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Sample records for electron transfer suppresses

  1. Blinking suppression of CdTe quantum dots on epitaxial graphene and the analysis with Marcus electron transfer

    SciTech Connect

    Hirose, Takuya; Tamai, Naoto; Kutsuma, Yasunori; Kurita, Atsusi; Kaneko, Tadaaki

    2014-08-25

    We have prepared epitaxial graphene by a Si sublimation method from 4H-SiC. Single-particle spectroscopy of CdTe quantum dots (QDs) on epitaxial graphene covered with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) showed the suppression of luminescence blinking and ∼10 times decreased luminescence intensity as compared with those on a glass. The electronic coupling constant, H{sub 01}, between CdTe QDs and graphene was calculated to be (3.3 ± 0.4) × 10{sup 2 }cm{sup −1} in PVP and (3.7 ± 0.8) × 10{sup 2 }cm{sup −1} in PEG based on Marcus theory of electron transfer and Tang-Marcus model of blinking with statistical distribution.

  2. Suppression of self-heating effect in AlGaN/GaN high electron mobility transistors by substrate-transfer technology using h-BN

    SciTech Connect

    Hiroki, Masanobu Kumakura, Kazuhide; Kobayashi, Yasuyuki; Akasaka, Tetsuya; Makimoto, Toshiki; Yamamoto, Hideki

    2014-11-10

    We fabricated AlGaN/GaN high electron mobility transistors (HEMTs) on h-BN/sapphire substrates and transferred them from the host substrates to copper plates using h-BN as a release layer. In current–voltage characteristics, the saturation drain current decreased by about 30% under a high-bias condition before release by self-heating effect. In contrast, after transfer, the current decrement was as small as 8% owing to improved heat dissipation: the device temperature increased to 50 °C in the as-prepared HEMT, but only by several degrees in the transferred HEMT. An effective way to improve AlGaN/GaN HEMT performance by a suppression of self-heating effect has been demonstrated.

  3. Proton-Coupled Electron Transfer

    SciTech Connect

    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

  4. Suppressing Electron Cloud in Future Linear Colliders

    SciTech Connect

    Pivi, M; Kirby, R.E.; Raubenheimer, T.O.; Le Pimpec, F.; /PSI, Villigen

    2005-05-27

    Any accelerator circulating positively charged beams can suffer from a build-up of an electron cloud (EC) in the beam pipe. The cloud develops through ionization of residual gases, synchrotron radiation and secondary electron emission and, when severe, can cause instability, emittance blow-up or loss of the circulating beam. The electron cloud is potentially a luminosity limiting effect for both the Large Hadron Collider (LHC) and the International Linear Collider (ILC). For the ILC positron damping ring, the development of the electron cloud must be suppressed. This paper discusses the state-of-the-art of the ongoing SLAC and international R&D program to study potential remedies.

  5. Electron transfer in biological molecules

    SciTech Connect

    Gray, H.B.

    1995-12-01

    Electron-transfer reactions are key stemps in photosynthesis, respiration, drug metabolism, and many other biochemical processes. These reactions commonly occur between protein-bound prosthetic groups that are separated by large molecular distances (often greater than 10 {Angstrom}). Although the electron donors and acceptors are expected to be weakly coupled, the reactions are remarkably fast and proceed with high specificity. Recent work on structurally engineered iron and cooper proteins has shown that the chemical bonds in the intervening medium potentially can control the rates of these electron-transfer reactions.

  6. Two-Electron Transfer Pathways.

    PubMed

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

    2015-06-18

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

  7. Passive runaway electron suppression in tokamak disruptions

    SciTech Connect

    Smith, H. M.; Helander, P.

    2013-07-15

    Runaway electrons created in disruptions pose a serious problem for tokamaks with large current. It would be desirable to have a runaway electron suppression method which is passive, i.e., a method that does not rely on an uncertain disruption prediction system. One option is to let the large electric field inherent in the disruption drive helical currents in the wall. This would create ergodic regions in the plasma and increase the runaway losses. Whether these regions appear at a suitable time and place to affect the formation of the runaway beam depends on disruption parameters, such as electron temperature and density. We find that it is difficult to ergodize the central plasma before a beam of runaway current has formed. However, the ergodic outer region will make the Ohmic current profile contract, which can lead to instabilities that yield large runaway electron losses.

  8. 75 FR 31665 - Electronic Fund Transfers

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-04

    ... CFR Part 205 Electronic Fund Transfers AGENCY: Board of Governors of the Federal Reserve System..., which implements the Electronic Fund Transfer Act, and the official staff commentary to the regulation... implements the Electronic Fund Transfer Act (EFTA), limiting a financial institution's ability to assess...

  9. Electron acceptor dependence of electron shuttle secretion and extracellular electron transfer by Shewanella oneidensis MR-1.

    PubMed

    Wu, Chao; Cheng, Yuan-Yuan; Li, Bing-Bing; Li, Wen-Wei; Li, Dao-Bo; Yu, Han-Qing

    2013-05-01

    Shewanella oneidensis MR-1 is an extensively studied dissimilatory metal-reducing bacterium with a great potential for bioremediation and electricity generation. It secretes flavins as electron shuttles which play an important role in extracellular electron transfer. However, the influence of various environmental factors on the secretion of flavins is largely unknown. Here, the effects of electron acceptors, including fumarate, ferrihydrite, Fe(III)-nitrilotriacetic acid (NTA), nitrate and trimethylamine oxide (TMAO), on the secretion of flavins were investigated. The level of riboflavin and riboflavin-5'-phosphate (FMN) secreted by S. oneidensis MR-1 varied considerably with different electron acceptors. While nitrate and ferrihydrite suppressed the secretion of flavins in relative to fumarate, Fe(III)-NTA and TMAO promoted such a secretion and greatly enhanced ferrihydrite reduction and electricity generation. This work clearly demonstrates that electron acceptors could considerably affect the secretion of flavins and consequent microbial EET. Such impacts of electron acceptors in the environment deserve more attention.

  10. Modular electron transfer circuits for synthetic biology

    PubMed Central

    Agapakis, Christina M

    2010-01-01

    Electron transfer is central to a wide range of essential metabolic pathways, from photosynthesis to fermentation. The evolutionary diversity and conservation of proteins that transfer electrons makes these pathways a valuable platform for engineered metabolic circuits in synthetic biology. Rational engineering of electron transfer pathways containing hydrogenases has the potential to lead to industrial scale production of hydrogen as an alternative source of clean fuel and experimental assays for understanding the complex interactions of multiple electron transfer proteins in vivo. We designed and implemented a synthetic hydrogen metabolism circuit in Escherichia coli that creates an electron transfer pathway both orthogonal to and integrated within existing metabolism. The design of such modular electron transfer circuits allows for facile characterization of in vivo system parameters with applications toward further engineering for alternative energy production. PMID:21468209

  11. 75 FR 33681 - Electronic Fund Transfers

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-06-15

    ... From the Federal Register Online via the Government Publishing Office FEDERAL RESERVE SYSTEM 12 CFR Part 205 Electronic Fund Transfers June 4, 2010. AGENCY: Board of Governors of the Federal Reserve... following correction: PART 205--ELECTRONIC FUND TRANSFERS (REGULATION E) 1. On page 31671, in the...

  12. Coupled electron transfers in artificial photosynthesis

    PubMed Central

    Hammarström, Leif; Styring, Stenbjörn

    2007-01-01

    Light-induced charge separation in molecular assemblies has been widely investigated in the context of artificial photosynthesis. Important progress has been made in the fundamental understanding of electron and energy transfer and in stabilizing charge separation by multi-step electron transfer. In the Swedish Consortium for Artificial Photosynthesis, we build on principles from the natural enzyme photosystem II and Fe-hydrogenases. An important theme in this biomimetic effort is that of coupled electron-transfer reactions, which have so far received only little attention. (i) Each absorbed photon leads to charge separation on a single-electron level only, while catalytic water splitting and hydrogen production are multi-electron processes; thus there is the need for controlling accumulative electron transfer on molecular components. (ii) Water splitting and proton reduction at the potential catalysts necessarily require the management of proton release and/or uptake. Far from being just a stoichiometric requirement, this controls the electron transfer processes by proton-coupled electron transfer (PCET). (iii) Redox-active links between the photosensitizers and the catalysts are required to rectify the accumulative electron-transfer reactions, and will often be the starting points of PCET. PMID:17954432

  13. Geometric phase and quantum interference in photosynthetic reaction center: Regulation of electron transfer

    NASA Astrophysics Data System (ADS)

    Sun, Yuming; Su, Yuehua; Dai, Zhenhong; Wang, WeiTian

    2016-10-01

    Photosynthesis is driven by electron transfer in reaction centers in which the functional unit is composed of several simple molecules C2-symmetrically arranged into two branches. In view of quantum mechanism, both branches are possible pathways traversed by the transferred electron. Due to different evolution of spin state along two pathways in transmembrane electric potential (TEP), quantum state of the transferred electron at the bridged site acquires a geometric phase difference dependent on TEP, the most efficient electron transport takes place in a specific range of TEP beyond which electron transfer is dramatically suppressed. What's more, reaction center acts like elaborately designed quantum device preparing polarized spin dependent on TEP for the transferred electron to regulate the reduction potential at bridged site. In brief, electron transfer generates the TEP, reversely, TEP modulates the efficiency of electron transfer. This may be an important approach to maintaining an appreciable pH environment in photosynthesis.

  14. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, R.; Calvin, M.

    1984-01-24

    The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospholipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transferring electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

  15. Photo-induced electron transfer method

    DOEpatents

    Wohlgemuth, Roland; Calvin, Melvin

    1984-01-01

    The efficiency of photo-induced electron transfer reactions is increased and the back transfer of electrons in such reactions is greatly reduced when a photo-sensitizer zinc porphyrin-surfactant and an electron donor manganese porphyrin-surfactant are admixed into phospho-lipid membranes. The phospholipids comprising said membranes are selected from phospholipids whose head portions are negatively charged. Said membranes are contacted with an aqueous medium in which an essentially neutral viologen electron acceptor is admixed. Catalysts capable of transfering electrons from reduced viologen electron acceptor to hydrogen to produce elemental hydrogen are also included in the aqueous medium. An oxidizable olefin is also admixed in the phospholipid for the purpose of combining with oxygen that coordinates with oxidized electron donor manganese porphyrin-surfactant.

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

    PubMed

    Natali, Mirco; Campagna, Sebastiano; Scandola, Franco

    2014-06-21

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

  17. Local control approach to ultrafast electron transfer

    NASA Astrophysics Data System (ADS)

    Vindel-Zandbergen, Patricia; Meier, Christoph; Sola, Ignacio R.

    2016-10-01

    We study ultrafast electron transfer between separated nuclei using local control theory. By imposing electron ionization and electron transport through the continuum, different local control formulations are used to increase the yield of retrapping the electron at the desired nuclei. The control mechanism is based on impulsive de-excitation. Both symmetric and asymmetric nuclear arrangements are analyzed, as well as the role of the nuclear motion.

  18. Vectorial electron transfer in spatially ordered arrays

    SciTech Connect

    Fox, M.A.

    1993-02-01

    Progress was made on synthesis of new materials for directional electron transfer (block copolymers and helical oligopeptides), preparation and characterization of anisotropic composites bearing organics and inorganics, electrocatalysis (redox-activated catalysts), and surface modifications of metals and semiconductors.

  19. Photoinduced electron transfer in ordered polymers

    SciTech Connect

    Jones, G. II.

    1990-10-20

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

  20. Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

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

  1. Breaking the barrier to fast electron transfer.

    PubMed

    Demin, Soren; Hall, Elizabeth A H

    2009-09-01

    A study of the electron transfer for a non-glycosylated redox variant of GOx is reported, immobilised onto an electrode via a polyhistidine tag. The non-glycosylated variant allows the enzyme to be brought closer to the electrode, and within charge transfer distances predicted by Marcus' theory. The enzyme-electrode-hybrid shows direct very fast reversible electrochemical electron transfer, with a rate constant of approximately 350 s(-1) under anaerobic conditions. This is 2 orders of magnitude faster than the enzyme-free flavin adenine dinucleotide (FAD). These results are discussed in the context of the conformation of FAD in the active site of GOx. Further data, presented in the presence of oxygen, show a reduced electron transfer rate (approximately 160 s(-1)) that may be associated with the oxygen interaction with the histidines in the active site. These residues are implicated in the proton transfer mechanism and thus suggest that the presence of oxygen may have a profound effect in attenuating the direct electron transfer rate and thus moderating 'short-circuit' incidental electron transfer between proteins.

  2. Electron transfer statistics and thermal fluctuations in molecular junctions

    SciTech Connect

    Goswami, Himangshu Prabal; Harbola, Upendra

    2015-02-28

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

  3. Electron transfer induced fragmentation of acetic acid

    NASA Astrophysics Data System (ADS)

    Ferreira da Silva, F.; Meneses, G.; Almeida, D.; Limão-Vieira, P.

    2014-04-01

    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.

  4. Electron transfer across a thermal gradient

    PubMed Central

    Craven, Galen T.

    2016-01-01

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

  5. Ultrafast Photoinduced Electron Transfer from Peroxide Dianion.

    PubMed

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

    2015-06-18

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

  6. SUPPRESSION OF ENERGETIC ELECTRON TRANSPORT IN FLARES BY DOUBLE LAYERS

    SciTech Connect

    Li, T. C.; Drake, J. F.; Swisdak, M.

    2012-09-20

    During flares and coronal mass ejections, energetic electrons from coronal sources typically have very long lifetimes compared to the transit times across the systems, suggesting confinement in the source region. Particle-in-cell simulations are carried out to explore the mechanisms of energetic electron transport from the corona to the chromosphere and possible confinement. We set up an initial system of pre-accelerated hot electrons in contact with ambient cold electrons along the local magnetic field and let it evolve over time. Suppression of transport by a nonlinear, highly localized electrostatic electric field (in the form of a double layer) is observed after a short phase of free-streaming by hot electrons. The double layer (DL) emerges at the contact of the two electron populations. It is driven by an ion-electron streaming instability due to the drift of the back-streaming return current electrons interacting with the ions. The DL grows over time and supports a significant drop in temperature and hence reduces heat flux between the two regions that is sustained for the duration of the simulation. This study shows that transport suppression begins when the energetic electrons start to propagate away from a coronal acceleration site. It also implies confinement of energetic electrons with kinetic energies less than the electrostatic energy of the DL for the DL lifetime, which is much longer than the electron transit time through the source region.

  7. Photoinduced electron transfer in ordered polymers

    SciTech Connect

    Jones, G. II.

    1991-12-01

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

  8. Theory of directed electronic energy transfer.

    PubMed

    Andrews, David L; Crisp, Richard G

    2006-03-01

    The migration of electronic energy between molecules or chromophores in molecular solids is a well-studied phenomenon. The ability to exert control over the directionality of this transfer, by a variety of methods involving applied electrical or optical fields, holds promise for advances in fields including nanoelectronics and energy harvesting materials. In this paper, we review in detail a number of methods for directing energy transfer, also identifying potential applications.

  9. Suppression of shot noise and spontaneous radiation in electron beams

    SciTech Connect

    Litvinenko,V.

    2009-08-23

    Shot noise in the electron beam distribution is the main source of noise in high-gain FEL amplifiers, which may affect applications ranging from single- and multi-stage HGHG FELs to an FEL amplifier for coherent electron cooling. This noise also imposes a fundamental limit of about 10{sup 6} on FEL gain, after which SASE FELs saturate. There are several advantages in strongly suppressing this shot noise in the electron beam, and the corresponding spontaneous radiation. For more than a half-century, a traditional passive method has been used successfully in practical low-energy microwave electronic devices to suppress shot noise. Recently, it was proposed for this purpose in FELs. However, being passive, the method has some significant limitations and is hardly suitable for the highly inhomogeneous beams of modern high-gain FELs. I present a novel active method of suppressing, by many orders-of-magnitude, the shot noise in relativistic electron beams. I give a theoretical description of the process, and detail its fundamental limitation.

  10. Solvent gating of intramolecular electron transfer

    SciTech Connect

    Miller, R.M. ); Spears, K.G.; Gong, J.H.; Wach, M. )

    1994-02-03

    The rates for ionic photodissociation of malachite green leucocyanide to form cyanide ion and a malachite green carbonium ion were measured as a function of solvent and temperature. The observed rates in mixtures of polar and nonpolar solvents all had an activation energy of about 1 kcal/mol for a wide range of dielectric constants. This dissociative intramolecular electron transfer (DIET) is unusual because it is the first example where solvent configurational entropy changes are required to enable a large amplitude molecular distortion leading to a nonadiabatic electron transfer and ionic dissociation. This solvent gated intramolecular electron-transfer mechanism is supported by analysis of the preexponential and activation energy trends in dipolar aprotic solven mixtures and alcohol solvents. The large amplitude motion is not separately measurable due to the slow gating rates, but viscosity effects on both the preexponential and the activation energy are analyzed to demonstrate consistency with a barrierless diffusion model having a structural dependence on electron-transfer rate. The rate has an inverse dependence on viscosity raised to the 0.53 power. 36 refs., 6 figs., 4 tabs.

  11. 75 FR 16579 - Electronic Fund Transfers

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-04-01

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

  12. Electron transfer and energy transfer through bridged systems. I. Formalism

    NASA Astrophysics Data System (ADS)

    Reimers, J. R.; Hush, N. S.

    1989-07-01

    A time-dependent formalism is developed for reactions in which energy (vibrational or electronic excitation, electron or hole transfer, etc.) is transferred coherently between centres through a bridge. This approach is inspired by the Robinson and Frosch model of energy transfer within two-level systems. This formalism yields a completely general algorithm which, in particular limits, reduces to a generalised form of both Fermi's golden rule and Rabi's rate equation, and, in so doing, unifies many existing theories. It is shown that, only in the limit of the bridge states being non-resonant with the initial and final states, can the full problem be represented by an effective two-level model. Existing methods based upon Löwdin diagonalization are shown to be appropriate only when this limit applies, and ambiguities which arise from the ad hoc nature of these methods are resolved. Also, it is typically only in this limit that the transfer of energy proceeds exponentially in time and can be described by a simple single-parameter rate constant. Only problems which can be modelled using a single set of quantum numbers are treated in this paper. Applications and more general problems are treated in subsequent papers.

  13. Dynamics of electron transfer in photosystem II.

    PubMed

    Burda, Kvetoslava

    2007-01-01

    Photosystem II, being a constituent of light driven photosynthetic apparatus, is a highly organized pigment-protein-lipid complex. The arrangement of PSII active redox cofactors insures efficiency of electron transfer within it. Donation of electrons extracted from water by the oxygen evolving complex to plastoquinones requires an additional activation energy. In this paper we present theoretical discussion of the anharmonic fluctuations of the protein-lipid matrix of PSII and an experimental evidence showing that the fluctuations are responsible for coupling of its donor and acceptor side. We argue that the fast collective motions liberated at temperatures higher that 200 K are crucial for the two final steps of the water splitting cycle and that one can distinguish three different dynamic regimes of PSII action which are controlled by the timescales of forward electron transfer, which vary with temperature. The three regimes of the dynamical behavior are related to different spatial domains of PSII.

  14. Estimates of electronic coupling for excess electron transfer in DNA

    NASA Astrophysics Data System (ADS)

    Voityuk, Alexander A.

    2005-07-01

    Electronic coupling Vda is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of Vda for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an efficient strategy is established for calculating the ET matrix elements between base pairs in a π stack. Two approaches are considered. First, we employ the diabatic-state (DS) method in which donor and acceptor are represented with radical anions of the canonical base pairs adenine-thymine (AT) and guanine-cytosine (GC). In this approach, similar values of Vda are obtained with the standard 6-31G* and extended 6-31++G** basis sets. Second, the electronic couplings are derived from lowest unoccupied molecular orbitals (LUMOs) of neutral systems by using the generalized Mulliken-Hush or fragment charge methods. Because the radical-anion states of AT and GC are well reproduced by LUMOs of the neutral base pairs calculated without diffuse functions, the estimated values of Vda are in good agreement with the couplings obtained for radical-anion states using the DS method. However, when the calculation of a neutral stack is carried out with diffuse functions, LUMOs of the system exhibit the dipole-bound character and cannot be used for estimating electronic couplings. Our calculations suggest that the ET matrix elements Vda for models containing intrastrand thymine and cytosine bases are essentially larger than the couplings in complexes with interstrand pyrimidine bases. The matrix elements for excess electron transfer are found to be considerably smaller than the corresponding values for hole transfer and to be very responsive to structural changes in a DNA stack.

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

    SciTech Connect

    Not Available

    1989-04-12

    This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

  16. Theoretical analysis of a runaway electron suppression device

    SciTech Connect

    Niemer, K.A.; Gilligan, J.G. . Dept. of Nuclear Engineering); Croessmann, C.D. ); England, A.C. )

    1990-01-01

    A new runaway electron suppression paddle was designed with the PTA code package to reduce the runaway electron population in the Advanced Toroidal Facility (ATF), Oak Ridge National Laboratory. The PTA code package is a unique application of PATRAN, the Integrated TIGER Series, and ABAQUS for modeling high energy electron impact on magnetic fusion components and materials. By its nature, ATF is susceptible to runaway electron formation and confinement resulting in the production of a high level of hard x-rays near the machine. Four previous stainless steel paddles proved effective in reducing the runaway electron population; however, electrons above 15 MeV have still been observed. Melting and bending were observed in each of the previous paddles, reducing their effectiveness. Scoping experiments are under way to further characterize the runaway electrons in ATF. Data from these experiments will provide insight into runaway electron damage mechanisms. Proposals for the insertion of a new paddle in ATF are being considered. These analyses add to the knowledge of runaway electron damage and will aid in the design of future components to withstand runaway electron discharges in all magnetic fusion devices, including tokamaks. 8 refs., 3 figs., 1 tab.

  17. Flavin Electron Shuttles Dominate Extracellular Electron Transfer by Shewanella oneidensis

    PubMed Central

    Kotloski, Nicholas J.; Gralnick, Jeffrey A.

    2013-01-01

    ABSTRACT Shewanella oneidensis strain MR-1 is widely studied for its ability to respire a diverse array of soluble and insoluble electron acceptors. The ability to breathe insoluble substrates is defined as extracellular electron transfer and can occur via direct contact or by electron shuttling in S. oneidensis. To determine the contribution of flavin electron shuttles in extracellular electron transfer, a transposon mutagenesis screen was performed with S. oneidensis to identify mutants unable to secrete flavins. A multidrug and toxin efflux transporter encoded by SO_0702 was identified and renamed bfe (bacterial flavin adenine dinucleotide [FAD] exporter) based on phenotypic characterization. Deletion of bfe resulted in a severe decrease in extracellular flavins, while overexpression of bfe increased the concentration of extracellular flavins. Strains lacking bfe had no defect in reduction of soluble Fe(III), but these strains were deficient in the rate of insoluble Fe(III) oxide reduction, which was alleviated by the addition of exogenous flavins. To test a different insoluble electron acceptor, graphite electrode bioreactors were set up to measure current produced by wild-type S. oneidensis and the Δbfe mutant. With the same concentration of supplemented flavins, the two strains produced similar amounts of current. However, when exogenous flavins were not supplemented to bioreactors, bfe mutant strains produced significantly less current than the wild type. We have demonstrated that flavin electron shuttling accounts for ~75% of extracellular electron transfer to insoluble substrates by S. oneidensis and have identified the first FAD transporter in bacteria. PMID:23322638

  18. Collective microdynamics and noise suppression in dispersive electron beam transport

    SciTech Connect

    Gover, Avraham; Dyunin, Egor; Duchovni, Tamir; Nause, Ariel

    2011-12-15

    A general formulation is presented for deep collective interaction micro-dynamics in dispersive e-beam transport. In the regime of transversely coherent interaction, the formulation is applicable to both coherent and random temporal modulation of the electron beam. We demonstrate its use for determining the conditions for suppressing beam current noise below the classical shot-noise level by means of transport through a dispersive section with a small momentum compaction parameter.

  19. Biotechnological Aspects of Microbial Extracellular Electron Transfer

    PubMed Central

    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

  20. Bacterial Nanowires Facilitate Extracellular Electron Transfer

    NASA Astrophysics Data System (ADS)

    Gorby, Y.

    2005-12-01

    Dissimilatory metal reducing bacteria, including Shewanella oneidensis and Geobacter sulfurreducens, produce electrically conductive nanowires that facilitate electron transfer to solid phase iron oxides. Nanowires produced by S. oneidensis strain MR-1 are functionalized by decaheme cytochromes MtrC and OmcA that are distributed along the length of the nanowires, as confirmed by immunolocalization experiments using peptide specific antibodies. Mutants lacking MtrC and OmcA produce nanowires that were poorly conductive, are unable to reduce solid phase iron oxides, and do not produce electric current in microbial fuel cells. Although less completely characterized, nanowires are also produced by organisms throughout a broad metabolic spectrum, from sulfate reducing bacteria to oxygenic, phototrophic cyanobacteria. Our research suggests that electrically conductive nanowires may be common throughout the microbial world and may serve as structures for efficient electron transfer and energy dissemination in complex communities such as microbial mats and biofilms.

  1. Suppressing the spin relaxation of electrons in silicon

    NASA Astrophysics Data System (ADS)

    Chalaev, Oleg; Song, Yang; Dery, Hanan

    2017-01-01

    Uniaxial compressive strain along the [001] direction strongly suppresses the spin relaxation in silicon. When the strain level is large enough so that electrons are redistributed only in the two valleys along the strain axis, the dominant scattering mechanisms are quenched and electrons mainly experience intra-axis scattering processes (intravalley or intervalley scattering within valleys on the same crystal axis). We first derive the spin-flip matrix elements due to intra-axis electron scattering off impurities, and then provide a comprehensive model of the spin relaxation time due to all possible interactions of conduction-band electrons with impurities and phonons. We predict a nearly three orders of magnitude improvement in the spin relaxation time of ˜1019cm-3 antimony-doped silicon (Si:Sb) at low temperatures.

  2. Electron Transfer and Reaction Mechanism of Laccases

    PubMed Central

    Jones, Stephen M.; Solomon, Edward I.

    2015-01-01

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

  3. Suppression mechanism of inter-tube transfer in double-wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Uryu, Seiji

    2005-03-01

    Double-wall carbon nanotubes have incommensurate lattice structure and are quasi-periodic[1,2]. Therefore, inter-tube transfer of electrons between incommensurate tubes is the key to understanding of double-wall tubes. Although some theoretical studies reported suppression of inter-tube transfer in multiwall tubes[3], the mechanism has not been well understood. The purpose of this paper is to clarify effects of inter-tube transfer in double-wall tubes. Using a tight-binding model length-dependence of conductance due to inter-tube transfer is calculated. The conductance is negligibly small in comparison to the conductance quantum and oscillates around an average which is approximately independent of the length. It is revealed based on the first-order perturbation theory that the result is attributed to quasi-periodic oscillation of position dependence of small local effective inter-tube coupling. [1] M. Kociak, K. Suenaga, K. Hirahara, Y. Saito, T. Nakahira, and S. Iijima, Phys. Rev. Lett. 89 (2002) 155501. [2] J. M. Zuo, I. Vartanyants, M. Gao, R. Zhang, and L. A. Nagahara, Science 300 (2003) 1419. [3] Y.-G. Yoon, P. Delaney, and S. G. Louie, Phys. Rev. B 66 (2002) 073407.

  4. Promoting Interspecies Electron Transfer with Biochar

    PubMed Central

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

    2014-01-01

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

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

    SciTech Connect

    Gust, J.D. Jr.; Moore, T.A.

    1988-04-12

    This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind's energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

  6. 77 FR 40459 - Electronic Fund Transfers (Regulation E); Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-10

    ... 1005 RIN 3170-AA15 Electronic Fund Transfers (Regulation E); Correction AGENCY: Bureau of Consumer..., the Bureau published the Final Rule (77 FR 6194), which implements the Electronic Fund Transfer Act... made to Sec. 1005.3(a) in the interim final rule, Electronic Fund Transfers (Regulation E),...

  7. 14 CFR 1274.931 - Electronic funds transfer payment methods.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.931 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods July 2002 Payments under...

  8. 14 CFR 1260.69 - Electronic funds transfer payment methods.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Electronic funds transfer payment methods... COOPERATIVE AGREEMENTS General Special Conditions § 1260.69 Electronic funds transfer payment methods. Electronic Funds Transfer Payment Methods October 2000 (a) Payments under this grant will be made by...

  9. 31 CFR 208.3 - Payment by electronic funds transfer.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 31 Money and Finance:Treasury 2 2011-07-01 2011-07-01 false Payment by electronic funds transfer... DISBURSEMENTS § 208.3 Payment by electronic funds transfer. Subject to § 208.4, and notwithstanding any other... electronic funds transfer....

  10. 14 CFR 1260.69 - Electronic funds transfer payment methods.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

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

  11. Mixed valent sites in biological electron transfer.

    PubMed

    Solomon, Edward I; Xie, Xiangjin; Dey, Abhishek

    2008-04-01

    Many of the active sites involved in electron transfer (ET) in biology have more than one metal and are mixed valent in at least one redox state. These include Cu(A), and the polynuclear Fe-S clusters which vary in their extent of delocalization. In this tutorial review the relative contributions to delocalization are evaluated using S K-edge X-ray absorption, magnetic circular dichroism and other spectroscopic methods. The role of intra-site delocalization in ET is considered.

  12. Photochemical electron transfer reactions of tirapazamine.

    PubMed

    Poole, James S; Hadad, Christopher M; Platz, Matthew S; Fredin, Zachary P; Pickard, Laura; Guerrero, Elisa Levya; Kessler, Margarita; Chowdhury, Goutam; Kotandeniya, Delshanee; Gates, Kent S

    2002-04-01

    The absorption and fluorescence spectra of 3-aminobenzo-1,2,4-triazine di-N-oxide (tirapazamine) have been recorded and exhibit a dependence on solvent that correlates with the Dimroth ET30 parameter. Time-dependent density functional theory calculations reveal that the transition of tirapazamine in the visible region is pi-->pi* in nature. The fluorescence lifetime is 98+/-2 ps in water. The fluorescence quantum yield is approximately 0.002 in water. The fluorescence of tirapazamine is efficiently quenched by electron donors via an electron-transfer process. Linear Stern-Volmer fluorescence quenching plots are observed with sodium azide, potassium thiocyanate, guanosine monophosphate and tryptophan (Trp) methyl ester hydrochloride. Guanosine monophosphate, tyrosine (Tyr) methyl ester hydrochloride and Trp methyl ester hydrochloride appear to quench the fluorescence at a rate greater than diffusion control implying that these substrates complex with tirapazamine in its ground state. This complexation was detected by absorption spectroscopy.

  13. Photoinduced electron transfer in ordered polymers

    SciTech Connect

    Jones, G. II.

    1993-01-01

    The present report gives a brief account of the following elements of work related to photochemical electron transfer themes: (1) the synthesis and Photochemical characterization of chromophore-bound peptides and amino acid model compounds based on the amino acids, tryptophan and the spacer residue, alanine (Ala); (2) the study of binding of cationic organic dyes to a peptide electrolyte, for which cooperative dye loading and helix formation is important; (3) the completion of work on a new series of acridinium chromophores that have rod-like'' arrangements of linked aryl rings for assembly of electron donor-acceptor systems that exhibit long lived charge separation; and (4) use of the modified form of the peptide, poly-L-histidine, as a template for sulfide oxidation.

  14. Analytical and computational studies of intramolecular electron transfer pertinent to electron transfer and electron capture dissociation mass spectrometry.

    PubMed

    Neff, Diane; Simons, Jack

    2010-01-28

    Earlier work from this group has suggested that, in electron capture and electron-transfer mass spectrometry experiments on positively charged gas-phase samples of polypeptides, the initial electron attachment event most likely occurs at one of the peptide's positively charged sites (e.g., protonated side chains), although electron attachment can occur at a disulfide or amide site ca. 1-10% of the time. Focusing on the 90-99% dominant channel in which initial electron attachment occurs at a positive site, this paper addresses to what extent and over what distances electron transfer can take place from a positively charged site to a disulfide sigma* or amide pi* orbital, because it is thought that it is through such orbitals that disulfide or N-C(alpha) backbone bond cleavage occurs. Ab initio electronic structure calculations show that, as long as an SS sigma* (or OCN pi*) orbital experiences sufficient Coulomb stabilization from proximal positively charged groups, there are a myriad of excited Rydberg states located on positive sites that are able to induce such intrapeptide electron transfer. Computational data show that the transfer rates decay exponentially with distance for a given Rydberg orbital. An analytical model is developed that allows us to estimate the rates of Rydberg-to-valence and Rydberg-to-Rydberg electron transfers as functions of the Rydberg orbitals' n quantum numbers. This model suggests that transfer can occur over very long distances at rates that are more than competitive with the rates of radiationless relaxation within the manifold of Rydberg states (the latter processes eventually terminate the electron-transfer process an thus the disulfide or N-C(alpha) bond cleavages), and it gives formulas for how these rates depend on n (and thus the radial span of the Rydberg orbitals).

  15. Experimental Studies on Grooved Surfaces to Suppress Secondary Electron Emission

    SciTech Connect

    Suetsugu, Y.; Fukuma, H.; Shibata, K.; Pivi, M.; Wang, L.; /SLAC

    2010-06-15

    Grooved surfaces are effective to suppress the secondary electron emission, and can be a promising technique to mitigate the electron cloud effect in positron/proton storage rings. Aiming for the application in a dipole-type magnetic field, various shapes of triangular grooved surfaces have been studied at KEK. The grooves tested here have vertex angles of 20-30{sup o}, depths of 2.5-5.0 mm, and vertex roundness of 0.05-0.2 mm. In a laboratory, the secondary electron yields (SEY) of small test pieces were measured using an electron beam in a magnetic-free condition. The grooved surfaces clearly had low SEY compared to flat surfaces of the same materials. The grooves with sharper vertexes had smaller SEY. A test chamber installed in a wiggler magnet of the KEKB positron ring was used to investigate the efficacy of the grooved surface in a strong magnetic field. In the chamber, a remarkable reduction in the electron density around the beam orbit was observed compared to the case of a flat surface with TiN coating.

  16. A Perfect Electrode to Suppress Secondary Electrons inside the Magnets

    SciTech Connect

    Wang, L.; Fukuma, H.; Kurokawa, S.; Pivi, M.; Xia, G.; /DESY

    2006-07-19

    An electron cloud due to multipacting in the positron ring of B-factories and the damping ring of the International Linear Collider (ILC) is one of the main concerns. The electron cloud in the drift region can be suppressed by a solenoid. However, the solenoid doesn't work inside a magnet. Numerical studies show that there is strong multipacting in a dipole magnet of a B-factory positron ring. Electrons also can be trapped inside quadrupole and sextupole magnets. The electron cloud from dipole magnets and wigglers in the positron damping ring of the ILC gives a critical limitation on the choice of a circumference of the damping ring, which directly results in a choice of two 6 km rings as the baseline for the positron damping ring. Various electrodes have been studied using the program CLOUDLAND. Our studies show that a wire type of the electrode with a few hundred voltages works perfectly to kill the secondary electrons inside various magnets.

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

    PubMed Central

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

    2016-01-01

    Photons can carry angular momentum, not only due to their spin, but also due to their spatial structure. This extra twist has been used, for example, to drive circular motion of microscopic particles in optical tweezers as well as to create vortices in quantum gases. Here we excite an atomic transition with a vortex laser beam and demonstrate the transfer of optical orbital angular momentum to the valence electron of a single trapped ion. We observe strongly modified selection rules showing that an atom can absorb two quanta of angular momentum from a single photon: one from the spin and another from the spatial structure of the beam. Furthermore, we show that parasitic ac-Stark shifts from off-resonant transitions are suppressed in the dark centre of vortex beams. These results show how light's spatial structure can determine the characteristics of light–matter interaction and pave the way for its application and observation in other systems. PMID:27694805

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  19. Reversible Electron Beam Heating for Suppression of Microbunching Instabilities at Free-Electron Lasers

    SciTech Connect

    Behrens, Christopher; Huang, Zhirong; Xiang, Dao; /SLAC

    2012-05-30

    The presence of microbunching instabilities due to the compression of high-brightness electron beams at existing and future x-ray free-electron lasers (FELs) results in restrictions on the attainable lasing performance and renders beam imaging with optical transition radiation impossible. The instability can be suppressed by introducing additional energy spread, i.e., heating the electron beam, as demonstrated by the successful operation of the laser heater system at the Linac Coherent Light Source. The increased energy spread is typically tolerable for self-amplified spontaneous emission FELs but limits the effectiveness of advanced FEL schemes such as seeding. In this paper, we present a reversible electron beam heating system based on two transverse deflecting radio-frequency structures (TDSs) upstream and downstream of a magnetic bunch compressor chicane. The additional energy spread is introduced in the first TDS, which suppresses the microbunching instability, and then is eliminated in the second TDS. We show the feasibility of the microbunching gain suppression based on calculations and simulations including the effects of coherent synchrotron radiation. Acceptable electron beam and radio-frequency jitter are identified, and inherent options for diagnostics and on-line monitoring of the electron beam's longitudinal phase space are discussed.

  20. 78 FR 49365 - Electronic Fund Transfers (Regulation E); Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-08-14

    ... From the Federal Register Online via the Government Publishing Office ] BUREAU OF CONSUMER FINANCIAL PROTECTION 12 CFR Part 1005 RIN 3170-AA33 Electronic Fund Transfers (Regulation E); Correction... rules \\1\\ implements the Electronic Fund Transfer Act's provisions regarding remittance transfers...

  1. Electron transfer reactions in microporous solids

    SciTech Connect

    Mallouk, T.E.

    1992-05-01

    We have studied electron transfer quenching of the excited state of Ru(bpy){sub 3}{sup 2+} in aqueous suspensions of zeolites Y, L, and mordenite. The internal pore network of the zeolite is ion-exchanged with methylviologen cations, which quench the excited state of the surface-bound sensitizer. A detailed study of the quenching and charge recombination kinetics, using time-resolved luminescence quenching and transient diffuse reflectance spectroscopies, shows to remarkable effects: first, the excited state quenching is entirely dynamic is large-pore zeolites (L and Y), even when they are prepared as apparently dry'' powders (which still contain significant amounts of internally sited water). Second, a lower limit for the diffusion coefficient of the MV{sup 2+} ion in these zeolites, determined by this technique, is 10{sup {minus}7} cm{sup 2}sec, i.e., only about one order of magnitude slower than a typical ion in liquid water, and 2--3 orders of magnitude faster than charge transfer diffusion of cations in polyelectrolyte films or membranes such as Nafion. Surface sensitization of internally platinized layered oxide semiconductors such as K{sub 4-x}H{sub x}Nb{sub 6}O{sub 17}{center dot}nH{sub 2}O (x {approx} 2.5) yields photocatalysts for the production of H{sub 2} and I{sub 3{minus}} in aqueous iodide solutions. Layered alkali niobates and titanates form a class of zeolitic wide-bandap semiconductors, and are the first examples of photocatalysts that evolve hydrogen from an electrochemically reversible (i.e., non-sacrificial) electron donor with visible light excitation.

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

    PubMed

    Lakhno, V D

    2000-06-01

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

  3. Electronic and Nuclear Factors in Charge and Excitation Transfer

    SciTech Connect

    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.

  4. Metal ion modulated electron transfer in photosynthetic proteins.

    SciTech Connect

    Utschig, L. M.; Thurnauer, M. C.; Chemistry

    2004-07-01

    Photosynthetic purple bacterial reaction center (RC) proteins are ideal native systems for addressing basic questions regarding the nature of biological electron transfer because both the protein structure and the electron-transfer reactions are well-characterized. Metal ion binding to the RC can affect primary photochemistry and provides a probe for understanding the involvement of local protein environments in electron transfer. The RC has two distinct transition metal ion binding sites, the well-known non-heme Fe{sup 2+} site buried in the protein interior and a recently discovered Zn{sup 2+} site located on the surface of the protein. Fe{sup 2+} removal and Zn{sup 2+} binding systematically affect different electron-transfer steps in the RC. Factors involved in the metal ion alteration of RC electron transfer may provide a paradigm for other biological systems involved in electron transfer.

  5. 76 FR 29901 - Electronic Fund Transfers

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-05-23

    ... delivery may be available for a higher fee. International Wire Transfers Consumers may also send... institutions by international wire transfer. Consumers may choose to send funds by wire transfer when..., particularly when sending larger amounts. A wire transfer is generally an account-to- account...

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

    PubMed

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

    1998-01-01

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

  7. [Mechanistic examination of organometallic electron transfer reactions: Annual report, 1989

    SciTech Connect

    Not Available

    1989-12-31

    Our mechanistic examination of electron transfer reactions between organometallic complexes has required data from our stopped-flow infrared spectrophotometer that was constructed in the first year. Our research on organometallic electron transfer reaction mechanisms was recognized by an invitation to the Symposium on Organometallic Reaction Mechanisms at the National ACS meeting in Miami. We have obtained a reasonable understanding of the electron transfer reactions between metal cations and anions and between metal carbonyl anions and metal carbonyl dimers. In addition we have begun to obtain data on the outer sphere electron transfer between metal carbonyl anions and coordination complexes and on reactions involving cluster anions.

  8. Mechanism of Intermolecular Electron Transfer in Bionanostructures

    NASA Astrophysics Data System (ADS)

    Gruodis, A.; Galikova, N.; Šarka, K.; Saulė, R.; Batiuškaitė, D.; Saulis, G.

    Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide. Most patients are inoperable and hepatoma cells are resistant to conventional chemotherapies. Thus, the development of novel therapies for HCC treatment is of paramount importance. Amongst different alimentary factors, vitamin C and vitamin K3 In the present work, it has been shown that the treatment of mouse hepatoma MH-22A cells by vitamin C and vitamin K3 at the ratio of 100:1 greatly enhanced their cytotoxicity. When cells were subjected to vitamin C at 200 μM or to vitamin K3 at 2 μM separately, their viability reduced by only about 10%. However, when vitamins C and K3 were combined at the same concentrations, they killed more than 90% of cells. To elucidate the mechanism of the synergistic cytotoxicity of the C&K3 mixture, theoretical quantum-chemical analysis of the dynamics of intermolecular electron transfer (IET) processes within the complexes containing C (five forms) and K3 (one form) has been carried out. Optimization of the ground state complex geometry has been provided by means of GAUSSIAN03 package. Simulation of the IET has been carried out using NUVOLA package, in the framework of molecular orbitals (MO). The rate of IET has been calculated using Fermi Golden rule. The results of simulations allow us to create the preliminary model of the reaction pathway.

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

    SciTech Connect

    1993-03-01

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

  10. 14 CFR 1274.931 - Electronic funds transfer payment methods.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

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

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

    PubMed Central

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

    2012-01-01

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

  12. PROTON-COUPLED ELECTRON TRANSFER: A Reaction Chemist's View

    NASA Astrophysics Data System (ADS)

    Mayer, James M.

    2004-01-01

    Proton-coupled electron transfer (PCET) reactions involve the concerted transfer of an electron and a proton. Such reactions play an important role in many areas of chemistry and biology. Concerted PCET is thermochemically more favorable than the first step in competing consecutive processes involving stepwise electron transfer (ET) and proton transfer (PT), often by >=1 eV. PCET reactions of the form X-H + Y X + H-Y can be termed hydrogen atom transfer (HAT). Another PCET class involves outersphere electron transfer concerted with deprotonation by another reagent, Y+ + XH-B Y + X-HB+ . Many PCET/HAT rate constants are predicted well by the Marcus cross relation. The cross-relation calculation uses rate constants for self-exchange reactions to provide information on intrinsic barriers. Intrinsic barriers for PCET can be comparable to or larger than those for ET. These properties are discussed in light of recent theoretical treatments of PCET.

  13. Lipid and water suppression by selective 1H homonuclear polarization transfer.

    PubMed

    Hardy, C J; Dumoulin, C L

    1987-07-01

    A pulse sequence is presented which uses Polarization Transfer by a Selective Homonuclear Technique (POTSHOT) to retain all resonances, in phase, from a selected coupled spin system while suppressing all other peaks, from both coupled and noncoupled spins. This technique, which is a selective form of Homonuclear Polarization Transfer (HPT), has been used in a 1.5-T whole-body system to generate edited 1H lactate spectra from lactate/oil phantoms and from excised dog hearts.

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

    PubMed

    Guallar, Victor

    2008-10-23

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

  15. Electron transfer at thermally heterogeneous molecule-metal interfaces

    NASA Astrophysics Data System (ADS)

    Craven, Galen T.; Nitzan, Abraham

    2017-03-01

    The rate of electron transfer between a molecular species and a metal, each at a different local temperature, is examined theoretically through the implementation of a bithermal (characterized by two temperatures) Marcus formalism. Expressions for the rate constant and the electronic contribution to a heat transfer mechanism which is induced by the temperature gradient between a molecule and metal are constructed. The system of coupled dynamical equations describing the electronic and thermal currents are derived and examined over diverse ranges of reaction geometries and temperature gradients. It is shown that electron transfer across the molecule-metal interface is associated with heat transfer and that the electron exchange between metal and molecule makes a distinct contribution to the interfacial heat conduction even when the net electronic current vanishes.

  16. Variable Electron Transfer Pathways in an Amphibian Cryptochrome

    PubMed Central

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

    2013-01-01

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

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

    PubMed Central

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

    2016-01-01

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

  18. A molecular shift register based on electron transfer

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

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

    PubMed

    Mayer, James M

    2011-01-01

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

  20. Photoinduced electron transfer between benzyloxy dendrimer phthalocyanine and benzoquinone

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  1. Engineering of an alternative electron transfer path in photosystem II

    PubMed Central

    Larom, Shirley; Salama, Faris; Schuster, Gadi; Adir, Noam

    2010-01-01

    The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multistep pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor QB, is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the QA intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II. PMID:20457933

  2. Kinetics and Mechanism of Electron Transfer in Proteins

    NASA Astrophysics Data System (ADS)

    Kulys, J.

    1986-10-01

    The results of studies on the kinetics of the oxidation-reduction reactions of individual proteins (electron transfer agents and enzymes) are described. Attention has been concentrated on the effect of the nature of the active centres in the protein molecules and of the modification of individual aminoacid residues on the rate of electron transfer in a homogeneous medium. Questions associated with the electrochemical reactions of proteins and with the effect of the state of the interface on the rate of this process are considered in detail. Ideas concerning the theoretical calculation of the rate constants for electron transfer in proteins are described. The bibliography includes 154 references.

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

    SciTech Connect

    Brunschwig, B.S.

    2000-01-12

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

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

    PubMed

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

    1998-01-01

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

  5. Photosensitized electron transfer processes of nanocarbons applicable to solar cells.

    PubMed

    D'Souza, Francis; Ito, Osamu

    2012-01-07

    Photosensitized electron-transfer processes of nanocarbon materials hybridized with electron donating or electron accepting molecules have been surveyed in this tutorial review on the basis of the recent results reported mainly from our laboratories. As nano-carbon materials, fullerenes and single wall carbon nanotubes (SWCNTs) have been employed. Fullerenes act as photo-sensitizing electron acceptors with respect to a wide variety of electron donors; in addition, the fullerenes act as good ground state electron acceptors in the presence of light-absorbing electron donors such as porphyrins and phthalocyanines. In the case of SWCNTs, their ground states act as electron acceptor and electron donors, depending on the photosensitizers. For example, with respect to the photoexcited porphyrins and phthalocyanines, SWCNTs usually act as electron acceptors, whereas for the photoexcited fullerenes, SWCNTs act as electron donors. The diameter sorted semi-conductive SWCNTs have been used to verify the size-dependent electron transfer rates. For the confirmation of the electron transfer processes, the transient absorption methods have been widely used, in addition to the time-resolved fluorescence spectral measurements. The kinetic data thus obtained in solution are found to be quite useful to predict the efficiencies of photovoltaic cells constructed on semiconductor nanoparticle modified electrodes and their photocatalytic processes.

  6. Extracellular electron transfer mechanisms between microorganisms and minerals

    SciTech Connect

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

    2016-08-30

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

  7. Promoting Knowledge Transfer with Electronic Note Taking

    ERIC Educational Resources Information Center

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

    2005-01-01

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

  8. Supramolecular networks with electron transfer in two dimensions

    SciTech Connect

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

    2016-09-13

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

  9. Improved heterogeneous electron transfer kinetics of fluorinated graphene derivatives

    NASA Astrophysics Data System (ADS)

    Boopathi, Sidhureddy; Narayanan, Tharangattu N.; Senthil Kumar, Shanmugam

    2014-08-01

    Though graphitic carbons are commercially available for various electrochemical processes, their performance is limited in terms of various electrochemical activities. Recent experiments on layered carbon materials, such as graphene, demonstrated an augmented performance of these systems in all electrochemical activities due to their unique electronic properties, enhanced surface area, structure and chemical stabilities. Moreover, flexibility in controlling electronic, as well as electrochemical activities by heteroatom doping brings further leverage in their practical use. Here, we study the electron transfer kinetics of fluorinated graphene derivatives, known as fluorinated graphene oxide (FGO) and its reduced form, RFGO. Enhanced electron transfer kinetics (heterogeneous electron transfer (HET)) is observed from these fluorinated systems in comparison to their undoped systems such as graphene oxide (GO) and reduced GO. A detailed study has been conducted using standard redox probes and biomolecules revealing the enhanced electro-catalytic activities of FGO and RFGO, and electron transfer rates are simulated theoretically. This study reveals that fluorine not only induces defects in graphitic lattice leading to an enhanced HET process but also can modify the electronic structure of graphene surface.Though graphitic carbons are commercially available for various electrochemical processes, their performance is limited in terms of various electrochemical activities. Recent experiments on layered carbon materials, such as graphene, demonstrated an augmented performance of these systems in all electrochemical activities due to their unique electronic properties, enhanced surface area, structure and chemical stabilities. Moreover, flexibility in controlling electronic, as well as electrochemical activities by heteroatom doping brings further leverage in their practical use. Here, we study the electron transfer kinetics of fluorinated graphene derivatives, known as

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

    NASA Astrophysics Data System (ADS)

    Suzuki, Yasumitsu; Yamashita, Koichi

    2012-04-01

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

  11. MANAGING ELECTRONIC DATA TRANSFER IN ENVIRONMENTAL CLEANUPS

    EPA Science Inventory

    The use of computers and electronic information poses a complex problem for potential litigation in space law. The problem currently manifests itself in at least two ways. First, the Environmental Protection Agency (EPA) enforcement of Comprehensive Environmental Response, Compen...

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

    DTIC Science & Technology

    1983-10-31

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

  13. Electron transfer reactions in microporous solids

    SciTech Connect

    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

  14. Efficient phosphorescent polymer light-emitting diodes by suppressing triplet energy back transfer.

    PubMed

    Gong, Shaolong; Yang, Chuluo; Qin, Jingui

    2012-07-21

    Phosphorescent polymer light-emitting diodes (PhPLEDs) are promising devices in flat panel displays and solid state lighting sources since they can combine the advantages of the high efficiency of electrophosphorescence and low-cost, large-scale manufacture by using a solution process. However, their efficiencies are generally much lower than those of small-molecule-based devices fabricated by using a thermal deposition approach. One of the major reasons for their low efficiency is that energy is lost by back transfer to a polymer host. This tutorial review gives a brief introduction to the fundamentals of PhPLEDs, and then highlights recent progress in the main approaches to suppress triplet energy back transfer from the phosphor to the polymer host towards realizing highly efficient PhPLEDs. The suppressing mechanisms are discussed, and the achievement of high device efficiencies are demonstrated. Emphasis is placed on the relationships between molecular structure, the extent of suppressing triplet energy back transfer, and device performance.

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

    PubMed

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

    2012-10-23

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

  16. 14 CFR 1274.931 - Electronic funds transfer payment methods.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... processed. (c) In the event the Recipient, during the performance of this cooperative agreement, elects to... COOPERATIVE AGREEMENTS WITH COMMERCIAL FIRMS Other Provisions and Special Conditions § 1274.931 Electronic... cooperative agreement will be made by the Government by electronic funds transfer through the Treasury...

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

    PubMed

    Strouse, Gabrielle A; Ganea, Patricia A

    2017-04-01

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

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

    PubMed

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

    2014-10-01

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

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

    PubMed Central

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

    2012-01-01

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

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

    SciTech Connect

    Abriata, Luciano A.; Alvarez-Paggi, Damian; Ledesma, Gabirela N.; Blackburn, Ninian J.; Vila, Alejandro J.; Murgida, Daniel H.

    2012-10-10

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

  1. Effect of proton transfer on the electronic coupling in DNA

    NASA Astrophysics Data System (ADS)

    Rak, Janusz; Makowska, Joanna; Voityuk, Alexander A.

    2006-06-01

    The effects of single and double proton transfer within Watson-Crick base pairs on donor-acceptor electronic couplings, Vda, in DNA are studied on the bases of quantum chemical calculations. Four dimers [AT,AT], [GC,GC], [GC,AT] and [GC,TA)] are considered. Three techniques - the generalized Mulliken-Hush scheme, the fragment charge method and the diabatic states method - are employed to estimate Vda for hole transfer between base pairs. We show that both single- and double proton transfer (PT) reactions may substantially affect the electronic coupling in DNA. The electronic coupling in [AT,AT] is predicted to be most sensitive to PT. Single PT within the first base pair in the dimer leads to increase in the hole transfer efficiency by a factor of 4, while proton transfer within the second pair should substantially, by 2.7 times, decrease the rate of charge transfer. Thus, directional asymmetry of the PT effects on the electronic coupling is predicted. The changes in the Vda matrix elements correlate with the topological properties of orbitals of donor and acceptor and can be qualitatively rationalized in terms of resonance structures of donor and acceptor. Atomic pair contributions to the Vda matrix elements are also analyzed.

  2. Doping suppression and mobility enhancement of graphene transistors fabricated using an adhesion promoting dry transfer process

    SciTech Connect

    Cheol Shin, Woo; Hun Mun, Jeong; Yong Kim, Taek; Choi, Sung-Yool; Jin Cho, Byung E-mail: tskim1@kaist.ac.kr; Yoon, Taeshik; Kim, Taek-Soo E-mail: tskim1@kaist.ac.kr

    2013-12-09

    We present the facile dry transfer of graphene synthesized via chemical vapor deposition on copper film to a functional device substrate. High quality uniform dry transfer of graphene to oxidized silicon substrate was achieved by exploiting the beneficial features of a poly(4-vinylphenol) adhesive layer involving a strong adhesion energy to graphene and negligible influence on the electronic and structural properties of graphene. The graphene field effect transistors (FETs) fabricated using the dry transfer process exhibit excellent electrical performance in terms of high FET mobility and low intrinsic doping level, which proves the feasibility of our approach in graphene-based nanoelectronics.

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

    PubMed

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

    2014-08-01

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

  4. Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions

    SciTech Connect

    Whitten, D.G.

    1991-10-01

    The focus of the work described in this report is on single electron transfer reactions of excited states which culminate in the formation of stable or metastable even electron species. For the most part the studies have involved even electron organic substrates which are thus converted photochemically to odd electron species and then at some stage reconvert to even electron products. These reactions generally fall into two rather different categories. In one set of studies we have examined reactions in which the metastable reagents generated by single electron transfer quenching of an excited state undergo novel fragmentation reactions, chiefly involving C-C bond cleavage. These reactions often culminate in novel and potentially useful chemical reactions and frequently have the potential for leading to new chemical products otherwise unaffordable by conventional reaction paths. In a rather different investigation we have also studied reactions in which single electron transfer quenching of an excited state is followed by subsequent reactions which lead reversibly to metastable two electron products which, often stable in themselves, can nonetheless be reacted with each other or with other reagents to regenerate the starting materials with release of energy. 66 refs., 9 figs., 1 tab.

  5. Mapping protein electron transfer pathways with QM/MM methods

    PubMed Central

    Guallar, Victor; Wallrapp, Frank

    2008-01-01

    Mixed quantum mechanics/molecular mechanics (QM/MM) methods offer a valuable computational tool for understanding the electron transfer pathway in protein–substrate interactions and protein–protein complexes. These hybrid methods are capable of solving the Schrödinger equation on a small subset of the protein, the quantum region, describing its electronic structure under the polarization effects of the remainder of the protein. By selectively turning on and off different residues in the quantum region, we are able to obtain the electron pathway for short- and large-range interactions. Here, we summarize recent studies involving the protein–substrate interaction in cytochrome P450 camphor, ascorbate peroxidase and cytochrome c peroxidase, and propose a novel approach for the long-range protein–protein electron transfer. The results on ascorbate peroxidase and cytochrome c peroxidase reveal the importance of the propionate groups in the electron transfer pathway. The long-range protein–protein electron transfer has been studied on the cytochrome c peroxidase–cytochrome c complex. The results indicate the importance of Phe82 and Cys81 on cytochrome c, and of Asn196, Ala194, Ala176 and His175 on cytochrome c peroxidase. PMID:18445553

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

    DOE PAGES

    Abriata, Luciano A.; Alvarez-Paggi, Damian; Ledesma, Gabirela N.; ...

    2012-10-10

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

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

    NASA Astrophysics Data System (ADS)

    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

  8. Condensed phase electron transfer beyond the Condon approximation

    NASA Astrophysics Data System (ADS)

    Mavros, Michael G.; Hait, Diptarka; Van Voorhis, Troy

    2016-12-01

    Condensed phase electron transfer problems are often simplified by making the Condon approximation: the approximation that the coupling connecting two charge-transfer diabatic states is a constant. Unfortunately, the Condon approximation does not predict the existence of conical intersections, which are ubiquitous in both gas-phase and condensed-phase photochemical dynamics. In this paper, we develop a formalism to treat condensed-phase dynamics beyond the Condon approximation. We show that even for an extremely simple test system, hexaaquairon(ii)/hexaaquairon(iii) self-exchange in water, the electronic coupling is expected to fluctuate rapidly and non-Condon effects must be considered to obtain quantitatively accurate ultrafast nonequilibrium dynamics. As diabatic couplings are expected to fluctuate substantially in many condensed-phase electron transfer systems, non-Condon effects may be essential to quantitatively capture accurate short-time dynamics.

  9. Photo-induced electron-transfer reactions in heterogeneous media

    NASA Astrophysics Data System (ADS)

    Yang, J. M.

    1981-11-01

    The conversion of solar energy into chemical energy was pursued by two approaches. One is the photo-induced electron transfer reactions in heterogeneous media, and the other is the photo-decomposition of water with liquid-junction solar cells. Photo-induced electron-transfer reactions in heterogeneous media with colloidal silica or poly-acrylate were studied by flash photolysis. In an effort to illustrate that small band-gap semiconductors can be protected from photo-corrosion through surface modification, the surface of polycrystalline ZnO was chemically coated with zinc phthalocyanine and the electron-transfer process across the coated ZnO-electrolyte interface was studied by photo-electrochemical techniques.

  10. Reorganization of intramolecular high frequency vibrational modes and dynamic solvent effect in electron transfer reactions.

    PubMed

    Yudanov, Vladislav V; Mikhailova, Valentina A; Ivanov, Anatoly I

    2012-04-26

    The possibility of the multichannel stochastic model to adequately describe all principal regularities observed in thermal electron transfer kinetics has been demonstrated. The most important are as follows: (i) the model predicts the solvent controlled regime in the Marcus normal region and its almost full suppression in the Marcus inverted region as well as a continuous transition between them in the vicinity of the activationless region; (ii) the suppression of dynamic solvent effect (DSE) is principally caused by the reorganization of high frequency vibrational modes; (iii) an additional factor of the DSE suppression stems from fast solvent relaxation component; (iv) in the inverted region, the multichannel stochastic model predicts the apparent activation energy to be much less than that calculated with Marcus equation. The exploration of the multichannel stochastic model has allowed one to conclude that the reorganization of high frequency vibrational modes can (i) raise the maximum rate constant above the solvent controlled limit by 2 and more orders of magnitude, (ii) shift the rate constant maximum to larger values of the free energy gap, and (iii) approach the electron transfer kinetics to the nonadiabatic regime.

  11. Tracking multiple generation and suppression of secondary electrons on periodic triangular surface

    SciTech Connect

    Li, S.; Wang, J. G.; Zhu, M.; Peng, J. C.; Xie, J. L.; Wu, X. L.; Guo, L. T.; Chang, C.; Xiong, Z. F.

    2013-12-15

    To research the dynamic course of multipactor suppression on the periodically patterned surface, tens of electron collision processes are tracked by numerical calculation. The influences of microwave frequency, amplitude of RF electric field, slope angle, the local field enhancement, and the tilted incident electric field on the multipactor suppression are studied by tracking multi-generation electrons' trajectories, hopping and flight time, collision energy, and secondary emission yield. Meanwhile, the dynamic processes of secondary electrons on the periodic surface are analyzed by particle-in-cell (PIC) simulation. The PIC results are consistent with the analytical results in which the electrons fly reciprocatingly between the slopes and impact on the slopes; the methods of increasing the slope angle, enlarging the RF field, and lowering the frequency in a certain range are helpful to enhance the multipactor suppression steadily and persistently.

  12. Theory of electron transfer and molecular state in DNA

    NASA Astrophysics Data System (ADS)

    Endres, Robert Gunter

    2002-09-01

    In this thesis, a mechanism for long-range electron transfer in DNA and a systematic search for high conductance DNA are developed. DNA is well known for containing the genetic code of all living species. On the other hand, there are some experimental indications that DNA can mediate effectively long-range electron transfer leading to the concept of chemistry at a distance. This can be important for DNA damage and healing. In the first part of the thesis, a possible mechanism for long-range electron transfer is introduced. The weak distance dependent electron transfer was experimentally observed using transition metal intercalators for donor and acceptor. In our model calculations, the transfer is mediated by the molecular analogue of a Kondo bound state well known from solid state physics of mixed-valence rare-earth compounds. We believe this is quite realistic, since localized d orbitals of the transition metal ions could function as an Anderson impurity embedded in a reservoir of rather delocalized molecular orbitals of the intercalator ligands and DNA pi orbitals. The effective Anderson model is solved with a physically intuitive variational ansatz as well as with the essentially exact DMRG method. The electronic transition matrix element, which is important because it contains the donor-acceptor distance dependence, is obtained with the Mulliken-Hush algorithm as well as from Born-Oppenheimer potential energy surfaces. Our possible explanation of long-range electron transfer is put in context to other more conventional mechanisms which also could lead to similar behavior. Another important issue of DNA is its possible use for nano-technology. Although DNA's mechanical properties are excellent, the question whether it can be conducting and be used for nano-wires is highly controversial. Experimentally, DNA shows conducting, semi-conducting and insulating properties. Motivated by these wide ranging experimental results on the conductivity of DNA, we have

  13. Single-molecule interfacial electron transfer dynamics in solar energy conversion

    NASA Astrophysics Data System (ADS)

    Dhital, Bharat

    This dissertation work investigated the parameters affecting the interfacial electron transfer (ET) dynamics in dye-semiconductor nanoparticles (NPs) system by using single-molecule fluorescence spectroscopy and imaging combined with electrochemistry. The influence of the molecule-substrate electronic coupling, the molecular structure, binding geometry on the surface and the molecule-attachment surface chemistry on interfacial charge transfer processes was studied on zinc porphyrin-TiO2 NP systems. The fluorescence blinking measurement on TiO2 NP demonstrated that electronic coupling regulates dynamics of charge transfer processes at the interface depending on the conformation of molecule on the surface. Moreover, semiconductor surface charge induced electronic coupling of molecule which is electrostatically adsorbed on the semiconductor surface also predominantly alters the ET dynamics. Furthermore, interfacial electric field and electron accepting state density dependent ET dynamics has been dissected in zinc porphyrin-TiO2 NP system by observing the single-molecule fluorescence blinking dynamics and fluorescence lifetime with and without applied bias. The significant difference in fluorescence fluctuation and lifetime suggested the modulation of charge transfer dynamics at the interface with external electric field perturbation. Quasi-continuous distribution of fluorescence intensity with applied negative potential was attributed to the faster charge recombination due to reduced density of electron accepting states. The driving force and electron accepting state density ET dependent dynamics has also been probed in zinc porphyrin-TiO2 NP and zinc porphyrin-indium tin oxide (ITO) systems. Study of a molecule adsorbed on two different semiconductors (ITO and TiO2), with large difference in electron densities and distinct driving forces, allows us to observe the changes in rates of back electron transfer process reflected by the suppressed fluorescence blinking of

  14. Macrophages activated by C-reactive protein through Fc gamma RI transfer suppression of immune thrombocytopenia.

    PubMed

    Marjon, Kristopher D; Marnell, Lorraine L; Mold, Carolyn; Du Clos, Terry W

    2009-02-01

    C-reactive protein (CRP) is an acute-phase protein with therapeutic activity in mouse models of systemic lupus erythematosus and other inflammatory and autoimmune diseases. To determine the mechanism by which CRP suppresses immune complex disease, an adoptive transfer system was developed in a model of immune thrombocytopenic purpura (ITP). Injection of 200 microg of CRP 24 h before induction of ITP markedly decreased thrombocytopenia induced by anti-CD41. CRP-treated splenocytes also provided protection from ITP in adoptive transfer. Splenocytes from C57BL/6 mice were treated with 200 microg/ml CRP for 30 min, washed, and injected into mice 24 h before induction of ITP. Injection of 10(6) CRP-treated splenocytes protected mice from thrombocytopenia, as did i.v. Ig-treated but not BSA-treated splenocytes. The suppressive cell induced by CRP was found to be a macrophage by depletion, enrichment, and the use of purified bone marrow-derived macrophages. The induction of protection by CRP-treated cells was dependent on FcRgamma-chain and Syk activation, indicating an activating effect of CRP on the donor cell. Suppression of ITP by CRP-treated splenocytes required Fc gamma RI on the donor cell and Fc gamma RIIb in the recipient mice. These findings suggest that CRP generates suppressive macrophages through Fc gamma RI, which then act through an Fc gamma RIIb-dependent pathway in the recipient to decrease platelet clearance. These results provide insight into the mechanism of CRP regulatory activity in autoimmunity and suggest a potential new therapeutic approach to ITP.

  15. 45 CFR 162.1601 - Health care electronic funds transfers (EFT) and remittance advice transaction.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 45 Public Welfare 1 2013-10-01 2013-10-01 false Health care electronic funds transfers (EFT) and... Electronic Funds Transfers (EFT) and Remittance Advice § 162.1601 Health care electronic funds transfers (EFT) and remittance advice transaction. The health care electronic funds transfers (EFT) and...

  16. 45 CFR 162.1601 - Health care electronic funds transfers (EFT) and remittance advice transaction.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 45 Public Welfare 1 2012-10-01 2012-10-01 false Health care electronic funds transfers (EFT) and... Electronic Funds Transfers (EFT) and Remittance Advice § 162.1601 Health care electronic funds transfers (EFT) and remittance advice transaction. The health care electronic funds transfers (EFT) and...

  17. 45 CFR 162.1601 - Health care electronic funds transfers (EFT) and remittance advice transaction.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 45 Public Welfare 1 2014-10-01 2014-10-01 false Health care electronic funds transfers (EFT) and... Electronic Funds Transfers (EFT) and Remittance Advice § 162.1601 Health care electronic funds transfers (EFT) and remittance advice transaction. The health care electronic funds transfers (EFT) and...

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

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

    PubMed Central

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

    2017-01-01

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

  20. Accumulative electron transfer: multiple charge separation in artificial photosynthesis.

    PubMed

    Karlsson, Susanne; Boixel, Julien; Pellegrin, Yann; Blart, Errol; Becker, Hans-Christian; Odobel, Fabrice; Hammarström, Leif

    2012-01-01

    To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme.

  1. Opto-Electronic Oscillator Using Suppressed Phase Modulation

    NASA Technical Reports Server (NTRS)

    Dick, G. John; Yu, Nan

    2007-01-01

    A proposed opto-electronic oscillator (OEO) would generate a microwave signal having degrees of frequency stability and spectral purity greater than those achieved in prior OEOs. The design of this system provides for reduction of noise levels (including the level of phase noise in the final output microwave signal) to below some of the fundamental limits of the prior OEOs while retaining the advantages of photonic generation of microwaves.

  2. Suppression of x-rays generated by runaway electrons in ATF

    SciTech Connect

    Rasmussen, D.A.; England, A.C.; Eberle, C.C.; Devan, W.R.; Harris, J.H.; Jernigan, T.C.; Kindsfather, R.R.; Morris, R.N.; Murakami, M.; Neilson, G.H.

    1987-01-01

    X-ray emission from runaway electrons on ATF is a serious issue. Runaway suppression techniques used on Heliotron-E are not adequate for ATF. Three approaches have been developed to suppress runaway production. Monitoring devices have been installed in occupied areas and personnel access and exposure will be limited. Additional shielding will be added as required. These systems will be ready for installation and testing on ATF prior to commissioning or first plasma operation.

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

    SciTech Connect

    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.

  4. Tryptophan-to-heme electron transfer in ferrous myoglobins

    PubMed Central

    Monni, Roberto; Al Haddad, André; van Mourik, Frank; Auböck, Gerald; Chergui, Majed

    2015-01-01

    It was recently demonstrated that in ferric myoglobins (Mb) the fluorescence quenching of the photoexcited tryptophan 14 (*Trp14) residue is in part due to an electron transfer to the heme porphyrin (porph), turning it to the ferrous state. However, the invariance of *Trp decay times in ferric and ferrous Mbs raises the question as to whether electron transfer may also be operative in the latter. Using UV pump/visible probe transient absorption, we show that this is indeed the case for deoxy-Mb. We observe that the reduction generates (with a yield of about 30%) a low-valence Fe–porphyrin π [FeII(porph●−)] -anion radical, which we observe for the first time to our knowledge under physiological conditions. We suggest that the pathway for the electron transfer proceeds via the leucine 69 (Leu69) and valine 68 (Val68) residues. The results on ferric Mbs and the present ones highlight the generality of Trp–porphyrin electron transfer in heme proteins. PMID:25902517

  5. Quantum ergodicity breaking in semi-classical electron transfer dynamics.

    PubMed

    Goychuk, Igor

    2017-01-25

    Can the statistical properties of single-electron transfer events be correctly predicted within a common equilibrium ensemble description? This fundamental in nanoworld question of ergodic behavior is scrutinized within a very basic semi-classical curve-crossing problem. It is shown that in the limit of non-adiabatic electron transfer (weak tunneling) well-described by the Marcus-Levich-Dogonadze (MLD) rate the answer is yes. However, in the limit of the so-called solvent-controlled adiabatic electron transfer, a profound breaking of ergodicity occurs. Namely, a common description based on the ensemble reduced density matrix with an initial equilibrium distribution of the reaction coordinate is not able to reproduce the statistics of single-trajectory events in this seemingly classical regime. For sufficiently large activation barriers, the ensemble survival probability in a state remains nearly exponential with the inverse rate given by the sum of the adiabatic curve crossing (Kramers) time and the inverse MLD rate. In contrast, near to the adiabatic regime, the single-electron survival probability is clearly non-exponential, even though it possesses an exponential tail which agrees well with the ensemble description. Initially, it is well described by a Mittag-Leffler distribution with a fractional rate. Paradoxically, the mean transfer time in this classical on the ensemble level regime is well described by the inverse of the nonadiabatic quantum tunneling rate on a single particle level. An analytical theory is developed which perfectly agrees with stochastic simulations and explains our findings.

  6. 48 CFR 18.124 - Electronic funds transfer.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 48 Federal Acquisition Regulations System 1 2014-10-01 2014-10-01 false Electronic funds transfer. 18.124 Section 18.124 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities...

  7. 48 CFR 18.123 - Electronic funds transfer.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

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

  8. 48 CFR 18.124 - Electronic funds transfer.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 48 Federal Acquisition Regulations System 1 2011-10-01 2011-10-01 false Electronic funds transfer. 18.124 Section 18.124 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities...

  9. 48 CFR 18.124 - Electronic funds transfer.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 48 Federal Acquisition Regulations System 1 2012-10-01 2012-10-01 false Electronic funds transfer. 18.124 Section 18.124 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities...

  10. 48 CFR 18.124 - Electronic funds transfer.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 48 Federal Acquisition Regulations System 1 2013-10-01 2013-10-01 false Electronic funds transfer. 18.124 Section 18.124 Federal Acquisition Regulations System FEDERAL ACQUISITION REGULATION CONTRACTING METHODS AND CONTRACT TYPES EMERGENCY ACQUISITIONS Available Acquisition Flexibilities...

  11. Tryptophan-to-heme electron transfer in ferrous myoglobins.

    PubMed

    Monni, Roberto; Al Haddad, André; van Mourik, Frank; Auböck, Gerald; Chergui, Majed

    2015-05-05

    It was recently demonstrated that in ferric myoglobins (Mb) the fluorescence quenching of the photoexcited tryptophan 14 (*Trp(14)) residue is in part due to an electron transfer to the heme porphyrin (porph), turning it to the ferrous state. However, the invariance of *Trp decay times in ferric and ferrous Mbs raises the question as to whether electron transfer may also be operative in the latter. Using UV pump/visible probe transient absorption, we show that this is indeed the case for deoxy-Mb. We observe that the reduction generates (with a yield of about 30%) a low-valence Fe-porphyrin π [Fe(II)(porph(●-))] -anion radical, which we observe for the first time to our knowledge under physiological conditions. We suggest that the pathway for the electron transfer proceeds via the leucine 69 (Leu(69)) and valine 68 (Val(68)) residues. The results on ferric Mbs and the present ones highlight the generality of Trp-porphyrin electron transfer in heme proteins.

  12. 75 FR 51707 - Electronic Funds Transfer of Depository Taxes

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-23

    ..., 40, and 301 [REG-153340-09] RIN 1545-BJ13 Electronic Funds Transfer of Depository Taxes AGENCY... hearing. SUMMARY: This document contains proposed regulations relating to Federal tax deposits (FTDs) by...). SUPPLEMENTARY INFORMATION: Background This document contains proposed amendments to the Income Tax...

  13. A molecularly based theory for electron transfer reorganization energy.

    PubMed

    Zhuang, Bilin; Wang, Zhen-Gang

    2015-12-14

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

  14. A molecularly based theory for electron transfer reorganization energy

    SciTech Connect

    Zhuang, Bilin; Wang, Zhen-Gang

    2015-12-14

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

  15. 77 FR 30923 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-05-24

    ... Part 1005 [Docket No. CFPB-2012-0019] RIN 3170-AA22 Electronic Fund Transfers (Regulation E) AGENCY... interested in learning more about this product, including its costs, benefits, and risks to consumers. The Bureau intends to issue a proposal to extend the Regulation E protections to GPR cards. Your comments,...

  16. Correlating electronic and vibrational motions in charge transfer systems

    SciTech Connect

    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.

  17. 77 FR 77187 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-31

    ... From the Federal Register Online via the Government Publishing Office ] Vol. 77 Monday, No. 250 December 31, 2012 Part II Bureau of Consumer Financial Protection 12 CFR Part 1005 Electronic Fund Transfers (Regulation E); Proposed Rule #0;#0;Federal Register / Vol. 77 , No. 250 / Monday, December...

  18. Shewanella secretes flavins that mediate extracellular electron transfer

    PubMed Central

    Marsili, Enrico; Baron, Daniel B.; Shikhare, Indraneel D.; Coursolle, Dan; Gralnick, Jeffrey A.; Bond, Daniel R.

    2008-01-01

    Bacteria able to transfer electrons to metals are key agents in biogeochemical metal cycling, subsurface bioremediation, and corrosion processes. More recently, these bacteria have gained attention as the transfer of electrons from the cell surface to conductive materials can be used in multiple applications. In this work, we adapted electrochemical techniques to probe intact biofilms of Shewanella oneidensis MR-1 and Shewanella sp. MR-4 grown by using a poised electrode as an electron acceptor. This approach detected redox-active molecules within biofilms, which were involved in electron transfer to the electrode. A combination of methods identified a mixture of riboflavin and riboflavin-5′-phosphate in supernatants from biofilm reactors, with riboflavin representing the dominant component during sustained incubations (>72 h). Removal of riboflavin from biofilms reduced the rate of electron transfer to electrodes by >70%, consistent with a role as a soluble redox shuttle carrying electrons from the cell surface to external acceptors. Differential pulse voltammetry and cyclic voltammetry revealed a layer of flavins adsorbed to electrodes, even after soluble components were removed, especially in older biofilms. Riboflavin adsorbed quickly to other surfaces of geochemical interest, such as Fe(III) and Mn(IV) oxy(hydr)oxides. This in situ demonstration of flavin production, and sequestration at surfaces, requires the paradigm of soluble redox shuttles in geochemistry to be adjusted to include binding and modification of surfaces. Moreover, the known ability of isoalloxazine rings to act as metal chelators, along with their electron shuttling capacity, suggests that extracellular respiration of minerals by Shewanella is more complex than originally conceived. PMID:18316736

  19. Theory of ultrafast heterogeneous electron transfer: Contributions of direct charge transfer excitations to the absorbance

    SciTech Connect

    Wang, Luxia; Willig, Frank; May, Volkhard

    2007-04-07

    Absorption spectra related to heterogeneous electron transfer are analyzed with the focus on direct charge transfer transition from the surface attached molecule into the semiconductor band states. The computations are based on a model of reduced dimensionality with a single intramolecular vibrational coordinate but a complete account for the continuum of conduction band states. The applicability of this model to perylene on TiO{sub 2} has been demonstrated in a series of earlier papers. Here, based on a time-dependent formulation, the absorbance is calculated with the inclusion of charge transfer excitations. A broad parameter set inspired by the perylene TiO{sub 2} systems is considered. In particular, the description generalizes the Fano effect to heterogeneous electron transfer reactions. Preliminary simulations of measured spectra are presented for perylene-catechol attached to TiO{sub 2}.

  20. Quantum effect of intramolecular high-frequency vibrational modes on diffusion-controlled electron transfer rate: From the weak to the strong electronic coupling regions

    SciTech Connect

    Zhu, Wenjuan; Zhao, Yi

    2007-05-14

    The Sumi-Marcus theory is extended by introducing two approaches to investigate electron transfer reactions from weak-to-strong electronic coupling regime. One of these approaches is the quantum R-matrix theory, useful for dealing with the intramolecular vibrational motions in the whole electronic coupling domain. The other is the split operator approach that is employed to solve the reaction-diffusion equation. The approaches are then applied to electron transfer in the Marcus inverted regime to investigate the nuclear tunneling effect on the long time rate and the survival probabilities. The numerical results illustrate that the adiabatic suppression obtained from the R-matrix approach is much smaller than that from the Landau-Zener theory whereas it cannot be predicted by the perturbation theory. The jointed effects of the electronic coupling and solvent relaxation time on the rates are also explored.

  1. An Effective Secondary Electron Emission Suppression Treatment For Copper MDC

    NASA Technical Reports Server (NTRS)

    Curren, Arthur N.; Long, Kenwyn J.; Jensen, Kenneth A.; Roman, Robert F.

    1993-01-01

    Untreated oxygen-free, high-conductivity (OFHC) copper, commonly used for MDC electrodes, exhibits relatively high secondary electron emission characteristics. This paper describes a specialized ion-bombardment procedure for texturing copper surfaces which sharply reduces the emission properties relative to untreated copper. The resulting surface is a particle-free, robust, uniformly highly-textured all-metal structure. The use of this process requires no modifications to copper machining, brazing, or other MDC normal fabrication procedures. The flight TWT for a planned NASA deep space probe, the Cassini Mission, will incorporate copper MDC electrodes treated with the method described here.

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

    NASA Astrophysics Data System (ADS)

    Kundu, Prasanta; Dua, Arti

    2013-01-01

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

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

    PubMed

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

    2015-10-14

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

  4. Heat shock suppresses mating and sperm transfer in the rice leaf folder Cnaphalocrocis medinalis.

    PubMed

    Liao, H J; Qian, Q; Liu, X D

    2014-06-01

    Temperature is a key environmental factor in determining the population size of Cnaphalocrocis medinalis in summer. High temperatures inhibit survival, development and fecundity of this insect. However, biological responses of female and male adults to heat shock, and physiological mechanism of high temperature suppressing population development are still ambiguous. We experimentally tested the impact of heat shock (5 h day-1) on biological traits, spermatogenesis and sperm transfer of adults of C. medinalis. The result showed that heat exposure to 39 and 40 °C for 5 h reduced longevity and copulation frequency of adults, and hatchability of eggs. Immediate survival rate of males was lower than that of females after 3 days of exposure to 41 °C. The oviposition period, copulation frequency, fecundity of adults and hatchability of eggs were significantly lower when male adults were exposed to 40 or 41 °C for 3 days. Heat shock decreased frequency and success rate of mating when males were exposed, and it also resulted in postponement of mating behaviour and prolongation of mating duration as both the female and male adults were exposed. Heat shock did not affect spermatogenesis, but significantly inhibited sperms maturation. Moreover, males could not ejaculate sperm into females during copulation when these male moths received heat shock. Heat shock remarkably suppressed mating behaviour and sperm transfer, which led to a dramatic decline of rice leaf folder populations.

  5. The Role of Resonant Vibrations in Electronic Energy Transfer

    PubMed Central

    Somsen, Oscar J. G.; Novoderezhkin, Vladimir I.; Mančal, Tomáš; van Grondelle, Rienk

    2016-01-01

    Abstract Nuclear vibrations play a prominent role in the spectroscopy and dynamics of electronic systems. As recent experimental and theoretical studies suggest, this may be even more so when vibrational frequencies are resonant with transitions between the electronic states. Herein, a vibronic multilevel Redfield model is reported for excitonically coupled electronic two‐level systems with a few explicitly included vibrational modes and interacting with a phonon bath. With numerical simulations the effects of the quantized vibrations on the dynamics of energy transfer and coherence in a model dimer are illustrated. The resonance between the vibrational frequency and energy gap between the sites leads to a large delocalization of vibronic states, which then results in faster energy transfer and longer‐lived mixed coherences. PMID:26910485

  6. Syntrophic growth via quinone-mediated interspecies electron transfer

    PubMed Central

    Smith, Jessica A.; Nevin, Kelly P.; Lovley, Derek R.

    2015-01-01

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

  7. Generic suppression of conductance quantization of interacting electrons in graphene nanoribbons in a perpendicular magnetic field

    NASA Astrophysics Data System (ADS)

    Shylau, A. A.; Zozoulenko, I. V.; Xu, H.; Heinzel, T.

    2010-09-01

    The effects of electron interaction on the magnetoconductance of graphene nanoribbons (GNRs) are studied within the Hartree approximation. We find that a perpendicular magnetic field leads to a suppression instead of an expected improvement of the quantization. This suppression is traced back to interaction-induced modifications of the band structure leading to the formation of compressible strips in the middle of GNRs. It is also shown that the hard-wall confinement combined with electron interaction generates overlaps between forward and backward propagating states, which may significantly enhance backscattering in realistic GNRs. The relation to available experiments is discussed.

