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

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

    2007-01-01

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

  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

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

    2014-01-31

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

  5. Intermolecular and Intramolecular Excited State Charge Transfer

    Eisenthal, Kenneth B.

    1983-01-01

    A primary mechanism of energy relaxation and chemical change in organic molecules in excited electronic states is charge transfer. 1 The charge transfer process can be intermolecular, involving an excited molecule and a neighboring molecule, one serving as an acceptor and the other as a donor molecule, or intramolecular, involving a charge redistribution in the excited molecule which produces a very large excited state dipole moment.In our investigations of the dynamics of these various charg...

  6. 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

  7. 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.)

  8. 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-acceptor dyads. PMID:16571036

  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. 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.

  11. Donor-Bridge-Acceptor Systems with Varying Bridge Units for the Investigation of Intramolecular and Intermolecular Electron Transfer Processes

    Kaiser, Conrad

    2014-01-01

    Within this study, the influence of the energetics of the bridge unit on electron transfer (ET) in an electrode-bridge-donor system was investigated in a monolayer environment. This was realized by specifically designing molecules containing ferrocene carboxylic ester donors and hydroquinone derivatives as bridge units and by using a gold electrode as acceptor. The energetics of the hydroquinone derivatives was adjusted by synthetically varying its substituents with the intention of chang...

  12. Stability of Pyrimidine Nucleic Acid Bases with Respect to Intra- and Intermolecular Proton Transfer Reactions Induced by Excess Electrons

    Dabkowska, Iwona; Haranczyk, Maciej; Rak, Janusz; Gutowski, Maciej; Xu, Shoujun; Nilles, J. Michael; Radisic, Dunja; Bowen, Kit H.

    2003-03-01

    Chemically transformed nucleic acid bases are considered as sources of point mutations in genetic material. Our computational results and photoelectron spectra provide information about chemical transformations of pyrimidine bases induced by excess electrons. The isolated pyrimidine bases as well as their complexes with X (X= amino acid, carboxylic acid, or alcohol) have been studied with the B3LYP and MPW1K density functionals, as well as at the second order Moller-Plesset level of theory. The photoelectron spectra of some anionic complexes reveal broad features with maxima around 2 eV. These features cannot be associated with the anion of intact pyrimidine base solvated by X and indicate occurrence of chemical transformations. Our main findings are: (i) the excess electron attachment can induce a barrier-free proton transfer (BFPT) from X to the O8 atom of uracil or thymine, (ii) thymine in complexes with carboxylic acids is more resistant to BFPT than uracil, (iii) the instability of neutral rare tautomers of uracil or thymine can be significantly suppressed due to the interaction with zwitterionic amino acids.

  13. Fluorescence photoactivation by intermolecular proton transfer.

    Swaminathan, Subramani; Petriella, Marco; Deniz, Erhan; Cusido, Janet; Baker, James D; Bossi, Mariano L; Raymo, Françisco M

    2012-10-11

    We designed a strategy to activate fluorescence under the influence of optical stimulations based on the intermolecular transfer of protons. Specifically, the illumination of a 2-nitrobenzyl derivative at an activating wavelength is accompanied by the release of hydrogen bromide. In turn, the photogenerated acid encourages the opening of an oxazine ring embedded within a halochromic compound. This structural transformation extends the conjugation of an adjacent coumarin fluorophore and enables its absorption at an appropriate excitation wavelength. Indeed, this bimolecular system offers the opportunity to activate fluorescence in liquid solutions, within rigid matrixes and inside micellar assemblies, relying on the interplay of activating and exciting beams. Furthermore, this strategy permits the permanent imprinting of fluorescent patterns on polymer films, the monitoring of proton diffusion within such materials in real time on a millisecond time scale, and the acquisition of images with spatial resolution at the nanometer level. Thus, our operating principles for fluorescence activation can eventually lead to the development of valuable photoswitchable probes for imaging applications and versatile mechanisms for the investigation of proton transport. PMID:22994311

  14. 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 ISBN 9781617387623. - (MRS Symposium Proceedings. 1207). [MRS Fall Meeting 2009. Boston (US), 30.11.2009-04.12.2009] R&D Projects: GA MŠk ME 866; GA 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

  15. Nanophotonic boost of intermolecular energy transfer

    de Roque, P. M.; van Hulst, N. F.; Sapienza, R.

    2015-11-01

    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 Frster radius. A hybrid nanoantenna-waveguide system mediates the transmission of energy, showing enhancements up to 108 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 donoracceptor separations. The scheme we propose connects realistic emitters and could lead to practical on-chip implementations.

  16. 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.

  17. 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.

  18. Determination of stepsize parameters for intermolecular vibrational energy transfer

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

  19. The study of intermolecular energy transfers in electronic energy quenching for molecular collisions N{sub 2}-N{sub 2}, N{sub 2}-O{sub 2}, O{sub 2}-O{sub 2}

    Kirillov, A.S. [Kola Science Centre RAS, Apatity (Russian Federation). Polar Geophysical Inst.

    2008-07-01

    Contributions of intermolecular electron energy transfers in the electronic quenching are calculated for molecular collisions N{sub 2}(A{sup 3}{sigma}{sub u}{sup +}, W{sup 3}{delta}{sub u})+N{sub 2}(X{sup 1}{sigma}{sub g}{sup +}, v=0), N{sub 2}(A{sup 3}{sigma}{sub u}{sup +})+N{sub 2}(X{sup 1}{sigma}{sub g}{sup +}, v{>=}0), N{sub 2}(A{sup 3}{sigma}{sub u}{sup +})+O{sub 2}(X{sup 3}{sigma}{sub g}{sup -}, v=0-2), O{sub 2}(a{sup 1}{delta}{sub g}, b{sup 1}{sigma}{sub g}{sup +})+O{sub 2}(X{sup 3}{sigma}{sub g}{sup -}, v=0-2). The calculation has allowed one to estimate the product branching ratios. It is shown that there is a dependence of the calculated rate coefficients on the vibrational excitation of N{sub 2}(X{sup 1}{sigma}{sub g}{sup +}) and O{sub 2}(X{sup 3}{sigma}{sub g}{sup -}) molecules. In many cases, the calculated rate coefficients have a good agreement with available experimental data. (orig.)

  20. Determination of stepsize parameters for intermolecular vibrational energy transfer

    Tardy, D.C.

    1992-03-01

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

  1. 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

  2. Intermolecular resonance energy transfer in the presence of a dielectric cylinder

    Using a Green's tensor method, we investigate the rate of resonance electronic energy transfer between two molecules near a dielectric cylinder. Both the case of a real and frequency-independent dielectric constant ε and the case of a Drude-Lorentz model for ε(ω) are considered, the latter case including dispersion and absorption. If the donor is placed at a fixed position near the cylinder, we find that the energy transfer rate to the acceptor is enhanced compared to its vacuum value in a number of discrete hotspots, centered at the cylinder's surface. In the absence of dispersion and absorption the rate of energy transfer may be enhanced at most a few times. On the other hand, for the Drude-Lorentz model the enhancement may be huge (up to 106) and the hotspots are sharply localized at the surface. We show that these observations can be explained from the fact that in the resonance region of the Drude-Lorentz dielectric surface plasmons occur, which play the dominant role in transferring the electronic energy between the donor and the acceptor. The dependence of the energy transfer rate on the molecular transition frequency is investigated as well. For small intermolecular distances, the cylinder hardly affects the transfer rate, independent of frequency. For larger distances, the frequency dependence is quite strong, in particular in the stop-gap region. The role of the intermolecular distance in the frequency dependence may be explained qualitatively using Heisenberg's uncertainty principle to calculate the spread in the frequencies of the intermediate photons.

  3. 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

  4. 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

  5. Intermolecular energy transfer in the presence of dispersing and absorbing media

    Dung, H T; Welsch, D G; Dung, Ho Trung; Kn\\"{o}ll, Ludwig; Welsch, Dirk-Gunnar

    2002-01-01

    By making use of the Green function concept of quantization of the electromagnetic field in Kramers--Kronig consistent media, a rigorous quantum mechanical derivation of the rate of intermolecular energy transfer in the presence of arbitrarily shaped, dispersing, and absorbing material bodies is given. Applications to bulk material, multi-slab planar structures, and microspheres are studied. It is shown that when the two molecules are near a planar interface, then surface-guided waves can strongly affect the energy transfer and essentially modify both the (F\\"{o}rster) short-range $R^{-6}$ dependence of the transfer rate and the long-range $R^{-2}$ dependence, which are typically observed in free space. In particular, enhancement (inhibition) of energy transfer can be accompanied by inhibition (enhancement) of donor decay. Results for four- and five-layered planar structures are given and compared with experimental results. Finally, the energy transfer between two molecules located at diametrically opposite p...

  6. Oxidative inter-/intermolecular alkene diamination of hydroxy styrenes with electron-rich amines.

    Danneman, Michael W; Hong, Ki Bum; Johnston, Jeffrey N

    2015-05-15

    Doubly intermolecular alkene diamination is achieved with electron-rich, terminal alkenes through the use of a hypervalent iodine (PhI(OAc)2) reagent, iodide, and electron-rich amines. Mono- and disubstituted amines combine with electron-rich alkenes, particularly o-hydroxystyrenes, to achieve the greatest level of generality. This operationally straightforward protocol, unreliant on conventional metal-based activation, is compatible with a broad range of functional groups. PMID:25942322

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

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

    2015-02-25

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

  8. 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; Bräuner-Osborne, Hans

    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...

  9. 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....

  10. 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

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

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

  12. 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.

  13. Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(/sup 1/S) + H/sub 2/(B /sup 1/. sigma. /sub u//sup +/). [Solution for coupled channel equations

    Grimes, R.M.

    1986-11-01

    To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H/sub 2/(B /sup 1/..sigma../sub u//sup +/) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H/sub 2/(B /sup 1/..sigma../sub u//sup +/). 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 + H/sub 2/(E,F /sup 1/..sigma../sub g//sup +/) and with He + H/sub 2/(X /sup 1/..sigma../sub g//sup +/) and cause a local maximum and a deep minimum in the He + H/sub 2/(B /sup 1/..sigma../sub u//sup +/) PES, respectively. The crossing with He + H/sub 2/(X /sup 1/..sigma../sub g//sup +/) 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 H/sub 2/(B /sup 1/..sigma../sub u//sup +/) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs.

  14. Intermolecular hydrogen transfer catalyzed by a flavodehydrogenase, bakers' yeast flavocytochrome b2

    Bakers yeast flavocytochrome b2 is a flavin-dependent L-2-hydroxy acid dehydrogenase which also exhibits transhydrogenase activity. When a reaction takes place between [2-3H]lactate and a halogenopyruvate, tritium is found in water and at the halogenolactate C2 position. When the halogenopyruvate undergoes halide ion elimination, tritium is also found at the C3 position of the resulting pyruvate. The amount tau of this intermolecular tritium transfer depends on the initial keto acid-acceptor concentration. At infinite acceptor concentration, extrapolation yields a maximal transfer of 97 +/- 11%. This indicates that the hydroxy acid-derived hydrogen resides transiently on enzyme monoprotic heteroatoms and that exchange with bulk solvent occurs only at the level of free reduced enzyme. Using a minimal kinetic scheme, the rate constant for hydrogen exchange between Ered and solvent is calculated to be on the order of 10(2) M-1 S-1, which leads to an estimated pK approximately equal to 15 for the ionization of the substrate-derived proton while on the enzyme. It is suggested that this hydrogen could be shared between the active site base and Flred N5 anion. It is furthermore shown that some tritium is incorporated into the products when the transhydrogenation is carried out in tritiated water. Finally, with [2-2H]lactate-reduced enzyme, a deuterium isotope effect is observed on the rate of bromopyruvate disappearance. Extrapolation to infinite bromopyruvate concentration yields DV = 4.4. An apparent inverse isotope effect is determined for bromide ion elimination. These results strengthen the idea that oxidoreduction and elimination pathways involve a common carbanionic intermediate

  15. Effect of Intra-molecular Disorder and Inter-molecular Electronic Interactions on the Electronic Structure of Poly-p-Phenylene Vinylene (PPV)

    Yang, Ping; Batista, Enrique R.; Tretiak, Sergei; Saxena, Avadh; Martin, Richard L.; Smith, D. L.

    2007-01-01

    We investigate the role of intra-molecular conformational disorder and inter-molecular electronic interactions on the electronic structure of disorder clusters of poly-p-phenylene vinylene (PPV) oligomers. Classical molecular dynamics is used to determine probable molecular geometries, and first-principle density functional theory (DFT) calculations are used to determine electronic structure. Intra-molecular and inter-molecular effects are disentangled by contrasting results for densely packe...

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

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

  17. 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

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

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

  19. Identification of molecular crystals capable of undergoing an acyl-transfer reaction based on intermolecular interactions in the crystal lattice.

    Tamboli, Majid I; Krishnaswamy, Shobhana; Gonnade, Rajesh G; Shashidhar, Mysore S

    2013-09-16

    Investigation of the intermolecular acyl-transfer reactivity in molecular crystals of myo-inositol orthoester derivatives and its correlation with crystal structures enabled us to identify the essential parameters to support efficient acyl-transfer reactions in crystals: 1)?the favorable geometry of the nucleophile (-OH) and the electrophile (C-O) and 2)?the molecular assembly, reinforced by C-H???? interactions, which supports a domino-type reaction in crystals. These parameters were used to identify another reactive crystal through a data-mining study of the Cambridge Structural Database. A 2:1 co-crystal of 2,3-naphthalene diol and its di-p-methylbenzoate was selected as a potentially reactive crystal and its reactivity was tested by heating the co-crystals in the presence of solid sodium carbonate. A facile intermolecular p-toluoyl group transfer was observed as predicted. The successful identification of reactive crystals opens up a new method for the detection of molecular crystals capable of exhibiting acyl-transfer reactivity. PMID:23934729

  20. Detection of complex formation and determination of intermolecular geometry through electrical anharmonic coupling of molecular vibrations using electron-vibration-vibration two-dimensional infrared spectroscopy.

    Guo, Rui; Fournier, Frederic; Donaldson, Paul M; Gardner, Elizabeth M; Gould, Ian R; Klug, David R

    2009-10-14

    Electrical interactions between molecular vibrations can be non-linear and thereby produce intermolecular coupling even in the absence of a chemical bond. We use this fact to detect the formation of an intermolecular complex using electron-vibration-vibration two-dimensional infrared spectroscopy (EVV 2DIR) and also to determine the distance and angle between the two molecular species. PMID:19774270

  1. Kinetics of intra- and intermolecular excited-state proton transfer of ? -(2-hydroxynaphthyl-1)-decanoic acid in homogeneous and micellar solutions

    Solntsev, Kyril M.; Popov, Alexander V.; Solovyeva, Vera A.; Abou Al-Ainain, Sami; Ilichev, Yuri V.; Hernandez, Rigoberto; Kuzmin, Michael G.

    2016-03-01

    The bifunctional photoacid ?-(2-hydroxynaphthyl-1)-decanoic acid (1S2N) takes part both in intramolecular excited-state proton transfer (ESPT) to the anion of a fatty acid and in intermolecular ESPT in the presence of a water solvent. Excited-state intra- and intermolecular proton transfer of 1S2N was investigated in homogeneous ethanol/water solution and in micellar solutions of various surfactants. The interfacial potential of micelles was changed by using cationic (CTAB), non-ionic (Brij-35) and anionic (SDS) surfactants. With the decrease of the interfacial potential, the protolytic photodissociation of naphthol and the diffusion-controlled intramolecular ESPT to carboxylic anion were suppressed.

  2. 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.

  3. Proton-Coupled Electron Transfer

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

    2012-07-11

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

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

    Tardy, D.C.

    1992-03-01

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

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

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

    2011-01-01

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

  6. 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

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

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

    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(+) and K(+) ions in simulations, and it is likely to impact modeling of a wide range of systems for medical and technological applications. PMID:26723580

  8. 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

  9. 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.

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

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

  11. Electronic Mechanisms of Intra and Intermolecular J Couplings in Systems with C-HO Interactions

    Cavasotto, Claudio N.; Vizioli, Celia V.; Martin C. Ruiz de Azua; Claudia G. Giribet

    2003-01-01

    Abstract: Correlation effects on the change of 1J(CH) couplings in model systems I:NCH...H2O and II:CH4...H2O as a function of the H...O distance are discussed. RPA and SOPPA results follow a similar trend in system II. In system I RPA values decrease monotonously as the H...O distance decreases, while SOPPA ones exhibit flat maximum near equilibrium. Such different behavior is ascribed to the €-transmitted component. Intermolecular couplings at the equilibrium geometry of I are analyzed by...

  12. 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.

  13. 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

  14. Explosives sensing by using electron-rich supramolecular polymers: role of intermolecular hydrogen bonding in significant enhancement of sensitivity.

    Gole, Bappaditya; Song, Wentao; Lackinger, Markus; Mukherjee, Partha Sarathi

    2014-10-13

    We demonstrate here that supramolecular interactions enhance the sensitivity towards detection of electron-deficient nitro-aromatic compounds (NACs) over discrete analogues. NACs are the most commonly used explosive ingredients and are common constituents of many unexploded landmines used during World War II. In this study, we have synthesised a series of pyrene-based polycarboxylic acids along with their corresponding discrete esters. Due to the electron richness and the fluorescent behaviour of the pyrene moiety, all the compounds act as sensors for electron-deficient NACs through a fluorescence quenching mechanism. A Stern-Volmer quenching constant determination revealed that the carboxylic acids are more sensitive than the corresponding esters towards NACs in solution. The high sensitivity of the acids was attributed to supramolecular polymer formation through hydrogen bonding in the case of the acids, and the enhancement mechanism is based on an exciton energy migration upon excitation along the hydrogen-bond backbone. The presence of intermolecular hydrogen bonding in the acids in solution was established by solvent-dependent fluorescence studies and dynamic light scattering (DLS) experiments. In addition, the importance of intermolecular hydrogen bonds in solid-state sensing was further explored by scanning tunnelling microscopy (STM) experiments at the liquid-solid interface, in which structures of self-assembled monolayer of the acids and the corresponding esters were compared. The sensitivity tests revealed that these supramolecular sensors can even detect picric acid and trinitrotoluene in solution at levels as low as parts per trillion (ppt), which is much below the recommended permissible level of these constituents in drinking water. PMID:25187022

  15. 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)

  16. Electron Transfer and Proton-Coupled Electron Transfer Reactivity and Self-Exchange of Synthetic [2Fe–2S] Complexes: Models for Rieske and mitoNEET Clusters

    Saouma, Caroline T.; Pinney, Margaux M.; Mayer, James M.

    2014-01-01

    This report describes the thermochemistry, proton-coupled electron transfer (PCET) reactions and self-exchange rate constants for a set of bis-benzimidazolate-ligated [2Fe–2S] clusters. These clusters serve as a model for the chemistry of biological Rieske and mitoNEET clusters. PCET from [Fe2S2(Prbbim)(PrbbimH)]2– (4) and [Fe2S2(Prbbim)(PrbbimH2)]1– (5) to TEMPO occurs via concerted proton–electron transfer (CPET) mechanisms (PrbbimH2 = 4,4-bis-(benzimidazol-2-yl)heptane). Intermolecular ele...

  17. 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

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

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

  19. 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.

  20. Electron transfer reactions. Pt. 1

    The oxidation of the substituted ethylenes, 2,3-dimethylbutene-2 (1), 2-methylbutene-2 (8), and ?-methylstyrene (13), by ferriin or lead dioxide in water and/or methanol has been studied. Product analyses of the reactions, which lead to kinetically controlled product distributions, showed that lead dioxide, just as ferriin, reacts as a one-electron-oxidant. The product distributions, which arise from further reactions of the primary intermediates, i.e. the radical cations formed via one-electron transfer, were found to depend on substituents, acidity and solvent. The results are consistent with three separate reaction paths of the radical cation, each of which leads to specific products. The radical cation can either deprotonate, be nucleophilicly attacked by solvent, or lead to dimeric products. (orig.)

  1. 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...

  2. Molecular Choreography of Isomerization and Electron Transfer Using One and Two Dimensional Femtosecond Stimulated Raman Spectroscopy

    Hoffman, David Paul

    2014-01-01

    Chemical reactions are defined by the change in the relative positions and bonding of nuclei in molecules. I have used femtosecond stimulated Raman spectroscopy (FSRS) to probe these transformations with structural specificity and high time precision revealing the mechanisms of two important classes of reactions; isomerization about an N=N bond and interfacial/intermolecular electron transfer.Isomerization about a double bond is one of the simplest, yet most important, photochemical reactions...

  3. Absolute electron transfer efficiency of GEM

    We report on the absolute single-electron transfer efficiency of a Gas Electron Multiplier (GEM). It is shown that the electron transfer and thus the detection efficiency, depend not only on the GEM geometry and gain but mostly on the electric field and electron diffusion in the gas volume preceding the GEM. We have demonstrated that conditions can be found, including pre-amplification of the single electrons in the gap preceding the GEM, in which full detection efficiency is obtained. The experimental electron transfer efficiency results are confirmed by Monte Carlo simulations

  4. 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 to those of the reacting complex. However, at high temperatures, dissociation of the complex occurs, and the temperature dependence of the observed rate constants is affected also by the enthalpy of the hydrogen bond association. Finally, implications of this study for the mechanisms of enzyme proton transfers are discussed

  5. 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 equal to those of the reacting complex. However, at high temperatures, dissociation of the complex occurs, and the temperature dependence of the observed rate constants is affected also by the enthalpy of the hydrogen bond association. Finally, implications of this study for the mechanisms of enzyme proton transfers are discussed.

  6. Effects of electron coupling to intra- and inter-molecular vibrational modes on the transport properties of single crystal organic semiconductors

    Perroni, C. A.; Ramaglia, V. Marigliano; Cataudella, V.

    2011-01-01

    Electron coupling to intra- and inter-molecular vibrational modes is investigated in models appropriate to single crystal organic semiconductors, such as oligoacenes. Focus is on spectral and transport properties of these systems beyond perturbative approaches. The interplay between different couplings strongly affects the temperature band renormalization that is the result of a subtle equilibrium between opposite tendencies: band narrowing due to interaction with local modes, band widening d...

  7. Theory and assignment of intermolecular charge transfer states in squaraines and their impact on efficiency in bulk heterojunction solar cells (Presentation Recording)

    Collison, Christopher J.; Zheng, Chenyu; Hestand, Nicholas; Cona, Brandon; Penmetcha, Anirudh; Spencer, Susan; Cody, Jeremy; Spano, Frank

    2015-10-01

    Squaraines are targeted for organic photovoltaic devices because of their high extinction coefficients over a broad wavelength range from visible to near infra-red (NIR). Moreover, their side groups can be changed with profound effects upon their ability to crystallize, leading to improvements in charge mobility and exciton diffusion. The broadening in squaraine absorption is often qualitatively attributed to H- and J-aggregates based on the exciton model, proposed by Kasha. However, such assignment is misleading considering that spectral shifts can arise from sources other than excitonic coupling. Our group has shown that packing structure influences the rate of charge transfer; thus a complete and accurate reassessment of the excited states must be completed before the true charge transfer mechanism can be confirmed. In this work, we will show how squaraine H-aggregates can pack in complete vertical stacks or slipped vertical stacks depending upon sidegroups and processing conditions. Hence, we uncover the contribution of an intermolecular charge transfer (IMCT) state through essential states modeling validated by spectroscopic and X-Ray diffraction data. We further show external quantum efficiency data that describe the influence of the IMCT state on the efficiency of our devices. This comprehensive understanding of squaraine aggregates drives the development of more efficient organic photovoltaic devices, leading towards a prescription for derivatives that can be tailored for optimized exciton diffusion, charge transfer, higher mobilities and reduced recombination in small molecule OPV devices.

