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1

Au25 Clusters as Electron-Transfer Catalysts Induced the Intramolecular Cascade Reaction of 2-nitrobenzonitrile  

NASA Astrophysics Data System (ADS)

Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Here, for the first time, Au25z nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra also verified Au25z was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25z.

Chong, Hanbao; Li, Peng; Wang, Shuxin; Fu, Fangyu; Xiang, Ji; Zhu, Manzhou; Li, Yadong

2013-11-01

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

2012-11-26

3

Incorporation of Water-Oxidation Catalysts into Photoinduced Electron Transfer Systems: Toward Solar Fuel Generation via Artificial Photosynthesis  

NASA Astrophysics Data System (ADS)

A key goal of artificial photosynthesis is to mimic the photochemistry of photosystem II and oxidize water using light energy, with the ultimate aim of using the liberated electrons for reductive, fuel-forming reactions. One of the more recent challenges in the field of solar fuels chemistry is the efficient activation of molecular water-oxidation catalysts with photoinduced electron transfer, an effort that would benefit from detailed knowledge of the energetics and kinetics of each electron transfer step in a light-driven catalytic cycle. The focus of this thesis is the synthesis and photophysical characterization of covalent assemblies comprising a redox-active organic chromophore and the iridium(III)-based water-oxidation catalyst Cp*Ir(ppy)Cl (ppy = 2-phenylpyridine), and the rates and pathways for photogeneration of higher-valence states of the catalyst are determined with femtosecond transient absorption spectroscopy and other time-resolved spectroscopic techniques. In linking the photooxidant perylene-3,4:9,10-bis (dicarboximide) (PDI) to the Ir(III) catalyst, fast photoinduced electron transfer from the metal complex to PDI outcompetes heavy-atom quenching of the dye excited state, and the catalytic integrity of the complex is retained, as determined by electrocatalysis experiments. Long-lived higher-valence states of the catalyst are necessary for the accumulation of oxidizing equivalents for oxygen evolution, and the lifetime of photogenerated Ir(IV) has been extended by over two orders of magnitude by catalyst incorporation into a covalent electron acceptor--chromophore--catalyst triad, in which the dye is perylene-3,4-dicarboximide (PMI). Time resolved X-ray absorption studies of the triad confirm the photogeneration of an Ir(IV) metal center, a species that is too unstable to observe with chemical or electrochemical oxidation methods. This approach to preparing higher-valence states of water-oxidation catalysts has great promise for deducing catalytic mechanisms and probing highly-reactive intermediates, and it also establishes a basis in systems design for photodriving catalytic processes. Covalent dye-catalyst assemblies have been gaining recognition as a useful motif for incorporation into dye-sensitized photoanodes for photoelectrochemical water-splitting cells, and the PMI-Ir catalyst unit is well-poised, both in the energetics and kinetics of its electron transfer properties, to improve upon current solar-driven fuel-forming devices.

Vagnini, Michael Thomas

4

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

PubMed Central

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.

2012-01-01

5

Hydrogen Photogeneration Promoted by Efficient Electron Transfer from Iridium Sensitizers to Colloidal MoS2 Catalysts  

PubMed Central

We report the utilization of colloidal MoS2 nanoparticles (NPs) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir(III) sensitizers. The effects of the particle size and particle dispersion of MoS2 NPs catalyst, reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated. The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions. The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer, resulting in enhancement of hydrogen evolution relative to the non-attached systems. The highest apparent quantum yield, which was as high as 12.4%, for hydrogen evolution, was obtained (? = 400?nm). PMID:24509729

Yuan, Yong-Jun; Yu, Zhen-Tao; Liu, Xiao-Jie; Cai, Jian-Guang; Guan, Zhong-Jie; Zou, Zhi-Gang

2014-01-01

6

Hydrogen photogeneration promoted by efficient electron transfer from iridium sensitizers to colloidal MoS2 catalysts.  

PubMed

We report the utilization of colloidal MoS2 nanoparticles (NPs) for multicomponent photocatalytic water reduction systems in cooperation with a series of cyclometalated Ir(III) sensitizers. The effects of the particle size and particle dispersion of MoS2 NPs catalyst, reaction solvent and the concentration of the components on hydrogen evolution efficiency were investigated. The MoS2 NPs exhibited higher catalytic performance than did other commonly used water reduction catalysts under identical experiment conditions. The introduction of the carboxylate anchoring groups in the iridium complexes allows the species to be favorably chem-adsorbed onto the MoS2 NPs surface to increase the electron transfer, resulting in enhancement of hydrogen evolution relative to the non-attached systems. The highest apparent quantum yield, which was as high as 12.4%, for hydrogen evolution, was obtained (? = 400?nm). PMID:24509729

Yuan, Yong-Jun; Yu, Zhen-Tao; Liu, Xiao-Jie; Cai, Jian-Guang; Guan, Zhong-Jie; Zou, Zhi-Gang

2014-01-01

7

Electron-transfer sensitization of H2 oxidation and CO2 reduction catalysts using a single chromophore.  

PubMed

Energy-storing artificial-photosynthetic systems for CO2 reduction must derive the reducing equivalents from a renewable source rather than from sacrificial donors. To this end, a homogeneous, integrated chromophore/two-catalyst system is described that is thermodynamically capable of photochemically driving the energy-storing reverse water-gas shift reaction (CO2 + H2 ? CO + H2O), where the reducing equivalents are provided by renewable H2. The system consists of the chromophore zinc tetraphenylporphyrin (ZnTPP), H2 oxidation catalysts of the form [Cp(R)Cr(CO)3](-), and CO2 reduction catalysts of the type Re(bpy-4,4'-R2)(CO)3Cl. Using time-resolved spectroscopic methods, a comprehensive mechanistic and kinetic picture of the photoinitiated reactions of mixtures of these compounds has been developed. It has been found that absorption of a single photon by broadly absorbing ZnTPP sensitizes intercatalyst electron transfer to produce the substrate-active forms of each. The initial photochemical step is the heretofore unobserved reductive quenching of the low-energy T1 state of ZnTPP. Under the experimental conditions, the catalytically competent state decays with a second-order half-life of ?15 ?s, which is of the right magnitude for substrate trapping of sensitized catalyst intermediates. PMID:24961370

La Porte, Nathan T; Moravec, Davis B; Hopkins, Michael D

2014-07-01

8

Cinchona-based phase-transfer catalysts for asymmetric synthesis.  

PubMed

Phase-transfer catalysis is one of the most useful methodologies for practical syntheses given its operational simplicity and mild reaction conditions that enable its application in industrial processes. Cinchona alkaloids have been a popular, natural source of practical organocatalysts due largely to their excellent commercial availability and low cost. Since the first Cinchona alkaloid-derived phase-transfer catalysts was disclosed in 1981, diverse generations of Cinchona-derived phase-transfer catalysts have been developed and successfully applied to various asymmetric syntheses. In this feature article, we describe the generation of Cinchona-derived chiral phase-transfer catalysts according to the development stages and our efforts toward the design of polymeric Cinchona phase-transfer catalysts, the effects of the electronic functional group incorporated in the catalysts, and their application in asymmetric organic reactions. PMID:19920996

Jew, Sang-sup; Park, Hyeung-geun

2009-12-14

9

The electron is a catalyst  

NASA Astrophysics Data System (ADS)

The electron is an efficient catalyst for conducting various types of radical cascade reaction that proceed by way of radical and radical ion intermediates. But because electrons are omnipresent, catalysis by electrons often passes unnoticed. In this Review, a simple analogy between acid/base catalysis and redox catalysis is presented. Conceptually, the electron is a catalyst in much the same way that a proton is a catalyst. The 'electron is a catalyst' paradigm unifies mechanistically an assortment of synthetic transformations that otherwise have little or no apparent relationship. Diverse radical cascades, including unimolecular radical substitution reactions (SRN1-type chemistry), base-promoted homolytic aromatic substitutions (BHAS), radical Heck-type reactions, radical cross-dehydrogenative couplings (CDC), direct arene trifluoromethylations and radical alkoxycarbonylations, can all be viewed as electron-catalysed reactions.

Studer, Armido; Curran, Dennis P.

2014-09-01

10

The role of a dipeptide outer-coordination sphere on H2-production catalysts: influence on catalytic rates and electron transfer.  

PubMed

The outer-coordination sphere of enzymes acts to fine-tune the active site reactivity and control catalytic rates, suggesting that incorporation of analogous structural elements into molecular catalysts may be necessary to achieve rates comparable to those observed in enzyme systems at low overpotentials. In this work, we evaluate the effect of an amino acid and dipeptide outer-coordination sphere on [Ni(P(Ph)(2)N(Ph-R)(2))(2)](2+) hydrogen production catalysts. A series of 12 new complexes containing non-natural amino acids or dipeptides was prepared to test the effects of positioning, size, polarity and aromaticity on catalytic activity. The non-natural amino acid was either 3-(meta- or para-aminophenyl)propionic acid terminated as an acid, an ester or an amide. Dipeptides consisted of one of the non-natural amino acids coupled to one of four amino acid esters: alanine, serine, phenylalanine or tyrosine. All of the catalysts are active for hydrogen production, with rates averaging ?1000?s(-1), 40?% faster than the unmodified catalyst. Structure and polarity of the aliphatic or aromatic side chains of the C-terminal peptide do not strongly influence rates. However, the presence of an amide bond increases rates, suggesting a role for the amide in assisting catalysis. Overpotentials were lower with substituents at the N-phenyl meta position. This is consistent with slower electron transfer in the less compact, para-substituted complexes, as shown in digital simulations of catalyst cyclic voltammograms and computational modeling of the complexes. Combining the current results with insights from previous results, we propose a mechanism for the role of the amino acid and dipeptide based outer-coordination sphere in molecular hydrogen production catalysts. PMID:23233438

Reback, Matthew L; Ginovska-Pangovska, Bojana; Ho, Ming-Hsun; Jain, Avijita; Squier, Thomas C; Raugei, Simone; Roberts, John A S; Shaw, Wendy J

2013-02-01

11

The Role of a Dipeptide Outer-Coordination Sphere on H2 -Production Catalysts: Influence on Catalytic Rates and Electron Transfer  

SciTech Connect

The outer-coordination sphere of enzymes acts to fine-tune the active site reactivity and control catalytic rates, suggesting that incorporation of analogous structural elements into molecular catalysts may be necessary to achieve rates comparable to those observed in enzyme systems at low overpotentials. In this work, we evaluate the effect of an amino acid and dipeptide outer-coordination sphere on [Ni(PPh2NPh-R2)2]2+ hydrogen production catalysts. A series of 12 new complexes containing non-natural amino acids or dipeptides were prepared to test the effects of positioning, size, polarity and aromaticity on catalytic activity. The non-natural amino acid was either 3-(meta- or para-aminophenyl)propionic acid terminated as an acid, an ester or an amide. Dipeptides consisted of one of the non-natural amino acids coupled to one of four amino acid esters: alanine, serine, phenylalanine or tyrosine. All of the catalysts are active for hydrogen production, with rates averaging ~1000 s-1, 40% faster than the unmodified catalyst. Structure and polarity of the aliphatic or aromatic side chains of the C-terminal peptide do not strongly influence rates. However, the presence of an amide bond increases rates, suggesting a role for the amide in assisting catalysis. Overpotentials were lower with substituents at the N-phenyl meta position. This is consistent with slower electron transfer in the less compact, para-substituted complexes, as shown in digital simulations of catalyst cyclic voltammograms and computational modeling of the complexes. Combining the current results with insights from previous results, we propose a mechanism for the role of the amino acid and dipeptide based outer-coordination sphere in molecular hydrogen production catalysts.

Reback, Matthew L.; Ginovska-Pangovska, Bojana; Ho, Ming-Hsun; Jain, Avijita; Squier, Thomas C.; Raugei, Simone; Roberts, John A.; Shaw, Wendy J.

2013-02-04

12

Vectorial electron transfer in spatially ordered arrays  

SciTech Connect

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

Fox, M.A.

1993-02-01

13

Asymmetric cyclopropanation of chalcones using chiral phase-transfer catalysts  

PubMed Central

The first phase-transfer catalyzed cyclopropanation reaction of chalcones using bromomalonates as the nucleophiles in a Michael Initiated Ring Closing reaction (MIRC) was developed. Key to success was the use of a free OH-containing cinchona alkaloid ammonium salt catalyst and carefully optimized liquid/liquid reaction conditions. The reaction performed well for electron neutral and electron deficient chalcones giving the products in yields up to 98% and with enantiomeric ratios up to 91:9. PMID:24391288

Herchl, Richard; Waser, Mario

2013-01-01

14

A functionalised nickel cyclam catalyst for CO2 reduction: electrocatalysis, semiconductor surface immobilisation and light-driven electron transfer.  

PubMed

The immobilisation of electrocatalysts for CO2 reduction onto light harvesting semiconductors is proposed to be an important step towards developing more efficient CO2 reduction photoelectrodes. Here, we report a low cost nickel cyclam complex covalently anchored to a metal oxide surface. Using transient spectroscopy we validate the role of surface immobilisation on enhancing the rate of photoelectron transfer. Furthermore [Ni(1,4,8,11-tetraazacyclotetradecane-6-carboxylic acid)](2+) (2) is shown to be a very active electrocatalyst in solution. PMID:25460350

Neri, Gaia; Walsh, James J; Wilson, Calum; Reynal, Anna; Lim, Jason Y C; Li, Xiaoe; White, Andrew J P; Long, Nicholas J; Durrant, James R; Cowan, Alexander J

2015-01-21

15

Electron transfer in peptides.  

PubMed

In this review, we discuss the factors that influence electron transfer in peptides. We summarize experimental results from solution and surface studies and highlight the ongoing debate on the mechanistic aspects of this fundamental reaction. Here, we provide a balanced approach that remains unbiased and does not favor one mechanistic view over another. Support for a putative hopping mechanism in which an electron transfers in a stepwise manner is contrasted with experimental results that support electron tunneling or even some form of ballistic transfer or a pathway transfer for an electron between donor and acceptor sites. In some cases, experimental evidence suggests that a change in the electron transfer mechanism occurs as a result of donor-acceptor separation. However, this common understanding of the switch between tunneling and hopping as a function of chain length is not sufficient for explaining electron transfer in peptides. Apart from chain length, several other factors such as the extent of the secondary structure, backbone conformation, dipole orientation, the presence of special amino acids, hydrogen bonding, and the dynamic properties of a peptide also influence the rate and mode of electron transfer in peptides. Electron transfer plays a key role in physical, chemical and biological systems, so its control is a fundamental task in bioelectrochemical systems, the design of peptide based sensors and molecular junctions. Therefore, this topic is at the heart of a number of biological and technological processes and thus remains of vital interest. PMID:25619931

Shah, Afzal; Adhikari, Bimalendu; Martic, Sanela; Munir, Azeema; Shahzad, Suniya; Ahmad, Khurshid; Kraatz, Heinz-Bernhard

2015-02-10

16

Photo-induced electron transfer method  

DOEpatents

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

Wohlgemuth, Roland (2823 Hillegass Ave., Berkeley, CA 94705); Calvin, Melvin (2683 Buena Vista Way, Berkeley, CA 94708)

1984-01-01

17

Photo-induced electron transfer method  

DOEpatents

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

Wohlgemuth, R.; Calvin, M.

1984-01-24

18

Nonadiabatic anharmonic electron transfer  

SciTech Connect

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 {Delta}=-{Delta}G. The temperature insensitivity of the transfer rate is clearly seen when the exoergicity equals the collective reorganization energy ({Delta}={Lambda}{sub s}) along a maximum ln (w) vs. {Delta} ridge of the surface. The surface also reveals additional regions for {Delta} where ln (w) appears to be insensitive to temperature, or effectively activationless, for some kinds of inner sphere contributions.

Schmidt, P. P. [Molecular Physics Research, 6547 Kristina Ursula Court, Falls Church, Virginia 22044 (United States)

2013-03-28

19

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

20

Selective transfer semihydrogenation of alkynes with nanoporous gold catalysts.  

PubMed

A facile, highly chemo- and stereoselective transfer semihydrogenation of alkynes to Z-olefins has been achieved by use of unsupported nanoporous gold (AuNPore) as a heterogeneous catalyst together with formic acid as a hydrogen donor. A variety of terminal/internal and aromatic/aliphatic alkynes were reduced to the corresponding alkenes in high chemical yields with good functional-group tolerance. The catalyst is robust enough to be reused without leaching. PMID:25521623

Wagh, Yogesh S; Asao, Naoki

2015-01-16

21

Electron transfer: Lower tunnel barriers  

NASA Astrophysics Data System (ADS)

A better understanding of electron transfer through molecules could provide the basis for many technological breakthroughs. Now, the rate of electron transfer has been enhanced in a family of molecules by making them more rigid, and this phenomenon may be explained by the loss of electronic energy to vibrations.

Miller, John R.

2014-10-01

22

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

23

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

24

Vectorial electron transfer in spatially ordered arrays. Progress report, January 1992--January 1993  

SciTech Connect

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

Fox, M.A.

1993-02-01

25

Exploring the decomposition pathways of iron asymmetric transfer hydrogenation catalysts.  

PubMed

Our group has developed a series of iron-based asymmetric transfer hydrogenation (ATH) catalysts for the reduction of polar double bonds. The activation of the precatalysts as well as the catalytic mechanism have been thoroughly investigated, but the decomposition pathways of these systems are poorly understood. Herein, we report a study of the deactivation pathways for an iron ATH catalyst under catalytically relevant conditions. The decomposition pathways were examined using experimental techniques and density functional theory (DFT) calculations. The major decomposition products that formed, Fe(CO)((Et)2PCH2CH2CHCHNCH2CH2P(Et)2) () and Fe(CO)((Et)2PCH2CH2C(Ph)C(Ph)NCH2CH2P(Et)2) (), had two amido donors as well as a C[double bond, length as m-dash]C bond on the diamine backbone of the tetradentate ligand. These species were identified by NMR studies and one was isolated as a bimetallic complex with Ru(ii)Cp*. Two minor iron hydride species also formed concurrently with , as determined by NMR studies, one of which was isolated and contained a fully saturated ligand as well as a hydride ligand. None of the compounds that were isolated were found to be active ATH catalysts. PMID:25373607

Lagaditis, Paraskevi O; Sues, Peter E; Lough, Alan J; Morris, Robert H

2014-11-01

26

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

NASA Astrophysics Data System (ADS)

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

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

2015-02-01

27

Electron Energy Loss Spectroscopy (EELS) of Iron Fischer Tropsch Catalysts  

NASA Astrophysics Data System (ADS)

Electron energy loss spectroscopy (EELS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy have been used to study iron catalysts for Fischer Tropsch synthesis. When silica-containing iron oxide precursors are activated in flowing CO, the iron phase segregates into iron carbide crystallites, leaving behind some unreduced iron oxide in an amorphous state coexisting with the silica binder. The iron carbide crystallites are found covered by characteristic amorphous carbonaceous surface layers. These amorphous species are difficult to analyze by traditional catalyst characterization techniques, which lack spatial resolution. Even a surface-sensitive technique such as XPS shows only broad carbon or iron peaks in these catalysts. As we show in this work, EELS allows us to distinguish three different carbonaceous species: reactive amorphous carbon, graphitic carbon, and carbidic carbon in the bulk of the iron carbide particles. The carbidic carbon K edge shows an intense “[pi]*” peak with an edge shift of about 1 eV to higher energy loss compared to that of the [pi]* of amorphous carbon film or graphitic carbon. EELS analysis of the oxygen K edge allows us to distinguish the amorphous unreduced iron phase from the silica binder, indicating these are two separate phases. These results shed light onto the complex phase transformations that accompany the activation of iron catalysts for Fischer Tropsch synthesis.

Jin, Aming; Xu, Huifang; Datye, Abhaya K.

2006-04-01

28

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

29

Quantitative structural assessment of heterogeneous catalysts by electron tomography.  

PubMed

We present transmission electron microscope (TEM) tomography investigations of ruthenium-based fuel cell catalyst materials as employed in direct methanol fuel cells (DMFC). The digital three-dimensional representation of the samples not only enables detailed studies on number, size, and shape but also on the local orientation of the ruthenium particles to their support and their freely accessible surface area. The shape analysis shows the ruthenium particles deviate significantly from spherical symmetry which increases their surface to volume ratio. The morphological studies help to understand the structure formation mechanisms during the fabrication as well as the high effectiveness of these catalysts in the oxygen reduction reaction at the cathode side of fuel cells. PMID:21916435

Grothausmann, Roman; Zehl, Gerald; Manke, Ingo; Fiechter, Sebastian; Bogdanoff, Peter; Dorbandt, Iris; Kupsch, Andreas; Lange, Axel; Hentschel, Manfred P; Schumacher, Gerhard; Banhart, John

2011-11-16

30

Energetics of Electron Transfer Reactions Dmitry Matyushov  

E-print Network

-induced bands: FCi() = FCi,solvent(x)FCi,gas( - x)dx #12;Inhomogeneous Solvent-Induced Broadening Iabs/em() = 22Energetics of Electron Transfer Reactions Dmitry Matyushov Arizona State University MIT, November-Hush Theory of Electron Transfer Two-parameters model: Fact = ( + F0)2 4 is the reorganization energy F0

Matyushov, Dmitry

31

Chiral salen-metal complexes as novel catalysts for asymmetric phase transfer alkylations  

Microsoft Academic Search

Chiral, salen-metal complexes have been tested as catalysts for the C-alkylation of aldimine Schiff's bases of alanine esters with alkyl bromides under phase-transfer conditions (solid sodium hydroxide, toluene, ambient temperature, 1–10% of the catalyst). The best catalyst, which was derived from a Cu(II) complex of (1R,2R or 1S,2S)-[N,N?-bis(2?-hydroxybenzylidene)]-1,2-diaminocyclohexane, gave ?-methyl-?-amino acids with enantiomeric excesses of 70–96%.

Yuri N. Belokon; Michael North; Vadim S. Kublitski; Nikolai S. Ikonnikov; Pavel E. Krasik; Viktor I. Maleev

1999-01-01

32

Effects of catalyst loading amount on the synthesis of poly(3-hexylthiophene) via externally initiated Kumada catalyst-transfer polycondensation  

NASA Astrophysics Data System (ADS)

A series of model polymerization are carried out via the one-pot externally initiated Kumada catalyst-transfer polycondensation (KCTP) of 2-bromo-5-chloromagnesium thiophene monomers, and the excess amount of initiators or catalysts are found no need to be isolated during the polycondensation process. Especially, the impacts of the nickel catalyst loading variation on regioregularity (rr), yield, molecular weight ( M n), polydispersity (PDI) and initiation efficiency of poly(3-hexylthiophene) (P3HT) are systematically investigated. The 1H NMR, size-exclusion chromatography (SEC), and MALDI-TOF mass spectroscopy results indicated that an excess amount of catalyst does not influence yield, rr, M n, and PDI of P3HT, nor the initiation efficiency. However, the PDI of the product is broad, and the M n and rr values decreased in the absence of 1,3-bis (diphenylphosphino)propane (dppp). It can be concluded that the in-situ KCTP polymerization of P3HT is a practical and effective process. These results are especially valuable for the synthesis of all-conjugated block copolymers where macroinitiators are used.

Wang, Jin; Higashihara, Tomoya

2014-12-01

33

Enhanced electron transfer by dendritic architecture: energy transfer and electron transfer in snowflake-shaped Zn porphyrin dendrimers.  

PubMed

[structure: see text] Photoinduced electron transfer was observed for the snowflake-shaped dendrimer with the Zn porphyrin core and anthraquinonyl terminals. Comparison of the electron-transfer efficiency of the dendrimer with the linear analogues indicates the advantage of the dendritic structure for the electron-transfer process. PMID:17371035

Kozaki, Masatoshi; Akita, Kogen; Okada, Keiji

2007-04-12

34

Dynamic studies of catalysts for biofuel synthesis in an Environmental Transmission Electron Microscope  

E-print Network

Dynamic studies of catalysts for biofuel synthesis in an Environmental Transmission Electron@cen.dtu.dk Keywords: Biofuel, catalysis, environmental TEM The development of transportation fuels from sustainable

Dunin-Borkowski, Rafal E.

35

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

PubMed

Human society faces a fundamental challenge as energy consumption is projected to increase due to population and economic growth as fossil fuel resources decrease. Therefore the transition to alternative and sustainable energy sources is of the utmost importance. The conversion of solar energy into chemical energy, by splitting H2O to generate molecular O2 and H2, could contribute to solving the global energy problem. Developing such a system will require the combination of several complicated processes, such as light-harvesting, charge separation, electron transfer, H2O oxidation, and reduction of the generated protons. The primary processes of charge separation and catalysis, which occur in the natural photosynthetic machinery, provide us with an excellent blueprint for the design of such systems. This Account describes our efforts to construct supramolecular assemblies capable of carrying out photoinduced electron transfer and to develop artificial water oxidation catalysts (WOCs). Early work in our group focused on linking a ruthenium chromophore to a manganese-based oxidation catalyst. When we incorporated a tyrosine unit into these supramolecular assemblies, we could observe fast intramolecular electron transfer from the manganese centers, via the tyrosine moiety, to the photooxidized ruthenium center, which clearly resembles the processes occurring in the natural system. Although we demonstrated multi-electron transfer in our artificial systems, the bottleneck proved to be the stability of the WOCs. Researchers have developed a number of WOCs, but the majority can only catalyze H2O oxidation in the presence of strong oxidants such as Ce(IV), which is difficult to generate photochemically. By contrast, illumination of ruthenium(II) photosensitizers in the presence of a sacrificial acceptor generates [Ru(bpy)3](3+)-type oxidants. Their oxidation potentials are significantly lower than that of Ce(IV), but our group recently showed that incorporating negatively charged groups into the ligand backbone could decrease the oxidation potential of the catalysts and, at the same time, decrease the potential for H2O oxidation. This permitted us to develop both ruthenium- and manganese-based WOCs that can operate under neutral conditions, driven by the mild oxidant [Ru(bpy)3](3+). Many hurdles to the development of viable systems for the production of solar fuels remain. However, the combination of important features from the natural photosynthetic machinery and novel artificial components adds insights into the complicated catalytic processes that are involved in splitting H2O. PMID:23957573

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

2014-01-21

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

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.

2012-07-19

38

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. PMID:21381734

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

2011-01-01

39

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 ...

40

Magnetically Recoverable Supported Ruthenium Catalyst for Hydrogenation of Alkynes and Transfer Hydrogenation of Carbonyl Compounds  

EPA Science Inventory

A ruthenium (Ru) catalyst supported on magnetic nanoparticles (NiFe2O4) has been successfully synthesized and used for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The cata...

41

Electron transfer reactions within zeolites: Radical cation from benzonorbornadiene  

SciTech Connect

Zeolites are being used as solid acid catalysts in a number of commercial processes. Occasionally zeolites are also reported to perform as electron transfer agents. Recently, we observed that radical cations of certain olefins and thiophene oligomers can be generated spontaneously within ZSM-5 zeolites. We noticed that these radical cations generated from diphenyl polyenes and thiophene oligomers were remarkably stable (at room temperature) within ZSM-5 and can be characterized spectroscopically at leisure. We have initiated a program on electron transfer processes within large pore zeolites. The basis of this approach is that once a cation radical is generated within a large pore zeolite, it will have sufficient room to undergo a molecular transformation. Our aim is to identify a condition under which electron transfer can be routinely and reliably carried out within large pore zeolites such as faujasites. To our great surprise, when benzonorbornadiene A and a number of olefins were included in divalent cation exchanged faujasites. they were transformed into products very quickly (<15 min). This observation allowed us to explore the use of zeolites as oxidants. Results of our studies on benzonorbornadiene are presented in this communication. 16 refs., 1 fig.

Pitchumani, K.; Ramamurthy, V. [Tulane Univ., New Orleans, LA (United States)] [Tulane Univ., New Orleans, LA (United States); Corbin, D.R. [The Du Pont Company, Wilmington, DE (United States)] [The Du Pont Company, Wilmington, DE (United States)

1996-08-28

42

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

43

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

44

Versatile iridicycle catalysts for highly efficient and chemoselective transfer hydrogenation of carbonyl compounds in water.  

PubMed

Cyclometalated iridium complexes are shown to be highly efficient and chemoselective catalysts for the transfer hydrogenation of a wide range of carbonyl groups with formic acid in water. Examples include ?-substituted ketones (?-ether, ?-halo, ?-hydroxy, ?-amino, ?-nitrile or ?-ester), ?-keto esters, ?-keto esters and ?,?-unsaturated aldehydes. The reduction was carried out at substrate/catalyst ratios of up to 50?000 at pH?4.5 and required no organic solvent. The protocol provides a practical, easy and efficient way for the synthesis of ?-functionalised secondary alcohols, such as ?-hydroxyethers, ?-hydroxyamines and ?-hydroxyhalo compounds, which are valuable intermediates in pharmaceutical, fine chemical, perfume and agrochemical synthesis. PMID:25124283

Talwar, Dinesh; Wu, Xiaofeng; Saidi, Ourida; Salguero, Noemí Poyatos; Xiao, Jianliang

2014-09-26

45

A new method for recycling asymmetric catalysts via formation of charge transfer complexes.  

PubMed

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity. PMID:16435879

Chollet, Guillaume; Rodriguez, Fernand; Schulz, Emmanuelle

2006-02-01

46

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

47

Intramolecular electron transfer in bipyridinium disulfides.  

PubMed

Reductive cleavage of disulfide bonds is an important step in many biological and chemical processes. Whether cleavage occurs stepwise or concertedly with electron transfer is of interest. Also of interest is whether the disulfide bond is reduced directly by intermolecular electron transfer from an external reducing agent or mediated intramolecularly by internal electron transfer from another redox-active moiety elsewhere within the molecule. The electrochemical reductions of 4,4'-bipyridyl-3,3'-disulfide (1) and the di-N-methylated derivative (2(2+)) have been studied in acetonitrile. Simulations of the cyclic voltammograms in combination with DFT (density functional theory) computations provide a consistent model of the reductive processes. Compound 1 undergoes reduction directly at the disulfide moiety with a substantially more negative potential for the first electron than for the second electron, resulting in an overall two-electron reduction and rapid cleavage of the S-S bond to form the dithiolate. In contrast, compound 2(2+) is reduced at less negative potential than 1 and at the dimethyl bipyridinium moiety rather than at the disulfide moiety. Most interesting, the second reduction of the bipyridinium moiety results in a fast and reversible intramolecular two-electron transfer to reduce the disulfide moiety and form the dithiolate. Thus, the redox-active bipyridinium moiety provides a low energy pathway for reductive cleavage of the S-S bond that avoids the highly negative potential for the first direct electron reduction. Following the intramolecular two-electron transfer and cleavage of the S-S bond the bipyridinium undergoes two additional reversible reductions at more negative potentials. PMID:24528295

Hall, Gabriel B; Kottani, Rudresha; Felton, Greg A N; Yamamoto, Takuhei; Evans, Dennis H; Glass, Richard S; Lichtenberger, Dennis L

2014-03-12

48

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

NASA Astrophysics Data System (ADS)

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

Swierk, John R.

49

Prospects for Electron Holography of Nanoparticle Catalysts Rafal E. Dunin-Borkowski1, *  

E-print Network

Prospects for Electron Holography of Nanoparticle Catalysts Rafal E. Dunin-Borkowski1, * , Lionel, Netherlands * email: rdb@cen.dtu.dk Off-axis electron holography is a transmission electron microscopy metal nanoparticles, measured using off-axis electron holography, are substantially higher than those

Dunin-Borkowski, Rafal E.

50

Non-redox metal ion promoted oxygen transfer by a non-heme manganese catalyst.  

PubMed

This work demonstrates that non-redox metal ions as Lewis acids can sharply improve the oxygen transfer efficiency of a manganese(ii) catalyst having a non-heme ligand. In the absence of Lewis acid, oxidation of a manganese(ii) complex will generate the known di-?-oxo-bridged dinuclear Mn2(iii,iv) core which is very sluggish for olefin epoxidation. Adding non-redox metal ions causes the dissociation of the dinuclear core, leading to sharp improvement in its oxygen transfer efficiency. PMID:25525748

Chen, Zhuqi; Yang, Ling; Choe, Cholho; Lv, Zhanao; Yin, Guochuan

2015-01-20

51

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

2011-12-23

52

Heat and Mass Transfer in a Reforming Catalyst Bed: Quantitative Evaluation of the Controlling Factor by Experiment  

NASA Astrophysics Data System (ADS)

Heat and mass transfer characteristics in a reforming catalyst bed have been experimentally investigated. Experiments were carried out with a single bench-scaled reforming tube which was filled with reforming catalyst. The tube wall was uniformly heated, and mixtures of steam and methane or propane were reformed through the catalyst bed. Most part of the reaction was completed in the upper part of the test tube. The effects of space velocity, which is a ratio of volumetric flow rate of process gas to the catalyst volume, steam carbon molar ratio, wall temperature, bed temperature, and catalyst particle diameter on the transport phenomena with chemical reaction, were determined. A correlation to heat transfer coefficient was determined by Nu, Rep, Pr, dp/d, and Da. The prediction of the overall methane conversion rate was also presented.

Usami, Yutaka; Fukusako, Shoichiro; Yamada, Masahiko

53

Electron transfer processes in double lanthanide activated YPO 4  

Microsoft Academic Search

This work reviews electron transfer processes in double lanthanide doped YPO4 studied using a diversity of optical techniques. The aim is to identify those transfer processes and to relate them with the location of lanthanide electron donor and lanthanide electron acceptor states within the bandgap of YPO4. Electron transfer from the valence band to a trivalent lanthanide impurity or to

P. Dorenbos; A. J. J. Bos; N. R. J. Poolton

2011-01-01

54

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

55

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

56

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

57

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

Federal Register 2010, 2011, 2012, 2013

...Electronic Funds Transfer of Depository Taxes; Correction AGENCY: Internal Revenue...providing guidance relating to Federal tax deposits (FTDs) by Electronic Funds Transfer...List of Subjects 26 CFR Part 40 Excise taxes, Reporting and recordkeeping...

