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1

The study of electron transfer in advanced materials (electrodes for Li-ion batteries or catalysts)  

NASA Astrophysics Data System (ADS)

Mössbauer Spectroscopy (MS) is really suitable to study local electronic structures. Its hyperfine parameters, isomer shift (IS) and quadrupole splitting (QS) allow to characterize the oxidation state and coordination of the probed element. So, the capabilities of this powerful technique have been highlighted for the study of electron transfer occurring during electrochemical or catalytic processes. Several examples illustrate how MS can be used for the determination of reaction mechanisms in new electrode materials of Li-ion batteries (Sb or Sn-based, Ti oxides) or reforming catalysts (supported bimetallic PtSn catalysts). Deeper insight into the mechanisms determining the electrochemical or catalytic performances can be expected.

Jumas, Jean-Claude; Womes, Manfred; Lippens, Pierre-Emmanuel; Olivier-Fourcade, Josette

2008-02-01

2

Electron transfer in dye-sensitised semiconductors modified with molecular cobalt catalysts: photoreduction of aqueous protons.  

PubMed

A visible-light driven H(2) evolution system comprising of a Ru(II) dye (RuP) and Co(III) proton reduction catalysts (CoP) immobilised on TiO(2) nanoparticles and mesoporous films is presented. The heterogeneous system evolves H(2) efficiently during visible-light irradiation in a pH-neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self-assembled system occurs at the ligand framework of CoP, which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H(2) (mol CoP)(-1) and above 200,000 mol H(2) (mol?TiO(2) nanoparticles)(-1) in water. Our studies support that a molecular Co species, rather than metallic Co or a Co-oxide precipitate, is responsible for H(2) formation on TiO(2). Electron transfer in this system was studied by transient absorption spectroscopy and time-correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO(2) in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long-lived TiO(2) conduction band electron is formed with a half-lifetime of approximately 0.8 s. Electron transfer from the TiO(2) conduction band to the CoP catalysts occurs quantitatively on a 10 ?s timescale and is about a hundred times faster than charge-recombination with the oxidised RuP. This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors. PMID:23033059

Lakadamyali, Fezile; Reynal, Anna; Kato, Masaru; Durrant, James R; Reisner, Erwin

2012-10-02

3

Ultrafast photodriven intramolecular electron transfer from an iridium-based water-oxidation catalyst to perylene diimide derivatives.  

PubMed

Photodriving the activity of water-oxidation catalysts is a critical step toward generating fuel from sunlight. The design of a system with optimal energetics and kinetics requires a mechanistic understanding of the single-electron transfer events in catalyst activation. To this end, we report here the synthesis and photophysical characterization of two covalently bound chromophore-catalyst electron transfer dyads, in which the dyes are derivatives of the strong photooxidant perylene-3,4:9,10-bis(dicarboximide) (PDI) and the molecular catalyst is the Cp*Ir(ppy)Cl metal complex, where ppy = 2-phenylpyridine. Photoexcitation of the PDI in each dyad results in reduction of the chromophore to PDI(•-) in less than 10 ps, a process that outcompetes any generation of (3*)PDI by spin-orbit-induced intersystem crossing. Biexponential charge recombination largely to the PDI-Ir(III) ground state is suggestive of multiple populations of the PDI(•-)-Ir(IV) ion-pair, whose relative abundance varies with solvent polarity. Electrochemical studies of the dyads show strong irreversible oxidation current similar to that seen for model catalysts, indicating that the catalytic integrity of the metal complex is maintained upon attachment to the high molecular weight photosensitizer. PMID:22586073

Vagnini, Michael T; Smeigh, Amanda L; Blakemore, James D; Eaton, Samuel W; Schley, Nathan D; D'Souza, Francis; Crabtree, Robert H; Brudvig, Gary W; Co, Dick T; Wasielewski, Michael R

2012-05-14

4

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

PubMed

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

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

2009-01-01

5

Water Reduction with Visible Light: Synergy between Optical Transitions and Electron Transfer in Au-TiO2 Catalysts Visualized by In?situ EPR Spectroscopy.  

PubMed

Golden electrons: Visible light excites conduction electron transfer from gold particles to support vacancies where they are taken up by protons to produce hydrogen. This transfer process was visualized by in?situ EPR spectroscopy. PMID:24030724

Priebe, Jacqueline B; Karnahl, Michael; Junge, Henrik; Beller, Matthias; Hollmann, Dirk; Brückner, Angelika

2013-09-12

6

Electron transfer reactions  

NASA Astrophysics Data System (ADS)

During the tenure of this contract research was performed on a number of aspects of electron transfer reactions (solvent dynamics including vibrational effects, non-Debye solvent dynamics, early steps in bacterial photosynthesis) and of the use of artificial intelligence searching methods, the latter, in part, as a prelude to our current study of electron transfer reactions in structurally complicated systems such as proteins. Seven Technical Reports were issued during this period, and research on several topics was initiated: the study of the relation between charge transfer absorption and fluorescence spectra and the inverted region, a nonadiabatic/adiabatic coherent mechanism for electron transfers, and electron transfers between two immiscible-liquid phases and between a semiconductor and an electrolyte.

Marcus, R. A.

1989-07-01

7

Charge transfer dynamics between photoexcited CdS nanorods and mononuclear Ru water-oxidation catalysts.  

PubMed

We describe the charge transfer interactions between photoexcited CdS nanorods and mononuclear water oxidation catalysts derived from the [Ru(bpy)(tpy)Cl](+) parent structure. Upon excitation, hole transfer from CdS oxidizes the catalyst (Ru(2+) ? Ru(3+)) on a 100 ps to 1 ns timescale. This is followed by 10-100 ns electron transfer (ET) that reduces the Ru(3+) center. The relatively slow ET dynamics may provide opportunities for the accumulation of multiple holes at the catalyst, which is necessary for water oxidation. PMID:23406271

Tseng, Huan-Wei; Wilker, Molly B; Damrauer, Niels H; Dukovic, Gordana

2013-02-25

8

Nonadiabatic anharmonic electron transfer.  

PubMed

The effect of an inner sphere, local mode vibration on an electron transfer is modeled using the nonadiabatic transition probability (rate) expression together with both the anharmonic Morse and the harmonic oscillator potential. For an anharmonic inner sphere mode, a variational analysis uses harmonic oscillator basis functions to overcome the difficulties evaluating Morse-model Franck-Condon overlap factors. Individual matrix elements are computed with the use of new, fast, robust, and flexible recurrence relations. The analysis therefore readily addresses changes in frequency and/or displacement of oscillator minimums in the different electron transfer states. Direct summation of the individual Boltzmann weighted Franck-Condon contributions avoids the limitations inherent in the use of the familiar high-temperature, gaussian form of the rate constant. The effect of harmonic versus anharmonic inner sphere modes on the electron transfer is readily seen, especially in the exoergic, inverted region. The behavior of the transition probability can also be displayed as a surface for all temperatures and values of the driving force/exoergicity ? = -?G. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy (? = ?(s)) along a maximum ln?(w) vs. ? ridge of the surface. The surface also reveals additional regions for ? where ln?(w) appears to be insensitive to temperature, or effectively activationless, for some kinds of inner sphere contributions. PMID:23556710

Schmidt, P P

2013-03-28

9

Nonadiabatic anharmonic electron transfer  

NASA Astrophysics Data System (ADS)

The effect of an inner sphere, local mode vibration on an electron transfer is modeled using the nonadiabatic transition probability (rate) expression together with both the anharmonic Morse and the harmonic oscillator potential. For an anharmonic inner sphere mode, a variational analysis uses harmonic oscillator basis functions to overcome the difficulties evaluating Morse-model Franck-Condon overlap factors. Individual matrix elements are computed with the use of new, fast, robust, and flexible recurrence relations. The analysis therefore readily addresses changes in frequency and/or displacement of oscillator minimums in the different electron transfer states. Direct summation of the individual Boltzmann weighted Franck-Condon contributions avoids the limitations inherent in the use of the familiar high-temperature, Gaussian form of the rate constant. The effect of harmonic versus anharmonic inner sphere modes on the electron transfer is readily seen, especially in the exoergic, inverted region. The behavior of the transition probability can also be displayed as a surface for all temperatures and values of the driving force/exoergicity ? = -?G. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy (? = ?s) along a maximum ln (w) vs. ? ridge of the surface. The surface also reveals additional regions for ? where ln (w) appears to be insensitive to temperature, or effectively activationless, for some kinds of inner sphere contributions.

Schmidt, P. P.

2013-03-01

10

Electron transfer in biology  

NASA Astrophysics Data System (ADS)

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

Williams, R. J. P.

11

Theory of electron transfer reactions  

NASA Astrophysics Data System (ADS)

An objective of the research performed on this grant is the understanding of the detailed behavior of a variety of electron transfer processes. Theories were developed for (1) the rate of electron transfer between a reagent in one liquid phase and another in a second (immiscible) liquid or polymer, (2) the rate of long distance electron transfer in proteins, (3) charge transfers spectra in frozen media, (d) scanning tunneling microscopy (stm) of molecular adsorbates, and (4) analysis of models of solvents used in computer simulations of electron transfer, particularly examining the error incurred by their common neglect of the electronic and vibrational contributions of the solvent's dielectric response.

Marcus, Rudolph A.

1994-06-01

12

Electron transfer reactions in microporous solids  

NASA Astrophysics Data System (ADS)

The research program involves the use of microporous solids (zeolites, clays, layered, and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. The 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., H2 and I3(-), or H2 and O2) from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

Mallouk, T. E.

1993-01-01

13

Proton-Coupled Electron Transfer  

SciTech Connect

Proton-Coupled Electron Transfer (PCET) describes reactions in which there is a change in both electron and proton content between reactants and products. It originates from the influence of changes in electron content on acid?base properties and provides a molecular-level basis for energy transduction between proton transfer and electron transfer. Coupled electron?proton transfer or EPT is defined as an elementary step in which electrons and protons transfer from different orbitals on the donor to different orbitals on the acceptor. There is (usually) a clear distinction between EPT and H-atom transfer (HAT) or hydride transfer, in which the transferring electrons and proton come from the same bond. Hybrid mechanisms exist in which the elementary steps are different for the reaction partners. EPT pathways such as PhO•/PhOH exchange have much in common with HAT pathways in that electronic coupling is significant, comparable to the reorganization energy with H{sub DA} ~ ?. Multiple-Site Electron?Proton Transfer (MS-EPT) is an elementary step in which an electron?proton donor transfers electrons and protons to different acceptors, or an electron?proton acceptor accepts electrons and protons from different donors. It exploits the long-range nature of electron transfer while providing for the short-range nature of proton transfer. A variety of EPT pathways exist, creating a taxonomy based on what is transferred, e.g., 1e{sup -}/2H{sup +} MS-EPT. PCET achieves “redox potential leveling” between sequential couples and the buildup of multiple redox equivalents, which is of importance in multielectron catalysis. There are many examples of PCET and pH-dependent redox behavior in metal complexes, in organic and biological molecules, in excited states, and on surfaces. Changes in pH can be used to induce electron transfer through films and over long distances in molecules. Changes in pH, induced by local electron transfer, create pH gradients and a driving force for long-range proton transfer in Photosysem II and through other biological membranes. In EPT, simultaneous transfer of electrons and protons occurs on time scales short compared to the periods of coupled vibrations and solvent modes. A theory for EPT has been developed which rationalizes rate constants and activation barriers, includes temperature- and driving force (?G)-dependences implicitly, and explains kinetic isotope effects. The distance-dependence of EPT is dominated by the short-range nature of proton transfer, with electron transfer being far less demanding.Changes in external pH do not affect an EPT elementary step. Solvent molecules or buffer components can act as proton donor acceptors, but individual H2O molecules are neither good bases (pK{sub a}(H{sub 3}O{sup +}) = ?1.74) nor good acids (pK{sub a}(H{sub 2}O) = 15.7). There are many examples of mechanisms in chemistry, in biology, on surfaces, and in the gas phase which utilize EPT. PCET and EPT play critical roles in the oxygen evolving complex (OEC) of Photosystem II and other biological reactions by decreasing driving force and avoiding high-energy intermediates.

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

2012-01-01

14

Graphene oxide as a recyclable phase transfer catalyst.  

PubMed

We demonstrated a simple and green chemical method to obtain Michael adducts and their derivatives by using GO as a phase transfer catalyst with different kinds of bases in water and dichloromethane, and we also used GO multiple cycles almost without reduction in reaction yields. PMID:23689290

Kim, Youngmin; Some, Surajit; Lee, Hyoyoung

2013-05-20

15

Manifestations of sequential electron transfer  

SciTech Connect

An essential feature of efficient photo-initiated charge separation is sequential electron transfer. Charge separation is initiated by photoexcitation of an electron donor followed by rapid electron transfer steps from the excited donor through a series of electron acceptors, so that, after one or two successive steps, charge separation is stabilized by the physical separation between the oxidized donor and reduced acceptor. The prime example of this process is the sequential electron transfer that takes place in the purple photosynthetic bacterial reaction center, resulting in the charge separation between P{sup +} and Q{sub A}{sup -} across a biological membrane. We have developed magnetic resonance tools to monitor sequential electron transfer. We are applying these techniques to study charge separation in natural photo-synthetic systems in order to gain insights into the features of the reaction center proteins that promote efficient charge separation. As we establish what some of these factors are, we are beginning to design artificial photosynthetic systems that undergo photoinduced sequential electron transfer steps.

Thurnauer, M.C.; Tang, J.

1996-05-01

16

Engineering atom transfer radical polymerization: Catalyst technology  

Microsoft Academic Search

Atom transfer radical polymerization (ATRP) is a controlled\\/living radical polymerization process developed a decade ago that allows the synthesis of tailored macromolecules. It has been widely used in the laboratory for polymer synthesis since, but significant use is yet to be made of it at an industrial scale for polymer production. This is due to the low activity of the

Santiago Faucher

2007-01-01

17

Electron capture, femtosecond electron transfer and theory  

NASA Astrophysics Data System (ADS)

Complexes of doubly protonated 1,n-diaminoalkanes with one or two molecules of 18-crown-6-ether undergo consecutive and competitive dissociations upon electron capture from a free thermal electron and femtosecond collisional electron transfer from Na and Cs atoms. The electron capture dissociation (ECD) and electron capture-induced dissociation (ECID) mass spectra show very different products and product ion intensities. In ECD, the reduced precursor ions dissociate primarily by loss of an ammonium hydrogen and the crown ether ligand. In ECID, ions from many more dissociation channels are observed and depend on whether collisions occur with Na or Cs atoms. ECID induces highly endothermic CC bond cleavages along the diaminoalkane chain, which are not observed with ECD. Adduction of one or two crown ethers to diaminoalkanes results in different electron capture cross-sections that follow different trends for ECD and ECID. Electron structure calculations at the B3-PMP2/6-311++G(2d,p) level of theory were used to determine structures of ions and ion radicals and the energetics for protonation, electron transfer, and ion dissociations for most species studied experimentally. The calculations revealed that the crown ether ligand substantially affected the recombination energy of the diaminoalkane ion and the electronic states accessed by electron attachment.

Holm, Anne I. S.; Larsen, Mikkel K.; Panja, Subhasis; Hvelplund, Preben; Nielsen, Steen Brøndsted; Leib, Ryan D.; Donald, William A.; Williams, Evan R.; Hao, Changtong; Turecek, Frantisek

2008-10-01

18

Transmission electron microscopy investigation of auto catalyst and cobalt germanide  

Microsoft Academic Search

The modern ceria-zirconia based catalysts are used in automobiles to reduce exhaust pollutants. Cobalt germanides have potential applications as electrical contacts in the future Ge-based semiconductor devices. In this thesis, transmission electron microscopy (TEM) techniques were used to study the atomic scale interactions between metallic nanostructures and crystalline substrates in the two material systems mentioned above. The model catalyst samples

Haiping Sun

2005-01-01

19

Electron, proton and related transfers  

NASA Astrophysics Data System (ADS)

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

Marcus, R. A.

1982-09-01

20

Polar solvation and electron transfer  

SciTech Connect

The report is divided into the following sections: completion of previous studies on solvation dynamics, dipole lattice studies, inertial components of solvation response, simple models of solvation dynamics, rotational dynamics and dielectric friction, intramolecular electron transfer reactions, and intermolecular donor-acceptor complexes.

Not Available

1993-04-13

21

A nonadiabatic and nonlinear theory for electron transfer  

NASA Astrophysics Data System (ADS)

We propose a general theory both non adiabatic and nonlinear which extends those used for the standard theory of electron transfer (ET) in chemistry but also becomes equivalent to it far from the inversion point. In the vicinity of the inversion point, the model parameters may be finely tuned such that large amplitude electronic oscillations between the donor and an extrasite, associated with large amplitude and collective phonon oscillations at the same frequency, are spontaneously generated (coherent electron phonon oscillator or CEPO). This extrasite is not a true acceptor but could play the role of a catalyst because by the CEPO it may trigger irreversible and ultrafast ET at low temperature toward a third site which is a real acceptor (while in the absence of catalyst, ET cannot occur). Such a trimer system may be regulated by small perturbations and behaves as a molecular transistor. We illustrate this idea by explicit numerical simulations on trimer models of the type donor-catalyst-acceptor. We discuss the relevance of our approach for understanding the ultrafast electron transfer experimentally observed in biosystems such as the photosynthetic reaction center.

Aubry, Serge

2008-03-01

22

Environmental Effects on Photoinduced Electron Transfer Reactions.  

National Technical Information Service (NTIS)

Photoinduced electron transfer reactions between an electronically excited photosensitizer molecule and a reversible electron acceptor capable of hydrogen production were studied to determine the possible utility of these reactions in solar energy convers...

T. E. Casti

1985-01-01

23

State symmetry effects on electron transfer reactions  

Microsoft Academic Search

To study state symmetry effects on electron transfer reactions, three donor-spacer-acceptor electron transfer molecules were synthesized and structurally characterized. The electron donor was 1,4-dimethoxyanthracene. The electron acceptors were 1,1-dicyanoethylene or 1,2-dicarbomethoxyethylene. The spacers were saturated cyclic hydrocarbons. The spacer of the [open quotes]symmetry allowed[close quotes] molecules oriented the acceptor, 1,1-dicyanoethylene, in such a way that the electronic symmetry of the

Zeng

1992-01-01

24

Electron hole formation in acidic zeolite catalysts  

NASA Astrophysics Data System (ADS)

The formation of an electron hole on an AlO4H center of the H-ZSM-5 zeolite has been studied by a hybrid quantum mechanics/shell-model ion-pair potential approach. The Becke-3-Lee-Yang-Parr (B3LYP) and Becke-Half&Half-Lee-Yang-Parr (BHLYP) hybrid density functionals yield electron holes of different nature, a delocalized hole for B3LYP and a hole localized on one oxygen atom for BHLYP. Comparison with coupled cluster calculations including single and double substitutions and with perturbative treatment of triple substitutions CCSD(T) and with experimental data for similar systems indicate that the localized description obtained with BHLYP is more accurate. Generation of the electron hole produces a substantial geometry relaxation, in particular an elongation of the Al-O distance to the oxygen atom with the unpaired electron. The zeolite framework stabilizes the positive charge by long-range effects. Our best estimates for the vertical and adiabatic ionization energies are 9.6-10.1 and 8.4-8.9 eV, respectively. Calculations for silicalite, the all-silica form of ZSM-5, also yield a localized electron hole, but the energy cost of the process is larger by 0.6-0.7 eV. The deprotonation energy of H-ZSM-5 is found to decrease from 12.86 to 11.40 eV upon electron hole formation.

Solans-Monfort, Xavier; Branchadell, Vicenç; Sodupe, Mariona; Sierka, Marek; Sauer, Joachim

2004-09-01

25

Biomolecular electron transfer under high hydrostatic pressure  

Microsoft Academic Search

The dependence of the photoinduced electron transfer rate on hydrostatic pressure up to 8 kbar was studied at 295 K in a bridged Zn-porphyrin donor and pyromellitimide acceptor supermolecule dissolved in toluene. A picosecond fluorescence emission kinetics of the donor, limited by the electron transfer rate, was detected by using synchroscan streak camera. The experiment was complemented with model calculations

Märt Tars; Aleksandr Ellervee; Michael R. Wasielewski; Arvi Freiberg

1998-01-01

26

Fluorescent PET (photoinduced electron transfer) sensors  

Microsoft Academic Search

Fluorescent PET (photoinduced electron transfer) sensors are considered to be those molecular systems where the binding of ions and other species leads to the perturbation of the competition between the de-excitation pathways of fluorescence and electron transfer. The early developments in this field are traced and the design logic of these sensors is detailed. A variety of examples drawn from

Richard A. Bissell; A. Prasanna de Silva; H. Nimal Gunaratne; P. Mark Lynch; Glenn Maguire; Colin McCoy; K. Samankumara Sandanayake

27

Synthesis of cyclic disulfides using didecyldimethylammonium bromide as phase transfer catalyst  

Microsoft Academic Search

A convenient, practical and general method for the synthesis of symmetrical and unsymmetrical cyclic disulfides based on the reaction of sulfur with sodium sulfide in the presence of didecyldimethylammonium bromide (DDAB) as a phase transfer catalyst is described.

Sachin U. Sonavane; Mandan Chidambaram; Sanaa Khalil; Joseph Almog; Yoel Sasson

2008-01-01

28

Computer simulation of electron transfer in molecular electronic devices  

Microsoft Academic Search

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

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

2005-01-01

29

A polymer imidazole salt as phase-transfer catalyst in halex fluorination irradiated by microwave  

Microsoft Academic Search

A new imidazole polymer salt was synthesized in order to develop a high efficiency phase-transfer catalyst for multi-phase reactions. The polymer salt was prepared easily by co-polymerization of 1-1?-(1,4-butamethylene)bis(imidazole) and 1,2-dibromoethane, and has the properties of excellent chemical and thermal stability and high ionic conductivity. It was applied as phase-transfer catalyst in the fluorination of chloronitrobenzenes under the irradiation of

Zheng Yong Liang; Chun Xu Lü; Jun Luo; Li Bin Dong

2007-01-01

30

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer.  

PubMed

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 ? ? ?(*) charge-transfer transition that shifts electron density to the side of the flavin isoalloxazine ring that is adjacent to the docked thymine dimer. This shift in electron density enhances the FADH(-) - to - dimer electronic coupling, thus inducing rapid electron transfer. PMID:23226907

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

2007-01-01

31

Flavin Charge Transfer Transitions Assist DNA Photolyase Electron Transfer  

PubMed Central

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 ? ? ?* 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.

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

2012-01-01

32

Effect of mass transfer and catalyst layer thickness on photocatalytic reaction  

SciTech Connect

Semiconductor photocatalytic processes have been studied for nearly 20 years due to their intriguing advantages in environmental remediation. A rational approach in determining the effect of mass transfer and catalyst layer thickness during photocatalytic reactions is proposed. The reaction occurs at the liquid-catalyst interface, and therefore when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters--external mass-transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass-transfer coefficient, and effective diffusivity--were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. Even though all these parameters are critical to the design and development of photocatalytic processes, they are not available in the literature. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thicknesses under two different operating configurations was analyzed theoretically and experimentally verified. It was observed that an optimal catalyst layer thickness exists for substrate-to-catalyst illumination.

Chen, D.; Li, F.; Ray, A.K.

2000-05-01

33

Nuclear reorganization barriers to electron transfer  

NASA Astrophysics Data System (ADS)

The nuclear barrier to electron transfer arises from the need for reorganization of intramolecular and solvent internuclear distances prior to electron transfer. For reactions with relatively small driving force ( normal free-energy region) the nuclear factors and rates increase as intrinsic inner-shell and outer-shell barriers decrease; this is illustrated by data for transition metal complexes in their ground electronic states. By contrast, in the inverted free-energy region, rates and nuclear factors decrease with decreasing intrinsic barriers; this is illustrated by data for the decay of charge-transfer excited states. Several approaches to the evaluation of the outer-shell barrier are explored in an investigation of the distance dependence of the nuclear factor in intramolecular electron-transfer processes.

Sutin, Norman; Brunschwig, Bruce S.; Creutz, Carol; Winkler, Jay R.

34

Nuclear reorganization barriers to electron transfer  

SciTech Connect

The nuclear barrier to electron transfer arises from the need for reorganization of intramolecular and solvent internuclear distances prior to electron transfer. For reactions with relatively small driving force (''normal'' free-energy region) the nuclear factors and rates increase as intrinsic inner-shell and outer-shell barriers decrease; this is illustrated by data for transition metal complexes in their ground electronic states. By contrast, in the inverted free-energy region, rates and nuclear factors decrease with decreasing ''intrinsic'' barriers; this is illustrated by data for the decay of charge-transfer excited states. Several approaches to the evaluation of the outer-shell barrier are explored in an investigation of the distance dependence of the nuclear factor in intramolecular electron-transfer processes. 39 refs., 14 figs., 3 tabs.

Sutin, N.; Brunschwig, B.S.; Creutz, C.; Winkler, J.R.

1988-01-01

35

48 CFR 18.124 - Electronic funds transfer.  

Code of Federal Regulations, 2011 CFR

... 2011-10-01 2011-10-01 false Electronic funds transfer. 18.124 Section 18...Available Acquisition Flexibilities 18.124 Electronic funds transfer. Electronic funds transfer payments may be waived...

2011-10-01

36

Electron Transfer for Large Molecules through Delocalization  

SciTech Connect

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

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

2012-01-01

37

Electronic information transfer in a transport chain  

Microsoft Academic Search

Purpose – The purpose of this paper is to assess electronic information transfer in logistics organizations. The paper approaches information transfer as an elemental component of contemporary business to business (B2B) processes. Design\\/methodology\\/approach – The empirical material concerns companies that together comprise a logistical chain. The paper uses interview data to show information exchange patterns within one particular logistics chain.

Tommi Inkinen; Ulla Tapaninen; Hennariina Pulli

2009-01-01

38

Electronic Energy Transfer among Complex Molecules  

Microsoft Academic Search

Electronic energy transfer among complex molecules in gas phase and in polar solvents was studied by employing naphthalene and biacetyl as sensitizer and activator, respectively. Triplet -triplet energy transfer from naphthalene to biacetyl was observed. In the gas phase a 310 nm, in polar solvents 230 nm, 295 nm and 325 nm excitation bands were found as the starting points

Oktay Demir

1985-01-01

39

3-D Heterogeneous Electronics by Transfer Printing  

Microsoft Academic Search

Here we describe an approach, called transfer printing, to allow the combination of broad classes of materials into three-dimensional (3-D) heterogeneously integrated electronic devices. The process involves fabrication of source wafers that contain high performance single crystal devices from materials including, but not limited to, silicon, gallium arsenide and gallium nitride. These devices are then delineated and transferred to a

C. A. Bower; E. Menard; J. Carr; J. A. Rogers

2007-01-01

40

Quantum effects in biological electron transfer.  

PubMed

Over recent decades, quantum effects such as coherent electronic energy transfers, electron and hydrogen tunneling have been uncovered in biological processes. In this Perspective, we highlight some of the main conceptual and methodological tools employed in the field to investigate electron tunneling in proteins, with a particular emphasis on the methodologies we are currently developing. In particular, we describe our recent contributions to the development of a mixed quantum-classical framework aimed at describing physical systems lying at the border between the quantum and semi-classical worlds. We present original results obtained by combining our approach with constrained Density Functional Theory calculations. Moving to coarser levels of description, we summarize our latest findings on electron transfer between two redox proteins, thereby showing the stabilization of inter-protein, water-mediated, electron-transfer pathways. PMID:22434318

de la Lande, Aurélien; Babcock, Nathan S; Rezá?, Jan; Lévy, Bernard; Sanders, Barry C; Salahub, Dennis R

2012-03-20

41

Electron transfer to continuum states  

SciTech Connect

Gene Rudd`s analysis of doubly differential cross sections for the ionization of He atoms by proton impact suggested that electrons were being carried along by the proton for a short period of time after being ejected from the target region. Normally, this would represent an electron capture event in which an excited state of atomic hydrogen is formed. Because the electron ends up ionized it was recognized that these states of the proton must be continuum states. This insight was confirmed by observations of the continuum electron capture (CEC) cusp when the electron velocity equals the proton velocity in the final state. The impact of this idea upon the theory of ionization at high energies is reviewed.

Macek, J.H. [Univ. of Tenenssee, Knoxville, TN (United States)]|[Oak Ridge National Lab., TN (United States)

1994-12-31

42

Photoinduced Intermolecular and Intramolecular Electron Transfer  

NASA Astrophysics Data System (ADS)

The finite sink approximation to the Smoluchowski -Collins-Kimball expression is used here to parameterize intermolecular electron transfer fluorescence quenching data. Values are determined for the relative diffusion coefficient, D_{rm FQ} and the effective encounter diameter, R in both diffusion limited and influenced cases. The effective encounter diameter is seen to increase with decreasing oxidation potential of electron donating quenchers of similar dimensions; this finding suggests that a long range electron transfer mechanism is present under these conditions which explains the absence of a Marcus inverted region noted by Rehm and Weller in 1970. Values of the intrinsic rate constant for electron transfer, k^circ, recovered for diffusion influenced systems are found to be independent of both solvent and temperature. These results are consistent with electron tunneling as the long range electron transfer mechanism. Intramolecular electron transfer is studied spectroscopically for derivatives of p-terphenyl and bianthranyl. The results obtained lead to a detailed examination of the photophysical behavior of 4-nitro-4^{' '}-amino-p-terphenyl (NATP) for which a state diagram consistent with the observed results are presented.

Biver, Carl John, III

43

Properties of ceramic foam catalyst supports: one-dimensional and two-dimensional heat transfer correlations  

Microsoft Academic Search

Ceramic foam catalyst supports in structured reactors promise higher external surface areas, lower pressure drop and increased heat transfer than beds of packed particles, especially for reactions limited to the external surface. Heat transfer is an important factor in highly endothermic and exothermic reactions, with the latter more compelling since hot spots, once started, propagate through the bed and lead

Y. Peng; J. T. Richardson

2004-01-01

44

Effect of mass transfer on the reaction rate in a monolithic catalyst with porous walls  

Microsoft Academic Search

The influence of reacting gas flow on the heterogeneous reaction in catalyst volume of honeycomb porous monolith with triangular channels was studied. The spatial distributions of the reacting gas flow, the rates of local mass transfer between channel walls and gas flow, as well as the interaction of transfer processes and a catalytic reaction were determined on the basis of

O. P. Klenov; S. A. Pokrovskaya; N. A. Chumakova; S. N. Pavlova; V. A. Sadykov; A. S. Noskov

2009-01-01

45

Photoinduced Intermolecular and Intramolecular Electron Transfer  

Microsoft Academic Search

The finite sink approximation to the Smoluchowski -Collins-Kimball expression is used here to parameterize intermolecular electron transfer fluorescence quenching data. Values are determined for the relative diffusion coefficient, D_{rm FQ} and the effective encounter diameter, R in both diffusion limited and influenced cases. The effective encounter diameter is seen to increase with decreasing oxidation potential of electron donating quenchers of

Carl John Biver III

1993-01-01

46

Synthesis of Externally Initiated Poly(3-alkylthiophene)s via Kumada Catalyst Transfer Polymerization  

NASA Astrophysics Data System (ADS)

The ability of chemists to design and synthesize pi conjugated organic polymers with precise control over their physical and electronic properties remains the key to technological breakthroughs using polymeric material in electronic and photonic devices. Kumada catalyst transfer polymerization (KCTP) technique and Grignard metathesis (GRIM) method have enabled the synthesis of highly regioregular polymers with controlled molecular weights, narrow polydispersity index and uniform end groups. Applying this technique toward external initiation of polymers would enable the preparation of sophisticated and beneficial polymer architectures such as surface grafted polymers. This work presents an investigation of various mechanistic parameters for external initiation of poly(3-alkylthiophene). The effects of binding ligand variation on the Nickel catalyst were investigated utilizing a novel methodology allowing facile screening of ligands. Poly(3-hexylthiophene) was synthesized with high percentage initiator headgroup incorporation with triphenylphosphine ligand while the use of bidentate ligands such as diphenylphosphinopropane only resulted in quantitative initiation when ligand exchange followed initiation with the more active species. A variety of functionally substituted aryl and thiophene halides were explored for their potential to act as external small molecule initiators and the reaction intermediates were characterized via spectroscopic techniques as well as theoretical calculations. Aryl halides were found to be more stable than thiophene halides and the type and position of the initiator functionality has played a deciding role in the polymerization mechanism. Ortho substitution stabilized the aryl-Ni intermediate complex via favorable orbital overlap and kinetic effects as a result of steric hindrance were demonstrated to affect the success of the external initiation. Surface-grafted poly(3-methylthiophene) thin films were synthesized from indium tin oxide where polymer thin film thicknesses were regulated by the variation of monomer solution and polymerization time. Photoelectron spectroscopy analysis had demonstrated that electrochemical oxidation of surface grafted thin films affords the ability to tune the work function and ionization potential. Such materials with controllable thicknesses and electronic properties have the potential to be useful as components in organic photovoltaic devices.

D'Avanzo, Antonella

47

Single Molecule Spectroscopy of Electron Transfer  

SciTech Connect

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

Michael Holman; Ling Zang; Ruchuan Liu; David M. Adams

2009-10-20

48

Electronic energy transfer and electron transfer in flexible bichromophoric molecules studied in a supersonic jet  

Microsoft Academic Search

The objective of this dissertation is to use laser spectroscopy in supersonic jets to investigate the dynamics and mechanism of Electronic Energy Transfer (EET) and Photon-induced Electron Transfer (PET) in bichromophoric molecules with flexible bridges. Molecular geometry computations using molecular mechanism methods have been applied to the interpretations of experimental results. In the investigations of a series of molecules: (1-

Xin Wang

1999-01-01

49

Electron transfer reactions in microporous solids  

SciTech Connect

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

Mallouk, T.E.

1993-01-01

50

Photoinduced electron transfer in ordered polymers  

SciTech Connect

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.

Jones, G. II.

1991-12-01

51

Protein motifs that facilitate electron transfer reactions  

NASA Astrophysics Data System (ADS)

Intra-protein electron transfer reactions are strongly modified by the unique, heterogeneous environment of each redox cofactor binding site. Ionized side chains and polar groups such as the backbone create static fields. Electron transfer also induces changes in the protein and its surroundings. Reorientation of the solvent water and polar or ionized side chains stabilize each charge state of the cofactor. In addition, changes in protonation state of acidic and basic groups in the protein couple proton motion to electron transfer. All these contributions modify the reaction free energy relative to that found in reference solvents. However, in each protein site different factors are most important. Multi Conformation Continuum Electrostatics calculations identify protein motifs that are important in each protein. Examples from cytochromes and photosynthetic reaction centers will be described. Supported by N.S.F. MCB-9629047.

Gunner, Marilyn

2002-03-01

52

Dialkylzinc Compounds as Chain Transfer Agents in Ethylene and Propylene Polymerizations Catalyzed by Metallocene Catalysts  

Microsoft Academic Search

Dialkylzinc compounds (ZnR2) with the alkyl groups of different steric hindrance were used as chain transfer agents in ethylene and propylene polymerizations catalyzed by two conventional metallocene catalysts including rac-Et(Ind)2ZrCl2 and rac-Me2Si[2-Me-4-Ph-Ind]2ZrCl2. In general, catalyst activities for ethylene polymerizations are barely affected by chain transfer agents, regardless of the R type; however, there are significant activity reductions in propylene polymerizations

Chuan-Hui Zhang; Jin-Yong Dong

2010-01-01

53

Dynamics in electron transfer protein complexes.  

PubMed

Electron transfer proteins transport electrons safely between large redox enzymes. The complexes formed by these proteins are among the most transient. The biological function requires, on the one hand, sufficient specificity of the interaction to allow for rapid and selective electron transfer, and, on the other hand, a fast turnover of the complex. Recent progress in the characterization of the nature of these complexes has demonstrated that the encounter state plays an important role. This state of initial binding is dominated by electrostatic interactions, and consists of an ensemble of orientations. Paramagnetic relaxation enhancement NMR and chemical shift perturbation analysis provide ways for the experimental characterisation of the encounter state. Several studies that have used these techniques have shown that the surface area sample in the encounter state can be limited to the immediate environment of the final, specific complex. The encounter complex can represent a large fraction and, in some small complexes, no specific binding is detected at all. It can be concluded that, in electron transfer protein complexes, a fine balance is sought between the low-specificity encounter state and the high-specificity productive complex to meet the opposing requirements of rapid electron transfer and a high turnover rate. PMID:21352493

Bashir, Qamar; Scanu, Sandra; Ubbink, Marcellus

2011-03-22

54

Extracellular electron transfer via microbial nanowires  

NASA Astrophysics Data System (ADS)

Microbes that can transfer electrons to extracellular electron acceptors, such as Fe(III) oxides, are important in organic matter degradation and nutrient cycling in soils and sediments. Previous investigations on electron transfer to Fe(III) have focused on the role of outer-membrane c-type cytochromes. However, some Fe(III) reducers lack c-cytochromes. Geobacter species, which are the predominant Fe(III) reducers in many environments, must directly contact Fe(III) oxides to reduce them, and produce monolateral pili that were proposed, on the basis of the role of pili in other organisms, to aid in establishing contact with the Fe(III) oxides. Here we report that a pilus-deficient mutant of Geobacter sulfurreducens could not reduce Fe(III) oxides but could attach to them. Conducting-probe atomic force microscopy revealed that the pili were highly conductive. These results indicate that the pili of G. sulfurreducens might serve as biological nanowires, transferring electrons from the cell surface to the surface of Fe(III) oxides. Electron transfer through pili indicates possibilities for other unique cell-surface and cell-cell interactions, and for bioengineering of novel conductive materials.

Reguera, Gemma; McCarthy, Kevin D.; Mehta, Teena; Nicoll, Julie S.; Tuominen, Mark T.; Lovley, Derek R.