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

    Kyas, Gerold; May, Volkhard

    2011-01-21

    A microscopic theory of interacting molecule metal-nanoparticle (MNP) systems is presented and used to compute absorption spectra and the plasmon enhancement of intermolecular excitation energy transfer (EET). The approach is based on a nonperturbative consideration of the Coulomb coupling matrix elements responsible for EET between the molecules and the MNP. In this way, the need to determine the local fields induced by surface plasmon excitations of the MNP is removed, but the whole description is restricted to distances among the interacting species less than the wavelength of absorbed photons. Based on a density matrix theory, the approach accounts for the vibrational level structure of the molecules, intramolecular vibrational energy redistribution (IVR), and plasmon damping. Numerical results for linear absorbance spectra and EET dynamics are offered. In this respect the importance of energy dissipation in the MNP due to rapid surface plasmon decay is emphasized. PMID:21261378

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

    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.

  10. 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.

  11. Electron-electron Thomas peak in fast transfer ionization

    ''Thomas process'' is a name used for a family of singular two-step processes that can lead to electron transfer. The Thomas process of the ''second kind,'' occurring in reactions with both transfer and ionization, utilizes the e-e scattering in the second step, so this Thomas process requires the dynamics of the electron-electron interaction. We calculate numerically the second order element of an S matrix and corresponding cross sections for the transfer ionization process. We find that the position and shape of the Thomas peak depend on both electron-electron and the electron-nucleus interaction. Also the direct and exchange amplitudes are equal at the peak position. We test the peaking approximation used for transfer ionization. Our results can be compared to experimental results for p++He?H+He2++e-. (c) 2000 The American Physical Society

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

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

    2013-01-01

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

  13. 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.

  14. Biotechnological Aspects of Microbial Extracellular Electron Transfer

    Kato, Souichiro

    2015-01-01

    Extracellular electron transfer (EET) is a type of microbial respiration that enables electron transfer between microbial cells and extracellular solid materials, including naturally-occurring metal compounds and artificial electrodes. Microorganisms harboring EET abilities have received considerable attention for their various biotechnological applications, in addition to their contribution to global energy and material cycles. In this review, current knowledge on microbial EET and its appli...

  15. Electron Transfer for Large Molecules through Delocalization

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

    2012-01-01

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

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

    Raffalt, Anders Christer; Schmidt, L.; Christensen, Hans Erik Mølager; Chi, Qijin; Ulstrup, Jens

    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...

  17. 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.

  18. Quantifying electron transfer reactions in biological systems

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

    2015-01-01

    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...

  19. Medium effects in photoinduced electron transfer reactions

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

  20. 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.

  1. Electron transfer induced fragmentation of acetic acid

    We present negative ion formation driven by electron transfer in atom (K) molecule (acetic acid) collisions. Acetic acid has been found in the interstellar medium, is also considered a biological related compound and as such studying low energy electron interactions will bring new insights as far as induced chemistry is concerned.

  2. Single Molecule Spectroscopy of Electron Transfer

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

  3. Excited-state intermolecular proton transfer of the firefly's chromophore D-luciferin. 2. Water-methanol mixtures.

    Presiado, Itay; Erez, Yuval; Huppert, Dan

    2010-09-01

    Steady-state emission and time-resolved techniques were employed to study the photoprotolytic processes d-luciferin undergoes in water-methanol mixtures over a wide range of molar fractions (chi(MeOH)) of methanol. We found that in the concentration range of 0 0.8 the proton transfer rate constant decreases with an even steeper slope. The kinetic isotope effect (KIE) maintains a constant value of 2.4 +/- 0.2 at all the mixture's compositions. PMID:20704300

  4. 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

  5. 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

  6. Theory of Ultrafast Photoinduced Heterogeneous Electron Transfer

    May, Volkhard

    2006-01-01

    Abstract Ultrafast heterogeneous electron transfer (HET) between a molecule attached to a semiconductor surface and the conduction band of the semiconductor is discussed theoretically with emphasis on the perylene TiO_2 system. The used description accounts for the specialty of the molecule i.e. its particular electronic level scheme together with its vibrational degrees of freedom. The band continuum of the semiconductor is included and the approach is ready to describe different...

  7. 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...

  8. 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...

  9. Applications of free-electron lasers to measurements of energy transfer in biopolymers and materials

    Edwards, Glenn S.; Johnson, J. B.; Kozub, John A.; Tribble, Jerri A.; Wagner, Katrina

    1992-08-01

    Free-electron lasers (FELs) provide tunable, pulsed radiation in the infrared. Using the FEL as a pump beam, we are investigating the mechanisms for energy transfer between localized vibrational modes and between vibrational modes and lattice or phonon modes. Either a laser-Raman system or a Fourier transform infrared (FTIR) spectrometer will serve as the probe beam, with the attribute of placing the burden of detection on two conventional spectroscopic techniques that circumvent the limited response of infrared detectors. More specifically, the Raman effect inelastically shifts an exciting laser line, typically a visible frequency, by the energy of the vibrational mode; however, the shifted Raman lines also lie in the visible, allowing for detection with highly efficient visible detectors. With regards to FTIR spectroscopy, the multiplex advantage yields a distinct benefit for infrared detector response. Our group is investigating intramolecular and intermolecular energy transfer processes in both biopolymers and more traditional materials. For example, alkali halides contain a number of defect types that effectively transfer energy in an intermolecular process. Similarly, the functioning of biopolymers depends on efficient intramolecular energy transfer. Understanding these mechanisms will enhance our ability to modify biopolymers and materials with applications to biology, medecine, and materials science.

  10. 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

  11. 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

  12. Electron transfer and bond breaking: Recent advances

    After a reminder of concerted/stepwise mechanistic dichotomy and other basic concepts and facts in the field, a series of recent advances is discussed. Particular emphasis is laid on the interactions between the fragments formed upon bond cleavage. These interactions may persist even in polar solvents and have important consequences on dissociative electron transfer kinetics and on the competition between concerted and stepwise pathways. Cleavage of ion radicals and its reverse reaction are examples of single electron transfer reactions concerted with bond cleavage and bond formation, respectively. The case of aromatic carbon-heteroatom bonds is particularly worth examination since symmetry restrictions impose circumventing a conical intersection. Reductive dehalogenases are involved in 'dehalorespiration' of anaerobic bacteria in which the role of dioxygen in aerobic organisms is played by major polychloride pollutants such as tetrachloroethylene. They offer an interesting illustration of how the coupling of electron transfer with bond breaking may be an important issue in natural processes. Applications of dissociative electron transfer concepts and models to mechanistic analysis in this class of enzymes will be discussed

  13. Biotechnological Aspects of Microbial Extracellular Electron Transfer.

    Kato, Souichiro

    2015-01-01

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

  14. Electron Transfer Dissociation Mass Spectrometry in Proteomics

    Kim, Min-Sik; Pandey, Akhilesh

    2012-01-01

    Mass spectrometry has rapidly evolved to become the platform of choice for proteomic analysis. While CID remains the major fragmentation method for peptide sequencing, electron transfer dissociation (ETD) is emerging as a complementary method for characterization of peptides and post-translational modifications (PTMs). Here, we review the evolution of ETD and some of its newer applications including characterization of PTMs, non-tryptic peptides and intact proteins. We will also discuss some ...

  15. 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...

  16. Promoting Interspecies Electron Transfer with Biochar

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

    2014-01-01

    Biochar, a charcoal-like product of the incomplete combustion of organic materials, is an increasingly popular soil amendment designed to improve soil fertility. We investigated the possibility that biochar could promote direct interspecies electron transfer (DIET) in a manner similar to that previously reported for granular activated carbon (GAC). Although the biochars investigated were 1000 times less conductive than GAC, they stimulated DIET in co-cultures of Geobacter metallireducens with...

  17. Ab initio quantum chemical calculation of electron transfer matrix elements for large molecules

    Using a diabatic state formalism and pseudospectral numerical methods, we have developed an efficient ab initio quantum chemical approach to the calculation of electron transfer matrix elements for large molecules. The theory is developed at the Hartree endash Fock level and validated by comparison with results in the literature for small systems. As an example of the power of the method, we calculate the electronic coupling between two bacteriochlorophyll molecules in various intermolecular geometries. Only a single self-consistent field (SCF) calculation on each of the monomers is needed to generate coupling matrix elements for all of the molecular pairs. The largest calculations performed, utilizing 1778 basis functions, required ?14h on an IBM 390 workstation. This is considerably less cpu time than would be necessitated with a supermolecule adiabatic state calculation and a conventional electronic structure code. copyright 1997 American Institute of Physics

  18. Promoting interspecies electron transfer with biochar

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

    2014-01-01

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

  19. 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

  20. 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

  1. 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

  2. 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.

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

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

    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 ξ0 = ℏω0/k(B)T where ω0 is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (ξ0 hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode∕medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems. PMID:24359347

  4. Nonlinear quantum effects on electron transfer reactions

    Yoshimori, A.

    1995-03-01

    An approximate expression is developed for a nonadiabatic electron transfer rate to estimate quantum effects of nuclear rearrangements. The time-dependent formula for Fermi's golden rule is expanded by Plank's constant to the second order, using the Wigner transformation. The method of h̵- expansion is applicable to systems with nonlinear potentials or many degrees of freedom. Using a continuum approximation, from the expansion, a rate expression is obtained, including sizes of reactants and a distance between reactants explicitly. The ratio of the obtained rate to the classical rate agrees well with a ratio by a quantum Monte Carlo simulation.

  5. Double electron transfer in H- + H+ collisions

    Absolute cross sections for double electron transfer in H- + H+ collisions have been measured for center-of-mass energies from 0.5 keV to 12 keV. Clear oscillations in the cross section are observed which are in excellent agreement with earlier measurements at lower energies by Brouillard et al (1979) as well as Peart and Dolder (1979). After an oscillation maximum at 3 keV center-of-mass energy the cross section decreases for increasing energy with no indication of further oscillations

  6. Double electron transfer in H- + H+ collisions

    Bruning, H.; Helm, H.; Briggs, J. S.

    2007-11-01

    Absolute cross sections for double electron transfer in H- + H+ collisions have been measured for center-of-mass energies from 0.5 keV to 12 keV. Clear oscillations in the cross section are observed which are in excellent agreement with earlier measurements at lower energies by Brouillard et al (1979) as well as Peart and Dolder (1979). After an oscillation maximum at 3 keV center-of-mass energy the cross section decreases for increasing energy with no indication of further oscillations.

  7. Computational Approach to Electron Charge Transfer Reactions

    Jónsson, Elvar Örn

    account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems to...... 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...... structure modes. This is for a large iridium-iridium dimer complex which shows a dramatic structural (and vibrational) change upon electronic excitation....

  8. 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

  9. 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...... embedding model has been suggested (C. Curutchet, A. Muoz-Losa, S. Monti, J. Kongsted, G. D. Scholes, and B. Mennucci, J. Chem. Theory Comput., 2009 5 (7), 1838-1848). In this work, we further develop this computational model by extending it with an ab initio derived polarizable force field including...

  10. Electron transfer pathways in microbial oxygen biocathodes

    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 O2 reduction by heme compounds. Here we showed that 1 μM 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 O2 reduction to H2O2 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.

  11. Mediated Electron Transfer at Redox Active Monolayers

    Michael E.G. Lyons

    2001-12-01

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

  12. 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.

  13. Electronic excitation transfer in concentrated micelle solutions

    Electronic excitation transport among interacting clusters of chromophores is investigated as a function of chromophores is investigated as a function of chromophore and cluster concentration. The technique of time-correlated single photon counting is employed to obtain time-resolved fluorescence depolarization data on aqueous octadecylrhodamine B/triton X-100 micelle solutions. The time-dependent fluorescence anisotropy, the energy transport observable, is directly compared to a theory developed to model this system. The theory is based on a first-order cumulant approximation to the solution of the transport master equation. The model depicts the micelles as monodisperse hard spheres with chromophores (octadecylrhodamine B) distributed about their surfaces. At low micelle concentration, the dynamics of excitation transfer depend only on internal micelle structure. At high micelle concentration excitation transfer occurs among chromophores on different micelles in addition to intramicelle transfer. The theoretical treatment provides nearly quantitative descriptions of the time and concentration dependence of the excitation transport. It correctly predicts the concentration at which intermicelle transfer becomes significant. In the low micelle concentration limit (energy transport confined to isolated micelles) the model having a Poisson distribution of chromophores works well for small ? ([chromophores]/[micelle]), but progressively worse as ? is increased. Following the literature, a chromophere interaction parameter (in the form of a two dimensional second virial coefficient) is used to skew the probe distribution. This enables the transport theory to reproduce the data for all the values of ? investigated and provides a determination of the second virial coefficient. 34 refs., 4 figs., 2 tabs

  14. Electron-gas plus damped-dispersion model for intermolecular forces: the rare-gas and H2-He, H2-Ne, and H2-Ar potentials

    The modified Gordon-Kim (MGK) electron-gas model for the calculation of the short-range repulsive interactions between closed-shell atoms and molecules is used with a damped-dispersion term of a form suggested by Hepburn et al. to calculate the intermolecular potentials between the rare-gas atoms and H2-He, H2-Ne, and H2-Ar. The damping function for the dispersion energies is found by comparison with the experimental Ar-Ar potential and is then used without change for all other interactions. Except for interactions involving Ne atoms, the results for the atom-atom interactions are uniformly quite good, with an average deviation from experiment in the position of the minimum (neglecting those involving Ne atoms) of only 0.7%. Both the radical V0(r) and anisotropic V2(r) terms of the atom-molecule results are compared with experiment. The calculated V0(r) potentials for He-H2 and Ar-H2 show close agreement with experiment, though the V2 terms are less well determined. All interactions involving Ne atoms are too repulsive. The errors in the potentials involving Ne atoms are attributed to errors in the treatment of the exchange energy in the MGK model. 29 references, 11 figures, 5 tables

  15. 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.)

  16. Short range photoinduced electron transfer in proteins: QM-MM simulations of tryptophan and flavin fluorescence quenching in proteins

    Hybrid quantum mechanical-molecular mechanics (dynamics) were performed on flavin reductase (Fre) and flavodoxin reductase (Fdr), both from Escherichia coli. Each was complexed with riboflavin (Rbf) or flavin mononucleotide (FMN). During 50 ps trajectories, the relative energies of the fluorescing state (S1) of the isoalloxazine ring and the lowest charge transfer state (CT) were assessed to aid prediction of fluorescence lifetimes that are shortened due to quenching by electron transfer from tyrosine. The simulations for the four cases display a wide range in CT-S1 energy gap caused by the presence of phosphate, other charged and polar residues, water, and by intermolecular separation between donor and acceptor. This suggests that the Gibbs energy change (?G 0) and reorganization energy (?) for the electron transfer may differ in different flavoproteins

  17. 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 treated.Chapter 2 discusses present theories of photoinduced electron transfer. The following factors appear to effect the electron transfer rate constants:- donor-acceptor distance- nature of the linkin...

  18. 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...

  19. GPU-accelerated computation of electron transfer.

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

    2012-11-01

    Electron transfer is a fundamental process that can be studied with the help of computer simulation. The underlying quantum mechanical description renders the problem a computationally intensive application. In this study, we probe the graphics processing unit (GPU) for suitability to this type of problem. Time-critical components are identified via profiling of an existing implementation and several different variants are tested involving the GPU at increasing levels of abstraction. A publicly available library supporting basic linear algebra operations on the GPU turns out to accelerate the computation approximately 50-fold with minor dependence on actual problem size. The performance gain does not compromise numerical accuracy and is of significant value for practical purposes. PMID:22847673

  20. Theory of plasmon enhanced interfacial electron transfer

    Wang, Luxia; May, Volkhard

    2015-04-01

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

  1. Electron-phonon interactions, pair-transfer processes, and superconductivity in TTF[Ni(dmit){sub 2}]{sub 2}

    Ramakumar, R.; Tanaka, Y.; Yamaji, K. [Electrotechnical Laboratory, 1-1-4 Umezono, Tsukuba, Ibaraki 305 (Japan)

    1997-07-01

    A model is developed for superconductivity in TTF[Ni(dmit){sub 2}]{sub 2}. We include both electron-{ital intra}molecular and -{ital inter}molecular vibration couplings. These interactions are the principal sources of superconducting pairing. The electron-{ital intra}molecular vibration coupling constants are estimated after performing a complete normal-mode analysis. The electron-{ital inter}molecular vibration coupling constants are also estimated. The unique band structure of this material [with both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) derived bands crossing the Fermi level] leads to a pair-transfer term between the bands. Estimates for T{sub c} are in reasonable agreement with experimental results. We find that major contribution to the electron-phonon interaction, in this material, comes to the LUMO band from acoustic phonons and pair transfer processes reduce the effects of the intraband Coulomb repulsion. {copyright} {ital 1997} {ital The American Physical Society}

  2. Reactions involving electron transfer at semiconductor surfaces

    Rapid isotopic equilibration was observed upon contacting an equimolar mixture of (16O2 + 18O2) at 295 or 77 K with oxygen-deficient surfaces of pure and doped zinc oxides from which light was excluded at all stages. Kinetic expressions for opposing second-order reactions accurately described variations in mole fraction of 16O2, 16O18O and 18O2 in the gas phase during the approach to full isotopic equilibration at 295 or 77 K. Rate constants thereby derived for this R0-type exchange did not correlate with reported concentrations of conduction-band electrons for the zinc oxides, indicating that the rate-determining process for exchange was not collective-electron type charge transfer at the oxygen-deficient surfaces in the absence of illumination. Surfaces could be rendered inactive by extensive preoxidation in 16O2 at 650 K in the dark, but heating for 2 h periods in the dark under continuous evacuation restored activity to a progressively increasing extent at temperatures of 400 to 650 K. Preadsorption of H2O, H2 or (CH3)2CHOH at 295 K strongly inhibited activity. An explanation of the observed results is developed. (author)

  3. Electron transfer processes in photosynthetics biological systems

    This seminar presents a conceptual model of the sequence of primary light induced electron transfer (ET) steps in photosynthetic bacteria. The temperature dependence of some of these redox reactions, like ET process between cytochrome and bacteriochlorophyll in Chromatium, is characterized by a temperature-independent rate at low temperatures and exhibits the Arrhenius-type dependence at high temperatures. The other primary ET processes, like an ET reaction between bacteriopheophytin and Fe-quinone complex in Rps. spheroides, are temperature-independent in the broad range of 4-300K. The third type of ET processes, exemplified by back ET reactions between Fe-quinone and bacteriochlorophyll in Rhs. rubrum, exhibits negative activation energy at high temperatures. The theoretical approach, describing the primary ET processes in photosynthesis, is based on the non-adiabatic multiphonon ET theory, which incorporates both a continuous distribution of optical phonons in a polar solvent and discrete intramolecular vibrational modes. The last two types of the redox reactions are attributed to activationless ET processes which play an essential role in highly efficient charge separation in primary photosynthetic processes. The transition temperature, separating the tunneling region from the activated region indicates the range of phonon frequencies involved in the ET process. Comparing the low-temperature rates with calculated Franck-Condon factors one can determine the value of the electron-exchange matrix element, which in turn provides a rough estimate of the distance scale between a donor and an acceptor in the primary ET events

  4. Photoreduction of polyhalogenated anthraquinones by direct electron transfer from alcohol

    Inoue, Haruo; Ikeda, Kenji; Mihara, Hayao; Hida, Mitsuhiko

    1983-02-01

    Polyhalogenated anthraquinones such as perfluoroanthraquinone, 1,2,3,4-tetrafluoroanthraquinone, and 1,2,3,4-tetrachloroanthraquinone are photoreduced in ethanol via direct electron transfer from ethanol. A dramatic switch-over from hydrogen-atom abstraction to electron transfer is induced by mixing of?? with n? * states in their T 1 state and the enhanced electron-accepting character of polyhalogenated anthraquinones.

  5. Electronic and Nuclear Factors in Charge and Excitation Transfer

    Piotr Piotrowiak

    2004-09-28

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

  6. Soliton-like Solutions and Electron Transfer in DNA

    Lakhno, V. D.

    2000-01-01

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

  7. Transcriptomic and genetic analysis of direct interspecies electron transfer

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

    2013-01-01

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

  8. 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......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...

  9. Electrons cross transfer in multislit electromagnetic trap 'Jupiter 2M'

    The researches of cross electrons transfer in the central and parts of a trap are carried out. It is shown, that increased electrons transfer in a face part is connected to presence here toroidal area of the superseded magnetic field. The change of a magnetic configuration has resulted in reduction of a cross electrons transfer in a face part, increase of density and negative potential of plasma

  10. Disorder and intermolecular interactions in a family of tetranuclear Ni(II) complexes probed by high-frequency electron paramagnetic resonance.

    Lawrence, Jon; Yang, En-Che; Edwards, Rachel; Olmstead, Marilyn M; Ramsey, Chris; Dalal, Naresh S; Gantzel, Peter K; Hill, Stephen; Hendrickson, David N

    2008-03-17

    High-frequency electron paramagnetic resonance (HFEPR) data are presented for four closely related tetranuclear Ni(II) complexes, [Ni(hmp)(MeOH)Cl]4.H2O (1a), [Ni(hmp)(MeOH)Br]4.H2O (1b), [Ni(hmp)(EtOH)Cl]4.H2O (2), and [Ni(hmp)(dmb)Cl]4 (3) (where hmp(-) is the anion of 2-hydroxymethylpyridine and dmb is 3,3'-dimethyl-1-butanol), which exhibit magnetic bistability (hysteresis) and fast magnetization tunneling at low temperatures, properties which suggest they are single-molecule magnets (SMMs). The HFEPR spectra confirm spin S = 4 ground states and dominant uniaxial anisotropy (DSz(2), D ZFS) parameters. The broad EPR lines, meanwhile, may be attributed to ligand and solvent disorder, which results in additional distributions of microenvironments. In the case of complex 3, there are no solvate molecules in the structure, and only one distinct Ni 4 molecule in the lattice. Consequently, the HFEPR data for complex 3 are extremely sharp. As the temperature of a crystal of complex 3 is decreased, the HFEPR spectrum splits abruptly at approximately 46 K into two patterns with very slightly different ZFS parameters. Heat capacity data suggest that this is caused by a structural transition at 46.6 K. A single-crystal X-ray structure at 12(2) K indicates large thermal parameters on the terminal methyl groups of the dmb (3,3-dimethyl-1-butanol) ligand. Most likely there exists dynamic disorder of parts of the dmb ligand above 46.6 K; an order-disorder structural phase transition at 46.6 K then removes some of the motion. A further decrease in temperature (<6 K) leads to further fine structure splittings for complex 3. This behavior is thought to be due to the onset of short-range magnetic correlations/coherences between molecules caused by weak intermolecular magnetic exchange interactions. PMID:18284196

  11. Proton coupled electron transfer tunneling reactions in WO3 and MoO3 nanostructured films

    Gavrilyuk, A. I.