2011-01-06

58

Enhanced in situ ethanolysis of Jatropha curcas L. in the presence of cetyltrimethylammonium bromide as a phase transfer catalyst  

Microsoft Academic Search

Limited solubility of alcohols in vegetable oils hinders transesterification reaction process. Phase transfer catalysis can be of great advantage to enhance the reaction rates. Addition of cetyltrimethylammonium bromide as a phase transfer catalyst on in situ transesterification of Jatropha curcas L. with alkaline ethanol was investigated. Use of cetyltrimethylammonium bromide increased the yield of fatty acid ethyl esters. Optimum operating

Sintayehu Mekuria Hailegiorgis; Shuhaimi Mahadzir; Duvvuri Subbarao

2011-01-01

59

Electron transfer and reaction mechanism of laccases.  

PubMed

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

Jones, Stephen M; Solomon, Edward I

2015-03-01

60

Promoting Interspecies Electron Transfer with Biochar  

PubMed Central

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

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

2014-01-01

61

Cinchona alkaloid-based polymer-bound phase-transfer catalysts: Efficient enantioselective alkylation of benzophenone imine of glycine esters  

Microsoft Academic Search

Cross-linked polystyrene-bound and poly(ethylene glycol)-bound phase-transfer catalysts as well as homopolymers of cinchona alkaloid derivatives have been synthesised. Both soluble and insoluble polymers have been investigated. The enantioselective alkylation of N-diphenyl methylene glycine t-butyl ester has been successfully carried out in heterogeneous and homogeneous systems. High enantioselectivities (up to 96%) have been obtained. The polymer-bound catalysts have been easily recovered

Baptiste Thierry; Jean-Christophe Plaquevent; Dominique Cahard

2005-01-01

62

Chiral salen–metal complexes as novel catalysts for the asymmetric synthesis of ?-amino acids under phase transfer catalysis conditions  

Microsoft Academic Search

Chiral salen–metal complexes have been tested as catalysts for the C-alkylation of Schiff's bases of alanine and glycine esters with alkyl bromides under phase-transfer conditions (solid sodium hydroxide, toluene, ambient temperature, 1–10mol% of the catalyst). The best catalyst, which was derived from a Cu(II) complex of (1R, 2R or 1S,2S)-[N,N?-bis(2?-hydroxybenzylidene)]-1,2-diaminocyclohexane, gave ?-amino and ?-methyl-?-amino acids with enantiomeric excesses of 70–96%.

Yuri N Belokon; Michael North; Tatiana D Churkina; Nikolai S Ikonnikov; Victor I Maleev

2001-01-01

63

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

64

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. PMID:21446721

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

2011-01-01

65

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

PubMed Central

In the photosynthetic photosystem II, electrons are transferred from the manganese-containing oxygen evolving complex (OEC) to the oxidized primary electron-donor chlorophyll P680•+ by a proton-coupled electron transfer process involving a tyrosine-histidine pair. Proton transfer from the tyrosine phenolic group to a histidine nitrogen positions the redox potential of the tyrosine between those of P680•+ and the OEC. We report the synthesis and time-resolved spectroscopic study of a molecular triad that models this electron transfer. The triad consists of a high-potential porphyrin bearing two pentafluorophenyl groups (PF10), a tetracyanoporphyrin electron acceptor (TCNP), and a benzimidazole-phenol secondary electron-donor (Bi-PhOH). Excitation of PF10 in benzonitrile is followed by singlet energy transfer to TCNP (? = 41 ps), whose excited state decays by photoinduced electron transfer (? = 830 ps) to yield . A second electron transfer reaction follows (? < 12 ps), giving a final state postulated as BiH+-PhO•-PF10-TCNP•-, in which the phenolic proton now resides on benzimidazole. This final state decays with a time constant of 3.8 ?s. The triad thus functionally mimics the electron transfers involving the tyrosine-histidine pair in PSII. The final charge-separated state is thermodynamically capable of water oxidation, and its long lifetime suggests the possibility of coupling systems such as this system to water oxidation catalysts for use in artificial photosynthetic fuel production. PMID:22566659

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

2012-01-01

66

Heat transfer and thermographic analysis of catalyst surface during multiphase phenomena under spray-pulsed conditions for dehydrogenation of cyclohexane over Pt catalysts.  

PubMed

Dehydrogenation of cyclohexane over Pt/alumite and Pt/activated carbon catalysts has been carried out for hydrogen storage and supply to fuel cell applications. An unsteady state has been created using spray pulsed injection of cyclohexane over the catalyst surface to facilitate the endothermic reaction to occur efficiently. Higher temperature of the catalyst surface is more favorable for the reaction, thus the heat transfer phenomena and temperature profile under alternate wet and dry conditions created using spray pulsed injection becomes important. IR thermography has been used for monitoring of temperature profile of the catalyst surface simultaneously with product analysis. The heat flux from the plate-type heater to the catalyst has been estimated using a rapid temperature recording and thermocouple arrangement. The estimated heat flux under transient conditions was in the range of 10-15 kW/m(2), which equates the requirement for endothermic reactions to the injection frequency of 0.5 Hz, as used in this study. The analysis of temperature profiles, reaction products over two different supports namely activated carbon cloth and alumite, reveals that the more conductive support such as alumite is more suitable for dehydrogenation of cyclohexane. PMID:16494328

Biniwale, Rajesh B; Kariya, N; Yamashiro, H; Ichikawa, Masaru

2006-02-23

67

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

68

Electron Transfer and Localization in Endohederal Metallofullerenes  

SciTech Connect

Endohedral metallofullerenes constitute an appealing class of nanoscale building blocks for fabrication of a wide range of noval materials. One open question of fundamental importance is the precise nature of charge redistribution with the carbon cages (Cn) upon metal encapsulation. Using ab initio density functional theory, we systematically study the electronic structure of metallofullerenes, focusing on the spatial charge redistribution. For all large metallofullerenes (n >32), the valence electrons of the metal atoms are all transferred to the fullerene states. Surprisingly, the transferred charge is found to be highly localized inside the cage near the metal cations, rather than uniformly distributed on the surfaces of the carbon cage as traditionally belied. This counterintuitive charge localization picture is attributed to the strong metal-cage interactions within the systems. These findings may prove to be instrumental in the design of novel fullerene-based functional nanomaterials. 1Supported by the DMSE program and grant no. DE-FG02-05ER46209 of USDOE, grant no. DMR-0606485 of USNSF, and NSF of China.

Yang, Shenyuan [ORNL; Yoon, Mina [ORNL; Hicke, Christian [ORNL; Zhang, Zhenyu [ORNL

2008-01-01

69

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

SciTech Connect

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

Hong, Woo-Pyo [Department of Electronics Engineering, Catholic University of Daegu, Hayang 712-702 (Korea, Republic of); Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180-3590 (United States); Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 426-791 (Korea, Republic of)

2014-08-15

70

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

NASA Astrophysics Data System (ADS)

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

Hong, Woo-Pyo; Jung, Young-Dae

2014-08-01

71

Contributing Gifts of Stock TO ELECTRONICALLY TRANSFER STOCK  

E-print Network

2-12/LM Contributing Gifts of Stock TO ELECTRONICALLY TRANSFER STOCK Your broker can electronically transfer shares of stock to the University of Missouri. You will need the following information to complete) 882-2316 TO MANUALLY TRANSFER AN ENTIRE STOCK CERTIFICATE Step 1: Obtain and complete a stock power

Missouri-Rolla, University of

72

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. PMID:16144411

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

2005-01-01

73

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. PMID:20380445

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

2010-01-01

74

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

75

Electron Transfer Dissociation Mass Spectrometry in Proteomics  

PubMed Central

Mass spectrometry has rapidly evolved to become the platform of choice for proteomic analysis. While CID remains the major fragmentation method for peptide sequencing, electron transfer dissociation (ETD) is emerging as a complementary method for characterization of peptides and post-translational modifications (PTMs). Here, we review the evolution of ETD and some of its newer applications including characterization of PTMs, non-tryptic peptides and intact proteins. We will also discuss some of the unique features of ETD such as its complementarity with CID and the use of alternating CID/ETD along with issues pertaining to analysis of ETD data. The potential of ETD for applications such as multiple reaction monitoring and proteogenomics in the future will also be discussed. PMID:22246976

Kim, Min-Sik; Pandey, Akhilesh

2013-01-01

76

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

77

Single-element Electron-transfer Optical Detector System  

NASA Technical Reports Server (NTRS)

An optical detector system includes an electrically resistive screen that is substantially transparent to radiation energy having a wavelength of interest. An electron transfer element (e.g., a low work function photoactive material or a carbon nanotube (CNT)-based element) has a first end and a second end with its first end spaced apart from the screen by an evacuated gap. When radiation energy passes through the screen with a bias voltage being applied thereto, transfer of electrons through the electron transfer element is induced from its first to its second end such that a quantity indicative of the electrons transferred can be detected.

Jordan, Jeffrey D. (Inventor)

2004-01-01

78

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 time scales and are often strongly coupled. As a result, the theoretical description of these processes requires a combination of quantum and classical methods. This Perspective discusses three of the current theoretical challenges in the field of PCET. The first challenge is the calculation of electron proton nonadiabatic effects, which are significant for these reactions because the hydrogen tunneling is often faster than the electronic transition. The second challenge is the modeling of electron transfer coupled to proton transport along hydrogen-bonded networks. The third challenge is the simulation of the ultrafast dynamics of nonequilibrium photoinduced PCET reactions in solution. Insights provided by theoretical studies may assist in the design of more effective catalysts for energy conversion processes. The proton relay portion of this review is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences.

Hammes-Schiffer, Sharon

2011-06-16

79

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

80

Photochemical Generation of Strong One-Electron Reductants via Light-Induced Electron Transfer with Reversible Donors Followed by Cross Reaction with Sacrificial Donors.  

PubMed

This work illustrates a modified approach for employing photoinduced electron transfer reactions coupled to secondary irreversible electron transfer processes for the generation of strongly reducing equivalents in solution. Through irradiation of [Ru(LL)3](2+) (LL= diimine ligands) with tritolylamine (TTA) as quencher and various alkyl amines as sacrificial electron donors, yields in excess of 50% can be achieved for generation of reductants with E(0)(2+/1+) values between -1.0 and -1.2 V vs NHE. The key to the system is the fact that the TTA cation radical, formed in high yield in reaction with the photoexcited [Ru(LL)3](2+) complex, reacts irreversibly with various sacrificial electron donating amines that are kinetically unable to directly react with the photoexcited complex. The electron transfer between the TTA(+) and the sacrificial amine is an energetically uphill process. Kinetic analysis of these parallel competing reactions, consisting of bimolecular and pseudo first-order reactions, allows determination of electron transfer rate constants for the cross electron transfer reaction between the sacrificial donor and the TTA(+). A variety of amines were examined as potential sacrificial electron donors, and it was found that tertiary 1,2-diamines are most efficient among these amines for trapping the intermediate TTA(+). This electron-donating combination is capable of supplying a persistent reducing flux of electrons to catalysts used for hydrogen production. PMID:24882233

Shan, Bing; Schmehl, Russell

2014-11-13

81

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

82

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

83

Electron transfer and protein engineering studies of the soluble methane monooxygenase from Methylococcus capsulatus (Bath)  

E-print Network

Chapter 1. Introduction: Electron Transfer in Biological Systems In many biological processes, including oxidative phosphorylation and photosynthesis, electron transfer reactions play vital roles. Electrons must be transported ...

Blazyk, Jessica L. (Jessica Lee), 1974-

2003-01-01

84

Electron transfer processes in double lanthanide activated YPO 4  

NASA Astrophysics Data System (ADS)

This work reviews electron transfer processes in double lanthanide doped YPO 4 studied using a diversity of optical techniques. The aim is to identify those transfer processes and to relate them with the location of lanthanide electron donor and lanthanide electron acceptor states within the bandgap of YPO 4. Electron transfer from the valence band to a trivalent lanthanide impurity or to the conduction band was studied by traditional single photon excitation on single lanthanide doped YPO 4. This work reports on YPO 4 doped with the electron donor Ce 3+ and co-doped with an electron acceptor Pr 3+, Er 3+, Nd 3+, Ho 3+, Dy 3+, Tm 3+, or Sm 3+ studied by means of thermoluminescence and optical stimulated luminescence techniques. The same samples were studied by pump and probe two photon spectroscopy utilizing synchrotron photons to transfer electrons from Ce 3+ to Ln 3+ defects and 445 nm laser diode to probe the concentration of created Ln 2+.

Dorenbos, P.; Bos, A. J. J.; Poolton, N. R. J.

2011-05-01

85

Single Molecule Electron Transfer Process of Ruthenium Complexes.  

SciTech Connect

Transition metal complexes such as ruthenium complexes, having metal-to-ligand charge transfer states, are extensively used in solar energy conversion and electron transfer in biological systems and at interfaces. The dynamics of metal-to-ligand charge transfer and subsequent intermolecular, intramolecular, and interfacial electron transfer processes can be highly complex and inhomogeneous, especially when molecules are involved in interactions and perturbations from heterogeneous local environments and gated by conformation fluctuations. We have employed the single-molecule spectroscopy, a powerful approach for inhomogeneous systems to study the electron transfer dynamics of ruthenium complexes. We have applied a range of statistical analysis methods to reveal nonclassical photon emission behavior of the single ruthenium complex, i.e., photon antibunching, and photophysical ground-state recovering dynamics on a microsecond time scale. The use of photon antibunching to measure phosphorescence lifetimes and single-molecule electron transfer dynamics at room temperature is demonstrated.

Hu, Dehong; Lu, H PETER.

2006-03-01

86

Mechanism of Intermolecular Electron Transfer in Bionanostructures  

NASA Astrophysics Data System (ADS)

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

Gruodis, A.; Galikova, N.; Šarka, K.; Saul?, R.; Batiuškait?, D.; Saulis, G.

87

Charge remote fragmentation in electron capture and electron transfer dissociations  

PubMed Central

Secondary fragmentations of three synthetic peptides (human ?A crystallin peptide 1-11, the deamidated form of human ?B2 crystallin peptide 4-14, and amyloid ? peptide 25-35) were studied in both electron capture dissociation (ECD) and electron transfer dissociation (ETD) mode. In ECD, in addition to c and z• ion formations, charge remote fragmentations (CRF) of z• ions were abundant, resulting in internal fragment formation or partial/entire side chain losses from amino acids, sometimes several residues away from the backbone cleavage site, and to some extent multiple side chain losses. The internal fragments were observed in peptides with basic residues located in the middle of the sequences, which was different from most tryptic peptides with basic residues located at the C-terminus. These secondary cleavages were initiated by hydrogen abstraction at the ?-, ?-, or ?-position of the amino acid side chain. In comparison, ETD generates fewer CRF fragments than ECD. This secondary cleavage study will facilitate ECD/ETD spectra interpretation, and help de novo sequencing and database searching. PMID:20171118

Li, Xiaojuan; Lin, Cheng; Han, Liang; Costello, Catherine E.; O’Connor, Peter B.

2010-01-01

88

Long-distance electron transfer from a triplet excited state  

NASA Astrophysics Data System (ADS)

Electron transfer from the triplet excited state of N,N,N',N'-tetramethylphenylene diamine to phthalic anhydride has been monitored by phosphorescence emission decay. The kinetics of the transfer process were observed directly and the rate constant depends exponentially on the reacting distance, k(r) = 1 × 10 4 exp(-0.58 r) s -1. The electron transfer rate has been found to be invariant over the temperature interval 77-143 K.

Murtagh, James; Thomas, J. Kerry

89

Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions  

PubMed Central

The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection by NMR. The catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R = PCy3 or PPh3; IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene and a phosphine, are used here to catalyze SABRE. They react with acetonitrile and pyridine to produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 and [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand exchange on a time scale commensurate with observation of the SABRE effect, which is illustrated here by the observation of both pyridine and acetonitrile HP. In this study, the required symmetry breaking that underpins SABRE is provided for by the use of chemical inequivalence rather than the previously reported magnetic inequivalence. As a consequence, we show that the ligand sphere of the polarization transfer catalyst itself becomes hyperpolarized and hence that the high-sensitivity detection of a number of reaction intermediates is possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, and [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies are also described that employ the deuterium-labeled substrates CD3CN and C5D5N, and the labeled ligands P(C6D5)3 and IMes-d22, to demonstrate that dramatically improved levels of HP can be achieved as a consequence of reducing proton dilution and hence polarization wastage. By a combination of these studies with experiments in which the magnetic field experienced by the sample at the point of polarization transfer is varied, confirmation of the resonance assignments is achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 is examined, its hydride ligand signals are shown to become visible through para-hydrogen-induced polarization rather than SABRE. PMID:24215616

2013-01-01

90

Integrating proton coupled electron transfer (PCET) and excited states  

SciTech Connect

In many of the chemical steps in photosynthesis and artificial photosynthesis, proton coupled electron transfer (PCET) plays an essential role. An important issue is how excited state reactivity can be integrated with PCET to carry out solar fuel reactions such as water splitting into hydrogen and oxygen or water reduction of CO{sub 2} to methanol or hydrocarbons. The principles behind PCET and concerted electron–proton transfer (EPT) pathways are reasonably well understood. In Photosystem II antenna light absorption is followed by sensitization of chlorophyll P{sub 680} and electron transfer quenching to give P{sub 680}{sup +}. The oxidized chlorophyll activates the oxygen evolving complex (OEC), a CaMn4 cluster, through an intervening tyrosine–histidine pair, Y{sub Z}. EPT plays a major role in a series of four activation steps that ultimately result in loss of 4e{sup ?}/4H{sup +} from the OEC with oxygen evolution. The key elements in photosynthesis and artificial photosynthesis – light absorption, excited state energy and electron transfer, electron transfer activation of multiple-electron, multiple-proton catalysis – can also be assembled in dye sensitized photoelectrochemical synthesis cells (DS-PEC). In this approach, molecular or nanoscale assemblies are incorporated at separate electrodes for coupled, light driven oxidation and reduction. Separate excited state electron transfer followed by proton transfer can be combined in single semi-concerted steps (photo-EPT) by photolysis of organic charge transfer excited states with H-bonded bases or in metal-to-ligand charge transfer (MLCT) excited states in pre-associated assemblies with H-bonded electron transfer donors or acceptors. In these assemblies, photochemically induced electron and proton transfer occur in a single, semi-concerted event to give high-energy, redox active intermediates.

Gagliardi, Christopher J.; Westlake, Brittany C.; Kent, Caleb A.; Paul, Jared J.; Papanikolas, John M.; Meyer, Thomas J.

2010-01-01

91

N-doped graphene as an electron donor of iron catalysts for CO hydrogenation to light olefins.  

PubMed

N-doped graphene used as an efficient electron donor of iron catalysts for CO hydrogenation can achieve a high selectivity of around 50% for light olefins, significantly superior to the selectivity of iron catalysts on conventional carbon materials, e.g. carbon black with a selectivity of around 30% at the same reaction conditions. PMID:25407097

Chen, Xiaoqi; Deng, Dehui; Pan, Xiulian; Hu, Yongfeng; Bao, Xinhe

2015-01-01

92

Influence of intercrystalline mass transfer on catalytic properties of Pt/H-ZSM-5/Al sub 2 O sub 3 catalyst  

SciTech Connect

Influence of intercrystalline (macropore) mass transfer on the catalytic activity and product selectivity in o-xylene isomerization, isooctane cracking, and methanol-to-aromatics conversion reactions on Pt/H-ZSM-5/Al{sub 2}O{sub 3} has been investigated by varying the catalyst particle size. Effect of poisoning of both the inter- and intracrystalline acid sites of the catalyst on its catalytic activity and selectivity has also been investigated. The effective intercrystalline diffusivity of the zeolite catalyst under reaction conditions has been determined by studying a first-order reaction cracking of isooctane (which does not penetrate the zeolite channels) using the catalysts of different particle sizes and determining the effectiveness factor of the catalyst. Both the activity and the selectivity of the catalyst in the above reactions are strongly influenced by the intercrystalline mass transfer.

Choudhary, V.R.; Akolekar, D.B. (National Chemical Lab., Pune (India))

1989-03-01

93

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

94

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. PMID:21686056

Mayer, James M.

2011-01-01

95

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

PubMed

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. PMID:21686056

Mayer, James M

2011-01-01

96

Understanding catalyst behavior during in situ heating through simultaneous secondary and transmitted electron imaging  

NASA Astrophysics Data System (ADS)

By coupling techniques of simultaneous secondary (SE) and transmitted electron (TE) imaging at high resolution in a modern scanning transmission electron microscope (STEM), with the ability to heat specimens using a highly stable MEMS-based heating platform, we obtained synergistic information to clarify the behavior of catalysts during in situ thermal treatments. Au/iron oxide catalyst 'leached' to remove surface Au was heated to temperatures as high as 700°C. The Fe2O3 support particle structure tended to reduce to Fe3O4 and formed surface terraces; the formation, coalescence, and mobility of 1- to 2-nm particles on the terraces were characterized in SE, STEM-ADF, and TEM-BF modes. If combined with simultaneous nanoprobe spectroscopy, this approach will open the door to a new way of studying the kinetics of nano-scaled phenomena.

Howe, Jane Y.; Allard, Lawrence F.; Bigelow, Wilbur C.; Demers, Hendrix; Overbury, Steven H.

2014-11-01

97

A molecular shift register based on electron transfer  

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

98

Tin passivation of vanadium in metal-contaminated fluid-cracking catalysts: Electron paramagnetic resonance studies  

Microsoft Academic Search

Vanadium interactions with model fluid cracking catalysts and vanadium passivation with tin have been monitored by electron paramagnetic resonance (EPR). Model systems such as EuY, amorphous aluminosilicate gels, and EuY-gel mixtures have been investigated. Vanadium, introduced in the form of vanadyl naphthenate, is stabilized on the zeolite primarily as octahedrally coordinated VO{sup 2+} cations. In contrast, the gel preferentially sorbs

M. W. Anderson; S. L. Suib; M. L. Occelli

1990-01-01

99

Engineering of an alternative electron transfer path in photosystem II  

PubMed Central

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

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

2010-01-01

100

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. PMID:19331417

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

2009-01-01

101

Electron Transfer-Initiated Epoxidation and Isomerization Chain Reactions of ?-Caryophyllene.  

PubMed

The abundant sesquiterpene ?-caryophyllene can be epoxidized by molecular oxygen in the absence of any catalyst. In polar aprotic solvents, the reaction proceeds smoothly with epoxide selectivities exceeding 70?%. A mechanistic study has been performed and the possible involvement of free radical, spin inversion, and electron transfer mechanisms is evaluated using experimental and computational methods. The experimental data-including a detailed reaction product analysis, studies on reaction parameters, solvent effects, additives and an electrochemical investigation-all support that the spontaneous epoxidation of ?-caryophyllene constitutes a rare case of unsensitized electron transfer from an olefin to triplet oxygen under mild conditions (80?°C, 1?bar?O2 ). As initiation of the oxygenation reaction, the formation of a caryophyllene-derived radical cation via electron transfer is proposed. This radical cation reacts with triplet oxygen to a dioxetane via a chain mechanism with chain lengths exceeding 100 under optimized conditions. The dioxetane then acts as an in?situ-formed epoxidizing agent. Under nitrogen atmosphere, the presence of a one-electron acceptor leads to the selective isomerization of ?-caryophyllene to isocaryophyllene. Observations indicate that this isomerization reaction is a novel and elegant synthetic pathway to isocaryophyllene. PMID:25430783

Steenackers, Bart; Campagnol, Nicolò; Fransaer, Jan; Hermans, Ive; De Vos, Dirk

2014-11-27

102

Electrostatic influence on energetics of electron transfer reactions.  

PubMed Central

Electron transfer chains in biological systems must operate efficiently to satisfy metabolic energetic requirements. The component proteins in these chains are expected to exhibit characteristic structural features that facilitate electron transfer to the appropriate donor and acceptor proteins. A survey of soluble one-electron carrier proteins indicates a significant tendency for lower potential proteins to be more negatively charged than higher potential proteins. Consideration of the electrostatic consequences of this pattern of charge asymmetry suggests that the reduction potential difference between the two proteins will be minimized in the precursor complex associated with electron transfer. An equivalent statement is that the change in free energy accompanying electron transfer in the complex will approach zero. This behavior is consistent with theoretical arguments advanced by Albery and Knowles [Albery, W. J. & Knowles, J. R. (1976) Biochemistry 15, 5631-5640], which suggest that for the most efficient enzymes, the free energy difference between enzyme-bound species should approach zero. A more general derivation of this prediction is provided. The observed charge asymmetry in electron transfer proteins provides a structural mechanism for satisfying this requirement, thus accelerating the overall rate of electron transfer. PMID:3858805

Rees, D C

1985-01-01

103

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

Federal Register 2010, 2011, 2012, 2013

...Electronic Funds Transfer (EFT) Market Research Study AGENCY: Financial Management...Electronic Funds Transfer (EFT) Market Research Study.'' DATES: Written comments...Electronic Funds Transfer (EFT) Market Research Study. OMB Number:...

2012-11-28

104

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

...2014-10-01 2014-10-01 false Health care electronic funds transfers (EFT... ADMINISTRATIVE REQUIREMENTS Health Care Electronic Funds Transfers (EFT...Remittance Advice § 162.1601 Health care electronic funds transfers...

2014-10-01

105

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

Federal Register 2010, 2011, 2012, 2013

...Collection of Information: ``Notice of Reclamation Electronic Funds Transfer, Federal...concerning forms FMS-I33, ``Notice of Reclamation. Electronic Funds Transfer, Federal...described below: Title: ``Notice of Reclamation, Electronic Funds Transfer,...

2012-04-12

106

12 CFR 205.15 - Electronic fund transfer of government benefits.  

Code of Federal Regulations, 2010 CFR

...2010-01-01 2010-01-01 false Electronic fund transfer of government benefits...GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of government...

2010-01-01

107

12 CFR 205.15 - Electronic fund transfer of government benefits.  

Code of Federal Regulations, 2011 CFR

...2011-01-01 2011-01-01 false Electronic fund transfer of government benefits...GOVERNORS OF THE FEDERAL RESERVE SYSTEM ELECTRONIC FUND TRANSFERS (REGULATION E) § 205.15 Electronic fund transfer of government...

2011-01-01

108

Steam reforming of n-hexane on pellet and monolithic catalyst beds. A comparative study on improvements due to heat transfer  

NASA Technical Reports Server (NTRS)

Monolithic catalysts with higher available active surface areas and better thermal conductivity than conventional pellets beds, making possible the steam reforming of fuels heavier than naphtha, were examined. Performance comparisons were made between conventional pellet beds and honeycomb monolith catalysts using n-hexane as the fuel. Metal-supported monoliths were examined. These offer higher structural stability and higher thermal conductivity than ceramic supports. Data from two metal monoliths of different nickel catalyst loadings were compared to pellets under the same operating conditions. Improved heat transfer and better conversion efficiencies were obtained with the monolith having higher catalyst loading. Surface-gas interaction was observed throughout the length of the monoliths.

1981-01-01

109

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

2013-05-01

110

Global electronic funds transfer between small and medium sized companies  

E-print Network

Cross-border electronic funds transfer is a rapidly expanding field for business and consumer payments. Large multi-national corporations have been able to invest the capital necessary to create infrastructures or work ...

Stovall, Shawn Eric

2006-01-01

111

75 FR 51707 - Electronic Funds Transfer of Depository Taxes  

Federal Register 2010, 2011, 2012, 2013

...Funds Transfer of Depository Taxes AGENCY: Internal Revenue Service...regulations relating to Federal tax deposits (FTDs) by Electronic...hearing. Drafting Information The principal author of these proposed regulations...Subjects 26 CFR Part 1 Income taxes, Reporting and...

2010-08-23

112

An Auger electron spectroscopy study of the activation of iron Fischer-Tropsch catalysts. II. Carbon monoxide activation  

SciTech Connect

Activation procedures can have a dramatic effect on the activity of iron-based catalysts for Fischer-Tropsch (F-T) synthesis. CO conversion over a 100 Fe/3 Cu/0.2 K catalyst (parts by weight) can vary by nearly a factor of 3, depending on activation treatment. In contrast, a 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst displays little dependence of F-T activity on activation treatment. An ultra-high vacuum surface analysis chamber coupled to an atmospheric reactor has been used to measure the surface composition of these catalysts following activation in carbon monoxide at 280[degrees]C, while transmission electron microscopy (TEM) and BET surface area measurements have been used to investigate catalyst morphology. CO activation of the 100 Fe/5 Cu/4.2 K/25 SiO[sub 2] catalyst at 280[degrees]C results in partial reduction of iron to a mixture of Fe[sub x]O and Fe[sub 3]O[sub 4], and an overall surface composition very similar to that obtained following hydrogen activation at 220 or 280[degrees]C, consistent with the invariance of F-T activity with activation treatment for this catalyst. Activation of the 100 Fe/3 Cu/0.2 K catalyst in CO at 280[degrees]C results in the formation of iron carbide particles, growth of graphitic carbon (C[sub g]) filaments, and formation of a thick, porous, C[sub g] layer covering the carbide particles. Differences in F-T activity between the hydrogen- and CO-activated 100 Fe/3 Cu/0.2 K catalyst are discussed in terms of surface composition and catalyst morphology. The difference in sensitivity of the two catalysts to activation conditions is related to differences in the extent of reduction of the catalysts. 45 refs., 4 figs., 1 tab.

Sault, A.G. (Sandia National Laboratories, Albuquerque, NM (United States)); Datye, A.K. (Univ. of New Mexico, Albuquerque (United States))

1993-03-01

113

Chemical Reaction Dynamics accompanying Electron-Transfer Osamu SUGINO  

E-print Network

transfer as does in the redox, while the latter appears in the photochemical reactions. Simulating bothChemical Reaction Dynamics accompanying Electron-Transfer Osamu SUGINO Institute for Solid State Physics, the University of Tokyo 5-1-5 Kashiwanoha, Chiba 277-8581 1. Introduction Many chemical reactions

Katsumoto, Shingo

114

Protein Conformational Dynamics Probed by Single-Molecule Electron Transfer  

Microsoft Academic Search

Electron transfer is used as a probe for angstrom-scale structural changes in single protein molecules. In a flavin reductase, the fluorescence of flavin is quenched by a nearby tyrosine residue by means of photo-induced electron transfer. By probing the fluorescence lifetime of the single flavin on a photon-by-photon basis, we were able to observe the variation of flavin-tyrosine distance over

Haw Yang; Guobin Luo; Pallop Karnchanaphanurach; Tai-Man Louie; Ivan Rech; Sergio Cova; Luying Xun; X. Sunney Xie

2003-01-01

115

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

116

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

117

Electron beam induced radiation damage in the catalyst layer of a proton exchange membrane fuel cell.  

PubMed

Electron microscopy is an essential tool for the evaluation of microstructure and properties of the catalyst layer (CL) of proton exchange membrane fuel cells (PEMFCs). However, electron microscopy has one unavoidable drawback, which is radiation damage. Samples suffer temporary or permanent change of the surface or bulk structure under radiation damage, which can cause ambiguity in the characterization of the sample. To better understand the mechanism of radiation damage of CL samples and to be able to separate the morphological features intrinsic to the material from the consequences of electron radiation damage, a series of experiments based on high-angle annular dark-field-scanning transmission scanning microscope (HAADF-STEM), energy filtering transmission scanning microscope (EFTEM), and electron energy loss spectrum (EELS) are conducted. It is observed that for thin samples (0.3-1 times ?), increasing the incident beam energy can mitigate the radiation damage. Platinum nanoparticles in the CL sample facilitate the radiation damage. The radiation damage of the catalyst sample starts from the interface of Pt/C or defective thin edge and primarily occurs in the form of mass loss accompanied by atomic displacement and edge curl. These results provide important insights on the mechanism of CL radiation damage. Possible strategies of mitigating the radiation damage are provided. PMID:23897710

He, Qianping; Chen, Jihua; Keffer, David J; Joy, David C

2014-01-01

118

Femtosecond Dynamics of DNA Photolyase:  Energy Transfer of Antenna Initiation and Electron Transfer of Cofactor Reduction  

Microsoft Academic Search

Photolyase is an enzyme that uses light energy to repair UV-induced DNA damage. We report here our femtosecond studies of the complex dynamics of energy and electron transfer in E. coli photolyase. Under physiological conditions, the excitation energy transfer from the antenna molecule methenyltetrahydrofolate (MTHF) to the fully reduced cofactor flavin (FADH - ) occurs in 292 ps, but it

Chaitanya Saxena; Aziz Sancar; Dongping Zhong

2004-01-01

119

Ultrasound-assisted phase-transfer catalysis: benzoylation of sodium 4-acetylphenoxide by dual-site phase-transfer catalyst in a tri-liquid system.  

PubMed

A novel dual-site phase-transfer catalyst (PTC) was prepared and used to conduct the benzoylation of sodium 4-acetylphenoxide by ultrasound-assisted third-liquid phase-transfer catalysis. The catalyst 1,4-bis(tributylammoniomethyl)benzene dibromide (BTBAMBB) was synthesized from the reaction of p-xylylene dibromide and tributylamine in toluene at 70°C. The dual-site PTC was employed to form the third-liquid phase by extra addition of 0.04-0.05 mol of NaCl into 10 cm(3) of water. In the condition of 0.0425 mol of NaCl at 30°C, the catalytic intermediate in the third-liquid phase reached a maximum value. Almost 80% of the catalyst was transferred from the aqueous phase into the third-liquid phase. The distributions of the catalytic intermediate and dual-site PTC between phases and the kinetics of benzoylation of sodium 4-acetylphenoxide catalyzed by BTBAMBB with ultrasound irradiation were performed. The pseudo-first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (28 kHz/300 W) in a batch reactor, the yield of product 4-acetylphenyl benzoate in the organic phase was 98.1% in 2 min at 30°C and 250 rpm with the apparent rate constant k(app) to be 0.0075 s(-1), which was 6 times faster than that without using ultrasound (yield=14.4%, k(app)=0.0013 s(-1)). The present study provides a green method to synthesize esters by ultrasound-assisted third-liquid phase-transfer catalysis. PMID:20667759

Yang, Hung-Ming; Chiu, Chun-Cheng

2011-01-01

120

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

PubMed Central

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.

