temperatures. Hopping cannot yet be conclusively ruled out in reactions of trapped electrons. Hopping is expected to become important in many media near room temperature

  14. Single-electron transfer living radical copolymerization of SWCNT-g-PMMA via graft from approach.

    Czech Academy of Sciences Publication Activity Database

    Jaisankar, S. N.; Haridharan, N.; Murali, A.; Ponyrko, Sergii; Špírková, Milena; Mandal, A. B.; Mat?jka, Libor

    2014-01-01

    Ro?. 55, ?. 13 (2014), s. 2959-2966. ISSN 0032-3861 R&D Projects: GA ?R GAP108/12/1459 Institutional support: RVO:61389013 Keywords : single electron transfer * single-walled carbon nanotubes * controlled radical polymerization Subject RIV: CD - Macromolecular Chemistry Impact factor: 3.562, year: 2014

  15. Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions

    Science.gov (United States)

    Silverstein, Todd P.

    2012-01-01

    Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

  16. Charge distribution effects in polyatomic reactants involved in simple electron transfer reactions.

    Czech Academy of Sciences Publication Activity Database

    Fawcett, W. R.; Chavis, G. J.; Hromadová, Magdaléna

    2008-01-01

    Ro?. 53, ?. 23 (2008), s. 6787-6792. ISSN 0013-4686 Institutional research plan: CEZ:AV0Z40400503 Keywords : electron transfer kinetics * charge distribution effects * double-layer effects in electrode kinetics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.078, year: 2008

  17. QUANTUM CHEMICAL MODELING OF SPECTRAL PROPERTIES AND ELECTRON TRANSFER IN EXTENDED SYSTEMS.

    Czech Academy of Sciences Publication Activity Database

    Záliš, Stanislav; Kvapilová, Hana; Kratochvílová, Irena; Šebera, Jakub; Vl?ek Jr., Antonín; Winter, R. F.

    2011-01-01

    Ro?. 2011, ?. 1 (2011), P1299. ISSN 1708-5284 R&D Projects: GA AV ?R KAN100400702; GA MŠk LD11086 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z10100520 Keywords : quantum chemical modeling * electron transfer Subject RIV: CF - Physical ; Theoretical Chemistry

  18. Direct electron transfer from photosystem II to hematite in a hybrid photoelectrochemical cell.

    Science.gov (United States)

    Wang, Wangyin; Wang, Zhiliang; Zhu, Qingjun; Han, Guangye; Ding, Chunmei; Chen, Jun; Shen, Jian-Ren; Li, Can

    2015-11-17

    A hybrid photoanode integrating the cyanobacterial photosystem II (PSII) with a hematite film for water oxidation is constructed. Direct electron transfer from PSII to the excited Ti/Fe2O3 electrode occurs under light irradiation, resulting in a significant improvement of the photocurrent. PMID:26443427

  19. Solution of the proton radius puzzle? Low momentum transfer electron scattering data are not enough

    CERN Document Server

    Distler, Michael O; Bernauer, Jan C

    2015-01-01

    In two recent papers it is argued that the 'proton radius puzzle' can be explained by truncating the electron scattering data to low momentum transfer and fit the rms radius in the low momentum expansion of the form factor. It is shown that this procedure is inconsistent and violates the Fourier theorem. The puzzle cannot be explained in this way.

  20. Coupling of heterogeneous and homogeneous electron transfer: Transition from stability to chaotic behavior.

    Czech Academy of Sciences Publication Activity Database

    Hromadová, Magdaléna; Pospíšil, Lubomír; Fanelli, N.; Gál, Miroslav; Kolivoška, Viliam; Valášek, M.

    2012-01-01

    Ro?. 2012, - (2012), s. 72. ISSN 0872-1904. [Iberic Meeting of Electrochemistry /14./ and Meeting of the Portuguese Electrochemical Society /17./. 11.04.2012-14.04.2012, Madeira Island] R&D Projects: GA ?R GA203/09/0705; GA AV ?R IAA400400802 Institutional research plan: CEZ:AV0Z40400503 Keywords : electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

  1. Electron transfer and dissociation mechanism of ferrioxalate: A time resolved optical and EXAFS study

    Science.gov (United States)

    Chen, Jie; Zhang, Hua; Tomov, Ivan V.; Ding, Xunliang; Rentzepis, Peter M.

    2007-03-01

    By means of ultrafast optical transient spectroscopy and EXAFS we have measured the transient spectra kinetics and Fe-O bond length of the ferrioxalate redox reaction transients. Based on Fe-O bond distances of the photoredox intermediates and quantum chemistry DFT and H-F calculations we propose a photoredox mechanism where photodissociation precedes electron transfer.

  2. Numerical Simulation for Heat Transfer in Liquid Cooling System of Electronic Components

    Directory of Open Access Journals (Sweden)

    Vadim A. Pomytkin

    2012-05-01

    Full Text Available In this study, the task of optimizing the thermal liquid cooling system distributor of electronic components by means of numerical simulation of heat transfer in the investigated object. This task allowed us to find the optimal geometric parameters of the thermal spreader.

  3. Proton transfer in phenol-amine complexes: phenol electronic effects on free energy profile in solution.

    Science.gov (United States)

    Aono, Shinji; Kato, Shigeki

    2010-12-01

    Free energy profiles for the proton transfer reactions in hydrogen-bonded complex of phenol with trimethylamine in methyl chloride solvent are studied with the reference interaction site model self-consistent field method. The reactions in both the electronic ground and excited states are considered. The second-order Møller-Plesset perturbation (MP) theory or the second-order multireference MP theory is used to evaluate the effect of the dynamical electron correlation on the free energy profiles. The free energy surface in the ground state shows a discrepancy with the experimental results for the related hydrogen-bonded complexes. To resolve this discrepancy, the effects of chloro-substitutions in phenol are examined, and its importance in stabilizing the ionic form is discussed. The temperature effect is also studied. In contrast to the ground state, the ??* excited state of phenol-trimethylamine complex exhibits the proton transfer reaction with a low barrier. The reaction is almost thermoneutral. This is attributed to the reduction of proton affinity of phenol by the ??* electronic excitation. We further examine the possibility of the electron-proton-coupled transfer in the ??* state through the surface crossing with the charge transfer type ??* state. PMID:20602442

  4. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    KAUST Repository

    Alsam, Amani A.

    2015-09-02

    We explored the excited-state interactions of bimolecular, non-covalent systems consisting of cationic poly[(9,9-di(3,3’-N,N’-trimethyl-ammonium) propyl fluorenyl-2,7-diyl)-alt-co-(9,9-dioctyl-fluorenyl-2,7-diyl)] diiodide salt (PFN) and 1,4-dicyanobenzene (DCB) using steady-state and time-resolved techniques, including femto- and nanosecond transient absorption and femtosecond infrared spectroscopies with broadband capabilities. The experimental results demonstrated that photo-induced electron transfer from PFN to DCB occurs on the picosecond time scale, leading to the formation of PFN+• and DCB-• radical ions. Interestingly, real-time observations of the vibrational marker modes on the acceptor side provided direct evidence and insight into the electron transfer process indirectly inferred from UV-Vis experiments. The band narrowing on the picosecond time scale observed on the antisymmetric C-N stretching vibration of the DCB radical anion provides clear experimental evidence that a substantial part of the excess energy is channeled into vibrational modes of the electron transfer product and that the geminate ion pairs dissociate. More importantly, our nanosecond time-resolved data indicate that the charge-separated state is very long lived (? 30 ns) due to the dissociation of the contact radical ion pair into free ions. Finally, the fast electron transfer and slow charge recombination anticipate the current donor?acceptor system with potential applications in organic solar cells.

  5. Bibliography on electron transfer processes in ion-ion/atom/molecule collisions (updated 1993)

    International Nuclear Information System (INIS)

    Following our previous compilations [IPPJ-AM-45 (1986), NIFS-DATA-7 (1990)], bibliographic information on experimental and theoretical studies on electron transfer processes in ion-ion/atom/molecule collisions is up-dated. The references published through 1980-1992 are included. For easy finding references for particular combination of collision partners, a simple list is also provided. (author) 1542 refs

  6. 27 CFR 24.272 - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ...to effect an electronic fund transfer message as required by paragraph (b) (2...part of the required records. (d) Failure to make a taxpayment by EFT. The proprietor...6651, and 6656, as applicable, for failure to make a taxpayment by EFT on or...

  7. 27 CFR 53.158 - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ...to effect an electronic fund transfer message as required by paragraph (b)(2...part of the required records. (d) Failure to make a taxpayment by EFT. The taxpayer...6651 and 6656, as applicable, for failure to make a payment or deposit of tax...

  8. 27 CFR 41.115a - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

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  9. 27 CFR 26.112a - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

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  10. 27 CFR 19.524 - Payment of tax by electronic fund transfer.

    Science.gov (United States)

    2010-04-01

    ...to effect an electronic fund transfer message as required by paragraph (b)(2...as part of required records. (d) Failure to make a taxpayment by EFT. The taxpayer...6651, or 6656, as applicable, for failure to make a taxpayment by EFT on or...

  11. Energy partitioning in single-electron transfer events between gaseous dications and their neutral counterparts.

    Czech Academy of Sciences Publication Activity Database

    Schröder, Detlef

    2012-01-01

    Ro?. 18, ?. 2 (2012), s. 139-148. ISSN 1469-0667 R&D Projects: GA ?R GA203/09/1223 Institutional research plan: CEZ:AV0Z40550506 Keywords : coincidence techniques * dications * electron transfer * energy partitioning * synchrotron radiation Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.259, year: 2012

  12. Electron transfer reaction in the Marcus inverted region: Role of high frequency vibrational modes

    International Nuclear Information System (INIS)

    A theoretical study of the dynamics of photo-electron transfer reactions in the Marcus inverted regime is presented. This study is motivated partly by the recent proposal of Barbara et al. (J. Phys. Chem. 96, 3728, 1991) that a minimal model of an electron transfer reaction should consist of a polar solvent mode (X), a low frequency vibrational mode (Q) and one high frequency mode (q). Interplay between these modes may be responsible for the crossover observed in the dynamics from a solvent controlled to a vibrational controlled electron transfer. The following results have been obtained. (i) In the case of slowly relaxing solvents, the proximity of the point of excitation to an effective sink on the excited surface is critical in determining the decay of the reactant population. This is because the Franck-Condon overlap between the reactant ground and the product excited states decreases rapidly with increase in the quantum number of the product vibrational state. (ii) Non-exponential solvation dynamics has an important effect in determining the rates of electron transfer. Especially, a biphasic solvation and a large coupling between the reactant and the product states both may be needed to explain the experimental results

  13. Single step versus stepwise electron transfer in head-to-tail dipyridinium isomers.

    Czech Academy of Sciences Publication Activity Database

    Hromadová, Magdaléna; Lachmanová, Št?pánka; Pospíšil, Lubomír; Tarábek, Ján; Fortage, J.; Dupeyre, G.; Lainé, P. P.; Peltier, C.; Ciofini, I.