    2007-12-01

    WO3 and MoO3 are famous hydrogenphilics, hydrogen loving materials, capable of performing various functions concerning atomic hydrogen. They are active catalysts in photochemical reactions connected with detachment of hydrogen atoms, being, at the same time, capable of accomodating great quantities of the detached hydrogen atoms, and transporting them to other functional materials via employment of various heterostructures. It was shown that tunneling proton-coupled electron transfer is the mechanism of the photochemical hydrogen abstraction reaction on the surface of highly disordered nanostructured WO3 and MoO3 thin films. Specially selected hydrogen donor molecules were adsorbed on the oxide surface bonding via donor-acceptor and hydrogen bonds which yield a decrease in the energy barrier for the hydrogen transfer from the adsorbed hydrogen donor molecule to the oxide surface. The very rough and heterogeneous film surface yields space fluctuations of the energy barrier parameters whereas intermolecular vibrations yield time fluctuations; the fluctuative barrier preparation being responsible for the tunneling photo-stimulated proton-coupled electron transfer.

  12. Oxide/Electrolyte interface: Electron transfer phenomena

    Fernndez-Ibez, P.

    2000-08-01

    Full Text Available Electron transfer on a titanium dioxide/electrolyte solution interface has been studied. As observed by other researchers on similar interfaces (TiO2- and ZnO- electrolyte solution, slow consumption of OH- ions was found. A theoretical model has been developed for calculating the change in Fermi energy levels of both electrolyte solution and semiconductor, showing that ion consumption from the solution is favoured by a decreased difference in their Fermi energies. A kinetic constant (? is found to characterise the consumption process, its value increasing with electrolyte and semiconductor mass concentrations. Furthermore, this process may be used to estimate the point of zero charge of a titanium dioxide colloidal dispersion.

    En este trabajo se ha estudiado un proceso de transferencia de electrones en la interfase dixido de titanio/electrolito acuoso. Tal y como han observado otros investigadores en interfases similares (TiO2- y ZnO- electrolito, se ha detectado un consumo lento de iones OH-. Para dar explicacin a este proceso, se ha desarrollado un modelo terico basado en el clculo de las energas de Fermi en el semiconductor y en el electrolito. De este modo, se demuestra que dicho consumo de iones est favorecido por una disminucin de la diferencia entre ambos niveles de Fermi. Para caracterizar el proceso de consumo lento de OH- se define una constante cintica (?, cuyo valor aumenta a medida que crece la concentracin msica de semiconductor y de electrolito en la suspensin. Adicionalmente, este fenmeno proporciona una herramienta para determinar experimentalmente el punto de carga nula de la suspensin de dixido de titanio en el medio acuoso.

  13. Electron Transfer Dissociation of Milk Oligosaccharides

    Han, Liang; Costello, Catherine E.

    2011-06-01

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

  14. Quantum coherent contributions in biological electron transfer

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

    2011-01-01

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

  15. Activation entropy of electron transfer reactions

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

    2006-05-01

    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 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.

  16. 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

  17. Photoinduced electron transfer reaction in diaminostilbene-tethered DNA duplexes.

    Ito, Takeo; Hayashi, Aiko; Uchida, Tsukasa; Tanabe, Kazuhito; Yamada, Hisatsugu; Nishimoto, Sei-Ichi

    2009-01-01

    DNA duplexes containing diaminostilbene (DAS) as a photoinduced electron donor were synthesized to investigate mechanisms of electron injection into DNA and the succeeding electron transfer in the duplexes. DAS-Capped hairpin DNA showed a high structural stability thereby attains large interaction between DAS and the terminal base pair. DAS-Tethered DNA by a single linker at the end of the duplex was also synthesized and the yields of photoinduced electron transfer through mismatched base pairs were quantified. Both duplexes showed similar electron transfer efficiencies depending on the base pairs, which suggests DAS stacks well on the "pi-way" of the duplex DNA. PMID:19749330

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

    The thermodynamic stability of the mixed valence (one electron reduced) state between linked Ru3 units was studied by means of electrochemical methods for the series of the ligand-bridged triruthenium cluster dimer, [Ru3(μ3-O)(μ-CH3CO2)6(CO)(L)(μ-BL)Ru3(μ3-O)(μ-CH3CO2)6(CO)(L)] (BL = 1,4 pyrazine: L = 4-dimethylaminopyridine (dmap) (1a), pyridine (py) (1b), 4-cyanopyridine (cpy) (1c), 1-azabicyclo[2.2.2]octane (1d); BL = 4,4'-bipyridine: L= dmap (2a), py(2b), cpy (2c); BL 2,7-diazapyrene; L = dmap (3a); BL = 1,4-diazabicyclo[2.2.2]octane: L = dmap (4a), py(4b), cpy (4c). The mixed valence states undergoing rapid intermolecular electron transfers were observed by IR spectro-electrochemistry. By simulating dynamical effects on the observed ν(CO) absorption band shapes, the rate constants ke for electron transfer in the mixed valence states of 1a, 1b, 1c and 1d were estimated to be 9x1011 s-1 (at room temperature (rt)), 5x1011 s-1 (at rt), ca. 1x1011 s-1 (at rt), and 1x1012 s-1 (at -18 oC), respectively. Possible applications of this approach to asymmetric mixed valence systems were discussed. (author)

  19. 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...

  20. Probing active electron transfer branch in photosystem I reaction center.

    Savikhin, Sergei; Dashdorj, Naranbaatar; Xu, Wu; Martinsson, Peter; Chitnis, Parag

    2003-03-01

    Complimentary point mutations were introduced at the primary electron acceptor sites in A and B branches of the photosystem I (PS I) reaction center (RC) from Synechocystis sp. PCC 6803 and their effect on the kinetics of the electron transfer process was studied by means of ultrafast pump-probe spectroscopy. The results indicate that in these species the electron transfer occurs primarily along the A-branch. Previous optical experiments on PS I complexes from Chlorella sorokiniana demonstrated that both branches of RC are equally active. That suggests that the directionality of electron transfer in PS I is species dependent.

  1. Electron transfer in organic glass. Distance and energy dependence

    The authors have investigated the distance and energy dependence of electron transfer in rigid organic glasses containing randomly dispersed electron donor and electron acceptor molecules. Pulsed radiolysis by an electron beam from a linear accelerator was used for ionization resulting in charge deposition on donor molecules. The disappearance kinetics of donor radical anions due to electron transfer to acceptor was monitored spectroscopically by the change in optical density at the wavelength corresponding to that of donor radical anion absorbance. It was found that the rate of the electron transfer observed experimentally was higher than that computed using the Marcus-Levich theory assuming that the electron-transfer activation barrier is equal to the binding energy of electron on the donor molecule. This discrepancy between the experimental and computed results suggests that the open-quotes inertclose quotes media in which electron-transfer reaction takes place may be participating in the process, resulting in experimentally observed higher electron-transfer rates. 32 refs., 3 figs., 2 tabs

  2. 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.... Thus, consumers could benefit from consistent, accessible disclosures regarding remittance transfers... approximate fees and exchange rates. When asked about the usefulness of a storefront sign showing how much...

  3. Electronic Publishing and the Information Transfer Process.

    Aveney, Brian

    1983-01-01

    Discusses new information forms that promise to force changes in the information transfer process which is based on the organization, storage, and distribution of edition printed products. Roles of authors, publishers, jobbers, librarians, and users in the information transfer process are highlighted. (EJS)

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

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

  5. Electron Transfer Rate Maxima at Large Donor-Acceptor Distances.

    Kuss-Petermann, Martin; Wenger, Oliver S

    2016-02-01

    Because of their low mass, electrons can transfer rapidly over long (>15 Å) distances, but usually reaction rates decrease with increasing donor-acceptor distance. We report here on electron transfer rate maxima at donor-acceptor separations of 30.6 Å, observed for thermal electron transfer between an anthraquinone radical anion and a triarylamine radical cation in three homologous series of rigid-rod-like donor-photosensitizer-acceptor triads with p-xylene bridges. Our experimental observations can be explained by a weak distance dependence of electronic donor-acceptor coupling combined with a strong increase of the (outer-sphere) reorganization energy with increasing distance, as predicted by electron transfer theory more than 30 years ago. The observed effect has important consequences for light-to-chemical energy conversion. PMID:26800279

  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. Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics

    Jin, Shengye; Hsiang, Jung-Cheng; Zhu, Haiming; Song, Nianhui; Dickson, Robert M.; Lian, Tianquan

    2010-01-01

    The electron transfer (ET) dynamics from core/multi-shell (CdSe/CdS3MLZnCdS2MLZnS2ML) quantum dots (QDs) to adsorbed Fluorescein (F27) molecules have been studied by single particle spectroscopy to probe the relationship between single QD interfacial electron transfer and blinking dynamics. Electron transfer from the QD to F27 and the subsequent recombination were directly observed by ensemble-averaged transient absorption spectroscopy. Single QD-F27 complexes show correlated fluctuation of f...

  8. Intermolecular electrostatic energies using density fitting.

    Cisneros, G Andrs; Piquemal, Jean-Philip; Darden, Thomas A

    2005-07-22

    A method is presented to calculate the electron-electron and nuclear-electron intermolecular Coulomb interaction energy between two molecules by separately fitting the unperturbed molecular electron density of each monomer. This method is based on the variational Coulomb fitting method which relies on the expansion of the ab initio molecular electron density in site-centered auxiliary basis sets. By expanding the electron density of each monomer in this way the integral expressions for the intermolecular electrostatic calculations are simplified, lowering the operation count as well as the memory usage. Furthermore, this method allows the calculation of intermolecular Coulomb interactions with any level of theory from which a one-electron density matrix can be obtained. Our implementation is initially tested by calculating molecular properties with the density fitting method using three different auxiliary basis sets and comparing them to results obtained from ab initio calculations. These properties include dipoles for a series of molecules, as well as the molecular electrostatic potential and electric field for water. Subsequently, the intermolecular electrostatic energy is tested by calculating ten stationary points on the water dimer potential-energy surface. Results are presented for electron densities obtained at four different levels of theory using two different basis sets, fitted with three auxiliary basis sets. Additionally, a one-dimensional electrostatic energy surface scan is performed for four different systems (H2O dimer, Mg2+-H2O, Cu+-H2O, and n-methyl-formamide dimer). Our results show a very good agreement with ab initio calculations for all properties as well as interaction energies. PMID:16095348

  9. 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

  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. A tubular view of electron transfer in azurin

    A new theoretical approach emphasizes tubes (tightly grouped families of pathways) for electron transfer and looks for interaction between these families rather than focussing on individual paths. in some cases, for a given donor D and acceptor A, the electron transfer can be thought of as pathway-like wherein the protein bridge can be physically reduced to a tube without changing the overall coupling. In other cases, the transfer is characterized by multiple tubes which can interfere with one another, and a single path assumption will fail to identify all of the structural elements which control the coupling. Reducing the protein to only the relevant parts (tubes) that mediate the tunneling matrix element is a useful tool for understanding electron transfer in biological medium. An example is carried out on blue copper protein azurin that plays an important role as an electron carrier in biological systems. (N.T.)

  12. Theoretical aspects of electron transfer reactions of complex molecules

    Kuznetsov, A. M.; Ulstrup, Jens

    Features of electron transfer involving complex molecules are discussed. This notion presently refers to molecular reactants where charge transfer is accompanied by large molecular reorganization, and commonly used displaced harmonic oscillator models do not apply. It is shown that comprehensive...... theory of charge transfer in polar media offers convenient tools for the treatment of experimental data for such systems, with due account of large-amplitude strongly anharmonic intramolecular reorganization. Equations for the activation barrier and free energy relationships are provided, incorporating...

  13. Interfacial Electron Transfer into Functionalized Crystalline Polyoxotitanate Nanoclusters

    Snoeberger, Robert C.; Young, Karin J.; Tang, Jiji; Allen, Laura J.; Crabtree, Robert H.; Brudvig, Gary W.; Coppens, Philip; Batista, Victor S.; Jason B. Benedict

    2012-01-01

    Interfacial electron transfer (IET) between a chromophore and a semi-conductor nanoparticle is one of the key processes in a dye sensitized solar cell. Theoretical simulations of the electron transfer in polyoxotitanate nanoclusters Ti17O24(OPri)20 (Ti17) functionalized with four para-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established by X-ray diffraction measurements, are presented. Complementary experimental information showing IET has bee...

  14. Nuclear interlevel transfer driven by electronic transitions

    We show how a gamma-ray laser might be made by optically exciting a transfer of population from a long-lived isomer to an energetically adjacent short-lived state of the same nucleus. We compare the advantages of using transitions of high multipolarity versus transitions of low multi-polarity. Preliminary numerical investigations of the mechanism show it to be somewhat favorable. 35 refs., 4 figs

  15. Laser pulse control of bridge mediated heterogeneous electron transfer

    Ultrafast heterogeneous electron transfer from surface attached dye molecules into semiconductor band states is analyzed. The focus is on systems where the dye is separated from the surface by different bridge anchor groups. To simulate the full quantum dynamics of the transfer process a model of reduced dimensionality is used. It comprises the electronic levels of the dye, the bridge anchor group electronic levels and the continuum of semiconductor band states, all defined versus a single intramolecular vibrational coordinate. The effect of the bridge states is demonstrated, firstly, in studying the injection dynamics following an impulsive excitation of the dye. Then, by discussing different control tasks it is demonstrate in which way the charge injection process can be influenced by tailored laser pulses. To highlight the importance of electron wave function interference emphasis is put on asymmetric two-bridge molecule systems which are also characterized by different and complex valued electronic transfer matrix elements.

  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. Electron transfer reactions in microporous solids

    Mallouk, T.E.

    1993-01-01

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

  18. Electron and proton transfer in chemistry and biology

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

  19. Desensitization of metastable intermolecular composites

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

    2011-04-26

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

  20. 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.

  1. Hydrogen diffusion and radiationless electron transfer in metal hydrides

    The activation energies of the radiationless electron transfer are calculated from the optical spectra of some Sc, Y, La, Lu, Nb, Pd, and Mg2Ni hydrides. These are practically the same with the values of the activation energies for hydrogen diffusion, pointing out to the importance of electron transfer from localized states to the conduction band in the mechanism of hydrogen diffusion. The exponential temperature dependence of the radiationless electron transfer probability together with vibrational tunneling at low temperatures can account for the temperature dependence of H diffusion in the entire temperature range. A comparison between the electronic structures of NiH and PdH qualitatively explains the higher activation energy of H diffusion in Ni. Isotopic effects in Pd hydrides and a treatment based on Frenkel defects also support the proposed model. (author)

  2. 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

  3. Theory of electron transfer in ion-atom collisions

    Current development of the theory of electron transfer in ion-atom collisions is summarized. Preliminary results indicate that K-K capture cross sections at lower energies are sensitive to the proper treatment of the atomic model. It was shown that electron capture from outer shells of multielectron atoms can be calculated using the present method, in conjunction with the simple independent electron model. Some recent research is summarized. 8 references

  4. Correlated ab initio investigations on the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O2(-)(X2?g)-HF(X1?+) complex.

    Fawzy, Wafaa M; Elsayed, Mahmoud; Zhang, Yuchen

    2013-01-01

    This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O(2)(-)(X(2)?(g))-HF(X(1)?(+)) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2-5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and C(s) symmetry along the A" surface of the complex, whereas the A' surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-D(e)) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 , with elongation of the HF bond distance in the complex by 0.133 , and D(e) value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C(2v) symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm(-1). The calculated harmonic oscillator vibrational frequencies showed that the H-F stretch vibrational transition in the complex is redshifted by 2564 cm(-1) and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the O(2)(-)-HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer. PMID:23298038

  5. 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

  6. Electronic Mechanisms of Intra and Intermolecular J Couplings in Systems with C-H···O Interactions

    Claudio N. Cavasotto

    2003-04-01

    Full Text Available Abstract: Correlation effects on the change of 1J(CH couplings in model systems I:NCH...H2O and II:CH4...H2O as a function of the H...O distance are discussed. RPA and SOPPA results follow a similar trend in system II. In system I RPA values decrease monotonously as the H...O distance decreases, while SOPPA ones exhibit flat maximum near equilibrium. Such different behavior is ascribed to the π-transmitted component. Intermolecular couplings at the equilibrium geometry of I are analyzed by means of the CLOPPA approach. The larger absolute value of 2hJ(CO compared to 1hJ(HO is found to arise from contributions involving a vacant LMO localized in the C-H...O moiety.

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

    PravinMallaShrestha

    2014-05-01

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

  8. [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

  9. 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

    The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl{sub 4} and CF{sub 4}. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypical Ng-CCl{sub 4} and Ng-CF{sub 4} and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF{sub 4}, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl{sub 4}, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential suggested by the analysis of the experiments actually reflect two chemically meaningful contributions, namely, a stabilizing interaction arising from the anisotropy of the charge distribution around the Cl atom in 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.

  10. 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

    The systems studied in this work are gas-phase weakly bound adducts of the noble-gas (Ng) atoms with CCl4 and CF4. Their investigation was motivated by the widespread current interest for the intermolecular halogen bonding (XB), a structural motif recognized to play a role in fields ranging from elementary processes to biochemistry. The simulation of the static and dynamic behaviors of complex systems featuring XB requires the formulation of reliable and accurate model potentials, whose development relies on the detailed characterization of strength and nature of the interactions occurring in simple exemplary halogenated systems. We thus selected the prototypical Ng-CCl4 and Ng-CF4 and performed high-resolution molecular beam scattering experiments to measure the absolute scale of their intermolecular potentials, with high sensitivity. In general, we expected to probe typical van der Waals interactions, consisting of a combination of size (exchange) repulsion with dispersion/induction attraction. For the He/Ne-CF4, the analysis of the glory quantum interference pattern, observable in the velocity dependence of the integral cross section, confirmed indeed this expectation. On the other hand, for the He/Ne/Ar-CCl4, the scattering data unravelled much deeper potential wells, particularly for certain configurations of the interacting partners. The experimental data can be properly reproduced only including a shifting of the repulsive wall at shorter distances, accompanied by an increased role of the dispersion attraction, and an additional short-range stabilization component. To put these findings on a firmer ground, we performed, for selected geometries of the interacting complexes, accurate theoretical calculations aimed to evaluate the intermolecular interaction and the effects of the complex formation on the electron charge density of the constituting moieties. It was thus ascertained that the adjustments of the potential suggested by the analysis of the experiments actually reflect two chemically meaningful contributions, namely, a stabilizing interaction arising from the anisotropy of the charge distribution around the Cl atom in CCl4 and a stereospecific electron transfer that occurs at the intermolecular distances mainly probed by the experiments. Our model calculations suggest that the largest effect is for the vertex geometry of CCl4 while other geometries appear to play a minor to negligible role. PMID:25978888

  11. 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

    2015-05-01

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

  12. 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-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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr04942c

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

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

    2009-01-01

    Interspecies electron transfer is a key process in methanogenic and sulphate-reducing environments. Bacteria and archaea that live in syntrophic communities take advantage of the metabolic abilities of their syntrophic partner to overcome energy barriers and break down compounds that they cannot digest by themselves. Here, we review the transfer of hydrogen and formate between bacteria and archaea that helps to sustain growth in syntrophic methanogenic communities. We also describe the proces...

  14. Electron transfer statistics and thermal fluctuations in molecular junctions

    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

  15. Coherent single-electron transfer in coupled quantum dots

    Fountoulakis, Antonios; Terzis, Andreas F.; Paspalakis, Emmanuel

    2009-10-01

    We theoretically investigate the coherent transfer of one electron between the ground states of a double coupled quantum dot structure. The coherent transfer of the electron is externally controlled by applied electromagnetic fields with on- or close-resonance driving frequencies and various shapes and duration. We derive the analytical expressions for the parameters of the external fields by approximating the quantum dot system as a three-level ?-type system. The analytical solutions are compared with numerical results and good agreement is found. The control methods developed here are applicable in symmetric and asymmetric quantum dot nanostructures.

  16. 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.

  17. Marcus Electron Transfer Reactions with Bulk Metallic Catalysis

    Widom, A; Srivastava, Y N

    2015-01-01

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

  18. 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.

  19. Theory of the Control of Ultrafast Interfacial Electron Transfer

    Rasmussen, Andrew Musso

    This dissertation describes the theoretial exploration of electron transfer (ET) processes at the interface between bulk and molecular or nanoscale materials. Analysis of simple model Hamiltonians, those for the two- and three-level electronic systems as well as for a single electronic level coupled to a continuum, inform an understanding of electron transfer in nontrivial systems. A new treatment of the three-level system at an undergraduate level encapsulates the hopping and superexchange mechanisms of electron transfer. The elegance of the behavior of ET from a single-level/continuum system precedes a treatment of the reverse process---quasicontinuum-to-discrete level ET. This reverse process, relevant to ET from a bulk material to a semiconductor quantum dot (QD) offers a handle for the coherent control of ET at an interface: the shape of an electronic wavepacket within the quasicontinuum. An extension of the single-level-to-continuum ET process is the injection of an electron from a QD to a wide-bandgap semiconductor nanoparticle (NP). We construct a minimal model to explain trends in ET rates at the QD/NP interface as a function of QD size. Finally, we propose a scheme to gate ET through a molecular junction via the coherent control of the torsional mode(s) of a linking molecule within the junction.

  20. Kinetics and mechanisms of photoinduced electron-transfer reaction of zinc myoglobin

    Photoinduced electron transfer (ET) between zinc myoglobin (ZnPPMb) and a variety of quenchers, such as hexacyanoferrate(III)([Fe(CN)6]3-) and hexaammineruthenium(III)(Ru(NH3)6]3+ ions, cationic viologens, copper(II) protein (stellacyanin), and metmyoglobins, has been studied in aqueous degassed solutions. The excited triplet state of ZnPPMb(*ZnPPMb) was quenched by [Fe(CN)6]3- in a self-associated complex. Both quenching rate constant and formation constant of the self-associated complex decrease with increasing ionic strengths. The thermal backward ET reaction for this system was not observed; it is most likely that the backward ET step is much faster than the quenching reaction. All of the cationic quenchers examined in this work did not form a self-associated complex with *ZnPPMb, and the intermolecular quenching occurred. The thermal backward ET reaction was observed for these cationic quenchers. Not only photoinduced ET but also thermal backward ET reactions were insensitive to the driving force of the reactions, suggesting that the reactions are controlled by conformational changes in ZnPPMb. The quenching rate constants increase with increasing ionic strength for the cationic quenchers. The effects of poly-L-lysine hydrochloride, sodium poly-L-glutamate, and sodium cyclo-hexaphosphate were also examined. The active site of the *ZnPPMb toward both anionic and cationic quenchers is assumed to be the positively charged site near the heme pocket. (author)

  1. Quality assurance and data collection -- Electronic Data Transfer

    The Radiological Environmental Monitoring (REM) group at the Fernald Environmental Management Project is involved in an Electronic Data Transfer practice that will result in the improved quality assurance of collected data. This practice focuses on electronic data transfer from the recording instrument to reduce the manpower normally required for manual data entry and improve the quality of the data transferred. The application of this practice can enhance any data collection program where instruments with electronic memories and a signal output are utilized. Organizations employing this practice can strengthen the quality and efficiency of their data collection program. The use of these practices can assist in complying with Quality Assurance requirements under ASME NQA-1, RCRA, CERCLA, and DOE Order activities. Data from Pylon AB-5 instrumentation is typically configured to print data to a tape. The REM group has developed a process to electronically transfer stored data. The data are sent from the Pylon AB-5 field instrument to a HewlettPackard portable hand computer, model HP95LX. Data are recorded and stored on a 128 K-byte RAN card and later transferred to a PC database as an electronic file for analysis. The advantage of this system is twofold: (1) Data entry errors are eliminated and (2) considerable data collection and entry time is eliminated. Checks can then be conducted for data validity between recorded intervals due to light leaks etc. and the detection of outliers. This paper will discuss the interface and connector components that allow this transfer of data from the Pylon to the PC to take place and the process to perform that activity

  2. Electron transfer at semiconducting metal dichalcogenide/liquid electrolyte interfaces

    Howard, J.N.

