These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

Arsenate stabilized Cu?O nanoparticle catalyst for one-electron transfer reversible reaction.  

PubMed

The befitting capping capabilities of AsO4(3-) provide a stable Cu2O nanocatalyst from a galvanic reaction between a Cu(II) precursor salt and As(0) nanoparticles. This stable Cu2O hydrosol appears to be a suitable catalyst for the one-electron transfer reversible redox reaction between Eosin Y and NaBH4. The progress of the reaction relates to three different kinetic stages. In the presence of the new catalyst the reversible redox reaction of Eosin Y in air shows a periodic color change providing a new crowd-pleasing demonstration, i.e. a "clock reaction". PMID:24626596

Sahoo, Ramkrishna; Dutta, Soumen; Pradhan, Mukul; Ray, Chaiti; Roy, Anindita; Pal, Tarasankar; Pal, Anjali

2014-05-14

2

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

3

Polymer stabilized silver nanoparticle: An efficient catalyst for proton-coupled electron transfer reaction and the electrochemical recognition of biomolecule  

NASA Astrophysics Data System (ADS)

A facile in situ synthesis route [1] has been described for the preparation of polymer stabilized silver nanoparticles. Such in situ synthesized silver nanoparticles are shown to have excellent catalytic activity for the reduction of 4-nitrophenolate (4NP), an example of a proton-coupled electron transfer (PCET) reaction mechanism. Also, the silver-polymer nanocomposite material is shown to perform as an efficient electro-catalyst for the oxidation of ascorbic acid.

Choudhary, Meenakshi; Siwal, Samarjeet; Ul Islam, Rafique; Witcomb, Michael J.; Mallick, Kaushik

2014-07-01

4

Anisotropic gold nanoparticle doped mesoporous boehmite films and their use as reusable catalysts in electron transfer reactions.  

PubMed

Anisotropic Au nanoparticle (NP) doped mesoporous and oriented boehmite films of about 2 microm in thickness were prepared and used as reusable catalysts. The films were characterized by grazing incidence X-ray diffraction (GIXRD), field emission scanning electron and transmission electron microscopies, optical absorptions and surface area and pore size measurements. GIXRD of the doped films showed a preferential growth of boehmite crystallites in the (020) plane. The electron microscopy studies revealed existence of dispersed anisotropic Au NPs of approximately 15-40 nm size range and irregular Au aggregates of approximately 200-300 nm inside the mesoporous boehmite films. The optical absorption of the films showed Au-plasmon bands at 605 nm and broad absorption covering the near-infrared (NIR) region due to the anisotropic Au nanostructures. These films showed excellent catalytic activities in both the organic (p-nitrophenol to p-aminophenol by sodium borohydride) and inorganic (ferricyanide to ferrocyanide by thiosulphate) electron transfer (redox) reactions in aqueous solutions with high rate constant values. The films can be easily separated after the reaction and reused several times without any significant degradation of their original catalytic activity. PMID:20557082

Jana, Debrina; Dandapat, Anirban; De, Goutam

2010-07-20

5

Electron Transfer in Metalloproteins  

E-print Network

. The ability of transition metals to exist in more than one stable oxidation state makes them suitable catalysts for biological processes that require transfer of electrons. The oxidation/reduction centers Cytochrome f Plastocyanin Plastoquinone complex + cytochrome b6 hh Glucose ADP+P ATP ATP CO2 ADP+P NADP F0005

Tuscia, Università Degli Studi Della

6

A kinetic study of plutonium dioxide dissolution in hydrochloric acid using iron (II) as an electron transfer catalyst  

SciTech Connect

Effective dissolution of plutonium dioxide has traditionally been accomplished by contact with strong nitric acid containing a small amount of fluoride at temperatures of {approximately} 100 C. In spite of these aggressive conditions, PuO{sub 2} dissolution is sometimes incomplete requiring additional contact with the solvent. This work focused on an alternative to conventional dissolution in nitric acid where an electron transfer catalyst, Fe(II), was used in hydrochloric acid. Cyclic voltammetry was employed as an in-situ analytical technique for monitoring the dissolution reaction rate. The plutonium oxide selected for this study was decomposed plutonium oxalate with > 95% of the material having a particle diameter (< 70 {micro}m) as determined by a scanning laser microscopy technique. Attempts to dry sieve the oxide into narrow size fractions prior to dissolution in the HCl-Fe(II) solvent system failed, apparently due to significant interparticle attractive forces. Although sieve splits were obtained, subsequent scanning laser microscopy analysis of the sieve fractions indicated that particle segregation was not accomplished and the individual sieve fractions retained a particle size distribution very similar to the original powder assemblage. This phenomena was confirmed through subsequent dissolution experiments on the various screen fractions which illustrated no difference in kinetic behavior between the original oxide assemblage and the sieve fractions.

Fife, K.W.

1996-09-01

7

Inhibition by phase transfer catalysts  

Microsoft Academic Search

While phase transfer catalysts have generally a positive effect on substitution of halides by rhodanide ion in two-phase reaction systems changing the structure of alkyl halide from primary to tert.-alkyl groups, catalysis reverses into inhibition. The assumption that this is due to the change in reaction mechanism from SN2 to SN1 was proved on hydrolysis of triphenylmethyl chloride in a

J. Šilhánek; J. Bartl; R. Mat?ju; M. Zbirovský

1982-01-01

8

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

9

Polymer-protected Pt/Ru bimetallic cluster catalysts for visible-light-induced hydrogen generation from water and electron transfer dynamics  

NASA Astrophysics Data System (ADS)

Colloidal dispersions of platinum/ruthenium bimetallic clusters, as well as those of platinum and ruthenium monometallic clusters, were prepared by alcohol reduction and applied to visible-light-induced hydrogen generation in the electron transfer system of tris(bipyridine)ruthenium(II) dichloride/methyl viologen dichloride/metal cluster/ethylenediaminetetraacetic acid disodium salt. Hydrogen generation rates are in proportion to the concentration of cluster metal at low concentration (about 10 -6 to 10 -5 mol dm -3), where the platinum/ruthenium bimetallic cluster is more active as a catalyst than platinum and ruthenium monometallic clusters. In addition, even the physical mixture of platinum and ruthenium monometallic clusters is more active than platinum and ruthenium monometallic clusters. Electron transfer rates from the methyl viologen radical cation to metal clusters were measured as well and compared with the hydrogen generation rates. Thus, both rates are in proportion to each other, suggesting that the hydrogen generation rate can be controlled by the electron transfer rate.

Toshima, Naoki; Hirakawa, Kazutaka

1997-11-01

10

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

11

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

12

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

13

Electron transfer networks Murad Banaji  

E-print Network

Electron transfer networks Murad Banaji§ Stephen Baigent June 4, 2007 Abstract In this paper we study electron transfer networks. These are generalisations of electron transport chains, and consist electrons to the oxidised forms, and there are some electron inflow and outflow processes. We show

Banaji,. Murad

14

Manifestations of sequential electron transfer  

Microsoft Academic Search

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

M. C. Thurnauer; J. Tang

1996-01-01

15

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

16

Oligomer and mixed-metal compounds: Potential multielectron transfer catalysts  

SciTech Connect

Research continued on potential multi-electron transfer catalysts. A new ligand with an ethyl group bridging two 1,10-phenanthroline ligands was isolated. This ligand can be utilized for generating monometallic or bimetallic complexes. The copper(I) complex was prepared and illustrates the utility of the ligand. The copper(I) complex luminesced in fluid solution at room temperature. Several new luminescing complexes of platinum(II) based on the biphenyl ligand were isolated. Their photophysical properties were separated into two classes, those emitting from {sup 3 }LC state and those emitting from a {sup 3}MLCT state in the same compound. Temperature dependent emission lifetime studies of new ruthenium(II) complexes suggest that current explanations regarding the photophysics of these complexes may need to be reexamined. Barclay-Butler plots of the log of the preexponential factor vs {Delta}E, the Arrhenius activation energy, was linear for a wide range of ruthenium(II) complexes. Finally, progress continues to be made in understanding energy transfer processes in mixed metal ruthenium(II)/rhenium(I) ruthenium(II)/cobalt(III) complexes. Solvent plays a critical role in the luminescence from both the rhenium(I) and ruthenium(II) components in the bimetallic complex and this role was examined as a function of the heavy atom effect and other solvent properties. 34 refs., 2 figs.

Rillema, D.P.

1991-01-01

17

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

18

Electron transfer in pnicogen bonds.  

PubMed

As a new type of noncovalent interactions, pnicogen bond between a VA group element (N, P, and As) and an electron donor (Lewis base) has grabbed attention in recent several years. Here we employ the block-localized wave function (BLW) based energy decomposition scheme to probe the bonding nature in a series of substituted phosphines XnPH3-n complexed with ammonia. As the BLW method can derive the optimal monomer orbitals in a complex with the electron transfer among monomers quenched, we can effectively examine the HOMO-LUMO interaction in these pnicogen bonding systems. Among various energy components, electron transfer energy together with the polarization energy dominates the pnicogen bonding energy. Although usually it is assumed that the electron transfer from ammonia to substituted phosphines occurs in the form of n ? ?*(XP) hyperconjugative interaction, we identify a kind of new pathway when X = NO2 and CN, i.e., n ? d?*, which results from the interaction between the ? orbital of cyano or nitro substituent and d orbitals on P. But still this picture of electron transfer using a single pair of orbitals is greatly simplified, as the electron density difference (EDD) maps corresponding to the overall electron transfer processes show the accumulation of electron density on the P side opposite to the X-P bond, with insignificant or even negligible gain of electron density on the substituent group side. Thus, the EDD maps tend to support the concept of ?-hole in pnicogen bonds. PMID:24588109

Guan, Liangyu; Mo, Yirong

2014-10-01

19

Reactivity and mass transfer of low-dimensional catalysts.  

PubMed

Understanding the mechanisms governing chemical and morphological changes induced by an ambient-pressure gas and how such changes influence the activity of heterogeneous catalysts is central to the formation of a predictive capability for structure-reactivity relationships. With techniques such as ambient-pressure photoelectron spectroscopy, scanning tunneling microscopy, and surface X-ray diffraction, active phases and reaction intermediates can be probed in situ on relevant samples to form a comprehensive picture of this dynamic interplay between gases and surfaces. Of particular interest is the interaction of oxygen and carbon monoxide with catalysts. We will describe how model systems of increased complexity can be used to investigate gas-mediated mass transfer processes that may occur even at relatively modest temperatures. Furthermore, we will discuss how the morphology may be tailored to study specific contributions from defect sites and charge transfer to catalytic activity. PMID:25065579

Weissenrieder, Jonas; Gustafson, Johan; Stacchiola, Dario

2014-10-01

20

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

21

Discovery and application of doubly quaternized cinchona-alkaloid-based phase-transfer catalysts.  

PubMed

We report the discovery of novel N,N'-disubstituted cinchona alkaloids as efficient phase-transfer catalysts for the assembly of stereogenic quaternary centers. In comparison to traditional cinchona-alkaloid-based phase-transfer catalysts, these new catalysts afford substantial improvements in enantioselectivity and reaction rate for intramolecular spirocyclization reactions with catalyst loadings as low as 0.3?mol% under mild conditions. PMID:24961909

Xiang, Bangping; Belyk, Kevin M; Reamer, Robert A; Yasuda, Nobuyoshi

2014-08-01

22

Molecular dynamics study of phase transfer catalyst for ion transfer through water-chloroform interface  

NASA Astrophysics Data System (ADS)

Microscopic mechanism of phase transfer catalyst (PTC) is investigated by molecular dynamics simulation. As an example of PTC, tetrabutylammonium cation is treated which facilitates Cl transfer from water to chloroform phase. Calculated free energy profiles reveal the effects of PTC in relation to the pertinent change of interface structure. The ion pair formation changes the free energy profiles in the late stage of transfer, where large structural fluctuation emerges, called water finger. The PTC controls the formation of water finger and thereby influences on the free energy. These microscopic insight is important for PTC-assisted reactions at the interface.

Kikkawa, Nobuaki; Ishiyama, Tatsuya; Morita, Akihiro

2012-05-01

23

Engineering nanocarbon interfaces for electron transfer  

E-print Network

Electron-transfer reactions at nanometer-scale interfaces, such as those presented by single-walled carbon nanotubes (SWCNTs), are important for emerging optoelectronic and photovoltaic technologies. Electron transfer also ...

Hilmer, Andrew J. (Andrew Joseph)

2013-01-01

24

Intra-channel mass and heat-transfer modeling in diesel oxidation catalysts  

E-print Network

02FCC-140 Intra-channel mass and heat-transfer modeling in diesel oxidation catalysts Kalyana transfer in modeling the performance of diesel oxidation catalysts. Many modeling studies have assumed experimental measurements of CO and hydrocarbon oxidation in diesel exhaust re- veal that actual mass

Tennessee, University of

25

Analytical Model for Rates of Electron Attachment and Intramolecular Electron Transfer in Electron Transfer  

E-print Network

electron attachment to the gaseous parent ion. The basic questions arising in these studies can be sumAnalytical Model for Rates of Electron Attachment and Intramolecular Electron Transfer in Electron) experiments, one subjects a mass-to-charge-selected parent ion to very low-energy electrons (often boiled off

Simons, Jack

26

Modular electron transfer circuits for synthetic biology  

PubMed Central

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

Agapakis, Christina M

2010-01-01

27

Supramolecular electron transfer by anion binding.  

PubMed

Anion binding has emerged as an attractive strategy to construct supramolecular electron donor-acceptor complexes. In recent years, the level of sophistication in the design of these systems has advanced to the point where it is possible to create ensembles that mimic key aspects of the photoinduced electron-transfer events operative in the photosynthetic reaction centre. Although anion binding is a reversible process, kinetic studies on anion binding and dissociation processes, as well as photoinduced electron-transfer and back electron-transfer reactions in supramolecular electron donor-acceptor complexes formed by anion binding, have revealed that photoinduced electron transfer and back electron transfer occur at time scales much faster than those associated with anion binding and dissociation. This difference in rates ensures that the linkage between electron donor and acceptor moieties is maintained over the course of most forward and back electron-transfer processes. A particular example of this principle is illustrated by electron-transfer ensembles based on tetrathiafulvalene calix[4]pyrroles (TTF-C4Ps). In these ensembles, the TTF-C4Ps act as donors, transferring electrons to various electron acceptors after anion binding. Competition with non-redox active substrates is also observed. Anion binding to the pyrrole amine groups of an oxoporphyrinogen unit within various supramolecular complexes formed with fullerenes also results in acceleration of the photoinduced electron-transfer process but deceleration of the back electron transfer; again, this is ascribed to favourable structural and electronic changes. Anion binding also plays a role in stabilizing supramolecular complexes between sulphonated tetraphenylporphyrin anions ([MTPPS](4-): M = H(2) and Zn) and a lithium ion encapsulated C(60) (Li(+)@C(60)); the resulting ensemble produces long-lived charge-separated states upon photoexcitation of the porphyrins. PMID:22766725

Fukuzumi, Shunichi; Ohkubo, Kei; D'Souza, Francis; Sessler, Jonathan L

2012-10-11

28

Development of a Method for the Extraction of Oil from Clay by Friendly Phase Transfer Catalyst  

Microsoft Academic Search

The separation of waste oil from clay was studied using benzyl triethanol ammonium chloride as phase transfer catalyst. The study showed that the surface tension has an effect on oil recovery. An induced air flotation process was used and polymeric decyl phenol formaldehyde ethoxylate was used as the collector. The effects of various parameters including concentration of catalyst, collector, time

A. K. El Morsi; A. M. A. Omar

2010-01-01

29

Poly[Ethylene Glycol] Derivatives as Phase Transfer Catalysts and Solvents for Organic Reactions  

Microsoft Academic Search

The use of polyethers, specifically poly(ethylene glycol)'s (PEG), as reagents in organic synthesis can be arbitrarily divided into three areas: 1) phase transfer catalysts, 2) supported catalysts, and 3) reaction solvents. Other areas such as enzyme immobilization, aqueous biphase separation, e.g., media effects on separation, or the synthesis of ethanol from sucrose will not be covered here.

G. E. Totten; N. A. Clinton

1988-01-01

30

Light-driven microbial dissimilatory electron transfer to hematite.  

PubMed

The ability of dissimilatory metal-reducing microorganisms (DMRM) to conduct extracellular electron transfer with conductive cellular components grants them great potential for bioenergy and environmental applications. Crystalline Fe(iii) oxide, a type of widespread electron acceptor for DMRM in nature, can be excited by light for photocatalysis and microbial culture-mediated photocurrent production. However, the feasibility of direct electron transfer from living cells to light-excited Fe(iii) oxides has not been well documented and the cellular physiology in this process has not been clarified. To resolve these problems, an electrochemical system composed of Geobacter sulfurreducens and hematite (?-Fe2O3) was constructed, and direct electron transfer from G. sulfurreducens cells to the light-excited ?-Fe2O3 in the absence of soluble electron shuttles was observed. Further studies evidenced the efficient excitation of ?-Fe2O3 and the dependence of photocurrent production on the biocatalytic activity. Light-induced electron transfer on the cell-?-Fe2O3 interface correlated linearly with the rates of microbial respiration and substrate consumption. In addition, the G. sulfurreducens cells were found to survive on light-excited ?-Fe2O3. These results prove a direct mechanism behind the DMRM respiration driven by photo-induced charge separation in semiconductive acceptors and also imply new opportunities to design photo-bioelectronic devices with living cells as a catalyst. PMID:25238285

Li, Dao-Bo; Cheng, Yuan-Yuan; Li, Ling-Li; Li, Wen-Wei; Huang, Yu-Xi; Pei, Dan-Ni; Tong, Zhong-Hua; Mu, Yang; Yu, Han-Qing

2014-10-01

31

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

32

Polyoxometalate-mediated electron transfer-oxygen transfer oxidation of cellulose and hemicellulose to synthesis gas.  

PubMed

Terrestrial plants contain ~70% hemicellulose and cellulose that are a significant renewable bioresource with potential as an alternative to petroleum feedstock for carbon-based fuels. The efficient and selective deconstruction of carbohydrates to their basic components, carbon monoxide and hydrogen, so called synthesis gas, is an important key step towards the realization of this potential, because the formation of liquid hydrocarbon fuels from synthesis gas are known technologies. Here we show that by using a polyoxometalate as an electron transfer-oxygen transfer catalyst, carbon monoxide is formed by cleavage of all the carbon-carbon bonds through dehydration of initially formed formic acid. In this oxidation-reduction reaction, the hydrogen atoms are stored on the polyoxometalate as protons and electrons, and can be electrochemically released from the polyoxometalate as hydrogen. Together, synthesis gas is formed. In a hydrogen economy scenario, this method can also be used to convert carbon monoxide to hydrogen. PMID:25082188

Sarma, Bidyut Bikash; Neumann, Ronny

2014-01-01

33

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

NASA Astrophysics Data System (ADS)

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

D'Avanzo, Antonella

34

Related rhenium(V) catalysts adopt different mechanisms for oxygen atom transfer  

Microsoft Academic Search

The chemical mechanisms for three related rhenium(V) catalysts of oxygen atom transfer reactions are reviewed. Two of the catalysts are compounds with a single rhenium atom, [MeReE(mtp)(PPh3)], where E is either O (1) or S (2) and mtpH2 is 2-(mercaptomethyl)thiophenol; the third is the di-rhenium compound {MeReO(mtp)}2 (3). In each of them, the Re atom is square-pyramidal, sitting slightly above

James H. Espenson

2005-01-01

35

Molybdenum Imido Alkylidene Metathesis Catalysts That Contain Electron-Withdrawing Biphenolates or Binaphtholates  

E-print Network

Molybdenum Imido Alkylidene Metathesis Catalysts That Contain Electron-Withdrawing Biphenolates(pentafluorophenyl)binaphthol] with a bis(2,5-dimethylpyrrolide) complex. The pyrrolide approach can be employed either to isolate catalysts on a preparative scale or to generate catalysts in situ. Several simple preliminary ring-closing metathesis

Müller, Peter

36

Non-destructive transmission electron microscopy study of catalyst degradation under electrochemical treatment  

Microsoft Academic Search

A novel, non-destructive transmission electron microscopy technique is introduced, which enables the observation of the identical locations of a catalyst before and after electrochemical treatment (IL-TEM). The significance of this method is exemplified by the analysis of a standard, commercially available carbon supported platinum catalyst. We demonstrate that the observed changes of the catalyst particles are a direct consequence of

Karl J. J. Mayrhofer; Sean J. Ashton; Josef C. Meier; Gustav K. H. Wiberg; Marianne Hanzlik; Matthias Arenz

2008-01-01

37

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

38

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

2014-10-01

39

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

40

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.

41

Reaction of electron-transfer flavoprotein with electron-transfer flavoprotein-ubiquinone oxidoreductase  

Microsoft Academic Search

The oxidative half-reaction of electron-transfer flavoprotein (ETF), electron transfer from ETF to electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO), is dependent on complementary surface charges on the two proteins. ETF is the positively charged member of the redox pair. The evidence is based on the pH and ionic strength dependencies of the comproportionation of oxidized ETF and ETF hydroquinone catalyzed by ETF-QO and

Joe D. Beckmann; Frank E. Frerman

1985-01-01

42

Long-range electron transfer  

PubMed Central

Recent investigations have shed much light on the nuclear and electronic factors that control the rates of long-range electron tunneling through molecules in aqueous and organic glasses as well as through bonds in donor–bridge–acceptor complexes. Couplings through covalent and hydrogen bonds are much stronger than those across van der Waals gaps, and these differences in coupling between bonded and nonbonded atoms account for the dependence of tunneling rates on the structure of the media between redox sites in Ru-modified proteins and protein–protein complexes. PMID:15738403

Gray, Harry B.; Winkler, Jay R.

2005-01-01

43

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

44

Electron Transfer in Cyanobacterial Photosystem I II. DETERMINATION OF FORWARD ELECTRON TRANSFER RATES OF SITE-DIRECTED MUTANTS IN A  

E-print Network

, quinones function as the terminal electron acceptors, and electron transfer is known to be highlyElectron Transfer in Cyanobacterial Photosystem I II. DETERMINATION OF FORWARD ELECTRON TRANSFER RATES OF SITE-DIRECTED MUTANTS IN A PUTATIVE ELECTRON TRANSFER PATHWAY FROM A0 THROUGH A1 TO FX

45

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

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

Photoinduced electron transfer in ordered polymers  

SciTech Connect

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

Jones, G. II.

1991-12-01

48

Optimum Transfer Guide: Electronic Media & Communications Why Study Electronic Media?  

E-print Network

, and writing to provide a broad and thor- ough liberal arts education. Why Study EM&C at Texas Tech. Graduate Education The College of Mass Communications offers both the Masters of Arts and the DoctorOptimum Transfer Guide: Electronic Media & Communications Why Study Electronic Media

Gelfond, Michael

49

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

50

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...

51

Catalysts  

NSDL National Science Digital Library

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

Consortium, The C.

2011-12-11

52

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.

53

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

PubMed

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

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

2013-02-15

54

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

55

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

56

An efficient method for the preparation of methylcobalamin, nature's organometallic methyl transfer catalyst  

Microsoft Academic Search

Methylcobalamin (1), the structurally simplest organocobalamin and nature's organometallic methyl transfer catalyst, was prepared from aquocob(III)alamin and methyl iodide in > 90% yield in a previously unexplored, but experimentally simple procedure, using formate as reducing agent and exploiting the previously established tendency of cob(II)alamin to be alkylated by methyliodide. A thorough NMR-spectroscopic analysis of aqueous solutions of this organometallic B12-derivative

Martin Tollinger; Tomas Dérer; Robert Konrat; Bernhard Kräutler

1997-01-01

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

Electron Attachment Step in Electron Capture Dissociation (ECD) and Electron Transfer Dissociation (ETD)  

E-print Network

or protein cation. This produces a less-exothermic (i.e., more "gentle") electron-transfer reaction than used a Landau-Zener-Stueckelberg curve-crossing approximation to estimate the ETD rates for electron

Simons, Jack

59

Mixed Valent Sites in Biological Electron Transfer  

SciTech Connect

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

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

2009-05-26

60

Ultrafast Interfacial Proton-Coupled Electron Transfer  

SciTech Connect

Interfaces between metallic or semiconducting solids and protic solvent adsorbates or liquids represent one of the most important, and yet hardly explored material environments for proton coupled electron transfer (PCET) processes. PCET mediated dynamical phenomena driven by light, electron, and chemical potentials are central in energy transduction processes of vast economic and environmental importance including the photocatalytic splitting of H?O, the photo and electrochemical reduction of CO?, and the conversion of chemical to electrical energy in fuel cells. Experimental and theoretical investigations of the dynamical aspects of PCET at solid surfaces are particularly challenging because relatively localized charges within a solvent couple in the presence of strong interfacial potentials to delocalized states of electronic continua of semiconductor or metal electrodes. Moreover, the localized charges are never the bare protons and electrons that balance chemical equations, but rather are dressed particles with associated polarization clouds inhomogeneously distributed and comprised variously of free electrons, lattice ions, and solvent molecules. The polarization clouds screen the Coulomb potential on the medium specific time scales and impose energetic costs associated with transport through the inhomogeneous region of interfaces between the solid and molecular environments. We introduce some recent theoretical studies aimed at providing an atomistic description on metal-protic solvent interface and modeling of simple processes such as the discharge of H? at a metal interface. Because of the paucity of experimental research and embryonic stage of theory, our goal is to present some key theoretical concepts and early experimental efforts based primarily on a surface science approach to ultrafast electron induced dynamics. In order to introduce some key features of interfacial PCET in the strong and intermediate coupling regimes, we discuss specific examples of photoinduced dissociation of alkanes on metals and photoinduced PCET dynamics of methanol covered TiO? surfaces.

Petek, Hrvoje; Zhao, Jin

2010-12-08

61

Electron Transfer Interactome of Cytochrome c  

PubMed Central

Lying at the heart of many vital cellular processes such as photosynthesis and respiration, biological electron transfer (ET) is mediated by transient interactions among proteins that recognize multiple binding partners. Accurate description of the ET complexes – necessary for a comprehensive understanding of the cellular signaling and metabolism – is compounded by their short lifetimes and pronounced binding promiscuity. Here, we used a computational approach relying solely on the steric properties of the individual proteins to predict the ET properties of protein complexes constituting the functional interactome of the eukaryotic cytochrome c (Cc). Cc is a small, soluble, highly-conserved electron carrier protein that coordinates the electron flow among different redox partners. In eukaryotes, Cc is a key component of the mitochondrial respiratory chain, where it shuttles electrons between its reductase and oxidase, and an essential electron donor or acceptor in a number of other redox systems. Starting from the structures of individual proteins, we performed extensive conformational sampling of the ET-competent binding geometries, which allowed mapping out functional epitopes in the Cc complexes, estimating the upper limit of the ET rate in a given system, assessing ET properties of different binding stoichiometries, and gauging the effect of domain mobility on the intermolecular ET. The resulting picture of the Cc interactome 1) reveals that most ET-competent binding geometries are located in electrostatically favorable regions, 2) indicates that the ET can take place from more than one protein-protein orientation, and 3) suggests that protein dynamics within redox complexes, and not the electron tunneling event itself, is the rate-limiting step in the intermolecular ET. Further, we show that the functional epitope size correlates with the extent of dynamics in the Cc complexes and thus can be used as a diagnostic tool for protein mobility. PMID:23236271

Volkov, Alexander N.; van Nuland, Nico A. J.

2012-01-01

62

Gene Transfer to Rabbit Retina with Electron Avalanche Transfection  

E-print Network

Gene Transfer to Rabbit Retina with Electron Avalanche Transfection Thomas W. Chalberg,1 Alexander clinically acceptable methods for efficient gene transfer. Electroporation is widely used for transfection for the eye. METHODS. A novel method for nonviral DNA transfer, called electron avalanche transfection

Palanker, Daniel

63

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

64

Synthesis of TiO2-Poly(3-hexylthiophene) Hybrid Particles through Surface-Initiated Kumada Catalyst-Transfer Polycondensation.  

PubMed

TiO2/conjugated polymers are promising materials in solar energy conversion where efficient photoinduced charge transfers are required. Here, a "grafting-from" approach for the synthesis of TiO2 nanoparticles supported with conjugated polymer brushes is presented. Poly(3-hexylthiophene) (P3HT), a benchmark material for organic electronics, was selectively grown from TiO2 nanoparticles by surface-initiated Kumada catalyst-transfer polycondensation. The grafting of the polymer onto the surface of the TiO2 nanoparticles by this method was demonstrated by (1)H and (13)C solid-state NMR, X-ray photoelectron spectrometry, thermogravimetric analysis, transmission electron microscopy, and UV-visible spectroscopy. Sedimentation tests in tetrahydrofuran revealed improved dispersion stability for the TiO2@P3HT hybrid material. Films were produced by solvent casting, and the quality of the dispersion of the modified TiO2 nanoparticles was evaluated by atomic force microscopy. The dispersion of the P3HT-coated TiO2 NPs in the P3HT matrix was found to be homogeneous, and the fibrillar structure of the P3HT matrix was maintained which is favorable for charge transport. Fluorescence quenching measurements on these hybrid materials in CHCl3 indicated improved photoinduced electron-transfer efficiency. All in all, better physicochemical properties for P3HT/TiO2 hybrid material were reached via the surface-initiated "grafted-from" approach compared to the "grafting-onto" approach. PMID:25188446

Boon, Florian; Moerman, David; Laurencin, Danielle; Richeter, Sébastien; Guari, Yannick; Mehdi, Ahmad; Dubois, Philippe; Lazzaroni, Roberto; Clément, Sébastien

2014-09-30

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

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

67

Extensive conformational sampling in a ternary electron transfer complex  

Microsoft Academic Search

Here we report the crystal structures of a ternary electron transfer complex showing extensive motion at the protein interface. This physiological complex comprises the iron-sulfur flavoprotein trimethylamine dehydrogenase and electron transferring flavoprotein (ETF) from Methylophilus methylotrophus. In addition, we report the crystal structure of free ETF. In the complex, electron density for the FAD domain of ETF is absent, indicating

Jaswir Basran; François Talfournier; Michael J. Sutcliffe; Nigel S. Scrutton; David Leys

2003-01-01

68

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

69

Diameter dependent electron transfer kinetics in semiconductor-enzyme complexes.  

