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Sample records for intermolecular electron transfer

  1. Intra- and intermolecular electron transfer reactions in covalently linked donor-acceptor molecules

    We synthesized a homologous series of molecules (MVnn'Q) where a methylviologen (MV2+) and an amino-chloronaphthoquinone (Q) are linked to each other via a flexible chain. Using the electron pulse radiolysis technique, we have measured time-resolved spectra and determined rate constants for intra- and intermolecular electron transfer (ET) between donor and acceptor site of the MVnn'Q molecules in water and in sodium dodecyl sulfate (SDS) micellar solution. For comparison, we also irradiated a solution containing a 1:1 mixture of methylviologen and amino-chloronaphthoquinone and measured spectra and intermolecular ET reactions between the separated electron donor and acceptor molecules. We found a remarkably slow intramolecular electron transfer from the reduced methylviologen moiety to the quinone site of all MVnn'Q molecules both in water and in aqueous SDS micellar suspensions. The intramolecular rate constants measured in water increase with the number of intervening bonds, leading to the conclusion that electron transfer occurs by a through-space rather than through-bond mechanism. The intramolecular rate constants virtually lose their chain length dependence in SDS suspensions where, because of an extended configuration of the micellized MVnn'Q molecules, through-space interaction is not favored. (orig.)

  2. Rates of intra- and intermolecular electron transfers in hydrogenase deduced from steady-state activity measurements.

    Dementin, Sébastien; Burlat, Bénédicte; Fourmond, Vincent; Leroux, Fanny; Liebgott, Pierre-Pol; Abou Hamdan, Abbas; Léger, Christophe; Rousset, Marc; Guigliarelli, Bruno; Bertrand, Patrick

    2011-07-01

    Electrons are transferred over long distances along chains of FeS clusters in hydrogenases, mitochondrial complexes, and many other respiratory enzymes. It is usually presumed that electron transfer is fast in these systems, despite the fact that there has been no direct measurement of rates of FeS-to-FeS electron transfer in any respiratory enzyme. In this context, we propose and apply to NiFe hydrogenase an original strategy that consists of quantitatively interpreting the variations of steady-state activity that result from changing the nature of the FeS clusters which connect the active site to the redox partner, and/or the nature of the redox partner. Rates of intra- and intermolecular electron transfer are deduced from such large data sets. The mutation-induced variations of electron transfer rates cannot be explained by changes in intercenter distances and reduction potentials. This establishes that FeS-to-FeS rate constants are extremely sensitive to the nature and coordination of the centers. PMID:21615141

  3. Intermolecular electron transfer from intramolecular excitation and coherent acoustic phonon generation in a hydrogen-bonded charge-transfer solid.

    Rury, Aaron S; Sorenson, Shayne; Dawlaty, Jahan M

    2016-03-14

    Organic materials that produce coherent lattice phonon excitations in response to external stimuli may provide next generation solutions in a wide range of applications. However, for these materials to lead to functional devices in technology, a full understanding of the possible driving forces of coherent lattice phonon generation must be attained. To facilitate the achievement of this goal, we have undertaken an optical spectroscopic study of an organic charge-transfer material formed from the ubiquitous reduction-oxidation pair hydroquinone and p-benzoquinone. Upon pumping this material, known as quinhydrone, on its intermolecular charge transfer resonance as well as an intramolecular resonance of p-benzoquinone, we find sub-cm(-1) oscillations whose dispersion with probe energy resembles that of a coherent acoustic phonon that we argue is coherently excited following changes in the electron density of quinhydrone. Using the dynamical information from these ultrafast pump-probe measurements, we find that the fastest process we can resolve does not change whether we pump quinhydrone at either energy. Electron-phonon coupling from both ultrafast coherent vibrational and steady-state resonance Raman spectroscopies allows us to determine that intramolecular electronic excitation of p-benzoquinone also drives the electron transfer process in quinhydrone. These results demonstrate the wide range of electronic excitations of the parent of molecules found in many functional organic materials that can drive coherent lattice phonon excitations useful for applications in electronics, photonics, and information technology. PMID:26979698

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

    Highlights: • Mechanism of PIET reaction process for the Rh101+/DEA system is investigated. • The significant geometrical changes of the charge–transfer complex are explained. • Forward Electron transfer from DEA to Rh101+∗ 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+) 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+∗ occurs on a time scale of τFET = 425–560 fs. The backward ET (BET) occurs in the inverted region with a time constant of τBET = 46.16–51.40 ps. The intramolecular vibrational relaxation (IVR) process occurs on the excited state potential energy surface with the time constant of τIVR = 2.77–5.39 ps

  5. Studies on intra-supramolecular and intermolecular electron-transfer processes between zinc naphthalocyanine and imidazole-appended fullerene.

    el-Khouly, Mohamed E; Rogers, Lisa M; Zandler, Melvin E; Suresh, Gadde; Fujitsuka, Mamoru; Ito, Osamu; D'Souza, Francis

    2003-04-14

    Spectroscopic, computational, redox, and photochemical behavior of a self-assembled donor-acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand (2-(4'-imidazolylphenyl)-fulleropyrrolidine, C60Im) was investigated in noncoordinating solvents, toluene and o-dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile. The optical absorption and ab initio B3 LYP/3-21G(*) computational studies revealed self-assembled supramolecular 1:1 dyad formation between the ZnNc and C60Im entities. In the optimized structure, the HOMO was found to be entirely located on the ZnNc entity while the LUMO was found to be entirely on the fullerene entity. Cyclic voltammetry studies of the dyad exhibited a total of seven one-electron redox processes in o-dichlorobenzene, with 0.1 M tetrabutylammonium perchlorate. The excited-state electron-transfer processes were monitored by both optical-emission and transient-absorption techniques. Direct evidence for the radical-ion-pair (C60Im.-:ZnNC.+) formation was obtained from picosecond transient-absorption spectral studies, which indicated charge separation from the singlet-excited ZnNc to the C60Im moiety. The calculated rates of charge separation and charge recombination were 1.4 x 10(10) s-1 and 5.3 x 10(7) s-1 in toluene and 8.9 x 10(9) s-1 and 9.2 x 10(7) s-1 in o-dichlorobenzene, respectively. In benzonitrile, intermolecular electron transfer from the excited triplet state of ZnNc to C60Im occurs and the second-order rate constant (kqtriplet) for this quenching process was 5.3 x 10(8)M-1s-1. PMID:12785261

  6. Electronic transitions and intermolecular forces

    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. Potassium ion controlled switching of intra- to intermolecular electron transfer in crown ether appended free-base porphyrin-fullerene donor-acceptor systems.

    D'Souza, Francis; Chitta, Raghu; Gadde, Suresh; Zandler, Melvin E; McCarty, Amy L; Sandanayaka, Atula S D; Araki, Yasuyaki; Ito, Osamu

    2006-04-01

    Photoinduced electron transfer in intramolecularly interacting free-base porphyrin bearing one or four 18-crown-6 ether units at different positions of the porphyrin macrocycle periphery and pristine fullerene was investigated in polar benzonitrile and nonpolar o-dichlorobenzene and toluene solvents. Owing to the presence of two modes of binding, stable dyads were obtained in which the binding constants, K, were found to range between 4.2 x 10(3) and 10.4 x 10(3) M(-1) from fluorescence quenching data depending upon the location and number of crown ether entities on the porphyrin macrocycle and the solvent. Computational studies using the B3LYP/3-21G() method were employed to arrive at the geometry and electronic structure of the intramolecular dyads. The energetics of the redox states of the dyads were established from cyclic voltammetric studies. Under the intramolecular conditions, both the steady-state and time-resolved emission studies revealed efficient quenching of the singlet excited free-base porphyrin in these dyads, and the measured rates of charge separation, k(CS), were found to be in the 10(8)-10(9) s(-1) range. Nanosecond transient absorption studies were performed to characterize the electron-transfer products and to evaluate the charge-recombination rates. Shifting of the electron-transfer pathway from the intra- to intermolecular route was achieved by complexing potassium ions to the crown ether cavity(ies) in benzonitrile. This cation complexation weakened the intramolecular interactions between fullerene and the crown ether appended free-base porphyrin supramolecules, and under these conditions, intermolecular type interactions were mainly observed. Reversible inter- to intramolecular electron transfer was also accomplished by extracting the potassium ions of the complex with the addition of 18-crown-6. The present study nicely demonstrates the application of supramolecular methodology to control the excited-state electron-transfer path in donor

  8. Mechanistic information from the first volume profile analysis for a reversible intermolecular electron-transfer reaction involving pentaammine(isonicotinamide)ruthenium and cytochrome c

    Baensch, B.; Meier, M.; Martinez, P. [Univ. of Witten/Herdecke (Germany)] [and others

    1994-10-12

    The reversible intermolecular electron-transfer reaction between pentaammine(isonicotinamide)ruthenium(II/III) and horse-heart cytochrome c iron(III/II) was subjected to a detailed kinetic and thermodynamic study as a function of temperature and pressure. Theoretical calculations based on the Marcus-Hush theory were employed to predict all rate and equilibrium constants as well as activation parameters. There is an excellent agreement between the kinetically and thermodynamically determined equilibrium constants and associated pressure parameters. These data are used to construct a volume profile for the overall process, from which it follows that the transition state lies halfway between the reactant and product states on a volume basis. The reorganization in the transition state has reached a similar degree in both directions of the electron-transfer process and corresponds to a {lambda}{sup {double_dagger}} value of 0.44 for this reversible reaction. This is the first complete volume profile analysis for a reversible intermolecular electron-transfer reaction.

  9. Resonant intermolecular transfer of vibrational energy in liquid water

    Woutersen, Sander; Bakker, Huib J.

    1999-12-01

    Many biological, chemical and physical processes involve the transfer of energy. In the case of electronic excitations, transfer between molecules is rapid, whereas for vibrations in the condensed phase, resonant energy transfer is an unlikely process because the typical timescale of vibrational relaxation (a few picoseconds) is much shorter than that of resonant intermolecular vibrational energy transfer. For the OH-stretch vibration in liquid water, which is of particular importance due to its coupling to the hydrogen bond, extensive investigations have shown that vibrational relaxation takes place with a time constant of 740 +/- 25 femtoseconds (ref. 7). So for resonant intermolecular energy transfer to occur in liquid water, the interaction between the OH-stretch modes of different water molecules needs to be extremely strong. Here we report time-resolved pump-probe laser spectroscopy measurements that reveal the occurrence of fast resonant intermolecular transfer of OH-stretch excitations over many water molecules before the excitation energy is dissipated. We find that the transfer process is mediated by dipole-dipole interactions (the Förster transfer mechanism) and additional mechanisms that are possibly based on intermolecular anharmonic interactions involving hydrogen bonds. Our findings suggest that liquid water may play an important role in transporting vibrational energy between OH groups located on either different biomolecules or along extended biological structures. OH groups in a hydrophobic environment should accordingly be able to remain in a vibrationally excited state longer than OH groups in a hydrophilic environment.

  10. Broadband visible light-harvesting naphthalenediimide (NDI) triad: study of the intra-/intermolecular energy/electron transfer and the triplet excited state.

    Wu, Shuang; Zhong, Fangfang; Zhao, Jianzhang; Guo, Song; Yang, Wenbo; Fyles, Tom

    2015-05-21

    A triad based on naphthalenediimides (NDI) was prepared to study the intersystem crossing (ISC), the fluorescence-resonance-energy-transfer (FRET), as well as the photoinduced electron transfer (PET) processes. In the triad, the 2-bromo-6-alkylaminoNDI moiety was used as singlet energy donor and the spin converter, whereas 2,6-dialkylaminoNDI was used as the singlet/triplet energy acceptor. This unique structural protocol and thus alignment of the energy levels ensures the competing ISC and FRET in the triad. The photophysical properties of the triad and the reference compounds were studied with steady-state UV-vis absorption spectra, fluorescence spectra, nanosecond transient absorption spectra, cyclic voltammetry, and DFT/TDDFT calculations. FRET was confirmed with steady-state UV-vis absorption and fluorescence spectroscopy. Intramolecular electron transfer was observed in polar solvents, demonstrated by the quenching of both the fluorescence and triplet state of the energy acceptor. Nanosecond transient absorption spectroscopy shows that the T1 state of the triad is exclusively localized on the 2,6-dialkylaminoNDI moiety in the triad upon selective photoexcitation into the energy donor, which indicates the intramolecular triplet state energy transfer. The intermolecular triplet state energy transfer between the two reference compounds was investigated with nanosecond transient absorption spectroscopy. The photophysical properties were rationalized by TDDFT calculations. PMID:25919420

  11. Inter-molecular electronic transfer

    Král, Karel; Menšík, Miroslav

    Warrendale, PA: Materials Research Society, 2010 - (Steckel, J.; Kotov, N.; Norris, D.; Bawendi, M.; Kuno, M.), 1207N0905-1-7. ( MRS Symposium Proceedings. 1207). ISBN 9781617387623. [ MRS Fall Meeting 2009. Boston (US), 30.11.2009-04.12.2009] R&D Projects: GA MŠk ME 866; GA ČR 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

  12. Intermolecular Phosphoryl Transfer Between Serine and Histidine Residues

    Yu Qian SU; Ming Yu NIU; Shu Xia CAO; Jian Chen ZHANG; Yu Fen ZHAO

    2004-01-01

    A novel intermolecular phosphoryl transfer from O-trimethylsilyl-N-(O, O-diisopropyl) phosphoryl serine trimethylsilyl ester to N, N'-bis(trimethylsilyl) histidine trimethylsilyl ester was studied through electrospray ionization mass spectrometry (ESI-MS). It was proposed that the transfer reaction went through penta-coordinated phosphorus intermediate.

  13. Nanophotonic boost of intermolecular energy transfer

    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.

  14. A New Intermolecular Phosphoryl Transfer between Serine and Histidine Residues

    SU,Yu-Qian; NIU,Ming-Yu; CAO,Shu-Xia; ZHANG,Jian-Chen; QU,Ling-Bo; LIAO,Xin-Cheng; ZHAO,Yu-Fen

    2004-01-01

    @@ Phosphoryl transfer constitutes one of the most important reactions in functionalized molecules, bioorganic chemistry and biochemistry.[1] The transformations are involved in diverse processes, such as activated state change of phosphorus, DNA/RNA synthesis, energy metabolism and signal transduction. So, phosphoryl transfer reaction which can be performed by either intramolecular or intermolecular phosphorylation and dephosphorylation mechanism has been investigated by many scientists in wide fields.

  15. Intermolecular Hydrogen Transfer in Isobutane Hydrate

    Takeshi Sugahara

    2012-05-01

    Full Text Available Electron spin resonance (ESR spectra of butyl radicals induced with γ-ray irradiation in the simple isobutane (2-methylpropane hydrate (prepared with deuterated water were investigated. Isothermal annealing results of the γ-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 γ-ray-irradiated propane hydrate with deuterated water.

  16. Ultrafast photoinduced intra- und intermolecular charge transfer and solvation

    Bizjak, Tanja

    2004-01-01

    Intra- and intermolecular charge transfer as well as internal conversion processes are studied in various molecular systems. The dynamics of these fundamental photoinduced processes are investigated by pump-probe femtosecond spectroscopy and steady-state fluorescence. Transient spectra are obtained using white light continuum as probe, while time resolved measurements are performed by probing at specific wavelengths with non dispersive detec-tion. Noncollinearly phase matched optical parametr...

  17. Intermolecular electron transfer between coumarin dyes and aromatic amines in Triton-X-100 micellar solutions: Evidence for Marcus inverted region

    Photoinduced electron transfer (ET) between coumarin dyes and aromatic amines has been investigated in Triton-X-100 micellar solutions and the results have been compared with those observed earlier in homogeneous medium. Significant static quenching of the coumarin fluorescence due to the presence of high concentration of amines around the coumarin fluorophore in the micelles has been observed in steady-state fluorescence studies. Time-resolved studies with nanosecond resolutions mostly show the dynamic part of the quenching for the excited coumarin dyes by the amine quenchers. A correlation of the quenching rate constants, estimated from the time-resolved measurements, with the free energy changes (ΔG0) of the ET reactions shows the typical bell shaped curve as predicted by Marcus outer-sphere ET theory. The inversion in the ET rates for the present systems occurs at an exergonicity (-ΔG0) of ∼0.7-0.8 eV, which is unusually low considering the polarity of the Palisade layer of the micelles where the reactants reside. Present results have been rationalized on the basis of the two dimensional ET model assuming that the solvent relaxation in micellar media is much slower than the rate of the ET process. Detailed analysis of the experimental data shows that the diffusional model of the bimolecular quenching kinetics is not applicable for the ET reactions in the micellar solutions. In the present systems, the reactions can be better visualized as equivalent to intramolecular electron transfer processes, with statistical distribution of the donors and acceptors in the micelles. A low electron coupling (Vel) parameter is estimated from the correlation of the experimentally observed and the theoretically calculated ET rates, which indicates that the average donor-acceptor separation in the micellar ET reactions is substantially larger than for the donor-acceptor contact distance. Comparison of the Vel values in the micellar solution and in the donor-acceptor close

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

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H2(B 1Σ/sub u/+) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H2(B 1Σ/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 1Σ/sub g/+) and with He + H2(X 1Σ/sub g/+) and cause a local maximum and a deep minimum in the He + H2(B 1Σ/sub u/+) PES, respectively. The crossing with He + H2(X 1Σ/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 1Σ/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

  19. Intermolecular nonradiative energy transfer in clusters with plasmonic nanoparticles

    Kucherenko, M. G.; Stepanov, V. N.; Kruchinin, N. Yu.

    2015-01-01

    The influence of carbon (fullerenes, nanotubes) and metal (Ni, Co, Cu, Ag) nanoparticles on the nonradiative electronic excitation energy transfer between the molecules of organic dyes (acrylic orange as a donor and Nile blue as an acceptor) in alcohol solutions of polyvinylbutyral is studied. It is found that, at particular concentrations of the mixture components, plasmonic nanoparticles affect the nonradiative electronic excitation energy transfer, which is manifested in an increase in the intensity of sensitized fluorescence of acceptors with simultaneous quenching of the fluorescence of donors. A very simple model is proposed to illustrate the observed redistribution of luminescence intensity between the spectral bands of the general spectrum. Molecular-dynamic calculations of the structure of nanocomposites performed for the same purpose confirmed the formation of associated molecular plasmonic complexes fixed by macrochain links.

  20. Description of cross peaks induced by intermolecular vibrational energy transfer in two-dimensional infrared spectroscopy

    Villaeys, Albert A

    2013-01-01

    In the present work, the analytical description of an intermolecular vibrational energy transfer, analyzed by two dimensional infrared spectroscopy, is established. The energy transfer process takes place between the dark combination states of low frequency modes pertaining to different molecules. The appearance of the cross peaks results from coherent transfer between these combination states and an optically active state of the acceptor molecule. Such a process has recently been observed experimentally between the nitrile groups of acetonitrile-d3 and benzonitrile molecules. This molecular system will be used as a model for the simulations of their two-dimensional infrared spectra. The dependence of the cross-peak growth, which is a signature of the intermolecular energy transfer, will be discussed in detail as a function of the molecular dynamical constants.

  1. Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase

    Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via α-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion

  2. Electron transfer reactions

    Cannon, R D

    2013-01-01

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

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

    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...

  4. Energy Decomposition Analysis with a Stable Charge-Transfer Term for Interpreting Intermolecular Interactions.

    Lao, Ka Un; Herbert, John M

    2016-06-14

    Many schemes for decomposing quantum-chemical calculations of intermolecular interaction energies into physically meaningful components can be found in the literature, but the definition of the charge-transfer (CT) contribution has proven particularly vexing to define in a satisfactory way and typically depends strongly on the choice of basis set. This is problematic, especially in cases of dative bonding and for open-shell complexes involving cation radicals, for which one might expect significant CT. Here, we analyze CT interactions predicted by several popular energy decomposition analyses and ultimately recommend the definition afforded by constrained density functional theory (cDFT), as it is scarcely dependent on basis set and provides results that are in accord with chemical intuition in simple cases, and in quantitative agreement with experimental estimates of the CT energy, where available. For open-shell complexes, the cDFT approach affords CT energies that are in line with trends expected based on ionization potentials and electron affinities whereas some other definitions afford unreasonably large CT energies in large-gap systems, which are sometimes artificially offset by underestimation of van der Waals interactions by density functional theory. Our recommended energy decomposition analysis is a composite approach, in which cDFT is used to define the CT component of the interaction energy and symmetry-adapted perturbation theory (SAPT) defines the electrostatic, polarization, Pauli repulsion, and van der Waals contributions. SAPT/cDFT provides a stable and physically motivated energy decomposition that, when combined with a new implementation of open-shell SAPT, can be applied to supramolecular complexes involving molecules, ions, and/or radicals. PMID:27049750

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

    Jensen, Anders A.; Hansen, Jakob L; Sheikh, Søren P;

    2002-01-01

    -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...

  6. Electron transfer in proteins

    Farver, O; Pecht, I

    1991-01-01

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

  7. Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.

    Nishino, Tomoaki

    2014-01-01

    This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics. PMID:24420248

  8. Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

    Ye, ChuanXiang [Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Zhao, Yi, E-mail: yizhao@xmu.edu.cn, E-mail: liangwz@xmu.edu.cn [State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China); Liang, WanZhen, E-mail: yizhao@xmu.edu.cn, E-mail: liangwz@xmu.edu.cn [Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, and College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005 (China)

    2015-10-21

    The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT.

  9. Resonance Raman spectra of organic molecules absorbed on inorganic semiconducting surfaces: Contribution from both localized intramolecular excitation and intermolecular charge transfer excitation

    The time-dependent correlation function approach for the calculations of absorption and resonance Raman spectra (RRS) of organic molecules absorbed on semiconductor surfaces [Y. Zhao and W. Z. Liang, J. Chem. Phys. 135, 044108 (2011)] is extended to include the contribution of the intermolecular charge transfer (CT) excitation from the absorbers to the semiconducting nanoparticles. The results demonstrate that the bidirectionally interfacial CT significantly modifies the spectral line shapes. Although the intermolecular CT excitation makes the absorption spectra red shift slightly, it essentially changes the relative intensities of mode-specific RRS and causes the oscillation behavior of surface enhanced Raman spectra with respect to interfacial electronic couplings. Furthermore, the constructive and destructive interferences of RRS from the localized molecular excitation and CT excitation are observed with respect to the electronic coupling and the bottom position of conductor band. The interferences are determined by both excitation pathways and bidirectionally interfacial CT

  10. Evidence of pressure induced intermolecular proton transfer via mutarotation: the case of supercooled d-fructose.

    Cecotka, Adam; Tripathy, Satya N; Paluch, Marian

    2015-07-15

    This paper describes a systematic investigation on the role of pressure in mutarotation kinetics of supercooled d-fructose using dielectric spectroscopy. The structural relaxation time acts as a suitable dynamical observable to monitor the mutarotation process that enables the construction of the kinetic curves. The reaction kinetic shapes have been analyzed using the Avrami model. At low temperature, sigmoidal kinetic curves are noted, which correspond to the high concentration of furanosidic forms. The magnitude of activation energy of the process significantly decreases with increasing pressure and is comparable to the solvated systems at 100 MPa. A potential connection between cooperative motion and the origin of intermolecular proton transfer via mutarotation at elevated pressure is also discussed. These experimental observations have fundamental significance on theoretical explanation of the mechanism involving mutarotation in sugars. PMID:26144525

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

    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 (∼ 100 cm-1 or ∼ 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.

  12. Electron transfer in proteins.

    Gray, H B; Winkler, J R

    1996-01-01

    Electron-transfer (ET) reactions are key steps in a diverse array of biological transformations ranging from photosynthesis to aerobic respiration. A powerful theoretical formalism has been developed that describes ET rates in terms of two parameters: the nuclear reorganization energy (lambda) and the electronic-coupling strength (HAB). Studies of ET reactions in ruthenium-modified proteins have probed lambda and HAB in several metalloproteins (cytochrome c, myoglobin, azurin). This work has shown that protein reorganization energies are sensitive to the medium surrounding the redox sites and that an aqueous environment, in particular, leads to large reorganization energies. Analyses of electronic-coupling strengths suggest that the efficiency of long-range ET depends on the protein secondary structure: beta sheets appear to mediate coupling more efficiently than alpha-helical structures, and hydrogen bonds play a critical role in both. PMID:8811189

  13. Advances in electron transfer chemistry

    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

  14. Frenkel and Charge-Transfer Excitons in Quasi-One-Dimensional Molecular Crystals with Strong Intermolecular Orbital Overlap

    Hoffmann, Michael

    2000-01-01

    We present a theoretical and experimental study on the lowest electronically excited states in quasi-one-dimensional molecular crystals. The specific calculations and the experiments are performed for the model compounds MePTCDI (N-N'-dimethylperylene-3,4:9,10-dicarboximide) and TCDA(3,4:9,10-perylenetetracarboxylic dianhydride). The intermolecular interactions between nearest neighbors are quantum chemically analyzed on the basis of semi-empirical (ZINDO/S) Hartree-Fock calculations and a si...

  15. Electron transfer interactome of cytochrome C.

    Alexander N Volkov

    Full Text Available Lying at the heart of many vital cellular processes such as photosynthesis and respiration, biological electron transfer (ET is mediated by transient interactions among proteins that recognize multiple binding partners. Accurate description of the ET complexes - necessary for a comprehensive understanding of the cellular signaling and metabolism - is compounded by their short lifetimes and pronounced binding promiscuity. Here, we used a computational approach relying solely on the steric properties of the individual proteins to predict the ET properties of protein complexes constituting the functional interactome of the eukaryotic cytochrome c (Cc. Cc is a small, soluble, highly-conserved electron carrier protein that coordinates the electron flow among different redox partners. In eukaryotes, Cc is a key component of the mitochondrial respiratory chain, where it shuttles electrons between its reductase and oxidase, and an essential electron donor or acceptor in a number of other redox systems. Starting from the structures of individual proteins, we performed extensive conformational sampling of the ET-competent binding geometries, which allowed mapping out functional epitopes in the Cc complexes, estimating the upper limit of the ET rate in a given system, assessing ET properties of different binding stoichiometries, and gauging the effect of domain mobility on the intermolecular ET. The resulting picture of the Cc interactome 1 reveals that most ET-competent binding geometries are located in electrostatically favorable regions, 2 indicates that the ET can take place from more than one protein-protein orientation, and 3 suggests that protein dynamics within redox complexes, and not the electron tunneling event itself, is the rate-limiting step in the intermolecular ET. Further, we show that the functional epitope size correlates with the extent of dynamics in the Cc complexes and thus can be used as a diagnostic tool for protein mobility.

  16. Coherent electron transfer in polyacetylene

    Psiachos, D., E-mail: dpsi@physics.uoc.gr

    2014-06-03

    Highlights: • We study electron–ion dynamics in a donor–acceptor system. • We find two distinct electron-transfer regimes: hopping and tunnelling. • We establish conditions for achieving ballistic electron transfer. • Lattice vibrations can dramatically affect the rate of electron transfer. • Decoherence due to lattice vibrations is limited in the tunnelling regime. - Abstract: We examine, using mixed classical-quantum electron–ion dynamics, electron transfer in a donor–acceptor-like molecular junction system based on polyacetylene. We identify two qualitatively-different transfer regimes: hopping and tunnelling. We discuss the criteria for achieving each one and for minimising inelastic scattering and decoherence arising from the coupling to the ions, and we connect our main results to quantities derived from electron dynamics involving simpler, three-state model systems. We identify the requirements to have near-ballistic transfer.

  17. Coherence in electron transfer pathways

    Skourtis, Spiros S.; Beratan, David N.; Waldeck, David H.

    2011-01-01

    Central to the view of electron-transfer reactions is the idea that nuclear motion generates a transition state geometry at which the electron/hole amplitude propagates coherently from the electron donor to the electron acceptor. In the weakly coupled or nonadiabatic regime, the electron amplitude tunnels through an electronic barrier between the donor and acceptor. The structure of the barrier is determined by the covalent and noncovalent interactions of the bridge. Because the tunneling bar...

  18. Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: The case of Euglena gracilis

    In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A498, non fluorescent and B462, fluorescent. Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A498 becomes B462), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B462 form acts as donor for the non-fluorescent A498 form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.

  19. Skeletal Isomerization and Inter-molecular Hydrogen Transfer Reactions in Catalytic Cracking

    Gao Yongcan; Zhang Jiushun; Xie Chaogang; Long Jun

    2002-01-01

    Bimolecular hydrogen transfer and skeletal isomerization are the important secondary reac tions among catalytic cracking reactions, which affect product yield distribution and product quality.Catalyst properties and operating parameters have great impact on bimolecular hydrogen transfer and skeletal isomerization reactions. Bimolecular hydrogen transfer activity and skeletal isomerization activity of USY-containing catalysts are higher than that of ZSM-5-containing catalyst. Coke deposition on the active sites of catalyst may suppress bimolecular hydrogen transfer activity and skeletal isomerization activity of catalyst in different degrees. Short reaction time causes a decrease of hydrogen trans fer reaction, but an increase of skeletal isomerization reaction compared to cracking reaction in catalytic cracking process.

  20. Electronic fund transfer & the "unbanked"

    Luxman Nathan

    1998-01-01

    As the Federal Government moves to switch most federal payments from paper check delivery to Direct Deposit by January 2, 1999, the Electronic Fund Transfer Initiative (EFT) attempts to educate consumers and serve the "unbanked."

  1. Advances in electron transfer chemistry

    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

  2. Coherence in electron transfer pathways.

    Skourtis, Spiros S; Beratan, David N; Waldeck, David H

    2011-01-01

    Central to the view of electron-transfer reactions is the idea that nuclear motion generates a transition state geometry at which the electron/hole amplitude propagates coherently from the electron donor to the electron acceptor. In the weakly coupled or nonadiabatic regime, the electron amplitude tunnels through an electronic barrier between the donor and acceptor. The structure of the barrier is determined by the covalent and noncovalent interactions of the bridge. Because the tunneling barrier depends on the nuclear coordinates of the reactants (and on the surrounding medium), the tunneling barrier is highly anisotropic, and it is useful to identify particular routes, or pathways, along which the transmission amplitude propagates. Moreover, when more than one such pathway exists, and the paths give rise to comparable transmission amplitude magnitudes, one may expect to observe quantum interferences among pathways if the propagation remains coherent. Given that the effective tunneling barrier height and width are affected by the nuclear positions, the modulation of the nuclear coordinates will lead to a modulation of the tunneling barrier and hence of the electron flow. For long distance electron transfer in biological and biomimetic systems, nuclear fluctuations, arising from flexible protein moieties and mobile water bridges, can become quite significant. We discuss experimental and theoretical results that explore the quantum interferences among coupling pathways in electron-transfer kinetics; we emphasize recent data and theories associated with the signatures of chirality and inelastic processes, which are manifested in the tunneling pathway coherence (or absence of coherence). PMID:23833692

  3. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na+ and K+ ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications

  4. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    Yao, Yi; Berkowitz, Max L., E-mail: maxb@unc.edu, E-mail: ykanai@unc.edu; Kanai, Yosuke, E-mail: maxb@unc.edu, E-mail: ykanai@unc.edu [Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599 (United States)

    2015-12-28

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na{sup +} and K{sup +} ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  5. Communication: Modeling of concentration dependent water diffusivity in ionic solutions: Role of intermolecular charge transfer

    Yao, Yi; Berkowitz, Max L.; Kanai, Yosuke

    2015-12-01

    The translational diffusivity of water in solutions of alkali halide salts depends on the identity of ions, exhibiting dramatically different behavior even in solutions of similar salts of NaCl and KCl. The water diffusion coefficient decreases as the salt concentration increases in NaCl. Yet, in KCl solution, it slightly increases and remains above bulk value as salt concentration increases. Previous classical molecular dynamics simulations have failed to describe this important behavior even when polarizable models were used. Here, we show that inclusion of dynamical charge transfer among water molecules produces results in a quantitative agreement with experiments. Our results indicate that the concentration-dependent diffusivity reflects the importance of many-body effects among the water molecules in aqueous ionic solutions. Comparison with quantum mechanical calculations shows that a heterogeneous and extended distribution of charges on water molecules around the ions due to ion-water and also water-water charge transfer plays a very important role in controlling water diffusivity. Explicit inclusion of the charge transfer allows us to model accurately the difference in the concentration-dependent water diffusivity between Na+ and K+ ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications.

  6. Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: The case of Euglena gracilis

    Mercatelli, Raffaella; Quercioli, Franco [Istituto Sistemi Complessi, CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy); Barsanti, Laura; Evangelista, Valter [Istituto di Biofisica, CNR, Via Moruzzi 1, 56124 Pisa (Italy); Coltelli, Primo [ISTI, CNR, Via Moruzzi 1, 56124 Pisa (Italy); Passarelli, Vincenzo; Frassanito, Anna Maria [Istituto di Biofisica, CNR, Via Moruzzi 1, 56124 Pisa (Italy); Gualtieri, Paolo, E-mail: paolo.gualtieri@pi.ibf.cnr.it [Istituto di Biofisica, CNR, Via Moruzzi 1, 56124 Pisa (Italy)

    2009-07-24

    In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A{sub 498,} non fluorescent and B{sub 462}, fluorescent. Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A{sub 498} becomes B{sub 462}), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B{sub 462} form acts as donor for the non-fluorescent A{sub 498} form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.