2005-06-01

55

Electron-transfer reactions in polymer matrices  

NASA Astrophysics Data System (ADS)

This paper discusses the dark reactions and photoreactions that occur with transfer of an electron from a donor to an acceptor in polymer matrices under electron tunnelling conditions and when forming change-transfer complexes. The main emphasis is on an analysis of the factors that determine the rate of electron transfer, which, in accordance with the advanced theory of electron transfer, are the magnitude of the exchange interaction, the free energy of the process, and the reorganisation energies of the medium and the reacting donor and acceptor molecules. The existing models for the movement of charge carriers between single-type transport sites are discussed. The limits of applicability of the different models have been determined. The reorganisation energy of a polymer matrix is shown to have a considerable effect on the rate of movement of charge carriers on introduced transport molecules. The effect of the dielectric properties and free volume of polymer matrices on the characteristics of electron phototransfer in donor-acceptor complexes is discussed. The bibliography includes 126 references.

Vannikov, Anatolii V.; Grishina, Antonina D.

1989-12-01

56

Molecular Basis for Directional Electron Transfer*  

PubMed Central

Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of electron tunneling with distance. In this work intermolecular electron transfer was studied in kinetic experiments performed with the small tetraheme cytochrome from Shewanella oneidensis MR-1 and from Shewanella frigidimarina NCIMB400 using non-physiological redox partners. This choice allowed the effect of specific recognition and docking to be eliminated from the measured rates. The results were analyzed with a kinetic model that uses the extensive thermodynamic characterization of these proteins reported in the literature to discriminate the kinetic contribution of each heme to the overall rate of electron transfer. This analysis shows that, in this redox chain that spans 23 ?, the kinetic properties of the individual hemes establish a functional specificity for each redox center. This functional specificity combined with the thermodynamic properties of these soluble proteins ensures directional electron flow within the cytochrome even outside of the context of a functioning respiratory chain.

Paquete, Catarina M.; Saraiva, Ivo H.; Calcada, Eduardo; Louro, Ricardo O.

2010-01-01

57

Mechanism of cobalt self-exchange electron transfer.  

PubMed

A heptanuclear cobalt cluster was synthesized in two different oxidation states, Co(II)7 and a mixed valence Co(III)Co(II)6, as a soluble model of a cobalt-phosphate/borate (Co-OEC) water splitting catalyst. Crystallographic characterization indicates similar cluster cores, distinguished primarily at the central Co atom. An anion associates to the cluster cores via hydrogen bonding. Using an isotope exchange method, an anomalously slow self-exchange electron transfer rate constant (kobs = 1.53 × 10(-3) M(-1) s(-1) at 40 °C and 38 mM [OTf] in MeCN), as compared to that predicted from semiclassical Marcus theory, supports a charge transfer process that is accelerated by dissociation of the anion from the oxidized cluster. This mechanism sheds light on the inverse dependence of anions in the self-repair mechanism of Co-OECs. Moreover, because H2O cannot directly bridge cobalt centers, owing to the encapsulation of the central Co within the cluster core, the observed results address a long-standing controversy surrounding the Co(2+/3+) self-exchange electron transfer reaction of the hexaaqua complex. PMID:23987247

Ullman, Andrew M; Nocera, Daniel G

2013-09-30

58

Dynamics of electron transfer in photosystem II  

Microsoft Academic Search

Photosystem II, being a constituent of light driven photosynthetic apparatus, is a highly organized pigment-protein-lipid\\u000a complex. The arrangement of PSII active redox cofactors insures efficiency of electron transfer within it. Donation of electrons\\u000a extracted from water by the oxygen evolving complex to plastoquinones requires an additional activation energy. In this paper\\u000a we present theoretical discussion of the anharmonic fluctuations of

Kv?toslava Burda

2007-01-01

59

Time dependence of donor–acceptor electron transfer and back transfer in solid solution  

Microsoft Academic Search

Electron transfer from an optically excited donor to randomly distributed acceptors followed by electron back transfer is treated theoretically for donors and acceptors in a rigid solution. The forward electron transfer process is described in terms of the excited state population probabilityPex(t) of the donor molecules, while the electron back transfer from the radical anion to the radical cation is

Y. Lin; R. C. Dorfman; M. D. Fayer

1989-01-01

60

Experimental investigation of donor-acceptor electron transfer and back transfer in solid solutions  

Microsoft Academic Search

Electron transfer from an optically excited donor (rubrene) to randomly distributed acceptors (duroquinone) followed by electron back transfer in a rigid solution (sucrose octaacetate) has been studied experimentally. The forward electron-transfer process was observed by time-dependent fluorescence quenching measurements, while the electron back transfer from the radical anion to the radical cation was monitored by use of the picosecond transient

R. C. Dorfman; Y. Lin; M. D. Fayer

1989-01-01

61

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads  

SciTech Connect

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).

Not Available

1989-04-12

62

Solvent gating of intramolecular electron transfer  

SciTech Connect

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.

Miller, R.M. (California State Univ., Chico, CA (United States)); Spears, K.G.; Gong, J.H.; Wach, M. (Northwestern Univ., Evanston, IL (United States))

1994-02-03

63

Solvent dynamics and electron transfer reactions  

Microsoft Academic Search

Recent experimental and theoretical studies of the influence of solvent dynamics on electron transfer (ET) reactions are discussed. It is seen that the survival probabilities of the reactants and products can be obtained as the solution to an integral equation using experimental or simulation data on the solvation dynamics. The theory developed for ET between thermally equilibrated reactants in solution,

Jayendran C. Rasaiah; Jianjun Zhu

1994-01-01

64

Promoting Knowledge Transfer with Electronic Note Taking  

ERIC Educational Resources Information Center

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

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

2005-01-01

65

A nonadiabatic theory for electron transfer and application to ultrafast catalytic reactions  

NASA Astrophysics Data System (ADS)

We propose a general formalism which extends those used for the standard theory of electron transfer (ET) in chemistry but also becomes equivalent to it far from the inversion point. Our model yields different results essentially in the vicinity of the inversion point when the energy barrier for ET is small. In that regime, the electronic frequencies become of the order of the phonon frequencies and the process of electron tunnelling is nonadiabatic because it is strongly coupled to the phonons. The consequence of nonadiabaticity is that the effective electron dynamics becomes nonlinear and that there is energy dissipation through the phonon bath. Thermal fluctuations appears as a random force in the effective equation. We use this formalism for a careful investigation of the vicinity of the inversion point. We find that when the model parameters are finely tuned, ET between donor and acceptor becomes reversible. Then, large amplitude electronic oscillations, associated with large amplitude and collective phonon oscillations at the same frequency, are spontaneously generated. This system is a coherent electron-phonon oscillator (CEPO) which cannot be confused with a standard normal mode. The acceptor which does not capture the electron may play the role of a catalyst. Thus when the catalyst is finely tuned with the donor in order to form a CEPO, it may trigger an irreversible and ultrafast electron transfer at low temperature between the donor and an extra acceptor, while in the absence of a catalyst, ET cannot occur. Such a trimer system may be regulated by small perturbations and behaves as a molecular transistor. We illustrate this idea by explicit numerical simulations on trimer models of the type donor-catalyst-acceptor. We discuss the relevance of our approach for understanding the ultrafast electron transfer experimentally observed in biosystems such as the photosynthetic reaction centre.

Aubry, S.

2007-06-01

66

Efficient clocked electron transfer on superfluid helium.  

PubMed

Unprecedented transport efficiency is demonstrated for electrons on the surface of micron-scale superfluid helium-filled channels by co-opting silicon processing technology to construct the equivalent of a charge-coupled device. Strong fringing fields lead to undetectably rare transfer failures after over a billion cycles in two dimensions. This extremely efficient transport is measured in 120 channels simultaneously with packets of up to 20 electrons, and down to singly occupied pixels. These results point the way towards the large scale transport of either computational qubits or electron spin qubits used for communications in a hybrid qubit system. PMID:22243176

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

2011-12-19

67

Fluorescent analysis of excess electron transfer through DNA  

Microsoft Academic Search

The DNA base stack provides unique features for the efficient long-range charge transfer. For the purpose of investigating excess electron transfer process through DNA, we developed a new method for fluorescence analysis of excess electron transfer based on reductive cleavage of a disulfide bond and a thiol-specific fluorescent probe. Excess electron transfer was detected by monitoring the fluorescence of emissive

Tadao Takada; Chie Tanaka; Mitsunobu Nakamura; Kazushige Yamana

2010-01-01

68

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

PubMed Central

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

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

2011-01-01

69

BASE-CATALYZED DESTRUCTION OF PCBS-NEW DONORS, NEW TRANSFER AGENTS/CATALYSTS  

EPA Science Inventory

The use of hydrogen transfer agents and catalysts to improve the base-catalyzed decomposition of polychlorinated biphenyls (PCBs) was investigated. The reaction proceeded only in the presence of base, but the rate of PCB disappearance increased with increasing amount of hydrogen ...

70

Identification of a highly effective asymmetric phase-transfer catalyst derived from ?-methylnaphthylamine  

Microsoft Academic Search

A library of quaternary ammonium salts has been generated via reaction of simple chiral amines with a series of conformationally dynamic biphenyl units. Screening of this library against the alkylation of a glycine imine has led to the identification of a highly effective asymmetric phase-transfer catalyst derived from ?-methylnaphthylamine.

Barry Lygo; Bryan Allbutt; S. Russell James

2003-01-01

71

Mass transfer effects in the oxidation of aqueous organic compounds over a hydrophobic solid catalyst  

Microsoft Academic Search

The use of a Carberry-type reactor has been investigated for the complete oxidation by oxygen of various water-soluble organic compounds over a platinum on porous polydivinylbenzene catalyst. Studies with aqueous formaldehyde as the test reactant reveal important details of reactor hydrodynamics and possible reaction pathways. Two routes for the transfer of oxygen are apparent in this reaction system. At low

K Lavelle; J. B McMonagle

2001-01-01

72

Estimates of electronic coupling for excess electron transfer in DNA  

NASA Astrophysics Data System (ADS)

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 ? 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.

Voityuk, Alexander A.

2005-07-01

73

Photoinduced electron transfer in model systems of photosynthesis  

Microsoft Academic Search

This Thesis describes Investigations on photoinduced electron transfer (ET) for several compounds, serving as model systems of the natural photosynthesis. In addition, the properties of the systems, e.g. the conformation in solution and the electronic properties of the photoexcited states are treated.Chapter 2 discusses present theories of photoinduced electron transfer. The following factors appear to effect the electron transfer rate

U. Hofstra

1988-01-01

74

Covalent electron transfer chemistry of graphene with diazonium salts.  

PubMed

Graphene is an atomically thin, two-dimensional allotrope of carbon with exceptionally high carrier mobilities, thermal conductivity, and mechanical strength. From a chemist's perspective, graphene can be regarded as a large polycyclic aromatic molecule and as a surface without a bulk contribution. Consequently, chemistries typically performed on organic molecules and surfaces have been used as starting points for the chemical functionalization of graphene. The motivations for chemical modification of graphene include changing its doping level, opening an electronic band gap, charge storage, chemical and biological sensing, making new composite materials, and the scale-up of solution-processable graphene. In this Account, we focus on graphene functionalization via electron transfer chemistries, in particular via reactions with aryl diazonium salts. Because electron transfer chemistries depend on the Fermi energy of graphene and the density of states of the reagents, the resulting reaction rate depends on the number of graphene layers, edge states, defects, atomic structure, and the electrostatic environment. We limit our Account to focus on pristine graphene over graphene oxide, because free electrons in the latter are already bound to oxygen-containing functionalities and the resulting chemistries are dominated by localized reactivity and defects. We describe the reaction mechanism of diazonium functionalization of graphene and show that the reaction conditions determine the relative degrees of chemisorption and physisorption, which allows for controlled modulation of the electronic properties of graphene. Finally we discuss different applications for graphene modified by this chemistry, including as an additive in polymer matrices, as biosensors when coupled with cells and biomolecules, and as catalysts when combined with nanoparticles. PMID:22946516

Paulus, Geraldine L C; Wang, Qing Hua; Strano, Michael S

2012-09-04

75

Phase transfer catalysts drive diverse organic solvent solubility of single-walled carbon nanotubes helically wrapped by ionic, semiconducting polymers.  

PubMed

Use of phase transfer catalysts such as 18-crown-6 enables ionic, linear conjugated poly[2,6-{1,5-bis(3-propoxysulfonicacidsodiumsalt)}naphthylene]ethynylene (PNES) to efficiently disperse single-walled carbon nanotubes (SWNTs) in multiple organic solvents under standard ultrasonication methods. Steady-state electronic absorption spectroscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) reveal that these SWNT suspensions are composed almost exclusively of individualized tubes. High-resolution TEM and AFM data show that the interaction of PNES with SWNTs in both protic and aprotic organic solvents provides a self-assembled superstructure in which a PNES monolayer helically wraps the nanotube surface with periodic and constant morphology (observed helical pitch length = 10 ± 2 nm); time-dependent examination of these suspensions indicates that these structures persist in solution over periods that span at least several months. Pump-probe transient absorption spectroscopy reveals that the excited state lifetimes and exciton binding energies of these well-defined nanotube-semiconducting polymer hybrid structures remain unchanged relative to analogous benchmark data acquired previously for standard sodium dodecylsulfate (SDS)-SWNT suspensions, regardless of solvent. These results demonstrate that the use of phase transfer catalysts with ionic semiconducting polymers that helically wrap SWNTs provide well-defined structures that solubulize SWNTs in a wide range of organic solvents while preserving critical nanotube semiconducting and conducting properties. PMID:20809609

Deria, Pravas; Sinks, Louise E; Park, Tae-Hong; Tomezsko, Diana M; Brukman, Matthew J; Bonnell, Dawn A; Therien, Michael J

2010-10-13

76

Ultrafast spectroscopy of electron transfer dynamics in liquids; excitation transfer studies of phase transitions  

Microsoft Academic Search

The transfer of an electron from a donor to an acceptor is the fundamental step in a wide range of chemical and biological processes. As a result, electron-transfer reactions have been the focus of numerous theoretical and experimental efforts aimed at understanding the kinetics and mechanism of the transfer event. Liquid solvents are an important medium for electron-transfer processes. The

Alexei A. Goun

2008-01-01

77

Bacterial Nanowires Facilitate Extracellular Electron Transfer  

NASA Astrophysics Data System (ADS)

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.

Gorby, Y.

2005-12-01

78

Imidazole facilitates electron transfer from organic reductants.  

PubMed

In cyclic voltammetry studies at pH 8, imidazole facilitates oxidation of organic compounds that normally lose hydrogen atoms. High concentrations of imidazole shift the oxidizing wave of ascorbic acid, 2,3-dimethoxy-5-methyl-1,4-hydroquinone, and the vitamin E analogue Trolox toward lower potentials. By contrast, imidazole has no effect on the cyclic voltammogram of methyl viologen, which undergoes electron rather than hydrogen-atom transfer. The effect of imidazole is observed at pH 8.0 but only to a lesser extent at pH 5.5 indicating that imidazole must be unprotonated to facilitate oxidation. Digital simulation shows that these results are consistent with a mechanism in which imidazole acts as a proton acceptor permitting concerted proton/electron transfer by the organic reductant. PMID:15219240

Kipp, Brian H; Faraj, Chadi; Li, Guoliang; Njus, David

2004-08-01

79

Reaction coordinates for electron transfer reactions  

SciTech Connect

The polarization fluctuation and energy gap formulations of the reaction coordinate for outer sphere electron transfer are linearly related to the constant energy constraint Lagrangian multiplier m in Marcus' theory of electron transfer. The quadratic dependence of the free energies of the reactant and product intermediates on m and m+1, respectively, leads to similar dependence of the free energies on the reaction coordinates and to the same dependence of the activation energy on the reorganization energy and the standard reaction free energy. Within the approximations of a continuum model of the solvent and linear response of the longitudinal polarization to the electric field in Marcus' theory, both formulations of the reaction coordinate are expected to lead to the same results.

Rasaiah, Jayendran C. [Department of Chemistry, University of Maine, Orono, Maine 04469 (United States); Zhu Jianjun [Department of Chemistry, State University of New York, Stonybrook, New York 11790 (United States) and Department of Chemistry, Henan Normal University, Xinxiang, Henan (China)

2008-12-07

80

Role of iron-based catalyst and hydrogen transfer in direct coal liquefaction  

SciTech Connect

The aim of this research is to understand the major function of iron-based catalysts on direct coal liquefaction (DCL). Pyrolysis and direct liquefaction of Shenhua bituminous coal were carried out to investigate the effect of three solvents (wash-oil from coal-tar, cycle-oil from coal liquefaction, and tetralin) in a N{sub 2} or a H{sub 2} atmosphere and with or without catalyst. The hydrogen content in the solvent and liquid product and the H{sub 2} consumption for every run were calculated to understand the hydrogen transfer approach in DCL. The results showed that the iron-based catalyst promotes the coal pyrolysis, and the dominating function of the catalyst in DCL is to promote the formation of activated hydrogen and to accelerate the secondary distribution of H in the reaction system including the gas, liquid, and solid phases. The major transfer approach of the activated hydrogen is from molecular hydrogen to solvent and then from solvent to coal, and the solvent takes on the role of a 'bridge' in the hydrogen transfer approach. 31 refs., 5 figs., 3 tabs.

Xian Li; Shuxun Hu; Lijun Jin; Haoquan Hu [Dalian University of Technology, Dalian (China). Institute of Coal Chemical Engineering

2008-03-15

81

Electron Transfer in Photosynthetic Reaction Centers  

Microsoft Academic Search

The central importance of (bacterio)chlorophyll as a major photosynthetic pigment arises from its ability to both harvest\\u000a the sunlight and perform ultrafast electron transfer (ET) reactions. The main function of the reaction center (RC) is to convert\\u000a the photoexcitation in order to generate a trans-membrane potential in a series of ET steps. In bacterial RCs it is possible\\u000a to relate

Josef Wachtveitl; Wolfgang Zinth

82

Electron transfer reactions at conductive diamond electrodes  

Microsoft Academic Search

The electrochemical behavior of the iron(III)\\/iron(II) and the ferri\\/ferro–cyanide redox couples in aqueous media has been investigated at conductive diamond, to obtain information on the properties of this electrode material. The investigation has been carried out at as prepared and oxidized diamond surfaces, under conditions of different concentration and temperature. The electron transfer kinetics has been followed by cyclic voltammetry,

Sergio Ferro; Achille De Battisti

2002-01-01

83

Catalysts  

NSDL National Science Digital Library

There are two types of catalysis reactions: homogeneous and heterogeneous. In a homogeneous reaction, the catalyst is in the same phase as the reactants. In a heterogeneous reaction, the catalyst is in a different phase from the reactants. This activity addresses homogeneous catalysis.

Consortium, The C.

2011-12-11

84

Electronic parameters for charge transfer along DNA.  

PubMed

We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The pi molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wave functions and energies of DNA bases are discussed and then used for calculating the corresponding wave functions of the two B-DNA base-pairs (adenine-thymine and guanine-cytosine). The obtained HOMO and LUMO energies of the bases are in good agreement with available experimental values. Our results are then used for estimating the complete set of charge transfer parameters between neighboring bases and also between successive base-pairs, considering all possible combinations between them, for both electrons and holes. The calculated microscopic quantities can be used in mesoscopic theoretical models of electron or hole transfer along the DNA double helix, as they provide the necessary parameters for a tight-binding phenomenological description based on the pi molecular overlap. We find that usually the hopping parameters for holes are higher in magnitude compared to the ones for electrons. Our findings are also compared with existing calculations from first principles. PMID:20680380

Hawke, L G D; Kalosakas, G; Simserides, C

2010-08-01

85

Dynamic environmental transmission electron microscopy observation of platinum electrode catalyst deactivation in a proton-exchange-membrane fuel cell.  

PubMed

Spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied to study the catalytic activity of platinum/amorphous carbon electrode catalysts in proton-exchange-membrane fuel cells (PEMFCs). These electrode catalysts were characterized in different atmospheres, such as hydrogen and air, and a conventional high vacuum of 10(-5) Pa. A high-speed charge coupled device camera was used to capture real-time movies to dynamically study the diffusion and reconstruction of nanoparticles with an information transfer down to 0.1 nm, a time resolution below 0.2 s and an acceleration voltage of 300 kV. With such high spatial and time resolution, AC-ETEM permits the visualization of surface-atom behaviour that dominates the coalescence and surface-reconstruction processes of the nanoparticles. To contribute to the development of robust PEMFC platinum/amorphous carbon electrode catalysts, the change in the specific surface area of platinum particles was evaluated in hydrogen and air atmospheres. The deactivation of such catalysts during cycle operation is a serious problem that must be resolved for the practical use of PEMFCs in real vehicles. In this paper, the mechanism for the deactivation of platinum/amorphous carbon electrode catalysts is discussed using the decay rate of the specific surface area of platinum particles, measured first in a vacuum and then in hydrogen and air atmospheres for comparison. PMID:23340321

Yoshida, Kenta; Xudong, Zhang; Bright, Alexander N; Saitoh, Koh; Tanaka, Nobuo

2013-01-22

86

Dynamic environmental transmission electron microscopy observation of platinum electrode catalyst deactivation in a proton-exchange-membrane fuel cell  

NASA Astrophysics Data System (ADS)

Spherical-aberration-corrected environmental transmission electron microscopy (AC-ETEM) was applied to study the catalytic activity of platinum/amorphous carbon electrode catalysts in proton-exchange-membrane fuel cells (PEMFCs). These electrode catalysts were characterized in different atmospheres, such as hydrogen and air, and a conventional high vacuum of 10-5 Pa. A high-speed charge coupled device camera was used to capture real-time movies to dynamically study the diffusion and reconstruction of nanoparticles with an information transfer down to 0.1 nm, a time resolution below 0.2 s and an acceleration voltage of 300 kV. With such high spatial and time resolution, AC-ETEM permits the visualization of surface-atom behaviour that dominates the coalescence and surface-reconstruction processes of the nanoparticles. To contribute to the development of robust PEMFC platinum/amorphous carbon electrode catalysts, the change in the specific surface area of platinum particles was evaluated in hydrogen and air atmospheres. The deactivation of such catalysts during cycle operation is a serious problem that must be resolved for the practical use of PEMFCs in real vehicles. In this paper, the mechanism for the deactivation of platinum/amorphous carbon electrode catalysts is discussed using the decay rate of the specific surface area of platinum particles, measured first in a vacuum and then in hydrogen and air atmospheres for comparison.

Yoshida, Kenta; Xudong, Zhang; Bright, Alexander N.; Saitoh, Koh; Tanaka, Nobuo

2013-02-01

87

Horizontal gene transfer in nematodes: a catalyst for plant parasitism?  

PubMed

The origin of plant parasitism within the phylum Nematoda is intriguing. The ability to parasitize plants has originated independently at least three times during nematode evolution and, as more molecular data has emerged, it has become clear that multiple instances of horizontal gene transfer (HGT) from bacteria and fungi have played a crucial role in the nematode's adaptation to this new lifestyle. The first reported HGT cases in plant-parasitic nematodes were genes encoding plant cell wall-degrading enzymes. Other putative examples of HGT were subsequently described, including genes that may be involved in the modulation of the plant's defense system, the establishment of a nematode feeding site, and the synthesis or processing of nutrients. Although, in many cases, it is difficult to pinpoint the donor organism, candidate donors are usually soil dwelling and are either plant-pathogenic or plant-associated microorganisms, hence occupying the same ecological niche as the nematodes. The exact mechanisms of transfer are unknown, although close contacts with donor microorganisms, such as symbiotic or trophic interactions, are a possibility. The widespread occurrence of horizontally transferred genes in evolutionarily independent plant-parasitic nematode lineages suggests that HGT may be a prerequisite for successful plant parasitism in nematodes. PMID:21539433

Haegeman, Annelies; Jones, John T; Danchin, Etienne G J

2011-08-01

88

Advanced Electron Microscopy in Developing Nanostructured Heterogeneous Catalysts  

Microsoft Academic Search

\\u000a Catalysis is the science of chemical reactions on an atomic or molecular level. Using the modern language, we can define catalysis\\u000a as a process of facilitated self-assembly of atoms or molecules; and a catalyst acts as the facilitator. Heterogeneous catalysis\\u000a refers to chemical reactions that occur on a surface; it involves solid catalysts and gaseous or liquid reactants. Heterogeneous\\u000a catalysts

J. Liu

89

Transmission electron microscopy investigation of auto catalyst and cobalt germanide  

NASA Astrophysics Data System (ADS)

The modern ceria-zirconia based catalysts are used in automobiles to reduce exhaust pollutants. Cobalt germanides have potential applications as electrical contacts in the future Ge-based semiconductor devices. In this thesis, transmission electron microscopy (TEM) techniques were used to study the atomic scale interactions between metallic nanostructures and crystalline substrates in the two material systems mentioned above. The model catalyst samples consisted of precious metal nano-particles (Pd, Rh) supported on the surface of (Ce,Zr)O2 thin films. The response of the microstructure of the metal-oxide interface to the reduction and oxidation treatments was investigated by cross-sectional high resolution TEM. Atomic detail of the metal-oxide interface was obtained. It was found that Pd and Rh showed different sintering and interaction behaviors on the oxide surface. The preferred orientation of Pd particles in this study was Pd(111)//CZO(111). Partial encapsulation of Pd particles by reduced (Ce,Zr)O 2 surface was observed and possible mechanisms of the encapsulation were discussed. The characteristics of the metal-oxide interaction depend on the properties of the oxide, as well as their relative orientation. The results provide experimental evidence for understanding the thermodynamics of the equilibrium morphology of a solid particle supported on a solid surface that is not considered as inert. The reaction of Co with Ge to form epitaxial Co5Ge7 was studied by in situ ultra-high vacuum (UHV) TEM using two methods. One was reactive deposition of Co on Ge, in which the Ge substrate was maintained at 350°C during deposition. The other method was solid state reaction, in which the deposition of Co on Ge was carried out at room temperature followed by annealing to higher temperatures. During reactive deposition, the deposited Co reacted with Ge to form nanosized 3D Co 5Ge7 islands. During solid state reaction, a continuous epitaxial Co5Ge7 film on the (001) Ge substrate was formed at ˜300°C. With further annealing at a higher temperature, the continuous Co5Ge 7 layer broke into 3D islands in order to relieve the strain energy in the epitaxial Co5Ge7 layer. Electron diffraction and X-ray diffraction were used to identify the cobalt germanide phase and epitaxial orientation relationships with respect to the substrate.

Sun, Haiping

90

Electron transfer dissociation of peptide anions.  

PubMed

Ion/ion reactions of multiply deprotonated peptide anions with xenon radical cations result in electron abstraction to generate charge-reduced peptide anions containing a free-radical site. Peptide backbone cleavage then occurs by hydrogen radical abstraction from a backbone amide N to facilitate cleavage of the adjacent C-C bond, thereby producing a- and x-type product ions. Introduction of free-radical sites to multiply charged peptides allows access to new fragmentation pathways that are otherwise too costly (e.g., lowers activation energies). Further, ion/ion chemistry, namely electron transfer reactions, presents a rapid and efficient means of generating odd-electron multiply charged peptides; these reactions can be used for studying gas-phase chemistries and for peptide sequence analysis. PMID:15907703

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

2005-04-14

91

Electrosynthesis in systems of two immiscible liquids and a phase transfer catalyst. II. Aromatic nuclear acyloxylation  

Microsoft Academic Search

The anodic acetoxylation of 1,4-dimethoxybenzene in a methylene chloride\\/water emulsion and using a phase transfer catalyst to supply the acetate ion to the organic medium is discussed. The yield of 2,5-dimethoxyphenylacetate is shown to vary with the electrolysis conditions but this product can be obtained with an organic yield of 85% and current yield, 60%. Similar conditions are used to

S. R. Ellis; D. Pletcher; P. H. Gamlen; K. P. Healy

1982-01-01

92

Water-improved heterogeneous transfer hydrogenation using methanol as hydrogen donor over Pd-based catalyst  

Microsoft Academic Search

The heterogeneous catalytic transfer hydrogenation (CTH) of styrene and nitrobenzene over Pd-based catalyst using methanol as hydrogen donor was investigated in a fixed-bed reactor. With the increase of the molar ratio of water to methanol from 0 to 1, the conversions of styrene and nitrobenzene are increased from 26.3% and 7.1% to 100% and 31.9%, respectively, and the selectivity of

Yizhi Xiang; Xiaonian Li; Chunshan Lu; Lei Ma; Qunfeng Zhang

2010-01-01

93

Photoinduced electron transfer reactions in zeolite cages  

SciTech Connect

This report summarizes work in the two areas of zeolites and layered double hydroxides. Results of studies on structural aspects of Ru(bpy)[sub 3][sup 2+]-zeolite Y are summarized. Photoinduced electron transfer between entrapped Ru(bpy)[sub 3][sup 2+] and methylviologen (MV) in neighboring supercages was examined. Benzylviologen was also used. Since molecules larger than 13 [angstrom] cannot be accomodated in zeolite cages, the layered double metal hydroxides (LDH) LiAl[sub 2](OH)[sub 6][sup +]X[sup [minus

Dutta, P.K.

1992-01-01

94

Mixed Valent Sites in Biological Electron Transfer  

SciTech Connect

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.

Solomon, E.I.; Xie, X.; Dey, A.

2009-05-26

95

Electronic excitation transfer in organized molecular assemblies  

SciTech Connect

Dynamics of electronic excitation transfer under restricted molecular geometries was investigated by means of a picosecond time-resolved fluorescence spectrophotometer and was compared among several kinds of molecular assemblies such as vesicles, Langmuir-Blodgett films, and photosynthetic light-harvesting antenna. The form of fluorescence decay curves depends on (1) dimensionality of systems (2-D, 3-D, or stacking multilayers) and (2) distribution of functional chromophores in a supramolecular assembly framework. The fluorescence decay curves of photoexcited donors were analyzed and revealed fractal behaviors with respect to spatial distribution of chromophores or energetically hierarchical structure among different sites with slightly different energy levels.

Yamazaki, Iwao; Tamai, Naoto; Yamazaki, Tomoko (Hokkaido Univ., Sapporo (Japan))

1990-01-25

96

Transmembrane electron transfer catalyzed by phospholipid-linked manganese porphyrins  

SciTech Connect

Synthetic models can be very helpful in studying the effect of distance and orientation in electron transfer reactions in biological membrane processes such as occur in photosynthesis and mitochondria. To provide a model for the electron transfer where porphyrin pigments play the key role, the preparation of porphyrin derivatives that are capable of light-induced intra- or intermolecular electron transfer was reported. However, there has been little study of ground-state electron transfer between porphyrin complexes to provide insight into the effect of distance and orientation in the electron transfer so that a vectorial electron transfer system may be constructed in the biological membrane. We now report transmembrane electron transfer catalyzed by manganese complexes of bilayer-active phospholipid-linked porphyrins 1, PE-C{sub n}-MnTTP (n = 0, 5, 11) (Scheme I), which can be easily immersed into the lipid bilayer. The synthetic procedures leading are described.

Nango, Mamoru; Mizusawa, Atsushi; Miyake, Takenori; Yoshinaga, Junji (Univ. of Osaka Prefecture (Japan))

1990-02-14

97

Photoinduced electron transfer in ordered polymers  

SciTech Connect

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.

Jones, G. II.

1993-01-01

98

Electrosynthesis in systems of two immiscible liquids and a phase transfer catalyst. I. The anodic cyanation of naphthalene  

Microsoft Academic Search

The anodic cyanation of naphthalene in a methylene chloride\\/water emulsion using a phase transfer catalyst to supply cyanide ions to the organic medium has been re-examined. The effect of electrolysis parameters (e.g., current density, electrode material, concentration of cyanide, naphthalene and phase transfer catalyst) on the current and organic yields of products is reported. It is shown that by correct

S. R. Ellis; D. Pletcher; P. Gough; S. R. Korn

1982-01-01

99

Didecyldimethylammonium bromide (DDAB): a universal, robust, and highly potent phase-transfer catalyst for diverse organic transformations  

Microsoft Academic Search

Didecyldimethylammonium bromide (DDAB) has been scrutinized in comparison with traditional phase-transfer catalysts in variety of liquid–liquid reactions. It was found to be an exceptionally comprehensive, durable, and highly efficient phase-transfer catalyst (PTC) in a number of representative organic transformations such as C- and N-alkylations, isomerization, esterification, elimination, cyanation, bromination, and oxidation under very mild conditions of temperature and mixing. It

Mandan Chidambaram; Sachin U. Sonavane; Jaima de la Zerda; Yoel Sasson

2007-01-01

100

Electron Transfer versus Proton Transfer in Gas-Phase Ion/Ion Reactions of Polyprotonated Peptides  

PubMed Central

The ion/ion reactions of several dozen reagent anions with triply protonated cations of the model peptide KGAILKGAILR have been examined to evaluate predictions of a Landau–Zener-based model for the likelihood for electron transfer. Evidence for electron transfer was provided by the appearance of fragment ions unique to electron transfer or electron capture dissociation. Proton transfer and electron transfer are competitive processes for any combination of anionic and cationic reactants. For reagent anions in reactions with protonated peptides, proton transfer is usually significantly more exothermic than electron transfer. If charge transfer occurs at relatively long distances, electron transfer should, therefore, be favored on kinetic grounds because the reactant and product channels cross at greater distances, provided conditions are favorable for electron transfer at the crossing point. The results are consistent with a model based on Landau–Zener theory that indicates both thermodynamic and geometric criteria apply for electron transfer involving polyatomic anions. Both the model and the data suggest that electron affinities associated with the anionic reagents greater than about 60–70 kcal/mol minimize the likelihood that electron transfer will be observed. Provided the electron affinity is not too high, the Franck–Condon factors associated with the anion and its corresponding neutral must not be too low. When one or the other of these criteria is not met, proton transfer tends to occur essentially exclusively. Experiments involving ion/ion attachment products also suggest that a significant barrier exists to the isomerization between chemical complexes that, if formed, lead to either proton transfer or electron transfer.

Gunawardena, Harsha P.; He, Min; Chrisman, Paul A.; Pitteri, Sharon J.; Hogan, Jason M.; Hodges, Brittany D. M.; McLuckey, Scott A.

2005-01-01

101

NEGATIVE ELECTRON TRANSFER DISSOCIATION OF GLYCOSAMINOGLYCANS  

PubMed Central

Structural characterization of glycosaminoglycans (GAGs) has been a challenge in the field of mass spectrometry, and the application of electron detachment dissociation (EDD) Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) has shown great promise to GAG oligosaccharide characterization in a single tandem mass spectrometry experiment. In this work, we apply the technique of negative electron transfer dissociation (NETD) to GAGs on a commercial ion trap mass spectrometer. NETD of GAGs, using fluoranthene or xenon as the reagent gas, produces fragmentation very similar to previously observed EDD fragmentation. Using fluoranthene or xenon, both glycosidic and cross-ring cleavages are observed, as well as even- and odd-electron products. The loss of SO3 can be minimized and an increase in cross-ring cleavages is observed if a negatively-charged carboxylate is present during NETD, which can be controlled by the charge state or the addition of sodium. NETD effectively dissociates GAGs up to eight saccharides in length, but the low resolution of the ion trap makes assigning product ions difficult. Similar to EDD, NETD is also able to distinguish the epimers iduronic acid from glucuronic acid in heparan sulfate tetrasaccharides and suggests that a radical intermediate plays an important role in distinguishing these epimers. These results demonstrate that NETD is effective at characterizing GAG oligosaccharides in a single tandem mass spectrometry experiment on a widely available mass spectrometry platform.

Wolff, Jeremy J.; Leach, Franklin E.; Laremore, Tatiana N.; Kaplan, Desmond A.; Easterling, Michael L.; Linhardt, Robert J.; Amster, I. Jonathan

2010-01-01

102

Theory of Electron Transfer and Transport Pathways in Biomolecules  

NASA Astrophysics Data System (ADS)

Electron transfer in proteins and nucleic acids occurs over large distances by a combination of short and long range tunneling mechanisms. Electron tunneling is facilitated by virtual oxidized and reduced states of the bridging macromolecule, and theoretical analysis reveals how a macromolecule's fold, energetics, and fluctuations influence the electron-transfer kinetics. Recent studies of protein electron transfer indicate when and why electron tunneling kinetics is sensitive to the structure of the protein's tunneling pathways. Electron transfer across protein-protein interfaces involves thin structured water layers that play a key role in tunneling mediation as well. Tunneling analysis that takes the dynamical fluctuations of the macromolecules into explicit account provides a unified view that links structure and function in protein electron transfer. In the case of DNA electron transport, a critical role is found for structural fluctuations and transport mediated by carrier injection to intervening bases, even at very short distances.

Beratan, David

2008-03-01

103

Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production  

PubMed Central

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.

Horvath, Samantha; Fernandez, Laura E.; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2012-01-01

104

Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production  

SciTech Connect

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 cataly c 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 heterogeneous 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 nitrogen atoms become more mobile to facilitate the contraction of this distance. This approach assists in the identification of the favored mechanisms under various experimental conditions and provides insight into the qualitative impact of substituents on the nitrogen and phosphorous atoms. 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, under FWP 56073.

Horvath, Samantha; Fernandez, Laura; Soudackov, Alexander V.; Hammes-Schiffer, Sharon

2012-09-25

105

Insights into proton-coupled electron transfer mechanisms of electrocatalytic H2 oxidation and production.  

PubMed

The design of molecular electrocatalysts for H(2) 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 H(2) 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

Horvath, Samantha; Fernandez, Laura E; Soudackov, Alexander V; Hammes-Schiffer, Sharon

2012-04-23

106

Vectorial electron transfer in spatially ordered arrays. Progress report, January 1991--January 1994  

SciTech Connect

Objective was to find methods for rapid, controlled placement of light absorbers, relays, and multi-electron catalysts at defined sites with respect to a semiconductor or metal surface and thus to develop methods for preparing chemically modified photoactive surfaces as artificial photosynthetic units. Progress has been made in four areas: synthesis of new materials for directional electron transfer, preparation and characterization of anisotropic composites containing organic and inorganic components, elaboration of mechanisms of electrocatalysis, and development of new methods for surface modification of metals and semiconductors.