PubMed

Excited state electron transfer (ET) is a fundamental step for the catalytic conversion of solar energy into chemical energy. To understand the properties controlling ET between photoexcited nanoparticles and catalysts, the ET kinetics were measured for solution-phase complexes of CdTe quantum dots and Clostridium acetobutylicum [FeFe]-hydrogenase I (CaI) using time-resolved photoluminescence spectroscopy. Over a 2.0-3.5 nm diameter range of CdTe nanoparticles, the observed ET rate (kET) was sensitive to CaI concentration. To account for diameter effects on CaI binding, a Langmuir isotherm and two geometric binding models were created to estimate maximal CaI affinities and coverages at saturating concentrations. Normalizing the ET kinetics to CaI surface coverage for each CdTe diameter led to kET values that were insensitive to diameter, despite a decrease in the free energy for photoexcited ET (?GET) with increasing diameter. The turnover frequency (TOF) of CaI in CdTe-CaI complexes was measured at several molar ratios. Normalization for diameter-dependent changes in CaI coverage showed an increase in TOF with diameter. These results suggest that kET and H2 production for CdTe-CaI complexes are not strictly controlled by ?GET and that other factors must be considered. PMID:25244026

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

2014-10-28

70

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

71

Cyclic electron transfer in plant leaf  

PubMed Central

The turnover of linear and cyclic electron flows has been determined in fragments of dark-adapted spinach leaf by measuring the kinetics of fluorescence yield and of the transmembrane electrical potential changes under saturating illumination. When Photosystem (PS) II is inhibited, a cyclic electron flow around PSI operates transiently at a rate close to the maximum turnover of photosynthesis. When PSII is active, the cyclic flow operates with a similar rate during the first seconds of illumination. The high efficiency of the cyclic pathway implies that the cyclic and the linear transfer chains are structurally isolated one from the other. We propose that the cyclic pathway operates within a supercomplex including one PSI, one cytochrome bf complex, one plastocyanin, and one ferredoxin. The cyclic process induces the synthesis of ATP needed for the activation of the Benson–Calvin cycle. A fraction of PSI (?50%), not included in the supercomplexes, participates in the linear pathway. The illumination would induce a dissociation of the supercomplexes that progressively increases the fraction of PSI involved in the linear pathway. PMID:12119384

Joliot, Pierre; Joliot, Anne

2002-01-01

72

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

SciTech Connect

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

Not Available

1989-12-31

73

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

SciTech Connect

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

Not Available

1989-01-01

74

Spectroscopic Probes for Electron Transfer Phenomena.  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. This work concerns spectroscopic studies of the oxo-centred trinuclear carboxylate complexes of the type (M_3O(RCO_2) _6(L)_3) ^+ and (M_2M ^'O(RCO_2 )_6(L)_3) where M = Fe(III), Cr(III) and Mn(III); M_2 M^' = Fe _2Mn^{rm xx} , Fe_2Fe^ {rm xx}, Fe_2Co ^{rm xx}, Fe _2Ni^{rm xx} and Mn_2Mn^ {rm xx}; R = CH_3 , CD_3 and C(Me) _3, and L = H_2O, D_2O, py, d_5 -py, gamma-picoline and beta -picoline. The main purpose was to study electron delocalization in the Fe_2Fe ^{rm xx} systems. Three techniques have been used; nuclear magnetic resonance, inelastic neutron scattering, and infrared spectroscopy. From the criterion that the M_2M ^'O framework in mixed metal complexes has C_{rm 2v} symmetry, and the fully 'oxidized' M^{rm xxx}_3O complexes have D_ {rm 3h} symmetry, the mixed valence compounds will appear to have either C_ {rm 2v} or D_{ rm 3h} symmetry depending on the rate of intramolecular electron transfer in relation to the time scale of the measurement. For the pivalate complexes (R = C(Me)_3)^1H nmr spectra in CDC1_3 show that electron hopping in the mixed valence complex is fast enough to average any inequivalencies due to the different oxidation states of iron. Rationalization of the paramagnetic shift patterns reveal that a sigma through bond mechanism is dominant for delocalizing unpaired spin density onto the nmr nucleus. Conversely, infrared spectra of the same complex indicates partial valence trapping in the solid state up to at least 150^circ C, and in solution at room temperature. Valence trapping is also found in the Mn_2Mn compounds. Inelastic neutron scattering in the region 0 to 3000cm^{-1} for the acetate and deuteroacetate compounds clearly identifies vibrations of the bridging ligand, and also reveal an envelope of bands due to coordinated and non-coordinated water molecules. Exchange coupling constants extracted by this technique for the Cr_3(III) and Fe_3 (III) compounds are found to decrease with increasing temperature. For the homologues (Fe_2MO(O _2CCD_3) _6(d_5-py) _3) (d_5-py), M = Mn^{rm xx}, Fe ^{rm xx}, Co^ {rm xx}, the coupling constants are very similar, indicating complete electron localization in the mixed valence compound at 5K.

White, Ross Paul

75

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

76

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

77

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.

78

76 FR 29901 - Electronic Fund Transfers  

Federal Register 2010, 2011, 2012, 2013

...Similarly, if an agent at a retail establishment fails to provide the disclosures required...Act (12 U.S.C. 1752). (b) Permanent exception for transfers to certain...to the amount transferred. 32(b) Permanent Exception for Transfers to Certain...

2011-05-23

79

Ring-Opening Metathesis Polymerization of 18-e Cobalt(I)-Containing Norbornene and Application as Heterogeneous Macromolecular Catalyst in Atom Transfer Radical Polymerization.  

PubMed

In the last decades, metallopolymers have received great attention due to their various applications in the fields of materials and chemistry. In this article, a neutral 18-electron exo-substituted ?(4) -cyclopentadiene CpCo(I) unit-containing polymer is prepared in a controlled/"living" fashion by combining facile click chemistry and ring-opening meta-thesis polymerization (ROMP). This Co(I)-containing polymer is further used as a heterogeneous macromolecular catalyst for atom transfer radical polymerization (ATRP) of methyl methacrylate and styrene. PMID:25250694

Yan, Yi; Zhang, Jiuyang; Wilbon, Perry; Qiao, Yali; Tang, Chuanbing

2014-11-01

80

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

PubMed Central

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

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

2012-01-01

81

Solvent-controlled acceleration of electron transfer reaction  

Microsoft Academic Search

Summary form only given. Liquid phase electron transfer is one of the key reactions in nature and has been extensively studied. In his pioneering work, Marcus (1985) modelled electron transfer (ET) as thermally activated barrier hopping. Subsequent improvements of the theory that incorporated the influence of solvent dynamics on the ET process, led to the central conclusion that the inverse

M. S. Pshenichnikov; H. P. Den Hartog; A. Baltuska; A. Pugzlys; S. Umapathy; D. A. Wiersma

2000-01-01

82

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

83

Computer Simulation of Electron Transfer at Hematite Surfaces  

SciTech Connect

Molecular dynamics simulations in combination with ab initio calculations were carried out to determine the rate of electron transfer in bulk hematite (?-Fe2O3) and at two low-index surfaces, namely the (012) and (001) surfaces. The electron transfer reactions considered here involve the II/III valence interchange between nearest-neighbor iron atoms. Two electron transfer directions were investigated namely the basal plane and c direction charge transfers. Electron transfer rates obtained in bulk hematite were in good agreement with ab initio electronic structure calculations thus validating the potential model. The surfaces were considered both in vacuum and in contact with an equilibrated aqueous solution. The reorganization energy is found to increase significantly at the first surface layer and this value is little affected by the presence of water. In addition, in the case of the (012) surface, the electronic coupling matrix element for the topmost basal plane transfer was calculated at the Hartree-Fock level and was found to be weak compared to the corresponding charge transfer in the bulk. Therefore, most surfaces show a decrease in the rate of charge transfer at the surface. However, where iron atoms involved in the charge transfer reaction are directly coordinated to water molecules, water lowers the free energy of activation to a great extent and provides a large driving force for electrons to diffuse toward the bulk thus opposing the intrinsic surface effect. The surfaces considered in this work show different charge transfer properties. Hematite has been shown to exhibit anisotropic conductivity and thus different surfaces will show different intra- and inter-layer rates depending on their orientation. Moreover, the calculations of charge transfers at the hydroxyl- and iron-terminated (001) surfaces revealed that surface termination has a significant effect on the charge transfer parameters in the vicinity of the surface. Finally, our findings indicate that undercoordinated terminal iron atoms could act as electron traps at the surface.

Kerisit, Sebastien N.; Rosso, Kevin M.

2006-04-15

84

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

85

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

86

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

87

Electronic state of supported Rh catalysts and the selectivity for the hydrogenation of carbon monoxide  

Microsoft Academic Search

The electronic states of Rh crystallites highly dispersed on various oxides (SiOâ, ZnO, ZrOâ, and ZrOâ or TiOâ on SiOâ) and the catalytic hydrogenation of CO to form oxygenated hydrocarbons were examined. From XPS measurement Rh on Rh\\/SiOâ showed an electronic state similar to that of Rh metal. This catalyst was active in forming hydrocarbons. However, Rh on Rh\\/ZnO, which

Maki Kawai; M. Uda; Masaru Ichikawa

1985-01-01

88

Synthesis of (2 S,2? S)-bimorpholine N, N?-quaternary salts as chiral phase transfer catalysts  

Microsoft Academic Search

(2S,2?S)-Bimorpholine was synthesized starting from (R,R)-tartaric acid ester acetal in six steps in 50% of the total yield. Key steps include: cyanide catalyzed amidation and one-step cyclization with p-toluenesulfonyl imidazole. Derivatization of N,N?-dibenzyl bimorpholine afforded quaternary bimorpholinium salts, which were used as chiral phase transfer alkylation catalysts.

Kristin Lippur; Tõnis Kanger; Kadri Kriis; Tiiu Kailas; Aleksander-Mati Müürisepp; Tõnis Pehk; Margus Lopp

2007-01-01

89

Variable Electron Transfer Pathways in an Amphibian Cryptochrome  

PubMed Central

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

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

2013-01-01

90

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

91

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

Microsoft Academic Search

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

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

2009-01-01

92

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

93

Final Report: Vibrational Dynamics in Photoinduced Electron Transfer  

SciTech Connect

The objective of this grant was to understand how molecular vibrational states (geometry distortions) are involved in photoinduced electron transfer rates of molecules. This subject is an important component of understanding how molecular absorbers of light convert that energy into charge separation. This is important because the absorption usually excites molecular vibrations in a new electronic state prior to electron transfer to other molecules or semiconductor nanoparticles, as in some types of solar cells. The speeds of charge separation and charge recombination are key parameters that require experiments such as those in this work to test the rules governing electron transfer rates. Major progress was made on this goal. Some of the molecular structures selected for developing experimental data were bimolecular charge transfer complexes that contained metals of cobalt or vanadium. The experiments used the absorption of an ultrafast pulse of light to directly separate charges onto the two different molecular parts of the complex. The charge recombination then proceeds naturally, and one goal was to measure the speed of this recombination for different types of molecular vibrations. We used picosecond and femtosecond duration pulses with tunable colors at infrared wavelengths to directly observe vibrational states and their different rates of charge recombination (also called electron transfer). We discovered that different contact geometries in the complexes had very different electron transfer rates, and that one geometry had a significant dependence on the amount of vibration in the complex. This is the first and only measurement of such rates, and it allowed us to confirm our interpretation with a number of molecular models and test the sensitivity of electron transfer to vibrational states. This led us to develop a general theory, where we point out how molecular distortions can change the electron transfer rates to be much faster than prior theories predict. This provides a new method to predict electron transfer rates for particular conditions, and it will be important in designing new types of solar cells. A related set of studies were also done to understand how much the environment around the active charge transfer molecules can control the speed of charge transfer. We studied different complexes with femtosecond transient absorption spectroscopy to show that solvent or components of a matrix environment can directly control ultrafast electron transfer when the environmental relaxation time response is on a similar time-scale as the natural electron transfer. Understanding such processes in both liquids and in a matrix is essential for designing new types of solar cells.

Kenneth G. Spears

2006-04-19

94

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

Microsoft Academic Search

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

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

2010-01-01

95

Cross-strand histidine-aromatic interactions enhance acyl-transfer rates in beta-hairpin peptide catalysts.  

PubMed

A reactive tagging methodology was used to select the species most reactive to an acylation reagent from a solid phase library of beta hairpin peptides. Hits bearing an electron-rich aromatic residue across strand from a reactive histidine were found to competitively become N-acylated. In addition to displaying rapid N-acylation rates the hit peptide was additionally deacylated in the presence of a nucleophile, thus closing a putative catalytic cycle. Variants of the hit peptide were studied to elucidate both the magnitude (up to 18?000-fold over background, kcat/kuncat = 94?000?000, or 45-fold over Boc-histidine methyl ester) and mechanism of acyl transfer catalysis. A combination of CH-?, cation-? and HisH(+)-O interactions in the cationic imidazole transition state is implicated in the rate acceleration, in addition to the fidelity of the beta hairpin fold. Moreover, NMR structural data on key intermediates or models thereof suggest that a key feature of this catalyst is the ability to access several different stabilizing conformations along the catalysis reaction coordinate. PMID:25254932

Matsumoto, M; Lee, S J; Gagné, M R; Waters, M L

2014-10-15

96

Picosecond infrared study of vibrational dependent electron transfer rates  

SciTech Connect

Photoinduced electron transfer and thermal back electron transfer in the inorganic donor-acceptor {l_brace}A{sup +}D{sup {minus}}{r_brace} contact ion-pair {l_brace}Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup {minus}}{r_brace} have been observed in solution with picosecond time-resolved infrared absorption spectroscopy. Optical excitation of a charge transfer band created by cobalt interaction causes an immediate electron transfer to form a neutral pair, and the spontaneous return electron transfer is followed by monitoring the CO stretching frequencies of the Co(CO){sub 4}{sup {minus}} and Co(CO){sub 4} molecules. The authors have observed the back electron transfer decay for up to 3 quanta of the CO stretching mode in the neutral pair {l_brace}DA{r_brace} for dichloromethane (DCM) solvent. The arrival kinetics into the ion pair and ion pair vibrational relaxation rates for final return to the vibrationless level have been studied for up to 4 quanta of vibration. These are the first measurements of an electron transfer process with vibrational resolution, and comparison to models is in progress.

Spears, K.G.; Arrivo, S.M.; Wen, X. [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry

1994-12-31

97

REFLECTIONS ON THE TWO-STATE ELECTRON TRANSFER MODEL.  

SciTech Connect

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

Brunschwig, B.S.

2000-01-12

98

Proton-coupled electron transfer with photoexcited metal complexes.  

PubMed

Proton-coupled electron transfer (PCET) plays a crucial role in many enzymatic reactions and is relevant for a variety of processes including water oxidation, nitrogen fixation, and carbon dioxide reduction. Much of the research on PCET has focused on transfers between molecules in their electronic ground states, but increasingly researchers are investigating PCET between photoexcited reactants. This Account describes recent studies of excited-state PCET with d(6) metal complexes emphasizing work performed in my laboratory. Upon photoexcitation, some complexes release an electron and a proton to benzoquinone reaction partners. Others act as combined electron-proton acceptors in the presence of phenols. As a result, we can investigate photoinduced PCET involving electron and proton transfer in a given direction, a process that resembles hydrogen-atom transfer (HAT). In other studies, the photoexcited metal complexes merely serve as electron donors or electron acceptors because the proton donating and accepting sites are located on other parts of the molecular PCET ensemble. We and others have used this multisite design to explore so-called bidirectional PCET which occurs in many enzymes. A central question in all of these studies is whether concerted proton-electron transfer (CPET) can compete kinetically with sequential electron and proton transfer steps. Short laser pulses can trigger excited-state PCET, making it possible to investigate rapid reactions. Luminescence spectroscopy is a convenient tool for monitoring PCET, but unambiguous identification of reaction products can require a combination of luminescence spectroscopy and transient absorption spectroscopy. Nevertheless, in some cases, distinguishing between PCET photoproducts and reaction products formed by simple photoinduced electron transfer (ET) (reactions that don't include proton transfer) is tricky. Some of the studies presented here deal directly with this important problem. In one case study we employed a cyclometalated iridium(III) complex. Our other studies with ruthenium(II) complexes and phenols focused on systematic variations of the reaction free energies for the CPET, ET, and proton transfer (PT) steps to explore their influence on the overall PCET reaction. Still other work with rhenium(I) complexes concentrated on the question of how the electronic structure of the metal-to-ligand charge transfer (MLCT) excited states affects PCET. We used covalent rhenium(I)-phenol dyads to explore the influence of the electron donor-electron acceptor distance on bidirectional PCET. In covalent triarylamine-Ru(bpy)?²?/Os(bpy)?²?-anthraquinone triads (bpy = 2,2'-bipyridine), hydrogen-bond donating solvents significantly lengthened the lifetimes of photogenerated electron/hole pairs because of hydrogen-bonding to the quinone radical anion. Until now, comparatively few researchers have investigated this variation of PCET: the strengthening of H-bonds upon photoreduction. PMID:23402212

Wenger, Oliver S

2013-07-16

99

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

SciTech Connect

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

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

2008-01-01

100

Electron attachment step in electron capture dissociation (ECD) and electron transfer dissociation (ETD).  

PubMed

We have made use of classical dynamics trajectory simultions and ab initio electronic structure calculations to estimate the cross sections with which electrons are attached (in electron capture dissociation (ECD)) or transferred (in electron transfer dissociation (ETD)) to a model system that contained both an S-S bond that is cleaved and a -NH(3)(+) positively charged site. We used a Landau-Zener-Stueckelberg curve-crossing approximation to estimate the ETD rates for electron transfer from a CH(3)(-) anion to the -NH(3)(+) Rydberg orbital or the S-S sigma* orbital. We draw conclusions about ECD from our ETD results and from known experimental electron-attachment cross sections for cations and sigma-bonds. We predict the cross section for ETD at the positive site of our model compound to be an order of magnitude larger than that for transfer to the Coulomb-stabilized S-S bond site. We also predict that, in ECD, the cross section for electron capture at the positive site will be up to 3 orders of magnitude larger than that for capture at the S-S bond site. These results seem to suggest that attachment to such positive sites should dominate in producing S-S bond cleavage in our compound. However, we also note that cleavage induced by capture at the positive site will be diminished by an amount that is related to the distance from the positive site to the S-S bond. This dimunition can render cleavage through Coulomb-assisted S-S sigma* attachment competitive for our model compound. Implications for ECD and ETD of peptides and proteins in which SS or N-C(alpha) bonds are cleaved are also discussed, and we explain that such events are most likely susceptible to Coulomb-assisted attachment, because the S-S sigma* and C=O pi* orbitals are the lowest-lying antibonding orbitals in most peptides and proteins. PMID:16833914

Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Simons, Jack

2005-07-01

101

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

102

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

PubMed Central

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.

2014-01-01

103

Electronic coupling responsible for energy transfer in columnar liquid crystals  

Microsoft Academic Search

Electronic coupling is the driving force for energy transfer in molecular materials and consists of several components. We determine the strength of dipolar\\/multipolar coupling and coupling due to orbital overlap for excitation transport in triphenylene columnar liquid crystals. We use time-resolved fluorescence spectroscopy and computer simulations. The fit of the experimental and simulated fluorescence decays reveals that the transfer process

Dimitra Markovitsi; Sylvie Marguet; Lazaros K. Gallos; Hervé Sigal; Philippe Millié; Panos Argyrakis; Helmut Ringsdorf; Sandeep Kumar

1999-01-01

104

Solvent structure and hydrodynamic effects in photoinduced electron transfer  

Microsoft Academic Search

A previously developed statistical mechanical theory describing photo-induced electron transfer and geminate recombination in liquid solutions has been modified to account for realistic finite-volume solvent effects. This work introduces physically important effects caused by the solvent which fundamentally affect the rates and spatial distribution of charge transfer events. The finite volume of solvent molecules gives rise to a nonuniform distribution

S. F. Swallen; Kristin Weidemaier; M. D. Fayer

1996-01-01

105

Models for Proton-coupled Electron Transfer in Photosystem II  

Microsoft Academic Search

The coupling of proton and electron transfers is a key part of the chemistry of photosynthesis. The oxidative side of photosystem\\u000a II (PS II) in particular seems to involve a number of proton-coupled electron transfer (PCET) steps in the S-state transitions.\\u000a This mini-review presents an overview of recent studies of PCET model systems in the authors’ laboratory. PCET is defined

James M. Mayer; Ian J. Rhile; Frank B. Larsen; Elizabeth A. Mader; Todd F. Markle; Antonio G. DiPasquale

2006-01-01

106

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

107

Static and dynamic order of cooperative multi-electron transfer  

NASA Astrophysics Data System (ADS)

We report on high correlation and ordering of multi-electron transfer at neutral-ionic transformation in quasi one-dimensional prototype crystal of tetrathiafulvalene-chloranil (TTF-CA). We present experimental evidences that the ordering of lattice-relaxed charge-transfer strings, which are nano-scale objects, occurs under static thermal equilibrium condition and non-equilibrium one achieved by femto-second laser irradiation. We suggest that the transformation is a profound example of self-organized, cooperative electron transfer with tendency for phase separation driven by energetics of inter-chain interaction and ferroelectric ordering.

Luty, T.; Cailleau, H.; Koshihara, S.; Collet, E.; Takesada, M.; Lemée-Cailleau, M. H.; Buron-LeCointe, M.; Nagaosa, N.; Tokura, Y.; Zienkiewicz, E.; Ouladdiaf, B.

2002-08-01

108

Radiative and nonradioactive electron transfer in donor-acceptor phenanthrimidazoles.  

PubMed

Photoinduced electron transfer in a series of naphthyl substituted phenanthrimidazoles has been studied in solutions. The intramolecular charge transfer (CT) leads to a large Stokes shift and large dipole moment in the fluorescent state. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all the compounds studied. An analysis of the CT fluorescence lead to the quantities relevant for the electron transfer in the Marcus inverted region. PMID:25194432

Jayabharathi, J; Thanikachalam, V; Ramanathan, P; Arunpandiyan, A

2014-11-01

109

The application of aberration-corrected electron microscopy to the characterization of gold-based catalysts  

NASA Astrophysics Data System (ADS)

Electron microscopy has long been used to study the morphology of heterogeneous catalysts. Recent advances in electron optics now allow for the correction of the inherent spherical aberration (Cs) produced by the objective lens in the scanning transmission electron microscope (STEM, resulting in a significantly improved spatial resolution as well as the ability to use a much larger probe-current than was previously possible. In this thesis, the combination of high-angle annular dark-field (HAADF) imaging and microanalysis by x-ray energy dispersive spectroscopy (XEDS) in an aberration-corrected STEM has been applied for the first time to the characterization of gold-based heterogeneous catalysts. Multi-variate statistical analysis (MSA) has been employed in order to further improve the STEM-XEDS spectrum image data acquired with this technique. In addition, supplemental analysis using electron-energy loss spectroscopy (EELS) and energy-filtered transmission electron microscopy (EFTEM) in an aberration-corrected instrument has also been attempted. These techniques have proven extremely valuable in providing complimentary information to more traditional catalyst characterization techniques such as x-ray photoelectron spectroscopy and x-ray diffraction in four specific problems relating to catalysis. Firstly, the atomic-scale resolution of Cs-corrected HAADF imaging has been utilized to study Au/FeOx catalysts in order to determine the size and structure of the Au clusters present on the support surface. It was discovered that, while both inactive and active catalysts for low-temperature CO oxidation contained large Au particles (> 5 nm) and individual Au atoms, the active catalyst also contained sub-nm clusters comprised of only a few Au atoms. Secondly, novel CeO2 support materials for Au and Au-Pd catalysts were synthesized by precipitation with supercritical CO2. These supports were found to produce significantly more active catalysts than those based on CeO2 prepared using more traditional methods. The combination of STEM-HAADF imaging and XEDS mapping has been used to characterize these catalysts and a strong correlation between the catalytic activity and the enhanced degree of metal dispersion over the support is demonstrated. Thirdly, a systematic series of Au-Pd/Al2O3 catalysts has been studied in order to characterize the effects of various heat treatments on the development of core-shell morphologies within the bi-metallic particles and its subsequent effect on their catalytic performance for H2O 2 synthesis. STEM-XEDS spectrum imaging was employed in order to determine the degree of alloying and segregation behavior within the individual Au-Pd particles as a function of calcination/reduction temperature. It was found that the as prepared catalyst contained homogeneous Au-Pd alloy particles and that a Pd-rich shell/Au-rich core morphology gradually developed upon calcination. Subsequent reduction of the catalyst caused a large fraction of the particles to invert and form Pd-rich core/Au-rich shell structures. These changes are related to both the activity and stability of the catalyst. Finally, the washing of activated carbon support materials in acid was found to be extremely beneficial for producing Au-Pd catalysts for the direct synthesis of H2O2. STEM-HAADF imaging revealed that the acid-washing treatment increased the dispersion of the metal on the carbon supports. Aberration-corrected STEM-XEDS spectrum imaging demonstrated a strong size dependence of the Au-Pd particle composition. Crucially, the acid-washing pre-treatment enhanced the alloying of Au and Pd by suppressing the formation of large (> 25 nm) Au-rich particles. In summary, the application of aberration-corrected HAADF imaging and STEM-XEDS spectrum imaging to the characterization of Au-based catalysts has enhanced the understanding of the structural and chemical features that determine their catalytic behavior. Specifically, they have allowed us to achieve the following: (a) image individual metal atoms and clusters of just a few atoms

Herzing, Andrew A.

110

Accelerated Electron Transfer between Metal Complexes Mediated by DNA  

NASA Astrophysics Data System (ADS)

DNA-mediated long-range electron transfer from photoexcited 1,10-phenanthroline complexes of ruthenium, Ru(phen)32+, to isostructural complexes of cobalt(III), rhodium(III), and chromium(III) bound along the helical strand. The efficiency of transfer depended upon binding mode and driving force. For a given donor-acceptor pair, surface-bound complexes showed greater rate enhancements than those that were intercalatively bound. Even in rigid glycerol at 253 K, the rates for donor-acceptor pairs bound to DNA remained enhanced. For the series of acceptors, the greatest enhancement in electron-transfer rate was found with chromium, the acceptor of intermediate driving force. The DNA polymer appears to provide an efficient intervening medium to couple donor and acceptor metal complexes for electron transfer.

Purugganan, Michael D.; Kumar, Challa V.; Turro, Nicholas J.; Barton, Jacqueline K.

1988-09-01

111

Alternative ground states enable pathway switching in biological electron transfer  

PubMed Central

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

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

2012-01-01

112

Fluoroponytailed crown ethers and quaternary ammonium salts as solid-liquid phase transfer catalysts in organic synthesis.  

PubMed

Fluorous derivatives of dibenzo-18-crown-6 ether were prepared, and then successfully applied in representative solid-liquid phase transfer catalysis reactions, which were performed in standard organic solvents, such as chlorobenzene and toluene, as well as in fluorous solvents, such as perfluoro-1,3-dimethylcyclohexane. It was clearly shown that properly designed fluoroponytailed crown ethers could promote the disintegration of the crystal lattice of alkali salts, and transfer anions from the solid surface into an apolar, non-coordinating perfluorocarbon phase, for phase transfer catalysis reactions in organic synthesis. Furthermore, 3,5-bis(perfluorooctyl)benzyl bromide and triethylamine were reacted under mild conditions to provide an analogue of the versatile phase transfer catalyst, benzyltriethylammonium chloride, containing two fluoroponytails. This fluoroponytailed quaternary ammonium salt was also successfully employed as a catalyst in a variety of organic reactions conducted under solid-liquid phase transfer catalysis conditions, without a perfluorocarbon phase. Thus, being both hydrophobic and lipophobic, fluorous crown ethers and ammonium salts, could be rapidly recovered in quantitative yields, and reused without loss of activity, over several reaction cycles. PMID:21928010

Pozzi, Gianluca; Fish, Richard H

2012-01-01

113

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

PubMed

Electron transfer (ET) is a fundamental process in a wide range of biological systems, photovoltaics and molecular electronics. Therefore to understand the relationship between molecular structure and ET properties is of prime importance. For this purpose, photoinduced ET has been studied extensively using donor-bridge-acceptor molecules, in which ?-conjugated molecular wires are employed as bridges. Here, we demonstrate that carbon-bridged oligo-p-phenylenevinylene (COPV), which is both rigid and flat, shows an 840-fold increase in the ET rate compared with the equivalent flexible molecular bridges. A 120-fold rate enhancement is explained in terms of enhanced electronic coupling between the electron donor and the electron acceptor because of effective conjugation through the COPVs. The remainder of the rate enhancement is explained by inelastic electron tunnelling through COPV caused by electron-vibration coupling, unprecedented for organic molecular wires in solution at room temperature. This type of nonlinear effect demonstrates the versatility and potential practical utility of COPVs in molecular device applications. PMID:25242485

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

2014-10-01

114

Electron transfer through rigid organic molecular wires enhanced by electronic and electron–vibration coupling  

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

115

Plugging in or going wireless: strategies for interspecies electron transfer.  

PubMed

Interspecies exchange of electrons enables a diversity of microbial communities to gain energy from reactions that no one microbe can catalyze. The first recognized strategies for interspecies electron transfer were those that relied on chemical intermediates that are recycled through oxidized and reduced forms. Well-studied examples are interspecies H2 transfer and the cycling of sulfur intermediates in anaerobic photosynthetic communities. Direct interspecies electron transfer (DIET) in which two species establish electrical contact is an alternative. Electrical contacts documented to date include electrically conductive pili, as well as conductive iron minerals and conductive carbon moieties such as activated carbon and biochar. Interspecies electron transfer is central to the functioning of methane-producing microbial communities. The importance of interspecies H2 transfer in many methanogenic communities is clear, but under some circumstances DIET predominates. It is expected that further mechanistic studies and broadening investigations to a wider range of environments will help elucidate the factors that favor specific forms of interspecies electron exchange under different environmental conditions. PMID:24904551

Shrestha, Pravin Malla; Rotaru, Amelia-Elena

2014-01-01

116

Engineered electron-transfer chain in photosystem 1 based photocathodes outperforms electron-transfer rates in natural photosynthesis.  

PubMed

Photosystem?1 (PS1) triggers the most energetic light-induced charge-separation step in nature and the in vivo electron-transfer rates approach 50?e(-) ?s(-1) ?PS1(-1). Photoelectrochemical devices based on this building block have to date underperformed with respect to their semiconductor counterparts or to natural photosynthesis in terms of electron-transfer rates. We present a rational design of a redox hydrogel film to contact PS1 to an electrode for photocurrent generation. We exploit the pH-dependent properties of a poly(vinyl)imidazole Os(bispyridine)2Cl polymer to tune the redox hydrogel film for maximum electron-transfer rates under optimal conditions for PS1 activity. The PS1-containing redox hydrogel film displays electron-transfer rates of up to 335±14?e(-) ?s(-1) ?PS1(-1), which considerably exceeds the rates observed in natural photosynthesis or in other semiartificial systems. Under O2 supersaturation, photocurrents of 322±19??A?cm(-2) were achieved. The photocurrents are only limited by mass transport of the terminal electron acceptor (O2). This implies that even higher electron-transfer rates may be achieved with PS1-based systems in general. PMID:25066901

Kothe, Tim; Pöller, Sascha; Zhao, Fangyuan; Fortgang, Philippe; Rögner, Matthias; Schuhmann, Wolfgang; Plumeré, Nicolas

2014-08-25

117

Real-time electron transfer in respiratory complex I.  