    Liblice : International Society of Electrochemistry, 2013. s. o12. [International Conference on Electrified Interfaces ICEI 2013 /13./.. 30.06.2013-05.07.2013, Liblice] R&D Projects: GA ?R GA203/09/0705; GA AV ?R M200401202 Institutional support: RVO:61388955 ; RVO:61388963 Keywords : electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

  14. Single Step versus Stepwise Electron Transfer in Expanded Pyridiniums, Kinetic Aspects.

    Czech Academy of Sciences Publication Activity Database

    Hromadová, Magdaléna; Lachmanová, Št?pánka; Pospíšil, Lubomír; Tarábek, Ján; Fortage, J.; Dupeyre, G.; Lainé, P. P.; Peltier, C.; Ciofini, I.

    Paris : University of Paris, 2013. s. 72-72. [ElecNano5: The Nanoscale and Electroanalysis: Surface Nanostructuration, Nanobiological Systems, Coupled Techniques, Microsystems. 15.05.2013-17.05.2013, Bordeaux] R&D Projects: GA ?R GA203/09/0705 Institutional support: RVO:61388955 ; RVO:61388963 Keywords : electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

  15. The Fate of Electronically Excited States : Ultrafast Electron and Energy Transfer in Solvated Donor-Acceptor Systems

    OpenAIRE

    Wallin, Staffan

    2005-01-01

    Processes where a molecule absorbs visible light and then disposes of the excess energy via electron/energy transfer reactions have an important role both in nature (e.g. in photosynthesis) and in many technical applications (e.g. in photography and photovoltaics). This thesis uses different spectroscopical techniques, mainly ultrafast transient absorption, to study such processes. The thesis can roughly be divided into three parts. In the first part, donor-acceptor systems linked by differen...

  16. Electron transfer and ionization in collisions of highly stripped ions with neutral targets at intermediate velocities

    International Nuclear Information System (INIS)

    A highly-charged ion impinging upon a neutral target atom will capture electrons into excited states of the projectile. If the velocity is much less than that of the target electrons, little direct ionization is expected, although appreciable target ionization has been reported for very highly charged ions. Recent studies on both transfer and ionization for Arq+ (6?q?17) and O+8,7 on Ar and He target shave been performed for projectile velocities between 0.2 and 1.7 a.u. The measured quantities include charge-state-correlated differential cross sections, K-x-ray emission, and longitudinal recoil- ion momentum transfer, from which Q values can be deduced. Non-negligible direct ionization is observed. Information is extracted on both the primary transfer process and the decay of the multiply excited projectile states formed. Comparisons with model predictions will be made

  17. Electronic Couplings for Resonance Energy Transfer from CCSD Calculations: From Isolated to Solvated Systems.

    Science.gov (United States)

    Caricato, Marco; Curutchet, Carles; Mennucci, Benedetta; Scalmani, Giovanni

    2015-11-10

    Quantum mechanical (QM) calculations of electronic couplings provide great insights for the study of resonance energy transfer (RET). However, most of these calculations rely on approximate QM methods due to the computational limitations imposed by the size of typical donor-acceptor systems. In this work, we present a novel implementation that allows computing electronic couplings at the coupled cluster singles and doubles (CCSD) level of theory. Solvent effects are also taken into account through the polarizable continuum model (PCM). As a test case, we use a dimer of indole, a common model system for tryptophan, which is routinely used as an intrinsic fluorophore in Förster resonance energy transfer studies. We consider two bright ? ? ?* states, one of which has charge transfer character. Lastly, the results are compared with those obtained by applying TD-DFT in combination with one of the most popular density functionals, B3LYP. PMID:26574317

  18. Quantum molecular dynamics study on energy transfer to the secondary electron in surface collision process of an ion

    Energy Technology Data Exchange (ETDEWEB)

    Shibahara, M [Department of Mechanical Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Satake, S; Taniguchi, J [Department of Applied Electronics, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510 (Japan)], E-mail: siba@mech.eng.osaka-u.ac.jp

    2008-03-15

    In the present study the quantum molecular dynamics method was applied to an energy transfer problem to an electron during ionic surface collision process in order to elucidate how energy of ionic collision transfers to the emitted electrons. Effects of various physical parameters, such as the collision velocity and interaction strength between the observed electron and the classical particles on the energy transfer to the electron were investigated by the quantum molecular dynamics method when the potassium ion was collided with the surface so as to elucidate the energy path to the electron and the predominant factor of energy transfer to the electron. Effects of potential energy between the ion and the electron and that between the surface molecule and the electron on the electronic energy transfer were shown in the present paper. The energy transfer to the observed secondary electron through the potential energy term between the ion and the electron was much dependent on the ion collision energy although the energy increase to the observed secondary electron was not monotonous through the potential energy between the ion and surface molecules with the change of the ion collision energy.

  19. Quantum molecular dynamics study on energy transfer to the secondary electron in surface collision process of an ion

    International Nuclear Information System (INIS)

    In the present study the quantum molecular dynamics method was applied to an energy transfer problem to an electron during ionic surface collision process in order to elucidate how energy of ionic collision transfers to the emitted electrons. Effects of various physical parameters, such as the collision velocity and interaction strength between the observed electron and the classical particles on the energy transfer to the electron were investigated by the quantum molecular dynamics method when the potassium ion was collided with the surface so as to elucidate the energy path to the electron and the predominant factor of energy transfer to the electron. Effects of potential energy between the ion and the electron and that between the surface molecule and the electron on the electronic energy transfer were shown in the present paper. The energy transfer to the observed secondary electron through the potential energy term between the ion and the electron was much dependent on the ion collision energy although the energy increase to the observed secondary electron was not monotonous through the potential energy between the ion and surface molecules with the change of the ion collision energy

  20. Modeling intermolecular interactions of physisorbed organic molecules using pair potential calculations

    International Nuclear Information System (INIS)

    The understanding and control of epitaxial growth of organic thin films is of crucial importance in order to optimize the performance of future electronic devices. In particular, the start of the submonolayer growth plays an important role since it often determines the structure of the first layer and subsequently of the entire molecular film. We have investigated the structure formation of 3,4,9,10-perylene-tetracarboxylic dianhydride and copper-phthalocyanine molecules on Au(111) using pair-potential calculations based on van der Waals and electrostatic intermolecular interactions. The results are compared with the fundamental lateral structures known from experiment and an excellent agreement was found for these weakly interacting systems. Furthermore, the calculations are even suitable for chemisorptive adsorption as demonstrated for copper-phthalocyanine/Cu(111), if the influence of charge transfer between substrate and molecules is known and the corresponding charge redistribution in the molecules can be estimated. The calculations are of general applicability for molecular adsorbate systems which are dominated by electrostatic and van der Waals interaction.

  1. Constraint-Based Modeling of Carbon Fixation and the Energetics of Electron Transfer in Geobacter metallireducens

    Energy Technology Data Exchange (ETDEWEB)

    Feist, AM; Nagarajan, H; Rotaru, AE; Tremblay, PL; Zhang, T; Nevin, KP; Lovley, DR; Zengler, K

    2014-04-24

    Geobacter species are of great interest for environmental and biotechnology applications as they can carry out direct electron transfer to insoluble metals or other microorganisms and have the ability to assimilate inorganic carbon. Here, we report on the capability and key enabling metabolic machinery of Geobacter metallireducens GS-15 to carry out CO2 fixation and direct electron transfer to iron. An updated metabolic reconstruction was generated, growth screens on targeted conditions of interest were performed, and constraint-based analysis was utilized to characterize and evaluate critical pathways and reactions in G. metallireducens. The novel capability of G. metallireducens to grow autotrophically with formate and Fe(III) was predicted and subsequently validated in vivo. Additionally, the energetic cost of transferring electrons to an external electron acceptor was determined through analysis of growth experiments carried out using three different electron acceptors (Fe(III), nitrate, and fumarate) by systematically isolating and examining different parts of the electron transport chain. The updated reconstruction will serve as a knowledgebase for understanding and engineering Geobacter and similar species. Author Summary The ability of microorganisms to exchange electrons directly with their environment has large implications for our knowledge of industrial and environmental processes. For decades, it has been known that microbes can use electrodes as electron acceptors in microbial fuel cell settings. Geobacter metallireducens has been one of the model organisms for characterizing microbe-electrode interactions as well as environmental processes such as bioremediation. Here, we significantly expand the knowledge of metabolism and energetics of this model organism by employing constraint-based metabolic modeling. Through this analysis, we build the metabolic pathways necessary for carbon fixation, a desirable property for industrial chemical production. We further discover a novel growth condition which enables the characterization of autotrophic (i.e., carbon-fixing) metabolism in Geobacter. Importantly, our systems-level modeling approach helped elucidate the key metabolic pathways and the energetic cost associated with extracellular electron transfer. This model can be applied to characterize and engineer the metabolism and electron transfer capabilities of Geobacter for biotechnological applications.