  7. Evidence for alkali metal induced intermolecular acetylenic hydrogen atom transfer between hydrogen-bonded alkyne complexes in solid argon

    Condensation of acetylene, propyne, and 2-butyne/acetylene mixtures with heavy alkali metal atoms (Na, K, Cs) in an argon matrix at 15 K has led to the appearance of infrared absorptions due to ethylene, propylene, and trans-2-butene, respectively. These results stand in sharp contrast with the products obtained with lithium. Isotopic studies have shown that ethylene formation involved three different acetylene molecules and evidenced a difference in the product yield with hydrogen vs. deuterium as well as a preference for trans- vs. cis-C2H2D2 formation, which is discussed and rationalized by differences in the zero point energies for the different mixed deuterium isotopes of the intermediate vinyl radical. This trend is amplified by methyl substitution. Spectroscopic evidence was found in these experiments for cesium acetylide (Cs+C2H-) and a cesium-acetylene π complex, which are involved in the intermolecular acetylenic hydrogen atom transfer process. 26 references, 3 figures, 2 tables

  8. The electronic couplings in electron transfer and excitation energy transfer.

    Hsu, Chao-Ping

    2009-04-21

    The transport of charge via electrons and the transport of excitation energy via excitons are two processes of fundamental importance in diverse areas of research. Characterization of electron transfer (ET) and excitation energy transfer (EET) rates are essential for a full understanding of, for instance, biological systems (such as respiration and photosynthesis) and opto-electronic devices (which interconvert electric and light energy). In this Account, we examine one of the parameters, the electronic coupling factor, for which reliable values are critical in determining transfer rates. Although ET and EET are different processes, many strategies for calculating the couplings share common themes. We emphasize the similarities in basic assumptions between the computational methods for the ET and EET couplings, examine the differences, and summarize the properties, advantages, and limits of the different computational methods. The electronic coupling factor is an off-diagonal Hamiltonian matrix element between the initial and final diabatic states in the transport processes. ET coupling is essentially the interaction of the two molecular orbitals (MOs) where the electron occupancy is changed. Singlet excitation energy transfer (SEET), however, contains a Frster dipole-dipole coupling as its most important constituent. Triplet excitation energy transfer (TEET) involves an exchange of two electrons of different spin and energy; thus, it is like an overlap interaction of two pairs of MOs. Strategies for calculating ET and EET couplings can be classified as (1) energy-gap-based approaches, (2) direct calculation of the off-diagonal matrix elements, or (3) use of an additional operator to describe the extent of charge or excitation localization and to calculate the coupling value. Some of the difficulties in calculating the couplings were recently resolved. Methods were developed to remove the nondynamical correlation problem from the highly precise coupled cluster

  9. Intermolecular interactions and proton transfer in the hydrogen halide-superoxide anion complexes.

    Lee, Sebastian J R; Mullinax, J Wayne; Schaefer, Henry F

    2016-02-17

    The superoxide radical anion O2(-) is involved in many important chemical processes spanning different scientific disciplines (e.g., environmental and biological sciences). Characterizing its interaction with various substrates to help elucidate its rich chemistry may have far reaching implications. Herein, we investigate the interaction between O2(-) (X[combining tilde] (2)Πg) and the hydrogen halides (X[combining tilde] (1)Σ) with coupled-cluster theory. In contrast to the short (1.324 Å) hydrogen bond formed between the HF and O2(-) monomers, a barrierless proton transfer occurs for the heavier hydrogen halides with the resulting complexes characterized as long (>1.89 Å) hydrogen bonds between halide anions and the HO2 radical. The dissociation energy with harmonic zero-point vibrational energy (ZPVE) for FHO2(-) (X[combining tilde] (2)A'') → HF (X[combining tilde] (1)Σ) + O2(-) (X[combining tilde] (2)Πg) is 31.2 kcal mol(-1). The other dissociation energies with ZPVE for X(-)HO2 (X[combining tilde] (2)A'') → X(-) (X[combining tilde] (1)Σ) + HO2 (X[combining tilde] (2)A'') are 25.7 kcal mol(-1) for X = Cl, 21.9 kcal mol(-1) for X = Br, and 17.9 kcal mol(-1) for X = I. Additionally, the heavier hydrogen halides can form weak halogen bonds H-XO2(-) (X[combining tilde] (2)A'') with interaction energies including ZPVE of -2.3 kcal mol(-1) for HCl, -8.3 kcal mol(-1) for HBr, and -16.7 kcal mol(-1) for HI. PMID:26852733

  10. Benchmark Calculations of Three-Body Intermolecular Interactions and the Performance of Low-Cost Electronic Structure Methods.

    Řezáč, Jan; Huang, Yuanhang; Hobza, Pavel; Beran, Gregory J O

    2015-07-14

    Many-body noncovalent interactions are increasingly important in large and/or condensed-phase systems, but the current understanding of how well various models predict these interactions is limited. Here, benchmark complete-basis set coupled cluster singles, doubles, and perturbative triples (CCSD(T)) calculations have been performed to generate a new test set for three-body intermolecular interactions. This "3B-69" benchmark set includes three-body interaction energies for 69 total trimer structures, consisting of three structures from each of 23 different molecular crystals. By including structures that exhibit a variety of intermolecular interactions and packing arrangements, this set provides a stringent test for the ability of electronic structure methods to describe the correct physics involved in the interactions. Both MP2.5 (the average of second- and third-order Møller-Plesset perturbation theory) and spin-component-scaled CCSD for noncovalent interactions (SCS-MI-CCSD) perform well. MP2 handles the polarization aspects reasonably well, but it omits three-body dispersion. In contrast, many widely used density functionals corrected with three-body D3 dispersion correction perform comparatively poorly. The primary difficulty stems from the treatment of exchange and polarization in the functionals rather than from the dispersion correction, though the three-body dispersion may also be moderately underestimated by the D3 correction. PMID:26575743

  11. Electron Transfer to Vinylaromatic Polymers

    Aromatic polymers accept electrons from alkali metals to form polyradicalanions. These undergo chain scission as a result of electronic interaction between aromatic rings. Spectrophotometric and chemical evidence led to the conclusion that during the chain-breaking process polymeric fragments were formed which had the properties of ''living polymers'', i.e. the characteristic visible spectra and the capability of initiating the polymerization of a number of vinyl monomers. It was possible to follow the rate of chain scission in the case of poly (4-vinyl biphenyl) and poly(α-vinyl naphthalene) by means of viscosity and spectrophotometric measurements. The postulated mechanism was found to be consistent with the slow decrease in free spin concentration measured by means of the electron spin resonance technique. Chain scission in polyacenaphthalene takes place at a much faster rate than in poly (4-vinyl biphenyl) and this fact is in good agreement with simple LCAO MO calculations. Preliminary experiments indicate that electron transfer to poly-N-vinyl carbazole produces little if any degradation. These investigations led to the examination of the temperature effect on the electron-transfer reaction from sodium to some substituted aromatic hydrocarbons. The details of this effect are discussed. (author)

  12. Electron transfer in helical polyaromatics

    Pospíšil, Lubomír; Gál, Miroslav; Horáček, Michal; Teplý, Filip; Adriaenssens, Louis; Severa, Lukáš

    Xi´an: International Society of Electrochemistry, 2009. O06-O06. [International Symposium on Frontiers of Electrochemical Science and Technology . 12.08.2009-15.08.2009, Xi´an] R&D Projects: GA ČR GA203/08/1157; GA MŠk OC 140; GA ČR GA203/09/0705; GA ČR GP203/09/P502; GA MŠk ME09114 Institutional research plan: CEZ:AV0Z40400503; CEZ:AV0Z40550506 Keywords : electron transfer * helical polyaromatics Subject RIV: CG - Electrochemistry

  13. Heterostructure Intervalley Transferred Electron Effects

    XUE Fang-Shi

    2001-01-01

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

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

    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. The inclusion of electron correlation in intermolecular potentials: Applications to the formamide dimer and liquid formamide

    Brdarski, S.; Åstrand, P.-O.; Karlström, G.

    2000-01-01

    dipole moment is 11% lower at the MP2 level than at the Hartree-Fock (HF) level, whereas the isotropic part of the polarizability is increased by 36% by adding electron correlation and using a considerably larger basis set. The atomic charges, dipole moments and polarizabilities obtained at the HF level...

  16. Conformational analysis, inter-molecular interactions, electronic properties and vibrational spectroscopic studies on cis-4-hydroxy-d-proline

    Ambrish Kumar Srivastava

    2016-12-01

    Full Text Available The present study deals with a non-native amino acid, cis-4-hydroxy-d-proline (CHDP using density functional theory at B3LYP/6-31+G(d,p level. The potential energy surface scan reveals the global minimum structure of CHDP along with two potential conformers. Highest occupied molecular orbital, lowest unoccupied molecular orbital, and molecular electrostatic potential surfaces are used to explain the chemical reactivity of title molecule. The atomic charge analysis has been carried out using Mulliken and natural population schemes. The equilibrium geometry of CHDP dimer has been obtained and inter-molecular interactions are explored using QTAIM and Natural bonding orbital analyses. Vibrational spectroscopic analysis has been performed on CHDP monomer and dimer at the same level of theory. Assignments to all vibrational modes up to 400 cm−1 have been offered along with their potential energy distribution to the maximum possible accuracy. The calculated frequencies are scaled by an equation, rather than by a constant factor and then compared with experimental FT-IR frequencies obtained by KBr disc and Nujol mull techniques. A number of electronic and thermodynamic parameters have also been evaluated for CHDP monomer and dimer.

  17. Quantifying electron transfer reactions in biological systems

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

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling...... 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...

  18. Dynamic NMR studies of base-catalyzed intramolecular single vs. intermolecular double proton transfer of 1,3-bis(4-fluorophenyl)triazene

    In this paper, we explore the mechanisms of degenerate base-catalyzed intra- and intermolecular proton transfer using dynamic liquid state NMR. For this purpose, the model compound 1,3-bis(4-fluorophenyl)[1,3-15N2]triazene (1) was studied with and without the presence of dimethylamine (2), trimethylamine (3) and water, using tetrahydrofuran-d 8 and methylethylether-d 8 as solvents, down to 130 K. Compound 1 represents an analog of carboxylic acids and of diarylamidines forming cyclic dimers in which a fast double proton transfer takes place. By contrast, the structure of 1 was chosen in such a way that this double proton transfer is suppressed, thus revealing the base catalyzed transfer by dynamic 1H and 19F NMR. Surprisingly, both 2 and 3 can pick up the mobile proton of 1 at one nitrogen atom and carry it to the other nitrogen atom of 1, resulting in an intramolecular transfer process catalyzed each time by a different base molecule. Even more surprising is that the intramolecular transfer catalyzed by 2 is faster than the superimposed intermolecular double proton transfer. In the absence of added bases, a 1 is subject to a slow proton exchange with 2-amino-5,4'-difluoro-diphenyl-diazene (4) which is formed in small quantities from 1 in the presence of acid impurities. This process can be minimized by a proper sample preparation technique. The kinetic H/D isotope effects are small, especially in the catalysis by 2, indicating a major heavy atom rearrangement and absence of tunneling. Semi-empirical PM3 and ab initio DFT calculations indicate a reaction pathway via a hydrogen bond switch of the protonated amine representing the transition state. The Arrhenius curves of all processes exhibit strong convex curvatures. This phenomenon is explained in terms of the hydrogen bond association of 1 with the added bases, preceding the proton transfer. At low temperatures, all catalysts are in a hydrogen bonded reactive complex with 1, and the rate constants observed equal

  19. Dynamic NMR studies of base-catalyzed intramolecular single vs. intermolecular double proton transfer of 1,3-bis(4-fluorophenyl)triazene

    Limbach, Hans-Heinrich; Männle, Ferdinand; Detering, Carsten; Denisov, Gleb S.

    2005-12-01

    In this paper, we explore the mechanisms of degenerate base-catalyzed intra- and intermolecular proton transfer using dynamic liquid state NMR. For this purpose, the model compound 1,3-bis(4-fluorophenyl)[1,3- 15N 2]triazene ( 1) was studied with and without the presence of dimethylamine ( 2), trimethylamine ( 3) and water, using tetrahydrofuran- d8 and methylethylether- d8 as solvents, down to 130 K. Compound 1 represents an analog of carboxylic acids and of diarylamidines forming cyclic dimers in which a fast double proton transfer takes place. By contrast, the structure of 1 was chosen in such a way that this double proton transfer is suppressed, thus revealing the base catalyzed transfer by dynamic 1H and 19F NMR. Surprisingly, both 2 and 3 can pick up the mobile proton of 1 at one nitrogen atom and carry it to the other nitrogen atom of 1, resulting in an intramolecular transfer process catalyzed each time by a different base molecule. Even more surprising is that the intramolecular transfer catalyzed by 2 is faster than the superimposed intermolecular double proton transfer. In the absence of added bases, a 1 is subject to a slow proton exchange with 2-amino-5,4'-difluoro-diphenyl-diazene ( 4) which is formed in small quantities from 1 in the presence of acid impurities. This process can be minimized by a proper sample preparation technique. The kinetic H/D isotope effects are small, especially in the catalysis by 2, indicating a major heavy atom rearrangement and absence of tunneling. Semi-empirical PM3 and ab initio DFT calculations indicate a reaction pathway via a hydrogen bond switch of the protonated amine representing the transition state. The Arrhenius curves of all processes exhibit strong convex curvatures. This phenomenon is explained in terms of the hydrogen bond association of 1 with the added bases, preceding the proton transfer. At low temperatures, all catalysts are in a hydrogen bonded reactive complex with 1, and the rate constants observed

  20. Role of intermolecular interactions on the electronic and geometric structure of a large Pi-conjugated molecule adsorbed on a metal surface

    Kilian, L.; Hauschild, A.; Temirov, R.; Soubatch, S.; Schoell, A.; Bendounan, A.; Reinert, F.; Lee, T. L.; Tautz, F. S.; Sokolowski, M.; Umbach, E

    2008-01-01

    The organic semiconductor molecule 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) exhibits two adsorption states on the Ag(111) surface: one in a metastable disordered phase, prepared at low temperatures, the other in the long-range ordered monolayer phase obtained at room temperature. Notably, the two states differ substantial in their vertical bonding distances, intramolecular distortions, and electronic structures. The difference is explained by intermolecular interactions, which ar...

  1. Effects of inter-molecular charge-transfer excitons on the external quantum efficiency of zinc-porphyrin/C60 heterojunction photovoltaic cells

    Ryuzaki, Sou; Kai, Toshihiro; Toda, Yasunori; Adachi, Satoru; Onoe, Jun

    2011-04-01

    We have examined the structural effects of zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic heterojunction photovoltaic (OPV) cells [ITO/Zn(OEP)/C60/Al], and investigated what exactly causes the improvement of EQE. When the structure of the Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of around 35% for previously reported OPV cells using buffer materials (Peumans and Forrest 2001 Appl. Phys. Lett. 79 126). The crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge-transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE of the photoabsorption band under illumination due to the IMCT excitons.

  2. Hierarchical control of electron-transfer

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

    1997-01-01

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

  3. Photoselected electron transfer pathways in DNA photolyase

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

    2007-01-01

    Cyclobutane dimer photolyases are proteins that bind to UV-damaged DNA containing cyclobutane pyrimidine dimer lesions. They repair these lesions by photo-induced electron transfer. The electron donor cofactor of a photolyase is a two-electron-reduced flavin adenine dinucleotide (FADH−). When FADH− is photo-excited, it transfers an electron from an excited π → π* singlet state to the pyrimidine dimer lesion of DNA. We compute the lowest excited singlet states of FADH− using ab initio (time-de...

  4. Advances in electron transfer chemistry, v.6

    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.

  5. Heat Transfer Augmentation for Electronic Cooling

    Suabsakul Gururatana

    2012-01-01

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

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

    Raffalt, Anders Christer; Schmidt, L.; Christensen, Hans Erik Mølager;

    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...

  7. Imaging the electrons from transfer ionization collisions

    The electrons emitted into the continuum in transfer ionization of He2+ on helium collisions in the energy range of 75 - 400 keV were imaged using reaction microscope. The electron emission patterns show big difference for projectile velocity lower and upper than 1 a.u. in the present studies.

  8. Low Temperature Electronic Transport and Electron Transfer through Organic Macromolecules

    Zimbovskaya, N A

    2002-01-01

    It is shown that at low temperatures and moderate electron dephasing the electron transmission function reveales a structure containing information about donor/acceptor sites effectively participating in the electron transfer (ET) processes and primary pathways of electrons tunneling through molecular bridges in macromolecules. This important information can be obtained as a result of analysis of experimental low temperature current-voltage characteristics for chosen molecules.

  9. Electron transfer across a thermal gradient.

    Craven, Galen T; Nitzan, Abraham

    2016-08-23

    Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor-acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures. PMID:27450086

  10. Photoinduced electron transfer in ordered polymers

    Jones, G. II.

    1991-12-01

    Long range photoinduced electron transfer between electron donor and acceptor groups is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. As part of an extensive study of long range electron transfer involving biopolymers, we have carried out this year investigations of the assembly of electron transfer agents in a system of model short peptides. Also studied is a polyelectrolyte that can adopt a helical conformation when electrostatically complexed with organic dye counter-ions. The principal interest in these systems has to do with the well ordered secondary structures adopted by peptide polymers, and the capabilities for synthetic modification of peptide side chains and end groups with chromophores or electroactive substituents. The present report gives a brief account of the following elements of work related to photochemical electron transfer themes: (1) the synthesis and photochemical characterization of chromophore-bound peptides and amino acid model compounds based on the amino acids, tryptophan and the spacer residue, alanine (Ala); (2) the study of binding of the cationic organic dye to a peptide electrolyte, for which cooperative dye loading and helix formation is important; and (3) completion of the synthesis of a new series of acridinium chromophores that have rod-like'' arrangements of inked aryl rings for assembly of electron donor-acceptor systems that will exhibit especially long lived charge separation.

  11. Unusual distance dependences of electron transfer rates.

    Kuss-Petermann, Martin; Wenger, Oliver S

    2016-07-28

    Usually the rates for electron transfer (kET) decrease with increasing donor-acceptor distance, but Marcus theory predicts a regime in which kET is expected to increase when the transfer distance gets longer. Until recently, experimental evidence for such counter-intuitive behavior had been very limited, and consequently this effect is much less well-known than the Gaussian free energy dependence of electron transfer rates leading to the so-called inverted driving-force effect. This article presents the theoretical concepts that lead to the prediction of electron transfer rate maxima at large donor-acceptor distances, and it discusses conditions that are expected to favor experimental observations of such behavior. It continues with a consideration of specific recent examples in which electron transfer rates were observed to increase with increasing donor-acceptor distance, and it closes with a discussion of the importance of this effect in the context of light-to-chemical energy conversion. PMID:27353891

  12. Facile Interfacial Electron Transfer of Hemoglobin

    Chunhai Fan; Shiping Song; Haiping Wu; Lihua Wang; Xiaofang Hu; Runguang Sun; Bo Zhou

    2005-01-01

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

  13. Facile Interfacial Electron Transfer of Hemoglobin

    Chunhai Fan

    2005-12-01

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

  14. Facilitating electron transfer in bioelectrocatalytic systems

    Sekretaryova, Alina

    2016-01-01

    Bioelectrocatalytic systems are based on biological entities, such as enzymes, whole cells, parts of cells or tissues, which catalyse electrochemical processes that involve the interaction between chemical change and electrical energy. In all cases, biocatalysis is implemented by enzymes, isolated or residing inside cells or part of cells. Electron transfer (ET) phenomena, within the protein molecules and between biological redox systems and electronics, enable the development of various bioe...

  15. Resonant electron transfer between quantum dots

    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 superposition of electron s...

  16. DFT study of isocyanate chemisorption on Cu(100): Correlation between substrate-adsorbate charge transfer and intermolecular interactions

    Belelli, Patricia G.; Garda, Graciela R.; Ferullo, Ricardo M.

    2011-07-01

    The adsorption of isocyanate (- NCO) species on Cu(100) was studied using the density functional theory (DFT) and the periodic slab model. The calculations indicate that at low and intermediate coverages NCO adsorbs preferentially on bridge and hollow sites. Work function and dipole moment changes show a significant negative charge transfer from Cu to NCO. The resulting charged NCO species interact repulsively among themselves being these dipole-dipole interactions particularly intensive when they are adsorbed in adjacent sites. Consequently, isocyanates tend to be separated from each other generating the vacant sites required for the dissociation to N and CO. This condition for NCO dissociation has been suggested in the past from experimental observations. A comparison was also performed with the NCO adsorption on Pd(100). In particular, the calculated minimal energy barrier for NCO dissociation was found to be higher on Cu(100) than on Pd(100) in accord with the well known higher NCO stability on Cu(100).

  17. Electron transfer in dinucleoside phosphate anions

    The electron transfer reaction within various dinucleoside phosphate radical anions has been investigated by ESR spectroscopy and pulse radiolysis. In the ESR work electrons are produced by photolysis of K4Fe(CN)6 in a 12 M LiCl glass at 770K. Upon photobleaching the electrons react with the dinucleoside phosphate to form the anion radical. The anions of the four DNA nucleosides were also produced and their ESR spectra were appropriately weighted and summed by computer to simulate the spectra found for the dinucleoside phosphate anions. From the analysis the relative amounts of each of the nucleoside anions in the dinucleoside phosphate anion were determined. Evidence suggests the electron affinity of the pyrimidine bases are greater than the purine bases; however, the results are not sufficient to distinguish between the individual purine or pyrimidine. When dinucleoside phosphate anions containing thymidine are warmed, protonation occurs only on thymine to produce the well known ''thymyl'' spectrum. Pulse radiolysis experiments on individual nucleotides (TMP, dAMP), mixtures of these nucleotides and the dinucleoside phosphate, TdA, in aqueous solution at room temperature show that in the TdA anion electron transfer occurs from adenine to thymine, whereas no electron transfer is found for mixtures of individual nucleotides. Protonation is found to occur only on thymine in the TdA anion in agreement with the ESR results

  18. Photoinduced electron transfer in ordered polymers

    Jones, G. II.

    1990-10-20

    Photochemical studies on organic polymers or biopolymers (particularly synthetic peptides) that have been modified by covalent attachment (or other means of binding) of organic chromophores and electron transfer agents are described. Specific projects involve are: peptide conjugates bearing electroactive residues such as tryptophan and specifically labeled at the N- or C-terminus of peptide chains; the electrostatic binding of organic dyes to poly-electrolytes (polyacrylates) for which the formation of dimeric aggregates of bound dye that display unusual photophysical and electron transfer properties is important; a study of the binding of dyes and electron transfer agents to the protein mimic,'' polyvinyl-2-pyrrolidinone (PVP), in hydrophobic domains that depend on specific H-bond interaction; and completion of an earlier study having to do with the triplet state properties of charge-transfer (CT) complexes of a high potential quinone and various electron donors (investigation of the properties of triplet (contact) radical-ion pairs). 13 refs., 5 figs., 2 tabs.

  19. Quantum effects in biological electron transfer

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

    2012-01-01

    Roč. 14, č. 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

  20. Energy of the quasi-free electron in H2, D2, and O2: Probing intermolecular potentials within the local Wigner-Seitz model

    We present for the first time the quasi-free electron energy V0(ρ) for H2, D2, and O2 from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine V0(ρ) accurately in strongly absorbing fluids (e.g., O2) and fluids with extremely low critical temperatures (e.g., H2 and D2). We also show that the isotropic local Wigner-Seitz model for V0(ρ) — when coupled with thermodynamic data for the fluid — can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths

  1. Domain motions and electron transfer dynamics in 2Fe-superoxide reductase.

    Horch, Marius; Utesch, Tillmann; Hildebrandt, Peter; Mroginski, Maria Andrea; Zebger, Ingo

    2016-08-17

    Superoxide reductases are non-heme iron enzymes that represent valuable model systems for the reductive detoxification of reactive oxygen species. In the present study, we applied different theoretical methods to study the structural dynamics of a prototypical 2Fe-superoxide reductase and its influence on electron transfer towards the active site. Using normal mode and essential dynamics analyses, we could show that enzymes of this type are capable of well-defined, electrostatically triggered domain movements, which may allow conformational proofreading for cellular redox partners involved in intermolecular electron transfer. Moreover, these global modes of motion were found to enable access to molecular configurations with decreased tunnelling distances between the active site and the enzyme's second iron centre. Using all-atom classical molecular dynamics simulations and the tunnelling pathway model, however, we found that electron transfer between the two metal sites is not accelerated under these conditions. This unexpected finding suggests that the unperturbed enzymatic structure is optimized for intramolecular electron transfer, which provides an indirect indication of the biological relevance of such a mechanism. Consistently, efficient electron transfer was found to depend on a distinct route, which is accessible via the equilibrium geometry and characterized by a quasi conserved tyrosine that could enable multistep-tunnelling (hopping). Besides these explicit findings, the present study demonstrates the importance of considering both global and local protein dynamics, and a generalized approach for the functional analysis of these aspects is provided. PMID:27491757

  2. Electronic transfer between low-dimensional nanosystems

    Král, Karel

    Hoboken: Wiley, 2011 - (Nair, K.; Priya, S.; Jia, Q.), s. 33-40. (Ceramic Transactions. vol. 226). ISBN 9781118059999. [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

  3. Electron transfer theory revisit: Quantum solvation effect

    Han, P; Cui, P; Mo, Y; He, G; Yan, Y J; Han, Ping; Xu, Rui-Xue; Cui, Ping; Mo, Yan; He, Guozhong; Yan, YiJing

    2006-01-01

    The effect of solvation on the electron transfer (ET) rate processes is investigated on the basis of the exact theory constructed in J. Phys. Chem. B Vol. 110, (2006); quant-ph/0604071. The nature of solvation is studied in a close relation with the mechanism of ET processes. The resulting Kramers' turnover and Marcus' inversion characteristics are analyzed accordingly. The classical picture of solvation is found to be invalid when the solvent longitudinal relaxation time is short compared with the inverse temperature.

  4. Electron Transfer Phenomena in Interfacial Bioelectrochemistry

    Baier, Claudia

    2011-01-01

    Biomolecules at the solid-liquid interface have been investigated using electrochemical measurement techniques such as cyclic voltammetry and electrochemical scanning probe microscopies. Structure and function of the biomolecules, depending on the electron transfer and the used electrode material could be studied down to a single molecule level. Besides investigating natural electroactive proteins, e.g. the metalloprotein azurin or the iron storage protein ferritin, a method has been develope...

  5. Modeling Electronic-Nuclear Interactions for Excitation Energy Transfer Processes in Light-Harvesting Complexes.

    Lee, Mi Kyung; Coker, David F

    2016-08-18

    An accurate approach for computing intermolecular and intrachromophore contributions to spectral densities to describe the electronic-nuclear interactions relevant for modeling excitation energy transfer processes in light harvesting systems is presented. The approach is based on molecular dynamics (MD) calculations of classical correlation functions of long-range contributions to excitation energy fluctuations and a separate harmonic analysis and single-point gradient quantum calculations for electron-intrachromophore vibrational couplings. A simple model is also presented that enables detailed analysis of the shortcomings of standard MD-based excitation energy fluctuation correlation function approaches. The method introduced here avoids these problems, and its reliability is demonstrated in accurate predictions for bacteriochlorophyll molecules in the Fenna-Matthews-Olson pigment-protein complex, where excellent agreement with experimental spectral densities is found. This efficient approach can provide instantaneous spectral densities for treating the influence of fluctuations in environmental dissipation on fast electronic relaxation. PMID:27472379

  6. Electronic Energy Transfer in Polarizable Heterogeneous Environments

    Svendsen, Casper Steinmann; Kongsted, Jacob

    2015-01-01

    Theoretical prediction of transport and optical properties of protein-pigment complexes is of significant importance when aiming at understanding the structure versus function relationship in such systems. Electronic energy transfer (EET) couplings represent a key property in this respect since...... such couplings provide important insight into the strength of interaction between photo-active pigments in protein-pigment complexes. Recently, attention has been payed to how the environment modifies or even controls the electronic couplings. To enable such theoretical predictions, a fully polarizable embedding...... of transition densities in the calculation of the electronic couplings - also when including the explicit environment contribution - can be replaced by a much simpler transition point charge description without comprising the quality of the model predictions....

  7. Promoting interspecies electron transfer with biochar

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

    2014-01-01

    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, 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...

  8. Education and solar conversion. Demonstrating electron transfer

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

    1998-07-23

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

  9. Heat transfer in high density electronics packaging

    2001-01-01

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

  10. Kinetics and mechanism of elementary act of electron transfer in alcohol radicals oxidation by hydrated trivalent iron ions

    The method of competing reactions has been employed to measure the velocity constants of one-electron oxidation of oxyalkyl radicals by Fe(3) ions upon γ-radiolysis of aqueous methanol, ethanol and isopropanol in the presence of Fe(3) ions and tetranitromethane. It is shown that if such factors as non-adiabaticity, reorganization of intermolecular degrees of freedom, core tunnelling effects and spin effects are taken into account, the quantum theory of outerspheric electron transfer in polar media provides for quantitative agreement of the measured velocity constants with experimental results

  11. Variation of geometries and electron properties along proton transfer in strong hydrogen-bond complexes

    Pacios, L. F.; Gálvez, O.; Gómez, P. C.

    2005-06-01

    Proton transfer in hydrogen-bond systems formed by 4-methylimidazole in both neutral and protonated cationic forms and by acetate anion are studied by means of MP2/6-311++G(d,p) ab initio calculations. These two complexes model the histidine (neutral and protonated)-aspartate diad present in the active sites of enzymes the catalytic mechanism of which involves the formation of strong hydrogen bonds. We investigate the evolution of geometries, natural bond orbital populations of bonds and electron lone pairs, topological descriptors of the electron density, and spatial distributions of the electron localization function along the process N-H ⋯O→N⋯H⋯O→N⋯H-O, which represents the stages of the H-transfer. Except for a sudden change in the population of electron lone pairs in N and O at the middle N...H...O stage, all the properties analyzed show a smooth continuous behavior along the covalent → hydrogen bond transit inherent to the transfer, without any discontinuity that could identify a formation or breaking of the hydrogen bond. This way, the distinction between covalent or hydrogen-bonding features is associated to subtle electron rearrangement at the intermolecular space.

  12. 14 CFR 1260.69 - Electronic funds transfer payment methods.

    2010-01-01

    ... Government by electronic funds transfer through the Treasury Fedline Payment System (FEDLINE) or the... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment...

  13. Copper(II)-Mediated Intermolecular C(sp(2))-H Amination of Benzamides with Electron-Rich Anilines.

    Singh, Bijaya Kumar; Polley, Arghya; Jana, Ranjan

    2016-05-20

    Despite significant progress, copper-catalyzed/mediated C-H amination reactions with electron-rich anilines remain an unsolved problem due to catalyst deactivation and deleterious side reactions. Herein, we report a copper(II)-mediated C(sp(2))-H amination of benzamides with electronically neutral or electron-rich anilines. A dramatic influence of silver(I) and tetrabutylammonium bromide was observed on the reaction outcome. The present protocol also demonstrates the synthesis of a number of nonsteroidal anti-inflammatory drugs. PMID:27148754

  14. Electron transfer in branched expanded pyridinium molecules

    Hromadová, Magdaléna; Lachmanová, Štěpánka; 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 ČR(CZ) GA14-05180S Grant ostatní: Rada Programu interní porpory projektů mezinárodní spolupráce AV ČR M200401202 Institutional support: RVO:61388955 Keywords : electron transfer * electrochemistry * pyridinium Subject RIV: CG - Electrochemistry

  15. Direct heterogeneous electron transfer of theophylline oxidase

    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...

  16. Theory of intermolecular forces

    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

  17. An isotopic mass effect on the intermolecular potential

    Herman, Michael F.; Currier, Robert P.; Clegg, Samuel M.

    2015-10-01

    The impact of isotopic variation on the electronic energy and intermolecular potentials is often suppressed when calculating isotopologue thermodynamics. Intramolecular potential energy surfaces for distinct isotopologues are in fact equivalent under the Born-Oppenheimer approximation, which is sometimes used to imply that the intermolecular interactions are independent of isotopic mass. In this communication, the intermolecular dipole-dipole interaction between hetero-nuclear diatomic molecules is considered. It is shown that the intermolecular potential contains mass-dependent terms even though each nucleus moves on a Born-Oppenheimer surface. The analysis suggests that mass dependent variations in intermolecular potentials should be included in comprehensive descriptions of isotopologue thermodynamics.

  18. Electron transfer pathways in microbial oxygen biocathodes

    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.

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

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

    2010-01-01

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

  20. Electron transfer in gas surface collisions

    In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

  1. Activation entropy of electron transfer reactions

    Milischuk, A A; Newton, M D; Milischuk, Anatoli A.; Matyushov, Dmitry V.; Newton, Marshall D.

    2005-01-01

    We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by conti...

  2. Devices which transfer electrons one-by-one

    An introduction is given to the field of single-electron devices, which are electronic circuits across which electrons may be transferred one by one. Experiments are described on the single-junction box and the four-junction box, devices in which electrons were transferred to a metallic island and their presence detected using a single-electron electrometer. The single-junction box, the simpler of the two devices, allows one to control the thermally-averaged number of excess electrons on the metallic island, whereas with the four-junction box one can actually control the transfer of individual electrons. (author) 11 refs.; 5 figs

  3. Path integral approach to non-relativistic electron charge transfer

    A path integral approach has been generalized for the non-relativistic electron charge transfer processes. The charge transfer - the capture of an electron by an ion passing another atom, or more generally the problem of rearrangement collisions - is formulated in terms of influence functionals. It has been shown that the electron charge transfer process can be treated either as an electron transition problem or as ion and atom elastic scattering in the effective potential field. The first-order Born approximation for the electron charge transfer reaction cross section has been reproduced to prove the adequacy of the path integral approach for this problem. (author)

  4. 48 CFR 18.123 - Electronic funds transfer.

    2010-10-01

    ... 48 Federal Acquisition Regulations System 1 2010-10-01 2010-10-01 false Electronic funds transfer. 18.123 Section 18.123 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities 18.123 Electronic funds transfer. Electronic funds...

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

    M. Bekker

    2009-01-01

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

  6. Theoretical aspects of electron transfer reactions of complex molecules

    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 ...

  7. Transcriptomic and genetic analysis of direct interspecies electron transfer

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

    2013-01-01

    The possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in which Geobacter sulfurreducens was the elect...

  8. The Liability of banks in electronic fund transfer transaction

    Algudah, Fayyad

    1993-01-01

    The liability of banks in electronic fund transfer (EFT) transactions is discussed in this thesis under the British and the United States law. The thesis covers banks’ liability in electronic credit and debit transfers. It covers banks’ liability in Electronic Fund Transfer at the Point Of Sale (EFTPOS), Automatic Teller Machines (ATM) and home and office banking. Liability of banks in credit card transactions and cheque truncation falls outside the scope of this thesis. In ...

  9. Electron transfer and interfacial behavior of redox proteins

    2010-01-01

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

  10. Internal electron transfer within mitochondrial succinate-cytochrome C reductase

    Internal electron transfer within succinate-cytochrome C reductase from pigeon breast muscle mitochondria was followed by the pulse radiolytic technique. The electron equivalent is transferred from an unknown donor to b type cytochrome(s), in a first order process with a rate constant of: 660 +- 150s-1. This process might be the rate determining step of electron transfer in mitochondria, since it is similar in rate to the turnover number of the mitochondrial respiratory chain

  11. Intermolecular and surface forces

    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

  12. Electronic transfer of sensitive patient data.

    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

  13. Activation entropy of electron transfer reactions

    We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by continuum models is not supported by the microscopic theory. Also, the reorganization and overall solvation entropies are substantially larger in the microscopic theory compared to continuum models

  14. Intermolecular spectroscopy of gases

    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)

  15. Electric-field-driven electron-transfer in mixed-valence molecules

    Blair, Enrique P.; Corcelli, Steven A.; Lent, Craig S.