PubMed

Electron transfer in complex I from Escherichia coli was investigated by an ultrafast freeze-quench approach. The reaction of complex I with NADH was stopped in the time domain from 90 mus to 8 ms and analyzed by electron paramagnetic resonance (EPR) spectroscopy at low temperatures. The data show that after binding of the first molecule of NADH, two electrons move via the FMN cofactor to the iron-sulfur (Fe/S) centers N1a and N2 with an apparent time constant of approximately 90 mus, implying that these two centers should have the highest redox potential in the enzyme. The rate of reduction of center N2 (the last center in the electron transfer sequence) is close to that predicted by electron transfer theory, which argues for the absence of coupled proton transfer or conformational changes during electron transfer from FMN to N2. After fast reduction of N1a and N2, we observe a slow, approximately 1-ms component of reduction of other Fe/S clusters. Because all elementary electron transfer rates between clusters are several orders of magnitude higher than this observed rate, we conclude that the millisecond component is limited by a single process corresponding to dissociation of the oxidized NAD(+) molecule from its binding site, where it prevents entry of the next NADH molecule. Despite the presence of approximately one ubiquinone per enzyme molecule, no transient semiquinone formation was observed, which has mechanistic implications, suggesting a high thermodynamic barrier for ubiquinone reduction to the semiquinone radical. Possible consequences of these findings for the proton translocation mechanism are discussed. PMID:18316732

Verkhovskaya, Marina L; Belevich, Nikolai; Euro, Liliya; Wikström, Mårten; Verkhovsky, Michael I

2008-03-11

118

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

119

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

120

The role of excited Rydberg States in electron transfer dissociation.  

PubMed

Ab initio electronic structure methods are used to estimate the cross sections for electron transfer from donor anions having electron binding energies ranging from 0.001 to 0.6 eV to each of three sites in a model disulfide-linked molecular cation. The three sites are (1) the S-S sigma(*) orbital to which electron attachment is rendered exothermic by Coulomb stabilization from the nearby positive site, (2) the ground Rydberg orbital of the -NH(3)(+) site, and (3) excited Rydberg orbitals of the same -NH(3)(+) site. It is found that attachment to the ground Rydberg orbital has a somewhat higher cross section than attachment to either the sigma orbital or the excited Rydberg orbital. However, it is through attachment either to the sigma(*) orbital or to certain excited Rydberg orbitals that cleavage of the S-S bond is most likely to occur. Attachment to the sigma(*) orbital causes prompt cleavage because the sigma energy surface is repulsive (except at very long range). Attachment to the ground or excited Rydberg state causes the S-S bond to rupture only once a through-bond electron transfer from the Rydberg orbital to the S-S sigma(*) orbital takes place. For the ground Rydberg state, this transfer requires surmounting an approximately 0.4 eV barrier that renders the S-S bond cleavage rate slow. However, for the excited Rydberg state, the intramolecular electron transfer has a much smaller barrier and is prompt. PMID:16599533

Sobczyk, Monika; Simons, Jack

2006-04-13

121

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

122

Theory of electron transfer and molecular state in DNA  

NASA Astrophysics Data System (ADS)

In this thesis, a mechanism for long-range electron transfer in DNA and a systematic search for high conductance DNA are developed. DNA is well known for containing the genetic code of all living species. On the other hand, there are some experimental indications that DNA can mediate effectively long-range electron transfer leading to the concept of chemistry at a distance. This can be important for DNA damage and healing. In the first part of the thesis, a possible mechanism for long-range electron transfer is introduced. The weak distance dependent electron transfer was experimentally observed using transition metal intercalators for donor and acceptor. In our model calculations, the transfer is mediated by the molecular analogue of a Kondo bound state well known from solid state physics of mixed-valence rare-earth compounds. We believe this is quite realistic, since localized d orbitals of the transition metal ions could function as an Anderson impurity embedded in a reservoir of rather delocalized molecular orbitals of the intercalator ligands and DNA pi orbitals. The effective Anderson model is solved with a physically intuitive variational ansatz as well as with the essentially exact DMRG method. The electronic transition matrix element, which is important because it contains the donor-acceptor distance dependence, is obtained with the Mulliken-Hush algorithm as well as from Born-Oppenheimer potential energy surfaces. Our possible explanation of long-range electron transfer is put in context to other more conventional mechanisms which also could lead to similar behavior. Another important issue of DNA is its possible use for nano-technology. Although DNA's mechanical properties are excellent, the question whether it can be conducting and be used for nano-wires is highly controversial. Experimentally, DNA shows conducting, semi-conducting and insulating properties. Motivated by these wide ranging experimental results on the conductivity of DNA, we have embarked on a theoretical effort to ascertain what conditions might induce such remarkable behavior. We use a combination of an ab initio density functional theory method and a parameterized Huckel-Slater-Koster model. Our focus here is to examine whether any likely DNA structures or environments can yield reduced activation gaps to conduction or enhanced electronic overlaps. In particular, we study a hypothetical stretched ribbon structure, A-, and B-form DNA, and the effects of counterions and humidity. Unlike solids, DNA and other molecules are considered soft condensed matter. Hence, we study the influence of vibrations upon the electronic structure of DNA. We calculate parameters for charge transfer rates between adjacent bases. We find good agreement between our estimated rates and recent experimental data assuming that torsional vibrations limit the charge transfer most significantly.

Endres, Robert Gunter

2002-09-01

123

Intramolecular electron transfer in pentaammineruthenium(III)-modified cobaltocytochrome c  

SciTech Connect

The iron in the heme group of horse-heart cytochrome c was replaced by cobalt according to established methods. The resulting cobalticytochrome c was subsequently modified at histidine-33 with a pentaammineruthenium group. Proof of correct derivatization was obtained by atomic absorption analysis of cobalt and ruthenium, differential pulse voltammetry, and enzymatic proteolysis analyzed by diode-array HPLC. Cobalt(II)-to-ruthenium(III) intramolecular electron transfer rates were measured as a function of temperature by electron pulse radiolysis. The azide radical (N{sub 3}{sup {sm_bullet}}) was used to oxidize the fully reduced form in order to generate the desired electron transfer precursor. The intramolecular electron transfer rate is 1.28 {plus_minus} 0.04 s{sup {minus}1} at 25 {degrees}C ({Delta}H{sup {double_dagger}} = 5.7 {plus_minus} 0.2 kcal/mol, {Delta}S{sup {double_dagger}} = -38.7 {plus_minus} 0.5 cal/(deg mol)) for a driving force of 0.28 {plus_minus} 0.02 eV. The results are compared with those for analogous pentaammineruthenium-modified, native iron, and zinc-substituted cytochromes c. The 0.4 eV increase in driving force for intramolecular electron transfer when iron is replaced by cobalt is largely compensated by an increase in reorganization energy.

Sun, Ji; Su, Chang; Wishart, J.F. [Brookhaven National Lab., Upton, NY (United States)] [Brookhaven National Lab., Upton, NY (United States)

1996-09-25

124

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

SciTech Connect

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

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

2011-01-01

125

Molecular\\/electronic structure–surface acidity relationships of model-supported tungsten oxide catalysts  

Microsoft Academic Search

A series of model-supported WO3 catalysts were synthesized on preformed Al2O3, Nb2O5, TiO2, and ZrO2 supports by impregnation of aqueous ammonium metatungstate, (NH4)10W12O41?5H2O. The molecular and electronic structures of the supported tungsten oxide phases were determined with in situ Raman and UV–vis spectroscopy, respectively. The supported tungsten oxide structures are the same on all oxide supports as a function of

Taejin Kim; Andrew Burrows; Christopher J. Kiely; Israel E. Wachs

2007-01-01

126

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

127

Quality assurance and data collection -- Electronic Data Transfer  

SciTech Connect

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

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

1993-05-01

128

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

SciTech Connect

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

Wang, Luxia; Willig, Frank; May, Volkhard [Department of Physics, University of Science and Technology Beijing, Xueyuan Road 30, Haidian District, 100083 Beijing (China); Fritz-Haber-Institut der MPG, Faradayweg 4-6, 14195 Berlin (Germany); Institut fuer Physik, Humboldt-Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin (Germany)

2007-04-07

129

Highly enantioselective epoxidation of 2-methylnaphthoquinone (vitamin K3) mediated by new cinchona alkaloid phase-transfer catalysts.  

PubMed

In the area of catalytic asymmetric epoxidation, the highly enantioselective transformation of cyclic enones and quinones is an extremely challenging target. With the aim to develop new and highly effective phase-transfer catalysts for this purpose, we conducted a systematic structural variation of PTCs based on quinine and quinidine. In the total of 15 new quaternary ammonium PTCs, modifications included, for example, the exchange of the quinine methoxy group for a free hydroxyl or other alkoxy substituents, and the introduction of additional elements of chirality through alkylation of the alkaloid quinuclidine nitrogen atom by chiral electrophiles. For example, the well-established 9- anthracenylmethyl group was exchanged for a "chiral" anthracene in the form of 9-chloromethyl-[(1,8-S;4,5-R)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene. The asymmetric epoxidation of vitamin K(3) was used as the test reaction for our novel PTCs. The readily available PTC 10 (derived from quinine in three convenient and high-yielding steps) proved to be the most enantioselective catalyst for this purpose known to date: At a catalyst loading of only 2.50 mol %, the quinone epoxide was obtained in 76 % yield and with 85 % ee (previously: < or =34 % ee), using commercial bleach (aqueous sodium hypochlorite) as the oxidant. To rationalize the sense of induction effected by our novel phase-transfer catalysts, a computational analysis of steric interactions in the intermediate chlorooxy enolate-PTC ion pair was conducted. Based on this analysis, the sense of induction for all 15 novel PTCs could be consistently explained. PMID:17348045

Berkessel, Albrecht; Guixà, Maria; Schmidt, Friederike; Neudörfl, Jörg M; Lex, Johann

2007-01-01

130

Intramolecular Electron Scattering and Electron Transfer Following Autoionization in Dissociating Molecules  

NASA Astrophysics Data System (ADS)

Resonant Auger decay of core-excited molecules during ultrafast dissociation leads to a Doppler shift of the emitted electrons depending on the direction of the electron emission relative to the dissociation axis. We have investigated this process by angle-resolved electron-fragment ion coincidence spectroscopy. Electron energy spectra for selected emission angles for the electron relative to the molecular axis reveal the occurrence of intermolecular electron scattering and electron transfer following the primary emission. These processes amount to approximately 25% of the resonant atomic Auger intensity emitted in the studied transition.

Kugeler, O.; Prümper, G.; Hentges, R.; Viefhaus, J.; Rolles, D.; Becker, U.; Marburger, S.; Hergenhahn, U.

2004-07-01

131

Catalytic enantioselective reactions driven by photoinduced electron transfer.  

PubMed

Photoinduced electron transfer is an essential step in the conversion of solar energy into chemical energy in photosystems I and II (ref. 1), and is also frequently used by chemists to build complex molecules from simple precursors. During this process, light absorption generates molecules in excited electronic states that are susceptible to accepting or donating electrons. But although the excited states are straightforward to generate, their short lifetimes makes it challenging to control electron transfer and subsequent product formation-particularly if enantiopure products are desired. Control strategies developed so far use hydrogen bonding, to embed photochemical substrates in chiral environments and to render photochemical reactions enantioselective through the use of rigid chiral complexing agents. To go beyond such stoichiometric chiral information transmission, catalytic turnover is required. Here we present a catalytic photoinduced electron transfer reaction that proceeds with considerable turnover and high enantioselectivity. By using an electron accepting chiral organocatalyst that enforces a chiral environment on the substrate through hydrogen bonding, we obtain the product in significant enantiomeric excess (up to 70%) and in yields reaching 64%. This performance suggests that photochemical routes to chiral compounds may find use in general asymmetric synthesis. PMID:16121176

Bauer, Andreas; Westkämper, Felix; Grimme, Stefan; Bach, Thorsten

2005-08-25

132

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

PubMed

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

Yang, Hung-Ming; Chu, Wei-Ming

2014-01-01

133

Theoretical studies of electron transfer through dendrimeric architecture  

NASA Astrophysics Data System (ADS)

We have analyzed the steady-state electron transfer rate through a bridge of dendrimeric architecture. The difference between the linear chain and the dendrimeric architecture has also been demonstrated with steady-state rate as a main observable in the coherent and incoherent regimes of interactions. It is shown that generally the rate of electron transfer in dendrimeric architecture is faster than the rate associated with their linear chain counterpart with similar kind of bonding connectivities. The rate depends upon the size of the molecule, core branching, and the nature of the coupling among the different nodes on the dendrimer molecule. Depending upon the nature of the donor and acceptor, phenomenological dephasing coefficient due to environment and the geometry of the dendrimeric architecture, the modification of electron transfer rate has been studied. In the regime of fully coherent interactions where all quantum effects are considered the rate shows a multiple inversion due to the dendrimer architecture which is neither available in the regime of incoherent interaction nor in the linear chain case in similar condition. We have discussed about the applicability of our model in metal-molecule-metal junction, photoinduced electron transfer process, and molecular conductor.

Rana, Dipankar; Gangopadhyay, Gautam

2006-01-01

134

Electron transfer kinetics on mono- and multilayer graphene.  

PubMed

Understanding of the electrochemical properties of graphene, especially the electron transfer kinetics of a redox reaction between the graphene surface and a molecule, in comparison to graphite or other carbon-based materials, is essential for its potential in energy conversion and storage to be realized. Here we use voltammetric determination of the electron transfer rate for three redox mediators, ferricyanide, hexaammineruthenium, and hexachloroiridate (Fe(CN)6(3-), Ru(NH3)6(3+), and IrCl6(2-), respectively), to measure the reactivity of graphene samples prepared by mechanical exfoliation of natural graphite. Electron transfer rates are measured for varied number of graphene layers (1 to ca. 1000 layers) using microscopic droplets. The basal planes of mono- and multilayer graphene, supported on an insulating Si/SiO2 substrate, exhibit significant electron transfer activity and changes in kinetics are observed for all three mediators. No significant trend in kinetics with flake thickness is discernible for each mediator; however, a large variation in kinetics is observed across the basal plane of the same flakes, indicating that local surface conditions affect the electrochemical performance. This is confirmed by in situ graphite exfoliation, which reveals significant deterioration of initially, near-reversible kinetics for Ru(NH3)6(3+) when comparing the atmosphere-aged and freshly exfoliated graphite surfaces. PMID:25290250

Velický, Mat?j; Bradley, Dan F; Cooper, Adam J; Hill, Ernie W; Kinloch, Ian A; Mishchenko, Artem; Novoselov, Konstantin S; Patten, Hollie V; Toth, Peter S; Valota, Anna T; Worrall, Stephen D; Dryfe, Robert A W

2014-10-28

135

Shewanella secretes flavins that mediate extracellular electron transfer  

E-print Network

study by Lies et al. (4) also demonstrated reduction of Fe(III) oxides precipitated within nano- porous November 6, 2007) Bacteria able to transfer electrons to metals are key agents in bio- geochemical metal. Riboflavin adsorbed quickly to other surfaces of geochemi- cal interest, such as Fe(III) and Mn(IV) oxy(hydr)oxides

Weiblen, George D

136

Energetics of Electron-Transfer Reactions in Soft Condensed  

E-print Network

Energetics of Electron-Transfer Reactions in Soft Condensed Media DMITRY V. MATYUSHOV Department condensed solvents such as supercooled liquids, liquid crystals, and photosynthetic reaction centers soft condensed media such as liquid crystals,5 proteins,6 and structural glass formers.7

Matyushov, Dmitry

137

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

138

New and efficient technique for the synthesis of ?-caprolactone using KHSO 5 as an oxidising agent in the presence of a phase transfer catalyst  

Microsoft Academic Search

A new method for the synthesis of ?-caprolactone based on the Baeyer–Villiger oxidation of cyclohexanone was developed. In the proposed reaction, potassium peroxomonosulphate was used as an oxidising agent under phase transfer catalysis conditions. The effects of the reaction parameters, including the type of phase transfer catalyst, the concentration of the oxidising agent, the type of organic solvent and temperature,

Stefan Baj; Anna Chrobok; Agnieszka Siewniak

2011-01-01

139

Effects of heat and mass transfer on the kinetics of CO oxidation over RuO2(110) catalyst  

SciTech Connect

By combining first-principles kinetic Monte Carlo (KMC) simulation with a second-order finite difference continuum model, a hybrid computational model is developed to study the effects of heat and mass transfer in the surrounding gas phase on the heterogeneous reaction kinetics. The integrated computational framework consists of a surface phase where catalytic surface reactions occur and a gas-phase boundary layer imposed on the catalyst surface where the temperature and pressure gradients exist. The temperature and pressure gradients in the gas-phase boundary layer are the consequence of thermal and molecular diffusions of reactants and products under reaction conditions. The surface phase domain is modeled using the site-explicit first-principles KMC simulation. The gas-phase boundary layer domain is described using the grid-based Crank-Nicolson method. At each time step, the heat and mass fluxes between two domains are calculated simultaneously until the steady-state reaction condition is reached. At the steady-state reaction condition, the activity, the surface coverages of reaction intermediates, as well as the temperature and pressure gradient profiles in the gas-phase boundary layer are statistically constant with very small fluctuations. To demonstrate the idea that the proper consideration of heat and mass transfer in the reaction environment is essential to accurate measurement of the intrinsic reaction kinetics, we investigated the kinetics of CO oxidation over the RuO2(110) catalysts. By varying the thickness of the RuO2(110) catalyst, the pronounced temperature and pressure gradients are formed in the gas-phase boundary layer. Our simulation results indicate that the temperature and pressure gradients caused by the heat and mass transfer could dramatically affect the observed intrinsic reaction kinetics under presumed nominal operating reaction conditions. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy.

Mei, Donghai; Lin, Guang

2011-05-16

140

Protein dynamics modulated electron transfer kinetics in early stage photosynthesis  

NASA Astrophysics Data System (ADS)

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

Kundu, Prasanta; Dua, Arti

2013-01-01

141

Electronic coupling responsible for energy transfer in columnar liquid crystals  

NASA Astrophysics Data System (ADS)

Electronic coupling is the driving force for energy transfer in molecular materials and consists of several components. We determine the strength of dipolar/multipolar coupling and coupling due to orbital overlap for excitation transport in triphenylene columnar liquid crystals. We use time-resolved fluorescence spectroscopy and computer simulations. The fit of the experimental and simulated fluorescence decays reveals that the transfer process is dominated by short range interactions (multipolar and orbital overlap) but the contribution of long range dipolar interactions cannot be neglected.

Markovitsi, Dimitra; Marguet, Sylvie; Gallos, Lazaros K.; Sigal, Hervé; Millié, Philippe; Argyrakis, Panos; Ringsdorf, Helmut; Kumar, Sandeep

1999-06-01

142

Alternating electron and proton transfer steps in photosynthetic water oxidation  

PubMed Central

Water oxidation by cyanobacteria, algae, and plants is pivotal in oxygenic photosynthesis, the process that powers life on Earth, and is the paradigm for engineering solar fuel–production systems. Each complete reaction cycle of photosynthetic water oxidation requires the removal of four electrons and four protons from the catalytic site, a manganese–calcium complex and its protein environment in photosystem II. In time-resolved photothermal beam deflection experiments, we monitored apparent volume changes of the photosystem II protein associated with charge creation by light-induced electron transfer (contraction) and charge-compensating proton relocation (expansion). Two previously invisible proton removal steps were detected, thereby filling two gaps in the basic reaction-cycle model of photosynthetic water oxidation. In the S2 ? S3 transition of the classical S-state cycle, an intermediate is formed by deprotonation clearly before electron transfer to the oxidant (). The rate-determining elementary step (?, approximately 30 µs at 20?°C) in the long-distance proton relocation toward the protein–water interface is characterized by a high activation energy (Ea = 0.46 ± 0.05 eV) and strong H/D kinetic isotope effect (approximately 6). The characteristics of a proton transfer step during the S0 ? S1 transition are similar (?, approximately 100 µs; Ea = 0.34 ± 0.08 eV; kinetic isotope effect, approximately 3); however, the proton removal from the Mn complex proceeds after electron transfer to . By discovery of the transient formation of two further intermediate states in the reaction cycle of photosynthetic water oxidation, a temporal sequence of strictly alternating removal of electrons and protons from the catalytic site is established. PMID:22988080

Klauss, André; Haumann, Michael; Dau, Holger

2012-01-01

143

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

144

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

145

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

146

Electron propagator theory approach to ab initio calculations of electron transfer rate and molecular conductance  

NASA Astrophysics Data System (ADS)

The ab initio theoretical approach to calculations of molecular electron transfer rate and molecular junction conductance is presented. The implemented approach is founded on Landauer formalism coupled to electron propagator theory (Green-Keldysh functions formalism) of solving the Dyson equation for molecular junction. The electron transfer rate calculation algorithm implementing quantum chemistry computational software output is proposed. The conductance through a single molecular orbital is found to be equal to a quantum of conductance, 2e2/h. The existence of the maximal value of electron transfer rate through a single molecular orbital is proposed, (?2/4h)?L?RF, whose order-of-magnitude estimate is 1011-1013 s-1.

Kletsov, Aleksey A.

2014-09-01

147

Real-time Simulations of Photoinduced Coherent Charge Transfer and Proton-Coupled Electron Transfer.  

PubMed

Photoinduced electron transfer (ET) and proton-coupled electron transfer (PCET) are fundamental processes in natural phenomena, most noticeably in photosynthesis. Time-resolved spectroscopic evidence of coherent oscillatory behavior associated with these processes has been reported both in complex biological environments, as well as in biomimetic models for artificial photosynthesis. Here, we consider a few biomimetic models to investigate these processes in real-time simulations based on ab initio molecular dynamics and Ehrenfest dynamics. This allows for a detailed analysis on how photon-to-charge conversion is promoted by a coupling of the electronic excitation with specific vibrational modes and with proton displacements. The ET process shows a characteristic coherence that is linked to the nuclear motion at the interface between donor and acceptor. We also show real-time evidence of PCET in a benzimidazole-phenol redox relay. PMID:25224924

Eisenmayer, Thomas J; Buda, Francesco

2014-10-20

148

Molybdenum Imido Alkylidene Metathesis Catalysts that Contain Electron Withdrawing Biphenolates or Binaphtholates  

PubMed Central

We have prepared new Mo(NR)(CHCMe2Ph)(diolate) complexes (R = 2,6-i-Pr2C6H3, 2,6-Me2C6H3, 1-Adamantyl, or 2-CF3C6H4) that contain relatively electron-withdrawing binaphtholate (3,3?-bis-(9-anthracenyl), 3,3?-bispentafluorophenyl, or 3,3?-bis(3,5-bis(trifluoromethyl)phenyl) or biphenolate (3,3?-di-tert-butyl-5,5?-bistrifluoromethyl-6,6?-dimethyl-1,1?-biphenyl-2,2?-diolate) ligands. We also have prepared new monomeric Mo(NR)(CHCMe2Ph)(2,5-dimethylpyrrolide)2 complexes and have treated them with biphenols or binaphthols in order to prepare several Mo(NR)(CHCMe2Ph)(diolate) species. In one case the new Mo(NR)(CHCMe2Ph)(diolate) complexes could be prepared only through reaction of a binaphthol [3,3?-bis(pentafluorophenyl)binaphthol] with a bis(2,5-dimethylpyrrolide) complex. The pyrrolide approach can be employed either to isolate catalysts on a preparative scale or to generate catalysts in situ. Several simple preliminary ring-closing metathesis reactions show that the new complexes are catalytically competent. PMID:18953421

Singh, Rojendra; Czekelius, Constantin; Schrock, Richard R.; Muller, Peter; Hoveyda, Amir H.

2008-01-01

149

Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies.  

PubMed

Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Forster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Forster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene units placed between the chromophores. We find that the polarizability of the bridge significantly enhances the effective interaction. We compare our calculations to single molecule experiments on two types of dyads and find reasonable agreement between theory and experiment. PMID:18298155

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

2008-02-21

150

Electron transfer to sulfides and disulfides: intrinsic barriers and relationship between heterogeneous and homogeneous electron-transfer kinetics.  

PubMed

The electron-acceptor properties of series of related sulfides and disulfides were investigated in N,N-dimethylformamide with homogeneous (redox catalysis) and/or heterogeneous (cyclic voltammetry and convolution analysis) electrochemical techniques. The electron-transfer rate constants were determined as a function of the reaction free energy and the corresponding intrinsic barriers were determined. The dependence of relevant thermodynamic and kinetic parameters on substituents was assessed. The kinetic data were also analyzed in relation to corresponding data pertaining to reduction of diaryl disulfides. All investigated reductions take place by stepwise dissociative electron transfer (DET) which causes cleavage of the C(alkyl)--S or S--S bond. A generalized picture of how the intrinsic electron-transfer barrier depends on molecular features, ring substituents, and the presence of spacers between the frangible bond and aromatic groups was established. The reduction mechanism was found to undergo a progressive (and now predictable) transition between common stepwise DET and DET proceeding through formation of loose radical anions. The intrinsic barriers were compared with available results for ET to several classes of dissociative- and nondissociative-type acceptors, and this led to verification that the heterogeneous and the homogeneous data correlate as predicted by the Hush theory. PMID:17616962

Meneses, Ana Belèn; Antonello, Sabrina; Arévalo, Maria Carmen; González, Concepcion Carmen; Sharma, Jadab; Wallette, Andrea N; Workentin, Mark S; Maran, Flavio

2007-01-01

151

Modes of coenzyme Q function in electron transfer  

Microsoft Academic Search

Summary In the mitochondrial respiratory chain, coenzyme Q acts in different ways. A diffusable coenzyme Q pool as a common substrate-like intermediate links the low-potential complexes with complex III. Its diffusion in the lipids is not rate-limiting for electron transfer, but its content is not saturating for maximal rate of NADH oxidation. Protein-bound coenzyme Q is involved in energy conservation,

G. Lenaz; Carla Bovina; Cinzia Castelluccio; Marika Cavazzoni; E. Estornell; Romana Fato; J. R. Huertas; Milena Merlo Pich; F. Pallotti; Giovanna Parenti Castelli; Hana Rauchova

1995-01-01

152

Intramolecular electron transfer in pentaammineruthenium(III)-modified cobaltocytochrome c  

Microsoft Academic Search

The iron in the heme group of horse-heart cytochrome c was replaced by cobalt according to established methods. The resulting cobalticytochrome c was subsequently modified at histidine-33 with a pentaammineruthenium group. Proof of correct derivatization was obtained by atomic absorption analysis of cobalt and ruthenium, differential pulse voltammetry, and enzymatic proteolysis analyzed by diode-array HPLC. Cobalt(II)-to-ruthenium(III) intramolecular electron transfer rates

Ji Sun; Chang Su; James F. Wishart

1996-01-01

153

The electron transfer system of syntrophically grown Desulfovibrio vulgaris.  

PubMed

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. PMID:19581361

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

2009-09-01

154

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

155

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

156

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

157

Zwitterionic-surfactant-stabilized palladium nanoparticles as catalysts in the hydrogen transfer reductive amination of benzaldehydes.  

PubMed

Palladium nanoparticles (NPs) stabilized by a zwitterionic surfactant are revealed here to be good catalysts for the reductive amination of benzaldehydes using formate salts as hydrogen donors in aqueous isopropanol. In terms of environmental impact and economy, metallic NPs offer several advantages over homogeneous and traditional heterogeneous catalysts. NPs usually display greater activity due to the increased metal surface area and sometimes exhibit enhanced selectivity. Thus, it is possible to use very low loadings of expensive metal. The methodology eliminates the use of a hydrogen gas atmosphere or toxic or expensive reagents. A range of aromatic aldehydes were converted to benzylamines when reacted with primary and secondary amines in the presence of the Pd NPs, which also displayed good activity when supported on alumina. In every case, the Pd NPs could be easily recovered and reused up to three more times, and at the end of the process, the product was metal-free. PMID:24552129

Drinkel, Emma E; Campedelli, Roberta R; Manfredi, Alex M; Fiedler, Haidi D; Nome, Faruk

2014-03-21

158

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

159

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

160

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: "Atomic level investigation of the phase stability of transition metal surfaces under reactive environmentnm [001] [110] [001] 2 nm HAADF STEM atomic level of -Al2O3 from several low index zone axis. Derived

161

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...

162

Investigation of a traditional catalyst by contemporary methods: Parallel electron spectroscopic and catalytic studies on Pt black  

NASA Astrophysics Data System (ADS)

Results of electron spectroscopy (XPS and UPS) of platinum black catalyst measured in various states of the catalyst have been summarized. XPS showed up to almost 50% carbon and up to 20% oxygen on a sample stored in air. These, however, had almost no influence on the chemical state of Pt, except for the appearance of minor surface oxide. A Pt purity of ˜90% could be reached by regeneration with O 2 and H 2. The C 1s peak contained several components from individual C atoms to graphitic and polymeric hydrocarbon layers. Thus, the active catalyst was not clean Pt but metallic Pt; the impurities exerting little influence on catalytic activity. Regeneration and deactivation led also to slight structural rearrangement, as detected by XRD. Intentional deactivation with hydrocarbon-hydrogen mixtures was monitored by XPS, UPS and catalytic tests. Correlation was found between catalytic activity and selectivity in hexane reaction and the amount - and also the chemical state - of carbon accumulated during deactivating runs. A short summary of electron spectroscopy of supported Pt catalysts is also given. The main underlying idea regards solid catalyst and reactants as a dynamic system, including also solid-state changes of the former.

Paál, Zoltán; Schlögl, Robert

2009-06-01

163

Electron Transfer Dissociation (ETD) of Peptides Containing Intrachain Disulfide Bonds  

NASA Astrophysics Data System (ADS)

The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z + 33 Da, c + 32 Da, and z-32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N-C? backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N-C? bond was cleaved first, and radical-driven reactions caused cleavage at either an S-S bond or an S-C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%-100% of possible backbone fragmentation.

Cole, Scott R.; Ma, Xiaoxiao; Zhang, Xinrong; Xia, Yu

2012-02-01

164

Electron transfer dissociation (ETD) of peptides containing intrachain disulfide bonds.  

