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1

Intermittent Single-Molecule Interfacial Electron Transfer Dynamics  

International Nuclear Information System (INIS)

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

2

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

International Nuclear Information System (INIS)

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

3

Remote interfacial electron transfer processes on nanocrystalline TiO2 sensitized with polynuclear complexes  

Directory of Open Access Journals (Sweden)

Full Text Available The kinetic study of interfacial electron transfer in sensitized nanocrystalline semiconductor is essential to the design of molecular devices performing specific light induced functions in a microheterogeneous environment. A series of molecular assemblies performing direct and remote charge injection to the semiconductor have been discussed in the context of artificial photosynthesis. A particular attention in this article has been paid to the factors that control the interfacial electron transfer processes in nanocrystalline TiO2 films sensitized with mononuclear and polynuclear transition metal complexes.

G. J. Meyer

1999-01-01

4

Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy  

Science.gov (United States)

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

5

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

CERN Document Server

Interfacial electron transfer (IET) dynamics in 1,1'-dioctadecyl-3, 3, 3', 3'-tetramethylindodicarbocyanine (DiD) dye molecules / indium tin oxide (ITO) film system have been probed at the ensemble and single-molecule level by recording the change of fluorescence emission intensity. By comparing the difference of the external electric current (EEC) dependence of lifetime and intensity for enambles and single molecules, it is shown that the single-molecule probe can effcienly demonstrate the IET dynamics. The backward electron transfer and electron transfer of ground state induce the single molecules fluorescence quenching when an EEC is applied to ITO film.

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

2011-01-01

6

Investigation of liquid-liquid interfacial electron transfer kinetics using multicenter ferrocenyl complexes  

International Nuclear Information System (INIS)

The redox behavior of two novel multicenter redox molecules (triferrocenylmethane and triferrocenylmethanol) has been studied in a thin film of nitrobenzene (NB) imposed between a graphite electrode and an aqueous electrolyte. The well separated three sets of redox peaks indicate strong intramolecular electronic communications between the three ferrocene centers in each molecule. They were adapted as model compounds for the study of electron transfer kinetics across the liquid/liquid interface with varied overall driving force using only one-type redox couples in the organic and aqueous phase, respectively. It has been shown that in both cases the dependence of interfacial electron transfer rate on the increased overall driving force across the nitrobenzene/water interface is not monotonic.

7

Investigation of liquid-liquid interfacial electron transfer kinetics using multicenter ferrocenyl complexes  

Energy Technology Data Exchange (ETDEWEB)

The redox behavior of two novel multicenter redox molecules (triferrocenylmethane and triferrocenylmethanol) has been studied in a thin film of nitrobenzene (NB) imposed between a graphite electrode and an aqueous electrolyte. The well separated three sets of redox peaks indicate strong intramolecular electronic communications between the three ferrocene centers in each molecule. They were adapted as model compounds for the study of electron transfer kinetics across the liquid/liquid interface with varied overall driving force using only one-type redox couples in the organic and aqueous phase, respectively. It has been shown that in both cases the dependence of interfacial electron transfer rate on the increased overall driving force across the nitrobenzene/water interface is not monotonic.

Xiang Debo [Department of Chemistry, Faculty of Science, Beijing Institute of Technology, Beijing 100081 (China); Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Merbouh, Nabyl [Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada); Shao Huibo [Department of Chemistry, Faculty of Science, Beijing Institute of Technology, Beijing 100081 (China); Yu Huazhong, E-mail: hogan_yu@sfu.ca [Department of Chemistry, Simon Fraser University, Burnaby, British Columbia V5A 1S6 (Canada)

2011-06-30

8

Interfacial electron transfer dynamics of ru(II)-polypy6ridine sensitized TiO2  

Energy Technology Data Exchange (ETDEWEB)

Quantum dynamics simulations combined with density functional theory calculations are applied to study interfacial electron transfer (IET) from pyridine-4-phosphonic acid, [Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 2+} and [Ru(tpy)(bpy)(H{sub 2}O)-Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 4+} into the (101) surface of anatase TiO{sub 2}. IET rate from pyridine-4-phosphonic acid attached to the nanoparticle in bidentate mode ({tau} {approx} 100 fs) is an order of magnitude faster than the IET rate of the adsorbate attached in the monodentate mode ({tau} {approx} 1 ps). Upon excitation with visible light, [Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 2+} attached to TiO{sub 2} in bidentate binding mode will undergo IET with the rate of {approx} 1-10 ps, which is competitive with the excited state decay into the ground state. The probability of electron injection from [Ru(tpy)(bpy)(H{sub 2}O)-Ru(tpy)(tpy(PO{sub 3}H{sub 2}))]{sup 4+} is rather low, as the excitation with visible light localizes the excited electron in the tpy-tpy bridge, which does not have favorable coupling with the TiO{sub 2} nanoparticle. The results are relevant to better understanding of the adsorbate features important for promoting efficient interfacial electron transfer into the semiconductor.

Jakubikova, Elena [Los Alamos National Laboratory; Martin, Richard L [Los Alamos National Laboratory; Batista, Enrique R [Los Alamos National Laboratory; Snoeberger, Robert C [YALE UNIV.; Batista, Victor S [YALE UNIV.

2009-01-01

9

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

Energy Technology Data Exchange (ETDEWEB)

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

Lian, Tianquan

2014-04-22

10

Interfacial electrochemical electron transfer in biology – Towards the level of the single molecule  

DEFF Research Database (Denmark)

Physical electrochemistry has undergone a remarkable evolution over the last few decades, integrating advanced techniques and theory from solid state and surface physics. Single-crystal electrode surfaces have been a core notion, opening for scanning tunnelling microscopy directly in aqueous electrolyte (in situ STM). Interfacial electrochemistry of metalloproteins is presently going through a similar transition. Electrochemical surfaces with thiol-based promoter molecular monolayers (SAMs) as biomolecular electrochemical environments and the biomolecules themselves have been mapped with unprecedented resolution, opening a new area of single-molecule bioelectrochemistry. We consider first in situ STM of small redox molecules, followed by in situ STM of thiol-based SAMs as molecular views of bioelectrochemical environments. We then address electron transfer metalloproteins, and multi-centre metalloenzymes including applied single-biomolecular perspectives based on metalloprotein/metallic nanoparticle hybrids.

Zhang, Jingdong; Chi, Qijin

2012-01-01

11

Gold nanoparticle assisted assembly of a heme protein for enhancement of long-range interfacial electron transfer  

DEFF Research Database (Denmark)

Interfacial electron transfer (ET) of biological macromolecules such as metalloproteins is the key process in bioelectrochemistry, enzymatic electrocatalysis, artificial ET chains, single-molecule electronic amplification and rectification, and other phenomena associated with the area of bioelectronics. A key challenge in molecular bioelectronics is to improve the efficiency of long-range charge transfer. The present work shows that this can be achieved by nanoparticle (NP) assisted assembly of cytochrome c (cyt c) on macroscopic single-crystalline electrode surfaces. We present the synthesis and characterization of water-soluble gold nanoparticles (AuNPs) with core diameter 3-4 nm and their application for the enhancement of long-range interfacial ET of a heme protein. Gold nanoparticles were electrostatically conjugated with cyt c to form nanoparticle-protein hybrid ET systems with well-defined stoichiometry. The systems were investigated in homogeneous solution and at liquid/solid interface. Conjugation ofcyt c results in a small but consistent broadening of the nanoparticle plasmon band. This phenomenon can be explained in terms of long-range electronic interactions between the gold nanoparticle and the protein molecule. When the nanoparticle-protein conjugates are assembled on Au(111) surfaces, long-range interfacial ET across a physical distance of over 50 A via the nanoparticle becomes feasible. Moreover, significant enhancement of the interfacial ET rate by more than an order of magnitude compared with that of cyt c in the absence of AuNPs is observed. AuNPs appear to serve as excellent ET relays, most likely by facilitating the electronic coupling between the protein redox center and the electrode surface.

Jensen, Palle Skovhus; Chi, Qijin

2007-01-01

12

Kinetics of interfacial electron transfer at single-layer graphene electrodes in aqueous and nonaqueous solutions.  

Science.gov (United States)

We present a catalog of electron transfer mediators for investigating the heterogeneous electron transfer kinetics of large-area, single-layer graphene electrodes. Scanning electrochemical microscopy (SECM) was used to probe the apparent standard electron transfer rate constant of mediators in aqueous solutions and in acetonitrile and dimethylformamide, allowing for studies of graphene electroactivity at different potentials and in both aqueous and nonaqueous media. In aqueous solution, iron(III) ethylenediaminetetraacetic acid, hexacyanoruthenate(II), hexacyanoferrate(II), hexacyanoferrate(III), octacyanomalybdate(IV), cobalt(III) sepulchrate, and hydroxymethylferrocene exhibited quasi-reversible electron transfer behavior. The electron transfer kinetics of hexaammineruthenium(III), methyl viologen, and tris(2,2'-bipyridyl)ruthenium(II) were found to be reversible in these studies. The electron transfer rate constant of hydroxymethylferrocene and ferrocene, in organic media, was similar to that for hydroxymethylferrocene in water, which, although fast, shows clear kinetic complications that we believe are inherent to graphene. A series of viologens, known to be reversible at metal electrodes, exhibited quasi-reversible electron transfer. For [Co(dapa)(2)](2+), where dapa is 2,6-bis[1-(phenylimino)ethyl]pyridine, in dimethylformamide, the oxidation state of the redox pair investigated affected the observed kinetics. Under similar experimental conditions, the Co(I/II) couple exhibited nearly reversible behavior whereas Co(II/III) had finite kinetics. This behavior was ascribed to the large difference in self-exchange rates for these two processes. To demonstrate the utility of using these mediators for examining graphene electrodes, the kinetics of two mediators with quasi-reversible electron transfer behavior, iron ethylenediaminetetraacetic acid and hexacyanoruthenate, were measured in the presence of a redox-active species [Os(bpy)(2)(dipy)Cl]PF(6), where bpy is 2,2'-bipyridine and dipy is 4,4'-trimethylenedipyridine, adsorbed onto the graphene surface. The kinetics of both mediators were enhanced in the presence of one-hundredth of a monolayer of the osmium complex, showing that even small amounts of impurities on the graphene surface are capable of enhancing the observed kinetics. PMID:23305445

Ritzert, Nicole L; Rodríguez-López, Joaquín; Tan, Cen; Abruña, Héctor D

2013-02-01

13

Hafnium metallocene compounds used as cathode interfacial layers for enhanced electron transfer in organic solar cells  

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We have used hafnium metallocene compounds as cathode interfacial layers for organic solar cells [OSCs]. A metallocene compound consists of a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure. For the fabrication of the OSCs, poly[3,4-ethylenedioxythiophene]:poly(styrene sulfonate), poly(3-hexylthiophene-2,5-diyl) + [6,6]-phenyl C61 butyric acid methyl ester, bis-(ethylcyclopentadienyl)hafnium(IV) dichloride, and aluminum were deposited as a hole transport ...

Park, Keunhee; Oh, Seungsik; Jung, Donggeun; Chae, Heeyeop; Kim, Hyoungsub; Boo, Jin-hyo

2012-01-01

14

Long-Range Interfacial Electrochemical Electron Transfer of Pseudomonas aeruginosa Azurin-Gold Nanoparticle Hybrid Systems  

DEFF Research Database (Denmark)

We have prepared a "hybrid" of the blue copper protein azurin (Pseudomonas aeruginosa) and a 3 nm gold nanoparticle (AuNP). The AuNP/azurin hybrid was assembled on a Au(111)-electrode surface in a two-step process. The AuNP was first attached to the Au(111) electrode via Au-S chemisorption of a 4,4'-biphenyidithiol (4,4'-BPDT) monolayer. This was followed by 1-decanethiol modification of the bound AuNP and hydrophobic binding of azurin to the AuNP. The Au(111)/AuNP/azurin system was characterized by atomic force microscopy (AFM), cyclic voltammetry (CV), and in situ electrochemical scanning tunneling microscopy (in situ STM). AFM and STM point to the feasibility of preparing both dense and sparsely populated AuNP monolayers. CV shows two pairs of voltammetric peaks at high scan rates, both around the azurin equilibrium potential. One pair of redox peaks follows closely that of azurin hydrophobically immobilized directly on a Au(111)/1-tetradecanethiol reference surface. The other pair, tentatively assigned tothe AuNP/azurin hybrid, shows a 20-fold electron transfer rate enhancement over the reference system. This dual pattern is supported by in situ STM which shows two distinct contrasts. A strong contrast most likely arises either from azurin-free AuNPs or from AuNP-free azurin displaced onto the Au(111)/4,4'-BPDT surface. The other contrast, assigned to the AuNP/azurin hybrid, is weaker and fluctuates in time. Mechanisms of electronic conductivity of the AuNP/azurin system are discussed.

Jensen, Palle Skovhus; Chi, Qijin

2009-01-01

15

Adsorption and interfacial electron transfer of Saccharomyces cerevisiae yeast cytochrome c monolayers on Au(111) electrodes  

DEFF Research Database (Denmark)

We have studied the adsorption and electron-transfer dynamics of Saccharomyces cerevisiae (yeast) iso-1-cytochrome c adsorbed on Au(111) electrodes in aqueous phosphate buffer media. This cytochrome possesses a thiol group close to the protein surface (Cys102) suitable for linking the protein to gold without drastic protein unfolding. A comprehensive approach, based on linear sweep and differential pulse voltammetry, capacitance measurements, X-ray photoelectron spectroscopy (XPS), in situ scanning tunneling microscopy (STM), and microcantilever sensor (MCS) techniques has been used. The voltammetric data display a thiol reductive desorption signal corresponding to close to monolayer coverage. Reductive desorption is also reflected in a capacitance peak. Voltammetric signals from the heme group in both native and partially denatured states could also be detected. XPS shows clear Au-S bond formation, but this observation is not conclusive for aqueous buffer conditions, as the protein is extensively unfolded under ultrahigh vacuum conditions needed for XPS. In situ STM discloses clear sub-monolayer coverage to molecular resolution. Imaging is robust in a 0.2 V electrochemical potential range negative of the equilibrium potential of YCC, where the protein is electrochemically functional. The MCS data show tensile differential stress signals when YCC is adsorbed on a gold-coated MCS, with distinguishable adsorption phases in the time range from

Hansen, Allan Glargaard; Boisen, Anja

2003-01-01

16

Adsorption and Interfacial Electron Transfer of Saccharomyces Cerevisiae : Yeast Cytochrome c Monolayers on Au(111) Electrodes  

DEFF Research Database (Denmark)

We have studied the adsorption and electron-transfer dynamics of Saccharomyces cerevisiae (yeast) iso-l-cytochrome c adsorbed on Au(lll) electrodes in aqueous phosphate buffer media. This cytochrome possesses a thiol group dos e to the protein surface (Cysl02) suitable for linking the protein to gold without drastic protein unfolding. A comprehensive approach, based on linear sweep and differential pulse voltammetry, capacitance measurements, X-ray photoelectron spectroscopy (XPS) , in situscanning tunneling microscopy (STM), and microcantilever sensor (MCS) techniques has been used. The voltammetric data display a thiol reductive desorption signal corresponding to dase to monolayer coverage. Reductive desorption is also reflected in a capacitance peak. Voltammetric signals from the heme group in both native and partially denatured states could also be detected. XPS shows dear Au -S band formation, but this observation is not condusive for aqueous buffer conditions, as the protein is extensively unfolded under ultrahigh vacuum conditions needed for XPS. In situ STM disdoses de ar sub-monolayer coverage to molecular resolution. Imaging is robust in a 0.2 V electrochemical potential range negative ofthe equilibrium potential of YCC, where the protein is electrochemically functional. The MCS data show tensile differential stress signals when YCC is adsorbed on a gold-coate d MCS, with distinguishable adsorption phases in the time range from <102 s to several thousand seconds. Comprehensive approaches to the mapping of adsorbed functional redox metalloproteins toward the single-molecule level, such as in the present study, will be important in the construction of nanoscale devices for multifarious biological and environmental screening.

Andersen, Jens Enevold Thanulov

2003-01-01

17

Mechanisms of interfacial electron-transfer within high-surface-area metal-oxide thin films  

Science.gov (United States)

The direct conversion of solar photon energy into electrical power is achieved with photovoltaic technology, yet existing technology is too inefficient or expensive to implement on a global scale. Dye sensitized solar cells (DSSCs) based on earth abundant low cost materials could overcome the barriers for world-wide implantation of photovoltaic technology. Historically the most efficient regenerative DSSCs utilize iodide based redox mediators in nitrile solvents. Despite the dominance of iodide redox mediator in DSSCs, the chemical attribute(s) that make iodide based electrolytes superior to other electrolyte is yet unproven. Discovering the chemical cause of iodide's superiority as a redox mediator was and important aspect of this thesis research. In Chapter 2 the photoinitated formation and cleavage of I-I bonds is demonstrated at an un-sensitized potentiostatically controlled mesoporous nanocrystalline (anatase) TiO2 thin film. After pulsed laser excitation of a TiO2 thin film, I2·- was observed that disproportionated to yield I3- and I-, but did not react with TiO2. In contrast evidence for a quasi-Fermi level dependent reaction between TiO2(e -) and I3- was observed. In agreement with the findings at un-sensitized TiO2 in Chapter 2, the results presented in Chapter 3 demonstrate that after pulsed laser excitation of an operational DSSC: I2·- is observed, I2·-does not react with TiO 2, and that charge recombination between I3- and TiO2(e-) is operative. In addition to absorption changes attributed to iodide redox chemistry, evidence for a transient electric field induced Stark effect was observed in the operational DSSC. Absorption changes reporting on the electric field at the TiO2 surface were simultaneously quantified at specific power conditions fo the operational DSSC. Chapter 4 explores alternative redox mediators to the iodide/triiodide couple. The photophysical studies presented herein provide key mechanistic details on kinetic processes pertinent to operational DSSCs. Specifically, electron transfer to and from iodide species found in an operational DSSC were quantified. Taken together this research advances the body of knowledge quantifying the chemical properties that make iodide based electrolytes a superior redox mediator in dye sensitized solar cells.

Rowley, John G.

18

Solvent isotope effects on interfacial protein electron transfer in crystals and electrode films.  

Science.gov (United States)

D(2)O-grown crystals of yeast zinc porphyrin substituted cytochrome c peroxidase (ZnCcP) in complex with yeast iso-1-cytochrome c (yCc) diffract to higher resolution (1.7 A) and pack differently than H(2)O-grown crystals (2.4-3.0 A). Two ZnCcP's bind the same yCc (porphyrin-to-porphyrin separations of 19 and 29 A), with one ZnCcP interacting through the same interface found in the H(2)O crystals. The triplet excited-state of at least one of the two unique ZnCcP's is quenched by electron transfer (ET) to Fe(III)yCc (k(e) = 220 s(-1)). Measurement of thermal recombination ET between Fe(II)yCc and ZnCcP+ in the D(2)O-treated crystals has both slow and fast components that differ by 2 orders of magnitude (k(eb)(1) = 2200 s(-1), k(eb)(2) = 30 s(-1)). Back ET in H(2)O-grown crystals is too fast for observation, but soaking H(2)O-grown crystals in D(2)O for hours generates slower back ET, with kinetics similar to those of the D(2)O-grown crystals (k(eb)(1) = 7000 s(-1), k(eb)(2) = 100 s(-1)). Protein-film voltammetry of yCc adsorbed to mixed alkanethiol monolayers on gold electrodes shows slower ET for D(2)O-grown yCc films than for H(2)O-grown films (k(H) = 800 s(-1); k(D) = 540 s(-1) at 20 degrees C). Soaking H(2)O- or D(2)O-grown films in the counter solvent produces an immediate inverse isotope effect that diminishes over hours until the ET rate reaches that found in the counter solvent. Thus, D(2)O substitution perturbs interactions and ET between yCc and either CcP or electrode films. The effects derive from slow exchanging protons or solvent molecules that in the crystal produce only small structural changes. PMID:16478190

Kang, Seong A; Hoke, Kevin R; Crane, Brian R

2006-02-22

19

Solvent Isotope Effects on Interfacial Protein Electron Transfer in Crystals and Electode Films  

Energy Technology Data Exchange (ETDEWEB)

D{sub 2}O-grown crystals of yeast zinc porphyrin substituted cytochrome c peroxidase (ZnCcP) in complex with yeast iso-1-cytochrome c (yCc) diffract to higher resolution (1.7 Angstroms) and pack differently than H{sub 2}O-grown crystals (2.4-3.0 Angstroms). Two ZnCcP's bind the same yCc (porphyrin-to-porphyrin separations of 19 and 29 Angstroms), with one ZnCcP interacting through the same interface found in the H{sub 2}O crystals. The triplet excited-state of at least one of the two unique ZnCcP's is quenched by electron transfer (ET) to Fe(III)yCc (k{sub e} = 220 s{sup -1}). Measurement of thermal recombination ET between Fe(II)yCc and ZnCcP+ in the H{sub 2}O-treated crystals has both slow and fast components that differ by 2 orders of magnitude (k{sub eb}{sup 1}= 2200 s{sup -1}, k{sub eb}{sup 2}= 30 s{sup -1}). Back ET in H{sub 2}O-grown crystals is too fast for observation, but soaking H{sub 2}O-grown crystals in D{sub 2}O for hours generates slower back ET, with kinetics similar to those of the D{sub 2}O-grown crystals (k{sub eb}{sup 1} = 7000 s{sup -1}, k{sub eb}{sup 2}= 100 s{sup -1}). Protein-film voltammetry of yCc adsorbed to mixed alkanethiol monolayers on gold electrodes shows slower ET for D{sub 2}O-grown yCc films than for H{sub 2}O-grown films (k{sub H} = 800 s{sup -1}; k{sub D} = 540 s{sup -1} at 20 C). Soaking H{sub 2}O- or D{sub 2}O-grown films in the counter solvent produces an immediate inverse isotope effect that diminishes over hours until the ET rate reaches that found in the counter solvent. Thus, D{sub 2}O substitution perturbs interactions and ET between yCc and either CcP or electrode films. The effects derive from slow exchanging protons or solvent molecules that in the crystal produce only small structural changes.

Kang,S.; Hoke, K.; Crane, B.

2006-01-01

20

Excited nanoscale-TiO2 induced interfacial electron transfer reaction of redox active cobalt(III)–alkyl amine complex and the solid surface  

International Nuclear Information System (INIS)

Interfacial electron transfer reaction mechanism has been probed using ? = 254 nm excited TiO2 nanoparticles and cis-[CoIII(en)2(RNH2)Cl]Cl2 adsorbates (where RNH2 = MeNH2, EtNH2, PrnNH2, BunNH2, BuiNH2, PennNH2, HexnNH2, BznNH2) in aqueous 2-propanol. These tailor made complexes differing in coordination environment due to RNH2 adhere onto TiO2 surface producing compact nano-TiO2//cobalt(III)–(RNH2) surface compound. The surface of the anatase under UV irradiation is uniquely powerful as adsorbent due to inherent hydrophobic/hydrophilic properties. Therefore, the compact structure facilitates an efficient electron transfer to the Co(III) center resulting a high photoefficiency of formation of Co(II). A model for the electron transfer is arrived by considering: (i) the overlap of conduction band of TiO2 with the acceptor level (Co center): (e?, CB)/(e?, tr) + (CoIII, ad) ? CoII and (ii) electronic coupling of donor level (localized on Ti center) with acceptor level (Co center): Ti (center) + (CoIII, ad) ? CoII. These pathways indicate accumulation of electron and appropriately available for reduction of the adhered complex ion. Significant insights were gained on the role of RNH2 moiety in modifying compact structure of TiO2–cobalt(III)–RNH2 compound, redox power of semiconductor surface, and the proposed mechanism of interfacial electron transfer reactions. Highlights: ? Interfacial electron transfer reactions can be probed with tailor made complexes. ? Excited anatase surface acts as a uniquely powerful adsorbent. ? Structurally integrated cobalt(III) complexes adhere to form surface compounds. ? Compact surface compound can facilitate electron transfer.

 
 
 
 
21

Interfacial Electrochemical Electron Transfer Processes in Bacterial Biofilm Environments on Au(111)  

DEFF Research Database (Denmark)

We have studied Streptococcus mutans (S. mutans) biolilm growth and growth inhibition on Au(111)-surfaces using atomic force microscopy (AFM) and interfacial electrochemistry of a number of redox probe molecules. AFM of the biofilm growth and growth inhibition on both mica and Au(111)-surfaces was followed by sampling at given times, drying the samples naturally, and imaging. The electrochemical investigations were based on single-crystal Au(111)-electrode surfaces to exclude polycrystallinity as a cause of inhomogeneous voltammetric broadening on the biofilm covered electrode surfaces. The redox couples were chosen for their positive ([Ru(NH3)(6)](3+2+), [Co(terpy)(2)](3+/2+), terpy = 2,2',2 ''-terpyridine) or negative ([Fe(CN)(6)](3-/4-), [IrCl6](3-)/(4-)) electrostatic charge, [Co(NH3)(6)](3+2+) and [Co(phen)(3)](3+2+) (phen = 1,10-phenanthroline) were other inhibition factors investigated. The positively and negatively charged redox probe couples displayed antagonistic inhibition and voltammetric patterns. [Ru(NH3)(6)](3+2+) and the homologous compound [Co(NH3)(6)](3+/2+) were the only probe compounds to effect growth inhibition. On the other hand, cyclic voltammetry (CV) of both [Ru(NH3)(6)](3+2+) (positively charged, biofilm growth inhibitor) and [Co(terpy)(2)](3+2+) (positively charged, no biofilm growth inhibition) displayed fully reversible CV on biofilm covered electrodes, almost indistinguishable from CV at bare Au(111)-electrode surfaces. In comparison, CVs of [Fe(CN)(6)](3-/4-) and [IrCl6](3-/4-) (both negatively charged and no growth inhibition) were distorted from planar diffusion behavior on bare Au(111)-electrode surfaces toward spherical diffusion behavior on S. mutans biofilm covered Au(111)-electrode surfaces. DNAase teatment of the biofilm covered Au(111)-electrode surface partly restores planar diffusion CV of [Fe(CN)(6)](3-/4-) and [IrCl6](3-/4-). This is reflected in a decrease of the growth rate and the appearance of molecular-scale structures near the bacterial edges as imaged by AFM after DNAase treatment. A rationale for the different voltammetric behavior of positively and negatively charged redox probe molecules based on electrostatic properties of the local surface environment is offered.

Hu, Yifan; Zhang, Jingdong

2010-01-01

22

Excited nanoscale-TiO{sub 2} induced interfacial electron transfer reaction of redox active cobalt(III)-alkyl amine complex and the solid surface  

Energy Technology Data Exchange (ETDEWEB)

Interfacial electron transfer reaction mechanism has been probed using {lambda} = 254 nm excited TiO{sub 2} nanoparticles and cis-[Co{sup III}(en){sub 2}(RNH{sub 2})Cl]Cl{sub 2} adsorbates (where RNH{sub 2} = MeNH{sub 2}, EtNH{sub 2}, Pr{sup n}NH{sub 2,} Bu{sup n}NH{sub 2,} Bu{sup i}NH{sub 2,} Pen{sup n}NH{sub 2}, Hex{sup n}NH{sub 2}, Bz{sup n}NH{sub 2}) in aqueous 2-propanol. These tailor made complexes differing in coordination environment due to RNH{sub 2} adhere onto TiO{sub 2} surface producing compact nano-TiO{sub 2}//cobalt(III)-(RNH{sub 2}) surface compound. The surface of the anatase under UV irradiation is uniquely powerful as adsorbent due to inherent hydrophobic/hydrophilic properties. Therefore, the compact structure facilitates an efficient electron transfer to the Co(III) center resulting a high photoefficiency of formation of Co(II). A model for the electron transfer is arrived by considering: (i) the overlap of conduction band of TiO{sub 2} with the acceptor level (Co center): (e{sup -}, CB)/(e{sup -}, tr) + (Co{sup III}, ad) {yields} Co{sup II} and (ii) electronic coupling of donor level (localized on Ti center) with acceptor level (Co center): Ti (center) + (Co{sup III}, ad) {yields} Co{sup II}. These pathways indicate accumulation of electron and appropriately available for reduction of the adhered complex ion. Significant insights were gained on the role of RNH{sub 2} moiety in modifying compact structure of TiO{sub 2}-cobalt(III)-RNH{sub 2} compound, redox power of semiconductor surface, and the proposed mechanism of interfacial electron transfer reactions. Highlights: Black-Right-Pointing-Pointer Interfacial electron transfer reactions can be probed with tailor made complexes. Black-Right-Pointing-Pointer Excited anatase surface acts as a uniquely powerful adsorbent. Black-Right-Pointing-Pointer Structurally integrated cobalt(III) complexes adhere to form surface compounds. Black-Right-Pointing-Pointer Compact surface compound can facilitate electron transfer.

Anbalagan, K., E-mail: kanuniv@gmail.com [Department of Chemistry, Pondicherry University, Kalapet, Pondicherry 605 014 (India); Ganeshraja, A.S.; Maharaja Mahalakshmi, C. [Department of Chemistry, Pondicherry University, Kalapet, Pondicherry 605 014 (India)

2012-06-15

23

Interfacial heat transfer - State of the art  

International Nuclear Information System (INIS)

Interfacial heat exchanges control the interfacial mass exchange rate, depend on the interfacial area, and are tied to the prediction of thermal nonequilibrium. The nature of the problem usually requires the formulation of mechanistic laws and precludes the general use of universal correlations. This is partly due to the fact that the length scale controlling the interfacial exchanges varies widely from one situation to another and has a strong influence on the exchange coefficients. Within the framework of the ''two-fluid models'', the exchanges occurring at the interfaces are explicitly taken into consideration by the jump condition linking the volumetric mass exchange (evaporation) rate between the phases, to the interfacial energy transfer rates

24

Control of photosensitized electron transfer reactions in organized interfacial systems: vesicles, water-in-oil microemulsions, and colloidal silicon dioxide particles  

Energy Technology Data Exchange (ETDEWEB)

The separation of photoproducts formed in photosensitized electron transfer reactions is essential for efficient energy conversion and storage. The organization of the components involved in the photoinduced process in interfacial systems leads to efficient compartmentalization of the products. Several interfacial systems, e.g., lipid bilayer membranes (vesicles), water-in-oil microemulsions and a solid SiO/sub 2/ colloidal interface, have been designed to accomplish this goal. An electron transfer across a lipid bilayer membrane leading to the separation of the photoproducts at opposite sides of the membrane is facilitated by establishing a transmembrane potential and organizing the cotransport of cations with specific carriers. In the water-in-oil microemulsion the separation of photoproducts is achieved by means of the hydrophilic-hydrophobic nature of the products. Photosensitized electron transfer reactions analogous to those occurring in the two half-cells are presented. The colloidal SiO/sub 2/ particles provice a charged interface that interacts with charged photoproducts. The photosensitized reduction of a neutral acceptor, propylviologen sulfonate (PVS/sup 0/) by positively charged sensitizers such as Ru(bipy)/sub 3//sup 2 +/ and Zn-tetramethylpyridinium porphyrin, Zu-TMPyP/sup 4 +/, is described. The effect of the SiO/sub 2/ interface is attributed to a high surface potential that results in the separation of the intermediate photoproducts. The quantum yields of the photosensitized reactions are correlated to the interfacial surface potential and the electrical effects of other charged interfaces such as micelles are compared with those of SiO/sub 2/. The possible utilization of the energy stored in the stabilized photoproducts in further chemical reactions is discussed. Special attention is given to the photodecomposition of water as a reaction route. 12 figures.

Wilner, I.; Laane, C.; Otvos, J.W.; Calvin, M.

1982-01-01

25

Hydrated Interfacial Ions and Electrons  

Science.gov (United States)

Charged particles such as hydrated ions and transient hydrated electrons, the simplest anionic reducing agents in water, and the special hydronium and hydroxide ions at water interfaces play an important role in many fields of science, such as atmospheric chemistry, radiation chemistry, and biology, as well as biochemistry. This article focuses on these species near hydrophobic interfaces of water, such as the air or vacuum interface of water or water protein/membrane interfaces. Ions at interfaces as well as solvated electrons have been reviewed frequently during the past decade. Although all species have been known for some time with seemingly familiar features, recently the picture in all cases became increasingly diffuse rather than clearer. The current account gives a critical state-of-the art overview of what is known and what remains to be understood and investigated about hydrated interfacial ions and electrons.

Abel, Bernd

2013-04-01

26

Surface plasmon enhanced interfacial electron transfer and resonance Raman, surface-enhanced resonance Raman studies of cytochrome C mutants  

Energy Technology Data Exchange (ETDEWEB)

Surface plasmon resonance was utilized to enhance the electron transfer at silver/solution interfaces. Photoelectrochemical reductions of nitrite, nitrate, and CO{sub 2} were studied on electrochemically roughened silver electrode surfaces. The dependence of the photocurrent on photon energy, applied potential and concentration of nitrite demonstrates that the photoelectrochemical reduction proceeds via photoemission process followed by the capture of hydrated electrons. The excitation of plasmon resonances in nanosized metal structures resulted in the enhancement of the photoemission process. In the case of photoelectrocatalytic reduction of CO{sub 2}, large photoelectrocatalytic effect for the reduction of CO{sub 2} was observed in the presence of surface adsorbed methylviologen, which functions as a mediator for the photoexcited electron transfer from silver metal to CO{sub 2} in solution. Photoinduced reduction of microperoxidase-11 adsorbed on roughened silver electrode was also observed and attributed to the direct photoejection of free electrons of silver metal. Surface plasmon assisted electron transfer at nanostructured silver particle surfaces was further determined by EPR method.

Zheng, Junwei

1999-11-08

27

Metal-Mold interfacial heat transfer  

Science.gov (United States)

During the solidification of metal castings, an interfacial heat transfer resistance exists at the boundary between the metal and the mold. This heat transfer resistance usually varies with time even if the cast metal remains in contact with the mold, due to the time dependence of plasticity of the freezing metal and oxide growth on the surface. The present work has studied interfacial heat transfer on two related types of castings. In the first type, a copper chill was placed on the top of a cylindrical, bottom gated casting. Using the techniques of transducer displacements and electrical continuity, a clearance gap was detected between the solidified metal and the chill. The second type of casting had a similar design except that the chill was placed at the bottom. Owing to the effect of gravity, solid to solid contact was maintained at the metal-chill interface, but the high degree of interface nonconformity resulted in a relatively low thermal conductance as indicated by solution of the inverse heat conduction problem. Finally, the influence of interfacial heat transfer on solidification time with three mold ma-terials is compared by a numerical example, and criteria for utilizing Chvorinov's rule are discussed.

Ho, Kai; Pehlke, Robert D.

1985-09-01

28

Approach to Interfacial and Intramolecular Electron Transfer of the Diheme Protein Cytochrome c(4) Assembled on Au(111) Surfaces  

DEFF Research Database (Denmark)

Intramolecular electron transfer (ET) between metal centers is a core feature of large protein complexes in photosynthesis, respiration, and redox enzyme catalysis. The number of microscopic redox potentials and ET rate constants is, however, prohibitive for experimental cooperative ET mapping, but two-center proteins are simple enough to offer complete communication networks. At the same time, multicenter redox proteins operate in membrane environments where conformational dynamics may lead to gated ET features different from conditions in homogeneous solution. The bacterial respiratory diheme protein Pseudomonas stutzeri cytochrome c(4) has been a target for intramolecular, interheme ET. We report here voltammetric and in situ scanning tunneling microscopy (STM) data for P. stutzeri cyt c(4) at single-crystal, atomically planar Au(111)-electrode surfaces modified by variable-length omega-mercapto-alkanoic carboxylic acids. As evidenced by in situ STM, the strongly dipolar protein is immobilized in a close to vertical orientation at this surface with the positively charged high-potential heme domain adjacent to the electrode. This orientation gives asymmetric voltammograms with two one-ET peaks in the cathodic direction and a single two-ET peak in the anodic direction. Intramolecular, interheme ET with high, 8,000-30,000 s(-1), rate constants is notably an essential part of this mechanism. The high rate constants are in striking contrast to ET reactions of P. stutzeri cyt c4 with small reaction partners in homogeneous solution for which kinetic analysis clearly testifies to electrostatic cooperative effects but no intramolecular, interheme ET higher than 0.1-10 s(-1). This difference suggests a strong gating feature of the process. On the basis of the three-dimensional structure of P. stutzeri cyt c(4), gating is understandable due to the through-space, hydrogen-bonded electronic contact between the heme propionates which is highly sensitive to environmental configurational fluctuations.