    2016-07-01

    Molecular quantum-dot cellular automata is a computing paradigm in which digital information is encoded by the charge configuration of a mixed-valence molecule. General-purpose computing can be achieved by arranging these compounds on a substrate and exploiting intermolecular Coulombic coupling. The operation of such a device relies on nonequilibrium electron transfer (ET), whereby the time-varying electric field of one molecule induces an ET event in a neighboring molecule. The magnitude of the electric fields can be quite large because of close spatial proximity, and the induced ET rate is a measure of the nonequilibrium response of the molecule. We calculate the electric-field-driven ET rate for a model mixed-valence compound. The mixed-valence molecule is regarded as a two-state electronic system coupled to a molecular vibrational mode, which is, in turn, coupled to a thermal environment. Both the electronic and vibrational degrees-of-freedom are treated quantum mechanically, and the dissipative vibrational-bath interaction is modeled with the Lindblad equation. This approach captures both tunneling and nonadiabatic dynamics. Relationships between microscopic molecular properties and the driven ET rate are explored for two time-dependent applied fields: an abruptly switched field and a linearly ramped field. In both cases, the driven ET rate is only weakly temperature dependent. When the model is applied using parameters appropriate to a specific mixed-valence molecule, diferrocenylacetylene, terahertz-range ET transfer rates are predicted.

  16. Probing the Mechanism of Electron Capture and Electron Transfer Dissociation Using Tags with Variable Electron Affinity

    Sohn, Chang Ho; Chung, Cheol K.; Yin, Sheng; Ramachandran, Prasanna; Loo, Joseph A; Beauchamp, J. L.

    2009-01-01

    Electron capture dissociation (ECD) and electron transfer dissociation (ETD) of doubly protonated electron affinity (EA)-tuned peptides were studied to further illuminate the mechanism of these processes. The model peptide FQpSEEQQQTEDELQDK, containing a phosphoserine residue, was converted to EA-tuned peptides via β-elimination and Michael addition of various thiol compounds. These include propanyl, benzyl, 4-cyanobenzyl, perfluorobenzyl, 3,5-dicyanobenzyl, 3-nitrobenzyl, and 3,5-dinitrobenz...

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

    NONE

    1993-03-01

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

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

    Kato, Souichiro

    2016-01-01

    Summary Extracellular electron transfer (EET) is a microbial metabolism that enables efficient electron transfer between microbial cells and extracellular solid materials. Microorganisms harbouring EET abilities have received considerable attention for their various biotechnological applications, including bioleaching and bioelectrochemical systems. On the other hand, recent research revealed that microbial EET potentially induces corrosion of iron structures. It has been well known that corr...

  19. 14 CFR 1274.931 - Electronic funds transfer payment methods.

    2010-01-01

    ... cooperative agreement will be made by the Government by electronic funds transfer through the Treasury Fedline... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.931...

  20. Inelastic electron scattering at low momentum transfer

    Recent advances of high energy resolution (ΔE approx. 30 keV FWHM) inelastic electron scattering at low momentum transfer (q -1) using selected experimental data from the Darmstadt electron linear accelerator are discussed. Strong emphasis is given to a comparison of the data with theoretical nuclear model predictions. Of the low multipolarity electric transitions investigated, as examples only E1 transitions to unnatural parity states in 11B and E2 transitions of the very fragmented isoscalar quadrupole giant resonance in 208Pb are considered. In 11B the role of the Os hole in the configuration of the 1/2+, 3/2+ and 5/2+ states is quantitatively determined via an interference mechanism in the transition probability. By comparison of the high resolution data with RPA calculations the E2 EWSR in 208Pb is found to be much less exhausted than anticipated from previous medium energy resolution (e,e) and hadron scattering experiments. In the case of M1 transitions it is shown that the simplest idealized independent particle shell-model prediction breaks down badly. In 28Si, ground-state correlations influence largely the detected M1 strength and such ground-state correlations are also responsible for the occurence of a strong M1 transition to a state at Ex = 10.319 MeV in 40Ca. In 90Zr only about 10% of the theoretically expected M1 strength is seen in (e,e) and in 140Ce and 208Pb none (detection limit 1-2 μ2K). In the case of 208Pb high resolution spectra exist now up to an excitation energy of Ex = approx. 12MeV. The continuous decrease of the M1 strength with mass number is corroborated by the behaviour of strong but very fragmented M2 transitions which are detected in 28Si, 90Zr, 140Ce and 208Pb concentrated at an excitation energy E x approx. 44A-1/3MeV. In 90Zr, the distribution of spacings and widths of the many Jπ = 2 states are consistent with a Wigner and Porter-Thomas distribution, respectively. (orig.) 891 KBE/orig. 892 ARA

  1. Electron Transfer Pathways in Cholesterol Synthesis.

    Porter, Todd D

    2015-10-01

    Cholesterol synthesis in the endoplasmic reticulum requires electron input at multiple steps and utilizes both NADH and NADPH as the electron source. Four enzymes catalyzing five steps in the pathway require electron input: squalene monooxygenase, lanosterol demethylase, sterol 4α-methyl oxidase, and sterol C5-desaturase. The electron-donor proteins for these enzymes include cytochrome P450 reductase and the cytochrome b5 pathway. Here I review the evidence for electron donor protein requirements with these enzymes, the evidence for additional electron donor pathways, and the effect of deletion of these redox enzymes on cholesterol and lipid metabolism. PMID:26344922

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

    Hellingwerf, K.J.; Teixeira De Mattos, M.J.; Bekker, M.

    2009-01-01

    The respiratory chain that is housed in the bacterial cytoplasmic membrane, generally transfers electrons from NADH to oxygen; in the absence of oxygen it can use several alternative electron acceptors, such as nitrate and fumarate. Transfer of electrons through this chain is usually coupled to the translocation of protons across the membrane. The resulting gradient of protons is then used for the generation of ATP by the F0F1-ATPase, and for other free energy requiring processes such as solu...

  3. Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy

    Mančal T.; Milota F.; Hauer J; Christensson N.; Bixner O.; Lukeš V.; Kauffmann H. F.

    2013-01-01

    Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an en...

  4. Photoinduced electron transfers with carbon dots

    Wang, Xin; Cao, Li; Lu, Fushen; Meziani, Mohammed J.; Li, Heting; Qi, Gang; Zhou, Bing; Harruff, Barbara A.; Kermarrec, Fabien; Sun, Ya-Ping

    2009-01-01

    The photoluminescence in carbon dots (surface-passivated small carbon nanoparticles) could be quenched efficiently by electron acceptor or donor molecules in solution, namely that photo-excited carbon dots are both excellent electron donors and excellent electron acceptors, thus offering new opportunities for their potential uses in light energy conversion and related applications.

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

    Basilevsky, M. V.; Mitina, E. A. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); Odinokov, A. V. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); National Research Nuclear University “MEPhI,” 31, Kashirskoye shosse, Moscow (Russian Federation); Titov, S. V. [Karpov Institute of Physical Chemistry, 3-1/12, Building 6, Obuha pereulok, Moscow (Russian Federation)

    2013-12-21

    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 ξ{sub 0}=ℏω{sub 0}/k{sub B}T where ω{sub 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 (ξ{sub 0} < 1 − 3) and for low (ξ{sub 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

  6. Electron transfer and decay processes of highly charged iodine ions

    In the present experimental work we have investigated multi-electron transfer processes in Iq+ (q=10, 15, 20 and 25) + Ne, Ar, Kr and Xe collisions at 1.5q keV energy. The branching ratios between Auger and radiative decay channels have been measured in decay processes of multiply excited states formed by multi-electron transfer collisions. It has been shown that, in all the multi-electron transfer processes investigated, the Auger decays are far dominant over the radiative decay processes and the branching ratios are clearly characterized by the average principal quantum number of the initial excited states of projectile ions. We could express the branching ratios in high Rydberg states formed in multi-electron transfer processes by using the decay probability of one Auger electron emission. (author)

  7. Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy

    Mančal T.

    2013-03-01

    Full Text Available Two-dimensional electronic spectroscopy (2D-ES is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.

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

    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 10−2 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

  9. 76 FR 29901 - Electronic Fund Transfers

    2011-05-23

    ... Board anticipates that final rules on remittance transfers will be issued by the Bureau. \\26\\ 75 FR... recipient of the funds. For instance, a consumer may add his daughter, who is studying abroad, as an...'' made by foreign-born residents in the United States to households abroad totaled $37.6 billion in...

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

    Vlček Jr., Antonín; Kvapilová, Hana; Towrie, M.; Záliš, Stanislav

    2015-01-01

    Roč. 48, č. 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

  11. 77 FR 6310 - Electronic Fund Transfers (Regulation E)

    2012-02-07

    ... numbers of transactions as being outside the normal course of business. Nor did they suggest other means... the first transaction in a series of preauthorized remittance transfers the same as all other... electronic transfers of funds sent by consumers in the United States to recipients in other countries....

  12. Theory of interrelated electron and proton transfer processes

    Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

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

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

    2006-01-01

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

  14. A role for microbial palladium nanoparticles in extracellular electron transfer.

    Wu, X; Zhao, F; Rahunen, N; Varcoe, JR; Avignone-Rossa, C.; Thumser, AE; Slade, RC

    2011-01-01

    Herein we have demonstrated a DET mechanism used by D. desulfuricans; where the periplasmic cytochromes and hydrogenases play an important role, and Pd nanoparticles bound to the microbes may participate in the electron transfer process. The present work is of importance not only for the fundamental studies of electron transfer processes in microbial physiology and ecology, but also for increased understanding and improvement of the performance of bioelectrochemical techniques e.g. precious m...

  15. Proton-Coupled Electron Transfer Reactions with Photometric Bases Reveal Free Energy Relationships for Proton Transfer.

    Eisenhart, Thomas T; Howland, William C; Dempsey, Jillian L

    2016-08-18

    The proton-coupled electron transfer (PCET) oxidation of p-aminophenol in acetonitrile was initiated via stopped-flow rapid-mixing and spectroscopically monitored. For oxidation by ferrocenium in the presence of 7-(dimethylamino)quinoline proton acceptors, both the electron transfer and proton transfer components could be optically monitored in the visible region; the decay of the ferrocenium absorbance is readily monitored (λmax = 620 nm), and the absorbance of the 2,4-substituted 7-(dimethylamino)quinoline derivatives (λmax = 370-392 nm) red-shifts substantially (ca. 70 nm) upon protonation. Spectral analysis revealed the reaction proceeds via a stepwise electron transfer-proton transfer process, and modeling of the kinetics traces monitoring the ferrocenium and quinolinium signals provided rate constants for elementary proton and electron transfer steps. As the pKa values of the conjugate acids of the 2,4-R-7-(dimethylamino)quinoline derivatives employed were readily tuned by varying the substituents at the 2- and 4-positions of the quinoline backbone, the driving force for proton transfer was systematically varied. Proton transfer rate constants (kPT,2 = (1.5-7.5) × 10(8) M(-1) s(-1), kPT,4 = (0.55-3.0) × 10(7) M(-1) s(-1)) were found to correlate with the pKa of the conjugate acid of the proton acceptor, in agreement with anticipated free energy relationships for proton transfer processes in PCET reactions. PMID:27500804

  16. Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide

    This paper studies the intramolecular photoinduced electron-transfer (PET) of covalent bonded azobenzene-perylene diimide (AZO-PDI) in solvents by using steady-state and time-resolved fluorescence spectroscopy together with ultrafast transient absorption spectroscopic techniques. Fast fluorescence quenching is observed when AZO-PDI is excited at characteristic wavelengths of AZO and perylene moieties. Reductive electron-transfer with transfer rate faster than 1011 s−1 is found. This PET process is also consolidated by femtosecond transient absorption spectra

  17. Mathematics and electronics - the conceptual transfer problem

    Waks, S.

    1988-07-01

    The article deals with the gap between the technological-school student's mastery of pure mathematical principles and his/her competence in their implementation in electronics and suggests a means for narrowing this, using a case study. A cooperative effort by mathematics and electronics teachers, involving coordination of content, teaching strategies and timing, was implemented on two groups (treatment and control). The treatment group achieved significantly higher average scores in tests in those questions where the mathematical reinforcement provided in the treatment process could be used - and this in spite of the group's weaker standing in the electronics course. Moreover, it was establised that treatment students adopted a more analytical approach in their solution strategies, while control students tended to rely more on recall and 'ready-made' formulae. The main conclusion of our case study is that mastery of mathematical theory and principles is a prerequisite to efficient tackling of technological problems, but is not always enough. Cooperation between the maths and electronics teachers contributes to improvement of the teaching-learning process in a technological discipline.

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

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

    2016-01-01

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

  19. Electron transfer rates and equilibrium within cytochrome c oxidase

    Farver, O; Einarsdóttir, O; Pecht, I

    2000-01-01

    Intramolecular electron transfer (ET) between the CuA center and heme a in bovine cytochrome c oxidase was investigated by pulse radiolysis. CuA, the initial electron acceptor, was reduced by 1-methyl nicotinamide radicals in a diffusion-controlled reaction, as monitored by absorption changes at...

  20. Photoinduced electron transfer in model systems of photosynthesis.

    Hofstra, U.

    1988-01-01

    This Thesis describes Investigations on photoinduced electron transfer (ET) for several compounds, serving as model systems of the natural photosynthesis. In addition, the properties of the systems, e.g. the conformation in solution and the electronic properties of the photoexcited states are treate

  1. A tetrastable naphthalenediimide: anion induced charge transfer, single and double electron transfer for combinational logic gates.

    Ajayakumar, M R; Hundal, Geeta; Mukhopadhyay, Pritam

    2013-09-11

    Herein we demonstrate the formation of the first tetrastable naphthalenediimide (NDI, 1a) molecule having multiple distinctly readable outputs. Differential response of 1a to fluoride anions induces intramolecular charge transfer (ICT), single/double electron transfer (SET/DET) leading to a set of combinational logic gates for the first time with a NDI moiety. PMID:23752683

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

    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

  3. Electron transfer, ionization, and excitation atomic collisions

    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

  4. Electronic Energy Transfer in Polarizable Heterogeneous Environments

    Svendsen, Casper Steinmann; Kongsted, Jacob

    2015-01-01

    such couplings provide important insight into the strength of interaction between photo-active pigments in protein-pigment complexes. Recently, attention has been payed to how the environment modifies or even controls the electronic couplings. To enable such theoretical predictions, a fully polarizable...... higher-order multipole moments. We use this extended model to systematically examine three different ways of obtaining EET couplings in a heterogeneous medium ranging from use of the exact transition density to a point-dipole approximation. Several interesting observations are made including that...... explicit use of transition densities in the calculation of the electronic couplings - also when including the explicit environment contribution - can be replaced by a much simpler transition point charge description without comprising the quality of the model predictions....

  5. Electron transfer, ionization, and excitation in atomic collisions: Progress report

    The fundamental processes of electron transfer, ionization, and excitation in ion-atom collisions are being studied at Penn State by Winter. (The related work of Alston, who recently came to Penn State, is not described here since he is not at present funded by DOE.) 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. Three coupled-state calculations are being carried out over the present three-year period and are discussed here: a Sturmian-pseudostate study of electron transfer in collisions between protons and the hydrogenic ions He+, Li2+, Be3+, ...; a triple-center, atomic-state study of ionization in collisions between α particles and H(ls) atoms and between protons and He+(ls) ions; and a coupled-state study of electron transfer and excitation in collisions between protons and neutral He atoms

  6. Numerical modeling of fast electron energy transfer

    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

  7. Noise-assisted quantum electron transfer in photosynthetic complexes

    Nesterov, Alexander I; Berman, Gennady P.; 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 co...

  8. Computational Approach to Electron Charge Transfer Reactions

    Jónsson, Elvar Örn

    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...... 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...

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

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

    2014-10-01

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

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

    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 γ-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

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

    Pravin Malla Shrestha

    2014-05-01

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

  12. [Electron transfer, ionization, and excitation in atomic collisions

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

  13. Optimization of Plasmon Decay Through Scattering and Hot Electron Transfer

    DeJarnette, Drew

    Light incident on metal nanoparticles induce localized surface oscillations of conductive electrons, called plasmons, which is a means to control and manipulate light. Excited plasmons decay as either thermal energy as absorbed phonons or electromagnetic energy as scattered photons. An additional decay pathway for plasmons can exist for gold nanoparticles situated on graphene. Excited plasmons can decay directly to the graphene as through hot electron transfer. This dissertation begins by computational analysis of plasmon resonance energy and bandwidth as a function of particle size, shape, and dielectric environment in addition to diffractive coupled in lattices creating a Fano resonance. With this knowledge, plasmon resonance was probed with incident electrons using electron energy loss spectroscopy in a transmission electron microscope. Nanoparticles were fabricated using electron beam lithography on 50 nanometer thick silicon nitride with some particles fabricated with a graphene layer between the silicon nitride and metal structure. Plasmon resonance was compared between ellipses on and off graphene to characterize hot electron transfer as a means of plasmon decay. It was observed that the presence of graphene caused plasmon energy to decrease by as much as 9.8% and bandwidth to increase by 25%. Assuming the increased bandwidth was solely from electron transfer as an additional plasmon decay route, a 20% efficiency of plasmon decay to graphene was calculated for the particular ellipses analyzed.

  14. Distance dependence of intramolecular electron transfer through rigid hydrocarbon spacers

    The effects of energy, distance and molecular structure on rates of electron transfer between molecules are the subjects of continuing investigations in the authors laboratory. The use of rigid molecular spacers between electron donor and acceptor groups facilitates study of the above questions, and is a promising method to obtain energy storage with directed charge separation. Here they present recent results focusing principally on the effects of distance through rigid hydrocarbon spacers. Through-bond interaction is the dominant source of the electronic coupling which enables electron transfer to occur in a series of molecules of the type D-S-A. Pulse radiolysis measurements used molecules D (donor) = biphenyl and A (acceptor) = naphthalene attached to a series of spacer molecules, S, having 3,4,6,7 or 10 saturated hydrocarbon bonds between the D and A groups. The spacer groups were 1,3-cyclohexane (three bonds), 1,4-cyclohexane (four bonds), 2,7-decalin (six bonds), 2,6-decalin (seven bonds) and 3,16-androstance (ten bonds). They attached electrons to these molecules using Argonne's picosecond Linac and measured electron transfer rates (ET) from 3.5 x 109s-1 across three bonds to 1.5 x 106s-1 across ten bonds. The clearest understanding of the rates is obtained by comparing the electronic-coupling interactions. The electronic interactions decrease regularly with increasing number of bonds, but do not correlate very well with either edge-to-edge or center-to-center distance

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

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

    2015-12-01

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

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

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

    2015-05-14

    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. PMID:25978888

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

    Bartocci, Alessio; Cappelletti, David; Pirani, Fernando [Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia 06123 (Italy); Belpassi, Leonardo [Istituto di Scienze e Tecnologie Molecolari del CNR, Perugia 06123 (Italy); Falcinelli, Stefano [Dipartimento di Ingegneria Civile ed Ambientale, Università degli Studi di Perugia, 06125 Perugia (Italy); Grandinetti, Felice [Dipartimento per la Innovazione nei sistemi Biologici, Agroalimentari e Forestali (DIBAF), Università della Tuscia, 01100 Viterbo (Italy); Tarantelli, Francesco [Dipartimento di Chimica, Biologia e Biotecnologie, Università di Perugia, Perugia 06123 (Italy); Istituto di Scienze e Tecnologie Molecolari del CNR, Perugia 06123 (Italy)

    2015-05-14

    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 CCl{sub 4} 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 CCl{sub 4} while other geometries appear to play a minor to negligible role.

  18. Distance-dependent electron transfer in DNA hairpins

    Lewis, F.D.; Wu, T.; Zhang, Y. [Northwestern Univ., Evanston, IL (United States)] [and others

    1997-08-01

    The distance dependence of photoinduced electron transfer in duplex DNA was determined for a family of synthetic DNA hairpins in which a stilbene dicarboxamide forms a bridge connecting two oligonucleotide arms. Investigation of the fluorescence and transient absorption spectra of these hairpins established that no photoinduced electron transfer occurs for a hairpin that has six deoxyadenosine-deoxythymidine base pairs. However, the introduction of a single deoxyguanosine-deoxycytidine base pair resulted in distance-dependent fluorescence quenching and the formation of the stilbene anion radical. Kinetic analysis suggests that duplex DNA is somewhat more effective than proteins as a medium for electron transfer but that it does not function as a molecular wire.

  19. Electron transfer statistics and thermal fluctuations in molecular junctions

    Goswami, Himangshu Prabal; Harbola, Upendra

    2015-02-01

    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.

  20. Electron transfer statistics and thermal fluctuations in molecular junctions

    Goswami, Himangshu Prabal; Harbola, Upendra [Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560012 (India)

    2015-02-28

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

  1. Energy of the quasi-free electron in H{sub 2}, D{sub 2}, and O{sub 2}: Probing intermolecular potentials within the local Wigner-Seitz model

    Evans, C. M., E-mail: cherice.evans@qc.cuny.edu; Krynski, Kamil [Department of Chemistry and Biochemistry, Queens College – CUNY, Flushing, New York 11367 (United States); Streeter, Zachary; Findley, G. L., E-mail: findley@ulm.edu [School of Sciences, University of Louisiana at Monroe, Monroe, Louisiana 71209 (United States)

    2015-12-14

    We present for the first time the quasi-free electron energy V{sub 0}(ρ) for H{sub 2}, D{sub 2}, and O{sub 2} from gas to liquid densities, on noncritical isotherms and on a near critical isotherm in each fluid. These data illustrate the ability of field enhanced photoemission (FEP) to determine V{sub 0}(ρ) accurately in strongly absorbing fluids (e.g., O{sub 2}) and fluids with extremely low critical temperatures (e.g., H{sub 2} and D{sub 2}). We also show that the isotropic local Wigner-Seitz model for V{sub 0}(ρ) — when coupled with thermodynamic data for the fluid — can yield optimized parameters for intermolecular potentials, as well as zero kinetic energy electron scattering lengths.

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

    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.

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

    CAO Weixiao; ZHANG Peng; FENG Xinde

    1995-01-01

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

  4. High-pressure effects on intramolecular electron transfer compounds

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

    2002-01-01

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

  5. Numerical simulation of transient moisture transfer into an electronic enclosure

    Nasirabadi, P. Shojaee; Jabbari, M.; Hattel, J. H.

    2016-06-01

    Electronic systems are sometimes exposed to harsh environmental conditions of temperature and humidity. Moisture transfer into electronic enclosures and condensation can cause several problems such as corrosion and alteration in thermal stresses. It is therefore essential to study the local climate inside the enclosures to be able to protect the electronic systems. In this work, moisture transfer into a typical electronic enclosure is numerically studied using CFD. In order to reduce the CPU-time and make a way for subsequent factorial design analysis, a simplifying modification is applied in which the real 3D geometry is approximated by a 2D axial symmetry one. The results for 2D and 3D models were compared in order to calibrate the 2D representation. Furthermore, simulation results were compared with experimental data and good agreement was found.

  6. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    2010-01-01

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

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

    李象远; 肖顺清; 何福城

    1999-01-01

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

  8. Electron-Wavepacket Reaction Dynamics in Proton Transfer of Formamide

    Nagashima, Kengo; Takatsuka, Kazuo

    2009-10-01

    We apply the semiclassical Ehrenfest theory, which provides electron wavepacket dynamics coupled to nuclear motion, to a study of water-assisted proton relay in formamide compared with a forced proton transfer in gas phase, both of which are associated with the tautomerization. We start with the enol (imidic acid) form HO-CH═NH and track its proton transfer process to the keto (amide) form O═CH-NH2. Identifying the fact that this is indeed a "proton transfer process" rather than hydrogen-atom migration in terms of radical character on the proton, we show a collective quantum flux of electrons, which flows backward against the proton motion. This backward flux compensates the electrons tightly covering the proton, as represented in the Mulliken charge. The enol form formamide is one of the simplest species in the group O═CR1-NHR2, which is a unit of polypeptide. In the gas phase, the nitrogen atom may have a pyramidal structure as in the ammonium molecule; therefore, the C-N bond may allow low barrier rotation along it. This rotation is strongly prohibited by the formation of the double bond C═N induced by the proton transfer. Not only the dynamical process of proton transfer itself but also the electronic structures left behind are greatly affected by the presence of water molecule(s) and polar solvents. In discussing the relative stability of the formamide after the proton transfer, the following resonance structures are frequently mentioned, O--CH═N+H2 ↔ O═CH-NH2. Here we address the dynamical manifestation of the resonance structures in terms of our dynamical electron theory.

  9. Role of direct microbial electron transfer in corrosion of steels

    Mehanna, Maha; Basséguy, Régine; Délia, Marie-Line; Bergel, Alain

    2009-01-01

    It has recently been discovered that many microbial species have the capacity to connect their metabolism to solid electrodes, directly exchanging electrons with them through membrane-bound redox compounds,nevertheless such a direct electron transfer pathway has been evoked rarely in the domain of microbial corrosion. Here was evidenced for the first time that the bacterium Geobacter sulfurreducens is able to increase the free potential of 304 L stainless steel up to 443 mV in only a few hour...

  10. Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis*

    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...

  11. Photoinduced Reductive Electron Transfer in LNA:DNA Hybrids

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

    2012-01-01

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

  12. 76 FR 81019 - Electronic Fund Transfers (Regulation E)

    2011-12-27

    ... this rule. See 76 FR 43569 (July 21, 2011). \\4\\ Public Law 111-203, section 1002(14) (defining... response to a notice published at 76 FR 75825 (Dec. 5, 2011) concerning its efforts to identify priorities... that provide electronic fund transfer services jointly may contract among themselves to comply with...

  13. Electron transfer reactions involving porphyrins and chlorophyll a

    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

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

    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 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

  15. Electron transfer flavoprotein deficiency: Functional and molecular aspects

    Schiff, M; Froissart, R; Olsen, Rikke Katrine Jentoft; Acquaviva, C; Vianey-Saban, C

    2006-01-01

    Multiple acyl-CoA dehydrogenase deficiency (MADD) is a recessively inherited metabolic disorder that can be due to a deficiency of electron transfer flavoprotein (ETF) or its dehydrogenase (ETF-ubiquinone oxidoreductase). ETF is a mitochondrial matrix protein consisting of alpha- (30kDa) and beta...... mutations in the ETFB gene. Nine novel disease-causing ETF mutations are reported....

  16. 31 CFR 208.3 - Payment by electronic funds transfer.

    2010-07-01

    ... 31 Money and Finance: Treasury 2 2010-07-01 2010-07-01 false Payment by electronic funds transfer. 208.3 Section 208.3 Money and Finance: Treasury Regulations Relating to Money and Finance (Continued) FISCAL SERVICE, DEPARTMENT OF THE TREASURY FINANCIAL MANAGEMENT SERVICE MANAGEMENT OF FEDERAL...

  17. CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS

    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.

  18. A molecularly based theory for electron transfer reorganization energy

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

  19. Nanoscale and single-molecule interfacial electron transfer

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

    2003-01-01

    Electrochemical science and technology in the 21st century have reached high levels of sophistication. A fundamental quantum mechanical theoretical frame for interfacial electrochemical electron transfer (ET) was introduced by Revaz Dogonadze. This frame has remained for four decades as a basis f...

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

    Shaffer, C. J.; Marek, Aleš; Pepin, R.; Slováková, K.; Tureček, F.

    2015-01-01

    Roč. 50, č. 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

  1. Intramolecular electron transfer in single-site-mutated azurins

    Farver, O; Skov, L K; Pascher, T; Karlsson, B G; Nordling, M; Lundberg, L G; Vänngård, T; Pecht, I

    1993-01-01

    apparently only marginally involved in electron transfer in wild-type azurin. Pathway calculations also suggest that a longer, through-backbone path is more efficient than the shorter one involving Trp48. The former pathway yields an exponential decay factor, beta, of 6.6 nm-1. Another mutation, raising the...

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

    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.

  3. Electron transfer activity of a de novo designed copper center in a three-helix bundle fold.

    Plegaria, Jefferson S; Herrero, Christian; Quaranta, Annamaria; Pecoraro, Vincent L

    2016-05-01

    In this work, we characterized the intermolecular electron transfer (ET) properties of a de novo designed metallopeptide using laser-flash photolysis. α3D-CH3 is three helix bundle peptide that was designed to contain a copper ET site that is found in the β-barrel fold of native cupredoxins. The ET activity of Cuα3D-CH3 was determined using five different photosensitizers. By exhibiting a complete depletion of the photo-oxidant and the successive formation of a Cu(II) species at 400nm, the transient and generated spectra demonstrated an ET transfer reaction between the photo-oxidant and Cu(I)α3D-CH3. This observation illustrated our success in integrating an ET center within a de novo designed scaffold. From the kinetic traces at 400nm, first-order and bimolecular rate constants of 10(5)s(-1) and 10(8)M(-1)s(-1) were derived. Moreover, a Marcus equation analysis on the rate versus driving force study produced a reorganization energy of 1.1eV, demonstrating that the helical fold of α3D requires further structural optimization to efficiently perform ET. This article is part of a Special Issue entitled Biodesign for Bioenergetics - the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson. PMID:26427552

  4. Photoinduced electron transfer of chlorophyll in lipid bilayer system

    D K Lee; K W Seo; Y S Kang

    2002-12-01

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

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

    Bereau, Tristan; von Lilienfeld, O. Anatole

    2014-01-01

    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 e...

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

    Kundu, Prasanta; Dua, Arti

    2013-01-28

    A recent experiment has probed the electron transfer kinetics in the early stage of photosynthesis in Rhodobacter sphaeroides for the reaction center of wild type and different mutants [Science 316, 747 (2007)]. By monitoring the changes in the transient absorption of the donor-acceptor pair at 280 and 930 nm, both of which show non-exponential temporal decay, the experiment has provided a strong evidence that the initial electron transfer kinetics is modulated by the dynamics of protein backbone. In this work, we present a model where the electron transfer kinetics of the donor-acceptor pair is described along the reaction coordinate associated with the distance fluctuations in a protein backbone. The stochastic evolution of the reaction coordinate is described in terms of a non-Markovian generalized Langevin equation with a memory kernel and Gaussian colored noise, both of which are completely described in terms of the microscopics of the protein normal modes. This model provides excellent fits to the transient absorption signals at 280 and 930 nm associated with protein distance fluctuations and protein dynamics modulated electron transfer reaction, respectively. In contrast to previous models, the present work explains the microscopic origins of the non-exponential decay of the transient absorption curve at 280 nm in terms of multiple time scales of relaxation of the protein normal modes. Dynamic disorder in the reaction pathway due to protein conformational fluctuations which occur on time scales slower than or comparable to the electron transfer kinetics explains the microscopic origin of the non-exponential nature of the transient absorption decay at 930 nm. The theoretical estimates for the relative driving force for five different mutants are in close agreement with the experimental estimates obtained using electrochemical measurements. PMID:23387626

  7. 76 FR 35219 - Federal Acquisition Regulation; Information Collection; Payment by Electronic Fund Transfer

    2011-06-16

    ... contract by electronic fund transfer (EFT). The information necessary to make the EFT transaction is... Regulation; Information Collection; Payment by Electronic Fund Transfer AGENCY: Department of Defense (DOD... extension of a previously approved information collection requirement concerning payment by electronic...

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

    Nibbering Erik T.J.; Dreyer Jens; Verma Sandeep; Ghosh Hirendra N.; Adamczyk Katrin

    2013-01-01

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

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

    Nibbering Erik T. J.

    2013-03-01

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

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

    Lovley Derek

    2016-01-01

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

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

    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 α 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

  12. New type of dual solid-state thermochromism: modulation of intramolecular charge transfer by intermolecular pi-pi interactions, kinetic trapping of the aci-nitro group, and reversible molecular locking.

    Naumov, Pance; Lee, Sang Cheol; Ishizawa, Nobuo; Jeong, Young Gyu; Chung, Ihn Hee; Fukuzumi, Shunichi

    2009-10-22

    by intramolecular proton transfer of one amino proton to the nitro group, whereupon an aci-nitro form is thermally populated. Contrary to the numerous examples of solid thermochromic molecules based on either pericyclic reactions or keto-enol tautomerism, this system appears to be the first organic thermochromic family where the thermochromic change appears as an effect of intermolecular pi-pi interactions and thermal intramolecular proton transfer to aromatic nitro group. PMID:19780605

  13. New Type of Dual Solid-State Thermochromism: Modulation of Intramolecular Charge Transfer by Intermolecular π-π Interactions, Kinetic Trapping of the Aci-Nitro Group, and Reversible Molecular Locking

    Naumov, Panče; Lee, Sang Cheol; Ishizawa, Nobuo; Jeong, Young Gyu; Chung, Ihn Hee; Fukuzumi, Shunichi

    2009-09-01

    intramolecular proton transfer of one amino proton to the nitro group, whereupon an aci-nitro form is thermally populated. Contrary to the numerous examples of solid thermochromic molecules based on either pericyclic reactions or keto-enol tautomerism, this system appears to be the first organic thermochromic family where the thermochromic change appears as an effect of intermolecular π-π interactions and thermal intramolecular proton transfer to aromatic nitro group.

  14. Syntrophic Growth via Quinone-Mediated Interspecies Electron Transfer

    Jessica A Smith

    2015-02-01

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

  15. Ab Initio Study of the Electron Transfer in an Ionized Stacked Complex of Guanines

    Cauët, Emilie; Liévin, Jacques

    2009-08-01

    The charge transfer process in an ionized stacking of two consecutive guanines (G5'G3')+ has been studied by means of state-averaged CASSCF/MRCI and RASSCF/RASPT2 calculations. The ground and two first excited states of the radical cation have been characterized, and the topology of the corresponding potential energy surfaces (PESs) has been studied as a function of all intermolecular geometrical parameters. The results demonstrate that the charge transfer process in (G5'G3')+ is governed by the avoiding crossing between the ground and first excited states of the complex. Relative translation motions of both guanines in their molecular planes are shown to lead to the charge migration between G5' and G3'. Five stationary points (three minima and two saddle points) have been characterized along the reaction path describing the passage of the positive charge from G5' to G3'. The global minimum on the PES is found to correspond to the charge configuration G5'+G3'. The existence of an intermediate minimum along the reaction path has been established, characterizing a structure where the positive charge is equally distributed between the two guanines. The calculated energy profile allowed us to determine the height of the potential energy barrier (7.33 kcal/mol) and to evaluate the electronic coupling at a geometry close to the avoiding crossing (3.6 kcal/mol). Test calculations showed that the topology of the ground state PES of the complex GG+ is qualitatively conserved upon optimization of the intramolecular geometrical parameters of the stationary points.

  16. Electron Transfer Mechanisms of DNA Repair by Photolyase

    Zhong, Dongping

    2015-04-01

    Photolyase is a flavin photoenzyme that repairs two DNA base damage products induced by ultraviolet (UV) light: cyclobutane pyrimidine dimers and 6-4 photoproducts. With femtosecond spectroscopy and site-directed mutagenesis, investigators have recently made significant advances in our understanding of UV-damaged DNA repair, and the entire enzymatic dynamics can now be mapped out in real time. For dimer repair, six elementary steps have been characterized, including three electron transfer reactions and two bond-breaking processes, and their reaction times have been determined. A unique electron-tunneling pathway was identified, and the critical residues in modulating the repair function at the active site were determined. The dynamic synergy between the elementary reactions for maintaining high repair efficiency was elucidated, and the biological nature of the flavin active state was uncovered. For 6-4 photoproduct repair, a proton-coupled electron transfer repair mechanism has been revealed. The elucidation of electron transfer mechanisms and two repair photocycles is significant and provides a molecular basis for future practical applications, such as in rational drug design for curing skin cancer.