Fox, M.A.

1994-01-01

107

Fluorescent PET(Photoinduced Electron Transfer) reagents for thiols  

Microsoft Academic Search

Michael addition of thiois to an electron deficient alkene functional group in reagents (1)-(3) give rise to fluorescence quantum yield enhancements. In the absence of the thiol, photoinduced electron transfer (PET) takes place from the fluorophore to the alkene moiety. Such electron transfer is suppressed after the thiol reaction.

A. Prasanna de Silva; H. Q. Nimal Gunaratne; Thorfinnur Gunnlaugsson

1998-01-01

108

Electronic and Nuclear Factors in Charge and Excitation Transfer  

SciTech Connect

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.

Piotr Piotrowiak

2004-09-28

109

GPU-accelerated computation of electron transfer.  

PubMed

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

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

2012-07-30

110

Electron transfer reactions in microporous solids  

SciTech Connect

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.

Mallouk, T.E.

1992-05-01

111

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

PubMed

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

Simons, Jack

2010-05-26

112

Electron transfer of plurimodified DNA SAMs.  

PubMed

An STM-based current-voltage (I/V) investigation of deoxyribonucleic acid (DNA) 18 base pair (bp) oligonucleotide monolayers on gold is presented. Three bases of each of the immobilized and complementary strands were modified with either iodine or phenylethylene moieties. The oligonucleotides were immobilized on template stripped gold (tsg) surfaces and characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). AFM imaging showed that monolayers of the expected height were formed. A comparative study of normal, halogenated, and phenyl-modified DNA was made with the STM in tunneling spectroscopy (TS) mode. I/V spectroscopic measurements in the range +/-250 mV on both single- and double-stranded (ds) DNA monolayers (modified and unmodified) showed that for negative substrate bias (U(sub)) electron transfer is more efficient through a phenyl-modified monolayer than through normal or halogenated DNA. This effect was particularly clear below a threshold bias of -100 mV. For positive U(sub), unmodified ds DNA was found to conduct slightly better than the modified strands. This is presumably caused by greater order in the unmodified versus modified DNA monolayers. Modifications on the immobilized (thiolated) strand seem to improve electron transport through the DNA monolayer more than modifications on the complementary (not surface-bound) strand. PMID:17590024

Rospigliosi, Alessandro; Ehlich, Rudolf; Hoerber, Heinrich; Middelberg, Anton; Moggridge, Geoff

2007-06-23

113

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

SciTech Connect

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.

Not Available

1989-12-31

114

SCANNING ELECTRON MICROSCOPY STUDY OF CO-PRECIPITATED IRON OXIDE CATALYSTS  

Microsoft Academic Search

Iron oxide Fischer-Tropsch catalysts were prepared using a sol-gel method to incorporate varying amounts of silica (SiO2) and a constant amount of potassium oxide (K2O) promoters. The sol-gel slurries containing different Fe\\/Si ratios were dried using a spray dryer. The spray-dried materials were calcined at 300°C prior to the use as catalysts for the Fischer-Tropsch reaction. Scanning electron microscopy (SEM),

Ram Srinivasan; Robert L Spicer; Bob OBrien; Rolando Gonzalez; Fred Tungate; Burtron H. Davis

1997-01-01

115

Removal of VOCs by hybrid electron beam reactor with catalyst bed  

Microsoft Academic Search

Electron beam decomposition of volatile organic compounds (VOCs) was studied in order to obtain information for developing effective treatment method of off-gases from industries. We have examined the combination of electron beam and catalyst honeycomb which is either 1% platinum based or ceramic honeycomb- based aluminum oxide, using a hybrid reactor in order to improve removal efficiency and CO2 formation;

Jinkyu Kim; Bumsoo Han; Yuri Kim; Jae-Hyung Lee; Chong-Rae Park; Jong-Chul Kim; Jo-Chun Kim; Ki-Joon Kim

2004-01-01

116

Surface-initiated group transfer polymerization mediated by rare earth metal catalysts.  

PubMed

We present the first example of a surface-initiated group transfer polymerization (SI-GTP) mediated by rare earth metal catalysts for polymer brush synthesis. The experimentally facile method allows rapid grafting of polymer brushes with a thickness of >150 nm in <5 min at room temperature. We show the preparation of common poly(methacrylate) brushes and demonstrate that SI-GTP is a versatile route for the preparation of novel polymer brushes. The method gives access to both thermoresponsive and proton-conducting brush layers. PMID:22497672

Zhang, Ning; Salzinger, Stephan; Deubel, Frank; Jordan, Rainer; Rieger, Bernhard

2012-04-17

117

Transfer Hydrogenation Reaction Of Ketones And Formic Acid Under Hydrothermal Conditions Without A Catalyst  

NASA Astrophysics Data System (ADS)

The hydrothermal experiments with ketones and formic acid showed that the hydrogen transfer reduction of ketones can be conducted with formic acid as a hydride donor in the presence of NaOH at 300° C. The yield of alcohols was considerably higher at a much lower ratio of hydrogen source to ketones than the traditional Meerwein-Ponndorf-Verley reduction, reaching 60% for isopropanol from acetone and 70% for lactic acid from pyruvic acid. Water molecules as a catalyst may directly participate in the transition state by making a hydrogen-bond ring network with the substrate molecules.

Shen, Zheng; Zhang, Yalei; Zhou, Xuefei; Wu, Bing; Cao, Jianglin; Jin, Fangming

2010-11-01

118

Direct simulation of electron transfer reactions in DNA radical cations  

PubMed Central

The electron transfer properties of DNA radical cations are important in DNA damage and repair processes. Fast long-range charge transfer has been demonstrated experimentally, but the subtle influences that experimental conditions as well as DNA sequences and geometries have on the details of electron transfer parameters are still poorly understood. In this work, we employ an atomistic QM/MM approach, based on a one-electron tight binding Hamiltonian and a classical molecular mechanics forcefield, to conduct nanosecond length MD simulations of electron holes in DNA oligomers. Multiple spontaneous electron transfer events were observed in 100 ns simulations with neighbouring adenine or guanine bases. Marcus parameters of charge transfer could be extracted directly from the simulations. The reorganisation energy ? for hopping between neighbouring bases was found to be ca. 25 kcal/mol and charge transfer rates of 4.1×109 s?1 for AA hopping and 1.3×109 s?1 for GG hopping were obtained.

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

2009-01-01

119

31 CFR 208.3 - Payment by electronic funds transfer.  

Code of Federal Regulations, 2013 CFR

31 Money and Finance:Treasury...false Payment by electronic funds transfer... Section 208.3 Money and Finance: Treasury...Regulations Relating to Money and Finance (Continued...208.3 Payment by electronic funds...

2013-07-01

120

31 CFR 208.3 - Payment by electronic funds transfer.  

Code of Federal Regulations, 2010 CFR

31 Money and Finance: Treasury...false Payment by electronic funds transfer... Section 208.3 Money and Finance: Treasury...Regulations Relating to Money and Finance (Continued...208.3 Payment by electronic funds...

2010-07-01

121

31 CFR 208.3 - Payment by electronic funds transfer.  

Code of Federal Regulations, 2010 CFR

31 Money and Finance: Treasury...false Payment by electronic funds transfer... Section 208.3 Money and Finance: Treasury...Regulations Relating to Money and Finance (Continued...208.3 Payment by electronic funds...

2009-07-01

122

Hemicryptophane-assisted electron transfer: a structural and electronic study.  

PubMed

Three copper(II)@hemicryptophane complexes with various cavity sizes and shapes, Cu(II)@1, Cu(II)@2 and Cu(II)@3, were synthesized and characterized by near-IR/vis and EPR spectroscopies. The spectroscopic data are consistent with the presence of a trigonal-bipyramidal geometry of the N(4)Cu·H(2)O core, in accord with the energy-minimized structures obtained from DFT calculations. Cyclic voltammetry studies in CH(2)Cl(2) showed irreversible redox processes, whereas electrolysis coulometry indicated that Cu(II)/Cu(I) complexes could be interconverted. Electrochemistry data of the complexes stress the crucial role of the cage structure of the hemicryptophane in the thermodynamics of the electron transfer. PMID:23138197

Perraud, Olivier; Tommasino, Jean-Bernard; Robert, Vincent; Albela, Belén; Khrouz, Lhoussain; Bonneviot, Laurent; Dutasta, Jean-Pierre; Martinez, Alexandre

2012-11-08

123

Current Theoretical Challenges in Proton-Coupled Electron Transfer: Electron-Proton Nonadiabaticity, Proton Relays, and Ultrafast Dynamics  

SciTech Connect

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.

Hammes-Schiffer, Sharon

2011-06-16

124

Hydrogen peroxide oxidation of mustard-model sulfides catalyzed by iron and manganese tetraarylporphyrines. Oxygen transfer to sulfides versus H(2)O(2) dismutation and catalyst breakdown.  

PubMed

Fe(III)- and Mn(III)-meso-tetraarylporphyrin catalysis of H(2)O(2) oxidation of dibenzyl and phenyl-2-chloroethyl sulfides, 1, is investigated in ethanol with the aim of designing catalytic systems for mustard decontamination. The sulfide conversion, the sulfoxide and sulfone yields, the oxygen transfer from H(2)O(2) to the sulfide, and the catalyst stability depend markedly on the metal, on the substituents of its ligand, and on the presence or the absence of a cocatalyst, imidazole or ammonium acetate. With Fe, sulfones, the only oxidation products, are readily obtained whatever the ligand (TPP, F(20)TPP, or TDCPP) and the cocatalyst; the oxygen transfer is fairly good, up to 95% when the catalyst concentration is small ([1]/[Cat] = 420); the catalyst breakdown is insignificant only in the absence of any cocatalyst. With Mn, the sulfide conversion is achieved completely when the ligand is TDCPP or TSO(3)PP, but not F(20)TPP or TPP; a mixture of sulfoxide, 2, and sulfone, 3, is always obtained with [2]/[3] = 3.5-0.85 depending on the ligand and the cocatalyst (electron withdrawing substituents favor 3 and NH(4)OAc, 2). The catalyst stability is very good, but the oxygen transfer is poor whatever the ligand and the cocatalyst. These results are discussed in terms of a scheme in which sulfide oxygenation, H(2)O(2) dismutation, and oxidative ligand breaking compete. It is shown that the efficiency of the oxygen transfer is related not only to the rate constant of the dismutation route but also to the concentration of the active metal-oxo intermediate, most likely a perferryl or permanganyl species, i.e., to the rate of its formation. PMID:11701009

Marques, A; Marin, M; Ruasse, M F

2001-11-16

125

Vectorial electron transfer on designed surfaces  

NASA Astrophysics Data System (ADS)

Bipolar CdSe/CoS semiconductor photoelectrode panels, capable of vectorial electron transfer, were used in series arrays to photodecompose water to yield hydrogen and oxygen in stoichiometric ratio with a maximum solar efficiency of about 1 precent. An analytical model was developed for these arrays which addresses the question of watersplitting and electrical power generation efficiencies as functions of the number of panels, the overpotential of the gas generating electrodes, incident light intensity, and the concentrations of the redox couples. Hydrogen production using a self-assembling zeolite system was discovered. Sensitized anatase TiO2 electrodes were used in photoelectrochemical cells employing variety of solution redox couples. The photoassisted production of hydrogen from methanol-water solutions containing mixtures of small particles of CdS/SiO2 and a wide bandgap semiconductor (TiO, ZnO, SnO2, or WO3), supported on silica and platinized was studied. The phenomenon of interparticle charge separation for Cds/SiO2 was found to be operative for CdS/SiO2 with WS sub 2/SiO2.

Bard, A. J.; Campion, A.; Fox, M. A.; Mallouk, T. E.; Webber, S. E.

126

Photoinduced electron transfer from a conducting polymer to buckminsterfullerene  

Microsoft Academic Search

Evidence for photoinduced electron transfer form the excited state of a conducting polymer onto buckminsterfullerene, Cââ, is reported. After photo-excitation of the conjugated polymer with light of energy greater than the Ï-Ï gap, an electron transfer to the Cââ molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components,

N. S. Sariciftci; L. Smilowitz; A. J. Heeger; F. Wudl

1992-01-01

127

Electron transfer between molecules randomly distributed in a glass  

Microsoft Academic Search

A theoretical and experimental study of electron transfer from an optically excited donor to randomly distributed acceptors in a glassy medium is presented. The influence on time dependent observables of an electron transfer rate which is dependent on the orientation of donor and acceptors in a system with random distance and angular distributions is examined. It is formally proven that

R. P. Domingue; M. D. Fayer

1985-01-01

128

Distance-dependent electron transfer in DNA hairpins  

Microsoft Academic Search

The distance dependence of photoinduced electron transfer in duplex DNA was determined for a family of synthetic DNA hairpins in which a stilbene dicarboxamide forms a bridge connecting two oligonucleotide arms. Investigation of the fluorescence and transient absorption spectra of these hairpins established that no photoinduced electron transfer occurs for a hairpin that has six deoxyadenosine-deoxythymidine base pairs. However, the

F. D. Lewis; T. Wu; Y. Zhang

1997-01-01

129

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity  

PubMed Central

Despite over three decades of research into asymmetric phase transfer catalysis (APTC), a fundamental understanding of the factors that affect the rate and stereoselectivity of this important process are still obscure. This paper describes the initial stages of a long-term program aimed at elucidating the physical organic foundations of APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with a libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity oriented approach wherein the tandem inter[4+2]/intra[3+2] cycloaddition of nitroalkenes serves as the key transformation. A two part synthetic strategy comprised of: (1) preparation of enantioenriched scaffolds and (2) development of parallel synthesis procedures is described. The strategy allows for the facile introduction of four variable groups in the vicinity of a stereogenic quaternary ammonium ion. The quaternary ammonium ions exhibited a wide range of activity and to a lesser degree enantioselectivity. Catalyst activity and selectivity are rationalized in a qualitative way based on the effective positive potential of the ammonium ion.

Denmark, Scott E.; Gould, Nathan D.; Wolf, Larry M.

2011-01-01

130

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

PubMed

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

Aubry, Serge; Kopidakis, Georgios

2005-12-01

131

Desulfurization of coal: enhanced selectivity using phase transfer catalysts. Quarterly report, March 1 - May 31, 1996  

SciTech Connect

Due to environmental problems related to the combustion of high sulfur Illinois coal, there continues to be interest in the development in viable pre-combustion desulfurization processes. Recent studies by the authors have obtained very good sulfur removals but the reagents that are used are too expensive. Use of cheaper reagents leads to a loss of desired coal properties. This study investigated the application phase transfer catalysts to the selective oxidation of sulfur in coal using air and oxygen as oxidants. The phase transfer catalyst is expected to function as a selectivity moderator by permitting the use of milder reaction conditions that otherwise necessary. This would enhance the sulfur selectivity and help retain the heating value of the coal. The use of certain coal combustion wastes for desulfurization, and the application of cerium (IV) catalyzed air oxidation for selective sulfur oxidation are also being studied. If successful, this project could lead to the rapid development of a commercially viable desulfurization process. This would significantly improve the marketability of Illinois coal.

Palmer, S.R.; Hippo, E.J. [Southern Illinois Univ., Carbondale, IL (United States)

1996-12-31

132

The reaction of trimethylamine dehydrogenase with electron transferring flavoprotein.  

PubMed

The kinetics of electron transfer between trimethylamine dehydrogenase (TMADH) and its physiological acceptor, electron transferring flavoprotein (ETF), has been studied by static and stopped-flow absorbance measurements. The results demonstrate that reducing equivalents are transferred from TMADH to ETF solely through the 4Fe/4S center of the former. The intrinsic limiting rate constant (klim) and dissociation constant (Kd) for electron transfer from the reduced 4Fe/4S center of TMADH to ETF are about 172 s-1 and 10 microM, respectively. The reoxidation of fully reduced TMADH with an excess of ETF is markedly biphasic, indicating that partial oxidation of the iron-sulfur center in 1-electron reduced enzyme significantly reduces the rate of electron transfer out of the enzyme in these forms. The interaction of the two unpaired electron spins of flavin semiquinone and reduced 4Fe/4S center in 2-electron reduced TMADH, on the other hand, does not significantly slow down the electron transfer from the 4Fe/4S center to ETF. From a comparison of the limiting rate constants for the oxidative and reductive half-reactions, we conclude that electron transfer from TMADH to ETF is not rate-limiting during steady-state turnover. The overall kinetics of the oxidative half-reaction are not significantly affected by high salt concentrations, indicating that electrostatic forces are not involved in the formation and decay of reduced TMADH-oxidized ETF complex. PMID:7592591

Huang, L; Rohlfs, R J; Hille, R

1995-10-13

133

Designing and Refining Ni(II)diimine Catalysts Toward the Controlled Synthesis of Electron-Deficient Conjugated Polymers.  

PubMed

Electron-deficient ?-conjugated polymers are important for organic electronics, yet the ability to polymerize electron-deficient monomers in a controlled manner is challenging. Here we show that Ni(II)diimine catalysts are well suited for the controlled polymerization of electron-deficient heterocycles. The relative stability of the calculated catalyst-monomer (or catalyst-chain end) complex directly influences the polymerization. When the complex is predicted to be most stable (139.2 kJ/mol), these catalysts display rapid reaction kinetics, leading to relatively low polydispersities (?1.5), chain lengths that are controlled by monomer:catalyst ratio, controlled monomer consumption up to 60% conversion, linear chain length growth up to 40% conversion, and 'living' chain ends that can be readily extended by adding more monomer. These are desirable features that highlight the importance of catalyst design for the synthesis of new conjugated polymers. PMID:23937150

Bridges, Colin R; McCormick, Theresa M; Gibson, Gregory L; Hollinger, Jon; Seferos, Dwight S

2013-08-22

134

Effect of electron beam irradiation on CO 2 reforming of methane over Ni\\/Al 2O 3 catalysts  

Microsoft Academic Search

The effect of electron beam irradiation on the CO2 reforming of methane over Ni\\/Al2O3 was investigated. The conversion rate of CO2 and CH4 forming H2 and CO using various catalysts irradiated with an absorbed dose greater than 2MGy was 5–10% higher than when using an untreated catalyst. The Ni\\/O ratio on the catalyst surface increased after treatment with an electron

Jin Jun; Jo-Chun Kim; Joong-Hyeok Shin; Ki-Wan Lee; Young Soon Baek

2004-01-01

135

Electron transfer reactions in microporous solids. Progress report, September 1990--January 1993  

SciTech Connect

Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H{sub 2} and I{sub 3}{sup {minus}}, or H{sub 2} and O{sub 2)} from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

Mallouk, T.E.

1993-01-01

136

Harvesting singlet fission for solar energy conversion: one versus two-electron transfer electron transfer from the quantum superposition state  

NASA Astrophysics Data System (ADS)

Singlet fission (SF) is being explored to increase the efficiency of organic photovoltaics. A key question is how to effectively extract multiple electron-hole pairs from multiple excitons with the presence of other competing channels such as electron transfer from the singlet state. Recent experiments on the pentacene and tetracene show that a quantum superposition of the singlet (S1) and multiexciton (ME) state is formed during SF. However, little is known about the kinetics of electron transfer from this quantum superposition. Here, we apply time-resolved photoemission spectroscopy to the tetracene/C60 interface to probe one and two electron transfer from S1 and ME states, respectively. Because of the relatively slow ( 7 ps) SF in tetracene, both one- and two-electron transfer are allowed. We show evidence for the formation of two distinct charge transfer states due to electron transfer from photo-excited tetracene to the lowest unoccupied molecular orbital (LUMO) and the LUMO+1 levels in C60. Kinetic analysis shows that 60% of the quantum superposition transfers one electron through the S1 state to C60 while 40% undergoes two-electron transfer through the ME state.

Chan, Wai-Lun; Tritsch, John; Zhu, Xiaoyang

2013-03-01

137

Electron-transfer processes in dendrimers and their implication in biology, catalysis, sensing and nanotechnology  

NASA Astrophysics Data System (ADS)

The extraordinary development of the design and synthesis of dendrimers has allowed scientists to locate redox sites at precise positions (core, focal points, branching points, termini, cavities) of these perfectly defined macromolecules, which have generation-controlled sizes and topologies matching those of biomolecules. Redox-dendrimer engineering has led to fine modelling studies of electron-transfer metalloproteins, in which the branches of the dendrimers hinder access to the active site in a manner reminiscent of that of the protein. It has also enabled the construction of remarkable catalysts, sensors and printboards, including by sophisticated design of the interface between redox dendrimers and solid-state devices -- for example by functionalizing electrodes and other surfaces. Electron-transfer processes between dendrimers and a variety of other molecules hold promising applications in diverse areas that range from bio-engineering to sensing, catalysis and energy materials.

Astruc, Didier

2012-04-01

138

Inorganic and biological electron transfer across an electronically conductive composite polymer membrane. Interim report  

SciTech Connect

We describe in this paper an experiment involving an electronically conductive polymer that, to our knowledge, has not been described previously. A free-standing conductive polymer (polypyrrole)-based membrane separates a solution of an electron donor from a solution of an electron acceptor. Because the conductive polymer is both electronically and anionically conductive, the membrane can transport electrons from the donor solution to the acceptor solution, and anions in the opposite direction, such that a sustainable electron-transfer reaction is driven across the conductive polymer membrane. We demonstrate such transmembrane electron/ion-transfer processes using both an inorganic and a-biochemical electron donor/acceptor system. The biochemical case is of particular interest because we show that the reduced form of the enzyme glucose oxidase can give its electrons directly to the polypyrrolemembrane surface. Direct electron transfer is usually not possible at inorganic metals.... Biological electron transfer, Conducting polymers.

Lawson, D.R.; Liang, W.; Martin, C.R.

1993-02-22

139

Photochemical charge separation in zeolites: Electron transfer dynamics, nanocrystals and zeolitic membranes. Final technical report  

SciTech Connect

Aluminosilicate zeolites provide an excellent host for photochemical charge separation. Because of the constraints provided by the zeolite, the back electron transfer from the reduced acceptor to the oxidized sensitizer is slowed down. This provides the opportunity to separate the charge and use it in a subsequent reaction for water oxidation and reduction. Zeolite-based ruthenium oxide catalysts have been found to be efficient for the water splitting process. This project has demonstrated the usefulness of zeolite hosts for photolytic splitting of water.

Dutta, Prabir K.

2001-09-30

140

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

PubMed Central

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.

Mayer, James M.

2011-01-01

141

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

PubMed Central

Electron capture dissociation (ECD) and electron transfer dissociation (ETD) of doubly protonated electron affinity (EA)-tuned peptides were studied to further illuminate the mechanism of these processes. The model peptide FQpSEEQQQTEDELQDK, containing a phosphoserine residue, was converted to EA-tuned peptides via ?-elimination and Michael addition of various thiol compounds. These include propanyl, benzyl, 4-cyanobenzyl, perfluorobenzyl, 3,5-dicyanobenzyl, 3-nitrobenzyl and 3,5-dinitrobenzyl structural moieties, having a range of EA from -1.15 to 1.65 eV, excluding the propanyl group. Typical ECD or ETD backbone fragmentations are completely inhibited in peptides with substituent tags having EA over 1.00 eV, which are referred to as electron predators in this work. Nearly identical rates of electron capture by the dications substituted by the benzyl (EA = -1.15 eV) and 3-nitrobenzyl (EA = 1.00 eV) moieties are observed, which indicates the similarity of electron capture cross sections for the two derivatized peptides. This observation leads to the inference that electron capture kinetics are governed by the long range electron-dication interaction and are not affected by side chain derivatives with positive EA. Once an electron is captured to high-n Rydberg states, however, through-space or through-bond electron transfer to the EA-tuning tags or low-n Rydberg states via potential curve crossing occurs in competition with transfer to the amide ?* orbital. The energetics of these processes are evaluated using time-dependent density functional theory with a series of reduced model systems. The intramolecular electron transfer process is modulated by structure-dependent hydrogen bonds and is heavily affected by the presence and type of electron withdrawing groups in the EA-tuning tag. The anion radicals formed by electron predators have high proton affinities (approximately 1400 kJ/mol for the 3-nitrobenzyl anion radical) in comparison to other basic sites in the model peptide dication, facilitating exothermic proton transfer from one of the two sites of protonation. This interrupts the normal sequence of events in ECD or ETD leading to backbone fragmentation by forming a stable radical intermediate. The implications which these results have for previously proposed ECD and ETD mechanisms are discussed.

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

2009-01-01

142

Catalytic enantioselective reactions driven by photoinduced electron transfer  

Microsoft Academic Search

Photoinduced electron transfer is an essential step in the conversion of solar energy into chemical energy in photosystems I and II (ref. 1), and is also frequently used by chemists to build complex molecules from simple precursors. During this process, light absorption generates molecules in excited electronic states that are susceptible to accepting or donating electrons. But although the excited

Andreas Bauer; Felix Westkämper; Stefan Grimme; Thorsten Bach

2005-01-01

143

Deficiency of Electron Transfer Flavoprotein or Electron Transfer Flavoprotein:Ubiquinone Oxidoreductase in Glutaric Acidemia Type II Fibroblasts  

Microsoft Academic Search

Glutaric acidemia type II (GA II) is a human genetic disorder. It has been suggested that the primary defect in this disorder is a deficiency of a protein involved in electron transport between the acyl-CoA dehydrogenases and the bc1 complex of the mitochondrial respiratory chain. Antisera were raised to purified porcine electron transfer flavoprotein (ETF) and electron transfer flavoprotein:ubiquinone oxidoreductase

Frank E. Frerman; Stephen I. Goodman

1985-01-01

144

Characterization of carbon supported palladium catalysts: inference of electronic and particle size effects using reaction probes  

Microsoft Academic Search

Carbon supported palladium catalysts have been used in a wide range of industrial reactions, especially hydrogenation in the fine chemical industry. However, there are a lot of difficulties to characterize this system, mainly due to intrinsic characteristics of the carbon materials. This work aimed to evaluate the effect of dispersion and electronic density of palladium on the catalytic performance of

André L. Dantas Ramos; Péricles da Silva Alves; Donato A. G. Aranda; Martin Schmal

2004-01-01

145

Rate coefficients for electron transfer in symmetrical systems  

NASA Astrophysics Data System (ADS)

Kinetics of transient populations of the locally excited state and CT states produced due to electron transfer processes in donor—acceptor—donor (DAD) or acceptor—donor—acceptor (ADA) molecules in liquid solutions are investigated. The theoretical approach is based on the Zusman-type kinetic equations and applies to adiabatic and nonadiabatic electron transfer processes. Model calculations for the three-surface model show that for adiabatic processes the rate coefficients may display extreme values in the presence of the finite activation barrier. The effect is particularly strong for the electron transfer process in non-Debye solvents.

Najbar, Jan; Jarz?ba, W?odzimierz

1992-08-01

146

Electron transfer in SmHfCo alloys  

Microsoft Academic Search

The rare-earth electron-transfer concept in the rare-earth-transition-metal compounds was evaluated for the binary compounds Sm2Co17 and Sm1Co5 from published data. The cobalt moment was found to be consistent with a two-transferred-electron rigid-band model. These results were verified by saturation magnetization measurements on the mixed-valence pseudobinary Sm2(1-x)Hf2xCo17 alloys where the moment per cobalt atom was consistent with a tetravalent-hafnium divalent-samarium electron-transfer

J. Orehotsky; S. Washko; J. Gerboc; T. Wahl

1977-01-01

147

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts.  

PubMed

Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (?-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH(3)OH). By placing [(p-cymene)RuCl(2)](2) on a surface and spraying a solution of ?-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH(3)). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O(2) dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH(3). These results represent an example that species generated from the (?-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH(3)OH to HCOOCH(3). This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system. PMID:22315417

Perry, Richard H; Brownell, Kristen R; Chingin, Konstantin; Cahill, Thomas J; Waymouth, Robert M; Zare, Richard N

2012-02-06

148

Oxidation-resistant, sterically demanding phenanthrolines as supporting ligands for copper(I) nitrene transfer catalysts.  

PubMed

New 1,10-phenanthroline ligands have been synthesized with C6F5- or 2,4,6-(CF3)3C6H2- groups in the 2- and 9-positions; a cationic copper(I) complex of the latter catalyses nitrene transfer to the C-H bonds of electron-rich arenes. PMID:15263951

Hamilton, Charles W; Laitar, David S; Sadighi, Joseph P

2004-06-07

149

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

PubMed

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. PMID:23558182

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

2013-03-14

150

Desulfurization of coal: Enhanced selectivity using phase transfer catalysts. Technical report, September 1--November 30, 1995  

SciTech Connect

Due to environmental problems related to the combustion of high sulfur Illinois coal, there continues to be interest in the development of viable pre-combustion desulfurization processes. Recent studies by the authors have obtained very good sulfur removals but the reagents that are used are too expensive. Use of cheaper reagents leads to a loss of desired coal properties. This study investigates the application of phase transfer catalysts to the selective oxidation of sulfur in coal using air and oxygen as oxidants. The phase transfer catalyst is expected to function as a selectivity moderator by permitting the use of milder reaction conditions than otherwise necessary. This would enhance the sulfur selectivity and help retain the heating value of the coal. The use of certain coal combustion wastes for desulfurization, and the application of cerium (IV) catalyzed air oxidations for selective sulfur oxidation are also being studied. If successful this project could lead to the rapid development of a commercially viable desulfurization process. This would significantly improve the marketability of Illinois coal. During this quarter aliquots of the IBC-101 coal have been ground to various particle sizes in an attempt to find the optimum physical pretreatment for mineral, especially pyrite, removal. Analysis of these various aliquots shows them to be representative of the original coal. In addition, preliminary desulfurization reactions using fly ash and scrubber sludges have been performed on an unoxidized IBC-101 sample. Results will be available next quarter. Also, SEM-EDAX analysis of the fly ash indicates that it contains oxides that have shown activity in base desulfurization reactions.

Palmer, S.R.; Hippo, E.J.

1995-12-31

151

Coordinated photoinduced electron and proton transfer in a molecular triad  

SciTech Connect

Excitation of carotenoid-porphyrin-quinone (C-P-Q) triads yields the porphyrin first excited singlet state, which decays by electron transfer to give a C-P[sup [center dot]+]-Q[sup [center dot]-] charge-separated state. Competing with rapid charge recombination is electron transfer from the carotenoid to produce a long-lived C[sup [center dot]+]-P-Q[sup [center dot]-] species. High quantum yields of the final state require tuning of electronic and thermodynamic factors to favor forward electron transfer over charge recombination. Triad 1 illustrates a new strategy for slowing charge recombination based on coupling photoinduced electron transfer to a change in proton chemical potential. The quantum yields and lifetimes of the final charge-separated states in the triads were assessed by monitoring the transient carotenoid radical cation absorptions. The results demonstrate that the yield of charge separation in multicomponent molecular photovoltaics can be increased by a coordinated electron and proton transfer process. It is also interesting that in 1 a substantial fraction of the intramolecular redox potential produced by photoinduced electron transfer is transformed into proton chemical potential. Elaboration of this concept could lead to photoinduced generation of proton motive force in a heterogeneous system. 24 refs., 3 figs.

Hung, S.C.; Macpherson, A.N.; Lin, S.; Liddell, P.A.; Seely, G.R.; Moore, A.L.; Moore, T.A.; Gust, D. (Arizona State Univ., Tempe, AZ (United States))

1995-02-08

152

A polymer onium acting as phase-transfer catalyst in halogen-exchange fluorination promoted by microwave  

Microsoft Academic Search

A polymerized quaternary ammonium salt polydiallyldimethylammonium chloride, exhibiting high stability to heat and base, was prepared and applied as phase-transfer catalyst (PTC) in halogen-exchange (Halex) fluorination of chloronitrobenzenes to give excellent yields of corresponding fluoronitrobenzenes. Dimethyl sulfoxide was found to be the best solvent when microwave was applied as heating resource.

Jun Luo; Chunxu Lü; Chun Cai; Wenchao Qü

2004-01-01

153

Convective heat transfer of exothermic reactive gas flowing across a heating cylinder coated with platinum catalyst in a narrow duct  

Microsoft Academic Search

The effect of a catalytic surface reaction on the convective heat transfer is studied for a cross flow to a cylinder. Platinum catalyst is coated on the surface of the cylinder which is set horizontally in a rectangular duct. The fluid is a mixture of SO2 and O2 and the following exothermic reaction takes place on the surface of the

Yoshinori Itaya; Tooru Hiroi; Hitoki Matsuda; Masanobu Hasatani

2002-01-01

154

Dynamical Effects in Electron Transfer Reactions. 2. Numerical Solution.  

National Technical Information Service (NTIS)

In part I a reaction-diffusion equation was introduced for the description of electron transfer reactions which are induced by fluctuations in both the solvent polarization and in the intramolecular vibrational coordinates. We analyze the model employing ...

W. Nadler R. A. Marcus

1987-01-01

155

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

Federal Register 2010, 2011, 2012, 2013

...relating to Federal tax deposits (FTDs) by Electronic Funds Transfer (EFT). FOR FURTHER INFORMATION CONTACT: Michael E. Hara, (202) 622-4910 (not a toll-free number). SUPPLEMENTARY INFORMATION: Background The correction notice that is...

2010-08-26

156

A Description of Electronic Fund Transfer Activities in 28 States.  

National Technical Information Service (NTIS)

This document, sponsored in part by the National Commission on Electronic Fund Transfers, surveys existing and planned EFT systems in 28 states. It describes how the hardware is used in the systems, the nature of the institutional arrangements involved in...

1977-01-01

157

48 CFR 18.123 - Electronic funds transfer.  

Code of Federal Regulations, 2010 CFR

Electronic funds transfer payments may be waived for acquisitions to support unusual and compelling needs or emergency acquisitions. (See 32.1103(e).) [71 FR 38248, July 5, 2006. Redesignated at 72 FR 46344, Aug. 17,...

2007-10-01

158

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

Federal Register 2010, 2011, 2012, 2013

...Electronic Fund Transfers (Regulation E); Correction AGENCY: Bureau of Consumer Financial...Final rule; official interpretation; correction...clarificatory amendment and technical correction to a final rule and official...

2013-08-14

159

Electron energy transfer rates for vibrational excitation of N2.  

SciTech Connect

The calculation of the electron density and electron temperature distribution in our ionosphere (from {approx} 150-600 km) requires a knowledge of the various heating, cooling and energy flow processes that occur. The energy transfer from electrons to neutral gases and ions is one of the dominant electron cooling processes in the ionosphere, and the role of vibrationally excited N2 in this is particularly significant.

Campbell, L. (Laurence); Cartwright, D. C. (David C.); Tuebner, P. J. O.; Brunger, M. J. (Michael J.)

2003-01-01

160

26 CFR 1.6302-4 - Voluntary payments by electronic funds transfer.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 false Voluntary payments by electronic funds transfer. 1.6302-4 Section...Provisions § 1.6302-4 Voluntary payments by electronic funds transfer. (a) Electronic funds transfer. Any person may...

2011-04-01

161

12 CFR 205.14 - Electronic fund transfer service provider not holding consumer's account.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Electronic fund transfer service provider not holding consumer's...FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.14 Electronic fund transfer service provider not holding...

2013-01-01

162

12 CFR 1005.14 - Electronic fund transfer service provider not holding consumer's account.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Electronic fund transfer service provider not holding consumer's...FINANCIAL PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) General § 1005.14 Electronic fund transfer service provider not holding...

2013-01-01

163

12 CFR 205.15 - Electronic fund transfer of government benefits.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Electronic fund transfer of government benefits. 205.15 ...FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of government benefits. (a)...

2013-01-01

164

12 CFR 1005.15 - Electronic fund transfer of government benefits.  

Code of Federal Regulations, 2013 CFR

...2013-01-01 false Electronic fund transfer of government benefits. 1005.15...FINANCIAL PROTECTION ELECTRONIC FUND TRANSFERS (REGULATION E) General § 1005.15 Electronic fund transfer of government benefits. (a)...

2013-01-01

165

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

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Submission of Electronic Funds Transfer Information...Provisions and Clauses 52.232-38 Submission of Electronic Funds Transfer Information...insert the following provision: Submission of Electronic Funds Transfer...

2012-10-01

166

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

Code of Federal Regulations, 2013 CFR

... false Payment of tax by electronic fund transfer. 26.267...267 Payment of tax by electronic fund transfer. ...bank in making payment by electronic fund transfer (EFT), as...taxes by cash, check, or money order is not...

2013-04-01

167

Single-molecule electron transfer reactions in nanomaterials  

SciTech Connect

Here we report the study of single molecule electron transfer dynamics by coupling fluorescence microscopy at a conventional electrochemical cell. The single-molecule fluorescence spectroelectrochemistry of cresyl violet in aqueous solution and on nanoparticle surface were studied. We observed that the single-molecule fluorescence intensity of cresyl violet is modulated synchronously with the cyclic voltammetric potential scanning. We attribute the fluorescence intensity change of single cresyl violet molecules to the electron transfer reaction driven by the electrochemical potential.

Hu, Dehong; Lei, Chenghong; Ackerman, Eric J.

2009-07-26

168

Is ubiquinone diffusion rate-limiting for electron transfer?  