    1992-01-01

    Charge transfer at semiconductor/electrolyte interfaces is the critical process in photoelectrochemical systems. Many aspects of the theory for these interfaces have yet to be experimentally verified. There are few reliable measurements of the fundamental electron transfer rate at nonilluminated semiconductors. This situation stems from experimental limitations imposed by most semiconductor electrode surfaces. Layered metal dichalcogenide semiconductors have excellent properties as semiconductor electrodes, but edge sites and crystal defects must be masked so only the defect-free basal plane of the two-dimensional material is exposed to solution. Conventional epoxy encapsulation of the crystal epoxy can introduce deleterious effects. A minielectrochemical cell was developed to perform experiments in a single drop of electrolyte held against the working electrode. The electrochemical behavior and operational considerations of the cell for aqueous and nonaqueous systems were investigated. Spatially-resolved electrochemistry was demonstrated for n-WSe[sub 2] and highly ordered pyrolytic graphite. The minicell was used to investigate electron transfer at nonilluminated n-WSe[sub 2]/dimethylferrocene[sup +/0] interfaces. This semiconductor is resistant to corrosion and has stable interfacial energetics. Interfaces with excellent diode behavior could be obtained by probing different regions of the surface. Electron transfer at these high quality surfaces was studied over an extensive solution concentration range. The rate of electron transfer was independent of solution acceptor concentration from 5 [mu]M to 0.25 M. The electron transfer data can be explained by assuming a surface-state mediate mechanism. A second metal dichalcogenide, n-SnS[sub 2], was investigated to compare the behavior of this wide band gap material to the narrow band gap n-WSe[sub 2]. The n-SnS[sub 2] electrodes displayed undesirable electrochemical effects in several solvent systems.

  3. 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...

  4. Extremely efficient clocked electron transfer on superfluid helium

    Bradbury, F. R.; Takita, Maika; Gurrieri, T. M.; Wilkel, K. J.; Eng, Kevin; Carroll, M. S.; Lyon, S. A.

    2011-01-01

    Unprecedented transport efficiency is demonstrated for electrons on the surface of micron-scale superfluid helium filled channels by co-opting silicon processing technology to construct the equivalent of a charge-coupled device (CCD). Strong fringing fields lead to undetectably rare transfer failures after over a billion cycles in two dimensions. This extremely efficient transport is measured in 120 channels simultaneously with packets of up to 20 electrons, and down to singly occupied pixels...

  5. 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

    When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10(-7)-10(-6) s(-1) for BDB2 to about 0.1 s(-1) in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened pi-pi interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered 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

  6. 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

    When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10-7-10-6 s-1 for BDB2 to about 0.1 s-1 in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened π-π interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered 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 π-π interactions and thermal intramolecular proton transfer to aromatic nitro group.

  7. 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

  8. 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

  9. 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...

  10. 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

  11. Adsorption and Interfacial Electron Transfer of Saccharomyces Cerevisiae

    Andersen, Jens Enevold Thanulov

    2003-01-01

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

  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... an employer and to which electronic fund transfers of the consumer's wages, salary, or other...

  13. A molecularly based theory for electron transfer reorganization energy

    Zhuang, Bilin; Wang, Zhen-Gang

    2015-12-01

    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.

  14. 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...

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

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

    2016-01-14

    Proton-coupled electron transfer (PCET) reactions involve the transfer of a proton and an electron and play an important role in a number of chemical and biological processes. Here, we describe a novel phenomenon, plasmon-enhanced PCET, which is manifested using SiO2-coated Ag nanoparticles functionalized with gallic acid (GA), a natural antioxidant molecule that can perform PCET. These GA-functionalized nanoparticles show enhanced plasmonic response at near-IR wavelengths, due to particle agglomeration caused by the GA molecules. Near-IR laser irradiation induces strong local hot-spots on the SiO2-coated Ag nanoparticles, as evidenced by surface enhanced Raman scattering (SERS). This leads to plasmon energy transfer to the grafted GA molecules that lowers the GA-OH bond dissociation enthalpy by at least 2 kcal mol(-1) and therefore facilitates PCET. The nanoparticle-driven plasmon-enhancement of PCET brings together the so far unrelated research domains of nanoplasmonics and electron/proton translocation with significant impact on applications based on interfacial electron/proton transfer. PMID:26505730

  16. 77 FR 30923 - Electronic Fund Transfers (Regulation E)

    2012-05-24

    ... to gift cards, however, the Board was careful to note that a general-use prepaid card did not include... cards, payroll cards, electronic benefit transfers (EBTs), or gift cards. \\1\\ Mercator Advisory Group... fees, service fees, or expiration dates on gift cards, which might take the form of a gift...

  17. 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

  18. 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

  19. 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...

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

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

    2012-01-01

    deuteration and explain, thereby, recent experiments performed on Drosophila melanogaster. Our demonstration is based on known physical properties of biological electron transfer and on ab initio calculations on odorants carried out for the purpose of the present study. We identify a range of physical...

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

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

    1998-01-01

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

  2. 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.

  3. Reduced density matrix hybrid approach: Application to electronic energy transfer

    Berkelbach, Timothy C; Reichman, David R

    2011-01-01

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

  4. 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.

  5. 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.

  6. Charge-transfer properties in the gas electron multiplier

    The charge transfer properties of a gas electron multiplier (GEM) were systematically investigated over a broad range of electric field configurations. The electron collection efficiency and the charge sharing were found to depend on the external fields, as well as on the GEM voltage. The electron collection efficiency increased with the collection field up to 90%, but was essentially independent of the drift field strength. A double conical GEM has a 10% gain increase with time due to surface charging by avalanche ions whereas this effect was eliminated with the cylindrical GEM. The positive-ion feedback is also estimated. (author)

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

    2011-06-16

    ... 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 fund... contract by electronic fund transfer (EFT). The information necessary to make the EFT transaction...

  8. 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.

  9. The ferredoxin-NADP+ reductase/ferredoxin electron transfer system of Plasmodium falciparum.

    Balconi, Emanuela; Pennati, Andrea; Crobu, Danila; Pandini, Vittorio; Cerutti, Raffaele; Zanetti, Giuliana; Aliverti, Alessandro

    2009-07-01

    In the apicoplast of apicomplexan parasites, plastidic-type ferredoxin and ferredoxin-NADP(+) reductase (FNR) form a short electron transport chain that provides reducing power for the synthesis of isoprenoid precursors. These proteins are attractive targets for the development of novel drugs against diseases such as malaria, toxoplasmosis, and coccidiosis. We have obtained ferredoxin and FNR of both Toxoplasma gondii and Plasmodium falciparum in recombinant form, and recently we solved the crystal structure of the P. falciparum reductase. Here we report on the functional properties of the latter enzyme, which differ markedly from those of homologous FNRs. In the physiological reaction, P. falciparum FNR displays a k(cat) five-fold lower than those usually determined for plastidic-type FNRs. By rapid kinetics, we found that hydride transfer between NADPH and protein-bound FAD is slower in the P. falciparum enzyme. The redox properties of the enzyme were determined, and showed that the FAD semiquinone species is highly destabilized. We propose that these two features, i.e. slow hydride transfer and unstable FAD semiquinone, are responsible for the poor catalytic efficiency of the P. falciparum enzyme. Another unprecedented feature of the malarial parasite FNR is its ability to yield, under oxidizing conditions, an inactive dimeric form stabilized by an intermolecular disulfide bond. Here we show that the monomerdimer interconversion can be controlled by oxidizing and reducing agents that are possibly present within the apicoplast, such as H(2)O(2), glutathione, and lipoate. This finding suggests that modulation of the quaternary structure of P. falciparum FNR might represent a regulatory mechanism, although this needs to be verified in vivo. PMID:19523113

  10. 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.

  11. 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.

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

    Klauss, André; Haumann, Michael; Dau, Holger

    2012-10-01

    Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel-production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese-calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S(2) → S(3) transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (Y Z OX). The rate-determining elementary step (τ, approximately 30 µs at 20 °C) in the long-distance proton relocation toward the protein-water interface is characterized by a high activation energy (E(a) = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S(0) → S(1) transition are similar (τ, approximately 100 µs; E(a) = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established. PMID:22988080

  13. 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 to leave the crossing region. In the framework of open quantum systems, τFC is a short time approximation of the characteristic decoherence time of the electronic subsystem in interaction with its nuclear environment. The comparison of the respective values of τcoh and τFC allows us to probe the occurrence of non-Condon effects. We use ab initio MD simulations to analyze how decoherence appears in several biological cofactors. We conclude that we cannot account for its order of magnitude by considering only the atoms or bonds directly concerned with the transfer. Decoherence results from contributions from all atoms of the system appearing with a time delay that increases with the distance from the primarily concerned atoms or bonds. The delay and magnitude of the contributions depend on the chemical nature of the system. Finally, we present recent developments based on constrained DFT for efficient and accurate evaluations of the electronic coupling in ab initio MD simulations. These are promising methods to study the subtle fluctuations of the electronic coupling and the mechanisms of electronic decoherence in biological systems. PMID:25730126

  14. Electron Transfer in DNA through magnetic bound states

    Cox, D L; Pati, S K

    2000-01-01

    Electron transfer (ET) via quantum mechanical tunneling between well separated donor (D) and acceptor (A) complexes is part of such biological processes as respiration, photosynthesis, and possibly DNA repair or damage. Data and theory for ET in proteins give a typical tunneling length of 0.1 nm. In contrast, fluorescence quenching in DNA at D/A distances of 4 nm or more suggests ET with tunneling lengths of order 1 nm. We show how such long ranged ET can be mediated by rapidly forming magnetic Kondo bound states (KS) arising from: (1) strong electron interactions and magnetic moments on D and/or A complexes satisfying suitable energy requirements, and (2) "quantum deconfinement" of electrons through extended bridge molecular orbitals. Realistic long range Coulomb interaction strengths between bridge electrons and localized D/A charges modestly enhance these ET rates.

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

    2015-01-01

    Here we report a ternary catalyst system for the intramolecular hydroamidation of unactivated olefins using simple N-aryl amide derivatives. Amide activation in these reactions occurs via concerted proton-coupled electron transfer (PCET) mediated by an excited state iridium complex and weak phosphate base to furnish a reactive amidyl radical that readily adds to pendant alkenes. A series of H-atom, electron, and proton transfer events with a thiophenol cocatalyst furnish the product and regenerate the active forms of the photocatalyst and base. Mechanistic studies indicate that the amide substrate can be selectively homolyzed via PCET in the presence of the thiophenol, despite a large difference in bond dissociation free energies between these functional groups. PMID:26439818

  16. Transfer of angular momentum in electron collisions with alkali atoms

    Measurements of the transfer of angular momentum to rubidium and sodium atoms in collisions with electrons are reported. For excitation of the rubidium 52S1/2-52P3/2 transition, it is found that existing first order distorted wave Born approximation calculations show poor agreement with the data and that a model which includes the relativistic interaction between the electrons and the atoms in the potential is needed. For the de-excitation of the sodium 42S1/2-32P3/2 transition, a long standing proposal relating to the sign of the transferred angular momentum is not supported except at small scattering angles. A convergent close coupling calculation displays excellent agreement with the measured data. Copyright (1999) CSIRO Australia

  17. 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

  18. 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

  19. 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

  20. Insights into Proton-Coupled Electron Transfer from Computation

    Provorse, Makenzie R.

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

  1. 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.

  2. 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

  3. 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...

  4. 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

  5. Evaluation of the role of specific acidic amino acid residues in electron transfer between the flavodoxin and cytochrome c3 from Desulfovibrio vulgaris.

    Feng, Y; Swenson, R P

    1997-11-01

    A hypothetical model for electron transfer complex between cytochrome c3 and the flavodoxin from the sulfate-reducing bacteria Desulfovibrio vulgaris has been proposed, based on electrostatic potential field calculations and NMR data [Stewart, D. E., LeGall, J. , Moura, I., Moura, J. J. G., Peck, H. D., Jr., Xavier, A. V., Weiner, P. K., & Wampler, J. E. (1988) Biochemistry 27, 2444-2450]. This modeled complex relies primarily on the formation of five ion pairs between lysine residues of the cytochrome and acidic residues surrounding the flavin mononucleotide cofactor of the flavodoxin. In this study, the role of several acidic residues of the flavodoxin in the formation of this complex and in electron transfer between these two proteins was evaluated. A total of 17 flavodoxin mutants were studied in which 10 acidic amino acids--Asp62, Asp63, Glu66, Asp69, Asp70, Asp95, Glu99, Asp106, Asp127, and Asp129--had been permanently neutralized either individually or in various combinations by substitution with their amide amino acid equivalent (i.e., asparate to asparagine, glutamate to glutamine) through site-directed mutagenesis. The kinetic data for the transfer of electrons from reduced cytochrome c3 to the various flavodoxin mutants do not conform well to a simple bimolecular mechanism involving the formation of an intermediate electron transfer complex. Instead, a minimal electron transfer mechanism is proposed in which an initial complex is formed that is stabilized by intermolecular electrostatic interactions but is relatively inefficient in terms of electron transfer. This step is followed by a rate-limiting reorganization of that complex leading to efficient electron transfer. The apparent rate of this reorganization step was enhanced by the disruption of the initial electrostatic interactions through the neutralization of certain acidic amino acid residues leading to faster overall observed electron transfer rates at low ionic strengths. Of the five acidic residues involved in ion pairing in the modeled complex proposed by Stewart et al. (1988), the kinetic data strongly implicate Asp62, Glu66, and Asp95 in the formation of the electrostatic interactions that control electron transfer. Less certainty is provided by this study for the involvement of Asp69 and Asp129, although the data do not exclude their participation. It was not possible to determine whether the modeled complex represents the optimal configuration for electron transfer obtained after the reorganization step or actually represents the initial complex. The data do provide evidence for the importance of electrostatic interactions in electron transfer between these two proteins and for the existence of alternative binding modes involving acidic residues on the surface of the flavodoxin other than those proposed in that model. PMID:9354631

  6. Intermolecular Silacarbonyl Ylide Cycloadditions: A Direct Pathway to Oxasilacyclopentenes

    Bourque, Laura E.; Woerpel, K. A.

    2009-01-01

    Silacarbonyl ylides, generated by metal-catalyzed silylene transfer to carbonyls, participate in formal intermolecular 1,3-dipolar cycloaddition reactions with carbonyl compounds and alkynes to form dioxasilacyclopentane acetals and oxasilacyclopentenes in an efficient, one-step process. PMID:18922005

  7. 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.

  8. 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.

  9. 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.

  10. Water-mediated electron transfer between protein redox centers.

    Migliore, Agostino; Corni, Stefano; Felice, Rosa Di; Molinari, Elisa

    2007-04-12

    Recent experimental and theoretical investigations show that water molecules between or near redox partners can significantly affect their electron-transfer (ET) properties. Here we study the effects of intervening water molecules on the electron self-exchange reaction of azurin (Az), by performing a conformational sampling on the water medium and by using a newly developed ab initio method to calculate transfer integrals between molecular redox sites. We show that the insertion of water molecules at the interface between the copper active sites of Az dimers slightly increases the overall ET rate, while some favorable water conformations can considerably enhance the ET kinetics. These features are traced back to the interplay of two competing factors: the electrostatic interaction between the water and protein subsystems (mainly opposing the ET process for the water arrangements drawn from MD simulations) and the effectiveness of water in mediating ET coupling pathways. Such an interplay provides a physical basis for the found absence of correlation between the electronic couplings derived through ab initio electronic structure calculations and the related quantities obtained through the Empirical Pathways (EP) method. In fact, the latter does not account for electrostatic effects on the transfer integrals. Thus, we conclude that the water-mediated electron tunneling is not controlled by the geometry of a single physical pathway. We discuss the results in terms of the interplay between different ET pathways controlled by the conformational changes of one of the water molecules via its electrostatic influence. Finally, we examine the dynamical effects of the interfacial water and check the validity of the Condon approximation. PMID:17388538

  11. Electron transfer and projectile excitation in single collisions

    Studies of electron transfer (capture) and projectile excitation together in a single encounter are reviewed. This combined capture and excitation can result from either a correlated or an uncorrelated interaction. The correlated process is referred to as resonant transfer and excitation (RTE), while the uncorrelated process is called nonresonant transfer and excitation (NTE). RTE is analogous to dielectronic recombination (DR) which occurs in the interaction between an ion and a free electron. Experimental and theoretical works leading to establishing the existence of RTE are reviewed as well as considerations relevant to distinguishing RTE from NTE. The dependences of RTE on projectile atomic number (14 ≤ Z ≤ 23) for Li-like ions, and on projectile charge state for H-like to Ne-like ions have been measured and compared with theory. The effect of the target electron momentum distribution on RTE has been demonstrated by comparing measurements for H2 and He targets. Measurements of RTE involving L-shell excitation have been conducted and compared with K-shell results. All of the measured RTE cross sections to date for H2 and He targets are in reasonable agreement with calculations based on theoretical DR cross sections averaged over the target electron momentum distribution; however, systematic discrepancies between experiment and theory exist. Additionally, is has been found that RTE can contribute considerably to total single-electron capture cross sections in the region where RTE is important, accounting for nearly half of the total capture events for calcium ions colliding with H2. (orig.)

  12. Mapping intermolecular bonding in C??.

    Sundqvist, Bertil

    2014-01-01

    The formation of intermolecular bonds in C?? has been investigated in detail at pressures below 2.2?GPa and up to 750?K. Fullerene samples were heated in a temperature gradient to obtain data on the formation of dimers and low-dimensional polymers along isobars. Intermolecular bonding was analyzed ex situ by Raman scattering, using both intramolecular modes and intermolecular stretching modes. Semi-quantitative reaction maps are given for the formation of dimers and chains. The activation energy for dimer formation decreases by 0.2?meV pm(-1) when intermolecular distances decrease and dimer formation is noticeably affected by the rotational state of molecules. Above 400-450?K larger oligomers are formed; below 1.4?GPa most of these are disordered, with small domains of linear chains, but above this the appearance of stretching modes indicates the existence of ordered one-dimensional polymers. At the highest pressures and temperatures two-dimensional polymers are also observed. PMID:25145952

  13. Interfacial electron transfer into functionalized crystalline polyoxotitanate nanoclusters.

    Snoeberger, Robert C; Young, Karin J; Tang, Jiji; Allen, Laura J; Crabtree, Robert H; Brudvig, Gary W; Coppens, Philip; Batista, Victor S; Benedict, Jason B

    2012-05-30

    Interfacial electron transfer (IET) between a chromophore and a semiconductor nanoparticle is one of the key processes in a dye-sensitized solar cell. Theoretical simulations of the electron transfer in polyoxotitanate nanoclusters Ti(17)O(24)(OPr(i))(20) (Ti(17)) functionalized with four p-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established by X-ray diffraction measurements, are presented. Complementary experimental information showing IET has been obtained by EPR spectroscopy. Evolution of the time-dependent photoexcited electron during the initial 5 fs after instantaneous excitation to the NPA LUMO + 1 has been evaluated. Evidence for delocalization of the excitation over multiple chromophores after excitation to the NPA LUMO + 2 state on a 15 fs time scale is also obtained. While chromophores are generally considered electronically isolated with respect to neighboring sensitizers, our calculations show that this is not necessarily the case. The present work is the most comprehensive study to date of a sensitized semiconductor nanoparticle in which the structure of the surface and the mode of molecular adsorption are precisely defined. PMID:22548416

  14. 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

  15. Electron transfer rates and equilibrium within cytochrome c oxidase

    Farver, O; Einarsdóttir, O; Pecht, I

    2000-01-01

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

  16. Noise-assisted quantum electron transfer in photosynthetic complexes

    Nesterov, Alexander I; Martnez, Jos Manuel Snchez; 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 MECHANISM AT THE SOLID-LIQUID INTERFACE OF PHYLLOSILICATES

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

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

    2012-04-25

    ... 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 transactions involving TANF assistance in liquor stores, casinos, gambling casinos, or other gaming establishments,...

  20. 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...

  1. 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

  2. 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.

  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. 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.

  5. Electronic Energy Transfer: Localized Operator Partitioning of Electronic Energy in Composite Quantum Systems

    Khan, Yaser R.; Brumer, Paul

    2012-01-01

    A Hamiltonian based approach using spatially localized projection operators is introduced to give precise meaning to the chemically intuitive idea of the electronic energy on a quantum subsystem. This definition facilitates the study of electronic energy transfer in arbitrarily coupled quantum systems. In particular, the decomposition scheme can be applied to molecular components that are strongly interacting (with significant orbital overlap) as well as to isolated fragments. The result lead...

  6. 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 ...

  7. 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

  8. 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

  9. 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.

  10. 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

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. Large momentum transfer electron scattering from few-nucleon systems

    A review is given of the experimental results from a series of measurements at SLAC of large momentum transfer (Q2 > 20 fm-2) electron scattering at forward angles from nuclei with A less than or equal to 4. Theoretical interpretations of these data in terms of traditional nuclear physics models and in terms of quark constituent models are described. Some physics questions for future experiments are explored, and a preview of possible future measurements of magnetic structure functions of light nuclei at large Q2 is given

  16. Nanoscale and single-molecule interfacial electron transfer

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

    2003-01-01

    Electrochemical science and technology in the 21st century have reached high levels of sophistication. A fundamental quantum mechanical theoretical frame for interfacial electrochemical electron transfer (ET) was introduced by Revaz Dogonadze. This frame has remained for four decades as a basis for...... comprehensive later theoretical work and data interpretation in many areas of chemistry, electrochemistry, and biology. We discuss here some new areas of theoretical electrochemical ET science, with focus on nanoscale electrochemical and bioelectrochemical sciences. Particular attention is given to in situ...

  17. 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

  18. Promoting direct interspecies electron transfer with activated carbon

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

    2012-01-01

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

  19. Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration

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

    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....