  2. 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. PMID:16486988

  3. Regulation of electron transfer processes affects phototrophic mat structure and activity.

    Science.gov (United States)

    Ha, Phuc T; Renslow, Ryan S; Atci, Erhan; Reardon, Patrick N; Lindemann, Stephen R; Fredrickson, James K; Call, Douglas R; Beyenal, Haluk

    2015-01-01

    Phototrophic microbial mats are among the most diverse ecosystems in nature. These systems undergo daily cycles in redox potential caused by variations in light energy input and metabolic interactions among the microbial species. In this work, solid electrodes with controlled potentials were placed under mats to study the electron transfer processes between the electrode and the microbial mat. The phototrophic microbial mat was harvested from Hot Lake, a hypersaline, epsomitic lake located near Oroville (Washington, USA). We operated two reactors: graphite electrodes were polarized at potentials of -700 mVAg/AgCl [cathodic (CAT) mat system] and +300 mVAg/AgCl [anodic (AN) mat system] and the electron transfer rates between the electrode and mat were monitored. We observed a diel cycle of electron transfer rates for both AN and CAT mat systems. Interestingly, the CAT mats generated the highest reducing current at the same time points that the AN mats showed the highest oxidizing current. To characterize the physicochemical factors influencing electron transfer processes, we measured depth profiles of dissolved oxygen (DO) and sulfide in the mats using microelectrodes. We further demonstrated that the mat-to-electrode and electrode-to-mat electron transfer rates were light- and temperature-dependent. Using nuclear magnetic resonance (NMR) imaging, we determined that the electrode potential regulated the diffusivity and porosity of the microbial mats. Both porosity and diffusivity were higher in the CAT mats than in the AN mats. We also used NMR spectroscopy for high-resolution quantitative metabolite analysis and found that the CAT mats had significantly higher concentrations of osmoprotectants such as betaine and trehalose. Subsequently, we performed amplicon sequencing across the V4 region of the 16S rRNA gene of incubated mats to understand the impact of electrode potential on microbial community structure. These data suggested that variation in the electrochemical conditions under which mats were generated significantly impacted the relative abundances of mat members and mat metabolism. PMID:26388853

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

    DEFF Research Database (Denmark)

    Gilbert, Benjamin; Katz, Jordan E.

    2013-01-01

    An emerging area in chemical science is the study of solid-phase redox reactions using ultrafast time-resolved spectroscopy. We have used molecules of the photoactive dye 2?,7?-dichlorofluorescein (DCF) anchored to the surface of iron(iii) oxide nanoparticles to create iron(ii) surface atoms via 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. We addressed this topic by performing femtosecond transient absorption (TA) measurements of aqueous suspensions of uncoated and DCF-sensitized iron oxide and oxyhydroxide nanoparticles, and an aqueous iron(iii)–dye complex. Following light absorption, excited state relaxation times of the dye of 115–310 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 is energetically forbidden) even though the acceptor states are different. Comparison of the alignment of the excited states of the dye and the unoccupied states of these oxides showed that the dye injects into acceptor states of different symmetry (Ti t2g vs. Fe eg).

  5. Intramolecular electron transfer in ruthenium-modified cytochrome C: Driving force effects

    International Nuclear Information System (INIS)

    The measurement of intramolecular electron transfer rates in several cis- and trans- tetraammine(L)-ruthenium-His33-modified horse heart cytochromes c (L = isonicotinamide, pyridine, N-methylpyrazinium, and H2O/OH) is reported herein. Activation parameters have also been obtained for L = isonicotinamide and pyridine. Only modest rate increases are observed for large changes in driving force (from L = pyridine to N-methylpyrazinium). The heme-to-ruthenium electron transfer rates for L = isonicotinamide, pyridine, and N-methylpyrazinium were measured by oxidation of the fully reduced complexes by radiolytically-generated carbonate (CO3-) radical. From previously reported work and these results, it is clear that the oxidative and reductive methods do not result in production of the same electron transfer intermediate. Possible reasons for this will be discussed. It is important to consider the effects of the local protein environment on the properties of the ruthenium center. There is a general effect of moderation of reduction potentials; that is to say that protein-bound high-potential complexes have lower reduction potentials than their small molecule models. The reverse holds for the low potential complexes. This effect can be a significant source of error in driving force estimates based on model complexes. Identification of the operative electron transfer mechanism remains an unsolved problem. Efforts will be made to increase the driving force further (within the constraints of the heme-ruthenium system) to determine the applicable reorganization parameters. Interpretation will be aided by parallel investigations into the effects of protein conformation and the distance dependences of through-bond and through-space electron transfer mechanisms

  6. Study of photo-activated electron transfer reactions in the first excited singlet state by picosecond and nanosecond laser spectroscopy

    International Nuclear Information System (INIS)

    Picosecond laser spectroscopy has been used to study two photo-activated electron transfer reactions: - a bimolecular electron transfer reaction between a sensitizer, DODCI, and an electron acceptor, methylviologen. The two radical ions created with an electron transfer efficiency ? ? 0.07 have been identified in picosecond and nanosecond laser absorption spectroscopy by adding selective solutes such as para-benzoquinone (an electron acceptor) or L(+) ascorbic acid (an electron donor). - an intramolecular electron transfer reaction in a triad molecule consisting of a tetra-aryl-porphyrin covalently linked to both a carotenoid and a quinone. The photoinduced charge separation occurs within 30 ps and leads, with a yield of 25 pc, to the formation of a zwitterion whose half-life is 2.5 ?s. The experimental results obtained in these two studies show an effective decrease in the recombination rate of the two radical ions created in the encounter pair. (author)

  7. Colloidal silver catalyzed multi-electron transfer processes in aqueous solution

    International Nuclear Information System (INIS)

    (CH3)2COH radicals were ?-radiolytically produced in aqueous solutions of colloidal silver(2.5 x 10-4 mol/l, acetone(0.1 - 0.2 M)) and propanol-2(0.2-0.4). The radicals were able to reduce Cd2, N2O and NO3- with yields of practically 100%. In the absence of colloidal silver, Cd2+ was not reduced, but N2O or NONO-3 were reduced with yields of the order of 1%. The reduction processes in the presence of silver occurred in competition with the reduction of water by the organic radicals. The catalytic action of colloidal silver is explained by electron transfer from the organic radicals to the silver praticles that become a pool of electrons and adsorbed hydrogen atoms. The stored electrons are then used to carry out the reduction of water or of dissolved substances. Relative rate constants for a number of multi-electron transfer processes at the colloidal silver pool are given and details of the reaction mechanism including the action of adsorbed H3 - atoms are discussed. - Radiolytically produced Cd+ ions were also reduced at the colloidal silver pool. However, Zn+, Ni+, and Co+ were found to transfer an electron to the pool. The homogeneous reaction between NONO-3 and (CH3)2COH was also investigated. A rate constant of 28 M-1s-1 was found for this reaction. (orig.)

  8. Electron Transport, Energy Transfer, and Optical Response in Single Molecule Junctions

    Science.gov (United States)

    White, Alexander

    2015-03-01

    The field of molecular electronics has grown significantly since the first measurements of single molecule conductance. The single molecule junction, a device in which two conducting leads are spanned by a single molecule, has become a powerful tool for studying charge transfer at the molecular level. While early experiments were focused on elastic electron conductance, today measurements of vibronic effects, molecular optical response, spintronics, thermal conductance, and quantum interference and decoherence effects are prominent areas of research. These new experimental advancements demand improved theoretical treatments which properly account for the interactions between different degrees of freedom: charge, electronic, vibrational, spin, etc.; all in physically relevant parameter ranges. This talk focuses on using a many-body states based approach to investigate the regime of strong interaction between these degrees of freedom, with relatively weak coupling between the molecule and the electric reservoirs created by the conducting leads. We focused on three related processes, electron transfer, electronic energy transfer and molecular excitation. In collaboraton with Boris Fainberg, Faculty of Sciences, Holon Institute of Technology; Sergei Tretiak, Theoretical Division, Center for Integrated Nanotechnologies, Los Alamos National Laboratory; and Michael Galperin, Department of Chemistry and Biochemistry, University of California San Diego.

  9. Influence of chemical and structural evolution of dissolved organic matter on electron transfer capacity during composting

    International Nuclear Information System (INIS)

    Highlights: • Electron transfer capability (ETC) of compost-derived DOM was investigated. • Composting treatment increased the ETC of DOM from municipal solid wastes. • The ETC increase related to humic matter, and molecule weight, and N and S content. - Abstract: Dissolved organic matter (DOM) can mediate electron transfer and change chemical speciation of heavy metals. In this study, the electron transfer capability (ETC) of compost-derived DOM was investigated through electrochemical approaches, and the factors influencing the ETC were studied using spectral and elemental analysis. The results showed that the electron accepting capacity (EAC) and electron donating capacity (EDC) of compost-derived DOM were 3.29–40.14 ?mole? (g C)?1 and 57.1– 346.07 ?mole? (g C)?1, respectively. Composting treatment increased the fulvic- and humic-like substance content, oxygenated aliphatic carbon content, lignin-derived aromatic carbon content, molecule weight, and N and S content of DOM, but decreased the aliphatic carbon content and the C and H content. This conversion increased the EDC and EAC of the DOM during composting

  10. Distance, stereoelectronic effects, and the Marcus inverted region in intramolecular electron transfer in organic radical anions

    International Nuclear Information System (INIS)

    A series of molecules with the general structure A1-Sp-A2 have been synthesized. Pulse radiolysis was used to convert them into negative ions, and the rates of intramolecular electron transfer were measured. In the first series studied Sp is the androstane skeleton with the acceptors attached to the 3- and 16-positions. The series consisted of eight molecules with A2 = 4-biphenyl and eight different A1 groups differing in electron affinity by 2.4 eV. The electron transfer rates differ by more than 3 orders of magnitude throughout the series and depend in a very nonlinear fashion on the free energy of the reaction. The second series of molecules was designed to study the effect of the spacer which was varied from the steroid to decalins (eight compounds) and cyclohexanes (four compounds). No comprehensive distance dependence exists. Instead, the rates are strongly influenced by the donor-acceptor attachment geometry which influences the electronic coupling. For the type of spacers studied it was found that the electron transfer rates are slowed down by 1 order of magnitude for each 2.0 bonds for a constant reorganization energy

  11. Probing and Exploiting the Interplay between Nuclear and Electronic Motion in Charge Transfer Processes.

    Science.gov (United States)