  17. Efficiency of intramolecular electron transfer from the second excited state of the donor in molecular triads D-A1-A2

    Feskov, S. V.; Ivanov, A. I.

    2016-01-01

    It is found that intramolecular and intermolecular electron transfer from the second singlet excited state of the donor in all molecular dyads studied up to now is accompanied by ultrafast recombination into the first excited state, resulting in a low quantum yield of the thermalized state with separated charges. The ultrafast photoinduced intramolecular charge transfer in donor‒acceptor 1‒acceptor 2 molecular triads is studied to ascertain the possibilities of increasing the quantum yield of ionic state. It is demonstrated that nonthermal (hot) electron transfer from the primary acceptor to the secondary acceptor can, in parallel with relaxation of a polar solvent, efficiently suppress the ultrafast recombination of charges into the first excited state of the donor and increase the yield of the ionic state. It is established that the angle between the directions of reaction coordinates corresponding to the electron transfer from the donor to the primary acceptor and from the primary acceptor to the secondary acceptor play the most important role in describing these processes. It is concluded that the value of this angle is governed by the ratio between the reorganization energies of the three possible electron transfers in the triad and can vary within wide limits. The parametric regions with maximum quantum yield of the thermalized ionic state are revealed. The strong effect the geometry of a studied triad has on charge separation efficiency is observed.

  18. Electron transfer, decoherence, and protein dynamics: insights from atomistic simulations.

    Narth, Christophe; Gillet, Natacha; Cailliez, Fabien; Lévy, Bernard; de la Lande, Aurélien

    2015-04-21

    Electron transfer in biological systems drives the processes of life. From cellular respiration to photosynthesis and enzymatic catalysis, electron transfers (ET) are chemical processes on which essential biological functions rely. Over the last 40 years, scientists have sought understanding of how these essential processes function in biology. One important breakthrough was the discovery that Marcus theory (MT) of electron transfer is applicable to biological systems. Chemists have experimentally collected both the reorganization energies (λ) and the driving forces (ΔG°), two parameters of Marcus theory, for a large variety of ET processes in proteins. At the same time, theoretical chemists have developed computational approaches that rely on molecular dynamics and quantum chemistry calculations to access numerical estimates of λ and ΔG°. Yet another crucial piece in determining the rate of an electron transfer is the electronic coupling between the initial and final electronic wave functions. This is an important prefactor in the nonadiabatic rate expression, since it reflects the probability that an electron tunnels from the electron donor to the acceptor through the intervening medium. The fact that a protein matrix supports electron tunneling much more efficiently than vacuum is now well documented, both experimentally and theoretically. Meanwhile, many chemists have provided examples of the rich physical chemistry that can be induced by protein dynamics. This Account describes our studies of the dynamical effects on electron tunneling. We present our analysis of two examples of natural biological systems through MD simulations and tunneling pathway analyses. Through these examples, we show that protein dynamics sustain efficient tunneling. Second, we introduce two time scales: τcoh and τFC. The former characterizes how fast the electronic coupling varies with nuclear vibrations (which cause dephasing). The latter reflects the time taken by the system

  19. Promoting direct interspecies electron transfer with activated carbon

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

    2012-01-01

    Granular activated carbon (GAC) is added to methanogenic digesters to enhance conversion of wastes to methane, but the mechanism(s) for GAC’s stimulatory effect are poorly understood. GAC has high electrical conductivity and thus it was hypothesized that one mechanism for GAC stimulation of...... 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...

  20. Nile blue can photosensitize DNA damage through electron transfer.

    Hirakawa, Kazutaka; Ota, Kazuhiro; Hirayama, Junya; Oikawa, Shinji; Kawanishi, Shosuke

    2014-04-21

    The mechanism of DNA damage photosensitized by Nile blue (NB) was studied using (32)P-5'-end-labeled DNA fragments. NB bound to the DNA strand was possibly intercalated through an electrostatic interaction. Photoirradiated NB caused DNA cleavage at guanine residues when the DNA fragments were treated with piperidine. Consecutive guanines, the underlined G in 5'-GG and 5'-GGG, were selectively damaged through photoinduced electron transfer. The fluorescence lifetime of NB was decreased by guanine-containing DNA sequence, supporting this mechanism. Single guanines were also slightly damaged by photoexcited NB, and DNA photodamage by NB was slightly enhanced in D2O. These results suggest that the singlet oxygen mechanism also partly contributes to DNA photodamage by NB. DNA damage photosensitized by NB via electron transfer may be an important mechanism in medicinal applications of photosensitizers, such as photodynamic therapy in low oxygen. PMID:24576317

  1. Large scale oil lease automation and electronic custody transfer

    Typically, oil field production operations have only been automated at fields with long term production profiles and enhanced recovery. The automation generally consists of monitoring and control at the wellhead and centralized facilities. However, Union Pacific Resources Co. (UPRC) has successfully implemented a large scale automation program for rapid-decline primary recovery Austin Chalk wells where purchasers buy and transport oil from each individual wellsite. This project has resulted in two significant benefits. First, operators are using the system to re-engineer their work processes. Second, an inter-company team created a new electronic custody transfer method. This paper will describe: the progression of the company's automation objectives in the area; the field operator's interaction with the system, and the related benefits; the research and development of the new electronic custody transfer method

  2. Electron transfer between quasi-zero-dimensional nanostructures

    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

  3. Two-photon electron transfer between quantum dots

    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)

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

    2003-01-01

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

  5. Electron transfer reactions in chemistry. Theory and experiment

    Marcus, Rudolph A.

    1997-01-01

    Since the late 1940s, the field of electron transfer processes has grown enormously, both in chemistry and biology. The development of the field, experimentally and theoretically, as well as its relation to the study of other kinds of chemical reactions, represents to us an intriguing history, one in which many threads have been brought together. In this lecture, some history, recent trends, and my own involvement in this research are described.

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

    Levi, B.G.

    1993-01-01

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

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

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

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

    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 ČR 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

  9. Crossed Andreev reflection versus electron transfer in graphene nanoribbons

    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 devices, but CAR can...

  10. [Electron transfer, ionization and excitation in atomic collisions

    The research being carried out at Penn State by Winter and Alston addresses the fundamental atomic-collision processes of electron transfer, ionization, and excitation. Winter has focussed attention on intermediate and, more recently, higher collision energies -- proton energies of at least about 50 keV -- for which coupled-state approaches are appropriate. Alston has concentrated on perturbative approaches to symmetric ion-ion/atom collisions at high energies and to asymmetric collisions at intermediate to high energies

  11. Electron Transfer rate between a electrode and a bridged redox

    Cruz, A. V. B.; Mishra, A. K.; Schmickler, W.

    2009-01-01

    We derive an explict bias dependent expression for electron transfer reaction rate from a solvated redox to a electrode through a bridged molecule of arbitrary length. The interaction of the solvated redox with the solvent is modelled as a classical harmonic oscillator bath. The effect of competing process, namely resonance tunneling between redox and bridge and the solvation of the redox is investigated. Plots were produced for the case of 5 atom bridge. Our analysis shows that for certain s...

  12. The electron transfer system of syntrophically grown Desulfovibrio vulgaris

    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.

  13. The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris

    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.

  14. Electron transfer processs with excited molecules at semiconductor electrodes

    Memming, R.

    In the first part of the paper, energy levels used in solid-state physics, in electrochemistry and in photochemistry are introduced and combined in a l- electron energy concept. This is also applied to excited molecules being adsorbed at semiconductor electrodes. On the basis of this concept, theoretical models concerning electron-transfer processes between molecules in their ground and excited state and semiconductor electrodes are then developed. In the last part of the paper, a number of typical results are presented and discussed. It is shown that the primary step is an electron-transfer reaction between an excited molecule and the semiconductor, whereas energy transfer plays only a minor role, which leads mostly to quenching. Most processes can be interpreted on the basis of the theoretical model mentioned above. Various phenomena, such as quantum yield, supersensitization, quenching, and influence of pH and doping of the semiconductor are discussed in detail. Finally, a brief outlook at the applications in solar-energy conversion systems is given.

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

    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

  16. Noise-assisted quantum electron transfer in photosynthetic complexes

    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...

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

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

  18. 77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...

    2012-06-08

    ... Account (ETA) Financial Agency Agreement AGENCY: Financial Management Service, Fiscal Service, Treasury... Financial Management Service solicits comments concerning form FMS-111, ``Electronic Transfer Account (ETA...: Electronic Transfer Account (ETA) Financial Agency Agreement. OMB Number: 1510-0073. Form Number: FMS...

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

    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...... 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...

  20. Electron-transfer reactions of tryptophan and tyrosine derivatives

    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

  1. Electronic Energy transfer in light-harvesting antenna complexes

    Hossein-Nejad, Hoda

    The studies presented in this thesis explore electronic energy transfer (EET) in light-harvesting antenna complexes and investigate the role of quantum coherence in EET. The dynamics of energy transfer are investigated in three distinct length scales and a different formulation of the exciton transport problem is applied at each scale. These scales include: the scale of a molecular dimer, the scale of a single protein and the scale of a molecular aggregate. The antenna protein phycoerythrin 545 (PE545) isolated from the photosynthetic cryptophyte algae Rhodomonas CS4 is specifically studied in two chapters of this thesis. It is found that formation of small aggregates delocalizes the excitation across chromophores of adjacent proteins, and that this delocalization has a dramatic effect in enhancing the rate of energy transfer between pigments. Furthermore, we investigate EET from a donor to an acceptor via an intermediate site and observe that interference of coherent pathways gives a finite correction to the transfer rate that is sensitively dependent on the nature of the vibrational interactions in the system. The statistical fluctuations of a system exhibiting EET are investigated in the final chapter. The techniques of non-equilibrium statistical mechanics are applied to investigate the steady-state of a typical system exhibiting EET that is perturbed out of equilibrium due to its interaction with a fluctuating bath.

  2. Controlling time scales for electron transfer through proteins

    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.

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

    Kato, Souichiro

    2016-03-01

    Extracellular electron transfer (EET) is a microbial metabolism that enables efficient electron transfer between microbial cells and extracellular solid materials. Microorganisms harbouring EET abilities have received considerable attention for their various biotechnological applications, including bioleaching and bioelectrochemical systems. On the other hand, recent research revealed that microbial EET potentially induces corrosion of iron structures. It has been well known that corrosion of iron occurring under anoxic conditions is mostly caused by microbial activities, which is termed as microbiologically influenced corrosion (MIC). Among diverse MIC mechanisms, microbial EET activity that enhances corrosion via direct uptake of electrons from metallic iron, specifically termed as electrical MIC (EMIC), has been regarded as one of the major causative factors. The EMIC-inducing microorganisms initially identified were certain sulfate-reducing bacteria and methanogenic archaea isolated from marine environments. Subsequently, abilities to induce EMIC were also demonstrated in diverse anaerobic microorganisms in freshwater environments and oil fields, including acetogenic bacteria and nitrate-reducing bacteria. Abilities of EET and EMIC are now regarded as microbial traits more widespread among diverse microbial clades than was thought previously. In this review, basic understandings of microbial EET and recent progresses in the EMIC research are introduced. PMID:26863985

  4. A stochastic reorganizational bath model for electronic energy transfer

    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...

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

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

    2000-01-01

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

  6. 77 FR 24667 - TANF Assistance and Electronic Benefit Transfer Transactions; Request for Public Comment

    2012-04-25

    ... state for entertainment.'' The law defines an electronic benefit transfer transaction as ``the use of a... Electronic Benefit Transfer Transactions; Request for Public Comment AGENCY: Department of Health and Human... States have implemented policies and practices to prevent electronic benefit transfer...

  7. Extracellular electron transfer from cathode to microbes: application for biofuel production

    Choi, Okkyoung; Sang, Byoung-In

    2016-01-01

    Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter ...

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

    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.

  9. Charge-sharing and electron-transfer characteristics of a gas electron multiplier (GEM)

    The charge sharing and electron-transfer process of a gas electron multiplier (GEM) with a high density of holes (60 μm in diameter at 100 μm of pitch) were examined. The GEM operated at a lower applied voltage due to the smaller size of the GEM holes; thus, a higher electric field is seen in the multiplication channels. The electron collection efficiency and the charge sharing were found to depend on the external field, as well as on the GEM voltage. The electron collection efficiency approached 90 % with a full collection of primary electrons under optimized GEM field conditions, and the range of the drift field for efficient electron collection to reach a plateau increased with the GEM voltage. The positive-ion feedback is also estimated

  10. Charge-sharing and electron-transfer characteristics of a gas electron multiplier (GEM)

    Han, Sang Hyo; Kang, Hee Dong [Kyungpook National Univ., Daegu (Korea, Republic of); Kim, Yong Kyun; Moon, Byung Soo; Chung, Chong Eun [KAERI, Daejon (Korea, Republic of); Cho, Hyo Sung; Kang, Sang Mook [Yonsei Univ., Wonju (Korea, Republic of)

    2002-05-01

    The charge sharing and electron-transfer process of a gas electron multiplier (GEM) with a high density of holes (60 {mu}m in diameter at 100 {mu}m of pitch) were examined. The GEM operated at a lower applied voltage due to the smaller size of the GEM holes; thus, a higher electric field is seen in the multiplication channels. The electron collection efficiency and the charge sharing were found to depend on the external field, as well as on the GEM voltage. The electron collection efficiency approached 90 % with a full collection of primary electrons under optimized GEM field conditions, and the range of the drift field for efficient electron collection to reach a plateau increased with the GEM voltage. The positive-ion feedback is also estimated.

  11. Suppression of Electron Transfer to Dioxygen by Charge Transfer and Electron Transfer Complexes in the FAD-dependent Reductase Component of Toluene Dioxygenase*

    Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

    2012-01-01

    The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD+ at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD+. A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD+ and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductaseTOL with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

  12. Suppression of electron transfer to dioxygen by charge transfer and electron transfer complexes in the FAD-dependent reductase component of toluene dioxygenase.

    Lin, Tzong-Yuan; Werther, Tobias; Jeoung, Jae-Hun; Dobbek, Holger

    2012-11-01

    The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD(+) at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD(+). A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD(+) and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductase(TOL) with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

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

    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 (Δ Get) for electron transfer process has been calculated by applying Rehm-Weller equation.

  14. Light induced electron transfer reactions of metal complexes

    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

  15. Parton models of high momentum transfer electron-nuclear scattering

    High-energy electron-nuclear scattering processes are discussed from the point of view of a parton model description. The light-cone formalism is introduced in a schematic presentation emphasizing: (i) the connection to relativistic dynamics, (ii) the phenomenological construction of the far off-shell components of wave functions, and (iii) asymptotic scaling laws. A survey is made of some of the recent calculations based on a nucleon constituent parton model and their comparison with data for momentum transfers Q22. A prospective discussion is also made on multiquark nuclear components and the quark parton model in QCD

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

    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

  17. Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration

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

    1999-01-01

    Pulse radiolytic reduction of disulfide bridges in ceruloplasmin yielding RSSR(-) radicals induces a cascade of intramolecular electron transfer (ET) processes. Based on the three-dimensional structure of ceruloplasmin identification of individual kinetically active disulfide groups and type 1 (T1...... 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....

  18. Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives

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

    1999-01-01

    (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...... 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...

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

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

    1998-01-01

    The intramolecular electron transfer (ET) between the type 1 Cu(I) and the type 2 Cu(II) sites of Alcaligenes xylosoxidans dissimilatory nitrite reductase (AxNiR) has been studied in order to compare it with the analogous process taking place in ascorbate oxidase (AO). This internal process is......(I) and the trinuclear copper centre in ascorbate oxidase, and the characteristics of the internal ET processes of these enzymes are compared. The data are consistent with the faster ET observed in nitrite reductase arising from a more advantageous entropy of activation when compared with ascorbate...

  20. Electronic state selectivity in dication-molecule single electron transfer reactions: NO+ + NO

    Parkes, M. A.; Lockyear, J. F.; Schröder, Detlef; Roithová, J.; Price, S. D.

    2011-01-01

    Roč. 13, č. 41 (2011), s. 18386-18392. ISSN 1463-9076 R&D Projects: GA ČR GA203/09/1223 Institutional research plan: CEZ:AV0Z40550506 Keywords : coincidence experiments * dications * electron transfer * energy partitioning * state selectivity Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.573, year: 2011

  1. Electron transfer pathway analysis in bacterial photosynthetic reaction center

    Kitoh-Nishioka, Hirotaka

    2016-01-01

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

  2. The electronic transfer of information and aerospace knowledge diffusion

    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.

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

    Farver, Ole; Brunori, Maurizio; Cutruzzolà, Francesca;

    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 studies of the Pseudomonas stutzeri enzyme, we observed that a marked negative cooperativity is...... controlling this internal ET step. In this study we have investigated the internal ET in the wild-type and His369Ala mutant of P. aeruginosa nitrite reductases and have observed similar cooperativity to that of the Pseudomonas stutzeri enzyme. Heme-c was initially reduced, in an essentially diffusion...

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

    Mazinani, Shobeir Khezr Seddigh

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

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

    Scharf, Christian

    2014-01-01

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

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

    Milot, Rebecca Lee

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

  7. Cluster PEACE observations of electrons during magnetospheric flux transfer events

    C. J. Owen

    Full Text Available During the first quarter of 2001 the apogees of the Cluster spacecraft quartet precessed through midday local times. This provides the first opportunity for 4 spacecraft studies of the bow shock, magnetosheath and the dayside magnetopause current layer and boundary layers. In this paper, we present observations of electrons in the energy range ~ 10 eV–26 keV made by the Plasma Electron And Current Experiment (PEACE located just inside the magnetopause boundary, together with supporting observations by the Flux Gate Magnetometer (FGM. During these observations, the spacecraft have separations of ~ 600 km. This scale size is of the order or less than the typical size of flux transfer events (FTEs, which are expected to be observed following bursts of reconnection on the dayside magnetopause. We study, in detail, the 3-D configuration of electron populations observed around a series of enhancements of magnetosheath-like electrons which were observed within the magnetosphere on 2 February 2001. We find that individual spacecraft observe magnetic field and electron signatures that are consistent with previous observations of magnetospheric FTEs. However, the differences in the signatures between spacecraft indicate that these FTEs have substructure on the scale of the spacecraft separation. We use these differences and the timings of the 4 spacecraft observations to infer the motions of the electron populations and thus the configuration of these substructures. We find that these FTEs are moving from noon towards dusk. The inferred size and speed of motion across the magnetopause, in one example, is ~ 0.8 RE and ~ 70 km s-1 respectively. In addition, we observe a delay in and an extended duration of the signature at the spacecraft furthest from the magnetopause. We discuss the implications of these 4 spacecraft observations for the structure of these FTEs. We suggest that these may include a compression of the closed

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

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

    2014-08-01

    Thermodynamically unfavourable electron transfers are enabled by coupling to an energy-supplying reaction. How the energy is transduced from the exergonic to the endergonic process is largely unknown. Here we provide the structural basis for an energy transduction process in the reductive activation of B12-dependent methyltransferases. The transfer of one electron from an activating enzyme to the cobalamin cofactor is energetically uphill and relies on coupling to an ATPase reaction. Our results demonstrate that the key to coupling is, besides the oxidation state-dependent complex formation, the conformational gating of the electron transfer. Complex formation induces a substitution of the ligand at the electron-accepting Co ion. Addition of ATP initiates electron transfer by provoking conformational changes that destabilize the complex. We show how remodelling of the electron-accepting Co2+ promotes ATP-dependent electron transfer; an efficient strategy not seen in other electron-transferring ATPases.

  9. Coherent Transfer of Electronic Wavepacket Motion Between Atoms

    Zhou, Tao; Richards, B. G.; Jones, R. R.

    2016-05-01

    We have shown that electron correlations, induced by controlled dipole-dipole (DD) interactions, can enable the coherent transfer of electronic wavepacket motion from atoms to their neighbors. In the experiment, a 5 ns tunable dye laser excites Rb atoms in a MOT to the 25s state in a weak static electric field for which the tunable 25s 33 s 24p34p DD interaction is resonant. A picosecond THz pulse then further excites each Rydberg atom into a coherent superposition, of 25s and 24p states. The evolution of this mixed-parity wavepacket is characterized by time-dependent oscillations in the electric dipole moment, with a period of 2.9 ps. Approximately 5 ns after the wavepacket creation, a second 5 ns dye-laser promotes a second set of atoms from the 5p level into the 33s state. Because of the DD interaction, the second dye laser actually creates atom pairs whose electronic states are correlated via the resonant DD coupling. A 33 s + 34p wavepacket, oscillating with the same 2.9 ps period as the 25 s + 24p wavepacket, develops on the second set of atoms as a result of the correlation. A second, time-delayed ps THz pulse enables the detection of the coherent wavepacket motion on the two sets of atoms. This research has been supported by the NSF.

  10. Local Intermolecular Order Controls Photoinduced Charge Separation at Donor/Acceptor Interfaces in Organic Semiconductors

    Feier, Hilary M.; Reid, Obadiah G.; Pace, Natalie A.; Park, Jaehong; Bergkamp, Jesse J.; Sellinger, Alan; Gust, Devens; Rumbles, Garry

    2016-03-23

    How free charge is generated at organic donor-acceptor interfaces is an important question, as the binding energy of the lowest energy (localized) charge transfer states should be too high for the electron and hole to escape each other. Recently, it has been proposed that delocalization of the electronic states participating in charge transfer is crucial, and aggregated or otherwise locally ordered structures of the donor or the acceptor are the precondition for this electronic characteristic. The effect of intermolecular aggregation of both the polymer donor and fullerene acceptor on charge separation is studied. In the first case, the dilute electron acceptor triethylsilylhydroxy-1,4,8,11,15,18,22,25-octabutoxyphthalocyaninatosilicon(IV) (SiPc) is used to eliminate the influence of acceptor aggregation, and control polymer order through side-chain regioregularity, comparing charge generation in 96% regioregular (RR-) poly(3-hexylthiophene) (P3HT) with its regiorandom (RRa-) counterpart. In the second case, ordered phases in the polymer are eliminated by using RRa-P3HT, and phenyl-C61-butyric acid methyl ester (PC61BM) is used as the acceptor, varying its concentration to control aggregation. Time-resolved microwave conductivity, time-resolved photoluminescence, and transient absorption spectroscopy measurements show that while ultrafast charge transfer occurs in all samples, long-lived charge carriers are only produced in films with intermolecular aggregates of either RR-P3HT or PC61BM, and that polymer aggregates are just as effective in this regard as those of fullerenes.

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

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

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

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

    2015-12-07

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

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

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

  14. 27 CFR 27.48a - Payment of tax by electronic fund transfer.

    2010-04-01

    ... corporations, as defined in 26 U.S.C. 1563, and implementing regulations in 26 CFR 1.1563-1 through 1.1563-4.... (c) Electronic fund transfer or EFT means any transfer of funds, other than a transaction originated... electronic fund transfer. 27.48a Section 27.48a Alcohol, Tobacco Products and Firearms ALCOHOL AND...

  15. Electron Transfer Reactivity of the Aqueous Iron(IV)-Oxo Complex. Outer-Sphere vs Proton-Coupled Electron Transfer.

    Bataineh, Hajem; Pestovsky, Oleg; Bakac, Andreja

    2016-07-01

    The kinetics of oxidation of organic and inorganic reductants by aqueous iron(IV) ions, Fe(IV)(H2O)5O(2+) (hereafter Fe(IV)aqO(2+)), are reported. The substrates examined include several water-soluble ferrocenes, hexachloroiridate(III), polypyridyl complexes M(NN)3(2+) (M = Os, Fe and Ru; NN = phenanthroline, bipyridine and derivatives), HABTS(-)/ABTS(2-), phenothiazines, Co(II)(dmgBF2)2, macrocyclic nickel(II) complexes, and aqueous cerium(III). Most of the reductants were oxidized cleanly to the corresponding one-electron oxidation products, with the exception of phenothiazines which produced the corresponding oxides in a single-step reaction, and polypyridyl complexes of Fe(II) and Ru(II) that generated ligand-modified products. Fe(IV)aqO(2+) oxidizes even Ce(III) (E(0) in 1 M HClO4 = 1.7 V) with a rate constant greater than 10(4) M(-1) s(-1). In 0.10 M aqueous HClO4 at 25 °C, the reactions of Os(phen)3(2+) (k = 2.5 × 10(5) M(-1) s(-1)), IrCl6(3-) (1.6 × 10(6)), ABTS(2-) (4.7 × 10(7)), and Fe(cp)(C5H4CH2OH) (6.4 × 10(7)) appear to take place by outer sphere electron transfer (OSET). The rate constants for the oxidation of Os(phen)3(2+) and of ferrocenes remained unchanged in the acidity range 0.05 1.3 V. For proton-coupled electron transfer, the reduction potential is estimated at E(0) (Fe(IV)aqO(2+), H(+)/Fe(III)aqOH(2+)) ≥ 1.95 V. PMID:27320290

  16. Facile direct electron transfer in glucose oxidase modified electrodes

    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.

  17. Electron transfer kinetics at polarized nanoscopic liquid/liquid interfaces.

    Cai, Chenxin; Mirkin, Michael V

    2006-01-11

    Rapid kinetics of electron transfer (ET) reactions across the interface between water and 1,2-dichloroethane were measured by steady-state voltammetry at nanopipet electrodes (50- to 400-nm orifice radius). The origins of previously reported imperfect voltammetric responses of ET reactions at micropipets were investigated. Several new experimental systems were explored, and two of them yielded high-quality voltammograms suitable for kinetic experiments. The determined standard rate constants were compared to those measured previously at polarized and nonpolarized liquid/liquid interfaces. The effect of the interfacial dimensions on the magnitude of the apparent ET rate constant is discussed. A new approach to ET kinetic measurements based on the use of the scanning electrochemical microscope with a nanopipet tip and a metallic substrate has been developed and employed to check the validity of determined kinetic parameters. PMID:16390144

  18. Electron Transfer Reactions: Generalized Spin-Boson Approach

    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.

  19. Long-range intramolecular electron transfer in azurins

    Farver, O; Pecht, I

    1989-01-01

    The Cu(II) sites of azurins, the blue single copper proteins, isolated from Pseudomonas aeruginosa and Alcaligenes spp. (Iwasaki) are reduced by CO2- radicals, produced by pulse radiolysis, in two distinct reaction steps: (i) a fast bimolecular phase, at the rates (5.0 +/- 0.8) x 10(8) M-1.s-1 (P...... to -26 in these proteins is reduced to the RSSR- radical ion as evidenced by its characteristic absorption band centered at 410 nm. This radical ion decays in a unimolecular process with a rate identical to that of the slow Cu(II) reduction phase in the respective protein, thus clearly suggesting...... the reactive sites, their redox potential, and the nature of the separating medium. Thus, azurins with distinct structural and reactivity characteristics isolated from different bacteria or modified by site-directed mutagenesis can be used in comparing long-range electron transfer process between...

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

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

    2015-01-01

    in biological systems are only partly understood. We show here that insoluble high molecular weight lignin functions as a reservoir of electrons facilitating LPMO activity. The electrons are donated to the enzyme by long-range electron transfer involving soluble low molecular weight lignins present...... in plant cell walls. Electron transfer was confirmed by electron paramagnetic resonance spectroscopy showing that LPMO activity on cellulose changes the level of unpaired electrons in the lignin. The discovery of a long-range electron transfer mechanism links the biodegradation of cellulose and...... lignin and sheds new light on how oxidative enzymes present in plant degraders may act in concert....

  1. Quantum effects in ultrafast electron transfers within cryptochromes.

    Firmino, Thiago; Mangaud, Etienne; Cailliez, Fabien; Devolder, Adrien; Mendive-Tapia, David; Gatti, Fabien; Meier, Christoph; Desouter-Lecomte, Michèle; de la Lande, Aurélien

    2016-08-21

    Cryptochromes and photolyases are flavoproteins that may undergo ultrafast charge separation upon electronic excitation of their flavin cofactors. Charge separation involves chains of three or four tryptophan residues depending on the protein of interest. The molecular mechanisms of these processes are not completely clear. In the present work we investigate the relevance of quantum effects like the occurrence of nuclear tunneling and of coherences upon charge transfer in Arabidopsis thaliana cryptochromes. The possible breakdown of the Condon approximation is also investigated. We have devised a simulation protocol based on the realization of molecular dynamics simulations on diabatic potential energy surfaces defined at the hybrid constrained density functional theory/molecular mechanics level. The outcomes of the simulations are analyzed through various dedicated kinetics schemes related to the Marcus theory that account for the aforementioned quantum effects. MD simulations also provide a basic material to define realistic model Hamiltonians for subsequent quantum dissipative dynamics. To carry out quantum simulations, we have implemented an algorithm based on the Hierarchical Equations of Motion. With this new tool in hand we have been able to model the electron transfer chain considering either two- or three-state models. Kinetic models and quantum simulations converge to the conclusion that quantum effects have a significant impact on the rate of charge separation. Nuclear tunneling involving atoms of the tryptophan redox cofactors as well as of the environment (protein atoms and water molecules) is significant. On the other hand non-Condon effects are negligible in most simulations. Taken together, the results of the present work provide new insights into the molecular mechanisms controlling charge separation in this family of flavoproteins. PMID:27427185

  2. Electron transfer from flavin to iron in the Pseudomonas oleovorans rubredoxin reductase-rubredoxin electron transfer complex.

    Lee, H J; Basran, J; Scrutton, N S

    1998-11-01

    Rubredoxin reductase (RR) and rubredoxin form a soluble and physiological eT complex. The complex provides reducing equivalents for a membrane-bound omega-hydroxylase, required for the hydroxylation of alkanes and related compounds. The gene (alkT) encoding RR has been overexpressed and the enzyme purified in amounts suitable for studies of eT by stopped-flow spectroscopy. The eT reactions from NADH to the flavin of RR and from reduced RR to the 1Fe and 2Fe forms of rubredoxin have been characterized by transient kinetic and thermodynamic analysis. The reductive half-reaction proceeds in a one-step reaction involving oxidized enzyme and a two-electron-reduced enzyme-NAD+ charge-transfer complex. Flavin reduction is observed at 450 nm and charge-transfer formation at 750 nm; both steps are hyperbolically dependent on NADH concentration. The limiting flavin reduction rate (180 +/- 4 s-1) is comparable to the limiting rate for charge-transfer formation (189 +/- 7 s-1) and analysis at 450 and 750 nm yielded enzyme-NADH dissociation constants of 36 +/- 2 and 43 +/- 5 microM, respectively. Thermodynamic analysis of the reductive half-reaction yielded values for changes in entropy (DeltaS = -65.8 +/- 2.2 J mol-1 K-1), enthalpy (DeltaH = 37.8 +/- 0.6 kJ mol-1) and Gibbs free energy (DeltaG = 57.5 +/- 0.7 kJ mol-1 at 298 K) during hydride ion transfer to the flavin N5 atom. Spectral analysis of mixtures of 1Fe or 2Fe rubredoxin and RR suggest that conformational changes accompany eT complex assembly. Both the 1Fe (nonphysiological) and 2Fe (physiological) forms of rubredoxin were found to oxidize two electron-reduced rubredoxin reductase with approximately equal facility. Rates for the reduction of rubredoxin are hyperbolically dependent on rubredoxin concentration and the limiting rates are 72. 7 +/- 0.6 and 55.2 +/- 0.3 s-1 for the 1Fe and 2Fe forms, respectively. Analysis of the temperature dependence of eT to rubredoxin using eT theory revealed that the reaction is not

  3. Electron transfer in peptides: on the formation of silver nanoparticles.

    Kracht, Sonja; Messerer, Matthias; Lang, Matthieu; Eckhardt, Sonja; Lauz, Miriam; Grobéty, Bernard; Fromm, Katharina M; Giese, Bernd

    2015-03-01

    Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag(+) ions bound by peptides with histidine as the Ag(+)-binding amino acid and tyrosine as photoinducible electron donor cannot be reduced to Ag nanoparticles (AgNPs) under ET conditions because the peptide prevents the aggregation of Ag atoms to form AgNPs. Only in the presence of chloride ions, which generate AgCl microcrystals in the peptide matrix, does the synthesis of AgNPs occur. The reaction starts with the formation of 100 nm Ag@AgCl/peptide nanocomposites which are cleaved into 15 nm AgNPs. This defined transformation from large nanoparticles into small ones is in contrast to the usually observed Ostwald ripening processes and can be followed in detail by studying time-resolved UV/Vis spectra which exhibit an isosbestic point. PMID:25663127

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

    满宝元; 王象泰; 等

    1995-01-01

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

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

    Samec, Zdeněk

    2009-01-01

    Roč. 55, č. 2 (2009), s. 75-81. ISSN 0034-6691 R&D Projects: GA ČR(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

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

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

    2013-01-01

    Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy to supp...

  7. 77 FR 71035 - Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT...

    2012-11-28

    ... Transfer (EFT) Market Research Study AGENCY: Financial Management Service, Fiscal Service, Treasury. ACTION... Financial Management Service solicits comments concerning the ``Electronic Funds Transfer (EFT) Market...: Request for additional information should be directed to Walt Henderson, EFT Strategy Division, 401...

  8. Study of Electron Transfer Processes between Simple Plasma Ions and Electron Attaching Gases

    Williams, Ted; Adams, Nigel; Babcock, Lucia

    1998-11-01

    CCl4 and SF6 are gases that rapidly attach electrons. They are used in etchant plasmas and in high power switches to prevent breakdown. This attachment results in a simple negative ion chemistry that can be well characterized. A concurrent series of reactions involving positive ions also occurs, with ionization eventually being removed by ion-ion mutual neutralization. However, unlike the negative ion chemistry, the positive ion chemistry is more complex and has not been well characterized. Common plasma ions are those of the rare and diatomic gases, along with impurity ions such as H_2O^+ and H_3O^+. Reactions of these ions with CCl4 and SF6 generally occur rapidly by dissociative electron transfer. Some exceptions have been observed when the reactant ion contains an H-atom(s), such as the production of HCl when H_3^+ reacts with CCl_4. Since these reactions involve a fixed amount of energy, they bear similarity to photoelectron and photoelectron-photoion coincidence studies of these electron attaching gases in which only Franck-Condon transitions can occur. Comparision of product ions observed and rate coefficients gives better insights into the mechanism of the electron transfer process. Support by NSF AST-9415485 is gratefully acknowledged.