  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. Probing the role of a conserved salt bridge in the intramolecular electron transfer kinetics of human sulfite oxidase.

    Johnson-Winters, Kayunta; Davis, Amanda C; Arnold, Anna R; Berry, Robert E; Tollin, Gordon; Enemark, John H

    2013-08-01

    Sulfite oxidase (SO) is a vital metabolic enzyme that catalyzes the oxidation of toxic sulfite to sulfate. The proposed mechanism of this molybdenum cofactor dependent enzyme involves two one-electron intramolecular electron transfer (IET) steps from the molybdenum center to the iron of the b 5-type heme and two one-electron intermolecular electron transfer steps from the heme to cytochrome c. This work focuses on how the electrostatic interaction between two conserved amino acid residues, R472 and D342, in human SO (hSO) affects catalysis. The hSO variants R472M, R472Q, R472K, R472D, and D342K were created to probe the effect of the position of the salt bridge charges, along with the interaction between these two residues. With the exception of R472K, these variants all showed a significant decrease in their IET rate constants, k et, relative to wild-type hSO, indicating that the salt bridge between residues 472 and 342 is important for rapid IET. Surprisingly, however, except for R472K and R472D, all of the variants show k cat values higher than their corresponding k et values. The turnover number for R472D is about the same as k et, which suggests that the change in this variant is rate-limiting in catalysis. Direct spectroelectrochemical determination of the Fe(III/II) reduction potentials of the heme and calculation of the Mo(VI/V) potentials revealed that all of the variants affected the redox potentials of both metal centers, probably due to changes in their environments. Thus, the position of the positive charge of R472 and that of the negative charge of D342 are both important in hSO, and changing either the position or the nature of these charges perturbs IET and catalysis. PMID:23779234

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

    Yang, Li-Ping; Sun, C P

    2011-01-01

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

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

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

    2009-01-01

    The cd(1) nitrite reductases, which catalyze the reduction of nitrite to nitric oxide, are homodimers of 60 kDa subunits, each containing one heme-c and one heme-d(1). Heme-c is the electron entry site, whereas heme-d(1) constitutes the catalytic center. The 3D structure of Pseudomonas aeruginosa...... nitrite reductase has been determined in both fully oxidized and reduced states. Intramolecular electron transfer (ET), between c and d(1) hemes is an essential step in the catalytic cycle. In earlier 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. 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.

  5. 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.

  6. Topological characterisation of intermolecular lithium bonding

    Vila, Antonio [Departamento de Quimica Fisica, Universidade de Vigo, Lagoas-Marcosende, 36310-Vigo, Galicia (Spain); Vila, Esther [Departamento de Quimica Fisica, Universidade de Vigo, Lagoas-Marcosende, 36310-Vigo, Galicia (Spain); Mosquera, Ricardo A. [Departamento de Quimica Fisica, Universidade de Vigo, Lagoas-Marcosende, 36310-Vigo, Galicia (Spain)], E-mail: mosquera@uvigo.es

    2006-08-01

    Bader's atoms in molecules topological theory was employed to analyse the B3LYP/6-311++G(3d2f,3p2d) electron distributions of several adducts that contain LiF. The results indicate significant differences between lithium bonding (LB) and hydrogen bonding (HB): (i) in spite of their larger stability, the charge density at the intermolecular critical points of LB complexes is about half of its value in the corresponding HB complexes, suggesting a dominant role of electrostatic interactions in the former; (ii) the Li atom in LB compounds is more shared between the base atom and the attached fluorine than hydrogen in HB complexes; and (iii) the Li atom gains electron charge from the hydrogens in all the complexes here studied, undergoing energetic stabilisation.

  7. Topological characterisation of intermolecular lithium bonding

    Bader's atoms in molecules topological theory was employed to analyse the B3LYP/6-311++G(3d2f,3p2d) electron distributions of several adducts that contain LiF. The results indicate significant differences between lithium bonding (LB) and hydrogen bonding (HB): (i) in spite of their larger stability, the charge density at the intermolecular critical points of LB complexes is about half of its value in the corresponding HB complexes, suggesting a dominant role of electrostatic interactions in the former; (ii) the Li atom in LB compounds is more shared between the base atom and the attached fluorine than hydrogen in HB complexes; and (iii) the Li atom gains electron charge from the hydrogens in all the complexes here studied, undergoing energetic stabilisation

  8. Theoretical studies of excess electrons in fluids: structure and electron transfer. Progress report, August 1981-August 1982

    Research reported involved studies of electron transfer reactions, negative water clusters, spin pairing in metal ammonia solutions, water-water interactions, interaction of Hexa aquo iron complexes, and proton transfer

  9. Intermolecular interaction in TeO2 crystal.

    Gabuda, Svyatoslav P; Kozlova, Svetlana G

    2006-09-21

    It is shown that the abnormal long-range Te-Te intermolecular interaction in TeO(2) crystals may be related to the tunneling of electrons from the 5s(2) active lone pairs of Te(4+) ions and their partial delocalization on neighboring Te(4+). PMID:16970416

  10. 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...

  11. Characteristics and nature of the intermolecular interactions in boron-bonded complexes with carbene as electron donor: an ab initio, SAPT and QTAIM study.

    Esrafili, Mehdi D

    2012-05-01

    We report geometries, stabilization energies, symmetry adapted perturbation theory (SAPT) and quantum theory of atoms in molecules (QTAIM) analyses of a series of carbene-BX(3) complexes, where X = H, OH, NH(2), CH(3), CN, NC, F, Cl, and Br. The stabilization energies were calculated at HF, B3LYP, MP2, MP4 and CCSD(T)/aug-cc-pVDZ levels of theory using optimized geometries of all the complexes obtained from B3LYP/aug-cc-pVTZ. Quantitatively, all the complexes indicate the presence of B-C(carbene) interaction due to the short B-C(carbene) distances. Inspection of stabilization energies reveals that the interaction energies increase in the order NH(2) > OH > CH(3) > F > H > Cl > Br > NC > CN, which is the opposite trend shown in the binding distances. Considering the SAPT results, it is found that electrostatic effects account for about 50% of the overall attraction of the studied complexes. By comparison, the induction components of these interactions represent about 40% of the total attractive forces. Despite falling in a region of charge depletion with nabla(2)ρ(BCP) >0, the B-C(carbene) bond critical points (BCPs) are characterized by a reasonably large value of the electron density (ρ(BCP)) and H(BCP) kinetic energy density at BCP and the B-C(carbene) bond is a polar covalent bond. PMID:21877151

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

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

    2015-01-01

    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...

  13. 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.

  14. 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 flux tubes ahead of the FTE, which causes density and field strength enhancements; a circulation of open flux tubes within the FTE itself, which accounts for the delay in the arrival of the magnetosheath electron populations at locations deepest within the magnetosphere; and a possible trapping of magnetospheric electrons on the most recently opened flux tubes within the FTE.

    Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind - magnetosphere interactions

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

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Aklujkar, Muktak; Liu, Fanghua; Shrestha, Minita; Summers, Zarath M; Malvankar, Nikhil; Flores, Dan Carlo; Lovley, Derek R

    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...... dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration.......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...

  16. 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

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

    Jo, Mingyu; Uchida, Takafumi; Tsurumaki-Fukuchi, Atsushi; Arita, Masashi; Fujiwara, Akira; Ono, Yukinori; Nishiguchi, Katsuhiko; Inokawa, Hiroshi; Takahashi, Yasuo

    2015-12-01

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

  18. Layered Black Phosphorus: Strongly Anisotropic Magnetic, Electronic, and Electron-Transfer Properties.

    Sofer, Zden?k; Sedmidubsk, David; Huber, t?pn; Luxa, Jan; Boua, Daniel; Boothroyd, Chris; Pumera, Martin

    2016-03-01

    Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer- and inner-sphere molecular probes is highly anisotropic. The electron-transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field. PMID:26822395

  19. Facile direct electron transfer in glucose oxidase modified electrodes

    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 ?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.

  20. A stochastic reorganizational bath model for electronic energy transfer

    Environmentally induced fluctuations of the optical gap play a crucial role 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 (HSR) model, in which the energy-gap fluctuation is approximated as white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to account for excitation energies thermal fluctuations. On the other hand, since the original work of HSR, many groups have employed stochastic models to simulate the same transfer dynamics. 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 equations via the generalized Langevin approach. Based on this connection, we propose a novel scheme to take account of reorganization effects within the framework of stochastic models. The proposed scheme provides a better description of the population dynamics especially in the regime of strong exciton-phonon coupling. Finally, we discuss the effect of the bath reorganization in the absorption and fluorescence spectra of ideal J-aggregates in terms of the Stokes shifts. We find a simple expression that relates the reorganization contribution to the Stokes shifts the reorganization shift to the ideal or non-ideal exciton delocalization in a J-aggregate. The reorganization shift can be described by three parameters: the monomer reorganization energy, the relaxation time of the optical gap, and the exciton delocalization length. This simple relationship allows one to understand the physical origin of the Stokes shifts in molecular aggregates

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

    Renschler, C. L.; Faulkner, L. R.

    1980-01-01

    Quenching of fluoranthene (FA) singlets by tetrabromo-o-benzoquinone (TBBQ) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was studied both in xylene solutions and in spin-cast polystyrene (PS) films. Emphasis was placed on time-resolved fluorescence transients resulting from pulsed excitation. Linear Stern-Volmer plots were obtained for quenching in solution and gave diffusion-controlled rate constants, of 1.45 x 10/sup 10/ M/sup -1/ sec/sup -1/ and 1.53 x 10/sup 10/ M/sup -1/ sec/sup -1/ for TBBQ and TMPD, respectively. TBBQ was found to quench FA singlets in PS over the studied concentration range 12 mM < (TBBQ) < 48 mM, but in its presence FA singlets decayed nonexponentially. The results were interpreted quantitatively in terms of pure Foerster's transfer from FA to TBBQ without diffusion of excitons. The critical transfer radius R/sub 0/ was experimentally determined to be 24.3 A, which is in good agreement with the theoretical value of 23 A calculated from spectral data. Quenching of FA singlets in PS films was found to be independent of FA concentration over a 300 mM to 1200 mM FA concentration range for a constant TBBQ concentration of 24.0 mM. TMPD was only slightly effective as a quencher of FA singlets in PS because it apparently behaves strictly as a contact quencher based on reversible charge transfer. The implications of these results for the design of systems intended to exploit light-induced electron transfer are discussed.

  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 adequately described as a nonadiabatic eT reaction (HAB > 80 cm-1). eT to both the 1Fe and 2Fe forms of rubredoxin is therefore gated by an adiabatic process that precedes the eT reaction from flavin to iron. Possible origins of this adiabatic event are discussed. PMID:9799514

  3. Electron-transfer reactions induced by ionizing radiation and photoirradiation

    Photoirradiation of a methanol solution of ?-methylstyrene and EuCl3.6H2O with Pyrex filter resulted in the formation of 2,3-dimethyl-2,3-diphenylbutane and 3,4-dimethyl-3,4-diphenylpentanol in high yields. This reaction was initiated by the excitation of Eu(III)CH3OH CT-bands and followed by a successive photochemical reaction of Eu(II) ions formed. When 1,3-dimethyluracil was used as a substrate a regioselective hydroxymethylation took place in high efficiency, probably via an electron-transfer mechanism. ?-Radiolysis of 1,3-dimethyluracil and its derivatives in methanol also resulted in the regioselective hydroxymethylation at C-5 position of the pyrimidine ring. Analogous additions of ethanol, 2-propanol and tetrahydrofuran to 1,3-dimethyluracil occured in high efficiency. A mechanism via the one-electron reduction of 1,3-dimethyluracil is presented and compared with that of the photochemical reactions. (author)

  4. Time-optimal polarization transfer from an electron spin to a nuclear spin

    Yuan, Haidong; Zeier, Robert; Pomplun, Nikolas; Glaser, Steffen J.; Khaneja, Navin

    2015-01-01

    Polarization transfers from an electron spin to a nuclear spin are essential for various physical tasks, such as dynamic nuclear polarization in nuclear magnetic resonance and quantum state transformations on hybrid electron-nuclear spin systems. We present time-optimal schemes for electron-nuclear polarization transfers which improve on conventional approaches and will have wide applications.

  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. Identification of an electron transfer locus in plastocyanin by chromium(II) affinity labeling

    Farver, O; Pecht, I

    1981-01-01

    aromatic residues. These are proposed to be involved in the electron transfer process. A mechanism for that process is presented that involves interaction between the d electrons of the metal ions with d pi-pi* delocalization through a weakly coupled pi* system. The rationale of this electron transfer...

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

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

  8. 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

  9. 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.

  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. 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 the porphyrin ring and degree of fluorination of ring substituents were analyzed. Due to the high reduction potentials of these sensitizers, injection into TiO2 was generally not observed. Injection timescales from the porphyrins into SnO2 depended strongly on the identity of the central substituent and were affected by competition with excited-state deactivation processes. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but is typically not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency and water stability of several alternative anchoring groups, including phosphonic acid, hydroxamic acid, acerylacetone, and boronic acid, were evaluated. While all of the anchoring groups exhibited water stability superior to carboxylate, the hydroxamate anchor had the best combination of ease of handling and electron injection efficiency. The effects on photoconductivity due to metal oxide morphology and the addition of dopants were also analyzed. Mixtures of anatase and rutile TiO 2 nanoparticles are known to exhibit cooperative effects which increase the efficiency of DSSCs and photocatalysis relative to the pure-phase materials. Through analysis of TRTS measurements, the mechanism of this synergistic effect was found to involve electron transfer from the lower-mobility, higher surface area rutile nanoparticles to anatase particles, resulting in a higher charge collection efficiency. In addition to morphology, doping has been investigated as a means of expanding the spectral range of visible absorption of photocatalysts. Doping ZnO nanowires with manganese(II) was found to significantly decrease the electron mobility, and doping with cobalt(II) increased the timescale for electron trapping. These differences can be understood by considering the changes to the band structure of ZnO effected by the dopants. Preliminary analyses of the solvent and electrolyte dependence on the electron injection rate and efficiency suggest that electron injection can be affected by several components of a DSSC or water oxidation cell in addition to the sensitizer and metal oxide. Performing TRTS studies on fully assembled devices will therefore be essential for determining the relationship between electron injection and device efficiency.

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

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

  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. Competitive-channel of double electron transfer in ion-atom collision

    Full text: Recent development in the theoretical and experimental studies on electron transfer is highlighted. Validity of single collision condition and isolated atom concept were achieved by gas target measurement. Studies on subshell resolved electron transfer for solid targets were also extrapolated to vanishing thicknesses. Predictions of the recently developed theory of a Close Coupling Calculations (CCC) based on Two State Atomic Expansion (TSAE) and Continuum Distorted Wave eikonal initial state (CDW-EIS) were compared with the experimental results. The cross-section for the simultaneous transfer of two electrons is comparable to the singe electron transfer cross-sections as the symmetry of the collision system is approached

  16. 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.

  17. ELECTRONIC FUNDS TRANSFER: EXPLORING THE DIFFICULTIES OF SECURITY

    MPAKWANA ANNASTACIA MTHEMBU

    2010-09-01

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

  18. Electron transfer reactions of macrocyclic compounds of cobalt

    Heckman, R.A.

    1978-08-01

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

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

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

    1995-01-01

    At high altitudes and velocities equal to or greater than the geosynchronous return velocity (10 kilometers per second), the shock layer of a hypersonic flight will be in thermochemical nonequilibrium and partially ionized. The amount of ionization is determined by the velocity. For a trans atmospheric flight of 10 kilometers per second and at an altitude of 80 kilometers, a maximum of 1% ionization is expected. At a velocity of 12 - 17 kilometer per second, such as a Mars return mission, up to 30% of the atoms and molecules in the flow field will be ionized. Under those circumstances, electrons play an important role in determining the internal states of atoms and molecules in the flow field and hence the amount of radiative heat load and the distance it takes for the flow field to re-establish equilibrium. Electron collisions provide an effective means of transferring energy even when the electron number density is as low as 1%. Because the mass of an electron is 12,760 times smaller than the reduced mass of N2, its average speed, and hence its average collision frequency, is more than 100 times larger. Even in the slightly ionized regime with only 1% electrons, the frequency of electron-molecule collisions is equal to or larger than that of molecule-molecule collisions, an important consideration in the low density part of the atmosphere. Three electron-molecule collision processes relevant to hypersonic flows will be considered: (1) vibrational excitation/de-excitation of a diatomic molecule by electron impact, (2) electronic excitation/de-excitation, and (3) dissociative recombination in electron-diatomic ion collisions. A review of available data, both theory and experiment, will be given. Particular attention will be paid to tailoring the molecular physics to the condition of hypersonic flows. For example, the high rotational temperatures in a hypersonic flow field means that most experimental data carried out under room temperatures are not applicable. Also, the average electron temperature is expected to be between 10,000 and 20,000 K. Thus only data for low energy electrons are relevant to the model.

  20. 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.

  1. 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 0.25mA·cm(-2) for the ORR at T1Cu of the adsorbed laccase on carbon is 0.8V 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

  2. 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.

  3. 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.

  4. Electron transfer precedes ATP hydrolysis during nitrogenase catalysis.

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

    2013-10-01

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

  5. Electron transfer of peroxidase assemblies at tailored nanocarbon electrodes

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

  6. 77 FR 77187 - Electronic Fund Transfers (Regulation E)

    2012-12-31

    ... fees may be disclosed. If a remittance transfer provider does not have specific knowledge regarding... remittance transfer provider does not have specific knowledge regarding variables that affect the amount of... intermediary institutions in connection with an international wire transfer, and taxes imposed on a...

  7. 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,...

  8. Desensitization and recovery of metastable intermolecular composites

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

    2010-09-07

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

  9. Photoinduced tautomerism of 2,6-dicarbomethoxyphenol in DMFwater mixtures: Perturbation from intermolecular processes

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

    2014-06-01

    In this paper, we report the spectral signatures of photoinduced tautomerism of 4-methyl-2,6-dicarbomethoxyphenol (CMOH) in DMFwater 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 CMOHSolvent 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 CMOHDMF and CMOHwater clusters. These findings are expected to shed light on the mechanism of acidbase reactions of several hydrogen bonded systems that are part of many biologically relevant processes. -- Highlights: Photoinduced tautomerization of CMOH has been studied in DMFwater 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.

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

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

  11. Electron transfer-reactions on the surface of MgO nanoparticles

    The surface of MgO nanoparticles obtained by chemical vapour deposition (CVD) was subjected to combined EPR and IR studies. Surface colour centres (FS+) and superoxide anions (O2-) which are complexed by surface cations (Mg2+) were isolated and characterized on this material for the first time. The hydride groups emerging from the initial H2 chemisorption processes (heterolytic splitting) play an active role in consecutive surface reactions. They provide the electrons which are required for the UV induced formation of surface colour centres (FS+) and for the production of superoxide anions (redox reaction). Both the colour centres and the superoxide anions (O2-) are EPR active. The hydroxyl groups resulting from H2 chemisorption (OHC) do not actively participate in the consecutive reactions. Together with the OH groups formed in the course of colour centre formation (OHR) they rather play the role of an observer. They undergo specific electronic interactions with both the colour centre (FS+...HO) and the superoxide anion which are IR inactive surface species. They may, however, be observed by IR spectroscopy via the specifically influenced OH stretching vibrations (O2...HO). This proves the intimate interplay between IR and EPR spectroscopy applied to the surface processes under investigation. As a result two paths were found for the three consecutive surface reaction steps: H2 chemisorption, colour centre formation and superoxide anion formation. In the first one a single well defined surface area element is involved, namely, a low coordinated ion pair, the cation of which is a constituent of an anion vacancy. In the second path a diffusion controlled intermediate step has to be adopted in which the electron required for the colour centre is transported by an H atom travelling from a hydride group to a remote anion vacancy. In either case there is clear experimental evidence that the finally resulting superoxide anions are complexed by the colour centre cations. As a consequence the relative abundance of two O2-species, namely O2- [A] and O2- [B], depends sensitively on H2 pressure during UV irradiation in the course of colour centre formation. The mechanisms of intermolecular electron transfer reactions between surface hydride groups and O2 (coadsorption of H2 and O2 in the dark) were also studied using the respective OH groups a surface probes. At low H2 pressures (P(H2)=1 mbar) the reaction between the hydride groups of chemisorption complex I and O2 can take place and results in the formation of O2- [A]. This is monitored by the hydroxyl group OHC. With increasing H2 pressure during the coadsorption experiment the sites of chemisorption complex II are more and more involved in the course of formation of O2-[B]. In the last part a systematic investigation concerning the change of surface topology by thermal pretreatment was performed using O2- as cation selective surface probes. On raising the temperature a drastical decrease of the number of different cation types is observed. Finally, only three of them can be isolated on the surface of MgO (1073 K) via O2- probes. This indicates a remarkable reduction of the diversity of surface sites. The three cations, together with the two sites capable of heterolytic H2 splitting and two predominant types of anion vacancies survive thermal treatment above 1073 K and determine the surface reactivity of totally dehydroxylated MgO nanoparticles. (author)

  12. 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

  13. 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.

  14. 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 dot-}AH{sub 2} in DMF, were rationalized by evaluating the Marcus parameters from the temperature dependence of the charge-recombination rate constants.

  15. 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

  16. Electron and hole transfer in DNA: the role of tunneling and environment

    Owing to the biological significance of radiation induced DNA damage, electron and hole transfer processes in DNA have attracted considerable interest. Various mechanisms for these processes have been proposed including tunneling and hopping. In our efforts we have investigated electron transfer for DNA in glasses, ices and solids at low temperatures via electron spin resonance (ESR) spectroscopy. Electrons and holes generated by irradiation at 77 K are trapped on DNA and transfer to a randomly interspersed intercalator, mitoxantrone (MX). Monitoring the changes of ESR signals of MX radicals, one electron oxidized guanine (G·+), one-electron reduced cytosine [C(N3)H·], and thymine anion radicals (T·-) with time at 77 K allows for the direct observation of electron and hole transfer. For DNA in aqueous glasses at low temperatures we are able to isolate the tunneling of excess electrons and we report overall distances of travel and the tunneling decay constant, beta. Studies with the duplexes polydAdT·polydAdT and polydIdC·polydIdC randomly intercalated with mitoxantrone (MX) show the excess electron transfer distances to be longer for pdAdT·pdAdT, than for for pdIdC·pdIdC. The beta value for DNA (0.9Angstroms-1) lies intermediate between that for pdAdT·pdAdT (0.75 Angstroms-1) and that for pdIdC·pdIdC (1.4 Angstroms-1). These results suggest that proton transfer from I to C·- forming CH· significantly slows but does not stop electron transfer. Similarly in DNA proton transfer in GC anion radical is not found to prevent electron transfer. Electron and hole transfer processes in frozen solutions (D2O ices) show that electron/hole transfer in polyA·polyU is significantly further than in DNA and transfer distances in polyC·polyG are substantially less than in DNA. These findings confirm our results in aqueous glasses. Our investigations of the effect of hydration, space filling lipid amine cation complexes, and temperature will also be discussed. Our modeling of electron transfer rates and distances of electron transfer in DNA-complexes allow for estimates of the spacing between DNA double stranded helices in each complex. This research was supported by the NIH NCI Grant RO1 CA45424

  17. 77 FR 10373 - Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid...