PubMed

The fragmentation chemistry of peptides containing intrachain disulfide bonds was investigated under electron transfer dissociation (ETD) conditions. Fragments within the cyclic region of the peptide backbone due to intrachain disulfide bond formation were observed, including: c (odd electron), z (even electron), c-33 Da, z+33 Da, c+32 Da, and z-32 Da types of ions. The presence of these ions indicated cleavages both at the disulfide bond and the N-C? backbone from a single electron transfer event. Mechanistic studies supported a mechanism whereby the N-C? bond was cleaved first, and radical-driven reactions caused cleavage at either an S-S bond or an S-C bond within cysteinyl residues. Direct ETD at the disulfide linkage was also observed, correlating with signature loss of 33 Da (SH) from the charge-reduced peptide ions. Initial ETD cleavage at the disulfide bond was found to be promoted amongst peptides ions of lower charge states, while backbone fragmentation was more abundant for higher charge states. The capability of inducing both backbone and disulfide bond cleavages from ETD could be particularly useful for sequencing peptides containing intact intrachain disulfide bonds. ETD of the 13 peptides studied herein all showed substantial sequence coverage, accounting for 75%-100% of possible backbone fragmentation. PMID:22161508

Cole, Scott R; Ma, Xiaoxiao; Zhang, Xinrong; Xia, Yu

2012-02-01

165

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

166

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

167

Electron transfer, ionization, and excitation in atomic collisions  

SciTech Connect

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

Winter, T.G.; Alston, S.G.

1992-01-01

168

BIOINSPIRED CATALYSTS: SYNTHESIS, CHARACTERISATION AND SOME APPLICATIONS  

Microsoft Academic Search

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

István Pálinkó

169

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

170

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

171

Novel ruthenium-based metathesis catalysts containing electron-withdrawing ligands: synthesis, immobilization, and reactivity.  

PubMed

The syntheses and reactivity of seven different ruthenium-based metathesis catalysts are described. Ru(CF3COO)2(PCy3)(=CH-2-(2-PrO)C6H4) (1), Ru(CF3COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (2), and Ru(CF3COO)2(PCy(3))(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (3) were prepared via chlorine exchange by reacting RuCl2(PCy3)2(=CH-2-(2-PrO)C6H4), RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), and RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), respectively, with silver trifluoroacetate (Cy =cyclohexyl). In analogy, Ru(CF3CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (4) and Ru(CF3CF2CF2COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (5) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with CF3CF2COOAg and CF3CF2CF2COOAg, respectively. Ru(C6F5COO)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (6) and Ru(C6F5O)2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (7) were prepared from RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) via reaction with C6F5COOTl and C6F5OTl, respectively. Supported catalysts Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5) (8), Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(PCy3)(=CH-2-(2-PrO)C6H4) (9), and Ru(PS-DVB-CH2OOCCF2CF2CF2COO)(CF3COO)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4) (10) were synthesized by reaction of RuCl2(PCy3)(1,3-dimesityldihydroimidazolin-2-ylidene)(=CHC6H5), RuCl2(PCy3)(=CH-2-(2-PrO)C6H4), and RuCl2(1,3-dimesityldihydroimidazolin-2-ylidene)(=CH-2-(2-PrO)C6H4), respectively, with a perfluoroglutaric acid-derivatized poly(styrene-co-divinylbenzene) (PS-DVB) support (silver form). Halogen exchange in PCy3-containing systems had to be carried out in dichloromethane in order to suppress precipitation of AgCl.PCy3. The reactivity of all new catalysts in ring-closing metathesis (RCM) of hindered electron-rich and -poor substrates, respectively, at elevated temperature (45 degrees C) was compared with that of existing systems. Diethyl diallylmalonate (DEDAM, 11), diethyl allyl(2-methylallyl)malonate (12), N,N-diallyl-p-toluenesulfonamide (13), N-benzyl-N-but-1-en-4-ylbut-2-enecarboxylic amide (14), and N-allyl-N-(1-carboxymethyl)but-3-en-1-yl-p-toluenesulfonamide (15) were used as educts. Supported catalysts were prepared with high loadings (2.4, 22.1, and 160 mg of catalyst/g PS-DVB for 8, 9, and 10, respectively). Catalyst 8 showed higher and catalysts 9 and 10 sowed significantly reduced activities in RCM compared to their homogeneous analogues. Thus, with 8, turnover numbers (TONs) up to 4200 were realized in stirred-batch (carousel) RCM experiments. To elucidate the nature of the bound species, catalysts 8-10 were subjected to 13C- and 31P-MAS NMR spectroscopy. These investigations provided evidence for the proposed structures. Leaching of ruthenium into the reaction mixture was low, resulting in ruthenium contents <85 ppb (ng/g) in the final RCM-derived products. PMID:15932306

Halbach, Tobias S; Mix, Stefan; Fischer, Dirk; Maechling, Simon; Krause, Jens O; Sievers, Carsten; Blechert, Siegfried; Nuyken, Oskar; Buchmeiser, Michael R

2005-06-10

172

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

173

Theory of electron transfer in the presence of dissipation  

NASA Astrophysics Data System (ADS)

An analytic study of the density matrix and Wigner representation equations for dissipative electron transfer is presented. An explicit expression is derived for the off-diagonal Green's function, which shows a very fast relaxation in time if the barrier to reaction is greater than the thermal energy. This fast relaxation invalidates previous attempts to derive coupled equations for the density in the large friction limit. The fast off-diagonal relaxation disallows an adiabatic elimination of the momentum even in the large friction limit. We then show, with the aid of the boundary layer method, how one can use the same analysis to derive a set of two coupled equations for the diagonal densities. These equations are a generalization to phase space of the large friction Zusman equations [Chem. Phys. 49, 295 (1980)]. Adiabatic elimination of the momentum from these generalized Zusman equations is correct in the large friction limit and naturally leads back to the Zusman equations. Numerical solution of the generalized Zusman equations is presented for symmetric electron transfer for weak and strong electronic coupling, moderate and high barriers, and a large range of damping. The numerical results provide new insight into the friction dependence of the rate in the weak damping regime and show that previous analytic expressions for the rate are only qualitative in nature.

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

2003-12-01

174

Modeling biofilms with dual extracellular electron transfer mechanisms.  

PubMed

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

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

2013-11-28

175

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

176

Microbial interspecies electron transfer via electric currents through conductive minerals.  

PubMed

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

2012-06-19

177

Advances in Enhanced Boiling Heat Transfer From Electronic Components  

NASA Astrophysics Data System (ADS)

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

Honda, Hiroshi; Wei, Jinjia

178

Single Electron Transfer Living Radical Polymerization via a New Initiator  

NASA Astrophysics Data System (ADS)

Research and development of novel initiating system such as single electron transfer living radical polymerization (SET-LRP) is of high importance in polymer chemistry. A new SET-LRP initiator was synthesized and applied to prepare end-functionalized poly(methyl methacrylate) (PMMA) in this study. ?-Trichloromethyl benzyl alcohol was firstly synthesized, followed by preparation of PMMA under SET-LRP conditions. Conversion of MMA was 81.9%, and the molecular weight of PMMA was about 2.5 kDa at 60 °C for 1 h. Consistency of the number-average molecular weight of PMMA from NMR, GPC and theoretical calculation indicated that the polymerization featured controllable property. Broad molecular weight distribution (MWD) may be ascribed to branched polymers formed by initiation and chain transfer.

Bai, Xiongxiong; Hu, Ying; Zhang, Xu; Ai, Lingling; Cheng, Chuanjie

2014-08-01

179

Scanning electron microscopy in nematode-induced giant transfer cells.  

PubMed

A study of giant cells induced by the root-knot nematode, Meloidogyne incognita, in roots of Impatiens balsamina was made by scanning electron microscopy. The cytoplasmic contents of giant cells were removed by a procedure based on KOH digestion, to reveal inner wall structure. Wall ingrowths typical of transfer cells are present in giant cells from six days onwards after induction. They develop on walls adjacent to vascular tissues, and their distribution and development was examined. Pit fields contianing plasmodesmata become elaborated in walls between giant cells, but pit fields are lost between giant cells and cells outside them. The distribution of plasmodesmata in pit fields suggests that de novo formation of plasmodesmata occurs in walls between giant cells. Various aspects of giant cell formation and function are discussed and wall ingrowth development is compared in giant cells and normal transfer cells. PMID:1001022

Jones, M G; Dropkin, V H

1976-01-01

180

Copper(I)/ABNO-catalyzed aerobic alcohol oxidation: alleviating steric and electronic constraints of Cu/TEMPO catalyst systems.  

PubMed

Cu/TEMPO catalyst systems promote efficient aerobic oxidation of sterically unhindered primary alcohols and electronically activated substrates, but they show reduced reactivity with aliphatic and secondary alcohols. Here, we report a catalyst system, consisting of ((MeO)bpy)Cu(I)(OTf) and ABNO ((MeO)bpy = 4,4'-dimethoxy-2,2'-bipyridine; ABNO = 9-azabicyclo[3.3.1]nonane N-oxyl), that mediates aerobic oxidation of all classes of alcohols, including primary and secondary allylic, benzylic, and aliphatic alcohols with nearly equal efficiency. The catalyst exhibits broad functional group compatibility, and most reactions are complete within 1 h at room temperature using ambient air as the source of oxidant. PMID:24128057

Steves, Janelle E; Stahl, Shannon S

2013-10-23

181

pH-dependent reduction potentials and proton-coupled electron transfer mechanisms in hydrogen-producing nickel molecular electrocatalysts.  

PubMed

The nickel-based P2(Ph)N2(Bn) electrocatalysts comprised of a nickel atom and two 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane ligands catalyze H2 production in acetonitrile. Recent electrochemical experiments revealed a linear dependence of the Ni(II/I) reduction potential on pH with a slope of 57 mV/pH unit, implicating a proton-coupled electron transfer (PCET) process with the same number of electrons and protons transferred. The combined theoretical and experimental studies herein provide an explanation for this pH dependence in the context of the overall proposed catalytic mechanism. In the proposed mechanisms, the catalytic cycle begins with a series of intermolecular proton transfers from an acid to the pendant amine ligand and electrochemical electron transfers to the nickel center to produce the doubly protonated Ni(0) species, a precursor to H2 evolution. The calculated Ni(II/I) reduction potentials of the doubly protonated species are in excellent agreement with the experimentally observed reduction potential in the presence of strong acid, suggesting that the catalytically active species leading to the peak observed in these cyclic voltammetry (CV) experiments is doubly protonated. The Ni(I/0) reduction potential was found to be slightly more positive than the Ni(II/I) reduction potential, indicating that the Ni(I/0) reduction occurs spontaneously after the Ni(II/I) reduction, as implied by the experimental observation of a single CV peak. These results suggest that the PCET process observed in the CV experiments is a two-electron/two-proton process corresponding to an initial double protonation followed by two reductions. On the basis of the experimental and theoretical data, the complete thermodynamic scheme and the Pourbaix diagram were generated for this catalyst. The Pourbaix diagram, which identifies the most thermodynamically stable species at each reduction potential and pH value, illustrates that this catalyst undergoes different types of PCET processes for various pH ranges. These thermodynamic insights will aid in the design of more effective molecular catalysts for H2 production. PMID:23477912

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

2013-04-01

182

In situ electron paramagnetic resonance (EPR) study of surface oxygen species on Au\\/ZnO catalyst for low-temperature carbon monoxide oxidation  

Microsoft Academic Search

Some paramagnetic superoxide ions detectable by electron paramagnetic resonance (EPR) can be generated on Au\\/ZnO catalyst by oxygen adsorption at room temperature as well as at 553K. In both the cases, the O2? ions are present on the catalyst surface. The disappearance of the O2? signal by the introduction of carbon monoxide over the catalyst surface implies that the O2?

Zhengping Hao; Liangbo Fen; G. Q Lu; Jianjun Liu; Lidun An; Hongli Wang

2001-01-01

183

Light induced electron transfer reactions of metal complexes  

SciTech Connect

Properties of the excited states of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of chromium(III), iron(II), ruthenium(II), osmium(II), rhodium(III), and iridium(III) are described. The electron transfer reactions of the ground and excited states are discussed and interpreted in terms of the driving force for the reaction and the distortions of the excited states relative to the corresponding ground states. General considerations relevant to the conversion of light into chemical energy are presented and progress in the use of polypyridine complexes to effect the light decomposition of water into hydrogen and oxygen is reviewed.

Sutin, N.; Creutz, C.

1980-01-01

184

Disulfide bond cleavage: a redox reaction without electron transfer.  

PubMed

By using Car-Parrinello molecular dynamics (CPMD) simulations we have simulated a mechanically induced redox reaction. Previous single-molecule atomic force microscopy (AFM) experiments demonstrated that the reduction of disulfide bonds in proteins with the weak reducing agent dithiothreitol depends on a mechanical destabilization of the breaking bond. With reactive molecular dynamics simulations the single steps of the reaction mechanism can be elucidated and the motion of the electrons can be monitored. The simulations show that the redox reaction consists of the heterolytic cleavage of the S--S bond followed by a sequence of proton transfers. PMID:20349464

Hofbauer, Florian; Frank, Irmgard

2010-05-01

185

Electron transfer mechanism of cytochrome c at graphene electrode  

NASA Astrophysics Data System (ADS)

We report the direct electron transfer of cytochrome c (Cyt c) observed at graphene electrodes. Graphene nanosheets were chemically synthesized and immobilized on to a glassy carbon electrode. Cyclic voltammetry of Cyt c in phosphate buffered saline was performed at these electrodes. Results indicated a pair of reversible redox waves with a peak-to-peak separation value of 0.07 V in a diffusion controlled electrochemical process. Furthermore, the voltammetric response of these electrodes in Cyt c were found to be stable over time with negligible electrode fouling toward Cyt c.

Alwarappan, Subbiah; Joshi, Rakesh K.; Ram, Manoj K.; Kumar, Ashok

2010-06-01

186

Intercalation of Trioxatriangulenium Ion in DNA: Binding, Electron Transfer, X-ray Crystallography, and Electronic  

E-print Network

Intercalation of Trioxatriangulenium Ion in DNA: Binding, Electron Transfer, X-ray Crystallography orbital. It binds to duplex DNA by intercalation with a preference for G-C base pairs. Irradiation that affect DNA chemically or structurally is determined by the mode of binding.1,2 Intercalation and groove

Williams, Loren

187

Direct one-pot conversion of acylated carbohydrates into their alkylated derivatives under heterogeneous reaction conditions using solid NaOH and a phase transfer catalyst  

Microsoft Academic Search

A convenient one-pot protocol for the direct conversion of acyl-protected carbohydrates into their alkylated counterparts has been developed by using alkyl halides in the presence of solid sodium hydroxide and a phase transfer catalyst. These economically convenient, mild, two-phase reaction conditions allow the preparation of a variety of monosaccharide intermediates for use in the synthesis of complex oligosaccharides.

Soni Kamlesh Madhusudan; Geetanjali Agnihotri; Devendra S. Negi; Anup Kumar Misra

2005-01-01

188

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

189

Biochemical Mechanisms Controlling Terminal Electron Transfer in Geobacter sulfurreducens  

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

190

Photoinduced electron transfer in rhenium(i)-oligotriarylamine molecules.  

PubMed

Two molecular triads with an oligotriarylamine multielectron donor were synthesized and investigated with a view to obtaining charge-separated states in which the oligotriarylamine is oxidized 2-fold. Such photoinduced accumulation of multiple redox equivalents is of interest for artificial photosynthesis. The first triad was comprised of the oligotriarylamine and two rhenium(I) tricarbonyl diimine photosensitizers each of which can potentially accept one electron. In the second triad the oligotriarylamine was connected to anthraquinone, in principle an acceptor of two electrons, via a rhenium(I) tricarbonyl diimine unit. With nanosecond transient absorption spectroscopy (using an ordinary pump-probe technique) no evidence for the generation of 2-fold oxidized oligotriarylamine or 2-fold reduced anthraquinone was found. The key factors limiting the photochemistry of the new triads to simple charge separation of one electron and one hole are discussed, and the insights gained from this study are useful for further research in the area of charge accumulation in purely molecular (nanoparticle-free) systems. An important problem of the rhenium-based systems considered here is the short wavelength required for photoexcitation. In the second triad, photogenerated anthraquinone monoanion is protonated by organic acids, and the resulting semiquinone species leads to an increase in lifetime of the charge-separated state by about an order of magnitude. This shows that the proton-coupled electron transfer chemistry of quinones could be beneficial for photoinduced charge accumulation. PMID:25271567

Bonn, Annabell G; Neuburger, Markus; Wenger, Oliver S

2014-10-20

191

Structural changes in iron oxide and gold catalysts during nucleation of carbon nanotubes studied by in situ transmission electron microscopy.  

PubMed

We report a simple, versatile in situ transmission electron microscopy (TEM) approach for investigating the nucleation and growth mechanism of carbon nanotubes (CNTs), by which the composition, phase transition, and physical state of various catalysts can be clearly resolved. In our approach, catalyst nanoparticles (NPs) are placed in a multiwall CNT "tubular furnace" with two open ends, and a high temperature is obtained by Joule heating in the specimen chamber of a TEM. The carbon is supplied by electron irradiation-induced injection of carbon atoms. Comparative studies on the catalytic behavior of traditional iron oxide and recently discovered gold catalysts were performed. It was found that the growth of CNTs from iron oxide involves the reduction of Fe2O3 to Fe3C, nucleation and growth of CNTs from partially liquefied Fe3C, and finally the formation of elemental Fe when the growth stops. In contrast, while changes in shape, size, and orientation were also observed for the fluctuating Au NPs, no chemical reactions or phase transitions occurred during the nucleation of CNTs. These two distinct nucleation and growth processes and mechanisms would be valuable for the structure-controlled growth of CNTs by catalyst design and engineering. PMID:24354297

Tang, Dai-Ming; Liu, Chang; Yu, Wan-Jing; Zhang, Li-Li; Hou, Peng-Xiang; Li, Jin-Cheng; Li, Feng; Bando, Yoshio; Golberg, Dmitri; Cheng, Hui-Ming

2014-01-28

192

Solvent-controlled electron transfer in crystal violet lactone.  

PubMed

Steady-state and picosecond time-resolved emission experiments are used to examine the excited-state charge transfer reaction of crystal violet lactone (CVL) in aprotic solvents. Solvatochromic analysis using a dielectric continuum model suggests dipole moments of 9-12 D for the initially excited (LE) state and ?24 D for the charge-transfer (CT) state. Intensities of steady-state emission as well as kinetic data provide free energies for the LE ? CT reaction that range from +12 kJ/mol in nonpolar solvents to -10 kJ/mol in highly polar solvents at 25 °C. Reaction rates constants, which lie in the range of 10-100 ns(-1) in most solvents, depend on both solvent polarity and solvent friction. In highly polar solvents, rates are correlated to solvation times in a manner that indicates that the reaction is a solvent-controlled electron transfer on an adiabatic potential surface having a modest barrier. PMID:20831148

Li, Xiang; Maroncelli, Mark

2011-04-28

193

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

194

Photoinduced electron transfer modeling to simulate flavoprotein fluorescence decay.  

PubMed

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

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

2014-01-01

195

Concerted Proton-Electron Transfers: Fundamentals and Recent Developments  

NASA Astrophysics Data System (ADS)

Proton-coupled electron transfers (PCET) are ubiquitous in natural and synthetic processes. This review focuses on reactions where the two events are concerted. Semiclassical models of such reactions allow their kinetic characterization through activation versus driving force relationships, estimates of reorganization energies, effects of the nature of the proton acceptor, and H/D kinetic isotope effect as well as their discrimination from stepwise pathways. Several homogeneous reactions (through stopped-flow and laser flash-quench techniques) and electrochemical processes are discussed in this framework. Once the way has been rid of the improper notion of pH-dependent driving force, water appears as a remarkable proton acceptor in terms of reorganization energy and pre-exponential factor, thanks to its H-bonded and H-bonding properties, similarly to purposely synthesized “H-bond train” molecules. The most recent developments are in modeling and description of emblematic concerted proton-electron transfer (CPET) reactions associated with the breaking of a heavy-atom bond in an all-concerted process.

Savéant, Jean-Michel

2014-06-01

196

Molecular Computational Investigation of Electron Transfer Kinetics across Cytochrome-Iron Oxide Interfaces  

Microsoft Academic Search

The interface between electron transfer proteins such as cytochromes and solid phase mineral oxides is central to the activity of dissimilatory-metal reducing bacteria. A combination of potential-based molecular dynamics simulations and ab initio electronic structure calculations are used in the framework of Marcus electron transfer theory to compute elementary electron transfer rates from a well-defined cytochrome model, namely the small

Sebastien N. Kerisit; Kevin M. Rosso; Michel Dupuis; Marat Valiev

2007-01-01

197

Alternative mitochondrial electron transfer as a novel strategy for neuroprotection.  

PubMed

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

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

2011-05-01

198

Identification of Catalysts and Materials for a High-Energy Density Biochemical Fuel Cell: Cooperative Research and Development Final Report, CRADA Number CRD-09-345  

SciTech Connect

The proposed research attempted to identify novel biochemical catalysts, catalyst support materials, high-efficiency electron transfer agents between catalyst active sites and electrodes, and solid-phase electrolytes in order to maximize the current density of biochemical fuel cells that utilize various alcohols as substrates.

Ghirardi, M.; Svedruzic, D.

2013-07-01

199

Theoretical study on a corrole-azafullerene dyad: Electronic structure, spectra and photoinduced electron transfer  

NASA Astrophysics Data System (ADS)

Density Functional Theory and Time-Dependent Density Functional Theory calculations have been carried out on a recently synthesized amino-corrole and a corrole-azafullerene dyad which exhibits photoinduced electron transfer (PET). Good agreement of the theoretical results with experiment is obtained regarding the absorption and emission spectra of the corrole, the absorption spectra of the corrole-azafullerene dyad and the transient anionic and cationic radicals of azafullerene and corrole respectively. Application of Mulliken's theory for charge-transfer states yields the excitation energy of the charge-separated state of the dyad very close to the S1 excitation of amino-corrole, consistent with a PET process.

Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula

2014-08-01

200

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

201

Topological analyses of time-dependent electronic structures: application to electron-transfers in methionine enkephalin.  

PubMed

We have studied electron transfers (ET) between electron donors and acceptors, taking as illustrative example the case of ET in methionine enkephalin. Recent pulse and gamma radiolysis experiments suggested that an ultrafast ET takes place from the C-terminal tyrosine residue to the N-terminal, oxidized, methionine residue. According to standard theoretical frameworks like the Marcus theory, ET can be decomposed into two successive steps: i) the achievement through thermal fluctuations, of a set of nuclear coordinates associated with degeneracy of the two electronic states, ii) the electron tunneling from the donor molecular orbital to the acceptor molecular orbital. Here, we focus on the analysis of the time-dependent electronic dynamics during the tunneling event. This is done by extending the approaches based on the topological analyses of stationary electronic density and of the electron localization function (ELF) to the time-dependent domain. Furthermore, we analyzed isosurfaces of the divergence of the current density, showing the paths that are followed by the tunneling electron from the donor to the acceptor. We show how these functions can be calculated with constrained density functional theory. Beyond this work, the topological tools used here can open up new opportunities for the electronic description in the time-dependent domain. PMID:25060148

Pilmé, Julien; Luppi, Eleonora; Bergès, Jacqueline; Houée-Lévin, Chantal; de la Lande, Aurélien

2014-08-01

202

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

203

Electronic effects in Ziegler-Natta polymerization of propylene and ethylene using soluble metallocene catalysts  

SciTech Connect

({eta}{sup 5}-5,6-X{sub 2}C{sub 9}H{sub 5}){sub 2}ZrCl{sub 2} catalysts (4a, X = H; 4b, X = CH{sub 3}; 4d, X = OCH{sub 3}; 4e, X = Cl) were investigated as catalysts for the polymerization of ethylene. In addition, polymerization of propylene and ethylene was studied by using corresponding racemic, ethylene-bridged analogues (5a, X = H; 5b, X = CH{sub 3}; 5d, X = OCH{sub 3}). Both the bridged and non-bridged catalysts were effective as catalysts for both ethylene and propylene polymerization, but the molecular weights were generally lower with the ethylene-bridged catalyst. 19 refs., 3 tabs.

Lee, Ik-Mo; Gauthier, W.J.; Ball, J.M.; Iyengar, B.; Collins, S. [Univ. of Waterloo, Ontario (Canada)

1992-06-01

204

Experimental and Theoretical Analysis of Photoinduced Electron Transfer: Including the Role of Liquid Structure  

E-print Network

-transfer. Photoinduced charge separation is of particular interest due to its importance in photosynthesis, photochemical reactions, and technical applications. In addition, the initiation of the electron-transfer process by a fast light pulse enables dynamical studies to directly examine the kinetics of electron transfer

Fayer, Michael D.

205

Electron transfer through 3D monolayers on Au25 clusters.  

PubMed

The monolayer protecting small gold nanoparticles (monolayer-protected clusters, MPCs) is generally represented as the 3D equivalent of 2D self-assembled monolayers (SAMs) on extended gold surfaces. However, despite the growing relevance of MPCs in important applied areas, such as catalysis and nanomedicine, our knowledge of the structure of 3D SAMs in solution is still extremely limited. We prepared a large series of monodisperse Au25(SCnH2n+1)18 clusters (n=2, 4, 6, 8, 10, 12, 14, 16, 18) and studied how electrons tunnel through these monolayers. Electron transfer results, nicely supported by 1H NMR spectroscopy, IR absorption spectroscopy, and molecular dynamics results, show that there is a critical ligand length marking the transition between short ligands, which form a quite fluid monolayer structure, and longer alkyl chains, which self-organize into bundles. At variance with the truly protecting 2D SAMs, efficient electronic communication of the Au25 core with the outer environment is thus possible even for long alkyl chains. These conclusions provide a different picture of how an ultrasmall gold core talks with the environment through/with its protecting but not-so-shielding monolayer. PMID:24460378

Antonello, Sabrina; Arrigoni, Giorgio; Dainese, Tiziano; De Nardi, Marco; Parisio, Giulia; Perotti, Lorena; René, Alice; Venzo, Alfonso; Maran, Flavio

2014-03-25

206

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

207

Long range electron transfer in helical polyproline II oligopeptides  

NASA Astrophysics Data System (ADS)

A series of binuclear donor-acceptor complexes with helical polyproline bridges [(bpy) 2Ru IIL-(Pro) n-apy-Ru III(NH 3) 5] 5+, n = 6, 7, 9, where L = 4-carboxy-4'-methyl-2,2'-bipyridine, bpy = 4,4'-bipyridine, and apy = 4-aminopyridine, were synthesized and characterized by absorption spectra, electrochemistry and HPLC. The CD spectra of the complexes confirm that they exist in the helical polyproline II structure. Intramolecular electron transfer within these complexes was studied by generating the [(bpy) 2Ru IL ·-(Pro) n-apy-Ru III(NH 3) 5] intermediate from the reaction of eaq (from pulse radiolysis) with the [(bpy) 2Ru IIL-(Pro) n-apy-Ru III(NH 3) 5] species in aqueous solution. The driving force for this reaction is estimated to be |? G0| ? 1.5 V. The rates ( k, 25°C) and activation parameters (? H‡ (kcal/mol), ? S‡ (eu)) for the intramolecular electron transfer were found to be: 1.08×10 5 s -1, 5.6, -17; 6.40 × 10 4 s -1, 5.1, -19; 1.91 × 10 4 s -1, 4.0, and -26 for n = 6, 7, 9 respectively. The rate ( k, 25°C) and activation parameters (? H‡ (kcal/mol), ? S‡ (eu)) for the intermolecular reaction between [(bpy) 2Ru IL ·] and [(NH 3) 5Ru III-apy-Pro] were found to be 2.1 × 10 9 M -1 s -1, 3.3 and -5. This series extends our studies of the distance dependence of rate versus the number of helical prolines bridging a donor and acceptor ruthenium site to a metal-to-metal distance ? 40 Å. The weak dependence of rate versus the number of prolines observed for n = 6, 7, and 9 is very similar to that observed earlier for [(bpy) 2Ru IIL-(Pro) n-Co III(NH 3) 5], n = 4-6. The rapid rates observed at these long distances show that long range electron transfer can be observed between an appropriate donor and acceptor directly connected to the proline bridge via peptide bonds at distances similar to the diameter of a small protein.

Ogawa, Michael Y.; Moreira, Icaro; Wishart, James F.; Isied, Stephan S.

1993-10-01

208

Tetrathiomolybdate Modified Au Electrodes: Convenient Tuning of the kinetics of Electron Transfer and its application in Electrocatalysis  

E-print Network

Ammonium tetrathiomolybdate (ATM) spontaneously self assembles on Au electrodes forming a hydrophilic, air stable, pH (3-11) tolerant multilayer that is stable over a reasonably large potential window. The ATM functionalized Au electrodes can adsorb iron porphyrin catalysts and act as O2 reducing electrodes. These electrodes are stable enough to perform rotating disk electrochemistry (RDE) as well as rotating ring disk electrochemistry (RRDE) experiments. The X-ray photoelectron spectroscopy (XPS) data indicate that the sulphide atoms of ATM anchors a single ATM layer on to Au and the subsequent layers grow vertically due to the presence of hydrogen bonding NH4+ counter-ions. The formation and growth of these ATM adlayers is investigated using atomic force microscopy (AFM), scanning electron microscopy (SEM) and a series of electrochemical data. The ATM functionalized Au electrodes have double layer capacitance comparable to those reported for Au electrode bearing short chain alkyl thiol self assembled monolayer (SAM). Importantly, the rate of interfacial charge transfer (CT) can be tuned by controlling the thickness of the adlayers by simply adjusting the deposition time. Importantly the kinetics of a catalyst adsorbed on this ATM adlayer can be switched from mass transfer limited to CT limited regime by adjusting the deposition time.