Microsoft Academic Search

The different possible dispositions of the electron transfer components in electron transfer chains are discussed: (a) random distribution of complexes and ubiquinone with diffusion-controlled collisions of ubiquinone with the complexes, (b) random distribution as above, but with ubiquinone diffusion not rate-limiting, (c) diffusion and collision of protein complexes carrying bound ubiquinone, and (d) solid-state assembly. Discrimination among these possibilities requires

Giorgio Lenaz; Romana Fato

1986-01-01

169

Tetrathiafulvalene–flavin dyads: electron transfer promoted by metal cations  

Microsoft Academic Search

Tetrathiafulvalene–flavin dyads 1 and 2 are reported. Both absorption and ESR spectral studies show that the intramolecular electron transfer occurs from TTF to flavin units in dyads 1 and 2 in the presence of Pb2+\\/Sc3+. But, the electron transfer is more efficient for dyad 1 in the presence of Pb2+\\/Sc3+. Electrochemical studies manifest that coordination of dyads 1 and 2

Lina Jia; Guanxin Zhang; Deqing Zhang; Daoben Zhu

2010-01-01

170

Photoinduced electron transfer from DABCO to trans-nitrostilbenes  

NASA Astrophysics Data System (ADS)

The anion radical of the trans isomers of 4-nitro-, 4,4'-dinitro-, and 4-nitro-4'-methoxystilbene was generated by triplet quenching with 1,4-diazabicyclo[2.2.2]octane (DABCO) in polar solvents at room temperature using laser flash photolysis. Electron transfer and trans ? cis photoisomerization are competing processes. The radical ions decay by electron back-transfer yielding the initial ground states.

Görner, Helmut; Schulte-Frohlinde, Dietrich

171

Electron transfer in syntrophic communities of anaerobic bacteria and archaea  

Microsoft Academic Search

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

Caroline M. Plugge; Alfons J. M. Stams

2009-01-01

172

Theoretical analysis of proton relays in electrochemical proton-coupled electron transfer.  

PubMed

The coupling of long-range electron transfer to proton transport over multiple sites plays a vital role in many biological and chemical processes. Recently the concerted proton-coupled electron transfer (PCET) reaction in a molecule with a hydrogen-bond relay inserted between the proton donor and acceptor sites was studied electrochemically. The standard rate constants and kinetic isotope effects (KIEs) were measured experimentally for this double proton transfer system and a related single proton transfer system. In the present paper, these systems are studied theoretically using vibronically nonadiabatic rate constant expressions for electrochemical PCET. Application of this approach to proton relays requires the calculation of multidimensional proton vibrational wave functions and the incorporation of multiple proton donor-acceptor motions. The decrease in proton donor-acceptor distances due to thermal fluctuations and the contributions from excited electron-proton vibronic states play important roles in these systems. The calculated KIEs and the ratio of the standard rate constants for the single and double proton transfer systems are in agreement with the experimental data. The calculations indicate that the standard PCET rate constant is lower for the double proton transfer system because of the smaller overlap integral between the ground state reduced and oxidized proton vibrational wave functions, resulting in greater contributions from excited electron-proton vibronic states with higher free energy barriers. The theory predicts that this rate constant may be increased by modifying the molecule in a manner that decreases the equilibrium proton donor-acceptor distances or alters the molecular thermal motions to facilitate the concurrent decrease of these distances. These insights may guide the design of more efficient catalysts for energy conversion devices. PMID:21524104

Auer, Benjamin; Fernandez, Laura E; Hammes-Schiffer, Sharon

2011-05-11

173

Evolution of Gold Structure During Thermal Treatment of Au\\/FeOx Catalysts Revealed by Aberration-Corrected Electron Microscopy  

Microsoft Academic Search

High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au\\/FeO (WGC ref. no. 60C), prepared by co-precipitation and calcined in air at 400 C, and a catalyst prepared by leaching surface gold from the parent catalyst and exposed to various treatments, including use in the water-gas shift reaction at 250 C.

Steven H Overbury; Lawrence Frederick Allard Jr; Albina Y Borisevich; Weiling Deng; Rui Si; Maria Flytzani-Stephanopoulos

2009-01-01

174

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

SciTech Connect

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

Stevens, B.

1997-07-01

175

Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide  

NASA Astrophysics Data System (ADS)

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

Feng, Wen-Ke; Feng, Yi-Yu; Wang, Shu-Feng; Feng, Wei; Yi, Wen-Hui; Gong, Qi-Huang

2010-11-01

176

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...

177

Diameter-dependent electronic transport properties of Au-catalyst/Ge-nanowire Schottky diodes  

SciTech Connect

We present electronic transport measurements in individual Au-catalyst/Ge-nanowire interfaces demonstrating the presence of a Schottky barrier. Surprisingly, the small-bias conductance density increases with decreasing diameter. Theoretical calculations suggest that this effect arises because electron-hole recombination in the depletion region is the dominant charge transport mechanism, with a diameter dependence of both the depletion width and the electron-hole recombination time. The recombination time is dominated by surface contributions and depends linearly on the nanowire diameter.

Picraux, S Thomas [Los Alamos National Laboratory; Leonard, Francois [SNL; Swartzentruber, Brian S [SNL; Talin, A Alee [SNL

2008-01-01

178

Influence of diffusion on photoinduced electron transfer. [laser radiation  

SciTech Connect

Electron transfer from an optically excited donor (rubrene) to randomly distributed acceptors (duroquinone) has been investigated experimentally. The forward electron-transfer process under the influence of diffusion in liquid solution (diethyl sebacate) is compared with that in solid solution (sucrose octaacetate). Steady-state fluorescence yield and time-resolved fluorescence measurements were used to measure the excited-state population of the donor (rubrene). The parameters were used to analyze the electron-transfer dynamics under a variety of acceptor concentrations. The agreement between theoretical predictions and experiments is very good. The forward transfer parameters (a{sub f} and R{sub 0}) in liquid solution are almost identical with those obtained in solid solution.

Song, L.; Dorfman, R.C.; Swallen, S.F.; Fayer, M.D. (Stanford Univ., CA (United States))

1991-05-02

179

Electronic parameters for charge transfer along DNA  

Microsoft Academic Search

.  We systematically examine all the tight-binding parameters pertinent to charge transfer along DNA. The molecular structure of the four DNA bases (adenine, thymine, cytosine, and guanine) is investigated by using the linear combination\\u000a of atomic orbitals method with a recently introduced parametrization. The HOMO and LUMO wave functions and energies of DNA\\u000a bases are discussed and then used for calculating

L. G. D. Hawke; G. Kalosakas; C. Simserides

2010-01-01

180

Quantum interferences and electron transfer in photosystem I.  

PubMed

We have studied the electron transfer occurring in the photosystem I (PSI) reaction center from the special pair to the first iron-sulfur cluster. Electronic structure calculations performed at the DFT level were employed to determine the on-site energies of the fragments comprising PSI, as well as the charge transfer integrals between neighboring pairs. This electronic Hamiltonian was then used to compute the charge transfer dynamics, using the stochastic surrogate Hamiltonian approach to account for the coherent propagation of the electronic density but also for its energy relaxation and decoherence. These simulations give reasonable transfer time ranging from subpicoseconds to nanoseconds and predict coherent oscillations for several picoseconds. Due to these long-lasting coherences, the propagation of the electronic density can be enhanced or inhibited by quantum interferences. The impact of random fluctuations and asymmetries on these interferences is then discussed. Random fluctuations lead to a classical transport where both constructive and destructive quantum interferences are suppressed. Finally it is shown that an energy difference of 0.15 eV between the on-site energies of the phylloquinones leads to a highly efficient electron transfer even in presence of strong random fluctuations. PMID:23134639

Renaud, Nicolas; Powell, Daniel; Zarea, Mahdi; Movaghar, Bijan; Wasielewski, Michael R; Ratner, Mark A

2012-11-15

181

Studies of impulsive vibrational influence on ultrafast electronic excitation transfer.  

PubMed

We investigated electronic energy-transfer dynamics in three model dimers within which coherent intramonomer nuclear motion had been induced by impulsive Raman excitation using an optimized, electronically preresonant control pulse. Calculations of the donor-survival probability, the ultrafast pump-probe signal, and the pump-probe difference signal are presented for dithia-anthracenophane and homodimers of 2-difluoromethylanthracene and 2-trifluoromethylanthracene. Survival probabilities and signals, along with phase-space analyses, elucidated the mechanisms, extent, and spectroscopic manifestations of external vibrational or torsional control over electronic excitation transfer. PMID:22236325

Biggs, Jason D; Cina, Jeffrey A

2012-02-10

182

Membrane catalyst layer for fuel cells  

DOEpatents

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 {mu}m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm{sup 2}. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Wilson, M.S.

1991-02-19

183

Characterization of durable nanostructured thin film catalysts tested under transient conditions using analytical aberration-corrected electron microscopy  

SciTech Connect

The stability of Ru0.1Ir0.9 oxidation evolution reaction (OER) catalysts deposited on Pt-coated nanostructured thin films (NSTFs) has been investigated by aberration-corrected electron microscopy. Accelerated stress tests showed that the OER catalysts significantly improved the durability of the Pt under cell reversal conditions. High-resolution images of the end-of-life NSTFs showed significant Ir loss from the whisker surfaces, while no Pt loss was observed, indicating that the OER catalysts had protected the catalyst coated whisker surfaces from degradation.

Cullen, David A [ORNL; More, Karren Leslie [ORNL; Reeves, Kimberly Shawn [ORNL; Vernstrom, George [3M Industrial Mineral Products; Atanasoska, Liliana [3M Industrial Mineral Products; Haugen, Gregory [3M Industrial Mineral Products; Atanasoski, Radoslav [3M Industrial Mineral Products

2011-01-01

184

The dynamical correlation in spacer-mediated electron transfer couplings  

Microsoft Academic Search

The dynamical correlation effect in electron transfer (ET) coupling was studied in this work, for cases where electrons tunnel through a many-electron environment. The ET couplings for three different bridge-mediated model systems were calculated: (I) trans-alkyl chains [H2C-(CH2)n-CH2, n=2-10], (II) two isomers of trans-1,4-dimethylenecyclohexane, and (III) two ethylenes spaced by a saturated ethane molecule. The couplings were calculated as half

Chou-Hsun Yang; Chao-Ping Hsu

2006-01-01

185

Vectorial electron transfer in spatially ordered arrays. Progress report, August 1994--January 1997  

SciTech Connect

With DOE support from August 1994 to August 1997, this project sought to identify methods for controlled placement of light absorbers, relays, and multielectron catalysts at defined sites from a fixed semiconductor or metal surface and, thus, to develop methods for preparing chemically modified photoactive surfaces as artificial photosynthetic units. These designed materials have been evaluated as efficient light collection devices and as substrates for defining the key features that govern the efficiency of long distance electron transfer and energy migration. The authors have synthesized several different families of integrated chemical systems as soluble arrays, as solid thin films, and as adsorbates on solid electrodes, seeking to establish how spatial definition deriving from covalent attachment to a helical polymer backbone, from self assembly of functionalized tethers on gold or metal oxide surfaces, and from rigid or layered block polymers can lead to controlled electron and energy transfer. The authors have also conducted physical characterization of semiconductor-containing composites active in controlled interfacial electron transfer, with charge transport in these materials having been evaluated by photophysical and electrochemical methods.

Fox, M.A.

1997-01-01

186

Hydrogen atom vs electron transfer in catecholase-mimetic oxidations by superoxometal complexes. Deuterium kinetic isotope effects.  

PubMed

Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases. PMID:15616728

Simándi, Tatiana M; May, Zoltán; Szigyártó, Imola Cs; Simándi, László I

2004-12-06

187

Electronic energy transfer in actinyl crystals  

NASA Astrophysics Data System (ADS)

Using time resolved laser spectroscopy at 4·2 K we show that nearest neighbour species in single crystal caesium uranyl nitrate, whose resonant electronic energies have a difference comparable to the excitonic bandwidth, are effectively localized. Transport through the crystal must proceed through a phonon-assisted 'hopping' mechanism with a time constant of about 10 ?s.

Thorne, J. R. G.; Denning, R. G.

188

Vectorial electron transfer in spatially ordered arrays  

SciTech Connect

Progress has been made in four areas: the synthesis of new materials for directional electron; the preparation and characterization of anisotropic composites bearing organic and inorganic components; the elaboration of mechanisms of electrocatalysis; and the development of new methods for surface modification of metals and semiconductors.

Fox, M.A.

1992-01-01

189

Theory of photoinduced heterogeneous electron transfer  

NASA Astrophysics Data System (ADS)

We consider electron injection into the conduction band of a semiconductor, from an electronically excited state of a dye molecule, adsorbed on its surface. For arbitrary width of the conduction band, the survival probability of the excited state can be calculated using a Green's-function approach. We show that the existence of a split-off state can play an important role in the total injection probability. In the wide band limit, the survival probability decays exponentially, but for finite band widths it does not. We further investigate the effect of vibrations on the process. A Green's operator technique may be used to solve this too exactly. We show that the problem may be reduced to a non-Hermitian eigenvalue problem for the vibrational states alone. Exact results can be obtained for arbitrary bandwidth and for a few vibrational degrees of freedom. In the wide band limit, the dynamics is particularly simple and we find that (1) the survival probability of the excited state is unchanged by the inclusion of vibrational motion, but (2) each vibrational state now has a finite lifetime. Numerical results are presented for the effects of reorganization energy, energy of the injecting level, and the variation of the matrix element for the electron injection, on the survival probability of the electron in the excited state. As an illustration of the approach, we also present results of numerical calculation of the absorption spectrum of perylene adsorbed on TiO2 and compare it with experimental results.

Sebastian, K. L.; Tachiya, Masanori

2006-02-01

190

Effect of proton transfer on the electronic coupling in DNA  

NASA Astrophysics Data System (ADS)

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.

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

2006-06-01

191

Theory of reversible electron transfer reactions in a condensed phase.  

PubMed

We have derived an exact analytical expression for the average forward rate of a reversible electron transfer reaction, modeled through a reaction coordinate undergoing diffusive motion in arbitrary potential wells of the reactant and the product in presence of a localized sink of arbitrary location and strength. The dynamics of diffusive motion is described by employing two coupled generalized diffusion reaction (Smoluchowski) equations with coordinate dependent diffusivity and delta sink. The average forward electron transfer rate constant obtained here for the system, with equilibrium or nonequilibrium distributions as initial condition, is determined by the forward and backward rate constants calculated based on the transition state theory and the weighted average rate for the well dynamics. We also discuss various limiting cases for the rate of electron transfer reactions corresponding to the different experimental situations. As an illustrative example, we have considered back electron transfer (ET) reaction and shown that the present theory can explain the non-Marcus free energy gap dependence of the rate of ET reactions. More importantly, the approach presented here can easily be extended to systems describing the dynamics of diffusive motion in coupled multipotential surfaces associated with electron transfer reactions. PMID:20866692

Dhole, Kajal; Modak, Brindaban; Samanta, Alok; Ghosh, Swapan K

2010-07-20

192

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

SciTech Connect

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

Not Available

1992-12-31

193

Photo-induced intermolecular electron transfer from electron donating solvents to Coumarin dyes in bile salt aggregates: Role of diffusion in electron transfer reaction  

Microsoft Academic Search

The photo-induced electron transfer between Coumarin dyes and aromatic amines has been investigated using steady state and time-resolved fluorescence quenching studies. We have observed a Marcus type inversion in the electron transfer rate in correlation of quenching constant to the free energy change occurred during reaction. To justify the “inverted region” obtained in the correlation of quenching constant versus free

Anjan Chakraborty; Debdeep Chakrabarty; Debabrata Seth; Partha Hazra; Nilmoni Sarkar

2006-01-01

194

Plastocyanin, an electron-transfer protein  

Microsoft Academic Search

Plastocyanin (Pc) is a copper (Cu)-containing blue protein, that functions as a mobile electron carrier between cytochrome (cyt) f and Photosystem 1 (PS1) in oxygenic organisms. The atomic structure is known and can be described as a ß-barrel with hydrophobic residues in the interior of the protein. To increase the understanding about structure-function relationships, site-directed mutagenesis of Pc has proven

Kalle Sigfridsson

1998-01-01

195

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

SciTech Connect

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.

Whitten, D.G.

1991-10-01

196

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

SciTech Connect

The studies have focused on rapid, efficient bond-fragmentation reactions initiated through photoinduced electron transfer. Electron transfer induced fragmentation of a number of donors have been examined, especially 1,2 diamines and related compounds. Two of the amines fragment with rate constants of 3 [times] 10[sup 8] to 2 [times] 10[sup 9] M[sup [minus]1]sec[sup [minus]1]. A series of amino-substituted pinacols and related compounds have also been examined; they undergo similar but slower fragmentation processes when converted to their cation radicals by photoinduced electron transfer. The studies with linked and polymeric electron donor- electron acceptor coupled molecules have also progressed. Several polymers containing diamine repeat units and anthraquinone or nitroaromatic acceptors have also been prepared that can be photoactivated by visible irradiation; they fragment efficiently in solution and photodegrade even in the solid state. The studies of singlet oxygen initiated fragmentation reactions of diamines, amino alcohols, and aminoketones have nearly been completed. Attention have been turned to fragmentable electron acceptors such as p- cyanobenzyl bromide; irradiation of electron donors such as methyl- or methoxy-naphthalenes can initiate efficient fragmentation of the electron deficient bromide.

Whitten, D.G.

1992-12-01

197

Electron Transfer Between Colloidal ZnO Nanocrystals  

SciTech Connect

Colloidal ZnO nanocrystals capped with dodecylamine and dissolved in toluene can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction-band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals (e{sub CB}{sup -}:ZnO-S) with a solution of uncharged large nanocrystals (ZnO-L) caused changes in the EPR spectrum indicative of quantitative electron transfer from small to large nanocrystals. EPR spectra of the reverse reaction, e{sub CB}{sup -}:ZnO-L + ZnO-S, showed that electrons do not transfer from large to small nanocrystals. Stopped-flow kinetics studies monitoring the change in the UV bandedge absorption showed that reactions of 50 {micro}M nanocrystals were complete within the 5 ms mixing time of the instrument. Similar results were obtained for the reaction of charged nanocrystals with methyl viologen (MV{sup 2+}). These and related results indicate that the electron-transfer reactions of these colloidal nanocrystals are quantitative and very rapid, despite the presence of {approx}1.5 nm long dodecylamine capping ligands. These soluble ZnO nanocrystals are thus well-defined redox reagents suitable for studies of electron transfer involving semiconductor nanostructures.

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

2011-03-30

198

Improving the efficiency of water splitting in dye-sensitized solar cells by using a biomimetic electron transfer mediator.  

PubMed

Photoelectrochemical water splitting directly converts solar energy to chemical energy stored in hydrogen, a high energy density fuel. Although water splitting using semiconductor photoelectrodes has been studied for more than 40 years, it has only recently been demonstrated using dye-sensitized electrodes. The quantum yield for water splitting in these dye-based systems has, so far, been very low because the charge recombination reaction is faster than the catalytic four-electron oxidation of water to oxygen. We show here that the quantum yield is more than doubled by incorporating an electron transfer mediator that is mimetic of the tyrosine-histidine mediator in Photosystem II. The mediator molecule is covalently bound to the water oxidation catalyst, a colloidal iridium oxide particle, and is coadsorbed onto a porous titanium dioxide electrode with a Ruthenium polypyridyl sensitizer. As in the natural photosynthetic system, this molecule mediates electron transfer between a relatively slow metal oxide catalyst that oxidizes water on the millisecond timescale and a dye molecule that is oxidized in a fast light-induced electron transfer reaction. The presence of the mediator molecule in the system results in photoelectrochemical water splitting with an internal quantum efficiency of approximately 2.3% using blue light. PMID:22547794

Zhao, Yixin; Swierk, John R; Megiatto, Jackson D; Sherman, Benjamin; Youngblood, W Justin; Qin, Dongdong; Lentz, Deanna M; Moore, Ana L; Moore, Thomas A; Gust, Devens; Mallouk, Thomas E

2012-04-30

199

Electron transfer dynamics: Zusman equation versus exact theory  

SciTech Connect

The Zusman equation has been widely used to study the effect of solvent dynamics on electron transfer reactions. However, application of this equation is limited by the classical treatment of the nuclear degrees of freedom. In this paper, we revisit the Zusman equation in the framework of the exact hierarchical equations of motion formalism, and show that a high temperature approximation of the hierarchical theory is equivalent to the Zusman equation in describing electron transfer dynamics. Thus the exact hierarchical formalism naturally extends the Zusman equation to include quantum nuclear dynamics at low temperatures. This new finding has also inspired us to rescale the original hierarchical equations and incorporate a filtering algorithm to efficiently propagate the hierarchical equations. Numerical exact results are also presented for the electron transfer reaction dynamics and rate constant calculations.

Shi Qiang; Chen Liping; Nan Guangjun [Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190 (China); Xu Ruixue [Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Yan Yijing [Department of Chemistry, Hong Kong University of Science and Technology, Kowloon (Hong Kong)

2009-04-28

200

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

Federal Register 2010, 2011, 2012, 2013

...OMB Review; Payment by Electronic Fund Transfer AGENCY: Department of Defense (DOD...concerning payment by electronic fund transfer. A notice was published in the Federal...Collection 9000- 0144, Payment by Funds Transfer, by any of the following methods:...

2011-10-31

201

Electron transfer dissociation of peptide anions  

Microsoft Academic Search

Ion\\/ion reactions of multiply deprotonated peptide anions with xenon radical cations result in electron abstraction to generate\\u000a charge-reduced peptide anions containing a free-radical site. Peptide backbone cleavage then occurs by hydrogen radical abstraction\\u000a from a backbone amide N to facilitate cleavage of the adjacent C-C bond, thereby producing a- and x-type product ions. Introduction\\u000a of free-radical sites to multiply charged

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

2005-01-01

202

Correlated electron-nuclear dynamics in ultrafast photoinduced electron-transfer reactions at dye-semiconductor interfaces  

NASA Astrophysics Data System (ADS)

The correlated electron-nuclear dynamics in ultrafast photoinduced electron-transfer processes at dye-semiconductor interfaces is investigated, employing accurate quantum dynamical calculations. It is shown that—depending on the relative time scale of electronic and nuclear dynamics—electronic-vibrational coupling in dye-semiconductor systems may result in electron transfer driven by coherent vibrational motion, nuclear dynamics induced by ultrafast electron-transfer processes, as well as localization of the electron at the dye molecule.

Thoss, Michael; Kondov, Ivan; Wang, Haobin

2007-10-01

203

Length-Dependence of Electron Transfer in Conjugated Molecular Wires  

NASA Astrophysics Data System (ADS)

The electron transfer (ET) properties of ?-electron conjugated molecular wires consisting of polyene chain, [>C=C<]n, (n=1-11) has been investigated in the framework of ab initio molecular orbital theory. As expected, magnitude of the ET coupling matrix element VDA decreases exponentially with increase in the length of the molecular wire. However, in contrast with the rigid ?-bonded molecular wires, the decay constant, ?, for the conjugated systems exhibits three different regimes over the calculated length. This is attributed to the delocalized nature of the electrons along molecular length that facilitates retention of the electron coupling even at large separations between the donor and acceptor centers.

Karna, Shashi; Mallick, Govind; Pandey, Ravindra

2007-03-01

204

Optical Control of the Electron in the Simplest Electron Transfer Reaction  

Microsoft Academic Search

In this work,we show how a sequence of femtosecond laser pulses can be used to control the dynamics of electron transfer (ET) reactions. We focus on the ejection and subsquent reattachment of an electron from a sodium anion in solution. We first select the distance at which the electron localizes from its Na atom partner (either in an immediate or

Benjamin Schwartz

2002-01-01

205

Experimental and theoretical study of gas\\/solid mass transfer in metallic filters as supports for micro-structured catalysts  

Microsoft Academic Search

Commercial sintered metallic micro-fibers have been investigated in view of their adoption as enhanced catalyst carriers. The material herein studied has high porosity (86%) and very high interfacial area (22400m2\\/m3), thus appearing promising for application in fast, mass-transfer limited catalytic processes. It was catalytically activated by calcination and impregnation with Pt, and tested in the model reaction of CO oxidation.

G. Groppi; E. Tronconi; G. Bozzano; M. Dente

2010-01-01

206

Supported oxides as combustion catalysts and as humidity sensors. Tuning the surface behavior by inter-phase charge transfer  

Microsoft Academic Search

The changes of the electrical properties of semiconductor oxide catalysts, when measured in situ provide useful information about surface processes as adsorption\\/desorption\\/reaction occur with charge transfer. The electrical properties of polycrystalline powders, mainly controlled by inter-grain Schottky-type barriers, are sensible to the “quality” of the surface\\/inter-grain domains, to sample morphology and to changes in charge and coverage of the surface

Monica Caldararu; Cornel Munteanu; Paul Chesler; Mariana Carata; Cristian Hornoiu; Niculae I. Ionescu; Georgeta Postole; Veronica Bratan

2007-01-01

207

Recoverable organorhodium-functionalized polyhedral oligomeric silsesquioxane: a bifunctional heterogeneous catalyst for asymmetric transfer hydrogenation of aromatic ketones in aqueous medium.  

PubMed

A bifuctional heterogeneous chiral rhodium catalyst exhibited excellent catalytic activity and enantioselectivity in asymmetric transfer hydrogenation of aromatic ketones and their analogues in aqueous medium, which could be recovered easily and used repetitively without affecting obviously its enantioselectivity. PMID:22590711

Tang, Shuang; Jin, Ronghua; Zhang, Huaisheng; Yao, Hui; Zhuang, Jinglan; Liu, Guohua; Li, Hexing

2012-05-16

208

Desulfurization of coal: Enhanced selectivity using phase transfer catalysts. Final technical report, September 1, 1995--August 31, 1996  

SciTech Connect

Due to environmental problems related to the combustion of high sulfur Illinois coal, there continues to be interest in the development of viable pre-combustion desulfurization processes. Recent studies by the authors have obtained very good sulfur removals but the reagents that are used are too expensive. Use of cheaper reagents leads to a loss of desired coal properties. This study investigated the application of phase transfer catalysts to the selective oxidation of sulfur in coal using air and oxygen as oxidants. The phase transfer catalyst was expected to function as a selectivity moderator by permitting the use of milder reaction conditions than otherwise necessary. This would enhance the sulfur selectivity and help retain the heating value of the coal. The use of certain coal combustion wastes for desulfurization, and the application of cerium (IV) catalyzed air oxidations for selective sulfur oxidation were also studied. If successful this project would have lead to the rapid development of a commercially viable desulfurization process. This would have significantly improved the marketability of Illinois coal. However, the phase transfer catalysts, the cerium and the scrubber sledge did not catalize the sulfur removal significantly.

Palmer, S.R.; Hippo, E.J.

1997-05-01

209

Electrochemical proton-coupled electron transfer: Beyond the golden rule  

SciTech Connect

Electrochemical proton-coupled electron transfer rate constant expressions that interpolate between the golden rule and solvent-controlled limits are derived. These expressions include the effects of solvent dynamics and thus are applicable for a wide range of vibronic couplings and solvent relaxation times. The golden rule limit is defined in terms of weak vibronic coupling and fast solvent relaxation, and the solvent-controlled limit is defined in terms of strong vibronic coupling and slow solvent relaxation. In the golden rule limit, the rate constant is proportional to the square of the vibronic coupling and is independent of the solvent relaxation time. In the solvent-controlled limit, the rate constant is independent of the vibronic coupling and increases as the solvent relaxation time decreases. The interconversion between the solvent-controlled and golden rule limits can be induced by altering the proton donor-acceptor mode frequency and the overlap between the reactant and product proton vibrational wave functions, as well as the electronic coupling, the solvent relaxation time, and the overpotential. The kinetic isotope effect behaves differently in the solvent-controlled and golden rule limits and thus provides a unique probe for characterizing electrochemical proton-coupled electron transfer processes. The analogous rate constant expressions for electrochemical electron transfer and homogeneous proton-coupled electron transfer are also presented. The impact of electrode overpotential, solvent relaxation time, and proton donor-acceptor mode frequency on the rate constants are analyzed for model systems.

Navrotskaya, Irina; Hammes-Schiffer, Sharon [Department of Chemistry, Pennsylvania State University, 104 Chemistry Building, University Park, Pennsylvania 16802 (United States)

2009-07-14

210

Long-distance photoinitiated electron transfer through polyene molecular wires  

SciTech Connect

Long-chain polyenes can be used as molecular wires to facilitate electron transfer between a photo-excited donor and an acceptor in an artificial photosynthetic system. The authors present data here on two Zn-porphyrin-polyene-anthraquinone molecules possessing either 5 or 9 all trans double bonds between the donor and acceptor, 1 and 2. The center-to-center distances between the porphyrin and the quinone in these relatively rigid molecules are 25 A for 1 and 35 A for 2. Selective picosecond laser excitation of the Zn-porphyrin in 1 and 2 results in the very rapid transfer of an electron to the anthraquinone in < 2 ps and 10 ps, respectively. The resultant radical ion pairs recombine with tau = 10 ps for 1 and tau = 25 ps for 2. The electron transfer rates remain remarkably rapid over these long distances. The involvement of polyene radical cations in the mechanism of the radical ion pair recombination reaction is clear from the transient absorption spectra of 1 and 2, which show strong absorbances in the near-infrared. The strong electronic coupling between the Zn-porphyrin and the anthraquinone provided by low-lying states of the polyene make it possible to transfer an electron rapidly over very long distances.

Wasielewski, M.R.; Johnson, D.G.; Svec, W.A.; Kersey, K.M.; Cragg, D.E.; Minsek, D.W.

1988-01-01

211

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

NASA Astrophysics Data System (ADS)

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

Gavrilyuk, A. I.

2007-12-01

212

Electron-Wavepacket Reaction Dynamics in Proton Transfer of Formamide  

NASA Astrophysics Data System (ADS)

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

Nagashima, Kengo; Takatsuka, Kazuo

2009-10-01

213

Quality assurance and data collection -- Electronic Data Transfer  

SciTech Connect

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

Tomczak, L.M.; Lohner, W.G.; Ray, E.C.; Salesky, J.A. [Fernald Environmental Restoration Management Corp., Cincinnati, OH (United States). Fernald Environmental Management Project; Spitz, H.B. [Cincinnati Univ., OH (United States). Coll. of Nuclear Engineering

1993-05-01

214

Electron transfer at semiconducting metal dichalcogenide/liquid electrolyte interfaces  

SciTech Connect

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

Howard, J.N.

1992-01-01

215

Solvent structure and hydrodynamic effects in photoinduced electron transfer  

SciTech Connect

A previously developed statistical mechanical theory describing photo-induced electron transfer and geminate recombination in liquid solutions has been modified to account for realistic finite-volume solvent effects. This work introduces physically important effects caused by the solvent which fundamentally affect the rates and spatial distribution of charge transfer events. The finite volume of solvent molecules gives rise to a nonuniform distribution of particles around an electron donor, which is incorporated into the theory by a two-particle radial distribution function (rdf). The Percus{endash}Yevick solutions for the rdf can give numerically useful values for the solvent structure, {ital g}({ital R}) although any form of {ital g}({ital R}) can be used with the method. The nonuniform particle distribution significantly affects the electron transfer rates and the distribution of ion pairs formed by forward electron transfer, particularly at short times. In addition, finite solvent size affects the rate of relative diffusion between any donor{endash}acceptor pair. These {open_quote}{open_quote}hydrodynamic effects{close_quote}{close_quote} slow down the interparticle diffusion rates when near contact, resulting in a major change in the long time behavior of photoexcited electron transfer systems. This work formally introduces the mathematical modifications to charge transfer theory necessary to account for the solvent structure and hydrodynamic effect and illustrates the results with model calculations. These calculations show that analysis of experiments with theories that do not include the rdf and hydrodynamic effects can result in significant errors in the interpretation of data. {copyright} {ital 1996 American Institute of Physics.}

Swallen, S.F.; Weidemaier, K.; Fayer, M.D. [Department of Chemistry, Stanford University, Stanford, California 94305 (United States)

1996-02-01

216

Electric field effects on fluorescence quenching due to electron transfer  

Microsoft Academic Search

The effect of an external electric field on fluorescence quenching due to electron transfer from a photoexcited electron donor to an acceptor has been analyzed theoretically. The model predicts that at weak fields the variation DeltaI(c,F)\\/I(c,0) in the steady-state monomer fluorescence intensity induced by an external electric field is proportional to the square of the field strength F and to

Maria Hilczer; Sergey Traytak; M. Tachiya

2001-01-01

217

The electronic structure of iron and nickel catalysts and their activity in coal hydrogenation  

SciTech Connect

The thermodynamic and quantum-chemical aspects of hydrogenation of coal organic matter in the presence of iron and nickel compounds as catalysts were considered. A thermodynamic analysis of the formation reaction of catalytically active catalyst entities under hydrogenation conditions was performed. The electronic structure of FeO, FeS, FeS{sub 2}, NiO, and NiS with the minimal number of iron and nickel atoms and their activated complexes with an H{sub 2} molecule were calculated by the ab initio Hartree-Fock method using the STO 6-311G basis set. A comparative catalytic activity of transition states of this kind was evaluated.

A.M. Gyul'maliev; A.S. Maloletnev; M.Ya. Shpirt; L.A. Zekel; M.A. Gyul'malieva [Institute for Fossil Fuels, Moscow (Russian Federation). Scientific Research Center on Complex Processing of Solid Fossil Fuels

2009-07-01

218

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

219

Magnetic resonance studies of photo-induced electron transfer reactions  

SciTech Connect

Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ([pi]/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser excitation. Investigations of electron transfer reactions focused on porphyrin (donor) - quinone (acceptor) systems. First, two hydrogen abstraction reactions were studied with FT EPR: photoreduction of acetone with 2-propanol, yielding the acetone ketyl radical, and the reaction of 2-propanol with t-butoxy radicals. Then, the FT EPR study of benzoquinone or duroquinone anion radicals generated by pulsed-laser induced electron transfer from zinc tetraphenylporphyrin (ZnTPP) or tetrasulfonated Zn(TPP), was carried out in homogeneous solution, micellar solutions, and silica gel. Finally, FT EPR was used to study electron transfer quenching of triplet C[sub 60] by electron donors.

van Willigen, H.

1992-11-01

220

Fluctuations in Biological and Bioinspired Electron-Transfer Reactions  

PubMed Central

Central to theories of electron transfer (ET) is the idea that nuclear motion generates a transition state that enables electron flow to proceed, but nuclear motion also induces fluctuations in the donor-acceptor (DA) electronic coupling that is the rate-limiting parameter for nonadiabatic ET. The interplay between the DA energy gap and DA coupling fluctuations is particularly noteworthy in biological ET, where flexible protein and mobile water bridges take center stage. Here, we discuss the critical timescales at play for ET reactions in fluctuating media, highlighting issues of the Condon approximation, average medium versus fluctuation-controlled electron tunneling, gated and solvent relaxation controlled electron transfer, and the influence of inelastic tunneling on electronic coupling pathway interferences. Taken together, one may use this framework to establish principles to describe how macromolecular structure and structural fluctuations influence ET reactions. This framework deepens our understanding of ET chemistry in fluctuating media. Moreover, it provides a unifying perspective for biophysical charge-transfer processes and helps to frame new questions associated with energy harvesting and transduction in fluctuating media.

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

2010-01-01

221

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

SciTech Connect

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).

Not Available

1989-04-12

222

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

SciTech Connect

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).

Not Available

1990-02-14

223

Nonperturbative method of electron transfer via a midway molecule  

Microsoft Academic Search

In the theory of Sumi and Kakitani on electron transfer (ET) via a midway molecule, the overall ET was formulated using the second-order perturbation method and phenomenologically incorporating the renormalization factor in the intermediate state to escape from the divergence of the rate. In this Letter, we developed a nonperturbative theory of the ET via a midway molecule and we

A. Kimura; T. Kakitani

1998-01-01

224

Direct electron transfer bioelectronic interfaces: application to clinical analysis  

Microsoft Academic Search

Bioelectronic interfaces based on direct electron transfer to proteins and enzymes immobilised at functional electrode surfaces are currently under development and the potential of two such systems for application to clinical measurement will be outlined. The first is the detection of free radical production via direct electrochemistry of cytochrome c immobilised covalently at modified gold electrodes. The redox protein cytochrome

Calum J. McNeil; Dale Athey; Wah On Ho

1995-01-01

225

Non-linear quantum effects on electron transfer reactions  

Microsoft Academic Search

To study nuclear quantum effects on electron transfer reactions, the non-adiabatic rate constant is expanded in terms of Planck's constant. The expansion to the second order reproduces well the quantum correction in the activation free energy for a quantum Monte Carlo simulation of water. In addition, the spin-boson model is discussed using the expansion. The validity of the rate constant

A. Yoshimori

1997-01-01

226

Nuclear quantum effects on electron transfer reactions in DNA hairpins  

Microsoft Academic Search

The driving force dependence of photoinduced electron transfer rate constant in synthetic DNA hairpins in aqueous solutions has been analyzed by means of molecular dynamics simulations. The quantum energy gap law has thus been investigated from a fully atomistic point of view, well reproducing the experimental results with reduced ambiguities in the parameter fitting. Although the contribution from the high-frequency

Shigenori Tanaka; Yasuo Sengoku

2003-01-01

227

Long-Distance Photoinitiated Electron Transfer Through Polyene Molecular Wires.  

National Technical Information Service (NTIS)

Long-chain polyenes can be used as molecular wires to facilitate electron transfer between a photo-excited donor and an acceptor in an artificial photosynthetic system. The authors present data here on two Zn-porphyrin-polyene-anthraquinone molecules poss...

M. R. Wasielewski D. G. Johnson W. A. Svec K. M. Kersey D. E. Cragg

1988-01-01

228

Energy and electron transfer processes in polymethine dyes  

Microsoft Academic Search

Polymethine dyes and its derivatives are attractive for their interesting optical and photo-electric properties. They are used as very efficient spectral sensitizers and laser dyes. Due to the high rate constant of deactivation channels of such dyes the primary processes of bimolecular processes as energy or electron transfer proceed within not more than some picoseconds or even shorter. In the

Karl-Heinz Feller; Roaldas Gadonas

1996-01-01

229

Electron transfer dynamics: Zusman equation versus exact theory  

Microsoft Academic Search

The Zusman equation has been widely used to study the effect of solvent dynamics on electron transfer reactions. However, application of this equation is limited by the classical treatment of the nuclear degrees of freedom. In this paper, we revisit the Zusman equation in the framework of the exact hierarchical equations of motion formalism, and show that a high temperature

Qiang Shi; Liping Chen; Guangjun Nan; Ruixue Xu; Yijing Yan

2009-01-01

230

Direct electron transfer of glucose oxidase on carbon nanotubes  

Microsoft Academic Search

In this report, exploitation of the unique properties of single-walled carbon nanotubes (SWNT) leads to the achievement of direct electron transfer with the redox active centres of adsorbed oxidoreductase enzymes. Flavin adenine dinucleotide (FAD), the redox active prosthetic group of flavoenzymes that catalyses important biological redox reactions and the flavoenzyme glucose oxidase (GOx), were both found to spontaneously adsorb onto

Anthony Guiseppi-Elie; Chenghong Lei; Ray H. Baughman

2002-01-01

231

Photoinduced electron transfer in binary blends of conjugated polymers  

SciTech Connect

The authors report observations concerning the intermolecular photoinduced electron transfer through blends of n-type/p-type {pi}-conjugated organic polymers. The results of transient absorption spectroscopy, fluorescence quenching analysis, and delocalized radical ion pair generation studies imply that these materials are supramolecular materials.