2012-01-01

121

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...

122

Polyelectrolyte effects on electron transfer process  

NASA Astrophysics Data System (ADS)

Pulse radiolysis and gamma radiolysis have been used to study the kinetics of electron scavenging by viologens bound to poly(styrenesulfonate)-(PSS) in the temperature range 6-298 K. The rate of radiation-induced one-electron reduction of methylviologen (MV 2+), diquat (DQ 2+), ethidium bromide (EB), ruthenium tris(2,2'-bipyridine) (Ru(bpy) 32+) is greatly inhibited by the presence of polyelectrolyte. The origin of the inhibition effect is shown to be determined by electrostatic forces (repulsion of electrons by the negative potential field of polyelectrolyte with trapped scavenger) and by geometric factor (caused by overlapping of the capture spheres of scavenger molecules on the PSS chain).

Wolszczak, Marian; Hankiewicz, Ewa; Kroh, Jerzy

1997-01-01

123

Stable electron emission from ZnO nanoemitters grown with pseudo-catalyst  

NASA Astrophysics Data System (ADS)

A stable electron emission was obtained from ZnO nanoemitters with catalyst-free vapor phase transport to avoid impurity doping from the catalyst itself. The shape of nanoemitters were related to the growth conditions. Nanoemitters with a hexagonal dipyramidal structure and a bead-chain-like shape were vertically grown; the wedged-thread shaped nanoemitters were also found. The estimated angle of the wedge was approximately 120°. Hexagonal-prismatic tapered nanoemitters appeared while lateral \\{ 01\\bar{1}0\\} surfaces were grown. The growth of cylindrical round-top nanoemitters was observed as well. High aspect ratio of sheet- and leaf-shaped nanoemitters were grown at a high O2/N2 flow ratio of 60 : 70. The formation mechanisms of nanoemitters were investigated, and the electron emission properties were discussed as well. The turn-on electric field at an emission current density of 0.1 µA/cm2 was 0.18 MV/m. The variation of emission current was less than 14% during 5 h of measurement time, showing good stable in electron emission.

Yang, Su-Hua; Hsu, Yi-Ming; Tsai, Ming-Wei; Hsueh, Ting-Jen

2014-03-01

124

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

125

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

126

Photocurrent generation by direct electron transfer using photosynthetic reaction centres  

NASA Astrophysics Data System (ADS)

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

Mahmoudzadeh, A.; Saer, R.; Jun, D.; Mirvakili, S. M.; Takshi, A.; Iranpour, B.; Ouellet, E.; Lagally, E. T.; Madden, J. D. W.; Beatty, J. T.

2011-09-01

127

Prediction of electronic component-board transient conjugate heat transfer  

Microsoft Academic Search

Numerical analysis of electronic component transient heat transfer has generally been confined to nonconjugate methods. This study discusses the need for conjugate (conduction\\/convection) analysis, both for component temperature and thermo-mechanical behavior prediction in operational, assembly and reliability qualification environments. The capability of computational fluid dynamics (CFD) analysis to predict component transient conjugate heat transfer is investigated using an industry-standard CFD

Valérie Eveloy; Peter Rodgers

2005-01-01

128

Direct and mediated electron transfer catalyzed by anionic tobacco peroxidase  

Microsoft Academic Search

The properties of anionic tobacco peroxidase (TOP) adsorbed on graphite electrode have been studied in direct and mediated\\u000a electron transfer in a wall-jet flow injection system. The percentage of tobacco peroxidase molecules active in directelectron\\u000a transfer is about 83%, which is higher than that for horeradish peroxidase (40–50%). This observation is explained in terms\\u000a of the lower degree of glycosylation

Florentina-Daniela Munteanu; Lo Gorton; Annika Lindgren; Tautgirdas Ruzgas; Jenny Emnéus; Elisabeth Csöregi; Irina G. Gazaryan; Igor V. Ouporov; Elena A. Mareeva; L. Mark Lagrimini

2000-01-01

129

Probing electron transfer dynamics of pyranine with reduced graphene oxide.  

PubMed

A stable reduced graphene oxide (rGO) was prepared and characterized by X-ray diffraction (XRD) and laser Raman spectroscopy. Steady state and time-resolved fluorescence quenching studies have been carried out to elucidate the process of electron transfer from excited pyranine (POH) into the rGO dispersion. POH adsorbed strongly on rGO dispersion with an apparent association constant of 33.4 (mg ml)(-1), and its fluorescence emission was quenched with an apparent association constant of 33.7 (mg ml)(-1). Picosecond lifetime measurements gave the rate constant for the electron transfer process from the excited singlet state of POH into the rGO dispersion as 8.8 × 10(9) s(-1). Laser flash photolysis studies demonstrated the formation of radicals for the evidence of electron transfer between POH and rGO. PMID:25168852

Asha Jhonsi, M; Nithya, C; Kathiravan, A

2014-10-14

130

Multi-Element Electron-Transfer Optical Detector System  

NASA Technical Reports Server (NTRS)

A multi-element optical detector system includes an electrically resistive screen that is substantially transparent to radiation energy having a wavelength of interest. A plurality of electron transfer elements (e.g., a low work function photoactive material or a carbon nanotube (CNT)-based element) are provided with each having a first end and a second end. The first end of each element is spaced apart from the screen by an evacuated gap. When the radiation energy passes through the screen with a bias voltage applied thereto, transfer of electrons through each element is induced from the first end to the second end such that a quantity indicative of the electrons transferred through each element can be detected.

Jordan, Jeffrey D. (Inventor)

2004-01-01

131

Auger-assisted electron transfer from photoexcited semiconductor quantum dots.  

PubMed

Although quantum confined nanomaterials, such as quantum dots (QDs) have emerged as a new class of light harvesting and charge separation materials for solar energy conversion, theoretical models for describing photoinduced charge transfer from these materials remain unclear. In this paper, we show that the rate of photoinduced electron transfer from QDs (CdS, CdSe, and CdTe) to molecular acceptors (anthraquinone, methylviologen, and methylene blue) increases at decreasing QD size (and increasing driving force), showing a lack of Marcus inverted regime behavior over an apparent driving force range of ?0-1.3 V. We account for this unusual driving force dependence by proposing an Auger-assisted electron transfer model in which the transfer of the electron can be coupled to the excitation of the hole, circumventing the unfavorable Franck-Condon overlap in the Marcus inverted regime. This model is supported by computational studies of electron transfer and trapping processes in model QD-acceptor complexes. PMID:24359156

Zhu, Haiming; Yang, Ye; Hyeon-Deuk, Kim; Califano, Marco; Song, Nianhui; Wang, Youwei; Zhang, Wenqing; Prezhdo, Oleg V; Lian, Tianquan

2014-03-12

132

Mimicking the antenna-electron transfer properties of photosynthesis  

PubMed Central

A molecular assembly based on derivatized polystyrene is described, which mimics both the light-harvesting and energy-conversion steps of photosynthesis. The system is unique in that the two key parts of a photosynthetic system are incorporated in a functional assembly constructed from polypyridine complexes of RuII. This system is truly artificial, as none of the components used in construction of the assembly are present in a natural photosynthetic system. Quantitative evaluation of the energy and electron transfer dynamics after transient irradiation by visible light offers important insights into the mechanisms of energy transport and electron transfer that lead to photosynthetic light-to-chemical energy conversion. PMID:10884400

Sykora, Milan; Maxwell, Kimberly A.; DeSimone, Joseph M.; Meyer, Thomas J.

2000-01-01

133

A role for excreted quinones in extracellular electron transfer  

NASA Astrophysics Data System (ADS)

Respiratory processes in bacteria are remarkable because of their ability to use a variety of compounds, including insoluble minerals, as terminal electron acceptors. Although much is known about microbial electron transport to soluble electron acceptors, little is understood about electron transport to insoluble compounds such as ferric oxides. In anaerobic environments, humic substances can serve as electron acceptors and also as electron shuttles to ferric oxides. To explore this process, we identified mutants in Shewanella putrefaciens that are unable to respire on humic substances. Here we show that these mutants contain disruptions in a gene that is involved in the biosynthesis of menaquinone. During growth, the wild type releases a menaquinone-related redox-active small molecule into the medium that complements the mutants. This finding raises the possibility that electron transfer to a variety of oxidants, including poorly soluble minerals, may be mediated by microbially excreted quinones that have yet to be identified.

Newman, Dianne K.; Kolter, Roberto

2000-05-01

134

Influence of intercrystalline mass transfer on catalytic properties of Pt\\/H-ZSM-5\\/Al sub 2 O sub 3 catalyst  

Microsoft Academic Search

Influence of intercrystalline (macropore) mass transfer on the catalytic activity and product selectivity in o-xylene isomerization, isooctane cracking, and methanol-to-aromatics conversion reactions on Pt\\/H-ZSM-5\\/AlâOâ has been investigated by varying the catalyst particle size. Effect of poisoning of both the inter- and intracrystalline acid sites of the catalyst on its catalytic activity and selectivity has also been investigated. The effective intercrystalline

V. R. Choudhary; D. B. Akolekar

1989-01-01

135

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

136

Mechanism of back electron transfer in an intermolecular photoinduced electron transfer reaction: solvent as a charge mediator.  

PubMed

Back electron transfer (BET) is one of the important processes that govern the decay of generated ion pairs in intermolecular photoinduced electron transfer reactions. Unfortunately, a detailed mechanism of BET reactions remains largely unknown in spite of their importance for the development of molecular photovoltaic structures. Here, we examine the BET reaction of pyrene (Py) and 1,4-dicyanobenzene (DCB) in acetonitrile (ACN) by using time-resolved near- and mid-IR spectroscopy. The Py dimer radical cation (Py2(·+)) and DCB radical anion (DCB(·-)) generated after photoexcitation of Py show asynchronous decay kinetics. To account for this observation, we propose a reaction mechanism that involves electron transfer from DCB(·-) to the solvent and charge recombination between the resulting ACN dimer anion and Py2(·+). The unique role of ACN as a charge mediator revealed herein could have implications for strategies that retard charge recombination in dye-sensitized solar cells. PMID:25044892

Narra, Sudhakar; Nishimura, Yoshifumi; Witek, Henryk A; Shigeto, Shinsuke

2014-10-01

137

Optical Measurements of Secondary Electron Transfer in Photosystem I  

Microsoft Academic Search

All known photosynthetic reaction centers have symmetric structures, using two similar or identical integral membrane subunits\\u000a to form a dimeric core, which binds the cofactors through which electrons are shuttled across the membrane. This symmetric\\u000a arrangement gives rise to two similar branches of cofactors, down which light-driven electron transfer could proceed. The\\u000a first three members of each branch are chlorins,

Fabrice Rappaport; Bruce A. Diner; Kevin Redding

138

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

139

Application Scope and Limitations of TADDOL-Derived Chiral Ammonium Salt Phase-Transfer Catalysts  

PubMed Central

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 ?-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

2014-01-01

140

Shewanella secretes flavins that mediate extracellular electron transfer  

E-print Network

. This approach detected redox-active mole- cules within biofilms, which were involved in electron transfer. Riboflavin adsorbed quickly to other surfaces of geochemi- cal interest, such as Fe(III) and Mn(IV) oxy and Lovley (5), Shewanella. alga BrY reduced iron oxides trapped within porous alginate beads. A more recent

Weiblen, George D

141

Dynamical arrest of electron transfer in liquid crystalline solvents.  

PubMed

We argue that electron transfer reactions in slowly relaxing solvents proceed in the nonergodic regime, making the reaction activation barrier strongly dependent on the solvent dynamics. For typical dielectric relaxation times of polar nematics, electron transfer reactions in the subnanosecond time scale fall into nonergodic regime in which nuclear solvation energies entering the activation barrier are significantly lower than their thermodynamic values. The transition from isotropic to nematic phase results in weak discontinuities of the solvation energies at the transition point and the appearance of solvation anisotropy weakening with increasing solute size. The theory is applied to analyze experimental kinetic data for the electron transfer kinetics in the isotropic phase of 5CB liquid crystalline solvent. We predict that the energy gap law of electron transfer reactions in slowly relaxing solvents is characterized by regions of fast change of the rate at points where the reaction switches between the ergodic and nonergodic regimes. The dependence of the rate on the donor-acceptor separation may also be affected in a way of producing low values for the exponential falloff parameter. PMID:16805631

Kapko, Vitaliy; Matyushov, Dmitry V

2006-07-01

142

D Simulation for Maximizing Electron Transfer Efficiency in Thick GEMS  

NASA Astrophysics Data System (ADS)

Thick GEM for UV detector applications must provide high detection efficiency for a single photoelectron produced by UV light. Electron Transfer Efficiency (ETE) of GEM detector determines the detection efficiency. We have used GARFIELD simulation for estimation of ETE at various operating parameters, which are to be optimized for high detection efficiency.

Garai, Baishali; Rajanna, K.; Radhakrishna, V.

2012-08-01

143

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

SciTech Connect

The long-term goal of the proposed research is to understand electron transfer dynamics in nanoparticle/liquid interface. This knowledge is essential to many semiconductor nanoparticle based devices, including photocatalytic waste degradation and dye sensitized solar cells.

Lian, Tianquan

2014-04-22

144

Shewanella secretes flavins that mediate extracellular electron transfer  

PubMed Central

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

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

2008-01-01

145

Electron-transfer reactions at the plasma-liquid interface.  

PubMed

Electrochemical reactions are normally initiated in solution by metal electrodes such as Pt, which are expensive and limited in supply. In this Communication, we demonstrate that an atmospheric-pressure microplasma can act as a gaseous, metal-free electrode to mediate electron-transfer reactions in aqueous solutions. Ferricyanide is reduced to ferrocyanide by plasma electrons, and the reduction rate is found to depend on discharge current. The ability to initiate and control electrochemical reactions at the plasma-liquid interface opens a new direction for electrochemistry based on interactions between gas-phase electrons and ionic solutions. PMID:21985430

Richmonds, Carolyn; Witzke, Megan; Bartling, Brandon; Lee, Seung Whan; Wainright, Jesse; Liu, Chung-Chiun; Sankaran, R Mohan

2011-11-01

146

Spin selectivity in electron transfer in photosystem I.  

PubMed

Photosystem I (PSI) is one of the most studied electron transfer (ET) systems in nature; it is found in plants, algae, and bacteria. The effect of the system structure and its electronic properties on the electron transfer rate and yield was investigated for years in details. In this work we show that not only those system properties affect the ET efficiency, but also the electrons' spin. Using a newly developed spintronic device and a technique which enables control over the orientation of the PSI monolayer relative to the device (silver) surface, it was possible to evaluate the degree and direction of the spin polarization in ET in PSI. We find high-spin selectivity throughout the entire ET path and establish that the spins of the electrons being transferred are aligned parallel to their momenta. The spin selectivity peaks at 300?K and vanishes at temperatures below about 150?K. A mechanism is suggested in which the chiral structure of the protein complex plays an important role in determining the high-spin selectivity and its temperature dependence. Our observation of high light induced spin dependent ET in PSI introduces the possibility that spin may play an important role in ET in biology. PMID:24989350

Carmeli, Itai; Senthil Kumar, Karuppannan; Heifler, Omri; Carmeli, Chanoch; Naaman, Ron

2014-08-18

147

Temperature dependence of electron transfer in coupled quantum wells  

NASA Astrophysics Data System (ADS)

We report on the temperature dependence of electron transfer between coupled quantum wells in a voltage tunable two-color quantum-well infrared photodetector (QWIP). The detection peak of this QWIP switches from 7.1 ?m under positive bias to 8.6 ?m under negative bias for temperatures T?40 K. For T?40 K, the 7.1 ?m peak is present under both bias polarities and increases significantly with T while the 8.6 ?m peak decreases correspondingly. We determine the temperature dependence of electron densities in the two QWs from the detector absorption spectra that are deduced using corrugated QWIPs and find that electron transfer is efficient only when thermionic emission is not significant.

Majumdar, Amlan; Choi, K. K.; Reno, J. L.; Rokhinson, L. P.; Tsui, D. C.

2003-02-01

148

Rydberg electron transfer to SF6: Product ion lifetimes  

NASA Astrophysics Data System (ADS)

The lifetimes of SF6- ions produced by Rydberg electron transfer in K(np )/SF6 collisions at high n, n ?30, are examined using a Penning ion trap. The data point to the formation of ions with a range of lifetimes that extends from ˜1to?10ms. Sizable numbers of ions remain in the trap even 40ms after initial injection and at least part of this signal can be attributed to radiative stabilization. Measurements of free low-energy electron attachment to SF6 in the trap show that the product ions have lifetimes similar to those of SF6- ions formed by electron transfer in high-n collisions.

Liu, Y.; Suess, L.; Dunning, F. B.

2005-06-01

149

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

150

Understanding the electronic structure of 4d metal complexes: from molecular spinors to L-edge spectra of a di-Ru catalyst.  

PubMed

L(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(III)(2)O(H(2)O)(2)(bpy)(4)](4+) water oxidation catalyst. Spectra of the blue dimer and the monomeric [Ru(NH(3))(6)](3+) model complex show considerably different splitting of the Ru L(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(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(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(3))(6)](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. PMID:21866913

Alperovich, Igor; Smolentsev, Grigory; Moonshiram, Dooshaye; Jurss, Jonah W; Concepcion, Javier J; Meyer, Thomas J; Soldatov, Alexander; Pushkar, Yulia

2011-10-01

151

Regulating proton-coupled electron transfer for efficient water splitting by manganese oxides at neutral pH  

PubMed Central

Manganese oxides have been extensively investigated as model systems for the oxygen-evolving complex of photosystem II. However, most bioinspired catalysts are inefficient at neutral pH and functional similarity to the oxygen-evolving complex has been rarely achieved with manganese. Here we report the regulation of proton-coupled electron transfer involved in water oxidation by manganese oxides. Pyridine and its derivatives, which have pKa values intermediate to the water ligand bound to manganese(II) and manganese(III), are used as proton-coupled electron transfer induction reagents. The induction of concerted proton-coupled electron transfer is demonstrated by the detection of deuterium kinetic isotope effects and compliance of the reactions with the libido rule. Although proton-coupled electron transfer regulation is essential for the facial redox change of manganese in photosystem II, most manganese oxides impair these regulatory mechanisms. Thus, the present findings may provide a new design rationale for functional analogues of the oxygen-evolving complex for efficient water splitting at neutral pH. PMID:24977746

Yamaguchi, Akira; Inuzuka, Riko; Takashima, Toshihiro; Hayashi, Toru; Hashimoto, Kazuhito; Nakamura, Ryuhei

2014-01-01

152

Simulations of charge transfer in Electron Multiplying Charge Coupled Devices  

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

153

Hydrogen-bond relays in concerted proton-electron transfers.  

PubMed

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

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

2012-03-20

154

Spectroscopic investigation of photo-induced proton-coupled electron transfer and Dexter energy transfer in model systems  

E-print Network

Spectroscopic investigations of systems designed to advance the mechanistic interrogation of photo-induced proton coupled electron transfer (PCET) and proton-coupled (through-bond) energy transfer (PCEnT) are presented. ...

Young, Elizabeth R. (Elizabeth Renee), 1980-

2009-01-01

155

Mechanistic studies of photo-induced proton-coupled electron transfer and oxygen atom transfer reactions in model systems  

E-print Network

Time-resolved optical spectroscopy has been employed for mechanistic studies in model systems designed to undergo photo-induced proton-coupled electron transfer (PCET) and oxygen atom transfer (OAT) reactions, both of which ...

Hodgkiss, Justin M. (Justin Mark), 1978-

2007-01-01

156

In situ characterization of an iron catalyst by potassium ion desorption and electron emission measurements  

Microsoft Academic Search

The surface conditions of an industrial iron catalyst were monitoredin situ by work function measurements and measurements of thermal desorption of potassium ions. Changes in activation energy for\\u000a potassium ion desorption and in work function values during catalyst activation and deactivation are discussed in terms of\\u000a the potassium coverage and chemical composition of the catalyst surface.

Andrzej Kotarba; Magnus Hagström; Klas Engvall; Jan B. C. Pettersson

1998-01-01

157

Probing Atomic and Electronic Structure of Catalysts by Combination of In Situ and Ex Situ Chemical Imaging  

E-print Network

Probing Atomic and Electronic Structure of Catalysts by Combination of In Situ and Ex Situ Chemical Karim, Robert Dagle, Ja Hun Kwak, Janos Szanyi, Charles Peden Purpose Understand the structural capabilities that enable this understanding Directly relate structural information with the catalytic

158

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

159

Periplasmic electron carriers and photo-induced electron transfer in the photosynthetic bacterium Ectothiorhodospira sp  

Microsoft Academic Search

A detailed analysis of the periplasmic electron carriers of the photosynthetic bacterium Ectothiorhodospira sp. has been performed. Two low mid-point redox potential electron carriers, cytochrome c? and cytochrome c, are detected. A high potential iron–sulfur protein is the only high mid-point redox potential electron transfer component\\u000a present in the periplasm. Analysis of light-induced absorption changes shows that this high potential

André Buche; Rafael Picorel; Jean-Marc Moulis; André Verméglio

2000-01-01

160

Self-regeneration of Pd-LaFeO3 catalysts: new insight from atomic-resolution electron microscopy.  

PubMed

Aberration-corrected transmission electron microscopy was used to study atomic-scale processes in Pd-LaFeO(3) catalysts. Clear evidence for diffusion of Pd into LaFeO(3) and out of LaFe(0.95)Pd(0.05)O(3-?) under high-temperature oxidizing and reducing conditions, respectively, was found, but the extent to which these processes occurred was quite limited. These observations cast doubt that such phenomena play a significant role in a postulated mechanism of self-regeneration of this system as an automotive exhaust-gas catalyst. PMID:22007950

Katz, Michael B; Graham, George W; Duan, Yingwen; Liu, Hong; Adamo, Carolina; Schlom, Darrell G; Pan, Xiaoqing

2011-11-16

161

Photophysical and electron transfer studies of a stable carbocation  

NASA Astrophysics Data System (ADS)

Photophysical and electron transfer properties of the stable trioxatriangulenium carbocation ( 1) are reported. Photophysical studies include absorption, fluorescence and phosphorescence spectra, singlet and triplet state quantum yields and lifetimes. Both the singlet and triplet excited states of 1 can accept an electron from donor molecules leading to the formation of the donor radical cation and the radical of 1. In aqueous solution, 1 can photo-oxidize DNA nucleosides such as guanosine and adenosine indicating that 1 may have potential use as a DNA cleaving agent.

Dileesh, S.; Gopidas, K. R.

2000-11-01

162

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

163

Strong electronic correlations in superconducting organic charge transfer salts  

Microsoft Academic Search

We review the role of strong electronic correlations in quasi-two-dimensional organic charge transfer salts such as (BEDT-TTF)2X, (BETS)2Y, and ??-[Pd(dmit)2]2Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerized and is described by a half-filled Hubbard model; the second class is not strongly dimerized and

B. J. Powell; Ross H. McKenzie

2006-01-01

164

Clustering of Electron Transfer Components: Kinetic and Thermodynamic Consequences  

Microsoft Academic Search

This chapter is devoted to the effects of the organization of electron transfer chains, discussing issues related to compartmentalization\\u000a at various scales as opposed to homogeneous, solution-like behavior. Mobile carriers (like quinones, cytochrome c\\u000a 2, plastocyanin) are required as shuttles between the reaction center complexes and the cytochrome bc\\u000a 1 or b\\u000a 6\\u000a f complexes; the question under focus is

Jérôme Lavergne

165

Nanoparticle facilitated extracellular electron transfer in microbial fuel cells.  

PubMed

Microbial fuel cells (MFCs) have been the focus of substantial research interest due to their potential for long-term, renewable electrical power generation via the metabolism of a broad spectrum of organic substrates, although the low power densities have limited their applications to date. Here, we demonstrate the potential to improve the power extraction by exploiting biogenic inorganic nanoparticles to facilitate extracellular electron transfer in MFCs. Simultaneous short-circuit current recording and optical imaging on a nanotechnology-enabled platform showed substantial current increase from Shewanella PV-4 after the formation of cell/iron sulfide nanoparticle aggregates. Detailed characterization of the structure and composition of the cell/nanoparticle interface revealed crystalline iron sulfide nanoparticles in intimate contact with and uniformly coating the cell membrane. In addition, studies designed to address the fundamental mechanisms of charge transport in this hybrid system showed that charge transport only occurred in the presence of live Shewanella, and moreover demonstrated that the enhanced current output can be attributed to improved electron transfer at cell/electrode interface and through the cellular-networks. Our approach of interconnecting and electrically contacting bacterial cells through biogenic nanoparticles represents a unique and promising direction in MFC research and has the potential to not only advance our fundamental knowledge about electron transfer processes in these biological systems but also overcome a key limitation in MFCs by constructing an electrically connected, three-dimensional cell network from the bottom-up. PMID:25310721

Jiang, Xiaocheng; Hu, Jinsong; Lieber, Alexander M; Jackan, Charles S; Biffinger, Justin C; Fitzgerald, Lisa A; Ringeisen, Bradley R; Lieber, Charles M

2014-11-12

166

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

167

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

168

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

169

Correlated Single Quantum Dot Blinking and Interfacial Electron Transfer Dynamics  

PubMed Central

The electron transfer (ET) dynamics from core/multi-shell (CdSe/CdS3MLZnCdS2MLZnS2ML) quantum dots (QDs) to adsorbed Fluorescein (F27) molecules have been studied by single particle spectroscopy to probe the relationship between single QD interfacial electron transfer and blinking dynamics. Electron transfer from the QD to F27 and the subsequent recombination were directly observed by ensemble-averaged transient absorption spectroscopy. Single QD-F27 complexes show correlated fluctuation of fluorescence intensity and lifetime, similar to those observed in free QDs. With increasing ET rate (controlled by F27-to-QD ratio), the lifetime of on states decreases and relative contribution of off states increases. It was shown that ET is active for QDs in on states, the excited state lifetime of which reflects the ET rate, whereas in the off state QD excitons decay by Auger relaxation and ET is not a competitive quenching pathway. Thus, the blinking dynamics of single QDs modulate their interfacial ET activity. Furthermore, interfacial ET provides an additional pathway for generating off states, leading to correlated single QD interfacial ET and blinking dynamics in QD-acceptor complexes. Because blinking is a general phenomenon of single QDs, it appears that the correlated interfacial ET and blinking and the resulting intermittent ET activity are general phenomena for single QDs. PMID:21915369

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

2011-01-01

170

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

171

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

172

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

Code of Federal Regulations, 2012 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...

2012-04-01

173

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

174

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

...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...

2014-04-01

175

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

Code of Federal Regulations, 2011 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...

2011-04-01

176

ELECTRON TRANSFER MECHANISM AT THE SOLID-LIQUID INTERFACE OF PHYLLOSILICATES  

EPA Science Inventory

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

177

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

Code of Federal Regulations, 2012 CFR

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2012-01-01

178

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

Code of Federal Regulations, 2013 CFR

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2013-01-01

179

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

Code of Federal Regulations, 2013 CFR

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2013-01-01

180

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

Code of Federal Regulations, 2012 CFR

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2012-01-01

181

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

Code of Federal Regulations, 2011 CFR

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2011-01-01

182

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

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2014-01-01

183

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

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2014-01-01

184

Atomic level study of water-gas shift catalysts via transmission electron microscopy and x-ray spectroscopy  

NASA Astrophysics Data System (ADS)

Water-gas shift (WGS), CO + H2O ? CO2 + H2 (DeltaH° = -41 kJ mol -1), is an industrially important reaction for the production of high purity hydrogen. Commercial Cu/ZnO/Al2O3 catalysts are employed to accelerate this reaction, yet these catalysts suffer from certain drawbacks, including costly regeneration processes and sulfur poisoning. Extensive research is focused on developing new catalysts to replace the current technology. Supported noble metals stand out as promising candidates, yet comprise intricate nanostructures complicating the understanding of their working mechanism. In this study, the structure of the supported Pt catalysts is explored by transmission electron microscopy and X-ray spectroscopy. The effect of the supporting phase and the use of secondary metals on the reaction kinetics is investigated. Structural heterogeneities are quantified and correlated with the kinetic descriptors of the catalysts to develop a fundamental understanding of the catalytic mechanism. The effect of the reaction environment on catalyst structure is examined by in-situ techniques. This study benefitted greatly from the use of model catalysts that provide a convenient medium for the atomic level characterization of nanostructures. Based on these studies, Pt supported on iron oxide nano islands deposited on inert spherical alumina exhibited 48 times higher WGS turnover rate (normalized by the total Pt surface area) than Pt supported on bulk iron oxide. The rate of aqueous phase glycerol reforming reaction of Pt supported on multiwall carbon nanotubes (MWCNT) is promoted by co-impregnating with cobalt. The synthesis resulted in a variety of nanostructures among which Pt-Co bimetallic nanoparticles are found to be responsible for the observed promotion. The unprecedented WGS rate of Pt supported on Mo2C is explored by forming Mo 2C patches on top of MWCNTs and the rate promotion is found to be caused by the Pt-Mo bimetallic entities.

Akatay, Mehmed Cem

185

Redox active tyrosines in photosystem II: role in proton coupled electron transfer reactions.  

E-print Network

??Proton coupled electron transfer reactions often involve tyrosine residues, because when oxidized, the phenolic side chain deprotonates. Tyrosine Z (YZ) is responsible for extracting electrons… (more)

Keough, James M.

2013-01-01

186

Electron transfer associated to bond breaking: Passage from sequential mechanism to dissociative electron transfer as a function of molecular structure, environment and energy of the incoming electron  

SciTech Connect

A simple and approximate model for dissociative electron transfer, based on a Morse curve description, is presented. The quantitative rate data presently available are correctly reproduced by the model. Application of the theory allows the estimation of bond dissociation energies in starting compounds and of the standard potential and intrinsic barrier of the reaction. The model also leads to rationalize the concerted or stepwise character of the electron transfer-bond breaking process as a function of molecular structure and energy of the incoming electron.

Andrieux, C. P.; Robert, M.; Saveant, J-M. [Laboratoire d'Electrochimie Moleculaire, Universite Denis Diderot (Paris 7), URA CNRS 438, 2 Place Jussiaeu, 75251 Paris Cedex 05 (France)

1996-04-01

187

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

SciTech Connect

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

Hagmann, S. [Inst. f. Kernphysik Univ. Frankfurt (Germany); GSI-Helmholtz-Zentrum, Darmstadt (Germany); Stoehlker, Th.; Trotsenko, S. [GSI-Helmholtz-Zentrum, Darmstadt (Germany); Helmholtz-Institut Jena (Germany); Kozhuharov, Ch.; Spillmann, U.; Bosch, F.; Liesen, D.; Winters, D.; Hillenbrand, P.-M. [GSI-Helmholtz-Zentrum, Darmstadt (Germany); Shabaev, V.; Tupitsyn, I.; Kozhedub, Y. [Dept. of Physics, St. Petersburg State Univ., St Petersburg (Russian Federation); Rothard, H. [CIMAO-CIRIL-GANIL, Caen (France); Reuschl, R. [GSI-Helmholtz-Zentrum, Darmstadt (Germany); Univ. P. Marie Curie, ParisVI (France); Ullrich, J.; Moshammer, R.; Voitkiv, A.; Surzhykov, A.; Fischer, D. [Max Planck Inst. f. Kernphysik, Heidelberg (Germany); Doerner, R. [Inst. f. Kernphysik Univ. Frankfurt (Germany)

2011-06-01

188

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

189

Effect of protein dynamics on biological electron?transfer  

PubMed Central

Computer simulations of the effect of protein dynamics on the long distance tunneling mediated by the protein matrix have been carried out for a Ru-modified (His 126) azurin molecule. We find that the tunneling matrix element is a sensitive function of the atomic configuration of the part of the protein matrix in which tunneling currents (pathways) are localized. Molecular dynamics simulations show that fluctuations of the matrix element can occur on a time scale as short as 10 fs. These short time fluctuations are an indication of a strong dynamic coupling of a tunneling electron to vibrational motions of the protein nuclear coordinates. The latter results in a modification of the conventional Marcus picture of electron transfer in proteins. The new element in the modified theory is that the tunneling electron is capable of emitting or absorbing vibrational energy (phonons) from the medium. As a result, some biological reactions may occur in an activationless fashion. An analytical theoretical model is proposed to account for thermal fluctuations of the medium in long distance electron transfer reactions. The model shows that, at long distances, the phonon-modified inelastic tunneling always dominates over the conventional elastic tunneling. PMID:9108041

Daizadeh, Iraj; Medvedev, Emile S.; Stuchebrukhov, Alexei A.

1997-01-01

190

Derivation of rate expressions for nonadiabatic proton-coupled electron transfer reactions in solution  

E-print Network

Derivation of rate expressions for nonadiabatic proton-coupled electron transfer reactions, and the transferring proton s are treated quantum mechanically. In this formulation, a PCET reaction is described. For PCET reactions involving the transfer of one electron and one proton, these mixed electronic/proton

Hammes-Schiffer, Sharon

191

27 CFR 26.112a - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2012 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2012-04-01

192

27 CFR 26.112a - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2010 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

193

27 CFR 26.112a - Payment of tax by electronic fund transfer.  

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2014-04-01

194

27 CFR 19.524 - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2010 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

195

27 CFR 26.112a - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2011 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2011-04-01

196

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

Code of Federal Regulations, 2013 CFR

...institution to make an electronic fund transfer in the...later than the close of business on the last day for...institution to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2013-04-01

197

27 CFR 26.112a - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2013 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2013-04-01

198

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

Code of Federal Regulations, 2012 CFR

...institution to make an electronic fund transfer in the...later than the close of business on the last day for...institution to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2012-04-01

199

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

...institution to make an electronic fund transfer in the...later than the close of business on the last day for...institution to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2014-04-01

200

Frontispiece: Wettability-Regulated Extracellular Electron Transfer from the Living Organism of Shewanella loihica PV-4.  

PubMed

Electron Transfer Extracellular electron transfer from living microbes can be regulated by altering the surface wettability of the electrode. In their Communication on page?1446?ff., H. Liu, Y. Zhu, et?al. report that the electron transfer activity on a hydrophilic electrode is more than five times higher than that on a hydrophobic one. PMID:25612176

Ding, Chun-Mei; Lv, Mei-Ling; Zhu, Ying; Jiang, Lei; Liu, Huan

2015-01-26

201

Mechanisms for control of biological electron transfer reactions.  