  8. Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads. Technical progress report, 1989

    SciTech Connect

    Not Available

    1989-04-12

    This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

  9. Photoinitiated electron transfer in multi-chromophoric species: Synthetic tetrads and pentads

    SciTech Connect

    Not Available

    1990-02-14

    This research project involves the design, synthesis and study of the molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

  10. Reduction-Induced Suppression of Electron Flow (RISE) in the Photosynthetic Electron Transport System of Synechococcus elongatus PCC 7942.

    PubMed

    Shaku, Keiichiro; Shimakawa, Ginga; Hashiguchi, Masaki; Miyake, Chikahiro

    2016-07-01

    Accumulation of electrons under conditions of environmental stress produces a reduced state in the photosynthetic electron transport (PET) system and causes the reduction of O2 by PSI in the thylakoid membranes to produce the reactive oxygen species superoxide radical, which irreversibly inactivates PSI. This study aims to elucidate the molecular mechanism for the oxidation of reaction center Chl of PSI, P700, after saturated pulse (SP) light illumination of the cyanobacterium Synechococcus elongatus PCC 7942 under steady-state photosynthetic conditions. Both P700 and NADPH were transiently oxidized after SP light illumination under CO2-depleted photosynthesis conditions. In contrast, the Chl fluorescence intensity transiently increased. Compared with the wild type, the increase in Chl fluorescence and the oxidations of P700 and NADPH were greatly enhanced in a mutant (Δflv1/3) deficient in the genes encoding FLAVODIIRON 1 (FLV1) and FLV3 proteins even under high photosynthetic conditions. Furthermore, oxidation of Cyt f was also observed in the mutant. After SP light illumination, a transient suppression of O2 evolution was also observed in Δflv1/3. From these observations, we propose that the reduction in the plastquinone (PQ) pool suppresses linear electron flow at the Cyt b6/f complex, which we call the reduction-induced suppression of electron flow (RISE) in the PET system. The accumulation of the reduced form of PQ probably suppresses turnover of the Q cycle in the Cyt b6/f complex.

  11. Electron transfer through a self-assembled monolayer of a double-helix peptide with linking the terminals by ferrocene.

    PubMed

    Okamoto, Shinpei; Morita, Tomoyuki; Kimura, Shunsaku

    2009-03-03

    A unique molecular structure, a double-helix peptide, was self-assembled on gold, and the electron transfer through the monolayer was studied. The double-helix peptide consists of two 9mer 3(10)-helical peptide chains having a disulfide group at each N terminal and being linked by a ferrocene dicarboxylic acid between the C terminals. Each helical peptide chain has three naphthyl groups in a linear arrangement along the helix. The monolayer properties and the electron transfer from the ferrocene unit to gold were studied with reference peptides with a similar double helix but without naphthyl groups, a single helix with a dicarboxylic ferrocene unit, and a single helix with a monocarboxylic ferrocene unit. It was demonstrated that the naphthyl groups on the side chains had no effect on electron transfer, and the electron-transfer rate in the double-helix monolayer was not promoted, despite the two electron pathways in the molecule. We propose that in the double-helix monolayer, molecular motions are suppressed, possibly by its rigid structure tethered by the two linkers on gold to cancel out acceleration effects of the 2-fold electron pathways and the ferrocene substitution number. The factors that affect the electron-transfer reaction across the helical peptide SAMs are discussed in depth.

  12. Long-range electron transfer in a model for DNA

    NASA Astrophysics Data System (ADS)

    Endres, R. G.; Cox, D. L.

    2001-03-01

    Long-range electron transfer (ET) between well separated donor (D) and acceptor (A) sites through quantum mechanical tunneling is essential to many biological processes like respiration, photosynthesis and possibly DNA repair and damage. We are investigating the distance dependence of the electronic transition matrix element H_DA and hence of the electron transfer rate in a model for DNA. Fluorescence quenching in DNA at D-A distances of 40 Åand more suggests ET with an unusually high decay length β-1 of order 10 Å (S.O.Kelley and J.K.Barton, in:Metal Ions in Biological Systems), A.Sigel and H.Sigel, Eds., Marcel Dekker, New York, Vol.36, 1999. Assuming strong electron interactions on the D complex and suitable energetics, this could be explained by formation of a many electron Kondo boundstate. We obtain H_DA from the splitting between the two lowest adiabatic electronic eigenenergies, which constitute the potential energy surfaces (PES) of the nuclear motion in lowest order Born-Oppenheimer approximation. The PES are constructed by coupling D and A to local breathing modes and by making a semi-analytical variational ansatz for the adiabatic eigenstates. The results from the PES are compared with results from the Mulliken-Hush algorithm.

  13. Rotational And Rovibrational Energy Transfer In Electron Collisions With Molecules

    NASA Technical Reports Server (NTRS)

    Thuemmel, Helmar T.; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    Air flows around a hypervelocity reentry vehicle undergo dissociation, rovibrational excitation and ionization. More specifically the air, initially 80% N2 and 20% O2, in the shock layer consists of species such as N, O, N2, O2, NO, N+, O+, N+, O+, NO+ and 2 free electrons. It was pointed out in multi temperature models'' that the temperature of the rotational energy modes and the gas-kinetic translational temperature are quickly equilibrated by a few collisions and rise rapidly to high temperatures as 50000K before falling off to equilibrium value of 10000K. Contrary, the electronic and vibrational temperatures state energy distributions remain low (less than 15000K) because of the slow equilibration. Electron vibrational energy transfer is thought to play a crucial role in such a ionizing flow regime since chemical reaction rates and dissociation depend strongly on the vibrational temperatures. Modeling of these flowfields in principle require the rovibrational excitation and de-excitation cross section data for average electron energies from threshold up to several eV (leV=11605.4 K). In this lecture we focus on theoretical description of rotational effects i.e. energy transfer of electrons to molecules such that the molecular rotational (vojo goes to voj) or vibrational and rotational (v(sub 0)j(sub 0) goes to vj) states are changed. Excitation and de-excitation of electronic states was discussed in a previous talk at this conference.

  14. Fundamental research on convective heat transfer in electronic cooling technology

    NASA Astrophysics Data System (ADS)

    Ma, C. F.; Gan, Y. P.; Tian, Y. Q.; Lei, D. H.

    1992-03-01

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

  15. Electron Transfer Mechanisms of DNA Repair by Photolyase

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed Central

    Solov’yov, Ilia A.; Chang, Po-Yao; Schulten, Klaus

    2012-01-01

    Smell is a vital sense for animals. The mainstream explanation of smell is based on recognition of the odorant molecules through characteristics of their surface, e.g., shape, but certain experiments suggest that such recognition is complemented by recognition of vibrational modes. According to this suggestion an olfactory receptor is activated by electron transfer assisted through odorant vibrational excitation. The hundreds to thousands of different olfactory receptors in an animal recognize odorants over a discriminant landscape with surface properties and vibrational frequencies as the two major dimensions. In the present paper we introduce the vibrationally assisted mechanism of olfaction and demonstrate for several odorants that, indeed, a strong enhancement of an electron tunneling rate due to odorant vibrations can arise. We discuss in this regard the influence of odorant deuteration and explain, thereby, recent experiments performed on Drosophila melanogaster. Our demonstration is based on known physical properties of biological electron transfer and on ab initio calculations on odorants carried out for the purpose of the present study. We identify a range of physical characteristics which olfactory receptors and odorants must obey for the vibrationally assisted electron transfer mechanism to function. We argue that the stated characteristics are feasible for realistic olfactory receptors, noting, though, that the receptor structure presently is still unknown, but can be studied through homology modeling. PMID:22899100

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

    PubMed

    Klauss, André; Haumann, Michael; Dau, Holger

    2012-10-02

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

  18. Maternal antibody transfer can lead to suppression of humoral immunity in developing zebra finches (Taeniopygia guttata).

    PubMed

    Merrill, Loren; Grindstaff, Jennifer L

    2014-01-01

    Maternally transferred antibodies have been documented in a wide range of taxa and are thought to adaptively provide protection against parasites and pathogens while the offspring immune system is developing. In most birds, transfer occurs when females deposit immunoglobulin Y into the egg yolk, and it is proportional to the amount in the female's plasma. Maternal antibodies can provide short-term passive protection as well as specific and nonspecific immunological priming, but high levels of maternal antibody can result in suppression of the offspring's humoral immune response. We injected adult female zebra finches (Taeniopygia guttata) with one of two antigens (lipopolysaccharide [LPS] or keyhole limpet hemocyanin [KLH]) or a control and then injected offspring with LPS, KLH, or a control on days 5 and 28 posthatch to examine the impact of maternally transferred antibodies on the ontogeny of the offspring's humoral immune system. We found that offspring of females exposed to KLH had elevated levels of KLH-reactive antibody over the first 17-28 days posthatch but reduced KLH-specific antibody production between days 28 and 36. We also found that offspring exposed to either LPS or KLH exhibited reduced total antibody levels, compared to offspring that received a control injection. These results indicate that high levels of maternal antibodies or antigen exposure during development can have negative repercussions on short-term antibody production and may have long-term fitness repercussions for the offspring.

  19. Effect of cationic plastoquinone SkQ1 on electron transfer reactions in chloroplasts and mitochondria from pea seedlings.

    PubMed

    Samuilov, V D; Kiselevsky, D B

    2015-04-01

    Plastoquinone bound with decyltriphenylphosphonium cation (SkQ1) penetrating through the membrane in nanomolar concentrations inhibited H2O2 generation in cells of epidermis of pea seedling leaves that was detected by the fluorescence of 2',7'-dichlorofluorescein. Photosynthetic electron transfer in chloroplasts isolated from pea leaves is suppressed by SkQ1 at micromolar concentrations: the electron transfer in chloroplasts under the action of photosystem II or I (with silicomolybdate or methyl viologen as electron acceptors, respectively) is more sensitive to SkQ1 than under the action of photosystem II + I (with ferricyanide or p-benzoquinone as electron acceptors). SkQ1 reduced by borohydride is oxidized by ferricyanide, p-benzoquinone, and, to a lesser extent, by silicomolybdate, but not by methyl viologen. SkQ1 is not effective as an electron acceptor supporting O2 evolution from water in illuminated chloroplasts. The data on suppression of photosynthetic O2 evolution or consumption show that SkQ1, similarly to phenazine methosulfate, causes conversion of the chloroplast redox-chain from non-cyclic electron transfer mode to the cyclic mode without O2 evolution. Oxidation of NADH or succinate in mitochondria isolated from pea roots is stimulated by SkQ1.

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

    PubMed

    Chuev, G N; Lakhno, V D

    1993-07-07

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

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

    NASA Astrophysics Data System (ADS)

    Prada, Marta; Toonen, Ryan; Harrison, Paul

    2005-03-01

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

  2. Electron nuclear spin transfer in quantum-dot networks

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  3. Suppression of runaway electrons with a resonant magnetic perturbation in MST tokamak plasmas

    NASA Astrophysics Data System (ADS)

    Munaretto, Stefano; Chapman, B. E.; Almagri, A. F.; Cornille, B. S.; Dubois, A. M.; Goetz, J. A.; McCollam, K. J.; Sovinec, C. R.

    2016-10-01

    Runaway electrons generated in MST tokamak plasmas are now being probed with resonant magnetic perturbations (RMP's). An RMP with m =3 strongly suppresses the runaway electrons. Initial modeling of these plasmas with NIMROD shows the degradation of flux surfaces with an m =3 RMP, which may account for the runaway electron suppression. These MST tokamak plasmas have Bt =0.14 T, Ip =50kA, and q(a) =2.2, with a bulk electron density and temperature of 5x1017 m-3 and 150 eV. Runaway electrons are detected via x-ray emission. The RMP is produced by a poloidal array of 32 saddle coils at the narrow vertical insulated cut in MST's thick conducting shell. Each RMP has a single m but a broad n spectrum. A sufficiently strong m =3 RMP completely suppresses the runaway electrons, while a comparable m =1 RMP has little effect. The impact of the RMP's on the magnetic topology of these plasmas is being studied with the nonlinear MHD code, NIMROD. With an m =3 RMP, stochasticity is introduced in the outer third of the plasma. No such change is observed with the m =1 RMP. NIMROD also predicts regularly occurring sawtooth oscillations with a period comparable to MHD activity observed in the experiment. Work supported by USDOE.

  4. Effects of G-Quadruplex Topology on Electronic Transfer Integrals

    PubMed Central

    Sun, Wenming; Varsano, Daniele; Di Felice, Rosa

    2016-01-01

    G-quadruplex is a quadruple helical form of nucleic acids that can appear in guanine-rich parts of the genome. The basic unit is the G-tetrad, a planar assembly of four guanines connected by eight hydrogen bonds. Its rich topology and its possible relevance as a drug target for a number of diseases have stimulated several structural studies. The superior stiffness and electronic π-π overlap between consecutive G-tetrads suggest exploitation for nanotechnologies. Here we inspect the intimate link between the structure and the electronic properties, with focus on charge transfer parameters. We show that the electronic couplings between stacked G-tetrads strongly depend on the three-dimensional atomic structure. Furthermore, we reveal a remarkable correlation with the topology: a topology characterized by the absence of syn-anti G-G sequences can better support electronic charge transfer. On the other hand, there is no obvious correlation of the electronic coupling with usual descriptors of the helix shape. We establish a procedure to maximize the correlation with a global helix shape descriptor. PMID:28335314

  5. Distance dependence in photo-induced intramolecular electron transfer

    NASA Astrophysics Data System (ADS)

    Larsson, Sven; Volosov, Andrey

    1986-09-01

    The distance dependence of the rate of photo-induced electron transfer reactions is studied. A quantum mechanical method CNDO/S is applied to a series of molecules recently investigated by Hush et al. experimentally. The calculations show a large interaction through the saturated bridge which connects the two chromophores. The electronic matrix element HAB decreases a factor 10 in about 4 Å. There is also a decrease of the rate due to less exothermicity for the longer molecule. The results are in fair agreement with the experimental results.

  6. Solvent reorganizational red-edge effect in intramolecular electron transfer.

    PubMed Central

    Demchenko, A P; Sytnik, A I

    1991-01-01

    Polar solvents are characterized by statistical distributions of solute-solvent interaction energies that result in inhomogeneous broadening of the solute electronic spectra. This allows photoselection of the high interaction energy part of the distribution by excitation at the red (long-wavelength) edge of the absorption bands. We observe that intramolecular electron transfer in the bianthryl molecule from the locally excited (LE) to the charge-transfer (CT) state, which requires solvent relaxation and does not occur in vitrified polar solutions, is dramatically facilitated in low-temperature propylene glycol glass by the red-edge excitation. This allows one to obtain spectroscopically the pure CT form and observe its dependence upon the relaxational properties of the solvent. A qualitative potential model of this effect is presented. PMID:11607224

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

    PubMed

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

    2017-02-07

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

  8. DNA Intercalated Psoralen Undergoes Efficient Photoinduced Electron Transfer.

    PubMed

    Fröbel, Sascha; Reiffers, Anna; Torres Ziegenbein, Christian; Gilch, Peter

    2015-04-02

    The interaction of psoralens with DNA has been used for therapeutic and research purposes for decades. Still the photoinduced behavior of psoralens in DNA has never been observed directly. Femtosecond transient absorption spectroscopy is used here to gain direct insight into the photophysics of a DNA-intercalated psoralen (4'-aminomethyl-4,5',8-trimethyl-psoralen (AMT)). Intercalation reduces the excited singlet lifetime of AMT to 4 ps compared with 1400 ps for AMT in water. This singlet quenching prohibits the population of the triplet state that is accessed in free AMT. Instead, a DNA to AMT electron transfer takes place. The resulting radical pair decays primarily via charge recombination with a time constant of 30 ps. The efficient electron transfer observed here reveals a completely new aspect of the psoralen-DNA interaction.

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

    PubMed Central

    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

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

    NASA Astrophysics Data System (ADS)

    Zhu, Jianjun; Wang, Jianji; Stell, George

    2006-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed Central

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

    2017-01-01

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

  13. Intermittent Single-Molecule Interfacial Electron Transfer Dynamics

    SciTech Connect

    Biju, Vasudevan P.; Micic, Miodrag; Hu, Dehong; Lu, H. Peter

    2004-08-04

    We report on single molecule studies of photosensitized interfacial electron transfer (ET) processes in Coumarin 343 (C343)-TiO2 nanoparticle (NP) and Cresyl Violet (CV+)-TiO2 NP systems, using time-correlated single photon counting coupled with scanning confocal fluorescence microscopy. Fluorescence intensity trajectories of individual dye molecules adsorbed on a semiconductor NP surface showed fluorescence fluctuations and blinking, with time constrants distributed from sub-milliseconds to several seconds.

  14. Insights into Proton-Coupled Electron Transfer from Computation

    NASA Astrophysics Data System (ADS)

    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.

  15. Electron Spectroscopy In Heavy-Ion Storage Rings: Resonant and Non-Resonant Electron Transfer Processes

    SciTech Connect

    Hagmann, S.; Stoehlker, Th.; Trotsenko, S.; Kozhuharov, Ch.; Spillmann, U.; Bosch, F.; Liesen, D.; Winters, D.; Hillenbrand, P.-M.; Shabaev, V.; Tupitsyn, I.; Kozhedub, Y.; Rothard, H.; Reuschl, R.; Ullrich, J.; Moshammer, R.; Voitkiv, A.; Surzhykov, A.; Fischer, D.; Doerner, R.

    2011-06-01

    Whereas our understanding of total cross sections for ionization and capture processes in ion-atom collisions is widely viewed as having arrived at a state of adequate maturity, the same cannot be said at all about the dynamics of collisions, multi-electron processes or the electron continua (in target and projectile) which are at the origin of total cross sections. We depict how these processes can be studied favourably in storage ring environments. We present examples of resonant and non-resonant electron transfer processes, radiative and non-radiative. This is elucidated via the relation of the electron nucleus bremsstrahlung at the high energy tip of the bremsstrahlung spectrum to the radiative electron capture cusp (RECC) and a new approach to determining molecular orbital binding energies in superheavy quasi-molecules in resonant KK charge transfer.

  16. The electron transfer system of syntrophically grown Desulfovibrio vulgaris.

    PubMed

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

    2009-09-01

    Interspecies hydrogen transfer between organisms producing and consuming hydrogen promotes the decomposition of organic matter in most anoxic environments. Although syntrophic coupling between hydrogen producers and consumers is 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 on growth modality. During syntrophic growth on lactate with a hydrogenotrophic methanogen, numerous genes involved in electron transfer and energy generation were upregulated in D. vulgaris compared with their expression in 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 upregulated genes. Additionally, a predicted operon containing genes involved in lactate transport and oxidation exhibited upregulation, 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 effect on growth via sulfate respiration. These results demonstrate that syntrophic growth and sulfate respiration use largely independent energy generation pathways and imply that to understand microbial processes that sustain nutrient cycling, lifestyles not captured in pure culture must be considered.

  17. The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris

    SciTech Connect

    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.

  18. The electron transfer system of synthrophically grown desulfovibrio vulgaris

    SciTech Connect

    Walker, Christopher; He, Zhili; Yang, Zamin Koo; Ringbauer, Joseph; HE, Qiang; Zhou, Jizhong; Voordouw, Gerrit; Wall, Judy; Arkin, Adam; Hazen, Terry; Stolyar, Sergey; Stahl, David

    2009-01-01

    Interspecies hydrogen transfer between organisms producing and consuming hydrogen promotes the decomposition of organic matter in most anoxic environments. Although syntrophic coupling between hydrogen producers and consumers is 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 on growth modality. During syntrophic growth on lactate with a hydrogenotrophic methanogen, numerous genes involved in electron transfer and energy generation were upregulated in D. vulgaris compared with their expression in 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 upregulated genes. Additionally, a predicted operon containing genes involved in lactate transport and oxidation exhibited upregulation, 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 effect on growth via sulfate respiration. These results demonstrate that syntrophic growth and sulfate respiration use largely independent energy generation pathways and imply that to understand microbial processes that sustain nutrient cycling, lifestyles not captured in pure culture must be considered.

  19. The electron transfer system of syntrophically grown Desulfovibrio vulgaris

    SciTech Connect

    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.

  20. Adoptively transferred TRAIL+ T cells suppress GVHD and augment antitumor activity

    PubMed Central

    Ghosh, Arnab; Dogan, Yildirim; Moroz, Maxim; Holland, Amanda M.; Yim, Nury L.; Rao, Uttam K.; Young, Lauren F.; Tannenbaum, Daniel; Masih, Durva; Velardi, Enrico; Tsai, Jennifer J.; Jenq, Robert R.; Penack, Olaf; Hanash, Alan M.; Smith, Odette M.; Piersanti, Kelly; Lezcano, Cecilia; Murphy, George F.; Liu, Chen; Palomba, M. Lia; Sauer, Martin G.; Sadelain, Michel; Ponomarev, Vladimir; van den Brink, Marcel R.M.

    2013-01-01

    Current strategies to suppress graft-versus-host disease (GVHD) also compromise graft-versus-tumor (GVT) responses. Furthermore, most experimental strategies to separate GVHD and GVT responses merely spare GVT function without actually enhancing it. We have previously shown that endogenously expressed TNF-related apoptosis-inducing ligand (TRAIL) is required for optimal GVT activity against certain malignancies in recipients of allogeneic hematopoietic stem cell transplantation (allo-HSCT). In order to model a donor-derived cellular therapy, we genetically engineered T cells to overexpress TRAIL and adoptively transferred donor-type unsorted TRAIL+ T cells into mouse models of allo-HSCT. We found that murine TRAIL+ T cells induced apoptosis of alloreactive T cells, thereby reducing GVHD in a DR5-dependent manner. Furthermore, murine TRAIL+ T cells mediated enhanced in vitro and in vivo antilymphoma GVT response. Moreover, human TRAIL+ T cells mediated enhanced in vitro cytotoxicity against both human leukemia cell lines and against freshly isolated chronic lymphocytic leukemia (CLL) cells. Finally, as a model of off-the-shelf, donor-unrestricted antitumor cellular therapy, in vitro–generated TRAIL+ precursor T cells from third-party donors also mediated enhanced GVT response in the absence of GVHD. These data indicate that TRAIL-overexpressing donor T cells could potentially enhance the curative potential of allo-HSCT by increasing GVT response and suppressing GVHD. PMID:23676461

  1. Suppressing the image smear of the vibration modulation transfer function for remote-sensing optical cameras.

    PubMed

    Li, Jin; Liu, Zilong; Liu, Si

    2017-02-20

    In on-board photographing processes of satellite cameras, the platform vibration can generate image motion, distortion, and smear, which seriously affect the image quality and image positioning. In this paper, we create a mathematical model of a vibrating modulate transfer function (VMTF) for a remote-sensing camera. The total MTF of a camera is reduced by the VMTF, which means the image quality is degraded. In order to avoid the degeneration of the total MTF caused by vibrations, we use an Mn-20Cu-5Ni-2Fe (M2052) manganese copper alloy material to fabricate a vibration-isolation mechanism (VIM). The VIM can transform platform vibration energy into irreversible thermal energy with its internal twin crystals structure. Our experiment shows the M2052 manganese copper alloy material is good enough to suppress image motion below 125 Hz, which is the vibration frequency of satellite platforms. The camera optical system has a higher MTF after suppressing the vibration of the M2052 material than before.

  2. Myxoma virus suppresses proliferation of activated T lymphocytes yet permits oncolytic virus transfer to cancer cells

    PubMed Central

    Villa, Nancy Y.; Wasserfall, Clive H.; Meacham, Amy M.; Wise, Elizabeth; Chan, Winnie; Wingard, John R.; McFadden, Grant

    2015-01-01

    Allogeneic hematopoietic cell transplant (allo-HCT) can be curative for certain hematologic malignancies, but the risk of graft-versus-host disease (GVHD) is a major limitation for wider application. Ideally, strategies to improve allo-HCT would involve suppression of T lymphocytes that drive GVHD while sparing those that mediate graft-versus-malignancy (GVM). Recently, using a xenograft model, we serendipitously discovered that myxoma virus (MYXV) prevented GVHD while permitting GVM. In this study, we show that MYXV binds to resting, primary human T lymphocytes but will only proceed into active virus infection after the T cells receive activation signals. MYXV-infected T lymphocytes exhibited impaired proliferation after activation with reduced expression of interferon-γ, interleukin-2 (IL-2), and soluble IL-2Rα, but did not affect expression of IL-4 and IL-10. MYXV suppressed T-cell proliferation in 2 patterns (full vs partial) depending on the donor. In terms of GVM, we show that MYXV-infected activated human T lymphocytes effectively deliver live oncolytic virus to human multiple myeloma cells, thus augmenting GVM by transfer of active oncolytic virus to residual cancer cells. Given this dual capacity of reducing GVHD plus increasing the antineoplastic effectiveness of GVM, ex vivo virotherapy with MYXV may be a promising clinical adjunct to allo-HCT regimens. PMID:25904246

  3. Myxoma virus suppresses proliferation of activated T lymphocytes yet permits oncolytic virus transfer to cancer cells.

    PubMed

    Villa, Nancy Y; Wasserfall, Clive H; Meacham, Amy M; Wise, Elizabeth; Chan, Winnie; Wingard, John R; McFadden, Grant; Cogle, Christopher R

    2015-06-11

    Allogeneic hematopoietic cell transplant (allo-HCT) can be curative for certain hematologic malignancies, but the risk of graft-versus-host disease (GVHD) is a major limitation for wider application. Ideally, strategies to improve allo-HCT would involve suppression of T lymphocytes that drive GVHD while sparing those that mediate graft-versus-malignancy (GVM). Recently, using a xenograft model, we serendipitously discovered that myxoma virus (MYXV) prevented GVHD while permitting GVM. In this study, we show that MYXV binds to resting, primary human T lymphocytes but will only proceed into active virus infection after the T cells receive activation signals. MYXV-infected T lymphocytes exhibited impaired proliferation after activation with reduced expression of interferon-γ, interleukin-2 (IL-2), and soluble IL-2Rα, but did not affect expression of IL-4 and IL-10. MYXV suppressed T-cell proliferation in 2 patterns (full vs partial) depending on the donor. In terms of GVM, we show that MYXV-infected activated human T lymphocytes effectively deliver live oncolytic virus to human multiple myeloma cells, thus augmenting GVM by transfer of active oncolytic virus to residual cancer cells. Given this dual capacity of reducing GVHD plus increasing the antineoplastic effectiveness of GVM, ex vivo virotherapy with MYXV may be a promising clinical adjunct to allo-HCT regimens.

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

    NASA Astrophysics Data System (ADS)

    Pati, Ranjit; Karna, Shashi P.

    2000-03-01

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

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

    PubMed

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

    2015-10-22

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

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

    PubMed

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

    2017-02-06

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

  7. Guanine oxidation by electron transfer: one- versus two-electron oxidation mechanism.

    PubMed

    Kupan, Adam; Saulière, Aude; Broussy, Sylvain; Seguy, Christel; Pratviel, Geneviève; Meunier, Bernard

    2006-01-01

    The degeneracy of the guanine radical cation, which is formed in DNA by oxidation of guanine by electron transfer, was studied by a detailed analysis of the oxidation products of guanine on oligonucleotide duplexes and by labeling experiments. It was shown that imidazolone, the major product of guanine oxidation, is formed through a one-electron oxidation process and incorporates one oxygen atom from O2. The formation of 8-oxo-7,8-dihydroguanine by a two-electron oxidation process was a minor pathway. The two-electron oxidation mechanism was also evidenced by the formation of a tris(hydroxymethyl)aminomethane adduct.

  8. Evidence for the purely electronic character of primary electron transfer in purple bacteria Rh. Sphaeroides

    NASA Astrophysics Data System (ADS)

    Glebov, I. O.; Poddubnyy, V. V.; Eremin, V. V.

    2015-11-01

    A quantum-chemical calculation of the excited electronic states of a Rh. Sphaeroides reaction centre was performed. We discovered a new excited electronic state which can participate in electron transfer (ET). The energy gradient calculations showed that photoexcitation activates only high-frequency vibrational modes. This contradicts the widely accepted picture of ET resulting from vibrational wave packet motion. An alternative model is suggested where ET has a purely dissipative character and occurs only due to pigment--protein interaction. With this model, we demonstrate that oscillations in the femtosecond spectra can be caused by the new electronic state and non-Markovian character of dissipative dynamics.

  9. Transverse to longitudinal phase space coupling in an electron beam for suppression of microbunching instability

    NASA Astrophysics Data System (ADS)

    Huang, Dazhang; Feng, Chao; Deng, Haixiao; Gu, Qiang; Zhao, Zhentang

    2016-10-01

    The microbunching instability developed during the beam compression process in the linear accelerator (LINAC) of a free-electron laser (FEL) facility has always been a problem that degrades the lasing performance, and even no FEL is able to be produced if the beam quality is destroyed too much by the instability. A common way to suppress the microbunching instability is to introduce extra uncorrelated energy spread by the laser heater that heats the beam through the interaction between the electron and laser beam, as what has been successfully implemented in the Linac Coherent Light Source and Fermi@Elettra. In this paper, a simple and effective scheme is proposed to suppress the microbunching instability by adding two transverse gradient undulators (TGU) before and after the magnetic bunch compressor. The additional uncorrelated energy spread and the density mixing from the transverse spread brought up by the first TGU results in significant suppression of the instability. Meanwhile, the extra slice energy spread and the transverse emittance can also be effectively recovered by the second TGU. The magnitude of the suppression can be easily controlled by varying the strength of the magnetic fields of the TGUs. Theoretical analysis and numerical simulations demonstrate the capability of the proposed technique in the LINAC of an x-ray free-electron laser facility.

  10. Syntrophic anaerobic photosynthesis via direct interspecies electron transfer

    PubMed Central

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

    2017-01-01

    Microbial phototrophs, key primary producers on Earth, use H2O, H2, H2S and other reduced inorganic compounds as electron donors. Here we describe a form of metabolism linking anoxygenic photosynthesis to anaerobic respiration that we call ‘syntrophic anaerobic photosynthesis'. We show that photoautotrophy in the green sulfur bacterium Prosthecochloris aestaurii can be driven by either electrons from a solid electrode or acetate oxidation via direct interspecies electron transfer from a heterotrophic partner bacterium, Geobacter sulfurreducens. Photosynthetic growth of P. aestuarii using reductant provided by either an electrode or syntrophy is robust and light-dependent. In contrast, P. aestuarii does not grow in co-culture with a G. sulfurreducens mutant lacking a trans-outer membrane porin-cytochrome protein complex required for direct intercellular electron transfer. Syntrophic anaerobic photosynthesis is therefore a carbon cycling process that could take place in anoxic environments. This process could be exploited for biotechnological applications, such as waste treatment and bioenergy production, using engineered phototrophic microbial communities. PMID:28067226

  11. Suppression of the Beam Instability Related to Electron Cloud at PEP-II B-Factory

    SciTech Connect

    Kulikov, A.

    2004-12-06

    PEP-II B-factory operates at a record high circulating current--currently {approx}2.5 A in the positron ring. Electron cloud effects became apparent when the positron ring current reached {approx}0.7 A with a bunch current {approx}1.5 mA. Initially, electron cloud induced beam instabilities significantly limited collider luminosity. However, suppression of the electron cloud related beam instabilities have been achieved with {approx}30 Gauss solenoids covering the drift sections of LER vacuum chamber.

  12. Suppression of runaway electron generation by massive helium injection after induced disruptions on TEXTOR

    NASA Astrophysics Data System (ADS)

    Lvovskiy, A.; Koslowski, H. R.; Zeng, L.; Zeng

    2015-10-01

    > Disruptions with runaway electron generation have been deliberately induced by injection of argon using a disruption mitigation valve. A second disruption mitigation valve has been utilised to inject varying amounts of helium after a short time delay. No generation of runaway electrons has been observed when more than a critical amount of helium has been injected no later than 5 ms after the triggering of the first valve. The required amount of helium for suppression of runaway electron generation is up to one order of magnitude lower than the critical density according to Connor & Hastie (1975) and Rosenbluth & Putvinski (1997).

  13. Suppression of colitis by adoptive transfer of helminth antigen-treated dendritic cells requires interleukin-4 receptor-α signaling

    PubMed Central

    Matisz, C. E.; Faz-López, B.; Thomson, E.; Al Rajabi, A.; Lopes, F.; Terrazas, L. I.; Wang, A.; Sharkey, K. A.; McKay, D. M.

    2017-01-01

    Infection with helminth parasites has been explored as a treatment for autoimmune and inflammatory diseases. As helminth antigens have potent immunomodulation properties capable of inducing regulatory programs in a variety of cell types, transferring cells treated with helminth antigens represents a novel extension to helminth therapy. Previous work determined that transfer of bone marrow-derived dendritic cells (DC) pulsed with a crude extract of the tapeworm Hymenolepis diminuta (HD) can suppress colitis in recipient mice. The present study explored the mechanism of disease suppression and the importance of interleukin (IL)-4 signaling. Transfer of HD-DCs suppressed dinitrobenzene sulfonic acid (DNBS)-induced colitis through activation of recipient IL-4 receptor-α. The transferred HD-DCs required IL-4Rα and the capacity to secrete IL-10 to drive IL-4 and IL-10 production and to suppress colitis in recipient mice. Treatment of DCs with IL-4 evokes an alternatively activated phenotype, but adoptive transfer of these cells did not affect the outcome of colitis. Collectively, these studies demonstrate the complexity between IL-4 and IL-10 in donor cells and recipient, and the requirement for parasite- and host-derived factors in this novel form of cell therapy. Thus IL-4Rα signaling is revealed as a pathway that could be exploited for helminth antigen cell-based therapy. PMID:28094779

  14. Molecular mimicry of photosynthetic energy and electron transfer

    SciTech Connect

    Gust, D.; Moore, T.A.; Moore, A.L. )

    1993-04-01

    Proper application of reaction design considerations can yield artificial photosynthetic devices which credibility mimic the three natural photochemical processes. One approach is to use pigments and electron donors and acceptors related to those found in natural photosynthesis (and thus presumably optimal for that system), but to replace the protein with covalent bonds as an organizing precept. Molecular pentads described herein exemplify the success of this approach. At the heart of these molecules, are two covalently linked synthetic porphyrin moieties (P-P). One of these models for chlorophyll is attached to a carotenoid polyene (C), whereas the other is linked to a rigid diquinone (Q-Q). As discussed later in this paper, excitation of such a pentad is followed by photoinitiated electron transfer steps which ultimately give a C[sup [center dot]+]-P-P-Q-Q[sup [center dot]-] charge-separated state. Depending upon the structure of the pentad and the conditions, these states are formed with quantum yields of up to 0.83, have lifetimes approaching 0.5 ms, and store about one-half of the energy of the exciting singlet state. Related photosynthesis mimics display singlet-singlet energy transfer from carotenoid polyenes to porphyrins and among porphyrin chromophores, and rapid quenching of porphyrin triplet states by attached carotenoids. How have the structures of these and other successful artificial reaction centers evolved, and what will be the next steps in their development The authors will address these questions from the point of view of photoinitiated electron transfer, and then singlet and triplet energy transfer will briefly be considered. 37 refs., 4 figs.

  15. Mechanisms for control of biological electron transfer reactions

    PubMed Central

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

    2014-01-01

    Electron transfer (ET) through and between proteins is a fundamental biological process. The rates and mechanisms of these ET reactions are controlled by the proteins in which the redox centers that donate and accept electrons reside. The protein influences the magnitudes of the ET parameters, the electronic coupling and reorganization energy that are associated with the ET reaction. The protein can regulate the rates of the ET reaction by requiring reaction steps to optimize the system for ET, leading to kinetic mechanisms of gated or coupled ET. Amino acid residues in the segment of the protein through which long range ET occurs can also modulate the ET rate by serving as staging points for hopping mechanisms of ET. Specific examples are presented to illustrate these mechanisms by which proteins control rates of ET reactions. PMID:25085775

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

    DOE R&D Accomplishments Database

    Marcus, R. A.; Sutin, N.

    1985-03-23

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

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

    EPA Science Inventory

    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. Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads. Technical progress report

    SciTech Connect

    Gust, J.D. Jr.; Moore, T.A.

    1988-04-12

    This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind`s energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

  19. Hetero-cycloreversions mediated by photoinduced electron transfer.

    PubMed

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

    2014-04-15

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

  20. Modeling biofilms with dual extracellular electron transfer mechanisms

    SciTech Connect

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

    2013-11-28

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

  1. Modeling biofilms with dual extracellular electron transfer mechanisms

    PubMed Central

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

    2013-01-01

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

  2. Extracting electron transfer coupling elements from constrained density functional theory

    NASA Astrophysics Data System (ADS)

    Wu, Qin; Van Voorhis, Troy

    2006-10-01

    Constrained density functional theory (DFT) is a useful tool for studying electron transfer (ET) reactions. It can straightforwardly construct the charge-localized diabatic states and give a direct measure of the inner-sphere reorganization energy. In this work, a method is presented for calculating the electronic coupling matrix element (Hab) based on constrained DFT. This method completely avoids the use of ground-state DFT energies because they are known to irrationally predict fractional electron transfer in many cases. Instead it makes use of the constrained DFT energies and the Kohn-Sham wave functions for the diabatic states in a careful way. Test calculations on the Zn2+ and the benzene-Cl atom systems show that the new prescription yields reasonable agreement with the standard generalized Mulliken-Hush method. We then proceed to produce the diabatic and adiabatic potential energy curves along the reaction pathway for intervalence ET in the tetrathiafulvalene-diquinone (Q-TTF-Q) anion. While the unconstrained DFT curve has no reaction barrier and gives Hab≈17kcal /mol, which qualitatively disagrees with experimental results, the Hab calculated from constrained DFT is about 3kcal /mol and the generated ground state has a barrier height of 1.70kcal/mol, successfully predicting (Q-TTF-Q)- to be a class II mixed-valence compound.

  3. Photoinduced Electron Transfer Process Visualized on Single Silver Nanoparticles.

    PubMed

    Lei, Gang; Gao, Peng Fei; Yang, Tong; Zhou, Jun; Zhang, Hong Zhi; Sun, Shan Shan; Gao, Ming Xuan; Huang, Cheng Zhi

    2017-02-28

    Understanding the photoinduced electron transfer (PET) mechanism is vital to improving the photoelectric conversion efficiency for solar energy materials and photosensitization systems. Herein, we visually demonstrate the PET process by real-time monitoring the photoinduced chemical transformation of p-aminothiophenol (p-ATP), an important SERS signal molecule, to 4,4'-dimercaptoazobenzene on single silver nanoparticles (AgNPs) with a localized surface plasmon resonance (LSPR) spectroscopy coupled dark-field microscopy. The bidirectional LSPR scattering spectral shifts bathochromically at first and hypsochromically then, which are caused by the electron transfer delay of p-ATP, disclose the PET path from p-ATP to O2 through AgNPs during the reaction, and enable us to digitalize the corresponding electron loss and gain on the surface of AgNP at different time periods. This visualized PET process could provide a simple and efficient approach to explore the nature of PET and help to interpret the SERS mechanism in terms of p-ATP.

  4. MATHEMATICAL MODELING OF EXTRACELLULAR ELECTRON TRANSFER IN BIOFILMS

    SciTech Connect

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

    2015-09-12

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

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

    PubMed

    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.

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

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 12 Banks and Banking 2 2012-01-01 2012-01-01 false Electronic fund transfer of government benefits. 205.15 Section 205.15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of...

  7. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 12 Banks and Banking 2 2010-01-01 2010-01-01 false Electronic fund transfer of government benefits. 205.15 Section 205.15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of...

  8. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 12 Banks and Banking 2 2013-01-01 2013-01-01 false Electronic fund transfer of government benefits. 205.15 Section 205.15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of...

  9. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 12 Banks and Banking 2 2014-01-01 2014-01-01 false Electronic fund transfer of government benefits. 205.15 Section 205.15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of...

  10. 12 CFR 205.15 - Electronic fund transfer of government benefits.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Electronic fund transfer of government benefits. 205.15 Section 205.15 Banks and Banking FEDERAL RESERVE SYSTEM BOARD OF GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of...

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

    NASA Astrophysics Data System (ADS)

    Reed, W. E.

    1980-06-01

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

  12. Photoinduced electron transfer from dialkyl nitroxides to halogenated solvents

    SciTech Connect

    Chateauneuf, J. ); Lusztyk, J.; Ingold, K.U. )

    1990-02-02

    Laser flash photolysis (LFP) at wavelengths within the charge-transfer absorption present in CCl{sub 4} solutions of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) yields the oxoammonium chloride of TEMPO, 1 ({lambda}{sub max} = 460 nm), and the trichloromethyl radical in an essentially instantaneous ({le}18 ps) process. The primary photochemical event is an electron transfer from TEMPO to CCl{sub 4}, and this is followed by immediate decomposition of the CCl{sub 4}{sup {sm bullet}{minus}} radical anion to Cl{sup {minus}} and Cl{sub 3}C{sup {sm bullet}}. An independent synthesis of 1 confirmed that the absorption attributed to this species has been correctly assigned. The formation of Cl{sub 3}C{sup {sm bullet}} was inferred by its trapping by molecular oxygen. LFP of TEMPO in other halogenated solvents and of other nitroxides in halogenated solvents has confirmed the generality of these photoreactions.

  13. Polymers suppress the inverse transfers of energy and the enstrophy flux fluctuations in two-dimensional turbulence.

    PubMed

    Kellay, H

    2004-09-01

    The addition of minute amounts of a flexible polymer to two-dimensional turbulence produced in fast-flowing soap films affects large scales and small scales differently. For large scales, the inverse transfers of energy are suppressed. For small scales, where mean quantities are barely affected, the enstrophy flux fluctuations are significantly reduced, making the flow less chaotic.