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

    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

  10. Correlation properties of surface and percolation transfer of electrons

    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: ∫0ν0WnoncollF(ν) 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(ν) ∝ 1/να exp(-1/ν). 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/Vα. This indicate on fractal properties phase-space. (author)

  11. A comparative study of organic electron transfer redox mediators: electron transfer kinetics for triarylimidazole and triarylamine mediators in the oxidation of 4-methoxybenzyl alcohol

    The triarylimidazoles (TAIs) constitute a promising class of organic electron transfer redox mediators that have been used to achieve indirect electrochemical C-H bonds activation and functionalization. Herein we report the diffusion and electron transfer rates for the oxidation of 4-methoxybenzyl alcohol using TAI and compare its electrochemical behavior with that of tris(4-bromophenyl)amine (TBPA). The results contribute to our understanding of the electron transfer process of electrocatalytic oxidation using TAIs, and offer useful guidelines for their further development and use

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

    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, ωB97X, with an optimized range-separation parameter, ω. 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. Enantioselective Intermolecular [2 + 2] Photocycloaddition Reactions of 2(1H)-Quinolones Induced by Visible Light Irradiation.

    Tröster, Andreas; Alonso, Rafael; Bauer, Andreas; Bach, Thorsten

    2016-06-29

    In the presence of a chiral thioxanthone catalyst (10 mol %) the title compounds underwent a clean intermolecular [2 + 2] photocycloaddition with electron-deficient olefins at λ = 419 nm. The reactions not only proceeded with excellent regio- and diastereoselectivity but also delivered the respective cyclobutane products with significant enantiomeric excess (up to 95% ee). Key to the success of the reactions is a two-point hydrogen bonding between quinolone and catalyst enabling efficient energy transfer and high enantioface differentiation. Preliminary work indicated that solar irradiation can be used for this process and that the substrate scope can be further expanded to isoquinolones. PMID:27268908

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

    Hyun, Byung-Ryool

    2011-05-11

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

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

    K Senthil Kumar; Archita Patnaik

    2013-03-01

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

  16. When electron transfer meets electron transport in redox-active molecular nanojunctions.

    Janin, Marion; Ghilane, Jalal; Lacroix, Jean-Christophe

    2013-02-13

    A scanning electrochemical microscope (SECM) was used to arrange two microelectrodes face-to-face separated by a micrometric gap. Polyaniline (PANI) was deposited electrochemically from the SECM tip side until it bridged the two electrodes. The junctions obtained were characterized by following the current through the PANI as a function of its electrochemical potential measured versus a reference electrode acting as a gate electrode in a solid-state transistor. PANI nanojunctions showed conductances below 100 nS in the oxidized state, indicating control of the charge transport within the whole micrometric gap by a limited number of PANI wires. The SECM configuration makes it possible to observe in the same experiment and in the same current range the electron-transfer and electron-transport processes. These two phenomena are distinguished here and characterized by following the variation of the current with the bias voltage and the scan rate. The electron-transfer current changes with the scan rate, while the charge-transport current varies with the bias voltage. Finally, despite the initially micrometric gap, a junction where the conductance is controlled by a single oligoaniline strand is achieved. PMID:23331168

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

    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.

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

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

    2015-10-01

    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.

  19. Synthesis, Characterization, Photophysics and Photochemistry of Pyrylogen Electron Transfer Sensitizers

    Clennan, Edward L. [University of Wyoming, Laramie; Liao, Chen [ORNL

    2014-01-01

    A series of new dicationic sensitizers that are hybrids of pyrylium salts and viologens has been synthesized. The electrochemical and photophysical properties of these "pyrylogen" sensitizers are reported in sufficient detail to allow rationale design of new photoinduced electron transfer reactions. The range of their reduction potentials (+0.37-+0.05V vs SCE) coupled with their range of singlet (48-63 kcal mol(-1)) and triplet (48-57kcalmol(-1)) energies demonstrate that they are potent oxidizing agents in both their singlet and triplet excited states, thermodynamically capable of oxidizing substrates with oxidation potentials as high as 3.1eV. The pyrylogens are synthesized in three steps from readily available starting materials in modest overall 11.4-22.3% yields. These sensitizers have the added advantages that: (1) their radical cations do not react on the CV timescale with oxygen bypassing the need to run reactions under nitrogen or argon and (2) have long wavelength absorptions between 413 and 523nm well out of the range where competitive absorbance by most substrates would cause a problem. These new sensitizers do react with water requiring special precautions to operate in a dry reaction environment.

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

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

    2016-06-01

    The biocatalytic electroreduction of oxygen has been studied on large surface area graphite and Vulcan® carbon electrodes with adsorbed Trametes trogii laccase. The electrokinetics of the O2 reduction reaction (ORR) was studied at different electrode potentials, O2 partial pressures and concentrations of hydrogen peroxide. Even though the overpotential at 0.25 mA·cm(-2) for the ORR at T1Cu of the adsorbed laccase on carbon is 0.8 V lower than for Pt of similar geometric area, the rate of the reaction and thus the operative current density is limited by the enzyme reaction rate at the T2/T3 cluster site for the adsorbed enzyme. The transition potential for the rate determining step from the direct electron transfer (DET) to the enzyme reaction shifts to higher potentials at higher oxygen partial pressure. Hydrogen peroxide produced by the ORR on bare carbon support participates in an inhibition mechanism, with uncompetitive predominance at high H2O2 concentration, non-competitive contribution can be detected at low inhibitor concentration. PMID:26883057

  1. Protein dynamics and electron transfer: Electronic decoherence and non-Condon effects

    Skourtis, Spiros S.; Balabin, Ilya A.; Kawatsu, Tsutomu; Beratan, David N.

    2005-01-01

    We compute the autocorrelation function of the donor-acceptor tunneling matrix element 〈TDA(t)TDA(0)〉 for six Ru-azurin derivatives. Comparison of this decay time to the decay time of the time-dependent Franck-Condon factor {computed by Rossky and coworkers [Lockwood, D. M., Cheng, Y.-K. & Rossky, P. J. (2001) Chem. Phys. Lett. 345, 159-165]} reveals the extent to which non-Condon effects influence the electron-transfer rate. 〈TDA(t)TDA(0)〉 is studied as a function of donor-acceptor distance,...

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

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

    2011-11-30

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

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

    Badalyan, Artavazd; Stahl, Shannon S.

    2016-07-01

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

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

    Badalyan, Artavazd; Stahl, Shannon S

    2016-07-21

    electron-proton-transfer mediators, such as TEMPO, may be used in combination with first-row transition metals, such as copper, to achieve efficient two-electron electrochemical processes, thereby introducing a new concept for the development of non-precious-metal electrocatalysts. PMID:27350245

  5. Coherent transfer of light polarization to electron spins in a semiconductor

    Kosaka, Hideo; Shigyou, Hideki; Mitsumori, Yasuyoshi; Rikitake, Yoshiaki; Imamura, Hiroshi; Kutsuwa, Takeshi; Arai, Koichiro; Edamatsu, Keiichi

    2007-01-01

    We demonstrate that the superposition of light polarization states is coherently transferred to electron spins in a semiconductor quantum well. By using time-resolved Kerr rotation we observe the initial phase of Larmor precession of electron spins whose coherence is transferred from light. To break the electron-hole spin entanglement, we utilized the big discrepancy between the transverse g-factors of electrons and light holes. The result encourages us to make a quantum media converter betwe...

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

    Chih-Hung Hsu; Jia-Ren Wu; Lung-Chien Chen; Po-Shun Chan; Cheng-Chiang Chen

    2014-01-01

    The utilization of nanostructure graphene thin films as electron transfer layer in dye-sensitized solar cells (DSSCs) was demonstrated. The effect of a nanostructure graphene thin film in DSSC structure was examined. The nanostructure graphene thin films provides a great electron transfer channel for the photogenerated electrons from TiO2 to indium tin oxide (ITO) glass. Obvious improvements in short-circuit current density of the DSSCs were observed by using the graphene electron transport l...

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

    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

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

    Nagasawa, Yutaka, E-mail: nagasawa@chem.es.osaka-u.ac.jp [Division of Frontier Materials Science, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka 560-8531 (Japan); PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Yoneda, Yusuke; Nambu, Shohei; Muramatsu, Masayasu; Takeuchi, Eisuke; Tsumori, Hiroki; Morikawa, Soichiro [Division of Frontier Materials Science, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Katayama, Tetsuro [PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012 (Japan); Miyasaka, Hiroshi [Division of Frontier Materials Science, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka 560-8531 (Japan)

    2014-10-17

    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{sup −1}, respectively, with only a few frequency difference of 5–9 cm{sup −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.

  9. Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene

    Sandanayaka, Atula S. D.; Araki, Yasuyaki; Ito, Osamu; Deviprasad, Gollapalli R.; Smith, Phillip M.; Rogers, Lisa M.; Zandler, Melvin E.; D'Souza, Francis

    2006-06-01

    Photochemical properties of pyrene and fluorene appended fulleropyrrolidine triads (AH 1-C 60-AH 2; AH 1 = pyrene and fluorene; AH 2 = naphthalene and phenyl) are reported. Electrochemical studies using cyclic voltammetry technique and DFT calculations at B3LYP/3-21G( ∗) method revealed that the charge-separated states in pyrene and fluorene appended triads are pyrene-C60rad --AH2 and fluorene-C60rad --AH2, respectively; however, no such charge-separated states could be established for naphthalene and phenyl appended triads. As demonstrated from the time resolved fluorescence, upon excitation of AH moiety in nonpolar solvents, energy transfer predominantly occurred from the singlet excited fluorophore to the C 60 moiety, whereas in polar DMF charge-separation also contributed to the fluorescence quenching. Additionally, charge separation also occurred from the singlet excited C 60 to the pyrene or fluorene entities of the triads in DMF. The rates and quantum yields of charge separation obtained by time-resolved emission studies were around 10 9 s -1 and 0.9-0.6 for pyrene-C 60-AH 2 and fluorene-C 60-AH 2 triads. Nanosecond transient absorption spectral studies performed by using 355 nm laser light on the triads, exhibited transient bands corresponding to the C60rad - and pyrene rad + or fluorene rad + , thus establishing the occurrence of electron transfer in these triads in DMF. The rates of charge recombination obtained by monitoring the decay of the C60rad - were found to be around 10 6 s -1 in DMF which resulted in the lifetimes of the radical ion pairs up to 1000 ns indicating charge stabilization in pyrene-C 60-AH 2 and fluorene-C 60-AH 2 triads. The formations of long-lived charge-separated states, pyrene-C60rad --AH2 and fluorene-C60rad --AH2 in DMF, were rationalized by evaluating the Marcus parameters from the temperature dependence of the charge-recombination rate constants.

  10. Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene

    Sandanayaka, Atula S.D. [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai 980-8577 (Japan); Araki, Yasuyaki [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai 980-8577 (Japan); Ito, Osamu [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai 980-8577 (Japan)], E-mail: ito@tagen.tohoku.ac.jp; Deviprasad, Gollapalli R. [Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0051 (United States); Smith, Phillip M. [Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0051 (United States); Rogers, Lisa M. [Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0051 (United States); Zandler, Melvin E. [Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0051 (United States); D' Souza, Francis [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai 980-8577 (Japan)], E-mail: Francis.DSouza@wichita.edu

    2006-06-20

    Photochemical properties of pyrene and fluorene appended fulleropyrrolidine triads (AH{sub 1}-C{sub 60}-AH{sub 2}; AH{sub 1}=pyrene and fluorene; AH{sub 2}=naphthalene and phenyl) are reported. Electrochemical studies using cyclic voltammetry technique and DFT calculations at B3LYP/3-21G(*) method revealed that the charge-separated states in pyrene and fluorene appended triads are pyrene{sup dot+}-C{sub 60}{sup dot-}AH{sub 2} and fluorene{sup dot+}-C{sub 60}{sup dot-}AH{sub 2}, respectively; however, no such charge-separated states could be established for naphthalene and phenyl appended triads. As demonstrated from the time resolved fluorescence, upon excitation of AH moiety in nonpolar solvents, energy transfer predominantly occurred from the singlet excited fluorophore to the C{sub 60} moiety, whereas in polar DMF charge-separation also contributed to the fluorescence quenching. Additionally, charge separation also occurred from the singlet excited C{sub 60} to the pyrene or fluorene entities of the triads in DMF. The rates and quantum yields of charge separation obtained by time-resolved emission studies were around 10{sup 9}s{sup -1} and 0.9-0.6 for pyrene-C{sub 60}-AH{sub 2} and fluorene-C{sub 60}-AH{sub 2} triads. Nanosecond transient absorption spectral studies performed by using 355nm laser light on the triads, exhibited transient bands corresponding to the C{sub 60}{sup dot-} and pyrene{sup dot+} or fluorene{sup dot+}, thus establishing the occurrence of electron transfer in these triads in DMF. The rates of charge recombination obtained by monitoring the decay of the C{sub 60}{sup dot-} were found to be around 10{sup 6}s{sup -1} in DMF which resulted in the lifetimes of the radical ion pairs up to 1000ns indicating charge stabilization in pyrene-C{sub 60}-AH{sub 2} and fluorene-C{sub 60}-AH{sub 2} triads. The formations of long-lived charge-separated states, pyrene{sup dot+}-C{sub 60}{sup d}'o{sup t-}AH{sub 2} and fluorene{sup dot+}-C{sub 60}{sup

  11. Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene

    Photochemical properties of pyrene and fluorene appended fulleropyrrolidine triads (AH1-C60-AH2; AH1=pyrene and fluorene; AH2=naphthalene and phenyl) are reported. Electrochemical studies using cyclic voltammetry technique and DFT calculations at B3LYP/3-21G(*) method revealed that the charge-separated states in pyrene and fluorene appended triads are pyrenedot+-C60dot-AH2 and fluorenedot+-C60dot-AH2, respectively; however, no such charge-separated states could be established for naphthalene and phenyl appended triads. As demonstrated from the time resolved fluorescence, upon excitation of AH moiety in nonpolar solvents, energy transfer predominantly occurred from the singlet excited fluorophore to the C60 moiety, whereas in polar DMF charge-separation also contributed to the fluorescence quenching. Additionally, charge separation also occurred from the singlet excited C60 to the pyrene or fluorene entities of the triads in DMF. The rates and quantum yields of charge separation obtained by time-resolved emission studies were around 109s-1 and 0.9-0.6 for pyrene-C60-AH2 and fluorene-C60-AH2 triads. Nanosecond transient absorption spectral studies performed by using 355nm laser light on the triads, exhibited transient bands corresponding to the C60dot- and pyrenedot+ or fluorenedot+, thus establishing the occurrence of electron transfer in these triads in DMF. The rates of charge recombination obtained by monitoring the decay of the C60dot- were found to be around 106s-1 in DMF which resulted in the lifetimes of the radical ion pairs up to 1000ns indicating charge stabilization in pyrene-C60-AH2 and fluorene-C60-AH2 triads. The formations of long-lived charge-separated states, pyrenedot+-C60d'ot-AH2 and fluorenedot+-C60dot-AH2 in DMF, were rationalized by evaluating the Marcus parameters from the temperature dependence of the charge-recombination rate constants

  12. Spin radical enhanced magnetocapacitance effect in intermolecular excited states.

    Zang, Huidong; Wang, Jianguo; Li, Mingxing; He, Lei; Liu, Zitong; Zhang, Deqing; Hu, Bin

    2013-11-14

    This article reports the magnetocapacitance effect (MFC) based on both pristine polymer MEH-PPV and its composite system doped with spin radicals (6R-BDTSCSB). We observed that a photoexcitation leads to a significant positive MFC in the pristine MEH-PPV. Moreover, we found that a low doping of spin radicals in polymer MEH-PPV causes a significant change on the MFC signal: an amplitude increase and a line-shape narrowing under light illumination at room temperature. However, no MFC signal was observed under dark conditions in either the pristine MEH-PPV or the radical-doped MEH-PPV. Furthermore, the magnitude increase and line-shape narrowing caused by the doped spin radicals are very similar to the phenomena induced by increasing the photoexcitation intensity. Our studies suggest that the MFC is essentially originated from the intermolecular excited states, namely, intermolecular electron-hole pairs, generated by a photoexcitation in the MEH-PPV. More importantly, by comparing the effects of spin radicals and electrically polar molecules on the MFC magnitude and line shape, we concluded that the doped spin radicals can have the spin interaction with intermolecular excited states and consequently affect the internal spin-exchange interaction within intermolecular excited states in the development of MFC. Clearly, our experimental results indicate that dispersing spin radicals forms a convenient method to enhance the magnetocapacitance effect in organic semiconducting materials. PMID:24144347

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

    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.

  14. 76 FR 67153 - Federal Acquisition Regulation; Submission for OMB Review; Payment by Electronic Fund Transfer

    2011-10-31

    ... published in the Federal Register at 76 FR 35219, on June 16, 2011. No comments were received. Public... would enable the Government to make payments under the contract by electronic fund transfer (EFT). The... Regulation; Submission for OMB Review; Payment by Electronic Fund Transfer AGENCY: Department of Defense...

  15. 48 CFR 52.232-33 - Payment by Electronic Funds Transfer-Central Contractor Registration.

    2010-10-01

    ... CONTRACT CLAUSES Text of Provisions and Clauses 52.232-33 Payment by Electronic Funds Transfer—Central... Government under this contract shall be made by electronic funds transfer (EFT), except as provided in... Fedwire Transfer System. The rules governing Federal payments through the ACH are contained in 31 CFR...

  16. 41 CFR 102-118.70 - Must my agency make all payments via electronic funds transfer?

    2010-07-01

    ... 41 Public Contracts and Property Management 3 2010-07-01 2010-07-01 false Must my agency make all payments via electronic funds transfer? 102-118.70 Section 102-118.70 Public Contracts and Property... Services § 102-118.70 Must my agency make all payments via electronic funds transfer? Yes, under 31...

  17. Aminotroponiminates as tunable, redox-active ligands: reversible single electron transfer and reductive dimerisation.

    Lichtenberg, C; Krummenacher, I

    2016-08-21

    Aminotroponiminates (atis) are shown to be redox-active ligands. Under strongly reducing conditions, the result of electron transfer can be controlled by the choice of the metal bound to the ati ligand. Either reversible electron transfer or a reductively induced dimerisation is observed. The latter reaction is (regio- and diastereo-) selective and chemically reversible. PMID:27452905

  18. The second R. A. Robinson Memorial Lecture. Electron, proton and related transfers

    Marcus, Rudolph A.

    1982-01-01

    Past and current developments in electron and proton transfer and in related fields are described. Broad classes of reactions have been considered from a unified viewpoint which offers a variety of experimental predictions. This introductory lecture considers various aspects of this many-faceted field. A simple equation is given for a highly exothermic electron-transfer reaction.

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

    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.

  20. Ultrafast Spectroscopic Signatures of Coherent Electron-Transfer Mechanisms in a Transition Metal Complex.

    Guo, Zhenkun; Giokas, Paul G; Cheshire, Thomas P; Williams, Olivia F; Dirkes, David J; You, Wei; Moran, Andrew M

    2016-07-28

    The prevalence of ultrafast electron-transfer processes in light-harvesting materials has motivated a deeper understanding of coherent reaction mechanisms. Kinetic models based on the traditional (equilibrium) form of Fermi's Golden Rule are commonly employed to understand photoinduced electron-transfer dynamics. These models fail in two ways when the electron-transfer process is fast compared to solvation dynamics and vibrational dephasing. First, electron-transfer dynamics may be accelerated if the photoexcited wavepacket traverses the point of degeneracy between donor and acceptor states in the solvent coordinate. Second, traditional kinetic models fail to describe electron-transfer transitions that yield products which undergo coherent nuclear motions. We address the second point in this work. Transient absorption spectroscopy and a numerical model are used to investigate coherent back-electron-transfer mechanisms in a transition metal complex composed of titanium and catechol, [Ti(cat)3](2-). The transient absorption experiments reveal coherent wavepacket motions initiated by the back-electron-transfer process. Model calculations suggest that the vibrationally coherent product states may originate in either vibrational populations or coherences of the reactant. That is, vibrational coherence may be produced even if the reactant does not undergo coherent nuclear motions. The analysis raises a question of broader significance: can a vibrational population-to-coherence transition (i.e., a nonsecular transition) accelerate electron-transfer reactions even when the rate is slower than vibrational dephasing? PMID:27362388

  1. 27 CFR 53.158 - Payment of tax by electronic fund transfer.

    2010-04-01

    ... electronic fund transfer. 53.158 Section 53.158 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY (CONTINUED) FIREARMS MANUFACTURERS EXCISE TAXES... Taxes § 53.158 Payment of tax by electronic fund transfer. (a) In general. For return periods...

  2. 27 CFR 24.272 - Payment of tax by electronic fund transfer.

    2010-04-01

    ... electronic fund transfer. 24.272 Section 24.272 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE TREASURY LIQUORS WINE Removal, Return and Receipt of Wine Taxpaid Removals § 24.272 Payment of tax by electronic fund transfer. (a) General. (1) During a...

  3. Intramolecular electron transfer in cytochrome cd(1) nitrite reductase from Pseudomonas stutzeri; kinetics and thermodynamics

    Farver, Ole; Kroneck, Peter M H; Zumft, Walter G;

    2002-01-01

    , internal electron transfer between these sites is an inherent element in the catalytic cycle of this enzyme. We have investigated the internal electron transfer reaction employing pulse radiolytically produced N-methyl nicotinamide radicals as reductant which reacts solely with the heme-c in an essentially...

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

    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

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

    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

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

    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

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

    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

  8. Photoinduced electron transfer in perylene-TiO2 nanoassemblies.

    Llansola-Portoles, Manuel J; Bergkamp, Jesse J; Tomlin, John; Moore, Thomas A; Kodis, Gerdenis; Moore, Ana L; Cosa, Gonzalo; Palacios, Rodrigo E

    2013-01-01

    The photosensitization effect of three perylene dye derivatives on titanium dioxide nanoparticles (TiO2 NPs) has been investigated. The dyes used, 1,7-dibromoperylene-3,4,9,10-tetracarboxy dianhydride (1), 1,7-dipyrrolidinylperylene-3,4,9,10-tetracarboxy dianhydride (2) and 1,7-bis(4-tert-butylphenyloxy)perylene-3,4,9,10-tetracarboxy dianhydride (3) have in common bisanhydride groups that convert into TiO2 binding groups upon hydrolysis. The different substituents on the bay position of the dyes enable tuning of their redox properties to yield significantly different driving forces for photoinduced electron transfer (PeT). Recently developed TiO2 NPs having a small average size and a narrow distribution (4 ± 1 nm) are used in this work to prepare the dye-TiO2 systems under study. Whereas successful sensitization was obtained with 1 and 2 as evidenced by steady-state spectral shifts and transient absorption results, no evidence for the attachment of 3 to TiO2 was observed. The comparison of the rates of PeT (kPeT ) for 1- and 2-TiO2 systems studied in this work with those obtained for previously reported analogous systems, having TiO2 NPs covered by a surfactant layer (Hernandez et al. [2012] J. Phys. Chem. B., 117, 4568-4581), indicates that kPeT for the former systems is slower than that for the later. These results are interpreted in terms of the different energy values of the conduction band edge in each system. PMID:23742178

  9. Electron-phonon energy transfer in hot-carrier solar cells

    Luque López, Antonio; Martí Vega, Antonio

    2010-01-01

    Hot-carrier solar cells may yield very high efficiency if the heat transfer from electrons to phonons is low enough. In this paper we calculate this heat transfer for the two inelastic mechanisms known to limit the electric conductivity: the multi-valley scattering in non-polar semiconductors and the coupling of electrons to longitudinal optical phonons in polar semiconductors. Heat transfer is ruled by matrix elements deduced from electric conductivity measurements. The cell power extracted ...

  10. Separation of intra- and intermolecular contributions to the PELDOR signal

    Schöps, Philipp; Plackmeyer, Jörn; Marko, Andriy

    2016-08-01

    Pulsed Electron-electron Double Resonance (PELDOR) is commonly used to measure distances between native paramagnetic centers or spin labels attached to complex biological macromolecules. In PELDOR the energies of electron magnetic dipolar interactions are measured by analyzing the oscillation frequencies of the recorded time resolved signal. Since PELDOR is an ensemble method, the detected signal contains contributions from intramolecular, as well as intermolecular electron spin interactions. The intramolecular part of the signal contains the information about the structure of the studied molecules, thus it is very important to accurately separate intra- and intermolecular contributions to the total signal. This separation can become ambiguous, when the length of the PELDOR signal is not much longer than twice the oscillation period of the signal. In this work we suggest a modulation depth scaling method, which can use short PELDOR signals in order to extract the intermolecular contribution. Using synthetic data we demonstrate the advantages of the new approach and analyze its stability with regard to signal noise. The method was also successfully tested on experimental data of three systems measured at Q-Band frequencies, two model compounds in deuterated and protonated solvents and one biological sample, namely BetP. The application of the new method with an assigned value of the signal modulation depth enables us to determine the interspin distances in all cases. This is especially interesting for the model compound with an interspin distance of 5.2 nm in the protonated solvent and the biological sample, since an accurate separation of the intra- and intermolecular PELDOR signal contributions would be difficult with the standard approach in those cases.

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

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

    2016-02-01

    The dynamics of excess-electron transfer in DNA has attracted the attention of scientists from all kinds of research fields because of its importance in biological processes. To date, several studies on excess-electron transfer in consecutive adenine (A):thymine (T) sequences in donor-DNA-acceptor systems have been published. However, the reported excess-electron transfer rate constants for consecutive T's are in the range of 10(10)-10(11) s(-1) depending on the photosensitizing electron donor, which provides various driving forces for excess-electron injection into DNA. In this study, we employed a strongly electron-donating photosensitizer, a dimer of 3,4-ethylenedioxythiophene (2E), and an electron acceptor, diphenylacetylene (DPA), to synthesize a series of modified DNA oligomers (2-Tn, n = 3-6) in order to investigate the excess-electron transfer dynamics in these donor-DNA-acceptor systems using femtosecond laser flash photolysis. The relation between the free energy change for charge injection and the excess-electron transfer rate among consecutive T's provided an intrinsic excess-electron hopping rate constant of (3.8 ± 1.5) × 10(10) s(-1) in the DNA, which is consistent with the fluctuation frequency of the DNA sugar backbone and bases (3.3 × 10(10) s(-1)). Thus, we discuss the effect of structural fluctuations on the excess-electron hopping in DNA. PMID:26741048

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

    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.

  13. How fast is optically induced electron transfer in organic mixed valence systems?

    Lambert, C; Moos, M; Schmiedel, A; Holzapfel, M; Schäfer, J; Kess, M; Engel, V

    2016-07-28

    The rate of thermally induced electron transfer in organic mixed valence compounds has thoroughly been investigated by e.g. temperature dependent ESR spectroscopy. However, almost nothing is known about the dynamics of optically induced electron transfer processes in such systems. Therefore, we investigated these processes in mixed valence compounds based on triphenylamine redox centres bridged by conjugated spacers by NIR transient absorption spectroscopy with fs-time resolution. These experiments revealed an internal conversion (IC) process to be on the order of 50-200 fs which is equivalent to the back electron transfer after optical excitation into the intervalence charge transfer band. This IC is followed by ultrafast cooling to the ground state within 1 ps. Thus, in the systems investigated optically induced electron transfer is about 3-4 orders of magnitude faster than thermally induced ET. PMID:27376572

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

    Chih-Hung Hsu

    2014-01-01

    Full Text Available The utilization of nanostructure graphene thin films as electron transfer layer in dye-sensitized solar cells (DSSCs was demonstrated. The effect of a nanostructure graphene thin film in DSSC structure was examined. The nanostructure graphene thin films provides a great electron transfer channel for the photogenerated electrons from TiO2 to indium tin oxide (ITO glass. Obvious improvements in short-circuit current density of the DSSCs were observed by using the graphene electron transport layer modified photoelectrode. The graphene electron transport layer reduces effectively the back reaction in the interface between the ITO transparent conductive film and the electrolyte in the DSSC.

  15. Coherent transfer of light polarization to electron spins in a semiconductor.

    Kosaka, Hideo; Shigyou, Hideki; Mitsumori, Yasuyoshi; Rikitake, Yoshiaki; Imamura, Hiroshi; Kutsuwa, Takeshi; Arai, Koichiro; Edamatsu, Keiichi

    2008-03-01

    We demonstrate that the superposition of light polarization states is coherently transferred to electron spins in a semiconductor quantum well. By using time-resolved Kerr rotation, we observe the initial phase of Larmor precession of electron spins whose coherence is transferred from light. To break the electron-hole spin entanglement, we utilized the big discrepancy between the transverse g factors of electrons and light-holes. The result encourages us to make a quantum media converter between flying photon qubits and stationary electron-spin qubits in semiconductors. PMID:18352739

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

    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 ra...

  17. Allosteric control of internal electron transfer in cytochrome cd1 nitrite reductase

    Farver, Ole; Kroneck, Peter M H; Zumft, Walter G;

    2003-01-01

    Cytochrome cd1 nitrite reductase is a bifunctional multiheme enzyme catalyzing the one-electron reduction of nitrite to nitric oxide and the four-electron reduction of dioxygen to water. Kinetics and thermodynamics of the internal electron transfer process in the Pseudomonas stutzeri enzyme have...

  18. Calculation of electron transfer in ruthenium-modified derivatives of cytochrome b562

    Glukhova, O. E.; Prytkova, T. R.; Shunaev, V. V.

    2016-03-01

    Quantitative theoretical studies of long-range electron transfer are still quite rare and require further development of computational methods for the analysis of such reactions. We considered the electron transfer reaction in rutenium-modified derivatives of cytochrome b562 with advanced modeling techniques. We conducted a series of ab initio calculations of the donor/acceptor interaction in protein fragments and compared the calculated electron velocity with available experimental data. Our approach takes into account the co-factor of the electronic structure and the impact of the solution on a donor-acceptor interaction. This allows us to predict the absolute values of the electron transfer rate unlike other computational methods which provide only qualitative results. Our estimates with good accuracy repeat the experimental values of electron transfer rate. It was found that the electron transfer in certain derivatives of cytochrome b562 is mainly caused by "shortcut" conformations in which the donor/acceptor interactions are mediated by the interaction of Ru-unbound ligands with groups of the protein surface. We argue that a quantitative theoretical analysis is essential for detailed understanding of electron transfer in proteins and mechanisms of biological redox reactions.

  19. Electron-transfer reactions between viologen radical cations and quinones in AOT reverse micelles studied by electron pulse radiolysis

    Electron-transfer reactions between viologen radical cations (CnVsm-bullet+, n = 1-18) and various quinones have been studied in aqueous and reverse micellar (AOT/isooctane/H2O) solution by use of the electron pulse radiolysis technique. By use of dynamic light scattering measurements, the concentration of water pools was determined and the number of electron-transfer reactants per water pool could be calculated. Rate constants measured for the reaction between CnVsm-bullet+ radicals and anthraquinonesulfonate ions (AQS-) decreased with increasing length of the aliphatic chain of the viologens, caused by association of the viologen with the surfactant interface

  20. Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

    Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

    2009-01-01

    Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide. PMID:19197929

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

    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.

  2. Study of intermediates from transition metal excited-state electron-transfer reactions

    Hoffman, M. Z.

    1992-07-01

    Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes.

  3. Measured multipole moments of continuum electron transfer angular distributions

    The velocity space distribution of electrons emitted near the forward direction from collisions involving fast, highly stripped oxygen ions with gaseous and solid targets is presented and described in terms of multipole moments of the ejected charge distribution, which permits direct comparison with recent theory. The measurements are produced by employing position-sensitive electron detection to combine emission angle definition with conventional electrostatic spectrometry. Agreement obtained between theory and distributions observed for binary continuum electron loss processes coupled with a similar multipole content observed with solid targets suggests a model of convoy electron production dominated by electron loss from the projectile within the bulk of the target. Further, the connection between multipoles of the projectile electron emission distribution in single collisions and the state of excitation of that projectile excited states may provide the basis for a probe of the state of ions traversing bulk solid matter. 14 refs., 3 figs., 1 tab

  4. Visualizing coherent intermolecular dipole-dipole coupling in real space.

    Zhang, Yang; Luo, Yang; Zhang, Yao; Yu, Yun-Jie; Kuang, Yan-Min; Zhang, Li; Meng, Qiu-Shi; Luo, Yi; Yang, Jin-Long; Dong, Zhen-Chao; Hou, J G

    2016-03-31

    Many important energy-transfer and optical processes, in both biological and artificial systems, depend crucially on excitonic coupling that spans several chromophores. Such coupling can in principle be described in a straightforward manner by considering the coherent intermolecular dipole-dipole interactions involved. However, in practice, it is challenging to directly observe in real space the coherent dipole coupling and the related exciton delocalizations, owing to the diffraction limit in conventional optics. Here we demonstrate that the highly localized excitations that are produced by electrons tunnelling from the tip of a scanning tunnelling microscope, in conjunction with imaging of the resultant luminescence, can be used to map the spatial distribution of the excitonic coupling in well-defined arrangements of a few zinc-phthalocyanine molecules. The luminescence patterns obtained for excitons in a dimer, which are recorded for different energy states and found to resemble σ and π molecular orbitals, reveal the local optical response of the system and the dependence of the local optical response on the relative orientation and phase of the transition dipoles of the individual molecules in the dimer. We generate an in-line arrangement up to four zinc-phthalocyanine molecules, with a larger total transition dipole, and show that this results in enhanced 'single-molecule' superradiance from the oligomer upon site-selective excitation. These findings demonstrate that our experimental approach provides detailed spatial information about coherent dipole-dipole coupling in molecular systems, which should enable a greater understanding and rational engineering of light-harvesting structures and quantum light sources. PMID:27029277

  5. Visualizing coherent intermolecular dipole–dipole coupling in real space

    Zhang, Yang; Luo, Yang; Zhang, Yao; Yu, Yun-Jie; Kuang, Yan-Min; Zhang, Li; Meng, Qiu-Shi; Luo, Yi; Yang, Jin-Long; Dong, Zhen-Chao; Hou, J. G.

    2016-03-01

    Many important energy-transfer and optical processes, in both biological and artificial systems, depend crucially on excitonic coupling that spans several chromophores. Such coupling can in principle be described in a straightforward manner by considering the coherent intermolecular dipole–dipole interactions involved. However, in practice, it is challenging to directly observe in real space the coherent dipole coupling and the related exciton delocalizations, owing to the diffraction limit in conventional optics. Here we demonstrate that the highly localized excitations that are produced by electrons tunnelling from the tip of a scanning tunnelling microscope, in conjunction with imaging of the resultant luminescence, can be used to map the spatial distribution of the excitonic coupling in well-defined arrangements of a few zinc-phthalocyanine molecules. The luminescence patterns obtained for excitons in a dimer, which are recorded for different energy states and found to resemble σ and π molecular orbitals, reveal the local optical response of the system and the dependence of the local optical response on the relative orientation and phase of the transition dipoles of the individual molecules in the dimer. We generate an in-line arrangement up to four zinc-phthalocyanine molecules, with a larger total transition dipole, and show that this results in enhanced ‘single-molecule’ superradiance from the oligomer upon site-selective excitation. These findings demonstrate that our experimental approach provides detailed spatial information about coherent dipole–dipole coupling in molecular systems, which should enable a greater understanding and rational engineering of light-harvesting structures and quantum light sources.