    Delor, Milan; Sazanovich, Igor V; Towrie, Michael; Weinstein, Julia A

    2015-04-21

    The Born-Oppenheimer approximation refers to the assumption that the nuclear and electronic wave functions describing a molecular system evolve and can be determined independently. It is now well-known that this approximation often breaks down and that nuclear-electronic (vibronic) coupling contributes greatly to the ultrafast photophysics and photochemistry observed in many systems ranging from simple molecules to biological organisms. In order to probe vibronic coupling in a time-dependent manner, one must use spectroscopic tools capable of correlating the motions of electrons and nuclei on an ultrafast time scale. Recent developments in nonlinear multidimensional electronic and vibrational spectroscopies allow monitoring both electronic and structural factors with unprecedented time and spatial resolution. In this Account, we present recent studies from our group that make use of different variants of frequency-domain transient two-dimensional infrared (T-2DIR) spectroscopy, a pulse sequence combining electronic and vibrational excitations in the form of a UV-visible pump, a narrowband (12 cm(-1)) IR pump, and a broadband (400 cm(-1)) IR probe. In the first example, T-2DIR is used to directly compare vibrational dynamics in the ground and relaxed electronic excited states of Re(Cl)(CO)3(4,4'-diethylester-2,2'-bipyridine) and Ru(4,4'-diethylester-2,2'-bipyridine)2(NCS)2, prototypical charge transfer complexes used in photocatalytic CO2 reduction and electron injection in dye-sensitized solar cells. The experiments show that intramolecular vibrational redistribution (IVR) and vibrational energy transfer (VET) are up to an order of magnitude faster in the triplet charge transfer excited state than in the ground state. These results show the influence of electronic arrangement on vibrational coupling patterns, with direct implications for vibronic coupling mechanisms in charge transfer excited states. In the second example, we show unambiguously that electronic and vibrational movement are coupled in a donor-bridge-acceptor complex based on a Pt(II) trans-acetylide design motif. Time-resolved IR (TRIR) spectroscopy reveals that the rate of electron transfer (ET) is highly dependent on the amount of excess energy localized on the bridge following electronic excitation. Using an adaptation of T-2DIR, we are able to selectively perturb bridge-localized vibrational modes during charge separation, resulting in the donor-acceptor charge separation pathway being completely switched off, with all excess energy redirected toward the formation of a long-lived intraligand triplet state. A series of control experiments reveal that this effect is mode specific: it is only when the high-frequency bridging C?C stretching mode is pumped that radical changes in photoproduct yields are observed. These experiments therefore suggest that one may perturb electronic movement by stimulating structural motion along the reaction coordinate using IR light. These studies add to a growing body of evidence suggesting that controlling the pathways and efficiency of charge transfer may be achieved through synthetic and perturbative approaches aiming to modulate vibronic coupling. Achieving such control would represent a breakthrough for charge transfer-based applications such as solar energy conversion and molecular electronics. PMID:25789559

  12. Molecular control of electron and hole transfer processes: Theory and applications

    Energy Technology Data Exchange (ETDEWEB)

    Newton, M.D. [Brookhaven National Lab., Upton, NY (United States). Dept. of Chemistry; Cave, R.J. [Harvey Mudd Coll., Claremont, CA (United States). Dept. of Chemistry

    1996-02-01

    Recent decades have seen remarkable advances in microscopic understanding of electron transfer (ET) processes in widely ranging contexts, including solid-state, liquid solution, and complex biological assemblies. The primary goal of this chapter is to report recent advances in the modeling, calculation, and analysis of electronic coupling in complex molecular aggregates, thereby allowing an assessment of current progress toward the goal of molecular-level control and design. The control of electron transfer kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, system energetics (especially activation and reorganization energies) as well as electronic coupling, which is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate. Nevertheless, to focus the discussion in this chapter, the authors will consider such energetics, and the associated molecular and solvent coordinates which control then, only to the extent that they bear on the analysis of the electronic coupling. In the following sections they first discuss the formulation of basic ET models, including the definition of initial and final states, the role of orbitals and 1-particle models in a many-electron context, the utility of various effective Hamiltonians, and the role of vibronic as well as purely electronic effects. With these theoretical tools in hand, they then examine very recent applications to complex molecular systems using the techniques of computational quantum chemistry, followed by detailed analysis of the numerical results. They then conclude with some comments regarding the current ``state of the art`` and remaining challenges.

  13. Investigation of liquid-liquid interfacial electron transfer kinetics using multicenter ferrocenyl complexes

    Energy Technology Data Exchange (ETDEWEB)

    Xiang Debo [Department of Chemistry, Faculty of Science, Beijing Institute of Technology, Beijing 100081 (China); Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Merbouh, Nabyl [Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Shao Huibo [Department of Chemistry, Faculty of Science, Beijing Institute of Technology, Beijing 100081 (China); Yu Huazhong, E-mail: hogan_yu@sfu.ca [Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada)

    2011-06-30

    The redox behavior of two novel multicenter redox molecules (triferrocenylmethane and triferrocenylmethanol) has been studied in a thin film of nitrobenzene (NB) imposed between a graphite electrode and an aqueous electrolyte. The well separated three sets of redox peaks indicate strong intramolecular electronic communications between the three ferrocene centers in each molecule. They were adapted as model compounds for the study of electron transfer kinetics across the liquid/liquid interface with varied overall driving force using only one-type redox couples in the organic and aqueous phase, respectively. It has been shown that in both cases the dependence of interfacial electron transfer rate on the increased overall driving force across the nitrobenzene/water interface is not monotonic.

  14. Miniaturized biofuel cell based on direct electron transfer of fructose dehydrogenase and bilirubin oxidase

    International Nuclear Information System (INIS)

    One of the objectives during designing of enzymatic biofuel cells is to avoid using of electron mediators - substances, which mediate electron transfer between the electrode surface and the active centers of enzymes. During this configuration it is not necessary to separate the cathodic and anodic space by membrane, what facilitates the transport of protons from the anode to the cathode while allowing miniaturization of the entire facility effectively. This work presents a biofuel cell based on direct electron transfer of fructose dehydrogenase and bilirubin oxidase immobilized on an electrode modified by gold nanoparticles. The device showed a maximum power of 27.4 mW · cm-2 at 0.3 V and the value of the potential (without flowing current) 746 mV. Then for this cell an increase of the maximum performance during operation in a reduced volume of electrolyte was detected in accordance with the expected facilitated metabolism and cartridge diffusion. (authors)

  15. Nitrogen doped carbon nanoparticles enhanced extracellular electron transfer for high-performance microbial fuel cells anode.

    Science.gov (United States)

    Yu, Yang-Yang; Guo, Chun Xian; Yong, Yang-Chun; Li, Chang Ming; Song, Hao

    2015-12-01

    Nitrogen doped carbon nanoparticles (NDCN) were applied to modify the carbon cloth anodes of microbial fuel cells (MFCs) inoculated with Shewanella oneidensis MR-1, one of the most well-studied exoelectrogens. Experimental results demonstrated that the use of NDCN increased anodic absorption of flavins (i.e., the soluble electron mediator secreted by S. oneidensis MR-1), facilitating shuttle-mediated extracellular electron transfer. In addition, we also found that NDCN enabled enhanced contact-based direct electron transfer via outer-membrane c-type cytochromes. Taken together, the performance of MFCs with the NDCN-modified anode was enormously enhanced, delivering a maximum power density 3.5 times' higher than that of the MFCs without the modification of carbon cloth anodes. PMID:25439129

  16. Electron and Hydrogen Atom Transfers in the Hydride Carrier Protein EmoB.

    Science.gov (United States)

    Gillet, Natacha; Lévy, Bernard; Moliner, Vicent; Demachy, Isabelle; de la Lande, Aurélien

    2014-11-11

    In this article, we investigate the mechanism of hydride transfer taking place within the EmoB protein of the Mesorhizobium species. The reaction involves the net transfer of one proton and two electrons from a reduced flavin mononucleotide (FMN) cofactor, which is anchored in the protein scaffold, to a diffusible oxidized FMN cofactor, both being held together by ?-stacking interactions. To analyze the formal hydride transfer in terms of more elementary steps, electron transfer (ET), and hydrogen atom transfers (HAT), we employ a combination of classical molecular dynamics simulations and hybrid constrained Density Functional Theory/Molecular Mechanics (cDFT/MM) energy calculations to build the free energy profiles, for the ET before and after HAT occurs between the flavins. The main outcomes of our study are first to highlight the role of the protein in stabilizing the ?-stacked FMN dimer and second to reveal the coupling between the ET and HAT. Before HAT has taken place, ET is unfavorable by 8 kcal/mol and become favorable by 8 kcal/mol after HAT. Our simulations show that such a coupling is not present for the analogous process in water (ET is almost athermal). This suggests a functional role for the protein matrix to ensure EmoB a role of hydride carrier in the Mesorhizobium species. PMID:26584385

  17. Photoinduced electron transfer in some photosensitive molecules-incorporated semiconductor/zeolites: New photocatalytic systems

    Indian Academy of Sciences (India)

    Minjoong Yoon; Devendra P S Negi

    2002-12-01

    An intramolecular charge transfer (ICT) molecule, -N,N-dimethylaminobenzoic acid (DMABA) has been studied in zeolite and colloidal media. The ratio of ICT to normal emission (ICT/LE) is greatly enhanced in zeolites compared to that in polar solvents. The ICT emission of DMABA was quenched by increasing the concentration of TiO2 colloids, while the normal emission was slightly enhanced. Upon illumination of the heteropoly acid (HPA) incorporated TiO2 colloids, interfacial electron transfer takes place from the conduction band of TiO2 to the incorporated HPA which is also excited to catalyze the photoreduction of Methyl Orange. It is found that the interfacial electron transfer mechanism of HPA/TiO2 is quite analogous to the Z-scheme mechanism for plant photosynthetic systems. In DMABA-adsorbed TiO2/Y-zeolite the ICT/LE ratio of DMABA is quite small implying that electron transfer takes place from DMABA to the conduction band of TiO2. This results in drastic enhancement in the photocatalytic activity of DMABA-adsorbed TiO2/Y-zeolite compared to free TiO2/Y-zeolite.

  18. An application protocol for CAD to CAD transfer of electronic information

    Science.gov (United States)

    Azu, Charles C., Jr.

    1993-01-01

    The exchange of Computer Aided Design (CAD) information between dissimilar CAD systems is a problem. This is especially true for transferring electronics CAD information such as multi-chip module (MCM), hybrid microcircuit assembly (HMA), and printed circuit board (PCB) designs. Currently, there exists several neutral data formats for transferring electronics CAD information. These include IGES, EDIF, and DXF formats. All these formats have limitations for use in exchanging electronic data. In an attempt to overcome these limitations, the Navy's MicroCIM program implemented a project to transfer hybrid microcircuit design information between dissimilar CAD systems. The IGES (Initial Graphics Exchange Specification) format is used since it is well established within the CAD industry. The goal of the project is to have a complete transfer of microelectronic CAD information, using IGES, without any data loss. An Application Protocol (AP) is being developed to specify how hybrid microcircuit CAD information will be represented by IGES entity constructs. The AP defines which IGES data items are appropriate for describing HMA geometry, connectivity, and processing as well as HMA material characteristics.