Chi, Qijin; Zhang, Jingdong

2010-01-01

29

Enhanced photocatalytic degradation of dye pollutants under visible irradiation on Al(III)-modified TiO2: structure, interaction, and interfacial electron transfer.  

Science.gov (United States)

Aluminum(III)-modified TiO2 was prepared by sol-gel process via a sudden gelating method. The structure of the modified material and the local environment of aluminum were investigated using X-ray diffraction, HRTEM, XPS, 27Al MAS NMR, and xi-potential measurements. The effect of the aluminum modification on interaction between the dye and photocatalyst, the interfacial electron transfer process, and thereby the degradation of dye pollutants under visible irradiation were also examined by FTIR spectra and UV-vis diffuse reflectance spectra. It was found that, rather than incorporating into the crystal lattice of TiO2, the aluminum forms an overlayer of Al2O3 on the surface of TiO2, interfaced with Ti-O-Al bonds. It is interesting that the carboxylate-containing dyes such as Rhodamine B (RhB) adsorb preferentially on the Al2O3, rather than the Ti(IV) sites on the surface of TiO2. The photodegradation rate observed for RhB is nearly 5-fold faster than that obtained in the pristine TiO2 system. The photodegradation of dyes on the aluminum(III)-modified photocatalyst is of great dependence on the structure and anchoring group of the dyes. Structure with carboxylate as anchoring group and amino group as electron donor is favorable for degradation. The mechanistic details are discussed on the basis of experimental results. PMID:18350913

Zhao, Dan; Chen, Chuncheng; Wang, Yifeng; Ma, Wanhong; Zhao, Jincai; Rajh, Tijana; Zang, Ling

2008-01-01

30

Interfacial area and interfacial transfer in two-phase systems. DOE final report  

Energy Technology Data Exchange (ETDEWEB)

In the two-fluid model, the field equations are expressed by the six conservation equations consisting of mass, momentum and energy equations for each phase. The existence of the interfacial transfer terms is one of the most important characteristics of the two-fluid model formulation. The interfacial transfer terms are strongly related to the interfacial area concentration and to the local transfer mechanisms such as the degree of turbulence near interfaces. This study focuses on the development of a closure relation for the interfacial area concentration. A brief summary of several problems of the current closure relation for the interfacial area concentration and a new concept to overcome the problem are given.

Ishii, Mamoru; Hibiki, T.; Revankar, S.T.; Kim, S.; Le Corre, J.M.

2002-07-01

31

Increase in the coordination number of a cobalt porphyrin after photo-induced interfacial electron transfer into nanocrystalline TiO2.  

Science.gov (United States)

Spectroscopic, electrochemical, and kinetic data provide compelling evidence for a coordination number increase initiated by interfacial electron transfer. Light excitation of Co(I)(meso-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) anchored to a nanocrystalline TiO(2) thin film, abbreviated Co(I)P/TiO(2), immersed in an acetonitrile:pyridine electrolyte resulted in rapid excited state injection, k(inj) > 10(8) s(-1), to yield Co(II)P/TiO(2)(e(-)), followed by axial coordination of pyridine to the Co(II)P and hence an increase in coordination number from four to five. The formal oxidation state and coordination environment of the Co metalloporphyrin on TiO(2) were assigned through comparative studies in fluid solution as well as by comparisons to previously reported data. The kinetics for pyridine coordination were successfully modeled with a pseudo-first order kinetic model that yielded a second-order rate constant of k(+py) = 2 × 10(8) M(-1) s(-1). Spectro-electrochemical measurements showed that pyridine coordination resulted in a ?200 mV negative shift in the Co(II/I) reduction potential, E°(Co(II/I)/TiO(2)) = -0.72 V and E°(Co(II/I)(py)/TiO(2)) = -0.85 V vs NHE. With some assumptions, this indicated an equilibrium formation constant K(f) = 400 M(-1) for the Co(II)P(py)/TiO(2) compound. The kinetics for charge recombination were non-exponential under all conditions studied, but were successfully modeled by the Kohlrausch-Williams-Watts (KWW) function with observed rate constants that decreased by about a factor of 100 when pyridine was present. The possible mechanisms for charge recombination are discussed. PMID:22954468

Achey, Darren; Ardo, Shane; Meyer, Gerald J

2012-09-17

32

Interfacial structures - Thermodynamical and experimental studies of the interfacial mass transfer  

International Nuclear Information System (INIS)

In the first section, we put forward hypotheses concerning the structure of the interfacial regions between two immiscible liquid phases. It appears that the longitudinal structure is comparable with that of a crystallized solid and that the transversal structure is nearest of that of a liquid. In the second section, we present a thermodynamical treatment of the irreversible phenomena in the interfacial region. The equation of evolution of a system consisting of two immiscible liquid phases are deduced. The third part allows an experimental verification of the theoretical relations. We also make clear, in certain cases, the appearance of a great 'interfacial resistance' which slows down the interfacial mass transfer. (author)

33

Attachment of CdSe nanoparticles to TiO2 via aqueous linker-assisted assembly: influence of molecular linkers on electronic properties and interfacial electron transfer.  

Science.gov (United States)

CdSe nanoparticles (NPs) capped with cysteinate (Cys), 3-mercaptopropionate (MP), and mercaptosuccinate (MS) were adsorbed to TiO(2) from basic aqueous dispersions. Native capping groups served as molecular linkers to TiO(2). Thus, the materials-assembly chemistry was simplified and made more reproducible and environmentally benign. The electronic properties of CdSe and the electron-transfer reactivity at CdSe-linker-TiO(2) interfaces varied with the structure and functionality of the capping groups. Cys-capped CdSe NPs exhibited a narrow and intense first excitonic absorption band centered at 422 nm, suggesting that they were magic-sized nanocrystals (MSCs) with diameters less than 2 nm. MP- and MS-capped CdSe NPs had broader and lower-energy absorption bands, which are typical of regular quantum dots. Photocurrent action spectra of nanocrystalline TiO(2) films functionalized with Cys-CdSe, MP-CdSe, and MS-CdSe overlaid closely with absorption spectra, indicating that excitation of CdSe gave rise to the injection of electrons into TiO(2). Under white-light illumination, the global energy-conversion efficiency for Cys-capped CdSe ((0.45 ± 0.11)%) was 1.2-to-6-fold greater than for MP- and MS-capped CdSe. Similarly, the absorbed photon-to-current efficiency was 1.3-to-3.3-fold greater. These differences arose from linker-dependent variations of electron-injection and charge-recombination reactivity. Transient absorption measurements indicated that electron injection from Cys-capped CdSe was more efficient than from MS-capped CdSe. In addition, charge recombination at CdSe-MS-TiO(2) interfaces was complete within hundreds of nanoseconds, whereas the charge-separated-state lifetime at CdSe-Cys-TiO(2) interfaces was on the order of several microseconds. Thus, Cys-capped CdSe MSCs are readily attached to TiO(2) and exhibit unusual electronic properties and desirable electron-transfer reactivity. PMID:21970556

Nevins, Jeremy S; Coughlin, Kathleen M; Watson, David F

2011-11-01

34

Study of Interfacial Mass Transfer on Vapor Bubbles in Microgravity  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The knowledge of interfacial heat and mass transfer is important for environmental and technical applications, especially nowadays for numerical simulations of two phase problems. However, the data available up to now are inconsistent, because most experiments performed on earth suffer under buoyancy and convection, and thus the boundary conditions at the evaluation could not clearly be defined. Therefore, we seized the opportunity to investigate interfacial heat and mass transfer in microgra...

Johannes Straub; Gerold Picker

2005-01-01

35

Density functional study of the interfacial electron transfer pathway for monolayer-adsorbed InN on the TiO(2) anatase (101) surface.  

Science.gov (United States)

Density functional theory (DFT) in connection with ultrasoft pseudopotential (USP) and generalized gradient spin-polarized approximations (GGSA) is applied to calculate the adsorption energies and structures of monolayer-adsorbed InN on the TiO(2) anatase (101) surface and the corresponding electronic properties, that is, partial density of states (PDOS) for surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN, to shed light on the possible structural modes for initial photoexcitation within the UV/vis adsorption region followed by fast electron injection through the InN/TiO(2) interface for an InN/TiO(2)-based solar cell design. Our calculated adsorption energies found that the two most probable stable structural modes of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are (1) an end-on structure with an adsorption energy of 2.52 eV through N binding to surface 2-fold coordinated O (O(cn2)), that is, InN-O(cn2), and (2) a side-on structure with an adsorption energy of 3.05 eV through both N binding to surface 5-fold coordinated Ti (Ti(cn5)) and In bridging two surface O(cn2), that is, (O(cn2))(2)-InN-Ti(cn5). Our calculated band gaps for both InN-O(cn2) and (O(cn2))2-InN-Ti(cn5) (including a 1.0-eV correction using a scissor operator) of monolayer-adsorbed InN on the TiO(2) anatase (101) surface are red-shifted to 1.7 eV (730 nm) and 2.3 eV (540 nm), respectively, which are within the UV/vis adsorption region similar to Gratzel's black dye solar cell. Our analyses of calculated PDOS for both surface and bulk layers of the TiO(2) anatase (101) surface and monolayer-adsorbed InN on the TiO(2) anatase (101) surface suggest that the (O(cn2))(2)-InN-Ti(n5) configuration of monolayer-adsorbed InN on the TiO(2) anatase (101) surface would provide a more feasible structural mode for the electron injection through the InN/TiO(2) interface. This is due to the presence of both occupied and unoccupied electronic states for monolayer-adsorbed InN within the band gap TiO(2) anatase (101) surface, which will allow the photoexcitation within the UV/vis adsorption region to take place effectively, and subsequently the photoexcited electronic states will overlap with the unoccupied electronic states around the lowest conduction band of the TiO(2) anatase (101) surface, which will ensure the electron injection through the InN/TiO(2) interface. Finally, another thing worth our attention is our preliminary study of double-layer-adsorbed InN on the TiO(2) anatase (101) surface, that is, (O(cn2))(2)-(InN)(2)-Ti(cn5), with a calculated band gap red-shifted to 2.6 eV (477 nm) and a different overlap of electronic states between double-layer-adsorbed InN and the TiO(2) anatase (101) surface qualitatively indicated that there is an effect of the thickness of adsorbed InN on the TiO(2) anatase (101) surface on both photoexcitation and electron injection processes involved in the photoinduced interfacial electron transfer through InN/TiO(2). A more thorough and comprehensive study of different layers of InN adsorbed in all possible different orientations on the TiO(2) anatase (101) surface is presently in progress. PMID:17107198

Lin, Jyh Shing; Chou, Wen-Chi; Lu, Shao-Yu; Jang, Geng-Jya; Tseng, Bo-Rong; Li, Yung-Ting

2006-11-23

36

Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy)2((4,4'-PO3H2)2bpy)]2+ in TiO2 Nanoparticle Films in Aqueous Environments  

Energy Technology Data Exchange (ETDEWEB)

Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru(bpy){sub 2}(4,4?-(PO{sub 3}H{sub 2}){sub 2}bpy)]{sup 2+} surface-bound to TiO{sub 2} (TiO{sub 2}-Ru{sup II}). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, , were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO{sub 2}(e{sup ?})-Ru{sup 3+}{yields}TiO{sub 2}-Ru{sup 2+}. The appearance of pH-dependent decreases in the efficiency of formation of TiO{sub 2}-Ru{sup 3+} and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond–microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.

Brennaman, Kyle M; Song, Wenjing; Patrocinio, Antonio O T; Jurss, Jonah W.; Concepcion, Javier J; Hoertz, Paul G; Traub, Matthew C; Murakami Iha, Neyde Y; Meyer, Thomas J

2011-01-01

37

Photosensitized electron transfer processes in SiO2 colloids and sodium lauryl sulfate micellar systems: Correlation of quantum yields with interfacial surface potentials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effectiveness of negatively charged colloidal SiO2 particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO4) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS0) with tris(2,2?-bipyridinium)ruthenium(II) [Ru(bipy)32+] as the sensitizer and triethanolamine as the electron donor is found to have a quant...

Laane, Colja; Willner, Itamar; Otvos, John W.

1981-01-01

38

Interfacial electron-transfer kinetics of ferrocene through oligophenyleneethynylene bridges attached to gold electrodes as constituents of self-assembled monolayers: observation of a nonmonotonic distance dependence.  

Science.gov (United States)

The standard heterogeneous electron-transfer rate constants (k(n)0) between substrate gold electrodes and the ferrocene redox couple attached to the electrode surface by variable lengths of substituted or unsubstituted oligophenyleneethynylene (OPE) bridges as constituents of mixed self-assembled monolayers were measured as a function of temperature. The distance dependences of the unsubstituted OPE standard rate constants and of the preexponential factors (An) obtained from an Arrhenius analysis of the unsubstituted OPE k(n)0 versus temperature data are not monotonic. This surprising result, together with the distance dependence of the substituted OPE preexponential factors, may be assessed in terms of the likely conformational variability of the OPE bridges (as a result of the low intrinsic barrier to rotation of the phenylene rings in these bridges) and the associated sensitivity of the rate of electron transfer (and, hence, the single-molecule conductance which may be estimated using An) through these bridges to the conformation of the bridge. Additionally, the measured standard rate constants were independent of the identity of the diluent component of the mixed monolayer, and using an unsaturated OPE diluent has no effect on the rate of electron transfer through a long-chain alkanethiol bridge. These observations indicate that the diluent does not participate in the electron-transfer event. PMID:15521782

Smalley, John F; Sachs, Sandra B; Chidsey, Christopher E D; Dudek, Stephen P; Sikes, Hadley D; Creager, Stephen E; Yu, C J; Feldberg, Stephen W; Newton, Marshall D

2004-11-10

39

Interfacial charge transfer dynamics in small molecule-modified TiO2 nanoparticles  

Science.gov (United States)

Direct molecule-semiconductor interfacial charge transfer interactions have received considerable research attention for their applications in various fields. In this study, the dynamics of molecule-TiO2 interfacial charge transfer complexes is monitored with femtosecond fluorescence upconversion and transient absorption. Small molecules (catechol, dopamine, benzhydroxamic acid, acetyl acetonate and salicylate)-modified TiO2 nanoparticles are prepared and the complexation is followed with optical absorption measurements. Although little visible luminescence is observed from these molecule- TiO2 nanoparticles, ultrafast emission in broad range of wavelengths is detected with fluorescence upconversion which is ascribed to the interfacial charge transfer emission. The charge transfer emission arose out of the radiative recombination of the electrons in the conduction band of TiO2 with holes in the molecule. Femtosecond fluorescence anisotropy measurements have shown that the interfacial charge-transfer excitation is mostly a localized one for catechol, dopamine and benzhydroxamate modified TiO2 nanoparticles. However, the possibility of delocalized charge-transfer excitations is observed for salicylate and acetyl acetonate-TiO2 nanoparticles. The decay of the charge transfer emission is ascribed to the relaxation of the localized states to delocalized states in the TiO2 conduction band. Transient absorption measurements have shown long-lived charge separation in the case of surface-modified TiO2 nanoparticles. Further measurements on the influence of charge-transfer excitations on the interfacial electron transfer in surface-modified TiO2 nanoparticles are being carried out.

Varaganti, Shankar; Mghangha, Edwin; Hasan, Jameel A.; Ramakrishna, Guda

2010-08-01

40

Visualizing interfacial charge transfer in dye sensitized nanoparticles using x-ray transient absorption spectroscopy.  

Energy Technology Data Exchange (ETDEWEB)

A molecular level understanding of the structural reorganization accompanying interfacial electron transfer is important for rational design of solar cells. Here we have applied XTA (X-ray transient absorption) spectroscopy to study transient structures in a heterogeneous interfacial system mimicking the charge separation process in dye-sensitized solar cell (DSSC) with Ru(dcbpy){sub 2}(NCS){sub 2} (RuN3) dye adsorbed to TiO{sub 2} nanoparticle surfaces. The results show that the average Ru-NCS bond length reduces by 0.06 {angstrom}, whereas the average Ru-N(dcbpy) bond length remains nearly unchanged after the electron injection. The differences in bond-order change and steric hindrance between two types of ligands are attributed to their structural response in the charge separation. This study extends the application of XTA into optically opaque hybrid interfacial systems relevant to the solar energy conversion.

Zhang, X. Y.; Smolentsev, G.; Guo, J.; Attenkofer, K.; Kurtz, C.; Jennings, G.; Lockard, J. V.; Stickrath, A. B.; Chen, L. X. (X-Ray Science Division); (Southern Federal Univ.); (Lund Univ.); (Northwestern Univ.)

2011-01-01

 
 
 
 
41

New Ru(II)/Os(II)-polypyridyl complexes for coupling to TiO2 surfaces through acetylacetone functionality and studies on interfacial electron-transfer dynamics.  

Science.gov (United States)

New Ru(ii)- and Os(ii)-polypyridyl complexes have been synthesized with pendant acetylacetone (acac) functionality for anchoring on nanoparticulate TiO2 surfaces with a goal of developing an alternate sensitizer that could be utilized for designing an efficient dye-sensitized solar cell (DSSC). Time-resolved transient absorption spectroscopic studies in the femtosecond time domain have been carried out. The charge recombination rates are observed to be very slow, compared with those for strongly coupled dye molecules having catechol as the anchoring functionality. The results of such studies reveal that electron-injection rates from the metal complex-based LUMO to the conduction band of TiO2 are faster than one would expect for an analogous complex in which the chromophoric core and the anchoring moiety are separated with multiple saturated C-C linkages. Such an observation is rationalized based on computational studies, and a relatively smaller spatial distance between the dye LUMO and the TiO2 surface accounted for this. Results of this study are compared with those for analogous complexes having a gem-dicarboxy group as the anchoring functionality for covalent binding to the TiO2 surface to compare the role of binding functionalities on electron-transfer dynamics. PMID:25097122

Banerjee, Tanmay; Biswas, Abul Kalam; Sahu, Tuhin Subhra; Ganguly, Bishwajit; Das, Amitava; Ghosh, Hirendra Nath

2014-09-28

42

Multidimensional mechanistic modeling of interfacial heat and mass transfer  

International Nuclear Information System (INIS)

A combined theoretical and computational study in modeling multidimensional, diabatic vapor/liquid flows is presented. Models have been developed governing kinematic aspects of multiphase flow as well as interfacial mass and heat transfer for flows of condensable gas (vapor) and liquids. The modeling formulation is based on the Reynolds averaged Navier-Stokes (RANS) type multi-field approach which utilizes a complete set of conservation equations for each fluid component 1. The modeled interfacial interactions include energy, mass, and momentum transfer. Emphasis in the model development work has been placed on the mechanisms governing coupled interfacial heat and mass transfer between the liquid and vapor fields (condensation and/or boiling). A method for tracking changes in bubble size is presented and tested. Locally based models of multidimensional effects have been analyzed, including distributions of fluid temperatures and volume fractions. The overall model accounts for both kinematic and thermodynamic nonequilibrium between the component fluids including superheated vapor. The model has been implemented in the NPHASE-CMFD computer code. Results from the kinematic model are compared to experimental data and good agreement is demonstrated. The heat and mass transfer model is parametrically tested to show the multidimensional effects on the rate of heat and mass transfer. These effects are explained in terms of local characteristics of the two-phase flow. The modacteristics of the two-phase flow. The model is applied to a scenario of saturated vapor injected into a subcooled flow through a heated, porous wall. This provides a reasonable approximation to subcooled boiling. The results are found to be dependent on the partitioning of the wall heat flux between direct liquid heating and vapor generation. However, the observed dependencies are explained and the modeling is considered consistent. (authors)

43

Interfacial stress transfer in a graphene nanosheet toughened hydroxyapatite composite  

Science.gov (United States)

In recent years, graphene has emerged as potential reinforcing nanofiller in the composites for structural engineering due to its extraordinary high elastic modulus and mechanical strength. As recognized, the transfer of stress from a low modulus matrix to a high-modulus reinforcing graphene and the interfacial behavior at a graphene-matrix interface is the fundamental issue in these composites. In the case of graphene nanosheet (GNS) reinforced hydroxyapatite (HA) composite, this research presented analytical models and simulated that the number of graphene layers of GNSs has little effect on the maximum axial stress (˜0.35 GPa) and the maximum shear stress (˜0.14 GPa) at a GNS-HA interface, and the energy dissipation by GNS pull-out decreases with increasing the number of graphene layers due to weak bonding between them. Also, GNS-HA interfacial delamination and/or GNS rupture were also indentified to be the two key failure mechanisms. The computed results are expected to facilitate a better understanding of the interfacial behavior at a GNS-ceramic interface and to achieve tough ceramics reinforced with GNSs.

Zhang, L.; Zhang, X. G.; Chen, Y.; Su, J. N.; Liu, W. W.; Zhang, T. H.; Qi, F.; Wang, Y. G.

2014-10-01

44

Probing Transient Structures during interfacial charge transfer mimicking solar cells and heterogeneous catalysis  

Science.gov (United States)

Photoinduced charge transfer at interfaces is a key process in photocatalysis and dye sensitized solar cells (DSSCs). Using X-ray transient absorption (XTA) spectroscopy, we extracted metal center surrounding transient structural information in a DSSC mimic, namely the RuN3 dye on the TiO2 nanoparticle surfaces. Structural evolution of the adsorbed dye sensitizer and the rearrangement of the nanocrystal surface associated with the electron density shift during and after the interfacial charge injection were investigated. The other interfacial charge transfer system is a suspension of Pt nanoparticles on TiO2 where the photoexcitation induces redox reactions and generate hydrogen fuel. The preliminary XTA results demonstrate the feasibility of the method in probing heterogeneous catalytic systems.

Chen, Lin; Zhang, Xiaoyi; Smolentsev, Grigory; Guo, Jianchang; Attenkofer, Klaus; Stickrath, Andrew B.; Liu, Di-Jia; Gothard, Nosheen

2011-03-01

45

Study of Interfacial Mass Transfer on Vapor Bubbles in Microgravity  

Directory of Open Access Journals (Sweden)

Full Text Available The knowledge of interfacial heat and mass transfer is important for environmental and technical applications, especially nowadays for numerical simulations of two phase problems. However, the data available up to now are inconsistent, because most experiments performed on earth suffer under buoyancy and convection, and thus the boundary conditions at the evaluation could not clearly be defined. Therefore, we seized the opportunity to investigate interfacial heat and mass transfer in microgravity environment. In these experiments the growth and collapse in the overall superheated and subcooled bubles, respectively, liquid or free vapor bubbles were observed at various liquid temperature and pressure states and over periods of from a few seconds up to 300 seconds. It was for the first time that such very long periods of bubble growth could be observed. The experimental set-up allowed the control of the liquid supersaturation before the bubbles were initiated by a short heat pulse at a miniaturized heater. Therefore it was possible to perform a systematic parametric study. The measured curves for vapor bubble growth are in good agreement with our numerical simulation. Based on this model the kinetic coefficients for the evaporation and condensation according to Hertz-Knudsen have been derived from the experimental data.

Johannes Straub

2005-03-01

46

Interfacial load transfer in polymer/carbon nanotube nanocomposites with a nanohybrid shish kebab modification.  

Science.gov (United States)

Interfacial properties are known to have a critical effect on the mechanical properties of a nanocomposite material system. Here, the interfacial load transfer in a carbon nanotube (CNT)/nylon-11 composite was studied with a CNT/nylon-11 nanohybrid shish kebab (NHSK) structure modification using Raman spectroscopy. Characterization of the polymer crystal in the NHSK using differential scanning calorimetry (DSC) for the first time indicates that the NHSK structure formed a more perfect crystal structure than the bulk polymer. On the basis of transmission electron microscopy and DSC results, a new growth model for the NHSK crystal is hypothesized, indicating the formation of an initial uniform crystal layer on the CNT prior to the crystallization of the kebabs. Characterization of the nanocomposites using Raman spectroscopy, with the samples heated to introduce interfacial shear stress caused by thermal expansion mismatch, found that the D* band of the CNT in the NHSK/nylon-11 composite displayed a more pronounced shift with an increase in temperature, which is attributed to the NHSK structure being more effective at transferring load from the nylon matrix to the nanotube inclusions. The NHSK structure was also used to fabricate composites with two amorphous polymers, polycarbonate and poly(methyl methacrylate), to investigate the load transfer mechanism. It was found that when the compatibility between the polymer in the NHSK structure and the bulk polymer matrix at the molecular level is sufficiently high, the ensuing mechanical interlocking effect further enhances the interfacial load transfer for polymer nanocomposites. Additional mechanical characterization of polymer nanocomposites with 0.1 wt % NHSK reinforcement demonstrates how the moduli and ultimate tensile strength of the nanocomposites can be improved via this NHSK structure. PMID:25134606

Nie, Min; Kalyon, Dilhan M; Fisher, Frank T

2014-09-10

47

Lead methylammonium triiodide perovskite-based solar cells: an interfacial charge-transfer investigation.  

Science.gov (United States)

This work reports on an investigation into interfacial charge transfer in CH3 NH3 PbI3 perovskite solar cells by using anatase TiO2 nanocuboids enclosed by active {100} and {001} facets. The devices show 6.0 and 8.0?% power conversion efficiency with and without hole-transport material. Transient photovoltage/photocurrent decay and charge extraction, as well as impedance spectroscopy measurements, reveal that carbon materials are effective counter electrodes in perovskite solar cells. The photogenerated charges are observed to be stored in mesoporous TiO2 film under illumination and in the CH3 NH3 PbI3 layer in the dark. The use of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) as a hole-transport material accelerates interfacial charge recombination between the photogenerated electrons and holes. PMID:25213607

Xu, Xiaobao; Zhang, Hua; Cao, Kun; Cui, Jin; Lu, Jianfeng; Zeng, Xianwei; Shen, Yan; Wang, Mingkui

2014-11-01

48

Interfacial electron dynamics and hot-electron-driven surface photochemistry of carbon tetrachloride on Ag(111).  

Science.gov (United States)

We used time-resolved two-photon photoemission (2PPE) spectroscopy to investigate the photochemical behavior, the interfacial electronic structure, and the fate of photogenerated hot electron for carbon tetrachloride adsorbed on Ag(111). The photodissociation cross section was determined over a wide range of photon energy from 1.62 to 5.69 eV, which suggested a low-lying electron affinity level of adsorbed CCl4. A CCl4-derived unoccupied state located at 3.41 eV above the Fermi level was attributed to an image potential (IP) state based on its binding energy and effective mass. Polarization dependence of the 2PPE signal revealed that the IP state was populated by an indirect excitation process involving scattering of photoexcited hot electrons rather than direct electronic transition from a bulk band. The lifetime of the IP state was much shorter on the CCl4-covered Ag(111) surface than on the clean one, implying that the electron in the IP state is scavenged effectively by CCl4, probably through dissociative attachment to it. These results are significant in the sense that they provide dynamical evidence for a new relaxation pathway of the IP state in addition to the more common pathway involving back transfer of electron to the substrate. PMID:16392586

Ryu, Sunmin; Chang, Jinyoung; Kim, Seong Keun

2005-09-15

49

Relationship Between Casting Distortion, Mold Filling, and Interfacial Heat Transfer in Sand Molds  

Energy Technology Data Exchange (ETDEWEB)

This project sought to determine the relationship between casting dimensions and interfacial heat transfer in aluminum alloy sand castings. The program had four parts; measurement of interfacial heat transfer coefficients in resin bonded and green sand molds, the measurement of gap formation in these molds, the analysis of castings made in varying gatings, orientations and thicknesses, and the measurement of residual stresses in castings in the as-cast and gate removed condition. New values for interfacial heat transfer coefficients were measured, a novel method for gap formation was developed, and the variation of casting dimensions with casting method, gating, and casting orientation in the mold was documented.

J. K. Parker; K. A. Woodbury; T. S. Piwonka; Y. Owusu

1999-09-30

50

Effect of steam superheating on droplet interfacial heat transfer  

International Nuclear Information System (INIS)

Interfacial heat transfer between water droplets and superheated steam in a dispersed flow regime is often calculated using a Lee and Ryley type correlation in loss-of-coolant accident (LOCA) analysis. Inherent deficiency of the correlation when the steam superheating is high enough as in typical reflood situation is described and a modification of the correlation is proposed. A correction factor to Lee-Ryley Nusselt number is derived analytically from the simple heat balance across the interface and a slight modification of the Reynolds number is made according to its definition. New correlation can be represented by Nusselt number equation where the properties of non-dimensional numbers are evaluated at film temperature except the density of the Reynolds number, which is evaluated at ambient temperature. The correction factor is a ratio of the latent heat of evaporation to the enthalpy difference between superheated steam and saturated liquid. Implementing the modified correlation into RELAP5/MOD3.2, the improvement of steam and clad temperature prediction is confirmed using the experimental data of FLECHT-SEASET 31504. (J.P.N)

51

Contribution to the study of interfacial mass transfers: extraction of U and Pu  

International Nuclear Information System (INIS)

Interfacial mass transfer occuring during the extraction of uranyl and plutonium nitrates by TBP was studied by the single drop method. Limiting step in the chemical interfacial reaction. Order of this reaction is one for neutral species Pu(NO3)4 or UO2(NO3)2, in thermodynamical equilibrium with other metallic species in aqueous phase. Order of the interfacial reaction is two for TBP. The influence of HDBP on interfacial reaction was studied. The following hypothesis (the species TBP-HDBP reacts at the interface with the species UO2(DBP)2(HDBP)2) is substantiated by the experimental results

52

Mass transfer and interfacial properties in two-phase microchannel flows  

International Nuclear Information System (INIS)

Drop-based microfluidic devices are becoming more common, and molecular mass transfer and drop circulation are issues that often affect the performance of such devices. Moreover, interfacial properties and surfactant mass transfer rates govern emulsion behavior. Since these phenomena depend strongly on drop size, measurement methods using small drops and flow typical of applications are desired. Using mineral oil as a continuous phase, water droplets and an alcohol surfactant, we demonstrate here a microfluidic approach to measure the interrelated phenomena of dynamic interfacial tension, surfactant mass transfer and interfacial retardation that employs droplet flows in a microchannel with constrictions/expansions. Interfacial flow is influenced markedly by adsorption of surfactant: severe interfacial retardation (by a factor of 30) is observed at low surfactant concentrations and interface remobilization is observed at higher surfactant concentrations. The interfacial tension is described by Langmuir kinetics and the parameters for interfaces with mineral oil (studied here) compare closely with those previously found at air interfaces. For the conditions explored, the surfactant mass transfer is described well by a mixed kinetic-diffusion limited model, and the desorption rate coefficients are measured to be both approximately 70 s-1. The transition from a diffusion-controlled to mixed diffusion-kinetic mass transfer mechanism predicted with reducing drop er mechanism predicted with reducing drop size is verified. This experimental approach (i.e. adjustable geometry and drop size and height) can therefore probe interfacial dynamics in simple and complex flow.

53

Interfacial shear and waviness effects on laminar film flow heat transfer in vertical tubes  

International Nuclear Information System (INIS)

This study presents experimental data for local laminar-film heat transfer with interfacial waviness and shear stress effects, for two film-formation methods: condensation only and condensation on injected films. The results explain differences between correlations commonly used to predict heat transfer through liquid films. Wave evolution is significantly influenced by both the length of longitudinal development and by the film-formation method. This study of condensation inside a vertical tube demonstrates that for small amplitude wavy films, heat transfer enhancement by interfacial shear results primarily from thinning of the film, whereas for films with large disturbance waves, interfacially-induced turbulent enhancement becomes increasingly important. Contrary to the common assumption, when the film is fairly smooth, interfacial shear has little effect on film transition to turbulence

54

Interfacial Electron Transfer Dynamics Following Laser Flash Photolysis of [Ru(bpy){sub 2}((4,4?-PO{sub 3}H{sub 2}){sub 2}bpy)]{sup 2+} in TiO{sub 2} Nanoparticle Films in Aqueous Environments  

Energy Technology Data Exchange (ETDEWEB)

Nanosecond laser flash photolysis has been used to investigate injection and back electron transfer from the complex [(Ru(bpy){sub 2}(4,4?-(PO{sub 3}H{sub 2}){sub 2}bpy)]{sup 2+} surface-bound to TiO{sub 2} (TiO2-Ru{sup II}). The measurements were conducted under conditions appropriate for water oxidation catalysis by known single-site water oxidation catalysts. Systematic variations in average lifetimes for back electron transfer, , were observed with changes in pH, surface coverage, incident excitation intensity, and applied bias. The results were qualitatively consistent with a model involving rate-limiting thermal activation of injected electrons from trap sites to the conduction band or shallow trap sites followed by site-to-site hopping and interfacial electron transfer, TiO{sub 2}(e?)-Ru{sup 3+}{yields}TiO{sub 2}-Ru{sup 2+}. The appearance of pH-dependent decreases in the efficiency of formation of TiO{sub 2}-Ru{sup 3+} and in incident-photon-to-current efficiencies with the added reductive scavenger hydroquinone point to pH-dependent back electron transfer processes on both the sub-nanosecond and millisecond–microsecond time scales, which could be significant in limiting long-term storage of multiple redox equivalents.

Brennaman, Kyle M; Patrocinio, Antonio O T; Song, Wenjing; Jurss, Jonah W.; Concepcion, Javier J; Hoertz, Paul G.; Traub, Matthew C; Murakami Iha, Neyde Y; Meyer, Thomas J.

2011-01-01

55

Nonadiabatic anharmonic electron transfer  

International Nuclear Information System (INIS)

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

56

Nonadiabatic anharmonic electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

57

Electron transfer to sulfides:  

International Nuclear Information System (INIS)

The problem of characterizing the steps associated with the dissociative reduction of sulfides has been addressed. The electrochemical reduction of diphenylmethyl para-methoxyphenyl sulfide in N,N-dimethylformamide, on both glassy carbon and mercury electrodes, was chosen as a test system. The electrode process involves the slow heterogeneous outer-sphere electron transfer to the sulfide, the fast cleavage of the C-S bond, the reduction of the ensuing carbon radical, and the self-protonation triggered by the generation of the strong base Ph2CH-. The latter reaction is rather slow, in agreement with the large intrinsic barriers characterizing proton transfers between CH-acids and carbon bases. The dissociative reduction was studied in the presence of an exogenous acid. The results, obtained by convolution analysis, point to a stepwise DET mechanism in which the ET step is accompanied by rather large reorganization energy. Similar results were obtained on both electrode materials. Analysis of the heterogeneous electron transfer and associated C-S bond cleavage indicate that the reduction of this and other sulfides lies between the stepwise dissociative electron transfers leading to the formation of stiff ?* radical anions and those going through the intermediacy of loose ?* radical anions

58

Protein electron transfer: Dynamics and statistics  

Science.gov (United States)

Electron transfer between redox proteins participating in energy chains of biology is required to proceed with high energetic efficiency, minimizing losses of redox energy to heat. Within the standard models of electron transfer, this requirement, combined with the need for unidirectional (preferably activationless) transitions, is translated into the need to minimize the reorganization energy of electron transfer. This design program is, however, unrealistic for proteins whose active sites are typically positioned close to the polar and flexible protein-water interface to allow inter-protein electron tunneling. The high flexibility of the interfacial region makes both the hydration water and the surface protein layer act as highly polar solvents. The reorganization energy, as measured by fluctuations, is not minimized, but rather maximized in this region. Natural systems in fact utilize the broad breadth of interfacial electrostatic fluctuations, but in the ways not anticipated by the standard models based on equilibrium thermodynamics. The combination of the broad spectrum of static fluctuations with their dispersive dynamics offers the mechanism of dynamical freezing (ergodicity breaking) of subsets of nuclear modes on the time of reaction/residence of the electron at a redox cofactor. The separation of time-scales of nuclear modes coupled to electron transfer allows dynamical freezing. In particular, the separation between the relaxation time of electro-elastic fluctuations of the interface and the time of conformational transitions of the protein caused by changing redox state results in dynamical freezing of the latter for sufficiently fast electron transfer. The observable consequence of this dynamical freezing is significantly different reorganization energies describing the curvature at the bottom of electron-transfer free energy surfaces (large) and the distance between their minima (Stokes shift, small). The ratio of the two reorganization energies establishes the parameter by which the energetic efficiency of protein electron transfer is increased relative to the standard expectations, thus minimizing losses of energy to heat. Energetically efficient electron transfer occurs in a chain of conformationally quenched cofactors and is characterized by flattened free energy surfaces, reminiscent of the flat and rugged landscape at the stability basin of a folded protein.

Matyushov, Dmitry V.