PubMed

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

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

2014-12-01

202

Energy transfer over long distances by means of electron beams  

NASA Astrophysics Data System (ADS)

It is suggested that the effect of multiple contactless rotation of electrons in an electrified ring, which has been recently discovered by our group, be used for energy transfer over long distances. In experiments with the ring, electrons travel very long distances, ?107 km. Electron losses due to radiation and losses in a residual gas are analyzed. It is shown that these losses are much lower than 10-4 % over a distance of ?104 km. Analysis is performed with regard to the complicated profile of the track. The electrical power that can be transmitted through such a channel is estimated. It exceeds 1013 W at a channel diameter of several millimeters. If channels have the form of a solenoid or toroid, high magnetic fields arise in them, which may find different applications including magnetic plasma confinement.

Kumakhov, M. A.

2014-07-01

203

Noise-assisted quantum electron transfer in photosynthetic complexes  

E-print Network

Electron transfer (ET) between primary electron donors and acceptors is modeled in the photosystem II reaction center (RC). Our model includes (i) two discrete energy levels associated with donor and acceptor, interacting through a dipole-type matrix element and (ii) two continuum manifolds of electron energy levels ("sinks"), which interact directly with the donor and acceptor. Namely, two discrete energy levels of the donor and acceptor are embedded in their independent sinks through the corresponding interaction matrix elements. We also introduce classical (external) noise which acts simultaneously on the donor and acceptor (collective interaction). We derive a closed system of integro-differential equations which describes the non-Markovian quantum dynamics of the ET. A region of parameters is found in which the ET dynamics can be simplified, and described by coupled ordinary differential equations. Using these simplified equations, both sharp and flat redox potentials are analyzed. We analytically and nu...

Nesterov, Alexander I; Martínez, José Manuel Sánchez; Sayre, Richard T

2013-01-01

204

DNA Damage Induced by Low-Energy Electrons: Electron Transfer and Diffraction  

NASA Astrophysics Data System (ADS)

Thin films of the short single strand of DNA, GCAT, in which guanine (G) or adenine (A) have been removed, were bombarded under vacuum by 4 to 15 eV electrons. The fragments corresponding to base release and strand breaks (SB) were analyzed by high performance liquid chromatography and their yields compared with those obtained from unmodified GCAT. From such a comparison, it is shown that, using GCAT as a model system, (1) most SB result from electron capture by DNA bases followed by electron transfer to the phosphate group and (2) the initial capture probability depends on the coherence of the electron wave within the tetramer.

Zheng, Yi; Wagner, J. Richard; Sanche, Léon

2006-05-01

205

DNA Damage Induced by Low-Energy Electrons: Electron Transfer and Diffraction  

SciTech Connect

Thin films of the short single strand of DNA, GCAT, in which guanine (G) or adenine (A) have been removed, were bombarded under vacuum by 4 to 15 eV electrons. The fragments corresponding to base release and strand breaks (SB) were analyzed by high performance liquid chromatography and their yields compared with those obtained from unmodified GCAT. From such a comparison, it is shown that, using GCAT as a model system (1) most SB result from electron capture by DNA bases followed by electron transfer to the phosphate group and (2) the initial capture probability depends on the coherence of the electron wave within the tetramer.

Zheng Yi; Wagner, J. Richard; Sanche, Leon [Groupe de Recherche en Sciences des Radiations, Faculte de Medecine, Universite de Sherbrooke, Sherbrooke, QC J1H 5N4 (Canada)

2006-05-26

206

45 CFR 162.1602 - Standards for health care electronic funds transfers (EFT) and remittance advice transaction.  

...2014-10-01 false Standards for health care electronic funds transfers (EFT... ADMINISTRATIVE REQUIREMENTS Health Care Electronic Funds Transfers (EFT... § 162.1602 Standards for health care electronic funds transfers...

2014-10-01

207

45 CFR 162.1603 - Operating rules for health care electronic funds transfers (EFT) and remittance advice transaction.  

...2014-10-01 false Operating rules for health care electronic funds transfers (EFT... ADMINISTRATIVE REQUIREMENTS Health Care Electronic Funds Transfers (EFT...162.1603 Operating rules for health care electronic funds transfers...

2014-10-01

208

45 CFR 162.1603 - Operating rules for health care electronic funds transfers (EFT) and remittance advice transaction.  

Code of Federal Regulations, 2013 CFR

...REQUIREMENTS Health Care Electronic Funds Transfers (EFT) and...Operating rules for health care electronic funds transfers (EFT) and...following for the health care electronic funds transfers (EFT) and...Combinations for CORE-defined Business Scenarios for the...

2013-10-01

209

45 CFR 162.1603 - Operating rules for health care electronic funds transfers (EFT) and remittance advice transaction.  

Code of Federal Regulations, 2012 CFR

...REQUIREMENTS Health Care Electronic Funds Transfers (EFT) and...Operating rules for health care electronic funds transfers (EFT) and...following for the health care electronic funds transfers (EFT) and...Combinations for CORE-defined Business Scenarios for the...

2012-10-01

210

High-resolution electron tomography study of an industrial Ni-Mo/gamma-Al2O3 hydrotreating catalyst.  

PubMed

The growing demand for high-quality transportation fuels requires their cost-effective production by hydrodesulfurization of crude oils using heterogeneous catalysts. To study the three-dimensional (3D) structure of such a commercial, sulfided Ni-Mo/gamma-Al2O3 catalyst, electron tomography was applied. The MoS2 particles form an interconnected complex structure within the mesopores of the alumina support. Spatial organization, morphology, and orientation of the MoS2 particles in the pores were resolved with sufficient accuracy to display the 6-A-spaced MoS2 crystal planes. The proximity of the MoS2 edge planes and more loosely interacting MoS2 basal planes to the alumina support showed the presence of pores smaller than 3 nm, which was confirmed by physisorption experiments. The actual shape of the MoS2 particles cannot be described by simple models as derived from studies on model catalysts. Electron tomography is a unique tool to study the actual 3D structure of complex industrial catalysts with sub-nanometer resolution. PMID:16722716

de Jong, Krijn P; van den Oetelaar, Leon C A; Vogt, Eelco T C; Eijsbouts, Sonja; Koster, Abraham J; Friedrich, Heiner; de Jongh, Petra E

2006-06-01

211

Interprotein Electron Transfer in a Confined Space: Uncoupling Protein Dynamics from Electron Transfer by  

E-print Network

with a crystallographically defined interface (Natan, M. J.; Baxter, W. W.; Kuila, D.; Gingrich, D. J.; Martin, G. S.; Hoffman.; Kuila, D.; Gingrich, D. J.; Martin, G. S.; Hoffman, B. M. AdV. Chem. Ser. 1991, 228 (Electron, David D. Thomas, and Brian M. Hoffman*, Contribution from the Department of Chemistry, Northwestern Uni

Thomas, David D.

212

Electron-transfer reactions of tryptophan and tyrosine derivatives  

SciTech Connect

Oxidation of tryptophan, tyrosine, and derivatives by oxidizing radicals was studied by pulse radiolysis in aqueous solutions at 20 /sup 0/C. Rate constants for the oxidation of tryptophan derivatives with .N/sub 3/ and Br/sub 2//sup -/. radicals vary from 8 x 10/sup 8/ to 4.8 and 10/sup 9/ M/sup -1/ s/sup -1/ and oxidation goes to completion; no pH dependence was observed. Oxidation rate constants for tyrosine derivatives increase upon deprotonation of the phenolic residue at higher pH. Redox potentials for the indolyl and phenoxyl radicals were derived from the measured equilibrium constants by using p-methoxyphenol (E/sub 7.5/ = 0.6 and E/sub 13/ = 0.4 V), bisulfite (E/sub 3/ = 0.84 V), and guanosine (E/sub 7/ = 0.91 V) redox couples as reference systems. Redox potentials of tryptophan derivatives were found to be in dependent on the nature of the side chain and higher than the redox potentials of tryptophan derivatives. Electron transfer from tyrosine to tryptophyl radical was found to be slow in neutral media and is suggested to proceed via multiple steps, one of which is proton transfer from tyrosine to tryptophyl radical followed by electron transfer. 26 references, 2 figures, 4 tables.

Jovanovic, S.V.; Harriman, A.; Simic, M.G.

1986-04-24

213

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

214

Hetero-cycloreversions mediated by photoinduced electron transfer.  

PubMed

Discovered more than eight decades ago, the Diels-Alder (DA) cycloaddition (CA) remains one of the most versatile tools in synthetic organic chemistry. Hetero-DA processes are powerful methods for the synthesis of densely functionalized six-membered heterocycles, ubiquitous substructures found in natural products and bioactive compounds. These reactions frequently employ azadienes and oxadienes, but only a few groups have reported DA processes with thiadienes. The electron transfer (ET) version of the DA reaction, though less investigated, has emerged as a subject of increasing interest. In the last two decades, researchers have paid closer attention to radical ionic hetero-cycloreversions, mainly in connection with their possible involvement in the repair of pyrimidine(6-4)pyrimidone photolesions in DNA by photolyases. In biological systems, these reactions likely occur through a reductive photosensitization mechanism. In addition, photooxidation can lead to cycloreversion (CR) reactions, and researchers can exploit this strategy for DNA repair therapies. In this Account, we discuss electron-transfer (ET) mediated hetero-CR reactions. We focus on the oxidative and reductive ET splitting of oxetanes, azetidines, and thietanes. Photoinduced electron transfer facilitates the splitting of a variety of four-membered heterocycles. In this context, researchers have commonly examined oxetanes, both experimentally and theoretically. Although a few studies have reported the cycloreversion of azetidines and thietanes carried out under electron transfer conditions, the number of examples remains limited. In general, the cleavage of the ionized four-membered rings appears to occur via a nonconcerted two-step mechanism. The trapping of the intermediate 1,4-radical ions and transient absorption spectroscopy data support this hypothesis, and it explains the observed loss of stereochemistry in the products. In the initial step, either C-C or C-X bond breaking may occur, and the preferred route depends on the substitution pattern of the ring, the type of heteroatom, and various experimental conditions. To better accommodate spin and charge, C-X cleavage happens more frequently, especially in the radical anionic version of the reaction. The addition or withdrawal of a single electron provides a new complementary synthetic strategy to activate hetero-cycloreversions. Despite its potential, this strategy remains largely unexplored. However, it offers a useful method to achieve C?X/olefin metathesis or, upon ring expansion, to construct six-membered heterocyclic rings. PMID:24702062

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

2014-04-15

215

Thin layer of carbon-nano-fibers (CNFs) as catalyst support for fast mass transfer in hydrogenation of nitrite  

Microsoft Academic Search

CNF-foam ‘hairy foam’ and CNF aggregates supported Pd catalysts were studied for the reduction of aqueous nitrite solution and also compared with conventional catalysts. Relatively large Pd particle size and similar Pd particle size distribution on all the catalyst supports excludes any structure sensitive effects on reaction. Intrinsic rates over hairy foam catalysts were independent of CNF-layer thickness (8–28?m) and

Jitendra Kumar Chinthaginjala; Johannes Hendrik Bitter; Leon Lefferts

2010-01-01

216

Front-End Electron Transfer Dissociation: A New Ionization Source  

PubMed Central

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.

2013-01-01

217

Microbial interspecies electron transfer via electric currents through conductive minerals  

PubMed Central

In anaerobic biota, reducing equivalents (electrons) are transferred between different species of microbes [interspecies electron transfer (IET)], establishing the basis of cooperative behaviors and community functions. IET mechanisms described so far are based on diffusion of redox chemical species and/or direct contact in cell aggregates. Here, we show another possibility that IET also occurs via electric currents through natural conductive minerals. Our investigation revealed that electrically conductive magnetite nanoparticles facilitated IET from Geobacter sulfurreducens to Thiobacillus denitrificans, accomplishing acetate oxidation coupled to nitrate reduction. This two-species cooperative catabolism also occurred, albeit one order of magnitude slower, in the presence of Fe ions that worked as diffusive redox species. Semiconductive and insulating iron-oxide nanoparticles did not accelerate the cooperative catabolism. Our results suggest that microbes use conductive mineral particles as conduits of electrons, resulting in efficient IET and cooperative catabolism. Furthermore, such natural mineral conduits are considered to provide ecological advantages for users, because their investments in IET can be reduced. Given that conductive minerals are ubiquitously and abundantly present in nature, electric interactions between microbes and conductive minerals may contribute greatly to the coupling of biogeochemical reactions. PMID:22665802

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2012-01-01

218

Modeling biofilms with dual extracellular electron transfer mechanisms  

PubMed Central

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

2013-01-01

219

Modeling biofilms with dual extracellular electron transfer mechanisms  

SciTech Connect

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

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

2013-11-28

220

Dynamic Control of Electron Transfers in Diflavin Reductases  

PubMed Central

Diflavin reductases are essential proteins capable of splitting the two-electron flux from reduced pyridine nucleotides to a variety of one electron acceptors. The primary sequence of diflavin reductases shows a conserved domain organization harboring two catalytic domains bound to the FAD and FMN flavins sandwiched by one or several non-catalytic domains. The catalytic domains are analogous to existing globular proteins: the FMN domain is analogous to flavodoxins while the FAD domain resembles ferredoxin reductases. The first structural determination of one member of the diflavin reductases family raised some questions about the architecture of the enzyme during catalysis: both FMN and FAD were in perfect position for interflavin transfers but the steric hindrance of the FAD domain rapidly prompted more complex hypotheses on the possible mechanisms for the electron transfer from FMN to external acceptors. Hypotheses of domain reorganization during catalysis in the context of the different members of this family were given by many groups during the past twenty years. This review will address the recent advances in various structural approaches that have highlighted specific dynamic features of diflavin reductases. PMID:23203109

Aigrain, Louise; Fatemi, Fataneh; Frances, Oriane; Lescop, Ewen; Truan, Gilles

2012-01-01

221

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

222

Magnetic Silica-Supported Ruthenium Nanoparticles: An Efficient Catalyst for Transfer Hydrogenation of Carbonyl Compounds  

EPA Science Inventory

One-pot synthesis of ruthenium nanoparticles on magnetic silica is described which involve the in situ generation of magnetic silica (Fe3O4@ SiO2) and ruthenium nano particles immobilization; the hydration of nitriles and transfer hydrogenation of carbonyl compounds occurs in hi...

223

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

224

Long-range intramolecular electron transfer in azurins.  

PubMed Central

The Cu(II) sites of azurins, the blue single copper proteins, isolated from Pseudomonas aeruginosa and Alcaligenes spp. (Iwasaki) are reduced by CO2- radicals, produced by pulse radiolysis, in two distinct reaction steps: (i) a fast bimolecular phase, at the rates (5.0 +/- 0.8) x 10(8) M-1.s-1 (P. aeruginosa) and (6.0 +/- 1.0) x 10(8) M-1.s-1 (Alcaligenes); (ii) a slow unimolecular phase with specific rates of 44 +/- 7 s-1 in the former and 8.5 +/- 1.5 s-1 for the latter (all at 298 K, 0.1 M ionic strength). Concomitant with the fast reduction of Cu(II), the single disulfide bridge linking cysteine-3 to -26 in these proteins is reduced to the RSSR- radical ion as evidenced by its characteristic absorption band centered at 410 nm. This radical ion decays in a unimolecular process with a rate identical to that of the slow Cu(II) reduction phase in the respective protein, thus clearly suggesting that a long-range intramolecular electron transfer occurs between the RSSR- radicals and the Cu(II) site. The temperature dependence of the internal electron transfer process in both proteins was measured over the 4 degrees C to 42 degrees C range. The activation parameters derived are delta H* = 47.5 +/- 4.0 and 16.7 +/- 1.5 kJ.mol-1; and delta S not equal to = -56.5 +/- 7.0 and -171 +/- 18 J.K-1.mol-1, respectively. Using the Marcus theory, we found that the intramolecular electron transfer rates and their activation parameters observed for the two azurins correlate well with the distances between the reactive sites, their redox potential, and the nature of the separating medium. Thus, azurins with distinct structural and reactivity characteristics isolated from different bacteria or modified by site-directed mutagenesis can be used in comparing long-range electron transfer process between their conserved disulfide bridge and the Cu(II) sites. PMID:2506545

Farver, O; Pecht, I

1989-01-01

225

Linear energy relationships in ground state proton transfer and excited state proton-coupled electron transfer.  

PubMed

Proton-coupled electron transfer (PCET) processes are elementary chemical reactions involved in a broad range of radical and redox reactions. Elucidating fundamental PCET reaction mechanisms are thus of central importance for chemical and biochemical research. Here we use quantum chemical density functional theory (DFT), time-dependent density functional theory (TDDFT), and the algebraic diagrammatic-construction through second-order (ADC(2)) to study the mechanism, thermodynamic driving force effects, and reaction barriers of both ground state proton transfer (pT) and photoinduced proton-coupled electron transfer (PCET) between nitrosylated phenyl-phenol compounds and hydrogen-bonded t-butylamine as an external base. We show that the obtained reaction barriers for the ground state pT reactions depend linearly on the thermodynamic driving force, with a Brønsted slope of 1 or 0. Photoexcitation leads to a PCET reaction, for which we find that the excited state reaction barrier depends on the thermodynamic driving force with a Brønsted slope of 1/2. To support the mechanistic picture arising from the static potential energy surfaces, we perform additional molecular dynamics simulations on the excited state energy surface, in which we observe a spontaneous PCET between the donor and the acceptor groups. Our findings suggest that a Brønsted analysis may distinguish the ground state pT and excited state PCET processes. PMID:25485993

Gamiz-Hernandez, Ana P; Magomedov, Artiom; Hummer, Gerhard; Kaila, Ville R I

2015-02-12

226

Highly active catalysts for the transfer dehydrogenation of alkanes: synthesis and application of novel 7-6-7 ring-based pincer iridium complexes.  

PubMed

A series of Ir-PCP pincer precatalysts [(7-6-7-(R) PCP)Ir(H)(Cl)] and [(7-6-7-(Ar) PCP)Ir(H)(Cl)(MeCN)] bearing a novel "7-6-7" fused-ring skeleton have been synthesized based upon the postulate that the catalytic species would have durability due to their rather rigid structure and high activity owing to the low but sufficient flexibility of their backbones, which are not completely fixed. Treatment of these precatalysts with NaOtBu gave rise to the active 14 electron (14e) species [(7-6-7-(iPr) PCP)Ir] and [(7-6-7-(Ph) PCP)Ir], which can trap hydrogen and were spectroscopically characterized as the tetrahydride complexes. Both [(7-6-7-(iPr) PCP)Ir] and [(7-6-7-(Ph) PCP)Ir] were found to be highly effective in the transfer dehydrogenation of cyclooctane with tert-butylethylene as the hydrogen acceptor, the initial reaction rate at high temperature (230?°C) being higher for [(7-6-7-(iPr) PCP)Ir] than [(7-6-7-(Ph) PCP)Ir], and the turnover number (TON) of the overall hydrogen transfer being higher for the latter. Nonetheless, the estimated TONs were as high as 4600 and 4820 for the two complexes at this temperature, respectively, which are unprecedented absolute values. In terms of durability, the [(7-6-7-(Ph) PCP)Ir] complex is the catalyst of choice for this reaction. Structural analysis and computational studies support the importance of the low flexibility of the ligand core. PMID:23794532

Shi, Yuan; Suguri, Takuya; Dohi, Chisato; Yamada, Hirotsuna; Kojima, Satoshi; Yamamoto, Yohsuke

2013-08-01

227

Molecular structures of porphyrin-quinone models for electron transfer  

SciTech Connect

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

Fajer, J.; Barkigia, K.M.; Melamed, D.; Sweet, R.M. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States); Kurreck, H.; Gersdorff, J. von; Plato, M.; Rohland, H.C.; Elger, G.; Moebius, K. [Free Univ. of Berlin (Germany)] [Free Univ. of Berlin (Germany)

1996-08-15

228

ATP-induced electron transfer by redox-selective partner recognition  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

229

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

PubMed

Thermodynamically unfavourable electron transfers are enabled by coupling to an energy-supplying reaction. How the energy is transduced from the exergonic to the endergonic process is largely unknown. Here we provide the structural basis for an energy transduction process in the reductive activation of B12-dependent methyltransferases. The transfer of one electron from an activating enzyme to the cobalamin cofactor is energetically uphill and relies on coupling to an ATPase reaction. Our results demonstrate that the key to coupling is, besides the oxidation state-dependent complex formation, the conformational gating of the electron transfer. Complex formation induces a substitution of the ligand at the electron-accepting Co ion. Addition of ATP initiates electron transfer by provoking conformational changes that destabilize the complex. We show how remodelling of the electron-accepting Co(2+) promotes ATP-dependent electron transfer; an efficient strategy not seen in other electron-transferring ATPases. PMID:25109607

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

2014-01-01

230

Enantioselective ?-Amination Enabled by a BINAM-Derived Phase-Transfer Catalyst.  

PubMed

Chiral anion phase-transfer of aryldiazonium cations was utilized to achieve highly enantioselective ?-amination of carbonyl compounds. A broad scope of indanone- and benzosuberone-derived substrates was amenable to this strategy. Critical to obtaining high levels of enantioselectivity was the use of BINAM-derived phosphoric acids. The utility of this transformation was demonstrated through facile conversion of diazene products to valuable ?-amino acid derivatives. PMID:25485073

Nelson, H M; Patel, J S; Shunatona, H P; Toste, F D

2015-01-01

231

Determination of the electronics transfer function for current transient measurements  

E-print Network

We describe a straight-forward method for determining the transfer function of the readout of a sensor for the situation in which the current transient of the sensor can be precisely simulated. The method relies on the convolution theorem of Fourier transforms. The specific example is a planar silicon pad diode connected with a 50 $\\Omega $ cable to an amplifier followed by a 5 GS/s sampling oscilloscope. The charge carriers in the sensor were produced by picosecond lasers with light of wavelengths of 675 and 1060 nm. The transfer function is determined from the 1060 nm data with the pad diode biased at 1000 V. It is shown that the simulated sensor response convoluted with this transfer function provides an excellent description of the measured transients for the laser light of both wavelengths, at voltages 50 V above the depletion voltage of about 90 V up to the maximum applied voltage of 1000 V. The method has been developed for the precise measurement of the dependence of the drift velocity of electrons and holes in high-ohmic silicon on crystal orientation, electric field and temperature. It can also be applied for the analysis of transient-current measurements of radiation-damaged solid state sensors, as long as sensors properties, like high-frequency capacitance, are not too different.

Christian Scharf; Robert Klanner

2014-07-10

232

Synthesis and use of an asymmetric transfer hydrogenation catalyst based on iron(II) for the synthesis of enantioenriched alcohols and amines.  

PubMed

The catalytic hydrogenation of prochiral ketones and imines is an advantageous approach to the synthesis of enantioenriched alcohols and amines, respectively, which are two classes of compounds that are highly prized in pharmaceutical, fragrance and flavoring chemistry. This hydrogenation reaction is generally carried out using ruthenium-based catalysts. Our group has developed an alternative synthetic route that is based on the environmentally friendlier iron-based catalysis. This protocol describes the three-part synthesis of trans-[amine(imine)diphosphine]chlorocarbonyliron(II) tetrafluoroborate templated by iron salts and starting from commercially available chemicals, which provides the precatalyst for the efficient asymmetric transfer hydrogenation of ketones and imines. The use of the enantiopure (S,S) catalyst to reduce prochiral ketones to the (R)-alcohol in good to excellent yields and enantioenrichment is also detailed, as well as the reduction to the amine in very high yield and enantiopurity of imines substituted at the nitrogen with the N-(diphenylphosphinoyl) group (-P(O)Ph2). Although the best ruthenium catalysts provide alcohols in higher enantiomeric excess (ee) than the iron complex catalyst used in this protocol, they do so on much longer time scales or at higher catalyst loadings. This protocol can be completed in 2 weeks. PMID:25569331

Zuo, Weiwei; Morris, Robert H

2015-02-01

233

Chemical electron-transfer reactions in electrospray mass spectrometry: Effective oxidation potentials of electron-transfer reagents in methylene chloride  

Microsoft Academic Search

Cyclic voltammetry (CV), UV\\/visible absorption spectroscopy, and electrospray mass spectrometry (ES-MS) are used in conjunction to study the mono- and \\/or dications produced in solution from the reaction of three model compounds ([beta]-carotene, cobalt(II) octaethylporphyrin (Co[sup II]OEP), nickel(II) octaethylporphyrin (Ni[sup II]OEP), in three different solvent\\/electron-transfer reagent systems (methylene chloride\\/0.1% trifluoroacetic acid (TFA) (v\\/v), methylene chloride\\/0.1% TFA\\/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) v\\/v\\/200 [mu]M), methylene

Gary J. Van Berkel; Feimeng. Zhou

1994-01-01

234

Synergistic contributions by decreasing overpotential and enhancing charge-transfer in ?-Fe2O3/Mn3O4/graphene catalysts with heterostructures for photocatalytic water oxidation.  

PubMed

A novel nanocomposite consisting of ?-Fe2O3, Mn3O4 and reduced graphene oxide (r-GO) has been facilely synthesized through a two-step method: solvothermal reaction for Mn3O4-modified ?-Fe2O3 (?-Fe2O3/Mn3O4) and self-assembly process for combining ?-Fe2O3/Mn3O4 with r-GO (?-Fe2O3/Mn3O4/r-GO). The morphology and structure of the nanocomposite were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results demonstrated that rod-like hematite was modified by Mn3O4 and dispersed on the surface of r-GO. Raman and Fourier transform infrared spectra (FTIR) showed superior interfacial contacts between ?-Fe2O3/Mn3O4 and r-GO. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) and photoelectrochemical characterization revealed a high light-harvesting efficiency, a lowered overpotential for water oxidation and an excellent charge transfer performance of ?-Fe2O3/Mn3O4/r-GO nanocomposite with heterostructures. The photocatalytic oxygen evolution from the optimized photocatalyst was up to 1406.2 ?mol g(-1) in 10 h of UV-vis light irradiation and the quantum yield was ca. 4.35% at 365 nm. Our investigation suggests that constructing a catalyst with heterostructures is a promising method to enhance photocatalytic activity. PMID:24781029

Yin, Shunli; Wang, Xiaomei; Mou, Zhigang; Wu, Yijie; Huang, Hui; Zhu, Mingshan; Du, Yukou; Yang, Ping

2014-06-21

235

Catalysts for electrochemical generation of oxygen  

NASA Technical Reports Server (NTRS)

Single crystal surfaces of platinum and gold and transition metal oxides of the spinel type were studied to find more effective catalysts for the electrolytic evolution of oxygen and to understand the mechanism and kinetics for the electrocatalysis in relation to the surface electronic and lattice properties of the catalyst. The single crystal studies involve the use of low energy electron diffraction (LEED) and Auger electron spectroscopy as complementary tools to the electrochemical measurements. Modifications to the transfer system and to the thin-layer electrochemical cell used to facilitate the transfer between the ultrahigh vacuum environment of the electron surface physics equipment and the electrochemical environment with a minimal possibility of changes in the surface structure, are described. The electrosorption underpotential deposition of Pb onto the Au(111), (100) and (110) single crystal surfaces with the thin-layer cell-LEED-Auger system is discussed as well as the synthesis of spinels for oxygen evolution studies.

Hagans, P.; Yeager, E.

1978-01-01

236

Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy  

NASA Astrophysics Data System (ADS)

Terahertz spectroscopy is distinguished from other far infrared and millimeter wave spectroscopies by its inherent phase sensitivity and sub-picosecond time resolution making it a versatile technique to study a wide range of physical phenomena. As THz spectroscopy is still a relatively new field, many aspects of THz generation mechanisms have not been fully examined. Using terahertz emission spectroscopy (TES), THz emission from ZnTe(110) was analyzed and found to be limited by two-photon absorption and free-carrier generation at high excitation fluences. Due to concerns about the continued use of fossil fuels, solar energy has been widely investigated as a promising source of renewable energy. Dye-sensitized solar cells (DSSCs) have been developed as a low-cost alternative to conventional photovoltaic solar cells. To solve the issues of the intermittency and inefficient transport associated with solar energy, researchers are attempting to adapt DSSCs for water oxidation and chemical fuel production. Both device designs incorporate sensitizer molecules covalently bound to metal oxide nanoparticles. The sensitizer, which is comprised of a chromophore and anchoring group, absorbs light and transfers an electron from its excited state to the conduction band of the metal oxide, producing an electric current. Using time-resolved THz spectroscopy (TRTS), an optical pump/THz probe technique, the efficiency and dynamics of electron injection from sensitizers to metal oxides was evaluated as a function of the chromophore, its anchoring group, and the metal oxide identity. Experiments for studying fully functioning DSSCs and water oxidation devices are also described. Bio-inspired pentafluorophenyl porphyrin chromophores have been designed and synthesized for use in photoelectrochemical water oxidation cells. Influences on the efficiency and dynamics of electron injection from the chromophores into TiO2 and SnO2 nanoparticles due to changes in both the central substituent to the porphyrin ring and degree of fluorination of ring substituents were analyzed. Due to the high reduction potentials of these sensitizers, injection into TiO2 was generally not observed. Injection timescales from the porphyrins into SnO2 depended strongly on the identity of the central substituent and were affected by competition with excited-state deactivation processes. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but is typically not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency and water stability of several alternative anchoring groups, including phosphonic acid, hydroxamic acid, acerylacetone, and boronic acid, were evaluated. While all of the anchoring groups exhibited water stability superior to carboxylate, the hydroxamate anchor had the best combination of ease of handling and electron injection efficiency. The effects on photoconductivity due to metal oxide morphology and the addition of dopants were also analyzed. Mixtures of anatase and rutile TiO 2 nanoparticles are known to exhibit cooperative effects which increase the efficiency of DSSCs and photocatalysis relative to the pure-phase materials. Through analysis of TRTS measurements, the mechanism of this synergistic effect was found to involve electron transfer from the lower-mobility, higher surface area rutile nanoparticles to anatase particles, resulting in a higher charge collection efficiency. In addition to morphology, doping has been investigated as a means of expanding the spectral range of visible absorption of photocatalysts. Doping ZnO nanowires with manganese(II) was found to significantly decrease the electron mobility, and doping with cobalt(II) increased the timescale for electron trapping. These differences can be understood by considering the changes to the band structure of ZnO effected by the dopants. Preliminary analyses of the solvent and electrolyte dependence on the electron injection rate and efficiency suggest that electron injection can be affected by

Milot, Rebecca Lee

237

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

238

Probing electron transfer mechanisms in Shewanella oneidensis MR-1 using a nanoelectrode platform and single-cell imaging  

PubMed Central

Microbial fuel cells (MFCs) represent a promising approach for sustainable energy production as they generate electricity directly from metabolism of organic substrates without the need for catalysts. However, the mechanisms of electron transfer between microbes and electrodes, which could ultimately limit power extraction, remain controversial. Here we demonstrate optically transparent nanoelectrodes as a platform to investigate extracellular electron transfer in Shewanella oneidensis MR-1, where an array of nanoholes precludes or single window allows for direct microbe-electrode contacts. Following addition of cells, short-circuit current measurements showed similar amplitude and temporal response for both electrode configurations, while in situ optical imaging demonstrates that the measured currents were uncorrelated with the cell number on the electrodes. High-resolution imaging showed the presence of thin, 4- to 5-nm diameter filaments emanating from cell bodies, although these filaments do not appear correlated with current generation. Both types of electrodes yielded similar currents at longer times in dense cell layers and exhibited a rapid drop in current upon removal of diffusible mediators. Reintroduction of the original cell-free media yielded a rapid increase in current to ?80% of original level, whereas imaging showed that the positions of > 70% of cells remained unchanged during solution exchange. Together, these measurements show that electron transfer occurs predominantly by mediated mechanism in this model system. Last, simultaneous measurements of current and cell positions showed that cell motility and electron transfer were inversely correlated. The ability to control and image cell/electrode interactions down to the single-cell level provide a powerful approach for advancing our fundamental understanding of MFCs. PMID:20837546

Jiang, Xiaocheng; Hu, Jinsong; Fitzgerald, Lisa A.; Biffinger, Justin C.; Xie, Ping; Ringeisen, Bradley R.; Lieber, Charles M.

2010-01-01

239

Noise-assisted quantum electron transfer in photosynthetic complexes  

E-print Network

Electron transfer (ET) between primary electron donors and acceptors is modeled in the photosystem II reaction center (RC). Our model includes (i) two discrete energy levels associated with donor and acceptor, interacting through a dipole-type matrix element and (ii) two continuum manifolds of electron energy levels ("sinks"), which interact directly with the donor and acceptor. Namely, two discrete energy levels of the donor and acceptor are embedded in their independent sinks through the corresponding interaction matrix elements. We also introduce classical (external) noise which acts simultaneously on the donor and acceptor (collective interaction). We derive a closed system of integro-differential equations which describes the non-Markovian quantum dynamics of the ET. A region of parameters is found in which the ET dynamics can be simplified, and described by coupled ordinary differential equations. Using these simplified equations, both sharp and flat redox potentials are analyzed. We analytically and numerically obtain the characteristic parameters that optimize the ET rates and efficiency in this system.

Alexander I. Nesterov; Gennady P. Berman; José Manuel Sánchez Martínez; Richard T. Sayre

2013-04-30

240

Aqueous systems from first-principles : structure, dynamics and electron-transfer reactions  

E-print Network

In this thesis, we show for the first time how it is possible to calculated fully from first-principles the diabatic free-energy surfaces of electron-transfer reactions. The excitation energy corresponding to the transfer ...

Sit, Patrick Hoi Land

2006-01-01

241

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

...general transfer requirements apply to electronic records? 1235.44 Section 1235.44 Parks, Forests, and Public Property NATIONAL ARCHIVES AND RECORDS ADMINISTRATION RECORDS MANAGEMENT TRANSFER OF REC- ORDS TO THE NATIONAL...

2014-07-01

242

CNN pincer ruthenium catalysts for hydrogenation and transfer hydrogenation of ketones: experimental and computational studies.  