  19. Electronic Coupling between Heme Electron-Transfer Centers and Its Decay with Distance Depends Strongly on Relative Orientation

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Dayle MA; Rosso, Kevin M.; Dupuis, Michel; Valiev, Marat; Straatsma, TP

    2006-08-10

    A method for calculating the electron-transfer matrix element VRP using density functional theory Kohn-Sham orbitals is presented and applied to heme dimers of varying relative orientation. The electronic coupling decays with increased iron separation according to VRP ) V0RP exp(-?r/2) with a distance dependence parameter ? ? 2 Å-1 for hemes with parallel porphyrins and either 1.1 or 4.0 Å-1 when the porphyrin planes are perpendicular, depending on the alignment of the iron d? orbital. These findings are used to interpret the observed orientation of the hemes in tetraheme redox proteins such as Flavocytochrome c3 fumarate reductase (Ifc3, PDB code 1QJD) of Shewanella frigidimarina, another flavocytochrome from the same bacterium (Fcc3, 1E39) and a small tetraheme cytochrome of Shewanella oneidensis strain MR1 (1M1P). Our results show that shifting and rotating the hemes controls the adiabaticity of the three electron hopping steps.

  20. Large work function difference driven electron transfer from electrides to single-walled carbon nanotubes

    Science.gov (United States)

    Menamparambath, Mini Mol; Park, Jong-Ho; Yoo, Ho-Sung; Patole, Shashikant P.; Yoo, Ji-Beom; Kim, Sung Wng; Baik, Seunghyun

    2014-07-01

    A difference in work function plays a key role in charge transfer between two materials. Inorganic electrides provide a unique opportunity for electron transfer since interstitial anionic electrons result in a very low work function of 2.4-2.6 eV. Here we investigated charge transfer between two different types of electrides, [Ca2N]+.e- and [Ca24Al28O64]4+.4e-, and single-walled carbon nanotubes (SWNTs) with a work function of 4.73-5.05 eV. [Ca2N]+.e- with open 2-dimensional electron layers was more effective in donating electrons to SWNTs than closed cage structured [Ca24Al28O64]4+.4e- due to the higher electron concentration (1.3 × 1022 cm-3) and mobility (~200 cm2 V-1 s-1 at RT). A non-covalent conjugation enhanced near-infrared fluorescence of SWNTs as high as 52%. The field emission current density of electride-SWNT-silver paste dramatically increased by a factor of 46 000 (14.8 mA cm-2) at 2 V ?m-1 (3.5 wt% [Ca2N]+.e-) with a turn-on voltage of 0.85 V ?m-1.A difference in work function plays a key role in charge transfer between two materials. Inorganic electrides provide a unique opportunity for electron transfer since interstitial anionic electrons result in a very low work function of 2.4-2.6 eV. Here we investigated charge transfer between two different types of electrides, [Ca2N]+.e- and [Ca24Al28O64]4+.4e-, and single-walled carbon nanotubes (SWNTs) with a work function of 4.73-5.05 eV. [Ca2N]+.e- with open 2-dimensional electron layers was more effective in donating electrons to SWNTs than closed cage structured [Ca24Al28O64]4+.4e- due to the higher electron concentration (1.3 × 1022 cm-3) and mobility (~200 cm2 V-1 s-1 at RT). A non-covalent conjugation enhanced near-infrared fluorescence of SWNTs as high as 52%. The field emission current density of electride-SWNT-silver paste dramatically increased by a factor of 46 000 (14.8 mA cm-2) at 2 V ?m-1 (3.5 wt% [Ca2N]+.e-) with a turn-on voltage of 0.85 V ?m-1. Electronic supplementary information (ESI) available: The acronyms of base materials and synthesized specimens, field emission characteristics of PSWNT-Ag paste and HSWNT-Ag paste, additional XPS and Raman data, estimation of transferred electrons from electrides to nanotubes, optical images of C12A7:e--HSWNT films, a SEM image of the tape-activated PSWNT-Ag paste, and comparison of field emission properties. See DOI: 10.1039/c4nr01629g

  1. Positronium Inhibition and Quenching by Organic Electron Acceptors and Charge Transfer Complexes

    DEFF Research Database (Denmark)

    Jansen, P.; Eldrup, Morten Mostgaard; Jensen, Bror Skytte; Mogensen, O. E.

    1975-01-01

    Positron lifetime measurements were performed on a series of organic electron acceptors and charge-transfer complexes in solution. The acceptors cause both positronium (Ps) inhibition (with maybe one exception) and quenching, but when an acceptor takes part in a charge-transfer complex the inhibition intensifies and the quenching almost vanishes. The reaction constants between ortho-Ps and the acceptors were determinded to be: 1.5 × 1010 M?1 s?1 for SO2 in dioxane 3.7 × 1010 M?1 s?1 for SO2 in n...

  2. Potential for direct interspecies electron transfer in methanogenic wastewater digester aggregates

    DEFF Research Database (Denmark)

    Morita, Masahiko; Malvankar, Nikhil S

    2011-01-01

    Mechanisms for electron transfer within microbial aggregates derived from an upflow anaerobic sludge blanket reactor converting brewery waste to methane were investigated in order to better understand the function of methanogenic consortia. The aggregates were electrically conductive, with conductivities 3-fold higher than the conductivities previously reported for dual-species aggregates of Geobacter species in which the two species appeared to exchange electrons via interspecies electron transfer. The temperature dependence response of the aggregate conductance was characteristic of the organic metallic-like conductance previously described for the conductive pili of Geobacter sulfurreducens and was inconsistent with electron conduction through minerals. Studies in which aggregates were incubated with high concentrations of potential electron donors demonstrated that the aggregates had no significant capacity for conversion of hydrogen to methane. The aggregates converted formate to methane but at rates toolow to account for the rates at which that the aggregates syntrophically metabolized ethanol, an important component of the reactor influent. Geobacter species comprised 25% of 16S rRNA gene sequences recovered from the aggregates, suggesting that Geobacter species may have contributed to some but probably not all of the aggregate conductivity. Microorganisms most closely related to the acetate-utilizing Methanosaeta concilii accounted for more than 90% of the sequences that could be assigned to methane producers, consistent with the poor capacity for hydrogen and formate utilization. These results demonstrate for the first time that methanogenic wastewater aggregates can be electrically conductive and suggest that direct interspecies electron transfer could be an important mechanism for electron exchange in some methanogenic systems.

  3. Reaction Dynamics of Proton-Coupled Electron Transfer from Reduced ZnO Nanocrystals.

    Science.gov (United States)

    Braten, Miles N; Gamelin, Daniel R; Mayer, James M

    2015-10-27

    The creation of systems that efficiently interconvert chemical and electrical energies will be aided by understanding proton-coupled electron transfers at solution-semiconductor interfaces. Steps in developing that understanding are described here through kinetic studies of reactions of photoreduced colloidal zinc oxide (ZnO) nanocrystals (NCs) with the nitroxyl radical TEMPO. These reactions proceed by proton-coupled electron transfer (PCET) to give the hydroxylamine TEMPOH. They occur on the submillisecond to seconds time scale, as monitored by stopped-flow optical spectroscopy. Under conditions of excess TEMPO, the reactions are multiexponential in character. One of the contributors to this multiexponential kinetics may be a distribution of reactive proton sites. A graphical overlay method shows the reaction to be first order in [TEMPO]. Different electron concentrations in otherwise identical NC samples were achieved by three different methods: differing photolysis times, premixing with an unphotolyzed sample, or prereaction with TEMPO. The reaction velocities were consistently higher for NCs with higher numbers of electrons. For instance, NCs with an average of 2.6 e(-)/NC reacted faster than otherwise identical samples containing ?1 e(-)/NC. Surprisingly, NC samples with the same average number of electrons but prepared in different ways often had different reaction profiles. These results show that properties beyond electron content determine PCET reactivity of the particles. PMID:26369280

  4. Ultrafast Intramolecular Electron and Proton Transfer in Bis(imino)isoindole Derivatives.

    Science.gov (United States)

    Driscoll, Eric; Sorenson, Shayne; Dawlaty, Jahan M

    2015-06-01

    Concerted motion of electrons and protons in the excited state is pertinent to a wide range of chemical phenomena, including those relevant for solar-to-fuel light harvesting. The excited state dynamics of small proton-bearing molecules are expected to serve as models for better understanding such phenomena. In particular, for designing the next generation of multielectron and multiproton redox catalysts, understanding the dynamics of more than one proton in the excited state is important. Toward this goal, we have measured the ultrafast dynamics of intramolecular excited state proton transfer in a recently synthesized dye with two equivalent transferable protons. We have used a visible ultrafast pump to initiate the proton transfer in the excited state, and have probed the transient absorption of the molecule over a wide bandwidth in the visible range. The measurement shows that the signal which is characteristic of proton transfer emerges within ?710 fs. To identify whether both protons were transferred in the excited state, we have measured the ultrafast dynamics of a related derivative, where only a single proton was available for transfer. The measured proton transfer time in that molecule was ?427 fs. The observed dynamics in both cases were reasonably fit with single exponentials. Supported by the ultrafast observations, steady-state fluorescence, and preliminary computations of the relaxed excited states, we argue that the doubly protonated derivative most likely transfers only one of its two protons in the excited state. We have performed calculations of the frontier molecular orbitals in the Franck-Condon region. The calculations show that in both derivatives, the excitation is primarily from the HOMO to LUMO causing a large rearrangement of the electronic charge density immediately after photoexcitation. In particular, charge density is shifted away from the phenolic protons and toward the proton acceptor nitrogens. The proton transfer is hypothesized to occur both due to enhanced acidity of the phenolic proton and enhanced basicity of the nitrogen in the excited state. We hope this study can provide insight for better understanding of the general class of excited state concerted electron-proton dynamics. PMID:25932563

  5. Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production.

    Science.gov (United States)

    Zhu, Nan; Zheng, Kaibo; Karki, Khadga J; Abdellah, Mohamed; Zhu, Qiushi; Carlson, Stefan; Haase, Dörthe; Žídek, Karel; Ulstrup, Jens; Canton, Sophie E; Pullerits, Tõnu; Chi, Qijin

    2015-01-01

    Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 10(9) s(-1). Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications. PMID:25996307

  6. Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production

    DEFF Research Database (Denmark)

    Zhu, Nan; Zheng, Kaibo

    2015-01-01

    Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3?×?109 s?1. Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications.