2013-07-01

59

Effect of modification melt treatment on casting/chill interfacial heat transfer and electrical conductivity of Al-13% Si alloy  

International Nuclear Information System (INIS)

For successful modelling of the solidification process, a reliable heat transfer boundary condition data is required. These boundary conditions are significantly influenced by the casting and mould parameters. In the present work, the effect of sodium modification melt treatment on casting/chill interfacial heat transfer during upward solidification of an Al-13% Si alloy against metallic chills is investigated using thermal analysis and inverse modelling techniques. In the presence of chills, modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting/chill interfacial region. The corresponding interfacial heat flux transients and electrical conductivities are also found to be higher. This is attributed to (i) improvement in the casting/chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal on addition of sodium and (ii) increase in the electronic heat conduction in the initial solidified shell due to change in the morphology of silicon from a acicular type to a fine fibrous structure and increase in the ratio of the modification rating to the secondary dendrite arm spacing

60

A numerical investigation on the influence of liquid properties and interfacial heat transfer during microdroplet deposition onto a glass substrate  

CERN Document Server

This work investigates the impingement of a liquid microdroplet onto a glass substrate at different temperatures. A finite-element model is applied to simulate the transient fluid dynamics and heat transfer during the process. Results for impingement under both isothermal and non-isothermal conditions are presented for four liquids: isopropanol, water, dielectric fluid (FC-72) and eutectic tin-lead solder (63Sn-37Pb). The objective of the work is to select liquids for a combined numerical and experimental study involving a high resolution, laser-based interfacial temperature measurement to measure interfacial heat transfer during microdroplet deposition. Applications include spray cooling, micro-manufacturing and coating processes, and electronics packaging. The initial droplet diameter and impact velocity are 80 {\\mu}m and 5 m/s, respectively. For isothermal impact, our simulations with water and isopropanol show very good agreement with experiments. The magnitude and rates of spreading for all four liquids ...

Bhardwaj, Rajneesh; Attinger, Daniel

2010-01-01

 
 
 
 
61

Interplay of local and global interfacial electronic structure of a strongly coupled dipolar organic semiconductor  

Science.gov (United States)

We investigate the consequences of strong electronic coupling at the organic semiconductor/metal interface in both the ground and excited state manifold for the case of chloro-boron subphthalocyanine on Cu(111). Using a combination of low-temperature scanning tunneling microscopy and ultraviolet photoelectron spectroscopy and angle-resolved two-photon photoemission, we are able to connect local electronic interactions at the interface with thin film structure despite complex growth in the submonolayer regime. We show that strong coupling leads to charge transfer from the surface to the molecule, and we are able to correlate this observation with the specific molecular adsorption geometry. Strong coupling further results in molecular excited state anion resonances and is responsible for autoionization of highly excited image potential states, relating to the heterogeneous electronic environment in these thin films. This study provides a step towards disentangling interfacial electronic interactions at complex organic/metal interfaces.

Ilyas, Nahid; Monti, Oliver L. A.

2014-09-01

62

Determination of interfacial heat transfer coefficient and its application in high pressure die casting process  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper, the research progress of the interfacial heat transfer in high pressure die casting (HPDC is reviewed. Results including determination of the interfacial heat transfer coefficient (IHTC, influence of casting thickness, process parameters and casting alloys on the IHTC are summarized and discussed. A thermal boundary condition model was developed based on the two correlations: (a IHTC and casting solid fraction and (b IHTC peak value and initial die surface temperature. The boundary model was then applied during the determination of the temperature field in HPDC and excellent agreement was found.

Cao Yongyou

2014-07-01

63

An improved heat transfer prediction model for turbulent falling liquid films with or without interfacial shear  

International Nuclear Information System (INIS)

An improved method is presented for the prediction of heat transfer coefficients in turbulent falling liquid films with or without interfacial shear for both heating or condensation. A modified Mudawwar and El-Masri's semi-empirical turbulence model, particularly to extend its use for the turbulent falling film with high interfacial shear, is used to replace the eddy viscosity model incorporated in the unified approach proposed by Yih and Liu. The liquid film thickness and asymptotic heat transfer coefficients against the film Reynolds number for wide range of interfacial shear predicted by both present and existing methods are compared with experimental data. The results show that, in general, predictions of the modified model agree more closely with experimental data than that of existing models. 9 figs., 3 tabs., 15 refs. (Author)

64

Influence of Glass Coating Thickness on Interfacial Heat Transfer Coefficient during Forming of Nickel Based Superalloys  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The influence of glass coating thickness on the interfacial heat transfer coefficient has been examined using numerical modeling. Temperature and heat flux during working of a Inconel 718 work-piece and colder H13 dies have been simulated. The thickness of the glass coating is found to have a significant influence on the forming characteristic. © (2013) Trans Tech Publications, Switzerland.

Busuttil, M.; Lin, Yp; Gebelin, Jc; Reed, Rc

2013-01-01

65

Electron transfer: Lower tunnel barriers  

Science.gov (United States)

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

66

Charge transfer and interfacial magnetism in (LaNiO3)n/(LaMnO3)2 superlattices  

Digital Repository Infrastructure Vision for European Research (DRIVER)

(LaNiO3)n/(LaMnO3)2 superlattices were grown using ozone-assisted molecular beam epitaxy, where LaNiO3 is a paramagnetic metal and LaMnO3 is an antiferromagnetic insulator. The superlattices exhibit excellent crystallinity and interfacial roughness of less than 1 unit cell. X-ray spectroscopy and dichroism measurements indicate that electrons are transferred from the LaMnO3 to the LaNiO3, inducing magnetism in LaNiO3. Magnetotransport measurements reveal a transition from me...

Hoffman, Jason; Tung, I. C.; Nelson-cheeseman, Brittany; Liu, Ming; Freeland, John; Bhattacharya, Anand

2013-01-01

67

An extremely sensitive aptasensor based on interfacial energy transfer between QDS SAMs and GO.  

Science.gov (United States)

In this work we designed a fluorescent self-assemblied multilayers, with thrombin aptamers and ssDNA as aptamer fixed onto the outermost layer, respectively. This multilayers can effectively sense biomolecules by interfacial florescence resonance energy transfer from multilayers to graphene oxide. High fluorescence quenching efficiency of graphene oxide and self-assemblied membrane' concentration results in good sensitivity for biosensing. A new interfacial sensing method with extremely high sensitivity for thrombin and DNA sequence was established, and the detection limit for thrombin and DNA was 16.2pM and 72.6 fM, respectively. PMID:24835931

Sun, Xiangying; Liu, Bin; Yang, Chuanxiao; Li, Congcong

2014-10-15

68

An extremely sensitive aptasensor based on interfacial energy transfer between QDS SAMs and GO  

Science.gov (United States)

In this work we designed a fluorescent self-assemblied multilayers, with thrombin aptamers and ssDNA as aptamer fixed onto the outermost layer, respectively. This multilayers can effectively sense biomolecules by interfacial florescence resonance energy transfer from multilayers to graphene oxide. High fluorescence quenching efficiency of graphene oxide and self-assemblied membrane' concentration results in good sensitivity for biosensing. A new interfacial sensing method with extremely high sensitivity for thrombin and DNA sequence was established, and the detection limit for thrombin and DNA was 16.2 pM and 72.6 fM, respectively.

Sun, Xiangying; Liu, Bin; Yang, Chuanxiao; Li, Congcong

2014-10-01

69

Time-resolved x-ray photoelectron spectroscopy techniques for real-time studies of interfacial charge transfer dynamics  

Energy Technology Data Exchange (ETDEWEB)

X-ray based spectroscopy techniques are particularly well suited to gain access to local oxidation states and electronic dynamics in complex systems with atomic pinpoint accuracy. Traditionally, these techniques are applied in a quasi-static fashion that usually highlights the steady-state properties of a system rather than the fast dynamics that often define the system function on a molecular level. Novel x-ray spectroscopy techniques enabled by free electron lasers (FELs) and synchrotron based pump-probe schemes provide the opportunity to monitor intramolecular and interfacial charge transfer processes in real-time and with element and chemical specificity. Two complementary time-domain xray photoelectron spectroscopy techniques are presented that are applied at the Linac Coherent Light Source (LCLS) and the Advanced Light Source (ALS) to study charge transfer processes in N3 dye-sensitized ZnO semiconductor nanocrystals, which are at the heart of emerging light-harvesting technologies.

Shavorskiy, Andrey; Hertlein, Marcus; Guo Jinghua; Tyliszczak, Tolek [Advanced Light Source, Lawrence Berkeley National Laboratory (United States); Cordones, Amy; Vura-Weis, Josh [Department of Chemistry, University of California Berkeley (United States); Siefermann, Katrin; Slaughter, Daniel; Sturm, Felix; Weise, Fabian; Khurmi, Champak; Belkacem, Ali; Weber, Thorsten; Gessner, Oliver [Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); Bluhm, Hendrik [Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); Strader, Matthew; Cho, Hana; Coslovich, Giacomo; Kaindl, Robert A. [Materials Sciences Division, Lawrence Berkeley National Laboratory (United States); Lin, Ming-Fu [Department of Chemistry, University of California Berkeley (United States); Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory (United States); and others

2013-04-19

70

Interfacial condensation heat transfer for countercurrent steam-water wavy flow in a horizontal circular pipe  

International Nuclear Information System (INIS)

An experimental study of interfacial condensation heat transfer has been performed for countercurrent steam-water wavy flow in a horizontal circular pipe. A total of 105 local interfacial condensation heat transfer coefficients have been obtained for various combinations of test parameters. Two empirical Nusselt number correlations were developed and parametric effects of steam and water flow rates and the degree of water subcooling on the condensation heat transfer were examined. For the wavy interface condition, the local Nusselt number is more strongly sensitive to the steam Reynolds number than water Reynolds number as opposed to the case of smooth interface condition. Comparisons of the present circular pipe data with existing correlations showed that existing correlations developed for rectangular channels are not directly applicable to a horizontal circular pipe flow

71

Core-concrete molten pool dynamics and interfacial heat transfer  

International Nuclear Information System (INIS)

Theoretical models are derived for the heat transfer from molten oxide pools to an underlying concrete surface and from molten steel pools to a general concrete containment. To accomplish this, two separate effects models are first developed, one emphasizing the vigorous agitation of the molten pool by gases evolving from the concrete and the other considering the insulating effect of a slag layer produced by concrete melting. The resulting algebraic expressions, combined into a general core-concrete heat transfer representation, are shown to provide very good agreement with experiments involving molten steel pours into concrete crucibles

72

Visualizing interfacial charge transfer in Ru-dye sensitized TiO{sub 2} nanoparticles using x-ray transient absorption spectroscopy.  

Energy Technology Data Exchange (ETDEWEB)

A molecular level understanding of the structural reorganization accompanying interfacial electron transfer is important for rational design of solar cells. Here we have applied XTA (X-ray transient absorption) spectroscopy to study transient structures in a heterogeneous interfacial system mimicking the charge separation process in dye-sensitized solar cell (DSSC) with Ru(dcbpy){sub 2}(NCS){sub 2} (RuN3) dye adsorbed to TiO{sub 2} nanoparticle surfaces. The results show that the average Ru-NCS bond length reduces by 0.06 {angstrom}, whereas the average Ru?N(dcbpy) bond length remains nearly unchanged after the electron injection. The differences in bond-order change and steric hindrance between two types of ligands are attributed to their structural response in the charge separation. This study extends the application of XTA into optically opaque hybrid interfacial systems relevant to the solar energy conversion.

Zhang, X.; Smolentsev, G.; Guo, J.; Attenkofer, K.; Kurtz, C.; Jennings, G.; Lockard, J. V.; Stickrath, A. B.; Chen, L. X. (Chemical Sciences and Engineering Division); ( XSD); (Southern Federal Univ.); (Lund Univ.); (Northwestern Univ.)

2011-03-01

73

Modeling and database for melt-water interfacial heat transfer  

International Nuclear Information System (INIS)

A mechanistic model is developed to predict the transition superficial gas velocity between bulk cooldown and crust-limited heat transfer regimes in a sparged molten pool with a coolant overlayer. The model has direct applications in the analysis of ex-vessel severe accidents, where molten corium interacts with concrete, thereby producing sparging concrete decomposition gases. The analysis approach embodies thermal, mechanical, and hydrodynamic aspects associated with incipient crust formation at the melt/coolant interface. The model is validated against experiment data obtained with water (melt) and liquid nitrogen (coolant) simulants. Predictions are then made for the critical gas velocity at which crust formation will occur for core material interacting with concrete in the presence of water. In summary: To validate the model, bench-top experiments were performed which employed water (melt) and liquid nitrogen (coolant) simulants; decomposition gases were simulated using argon gas. The results of the experiments confirm the existence of distinct crust limited and bulk cooldown heat transfer regimes. The transition between the two regimes occurred gradually between j = 2 to 4 cm/s, with onset of bulk cooling occurring at j = 2 cm/s. The model predicts a transition gas velocity of j 2.5 cm/s without empirical adjustment. Application of the model to the case of oxidic corium over concrete indicates that efficient bulk cooling of melt will occur as long as the concreteof melt will occur as long as the concrete decomposition gas velocity lies above 6 cm/s. When the gas velocity falls below this value, an interstitial crust is predicted to form. Thereafter, heat transfer from the MCCI zone to the coolant will be crust-limited

74

Interfacial heat transfer in multiphase molten pools with gas injection  

Science.gov (United States)

In the very unlikely event of a severe reactor accident involving core meltdown and pressure vessel failure, it is vital to identify the circumstances that would allow the molten core material to cool down and resolidify, bringing core debris to a safe and stable state. In this type of accident, the molten material which escapes from the reactor pressure vessel will accumulate as a molten pool in the reactor cavity below. To achieve coolability of the corium in this configuration it has been proposed to flood the cavity with water from above forming a layered structure where upward heat loss from the molten pool to the water will cause the core material to quench and solidify. The effectiveness of this procedure depends largely on the rate of upward heat loss as well as on the formation and stability of an upper crust. In this situation the molten pool becomes a three phase mixture: the solid and liquid slurry formed by the molten pool cooled to a temperature below the temperature of liquidus, agitated by the gases formed in the concrete ablation process. The present work quantifies the partition of the heat losses upward and downward considering the influence of the solid fraction in the pool and the viscosity effects, and the rate of heat loss through a solid layer. To complete this task a intermediate scale experimental test section has been designed and built at the University of Wisconsin - Madison, in which simulant materials are used to model the process of heat and mass transfer which involves the molten pool, the solid layer atop and the coolant layer above. The design includes volumetric heating, gas injection from the bottom and solids within the pool. New experimental results showing the heat transfer behavior for pools with different viscosities and various solid fractions are presented. The current results indicate a power split which favors heat transfer upward to the coolant simulant above by a 2:1 or 3:1 ratio. In addition, the power split is unaffected by the viscosity of the pool, the solid fractions in the pool and the superficial velocity.

Bilbao Y Leon, Rosa Marina

75

Modeling and database for melt-water interfacial heat transfer  

International Nuclear Information System (INIS)

A mechanistic model is developed to predict the transition superficial gas velocity between bulk cooldown and crust-limited heat transfer regimes in a sparged molten pool with a coolant overlayer. The model has direct applications in the analysis of ex-vessel severe accidents, where molten corium interacts with concrete, thereby producing sparging concrete decomposition gases. The analysis approach embodies thermal, mechanical, and hydrodynamic aspects associated with incipient crust formation at the melt/coolant interface. The model is validated against experiment data obtained with water (melt) and liquid nitrogen (coolant) simulants. Predictions are then made for the critical gas velocity at which crust formation will occur for core material interacting with concrete in the presence of water

76

Photoelectric conversion behavior based on direct interfacial charge-transfer from porphyrin derivative to silicon nanowires  

Science.gov (United States)

A porphyrin derivative was prepared, and the photoelectric conversion behaviors of porphyrin derivative sensitized silicon nanowires had been studied that showed the maximum photocurrent generation that occurred at the near infrared region, which can be attributed to the direct interfacial charge-transfer from the highest occupied molecular orbital of porphyrin derivative to the conduction band of silicon nanowires. These properties open up the possibility of constructing photovoltaic devices and light-harvesting systems using various dyes and semiconductors.

Wen, Liping; Liu, Xiaofeng; Yang, Nailiang; Zhai, Jin; Huang, Changshui; Li, Yuliang; Jiang, Lei

2010-12-01

77

Electron transfer in pnicogen bonds.  

Science.gov (United States)

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 X(n)PH(3-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

78

Interfacial electronic structure at a metal—phthalocyanine/graphene interface: Copper—phthalocyanine versus iron—phthalocyanine  

Science.gov (United States)

The energy level alignment of CuPc and FePc on single-layer graphene/Ni(111) (SLG/Ni) substrate was investigated by using ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). The highest occupied molecular orbitals (HOMOs) in a thick layer of CuPc and FePc lie at 1.04 eV and 0.90 eV, respectively, below the Fermi level of the SLG/Ni substrate. Weak adsorbate—substrate interaction leads to negligible interfacial dipole at the CuPc/SLG/Ni interface, while a large interfacial dipole (0.20 eV) was observed in the case of FePc/SLG/Ni interface, due to strong adsorbate—substrate coupling. In addition, a new interfacial electronic feature was observed for the first time in the case of FePc on SLG/Ni substrate. This interfacial state can be attributed to a charge transfer from the SLG/Ni substrate to unoccupied orbitals of FePc.

Ye, Wei-Guo; Liu, Dan; Peng, Xiao-Feng; Dou, Wei-Dong

2013-11-01

79

Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume IV. Chapters 15-19)  

Energy Technology Data Exchange (ETDEWEB)

Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

Guo, T.; Park, J.; Kojasoy, G.

2003-03-15

80

Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume II. Chapters 6-10)  

Energy Technology Data Exchange (ETDEWEB)

Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

Guo, T.; Park, J.; Kojasoy, G.

2003-03-15

 
 
 
 
81

Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume I. Chapters 1-5)  

Energy Technology Data Exchange (ETDEWEB)

Experiments were performed on horizontal air-water bubbly two-phase flow, axial flow, stratified wavy flow, and annular flow. Theoretical studies were also undertaken on interfacial parameters for a horizontal two-phase flow.

Guo, T.; Park, J.; Kojasoy, G.

2003-03-15

82

Control of ferromagnetic relaxation in magnetic thin films through thermally induced interfacial spin transfer.  

Science.gov (United States)

Relaxation control in magnetic thin films via thermally induced interfacial spin transfers was demonstrated for the first time. The experiments used a trilayered structure that consisted of an yttrium iron garnet (YIG) thin film grown on a gadolinium gallium garnet substrate and capped with a nanometer-thick Pt layer. As a temperature gradient is applied across the thickness of the structure, there exists a spin angular momentum transfer across the YIG/Pt interface. This spin transfer results in a torque on YIG magnetic moments. The torque can either speed up or slow down the relaxation in the YIG film, depending on the sign of the temperature gradient with respect to the trilayered structure. PMID:23004648

Lu, Lei; Sun, Yiyan; Jantz, Michael; Wu, Mingzhong

2012-06-22

83

An experimental investigation o the interfacial condensation heat transfer in steam/water countercurrent stratified flow in a horizontal pipe  

International Nuclear Information System (INIS)

An interfacial condensation heat transfer phenomenon in a steam/water countercurrent stratified flow in a nearly horizontal pipe has been experimentally investigated. The present study has been focused on the measurement of the temperature and velocity distributions within the water layer. In particular, the water layer thickness used in the present work is large enough so that the turbulent mixing is limited and the thermal stratification is established. As a result, the thermal resistance of the water layer to the condensation heat transfer is increased significantly. An empirical correlation of the interfacial condensation heat transfer has been developed. The present correlation agrees with the data within ±15%

84

An experimental investigation of the interfacial condensation heat transfer in steam/water countercurrent stratified flow in a horizontal pipe  

Energy Technology Data Exchange (ETDEWEB)

An interfacial condensation heat transfer phenomenon in a steam/water countercurrent stratified flow in a nearly horizontal pipe has been experimentally investigated. The present study has been focused on the measurement of the temperature and velocity distributions within the water layer. In particular, the water layer thickness used in the present work is large enough so that the turbulent mixing is limited and the thermal stratification is established. As a result, the thermal resistance of the water layer to the condensation heat transfer is increased significantly. An empirical correlation of the interfacial condensation heat transfer has been developed. The present correlation agrees with the data within {+-} 15%. 5 refs., 6 figs. (Author)

Chu, In Cheol; Yu, Seon Oh; Chun, Moon Hyun [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of); Kim, Byong Sup; Kim, Yang Seok; Kim, In Hwan; Lee, Sang Won [Korea Electric Power Research Institute, Taejon (Korea, Republic of)

1998-12-31

85

Functional 2D nanoparticle/polymer array: Interfacial assembly, transfer, characterization, and coupling to photonic crystal cavities  

Science.gov (United States)

We developed a universal, facile and robust method to prepare free-standing, ordered and patternable nanoparticle/polymer monolayer arrays by evaporation-induced self-assembly at a fluid interface. The ultra-thin monolayer nanoparticle/polymer arrays are sufficiently robust that they can be transferred to arbitrary substrates, even with complex topographies. More importantly, the Poly (methyl methacrylate) (PMMA) in the system serves as a photoresist enabling two modes of electron beam (e-beam) nanoparticle patterning. These ultra-thin films of monolayer nanoparticle arrays are of fundamental interest as 2D artificial solids for electronic, magnetic and optical properties and are also of technological interest for a diverse range of applications in micro- and macro-scale devices including photovoltaics, sensors, catalysis, and magnetic storage. By co-assembly with block co-polymers, the nanoparticles were selectively positioned in one specific phase, representing a high throughput route for creating nanoparticle patterns. The self-assembly process was investigated by combined in-situ grazing incidence small angle x-ray scattering (GISAXS) and numerical simulation. By e-beam irradiation of free-standing 2D NP/polymer arrays, anisotropic nanowire arrays have been fabricated. Additionally, preliminary investigation on assembly of binary nanoparticle arrays has also been introduced, serving as promising future directions of interfacial assembly. Controlling the rate of spontaneous emission and thus promoting the photon generation efficiency is a key step toward fabrication of Quantum dot based single-photon sources, and harnessing of light energy from emitters with a broad emitting spectrum. Coupling of photo emitters to photonic cavities without perturbing the optical performance of cavities remains as a challenge in study of Purcell effect based on quantum electrodynamics. Taking advantage of interfacial assembly and transfer, we have achieved controlled deposition of quantum dots into high Q photonic microcavities and studied the modification of their optical properties. Anomalous enhanced spontaneous emission and Fabry-Perot resonance have been observed.

Xiong, Shisheng

86

Controlled interfacial electron dynamics in highly efficient Zn2 SnO4 -based dye-sensitized solar cells.  

Science.gov (United States)

Among ternary oxides, Zn2 SnO4 (ZSO) is considered for dye-sensitized solar cells (DSSCs) because of its wide bandgap, high optical transmittance, and high electrical conductivity. However, ZSO-based DSSCs have a poor performance record owing largely to the absence of systematic efforts to enhance their performance. Herein, general strategies are proposed to improve the performance of ZSO-based DSSCs involving interfacial engineering/modification of the photoanode. A conformal ZSO thin film (blocking layer) deposited at the fluorine-doped tin oxide-electrolyte interface by pulsed laser deposition suppressed the back-electron transfer effectively while maintaining a high optical transmittance, which resulted in a 22 % improvement in the short-circuit photocurrent density. Surface modification of ZSO nanoparticles (NPs) resulted in an ultrathin ZnO shell layer, a 9 % improvement in the open-circuit voltage, and a 4 % improvement in the fill factor because of the reduced electron recombination at the ZSO NPs-electrolyte interface. The ZSO-based DSSCs exhibited a faster charge injection and electron transport than their TiO2 -based counterparts, and their superior properties were not inhibited by the ZnO shell layer, which indicates their feasibility for highly efficient DSSCs. Each interfacial engineering strategy could be applied to the ZSO-based DSSC independently to lead to an improved conversion efficiency of 6 %, a very high conversion efficiency for a non-TiO2 based DSSC. PMID:24347268

Shin, Seong Sik; Kim, Dong Wook; Hwang, Daesub; Suk, Jae Ho; Oh, Lee Seul; Han, Byung Suh; Kim, Dong Hoe; Kim, Ju Seong; Kim, Dongho; Kim, Jin Young; Hong, Kug Sun

2014-02-01

87

Electron Transfer to Vinylaromatic Polymers  

International Nuclear Information System (INIS)

Aromatic polymers accept electrons from alkali metals to form polyradicalanions. These undergo chain scission as a result of electronic interaction between aromatic rings. Spectrophotometric and chemical evidence led to the conclusion that during the chain-breaking process polymeric fragments were formed which had the properties of ''living polymers'', i.e. the characteristic visible spectra and the capability of initiating the polymerization of a number of vinyl monomers. It was possible to follow the rate of chain scission in the case of poly (4-vinyl biphenyl) and poly(?-vinyl naphthalene) by means of viscosity and spectrophotometric measurements. The postulated mechanism was found to be consistent with the slow decrease in free spin concentration measured by means of the electron spin resonance technique. Chain scission in polyacenaphthalene takes place at a much faster rate than in poly (4-vinyl biphenyl) and this fact is in good agreement with simple LCAO MO calculations. Preliminary experiments indicate that electron transfer to poly-N-vinyl carbazole produces little if any degradation. These investigations led to the examination of the temperature effect on the electron-transfer reaction from sodium to some substituted aromatic hydrocarbons. The details of this effect are discussed. (author)

88

Section thickness-dependant interfacial heat transfer in squeeze casting of aluminum alloy A443  

International Nuclear Information System (INIS)

Five-step castings of aluminum alloy A443 with different section thicknesses (2, 6, 8, 10, 20 mm) were squeezed under a hydraulic pressure of 60 MPa. Temperatures inside the P20 steel die mold and at the casting surface were recorded by fine type-K thermocouples. A numerical solution, i.e. inverse method was employed to determine the casting-die interfacial heat transfer coefficients (IHTCs). The results show the IHTCs initially reached a maximum peak value followed by a gradually decline to a lower level. With the applied pressure of 60MPa, the peak IHTC values from steps 1 to 5 varied from 5629 W/m2K to 9419 W/m2K. The section thickness affected IHTC peak values significantly. Compared to the thin steps at upper cavity, the lower thick steps obtained higher peak IHTCs and heat flux values due to high local pressures and high melt temperature.

89

"Butterfly Effect" in CuO/Graphene Composite Nanosheets: A Small Interfacial Adjustment Triggers Big Changes in Electronic Structure and Li-Ion Storage Performance.  

Science.gov (United States)

Generally speaking, excellent electrochemical performance of metal oxide/graphene nanosheets (GNSs) composite is attributed to the interfacial interaction (or "synergistic effect") between constituents. However, there are no any direct observations on how the electronic structure is changed and how the properties of Li-ion storage are affected by adjusting the interfacial interaction, despite of limited investigations on the possible nature of binding between GNSs and metal oxide. In this paper, CuO nanosheets/GNSs composites with a little Cu2O (ca. 4 wt %) were utilized as an interesting model to illustrate directly the changes of interfacial nature as well as its deep influence on the electronic structure and Li-ion storage performance of composite. The interfacial adjustment was successfully fulfilled by removal of Cu2O in the composite by NH3·H2O. Formation of Cu-O-C bonds on interfaces both between CuO and GNSs, and Cu2O and GNSs in the original CuO/GNSs composites was detected. The small interfacial alteration by removal of the little Cu2O results in the obvious changes in electronic structure, such as weakening of covalent Cu-O-C interfacial interaction and recovery of ? bonds in graphene, and simultaneously leads to variations in electrochemical performance of composites, including a 21% increase of reversible capacity, degradation of cyclic stability and rate-performance, and obvious increase of charge-transfer resistance, which can be called a "butterfly effect" in graphene-based metal oxide composites. These interesting phenomena could be helpful to design not only the high-performance graphene/metal oxide anode materials but also various advanced graphene-based composites used in the other fields such as sensors, catalysis, fuel cells, solar cells, etc. PMID:25226227

Zhang, Xiaoting; Zhou, Jisheng; Song, Huaihe; Chen, Xiaohong; Fedoseeva, Yu V; Okotrub, A V; Bulusheva, L G

2014-10-01

90

Experimental measurement of the interfacial heat transfer coefficients of subcooled flow boiling using micro-thermocouple and double directional images  

International Nuclear Information System (INIS)

Full text of publication follows: Models or correlations for phase interface are needed to analyze the multi-phase flow. Interfacial heat transfer coefficients are important to constitute energy equation of multi-phase flow, specially. In subcooled boiling flow, bubble condensation at the bubble-liquid interface is a major mechanism of heat transfer within bulk subcooled liquid. Bubble collapse rates and temperatures of each phase are needed to determine the interfacial heat transfer coefficient for bubble condensation. Bubble collapse rates were calculated through image processing in single direction, generally. And in case of liquid bulk temperature, which has been obtained by general temperature sensor such as thermocouple, was used. However, multi-directional images are needed to analyze images due to limitations of single directional image processing. Also, temperature sensor, which has a fast response time, must be used to obtain more accurate interfacial heat transfer coefficient. Low pressure subcooled water flow experiments using micro-thermocouple and double directional image processing with mirrors were conducted to investigate bubble condensation phenomena and to modify interfacial heat transfer correlation. Experiments were performed in a vertical subcooled boiling flow of a rectangular channel. Bubble condensing traces with respect to time were recorded by high speed camera in double direction and bubble collapse rates were calculated by processing recor rates were calculated by processing recorded digital images. Temperatures were measured by micro-thermocouple, which is a K-type with a 12.7 ?m diameter. The liquid temperature was estimated by the developed algorithm to discriminate phases and find each phase temperature in the measured temperature including both liquid and bubble temperature. The interfacial heat transfer coefficient for bubble condensation was calculated from the bubble collapse rates and the estimated liquid temperature, and its correlation was modified. The modified correlation has been compared with other correlations. (authors)

91

Kinetic and structural studies, origins of selectivity, and interfacial charge transfer in the artificial photosynthesis of CO  

Energy Technology Data Exchange (ETDEWEB)

The effective design of an artificial photosynthetic system entails the optimization of several important interactions. Herein we report stopped-flow UV-visible (UV-vis) spectroscopy, X-ray crystallographic, density functional theory (DFT), and electrochemical kinetic studies of the Re(bipy-tBu) (CO)3(L) catalyst for the reduction of CO2 to CO. A remarkable selectivity for CO2 over Hþ was observed by stopped-flow UV-vis spectroscopy of [Re(bipy-tBu)3]-1. The reaction with CO2 is about 25 times faster than the reaction with water or methanol at the same concentrations. X-ray crystallography and DFT studies of the doubly reduced anionic species suggest that the highest occupied molecular orbital (HOMO) has mixed metal-ligand character rather than being purely doubly occupied dz2, which is believed to determine selectivity by favoring CO2 (?+?) over H+ (? only) binding. Electrocatalytic studies performed with the addition of Brönsted acids reveal a primary H/D kinetic isotope effect, indicating that transfer of protons to Re-CO2 is involved in the rate limiting step. Lastly, the effects of electrode surface modification on interfacial electron transfer between a semiconductor and catalyst were investigated and found to affect the observed current densities for catalysis more than threefold, indicating that the properties of the electrode surface need to be addressed when developing a homogeneous artificial photosynthetic system.

Smieja, Jonathan M.; Benson, Eric E.; Kumar, Bhupendra; Grice, Kyle A.; Seu, Candace; Miller, Alexander J.; Mayer, James M.; Kubiak, Cliff

2012-09-25

92

Inverse identification of interfacial heat transfer coefficient between the casting and metal mold using neural network  

International Nuclear Information System (INIS)

The effect of the heat transfer coefficient at the casting-mold interface is of prime importance to improve the casting quality, especially for castings in metal molds. However, it is difficult to determine the values of heat transfer coefficient from experiments due to the influence of various factors, such as contacting pressure, oxides on surfaces, roughness of surfaces, coating material, coating thickness and gap formation caused by the deformation of casting and mold, etc. In the present paper, the interfacial heat transfer coefficient (IHTC) between the casting and metal mold is identified by using the method of inverse analysis based on measured temperatures, neural network with back-propagation algorithm and numerical simulation. Then, by applying the identified IHTC in finite element analysis, the comparison between numerical calculated and experimental results is made to verify the correctness of method. The results show that the numerical calculated temperatures are in good agreement with experimental ones. These demonstrate that the method of inverse analysis is a feasible and effective tool for determination of the casting-mold IHTC. In addition, it is found that the identified IHTC varies with time during the casting solidification and varies in the range of about 100-3200 Wm-2K-1. The characteristics of the time-varying IHTC have also been discussed.

93

Inverse identification of interfacial heat transfer coefficient between the casting and metal mold using neural network  

Energy Technology Data Exchange (ETDEWEB)

The effect of the heat transfer coefficient at the casting-mold interface is of prime importance to improve the casting quality, especially for castings in metal molds. However, it is difficult to determine the values of heat transfer coefficient from experiments due to the influence of various factors, such as contacting pressure, oxides on surfaces, roughness of surfaces, coating material, coating thickness and gap formation caused by the deformation of casting and mold, etc. In the present paper, the interfacial heat transfer coefficient (IHTC) between the casting and metal mold is identified by using the method of inverse analysis based on measured temperatures, neural network with back-propagation algorithm and numerical simulation. Then, by applying the identified IHTC in finite element analysis, the comparison between numerical calculated and experimental results is made to verify the correctness of method. The results show that the numerical calculated temperatures are in good agreement with experimental ones. These demonstrate that the method of inverse analysis is a feasible and effective tool for determination of the casting-mold IHTC. In addition, it is found that the identified IHTC varies with time during the casting solidification and varies in the range of about 100-3200 Wm{sup -2}K{sup -1}. The characteristics of the time-varying IHTC have also been discussed.

Zhang Liqiang [State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, 410082 Hunan (China); College of Materials Science Engineering, Hunan University, Changsha, 410082 Hunan (China); Li Luoxing, E-mail: llxly2000@163.co [State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, Hunan University, Changsha, 410082 Hunan (China) and College of Materials Science Engineering, Hunan University, Changsha, 410082 Hunan (China); Ju Hui; Zhu Biwu [College of Materials Science Engineering, Hunan University, Changsha, 410082 Hunan (China)

2010-10-15

94

Determination of the metal/die interfacial heat transfer coefficient of high pressure die cast B390 alloy  

Science.gov (United States)

High-pressure die cast B390 alloy was prepared on a 350 ton cold chamber die casting machine. The metal/die interfacial heat transfer coefficient of the alloy was investigated. Considering the filling process, a "finger"-shaped casting was designed for the experiments. This casting consisted of five plates with different thicknesses (0.05 inch or 1.27 mm to 0.25 inch or 6.35 mm) as well as individual ingates and overflows. Experiments under various operation conditions were conducted, and temperatures were measured at various specific locations inside the die. Based on the results, the interfacial heat transfer coefficient and heat flux were determined by solving the inverse heat transfer problem. The influence of the mold-filling sequence, sensor locations, as well as processing parameters including the casting pressure, die temperature, and fast/slow shot speeds on the heat transfer coefficient were discussed.

Cao, Yongyou; Guo, Zhipeng; Xiong, Shoumei

2012-07-01

95

The effect of molecular aggregates over the interfacial charge transfer processes on dye sensitized solar cells  

Science.gov (United States)

The electron transfer reaction between the photoinjected electrons in the nanocrystalline TiO2 mesoporous sensitized films and the oxidized electrolyte in dye sensitized solar cells (DSSC) plays a major role on the device efficiency. In this communication we show that, although the presence of molecular aggregates on the free base porphyrin DSSC limits the device photocurrent response under illumination, they form an effective hydrophobic barrier against the oxidized electrolyte impeding fast back-electron transfer kinetics. Therefore, their drawback can be overcome by designing dyes with peripheral moieties that prevent the formation of the aggregates and are able to achieve efficiencies as high as 3.2% under full sun.

Planells, Miquel; Forneli, Amparo; Martínez-Ferrero, Eugenia; Sánchez-Díaz, Antonio; Sarmentero, Maria Angeles; Ballester, Pablo; Palomares, Emilio; O'Regan, Brian C.