  14. Cross-Modal Transfer of Conditioned Suppression in Rats: Effects of US Intensity and Extinction of the Initial Conditioning Task

    ERIC Educational Resources Information Center

    Doe, Nobutaka; Nakajima, Sadahiko; Tamai, Noriko

    2004-01-01

    In conditioned suppression of water licking behavior by rats, we obtained data indicating general transfer of fear conditioning. A series of experiments resulted in two major findings. First, pairing of a neutral stimulus with a shock in the initial conditioning task facilitated acquisition of subsequent fear conditioning to another neutral…

  15. Transcriptomic and Genetic Analysis of Direct Interspecies Electron Transfer

    PubMed Central

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

    2013-01-01

    The possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in which Geobacter sulfurreducens was the electron-accepting partner for either Geobacter metallireducens, which performs DIET, or Pelobacter carbinolicus, which relies on HIT. Transcript abundance for G. sulfurreducens uptake hydrogenase genes was 7-fold lower in cocultures with G. metallireducens than in cocultures with P. carbinolicus, consistent with DIET and HIT, respectively, in the two cocultures. Transcript abundance for the pilus-associated cytochrome OmcS, which is essential for DIET but not for HIT, was 240-fold higher in the cocultures with G. metallireducens than in cocultures with P. carbinolicus. The pilin gene pilA was moderately expressed despite a mutation that might be expected to repress pilA expression. Lower transcript abundance for G. sulfurreducens genes associated with acetate metabolism in the cocultures with P. carbinolicus was consistent with the repression of these genes by H2 during HIT. Genes for the biogenesis of pili and flagella and several c-type cytochrome genes were among the most highly expressed in G. metallireducens. Mutant strains that lacked the ability to produce pili, flagella, or the outer surface c-type cytochrome encoded by Gmet_2896 were not able to form cocultures with G. sulfurreducens. These results demonstrate that there are unique gene expression patterns that distinguish DIET from HIT and suggest that metatranscriptomics may be a promising route to investigate interspecies electron transfer pathways in more-complex environments. PMID:23377933

  16. Suppression of microbunching instability using bending magnets in free-electron-laser linacs.

    PubMed

    Qiang, Ji; Mitchell, Chad E; Venturini, Marco

    2013-08-02

    The microbunching instability driven by collective effects of the beam inside an accelerator can significantly degrade the final electron beam quality for free electron laser (FEL) radiation. In this Letter, we propose an inexpensive scheme to suppress such an instability in accelerators for next generation FEL light sources. Instead of using an expensive device such as a laser heater or RF deflecting cavities, this scheme uses longitudinal mixing associated with the transverse spread of the beam through bending magnets inside the accelerator transport system to suppress the instability. The final uncorrelated energy spread increases roughly by the current compression factor, which is important in seeded FEL schemes in order to achieve high harmonic short-wavelength x-ray radiation.

  17. Ab initio quantum chemical study of electron transfer in carboranes

    NASA Astrophysics Data System (ADS)

    Pati, Ranjit; Pineda, Andrew C.; Pandey, Ravindra; Karna, Shashi P.

    2005-05-01

    The electron transfer (ET) properties of 10- and 12-vertex carboranes are investigated by the ab initio Hartree-Fock method within the Marcus-Hush (MH) two-state model and the Koopman theorem (KT) approach. The calculated value of the ET coupling matrix element, VAB, is consistently higher in the KT approach than in the MH two-state model. For the carborane molecules functionalized by -CH 2 groups at C-vertices, VAB strongly depends on the relative orientation of the planes containing the terminal -CH 2 groups. The predicted conformation dependence of VAB offers a molecular mechanism to control ET between two active centers in molecular systems.

  18. Photoinduced electron transfer based ion sensing within an optical fiber.

    PubMed

    Englich, Florian V; Foo, Tze Cheung; Richardson, Andrew C; Ebendorff-Heidepriem, Heike; Sumby, Christopher J; Monro, Tanya M

    2011-01-01

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

  19. Artificial photosynthesis: from nanosecond electron transfer to catalytic water oxidation.

    PubMed

    Kärkäs, Markus D; Johnston, Eric V; Verho, Oscar; Akermark, Björn

    2014-01-21

    Human society faces a fundamental challenge as energy consumption is projected to increase due to population and economic growth as fossil fuel resources decrease. Therefore the transition to alternative and sustainable energy sources is of the utmost importance. The conversion of solar energy into chemical energy, by splitting H2O to generate molecular O2 and H2, could contribute to solving the global energy problem. Developing such a system will require the combination of several complicated processes, such as light-harvesting, charge separation, electron transfer, H2O oxidation, and reduction of the generated protons. The primary processes of charge separation and catalysis, which occur in the natural photosynthetic machinery, provide us with an excellent blueprint for the design of such systems. This Account describes our efforts to construct supramolecular assemblies capable of carrying out photoinduced electron transfer and to develop artificial water oxidation catalysts (WOCs). Early work in our group focused on linking a ruthenium chromophore to a manganese-based oxidation catalyst. When we incorporated a tyrosine unit into these supramolecular assemblies, we could observe fast intramolecular electron transfer from the manganese centers, via the tyrosine moiety, to the photooxidized ruthenium center, which clearly resembles the processes occurring in the natural system. Although we demonstrated multi-electron transfer in our artificial systems, the bottleneck proved to be the stability of the WOCs. Researchers have developed a number of WOCs, but the majority can only catalyze H2O oxidation in the presence of strong oxidants such as Ce(IV), which is difficult to generate photochemically. By contrast, illumination of ruthenium(II) photosensitizers in the presence of a sacrificial acceptor generates [Ru(bpy)3](3+)-type oxidants. Their oxidation potentials are significantly lower than that of Ce(IV), but our group recently showed that incorporating negatively

  20. Model for primary electron transfer and coupling of electronic states at reaction centers of purple bacteria

    NASA Astrophysics Data System (ADS)

    Pavlovich, V. S.

    2006-05-01

    A detailed derivation is presented for relations making it possible to describe the effect of temperature on the halfwidth of the P960 and P870 absorption bands and also on the electron transfer (ET) rate at reaction centers (RCs) of the purple bacteria Rps. viridis and Rb. sphaeroides. Primary electron transfer is considered as a resonant nonradiative transition between P* and P+B L - states (where P is a special pair, BL is an additional bacteriochlorophyll in the L branch of the reaction center). It has been shown that the vibrational hα mode with frequency 130 150 cm-1 controls primary electron transfer. It has been found that the matrix element of the electronic transition between the states P* and P+B L - is equal to 12.7 ± 0.9 and 12.0 ± 1.2 cm-1 for Rps. viridis and Rb. sphaeroides respectively. The mechanism is discussed for electron transport from P* and BL and then to bacteriopheophytin HL.

  1. The electronic transfer of information and aerospace knowledge diffusion

    NASA Technical Reports Server (NTRS)

    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.

  2. Molecular structures of porphyrin-quinone models for electron transfer

    SciTech Connect

    Fajer, J.; Barkigia, K.M.; Melamed, D.; Sweet, R.M.; Kurreck, H.; Gersdorff, J. von; Plato, M.; Rohland, H.C.; Elger, G.; Moebius, K.

    1996-08-15

    Synthetic porphyrin-quinone complexes are commonly used to mimic electron transport in photosynthetic reaction centers and to probe the effects of energetics, distances, and relative orientations on rates of electron transfer between donor-acceptor couples. The structures of two such models have been determined by X-ray diffraction. The redox pairs consist of a zinc porphyrin covalently linked to benzoquinone in cis and trans configurations via a cyclohexanediyl bridge. The crystallographic studies were undertaken to provide a structural foundation for the extensive body of experimental and theoretical results that exists for these compounds in both the ground and photoinduced charge-separated states. The results validate conclusions reached from theoretical calculations, EPR and two-dimensional NMR results for these states. 15 refs., 6 figs., 2 tabs.

  3. Electronic energy transfer: Localized operator partitioning of electronic energy in composite quantum systems

    NASA Astrophysics Data System (ADS)

    Khan, Yaser; Brumer, Paul

    2012-11-01

    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 defines a consistent electronic energy at all internuclear distances, including the case of separated fragments, and reduces to the well-known Förster and Dexter results in their respective limits. Numerical calculations of coherent energy and charge transfer dynamics in simple model systems are presented and the effect of collisionally induced decoherence is examined.

  4. Acid Treatment Enables Suppression of Electron-Hole Recombination in Hematite for Photoelectrochemical Water Splitting.

    PubMed

    Yang, Yi; Forster, Mark; Ling, Yichuan; Wang, Gongming; Zhai, Teng; Tong, Yexiang; Cowan, Alexander J; Li, Yat

    2016-03-01

    We report a strategy for efficient suppression of electron-hole recombination in hematite photoanodes. Acid-treated hematite showed a substantially enhanced photocurrent density compared to untreated samples. Electrochemical impedance spectroscopy studies revealed that the enhanced photocurrent is partly due to improved efficiency of charge separation. Transient absorption spectroscopic studies coupled to electrochemical measurements indicate that, in addition to improved bulk electrochemical properties, acid-treated hematite has significantly decreased surface electron-hole recombination losses owing to a greater yield of the trapped photoelectrons being extracted to the external circuit.

  5. Biochemical Mechanisms Controlling Terminal Electron Transfer in Geobacter sulfurreducens

    NASA Astrophysics Data System (ADS)

    Helmus, R.; Liermann, L. J.; Brantley, S. L.; Tien, M.

    2009-04-01

    The ability of Geobacter sulfurreducens to use a variety of metals as terminal electron acceptors (TEAs) for cellular respiration makes it attractive for use in bioremediation and implies its importance to mineral cycling in the environment. This study is aimed at understanding the biochemical mechanisms that allow Geobacter sulfurreducens to use soluble and insoluble iron and manganese forms as TEAs for cellular respiration and is the first of its kind to address the kinetics of manganese use as a TEA by G. sulfurreducens. First, G. sulfurreducens was conditioned to grow on various soluble and insoluble iron and manganese forms. G. sulfurreducens demonstrated enhanced growth rates when cultured using soluble TEAs compared with insoluble TEAs. However, the lower growth rate on insoluble iron compared with soluble iron was observed concomitantly with a 1-2 log lower cell density in stationary phase in insoluble iron cultures and a lower growth yield per electron donor used in log growth phase. Furthermore, the growth yield per electron was similar with both soluble and insoluble iron. These results suggest that the net amount of energy available for biomass production achieved from reducing insoluble iron is lower than with soluble iron, which may be due to a different biochemical mechanism catalyzing the electron transfer to TEA dependent upon the solubility of the TEA. One scenario consistent with this notion is that protein(s) in the outer membrane of G. sulfurreducens that transfers electrons to insoluble TEAs does so in a manner that uncouples electron flow from the proton pump in the cellular membrane, similar to what we have observed with Shewanella oneidensis MR-1. Both the growth rate and growth yield of G. sulfurreducens on insoluble manganese were higher than on insoluble iron, indicating that there is a difference in the flow of electrons to the TEA in these two situations. While the different redox potentials of these elements may affect these values

  6. Exciton Relaxation and Electron Transfer Dynamics of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Liu, Cunming

    Quantum dots (QDs), also referred to as colloidal semiconductor nanocrystals, exhibit unique electronic and optical properties arising from their three-dimensional confinement and strongly enhanced coulomb interactions. Developing a detailed understanding of the exciton relaxation dynamics within QDs is important not only for sake of exploring the fundamental physics of quantum confinement processes, but also for their applications. Ultrafast transient absorption (TA) spectroscopy, as a powerful tool to explore the relaxation dynamics of excitons, was employed to characterize the hot single/multiexciton relaxation dynamics at the first four exciton states of CdSe/CdZnS QDs. We observed for the first time that the hot hole can relax through two possible pathways: Intraband multiple phonon coupling and intrinsic defect trapping, with a lifetime of ˜7 ps. Additionally, an ultra-short component of ˜ 8 ps, directly associated with the Auger recombination of highly energetic exciton states, was discovered. After exploring the exciton relaxation inside QDs, ultrafast TA spectroscopy was further applied to study the electron transferring outside from QDs. By using a brand-new photocatalytic system consisting of CdSe QDs and Ni-dihydrolipoic acid (Ni-DHLA) catalyst, which has represented a robust photocatalysis of H2 from water, the photoinduced electron transfer (ET) dynamics between QD and the catalyst, one of most important steps during H2 generation, was studied. We found smaller bare CdSe QDs exhibit a better ET performance and CdS shelling on the bare QDs leads to worsen the ET. The calculations of effective mass approximation (EMA) and Marcus theory show the ET process is mainly dominated by driving force, electronic coupling strength and reorganization energy between QD and the catalyst.

  7. Universality of energy and electron transfer processes in photosystem I.

    PubMed

    Hastings, G; Hoshina, S; Webber, A N; Blankenship, R E

    1995-11-28

    Femtosecond transient absorption spectroscopy has been used to investigate the photoinduced energy and electron transfer processes in photosystem I (PS I) particles from cyanobacteria, green algae, and higher plants. At room temperature, the kinetics observed in all three species are very similar: Following 590 nm excitation, an equilibration process(es) with a 3.7-7.5 ps lifetime was observed, followed by a 19-24 ps process that is associated with trapping. In all three species long-wavelength pigments (pigments that absorb at longer wavelengths than the primary electron donor) were observed. The difference spectrum associated with reduction of the primary electron acceptor [Ao(-)-Ao) difference spectrum] was obtained for all three species. The (Ao(-)-Ao) difference spectra obtained from measurements using detergent-isolated PS I particles from spinach and Chlamydomonas reinhardtii are similar but clearly membrane fragments. In all three species the reduced primary electron acceptor (Ao(-)) is reoxidized extremely rapidly, in about 20 ps. The difference spectrum associated with Ao reduction appears to contain contributions from more than a single chlorophyll pigment.

  8. Spatial resolution and information transfer in scanning transmission electron microscopy.

    PubMed

    Peng, Yiping; Oxley, Mark P; Lupini, Andrew R; Chisholm, Matthew F; Pennycook, Stephen J

    2008-02-01

    The relation between image resolution and information transfer is explored. It is shown that the existence of higher frequency transfer in the image is just a necessary but not sufficient condition for the achievement of higher resolution. Adopting a two-point resolution criterion, we suggest that a 10% contrast level between two features in an image should be used as a practical definition of resolution. In the context of scanning transmission electron microscopy, it is shown that the channeling effect does not have a direct connection with image resolution because sharp channeling peaks do not move with the scanning probe. Through a quantitative comparison between experimental image and simulation, a Fourier-space approach is proposed to estimate defocus and sample thickness. The effective atom size in Z-contrast imaging depends on the annular detector's inner angle. Therefore, an optimum angle exists for the highest resolution as a trade-off between reduced atom size and reduced signal with limited information transfer due to noise.

  9. Electron transfer in native and mutated photosystem I reaction centers

    NASA Astrophysics Data System (ADS)

    Savikhin, Sergei; Xu, Wu; Chitnis, Parag; Struve, Walter

    2002-03-01

    Femtosecond time-resolved absorption difference studies were performed on photosystem I complexes from the cyanobacterium Synechocystis sp. PCC 6803. The overal electron transfer from the special pair P700 to the secondary acceptor A1 has been shown to be 10 ps, twice shorter than the previously estimated value. Similar studies were performed on more than 10 genetically engineered species, where protein structure was altered in the visinity of the reaction center (RC). The functioning of the PS I complex was found to be extremelly sensitive to the protein sequence in the immediate proximity of the RC: less than half of the studied mutations resulted in photosynthetically active complexes, and all of the latter had electron transfer dynamics indistinguishable from that of the wild type. Most of the mutations in the other areas of the PS I, including antenna, did not affect the photosynthetic function of this complex radically. These results confirm the extreme importance of the precise RC structure and demonstrate why millions of years of evolution resulted in only two types of topologically similar RC's shared by all photosynthetic organisms.

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

    NASA Astrophysics Data System (ADS)

    Giles, Alex; Spooner, Jacob; Weinberg, Noham

    2013-06-01

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

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

    SciTech Connect

    Spears, K.G.

    1993-09-08

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  13. Strong suppression of shot noise in a feedback-controlled single-electron transistor.

    PubMed

    Wagner, Timo; Strasberg, Philipp; Bayer, Johannes C; Rugeramigabo, Eddy P; Brandes, Tobias; Haug, Rolf J

    2017-03-01

    Feedback control of quantum mechanical systems is rapidly attracting attention not only due to fundamental questions about quantum measurements, but also because of its novel applications in many fields in physics. Quantum control has been studied intensively in quantum optics but progress has recently been made in the control of solid-state qubits as well. In quantum transport only a few active and passive feedback experiments have been realized on the level of single electrons, although theoretical proposals exist. Here we demonstrate the suppression of shot noise in a single-electron transistor using an exclusively electronic closed-loop feedback to monitor and adjust the counting statistics. With increasing feedback response we observe a stronger suppression and faster freezing of charge current fluctuations. Our technique is analogous to the generation of squeezed light with in-loop photodetection as used in quantum optics. Sub-Poisson single-electron sources will pave the way for high-precision measurements in quantum transport similar to optical or optomechanical equivalents.

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

    SciTech Connect

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

    2015-12-07

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

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

    PubMed

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

    2015-11-19

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

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

    NASA Astrophysics Data System (ADS)

    Sheu, Sheh-Yi; Yang, Dah-Yen

    2017-01-01

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

  17. Structural basis of interprotein electron transfer in bacterial sulfite oxidation

    PubMed Central

    McGrath, Aaron P; Laming, Elise L; Casas Garcia, G Patricia; Kvansakul, Marc; Guss, J Mitchell; Trewhella, Jill; Calmes, Benoit; Bernhardt, Paul V; Kappler, Ulrike; Maher, Megan J

    2015-01-01

    Interprotein electron transfer underpins the essential processes of life and relies on the formation of specific, yet transient protein-protein interactions. In biological systems, the detoxification of sulfite is catalyzed by the sulfite-oxidizing enzymes (SOEs), which interact with an electron acceptor for catalytic turnover. Here, we report the structural and functional analyses of the SOE SorT from Sinorhizobium meliloti and its cognate electron acceptor SorU. Kinetic and thermodynamic analyses of the SorT/SorU interaction show the complex is dynamic in solution, and that the proteins interact with Kd = 13.5 ± 0.8 μM. The crystal structures of the oxidized SorT and SorU, both in isolation and in complex, reveal the interface to be remarkably electrostatic, with an unusually large number of direct hydrogen bonding interactions. The assembly of the complex is accompanied by an adjustment in the structure of SorU, and conformational sampling provides a mechanism for dissociation of the SorT/SorU assembly. DOI: http://dx.doi.org/10.7554/eLife.09066.001 PMID:26687009

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

    PubMed Central

    Sheu, Sheh-Yi; Yang, Dah-Yen

    2017-01-01

    Proteins are of interest in nano-bio electronic devices due to their versatile structures, exquisite functionality and specificity. However, quantum transport measurements produce conflicting results due to technical limitations whereby it is difficult to precisely determine molecular orientation, the nature of the moieties, the presence of the surroundings and the temperature; in such circumstances a better understanding of the protein electron transfer (ET) pathway and the mechanism remains a considerable challenge. Here, we report an approach to mechanically drive polypeptide flip-flop motion to achieve a logic gate with ON and OFF states during protein ET. We have calculated the transmission spectra of the peptide-based molecular junctions and observed the hallmarks of electrical current and conductance. The results indicate that peptide ET follows an NC asymmetric process and depends on the amino acid chirality and α-helical handedness. Electron transmission decreases as the number of water molecules increases, and the ET efficiency and its pathway depend on the type of water-bridged H-bonds. Our results provide a rational mechanism for peptide ET and new perspectives on polypeptides as potential candidates in logic nano devices. PMID:28051140

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

    PubMed

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

    2014-08-19

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    PubMed

    Sofer, Zdeněk; Sedmidubský, David; Huber, Štěpán; Luxa, Jan; Bouša, 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.

  2. Water promoting electron hole transport between tyrosine and cysteine in proteins via a special mechanism: double proton coupled electron transfer.

    PubMed

    Chen, Xiaohua; Ma, Guangcai; Sun, Weichao; Dai, Hongjing; Xiao, Dong; Zhang, Yanfang; Qin, Xin; Liu, Yongjun; Bu, Yuxiang

    2014-03-26

    The proton/electron transfer reactions between cysteine residue (Cys) and tyrosinyl radical (Tyr(•)) are an important step for many enzyme-catalyzed processes. On the basis of the statistical analysis of protein data bank, we designed three representative models to explore the possible proton/electron transfer mechanisms from Cys to Tyr(•) in proteins. Our ab initio calculations on simplified models and quantum mechanical/molecular mechanical (QM/MM) calculations on real protein environment reveal that the direct electron transfer between Cys and Tyr(•) is difficult to occur, but an inserted water molecule can greatly promote the proton/electron transfer reactions by a double-proton-coupled electron transfer (dPCET) mechanism. The inserted H2O plays two assistant roles in these reactions. The first one is to bridge the side chains of Tyr(•) and Cys via two hydrogen bonds, which act as the proton pathway, and the other one is to enhance the electron overlap between the lone-pair orbital of sulfur atom and the π-orbital of phenol moiety and to function as electron transfer pathway. This water-mediated dPCET mechanism may offer great help to understand the detailed electron transfer processes between Tyr and Cys residues in proteins, such as the electron transfer from Cys439 to Tyr730(•) in the class I ribonucleotide reductase.

  3. Charge transfer emission in coumarin 343 sensitized TiO{sub 2} nanoparticle: A direct measurement of back electron transfer

    SciTech Connect

    Ghosh, H.N.

    1999-11-25

    Electron injection and back electron transfer dynamics in coumarin 343 (C-343) adsorbed on TiO{sub 2} nanoparticles are studied by picosecond transient absorption and time-resolved fluorescence spectroscopy. The direct detection of electrons in the nanoparticles and the parent cation are monitored using picosecond transient absorption spectroscopy, and the corresponding dynamics of the adsorbate are monitored by time-resolved absorption spectra of the cation radical of C-343 in the visible region. When the electron returns from the nanoparticles to the present cation, a low quantum yield red-shifted charge transfer emission is observed. Measuring the charge transfer emission lifetimes by a picosecond time-resolved fluorimeter, the author gets an exact rate of back electron transfer reaction from the nanoparticle to the parent cation.

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

    SciTech Connect

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

    2016-06-14

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

  5. Electron transfer dissociation of modified peptides and proteins.

    PubMed

    Zhou, Yuping; Dong, Jia; Vachet, Richard W

    2011-10-01

    Mass spectrometry is the method of choice for sequencing peptides and proteins and is the preferred choice for characterizing post-translational modifications (PTMs). The most commonly used dissociation method to characterize peptides (i.e. collision-induced dissociation (CID)), however, has some limitations when it comes to analyzing many PTMs. Because CID chemistry is influenced by amino acid side-chains, some modifications can alter or inhibit dissociation along the peptide backbone, thereby limiting sequence information and hindering identification of the modification site. Electron transfer dissociation (ETD) has emerged as an alternate dissociation technique that, in most cases, overcomes these limitations of CID because it is less affected by side chain chemistry. Here, we review recent applications of ETD for characterizing peptide and protein PTMs with a particular emphasis on the advantages of ETD over CID, the ways in which ETD and CID have been used in a complementary manner, and how peptide modifications can still influence ETD dissociation pathways.

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

    PubMed Central

    2016-01-01

    Proton-coupled electron transfer (PCET) is ubiquitous throughout chemistry and biology. This Perspective discusses recent advances and current challenges in the field of PCET, with an emphasis on the role of theory and computation. The fundamental theoretical concepts are summarized, and expressions for rate constants and kinetic isotope effects are provided. Computational methods for calculating reduction potentials and pKa’s for molecular electrocatalysts, as well as insights into linear correlations and non-innocent ligands, are also described. In addition, computational methods for simulating the nonadiabatic dynamics of photoexcited PCET are discussed. Representative applications to PCET in solution, proteins, electrochemistry, and photoinduced processes are presented, highlighting the interplay between theoretical and experimental studies. The current challenges and suggested future directions are outlined for each type of application, concluding with an overall view to the future. PMID:26110700

  7. Heat transfer model to characterize the focal cooling necessary to suppress spontaneous epileptiform activity (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Guerra, Reynaldo G.; Davalos, Rafael V.; Garcia, Paul A.; Rubinsky, Boris; Berger, Mitchel

    2005-04-01

    Epilepsy is characterized by paroxysmal transient disturbances of the electrical activity of the brain. Symptoms are manifested as impairment of motor, sensory, or psychic function with or without loss of consciousness or convulsive seizures. This paper presents an initial post-operative heat transfer analysis of surgery performed on a 41 year-old man with medically intractable Epilepsy. The surgery involved tumor removal and the resection of adjacent epileptogenic tissue. Electrocorticography was performed before resection. Cold saline was applied to the resulting interictal spike foci resulting in transient, complete cessation of spiking. A transient one dimensional semi-infinite finite element model of the surface of the brain was developed to simulate the surgery. An approximate temperature distribution of the perfused brain was developed by applying the bioheat equation. The model quantifies the surface heat flux reached in achieving seizure cessation to within an order of magnitude. Rat models have previously shown that the brain surface temperature range to rapidly terminate epileptogenic activity is 20-24°C. The developed model predicts that a constant heat flux of approximately -13,000W/m2, applied at the surface of the human brain, would achieve a surface temperature in this range in approximately 3 seconds. A parametric study was subsequently performed to characterize the effects of brain metabolism and brain blood perfusion as a function of the determined heat flux. The results of these findings can be used as a first approximation in defining the specifications of a cooling device to suppress seizures in human models.

  8. Electron transfer in systems of well-defined geometry

    SciTech Connect

    Overfield, R.E.; Kaufmann, K.J.; Wasielewski, M.R.

    1980-01-01

    Two mesopyropheophorbide macrocycles can be joined via two covalent linkages to produce a cyclophane. It is possible to insert one or two Mg atoms into the cyclophane. The Qy transitions of the macrocycles are nearly orthogonal. The visible absorption spectrum of the monometal cyclophane is nearly a superposition of the spectra of the monomers. Emission from the monometal cyclophane arises primarily from the red most absorbing chromophore. The excited state difference spectrum shows that both macrocycles are excited. Fluorescence lifetimes of the monometal cyclophane decrease with increasing dielectric strength. Changes in the fluorescence and the triplet yield parallel the shortening of the singlet lifetime. Thus the radiative rate is solvent independent. This is in contrast to what one would expect if the emitting state had charge transfer character. Since the fluorescence lifetime is dependent on dielectric, the nonradiative relaxation from the singlet state is due to formation of a radical pair. The decay rate of the postulated radical pair was monitored by observing the kinetics of ground state repopulation. For the geometry of this cyclophane, electron transfer proceeds relatively slowly (k = 3 x 10/sup 9/ sec/sup -1/) in the forward direction. Modeling calculations indicate that the rate of annihilation of the radical pair may decrease as the solvent dielectric decreases.

  9. Experiments in DIII-D toward achieving rapid shutdown with runaway electron suppression

    SciTech Connect

    Hollmann, E. M.; Commaux, Nicolas JC; Eidietis, N. W.; Evans, T. E.; Humphreys, D. A.; James, A. N.; Jernigan, T. C.; Parks, P. B.; Strait, E. J.; Wesley, J. C.; Yu, J.H.; Austin, M. E.; Baylor, Larry R; Brooks, N. H.; Izzo, V. A.; Jackson, G. L.; Van Zeeland, M. A.; Wu, W.

    2010-01-01

    Experiments have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] toward understanding runaway electron formation and amplification during rapid discharge shutdown, as well as toward achieving complete collisional suppression of these runaway electrons via massive delivery of impurities. Runaway acceleration and amplification appear to be well explained using the zero-dimensional (0D) current quench toroidal electric field. 0D or even one-dimensional modeling using a Dreicer seed term, however, appears to be too small to explain the initial runaway seed formation. Up to 15% of the line-average electron density required for complete runaway suppression has been achieved in the middle of the current quench using optimized massive gas injection with multiple small gas valves firing simultaneously. The novel rapid shutdown techniques of massive shattered pellet injection and shell pellet injection have been demonstrated for the first time. Experiments using external magnetic perturbations to deconfine runaways have shown promising preliminary results. (C) 2010 American Institute of Physics. [doi:10.1063/1.3309426

  10. Experiments in DIII-D toward achieving rapid shutdown with runaway electron suppression

    SciTech Connect

    Hollmann, E. M.; James, A. N.; Yu, J. H.; Izzo, V. A.; Commaux, N.; Jernigan, T. C.; Baylor, L. R.; Eidietis, N. W.; Parks, P. B.; Wesley, J. C.; Brooks, N. H.; Jackson, G. L.; Zeeland, M. A. van; Wu, W.; Evans, T. E.; Humphreys, D. A.; Strait, E. J.; Austin, M. E.

    2010-05-15

    Experiments have been performed in the DIII-D tokamak [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] toward understanding runaway electron formation and amplification during rapid discharge shutdown, as well as toward achieving complete collisional suppression of these runaway electrons via massive delivery of impurities. Runaway acceleration and amplification appear to be well explained using the zero-dimensional (0D) current quench toroidal electric field. 0D or even one-dimensional modeling using a Dreicer seed term, however, appears to be too small to explain the initial runaway seed formation. Up to 15% of the line-average electron density required for complete runaway suppression has been achieved in the middle of the current quench using optimized massive gas injection with multiple small gas valves firing simultaneously. The novel rapid shutdown techniques of massive shattered pellet injection and shell pellet injection have been demonstrated for the first time. Experiments using external magnetic perturbations to deconfine runaways have shown promising preliminary results.

  11. Suppression of Secondary Electron Emission using Triangular Grooved Surface in the ILC Dipole and Wiggler Magnets

    SciTech Connect

    Wang, L.; Bane, K.; Chen, C.; Himel, T.; Munro, M.; Pivi, M.; Raubenheimer, T.; Stupakov, G.; /SLAC

    2007-07-06

    The development of an electron cloud in the vacuum chambers of high intensity positron and proton storage rings may limit machine performance. The suppression of electrons in a magnet is a challenge for the positron damping ring of the International Linear Collider (ILC) as well as the Large Hadron Collider. Simulation show that grooved surfaces can significantly reduce the electron yield in a magnet. Some of the secondary electrons emitted from the grooved surface return to the surface within a few gyrations, resulting in a low effective secondary electron yield (SEY) of below 1.0 A triangular surface is an effective, technologically attractive mitigation with a low SEY and a weak dependence on the scale of the corrugations and the external magnetic field. A chamber with triangular grooved surface is proposed for the dipole and wiggler sections of the ILC and will be tested in KEKB in 2007. The strategy of electron cloud control in ILC and the optimization of the grooved chamber such as the SEY, impedance as well as the manufacturing of the chamber, are also discussed.

  12. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Suppression of Anti-resonant Effect in Presence of Band Overlap

    NASA Astrophysics Data System (ADS)

    Xiong, Gang

    2010-07-01

    By exact resolution of coupled ideal chains connecting an extra side site, we show that the so-called "anti-resonant effect" is suppressed when the electron energy is inside the overlap region of extended bands of the ideal tight-binding chains. When the electronic energy is outside the band overlap region, the existence of "anti-resonant effect" is tuned by details of local connectivity around the extra side site and can be suppressed by introduction of magnetic flux.

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

    PubMed

    Paul, Nandadulal; Samanta, Subhas; Goswami, Sreebrata

    2010-03-15

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

  14. Substrate entasis and electronic coupling elements in electron transfer from FeII in a multicopper ferroxidase

    PubMed Central

    Kosman, Daniel J.

    2008-01-01

    Outersphere electron transfer in multicopper oxidases occurs at the type 1, blue CuII. One class of MCO proteins exhibits a specificity in this reaction towards FeII. In work carried out in collaboration with the Solomon lab over the past 7 years, we have delineated the structural motifs that support this ferroxidase specificity and have quantified the contributions that each makes to this outersphere electron transfer reaction from FeII to the type 1 CuII. Two features of this electron transfer catalysis stand out. First, the protein provides a binding site for FeII that actually favors FeIII; this coordination sphere places the bound FeII in a state of “entasis” that can be relieved by loss of an electron. In short, the EO of the bound FeII is lowered relative to that of aqueous ferrous iron making electron transfer thermodynamically favorable. Second, carboxylates within this coordination sphere provide an electronic coupling pathway for the electron transfer via their H-bond network with type 1 Cu histidine ligands thus making electron transfer kinetically efficient. This brief report breaks down these contributions to ferroxidase specificity in terms of the semi-classical Marcus equation describing outersphere electron transfer. PMID:18443651

  15. Electron Suppression and Simulation Fidelity in the Strawman Design of SXTF.

    DTIC Science & Technology

    1978-12-31

    DESCRIPTION OF THE SXTF The tank simulator is sketched in Figure 1. Basically, it con- sists of a spherical vacuum tank (stainless steel ) 15 m in...irid Sd. 34 a. Free Space b. Perfect Suppression 5 x1O-10 - 6xlo-O - - - ! ,1 4340 C "- - --- . . -__ _--- L__ S3x1-O - L" L f~.. ’L ’ . .. . ... t...Dev & Acq ATTN: ESR , E. Burke Department of the Army ATTN: DAMA-CSS-N Strategic Air CommandDepartment of the Air Force Electronics Tech & Devices Lab

  16. Critical Role of Energy Transfer Between Terbium Ions for Suppression of Back Energy Transfer in Nonanuclear Terbium Clusters.

    PubMed

    Omagari, Shun; Nakanishi, Takayuki; Kitagawa, Yuichi; Seki, Tomohiro; Fushimi, Koji; Ito, Hajime; Meijerink, Andries; Hasegawa, Yasuchika

    2016-11-15

    Lanthanide (Ln(III)) complexes form an important class of highly efficient luminescent materials showing characteristic line emission after efficient light absorption by the surrounding ligands. The efficiency is however lowered by back energy transfer from Ln(III) ion to the ligands, especially at higher temperatures. Here we report a new strategy to reduce back energy transfer losses. Nonanuclear lanthanide clusters containing terbium and gadolinium ions, TbnGd9-n clusters ([TbnGd9-n(μ-OH)10(butylsalicylate)16](+)NO3(-), n = 0, 1, 2, 5, 8, 9), were synthesized to investigate the effect of energy transfer between Tb(III) ions on back energy transfer. The photophysical properties of TbnGd9-n clusters were studied by steady-state and time-resolved spectroscopic techniques and revealed a longer emission lifetime with increasing number of Tb(III) ions in TbnGd9-n clusters. A kinetic analysis of temperature dependence of the emission lifetime show that the energy transfer between Tb(III) ions competes with back energy transfer. The experimental results are in agreement with a theoretical rate equation model that confirms the role of energy transfer between Tb(III) ions in reducing back energy transfer losses. The results provide a new strategy in molecular design for improving the luminescence efficiency in lanthanide complexes which is important for potential applications as luminescent materials.

  17. Critical Role of Energy Transfer Between Terbium Ions for Suppression of Back Energy Transfer in Nonanuclear Terbium Clusters

    PubMed Central

    Omagari, Shun; Nakanishi, Takayuki; Kitagawa, Yuichi; Seki, Tomohiro; Fushimi, Koji; Ito, Hajime; Meijerink, Andries; Hasegawa, Yasuchika

    2016-01-01

    Lanthanide (Ln(III)) complexes form an important class of highly efficient luminescent materials showing characteristic line emission after efficient light absorption by the surrounding ligands. The efficiency is however lowered by back energy transfer from Ln(III) ion to the ligands, especially at higher temperatures. Here we report a new strategy to reduce back energy transfer losses. Nonanuclear lanthanide clusters containing terbium and gadolinium ions, TbnGd9−n clusters ([TbnGd9−n(μ-OH)10(butylsalicylate)16]+NO3−, n = 0, 1, 2, 5, 8, 9), were synthesized to investigate the effect of energy transfer between Tb(III) ions on back energy transfer. The photophysical properties of TbnGd9−n clusters were studied by steady-state and time-resolved spectroscopic techniques and revealed a longer emission lifetime with increasing number of Tb(III) ions in TbnGd9−n clusters. A kinetic analysis of temperature dependence of the emission lifetime show that the energy transfer between Tb(III) ions competes with back energy transfer. The experimental results are in agreement with a theoretical rate equation model that confirms the role of energy transfer between Tb(III) ions in reducing back energy transfer losses. The results provide a new strategy in molecular design for improving the luminescence efficiency in lanthanide complexes which is important for potential applications as luminescent materials. PMID:27845407

  18. Critical Role of Energy Transfer Between Terbium Ions for Suppression of Back Energy Transfer in Nonanuclear Terbium Clusters

    NASA Astrophysics Data System (ADS)

    Omagari, Shun; Nakanishi, Takayuki; Kitagawa, Yuichi; Seki, Tomohiro; Fushimi, Koji; Ito, Hajime; Meijerink, Andries; Hasegawa, Yasuchika

    2016-11-01

    Lanthanide (Ln(III)) complexes form an important class of highly efficient luminescent materials showing characteristic line emission after efficient light absorption by the surrounding ligands. The efficiency is however lowered by back energy transfer from Ln(III) ion to the ligands, especially at higher temperatures. Here we report a new strategy to reduce back energy transfer losses. Nonanuclear lanthanide clusters containing terbium and gadolinium ions, TbnGd9‑n clusters ([TbnGd9‑n(μ-OH)10(butylsalicylate)16]+NO3‑, n = 0, 1, 2, 5, 8, 9), were synthesized to investigate the effect of energy transfer between Tb(III) ions on back energy transfer. The photophysical properties of TbnGd9‑n clusters were studied by steady-state and time-resolved spectroscopic techniques and revealed a longer emission lifetime with increasing number of Tb(III) ions in TbnGd9‑n clusters. A kinetic analysis of temperature dependence of the emission lifetime show that the energy transfer between Tb(III) ions competes with back energy transfer. The experimental results are in agreement with a theoretical rate equation model that confirms the role of energy transfer between Tb(III) ions in reducing back energy transfer losses. The results provide a new strategy in molecular design for improving the luminescence efficiency in lanthanide complexes which is important for potential applications as luminescent materials.

  19. Ions interacting with planar aromatic molecules: Modeling electron transfer reactions

    SciTech Connect

    Forsberg, B. O.; Alexander, J. D.; Chen, T.; Pettersson, A. T.; Gatchell, M.; Cederquist, H.; Zettergren, H.

    2013-02-07

    We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C{sub 14}H{sub 10}, coronene C{sub 24}H{sub 12}, or circumcoronene C{sub 54}H{sub 18}. These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

  20. Chlorophyll-quinone photochemical electron transfer in liposomes

    SciTech Connect

    Hurley, J.K.; Castelli, F.; Tollin, G.

    1981-09-01

    The study described involves the reduction of electron acceptors (quinones) by photoexcited Chloroplasts (Chl). Chl a (from spinach) is incorporated into phosphatidylcholine (either synthetic or from hen egg yolks) liposomes suspended in 10 mM phosphate buffer (pH 7.0). The quinones are either present during liposome formation or added later, depending upon their water solubility. The measurement technique employed is laser flash photolysis. A pulsed nitrogen laser pumps a dye laser, which delivers a short light flash (10 ns) to the sample at a wavelength (655-660 nm) within an absorption band of Chl. This raises Chl to an excited singlet level, which can rapidly cross to the lowest excited triple level (/sup 3/Chl). From this state Chl can transfer an electron to acceptors such as quinones, resulting in the formation of the Chl cation radical (Chl./sup +/) and the semiquinone anion radical (Q./sup +/). Transient absorbance changes ocurring within the sample cell are monitored and can be attributed to processes such as excited state quenching (of /sup 3/Chl by Q) and radical product formation and decay. (JMT)

  1. Long-range electron transfer in biomolecules. Tunneling or hopping?

    PubMed

    Voityuk, Alexander A

    2011-10-27

    Two competing mechanisms are relevant for long-range electron transfer (ET) in biomolecules: direct electron tunneling between donor (D) and acceptor (A), D → A, and multistep hopping D → X → A, where an electron or an electron hole is transiently localized on intermediate sites X. Which of these mechanisms dominates the ET reaction is determined by the arrangement and electronic properties of the redox centers. For thermal ET, it is shown that single-step tunneling is overcome by hopping when the energy gap E between D and X is smaller than the crossover barrier E(C), E(C) = (ΔG/2) + (3/4)k(B)TβR(DA), where ΔG is the driving force, β the decay parameter, and R(DA) the donor-acceptor distance. In proteins at T = 300 K, hopping will dominate when E < E(C) = (ΔG/2) + (R(DA)/50) (E and ΔG are in eV, R(DA) in Å); single-step tunneling will be operative when E > E(C). Thus, one can explore the ET mechanism using three quantities E, ΔG, and R(DA). When ΔG = 0 and E = 0.5 eV (the difference in redox potentials of D and X is 0.5 V), two-step hopping D → X → A will be favored at R(DA) >25 Å. In protein ET chains, the distance between redox cofactors is often smaller than 20 Å, but the gap E between the cofactors and surrounding amino acid residues is larger than 0.5 eV. Therefore, ET in the systems should occur by single-step tunneling D → A. In the activationless regime (ΔG ≈ -λ, λ is the reorganization energy) often observed for photoinduced ET, the crossing point energy is determined by E(C) = (2λkTβR(DA))(1/2) - λ. The suggested expressions for the threshold barrier may be useful to predict the ET mechanism in natural and artificial redox systems.