Sudipta Chatterjee; Kushal Sengupta; Abhishek Dey

2014-09-10

209

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

210

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

PubMed

Despite the importance of exogenous electron shuttles (ESs) in extracellular electron transfer (EET), a lack of understanding of the key properties of ESs is a concern given their different influences on EET processes. Here, the ES-mediated EET capacity of Shewanella putrefaciens 200 (SP200) was evaluated by examining the electricity generated in a microbial fuel cell. The results indicated that all the ESs substantially accelerated the current generation compared to only SP200. The current and polarization parameters were linearly correlated with both the standard redox potential (E(ES)(0)) and the electron accepting capacity (EAC) of the ESs. A thermodynamic analysis of the electron transfer from the electron donor to the electrode suggested that the EET from c-type cytochromes (c-Cyts) to ESs is a crucial step causing the differences in EET capacities among various ESs. Based on the derived equations, both E(ES)(0) and EAC can quantitatively determine potential losses (?E) that reflect the potential loss of the ES-mediated EET. In situ spectral kinetic analysis of ES reduction by c-Cyts in a living SP200 suspension was first investigated with the E(ES), E(c-Cyt), and ?E values being calculated. This study can provide a comprehensive understanding of the role of ESs in EET. PMID:25058026

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

2014-08-19

211

A stochastic reorganizational bath model for electronic energy transfer  

NASA Astrophysics Data System (ADS)

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

Fujita, Takatoshi; Huh, Joonsuk; Aspuru-Guzik, Alán

2014-06-01

212

Electron transfer in systems of well-defined geometry  

SciTech Connect

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

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

1980-01-01

213

Structural studies of photoinduced intramolecular electron transfer in cyclopentadienylnickelnitrosyl  

SciTech Connect

A structural study based on EXAFS, FTIR, and optical absorption spectroscopies has been conducted on a photogenerated, metastable state of cyclopentadienylnickelnitrosyl (CpNiNO) produced by a reversible photochemical reaction. The photogenerated, metastable state with distinctively different EXAFS, IR, and optical absorption spectra from those of the ground state molecules was created by irradiating the sample with the 365 nm line of a mercury lamp at 20K . At the same temperature, the reverse reaction was induced by irradiation with the 313 nm line from the mercury lamp. Based on the analysis of the EXAFS data, the photogenerated, metastable state of CpNiNO has undergone considerable nuclear rearrangements compared to its ground state. The nuclear movement is characterized by a 0.12{angstrom} elongation of Ni-N bond and by a bending of Ni-N-O. A shift of the N-O stretching frequency from 1824 to 1387 cm{sup {minus}1} was observed in the photoinduced reaction with 365 nm light, implying that a NO{sup {minus}} like species results from intramolecular electron transfer from Ni to NO. The changes in the absorption spectra for the same reaction showed reduced absorption of the 385 nm band and a newly generated broad band near IR region. Temperature dependence of the Debye-Waller factor of CpNiNO was in good agreement with the diatomic harmonic oscillator for the Ni-N bond, but deviated for the Ni-O and the Ni-C bonds. Based on the structures obtained from EXAFS, ZINDO calculations for both the ground state and the photogenerated, metastable state of CpNiNO reproduced the general features of the observed absorption spectra and qualitatively explained the wavelength dependence of the reaction. The calculated partial charges on each atom in the ground state and the photogenerated, metastable state of CpNiNO are consistent with intramolecular electron transfer upon photoexcitation by 365 nm light.

Chen, L.X.; Bowman, M.K. [Argonne National Lab., IL (United States); Wang, Zhiyu; Norris, J.R. [Argonne National Lab., IL (United States)]|[Univ. of Chicago, IL (United States). Dept. of Chemistry; Montano, P.A. [Argonne National Lab., IL (United States)]|[Univ. of Illinois, Chicago, IL (United States). Dept. of Physics

1994-03-01

214

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

Code of Federal Regulations, 2011 CFR

...international standards organization. Acceptable transfer formats include the Geography Markup Language (GML) as defined by the Open GIS Consortium. (d) Textual documents . Electronic textual documents must be transferred as plain ASCII files;...

2011-07-01

215

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

Code of Federal Regulations, 2010 CFR

...international standards organization. Acceptable transfer formats include the Geography Markup Language (GML) as defined by the Open GIS Consortium. (d) Textual documents . Electronic textual documents must be transferred as plain ASCII files;...

2010-07-01

216

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

217

Fast transfer hydrogenation using a highly active orthometalated heterocyclic carbene ruthenium catalyst  

Microsoft Academic Search

The free carbene 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene reacts with trans,cis-RuHCl(PPh3)2(ampy) (ampy=2-(aminomethyl)pyridine) affording an orthometalated N-heterocyclic carbene complex characterized by an X-ray diffraction study. This compound in presence of NaOH shows very high catalytic activity for the transfer hydrogenation of several ketones to alcohols using 2-propanol as hydrogen source, affording TOF values up to 120,000h?1 (at 50% conversion).

Walter Baratta; Jan Schütz; Eberhardt Herdtweck; Wolfgang A. Herrmann; Pierluigi Rigo

2005-01-01

218

Mechanistic insights into hydride-transfer and electron-transfer reactions by a manganese(IV)-oxo porphyrin complex.  

PubMed

Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogs to a manganese(IV)-oxo porphyrin complex, (TMP)Mn(IV)(O) [TMP = 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrin], occurs via disproportionation of (TMP)Mn(IV)(O) to [(TMP)Mn(III)](+) and [(TMP)Mn(V)(O)](+) that acts as the actual hydride acceptor. In contrast, electron transfer from ferrocene derivatives to (TMP)Mn(IV)(O) occurs directly to afford ferricenium ions and (TMP)Mn(III)(OH) products. The disproportionation rate constant of (TMP)Mn(IV)(O) was determined by the dependence of the observed second-order rate constants on concentrations of NADH analogs to be (8.0 +/- 0.6) x 10(6) M(-1) s(-1) in acetonitrile at 298 K. The disproportionation rate constant of (TMP)Mn(IV)(O) in hydride-transfer reactions increases linearly with increasing acid concentration, whereas the rate constant of electron transfer from ferrocene to (TMP)Mn(IV)(O) remains constant irrespective of the acid concentration. The rate constants of electron transfer from a series of ferrocene derivatives to (TMP)Mn(IV)(O) were evaluated in light of the Marcus theory of electron transfer to determine the reorganization energy of electron transfer by the (TMP)Mn(IV)(O) complex. PMID:19888722

Fukuzumi, Shunichi; Fujioka, Naofumi; Kotani, Hiroaki; Ohkubo, Kei; Lee, Yong-Min; Nam, Wonwoo

2009-12-01

219

Ions interacting with planar aromatic molecules: modeling electron transfer reactions.  

PubMed

We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C(14)H(10), coronene C(24)H(12), or circumcoronene C(54)H(18). These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies. PMID:23406118

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

2013-02-01

220

Long-Range Photoinduced Electron Transfer Through a DNA Helix  

NASA Astrophysics Data System (ADS)

Rapid photoinduced electron transfer is demonstrated over a distance of greater than 40 angstroms between metallointercalators that are tethered to the 5' termini of a 15-base pair DNA duplex. An oligomeric assembly was synthesized in which the donor is Ru(phen)_2dppz^2+ (phen, phenanthroline, and dppz, dipyridophenazine) and the acceptor is Rh(phi)_2phen^3+ (phi, phenanthrenequinone diimine). These metal complexes are intercalated either one or two base steps m from the helix termini. Although the ruthenium-modified oligonucleotide hybridized to an unmodified complement luminesces intensely, the ruthenium-modified oligomer hybridized to the rhodium-modified oligomer shows no detectable luminescence. Time-resolved studies point to a lower limit of 109 per second for the quenching rate. No quenching was observed upon metallation of two complementary octamers by Ru(phen)_32+ and Rh(phen)_33+ under conditions where the phen complexes do not intercalate. The stacked aromatic heterocycles of the DNA duplex therefore serve as an efficient medium for coupling electron donors and acceptors over very long distances.

Murphy, C. J.; Arkin, M. R.; Jenkins, Y.; Ghatlia, N. D.; Bossmann, S. H.; Turro, N. J.; Barton, J. K.

1993-11-01

221

Contrasting effects of axial ligands on electron-transfer versus proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes.  

PubMed

The effects of axial ligands on electron-transfer and proton-coupled electron-transfer reactions of mononuclear nonheme oxoiron(IV) complexes were investigated by using [Fe(IV)(O)(tmc)(X)](n+) (1-X) with various axial ligands, in which tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is CH(3)CN (1-NCCH(3)), CF(3)COO(-) (1-OOCCF(3)), or N(3) (-) (1-N(3)), and ferrocene derivatives as electron donors. As the binding strength of the axial ligands increases, the one-electron reduction potentials of 1-X (E(red), V vs. saturated calomel electrode (SCE)) are more negatively shifted by the binding of the more electron-donating axial ligands in the order of 1-NCCH(3) (0.39) > 1-OOCCF(3) (0.13) > 1-N(3) (-0.05 V). Rate constants of electron transfer from ferrocene derivatives to 1-X were analyzed in light of the Marcus theory of electron transfer to determine reorganization energies (lambda) of electron transfer. The lambda values decrease in the order of 1-NCCH(3) (2.37) > 1-OOCCF(3) (2.12) > 1-N(3) (1.97 eV). Thus, the electron-transfer reduction becomes less favorable thermodynamically but more favorable kinetically with increasing donor ability of the axial ligands. The net effect of the axial ligands is the deceleration of the electron-transfer rate in the order of 1-NCCH(3) > 1-OOCCF(3) > 1-N(3). In sharp contrast to this, the rates of the proton-coupled electron-transfer reactions of 1-X are markedly accelerated in the presence of an acid in the opposite order: 1-NCCH(3) < 1-OOCCF(3) < 1-N(3). Such contrasting effects of the axial ligands on the electron-transfer and proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes are discussed in light of the counterintuitive reactivity patterns observed in the oxo transfer and hydrogen-atom abstraction reactions by nonheme oxoiron(IV) complexes (Sastri et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 19 181-19 186). PMID:19937616

Fukuzumi, Shunichi; Kotani, Hiroaki; Suenobu, Tomoyoshi; Hong, Seungwoo; Lee, Yong-Min; Nam, Wonwoo

2010-01-01

222

Pyrylogens: synthesis, structural, electrochemical, and photophysical characterization of a new class of electron transfer sensitizers.  

PubMed

The synthesis and photophysical properties of a new series of dicationic electron transfer sensitizers have been reported. These new materials, pyrylogens, are hybrids of pyrylium cations and Viologen dications. Electron transfer reactions of neutral organic substrates using these new sensitizers generate radical-cation/radical-cation pairs whose repulsive (repellent) interaction is designed to compete with energy wasting return electron transfer (RET) by enhancing diffusive separation and formation of solvent separated ions. PMID:18500798

Clennan, Edward L; Liao, Chen; Ayokosok, Erambo

2008-06-18

223

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

PubMed

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

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

2011-03-21

224

Nitrate storage behavior of Ba/MnOx-CeO2 catalyst and its activity for soot oxidation with heat transfer limitations.  

PubMed

A BaMnCe ternary catalyst was prepared by impregnating barium acetate on MnO(x)-CeO(2) mixed oxides, with the monoxide supported catalysts and the solid solution support as references. The activities of the catalysts for soot oxidation were evaluated in the presence of NO under an energy transference controlled regime. BaMnCe presented the lowest maximal soot oxidation rate temperature at 393 degrees C among the catalysts investigated. Although BaMnCe experienced a loss in the specific surface area and low-temperature redox property due to blocking of the support pores by barium carbonate, its superior soot oxidation activity highlighted the importance of relatively stable bidentate/monodentate nitrates coordinated to Mn(x+) and Ce(x+) sites and more stable ionic barium nitrate. About half of the nitrates stored on this catalyst decomposed within the temperature interval of 350-450 degrees C, and the ignition temperature of soot decreased significantly with involvement of the nitrates or NO(2) released. PMID:20538410

Wu, Xiaodong; Liu, Shuang; Lin, Fan; Weng, Duan

2010-09-15

225

"Sticky electrons" transport and interfacial transfer of electrons in the dye-sensitized solar cell.  

PubMed

Dye-sensitized solar cells (DSCs, also known as Gratzel cells) mimic the photosynthetic process by using a sensitizer dye to harvest light energy to generate electrical power. Several functional features of these photochemical devices are unusual, and DSC research offers a rewarding arena in which to test new ideas, new materials, and new methodologies. Indeed, one of the most attractive chemical features of the DSC is that the basic concept can be used to construct a range of devices, replacing individual components with alternative materials. Despite two decades of increasing research activity, however, many aspects of the behavior of electrons in the DSC remain puzzling. In this Account, we highlight current understanding of the processes involved in the functioning of the DSC, with particular emphasis on what happens to the electrons in the mesoporous film following the injection step. The collection of photoinjected electrons appears to involve a random walk process in which electrons move through the network of interconnected titanium dioxide nanoparticles while undergoing frequent trapping and detrapping. During their passage to the cell contact, electrons may be lost by transfer to tri-iodide species in the redox electrolyte that permeates the mesoporous film. Competition between electron collection and back electron transfer determines the performance of a DSC: ideally, all injected electrons should be collected without loss. This Account then goes on to survey recent experimental and theoretical progress in the field, placing particular emphasis on issues that need to be resolved before we can gain a clear picture of how the DSC works. Several important questions about the behavior of "sticky" electrons, those that undergo multiple trapping and detrapping, in the DSC remain unanswered. The most fundamental of these concerns is the nature of the electron traps that appear to dominate the time-dependent photocurrent and photovoltage response of DSCs. The origin of the nonideality factor in the relationship between the intensity and the DSC photovoltage is also unclear, as is the discrepancy in electron diffusion length values determined by steady-state and non-steady-state methods. With these unanswered questions, DSC research is likely to remain an active and fruitful area for some years to come. PMID:19637905

Peter, Laurence

2009-11-17

226

Photoinitiated proton-coupled electron transfer and radical transport kinetics in class la ribonucleotide reductase  

E-print Network

Proton-coupled electron transfer (PCET) is a critical mechanism in biology, underpinning key processes such as radical transport, energy transduction, and enzymatic substrate activation. Ribonucleotide reductases (RNRs) ...

Pizano, Arturo A. (Arturo Alejandro)

2013-01-01

227

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

228

Selectivity in the electron transfer catalyzed Diels-Alder reaction of (R)-alpha-phellandrene and 4-methoxystyrene.  

PubMed

Electron transfer catalysis is an effective method for the acceleration of Diels-Alder reactions between two substrates of similar electron density. The dependence of the selectivity of the Diels-Alder reaction between (R)-alpha-phellandrene and 4-methoxystyrene catalyzed by photoinduced electron transfer with tris(4-methoxyphenyl) pyrylium tetrafluoroborate is studied. Despite the fact that the radical ions involved are highly reactive species, complete regioselectivity favoring attack on the more highly substituted double bond is observed. The endo/exo selectivity and the periselectivity between [4 + 2] and [2 + 2] cycloaddition is found to be solvent-dependent. Stereochemical analysis showed that the periselectivity is correlated with the facial selectivity, with attack trans to the isopropyl group leading to the [4 + 2] product and cis attack leading to the formation of the [2 + 2] product. A good correlation between the dielectric constant of the solvent and the endo/ exo ratio is found, but more polar solvents lead to lower periselectivity. The effect of reactant and catalyst concentrations is found to be smaller. These results are rationalized in the context of the relative stability of the ion-molecule complexes and the singly linked intermediate of the reaction. PMID:18785777

Sevov, Christo S; Wiest, Olaf

2008-10-17

229

Theoretical study on the electronic structure of triphenyl sulfonium salts: Electronic excitation and electron transfer processes  

NASA Astrophysics Data System (ADS)

Density functional theory (DFT) and Time Dependent DFT calculations on triphenyl sulfonium cation (TPS) and the salts of TPS with triflate, nonaflate, perfluoro-1-octanesulfonate and hexafluoro antimonate anions are presented. These systems are widely used as cationic photoinitiators and as electron ejection layer for polymer light-emitting diodes. While some differences exist in the electronic structure of the different salts, their lowest energy intense absorption maxima are calculated at nearly the same energy for all systems. The first excited state of TPS and of the TPS salts is dissociating. Electron addition to the TPS salts lowers their energy by 1.0-1.33 eV.

Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula; Lathiotakis, Nektarios N.; Georgiadou, Dimitra G.; Vasilopoulou, Maria; Argitis, Panagiotis

2014-05-01

230

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. Kinetic and thermodynamic results preclude stepwise mechanisms of sequential proton and then electron) Meunier, B., Ed. Biomimetic Oxidations Catalyzed by Transition Metal Complexes; Imperial College Press

Roth, Justine P.

231

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

Code of Federal Regulations, 2011 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...

2011-04-01

232

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

233

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

234

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

235

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...

236

[Mechanisms of electron transfer to insoluble terminal acceptors in chemoorganotrophic bacteria].  

PubMed

The mechanisms of electron transfer of association of chemoorganotrophic bacteria to the anode in microbial fuel cells are summarized in the survey. These mechanisms are not mutually exclusive and are divided into the mechanisms of mediator electron transfer, mechanisms of electron transfer with intermediate products of bacterial metabolism and mechanism of direct transfer of electrons from the cell surface. Thus, electron transfer mediators are artificial or synthesized by bacteria riboflavins and phenazine derivatives, which also determine the ability of bacteria to antagonism. The microorganisms with hydrolytic and exoelectrogenic activity are involved in electron transfer mechanisms that are mediated by intermediate metabolic products, which are low molecular carboxylic acids, alcohols, hydrogen etc. The direct transfer of electrons to insoluble anode is possible due to membrane structures (cytochromes, pili, etc.). Association of microorganisms, and thus the biochemical mechanisms of electron transfer depend on the origin of the inoculum, substrate composition, mass transfer, conditions of aeration, potentials and location of electrodes and others, that are defined by technological and design parameters. PMID:24868908

Samarukha, I A

2014-01-01

237

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

238

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

239

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

PubMed Central

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

Beyenal, Haluk; Babauta, Jerome T.

2014-01-01

240

77 FR 6310 - Electronic Fund Transfers (Regulation E)  

Federal Register 2010, 2011, 2012, 2013

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

2012-02-07

241

Synthesis, characterization, photophysics and photochemistry of pyrylogen electron transfer sensitizers.  

PubMed

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-+0.05 V vs SCE) coupled with their range of singlet (48-63 kcal mol(-1)) and triplet (48-57 kcal mol(-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 3.1 eV. 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 523 nm 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. PMID:24112032

Clennan, Edward L; Liao, Chen

2014-01-01

242

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

243

Chemical Bonding: The Classical Description sharing or transferring electrons between atoms  

E-print Network

Chemical Bonding: The Classical Description sharing or transferring electrons between atoms LEWIS electron dot diagram -> formula (SF6) VSEPR (valence-shell electron-pair repulsion) theory Molecular Structure (w/o quantum mechanics) Chapter. 3 Two or more atoms approach -> their electrons interact and form

Ihee, Hyotcherl

244

Fabrication of all-carbon nanotube electronic devices on flexible substrates through CVD and transfer methods.  

PubMed

SWNT thin films with different nanotube densities are fabricated by CVD while controlling the concentration of catalyst and growth time. Three layers of SWNT films are transferred to flexible substrates serving as electrodes and channel materials, respectively. All-carbon nanotube TFTs with an on/off ratio as high as 10(5) are obtained. Inverters are fabricated on top of the flexible substrates with symmetric input/output behavior. PMID:24123547

Zou, Yuan; Li, Qunqing; Liu, Junku; Jin, Yuanhao; Qian, Qingkai; Jiang, Kaili; Fan, Shoushan

2013-11-13

245

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

246

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) the proton transfer reaction becomes more exothermic, (4) the electron transfer reaction becomes more as the temperature increases and as the electron transfer reaction becomes more exothermic in the normal Marcus

Hammes-Schiffer, Sharon

247

Primary reactions in photosynthetic reaction centers of Rhodobacter sphaeroides - Time constants of the initial electron transfer  

NASA Astrophysics Data System (ADS)

The primary dynamics of reaction centers from Rhodobacter sphaeroides at room temperature are studied at low excitation intensities and low excitation rates. Analysis based on singular value decomposition yields three time constants in the picosecond range (ca. 1.2 ps, 3.5 ps and 220 ps). The spectral and temporal signatures are fully consistent with the step-wise electron transfer model published previously, with a first electron transfer to the bacteriochlorophyll with a time constant of 3.5 ps and a second 1.2 ps transfer to the bacteriopheophytin. No indications for adiabatic electron transfer are found in the time range >0.5 ps.

Dominguez, Pablo Nahuel; Himmelstoss, Matthias; Michelmann, Jeff; Lehner, Florian Thomas; Gardiner, Alastair T.; Cogdell, Richard J.; Zinth, Wolfgang

2014-05-01

248

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

249

Sub-Tc electron transfer at the HTSC/polymer interface.  

PubMed

The first kinetic measurements for electron transfer (ferrocene/ferricinium reaction) at the interface between an HTSC (Tl,Pb1223) and a redox polymer (ferrocene-tagged poly-pyrrole) show that superconductivity affects electron transfer rate, which thus offers a novel probe of the superconducting state. PMID:12669863

Le-Poul, Nicolas; Green, Stephen J; Attfield, J Paul; Bedford, Robin B; Lyons, Michael E G; Patterson, Aileen M

2003-03-01

250

Electron-transfer photochromism to switch bulk second-order nonlinear optical properties with high contrast.  

PubMed

The first bulk electron-transfer photochromic compound with intrinsic second-order nonlinear optical (NLO) photoswitching properties has been synthesized. This system employs an electron-transfer photoactive asymmetric viologen ligand coordinated to a zinc(II) center. PMID:25195919

Li, Pei-Xin; Wang, Ming-Sheng; Zhang, Ming-Jian; Lin, Chen-Sheng; Cai, Li-Zhen; Guo, Sheng-Ping; Guo, Guo-Cong

2014-10-20

251

49 CFR 225.37 - Optical media transfer and electronic submission.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Optical media transfer and electronic submission. ...AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. ...updates, and amendments by way of optical media (CD-ROM), or by means of...

2013-10-01

252

49 CFR 225.37 - Optical media transfer and electronic submission.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Optical media transfer and electronic submission. ...AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. ...updates, and amendments by way of optical media (CD-ROM), or by means of...

2012-10-01

253

49 CFR 225.37 - Optical media transfer and electronic submission.  

Code of Federal Regulations, 2011 CFR

...2011-10-01 2011-10-01 false Optical media transfer and electronic submission. ...AND INVESTIGATIONS § 225.37 Optical media transfer and electronic submission. ...updates, and amendments by way of optical media (CD-ROM), or by means of...

2011-10-01

254

Redox Modulation of Flavin and Tyrosine Determines Photoinduced Proton-coupled Electron Transfer and  

E-print Network

-coupled electron transfer between a tyrosine and the flavin cofactor is the key reaction to switch from a dark reactions. Photoinduced electron transfer in biological systems, espe- cially in proteins, is a highly in the amino acid composition of the flavin binding pocket, the reaction rates of the forward reaction differ

van Stokkum, Ivo

255

Evidence for two active branches for electron transfer in photosystem I  

E-print Network

, the electrons are transferred to an iron-sulfur cluster, FX, and then to the terminal iron-sulfur acceptors, FA is used as a terminal acceptor. PS I uses iron-sulfur clusters as terminal acceptors, and the quinone of the photosystem (PS) I primary donor (P700), an electron is transferred to the primary acceptor, A0 (a chlorophyll

256

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

257

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

258

The Iron-Sulfur Cluster of Electron Transfer Flavoprotein-ubiquinone Oxidoreductase (ETF-QO) is the Electron Acceptor for Electron Transfer Flavoprotein†  

PubMed Central

Electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) accepts electrons from electron-transfer flavoprotein (ETF) and reduces ubiquinone from the ubiquinone-pool. It contains one [4Fe-4S]2+,1+ and one FAD, which are diamagnetic in the isolated oxidized enzyme and can be reduced to paramagnetic forms by enzymatic donors or dithionite. In the porcine protein, threonine 367 is hydrogen bonded to N1 and O2 of the flavin ring of the FAD. The analogous site in Rhodobacter sphaeroides ETF-QO is asparagine 338. Mutations N338T and N338A were introduced into the R. sphaeroides protein by site-directed mutagenesis to determine the impact of hydrogen bonding at this site on redox potentials and activity. The mutations did not alter the optical spectra, EPR g-values, spin-lattice relaxation rates, or the [4Fe-4S]2+,1+ to FAD point-dipole interspin distances. The mutations had no impact on the reduction potential for the iron-sulfur cluster, which was monitored by changes in the continuous wave EPR signals of the [4Fe-4S]+ at 15 K. For the FAD semiquinone, significantly different potentials were obtained by monitoring the titration at 100 or 293 K. Based on spectra at 293 K the N338T mutation shifted the first and second midpoint potentials for the FAD from +47 mV and ?30 mV for wild type to ?11 mV and ?19 mV, respectively. The N338A mutation decreased the potentials to ?37 mV and ?49 mV. Lowering the midpoint potentials resulted in a decrease in the quinone reductase activity and negligible impact on disproportionation of ETF1e? catalyzed by ETF-QO. These observations indicate that the FAD is involved in electron transfer to ubiquinone, but not in electron transfer from ETF to ETF-QO. Therefore the iron-sulfur cluster is the immediate acceptor from ETF. PMID:18672901

Swanson, Michael A.; Usselman, Robert J.; Frerman, Frank E.; Eaton, Gareth R.; Eaton, Sandra S.

2011-01-01

259

In situ monitoring of bare and K-doped Mo 2C catalysts surface depassivation based on emission of electrons and K + ions  

NASA Astrophysics Data System (ADS)

The method for in situ characterization of surface transformations on heterogeneous catalyst is described. The method is based on the measurements of thermal electron and ion emissions from the catalyst surface. It is demonstrated by investigating the depassivation process of undoped and K-doped Mo 2C catalysts exposed to air after synthesis and use to identify characteristic steps of reduction-carburization by flowing CH 4/H 2 gas mixture. The information obtained from thermal emission experiments is consistent with the methane consumption profile, which provided an independent observation of the recarburization step.

Kotarba, Andrzej; Adamski, Grzegorz; Sojka, Zbigniew; Djega-Mariadassou, Gerald; Pettersson, Jan B. C.

2006-04-01

260

Characterization of Catalysts for Synthesis of Higher Alcohols using Electron Microscopy  

E-print Network

interest in developing transportation fuels from sustainable resources demands new and better production paths. One of these is using biogas to create alcohol as a fuel. Higher they are working [2],[3]. The catalysts for sustainable energy project (CASE) at DTU aims

Dunin-Borkowski, Rafal E.

261

Heterogeneous electron transfer at nanoscopic electrodes: importance of electronic structures and electric double layers.  

PubMed

Heterogeneous electron-transfer (ET) processes at solid electrodes play key roles in molecular electronics and electrochemical energy conversion and sensing. Electrode nanosization and/or nanostructurization are among the major current strategies for performance promotion in these fields. Besides, nano-sized/structured electrodes offer great opportunities to characterize electrochemical structures and processes with high spatial and temporal resolution. This review presents recent insights into the nanoscopic size and structure effects of electrodes and electrode materials on heterogeneous ET kinetics, by emphasizing the importance of the electric double-layer (EDL) at the electrode/electrolyte interface and the electronic structure of electrode materials. It is shown, by general conceptual analysis and recent example demonstrations of representative electrode systems including electrodes of nanometer sizes and gaps and of nanomaterials such as sp(2) hybridized nanocarbons and semiconductor quantum dots, how the heterogeneous ET kinetics, the electronic structures of electrodes, the EDL structures at the electrode/electrolyte interface and the nanoscopic electrode sizes and structures may be related. PMID:24871071

Chen, Shengli; Liu, Yuwen; Chen, Junxiang

2014-08-01

262

Electron transfer catalysis with monolayer protected Au25 clusters  

NASA Astrophysics Data System (ADS)

Au25L18 (L = S(CH2)2Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au25L18+ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au25L18+ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au25L18/Au25L18- and the Au25L18+/Au25L18 redox couples as redox mediators. Simulation of the CV curves led to determination of the ET rate constant (kET) values for concerted dissociative ET to the peroxides. The ET free energy ?G° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log kETvs. ?G°) relationship. Comparison with the kET obtained using a ferrocene-type donor with a formal potential similar to that of Au25L18/Au25L18- showed that the presence of the capping monolayer affects the ET rate rather significantly, which is attributed to the intrinsic nonadiabaticity of peroxide acceptors.Au25L18 (L = S(CH2)2Ph) clusters were prepared and characterized. The resulting monodisperse clusters were reacted with bis(pentafluorobenzoyl) peroxide in dichloromethane to form Au25L18+ quantitatively. The kinetics and thermodynamics of the corresponding electron transfer (ET) reactions were characterized via electrochemistry and thermochemical calculations. Au25L18+ was used in homogeneous redox catalysis experiments with a series of sym-substituted benzoyl peroxides, including the above peroxide, bis(para-cyanobenzoyl) peroxide, dibenzoyl peroxide, and bis(para-methoxybenzoyl) peroxide. Peroxide dissociative ET was catalyzed using both the Au25L18/Au25L18- and the Au25L18+/Au25L18 redox couples as redox mediators. Simulation of the CV curves led to determination of the ET rate constant (kET) values for concerted dissociative ET to the peroxides. The ET free energy ?G° could be estimated for all donor-acceptor combinations, leading to observation of a nice activation-driving force (log kETvs. ?G°) relationship. Comparison with the kET obtained using a ferrocene-type donor with a formal potential similar to that of Au25L18/Au25L18- showed that the presence of the capping monolayer affects the ET rate rather significantly, which is attributed to the intrinsic nonadiabaticity of peroxide acceptors. This article was submitted as part of a Themed Issue on metallic clusters. Other papers on this topic can be found in issue 14 of vol. 4 (2012). This issue can be found from the Nanoscale homepage [http://www.rsc.org/nanoscale].

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

2012-08-01

263

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

264

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

SciTech Connect

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

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

2012-03-01

265

Photopolymerization Sensitized by CdTe Nanocrystals in Ionic Liquid: Highly Efficient Photoinduced Electron Transfer  

Microsoft Academic Search

We demonstrate a photopolymerization sensitized by CdTe nanocrystals in room temperature ionic liquid. The kinetics of photoinduced electron transfer from cationic CdTe nanocrystals to polymerization initiators in several kinds of ionic liquids is also studied. From the analyses of photoluminescence quenching measurement, the electron transfer rates from CdTe nanocrystals to organic electron acceptors are anomalously large in the ionic liquid

Yoshiyuki Nonoguchi; Takuya Nakashima; Makiko Sakashita; Tsuyoshi Kawai

2008-01-01

266

Rate expressions for excitation transfer. III. An ab initio study of electronic factors in excitation transfer and exciton resonance interactions  

NASA Astrophysics Data System (ADS)

A detailed theory for electronic aspects of electronic excitation (energy) transfer (EET) for sandwich dimers was derived in paper II of this series [J. Chem. Phys. 101, 10 521 (1994)]. In II, the electronic transfer matrix element for EET was evaluated, then simplified to various levels of approximation. The results of ab initio molecular orbital calculations on an ethene sandwich dimer are reported here in order to test and quantify the theory of II. The calculations were undertaken using a STO-6G basis set and localized molecular orbitals, with separations of 4, 5, and 6 Å between the molecules. It is demonstrated that the important electronic factors contributing to EET are the Coulombic interaction (for direct singlet-singlet transfer) and, for both singlet-singlet and triplet-triplet EET, orbital overlap-dependent interactions. The dominant orbital overlap-dependent terms arise from through-configuration interaction, which involves successive one-electron transfers mediated via bridging ionic configurations, first presented in II. The results confirm that the Dexter-type exchange interaction is small in comparison.

Scholes, Gregory D.; Harcourt, Richard D.; Ghiggino, Kenneth P.