2008-04-01

96

Solar energy conversion dynamics of interfacial electron and excitation transfer  

CERN Document Server

The importance of developing new, clean and renewable sources of energy will continue to grow in the foreseeable future and so will the need for the education of researchers in this field of research. The interest and challenges of the field continue to shift from simple homogeneous solutions to increasingly more complex heterogeneous systems and interfaces. Over the past decade there have been numerous theoretical and experimental breakthroughs many of which still exist only in the primary literature. The aim of this book is to gather in one volume the description of modern, sometimes explora

Piotrowiak, Piotr

2013-01-01

97

Interfacial electron transfer dynamics of photosensitized zinc oxide nanoclusters  

Energy Technology Data Exchange (ETDEWEB)

The authors have prepared and characterized photosensitized zinc oxide (ZnO) nanoclusters, dispersed in methanol, using carboxylated coumarin dyes for surface adsorption. Femtosecond time-resolved emission spectroscopy allows the authors to measure the photo-induced charge carrier injection rate constant from the adsorbed photosensitizer to the n-type semiconductor nanocluster. These results are compared with other photosensitized semiconductors.

Murakoshi, Kei; Yanagida, Shozo [Osaka Univ. (Japan). Graduate School of Engineering; Capel, M. [Brookhaven National Lab., Upton, NY (United States)] [and others

1997-06-01

98

Interfacial electron and phonon scattering processes in high-powered nanoscale applications.  

Energy Technology Data Exchange (ETDEWEB)

The overarching goal of this Truman LDRD project was to explore mechanisms of thermal transport at interfaces of nanomaterials, specifically linking the thermal conductivity and thermal boundary conductance to the structures and geometries of interfaces and boundaries. Deposition, fabrication, and post possessing procedures of nanocomposites and devices can give rise to interatomic mixing around interfaces of materials leading to stresses and imperfections that could affect heat transfer. An understanding of the physics of energy carrier scattering processes and their response to interfacial disorder will elucidate the potentials of applying these novel materials to next-generation high powered nanodevices and energy conversion applications. An additional goal of this project was to use the knowledge gained from linking interfacial structure to thermal transport in order to develop avenues to control, or 'tune' the thermal transport in nanosystems.

Hopkins, Patrick E.

2011-10-01

99

Interfacial electron and phonon scattering processes in high-powered nanoscale applications  

International Nuclear Information System (INIS)

The overarching goal of this Truman LDRD project was to explore mechanisms of thermal transport at interfaces of nanomaterials, specifically linking the thermal conductivity and thermal boundary conductance to the structures and geometries of interfaces and boundaries. Deposition, fabrication, and post possessing procedures of nanocomposites and devices can give rise to interatomic mixing around interfaces of materials leading to stresses and imperfections that could affect heat transfer. An understanding of the physics of energy carrier scattering processes and their response to interfacial disorder will elucidate the potentials of applying these novel materials to next-generation high powered nanodevices and energy conversion applications. An additional goal of this project was to use the knowledge gained from linking interfacial structure to thermal transport in order to develop avenues to control, or 'tune' the thermal transport in nanosystems.

100

Interfacial condensation heat transfer for countercurrent steam-water stratified flow in a circular pipe  

International Nuclear Information System (INIS)

An experimental study of steam condensation on a subcooled thick water layer (0.018 ? 0.031 m) in a countercurrent stratified flow has been performed using a nearly horizontal circular pipe. A total of 103 average interfacial condensation heat transfer coefficients were obtained and parametric effects of steam and water flow rates and the degree of subcooling on condensation heat transfer were examined. The measured local temperature and velocity distributions in the thick water layer revealed that there was a thermal stratification due to the lack of full turbulent thermal mixing in the lower region of the water layer. Two empirical Nusselt number correlations, one in items of average steam and water Reynolds numbers, and the water Prandtl number, and the other in terms of the Jacob number in place of the Prandtl number, which agree with most of the data within ±25 percent were developed based on the bulk flow properties. Comparisons of the present data with existing correlations showed that the present data were significantly lower than the values predicted by existing correlations. (author)

 
 
 
 
101

Evaluation of interfacial mass transfer coefficient as a function of temperature and pressure in carbon dioxide/normal alkane systems  

Science.gov (United States)

CO2 gas injection is known as one of the most popular enhanced oil recovery techniques for light and medium oil reservoirs, therefore providing an acceptable mass transfer mechanism for CO2-oil systems seems necessary. In this study, interfacial mass transfer coefficient has been evaluated for CO2-normal heptane and CO2-normal hexadecane systems using equilibrium and dynamic interfacial tension data, which have been measured using the pendant drop method. Interface mass transfer coefficient has been calculated as a function of temperature and pressure in the range of 313-393 K and 1.7-8.6 MPa, respectively. The results showed that the interfacial resistance is a parameter that can control the mass transfer process for some CO2-normal alkane systems, and cannot be neglected. Additionally, it was found that interface mass transfer coefficient increased with pressure. However, the variation of this parameter with temperature did not show a clear trend and it was strongly dependent on the variation of diffusivity and solubility of CO2 in the liquid phase.

Nikkhou, Fatemeh; Keshavarz, Peyman; Ayatollahi, Shahab; Jahromi, Iman Raoofi; Zolghadr, Ali

2014-09-01

102

Air/sea DMS gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed  

Science.gov (United States)

Shipboard measurements of eddy covariance DMS air/sea fluxes and seawater concentration were carried out in the North Atlantic bloom region in June/July 2011. Gas transfer coefficients (k660) show a linear dependence on mean horizontal wind speed at wind speeds up to 11 m s-1. At higher wind speeds the relationship between k660 and wind speed weakens. At high winds, measured DMS fluxes were lower than predicted based on the linear relationship between wind speed and interfacial stress extrapolated from low to intermediate wind speeds. In contrast, the transfer coefficient for sensible heat did not exhibit this effect. The apparent suppression of air/sea gas flux at higher wind speeds appears to be related to sea state, as determined from shipboard wave measurements. These observations are consistent with the idea that long waves suppress near surface water side turbulence, and decrease interfacial gas transfer. This effect may be more easily observed for DMS than for less soluble gases, such as CO2, because the air/sea exchange of DMS is controlled by interfacial rather than bubble-mediated gas transfer under high wind speed conditions.

Bell, T. G.; De Bruyn, W.; Miller, S. D.; Ward, B.; Christensen, K.; Saltzman, E. S.

2013-05-01

103

Air/sea DMS gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed  

Directory of Open Access Journals (Sweden)

Full Text Available Shipboard measurements of eddy covariance DMS air/sea fluxes and seawater concentration were carried out in the North Atlantic bloom region in June/July 2011. Gas transfer coefficients (k660 show a linear dependence on mean horizontal wind speed at wind speeds up to 11 m s?1. At higher wind speeds the relationship between k660 and wind speed weakens. At high winds, measured DMS fluxes were lower than predicted based on the linear relationship between wind speed and interfacial stress extrapolated from low to intermediate wind speeds. In contrast, the transfer coefficient for sensible heat did not exhibit this effect. The apparent suppression of air/sea gas flux at higher wind speeds appears to be related to sea state, as determined from shipboard wave measurements. These observations are consistent with the idea that long waves suppress near surface water side turbulence, and decrease interfacial gas transfer. This effect may be more easily observed for DMS than for less soluble gases, such as CO2, because the air/sea exchange of DMS is controlled by interfacial rather than bubble-mediated gas transfer under high wind speed conditions.

T. G. Bell

2013-05-01

104

Measurements of electron—phonon coupling factor and interfacial thermal resistance of metallic nano-films using a transient thermoreflectance technique  

International Nuclear Information System (INIS)

Using a transient thermoreflectance (TTR) technique, several Au films with different thicknesses on glass and SiC substrates are measured for thermal characterization of metallic nano-films, including the electron-phonon coupling factor G, interfacial thermal resistance R, and thermal conductivity Ks of the substrate. The rear heating-front detecting (RF) method is used to ensure the femtosecond temporal resolution. An intense laser beam is focused on the rear surface to heat the film, and another weak laser beam is focused on the very spot of the front surface to detect the change in the electron temperature. By varying the optical path delay between the two beams, a complete electron temperature profile can be scanned. Different from the normally used single-layer model, the double-layer model involving interfacial thermal resistance is studied here. The electron temperature cooling profile can be affected by the electron energy transfer into the substrate or the electron-phonon interactions in the metallic films. For multiple-target optimization, the genetic algorithm (GA) is used to obtain both G and R. The experimental result gives a deep understanding of the mechanism of ultra-fast heat transfer in metals. (general)

105

Impact of bidirectional charge transfer and molecular distortions on the electronic structure of a metal-organic interface.  

Science.gov (United States)

Interface energetics are of fundamental importance in organic and molecular electronics. By combining complementary experimental techniques and first-principles calculations, we resolve the complex interplay among several interfacial phenomena that collectively determine the electronic structure of the strong electron acceptor tetrafluoro-tetracyanoquinodimethane chemisorbed on copper. The combination of adsorption-induced geometric distortion of the molecules, metal-to-molecule charge transfer, and molecule-to-metal back transfer leads to a net increase of the metal work function. PMID:18233542

Romaner, Lorenz; Heimel, Georg; Brédas, Jean-Luc; Gerlach, Alexander; Schreiber, Frank; Johnson, Robert L; Zegenhagen, Jörg; Duhm, Steffen; Koch, Norbert; Zojer, Egbert

2007-12-21

106

Light induced electron transfer of metal complexes  

International Nuclear Information System (INIS)

Light induced electron transfer of metal complexes has been studied extensively during the last decade. This interest was stimulated by attempts to develop an artificial photosynthesis for the conversion and chemical storage of solar energy. Even if this goal has not yet been achieved photochemical redox processes of coordination compounds are now much better understood. In this review the various possibilities of photoinduced electron transfer are discussed and illustrated by selected samples. A distinction is made between intra- and intermolecular electron transfer which may occur as a direct optical transition or by an excited state electron transfer mechanism. (author). 52 refs.; 1 fig

107

Defining new frontiers in electronic devices with high ? dielectrics and interfacial engineering  

International Nuclear Information System (INIS)

Ga2O3(Gd2O3), a high ? gate dielectric, ultrahigh vacuum (UHV)-deposited on GaAs and InGaAs has unpinned the Fermi level in the high-electron-mobility III-V compound semiconductors for the first time. Systematic heat treatments under various gases and temperatures were studied to achieve low leakage currents of 10-8-10-9 A/cm2 and low interfacial density of states (D it's) in the range of 11 cm-2 eV-1. By removing moisture from the oxide, thermodynamic stability of the Ga2O3(Gd2O3)/GaAs heterostructures and the interfaces were achieved with high temperature annealing, the oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. The Fermi-level unpinning in atomic layer deposition (ALD) Al2O3 ex-situ deposited on InGaAs was achieved. Recent work of extremely high-quality nano-thick single crystal oxides of gamma-Al2O3 and bixbyite cubic Sc2O3 epitaxially grown on Si (111) is discussed. Interfacial manipulation is essential in giving excellent results presented in the paper. X-ray diffraction, reflectivity, and X-ray photoelectron spectroscopy using synchrotron radiation are critical in probing the interfacial properties

108

Kinetic and structural studies, origins of selectivity, and interfacial charge transfer in the artificial photosynthesis of CO  

Energy Technology Data Exchange (ETDEWEB)

The effective design of an artificial photosynthetic system entails the optimization of several important interactions. Herein we report stopped-flow UV-Vis spectroscopy, X-ray crystallography, DFT, and electrochemical kinetic studies of the Re(bipy-tBu)(CO)3(L) catalyst system. A remarkable selectivity for CO2 over H+ was observed by stopped-flow UV-Vis spectroscopy of [Re(bipy-tBu)(CO)3]-. The pseudo-first order rate constant for the reaction with 10 mM CO2 in THF is 35 s-1. This is ca. 15-20 times faster than the reactions with water or methanol at the same concentration in THF. X-ray crystallography and DFT studies of the doubly-reduced anionic species suggest that the HOMO has mixed metal-ligand character rather than being purely dz 2, which is thought to aid catalytic selectivity by favoring binding of CO2 over H+. Electrocatalytic studies performed with the addition of Brönsted acids reveal a primary H/D kinetic isotope effect, indicating that transfer of protons to Re-CO2 is involved in the rate limiting step. Lastly, the effects of electrode surface modification on interfacial electron transfer between a semiconductor and catalyst were investigated and found to affect the observed catalytic rates up to seven-fold, indicating that the properties of the electrode surface should not be overlooked when developing a homogeneous artificial photosynthetic system. This research was supported at the University of Washington, Seattle by the Camille and Henry Dreyfus Postdoctoral Program in Environmental Chemistry (for a fellowship to A. J. M. M.), and, for funds to purchase the stopped-flow instrument, the U.S. National Institutes of Health 13 (Grant GM-50422 to JMM), and 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.

Smieja, Jonathan M.; Benson, Eric E.; Kumar, Bhupendra; Grice, Kyle A.; Seu, Candace; Miller, Alexander J.; Mayer, James M.; Kubiak, Cliff

2012-09-25

109

Flavin Electron Shuttles Dominate Extracellular Electron Transfer by Shewanella oneidensis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Shewanella oneidensis strain MR-1 is widely studied for its ability to respire a diverse array of soluble and insoluble electron acceptors. The ability to breathe insoluble substrates is defined as extracellular electron transfer and can occur via direct contact or by electron shuttling in S. oneidensis. To determine the contribution of flavin electron shuttles in extracellular electron transfer, a transposon mutagenesis screen was performed with S. oneidensis to identify mutants unable to ...

Kotloski, Nicholas J.; Gralnick, Jeffrey A.

2013-01-01

110

Concatenation of reversible electronic energy transfer and photoinduced electron transfer to control a molecular piston.  

Science.gov (United States)

Reversible electronic energy transfer and photoinduced electron transfer conspire in the light-driven dethreading of a molecular piston, showing the potential of combining these processes in supramolecular systems. PMID:22428161

Scarpantonio, Luca; Tron, Arnaud; Destribats, Carole; Godard, Pascale; McClenaghan, Nathan D

2012-04-25

111

Kinetics and mechanism of the interfacial mass transfer of Eu3+ and Am3+ in the system bis(2-ethylhexyl) phosphate-n-dodecane-NaCl-HCl-water  

International Nuclear Information System (INIS)

The mass-transfer kinetics of Eu3+ and Am3+ between aqueous chloride solutions and n-dodecane solutions of bis(2-ethylhexyl) phosphate (HDEHP) have been investigated by using a constant-interfacial-area stirred cell. The results have been interpreted according to two alternative models: (1) the mass-transfer rate is controlled by interfacial film diffusion and (2) the mass-transfer rate is controlled by a series of slow reversible interfacial reactions. According to the latter model an interfacial complex between the metal cation and HDEHP is the main intermediate of the series of chemical reactions. The equilibrium constants which describe the heterogeneous reactions between Am3+, Eu3+, and HDEHP also have been evaluated

112

Computer simulation of electron transfer in molecular electronic devices  

Energy Technology Data Exchange (ETDEWEB)

The study of electron transfer through individual molecules bound to metal electrodes has become important due to the potential application in molecular electronic devices. Since the electronic and atomic motions in these molecules influence each other, they need to be treated self-consistently. We have used self-consistent quantum chemistry molecular dynamics calculations to discuss some of the issues related to electron transfer through a spatially symmetric [9,10-bis((2'-para-mercaptophenyl)-ethinyl)-anthracene] and an asymmetric [1,4-bis((2'-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene] molecule bound to metal electrodes. Specifically addressed are the effects of voltage inversion on electron transfer between electrodes through both molecules. Our results show an electron transfer behaviour that reproduces the spatial symmetry of the molecules in agreement with experimental current-voltage data. The change in time of electron density and dimerisation at specific atomic sites is also discussed.

Correia, Helena M.G. [Departamento de Fisica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal); Ramos, Marta M.D. [Departamento de Fisica, Universidade do Minho, Campus de Gualtar, 4710-057 Braga (Portugal)]. E-mail: marta@fisica.uminho.pt

2005-12-15

113

Interfacial charge transfer events of BODIPY molecules: single molecule spectroelectrochemistry and substrate effects.  

Science.gov (United States)

We present single molecule fluorescence and spectroelectrochemistry characteristics of 4,4'-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) bearing two carboxylic acid groups at its 2 and 6 positions. Our study shows a heterogeneous half redox potential distribution for the BODIPY molecules embedded in polystyrene film because of the heterogeneity in their charge transfer rates. Single molecules adsorbed onto a TiO2 surface with ordered nanostructures show surprising fluorescence blinking activity with the shortest ON duration time in comparison to bare glass and indium-tin oxide (ITO) surfaces. Single molecule stability tests show longer ON duration time and a stable fluorescence feature when dispersed in polystyrene thin film than molecules exposed to air. Shorter ON times are observed for molecules. In intimate contact with ITO in comparison to glass substrates. Such a decrease in their fluorescence stability or intensity is explained by charge transfer activities from the dye molecules to the metal oxide surface. Electron transfer and back transfer rates are calculated to illustrate the substrate effects by using a well-established model. PMID:25252244

Liu, Jia; Hill, Caleb M; Pan, Shanlin; Liu, Haiying

2014-10-01

114

Defining new frontiers in electronic devices with high {kappa} dielectrics and interfacial engineering  

Energy Technology Data Exchange (ETDEWEB)

Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3}), a high {kappa} gate dielectric, ultrahigh vacuum (UHV)-deposited on GaAs and InGaAs has unpinned the Fermi level in the high-electron-mobility III-V compound semiconductors for the first time. Systematic heat treatments under various gases and temperatures were studied to achieve low leakage currents of 10{sup -8}-10{sup -9} A/cm{sup 2} and low interfacial density of states (D {sub it'}s) in the range of < 10{sup 11} cm{sup -2} eV{sup -1}. By removing moisture from the oxide, thermodynamic stability of the Ga{sub 2}O{sub 3}(Gd{sub 2}O{sub 3})/GaAs heterostructures and the interfaces were achieved with high temperature annealing, the oxide remains amorphous and the interface remains intact with atomic smoothness and sharpness. The Fermi-level unpinning in atomic layer deposition (ALD) Al{sub 2}O{sub 3} ex-situ deposited on InGaAs was achieved. Recent work of extremely high-quality nano-thick single crystal oxides of gamma-Al{sub 2}O{sub 3} and bixbyite cubic Sc{sub 2}O{sub 3} epitaxially grown on Si (111) is discussed. Interfacial manipulation is essential in giving excellent results presented in the paper. X-ray diffraction, reflectivity, and X-ray photoelectron spectroscopy using synchrotron radiation are critical in probing the interfacial properties.

Hong, M. [Department of Materials Science and Eng., National Tsing Hua University, Hsinchu, Taiwan (China)]. E-mail: mhong@mx.nthu.edu.tw; Lee, W.C. [Department of Materials Science and Eng., National Tsing Hua University, Hsinchu, Taiwan (China); Huang, M.L. [Department of Materials Science and Eng., National Tsing Hua University, Hsinchu, Taiwan (China); Chang, Y.C. [Department of Materials Science and Eng., National Tsing Hua University, Hsinchu, Taiwan (China); Lin, T.D. [Department of Materials Science and Eng., National Tsing Hua University, Hsinchu, Taiwan (China); Lee, Y.J. [Department of Materials Science and Eng., National Tsing Hua University, Hsinchu, Taiwan (China); Kwo, J. [Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China); Hsu, C.H. [Synchrotron Radiation Research Center, Hsinchu, Taiwan (China); Lee, H.Y. [Synchrotron Radiation Research Center, Hsinchu, Taiwan (China)

2007-05-23

115

Interfacial ion-transfer mechanism for the intense luminescence observed when opening self-seal envelopes.  

Science.gov (United States)

The unusually intense luminescence (commonly called triboluminescence) observed when opening self-seal envelopes has been studied using spectroscopy. Emissions from gas-phase species due to electrical discharge were observed, which in the case of air consists of vibronic transitions of N(2)(C(3)?(u)-B(3)?(g)) in the ultraviolet (UV) region (280-400 nm). However, the major cause of the intense blue luminescence (around 435 nm) is attributed to optical brightening agents added to the white paper. The results suggest that the emission from the brightening agents may be caused by two mechanisms: (i) fluorescence due to excitation by the UV light from the gas discharge and (ii) nonoptically, by electron transfer. The electrical discharge results from contact electrification; we propose a mechanism for the charge transfer involving a net migration of hydroxide anions out of the paper into the wet latex-adhesive during drying. PMID:22924818

Alexander, Andrew J

2012-09-18

116

Nuclear reorganization barriers to electron transfer  

International Nuclear Information System (INIS)

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

117

Hierarchical control of electron-transfer  

DEFF Research Database (Denmark)

In this chapter the role of electron transfer in determining the behaviour of the ATP synthesising enzyme in E. coli is analysed. It is concluded that the latter enzyme lacks control because of special properties of the electron transfer components. These properties range from absence of a strong back pressure by the protonmotive force on the rate of electron transfer to hierarchical regulation of the expression of the gens that encode the electron transfer proteins as a response to changes in the bioenergetic properties of the cell.The discussion uses Hierarchical Control Analysis as a paradigm. This allows one to analyse a complex system of regulatory interactions in terms of the importance of the contributing factors.

Jensen, Peter Ruhdal

1997-01-01

118

Effect of casting/mould interfacial heat transfer during solidification of aluminium alloys cast in CO2-sand mould  

Science.gov (United States)

The ability of heat to flow across the casting and through the interface from the casting to the mold directly affects the evolution of solidification and plays a notable role in determining the freezing conditions within the casting, mainly in foundry systems of high thermal diffusivity such as chill castings. An experimental procedure has been utilized to measure the formation process of an interfacial gap and metal-mould interfacial movement during solidification of hollow cylindrical castings of Al-4.5 % Cu alloy cast in CO2-sand mould. Heat flow between the casting and the mould during solidification of Al-4.5 % Cu alloy in CO2-sand mould was assessed using an inverse modeling technique. The analysis yielded the interfacial heat flux ( q), heat transfer coefficient ( h) and the surface temperatures of the casting and the mould during solidification of the casting. The peak heat flux was incorporated as a dimensionless number and modeled as a function of the thermal diffusivities of the casting and the mould materials. Heat flux transients were normalized with respect to the peak heat flux and modeled as a function of time. The heat flux model proposed was to estimate the heat flux transients during solidification of Al-4.5 % Cu alloy cast in CO2-sand moulds.

Kulkarni, S. N.; Radhakrishna, D. K.

2011-06-01

119

Hierarchical assembly of BiOCl nanosheets onto bicrystalline TiO2 nanofiber: Enhanced photocatalytic activity based on photoinduced interfacial charge transfer.  

Science.gov (United States)

One-dimensional ternary hierarchical heterostructures based on BiOCl nanosheets and bicrystalline TiO2 nanofiber frameworks that consist of anatase-rutile (AR) mixed phase TiO2 nanoparticles were successfully designed by combining the electrospinning technique and solvothermal method. The BiOCl nanosheets were uniformly grown onto the electrospun TiO2 nanofibers, and the density of the secondary BiOCl nanosheets could be controlled by adjusting the precursor concentration. Photocatalytic tests displayed that the ternary BiOCl/TiO2 (AR) hierarchical heterostructures possessed a much higher degradation rate than the bare bicrystalline TiO2 (AR) nanofibers, BiOCl/TiO2 (A) or BiOCl/TiO2 (R) composite. It is mainly attributed to the photogenerated interfacial charge transfer based on the photosynergistic effect of the heterojunctions, which results in the high separation efficiency of photogenerated electron-hole pairs. PMID:25217727

Li, Lu; Zhang, Mingyi; Liu, Ying; Zhang, Xitian

2014-12-01

120

Decoupling interfacial reactions between plasmas and liquids: charge transfer vs plasma neutral reactions.  

Science.gov (United States)

Plasmas (gas discharges) formed at the surface of liquids can promote a complex mixture of reactions in solution. Here, we decouple two classes of reactions, those initiated by electrons (electrolysis) and those initiated by gaseous neutral species, by examining an atmospheric-pressure microplasma formed in different ambients at the surface of aqueous saline (NaCl) solutions. Electrolytic reactions between plasma electrons and aqueous ions yield an excess of hydroxide ions (OH(-)), making the solution more basic, while reactions between reactive neutral species formed in the plasma phase and the solution lead to nitrous acid (HNO2), nitric acid (HNO3), and hydrogen peroxide (H2O2), making the solution more acidic. The relative importance of either reaction path is quantified by pH measurements, and we find that it depends directly on the composition of the ambient background gas. With a background gas of oxygen or argon, electron transfer reactions yielding excess OH(-) dominate, while HNO2 and HNO3 formed in the plasma and by the dissolution of nitrogen oxide (NOx) species dominate in the case of air and nitrogen. For pure nitrogen (N2) gas, we observe a unique coupling between both reactions, where oxygen (O2) gas formed via water electrolysis reacts in the bulk of the plasma to form NOx, HNO2, and HNO3. PMID:24144120

Rumbach, Paul; Witzke, Megan; Sankaran, R Mohan; Go, David B

2013-11-01

 
 
 
 
121

Electron transfer induced fragmentation of acetic acid  

Science.gov (United States)

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

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

2014-04-01

122

Photon-induced electron transfer transitions of the solvated electrons  

Energy Technology Data Exchange (ETDEWEB)

The role of electron transfer transitions in the absorption spectrum of the solvated electron in liquid water is studied in terms of the generalized line shape function. When the density of trapping sites is greater than one third of the density of solvent molecules, the transition-dipole moment for photon-induced electron transfers was found to be greater than that of the single-site 1s..-->..2p transition. The solvated electron is assumed to be coupled with low-frequency solvent modes and a high-frequency molecular mode. The latter mode is responsible for a small isotope shift in the peak energy. The spectrum consists of contributions from short-distance transfers (''bound--bound'') and long-distance (''bound--free'') transfers, the latter being the minor component of the total spectrum.

Funabashi, K.; Carmichael, I.; Hamill, W.H.

1978-09-15

123

Excited state electron transfer after visible light absorption by the Co(i) state of vitamin B12.  

Science.gov (United States)

The first example of excited state electron transfer from cob(i)alamin is reported herein. Vitamin B12 was anchored to a mesoporous TiO2 thin film and electrochemically reduced to the cob(i)alamin form. Pulsed laser excitation resulted in rapid excited state electron transfer, ket > 10(8) s(-1), followed by microsecond interfacial charge recombination to re-form cob(i)alamin. The supernucleophilic cob(i)alamin was found to be a potent photoreductant. The yield of excited state electron transfer was found to be excitation wavelength dependent. The implications of this dependence are discussed. PMID:25232558

Achey, Darren; Brigham, Erinn C; DiMarco, Brian N; Meyer, Gerald J

2014-10-01

124

A perspective of biological supramolecular electron transfer.  

Science.gov (United States)

Electron transfer is an essential activity in biological systems. The migrating electron originates from water-oxygen in photosynthesis and reverts to dioxygen in respiration. In this cycle two metal porphyrin complexes possessing circular conjugated system and macrocyclic pi-clouds, chlorophyll and heme, play a decisive role in mobilising electrons for travel over biological structures as extraneous electrons. Transport of electrons within proteins (as in cytochromes) and within DNA (during oxidative damage and repair) is known to occur. Initial evaluations did not favour formation of semiconducting pathways of delocalized electrons of the peptide bonds in proteins and of the bases in nucleic acids. Direct measurement of conductivity of bulk material and quantum chemical calculations of their polymeric structures also did not support electron transfer in both proteins and nucleic acids. New experimental approaches have revived interest in the process of charge transfer through DNA duplex. The fluorescence on photo-excitation of Ru-complex was found to be quenched by Rh-complex, when both were tethered to DNA and intercalated in the base stack. Similar experiments showed that damage to G-bases and repair of T-T dimers in DNA can occur by possible long range electron transfer through the base stack. The novelty of this phenomenon prompted the apt name, "chemistry at a distance". Based on experiments with ruthenium modified proteins, intramolecular electron transfer in proteins is now proposed to use pathways that include C-C sigma-bonds and surprisingly hydrogen bonds which remained out of favour for a long time. In support of this, some experimental evidence is now available showing that hydrogen bond-bridges facilitate transfer of electrons between metal-porphyrin complexes. By molecular orbital calculations over 20 years ago we found that "delocalization of an extraneous electron is pronounced when it enters low-lying virtual orbitals of the electronic structures of peptide units linked by hydrogen bonds". This review focuses on supramolecular electron transfer pathways that can emerge on interlinking by hydrogen bonds and metal coordination of some unnoticed structures with pi-clouds in proteins and nucleic acids, potentially useful in catalysis and energy missions. PMID:10844992

Ramasarma, T

1999-12-01

125

Bioinspired electron-transfer systems and applications  

International Nuclear Information System (INIS)

Bioinspired electron-transfer systems including artificial photosynthesis and respiration are presented herein together with some of their applications. First, multi-step electron-transfer systems composed of electron donor-acceptor ensembles have been developed, mimicking functions of the photosynthetic reaction center. However, a significant amount of energy is lost during the multi-step electron-transfer processes. Then, as an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer within redox cascades, simple donor-acceptor dyads have been developed to attain along-lived and high energy charge-separated state without significant loss of excitation energy, by fine control of the redox potentials and of the geometry of donor-acceptor dyads that have small reorganization energies of electron transfer. Such simple molecular dyads, capable of fast charge separation but extremely slow charge recombination, have significant advantages with regard to synthetic feasibility, providing a variety of applications including construction of organic solar cells and development of efficient photo-catalytic systems for the solar energy conversion. An efficient four-electron reduction of dioxygen to water by one-electron reductants such as ferrocene derivatives as well as by an NADH analog has also been achieved as a respiration model by using a cofacial dicobalt porphyrin that can form the ?-peroxo Co(III)-O2Co(III) complex. The catalytic mechanism of the four-electron reduction of dioxygen has been clarified based on the detailed kinetic study and the detection of the intermediate. (author)

126

Intramolecular electron transfer in bipyridinium disulfides.  

Science.gov (United States)

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

127

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

128

Influence of the interfacial roughness on electron channelling in Fe/Au(001) multilayers  

International Nuclear Information System (INIS)

Fe/Au(001) multilayers have been grown by molecular beam epitaxy using a new technique for the preparation of Au buffer layers on MgO(001) substrates. Scanning tunnelling microscopy and grazing incidence x-ray scattering reveal that the Au buffers have extremely low interface roughness and a long in-plane correlation length. X-ray scattering and diffraction show that multilayers grown on the new buffers, although having little difference in their crystalline structure, have much smoother interfaces than those grown on previous buffers. Compared with earlier multilayers with rougher interfaces, the giant magnetoresistance has increased by 20% due to more complete antiferromagnetic exchange coupling. Measurement of the saturation conductivity shows that the number of specular reflections occurring during electron channelling remains unchanged even though the interfacial roughness is reduced by a factor of six. It is postulated that the cause of this is either that spin-dependent scattering at the interface is being driven solely by the difference in the band structure, not by diffuse scatter at the interfaces, or that the wavelength of the transport electrons is such that the change in the roughness has no effect upon the specular scattering

129

Interfacial Electronic and Magnetic Coupling in Organic-metal System Studied by Scanning Tunneling Microscopy  

Science.gov (United States)

Organic materials have drawn much attention in spintronics studies because of their tunable properties by functional groups and potential to achieve molecular magnets. An important factor influencing these properties is the interfacial effect. In organic-metal systems, different interfaces lead to strong modulation of electronic structures and even magnetic behaviors like spin coupling. In our study, Mn-phthalocyanine (MnPc) deposited on Cu(111) surface have been measured by scanning tunneling microscopy (STM) and spectroscopy (STS) at 4.5 K. With different deposition amount, MnPc are adsorbed as isolated molecules or in an ordered assembled structure. From STS curves, assembled MnPc possess a broadened state near the onset of Cu(111) surface state comparing to islolated ones. According to ab initio calculation, distance between the central Mn atom and the substrate in assembled molecules is reduced due to intermolecular interaction and affects the electronic structures. Magnetic behaviors of MnPc on ferromagnetic metal substrate are further investigated by spin-polarized STM (SP-STM). Spin contrast of isolated molecules on Co nanoislands on Cu(111) is found near the Fermi level in STS maps, which is considered to be ferromagnetic coupling between MnPc and Co islands.

Chu, Yu-Hsun; Hsu, C. H.; Hsu, P. J.; Hsieh, W. J.; Lu, C. I.; Chen, S. W.; Butler, C. J.; Kaun, Chao-Cheng; Lin, Minn-Tsong

2012-02-01

130

Electron transfer in weakly interacting systems  

International Nuclear Information System (INIS)

A recently proposed semiclassical model, in which an electronic transmission coefficient and a nuclear tunneling factor are introduced as corrections to the classical activated-complex expression, is described. The nuclear tunneling corrections are shown to be important only at low temperatures or when the electron transfer is very exothermic. By contrast, corrections for nonadiabaticity may be significant for most outer-sphere reactions of metal complexes. The rate constants for the Fe(H2O)62+-Fe(H2O)63+, Ru(NH3)62+-Ru(NH3)63+ and Ru(bpy)32+-Ru(bpy)33+ electron exchange reactions predicted by the semiclassical model are in very good agreement with the observed values. The implications of the model for optically-induced electron transfer in mixed-valence systems are noted

131

Interfacial Charge Transport in Organic Electronic Materials: the Key to a New Electronics Technology  

Energy Technology Data Exchange (ETDEWEB)

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). The primary aim of this project is to obtain a basic scientific understanding of electrical transport processes at interfaces that contain an organic electronic material. Because of their processing advantages and the tunability of their electronic properties, organic electronic materials are revolutionizing major technological areas such as information display. We completed an investigation of the fundamental electronic excitation energies in the prototype conjugated polymer MEH-PPV. We completed a combined theoretical/experimental study of the energy relation between charged excitations in a conjugated polymer and the metal at a polymer/metal interface. We developed a theoretical model that explains injection currents at polymer/metal interfaces. We have made electrical measurements on devices fabricated using the conjugated polymer MEH-PPV a nd a series of metals.

Smith, D.L.; Campbell, I.H.; Davids, P.S.; Heller, C.M.; Laurich, B.K.; Crone, B.K.; Saxena, A.; Bishop, A.R.; Ferraris, J.P.; Yu, Z.G.

1999-06-04

132

Cycloreversion of ?-lactams via photoinduced electron transfer.  

Science.gov (United States)

The radical anions of ?-lactams, photogenerated in the presence of DABCO as an electron donor, undergo cycloreversion via N-C4 bond cleavage, back electron transfer and final C2-C3 bond cleavage, leading to olefins. The involved intermediates are 1,4-radical anions and 1,4-biradicals. The experimental observations are consistent with the results of DFT calculations. PMID:25223340

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

2014-10-01

133

Tomography based determination of permeability, Dupuit-Forchheimer coefficient, and interfacial heat transfer coefficient in reticulate porous ceramics  

International Nuclear Information System (INIS)

A computer tomography based methodology is applied to determine the transport properties of fluid flow across porous media. A 3D digital representation of a 10-ppi reticulate porous ceramic (RPC) sample was generated by X-ray tomographic scans. Structural properties such as the porosity, specific interfacial surface area, pore-size distribution, mean survival time, two-point correlation function s2, and local geometry distribution of the RPC sample are directly extracted from the tomographic data. Reference solutions of the fluid flow governing equations are obtained for Re = 0.2-200 by applying finite volume direct pore-level numerical simulation (DPLS) using unstructured, body-fitted, tetrahedral mesh discretization. The permeability and the Dupuit-Forchheimer coefficient are determined from the reference solutions by DPLS, and compared to the values predicted by selected porous media flow models, namely: conduit-flow, hydraulic radius theory, drag models, mean survival time bound, s2-bound, fibrous bed correlations, and local porosity theory-based models. DPLS is further employed to determine the interfacial heat transfer coefficient and to derive a corresponding Nu-correlation, which is compared to empirical correlations

134

Tailoring liquid/solid interfacial energy transfer: fabrication and application of multiscale metallic surfaces with engineered heat transfer and electrolysis properties via femtosecond laser surface processing techniques  

Science.gov (United States)

Femtosecond Laser Surface Processing (FLSP) is a powerful technique for the fabrication of self-organized multiscale surface structures on metals that are critical for advanced control over energy transfer at a liquid/solid interface in applications such as electrolysis. The efficiency of the hydrogen evolution reaction on stainless steel 316 electrodes in a 1 molar potassium hydroxide solution is used to analyze the role of surface geometry to facilitate the phase conversion of the liquid to a gaseous state in the vicinity of the interface. It is found that the efficiency of the electrolysis process is directly related to the separation of micro-scale features on an electrode surface. The enhancement is attributed to the size of the valleys between microstructures controlling the contact between an evolving vapor bubble and the electrode surface. The results suggest an alternative pathway for the tailoring of interfacial energy transfer on structured surfaces separate from traditional benchmarks such as surface area and contact angle.