PubMed

Reaction of [RuCl(CNN)(dppb)] (1-Cl) (HCNN=2-aminomethyl-6-(4-methylphenyl)pyridine; dppb=Ph2 P(CH2 )4 PPh2 ) with NaOCH2 CF3 leads to the amine-alkoxide [Ru(CNN)(OCH2 CF3 )(dppb)] (1-OCH2 CF3 ), whose neutron diffraction study reveals a short RuO???HN bond length. Treatment of 1-Cl with NaOEt and EtOH affords the alkoxide [Ru(CNN)(OEt)(dppb)]?(EtOH)n (1-OEt?n?EtOH), which equilibrates with the hydride [RuH(CNN)(dppb)] (1-H) and acetaldehyde. Compound 1-OEt?n?EtOH reacts reversibly with H2 leading to 1-H and EtOH through dihydrogen splitting. NMR spectroscopic studies on 1-OEt?n?EtOH and 1-H reveal hydrogen bond interactions and exchange processes. The chloride 1-Cl catalyzes the hydrogenation (5 atm of H2 ) of ketones to alcohols (turnover frequency (TOF) up to 6.5×10(4) h(-1) , 40?°C). DFT calculations were performed on the reaction of [RuH(CNN')(dmpb)] (2-H) (HCNN'=2-aminomethyl-6-(phenyl)pyridine; dmpb=Me2 P(CH2 )4 PMe2 ) with acetone and with one molecule of 2-propanol, in alcohol, with the alkoxide complex being the most stable species. In the first step, the Ru-hydride transfers one hydrogen atom to the carbon of the ketone, whereas the second hydrogen transfer from NH2 is mediated by the alcohol and leads to the key "amide" intermediate. Regeneration of the hydride complex may occur by reaction with 2-propanol or with H2 ; both pathways have low barriers and are alcohol assisted. PMID:25195979

Baratta, Walter; Baldino, Salvatore; Calhorda, Maria José; Costa, Paulo J; Esposito, Gennaro; Herdtweck, Eberhardt; Magnolia, Santo; Mealli, Carlo; Messaoudi, Abdelatif; Mason, Sax A; Veiros, Luis F

2014-10-13

243

27 CFR 25.165 - Payment of tax by electronic fund transfer.  

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund...

2014-04-01

244

27 CFR 25.165 - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2012 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund...

2012-04-01

245

27 CFR 25.165 - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2011 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund...

2011-04-01

246

27 CFR 25.165 - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2010 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund...

2010-04-01

247

27 CFR 25.165 - Payment of tax by electronic fund transfer.  

Code of Federal Regulations, 2013 CFR

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund...

2013-04-01

248

Kinetics and mechanism of electron transfer in intact photosystem II and in the isolated reaction center  

E-print Network

Kinetics and mechanism of electron transfer in intact photosystem II and in the isolated reaction center: Pheophytin is the primary electron acceptor A. R. Holzwarth , M. G. Mu¨ ller , M. Reus , M and kinetics of electron transfer in isolated D1 D2-cytb559 photosystem (PS) II reaction centers (RCs

Roegner, Matthias

249

Competition between electron transfer, trapping, and recombination in CdS nanorod-hydrogenase complexes.  

PubMed

Electron transfer from photoexcited CdS nanorods to [FeFe]-hydrogenase is a critical step in photochemical H2 production by CdS-hydrogenase complexes. By accounting for the distributions in the numbers of electron traps and enzymes adsorbed, we determine rate constants and quantum efficiencies for electron transfer from transient absorption measurements. PMID:25623885

Utterback, James K; Wilker, Molly B; Brown, Katherine A; King, Paul W; Eaves, Joel D; Dukovic, Gordana

2015-02-10

250

Electronic shift register memory based on molecular electron-transfer reactions  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

251

Fast electron transfer processes in cytochrome C and related metalloproteins.  

PubMed Central

Various free radicals formed on pulse radiolysis of aqueous solutions have been used to investigate the mechanisms of reduction of cytochrome(III) c by inter- and intramolecular electron transfer. The rapid formation of free radicals (t less than 1 mus) and their high reactivity with cytochrome (k approximately 10(8)(-5) x 10(10)M(-1)s(-1)) make such studies feasible. Reduction of cytochrome by free radicls is monitored by optical methods. Fast optical changes in the 1(-500)-mus region correspond to reduction of the iron center; whereas the slower changes in the 10(-500)-ms region are attributed to postreduction conformational changes. It has been concluded that the reduction path is mediated through the crevice and that no reduction intermediates are being formed. PMID:213135

Simic, M G; Taub, I A

1978-01-01

252

Electron Transfer Reactions: Generalized Spin-Boson Approach  

E-print Network

We introduce a mathematically rigorous analysis of a generalized spin-boson system for the treatment of a donor-acceptor (reactant-product) quantum system coupled to a thermal quantum noise. The donor/acceptor probability dynamics describes transport reactions in chemical processes in presence of a noisy environment -- such as the electron transfer in a photosynthetic reaction center. Besides being rigorous, our analysis has the advantages over previous ones that (1) we include a general, non energy-conserving system-environment interaction, and that (2) we allow for the donor or acceptor to consist of multiple energy levels lying closely together. We establish explicit expressions for the rates and the efficiency (final donor-acceptor population difference) of the reaction. In particular, we show that the rate increases for a multi-level acceptor, but the efficiency does not.

Marco Merkli; Gennady Berman; Richard Sayre

2012-09-04

253

Electron Transfer Reactions: Generalized Spin-Boson Approach  

E-print Network

We introduce a mathematically rigorous analysis of a generalized spin-boson system for the treatment of a donor-acceptor (reactant-product) quantum system coupled to a thermal quantum noise. The donor/acceptor probability dynamics describes transport reactions in chemical processes in presence of a noisy environment -- such as the electron transfer in a photosynthetic reaction center. Besides being rigorous, our analysis has the advantages over previous ones that (1) we include a general, non energy-conserving system-environment interaction, and that (2) we allow for the donor or acceptor to consist of multiple energy levels lying closely together. We establish explicit expressions for the rates and the efficiency (final donor-acceptor population difference) of the reaction. In particular, we show that the rate increases for a multi-level acceptor, but the efficiency does not.

Merkli, Marco

2012-01-01

254

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. PMID:23535590

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

2013-01-01

255

Steric guided change of electron transfer mechanism in benzene  

NASA Astrophysics Data System (ADS)

In fluorescence quenching study via electron transfer (ET), the quenching rate constant ( kq) values generally decrease with lowering of quencher concentration, since smaller concentration of quencher always leads to a red shift in the donor-acceptor (D-A) distance in ET [M. Tachiya, S. Murata, J. Phys. Chem. 96 (1992) 8441; S. Murata, M. Tachiya, J. Phys. Chem. 100 (1996) 4064; L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A 103 (1999) 5882]. However, while doing a comparative study with different carbazole (CZ) derivatives-1,4-dicyanobenzene (DCB) systems in benzene (BZ), we observed a deviation from that normal behaviour. It was found that for all of them with lower quencher (DCB) concentration, kq values actually increase instead of the expected reduction. Exceptionally, for simple CZ (C 12H 9N) with decrease in concentration of DCB, kq values can even reach the order of energy transfer (10 11 s -1). Interestingly, it is not observed when toluene (TL) or xylene (XY) is used as solvent. To explain this unique observation, a sandwich type of molecular structure is predicted, where BZ sliding in between CZ and DCB brings them closer enough, imparting more through bond character to CZ-DCB interaction and hence a higher rate of ET ( kq) is observed [L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A. 103 (1999) 5882].

Chatterjee, Suchandra; Basu, Samita; Ghosh, Nandita; Chakrabarty, Manas

2005-06-01

256

Steric guided change of electron transfer mechanism in benzene.  

PubMed

In fluorescence quenching study via electron transfer (ET), the quenching rate constant (k(q)) values generally decrease with lowering of quencher concentration, since smaller concentration of quencher always leads to a red shift in the donor-acceptor (D-A) distance in ET [M. Tachiya, S. Murata, J. Phys. Chem. 96 (1992) 8441; S. Murata, M. Tachiya, J. Phys. Chem. 100 (1996) 4064; L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A 103 (1999) 5882]. However, while doing a comparative study with different carbazole (CZ) derivatives-1,4-dicyanobenzene (DCB) systems in benzene (BZ), we observed a deviation from that normal behaviour. It was found that for all of them with lower quencher (DCB) concentration, k(q) values actually increase instead of the expected reduction. Exceptionally, for simple CZ (C12H9N) with decrease in concentration of DCB, k(q) values can even reach the order of energy transfer (10(11) s(-1)). Interestingly, it is not observed when toluene (TL) or xylene (XY) is used as solvent. To explain this unique observation, a sandwich type of molecular structure is predicted, where BZ sliding in between CZ and DCB brings them closer enough, imparting more through bond character to CZ-DCB interaction and hence a higher rate of ET (k(q)) is observed [L. Burel, M. Mastafavi, S. Murata, M. Tachiya, J. Phys. Chem. A. 103 (1999) 5882]. PMID:15863061

Chatterjee, Suchandra; Basu, Samita; Ghosh, Nandita; Chakrabarty, Manas

2005-06-01

257

Smooth landscape solvent dynamics in electron transfer reactions  

NASA Astrophysics Data System (ADS)

Solvent effects play a major role in controlling electron-transfer reactions. The solvent dynamics happens on a very high-dimensional surface, and this complex landscape is populated by a large number of minima. A critical problem is to understand the conditions under which the solvent dynamics can be represented by a single collective reaction coordinate. When this unidimensional representation is valid, one recovers the successful Marcus theory. In this study the approach used in a previous work [V. B. P. Leite and J. N. Onuchic; J. Phys. Chem. 100, 7680 (1996)] is extended to treat a more realistic solvent model, which includes energy correlation. The dynamics takes place in a smooth and well behaved landscape. The single shell of solvent molecules around a cavity is described by a two-dimensional system with periodic boundary conditions with nearest neighbor interaction. It is shown how the polarization-dependent effects can be inferred. The existence of phase transitions depends on a factor ? proportional to the contribution from the two parameters of the model. For the present model, ? suggests the existence of "weak kinetic phase transitions," which are used in the analysis of solvent effects in charge-transfer reactions.

Leite, Vitor B. P.

1999-05-01

258

Direct electron transfer with enzymes on nanofiliform titanium oxide films with electron-transport ability.  

PubMed

Direct electron transfer (DET) from biomolecules to electrode is a process without electron-mediators, thus superior selectivity and sensitivity is expected in order to monitor electron transfer between electrode and biomolecules without any mediator interference. However, DET is difficult because a redox center which is an electron active center of proteins such as enzymes is buried deep. So, a unique electrode nanostructure to reach the redox center is a critical factor. Here we have systematically investigated terms for DET using various nanofiliformed electrode morphologies and enzyme concentrations. It is pointed out that the reaction site is below 100 nm, the ration amounts of adsorbed enzyme per surface area are below 1.0 are contributed to the DET. As a great application, we have developed a biosensor monitoring the hydrogen peroxide (H(2)O(2)) detecting capability from peroxidase directly. For the fabricated HRP/nTOF/Ti-electrodes observed the catalytic current value was linear according to the increase in the concentration of H(2)O(2) up to 100 ?M, which indicates a good potential for an H(2)O(2) biosensor. PMID:23040371

Lee, So-Yoon; Matsuno, Ryosuke; Ishihara, Kazuhiko; Takai, Madoka

2013-03-15

259

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

260

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

261

Rapid estimation of catalyst nanoparticle morphology and atomic-coordination by high-resolution Z-contrast electron microscopy.  

PubMed

Heterogeneous nanoparticle catalyst development relies on an understanding of their structure-property relationships, ideally at atomic resolution and in three-dimensions. Current transmission electron microscopy techniques such as discrete tomography can provide this but require multiple images of each nanoparticle and are incompatible with samples that change under electron irradiation or with surveying large numbers of particles to gain significant statistics. Here, we make use of recent advances in quantitative dark-field scanning transmission electron microscopy to count the number atoms in each atomic column of a single image from a platinum nanoparticle. These atom-counts, along with the prior knowledge of the face-centered cubic geometry, are used to create atomistic models. An energy minimization is then used to relax the nanoparticle's 3D structure. This rapid approach enables high-throughput statistical studies or the analysis of dynamic processes such as facet-restructuring or particle damage. PMID:25340541

Jones, Lewys; MacArthur, Katherine E; Fauske, Vidar T; van Helvoort, Antonius T J; Nellist, Peter D

2014-11-12

262

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...

263

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

Code of Federal Regulations, 2011 CFR

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2011-04-01

264

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

265

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

...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...

2014-04-01

266

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

Code of Federal Regulations, 2012 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...

2012-04-01

267

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

268

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

DOEpatents

Cooling apparatuses and coolant-cooled electronic systems are provided which include thermal transfer structures configured to engage with a spring force one or more electronics cards with docking of the electronics card(s) within a respective socket(s) of the electronic system. A thermal transfer structure of the cooling apparatus includes a thermal spreader having a first thermal conduction surface, and a thermally conductive spring assembly coupled to the conduction surface of the thermal spreader and positioned and configured to reside between and physically couple a first surface of an electronics card to the first surface of the thermal spreader with docking of the electronics card within a socket of the electronic system. The thermal transfer structure is, in one embodiment, metallurgically bonded to a coolant-cooled structure and facilitates transfer of heat from the electronics card to coolant flowing through the coolant-cooled structure.

David, Milnes P; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Parida, Pritish R; Schmidt, Roger R

2014-12-16

269

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. PMID:22375846

Niklas, Jens; Mardis, Kristy L.; Rakhimov, Rakhim R.; Mulfort, Karen L.; Tiede, David M.; Poluektov, Oleg G.

2012-01-01

270

Structural factors influencing the intramolecular charge transfer and photoinduced electron transfer in tetrapyrazinoporphyrazines.  

PubMed

A series of unsymmetrical tetrapyrazinoporphyrazines (TPyzPzs) from the group of azaphthalocyanines with one peripherally attached amino substituent (donor) were synthesized, and their photophysical properties (fluorescence quantum yield and singlet oxygen quantum yield) were determined. The synthesized TPyzPzs were expected to undergo intramolecular charge transfer (ICT) as the main pathway for deactivating their excited states. Several structural factors were found to play a critical role in ICT efficiency. The substituent in the ortho position to the donor center significantly influences the ICT, with tert-butylsulfanyl and butoxy substituents inducing the strongest ICTs, whereas chloro, methyl, phenyl, and hydrogen substituents in this position reduce the efficiency. The strength of the donor positively influences the ICT efficiency and correlates well with the oxidation potential of the amines used as the substituents on the TPyzPz as follows: n-butylamine < N,N-diethylamine < aniline < phenothiazine. The ICT (with conjugated donors and acceptors) in the TPyzPz also proved to be much stronger than a photoinduced electron transfer in which the donor and the acceptor are connected through an aliphatic linker. PMID:24509513

Novakova, Veronika; Hladík, Petr; Filandrová, Tereza; Zajícová, Ivana; Krepsová, Veronika; Miletin, Miroslav; Len?o, Juraj; Zimcik, Petr

2014-03-21

271

Ultrasound assisted the preparation of 1-(4-nitrophenyl) imidazole under a new multi-site phase-transfer catalyst--kinetic study.  

PubMed

In this work, the nitroarylation of imidazole catalyzed by a new novel dual-site phase-transfer catalyst was carried out in an alkaline solution/imidazole in chlorobenzene two-phase medium with ultrasonic irradiation (40 kHz, 300 W). This new synthesized phase-transfer catalyst, N(1),N(6)-diethyl-N(1),N(1),N(6),N(6)-tetraisopropylhexane-1,6-diaminium dichloride (MPTC), which possesses two-site activity, was obtained from the reaction of 1,6-dichlorohexane and N-ethyl-N-isopropylpropane-2-amine. The reaction of imidazole and alkali was carried out at the interface to generate sodium imidazole anion which can further react with MPTC form quaternary ammonium imidazole anion along with ultrasonic irradiation (40 kHz, 300 W). This ion-pair further react with 1-chloro-4-nitrobenzene which is present in the organic phase to produce 1-(4-nitropheny) imidazole. The reaction follows a pseudo first-order rate law. Kinetics of the reactions such as effect of the catalysts, ultrasonic effect, agitation speed, temperature, alkaline concentration, amount of 4-nitrochlorobenzene and the solvent effect on the reaction rate were investigated in detail. Peculiar phenomenon for the dependence of the reaction rate on the amount of MPTC and ultrasonication are explained satisfactorily. PMID:24409465

Selvaraj, Varathan; Rajendran, Venugopal

2014-03-01

272

SO 2 adsorption and thermal stability and reducibility of sulfates formed on the magnesium-aluminate spinel sulfur-transfer catalyst  

NASA Astrophysics Data System (ADS)

Magnesium-aluminate spinel used as a sulfur-transfer catalyst in the fluid catalytic cracking units for SO x emission control was prepared by the precipitation method. The crystalline structure, textural property, and surface dehydroxylation of the sample were characterized by thermogravimetry-derivative thermogravimetry (TG-DTG), differential thermal analysis (DTA), X-ray diffraction (XRD), liquid N 2 adsorption-desorption and infrared spectroscopy (IR) measurements. The behavior of SO 2 adsorption and oxidation on the surface of catalyst was evaluated with IR from 50°C to 600°C. Particularly, the thermal stability and H 2-reducibility of the formed sulfite or sulfate during SO 2 adsorption or oxidation were tested under various conditions. In the absence of oxygen in the feed mixture, weak physically adsorbed SO 2 species and surface sulfite were identified. In the case of SO 2 oxidative adsorption, both surface sulfate and bulk-like sulfate were formed. When the sulfated sample was reduced with hydrogen, the surface sulfite and sulfates were completely removed below 550°C in vacuum. The bulk-like sulfate, however, showed a high ability to resist H 2-reduction, which indicates that the reducibility of bulk-like sulfate formed on magnesium-aluminate spinel must be enhanced when it is used as a sulfur-transfer catalyst.

Wang, Jin-an; Li, Cheng-lie

2000-07-01

273

Electronic resonance with anticorrelated pigment vibrations drives photosynthetic energy transfer outside the adiabatic framework  

PubMed Central

The delocalized, anticorrelated component of pigment vibrations can drive nonadiabatic electronic energy transfer in photosynthetic light-harvesting antennas. In femtosecond experiments, this energy transfer mechanism leads to excitation of delocalized, anticorrelated vibrational wavepackets on the ground electronic state that exhibit not only 2D spectroscopic signatures attributed to electronic coherence and oscillatory quantum energy transport but also a cross-peak asymmetry not previously explained by theory. A number of antennas have electronic energy gaps matching a pigment vibrational frequency with a small vibrational coordinate change on electronic excitation. Such photosynthetic energy transfer steps resemble molecular internal conversion through a nested intermolecular funnel. PMID:23267114

Tiwari, Vivek; Peters, William K.; Jonas, David M.

2013-01-01

274

Electronic resonance with anticorrelated pigment vibrations drives photosynthetic energy transfer outside the adiabatic framework.  

PubMed

The delocalized, anticorrelated component of pigment vibrations can drive nonadiabatic electronic energy transfer in photosynthetic light-harvesting antennas. In femtosecond experiments, this energy transfer mechanism leads to excitation of delocalized, anticorrelated vibrational wavepackets on the ground electronic state that exhibit not only 2D spectroscopic signatures attributed to electronic coherence and oscillatory quantum energy transport but also a cross-peak asymmetry not previously explained by theory. A number of antennas have electronic energy gaps matching a pigment vibrational frequency with a small vibrational coordinate change on electronic excitation. Such photosynthetic energy transfer steps resemble molecular internal conversion through a nested intermolecular funnel. PMID:23267114

Tiwari, Vivek; Peters, William K; Jonas, David M

2013-01-22

275

Modeling Charge Transfer in Fullerene Collisions via Real-Time Electron Dynamics  

SciTech Connect

An approach for performing real-time dynamics of electron transfer in a prototype redox reaction that occurs in reactive collisions between neutral and ionic fullerenes is discussed. The quantum dynamical simulations show that the electron transfer occurs within 60 fs directly preceding the collision of the fullerenes, followed by structural changes and relaxation of electron charge. The consequences of real-time electron dynamics are fully elucidated for the far from equilibrium processes of collisions between neutral and multiply charged fullerenes.

Jakowski, Jacek [ORNL; Irle, Stephan [ORNL; Morokuma, Keiji [ORNL; Sumpter, Bobby G [ORNL

2012-01-01

276

Catalyst by Design  

SciTech Connect

The development of new catalytic materials is still dominated by trial and error methods. Although it has been successful, the empirical development of catalytic materials is time consuming and expensive with no guarantee of success. In our laboratories, we are developing a comprehensive catalysts by design that involves state-of-the-art first principle density functional theory calculations, experimental design of catalyst sites, and sub- ngstr m resolution imaging with an aberration-corrected electron microscope to characterize the microstructure. In this chapter, we focus on supported platinum cluster catalyst systems which are one of the most important industrial catalysts and attempt to demonstrate the feasibility of the catalyst by design concept.

Narula, Chaitanya Kumar [ORNL] [ORNL; DeBusk, Melanie Moses [ORNL] [ORNL

2014-01-01

277

Model Proton-Coupled Electron Transfer Reactions in Solution: Predictions of Rates, Mechanisms, and Kinetic Isotope Effects  

E-print Network

Model Proton-Coupled Electron Transfer Reactions in Solution: Predictions of Rates, Mechanisms isotope effects for proton-coupled electron transfer (PCET) reactions. These studies are based) the proton transfer reaction becomes more exothermic, (4) the electron transfer reaction becomes more

Hammes-Schiffer, Sharon

278

Photoinduced electron transfer from semiconductor quantum dots to metal oxide nanoparticles  

PubMed Central

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

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

2011-01-01

279

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

2011-12-01

280

Pattern transfer of electron beam modified self-assembled monolayers for high-resolution lithography  

E-print Network

. An Hitachi S-800 scan- ning electron microscope with a pattern generator was used for 1­25 keV exposures-resolution electron beam lithography. Focused electron beams from 1 to 50 keV and scanning tunneling microscopy at 10Pattern transfer of electron beam modified self-assembled monolayers for high

Parikh, Atul N.

281

Probing concerted proton–electron transfer in phenol–imidazoles  

PubMed Central

A series of seven substituted 4,6-di-tert-butyl-2-(4,5-diarylimidazolyl)-phenols have been prepared and characterized, along with two related benzimidazole compounds. X-ray crystal structures of all of the compounds show that the phenol and imidazole rings are close to coplanar and are connected by an intramolecular ArOH?N hydrogen bond. One-electron oxidation of these compounds occurs with movement of the phenolic proton to the imidazole base by concerted proton–electron transfer (CPET) to yield fairly stable distonic radical cations. These phenol–base compounds are a valuable system in which to examine the key features of CPET. Kinetic measurements of bimolecular CPET oxidations, with Erxn between +0.04 and ?0.33 V, give rate constants from (6.3 ± 0.6) × 102 to (3.0 ± 0.6) × 106 M?1 s?1. There is a good correlation of log(k) with ?G°, with only one of the 15 rate constants falling more than a factor of 5.2 from the correlation line. Substituents on the imidazole affect the (O–H?N) hydrogen bond, as marked by variations in the 1H NMR and calculated vibrational spectra and geometries. Crystallographic dO?N values appear to be more strongly affected by crystal packing forces. However, there is almost no correlation of rate constants with any of these measured or computed parameters. Over this range of compounds from the same structural family, the dominant contributor to the differences in rate constant is the driving force ?G°. PMID:18212121

Markle, Todd F.; Rhile, Ian J.; DiPasquale, Antonio G.; Mayer, James M.

2008-01-01

282

Signal and charge transfer efficiency of few electrons clocked on microscopic superfluid helium channels  

Microsoft Academic Search

Electrons floating on the surface of liquid helium are possible spin qubits for quantum information processing. Varying electric potentials are not expected to modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This approach depends upon efficient intergate transfer of individual electrons. Measurements are presented here of the charge transfer efficiency

G. Sabouret; F. R. Bradbury; S. Shankar; J. A. Bert; S. A. Lyon

2008-01-01

283

Theory for electron-transfer reactions involving two Marcus surfaces with a different force constant  

SciTech Connect

Theory for electron-transfer reactions at high temperature involving two Marcus parabolic surfaces with a different force constant is presented. The dynamic solvent effects are also considered using the stochastic Liouville equation, assuming an overdamped Debye solvent. An analytical expression for the adiabatic/nonadiabatic electron-transfer rate constant is derived.

Tang, Jau

1994-02-01

284

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

285

Proton-coupled electron transfer reactions in solution: Molecular dynamics with quantum transitions for model systems  

E-print Network

Proton-coupled electron transfer reactions in solution: Molecular dynamics with quantum transitions A general minimal model for proton-coupled electron transfer PCET reactions in solution is presented of PCET reactions. This represents the first application of MDQT to a system in which both a proton

Hammes-Schiffer, Sharon

286

Energetics of Quinone-Dependent Electron and Proton Transfers in Rhodobacter sphaeroides Photosynthetic Reaction Centers  

E-print Network

are found in many transmembrane proteins that coupled electron and proton transfer reactions (1, 2), includ. The quinone-dependent electron and proton transfers in bacterial reaction centers (RCs) of Rhodobacter a second proton, yielding the dihydroquinone. Overall, two cycles of light-driven reactions oxidize two

Gunner, Marilyn

287

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

Federal Register 2010, 2011, 2012, 2013

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2012-01-10

288

Probing the Coupling between Proton and Electron Transfer in Photosystem II Core Complexes Containing a  

E-print Network

Probing the Coupling between Proton and Electron Transfer in Photosystem II Core Complexes associated with either the electron or proton transfer. We have performed such a study here in Photosystem II-fluorotyrosine (3F-TyrZ) for TyrZ. In Mn-depleted Photosystem II, the dependence upon pH of the oxidation rates

289

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

290

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

Code of Federal Regulations, 2010 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...

2010-04-01

291

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

Code of Federal Regulations, 2011 CFR

...240 Payment of tax by electronic fund transfer. (a) General...by no later than close of business on the last day for filing the...tax payment before close of business on the last day for filing...entitled “Payment of Tax by Electronic Fund Transfer”. This...

2011-04-01

292

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

Code of Federal Regulations, 2011 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...

2011-04-01

293

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

...240 Payment of tax by electronic fund transfer. (a) General...by no later than close of business on the last day for filing the...tax payment before close of business on the last day for filing...entitled “Payment of Tax by Electronic Fund Transfer”. This...

2014-04-01

294

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

Code of Federal Regulations, 2012 CFR

...240 Payment of tax by electronic fund transfer. (a) General...by no later than close of business on the last day for filing the...tax payment before close of business on the last day for filing...entitled “Payment of Tax by Electronic Fund Transfer”. This...

2012-04-01

295

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

Code of Federal Regulations, 2013 CFR

...240 Payment of tax by electronic fund transfer. (a) General...by no later than close of business on the last day for filing the...tax payment before close of business on the last day for filing...entitled “Payment of Tax by Electronic Fund Transfer”. This...

2013-04-01

296

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

Code of Federal Regulations, 2012 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...

2012-04-01

297

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

...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...

2014-04-01

298

Functional LH1 antenna complexes influence electron transfer in bacterial photosynthetic reaction centers  

Microsoft Academic Search

The effect of the light harvesting 1 (LH1) antenna complex on the driving force for light-driven electron transfer in the Rhodobacter sphaeroides reaction center has been examined. Equilibrium redox titrations show that the presence of the LH1 antenna complex influences the free energy change for the primary electron transfer reaction through an effect on the reduction potential of the primary

Ronald W. Visschers; Simone I. E. Vulto; Michael R. Jones; Rienk van Grondelle; Ruud Kraayenhof

1999-01-01

299

Functional LH1 antenna complexes influence electron transfer in bacterial photosynthetic reaction centers  

Microsoft Academic Search

The effect of the light harvesting 1 (LH1) antenna complex on the driving force for light-driven electron transfer in the Rhodobacter sphaeroidesreaction center has been examined. Equilibrium redox titrations show that the presence of the LH1 antenna complex influences the free energy change for the primary electron transfer reaction through an effect on the reduction potential of the primary donor.

Ronald W. Visschers; Simone I. E. Vulto; Michael R. Jones; Rienk van Grondelle; Ruud Kraayenhof

1999-01-01

300

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

Federal Register 2010, 2011, 2012, 2013

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2012-07-10

301

77 FR 6310 - Electronic Fund Transfers (Regulation E)  

Federal Register 2010, 2011, 2012, 2013

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2012-02-07

302

Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer–fullerene blends  

NASA Astrophysics Data System (ADS)

The conversion of photoexcitations into charge carriers in organic solar cells is facilitated by the dissociation of excitons at the donor/acceptor interface. The ultrafast timescale of charge separation demands sophisticated theoretical models and raises questions about the role of coherence in the charge-transfer mechanism. Here, we apply two-dimensional electronic spectroscopy to study the electron transfer process in poly(3-hexylthiophene)/PCBM (P3HT/PCBM) blends. We report dynamics maps showing the pathways of charge transfer that clearly expose the significance of hot electron transfer. During this ultrafast electron transfer, vibrational coherence is directly transferred from the P3HT exciton to the P3HT hole polaron in the crystalline domain. This result reveals that the exciton converts to a hole with a similar spatial extent on a timescale far exceeding other photophysical dynamics including vibrational relaxation.

Song, Yin; Clafton, Scott N.; Pensack, Ryan D.; Kee, Tak W.; Scholes, Gregory D.

2014-09-01

303

Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer-fullerene blends.  

PubMed

The conversion of photoexcitations into charge carriers in organic solar cells is facilitated by the dissociation of excitons at the donor/acceptor interface. The ultrafast timescale of charge separation demands sophisticated theoretical models and raises questions about the role of coherence in the charge-transfer mechanism. Here, we apply two-dimensional electronic spectroscopy to study the electron transfer process in poly(3-hexylthiophene)/PCBM (P3HT/PCBM) blends. We report dynamics maps showing the pathways of charge transfer that clearly expose the significance of hot electron transfer. During this ultrafast electron transfer, vibrational coherence is directly transferred from the P3HT exciton to the P3HT hole polaron in the crystalline domain. This result reveals that the exciton converts to a hole with a similar spatial extent on a timescale far exceeding other photophysical dynamics including vibrational relaxation. PMID:25215959

Song, Yin; Clafton, Scott N; Pensack, Ryan D; Kee, Tak W; Scholes, Gregory D

2014-01-01

304

Carbon electrodes for direct electron transfer type laccase cathodes investigated by current density-cathode potential behavior.  

PubMed

Direct electron transfer from carbon electrodes to adsorbed laccase (EC 1.10.3.2) from Trametes versicolor is widely used to enable mediatorless enzymatic biofuel cell cathodes. However, data published so far are poorly comparable in terms of oxygen reduction performance. We thus present a comparative characterization of carbon-based electrode materials as cathode in half-cell configuration, employing adsorbed laccase as oxygen reduction catalyst. Open circuit potentials and performances were significantly increased by laccase adsorption, indicating the occurrence of direct electron transfer. At a potential of 0.5 V vs. SCE volume-normalized current densities of approximately 10, 37, 40, 70, and 77 ?A cm(-3) were measured for cathodes nanotubes, carbon nanofibers and multi-walled carbon nanotubes, respectively. In addition, we could show that both, carbon nanotubes and porous carbon tubes exhibit dramatically lower current densities compared to graphite felt and carbon nanofibers when normalized to BET surface instead of electrode volume. Further work will be required to clarify whether this stems from material-dependent interaction of enzyme and electrode surface or constricted enzyme adsorption due to agglomeration of the nanotubes. In case of the latter, an improved dispersion of the nanotubes upon electrode fabrication may greatly enhance their performance. PMID:20627511

Rubenwolf, Stefanie; Strohmeier, Oliver; Kloke, Arne; Kerzenmacher, Sven; Zengerle, Roland; von Stetten, Felix

2010-10-15

305

Electronic coulombic coupling of excitation-energy transfer in xanthorhodopsin.  

PubMed

Electronic coupling of excitation-energy transfer (EET) in a retinal (RET) protein, xanthorhodopsin (xR), was studied theoretically. The protein, functioning as a light driven proton pump, contains a carotenoid antenna, salinixanthin (SXN), to collect light energy for an RET chromophore through EET. The pseudo-Coulombic interaction (PCI) between the donor SXN and the acceptor RET molecules was calculated by a transition density fragment interaction (TDFI) method, which overcomes difficulty arising in the evaluation of PCI in xR by a conventional dipole-dipole (dd) method, at the ab initio TDDFT/SAC-CI level of theory. The result nicely agrees with the experimentally observed PCI. To examine the correlation between the SXN-RET alignment and the EET efficiency, we computed PCIs for SXN conformations that are virtually generated around the protein. The calculation shows that the optimal SXN alignment for the maximally tuned efficiency of EET is attained in the native xR. PCI in another retinal protein, archaerhodopsin-2, which also binds a carotenoid but lacks EET activity, was also evaluated. The computed PCI is negligibly small, well explaining the lack of EET efficiency. PMID:19772318

Fujimoto, Kazuhiro J; Hayashi, Shigehiko

2009-10-14

306

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

307

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

SciTech Connect

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

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

2014-01-01

308

Electron transfer precedes ATP hydrolysis during nitrogenase catalysis  

PubMed Central

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

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

2013-01-01

309

Performance of alumina-supported Pt catalysts in an electron-beam-sustained CO2 laser amplifier  

NASA Astrophysics Data System (ADS)

The performance of an alumina-supported Pt catalyst system used to maintain the gas purity in an electron-beam-sustained (636) isotope CO2 laser amplifier has been tested. The system characteristics using the two-zone, parallel flow reactor were determined for both continuous- and end-of-day reactor operation using on-line mass spectrometric sampling. The laser amplifier was run with an energy loading of typically 110 J-l/atm and an electron-beam current of 4 mA/sq cm. With these conditions and a pulse repetition frequency of 10 Hz for up to 10,000 shots, increases on the order of 100 ppm O2 were observed with the purifier on and 150 ppm with it off. The 1/e time recovery time was found to be approximately 75 minutes.