  2. Photoinduced electron transfer reaction in polymer-surfactant aggregates: Photoinduced electron transfer between N,N-dimethylaniline and 7-amino coumarin dyes

    SciTech Connect

    Chakraborty, Anjan; Seth, Debabrata; Setua, Palash; Sarkar, Nilmoni

    2008-05-28

    Photoinduced electron transfer between coumarin dyes and N,N-dimethylaniline has been investigated by using steady state and picosecond time resolved fluorescence spectroscopy in sodium dodecyl sulphate (SDS) micelles and PVP-polyvinyl pyrrolidone (SDS) polymer-surfactant aggregates. A slower rate of electron transfer is observed in PVP-SDS aggregates than in polymer-free SDS micelles. A Marcus type inversion is observed in the correlation of free energy change in comparison with the electron transfer rate. The careful investigation reveals that C-151 deviates from the normal Marcus inverted region compared to its analogs C-152 and C-481 due to slower rotational relaxation and smaller translational diffusion coefficient.

  3. Modular electron transfer circuits for synthetic biology: insulation of an engineered biohydrogen pathway.

    PubMed

    Agapakis, Christina M; Silver, Pamela A

    2010-01-01

    Electron transfer is central to a wide range of essential metabolic pathways, from photosynthesis to fermentation. The evolutionary diversity and conservation of proteins that transfer electrons makes these pathways a valuable platform for engineered metabolic circuits in synthetic biology. Rational engineering of electron transfer pathways containing hydrogenases has the potential to lead to industrial scale production of hydrogen as an alternative source of clean fuel and experimental assays for understanding the complex interactions of multiple electron transfer proteins in vivo. We designed and implemented a synthetic hydrogen metabolism circuit in Escherichia coli that creates an electron transfer pathway both orthogonal to and integrated within existing metabolism. The design of such modular electron transfer circuits allows for facile characterization of in vivo system parameters with applications toward further engineering for alternative energy production.

  4. Directionality of electron-transfer reactions in photosystem I of prokaryotes: universality of the bidirectional electron-transfer model.

    PubMed

    Santabarbara, Stefano; Kuprov, Ilya; Poluektov, Oleg; Casal, Antonio; Russell, Charlotte A; Purton, Saul; Evans, Michael C W

    2010-11-25

    The electron-transfer (ET) reactions in photosystem I (PS I) of prokaryotes have been investigated in wild-type cells of the cyanobacterium Synechocystis sp. PCC 6803, and in two site-directed mutants in which the methionine residue of the reaction center subunits PsaA and PsaB, which acts as the axial ligand to the primary electron chlorophyll acceptor A(0), was substituted with histidine. Analysis by pulsed electron paramagnetic resonance spectroscopy at 100 K indicates the presence of two forms of the secondary spin-correlated radical pairs, which are assigned to [P(700)(+)A(1A)(-)] and [P(700)(+)A(1B)(-)], where A(1A) and A(1B) are the phylloquinone molecules bound to the PsaA and the PsaB reaction center subunits, respectively. Each of the secondary radical pair forms is selectively observed in either the PsaA-M688H or the PsaB-M668H mutant, whereas both radical pairs are observed in the wild type following reduction of the iron-sulfur cluster F(X), the intermediate electron acceptor between A(1) and the terminal acceptors F(A) and F(B). Analysis of the time and spectral dependence of the light-induced electron spin echo allows the resolution of structural differences between the [P(700)(+)A(1A)(-)] and [P(700)(+)A(1B)(-)] radical pairs. The interspin distance is 25.43 ± 0.01 Å for [P(700)(+)A(1A)(-)] and 24.25 ± 0.01 Å for [P(700)(+)A(1B)(-)]. Moreover, the relative orientation of the interspin vector is rotated by ~60° with respect to the g-tensor of the P(700)(+) radical. These estimates are in agreement with the crystallographic structural model, indicating that the cofactors bound to both reaction center subunits of prokaryotic PS I are actively involved in electron transport. This work supports the model that bidirectionality is a general property of type I reaction centers from both prokaryotes and eukaryotes, and contrasts with the situation for photosystem II and other type II reaction centers, in which ET is strongly asymmetric. A revised model

  5. Suppression of Emittance Growth Using a Shaped Cold Atom Electron and Ion Source.

    PubMed

    Thompson, D J; Murphy, D; Speirs, R W; van Bijnen, R M W; McCulloch, A J; Scholten, R E; Sparkes, B M

    2016-11-04

    We demonstrate precise control of charged particle bunch shape with a cold atom electron and ion source to create bunches with linear and, therefore, reversible Coulomb expansion. Using ultracold charged particles enables detailed observation of space-charge effects without loss of information from thermal diffusion, unambiguously demonstrating that shaping in three dimensions can result in a marked reduction of Coulomb-driven emittance growth. We show that the emittance growth suppression is accompanied by an increase in bunch focusability and brightness, improvements necessary for the development of sources capable of coherent single-shot ultrafast electron diffraction of noncrystalline objects, with applications ranging from femtosecond chemistry to materials science and rational drug design.

  6. Suppression of Emittance Growth Using a Shaped Cold Atom Electron and Ion Source

    NASA Astrophysics Data System (ADS)

    Thompson, D. J.; Murphy, D.; Speirs, R. W.; van Bijnen, R. M. W.; McCulloch, A. J.; Scholten, R. E.; Sparkes, B. M.

    2016-11-01

    We demonstrate precise control of charged particle bunch shape with a cold atom electron and ion source to create bunches with linear and, therefore, reversible Coulomb expansion. Using ultracold charged particles enables detailed observation of space-charge effects without loss of information from thermal diffusion, unambiguously demonstrating that shaping in three dimensions can result in a marked reduction of Coulomb-driven emittance growth. We show that the emittance growth suppression is accompanied by an increase in bunch focusability and brightness, improvements necessary for the development of sources capable of coherent single-shot ultrafast electron diffraction of noncrystalline objects, with applications ranging from femtosecond chemistry to materials science and rational drug design.

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

    NASA Astrophysics Data System (ADS)

    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

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

    PubMed

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

    2015-08-03

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

  9. 75 FR 59172 - Electronic Funds Transfer of Depository Taxes; Hearing Cancellation

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-09-27

    ... 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...

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

    PubMed

    Li, Yongquan; Li, Hongyu

    2014-03-01

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

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

    PubMed

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

    2013-02-13

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

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

    NASA Technical Reports Server (NTRS)

    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

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

    EPA Science Inventory

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

  14. 77 FR 1555 - Administrative Simplification: Adoption of Standards for Health Care Electronic Funds Transfers...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-01-10

    ... and 162 Administrative Simplification: Adoption of Standards for Health Care Electronic Funds... Health Care Electronic Funds Transfers (EFTs) and Remittance Advice AGENCY: Office of the Secretary, HHS... facilitate health care EFT transmissions. DATES: Effective Date: These regulations are effective on...

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

    DOEpatents

    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.

  16. Photoinduced electron transfer from triplet fullerene, [sup 3]C[sub 60], to tetracyanoethylene. Fourier transform electron paramagnetic resonance study

    SciTech Connect

    Michaeli, S.; Meiklyar, V.; Levanon, H. ); Schulz, M.; Moebius, K. )

    1994-08-04

    Fourier transform EPR spectroscopy was employed in studying the electron transfer (ET) and the quenching mechanisms of the photoexcited triplet state of C[sub 60] (electron donor) in the presence of the electron acceptor tetracyanoethylene (TCNE) in a benzonitrile solution. The ET reaction product, which is the stable anion radical TCNE[sup [minus

  17. Comprehensive comparison of collision induced dissociation and electron transfer dissociation.

    PubMed

    Molina, Henrik; Matthiesen, Rune; Kandasamy, Kumaran; Pandey, Akhilesh

    2008-07-01

    Electron transfer dissociation (ETD) is a recently introduced mass spectrometric technique which has proven to be an excellent tool for the elucidation of labile post-translational modifications such as phosphorylation and O-GlcNAcylation of serine and threonine residues. However, unlike collision induced dissociation (CID), which has been studied for decades, the intricacies of ETD-based fragmentation have not yet been firmly established or systematically addressed. In this analysis, we have systematically compared the CID and ETD fragmentation patterns for the large majority of the peptides that do not contain such labile modifications. Using a standard 48 protein mix, we were able to measure false-positive rates for the experiments and also assess a large number of peptides for a detailed comparison of CID and ETD fragmentation pattern. Analysis of approximately 19,000 peptides derived from both standard proteins and complex protein samples revealed that (i) CID identified 50% more peptides than ETD; (ii) ETD resulted in approximately 20% increase in amino acid sequence coverage over CID; and (iii) combining CID and ETD fragmentation increased the sequence coverage for an average tryptic peptide to 92%. Interestingly, our analysis revealed that nearly 60% of all ETD-identified peptides carried two positive charges, which is in sharp contrast to what has been generally accepted. We also present a novel strategy for automatic validation of peptide assignments based on identification of a peptide by consecutive CID and ETD fragmentation in an alternating mode.

  18. Mechanism of teratogenesis: electron transfer, reactive oxygen species, and antioxidants.

    PubMed

    Kovacic, Peter; Somanathan, Ratnasamy

    2006-12-01

    Teratogenesis has been a topic of increasing interest and concern in recent years, generating controversy in association with danger to humans and other living things. A veritable host of chemicals is known to be involved, encompassing a wide variety of classes, both organic and inorganic. Contact with these chemicals is virtually unavoidable due to contamination of air, water, ground, food, beverages, and household items, as well as exposure to medicinals. The resulting adverse effects on reproduction are numerous. There is uncertainty regarding the mode of action of these chemicals, although various theories have been advanced, e.g., disruption of the central nervous system (CNS), DNA attack, enzyme inhibition, interference with hormonal action, and insult to membranes, proteins, and mitochondria. This review provides extensive evidence for involvement of oxidative stress (OS) and electron transfer (ET) as a unifying theme. Successful application of the mechanistic approach is made to all of the main classes of toxins, in addition to large numbers of miscellaneous types. We believe it is not coincidental that the vast majority of these substances incorporate ET functionalities (quinone, metal complex, ArNO2, or conjugated iminium) either per se or in metabolites, potentially giving rise to reactive oxygen species (ROS) by redox cycling. Some categories, e.g., peroxides and radiation, appear to generate ROS by non-ET routes. Other mechanisms are briefly addressed; a multifaceted approach to mode of action appears to be the most logical. Our framework should increase understanding and contribute to preventative measures, such as use of antioxidants.

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

    SciTech Connect

    Clennan, Edward L.; Liao, Chen

    2014-01-01

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

  20. Diameter dependent electron transfer kinetics in semiconductor-enzyme complexes.

    PubMed

    Brown, Katherine A; Song, Qing; Mulder, David W; King, Paul W

    2014-10-28

    Excited state electron transfer (ET) is a fundamental step for the catalytic conversion of solar energy into chemical energy. To understand the properties controlling ET between photoexcited nanoparticles and catalysts, the ET kinetics were measured for solution-phase complexes of CdTe quantum dots and Clostridium acetobutylicum [FeFe]-hydrogenase I (CaI) using time-resolved photoluminescence spectroscopy. Over a 2.0-3.5 nm diameter range of CdTe nanoparticles, the observed ET rate (kET) was sensitive to CaI concentration. To account for diameter effects on CaI binding, a Langmuir isotherm and two geometric binding models were created to estimate maximal CaI affinities and coverages at saturating concentrations. Normalizing the ET kinetics to CaI surface coverage for each CdTe diameter led to k(ET) values that were insensitive to diameter, despite a decrease in the free energy for photoexcited ET (ΔGET) with increasing diameter. The turnover frequency (TOF) of CaI in CdTe-CaI complexes was measured at several molar ratios. Normalization for diameter-dependent changes in CaI coverage showed an increase in TOF with diameter. These results suggest that k(ET) and H2 production for CdTe-CaI complexes are not strictly controlled by ΔG(ET) and that other factors must be considered.

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

    SciTech Connect

    Hammes-Schiffer, Sharon

    2015-07-22

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

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

    NASA Astrophysics Data System (ADS)

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

    NASA Astrophysics Data System (ADS)

    Badalyan, Artavazd; Stahl, Shannon S.

    2016-07-01

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

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

    PubMed

    Badalyan, Artavazd; Stahl, Shannon S

    2016-07-21

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

  5. 77 FR 6193 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-07

    ... instance through wire transfers or automated clearing house (ACH) transactions. Furthermore, consumers in... Dodd-Frank Amendments, Congress had specifically structured the EFTA to exclude wire transfers,\\13\\ and... of certain methods, particularly consumer wire transfers, is very limited, but the Bureau...

  6. Photoinitiated electron transfer in multi-chromophoric species: Synthetic tetrads and pentads. Technical progress report, 1987--1990

    SciTech Connect

    Not Available

    1990-02-14

    This research project involves the design, synthesis and study of the molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. Specifically, the molecules are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties. In addition, they model carotenoid antenna function in photosynthesis (singlet-singlet energy transfer from carotenoid polyenes to chlorophyll) and carotenoid photoprotection from singlet oxygen damage (triplet-triplet energy transfer from chlorophyll to carotenoids).

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

    PubMed

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

    2015-03-17

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

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

    PubMed Central

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

    2011-01-01

    Quantum dot-metal oxide junctions are an integral part of next-generation solar cells, light emitting diodes, and nanostructured electronic arrays. Here we present a comprehensive examination of electron transfer at these junctions, using a series of CdSe quantum dot donors (sizes 2.8, 3.3, 4.0, and 4.2 nm in diameter) and metal oxide nanoparticle acceptors (SnO2, TiO2, and ZnO). Apparent electron transfer rate constants showed strong dependence on change in system free energy, exhibiting a sharp rise at small driving forces followed by a modest rise further away from the characteristic reorganization energy. The observed trend mimics the predicted behavior of electron transfer from a single quantum state to a continuum of electron accepting states, such as those present in the conduction band of a metal oxide nanoparticle. In contrast with dye-sensitized metal oxide electron transfer studies, our systems did not exhibit unthermalized hot-electron injection due to relatively large ratios of electron cooling rate to electron transfer rate. To investigate the implications of these findings in photovoltaic cells, quantum dot-metal oxide working electrodes were constructed in an identical fashion to the films used for the electron transfer portion of the study. Interestingly, the films which exhibited the fastest electron transfer rates (SnO2) were not the same as those which showed the highest photocurrent (TiO2). These findings suggest that, in addition to electron transfer at the quantum dot-metal oxide interface, other electron transfer reactions play key roles in the determination of overall device efficiency. PMID:21149685

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

    PubMed Central

    Westereng, Bjørge; Cannella, David; Wittrup Agger, Jane; Jørgensen, 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

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

    PubMed

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

    2015-12-21

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

  11. Photoinduced bimolecular electron transfer kinetics in small unilamellar vesicles

    SciTech Connect

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

    2007-11-21

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

  12. Revising Intramolecular Photoinduced Electron Transfer (PET) from First-Principles.

    PubMed

    Escudero, Daniel

    2016-09-20

    Photoinduced electron transfer (PET) plays relevant roles in many areas of chemistry, including charge separation processes in photovoltaics, natural and artificial photosynthesis, and photoluminescence sensors and switches. As in many other photochemical scenarios, the structural and energetic factors play relevant roles in determining the rates and efficiencies of PET and its competitive photodeactivation processes. Particularly, in the field of fluorescent sensors and switches, intramolecular PET is believed (in many cases without compelling experimental proof) to be responsible of the quench of fluorescence. There is an increasing experimental interest in fluorophore's molecular design and on achieving optimal excitation/emission spectra, excitation coefficients, and fluorescence quantum yields (importantly for bioimaging purposes), but less efforts are devoted to fundamental mechanistic studies. In this Account, I revise the origins of the fluorescence quenching in some of these systems with state-of-the-art quantum chemical tools. These studies go beyond the common strategy of analyzing frontier orbital energy diagrams and performing PET thermodynamics calculations. Instead, the potential energy surfaces (PESs) of the lowest-lying excited states are explored with time-dependent density functional theory (TD-DFT) and complete active space self-consistent field (CASSCF) calculations and the radiative and nonradiative decay rates from the involved excited states are computed from first-principles using a thermal vibration correlation function formalism. With such a strategy, this work reveals the real origins of the fluorescence quenching, herein entitled as dark-state quenching. Dark states (those that do not absorb or emit light) are often elusive to experiments and thus, computational investigations can provide novel insights into the actual photodeactivation mechanisms. The success of the dark-state quenching mechanism is demonstrated for a wide variety of

  13. Control of interspecies electron flow during anaerobic digestion: significance of formate transfer versus hydrogen transfer during syntrophic methanogenesis in flocs. [Methanobacterium formicicum; Desulfovibrio vulgaris

    SciTech Connect

    Thiele, J.H.; Zeikus, J.G.

    1988-01-01

    Microbial formate production and consumption during syntrophic conversion of ethanol or lactate to methane was examined in purified flocs and digestor contents obtained from a whey-processing digestor. Formate production by digestor contents or purified digestor flocs was dependent on CO/sub 2/ and either ethanol or lactate but not H/sub 2/ gas as an electron donor. Floc preparations accumulated fourfold-higher levels of formate (40 ..mu..M) than digestor contents, and the free flora was the primary site for formate cleavage to CO/sub 2/ and H/sub 2/ (90 ..mu..M formate per h). Inhibition of methanogenesis by CHCl/sub 3/ resulted in formate accumulation and suppression of syntrophic ethanol oxidation. H/sub 2/ gas was an insignificant intermediary metabolite of syntrophic ethanol conversion by flocs, and it exogenous addition neither stimulated methanogenes nor inhibited the initial rate of ethanol oxidation. These results demonstrated that >90% of the syntrophic ethanol conversion to methane by mixed cultures containing primarily Desulfovibrio vulgaris and Methanobacterium formicicum was mediated via interspecies formate transfer and the <10% was mediated via interspecies H/sub 2/ transfer. The results are discussed in relation to biochemical thermodynamics. A model is presented which describes the dynamics of a bicarbonate-formate electron shuttle mechanism for control of carbon and electron flow during syntrophic methanogenesis and provides a novel mechanism for energy conservation by syntrophic acetogens.

  14. 27 CFR 26.267 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... transfer (EFT), as defined in paragraph (c) of this section, of such taxes during the succeeding calendar... make remittances by EFT. For purposes of this section, the dollar amount of tax liability is to be... to make remittances by EFT. (c) Electronic fund transfer or EFT means any transfer of funds,...

  15. 27 CFR 26.267 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... transfer (EFT), as defined in paragraph (c) of this section, of such taxes during the succeeding calendar... make remittances by EFT. For purposes of this section, the dollar amount of tax liability is to be... to make remittances by EFT. (c) Electronic fund transfer or EFT means any transfer of funds,...

  16. 27 CFR 26.267 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... transfer (EFT), as defined in paragraph (c) of this section, of such taxes during the succeeding calendar... make remittances by EFT. For purposes of this section, the dollar amount of tax liability is to be... to make remittances by EFT. (c) Electronic fund transfer or EFT means any transfer of funds,...

  17. 27 CFR 26.267 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... transfer (EFT), as defined in paragraph (c) of this section, of such taxes during the succeeding calendar... make remittances by EFT. For purposes of this section, the dollar amount of tax liability is to be... to make remittances by EFT. (c) Electronic fund transfer or EFT means any transfer of funds,...

  18. 27 CFR 26.267 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... transfer (EFT), as defined in paragraph (c) of this section, of such taxes during the succeeding calendar... make remittances by EFT. For purposes of this section, the dollar amount of tax liability is to be... to make remittances by EFT. (c) Electronic fund transfer or EFT means any transfer of funds,...

  19. 49 CFR 225.37 - Magnetic media transfer and electronic submission.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 49 Transportation 4 2010-10-01 2010-10-01 false Magnetic media transfer and electronic submission..., AND INVESTIGATIONS § 225.37 Magnetic media transfer and electronic submission. (a) A railroad has the option of submitting the following reports, updates, and amendments by way of magnetic media...

  20. 49 CFR 225.37 - Optical media transfer and electronic submission.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 49 Transportation 4 2011-10-01 2011-10-01 false Optical media transfer and electronic submission..., AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. (a) A railroad has the option of submitting the following reports, updates, and amendments by way of optical media (CD-ROM),...

  1. 27 CFR 40.165a - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

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

  2. 27 CFR 41.115a - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

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

  3. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

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

  4. 27 CFR 40.357 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

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

  5. Distance dependence of electron transfer from liposome-embedded (alkanephosphocholine-porphinato) zinc

    SciTech Connect

    Tsuchida, E.; Kaneko, M.; Nishide, H.; Hoshino, M.

    1986-05-22

    (Alkanephosphocholine-porphinato)zinc forms a geometrically well-defined bilayer liposome with phospholipid. Electron transfer from the liposome-embedded (porphinato)zincs with different alkyl chain lengths to methylviologen present in the outer bulk solution is measured by laser flash photolysis: the intermolecular electron transfer was observed only when the porphyrin plane is located within 12 A from the surface.

  6. 41 CFR 102-118.70 - Must my agency make all payments via electronic funds transfer?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

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

  7. 41 CFR 102-118.70 - Must my agency make all payments via electronic funds transfer?

    Code of Federal Regulations, 2011 CFR

    2011-01-01

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

  8. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... commercial bank in making payment by electronic fund transfer (EFT) of such taxes during the succeeding... is required, by this section, to make remittances by EFT. For purposes of this section, the dollar... required to make remittances by EFT. (c) For the purposes of this section, (1) electronic fund transfer...

  9. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... commercial bank in making payment by electronic fund transfer (EFT) of such taxes during the succeeding... is required, by this section, to make remittances by EFT. For purposes of this section, the dollar... required to make remittances by EFT. (c) For the purposes of this section, (1) electronic fund transfer...

  10. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... commercial bank in making payment by electronic fund transfer (EFT) of such taxes during the succeeding... is required, by this section, to make remittances by EFT. For purposes of this section, the dollar... required to make remittances by EFT. (c) For the purposes of this section, (1) electronic fund transfer...

  11. 27 CFR 41.63 - Payment of tax by electronic fund transfer.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... commercial bank in making payment by electronic fund transfer (EFT) of such taxes during the succeeding... is required, by this section, to make remittances by EFT. For purposes of this section, the dollar... required to make remittances by EFT. (c) For the purposes of this section, (1) electronic fund transfer...

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

    PubMed

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

    2000-06-01

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

  13. Particle simulation of runaway electrons in rippled tokamaks with pellet suppression effects

    NASA Astrophysics Data System (ADS)

    Spong, D. A.; Carbajal Gomez, L.; Del-Castillo-Negrete, D.; Baylor, L.; Seal, S.

    2016-10-01

    Runaway electrons are of significant concern for large tokamak devices both due to gradual acceleration by the Ohmic heating field and the more rapid acceleration and avalanche production that can occur during major disruptions. We have developed a simulation model (KORCGC) that follows large number of runaway guiding center (GC) orbits, taking into account Coulomb collisions, impurities, synchrotron radiation, rippled (3D) fields, and electric field acceleration, including inductive effects. Applications to pellet suppression experiments have been made and show similar effects (current/energy decay rates) as the observations. The model uses a hybrid (MPI/OpenMP) design and shows excellent parallel scaling. The energy parameters of runaway pellet suppression and formation fit within the limits of the GC approximation and the longer timesteps allowed by GC facilitate modeling over relevant timescales. Simulations of impurity injection dissipation experiments on DIIID and ITER will be discussed. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy and by U.S. Department of Energy, Office of Science Contract No. DE-AC05-00OR2.

  14. Suppression of infrared absorption in nanostructured metals by controlling Faraday inductance and electron path length.

    PubMed

    Han, Sang Eon

    2016-02-08

    Nanostructured metals have been intensively studied for optical applications over the past few decades. However, the intrinsic loss of metals has limited the optical performance of the metal nanostructures in diverse applications. In particular, light concentration in metals by surface plasmons or other resonances causes substantial absorption in metals. Here, we avoid plasmonic excitations for low loss and investigate methods to further suppress loss in nanostructured metals. We demonstrate that parasitic absorption in metal nanostructures can be significantly reduced over a broad band by increasing the Faraday inductance and the electron path length. For an example structure, the loss is reduced in comparison to flat films by more than an order of magnitude over most of the very broad spectrum between short and long wavelength infrared. For a photodetector structure, the fraction of absorption in the photoactive material increases by two orders of magnitude and the photoresponsivity increases by 15 times because of the selective suppression of metal absorption. These findings could benefit many metal-based applications that require low loss such as photovoltaics, photoconductive detectors, solar selective surfaces, infrared-transparent defrosting windows, and other metamaterials.

  15. Electron temperature fluctuations changes associated with ELM suppression by RMP in DIII-D

    NASA Astrophysics Data System (ADS)

    Sung, C.; Wang, G.; Rhodes, T.; Peebles, W.

    2015-11-01

    New results in this presentation show an increase in broadband electron temperature fluctuations (T~e) during ELM suppression by resonant magnetic perturbations (RMP). This measurement is obtained via correlation ECE (CECE) near the top of the pedestal (ρ ~ 0.9 - 0.96). This T~e increase is significant, (>40%), and occurs after the ELM suppression but not between ELMS. This may imply an increase in thermal transport facilitated by the increased T~e levels. Considering that the changes in gradient scale length during ELMs with RMP are complicated, it is possible that the mechanism responsible for changing T~e is different compared to previously observed changes in ñe [G. R. McKee et al NF 2013]. This possibility, and the nature of the T~e , will be studied through profile analysis and linear gyrokinetic analysis using TGLF [J. E. Kinsey et al PoP 2008]. In addition, the relation between the T~e and an observed low frequency coherent mode will be investigated. Work supported by the US DOE under DE-FG02-08ER54984 and DE-FC02-04ER54698.

  16. Activated-ion electron transfer dissociation improves the ability of electron transfer dissociation to identify peptides in a complex mixture.

    PubMed

    Ledvina, Aaron R; Beauchene, Nicole A; McAlister, Graeme C; Syka, John E P; Schwartz, Jae C; Griep-Raming, Jens; Westphall, Michael S; Coon, Joshua J

    2010-12-15

    Using a modified electron transfer dissociation (ETD)-enabled quadrupole linear ion trap (QLT) mass spectrometer, we demonstrate the utility of IR activation concomitant with ETD ion-ion reactions (activated-ion ETD, AI-ETD). Analyzing 12 strong cation exchanged (SCX) fractions of a LysC digest of human cell protein extract using ETD, collision-activated dissociation (CAD), and AI-ETD, we find that AI-ETD generates 13 405 peptide spectral matches (PSMs) at a 1% false-discovery rate (1% FDR), surpassing both ETD (7 968) and CAD (10 904). We also analyze 12 SCX fractions of a tryptic digest of human cell protein extract and find that ETD produces 6 234 PSMs, AI-ETD 9 130 PSMs, and CAD 15 209 PSMs. Compared to ETD with supplemental collisional activation (ETcaD), AI-ETD generates ∼80% more PSMs for the whole cell lysate digested with trypsin and ∼50% more PSMs for the whole cell lysate digested with LysC.

  17. Suppressed decomposition of organometal halide perovskites by impermeable electron-extraction layers in inverted solar cells

    PubMed Central

    Brinkmann, K.O.; Zhao, J.; Pourdavoud, N.; Becker, T.; Hu, T.; Olthof, S.; Meerholz, K.; Hoffmann, L.; Gahlmann, T.; Heiderhoff, R.; Oszajca, M. F.; Luechinger, N. A.; Rogalla, D.; Chen, Y.; Cheng, B.; Riedl, T

    2017-01-01

    The area of thin-film photovoltaics has been overwhelmed by organometal halide perovskites. Unfortunately, serious stability concerns arise with perovskite solar cells. For example, methyl-ammonium lead iodide is known to decompose in the presence of water and, more severely, even under inert conditions at elevated temperatures. Here, we demonstrate inverted perovskite solar cells, in which the decomposition of the perovskite is significantly mitigated even at elevated temperatures. Specifically, we introduce a bilayered electron-extraction interlayer consisting of aluminium-doped zinc oxide and tin oxide. We evidence tin oxide grown by atomic layer deposition does form an outstandingly dense gas permeation barrier that effectively hinders the ingress of moisture towards the perovskite and—more importantly—it prevents the egress of decomposition products of the perovskite. Thereby, the overall decomposition of the perovskite is significantly suppressed, leading to an outstanding device stability. PMID:28067308

  18. Suppressed decomposition of organometal halide perovskites by impermeable electron-extraction layers in inverted solar cells

    NASA Astrophysics Data System (ADS)

    Brinkmann, K. O.; Zhao, J.; Pourdavoud, N.; Becker, T.; Hu, T.; Olthof, S.; Meerholz, K.; Hoffmann, L.; Gahlmann, T.; Heiderhoff, R.; Oszajca, M. F.; Luechinger, N. A.; Rogalla, D.; Chen, Y.; Cheng, B.; Riedl, T.

    2017-01-01

    The area of thin-film photovoltaics has been overwhelmed by organometal halide perovskites. Unfortunately, serious stability concerns arise with perovskite solar cells. For example, methyl-ammonium lead iodide is known to decompose in the presence of water and, more severely, even under inert conditions at elevated temperatures. Here, we demonstrate inverted perovskite solar cells, in which the decomposition of the perovskite is significantly mitigated even at elevated temperatures. Specifically, we introduce a bilayered electron-extraction interlayer consisting of aluminium-doped zinc oxide and tin oxide. We evidence tin oxide grown by atomic layer deposition does form an outstandingly dense gas permeation barrier that effectively hinders the ingress of moisture towards the perovskite and--more importantly--it prevents the egress of decomposition products of the perovskite. Thereby, the overall decomposition of the perovskite is significantly suppressed, leading to an outstanding device stability.

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

    NASA Astrophysics Data System (ADS)

    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

  20. Electron transfer catalysis with monolayer protected Au25 clusters

    NASA Astrophysics Data System (ADS)

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

    2012-08-01

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

  1. Bridge-mediated hopping or superexchange electron-transfer processes in bis(triarylamine) systems

    NASA Astrophysics Data System (ADS)

    Lambert, Christoph; Nöll, Gilbert; Schelter, Jürgen

    2002-09-01

    Hopping and superexchange are generally considered to be alternative electron-transfer mechanisms in molecular systems. In this work we used mixed-valence radical cations as model systems for the investigation of electron-transfer pathways. We show that substituents attached to a conjugated bridge connecting two triarylamine redox centres have a marked influence on the near-infrared absorption spectra of the corresponding cations. Spectral analysis, followed by evaluation of the electron-transfer parameters using the Generalized Mulliken-Hush theory and simulation of the potential energy surfaces, indicate that hopping and superexchange are not alternatives, but are both present in the radical cation with a dimethoxybenzene bridge. We found that the type of electron-transfer mechanism depends on the bridge-reorganization energy as well as on the bridge-state energy. Because superexchange and hopping follow different distance laws, our findings have implications for the design of new molecular and polymeric electron-transfer materials.

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

    PubMed

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

    2009-03-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    SciTech Connect

    Müller, Eric; Mahns, Benjamin; Büchner, Bernd; Knupfer, Martin

    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.

  5. SO2−· Electron Transfer Ion/Ion Reactions with Disulfide Linked Polypeptide Ions

    PubMed Central

    Chrisman, Paul A.; Pitteri, Sharon J.; Hogan, Jason M.; McLuckey, Scott A.

    2005-01-01

    Multiply-charged peptide cations comprised of two polypeptide chains (designated A and B) bound via a disulfide linkage have been reacted with SO2−· in an electrodynamic ion trap mass spectrometer. These reactions proceed through both proton transfer (without dissociation) and electron transfer (with and without dissociation). Electron transfer reactions are shown to give rise to cleavage along the peptide backbone, loss of neutral molecules, and cleavage of the cystine bond. Disulfide bond cleavage is the preferred dissociation channel and both Chain A (or B)—S· and Chain A (or B)—SH fragment ions are observed, similar to those observed with electron capture dissociation (ECD) of disulfide-bound peptides. Electron transfer without dissociation produces [M + 2H]+· ions, which appear to be less kinetically stable than the proton transfer [M + H]+ product. When subjected to collision-induced dissociation (CID), the [M + 2H]+· ions fragment to give products that were also observed as dissociation products during the electron transfer reaction. However, not all dissociation channels noted in the electron transfer reaction were observed in the CID of the [M + 2H]+· ions. The charge state of the peptide has a significant effect on both the extent of electron transfer dissociation observed and the variety of dissociation products, with higher charge states giving more of each. PMID:15914021

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

    SciTech Connect

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

    2012-03-01

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

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

    PubMed Central

    Kato, Yuki; Nagao, Ryo; Noguchi, Takumi

    2016-01-01

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

  8. 77 FR 50243 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-08-20

    ... course of business'' in the definition of ``remittance transfer provider,'' which determines whether a... in the United States to individuals and businesses in foreign countries. For covered transactions... providing remittance transfers in the ``normal course of business,'' and thus is a ``remittance...

  9. 77 FR 6310 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-02-07

    ... discontinue providing a small number of transfers per year to accommodate customers of its regular business... phrase ``normal course of business'' in the definition of ``remittance transfer provider.'' This... 1700 G Street, NW., Washington, DC 20006, on official business days between the hours of 10 a.m. and...

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

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

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

  11. Technique for suppressing the electronic offset drift of interferometric open-loop fiber optic gyroscopes.

    PubMed

    Bacurau, Rodrigo M; Spengler, Anderson W; Dante, Alex; Morais, Flávio J O; Duarte, Luis F C; Ribeiro, Luiz E B; Ferreira, Elnatan C

    2016-11-15

    A technique to eliminate the offset drift in the demodulator circuitry of open-loop interferometric fiber optic gyroscopes is presented. This technique employs a demodulation scheme that uses the area of the negative half-cycles of the output signal of a sinusoidally modulated gyroscope to obtain the angular velocity. We propose an electronic circuitry that periodically reverses the demodulator input, allowing for the acquisition of two samples of the gyroscope signal with the same magnitude and opposite polarities. The angular velocity is obtained from the subtraction of these two samples, suppressing the electronic offset. Experiments showed that the proposed method reduces the demodulator offset drift from 4.4 μV/°C to about 14 nV/°C, which is equivalent to a reduction, from 0.2 deg/h/°C to about 0.0006 deg/h/°C in the tested gyroscope. The proposed technique improved the bias stability of the tested gyroscope from 0.0162 to 0.0071 deg/h.

  12. Fine-Scale Zonal Flow Suppression of Electron Temperature Gradient Turbulence

    SciTech Connect

    Parker, S. E.; Kohut, J. J.; Chen, Y.; Lin, Z.; Hinton, F. L.; Lee, W. W.

    2006-11-30

    It is found in collisionless Electron Temperature Gradient (ETG) turbulence simulations that, while zonal flows are weak at early times, the zonal flows continue to grow algebraically (proportional to time). These fine-scale zonal flows have a radial wave number such that kr{rho}i > 1 and kr{rho}e < 1. Eventually, the zonal flows grow to a level that suppresses the turbulence due to ExB shearing. The final electron energy flux is found to be relatively low. These conclusions are based on particle convergence studies with adiabatic ion electrostatic flux-tube gyrokinetic {delta}f particle simulations run for long times. The Rosenbluth-Hinton random walk mechanism is given as an explanation for the long time build up of the zonal flow in ETG turbulence and it is shown that the generation is (k perpendicular {rho}e)2 smaller than for isomorphic Ion Temperature Gradient (ITG) problem. This mechanism for zonal flow generation here is different than the modulational instability mechanism for ITG turbulence. These results are important because previous results indicated zonal flows were unimportant for ETG turbulence. Weak collisional damping of the zonal flow is also shown to be a n important effect.

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

    PubMed

    Fukuzumi, Shunichi

    2015-04-21

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

  14. Transferable pseudoclassical electrons for aufbau of atomic ions.

    PubMed

    Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

    2014-06-05

    Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species.

  15. Influence of environment induced correlated fluctuations in electronic coupling on coherent excitation energy transfer dynamics in model photosynthetic systems

    NASA Astrophysics Data System (ADS)

    Huo, Pengfei; Coker, David F.

    2012-03-01

    Two-dimensional photon-echo experiments indicate that excitation energy transfer between chromophores near the reaction center of the photosynthetic purple bacterium Rhodobacter sphaeroides occurs coherently with decoherence times of hundreds of femtoseconds, comparable to the energy transfer time scale in these systems. The original explanation of this observation suggested that correlated fluctuations in chromophore excitation energies, driven by large scale protein motions could result in long lived coherent energy transfer dynamics. However, no significant site energy correlation has been found in recent molecular dynamics simulations of several model light harvesting systems. Instead, there is evidence of correlated fluctuations in site energy-electronic coupling and electronic coupling-electronic coupling. The roles of these different types of correlations in excitation energy transfer dynamics are not yet thoroughly understood, though the effects of site energy correlations have been well studied. In this paper, we introduce several general models that can realistically describe the effects of various types of correlated fluctuations in chromophore properties and systematically study the behavior of these models using general methods for treating dissipative quantum dynamics in complex multi-chromophore systems. The effects of correlation between site energy and inter-site electronic couplings are explored in a two state model of excitation energy transfer between the accessory bacteriochlorophyll and bacteriopheophytin in a reaction center system and we find that these types of correlated fluctuations can enhance or suppress coherence and transfer rate simultaneously. In contrast, models for correlated fluctuations in chromophore excitation energies show enhanced coherent dynamics but necessarily show decrease in excitation energy transfer rate accompanying such coherence enhancement. Finally, for a three state model of the Fenna-Matthews-Olsen light

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

    PubMed

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

    1999-06-01

    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 solvent reorganization energy are provided as a basis for understanding and interpreting a long-range electron transfer experiment. The difficulties and problems of the polaron treatment of long-range electron transfers are discussed, and suggestions for new experiments are made.

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

    PubMed

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

    2014-02-01

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

  18. Orexin gene transfer into the amygdala suppresses both spontaneous and emotion-induced cataplexy in orexin-knockout mice.

    PubMed

    Liu, Meng; Blanco-Centurion, Carlos; Konadhode, Roda Rani; Luan, Liju; Shiromani, Priyattam J

    2016-03-01

    Narcolepsy is a chronic sleep disorder linked to the loss of orexin-producing neurons in the hypothalamus. Cataplexy, a sudden loss of muscle tone during waking, is an important distinguishing symptom of narcolepsy and it is often triggered by strong emotions. The neural circuit underlying cataplexy attacks is not known, but is likely to involve the amygdala, a region implicated in regulating emotions. In mice models of narcolepsy, transfer of the orexin gene into surrogate neurons has been successful in ameliorating narcoleptic symptoms. However, it is not known whether this method also blocks cataplexy triggered by strong emotions. To examine this possibility, the gene encoding mouse prepro-orexin was transferred into amygdala neurons of orexin-knockout (KO) mice (rAAV-orexin; n = 8). Orexin-KO mice that did not receive gene transfer (no-rAAV; n = 7) or received only the reporter gene (rAAV-GFP; n = 7) served as controls. Three weeks later, the animal's sleep and behaviour were recorded at night (no-odour control night), followed by another recording at night in the presence of predator odour (odour night). Orexin-KO mice given the orexin gene transfer into surrogate amygdala neurons had significantly less spontaneous bouts of cataplexy, and predator odour did not induce cataplexy compared with control mice. Moreover, the mice with orexin gene transfer were awake more during the odour night. These results demonstrate that orexin gene transfer into amygdala neurons can suppress both spontaneous and emotion-induced cataplexy attacks in narcoleptic mice. It suggests that manipulating amygdala pathways is a potential strategy for treating cataplexy in narcolepsy.

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

    PubMed Central

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

    2013-01-01

    Molecules typically must point in specific relative directions to participate efficiently in energy transfer and reactions. For example, Förster energy transfer favors specific relative directions of each molecule’s transition dipole [Förster T (1948) Ann Phys 2(1-2):55–75] and electron transfer between gas-phase molecules often depends on the relative orientation of orbitals [Brooks PR, et al. (2007) J Am Chem Soc 129(50):15572–15580]. Surface chemical reactions can be many orders of magnitude faster than their gas-phase analogs, a fact that underscores the importance of surfaces for catalysis. One reason surface reactions can be so fast is the labile change of oxidation state that commonly takes place upon adsorption, a process involving electron transfer between a solid metal and an approaching molecule. By transferring electrons to or from the adsorbate, the process of bond weakening and/or cleavage is initiated, chemically activating the reactant [Yoon B, et al. (2005) Science 307(5708):403–407]. Here, we show that the vibrational relaxation of NO—an example of electronically nonadiabatic energy transfer that is driven by an electron transfer event [Gadzuk JW (1983) J Chem Phys 79(12):6341–6348]—is dramatically enhanced when the molecule approaches an Au(111) surface with the N atom oriented toward the surface. This represents a rare opportunity to investigate the steric influences on an electron transfer reaction happening at a surface. PMID:24127598

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

    NASA Astrophysics Data System (ADS)

    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

  1. A framework for modeling electroactive microbial biofilms performing direct electron transfer.

    PubMed

    Korth, Benjamin; Rosa, Luis F M; Harnisch, Falk; Picioreanu, Cristian

    2015-12-01

    A modeling platform for microbial electrodes based on electroactive microbial biofilms performing direct electron transfer (DET) is presented. Microbial catabolism and anabolism were coupled with intracellular and extracellular electron transfer, leading to biofilm growth and current generation. The model includes homogeneous electron transfer from cells to a conductive biofilm component, biofilm matrix conduction, and heterogeneous electron transfer to the electrode. Model results for Geobacter based anodes, both at constant electrode potential and in voltammetric (dynamic electrode potential) conditions, were compared to experimental data from different sources. The model can satisfactorily describe microscale (concentration, pH and redox gradients) and macroscale (electric currents, biofilm thickness) properties of Geobacter biofilms. The concentration of electrochemically accessible redox centers, here denominated as cytochromes, involved in the extracellular electron transfer, plays the key role and may differ between constant potential (300 mM) and dynamic potential (3mM) conditions. Model results also indicate that the homogeneous and heterogeneous electron transfer rates have to be within the same order of magnitude (1.2 s(-1)) for reversible extracellular electron transfer.