  7. Genome-wide expression links the electron transfer pathway of Shewanella oneidensis to chemotaxis

    Directory of Open Access Journals (Sweden)

    Yuan Shinsheng

    2010-05-01

    Full Text Available Abstract Background By coupling the oxidation of organic substrates to a broad range of terminal electron acceptors (such as nitrate, metals and radionuclides, Shewanella oneidensis MR-1 has the ability to produce current in microbial fuel cells (MFCs. omcA, mtrA, omcB (also known as mtrC, mtrB, and gspF are some known genes of S. oneidensis MR-1 that participate in the process of electron transfer. How does the cell coordinate the expression of these genes? To shed light on this problem, we obtain the gene expression datasets of MR-1 that are recently public-accessible in Gene Expression Omnibus. We utilize the novel statistical method, liquid association (LA, to investigate the complex pattern of gene regulation. Results Through a web of information obtained by our data analysis, a network of transcriptional regulatory relationship between chemotaxis and electron transfer pathways is revealed, highlighting the important roles of the chemotaxis gene cheA-1, the magnesium transporter gene mgtE-1, and a triheme c-type cytochrome gene SO4572. Conclusion We found previously unknown relationship between chemotaxis and electron transfer using LA system. The study has the potential of helping researchers to overcome the intrinsic metabolic limitation of the microorganisms for improving power density output of an MFC.

  8. Distance-dependent electron transfer rate of immobilized redox proteins: A statistical physics approach

    Science.gov (United States)

    Georg, Sören; Kabuss, Julia; Weidinger, Inez M.; Murgida, Daniel H.; Hildebrandt, Peter; Knorr, Andreas; Richter, Marten

    2010-04-01

    The electron transfer kinetics of redox proteins adsorbed on metal electrodes coated with self-assembled monolayers (SAMs) of mercaptanes shows an unusual distance-dependence. For thick SAMs, the experimentally measured electron transfer rate constant kexp obeys the behavior predicted by Marcus theory [R. A. Marcus and N. Sutin, Biochim. Biophys. Acta 811, 265 (1985)], whereas for thin SAMs, kexp remains virtually constant [Z. Q. Feng , J. Chem. Soc., Faraday Trans. 93, 1367 (1997)]. In this work, we present a simple theoretical model system for the redox protein cytochrome c electrostatically bound to a SAM-coated electrode. A statistical average of the electron tunneling rate is calculated by accounting for all possible orientations of the model protein. This approach, which takes into account the electric field dependent orientational distribution, allows for a satisfactory description of the “saturation” regime in the high electric field limit. It further predicts a nonexponential behavior of the average electron transfer processes that may be experimentally checked by extending kinetic experiments to shorter sampling times, i.e., ?1/kexp . For a comprehensive description of the overall kinetics in the saturation regime at sampling times of the order of 1/kexp , it is essential to consider the dynamics of protein reorientation, which is not implemented in the present model.

  9. NI (II AND PB (II INHIBIT THE ENZYMATIC ACTIVITY OF DNA IN AN ELECTRON TRANSFER REACTION

    Directory of Open Access Journals (Sweden)

    B FARZAMI

    2002-03-01

    Full Text Available Introduction. Ni and Pb are metals with several suggested mechanisms for their toxicity on the biological systems. We have recently investigated involvement of DNA in an electron transfer reaction as an enzyme. In this reaction non- fluorescent dichlorofluorescin (LDCF is converted to the dichlorofluorescein (DCF in the presence of peroxides and hematin. Methods. The fluorometric technique was used in this study. The pH effect on the reaction rate was investigated. The results showed that DCF has the maximum emission on tris buffer 0.05 Mat pH 8.4. Results. DNA and carnosine catalyze the reaction, which proceeds by the electron transfer mechanism. The presence of carnosine is necessary for the catalytic action of DNA as a cofactor. Ni (II and Pb (11 are the potent inhibitors of the reaction. The kinetic parameters and determined in the presence and absence of the above ligands. Discussion. DNA, which has the electrical properties only in the double helical forms, acts as a catalyst in the conversion of LDCF to DCF. The existence of the carnosine, an endogenous dipeptide with antioxidant and free radical scavenging roles, is an important factor for the progress of the reaction. Both Ni (11 and Pb (II inhibit the reaction. These metals could act as the electron pool to cause inhibition in such electron transfer reaction. This phenomenon could be related to the carcinogenic effect of these metals.

  10. Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production

    Science.gov (United States)

    Zhu, Nan; Zheng, Kaibo; Karki, Khadga J.; Abdellah, Mohamed; Zhu, Qiushi; Carlson, Stefan; Haase, Dörthe; Žídek, Karel; Ulstrup, Jens; Canton, Sophie E.; Pullerits, Tõnu; Chi, Qijin

    2015-05-01

    Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3?×?109 s-1. Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid nanofilm acts as a photoanode. We thereby demonstrate a cost-effective method to construct large-area QD-graphene hybrid nanofilms with straightforward scale-up potential for optoelectronic applications.

  11. 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.

  12. Toward transferable interatomic van der Waals interactions without electrons: The role of multipole electrostatics and many-body dispersion

    International Nuclear Information System (INIS)

    We estimate polarizabilities of atoms in molecules without electron density, using a Voronoi tesselation approach instead of conventional density partitioning schemes. The resulting atomic dispersion coefficients are calculated, as well as many-body dispersion effects on intermolecular potential energies. We also estimate contributions from multipole electrostatics and compare them to dispersion. We assess the performance of the resulting intermolecular interaction model from dispersion and electrostatics for more than 1300 neutral and charged, small organic molecular dimers. Applications to water clusters, the benzene crystal, the anti-cancer drug ellipticine—intercalated between two Watson-Crick DNA base pairs, as well as six macro-molecular host-guest complexes highlight the potential of this method and help to identify points of future improvement. The mean absolute error made by the combination of static electrostatics with many-body dispersion reduces at larger distances, while it plateaus for two-body dispersion, in conflict with the common assumption that the simple 1/R6 correction will yield proper dissociative tails. Overall, the method achieves an accuracy well within conventional molecular force fields while exhibiting a simple parametrization protocol

  13. Computational methods for intramolecular electron transfer in a ferrous-ferric iron complex.

    Science.gov (United States)

    Zarzycki, Piotr; Kerisit, Sebastien; Rosso, Kevin

    2011-09-01

    The limitations of common theoretical and molecular computational approaches for predicting electron transfer quantities were assessed, using an archetypal bridged ferrous-ferric electron transfer system in aqueous solution. The basis set effect on the magnitude of the electronic coupling matrix element computed using the quasi-diabatic method was carefully examined, and it was found that the error related to a poor basis set could exceed the thermal energy at room temperature. A range of approaches to determining the external (solvent) reorganization energy were also investigated. Significant improvements from the Marcus continuum model can be obtained by including dipolar Born-Kirkwood-Onsager correction. In this regard, we also found that Klamt's Conductor-Like Screening Model (COSMO) yields estimations of the external reorganization energy similar to those obtained with explicit solvent molecular dynamics simulations if the fast-frequency modes are neglected, which makes it an attractive alternative to laborious umbrella sampling simulations. By using the COSMO model, we also confirm that a decrease in curvature of the potential energy surface is a manifestation of the dielectric saturation observed in the first solvation layer. The linearity of solvent response to the charge redistribution was assessed by analyzing the energy gap autocorrelation function as well as the solvent density and dipole moment fluctuations. Molecular dynamics was also used to evaluate the sign and magnitude of the solvent reorganization entropy and to determine its effect on the predicted electron transfer rate. Finally, we present a simple way of estimating the vibration frequency along the reaction coordinate, which also enables prediction of the mass-dependent isotopic signature of electron transfer reactions. PMID:21696749

  14. Study of the electron transfer in analog compounds of the Prussia blue

    International Nuclear Information System (INIS)

    As answer to the necessity of the search of new nano structured materials, the present work was carried out that it studies the electron transfer in compound similar of the Prussia blue (CAAP), which are representative molecular materials, because its chromophore, magnetic, and electric properties, depend mainly on the processes that are made in their levels or orbital energy. It is known that these made up with octahedra symmetry that its are presented in form of powders, suffer processes of electron transfer when its are exposed to external stimulation by means of light (embracing the regions from the ultraviolet one until the infrared in the electromagnetic spectrum), because they are made up of mixed valency. To know that types of electronic transfers are those that are made in the study materials, 4 series of CAAP its were synthesized by the method of mixtures of aqueous solutions: M[Fe+3CN)6]2nH2O, M[Cr+3(CN)6]2nH2O, M[Mn+3(CN)6]3nH2O y M[Co+3(CN)6]3nH2O, and later on studied by means of the electron spectroscopy technique with a UV-SENSE spectrophotometer (Perkin-Elmer) in or n range of work of 250 to 1100 nm. Because to discuss the electronic structures of any compound, it is required the calculation of the energy levels, they took like reference the data tabulated by John Alexander and Harry Gray calculated by the modified theoretical approach of Wolfsberg-Helmhoz. When comparing the obtained spectra with the theoretical data, it was concludes that in the CAAP, its are carried out electronic transfers among orbital molecular metallic of the type d ? d, and load transfer (TC) among orbital molecular of the ligand and metal. When being carried out a load transfer in the CAAP that initially are made up of under-spin these its are photoinduced to an excited state of high spin. In consequence it is possible to vary the interactions among the metals of transition of the CAAP and the ligands, allowing the extension of coordinated phenomena (as the magnetism) through the crystalline lattice. This strengthens the idea that these materials are good candidates to be employees as molecular magnets with photoinduced control. (Author)

  15. Boiling heat transfer in narrow channels with offset strip fins: Application to electronic chipsets cooling

    International Nuclear Information System (INIS)

    An experimental study on saturated flow boiling heat transfer of HFE-7100 in vertical rectangular channels with offset strip fins is presented. The experiments have been carried out at atmospheric pressure, over a wide range of vapour quality and heat fluxes up to 1.8 x 105 W/m2. The local boiling heat transfer coefficient has been obtained from experiments and analysed by means of Chen superposition method. Some correlations for convective boiling and nucleate boiling heat transfer coefficients have been considered. A good agreement has been found with Feldman et al. correlation for convective boiling heat transfer and Kim and Sohn correlations for nucleate boiling heat transfer. A closed circuit for electronic chipsets cooling, with the same evaporator as that studied in the first part of the paper, has been studied. Thermal performances of this system have been measured and compared with those of a circuit with the same components but no internal fins in the evaporator. The results have shown that for high heat loads the inner geometry of evaporator does not influence the two-phase heat transfer. For low heat loads, offset strip fins evaporator gives better performances than no fins evaporator.