Cunningham, D. L.; Jones, P. L.; Miyake, C. I.; Moody, S. E.

1990-06-01

310

Performance of alumina-supported Pt catalysts in an electron-beam-sustained CO2 laser amplifier  

NASA Technical Reports Server (NTRS)

The performance of an alumina-supported Pt catalyst system used to maintain the gas purity in an electron-beam-sustained (636) isotope CO2 laser amplifier has been tested. The system characteristics using the two-zone, parallel flow reactor were determined for both continuous- and end-of-day reactor operation using on-line mass spectrometric sampling. The laser amplifier was run with an energy loading of typically 110 J-l/atm and an electron-beam current of 4 mA/sq cm. With these conditions and a pulse repetition frequency of 10 Hz for up to 10,000 shots, increases on the order of 100 ppm O2 were observed with the purifier on and 150 ppm with it off. The 1/e time recovery time was found to be approximately 75 minutes.

Cunningham, D. L.; Jones, P. L.; Miyake, C. I.; Moody, S. E.

1990-01-01

311

Theory of Proton-Coupled Electron Transfer in Energy Conversion Processes  

PubMed Central

Conspectus Proton-coupled electron transfer (PCET) reactions play an essential role in a broad range of energy conversion processes, including photosynthesis and respiration. These reactions also form the basis of many types of solar fuel cells and electrochemical devices. Recent advances in the theory of PCET enable the prediction of the impact of system properties on the reaction rates. These predictions may guide the design of more efficient catalysts for energy production, including those based on artificial photosynthesis and solar energy conversion. This Account summarizes the theoretically predicted dependence of PCET rates on system properties and illustrates potential approaches for tuning the reaction rates in chemical systems. A general theoretical formulation for PCET reactions has been developed over the past decade. In this theory, PCET reactions are described in terms of nonadiabatic transitions between the reactant and product electron-proton vibronic states. A series of nonadiabatic rate constant expressions for both homogeneous and electrochemical PCET reactions have been derived in various well-defined limits. Recently this theory has been extended to include the effects of solvent dynamics and to describe ultrafast interfacial PCET. Analysis of the rate constant expressions provides insight into the underlying physical principles of PCET and enables the prediction of the dependence of the rates on the physical properties of the system. Moreover, the kinetic isotope effect, which is the ratio of the rates for hydrogen and deuterium, provides a useful mechanistic probe. Typically the PCET rate will increase as the electronic coupling and temperature increase and as the total reorganization energy and equilibrium proton donor-acceptor distance decrease. The rate constant is predicted to increase as the driving force becomes more negative, rather than exhibit turnover behavior in the inverted region, because excited vibronic product states associated with low free energy barriers and relatively large vibronic couplings become accessible. The physical basis for the experimentally observed pH dependence of PCET reactions has been debated in the literature. When the proton acceptor is a buffer species, the pH dependence may arise from the protonation equilibrium of the buffer. It could also arise from kinetic complexity of competing concerted and sequential PCET reaction pathways. In electrochemical PCET, the heterogeneous rate constants and current densities depend strongly on the overpotential. The change in equilibrium proton donor-acceptor distance upon electron transfer may lead to asymmetries in the Tafel plots and deviations of the transfer coefficient from the standard value of one-half at zero overpotential. Applications of this theory to experimentally studied systems illustrate approaches that can be utilized to tune the PCET rate. For example, the rate can be tuned by changing the pH or using different buffer species as proton acceptors. The rate can also be tuned with site-specific mutagenesis in biological systems or chemical modifications that vary the substituents on the redox species in chemical systems. Understanding the impact of these changes on the PCET rate may assist experimental efforts to enhance energy conversion processes. PMID:19807148

Hammes-Schiffer, Sharon

2010-01-01

312

Localization of alkali metal ions in sodium-promoted palladium catalysts as studied by low energy ion scattering and transmission electron microscopy  

SciTech Connect

Three series of palladium-based catalysts have been studied by Low Energy Ion Scattering (LEIS) and Transmission Electron Microscopy (TEM). The first series is comprised of Na-Pd/SiO{sub 2} catalysts, obtained by addition of palladium to a silica support and by further addition of sodium ions with a Na/Pd atomic ratio (R) equal to 0,6.4 and 25.6. The second series consists of palladium catalysts supported on natural pumice, in which, due to a different loading of supported palladium, R{prime}, the (Na+K)/Pd atomic ratio, is equal to 17.0 and 39.4. The third series is represented by two palladium-based catalysts supported on {open_quotes}model pumices,{close_quotes} synthetic silico-aluminates, obtained by sol-gel techniques, with a different amount of sodium, and R equal to 2.1 and 6.1 respectively. LEIS experiments and electron microscopy demonstrate a different location of alkali metal ions in the first two series: in the Na-Pd/SiO{sub 2} catalysts sodium is distributed in a way which is not uniform on the support and on the palladium metal, which is partly decorated with Na ions, whereas in the Pd/natural-pumice series the palladium surface is sodium-free. The results on the third series of catalysts, Pd/model pumice, are not definitive on the basis of the LEIS and TEM analyses, but by FTIR study of CO and CO{sub 2} adsorption, the decoration of palladium by sodium ions could be excluded. The results confirm the importance of the alkali metal ion location in alkali-promoted palladium catalysts and open new possibilities in the design of palladium-supported catalysts by a better control of promoter location. 18 refs., 5 figs., 2 tabs.

Liotta, L.F.; Deganello, G.; Delichere, P. [Istituto di Chimica e Tecnologia dei Prodotti Naturali, Palermo (Italy)] [and others] [Istituto di Chimica e Tecnologia dei Prodotti Naturali, Palermo (Italy); and others

1996-12-01

313

Kinetic resolution of racemic 2-hydroxy-?-butyrolactones by asymmetric esterification using diphenylacetic acid with pivalic anhydride and a chiral acyl-transfer catalyst.  

PubMed

Various optically active 2-hydroxy-?-butyrolactone derivatives are produced via the kinetic resolution of racemic 2-hydroxy-?-butyrolactones with diphenylacetic acid using pivalic anhydride and (R)-benzotetramisole ((R)-BTM), a chiral acyl-transfer catalyst. Importantly, the substrate scope of this novel protocol is fairly broad (12 examples, s-value; up to over 1000). In addition, we succeeded in disclosing the reaction mechanism to afford high enantioselectivity using theoretical calculations and expounded on the substituent effects at the C-3 positions in 2-hydroxylactones. PMID:23461674

Nakata, Kenya; Gotoh, Kouya; Ono, Keisuke; Futami, Kengo; Shiina, Isamu

2013-03-15

314

Ab initio quantum mechanical/molecular mechanical simulation of electron transfer process: Fractional electron approach  

SciTech Connect

Electron transfer (ET) reactions are one of the most important processes in chemistry and biology. Because of the quantum nature of the processes and the complicated roles of the solvent, theoretical study of ET processes is challenging. To simulate ET processes at the electronic level, we have developed an efficient density functional theory (DFT) quantum mechanical (QM)/molecular mechanical (MM) approach that uses the fractional number of electrons as the order parameter to calculate the redox free energy of ET reactions in solution. We applied this method to study the ET reactions of the aqueous metal complexes Fe(H{sub 2}O){sub 6}{sup 2+/3+} and Ru(H{sub 2}O){sub 6}{sup 2+/3+}. The calculated oxidation potentials, 5.82 eV for Fe(II/III) and 5.14 eV for Ru(II/III), agree well with the experimental data, 5.50 and 4.96 eV, for iron and ruthenium, respectively. Furthermore, we have constructed the diabatic free energy surfaces from histogram analysis based on the molecular dynamics trajectories. The resulting reorganization energy and the diabatic activation energy also show good agreement with experimental data. Our calculations show that using the fractional number of electrons (FNE) as the order parameter in the thermodynamic integration process leads to efficient sampling and validate the ab initio QM/MM approach in the calculation of redox free energies.

Zeng Xiancheng; Hu Hao; Hu Xiangqian; Cohen, Aron J.; Yang Weitao [Department of Chemistry, Duke University, Durham, North Carolina 27708 (United States)

2008-03-28

315

Kinetics, energetics, and electronic coupling of the primary electron transfer reactions in mutated reaction centers of Blastochloris viridis.  

PubMed Central

Femtosecond spectroscopy in combination with site-directed mutagenesis has been used to study the dynamics of primary electron transfer in native and 12 mutated reaction centers of Blastochloris (B) (formerly called Rhodopseudomonas) viridis. The decay times of the first excited state P* vary at room temperature between of 0.6 and 50 ps, and at low temperatures between 0.25 and 90 ps. These changes in time constants are discussed within the scope of nonadiabatic electron transfer theory using different models: 1) If the mutation is assumed to predominantly influence the energetics of the primary electron transfer intermediates, the analysis of the room temperature data for the first electron transfer step to the intermediate P(+)B(A)(-) yields a reorganization energy lambda = 600 +/- 200 cm(-1) and a free energy gap Delta G ranging from -600 cm(-1) to 800 cm(-1). However, this analysis fails to describe the temperature dependence of the reaction rates. 2) A more realistic description of the temperature dependence of the primary electron transfer requires different values for the energetics and specific variations of the electronic coupling upon mutation. Apparently the mutations also lead to pronounced changes in the electronic coupling, which may even dominate the change in the reaction rate. One main message of the paper is that a simple relationship between mutation and a change in one reaction parameter cannot be given and that at the very least the electronic coupling is changed upon mutation. PMID:12023243

Huppman, P; Arlt, T; Penzkofer, H; Schmidt, S; Bibikova, M; Dohse, B; Oesterhelt, D; Wachtveit, J; Zinth, W

2002-01-01

316

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. PMID:9591682

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

1998-01-01

317

Photoinduced electron transfer in perylene-TiO2 nanoassemblies.  

PubMed

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

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

2013-01-01

318

Temperature Invariance of the Nitrogenase Electron Transfer Mechanism  

PubMed Central

Earlier studies on electron transfer (ET) from the nitrogenase Fe protein to the MoFe protein concluded that the mechanism for ET changed during cooling from 25°C to 5°C, based on the observation that the rate constant for Fe protein to MoFe protein ET decreases strongly, with a non-linear Arrhenius plot. They further indicated that the ET was reversible, with complete ET at ambient but with an equilibrium constant near unity at 5°C. These studies were carried out with buffers having a strong temperature coefficient. We have examined the temperature variation in the kinetics of oxidation of the Fe protein by the MoFe protein at constant pH = 7.4 fixed by the buffer MOPS, which has a very small temperature coefficient. Using MOPS, we also observe temperature dependent ET rate constants, with non-linear Arrhenius plots. But, we find that ET is gated across the temperature range by a conformational change that involves the binding of numerous water molecules, consistent with an unchanging ET mechanism. Furthermore, there is no sKIE throughout the temperature range studied, again consistent with an unchanging mechanism In addition, the non-linear Arrhenius plots are explained by the change in heat capacity caused by the binding of waters in an invariant gating ET mechanism. Together, these observations contradict the idea of a change in ET mechanism with cooling. Finally, the extent of ET at constant pH does not change significantly with temperature, in contrast to the previously proposed change in ET equilibrium. PMID:23050654

Mayweather, Diana; Danyal, Karamatullah; Dean, Dennis R.; Seefeldt, Lance C.; Hoffman, Brian M.

2012-01-01

319

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

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

320

Gene Transfer to Rabbit Retina with Electron Avalanche Transfection  

E-print Network

clinically acceptable methods for efficient gene transfer. Electroporation is widely used for transfection electroporation. Also demonstrated was efficient plasmid DNA transfer to the rabbit retina after subretinal DNA many drawbacks: they can be immunogenic and toxic and, most notably for adenoassociated virus, have

Palanker, Daniel

321

The Potential Use of Electronic File Transfer in the National Archives.  

ERIC Educational Resources Information Center

This paper reviews the incompatibilities among federal government electronic records and explores the potential use of electronic file transfer in the National Archives. It begins by explaining the procedures of the current Center for Electronic Records (NNX) for dealing with accessioning, preservation, and reference tapes. The advantages and…

Thornton, Roberta

322

Development of electron spin polarization in photosynthetic electron transfer by the radical pair mechanism.  

PubMed Central

We have extended the radical pair theory to treat systems of membrane-bound radicals with g tensor anisotropy. Analysis of the polarized electron paramagnetic resonance (EPR) signals of P700+, originating from photosystem I of higher plants, in terms of the radical pair mechanism provides information about the sequence of early electron acceptors. To account for the orientation dependence of the line shape and integrated area of this polarized signal, we propose the electron transfer sequence to be P700 leads to A1 leads to X leads to Fd(A, B), where A1 is a small organic molecule (possibly chlorophyll), X is the acceptor species observed recently in low-temperature EPR studies, and Fd(A, B) are the ferredoxin iron-sulfur centers A and B. Our calculations provide information about the life-times of A1-, and X-, and their exchange interactions with P700+. We also find supporting evidence for the orientation of X- in the thylakoid membrane reported recently by G. C. Dismukes and K. Sauer (Biochim. Biophys. Acta. 504:431-445.). PMID:233573

Friesner, R; Dismukes, G C; Sauer, K

1979-01-01

323

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. PMID:19778106

Migliore, Agostino

2009-01-01

324

Computational insight into the initial steps of the Mars-van Krevelen mechanism: electron transfer and surface defects in the reduction of polyoxometalates.  

PubMed

Metal oxides as a rule oxidize and oxygenate substrates via the Mars-van Krevelen mechanism. A well-defined ?-Keggin polyoxometalate, H(5)PV(2)Mo(10)O(40), can be viewed as an analogue of discrete structure that reacts via the Mars-van Krevelen mechanism both in solution and in the gas phase. Guided by previous experimental observations, we have studied the key intermediates on the reaction pathways of its reduction by various compounds using high-level DFT calculations. These redox reactions of polyoxometalates require protons, and thus such complexes were explicitly considered. First, the energetics of outer-sphere proton and electron transfer as well as coupled proton and electron transfer were calculated for seven substrates. This was followed by identification of possible key intermediates on the subsequent reaction pathways that feature displacement of the metal atom from the Keggin structure and coordinatively unsaturated sites on the H(5)PV(2)Mo(10)O(40) surface. Such metal defects are favored at vanadium sites. For strong reducing agents the initial outer-sphere electron transfer, alone or possibly coupled with proton transfer, facilitates formation of metal defects. Subsequent coordination allows for formation of reactive ensembles on the catalyst surface, for which the selective oxygen-transfer step becomes feasible. Weak reducing agents do not facilitate defect formation by outer-sphere electron and/or proton transfers, and thus formation of metal defect structures prior to the substrate activation is suggested as an initial step. Calculated geometries and energies of metal defect structures support experimentally observed intermediates and demonstrate the complex nature of the Mars-van Krevelen mechanism. PMID:23210519

Efremenko, Irena; Neumann, Ronny

2012-12-26

325

Oxidation catalyst  

DOEpatents

The present invention generally relates to catalyst systems and methods for oxidation of carbon monoxide. The invention involves catalyst compositions which may be advantageously altered by, for example, modification of the catalyst surface to enhance catalyst performance. Catalyst systems of the present invention may be capable of performing the oxidation of carbon monoxide at relatively lower temperatures (e.g., 200 K and below) and at relatively higher reaction rates than known catalysts. Additionally, catalyst systems disclosed herein may be substantially lower in cost than current commercial catalysts. Such catalyst systems may be useful in, for example, catalytic converters, fuel cells, sensors, and the like.

Ceyer, Sylvia T. (Cambridge, MA); Lahr, David L. (Cambridge, MA)

2010-11-09

326

Transferable pseudoclassical electrons for aufbau of atomic ions.  

PubMed

Generalizing the LEWIS reactive force field from electron pairs to single electrons, we present LEWIS• in which explicit valence electrons interact with each other and with nuclear cores via pairwise interactions. The valence electrons are independently mobile particles, following classical equations of motion according to potentials modified from Coulombic as required to capture quantum characteristics. As proof of principle, the aufbau of atomic ions is described for diverse main group elements from the first three rows of the periodic table, using a single potential for interactions between electrons of like spin and another for electrons of unlike spin. The electrons of each spin are found to distribute themselves in a fashion akin to the major lobes of the hybrid atomic orbitals, suggesting a pointillist description of the electron density. The broader validity of the LEWIS• force field is illustrated by predicting the vibrational frequencies of diatomic and triatomic hydrogen species. PMID:24752384

Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

2014-06-01

327

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

E-print Network

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

Nesterov, Alexander I

2014-01-01

328

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

E-print Network

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

Alexander I. Nesterov; Gennady P. Berman

2014-11-28

329

On the connection of semiclassical instanton theory with Marcus theory for electron transfer in solution  

SciTech Connect

We present a derivation of Marcus theory of electron transfer in solution starting from semiclassical instanton theory. The conventional semiclassical instanton theory provides an inadequate description of the electron transfer process in the inverted Marcus regime. This has been attributed to the lack of backscattering in the product region, which is represented as a semi-infinite continuum of states. For electron transfer processes in condensed phase, the electronic states in the acceptor well are bound, which violates the continuum assumption. We show by detailed analysis of the minimum action path of a model system for electron transfer that the proper tunneling coordinate is a delocalized, 'bead-count' mode. The tunneling mode is analytically continued in the complex plane as in the traditional derivation. Unlike the traditional analysis where the method of steepest descent is used, the tunneling coordinate is treated as a quasi-zero mode. This feature allows including the influence of backscattering in the acceptor well and leads to the recovery of the Marcus formula for the rate of electron transfer. The results have implications on the performance of ring polymer molecular dynamics for the study of electron transfer dynamics.

Shushkov, Philip [Department of Chemistry, Yale University, New Haven, Connecticut 06520 (United States)

2013-06-14

330

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

SciTech Connect

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

Neta, P.

1995-02-01

331

Exciton/Charge-transfer Electronic Couplings in Organic Semiconductors  

E-print Network

Charge transfer (CT) states and excitons are important in energy conversion processes that occur in organic light emitting devices (OLEDS) and organic solar cells. An ab initio density functional theory (DFT) method for ...

Difley, Seth

332

Electron transfer dynamics and excited state branching in a charge-transfer platinum(ii) donor-bridge-acceptor assembly.  

PubMed

A linear asymmetric Pt(ii) trans-acetylide donor-bridge-acceptor triad designed for efficient charge separation, NAP[triple bond, length as m-dash]Pt(PBu3)2[triple bond, length as m-dash]Ph-CH2-PTZ (), containing strong electron acceptor and donor groups, 4-ethynyl-N-octyl-1,8-naphthalimide (NAP) and phenothiazine (PTZ) respectively, has been synthesised and its photoinduced charge transfer processes characterised in detail. Excitation with 400 nm, ?50 fs laser pulse initially populates a charge transfer manifold stemming from electron transfer from the Pt-acetylide centre to the NAP acceptor and triggers a cascade of charge and energy transfer events. A combination of ultrafast time-resolved infrared (TRIR) and transient absorption (TA) spectroscopies, supported by UV-Vis/IR spectroelectrochemistry, emission spectroscopy and DFT calculations reveals a self-consistent photophysical picture of the excited state evolution from femto- to milliseconds. The characteristic features of the NAP-anion and PTZ-cation are clearly observed in both the TRIR and TA spectra, confirming the occurrence of electron transfer and allowing the rate constants of individual ET-steps to be obtained. Intriguingly, has three separate ultrafast electron transfer pathways from a non-thermalised charge transfer manifold directly observed by TRIR on timescales ranging from 0.2 to 14 ps: charge recombination to form either the intraligand triplet (3)NAP with 57% yield, or the ground state, and forward electron transfer to form the full charge-separated state (3)CSS ((3)[PTZ(+)-NAP(-)]) with 10% yield as determined by target analysis. The (3)CSS decays by charge-recombination to the ground state with ?1 ns lifetime. The lowest excited state is (3)NAP, which possesses a long lifetime of 190 ?s and efficiently sensitises singlet oxygen. Overall, molecular donor-bridge-acceptor triad demonstrates excited state branching over 3 different pathways, including formation of a long-distant (18 Å) full charge-separated excited state from a directly observed vibrationally hot precursor state. PMID:25361227

Scattergood, Paul A; Delor, Milan; Sazanovich, Igor V; Bouganov, Oleg V; Tikhomirov, Sergei A; Stasheuski, Alexander S; Parker, Anthony W; Greetham, Gregory M; Towrie, Michael; Davies, E Stephen; Meijer, Anthony J H M; Weinstein, Julia A

2014-12-21

333

26 CFR 25.6302-1 - Voluntary payments of gift taxes by electronic funds transfer.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 false Voluntary payments of gift taxes by electronic funds transfer. 25.6302-1...DEPARTMENT OF THE TREASURY (CONTINUED) ESTATE AND GIFT TAXES GIFT TAX; GIFTS MADE AFTER DECEMBER 31, 1954...

2010-04-01

334

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

Code of Federal Regulations, 2010 CFR

...and Public Property NATIONAL ARCHIVES AND RECORDS ADMINISTRATION RECORDS MANAGEMENT TRANSFER OF RECORDS TO THE NATIONAL ARCHIVES...requirements available on the NARA Electronic Records Management Initiative Web page at...

2010-07-01

335

36 CFR 1235.48 - What documentation must agencies transfer with electronic records?  

Code of Federal Regulations, 2010 CFR

...and Public Property NATIONAL ARCHIVES AND RECORDS ADMINISTRATION RECORDS MANAGEMENT TRANSFER OF RECORDS TO THE NATIONAL ARCHIVES...formats are available on the NARA Electronic Records Management Initiative Web page at...

2010-07-01

336

26 CFR 20.6302-1 - Voluntary payments of estate taxes by electronic funds transfer.  

Code of Federal Regulations, 2010 CFR

... 2010-04-01 false Voluntary payments of estate taxes by electronic funds transfer. 20.6302-1...SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) ESTATE AND GIFT TAXES ESTATE TAX; ESTATES OF DECEDENTS DYING AFTER AUGUST...

2010-04-01

337

26 CFR 20.6302-1 - Voluntary payments of estate taxes by electronic funds transfer.  

Code of Federal Regulations, 2011 CFR

... 2010-04-01 true Voluntary payments of estate taxes by electronic funds transfer. 20.6302-1...SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) ESTATE AND GIFT TAXES ESTATE TAX; ESTATES OF DECEDENTS DYING AFTER AUGUST...

2011-04-01

338

26 CFR 20.6302-1 - Voluntary payments of estate taxes by electronic funds transfer.  

Code of Federal Regulations, 2013 CFR

... 2013-04-01 false Voluntary payments of estate taxes by electronic funds transfer. 20.6302-1...SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) ESTATE AND GIFT TAXES ESTATE TAX; ESTATES OF DECEDENTS DYING AFTER AUGUST...

2013-04-01

339

26 CFR 20.6302-1 - Voluntary payments of estate taxes by electronic funds transfer.  

... 2013-04-01 true Voluntary payments of estate taxes by electronic funds transfer. 20.6302-1...SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) ESTATE AND GIFT TAXES ESTATE TAX; ESTATES OF DECEDENTS DYING AFTER AUGUST...

2014-04-01

340

26 CFR 20.6302-1 - Voluntary payments of estate taxes by electronic funds transfer.  

Code of Federal Regulations, 2012 CFR

... 2012-04-01 false Voluntary payments of estate taxes by electronic funds transfer. 20.6302-1...SERVICE, DEPARTMENT OF THE TREASURY (CONTINUED) ESTATE AND GIFT TAXES ESTATE TAX; ESTATES OF DECEDENTS DYING AFTER AUGUST...

2012-04-01

341

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

Code of Federal Regulations, 2010 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2010-04-01

342

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

Code of Federal Regulations, 2012 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2012-04-01

343

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

Code of Federal Regulations, 2013 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2013-04-01

344

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

Code of Federal Regulations, 2011 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2011-04-01

345

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

Code of Federal Regulations, 2010 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2010-04-01

346

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

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2014-04-01

347

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

Code of Federal Regulations, 2011 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2011-04-01

348

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

Code of Federal Regulations, 2013 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2013-04-01

349

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

Code of Federal Regulations, 2012 CFR

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2012-04-01

350

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

...in taxes on tobacco products, cigarette papers, and cigarette tubes combining tax liabilities...commercial bank in making payment by electronic fund transfer (EFT) of taxes on tobacco products, cigarette papers, and cigarette...

2014-04-01

351

Proton-coupled electron transfer : from basic principles to small molecule activation  

E-print Network

Proton-coupled electron transfer (PCET) is the basic mechanism for bioenergetic conversion. Hallmark examples of such reactivities include water oxidation which is coupled to photosynthesis and oxygen reduction which is ...

Rosenthal, Joel, 1979-

2007-01-01

352

Electron Transfer and the Roles of Flavins during Iron(III) Reduction by Shewanella Oneidensis.  

E-print Network

??The purpose of our investigation is to explore the terminal electron-transfer reaction of Shewanella oneidensis, a dissimilatory metal-reducing bacterium (DMRB), during the anaerobic respiration of… (more)

Puls, Brendan

2013-01-01

353

The Secure Electronic Transfer of Prescriptions David Chadwick, University of Salford  

E-print Network

1 The Secure Electronic Transfer of Prescriptions David Chadwick, University of Salford Darren of confidentiality, integrity and availability, and then uses these to determine the security requirements for ETP. Introduction Information security is traditionally viewed as providing confidentiality, integrity

Kent, University of

354

Crossed-beam studies of electron transfer to oriented trichloronitromethane, CCl3NO2, molecules  

E-print Network

of the NO orbital. We have extended these studies to trichloronitromethane, CCl3NO2, also known as chloropicrin . Electron transfer collisions produce a positive and negative ion pair which are separated and detected

Brooks, Philip R.

355

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

NASA Technical Reports Server (NTRS)

A molecular shift register memory at the molecular level is described. The memory elements consist of molecules can exit in either an oxidized or reduced state and the bits are shifted between the cells with photoinduced electron transfer reactions.

Beratan, D.

1993-01-01

356

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

NASA Astrophysics Data System (ADS)

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

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

2010-03-01

357

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

SciTech Connect

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

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

2013-10-01

358

Electron transfer in collisions of keV potassium ions with methane molecules  

NASA Astrophysics Data System (ADS)

Absolute total electron transfer cross sections have been measured for the K+-CH4 system, at impact energies 0.5-3.5 keV. The charge transfer cross sections show a monotonic increasing behaviour as a function of the incident energy. Semiempirical calculation is in good agreement with the present cross-section data.

Alarcón, F. B.; Martínez, H.

2013-03-01

359

Theoretical formulation for electron transfer coupled to multiple protons: Application to amidiniumcarboxylate interfaces  

E-print Network

for the two systems, leading to an endothermic reaction for the donor­ amidinium­carboxylate ­acceptor system and an exothermic reaction for the donor­ carboxylate­amidinium ­acceptor system. The deuterium kinetic isotope the electron transfer reaction is coupled to the motion of two protons at the proton transfer interface

Hammes-Schiffer, Sharon

360

Charge Transfer in Fullerene-Conducting Polymer Compositex: Electronic and Excitonic Properties  

Microsoft Academic Search

C60 doping into conducting polymer with highly extended ?-electron system in the main chain induces remarkable quenching of photoluminescence in conducting polymer and drastic enhancement of photoconductivity. These results can be explained in terms of photo-induced charge transfer between conducting polymer and C60. That is, photoexcited excitons or exciton-polarons on conducting polymer are effectively dissociated at C60 molecules transferring electrons

Katsumi Yoshino; Kazuya Tada; Akihiko Fujii; Kazuhisa Hosoda; Shin-ichi Kawabe; Hirotake Kajii; Masaharu Hirohata; Rahmat Hidayat; Hisashi Araki; Anvar A. Zakhidov; Ryu-ichi Sugmoto; Masahiko Iyoda; Mitsuo Ishikawa; Toshio Masuda

1997-01-01

361

Very fast electron transfer from cytochrome to the bacterial photosynthetic reaction center at low temperature  

Microsoft Academic Search

Electron transfer from the proximal heme c-559 to the primary donor P has been studied in reaction centers of the photosynthetic bacterium Rhodopseudomonas viridis in which the tyrosine residue L162 was replaced by threonine. In the wild type, when the two high-potential hemes of the tetraheme cytochrome are reduced before flash excitation, a rapid electron transfer (t1\\/2=190 ns) observed at

José M Ortega; Barbara Dohse; Dieter Oesterhelt; Paul Mathis

1997-01-01

362

Analysis of the trypanosome flagellar proteome using a combined electron transfer\\/collisionally activated dissociation strategy  

Microsoft Academic Search

The use of electron-transfer dissociation as an alternative peptide ion activation method for generation of protein sequence\\u000a information is examined here in comparison with the conventional method of choice, collisionally activated dissociation, using\\u000a a linear ion trapping instrument. Direct comparability between collisionally and electron-transfer-activated product ion data\\u000a were ensured by employing an activation-switching method during acquisition, sequentially activating precisely the

Sarah R. Hart; King Wai Lau; Zhiqi Hao; Richard Broadhead; Neil Portman; Andreas Hühmer; Keith Gull; Paul G. McKean; Simon J. Hubbard; Simon J. Gaskell

2009-01-01

363

Reaction dynamics and proton coupled electron transfer: studies of tyrosine-based charge transfer in natural and biomimetic systems.  

PubMed

In bioenergetic reactions, electrons are transferred long distances via a hopping mechanism. In photosynthesis and DNA synthesis, the aromatic amino acid residue, tyrosine, functions as an intermediate that is transiently oxidized and reduced during long distance electron transfer. At physiological pH values, oxidation of tyrosine is associated with a deprotonation of the phenolic oxygen, giving rise to a proton coupled electron transfer (PCET) reaction. Tyrosine-based PCET reactions are important in photosystem II, which carries out the light-induced oxidation of water, and in ribonucleotide reductase, which reduces ribonucleotides to form deoxynucleotides. Photosystem II contains two redox-active tyrosines, YD (Y160 in the D2 polypeptide) and YZ (Y161 in the D1 polypeptide). YD forms a light-induced stable radical, while YZ functions as an essential charge relay, oxidizing the catalytic Mn?CaO? cluster on each of four photo-oxidation reactions. In Escherichia coli class 1a RNR, the ?2 subunit contains the radical initiator, Y122O•, which is reversibly reduced and oxidized in long range electron transfer with the ?2 subunit. In the isolated E. coli ?2 subunit, Y122O• is a stable radical, but Y122O• is activated for rapid PCET in an ?2?2 substrate/effector complex. Recent results concerning the structure and function of YD, YZ, and Y122 are reviewed here. Comparison is made to recent results derived from bioengineered proteins and biomimetic compounds, in which tyrosine-based charge transfer mechanisms have been investigated. This article is part of a Special Issue entitled: Vibrational spectroscopies and bioenergetic systems. PMID:25260243

Barry, Bridgette A

2015-01-01

364

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

NASA Astrophysics Data System (ADS)

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

Ramakrishnan, Raghunathan; Nest, Mathias

2015-01-01

365

pH-Dependent Reduction Potentials and Proton-Coupled Electron Transfer Mechanisms in Hydrogen-Producing Nickel Molecular Electrocatalysts  

SciTech Connect

The nickel-based Ph Bz 2 2 P N electrocatalysts, which are comprised of a nickel atom and two 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane ligands, have been shown to effectively catalyze H2 production in acetonitrile. Recent electrochemical experiments revealed a linear dependence of the NiII/I reduction potential on pH, suggesting a proton-coupled electron transfer (PCET) reaction. In the proposed mechanism, the catalytic cycle begins with a PCET process involving electrochemical electron transfer to the nickel center and intermolecular proton transfer from an acid to the pendant amine ligand. This paper presents quantum mechanical calculations of this PCET process to examine the thermodynamics of the sequential mechanisms, in which either the electron or the proton transfers first (ET–PT and PT–ET, respectively), and the concerted mechanism (EPT). The favored mechanism depends on a balance among many factors, including the acid strength, association free energy for the acid–catalyst complex, PT free energy barrier, and ET reduction potential. The ET reduction potential is less negative after PT, favoring the PT–ET mechanism, and the association free energy is less positive after reduction, favoring the ET–PT mechanism. The calculations, along with analysis of the experimental data, indicate that the sequential ET–PT mechanism is favored for weak acids because of the substantial decrease in the association free energy after reduction. For strong acids, however, the PT–ET mechanism may be favored because the association free energy is somewhat smaller and PT is more thermodynamically favorable. The concerted mechanism could also occur, particularly for intermediate acid strengths. In the context of the entire catalytic cycle for H2 production, the initial PCET process involving intermolecular PT has a more negative reduction potential than the subsequent PCET process involving intramolecular PT. As a result, the second PCET should occur spontaneously, which is consistent with cyclic voltammogram experiments. 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.

Horvath, Samantha; Fernandez, Laura; Appel, Aaron M.; Hammes-Schiffer, Sharon

2013-04-01

366

Structural basis of inter-protein electron transfer for nitrite reduction in denitrification.  

PubMed

Recent earth science studies have pointed out that massive acceleration of the global nitrogen cycle by anthropogenic addition of bio-available nitrogen has led to a host of environmental problems. Nitrous oxide (N(2)O) is a greenhouse gas that is an intermediate during the biological process known as denitrification. Copper-containing nitrite reductase (CuNIR) is a key enzyme in the process; it produces a precursor for N(2)O by catalysing the one-electron reduction of nitrite (NO2-) to nitric oxide (NO). The reduction step is performed by an efficient electron-transfer reaction with a redox-partner protein. However, details of the mechanism during the electron-transfer reaction are still unknown. Here we show the high-resolution crystal structure of the electron-transfer complex for CuNIR with its cognate cytochrome c as the electron donor. The hydrophobic electron-transfer path is formed at the docking interface by desolvation owing to close contact between the two proteins. Structural analysis of the interface highlights an essential role for the loop region with a hydrophobic patch for protein-protein recognition; it also shows how interface construction allows the variation in atomic components to achieve diverse biological electron transfers. PMID:19890332

Nojiri, Masaki; Koteishi, Hiroyasu; Nakagami, Takuya; Kobayashi, Kazuo; Inoue, Tsuyoshi; Yamaguchi, Kazuya; Suzuki, Shinnichiro

2009-11-01

367

Building model systems to understand Proton-Coupled Electron Transfer in heme : spectroscopic investigation of charge transfer to axially bound diimide acceptors  

E-print Network

Proton-Coupled Electron Transfer (PCET) is an important mechanistic motif in chemistry, which allows for efficient charge transport in many biological systems. We seek to understand how the proton and electron motions are ...