    2012-02-22

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

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

    Westereng, Bjrge; Cannella, David; Wittrup Agger, Jane; Jrgensen, Henning; Larsen Andersen, Mogens; Eijsink, Vincent G.H.; Felby, Claus

    2015-01-01

    Enzymatic oxidation of cell wall polysaccharides by lytic polysaccharide monooxygenases (LPMOs) plays a pivotal role in the degradation of plant biomass. While experiments have shown that LPMOs are copper dependent enzymes requiring an electron donor, the mechanism and origin of the electron supply in biological systems are only partly understood. We show here that insoluble high molecular weight lignin functions as a reservoir of electrons facilitating LPMO activity. The electrons are donated to the enzyme by long-range electron transfer involving soluble low molecular weight lignins present in plant 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. PMID:26686263

  19. 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.

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

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

    , 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...

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

    2010-10-01

    ... CLAUSES Text of Provisions and Clauses 52.232-38 Submission of Electronic Funds Transfer Information with... 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...

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

    Kuznetsov, A. M.; Sokolov, V. V.; Ulstrup, Jens

    adiabatic electron transfer reactions is elaborated. A new formula for the transition probability of non-adiabatic electron transfer reactions is obtained in an improved Condon approximation A regular method for the calculation of non-Condon corrections is suggested. The importance of these effects for some...

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

    Loukova G.V.

    2013-09-01

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

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

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

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

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

    1999-01-01

    The polaron approach is used to treat long-range electron transfers between globular proteins. A rate expression for the polaron transfer model is given along with a description of appropriate conditions for its use. Assuming that electrons transfer via a superexchange coupling due to a polaron excitation, we have estimated the distance dependence of the rate constant for the self-exchange reactions between globular proteins in solutions. The distance dependence of the polaron coupling and so...

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

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

  8. An electron energy-loss study of picene and chrysene based charge transfer salts

    Mller, Eric; Mahns, Benjamin; Bchner, Bernd; Knupfer, Martin [IFW Dresden, P.O. Box 270116, D-01171 Dresden (Germany)

    2015-05-14

    The electronic excitation spectra of charge transfer compounds built from the hydrocarbons picene and chrysene, and the strong electron acceptors F{sub 4}TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and TCNQ (7,7,8,8-tetracyanoquinodimethan) have been investigated using electron energy-loss spectroscopy. The corresponding charge transfer compounds have been prepared by co-evaporation of the pristine constituents. We demonstrate that all investigated combinations support charge transfer, which results in new electronic excitation features at low energy. This might represent a way to synthesize low band gap organic semiconductors.

  9. Pulse radiolytic and electrochemical investigations of intramolecular electron transfer in carotenoporphyrins and carotenoporphyrin-quinone triads

    Thermodynamic and kinetic aspects of intramolecular electron-transfer reactions in carotenoporphyrin dyads and carotenoid-porphyrin-quinone triads have been studied by using pulse radiolysis and cyclic voltammetry. Rapid (<1 μs) electron transfer from carotenoid radical anions to attached porphyrins has been inferred. Carotenoid cations, on the other hand, do not readily accept electrons from attached porphyrins or pyropheophorbides. Electrochemical studies provide the thermodynamic basis for these observations and also allow estimation of the energetics of photoinitiated two-step electron transfer and two-step charge recombination in triad models for photosynthetic charge separation

  10. An electron energy-loss study of picene and chrysene based charge transfer salts

    The electronic excitation spectra of charge transfer compounds built from the hydrocarbons picene and chrysene, and the strong electron acceptors F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) and TCNQ (7,7,8,8-tetracyanoquinodimethan) have been investigated using electron energy-loss spectroscopy. The corresponding charge transfer compounds have been prepared by co-evaporation of the pristine constituents. We demonstrate that all investigated combinations support charge transfer, which results in new electronic excitation features at low energy. This might represent a way to synthesize low band gap organic semiconductors

  11. Coulomb effects in polarization transfer in elastic antiproton and proton electron scattering at low energies

    Arenhoevel, H.

    2007-01-01

    The influence of Coulomb distortion on the polarization transfer in elastic proton and antiproton electron scattering at low energies is calculated in a distorted wave Born approximation. For antiproton electron scattering Coulomb effects reduce substantially the spin transfer cross section compared to the plane wave Born approximation whereas for proton electron scattering they lead to a dramatic increase for kinetic proton lab energies below about 20 keV.

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

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

  13. Optical and thermal electron transfer in rigid difunctional molecules of fixed distance and orientation

    Pulse radiolysis has been used to investigate intramolecular electron transfer in a series of molecules in which dimethoxynapththalene (M2N) and dicyanovinyl (DCV) groups are held at fixed distance and orientation by rigid saturated hydrocarbon bridges. Electron transfer from M2N- to DCV is faster than 1 x 109 s-1 for compounds in which the two groups are separated by 4, 6, 8, 10, or 12 saturated carbon-carbon bonds. For the 4-, 6-, and 8-bond compounds, optical electron transfer bands are present in the visible - near-infrared absorption spectra of the anions. The positions shift to higher energies with increasing solvent polarity. Their intensities are large (epsilon ? 2000 M-1 cm-1 for the 4-bond compound) and decrease rapidly as the length of the bridge increases. It is clear that exceptionally large, long-distance electronic coupling of the two ? systems occurs through the saturated bonds of the bridge. These electronic couplings are 0.16, 0.06, and 0.03 eV across 4-, 6-, and 8-bond bridges. Even larger couplings have been observed previously by photoelectron spectroscopy, but not for such large ? systems. With these large electronic couplings, long-distance electron transfer in the 4- and 6-bond compounds is expected to be adiabatic. Even for the 8-bond compound with a center-to-center distance of ?12 A the electron-transfer rate reduced from the optical electron-transfer absorption band is > 1012 s-1

  14. 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.

  15. 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.

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

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

    2014-03-01

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

  17. Specific intermolecular interactions of organic compounds

    Baev, Alexei K

    2012-01-01

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

  18. Effect of excess charge of cadmium sulfide colloid particles on interphase rate of electron transfer

    Kinetics of photodecolorization relaxation of aqueous solutions containing CdS colloid with particle size approx 50 A, L-cysteine as electron donor and oxygen as electron acceptor, has been studied. Photodecolorization relaxation kinetics reflects of nonequilibrium electron transfer from CdS particles to oxygen molecules in solution. The regularities defined are explained proceeding from the assumption on the effect of excess electrons charge on potential of colloid particles double layer, i.e. on apparent activation energy of electron interphase transfer

  19. Sequential energy and electron transfer in a three-component system aligned on a clay nanosheet.

    Fujimura, Takuya; Ramasamy, Elamparuthi; Ishida, Yohei; Shimada, Tetsuya; Takagi, Shinsuke; Ramamurthy, Vaidhyanathan

    2016-02-10

    To achieve the goal of energy transfer and subsequent electron transfer across three molecules, a phenomenon often utilized in artificial light harvesting systems, we have assembled a light absorber (that also serves as an energy donor), an energy acceptor (that also serves as an electron donor) and an electron acceptor on the surface of an anionic clay nanosheet. Since neutral organic molecules have no tendency to adsorb onto the anionic surface of clay, a positively charged water-soluble organic capsule was used to hold neutral light absorbers on the above surface. A three-component assembly was prepared by the co-adsorption of a cationic bipyridinium derivative, cationic zinc porphyrin and cationic octaamine encapsulated 2-acetylanthracene on an exfoliated anionic clay surface in water. Energy and electron transfer phenomena were monitored by steady state fluorescence and picosecond time resolved fluorescence decay. The excitation of 2-acetylanthracene in the three-component system resulted in energy transfer from 2-acetylanthracene to zinc porphyrin with 71% efficiency. Very little loss due to electron transfer from 2-acetylanthracene in the cavitand to the bipyridinium derivative was noticed. Energy transfer was followed by electron transfer from the zinc porphyrin to the cationic bipyridinium derivative with 81% efficiency. Analyses of fluorescence decay profiles confirmed the occurrence of energy transfer and subsequent electron transfer. Merging the concepts of supramolecular chemistry and surface chemistry we realized sequential energy and electron transfer between three hydrophobic molecules in water. Exfoliated transparent saponite clay served as a matrix to align the three photoactive molecules at a close distance in aqueous solutions. PMID:26820105

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

    Horáček, Miroslav

    2005-01-01

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

  1. 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...

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

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

    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...

  3. 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

  4. 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.

  5. Photo-induced electron transfer at nanostructured semiconductor-zinc porphyrin interface

    Hakola, Hanna; Pyymaki Perros, Alexander; Myllyperkiö, Pasi; Kurotobi, Kei; Lipsanen, Harri; Imahori, Hiroshi; Lemmetyinen, Helge; Tkachenko, Nikolai V.

    2014-01-01

    Electron transfer at metal oxide-organic dye interface on ZnO nanorod (ZnOr) templates was studied by femtosecond absorption spectroscopy method. Further confirmation of the electron transfer was obtained from photoelectrical studies. The fastest electron transfer from zinc porphyrin (ZnP) to semiconductor was observed for ZnOr modified by a 5 nm layer of TiO2 (nanoparticle and ZnP. This indicates that the charge recombination depends mainly on semiconductor bulk properties whereas the charge separation is determined by the organic-semiconductor interface.

  6. Reversible electron transfer reaction between polyaniline and thiol/disulfide couples

    Tatsuma, Tetsu; Matsui, Hiroshi; Shouji, Eiichi; Oyama, Noboru [Tokyo Univ. of Agriculture and Technology (Japan)

    1996-08-15

    Reversible electron transfer was observed between polyaniline (PAn) and thiol/disulfide couples of 2,5-dimercapto-1,3,4-thiadazole (DMcT), 2-mercapto-5-methyl-1,3,4-thiadiazole, 2-mercaptopyridine, and thiophenol. Thus, PAn can be used as a molecular current collector for those insulating organosulfur compounds, which are promising high-capacity energy storage materials. Among those couples, DMc Tex hibits the fastest reversible electron transfer. Electron transfer from other aromatic and aliphatic thiols to oxidized PAn is also observed. Effects of protons on the reactions and reaction kinetics are discussed. 10 refs., 10 figs., 1 tab.

  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 attached to electrodes show two distinct regimes: hopping and tunnelling, where in the latter, the current increases as a function of the energy of the transferred electron, a regime inaccessible by conventional scattering theory.

  8. 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 ?-conjugated core between molecules. We present here the electron density distribution in rubrene at 20?K and at 100?K obtained using a combination of high-resolution X-ray and neutron diffraction data. The topology of the electron density and energies of intermolecular interactions are studied quantitatively. Specifically, the presence of C?...C? interactions between neighbouring tetracene backbones of the rubrene molecules is experimentally confirmed from a topological analysis of the electron density, Non-Covalent Interaction (NCI analysis and the calculated interaction energy of molecular dimers. A significant contribution to the lattice energy of the crystal is provided by HH interactions. The electron density features of HH bonding, and the interaction energy of molecular dimers connected by HH 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.

  9. 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

  10. Extracellular electron transfer mechanism in Shewanella loihica PV-4 biofilms formed at indium tin oxide and graphite electrodes

    Jain, A.; Connolly, J.O.; Woolley, R.; Krishnamurthy, S.; Marsili, E.

    , secreted redox mediators accumulated at biofilm/graphite interface, thus increasing mediated electron transfer as the biofilm grows over five days. Our results showed that the electrode material determined the prevalent electron transfer mechanism...

  11. Electron transfer of nitrogen, oxygen and silicon in vanadium

    In order to assess the possibility of refining vanadium by the electricity transfer method, the process of electricity transfer of impurities of nitrogen, oxygen and silicon in vanadium is studied. The diffusion coefficients for these impurities in the temperature range of 1565-16650C are determined. The distribution of impurities over the length of a specimen is determined by methods of potentials and eddy currents. The electricity transfer is performed in a hermetically sealed flask in argon atmosphere. The diffusion coefficient values for O2, N2, Si in V at 16650C are measured to be 1.0x10-5; 0.38x10-5; 4.7x10-5cm.g/sec, respectively, which corresponds to an activation energy of 12, 20 and 24 kcal/mol. Also estimated are their effective valence and charge carrier density per atom of vanadium. The data obtained stubstantiate the ''hole'' mechanism of vanadium conductivity

  12. Direct Delocalization for Calculating Electron Transfer in Fullerenes

    Arntsen, Christopher D.; Reslan, Randa; Hernandez, Samuel; Gao, Yi; Neuhauser, Daniel

    2013-08-05

    A method is introduced for simple calculation of charge transfer between very large solvated organic dimers (fullerenes here) from isolated dimer calculations. The individual monomers in noncentrosymmetric dimers experience different chemical environments, so that the dimers do not necessarily represent bulk-like molecules. Therefore, we apply a delocalizing bias directly to the Fock matrix of the dimer system, and verify that this is almost as accurate as self-consistent solvation. As large molecules like fullerenes have a plethora of excited states, the initially excited state orbitals are thermally populated, so that the rate is obtained as a thermal average over Marcus thermal transfers.

  13. The Role of Protein Fluctuation Correlations in Electron Transfer in Photosynthetic Complexes

    Nesterov, Alexander I

    2014-01-01

    We consider the dependence of the electron transfer in photosynthetic complexes on correlation properties of random fluctuations of the protein environment. The electron subsystem is modeled by a finite network of connected electron (exciton) sites. The fluctuations of the protein environment are modeled by random telegraph processes, which act either collectively (correlated) or independently (uncorrelated) on the electron sites. We derived an exact closed system of first-order linear differential equations with constant coefficients, for the average density matrix elements and for their first moments. Under some conditions, we obtain analytic expressions for the electron transfer rates. We compare the correlated and uncorrelated regimes, and demonstrated numerically that the uncorrelated fluctuations of the protein environment can, under some conditions, either increase or decrease the electron transfer rates.

  14. Pulse radiolytic studies of electron transfer processes and applications to solar photochemistry. Progress report

    Neta, P.

    1995-02-01

    The pulse radiolysis technique is applied to the study of electron transfer processes in a variety of chemical systems. Reactive intermediates are produced in solution by electron pulse irradiation and the kinetics of their reactions are followed by time resolved absorption spectrophotometry. Complementary experiments are carried out with excimer laser flash photolysis. These studies are concerned with mechanisms, kinetics, and thermodynamics of reactions of organic and inorganic radicals and unstable oxidation states of metal ions. Reactions are studied in both aqueous and non-aqueous solutions. The studies focus on the unique ability of pulse radiolysis to provide absolute rate constants for reactions of many inorganic radicals and organic peroxyl radicals, species that are key intermediates in many chemical processes. A special concern of this work is the study of electron transfer reactions of metalloporphyrins, which permits evaluation of these molecules as intermediates in solar energy conversion. Metalloporphyrins react with free radicals via electron transfer, involving the ligand or the metal center, or via bonding to the metal, leading to a variety of chemical species whose behavior is also investigated. The highlights of the results during the past three years are summarized below under the following sections: (a) electron transfer reactions of peroxyl radicals, concentrating on the characterization of new peroxyl radicals derived from vinyl, phenyl, other aryl, and pyridyl; (b) solvent effects on electron transfer reactions of inorganic and organic peroxyl radicals, including reactions with porphyrins, and (c) electron transfer and alkylation reactions of metalloporphyrins and other complexes.

  15. 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...

  16. Photochemical reactions of electron-deficient olefins with N,N,N',N'-tetramethylbenzidine via photoinduced electron-transfer

    Photoinduced electron transfer reactions of several electron-deficient olefins with N,N,N',N'-tetramethylbenzidine (TMB) in acetonitrile solution have been studied by using laser flash photolysis technique and steady-state fluorescence quenching method. Laser pulse excitation of TMB yields 3TMB* after rapid intersystem crossing from 1TMB*. The triplet which located at 480 nm is found to undergo fast quenching with the electron acceptors fumaronitrile (FN), dimethyl fumarate (DMF), diethyl fumarate (DEF), cinnamonitrile (CN), α-acetoxyacrylonitrile (AAN), crotononitrile (CrN) and 3-methoxyacrylonitrile (MAN). Substituents binding to olefin molecule own different electron-donating/withdrawing powers, which determine the electron-deficient property (π-cloud density) of olefin molecule as well as control the electron transfer rate constant directly. The detection of ion radical intermediates in the photolysis reactions confirms the proposed electron transfer mechanism, as expected from thermodynamics. The quenching rate constants of triplet TMB by these olefins have been determined at 510 nm to avoid the disturbance of formed TMB cation radical around 475 nm. All the kqT values approach or reach to the diffusion-controlled limit. In addition, fluorescence quenching rate constants kqS have been also obtained by calculating with Stern-Volmer equation. A correlation between experimental electron transfer rate constants and free energy changes has been explained by Marcus theory of adiabatic outer-sphere electron transfer. Disharmonic kq values for CN and CrN in endergonic region may be the disturbance of exciplexs formation. e of exciplex formation

  17. Dynamic modulation of electron correlation by intramolecular modes in charge transfer compounds

    Meneghetti, M

    1999-01-01

    Electron-phonon and electron-electron interactions are in competition in determining the properties of molecular charge transfer conductors and superconductors. The direct influence of phonons on the electron-electron interaction was not before considered and in the present work the coupling of intramolecular modes to electron-electron interaction (U-vib interaction) is investigated.The effect of this coupling on the frequency of the normal modes of a dimer model is obtained and it is shown that frequency shifts of the Raman active modes are directly related to this coupling. The results are used to obtain the values of the U-vib coupling constants of intramolecular modes of a representative molecule of charge transfer conductors, like tetramethyltetratiafulvalene. Consequences of this coupling on the electron pairing are also suggested.

  18. 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.

  19. 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

  20. 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.

  1. 77 FR 6310 - Electronic Fund Transfers (Regulation E)

    2012-02-07

    ... information on whether it should revise these threshold numbers in Regulation Z. See 76 FR 75825 (Dec. 5, 2011... would complete the rulemaking process. 76 FR 29902 (May 23, 2011). This proposal has two parts. First... disclosure and two receipts) for each transfer described above would create information overload...

  2. Rhodamine-6G can photosensitize folic acid decomposition through electron transfer

    Hirakawa, Kazutaka; Ito, Hiroki

    2015-05-01

    Rhodamine-6G photosensitized folic acid decomposition in aqueous solution, and its quantum yield in the presence of 10 ?M folic acid was 9.9 10-6. A possible mechanism of this photodecomposition is direct oxidation through an electron transfer from folic acid to rhodamine-6G. The fluorescence lifetime of rhodamine-6G was slightly decreased by folic acid, suggesting electron transfer in the excited singlet state of rhodamine-6G. The quenching rate coefficient estimated from the Stern-Volmer plot of the fluorescence quenching supported that this electron transfer proceeds as a diffusion-controlled reaction. The quantum yields of the electron transfer and the following reaction could be determined.

  3. Radiation and photo induced electron transfer processes: Exciting possibilities for basic research and applications

    Radiation and/or photo induced electron transfer reaction results in retrievable storage of information, with extensive applications ranging from dosimetry, efficient light conversion molecular devices (LCMD), photo refraction, optical phase conjunction and holography. These areas gives ample new opportunities to conduct basic investigations to elucidate the mechanistic aspects of photo (radiation) induced electron transfer, and to translate the acquired knowledge into making a device. The talk will focus on the investigation by the author on photo induced electron transfer reaction in photorefractive systems and also on the radiation induced electron transfer processes in dosimetric materials. Furthermore, the recent trends in the light conversion molecular devices using rare earth complexes and the fluorescent molecular sensors for cation recognition will be discussed. (author)

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

    Rosspeintner Arnulf; Lang Bernhard; Vauthey Eric

    2013-01-01

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

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

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

    2010-03-01

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

  6. An Electron Transfer Approach to the Preparation of Highly Functionalized Anthraquinones

    Patrice Vanelle

    2005-01-01

    Full Text Available A series of highly functionalized quinones was prepared by an original reaction of 2,3-bis(chloromethyl-1,4-dimethoxyanthraquinone (6 with various nitronate anions under electron transfer reaction conditions.

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

    Patrice Vanelle

    2002-12-01

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

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

    Patrice Vanelle; Vincent Rémusat; Pascal Rathelot

    2002-01-01

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

  9. 77 FR 71035 - Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT...

    2012-11-28

    ... Fiscal Service Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT) Market Research Study AGENCY: Financial Management Service, Fiscal Service, Treasury. ACTION: Notice and Request for comments. SUMMARY: The Financial Management Service, as part of its...

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

    Sontakke, Atul D.; Ueda, Jumpei; Katayama, Yumiko; Dorenbos, Pieter; Tanabe, Setsuhisa

    2015-03-01

    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.

  11. 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

  12. 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... Electronic Funds Transfer Information. As prescribed in 32.1110(c), insert the following clause: Designation of Office for Government Receipt of Electronic Funds Transfer Information (MAY 1999) (a) As...

  13. 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

  14. 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.

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

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

    2015-01-01

    Various biological processes involve the conversion of energy into forms that are usable for chemical transformations and are quantum mechanical in nature. Such processes involve light absorption, excited electronic states formation, excitation energy transfer, electrons and protons tunnelling which for example occur in photosynthesis, cellular respiration, DNA repair, and possibly magnetic field sensing. Quantum biology uses computation to model biological interactions in light of quantum mechanical effects and has primarily developed over the past decade as a result of convergence between quantum physics and biology. In this paper we consider electron transfer in biological processes, from a theoretical view-point; namely in terms of quantum mechanical and semi-classical models. We systematically characterize the interactions between the moving electron and its biological environment to deduce the driving force for the electron transfer reaction and to establish those interactions that play the major role in propelling the electron. The suggested approach is seen as a general recipe to treat electron transfer events in biological systems computationally, and we utilize it to describe specifically the electron transfer reactions in Arabidopsis thaliana cryptochrome-a signaling photoreceptor protein that became attractive recently due to its possible function as a biological magnetoreceptor. PMID:26689792

  16. 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.

  17. Enhanced ionization of embedded clusters by Electron Transfer Mediated Decay in helium nanodroplets

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

    2015-01-01

    Here, we report the observation of electron transfer mediated decay For Mg clusters embedded in He nanodroplets. The process is mediated by the initial ionization of helium followed by an autoionization process by electron transfer in the Mg clusters. The photoelectron spectrum (PES) reveal a low energy ETMD peak. For Mg clusters larger than 7 atoms, we observe the formation of stable doubly ionized clusters. The process is shown to be the primamry ionization mechanism for embedded clusters.

  18. 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...