Anderson, Troy P.; Wilson, Chris; Zuhlke, Craig A.; Kruse, Corey; Hassebrook, Anton; Somanas, Isra; Ndao, Sidy; Gogos, George; Alexander, Dennis

2014-03-01

135

75 FR 51707 - Electronic Funds Transfer of Depository Taxes  

Science.gov (United States)

...impact on small business. Comments...copies) or electronic comments that...or place of business in the United...Deposits by electronic funds transfer...is made by electronic funds transfer by the next business day,...

2010-08-23

136

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1990-10-20

137

A Study Looking the Electronic Funds Transfer  

Directory of Open Access Journals (Sweden)

Full Text Available The aim of this paper is to present the characteristics of the most important electronic funds transfer in the world, both interperson and interbank. We identified the following informations: location, type, owner, operator, number of transactions, transsactions value, clients, financial scheme and the message format.

Codruta POENAR

2008-01-01

138

Ultrafast electron and energy transfer in dye-sensitized iron oxide and oxyhydroxide nanoparticles  

DEFF Research Database (Denmark)

An emerging area in chemical science is the study of solid-phase redox reactions using ultrafast time-resolved spectroscopy. We have used molecules of the photoactive dye 2?,7?-dichlorofluorescein (DCF) anchored to the surface of iron(iii) oxide nanoparticles to create iron(ii) surface atoms via photo-initiated interfacial electron transfer. This approach enables time-resolved study of the fate and mobility of electrons within the solid phase. However, complete analysis of the ultrafast processes following dye photoexcitation of the sensitized iron(iii) oxide nanoparticles has not been reported. We addressed this topic by performing femtosecond transient absorption (TA) measurements of aqueous suspensions of uncoated and DCF-sensitized iron oxide and oxyhydroxide nanoparticles, and an aqueous iron(iii)–dye complex. Following light absorption, excited state relaxation times of the dye of 115–310 fs were found for all samples. Comparison between TA dynamics on uncoated and dye-sensitized hematite nanoparticles revealed the dye de-excitation pathway to consist of a competition between electron and energy transfer to the nanoparticles. We analyzed the TA data for hematite nanoparticles using a four-state model of the dye-sensitized system, finding electron and energy transfer to occur on the same ultrafast timescale. The interfacial electron transfer rates for iron oxides are very close to those previously reported for DCF-sensitized titanium dioxide (for which dye–oxide energy transfer is energetically forbidden) even though the acceptor states are different. Comparison of the alignment of the excited states of the dye and the unoccupied states of these oxides showed that the dye injects into acceptor states of different symmetry (Ti t2g vs. Fe eg).

Gilbert, Benjamin; Katz, Jordan E.

2013-01-01

139

Ultrafast electron and energy transfer in dye-sensitized iron oxide and oxyhydroxide nanoparticles.  

Science.gov (United States)

An emerging area in chemical science is the study of solid-phase redox reactions using ultrafast time-resolved spectroscopy. We have used molecules of the photoactive dye 2',7'-dichlorofluorescein (DCF) anchored to the surface of iron(III) oxide nanoparticles to create iron(II) surface atoms via photo-initiated interfacial electron transfer. This approach enables time-resolved study of the fate and mobility of electrons within the solid phase. However, complete analysis of the ultrafast processes following dye photoexcitation of the sensitized iron(III) oxide nanoparticles has not been reported. We addressed this topic by performing femtosecond transient absorption (TA) measurements of aqueous suspensions of uncoated and DCF-sensitized iron oxide and oxyhydroxide nanoparticles, and an aqueous iron(III)-dye complex. Following light absorption, excited state relaxation times of the dye of 115-310 fs were found for all samples. Comparison between TA dynamics on uncoated and dye-sensitized hematite nanoparticles revealed the dye de-excitation pathway to consist of a competition between electron and energy transfer to the nanoparticles. We analyzed the TA data for hematite nanoparticles using a four-state model of the dye-sensitized system, finding electron and energy transfer to occur on the same ultrafast timescale. The interfacial electron transfer rates for iron oxides are very close to those previously reported for DCF-sensitized titanium dioxide (for which dye-oxide energy transfer is energetically forbidden) even though the acceptor states are different. Comparison of the alignment of the excited states of the dye and the unoccupied states of these oxides showed that the dye injects into acceptor states of different symmetry (Ti t2gvs. Fe eg). PMID:24018485

Gilbert, Benjamin; Katz, Jordan E; Huse, Nils; Zhang, Xiaoyi; Frandsen, Cathrine; Falcone, Roger W; Waychunas, Glenn A

2013-10-28

140

Interfacial electronic structure of gold nanoparticles on Si(100): alloying versus quantum size effects.  

Science.gov (United States)

Gold nanoparticles (Au NPs) were prepared on a native-oxide-covered Si(100) substrate by sputter-deposition followed by thermal annealing. The size of Au NPs could be controlled in the range of 8-48 nm by varying the sputter-deposition time and post-annealing temperature. The interparticle separation was found to be directly related to the size of Au NPs, with smaller separations for particles of smaller size. The surface morphology, crystal structure, and interfacial composition of the chemical states of these supported Au NPs were studied as a function of their average size by using scanning electron microscopy, glancing-incidence X-ray diffraction, and depth-profiling X-ray photoelectron spectroscopy (XPS), respectively. The new Au 4f7/2 peak found at 1.1-1.2 eV higher in binding energy than that for the metallic Au feature (at 84.0 eV) can be attributed to the formation of Au silicide at the interface between Au NPs and the Si substrate. Depth-profiling XPS experiments revealed no discernible change in the binding energies of the Au silicide and metallic Au 4f features with increasing Ar+ sputtering time, indicating that the Au-to-silicide interface is abrupt. Furthermore, the shift in the Au 5d5/2 valence band to a higher binding energy and the reduction of the Au 5d spin-orbit splitting with increasing Ar+ sputtering time also support the formation of Au silicide. No clear evidence for the quantum size effect was observed for the supported NPs. The finite density of state at the Fermi level and the fixed Au 4f7/2 peak position clearly indicate the metallic nature of the Au silicide at the Au-Si interface. PMID:19518081

Sohn, Youngku; Pradhan, Debabrata; Radi, Abdullah; Leung, K T

2009-08-18

 
 
 
 
141

Electron transfer theory revisit: Quantum solvation effect  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of solvation on the electron transfer (ET) rate processes is investigated on the basis of the exact theory constructed in J. Phys. Chem. B Vol. 110, (2006); quant-ph/0604071. The nature of solvation is studied in a close relation with the mechanism of ET processes. The resulting Kramers' turnover and Marcus' inversion characteristics are analyzed accordingly. The classical picture of solvation is found to be invalid when the solvent longitudinal relaxation time is...

Han, Ping; Xu, Rui-xue; Cui, Ping; Mo, Yan; He, Guozhong; Yan, Yijing

2006-01-01

142

Electron transfer control in soluble methane monooxygenase.  

Science.gov (United States)

The hydroxylation or epoxidation of hydrocarbons by bacterial multicomponent monooxygenases (BMMs) requires the interplay of three or four protein components. How component protein interactions control catalysis, however, is not well understood. In particular, the binding sites of the reductase components on the surface of their cognate hydroxylases and the role(s) that the regulatory proteins play during intermolecular electron transfer leading to the hydroxylase reduction have been enigmatic. Here we determine the reductase binding site on the hydroxylase of a BMM enzyme, soluble methane monooxygenase (sMMO) from Methylococcus capsulatus (Bath). We present evidence that the ferredoxin domain of the reductase binds to the canyon region of the hydroxylase, previously determined to be the regulatory protein binding site as well. The latter thus inhibits reductase binding to the hydroxylase and, consequently, intermolecular electron transfer from the reductase to the hydroxylase diiron active site. The binding competition between the regulatory protein and the reductase may serve as a control mechanism for regulating electron transfer, and other BMM enzymes are likely to adopt the same mechanism. PMID:24937475

Wang, Weixue; Iacob, Roxana E; Luoh, Rebecca P; Engen, John R; Lippard, Stephen J

2014-07-01

143

Analysis of anodic current transient measured on Pd electrode with fractal surface: Hydrogen diffusion coupled with interfacial charge transfer  

Energy Technology Data Exchange (ETDEWEB)

Hydrogen transport through Pd electrode with fractally rough surface was investigated in 0.1 M NaOH solution by analysis of the anodic current transient. The Pd electrode surfaces were electrochemically modified to be rough by redox cycling in 1 M H{sub 2}SO{sub 4} solution. From the triangulation analysis of the atomic force microscopy images, it was found that the modified electrode surfaces exhibited self-similar scaling properties with different fractal dimensions, depending upon the number of redox cycles. The anodic current transient measured on the surface-modified fractal electrode subjected to the hydrogen discharging potentials of 0.3-0.7 V reversible hydrogen electrode, (RHE) showed the non-generalised Cottrell behaviour, which resulted from the constraint of hydrogen diffusion mixed with interfacial charge transfer during hydrogen transport. Especially, it displayed an inflexion point at the time that corresponds to the temporal outer cut-off of fractality, i.e. the crossover time required for the fractal to flat transition. In addition, the temporal outer cut-off under the constraint of mixed control was observed to be shortened with increasing hydrogen discharging potential, which could be accounted for by the increased growth rate of diffusion layer in the electrode accompanying the facilitated charge transfer kinetics at the electrode/electrolyte interface. (author)

Lee, Jong-Won; Pyun, Su-Il [Korea Advanced Institute of Science and Technology, Yuseong-Gu, Daejeon (Korea). Department of Materials Science and Engineering

2005-11-01

144

Analysis of anodic current transient measured on Pd electrode with fractal surface: Hydrogen diffusion coupled with interfacial charge transfer  

International Nuclear Information System (INIS)

Hydrogen transport through Pd electrode with fractally rough surface was investigated in 0.1 M NaOH solution by analysis of the anodic current transient. The Pd electrode surfaces were electrochemically modified to be rough by redox cycling in 1 M H2SO4 solution. From the triangulation analysis of the atomic force microscopy images, it was found that the modified electrode surfaces exhibited self-similar scaling properties with different fractal dimensions, depending upon the number of redox cycles. The anodic current transient measured on the surface-modified fractal electrode subjected to the hydrogen discharging potentials of 0.3-0.7 V reversible hydrogen electrode (RHE) showed the non-generalised Cottrell behaviour, which resulted from the constraint of hydrogen diffusion mixed with interfacial charge transfer during hydrogen transport. Especially, it displayed an inflexion point at the time that corresponds to the temporal outer cut-off of fractality, i.e. the crossover time required for the fractal to flat transition. In addition, the temporal outer cut-off under the constraint of mixed control was observed to be shortened with increasing hydrogen discharging potential, which could be accounted for by the increased growth rate of diffusion layer in the electrode accompanying the facilitated charge transfer kinetics at the electrode/electrolyte interface

145

Charge-transfer interfaces between metal and redox arylamine molecular films: As probed with anode interfacial engineering approach in single-layer organic diodes  

CERN Document Server

We investigate the charge-transfer interfaces between metal and redox arylamine molecular films through studying the current-voltage characteristics of single-layer organic diodes with the aid of anode interfacial engineering method. The diode turn-on voltage is shown to be highly sensitive to the arylamine/metal charge-transfer interfaces and thus can serve as a probe in detecting such organic/metal interfaces. We show that the diode electrical performance could be tuned through engineering the arylamine/metal interfaces via controlling the factors of anode work function, arylamine substitute groups, and active layer surface morphology etc. The conduction mechanism of the diodes is shown to be injection limited, which could be well described with Richardson-Schottky thermonic emission model. Our work may provide some insight into the use of single-layer organic diode and interfacial engineering method to rapidly probe the organic/metal and even organic/organic charge-transfer interfaces.

Li, J C; Szulczewski, G J

2005-01-01

146

Core-concrete molten pool dynamics and interfacial heat transfer. [PWR; BWR  

Energy Technology Data Exchange (ETDEWEB)

Theoretical models are derived for the heat transfer from molten oxide pools to an underlying concrete surface and from molten steel pools to a general concrete containment. To accomplish this, two separate effects models are first developed, one emphasizing the vigorous agitation of the molten pool by gases evolving from the concrete and the other considering the insulating effect of a slag layer produced by concrete melting. The resulting algebraic expressions, combined into a general core-concrete heat transfer representation, are shown to provide very good agreement with experiments involving molten steel pours into concrete crucibles.

Benjamin, A.S.

1980-01-01

147

Computational micromechanics analysis of electron hopping and interfacial damage induced piezoresistive response in carbon nanotube-polymer nanocomposites  

Science.gov (United States)

Carbon nanotube (CNT)-polymer nanocomposites have been observed to exhibit an effective macroscale piezoresistive response, i.e., change in macroscale resistivity when subjected to applied deformation. The macroscale piezoresistive response of CNT-polymer nanocomposites leads to deformation/strain sensing capabilities. It is believed that the nanoscale phenomenon of electron hopping is the major driving force behind the observed macroscale piezoresistivity of such nanocomposites. Additionally, CNT-polymer nanocomposites provide damage sensing capabilities because of local changes in electron hopping pathways at the nanoscale because of initiation/evolution of damage. The primary focus of the current work is to explore the effect of interfacial separation and damage at the nanoscale CNT-polymer interface on the effective macroscale piezoresistive response. Interfacial separation and damage are allowed to evolve at the CNT-polymer interface through coupled electromechanical cohesive zones, within a finite element based computational micromechanics framework, resulting in electron hopping based current density across the separated CNT-polymer interface. The macroscale effective material properties and gauge factors are evaluated using micromechanics techniques based on electrostatic energy equivalence. The impact of the electron hopping mechanism, nanoscale interface separation and damage evolution on the effective nanocomposite electrostatic and piezoresistive response is studied in comparison with the perfectly bonded interface. The effective electrostatic/piezoresistive response for the perfectly bonded interface is obtained based on a computational micromechanics model developed in the authors’ earlier work. It is observed that the macroscale effective gauge factors are highly sensitive to strain induced formation/disruption of electron hopping pathways, interface separation and the initiation/evolution of interfacial damage.

Chaurasia, A. K.; Ren, X.; Seidel, G. D.

2014-07-01

148

Monitoring molecule dynamics by free electron transfer  

International Nuclear Information System (INIS)

Complete text of publication follows. Phenol radical cations and phenoxyl radicals were observed as direct products of free electron transfer from phenol-type solute molecules to solvent parent radical cations generated by ionizing irradiation. The finding of the two species in comparable amounts is attributed to the dynamics of the phenol molecule oscillating in the femtosecond range by vibration, rotation and other motions. Analyzing the hetero group rotation around the C-OH bond, two border line conformer structures can be distinguished such as the plane molecule and a rotated one where the substituent is twisted by 90 deg. Assuming a promt free electron transfer (FET) in each encounter, ionization of all rotation-caused conformer states should happen, resulting in different products. This seem reasonable under the aspect that accompanied with the rotation also electron distribution should change. Quantum-chemical calculations indicate that for phenol as solute primarily its conformers with perpendicular C-OH axis orientation to the aromatic ring tend to deprotonate after ionization. A quite similar behavior could be predicted for the heteroanalogous thio- and selenophenols. Quite generally considerable changes in the electron distribution of the ground state molecules with the twisting angle of the -OH, -SH and -SeH groups could be calculated, with the greatest differences between 'parallel' and 'perpendicular' conformations. On the assumption that FET projects the equilibrium solute conformer distribution onto the solute cation conformer one it is demonstrated that the experimental findings are compatible with a simple solute-cation internal relaxation model

149

Nanoscale characterization of interfacial electronic properties and degradation mechanisms of organic thin films for electroluminescence displays  

Science.gov (United States)

For the first time, the promising organic light-emitting diode (OLED), indium tin oxide (ITO)/copper phthalocyanine (CuPc)/N,N '-di(naphthalene-l-yl)-N,N'-diphthalbenzidine (NPB)/tris(8-quinolinolatoline) aluminum (Alq3) (ITO/CuPc/NPB/Alq 3), has been selected for investigating its interfacial properties, and morphological degradation mechanisms induced by moisture and temperature through the systematic visualization by the state-of-the-art scanning probe microscopy (SPM). The motivation of this thesis lies in the importance of the OLED interfaces associated with the OLED's quantum efficiency, and morphological alteration in respect to device lifetime and luminance. Variable-temperature ultrahigh vacuum scanning tunnelling microscopy and spectroscopy (VT-UHV/STM and STS) are used to investigate the interfacial electronic properties at the Au(111)/CuPc interface. The energy band gap of CuPc ultrathin films on Au(111) measured by the charge injection from the STM tip into the highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) levels of CuPc is ˜1.9--2.1 eV, which is comparable to the optical band gap (˜1.7 eV). This result indicates that a dipole layer and/or image forces is present right at the Au(111)/CuPc interface, and confirms that the common vacuum level alignment at the interface is invalid. Also, it is found that the morphological features probably affect the tunnelling current. To scrutinize the degradation associated with morphological variations of the Alga-based OLED structures, a variable-temperature tapping mode atomic force microscope (VT-AFM) and other complementary techniques such as thickness-shear mode (TSM) acoustic wave mass sensor and micro-Raman spectroscopy have been employed to sift the degradation mechanisms induced by ambient atmosphere and Joule heating. A volatile species released from the Alq3 thin films under exposure to moisture has been traced by the TSM acoustic wave mass sensor. This volatile species is most likely to be the freed 8-quinolinolatoline (8-Hq), a product of the reaction by Alq3 with water. As a result, the degradation mechanisms associated with morphological change of Alq 3 thin film by moisture are the crystallization of Alq3, the hydration of Alq3, and the reaction by Alq3 complex with moisture. Moreover, it has been visualized that the hydrated Alq 3 can be transformed into crystalline Alq3 structures and dark holes by the captioned reactions. Similarly, the ambient-induced morphological changes of ITO/CuPc, ITO/CuPc/NPB and ITO/CuPc/NPB/Alq3 structures have also been investigated. It is found that indium diffusion from the ITO substrate into organic layers possibly exists. After stored in an ambient atmosphere, crystallization of NPB thin films takes place. Photoluminescence (PL) investigation and local current map of the various degrading/degraded thin films suggest that the morphological changes, e.g., the formation of dark holes and Alq3 crystalline structures, essentially affect the PL and electrical characteristics. (Abstract shortened by UMI.)

Xu, Mingsheng

150

Promoting interspecies electron transfer with biochar  

DEFF Research Database (Denmark)

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

Chen, Shanshan; Rotaru, Amelia-Elena

2014-01-01

151

Promoting Interspecies Electron Transfer with Biochar  

Science.gov (United States)

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

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

2014-01-01

152

Promoting interspecies electron transfer with biochar.  

Science.gov (United States)

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

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

2014-01-01

153

Driving force dependent, photoinduced electron transfer at degenerately doped, optically transparent semiconductor nanoparticle interfaces.  

Science.gov (United States)

Photoinduced, interfacial electron injection and back electron transfer between surface-bound [Ru(II)(bpy)2(4,4'-(PO3H2)2-bpy)](2+) and degenerately doped In2O3:Sn nanoparticles, present in mesoporous thin films (nanoITO), have been studied as a function of applied external bias. Due to the metallic behavior of the nanoITO films, application of an external bias was used to vary the Fermi level in the oxide and, with it, the driving force for electron transfer (?G(o)'). By controlling the external bias, ?G(o)' was varied from 0 to -1.8 eV for electron injection and from -0.3 to -1.3 eV for back electron transfer. Analysis of the back electron-transfer data, obtained from transient absorption measurements, using Marcus-Gerischer theory gave an experimental estimate of ? = 0.56 eV for the reorganization energy of the surface-bound Ru(III/II) couple in acetonitrile with 0.1 M LiClO4 electrolyte. PMID:25330285

Farnum, Byron H; Morseth, Zachary A; Brennaman, M Kyle; Papanikolas, John M; Meyer, Thomas J

2014-11-12

154

Electron Transfer-Based Single Molecule Fluorescence as a Probe for Nano-Environment Dynamics  

Directory of Open Access Journals (Sweden)

Full Text Available Electron transfer (ET is one of the most important elementary processes that takes place in fundamental aspects of biology, chemistry, and physics. In this review, we discuss recent research on single molecule probes based on ET. We review some applications, including the dynamics of glass-forming systems, surface binding events, interfacial ET on semiconductors, and the external field-induced dynamics of polymers. All these examples show that the ET-induced changes of fluorescence trajectory and lifetime of single molecules can be used to sensitively probe the surrounding nano-environments.

Ruiyun Chen

2014-02-01

155

Education and solar conversion. Demonstrating electron transfer  

Energy Technology Data Exchange (ETDEWEB)

A simplified solar cell fabrication procedure is presented that uses natural anthocyanin or chlorophyll dyes extracted from plants. This procedure illustrates how interdisciplinary science can be taught at lower division university and upper division high school levels for an understanding of renewable energy as well as basic science concepts. Electron transfer occurs on the Earth in the mitochondrial membranes found in living cells, and in the thylakoid membranes found in the photosynthetic cells of green plants. Since we depend on the results of this electron and energy transfer, e.g. in our use of petroleum and agricultural products, it is desirable to understand and communicate how the electron transfer works. The simplified solar cell fabrication procedure, based on nanocrystalline dye-sensitized solar cells, has therefore been developed so that it can be inexpensively reproduced and utilized in the teaching of basic principles in biology, chemistry, physics, and environmental science. A water-based solution of commercial nanocrystalline titanium dioxide (TiO{sub 2}) powder is used to deposit a highly porous semiconductor electron acceptor. This acceptor couples the light-driven processes occurring at an organic dye to the macroscopic world and an external electrical circuit. Materials science and semiconductor physics are emphasized during the deposition of the sintered TiO{sub 2} nanocrystalline ceramic film. Chelation, complexation and molecular self-assembly are demonstrated during the attachment of the dye molecule to the surface of the TiO{sub 2} semiconductor particles. Environmental chemistry and energy conversion can be linked to these concepts via the regenerative oxidation and reduction cycle found in the cell. The resulting device, made in under 3 h, can be used as a light detector or power generator that produces 0.4-0.5 V at open circuit, and 1-2 mA per square cm under solar illumination

Smestad, Greg P. [Institute of Physical Chemistry, ICP-2, Swiss Federal Institute of Technology, EPFL, CH-1015 Lausanne (Switzerland)

1998-07-23

156

Long-Range Electron Transfer and Electronic Transport Through Macromolecules  

CERN Document Server

A theory of electrical transport through molecular wires is used to estimate the electronic factor in the intramolecular electron transfer (ET) in porphyrin-nitrobenzene supermolecules, and to analyze its structure. The chosen molecules have complex donor and acceptor configurations, and relatively simple structure of the bridge, which enables us to concentrate our studies on the donor/acceptor coupling to the bridge. We present analytical and numerical results concerning the effect of donor/acceptor coupling to the bridge on the ET process in molecules with complex donor/acceptor subsystems. PACS 05.60.Gg, 36.20.-r

Zimbovskaya, N A; Zimbovskaya, Natalya; Gumbs, Godfrey

2002-01-01

157

TiO2-SnO2:F interfacial electronic structure investigated by soft x-ray absorption spectroscopy  

Science.gov (United States)

The electronic structure of the titanium dioxide (TiO2)-fluorine-doped tin dioxide (SnO2:F) interface is investigated by soft x-ray absorption spectroscopy using synchrotron radiation. The measurements probe the site- and symmetry-selected unoccupied density of states and reflect the interaction between an early transition-metal-oxide (d0) semiconductor and a post-transition-metal-oxide (d10) degenerate semiconductor. The distinct interfacial electronic structure of TiO2-SnO2:F is established by contrasting spectra with those for anatase and rutile TiO2, SnO2:F, and ZnO-SnO2:F and CdO-SnO2:F interfaces. Oxygen 1s absorption spectra, which relate to the O 2p partial density of states of the conduction band, indicate that the interface is associated with a reduction in Ti d-O p orbital hybridization and an alteration of the TiO2 crystal field. These observations are consistent with measured titanium 2p absorption spectra, which in addition provide evidence for distortion of long-range order around the cation site in the interfacial TiO2. The TiO2-SnO2:F interface is a functional component of a number of optoelectronic devices, perhaps most notably within the anode structure of solar cell architectures. In nonequilibrium conditions, such as those found in operating solar cells, interfacial electronic structure directly influences performance by modifying, for instance, the quasi-Fermi level electrons and the potential distribution at the transparent electrode.

Kronawitter, Coleman X.; Kapilashrami, Mukes; Bakke, Jonathan R.; Bent, Stacey F.; Chuang, Cheng-Hao; Pong, Way-Faung; Guo, Jinghua; Vayssieres, Lionel; Mao, Samuel S.

2012-03-01

158

Interfacial wave effects on heat transfer to a falling liquid film  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Experiments were performed to provide insight into the heat transfer aspects of a wavy liquid film. Local film thickness and liquid temperature were measured simultaneously using a thermal conductance thickness probe and fast response thermocouples as the wavy film fell over an electrically heated wall. Liquid temperature at a fixed distance from the wall generally increased in the thin substrate portion of the film and decreased within the large waves. Temperature showed complex excursions w...

Lyu, Tae-hwan

1990-01-01

159

Air-sea dimethylsulfide (DMS) gas transfer in the North Atlantic: evidence for limited interfacial gas exchange at high wind speed  

Science.gov (United States)

Shipboard measurements of eddy covariance dimethylsulfide (DMS) air-sea fluxes and seawater concentration were carried out in the North Atlantic bloom region in June/July 2011. Gas transfer coefficients (k660) show a linear dependence on mean horizontal wind speed at wind speeds up to 11 m s-1. At higher wind speeds the relationship between k660 and wind speed weakens. At high winds, measured DMS fluxes were lower than predicted based on the linear relationship between wind speed and interfacial stress extrapolated from low to intermediate wind speeds. In contrast, the transfer coefficient for sensible heat did not exhibit this effect. The apparent suppression of air-sea gas flux at higher wind speeds appears to be related to sea state, as determined from shipboard wave measurements. These observations are consistent with the idea that long waves suppress near-surface water-side turbulence, and decrease interfacial gas transfer. This effect may be more easily observed for DMS than for less soluble gases, such as CO2, because the air-sea exchange of DMS is controlled by interfacial rather than bubble-mediated gas transfer under high wind speed conditions.

Bell, T. G.; De Bruyn, W.; Miller, S. D.; Ward, B.; Christensen, K.; Saltzman, E. S.

2013-11-01

160

Electric field induced enhancement in the interfacial charge transfer kinetics of a solid polymer electrolyte  

International Nuclear Information System (INIS)

A novel electrostatic method for preparing modified solid polymer electrolytes (SPEs) is reported. Application of an electric field on an evaporating mixture of KYNAR, ethylene carbonate (EC), propylene carbonate (PC) and LiPF6 dissolved in tetra hydro furan (THF) resulted in a solid polymer electrolyte whose charge transfer resistance was at least an order of magnitude lower than that formed without the application of an electric field. We believe that the observed enhancement is probably due to an electric field induced orientation of dipoles in the polymer chain

 
 
 
 
161

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1993-01-01

162

Studies of interfacial heat transfer resistances and characterization of strip microstructures for Al-Mg alloys cast on a single belt casting simulator  

International Nuclear Information System (INIS)

Interfacial heat transfer resistances during the solidification of aluminum-magnesium alloy strips were measured using the IHCP (Inverse Heat Conduction Problem) method. For these experiments, a small simulator of a single belt caster was used and interfacial heat fluxes and heat transfer coefficients were obtained assuming unidirectional heat flow. The influence of thermophysical properties of substrate, melt superheat and roughness of substrates on strip microstructures in the longitudinal and transverse directions were also investigated. Experimental studies revealed that low superheats (? 2 oC) produced finer grain sizes (?40?m) and homogeneous microstructures were obtained. High thermal conductivity substrates such as copper resulted in strips that were more uniform in thickness and had improved surface quality. It was also found that there was a critical substrate roughness which provided more nucleation sites at the metal/substrate interface resulting in a fine grain distribution throughout the strip produced. (author)

163

Effects of interfacial waves on heat transfer to free-falling turbulent liquid films  

International Nuclear Information System (INIS)

Turbulent liquid films are encountered in a wide variety of thermal devices. To better characterize film flow, experiments have been performed to establish a data base for sensible and evaporative heating of free-falling turbulent liquid films. Experiments were conducted by heating water as it fell on the outside of a vertical tube having a diameter of 25.4mm. The tube consisted of a porous plastic film distributor, an adiabatic hydrodynamic development section and a thin-walled 781mm long electrically heated stainless steel tube which provided a uniform wall heat flux. Seventeen pairs of thermocouples were used to monitor the inner wall temperature of the tube and sampling scoops were used to determine the mean film temperature. The test section was contained within a sealed chamber to facilitate testing at subatmospheric pressures for accurate determination of evaporation heat transfer coefficients. Fluid conditions were controlled through a high purity fluid delivery system

164

Study on interfacial heat transfer coefficient at metal/die interface during high pressure die casting process of AZ91D alloy  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The high pressure die casting (HPDC) process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today’s manufacturing industry.In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were Measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (I...

Guo, Zhi-peng; Xiong, Shou-mei

2007-01-01

165

Mediated Electron Transfer at Redox Active Monolayers  

Directory of Open Access Journals (Sweden)

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

Michael E.G. Lyons

2001-12-01

166

Interfacial electronic transport phenomena in single crystalline Fe-MgO-Fe thin barrier junctions  

Energy Technology Data Exchange (ETDEWEB)

Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3–8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2?eV) interfacial resonance states: a mixture of ?{sub 1}-like and ?{sub 5}-like symmetries.

Gangineni, R. B., E-mail: rameshg.phy@pondiuni.edu.in [Department of Physics, School of Physical, Chemical and Applied Sciences, Pondicherry University, R. V. Nagar, Kalapet, Pondicherry 605 014 (India); SPINTEC, UMR 8191 CEA/CNRS/UJF-Grenoble 1/Grenoble INP, INAC, 17 rue des Martyrs, F-38054 Grenoble Cedex (France); Bellouard, C., E-mail: christine.bellouard@ijl.nancy-universite.fr; Duluard, A. [Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, BP 239, 54506 Vandoeuvre (France); Negulescu, B. [Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, BP 239, 54506 Vandoeuvre (France); UFR de Sciences et Techniques, Matériaux, microélectronique, acoustique, nanotechnologies (GREMAN), University François Rabelais, Parc de Grandmont, 37200 Tours (France); Baraduc, C.; Gaudin, G. [SPINTEC, UMR 8191 CEA/CNRS/UJF-Grenoble 1/Grenoble INP, INAC, 17 rue des Martyrs, F-38054 Grenoble Cedex (France); Tiusan, C., E-mail: coriolan.tiusan@phys.utcluj.ro [Institut Jean Lamour, UMR 7198, CNRS-Université de Lorraine, BP 239, 54506 Vandoeuvre (France); Department of Physics and Chemistry, Center of Superconductivity, Spintronics and Surface Science, Technical University of Cluj Napoca, Str. Memorandumului No. 28, RO-400114 Cluj-Napoca (Romania)

2014-05-05

167

Interfacial electronic transport phenomena in single crystalline Fe-MgO-Fe thin barrier junctions  

International Nuclear Information System (INIS)

Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3–8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2?eV) interfacial resonance states: a mixture of ?1-like and ?5-like symmetries

168

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

Science.gov (United States)

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

Hong, Woo-Pyo; Jung, Young-Dae

2014-08-01

169

Electron transfer in gas surface collisions  

International Nuclear Information System (INIS)

In this thesis electron transfer between atoms and metal surfaces in general is discussed and the negative ionization of hydrogen by scattering protons at a cesiated crystalline tungsten (110) surface in particular. Experimental results and a novel theoretical analysis are presented. In Chapter I a theoretical overview of resonant electron transitions between atoms and metals is given. In the first part of chapter II atom-metal electron transitions at a fixed atom-metal distance are described on the basis of a model developed by Gadzuk. In the second part the influence of the motion of the atom on the atomic charge state is incorporated. Measurements presented in chapter III show a strong dependence of the fraction of negatively charged H atoms scattered at cesiated tungsten, on the normal as well as the parallel velocity component. In chapter IV the proposed mechanism for the parallel velocity effect is incorporated in the amplitude method. The scattering process of protons incident under grazing angles on a cesium covered surface is studied in chapter V. (Auth.)

170

Activation entropy of electron transfer reactions  

CERN Document Server

We report microscopic calculations of free energies and entropies for intramolecular electron transfer reactions. The calculation algorithm combines the atomistic geometry and charge distribution of a molecular solute obtained from quantum calculations with the microscopic polarization response of a polar solvent expressed in terms of its polarization structure factors. The procedure is tested on a donor-acceptor complex in which ruthenium donor and cobalt acceptor sites are linked by a four-proline polypeptide. The reorganization energies and reaction energy gaps are calculated as a function of temperature by using structure factors obtained from our analytical procedure and from computer simulations. Good agreement between two procedures and with direct computer simulations of the reorganization energy is achieved. The microscopic algorithm is compared to the dielectric continuum calculations. We found that the strong dependence of the reorganization energy on the solvent refractive index predicted by conti...

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

2005-01-01

171

Electron transfer reactions of organometallic compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The mixed valence states of the twelve ligand bridged hexaruthenium clusters $\\rm Ru\\sb3(\\mu\\sb3$-O)($\\mu$-$\\rm CH\\sb3CO\\sb2)\\sb6(CO)(L\\sp\\prime)(\\mu$-L)$\\rm Ru\\sb3(\\mu\\sb3$-O)($\\mu$-$\\rm CH\\sb3CO\\sb2)\\sb6(CO)(L\\sp{\\prime\\prime})$ (L = 1,4-pyrazine or 4,4$\\sp\\prime$-bipyridine; L$\\sp\\prime$ (or L$\\sp{\\prime\\prime})$ = 4-dimethyl-aminopyridine, pyridine, 4-cyanopyridine, undergo rapid intramolecular electron transfer. The splitting of the reduction waves in cyclic voltammetry depends on the el...

Zavarine, Igor S.

1998-01-01

172

GPU-accelerated computation of electron transfer.  

Science.gov (United States)

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

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

2012-11-01

173

A study of interfacial heat transfer and process parameters in squeeze casting and low pressure permanent mold casting  

Science.gov (United States)

With the emerging demand for energy efficient and environment-friendly automobiles, cast aluminum alloys are increasingly being used in their manufacture. In this context, two permanent mold casting processes, namely, Squeeze Cast Permanent Mold and Low Pressure Permanent Mold (LPPM) have become very popular in the production of high integrity shape-cast aluminum components. However, many industries are yet to benefit from the full potential of these processes due to limited understanding of the effect of process parameters on casting quality and the necessary boundary conditions for computer modeling and simulation so as to minimize costly field trials. This dissertation attempts to address some of these concerns facing today's foundry industry. An experimental investigation of the Indirect Squeeze Casting Process was conducted by pouring molten Al-7Si-0.3Mg (A356) alloy into a specially designed and instrumented mold, mounted on a horizontal clamped-vertical shot squeeze caster (HVSC). Temperature measurements close to the metal/mold interface were made and compared with the results of the numerical simulation of heat flow during solidification and cooling of castings. The Heat Transfer Coefficient (HTC), a critical parameter essential for any solidification simulation, was estimated based on the simulation that gave the best fit to the experimental temperature data. During the solidification process, the HTC is relatively uniform over the entire casting and on reaching a critical solidification pressure, the HTC is close to 4500 W/m2 K. The work has also provided a correlation of Secondary Dendrite Arm Spacing (SDAS) with cooling rate for a modified A356 alloy. Low Pressure Permanent Mold Casting experiments were conducted by pouring a nearly identical aluminum alloy into an instrumented, coated mold mounted on a low pressure casting machine. The pressure levels, along with the time required to achieve complete filling, were microprocessor controlled in the casting machine. The HTC evaluation and SDAS-Cooling Rate Correlation were made in a similar manner to the Squeeze Casting study. A novel approach to estimating the HTC, accounting for the temporal and spatial temperature and thermal property variations, is presented. The maximum and minimum values of the HTC in this case were close to 2000 W/m2 K with no air gap and 400 W/m2 K with an air gap formation. The influences of air gap formation and mold coatings in controlling interfacial heat transfer were also modeled. It is expected that the HTCs and SDAS-Cooling Rate Correlations for the two casting processes will assist foundry engineers in deriving maximum benefits from each process.