Jenekhe, A.A.; Paor, L.R. de; Chen, X.L.; Tarkka, R.M. [Univ. of Rochester, NY (United States)

1996-10-01

232

Probing Inhomogeneous Vibrational Reorganization Energy Barriers of Interfacial Electron Transfer  

SciTech Connect

We report an atomic force microscopy (AFM) and confocal Raman microscopy study on the interfacial electron transfer of a dye-sensitization system, alizarin adsorbed upon TiO2 nanoparticles. Resonance Raman and absorption spectral analyses revealed the distribution of the mode-specific vibrational reorganization energies encompassing different local sites (~250 nm spatial resolution), suggesting spatially inhomogeneous vibrational reorganization energy and different Franck-Condon coupling factors of the interfacial electron transfer. We found that the total vibrational reorganization energy was inhomogeneous from site to site, and specifically, the mode-specific analyses indicated that the energy distributions were inhomogeneous for bridging normal modes and homogeneous for nonbridging normal modes, especially for modes far away from the alizarin- TiO2 coupling hydroxyl modes. Our results demonstrate a significant step forward in characterizing site-specific inhomogeneous interfacial charge transfer dynamics.

Pan, Duohai; Hu, Dehong; Lu, H. Peter

2005-09-01

233

Phonon-mediated path-interference in electronic energy transfer  

NASA Astrophysics Data System (ADS)

Motivated by the recent observations of quantum coherence in light-harvesting antennae, we present a formalism to quantify the contribution of path-interference in phonon-mediated electronic energy transfer. The transfer rate between two molecules is computed by considering the quantum mechanical amplitudes associated with pathways connecting the initial and final sites. This includes contributions from classical pathways, but also terms arising from their interference. By treating the vibrational modes of the molecules as a non-Markovian harmonic oscillator bath, we compute the first-order path-interference correction to the classical transfer rate. We show that the correction due to path-interference may have either a vibrational or an electronic character, and may exceed the contribution of the indirect classical pathways.

Hossein-Nejad, Hoda; Olaya-Castro, Alexandra; Scholes, Gregory D.

2011-03-01

234

Polarization transfer of bremsstrahlung arising from spin-polarized electrons.  

PubMed

We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. By means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. For the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy. PMID:23004992

Märtin, R; Weber, G; Barday, R; Fritzsche, Y; Spillmann, U; Chen, W; DuBois, R D; Enders, J; Hegewald, M; Hess, S; Surzhykov, A; Thorn, D B; Trotsenko, S; Wagner, M; Winters, D F A; Yerokhin, V A; Stöhlker, Th

2012-06-26

235

Polarization Transfer of Bremsstrahlung Arising from Spin-Polarized Electrons  

NASA Astrophysics Data System (ADS)

We report on a study of the polarization transfer between transversely polarized incident electrons and the emitted x rays for electron-atom bremsstrahlung. By means of Compton polarimetry we performed for the first time an energy-differential measurement of the complete properties of bremsstrahlung emission related to linear polarization, i.e., the degree of linear polarization as well as the orientation of the polarization axis. For the high-energy end of the bremsstrahlung continuum the experimental results for both observables show a high sensitivity on the initial electron spin polarization and prove that the polarization orientation is virtually independent of the photon energy.

Märtin, R.; Weber, G.; Barday, R.; Fritzsche, Y.; Spillmann, U.; Chen, W.; DuBois, R. D.; Enders, J.; Hegewald, M.; Hess, S.; Surzhykov, A.; Thorn, D. B.; Trotsenko, S.; Wagner, M.; Winters, D. F. A.; Yerokhin, V. A.; Stöhlker, Th.

2012-06-01

236

Synthesis and characterization of novel antibacterial polymers and clay delivery systems and polymeric phase transfer catalysts  

NASA Astrophysics Data System (ADS)

The research presented in this dissertation involves the syntheses of both novel antibacterial polymers and nanocomposites and polymeric phase transfer catalysts. The first section describes the synthesis, characterization, and antibacterial activities of new acrylate/methacrylate and acrylamide/methacrylamide polymers containing pendant quaternary ammonium compounds and norfloxacin. The first part of this section focuses on the syntheses and antibacterial activities of new water-soluble bis-quaternary ammonium methacrylate monomers and polymers (Chapter II). The monomers and polymers showed antibacterial activities against Staphylococcus aureus and Escherichia coli and the activity increased as the alkyl chain length in ammonium groups increased from 4 to 6 carbons. The results are very encouraging since polymers with quaternary ammonium compounds containing short alkyl chains are generally not active against bacteria. The second part of the first section involves the syntheses and antibacterial activities of various new monomers and polymers with amine and mono-quaternary ammonium groups on the side chain (Chapter III). The monomers were either the derivatives of 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHM) or based on acrylamide and methacrylamide derivatives. All monomers were homopolymerized and copolymerized with 2-hydroxyethylmethacrylate (HEMA). Amine monomers, their homopolymers and copolymers did not show any antibacterial activity against S. aureus and E. coli while the quaternized AHM-3-(aminomethyl) pyridine monomer, its homopolymer and copolymer with HEMA showed antibacterial activities against both bacteria. It was also found that the antibacterial activity of the quaternized methacrylamide-3-(aminomethyl) pyridine monomers and polymers increased as the alkyl chain length in ammonium groups increased. (Abstract shortened by UMI.)

Dizman, Bekir

237

Protein dynamics modulated electron transfer kinetics in early stage photosynthesis.  

PubMed

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

Kundu, Prasanta; Dua, Arti

2013-01-28

238

Protein dynamics modulated electron transfer kinetics in early stage photosynthesis  

NASA Astrophysics Data System (ADS)

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.

Kundu, Prasanta; Dua, Arti

2013-01-01

239

Electron transfer between distant quantum dots by surface acoustic waves  

NASA Astrophysics Data System (ADS)

Quantum dots (QDs) provide a useful system for manipulating and storing quantum information. Tunneling of electrons between double dots has been demonstrated but over larger distances a tunnel barrier is inadequate. We show such long range transfer of single electrons between QDs through a depleted 1D channel using a surface acoustic wave (SAW) pulse. Surface gates define two QDs (RQD & LQD) connected by a 4?m channel. Electrons trapped in RQD are raised above the Fermi energy by a gate sequence. Having set RQD to be ``full'' and LQD ``empty'' a SAW pulse is sent through the RQD towards the LQD. The SAW potential lifts and carries any electrons from RQD to LQD where they are trapped by a large exit gate voltage (transfer reliability 70%.) Changes in QD occupation are monitored by 1D charge detectors. We have demonstrated the transfer of electrons between static and dynamic QDs. This technique may allow the movement of quantum information (spin) between processor and storage, or to a region of holes for conversion to photon qubits.

McNeil, R. P. G.; Kataoka, M.; Ford, C. J. B.; Barnes, C. H. W.; Anderson, D.; Jones, G. A. C.; Farrer, I.; Ritchie, D. A.

2010-03-01

240

Nanostructural and Chemical Characterization of Supported Metal Oxide Catalysts by Aberration Corrected Analytical Electron Microscopy  

NASA Astrophysics Data System (ADS)

In this thesis, aberration corrected STEM imaging and chemical analysis techniques have been extensively applied in the structural and chemical characterization of supported tungsten oxide catalysts in an attempt to reveal the structure-activity relationships at play in these catalyst systems. The supported WO3/ZrO2 solid acid catalyst system is a major focal point of this thesis, and detailed aberration-corrected STEM-HAADF imaging studies were performed on a systematic set of catalysts showing different level of catalytic performance. The nature of the catalytically most active WOx species was identified by correlating structural information, obtained from STEM-HAADF and in-situ optical spectroscopy studies, with catalytic testing results. Specifically, ˜1nm distorted Zr-WOx mixed oxide clusters were identified to be the most active species for both the methanol dehydration and n-pentane isomerization reactions in the WO3/ZrO2 catalyst system. The use of amorphous zirconia as a precursor support material makes it much easier to extract and incorporate Zr cations into the surface WOx clusters during calcination. The calcination temperature was also identified to also play an important role in the formation of these most active Zr-WOx clusters. When the calcination temperature is comparable to or higher than the 896K Huttig temperature of ZrO2 (at which surface ZrO x species have sufficient mobility to agglomerate and sinter), the chance for successful surface WOx and ZrOx intermixing is significantly increased. Based on this perceived structure-activity relationship, several new catalyst synthesis strategies were developed in an attempt to optimize the catalytic performance of WOx-based catalysts. We have demonstrated in Chapter 3 that co-impregnation of WOx and ZrOx precursors onto an inactive model WO3/ZrO2 catalyst, followed by a calcination treatment above the 896K Huttig temperature of ZrO 2, promotes the surface diffusion of ZrO2 and intermixing of ZrOx with WOx. As a consequence, the catalytic activity of the co-impregnated material is dramatically increased by more than two orders of magnitude. We further showed in Chapter 5 that the Keggin structure based on phosphotungstic acid hydrate (i.e. an ˜ 1nm P-WOx mixed oxide cluster) can be successfully immobilized on an amorphous SiO2 support surface. Such catalyst design experiments further support our postulated structure-activity model, in which WO x clusters mixed with some low valence heteroatoms are the most active entities for the methanol dehydration and n-pentane isomerization reactions. Another major theme of this thesis is the analysis of model double-supported metal oxide catalysts, in which a high surface area oxide support material (amorphous SiO2) is modified by the presence of a second metal oxide surface species (TiO2 or ZrO2) added to control the distribution and activity of the active surface WOx component. These complex double-supported metal oxide catalysts represent a very significant challenge in terms of structural characterization. A new electron microscopy characterization strategy was developed for this purpose which combined aberration corrected STEM imaging with concurrent EELS and XEDS analysis. We demonstrated that the various components in a double-supported WO3/TiO 2/SiO2 catalyst system can be effectively visualized using complementary HAADF and STEM-BF imaging within an aberration corrected STEM. Furthermore, when combined with chemical analysis by STEM-EELS and XEDS within the same STEM instrument, it is possible to map out the relative spatial distribution of all the metal oxide components within the WO3/TiO2/SiO 2 catalyst. By comparing the structures of a systematic set of WO 3/TiO2/SiO2 samples displaying high, intermediate and low activity for the methanol dehydration reaction, we showed that the acidic catalytic activity seems to benefit from having (i) a more localized electron density on the TiOx support and (ii) a larger WOx domain that can better disperse the electron density. The results presented in this thesis clear

Zhou, Wu

241

Studying Fischer-Tropsch catalysts using transmission electron microscopy and model systems of nanoparticles on planar supports.  

SciTech Connect

Nanoparticle model systems on planar supports form a versatile platform for studying morphological and compositional changes of catalysts due to exposure to realistic reaction conditions. We review examples from our work on iron and cobalt catalysts, which can undergo significant rearrangement in the reactive environment of the Fischer-Tropsch synthesis. The use of specially designed, silicon based supports with thin film SiO{sub 2} enables the application of transmission electron microscopy, which has furnished important insight into e.g. the mechanisms of catalyst regeneration.

Thune, P. C.; Weststrate, C. J.; Moodley, P.; Saib, A. M.; van de Loosdrecht, J.; Miller, J. T.; Niemantsverdriet, J. W. (Chemical Sciences and Engineering Division); (Eindhoven Univ. of Technology); (Sasol Technology)

2011-01-01

242

Electron transfer collisions between isolated fullerene dianions and SF6  

NASA Astrophysics Data System (ADS)

Electron transfer collisions of trapped doubly charged fullerene anions C762-, C782-, and C842- with SF6 are studied in a Fourier transform ion cyclotron resonance mass spectrometer at center-of-mass collisional energies ranging from thermal energy to 77 eV. Collision energy dependencies manifest threshold energies for (nominally exoergic) single electron transfer onto SF6 of 1.46+/-0.3 eV, 1.56+/-0.3 eV, and 1.63+/-0.3 eV for C762-, C782-, and C842-, respectively. Kinetics studies reveal charge-transfer cross sections of up to 430+/-200 A?2 for C842- at a collision energy of 77 eV. The mechanism and the energetics are discussed in terms of classical electrostatic model calculations. Additionally, we rationalize the collision energy dependencies of the charge-transfer cross sections using the two-state Landau-Zener formalism to describe the associated resonant electron tunneling probability.

Neumaier, Marco; Hampe, Oliver; Kappes, Manfred M.

2005-08-01

243

A device for measuring spin selectivity in electron transfer.  

PubMed

A new type of device is presented that allows direct measurement of spin selectivity in charge transfer processes occurring in adsorbed molecules. The new device provides direct information about the nature of the charge being transferred (electrons or holes) and on spin selectivity, if it exists. Here the device is applied for establishing the spin-dependent electron transfer through double-stranded DNA and its variation with the length of the oligomer. The DNA is self-assembled on a silver substrate and is measured under ambient conditions. The device is based on monitoring the electric potential between a ferromagnetic Ni layer and a silver layer, on top of which the DNA is self-assembled. When a dye molecule, attached to the DNA, is photoexcited, a charge transfer between the dye and the silver substrate takes place, resulting in a change in the electric potential between the Ni and the silver. If the charge transfer is spin selective, the electric potential measured depends on the direction of magnetization of the Ni. PMID:24077104

Senthil Kumar, Karuppannan; Kantor-Uriel, Nirit; Mathew, Shinto Pulinthanathu; Guliamov, Rahamim; Naaman, Ron

2013-10-01

244

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

PubMed

Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ?G°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -?G° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-?G°) can restore fast rates of electron transfer. PMID:23869871

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

2013-08-21

245

Electric field effect on electron transfer between donor and acceptor in polymer matrix  

Microsoft Academic Search

Theoretical investigations on the effect of an external electric field on electron transfer from a photoexcited electron donor to an acceptor doped in a rigid polymer matrix have been described. Four cases are considered: (I) intramolecular electron transfer in donor–acceptor pairs linked by a spacer, (II) intermolecular electron transfer between donor and acceptor molecules which are both randomly distributed in

Maria Hilczer; T Bandyopadhyay; M Tachiya

2004-01-01

246

Long-range electron transfer in a model for DNA  

NASA Astrophysics Data System (ADS)

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 ?-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.

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

2001-03-01

247

Inclusive electron - nucleus scattering at large momentum transfer  

SciTech Connect

Inclusive electron scattering is measured with 4.045 GeV incident beam energy from C, Fe, and Au targets. The measured energy transfers and angles correspond to a kinematic range for Bjorken x>1 and momentum transfers from Q2 = 1-7 (GeV/c)2. When analyzed in terms of the y-scaling function the data show for the first time an approach to scaling for values of the initial nucleon momenta significantly greater than the nuclear matter Fermi momentum (i.e., >0.3 GeV/c).

J. Arrington; C. S. Armstrong; T. Averett; O. K. Baker; L. de Bever; C. W. Bochna; W. Boeglin; B. Bray; R. D. Carlini; G. Collins; C. Cothran; D. Crabb; D. Day; J. A. Dunne; D. Dutta; R. Ent; B. W. Filippone; A. Honegger; E. W. Hughes; J. Jensen; J. Jourdan; C. E. Keppel; D. M. Koltenuk; R. Lindgren; A. Lung; D. J. Mack; J. McCarthy; R. D. McKeown; D. Meekins; J. H. Mitchell; H. G. Mkrtchyan; G. Niculescu; I. Niculescu; T. Petitjean; O. Rondon; I. Sick; C. Smith; B. Terburg; W. F. Vulcan; S. A. Wood; C. Yan; J. Zhao; and B. Zihlmann

1999-03-01

248

Electronic energy transfer: vibrational control and nonlinear wavepacket interferometry  

NASA Astrophysics Data System (ADS)

The time-development of photoexcitations in molecular aggregates exhibits specific dynamics of electronic states and vibrational wavefunction. We discuss the dynamical formation of entanglement between electronic and vibrational degrees of freedom in molecular aggregates with theory of electronic energy transfer and the method of vibronic 2D wavepackets [ J. Chem. Phys. 118, 46 (2003); quant-ph/0412219]. The vibronic dynamics is also described by applying Jaynes-Cummings model to the electronic energy transfer [J. Chem. Phys. 120, 11209 (2004); math-ph/0403023]. Following the ultrafast excitation of donor [ J. Phys. Chem 99, 2568 (1995); chem-ph/9411004] the population of acceptor rises by small portions per each vibrational period, oscillates force and back between donor and acceptor with later damping and partial revivals of this oscillation. The transfer rate gets larger as donor wavepacket approaches the acceptor equilibrium configuration, which is possible at specific energy differences of donor and acceptor and at maximal amount of the vibrational motion along the line that links donor and acceptor equilibria positions. The four-pulse phase-locked nonlinear wavepacket 2D interferograms reflect the shape of the relevant 2D vibronic wavepackets and have maxima at longer delay between excitation pulses for dimers with equal donor-acceptor energy difference compare to dimers with activationless energy configuration [Cina, Fleming, J. Phys. Chem. A. 108, 11196 (2004)].

Prezhdo, Oleg V.; Cina, Jeffrey A.; Kilin, Dmitri S.

2005-04-01

249

Esterification of sodium 4-hydroxybenzoate by ultrasound-assisted solid-liquid phase-transfer catalysis using dual-site phase-transfer catalyst.  

PubMed

The catalytic esterification of sodium 4-hydroxybenzoate with benzyl bromide by ultrasound-assisted solid-liquid phase-transfer catalysis (U-SLPTC) was investigated using the novel dual-site phase-transfer catalyst 4,4'-bis(tributylammoniomethyl)-1,1'-biphenyl dichloride (BTBAMBC), which was synthesized from the reaction of 4,4'-bis(chloromethyl)-1,1'-biphenyl and tributylamine. Without catalyst and in the absence of water, the product yield at 60°C was only 0.36% in 30min of reaction even under ultrasound irradiation (28kHz/300W) and 250rpm of stirring speed. When 1cm(3) of water and 0.5mmol of BTBAMBC were added, the yield increased to 84.3%. The catalytic intermediate 4,4'-bis(tributylammoniomethyl)-1,1'-biphenyl di-4-hydroxybenzoate was also synthesized to verify the intrinsic reaction which was mainly conducted in the quasi-aqueous phase locating between solid and organic phases. Pseudo-first-order kinetic equation was used to correlate the overall reaction, and the apparent rate coefficient with ultrasound (28kHz/300W) was 0.1057min(-1), with 88% higher than that (0.0563min(-1)) without ultrasound. The esterification under ultrasonic irradiation using BTBAMBC by solid-liquid phase-transfer catalysis was developed. PMID:23972326

Yang, Hung-Ming; Chu, Wei-Ming

2013-08-13

250

Electron donor-acceptor quenching and photoinduced electron transfer for coumarin dyes  

NASA Astrophysics Data System (ADS)

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.

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

1983-10-01

251

Atomic-orbital expansion representation of electron transfer in two-electron systems  

SciTech Connect

Election transfer in two electron ion-atom collision systems is examined using united-atom orbitals (AO+) basic sets. The Hamiltonian is the sum of H/sub 0/ (i), the Hamiltonian of electron i with respect to the two nuclei (or atomic cores), and the electron-electron interaction. With the electron wavefunction expanded in the AO+ basis sets, with the Hamiltonian and with a curved-line inter-nuclear trajectory, the time-dependent Schroedinger equation is solved within the basis space without further approximations. 8 refs., 1 fig.

Fritsch, W.; Lin, C.D.

1985-01-01

252

Au-to-CO electron transfer evidenced by surface-enhanced Raman scattering of 2,6-dimethylphenyl isocyanide  

NASA Astrophysics Data System (ADS)

Au nanoparticles are known to be efficient CO oxidation catalysts under ambient conditions. Investigation of the interaction of CO with Au is difficult particularly using Raman spectroscopy. Although indirect, we demonstrate the transfer of electrons from Au to CO by means of surface-enhanced Raman scattering of 2,6-dimethylphenyl isocyanide, exploiting the susceptibility of the NC stretching band of isocyanide to the variation of the surface potential of Au nanoparticles. The back-bonding from Au to the CO 2?b orbital must be dominant over the 5? donation of CO to Au.

Kim, Kwan; Lee, Seung Hun; Kim, Kyung Lock; Shin, Kuan Soo

2013-10-01

253

Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies  

NASA Astrophysics Data System (ADS)

Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Förster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Förster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene units placed between the chromophores. We find that the polarizability of the bridge significantly enhances the effective interaction. We compare our calculations to single molecule experiments on two types of dyads and find reasonable agreement between theory and experiment.

Fückel, Burkhard; Köhn, Andreas; Harding, Michael E.; Diezemann, Gregor; Hinze, Gerald; Basché, Thomas; Gauss, Jürgen

2008-02-01

254

Indium phosphide and gallium arsenide transferred-electron devices  

NASA Astrophysics Data System (ADS)

The internal physical processes involved in TEDs (Transferred Electron Devices) are reviewed to identify those parameters critical to the transferred-electron (Gunn) effect at millimeter-wave frequencies. Emphasis is on the relation of theoretical device performance to existing practical device behavior. The theoretical work is also used to highlight those areas of internal device physics that are likely to provide the improved performance characteristics demanded by system designers. The TED is approached both as an oscillator and as a reflection amplifier device. Practical equipment results are quoted to illustrate the potential of the TED before consideration is given to the future prospects of this class of device in the vitally important field of millimeter-wave technology.

Eddison, I. G.

255

Electron transfer into self-assembling monolayers on gold electrodes  

SciTech Connect

Electron transfer through a nonconjugated hydrocarbon film was studied. 1-Methyl-1{prime}-(10-(octadecylthio)decyl)-4,4{prime}-bipyridinium dibromide, 1-(7-(octadecylthio)heptyl)-1{prime}-propyl-4,4{prime}-bipyridinium dibromide, and 1-hexyl-1{prime}-(5-(octadecylthio)pentyl)-4,4{prime}-bipyridinium dibromide were synthesized and were separately self-assembled with octadecyl mercaptan onto Au electrodes. The sulfide attached to the gold, and the hydrocarbon chains oriented such that the resulting monolayer films had the electroactive group fixed a distance of 5, 7, or 10 CH{sub 2} groups from the surface, which was about 7-12 {angstrom}, depending on the angle of the chains to the surface. The films were characterized by cyclic voltammetry, FTIR, and ellipsometry. Electron transfer depended on the distance of the electroactive group from the surface and was facile in all cases.

Bunding Lee, K.A. (S.C. Johnson and Son, Inc., Racine, WI (USA))

1990-03-01

256

SF4: electron affinity determination by charge-transfer reactions  

NASA Astrophysics Data System (ADS)

A selected-ion flow drift tube was used to conduct an extensive study of the negative ion/molecule reaction of SF4 and SF-4. Thirteen reactions proceed by electron transfer. Data from these reactions, and information from systems that do not react at all, are used to determine the electron affinity of SF4, EA(SF4) = 1.5 ± 0.2 eV. Additional thermochemical data are used to determine the fluoride affinity of SF3, D(SF3-F-) = 1.8 ± 0.3 eV.

Viggiano, A. A.; Miller, Thomas M.; Stevens Miller, Amy E.; Morris, Robert A.; van Doren, Jane M.; Paulson, John F.

1991-11-01

257

Structural control of electron-transfer properties in metalloproteins  

Microsoft Academic Search

Summary The factors that control long-range electron transfer between two redox centers in a protein are summarized. Rack-induced bonding in blue copper proteins is described. The protein conformation forces the Cu(II) ion into a distorted geometry, lying at least 70 kJ mol-1 above the preferred square-planar geometry in energy. The distortion has the effect that the structural change associated with

Bo G. Malmström

1990-01-01

258

Advances in Enhanced Boiling Heat Transfer From Electronic Components  

Microsoft Academic Search

This paper reviews recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids by use of surface microstructures. The microstructures developed include rough surfaces produced by sanding, vapor blasting hard particles, sputtering of SiO2 followed by wet etching of the surface, chemical vapor deposition of SiO2 film etc., laser-drilled cavities, a brush-like structure (dendritic structure), reentrant

Hiroshi Honda; Jinjia Wei

2003-01-01

259

A coumarin based fluorescent photoinduced electron transfer cation sensor  

Microsoft Academic Search

We wish to report 4-[(Bis(pyridin-2-ylmethyl)amino)methyl]-7-methoxychromen-2-one, 1, as a fluorescent photoinduced electron transfer cation sensor that is capable of indicating the presence of Zn2+, Cd2+ and Pb2+ ions via a fluorescence signal. The log binding constants, ?, for these metal ions have been measured, and were found to be 6.10±0.4, 6.37±0.3, and 5.67±0.3, respectively.

Chandrika P. Kulatilleke; Saliya A. de Silva; Yair Eliav

2006-01-01

260

Photoinduced electron-transfer processes involving substituted stilbene oxides  

Microsoft Academic Search

Electron-transfer interactions of several substituted stilbene oxides (oxiranes) containing cyano and carbomethoxy groups at 2,3-positions with the singlet and triplet states of 1,4-dicyanonaphthalene (DCN) and N,N,N',N'-tetramethylbenzidine (TMB) have been investigated by steady-state fluorescence quenching, pulse radiolysis, and laser flash photolysis. The results are examined in the context of the behaviors of the oxiranes with respect to photosensitized isomerization and degradation

P. K. Das; A. J. Muller; G. W. Griffin

1977-01-01

261

Intermittent Single-Molecule Interfacial Electron Transfer Dynamics  

SciTech Connect

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.

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

2004-08-04

262

Electron transfer coupled with ATP hydrolysis in nitrogenase  

Microsoft Academic Search

Nitrogenase, which is not a membrane protein in vivo, performs energy coupling: the transfer of an electron coupled with ATP hydrolysis from one protein component of nitrogenase, Fe protein (Av2), to another its protein component, MoFe protein (Av1), to form the so-called “super-reduced state” of the active site responsible for the reduction of the substrates, FeMo cofactor (FeMoco) containing Fe,

L. A. Syrtsova; E. A. Timofeeva

2001-01-01

263

Mechanically mediated electron transfer in model metallo-enzyme interfaces  

Microsoft Academic Search

In this paper, we develop a physical analysis of charge transfer in the model ‘metallo-enzyme’ complex which consists of a synthetic redox-addressed assembly (a ‘reaction center’) hybridized with a quantum dot (a gold nanoparticle) and attached via molecular bridge (a spacer) to the electrode. This artificial system allows us to model electronic transduction in experimental redox ezyme-gold nanoparticle hybrid structure

L. Yu. Gorelik; M. V. Voinova

2006-01-01

264

Photochemical electron transfer mediated addition of naphthylamine derivatives to electron-deficient alkenes.  

PubMed

Using photochemical electron transfer, N,N-dimethylnaphthylamine derivatives are added to ?,?-unsaturated carboxylates. The addition takes place exclusively in the ?-position of electron-deficient alkenes and mainly in the 4-position of N,N-dimethylnaphthalen-1-amine. A minor regioisomer results from the addition in the 5-position of this naphthylamine. A physicochemical study reveals that the fluorescence quenching of N,N-dimethylnaphthalen-1-amine is diffusion-controlled and that the back electron transfer is highly efficient. Therefore no transformation is observed at lower concentrations. To overcome this limitation and to induce an efficient transformation, minor amounts of water or another proton donor as well as an excess of the naphthylamine derivative are necessary. A mechanism involving a contact radical ion pair is discussed. Isotopic labeling experiments reveal that no hydrogen is directly transferred between the substrates. The hydrogen transfer to the furanone moiety observed in the overall reaction therefore results from an exchange with the reaction medium. An electrophilic oxoallyl radical generated from the furanone reacts with the naphthylamine used in excess. Concerning some mechanistic details, the reaction is compared with radical and electrophilic aromatic substitutions. The transformation was carried out with a variety of electron-deficient alkenes. Sterically hindered furanone derivatives are less reactive under standard conditions. In a first experiment, such a compound was transformed using heterogeneous electron transfer photocatalysis with TiO(2). PMID:21806039

Jahjah, Rabih; Gassama, Abdoulaye; Dumur, Frédéric; Marinkovi?, Siniša; Richert, Sabine; Landgraf, Stephan; Lebrun, Aurélien; Cadiou, Cyril; Sellès, Patrice; Hoffmann, Norbert

2011-08-10

265

The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris? †  

PubMed Central

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.

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.

2009-01-01

266

The electron transfer system of synthrophically grown desulfovibrio vulgaris  

SciTech Connect

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.

Walker, Christopher [University of Washington, Seattle; He, Zhili [University of Oklahoma; Yang, Zamin Koo [ORNL; Ringbauer, Joseph [University of Washington, Seattle; HE, Qiang [ORNL; Zhou, Jizhong [University of Oklahoma; Voordouw, Gerrit [University of Calgary, ALberta, Canada; Wall, Judy [University of Missouri, Columbia; Arkin, Adam [Lawrence Berkeley National Laboratory (LBNL); Hazen, Terry [Lawrence Berkeley National Laboratory (LBNL); Stolyar, Sergey [University of Washington; Stahl, David [University of Washington

2009-01-01

267

Superexchange-mediated electronic energy transfer in a model dyad.  

PubMed

On the basis of time-dependent density functional theory (TD-DFT) calculations coupled to the polarizable continuum model (PCM) and single molecule spectroscopic studies, we provide a detailed investigation of excitation energy transfer within a model bi-chromophoric system where a perylene monoimide (PMI) donor is bridged to a terrylene diimide (TDI) acceptor through a ladder-type pentaphenylene (pPh) spacer. We find that the electronic excitation on the PMI donor significantly extends over the bridge giving rise to a partial charge transfer character and inducing a approximately 3-fold increase in the electronic interaction between the chromophores, which explains the failure of the Förster model in reproducing the observed energy migration rates when treating PMI as the donor. However, despite an increased charge transfer contribution in the effective donor state, the increase in solvent polarity is not accompanied by an enhancement in the electronic coupling between the subunits, which is rationalized from a detailed analysis of the excited-state wavefunctions. PMID:20544101

Curutchet, Carles; Feist, Florian A; Van Averbeke, Bernard; Mennucci, Benedetta; Jacob, Josemon; Müllen, Klaus; Basché, Thomas; Beljonne, David

2010-06-12

268

Electronic structure and charge transfer states of a multichromophoric heptad  

NASA Astrophysics Data System (ADS)

A multichromophoric Heptad molecule containing Zn-tetraphenyl porphyrin, BDPY dye, bisphenyl anthracene, and C60 attached to a hexaphenyl -benzene core was synthesized by Gust et al. (J. Phys. Chem. B, 113, 7147 (2009)). The snowflake like molecule behaves like an antenna capturing photons at different wavelengths and transferring the energy to the porphyrin. We present a DFT based study on the ground state of the complex and also on the lowest two charge transfer (CT) states of the complex carried out using a perturbative delta-SCF method. The calculations, done using a mixed all-electron and pseudo-potential approach, show that the ionization potential of porphyrin and the electron affinity of C60 in the complex changes significantly from isolated molecules. Our calculated value of the lowest CT state is within 0.2 eV of the experimental estimate. This CT state contains a hole on porphyrin HOMO and a particle on the C60 LUMO. A comparison of the energetics with experiment indicates that the process probably involves excitation from the HOMO-1 of porphyrin to the porphyrin LUMO followed by electron transfer and hole bubbling up resulting in a CT state with the hole on porphyrin HOMO and particle on C60 LUMO.

Basurto, Luis; Zope, Rajendra; Baruah, Tunna

2013-03-01

269

The electron transfer system of syntrophically grown Desulfovibrio vulgaris  

SciTech Connect

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.

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

270

The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris  

SciTech Connect

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.

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

271

36 CFR 1235.44 - What general transfer requirements apply to electronic records?  

Code of Federal Regulations, 2012 CFR

...2012-07-01 false What general transfer requirements apply to electronic records...ADMINISTRATION RECORDS MANAGEMENT TRANSFER OF RECORDS TO THE NATIONAL ARCHIVES OF THE UNITED STATES Transfer Specifications and Standards §...

2012-07-01

272

Frontier orbital symmetry control of intermolecular electron transfer. Progress report, November 1, 1989-October 31, 1990.  

National Technical Information Service (NTIS)

Research continued on the study of intermolecular electron transfer. This report discusses the following topics: fluorescence quenching by electron transfer and the modification of quenching dynamics by solvent properties and net free energy change; trans...

B. Stevens

1990-01-01

273

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

Code of Federal Regulations, 2013 CFR

...TOBACCO PRODUCTS, CIGARETTE PAPERS AND TUBES...TOBACCO Manufacture of Cigarette Papers and Tubes ...Payment of tax by electronic fund transfer. ...in making payment by electronic fund transfer (EFT...tobacco products, cigarette papers, and...

2013-04-01

274

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

Code of Federal Regulations, 2010 CFR

...TOBACCO PRODUCTS, CIGARETTE PAPERS AND TUBES...TOBACCO Manufacture of Cigarette Papers and Tubes ...Payment of tax by electronic fund transfer. ...in making payment by electronic fund transfer (EFT...tobacco products, cigarette papers, and...

2010-04-01

275

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

Code of Federal Regulations, 2010 CFR

...TOBACCO PRODUCTS AND CIGARETTE PAPERS AND TUBES ...Payment of tax by electronic fund transfer. ...cigarette papers, and cigarette tubes combining tax...in making payment by electronic fund transfer (EFT...tobacco products, cigarette papers, and...

2009-04-01

276

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

Code of Federal Regulations, 2010 CFR

...TOBACCO PRODUCTS AND CIGARETTE PAPERS AND TUBES Manufacture of Cigarette Papers and Tubes...Payment of tax by electronic fund transfer...making payment by electronic fund transfer...tobacco products, cigarette papers,...

2009-04-01

277

Photoinduced electron transfer between a donor and an acceptor separated by a capsular wall.  

PubMed

The efficient photoinduced electron transfer from a stilbene derivative incarcerated within a negatively charged organic nanocapsule to positively charged acceptors (methyl viologen and a pyridinium salt) adsorbed outside and the back electron transfer were controlled by supramolecular effects. PMID:22301470

Porel, Mintu; Jockusch, Steffen; Parthasarathy, Anand; Rao, V Jayathirtha; Turro, Nicholas J; Ramamurthy, V

2012-02-03

278

TTP: Secure ACID Transfer Protocol for Electronic Ticket between Personal Tamper-Proof Devices  

Microsoft Academic Search

The expanding market for digital content increases the demand to transfer electronic value through open networks. This paper describes the Ticket Transfer Protocol (TTP), which enables electronically transferable tickets to directly move between two personal tamper-proof devices. The applied two-phase commit protocol for the transfer realizes the ACID (atomicity, consistency, isolation, durability) transaction properties without any external coordinators. Moreover, this

Kimio Kuramitsu; Tadashi Murakami; Hajime Matsuda; Ken Sakamura

2000-01-01

279

Intramolecular photochemical electron transfer. 6. Bridge and solvent dependence of electron transfer in covalently linked porphyrin-peptide-quinone compounds  

SciTech Connect

Intramolecular electron transfer (ET) rate constants k{sub ET} for three covalently linked porphyrin-peptide-quinone compounds have been measured in several solvents. The results show that not only through-bridge, but also through-solvent interactions play important roles in the intramolecular ET process. This latter effect is deduced from the observation that aromatic groups, as both side groups in the bridge and in the solvent, appear to induce a significant increase in the ET rate.

Liu, Jingyao; Schmidt, J.A.; Bolton, J.R. (Univ. of Western Ontario, London (Canada))

1991-09-05

280

Optical Control of the Electron in the Simplest Electron Transfer Reaction  

NASA Astrophysics Data System (ADS)

In this work,we show how a sequence of femtosecond laser pulses can be used to control the dynamics of electron transfer (ET) reactions. We focus on the ejection and subsquent reattachment of an electron from a sodium anion in solution. We first select the distance at which the electron localizes from its Na atom partner (either in an immediate or solvent-separated contact pair) by proper choice of the excitation wavelength used to eject the electron. Once ejected, the electrons in these contact pairs undergo a spontaneous back ET reaction to regenerate the parent Na¯. By re-exciting the electron immediately after it is ejected, we can alter the course of the ET reaction. We find that when the electrons in immediate contact pairs are re-excited, the back ET process is shut off. This is because the delocalization of the electron's wavefunction that occurs upon excitation increases the probability to find the electron outside the immediate solvent cavity, where it can no longer undergo rapid back electron transfer. In a similar experiment in which the re-excitation pulse is applied some time after the electron is ejected, all the electrons in immediate contact pairs have recombined into sodium anions, so the only electrons left are in solvent-separated contact pairs. Delocalizing the electronic wavefunction in the solvent-separated pairs gives some probability to increase the electron density in the adjacent cavity that contains the sodium atom, enhancing the rate of the back ET. There is also some probability that the excited electrons can localize even further from the Na atom, so that the re-excitation pulse both enhances and hinders the back electron transfer reaction. With a careful analysis of the data, we have been able to unravel exactly how far the electron moves upon re-excitation, allowing us to manipulate the electron-sodium atom distance at any time during the back ET reaction that we choose. This represents a degree of optical control over ET reaction dynamics that has yet to be achieved for the nuclear degrees of freedom in photodissociation reactions.