Hanson, Christina J

2013-01-01

368

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

PubMed Central

The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

Liu, Jian; McLuckey, Scott A.

2012-01-01

369

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

PubMed

We report a simple, versatile, and wafer-scale water-assisted transfer printing method (WTP) that enables the transfer of nanowire devices onto diverse nonconventional substrates that were not easily accessible before, such as paper, plastics, tapes, glass, polydimethylsiloxane (PDMS), aluminum foil, and ultrathin polymer substrates. The WTP method relies on the phenomenon of water penetrating into the interface between Ni and SiO(2). The transfer yield is nearly 100%, and the transferred devices, including NW resistors, diodes, and field effect transistors, maintain their original geometries and electronic properties with high fidelity. PMID:21696196

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

2011-08-10

370

A new semiclassical decoupling scheme for electronic transitions in molecular collisions - Application to vibrational-to-electronic energy transfer  

NASA Technical Reports Server (NTRS)

A new semiclassical decoupling scheme (the trajectory-based decoupling scheme) is introduced in a computational study of vibrational-to-electronic energy transfer for a simple model system that simulates collinear atom-diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic-energy separation (lambda), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate-based decoupling scheme) failed. Interference effects are not exhibited in P vs lambda results.

Lee, H.-W.; Lam, K. S.; Devries, P. L.; George, T. F.

1980-01-01

371

Electron transfer of carbonylmetalate radical pairs: femtosecond visible spectroscopy of optically excited ion pairs  

SciTech Connect

Charge transfer excitation at 640 nm of the cobaltocenium tetracarbonylcobaltate ion pair, [Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup -}], was monitored in 1,2- dichloroethane solution by femtosecond transient visible absorption spectroscopy. The absorption prepares a neutral radical pair that can undergo spontaneous back electron transfer, and which shows a double peaked spectrum with features at 760 and 815 nm at 3 ps delay time. Transient decay times of 5.8{+-}0.5 ps were measured by monitoring the decay of Co(CO){sub 4} at 757 nm and 780 nm, and these are assigned to the back electron transfer step. The ET kinetics are consistent with the previously reported rates of electron transfer that were measured for specific vibrational states by picosecond transient IR.

Wen, X.; Spears, K.G. [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Wiederrecht, G.P.; Wasielewski, M.R. [Argonne National Lab., IL (United States)

1997-02-01

372

Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band  

PubMed Central

The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co–O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal–oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism. PMID:18832175

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

2008-01-01

373

THE BENEFITS IN AND BARRIERS TO THE IMPLEMENTATION OF THE ELECTRONIC TRANSFER OF PRESCRIPTIONS  

E-print Network

1 THE BENEFITS IN AND BARRIERS TO THE IMPLEMENTATION OF THE ELECTRONIC TRANSFER OF PRESCRIPTIONS of a study into the benefits and barriers in implementing a system for the Electronic Transmission was to gain a complete appreciation of the expected benefits in and barriers to project success. Without

Kent, University of

374

Excited state dynamics with nonadiabatic transitions for model photoinduced proton-coupled electron transfer reactions  

E-print Network

PCET reactions, the electron and proton coordinates are treated quantum me- chanically, whileExcited state dynamics with nonadiabatic transitions for model photoinduced proton-coupled electron transfer reactions Jian-Yun Fang and Sharon Hammes-Schiffera) Department of Chemistry and Biochemistry

Hammes-Schiffer, Sharon

375

Intermolecular electron transfer may play a major role in biological regulation, defense, and cancer  

Microsoft Academic Search

strong oxidizing agents is incompatible with life, and we have no light in our body to move electrons (except in the eye and skin). So charge transfer re- mained, for the hiologist, more or less a chemical curiosity. Using the method of electron spin resonance (5). I could show that even molecules with low reactivity, which play a major role

Albert Szent-Gy

376

Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes  

E-print Network

Intrinsic Barriers for Electron and Hydrogen Atom Transfer Reactions of Biomimetic Iron Complexes: Self-exchange reactions between high-spin iron complexes of 2,2-bi-imidazoline (H2bim) have been.3 ( 0.3 at 324 K, whereas no such effect is detected in the electron exchange reaction. Proton self

Roth, Justine P.

377

Proton-coupled electron transfer: Free radicals under control  

NASA Astrophysics Data System (ADS)

Biological solar energy conversion requires the coordinated and rapid movement of protons and electrons through complex proteins, called reaction centres. Now, an artificial and structurally simple reaction centre has been synthesized that mimics an important, photosynthetic charge relay.

Barry, Bridgette A.

2014-05-01

378

Electron transfer reaction dynamics of p-nitroaniline in water from liquid to supercritical conditions.  

PubMed

Photoexcitation dynamics of p-nitroaniline (pNA) have been investigated by femto-second transient absorption spectroscopy in water from liquid to supercritical conditions; along the isochoric line from the ambient condition to 664 K at 40.1 MPa and along the isothermal line from 40.1 to 36.1 MPa at 664 K. The rates of the back electron transfer reaction from the photoexcited charge transfer state to the electronic ground state was determined by the bleach recovery of the ground state absorption, and the successive vibrational relaxation in the electronic ground state was determined by the hot-band decay which was apparent at the red edge of the absorption. The variation of the back electron transfer rate was compared with the prediction based on the electron transfer theory including the Franck-Condon active vibrational modes. The results indicated that both the free energy change of the reaction and the change of the intramolecular vibrational reorganization energy cause the characteristic density (or temperature) dependence of the back electron transfer rate. The density dependence of the vibrational relaxation rate was compared with the collision frequency and the coordination number of the solvent molecule around the solute estimated by the molecular dynamics simulations. The density dependence of the coordination of a water oxygen atom to an amino hydrogen atom of pNA was found to be correlated with the density dependence of vibrational relaxation rate. PMID:22909090

Osawa, Koji; Terazima, Masahide; Kimura, Yoshifumi

2012-09-20

379

Electrostatic effects on electron-transfer kinetics in the cytochrome f-plastocyanin complex.  

PubMed

In a complex of two electron-transfer proteins, their redox potentials can be shifted due to changes in the dielectric surroundings and the electrostatic potentials at each center caused by the charged residues of the partner. These effects are dependent on the geometry of the complex. Three different docking configurations (DCs) for intracomplex electron transfer between cytochrome f and plastocyanin were studied, defined by 1) close contact of the positively charged region of cytochrome f and the negatively charged regions of plastocyanin (DC1) and by (2, 3) close contact of the surface regions adjacent to the Fe and Cu redox centers (DC2 and DC3). The equilibrium energetics for electron transfer in DC1-DC3 are the same within approximately +/-0.1 kT. The lower reorganization energy for DC2 results in a slightly lower activation energy for this complex compared with DC1 and DC3. The long heme-copper distance (approximately 24 A) in the DC1 complex drastically decreases electronic coupling and makes this complex much less favorable for electron transfer than DC2 or DC3. DC1-like complexes can only serve as docking intermediates in the pathway toward formation of an electron-transfer-competent complex. Elimination of the four positive charges arising from the lysine residues in the positive patch of cytochrome f, as accomplished by mutagenesis, exerts a negligible effect (approximately 3 mV) on the redox potential difference between cyt f and PC. PMID:9414237

Soriano, G M; Cramer, W A; Krishtalik, L I

1997-12-01

380

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

SciTech Connect

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

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

2014-03-03

381

Electron transfer-induced blinking in Ag nanodot fluorescence  

PubMed Central

Various single-standed DNA-encapsulated Ag nanoclusters (nanodots) exhibit strong, discrete fluorescence with solvent polarity-dependent absorption and emission throughout the visible and near-IR. All species examined, regardless of their excitation and emission energies, show similar µs single-molecule blinking dynamics and near IR transient absorptions. The polarity dependence, µsec blinking, and indistinguishable µsec-decaying transient absorption spectra for multiple nanodots suggest a common charge transfer-based mechanism that gives rise to nanodot fluorescence intermittency. Photoinduced charge transfer that is common to all nanodot emitters is proposed to occur from the Ag cluster into the nearby DNA bases to yield a long-lived charge-separated trap state that results in blinking on the single molecule level. PMID:20161463

Patel, Sandeep A.; Cozzuol, Matteo; Hales, Joel M.; Richards, Chris I.; Sartin, Matthew; Hsiang, Jung-Cheng; Vosch, Tom; Perry, Joseph. W.; Dickson, Robert M.

2009-01-01

382

Design of new chiral phase-transfer catalysts with dual functions for highly enantioselective epoxidation of alpha,beta-unsaturated ketones.  

PubMed

A new chiral ammonium bromide, 1-Br, possessing diarylmethanol functionality as a substrate recognition site has been designed as a promising, dual-functioning catalyst for the highly enantioselective epoxidation of alpha,beta-unsaturated ketones under mild phase-transfer conditions. For instance, vigorous stirring of a mixture of chalcone, 1-Br (3 mol %), and 13% NaOCl in toluene at 0 degrees C for 24 h gave rise to epoxy chalcone quantitatively with 96% ee. A variety of alpha,beta-unsaturated ketones can also be epoxidized with rigorous stereochemical control, clearly demonstrating the effectiveness and utility of the present system. Further, a successful single-crystal X-ray diffraction analysis of 1-PF6 uncovered its distinctive three-dimensional molecular architecture and provided useful information for postulating the transition state. PMID:15174835

Ooi, Takashi; Ohara, Daisuke; Tamura, Masazumi; Maruoka, Keiji

2004-06-01

383

Whitehead Institute stock gift instructions > Donating securities is best accomplished by electronic transfer via a broker > Following the stock transfer, please notify the  

E-print Network

Whitehead Institute stock gift instructions > Donating securities is best accomplished by electronic transfer via a broker > Following the stock transfer, please notify the Whitehead Institute 02110 617.261.1000 800.225.2374 Following the stock transfer, please notify the Whitehead Institute

Sabatini, David M.

384

Electron transfer and coupling in graphene-tungsten disulfide van der Waals heterostructures.  

PubMed

The newly discovered two-dimensional materials can be used to form atomically thin and sharp van der Waals heterostructures with nearly perfect interface qualities, which can transform the science and technology of semiconductor heterostructures. Owing to the weak van der Waals interlayer coupling, the electronic states of participating materials remain largely unchanged. Hence, emergent properties of these structures rely on two key elements: electron transfer across the interface and interlayer coupling. Here we show, using graphene-tungsten disulfide heterostructures as an example, evidence of ultrafast and highly efficient interlayer electron transfer and strong interlayer coupling and control. We find that photocarriers injected in tungsten disulfide transfer to graphene in 1?ps and with near-unity efficiency. We also demonstrate that optical properties of tungsten disulfide can be effectively tuned by carriers in graphene. These findings illustrate basic processes required for using van der Waals heterostructures in electronics and photonics. PMID:25421098

He, Jiaqi; Kumar, Nardeep; Bellus, Matthew Z; Chiu, Hsin-Ying; He, Dawei; Wang, Yongsheng; Zhao, Hui

2014-01-01

385

Electron transfer and coupling in graphene–tungsten disulfide van der Waals heterostructures  

NASA Astrophysics Data System (ADS)

The newly discovered two-dimensional materials can be used to form atomically thin and sharp van der Waals heterostructures with nearly perfect interface qualities, which can transform the science and technology of semiconductor heterostructures. Owing to the weak van der Waals interlayer coupling, the electronic states of participating materials remain largely unchanged. Hence, emergent properties of these structures rely on two key elements: electron transfer across the interface and interlayer coupling. Here we show, using graphene–tungsten disulfide heterostructures as an example, evidence of ultrafast and highly efficient interlayer electron transfer and strong interlayer coupling and control. We find that photocarriers injected in tungsten disulfide transfer to graphene in 1?ps and with near-unity efficiency. We also demonstrate that optical properties of tungsten disulfide can be effectively tuned by carriers in graphene. These findings illustrate basic processes required for using van der Waals heterostructures in electronics and photonics.

He, Jiaqi; Kumar, Nardeep; Bellus, Matthew Z.; Chiu, Hsin-Ying; He, Dawei; Wang, Yongsheng; Zhao, Hui

2014-11-01

386

Transfer printing of thermoreversible ion gels for flexible electronics.  

PubMed

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

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

2013-10-01

387

Resolution of proton and electron transfer events in the photosynthetic reaction center and the cytochrome-bc1 complex of  

E-print Network

S12-005 Resolution of proton and electron transfer events in the photosynthetic reaction center; Keywords: proton transfer, electron transfer, bc1 complex, Rhodobacter capsulatus. 1. Introduction. Flashes in the photochemical reaction center (RC) and lead to the reduction of a bound ubiquinone QB to a quinol QBH2

Steinhoff, Heinz-Jürgen

388

Photoinduced electron and energy transfer processes in fullerene C 60–metal complex hybrid assemblies  

Microsoft Academic Search

The electron and energy accepting properties of fullerene C60 can be readily exploited upon the selection of suitable donating species to construct supramolecular assemblies which display photoinduced electron and\\/or energy transfer processes. In this account we focus on the use of transition metal complexes in the role of the electron\\/energy donor, in particular we discuss the photophysical properties of some

John N. Clifford; Gianluca Accorsi; François Cardinali; Jean-François Nierengarten; Nicola Armaroli

2006-01-01

389

Structural and mechanistic aspects of flavoproteins: electron transfer through the nitric oxide synthase flavoprotein domain  

PubMed Central

Nitric oxide synthases belong to a family of dual-flavin enzymes that transfer electrons from NAD(P)H to a variety of heme protein acceptors. During catalysis, their FMN subdomain plays a central role by acting as both an electron acceptor (receiving electrons from FAD) and an electron donor, and is thought to undergo large conformational movements and engage in two distinct protein–protein interactions in the process. This minireview summarizes what we know about the many factors regulating niric oxide synthase flavoprotein domain function, primarily from the viewpoint of how they impact electron input/output and conformational behaviors of the FMN subdomain. PMID:19583767

Stuehr, Dennis J.; Tejero, Jesús; Haque, Mohammad M.

2010-01-01

390

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

PubMed Central

Photobiological hydrogen production is an attractive, carbon-neutral means to convert solar energy to hydrogen. We build on previous research improving the Alteromonas macleodii “Deep Ecotype” [NiFe] hydrogenase, and report progress towards creating an artificial electron transfer pathway to supply the hydrogenase with electrons necessary for hydrogen production. Ferredoxin is the first soluble electron transfer mediator to receive high-energy electrons from photosystem I, and bears an electron with sufficient potential to efficiently reduce protons. Thus, we engineered a hydrogenase-ferredoxin fusion that also contained several other modifications. In addition to the C-terminal ferredoxin fusion, we truncated the C-terminus of the hydrogenase small subunit, identified as the available terminus closer to the electron transfer region. We also neutralized an anionic patch surrounding the interface Fe-S cluster to improve transfer kinetics with the negatively charged ferredoxin. Initial screening showed the enzyme tolerated both truncation and charge neutralization on the small subunit ferredoxin-binding face. While the enzyme activity was relatively unchanged using the substrate methyl viologen, we observed a marked improvement from both the ferredoxin fusion and surface modification using only dithionite as an electron donor. Combining ferredoxin fusion and surface charge modification showed progressively improved activity in an in vitro assay with purified enzyme. PMID:25603181

Yonemoto, Isaac T.; Smith, Hamilton O.; Weyman, Philip D.

2015-01-01

391

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

PubMed

Photobiological hydrogen production is an attractive, carbon-neutral means to convert solar energy to hydrogen. We build on previous research improving the Alteromonas macleodii "Deep Ecotype" [NiFe] hydrogenase, and report progress towards creating an artificial electron transfer pathway to supply the hydrogenase with electrons necessary for hydrogen production. Ferredoxin is the first soluble electron transfer mediator to receive high-energy electrons from photosystem I, and bears an electron with sufficient potential to efficiently reduce protons. Thus, we engineered a hydrogenase-ferredoxin fusion that also contained several other modifications. In addition to the C-terminal ferredoxin fusion, we truncated the C-terminus of the hydrogenase small subunit, identified as the available terminus closer to the electron transfer region. We also neutralized an anionic patch surrounding the interface Fe-S cluster to improve transfer kinetics with the negatively charged ferredoxin. Initial screening showed the enzyme tolerated both truncation and charge neutralization on the small subunit ferredoxin-binding face. While the enzyme activity was relatively unchanged using the substrate methyl viologen, we observed a marked improvement from both the ferredoxin fusion and surface modification using only dithionite as an electron donor. Combining ferredoxin fusion and surface charge modification showed progressively improved activity in an in vitro assay with purified enzyme. PMID:25603181

Yonemoto, Isaac T; Smith, Hamilton O; Weyman, Philip D

2015-01-01

392

Rhodium Catalysts in the Oxidation of CO by O2 and NO: Shape, Composition, and Hot Electron Generation  

SciTech Connect

It is well known that the activity, selectivity, and deactivation behavior of heterogeneous catalysts are strongly affected by a wide variety of parameters, including but not limited to nanoparticle size, shape, composition, support, pretreatment conditions, oxidation state, and electronic state. Enormous effort has been expended in an attempt to understand the role of these factors on catalytic behavior, but much still remains to be discovered. In this work, we have focused on deepening the present understanding of the role of nanoparticle shape, nanoparticle composition, and hot electrons on heterogeneous catalysis in the oxidation of carbon monoxide by molecular oxygen and nitric oxide. These reactions were chosen because they are important for environmental applications, such as in the catalytic converter, and because there is a wide range of experimental and theoretical insight from previous single crystal work as well as experimental data on nanoparticles obtained using new state-of-the-art techniques that aid greatly in the interpretation of results on complex nanoparticle systems. In particular, the studies presented in this work involve three types of samples: {approx} 6.5 nm Rh nanoparticles of different shapes, {approx} 15 nm Rh1-xPdx core-shell bimetallic polyhedra nanoparticles, and Rh ultra-thin film ({approx} 5 nm) catalytic nanodiodes. The colloidal nanoparticle samples were synthesized using a co-reduction of metal salts in alcohol and supported on silicon wafers using the Langmuir-Blodgett technique. This synthetic strategy enables tremendous control of nanoparticle size, shape, and composition. Nanoparticle shape was controlled through the use of different organic polymer capping layers. Bimetallic core-shell nanoparticles were synthesized by careful choice of metal salt precursors. Rh/TiO{sub x} and Rh/GaN catalytic nanodiodes were fabricated using a variety of thin film device fabrication techniques, including reactive DC magnetron sputtering, electron beam evaporation, and rapid thermal annealing. The combination of these techniques enabled control of catalytic nanodiode morphology, geometry, and electrical properties.

Renzas, James R.

2010-03-08

393

Electron paramagnetic resonance analysis of La(1-x)M(x)MnO(3+?) (M = Ce, Sr) perovskite-like nanostructured catalysts.  

PubMed

The physical-chemical properties of some nanostructured perovskite-like catalysts of general formula La(1-x)M(x)MnO(3+?) (M = Ce, Sr) have been investigated, in particular by using the electron paramagnetic resonance (EPR) technique. We show that the interplay between the -O-Mn(3+)-O-Mn(4+)-O- electron double-exchange and the electron mobility is strictly dependent on the dopant nature and the annealing conditions in air. A relationship between the observed properties of these samples and their activity in the methane flameless catalytic combustion is proposed. PMID:22799746

Oliva, Cesare; Allieta, Mattia; Scavini, Marco; Biffi, Cesare; Rossetti, Ilenia; Forni, Lucio

2012-08-01

394

Electron-impact ionization of helium with large energy transfer  

SciTech Connect

We consider the recently measured case of 730 eV electron-impact ionization of the ground state of helium with 205 and 500 eV coplanar outgoing electrons by Catoire et al. [J. Phys. B 39, 2827 (2006)]. These measurements, which are on a relative scale, show some unexpected structure and variation from the second-order distorted-wave Born approximation R-matrix and Brauner-Briggs-Klar theories. Using the convergent close-coupling method we provide an improved agreement with experiment, but some discrepancies still remain.

Bray, I.; Fursa, D. V.; Stelbovics, A. T. [ARC Centre of Excellence for Antimatter-Matter Studies, Murdoch University, Perth, 6150 (Australia)

2006-09-15

395

Poisson-distributed electron-transfer dynamics from single quantum dots to C60 molecules.  

PubMed

Functional quantum dot (QD)-based nanostructures are often constructed through the self-assembly of QDs with binding partners (molecules or other nanoparticles), a process that leads to a statistical distribution of the number of binding partners. Using single QD fluorescence spectroscopy, we probe this distribution and its effect on the function (electron-transfer dynamics) in QD-C60 complexes. Ensemble-averaged transient absorption and fluorescence decay as well as single QD fluorescence decay measurements show that the QD exciton emission was quenched by electron transfer from the QD to C60 molecules and the electron-transfer rate increases with the C60-to-QD ratio. The electron-transfer rate of single QD-C60 complexes fluctuates with time and varies among different QDs. The standard deviation increases linearly with the average of electron-transfer rates of single QD-C60 complexes, and the distributions of both quantities obey Poisson statistics. The observed distributions of single QD-C60 complexes and ensemble-averaged fluorescence decay kinetics can be described by a model that assumes a Poisson distribution of the number of adsorbed C60 molecules per QD. Our findings suggest that, in self-assembled QD nanostructures, the statistical distribution of the number of adsorbed partners can dominate the distributions of the averages and standard deviation of their interfacial dynamical properties. PMID:21190376

Song, Nianhui; Zhu, Haiming; Jin, Shengye; Zhan, Wei; Lian, Tianquan

2011-01-25

396

A Secure Electronic Market for Anonymous Transferable Emission Permits  

Microsoft Academic Search

Electronic Markets as new mechanisms for co-ordinating allocation of goods, are supposed to reduce the trading immanent transaction costs, especially when the traded goods are digitally represented. A market with no transaction costs is theoretically the most efficient possible allocation mechanism. The US government has recently passed the Acid Rain Act, which uses a system of tradable permits to reduce

Markus Gerhard; Alexander W. Röhm

1998-01-01

397

Anchored [RuCl2(p-cymene)]2 in hybrid zirconium phosphate-phosphonate coated and pillared with double-stranded hydrophobic linear polystyrene as heterogeneous catalyst suitable for aqueous asymmetric transfer hydrogenation.  

PubMed

A novel type of phosphonate-containing polystyrene copolymers 1a-e bearing an N'-alkylated TsDPEN chiral ligand and double-stranded polystyrene chains were prepared for the first time using simple radical copolymerization of 1-phosphonate styrene with (R,R)-N'-4'-vinylbenzyl-N-4-vinylbenzenesulfonyl-1,2-diphenylethylene-1,2-diamine. Through the coprecipitation of their supported Ru polystyrene copolymers 2a-e and NaH2PO4 with ZrOCl2, pillared hybrid zirconium phosphate-phosphonate-anchored Ru catalysts 3a-e and 4d1-d5 were obtained as heterogeneous catalysts suitable for aqueous asymmetric transfer hydrogenation. In the aqueous asymmetric transfer hydrogenation of aromatic ketones, the anchored Ru catalysts showed good catalytic activities, chemoselectivities (~100%), and enantioselectivities (73.6% ee to 95.6% ee). The Ru catalysts retained their catalytic properties even at the fifth recycle time (92.2% conv., 92.1% ee). However, corresponding supported Ru catalyst 3d' resulted in disappointing reusability because of the loss of ruthenium in every recycle process. The conversions of aromatic ketones were closely related to the o-, m- or p-positions of the substituents on the aromatic ring caused by shape-selective matching. PMID:23474609

Wang, Rui; Wan, Jingwei; Ma, Xuebing; Xu, Xiao; Liu, Liu

2013-05-14

398

The seamless transfer of care: a pilot study assessing the usability of an electronic transfer of care communication tool.  

PubMed

The purpose of this pilot study was to explore the feasibility of implementing a new electronic transfer of care (TOC) tool. The study was conducted in a Canadian tertiary care center. Brief survey instruments were completed by acute care physicians, community-based physicians, and patients to assess providers' perspectives on the usability of the novel electronic tool. The units of analysis were physician and patient perceptions. Mixed methods were used including descriptive statistical analyses and qualitative thematic analysis. Twenty-eight unique acute care physicians completed 100 electronic TOC summaries, and 44 unique community-based physicians rated quality and pertinence of the summaries. Twenty-two patients responded to a follow-up telephone call. The novel TOC communication tool was generally well received by physicians and patients, and it is now being evaluated in a large-scale clinical trial assessing hard clinical outcomes. The information presented herein provides a template for assessment of such information system innovations. PMID:24052455

Santana, Maria Jose; Holroyd-Leduc, Jayna; Flemons, William Ward; O'Beirne, Maeve; White, Deborah; Clayden, Nancy; Forster, Alan J; Ghali, William A

2014-01-01

399

Photoinduced electron transfer from N,N-dimethylaniline to 7-amino Coumarins in protein-surfactant complex: Slowing down of electron transfer dynamics compared to micelles  

NASA Astrophysics Data System (ADS)

Photoinduced electron transfer from N,N-dimethylaniline to different Coumarin dyes has been investigated in dodecyl trimethyl ammonium bromide (DTAB) micelles and in Bovine serum albumin (BSA)-DTAB protein-surfactant complex using steady-state and picosecond time-resolved fluorescence spectroscopy. We observed a slower fluorescence quenching rate in the DTAB micelles and in the protein-surfactant complex as compared to that in pure acetonitrile solution. Moreover, the observed fluorescence quenching in BSA-DTAB complex was found to be slower than that in DTAB micelles. In the correlation of free-energy change with the fluorescence quenching constant we observed a deviation in the fluorescence quenching electron transfer rate for Coumarin 151 (C-151) from the normal Marcus curve. This observation is ascribed to the stronger interaction of C-151 with the surfactant molecules present in the micelles. This is evident from the slower translation diffusion (DL) of Coumarin 151 compared to other probe molecules.

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

2006-02-01

400

Formation of a long-lived electron-transfer state in mesoporous silica-alumina composites enhances photocatalytic oxygenation reactivity  

PubMed Central

A simple donor-acceptor linked dyad, 9-mesityl-10-methylacridinium ion (Acr+-Mes) was incorporated into nanosized mesoporous silica-alumina to form a composite, which in acetonitrile is highly dispersed. In this medium, upon visible light irradiation, the formation of an extremely long-lived electron-transfer state (Acr•-Mes•+) was confirmed by EPR and laser flash photolysis spectroscopic methods. The composite of Acr+-Mes-incorporated mesoporous silica-alumina with an added copper complex [(tmpa)CuII] (tmpa = tris(2-pyridylmethyl)amine) acts as an efficient and robust photocatalyst for the selective oxygenation of p-xylene by molecular oxygen to produce p-tolualdehyde and hydrogen peroxide. Thus, incorporation of Acr+-Mes into nanosized mesoporous silica-alumina combined with an O2-reduction catalyst ([(tmpa)CuII]2+) provides a promising method in the development of efficient and robust organic photocatalysts for substrate oxygenation by dioxygen, the ultimate environmentally benign oxidant. PMID:22543164

Fukuzumi, Shunichi; Doi, Kaoru; Itoh, Akinori; Suenobu, Tomoyoshi; Ohkubo, Kei; Yamada, Yusuke; Karlin, Kenneth D.

2012-01-01

401

Electron transfer in N-hydroxyurea complexes with iron(III).  

PubMed

Redox behaviour of the iron(III) complex with the antitumour drug hydroxyurea was studied by cyclic voltammetry. The complex underwent a one-electron reduction, followed by an irreversible chemical reaction (EC mechanism) in which a ligand was released. In addition, it was found that the hydroxyurea gave up an electron to iron(III) in solution. Differential-pulse voltammetry revealed an increase in the concentration of the generated iron(II) species. Electron paramagnetic resonance (EPR) spectroscopy studies of the oxidative degradation of hydroxyurea confirmed formation of the radical species H2N-CO-NHO*. Electrochemical data for iron(III) complexes of hydroxyurea and its structural analogue 3-ethylhydroxyurea, which also exhibits antitumour activity, show the same mechanism involved in the electron transfer. The observed redox properties indicate that hydroxyurea may interfere with electron transfer processes in biological systems after binding to iron-containing ribonucleotide reductase. PMID:15642408

Nigovi?, Biljana; Kujundzi?, Nikola; Sankovi?, Kresimir

2005-01-01

402

40 CFR Table I-2 to Subpart I - Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry  

Code of Federal Regulations, 2012 CFR

...Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics...Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics...type Fluorinated GHGs and fluorinated heat transfer fluids used during...

2012-07-01

403

40 CFR Table I-2 to Subpart I of... - Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry  

Code of Federal Regulations, 2013 CFR

...Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics...Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics...type Fluorinated GHGs and fluorinated heat transfer fluids used during...

2013-07-01

404

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

SciTech Connect

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

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

2012-12-14

405

Charge transfer across transition-metal oxide interfaces: Emergent conductance and electronic structure  

NASA Astrophysics Data System (ADS)

We perform density functional theory plus dynamical mean-field theory calculations to investigate internal charge transfer in a superlattice composed of alternating layers of vanadate and manganite perovskite and Ruddlesden-Popper structure materials. We show that the electronegativity difference between vanadium and manganese causes moderate charge transfer from VO2 to MnO2 layers in both perovskite and Ruddlesden-Popper-based superlattices, leading to hole doping of the VO2 layer and electron doping of the MnO2 layer. Comparison of the perovskite and Ruddlesden-Popper-based heterostructures shows that apical oxygen motion in the perovskite superlattice enhances charge transfer. Our first principles simulations demonstrate that the combination of internal charge transfer and quantum confinement provided by heterostructuring is a powerful approach to engineering electronic structure and tailoring correlation effects in transition metal oxides.

Chen, Hanghui; Park, Hyowon; Millis, Andrew J.; Marianetti, Chris A.

2014-12-01

406

Exploiting the interparticle electron transfer process in the photocatalysed oxidation of phenol, 2-chlorophenol and pentachlorophenol: chemical evidence for electron and hole transfer between coupled semiconductors  

Microsoft Academic Search

The photocatalysed oxidation of phenol, 2-chlorophenol and pentachlorophenol was re-examined under conditions in which TiO2 anatase was sensitized by CdS in air-equilibrated aqueous media; this was to assess whether or not the interparticle electron transfer pathway, first discovered a decade ago (N. Serpone, E. Borgarello and M. Gratzel, J. Chem. Soc., Chem. Commun., (1984) 342) and subsequently applied to enhance

N. Serpone; P. Maruthamuthu; P. Pichat; E. Pelizzetti; H. Hidaka

1995-01-01

407

Effect of water sorption on the electronic conductivity of porous polymer electrolyte membrane fuel cell catalyst layers.  

PubMed

A method is described for measuring the effective electronic conductivity of porous fuel cell catalyst layers (CLs) as a function of relative humidity (RH). Four formulations of CLs with different carbon black (CB) contents and ionomer equivalent weights (EWs) were tested. The van der Pauw method was used to measure the sheet resistance (RS), which increased with RH for all samples. The increase was attributed to ionomer swelling upon water uptake, which affects the connectivity of CB aggregates. Greater increases in RS were observed for samples with lower EW, which uptake more water on a mass basis per mass ionomer. Transient RS measurements were taken during absorption and desorption, and the resistance kinetics were fit using a double exponential decay model. No hysteresis was observed, and the absorption and desorption kinetics were virtually symmetric. Thickness measurements were attempted at different RHs, but no discernible changes were observed. This finding led to the conclusion that the conducting Pt/C volume fraction does not change with RH, which suggests that effective medium theory models that depend on volume fraction alone cannot explain the reduction in conductivity with RH. The merits of percolation-based models were discussed. Optical micrographs revealed an extensive network of "mud cracks" in some samples. The influence of water sorption on CL conductivity is primarily explained by ionomer swelling, and its effects on the quantity and quality of interaggregate contacts were discussed. PMID:25275957

Morris, David R P; Liu, Selina P; Villegas Gonzalez, David; Gostick, Jeff T

2014-11-12

408

Bacterial Nanowires Facilitate Electron Transfer in Saturated Porous Media  

NASA Astrophysics Data System (ADS)

Bacterial nanowires are electrically conductive appendages produced by bacteria in response to electron acceptor limitation and may contribute to biogeophysical signatures in saturated subsurface sediments. Using Shewanella oneidensis strain MR-1 as a model organism, we performed controlled laboratory column experiments that conclusively demonstrated that nanowires are necessary to develop self potential (SP) signals spanning more than 500mV. Oxygen, which served as the sole terminal electron acceptor and diffused into the upper portion of the open column, supported cell respiration and viability. Scanning electron microscopy verified the presence of nanowire network that physically and presumably electrically connected cells throughout the column. Sterile control columns and columns inoculated with a mutant strain of S. oneidensis that produced significantly less conductive nanowires developed minor SP signals (up to 10mV). Our results suggest that microbial activity and nanowires greatly impact the electrical properties of porous materials and contribute to our understanding of the mechanisms that underlie geophysical methods for mapping microbial activity in near subsurface environments.

Ntarlagiannis, D.; Atekwana, E.; Hill, E.; Gorby, Y.

2006-12-01

409

Characterization of Electron Transfer Dissociation in the Orbitrap Velos HCD Cell  

NASA Astrophysics Data System (ADS)

Electron transfer dissociation (ETD) is commonly employed in ion traps utilizing rf fields that facilitate efficient electron transfer reactions. Here, we explore performing ETD in the HCD collision cell on an Orbitrap Velos instrument by applying a static DC gradient axially to the rods. This gradient enables simultaneous three dimensional, charge sign independent, trapping of cations and anions, initiating electron transfer reactions in the center of the HCD cell where oppositely charged ions clouds overlap. Here, we evaluate this mode of operation for a number of tryptic peptide populations and the top-down sequence analysis of ubiquitin. Our preliminary data show that performing ETD in the HCD cell provides similar fragmentation as ion trap-ETD but requires further optimization to match performance of ion trap-ETD.