Krishna, Prasad

2001-08-01

174

Single-element Electron-transfer Optical Detector System  

Science.gov (United States)

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

Jordan, Jeffrey D. (Inventor)

2004-01-01

175

Electron transfer reactions of metal complexes in solution  

International Nuclear Information System (INIS)

A few representative electron-transfer reactions are selected and their kinetic parameters compared with the predictions of activated complex models. Since Taube has presented an elegant treatment of intramolecular electron-transfer reactions, emphasis is on bimolecular reactions. The latter electron-transfer reactions are more complicated to treat theoretically since the geometries of their activated complexes are not as well known as for the intramolecular case. In addition in biomolecular reactions, the work required to bring the two reactants together needs to be calculated. Since both reactants generally carry charges this presents a non-trivial problem at the ionic strengths usually used to study bimolecular electron transfer

176

Condensation of two-dimensional oxide-interfacial charges into one-dimensional electron chains by the misfit-dislocation strain field.  

Science.gov (United States)

The success of semiconductor technology is largely ascribed to controlled impacts of strains and defects on the two-dimensional interfacial charges. Interfacial charges also appear in oxide heterojunctions such as LaAlO3/SrTiO3 and (Nd0.35Sr0.65)MnO3/SrTiO3. How the localized strain field of one-dimensional misfit dislocations, defects resulting from the intrinsic misfit strains, would affect the extended oxide-interfacial charges is intriguing and remains unresolved. Here we show the atomic-scale observation of one-dimensional electron chains formed in (Nd0.35Sr0.65)MnO3/SrTiO3 by the condensation of characteristic two-dimensional interfacial charges into the strain field of periodically arrayed misfit dislocations, using chemical mapping and quantification by scanning transmission electron microscopy. The strain-relaxed inter-dislocation regions are readily charge depleted, otherwise decorated by the pristine charges, and the corresponding total-energy calculations unravel the undocumented charge-reservoir role played by the dislocation-strain field. This two-dimensional-to-one-dimensional electronic condensation represents a novel electronic-inhomogeneity mechanism at oxide interfaces and could stimulate further studies of one-dimensional electron density in oxide heterostructures. PMID:24663109

Chang, C-P; Chu, M-W; Jeng, H T; Cheng, S-L; Lin, J G; Yang, J-R; Chen, C H

2014-01-01

177

Oxide/Electrolyte interface: Electron transfer phenomena  

Directory of Open Access Journals (Sweden)

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

En este trabajo se ha estudiado un proceso de transferencia de electrones en la interfase dióxido de titanio/electrolito acuoso. Tal y como han observado otros investigadores en interfases similares (TiO2- y ZnO- electrolito, se ha detectado un consumo lento de iones OH-. Para dar explicación a este proceso, se ha desarrollado un modelo teórico basado en el cálculo de las energías de Fermi en el semiconductor y en el electrolito. De este modo, se demuestra que dicho consumo de iones está favorecido por una disminución de la diferencia entre ambos niveles de Fermi. Para caracterizar el proceso de consumo lento de OH- se define una constante cinética (?, cuyo valor aumenta a medida que crece la concentración másica de semiconductor y de electrolito en la suspensión. Adicionalmente, este fenómeno proporciona una herramienta para determinar experimentalmente el punto de carga nula de la suspensión de dióxido de titanio en el medio acuoso.

Fernández-Ibáñez, P.

2000-08-01

178

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads  

Energy Technology Data Exchange (ETDEWEB)

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

NONE

1993-03-01

179

Quantum coherent contributions in biological electron transfer  

CERN Document Server

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

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

2011-01-01

180

Photoinduced Electron-transfer Reaction of Pentafluoroiodobenzene with Alkenes  

Directory of Open Access Journals (Sweden)

Full Text Available Irradiation of pentafluoroiodobenzene and alkenes gave the corresponding adducts. The presence of single electron-transfer scavengers, (p-dinitrobenzene and t-Bu2NO and the free radical inhibitor (hydroquinone suppressed the reaction. A photoinduced electron-transfer mechanism is proposed.

Qing-Yun Chen

1997-01-01

 
 
 
 
181

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

Science.gov (United States)

...Bureau finds that there is good cause to publish this...interim final rule, Electronic Fund Transfers (Regulation...which the Bureau found good cause to conclude that...This part applies to any electronic fund transfer that authorizes...to debit or credit a consumer's account....

2012-07-10

182

Interfacial Chemistry and the Design of Solid-Phase Nucleic Acid Hybridization Assays Using Immobilized Quantum Dots as Donors in Fluorescence Resonance Energy Transfer  

Science.gov (United States)

The use of quantum dots (QDs) as donors in fluorescence resonance energy transfer (FRET) offer several advantages for the development of multiplexed solid-phase QD-FRET nucleic acid hybridization assays. Designs for multiplexing have been demonstrated, but important challenges remain in the optimization of these systems. In this work, we identify several strategies based on the design of interfacial chemistry for improving sensitivity, obtaining lower limits of detection (LOD) and enabling the regeneration and reuse of solid-phase QD-FRET hybridization assays. FRET-sensitized emission from acceptor dyes associated with hybridization events at immobilized QD donors provides the analytical signal in these assays. The minimization of active sensing area reduces background from QD donor PL and allows the resolution of smaller amounts of acceptor emission, thus lowering the LOD. The association of multiple acceptor dyes with each hybridization event can enhance FRET efficiency, thereby improving sensitivity. Many previous studies have used interfacial protein layers to generate selectivity; however, transient destabilization of these layers is shown to prevent efficient regeneration. To this end, we report a protein-free interfacial chemistry and demonstrate the specific detection of as little as 2 pmol of target, as well as an improved capacity for regeneration. PMID:22163951

Algar, W. Russ; Krull, Ulrich J.

2011-01-01

183

Electron Transfer in Porphyrin Complexes in Different Solvents  

CERN Document Server

The electron transfer in different solvents is investigated for systems consisting of donor, bridge and acceptor. It is assumed that vibrational relaxation is much faster than the electron transfer. Electron transfer rates and final populations of the acceptor state are calculated numerically and in an approximate fashion analytically. In wide parameter regimes these solutions are in very good agreement. The theory is applied to the electron transfer in ${\\rm H_2P-ZnP-Q}$ with free-base porphyrin (${\\rm H_2P}$) being the donor, zinc porphyrin (${\\rm ZnP}$) the bridge, and quinone (${\\rm Q}$) the acceptor. It is shown that the electron transfer rates can be controlled efficiently by changing the energy of the bridging level which can be done by changing the solvent. The effect of the solvent is determined for different models.

Kilin, D S; Schreiber, M

2000-01-01

184

Computational Approach to Electron Charge Transfer Reactions  

DEFF Research Database (Denmark)

The step from ab initio atomic and molecular properties to thermodynamic - or macroscopic - properties requires the combination of several theoretical tools. This dissertation presents constant temperature molecular dynamics with bond length constraints, a hybrid quantum mechanics-molecular mechanics scheme, and tools to analyse statistical data and generate relative free energies and free energy surfaces. The methodology is applied to several charge transfer species and reactions in chemical environments - chemical in the sense that solvent, counter ions and substrate surfaces are taken in to account - which directly influence the reactants and resulting reaction through both physical and chemical interactions. All methods are though general and can be applied to different types of chemistry. First, the basis of the various theoretical tools is presented and applied to several test systems to show general (or expected) properties. Properties such as in the physical and (semi-)chemical interface between classical and quantum systems and the effects of molecular bond length constraints on the temperature during simulations. As a second step the methodology is applied to the symmetric and asymmetric charge transfer reactions between several first-row transition metals in water. The results are compared to experiments and rationalised with classical analytic expressions. Shortcomings of the methods are accounted for with clear steps towards improved accuracy. Later the analysis is extended to more complex systems composed of a larger osmium complex in solution and at the solute-substrate interfaces, where in particular the redox state of the complex is controlled through chemical means. The efficiency of the hybrid-classical and quantum mechanics method is used to generate adequate statistics and a simple post-sampling scheme used to generate free energy surfaces - which compare to full ab initio calculations. In the last part both the molecular dynamics and hybrid classical and quantum mechanics method are used to generate a vast data set for the accurate analysis of dynamical structure modes. This is for a large iridium-iridium dimer complex which shows a dramatic structural (and vibrational) change upon electronic excitation.

Jónsson, Elvar Örn

2013-01-01

185

Controllable interfacial adhesion applied to transfer light and fragile objects by using gecko inspired mushroom-shaped pillar surface.  

Science.gov (United States)

Gecko-inspired surfaces are smart dry adhesive surfaces that have attracted much attention because of their wide range of potential applications. However, strong frictional force, rather than adhesive force, is frequently targeted in most of research in this area. In this study, the interfacial adhesive and frictional properties of a gecko-inspired mushroom-shaped polyurethane pillar array surface have been systematically characterized to design and control the interfacial adhesion of the surface by considering the nanoscale interfacial adhesion, the microscale structural compliance and deformation, and the macro-scale actuation. Matching the movement of the leg springs and the interfacial adhesive characteristics between the pillar array surfaces and substrates, a three-legged clamp prototype has been designed and fabricated to successfully pick up and release light and fragile objects with a smooth upper surface, such as a silicon wafer. These results provide a new insight into not only the theoretical understanding of the integrating adhesion mechanisms, but also the practical applications of utilizing and controlling the adhesive and frictional forces of gecko-inspired surfaces. PMID:24041007

Zhou, Ming; Tian, Yu; Sameoto, Dan; Zhang, Xiangjun; Meng, Yonggang; Wen, Shizhu

2013-10-23

186

Electron transfer in proteins : in search of preferential pathways  

DEFF Research Database (Denmark)

Electron migration between and within proteins is one of the most prevalent forms of biological energy conversion processes. Electron transfer reactions take place between active centers such as transition metal ions or organic cofactors over considerable distances at fast rates and with remarkable specificity. The electron transfer is attained through weak electronic interaction between the active sites, so that considerable research efforts are centered on resolving the factors that control the rates of long-distance electron transfer reactions in proteins. These factors include (in addition to the distance and nature of the microenvironment separating the reactants) thermodynamic driving force and the configurational changes required upon reaction. Several of these aspects are addressed in this review, which is based primarily on recent work performed by the authors on model systems of blue copper-containing proteins. These proteins serve almost exclusively in electron transfer reactions, and as it turns out, their metal coordination sites are endowed with properties uniquely optimized for their function.

Farver, O; Pecht, I

1991-01-01

187

The distance and temperature dependence of electron-transfer rates  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer occurs over relatively long distances in a variety of systems. In interpreting the measured electron-transfer rates it is usually assumed that the rate constants depend exponentially on the distance separating the two redox sites and that this distance dependence arises from the decrease in the electronic coupling of the redox sites with increasing separation. Although the electronic coupling is an important factor determining the distance dependence of the rate, theoretical considerations suggest that the nuclear factors are also important. The various factors determining long-range electron-transfer rates are discussed and it is shown that very different distance dependences are predicted for reactions in the normal and inverted free-energy regions. The effect of the enthalpy change on the electron-transfer rate is also considered; three enthalpy regions are identified depending on the overall free energy and entropy changes for the reaction.

Sutin, N.

1987-01-01

188

Electronic and magnetic interfacial states of Ag in an Ni81Fe19 /Ag coupled multilayer  

Science.gov (United States)

Studies of the Ag induced magnetic moments at the interfaces in an [Ni81Fe19(29 Å)/Ag(11 Å)]135 multilayer by x-ray magnetic circular dichroism (XMCD) and x-ray resonant magnetic scattering (XRMS) at the Ag L2,3 edges are reported. This allows us to quantify the interfacial magnetic moments as well as the extension through the silver layer. From the experimental XMCD spectra and thanks to the use of full relativistic band structure calculations, we succeed in extracting quantitative spin and orbital magnetic moments held by the 4d states of silver. Moreover, we show that, although silver has an almost full 4d band, magneto-optical sum rules can be safely applied in the case of the noble metal L edges. We find from XMCD that Ag is polarized by Ni81Fe19 and has a total magnetic moment of 0.0136 ?B spatially averaged over the 11 Å layer thickness. XRMS analysis indicates that this induced polarization is enhanced at the interface but remains present inside the whole Ag layer, demonstrating the existence of an indirect coupling between the NiFe layers through the non-magnetic spacer.

Jaouen, N.; Wilhelm, F.; Rogalev, A.; Goulon, J.; Ortega, L.; Tonnerre, J. M.; Yaresko, A.

2008-03-01

189

Shewanella secretes flavins that mediate extracellular electron transfer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 acc...

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

2008-01-01

190

Momentum transfer to small particles by aloof electron beams  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The force exerted on nanoparticles and atomic clusters by fast passing electrons like those employed in transmission electron microscopes are calculated and integrated over time to yield the momentum transferred from the electrons to the particles. Numerical results are offered for metallic and dielectric particles of different sizes (0-500 nm in diameter) as well as for carbon nanoclusters. Results for both linear and angular momentum transfers are presented. For the electr...

Abajo, F. J. Garcia

2007-01-01

191

Momentum transfer to small particles by aloof electron beams  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The force exerted on nanoparticles and atomic clusters by fast passing electrons like those employed in transmission electron microscopes are calculated and integrated over time to yield the momentum transferred from the electrons to the particles. Numerical results are offered for metallic and dielectric particles of different sizes (0-500 nm in diameter) as well as for carbon nanoclusters. Results for both linear and angular momentum transfers are presented. For the electr...

Abajo, F. J. Garcia

2004-01-01

192

76 FR 29901 - Electronic Fund Transfers  

Science.gov (United States)

...face significant compliance risk if the error resolution requirements...the requested transfer could travel. (4) Other taxes imposed...requested remittance transfer may travel. Paragraph 32(c)(4) 1...send US$250 to a relative in India to an U.S....

2011-05-23

193

Versatile electron-collecting interfacial layer by in situ growth of silver nanoparticles in nonconjugated polyelectrolyte aqueous solution for polymer solar cells.  

Science.gov (United States)

Novel PEIE-Ag composites by in situ growth of silver nanoparticles in poly(ethylenimine)-ethoxylated (PEIE) aqueous solution are explored as an efficient interfacial layer for improving inverted polymer solar cells (PSCs) performance. The hybrid PEIE-Ag interfacial material is simple to fabricate only via ultraviolet irradiation with good water-solubility and unique film formation. The generated Ag nanoparticles can anchor in the PEIE polymer chains to form a conductive continuous interpenetrating network structure. Combining of the advantages of PEIE and Ag nanoparticles, the PEIE-Ag shows enhanced charge transport, electron selective and collection, and improved light-harvesting, mainly due to the surface plasmon resonance effect, better energy alignment induced by the formation of ideal dipole layer, as well as the improved conductivity. These distinguished interfacial properties result in the power conversion efficiency of inverted PSCs based on poly[4,8-bis(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b]dithiophene-2,6-diyl]-alt-[2-(2-ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl] (PBDTTT-C-T) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) photoactive layer substantially improved up to 7.66% from 6.11%. Moreover, the device performance is insensitively dependent on the thickness of the PEIE-Ag interfacial layer, broadening the thicknesses selection window for interfacial materials. These results demonstrate that PEIE-Ag is a potential interfacial material compatible with roll-to-roll techniques and suitable for printed electronic devices. PMID:25207753

Yuan, Kai; Chen, Lie; Chen, Yiwang

2014-10-01

194

A molecular shift register based on electron transfer  

Science.gov (United States)

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

195

A study of the dispersed flow interfacial heat transfer model of RELAP5/MOD2.5 and RELAP5/MOD3  

International Nuclear Information System (INIS)

The model of interfacial heat transfer for the dispersed flow regime used in the RELAP5 computer codes is investigated in the present paper. Short-transient calculations of two low flooding rate tube reflooding experiments have been performed, where the hydraulic conditions and the heat input to the vapour in the post-dryout region were controlled for the predetermined position of the quench front. Both RELAP5/MOD2.5 and RELAP5/MOD3 substantially underpredicted the exit vapour temperature. The mass flow rate and quality, however, were correct and the heat input to the vapour was larger than the actual one. As the vapour superheat at the tube exit depends on the balance between the heat input from the wall and the heat exchange with the droplets, the discrepancy between the calculated and the measured exit vapour temperature suggested that the inability of both codes to predict the vapour superheat in the dispersed flow region is due to the overprediction of the interfacial heat transfer rate

196

Dissociative electron attachment and charge transfer in condensed matter  

International Nuclear Information System (INIS)

Experiments using energy-selected beams of electrons incident from vacuum upon thin vapour deposited solids show that, as in the gas-phase, scattering cross sections at low energies are dominated by the formation of temporary negative ions (or resonances) and that molecular damage may be effected via dissociative electron attachment (DEA). Recent results also show that charge transfer between anionic states of target molecules and their environment is often crucial in determining cross sections for electron driven processes. Here, we review recent work from our laboratory, in which charge transfer is observed. For rare gas solids, electron exchange between the electron-exciton complex and either a metal substrate or co-adsorbed molecule enhances the desorption of metastable atoms and/or molecular dissociation. We discuss how transient electron capture by surface electron states of a substrate and subsequent electron transfer to a molecular adsorbate enhances the effective cross sections for DEA. We also consider the case of DEA to CF2Cl2 condensed on water and ammonia ices, where electron exchange between pre-solvated electron states of ice and transient molecular anions can also increase DEA cross sections. Electron transfer from molecular resonances into pre-solvated electron states of ice is also discussed

197

Dissociative electron attachment and charge transfer in condensed matter  

Energy Technology Data Exchange (ETDEWEB)

Experiments using energy-selected beams of electrons incident from vacuum upon thin vapour deposited solids show that, as in the gas-phase, scattering cross sections at low energies are dominated by the formation of temporary negative ions (or resonances) and that molecular damage may be effected via dissociative electron attachment (DEA). Recent results also show that charge transfer between anionic states of target molecules and their environment is often crucial in determining cross sections for electron driven processes. Here, we review recent work from our laboratory, in which charge transfer is observed. For rare gas solids, electron exchange between the electron-exciton complex and either a metal substrate or co-adsorbed molecule enhances the desorption of metastable atoms and/or molecular dissociation. We discuss how transient electron capture by surface electron states of a substrate and subsequent electron transfer to a molecular adsorbate enhances the effective cross sections for DEA. We also consider the case of DEA to CF{sub 2}Cl{sub 2} condensed on water and ammonia ices, where electron exchange between pre-solvated electron states of ice and transient molecular anions can also increase DEA cross sections. Electron transfer from molecular resonances into pre-solvated electron states of ice is also discussed.

Bass, A.D. E-mail: andrew.bass@usherbrooke.ca; Sanche, L

2003-09-01

198

Coincidence spectroscopy of continuum electron transfer in heavy ion collisions  

International Nuclear Information System (INIS)

Progress is reviewed in heavy ion continuum transfer processes. Faster, heavier, bare and highly ionized ions (permitting wide projectile charge state variation) are used to perform both singles and coincidence experiments concerning electron capture to the continuum in ion-atom collisions, electron loss to the continuum in ion-atom collisions, and convoy electron production in solids. 27 references

199

Electron transfer in SmHfCo alloys  

International Nuclear Information System (INIS)

The rare-earth electron-transfer concept in the rare-earth--transition-metal compounds was evaluated for the binary compounds Sm2Co17 and Sm1Co5 from published data. The cobalt moment was found to be consistent with a two-transferred-electron rigid-band model. These results were verified by saturation magnetization measurements on the mixed-valence pseudobinary Sm/sub 2(1-x)/Hf/sub 2x/Co17 alloys where the moment per cobalt atom was consistent with a tetravalent-hafnium divalent-samarium electron-transfer mechanism

200

Evaluating zirconium–zirconium hydride interfacial strains by nano-beam electron diffraction  

International Nuclear Information System (INIS)

Nano-beam electron diffraction has been used to quantify the elastic strain field associated with ?-hydride needles embedded in an ?-Zr matrix. It has been found that the volume misfit associated with precipitation results in elastic strains that are ?4× greater in the matrix than the hydride. Electron energy loss spectroscopy was used to detect hydrogen enrichment at the matrix–hydride interface by a shift in the zirconium plasmon peak. This work highlights that ?-hydride is metastable and acts as a precursor to equilibrium ?-hydride and that compositional variations within the hydride can be detected using electron energy loss spectroscopy.

 
 
 
 
201

Theory of electron transfer and ionization  

International Nuclear Information System (INIS)

The main effort reported is directed toward charge transfer and ionization in high energy atomic collisions. The research may be divided into classical trajectory calculations, quantum - mechanical collision theory, and phenomenological treatments of quantal interference effects in heavy ion collisions

202

Theory of electron transfer and ionization  

Energy Technology Data Exchange (ETDEWEB)

The main effort reported is directed toward charge transfer and ionization in high energy atomic collisions. The research may be divided into classical trajectory calculations, quantum - mechanical collision theory, and phenomenological treatments of quantal interference effects in heavy ion collisions.

Becker, R. L.

1979-01-01

203

Vectorially photoinduced electron-transfer processes across water-in-oil interfaces of microemulsions  

Energy Technology Data Exchange (ETDEWEB)

Artificial photosynthetic devices are potential fuel sources. The basic idea in the design of such devices is a photosensitized electron-transfer that yields chemical species capable of reducing and oxidizing water to hydrogen and oxygen. A fundamental difficulty in effecting this transfer is the thermodynamically favored back reactions of the intermediary redox species. An interfacial model composed of a water-in-oil microemulsion is suggested to provide the separation of these redox species, thereby preventing back-reactions. This model is designed to accomplish the photodecomposition of water in two separate water-in-oil microemulsions coupled by a redox reaction. Phase-transfer of one of the redox products from the water-in-oil interface to the continuous organic phase is the principle by which separation is achieved. The oxidation and reduction sites of the general model have been constructed. One system includes the photosensitized oxidation of a donor, EDTA, solubilized in the water pool, benzylnicotinamide acts as a primary acceptor that mediates by the phase transfer principle the reduction of a secondary acceptor, dimethylamino-azobenzene, solubilized in the continuous organic phase. In system two, involving the photosensitized reduction of methyl viologen, by tris(2,2'bipyridine)Ru(2+), thioophenol is used as the donor and its oxidation product is phase transferred to the continuous organic phase. The photoinduced processes accomplished in the two systems proceed along an uphill gradient of free energy. Two water soluble zinc-porphyrins can substitute for the Ru(2+) complex in the second system. As the two Zn-porphyrins are oppositely charged, the effect of electrostatic interactions on the quantum yields of viologen reduction could be evaluated. The results suggest that the surface charge of the wateroil interface strongly influences the efficiency of electron-transfer.

Willner, I.; Otvos, J.W.; Calvin, M.

1980-07-01

204

Kinetics and mechanism of the interfacial mass transfer of Eu(III) in the system: bis(2-ethylhexyl)phosphoric acid, n-dodecane-NaCl, lactic acid, polyaminocarboxylic acid, water  

International Nuclear Information System (INIS)

The rate laws which characterize the interfacial mass transfer of Eu3+ between aqueous phases containing a mixture of lactic acid and a polyaminocarboxylic acid (DTPA or HEDTA) and organic phases containing HDEHP in n-dodecane have been experimentally determined. The data demonstrate that in a wide range of stirring conditions the mass transfer process is entirely controlled by the rate of interfacial chemical reactions. A reaction mechanism where the four aqueous species, Eu3+, Eu-lactate, Eu-polyaminocarboxylate, and the mixed complex Eu-lactate-polyaminocarboxylate, are simultaneously reacting with the interfacially adsorbed HDEHP molecules has been worked out. This mechanism fully agrees with the experimental kinetic data. The rate constants which characterize most of the rate-determining steps have been calculated. Some practical implications of the faster mass transfer kinetics obtained with HEDTA are briefly discussed in relation to tervalent actinide-lanthanide group separations. 5 figures, 4 tables

205

Proton-coupled electron transfer with photoexcited metal complexes.  

Science.gov (United States)

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

206

Chirped pulse control of long range electron transfer  

International Nuclear Information System (INIS)

We have studied the capabilities of intense ultrashort chirped pulses for controlling the long range electron transfer in systems strongly coupled to a polar medium. We considered a two state electronic donor/acceptor system, possessing a large difference of permanent dipole moments between donor and acceptor states, with relaxation treated as a diffusion on electronic potential energy surfaces. This relaxation model has enabled us to trace continuously the transition from a coherent population transfer to incoherent one. In addition to the field controlled electron transfer, we take into account a possibility of the direct optical transition between electronic states under study as well. We have introduced the generalized Rabi frequency that enabled us to extend the concepts and ideas of population transfer, developed for optical transitions, to the electron transfer (radiationless process) controlled with strong electromagnetic field. We have shown that it is possible to realize the 'radiationless' analogies to ?-pulse excitation, adiabatic rapid passage and pump-dump process. We have obtained a physically clear picture of the analogy to the adiabatic rapid passage for the chirped controlled long-range electron transfer by studying vibrationally non-equilibrium populations behavior and careful examination of all the conditions needed for adiabatic rapid passage

207

Determining the effect of solid and liquid vectors on the gaseous interfacial area and oxygen transfer rates in two-phase partitioning bioreactors  

International Nuclear Information System (INIS)

The effect of liquid and solid transfer vectors (silicone oil and Desmopan, respectively) on the gaseous interfacial area (ag) was evaluated in a two-phase partitioning bioreactor (TPPB) using fresh mineral salt medium and the cultivation broth of a toluene degradation culture (Pseudomonas putida DOT-T1E cultures continuously cultivated with and without silicone oil at low toluene loading rates). Higher values of ag were recorded in the presence of both silicone oil and Desmopan compared to the values obtained in the absence of a vector, regardless of the aqueous medium tested (1.6 and 3 times higher, respectively, using fresh mineral salt medium). These improvements in ag were well correlated to the oxygen mass transfer enhancements supported by the vectors (1.3 and 2.5 for liquid and solid vectors, respectively, using fresh medium). In this context, oxygen transfer rates of 2.5 g O2 L-1 h-1 and 1.3 g O2 L-1 h-1 were recorded in the presence of Desmopan and silicone oil, respectively, which are in agreement with previously reported values in literature. These results suggest that mass transfer enhancements in TPPBs might correspond to an increase in ag rather than to the establishment of a high-performance gas/vector/water transfer pathway.

208

Determining the effect of solid and liquid vectors on the gaseous interfacial area and oxygen transfer rates in two-phase partitioning bioreactors  

Energy Technology Data Exchange (ETDEWEB)

The effect of liquid and solid transfer vectors (silicone oil and Desmopan, respectively) on the gaseous interfacial area (a{sub g}) was evaluated in a two-phase partitioning bioreactor (TPPB) using fresh mineral salt medium and the cultivation broth of a toluene degradation culture (Pseudomonas putida DOT-T1E cultures continuously cultivated with and without silicone oil at low toluene loading rates). Higher values of a{sub g} were recorded in the presence of both silicone oil and Desmopan compared to the values obtained in the absence of a vector, regardless of the aqueous medium tested (1.6 and 3 times higher, respectively, using fresh mineral salt medium). These improvements in a{sub g} were well correlated to the oxygen mass transfer enhancements supported by the vectors (1.3 and 2.5 for liquid and solid vectors, respectively, using fresh medium). In this context, oxygen transfer rates of 2.5 g O{sub 2} L{sup -1} h{sup -1} and 1.3 g O{sub 2} L{sup -1} h{sup -1} were recorded in the presence of Desmopan and silicone oil, respectively, which are in agreement with previously reported values in literature. These results suggest that mass transfer enhancements in TPPBs might correspond to an increase in a{sub g} rather than to the establishment of a high-performance gas/vector/water transfer pathway.

Quijano, Guillermo [Departmento de Ingenieria Quimica y Tecnologia del Medio Ambiente, Universidad de Valladolid, Paseo del Prado de la Magdalena, s/n, 47005 Valladolid (Spain); Departamento de Biotecnologia y Bioingenieria, Centro de Investigacion y de Estudios, Avanzados del IPN (Cinvestav), Apdo. Postal 14-740, 07360 Mexico, D.F. (Mexico); Rocha-Rios, Jose [Departmento de Ingenieria Quimica y Tecnologia del Medio Ambiente, Universidad de Valladolid, Paseo del Prado de la Magdalena, s/n, 47005 Valladolid (Spain); Departamento de Ingenieria de Procesos e Hidraulica (IPH), Universidad Autonoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco No. 186, 09340 Mexico, D.F. (Mexico); Hernandez, Maria; Villaverde, Santiago [Departmento de Ingenieria Quimica y Tecnologia del Medio Ambiente, Universidad de Valladolid, Paseo del Prado de la Magdalena, s/n, 47005 Valladolid (Spain); Revah, Sergio [Departamento de Procesos y Tecnologia, Universidad Autonoma Metropolitana-Cuajimalpa, c/o IPH, UAM-Iztapalapa, Av. San Rafael Atlixco No. 186, 09340 Mexico, D.F. (Mexico); Munoz, Raul, E-mail: mutora@iq.uva.es [Departmento de Ingenieria Quimica y Tecnologia del Medio Ambiente, Universidad de Valladolid, Paseo del Prado de la Magdalena, s/n, 47005 Valladolid (Spain); Thalasso, Frederic [Departamento de Biotecnologia y Bioingenieria, Centro de Investigacion y de Estudios, Avanzados del IPN (Cinvestav), Apdo. Postal 14-740, 07360 Mexico, D.F. (Mexico)

2010-03-15

209

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

Science.gov (United States)

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

210

Spin-polarized electron transfer in ferromagnet/C60 interfaces  

Science.gov (United States)

The contact between a molecule and a metallic electrode contributes to or even determines the characteristics of organic devices, such as their electronic properties. This is partly due to the charge transfer that takes place when two materials with different chemical potentials are put together. In the case of magnetic electrodes, the transfer can be accompanied by the transmission of a net spin polarization or spin doping. In nanocarbon systems, hybridization and spin doping can suppress the moment of a transition metal ferromagnet through the loss of majority spin electrons to the organic. Here, C60 is shown to become ferromagnetic as a result of spin doping from cobalt with an induced moment of 1.2 ?B per cage while suppressing the moment of the ferromagnet by up to 21%. Polarized neutron reflectivity and x-ray magnetic circular dichroism reveal the presence of an antiferromagnetic coupling of the interfacial layers of cobalt and C60, and weakly coupled induced magnetism propagating into the bulk organic. Thus, it is shown that the deposition of molecules with high electron affinity can be used to induce zero-voltage spin injection.

Moorsom, Timothy; Wheeler, May; Mohd Khan, Taukeer; Al Ma'Mari, Fatma; Kinane, Christian; Langridge, Sean; Ciudad, David; Bedoya-Pinto, Amílcar; Hueso, Luis; Teobaldi, Gilberto; Lazarov, Vlado K.; Gilks, Daniel; Burnell, Gavin; Hickey, Bryan J.; Cespedes, Oscar

2014-09-01

211

Effect of Electron Beam Irradiation of the Characteristics of Jute Fibers and the Interfacial Properties of Jute/PLA Green Composites  

International Nuclear Information System (INIS)

Cellulose-based natural fibers such as jute, knife and hemp have promising potential as a replacement for glass fibers in a polymer composite system because of their many advantages like natural abundance, low cost, light weight, biodegradability, carbon dioxide reduction in nature and acceptable mechanical properties. However, natural fibers need an appropriate surface treatment modifying their surface characteristics in order to effectively improve the interfacial properties as well as the mechanical and thermal properties. Electron beam irradiation technique is particularly interesting as it may offer the possibility to modify the surfaces and to enhance the properties of polymer materials such as fibers, films and composites. In addition, electron beam processing has a merit because it is a dry, solvent free and eco-friendly method with a fast throughput rate. In the present study, Jute fibers were irradiated at different dosages of electron beam from 10 to 100 kGy. The result was compared with raw jute fibers un-irradiated, showing the effect on the interfacial shear strength between jute fibers and PLA in terms of single fiber tensile property, fiber surface topology, and chemical composition occurring in jute fibers upon irradiation. It has been found that the surface topology and chemical characteristics of jute fibers significantly depended on the electron beam dosage irradiated, directly influencing the interfacial shear strength and interlaminar shear strength of jute-PLA green composites. It was concluded that electron beam irradiation played a contributing role not only in physically modifying the jute fiber surfaces but also in improving the interfacial properties between jute fibers and poly in the green composite, exhibiting the most effectiveness at a low electron beam energy of 10 kGy

212

A kinetic model for evaluating the dependence of the quantum yield of nano-TiO{sub 2} based photocatalysis on light intensity, grain size, carrier lifetime, and minority carrier diffusion coefficient: Indirect interfacial charge transfer  

Energy Technology Data Exchange (ETDEWEB)

A model based on spherical TiO{sub 2} nanoparticles was developed to study heterogeneous photocatalysis based on TiO{sub 2} in the case of indirect interfacial charge transfer. In this model, the effect of light intensity (I{sub 0}), grain size (r{sub 0}), carrier lifetime (tau{sub p}), and minority carrier diffusion coefficient (D{sub p}) on the quantum yield (QY) of photocatalytic reactions was investigated in detail. Under conditions of sufficiently low incident-light intensity, the QY was found to be propor toI{sub 0}, while it decreased rapidly with an increase in I{sub 0}. In addition, the QY went to zero at a critically high light intensity. Furthermore, the QY was found to decrease with increasing r{sub 0} due to the bulk-recombination loss, and the effect of r{sub 0} on the QY became increasingly stronger with the increase in I{sub 0}. The QY decreased with the decrease in tau{sub p} and D{sub p}, which was more apparent at the critically high I{sub 0}. Under conditions of low [(RH{sub 2}){sub aq}], the QY increased with an increase in [(RH{sub 2}){sub aq}], while it remained nearly constant at high [(RH{sub 2}){sub aq}] due to the fact that the photoinduced electron interfacial transfer became the limiting step for photocatalytic reactions in the case of high [(RH{sub 2}){sub aq}].

Liu Baoshun, E-mail: liubaoshun@126.co [Key Laboratory of Silicate Materials Science and Engineering, Ministry of Education, Wuhan, Hubei 430070 (China) and School of Material Science and Technology, Wuhan University of Technology, Wuhan, Hubei 430070 (China); Zhao Xiujian [Key Laboratory of Silicate Materials Science and Engineering, Ministry of Education, Wuhan, Hubei 430070 (China)

2010-04-30

213

Freezing hot electrons. Electron transfer and solvation dynamics at D{sub 2}O and NH{sub 3}-metal interfaces  

Energy Technology Data Exchange (ETDEWEB)

The present work investigates the electron transfer and solvation dynamics at the D{sub 2}O/Cu(111), D{sub 2}O/Ru(001), and NH{sub 3}/Cu(111) interfaces using femtosecond time-resolved two-photon photoelectron spectroscopy. Within this framework, the influence of the substrate, adsorbate structure and morphology, solvation site, coverage, temperature, and solvent on the electron dynamics are studied, yielding microscopic insight into the underlying fundamental processes. Transitions between different regimes of ET, substrate-dominated, barrier-determined, strong, and weak coupling are observed by systematic variation of the interfacial properties and development of empirical model descriptions. It is shown that the fundamental steps of the interfacial electron dynamics are similar for all investigated systems: Metal electrons are photoexcited to unoccupied metal states and transferred into the adlayer via the adsorbate's conduction band. The electrons localize at favorable sites and are stabilized by reorientations of the surrounding polar solvent molecules. Concurrently, they decay back two the metal substrate, as it offers a continuum of unoccupied states. However, the detailed characteristics vary for the different investigated interfaces: For amorphous ice-metal interfaces, the electron transfer is initially, right after photoinjection, dominated by the substrate's electronic surface band structure. With increasing solvation, a transient barrier evolves at the interface that increasingly screens the electrons from the substrate. Tunneling through this barrier becomes the rate-limiting step for ET. The competition of electron decay and solvation leads to lifetimes of the solvated electrons in the order of 100 fs. Furthermore, it is shown that the electrons bind in the bulk of the ice layers, but on the edges of adsorbed D{sub 2}O clusters and that the ice morphology strongly influences the electron dynamics. For the amorphous NH{sub 3}/Cu(111) interface, two isomers of solvated electrons are found. One exhibits electron dynamics on femtosecond, the other one on picosecond timescales. A similar transition between ET regimes is observed as for ice, but, furthermore, it is shown that - depending on layer thickness - the weak coupling limit is reached, where ET is mediated by thermally activated rearrangement of the solvent. Upon crystallization, the electron dynamics change significantly. Instead of femto- or picoseconds, the electrons reside for minutes in the adlayer. The observation of their formation dynamics allows analysis of their energetic stabilization over 17 orders of magnitude in time. It is shown that their high degree of screening is achieved by localization at orientational defects at the adsorbate-vacuum interface. (orig.)