  16. Spin polarized electron source technology transferred from HE accelerators to LE electron microscopes

    International Nuclear Information System (INIS)

    For more than 25 years, our group has developed the technology of spin-polarized-electron-source (PES) for a future linear collider project (ILC). Various new techniques for achieving high polarization, high quantum efficiency, high current density, sub-nanosecond multi-bunch generation etc. were developed. Two fundamental technologies; 1) reduction of dark current and 2) preparation of extremely high vacuum environment for preserving the NEA (Negative Electron Affinity) surface have been also developed. Using these PES technologies and a new transmission type of semiconductor photocathode, we recently succeeded in producing the high brightness and high polarization electron beam for the low energy electron microscope (LEEM). Our Spin-LEEM system enables the world-first video-observation (?10 pictures/sec) of the surface magnetic domains of evaporated Co on the W (110) substrate with ?20nm space resolution. (author)

  17. Photochemical generation of strong one-electron reductants via light-induced electron transfer with reversible donors followed by cross reaction with sacrificial donors.

    Science.gov (United States)

    Shan, Bing; Schmehl, Russell

    2014-11-13

    This work illustrates a modified approach for employing photoinduced electron transfer reactions coupled to secondary irreversible electron transfer processes for the generation of strongly reducing equivalents in solution. Through irradiation of [Ru(LL)3](2+) (LL= diimine ligands) with tritolylamine (TTA) as quencher and various alkyl amines as sacrificial electron donors, yields in excess of 50% can be achieved for generation of reductants with E(0)(2+/1+) values between -1.0 and -1.2 V vs NHE. The key to the system is the fact that the TTA cation radical, formed in high yield in reaction with the photoexcited [Ru(LL)3](2+) complex, reacts irreversibly with various sacrificial electron donating amines that are kinetically unable to directly react with the photoexcited complex. The electron transfer between the TTA(+) and the sacrificial amine is an energetically uphill process. Kinetic analysis of these parallel competing reactions, consisting of bimolecular and pseudo first-order reactions, allows determination of electron transfer rate constants for the cross electron transfer reaction between the sacrificial donor and the TTA(+). A variety of amines were examined as potential sacrificial electron donors, and it was found that tertiary 1,2-diamines are most efficient among these amines for trapping the intermediate TTA(+). This electron-donating combination is capable of supplying a persistent reducing flux of electrons to catalysts used for hydrogen production. PMID:24882233

  18. The [(NH3)5Ru-Pyz-Ru(NH3)5]5+ complex: electronic structure, spectrum and modeling of intramolecular electron transfer

    International Nuclear Information System (INIS)

    Semiempirical method INDO+CI was used to calculate the electronic structure of base and excited states of binuclear mixed-valent complex [Ru(NH3)5]2(Pyz)5+. Referral of electron spectra was given. Theoretical model of electron transfer between Ru(2) and Ru(3) metal centers was approved on the basis of multielectron wave functions

  19. Specific intermolecular interactions of element-organic compounds

    CERN Document Server

    Baev, Alexei K

    2014-01-01

    This book extends the development of the thermodynamic theory of specific intermolecular interactions to element-organic and specific organometallic compounds. The fundamentals of an unconventional approach to the theory of H-bonding and specific interactions are formulated, based on a concept of pentacoordinate carbon atoms. Prof. Baev has introduced the theory already in his successful books ""Specific Intermolecular Interactions of Organic Compounds"" and ""Specific Intermolecular Interactions of Nitrogenated and Bioorganic Compounds"". In this book he also demonstrates it for element organ

  20. Photo- and radiation chemical studies of intermediates involved in excited-state electron-transfer reactions

    International Nuclear Information System (INIS)

    Excited-state inter- and intramolecular electron-transfer reactions lie at the heart of the most photochemical solar energy conversion schemes. The authors research, which has utilized the techniques of continuous and pulsed photolysis and radiolysis, has focused on three general aspects of these reactions involving transition metal coordination complexes and electron donor-acceptor complexes: i) the effect of solution medium on the properties and quenching of the excited states; ii) the control of the quantum yields of formation of redox products; iii) the mechanism by which reduced species interact with water to yield H2 homogeneously and heterogeneously. EDTA is among the most popular sacrificial electron donors used in model systems. Its role is to scavenge the oxidized form of the photosensitizer in order to prevent its rapid reaction with the reduced form of the electron relay species that results from the electron-transfer quenching of the excited photosensitizer. In systems involving MV2+, the radicals resulting from the oxidation of EDTA can eventually lead to the generation of a second equivalent of MV+; the reducing agent is believed to be a radical localized on the carbon atom alpha to the carboxylate group. The reaction of radiolytically-generated OH/H with EDTA produces this radical directly via H-abstraction or indirectly via deprotonation of the carbon atom adjacent to the nitrogen radical site in the oxidized amine moiety; it reduces MV2+ with rate constants of 2.8 x 109, 7.6 x 109, and 8.5 x 106M-1s-1 at pH 12.5, 8.3, and 4.7, respectively. Degradative decarboxylation of EDTA-radicals and their back electron-transfer reactions are enhanced in acidic solution causing the yield of MV+ to be severely diminished

  1. Electron transfer reactions in microporous solids. Progress report, September 1990--January 1993

    Energy Technology Data Exchange (ETDEWEB)

    Mallouk, T.E.

    1993-01-01

    Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H{sub 2} and I{sub 3}{sup {minus}}, or H{sub 2} and O{sub 2)} from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

  2. Electron transfer within charge-localized arylhydrazine-centered mixed valence radical cations having larger bridges.

    Science.gov (United States)

    Nelsen, Stephen F; Schultz, Kevin P

    2009-05-14

    Kinetics for intramolecular charge transfer between two diarylhydrazine units, measured by ESR, are reported for six charge-localized mixed valence compounds having 9, 11, 13, and 16 bonds between the nitrogen atoms. A 17-bond bridged compound had too slow electron transfer to measure the rate constant by ESR. The optical spectra of these radical cations are compared with tert-butyl,aryl-substituted hydrazines, and rate constants calculated using parameters derived from the optical spectra are compared with the experimental values where possible. The charge-transfer band overlapped too badly with bridge-centered absorption for the 16-bond bridged compound to allow the comparison to be made. The 13-bond bridged compound gave worse agreement than the other compounds. Its optical rate constant was about 5.4 times the ESR rate constant at a temperature between the ranges in which the data were collected. PMID:19374409

  3. 3-Coil resonance-based wireless power transfer system for implantable electronic

    KAUST Repository

    Yi, Ying

    2013-05-01

    This paper presents a 3-coil resonance-based wireless power transfer (R-WPT) system using a single layer of inductor coil windings, in a pancake configuration, in order to obtain a compact system for implantable electronic applications. A theoretical analysis and experimental measurements in terms of quality factor Q and power transfer efficiency (PTE), was done. Our proposed 3-coil scheme can achieve a high PTE with a resonance frequency of 2.46 MHz over a transfer distance of up to 30 mm, by using two 15-mm radius implant coils. The achieved experimental PTE is more than 85%at a 5 mm separation distance, and about 50% PTE at a distance of 20 mm. © 2013 IEEE.

  4. New Oxime Ligand with Potential for Proton-Coupled Electron-Transfer Reactions

    DEFF Research Database (Denmark)

    Deville, Claire; Sundberg, Jonas

    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 site.2 Metal complex of ligands possessing both H-donor and H-acceptor sites in the second coordination sphere should be interesting candidates for proton transfer reactions induced by photooxidation of the metal ion. We have prepared new oxime-containing ligands which coordinate to metal ions such that a pyridine group is sterically restricted so it does not coordinate. Instead it can act as proximal base for accepting the oxime proton. [1] M. H. V. Huynh, T. J. Meyer, Chem. Rev. 2007, 107, 5004-5064. [2] T. Irebo, O. Johansson, L. Hammarström, J. Am. Chem. Soc., 2008, 130, 9194-9195.

  5. Blue Copper Proteins: A rigid machine for efficient electron transfer, a flexible device for metal uptake.

    Science.gov (United States)

    Pérez-Henarejos, Sergio Alejo; Alcaraz, Luis A; Donaire, Antonio

    2015-10-15

    Blue Copper Proteins (BCPs) are small and generally soluble copper-containing proteins which participate in monoelectron transfer processes in biological systems. An overview of their electronic and tertiary structure is detailed here. The well-established entatic/rack-induced mechanism is explained by comparing thermodynamic parameters between the folded (tense) and the unfolded (relaxed) forms of the BCP rusticyanin. Recently, NMR solution data have shown that the active sites of BCPs in absence of the metal ion, i.e. in the apoforms, are flexible in the micro-to-second timescale. The rigidity proposed by the entatic/rack-induced mechanism is an imperative for the holoprotein to perform electron transfer; while the flexibility of the apocupredoxin is necessary to uptake the metal ion from the metallochaperones. These apparently contradictory requirements are discussed in the present work. Finally, the role of azurin and some peptides derived from it in anticancer therapy are also described. PMID:26334718

  6. Synergetic mechanisms of structural regulation of the electron transfer and other reactions of biological macromolecules

    International Nuclear Information System (INIS)

    A general concept of self-regulation of biomolecule function due to the interaction of fast reaction (in particular, electron transfer) events and slow structural re-arrangements is expounded. It proceeds from the fact that the structural changes produced by each elementary reaction act can be accumulated, up to drastic modification of the reaction turnover. Thus, conformational control of biomolecule functioning is realized along synergetic scenarios at the single-molecule level. A proper theoretical formalism and its application to the analysis of electron transfer reactions in photosynthetic reaction centers (RCs) are described. The peculiarities of bistability and hysteresis phenomena as well as of corresponding effects of RC protein memory, revealed both theoretically and experimentally, are discussed

  7. Direct observation of multistep energy transfer in LHCII with fifth-order 3D electronic spectroscopy

    Science.gov (United States)

    Zhang, Zhengyang; Lambrev, Petar H.; Wells, Kym L.; Garab, Gy?z?; Tan, Howe-Siang

    2015-07-01

    During photosynthesis, sunlight is efficiently captured by light-harvesting complexes, and the excitation energy is then funneled towards the reaction centre. These photosynthetic excitation energy transfer (EET) pathways are complex and proceed in a multistep fashion. Ultrafast two-dimensional electronic spectroscopy (2DES) is an important tool to study EET processes in photosynthetic complexes. However, the multistep EET processes can only be indirectly inferred by correlating different cross peaks from a series of 2DES spectra. Here we directly observe multistep EET processes in LHCII using ultrafast fifth-order three-dimensional electronic spectroscopy (3DES). We measure cross peaks in 3DES spectra of LHCII that directly indicate energy transfer from excitons in the chlorophyll b (Chl b) manifold to the low-energy level chlorophyll a (Chl a) via mid-level Chl a energy states. This new spectroscopic technique allows scientists to move a step towards mapping the complete complex EET processes in photosynthetic systems.