1995-06-01

267

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

268

Pathways for photoinduced electron transfer within a mixed-metal bisporphyrin  

SciTech Connect

The photophysical properties of an oblique bisporphyrin, comprised of gold(III) and zinc(II) porphyrinic subunits separated by a 2,9-diphenyl-1, 10-phenanthroline spacer moiety, have been studied. Upon selective excitation of either porphyrin, rapid electron transfer occurs from the zinc porphyrin to the appended gold porphyrin and the ground-state system is restored by relatively slow reverse electron transfer. The rates of the various electron transfer steps correlate with both reaction exergonicity and temperature but only poorly with the solvent polarity because of limited applicability of the dielectric continuum model to this system and solvent-induced changes in redox potentials. The magnitude of electronic coupling between the reactants shows a marked dependence on the energy gap between relevant orbitals on the porphyrin and the spacer group, consistent with through-bond interaction. It is concluded that reaction via the zinc porphyrin excited singlet and triplet states proceeds via electron transfer through the LUMO of the spacer, while the gold porphrin triplet excited state reacts via hole transfer through the HOMO of the spacer moiety. Reverse electron transfer seems to show no preferred pathway and may involve through-space electron transfer. 43 refs., 6 figs., 5 tabs.

Harriman, A. (Univ. of Texas, Austin (United States)); Heitz, V. (Univ. of Texas, Austin (United States) Universite Louis Pasteur, Strasbourg (France)); Sauvage, J.P. (Universite Louis Pasteur, Strasbourg (France))

1993-06-03

269

Coherent transfer of light polarization to electron spins in a semiconductor  

E-print Network

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

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

2007-10-20

270

Effects of ionic polymer environment on the photoinduced electron transfer from zinc porphyrin to viologen  

SciTech Connect

The effect of ionic polymer environment on photoinduced electron transfer from zinc porphyrin to viologen was investigated for aqueous Nylon containing pendant viologen and quaternized amino groups. The quantum yield for the photoinduced reduction of the viologen group with zinc porphyrins was found to be variable as functions of the fraction of pendant viologen, the concentration of the electron donor, and the ionic strength of the solution. By laser flash photolysis experiments, the reaction rates for electron transfer from the excited porphyrin to the viologen group in the polymer and for back electron transfer from the reduced viologen to the oxidized porphyrin were measured. As a result, it was found that the cationic and/or hydrophobic polymer environment retards the back electron transfer, which increases the quantum yield for the formation of viologen cation radicals. 42 references, 6 figures, 3 tables.

Nosaka, Y.; Kuwabara, A.; Miyama, H.

1986-03-27

271

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

PubMed

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). PMID:24562190

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

2014-04-01

272

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

273

Dispersion solute-solvent coupling in electron transfer reactions. I. Effective potential  

E-print Network

Dispersion solute-solvent coupling in electron transfer reactions. I. Effective potential Dmitry V in the present paper a system composed of a polar polarizable solute immersed in a solvent of polar polarizable by averaging over the electronic degrees of freedom of the solute and the solvent. Electronic polarizabilities

Matyushov, Dmitry

274

Isotope effect with deuterated media in photo- and dark-electron transfer reactions  

Microsoft Academic Search

The effects of isotope substitution were in solvent and acceptor molecules on the efficiency of electron tunneling from electronically excited molecules to acceptor particles in vitreous matrices were studied. Photoelectron transfer from magnesium etio-I-porphyrin to chloroform and carbon tetrachloride were investigated. Ethanol and methanol, deuterated and solidified in the form of transparent glass, served as the matrix. Optical and electron

R. G. Yusupov; R. F. Khairutdinov

1988-01-01

275

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

276

Gene expression and deletion analysis of mechanisms for electron transfer from electrodes to Geobacter sulfurreducens.  

PubMed

Geobacter sulfurreducens is one of the few microorganisms available in pure culture known to directly accept electrons from a negatively poised electrode. Microarray analysis was used to compare gene transcript abundance in biofilms of G. sulfurreducens using a graphite electrode as the sole electron donor for fumarate reduction compared with transcript abundance in biofilms growing on the same material, but not consuming current. Surprisingly, genes for putative cell-electrode connections, such as outer-surface cytochromes and pili, which are highly expressed in current-producing biofilms, were not highly expressed in current-consuming biofilms. Microarray analysis of G. sulfurreducens gene transcript abundance in current-consuming biofilms versus current-producing biofilms gave similar results. In both comparative studies current-consuming biofilms had greater transcript abundance for a gene (GSU3274) encoding a putative monoheme, c-type cytochrome. Deletion of genes for outer-surface proteins previously shown to be essential for optimal electron transfer to electrodes had no impact on electron transfer from electrodes. Deletion of GSU3274 completely inhibited electron transfer from electrodes, but had no impact on electron transfer to electrodes. These differences in gene expression patterns and the impact of gene deletions suggest that the mechanisms for electron transfer from electrodes to G. sulfurreducens differ significantly from the mechanisms for electron transfer to electrodes. PMID:20696622

Strycharz, Sarah M; Glaven, Richard H; Coppi, Maddalena V; Gannon, Sarah M; Perpetua, Lorrie A; Liu, Anna; Nevin, Kelly P; Lovley, Derek R

2011-02-01

277

Unique Mechanisms of Excitation Energy Transfer, Electron Transfer and Photoisomerization in Biological Systems  

Microsoft Academic Search

We discuss unique mechanisms typical in the elementary processes ofbiological functions. We focus on three topics. Excitation energytransfer in the light-harvesting antenna systems of photosyntheticbacteria is unique in its structure and the energy transfer mechanism. Inthe case of LH2 of Rhodopseudomonas acidophila, the B850 intra-ringenergy transfer and the inter-ring energy transfer between B800 and B850take place by the intermediate coupling

T. Kakitani; T. Kawatsu; A. Kimura; A. Yamada; T. Yamato; S. Yamamoto

2002-01-01

278

Electron transfer reactions in electrolyte solutions: effects of ion atmosphere and solvent relaxation  

NASA Astrophysics Data System (ADS)

A molecular theory of the effects of solution dynamics on the rates of adiabatic outer-sphere electron transfer reactions in electrolyte solutions is presented. The theory correctly includes the dynamics of both ions and solvent molecules through frequency dependent ion and solvent susceptibilities. The rate of electron transfer is calculated by employing the well-known Grote-Hynes theory. The barrier-crossing frequency of electron transfer is found to depend rather strongly on the salt concentration dependent solvent longitudinal relaxation time and on the ionic conductivity. Numerical results are presented for some common aqueous and non-aqueous electrolyte solutions.

Chandra, Amalendu

1996-05-01

279

77 FR 6193 - Electronic Fund Transfers (Regulation E)  

Federal Register 2010, 2011, 2012, 2013

...may also affect some consumers' decisions about whether...transfers made by migrant consumers sending remittances...summarizing results of consumer research conducted by the Board...Migrant Remittances,'' Journal of Economic...

2012-02-07

280

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

281

How Does the Solvent Control Electron Transfer? Experimental and Theoretical Studies of the Simplest Charge Transfer Reaction  

Microsoft Academic Search

The standard theoretical description used to describe electron transfer is Marcus theory, which maps the polarization of the solvent surrounding the reactants onto a reaction coordinate, q. The questions we address in this paper are: How many and what types of solvent degrees of freedom constitute q? Is it appropriate to treat the solvent as a dielectric continuum? Our approach

Erik R. Barthel; Ignacio B. Martini; Benjamin J. Schwartz

2001-01-01

282

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

283

-GAB and pH Dependence of the Electron Transfer from P+ in Rhodobacter sphaeroides Reaction Centers  

E-print Network

-G°AB and pH Dependence of the Electron Transfer from P+ QA - QB to P+ QAQB - in Rhodobacter in the reaction cycle. The early, fast electron-transfer reactions forming P+QA - show little temperature or pH from QA - to QB has significant temperature and pH dependence (8, 15, 16). An electron transfer from QA

Li, Jiali

284

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

PubMed

The free radical scavenging activity of six 2'-hydroxychalcones has been studied in gas phase and solvents using the density functional theory (DFT) method. The three main working mechanisms, hydrogen atom transfer (HAT), stepwise electron-transfer-proton-transfer (ET-PT) and sequential-proton-loss-electron-transfer (SPLET) have been considered. The O-H bond dissociation enthalpy (BDE), ionization potential (IP), proton affinity (PA) and electron transfer energy (ETE) parameters have been computed in gas phase and solvents. The theoretical results confirmed the important role of the B ring in the antioxidant properties of hydroxychalcones. In addition, the calculated results matched well with experimental values. The results suggested that HAT would be the most favorable mechanism for explaining the radical-scavenging activity of hydroxychalcone in gas phase, whereas SPLET mechanism is thermodynamically preferred pathway in aqueous solution. PMID:23801254

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

2013-09-01

285

Measured multipole moments of continuum electron transfer angular distributions  

SciTech Connect

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

Elston, S.B.

1986-01-01

286

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

2014-11-12

287

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

...2014-04-01 2013-04-01 true 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...

2014-04-01

288

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

289

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

Code of Federal Regulations, 2013 CFR

...2013-04-01 2013-04-01 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...

2013-04-01

290

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

Code of Federal Regulations, 2011 CFR

...2011-04-01 2010-04-01 true 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...

2011-04-01

291

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

Code of Federal Regulations, 2012 CFR

...2012-04-01 2012-04-01 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...

2012-04-01

292

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

Code of Federal Regulations, 2010 CFR

...DEPARTMENT OF THE TREASURY LIQUORS LIQUORS AND ARTICLES FROM PUERTO RICO AND THE VIRGIN ISLANDS Procedure at Port of Entry From the Virgin Islands § 26.267 Payment of tax by electronic fund transfer. (a) Each...

2010-04-01

293

26 CFR 40.6302(a)-1 - Voluntary payments of excise taxes by electronic funds transfer.  

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 true Voluntary payments of excise taxes by electronic funds transfer. 40.6302...DEPARTMENT OF THE TREASURY (CONTINUED) MISCELLANEOUS EXCISE TAXES EXCISE TAX PROCEDURAL REGULATIONS §...

2010-04-01

294

26 CFR 40.6302(a)-1 - Voluntary payments of excise taxes by electronic funds transfer.  

Code of Federal Regulations, 2011 CFR

...2011-04-01 2011-04-01 false Voluntary payments of excise taxes by electronic funds transfer. 40.6302...DEPARTMENT OF THE TREASURY (CONTINUED) MISCELLANEOUS EXCISE TAXES EXCISE TAX PROCEDURAL REGULATIONS §...

2011-04-01

295

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

296

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

297

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

298

Photochemical ribonucleotide reductase for the study of proton-coupled electron transfer  

E-print Network

Charge transport and catalysis in enzymes often rely on amino acid radicals as intermediates. The generation and transport of these radicals are synonymous with proton-coupled electron transfer (PCET), which intrinsically ...

Reece, Steven Y., 1980-

2007-01-01

299

Electron-transfer reactions in coal-model compounds. Annual report, January-December 1987  

SciTech Connect

Oxidation of benzpinacol (BPC) was effected with two Fe(III) (1,10-phenanthroline)3 complexes. The product of these reactions is exclusively benzophenone when 2,6-di-t-butylpyridine is added to the solution. The rates of the electron-transfer process were determined by monitoring the change of the Fe(III) and Fe(II) concentrations by uv-vis spectroscopy. By measuring the rates of the electron transfer as a function of temperature, activation parameters for the electron-transfer process from BPC to Fe(III) (1,10-phenanthroline)3 and to Fe(III) (4,7-diphenyl-1,10-phenanthroline)3 were determined. These data indicate the importance of entropy in potential electron-transfer reactions. Novel bond-cleavage reactions have been observed through the use of added oxygen indicating a new mechanistic pathway for coal-polymer fragmentation.

Penn, J.H.

1988-03-01

300

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

Federal Register 2010, 2011, 2012, 2013

...January 10, 2012 Part II Department of Health and Human Services...Simplification: Adoption of Standards for Health Care Electronic Funds Transfers (EFTs...DEPARTMENT OF HEALTH AND HUMAN SERVICES Office of the...

2012-01-10

301

Theoretical study of electron, proton, and proton-coupled electron transfer in iron bi-imidazoline complexes.  

PubMed

A comparative theoretical investigation of single electron transfer (ET), single proton transfer (PT), and proton-coupled electron transfer (PCET) reactions in iron bi-imidazoline complexes is presented. These calculations are motivated by experimental studies showing that the rates of ET and PCET are similar and are both slower than the rate of PT for these systems (Roth, J. P.; Lovel, S.; Mayer, J. M. J. Am. Chem. Soc. 2000, 122, 5486). The theoretical calculations are based on a multistate continuum theory, in which the solute is described by a multistate valence bond model, the transferring hydrogen nucleus is treated quantum mechanically, and the solvent is represented as a dielectric continuum. For electronically nonadiabatic electron transfer, the rate expressions for ET and PCET depend on the inner-sphere (solute) and outer-sphere (solvent) reorganization energies and on the electronic coupling, which is averaged over the reactant and product proton vibrational wave functions for PCET. The small overlap of the proton vibrational wave functions localized on opposite sides of the proton transfer interface decreases the coupling for PCET relative to ET. The theory accurately reproduces the experimentally measured rates and deuterium kinetic isotope effects for ET and PCET. The calculations indicate that the similarity of the rates for ET and PCET is due mainly to the compensation of the smaller outer-sphere solvent reorganization energy for PCET by the larger coupling for ET. The moderate kinetic isotope effect for PCET arises from the relatively short proton transfer distance. The PT reaction is found to be dominated by solute reorganization (with very small solvent reorganization energy) and to be electronically adiabatic, leading to a fundamentally different mechanism that accounts for the faster rate. PMID:11457104

Iordanova, N; Decornez, H; Hammes-Schiffer, S

2001-04-25

302

Electron impact excitation of SO2 - Differential, integral, and momentum transfer cross sections  

NASA Technical Reports Server (NTRS)

Electron impact excitation of the electronic states of SO2 was investigated. Differential, integral, and inelastic momentum transfer cross sections were obtained by normalizing the relative measurements to the elastic cross sections. The cross sections are given for seven spectral ranges of the energy-loss spectra extending from the lowest electronic state to near the first ionization limit. Most of the regions represent the overlap of several electronic transitions. No measurements for these cross sections have been reported previously.

Vuskovic, L.; Trajmar, S.

1982-01-01

303

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

E-print Network

-CNISM, Universita della Tuscia, I-01100 Viterbo, Italy 2 Institute of Agro-environmental and Forest Biology-tin oxide, in resonance with its ligand-to-metal charge transfer absorption band, resulted in a light. The capability of controlling electron transfer processes through light pulses opens interesting perspectives

Tuscia, Università Degli Studi Della

304

Electron transfer rates in highly exothermic reactions on semiconductor electrolyte interfaces, and the deuterium isotope effect  

Microsoft Academic Search

Highly exothermic electron transfer rates were measured by semiconductor electrochemical techniques. Experiments demonstrate that the decreases in the electron transfer rates with the exothermicity of the reactions in so-called abnormal regions are much more moderate than the classical predictions, and that this is probably due to the effects of intramolecular vibrations such as C-H stretching and\\/or bending. 3 figures.

Seiichiro Nakabayashi; Kiminori Itoh; Akira Fujishima; Kenichi Honda

1983-01-01

305

Diameter selective electron transfer from encapsulated ferrocenes to single-walled carbon nanotubes.  

PubMed

The diameter selective photoluminescence quenching of single-walled carbon nanotubes (SWCNTs) is observed upon ferrocene encapsulation, which can be attributed to electron transfer from the encapsulated ferrocenes to the SWCNTs. Interestingly, the dependence of the electron transfer process on the nanotube diameter is governed by the molecular orientation of the ferrocenes in the SWCNT rather than the reduction potentials of the SWCNT. PMID:25310793

Iizumi, Yoko; Suzuki, Hironori; Tange, Masayoshi; Okazaki, Toshiya

2014-10-24

306

Effects of heterocyclic and tertiary permeant amines on the electron transfer in thylakoid membranes  

Microsoft Academic Search

The effect of low concentrations (up to 50 ?M) of lipophilic permeant amines on the electron transfer in thylakoid membranes\\u000a of pea chloroplasts has been investigated. In the presence of heterocyclic amines (9-aminoacridine and neutral red), the electron\\u000a transfer, initiated from H2O to PS I acceptors, has been shown to be inhibited to a level amounting to less than 50%

Vera Opanasenko; Alexey Agafonov; Raissa Demidova

2002-01-01

307

Electron-transfer reactions in coal-model compounds. Annual report, January-December 1987  

Microsoft Academic Search

Oxidation of benzpinacol (BPC) was effected with two Fe(III) (1,10-phenanthroline)3 complexes. The product of these reactions is exclusively benzophenone when 2,6-di-t-butylpyridine is added to the solution. The rates of the electron-transfer process were determined by monitoring the change of the Fe(III) and Fe(II) concentrations by uv-vis spectroscopy. By measuring the rates of the electron transfer as a function of temperature,

Penn

1988-01-01

308

Coupling of light-induced electron transfer to proton uptake in photosynthesis  

Microsoft Academic Search

Light energy is transformed into chemical energy in photosynthesis by coupling a light-induced electron transfer to proton uptake. The resulting proton gradient drives ATP synthesis. In this study, we monitored the light-induced reactions in a 100-kDa photosynthetic protein from 30 ns to 35 s by FTIR difference spectroscopy. The results provide detailed mechanistic insights into the electron and proton transfer

André Remy; Klaus Gerwert

2003-01-01

309

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

Microsoft Academic Search

Solvent kinetic isotope effect studies of electron transfer within xanthine oxidase have been performed, using a stopped-flow pH-jump technique to perturb the distribution of reducing equivalents within partially reduced enzyme and follow the kinetics of reequilibration spectrophotometrically. It is found that the rate constant for electron transfer between the flavin and one of the iron-sulfur centers of the enzyme observed

Russ Hille

1991-01-01

310

Electron capture and transfer dissociation: Peptide structure analysis at different ion internal energy levels  

Microsoft Academic Search

We decoupled electron-transfer dissociation (ETD) and collision-induced dissociation of charge-reduced species (CRCID) events\\u000a to probe the lifetimes of intermediate radical species in ETD-based ion trap tandem mass spectrometry of peptides. Short-lived\\u000a intermediates formed upon electron transfer require less energy for product ion formation and appear in regular ETD mass spectra,\\u000a whereas long-lived intermediates require additional vibrational energy and yield product

Hisham Ben Hamidane; Diego Chiappe; Ralf Hartmer; Aleksey Vorobyev; Marc Moniatte; Yury O. Tsybin

2009-01-01

311

Photoinduced electron transfer between fullerenes (C 60\\/C 70) and disubstituted naphthalenes using laser flash photolysis  

Microsoft Academic Search

Photoinduced electron-transfer processes between fullerenes C60\\/C70 and disubstituted-naphthalenes have been studied by laser flash photolysis. Quantum yields (?etT) and rate constants (ket) of electron transfer from naphthalenes to the excited triplet states of C60 (3C60?) and C70 (3C70?) have been determined by observing the transient absorption bands in the wide wavelength VIS\\/NIR regions. The observed ?etT and ket values depend

Mohamed El-Khouly; Mamoru Fujitsuka; Osamu Ito; Maged El-Kemary

2001-01-01

312

Kinetics of Electron Transfer within Cytochrome bc 1 and Between Cytochrome bc 1 and Cytochrome c  

Microsoft Academic Search

In this minireview an overview is presented of the kinetics of electron transfer within the cytochrome bc\\u000a 1 complex, as well as from cytochrome bc\\u000a 1 to cytochrome c. The cytochrome bc\\u000a 1 complex (ubiquinone:cytochrome c oxidoreductase) is an integral membrane protein found in the mitochondrial respiratory chain as well as the electron transfer\\u000a chains of many respiratory and photosynthetic

Francis Millett; Bill Durham

2004-01-01

313

Frontier orbital symmetry control of intermolecular electron transfer  

SciTech Connect

This report contains sections describing the selection of electron donor-acceptor systems, the synthesis and photophysical properties of linked electron-donor-acceptor systems, the estimation of photoinduced charge-separation rate constants from fluorescence quenching data, and radical ion-pair recombination by picosecond transient absorption spectroscopy. 9 refs., 1 fig., 7 tabs.

Stevens, B.

1991-09-01

314

Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory  

E-print Network

and on the properties of the liquid solvent. For example, solvent dielectric properties affect free energies of transfer a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants

Fayer, Michael D.

315

Reversible in situ catalyst formation.  

PubMed

Acid catalysts play a vital role in the industrial synthesis and production of a plethora of organic chemicals. But, their subsequent neutralization and disposal is also a giant source of waste. For example, for a Friedel-Crafts acylation with AlCl 3, a kilogram of product yields up to 20 kg of (contaminated) waste salt. Other processes are even worse, and this waste is both an environmental and economic shortcoming. Here we address this issue by showing a series of acid catalysts where the neutralization is "built in" to the system and thus eliminates waste. Clearly these will not replace all organic and mineral acid catalysts, but they can replace many. Further, we show how these self-neutralizing catalysts can often eliminate unwanted byproducts, improve selectivity, or elimination of mass transfer limitations by changing from heterogeneous to homogeneous systems. They readily facilitate separations and promote recycling, to promote both green chemistry and good economics. First is near-critical water, or liquid water under pressure, where the K W for dissociation goes up 3-4 decades between 0 degrees C and 250 degrees C, thus facilitating both acid and base catalysis. Moreover, as the exothermic hydrogen bonding diminishes, the dielectric constant goes down to the point at which both salts and organics are soluble in this very hot water. For example, toluene and water are completely miscible at 305 degrees C. This eliminates mass transfer limitations for the reactions, and postreaction cooling not only lowers the K W to neutralize the ions without waste but also results in facile separations from simple liquid-liquid immiscibility. Further, we show the formation of catalysts with alkylcarbonic acids from alcohols and CO2, analogous to carbonic acid from water and CO2. We show a number of applications for these self-neutralizing catalysts, including the formation of ketals, the formation of diazonium intermediates to couple with electron-rich aromatics to produce dye molecules, and the hydration of beta-pinene. Here also these systems often enhance phase behavior to cut mass transfer resistance. In an analogous application we show that peroxide and CO2 gives peroxycarbonic acid, also reversible upon the removal of the CO2, and we show application to epoxidation reactions. The bottom line is that these catalysts afford profound advantages for both green chemistry and improved economics. The methods outlined here have potential for abundant applications, and we hope that this work will motivate such opportunities. PMID:18251512

Hallett, Jason P; Pollet, Pamela; Liotta, Charles L; Eckert, Charles A

2008-03-01

316

Preparation of 1,3-bis(allyloxy)benzene under a new multi-site phase-transfer catalyst combined with ultrasonication--a kinetic study.  

PubMed

In the present work, kinetics of synthesis of 1,3-bis(allyloxy)benzene was successfully carried out by O-allylation of resorcinol with allyl bromide using aqueous potassium hydroxide and catalyzed by a new multi-site phase-transfer catalyst viz., 1,3,5,7-tetrabenzylhexamethylenetetraammonium tetrachloride, MPTC under ultrasonic (40 kHz, 300 W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40 kHz, 300 W) in a batch reactor, it shows that the overall reaction rate can be greatly enhanced to seven fold faster with ultrasound irradiation than without ultrasound. The present study provides a method to synthesize ethers by ultrasound assisted liquid-liquid phase-transfer catalysis condition. PMID:23545104

Selvaraj, Varathan; Rajendran, Venugopal

2013-09-01

317

Ultrasound assisted the preparation of 1-butoxy-4-nitrobenzene under a new multi-site phase-transfer catalyst--kinetic study.  

PubMed

In the present research work deals with the preparation of 1-butoxy-4-nitrobenzene was successfully carried out by 4-nitrophenol with n-butyl bromide using aqueous potassium carbonate and catalyzed by a new multi-site phase-transfer catalyst (MPTC) viz., N(1),N(4)-diethyl-N(1),N(1),N(4),N(4)-tetraisopropylbutane-1,4-diammonium dibromide, under ultrasonic (40 kHz, 300 W) assisted organic solvent condition. The pseudo first-order kinetic equation was applied to describe the overall reaction. Under ultrasound irradiation (40 kHz, 300 W) in a batch reactor, it shows that the overall reaction greatly enhanced with ultrasound irradiation than without ultrasound. The present study provides a method to synthesize nitro aromatic ethers by ultrasound assisted liquid-liquid multi-site phase-transfer catalysis condition. PMID:23948491

Harikumar, Kuppuswamy; Rajendran, Venugopal

2014-01-01

318

Relationship between the oxidation potential of the bacteriochlorophyll dimer and electron transfer in photosynthetic reaction centers.  

PubMed

The primary electron donor in the photosynthetic reaction center from purple bacteria is a bacteriochlorophyll dimer containing four conjugated carbonyl groups that may form hydrogen bonds with amino acid residues. Spectroscopic analyses of a set of mutant reaction centers confirm that hydrogen bonds can be formed between each of these carbonyl groups and histidine residues in the reaction center subunits. The addition of each hydrogen bond is correlated with an increase in the oxidation potential of the dimer, resulting in a 355-mV range in the midpoint potential. The resulting changes in the free-energy differences for several reactions involving the dimer are related to the electron transfer rates using the Marcus theory. These reactions include electron transfer from cytochrome c2 to the oxidized dimer, charge recombination from the primary electron acceptor quinone, and the initial forward electron transfer. PMID:8847341

Allen, J P; Williams, J C

1995-06-01

319

Hydrogen Transfer, Coke Formation, and Catalyst Decay and Their Role in the Chain Mechanism of Catalytic Cracking  

Microsoft Academic Search

Understanding of the process of hydrogen redistribution in catalytic cracking has long been recognized as essential to understanding of the coking processes responsible for catalyst decay. Hydrogen redistribution is also thought to be behind the puzzling excess of paraffins over olefins that has been noted by several authors [1-3], and to hold the key to determining the selectivity of cracking

K. A. CUMMING; B. W. WOJCIECHOWSKI

1996-01-01

320

Electron-transfer reactions of coal model compounds. Final report, January 1986-August 1988  

SciTech Connect

Oxidation of benzpinacol (BPC) and diphenyldimethylpinacol (DPB) was effected with two Fe(3)(1,10-phenanthroline)3 complexes. The products of these reactions are exclusively the corresponding ketones when 2,6-di-t-butylpyridine is added to the solution. The rates of the electron-transfer processes were determined by monitoring the change of the Fe(2) and Fe(3) species by uv-vis spectroscopy. The energy required for the reactions was found to be ca. 10 kcal/mole lower than predicted, based on the redox potentials of the electron-donor and the electron acceptor. The mechanism of these electron-transfer reactions appears to be complex. In addition, electron transfer reactions utilizing 9,10-dicyanoanthracene were shown to cause the bond cleavage of model coal compounds. Mechanistic studies have shown that molecular oxygen causes a radical chain-reaction mechanism for bond cleavage following the electron-transfer event, signifying that a minimum of 4 bonds are cleaved in each electron-transfer event.

Penn, J.H.

1989-04-01

321

Electron Transfer DOI: 10.1002/anie.200603822  

E-print Network

at a potential (E1 = Ã?0.1 V) where all the TPyP molecules were reduced.[13] A short oxidation potential pulse (E2 to areas such as molecular electronics, electro- chemistry, biology, catalysis, information storage

Borguet, Eric

322

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

323

Sulfated SnO2 modified multi-walled carbon nanotubes - A mixed proton-electron conducting support for Pt catalysts in direct ethanol fuel cells  

NASA Astrophysics Data System (ADS)

We report on the synthesis of sulfated SnO2 modified multi-walled carbon nanotubes (MWCNTs) composites as new supports of Pt catalyst (Pt-S-SnO2/MWCNTs) with the aims to enhance electron and proton conductivity and also catalytic activity for ethanol oxidation. The Pt-S-SnO2/MWCNTs catalyst is synthesized by a combination of improved sol-gel and pulse-microwave assisted polyol methods. The surface presence, morphology and structure of the Pt-S-SnO2/MWCNTs catalyst are characterized by Fourier transform infrared spectroscopy (FT-IR), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively. The electrocatalytic properties of the Pt-S-SnO2/MWCNTs catalyst for ethanol oxidation reactions are investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. The results show that Pt-S-SnO2/MWCNTs catalyst exhibits higher catalytic activity for ethanol oxidation than Pt supported on non-sulfated SnO2/MWCNTs composites.

Zhang, Xinwei; Zhu, Hong; Guo, Zhijun; Wei, Yongsheng; Wang, Fanghui

2011-03-01

324

Concerted proton-electron transfer in the oxidation of hydrogen-bonded phenols.  

PubMed

Three phenols with pendant, hydrogen-bonded bases (HOAr-B) have been oxidized in MeCN with various one-electron oxidants. The bases are a primary amine (-CPh(2)NH(2)), an imidazole, and a pyridine. The product of chemical and quasi-reversible electrochemical oxidations in each case is the phenoxyl radical in which the phenolic proton has transferred to the base, (*)OAr-BH(+), a proton-coupled electron transfer (PCET) process. The redox potentials for these oxidations are lower than for other phenols, predominately from the driving force for proton movement. One-electron oxidation of the phenols occurs by a concerted proton-electron transfer (CPET) mechanism, based on thermochemical arguments, isotope effects, and DeltaDeltaG(++)/DeltaDeltaG degrees . The data rule out stepwise paths involving initial electron transfer to form the phenol radical cations [(*)(+)HOAr-B] or initial proton transfer to give the zwitterions [(-)OAr-BH(+)]. The rate constant for heterogeneous electron transfer from HOAr-NH(2) to a platinum electrode has been derived from electrochemical measurements. For oxidations of HOAr-NH(2), the dependence of the solution rate constants on driving force, on temperature, and on the nature of the oxidant, and the correspondence between the homogeneous and heterogeneous rate constants, are all consistent with the application of adiabatic Marcus theory. The CPET reorganization energies, lambda = 23-56 kcal mol(-)(1), are large in comparison with those for electron transfer reactions of aromatic compounds. The reactions are not highly non-adiabatic, based on minimum values of H(rp) derived from the temperature dependence of the rate constants. These are among the first detailed analyses of CPET reactions where the proton and electron move to different sites. PMID:16669677

Rhile, Ian J; Markle, Todd F; Nagao, Hirotaka; DiPasquale, Antonio G; Lam, Oanh P; Lockwood, Mark A; Rotter, Katrina; Mayer, James M

2006-05-10

325

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

326

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

327

The influence of diffusion on photoinduced electron transfer and geminate recombination  

E-print Network

The influence of diffusion on photoinduced electron transfer and geminate recombination R. C 7 November 1991; accepted 5 February 1992) The influence of diffusion on photoinduced electron media whose properties govern life processes.' Before current can flow in a fuel cell, the fuel has

Fayer, Michael D.