Staehler, A.J.

2007-05-15

214

Microbial interspecies electron transfer via electric currents through conductive minerals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 electric...

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2012-01-01

215

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

Science.gov (United States)

... false Payment of tax by electronic fund transfer. 41.63...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...41.63 Payment of tax by electronic fund transfer. ...bank in making payment by electronic fund transfer...

2010-04-01

216

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

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... false Payment of tax by electronic fund transfer. 19.524...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...524 Payment of tax by electronic fund transfer. (a) General...bank in making payment by electronic fund transfer...

2010-04-01

217

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

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... false Payment of tax by electronic fund transfer. 25.165...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...165 Payment of tax by electronic fund transfer. (a) Eligible...bank in making payment by electronic fund transfer...

2010-04-01

218

27 CFR 27.48a - Payment of tax by electronic fund transfer.  

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... false Payment of tax by electronic fund transfer. 27.48a...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...48a Payment of tax by electronic fund transfer. ...bank in making payment by electronic fund transfer...

2010-04-01

219

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

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... false Payment of tax by electronic fund transfer. 40.357...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...357 Payment of tax by electronic fund transfer. (a) General...bank in making payment by electronic fund transfer...

2010-04-01

220

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

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... false Payment of tax by electronic fund transfer. 53.158...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...158 Payment of tax by electronic fund transfer. (a) In...the taxes (taxpayments) by electronic fund transfer...

2010-04-01

 
 
 
 
221

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

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... false Payment of tax by electronic fund transfer. 26.267...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...267 Payment of tax by electronic fund transfer. ...bank in making payment by electronic fund transfer...

2010-04-01

222

Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide  

International Nuclear Information System (INIS)

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

223

Radiative and nonradioactive electron transfer in donor-acceptor phenanthrimidazoles.  

Science.gov (United States)

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

224

Electron and proton transfer in chemistry and biology  

International Nuclear Information System (INIS)

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

225

Photoinduced electron transfer between a carotenoid and TiO2 nanoparticle.  

Science.gov (United States)

The dynamics of photoinduced electron injection and recombination between all-trans-8'-apo-beta-caroten-8'-oic acid (ACOA) and a TiO(2) colloidal nanoparticle have been studied by means of transient absorption spectroscopy. We observed an ultrafast ( approximately 360 fs) electron injection from the initially excited S(2) state of ACOA into the TiO(2) conduction band with a quantum yield of approximately 40%. As a result, the ACOA(*)(+) radical cation was formed, as demonstrated by its intense absorption band centered at 840 nm. Because of the competing S(2)-S(1) internal conversion, approximately 60% of the S(2)-state population relaxes to the S(1) state. Although the S(1) state is thermodynamically favorable to donate electrons to the TiO(2), no evidence was found for electron injection from the ACOA S(1) state, most likely as a result of a complicated electronic nature of the S(1) state, which decays with a approximately 18 ps time constant to the ground state. The charge recombination between the injected electrons and the ACOA(*)(+) was found to be a highly nonexponential process extending from picoseconds to microseconds. Besides the usual pathway of charge recombination forming the ACOA ground state, about half of the ACOA(*)(+) recombines via the ACOA triplet state, which was monitored by its absorption band at 530 nm. This second channel of recombination proceeds on the nanosecond time scale, and the formed triplet state decays to the ground state with a lifetime of approximately 7.3 micros. By examination of the process of photoinduced electron transfer in a carotenoid-semiconductor system, the results provide an insight into the photophysical properties of carotenoids, as well as evidence that the interfacial electron injection occurs from the initially populated excited state prior to electronic and nuclear relaxation of the carotenoid molecule. PMID:12431127

Pan, Jie; Benkö, Gábor; Xu, Yunhua; Pascher, Torbjörn; Sun, Licheng; Sundström, Villy; Polívka, Tomás

2002-11-20

226

The bulk and interfacial electronic and chemical structure of amorphous hydrogenated boron carbide  

Science.gov (United States)

The chemical and electronic structure, as related to the surface, interface and bulk of amorphous hydrogenated boron carbide (a-BxC:H y), is of interest in neutron detection and microelectronics. This dissertation investigates the chemical and electronic structure of semiconducting thin-film a-BxC:Hy grown by plasma enhanced chemical vapor deposition (PECVD) of ortho-carborane (1,2-C2B10H12). Experimental methods used include: x-ray and ultraviolet photoelectron spectroscopies (XPS/UPS) and x-ray absorption/emission spectroscopies (XAS/XES). These methods were used to investigate the chemical species, bonding and hybridizations, and band gaps of a-BxC:Hy prepared or treated under varying conditions. Additionally, a detailed examination of the formation of Schottky barriers was implemented. Throughout this dissertation the chemical structure was studied. One study was to understand various growth conditions. The effects of the PECVD growth parameters were evaluated by comparing changes in atomic percentages (at.%'s) between thin-films from various substrate temperatures. Additionally, detailed studies of the photoelectron core level under two different growth conditions were undertaken to evaluate the effects of pre-/post- argon ion etching (Ar+) for the following: the chemical structural change for both an as grown (AG) and in-situ thermal treatment (500°C), and post Ar+ etch of samples thermally treated ranging from as grown to 850°C. The as grown and in-situ treated samples were used in conjunction to determine the formation of the Schottky barrier. The electronic structure was determined by the changes within the valence band of the thermally treated samples and formation of Schottky barrier. Thermally treated samples (as grown to 850°C) were further evaluated with respect to their occupied and unoccupied electronic states. The atomic percentage gave a stoichiometry range for a-B xC:Hy (given as x=1.5 to 3.0 with y= decreases with thermal treatment and Oz: z= 0.2 to 0.5). Studies of films with respect to thermal treatment reveal two discrete state changes that occur at 400°C and 850°C These changes are due to segregation of carbon and oxygen by the reorganization of the hydrocarbon chains between icosahedra. Additionally, the Schottky barrier study indicates that a clean surface was necessary before deposition of an ohmic contact and from the metals studied. Such studies are important to applications for high temperature thermoelectric converters, high-efficiency direct-conversion solid-state neutron detectors and microelectronics.

Driver, Marcus Sky

227

Accelerated Electron Transfer between Metal Complexes Mediated by DNA  

Science.gov (United States)

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

228

Reactions of electron transfer with participation of porphyrins  

International Nuclear Information System (INIS)

Radiation-chemical yields of radiolysis and electronic absorption spectra of solutions are given. It is ascertained that reactions of electron transfer take place during interactions of alcohol radicals both with metalloporphyrins and porphyrin-ligands. The presence of metal ion results in the change of its valency state and protection of ?-system of macroring

229

Electron transfer in the Hf1Co6 magnetic alloy  

International Nuclear Information System (INIS)

The cobalt atomic magnetic moment in Hf1Co6 was determined from the measured saturation magnetization and compared with predictions of an electron transfer model. Good agreement was found when hafnium contributes only two of its four valence electrons to the empty states in the minority spin band of cobalt

230

Electronic and Interfacial Properties of PD/6H-SiC Schottky Diode Gas Sensors  

Science.gov (United States)

Pd/SiC Schottky diodes detect hydrogen and hydrocarbons with high sensitivity. Variation of the diode temperature from 100 C to 200 C shows that the diode sensitivity to propylene is temperature dependent. Long-term heat treating at 425 C up to 140 hours is carried out to determine the effect of extended heat treating on the diode properties and gas sensitivity. The heat treating significantly affects the diode's capacitive characteristics, but the diode's current carrying characteristics are much more stable with a large response to hydrogen. Scanning Electron Microscopy and X-ray Spectrometry studies of the Pd surface after the heating show cluster formation and background regions with grain structure observed in both regions. The Pd and Si concentrations vary between grains. Auger Electron Spectroscopy depth profiles revealed that the heat treating promoted interdiffusion and reaction between the Pd and SiC dw broadened the interface region. This work shows that Pd/SiC Schottky diodes have significant potential as high temperature gas sensors, but stabilization of the structure is necessary to insure their repeatability in long-term, high temperature applications.

Chen, Liang-Yu; Hunter, Gary W.; Neudeck, Philip G.; Bansal, Gaurav; Petit, Jeremy B.; Knight, Dak; Liu, Chung-Chiun; Wu, Qinghai

1996-01-01

231

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

Science.gov (United States)

The transfer of an electron from a donor to an acceptor is the fundamental step in a wide range of chemical and biological processes. As a result, electron-transfer reactions have been the focus of numerous theoretical and experimental efforts aimed at understanding the kinetics and mechanism of the transfer event. Liquid solvents are an important medium for electron-transfer processes. The influences of the distance dependence, diffusion, the radial distribution function, and the hydrodynamic effect have been incorporated into the theory of electron transfer in solution, as well as into the theory of electron transfer between donors and acceptors in the head group regions of micelles. The development of new laser system with a pulse duration of tens of femtoseconds, with tunable wavelength allowed us to study these processes on a considerably shorter time scale than previous studies. This allowed us to observe not only the diffusion controlled but also the kinetics of electron transfer for donor/acceptor pairs that are in close proximity. In one set of experiments we have studied the kinetics of electron transfer in electron accepting molecule (rhodamine 3B) dissolved in electron donating solvent (N,N-dimethylaniline). The data for the forward electron transfer and geminate recombination are approximated by the statistical theory of the electron transfer. Optical anisotropy observed in the experiment demonstrates the orientation dependence of the electron transfer rate. In further experiments we investigated the electron transfer in non-hydrogen bonding liquids of increasing viscosity. The effective value of the donor/acceptor electronic coupling was found to decrease with viscosity. Electron transfer experiments were also carried out on the surface of micelles. The systems studied are the hole donor octadecyl-rhodamine B (ODRB) and the hole acceptor N,N-dimethyl-aniline (DMA) in micelles made of dodecyltrimethylammonium bromide (DTAB) and tetradecyltrimethylammonium bromide (TTAB). It was found that the effective coupling is reduced compared to donor/acceptor pairs dissolved in simple liquids. In the 2nd half of thesis we have addressed the question of the dynamics of phase transitions. We have demonstrated the ability to use the fluorescent excitation-transfer technique to study the demixing of liquids specifically, kinetics of demixing water and 2,6-dimethylpyridine. These two liquids possess a low critical temperature point, which allowed us to use a temperature jump from a laser pulse to initiate the process of phase separation. It was found that Coumarin480 laser dye and HPTS (8-Hydroxypyrene-1,3,6-trisulfonic acid) fluorescent dye have significantly different solubilities in the components of the mixture. These dyes undergo excitation transfer from Coumarin480 to HPTS in the uniform state, but not in the phase-separated state. A system with a temperature jump pump and an excitation transfer probe measured the time scale of the initial step of the phase separation.

Goun, Alexei A.

232

Quantum interferences and electron transfer in photosystem I.  

Science.gov (United States)

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

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

2013-07-25

233

Hydrogen diffusion and radiationless electron transfer in metal hydrides  

International Nuclear Information System (INIS)

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

234

Electronic energy transfer in actinyl crystals  

International Nuclear Information System (INIS)

Time-resolved luminescence and excitation spectra of single crystals of caesium uranyl chloride containing a wide range of concentrations of bromide ion impurity have been studied between 4.2 K and room temperature. There is no evidence that the trapping process is diffusion controlled even in crystals containing one trap centre in 104. It follows that a lower limit on the resonant transfer rate at 4.2 K is 1010 s-1. The observation of distinct spectroscopic features characterizing sites adjacent to the trap site enables the anisotropy of the trapping rate to be demonstrated. (author)

235

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

Science.gov (United States)

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

Kosman, Daniel J

2008-03-01

236

Coupling of narrow and wide band-gap semiconductors on uniform films active in bacterial disinfection under low intensity visible light: Implications of the interfacial charge transfer (IFCT)  

International Nuclear Information System (INIS)

Highlights: • Design, preparation, testing and characterization of uniform sputtered films. • Interfacial charge transfer from the Ag2O (cb) to the lower laying Ta2O5 (cb). • The optical absorption of TaON and TaON/Ag was proportional to E. coli inactivation. • Self-cleaning of the TaON/Ag polyester enables repetitive E. coli inactivation. -- Abstract: This study reports the design, preparation, testing and surface characterization of uniform films deposited by sputtering Ag and Ta on non-heat resistant polyester to evaluate the Escherichia coli inactivation by TaON, TaN/Ag, Ag and TaON/Ag polyester. Co-sputtering for 120 s Ta and Ag in the presence of N2 and O2 led to the faster E. coli inactivation by a TaON/Ag sample within ?40 min under visible light irradiation. The deconvolution of TaON/Ag peaks obtained by X-ray photoelectron spectroscopy (XPS) allowed the assignment of the Ta2O5 and Ag-species. The shifts observed for the XPS peaks have been assigned to AgO to Ag2O and Ag0, and are a function of the applied sputtering times. The mechanism of interfacial charge transfer (IFCT) from the Ag2O conduction band (cb) to the lower laying Ta2O5 (cb) is discussed suggesting a reaction mechanism. The optical absorption of the TaON and TaON/Ag samples found by diffuse reflectance spectroscopy (DRS) correlated well with the kinetics of E. coli inactivation. The TaON/Ag sample microstructure was characterized by contact angle (CA) and by atomic force microscopy (AFM). Self-cleaning of the TaON/Ag polyester after each disinfection cycle enabled repetitive E. coli inactivation

237

Interfacial dissipation in two-phase flow  

International Nuclear Information System (INIS)

Advanced generation computer codes for the thermal-hydraulics of light water reactors often use two-fluid models in which the interfacial momentum transfer laws must be specified. In this paper, the authors examine the necessary conditions on the interfacial momentum transfer laws in order that the model be properly dissipative. 3 refs

238

Electron transfer properties of organic dye-sensitized solar cells based on indoline sensitizers with ZnO nanoparticles  

Science.gov (United States)

Two indoline dyes, coded D149 and D205, were used as the sensitizers of ZnO dye-sensitized solar cells (DSCs) with optimal energy conversion efficiencies of more than 5%, under AM 1.5 full sunlight illumination (100 mW cm - 2). Higher interfacial charge transfer rate and retardant fluorescence decay confirmed from transient fluorescence illustrated that D205-sensitized ZnO DSCs could possess better electron transport than D149-sensitized ZnO DSCs. The enhancement of Voc and Jsc for D205-sensitized ZnO DSCs was ascribed to the effective suppression of electron recombination by extending the alkyl chain on the terminal rhodanine moiety from ethyl to octyl. The evidence of enhanced electron diffusion coefficient was further shown by electrochemical impedance spectroscopy (EIS).

Cheng, Hsin-Ming; Hsieh, Wen-Feng

2010-12-01

239

Electron transfer properties of organic dye-sensitized solar cells based on indoline sensitizers with ZnO nanoparticles  

International Nuclear Information System (INIS)

Two indoline dyes, coded D149 and D205, were used as the sensitizers of ZnO dye-sensitized solar cells (DSCs) with optimal energy conversion efficiencies of more than 5%, under AM 1.5 full sunlight illumination (100 mW cm-2). Higher interfacial charge transfer rate and retardant fluorescence decay confirmed from transient fluorescence illustrated that D205-sensitized ZnO DSCs could possess better electron transport than D149-sensitized ZnO DSCs. The enhancement of Voc and Jsc for D205-sensitized ZnO DSCs was ascribed to the effective suppression of electron recombination by extending the alkyl chain on the terminal rhodanine moiety from ethyl to octyl. The evidence of enhanced electron diffusion coefficient was further shown by electrochemical impedance spectroscopy (EIS).

240

Electron transfer properties of organic dye-sensitized solar cells based on indoline sensitizers with ZnO nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Two indoline dyes, coded D149 and D205, were used as the sensitizers of ZnO dye-sensitized solar cells (DSCs) with optimal energy conversion efficiencies of more than 5%, under AM 1.5 full sunlight illumination (100 mW cm{sup -2}). Higher interfacial charge transfer rate and retardant fluorescence decay confirmed from transient fluorescence illustrated that D205-sensitized ZnO DSCs could possess better electron transport than D149-sensitized ZnO DSCs. The enhancement of V{sub oc} and J{sub sc} for D205-sensitized ZnO DSCs was ascribed to the effective suppression of electron recombination by extending the alkyl chain on the terminal rhodanine moiety from ethyl to octyl. The evidence of enhanced electron diffusion coefficient was further shown by electrochemical impedance spectroscopy (EIS).

Cheng, Hsin-Ming; Hsieh, Wen-Feng, E-mail: SMCheng@itri.org.tw, E-mail: wfhsieh@mail.nctu.edu.tw [Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan (China)

2010-12-03

 
 
 
 
241

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

Science.gov (United States)

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

242

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

Science.gov (United States)

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

243

Plugging in or going wireless: strategies for interspecies electron transfer  

Science.gov (United States)

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

244

Plugging in or Going Wireless: Strategies for Interspecies Electron Transfer  

Directory of Open Access Journals (Sweden)

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

PravinMallaShrestha

2014-05-01

245

Plugging in or Going Wireless : Strategies for Interspecies Electron Transfer  

DEFF Research Database (Denmark)

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.

Shrestha, Pravin; Rotaru, Amelia-Elena

2014-01-01

246

Theory of reversible electron transfer reactions in a condensed phase  

Science.gov (United States)

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

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

2010-07-01

247

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

Science.gov (United States)

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

248

Non-Nernstian two-electron transfer photocatalysis at metalloporphyrin-TiO2 interfaces.  

Science.gov (United States)

A long-standing question in the photochemical sciences concerns how to integrate single-electron transfers to catalytic multielectron transfer reactions that produce useful chemical fuels. Here we provide a strategy for the two-electron formation of C-C bonds with molecular catalysts anchored to semiconductor nanocrystallites. The blue portion of the solar spectrum provides band gap excitation of the semiconductor while longer wavelengths of light initiate homolytic cleavage of metal-carbon bonds that, after interfacial charge transfer, restore the catalyst. The semiconductor utilized was the anatase polymorph of TiO(2) present as a nanocrystalline, mesoporous thin film. The catalyst was cobalt meso-5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin chloride, Co(TCPP)Cl. For this catalyst and iron protoporphyrin IX chloride, Fe(PPIX)Cl, two distinct and sequential metal-based M(III/II) and M(II/I) reductions were observed under band gap illumination. Spectroelectrochemical characterization indicated that both reductions were non-Nernstian, behavior attributed to an environmentally dependent potential drop across the molecule-semiconductor interface. Reaction of Co(I)(TCPP)/TiO(2) with organobromides (RBr = 1-Br-hexane or benzyl bromide) resulted in the formation of Co(III)-R(TCPP)/TiO(2). Visible light excitation induced homolytic cleavage of the Co-C bond and the formation of C-C-bonded products. The reactions were catalytic when band gap excitation or an electrochemical bias provided TiO(2) electrons to the oxidized catalyst. Sustained photocurrents were quantified in photoelectrosynthetic solar cells under forward bias. PMID:21888402

Ardo, Shane; Achey, Darren; Morris, Amanda J; Abrahamsson, Maria; Meyer, Gerald J

2011-10-19

249

Electron Delocalization and Charge Transfer in Polypeptide Chains  

Science.gov (United States)

In this work, the electron structure and charge-transfer mechanism in polypeptide chains are investigated according to natural bond orbitals (NBO) analysis at the level of B3LYP/6-311++G**. The results indicate that the delocalization of electrons between neighboring peptide subgroups can occur in two opposite directions, and the delocalization effect in the direction from the carboxyl end to the amino end has an obvious advantage. As a result of a strong hyperconjugative interaction, the lowest unoccupied NBO of the peptide subgroup, ?*C-O, has significant delocalization to neighboring subgroups, and the energies of these NBOs decrease from the carboxyl end to the amino end. The formation of intramolecular O···H-N type hydrogen bonds also helps to delocalize the electron from the carboxyl end to the amino end. Thus, the electron will flow to the amino end. The superexchange mechanism is suggested in the electron-transfer process.

Wang, Ye-Fei; Yu, Zhang-Yu; Wu, Jian; Liu, Cheng-Bu

2009-09-01

250

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

Energy Technology Data Exchange (ETDEWEB)

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

251

Direct interspecies electron transfer between Geobacter metallireducens and Methanosarcina barkeri.  

Science.gov (United States)

Direct interspecies electron transfer (DIET) is potentially an effective form of syntrophy in methanogenic communities, but little is known about the diversity of methanogens capable of DIET. The ability of Methanosarcina barkeri to participate in DIET was evaluated in coculture with Geobacter metallireducens. Cocultures formed aggregates that shared electrons via DIET during the stoichiometric conversion of ethanol to methane. Cocultures could not be initiated with a pilin-deficient G. metallireducens strain, suggesting that long-range electron transfer along pili was important for DIET. Amendments of granular activated carbon permitted the pilin-deficient G. metallireducens isolates to share electrons with M. barkeri, demonstrating that this conductive material could substitute for pili in promoting DIET. When M. barkeri was grown in coculture with the H2-producing Pelobacter carbinolicus, incapable of DIET, M. barkeri utilized H2 as an electron donor but metabolized little of the acetate that P.carbinolicus produced. This suggested that H2, but not electrons derived from DIET, inhibited acetate metabolism. P. carbinolicus-M. barkeri cocultures did not aggregate, demonstrating that, unlike DIET, close physical contact was not necessary for interspecies H2 transfer. M. barkeri is the second methanogen found to accept electrons via DIET and the first methanogen known to be capable of using either H2 or electrons derived from DIET for CO2 reduction. Furthermore, M. barkeri is genetically tractable,making it a model organism for elucidating mechanisms by which methanogens make biological electrical connections with other cells. PMID:24837373

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

2014-08-01

252

Photocurrent generation by direct electron transfer using photosynthetic reaction centres  

International Nuclear Information System (INIS)

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-baong term efforts to demonstrate RC-based photovoltaic devices

253

The role of excited Rydberg States in electron transfer dissociation.  

Science.gov (United States)

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

254

Light-driven microbial dissimilatory electron transfer to hematite.  

Science.gov (United States)

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

255

Phonon-mediated path-interference in electronic energy transfer.  

Science.gov (United States)

We present a formalism to quantify the contribution of path-interference in phonon-mediated electronic energy transfer. The transfer rate between two molecules is computed by considering the quantum mechanical amplitudes associated with pathways connecting the initial and final sites. This includes contributions from classical pathways, but also terms arising from interference of different pathways. We treat the vibrational modes coupled to the molecules as a non-Markovian harmonic oscillator bath, and investigate the correction to transfer rates due to the lowest-order interference contribution. We show that depending on the structure of the harmonic bath, the correction due to path-interference may have a dominant vibrational or electronic character, and can make a notable contribution to the transfer rate in the steady state. PMID:22260569

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

2012-01-14

256

Universal nanopatternable interfacial bonding.  

Science.gov (United States)

A nanopatternable polydimethylsiloxane (PDMS) oligomer layer is demonstrated as an interfacial adhesive for its intrinsic transferability and universal adhesiveness. Utilizing the well-established surface modification and bonding techniques of PDMS surfaces, irreversible bonding is formed (up to 400 kPa) between a wide range of substrate pairs, representing ones within and across different materials categories, including metals, ceramics, thermoset, and thermoplastic polymers. PMID:22028210

Ding, Yuzhe; Garland, Shaun; Howland, Michael; Revzin, Alexander; Pan, Tingrui

2011-12-01

257

Heavy particle interference and diffraction in fast electron transfer collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis presents experimental results from the synchrotron cooler and storage ring CRYRING on charge transfer processes in fast electron transfer collisions using high-resolution cold target recoil-ion momentum spectroscopy. The main focus of these studies was to investigate a key concept of quantum mechanics: the wave-particle duality. One series of experiments has been dedicated to the study of heavy particle de Broglie wave interference due to scattering on a molecular ’double slit?...

Gudmundsson, Magnus

2011-01-01

258

Magneto-controlled Quantized Electron Transfer to Surface-confined Redox Units and Metal Nanoparticles  

Directory of Open Access Journals (Sweden)

Full Text Available Hydrophobic magnetic nanoparticles (NPs consisting of undecanoate-cappedmagnetite (Fe3O4, average diameter ca. 5 nm are used to control quantized electron transferto surface-confined redox units and metal NPs. A two-phase system consisting of anaqueous electrolyte solution and a toluene phase that includes the suspended undecanoate-capped magnetic NPs is used to control the interfacial properties of the electrode surface.The attracted magnetic NPs form a hydrophobic layer on the electrode surface resulting inthe change of the mechanisms of the surface-confined electrochemical processes. Aquinone-monolayer modified Au electrode demonstrates an aqueous-type of theelectrochemical process (2e- 2H+ redox mechanism for the quinone units in the absence ofthe hydrophobic magnetic NPs, while the attraction of the magnetic NPs to the surfaceresults in the stepwise single-electron transfer mechanism characteristic of a dry non-aqueous medium. Also, the attraction of the hydrophobic magnetic NPs to the Au electrodesurface modified with Au NPs (ca. 1.4 nm yields a microenvironment with a low dielectricconstant that results in the single-electron quantum charging of the Au NPs.

Itamar Willner

2006-04-01

259

Multi-Element Electron-Transfer Optical Detector System  

Science.gov (United States)

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

Jordan, Jeffrey D. (Inventor)

2004-01-01

260

Probing electron transfer dynamics of pyranine with reduced graphene oxide.  

Science.gov (United States)

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

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

2014-10-14

 
 
 
 
261

Electron transfer dynamics: Zusman equation versus exact theory  

International Nuclear Information System (INIS)

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

262

Vibrational coherence in electron transfer: The tetracyanoethylene-pyrene complex  

Science.gov (United States)

Coherent vibrational wave packet motion is created in the excited charge-transfer state of the electron donor-acceptor complex between tetracyanoethylene (TCNE) and pyrene by an ultrashort (40 fs) 810 nm pump pulse. Observations of the dynamics of the TCNE-anion transient absorption and the disappearance of the bleach of the ground state absorption show that the electron-transfer reaction back to the ground state of the complex occurs on a 250 fs-1.5 ps time scale. The bleach recovery signal shows clear oscillations and both impulsive stimulated Raman scattering in the ground state and coherent repopulation of the ground state surface due to a vibrationally coherent electron transfer reaction were considered as the cause. Vibrational coherence has also been monitored by observing quantum beats in the stimulated emission from the charge transfer state back to the ground state in the near-ir. This observation strongly suggests that the electron transfer reaction is indeed vibrationally coherent and that the reaction rate is modulated by this coherence. This interpretation is corroborated by a classical Monte Carlo simulation of vibrationally coherent reactions in the inverted regime.

Wynne, Klaas; Reid, Gavin D.; Hochstrasser, Robin M.

1996-08-01

263

Auger-assisted electron transfer from photoexcited semiconductor quantum dots.  

Science.gov (United States)

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

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

2014-03-12

264

Theoretical aspects of electron transfer reactions of complex molecules  

DEFF Research Database (Denmark)

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

Ulstrup, Jens

2001-01-01

265

Conformational dependence of electron transfer across de novo designed metalloproteins.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Flash photolysis and pulse radiolysis measurements demonstrate a conformational dependence of electron transfer rates across a 16-mer helical bundle (three-helix metalloprotein) modified with a capping CoIII(bipyridine)3 electron acceptor at the N terminus and a 1-ethyl-1'-ethyl-4,4'- bipyridinium donor at the C terminus. For the CoIII(peptide)3-1-ethyl-1'-ethyl-4,4'-bipyridinium maquettes, the observed transfer is a first order, intramolecular process, independent of peptide concentration or...

Mutz, M. W.; Mclendon, G. L.; Wishart, J. F.; Gaillard, E. R.; Corin, A. F.

1996-01-01

266

High-pressure effects on intramolecular electron transfer compounds  

CERN Document Server

We explore the effect of pressure on the fluorescence spectra of the intramolecular electron transfer compound N-(1-pyrenylmethyl), N-methyl-4-methoxyaniline (Py-Am) and its model version, with poly(methyl methacrylate) blended in, at high pressure up to 7 GPa. The emission properties of Py-Am and pyrene show distinct difference with the increase of pressure. This difference indicates the strength of the charge transfer interaction resulting from the adjusting of the conformation of Py-Am with increase of pressure. The relationship between the electronic state of the molecule and pressure is discussed.

He Li Ming; Li Hong; Zhang Bao Wen; Li Yi; Yang Guo Qiang

2002-01-01

267

Theory of electron transfer and molecular state in DNA  

Science.gov (United States)

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

268

Energy and electron transfer processes in polymethine dyes  

International Nuclear Information System (INIS)

Polymethine dyes and its derivatives are attractive for their interesting optical and photo-electric properties. They are used as very efficient spectral sensitizers and laser dyes. Due to the high rate constant of deactivation channels of such dyes the primary processes of bimolecular processes as energy or electron transfer proceed within not more than some picoseconds or even shorter. In the case of a polymethine which does not isomerize we were able to show by means of time-resolved absorption spectroscopy that the singlet state photoelectron transfer to methyl- and benzylviologen had an efficiency of 0.15 with rate constants of 6.7·109 and 4.6·109 l/mole·s, respectively, yielding the polymethine dication radical. The photoreduction with tetraphenylborate and potassium rhodanide is also very efficient with an efficiency of about 0.10 with rate constants of 2.4·1010 and 1.6·1010 l/mole·s, respectively, yielding the polymethine neutral radical. The spectral differences of the observed radical spectra are small. The investigation of the temperature dependence of the photo induced electron transfer of the investigated polymethine to methylviologen results in an activation energy ?G*=24 kJ/mole and a value of the frequency factor of A=4.7·1014 l/mole·s. Strong deviation from a linear Arrhenius plot was observed at low temperatures which can be explained by solvent-solute interaction decreasing the electronteraction decreasing the electron transfer rate constant at lower temperatures. The calculated electron transfer rate constants agree with the assumption of the investigated process as a diffusion-controlled one. Energy transfer occurs as a efficient competitive deactivation channel from photo excited polymethine dyes to other chromophore systems with a strong overlapping of the fluorescence and the absorption bands of the donor and the acceptor, respectively. We have investigated the time and spectral evolution of the energy transfer process from a polymethine dye to different energy acceptor dyes in solution. The general question within this respect was the involvement of an intermediate electron transfer as competitive process in the energy transfer process. Whereas the Foerster energy transfer radius calculated from the time-resolved data exceeds the value received from the overlap integral by 15%, indicating deviation from a normal Foerster decay type the semilogarithmic plot of the ground state recovery kinetics vs. square root of time results in an ideal straight line dependence. No intermediate spectra as well as intermediate time behaviour was found in these complexes

269

Quality assurance and data collection -- Electronic Data Transfer  

International Nuclear Information System (INIS)

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

270

Effect of Process Parameters, Casting Thickness, and Alloys on the Interfacial Heat-Transfer Coefficient in the High-Pressure Die-Casting Process  

Science.gov (United States)

The heat transfer at the metal-die interface is believed to have great influence on the solidification process and cast structure of the high-pressure die-casting (HPDC) process. The present article focused on the effects of process parameters, casting thickness, and alloys on the metal-die interfacial heat-transfer coefficient (IHTC) in the HPDC process. Experiment was carried out on a cold-chamber die-casting machine with two casting alloys AM50 and ADC12. A special casting, namely, “step-shape” casting, was used and cast against a H13 steel die. The IHTC was determined using an inverse approach based on the temperature measurements inside the die. Results show that the IHTC is different at different steps and changes as the solidification of the casting proceeds. Process parameters only influence the IHTC in its peak value, and for both AM50 and ADC12 alloys, a greater fast shot velocity leads to a greater IHTC peak value at steps 1 and 2. The initial die surface temperature has a more prominent influence on the IHTC peak values at the thicker steps, especially step 5. Results also show that a closer contact between the casting and die could be achieved when the casting alloy is ADC12 instead of AM50, which consequently leads to a higher IHTC.

Guo, Zhi-Peng; Xiong, Shou-Mei; Liu, Bai-Cheng; Li, Mei; Allison, John

2008-12-01

271

Electron-transfer processes in fast ion-atom collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The subject of this thesis is experimental studies of electron-transfer processes in ion-atom collisions at velocities significantly higher than typical orbital velocities of electrons in bound states of atoms or molecules. The experimental technique applied combines the high beam intensity of heavy-ion storage rings with a supersonic gas-jet target equipped with a recoil-ion-momentum spectrometer. In singleelectron capture to fast protons from helium atoms, we have for the first time achieve...

Støchkel, Kristian

2005-01-01

272

Intramolecular Electron Scattering and Electron Transfer Following Autoionization in Dissociating Molecules  

Science.gov (United States)

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

273

Magnetic resonance studies of photo-induced electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

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

van Willigen, H.

1992-11-01

274

Energy and photoinduced electron transfer in porphyrin-fullerene dyads  

Energy Technology Data Exchange (ETDEWEB)

Time-resolved fluorescence and absorption techniques have been used to investigate energy and photoinduced electron transfer in a covalently linked free-base porphyrin-fullerene dyad and its zinc analogue. In toluene, the porphyrin first excited singlet states decay in about 20 ps by singlet-singlet energy transfer to the fullerene. The fullerene first excited singlet state is not quenched and undergoes intersystem crossing to the triplet, which exists in equilibrium with the porphyrin triplet state. In benzonitrile, photoinduced electron transfer from the porphyrin first excited singlet state to the fullerene competes with energy transfer. The fullerene excited singlet state is also quenched by electron transfer from the porphyrin. Overall, the charge-separated state is produced with a quantum yield approaching unity. This state lives for 290 ps in the free-base dyad and 50 ps in the zinc analog. These long lifetimes suggest that such dyads may be useful as components of more complex light-harvesting systems. 32 refs., 12 figs., 1 tab.

Kuciauskas, D.; Lin, S.; Seely, G.R.; Moore, A.L.; Moore, T.A.; Gust, D. [Arizona State Univ., Tempe, AZ (United States); Drovetskaya, T.; Reed, C.A. [Univ. of Southern California, Los Angeles, CA (United States); Boyd, P.D.W. [Univ. of Auckland (New Zealand)

1996-09-26

275

Scanning Electron Microscopic Evaluation of Composite Resin-Dentin, Calcium Hydroxide-Dentin and Resin- Calcium Hydroxide Interfacial Gap with Composite Resin Restorations- An in vitro Study  

Directory of Open Access Journals (Sweden)

Full Text Available The dental pulp has been shown to have its own reparative capacity and is capable not only of healing but alsoof providing a dentinal bridge in the absence of calcium hydroxide. The present study was performed to evaluateinterfacial gaps formed due to polymerization shrinkage of composite resin. 20 Maxillary or Mandibular, freshly extractedhuman third molars were prepared and filled using composite with a calcium hydroxide base. The samples were dividedinto two groups based on primer/bonding agent used i.e. Scotchbond multipurpose (Group I and Single bond (GroupII.Sectioned samples were gold sputtered and analyzed using Scanning Electron Microscope (SEM. The interfacial gap inspecimens belonging to group I and II was observed at the 3 interfaces viz; Calcium hydroxide-dentin interface (A,Composite resin - calcium hydroxide interface (B and Composite resin - dentin interface (C. The interfacial gap formedbetween calcium hydroxide and dentin (A was highly significant (p <0.01 in both groups i.e. Group I and Group II, whenit was compared with ‘B’ and ‘C’ of the same group. There was no statistical significant difference between group ‘B’ and‘C’. Thus in both the groups an interfacial gap was found between the calcium hydroxide and dentin. Interposition ofcalcium hydroxide between tooth and resin possesses some clinical disadvantages and is recommended in selectiveclinical situations.

Manoranjan Reddy,

2011-07-01

276

Electron transfer kinetics on mono- and multilayer graphene.  

Science.gov (United States)

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

277

Theoretical studies of electron transfer through dendrimeric architecture  

Science.gov (United States)

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

278

Local operator partitioning of electronic energy for electronic energy transfer: An efficient algorithm  

Digital Repository Infrastructure Vision for European Research (DRIVER)

An efficient computational algorithm to implement a local operator approach to partitioning electronic energy in general molecular systems is presented. This approach, which rigorously defines the electronic energy on any subsystem within a molecule, gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. We apply the technique to the $9-$(($1-$naphthyl)$-$methyl)-an...

Nagesh, Jayashree; Izmaylov, Artur F.; Brumer, Paul

2013-01-01

279

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

Energy Technology Data Exchange (ETDEWEB)

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

1990-02-14

280

Multicopper oxidases : intramolecular electron transfer and O2 reduction  

DEFF Research Database (Denmark)

The multicopper oxidases are an intriguing, widespread family of enzymes that catalyze the reduction of O2 to water by a variety of single-electron and multiple-electron reducing agents. The structure and properties of the copper binding sites responsible for the latter chemical transformations have been studied for over 40 years and a detailed picture is emerging. This review focuses particularly on the kinetics of internal electron transfer between the type 1 (blue) copper site and the trinuclear center, as well as on the nature of the intermediates formed in the oxygen reduction process.