  19. Electron transfer and photophosphorylation in mitochondria of buckwheat after irradiation of seeds with ?-rays

    Pre-sowing irradiation of seeds at 500 R activates the transfer of electrons by photosynthetic electron transfer path of isolated buchwheat chloroplasts in the ontogenesis and stimulates the conjugated photosynthetic phosphorilation. An increased content of NADPxH2 is observed along with an elevated level of ATP production. Intensification of oxidative phosphorilation and growth of the P/O ratio of mitochondria has been shown in the ''irradiated'' plants, together with a concomitant increase of ATPhase activity in chloroplasts and mitochondria

  20. 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

  1. Microbial Electrochemical System: extracellular electron transfer from photosynthesis and respiration to electrode

    Hasan, Kamrul

    2016-01-01

    The electrochemical communication between microorganisms and electrodes has substantial implications both for basic understanding of biological electron transfer as well as in diverse applications, such as, microbial electrochemical system (MES), microbial biosensors and in production of valuable chemicals. In these systems the extracellular electron transfer (EET) from microbial metabolism to electrodes is restricted due to the insulated cellular exterior made of lipid structures. To obtain ...

  2. 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. Y5KF211CJ1).

  3. 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...

  4. Average electron tunneling route of the electron transfer in protein media.

    Nishioka, Hirotaka; Kakitani, Toshiaki

    2008-08-14

    We present a new theoretical method to determine and visualize the average tunneling route of the electron transfer (ET) in protein media. In this, we properly took into account the fluctuation of the tunneling currents and the quantum-interference effect. The route was correlated with the electronic factor in the case of ET by the elastic tunneling mechanism. We expanded by the interatomic tunneling currents 's. Incorporating the quantum-interference effect into the mean-square interatomic tunneling currents, denoted as , we could express as a sum of variant Planck's over 2pi(2). Drawing the distribution of on the protein structure, we obtain the map which visually represents which parts of bonds and spaces most significantly contribute to . We applied this method to the ET from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobacter sphaeroides. We obtained 's by a combined method of molecular dynamics simulations and quantum chemical calculations. In calculating , we found that much destructive interference works among the interatomic tunneling currents even after taking the average. We drew the map by a pipe model where atoms a and b are connected by a pipe with width proportional to the magnitude of . We found that two groups of 's, which are mutually coupled with high correlation in each group, have broad pipes and form the average tunneling routes, called Trp route and Met route. Each of the two average tunneling routes is composed of a few major pathways in the Pathways model which are fused at considerable part to each other. We also analyzed the average tunneling route for the ET by the inelastic tunneling mechanism. PMID:18630851

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

    Scharf, Christian, E-mail: Christian.Scharf@desy.de; Klanner, Robert

    2015-04-11

    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. The charge carriers in the sensor are 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 laser light of both wavelengths. The method has been applied successfully for the simulation of current transients of several different silicon pad diodes. It can also be applied for the analysis of transient-current measurements of radiation-damaged solid state sensors, as long as sensors properties, like high-frequency capacitance, are not too different.

  6. 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

  7. 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.

  8. 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

  9. Use of electron-excitation energy transfer in dye laser active media

    Rodchenkova, V.V.; Reva, M.G.; Akimov, A.I.; Uzhinov, B.M.

    1984-01-01

    A study was made of the spectral luminescence and lasing characteristics of two-component dye mixtures, and of the use of electron-excitation energy transfer to improve the laser emission parameters. A considerable increase in the lasing efficiencyu was found on exciting Trypaflavine by energy transfer from coumarin dyes. The use of electron-excitation energy transfer enabled the laser emission spectrum to be broadened. It was found that by varying the energy donor and acceptor concentrations one could produce laser emission of constant intensity in the spectral range between the donor and acceptor lasing regions.

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

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

    2011-05-24

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

  11. Exclusive electron scattering from deuterium at high momentum transfer

    Cross sections are presented for the reaction 2H(e,e'p)n for momentum transfers in the range 1.2≤Q2≤6.8(GeV/c)2 and for missing momenta from 0 to 250 MeV/c. The longitudinal-transverse interference structure function has been separated at Q2=1.2(GeV/c)2. The observables are compared to calculations performed in nonrelativistic and relativistic frameworks. The data are best described by a fully relativistic calculation

  12. Fabrication of nanowire electronics on nonconventional substrates by water-assisted transfer printing method

    Lee, Chi Hwan; Kim, Dong Rip; Zheng, Xiaolin

    2015-06-01

    We report a simple, versatile, and wafer-scale water-assisted transfer printing method (WTP) that enables the transfer of nanowire devices onto diverse nonconventional substrates that were not easily accessible before, such as paper, plastics, tapes, glass, polydimethylsiloxane (PDMS), aluminum foil, and ultrathin polymer substrates. The WTP method relies on the phenomenon of water penetrating into the interface between Ni and SiO2. The transfer yield is nearly 100%, and the transferred devices, including NW resistors, diodes, and field effect transistors, maintain their original geometries and electronic properties with high fidelity.

  13. Vibrational coherence transfer in an electronically decoupled molecular dyad

    Schweighfer, Felix; Dworak, Lars; Braun, Markus; Zastrow, Marc; Wahl, Jan; Burghardt, Irene; Rck-Braun, Karola; Wachtveitl, Josef

    2015-03-01

    The ring opening of a dithienylethene photoswitch incorporated in a bridged boron-dipyrromethene - dithienylethene molecular dyad was investigated with ultrafast spectroscopy. Coherent vibrations in the electronic ground state of the boron-dipyrromethene are triggered after selective photoexcitation of the closed dithienylethene indicating vibrational coupling although the two moieties are electronically isolated. A distribution of short-lived modes and a long-lived mode at 143 cm-1 are observed. Analysis of the theoretical frequency spectrum indicates two modes at 97 cm-1 and 147 cm-1 which strongly modulate the electronic transition energy. Both modes exhibit a characteristic displacement of the bridge suggesting that the mechanical momentum of the initial geometry change after photoexcitation of the dithienylethene is transduced to the boron-dipyrromethene. The relaxation to the dithienylethene electronic ground state is accompanied by significant heat dissipation into the surrounding medium. In the investigated dyad, the boron-dipyrromethene acts as probe for the ultrafast photophysical processes in the dithienylethene.

  14. 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

  15. 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

  16. Influence of intermolecular interactions on magnetic observables

    Schnack, Jürgen

    2016-02-01

    Very often it is an implied paradigm of molecular magnetism that magnetic molecules in a crystal interact so weakly that measurements of dc magnetic observables reflect ensemble properties of single molecules. But the number of cases where the assumption of virtually noninteracting molecules does not hold grows steadily. A deviation from the noninteracting case can especially clearly be seen in clusters with antiferromagnetic couplings, where steps of the low-temperature magnetization curve are smeared out with increasing intermolecular interaction. In this investigation we demonstrate with examples in one, two, and three space dimensions how intermolecular interactions influence typical magnetic observables such as magnetization, susceptibility, and specific heat.

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

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

    2011-01-01

    Mechanisms for electron transfer within microbial aggregates derived from an upflow anaerobic sludge blanket reactor converting brewery waste to methane were investigated in order to better understand the function of methanogenic consortia. The aggregates were electrically conductive, with...... assigned to methane producers, consistent with the poor capacity for hydrogen and formate utilization. These results demonstrate for the first time that methanogenic wastewater aggregates can be electrically conductive and suggest that direct interspecies electron transfer could be an important mechanism...... for electron exchange in some methanogenic systems....

  18. An expression for the bridge-mediated electron transfer rate in dye-sensitized solar cells.

    Maggio, Emanuele; Troisi, Alessandro

    2014-04-13

    We have derived an expression for the rate of electron transfer between a semiconductor and a redox centre connected to the semiconductor via a molecular bridge. This model is particularly useful to study the charge recombination (CR) process in dye-sensitized solar cells, where the dye is often connected to the semiconductor by a conjugated bridge. This formalism, designed to be coupled with density functional theory electronic structure calculations, can be used to explore the effect of changing the bridge on the rate of interfacial electron transfer. As an example, we have evaluated the CR rate for a series of systems that differ in the bridge length. PMID:24615149

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

    Kuznetsov, A. M.; Ulstrup, Jens

    1981-01-01

    the coupling between the metal centers [(Ru(II)/Ru(III) and Ru(II)/Co(III) couples] is sufficiently weak (class I or II mixed valence compounds). The ET mechanism can involve either direct transfer between the donor and acceptor groups or a higher order mechanism in which ET proceeds through......Intramolecular electron transfer (ET) over distances up to about 10 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...

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

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

    2014-03-03

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

  1. Low-temperature electron-phonon heat transfer in metal films

    Cojocaru, S.; Anghel, D. V.

    2016-03-01

    We consider the deformation potential mechanism of the electron-phonon coupling in metal films and investigate the intensity of the associated heat transfer between the electron and phonon subsystems. The focus is on the temperature region below dimensional crossover T Fermi gas. We derive an explicit expression for the power P (T ) of the electron-phonon heat transfer which explains the behavior observed in some experiments including the case of metallic film supported by an insulating membrane with different acoustic properties. It is shown that at low temperatures the main contribution is due to the coupling with Lamb's dilatational and flexural acoustic modes.

  2. Collective and Plasma Screening Effects on Electron Transfer Processes in Nonideal Plasmas

    Collective and plasma screening effects on the maximum principal quantum number and the maximum internuclear distance in electron transfers in nonideal plasmas are investigated. An effective pseudopotential model taking into account collective and plasma screening effects is applied to obtain the interaction potential and screened effective charge in nonideal plasmas. The screened over the barrier model is applied to obtain the electron capture radius and the maximum principal quantum number of the final state of the transferred electron. The results show that the electron capture radius is more sensitive to the collective effect rather than the plasma screening effect. The electron capture radius is found to increase with increasing nonideality plasmas parameter. It is also found that the maximum principal quantum number of the final state of the electron increases with increasing nonideality plasma parameter and reciprocal Debye length

  3. Electron transfer within xanthine oxidase: A solvent kinetic isotope effect study

    Solvent kinetic isotope effect studies of electron transfer within xanthine oxidase have been performed, using a stopped-flow pH-jump technique to perturb the distribution of reducing equivalents within partially reduced enzyme and follow the kinetics of reequilibration spectrophotometrically. It is found that the rate constant for electron transfer between the flavin and one of the iron-sulfur centers of the enzyme observed when the pH is jumped from 10 to 6 decreases from 173 to 25 s-1 on going from HJ2O to D2O, giving an observed solvent kinetic isotope effect of 6.9. An effect of comparable magnitude is observed for the pH jump in the opposite direction, the rate constant decreasing form 395 to 56 s-1. The solvent kinetic isotope effect on kobs is found to be directly proportional to the mole fraction of D2O in the reaction mix for the pH jump in each direction, consistent with the effect arising from a single exchangeable proton. Calculations of the microscopic rate constants for electron transfer between the flavin and the iron-sulfur center indicate that the intrinsic solvent kinetic isotope effect for electron transfer from the neutral flavin semiquinone to the iron-sulfur center designated Fe/S I is substantially greater than for electron transfer in the opposite direction and that the observed solvent kinetic isotope effect is a weighted average of the intrinsic isotope effects for the forward and reverse microscopic electron-transfer steps. The results emphasize the importance of prototropic equilibria in the kinetic as well as thermodynamic behavior of xanthine oxidase and indicate that protonation/deprotonation of the isoalloxazine ring is concomitant with electron transfer in the xanthine oxidase system

  4. 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 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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr05165c

  5. 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

  6. 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

    Quantum dots (QDs) and graphene are both promising materials for the development of new-generation optoelectronic devices. Towards this end, synergic assembly of these two building blocks is a key step but remains a challenge. Here, we show a one-step strategy for organizing QDs in a graphene...... matrix via interfacial self-assembly, leading to the formation of sandwiched hybrid QD-graphene nanofilms. We have explored structural features, electron transfer kinetics and photocurrent generation capacity of such hybrid nanofilms using a wide variety of advanced techniques. Graphene nanosheets...... interlink QDs and significantly improve electronic coupling, resulting in fast electron transfer from photoexcited QDs to graphene with a rate constant of 1.3 × 109 s−1. Efficient electron transfer dramatically enhances photocurrent generation in a liquid-junction QD-sensitized solar cell where the hybrid...

  7. Coherent electron transfer in a coupled quantum dot nanostructure using stimulated Raman adiabatic passage

    Fountoulakis, Antonios; Paspalakis, Emmanuel

    2013-05-01

    We study the potential for coherent transfer of a single electron between the ground states of two anharmonic coupled quantum dots using an adiabatic passage method. We consider the interaction of a quantum dot structure characterized by an asymmetric confining potential by two external electromagnetic fields. We use the method of stimulated Raman adiabatic passage (STIRAP) for control of the dynamics of the electron, and ultimately for succeeding the transfer of the electron from the initially occupied quantum dot to the other quantum dot. Results for several values of the parameters of the applied electromagnetic fields are presented, and we show that STIRAP can lead to efficient coherent single electron transfer for a wide range of these parameters.

  8. Interspecies electron transfer in methanogenic propionate degrading consortia

    de Bok, F. A. M.; Plugge, C. M.; Stams, A.J.M.

    2004-01-01

    Propionate is a key intermediate in the conversion of complex organic matter under methanogenic conditions. Oxidation of this compound requires obligate syntrophic consortia of acetogenic proton- and bicarbonate reducing bacteria and methanogenic archaea. Although H2 acts as an electron-carrier in these consortia, evidence accumulates that formate plays an even more important role. To make energy yield from propionate oxidation energetically feasible for the bacteria and archaea involved, the...

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

    Klauss, André; Haumann, Michael; Dau, Holger

    2012-01-01

    Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel–production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese–calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent ...

  10. 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...

  11. 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)

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

    Highlights: We model electron dynamics across cyano alkanethiolates attached to gold cluster. We present electron transfer time scales from TD-DFT and TD-CI based simulations. Both DFT and CI methods qualitatively predict the trend in time scales. TD-CI predicts the experimental relative time scale very accurately. - Abstract: We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual ?? molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process

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

    Ramakrishnan, Raghunathan, E-mail: r.ramakrishnan@unibas.ch [Institute of Physical Chemistry, National Center for Computational Design and Discovery of Novel Materials (MARVEL), Department of Chemistry, University of Basel, Klingelbergstrasse 80, CH-4056 Basel (Switzerland); Nest, Mathias [Theoretische Chemie, Technische Universitt Mnchen, Lichtenbergstr. 4, 85747 Garching (Germany)

    2015-01-13

    Highlights: We model electron dynamics across cyano alkanethiolates attached to gold cluster. We present electron transfer time scales from TD-DFT and TD-CI based simulations. Both DFT and CI methods qualitatively predict the trend in time scales. TD-CI predicts the experimental relative time scale very accurately. - Abstract: We employ wavepacket simulations based on many-body time-dependent configuration interaction (TD-CI), and single active electron theories, to predict the ultrafast molecule/metal electron transfer time scales, in cyano alkanethiolates bonded to model gold clusters. The initial states represent two excited states where a valence electron is promoted to one of the two virtual ?{sup ?} molecular orbitals localized on the cyanide fragment. The ratio of the two time scales indicate the efficiency of one charge transfer channel over the other. In both our one-and many-electron simulations, this ratio agree qualitatively with each other as well as with the previously reported experimental time scales (Blobner et al., 2012), measured for a macroscopic metal surface. We study the effect of cluster size and the description of electron correlation on the charge transfer process.

  14. 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

  15. 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 4.14.2 ppm at proton nuclear magnetic resonance spectroscopy results clearly confirms the living nature of the polymerization. Thermogravimetric analysis shows that thermal stability of the nanocomposites increases by adding nanoparticles content. Decrease of glass transition temperature is also demonstrated by the addition of 3 wt% of silica nanoparticles according to the differential scanning calorimetry results.

  16. 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 thermal stability of the nanocomposites increases by adding nanoparticles content. Decrease of glass transition temperature is also demonstrated by the addition of 3 wt% of silica nanoparticles according to the differential scanning calorimetry results

  17. 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.

  18. Mapping intermolecular bonding in C60

    Sundqvist, Bertil

    2014-08-01

    The formation of intermolecular bonds in C60 has been investigated in detail at pressures below 2.2 GPa and up to 750 K. Fullerene samples were heated in a temperature gradient to obtain data on the formation of dimers and low-dimensional polymers along isobars. Intermolecular bonding was analyzed ex situ by Raman scattering, using both intramolecular modes and intermolecular stretching modes. Semi-quantitative reaction maps are given for the formation of dimers and chains. The activation energy for dimer formation decreases by 0.2 meV pm-1 when intermolecular distances decrease and dimer formation is noticeably affected by the rotational state of molecules. Above 400-450 K larger oligomers are formed; below 1.4 GPa most of these are disordered, with small domains of linear chains, but above this the appearance of stretching modes indicates the existence of ordered one-dimensional polymers. At the highest pressures and temperatures two-dimensional polymers are also observed.

  19. 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. © 2014 American Chemical Society.

  20. A nonadiabatic theory for ultrafast catalytic electron transfer: a model for the photosynthetic reaction center.

    Aubry, Serge; Kopidakis, Georgios

    2005-12-01

    A non-adiabatic theory of Electron Transfer (ET), which improves the standard theory near the inversion point and becomes equivalent to it far from the inversion point, is presented. The complex amplitudes of the electronic wavefunctions at different sites are used as Kramers variables for describing the quantum tunneling of the electron in the deformable potential generated by its environment (nonadiabaticity) which is modeled as a harmonic classical thermal bath. After exact elimination of the bath, the effective electron dynamics is described by a discrete nonlinear Schrödinger equation with norm preserving dissipative terms and a Langevin random force, with a frequency cut-off, due to the thermalized phonons.This theory reveals the existence of a specially interesting marginal case when the linear and nonlinear coefficients of a two electronic states system are appropriately tuned for forming a Coherent Electron-Phonon Oscillator (CEPO). An electron injected on one of the electronic states of a CEPO generates large amplitude charge oscillations (even at zero temperature) associated with coherent phonon oscillations and electronic level oscillations. This fluctuating electronic level may resonate with a third site which captures the electron so that Ultrafast Electron Transfer (UFET) becomes possible. Numerical results are shown where two weakly interacting sites, a donor and a catalyst, form a CEPO that triggers an UFET to an acceptor. Without a catalytic site, a very large energy barrier prevents any direct ET. This UFET is shown to have many qualitative features similar to those observed in the primary charge separation in photosynthetic reaction centers. We suggest that more generally, CEPO could be a paradigm for understanding many selective chemical reactions involving electron transfer in biosystems. PMID:23345905

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

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

    2011-01-01

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

  2. 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.

  3. Photoinduced electron transfer in a chromophore-catalyst assembly anchored to TiO2.

    Ashford, Dennis L; Song, Wenjing; Concepcion, Javier J; Glasson, Christopher R K; Brennaman, M Kyle; Norris, Michael R; Fang, Zhen; Templeton, Joseph L; Meyer, Thomas J

    2012-11-21

    Photoinduced formation, separation, and buildup of multiple redox equivalents are an integral part of cycles for producing solar fuels in dye-sensitized photoelectrosynthesis cells (DSPECs). Excitation wavelength-dependent electron injection, intra-assembly electron transfer, and pH-dependent back electron transfer on TiO(2) were investigated for the molecular assembly [((PO(3)H(2)-CH(2))-bpy)(2)Ru(a)(bpy-NH-CO-trpy)Ru(b)(bpy)(OH(2))](4+) ([TiO(2)-Ru(a)(II)-Ru(b)(II)-OH(2)](4+); ((PO(3)H(2)-CH(2))(2)-bpy = ([2,2'-bipyridine]-4,4'-diylbis(methylene))diphosphonic acid); bpy-ph-NH-CO-trpy = 4-([2,2':6',2″-terpyridin]-4'-yl)-N-((4'-methyl-[2,2'-bipyridin]-4-yl)methyl) benzamide); bpy = 2,2'-bipyridine). This assembly combines a light-harvesting chromophore and a water oxidation catalyst linked by a synthetically flexible saturated bridge designed to enable long-lived charge-separated states. Following excitation of the chromophore, rapid electron injection into TiO(2) and intra-assembly electron transfer occur on the subnanosecond time scale followed by microsecond-millisecond back electron transfer from the semiconductor to the oxidized catalyst, [TiO(2)(e(-))-Ru(a)(II)-Ru(b)(III)-OH(2)](4+)→[TiO(2)-Ru(a)(II)-Ru(b)(II)-OH(2)](4+). PMID:23101955

  4. Electron transfer beyond the static picture: a TDDFT∕TD-ZINDO study of a pentacene dimer.

    Reslan, Randa; Lopata, Kenneth; Arntsen, Christopher; Govind, Niranjan; Neuhauser, Daniel

    2012-12-14

    We use time-dependent density functional theory and time-dependent ZINDO (a semi-empirical method) to study transfer of an extra electron between a pair of pentacene molecules. A measure of the electronic transfer integral is computed in a dynamic picture via the vertical excitation energy from a delocalized anionic ground state. With increasing dimer separation, this dynamical measurement of charge transfer is shown to be significantly larger than the commonly used static approximation (i.e., LUMO+1-LUMO of the neutral dimer, or HOMO-LUMO of the charged dimer), up to an order of magnitude higher at 6 Å. These results offer a word of caution for calculations involving large separations, as in organic photovoltaics, where care must be taken when using a static picture to model charge transfer. PMID:23249039

  5. Electron transfer beyond the static picture: A TDDFT/TD-ZINDO study of a pentacene dimer

    Reslan, Randa; Lopata, Kenneth A.; Arntsen, Christopher D.; Govind, Niranjan; Neuhauser, Daniel

    2012-12-14

    We use time-dependent density functional theory and time-dependent ZINDO (a semi-empirical method) to study transfer of an extra electron between a pair of pentacene dimers. A measure of the electronic transfer integral is computed in a dynamic picture via the vertical excitation energy from a delocalized anionic ground state. With increasing dimer separation, this dynamical measurement of charge transfer is shown to be significantly larger than the commonly used static approximation (i.e., LUMO+1 - LUMO of the neutral dimer, or HOMO - LUMO of the charged dimer), up to an order of magnitude higher at 6 Å. These results offer a word of caution for calculations involving large separations, as in organic photovoltaics, where care must be taken when using a static picture to model charge transfer.

  6. Electron transfer beyond the static picture: A TDDFT/TD-ZINDO study of a pentacene dimer

    Reslan, Randa; Lopata, Kenneth; Arntsen, Christopher; Govind, Niranjan; Neuhauser, Daniel

    2012-12-01

    We use time-dependent density functional theory and time-dependent ZINDO (a semi-empirical method) to study transfer of an extra electron between a pair of pentacene molecules. A measure of the electronic transfer integral is computed in a dynamic picture via the vertical excitation energy from a delocalized anionic ground state. With increasing dimer separation, this dynamical measurement of charge transfer is shown to be significantly larger than the commonly used static approximation (i.e., LUMO+1-LUMO of the neutral dimer, or HOMO-LUMO of the charged dimer), up to an order of magnitude higher at 6 Å. These results offer a word of caution for calculations involving large separations, as in organic photovoltaics, where care must be taken when using a static picture to model charge transfer.

  7. 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 artists 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.

  8. 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.

  9. 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.

  10. Time-resolved spectroscopy of energy and electron transfer processes in the photosynthetic bacterium Heliobacillus mobilis.