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

    PubMed

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

    2016-02-21

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

  3. 48 CFR 52.232-33 - Payment by Electronic Funds Transfer-Central Contractor Registration.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Government under this contract shall be made by electronic funds transfer (EFT), except as provided in... 48 Federal Acquisition Regulations System 2 2010-10-01 2010-10-01 false Payment by Electronic... CONTRACT CLAUSES Text of Provisions and Clauses 52.232-33 Payment by Electronic Funds...

  4. Electronic coherence and the kinetics of energy transfer in light-harvesting systems

    NASA Astrophysics Data System (ADS)

    Huo, Pengfei; Coker, David; Miller, Thomas

    Recent 2D-spectroscopy experiments have observed transient electronic coherence in natural and artificial light harvesting systems, which raises questions about the role of electronic coherence in facilitating excitation energy transfer (EET) processes. In this talk, we introduce the recently developed partial linearized path-integral (PLPI) method, which can accurately simulate exciton transfer dynamics across multiple reaction regimes, as well as reliably describe the electronic coherence among excitonic states. Further, we develop a strategy that enables the analysis of the relative impact of static and dynamic electronic coherence. With PLPI simulations, we find that energy transfer dynamics are almost entirely dominated by static coherence effects; dynamic coherence is found to cause only minor effects. These conclusions are consistent with the historical view that emphasizes the importance of energy-level alignment for efficient incoherent energy transfer,while suggesting a less important role for more exotic electronic coherence effects that have been recently emphasized.

  5. Intercalation of trioxatriangulenium ion in DNA: binding, electron transfer, x-ray crystallography, and electronic structure.

    PubMed

    Reynisson, Jóhannes; Schuster, Gary B; Howerton, Sheldon B; Williams, Loren Dean; Barnett, Robert N; Cleveland, Charles L; Landman, Uzi; Harrit, Niels; Chaires, Jonathan B

    2003-02-26

    Trioxatriangulenium ion (TOTA(+)) is a flat, somewhat hydrophobic compound that has a low-energy unoccupied molecular orbital. It binds to duplex DNA by intercalation with a preference for G-C base pairs. Irradiation of intercalated TOTA(+) causes charge (radical cation) injection that results in strand cleavage (after piperidine treatment) primarily at GG steps. The X-ray crystal structure of TOTA(+) intercalated in the hexameric duplex d[CGATCG](2) described here reveals that intercalation of TOTA(+) results in an unusually large extension of the helical rise of the DNA and that the orientation of TOTA(+) is sensitive to hydrogen-bonding interactions with backbone atoms of the DNA. Electronic structure calculations reveal no meaningful charge transfer from DNA to TOTA(+) because the lowest unoccupied molecular orbital of TOTA(+), (LUMO)(T), falls in the gap between the highest occupied molecular orbital, (HOMO)(D), and the (LUMO)(D) of the DNA bases. These calculations reveal the importance of backbone, water, and counterion interactions, which shift the energy levels of the bases and the intercalated TOTA(+) orbitals significantly. The calculations also show that the inserted TOTA(+) strongly polarizes the intercalation cavity where a sheet of excess electron density surrounds the TOTA(+).

  6. Electron donor-acceptor quenching and photoinduced electron transfer for coumarin dyes. Technical report, 1 January-31 October 1982

    SciTech Connect

    Jones, G. II; Griffin, S.F.; Choi, C.; Bergmark, W.R.

    1983-10-31

    The fluorescence of 7-aminocoumarins is quenched by a variety of organic electron donors or acceptors in acetonitrile. In general, donors with half-wave oxidation potentials less positive than 1.0 V vs SCE and acceptors with reduction potentials less negative than -1.5 V vs SCE are candidates for diffusion limited quenching of coumarin singlet states. Profiles of quenching rates are consistent with calculated free energies for electron transfer between excited coumarins and donors or acceptors. In flash photolysis experiments electron transfer for several dyes and quenchers (e.g., methyl viologen) is demonstrated. Relatively low yields of net electron transfer are consistently obtained due to inefficient ionic photodissociation via singlet quenching or a low yield of more photoactive coumarin triplets. Electrochemical properties of the coumarins have been investigated by cyclic voltammetry with the indications of reversible oxidation and irreversible reduction as important processes.

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

    PubMed

    Petrenko, Alexander; Stein, Matthias

    2015-10-29

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

  8. N-Nicotinoyl dopamine inhibits skin pigmentation by suppressing of melanosome transfer.

    PubMed

    Kim, Bora; Hwang, Jae Sung; Kim, Hyun-Soo

    2015-12-15

    We investigated the inhibitory effects of a niacinamide derivative, N-Nicotinoyl dopamine (NND) on melanogenesis. NND inhibits melanosome transfer in a normal human melanocyte-keratinocyte co-culture system and through phagocytic ability without affecting viability of cells while it did not show inhibitory effects of tyrosinase and melanin synthesis in B16F10 mouse melanoma cells. In addition, safety of NND was verified through performing neural stem cell morphology assay. Our findings indicate that NND may potentially be used for cosmetic industry for improvement of skin whitening and therapies related with several skin disorders, and the effect of NND may be acquired via reduction of melanosome transfer.

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

    PubMed

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

    2011-08-14

    Interfacial electron transfer (IET) dynamics in a 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine (DiD) dye molecule/indium tin oxide (ITO) film system have been probed at the ensemble and single-molecule levels. By comparing the difference in the external electric current (EEC) dependence of the fluorescence intensities and lifetimes of the ensembles and single molecules, it is shown that the single-molecule probe can effectively demonstrate IET dynamics. The backward electron transfer and electron transfer from the ground state induce single-molecule fluorescence quenching when an EEC is applied to the DiD/ITO film system.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  11. Proton-Coupled Electron-Transfer Processes in Ultrafast Time Domain: Evidence for Effects of Hydrogen-Bond Stabilization on Photoinduced Electron Transfer.

    PubMed

    Dey, Ananta; Dana, Jayanta; Aute, Sunil; Maity, Partha; Das, Amitava; Ghosh, Hirendra N

    2017-03-08

    The proton-coupled electron-transfer (PCET) reaction is investigated for a newly synthesized imidazole-anthraquinone biomimetic model with a photoactive Ru(II) -polypyridyl moiety that is covalently coupled to the imidazole fragment. Intramolecular H-bonding interactions between imidazole and anthraquinone moieties favor the PCET process; this can be correlated to an appreciable positive shift in the one-electron reduction potential of the coordinated anthraquinone moiety functionalized with the imidazole fragment. This can also be attributed to the low luminescence quantum yield of the Ru(II) -polypyridyl complex used. The dynamics of the intramolecular electron-transfer (ET) and PCET processes are studied by using femtosecond transient absorption spectroscopy. The steady-state spectroscopic studies and the results of the time-resolved absorption studies confirm that H-bonded water molecules play a major role in both ET and PCET dynamics as a proton relay in the excited state. The electron-transfer process is followed by a change in the H-bonding equilibrium between AQ and imidazole in acetonitrile solvent, and protonation of AQ(.-) by water leads to PCET in the presence of water. A slower forward and backward electron-transfer rate is observed in the presence of D2 O compared with that in H2 O. These results provide further experimental support for a detailed understanding of the PCET process.

  12. 75 FR 52485 - Electronic Funds Transfer of Depository Taxes; Correction

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-08-26

    ... Depository Taxes; Correction AGENCY: Internal Revenue Service (IRS), Treasury. ACTION: Correction to notice... Federal Register on Monday, August 23, 2010, relating to Federal tax deposits (FTDs) by Electronic...

  13. Role for bound water and CH-pi aromatic interactions in photosynthetic electron transfer.

    PubMed

    Sacksteder, Colette A; Bender, Shana L; Barry, Bridgette A

    2005-06-01

    Photosystem I (PSI) is one of two photosynthetic reaction centers present in plants, algae, and cyanobacteria and catalyzes the reduction of ferredoxin and the oxidation of cytochrome c or plastocyanin. The PSI primary chlorophyll donor, which is oxidized in the primary electron-transfer events, is a heterodimer of chl a and a' called P700. It has been suggested that protein relaxation accompanies light-induced electron transfer in this reaction center (Dashdorj, N.; Xu, W.; Martinsson, P.; Chitnis, P. R.; Savikhin, S. Biophys. J. 2004, 86, 3121. Kim, S.; Sacksteder, C. A.; Bixby, K. A.; Barry, B. A. Biochemistry 2001, 40, 15384). To investigate the details of electron transfer and relaxation events in PSI, we have employed several experimental approaches. First, we report a pH-dependent viscosity effect on P700+ reduction; this result suggests a role for proton transfer in the PSI electron-transfer reactions. Second, we find that changes in hydration alter the rate of P700+ reduction and the interactions of P700 with the protein environment. This result suggests a role for bound water in electron transfer to P700+. Third, we present evidence that deuteration of the tyrosine aromatic side chain perturbs the vibrational spectrum, associated with P700+ reduction. We attribute this result to a linkage between CH-pi interactions and electron transfer to P700+.

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

    PubMed Central

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

    2016-01-01

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

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

    SciTech Connect

    Neta, P.

    1995-02-01

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

  16. The Mechanism and Properties of Electron Transfer in the Biological Organism

    NASA Astrophysics Data System (ADS)

    Pang, Xiao-Feng

    2013-08-01

    The mechanism and properties of electron transfer along protein molecules at finite temperature T ≠ 0 in the life systems are studied using nonlinear theory of bio-energy transport and Green function method, in which the electrons are transferred from donors to acceptors in virtue of the supersound soliton excited by the energy released in ATP hydrolysis. The electron transfer is, in essence, a process of oxidation-reduction reaction. In this study we first give the Hamiltonian and wavefunction of the system and find out the soliton solution of the dynamical equation in the protein molecules with finite temperature, and obtain the dynamical coefficient of the electron transfer. The results show that the speed of the electron transfer is related to the velocity of motion of the soliton, distribution of electrons in the donor and acceptor as well as the interaction strength among them. We finally concluded the changed rule of electric current, arising from the electron transfer, with increasing time. These results are useful in molecular and chemical biology.

  17. Nanoparticle Facilitated Extracellular Electron Transfer in Microbial Fuel Cells

    DTIC Science & Technology

    2014-10-13

    KEYWORDS: Bacteria, facilitated electron transport, electrochemically active, iron sulfide, Shewanella Microbial fuel cells (MFCs) are capable of...to MFC technology is the unique capability of electrochemically active bacteria, such as Shewanella and Geobacter, to divert electrons from the... electrochemical studies also demonstra- ted that the current contribution from remote bacterial cells was significantly diminished at longer cell−electrode dis

  18. Theoretical study on the antioxidant properties of 2'-hydroxychalcones: H-atom vs. electron transfer mechanism.

    PubMed

    Xue, Yunsheng; Zheng, Youguang; Zhang, Ling; Wu, Wenya; Yu, Ding; Liu, Yi

    2013-09-01

    The free radical scavenging activity of six 2'-hydroxychalcones has been studied in gas phase and solvents using the density functional theory (DFT) method. The three main working mechanisms, hydrogen atom transfer (HAT), stepwise electron-transfer-proton-transfer (ET-PT) and sequential-proton-loss-electron-transfer (SPLET) have been considered. The O-H bond dissociation enthalpy (BDE), ionization potential (IP), proton affinity (PA) and electron transfer energy (ETE) parameters have been computed in gas phase and solvents. The theoretical results confirmed the important role of the B ring in the antioxidant properties of hydroxychalcones. In addition, the calculated results matched well with experimental values. The results suggested that HAT would be the most favorable mechanism for explaining the radical-scavenging activity of hydroxychalcone in gas phase, whereas SPLET mechanism is thermodynamically preferred pathway in aqueous solution.

  19. Suppression of Beam-Ion Instability in Electron Rings with Multi-Bunch Train Beam Fillings

    SciTech Connect

    Wang, L.; Cai, Y.; Raubenheimer, T.O.; Fukuma, H.; /KEK, Tsukuba

    2011-08-18

    The ion-caused beam instability in the future light sources and electron damping rings can be serious due to the high beam current and ultra-small emittance of picometer level. One simple and effective mitigation of the instability is a multi-bunch train beam filling pattern which can significantly reduce the ion density near the beam, and therefore reduce the instability growth rate up to two orders of magnitude. The suppression is more effective for high intensity beams with low emittance. The distribution and the field of trapped ions are benchmarked to validate the model used in the paper. The wake field of ion-cloud and the beam-ion instability is investigated both analytically and numerically. We derived a simple formula for the build-up of ion-cloud and instability growth rate with the multi-bunch-train filling pattern. The ion instabilities in ILC damping ring, SuperKEKB and SPEAR3 are used to compare with our analyses. The analyses in this paper agree well with simulations.

  20. Assessment of bitterness intensity and suppression effects using an Electronic Tongue

    NASA Astrophysics Data System (ADS)

    Legin, A.; Rudnitskaya, A.; Kirsanov, D.; Frolova, Yu.; Clapham, D.; Caricofe, R.

    2009-05-01

    Quantification of bitterness intensity and effectivness of bitterness suppression of a novel active pharmacological ingredient (API) being developed by GSK was performed using an Electronic Tongue (ET) based on potentiometric chemical sensors. Calibration of the ET was performed with solutions of quinine hydrochloride in the concentration range 0.4-360 mgL-1. An MLR calibration model was developed for predicting bitterness intensity expressed as "equivalent quinine concentration" of a series of solutions of quinine, bittrex and the API. Additionally the effectiveness of sucralose, mixture of aspartame and acesulfame K, and grape juice in masking the bitter taste of the API was assessed using two approaches. PCA models were produced and distances between compound containing solutions and corresponding placebos were calculated. The other approach consisted in calculating "equivalent quinine concentration" using a calibration model with respect to quinine concentration. According to both methods, the most effective taste masking was produced by grape juice, followed by the mixture of aspartame and acesulfame K.

  1. Suppression of stimulated Raman scattering due to localization of electron plasma wave in laser beam filaments

    SciTech Connect

    Sharma, Prerana; Sharma, R. P.

    2009-03-15

    The filamentation of the high power laser beam by taking off-axial contribution is investigated when ponderomotive nonlinearity is taken into account. The splitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays. It is observed that the weak electron plasma wave (EPW) propagating in the z direction is nonlinearly coupled in the modified filamentary regions of the laser beam. The semianalytical solution of the nonlinear coupled EPW equation in the presence of laser beam filaments has been found and it is observed that the nonlinear coupling between these two waves leads to localization of the EPW. Stimulated Raman scattering (SRS) of this EPW is studied and backreflectivity has been calculated. Further, the localization of EPW affects the eigenfrequency and damping of plasma wave. As a result of this, mismatch and modified enhanced Landau damping lead to the disruption of SRS process and a substantial reduction in the backreflectivity. For the typical laser beam and plasma parameters with wavelength ({lambda}=1064 nm), power flux ({approx_equal}10{sup 16} W cm{sup -2}), and plasma density (n/n{sub cr})=0.2; the backreflectivity was found to be suppressed by a factor of around 20%.

  2. Suppression of stimulated Raman scattering due to localization of electron plasma wave in laser beam filaments

    NASA Astrophysics Data System (ADS)

    Sharma, Prerana; Sharma, R. P.

    2009-03-01

    The filamentation of the high power laser beam by taking off-axial contribution is investigated when ponderomotive nonlinearity is taken into account. The splitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays. It is observed that the weak electron plasma wave (EPW) propagating in the z direction is nonlinearly coupled in the modified filamentary regions of the laser beam. The semianalytical solution of the nonlinear coupled EPW equation in the presence of laser beam filaments has been found and it is observed that the nonlinear coupling between these two waves leads to localization of the EPW. Stimulated Raman scattering (SRS) of this EPW is studied and backreflectivity has been calculated. Further, the localization of EPW affects the eigenfrequency and damping of plasma wave. As a result of this, mismatch and modified enhanced Landau damping lead to the disruption of SRS process and a substantial reduction in the backreflectivity. For the typical laser beam and plasma parameters with wavelength (λ =1064 nm), power flux (≈1016 W cm-2), and plasma density (n /ncr)=0.2; the backreflectivity was found to be suppressed by a factor of around 20%.

  3. Suppression of stimulated Raman scattering due to localization of electron plasma wave in laser beam filaments

    NASA Astrophysics Data System (ADS)

    Sharma, Prerana; Sharma, Rampal

    2009-11-01

    The filamentation of the high power laser beam by taking off-axial contribution is investigated when ponderomotive nonlinearity is taken into account. The splitted profile of the laser beam is obtained due to uneven focusing of the off-axial rays. It is observed that the weak electron plasma wave (EPW) propagating in the z direction is nonlinearly coupled in the modified filamentary regions of the laser beam. The semi-analytical solution of the nonlinear coupled EPW equation in the presence of laser beam filaments has been found and it is observed that the nonlinear coupling between these two waves leads to localization of the EPW. Stimulated Raman scattering (SRS) of this EPW is studied and back reflectivity has been calculated. Further, the localization of EPW affects the eigen frequency and damping of plasma wave. As a result of this, mismatch and modified enhanced Landau damping lead to the disruption of SRS process and a substantial reduction in the back reflectivity. For the typical laser beam and plasma parameters with wavelength (λ=1064nm), power flux ( 10^16 W cm-2), and plasma density (n/ncr) = 0.2; the back reflectivity was found to be suppressed by a factor of around 20%.

  4. [Long-range electron transfer in globular proteins by polaron excitation].

    PubMed

    Lakhno, V L; Chuev, G N

    1997-01-01

    Considering polaron model, we have calculated an electron state localized in the protein heme. Using these calculations: the electron density and electron energy, we estimated the self-exchange rate constant for cyt c (horse heart), its reorganization energy, matrix element, and dependence of this rate on the distance between hemes. The results are compared with the experimental data and other theoretical estimations. We discuss the role of polaron excitations in the long-range electron transfer in globular proteins.

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

    SciTech Connect

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

    2015-09-28

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

  6. An electron-transfer photochromic crystalline MOF accompanying photoswitchable luminescence in a host-guest system.

    PubMed

    Liu, Yu-Shuang; Luo, Yu-Hui; Li, Li; Zhang, Hong

    2017-03-23

    A new electron transfer type photoactive host-guest supramolecule was constructed by introducing (CH3)2NH2(+) cations to the MOF framework. The resulting compound 1 exhibits reversible photochromic property without using photochromic components, resulting from photoinduced electron-transfer between the electron-rich anionic framework and the electron-deficient guest ions. In addition, a photoluminescence "on/off switch" occurs during the coloration-decoloration process. The raw materials are non-poisonous and harmless, hence compound 1 may be more cost-effective, clean, and harmless to the heath than existing photochromic materials.

  7. Investigation of the Mechanism of Electron Capture and Electron Transfer Dissociation of Peptides with a Covalently Attached Free Radical Hydrogen Atom Scavenger.

    PubMed

    Sohn, Chang Ho; Yin, Sheng; Peng, Ivory; Loo, Joseph A; Beauchamp, J L

    2015-11-15

    The mechanisms of electron capture and electron transfer dissociation (ECD and ETD) are investigated by covalently attaching a free-radical hydrogen atom scavenger to a peptide. The 2,2,6,6-tetramethylpiperidin-l-oxyl (TEMPO) radical was chosen as the scavenger due to its high hydrogen atom affinity (ca. 280 kJ/mol) and low electron affinity (ca. 0.45 ev), and was derivatized to the model peptide, FQX(TEMPO)EEQQQTEDELQDK. The X(TEMPO) residue represents a cysteinyl residue derivatized with an acetamido-TEMPO group. The acetamide group without TEMPO was also examined as a control. The gas phase proton affinity (882 kJ/mol) of TEMPO is similar to backbone amide carbonyls (889 kJ/mol), minimizing perturbation to internal solvation and sites of protonation of the derivatized peptides. Collision induced dissociation (CID) of the TEMPO tagged peptide dication generated stable odd-electron b and y type ions without indication of any TEMPO radical induced fragmentation initiated by hydrogen abstraction. The type and abundance of fragment ions observed in the CID spectra of the TEMPO and acetamide tagged peptides are very similar. However, ECD of the TEMPO labeled peptide dication yielded no backbone cleavage. We propose that a labile hydrogen atom in the charge reduced radical ions is scavenged by the TEMPO radical moiety, resulting in inhibition of N-Cα backbone cleavage processes. Supplemental activation after electron attachment (ETcaD) and CID of the charge-reduced precursor ion generated by electron transfer of the TEMPO tagged peptide dication produced a series of b + H (b(H)) and y + H (y(H)) ions along with some c ions having suppressed intensities, consistent with stable O-H bond formation at the TEMPO group. In summary, the results indicate that ECD and ETD backbone cleavage processes are inhibited by scavenging of a labile hydrogen atom by the localized TEMPO radical moiety. This observation supports the conjecture that ECD and ETD processes involve long

  8. Design of a Molecular Memory Device: The Electron Transfer Shift Register Memory

    NASA Technical Reports Server (NTRS)

    Beratan, D.

    1993-01-01

    A molecular shift register memory at the molecular level is described. The memory elements consist of molecules can exit in either an oxidized or reduced state and the bits are shifted between the cells with photoinduced electron transfer reactions.

  9. Density Functional Reactivity Theory Characterizes Charge Separation Propensity in Proton-Coupled Electron Transfer Reactions

    SciTech Connect

    Liu, Shubin; Ess, Daniel H.; Schauer, Cynthia

    2011-04-20

    Proton-coupled electron transfer (PCET) reactions occur in many biological and artificial solar energy conversion processes. In these reactions the electron is often transferred to a site distant to the proton acceptor site. In this work, we employ the dual descriptor and the electrophilic Fukui function from density functional reactivity theory (DFRT) to characterize the propensity for an electron to be transferred to a site other than the proton acceptor site. The electrophilic regions of hydrogen bond or van der Waal reactant complexes were examined using these DFRT descriptors to determine the region of space to which the electron is most likely to be transferred. This analysis shows that in PCET reactions the electrophilic region of the reactant complex does not include the proton acceptor site.

  10. Determination of electron transfer kinetic parameters by fourier transform electrochemical impedance spectroscopic analysis.

    PubMed

    Chang, Byoung-Yong; Hong, Sung-Young; Yoo, Jung-Suk; Park, Su-Moon

    2006-10-05

    A new attempt to obtain electron transfer kinetic parameters at an electrified electrode/electrolyte interface using Fourier transform electrochemical impedance spectroscopic (FTEIS) analyses of small potential step chronoamperometric currents is presented. The kinetic parameters thus obtained allowed mass transport free voltammograms to be constructed in an overpotential region, where the diffusion limits the electron transfer reaction, using the Butler-Volmer (B-V) relation. The B-V voltammograms clearly distinguish electrode reactions that are not much different in their electron transfer kinetic parameters, thus showing very similar normal linear sweep voltammetric (SCV) behaviors. Electrochemical reduction of p-benzoquinone, which displays nearly the same SCV responses at a gold electrode regardless whether the electrode is covered by a thiolated beta-cyclodextrin self-assembled monolayer, was taken as an example for the demonstration. The results show that the two voltametrically similar systems display very different electron transfer characteristics.

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

    NASA Astrophysics Data System (ADS)

    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 μM 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.

  12. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... information that is required to make payment by electronic funds transfer (EFT) under any contract that results from this solicitation. This submission satisfies the requirement to provide EFT information...

  13. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... information that is required to make payment by electronic funds transfer (EFT) under any contract that results from this solicitation. This submission satisfies the requirement to provide EFT information...

  14. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... information that is required to make payment by electronic funds transfer (EFT) under any contract that results from this solicitation. This submission satisfies the requirement to provide EFT information...

  15. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... information that is required to make payment by electronic funds transfer (EFT) under any contract that results from this solicitation. This submission satisfies the requirement to provide EFT information...

  16. 48 CFR 52.232-38 - Submission of Electronic Funds Transfer Information with Offer.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... information that is required to make payment by electronic funds transfer (EFT) under any contract that results from this solicitation. This submission satisfies the requirement to provide EFT information...

  17. 77 FR 71035 - Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer (EFT...

    Federal Register 2010, 2011, 2012, 2013, 2014

    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...

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

    SciTech Connect

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

    2013-10-01

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

  19. Vectorial electron transfer in spatially ordered arrays. Progress report, January 1992--January 1993

    SciTech Connect

    Fox, M.A.

    1993-02-01

    Progress was made on synthesis of new materials for directional electron transfer (block copolymers and helical oligopeptides), preparation and characterization of anisotropic composites bearing organics and inorganics, electrocatalysis (redox-activated catalysts), and surface modifications of metals and semiconductors.

  20. 77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-08

    ... Fiscal Service Financial Management Service; Proposed Collection of Information: Electronic Transfer Account (ETA) Financial Agency Agreement AGENCY: Financial Management Service, Fiscal Service, Treasury. ACTION: Notice and Request for comments. SUMMARY: The Financial Management Service, as part of...

  1. COMPLETE SUPPRESSION OF THE M=2/N-1 NEOCLASSICAL TEARING MODE USING ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D

    SciTech Connect

    PETTY,CC; LAHAYE,LA; LUCE,TC; HUMPHREYS,DA; HYATT,AW; PRATER,R; STRAIT,EJ; WADE,MR

    2003-03-01

    A271 COMPLETE SUPPRESSION OF THE M=2/N-1 NEOCLASSICAL TEARING MODE USING ELECTRON CYCLOTRON CURRENT DRIVE ON DIII-D. The first suppression of the important and deleterious m=2/n=1 neoclassical tearing mode (NTM) is reported using electron cyclotron current drive (ECCD) to replace the ''missing'' bootstrap current in the island O-point. Experiments on the DIII-D tokamak verify the maximum shrinkage of the m=2/n=1 island occurs when the ECCD location coincides with the q = 2 surface. The DIII-D plasma control system is put into search and suppress mode to make small changes in the toroidal field to find and lock onto the optimum position, based on real time measurements of dB{sub {theta}}/dt, for complete m=2/n=1 NTM suppression by ECCD. The requirements on the ECCD for complete island suppression are well modeled by the modified Rutherford equation for the DIII-D plasma conditions.

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

    PubMed

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

    2015-12-22

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

  3. Electron transfer from humic substances to biogenic and abiogenic Fe(III) oxyhydroxide minerals.

    PubMed

    Piepenbrock, Annette; Schröder, Christian; Kappler, Andreas

    2014-01-01

    Microbial humic substance (HS) reduction and subsequent abiotic electron transfer from reduced HS to poorly soluble Fe(III) (oxyhydr)oxides, a process named electron shuttling, significantly increases microbial Fe(III) mineral reduction rates. However, the importance of electron shuttling in nature and notably the electron transfer from HS to biogenic Fe(III) (oxyhydr)oxides have thus far not been determined. In this study, we have quantified the rate and extent of electron transfer from reduced and nonreduced Pahokee Peat humic acids (PPHA) and fresh soil organic matter (SOM) extracts to both synthetic and environmentally relevant biogenic Fe(III) (oxyhydr)oxides. We found that biogenic Fe(III) minerals were reduced faster and to an equal or higher degree than their abiogenic counterparts. Differences were attributed to differences in crystallinity and the association of bacterial biomass with biogenic minerals. Compared to purified PPHA, SOM extract transferred fewer electrons per milligram of carbon and electron transfer was observed only to poorly crystalline ferrihydrite but not to more crystalline goethite. This indicates a difference in redox potential distribution of the redox-active functional groups in extracted SOM relative to the purified PPHA. Our results suggest that HS electron shuttling can also contribute to iron redox processes in environments where biogenic Fe(III) minerals are present.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    PubMed Central

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

    2015-01-01

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

  6. 76 FR 81019 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-27

    ...Title X of the Dodd-Frank Wall Street Reform and Consumer Protection Act (Dodd-Frank Act) transferred rulemaking authority for a number of consumer financial protection laws from seven Federal agencies to the Bureau of Consumer Financial Protection (Bureau) as of July 21, 2011. The Bureau is in the process of republishing the regulations implementing those laws with technical and conforming......

  7. 78 FR 30661 - Electronic Fund Transfers (Regulation E)

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-22

    ... involved in open network transfers may learn about each other's practices regarding fees or other matters..., even a large correspondent bank, attempting to learn and accurately disclose these fees. Relatedly... introductory language in Sec. 1005.30 states that ``for purposes of this subpart, the following...

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

    SciTech Connect

    Yang, Jin-Guo; Kam, Fong-Yu; Chua, Lay-Lay

    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.

  9. The Historian and Electronic Research: File Transfer Protocol (FTP).

    ERIC Educational Resources Information Center

    McCarthy, Michael J.

    1993-01-01

    Asserts that the Internet will become the academic communication medium for historians in the 1990s. Describes the "file transfer protocol" (FTP) access approach to the Internet and discusses its significant for historical research. Includes instructions for using FTP and a list of history-related FTP sites. (CFR)

  10. An in situ transmission electron microscope deformation study of the slip transfer mechanisms in metals

    SciTech Connect

    Lee, T.C.; Robertson, I.M.; Birnbaum, H.K. . Dept. of Materials Science and Engineering)

    1990-09-01

    The slip transfer mechanisms across grain boundaries in 310 stainless steel, high-purity aluminum, and a Ni-S alloy have been studied by using the in situ transmission electron microscope (TEM) deformation technique. Several interactions between mobile lattice dislocations and grain boundaries have been observed, including the transfer and generation of dislocations at grain boundaries and the nucleation and propagation of a grain boundary crack. Quantitative condition have been established to correctly predict the slip transfer mechanism.

  11. Electron Transfer Studies of Ruthenium(II) Complexes with Biologically Important Phenolic Acids and Tyrosine.

    PubMed

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

    2016-03-01

    The ruthenium(II) complexes having 2,2'-bipyridine and phenanthroline derivatives are synthesized and characterized. The photophysical properties of these complexes at pH 12.5 are studied. The electron transfer reaction of biologically important phenolic acids and tyrosine are studied using absorption, emission and transient absorption spectral techniques. Semiclassical theory is applied to calculate the rate of electron transfer between ruthenium(II) complexes and biologically important phenolic acids.

  12. 36 CFR 1235.48 - What documentation must agencies transfer with electronic records?

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... NARA Form 14097, Technical Description for Transfer of Electronic Records, for magnetic tape media, and... format and codes as transferred. (c) Digital geospatial data files. Digital geospatial data files must... digital geospatial data files can include metadata that conforms to the Federal Geographic Data...

  13. 12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... initiates a transfer to effect a provisional credit in accordance with § 205.11(c)(2)(ii). (iii) If the..., in the appropriate amount and within the applicable time period, in accordance with § 205.11(c)(2)(i... 12 Banks and Banking 2 2014-01-01 2014-01-01 false Electronic fund transfer service provider...

  14. 12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... initiates a transfer to effect a provisional credit in accordance with § 205.11(c)(2)(ii). (iii) If the..., in the appropriate amount and within the applicable time period, in accordance with § 205.11(c)(2)(i... 12 Banks and Banking 2 2012-01-01 2012-01-01 false Electronic fund transfer service provider...

  15. 12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... initiates a transfer to effect a provisional credit in accordance with § 205.11(c)(2)(ii). (iii) If the..., in the appropriate amount and within the applicable time period, in accordance with § 205.11(c)(2)(i... 12 Banks and Banking 2 2010-01-01 2010-01-01 false Electronic fund transfer service provider...

  16. 12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... initiates a transfer to effect a provisional credit in accordance with § 205.11(c)(2)(ii). (iii) If the..., in the appropriate amount and within the applicable time period, in accordance with § 205.11(c)(2)(i... 12 Banks and Banking 2 2013-01-01 2013-01-01 false Electronic fund transfer service provider...

  17. 12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... initiates a transfer to effect a provisional credit in accordance with § 205.11(c)(2)(ii). (iii) If the..., in the appropriate amount and within the applicable time period, in accordance with § 205.11(c)(2)(i... 12 Banks and Banking 2 2011-01-01 2011-01-01 false Electronic fund transfer service provider...

  18. 36 CFR 1235.50 - What specifications and standards for transfer apply to electronic records?

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ...-proprietary, published open standard maintained by or for a Federal, national, or international standards... standards for transfer apply to electronic records? 1235.50 Section 1235.50 Parks, Forests, and Public... NATIONAL ARCHIVES OF THE UNITED STATES Transfer Specifications and Standards § 1235.50 What...

  19. Amber suppression in Escherichia coli by unusual mitochondria-like transfer RNAs.

    PubMed

    Bourdeau, V; Steinberg, S V; Ferbeyre, G; Emond, R; Cermakian, N; Cedergren, R

    1998-02-17

    The "cloverleaf" base-pairing pattern was established as the structural paradigm of active tRNA species some 30 years ago. Nevertheless, this pattern does not accommodate the folding of certain mitochondrial tRNAs. For these recalcitrant tRNAs, we have proposed structures having from 5 to 10 base pairs in the anticodon stem rather than the canonical 6. The absence of these types of tRNAs in cytoplasmic translation systems, however, raises the possibility that they may not be bona fide alternate folding patterns for active tRNA molecules. For this reason, we have designed new tRNA genes based on our model of unusual mitochondrial tRNAs, having 7, 8, 9, and 10 base pairs in the anticodon stem with other modifications to the D-stem and connector regions. We show here that these synthetic genes produce tRNAs that actively suppress amber codons in vivo.

  20. Photoinduced Electron Transfer in DNA: Charge Shift Dynamics Between 8-Oxo-Guanine Anion and Adenine.

    PubMed

    Zhang, Yuyuan; Dood, Jordan; Beckstead, Ashley A; Li, Xi-Bo; Nguyen, Khiem V; Burrows, Cynthia J; Improta, Roberto; Kohler, Bern

    2015-06-18

    Femtosecond time-resolved IR spectroscopy is used to investigate the excited-state dynamics of a dinucleotide containing an 8-oxoguanine anion at the 5'-end and neutral adenine at the 3'-end. UV excitation of the dinucleotide transfers an electron from deprotonated 8-oxoguanine to its π-stacked neighbor adenine in less than 1 ps, generating a neutral 8-oxoguanine radical and an adenine radical anion. These species are identified by the excellent agreement between the experimental and calculated IR difference spectra. The quantum efficiency of this ultrafast charge shift reaction approaches unity. Back electron transfer from the adenine radical anion to the 8-oxguanine neutral radical occurs in 9 ps, or approximately 6 times faster than between the adenine radical anion and the 8-oxoguanine radical cation (Zhang, Y. et al. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 11612-11617). The large asymmetry in forward and back electron transfer rates is fully rationalized by semiclassical nonadiabatic electron transfer theory. Forward electron transfer is ultrafast because the driving force is nearly equal to the reorganization energy, which is estimated to lie between 1 and 2 eV. Back electron transfer is highly exergonic and takes place much more slowly in the Marcus inverted region.

  1. Evidence for concerted pathways in ion-pairing coupled electron transfers.

    PubMed

    Savéant, Jean-Michel

    2008-04-09

    Ion-pairing with electro-inactive metal ions may change drastically the thermodynamic and kinetic reactivity of electron transfer in chemical and biochemical processes. Besides the classical stepwise pathways (electron-transfer first, followed by ion-pairing or vice versa), ion-pairing may also occur concertedly with electron transfer. The latter pathway avoids high-energy intermediates but a key issue is that of the kinetic price to pay to benefit from this thermodynamic advantage. A model is proposed leading to activation/driving force relationships characterizing such concerted associative electron transfers for intermolecular and intramolecular homogeneous reactions and for electrochemical reactions. Contrary to previous assertions, the driving force of the reaction (defined as the opposite of the reaction standard free energy), as well as the intrinsic barrier, does not depend on the concentration of the ion-pairing agent, which simply plays the role of one of the reactants. Besides solvent and intramolecular reorganization, the energy of the bond being formed is the main component of the intrinsic barrier. Application of these considerations to reactions reported in recent literature illustrates how concerted ion-pairing electron-transfer reactions can be diagnosed and how competition between stepwise and concerted pathways can be analyzed. It provided the first experimental evidence of the viability of concerted ion-pairing electron-transfer reactions.

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

    PubMed Central

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

    2014-01-01

    Bioelectrochemical systems (BESs) share the principle of the microbially catalyzed anodic substrate oxidation. Creating an electrode interface to promote extracellular electron transfer from microbes to electrode and understanding such mechanisms are crucial for engineering BESs. In this study, significantly promoted electron transfer and a 10-times increase in current generation in a BES were achieved by the utilization of carbon nanotube (CNT) network, compared with carbon paper. The mechanisms for the enhanced current generation with the CNT network were elucidated with both experimental approach and molecular dynamic simulations. The fabricated CNT network was found to be able to substantially enhance the interaction between the c-type cytochromes and solid electron acceptor, indicating that the direct electron transfer from outer-membrane decaheme c-type cytochromes to electrode might occur. The results obtained in this study will benefit for the optimized design of new materials to target the outer membrane proteins for enhanced electron exchanges. PMID:24429552

  3. A new semiclassical decoupling scheme for electronic transitions in molecular collisions - Application to vibrational-to-electronic energy transfer

    NASA Technical Reports Server (NTRS)

    Lee, H.-W.; Lam, K. S.; Devries, P. L.; George, T. F.

    1980-01-01

    A new semiclassical decoupling scheme (the trajectory-based decoupling scheme) is introduced in a computational study of vibrational-to-electronic energy transfer for a simple model system that simulates collinear atom-diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic-energy separation (lambda), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate-based decoupling scheme) failed. Interference effects are not exhibited in P vs lambda results.

  4. Axonal and synaptic failure suppress the transfer of firing rate oscillations, synchrony and information during high frequency deep brain stimulation.

    PubMed

    Rosenbaum, Robert; Zimnik, Andrew; Zheng, Fang; Turner, Robert S; Alzheimer, Christian; Doiron, Brent; Rubin, Jonathan E

    2014-02-01

    High frequency deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a widely used treatment for Parkinson's disease, but its effects on neural activity in basal ganglia circuits are not fully understood. DBS increases the excitation of STN efferents yet decouples STN spiking patterns from the spiking patterns of STN synaptic targets. We propose that this apparent paradox is resolved by recent studies showing an increased rate of axonal and synaptic failures in STN projections during DBS. To investigate this hypothesis, we combine in vitro and in vivo recordings to derive a computational model of axonal and synaptic failure during DBS. Our model shows that these failures induce a short term depression that suppresses the synaptic transfer of firing rate oscillations, synchrony and rate-coded information from STN to its synaptic targets. In particular, our computational model reproduces the widely reported suppression of parkinsonian β oscillations and synchrony during DBS. Our results support the idea that short term depression is a therapeutic mechanism of STN DBS that works as a functional lesion by decoupling the somatic spiking patterns of STN neurons from spiking activity in basal ganglia output nuclei.

  5. Adeno-associated virus-mediated human IL-10 gene transfer suppresses the development of experimental autoimmune orchitis.

    PubMed

    Watanabe, M; Kashiwakura, Y; Kusumi, N; Tamayose, K; Nasu, Y; Nagai, A; Shimada, T; Daida, H; Kumon, H

    2005-07-01

    Testicular germ cell-induced autoimmune orchitis is characterized by inflammatory cell infiltration followed by disturbance of spermatogenesis. Experimental autoimmune orchitis (EAO) is an animal model for human immunological male infertility; delayed-type hypersensitivity (DTH) response plays a key role in its induction. Interleukin-10 (IL-10) is a regulatory cytokine that is critical in preventing organ-specific autoimmune inflammation. To determine the effects on EAO of human IL-10 (hIL-10) gene transfer, C3H/He mice immunized by unilateral testicular injury were administered intramuscular (i.m.) injections of adeno-associated viral (AAV) vector-encoding hIL-10 on the day of immunization. Serum hIL-10 was detected beginning at 1 week postinjection, and peaked at 3 weeks. Histological examinations showed a significantly low incidence of orchitis and disturbance of spermatogenesis in AAV hIL-10-treated mice, and the DTH response to autologous testicular cells was significantly suppressed. Immunohistochemical analysis of IFN- and IL-2, T-cell-associated cytokines, in the spleen and testes revealed significantly fewer cytokine-expressing cells after treatment. We conclude that a single i.m. administration of AAV hIL-10 significantly suppresses EAO and hypospermatogenesis by regulating cell-mediated immunity in the testes.

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

    PubMed Central

    Liu, Jian; McLuckey, Scott A.

    2012-01-01

    The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

  7. The dipole moment of the electron carrier adrenodoxin is not critical for redox partner interaction and electron transfer.