  8. Peptide Sequence Analysis by Electron Transfer Dissociation Mass Spectrometry: A Web-Based Tutorial

    Science.gov (United States)

    Hunt, Donald F.; Shabanowitz, Jeffrey; Bai, Dina L.

    2015-07-01

    We created a web-based tutorial designed to teach manual interpretation and identification of spectra acquired using electron transfer dissociation (ETD). The tutorial provides an explanation of the ETD fragmentation process with the goal of identifying all of the significant peaks in a spectrum. We discuss determination of the precursor mass and charge state, neutral losses, electron transfer without dissociation (ETnoD), and the mechanisms by which fragment ions are created. Our hope is to provide a tool that presents the information already taught in D.F.H.'s short courses in a way that is easy for any student or researcher in the mass spectrometry community to access. The tutorial may be found at http://www.huntlab.org.

  9. Light- induced electron transfer and ATP synthesis in a carotene synthesizing insect

    Science.gov (United States)

    Valmalette, Jean Christophe; Dombrovsky, Aviv; Brat, Pierre; Mertz, Christian; Capovilla, Maria; Robichon, Alain

    2012-08-01

    A singular adaptive phenotype of a parthenogenetic insect species (Acyrthosiphon pisum) was selected in cold conditions and is characterized by a remarkable apparition of a greenish colour. The aphid pigments involve carotenoid genes well defined in chloroplasts and cyanobacteria and amazingly present in the aphid genome, likely by lateral transfer during evolution. The abundant carotenoid synthesis in aphids suggests strongly that a major and unknown physiological role is related to these compounds beyond their canonical anti-oxidant properties. We report here that the capture of light energy in living aphids results in the photo induced electron transfer from excited chromophores to acceptor molecules. The redox potentials of molecules involved in this process would be compatible with the reduction of the NAD+ coenzyme. This appears as an archaic photosynthetic system consisting of photo-emitted electrons that are in fine funnelled into the mitochondrial reducing power in order to synthesize ATP molecules.

  10. Semiclassical Green's functions and an instanton formulation of electron-transfer rates in the nonadiabatic limit

    Science.gov (United States)

    Richardson, Jeremy O.; Bauer, Rainer; Thoss, Michael

    2015-10-01

    We present semiclassical approximations to Green's functions of multidimensional systems, extending Gutzwiller's work to the classically forbidden region. Based on steepest-descent integrals over these functions, we derive an instanton method for computing the rate of nonadiabatic reactions, such as electron transfer, in the weak-coupling limit, where Fermi's golden-rule can be employed. This generalizes Marcus theory to systems for which the environment free-energy curves are not harmonic and where nuclear tunnelling plays a role. The derivation avoids using the Im F method or short-time approximations to real-time correlation functions. A clear physical interpretation of the nuclear tunnelling processes involved in an electron-transfer reaction is thus provided. In Paper II [J. O. Richardson, J. Chem. Phys. 143, 134116 (2015)], we discuss numerical evaluation of the formulae.

  11. Semiclassical Green's functions and an instanton formulation of electron-transfer rates in the nonadiabatic limit

    CERN Document Server

    Richardson, Jeremy O; Thoss, Michael

    2015-01-01

    We present semiclassical approximations to Green's functions of multidimensional systems, extending Gutzwiller's work to the classically forbidden region. Based on steepest-descent integrals over these functions, we derive an instanton method for computing the rate of nonadiabatic reactions, such as electron transfer, in the weak-coupling limit, where Fermi's golden-rule can be employed. This generalizes Marcus theory to systems for which the environment free-energy curves are not harmonic and where nuclear tunnelling plays a role. The derivation avoids using the Im F method or short-time approximations to real-time correlation functions. A clear physical interpretation of the nuclear tunnelling processes involved in an electron-transfer reaction is thus provided. In the following paper, we discuss numerical evaluation of the formulae.

  12. Electron-transfer processes in dendrimers and their implication in biology, catalysis, sensing and nanotechnology

    Science.gov (United States)

    Astruc, Didier

    2012-04-01

    The extraordinary development of the design and synthesis of dendrimers has allowed scientists to locate redox sites at precise positions (core, focal points, branching points, termini, cavities) of these perfectly defined macromolecules, which have generation-controlled sizes and topologies matching those of biomolecules. Redox-dendrimer engineering has led to fine modelling studies of electron-transfer metalloproteins, in which the branches of the dendrimers hinder access to the active site in a manner reminiscent of that of the protein. It has also enabled the construction of remarkable catalysts, sensors and printboards, including by sophisticated design of the interface between redox dendrimers and solid-state devices -- for example by functionalizing electrodes and other surfaces. Electron-transfer processes between dendrimers and a variety of other molecules hold promising applications in diverse areas that range from bio-engineering to sensing, catalysis and energy materials.

  13. Modulation of electron transfer kinetics by protein conformational fluctuations during early-stage photosynthesis

    Science.gov (United States)

    Chaudhury, Srabanti; Cherayil, Binny J.

    2007-10-01

    The kinetics of electron transfer during the early stages of the photosynthetic reaction cycle has recently been shown in transient absorption experiments carried out by Wang et al. [Science 316, 747 (2007)] to be strongly influenced by fluctuations in the conformation of the surrounding protein. A model of electron transfer rates in polar solvents developed by Sumi and Marcus using a reaction-diffusion formalism [J. Chem. Phys. 84, 4894 (1986)] was found to be successful in fitting the experimental absorption curves over a roughly 200ps time interval. The fits were achieved using an empirically determined time-dependent function that described protein conformational relaxation. In the present paper, a microscopic model of this function is suggested, and it is shown that the function can be identified with the dynamic autocorrelation function of intersegment distance fluctuations that occur in a harmonic potential of mean force under the action of fractional Gaussian noise.

  14. Prospect for observation of polarization in electron-deuteron elastic scattering at high momentum transfer

    International Nuclear Information System (INIS)

    A measurement of the charge and quadrupole form factors of the deuteron would address the most fundamental questions in nuclear physics: validity of perturbative QCD at relatively low momentum transfer, effect of isoscalar meson-exchange currents, and the deuteron structure at short range. Polarization methods will be required in order to provide the separation of these form factors. We propose that the high current of electrons in a storage ring be employed in order to scatter electrons from a gaseous, tensor-polarized, deuterium target. (orig.)

  15. Dielectric losses and charge transfer in electron-irradiated TIGaS2 single crystal

    International Nuclear Information System (INIS)

    Full text: This study presents the results of studying the frequency dependence of real and imaginary componenets of the complex dielectric permittivity, loss tangent, conductivity across the layers of high-resistive of TIGaS2 single crystals at frequencies from 50 kHz up to 35 MHz and the effect of electron-irradiation on themSample from TiGaS2 were made inn sandwich form with electrodes of silver plate. The investigation of the frequency dependences af ac-conductivity of the electron-irradiated TiGaS2 single crystal made it possible to elucidate the hopping charge-transfer mechanism

  16. Photoinduced Electron Transfer in Ordered Macromolecular Assemblies. Final report for May 1, 1988 - June 30, 2002

    Energy Technology Data Exchange (ETDEWEB)

    Jones, G.

    2005-02-11

    The final report describes studies over a 13 year period having to do with photoinduced electron transfer for active chromophores and redox agents, including assembly of the components in water soluble polymers or polypeptides. The findings include observation of long range charge separation and electron transport using laser phototransient spectroscopy. The systems targeted in these studies include peptide assemblies for which helical conformations and aggregation are documented. Oligomeric peptides modified with non-native redox active groups were also selected for investigation. Highly charged polymers or peptides were investigated as host agents that resemble proteins. The overall goal of these investigations focused on the design and characterization of systems capable of artificial photosynthesis.

  17. Direct measurement of electron transfer distance decay constants of single redox proteins by electrochemical tunneling spectroscopy.

    Science.gov (United States)

    Artés, Juan M; Díez-Pérez, Ismael; Sanz, Fausto; Gorostiza, Pau

    2011-03-22

    We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current?distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (?) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains. PMID:21539019

  18. Radical anion salts and charge transfer complexes based on tetracyanoquinodimethane and other strong ?-electron acceptors

    Science.gov (United States)

    Starodub, V. A.; Starodub, T. N.

    2014-05-01

    The unique properties of radical anion salts and charge transfer complexes formed by tetracyanoquinodimethane and other strong ?-electron acceptors are analyzed. Their ability to form fusible conductive materials and magnetically ordered structures, including ferromagnetic ones with high Curie temperatures, spin ladders and quasi-two-dimensional organic conductors and superconductors is considered. Particular attention is given to the possible areas of application of these radical anion salts in electronic industry as nanomaterials, materials for the fabrication of field effect transistors, photodiodes and ion selective electrodes. The bibliography includes 421 references.

  19. Measurement of Tensor Polarization in Elastic Electron-Deuteron Scattering at Large Momentum Transfer

    International Nuclear Information System (INIS)

    Tensor polarization observables (t20, t21 and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c) 2. The experiment was performed at the Jefferson Laboratory in Hall C using the electron HMS Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q 2 the deuteron charge form factors GC and GQ. They are in good agreement with relativistic calculations and disagree with pQCD predictions

  20. Measurement of Tensor Polarization in Elastic Electron-Deuteron Scattering at Large Momentum Transfer

    International Nuclear Information System (INIS)

    Tensor polarization observables (t20, t21 and t22) have been measured in elastic electron-deuteron scattering for six values of momentum transfer between 0.66 and 1.7 (GeV/c)2. The experiment was performed at the Jefferson Laboratory in Hall C using the electron HMS Spectrometer, a specially designed deuteron magnetic channel and the recoil deuteron polarimeter POLDER. The new data determine to much larger Q2 the deuteron charge form factors GC and GQ. They are in good agreement with relativistic calculations and disagree with pQCD predictions