  6. Interspecies electron transfer via hydrogen and formate rather than direct electrical connections in cocultures of Pelobacter carbinolicus and Geobacter sulfurreducens

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

    2012-01-01

    Direct interspecies electron transfer (DIET) is an alternative to interspecies H(2)/formate transfer as a mechanism for microbial species to cooperatively exchange electrons during syntrophic metabolism. To understand what specific properties contribute to DIET, studies were conducted with Peloba...

  7. Direct electron transfer of glucose oxidase on the carbon nanotube electrode

    CAI Chenxin; CHEN Jing; LU Tianhong

    2004-01-01

    The direct electron transfer of glucose oxidase (Gox) immobilized onto the surface of the carbon nanotube (CNT)-modified glassy carbon (CNT/GC) electrode is reported. The direct electron transfer rate of Gox is greatly enhanced when it was immobilized onto the surface of CNT/GC electrode. Cyclic voltammetric results show a pair of well-defined and nearly sym metric redox peaks, which corresponds to the direct electron transfer of Gox, with the formal potential (E0′), which is almost independent on the scan rates, of about -0.456 V (vs. SCE) in the phosphate buffer solution (pH 6.9). The apparent heterogeneous electron transfer rate constant (ks) of Gox at the CNT/GC electrode surface is estimated to be (1.74 ± 0.42) s-1, which is much higher than that reported previously. The dependence of E0′on solution pH indicates that the direct electron transfer of Gox is a two-electron-transfer coupled with two-proton-transfer reaction process. The experimental results also demonstrate that the immobilized Gox retains its bioelectrocatalytic activity toward the oxidation of glucose. The method presented here can be easily extended to obtain the direct electrochemistry of other enzymes or proteins.

  8. Near-IR excitation transfer and electron transfer in a BF2-chelated dipyrromethane-azadipyrromethane dyad and triad.

    El-Khouly, Mohamed E; Amin, Anu N; Zandler, Melvin E; Fukuzumi, Shunichi; D'Souza, Francis

    2012-04-23

    A molecular dyad and triad, comprised of a known photosensitizer, BF(2)-chelated dipyrromethane (BDP), covalently linked to its structural analog and near-IR emitting sensitizer, BF(2)-chelated tetraarylazadipyrromethane (ADP), have been newly synthesized and the photoinduced energy and electron transfer were examined by femtosecond and nanosecond laser flash photolysis. The structural integrity of the newly synthesized compounds has been established by spectroscopic, electrochemical, and computational methods. The DFT calculations revealed a molecular-clip-type structure for the triad, in which the BDP and ADP entities are separated by about 14 Å with a dihedral angle between the fluorophores of around 70°. Differential pulse voltammetry studies have revealed the redox states, allowing estimation of the energies of the charge-separated states. Such calculations revealed a charge separation from the singlet excited BDP ((1)BDP*) to ADP (BDP(.+)-ADP(.-)) to be energetically favorable in nonpolar toluene and in polar benzonitrile. In addition, the excitation transfer from the singlet BDP to ADP is also envisioned due to good spectral overlap of the BDP emission and ADP absorption spectra. Femtosecond laser flash photolysis studies provided concrete evidence for the occurrence of energy transfer from (1)BDP* to ADP (in benzonitrile and toluene) and electron transfer from BDP to (1)ADP* (in benzonitrile, but not in toluene). The kinetic study of energy transfer was measured by monitoring the rise of the ADP emission and revealed fast energy transfer (ca. 10(11) s(-1)) in these molecular systems. The kinetics of electron transfer via (1)ADP*, measured by monitoring the decay of the singlet ADP at λ=820 nm, revealed a relatively fast charge-separation process from BDP to (1)ADP*. These findings suggest the potential of the examined ADP-BDP molecules to be efficient photosynthetic antenna and reaction center models. PMID:22416038

  9. Role of coherence and delocalization in photo-induced electron transfer at organic interfaces.

    Abramavicius, V; Pranculis, V; Melianas, A; Inganäs, O; Gulbinas, V; Abramavicius, D

    2016-01-01

    Photo-induced charge transfer at molecular heterojunctions has gained particular interest due to the development of organic solar cells (OSC) based on blends of electron donating and accepting materials. While charge transfer between donor and acceptor molecules can be described by Marcus theory, additional carrier delocalization and coherent propagation might play the dominant role. Here, we describe ultrafast charge separation at the interface of a conjugated polymer and an aggregate of the fullerene derivative PCBM using the stochastic Schrödinger equation (SSE) and reveal the complex time evolution of electron transfer, mediated by electronic coherence and delocalization. By fitting the model to ultrafast charge separation experiments, we estimate the extent of electron delocalization and establish the transition from coherent electron propagation to incoherent hopping. Our results indicate that even a relatively weak coupling between PCBM molecules is sufficient to facilitate electron delocalization and efficient charge separation at organic interfaces. PMID:27605035

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

    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.

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

    Kar, Durga P.; Nayak, Praveen P.; Bhuyan, Satyanarayan; Mishra, Debasish [Department of Electronics and Instrumentation Engineering, Institute of Technical Education and Research, Siksha ‘O’ Anushandhan University, Bhubaneswar 751030 (India)

    2015-09-28

    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.

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

    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

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

    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...

  14. 78 FR 30661 - Electronic Fund Transfers (Regulation E)

    2013-05-22

    ... closed network transactions, which generally can only be sent to agents or other entities that have... consumers in the United States to designated recipients in other countries and, for covered transactions... by a person other than the remittance transfer provider. In place of these two former...

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

    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.

  16. Intramolecular versus intermolecular hydrogen bonding in solution

    Vliegenthart, J. F. G.; Kroon, Jan; Kroon-Batenburg, L.M.J.; Leeflang, B.R.

    1994-01-01

    The balance between intra- and intermolecular hydrogen bonding is studied for a solution of methyl beta-cellobioside in water and dimethylsulfoxide by 1H NMR and molecular dynamics simulations. In water O(3) predominantly interacts with water molecules, whereas in dimethylsulfoxide it is intramolecularly hydrogen bonded to O(5Œ). The temperature coefficient of the chemical shift of the hydroxy groups appears to be a reliable indicator of intermolecular hydrogen-bond formation, whereas the ex...

  17. Coexistence of Different Electron-Transfer Mechanisms in the DNA Repair Process by Photolyase.

    Lee, Wook; Kodali, Goutham; Stanley, Robert J; Matsika, Spiridoula

    2016-08-01

    DNA photolyase has been the topic of extensive studies due to its important role of repairing photodamaged DNA, and its unique feature of using light as an energy source. A crucial step in the repair by DNA photolyase is the forward electron transfer from its cofactor (FADH(-) ) to the damaged DNA, and the detailed mechanism of this process has been controversial. In the present study, we examine the forward electron transfer in DNA photolyase by carrying out high-level ab initio calculations in combination with a quantum mechanical/molecular mechanical (QM/MM) approach, and by measuring fluorescence emission spectra at low temperature. On the basis of these computational and experimental results, we demonstrate that multiple decay pathways exist in DNA photolyase depending on the wavelength at excitation and the subsequent transition. This implies that the forward electron transfer in DNA photolyase occurs not only by superexchange mechanism but also by sequential electron transfer. PMID:27362906

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

    Gates, Andrew J. [Univ. of East Anglia, Norwich (United Kingdom); Marritt, Sophie [Univ. of East Anglia, Norwich (United Kingdom); Bradley, Justin [Univ. of East Anglia, Norwich (United Kingdom); Shi, Liang [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); McMillan, Duncan G. [Univ. of Leeds (United Kingdom); Jeuken, Lars J. [Univ. of Leeds (United Kingdom); Richardson, David [Univ. of East Anglia, Norwich (United Kingdom); Butt, Julea N. [Univ. of East Anglia, Norwich (United Kingdom)

    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.

  19. Electron transfer from CO2lg-bullet- to perylene in cyclohexane

    CO2lg-bullet- formed by the reactions of the electron with CO2 in cyclohexane transfers an electron to perylene with a rate constant of 2.9 x 1010 M-1s-1. Gε580nm for the perylene radical anion is 9 x 103 molecules (100 eV)-1 M -1 cm-1. The transfer of an electron from CO2lg-bullet+ to an aromatic molecule is a significant process when CO2 is used as an electron scavenger in solution where the production of excited states of the aromatic molecule is studied. 24 refs., 6 figs

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

    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.

  1. Microbe-electrode interactions: The chemico-physical environment and electron transfer

    Gardel, Emily Jeanette

    2013-01-01

    This thesis presents studies that examine microbial extracellular electron transfer that an emphasis characterizing how environmental conditions influence electron flux between microbes and a solid-phase electron donor or acceptor. I used bioelectrochemical systems (BESs), fluorescence and electron microscopy, chemical measurements, 16S rRNA analysis, and qRT-PCR to study these relationships among chemical, physical and biological parameters and processes.

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

    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

  3. Quantifying electron transfer reactions in biological systems: what interactions play the major role?

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

    2015-12-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor.

  4. Ultrafast Electron Transfer in Solutions Studied by Picosecond Pulse Radiolysis

    Ma, Jun

    2015-01-01

    The interaction of energetic particles with water results in the excitation and ionization of water molecules. The ionization process refers to the generation of the excess electrons detached from their parent molecules and leaving behind the positive hole (denoted as H₂O•⁺). This occurs on the timescale of an electronic transition ~10⁻¹⁵ s. The earliest chemical processes of H₂O•⁺ and excess electron towards other matter followed water ionizing in bulk still remain relative little known and ...

  5. Synthesis and photoinduced electron transfer studies of a tri(phenothiazine)-subphthalocyanine-fullerene pentad.

    KC, Chandra B; Lim, Gary N; Zandler, Melvin E; D'Souza, Francis

    2013-09-01

    A novel donor-acceptor pentad featuring subphthalocyanine and fullerene as the primary electron donor and acceptor, and three phenothiazine entities as secondary hole transferring agents, have been newly synthesized and characterized as an photosynthetic reaction center model compound. Occurrences of ultrafast photoinduced electron transfer (PET) and slower charge recombination are witnessed in the pentad from the femtosecond and nanosecond transient absorption studies. PMID:23981125

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

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

    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 opposi...

  7. Explicitly Time-Dependent Electron Transfer in Donor-Bridge-Acceptor Systems

    Psiachos, Demetra

    2016-01-01

    We discuss electron transfer in benchmark donor-bridge-acceptor systems using time-dependent methods based on exact diagonalizations. For the small bridge sizes studied, the exact solution leads to results far different from perturbation theory. Notably, we do not obtain destructive interferences in the electron transfer for the arrangements of the bridge molecules which lead to this result using the perturbation theory. The calculated currents for various donor-bridge-acceptor configurations...

  8. Electronic transfer of prescription-related information: comparing views of patients, general practitioners, and pharmacists.

    Porteous, Terry; Bond, Christine; Robertson, Roma; Hannaford, Philip; Reiter, Ehud

    2003-01-01

    BACKGROUND: The National Health Service (NHS) intends to introduce a system of electronic transfer of prescription-related information between general practitioners (GPs) and community pharmacies. The NHS Plan describes how this will be achieved. AIM: To gather opinions of patients, GPs, and community pharmacists on the development of a system of electronic transfer of prescription-related information between GPs and community pharmacies. DESIGN OF STUDY: Survey combining interviews, focus gr...

  9. Quantitative analysis of intermolecular interactions in orthorhombic rubrene

    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 π-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 Cπ...Cπ 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.

  10. Electron Transfer Between Colloidal ZnO Nanocrystals

    Hayoun, Rebecca; Whitaker, Kelly M.; Gamelin, Daniel R.; Mayer, James M.

    2011-01-01

    Colloidal ZnO nanocrystals, capped with dodecylamine and dissolved in toluene, can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals with a solution of uncharged large nanocrystals, e-CB:ZnO–S + ZnO–L, causes changes in the EPR spectrum i...

  11. Electrostatic effect on electron transfer between cytochrome b5 and cytochrome c

    2000-01-01

    The binding and electron transfer between wild type, E44A, E56A, E44/56A, E44/48/56A/D60Aand F35Y variants of cytochrome b5 and cytochrome c were studied. When mixed with cytochrome c, the cytochrome b5E44/48/56A/D60A did not show the typical UV-vis difference spectrum of absorption, indicating that the alteration ofthe surface electrostatic potential obviously influenced the spectrum. The electron transfer rates of wild type cytochromeb5, its variants and cytochrome e at different temperature and ionic strength exhibited an order of F35Y > wild type >E56A > E44A > E44/48/56A/D60A. The enthalpy and entropy of the reaction did not change obviously, suggestingthat the mutation did not significantly disturb the electron transfer conformation. The investigation of electron transfer rateconstants at different ionic strength demonstrated that electrostatic interaction obviously affected the electron transfer pro-cess. The significant difference of Cyt b5 F35Y and E44/48/56A/D60A from the wild type protein further confirmed thegreat importance of the electrostatic interaction in the protein electron transfer.

  12. Transetherification on polyols by intra- and intermolecular nucleophilic substitutions.

    Takahiro Muraoka

    Full Text Available Transetherification on polyols involving intra- and intermolecular nucleophilic substitutions is reported. Di- or trialkoxide formation of propane-1,3-diol or 2-(hydroxymethylpropane-1,3-diol derivatives by NaH triggers the reaction via oxetanes formation, where the order to add NaH and a polyol significantly influences the yields of products. It was demonstrated that the protective group on the pentaerythritol skeleton is apparently transferred to the hydrophilic and hydrophobic chain molecules bearing a leaving group in one-step, and a protective group conversion from tosyl to benzyl was successful using a benzyl-appending triol to afford a desired product in 67% yield.

  13. Transfer printing of thermoreversible ion gels for flexible electronics.

    Lee, Keun Hyung; Zhang, Sipei; Gu, Yuanyan; Lodge, Timothy P; Frisbie, C Daniel

    2013-10-01

    Thermally assisted transfer printing was employed to pattern thin films of high capacitance ion gels on polyimide, poly(ethylene terephthalate), and SiO2 substrates. The ion gels consisted of 20 wt % block copolymer poly(styrene-b-ethylene oxide-b-styrene and 80 wt % ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)amide. Patterning resolution was on the order of 10 μm. Importantly, ion gels containing the block polymer with short PS end blocks (3.4 kg/mol) could be transfer-printed because of thermoreversible gelation that enabled intimate gel-substrate contact at 100 °C, while gels with long PS blocks (11 kg/mol) were not printable at the same temperature due to poor wetting contact between the gel and substrates. By using printed ion gels as high-capacitance gate insulators, electrolyte-gated thin-film transistors were fabricated that operated at low voltages (<1 V) with high on/off current ratios (∼10(5)). Statistical analysis of carrier mobility, turn-on voltage, and on/off ratio for an array of printed transistors demonstrated the excellent reproducibility of the printing technique. The results show that transfer printing is an attractive route to pattern high-capacitance ion gels for flexible thin-film devices. PMID:24028461

  14. Reductive cleavage of dichalcogenide bonds. Communication 3. Selectivity of electron exchange in diaryldichalcogenide-bispyridinium systems

    The kinetics of reductive cleavage of the dichalcogenide bond in dimeric Schiff's bases ArEEAr (E = S, Te) induced by indirect electron transfer by the in situ generated bridged bispyridinium radical cations and biradicals was studied by cyclic voltammetry. It is found that the dependence between the apparent rate constants of intermolecular electron transfer and the electron-withdrawing properties of diaryldichalcogenides is violated. The mechanisms of homogeneous (chemical) and heterogeneous (electrochemical) reductive cleavage of diaryldichalcogenides are discussed

  15. Effect of resonant-to-bulk electron momentum transfer on the efficiency of electron-cyclotron current drive

    Efficiency of current drive by electron-cyclotron waves is investigated numerically by a bounce-average Fokker-Planck code to elucidate the effects of momentum transfer from resonant to bulk electrons, finite bulk temperature relative to the energy of resonant electrons, and trapped electrons. Comparisons are made with existing theories to assess their validity and quantitative difference between theory and code results. Difference of nearly a factor of 2 was found in efficiency between some theory and code results. 4 refs., 4 figs

  16. Identification of a new electron-transfer relaxation pathway in photoexcited pyrrole dimers

    Neville, Simon P.; Kirkby, Oliver M.; Kaltsoyannis, Nikolas; Worth, Graham A.; Fielding, Helen H.

    2016-04-01

    Photoinduced electron transfer is central to many biological processes and technological applications, such as the harvesting of solar energy and molecular electronics. The electron donor and acceptor units involved in electron transfer are often held in place by covalent bonds, π-π interactions or hydrogen bonds. Here, using time-resolved photoelectron spectroscopy and ab initio calculations, we reveal the existence of a new, low-energy, photoinduced electron-transfer mechanism in molecules held together by an NH⋯π bond. Specifically, we capture the electron-transfer process in a pyrrole dimer, from the excited π-system of the donor pyrrole to a Rydberg orbital localized on the N-atom of the acceptor pyrrole, mediated by an N-H stretch on the acceptor molecule. The resulting charge-transfer state is surprisingly long lived and leads to efficient electronic relaxation. We propose that this relaxation pathway plays an important role in biological and technological systems containing the pyrrole building block.

  17. Extracellular electron transfer from cathode to microbes: application for biofuel production.

    Choi, Okkyoung; Sang, Byoung-In

    2016-01-01

    Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter showed that both directions for electron transfer would be possible. It was proposed that gram-positive bacteria, in the absence of cytochrome C, would accept electrons using a cascade of membrane-bound complexes such as membrane-bound Fe-S proteins, oxidoreductase, and periplasmic enzymes. Modification of the cathode with the addition of positive charged species such as chitosan or with an increase of the interfacial area using a porous three-dimensional scaffold electrode led to increased current consumption. The extracellular electron transfer from the cathode to the microbe could catalyze various bioelectrochemical reductions. Electrofermentation used electrons from the cathode as reducing power to produce more reduced compounds such as alcohols than acids, shifting the metabolic pathway. Electrofuel could be generated through artificial photosynthesis using electrical energy instead of solar energy in the process of carbon fixation. PMID:26788124

  18. Electron transfer from end-capped quaterthiophene to photoexcited C60: a pulsed EPR investigation

    We report on a pulsed EPR investigation of the photoinduced electron transfer from end-capped quaterthiophene to the photoexcited triplet state of C60 in liquid solutions. Fourier transform of the free induction decays results in spectra of the transient triplet state and of the transient C60 monoradical anion. Electron transfer rates were deduced from the observed triplet quenching rates at different temperatures. The results give evidence for the formation of an intermediate donor-acceptor exciplex in the charge transfer mechanism. (orig.)

  19. Intermolecular Hydropyridylation of Unactivated Alkenes.

    Ma, Xiaoshen; Herzon, Seth B

    2016-07-20

    A general method for the hydropyridylation of unactivated alkenes is described. The transformation connects metal-mediated hydrogen atom transfer to alkenes and Minisci addition reactions. The reaction proceeds under mild conditions with high site-selectivities and allows for the construction of tertiary and quaternary centers from simple alkene starting materials. PMID:27384921

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

    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 π 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. Y5

  1. 77 FR 30923 - Electronic Fund Transfers (Regulation E)

    2012-05-24

    ... protections given to checking accounts and electronic transactions involving checking accounts under federal... comments, in conjunction with other outreach and analysis, will help the Bureau better understand and... inspect the documents by calling (202) 435- 7275. All comments, including attachments and other...

  2. Cellular electron transfer and radical mechanisms for drug metabolism

    Aerobic and anaerobic reductions of various nitroaromatic compounds by mammalian cells result in the production of reactive intermediates. Drug reduction is dependent upon glucose, nonprotein thiols, endogenous enzyme levels, and drug electron affinity. Drugs with electron affinities approaching that of oxygen are reduced, in the presence of oxygen, beyond a one-electron radical anion. Nitroaromatic radical anion inactivation occurs by reaction with cellular ferricytochrome c, endogenous thiols, and with oxygen. In the latter case the reaction results in the production of peroxide. Drugs that are substrates for the enzyme glutathione-S-transferase remove endogeneous thiols and demonstrate peroxide production without prior thiol removal. Less electron affinic drugs such as misonidazole require thiol removal as well as the presence of cyanide or azide for maximal peroxide production. Under anaerobic conditions radical anion and nitroso intermediates are reactive with glutathione. Removal of endogenous thiols by hypoxic preincubation with misonidazole may be related to the enhanced radiation response and cytotoxicity of this drug. Reduction of nitro compounds in the presence of DNA and chemicals such as dithionite, zinc dust, or polarographic techniques causes binding to macromolecules and DNA breaks. Chemical-reduction of nitro compounds by ascorbate in the presence of cells enhances drug cytotoxic effects

  3. Nuclear interlevel transfer driven by collective outer shell electron oscillations

    The general problem of dynamic electron-nucleus coupling is discussed, and the possibility of using this mechanism to initiate gamma-ray lasing. Single-particle and collective mechanisms are considered. The problems associated with accurate calculation of these processes are discussed, and some numerical results are given. Work in process in described. 10 refs., 7 figs

  4. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    2010-10-01

    ... information that is required to make payment by electronic funds transfer (EFT) under any contract that... 48 Federal Acquisition Regulations System 2 2010-10-01 2010-10-01 false Submission of Electronic... System FEDERAL ACQUISITION REGULATION (CONTINUED) CLAUSES AND FORMS SOLICITATION PROVISIONS AND...

  5. A semiclassical theory of electron transfer reactions in Condon approximation and beyond

    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 ...

  6. MAGNETIC PROPERTIES AND ELECTRON TRANSFER IN BINUCLEAR ORGANO-IRON SANDWICHES

    Guillin, J.; Desbois, M.; Lacoste , M; Astruc, D.; Varret, F.

    1988-01-01

    Bi-iron electron reservoirs complexes, of sandwich structure, have been studied in the 36, 37, 38 e- states, by Mössbauer spectroscopy in external magnetic fields. The nature of the various couplings between the 19 e- subunits has been elucidated, and correlated to the electron transfer to the bridge in the mixed valence state.

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

    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

  8. Explanation of Turbulent Suppression of Electron Heat Transfer in GOL-3 Facility at the Stage of Relativistic Electron Beam Injection

    The effect of the electron heat transfer suppression during the stage of relativistic electron beam injection into a plasma was discovered experimentally more than a decade ago. It is now widely adopted that the suppression is a side sequel of Langmuir turbulence excited by the beam, however neither quantitative theory nor even rough estimates of the phenomena were available so far. We argue that the coefficient of turbulent thermal conductivity can be evaluated from a robust judgement based on the energy balance consideration

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

    Takeda, Kouta; Matsumura, Hirotoshi; Ishida, Takuya; Yoshida, Makoto; Igarashi, Kiyohiko; Samejima, Masahiro; Ohno, Hiroyuki; Nakamura, Nobuhumi

    2016-08-26

    A pyranose dehydrogenase from Coprinopsis cinerea (CcPDH) is an extracellular quinohemoeprotein, which consists a b-type cytochrome domain, a pyrroloquinoline-quinone (PQQ) domain, and a family 1-type carbohydrate-binding module. The electron transfer reaction of CcPDH was studied using some electron acceptors and a carbon electrode at various pH levels. Phenazine methosulfate (PMS) reacted directly at the PQQ domain, whereas cytochrome c (cyt c) reacted via the cytochrome domain of intact CcPDH. Thus, electrons are transferred from reduced PQQ in the catalytic domain of CcPDH to heme b in the N-terminal cytochrome domain, which acts as a built-in mediator and transfers electron to a heterogenous electron transfer protein. The optimal pH values of the PMS reduction (pH 6.5) and the cyt c reduction (pH 8.5) differ. The catalytic currents for the oxidation of l-fucose were observed within a range of pH 4.5 to 11. Bioelectrocatalysis of CcPDH based on direct electron transfer demonstrated that the pH profile of the biocatalytic current was similar to the reduction activity of cyt c characters. PMID:27338639

  10. Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets.

    LaForge, A C; Stumpf, V; Gokhberg, K; von Vangerow, J; Stienkemeier, F; Kryzhevoi, N V; O'Keeffe, P; Ciavardini, A; Krishnan, S R; Coreno, M; Prince, K C; Richter, R; Moshammer, R; Pfeifer, T; Cederbaum, L S; Mudrich, M

    2016-05-20

    We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets. PMID:27258866

  11. Ultrafast Electron Transfer Kinetics in the LM Dimer of Bacterial Photosynthetic Reaction Center from Rhodobacter sphaeroides.

    Sun, Chang; Carey, Anne-Marie; Gao, Bing-Rong; Wraight, Colin A; Woodbury, Neal W; Lin, Su

    2016-06-23

    It has become increasingly clear that dynamics plays a major role in the function of many protein systems. One system that has proven particularly facile for studying the effects of dynamics on protein-mediated chemistry is the bacterial photosynthetic reaction center from Rhodobacter sphaeroides. Previous experimental and computational analysis have suggested that the dynamics of the protein matrix surrounding the primary quinone acceptor, QA, may be particularly important in electron transfer involving this cofactor. One can substantially increase the flexibility of this region by removing one of the reaction center subunits, the H-subunit. Even with this large change in structure, photoinduced electron transfer to the quinone still takes place. To evaluate the effect of H-subunit removal on electron transfer to QA, we have compared the kinetics of electron transfer and associated spectral evolution for the LM dimer with that of the intact reaction center complex on picosecond to millisecond time scales. The transient absorption spectra associated with all measured electron transfer reactions are similar, with the exception of a broadening in the QX transition and a blue-shift in the QY transition bands of the special pair of bacteriochlorophylls (P) in the LM dimer. The kinetics of the electron transfer reactions not involving quinones are unaffected. There is, however, a 4-fold decrease in the electron transfer rate from the reduced bacteriopheophytin to QA in the LM dimer compared to the intact reaction center and a similar decrease in the recombination rate of the resulting charge-separated state (P(+)QA(-)). These results are consistent with the concept that the removal of the H-subunit results in increased flexibility in the region around the quinone and an associated shift in the reorganization energy associated with charge separation and recombination. PMID:27243380

  12. Tuning the reorganization energy of electron transfer in supramolecular ensembles - metalloporphyrin, oligophenylenevinylenes, and fullerene - and the impact on electron transfer kinetics

    Stangel, Christina; Schubert, Christina; Kuhri, Susanne; Rotas, Georgios; Margraf, Johannes T.; Regulska, Elzbieta; Clark, Timothy; Torres, Tomás; Tagmatarchis, Nikos; Coutsolelos, Athanassios G.; Guldi, Dirk M.

    2015-01-01

    Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions between electron donors and acceptors in the ground and excited states. No appreciable electron interactions were noted in the ground state, which was being probed by electrochemistry, absorption spectroscopy, etc.; the electron acceptors are sufficiently decoupled from the electron donors. In the excited state, a different picture evolved. In particular, steady-state and time-resolved fluorescence and transient absorption measurements revealed substantial electron donor-acceptor interactions. These led, upon photoexcitation of the porphyrins, to tunable intramolecular electron-transfer processes, that is, the oxidation of porphyrin and the reduction of C60. In this regard, the largest impact stems from a rather strong distance dependence of the total reorganization energy in stark contrast to the distance independence seen for covalently linked conjugates.Oligo(p-phenylenevinylene) (oPPV) wires of various lengths featuring pyridyls at one terminal and C60 moieties at the other, have been used as molecular building blocks in combination with porphyrins to construct a novel class of electron donor-acceptor architectures. These architectures, which are based on non-covalent, directional interactions between the zinc centers of the porphyrins and the pyridyls, have been characterized by nuclear magnetic resonance spectroscopy and mass spectrometry. Complementary physico-chemical assays focused on the interactions

  13. The transfer of energy between electrons and ions in solids

    In this review we consider those processes in condensed matter that involve the irreversible flow of energy between electrons and nuclei that follows from a system being taken out of equilibrium. We survey some of the more important experimental phenomena associated with these processes, followed by a number of theoretical techniques for studying them. The techniques considered are those that can be applied to systems containing many non-equivalent atoms. They include both perturbative approaches (Fermi's Golden Rule and non-equilibrium Green's functions) and molecular dynamics based (the Ehrenfest approximation, surface hopping, semi-classical Gaussian wavefunction methods and correlated electron-ion dynamics). These methods are described and characterized, with indications of their relative merits

  14. Challenges in reduction of dinitrogen by proton and electron transfer.

    van der Ham, Cornelis J M; Koper, Marc T M; Hetterscheid, Dennis G H

    2014-08-01

    Ammonia is an important nutrient for the growth of plants. In industry, ammonia is produced by the energy expensive Haber-Bosch process where dihydrogen and dinitrogen form ammonia at a very high pressure and temperature. In principle one could also reduce dinitrogen upon addition of protons and electrons similar to the mechanism of ammonia production by nitrogenases. Recently, major breakthroughs have taken place in our understanding of biological fixation of dinitrogen, of molecular model systems that can reduce dinitrogen, and in the electrochemical reduction of dinitrogen at heterogeneous surfaces. Yet for efficient reduction of dinitrogen with protons and electrons major hurdles still have to be overcome. In this tutorial review we give an overview of the different catalytic systems, highlight the recent breakthroughs, pinpoint common grounds and discuss the bottlenecks and challenges in catalytic reduction of dinitrogen. PMID:24802308

  15. Comparison of three methods for calculation of electron transfer probability in H+ + Ne

    We have developed a theoretical model of ion-atom collisions where we described electron dynamics by the time-dependent density-functional theory (TDDFT) and the ion dynamics by classical mechanics through the Ehrenfest method. We have compared three methods to calculate the probability of electron transfer during H+ + Ne collision. By discussing these issues we shall be able to understand how these methods work, what their limitations are and whether they admit of any improvements. -- Highlights: ► We have developed a theoretical model of ion-atom collisions based on TDDFT. ► We have compared three methods to calculate the probability of electron transfer in H+ + Ne. ► Electron transfer cross sections showed a good agreement with available experimental data.

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

    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...

  17. ELECTRON TRANSFER IN Hg1-xCdxTe-CdTe HETEROSTRUCTURES

    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.

  18. Dynamics of Electron Transfer Processes at the Surface of Dye-Sensitized Mesoporous Semiconductor Films

    Teuscher, Joël

    2010-01-01

    Electron transfer reactions taking place at the surface of dye-sensitized semiconductors are key processes in dye-sensitized solar cells (DSSCs). After light absorption, the excited state of a dye injects an electron into a wide-bandgap semiconductor, usually titanium dioxyde, TiO2. The formed oxidized dye can then be intercepted by a redox mediator, typically iodide, before charge recombination between the injected electron and the oxidized dye...

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

    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)

  20. Radiation forces to electrons in laser fields explained as scattering for ponderomotive momentum transfers

    The ponderomotive momentum exchange in laser interaction with electrons is derived using a scattering model. This explains how the momentum is exchanged globally when an electron is emitted radially from a laser beam while the axial exchange of momentum is coupled with the momentum of the electromagnetic energy transferred from the laser field to the electron in the form of kinetic energy. Special attention is given to the forces acting on electrons in a laser beam and expelling the electrons laterally from the beam. 14 refs

  1. Femtosecond dynamics of electron transfer in a neutral organic mixed-valence compound

    In this article we report a femtosecond time-resolved transient absorption study of a neutral organic mixed-valence (MV) compound with the aim to gain insight into its charge-transfer dynamics upon optical excitation. The back-electron transfer was investigated in five different solvents, toluene, dibutyl ether, methyl-tert-butyl ether (MTBE), benzonitrile and n-hexane. In the pump step, the molecule was excited at 760 nm and 850 nm into the intervalence charge-transfer band. The resulting transients can be described by two time constant. We assign one time constant to the rearrangement of solvent molecules in the charge-transfer state and the second time constant to back-electron transfer to the electronic ground state. Back-electron transfer rates range from 1.5 x 1012 s-1 in benzonitrile through 8.3 x 1011 s-1 in MTBE, around 1.6 x 1011 s-1 in dibutylether and toluene and to 3.8 x 109 s-1 in n-hexane

  2. Electronic Structure of the Perylene / Zinc Oxide Interface: A Computational Study of Photoinduced Electron Transfer and Impact of Surface Defects

    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.

  3. Intramolecular and intermolecular hydrogen bonds in aminophenols

    IR-Fourier spectroscopy methods are adopted to study intramolecular and intermolecular hydrogen bonds that form in CCl4 solutions of aminophenol derivatives and in a solid phase of these compounds pressed in KBr. If a hydroxyl group is present in the molecule in the ortho-position to an amino group, then intramolecular interactions between OH and NH groups will take place in aminophenol solutions. Intramolecular O-HO=S=O and N-H...O=S=O hydrogen bonds are found in solutions of compounds containing a sulfonamide fragment. Additional acylation of the amino group causes an intramolecular O-H...O=C hydrogen bond to form in solutions. Functional groups OH, NH, SO2, and C=O interact with one another in various ways in the solid phase to form intermolecular hydrogen bonds in aminophenols. (authors) Keywords aminophenol - IR spectrum - intramolecular hydrogen bond - intermolecular hydrogen bond

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

    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

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

    Khezri, Khezrollah, E-mail: kh.khezri@ut.ac.ir [School of Chemistry, University College of Science, University of Tehran, PO Box 14155-6455, Tehran (Iran, Islamic Republic of); Roghani-Mamaqani, Hossein [Department of Polymer Engineering, Sahand University of Technology, PO Box 51335-1996, Tabriz (Iran, Islamic Republic of)

    2014-11-15

    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 T{sub g} 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{sup −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

  6. Expanding the Diet for DIET: Electron Donors Supporting Direct Interspecies Electron Transfer (DIET) in Defined Co-Cultures

    Wang, Li-Ying; Nevin, Kelly P.; Woodard, Trevor L.; Mu, Bo-Zhong; Lovley, Derek R.