328

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

NASA Astrophysics Data System (ADS)

Kinetic models based on Fermi's Golden Rule are commonly employed to understand photoinduced electron transfer dynamics at molecule-semiconductor interfaces. Implicit in such second-order perturbative descriptions is the assumption that nuclear relaxation of the photoexcited electron donor is fast compared to electron injection into the semiconductor. This approximation breaks down in systems where electron transfer transitions occur on 100-fs time scale. Here, we present a fourth-order perturbative model that captures the interplay between time-coincident electron transfer and nuclear relaxation processes initiated by light absorption. The model consists of a fairly small number of parameters, which can be derived from standard spectroscopic measurements (e.g., linear absorbance, fluorescence) and/or first-principles electronic structure calculations. Insights provided by the model are illustrated for a two-level donor molecule coupled to both (i) a single acceptor level and (ii) a density of states (DOS) calculated for TiO2 using a first-principles electronic structure theory. These numerical calculations show that second-order kinetic theories fail to capture basic physical effects when the DOS exhibits narrow maxima near the energy of the molecular excited state. Overall, we conclude that the present fourth-order rate formula constitutes a rigorous and intuitive framework for understanding photoinduced electron transfer dynamics that occur on the 100-fs time scale.

Li, Lesheng; Giokas, Paul G.; Kanai, Yosuke; Moran, Andrew M.

2014-06-01

329

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

PubMed

Kinetic models based on Fermi's Golden Rule are commonly employed to understand photoinduced electron transfer dynamics at molecule-semiconductor interfaces. Implicit in such second-order perturbative descriptions is the assumption that nuclear relaxation of the photoexcited electron donor is fast compared to electron injection into the semiconductor. This approximation breaks down in systems where electron transfer transitions occur on 100-fs time scale. Here, we present a fourth-order perturbative model that captures the interplay between time-coincident electron transfer and nuclear relaxation processes initiated by light absorption. The model consists of a fairly small number of parameters, which can be derived from standard spectroscopic measurements (e.g., linear absorbance, fluorescence) and/or first-principles electronic structure calculations. Insights provided by the model are illustrated for a two-level donor molecule coupled to both (i) a single acceptor level and (ii) a density of states (DOS) calculated for TiO2 using a first-principles electronic structure theory. These numerical calculations show that second-order kinetic theories fail to capture basic physical effects when the DOS exhibits narrow maxima near the energy of the molecular excited state. Overall, we conclude that the present fourth-order rate formula constitutes a rigorous and intuitive framework for understanding photoinduced electron transfer dynamics that occur on the 100-fs time scale. PMID:24952525

Li, Lesheng; Giokas, Paul G; Kanai, Yosuke; Moran, Andrew M

2014-06-21

330

Many heme-binding proteins with diverse functions are known, including electron-transferring cytochromes,  

E-print Network

regulatory proteins; hence, a search for matches in non-coding DNA sequences would not be expectedMany heme-binding proteins with diverse functions are known, including electron. They are not commonly implicated in catalysis or electron transfer; instead, the heme-bound iron stays in its 2+ (Fe

Hardison, Ross C.

331

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

332

Molecular view of an electron transfer process essential for iron-sulfur protein biogenesis  

PubMed Central

Biogenesis of iron–sulfur cluster proteins is a highly regulated process that requires complex protein machineries. In the cytosolic iron–sulfur protein assembly machinery, two human key proteins—NADPH-dependent diflavin oxidoreductase 1 (Ndor1) and anamorsin—form a stable complex in vivo that was proposed to provide electrons for assembling cytosolic iron–sulfur cluster proteins. The Ndor1–anamorsin interaction was also suggested to be implicated in the regulation of cell survival/death mechanisms. In the present work we unravel the molecular basis of recognition between Ndor1 and anamorsin and of the electron transfer process. This is based on the structural characterization of the two partner proteins, the investigation of the electron transfer process, and the identification of those protein regions involved in complex formation and those involved in electron transfer. We found that an unstructured region of anamorsin is essential for the formation of a specific and stable protein complex with Ndor1, whereas the C-terminal region of anamorsin, containing the [2Fe-2S] redox center, transiently interacts through complementary charged residues with the FMN-binding site region of Ndor1 to perform electron transfer. Our results propose a molecular model of the electron transfer process that is crucial for understanding the functional role of this interaction in human cells. PMID:23596212

Banci, Lucia; Bertini, Ivano; Calderone, Vito; Ciofi-Baffoni, Simone; Giachetti, Andrea; Jaiswal, Deepa; Mikolajczyk, Maciej; Piccioli, Mario; Winkelmann, Julia

2013-01-01

333

Molecular view of an electron transfer process essential for iron-sulfur protein biogenesis.  

PubMed

Biogenesis of iron-sulfur cluster proteins is a highly regulated process that requires complex protein machineries. In the cytosolic iron-sulfur protein assembly machinery, two human key proteins--NADPH-dependent diflavin oxidoreductase 1 (Ndor1) and anamorsin--form a stable complex in vivo that was proposed to provide electrons for assembling cytosolic iron-sulfur cluster proteins. The Ndor1-anamorsin interaction was also suggested to be implicated in the regulation of cell survival/death mechanisms. In the present work we unravel the molecular basis of recognition between Ndor1 and anamorsin and of the electron transfer process. This is based on the structural characterization of the two partner proteins, the investigation of the electron transfer process, and the identification of those protein regions involved in complex formation and those involved in electron transfer. We found that an unstructured region of anamorsin is essential for the formation of a specific and stable protein complex with Ndor1, whereas the C-terminal region of anamorsin, containing the [2Fe-2S] redox center, transiently interacts through complementary charged residues with the FMN-binding site region of Ndor1 to perform electron transfer. Our results propose a molecular model of the electron transfer process that is crucial for understanding the functional role of this interaction in human cells. PMID:23596212

Banci, Lucia; Bertini, Ivano; Calderone, Vito; Ciofi-Baffoni, Simone; Giachetti, Andrea; Jaiswal, Deepa; Mikolajczyk, Maciej; Piccioli, Mario; Winkelmann, Julia

2013-04-30

334

Electron transfer from sulfate-reducing becteria biofilm promoted by reduced graphene sheets  

NASA Astrophysics Data System (ADS)

Reduced graphene sheets (RGSs) mediate electron transfer between sulfate-reducing bacteria (SRB) and solid electrodes, and promote the development of microbial fuel cells (MFC). We have investigated RSG-promoted electron transfer between SRB and a glassy carbon (GC) electrode. The RGSs were produced at high yield by a chemical sequence involving graphite oxidation, ultrasonic exfoliation of nanosheets, and N2H4 reduction. Cyclic voltammetric testing showed that the characteristic anodic peaks (around 0.3 V) might arise from the combination of bacterial membrane surface cytochrome c3 and the metabolic products of SRB. After 6 d, another anodic wave gradually increased to a maximum current peak and a third anodic signal became visible at around 0 V. The enhancements of two characteristic anodic peaks suggest that RSGs mediate electron-transfer kinetics between bacteria and the solid electrode. Manipulation of these recently-discovered electron-transport mechanisms will lead to significant advances in MFC engineering.

Wan, Yi; Zhang, Dun; Wang, Yi; Wu, Jiajia

2012-01-01

335

Modulating the electronic structure of chromophores by chemical substituents for efficient energy transfer: application to fluorone.  

PubMed

Strong electron correlation within a quasi-spin model of chromophores was recently shown to enhance exciton energy transfer significantly. Here we investigate how the modulation of the electronic structure of the chromophores by chemical substitution can enhance energy-transfer efficiency. Unlike previous work that does not consider the direct effect of the electronic structure on exciton dynamics, we add chemical substituents to the fluorone dimer to study the effect of electron-donating and electron-withdrawing substituents on exciton energy transfer. The exciton dynamics are studied from the solution of a quantum Liouville equation for an open system whose model Hamiltonian is derived from excited-state electronic structure calculations. Both van der Waals energies and coupling energies, arising from the Hellmann-Feynman force generated upon transferring the dimers from infinity to a finite separation, are built into the model Hamiltonian. Though these two effects are implicitly treated in dipole-based models, their explicit and separate treatment as discussed here is critical to forging the correct connection with the electronic structure calculations. We find that the addition of electron-donating substituents to the fluorone system results in an increase in exciton-transfer rates by factors ranging from 1.3-1.9. The computed oscillator strength is consistent with the recent experimental results on a larger heterodimer system containing fluorone. The oscillator strength increases with the addition of electron-donating substituents. Our results indicate that the study of chromophore networks via electronic structure will help in the future design of efficient synthetic light-harvesting systems. PMID:25062094

Sand, Andrew M; Liu, Claire; Valentine, Andrew J S; Mazziotti, David A

2014-08-01

336

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

337

Acceptor side effects on the electron transfer at cryogenic temperatures in intact photosystem II  

Microsoft Academic Search

In intact PSII, both the secondary electron donor (TyrZ) and side-path electron donors (Car\\/ChlZ\\/Cytb559) can be oxidized by P680+ at cryogenic temperatures. In this paper, the effects of acceptor side, especially the redox state of the non-heme iron, on the donor side electron transfer induced by visible light at cryogenic temperatures were studied by EPR spectroscopy. We found that the

Han Bao; Chunxi Zhang; Keisuke Kawakami; Yanan Ren; Jian-Ren Shen; Jingquan Zhao

2008-01-01

338

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

339

Balancing the two photosystems: photosynthetic electron transfer governs  

E-print Network

In photosynthesis in chloroplasts, two separate light- driven reactions each move an electron from a donor-scheme'. Each photosystem contains a photochemical reaction centre and its own array of light-harvesting antenna pigments. Reaction centres and light-harvesting pigments are associated with speci¢c protein complexes

Allen, John F.

340

Kinetics of electron transfer through the respiratory chain.  

PubMed Central

We show that the rate at which electrons pass through the respiratory chain in mitochondria and respiring prokaryotic cells is described by the product of three terms, one describing electron donation, one acceptance, and a third, the thermodynamic drive. We apply the theory of nonequilibrium thermodynamics in the context of the chemiosmotic model of proton translocation and energy conservation. This approach leads to a closed-form expression that predicts steady-state electron flux as a function of chemical conditions and the proton motive force across the mitochondrial inner membrane or prokaryotic cytoplasmic membrane. The rate expression, derived considering reverse and forward electron flow, is the first to account for both thermodynamic and kinetic controls on the respiration rate. The expression can be simplified under specific conditions to give rate laws of various forms familiar in cellular physiology and microbial ecology. The expression explains the nonlinear dependence of flux on electrical potential gradient, its hyperbolic dependence on substrate concentration, and the inhibiting effects of reaction products. It provides a theoretical basis for investigating life under unusual conditions, such as microbial respiration in alkaline waters. PMID:12324402

Jin, Qusheng; Bethke, Craig M

2002-01-01

341

The transfer between electron bulk kinetic energy and thermal energy in collisionless magnetic reconnection  

SciTech Connect

By performing two-dimensional particle-in-cell simulations, we investigate the transfer between electron bulk kinetic and electron thermal energy in collisionless magnetic reconnection. In the vicinity of the X line, the electron bulk kinetic energy density is much larger than the electron thermal energy density. The evolution of the electron bulk kinetic energy is mainly determined by the work done by the electric field force and electron pressure gradient force. The work done by the electron gradient pressure force in the vicinity of the X line is changed to the electron enthalpy flux. In the magnetic island, the electron enthalpy flux is transferred to the electron thermal energy due to the compressibility of the plasma in the magnetic island. The compression of the plasma in the magnetic island is the consequence of the electromagnetic force acting on the plasma as the magnetic field lines release their tension after being reconnected. Therefore, we can observe that in the magnetic island the electron thermal energy density is much larger than the electron bulk kinetic energy density.

Lu, San; Lu, Quanming; Huang, Can; Wang, Shui [CAS Key Lab of Basic Plasma Physics, University of Science and Technology of China, Hefei 230026 (China)] [CAS Key Lab of Basic Plasma Physics, University of Science and Technology of China, Hefei 230026 (China)

2013-06-15

342

Manipulation of microbial extracellular electron transfer by changing molecular structure of phenazine-type redox mediators.  

PubMed

Phenazines, as a type of electron shuttle, are involved in various biological processes to facilitate microbial energy metabolism and electron transfer. They constitute a large group of nitrogen-containing heterocyclic compounds, which can be produced by a diverse range of bacteria or by artificial synthesis. They vary significantly in their properties, depending mainly on the nature and position of substitutent group. Thus, it is of great interest to find out the most favorable substituent type and molecular structure of phenazines for electron transfer routes. Here, the impacts of the substituent group on the reduction potentials of phenazine-type redox mediators in aqueous solution were investigated by quantum chemical calculations, and the calculation results were further validated with experimental data. The results show that the reaction free energy was substantially affected by the location of substituent groups on the phenazine molecule and the protonated water clusters. For the main proton addition process, the phenazines substituted with electron-donating groups and those with electron-withdrawing groups interacted with different protonated water clusters, attributed to the proximity effect of water molecules on proton transfer. Thus, high energy conversion efficiency could be achieved by controlling electron flow route with appropriate substituted phenazines to reduce the biological energy acquisition. This study provides useful information for designing efficient redox mediators to promote electron transfer between microbes and terminal acceptors, which are essential to bioenergy recovery from wastes and environmental bioremediation. PMID:23244024

Chen, Jie-Jie; Chen, Wei; He, Hui; Li, Dao-Bo; Li, Wen-Wei; Xiong, Lu; Yu, Han-Qing

2013-01-15

343

Electronic energies for Neon dimer dication radiative charge transfer  

NASA Astrophysics Data System (ADS)

This research was conducted to find the shape of the potential energy surfaces for the Neon dimer dication, designated Ne2(+2), to include all symmetries which dissociate to two ground state Ne(+) ions or a ground state Ne atom and Ne(+2) ion. The motivation is to investigate whether there is a minimum in the upper level, the Ne(+2) and Ne level, located in such a way that populations of bound dimer molecules can be built up without dissociating or transitioning to the lower level other than by radiative charge transfer. It is also of interest to show that the ground state is dissociative, that is that its energy is monotonically decreasing with increasing nuclear separation. Calculations were completed using programs known as Gaussian-86, and Diatom. Diatom produced excellent results for the He2(+2)test case. Ne2(+2) calculations were not as accurate as He2(+2), but results did indicate that bound upper level states exist which can only undergo charge transfer radiatively. This research computed Neon dimer dication potential energies for nuclear separations from 0.9 to 20 a.u. of Ne2(+2) sigma, pi, and delta states.

Deemer, Roger Alan

1989-12-01

344

Photoinduced electron transfer and geminate recombination for photoexcited acceptors in a pure donor solvent.  

PubMed

Photoinduced electron transfer and geminate recombination are studied for the systems rhodamine 3B (R3B(+)) and rhodamine 6G (R6G(+)), which are cations, in neat neutral N,N-dimethylaniline (DMA). Following photoexcitation of R3B(+) or R6G(+) (abbreviated as R(+)), an electron is transferred from DMA to give the neutral radical R and the cation DMA(+). Because the DMA hole acceptor is the neat solvent, the forward transfer rate is very large, approximately 5x10(12) s(-1). The forward transfer is followed by geminate recombination, which displays a long-lived component suggesting several percent of the radicals escape geminate recombination. Spectrally resolved pump-probe experiments are used in which the probe is a "white" light continuum, and the full time-dependent spectrum is recorded with a spectrometer/charge-coupled device. Observations of stimulated emission (excited state decay-forward electron transfer), the R neutral radical spectrum, and the DMA(+) radical cation spectrum as well as the ground-state bleach recovery (geminate recombination) make it possible to unambiguously follow the electron transfer kinetics. Theoretical modeling shows that the long-lived component can be explained without invoking hole hopping or spin-forbidden transitions. PMID:15267972

Saik, V O; Goun, A A; Fayer, M D

2004-05-22

345

Flavin Redox Bifurcation as a Mechanism for Controlling the Direction of Electron Flow during Extracellular Electron Transfer.  

PubMed

The iron-reducing bacterium Shewanella oneidensis MR-1 has a dual directional electronic conduit involving 40 heme redox centers in flavin-binding outer-membrane c-type cytochromes (OM c-Cyts). While the mechanism for electron export from the OM c-Cyts to an anode is well understood, how the redox centers in OM c-Cyts take electrons from a cathode has not been elucidated at the molecular level. Electrochemical analysis of live cells during switching from anodic to cathodic conditions showed that altering the direction of electron flow does not require gene expression or protein synthesis, but simply redox potential shift about 300?mV for a flavin cofactor interacting with the OM c-Cyts. That is, the redox bifurcation of the riboflavin cofactor in OM c-Cyts switches the direction of electron conduction in the biological conduit at the cell-electrode interface to drive bacterial metabolism as either anode or cathode catalysts. PMID:25156475

Okamoto, Akihiro; Hashimoto, Kazuhito; Nealson, Kenneth H

2014-10-01

346

Frontispiece: Aligning Electronic and Protonic Energy Levels of Proton-Coupled Electron Transfer in Water Oxidation on Aqueous TiO2.  

PubMed

Proton-Coupled Electron Transfer In their Communication on page?12046?ff., J. Cheng et?al. propose the concept of protonic energy levels to visualize the thermodynamics of proton-coupled electron transfer. Their method helps to elucidate the electronic and protonic components of thermodynamic overpotentials in photocatalysis. PMID:25350943

Cheng, Jun; Liu, Xiandong; Kattirtzi, John A; VandeVondele, Joost; Sprik, Michiel

2014-11-01

347

Elastic electron scattering cross sections at high momentum transfer  

NASA Astrophysics Data System (ADS)

The elastic scattering cross section of keV electrons over large angles (>90°) is discussed. A comparison is made of the Rutherford cross section, the cross section obtained in the first Born approximation and that obtained by a partial wave calculation. The last approach differs significantly from the first two. For compounds, the recoil energy makes it possible to distinguish experimentally from which atom the electron has scattered. We compare the elastic peak ratio of H and O in water at several keV and for Hf and O in HfO2 at 20-40 keV with the calculated ratios. Reasonable (but not perfect) agreement is obtained between the experiment and theory for the partial wave calculations.

Vos, M.; McEachran, R. P.; Weigold, E.; Bonham, R. A.

2013-04-01

348

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

PubMed

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

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

2011-07-01

349

Multi-scale modeling of moisture transfer in electronic packaging  

Microsoft Academic Search

Interfacial delamination is one of the primary concerns in electronic package design. Pop-corning in plastic-encapsulated IC packages is a defect frequently occurring during the solder reflow due to moisture penetration into the packages. Moisture absorption has a detrimental effect on the EMC\\/Cu interfacial adhesion and drastically reduces the reliability of the encapsulated package. To obtain good reliability and to prevent

H. B. Fan; M. M. F. Yuen

2010-01-01

350

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

2014-11-01

351

On the origin of matrix elements for electronic excitation (energy) transfer  

NASA Astrophysics Data System (ADS)

The origin of electronic energy transfer (EET) between two chromophores (D and A) is explored further for several molecular situations that may be encountered in experiment—namely, nonoverlapping active-space orbitals of the D and A chromophores, forbidden electronic excitations for both chromophores, and an allowed and a forbidden electronic excitation for the D and A chromophores, respectively. The theory is illustrated via the results of calculations of the EET matrix elements for model systems with both four-eight active-space electrons and all of the electrons included explicitly. In each case, it is found that any overlap contribution to these matrix elements is associated much more with charge-transfer and penetration terms rather than it is with the Dexter exchange integral. The calculated magnitude of the latter integral is always smaller than that of the Coulomb integral.

Harcourt, Richard D.; Ghiggino, Kenneth P.; Scholes, Gregory D.; Speiser, Shammai

1996-08-01

352

Analyzing the electric response of molecular conductors using "electron deformation" orbitals and occupied-virtual electron transfer.  

PubMed

The concept of "electron deformation orbitals" (EDOs) is used to investigate the electric response of conducting metals and oligophenyl chains. These orbitals and their eigenvalues are obtained by diagonalization of the deformation density matrix (difference between the density matrices of the perturbed and unperturbed systems) and can be constructed as linear combinations of the unperturbed molecular orbitals within "frozen geometry" conditions. This form of the EDOs allows calculating the part of the electron deformation density associated to an effective electron transfer from occupied to virtual orbitals (valence to conduction band electron transfer in the band model of conductivity). It is found that the "electron deformation" orbitals pair off, displaying the same eigenvalue but opposite sign. Each pair represents an amount of accumulation/depletion of electron charge at different molecular regions. In the oligophenyl systems investigated only one pair contributes effectively to the charge flow between molecular ends, resulting from the promotion of electrons from occupied orbitals to close in energy virtual orbitals of appropriate symmetry and overlapping. Analysis of this pair along explains the differences in conductance of olygophenyl chains based on phenyl units. PMID:24676839

Mandado, Marcos; Ramos-Berdullas, Nicolás

2014-06-30

353

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

SciTech Connect

Electron-transfer reactions between viologen radical cations (C{sub n}V{sup {sm bullet}+}, n = 1-18) and various quinones have been studied in aqueous and reverse micellar (AOT/isooctane/H{sub 2}O) solution by use of the electron pulse radiolysis technique. By use of dynamic light scattering measurements, the concentration of water pools was determined and the number of electron-transfer reactants per water pool could be calculated. Rate constants measured for the reaction between C{sub n}V{sup {sm bullet}+} radicals and anthraquinonesulfonate ions (AQS{sup {minus}}) decreased with increasing length of the aliphatic chain of the viologens, caused by association of the viologen with the surfactant interface.

Hubig, S.M. (Univ. of Texas, Austin (USA)); Rodgers, M.A.J. (Bowling Green State Univ., OH (USA))

1990-03-08

354

A redox beginning: Which came first phosphoryl, acyl, or electron transfer ?. [Abstract only  

NASA Technical Reports Server (NTRS)

Thermodynamic and kinetic information available on the synthesis of prebiotic monomers and polymers will be examined in order to illuminate the prebiotic plausibility of polymer syntheses based on (a) phosphoryl transfer that yields phosphodiester polymers, (b) acyl transfer that gives polyamides, and (c) electron transfer that produces polydisulfide or poly(thio)ester polymers. New experimental results on the oxidative polymerization of 2,3-dimercaptopropanol by ferric ions on the surface of ferric hydroxide oxide will be discussed as a chemical model of polymerization by electron transfer. This redox polymerization that yields polymers with a polydisulfide backbone was found to give oligomers up to the 15-mer from 1 mM of 2,3-dimercaptopropanol after one day at 25 C. High pressure liquid chromatography (HPLC) analysis of the oligomers was carried out on an Alltech OH-100 column eluted with acetonitrile-water.

Weber, Arthur L.

1994-01-01

355

Use of laser transfer processing for producing Al-Bi doped silicon electronic devices  

NASA Astrophysics Data System (ADS)

This work explores the combination of laser transfer and laser doping in a single process, as a way to produce highly defined, heavily doped volumes on semiconductors, to produce electronic devices. The process has been realized on mono and multicrystalline silicon by means of nanosecond laser pulses. The paper studies the mechanism of the process and the requirements in terms of beam shaping, energy levels and specific constrains of the setup to get proper dopant transfer and diffusion, as well as high compositional gradient. Bismuth is selected as n-dopant, and aluminum is used as an already well known solution for laser driven heavy p-doping on silicon. The suitability of laser transfer doping for direct writing of electronic devices is assessed in terms of transfer, melting and doping capability, and compared with other State-of-the-Art laser doping processes.

Romero, Pablo; Otero, Nerea; Leira, Cristina; Coto, Ivette

2013-03-01

356

Electron spin polarization in photosynthesis and the mechanism of electron transfer in photosystem I. Experimental observations.  

PubMed Central

Transient electron paramagnetic resonance (EPR) methods are used to examine the spin populations of the light-induced radicals produced in spinach chloroplasts, photosystem I particles, and Chlorella pyrenoidosa. We observe both emission and enhanced absorption within the hyperfine structure of the EPR spectrum of P700+, the photooxidized reaction-center chlorophyll radical (Signal I). By using flow gradients or magnetic fields to orient the chloroplasts in the Zeeman field, we are able to influence both the magnitude and sign of the spin polarization. Identification of the polarized radical and P700+ is consistent with the effects of inhibitors, excitation light intensity and wavelength, redox potential, and fractionation of the membranes. The EPR signal of the polarized P700+ radical displays a 30% narrower line width than P700+ after spin relaxation. This suggests a magnetic interaction between P700+ and its reduced (paramagnetic) acceptor, which leads to a collapse of the P700+ hyperfine structure. Narrowing of the spectrum is evident only in the spectrum of polarized P700+, because prompt electron transfer rapidly separates the radical pair. Evidence of cross-relaxation between the adjacent radicals suggests the existence of an exchange interaction. The results indicate that polarization is produced by a radical pair mechanism between P700+ and the reduced primary acceptor of photosystem I. The orientation dependence of the spin polarization of P700+ is due to the g-tensor anisotropy of the acceptor radical to which it is exchange-coupled. The EPR spectrum of P700+ is virtually isotropic once the adjacent acceptor radical has passed the photoionized electron to a later, more remote acceptor molecule. This interpretation implies that the acceptor radical has g-tensor anisotropy significantly greater than the width of the hyperfine field on P700+ and that the acceptor is oriented with its smallest g-tensor axis along the normal to the thylakoid membranes. Both the ferredoxin-like iron-sulfur centers and the X- species observed directly by EPR at low temperatures have g-tensor anisotropy large enough to produce the observed spin polarization; however, studies on oriented chloroplasts show that the bound ferredoxin centers do not have this orientation of their g tensors. In contrast, X- is aligned with its smallest g-tensor axis predominantly normal to the plane of the thylakoid membranes. This is the same orientation predicted for the acceptor radical based on analysis of the spin polarization of P700+, and indicates that the species responsible for the anisotropy of the polarized P700+ spectrum is probably X-. The dark EPR Signal II is shown to possess anisotropic hyperfine structure (and possibly g-tensor anisotropy), which serves as a good indicator of the extent of membrane alignment. PMID:204369

Dismukes, G C; McGuire, A; Blankenship, R; Sauer, K

1978-01-01

357

Inter-flavin electron transfer in cytochrome P450 reductase effects of solvent and pH identify hidden  

E-print Network

Inter-flavin electron transfer in cytochrome P450 reductase ­ effects of solvent and pH identify to the endoplasmic retic- ulum by a hydrophobic N-terminal membrane anchor Keywords electron transfer; pH dependence and kinetic effects of pH and solvent on two- and four-electron reduction in this diflavin enzyme. p

358

Electron transfer in supercritical carbon dioxide: ultraexothermic charge recombination at the end of the "inverted region".  

PubMed

Charge-recombination rates in contact radical-ion pairs, formed between aromatic hydrocarbons and nitriles in supercritical CO(2) and heptane, decrease with the exothermicity of the reactions until they reach -70 kcal mol(-1), but from there on an increase is observed. The first decrease in rate is typical of the "inverted region" of electron-transfer reactions. The change to an increase in the rate for ultra-exothermic electron transfer indicates a new free-energy relationship. We show that the resulting "double-inverted region" is not due to a change in mechanism. It is an intrinsic property of electron-transfer reactions, and it is due to the increase of the reorganisation energy with the reaction exothermicity. PMID:16548016

Serpa, Carlos; Gomes, Paulo J S; Arnaut, Luis G; Formosinho, Sebastião J; Pina, João; de Melo, J Seixas

2006-06-23

359

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

PubMed

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

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

2010-09-10

360

Reprint of: Ultrafast photoinduced electron transfer in conducting polymer-buckminsterfullerene composites  

NASA Astrophysics Data System (ADS)

We report time-resolved photoinduced absorption and time-resolved photoconductivity in conducting polymer-C60 composites. Photoinduced electron transfer occurs at times <1 ps. Two subgap features are observed in the photoinduced absorption of pure poly (3-octylthiophene) (P3OT); these form earlier than 1 ps and decay with ? < 5 ps. P3OT mixed with C60 shows similar spectral features at early times (<1 ps); however, a new spectrum evolves after ? 1 ps as a result of electron transfer from P3OT to C60. Ultrafast photoinduced electron transfer improves the quantum efficiency for photogeneration of charge carriers; in the ps domain the photoconductivity of the conducting polymer host is enhanced by more than an order of magnitude upon mixing in a few percent C60.

Kraabel, B.; Lee, C. H.; McBranch, D.; Moses, D.; Sariciftci, N. S.; Heeger, A. J.

2013-12-01

361

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

362

[Comparison of group transfer, inner shere and outer sphere electron transfer mechanisms for organometallic complexes]. Summary  

SciTech Connect

Our studies of reactions of metal carbonyl cations and anions have shown that metal carbonyl cations can catalyze CO exchange reactions on metal carbonyl anions. This result provides further evidence for a mechanism involving attack of the metal carbonyl anion on a carbon of the metal carbonyl cation in CO{sup 2+} transfer reactions. Reaction of metal carbonyl anions with metal carbonyl halides is a common approach to formation of metal-metal bonds. We have begun to use kinetic data and product analysis to understand the formation of homobimetallic versus heterobimetallic products in such reactions. Initial data indicate a nucleophilic attack, possibly through a ring-slippage mechanism.

Not Available

1991-12-31

363

Gold nanoparticles as electron reservoir redox catalysts for 4-nitrophenol reduction: a strong stereoelectronic ligand influence.  

PubMed

The stereoelectronic properties of the stabilizing ligands of gold nanoparticles (AuNPs) are shown to play a considerable role in their catalytic efficiency for 4-nitrophenol reduction by NaBH4, consistent with a mechanism involving restructuration of the AuNP surface that behaves as an "electron reservoir". PMID:25051189

Ciganda, Roberto; Li, Na; Deraedt, Christophe; Gatard, Sylvain; Zhao, Pengxiang; Salmon, Lionel; Hernández, Ricardo; Ruiz, Jaime; Astruc, Didier

2014-09-11

364

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

365

Improvement of a direct electron transfer-type fructose/dioxygen biofuel cell with a substrate-modified biocathode.  

PubMed

The fructose/dioxygen biofuel cell, one of the direct electron transfer (DET)-type bioelectrochemical devices, utilizes fructose dehydrogenase (FDH) on the anode and multi-copper oxidase such as bilirubin oxidase (BOD) on the cathode as catalysts. The power density in the literature is limited by the biocathode performance. We show that the DET-type biocathode performance is greatly improved, when bilirubin or some related substances are adsorbed on electrodes before the BOD adsorption. Several data show that the substrate modification induces the appropriate orientation of BOD on the electrode surface for the DET. The substrate-modification method has successfully been applied to air-breathing gas-diffusion-type biocathodes. We have also optimized the conditions of the FDH adsorption on carbon cryogel electrodes. Finally, a one-compartment DET-type biofuel cell without separators has been constructed, and the maximum power density of 2.6 mW cm(-2) was achieved at 0.46 V of cell voltage under quiescent (passive) and air atmospheric conditions. PMID:24469104

So, Keisei; Kawai, Shota; Hamano, Yasuyuki; Kitazumi, Yuki; Shirai, Osamu; Hibi, Makoto; Ogawa, Jun; Kano, Kenji

2014-03-14

366

The mechanism of homogeneous CO2 reduction by Ni(cyclam): product selectivity, concerted proton-electron transfer and C-O bond cleavage.  