Schwartz, Benjamin

2002-03-01

281

Molecular mimicry of photosynthetic energy and electron transfer  

SciTech Connect

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.

Gust, D.; Moore, T.A.; Moore, A.L. (Arizona State Univ., Tempe (United States))

1993-04-01

282

Electron solvation in water clusters following charge transfer from iodide  

SciTech Connect

The dynamics following charge transfer to solvent from iodide to a water cluster are studied using time-resolved photoelectron imaging of I{sup -}(H{sub 2}O){sub n} and I{sup -}(D{sub 2}O){sub n} clusters with n{<=}28. The results show spontaneous conversion, on a time scale of {approx}1 ps, from water cluster anions with surface-bound electrons to structures in which the excess electron is more strongly bound and possibly more internalized within the solvent network. The resulting dynamics provide valuable insight into the electron solvation dynamics in water clusters and the relative stabilities between recently observed isomers of water cluster anions.

Verlet, Jan R.R.; Kammrath, Aster; Griffin, Graham B.; Neumark, Daniel M. [Department of Chemistry, University of California, Berkeley, California 94720 and Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

2005-12-15

283

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

Code of Federal Regulations, 2013 CFR

...made when the taxpayment by electronic fund transfer is received...section, a taxpayment by electronic fund transfer shall be considered...directs the bank to effect an electronic fund transfer message as required...taxpayer, through normal banking procedures, will serve...

2013-04-01

284

Photoinduced electron transfer from dimethyl aniline to coumarin dyes in reverse micelles  

Microsoft Academic Search

Photoinduced electron transfer between different coumarin dyes and N,N-dimethyl aniline has been investigated in AOT reverse micelle using steady state and time resolved fluorescence spectroscopy. We have observed a slower electron transfer rate in reverse micelle in comparison to that in the neat solvent. Moreover, we have observed retardation in the electron transfer rate in the correlation of the free

Anjan Chakraborty; Debabrata Seth; Debdeep Chakrabarty; Partha Hazra; Nilmoni Sarkar

2005-01-01

285

PHOTOINDUCED INTRAMOLECULAR ELECTRON-TRANSFER OF SUBSTITUTED BENZOATE ESTERS OF 9-ANTHR.ACENEMETPIANOL IN METHANOL  

Microsoft Academic Search

The photoinduced intramolecular electron transfer is a complex phenomena. The role of the solvent and the substituents on the chromophore are important in electron transfer. The higher dipole moment difference between the excited and ground states is direct evidence for such an intramolecular electron transfer. In this study six esters of 9-anthracene methanol were synthesised and characterised. The Stoke shifts

M. D. P. DE COSTA; P. K. CUMARANATUNGA; SRIYANI MALLIKA

286

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

Code of Federal Regulations, 2013 CFR

... false Payment of tax by electronic fund transfer. 24.272...272 Payment of tax by electronic fund transfer. (a) General...institution in making payment by electronic fund transfer (EFT) of...taxes by cash, check, or money order as described in §...

2013-04-01

287

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

NASA Astrophysics Data System (ADS)

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.

Reed, W. E.

1980-06-01

288

Reduced density matrix hybrid approach: Application to electronic energy transfer  

SciTech Connect

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

Berkelbach, Timothy C.; Reichman, David R. [Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027 (United States); Markland, Thomas E. [Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305 (United States)

2012-02-28

289

Advanced oxidation of aromatic VOCs using a pilot system with electron beam-catalyst coupling  

NASA Astrophysics Data System (ADS)

The decomposition of volatile organic compounds (VOCs) using a pilot system of electron beam (EB)-catalyst coupling was investigated. Two aromatic VOCs, toluene (1800 ppmC) and o-xylene (1500 ppmC), were irradiated with a dose range of 0-10 kGy at room temperature. The removal efficiencies for toluene and o-xylene were 92.4% and 94.5%, respectively, under a 10 kGy absorbed dose condition, which were higher than the results of 45.7% and 52.3% when EB-only was used, respectively. The CO2 selectivity approached 100% for both toluene and o-xylene using the EB-catalyst coupling system, while the concentrations of O3 formed were 0.02 ppm (toluene) and 0.003 ppm (o-xylene) at 10 kGy. The aerosol concentration was also measured as 43.2 ?g/m3 (toluene) and 53.4 ?g/m3 (o-xylene) at 10 kGy absorbed dose.

Kim, Ki-Joon; Kim, Junghwan; Son, Youn-Suk; Chung, Sang-Gwi; Kim, Jo-Chun

2012-05-01

290

Long-range electron transfer across a ? -conjugated chain: Role of electron correlations  

NASA Astrophysics Data System (ADS)

We consider a prototype polyene chain donor- ? (bridge)-acceptor. The distance between the donor and the acceptor is varied by increasing the number of atoms in the bridge and the rate of electron transfer kET is studied for a series of different donors D=NH2,OCH3,SCH3 , and a fixed acceptor A=NO2 . We observe a large kET even at a D-A separation of ˜45Å , unexpected from the standard noninteracting theories. Such a long-range electron transfer is primarily due to the formation of bound electron-hole pair (exciton) across the donor-bridge-acceptor atoms. Calculations at various levels, semi-empirical (with inclusion of configuration interactions) and many-body models (using density matrix renormalization group theory), have been performed to accurately account for such electron correlations.

Lakshmi, S.; Datta, Ayan; Pati, Swapan K.

2005-07-01

291

Application scope and limitations of TADDOL-derived chiral ammonium salt phase-transfer catalysts.  

PubMed

We have recently introduced a new class of chiral ammonium salt catalysts derived from easily available TADDOLs. To get a full picture of the scope of application and limitations of our catalysts we tested them in a variety of different important transformations. We found that, although these compounds have recently shown their good potential in the asymmetric ?-alkylation of glycine Schiff bases, they clearly failed when we attempted to control more reactive nucleophiles like b-keto esters. On the other hand, when using them to catalyse the addition of glycine Schiff bases to different Michael acceptors it was found necessary to carefully optimize the reaction conditions for every single substrate class, as seemingly small structural changes sometimes required the use of totally different reaction conditions. Under carefully optimized conditions enantiomeric ratios up to 91:9 could be achieved in the addition of glycine Schiff bases to acrylates, whereas acrylamides and methyl vinyl ketone gave slightly lower selectivities (up to e.r. 77:23 in these cases). Thus, together with additional studies towards the syntheses of these catalysts we have now a very detailed understanding about the scope and limitations of the synthesis sequence to access our PTCs and about the application scope of these catalysts in asymmetric transformations. PMID:23584056

Gururaja, Guddeangadi N; Herchl, Richard; Pichler, Antonia; Gratzer, Katharina; Waser, Mario

2013-04-12

292

Modeling biofilms with dual extracellular electron transfer mechanisms.  

PubMed

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

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

2013-10-23

293

Advances in Enhanced Boiling Heat Transfer From Electronic Components  

NASA Astrophysics Data System (ADS)

This paper reviews recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids by use of surface microstructures. The microstructures developed include rough surfaces produced by sanding, vapor blasting hard particles, sputtering of SiO2 followed by wet etching of the surface, chemical vapor deposition of SiO2 film etc., laser-drilled cavities, a brush-like structure (dendritic structure), reentrant and micro-reentrant cavities, microfins, and porous structures fabricated by alumina particle spraying and painting of silver flakes, diamond particles, aluminum particles and copper particles. Heat sink studs with drilled holes, microfins, multi-layered micro-channels and pores, and pin fins with and without microporous coating have also been developed. The height of microstructure ranges from 0 to 12mm. The primary issues discussed are the mitigation of temperature overshoot at boiling incipience, enhancement of nucleate boiling heat transfer and increasing the critical heat flux.

Honda, Hiroshi; Wei, Jinjia

294

Photoinduced electron transfer from dialkyl nitroxides to halogenated solvents  

SciTech Connect

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.

Chateauneuf, J. (National Research Council of Canada, Ottawa, Ontario (Canada)); Lusztyk, J.; Ingold, K.U. (Univ. of Notre Dame, IN (United States))

1990-02-02

295

Front-end electron transfer dissociation: a new ionization source.  

PubMed

Electron transfer dissociation (ETD), a technique that provides efficient fragmentation while depositing little energy into vibrational modes, has been widely integrated into proteomics workflows. Current implementations of this technique, as well as other ion-ion reactions like proton transfer, involve sophisticated hardware, lack robustness, and place severe design limitations on the instruments to which they are attached. Described herein is a novel, electrical discharge-based reagent ion source that is located in the first differentially pumped region of the mass spectrometer. The reagent source was found to produce intense reagent ion signals over extended periods of time while having no measurable impact on precursor ion signal. Further, the source is simple to construct and enables implementation of ETD on any instrument without modification to footprint. Finally, in the context of hybrid mass spectrometers, relocation of the reagent ion source to the front of the mass spectrometer enables new approaches to gas phase interrogation of intact proteins. PMID:23909443

Earley, Lee; Anderson, Lissa C; Bai, Dina L; Mullen, Christopher; Syka, John E P; English, A Michelle; Dunyach, Jean-Jacques; Stafford, George C; Shabanowitz, Jeffrey; Hunt, Donald F; Compton, Philip D

2013-08-19

296

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

PubMed Central

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

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

2012-01-01

297

Understanding the Electronic Structure of 4d Metal Complexes: From Molecular Spinors to L-Edge Spectra of a di-Ru Catalyst  

SciTech Connect

L{sub 2,3}-edge X-ray absorption spectroscopy (XAS) has demonstrated unique capabilities for the analysis of the electronic structure of di-Ru complexes such as the blue dimer cis,cis-[Ru{sub 2}{sup III}O(H{sub 2}O){sub 2}(bpy){sub 4}]{sup 4+} water oxidation catalyst. Spectra of the blue dimer and the monomeric [Ru(NH{sub 3}){sub 6}]{sup 3+} model complex show considerably different splitting of the Ru L{sub 2,3} absorption edge, which reflects changes in the relative energies of the Ru 4d orbitals caused by hybridization with a bridging ligand and spin-orbit coupling effects. To aid the interpretation of spectroscopic data, we developed a new approach, which computes L{sub 2,3}-edges XAS spectra as dipole transitions between molecular spinors of 4d transition metal complexes. This allows for careful inclusion of the spin-orbit coupling effects and the hybridization of the Ru 4d and ligand orbitals. The obtained theoretical Ru L{sub 2,3}-edge spectra are in close agreement with experiment. Critically, existing single-electron methods (FEFF, FDMNES) broadly used to simulate XAS could not reproduce the experimental Ru L-edge spectra for the [Ru(NH{sub 3}){sub 6}]{sup 3+} model complex nor for the blue dimer, while charge transfer multiplet (CTM) calculations were not applicable due to the complexity and low symmetry of the blue dimer water oxidation catalyst. We demonstrated that L-edge spectroscopy is informative for analysis of bridging metal complexes. The developed computational approach enhances L-edge spectroscopy as a tool for analysis of the electronic structures of complexes, materials, catalysts, and reactive intermediates with 4d transition metals.

Alperovich, Igor; Smolentsev, Grigory; Moonshiram, Dooshaye; Jurss, Jonah W.; Concepcion, Javier J.; Meyer, Thomas J.; Soldatov, Alexander; Pushkar, Yulia (SFU-Russia); (Purdue); (UNC); (LIT)

2011-12-09

298

Mechanisms of bridge-mediated electron transfer: A TDDFT electronic dynamics study  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

299

Transcriptomic and genetic analysis of direct interspecies electron transfer.  

PubMed

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

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

2013-02-01

300

Transcriptomic and Genetic Analysis of Direct Interspecies Electron Transfer  

PubMed Central

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.

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

2013-01-01

301

Photoinduced electron transfer from phycoerythrin to colloidal metal semiconductor nanoparticles  

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

302

Photoinduced electron and energy transfer in molecular pentads  

SciTech Connect

A series of molecular pentads, each consisting of a porphyrin dyad (P-P) covalently linked to a carotenoid polyene (C) and a diquinone moiety (Q[sub A]-Q[sub B]), have been prepared, and the photochemical properties of these molecules have been studied using steady-state and transient absorption and emission spectroscopies. Each of the pentads undergoes photoinduced electron transfer from the C-P-[sup 1]P-Q[sub A]-Q[sub B] singlet state to yield the charge-separated state C-P-P[sup [sm bullet]+]-Q[sub A][sup [sm bullet][minus

Gust, D.; Moore, T.A.; Moore, A.L.; Macpherson, A.N.; Lopez, A.; DeGraziano, J.M.; Gouni, I.; Bittersmann, E.; Seely, G.R.; Gao, F.; Nieman, R.A.; Ma, X.C.; Demanche, L.J.; Hung, S.C.; Luttrull, D.K.; Lee, S.J.; Kerrigan, P.K. (Arizona State Univ., Tempe, AZ (United States))

1993-12-01

303

Importance of Charge Transfer Excitations in DNA Electron Spectrum:  

NASA Astrophysics Data System (ADS)

Electron spectra of DNA model compounds, adenosine-thymidine and guanosine-cytidine nucleoside base pairs, as well as the relevant homogeneous stacked base pair steps in A-DNA and B-DNA conformations, were investigated using ZINDO semiempirical quantum-chemical method. This work confirms that, in DNA with intact Watson-Crick hydrogen bonding and base stacking, the highest occupied molecular orbitals (HOMO) are residing on purine base residues, whereas the lowest unoccupied molecular orbitals (LUMO) — on pyrimidine base residues. In general, the present results are satisfactorily comparable with the available experimental data. The role of charge transfer excitations in the polymer DNA 260 nm spectral band is discussed.

Starikov, E. B.

304

Improving electronic structure methods to predict nano-optoelectronics and nano-catalyst functions.  

SciTech Connect

This report focuses on quantum chemistry and ab initio molecular dynamics (AIMD) calculations applied to elucidate the mechanism of the multi-step, 2-electron, electrochemical reduction of the green house gas molecule carbon dioxide (CO{sub 2}) to carbon monoxide (CO) in aqueous media. When combined with H{sub 2} gas to form synthesis ('syn') gas, CO becomes a key precursor to methane, methanol, and other useful hydrocarbon products. To elucidate the mechanism of this reaction, we apply computational electrochemistry which is a fledgling, important area of basic science critical to energy storage. This report highlights several approaches, including the calculation of redox potentials, the explicit depiction of liquid water environments using AIMD, and free energy methods. While costly, these pioneering calculations reveal the key role of hydration- and protonation-stabilization of reaction intermediates, and may inform the design of CO{sub 2}-capture materials as well as its electrochemical reduction. In the course of this work, we have also dealt with the challenges of identifying and applying electronic structure methods which are sufficiently accurate to deal with transition metal ion complex-based catalyst. Such electronic structure methods are also pertinent to the accurate modeling of actinide materials and therefore to nuclear energy research. Our multi-pronged effort towards achieving this titular goal of the LDRD is discussed.

Nielsen, Ida Marie B.; Marzari, Nicola (Massachusetts Institute of Technology); Shelnutt, John Allen; Kulik, Heather J. (Massachusetts Institute of Technology); Medforth, Craig John (University of New Mexico, Albuquerque, NM); Leung, Kevin

2009-10-01

305

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

SciTech Connect

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.

Spears, K.G.

1993-09-08

306

Analysis of electron correlation in simultaneous electron transfer and excitation in atomic collisions  

SciTech Connect

The two-electron process of simultaneous electron transfer and excitation (TE) in atomic collisions is studied within the close-coupling method for the example of the system He/sup +/+H. The calculated energy dependence of the population of various helium doubly excited states is analyzed for the role of electron correlations in the resonant and nonresonant contributions to the TE process which are included coherently. It is predicted that the impact-parameter--dependent state-selective TE probabilities for this process show conspicuous peak structures.

Fritsch, W.; Lin, C.D.

1988-08-08

307

BIOINSPIRED CATALYSTS: SYNTHESIS, CHARACTERISATION AND SOME APPLICATIONS  

Microsoft Academic Search

Our recent work concerning the synthesis, characterisation and some applications of bioinspired electron-transfer catalysts is reviewed in this contribution. The catalysts were various mono- or heterobimetallic complexes having either Cu(II) or Cu(II) and Zn(II) as central ions and amino acids, their derivatives or various N- containing organic molecules as ligands. Emphasis was based upon the solid support immobilised versions of

István Pálinkó

308

Organometallic ruthenium and iridium transfer-hydrogenation catalysts using coenzyme NADH as a cofactor.  

PubMed

Artificial enzymes: half-sandwich arene ruthenium(II) and cyclopentadienyl iridium(III) complexes containing N,N-chelated ligands can use NADH as a source of hydride for the reduction of ketones. Moreover, cyclopentadienyl phenanthroline iridium(III) derivatives at micromolar concentrations are robust catalysts for the production of H(2) from NADH in water and can raise the NAD(+)/NADH ratio in cancer cells. PMID:22415924

Betanzos-Lara, Soledad; Liu, Zhe; Habtemariam, Abraha; Pizarro, Ana M; Qamar, Bushra; Sadler, Peter J

2012-03-13

309

Efficient multistep photoinitiated electron transfer in a molecular pentad  

SciTech Connect

A synthetic five-part molecular device has been prepared that uses a multistep electron transfer strategy similar to that of photosynthetic organisms to capture light energy and convert it to chemical potential in the form of long-lived charge separation. It consists of two covalently linked porphyrin moieties, one containing a zinc ion (P{sub Zn}) and the other present as the free base (P). The metallated porphyrin bears a carotenoid polyene (C) and the other a diquinone species (Q{sub A}-Q{sub B}). Excitation of the free-base porphyrin in a chloroform solution of the pentad yields an initial charge-separated state, C-P{sub Zn}-P{sup {center dot}+}-Q{sub A}{sup {center dot}{minus}}-Q{sub B}, with a quantum yield of 0.85. Subsequent electron transfer steps lead to a final charge-separated state, C{sup {center dot}+}-P{sub Zn}-P-Q{sub A}-Q{sub B}{sup {center dot}{minus}}, which is formed with an overall quantum yield of 0.83 and has a lifetime of 55 microseconds. Irradiation of the free-base form of the pentad, C-P-P-Q{sub A}-Q{sub B}, gives a similar charge-separated state with a lower quantum yield (0.15 in dichloromethane), although the lifetime is increased to {approximately}340 microseconds. The artificial photosynthetic system preserves a significant fraction ({approximately}1.0 electron volt) of the initial excitation energy (1.9 electron volts) in the long-lived, charge-separated state.

Gust, D.; Moore, T.A.; Moore, A.L.; Lee, Seung-Joo; Bittersmann, E.; Luttrull, D.K.; Rehms, A.A.; DeGraziano, J.M.; Xiaochun C. Ma; Feng Gao; Belford, R.E.; Trier, T.T. (Arizona State Univ., Tempe (USA))

1990-04-13

310

Effects of molecular orientation on electron-transfer collisions  

SciTech Connect

K{sup +} ions have been detected from the intersection of a beam of K atoms (5-30 eV) with beams of various simple molecules, such as CH{sub 3}Br and CF{sub 3}Br, which had been oriented prior to the collision. Production of ions in the collision is found to be highly dependent on orientation. The effect is most pronounced near threshold ({approx}5 eV) and almost disappears at higher (30 eV) energies. Attack at the reactive halogen end produces the most ions, regardless of the polarity of that end. For each molecule, the reactive end seems to have the lower threshold energy. These observations may be a result of the electron being transferred to a specific end of the molecule, but the experiments measure only the net result of an electron transfer followed by the separation of the ions. Whether or not electron jump per se depends on orientation is still an open question, but the authors are able to qualitatively interpret the experimental results as being due to interactions between the ions as they separate in the exit channel. Most of the negative molecular ions dissociate, ejecting a halogen X{sup {minus}} in the direction of the (oriented) molecular axis. If the X end is oriented away from the incoming K atom, the ejected X{sup {minus}} will travel in the same direction as the K{sup +}, making the electron more likely to return to the K{sup +} ion and reducing the K{sup +} signal in this unfavorable orientation.

Harland, P.W.; Carman, H.S. Jr.; Phillips, L.F.; Brooks, P.R. (Rice Univ., Houston, TX (United States))

1991-10-17

311

Photoinduced Electron Transfer Counter to the Bias Field in Coupled Quantum Wells.  

National Technical Information Service (NTIS)

Optical excitation of electrons in an asymmetric double quantum well is theoretically examined. The well is biased to align the excited levels and permit resonant electron tunneling. Emphasis is made on the photoinduced transfer of electrons counter to th...

M. I. Stockman L. S. Muratov L. N. Pandey T. F. George

1992-01-01

312

Selected Electronic Funds Transfer Issues: Privacy, Security, and Equity. Volume II - Working Papers.  

National Technical Information Service (NTIS)

Electronic funds transfer (EFT) is the application of computer technology to the delivery of financial services. Electronic banking, as it is frequently called, is a communications process that relies on electronic messages instead of paper for financial ...

1982-01-01

313

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

Federal Register 2010, 2011, 2012, 2013

...2060-AR09 Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer...finalizing technical revisions to the electronics manufacturing source category of the...address any other changes related to the electronics manufacturing source category....

2012-02-22

314

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

NASA Astrophysics Data System (ADS)

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.

Khan, Yaser; Brumer, Paul

2012-11-01

315

The dynamical correlation in spacer-mediated electron transfer couplings  

NASA Astrophysics Data System (ADS)

The dynamical correlation effect in electron transfer (ET) coupling was studied in this work, for cases where electrons tunnel through a many-electron environment. The ET couplings for three different bridge-mediated model systems were calculated: (I) trans-alkyl chains [H2C-(CH2)n-CH2, n=2-10], (II) two isomers of trans-1,4-dimethylenecyclohexane, and (III) two ethylenes spaced by a saturated ethane molecule. The couplings were calculated as half energy gaps of the two lowest adiabatic states. The dynamical correlation was included with spin-flip (SF) and ionization potential or electron affinity coupled-cluster singles and doubles (SF-CCSD and IP/EA-CCSD) and a ?CCSD scheme. The direct coupling (DC) scheme is also used as a way to obtain a solution with nondynamical correlation, since DC uses approximated eigenstates that are symmetry-restoring linear combinations of two symmetry-broken unrestricted Hartree-Fock configurations. For all cases tested except for one, results from the DC scheme closely follow the CCSD data, indicating that the dual-configuration solutions can be a good approximation of wave functions with nondynamical correlation included, but there exist exceptions. Comparing the DC results with SF-CCSD and IP or EA-CCSD data, we concluded that the dynamical correlation effect is small for most of the cases we tested.

Yang, Chou-Hsun; Hsu, Chao-Ping

2006-06-01

316

Wireless transfer of sensor data into electronic health records.  

PubMed

The purpose of this study is to explore how wireless transfer of sensor data can be implemented in existing Electronic Health Record (EHR) systems. Blood glucose data from people with diabetes Type 1 has been selected as the case.As proof of concept, a prototype for sending blood glucose measurements into an EHR system was developed for the DIPS EHR system. For the prototype to be transferable to a general setting, care was taken not to introduce any additional workload for the diabetes nurses or the diabetes Type 1 patients. In the prototype, the transfer of blood glucose data is automatic and invisible to the user, and the data is presented to the nurses within the existing DIPS laboratory module.To determine whether deployment of such a system would present any risks or hazards to patients (medical or financial), a risk analysis was performed. The analysis indicates that storing blood glucose values in the patient's EHR does not represent any significantly increased risks for the diabetes patient.The study shows that existing EHR systems are well suited to receive sensor data. The three main EHR systems in Norwegian hospitals are all supported with application programming interfaces (APIs), enabling external vendors to add modules. These APIs are sufficient to implement modules for receiving sensor data. However, none of the systems currently have commercially available modules for receiving such data. PMID:16160281

Walseth, Ole Anders; Arsand, Eirik; Sund, Torbjørn; Skipenes, Eva

2005-01-01

317

Photoinduced electron transfer probes for the observation of enzyme activities  

NASA Astrophysics Data System (ADS)

Enzymes engage key roles in a wide variety of important physical and medical processes, which thus can be altered by manipulating the behavior of enzymes in charge. The capability for manipulation requires an exact understanding of enzymatic operation modes though, which can be increased by employing fluorescence spectroscopy techniques. To date several fluorescence-based assays using labeled substrates have been developed to examine different subclasses of hydrolases. We developed a method that circumvents the unspecific probe enzyme interactions and affinity problems occurring in common probes as those based on fluorescence resonance energy transfer (FRET) by taking advantage of the comparably strong electron donating properties of the naturally occurring nucleic acid guanosine (G). Combined with an appropriate fluorophore this compound shows efficient photoinduced electron transfer (PET) quenching reactions only upon contact formation. Thus, initially quenched enzyme substrates, e.g. specific nucleic acid sequences, can be designed that cause a distinct increase in fluorescence signal upon specific hydrolysis. Here we demonstrate the general validity of PET probes for the observation of various nucleases at the ensemble and single molecule level. The rapid response time of the probes enables real-time monitoring of enzyme activities and provides quantitative data which are compared to those of commonly available and recently published, more complex probes. Additionally the applicability of this method is demonstrated for peptidases via fluorophore tryptophan (Trp) interaction.

Henkenjohann, S.; Sauer, M.

2009-02-01

318

Photoinduced electron transfer modeling to simulate flavoprotein fluorescence decay.  

PubMed

A method of analysis is described on the photoinduced electron transfer (PET) from aromatic amino acids as tryptophans (Trp) and tyrosines (Tyr) to the excited isoalloxazine (Iso*) in FMN-binding proteins (FBP) from Desulfovibrio vulgaris (strain, Miyazaki F). Time-dependent geometrical factors as the donor-acceptor distances are determined by means of a molecular dynamics simulation (MDS) of the proteins. Fluorescence decays of the single mutated isoforms of FBP are used as experimental data. The electrostatic (ES) energy between the photoproducts and ionic groups in the proteins is introduced into the Kakitani and Mataga (KM) model, which is modeled for an electron transfer process in solution. The PET parameters contained in the KM rate are determined by means of a nonlinear least square method, according to the Marquardt algorithm. The agreement between the observed and calculated decays is quite good, but not optimal. Characteristics on PET in flavoproteins, obtained by the present method, are described. Possible improvements of the method are discussed. PMID:24108633

Nunthaboot, Nadtanet; Lugsanangarm, Kiattisak; Nueangaudom, Arthit; Pianwanit, Somsak; Kokpol, Sirirat; Tanaka, Fumio

2014-01-01

319

Polar solvent dynamics and electron-transfer reactions.  

PubMed

Polar solvents often exert a dramatic influence on reactions in solution. Equilibrium aspects of this influence involve differential solvation of reactants compared to the transition state that lead to alteration of the free-energy barrier to reaction. Such effects are well known, and often give rise changes in reaction rates of many orders of magnitude. Less well understood are effects arising from non-equilibrium, dynamical aspects of solvation. During the course of reaction, charge is rapidly redistributed among reactants. How the reaction couples to its solvent environment depends critically on how fast the solvent can respond to these changes in reactant charge distribution. In this article the dynamics of solvation in polar liquids and the influence of this dynamics on electron-transfer reactions are discussed. A molecular picture suggests that polar solvation occurs on multiple time scales as a result of the involvement of different types of solvent motion. A hierarchy of models from a homogeneous continuum model to one incorporating molecular aspects of solvation, combined with computer simulations, gives insight into the underlying dynamics. Experimental measures of solvation dynamics from picosecond and subpicosecond time-dependent Stokes shift studies are compared with the predictions of theoretical models. The implication of these results for electron-transfer reactions in solution are then briefly considered. PMID:17751278

Maroncelli, M; Macinnis, J; Fleming, G R

1989-03-31

320

New XAFS beamline for structural and electronic dynamics of nanoparticle catalysts in fuel cells under operating conditions  

NASA Astrophysics Data System (ADS)

We are currently constructing a new X-ray absorption fine structure (XAFS) beamline BL36XU at SPring-8 dedicated for the structural and electronic analysis of the dynamic events on polymer electrolyte fuel cell (PEFC) cathode catalysts for the development of next-generation PEFCs. To investigate the cathode catalyst nanoparticles in PEFCs under the operating conditions, the beamline is designed to provide time- and spatially resolved XAFS techniques having a time resolution of 100 ?s, spatial resolution of 200 nm, and depth resolution of 1 ?m. We report the outline and design of the new beamline.

Sekizawa, O.; Uruga, T.; Tada, M.; Nitta, K.; Kato, K.; Tanida, H.; Takeshita, K.; Takahashi, S.; Sano, M.; Aoyagi, H.; Watanabe, A.; Nariyama, N.; Ohashi, H.; Yumoto, H.; Koyama, T.; Senba, Y.; Takeuchi, T.; Furukawa, Y.; Ohata, T.; Matsushita, T.; Ishizawa, Y.; Kudo, T.; Kimura, H.; Yamazaki, H.; Tanaka, T.; Bizen, T.; Seike, T.; Goto, S.; Ohno, H.; Takata, M.; Kitamura, H.; Ishikawa, T.; Yokoyama, T.; Iwasawa, Y.

2013-04-01

321

How Much Is Transferred from Training to the Job? The 10% Delusion as a Catalyst for Thinking about Transfer  

ERIC Educational Resources Information Center

|This article explores the common belief that only a small amount of what is taught in a training program is actually transferred to the job. After providing evidence of the source of the generalization and the acceptance of the notion despite the lack of empirical, behavioral evidence, we take the opportunity to examine the likely reasons for…

Ford, J. Kevin; Yelon, Stephen L.; Billington, Abigail Q.

2011-01-01

322

Low-temperature electronic transport through macromolecules and characteristics of intramolecular electron transfer  

NASA Astrophysics Data System (ADS)

Long-distance electron transfer (ET) plays an important part in many biological processes. Also, fundamental understanding of ET processes could give grounds for designing miniaturized electronic devices. So far, experimental data on the ET mostly concern ET rates which characterize ET processes as a whole. Here, we develop a different approach which could provide more information about intrinsic characteristics of the long-range intramolecular ET. A starting point of the studies is an obvious resemblance between ET processes and electric transport through molecular wires placed between metallic contacts. Accordingly, the theory of electronic transport through molecular wires is applied to analyze characteristics of a long-range electron transfer through molecular bridges. Assuming a coherent electron tunneling to be a predominant mechanism of ET at low temperatures, it is shown that low-temperature current-voltage characteristics could exhibit a special structure, and the latter contains information concerning intrinsic features of the intramolecular ET. Using the Buttiker dephasing model within the scattering matrix formalism, we analyze the effect of dephasing on the electron transmission function and current-voltage curves.

Zimbovskaya, Natalya A.

2005-09-01

323

Smart Universal Multiple-Valued Logic Gates by Transferring Single Electrons  

Microsoft Academic Search

This paper proposes smart universal multiple-valued (MV) logic gates by transferring single electrons (SEs). The logic gates are based on mosfet based SE turnstiles that can accurately transfer SEs with high speed at high temperature. The number of electrons transferred per cycle by the SE turnstile is a quantized function of its gate voltage, and this characteristic is fully exploited

Wan-Cheng Zhang; Nan-Jian Wu

2008-01-01

324

78 FR 6025 - Electronic Fund Transfers (Regulation E) Temporary Delay of Effective Date  

Federal Register 2010, 2011, 2012, 2013

...CFPB-2012-0050] RIN 3170-AA33 Electronic Fund Transfers (Regulation E) Temporary Delay of Effective...which implements the Electronic Fund Transfer Act (EFTA). The 2012 Final Rule implements...Dodd- Frank Act) regarding remittance transfers. The Bureau is delaying the...

2013-01-29

325

Alternative mitochondrial electron transfer as a novel strategy for neuroprotection.  

PubMed

Neuroprotective strategies, including free radical scavengers, ion channel modulators, and anti-inflammatory agents, have been extensively explored in the last 2 decades for the treatment of neurological diseases. Unfortunately, none of the neuroprotectants has been proved effective in clinical trails. In the current study, we demonstrated that methylene blue (MB) functions as an alternative electron carrier, which accepts electrons from NADH and transfers them to cytochrome c and bypasses complex I/III blockage. A de novo synthesized MB derivative, with the redox center disabled by N-acetylation, had no effect on mitochondrial complex activities. MB increases cellular oxygen consumption rates and reduces anaerobic glycolysis in cultured neuronal cells. MB is protective against various insults in vitro at low nanomolar concentrations. Our data indicate that MB has a unique mechanism and is fundamentally different from traditional antioxidants. We examined the effects of MB in two animal models of neurological diseases. MB dramatically attenuates behavioral, neurochemical, and neuropathological impairment in a Parkinson disease model. Rotenone caused severe dopamine depletion in the striatum, which was almost completely rescued by MB. MB rescued the effects of rotenone on mitochondrial complex I-III inhibition and free radical overproduction. Rotenone induced a severe loss of nigral dopaminergic neurons, which was dramatically attenuated by MB. In addition, MB significantly reduced cerebral ischemia reperfusion damage in a transient focal cerebral ischemia model. The present study indicates that rerouting mitochondrial electron transfer by MB or similar molecules provides a novel strategy for neuroprotection against both chronic and acute neurological diseases involving mitochondrial dysfunction. PMID:21454572

Wen, Yi; Li, Wenjun; Poteet, Ethan C; Xie, Luokun; Tan, Cong; Yan, Liang-Jun; Ju, Xiaohua; Liu, Ran; Qian, Hai; Marvin, Marian A; Goldberg, Matthew S; She, Hua; Mao, Zixu; Simpkins, James W; Yang, Shao-Hua

2011-03-18

326

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

PubMed

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

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

2006-02-01

327

Collisional electron transfer to photoexcited acceptor radical anions  

NASA Astrophysics Data System (ADS)

In this article, we show that photoexcitation of radical anions facilitates electron transfer from sodium atoms in femtosecond encounters. Thus, excitation of 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and fluorinated TCNQ (TCNQ-F4) anions to the second optically active state at 478 nm led to increases in the yields of dianions of about 20% and 10%, respectively. Photoexcitation with a nanosecond-long laser pulse was done a few microseconds before the ions entered the sodium collision cell so that none of the ions would be in any of the initially reached doublet-excited states. We suggest an explanation for the higher electron capture cross section based on the formation of long-lived quartet state anions. Excitation of TCNQ anions within the lowest-energy absorption band, where there are no accessible quartet states, led instead to a lower yield of dianions. There are at least three explanations for the lower dianion yields: (1) Depletion of the monoanion beam due to photodetachment after the absorption of minimum two photons; (2) Formation of short-lived vibrationally excited dianions that decay by electron autodetachment prior to identification; and (3) Lower electron capture cross sections of vibrationally excited monoanions. Similar losses in dianion signal can occur at 478 nm so the actual yield of dianions at this wavelength due to the population of quartet states is therefore greater than that observed. Our methodology devises a more efficient route for the production of molecular dianions, and at the same time it may provide information on long-lived electronic states.

Wyer, Jean Ann; Støchkel, Kristian; Nielsen, Steen Brøndsted

2012-02-01

328

Evolution of gold structure during thermal treatment of Au/FeOx catalysts revealed by aberration-corrected electron microscopy.  

PubMed

High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au/Fe(2)O(3) (WGC ref. no. 60C), prepared by co-precipitation and calcined in air at 400 degrees C, and a catalyst prepared by leaching surface gold from the parent catalyst and exposed to various treatments, including use in the water-gas shift reaction at 250 degrees C. Aberration-corrected JEOL 2200FS (JEOL USA, Peabody, MA) and Vacuum Generators HB-603U STEM instruments were used to image fresh, reduced, leached, used and re-oxidized catalyst samples. A new in situ heating technology (Protochips Inc., Raleigh, NC, USA), which permits full sub-Angström imaging resolution in the JEOL 2200FS was used to study the effects of temperature on the behavior of gold species. A remarkable stability of gold to redox treatments up to 400 degrees C, with atomic gold decorating step surfaces of iron oxide was identified. On heating the samples in vacuum to 700 degrees C, it was found that monodispersed gold began to sinter to form nanoparticles above 500 degrees C. Gold species internal to the iron oxide support material was shown to diffuse to the surface at elevated temperature, coalescing into discrete nanocrystals. The results demonstrate the value of in situ heating for understanding morphological changes in the catalyst with elevated temperature treatments. PMID:19339311

Allard, Lawrence F; Borisevich, Albina; Deng, Weiling; Si, Rui; Flytzani-Stephanopoulos, Maria; Overbury, Steven H

2009-04-01

329

Evolution of Gold Structure During Thermal Treatment of Au/FeOx Catalysts Revealed by Aberration-Corrected Electron Microscopy  

SciTech Connect

High-resolution aberration-corrected electron microscopy was performed on a series of catalysts derived from a parent material, 2 at.% Au/Fe{sub 2}O{sub 3} (WGC ref. no. 60C), prepared by co-precipitation and calcined in air at 400 C, and a catalyst prepared by leaching surface gold from the parent catalyst and exposed to various treatments, including use in the water-gas shift reaction at 250 C. Aberration-corrected JEOL 2200FS (JEOL USA, Peabody, MA) and Vacuum Generators HB-603U STEM instruments were used to image fresh, reduced, leached, used and re-oxidized catalyst samples. A new in situ heating technology (Protochips Inc., Raleigh, NC, USA), which permits full sub-Angstrom imaging resolution in the JEOL 2200FS was used to study the effects of temperature on the behavior of gold species. A remarkable stability of gold to redox treatments up to 400 C, with atomic gold decorating step surfaces of iron oxide was identified. On heating the samples in vacuum to 700 C, it was found that monodispersed gold began to sinter to form nanoparticles above 500 C. Gold species internal to the iron oxide support material was shown to diffuse to the surface at elevated temperature, coalescing into discrete nanocrystals. The results demonstrate the value of in situ heating for understanding morphological changes in the catalyst with elevated temperature treatments.

Overbury, Steven {Steve} H [ORNL; Allard Jr, Lawrence Frederick [ORNL; Borisevich, Albina Y [ORNL; Deng, Weiling [Tufts University; Si, Rui [Tufts University; Flytzani-Stephanopoulos, Prof. Maria [Tufts University

2009-01-01

330

Coupled proton and electron transfer reactions in cytochrome oxidase.  