    2016-01-01

    Direct interspecies electron transfer (DIET) has been recognized as an alternative to interspecies H2 transfer as a mechanism for syntrophic growth, but previous studies on DIET with defined co-cultures have only documented DIET with ethanol as the electron donor in the absence of conductive materials. Co-cultures of Geobacter metallireducens and Geobacter sulfurreducens metabolized propanol, butanol, propionate, and butyrate with the reduction of fumarate to succinate. G. metallireducens utilized each of these substrates whereas only electrons available from DIET supported G. sulfurreducens respiration. A co-culture of G. metallireducens and a strain of G. sulfurreducens that could not metabolize acetate oxidized acetate with fumarate as the electron acceptor, demonstrating that acetate can also be syntrophically metabolized via DIET. A co-culture of G. metallireducens and Methanosaeta harundinacea previously shown to syntrophically convert ethanol to methane via DIET metabolized propanol or butanol as the sole electron donor, but not propionate or butyrate. The stoichiometric accumulation of propionate or butyrate in the propanol- or butanol-fed cultures demonstrated that M. harundinaceae could conserve energy to support growth solely from electrons derived from DIET. Co-cultures of G. metallireducens and Methanosarcina barkeri could also incompletely metabolize propanol and butanol and did not metabolize propionate or butyrate as sole electron donors. These results expand the range of substrates that are known to be syntrophically metabolized through DIET, but suggest that claims of propionate and butyrate metabolism via DIET in mixed microbial communities warrant further validation. PMID:26973614

  7. Photoinduced 2-way electron transfer in composites of metal nanoclusters and semiconductor quantum dots

    Mondal, Navendu; Paul, Sneha; Samanta, Anunay

    2016-07-01

    In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation between the QDs and NCs in a giant BSA-capped system, a higher electron transfer rate in this composite suggests that unlike other smaller capping agents, which act more like insulators, BSA allows much better electron conduction, as indicated previously.In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation

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

    Morita, Masahiko; Malvankar, Nikhil S; Franks, Ashley E;

    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...

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

    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 (α) 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.

  10. Influence of Complex Stabilities on Electron-Transfer Reactions

    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 |Δlog10K|, where Δ 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 + bΔlog 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

  11. Technology transfer present and futures in the electronic arts

    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.

  12. Spectrophotometric study of the charge transfer complexation of some porphyrin derivatives as electron donors with tetracyanoethylene

    El-Zaria, Mohamed E.

    2008-01-01

    Charge transfer complexes (CTC) of 5,10,15,20-tetraphenylporphyrin (TPP), 5,10,15,20-tetra(4-tolyl)porphyrin (TTP), 5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMP), Zn-5,10,15,20-tetraphenylporphyrin (Zn-TPP), and Zn-5,10,15,20-tetra(4-tolyl)porphyrin (Zn-TTP) with tetracyanoethylene (TCNE) have been studied at various temperatures in CH 2Cl 2 and CCl 4. The data are discussed in terms of equilibrium constant ( KCT), molar extinction coefficient ( ɛCT), thermodynamic standard reaction quantities (Δ G°, Δ H° and Δ S°), oscillator strength ( f), and transition dipole moment ( μ). The spectrum obtained for TPP/TCNE, TTP/TCNE, and TMP/TCNE systems shows two main absorption bands at 475 and 690 nm, which are not due to the absorption of any of the reactants. These bands are characteristic of an intermolecular charge transfer involving the overlap of the lowest unoccupied molecular orbital (LUMO) of the acceptor with the highest occupied molecular orbital (HOMO) of the donor. The results reveal that the interaction between the donors and acceptor is due to π-π * transitions by the formation of radical ion pairs. The stoichiometry of the complexes was found to be 1:1 ratio by the Job and straight line methods between donors and acceptor with the maximum absorption bands at wavelengths of 475 and 690 nm. The observed data show salvation effects on the spectral and thermodynamics properties of CTC. The ionization potential of the donors and the dissociation energy of the CTC were also determined and are found to be constant.

  13. An analysis of conjugate heat transfer in the heat sink of an electronic chip

    Horvat, Andrej; Catton, Ivan

    2015-01-01

    This paper describes the construction of an algorithm for conjugate heat-transfer calculations in order to find the most suitable form for the heat sink of an electronic chip. Applying volume averaging theory (VAT) to a system of transport equations, a heat-sink structure was modeled as a homogeneous porous medium. The geometry of the simulation domain and the boundary conditions followed the experimental setup used in the Morrin-Martinelly-Gier Memorial Heat Transfer Laboratory at the Univer...

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

    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

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

    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

  16. Excited state electron transfer in systems with a well-defined geometry. [cyclophane

    Kaufmann, K.J.

    1980-12-01

    The effect of temperature, dielectric strength and ligand on the structure of the mesopyropheophorbide cyclophanes will be studied. ESR, NMR, emission and absorption spectroscopy, as well as circular dichroism will be used. The changes in structure will be correlated with changes in the photochemical activity. Electron acceptors such as benzoquinone will be utilized to stabilize the charge separation. Charge separation in porphyrin quinone dimers will also be studied. It was found that electron transfer in the cyclophane system is relatively slow. This is presumably due to an orientation requirement for fast electron transfer. Solvent dielectric also is important in producing a charge separation. Decreasing the temperature effects the yield of charge transfer, but not the kinetics.

  17. Spin Chains and Electron Transfer at Stepped Silicon Surfaces.

    Aulbach, J; Erwin, S C; Claessen, R; Schäfer, J

    2016-04-13

    High-index surfaces of silicon with adsorbed gold can reconstruct to form highly ordered linear step arrays. These steps take the form of a narrow strip of graphitic silicon. In some cases-specifically, for Si(553)-Au and Si(557)-Au-a large fraction of the silicon atoms at the exposed edge of this strip are known to be spin-polarized and charge-ordered along the edge. The periodicity of this charge ordering is always commensurate with the structural periodicity along the step edge and hence leads to highly ordered arrays of local magnetic moments that can be regarded as "spin chains." Here, we demonstrate theoretically as well as experimentally that the closely related Si(775)-Au surface has-despite its very similar overall structure-zero spin polarization at its step edge. Using a combination of density-functional theory and scanning tunneling microscopy, we propose an electron-counting model that accounts for these differences. The model also predicts that unintentional defects and intentional dopants can create local spin moments at Si(hhk)-Au step edges. We analyze in detail one of these predictions and verify it experimentally. This finding opens the door to using techniques of surface chemistry and atom manipulation to create and control silicon spin chains. PMID:26974012

  18. A structural basis for electron transfer in bacterial photosynthesis

    Triplet data for the primary donor in single crystals of bacterial reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis are interpreted in terms of the corresponding x-ray structures. The analysis of electron paramagnetic resonance data from single crystals (triplet zero field splitting and cation and triplet linewidth of the primary special pair donor of bacterial reaction centers) is extended to systems of a non-crystalline nature. A unified interpretation based on frontier molecular orbitals concludes that the special pair behaves like a supermolecule in all wild-type bacteria investigated here. However, in heterodimers of Rb. capsulatus (HisM200 changed to Leu or Phe with the result that the M-half of the special pair is converted to bacteriopheophytin) the special pair possesses the EPR properties more appropriately described in terms of a monomer. In all cases the triplet state and cation EPR properties appear to be dominated by the highest occupied molecular orbitals. These conclusions derived from EPR experiments are supplemented by data from Stark spectroscopy of reaction centers from Rb. capsulatus. 41 refs., 3 tabs

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

    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...

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

    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.

  1. Electric Field Induced Fluorescence Modulation of Single Molecules in PMMA Based on Electron Transfer

    Suotang Jia

    2012-09-01

    Full Text Available We present a method to modulate the fluorescence of non-polar single squaraine-derived rotaxanes molecules embedded in a polar poly(methyl methacrylate (PMMA matrix under an external electric field. The electron transfer between single molecules and the electron acceptors in a PMMA matrix contributes to the diverse responses of fluorescence intensities to the electric field. The observed instantaneous and non-instantaneous electric field dependence of single-molecule fluorescence reflects the redistribution of electron acceptors in PMMA induced by electronic polarization and orientation polarization of polar polymer chains in an electric field.

  2. Electron emitted in transfer ionization in He2+ on helium collisions

    A complete experiment for He2+ on helium collisions was performed over a relatively broad energy range by using a reaction microscope in Lanzhou in order to clarify the emission properties. In the experiment the momenta of recoil ions, the emitted electron, and the charge state of the scattered projectiles were recorded in coincidence in event-by-event mode. By reconstruction of the momentum vector of electrons, the momentum distributions of the continuum electrons in the scattering plane were obtained. The distributions show characteristics of the electrons originated from transfer ionization in the collisions.

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

    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

  4. Electronic State-Resolved Electron-Phonon Coupling in an Organic Charge Transfer Material from Broadband Quantum Beat Spectroscopy.

    Rury, Aaron S; Sorenson, Shayne; Driscoll, Eric; Dawlaty, Jahan M

    2015-09-17

    The coupling of electron and lattice phonon motion plays a fundamental role in the properties of functional organic charge-transfer materials. In this Letter we extend the use of ultrafast vibrational quantum beat spectroscopy to directly elucidate electron-phonon coupling in an organic charge-transfer material. As a case study, we compare the oscillatory components of the transient reflection (TR) of a broadband probe pulse from single crystals of quinhydrone, a 1:1 cocrystal of hydroquinone and p-benzoquinone, after exciting nonresonant impulsive stimulated Raman scattering and resonant electronic transitions using ultrafast pulses. Spontaneous resonance Raman spectra confirm the assignment of these oscillations as coherent lattice phonon excitations. Fourier transforms of the vibrational quantum beats in our broadband TR measurements allow construction of spectra that we show report the ability of these phonons to directly modulate the electronic structure of quinhydrone. These results demonstrate how coherent ultrafast processes can characterize the complex interplay of charge transfer and lattice motion in materials of fundamental relevance to chemistry, materials sciences, and condensed matter physics. PMID:26722724

  5. The effects of fulvic acid on microbial denitrification: promotion of NADH generation, electron transfer, and consumption.

    Li, Mu; Su, Yinglong; Chen, Yinguang; Wan, Rui; Zheng, Xiong; Liu, Kun

    2016-06-01

    The heterotrophic denitrification requires the participation of electrons which are derived from direct electron donor (usually nicotinamide adenine dinucleotide (NADH)), and the electrons are transferred via electron transport system in denitrifiers and then consumed by denitrifying enzymes. Despite the reported electron transfer ability of humic substances (HS), the influences of fulvic acid (FA), an ubiquitous major component of HS, on promoting NADH generation, electron transfer, and consumption in denitrification process have never been reported. The presence of FA, compared with the control, was found not only significantly improved the total nitrogen (TN) removal efficiency (99.9 % versus 74.8 %) but remarkably reduced the nitrite accumulation (0.2 against 43.8 mg/L) and N2O emission (0.003 against 0.240 mg nitrogen/mg TN removed). The mechanisms study showed that FA increased the metabolism of carbon source via glycolysis and tricarboxylic acid (TCA) cycle pathways to produce more available NADH. FA also facilitated the electron transfer activities from NADH to denitrifying enzymes via complex I and complex III in electron transport system, which improved the reduction of nitrate and accelerated the transformations of nitrite and N2O, and lower nitrite and N2O accumulations were therefore observed. In addition, the consumption of electrons in denitrification was enhanced due to FA stimulating the synthesis and the catalytic activity of key denitrifying enzymes, especially nitrite reductase and N2O reductase. It will provide an important new insight into the potential effect of FA on microbial denitrification metabolism process and even nitrogen cycle in nature niches. PMID:26894403

  6. Three-dimensional model of stellacyanin and its implications for electron transfer reactivity

    Wherland, S; Farver, O; Pecht, I

    1988-01-01

    system. The structure also indicates that a carbonyl oxygen atom is near the copper, thus the site may have analogy to the Alcaligenes denitrificans azurin (Az) site, although the amino acid sequence is more homologous to that of Pc. The model indicates that aspartate 49, reductively labeled by Cr......(III), is near the copper center and homologous to the site labeled by Cr(III) on Pc. Also homologous to Pc is a tyrosine residue adjacent to the aspartate. This tyrosine has been implicated in Pc electron transfer and thus is probably involved in electron transfer reactivity of St as well. The higher...

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

    Gao, Shiwu

    2015-06-01

    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.

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

    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.

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

    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.)

  10. Non-Markovian theory for the waiting time distributions of single electron transfers.

    Welack, Sven; Yan, YiJing

    2009-09-21

    We derive a non-Markovian theory for waiting time distributions of consecutive single electron transfer events. The presented microscopic Pauli rate equation formalism couples the open electrodes to the many-body system, allowing to take finite bias and temperature into consideration. Numerical results reveal transient oscillations of distinct system frequencies due to memory in the waiting time distributions. Memory effects can be approximated by an expansion in non-Markovian corrections. This method is employed to calculate memory landscapes displaying preservation of memory over multiple consecutive electron transfers. PMID:19778104

  11. A Novel Micro—hole Electrode Used to Investigate Electron Transfer Reactions at ITIES

    DongPingZHAN; BingLiangWU

    2002-01-01

    A novel micro-hole electrode was fabricated to investigate the electron transfer reaction at the interface between two immiscible electrolyte solutions (ITIES). The electron transfer reaction between feero/ferricyanide in aqueous phase(W) and ferrocene in 1,2-dichloroethane (O) phase was studied as a test experiment. The results showed that the diffusion coefficient obtained from the micro-hole electrode was consistent with that obtained at macro-interface. Due to its simplicity and the very small IR drop it will be a useful tool for the study of ITIES systems.

  12. A Novel Micro-hole Electrode Used to Investigate Electron Transfer Reactions at ITIES

    2002-01-01

    A novel micro-hole electrode was fabricated to investigate the electron transfer reaction at the interface between two immiscible electrolyte solutions (ITIES). The electron transfer reaction between ferro/ferricyanide in aqueous phase (W) and ferrocene in 1, 2-dichloroethane (O) phase was studied as a test experiment. The results showed that the diffusion coefficient obtained from the micro-hole electrode was consistent with that obtained at macro-interface. Due to its simplicity and the very small IR drop it will be a useful tool for the study of ITIES systems.

  13. The single electron transfer chemistry of coals. Final report

    Larsen, J.W.; Flowers, R.A. II

    1994-12-31

    This research addressed electron donar properties and radical reactions in coal. Solid residues from pyridine Soxhlet extractions of Pocahontas No. 3, Upper Freeport, Pittsburgh No. 8, Illinois No. 6 and Wyodak coals were exposed to 4-vinylpyridine vapors and swelled. All of the 4-vinylpyridine could not be removed under vacuum at 100{degree}C. Diffuse reflectance FTIR revealed the presence of poly-(4-vinylpyridine) in the Illinois No. 6 and Wyodak coals. EPR spectra displayed the loss of inertinite radicals in Upper Freeport, Illinois No. 6 and Wyodak residues after exposure to 4-vinylpyridine. There was little change in the vitrinite radical density or environment. The molecule N,N{prime}-Diphenyl-p-phenylene diamine (DPPD) was exposed to the solid residues from pyridine Soxhlet extractions of the above coals. Diffuse reflectance FTIR failed to detect the imine product from radical reaction with DPPD. EPR spectra displayed the loss of inertinite radicals in Upper Freeport and Wyodak residues. 7,7,8,8-Tetracyanoquinodimethane (TCNQ) and Tetracyanoethylene (TCNE) were deposited into coals in pyridine. FTIR indicated complete conversion of TCNQ to a material with a singly occupied LUMO. In TCNE the LUMO is about 30% occupied. TCNQ and TCNE were deposited into the pyridine extracts and residues of Illinois No. 6 and Pittsburgh No. 8 coals. Only a small amount of the TCNQ and TCNE displayed nitrile shifts in the IR spectrum of a material with an occupied LUMO. It has been concluded that TCNQ must be part of the aromatic stacks in coal and the TCNQ LUMO is part of an extended band.

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

    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

  15. Ru(II)-diimine functionalized metalloproteins: From electron transfer studies to light-driven biocatalysis.

    Lam, Quan; Kato, Mallory; Cheruzel, Lionel

    2016-05-01

    The unique photochemical properties of Ru(II)-diimine complexes have helped initiate a series of seminal electron transfer studies in metalloenzymes. It has thus been possible to experimentally determine rate constants for long-range electron transfers. These studies have laid the foundation for the investigation of reactive intermediates in heme proteins and for the design of light-activated biocatalysts. Various metalloenzymes such as hydrogenase, carbon monoxide dehydrogenase, nitrogenase, laccase and cytochrome P450 BM3 have been functionalized with Ru(II)-diimine complexes. Upon visible light-excitation, these photosensitized metalloproteins are capable of sustaining photocatalytic activity to reduce small molecules such as protons, acetylene, hydrogen cyanide and carbon monoxide or activate molecular dioxygen to produce hydroxylated products. The Ru(II)-diimine photosensitizers are hence able to deliver multiple electrons to metalloenzymes buried active sites, circumventing the need for the natural redox partners. In this review, we will highlight the key achievements of the light-driven biocatalysts, which stem from the extensive electron transfer investigations. This article is part of a Special Issue entitled Biodesign for Bioenergetics--the design and engineering of electronic transfer cofactors, proteins and protein networks, edited by Ronald L. Koder and J.L. Ross Anderson. PMID:26392147

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

    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

  17. Role of electron transfer in Ce3+ sensitized Yb3+ luminescence in borate glass

    In a Ce3+-Yb3+ system, two mechanisms are proposed so far namely, the quantum cutting mechanism and the electron transfer mechanism explaining Yb3+ infrared luminescence under Ce3+ excitation. Among them, the quantum cutting mechanism, where one Ce3+ photon (ultraviolet/blue) gives rise to two Yb3+ photons (near infrared) is widely sought for because of its huge potential in enhancing the solar cell efficiency. In present study on Ce3+-Yb3+ codoped borate glasses, Ce3+ sensitized Yb3+ luminescence at ∼1 μm have been observed on Ce3+ 5d state excitation. However, the intensity of sensitized Yb3+ luminescence is found to be very weak compared to the strong quenching occurred in Ce3+ luminescence in Yb3+ codoped glasses. Moreover, the absolute luminescence quantum yield also showed a decreasing trend with Yb3+ codoping in the glasses. The overall behavior of the luminescence properties and the quantum yield is strongly contradicting with the quantum cutting phenomenon. The results are attributed to the energetically favorable electron transfer interactions followed by Ce3+-Yb3+ ⇌ Ce4+-Yb2+ inter-valence charge transfer and successfully explained using the absolute electron binding energies of dopant ions in the studied borate glass. Finally, an attempt has been presented to generalize the electron transfer mechanism among opposite oxidation/reduction property dopant ions using the vacuum referred electron binding energy (VRBE) scheme for lanthanide series

  18. A new intermolecular mechanism to selectively drive photoinduced damages

    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.

  19. Magnetic field effect as a probe of distance-dependent electron transfer in systems undergoing free diffusion

    Krissinel, Evgenii B.; Burshtein, Anatoly I.; Lukzen, Nikita N.; Steiner, Ulrich

    1999-01-01

    A theoretical analysis is presented of the problem of how distance-dependent electron transfer in photoinduced forward electron transfer followed by geminate backward electron transfer in liquid solution is reflected in the viscosity dependence of the magnetic field effect (MFE) on the efficiency of free radical formation (φce) in such reactions. The stochastic Liouville equation formalism is employed to model the reaction behaviour of distance-distributed, triplet-born radical pairs (RPs) un...

  20. Interfacial electron transfer and bioelectrocatalysis of carbonized plant material as effective anode of microbial fuel cell

    ABSTRACT: Effective use of natural materials to fabricate porous carbonaceous structures for anodes of microbial fuel cells (MFCs) has a high potential for substantial cost reduction in MFC. In this study, three kinds of plant materials, i.e. king mushroom, wild mushroom and corn stem, were investigated for fabrication of conductive electrode materials by simple carbonization procedures. Structure–reactivity relationships of these electrodes were systematically studied with electrochemical redox probe ([Fe(CN)6]3−/4−) and biofilm electroactivity. The electrochemical and bioelectrochemical accessibilities of the carbonized electrodes were evaluated by impedance, cyclic voltammetry and chronoamperometry techniques in order to study the electron transfer rate (Kapp), charge transfer resistances, oxidative current density and bioelectroactive moieties. The results showed that the electron transfer resistance (Rct) was 94 Ω for carbonized corn stem electrode with an electron transfer rate (Kapp) of 3.44 × 10−2 cm s−1 for Fe2+/Fe3+ redox probe. Higher bioelectroactivity (9.29 × 10−8 mol cm−2) was found from biofilm on carbonized corn stem (Rbiofilm, 45 Ω) with an electron transfer rate (bacteria-anode) of 63 × 10−5 cm s−1. The maximum bioelectrocatalytic current (imax) of 3.12 mA cm−2 was obtained on carbon electrode derived from corn stem. That is 8 times higher than plain graphite electrode. The porous architecture, high electron transfer rate and high electroactive biofilm growth are attributes that qualify natural-material carbon anodes as low-cost alternative for MFC

  1. Peptide and protein sequence analysis by electron transfer dissociation mass spectrometry

    Syka, John E. P.; Coon, Joshua J.; Schroeder, Melanie J.; Shabanowitz, Jeffrey; Hunt, Donald F.

    2004-01-01

    Peptide sequence analysis using a combination of gas-phase ion/ion chemistry and tandem mass spectrometry (MS/MS) is demonstrated. Singly charged anthracene anions transfer an electron to multiply protonated peptides in a radio frequency quadrupole linear ion trap (QLT) and induce fragmentation of the peptide backbone along pathways that are analogous to those observed in electron capture dissociation. Modifications to the QLT that enable this ion/ion chemistry are presented, and automated ac...

  2. Promotion of the Direct Electron Transfer of Hemoglobin by the Carbon Nanotube

    Jing CHEN; Chen Xin CAI

    2004-01-01

    It is reported that the direct electron transfer of hemoglobin (Hb) can be effectively promoted by carbon nanotubes when Hb was immobilized on the surface of the carbon nanotubes modified electrode. The results indicated that the conversion of Hb-Fe(III)/Hb-Fe(II) is a one-electron coupled one-proton reaction process. The method presented can be easily extended to study the direct electrochemistry of other proteins or enzymes.

  3. Vibrational transition rule during a through-bond electron transfer process

    Monturet, Serge; Kepenekian, M.; Robles, Roberto; Lorente, N.; Joachim, Christian

    2013-01-01

    The transition rule governing the inelastic excitations of molecular vibrations occurring during a molecular through-state electron transfer process is presented. Using an effective Hamiltonian model, it is shown that the quantum time oscillation of the intermediate electronic state population triggers this transition. Its corresponding quantum oscillation frequency has to be equal to a quantum of vibration. This transition rule is extended to the full spectrum of a quantum vibrator. This new...

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

    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 the polarization me...

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

    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 β (exponent η) 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 β for the exponential fit k=k0exp(-βd) and the exponent η for the power-law fit k=k0′N-η are computed. β≈ 0.2–2 Å−1, k0 is usually 10−2–10−1 PHz, generally ≈10−4–10 PHz. η≈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

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

    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.

  7. Photoinduced 2-way electron transfer in composites of metal nanoclusters and semiconductor quantum dots.

    Mondal, Navendu; Paul, Sneha; Samanta, Anunay

    2016-08-01

    In order to explore the potential of nanocomposites comprising semiconductor quantum dots (QDs) and metal nanoclusters (NCs) in photovoltaic and catalytic applications, the interaction between CdTe QDs and gold NCs, Au10 and Au25, stabilized by histidine, bovine serum albumin (BSA) and glutathione, is studied by an ultrafast transient absorption (TA) technique. Temporal and spectral studies of the transients reveal photoinduced 2-way electron transfer between the two constituents of the nanocomposites, where Au NCs, which generally act as electron donors when used as photosensitizers, perform the role of the efficient electron acceptor. Interestingly, it is found that the electron transfer dynamics in these composites is governed not by the distance of separation of the constituents but by the nature of the surface capping ligands. Despite a large separation between the QDs and NCs in a giant BSA-capped system, a higher electron transfer rate in this composite suggests that unlike other smaller capping agents, which act more like insulators, BSA allows much better electron conduction, as indicated previously. PMID:27396603

  8. Density functional investigation of the electronic structure and charge transfer excited states of a multichromophoric antenna

    Basurto, Luis; Zope, Rajendra R.; Baruah, Tunna

    2016-05-01

    We report an electronic structure study of a multichromophoric molecular complex containing two of each borondipyrromethane dye, Zn-tetraphenyl-porphyrin, bisphenyl anthracene and a fullerene. The snowflake shaped molecule behaves like an antenna capturing photon at different frequencies and transferring the photon energy to the porphyrin where electron transfer occurs from the porphyrin to the fullerene. The study is performed within density functional formalism using large polarized Guassian basis sets (12,478 basis functions in total). The energies of the HOMO and LUMO states in the complex, as adjudged by the ionization potential and the electron affinity values, show significant differences with respect to their values in participating subunits in isolation. These differences are also larger than the variations of the ionization potential and electron affinity values observed in non-bonded C60-ZnTPP complexes in co-facial arrangement or end-on orientations. An understanding of the origin of these differences is obtained by a systematic study of the effect of structural strain, the presence of ligands, the effect of orbital delocalization on the ionization energy and the electron affinity. Finally, a few lowest charge transfer energies involving electronic transitions from the porphyrin component to the fullerene subunit of the complex are predicted.

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

    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

    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. Powering microbes with electricity: direct electron transfer from electrodes to microbes

    Lovley, DR

    2010-09-16

    P>The discovery of electrotrophs, microorganisms that can directly accept electrons from electrodes for the reduction of terminal electron acceptors, has spurred the investigation of a wide range of potential applications. To date, only a handful of pure cultures have been shown to be capable of electrotrophy, but this process has also been inferred in many studies with undefined consortia. Potential electron acceptors include: carbon dioxide, nitrate, metals, chlorinated compounds, organic acids, protons and oxygen. Direct electron transfer from electrodes to cells has many advantages over indirect electrical stimulation of microbial metabolism via electron shuttles or hydrogen production. Supplying electrons with electrodes for the bioremediation of chlorinated compounds, nitrate or toxic metals may be preferable to adding organic electron donors or hydrogen to the subsurface or bioreactors. The most transformative application of electrotrophy may be microbial electrosynthesis in which carbon dioxide and water are converted to multi-carbon organic compounds that are released extracellularly. Coupling photovoltaic technology with microbial electrosynthesis represents a novel photosynthesis strategy that avoids many of the drawbacks of biomass-based strategies for the production of transportation fuels and other organic chemicals. The mechanisms for direct electron transfer from electrodes to microorganisms warrant further investigation in order to optimize envisioned applications.

  12. An energy decomposition analysis for intermolecular interactions from an absolutely localized molecular orbital reference at the coupled-cluster singles and doubles level

    We propose a wave function-based method for the decomposition of intermolecular interaction energies into chemically-intuitive components, isolating both mean-field- and explicit correlation-level contributions. We begin by solving the locally-projected self-consistent field for molecular interactions equations for a molecular complex, obtaining an intramolecularly polarized reference of self-consistently optimized, absolutely-localized molecular orbitals (ALMOs), determined with the constraint that each fragment MO be composed only of atomic basis functions belonging to its own fragment. As explicit inter-electronic correlation is integral to an accurate description of weak forces underlying intermolecular interaction potentials, namely, coordinated fluctuations in weakly interacting electronic densities, we add dynamical correlation to the ALMO polarized reference at the coupled-cluster singles and doubles level, accounting for explicit dispersion and charge-transfer effects, which map naturally onto the cluster operator. We demonstrate the stability of energy components with basis set extension, follow the hydrogen bond-breaking coordinate in the Cs-symmetry water dimer, decompose the interaction energies of dispersion-bound rare gas dimers and other van der Waals complexes, and examine charge transfer-dominated donor-acceptor interactions in borane adducts. We compare our results with high-level calculations and experiment when possible.

  13. Long-range protein electron transfer observed at the single-molecule level

    Chi, Qijin; Farver, Ole; Ulstrup, Jens

    2005-01-01

    A biomimetic long-range electron transfer (ET) system consisting of the blue copper protein azurin, a tunneling barrier bridge, and a gold single-crystal electrode was designed on the basis of molecular wiring self-assembly principles. This system is sufficiently stable and sensitive in a quasi...

  14. Bibliography on electron transfer processes in ion-ion/atom/molecule collisions (updated 1993)

    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

  15. Bistable switching in supercritical n+-n-n+GaAs transferred electron devices

    Jøndrup, Peter; Jeppesen, Palle; Jeppson, Bert

    1976-01-01

    Bistable switching in supercritically doped n+-n-n+GaAs transferred electron devices (TED's) is investigated experimentally and interpreted in computer simulations, for which details of the computer program are given. Three switching modes all leading to stable anode domains are discussed, namely...

  16. ZnO-nanorods/graphene heterostructure: a direct electron transfer glucose biosensor.

    Zhao, Yu; Li, Wenbo; Pan, Lijia; Zhai, Dongyuan; Wang, Yu; Li, Lanlan; Cheng, Wen; Yin, Wei; Wang, Xinran; Xu, Jian-Bin; Shi, Yi

    2016-01-01

    ZnO-nanorods/graphene heterostructure was synthesized by hydrothermal growth of ZnO nanorods on chemically reduced graphene (CRG) film. The hybrid structure was demonstrated as a biosensor, where direct electron transfer between glucose oxidase (GOD) and electrode was observed. The charge transfer was attributed to the ZnO nanorod wiring between the redox center of GOD and electrode, and the ZnO/graphene heterostructure facilitated the transport of electrons on the hybride electrode. The glucose sensor based on the GOD-ZnO/CRG/Pt electrode had a high sensitivity of 17.64 μA mM(-1), which is higher than most of the previously reported values for direct electron transfer based glucose biosensors. Moreover, this biosensor is linearly proportional to the concentration of glucose in the range of 0.2-1.6 mM. The study revealed that the band structure of electrode could affect the detection of direct electron transfer of GOD, which would be helpful for the design of the biosensor electrodes in the future. PMID:27572675

  17. Bimolecular Excited-State Electron Transfer with Surprisingly Long-Lived Radical Ions

    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.

  18. Electron transfer reaction in the Marcus inverted region: Role of high frequency vibrational modes

    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

  19. Surface residues dynamically organize water bridges to enhance electron transfer between proteins

    de la Lande, A.; Babcock, N. S.; Řezáč, Jan; Sanders, B. C.; Salahub, D. R.

    2010-01-01

    Roč. 107, č. 26 (2010), s. 11799-11804. ISSN 0027-8424 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron transfer * pathway model * mutations Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 9.771, year: 2010

  20. Global proteomic profiling of phosphopeptides using electron transfer dissociation tandem mass spectrometry

    Molina, Henrik; Horn, David M; Tang, Ning; Mathivanan, Suresh; Pandey, Akhilesh

    2007-01-01

    Electron transfer dissociation (ETD) is a recently introduced mass spectrometric technique that provides a more comprehensive coverage of peptide sequences and posttranslational modifications. Here, we evaluated the use of ETD for a global phosphoproteome analysis. In all, we identified a total of...... method for localization of phosphorylation sites and should be an integral component of any strategy for comprehensive phosphorylation analysis....

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

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

    2014-01-01

    Roč. 55, č. 13 (2014), s. 2959-2966. ISSN 0032-3861 R&D Projects: GA ČR 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

  2. Electron transfer through time dependent bridges: Differences between Franck-Condon and Born-Oppenheimer breakdown

    We consider tunneling-mediated electron transfer through time dependent bridges. An approach is developed for computing corrections to the time dependent tunneling matrix element that arise from the breakdown of the Born-Oppenheimer Adiabatic approximation. Differences between Franck-Condon and Born-Oppenheimer breakdown are discussed in the context of bridge-mediated tunneling

  3. Electron transfer reactions, cyanide and O2 binding of truncated hemoglobin from Bacillus subtilis

    Fernandez, Esther; Larsson, Jonas T.; McLean, Kirsty J.;

    2013-01-01

    The truncated hemoglobin from Bacillus subtilis (trHb-Bs) possesses a surprisingly high affinity for oxygen and resistance to (auto)oxidation; its physiological role in the bacterium is not understood and may be connected with its very special redox and ligand binding reactions. Electron transfer...

  4. Blue copper proteins as a model for investigating electron transfer processes within polypeptide matrices

    Farver, O; Pecht, I

    1994-01-01

    Cu(II) ion bound at a distance of approximately 2.6 nm has been studied, in naturally occurring and in single-site mutated azurins. The role of changing specific amino acid residues on the internal long-range electron transfer (LRET) process and its potential pathways has been investigated. It is...

  5. Sandwiched confinement of quantum dots in graphene matrix for efficient electron transfer and photocurrent production

    Zhu, Nan; Zheng, Kaibo; J. Karki, Khadga; Abdellah, Mohamed; Zhu, Qiushi; Carlson, Stefan; Haase, Dörthe; Žídek, Karel; Ulstrup, Jens; Canton, Sophie E.; Pullerits, Tonu; Chi, Qijin

    2015-01-01

    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...

  6. 77 FR 22067 - Proposed Collection of Information: Trace Request for Electronic Funds Transfer (EFT) Payment...

    2012-04-12

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE TREASURY Fiscal Service Proposed Collection of Information: Trace Request for Electronic Funds Transfer (EFT...: Trace Request for EFT Payment; and Trace Request Direct Deposit. OMB Number: 1510-0045. Form Number:...

  7. Long-range electron transfer in engineered azurins exhibits marcus inverted region behavior

    Farver, Ole; Hosseinzadeh, Parisa; Marshall, Nicholas M.;

    2015-01-01

    The Marcus theory of electron transfer (ET) predicts that while the ET rate constants increase with rising driving force until it equals a reaction’s reorganization energy, at higher driving force the ET rate decreases, having reached the Marcus inverted region. While experimental evidence of the...

  8. Application of EIS with Au-Hg microelectrode in determining electron transfer mechanisms

    Bai, X. [College of Marine Studies, University of Delaware, Lewes, DE 19958 (United States); Dexter, S.C. [College of Marine Studies, University of Delaware, Lewes, DE 19958 (United States)]. E-mail: dexter@udel.edu; Luther, G.W. [College of Marine Studies, University of Delaware, Lewes, DE 19958 (United States)

    2006-01-20

    The objective of this study was to investigate the application of microelectrodes with electrochemical impedance spectroscopy (EIS) for distinguishing between one- and two-electron transfer electrochemical reactions occurring within marine microbial biofilms. In our study, both gold and gold-mercury amalgam microelectrodes with tip diameters of 100 {mu}m were used. EIS measurements were performed at the half-wave potentials of the chemicals of interest in 0.5 M NaCl aqueous solutions containing 100 {mu}M each of FeCl{sub 3}, [Fe(Cat){sub 2}]{sup -}, [Fe(Cat){sub 3}]{sup 3-}, [Fe(4NCat){sub 3}]{sup 3-}, MnCl{sub 2}, FeCl{sub 2} and mixed solutions with two of those chemicals in NaCl solution or seawater. The results showed that there was a linear relationship between the impedance Z {sub re}, Z {sub im} and angular frequency {omega} {sup -1/2} obtained at phase angle of 45{sup o} for both one- and two-electron transfer reactions. One-electron transfer reactions could then be distinguished from two-electron transfer reactions by the slopes.