PubMed

Homogeneous CO2 reduction catalyzed by [Ni(I)(cyclam)](+) (cyclam = 1,4,8,11-tetraazacyclotetradecane) exhibits high efficiency and selectivity yielding CO only at a relatively low overpotential. In this work, a density functional theory study of the reaction mechanism is presented. Earlier experiments have revealed that the same reaction occurring on mercury surfaces generates a mixture of CO and formate. According to the proposed mechanism, an ?(1)-CO2 adduct is the precursor for CO evolution, whereas formate is obtained from an ?(1)-OCO adduct. Our calculations show that generation of the ?(1)-CO2 adduct is energetically favored by ?14.0 kcal/mol relative to that of the ?(1)-OCO complex, thus rationalizing the product selectivity observed experimentally. Binding of ?(1)-CO2 to Ni(I) only leads to partial electron transfer from the metal center to CO2. Hence, further CO2 functionalization likely proceeds via an outer-sphere electron-transfer mechanism, for which concerted proton coupled electron transfer (PCET) is calculated to be the most feasible route. Final C-O bond cleavage involves rather low barriers in the presence of H3O(+) and H2CO3 and is therefore essentially concerted with the preceding PCET. As a result, the entire reaction mechanism can be described as concerted proton-electron transfer and C-O bond cleavage. On the basis of the theoretical results, the limitations of the catalytic activity of Ni(cyclam) are discussed, which sheds light on future design of more efficient catalysts. PMID:24957425

Song, Jinshuai; Klein, Eric L; Neese, Frank; Ye, Shengfa

2014-07-21

367

Titanium salan catalysts for the asymmetric epoxidation of alkenes: steric and electronic factors governing the activity and enantioselectivity.  

PubMed

A new insight into the highly enantioselective (up to >99.5?% ee) epoxidation of olefins in the presence of chiral titanium(IV) salan complexes is reported. A series of 14 chiral ligands with varying steric and electronic properties have been designed, and it was found that electronic effects modulate the catalytic activity (without affecting the enantioselectivity), whereas the steric properties account for the enantioselectivity of the epoxidation. Competitive oxidations of p-substituted styrenes reveal the electrophilic nature of the oxygen-transferring active species, with a Hammett ? value of -0.51; the enantioselectivity is unaffected by the electron-donating (or withdrawing) ability of the p-substituents. Mechanistic studies provide evidence in favor of a stepwise reaction mechanism: in the first (rate-determining) stage, olefin most probably coordinates to the active species, followed by intramolecular enantioselective oxygen transfer. The enantioselectivity increases with decreasing temperature. The modified Eyring plots for the epoxidation of styrene and (Z)-?-methylstyrene are linear, indicating a single, enthalpy-controlled mechanism of stereoselectivity, with ??H(?) =-6.6?kJ?mol(-1) and -5.4?kJ?mol(-1) , respectively. PMID:25213492

Talsi, Evgenii P; Samsonenko, Denis G; Bryliakov, Konstantin P

2014-10-27

368

Fast electron transfer from PbSe quantum dots to TiO2  

NASA Astrophysics Data System (ADS)

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

Masumoto, Yasuaki; Takagi, Hayato; Umino, Hikaru; Suzumura, Eri

2013-12-01

369

Alignment Effects in Collisionally Induced Electronic Energy Transfer: Experiment and Theory  

Microsoft Academic Search

The work presented here investigates how electronic energy transfer in atoms is affected by the geometry with which the atoms collide. Orbital alignment effects and branching fractions are measured for collisionally-induced electronic energy transfer from the Sr 5s6p ^1 P_1 state to seven near resonant states: 5s6p ^3P_ {2,1,0}, 4d5p ^1D _2, and 4d5p ^1F _{4,3,2}. The measurements are carried

Laurie Joan Kovalenko

1989-01-01

370

Electron transfer reactions of ruthenium(II)-bipyridine complexes carrying tyrosine moiety with quinones.  

PubMed

Three ruthenium(II)-bipyridine complexes carrying a tyrosine moiety were synthesized and photophysical and electron transfer studies with quinones were carried out using absorption and emission spectral techniques. The binding efficiency of quinones with ruthenium(II)-bipyridine complexes was also studied using these techniques. The binding efficiency was moderate and similar for all complexes with all quinones. The quenching modes were also similar and efficient for all complexes with all quinones. The quenching processes were diffusion controlled. The rate of electron transfer was calculated using semiclassical theory. Copyright © 2013 John Wiley & Sons, Ltd. PMID:24343838

Mareeswaran, Paulpandian Muthu; Rajkumar, Eswaran; Sathish, Veerasamy; Rajagopal, Seenivasan

2014-11-01

371

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

SciTech Connect

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

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

2013-12-04

372

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

NASA Astrophysics Data System (ADS)

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

Getoff, Nikola; Hartmann, Johannes; Schittl, Heike; Gerschpacher, Marion; Quint, Ruth Maria

2011-08-01

373

Electron Transfer Mechanism in Gold Surface Modified with Self-Assembly Monolayers from First Principles  

NASA Astrophysics Data System (ADS)

We report the investigation of electron tunneling mechanism of peptide ferrocenyl-glycylcystamine self-assembled monolayers (SAMs) onto Au (111) electrode surfaces. Recent experimental investigations showed that electron transfer in peptides can occur across long distances by separating the donor from the acceptor. This mechanism can be further fostered by the presence of electron donor terminations of Fc terminal units on SAMs but the charge transfer mechanism is still not clear. We study the interaction of the peptide ferrocenyl-glycylcystamine on the Au (111) from first principles calculations to evaluate the electron transfer mechanism. For this purpose, we used the Kohn Sham (KS) scheme for the Density Functional Theory (DFT) as implemented in the Quantum-ESPRESSO suit of codes, using Vandebilt ultrasoft pseudopotentials and GGA-PBE exchange correlation functional to evaluate the ground-state atomic and electronic structure of the system. The analysis of KS orbital at the Fermi Energy showed high electronic density localized in Fc molecules and the observation of a minor contribution from the solvent and counter ion. Based on the results, we infer evidences of electron tunneling mechanism from the molecule to the Au(111).

Lima, Filipe C. D. A.; Iost, Rodrigo M.; Crespilho, Frank N.; Caldas, Marília J.; Calzolari, Arrigo; Petrilli, Helena M.

2013-03-01

374

Experimental studies of fundamental issues in electron transfer through nanometer scale devices  

NASA Astrophysics Data System (ADS)

Electron transfer reactions constitute many of the primary events in materials science, chemistry, physics, and biochemistry, e.g. the electron transport properties and photoexcited processes in solids and molecules, chemical reactions, corrosion, photosynthesis, respiration, and so forth. A self-assembled monolayer (SAM) film provides us with a unique environment not only to understand and manipulate the surface electronic properties of a solid, but also to control electron transfer processes at the interface. The first topic in this thesis describes the structure and electron tunneling characterization of alkanethiol SAMs on InP(100). Angle-resolved X-ray photoelectron spectroscopy was used to characterize the bonding of alkanethiols to n-InP surfaces and to measure the monolayer thickness. The results showed that the sulfur binds to In atoms on the surface, and provided film thicknesses of 6.4 A for C8H17SH, 11.1 A for C12H25SH, and 14.9 A for C16H 33SH, resulting in an average tilt angle of 55°. The analysis indicated that super-exchange coupling between the alkane chains plays an important role in defining electron tunneling barriers, especially for highly tilted chains. The second topic describes studies of cytochrome c bound to pure and mixed SAMs of o-terminated alkanethiol (terminated with pyridine, imidazole or nitrile groups) and alkanethiol on gold. Electrochemical methods are used to determine electron transfer rate constants of cytochrome c, and scanning tunneling microscopy to observe the cytochrome c on the SAM. Detailed analysis revealed direct association of the heme of cytochrome c with the terminal groups of the SAMs and a 'turning-over' of the electron transfer of cytochrome c from adiabatic to non-adiabatic regime. The third topic describes studies of oxidation and reduction of cytochrome c in solution through eleven different self-assembled monolayers (SAMs) on gold electrodes by cyclic voltammetry. Electron transfer rate constants of cytochrome c through the eleven SAMs ranged from ?10-4 to ˜10-1 cm/sec. A strong correlation between the electron transfer rate constants and the hydrogen bonding ability of the SAM is identified. This correlation is discussed in terms of the dependence of the rate constant on the outer-sphere reorganization energy and the electronic coupling between the cytochrome and the differently terminated monolayer films.

Yamamoto, Hiromichi

375

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

376

Hydrodesulfurization catalysts prepared by two methods analyzed by transmission electron microscopy  

Microsoft Academic Search

Samples of molybdenum sulfide, cobalt sulfide and mixtures in atomic rations r = Co\\/(Co + Mo) of 0.0, 0.3, 0.5, 0.7, and 1.0 were prepared by two different methods, homogeneous sulfide precipitation (HSP) and impregnated thiosalt decomposition (ITD). Samples were observed by high-resolution electron microscopy using imaging and diffraction modes. Both preparation methods present the rag structure typical of MoSâ-2H

J. Cruz Reyes; M. Avalos Borja; M. H. Farias; S. Fuentes

1992-01-01

377

Inner reorganization limiting electron transfer controlled hydrogen bonding: intra- vs. intermolecular effects.  

PubMed

In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. log?KB[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate k, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, ?i,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental k. PMID:24653999

Martínez-González, Eduardo; Frontana, Carlos

2014-05-01

378

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

PubMed

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; Nagata, Kazuhiro

2013-09-16

379

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

380

Photoinduced electron transfer in donor-acceptor complexes of ethylene with molecular and atomic iodine.  

PubMed

Building upon our recent studies of radical addition pathways following excitation of the I2 chromophore in the donor-acceptor complex of ethylene and I2 (C2H4···I2), in this article, we extend our studies to examine photoinduced electron transfer. Thus, irradiation into the intense charge-transfer band of the complex (?max = 247 nm) gave rise to a band at 366 nm that is assigned to the bridged ethylene-I radical complex on the basis of our prior work. The formation of the radical complex is explained by a mechanism that involves rapid back electron transfer leading to I-I bond fission. Excitation into the charge-transfer band of the radical complex led to regeneration of the parent complex and the formation of the final photoproduct, anti- and gauche-1,2-diiodoethane, which confirms that the reaction proceeds ultimately by a radical addition mechanism. This finding is contrasted with our previous study of the C2H4···Br2 complex, where CT excitation led to only one product, anti-1,2-dibromoethane, a result explained by a single electron-transfer mechanism proceeding via a bridged bromonium ion intermediate. For the I2 complex, the breakup of the photolytically generated I2(-•) anion radical is apparently sufficiently slow to render it uncompetitive with back electron transfer. Finally, we report a detailed computational examination of the parent and radical complexes of both bromine and iodine, using high-level single- and multireference methods, which provide insight into the different behaviors of the charge-transfer states of the two radicals and the role of spin-orbit coupling. PMID:25075444

Kalume, Aimable; George, Lisa; Powell, Andrew D; Dawes, Richard; Reid, Scott A

2014-08-28

381

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.

382

Heterogeneous electron transfer studies with ligninolytic redox enzymes and living bacteria. Applications in biosensors and biofuel cells.  

E-print Network

??The catalytic properties and the inter-domain electron transfer of cellobiose dehydrogenase (CDH) from the ascomycete fungus Myriococcum thermophilum adsorbed on graphite and thiol (SAM) modified… (more)

Coman, Vasile

2009-01-01

383

Electronic materials high-T(sub c) superconductivity polymers and composites structural materials surface science and catalysts industry participation  

NASA Technical Reports Server (NTRS)

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

1988-01-01

384

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

385

Electron transfer and capture dynamics in ZnSe quantum wells grown on GaAs  

SciTech Connect

We investigate the transfer and capture dynamics of electrons in phase coherent photorefractive ZnSe quantum wells grown on GaAs using degenerate three-beam four-wave-mixing. The measurements reveal electron capture times by the quantum well in the order of several tens of picoseconds and a transit time of approximately 5 picoseconds from the GaAs substrate through the ZnMgSe barrier.

Dongol, A.; Wagner, H. P. [Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221 (United States)

2013-12-04

386

New degenerate metal-oxide electrodes for nearly reversible direct electron transfer to the redox proteins  

Microsoft Academic Search

Heavily doped cadmium tin oxide (CTO) film electrodes were developed for fast electron exchange with redox proteins. The metal oxide films showed nearly reversible electron transfer for the [2Fe–2S] proteins spinach ferredoxin (Sp fd) and putidaredoxin (Pdx), and the well-studied heme protein horse heart cytochrome c. These represent a family of proteins that are of comparable size, but vary significantly

Gintaras Valincius; Vytas Reipa; Martin P. Mayhew; Vincent L. Vilker

2002-01-01

387

Role of solvent dynamics in ultrafast photoinduced proton-coupled electron transfer reactions in solution.  

PubMed

A theoretical formulation for modeling photoinduced nonequilibrium proton-coupled electron transfer (PCET) reactions in solution is presented. In this formulation, the PCET system is described by donor and acceptor electron-proton vibronic free energy surfaces that depend on a single collective solvent coordinate. Dielectric continuum theory is used to obtain a generalized Langevin equation of motion for this collective solvent coordinate. The terms in this equation depend on the solvent properties, such as the dielectric constants, relaxation time, and molecular moment of inertia, as well as the solute properties characterizing the vibronic surfaces. The ultrafast dynamics following photoexcitation is simulated using a surface hopping method in conjunction with the Langevin equation of motion. This methodology is used to examine a series of model photoinduced PCET systems, where the initial nonequilibrium state is prepared by vertical photoexcitation from the ground electronic state to the donor electronic state. Analysis of the dynamical trajectories provides insight into the interplay between the solvent dynamics and the electron-proton transfer for these types of processes. In addition, these model studies illustrate how the coupling between the electron-proton transfer and the solvent dynamics can be tuned by altering the solute and solvent properties. PMID:20809583

Hazra, Anirban; Soudackov, Alexander V; Hammes-Schiffer, Sharon

2010-09-30

388

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

389

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

390

Fast electron transfer through a single molecule natively structured redox protein  

NASA Astrophysics Data System (ADS)

The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b562 in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum-iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be `gated' through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b562 molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent.The electron transfer properties of proteins are normally measured as molecularly averaged ensembles. Through these and related measurements, proteins are widely regarded as macroscopically insulating materials. Using scanning tunnelling microscopy (STM), we present new measurements of the conductance through single-molecules of the electron transfer protein cytochrome b562 in its native conformation, under pseudo-physiological conditions. This is achieved by thiol (SH) linker pairs at opposite ends of the molecule through protein engineering, resulting in defined covalent contact between a gold surface and a platinum-iridium STM tip. Two different orientations of the linkers were examined: a long-axis configuration (SH-LA) and a short-axis configuration (SH-SA). In each case, the molecular conductance could be `gated' through electrochemical control of the heme redox state. Reproducible and remarkably high conductance was observed in this relatively complex electron transfer system, with single-molecule conductance values peaking around 18 nS and 12 nS for the SH-SA and SH-LA cytochrome b562 molecules near zero electrochemical overpotential. This strongly points to the important role of the heme co-factor bound to the natively structured protein. We suggest that the two-step model of protein electron transfer in the STM geometry requires a multi-electron transfer to explain such a high conductance. The model also yields a low value for the reorganisation energy, implying that solvent reorganisation is largely absent. Electronic supplementary information (ESI) available: Experimental methods, DNA and protein sequences, additional STM statistical analysis and images, electrochemical data and It-z data analysis. See DOI: 10.1039/c2nr32131a

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

2012-10-01

391

The Fragments of the Photosynthetic Electron Transfer Chain in Model Systems  

PubMed Central

In this paper the recent research from our laboratory is reviewed. Short fragments of the photochemical electron transfer chain of photosynthesis were reproduced in aqueous detergent solutions or in organic solvents. The function of photosystem I is reproduced in a ternary system of chlorophylls, electron donors (dienols, sulfhydryl compounds, hydrazine, etc.), and electron acceptors (viologens, nicotinamide-adenine dinucleotide [NAD], flavines, etc.). Chlorophyll-photosensitized reduction of viologens in some cases is activated by oxygen at the expense of active reductants formed during the photosensitized oxidation of an initial electron donor (thiourea). Chlorophyll-photosensitized oxidoreduction of cytochromes is activated by flavines, viologens, vitamin K derivatives, and some other redox systems (cofactors of cyclic photophosphorylation). The primary mechanism of the reactions studied depends on the reversible chlorophyll photooxidoreduction. In binary systems, chlorophyll (monomeric or aggregated) and electron donor or electron acceptor, reversible photoreduction or photooxidation is observed. Irreversible bacteriochlorophyll oxidation leads to the formation of chlorophyll and protochlorophyll analogues; irreversible protochlorophyll photoreduction results in chlorophyll-like pigment appearance. The photodisaggregation of chlorophyll was observed. The models of photosystem II studied were the photochemical oxygen evolution in aqueous solutions of electron acceptors (ferric compounds, quinone), photosensitized in the near UV part of the spectrum by inorganic semiconductors (tungsten, titanium, and zinc oxides). All reactions described are based on electron (hydrogen) transfer photosensitized by pigment system. PMID:4338745

Krasnovsky, A. A.

1972-01-01

392

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

...Fluorinated Heat Transfer Fluids Used by the Electronics Industry I Table I-2 to Subpart...MANDATORY GREENHOUSE GAS REPORTING Electronics Manufacturing Pt. 98, Subpt. I...Fluorinated Heat Transfer Fluids Used by the Electronics Industry Product type...

2014-07-01

393

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

...Fluorinated Heat Transfer Fluids Used by the Electronics Industry I Table I-2 to Subpart...MANDATORY GREENHOUSE GAS REPORTING Electronics Manufacturing Pt. 98, Subpt. I...Fluorinated Heat Transfer Fluids Used by the Electronics Industry Product type...

2013-07-01

394

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

395

Influence of adsorption on photoinduced electron transfer in supported liquid membranes: the case of C 60  

Microsoft Academic Search

Porous polymer membranes modified by the incorporation of a decane mixture of fullerene and phospholipids have photoconducting properties which depend on the nature of the polymer. We show that the mechanism of bilayer lipid membrane formation usually used to explain these photoconducting properties by electron transfer, is not pertinent when explaining the influence of the membrane surface properties on the

E. Tronelpeyroz; G. Miquelmercier; P. Vanel; P. Seta

1998-01-01

396

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

397

Light-induced electron transfer in Arabidopsis cryptochrome-1 correlates with in vivo function.  

PubMed

Cryptochromes are blue light-activated photoreceptors found in multiple organisms with significant similarity to photolyases, a class of light-dependent DNA repair enzymes. Unlike photolyases, cryptochromes do not repair DNA and instead mediate blue light-dependent developmental, growth, and/or circadian responses by an as yet unknown mechanism of action. It has recently been shown that Arabidopsis cryptochrome-1 retains photolyase-like photoreduction of its flavin cofactor FAD by intraprotein electron transfer from tryptophan and tyrosine residues. Here we demonstrate that substitution of two conserved tryptophans that are constituents of the flavin-reducing electron transfer chain in Escherichia coli photolyase impairs light-induced electron transfer in the Arabidopsis cryptochrome-1 photoreceptor in vitro. Furthermore, we show that these substitutions result in marked reduction of light-activated autophosphorylation of cryptochrome-1 in vitro and of its photoreceptor function in vivo, consistent with biological relevance of the electron transfer reaction. These data support the possibility that light-induced flavin reduction via the tryptophan chain is the primary step in the signaling pathway of plant cryptochrome. PMID:15774475

Zeugner, Anke; Byrdin, Martin; Bouly, Jean-Pierre; Bakrim, Nadia; Giovani, Baldissera; Brettel, Klaus; Ahmad, Margaret

2005-05-20

398

Histidine is involved in coupling proton uptake to electron transfer in photosynthetic proteins  

Microsoft Academic Search

In photosynthesis, the central step in transforming light energy into chemical energy is the coupling of light-induced electron transfer to proton uptake and release. Despite intense investigations of different photosynthetic protein complexes, including the photosystem II (PS II) in plants and the reaction center (RC) in bacteria, the molecular details of this fundamental process remain incompletely understood. In the RC

Delphine Onidas; Joanna M. Stachnik; Sven Brucker; Steffen Krätzig; Klaus Gerwert

2010-01-01

399

Solvent-Induced Electron Transfer and Delocalization in Mixed-Valence Complexes. Electrochemistry  

E-print Network

. For unsymmetrical complexes G� * 0, and the free energy change is usually solvent dependent as well.1f,5d,8Solvent-Induced Electron Transfer and Delocalization in Mixed-Valence Complexes. Electrochemistry,2-bipyridine; 4,4-bpy ) 4,4- bipyridine), E1/2 varies linearly with the donor number (DN) of the solvent

400

Quantum correction for electron transfer rates. Comparison of polarizable versus nonpolarizable descriptions of solvent  

E-print Network

descriptions of solvent Xueyu Song and R. A. Marcus Arthur Amos NoyesLaboratory of Chemical Physics,`) 127 of the frequency spectrum. I. INTRODUCTION Electron transfer reactions are among the most funda- mental chemical the dielec- tric response in one region important for the quantum cor- rection and underestimate

Song, Xueyu

401

Evidence for Orbital-Specific Electron Transfer to Oriented Haloform Molecules  

E-print Network

molecules have been oriented by "brute force" techniques,14,15 and a number of small symmetric tops have for their intrinsic interest. Whereas most small molecules are near-prolate tops18 which are difficult to spin aboutEvidence for Orbital-Specific Electron Transfer to Oriented Haloform Molecules Beike Jia, Jonathan

Brooks, Philip R.

402

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

403

Laser pulse control of ultrafast heterogeneous electron transfer: A computational study  

E-print Network

Laser pulse control of ultrafast heterogeneous electron transfer: A computational study Luxia Wang, Germany Received 31 March 2004; accepted 30 July 2004 Laser pulse control of the photoinduced 90 fs charge in which way the charge injection time can be changed by tailored laser pulses. In a second step a pump

Röder, Beate

404

Ground and Excited State Intramolecular Proton Transfer in Salicylic Acid: an Ab Initio Electronic Structure Investigation  

E-print Network

emission in the fluorescence spectrum of salicylic acid and methyl salicylate and attributedGround and Excited State Intramolecular Proton Transfer in Salicylic Acid: an Ab Initio Electronic in salicylic acid have been studied by ab initio molecular orbital calculations using the 6-31G** basis set

Chowdhury, Arindam

405

Triphenylmethane dyes, an alternative for mediated electronic transfer systems in glucose oxidase biofuel cells  

Microsoft Academic Search

The bioelectrochemical behavior of three triphenylmethane (TPM) dyes commonly used as pH indicators, and their application in mediated electron transfer systems for glucose oxidase bioanodes in biofuel cells was investigated. Bromophenol Blue, Bromothymol Blue, Bromocresol Green were compared bioelectrochemically against two widely used mediators, benzoquinone and ferrocene carboxy aldehyde. Biochemical studies were performed in terms of enzymatic oxidation, enzyme affinity,

Gustavo P. M. K. Ciniciato; Ernesto R. González

2011-01-01

406

Release of oxidized plastocyanin from photosystem I limits electron transfer between photosystem I and  

E-print Network

), and cytochrome (cyt) f oxidation kinetics in Chlamydomonas reinhardtii mutants in which either the bindingRelease of oxidized plastocyanin from photosystem I limits electron transfer between photosystem I and cytochrome b6f complex in vivo Giovanni Finazzi* , Frederik Sommer , and Michael Hippler *Unite´ Mixte de

407

De Novo Design of a Cytochrome b Maquette for Electron Transfer and Coupled Reactions on Electrodes  

E-print Network

for cytochrome b as well as the coupling of the b-heme oxidation and reduction to proton exchange. The pDe Novo Design of a Cytochrome b Maquette for Electron Transfer and Coupled Reactions on Electrodes maquettes that bis-histidine ligate protoporphyrin IX (heme), much like native b cytochromes, as well

Gibney, Brian R.

408

Novel [4+2] cycloaddition between thiobenzophenone and aryl-substituted alkenes via photoinduced electron transfer.  

PubMed

The [4+2] cycloaddition products between thiobenzophenone (1) and arylalkenes (2) were obtained in the presence of (thia)pyrylium salts (sensitizer=3 or 4) as electron transfer photosensitizers. Although both radical cations 1*+ and 2*+ are generated, only the former is involved in the process. PMID:17672473

Argüello, Juan E; Pérez-Ruiz, Raúl; Miranda, Miguel A

2007-08-30

409

Marcus Theory: Thermodynamics CAN Control the Kinetics of Electron Transfer Reactions  

ERIC Educational Resources Information Center

Although it is generally true that thermodynamics do not influence kinetics, this is NOT the case for electron transfer reactions in solution. Marcus Theory explains why this is so, using straightforward physical chemical principles such as transition state theory, Arrhenius' Law, and the Franck-Condon Principle. Here the background and…

Silverstein, Todd P.

2012-01-01

410

Biosensors based on novel peroxidases with improved properties in direct and mediated electron transfer  

Microsoft Academic Search

Native horseradish peroxidase (HRP) on graphite has revealed ?50% of the active enzyme molecules to be in direct electron transfer (ET) contact with the electrode surface. Some novel plant peroxidases from tobacco, peanut and sweet potato were kinetically characterised on graphite in order to find promising candidates for biosensor applications and to understand the nature of the direct ET in

Annika Lindgren; Tautgirdas Ruzgas; Lo Gorton; Elisabeth Csöregi; Gerardo Bautista Ardila; Ivan Yu Sakharov; Irina G Gazaryan

2000-01-01

411

ELUCIDATING THE ROLE OF ELECTRON TRANSFER MEDIATORS IN REDUCTIVE TRANSFORMATIONS IN NATURAL SEDIMENTS  

EPA Science Inventory

To study the identity and reactivity of electron transfer mediators (ETMs) in natural sediments, the reduction kinetics of a glass bead-azo dye complex were measured in abiotic and biotic model systems, as well as in natural sediments. In abiotic model systems, the bead-dye comp...

412

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

SciTech Connect

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M.R.

1992-08-01

413

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: From charge separation and storage to molecular switches  

SciTech Connect

Photoinduced charge separation reactions form the basis for energy storage processes in both natural and artificial photosynthesis. Moreover, rapid reversible photoinduced electron transfer reactions are a class of photophysical phenomena that can be exploited to develop schemes for optical switching. Examples from each of these fields are discussed.

Wasielewski, M.R.

1992-01-01

414

Computational studies on electron and proton transfer in phenol-imidazole-base triads.  

PubMed

The electron and proton transfer in phenol-imidazole-base systems (base = NH(2)(-) or OH(-)) were investigated by density-functional theory calculations. In particular, the role of bridge imidazole on the electron and proton transfer was discussed in comparison with the phenol-base systems (base = imidazole, H(2)O, NH(3), OH(-), and NH(2)(-)). In the gas phase phenol-imidazole-base system, the hydrogen bonding between the phenol and the imidazole is classified as short strong hydrogen bonding, whereas that between the imidazole and the base is a conventional hydrogen bonding. The n value in sp(n) hybridization of the oxygen and carbon atoms of the phenolic CO sigma bond was found to be closely related to the CO bond length. From the potential energy surfaces without and with zero point energy correction, it can be concluded that the separated electron and proton transfer mechanism is suitable for the gas-phase phenol-imidazole-base triads, in which the low-barrier hydrogen bond is found and the delocalized phenolic proton can move freely in the single-well potential. For the gas-phase oxidized systems and all of the triads in water solvent, the homogeneous proton-coupled electron transfer mechanism prevails. PMID:19479733

Yan, Shihai; Kang, Sunwoo; Hayashi, Tomoyuki; Mukamel, Shaul; Lee, Jin Yong

2010-01-30

415

Distance Dependence of Electron Transfer in DNA: The Role of the Reorganization Energy and Free Energy  

E-print Network

Distance Dependence of Electron Transfer in DNA: The Role of the Reorganization Energy and Free of the solvent reorganization energy and free energy in the heterogeneous DNA environment. DNA is modeled represents water. Model calculations show the importance of including the reorganization energy and the free

Fayer, Michael D.

416

Modeling the free energy surfaces of electron transfer in condensed phases  

E-print Network

PROOF COPY 509037JCP Modeling the free energy surfaces of electron transfer in condensed phases analytical solution for the ET free energy surfaces demonstrates the following features: i the range of ET reaction coordinates is limited by a one-sided fluctuation band, ii the ET free energies are infinite

Matyushov, Dmitry

417

Non-adiabatic molecular dynamics simulation of ultrafast solar cell electron transfer  

E-print Network

effects are incorporated by the quantum-classical mean-field approach. A novel procedure separating the NANon-adiabatic molecular dynamics simulation of ultrafast solar cell electron transfer William Stier Received 7 August 2002; accepted 15 November 2002 Abstract A non-adiabatic (NA) molecular dynamics (MD

418

Oxygen Isotope Effects as Probes of Electron Transfer Mechanisms and Structures of  

E-print Network

Oxygen Isotope Effects as Probes of Electron Transfer Mechanisms and Structures of Activated O2, Maryland 21218 RECEIVED ON JULY 26, 2008 C O N S P E C T U S Competitively determined oxygen (18 O) isotope- dative processes. This Account describes efforts to advance oxygen kinetic isotope effects (18 O KIEs

Roth, Justine P.

419

Nonadiabatic electron transfer at the nanoscale tin-oxide semiconductor/aqueous solution interface  

E-print Network

conversion � for example, Gr�tzel cells.1�3 We have examined the kinetics of back electron transfer (bET the semiconductor surface states.4 For a variety of experimental reasons, we have focused on bET from negatively described by semi-classical Marcus theory.8,9 At modest driving forces, bET rates increase with increasing

420

Photoinduced electron transfer from rail to rung within a self-assembled oligomeric porphyrin ladder  

SciTech Connect

Photoinduced electron transfer in a self-assembled supramolecular ladder structure comprising oligomeric porphyrin rails and ligated dipyridyltetrazine rungs was characterized by transient absorption spectroscopy and transient direct current photoconductivity to be mainly from an oligomer (rail) to the center of a terminal tetrazine (rung), with the remaining hole being delocalized on the oligomer and subsequent charge recombination in 0.19 ns.

She, Chunxing; Lee, Suk Joong; McGarrah, James E.; Vura-Weis, Josh; Wasielewski, Michael; Chen, Hanning; Schatz, George C.; Ratner, Mark A.; Hupp, Joseph T.

2010-01-01