PubMed

Cytochrome oxidase catalyzes the four-electron reduction of O2 to water and conserves the substantial free energy of the reaction in the form of a protonmotive force. For each electron, two full charges are translocated across the membrane, resulting in a voltage. One of the mechanisms to generate the charge separation in cytochrome oxidase is via a proton pump. A single reaction cycle can be monitored over the course of about 1 msec using absorption spectroscopy, revealing distinct intermediates. Thus, the reaction cycle can be studied as a series of steps. Each of the reaction steps in the catalytic cycle involves a sequence of coupled electron and proton transfer reaction, where protons are either consumed in the chemistry of water formation or pumped across the membrane. The pumping mechanism requires consideration of both the thermodynamics of the various species but also the favored kinetic pathways that assure proton pumping is unidirectional. Hence, a knowledge of transition states and transiently, poorly populated intermediates is likely to be important to understand the mechanism of the pump. PMID:14766393

Gennis, Robert B

2004-01-01

331

Dissociative electron capture of halocarbon caused by the internal electron transfer from water trimer anion.  

PubMed

Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF(2)Cl(2) molecule and a water trimer anion e(-)(H(2)O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H(2)O)(3)-CF(2)Cl(2), was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF(2)Cl(2) as a function of time. Immediately, the Cl(-) ion was dissociated from CF(2)Cl(2)(-) adsorbed on the water cluster. The reaction was schematically expressed by e(-)(H(2)O)(3)-CF(2)Cl(2)-->[(H(2)O)(3)-->-CF(2)CL(2)](-) --> (H(2O)(3) + CF(2)CL + CI(-) (I) where [(H(2)O)(3)-CF(2)Cl(2)](-) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF(2)Cl(2). The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF(2)Cl(2) and CF(2)Cl(2)-(H(2)O)(3), i.e. e(-) + CF(2)Cl(2), and e(-) + CF(2)Cl(2)-(H(2)O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310]. PMID:18404226

Tachikawa, Hiroto

2008-03-03

332

Low Temperature Electronic Transport through Macromolecules and Characteristics of Intramolecular Electron Transfer Processes  

NASA Astrophysics Data System (ADS)

A theory of electronic transport through molecular wires is applied to analyze characteristics of a long-range electron transfer (ET) through molecular bridges in macromolecules with complex donor/acceptor subsystems. Assuming a coherent electron tunneling through the bridge to be the predominant mechanism of ET at low temperatures it is shown that low temperature current-voltage curves can exhibit a step-like structure, which contains information concerning intrinsic features of ET processes such as the effect of donor/acceptor coupling to the bridge and primary pathways of electrons tunneling through the bridge. By contacting the proposed theoretical analysis with such experimental data a variety of valuable characteristics of long-range intramolecular ET can be identified.

Zimbovskiy, Gregoriy; Zimbovskaya, Natalya

2003-03-01

333

Double electron transfer in slow, highly charged ion-molecule collisions  

Microsoft Academic Search

During collisions between slow highly charged ions and neutral atoms or molecules, a lot of electrons can be transferred into multiply excited levels of the highly charged ions, and finally the product ions are stabilized by ejection of electrons (autoionization decay) or photons (radiative decay). The ratios of the radiative decay to the autoionization decay after double-electron transfer processes in

F. Krok; H. Tawara; I. Yu Tolstikhina; H. A. Sakaue; I. Yamada; K. Hosaka; M. Kimura; A. Matsumoto; N. Nakamura; S. Ohtani; M. Sakurai; H. Watanabe; M. Yoshino

1997-01-01

334

Quantum mechanical methods for calculating proton tunneling splittings and proton-coupled electron transfer vibronic couplings  

Microsoft Academic Search

Development of quantum mechanical methods for the calculation of proton tunneling splittings and proton-coupled electron transfer vibronic couplings is presented in this thesis. The fundamental physical principles underlying proton transfer in the electronically adiabatic and nonadiabatic limits are illustrated by applying the quantum mechanical methods we developed to chemical systems exemplary of the electronically adiabatic and nonadiabatic proton-tunneling regimes. Overall,

Jonathan H. Skone

2008-01-01

335

27 CFR 19.240 - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2013 CFR

... false Payment of tax by electronic fund transfer. 19.240...240 Payment of tax by electronic fund transfer. (a) General...payments by cash, check, or money order. Instead...entitled âPayment of Tax by Electronic Fund Transferâ. This...

2013-04-01

336

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

National Technical Information Service (NTIS)

This report discusses the following topics: the recovery of intermolecular transfer parameters from fluorescence quenching in liquids; photoinduced intramolecular electron transfer in flexible donor/space/acceptor systems containing an extended unsaturate...

B. Stevens

1997-01-01

337

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

NASA Astrophysics Data System (ADS)

Intramolecular electron transfer in chiral dyads has been investigated by spin chemistry methods. It is observed intramolecular photoelectron transfer in the dyads. The study of spin effects shows the exciplex formation during excited state quenching of the dyad.

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

2011-11-01

338

Hindered intramolecular electron transfer in room-temperature ionic liquid.  

PubMed

Three perylene tetracarboxylic diimide (PDI) compounds, namely, N,N'- di(2-N'',N''-dimethylamino)ethylperylene-3,4:9,10-tetracarboxylic diimide (1), N,N'-di(2-N'',N''-dimethylamino)propylperylene-3,4:9,10-tetracarboxylic diimide (2), and N,N'- dicyclohexyl-1,7-pyrrolidinylperylene-3,4:9,10-tetracarboxylic diimide (3), have been designed and prepared. Their photophysical properties in room-temperature ionic liquid (RTILs) were studied by steady-state absorption and emission spectra and fluorescence lifetime measurements. The intramolecular photoinduced electron transfer from dimethylamine to PDI in 1 and 2 has been efficiently hindered because of the solvation of RTILs. A two-conformation mechanism for the PET in 1 and 2 is proposed, which explains the results of the fluorescence lifetime measurements well. The solvation of RTILs to 3 resembled that of a normal polar organic solvent with polarity larger than that of DMF. PMID:20377182

Wu, Haixia; Wang, Haixia; Xue, Lin; Shi, Yan; Li, Xiyou

2010-04-08

339

Structures of Protein-Protein Complexes involved in electron transfer  

PubMed Central

Electron transfer (ET) reactions are essential for life since they underpin oxidative phosphorylation and photosynthesis, processes leading to the generation of ATP, and are involved in many reactions of intermediary metabolism1. Key to these roles is the formation of transient inter-protein ET complexes. The structural basis for the control of specificity between partner proteins is lacking since these weak transient complexes have remained largely intractable for crystallographic studies2,3. Inter-protein ET processes are central to all of the key steps of denitrification, an alternative form of respiration in which bacteria reduce nitrate or nitrite to N2 via the gaseous intermediates nitric oxide (NO) and nitrous oxide (N2O) when oxygen concentrations are limiting. The one electron reduction of nitrite to NO, a precursor to N2O, is performed by either a heme- or copper-containing nitrite reductase (CuNiR) where they receive an electron from redox partner proteins a cupredoxin or a c-type cytochrome4,5. Here we report the structures of the newly characterized three-domain hemec-Cu nitrite reductase from Ralstonia pickettii (RpNiR) at 1.01Å resolution and its M92A and P93A mutains. Very high resolution provides the first view of the atomic detail of the interface between the core trimeric cupredoxin structure of CuNiR and the tethered cytochrome c domain that allows the enzyme to function as an effective self-electron transfer system i.e. where the donor and acceptor proteins are fused together by genomic acquisition for functional advantage. Comparison of RpNiR with the binary complex of a CuNiR with a donor protein, AxNiR-cytc5516, and mutagenesis studies provide direct evidence for the importance of a hydrogen bonded water at the interface in ET. The structure also provides an explanation for the preferential binding of nitrite to the reduced copper ion at the active site in RpNiR, in contrast to other CuNiRs where reductive inactivation occurs, preventing substrate binding.

Antonyuk, Svetlana V.; Cong, Han; Eady, Robert R.; Hasnain, S. Samar

2013-01-01

340

Electron transfer in systems of well-defined geometry  

SciTech Connect

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.

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

1980-01-01

341

Application of X\\/sub. cap alpha. \\/-scattered-wave method to the analysis of electronic structure of catalysts for hydrogenation processes and selective hydrogenation of unsaturated compounds. II. Modeling of electronic structure of palladized alumina catalyst  

Microsoft Academic Search

The SCF-X\\/sub ..cap alpha..\\/-SW method has been used within the framework of the cluster model to calculate the electronic structure of Pd\\/AlâOâ. The structure of the energy levels of the system and their partial composition are consistent with the x-ray photoelectron spectrum of the catalyst. It has been shown that the interaction of the metal with the support is manifested

S. G. Gagarin; A. L. Gubskii; A. P. Kovtun; A. A. Kirchko; V. P. Sachenko

1983-01-01

342

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

SciTech Connect

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.

Chakraborty, Anjan; Seth, Debabrata; Setua, Palash; Sarkar, Nilmoni [Department of Chemistry, Indian Institute of Technology, Kharagpur 721 302, West Bengal (India)

2008-05-28

343

Limited reversibility of transmembrane proton transfer assisting transmembrane electron transfer in a dihaem-containing succinate:quinone oxidoreductase  

Microsoft Academic Search

Membrane protein complexes can support both the generation and utilisation of a transmembrane electrochemical proton potential (?p), either by supporting transmembrane electron transfer coupled to protolytic reactions on opposite sides of the membrane or by supporting transmembrane proton transfer. The first mechanism has been unequivocally demonstrated to be operational for ?p-dependent catalysis of succinate oxidation by quinone in the case

M. Gregor Madej; Florian G. Müller; Julian Ploch; C. Roy D. Lancaster

2009-01-01

344

Kinetics of fluorescence quenching for electron transfer and for energy transfer: Molecular dynamics tests for spherical molecules  

Microsoft Academic Search

The Smoluchowski approach to description of fluorescence quenching is tested by comparing the theory with computer simulations for the case of spherical molecules. The distance dependent sink terms describing the electron transfer mechanism and the Forster model for the energy transfer are considered. It is shown that the agreement between the rate coefficient from the model and from simulations depends

Marek Litniewski; Jerzy Gorecki

2005-01-01

345

Surface activation of electrocatalysis at oxide electrodes. Concerted electron-proton transfer.  

PubMed

Dramatic rate enhancements are observed for the oxidation of phenols, including tyrosine, at indium-tin oxide electrodes modified by the addition of the electron-transfer relays [M(II)(bpy)(2)(4,4'-(HO)(2)P(O)CH(2))(2)bpy)](2+) (M = Ru, Os) with clear evidence for the importance of proton-coupled electron transfer and concerted electron-proton transfer. PMID:21302912

Gagliardi, Christopher J; Jurss, Jonah W; Thorp, H Holden; Meyer, Thomas J

2011-02-08

346

Photoinduced electron transfer reaction of mono-(6-deoxy-p-nitrobenzylamino)-?-cyclodextrin with naphthalene derivatives  

Microsoft Academic Search

The fluorescence of a number of naphthalene derivatives was quenched by 6-deoxy-p-nitrobenzylamino-ß-cyclodextrin (NACD) in aqueous solution. The origin of the quenching was attributed to the electron transfer from the excited naphthalene groups to the ground state p-nitrobenzyl group of NACD. Both steady-state and time-resolved fluorescence measurements revealed that there were two routes of electron transfer, i.e. (1) electron transfer between

Yong-Hui Wang; Yao Fu; Hai-Ming Zhang; Jian-Ping Ye; Qing-Xiang Guo

2003-01-01

347

Electronic structure and proton transfer in ground-state hexafluoroacetylacetone.  

PubMed

The ground electronic state (X(1)A(1)) of hexafluoroacetylacetone (HFAA) has been subjected to synergistic experimental and theoretical investigations designed to resolve controversies surrounding the nature of intramolecular hydrogen bonding for the enol tautomer. Cryogenic (93K) X-ray diffraction studies were conducted on single HFAA crystals grown in situ by means of the zone-melting technique, with the resulting electron density maps affording clear evidence for distinguishable O(1)-H and H...O(2) bonds that span an interoxygen distance of 2.680 +/- 0.003 A. Such laboratory findings have been corroborated by a variety of quantum chemical methods including Hartree-Fock (HF), density functional [DFT (B3LYP)], Møller-Plesset perturbation (MPn), and coupled cluster [CCSD, CCSD(T)] treatments built upon extensive sets of correlation-consistent basis functions. Geometry optimizations performed at the CCSD(T)/aug-cc-pVDZ level of theory predict an asymmetric (C(s)) equilibrium configuration characterized by an O...O donor-acceptor separation of 2.628 A. Similar analyses of the transition state for proton transfer reveal a symmetric (C(2v)) structure that presents a potential barrier of 21.29 kJ/mol (1779.7 cm(-1)) height. The emerging computational description of HFAA is in reasonable accord with crystallographic measurements and suggests a weakening of hydrogen-bond strength relative to that of the analogous acetylacetone molecule. PMID:20507165

Chatterjee, Chandrima; Incarvito, Christopher D; Burns, Lori A; Vaccaro, Patrick H

2010-06-24

348

Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory  

NASA Astrophysics Data System (ADS)

Photoinduced intermolecular electron transfer between Rhodamine 3B and N,N-dimethylaniline has been studied in a series of seven liquids: acetonitrile, ethanol, propylene glycol, and mixtures of ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol. In each liquid, the donor and acceptors have different diffusion constants and experience distinct dielectric properties. Ps time-dependent fluorescence measurements and steady-state fluorescence yield measurements were made and analyzed using a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants, diffusion constants, and redox potentials, leaving the electronic coupling unknown. Taking the distance-dependence of the coupling to be ?=1 Å-1, data were fit to a single parameter, the coupling matrix element at contact, J0. The theory is able to reproduce both the functional form of the time-dependence and the concentration-dependence of the data in all seven liquids by fitting only J0. Despite the substantial differences in the properties of the experimental systems studied, fits to the data are very good and the values for J0 are very similar for all solvents.

Tavernier, H. L.; Kalashnikov, M. M.; Fayer, M. D.

2000-12-01

349

Electronic materials high- Tc superconductivity polymers and composites structural materials surface science and catalysts industry participation  

SciTech Connect

The fifth year of the Center for Advanced Materials was marked primarily by the significant scientific accomplishments of the research programs. The Electronics Materials program continued its work on the growth and characterization of gallium arsenide crystals, and the development of theories to understand the nature and distribution of defects in the crystals. The High-{Tc} Superconductivity Program continued to make significant contributions to the field in theoretical and experimental work on both bulk materials and thin films and devices. The Ceramic Processing group developed a new technique for cladding YBCO superconductors for high current applications in work with the Electric Power Research Institute. The Polymers and Composites program published a number of important studies involving atomistic simulations of polymer surfaces with excellent correlations to experimental results. The new Enzymatic Synthesis of Materials project produced its first fluorinated polymers and successfully began engineering enzymes designed for materials synthesis. The Structural Materials Program continued work on novel alloys, development of processing methods for advanced ceramics, and characterization of mechanical properties of these materials, including the newly-documented characterization of cyclic fatigue-crack propagation behavior in toughened ceramics. Finally, the Surface Science and Catalysis program made significant contributions to the understanding of microporous catalysts and the nature of surface structures and interface compounds.

Not Available

1988-01-01

350

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

Federal Register 2010, 2011, 2012, 2013

...TREASURY Fiscal Service Financial Management Service; Proposed Collection of Information: Electronic Funds Transfer...written comments to Financial Management Service, Records and Information Management Branch, Room 135, 3700...

2012-11-28

351

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation  

SciTech Connect

Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

Wasielewski, M.R.; Wiederrecht, G.P.; Svec, W.A.

1993-05-01

352

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation  

SciTech Connect

Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

Wasielewski, M.R.; Wiederrecht, G.P.; Svec, W.A.

1993-01-01

353

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation  

NASA Astrophysics Data System (ADS)

Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

Wasielewski, M. R.; Wiederrecht, G. P.; Svec, W. A.

354

Application of the photoinduced electron transfer model to the hydrated electron spectrum  

SciTech Connect

A reinvestigation of the photoinduced electron transfer model for the hydrated electron is presented. This entails a number of modifications. A class of polarization-based models for the localized electron is employed which allows a consistent treatment of both wave function and medium reorganization energy. The dipole-velocity transition operator is adopted to ensure the origin independence of the transition moment. Difficulties in the construction of a final state manifold are alleviated by a symmetric orthogonalization procedure. This entails the assumption of a lattice model, taken to be characteristic of the bulk solvent. For certain of the models, the optical absorption line shape, calculated as a sum over sites, is in reasonable accord with the experimentally observed half-width and asymmetry.

Hug, G.L.; Carmichael, I.

1982-08-19

355

Membrane catalyst layer for fuel cells  

DOEpatents

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 .mu.m in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm.sup.2. The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na.sup.+ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Wilson, Mahlon S. (Los Alamos, NM)

1993-01-01

356

Alkali Doping Heterogeneous Catalysts.  

National Technical Information Service (NTIS)

Alkali doping mechanisms were considered: catalytic action of the alkali; creation of basic centers; neutralization of acid centers; alteration of the electronic properties of the catalyst surface; remedies for catalyst preparation; influencing the physic...

W. D. Mross

1983-01-01

357

Studies on adhesion of polyethylene. Part I. Influence of functionality and phase transfer catalyst  

Microsoft Academic Search

Low-density polyethylene (LDPE) has been oxidized using phase transferred permanganate as an oxidant. The resulting surface modifications have been characterized by different methods and the consequent adhesion promotion has been characterized in terms of contact angle and peel strength measurements. From contact angle measurements using water and formamide liquid drops, reversible work of adhesion, and thence ? s and ?-

J. Konar; R. Ghosh

1989-01-01

358

Tuning photoinduced intramolecular electron transfer by electron accepting and donating substituents in oxazolones.  

PubMed

The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31?+?G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the ?-electron mobility, however, the 3,5-dinitro substituent decreased the ?-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the ?-conjugated linker and may find applications in photovoltaic cells and light emitting diodes. PMID:23494168

Oztürk, Gülsiye; Karab?y?k, Hasan; Aygün, Muhittin; Alp, Serap; Ozçelik, Serdar

2013-03-15

359

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

Code of Federal Regulations, 2010 CFR

...TOBACCO PRODUCTS AND CIGARETTE PAPERS AND TUBES...Payment of tax by electronic fund transfer...cigars, cigarettes, cigarette papers, and cigarette tubes combining...making payment by electronic fund...

2009-04-01

360

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

Code of Federal Regulations, 2010 CFR

...TOBACCO PRODUCTS, CIGARETTE PAPERS AND TUBES...Payment of tax by electronic fund transfer...cigars, cigarettes, cigarette papers, and cigarette tubes combining...making payment by electronic fund...

2010-04-01

361

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

Code of Federal Regulations, 2013 CFR

...TOBACCO PRODUCTS, CIGARETTE PAPERS AND TUBES...Payment of tax by electronic fund transfer...cigars, cigarettes, cigarette papers, and cigarette tubes combining...making payment by electronic fund...

2013-04-01

362

Method of and apparatus for the electron beam treatment of powders and aggregates in pneumatic transfer  

US Patent & Trademark Office Database

Powders and aggregates are treated in pneumatic transfer as a thin layer moving at high velocity which electrons from a selfshielded electron beam processor of voltage less than or equal to 500 kilovolts.

1998-09-01

363

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...

364

Electronically conducting proton exchange polymers as catalyst supports for proton exchange membrane fuel cells. Electrocatalysis of oxygen reduction, hydrogen oxidation, and methanol oxidation  

SciTech Connect

A variety of supported catalysts were prepared by the chemical deposition of Pt and Pt-Ru particles on chemically prepared poly(3,4-ethylenedioxythiophene)/poly(styrene-4-sulfonate) (PEDOT/PSS) and PEDOT/polyvinylsulfate (PVS) composites. The polymer particles were designed to provide a porous, proton-conducting and electron-conducting catalyst support for use in fuel cells. These polymer-supported catalysts were characterized by electron microscopy, impedance spectroscopy, cyclic voltammetry, and conductivity measurements. Their catalytic activities toward hydrogen and methanol oxidation and oxygen reduction were evaluated in proton exchange membrane fuel-cell-type gas diffusion electrodes. Activities for oxygen reduction comparable to that obtained with a commercial carbon-supported catalyst were observed, whereas those for hydrogen and methanol oxidation were significantly inferior, although still high for prototype catalysts.

Lefebvre, M.C.; Qi, Z.; Pickup, P.G. [Memorial Univ. of Newfoundland, St. John`s, Newfoundland (Canada). Dept. of Chemistry

1999-06-01

365

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

SciTech Connect

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).

Not Available

1990-02-14

366

Photoinduced electron transfer processes in dye-semiconductor systems with different spacer groups  

NASA Astrophysics Data System (ADS)

Photoinduced electron transfer processes in perylene-titanium dioxide dye-semiconductor systems are studied. In particular, the influence of saturated and unsaturated aliphatic spacer groups inserted between the chromophore and the semiconductor substrate is investigated. The study is based on a recently developed method that combines first-principles electronic structure calculations to characterize the dye-semiconductor systems and accurate multilayer multiconfiguration time-dependent Hartree simulations to reveal the underlying nonadiabatic dynamics. The results show that, in agreement with previous experimental studies, the spacer groups may affect the electron transfer dynamics significantly. Furthermore, the influence of electronic-vibrational coupling on the electron transfer dynamics and absorption spectra is discussed.

Li, Jingrui; Wang, Haobin; Persson, Petter; Thoss, Michael

2012-12-01

367

Sensitization of ultra-long-range excited-state electron transfer by energy transfer in a polymerized film.  

PubMed

Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state Ru(bpy)3(2+*) to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, Ru(bpy)3(2+*) to Acr-An triplet energy transfer occurs followed by long-range, Acr-(3)An-Acr-An ? Acr-An-Acr-(3)An, energy migration. With methyl viologen dication (MV(2+)) added as a trap, Acr-(3)An + MV(2+) ? Acr-An(+) + MV(+) electron transfer results in sensitized electron transfer quenching over a distance of approximately 90 Å. PMID:22949698

Ito, Akitaka; Stewart, David J; Fang, Zhen; Brennaman, M Kyle; Meyer, Thomas J

2012-09-04

368

Photoinduced electron transfer for an eosin-tyrosine conjugate. Activity of the tyrosinate anion in long-range electron transfer in a protein-like polymer matrix  

Microsoft Academic Search

The Xanthene dye eosin Y has been modified via a thiohydantoin link to the amine terminus of the amino acid L-tyrosine. Photochemical electron transfer involving the singlet state of the dye and the attached phenol-containing residue led to a reduction in eosin fluorescence quantum yield and lifetime for aqueous solutions at elevated pH. The conjugate provided an electron transfer product

Guilford Jones; Zhiming Feng; Churl Oh

1995-01-01

369

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

Microsoft Academic Search

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

Anjan Chakraborty; Debabrata Seth; Palash Setua; Nilmoni Sarkar

2008-01-01

370

Three-dimensional representations of photo-induced electron transfer rates in pyrene-(CH 2) n -N,N?-dimethylaniline systems obtained by three electron transfer theories  

Microsoft Academic Search

The observed rates of photo-induced electron transfer (ET) from N,N?-dimethylaniline (DMA) to the excited pyrene (Py) in confined systems of pyrene-(CH2)n-N,N?- dimethylaniline (PnD: n=1–3) were studied by molecular dynamic simulation (MD) and three kinds of electron transfer theories. ET parameters contained in Marcus theory (M theory), Bixon and Jortner theory (BJ theory) and Kakitani and Mataga theory (KM theory) were

Rong Rujkorakarn; Fumio Tanaka

2009-01-01

371

Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene  

NASA Astrophysics Data System (ADS)

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

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

2006-06-01

372

Quantum dynamics simulations of interfacial electron transfer in sensitized TiO2 semiconductors  

Microsoft Academic Search

A mixed quantum-classical method combining ab initio-DFT molecular dynamics simulations with electronic relaxation calculations is used to investigate interfacial electron transfer in catechol\\/TiO2-anatase nanostructures under vacuum conditions at finite temperature. The calculations demonstrate that the injection mechanism is accelerated by thermal nuclear motion. In particular, electron-phonon scattering leads to ultrafast adsorbate monolayer electron transfer and the disappearance of the anisotropic

Sabas G. Abuabara; Luis G. C. Rego; Victor S. Batista

2005-01-01

373

Microscale gradients and their role in electron-transfer mechanisms in biofilms.  

PubMed

The chemical and electrochemical gradients in biofilms play a critical role in electron-transfer processes between cells and a solid electron acceptor. Most of the time, electron-transfer processes have been investigated in the bulk phase, for a biofilm electrode or for an isolated component of a biofilm. Currently, the knowledge of chemical and electrochemical gradients in living biofilms respiring on a solid surface is limited. We believe the chemical and electrochemical gradients are critical for explaining electron-transfer mechanisms. The bulk conditions, an isolated part of a biofilm or a single cell cannot be used to explain electron-transfer mechanisms in biofilm systems. In addition, microscale gradients explain how the reactor configuration plays a critical role in electron-transfer processes. PMID:23176474

Beyenal, Haluk; Babauta, Jerome T

2012-12-01

374

Copper(I) catalyst for carbene and nitrene transfer to form cyclopropanes, cyclopropenes, and aziridines  

SciTech Connect

The copper(I) complex Tp[prime]Cu(C[sub 2]H[sub 4]) (1; Tp[prime] = hydrotris (3,5-dimethyl-1-pyrazolyl)borate) catalyzes reactions of ethyl diazoacetate with alkenes or alkynes to form cyclopropanes or cyclopropenes, respectively. Yields are moderate to high, and the reactions are performed under mild conditions. Complex 1 also catalyzes nitrene transfer from PhI=NTs to alkenes to produce aziridines in high yield. 20 refs., 3 tabs.

Perez, P.J.; Brookhart, M.; Templeton, J.L. (Univ. of North Carolina, Chapel Hill (United States))

1993-02-01

375

Intermolecular Electron-Transfer Reactions in Soluble Methane Monooxygenase: A Role for Hysteresis in Protein Function  

PubMed Central

Electron transfer from reduced nicotinamide adenine dinucleotide (NADH) to the hydroxylase component (MMOH) of soluble methane monooxygenase (sMMO) primes its non-heme diiron centers for reaction with dioxygen to generate high-valent iron intermediates that convert methane to methanol. This intermolecular electron-transfer step is facilitated by a reductase (MMOR), which contains [2Fe-2S] and flavin adenine dinucleotide (FAD) prosthetic groups. To investigate interprotein electron transfer, chemically reduced MMOR was mixed rapidly with oxidized MMOH in a stopped-flow apparatus, and optical changes associated with reductase oxidation were recorded. The reaction proceeds via four discrete kinetic phases corresponding to the transfer of four electrons into the two dinuclear iron sites of MMOH. Pre-equilibrating the hydroxylase with sMMO auxiliary proteins MMOB or MMOD severely diminishes electron-transfer throughput from MMOR, primarily by shifting the bulk of electron transfer to the slowest pathway. The biphasic reactions for electron transfer to MMOH from several MMOR ferredoxin analogues are also inhibited by MMOB and MMOD. These results, in conjunction with the previous finding that MMOB enhances electron-transfer rates from MMOR to MMOH when preformed MMOR-MMOH-MMOB complexes are allowed to react with NADH [Gassner, G. T.; Lippard, S. J. Biochemistry 1999, 38, 12768-12785], suggest that isomerization of the initial ternary complex is required for maximal electron-transfer rates. To account for the slow electron transfer observed for the ternary precomplex in this work, a model is proposed in which conformational changes imparted to the hydroxylase by MMOR are retained throughout the catalytic cycle. Several electron-transfer schemes are discussed with emphasis on those that invoke multiple interconverting MMOH populations.

Blazyk, Jessica L.; Gassner, George T.

2005-01-01

376

The electron transfer complex between nitrous oxide reductase and its electron donors.  

PubMed

Identifying redox partners and the interaction surfaces is crucial for fully understanding electron flow in a respiratory chain. In this study, we focused on the interaction of nitrous oxide reductase (N(2)OR), which catalyzes the final step in bacterial denitrification, with its physiological electron donor, either a c-type cytochrome or a type 1 copper protein. The comparison between the interaction of N(2)OR from three different microorganisms, Pseudomonas nautica, Paracoccus denitrificans, and Achromobacter cycloclastes, with their physiological electron donors was performed through the analysis of the primary sequence alignment, electrostatic surface, and molecular docking simulations, using the bimolecular complex generation with global evaluation and ranking algorithm. The docking results were analyzed taking into account the experimental data, since the interaction is suggested to have either a hydrophobic nature, in the case of P. nautica N(2)OR, or an electrostatic nature, in the case of P. denitrificans N(2)OR and A. cycloclastes N(2)OR. A set of well-conserved residues on the N(2)OR surface were identified as being part of the electron transfer pathway from the redox partner to N(2)OR (Ala495, Asp519, Val524, His566 and Leu568 numbered according to the P. nautica N(2)OR sequence). Moreover, we built a model for Wolinella succinogenes N(2)OR, an enzyme that has an additional c-type-heme-containing domain. The structures of the N(2)OR domain and the c-type-heme-containing domain were modeled and the full-length structure was obtained by molecular docking simulation of these two domains. The orientation of the c-type-heme-containing domain relative to the N(2)OR domain is similar to that found in the other electron transfer complexes. PMID:21739254

Dell'acqua, Simone; Moura, Isabel; Moura, José J G; Pauleta, Sofia R

2011-07-08

377

Excess electron transfer dynamics in DNA hairpins conjugated with N,N-dimethylaminopyrene as a photosensitizing electron donor.  

PubMed

Excess electron transfer dynamics in DNA hairpins was investigated by femtosecond laser flash photolysis of a donor-DNA-acceptor system using N,N-dimethylaminopyrene and diphenylacetylene as an electron donor and acceptor, respectively. It was revealed that the excess electron hopping rate between T's is faster than that of the hole. PMID:23037011

Park, Man Jae; Fujitsuka, Mamoru; Nishitera, Haruhiro; Kawai, Kiyohiko; Majima, Tetsuro

2012-11-18

378

Photo-induced charge transfer. A critical test of the mechanism and range of biological electron transfer processes.  

PubMed Central

The vibronic coupling theory of electron tunneling between biomolecules requires that all such tunnelings involve vibronic coupling, finds temperature dependence to tunneling at finite temperatures, and predicts relatively short tunneling distances. This theory might be expected to apply to most electron transfers involved in the membrane-bound electron transfer reactions of photosynthesis and oxidative phosphorylation. This paper calculates the properties of a weak charge-transfer optical absorption band, whose predicted characteristics are a direct and simple consequence of the model that describes vibronically coupled tunneling. The new absorption band provides the basis for a critical experimental test of the constructs and parameters of the tunneling theory. If the tunneling theory is valid, the oscillator strength of such bands will be the most reliable measure of the tunneling matrix element and of the distance between the sites exchanging an electron.

Hopfield, J J

1977-01-01

379

Synthetic control over photoinduced electron transfer in phosphorescence zinc sensors.  

PubMed

Despite the promising photofunctionalities, phosphorescent probes have been examined only to a limited extent, and the molecular features that provide convenient handles for controlling the phosphorescence response have yet to be identified. We synthesized a series of phosphorescence zinc sensors based on a cyclometalated heteroleptic Ir(III) complex. The sensor construct includes two anionic cyclometalating ligands and a neutral diimine ligand that tethers a di(2-picolyl)amine (DPA) zinc receptor. A series of cyclometalating ligands with a range of electron densities and band gap energies were used to create phosphorescence sensors. The sensor series was characterized by variable-temperature steady-state and transient photoluminescence spectroscopy studies, electrochemical measurements, and quantum chemical calculations based on time-dependent density functional theory. The studies demonstrated that the suppression of nonradiative photoinduced electron transfer (PeT) from DPA to the photoexcited Ir(IV) species provided the underlying mechanism that governed the phosphorescent response to zinc ions. Importantly, the Coulombic barrier, which was located on either the cyclometalating ligand or the diimine ligand, negligibly influenced the PeT process. Phosphorescence modulation by PeT strictly obeyed the Rehm-Weller principle, and the process occurred in the Marcus-normal region. These findings provide important guidelines for improving sensing performance; an efficient phosphorescence sensor should include a cyclometalating ligand with a wide band gap energy and a deep oxidation potential. Finally, the actions of the sensor were demonstrated by visualizing the intracellular zinc ion distribution in HeLa cells using a confocal laser scanning microscope and a photoluminescence lifetime imaging microscope. PMID:23458333

Woo, Hana; Cho, Somin; Han, Yejee; Chae, Weon-Sik; Ahn, Dae-Ro; You, Youngmin; Nam, Wonwoo

2013-03-13

380

Electron transfer reactions in condensed phase: effect of reversibility.  

PubMed

We propose a generalized one-dimensional kinetic equation for multidimensional reversible electron transfer (ET) reaction with a nonequilibrium situation as the initial condition. The rate constant for the forward reversible ET reaction obtained here consists of the rate for the corresponding irreversible ET reaction, and an extra term due to reversibility of the ET process which includes the rates of diffusion dynamics in the reactant and product wells. In order to understand the effect of reversibility, we consider back ET reaction in a system consisting of an electron donor-acceptor pair in a solvent modeled through low frequency solvent collective coordinates (multidimensional) characterized by the orientational polarization and slowly relaxing one-dimensional vibrational mode. We propose here a new generalized polarization energy functional corresponding to the extension of the continuum version for the same, which has opened up the possibility of inclusion of molecular nature of the solvent into the solvent reorganization energy. We then derive an exact expression for the ET rate for this model system. The numerical results calculated by using the proposed one-dimensional approach are shown to be in good agreement with the available experimental results. Non-Marcus free energy gap dependence of the rates observed here for the reversible and irreversible ET reactions are very close to each other in the barrierless region, while for other situations, the rate for the former process is found to be less than the latter. The extra term, which makes the difference between the rate constants for irreversible and reversible ET reactions, is found to be contributed by the diffusion dynamics from both reactant and product wells but the dominating contribution is provided mainly by the product well. PMID:22463277

Dhole, Kajal; Jena, Naresh K; Samanta, Alok; Ghosh, Swapan K

2012-02-07

381

Proton-coupled electron-transfer reduction of dioxygen catalyzed by a saddle-distorted cobalt phthalocyanine.  

PubMed

Proton-coupled electron-transfer reduction of dioxygen (O(2)) to afford hydrogen peroxide (H(2)O(2)) was investigated by using ferrocene derivatives as reductants and saddle-distorted (?-octaphenylphthalocyaninato)cobalt(II) (Co(II)(Ph(8)Pc)) as a catalyst under acidic conditions. The selective two-electron reduction of O(2) by dimethylferrocene (Me(2)Fc) and decamethylferrocene (Me(10)Fc) occurs to yield H(2)O(2) and the corresponding ferrocenium ions (Me(2)Fc(+) and Me(10)Fc(+), respectively). Mechanisms of the catalytic reduction of O(2) are discussed on the basis of detailed kinetics studies on the overall catalytic reactions as well as on each redox reaction in the catalytic cycle. The active species to react with O(2) in the catalytic reaction is switched from Co(II)(Ph(8)Pc) to protonated Co(I)(Ph(8)PcH), depending on the reducing ability of ferrocene derivatives employed. The protonation of Co(II)(Ph(8)Pc) inhibits the direct reduction of O(2); however, the proton-coupled electron transfer from Me(10)Fc to Co(II)(Ph(8)Pc) and the protonated [Co(II)(Ph(8)PcH)](+) occurs to produce Co(I)(Ph(8)PcH) and [Co(I)(Ph(8)PcH(2))](+), respectively, which react immediately with O(2). The rate-determining step is a proton-coupled electron-transfer reduction of O(2) by Co(II)(Ph(8)Pc) in the Co(II)(Ph(8)Pc)-catalyzed cycle with Me(2)Fc, whereas it is changed to the electron-transfer reduction of [Co(II)(Ph(8)PcH)](+) by Me(10)Fc in the Co(I)(Ph(8)PcH)-catalyzed cycle with Me(10)Fc. A single crystal of monoprotonated [Co(III)(Ph(8)Pc)](+), [Co(III)Cl(2)(Ph(8)PcH)], produced by the proton-coupled electron-transfer reduction of O(2) by Co(II)(Ph(8)Pc) with HCl, was obtained, and the crystal structure was determined in comparison with that of Co(II)(Ph(8)Pc). PMID:22299646

Honda, Tatsuhiko; Kojima, Takahiko; Fukuzumi, Shunichi

2012-02-21

382

77 FR 6310 - Electronic Fund Transfers (Regulation E)  

Federal Register 2010, 2011, 2012, 2013

...described above would create information overload for consumers. Subsequent...transfer that contains accurate information about the transfer. The Bureau...described above would create information overload for consumers. The...

2012-02-07

383

Intramolecular electron transfer across amino acid spacers in the picosecond time regime. Charge-transfer interaction through peptide bonds  

SciTech Connect

For a series of alanine-based peptides having 1--3 amino acid residues as spacers, the chromophore, pyrenesulfonyl (Pyr), has been attached at the N-terminus and an electron donor, dimethyl-1,4-benzenediamine (DMPD), covalently bound at the C-terminus. Evidence for an intramolecular charge-transfer interaction involving the electron donor and acceptor groups has been obtained from absorption spectra. Intramolecular electron transfer involving the end groups, Pyr (electron acceptor) and DMPD (electron donor) has been confirmed by ultrafast pump-probe methods. The radical-ion pair states that are generated on Ti/sapphire laser excitation at 400 nm decay in the picosecond to nanosecond time domain and generally show multiexponential decay kinetics. These rates of charge recombination are among the fastest yet observed involving electron transfer between terminal groups for peptide oligomers. The falloff of rate constants for ion pair recombination is irregular in terms of the through-bond distance that separates Pyr and DMPD groups for the various peptide links; i.e., back electron transfer remains fast for the tripeptide, Pyr-Ala-Ala-Ala-DMPD, despite an average through-bond distance between photoactive groups that reaches 18 {angstrom}. Molecular modeling studies show that the peptides are free to adopt conformations in essentially random fashion, without showing evidence for long range ordering of the peptide chain.