Frese, Christian K.; Nolting, Dirk; Altelaar, A. F. Maarten; Griep-Raming, Jens; Mohammed, Shabaz; Heck, Albert J. R.

2013-11-01

410

Low temperature extension of the generalized Zusman phase space equations for electron transfer.  

PubMed

In a previous paper [J. Chem. Phys. 119, 11864 (2003)], we derived a set of two coupled equations which describe electron transfer in the presence of dissipation at high temperature. Employing the low temperature extension of the Fokker-Planck operator, suggested by Haake and Reibold [Phys. Rev. A 32, 2462 (1985)] and Ankerhold [Europhys. Lett. 61, 301 (2003)], we show that one may extend the generalized Zusman equations in a similar manner to low temperature. Numerical simulation shows that addition of the temperature-dependent term which couples the coordinate and momentum causes an increase in the electron transfer rate as compared to the rate obtained from the previous high temperature equations. The increase in the rate comes from the increase in the equilibrium variances of the coordinate and momentum. The low temperature quantum theory allows for higher energy portions of phase space to contribute to the electron transfer rate where the rate is higher thus enhancing the overall rate. PMID:15267976

Zhang, Ming-Liang; Zhang, Shesheng; Pollak, Eli

2004-05-22

411

Low temperature extension of the generalized Zusman phase space equations for electron transfer  

NASA Astrophysics Data System (ADS)

In a previous paper [J. Chem. Phys. 119, 11864 (2003)], we derived a set of two coupled equations which describe electron transfer in the presence of dissipation at high temperature. Employing the low temperature extension of the Fokker-Planck operator, suggested by Haake and Reibold [Phys. Rev. A 32, 2462 (1985)] and Ankerhold [Europhys. Lett. 61, 301 (2003)], we show that one may extend the generalized Zusman equations in a similar manner to low temperature. Numerical simulation shows that addition of the temperature-dependent term which couples the coordinate and momentum causes an increase in the electron transfer rate as compared to the rate obtained from the previous high temperature equations. The increase in the rate comes from the increase in the equilibrium variances of the coordinate and momentum. The low temperature quantum theory allows for higher energy portions of phase space to contribute to the electron transfer rate where the rate is higher thus enhancing the overall rate.

Zhang, Ming-Liang; Zhang, Shesheng; Pollak, Eli

2004-05-01

412

Single electron transfer between selectfluor and chloride: A mass spectrometric and theoretical study  

NASA Astrophysics Data System (ADS)

The reaction between 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis-tetrafluoroborate (selectfluor) and chloride has been studied experimentally and modeled computationally at the ab initio levels. Based on the interception experiments by electrospray ionization-mass spectrometry (ESI-MS), it is found that only 5,5-dimethyl-l-pyrroline N-oxide (DMPO) succeeds in trapping the chlorine free radical. This result indicates that the single electron transfer (SET) is likely to occur between selectfluor and chloride. According to the Marcus' theory, the activation and reaction free energies for this electron transfer have been calculated. The theoretical study shows that the electron transfer reaction is both thermodynamically and kinetically beneficial, which is consistent with the experiment.

Zhang, Xiang

2013-10-01

413

Efficient electron transfer in functional assemblies of pyridine-modified NQDs on SWNTs.  

PubMed

Nanocrystal quantum dot (NQD)/single-walled carbon nanotube (SWNT) hybrid nanomaterials were synthesized, assembled into field effect transistors (FETs) via dielectrophoresis (DEP), and characterized optically and electronically. The pyridine moiety functioned as a short, noncovalent linker between the NQDs and SWNTs and allowed more efficient carrier transfer through the assemblies without deleteriously altering electronic structures. Photoluminescence studies of the resulting assemblies support an efficient carrier transfer process in CdSe-py-SWNTs unlike that of CdSe/ZnS-py-SWNTs. The use of DEP as a means of controlling the assembly process allowed the creation of a SWNT array containing densely packed CdSe NQDs across a 2 mum gap between electrodes. Observations and characterization of the photocurrent, resistivity, gate dependence, and optical properties of these systems suggest efficient electron transfer from photoexcited NQDs to SWNTs. PMID:20028098

Jeong, Sohee; Shim, Hyung Cheoul; Kim, Soohyun; Han, Chang-Soo

2010-01-26

414

Electron-transfer kinetics in cyanobacterial cells: Methyl viologen is a poor inhibitor of linear electron flow.  

PubMed

The inhibitor methyl viologen (MV) has been widely used in photosynthesis to study oxidative stress. Its effects on electron transfer kinetics in Synechocystis sp. PCC6803 cells were studied to characterize its electron-accepting properties. For the first hundreds of flashes following MV addition at submillimolar concentrations, the kinetics of NADPH formation were hardly modified (less than 15% decrease in signal amplitude) with a significant signal decrease only observed after more flashes or continuous illumination. The dependence of the P700 photooxidation kinetics on the MV concentration exhibited a saturation effect at 0.3mM MV, a concentration which inhibits the recombination reactions in photosystem I. The kinetics of NADPH formation and decay under continuous light with MV at 0.3mM showed that MV induces the oxidation of the NADP pool in darkness and that the yield of linear electron transfer decreased by only 50% after 1.5-2 photosystem-I turnovers. The unexpectedly poor efficiency of MV in inhibiting NADPH formation was corroborated by in vitro flash-induced absorption experiments with purified photosystem-I, ferredoxin and ferredoxin-NADP(+)-oxidoreductase. These experiments showed that the second-order rate constants of MV reduction are 20 to 40-fold smaller than the competing rate constants involved in reduction of ferredoxin and ferredoxin-NADP(+)-oxidoreductase. The present study shows that MV, which accepts electrons in vivo both at the level of photosystem-I and ferredoxin, can be used at submillimolar concentrations to inhibit recombination reactions in photosystem-I with only a moderate decrease in the efficiency of fast reactions involved in linear electron transfer and possibly cyclic electron transfer. PMID:25448535

Sétif, Pierre

2015-02-01

415

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

E-print Network

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

Simserides, Constantinos

2014-01-01

416

Blue light drives B-side electron transfer in bacterial photosynthetic reaction centers.  

PubMed

The core of the photosynthetic reaction center from the purple non-sulfur bacterium Rhodobacter sphaeroides is a quasi-symmetric heterodimer, providing two potential pathways for transmembrane electron transfer. Past measurements have demonstrated that only one of the two pathways (the A-side) is used to any significant extent upon excitation with red or near-infrared light. Here, it is shown that excitation with blue light into the Soret band of the reaction center gives rise to electron transfer along the alternate or B-side pathway, resulting in a charge-separated state involving the anion of the B-side bacteriopheophytin. This electron transfer is much faster than normal A-side transfer, apparently occurring within a few hundred femtoseconds. At low temperatures, the B-side charge-separated state is stable for at least 1 ns, but at room temperature, the B-side bacteriopheophytin anion is short-lived, decaying within approximately 15 ps. One possible physiological role for B-side electron transfer is photoprotection, rapidly quenching higher excited states of the reaction center. PMID:11705365

Lin, S; Katilius, E; Haffa, A L; Taguchi, A K; Woodbury, N W

2001-11-20

417

Influences of acid on molecular forms of fluorescein and photoinduced electron transfer in fluorescein-dispersing sol-gel titania films.  

PubMed

Fluorescein-dispersing titania gel films were prepared by the acid-catalyzed sol-gel reaction using a titanium alkoxide solution containing fluorescein. The molecular forms of fluorescein in the films, depending on its acid-base equilibria, and the complex formation and photoinduced electron transfer process between the dye and titania surface were investigated by fluorescence and photoelectric measurements. The titanium species were coordinated to the carboxylate and phenolate-like groups of the fluorescein species. The quantum efficiencies of the fluorescence quenching and photoelectric conversion were higher upon excitation of the dianion species interacting with the titania, i.e. the dye-titania complex. This result indicated that the dianion form was the most favorable for formation of the dye-titania complex exhibiting the highest electron transfer efficiency. Using nitric acid as the catalyst, the titania surface bonded to the fluorescein instead of the adsorbed nitrate ion during the steam treatment. The dye-titania complex formation played an important role in the electron injection from the dye to the titania conduction band. PMID:24502447

Nishikiori, Hiromasa; Setiawan, Rudi Agus; Miyashita, Kyohei; Teshima, Katsuya; Fujii, Tsuneo

2014-01-01

418

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

PubMed Central

Aspects of intramolecular light energy and electron transfer will be discussed for three protein--cofactor complexes, whose three-dimensional structures have been elucidated by X-ray crystallography: components of light-harvesting cyanobacterial phycobilisomes; the purple bacterial reaction centre; and the blue multi-copper oxidases. A wealth of functional data is available for these systems which allows specific correlations between structure and function and general conclusions about light energy and electron transfer in biological materials to be made. Images PMID:2676513

Huber, R

1989-01-01

419

Promoted electron transfer of mitoxantrone binding with DNA by cytochrome c  

SciTech Connect

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

Li Nan [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Remin Street 5625, ChangChun Jilin 130022 (China); Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China); Yang Xiurong [State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Remin Street 5625, ChangChun Jilin 130022 (China)]. E-mail: xryang@ns.ciac.jl.cn

2005-06-17

420

On-demand single-electron transfer between distant quantum dots.  

PubMed

Single-electron circuits of the future, consisting of a network of quantum dots, will require a mechanism to transport electrons from one functional part of the circuit to another. For example, in a quantum computer decoherence and circuit complexity can be reduced by separating quantum bit (qubit) manipulation from measurement and by providing a means of transporting electrons between the corresponding parts of the circuit. Highly controlled tunnelling between neighbouring dots has been demonstrated, and our ability to manipulate electrons in single- and double-dot systems is improving rapidly. For distances greater than a few hundred nanometres, neither free propagation nor tunnelling is viable while maintaining confinement of single electrons. Here we show how a single electron may be captured in a surface acoustic wave minimum and transferred from one quantum dot to a second, unoccupied, dot along a long, empty channel. The transfer direction may be reversed and the same electron moved back and forth more than sixty times-a cumulative distance of 0.25 mm-without error. Such on-chip transfer extends communication between quantum dots to a range that may allow the integration of discrete quantum information processing components and devices. PMID:21938065

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

2011-09-22

421

Discovery and characterization of electron transfer proteins in the photosynthetic bacteria.  

PubMed

Research on photosynthetic electron transfer closely parallels that of other electron transfer pathways and in many cases they overlap. Thus, the first bacterial cytochrome to be characterized, called cytochrome c (2), is commonly found in non-sulfur purple photosynthetic bacteria and is a close homolog of mitochondrial cytochrome c. The cytochrome bc (1) complex is an integral part of photosynthetic electron transfer yet, like cytochrome c (2), was first recognized as a respiratory component. Cytochromes c (2) mediate electron transfer between the cytochrome bc (1) complex and photosynthetic reaction centers and cytochrome a-type oxidases. Not all photosynthetic bacteria contain cytochrome c (2); instead it is thought that HiPIP, auracyanin, Halorhodospira cytochrome c551, Chlorobium cytochrome c555, and cytochrome c (8) may function in a similar manner as photosynthetic electron carriers between the cytochrome bc (1) complex and reaction centers. More often than not, the soluble or periplasmic mediators do not interact directly with the reaction center bacteriochlorophyll, but require the presence of membrane-bound intermediates: a tetraheme cytochrome c in purple bacteria and a monoheme cytochrome c in green bacteria. Cyclic electron transfer in photosynthesis requires that the redox potential of the system be delicately poised for optimum efficiency. In fact, lack of redox poise may be one of the defects in the aerobic phototrophic bacteria. Thus, large concentrations of cytochromes c (2) and c' may additionally poise the redox potential of the cyclic photosystem of purple bacteria. Other cytochromes, such as flavocytochrome c (FCSD or SoxEF) and cytochrome c551 (SoxA), may feed electrons from sulfide, sulfur, and thiosulfate into the photosynthetic pathways via the same soluble carriers as are part of the cyclic system. PMID:16228571

Meyer, Terrance E; Cusanovich, Michael A

2003-01-01

422

Ionic liquids as oxidic media for electron transfer studies  

NASA Astrophysics Data System (ADS)

We review the basic ideas underlying the electron free energy level diagrams that have been found useful in considering the thermodynamics of redox processes in molten silicates and related high temperature ionic liquid (IL) solvents, and then show how closely they link to behavior observable in ambient temperature ionic liquids. Much of the information available on redox levels in molten oxides has been gleaned from chemical analysis and spectroscopic species distribution studies, but it is simpler to obtain the data electrochemically. Here, we report some cyclic voltammetry measurements of the Fe(II)/Fe(III) redox equilibrium in aprotic ionic liquids whose anions provide oxide environments for the redox species that are of different electronic polarizability character from the high temperature solvents, and relate the observations to those of the earlier studies. Quasi-reversible behavior is found in each of the cases studied. As might be expected, the Fe(II)/Fe(III) equilibrium experiences a more basic environment in an acetate IL than it experiences in any of the common glassforming oxide media, while triflate anions contrast by providing a more acid environment than does the most acid of the molten oxide glassformers studied (an alkali phosphate). The difference can amount to well over 1 V, suggesting the possibility of a "basicity cell" where the same redox couple locates in anode and cathode compartments of the cell, and only the anion environment is different.

Ueno, Kazuhide; Angell, C. Austen

2012-06-01

423

Ionic liquids as oxidic media for electron transfer studies.  

PubMed

We review the basic ideas underlying the electron free energy level diagrams that have been found useful in considering the thermodynamics of redox processes in molten silicates and related high temperature ionic liquid (IL) solvents, and then show how closely they link to behavior observable in ambient temperature ionic liquids. Much of the information available on redox levels in molten oxides has been gleaned from chemical analysis and spectroscopic species distribution studies, but it is simpler to obtain the data electrochemically. Here, we report some cyclic voltammetry measurements of the Fe(II)?Fe(III) redox equilibrium in aprotic ionic liquids whose anions provide oxide environments for the redox species that are of different electronic polarizability character from the high temperature solvents, and relate the observations to those of the earlier studies. Quasi-reversible behavior is found in each of the cases studied. As might be expected, the Fe(II)?Fe(III) equilibrium experiences a more basic environment in an acetate IL than it experiences in any of the common glassforming oxide media, while triflate anions contrast by providing a more acid environment than does the most acid of the molten oxide glassformers studied (an alkali phosphate). The difference can amount to well over 1 V, suggesting the possibility of a "basicity cell" where the same redox couple locates in anode and cathode compartments of the cell, and only the anion environment is different. PMID:22755581

Ueno, Kazuhide; Angell, C Austen

2012-06-28

424

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

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

425

The First Events in Photosynthesis: Electronic Coupling and Energy Transfer Dynamics in the Photosynthetic Reaction Center from Rhodobacter sphaeroides  

E-print Network

The First Events in Photosynthesis: Electronic Coupling and Energy Transfer Dynamics in photosynthesis. The reaction center contains six chlorophyll-like pigments arranged with approximate C2 symmetry

Scherer, Norbert F.

426

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

SciTech Connect

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

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

2008-04-30

427

Synthesis and application of a microgel-supported acylating reagent by coupled ring-opening metathesis polymerization and activators re-generated by electron transfer for atom transfer radical polymerization.  

PubMed

A novel microgel-supported acylating reagent (MGAR) was prepared by combining ring-opening metathesis polymerization (ROMP) and Activators Re-Generated by Electron Transfer for Atom Transfer Radical Polymerization (ARGET ATRP): (1) synthesis of an ATRP macroinitiator 3 by living ROMP of oxanorbornene-based activated ester 1, derived from N-hydroxysuccinimide, using the Grubbs initiator RuCl(2)(PCy(3))(2)(=CHPh) and (Z)-but-2-ene-1,4-diyl bis(2-bromopropanoate) (BDBP) as a terminating agent; (2) synthesis of MGAR 4 by ARGET ATRP of styrene (S) and divinylbenzene (DVB) using the prepared macroinitiator 3, a CuCl(2)/Me(6)TREN (tris[2-(dimethylamino)ethyl]amine) catalyst system, a Sn(Oct)(2) [tin(II)2-ethylhexanoate] reducing agent. The synthesized microgels 4 exhibit excellent acyl (acetyl, benzoyl, phenylsulfonyl) transfer properties for primary and secondary amines (n-BuNH(2), Et(2)NH, morpholine, etc.) under mild conditions (25 degrees C, 13.5-14 h) affording N-acylamines with high yield (95.6-100%) and purity (94.1-96.0%). PMID:20073476

Li, Hong; Pang, Zi-Bo; Jiao, Zhi-Feng; Lin, Fei

2010-03-01

428

Opto-electronic conversion logic behaviour through dynamic modulation of electron/energy transfer states at the TiO2-carbon quantum dot interface.  

PubMed

Here we show a bias-mediated electron/energy transfer process at the CQDs-TiO(2) interface for the dynamic modulation of opto-electronic properties. Different energy and electron transfer states have been observed in the CQDs-TNTs system due to the up-conversion photoluminescence and the electron donation/acceptance properties of the CQDs decorated on TNTs. PMID:23386113

Wang, Fang; Zhang, Yonglai; Liu, Yang; Wang, Xuefeng; Shen, Mingrong; Lee, Shuit-Tong; Kang, Zhenhui

2013-03-01

429

Ero1-? and PDIs constitute a hierarchical electron transfer network of endoplasmic reticulum oxidoreductases  

PubMed Central

Ero1-? and endoplasmic reticulum (ER) oxidoreductases of the protein disulfide isomerase (PDI) family promote the efficient introduction of disulfide bonds into nascent polypeptides in the ER. However, the hierarchy of electron transfer among these oxidoreductases is poorly understood. In this paper, Ero1-?–associated oxidoreductases were identified by proteomic analysis and further confirmed by surface plasmon resonance. Ero1-? and PDI were found to constitute a regulatory hub, whereby PDI induced conformational flexibility in an Ero1-? shuttle cysteine (Cys99) facilitated intramolecular electron transfer to the active site. In isolation, Ero1-? also oxidized ERp46, ERp57, and P5; however, kinetic measurements and redox equilibrium analysis revealed that PDI preferentially oxidized other oxidoreductases. PDI accepted electrons from the other oxidoreductases via its a? domain, bypassing the a domain, which serves as the electron acceptor from reduced glutathione. These observations provide an integrated picture of the hierarchy of cooperative redox interactions among ER oxidoreductases in mammalian cells. PMID:24043701

Araki, Kazutaka; Iemura, Shun-ichiro; Kamiya, Yukiko; Ron, David; Kato, Koichi; Natsume, Tohru

2013-01-01

430

Ruthenium supported on magnetic nanoparticles: An efficient and recoverable catalyst for hydrogenation of alkynes and transfer hydrogenation of carbonyl compounds  

EPA Science Inventory

Ruthenium supported on surface modified magnetic nanoparticles (NiFe2O4) has been successfully synthesized and applied for hydrogenation of alkynes at room temperature as well as transfer hydrogenation of a number of carbonyl compounds under microwave irradiation conditions. The ...

431

Electronic Energy Transfer on CaO Surfaces  

SciTech Connect

We excite low-coordinated surface sites of nanostructured CaO samples using tunable UV laser pulses and observe hyperthermal O-atom emission indicative of an electronic excited-state desorption mechanism. The O-atom yield increases dramatically with photon energy, between 3.75 and 5.4 eV, below the bulk absorption threshold. The peak of the kinetic energy distribution does not increase with photon energy in the range 3.9 to 5.15 eV. These results are analyzed in the context of a laser desorption model developed previously for nanostructured MgO samples. The data are consistent with desorption induced by exciton localization at corner-hole trapped surface sites following either direct corner excitation or diffusion and localization of excitons from higher coordinated surface sites.

Joly, Alan G.; Beck, Kenneth M.; Hess, Wayne P.

2008-09-28

432

Negative Polarization through Photon to Electron Spin Polarization Transfer in GaAs Quantum Wells  

E-print Network

We demonstrate negative polarization created by light-hole exciton excitation in g-factor engineered GaAs quantum wells measured by time-resolved Kerr rotation and polarization-resolved photoluminescence. This negative polarization is a result of polarization transfer from a photon to an electron spin mediated by a light hole. This demonstration is an important step towards achieving quantum media conversion from a photonic qubit to an electron spin qubit required for building a quantum repeater.

H. Kosaka; Y. Rikitake; H. Imamura; Y. Mitsumori; K. Edamatsu

2006-09-20

433

Transient Interactions Between Soluble Electron Transfer Proteins. The Case of Plastocyanin and Cytochrome f  

Microsoft Academic Search

\\u000a Oxygenic photosynthesis depends absolutely on electron transfer between cytochrome f and plastocyanin (or cytochrome c\\u000a 6). The reaction must be very fast if it is not to limit the rate of photosynthesis; it also depends on diffusional interaction\\u000a between the two proteins. This implies that it is highly transient, and involves specific binding in a configuration that\\u000a allows rapid electron

Derek S. Bendall; Beatrix G. Schlarb-Ridley; Christopher J. Howe

434

The arginine anomaly: arginine radicals are poor hydrogen atom donors in electron transfer induced dissociations.  

PubMed

Arginine amide radicals are generated by femtosecond electron transfer to protonated arginine amide cations in the gas phase. A fraction of the arginine radicals formed (2-amino-5-dihydroguanid-1'-yl-pentanamide, 1H) is stable on the 6.7 micros time scale and is detected after collisional reionization. The main dissociation of 1H is loss of a guanidine molecule from the side chain followed by consecutive dissociations of the 2-aminopentanamid-5-yl radical intermediate. Intramolecular hydrogen atom transfer from the guanidinium group onto the amide group is not observed. These results are explained by ab initio and density functional theory calculations of dissociation and transition state energies. Loss of guanidine from 1H is calculated to require a transition state energy of 68 kJ mol(-)(1), which is substantially lower than that for hydrogen atom migration from the guanidine group. The loss of guanidine competes with the reverse migration of the arginine alpha-hydrogen atom onto the guanidyl radical. RRKM calculations of dissociation kinetics predict the loss of guanidine to account for >95% of 1H dissociations. The anomalous behavior of protonated arginine amide upon electron transfer provides an insight into electron capture and transfer dissociations of peptide cations containing arginine residues as charge carriers. The absence of efficient hydrogen atom transfer from charge-reduced arginine onto sterically proximate amide group blocks one of the current mechanisms for electron capture dissociation. Conversely, charge-reduced guanidine groups in arginine residues may function as radical traps and induce side-chain dissociations. In light of the current findings, backbone dissociations in arginine-containing peptides are predicted to involve excited electronic states and proceed by the amide superbase mechanism that involves electron capture in an amide pi* orbital, which is stabilized by through-space coulomb interaction with the remote charge carriers. PMID:16984203

Chen, Xiaohong; Turecek, Frantisek

2006-09-27

435

Structural insights into electron transfer in caa3-type cytochrome oxidase  

PubMed Central

Summary Paragraph Cytochrome c oxidase is a member of the heme copper oxidase superfamily (HCO)1. HCOs function as the terminal enzymes in the respiratory chain of mitochondria and aerobic prokaryotes, coupling molecular oxygen reduction to transmembrane proton pumping. Integral to the enzyme’s function is the transfer of electrons from cytochrome c to the oxidase via a transient association of the two proteins. Electron entry and exit are proposed to occur from the same site on cytochrome c2–4. Here we report the crystal structure of the caa3-type cytochrome oxidase from Thermus thermophilus, which has a covalently tethered cytochrome c domain. Crystals were grown in a bicontinuous mesophase using a synthetic short-chain monoacylglycerol as the hosting lipid. From the electron density map, at 2.36 Å resolution, a novel integral membrane subunit and a native glycoglycerophospholipid embedded in the complex were identified. Contrary to previous electron transfer mechanisms observed for soluble cytochrome c, the structure reveals the architecture of the electron transfer complex for the fused cupredoxin/cytochrome c domain which implicates different sites on cytochrome c for electron entry and exit. Support for an alternative to the classical proton gate characteristic of this HCO class is presented. PMID:22763450

Lyons, Joseph A.; Aragão, David; Slattery, Orla; Pisliakov, Andrei V.; Soulimane, Tewfik; Caffrey, Martin

2012-01-01

436

Constraint-Based Modeling of Carbon Fixation and the Energetics of Electron Transfer in Geobacter metallireducens  

PubMed Central

Geobacter species are of great interest for environmental and biotechnology applications as they can carry out direct electron transfer to insoluble metals or other microorganisms and have the ability to assimilate inorganic carbon. Here, we report on the capability and key enabling metabolic machinery of Geobacter metallireducens GS-15 to carry out CO2 fixation and direct electron transfer to iron. An updated metabolic reconstruction was generated, growth screens on targeted conditions of interest were performed, and constraint-based analysis was utilized to characterize and evaluate critical pathways and reactions in G. metallireducens. The novel capability of G. metallireducens to grow autotrophically with formate and Fe(III) was predicted and subsequently validated in vivo. Additionally, the energetic cost of transferring electrons to an external electron acceptor was determined through analysis of growth experiments carried out using three different electron acceptors (Fe(III), nitrate, and fumarate) by systematically isolating and examining different parts of the electron transport chain. The updated reconstruction will serve as a knowledgebase for understanding and engineering Geobacter and similar species. PMID:24762737

Feist, Adam M.; Nagarajan, Harish; Rotaru, Amelia-Elena; Tremblay, Pier-Luc; Zhang, Tian; Nevin, Kelly P.; Lovley, Derek R.; Zengler, Karsten

2014-01-01

437

A structural basis for electron transfer in bacterial photosynthesis  

SciTech Connect

Triplet data for the primary donor in single crystals of bacterial reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis are interpreted in terms of the corresponding x-ray structures. The analysis of electron paramagnetic resonance data from single crystals (triplet zero field splitting and cation and triplet linewidth of the primary special pair donor of bacterial reaction centers) is extended to systems of a non-crystalline nature. A unified interpretation based on frontier molecular orbitals concludes that the special pair behaves like a supermolecule in all wild-type bacteria investigated here. However, in heterodimers of Rb. capsulatus (His/sup M200/ changed to Leu or Phe with the result that the M-half of the special pair is converted to bacteriopheophytin) the special pair possesses the EPR properties more appropriately described in terms of a monomer. In all cases the triplet state and cation EPR properties appear to be dominated by the highest occupied molecular orbitals. These conclusions derived from EPR experiments are supplemented by data from Stark spectroscopy of reaction centers from Rb. capsulatus. 41 refs., 3 tabs.

Norris, J.R.; DiMagno, T.J.; Angerhofer, A.; Chang, C.H.; El-Kabbani, O.; Schiffer, M.

1989-01-01

438

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

SciTech Connect

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

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

2012-05-30

439

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

PubMed

The reduced density matrix completely describes the quantum state of an electron scattered by an object in transmission electron microscopy. However, the detection process restricts access to the diagonal elements only. The off-diagonal elements, determining the coherence of the scattered electron, may be obtained from electron holography. In order to extract the influence of the object from the off-diagonals, however, a rigorous consideration of the electron microscope influences like aberrations of the objective lens and the Möllenstedt biprism in the presence of partial coherence is required. Here, we derive a holographic transfer theory based on the generalization of the transmission cross-coefficient including all known holographic phenomena. We furthermore apply a particular simplification of the theory to the experimental analysis of aloof beam electrons scattered by plane silicon surfaces. PMID:25156951

Röder, Falk; Lubk, Axel

2014-11-01

440

Evidence for coupled electron and proton transfer in the [8Fe-7S] cluster of nitrogenase.  

PubMed

Substrate reduction by nitrogenase requires electron transfer from a [4Fe-4S] cluster in the iron (Fe) protein component to an FeMo cofactor in the molybdenum-iron (MoFe) protein component in a reaction that is coupled to MgATP hydrolysis and component protein association and dissociation. An [8Fe-7S] (or P-) cluster in the MoFe protein has been proposed as an intermediate electron-transfer site, although how this cluster functions in electron-transfer remains unclear. In the present work, it is demonstrated that one redox couple of the P-cluster (P2+/1+) undergoes coupled electron and proton transfer, whereas a more reduced couple (P1+/N) does not involve a coupled proton transfer. Redox titrations of the MoFe protein P-cluster were performed, and the midpoint potential of the P2+/1+ couple (Em2) was found to be pH dependent, ranging from -224 mV at pH 6.0 to -348 mV at pH 8.5. A plot of Em2 versus the pH for this redox couple was linear and revealed a change of -53 mV/pH unit, indicating a single protonation event associated with reduction. From this plot, it was concluded that p is <6.0 and p is >8.5 in a proton-modified Nernst equation. In contrast, the midpoint potential for the P1+/N couple (Em1) was found to be -290 mV and was invariant over the pH range 6.0-8.5. These results indicate that the protonated species does not influence either the P1+ or the PN oxidation states. In addition, at physiological pH values, electron transfer is coupled to proton transfer for the P2+/1+ couple. The P-clusters are unique among [Fe-S] clusters in that they appear to be ligated to the protein through a serinate-gammaO ligand (betaSer188) and a peptide bond amide-N ligand (alphaCys88), in addition to cysteinate-S ligands. Elimination of the serinate ligand by replacement with a glycine was found to shift the Em values for both P-cluster couples by greater than +60 mV, however the pH dependence of Em2 was unchanged. These results rule out Ser188 as the protonated ligand responsible for the pH dependence of Em2. The implications of these results in understanding the nitrogenase electron-transfer mechanism are discussed. PMID:9698385

Lanzilotta, W N; Christiansen, J; Dean, D R; Seefeldt, L C

1998-08-11

441

Electron transfer as the initiation mechanism of photocurable maleimide–vinyl ether based resins  

Microsoft Academic Search

Maleimide–vinyl ether resins polymerise upon UV irradiation without the addition of a photoinitiator. The first step of initiation is an electron transfer from a ground state vinyl ether molecule to the triplet maleimide. Absolute rate constants for the reaction of triplet maleimide (?max=260 and 320 nm) with maleimide itself, unsaturated monomers, inorganic ions, and alcohols were determined by laser flash photolysis.

Justus von Sonntag; Dieter Beckert; Wolfgang Knolle; Reiner Mehnert

1999-01-01

442

The search for relay stations. Long-distance electron transfer in peptides.  

PubMed

Nature uses peptide aggregates as soft materials for electron transfer over long distances. These reactions occur in a multistep hopping reaction with various functional groups as relay stations that are located in the side chain and in the backbone of the peptides. PMID:24594326

Giese, Bernd; Kracht, Sonja; Cordes, Meike

2013-01-01

443

Photo-Induced Electron Transfer Between Photosystem 2 via Cross-linked Redox Hydrogels  

E-print Network

Full Paper Photo-Induced Electron Transfer Between Photosystem 2 via Cross-linked Redox Hydrogels was wired to electrode surfaces via osmium-containing redox polymers based on poly(vinyl)imidazol. The redox illumination, the enzymatic reaction could be switched on and a catalytic current was observed at the electrode

Roegner, Matthias

444

Electrochemical analysis of proton and electron transfer equilibria of the reducible moieties in humic acids.  

PubMed

Humic substances play a key role in biogeochemical and pollutant redox reactions. The objective of this work was to characterize the proton and electron transfer equilibria of the reducible moieties in different humic acids (HA). Cyclic voltammetry experiments demonstrated that diquat and ethylviologen mediated electron transfer between carbon working electrodes and HA. These compounds were used also to facilitate attainment of redox equilibria between redox electrodes and HA in potentiometric E(h) measurements. Bulk electrolysis of HA combined with pH-stat acid titration demonstrated that electron transfer to the reducible moieties in HA also resulted in proton uptake, suggesting decreasing reduction potentials E(h) of HA with increasing pH. This was confirmed by potentiometric E(h)-pH titrations of HA at different redox states. E(h) measurements of HA samples prereduced to different redox states by bulk electrolysis revealed reducible moieties in HA that cover a wide range of apparent standard reduction potentials at pH 7 from E(h)(0)* = +0.15 to -0.3 V. Modeling revealed an overall increase in the relative abundance of reducible moieties with decreasing E(h). The wide range of HA is consistent with its involvement in numerous environmental electron transfer reactions under various redox conditions. PMID:21823669

Aeschbacher, Michael; Vergari, Daniele; Schwarzenbach, René P; Sander, Michael

2011-10-01

445

Ultrafast Electron Transfer Dynamics in Ruthenium Polypyridyl Complexes with a -Conjugated Ligand  

E-print Network

Ultrafast Electron Transfer Dynamics in Ruthenium Polypyridyl Complexes with a -Conjugated LigandVised Manuscript ReceiVed: June 16, 2010 The excited-state dynamics of two mixed-ligand mononuclear ruthenium on the bipyridyl end of ligand L closest to the ruthenium atom. Vibrational cooling in the charge-separated state

Dutta, Prabir K.

446

RNA with iron(II) as a cofactor catalyses electron transfer  

E-print Network

RNA with iron(II) as a cofactor catalyses electron transfer Chiaolong Hsiao, I-Chun Chou, C. Denise with abundant and benign Fe21 . We hypothesize that Fe21 was an RNA cofactor when iron was abundant iron and essentially no O2 (refs 1,2). The `great oxidation' led to Fe2þ /O2-mediated cellular damage3

Williams, Loren

447

Simulation study of the ferrous ferric electron transfer at a metal-aqueous electrolyte interface  

Microsoft Academic Search

We report a new simulation study of the rate of ferrous–ferric electron transfer at a metal electrolyte interface. In contrast with earlier work, new features in our study include a detailed account of the effects of the field associated with the charging of the electrode, inclusion of entropic effects in the calculated free energy barriers, and a study of the

B. B. Smith; J. W. Halley

1994-01-01

448

Numerical technique for modeling conjugate heat transfer in an electronic device heat sink  

Microsoft Academic Search

A fast running computational algorithm based on the volume averaging technique (VAT) is developed to simulate conjugate heat transfer process in an electronic device heat sink. The goal is to improve computational capability in the area of heat exchangers and to help eliminate some of empiricism that leads to overly constrained designs with resulting economic penalties.VAT is tested and applied

Andrej Horvat; Ivan Catton

2003-01-01</