    Lin, S.; Chiou, H C; Kleinherenbrink, F A; Blankenship, R E

    1994-01-01

    The kinetics of excitation energy transfer and electron transfer processes within the membrane of Heliobacillus mobilis were investigated using femtosecond transient absorption difference spectroscopy at room temperature. The kinetics in the 725- to 865-nm region, upon excitation at 590 and 670 nm, were fit using global analysis. The fits returned three kinetic components with lifetimes of 1-2 ps and 27-30 ps, and a component that does not decay within several nanoseconds. The 1- to 2-ps comp...

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

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

  12. 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

  13. Ion-mediated electron transfer in a supramolecular donor-acceptor ensemble.

    Park, Jung Su; Karnas, Elizabeth; Ohkubo, Kei; Chen, Ping; Kadish, Karl M; Fukuzumi, Shunichi; Bielawski, Christopher W; Hudnall, Todd W; Lynch, Vincent M; Sessler, Jonathan L

    2010-09-10

    Ion binding often mediates electron transfer in biological systems as a cofactor strategy, either as a promoter or as an inhibitor. However, it has rarely, if ever, been exploited for that purpose in synthetic host-guest assemblies. We report here that strong binding of specific anions (chloride, bromide, and methylsulfate but not tetrafluoroborate or hexafluorophosphate) to a tetrathiafulvalene calix[4]pyrrole (TTF-C4P) donor enforces a host conformation that favors electron transfer to a bisimidazolium quinone (BIQ2+) guest acceptor. In contrast, the addition of a tetraethylammonium cation, which binds more effectively than the BIQ2+ guest in the TTF-C4P cavity, leads to back electron transfer, restoring the initial oxidation states of the donor and acceptor pair. The products of these processes were characterized via spectroscopy and x-ray crystallography. PMID:20829481

  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. Electron transfer mechanism in Shewanella loihica PV-4 biofilms formed at graphite electrode.

    Jain, Anand; Zhang, Xiaoming; Pastorella, Gabriele; Connolly, Jack O; Barry, Niamh; Woolley, Robert; Krishnamurthy, Satheesh; Marsili, Enrico

    2012-10-01

    Electron transfer mechanisms in Shewanella loihica PV-4 viable biofilms formed at graphite electrodes were investigated in potentiostat-controlled electrochemical cells poised at oxidative potentials (0.2V vs. Ag/AgCl). Chronoamperometry (CA) showed a repeatable biofilm growth of S. loihica PV-4 on graphite electrode. CA, cyclic voltammetry (CV) and its first derivative shows that both direct electron transfer (DET) mediated electron transfer (MET) mechanism contributes to the overall anodic (oxidation) current. The maximum anodic current density recorded on graphite was 90 μA cm(-2). Fluorescence emission spectra shows increased concentration of quinone derivatives and riboflavin in the cell-free supernatant as the biofilm grows. Differential pulse voltammetry (DPV) show accumulation of riboflavin at the graphite interface, with the increase in incubation period. This is the first study to observe a gradual shift from DET to MET mechanism in viable S. loihica PV-4 biofilms. PMID:22281091

  16. Recent Advances in Photoinduced Electron Transfer Processes of Fullerene-Based Molecular Assemblies and Nanocomposites

    Osamu Ito

    2012-05-01

    Full Text Available Photosensitized electron-transfer processes of fullerenes hybridized with electron donating or other electron accepting molecules have been surveyed in this review on the basis of the recent results reported mainly from our laboratories. Fullerenes act as photo-sensitizing electron acceptors with respect to a wide variety of electron donors; in addition, fullerenes in the ground state also act as good electron acceptors in the presence of light-absorbing electron donors such as porphyrins. With single-wall carbon nanotubes (SWCNTs, the photoexcited fullerenes act as electron acceptor. In the case of triple fullerene/porphyrin/SWCNT architectures, the photoexcited porphyrins act as electron donors toward the fullerene and SWCNT. These mechanisms are rationalized with the molecular orbital considerations performed for these huge supramolecules. For the confirmation of the electron transfer processes, transient absorption methods have been used, in addition to time-resolved fluorescence spectral measurements. The kinetic data obtained in solution are found to be quite useful to predict the efficiencies of photovoltaic cells.

  17. 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

  18. 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...

  19. Intra- and intermolecular reaction selectivities of γ-substituted adamantanylidenes.

    Knoll, Wolfgang; Kaneno, Daisuke; Bobek, Michael M; Brecker, Lothar; Rosenberg, Murray G; Tomoda, Shuji; Brinker, Udo H

    2012-02-01

    A study of adamantanylidenes having a γ-substituent (R) was undertaken to gauge how inductive and steric effects of remotely positioned functional groups influence intra- and intermolecular product selectivity. 3H-Diazirines were thermolyzed or photolyzed to generate the corresponding carbenes. On rapid heating, the resulting carbenes isomerized to 2,4-didehydroadamantanes by intramolecular 1,3-CH insertions. When R was an electron donor (R(D)) mostly asymmetric 1-substituted derivatives were produced but when it was an electron acceptor (R(A)) the symmetric 7-substituted ones were formed. When solutions were exposed to UV-A light, intermolecular adducts from the carbenes and solvent predominated with lesser amounts of intramolecular product being formed. Valence isomerization of 3H-diazirines also afforded diazo compounds. In methanol, protonation of diazo compounds to give the corresponding 2-adamantyl cations exceeds their coupling. This diversion was controlled with fumaronitrile by trapping the diazo compounds. The adducts possessed mostly anti configurations with R = R(D) and syn arrangements with R = R(A). The connection between as- and anti-product formation and that of s- and syn-products was deemed to be the consequence of a rapid equilibrium between two distinct carbene conformations. This was qualified and quantified using ab initio calculations and NBO analyses. PMID:22168480

  20. Using triazine as coupling unit for intra and intermolecular ferromagnetic coupling I

    Zhang, Jingping; Baumgarten, Martin

    1997-01-01

    Novel high spin bi- and triradicals composed of triazine coupling units and different kinds of radical centers ( +NH 2, .NH, .CH 2, HNO ., :N, :C), are predicted from AM1-CI calculations. It is found that when +.NH, and .N serve as spin centers, the high spin ground states of bi- and triradicals with triazine coupling units are more stable than those with phenylene and benzenetriyl ones, respectively. For a biradical with triazine coupling unit and +NH spin center, intermolecular hydrogen bonds can be formed between this biradical and a diamagnetic cyanuric acid or between two biradicals themselves as well, which may be considered as the basic units of supramolecular aggregates. For these two cases, it is shown that intermolecular hydrogen bonds between high spin molecules and diamagnetic molecules reduce the stability of high spin ground state, but the intermolecular ferromagnetic coupling of biradical dimer can be transferred although weakly through hydrogen bonds.

  1. Excitational energy and photoinduced electron transfer reactions in Ge(IV) corroleporphyrin hetero dimers

    We have constructed hetero dimers by utilizing the axial bonding capabilities as well as known oxophilicity of Germanium(IV) ion of Germanium(IV) corroles as basal scaffolding unit and either free-base or ZnII porphyrin at axial position for the first time. Both the hetero dimers have been completely characterized by elemental analysis, UVvisible, proton nuclear magnetic resonance (1D and 1H1H COSY) and fluorescence spectroscopies as well as electrochemical methods. The ground state properties indicate that there exists a minimum ?? interactions between the macrocyclic units of these dyads. Excited state properties showed that there is an electronic energy transfer competing photoinduced electron transfer from singlet state of basal metalloid corrole to the axial porphyrin and a photoinduced electron transfer from excited state of axial porphyrin to the ground state of central metalloid corrole are possible. -- Highlights: ? We have constructed hetero dimers based on corroleporphyrin by utilizing axial position of Ge(IV) corrole. There exists mimum ?? interactions between the macrocyclic units. The excited state properties indicate that both excitation energy transfer and photoinduced electron transfer reactions are possible in these hetero dimers

  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. Contribution of transfer ionization to total electron capture from a helium target

    Tanis, J. A.; Clark, M. W.; Price, R.; Olson, R. E.

    1987-08-01

    The contribution of transfer ionization (TI) to total electron capture has been measured for Oq+ ions (q=5, 6, 7, and 8) colliding with helium at energies from 0.5 to 1.5 MeV/u. These measurements, along with other published results, suggest a maximum TI contribution to total capture of ~0.15q0.5 at E (in keV/u)/q0.5~=100. The results demonstrate that the failure to account for transfer ionization in total single-charge-transfer cross sections may lead to large discrepancies between experiment and theory.

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

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

    2016-01-01

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

  6. 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

  7. Fast electron transfer from PbSe quantum dots to TiO2

    Fast electron transfer from PbSe quantum dots (QDs) to the porous anatase TiO2 film was observed in transient absorption, when the lowest unoccupied molecular orbital level of PbSe QDs is higher than that of TiO2. In PbSe QDs 2.7nm in diameter linked to the TiO2 film the bleaching recovery decay shortened to 1ps from 650ps observed in the non-linked PbSe QDs. The electron transfer from the quantum state in small PbSe QDs to TiO2 takes place fast and efficiently

  8. Fast electron transfer from PbSe quantum dots to TiO{sub 2}

    Masumoto, Yasuaki; Takagi, Hayato; Umino, Hikaru; Suzumura, Eri [Institute of Physics, University of Tsukuba, Tsukuba 305-8571 (Japan)

    2013-12-04

    Fast electron transfer from PbSe quantum dots (QDs) to the porous anatase TiO{sub 2} film was observed in transient absorption, when the lowest unoccupied molecular orbital level of PbSe QDs is higher than that of TiO{sub 2}. In PbSe QDs 2.7nm in diameter linked to the TiO{sub 2} film the bleaching recovery decay shortened to 1ps from 650ps observed in the non-linked PbSe QDs. The electron transfer from the quantum state in small PbSe QDs to TiO{sub 2} takes place fast and efficiently.

  9. Linear free-enthalpy relation for radical yield in fluorescence quenching by electron transfer

    Iwa, Peter; Steiner, Ulrich; Vogelmann, Ekehardt; Kramer, Horst E.A.

    1982-01-01

    The rate constant (kq) and net electron-transfer yield (Φr) in the quenching of an excited oxonine singlet by 24 aromatic amines and methoxy compounds were determined in methanol from stationary fluorescence measurements and flash spectroscopy. The systems investigated correspond to a variation of ΔGet°, the standard free reaction enthalpy of the electron transfer from the quencher to excited singlet oxonine, between -0.12 and -1.56 eV. Whereas the kq values observed are all close to the diff...

  10. 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...

  11. Promoted electron transfer of mitoxantrone binding with DNA by cytochrome c

    A promoted electron transfer of an antitumor drug, mitoxantrone (MTX), intercalating into DNA duplex was successfully obtained upon addition of cytochromes c (cyt. c) in NaAc-HAc buffer solution (pH 4.5). The experimental results suggested that co-existence of MTX and cyt. c in the DNA helix is an important factor for accelerated electron transfer of MTX, where the promoter, cyt. c, operated smoothly through the DNA bridge. The UV/Vis spectroscopic experiments further confirmed the interaction process. Furthermore, a possible mechanism of such reaction was also discussed in this paper

  12. A structural basis of light energy and electron transfer in biology (Nobel lecture)

    Huber, R.

    1989-07-01

    Aspects of intramolecular light energy and electron transfer are discussed for three protein cofactor complexes whose three-dimensional structures have been elucidated by X-ray crystallography: the light harvesting phycobilisomes of cyanobacteria, the reaction center of purple bacteria, and the blue multi-copper oxidases. A wealth of functional data is available for these systems which allows specific correlations to be made between structure and function and general conclusions to be drawn about light energy and electron transfer in biological materials. (orig.).

  13. 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

  14. 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.

  15. Spin effects in intramolecular electron transfer in naproxen- N -methylpyrrolidine dyad

    Magin, I. M.; Polyakov, N. E.; Khramtsova, E. A.; Kruppa, A. I.; Tsentalovich, Yu. P.; Leshina, T. V.; Miranda, M. A.; Nuin, E.; Marin, M. L.

    2011-11-01

    The intramolecular electron transfer in the naproxen- N-methylpyrrolidine dyad has been investigated by spin chemistry methods. The existence of CIDNP in a high magnetic field points to electron transfer as a possible mechanism of the quenching of the excited state of a dyad. However, the failure to detect magnetic field effects on triplet yield makes us conclude that this quenching mechanism is not the only one. The observation of CIDNP effects in the dyad in the media of low polarity and the short risetime of triplet state formation indicate a potential role of exciplex in the quenching of the excited state of the dyad.

  16. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    Farver, O.; Zhang, Jingdong; Chi, Qijin; Precht, I.; Ulstrup, Jens

    2001-01-01

    positive rather than negative. Isotope effects are, however, also inherent in the nuclear reorganization Gibbs free energy and in the tunneling factor for the electron transfer process. A slightly larger thermal protein expansion in H2O than in D2O (0.001 nm K-1) is sufficient both to account for the......Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1)) and...

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

    Freire Renato S.

    2003-01-01

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

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

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

  19. 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.

  20. 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

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

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

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

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

    2011-08-15

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

  3. Tuning of Hemes b Equilibrium Redox Potential Is Not Required for Cross-Membrane Electron Transfer*

    Pintscher, Sebastian; Kuleta, Patryk; Cieluch, Ewelina; Borek, Arkadiusz; Sarewicz, Marcin; Osyczka, Artur

    2016-01-01

    In biological energy conversion, cross-membrane electron transfer often involves an assembly of two hemes b. The hemes display a large difference in redox midpoint potentials (ΔEm_b), which in several proteins is assumed to facilitate cross-membrane electron transfer and overcome a barrier of membrane potential. Here we challenge this assumption reporting on heme b ligand mutants of cytochrome bc1 in which, for the first time in transmembrane cytochrome, one natural histidine has been replaced by lysine without loss of the native low spin type of heme iron. With these mutants we show that ΔEm_b can be markedly increased, and the redox potential of one of the hemes can stay above the level of quinone pool, or ΔEm_b can be markedly decreased to the point that two hemes are almost isopotential, yet the enzyme retains catalytically competent electron transfer between quinone binding sites and remains functional in vivo. This reveals that cytochrome bc1 can accommodate large changes in ΔEm_b without hampering catalysis, as long as these changes do not impose overly endergonic steps on downhill electron transfer from substrate to product. We propose that hemes b in this cytochrome and in other membranous cytochromes b act as electronic connectors for the catalytic sites with no fine tuning in ΔEm_b required for efficient cross-membrane electron transfer. We link this concept with a natural flexibility in occurrence of several thermodynamic configurations of the direction of electron flow and the direction of the gradient of potential in relation to the vector of the electric membrane potential. PMID:26858251

  4. Tuning of Hemes b Equilibrium Redox Potential Is Not Required for Cross-Membrane Electron Transfer.

    Pintscher, Sebastian; Kuleta, Patryk; Cieluch, Ewelina; Borek, Arkadiusz; Sarewicz, Marcin; Osyczka, Artur

    2016-03-25

    In biological energy conversion, cross-membrane electron transfer often involves an assembly of two hemesb The hemes display a large difference in redox midpoint potentials (ΔEm_b), which in several proteins is assumed to facilitate cross-membrane electron transfer and overcome a barrier of membrane potential. Here we challenge this assumption reporting on hemebligand mutants of cytochromebc1in which, for the first time in transmembrane cytochrome, one natural histidine has been replaced by lysine without loss of the native low spin type of heme iron. With these mutants we show that ΔEm_b can be markedly increased, and the redox potential of one of the hemes can stay above the level of quinone pool, or ΔEm_b can be markedly decreased to the point that two hemes are almost isopotential, yet the enzyme retains catalytically competent electron transfer between quinone binding sites and remains functionalin vivo This reveals that cytochromebc1can accommodate large changes in ΔEm_b without hampering catalysis, as long as these changes do not impose overly endergonic steps on downhill electron transfer from substrate to product. We propose that hemesbin this cytochrome and in other membranous cytochromesbact as electronic connectors for the catalytic sites with no fine tuning in ΔEm_b required for efficient cross-membrane electron transfer. We link this concept with a natural flexibility in occurrence of several thermodynamic configurations of the direction of electron flow and the direction of the gradient of potential in relation to the vector of the electric membrane potential. PMID:26858251

  5. Intermolecular Interactions of Noble-Gas-Containing Species

    Lignell, Antti

    2008-01-01

    The importance of intermolecular interactions to chemistry, physics, and biology is difficult to overestimate. Without intermolecular forces, condensed phase matter could not form. The simplest way to categorize different types of intermolecular interactions is to describe them using van der Waals and hydrogen bonded (H-bonded) interactions. In the H-bond, the intermolecular interaction appears between a positively charged hydrogen atom and electronegative fragments and it originates from str...

  6. Tuning electron transfer rates through molecular bridges in quantum dot sensitized oxides.

    Wang, Hai; McNellis, Erik R; Kinge, Sachin; Bonn, Mischa; Cánovas, Enrique

    2013-11-13

    Photoinduced electron transfer processes from semiconductor quantum dots (QDs) molecularly bridged to a mesoporous oxide phase are quantitatively surveyed using optical pump-terahertz probe spectroscopy. We control electron transfer rates in donor-bridge-acceptor systems by tuning the electronic coupling strength through the use of n-methylene (SH-[CH2]n-COOH) and n-phenylene (SH-[C6H4](n)-COOH) molecular bridges. Our results show that electron transfer occurs as a nonresonant quantum tunneling process with characteristic decay rates of β(n) = 0.94 ± 0.08 and β(n) = 1.25 per methylene and phenylene group, respectively, in quantitative agreement with reported conductance measurements through single molecules and self-assembled monolayers. For a given QD donor-oxide acceptor separation distance, the aromatic n-phenylene based bridges allow faster electron transfer processes when compared with n-methylene based ones. Implications of these results for QD sensitized solar cell design are discussed. PMID:24093529

  7. 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

  8. 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

  9. 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

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

    Azar, R. Julian; Head-Gordon, Martin

    2012-01-01

    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.

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

    Azar, R. Julian; Head-Gordon, Martin [Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720 (United States) and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2012-01-14

    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 C{sub s}-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.

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

    Smirnov, Anatoly Yu; Nori, Franco

    2010-01-01

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

  14. Electron transfer from purine deoxynucleotides to deoxynucleotides deprotonated radical cations. in aqueous solution

    Shi, Yimin; Huang, Chungyang; Wang, Wengfeng; Kang, Jiuhong; Yao, Side; Lin, Nianyun; Zheng, Rongliang

    2000-05-01

    In aqueous solution, the deprotonated radical cations of dCMP, TMP and Poly C created by SO 4rad - can react with dAMP at a close to diffusion control rate constants which indicates a rapid electron transfer from dAMP to deprotonated radical cations of deoxynucleotides. Analogous reaction was found to occur between the deprotonated radical cation of dAMP, dCMP, TMP or Poly C and dGMP. The rate constants were determined to be 0.64-1.310 8 M -1 s -1 for electron transfer from dAMP toward deprotonated radical cations and 1.2-3.310 8 M -1 s -1 for the case of dGMP. Thus, the electron loss center caused by one electron oxidant or by ionizing radiation will end up at guanine in DNA.

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

    Swierk, John R.

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

  16. 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

  17. 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.

  18. Quantum Dynamics of Ultrafast Electron Transfer Processes in Dye-Semiconductor Systems

    Li, Jingrui

    2012-01-01

    Ultrafast photoinduced electron transfer (ET) processes in dye-semiconductor systems are studied employing a first-principles based methodology. Electronic structure calculations are used to characterize the systems and to parametrize a model Hamiltonian. On the basis of this modeling procedure, accurate quantum dynamical simulations are performed employing the multilayer multiconfiguration time-dependent Hartree method. As representative examples, several dye molecules adsorbed at titanium o...

  19. Influence of the temperature in the electronic transfer mechanism of Geobacter sulfurreducens

    Peixoto, L.; Santos, Andréa F. S.; Machado, Idalina; Sousa, Ana Margarida; A. G. Brito; Parpot, Pier; Pereira, Maria Olívia; Nogueira, R.

    2011-01-01

    Geobacter species are important in the reduction of metals (e.g. Fe, Mn) in soils and sediments and constitute one of the most effective microorganisms known to use electrodes as the sole electron acceptor in microbial fuel cells to generate electricity. G. sulfurreducens transfers electrons directly to the electrode from different external membrane cytochromes. Each cytochrome is associated with a range of electrical potentials, being energetically more favourable than some others. Diffe...

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

    Bauer, Christophe; Teuscher, Jol; Brauer, Jan Cornelius; Punzi, Angela; Marchioro, Arianna; Ghadiri, Elham; De Jonghe, Jelissa; Wielopolski, Mateusz; Banerji, Natalie; Moser, Jacques-E

    2011-01-01

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

  1. 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

  2. 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.

  3. 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...

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

    Röder, Falk, E-mail: Falk.Roeder@Triebenberg.de; Lubk, Axel

    2014-11-15

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

  5. 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.

  6. Long-range electron transfer in engineered azurins exhibits marcus inverted region behavior

    Farver, Ole; Hosseinzadeh, Parisa; Marshall, Nicholas M.; Wherland, Scot; Lu, Yi; Pecht, Israel

    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...

  7. 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

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

    Farver, O; Jeuken, L J; Canters, G W; Pecht, I

    2000-01-01

    Azurin contains two potential redox sites, a copper centre and, at the opposite end of the molecule, a cystine disulfide (RSSR). Intramolecular electron transfer between a pulse radiolytically produced RSSR- radical anion and the blue Cu(II) ion was studied in a series of azurins in which single-...

  9. 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

  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. 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.

  12. 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...

  13. 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

  14. 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

  15. 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

  16. 27 CFR 40.357 - Payment of tax by electronic fund transfer.

    2010-04-01

    ... of corporations, as defined in 26 U.S.C. 1563, and implementing regulations in 26 CFR 1.563-1... electronic fund transfer. 40.357 Section 40.357 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO..., CIGARETTE PAPERS AND TUBES, AND PROCESSED TOBACCO Manufacture of Cigarette Papers and Tubes Taxes ...

  17. 27 CFR 40.165a - Payment of tax by electronic fund transfer.

    2010-04-01

    ... making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and... group of corporations, as defined in 26 U.S.C. 1563, and implementing regulations in 26 CFR 1.1563-1... citations affecting 40.165a, see the List of CFR Sections Affected, which appears in the Finding...

  18. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    2010-04-01

    ... controlled group of corporations, as defined in 26 U.S.C. 1563, and implementing regulations in 26 CFR 1.1563... electronic fund transfer. 41.63 Section 41.63 Alcohol, Tobacco Products and Firearms ALCOHOL AND TOBACCO TAX..., CIGARETTE PAPERS AND TUBES, AND PROCESSED TOBACCO Taxes Customs' Collection of Taxes 41.63 Payment of...

  19. 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

  20. 36 CFR 1235.50 - What specifications and standards for transfer apply to electronic records?

    2010-07-01

    ... Property NATIONAL ARCHIVES AND RECORDS ADMINISTRATION RECORDS MANAGEMENT TRANSFER OF RECORDS TO THE... electronic records in a format that is independent of specific hardware or software. Except as specified in... a request from NARA to provide the software to decompress the records. (3) Agencies interested...