Jones, G. II; Lu, L.N.; Fu, H.; Farahat, C.W.; Oh, C. [Boston Univ., MA (United States); Greenfield, S.R.; Gosztola, D.J. [Argonne National Lab., IL (United States). Chemistry Div.; Wasielewski, M.R. [Argonne National Lab., IL (United States). Chemistry Div.]|[Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry

1999-01-21

384

Simulations of fluorescence quenching using theoretical models of energy and electron transfer in random arrays  

Microsoft Academic Search

A master equation is solved numerically for investigating energy transfer and trapping in two-dimensional disordered systems of chlorophylls and quinones. Quenching of the excitation occurs both by electron transfer from a chlorophyll to a neighbouring quinone and by energy transfer to self-quenching traps consisting of statistical pairs of chlorophyll molecules closer than a critical distance. The quinone concentration dependence of

Laurent G. Boulu; John J. Kozak

1988-01-01

385

Effects of quantum coherence in metalloprotein electron transfer.  

PubMed

Many intramolecular electron transfer (ET) reactions in biology are mediated by metal centers in proteins. This process is commonly described by a model of diffusive hopping according to the semiclassical theories of Marcus and Hopfield. However, recent studies have raised the possibility that nontrivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we investigate the potential effects of quantum coherence in biological ET by extending the semiclassical model to allow for the possibility of quantum coherent phenomena using a quantum master equation based on the Holstein Hamiltonian. We test the model on the structurally defined chain of seven iron-sulfur clusters in nicotinamide adenine dinucleotide plus hydrogen:ubiquinone oxidoreductase (complex I), a crucial respiratory enzyme and one of the longest chains of metal centers in biology. Using experimental parameters where possible, we find that, in limited circumstances, a small quantum mechanical contribution can provide a marked increase in the ET rate above the semiclassical diffusive-hopping rate. Under typical biological conditions, our model reduces to well-known diffusive behavior. PMID:23030959

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

2012-09-26

386

Statistical analysis of electron transfer dissociation pairwise fragmentation patterns.  

PubMed

Electron transfer dissociation (ETD) is an alternative peptide dissociation method developed in recent years. Compared with the traditional collision induced dissociation (CID) b and y ion formation, ETD generates c and z ions and the backbone cleavage is believed to be less selective. We have reported previously the application of a statistical data mining strategy, K-means clustering, to discover fragmentation patterns for CID, and here we report application of this approach to ETD spectra. We use ETD data sets from digestions with three different proteases. Data analysis shows that selective cleavages do exist for ETD, with the fragmentation patterns affected by protease, charge states, and amino acid residue compositions. It is also noticed that the c(n-1) ion, corresponding to loss of the C-terminal amino acid residue, is statistically strong regardless of the residue at the C-terminus of the peptide, which suggests that the peptide gas phase conformation plays an important role in the dissociation pathways. These patterns provide a basis for mechanism elucidation, spectral prediction, and improvement of ETD peptide identification algorithms. PMID:22022956

Li, Wenzhou; Song, Chi; Bailey, Derek J; Tseng, George C; Coon, Joshua J; Wysocki, Vicki H

2011-11-28

387

Effects of quantum coherence in metalloprotein electron transfer  

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

388

Electron transfer catalysis with monolayer protected Au?? clusters.  

PubMed

Au??L?? (L = S(CH?)?Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au??L??? quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au??L??? 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 Au??L??/Au??L??? and the Au??L???/Au??L?? redox couples as redox mediators. Simulation of the CV curves led to determination of the ET rate constant (k(ET)) values for concerted dissociative ET to the peroxides. The ET free energy ?G° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log k(ET)vs.?G°) relationship. Comparison with the k(ET) obtained using a ferrocene-type donor with a formal potential similar to that of Au??L??/Au??L??? showed that the presence of the capping monolayer affects the ET rate rather significantly, which is attributed to the intrinsic nonadiabaticity of peroxide acceptors. PMID:22772766

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

2012-07-09

389

Statistical Analysis of Electron Transfer Dissociation Pairwise Fragmentation Patterns  

PubMed Central

Electron transfer dissociation (ETD) is an alternative peptide dissociation method developed in recent years. Compared with the traditional collision induced dissociation (CID) b and y ion formation, ETD generates c and z ions and the backbone cleavage is believed to be less selective. We have reported previously the application of a statistical data mining strategy, K-means clustering, to discover fragmentation patterns for CID, and here we report application of this approach to ETD spectra. We use ETD data sets from digestions with three different proteases. Data analysis shows that selective cleavages do exist for ETD, with the fragmentation patterns affected by protease, charge states, and amino acid residue compositions. It is also noticed that the cn-1 ion, corresponding to loss of the C-terminal amino acid residue, is statistically strong regardless of the residue at the C-terminus of the peptide, which suggest that peptide gas phase conformation plays important roles in the dissociation pathways. These patterns provide a basis for mechanism elucidation, spectral prediction, and improvement of ETD peptide identification algorithms.

Li, Wenzhou; Song, Chi; Bailey, Derek J.; Tseng, George C.; Coon, Joshua J.; Wysocki, Vicki H.

2012-01-01

390

Theoretical study of photoinduced electron transfer from tetramethylethylene to tetracyanoethylene  

NASA Astrophysics Data System (ADS)

Using ab initio and density functional calculations, we studied photoexcitation of a charge-balanced electron donor-acceptor (DA) complex comprised of tetracyanoethylene (TCE) and tetramethylethylene (TME). We considered both the TCE-TME stacked conformer and a possible conformer with a solvent molecule (dichloromethane) inserted between TCE and TME. The photoexcitation of the DA complex can directly form a charge transfer (CT) state. Our theoretical investigations show that the CT state can also be produced from the decay of higher excited states. Using the continuum model, we investigated the solvent effects on CT absorption, local excitation, and CT emission in the polar solvent. The equilibrium solvation energies of the ground and excited states of the DA complex were calculated using the self-consistent reaction field method, and then the correction of nonequilibrium solvation energies for the vertical transitions was made. The transition energies (i.e., CT absorption for the DA complexes and CT emission for the contact ion pair complexes) in the polar solvent show redshifts relative to those in the gas phase.

Yi, Hai-Bo; Duan, Xiao-Hui; Lee, Jin Yong; Lee, Han Myoung; Li, Xiang-Yuan; Kim, Kwang S.

2003-11-01

391

Calculation of Electron Transfer Reorganization Energies Using the Finite Difference Poisson-Boltzmann Model  

Microsoft Academic Search

A description is given of a method to calculate the electron transfer reorganization energy (?) in proteins using the linear or nonlinear Poisson-Boltzmann (PB) equation. Finite difference solutions to the linear PB equation are then used to calculate ? for intramolecular electron transfer reactions in the photosynthetic reaction center from Rhodopseudomonas viridis and the ruthenated heme proteins cytochrome c, myoglobin,

Kim A. Sharp

1998-01-01

392

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

Code of Federal Regulations, 2013 CFR

...no later than the close of business on the last day for making...financial institution to effect an electronic fund transfer message as...on or before the close of business on the prescribed last day...entitled Payment of Tax by Electronic Fund Transfer. This...

2013-04-01

393

Thermochemistry of Proton-Coupled Electron Transfer Reagents and its Implications  

Microsoft Academic Search

Many, if not most, redox reactions are coupled to proton transfers. This includes most common sources of chemical potential energy, from the bioenergetic processes that power cells to the fossil fuel combustion that powers cars. These proton-coupled electron transfer or PCET processes may involve multiple electrons and multiple protons, as in the 4 e, 4 H+ reduction of dioxygen (O2)

Jeffrey J. Warren; Tristan A. Tronic; James M. Mayer

2010-01-01

394

Coherent phonons in CdSe quantum dots triggered by ultrafast electron transfer  

NASA Astrophysics Data System (ADS)

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

Dworak, L.; Braun, M.; Wachtveitl, J.

2013-03-01

395

Multiple electron transfer in slow collisions of highly charged ions and atoms  

NASA Astrophysics Data System (ADS)

Multi-electron transfer processes in slow collisions Arq++Ar (/q=5,...,10) have been studied theoretically by means of a molecular dynamics approach. We discuss the electron transfer dynamics, in particular with respect to the assumptions made in overbarrier models. Furthermore, absolute cross-sections are defined and compared to experimental data.

Zarour, Bilel; Saalmann, Ulf

2003-05-01

396

Multiple electron transfer in slow collisions of highly charged ions and atoms  

Microsoft Academic Search

Multi-electron transfer processes in slow collisions Arq++Ar (q=5,…,10) have been studied theoretically by means of a molecular dynamics approach. We discuss the electron transfer dynamics, in particular with respect to the assumptions made in overbarrier models. Furthermore, absolute cross-sections are defined and compared to experimental data.

Bilel Zarour; Ulf Saalmann

2003-01-01

397

Analog CMOS charge model for molecular redox electron-transfer reactions and bio-chemical pathways  

Microsoft Academic Search

Oxidation and reduction (Redox) reactions are known to constitute an electron transfer chain in many biochemical pathways in living organisms (systems). Mathematical modeling of these bio-chemical pathways is of growing focus in the emerging area of systems biology. In this brief paper an effort is made to develop a CMOS integrated circuit model for the electron transfer chain in the

S. M. Rezaul Hasan; Nazmul Ula

2008-01-01

398

Demonstrating Electron Transfer and Nanotechnology: A Natural Dye-Sensitized Nanocrystalline Energy Converter  

Microsoft Academic Search

A unique solar cell fabrication procedure has been developed using natural anthocyanin dyes extracted from berries. It can be reproduced with a minimum amount of resources in order to provide an interdisciplinary approach for lower-division undergraduate students learning the basic principles of biological extraction, physical chemistry, and spectroscopy as well as environmental science and electron transfer. Electron transfer is the

Greg P. Smestad; Michael Gratzel

1998-01-01

399

Facile Fabrication of Biocompatible and Tunable Multifunctional Nanomaterials via Iron-Mediated Atom Transfer Radical Polymerization with Activators Generated by Electron Transfer.  

PubMed

A novel strategy of preparing multifunctional nanoparticles (NPs) with near infra red (NIR) fluorescence and magnetism showing good hydrophilicity and low toxicity was developed via surface-initiated atom transfer radical polymerization with activators generated by electron transfer (AGET ATRP) of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA) and glycidyl methacrylate (GMA) employing biocompatible iron as the catalyst on the surface of silica coated iron oxide (Fe3O4@SiO2) NPs. The small molecules (CS2), a NIR fluorescent chromophore, can be fixed into the covalently grafted polymer shell of the NPs by chemical reaction through a covalent bond to obtain stable CS2 dotted NPs Fe3O4@SiO2@PPEGMA-co-PGMA@CS2. The fluorescence intensity of the as-prepared NPs could be conveniently regulated by altering the silica shell thickness (varying the feed of silica source TEOS), CS2 feed, or the feed ratio of VPEGMA/VGMA, which are easily realized in the preparation process. Thorough investigation of the properties of the final NPs including in vivo dual modal imaging indicate that such NPs are one of the competitive candidates as imaging agents proving a promising potential in the biomedical area. PMID:24079826

He, Weiwei; Cheng, Liang; Zhang, Lifen; Liu, Zhuang; Cheng, Zhenping; Zhu, Xiulin

2013-09-30

400

Effect of ultrafast electron transfer on photon echo signal: Decoherence process in electron-donating solvents  

NASA Astrophysics Data System (ADS)

The effect of ultrafast electron transfer (ET) on the coherent state was investigated by means of three pulse photon echo for an azaporphyrin (AzP) derivative, 2,7,12,17-Tetra- tert-butyl-5,10,15,20-tetraaza-21 H,23 H-porphine, in electron-donating solvents. The peak shift and fwhm of the echo signal substantially decreased in the reactive solvents, indicating that the ultrafast ET affected the coherent state of the chromophore significantly. By integrating the present results in reactive and inert solvents with those previously performed for other systems, the role of the rapid reaction in the decoherence process was discussed from the viewpoints of the strength of the solute-solvent coupling.

Nagasawa, Yutaka; Mukai, Ryusuke; Mori, Kazuya; Muramatsu, Masayasu; Miyasaka, Hiroshi

2009-11-01

401

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

SciTech Connect

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

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

1993-06-05

402

Marked detergents effects on safranine T-mediated photo-induced electron transfer in cytochrome P-450 1A2  

Microsoft Academic Search

Cytochrome P-450 accepts electrons from electron transfer proteins to facilitate monooxidation reactions. It is suggested that basic amino acids such as Lys and Arg on the P-450 molecular surface interact with acidic amino acids such as Gin and Asp of the electron transfer protein. Safranine T is a basic compound which mediates electron transfer with illumination. It was found with

Ryosuke Nakano; Hideo Konami; Hideaki Sato; Osamu Ito; Toru Shimizu

1995-01-01

403

The structure and function of the cytochrome c 2 : reaction center electron transfer complex from Rhodobacter sphaeroides  

Microsoft Academic Search

In the photosynthetic bacterium, Rhodobacter sphaeroides, the mobile electron carrier, cytochrome c2 (cyt c2) transfers an electron from reduced heme to the photooxidized bacteriochlorophyll dimer in the membrane bound reaction center (RC) as part of the light induced cyclic electron transfer chain. A complex between these two proteins that is active in electron transfer has been crystallized and its structure

Herbert L. Axelrod; Melvin Y. Okamura

2005-01-01

404

Probing the ultrafast electron transfer at the CuPc/Au(111) interface  

SciTech Connect

Core-hole clock spectroscopy and near-edge x-ray-absorption fine structure measurements have been used to investigate the ultrafast electron transfer dynamics at the Copper(II) phthalocyanine (CuPc)/Au(111) interface. It was found that the strong electronic coupling between the first layer of CuPc molecules and Au(111) substrate favors ultrafast electron transfer from the lowest unoccupied molecular orbital of the CuPc molecules to the conduction band of Au(111) in the time scale of {approx}6 fs. In contrast, the intermolecular electron transfer within multilayers of CuPc molecules via the weak van der Waals interaction was much slower.

Chen Wei; Wang Li; Qi Dongchen; Chen Shi; Gao Xingyu; Wee, Andrew Thye Shen [Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore)

2006-05-01

405

The general treatment of superexchange versus sequential electron transfer in a three-component system  

SciTech Connect

The mechanisms of superexchange vs sequential electron transfer in a three-component system involving reactant, intermediate, and product are investigated by using the Zusman equation. This approach is nonperturbative with regard to the electronic coupling and thus, in principle, the contributions from all higher order terms are included. This treatment allows examination of a wide range of conditions from nondegenerate to degenerate cases, as well as from nonadiabatic to adiabatic cases for electron transfer processes involving three Marcus parabolas such as believed to occur in photosynthetic reaction centers. New effects of superexchange on electron-transfer rate resulting from degenerate energy-level crossings are predicted.

Tang, J. (Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)); Wang, Z. (Department of Chemistry, The University of Chicago, Chicago, Illinois 60637 (United States)); Norris, J.R. (Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States) Department of Chemistry, The University of Chicago, Chicago, Illinois 60637 (United States))

1993-07-15

406

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

NASA Astrophysics Data System (ADS)

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

Winter, Bernd

2009-03-01

407

Photoinduced bimolecular electron transfer kinetics in small unilamellar vesicles  

SciTech Connect

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 observed in the correlation of the fluorescence quenching rate constants k{sub q} with the free energy change, {delta}G{sup 0} of the reactions. However, the coumarin dyes, C152 and C481 (cf. Scheme 1), show unusually high k{sub q} values and high activation barriers, which is not expected from Marcus ET theory. This unusual behavior is explained on the basis of participation of the twisted intramolecular charge transfer states of these two dyes in the ET kinetics.

Choudhury, Sharmistha Dutta; Kumbhakar, Manoj; Nath, Sukhendu; Pal, Haridas [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085 (India)

2007-11-21

408

Development of durable high-temperature catalysts for natural gas combustion. Analysis of heterogeneous reactions, heat transfer, and thermal stresses in combustion catalyst monoliths. Topical report No. 4, July 1, 1991-February 28, 1994  

SciTech Connect

The topical report describes the development of a numerical model for predicting the transient performance and thermal stresses in combustion catalyst monoliths. The authors simulated the temperature and thermal stress distributions in a monolith during combustion of premixed methane and air at 10-atm. These simulations show that the high heat transfer coefficient at the entrance of a honeycomb channel leads to very high thermal stress during abrupt fuel cut-off and, surprisingly, during some catalyst 'light-off' conditions. Thermal conductivity along the substrate wall moderates the impact of transient cooling on therml stresses near the entrance. Very high temperatures are required before creep rates (in mullite) provide relief of residual stresses under long-term steady-state operation.

Boehman, A.L.; Simons, J.W.; McCarty, J.G.

1994-02-01

409

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

SciTech Connect

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.

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

410

Biomimetic Catalysis: Hydroxylation of C2 , C3 , and CycloC6 Hydrocarbons by Managanese Porphyrin and Non-Porphyrin Catalysts in the Presence of Monooxygen Transfer Reagents.  

National Technical Information Service (NTIS)

Metal complexes that mimic the active site of monooxygenase enzymes and convert carbon-hydrogen bonds to carbon-hydroxyl in the presence of a monooxygen transfer reagent are called biomimetic catalysts. Studies concerning the activation of methane, ethane...

R. H. Fish R. H. Fong R. T. Price J. B. Vincent G. Christou

1988-01-01

411

Electron transfer catalysis with monolayer protected Au25 clusters  

NASA Astrophysics Data System (ADS)

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 ?G° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log kETvs. ?G°) 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 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 ?G° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log kETvs. ?G°) 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. This article was submitted as part of a Themed Issue on metallic clusters. Other papers on this topic can be found in issue 14 of vol. 4 (2012). This issue can be found from the Nanoscale homepage [http://www.rsc.org/nanoscale].

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

2012-08-01

412

Electron transfer and protein dynamics in the photosynthetic reaction center.  

PubMed Central

We have measured the kinetics of electron transfer (ET) from the primary quinone (Q(A)) to the special pair (P) of the reaction center (RC) complex from Rhodobacter sphaeroides as a function of temperature (5-300 K), illumination protocol (cooled in the dark and under illumination from 110, 160, 180, and 280 K), and warming rate (1.3 and 13 mK/s). The nonexponential kinetics are interpreted with a quantum-mechanical ET model (Fermi's golden rule and the spin-boson model), in which heterogeneity of the protein ensemble, relaxations, and fluctuations are cast into a single coordinate that relaxes monotonically and is sensitive to all types of relaxations caused by ET. Our analysis shows that the structural changes that occur in response to ET decrease the free energy gap between donor and acceptor states by 120 meV and decrease the electronic coupling between donor and acceptor states from 2.7 x 10(-4) cm(-1) to 1.8 x 10(-4) cm(-1). At cryogenic temperatures, conformational changes can be slowed or completely arrested, allowing us to monitor relaxations on the annealing time scale (approximately 10(3)-10(4) s) as well as the time scale of ET (approximately 100 ms). The relaxations occur within four broad tiers of conformational substates with average apparent Arrhenius activation enthalpies of 17, 50, 78, and 110 kJ/mol and preexponential factors of 10(13), 10(15), 10(21), and 10(25) s(-1), respectively. The parameterization provides a prediction of the time course of relaxations at all temperatures. At 300 K, relaxations are expected to occur from 1 ps to 1 ms, whereas at lower temperatures, even broader distributions of relaxation times are expected. The weak dependence of the ET rate on both temperature and protein conformation, together with the possibility of modeling heterogeneity and dynamics with a single conformational coordinate, make RC a useful model system for probing the dynamics of conformational changes in proteins.

McMahon, B H; Muller, J D; Wraight, C A; Nienhaus, G U

1998-01-01

413

Photoinduced electron transfer in ordered polymers: Progress report, May 1, 1988December 31, 1988  

Microsoft Academic Search

Long-range photoinduced electron transfer between potential electron donors and acceptors is of considerable current interest in terms of strategies for artificial photosynthesis and studies regarding the redox properties of proteins. Electron transfer over organized arrays of significant dimension (e.g., 10 nm) may also be important for molecule-based bistable switches or rectifiers. As part of a program of study of long

G. II

1988-01-01

414

Elementary events of electron transfer in a voltage-driven quantum point contact.  

PubMed

We find that the statistics of electron transfer in a coherent quantum point contact driven by an arbitrary time-dependent voltage is composed of elementary events of two kinds: unidirectional one-electron transfers determining the average current and bidirectional two-electron processes contributing to the noise only. This result pertains at vanishing temperature while the extended Keldysh-Green's function formalism in use also enables the systematic calculation of the higher-order current correlators at finite temperatures. PMID:17930910

Vanevi?, Mihajlo; Nazarov, Yuli V; Belzig, Wolfgang

2007-08-13

415

Reproductive toxins: pervasive theme of oxidative stress and electron transfer.  

PubMed

Reproductive toxicity 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. Exposure is pervasive and virtually unavoidable due to contamination of air, water, ground, food, beverages, drugs, and household items. The corresponding adverse effects on reproduction are numerous. There is uncertainty regarding mode of action although various theories have been advanced, e.g., disruption of the CNS, DNA attack, enzyme inhibition, interference with hormonal action, and insult to membranes and proteins. This review provides extensive evidence for involvement of oxidative stress (OS) and electron transfer (ET) as a unifying theme. Successful application 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. For completeness, other theories are also addressed; a multifaceted approach appears to be the most logical. Our framework should increase understanding and contribute to preventative measures, such as use of antioxidants (AOs). The ET-OS theory has recently been used as the central theme by us in reviews of biomechanisms involved with anti-infective drugs, anticancer agents, and carcinogens. PMID:11375756

Kovacic, P; Jacintho, J D

2001-06-01

416

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

PubMed

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. PMID:17315244

Kovacic, Peter; Somanathan, Ratnasamy

2006-12-01

417

Electron spin polarization in sequential electron transfer. An example from iron-containing photosynthetic bacterial reaction center proteins  

SciTech Connect

Characteristic electron spin polarization (ESP) is observed during the initial energy conversion steps of natural and artificial photosynthetic systems when they are monitored by time-resolved electron paramagnetic resonance (EPR). Correct interpretation of this ESP is essential for elucidating the details of sequential electron transfer leading to stabilized charge separation in these systems. An extended model that describes ESP in sequential electron transfer has been developed. This model has been applied specifically to the primary reactions of photosynthetic bacteria. We report ESP EPR spectra obtained from native protonated and deuterated (99.7%) iron-containing bacterial reaction centers (rcs) of Rb. sphaeroides R26 and interpret the results together with those from quinone-replaced rcs using the extended ESP model for sequential electron transfer. The time-resolved P[sup +] EPR signals from P[sup +]H[QFe[sup 2+

Snyder, S.W.; Bondeson, S.R.; Norris, J.R.; Thurnauer, M.C. (Argonne National Lab., IL (United States)); Morris, A.L. (Univ. of Chicago, IL (United States))

1993-05-05

418

Metalloporphyrins as energy transfer catalysts: Progress report, August 1, 1984-July 31, 1987  

SciTech Connect

Porphyrin excited state dynamics have been explored initially using a simple stationary sample cw laser technique to pump a steady state; the ground state spectrum is obtained by spinning the sample, and the excited state spectrum is obtained by subtraction. In this way triplet state Resoannce Rama (RR) spectra were obtained for the tetraphenylporphine (TPP) complexes of magnesium, zinc, and palladium, and excited state deligation was studied for pyridine and piperidine complexes of nickel TPP. In connection with the latter study, the systematics of RR frequencies and core size were established for 4- and 6-coordinate nickel porphyrins, and a 5-coordinate high-spin complex was definitively characterized. In addition RR spectra were analyzed for ruthenium porphyrins, as background for future excited state studies, and backbonding charcteristics were established. Charge transfer excited states of a 4,4'-bipyridine complex of ruthenium(II) were studied via the power-dependent photoinduced RR spectra produced with a YAG laser. RR spectra of metallo-OEP (octaethylporphyrin) cation radicals have also been studied.

Sprio, T.G.

1987-01-01

419

Effects of hydrogen bonding on metal ion-promoted intramolecular electron transfer and photoinduced electron transfer in a ferrocene-quinone dyad with a rigid amide spacer.  

PubMed

A ferrocene-quinone dyad (Fc-Q) with a rigid amide spacer and Fc-(Me)Q dyad, in which the amide proton acting as a hydrogen-bonding acceptor is replaced by the methyl group, are employed to examine the effects of hydrogen bonding on both the thermal and the photoinduced electron-transfer reactions. The hydrogen bonding of the semiquinone radical anion with the amide proton in Fc-Q(.-) produced by the electron-transfer reduction of Fc-Q is indicated by the significant positive shift of the one-electron reduction potential of Fc-Q. The hyperfine coupling constants of Fc-Q(.-) also indicate the existence of hydrogen bonding, agreeing with those predicted by the density functional calculation. The hydrogen-bonding dynamics in the photoinduced electron transfer from the ferrocene (Fc) to the quinone moiety (Q) in Fc-Q have been successfully detected in the femtosecond laser flash photolysis experiments. Thermal intramolecular electron transfer from Fc to Q in Fc-Q and Fc-(Me)Q also occurs efficiently in the presence of metal ions in acetonitrile at 298 K. The hydrogen bond formed between the semiquinone radical anion and the amide proton in Fc-Q results in remarkable acceleration of the rate of metal ion-promoted electron transfer as compared to the rate of Fc-(Me)Q in which hydrogen bonding is prohibited. The metal ion-promoted electron-transfer rates are well correlated with the binding energies of superoxide ion-metal ion complexes, which are derived from the g(zz) values of the ESR spectra. PMID:12537500

Fukuzumi, Shunichi; Okamoto, Ken; Yoshida, Yutaka; Imahori, Hiroshi; Araki, Yasuyuki; Ito, Osamu

2003-01-29

420

The Hydrogen Catalyst Cobaloxime - a Multifrequency EPR & DFT Study of Cobaloxime's Electronic Structure  

PubMed Central

Solar fuels research aims to mimic photosynthesis and devise integrated systems that can capture, convert, and store solar energy in the form of high-energy molecular bonds. Molecular hydrogen is generally considered an ideal solar fuel as its combustion is essentially pollution-free. Cobaloximes rank among the most promising earth-abundant catalysts for the reduction of protons to molecular hydrogen. We have used multifrequency EPR spectroscopy at X-band, Q-band, and D-band combined with DFT calculations to reveal electronic structure and establish correlations between structure, surroundings and catalytic activity of these complexes. To assess the strength and nature of ligand cobalt interactions, the BF2-capped cobaloxime, Co(dmgBF2)2, was studied in a variety of different solvents with a range of polarities and stoichiometric amounts of potential ligands to the cobalt ion. This allows the differentiation of labile and strongly coordinating axial ligands for the Co(II) complex. Labile, or weakly coordinating, ligands like methanol result in larger g-tensor anisotropy than strongly coordinating ligands like pyridine. Additionally, a coordination number effect is seen for the strongly coordinating ligands with both singly-ligated LCo(dmgBF2)2 and doubly-ligated L2Co(dmgBF2)2. The presence of two strongly coordinating axial ligands leads to the smallest g-tensor anisotropy. The relevance of the strength of the axial ligand(s) to the catalytic efficiency of Co(dmgBF2)2 is discussed. Finally, the influence of molecular oxygen and formation of Co(III) superoxide radicals LCo(dmgBF2)2O2• is studied. The experimental results are compared with a comprehensive set of DFT calculations on Co(dmgBF2)2 model systems with various axial ligands. Comparison with experimental values for the “key” magnetic parameters like g-tensor and 59Co hyperfine coupling tensor allows the determination of the conformation of the axially ligated Co(dmgBF2)2 complexes. The data presented here are vital for understanding the influence of solvent and ligand coordination on the catalytic efficiency of cobaloximes.

Niklas, Jens; Mardis, Kristy L.; Rakhimov, Rakhim R.; Mulfort, Karen L.; Tiede, David M.; Poluektov, Oleg G.

2012-01-01

421

Photo-Induced Single Molecule Electron Transfer at the Molecule-Nanoparticle Interface  

NASA Astrophysics Data System (ADS)

Single molecule fluorescence spectroscopy was used to study photoinduced electron transfer (ET) dynamics across single donor-bridge-acceptor junctions consisting of perylene-3,4:9,10-bis(dicarboximide) (PDI), n-phenylene bridge with COOH anchoring group, and antimony doped Tin Oxide(ATO) nanoparticles. Photo-excitation of PDI initiates electron transfer from its excited state into ATO nanoparticles. Electron transfer was confirmed and ensemble average rate was measured by transient infrared absorption spectroscopy, in which injected electrons in ATO were directly monitored. Single molecule fluorescence from donor molecule was confirmed by the observed blinking behavior, fluorescence spectrum, and excitation polarization dependence. Single molecule fluorescence lifetime was measured by time-correlated single photon counting, from which forward electron transfer rate from adsorbate excited state to nanoparticle was determined. The dependence of these single molecule ET rates and their fluctuation on the length of phenylene bridge and the nature of semiconductors are being investigated.

Lian, Tianquan; Goh, Wanhee; Guo, Jianchang; Liu, Xi; Ahrens, Michael; Schierloh, Emilie; Wasielewski, Michael

2006-03-01

422

Electron transfer kinetics at single-walled carbon nanotube paper: The role of band structure  

NASA Astrophysics Data System (ADS)

The role of band structure of individual tubules from single-walled carbon nanotube paper in the electron transfer process was considered within Gerischer-Marcus theory using Raman scattering spectroscopy, cyclic voltammetry and electrochemical impedance spectroscopy data. A heterogeneous electron transfer rate of 1.06×10-3cms was observed for ferri/ferrocyanid. A position of the Raman radial breathing mode was used for determination of the chiral vectors of tubules being in resonance with excitation laser light of 1.17 eV. For these tubules, the calculated electron transfer rates are similar. It has been shown that nanotube electronic states away from the Fermi level contribute to the electron transfer kinetics due to the broad distribution of the redox states in electrolyte.

Szroeder, Pawe?

2011-11-01

423

The effect of mass transfer on the catalytic combustion of benzene and methane over palladium catalysts supported on porous materials  

Microsoft Academic Search

Catalytic combustion of benzene and methane over palladium catalysts supported on FAU and MOR zeolites and MCM-41 and KIT-1 mesoporous materials were studied to illustrate the effect of pore size and shape of supports on their catalytic activities. The palladium catalysts supported on mesoporous materials showed high activity and a steep increase in the conversion of benzene with rising temperature.

Min-Woong Ryoo; Sang-Gwi Chung; Jong-Ho Kim; Yo Soon Song; Gon Seo

2003-01-01

424

Controlling photoinduced electron transfer rates in donor-spacer-acceptor molecules by changing the electronic properties of the spacer  

NASA Astrophysics Data System (ADS)

Electron transfer in photosynthetic reaction centers was examined. Specifically, the nature of the medium that lies between the electron donors and acceptors in the reaction centers was studied. The approach was to synthesize four fixed-distance porphyrin-quinone molecules in order to study the effects of changing the orbital energies of the donor, acceptor, and intervening spacer molecules.

Wasielewski, Michael R.; Niemczyk, Mark P.; Johnson, Douglas G.

425

Sulfated SnO 2 modified multi-walled carbon nanotubes – A mixed proton–electron conducting support for Pt catalysts in direct ethanol fuel cells  

Microsoft Academic Search

We report on the synthesis of sulfated SnO2 modified multi-walled carbon nanotubes (MWCNTs) composites as new supports of Pt catalyst (Pt–S-SnO2\\/MWCNTs) with the aims to enhance electron and proton conductivity and also catalytic activity for ethanol oxidation. The Pt–S-SnO2\\/MWCNTs catalyst is synthesized by a combination of improved sol–gel and pulse-microwave assisted polyol methods. The surface presence, morphology and structure of

Xinwei Zhang; Hong Zhu; Zhijun Guo; Yongsheng Wei; Fanghui Wang

2011-01-01

426

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

SciTech Connect

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

Hoffman, M.Z.

1992-07-31

427

Electron transfer reactions of metalloproteins at peptide-modified gold electrodes.  

PubMed

The electron transfer reactions of four small redox proteins, cytochrome c. ferredoxin, plastocyanin and azurin, have been investigated at novel peptide-modified gold electrodes. These proved to be effective and selective in facilitating electron transfer. Good, quasi-reversible electron transfer was achieved selectively at different peptide-protein configurations by changing the pH or the ionic strength of the solution. The use of peptides as promoters for protein electrochemistry opens up the possibility of designing very specific electrode surfaces for larger molecules like enzymes. PMID:2163832

Barker, P D; Di Gleria, K; Hill, H A; Lowe, V J

1990-05-31

428

FI catalysts: new olefin polymerization catalysts for the creation of value-added polymers.  

PubMed

This contribution reports the discovery and application of phenoxy-imine-based catalysts for olefin polymerization. Ligand-oriented catalyst design research has led to the discovery of remarkably active ethylene polymerization catalysts (FI Catalysts), which are based on electronically flexible phenoxy-imine chelate ligands combined with early transition metals. Upon activation with appropriate cocatalysts, FI Catalysts can exhibit unique polymerization catalysis (e.g., precise control of product molecular weights, highly isospecific and syndiospecific propylene polymerization, regio-irregular polymerization of higher alpha-olefins, highly controlled living polymerization of both ethylene and propylene at elevated temperatures, and precise control over polymer morphology) and thus provide extraordinary opportunities for the syntheses of value-added polymers with distinctive architectural characteristics. Many of the polymers that are available via the use of FI Catalysts were previously inaccessible through other means of polymerization. For example, FI Catalysts can form vinyl-terminated low molecular weight polyethylenes, ultra-high molecular weight amorphous ethylene-propylene copolymers and atactic polypropylenes, highly isotactic and syndiotactic polypropylenes with exceptionally high peak melting temperatures, well-defined and controlled multimodal polyethylenes, and high molecular weight regio-irregular poly(higher alpha-olefin)s. In addition, FI Catalysts combined with MgCl(2)-based compounds can produce polymers that exhibit desirable morphological features (e.g., very high bulk density polyethylenes and highly controlled particle-size polyethylenes) that are difficult to obtain with conventionally supported catalysts. In addition, FI Catalysts are capable of creating a large variety of living-polymerization-based polymers, including terminally functionalized polymers and block copolymers from ethylene, propylene, and higher alpha-olefins. Furthermore, some of the FI Catalysts can furnish living-polymerization-based polymers catalytically by combination with appropriate chain transfer agents. Therefore, the development of FI Catalysts has enabled some crucial advances in the fields of polymerization catalysis and polymer syntheses. PMID:15293336

Mitani, Makoto; Saito, Junji; Ishii, Sei-Ichi; Nakayama, Yasushi; Makio, Haruyuki; Matsukawa, Naoto; Matsui, Shigekazu; Mohri, Jun-Ichi; Furuyama, Rieko; Terao, Hiroshi; Bando, Hideki; Tanaka, Hidetsugu; Fujita, Terunori

2004-01-01

429

Full-electron calculation of effective electronic couplings and excitation energies of charge transfer states: Application to hole transfer in DNA ?-stacks  

PubMed Central

In this work I develop and apply a theoretical method for calculating effective electronic couplings (or transfer integrals) between redox sites involved in hole or electron transfer reactions. The resulting methodology is a refinement and a generalization of a recently developed approach for transfer integral evaluation. In fact, it holds for any overlap between the charge-localized states used to represent charge transfer (CT) processes in the two-state model. The presented theoretical and computational analyses show that the prototype approach is recovered for sufficiently small overlaps. The method does not involve any empirical parameter. It allows a complete multielectron description, therefore including electronic relaxation effects. Furthermore, its theoretical formulation holds at any value of the given reaction coordinate and yields a formula for the evaluation of the vertical excitation energy (i.e., the energy difference between the adiabatic ground and first-excited electronic states) that rests on the same physical quantities used in transfer integral calculation. In this paper the theoretical approach is applied to CT in B-DNA base dimers within the framework of Density Functional Theory (DFT), although it can be implemented in other computational schemes. The results of this work, as compared with previous Hartree–Fock (HF) and post-HF evaluations, support the applicability of the current implementation of the method to larger ?-stacked arrays, where post-HF approaches are computationally unfeasible.

Migliore, Agostino

2009-01-01

430

The hydrogenation/transfer hydrogenation network: asymmetric hydrogenation of ketones with chiral eta6-arene/N-Tosylethylenediamine-ruthenium(II) catalysts.  

PubMed

Chiral eta6-arene/N-tosylethylenediamine-Ru(II) complexes, known as excellent catalysts for asymmetric transfer hydrogenation of aromatic ketones in basic 2-propanol, can be used for asymmetric hydrogenation using H2 gas. Active catalysts are generated from RuCl[(S,S)-TsNCH(C6H5)CH(C6H5)NH2](eta6-p-cymene) in methanol, but not 2-propanol, or by combination of Ru[(S,S)-TsNCH(C6H5)CH(C6H5)NH](eta6-p-cymene) and CF3SO3H or other non-nucleophilic acids. This method allows, for the first time, asymmetric hydrogenation of simple ketones under acidic conditions. Hydrogenation of base-sensitive 4-chromanone and its derivatives with the S,S catalyst proceeds in methanol with a substrate-to-catalyst molar ratio of 1000-3000 (10 atm) to 7000 (100 atm), giving (S)-4-chromanols with 97% ee quantitatively. The reaction can be achieved even on a 2.4 kg scale. The mechanistic rationale for the catalytic efficiency is presented. PMID:16819854

Ohkuma, Takeshi; Utsumi, Noriyuki; Tsutsumi, Kunihiko; Murata, Kunihiko; Sandoval, Christian; Noyori, Ryoji

2006-07-12