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

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

    2011-01-01

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

  10. 75 FR 59172 - Electronic Funds Transfer of Depository Taxes; Hearing Cancellation

    2010-09-27

    ... Register on Thursday, August ] 26, 2010, (75 FR 52485) announced that a public hearing was scheduled for... Depository Taxes; Hearing Cancellation AGENCY: Internal Revenue Service (IRS), Treasury. ACTION: Cancellation... on proposed regulation relating to Federal tax deposits (FTDs) by Electronic Funds Transfer...

  11. Single Step versus Stepwise Electron Transfer in Expanded Pyridiniums, Kinetic Aspects

    Hromadová, Magdaléna; Lachmanová, Štěpánka; 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 ČR GA203/09/0705 Institutional support: RVO:61388955 ; RVO:61388963 Keywords : electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

  12. Single step versus stepwise electron transfer in head-to-tail dipyridinium isomers

    Hromadová, Magdaléna; Lachmanová, Štěpánka; 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 ČR GA203/09/0705; GA AV ČR M200401202 Institutional support: RVO:61388955 ; RVO:61388963 Keywords : electron transfer * electrochemistry Subject RIV: CG - Electrochemistry

  13. The Energy Transfer Processes between Carotenoid and Chlorophyll Regulated by Electron Exchange Mechanism

    2001-01-01

    The energy transfer efficiency between carotenoids and chlorophyll depend on temperature and viscosity of the media. A 3.5 ps process was detected by the pico-second time-resolved spectra and the process was proved to be regulated by electron exchange mechanism.

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

    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…

  15. Promotion of multi-electron transfer for enhanced photocatalysis: A review focused on oxygen reduction reaction

    Wang, Changhua; Zhang, Xintong; Liu, Yichun

    2015-12-01

    Semiconductor photocatalysis has attracted significant interest for solar light induced environmental remediation and solar fuel generation. As is well known, photocatalytic performance is determined by three steps: photoexcitation, separation and transport of photogenerated charge carriers, and surface reactions. To achieve higher efficiency, significant efforts have been made on improvement of efficiency of above first two steps, which have been well documented in recent review articles. In contrast, this review intends to focus on strategies moving onto the third step of improvement for enhanced photocatalysis wherein active oxygen species including superoxide radical, hydrogen peroxide, hydroxyl radical are in situ detected. Particularly, surface electron-transfer reduction of oxygen over single component photocatalysts is reviewed and systems enabling multi-electron transfer induced oxygen reduction reaction (ORR) are highlighted. It is expected this review could provide a guideline for readers to better understand the critical role of ORR over photocatalyst in charge carrier separation and transfer and obtain reliable results for enhanced aerobic photocatalysis.

  16. Electron transfer and ionization in collisions of highly stripped ions with neutral targets at intermediate velocities

    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.

    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 π → π* 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. Convective and conduction heat transfer study on a mig-type electron gun

    A convective and conducting heat transfer study of a magnetron injection electron gun has been made to minimize the temperature distribution in the gun elements while keeping the required operating temperature at 10000 C of the emitter. Appropriate materials were selected to reduce thermal losses and to improve the gun design from a constructional point of view aiming at extending the capabilities of the electron gun. A thermal probe to determine the air velocity and the convective heat transfer coefficient has been constructed to determine the external boundary condition of the ceramic shell and external flanges. A study the contact resistance for all the gun elements has been made to minimize the conduction thermal losses. A software has been used to simulate a thermal model considering the three processes of thermal transfer, namely, conduction, convection and radiation and the influence of the physical properties of the materials used. (author). 7 refs., 5 figs., 1 tab

  19. Local intermolecular interactions for selective CO2 capture by zeolitic imidazole frameworks: energy decomposition analysis

    Intermolecular energy decomposition analysis (EDA) is reported for the binding of CO2 with zeolitic imidazole frameworks (ZIF) to provide a molecular level interpretation of the recent capacity and selectivity measurements of several ZIFs and to suggest a theoretical guideline to improve their performance further, using 1 nm size of organic linker fragment of the ZIFs as a target molecule. The EDA suggests that the local electronic interaction of CO2 and the substituent groups, mainly frozen density and polarization interactions with little charge transfer, is the primary binding interaction, but the electron correlation effects can be equally or more important depending on the binding geometry and functional groups. The present correlated calculations identify the preferred ZIF binding sites for various gases including CO2 to be mostly near the benzene substituent groups rather than the plane of imidazole rings. We predict that the NH2-substituted ZIF would have an enhanced capacity of CO2 as compared to the NO2-substituted ZIF that was recently synthesized and reported to be one of the materials with the best capacity results along with high gas selectivity. The present calculations may imply that the local functionality of the linking organics, rather than detailed framework structures, may be of primary importance in designing certain high capacity MOF or ZIF materials.

  20. Theoretical analysis of proton relays in electrochemical proton-coupled electron transfer.

    Auer, Benjamin; Fernandez, Laura E; Hammes-Schiffer, Sharon

    2011-06-01

    The coupling of long-range electron transfer to proton transport over multiple sites plays a vital role in many biological and chemical processes. Recently the concerted proton-coupled electron transfer (PCET) reaction in a molecule with a hydrogen-bond relay inserted between the proton donor and acceptor sites was studied electrochemically. The standard rate constants and kinetic isotope effects (KIEs) were measured experimentally for this double proton transfer system and a related single proton transfer system. In the present paper, these systems are studied theoretically using vibronically nonadiabatic rate constant expressions for electrochemical PCET. Application of this approach to proton relays requires the calculation of multidimensional proton vibrational wave functions and the incorporation of multiple proton donor-acceptor motions. The decrease in proton donor-acceptor distances due to thermal fluctuations and the contributions from excited electron-proton vibronic states play important roles in these systems. The calculated KIEs and the ratio of the standard rate constants for the single and double proton transfer systems are in agreement with the experimental data. The calculations indicate that the standard PCET rate constant is lower for the double proton transfer system because of the smaller overlap integral between the ground state reduced and oxidized proton vibrational wave functions, resulting in greater contributions from excited electron-proton vibronic states with higher free energy barriers. The theory predicts that this rate constant may be increased by modifying the molecule in a manner that decreases the equilibrium proton donor-acceptor distances or alters the molecular thermal motions to facilitate the concurrent decrease of these distances. These insights may guide the design of more efficient catalysts for energy conversion devices. PMID:21524104

  1. Constraint-Based Modeling of Carbon Fixation and the Energetics of Electron Transfer in Geobacter metallireducens

    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

  2. Mechanically induced intramolecular electron transfer in a mixed-valence molecular shuttle

    Barnes, Jonathan C.; Fahrenbach, Albert C.; Dyar, Scott M.; Frasconi, Marco; Giesener, Marc A.; Zhu, Zhixue; Liu, Zhichang; Hartlieb, Karel J.; Carmieli, Ranaan; Wasielewski, Michael R.; Stoddart, J. Fraser

    2012-01-01

    The kinetics and thermodynamics of intramolecular electron transfer (IET) can be subjected to redox control in a bistable [2]rotaxane comprised of a dumbbell component containing an electron-rich 1,5-dioxynaphthalene (DNP) unit and an electron-poor phenylene-bridged bipyridinium (P-BIPY2+) unit and a cyclobis (paraquat-p-phenylene) (CBPQT4+) ring component. The [2]rotaxane exists in the ground-state co-conformation (GSCC) wherein the CBPQT4+ ring encircles the DNP unit. Reduction of the CBPQT...

  3. Relationship between conformational dynamics and electron transfer in a desolvated peptide. Part II. Temperature dependence.

    Parks, Joel H; Semrouni, David; Clavaguéra, Carine; Ohanessian, Gilles

    2013-02-14

    Recent time-resolved lifetime measurements studied the quenching of the fluorescence emitted by a dye covalently bound to the desolvated peptide Dye-Pro(4)-Arg(+)-Trp. This peptide sequence was chosen for study since intramolecular interactions constrain all large-scale fluctuations except for those of the interacting dye and Trp side chain. It was shown that quenching occurred as a result of interaction between the excited dye and tryptophan side chain. These measurements exhibited a temperature dependence that suggested the quenching mechanism was related to electron transfer. This paper presents a comparison of the experimental quenching rate with the Marcus electron transfer model performed with molecular dynamics (MD) calculations. Taking advantage of the AMOEBA force field that explicitly includes polarizability ensures that the intramolecular electrostatic and polarization interactions in this desolvated peptide ion are treated realistically. MD calculations identify both large-scale fluctuations between conformations as well as small-scale fluctuations within a conformation that are shown to be correlated with torsional dynamics of the Trp side chain. Trajectories of the Dye-Trp distance identify the occurrence of close separations required for efficient electron transfer. The temperature dependence of the quenching rate closely follows the rate predicted by the Marcus electron transfer model within uncertainties resulting from statistical averages. Estimates of the energy parameters characterizing the Marcus model indicate the electronic coupling matrix element and the reaction free energy derived from the fits are consistent with published values for transfer in polyproline bridged peptides. These calculations help to provide a molecular basis for investigating conformational changes in desolvated biomolecular ions by fluorescence quenching measurements. PMID:23297809

  4. Intramolecular electron transfer in ruthenium-modified cytochrome C: Driving force effects

    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

  5. Ultrafast photoinduced energy and electron transfer in multi-modular donor-acceptor conjugates.

    El-Khouly, Mohamed E; Wijesinghe, Channa A; Nesterov, Vladimir N; Zandler, Melvin E; Fukuzumi, Shunichi; D'Souza, Francis

    2012-10-22

    New multi-modular donor-acceptor conjugates featuring zinc porphyrin (ZnP), catechol-chelated boron dipyrrin (BDP), triphenylamine (TPA) and fullerene (C(60)), or naphthalenediimide (NDI) have been newly designed and synthesized as photosynthetic antenna and reaction-center mimics. The X-ray structure of triphenylamine-BDP is also reported. The wide-band capturing polyad revealed ultrafast energy-transfer (k(ENT) =1.0 × 10(12) s(-1)) from the singlet excited BDP to the covalently linked ZnP owing to close proximity and favorable orientation of the entities. Introducing either fullerene or naphthalenediimide electron acceptors to the TPA-BDP-ZnP triad through metal-ligand axial coordination resulted in electron donor-acceptor polyads whose structures were revealed by spectroscopic, electrochemical and computational studies. Excitation of the electron donor, zinc porphyrin resulted in rapid electron-transfer to coordinated fullerene or naphthalenediimide yielding charge separated ion-pair species. The measured electron transfer rate constants from femtosecond transient spectral technique in non-polar toluene were in the range of 5.0 × 10(9)-3.5 × 10(10) s(-1). Stabilization of the charge-separated state in these multi-modular donor-acceptor polyads is also observed to certain level. PMID:22996909

  6. Large work function difference driven electron transfer from electrides to single-walled carbon nanotubes

    Menamparambath, Mini Mol

    2014-06-23

    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 [Ca 24Al28O64]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 cm 2 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 46000 (14.8 mA cm-2) at 2 V μm-1 (3.5 wt% [Ca2N]+·e-) with a turn-on voltage of 0.85 V μm-1. This journal is © the Partner Organisations 2014.

  7. Influence of chemical and structural evolution of dissolved organic matter on electron transfer capacity during composting

    He, Xiao-Song [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Innovation base of Ground Water and Environmental System Engineering, Chinese Research Academy of Environmental Science, Beijing 100012 (China); Xi, Bei-Dou, E-mail: hexs82@126.com [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Innovation base of Ground Water and Environmental System Engineering, Chinese Research Academy of Environmental Science, Beijing 100012 (China); Cui, Dong-Yu [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Innovation base of Ground Water and Environmental System Engineering, Chinese Research Academy of Environmental Science, Beijing 100012 (China); Liu, Yong [Guangdong Key Laboratory of Agro-Environmental Integrated Control, Guangdong Institute of Eco-Environmental and Soil Sciences, Guangzhou 510650 (China); Tan, Wen-Bin; Pan, Hong-Wei; Li, Dan [State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012 (China); Innovation base of Ground Water and Environmental System Engineering, Chinese Research Academy of Environmental Science, Beijing 100012 (China)

    2014-03-01

    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 μmol{sub e−} (g C){sup −1} and 57.1– 346.07 μmol{sub e−} (g C){sup −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.

  8. Influence of chemical and structural evolution of dissolved organic matter on electron transfer capacity during composting

    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 μmole− (g C)−1 and 57.1– 346.07 μmole− (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

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

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

    2016-09-01

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

  10. The role of electronic symmetry in charge-transfer-to-solvent reactions: Quantum nonadiabatic computer simulation of photoexcited sodium anions

    Smallwood, C J; Bosma, W B; Larsen, R E; Schwartz, Benjamin J.

    2003-01-01

    Since charge-transfer-to-solvent (CTTS) reactions represent the simplest class of solvent-driven electron transfer reactions, there has been considerable interest in understanding the solvent motions responsible for electron ejection. The major question that we explore in this paper is what role the symmetry of the electronic states plays in determining the solvent motions that account for CTTS. To this end, we have performed a series of one-electron mixed quantum/classical nonadiabatic molec...

  11. Molecular control of electron and hole transfer processes: Theory and applications

    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.

  12. First Observation of Electron Transfer Mediated Decay in Aqueous Solutions: A Novel Probe of Ion Pairing

    Unger, I; Thürmer, S; Aziz, E F; Cederbaum, L S; Muchová, E; Slavíček, P; Winter, B; Kryzhevoi, N V

    2016-01-01

    A major goal of many spectroscopic techniques is to provide comprehensive information on the local chemical environment. Electron transfer mediated decay (ETMD) is a sensitive probe of the environment since it is actively involved in this non-local radiationless decay process through electron and energy transfer steps. We report the first experimental observation of ETMD in the liquid phase. Using liquid-jet X-ray photoelectron spectroscopy we explore LiCl aqueous solution, and detect low-energy electrons unambiguously emerging from the ETMD processes of core-ionized Li+. We interpret the experimental results with molecular dynamics and high-level ab initio calculations. By considering various solvation-structure models we show that both water molecules and Cl- anions can participate in ETMD, with each process having its characteristic spectral fingerprint. Different ion associations lead to different spectral shapes. The potential application of the unique sensitivity of the ETMD spectroscopy to the local hy...

  13. Large electron transfer rate effects from the Duschinsky mixing of vibrations

    Sando, Gerald M.; Spears, Kenneth G; Hupp, Joseph T;

    2001-01-01

    vibrations are very important. The Duschinsky effect arises when two electronic states have vibrational normal mode coordinate systems that are rotated and translated relative to each other. We use a conventional quantum rate model for ET, and the examples include 6-8 vibrations, where two vibrational modes......We systematically test how the Duschinsky mixing of normal coordinate vibrations affects transition rates for electron transfer (ET). We find that ET rates in the inverted region can increase many orders of magnitude from Duschinsky mixing, and both totally symmetric and nontotally symmetric...... magnitude for inverted electron transfer reactions and modest mixing. The peak location in a rate vs energy gap plot can depend on the degree of Duschinsky mixing, and therefore it corresponds to a sum of solvent and an effective vibrational reorganization energy that is not predictable by simple models...

  14. Characterization and modelling of interspecies electron transfer mechanisms and microbial community dynamics of a syntrophic association

    Nagarajan, Harish; Embree, Mallory; Rotaru, Amelia-Elena;

    2013-01-01

    complex nutritional and energetic dependencies and their functioning. Here we apply a multi-omic modelling workflow that combines genomic, transcriptomic and physiological data with genome-scale models to investigate dynamics and electron flow mechanisms in the syntrophic association of Geobacter......Syntrophic associations are central to microbial communities and thus have a fundamental role in the global carbon cycle. Despite biochemical approaches describing the physiological activity of these communities, there has been a lack of a mechanistic understanding of the relationship between...... metallireducens and Geobacter sulfurreducens. Genome-scale modelling of direct interspecies electron transfer reveals insights into the energetics of electron transfer mechanisms. While G. sulfurreducens adapts to rapid syntrophic growth by changes at the genomic and transcriptomic level, G. metallireducens...

  15. Electron transfer of Pseudomonas aeruginosa CP1 in electrochemical reduction of nitric oxide.

    Zhou, Shaofeng; Huang, Shaobin; He, Jiaxin; Li, Han; Zhang, Yongqing

    2016-10-01

    This study reports catalytic electro-chemical reduction of nitric oxide (NO) enhanced by Pseudomonas aeruginosa strain CP1. The current generated in the presence of bacteria was 4.36times that in the absence of the bacteria. The strain was able to catalyze electro-chemical reduction of NO via indirect electron transfer with an electrode, revealed by a series of cyclic voltammetry experiments. Soluble electron shuttles secreted into solution by live bacteria were responsible for the catalytic effects. The enhancement of NO reduction was also confirmed by detection of nitrous oxide; the level of this intermediate was 46.4% higher in the presence of bacteria than in controls, illustrated that the electron transfer pathway did not directly reduce nitric oxide to N2. The findings of this study may offer a new model for bioelectrochemical research in the field of NO removal by biocatalysts. PMID:27426634

  16. Tetrakis-acridinyl peptide: Distance dependence of photoinduced electron transfer in deoxyribonucleic acid assemblies

    The distance dependence of photoinduced electron transfer in deoxyribonucleic acid (DNA) duplex was investigated using the 'TAP cassette' systems of the general formula (AT)6A nXA9-n (X denote guanine (G) or cytosine (C)). The tetrakis-9-acridinyl peptide (TAP) binds tightly with (AT)6 duplex region showing strong fluorescence that was not quenched by the A nXA9-n single-stranded region. Quenching was observed after duplex formation with the complementary T9-nXT n strand (G-C pairing), showing clear dependence on the distance between the TAP and a guanine. An extremely low β value of 0.22 was obtained in our electron transfer (ET) system that suggests exceptional good mediation of ET process. Experiments with G-mismatches showed negligible quenching for systems with guanine separated by more than one AT base pair that indicated rather inefficient ET process for duplexes containing disrupted π-electronic system

  17. Intervalley transfer of electrons in ZnS-type thin film electroluminescent devices

    Based on calculation about intervalley scattering rates in ZnS, the intervalley transfer process in ZnS-type thin film electroluminescent devices is investigated through Monte Carlo simulation. The transient time of intervalley transfer is about 0.2-0.3 ps, it coincides with that of electron average energy. Intervalley distribution shifts to high valleys as the electric field increased. The electron kinetic energy distributions in different valleys are also gained. We propose that high valleys could store energies, which could prolong the decay of the electron average energy as the field is removed. These results could be used as a basic data on the study of electroluminescent process and the citation of valley parameters in analytic models should be carefully considered. (author)

  18. Modulation of the electron transfer processes in Au-ZnO nanostructures

    Aguirre, M. E.; Armanelli, A.; Perelstein, G.; Feldhoff, A.; Tolley, A. J.; Grela, M. A.

    2015-04-01

    Plasmonic nanostructures comprising Au and ZnO nanoparticles synthesized by the spontaneous reduction of HAuCl4 in ethylene glycol were used to assess the possibility of modulating the direction of the electron transfer processes at the interface. One electron UV reduction and visible oxidation of the reversible couple TEMPOL/TEMPOL-H was confirmed by EPR spectroscopy. The apparent quantum yield for TEMPOL-H conversion under continuous wave visible excitation depends on the irradiation wavelength, being 0.57% and 0.27% at 450 +/- 12 and 530 +/- 12 nm, respectively. These results indicate that both the surface plasmon resonance and the interband transition from the 5d to the 6s level of Au nanoparticles contribute to the visible activity of the nanostructure. In addition, by detecting free electron conduction band electrons in ZnO, after the visible excitation of Au/ZnO nanostructures, we provide direct evidence of the photoexcited electron transfer from gold nanoparticles to ZnO.Plasmonic nanostructures comprising Au and ZnO nanoparticles synthesized by the spontaneous reduction of HAuCl4 in ethylene glycol were used to assess the possibility of modulating the direction of the electron transfer processes at the interface. One electron UV reduction and visible oxidation of the reversible couple TEMPOL/TEMPOL-H was confirmed by EPR spectroscopy. The apparent quantum yield for TEMPOL-H conversion under continuous wave visible excitation depends on the irradiation wavelength, being 0.57% and 0.27% at 450 +/- 12 and 530 +/- 12 nm, respectively. These results indicate that both the surface plasmon resonance and the interband transition from the 5d to the 6s level of Au nanoparticles contribute to the visible activity of the nanostructure. In addition, by detecting free electron conduction band electrons in ZnO, after the visible excitation of Au/ZnO nanostructures, we provide direct evidence of the photoexcited electron transfer from gold nanoparticles to ZnO. Electronic

  19. Simulations of the THz spectrum of liquid water incorporating the effects of intermolecular charge fluxes through hydrogen bonds

    The intensity of the band at ∼200 cm−1 (∼6 THz) in the Terahertz spectrum of liquid water mainly arises from the modulations of the extent of intermolecular charge transfer through hydrogen bonds, called intermolecular charge fluxes, occurring upon molecular translations along the O…H hydrogen bonds. To obtain reasonable spectral profiles from simulations, it is necessary to effectively incorporate the effects of those intermolecular charge fluxes, but apparently it is not possible by simple classical molecular dynamics simulations with fixed atomic partial charges even if they are amended by molecular induced dipoles due to intermolecular electrostatic interactions. The present paper shows how we can do reasonably correct spectral simulations, without resorting to fully ab initio molecular dynamics

  20. Simulations of the THz spectrum of liquid water incorporating the effects of intermolecular charge fluxes through hydrogen bonds

    Torii, Hajime, E-mail: torii.hajime@shizuoka.ac.jp [Department of Chemistry, Faculty of Education, and Department of Optoelectronics and Nanostructure Science, Graduate School of Science and Technology, Shizuoka University, 836 Ohya, Shizuoka 422-8529 (Japan)

    2015-12-31

    The intensity of the band at ∼200 cm{sup −1} (∼6 THz) in the Terahertz spectrum of liquid water mainly arises from the modulations of the extent of intermolecular charge transfer through hydrogen bonds, called intermolecular charge fluxes, occurring upon molecular translations along the O…H hydrogen bonds. To obtain reasonable spectral profiles from simulations, it is necessary to effectively incorporate the effects of those intermolecular charge fluxes, but apparently it is not possible by simple classical molecular dynamics simulations with fixed atomic partial charges even if they are amended by molecular induced dipoles due to intermolecular electrostatic interactions. The present paper shows how we can do reasonably correct spectral simulations, without resorting to fully ab initio molecular dynamics.

  1. Electrochemical control over photoinduced electron transfer and trapping in CdSe-CdTe quantum-dot solids.

    Boehme, Simon C; Walvis, T Ardaan; Infante, Ivan; Grozema, Ferdinand C; Vanmaekelbergh, Daniël; Siebbeles, Laurens D A; Houtepen, Arjan J

    2014-07-22

    Understanding and controlling charge transfer between different kinds of colloidal quantum dots (QDs) is important for devices such as light-emitting diodes and solar cells and for thermoelectric applications. Here we study photoinduced electron transfer between CdTe and CdSe QDs in a QD film. We find that very efficient electron trapping in CdTe QDs obstructs electron transfer to CdSe QDs under most conditions. Only the use of thiol ligands results in somewhat slower electron trapping; in this case the competition between trapping and electron transfer results in a small fraction of electrons being transferred to CdSe. However, we demonstrate that electron trapping can be controlled and even avoided altogether by using the unique combination of electrochemistry and transient absorption spectroscopy. When the Fermi level is raised electrochemically, traps are filled with electrons and electron transfer from CdTe to CdSe QDs occurs with unity efficiency. These results show the great importance of knowing and controlling the Fermi level in QD films and open up the possibility of studying the density of trap states in QD films as well as the systematic investigation of the intrinsic electron transfer rates in donor-acceptor films. PMID:24883930

  2. An OODR study of collision induced energy transfer between unperturbed electronic states

    A two laser, optical-optical double resonance (OODR) technique has been used as a direct probe of the electronic energy transfer process between rovibronic levels of the A and X states of 14N2+. For the first time collisional selection or propensity rules are obtained for a homonuclear molecule which has no perturbations or ''gates'' between the states involved. The electronic transfer rate between the A(v = 4) and X(v = 8) rotational manifolds is shown to be comparable to that for rotational energy transfer (RET) and in spite of the competition between these two mechanisms it is demonstrated that there is a propensity towards ΔJ approx. = O rather than ΔE (energy gap) approx. = O. In addition, the selection rule s a is shown to apply for this process. Other pairs of vibronic levels show similar propensity rules and demonstrate that these are truly electronic energy transfer processes rather than a form of RET as occurs when the rotational levels are known to be perturbed in the isolated molecule

  3. An application protocol for CAD to CAD transfer of electronic information

    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.

  4. Contrast in electron-transfer mediation between graphene oxide and reduced graphene oxide.

    Hongthani, Wiphada; Patil, Avinash J; Mann, Stephen; Fermín, David J

    2012-08-27

    The properties of graphene oxide (GO) and DNA-stabilised reduced graphene-oxide (rGO) sheets as electron-transfer mediators in partially blocked electrodes are evaluated employing electrochemical impedance spectroscopy. Evidences obtained from UV/Vis, Raman and FTIR spectroscopies, as well as atomic force microscopy, confirm that the reduction of exfoliated GO single sheets by hydrazine yields partially reduced graphene oxide featuring a high defect density. Two-dimensional assemblies of GO and rGO were formed through electrostatic adsorption at Au electrodes, sequentially modified with 11-mercaptoundecanoic acid (MUA) and poly-diallyldimethylammonium chloride (PDADMAC). The MUA:PDADMAC generates a strong blocking layer to the electron-transfer reaction involving the ferri/ferrocyanide redox couple. This blocking behaviour is not significantly affected upon adsorption of GO. However, adsorption of a sub-monolayer of rGO decreases the charge-transfer resistance by more than two orders of magnitude. Analysis of cyclic voltammograms and impedance spectra suggests that electron transfer in rGO assemblies is mediated by occupied states located just below the redox Fermi energy of the probe. These findings are discussed in the context of on-going controversies regarding the electrochemical reactivity of sp(2)-carbon basal planes. PMID:22865797

  5. Photoinduced electron transfer in some photosensitive molecules-incorporated semiconductor/zeolites: New photocatalytic systems

    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.

  6. Computational Analysis of Intermolecular Coulombic Decay Effects in DNA nucleotide Photoionization

    Vargas, E. L.; Robertson, J.; Andrianarijaona, V. M.

    2016-03-01

    Intermolecular Coulombic Decay (ICD) is the process of how electrons return to their original state after excitation and how this affects their immediate environment. In a previous research presentationwe had considered the hypothetical applications of Intermolecular Coulombic Decay on the adhesiveness of coding proteins within DNA molecules. This presentation is a continuation of the previous in that the results of our DFT-based computational calculations of the ionization potentials of nucleotides and their excitation energies will be presented, as well as how they influence their surroundings. Author would like to acknowledge the PUC Student Senate for financial assistance.

  7. Study of photo-activated electron transfer reactions in the first excited singlet state by picosecond and nanosecond laser spectroscopy

    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 γ ≅ 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 μs. 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)

  8. Charge transfer mobility of naphthodithiophenediimide derivative: Normal-mode and bond length relaxation analysis

    Liu, Xiaoyan; Liu, Yujuan; Zheng, Yujun

    2016-02-01

    In this letter, the charge transfer mobility of naphthalenediimide (NDTI) derivative is investigated. By employing the normal-mode analysis and bond length relaxation analysis, the influences of chemical elements on reorganization energies and intermolecular electronic couplings are investigated in NDTI derivative. The results show that the introduction of atom O would decrease reorganization energy in hole-hopping process and increase electronic coupling. This analysis encourages the molecular and material design in organic semiconductors.

  9. 48 CFR 52.232-35 - Designation of Office for Government Receipt of Electronic Funds Transfer Information.

    2010-10-01

    ... Government Receipt of Electronic Funds Transfer Information. 52.232-35 Section 52.232-35 Federal Acquisition... CONTRACT CLAUSES Text of Provisions and Clauses 52.232-35 Designation of Office for Government Receipt of Electronic Funds Transfer Information. As prescribed in 32.1110(c), insert the following clause:...

  10. 48 CFR 52.232-34 - Payment by Electronic Funds Transfer-Other than Central Contractor Registration.

    2010-10-01

    ... PROVISIONS AND CONTRACT CLAUSES Text of Provisions and Clauses 52.232-34 Payment by Electronic Funds Transfer... payment. (1) All payments by the Government under this contract shall be made by electronic funds transfer... governing Federal payments through the ACH are contained in 31 CFR part 210. (d) Suspension of payment....

  11. Pulse Radiolysis Studies of Temperature Dependent Electron Transfers among Redox Centers in ba(3)-Cytochrome c Oxidase from Thermus thermophilus

    Farver, Ole; Wherland, Scot; Antholine, William E;

    2010-01-01

    The functioning of cytochrome c oxidases involves orchestration of long-range electron transfer (ET) events among the four redox active metal centers. We report the temperature dependence of electron transfer from the Cu(A)(r) site to the low-spin heme-(a)b(o) site, i.e., Cu(A)(r) + heme-a(b)(o) ...

  12. DFT study of electronic transfer properties of carboxyl and nitro substituted benzene

    The electronic and optical transfer properties of Benzene, Benzoic Acid (BA), Nitrobenzene (NB) and Para Nitro Benzoic Acid (PNBA) at ground and first excited state has been investigated by the Density functional theory (DFT)and Time Dependent Density Functional Theory (TDDFT) using SVWN functional/3-21G basis set respectively. Possible intra-molecular charge transfer and n to π* transitions in the ground and the first excitation states have been predicted by the molecular orbitals and the Natural Bond Orbital (NBO) analysis. The simulated absorption spectra have been generated and the result compared with existing experimental results

  13. Hot-electron-transfer enhancement for the efficient energy conversion of visible light.

    Yu, Sungju; Kim, Yong Hwa; Lee, Su Young; Song, Hyeon Don; Yi, Jongheop

    2014-10-13

    Great strides have been made in enhancing solar energy conversion by utilizing plasmonic nanostructures in semiconductors. However, current generation with plasmonic nanostructures is still somewhat inefficient owing to the ultrafast decay of plasmon-induced hot electrons. It is now shown that the ultrafast decay of hot electrons across Au nanoparticles can be significantly reduced by strong coupling with CdS quantum dots and by a Schottky junction with perovskite SrTiO3 nanoparticles. The designed plasmonic nanostructure with three distinct components enables a hot-electron-assisted energy cascade for electron transfer, CdS→Au→SrTiO3, as demonstrated by steady-state and time-resolved photoluminescence spectroscopy. Consequently, hot-electron transfer enabled the efficient production of H2 from water as well as significant electron harvesting under irradiation with visible light of various wavelengths. These findings provide a new approach for overcoming the low efficiency that is typically associated with plasmonic nanostructures. PMID:25169852

  14. Rhodium thin film-carbon nanotube nanostructures: Synthesis, characterization and electron transfer properties

    Rh thin films have been synthesized onto carbon nanotubes by pulsed laser deposition under vacuum and under 266 Pa of helium background pressure. Field emission scanning electron microscopy revealed two types of Rh films: (i) Rh film fabricated under vacuum was smooth and of closed structure and (ii) Rh prepared at 266 Pa of He was porous. Transmission electron microscopy showed that the smooth Rh film was made of highly interconnected particles of 2 nm diameter, whereas the porous film had a morphology of particles arranged into columns with particles having an average diameter of 5 nm. In addition, using high resolution transmission electron microscopy images, the Rh film thickness could be estimated to be about 20 nm. X-ray diffraction pattern showed well-crystallized thin films with a (111) intense orientation. X-ray photoelectron spectroscopy confirmed the presence of metallic Rh at the surface of the carbon nanotubes. Preliminary evaluation of the electron transfer properties showed that porous Rh-carbon nanotubes exhibited reduced oxophilicity than smooth Rh. In addition, the porous Rh film offered larger electrochemical stability window between the onset of hydrogen adsorption and Rh oxide formation. Such interesting properties have important implications in many electroanalytical applications. - Highlights: • Pulsed laser synthesis used to deposit rhodium thin films onto carbon nanotubes. • Smooth and porous rhodium films verified by electron microscopy analyses • Electron transfer properties studied in sulfuric acid solution

  15. A general theoretical model for electron transfer reactions in complex systems.

    Amadei, Andrea; Daidone, Isabella; Aschi, Massimiliano

    2012-01-28

    In this paper we present a general theoretical-computational model for treating electron transfer reactions in complex atomic-molecular systems. The underlying idea of the approach, based on unbiased first-principles calculations at the atomistic level, utilizes the definition and the construction of the Diabatic Perturbed states of the involved reactive partners (i.e. the quantum centres in our perturbation approach) as provided by the interaction with their environment, including their mutual interaction. In this way we reconstruct the true Adiabatic states of the reactive partners characterizing the electron transfer process as the fluctuation of the electronic density due to the fluctuating perturbation. Results obtained by using a combination of Molecular Dynamics simulation and the Perturbed Matrix Method on a prototypical intramolecular electron transfer (from 2-(9,9'-dimethyl)fluorene to the 2-naphthalene group separated by a steroidal 5-α-androstane skeleton) well illustrate the accuracy of the method in reproducing both the thermodynamics and the kinetics of the process. PMID:22158942

  16. NI (II AND PB (II INHIBIT THE ENZYMATIC ACTIVITY OF DNA IN AN ELECTRON TRANSFER REACTION

    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.

  17. Study of the electron transfer in analog compounds of the Prussia blue

    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

  18. Trans-membrane electron transfer in red blood cells immobilized in a chitosan film on a glassy carbon electrode

    We have studied the trans-membrane electron transfer in human red blood cells (RBCs) immobilized in a chitosan film on a glassy carbon electrode (GCE). Electron transfer results from the presence of hemoglobin (Hb) in the RBCs. The electron transfer rate (ks) of Hb in RBCs is 0.42 s−1, and <1.13 s−1 for Hb directly immobilized in the chitosan film. Only Hb molecules in RBCs that are closest to the plasma membrane and the surface of the electrode can undergo electron transfer to the electrode. The immobilized RBCs displayed sensitive electrocatalytic response to oxygen and hydrogen peroxide. It is believed that this cellular biosensor is of potential significance in studies on the physiological status of RBCs based on observing their electron transfer on the modified electrode. (author)

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

    Bereau, Tristan, E-mail: bereau@mpip-mainz.mpg.de [Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany and Department of Chemistry, University of Basel, 4056 Basel (Switzerland); Lilienfeld, O. Anatole von [Department of Chemistry, Institute of Physical Chemistry, University of Basel, 4056 Basel, Switzerland and Argonne Leadership Computing Facility, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

    2014-07-21

    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/R{sup 6} correction will yield proper dissociative tails. Overall, the method achieves an accuracy well within conventional molecular force fields while exhibiting a simple parametrization protocol.

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

    Bereau, Tristan; von Lilienfeld, O. Anatole

    2014-07-01

    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.