    PubMed

    Hannemann, Frank; Guyot, Arnaud; Zöllner, Andy; Müller, Jürgen J; Heinemann, Udo; Bernhardt, Rita

    2009-07-01

    Dipole moments of proteins arise from helical dipoles, hydrogen bond networks and charged groups at the protein surface. High protein dipole moments were suggested to contribute to the electrostatic steering between redox partners in electron transport chains of respiration, photosynthesis and steroid biosynthesis, although so far experimental evidence for this hypothesis was missing. In order to probe this assumption, we changed the dipole moment of the electron transfer protein adrenodoxin and investigated the influence of this on protein-protein interactions and electron transfer. In bovine adrenodoxin, the [2Fe-2S] ferredoxin of the adrenal glands, a dipole moment of 803 Debye was calculated for a full-length adrenodoxin model based on the Adx(4-108) and the wild type adrenodoxin crystal structures. Large distances and asymmetric distribution of the charged residues in the molecule mainly determine the observed high value. In order to analyse the influence of the resulting inhomogeneous electric field on the biological function of this electron carrier the molecular dipole moment was systematically changed. Five recombinant adrenodoxin mutants with successively reduced dipole moment (from 600 to 200 Debye) were analysed for their redox properties, their binding affinities to the redox partner proteins and for their function during electron transfer-dependent steroid hydroxylation. None of the mutants, not even the quadruple mutant K6E/K22Q/K24Q/K98E with a dipole moment reduced by about 70% showed significant changes in the protein function as compared with the unmodified adrenodoxin demonstrating that neither the formation of the transient complex nor the biological activity of the electron transfer chain of the endocrine glands was affected. This is the first experimental evidence that the high dipole moment observed in electron transfer proteins is not involved in electrostatic steering among the proteins in the redox chain.

  8. A dynamic periplasmic electron transfer network enables respiratory flexibility beyond a thermodynamic regulatory regime

    PubMed Central

    Sturm, Gunnar; Richter, Katrin; Doetsch, Andreas; Heide, Heinrich; Louro, Ricardo O; Gescher, Johannes

    2015-01-01

    Microorganisms show an astonishing versatility in energy metabolism. They can use a variety of different catabolic electron acceptors, but they use them according to a thermodynamic hierarchy, which is determined by the redox potential of the available electron acceptors. This hierarchy is reflected by a regulatory machinery that leads to the production of respiratory chains in dependence of the availability of the corresponding electron acceptors. In this study, we showed that the γ-proteobacterium Shewanella oneidensis produces several functional electron transfer chains simultaneously. Furthermore, these chains are interconnected, most likely with the aid of c-type cytochromes. The cytochrome pool of a single S. oneidensis cell consists of ca. 700 000 hemes, which are reduced in the absence on an electron acceptor, but can be reoxidized in the presence of a variety of electron acceptors, irrespective of prior growth conditions. The small tetraheme cytochrome (STC) and the soluble heme and flavin containing fumarate reductase FccA have overlapping activity and appear to be important for this electron transfer network. Double deletion mutants showed either delayed growth or no growth with ferric iron, nitrate, dimethyl sulfoxide or fumarate as electron acceptor. We propose that an electron transfer machinery that is produced irrespective of a thermodynamic hierarchy not only enables the organism to quickly release catabolic electrons to a variety of environmental electron acceptors, but also offers a fitness benefit in redox-stratified environments. PMID:25635641

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

    NASA Astrophysics Data System (ADS)

    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.

  10. Design of photoactive ruthenium complexes to study electron transfer and proton pumping in cytochrome oxidase.

    PubMed

    Durham, Bill; Millett, Francis

    2012-04-01

    This review describes the development and application of photoactive ruthenium complexes to study electron transfer and proton pumping reactions in cytochrome c oxidase (CcO). CcO uses four electrons from Cc to reduce O(2) to two waters, and pumps four protons across the membrane. The electron transfer reactions in cytochrome oxidase are very rapid, and cannot be resolved by stopped-flow mixing techniques. Methods have been developed to covalently attach a photoactive tris(bipyridine)ruthenium group [Ru(II)] to Cc to form Ru-39-Cc. Photoexcitation of Ru(II) to the excited state Ru(II*), a strong reductant, leads to rapid electron transfer to the ferric heme group in Cc, followed by electron transfer to Cu(A) in CcO with a rate constant of 60,000s(-1). Ruthenium kinetics and mutagenesis studies have been used to define the domain for the interaction between Cc and CcO. New ruthenium dimers have also been developed to rapidly inject electrons into Cu(A) of CcO with yields as high as 60%, allowing measurement of the kinetics of electron transfer and proton release at each step in the oxygen reduction mechanism.

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

    PubMed

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

    2015-10-28

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

  12. Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production

    PubMed Central

    Horvath, Samantha; Fernandez, Laura E.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

    2012-01-01

    The design of molecular electrocatalysts for H2 oxidation and production is important for the development of alternative renewable energy sources that are abundant, inexpensive, and environmentally benign. Recently, nickel-based molecular electrocatalysts with pendant amines that act as proton relays for the nickel center were shown to effectively catalyze H2 oxidation and production. We developed a quantum mechanical approach for studying proton-coupled electron transfer processes in these types of molecular electrocatalysts. This theoretical approach is applied to a nickel-based catalyst in which phosphorous atoms are directly bonded to the nickel center, and nitrogen atoms of the ligand rings act as proton relays. The catalytic step of interest involves electron transfer between the nickel complex and the electrode as well as intramolecular proton transfer between the nickel and nitrogen atoms. This process can occur sequentially, with either the electron or proton transferring first, or concertedly, with the electron and proton transferring simultaneously without a stable intermediate. The electrochemical rate constants are calculated as functions of overpotential for the concerted electron-proton transfer reaction and the two electron transfer reactions in the sequential mechanisms. Our calculations illustrate that the concerted electron-proton transfer standard rate constant will increase as the equilibrium distance between the nickel and nitrogen atoms decreases and as the pendant amines become more flexible to facilitate the contraction of this distance with a lower energy penalty. This approach identifies the favored mechanisms under various experimental conditions and provides insight into the impact of substituents on the nitrogen and phosphorous atoms. PMID:22529352

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

    NASA Astrophysics Data System (ADS)

    Scharf, Christian; Klanner, Robert

    2015-04-01

    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. 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.

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

    PubMed

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

    2013-10-09

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

  15. Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols.

    PubMed

    Rhile, Ian J; Markle, Todd F; Nagao, Hirotaka; DiPasquale, Antonio G; Lam, Oanh P; Lockwood, Mark A; Rotter, Katrina; Mayer, James M

    2006-05-10

    Three phenols with pendant, hydrogen-bonded bases (HOAr-B) have been oxidized in MeCN with various one-electron oxidants. The bases are a primary amine (-CPh(2)NH(2)), an imidazole, and a pyridine. The product of chemical and quasi-reversible electrochemical oxidations in each case is the phenoxyl radical in which the phenolic proton has transferred to the base, (*)OAr-BH(+), a proton-coupled electron transfer (PCET) process. The redox potentials for these oxidations are lower than for other phenols, predominately from the driving force for proton movement. One-electron oxidation of the phenols occurs by a concerted proton-electron transfer (CPET) mechanism, based on thermochemical arguments, isotope effects, and DeltaDeltaG(++)/DeltaDeltaG degrees . The data rule out stepwise paths involving initial electron transfer to form the phenol radical cations [(*)(+)HOAr-B] or initial proton transfer to give the zwitterions [(-)OAr-BH(+)]. The rate constant for heterogeneous electron transfer from HOAr-NH(2) to a platinum electrode has been derived from electrochemical measurements. For oxidations of HOAr-NH(2), the dependence of the solution rate constants on driving force, on temperature, and on the nature of the oxidant, and the correspondence between the homogeneous and heterogeneous rate constants, are all consistent with the application of adiabatic Marcus theory. The CPET reorganization energies, lambda = 23-56 kcal mol(-)(1), are large in comparison with those for electron transfer reactions of aromatic compounds. The reactions are not highly non-adiabatic, based on minimum values of H(rp) derived from the temperature dependence of the rate constants. These are among the first detailed analyses of CPET reactions where the proton and electron move to different sites.

  16. The thermodynamics of charge transfer in DNA photolyase: using thermodynamic integration calculations to analyse the kinetics of electron transfer reactions.

    PubMed

    Krapf, Sebastian; Koslowski, Thorsten; Steinbrecher, Thomas

    2010-08-28

    DNA Photolyases are light sensitive oxidoreductases present in many organisms that participate in the repair of photodamaged DNA. They are capable of electron transfer between a bound cofactor and a chain of tryptophan amino acid residues. Due to their unique mechanism and important function, photolyases have been subject to intense study in recent times, with both experimental and computational efforts. In this work, we present a novel application of classical molecular dynamics based free energy calculations, combined with quantum mechanical computations, to biomolecular charge transfer. Our approach allows for the determination of all reaction parameters in Marcus' theory of charge transport. We were able to calculate the free energy profile for the movement of a positive charge along protein sidechains involved in the biomolecule's function as well as charge-transfer rates that are in good agreement with experimental results. Our approach to simulate charge-transfer reactions explicitly includes the influence of protein flexibility and solvent dynamics on charge-transfer energetics. As applied here to a biomolecular system of considerable scientific interest, we believe the method to be easily adaptable to the study of charge-transfer phenomena in biochemistry and other fields.

  17. Low frequency magnetic field suppression in an atomic spin co-magnetometer with a large electron magnetic field

    NASA Astrophysics Data System (ADS)

    Fang, Jiancheng; Chen, Yao; Zou, Sheng; Liu, Xuejing; Hu, Zhaohui; Quan, Wei; Yuan, Heng; Ding, Ming

    2016-03-01

    In a K-Rb-21Ne co-magnetometer, the Rb electron magnetic field which is experienced by the nuclear spin is about 100 times larger than that of the K in a K-3He co-magnetometer. The large electron magnetic field which is neglected in the K-3He co-magnetometer coupled Bloch equations model is considered here in the K-Rb-21Ne co-magnetometer to study the low frequency magnetic field suppression effect. Theoretical analysis and experimental results shows that in the K-Rb-21Ne spin co-magnetometer, not only the nuclear spin but also the large electron spin magnetic field compensate the external magnetic field noise. By comparison, only the 3He nuclear spins mainly compensate the external magnetic field noise in a K-3He co-magnetometer. With this study, in addition to just increasing the magnetic field of the nuclear spins, we can suppress the magnetic field noise by increasing the density of the electron spin. We also studied how the magnetic field suppression effect relates to the scale factor of the K-Rb-21Ne co-magnetometer and we compared the scale factor with that of the K-3He co-magnetometer. Lastly, we show the sensitivity of our co-magnetometer. The magnetic field noise, the air density fluctuation noise and pumping power optimization are studied to improve the sensitivity of the co-magnetometer.

  18. Classical model for electronically non-adiabatic collision processes resonance effects in electronic-vibrational energy transfer

    SciTech Connect

    Orel, Ann E.; Ali, Dominic P.; Miller, William H.

    1981-02-01

    In this paper, a classical model for electronically non-adiabatic collision processes is applied to E → V energy transfer in a collinear system, A + BC (v = 1) → A* + BC (v = 0), resembling Br-H2. Finally, the model, which treats electronic as well as translational, rotational, and vibrational degrees of freedom by classical mechanics, describes the resonance features in this process reasonably well.

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

    PubMed

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

    2011-05-24

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

  20. Mediation by indole analogues of electron transfer during oxygen activation in variants of Escherichia coli ribonucleotide reductase R2 lacking the electron-shuttling tryptophan 48.

    PubMed

    Saleh, Lana; Kelch, Brian A; Pathickal, Betsy A; Baldwin, Jeffrey; Ley, Brenda A; Bollinger, J Martin

    2004-05-25

    Activation of dioxygen by the carboxylate-bridged diiron(II) cluster in the R2 subunit of class I ribonucleotide reductase from Escherichia coli results in the one-electron oxidation of tyrosine 122 (Y122) to a stable radical (Y122*). A key step in this reaction is the rapid transfer of a single electron from a near-surface residue, tryptophan 48 (W48), to an adduct between O(2) and diiron(II) cluster to generate a readily reducible cation radical (W48(+)(*)) and the formally Fe(IV)Fe(III) intermediate known as cluster X. Previous work showed that this electron injection step is blocked in the R2 variant with W48 replaced by phenylalanine [Krebs, C., Chen, S., Baldwin, J., Ley, B. A., Patel, U., Edmondson, D. E., Huynh, B. H., and Bollinger, J. M., Jr. (2000) J. Am. Chem. Soc. 122, 12207-12219]. In this study, we show that substitution of W48 with alanine similarly disables the electron transfer (ET) but also permits its chemical mediation by indole compounds. In the presence of an indole mediator, O(2) activation in the R2-W48A variant produces approximately 1 equiv of stable Y122* and more than 1 equiv of the normal (micro-oxo)diiron(III) product. In the absence of a mediator, the variant protein generates primarily altered Fe(III) products and only one-fourth as much stable Y122* because, as previously reported for R2-W48F, most of the Y122* that is produced decays as a consequence of the inability of the protein to mediate reductive quenching of one of the two oxidizing equivalents of the initial diiron(II)-O(2) complex. Mediation of ET is effective in W48A variants containing additional substitutions that also impact the reaction mechanism or outcome. In the reaction of R2-W48A/F208Y, the presence of mediator suppresses formation of the Y208-derived diiron(III)-catecholate product (which is predominant in R2-F208Y in the absence of reductants) in favor of Y122*. In the reaction of R2-W48A/D84E, the presence of mediator affects the outcome of decay of the

  1. Distance dependence in photoinduced intramolecular electron transfer. Additional remarks and calculations

    NASA Astrophysics Data System (ADS)

    Larsson, Sven; Volosov, Andrey

    1987-12-01

    Rate constants for photoinduced intramolecular electron transfer are calculated for four of the molecules studied by Hush et al. The electronic factor is obtained in quantum chemical calculations using the CNDO/S method. The results agree reasonably well with experiments for the forward reaction. Possible reasons for the disagreement for the charge recombination process are offered.

  2. Computational studies of suppression of microwave gas breakdown by crossed dc magnetic field using electron fluid model

    NASA Astrophysics Data System (ADS)

    Zhao, Pengcheng; Guo, Lixin; Shu, Panpan

    2016-08-01

    The gas breakdown induced by a square microwave pulse with a crossed dc magnetic field is investigated using the electron fluid model, in which the accurate electron energy distribution functions are adopted. Simulation results show that at low gas pressures the dc magnetic field of a few tenths of a tesla can prolong the breakdown formation time by reducing the mean electron energy. With the gas pressure increasing, the higher dc magnetic field is required to suppress the microwave breakdown. The electric field along the microwave propagation direction generated due to the motion of electrons obviously increases with the dc magnetic field, but it is much less than the incident electric field. The breakdown predictions of the electron fluid model agree very well with the particle-in-cell-Monte Carlo collision simulations as well as the scaling law for the microwave gas breakdown.

  3. Plasmon Enhancement of Electronic Energy Transfer Between Quantum Dots on the Surface of Nanoporous Silica

    NASA Astrophysics Data System (ADS)

    Tikhomirova, N. S.; Myslitskaya, N. A.; Samusev, I. G.; Bryukhanov, V. V.

    2016-01-01

    We use spectral kinetic methods to study electronic energy transfer processes between semiconductor quantum dots on the surface of wide-pore silica in the absence of and in the presence of silver nanoparticles, obtained by laser ablation methods. We have determined the efficiencies of dipole-dipole energy transfer between two-shell (CdSe/CdS/ZnS) and one-shell (CdSe/ZnS) quantum dots on the surface, the luminescence lifetimes and quantum yields, transfer distances and transfer rate constants. We have studied enhancement of photoprocesses in individual quantum dots and in a pair under the influence of resonant localized plasmons of ablative silver nanoparticles.

  4. Experimental exploration of the Mulliken-Hush relationship for intramolecular electron transfer reactions.

    PubMed

    Mukherjee, Tamal; Ito, Naoki; Gould, Ian R

    2011-03-17

    The Mulliken-Hush (M-H) relationship provides the critical link between optical and thermal electron transfer processes, and yet very little direct experimental support for its applicability has been provided. Dicyanovinylazaadamantane (DCVA) represents a simple two-state (neutral/charge-transfer) intramolecular electron transfer system that exhibits charge-transfer absorption and emission spectra that are readily measurable in solvents with a wide range of polarities. In this regard it represents an ideal model system for studying the factors that control both optical charge separation (absorption) and recombination (emission) processes in solution. Here we explore the applicability of the M-H relation to quantitative descriptions of the optical charge-transfer processes in DCVA. For DCVA, the measured radiative rate constants exhibit a linear dependence on transition energy, and transition dipole moments exhibit an inverse dependence on transition energy, consistent with the M-H relationship.

  5. Suppression of electron emission from metal electrodes : LDRD 28771 final report.

    SciTech Connect

    Stygar, William A.; Savage, Mark Edward; Ives, Harry Crockett, III; Johnson, David J.; Fowler, William E.

    2003-11-01

    This research consisted of testing surface treatment processes for stainless steel and aluminum for the purpose of suppressing electron emission over large surface areas to improve the pulsed high voltage hold-off capabilities of these metals. Improvements to hold-off would be beneficial to the operation of the vacuum-insulator grading rings and final self-magnetically insulated transmission line on the ZR-upgrade machine and other pulsed power applications such as flash radiograph and pulsed-microwave machines. The treatments tested for stainless steel include the Z-protocol (chemical polish, HVFF, and gold coating), pulsed E-beam surface treatments by IHCE, Russia, and chromium oxide coatings. Treatments for aluminum were anodized and polymer coatings. Breakdown thresholds also were measured for a range of surface finishes and gap distances. The study found that: (1.) Electrical conditioning and solvent cleaning in a filtered air environment each improve HV hold-off 30%. (2.) Anodized coatings on aluminum give a factor of two improvement in high voltage hold-off. However, anodized aluminum loses this improvement when the damage is severe. Chromium oxide coatings on stainless steel give a 40% and 20% improvement in hold-off before and after damage from many arcs. (3.) Bare aluminum gives similar hold-off for surface roughness, R{sub a}, ranging from 0.08 to 3.2 {micro}m. (4.) The various EBEST surfaces tested give high voltage hold-off a factor of two better than typical machined and similar to R{sub a} = 0.05 {micro}m polished stainless steel surfaces. (5.) For gaps > 2 mm the hold-off voltage increases as the square root of the gap for bare metal surfaces. This is inconsistent with the accepted model for metals that involves E-field induced electron emission from dielectric inclusions. Micro-particles accelerated across the gap during the voltage pulse give the observed voltage dependence. However the similarity in observed breakdown times for large and small

  6. Kinetics of electron transfer through the respiratory chain.

    PubMed Central

    Jin, Qusheng; Bethke, Craig M

    2002-01-01

    We show that the rate at which electrons pass through the respiratory chain in mitochondria and respiring prokaryotic cells is described by the product of three terms, one describing electron donation, one acceptance, and a third, the thermodynamic drive. We apply the theory of nonequilibrium thermodynamics in the context of the chemiosmotic model of proton translocation and energy conservation. This approach leads to a closed-form expression that predicts steady-state electron flux as a function of chemical conditions and the proton motive force across the mitochondrial inner membrane or prokaryotic cytoplasmic membrane. The rate expression, derived considering reverse and forward electron flow, is the first to account for both thermodynamic and kinetic controls on the respiration rate. The expression can be simplified under specific conditions to give rate laws of various forms familiar in cellular physiology and microbial ecology. The expression explains the nonlinear dependence of flux on electrical potential gradient, its hyperbolic dependence on substrate concentration, and the inhibiting effects of reaction products. It provides a theoretical basis for investigating life under unusual conditions, such as microbial respiration in alkaline waters. PMID:12324402

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

    SciTech Connect

    Rinker, G.A.; Solem, J.G.; Biedenharn, L.C.

    1986-10-20

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

  8. Rates of primary electron transfer reactions in the photosystem I reaction center reconstituted with different quinones as the secondary acceptor

    SciTech Connect

    Kumazaki, Shigeichi; Kandori, Hideki; Yoshihara, Keitaro ); Iwaki, Masayo; Itoh, Shigeru ); Ikegamu, Isamu )

    1994-10-27

    Rates of sequential electron transfer reactions from the primary electron donor chlorophyll dimer (P700) to the electron acceptor chlorophyll a-686 (A[sub 0]) and to the secondary acceptor quinone (Q[sub [phi

  9. Length-dependence of intramolecular electron transfer in σ-bonded rigid molecular rods: an ab initio molecular orbital study

    NASA Astrophysics Data System (ADS)

    Pati, Ranjit; Karna, Shashi P.

    2002-01-01

    The dependence of electron transfer (ET) coupling element, VAB, on the length of rigid-rod-like systems consisting of bicyclo[1.1.1]pentane (BCP), cubane (CUB), and bicyclo[2.2.2]octane (BCO) monomers, has been investigated with the use of ab initio Hartree-Fock (HF) method employing Marcus-Hush two-state (TS) model. The value of VAB decreases exponentially with increase in the number of the cage units of the σ-bonded molecules. The calculated decay constant, β, shows good agreement with previously reported data. For molecular length⩾15 Å, the value of VAB becomes negligibly small, suggesting complete suppression of the through bond direct tunneling contribution to ET process.

  10. Electronic spectroscopy and energy transfer in cadmium selenide quantum dots and conjugated oligomers

    NASA Astrophysics Data System (ADS)

    Javier, Artjay

    The electronic excited state kinetics of CdSe quantum dots (QD) are studied through optical spectroscopy, by subjecting the quantum dots to different experimental conditions, as well as coupling them to phenylene-ethynylene oligomers. CdSe QDs feature a quantum-confined exciton state which pursues a variety of pathways once formed, such as band-edge recombination, charge separation by trapping at the dot surface, and electronic energy transfer (EnT). These phenomena are studied using different CdSe sizes, highlighting the effects of quantum confinement and surface energies on exciton decay. The size dependence of the exciton lifetime is studied, and correlation of the radiative lifetime to theoretical expectations are found, as well as evidence that nonradiative relaxation through crystal vibrations follows the Energy Gap Law and Marcus Inverted Region kinetics. A detailed analysis of the lifetime decays using the Maximum Entropy Method (MEM) reveal the presence of distributed, dual excited states, which are assigned to band-edge recombination and charged exciton decay. Complementary time-resolved PL allows for direct measurement of excited state populations, which changes dramatically upon addition of an inorganic capping layer to the QD, reflecting the suppression of surface carrier trapping. A strong excitation power-dependence of the photo-activated photoluminescence (PL) is correlated to the established observation of PL intermittency. Forming a hybrid nanocomposite of CdSe QDs and phenylene-ethynylene oligomers allows a detailed study of EnT between the organic phase and the inorganic phase, as well as complex energy migration kinetics within the organic phase. The size-dependent, and chain length-dependent EnT is found to arise from the spectral overlap dependence between the phases. Finally, CdSe QDs are mixed into phenylene-ethynylene oligomers at dopant-level concentrations to study the photo-induced phase transformations and subsequent electronic energy

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  12. Molecular view of an electron transfer process essential for iron–sulfur protein biogenesis

    PubMed Central

    Banci, Lucia; Bertini, Ivano; Calderone, Vito; Ciofi-Baffoni, Simone; Giachetti, Andrea; Jaiswal, Deepa; Mikolajczyk, Maciej; Piccioli, Mario; Winkelmann, Julia

    2013-01-01

    Biogenesis of iron–sulfur cluster proteins is a highly regulated process that requires complex protein machineries. In the cytosolic iron–sulfur protein assembly machinery, two human key proteins—NADPH-dependent diflavin oxidoreductase 1 (Ndor1) and anamorsin—form a stable complex in vivo that was proposed to provide electrons for assembling cytosolic iron–sulfur cluster proteins. The Ndor1–anamorsin interaction was also suggested to be implicated in the regulation of cell survival/death mechanisms. In the present work we unravel the molecular basis of recognition between Ndor1 and anamorsin and of the electron transfer process. This is based on the structural characterization of the two partner proteins, the investigation of the electron transfer process, and the identification of those protein regions involved in complex formation and those involved in electron transfer. We found that an unstructured region of anamorsin is essential for the formation of a specific and stable protein complex with Ndor1, whereas the C-terminal region of anamorsin, containing the [2Fe-2S] redox center, transiently interacts through complementary charged residues with the FMN-binding site region of Ndor1 to perform electron transfer. Our results propose a molecular model of the electron transfer process that is crucial for understanding the functional role of this interaction in human cells. PMID:23596212

  13. Hot-electron-transfer enhancement for the efficient energy conversion of visible light.

    PubMed

    Yu, Sungju; Kim, Yong Hwa; Lee, Su Young; Song, Hyeon Don; Yi, Jongheop

    2014-10-13

    Great strides have been made in enhancing solar energy conversion by utilizing plasmonic nanostructures in semiconductors. However, current generation with plasmonic nanostructures is still somewhat inefficient owing to the ultrafast decay of plasmon-induced hot electrons. It is now shown that the ultrafast decay of hot electrons across Au nanoparticles can be significantly reduced by strong coupling with CdS quantum dots and by a Schottky junction with perovskite SrTiO3 nanoparticles. The designed plasmonic nanostructure with three distinct components enables a hot-electron-assisted energy cascade for electron transfer, CdS→Au→SrTiO3, as demonstrated by steady-state and time-resolved photoluminescence spectroscopy. Consequently, hot-electron transfer enabled the efficient production of H2 from water as well as significant electron harvesting under irradiation with visible light of various wavelengths. These findings provide a new approach for overcoming the low efficiency that is typically associated with plasmonic nanostructures.

  14. Generalization of the Mulliken-Hush treatment for the calculation of electron transfer matrix elements

    NASA Astrophysics Data System (ADS)

    Cave, Robert J.; Newton, Marshall D.

    1996-01-01

    A new method for the calculation of the electronic coupling matrix element for electron transfer processes is introduced and results for several systems are presented. The method can be applied to ground and excited state systems and can be used in cases where several states interact strongly. Within the set of states chosen it is a non-perturbative treatment, and can be implemented using quantities obtained solely in terms of the adiabatic states. Several applications based on quantum chemical calculations are briefly presented. Finally, since quantities for adiabatic states are the only input to the method, it can also be used with purely experimental data to estimate electron transfer matrix elements.

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

    PubMed Central

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

    2004-01-01

    Peptide sequence analysis using a combination of gas-phase ion/ion chemistry and tandem mass spectrometry (MS/MS) is demonstrated. Singly charged anthracene anions transfer an electron to multiply protonated peptides in a radio frequency quadrupole linear ion trap (QLT) and induce fragmentation of the peptide backbone along pathways that are analogous to those observed in electron capture dissociation. Modifications to the QLT that enable this ion/ion chemistry are presented, and automated acquisition of high-quality, single-scan electron transfer dissociation MS/MS spectra of phosphopeptides separated by nanoflow HPLC is described. PMID:15210983

  16. Riboflavin-shuttled extracellular electron transfer from Enterococcus faecalis to electrodes in microbial fuel cells.

    PubMed

    Zhang, Enren; Cai, Yamin; Luo, Yue; Piao, Zhe

    2014-11-01

    Great attention has been focused on Gram-negative bacteria in the application of microbial fuel cells. In this study, the Gram-positive bacterium Enterococcus faecalis was employed in microbial fuel cells. Bacterial biofilms formed by E. faecalis ZER6 were investigated with respect to electricity production through the riboflavin-shuttled extracellular electron transfer. Trace riboflavin was shown to be essential for transferring electrons derived from the oxidation of glucose outside the peptidoglycan layer in the cell wall of E. faecalis biofilms formed on the surface of electrodes, in the absence of other potential electron mediators (e.g., yeast extract).

  17. Electron transfer and coupling in graphene-tungsten disulfide van der Waals heterostructures.

    PubMed

    He, Jiaqi; Kumar, Nardeep; Bellus, Matthew Z; Chiu, Hsin-Ying; He, Dawei; Wang, Yongsheng; Zhao, Hui

    2014-11-25

    The newly discovered two-dimensional materials can be used to form atomically thin and sharp van der Waals heterostructures with nearly perfect interface qualities, which can transform the science and technology of semiconductor heterostructures. Owing to the weak van der Waals interlayer coupling, the electronic states of participating materials remain largely unchanged. Hence, emergent properties of these structures rely on two key elements: electron transfer across the interface and interlayer coupling. Here we show, using graphene-tungsten disulfide heterostructures as an example, evidence of ultrafast and highly efficient interlayer electron transfer and strong interlayer coupling and control. We find that photocarriers injected in tungsten disulfide transfer to graphene in 1 ps and with near-unity efficiency. We also demonstrate that optical properties of tungsten disulfide can be effectively tuned by carriers in graphene. These findings illustrate basic processes required for using van der Waals heterostructures in electronics and photonics.

  18. Reaction electronic flux and its role in DNA intramolecular proton transfers.

    PubMed

    Durán, Rocío; Vöhringer-Martinez, Esteban; Toro-Labbé, Alejandro; Herrera, Bárbara

    2016-06-01

    Proton transfer reactions present a key step in many biological and chemical processes. Here, we focused on the electronic changes in the proton transfer reactions of the four DNA bases. In combination with the previous structural analysis the reaction electronic flux together with local descriptors as the Hirshfeld-I charges allow us to identify chemical events and rationalize the underlying reaction mechanism. Our results show that imine-enamine in adenine and citosyne, and keto-enol tautomerizations in thymine and guanine have different reaction mechanisms. The former involve net structural rearrangements driven by favoured electrostatic interactions between the proton and the acceptor atom whereas the keto-enol tautomerizations require electronic changes reflected in the reaction electronic flux and changes in the NBO bond orders which favour the proton transfer reaction.

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

    PubMed

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

    2014-08-07

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

  20. Direct observation of electron-to-hole energy transfer in CdSe quantum dots.

    PubMed

    Hendry, E; Koeberg, M; Wang, F; Zhang, H; de Mello Donegá, C; Vanmaekelbergh, D; Bonn, M

    2006-02-10

    We independently determine the subpicosecond cooling rates for holes and electrons in CdSe quantum dots. Time-resolved luminescence and terahertz spectroscopy reveal that the rate of hole cooling, following photoexcitation of the quantum dots, depends critically on the electron excess energy. This constitutes the first direct, quantitative measurement of electron-to-hole energy transfer, the hypothesis behind the Auger cooling mechanism proposed in quantum dots, which is found to occur on a 1 +/- 0.15 ps time scale.

  1. The transfer between electron bulk kinetic energy and thermal energy in collisionless magnetic reconnection

    SciTech Connect

    Lu, San; Lu, Quanming; Huang, Can; Wang, Shui

    2013-06-15

    By performing two-dimensional particle-in-cell simulations, we investigate the transfer between electron bulk kinetic and electron thermal energy in collisionless magnetic reconnection. In the vicinity of the X line, the electron bulk kinetic energy density is much larger than the electron thermal energy density. The evolution of the electron bulk kinetic energy is mainly determined by the work done by the electric field force and electron pressure gradient force. The work done by the electron gradient pressure force in the vicinity of the X line is changed to the electron enthalpy flux. In the magnetic island, the electron enthalpy flux is transferred to the electron thermal energy due to the compressibility of the plasma in the magnetic island. The compression of the plasma in the magnetic island is the consequence of the electromagnetic force acting on the plasma as the magnetic field lines release their tension after being reconnected. Therefore, we can observe that in the magnetic island the electron thermal energy density is much larger than the electron bulk kinetic energy density.

  2. Diffusion mass transfer in ionic materials under intense electron irradiation

    NASA Astrophysics Data System (ADS)

    Bochkarev, I. G.; Ghyngazov, S. A.; Frangulyan, T. S.; Petrova, A. B.; Chernyavskii, A. V.

    2017-01-01

    The results of studies on the impact of an electron beam with the energy of 1-2 MeV on diffusion processes in materials with ionic bonds are presented in the paper. Used electron beam intensity is allowed to provide heating of the material to temperatures of 1600 K. Diffusion of Na, Mg, Al ions into single crystals KBr in the temperature range 573-883 K, Al ions in the NiO-AlO system at 1373-1573 K, was studied. Diffusion annealing carried out under thermal and radiation-thermal heating of the samples. Then diffusion coefficients were determined. It was found stimulating action of irradiation on diffusion processes of Mg, Al ions in Kbr and Al ions in the NiO-Al2O3 system, which consists in increasing the diffusion coefficients at radiation-thermal annealing. The observed effect is achieved by increasing the effective rate of diffusion jumps.

  3. Electronic Energies for Neon Dimer Dication Radiative Charge Transfer

    DTIC Science & Technology

    1989-12-01

    E+ or E- symmetry, but Herzberg indicates that they are both E- The electronic energy levels shown can be verified by examining their values at large... Herzberg , Molecular Spectra and Molecular Structure: 1. Spectra of Diatomic Molecules, Second Ed., Princeton, New Jersey: D. Van Nostrand Company, Inc...tlerzherg, Gerhard , F.R.S. Molecular Spectra and Molecular Structure: 1. Spectra of Diatomic .M,,leculcs. Second Ed., Princeton, New Jersey: D. Van

  4. Electron transfer dynamics of Rhodothermus marinus caa3 cytochrome c domains on biomimetic films.

    PubMed

    Molinas, Maria F; De Candia, Ariel; Szajnman, Sergio H; Rodríguez, Juan B; Martí, Marcelo; Pereira, Manuela; Teixeira, Miguel; Todorovic, Smilja; Murgida, Daniel H

    2011-10-28

    The subunit II of the caa(3) oxygen reductase from Rhodothermus marinus contains, in addition to the Cu(A) center, a c-type heme group in the cytochrome c domain (Cyt-D) that is the putative primary electron acceptor of the enzyme. In this work we have combined surface-enhanced resonance Raman (SERR) spectroelectrochemistry, molecular dynamics (MD) simulations and electron pathway calculations to assess the most likely interaction domains and electron entry/exit points of the truncated Cyt-D of subunit II in the reactions with its electron donor, HiPIP and electron acceptor, Cu(A). The results indicate that the transient interaction between Cyt-D and HiPIP relies upon a delicate balance of hydrophobic and polar contacts for establishing an optimized electron transfer pathway that involves the exposed edge of the heme group and guaranties efficient inter-protein electron transfer on the nanosecond time scale. The reorganization energy of ca. 0.7 eV was determined by time-resolved SERR spectroelectrochemistry. The intramolecular electron transfer pathway in integral subunit II from Cyt-D to the Cu(A) redox center most likely involves the iron ligand histidine 20 as an electron exit point in Cyt-D.

  5. Observation of suppressed Auger mechanism in type-I quantum well structures with delocalized electron-hole wavefunctions

    SciTech Connect

    Hassani Nia, Iman; Fathipour, Vala; Mohseni, Hooman

    2015-08-15

    We report the first observation of non-threshold Auger mechanism for a quantum well structure with Type-I band alignment. Excitation-dependent photoluminescence measurements were used to extract the Auger recombination coefficients from 77 K up to room temperature. The results verify the role of interface mediated momentum exchange as well as suppression of Auger recombination for delocalized electron-hole wavefunctions.

  6. DFT/B3LYP study of the substituent effect on the reaction enthalpies of the individual steps of single electron transfer-proton transfer and sequential proton loss electron transfer mechanisms of phenols antioxidant action.

    PubMed

    Klein, Erik; Lukes, Vladimír

    2006-11-09

    The reaction enthalpies related to the individual steps of two phenolic antioxidants action mechanisms, single electron transfer-proton transfer (SET-PT) and sequential proton loss electron transfer (SPLET), for 30 meta and para-substituted phenols (ArOH) were calculated using DFT/B3LYP method. These mechanisms represent the alternative ways to the extensively studied hydrogen atom transfer (HAT) mechanism. Except the comparison of calculated reaction enthalpies with available experimental and/or theoretical values, obtained enthalpies were correlated with Hammett constants. We have found that electron-donating substituents induce the rise in the enthalpy of proton dissociation (PDE) from ArOH+* radical cation (second step in SET-PT) and in the proton affinities of phenoxide ions ArO- (reaction enthalpy of the first step in SPLET). Electron-withdrawing groups cause the increase in the reaction enthalpies of the processes where electron is abstracted, i.e., in the ionization potentials of ArOH (first step in SET-PT) and in the enthalpy of electron transfer from ArO- (second step in SPLET). Found results indicate that all dependences of reaction enthalpies on Hammett constants of the substituents are linear. The calculations of liquid-phase reaction enthalpies for several para-substituted phenols indicate that found trends hold also in water, although substituent effects are weaker. From the thermodynamic point of view, entering SPLET mechanism represents the most probable process in water.

  7. Current Theoretical Challenges in Proton-Coupled Electron Transfer: Electron-Proton Nonadiabaticity, Proton Relays, and Ultrafast Dynamics

    SciTech Connect

    Hammes-Schiffer, Sharon

    2011-06-16

    Proton-coupled electron transfer (PCET) reactions play an important role in a wide range of biological and chemical processes. The motions of the electrons, transferring protons, solute nuclei, and solvent nuclei occur on a wide range of timescales and are often strongly coupled. As a result, the theoretical description of these processes requires a combination of quantum and classical methods. This perspective discusses three of the current theoretical challenges in the field of PCET. The first challenge is the calculation of electron-proton nonadiabatic effects, which are significant for these reactions because the hydrogen tunneling is often faster than the electronic transition. The second challenge is the modeling of electron transfer coupled to proton transport along hydrogen-bonded networks. The third challenge is the simulation of the ultrafast dynamics of nonequilibrium photoinduced PCET reactions in solution. Insights provided by theoretical studies may assist in the design of more effective catalysts for energy conversion processes. The proton relay portion of this review is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

  8. Current Theoretical Challenges in Proton-Coupled Electron Transfer: Electron Proton Nonadiabaticity, Proton Relays, and Ultrafast Dynamics

    SciTech Connect

    Hammes-Schiffer, Sharon

    2011-06-16

    Proton-coupled electron transfer (PCET) reactions play an important role in a wide range of biological and chemical processes. The motions of the electrons, transferring protons, solute nuclei, and solvent nuclei occur on a wide range of time scales and are often strongly coupled. As a result, the theoretical description of these processes requires a combination of quantum and classical methods. This Perspective discusses three of the current theoretical challenges in the field of PCET. The first challenge is the calculation of electron proton nonadiabatic effects, which are significant for these reactions because the hydrogen tunneling is often faster than the electronic transition. The second challenge is the modeling of electron transfer coupled to proton transport along hydrogen-bonded networks. The third challenge is the simulation of the ultrafast dynamics of nonequilibrium photoinduced PCET reactions in solution. Insights provided by theoretical studies may assist in the design of more effective catalysts for energy conversion processes. The proton relay portion of this review is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  10. Electron-transfer and acid-base properties of a two-electron oxidized form of quaterpyrrole that acts as both an electron donor and an acceptor.

    PubMed

    Zhang, Min; E, Wenbo; Ohkubo, Kei; Sanchez-Garcia, David; Yoon, Dae-Wi; Sessler, Jonathan L; Fukuzumi, Shunichi; Kadish, Karl M

    2008-02-21

    Electron-transfer interconversion between the four-electron oxidized form of a quaterpyrrole (abbreviated as P4 for four pyrroles) and the two-electron oxidized form (P4H2) as well as between P4H2 and its fully reduced form (P4H4) bearing analogous substituents in the alpha- and beta-pyrrolic positions was studied by means of cyclic voltammetry and UV-visible spectroelectrochemistry combined with ESR and laser flash photolysis measurements. The two-electron oxidized form, P4H2, acts as both an electron donor and an electron acceptor. The radical cation (P4H2*+) and radical anion (P4H2*-) are both produced by photoinduced electron transfer from dimeric 1-benzyl-1,4-dihydronicotinamide to P4H2, whereas the cation radical form of the compound is also produced by electron-transfer oxidation of P4H2 with [Ru(bpy)3]3+. The ESR spectra of P4H2*+ and P4H2*- were recorded at low temperature and exhibit spin delocalization over all four pyrrole units. Thus, the two-electron oxidized form of the quaterpyrrole (P4H2) displays redox and electronic features analogous to those seen in the case of porphyrins and may be considered as a simple, open-chain model of this well-studied tetrapyrrolic macrocycle. The dynamics of deprotonation from P4H2*+ and disproportionation of P4H2 were examined by laser flash photolysis measurements of photoinduced electron-transfer oxidation and reduction of P4H2, respectively.

  11. Electronic promotion effect of double proton transfer on conduction of DNA through improvement of transverse electronic communication of base pairs

    NASA Astrophysics Data System (ADS)

    Liu, Haiying; Li, Genqin; Zhang, Laibin; Li, Jilai; Wang, Meishan; Bu, Yuxiang

    2011-10-01

    The effect of double proton transfer (DPT) on charge migration of DNA was investigated by the nonequilibrium Green's function method combined with density functional theory. The results revealed that DPT not only lowers ionization potentials, but also improves the delocalization of the localized π-orbitals at each base moiety through adjusting energy levels and spatial distributions of their molecular orbitals. Furthermore, DPT leads to both the strengthening of the second-order interactions of the Watson-Crick H-bond zones, and the promotion of the charge transfer transitions between two pairing bases in the UV absorption spectra. Electronic transport calculations indicated that DPT can improve the charge migration along the DNA duplex for specific sequences through enhancing transverse base-to-base electronic communication. This work will provide a new insight into the understanding of DNA charge conduction which can be electronically promoted or regulated by DPT.

  12. Rates of primary electron transfer in photosynthetic reaction centres and their mechanistic implications

    NASA Astrophysics Data System (ADS)

    Fleming, G. R.; Martin, J. L.; Breton, J.

    1988-05-01

    The conversion of light energy to chemical energy during photosyn-thesis involves the transfer of electrons between pigments embedded in a membrane protein. This process occurs with high quantum efficiency, the result of extremely fast electron transfer over a long distance preventing back transfer and energy loss. Recently the three-dimensional structures of the photosynthetic reaction centres of the bacteria Rhodopseudomonas viridis1 and Rhodobacter sphaeroides2 have been determined, allowing a molecular descrip-tion of the primary charge separation process. There are two symmetrically related branches of pigments in the structure (L and M), extending from the special pair of bacteriochlorophyll molecules (P) to the two bacteriopheophytins (HL and HM) via two bacteriochlorophylls (BLand BM). Many features of the electron transfer process are poorly understood, such as the nature of the excited states involved, the identity of the primary charge separation step and the roles of the protein and of B3-13. We have determined the rates of electron transfer in isolated reaction centre complexes of Rps. viridis and Rb. sphaeroides as a function of temperature. The rates increase as temperature is decreased, which may be due to either changes in electronic coupling of the pigments or changes in the population of coupled vibrational modes, or a combination of the two. We see no evidence of a B-L intermediate, which sets a lower limit on the rate of electron transfer from BL to HL. This is so high as to rule out transfer by two non-adiabatic steps.

  13. Tuning the Electronic Coupling and Electron Transfer in Mo2 Donor-Acceptor Systems by Variation of the Bridge Conformation.

    PubMed

    Kang, Mei Ting; Meng, Miao; Tan, Ying Ning; Cheng, Tao; Liu, Chun Y

    2016-02-24

    Assembling two quadruply bonded dimolybdenum units [Mo2 (DAniF)3 ](+) (DAniF=N,N'-di(p-anisyl)formamidinate) with 1,4-naphthalenedicarboxylate and its thiolated derivatives produced three complexes [{Mo2 (DAniF)3 }2 (μ-1,4-O2 CC10 H6 CO2 )], [{Mo2 (DAniF)3 }2 (μ-1,4-OSCC10 H6 COS)], and [{Mo2 (DAniF)3 }2 (μ-1,4-S2 CC10 H6 CS2 )]. In the X-ray structures, the naphthalene bridge deviates from the plane defined by the two Mo-Mo bond vectors with the torsion angle increasing as the chelating atoms of the bridging ligand vary from O to S. The mixed-valent species exhibit intervalence transition absorption bands with high energy and very low intensity. In comparison with the data for the phenylene analogues, the optically determined electronic coupling matrix elements (Hab =258-345 cm(-1) ) are lowered by a factor of two or more, and the electron-transfer rate constants (ket ≈10(11)  s(-1) ) are reduced by about one order of magnitude. These results show that, when the electron-transporting ability of the bridge and electron-donating (electron-accepting) ability of the donor (acceptor) are both variable, the former plays a dominant role in controlling the intramolecular electron transfer. DFT calculations revealed that increasing the torsion angle enlarges the HOMO-LUMO energy gap by elevating the (bridging) ligand-based LUMO energy. Therefore, our experimental results and theoretical analyses verify the superexchange mechanism for electronic coupling and electron transfer.

  14. Chlorophyll-quinone photochemical electron transfer in liposomes

    SciTech Connect

    Hurley, J.K.; Castelli, F.; Tollin, G.

    1981-09-01

    A study is described which involves the reduction of electron acceptors (quinones) by photoexcited chlorophyll (Chl). The experimental samples consisted of Chl a (from spinach) incorporated into phosphatidylcholine (either synthetic or from hen egg yolks) liposomes suspended in 10 mM phosphate buffer (pH 7.0). The quinones were either present during liposome formation or added later, depending on their water solubility. The measurement technique employed was laser flash photolysis. Results have provided considerable insight into the ways in which membranes may modify the photochemical properties of Chl by allowing molecular compartmentalization and by permitting cooperative interactions.

  15. Mapping the Long-Range Electron Transfer Route in Ligninolytic Peroxidases.

    PubMed

    Acebes, Sandra; Ruiz-Dueñas, Francisco J; Toubes, Mario; Saez-Jimenez, Veronica; Perez-Boada, Marta; Lucas, Maria Fatima; Martínez, Angel T; Guallar, Victor

    2017-04-04

    Combining a computational analysis with site-directed mutagenesis, we have studied the long-range electron transfer pathway in versatile and lignin peroxidases, two enzymes of biotechnological interest that play a key role for fungal degradation of lignin in plant biomass. The in silico study established two possible electron transfer routes starting at the surface tryptophan residue previously identified as responsible for oxidation of the bulky lignin polymer. Moreover, in both enzymes, a second buried tryptophan residue appears as a top electron transfer carrier, indicating the prevalence of one pathway. Site-directed mutagenesis of versatile peroxidase (from Pleurotus eryngii) allowed us to corroborate the computational analysis and the role played by the buried tryptophan (Trp244) and a neighbor phenylalanine residue (Phe198), together with the surface tryptophan, in the electron transfer. These three aromatic residues are highly conserved in all the sequences analyzed (up to a total of 169). The importance of the surface (Trp171) and buried (Trp251) tryptophan residues in lignin peroxidase has been also confirmed by directed mutagenesis of the Phanerochaete chrysosporium enzyme. Overall, the combined procedure identifies analogous electron transfer pathways in the long-range oxidation mechanism for both ligninolytic peroxidases, constituting a good example of how computational analysis avoids making extensive trial-error mutagenic experiments.

  16. Poisson-distributed electron-transfer dynamics from single quantum dots to C60 molecules.

    PubMed

    Song, Nianhui; Zhu, Haiming; Jin, Shengye; Zhan, Wei; Lian, Tianquan

    2011-01-25

    Functional quantum dot (QD)-based nanostructures are often constructed through the self-assembly of QDs with binding partners (molecules or other nanoparticles), a process that leads to a statistical distribution of the number of binding partners. Using single QD fluorescence spectroscopy, we probe this distribution and its effect on the function (electron-transfer dynamics) in QD-C60 complexes. Ensemble-averaged transient absorption and fluorescence decay as well as single QD fluorescence decay measurements show that the QD exciton emission was quenched by electron transfer from the QD to C60 molecules and the electron-transfer rate increases with the C60-to-QD ratio. The electron-transfer rate of single QD-C60 complexes fluctuates with time and varies among different QDs. The standard deviation increases linearly with the average of electron-transfer rates of single QD-C60 complexes, and the distributions of both quantities obey Poisson statistics. The observed distributions of single QD-C60 complexes and ensemble-averaged fluorescence decay kinetics can be described by a model that assumes a Poisson distribution of the number of adsorbed C60 molecules per QD. Our findings suggest that, in self-assembled QD nanostructures, the statistical distribution of the number of adsorbed partners can dominate the distributions of the averages and standard deviation of their interfacial dynamical properties.

  17. Photoinduced electron transfer in a protein-surfactant complex: probing the interaction of SDS with BSA.

    PubMed

    Chakraborty, Anjan; Seth, Debabrata; Setua, Palash; Sarkar, Nilmoni

    2006-08-24

    Photoinduced fluorescence quenching electron transfer from N,N-dimethyl aniline to different 7-amino coumarin dyes has been investigated in sodium dodecyl sulfate (SDS) micelles and in bovine serum albumin (BSA)-SDS protein-surfactant complexes using steady state and picosecond time resolved fluorescence spectroscopy. The electron transfer rate has been found to be slower in BSA-SDS protein-surfactant complexes compared to that in SDS micelles. This observation has been explained with the help of the "necklace-and-bead" structure formed by the protein-surfactant complex due to coiling of protein molecules around the micelles. In the correlation of free energy change to the fluorescence quenching electron transfer rate, we have observed that coumarin 151 deviates from the normal Marcus region, showing retardation in the electron transfer rate at higher negative free energy region. We endeavored to establish that the retardation in the fluorescence quenching electron transfer rate for coumarin 151 at higher free energy region is a result of slower rotational relaxation and slower translational diffusion of coumarin 151 (C-151) compared to its analogues coumarin 152 and coumarin 481 in micelles and in protein-surfactant complexes. The slower rotational relaxation and translational diffusion of C-151 are supposed to be arising from the different location of coumarin 151 compared to coumarin 152 and coumarin 481.

  18. Redox-linked conformation change and electron transfer between monoheme c-type cytochromes and oxides

    NASA Astrophysics Data System (ADS)

    Khare, Nidhi; Lovelace, David M.; Eggleston, Carrick M.; Swenson, Michael; Magnuson, Timothy S.

    2006-09-01

    Electron transfer between redox active proteins and mineral oxides is important in a variety of natural as well as technological processes, including electron transfer from dissimilatory metal-reducing bacteria to minerals. One of the pathways that could trigger electron transfer between proteins and minerals is redox-linked conformation change. We present electrochemical evidence that mitochondrial cytochrome c (Mcc) undergoes significant conformation change upon interaction with hematite and indium-tin oxide (ITO) surfaces. The apparent adsorption-induced conformation change causes the protein to become more reducing, which makes it able to transfer electrons to the hematite conduction band. Although Mcc is not a protein thought to be involved in interaction with mineral surfaces, it shares (or can be conformed so as to share) some characteristics with multiheme outer-membrane cytochromes thought to be involved in the transfer of electrons from dissimilatory iron-reducing bacteria to ferric minerals during respiration. We present evidence that a 10.1 kDa monohoeme cytochrome isolated and purified from Acidiphilium cryptum, with properties similar to those of Mcc, also undergoes conformation change as a result of interaction with hematite surfaces.

  19. 45 CFR 162.1603 - Operating rules for health care electronic funds transfers (EFT) and remittance advice transaction.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... transfers (EFT) and remittance advice transaction. 162.1603 Section 162.1603 Public Welfare Department of... REQUIREMENTS Health Care Electronic Funds Transfers (EFT) and Remittance Advice § 162.1603 Operating rules for health care electronic funds transfers (EFT) and remittance advice transaction. On and after January...

  20. Electron-transfer kinetics in cyanobacterial cells: methyl viologen is a poor inhibitor of linear electron flow.

    PubMed

    Sétif, Pierre

    2015-02-01

    The inhibitor methyl viologen (MV) has been widely used in photosynthesis to study oxidative stress. Its effects on electron transfer kinetics in Synechocystis sp. PCC6803 cells were studied to characterize its electron-accepting properties. For the first hundreds of flashes following MV addition at submillimolar concentrations, the kinetics of NADPH formation were hardly modified (less than 15% decrease in signal amplitude) with a significant signal decrease only observed after more flashes or continuous illumination. The dependence of the P700 photooxidation kinetics on the MV concentration exhibited a saturation effect at 0.3 mM MV, a concentration which inhibits the recombination reactions in photosystem I. The kinetics of NADPH formation and decay under continuous light with MV at 0.3 mM showed that MV induces the oxidation of the NADP pool in darkness and that the yield of linear electron transfer decreased by only 50% after 1.5-2 photosystem-I turnovers. The unexpectedly poor efficiency of MV in inhibiting NADPH formation was corroborated by in vitro flash-induced absorption experiments with purified photosystem-I, ferredoxin and ferredoxin-NADP(+)-oxidoreductase. These experiments showed that the second-order rate constants of MV reduction are 20 to 40-fold smaller than the competing rate constants involved in reduction of ferredoxin and ferredoxin-NADP(+)-oxidoreductase. The present study shows that MV, which accepts electrons in vivo both at the level of photosystem-I and ferredoxin, can be used at submillimolar concentrations to inhibit recombination reactions in photosystem-I with only a moderate decrease in the efficiency of fast reactions involved in linear electron transfer and possibly cyclic electron transfer.

  1. Effectiveness of perturbation theory approaches for computing non-condon electron transfer dynamics in condensed phases.

    PubMed

    Cook, William R; Coalson, Rob D; Evans, Deborah G

    2009-08-20

    A description of electron transfer in condensed-phase media requires models that adequately describe the coupling of the electronic degrees of freedom to the surrounding nuclear coordinates. The spin-boson model has been the canonical model used to understand quantum dynamic processes in condensed-phase media over the last 25 years. Inherent in the standard model of a two-state quantum system coupled to a bosonic bath is the assumption that the Condon approximation is valid. In this context, the Condon approximation assumes that the bath configurations (coordinates) have no effect on the nonadiabatic coupling matrix element. While this is a useful model for electron transfer in small molecular systems, the validity of this approximation is less likely when large-scale motions of solvent molecules are strongly coupled to the electron transfer event, e.g., in molecular clamps and long-range electron transfer in biopolymers. In the present paper a general model for two-state electron transfer which allows for system-bath coupling in both the diagonal and off-diagonal (nonadiabatic) terms is studied. Time-dependent perturbation theory for this Hamiltonian is developed using a small polaron transformation. As noted in several recent studies, in a certain regime of parameter space, the relevant Hamiltonian admits an exact solution, termed the exactly solvable non-Condon Hamiltonian (or NCE). This limit, for which exact solutions are available, is used to benchmark the short- and long-time accuracy of various perturbative approaches. The validated perturbation equations are subsequently used to explore the role of non-Condon effects on electron transfer by systematically increasing the strength of the non-Condon coupling term from zero (i.e., the canonical spin-boson model) to the value that pertains to the exactly solvable non-Condon model (where non-Condon effects are significant).

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

    NASA Astrophysics Data System (ADS)

    Mondal, Navendu; Paul, Sneha; Samanta, Anunay

    2016-07-01

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

  3. Hydrogen forms in water by proton transfer to a distorted electron.

    PubMed

    Marsalek, Ondrej; Frigato, Tomaso; VandeVondele, Joost; Bradforth, Stephen E; Schmidt, Burkhard; Schütte, Christof; Jungwirth, Pavel

    2010-01-21

    Solvated electrons are ubiquitous intermediates in radiation-induced processes, with their lifetime being determined by quenching processes, such as the direct reaction with protons under acidic conditions. Ab initio molecular dynamics simulations allow us to unravel with molecular resolution the ultrafast reaction mechanism by which the electron and proton react in water. The path to a successful reaction involves a distortion and contraction of the hydrated electron and a rapid proton motion along a chain of hydrogen bonds, terminating on the water molecule most protruding into the electron cloud. This fundamental reaction is thus decidedly shown to be of a proton-transfer rather than electron-transfer character. Due to the desolvation penalty connected with breaking of the hydration shells of these charged particles, the reaction is, however, not diffusion-limited, in agreement with the interpretation of kinetics measurements.

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

    SciTech Connect

    Khezri, Khezrollah; Roghani-Mamaqani, Hossein

    2014-11-15

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

  5. Distal [FeS]-Cluster Coordination in [NiFe]-Hydrogenase Facilitates Intermolecular Electron Transfer

    PubMed Central

    Petrenko, Alexander; Stein, Matthias

    2017-01-01

    Biohydrogen is a versatile energy carrier for the generation of electric energy from renewable sources. Hydrogenases can be used in enzymatic fuel cells to oxidize dihydrogen. The rate of electron transfer (ET) at the anodic side between the [NiFe]-hydrogenase enzyme distal iron–sulfur cluster and the electrode surface can be described by the Marcus equation. All parameters for the Marcus equation are accessible from Density Functional Theory (DFT) calculations. The distal cubane FeS-cluster has a three-cysteine and one-histidine coordination [Fe4S4](His)(Cys)3 first ligation sphere. The reorganization energy (inner- and outer-sphere) is almost unchanged upon a histidine-to-cysteine substitution. Differences in rates of electron transfer between the wild-type enzyme and an all-cysteine mutant can be rationalized by a diminished electronic coupling between the donor and acceptor molecules in the [Fe4S4](Cys)4 case. The fast and efficient electron transfer from the distal iron–sulfur cluster is realized by a fine-tuned protein environment, which facilitates the flow of electrons. This study enables the design and control of electron transfer rates and pathways by protein engineering. PMID:28067774

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

    PubMed Central

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

    2015-01-01

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

  7. A redox beginning: Which came first phosphoryl, acyl, or electron transfer ?. [Abstract only

    NASA Technical Reports Server (NTRS)

    Weber, Arthur L.

    1994-01-01

    Thermodynamic and kinetic information available on the synthesis of prebiotic monomers and polymers will be examined in order to illuminate the prebiotic plausibility of polymer syntheses based on (a) phosphoryl transfer that yields phosphodiester polymers, (b) acyl transfer that gives polyamides, and (c) electron transfer that produces polydisulfide or poly(thio)ester polymers. New experimental results on the oxidative polymerization of 2,3-dimercaptopropanol by ferric ions on the surface of ferric hydroxide oxide will be discussed as a chemical model of polymerization by electron transfer. This redox polymerization that yields polymers with a polydisulfide backbone was found to give oligomers up to the 15-mer from 1 mM of 2,3-dimercaptopropanol after one day at 25 C. High pressure liquid chromatography (HPLC) analysis of the oligomers was carried out on an Alltech OH-100 column eluted with acetonitrile-water.

  8. The impact of symmetric modes on intramolecular electron transfer: A semi-classical approach

    NASA Astrophysics Data System (ADS)

    Coropceanu, Veaceslav; Boldyrev, Sergei I.; Risko, Chad; Brédas, Jean-Luc

    2006-07-01

    We have generalized the Hush equations developed for the analysis of intervalence charge-transfer bands by including into the model the interaction with symmetric vibrations. Our results indicate that in symmetric class-II systems the maximum of the intervalence charge-transfer band is equal to the reorganization energy λ related to the antisymmetric vibrations as is the case in the conventional Hush model. In contrast, the corresponding transition dipole moment and the activation barrier for thermal electron transfer, in addition to their dependence on λ, also depend on the reorganization energy L related to symmetric vibrational modes. We show that the interaction with symmetric vibrational modes reduces the activation barrier and that the thermal electron-transfer rates derived on the basis of a Hush-type analysis of the optical data are generally underestimated.

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

    SciTech Connect

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

    2008-04-30

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

  10. Proton-Coupled Electron Transfer in Biology: Results from Synergistic Studies in Natural and Model Systems

    PubMed Central

    Reece, Steven Y.; Nocera, Daniel G.

    2015-01-01

    Proton-coupled electron transfer (PCET) underpins energy conversion in biology. PCET may occur with the unidirectional or bidirectional transfer of a proton and electron and may proceed synchronously or asynchronously. To illustrate the role of PCET in biology, this review presents complementary biological and model systems that explore PCET in electron transfer (ET) through hydrogen bonds [azurin as compared to donor-acceptor (D–A) hydrogen-bonded networks], the activation of C–H bonds [alcohol dehydrogenase and soybean lipoxygenase (SLO) as compared to Fe(III) metal complexes], and the generation and transport of amino acid radicals [photosystem II (PSII) and ribonucleotide reductase (RNR)as compared to tyrosine-modified photoactive Re(I) and Ru(II) complexes]. In providing these comparisons, the fundamental principles of PCET in biology are illustrated in a tangible way. PMID:19344235

  11. Theory and experiment on the cuprous-cupric electron transfer rate at a copper electrode

    NASA Astrophysics Data System (ADS)

    Halley, J. W.; Smith, B. B.; Walbran, S.; Curtiss, L. A.; Rigney, R. O.; Sutjianto, A.; Hung, N. C.; Yonco, R. M.; Nagy, Z.

    1999-04-01

    We describe results of experiment and theory of the cuprous-cupric electron transfer rate in an aqueous solution at a copper electrode. The methods are similar to those we reported earlier for the ferrous-ferric rate. The comparison strongly suggests that, in marked distinction to the ferrous-ferric case, the electron transfer reaction is adiabatic. The model shows that the activation barrier is dominated by the energy required for the ion to approach the electrode, rather than by the energy required for rearrangement of the solvation shell, also in sharp distinction to the case of the ferric-ferrous electron transfer at a gold electrode. Calculated activation barriers based on this image agree with the experimental results reported here.

  12. Studies of Photosynthetic Energy and Charge Transfer by Two-dimensional Fourier transform electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Ogilvie, Jennifer

    2010-03-01

    Two-dimensional (2D) Fourier transform electronic spectroscopy has recently emerged as a powerful tool for the study of energy transfer in complex condensed-phase systems. Its experimental implementation is challenging but can be greatly simplified by implementing a pump-probe geometry, where the two phase-stable collinear pump pulses are created with an acousto-optic pulse-shaper. This approach also allows the use of a continuum probe pulse, expanding the available frequency range of the detection axis and allowing studies of energy transfer and electronic coupling over a broad range of frequencies. We discuss several benefits of 2D electronic spectroscopy and present 2D data on the D1-D2 reaction center complex of Photosystem II from spinach. We discuss the ability of 2D spectroscopy to distinguish between current models of energy and charge transfer in this system.

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

    PubMed

    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.

  14. Subpicosecond time-resolved intramolecular electronic energy transfer in flexible bichromophoric Coumarin molecules

    SciTech Connect

    Kaschke, M.; Ernsting, N.P. ); Valeur, B.; Bourson, J. )

    1990-07-26

    By excite-and-probe spectroscopy with subpicosecond time resolution, the authors have measured the intramolecular electronic energy transfer in bichromophoric coumarins linked by a flexible polymethylene chain. The transfer proceeds on a time scale between 1 and 20 ps depending on the polymethylene chain length. The results can be well described by a dipole-dipole interaction model that takes into account the statistical distribution of intramolecular distances between the two chromophores.

  15. Effect of energy transfer from atomic electron shell to an α particle emitted by decaying nucleus

    NASA Astrophysics Data System (ADS)

    Igashov, S. Yu.; Tchuvil'sky, Yu. M.

    2016-12-01

    The process of energy transfer from the electron shell of an atom to an α particle propagating through the shell is formulated mathematically. Using the decay of the 226Ra nucleus as an example, it is demonstrated that this phenomenon increases the α-decay intensity in contrast with other known effects of similar type. Moreover, the α decay of the nucleus is more strongly affected by the energy transfer than by all other effects taken together.

  16. Femtosecond laser field induced modifications of electron-transfer processes in Ne{sup +}-He collisions

    SciTech Connect

    Lu Zhenzhong; Chen Deying; Fan Rongwei; Xia Yuanqin

    2012-01-02

    We demonstrate the presence of femtosecond laser induced charge transfer in Ne{sup +}-He collisions. Electron transfer in ion-atom collisions is considerably modified when the collision is embedded in a strong laser field with the laser intensity of {approx}10{sup 15} W/cm{sup 2}. The observed anisotropy of the He{sup +} angular distribution confirms the prediction of early work that the capture probability varies significantly with the laser polarization angle.

  17. Energy transfer enhancement by oxygen perturbation of spin-forbidden electronic transitions in aromatic systems

    NASA Astrophysics Data System (ADS)

    Monguzzi, A.; Tubino, R.; Salamone, M. M.; Meinardi, F.

    2010-09-01

    Triplet-triplet energy transfer in multicomponent organic systems is usually entirely ascribed to a Dexter-type mechanism involving only short-range donor/acceptor interactions. We demonstrate that the presence of molecular oxygen introduces a perturbation to the electronic structure of one of the involved moieties which can induce a large increase in the spin-forbidden transition oscillator strength so that the otherwise negligible Förster contribution dominates the overall energy transfer rate.

  18. Effect of Small Changes in Secondary Structure on the Electron Transfer Rate in Proteins

    NASA Astrophysics Data System (ADS)

    Wolfgang, J.; Risser, S. M.

    1996-03-01

    In the non-adiabatic limit, the rate of electron transfer reactions is proportional to the square of the electronic coupling between donor and acceptor. The distance decay of the coupling in a protein is sensitive to the protein geometry and the tunneling energy of the electron. In this paper, we use Green's function methods combined with molecular dynamics simulations to examine how the electronic coupling is modulated by the primary, secondary and tertiary structure of polypeptides. We also will explore the sensitivity of the coupling to small changes in atomic coordinates. This work was supported by the Research Corporation and East Texas State University.

  19. Interplay between structure, stoichiometry, and electron transfer dynamics in SILAR-based quantum dot-sensitized oxides.

    PubMed

    Wang, Hai; Barceló, Irene; Lana-Villarreal, Teresa; Gómez, Roberto; Bonn, Mischa; Cánovas, Enrique

    2014-10-08

    We quantify the rate and efficiency of picosecond electron transfer (ET) from PbS nanocrystals, grown by successive ionic layer adsorption and reaction (SILAR), into a mesoporous SnO2 support. Successive SILAR deposition steps allow for stoichiometry- and size-variation of the QDs, characterized using transmission electron microscopy. Whereas for sulfur-rich (p-type) QD surfaces substantial electron trapping at the QD surface occurs, for lead-rich (n-type) QD surfaces, the QD trapping channel is suppressed and the ET efficiency is boosted. The ET efficiency increase achieved by lead-rich QD surfaces is found to be QD-size dependent, increasing linearly with QD surface area. On the other hand, ET rates are found to be independent of both QD size and surface stoichiometry, suggesting that the donor-acceptor energetics (constituting the driving force for ET) are fixed due to Fermi level pinning at the QD/oxide interface. Implications of our results for QD-sensitized solar cell design are discussed.

  20. Fe electron transfer and atom exchange in goethite: influence of Al-substitution and anion sorption.

    PubMed

    Latta, Drew E; Bachman, Jonathan E; Scherer, Michelle M

    2012-10-02

    The reaction of Fe(II) with Fe(III) oxides and hydroxides is complex and includes sorption of Fe(II) to the oxide, electron transfer between sorbed Fe(II) and structural Fe(III), reductive dissolution coupled to Fe atom exchange, and, in some cases mineral phase transformation. Much of the work investigating electron transfer and atom exchange between aqueous Fe(II) and Fe(III) oxides has been done under relatively simple aqueous conditions in organic buffers to control pH and background electrolytes to control ionic strength. Here, we investigate whether electron transfer is influenced by cation substitution of Al(III) in goethite and the presence of anions such as phosphate, carbonate, silicate, and natural organic matter. Results from (57)Fe Mössbauer spectroscopy indicate that both Al-substitution (up to 9%) and the presence of common anions (PO(4)(3-), CO(3)(2-), SiO(4)(4-), and humic acid) does not inhibit electron transfer between aqueous Fe(II) and Fe(III) in goethite under the conditions we studied. In contrast, sorption of a long-chain phospholipid completely shuts down electron transfer. Using an enriched isotope tracer method, we found that Al-substitution in goethite (10%), does, however, significantly decrease the extent of atom exchange between Fe(II) and goethite (from 43 to 12%) over a month's time. Phosphate, somewhat surprisingly, appears to have little effect on the rate and extent of atom exchange between aqueous Fe(II) and goethite. Our results show that electron transfer between aqueous Fe(II) and solid Fe(III) in goethite can occur under wide range of geochemical conditions, but that the extent of redox-driven Fe atom exchange may be dependent on the presence of substituting cations such as Al.

  1. Imaging charge and energy transfer in molecules using free-electron lasers

    NASA Astrophysics Data System (ADS)

    Rudenko, Artem

    2014-05-01

    Charge and energy transfer reactions drive numerous important processes in physics, chemistry and biology, with applications ranging from X-ray astrophysics to artificial photosynthesis and molecular electronics. Experimentally, the central goal in studies of transfer phenomena is to trace the spatial localization of charge at a given time. Because of their element and site sensitivity, ultrafast X-rays provide a promising tool to address this goal. In this talk I will discuss several experiments where free-electron lasers were employed to study charge and energy transfer dynamics in fragmenting molecules. In a first example, we used intense, 70 femtosecond 1.5 keV pulses from the Linac Coherent Light Source (LCLS) to study distance dependence of electron transfer in laser-dissociated methyl iodide molecules. Inducing well-localized positive charge on the heavy iodine atom, we observe signature of electron transition from the separated methyl group up to the distances of 35 atomic units. In a complementary experiment, we studied charge exchange between two partners in a dissociating molecular iodine employing a pump-probe arrangement with two identical 90 eV pulses from the Free-Electron LASer in Hamburg (FLASH). In both cases, the effective spatial range of the electron transfer can be reasonably described by a classical over-the-barrier model developed for ion-atom collisions. Finally, I will discuss a time-resolved measurement on non-local relaxation mechanism based on a long-range energy transfer, the so-called interatomic Coulombic decay. This work was supported by Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, US Department of Energy and by the Kansas NSF ``First Award'' program.

  2. Use of Ruthenium Photooxidation Techniques to Study Electron Transfer in the Cytochrome bc1 Complex

    PubMed Central

    Millett, Francis; Durham, Bill

    2009-01-01

    Ruthenium photooxidation methods are presented to study electron transfer between the cytochrome bc1 complex and cytochrome c, and within the cytochrome bc1 complex. Methods are described to prepare a ruthenium cytochrome c derivative, Ruz-39-Cc, by labeling the single sulfhydryl on yeast H39C;C102T iso-1-Cc with the reagent Ru(bpz)2(4-bromomethyl-4′-methylbipyridine). The ruthenium complex attached to Cys-39 on the opposite side of Cc from the heme crevice does not affect the interaction with cyt bc1. Laser excitation of reduced Ruz-39-Cc results in photooxidation of heme c within 1 μs with a yield of 20%. Flash photolysis of a 1:1 complex between reduced yeast cytochrome bc1 and Ruz-39-Cc leads to electron transfer from heme c1 to heme c with a rate constant of 1.4 × 104 s-1. Methods are described for the use of the ruthenium dimer, Ru2D, to photooxidize cyt c1 in the cytochrome bc1 complex within 1 μs with a yield of 20%. Electron transfer from the Rieske iron-sulfur center [2Fe2S] to cyt c1 was detected with a rate constant of 6 × 104 s-1 in R. sphaeroides cyt bc1 using this method. This electron transfer step is rate-limited by the rotation of the Rieske iron-sulfur protein in a conformational gating mechanism. This method provides critical information on the dynamics of rotation of the iron-sulfur protein (ISP) as it transfers electrons from QH2 in the Qo site to cyt c1 These ruthenium photooxidation methods can be used to measure many of the electron transfer reactions in cytochrome bc1 complexes from any source. PMID:19348884

  3. Catalytic electron-transfer oxygenation of substrates with water as an oxygen source using manganese porphyrins.

    PubMed

    Fukuzumi, Shunichi; Mizuno, Takuya; Ojiri, Tetsuya

    2012-12-03

    Manganese(V)-oxo-porphyrins are produced by the electron-transfer oxidation of manganese-porphyrins with tris(2,2'-bipyridine)ruthenium(III) ([Ru(bpy)(3)](3+); 2 equiv) in acetonitrile (CH(3)CN) containing water. The rate constants of the electron-transfer oxidation of manganese-porphyrins have been determined and evaluated in light of the Marcus theory of electron transfer. Addition of [Ru(bpy)(3)](3+) to a solution of olefins (styrene and cyclohexene) in CH(3)CN containing water in the presence of a catalytic amount of manganese-porphyrins afforded epoxides, diols, and aldehydes efficiently. Epoxides were converted to the corresponding diols by hydrolysis, and were further oxidized to the corresponding aldehydes. The turnover numbers vary significantly depending on the type of manganese-porphyrin used owing to the difference in their oxidation potentials and the steric bulkiness of the ligand. Ethylbenzene was also oxidized to 1-phenylethanol using manganese-porphyrins as electron-transfer catalysts. The oxygen source in the substrate oxygenation was confirmed to be water by using (18)O-labeled water. The rate constant of the reaction of the manganese(V)-oxo species with cyclohexene was determined directly under single-turnover conditions by monitoring the increase in absorbance attributable to the manganese(III) species produced in the reaction with cyclohexene. It has been shown that the rate-determining step in the catalytic electron-transfer oxygenation of cyclohexene is electron transfer from [Ru(bpy)(3)](3+) to the manganese-porphyrins.

  4. Photoinduced electron transfer in ruthenium(II)/Tin(IV) multiporphyrin arrays.

    PubMed

    Indelli, M Teresa; Chiorboli, Claudio; Ghirotti, Marco; Orlandi, Michele; Scandola, Franco; Kim, Hyun Jung; Kim, Hee-Joon

    2010-11-18

    The photophysical behavior of a series of heterometallic arrays made of a central Sn(IV) porphyrin connected, respectively, to two (SnRu(2)), four (SnRu(4)), or six (SnRu(6)) ruthenium porphyrin units has been studied in dichloromethane. Two different motifs connect the ruthenium porphyrin units to central tin porphyrin core, axial coordination via ditopic bridging ligands and/or coordination to peripheral pyridyl groups of the central porphyrin ring. A remarkable number of electron transfer processes (photoinduced charge separation and recombination processes) have been time-resolved using a combination of emission spectroscopy and fast (nanosecond) and ultrafast (femtosecond) absorption techniques. In these systems both types of molecular components can be selectively populated by light absorption. In all the arrays, the local excited states of these units (the tin porphyrin singlet excited state and the ruthenium porphyrin triplet state) are quenched by electron transfer leading to a charge-separated state where the ruthenium porphyrin unit is oxidized and the tin porphyrin unit is reduced. For each array, the two forward electron transfer processes, as well as the charge recombination process leading back to the ground state, have been kinetically resolved. The rate constants obey standard free-energy correlations with the forward processes lying in the normal free-energy regime and the back reactions in the Marcus inverted region. The comparison between the trimeric (SnRu(2)) and pentameric (SnRu(4)) arrays shows that all the electron transfer processes are faster in the latter than in the former system. This can be rationalized in terms of differences in electronic factors (due to the different connecting motifs) and driving force. In less polar solvents, such as toluene, the energy of the charge-separated states is substantially lifted, leading to a switch (from electron transfer to triplet energy transfer) in the deactivation mechanism of the excited

  5. Characterisation of the signal and noise transfer of CCD cameras for electron detection.

    PubMed

    Meyer, R R; Kirkland, A I

    2000-05-01

    Methods to characterise the performance of CCD cameras for electron detection are investigated with particular emphasis on the difference between the transfer of signal and noise. Similar to the Modulation Transfer Function MTF, which describes the spatial frequency dependent attenuation of contrast in the image, we introduce a Noise Transfer Function NTF that describes the transfer of the Poisson noise that is inevitably present in any electron image. A general model for signal and noise transfer by an image converter is provided. This allows the calculation of MTF and NTF from Monte-Carlo simulations of the trajectories of electrons and photons in the scintillator and the optical coupling of the camera. Furthermore, accurate methods to measure the modulation and noise transfer functions experimentally are presented. The spatial-frequency dependent Detection Quantum Efficiency DQE, an important figure of merit of the camera which has so far not been measured experimentally, can be obtained from the measured MTF and NTF. The experimental results are in good agreement with the simulations and show that the NTF at high spatial frequencies is in some cases by a factor of four higher than the MTF. This implies that the noise method, which is frequently used to measure the MTF, but in fact measures the NTF, gives over-optimistic results. Furthermore, the spatial frequency dependent DQE is lower than previously assumed.

  6. A structural basis for electron transfer in bacterial photosynthesis

    SciTech Connect

    Norris, J.R.; DiMagno, T.J.; Angerhofer, A.; Chang, C.H.; El-Kabbani, O.; Schiffer, M.

    1989-01-01

    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 (His/sup M200/ 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.

  7. Conceptual density functional theory for electron transfer and transport in mesoscopic systems.

    PubMed

    Bueno, Paulo R; Miranda, David A

    2017-02-22

    Molecular and supramolecular systems are essentially mesoscopic in character. The electron self-exchange, in the case of energy fluctuations, or electron transfer/transport, in the case of the presence of an externally driven electrochemical potential, between mesoscopic sites is energetically driven in such a manner where the electrochemical capacitance (C[small mu, Greek, macron]) is fundamental. Thus, the electron transfer/transport through channels connecting two distinct energetic (ΔE[small mu, Greek, macron]) and spatially separated mesoscopic sites is capacitively modulated. Remarkably, the relationship between the quantum conductance (G) and the standard electrochemical rate constant (kr), which is indispensable to understanding the physical and chemical characteristics governing electron exchange in molecular scale systems, was revealed to be related to C[small mu, Greek, macron], that is, C[small mu, Greek, macron] = G/kr. Accordingly, C[small mu, Greek, macron] is the proportional missing term that controls the electron transfer/transport in mesoscopic systems in a wide-range, and equally it can be understood from first principles density functional quantum mechanical approaches. Indeed the differences in energy between states is calculated (or experimentally accessed) throughout the electrochemical capacitance as ΔE[small mu, Greek, macron] = β/C[small mu, Greek, macron], and thus constitutes the driving force for G and/or kr, where β is only a proportional constant that includes the square of the unit electron charge times the square of the number of electron particles interchanged.

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

    NASA Astrophysics Data System (ADS)

    Getoff, Nikola; Hartmann, Johannes; Schittl, Heike; Gerschpacher, Marion; Quint, Ruth Maria

    2011-08-01

    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.

  9. Electron Transfer Mechanism in Gold Surface Modified with Self-Assembly Monolayers from First Principles

    NASA Astrophysics Data System (ADS)

    Lima, Filipe C. D. A.; Iost, Rodrigo M.; Crespilho, Frank N.; Caldas, Marília J.; Calzolari, Arrigo; Petrilli, Helena M.

    2013-03-01

    We report the investigation of electron tunneling mechanism of peptide ferrocenyl-glycylcystamine self-assembled monolayers (SAMs) onto Au (111) electrode surfaces. Recent experimental investigations showed that electron transfer in peptides can occur across long distances by separating the donor from the acceptor. This mechanism can be further fostered by the presence of electron donor terminations of Fc terminal units on SAMs but the charge transfer mechanism is still not clear. We study the interaction of the peptide ferrocenyl-glycylcystamine on the Au (111) from first principles calculations to evaluate the electron transfer mechanism. For this purpose, we used the Kohn Sham (KS) scheme for the Density Functional Theory (DFT) as implemented in the Quantum-ESPRESSO suit of codes, using Vandebilt ultrasoft pseudopotentials and GGA-PBE exchange correlation functional to evaluate the ground-state atomic and electronic structure of the system. The analysis of KS orbital at the Fermi Energy showed high electronic density localized in Fc molecules and the observation of a minor contribution from the solvent and counter ion. Based on the results, we infer evidences of electron tunneling mechanism from the molecule to the Au(111). We acknowledge FAPESP for grant support. Also, LCCA/USP, RICE and CENAPAD for computational resources.

  10. A kinetic perspective on extracellular electron transfer by anode-respiring bacteria.

    PubMed

    Torres, César I; Marcus, Andrew Kato; Lee, Hyung-Sool; Parameswaran, Prathap; Krajmalnik-Brown, Rosa; Rittmann, Bruce E

    2010-01-01

    In microbial fuel cells and electrolysis cells (MXCs), anode-respiring bacteria (ARB) oxidize organic substrates to produce electrical current. In order to develop an electrical current, ARB must transfer electrons to a solid anode through extracellular electron transfer (EET). ARB use various EET mechanisms to transfer electrons to the anode, including direct contact through outer-membrane proteins, diffusion of soluble electron shuttles, and electron transport through solid components of the extracellular biofilm matrix. In this review, we perform a novel kinetic analysis of each EET mechanism by analyzing the results available in the literature. Our goal is to evaluate how well each EET mechanism can produce a high current density (> 10 A m(-2)) without a large anode potential loss (less than a few hundred millivolts), which are feasibility goals of MXCs. Direct contact of ARB to the anode cannot achieve high current densities due to the limited number of cells that can come in direct contact with the anode. Slow diffusive flux of electron shuttles at commonly observed concentrations limits current generation and results in high potential losses, as has been observed experimentally. Only electron transport through a solid conductive matrix can explain observations of high current densities and low anode potential losses. Thus, a study of the biological components that create a solid conductive matrix is of critical importance for understanding the function of ARB.

  11. Electronic Warfare: Comprehensive Strategy Still Needed for Suppressing Enemy Air Defenses

    NASA Astrophysics Data System (ADS)

    2002-11-01

    U.S. military aircraft are often at great risk from enemy air defenses, and the services use specialized aircraft to neutralize or destroy them. In January 2001, GAO reported that a gap existed between the services' suppression capabilities and their needs and recommended that a comprehensive strategy was needed to fix the situation. In response to GAO's report, DOD emphasized that a major study underway at the time would provide the basis for a Department-wide strategy and lead to a balanced set of acquisition programs between the services. This report updates our previous work and assesses actions that DOD has taken to improve its suppression capabilities.

  12. Photoinduced direct electron transfer from InSe to GaSe semiconductor nanoparticles.

    PubMed

    Tu, Haohua; Kelley, David F

    2006-01-01

    Direct electron transfer from InSe nanoparticles to GaSe nanoparticles in mixed solution-phase aggregates has been found to occur upon photoexcitation. Mixed aggregates exhibit a strong charge-transfer absorption band at an energy slightly higher than the InSe band gap. Photoexcitation of this band results in a polarized transient absorption spectrum and transient absorption kinetics characteristic of InSe valence-band holes and GaSe conduction-band electrons. The kinetics indicate that charge separation persists for at least several hundred picoseconds.

  13. Short-lived electron transfer in donor-bridge-acceptor systems

    NASA Astrophysics Data System (ADS)

    Psiachos, D.

    2016-10-01

    We investigate time-dependent electron transfer (ET) in benchmark donor-bridge-acceptor systems. For the small bridge sizes studied, we obtain results far different from the perturbation theory which underlies scattering-based approaches, notably a lack of destructive interference in the ET for certain arrangements of bridge molecules. We also calculate wavepacket transmission in the non-steady-state regime, finding a featureless spectrum, while for the current we find two types of transmission: sequential and direct, where in the latter, the current transmission increases as a function of the energy of the transferred electron, a regime inaccessible by conventional scattering theory.

  14. Nobel lecture. A structural basis of light energy and electron transfer in biology.

    PubMed Central

    Huber, R

    1989-01-01

    Aspects of intramolecular light energy and electron transfer will be discussed for three protein--cofactor complexes, whose three-dimensional structures have been elucidated by X-ray crystallography: components of light-harvesting cyanobacterial phycobilisomes; the purple bacterial reaction centre; and the blue multi-copper oxidases. A wealth of functional data is available for these systems which allows specific correlations between structure and function and general conclusions about light energy and electron transfer in biological materials to be made. Images PMID:2676513

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

    SciTech Connect

    Masumoto, Yasuaki; Takagi, Hayato; Umino, Hikaru; Suzumura, Eri

    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.

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

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hiromichi

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

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

    SciTech Connect

    Atwood, J.

    1990-01-01

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

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

    SciTech Connect

    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.

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

    PubMed

    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.

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

    PubMed

    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.