Wherland, Scot; Farver, Ole

2014-01-01

 
 
 
 
281

Protein dynamics modulated electron transfer kinetics in early stage photosynthesis  

Science.gov (United States)

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

282

Charge transfer and electron emission in ion-surface interactions  

International Nuclear Information System (INIS)

The formation and decay of multiply excited projectiles during collisions of slow highly charged ions with metal and insulator surfaces have been simulated based on a classical over-barrier model. Simulations including the full trajectory of the projectile have recently allowed the simultaneous evaluation of projectile kinetic energy gains, final charge-state distributions and emitted Auger electron yields in reasonable agreement with experiments. Due to the many-electron nature of these interactions, no detailed quantum mechanical calculations are available. In contrast, for low charge states of the incident ion, quantum mechanical close-coupling calculations have been performed that provide detailed information on resonance formation, hybridization, and electron transfer, including the effects of external electric fields. In this paper, some aspects of ion-surface collisions are reviewed within both (many-electron) over-barrier models and quantum mechanical single-electron expansion methods

283

Mechanism of electron transfer processes photoinduced by lumazine.  

Science.gov (United States)

UV-A (320-400 nm) and UV-B (280-320 nm) radiation causes damage to DNA and other biomolecules through reactions induced by different endogenous or exogenous photosensitizers. Lumazines are heterocyclic compounds present in biological systems as biosynthetic precursors and/or products of metabolic degradation. The parent and unsubstituted compound called lumazine (pteridine-2,4(1,3H)-dione; Lum) is able to act as photosensitizer through electron transfer-initiated oxidations. To get further insight into the mechanisms involved, we have studied in detail the oxidation of 2'-deoxyadenosine 5'-monophosphate (dAMP) photosensitized by Lum in aqueous solution. After UV-A or UV-B excitation of Lum and formation of its triplet excited state ((3)Lum*), three reaction pathways compete for the deactivation of the latter: intersystem crossing to singlet ground state, energy transfer to O(2), and electron transfer between dAMP and (3)Lum* yielding the corresponding pair of radical ions (Lum?(-) and dAMP?(+)). In the following step, the electron transfer from Lum?(-) to O(2) regenerates Lum and forms the superoxide anion (O(2)?(-)), which undergoes disproportionation into H(2)O(2) and O(2). Finally dAMP?(+) participates in subsequent reactions to yield products. PMID:22212735

Denofrio, M Paula; Dántola, M Laura; Vicendo, Patricia; Oliveros, Esther; Thomas, Andrés H; Lorente, Carolina

2012-02-01

284

Effect of gold nanoparticles on the structure and electron-transfer characteristics of glucose oxidase redox polyelectrolyte-surfactant complexes.  

Science.gov (United States)

Efficient electrical communication between redox proteins and electrodes is a critical issue in the operation and development of amperometric biosensors. The present study explores the advantages of a nanostructured redox-active polyelectrolyte-surfactant complex containing [Os(bpy)2Clpy](2+) (bpy=2,2'-bipyridine, py= pyridine) as the redox centers and gold nanoparticles (AuNPs) as nanodomains for boosting the electron-transfer propagation throughout the assembled film in the presence of glucose oxidase (GOx). Film structure was characterized by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM), GOx incorporation was followed by surface plasmon resonance (SPR) and quartz-crystal microbalance with dissipation (QCM-D), whereas Raman spectroelectrochemistry and electrochemical studies confirmed the ability of the entrapped gold nanoparticles to enhance the electron-transfer processes between the enzyme and the electrode surface. Our results show that nanocomposite films exhibit five-fold increase in current response to glucose compared with analogous supramolecular AuNP-free films. The introduction of colloidal gold promotes drastic mesostructural changes in the film, which in turn leads to a rigid, amorphous interfacial architecture where nanoparticles, redox centers, and GOx remain in close proximity, thus improving the electron-transfer process. PMID:25171096

Cortez, M Lorena; Marmisollé, Waldemar; Pallarola, Diego; Pietrasanta, Lía I; Murgida, Daniel H; Ceolín, Marcelo; Azzaroni, Omar; Battaglini, Fernando

2014-10-01

285

Single electron transfer in thermally annealed nanoparticle dropcast thick films  

Science.gov (United States)

A very simple and effective procedure based on thermal annealing was reported in inducing discrete charge transfer in nanoparticle solid films. The particle ensembles were prepared by dropcasting a particle solution onto an interdigitated array electrode. The as-prepared particle films exhibited only linear featureless current-potential profiles in conductivity measurements, whereas after thermal annealing, well-defined staircase features of single electron transfer started to emerge at temperatures higher than 300 K. This was accounted for by the combined consequence of structural rearrangements of nanoparticle cores within the organic protecting matrix and thermal activation of interparticle charge transport.

Pradhan, Sulolit; Kang, Xiongwu; Mendoza, Ernesto; Chen, Shaowei

2009-01-01

286

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

DEFF Research Database (Denmark)

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

Solov'yov, Ilia; Chang, Po-Yao

2012-01-01

287

Photoinduced electron-transfer reactions of aryl glycosides  

Energy Technology Data Exchange (ETDEWEB)

The photolytic effects of ultraviolet, as well as other electromagnetic, radiation on carbohydrates are of interest in connection with photodegradation of cellulose and potential application in the photolytic cleavage of lignocellulosic bonds. Aryl glycosides, model compounds for lignocellulosic systems, were irradiated under conditions selected to achieve photoinduced electron-transfer. Various anomeric phenyl D-gluco- and D-galacto-pyranoside solutions in acetonitrile saturated with oxygen, air, or nitrogen and containing 1,4-dicyanonaphthalene (DCN) were irradiated at 350 nm for extended periods, and cleavage of the radical cation formed upon electron transfer to give the simple monosaccharide and phenol was observed. In the presence of methanol, it is possible to intercept the cationic intermediate, with formation of the corresponding methyl glycosides. Control experiments conducted in the presence of oxygen, air, or nitrogen in the absence of DCN showed little or no conversion. Comparison of the modes of fragmentation in solution with those observed in the gas phase upon electron impact in the mass spectrometer was made, and mechanisms for the reactions induced by electron transfer under these conditions are proposed.

Timpa, J.D.; Legendre, M.G.; Griffin, G.W.; Das, P.K.

1983-01-01

288

Unveiling the details of electron transfer in multicenter redox proteins.  

Science.gov (United States)

Metalloproteins modulate the intrinsic properties of transition metals to achieve controlled catalysis, electron transfer, or structural stabilization. Those performing electron transport, redox proteins, are a diverse class of proteins with central roles in numerous metabolic and signaling pathways, including respiration and photosynthesis. Many redox proteins have applications in industry, especially biotechnology, making them the focus of intense research. Redox proteins may contain one or multiple redox centers of the same or a different type. The complexity of proteins with multiple redox centers makes it difficult to establish a detailed molecular mechanism for their activity. Thermodynamic and kinetic information can be interpreted using the molecular structure to elucidate the protein's functional mechanism. This Account reviews experimental strategies developed in recent years to determine the detailed thermodynamic properties of multicenter redox proteins and their kinetic properties during interactions with redox partners. These strategies allow the discrimination of thermodynamic and kinetic properties of each individual redox center. The thermodynamic characterization of the redox transitions results from the combined analysis of data from NMR and UV-visible spectroscopy. Meanwhile, the kinetic characterization of intermolecular electron transfer comes from stopped-flow spectrophotometry. We illustrate an application of these strategies to a particular redox protein, the small tetraheme cytochrome from the periplasmic space of Shewanella oneidensis MR-1. This protein is a convenient prototype for developing methods for the detailed analysis of multicenter electron transfer proteins because hemes have strong UV-visible absorption bands and because heme resonances have exquisite discrimination in NMR spectra. Nonetheless, the methods are fully generalizable. Ultimately, this Account highlights the relevance of detailed characterization of the thermodynamic and kinetic properties of redox proteins. These properties are responsible for the directionality and specificity of the electron transfer process in bioenergetic pathways; a more thorough characterization of these properties should allow better-designed proteins for industrial applications. PMID:23984680

Paquete, Catarina M; Louro, Ricardo O

2014-01-21

289

A New Formulation of the Frequency Factor in the Expression for the Rate Constant of Interfacial Charge Transfers  

Scientific Electronic Library Online (English)

Full Text Available SciELO Portugal | Language: English Abstract in english A new way for deriving the fundamental equation of the electrochemistry has been developed in the potential range in which Butler-Volmer behaviour is found. In this approach the frequency factor is considered to be a function of the potential instead of the activation energy. The frequency factor is [...] calculated by means of a classical statistical mechanics treatment giving rise to a new definition for the symmetry factor. A new expression for the standard rate constant in adiabatic heterogeneous charge transfer reactions has been derived.

Jaime González, Velasco.

290

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

Science.gov (United States)

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

291

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

Science.gov (United States)

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

292

Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies.  

Science.gov (United States)

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

293

Electron transfer to Ar2+ from rare-gas atoms  

International Nuclear Information System (INIS)

Two generally applicable models for electron transfer have been compared with new measurements of the ?21 cross section for Ar2+, in targets of helium and xenon made between 60 and 200 KeV, and with previous measurements in the other stable rare-gas targets. Level crossing calculations with the Landau-Zener model indicate that this mechanism is unimportant in all the targets except helium and neon. An improved version of the Rapp-Francis non-crossing theory (J. Chem. Phys.; 37: 2631 (1962)) gives reasonable predictions for both heavy and light rare-gas targets and this is probably the dominant electron transfer process at these energies. (U.K.)

294

Large scale oil lease automation and electronic custody transfer  

International Nuclear Information System (INIS)

Typically, oil field production operations have only been automated at fields with long term production profiles and enhanced recovery. The automation generally consists of monitoring and control at the wellhead and centralized facilities. However, Union Pacific Resources Co. (UPRC) has successfully implemented a large scale automation program for rapid-decline primary recovery Austin Chalk wells where purchasers buy and transport oil from each individual wellsite. This project has resulted in two significant benefits. First, operators are using the system to re-engineer their work processes. Second, an inter-company team created a new electronic custody transfer method. This paper will describe: the progression of the company's automation objectives in the area; the field operator's interaction with the system, and the related benefits; the research and development of the new electronic custody transfer method

295

Photophysical and electron transfer studies of a stable carbocation  

Science.gov (United States)

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

Dileesh, S.; Gopidas, K. R.

2000-11-01

296

Molecular model for aqueous ferrous--ferric electron transfer  

Energy Technology Data Exchange (ETDEWEB)

We present a molecular model for studying the prototypical ferric--ferrous electron transfer process in liquid water, and we discuss its structural implications. Treatment of the nonequilibrium dynamics will be the subject of future work. The elementary constituents in the model are classical water molecules, classical ferric ions (i.e., Fe/sup 3 +/ particles), and a quantal electron. Pair potentials and pseudopotentials describing the interactions between these constituents are presented. These interactions lead to ligand structures of the ferric and ferrous ions that are in good agreement with those observed in nature. The validity of the tight binding model is examined. With umbrella sampling, we have computed the diabatic free energy of activation for electron transfer. The number obtained, roughly 20 kcal/mol, is in reasonable accord with the aqueous ferric--ferrous transfer activation energy of about 15 to 20 kcal/mol estimated from experiment. The Marcus relation for intersecting parabolic diabatic free energy surfaces is found to be quantitatively accurate in our model. Due to its significance to future dynamical studies, we have computed the tunnel splitting for our model in the absence of water molecules. Its value is about 1 k/sub B/ T at room temperature for ferrous--ferric separations around 5.5 A. This indicates that the dynamics of the electron transfer are complex involving both classical adiabatic dynamics and quantal nonadiabatic transitions. The dynamics may also be complicated due to glassy behavior of tightly bound ligand water molecules. We discuss this glassy behavior and also describe contributions to the solvation energetics from water molecules in different solvation shells. Finally, the energetics associated with truncating long ranged forces is discussed and analyzed.

Kuharski, R.A.; Bader, J.S.; Chandler, D.; Sprik, M.; Klein, M.L.; Impey, R.W.

1988-09-01

297

Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2011-01-01

298

Electrochemical studies on small electron transfer proteins using membrane electrodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Membrane electrodes (ME) were constructed using gold, glassy carbon and pyrolytic graphite supports and a dialysis membrane, and used to study the electrochemical behavior of small size electron transfer proteins: monohemic cytochrome c522 from Pseudomonas nautica and cytochrome c533 as well as rubredoxin from Desulfovibrio vulgaris . Different electrochemical techniques were used including cyclic voltammetry (CV), square wave voltammetry (SW) and differential pulse voltammetry (DP). A ...

Moura, Jose? J. G.; Santos, M. M. Correia Dos; Sousa, P. M. Paes; Gonc?alves, M. L. Simo?es; Krippahl, L.; Lojou, E?; Bianco, P.

2003-01-01

299

Marcus wins nobel prize in chemistry for electron transfer theory  

International Nuclear Information System (INIS)

This article describes the work of Rudolf Marcus of Caltech leading to his receipt of the 1992 Nobel Prize in Chemistry open-quotes for his contributions to the theory of electron transfer reactions in chemical systems.close quotes Applications of Marcus' theory include such diverse phenomena as photosynthesis, electrically conducting polymers, chemiluminescence, and corrosion. Historical aspects of his career are given. 10 refs., 1 fig

300

Low activation barriers characterize intramolecular electron transfer in ascorbate oxidase  

DEFF Research Database (Denmark)

Anaerobic reduction kinetics of the zucchini squash ascorbate oxidase (AO; L-ascorbate:oxygen oxidoreductase, EC 1.10.3.3) by pulse radiolytically produced CO2- radical ions were investigated. Changes in the absorption bands of type 1 [Cu(II)] (610 nm) and type 3 [Cu(II)] (330 nm) were monitored over a range of reactant concentrations, pH, and temperature. The direct bimolecular reduction of type 1 [Cu(II)] [(1.2 +/- 0.2) x 10(9) M-1.s-1] was followed by its subsequent reoxidation in three distinct phases, all found to be unimolecular processes with the respective specific rates of 201 +/- 8, 20 +/- 4, and 2.3 +/- 0.2 s-1 at pH 5.5 and 298 K. While at this pH no direct bimolecular reduction was resolved in the 330-nm band, at pH 7.0 such a direct process was observed [(6.5 +/- 1.2) x 10(8) M-1.s-1]. In the same slower time domains where type 1 [Cu(I)] reoxidation was monitored, reduction of type 3 [Cu(II)] was observed, which was also concentration independent and with identical rate constants and amplitudes commensurate with those of type 1 [Cu(II)] reoxidation. These results show that after electron uptake by type 1 [Cu(II)], its reoxidation takes place by intramolecular electron transfer to type 3 [Cu(II)]. The observed specific rates are similar to values reported for the limiting-rate constants of AO reduction by excess substrate, suggesting that internal electron transfer is the rate-determining step of AO activity. The temperature dependence of the intramolecular electron transfer rate constants was measured from 275 to 308 K at pH 5.5 and, from the Eyring plots, low activation enthalpies were calculated--namely, 9.1 +/- 1.1 and 6.8 +/- 1.0 kJ.mol-1 for the fastest and slowest phases, respectively. The activation entropies observed for these respective phases were -170 +/- 9 and -215 +/- 16 J.K-1.mol-1. The exceptionally low enthalpy barriers imply the involvement of highly optimized electron transfer pathways for internal electron transfer.

Farver, O; Pecht, I

1992-01-01

 
 
 
 
301

Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives  

DEFF Research Database (Denmark)

A novel method for the initiation of intramolecular electron transfer reactions in azurin is reported. The method is based on laser photoexcitation of covalently attached thiouredopyrenetrisulfonate (TUPS), the reaction that generates the low potential triplet state of the dye with high quantum efficiency. TUPS derivatives of azurin, singly labeled at specific lysine residues, were prepared and purified to homogeneity by ion exchange HPLC. Transient absorption spectroscopy was used to directly monitor the rates of the electron transfer reaction from the photoexcited triplet state of TUPS to Cu(II) and the back reaction from Cu(I) to the oxidized dye. For all singly labeled derivatives, the rate constants of copper ion reduction were one or two orders of magnitude larger than for its reoxidation, consistent with the larger thermodynamic driving force for the former process. Using 3-D coordinates of the crystal structure of Pseudomonas aeruginosa azurin and molecular structure calculation of the TUPS modified proteins, electron transfer pathways were calculated. Analysis of the results revealed a good correlation between separation distance from donor to Cu ligating atom (His-N or Cys-S) and the observed rate constants of Cu(II) reduction.

Borovok, N; Kotlyar, A B

1999-01-01

302

The electron transfer system of syntrophically grown Desulfovibrio vulgaris  

Energy Technology Data Exchange (ETDEWEB)

Interspecies hydrogen transfer between organisms producing and consuming hydrogen promotes the decomposition of organic matter in most anoxic environments. Although syntrophic couplings between hydrogen producers and consumers are a major feature of the carbon cycle, mechanisms for energy recovery at the extremely low free energies of reactions typical of these anaerobic communities have not been established. In this study, comparative transcriptional analysis of a model sulfate-reducing microbe, Desulfovibrio vulgaris Hildenborough, suggested the use of alternative electron transfer systems dependent upon growth modality. During syntrophic growth on lactate with a hydrogenotrophic methanogen, D. vulgaris up-regulated numerous genes involved in electron transfer and energy generation when compared with sulfate-limited monocultures. In particular, genes coding for the putative membrane-bound Coo hydrogenase, two periplasmic hydrogenases (Hyd and Hyn) and the well-characterized high-molecular weight cytochrome (Hmc) were among the most highly expressed and up-regulated. Additionally, a predicted operon coding for genes involved in lactate transport and oxidation exhibited up-regulation, further suggesting an alternative pathway for electrons derived from lactate oxidation during syntrophic growth. Mutations in a subset of genes coding for Coo, Hmc, Hyd and Hyn impaired or severely limited syntrophic growth but had little affect on growth via sulfate-respiration. These results demonstrate that syntrophic growth and sulfate-respiration use largely independent energy generation pathways and imply that understanding of microbial processes sustaining nutrient cycling must consider lifestyles not captured in pure culture.

Walker, C.B.; He, Z.; Yang, Z.K.; Ringbauer, Jr., J.A.; He, Q.; Zhou, J.; Voordouw, G.; Wall, J.D.; Arkin, A.P.; Hazen, T.C.; Stolyar, S.; Stahl, D.A.

2009-05-01

303

The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris  

Energy Technology Data Exchange (ETDEWEB)

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

304

Electron transfer reactions within zeolites: Radical cation from benzonorbornadiene  

Energy Technology Data Exchange (ETDEWEB)

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); Corbin, D.R. [The Du Pont Company, Wilmington, DE (United States)

1996-08-28

305

Nanoparticle facilitated extracellular electron transfer in microbial fuel cells.  

Science.gov (United States)

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

306

Effects of solution viscosity on heterogeneous electron transfer across a liquid/liquid interface  

International Nuclear Information System (INIS)

Scanning electrochemical microscopy (SECM) is employed to investigate the effect of solution viscosity on the rate constants of electron transfer (ET) reaction between potassium ferricyanide in water and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-dichloroethane. Either tetrabutylammonium (TBA+) or ClO4- is chosen as the common ion in both phases to control the interfacial potential drop. The rate constant of heterogeneous ET reaction between TCNQ and ferrocyanide produced in-situ, k12, is evaluated by SECM and is inversely proportional to the viscosity of the aqueous solution and directly proportional to the diffusion coefficient of K4Fe(CN)6 in water when the concentration of TCNQ in the DCE phase is in excess. The k12 dependence on viscosity is explained in terms of the longitudinal relaxation time of the solution. The rate constant of the heterogeneous ET reaction between TCNQ- and ferricyanide, k21, is also obtained by SECM and these results cannot be explained by the same manner

307

Effects of solution viscosity on heterogeneous electron transfer across a liquid/liquid interface  

Energy Technology Data Exchange (ETDEWEB)

Scanning electrochemical microscopy (SECM) is employed to investigate the effect of solution viscosity on the rate constants of electron transfer (ET) reaction between potassium ferricyanide in water and 7,7,8,8-tetracyanoquinodimethane (TCNQ) in 1,2-dichloroethane. Either tetrabutylammonium (TBA{sup +}) or ClO{sub 4}{sup -} is chosen as the common ion in both phases to control the interfacial potential drop. The rate constant of heterogeneous ET reaction between TCNQ and ferrocyanide produced in-situ, k{sub 12}, is evaluated by SECM and is inversely proportional to the viscosity of the aqueous solution and directly proportional to the diffusion coefficient of K{sub 4}Fe(CN){sub 6} in water when the concentration of TCNQ in the DCE phase is in excess. The k{sub 12} dependence on viscosity is explained in terms of the longitudinal relaxation time of the solution. The rate constant of the heterogeneous ET reaction between TCNQ{sup -} and ferricyanide, k{sub 21}, is also obtained by SECM and these results cannot be explained by the same manner.

Bai Yamin; Sun Peng; Zhang Meiqin; Gao Zhao; Yang Zhengyu; Shao Yuanhua

2003-10-15

308

Electron transfer and multi-electron accumulation in ExBox??.  

Science.gov (United States)

Molecules capable of accepting and storing multiple electrons are crucial components of artificial photosynthetic systems designed to drive catalysts, such as those used to reduce protons to hydrogen. ExBox(4+), a boxlike cyclophane comprising two ?-electron-poor extended viologen units tethered at both ends by two p-xylylene linkers, has been shown previously to accept an electron through space from a photoexcited guest. Herein is an investigation of an alternate, through-bond intramolecular electron-transfer pathway involving ExBox(4+) using a combination of transient absorption and femtosecond stimulated Raman spectroscopy (FSRS). Upon photoexcitation of ExBox(4+), an electron is transferred from one of the p-xylylene linkers to one of the extended viologen units in ca. 240?ps and recombines in ca. 4?ns. A crystal structure of the doubly reduced species ExBox(2+) was obtained. PMID:24828229

Dyar, Scott M; Barnes, Jonathan C; Jurí?ek, Michal; Stoddart, J Fraser; Co, Dick T; Young, Ryan M; Wasielewski, Michael R

2014-05-19

309

Long range electron transfer across $\\pi$-conjugated systems: role of electron correlations  

CERN Document Server

We consider a prototype polyene chain: donor-$\\pi$(bridge)-acceptor. The distance between the donor and the acceptor is varied by increasing the number of bridged atoms and rate of electron transfer, k$_{et}$ is studied for a series of different donors, D=NH$_2$, SH, OH, and a fixed acceptor, A=NO$_2$. We observe a large k$_{et}$ even at a very large D-A separation of $\\sim$ 45 $\\AA$, unexpected from the well-known and standard theories like the Forster theory. Such a long range electron transfer is due to the strong electron-electron interactions in the bridged orbitals that result in deconfinment of electrons in donor orbitals. Calculations at various levels: semi-empirical and many-body exact, have been performed to accurately account for such correlations.

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

2005-01-01

310

Electron transfer between ? and ? haem groups in haemoglobin  

International Nuclear Information System (INIS)

We have previously shown that when haemoglobin hybrids containing Fe III and (FeO2) units are exposed to 60Co ?-rays, ejected electrons add in a highly specific manner to both units, addition to the (FeO2) units being preferred. This suggested that intramolecular electron transfer from the unstable (FeO2)- centres to FeIII to give the stable FeII form is immeasurably slow in the 77-150 K range. [We cannot use higher temperatures because the (FeO2)- units change, probably as a result of protonation to give Fe-O2H units]. This result was unexpected in view of the relatively fast reactions occurring over similar distances in proteins, including haemoglobin hybrids. One possible error in our argument lies in the cooperative effect of oxygen binding which could negate the results, since the transfer considered is clearly impossible within (FeO2)3(FeO2-) molecules. Thus, even if the transfer within hybrid units were rapid, (FeO2)- centres would remain unchanged in (FeO2)3(FeO2-) molecules, and it could have been these (FeO2)- units that were studied, those formed in hybrids having undergone electron transfer so rapidly that they were lost prior to e.s.r. studies. Working at low concentrations of (FeO2), we have estrations of (FeO2), we have established that reaction to give (FeO2)- remains favourable and that the units remain stable. The results rule out the possibility of fast electron transfer. As a further check, we have studied the stability of (FeO2)- units in the mutant haemoglobin M Iwate. The form used has all its ? chains fixed as Fe111, whereas the ?-chains take up oxygen normally to give oxyhaem units. Again, electron capture on irradiation was favoured at the (FeO2) units, and, at low doses, these must be in molecules containing at least one Fe111 unit. (author)

311

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

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...Electronic Funds Transfer—Central Contractor Registration...Electronic Funds Transfer—Central Contractor Registration (OCT...information contained in the Central Contractor Registration (CCR) database. In the event that the...

2010-10-01

312

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

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2010-01-01

313

Effects of molecular orientation on electron-transfer collisions  

International Nuclear Information System (INIS)

K+ ions have been detected from the intersection of a beam of K atoms (5-30 eV) with beams of various simple molecules, such as CH3Br and CF3Br, which had been oriented prior to the collision. Production of ions in the collision is found to be highly dependent on orientation. The effect is most pronounced near threshold (?5 eV) and almost disappears at higher (30 eV) energies. Attack at the reactive halogen end produces the most ions, regardless of the polarity of that end. For each molecule, the reactive end seems to have the lower threshold energy. These observations may be a result of the electron being transferred to a specific end of the molecule, but the experiments measure only the net result of an electron transfer followed by the separation of the ions. Whether or not electron jump per se depends on orientation is still an open question, but the authors are able to qualitatively interpret the experimental results as being due to interactions between the ions as they separate in the exit channel. Most of the negative molecular ions dissociate, ejecting a halogen X- in the direction of the (oriented) molecular axis. If the X end is oriented away from the incoming K atom, the ejected X- will travel in the same direction as the K+, making the electron more likely to return to the K+ ion and reducing the K+ signal in this unfavorable orientationientation

314

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

Science.gov (United States)

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

315

Electron transfer. 88. Cobalt(III)-bound phosphite and hypophosphite  

International Nuclear Information System (INIS)

Phosphite and hypophosphite coordinate to cobalt(III) in (NH3)5Co/sup III/ through oxygen, rather than through phosphorus. The resulting complexes undergo electron-transfer reactions with Ru(NH3)62+ much more slowly than with Eu2+ or V2+, indicating that the latter two reactants preferentially utilize ligand bridging. Reductions with Cr2+ are shown to accompanied by transfer of the phosphorus-containing ligands, and reaction of the protonated phosphito (biphosphito) derivative (pK/sub A/ = 3.06 at 230C) proceeds through a combination of acid-independent and inverse-acid paths, both routes yielding the same phosphito-bound Cr(III) product. The hypophosphito, but not the biphosphito, complex reacts with Ce(IV), producing Co2+ in an induced electron-transfer process. The yield of Co2+ falls off progressively as [Ce/sup IV/] is increased, pointing to a sequence in which a Co(III)-bound P(II) radical is formed in initial attack by Ce(IV) but subsequently undergoes partition between competing reaction paths, i.e. internal electron transfer to Co(III) vs external oxidation by a second Ce(IV) center. The hypophosphito complex, but not the biphosphito complex, smoothly decomposes in basic media via an internal redox reaction, yielding Co(II) quantitatively, along with a 1:1 mixture of phosphite, and hypophosphite. This transformation, which fails with mixtures of (NH3)5Co(H2O)3+ and H2PO2- appears to be catalyzed specifically by OH-. Deuterium-labeling experiments disclose a solvent isotope effect. Reaction mechanisms are suggested for all the observed results. 54 references, 5 tables

316

Charge amplification and transfer processes in the gas electron multiplier  

CERN Document Server

We report the results of systematic investigations on the operating properties of detectors based on the gas electron multiplier (GEM). The dependence of gain and charge collection efficiency on the external fields has been studied in a range of values for the hole diameter and pitch. The collection efficiency of ionization electrons into the multiplier, after an initial increase, reaches a plateau extending to higher values of drift field the larger the GEM voltage and its optical transparency. The effective gain, fraction of electrons collected ba an electrode following the multiplier, increases almost linearly with the collection field, until entering a steeper parallel plate multiplication regime. The maximum effective gain attainable increases with the reduction in the hole diameter, stabilizing to a constant value at a diameter approximately corresponding to the foil thickness. Charge transfer properties appear to depend only on ratios of fields outside mad and the channels, with no interaction between ...

Bachmann, S; Ropelewski, Leszek; Sauli, Fabio; Sharma, A; Mörmann, D

1999-01-01

317

Effects of electrostatic interactions on electron transfer reactions  

International Nuclear Information System (INIS)

The fast reactions of electron transfer are studied by pulse radiolysis. This technique allows the creation in about 10-8 second radicals and radical ions with high redox potentials. For solvated electrons electrostatic interaction on the kinetics of reactions limited by diffusion is described by Debye's equation when ion mobility is known. Deviation from theory can occur in ion pairs formation. This is evidenced experimentally for anions by cation complexation with a cryptate. Relatively slow reactions are more sensitive to electrostatic interactions than limited by diffusion. If ion pairs are not formed kinetics constant depends on dielectric constant of solvent and reaction radius. Experimentally is studied the effect of electrostatic interaction on the rate constants of solvated electrons with anions and cations in water-ethanol mixtures where the dielectric constant change from 80 to 25 at room temperature. 17 refs

318

Noise-assisted quantum electron transfer in photosynthetic complexes  

CERN Document Server

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

319

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

International Nuclear Information System (INIS)

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

320

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

Science.gov (United States)

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

 
 
 
 
321

Angular momentum transfer and polarization degree of ions with two-valence electrons by electron impact  

Energy Technology Data Exchange (ETDEWEB)

We study for electron-impact excitation of ions with two valence electrons (Be{sup 2+}, C{sup 2+} and Si{sup 2+}) from the ground state to the first {sup 1}P{sup 0} state using the R-matrix method. The integral cross sections and polarization degree for this transition of each ion are obtained. The differential cross sections and angular momentum transfer are also shown at a few energies in the non-resonant region. The present angular momentum transfer for Be{sup 2+} and C{sup 2+} at small scattering angles has positive values, while it is negative for Si{sup 2+}.

Akita, Kenichi; Nakazaki, Shinobu; Igarashi, Akinori [Department of Applied Physics, Faculty of Engineering, University of Miyazaki, Miyazaki 889-2192 (Japan); Kai, Takeshi, E-mail: akita@phys.miyazaki-u.ac.j [Quantum Beam Science Directorate, Japan Atomic Energy Agency 8-1 Umemidai Kizugawa-city Kyoto 619-0215 (Japan)

2009-04-01

322

Direct probing of the structure and electron transfer of fullerene/ferrocene hybrid on Au(111) electrodes by in situ electrochemical STM.  

Science.gov (United States)

The electron donor-acceptor dyads are an emerging class of materials showing important applications in nonlinear optics, dye-sensitized solar cells, and molecular electronics. Investigation of their structure and electron transfer at the molecular level provides insights into the structure-property relationship and can benefit the design and preparation of electron donor-acceptor dyad materials. Herein, the interface adstructure and electron transfer of buckyferrocene Fe(C60Me5)Cp, a typical electron donor-acceptor dyad, is directly probed using in situ electrochemical scanning tunneling microscopy (STM) combined with theoretical simulations. It is found that the adsorption geometry and assembled structure of Fe(C60Me5)Cp is significantly affected by the electrochemical environments. In 0.1 M HClO4 solution, Fe(C60Me5)Cp forms well-ordered monolayers and multilayers on Au(111) surfaces with molecular dimer as the building block. In 0.1 M NaClO4 solution, typical six-fold symmetric close-packed monolayer with vertically adsorbed Fe(C60Me5)Cp is formed. Upon electrochemical oxidation, the oxidized Fe(C60Me5)Cp shows higher brightness in an STM image, which facilitates the direct visualization of the interfacial electrochemical electron transfer process. Theoretical simulation indicates that the electrode potential-activated, one-electron transfer from Fe(C60Me5)Cp to the electrode leads to the change of the delocalization character of the frontier orbital in the molecule, which is responsible for the STM image contrast change. This result is beneficial for understanding the structure and property of single electron donor-acceptor dyads. It also provides a direct approach to study the electron transfer of electron donor-acceptor compounds at the molecular level. PMID:24483295

Chen, Ting; Wang, Dong; Gan, Li-Hua; Matsuo, Yutaka; Gu, Jing-Ying; Yan, Hui-Juan; Nakamura, Eiichi; Wan, Li-Jun

2014-02-26

323

Concerted proton-electron transfers: electrochemical and related approaches.  

Science.gov (United States)

Proton-coupled electron transfers (PCETs) are omnipresent in natural and artificial chemical processes. Given the contemporary challenges associated with energy conversion, pollution abatement, and the development of high-performance sensors, a greater understanding of the mechanisms that underlie the practical efficiency of PCETs is a timely research topic. In contrast to hydrogen-atom transfers, proton and electron transfers involve different centers in PCET reactions. The reaction may go through an electron- or proton-transfer intermediate, giving rise to the electron-proton transfer (EPT) and the proton-electron transfer (PET) pathways. When the proton and electron transfers are concerted (the CPET pathway), the high-energy intermediates of the stepwise pathways are bypassed, although this thermodynamic benefit may have a kinetic cost. The primary task of kinetics-based mechanism analysis is therefore to distinguish the three pathways, quantifying the factors that govern the competition between them, which requires modeling of CPET reactivity. CPET models of varying sophistication have appeared, but the large number of parameters involved and the uncertainty of the quantum chemical calculations they may have to resort to make experimental confrontation and inspiration a necessary component of model testing and refinement. Electrochemical PCETs are worthy of particular attention, if only because most applications in which PCET mechanisms are operative involve collection or injection of electricity through electrodes. More fundamentally, changing the electrode potential is an easy and continuous means of varying the driving force of the reaction, whereas the current flowing through the electrode is a straightforward measure of its rate. Consequently, the current-potential response in nondestructive techniques (such as cyclic voltammetry) can be read as an activation-driving force relationship, provided the contribution of diffusion has been taken into account. Intrinsic properties (properties at zero driving force) are consequently a natural outcome of the electrochemical approach. In this Account, we begin by examining the modeling of CPET reactions and then describe illustrating experimental examples inspired by two biological systems, photosystem II and superoxide dismutase. One series of studies examined the oxidation of phenols with, as proton acceptor, either an attached nitrogen base or water (in water as solvent). Another addressed interconversion of aquo-hydroxo-oxo couples of transition metal complexes, using osmium complexes as prototypes. Finally, the reduction of superoxide ion, which is closely related to its dismutation, allowed the observation and rationalization of the remarkable properties of water as a proton donor. Water is also an exceptional proton acceptor in the oxidation of phenols, requiring very small reorganization energies, both in the electrochemical and homogeneous cases. These varied examples reveal general features of PCET reactions that may serve as guidelines for future studies, suggesting that research emphasis might be profitably directed toward new biological systems on the one hand and on the role of hydrogen bonding and hydrogen-bonded environments (such as water or proteins) on the other. PMID:20232879

Costentin, Cyrille; Robert, Marc; Savéant, Jean-Michel

2010-07-20

324

Photoinduced electron transfer in a dynamic supramolecular system with curved ?-structures.  

Science.gov (United States)

Photoinduced electron-transfer processes in a carbonaceous supramolecular combination of a tubular host and a C60 guest were investigated with time-resolved transient absorption spectra upon laser flash photolysis. Following the formation of triplet charge-separated species via electron transfer from the host to the guest, a rapid back electron transfer proceeded to afford triplet C60. PMID:24918189

Hitosugi, Shunpei; Ohkubo, Kei; Iizuka, Ryosuke; Kawashima, Yuki; Nakamura, Kosuke; Sato, Sota; Kono, Hirohiko; Fukuzumi, Shunichi; Isobe, Hiroyuki

2014-06-20

325

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

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... false Payment of tax by electronic fund transfer. 40.165a...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...165a Payment of tax by electronic fund transfer. (a) General...bank in making payment by electronic fund transfer...

2010-04-01

326

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

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2010-04-01

327

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

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... false Payment of tax by electronic fund transfer. 41.115a...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...115a Payment of tax by electronic fund transfer. (a) General...bank in making payment by electronic fund transfer...

2010-04-01

328

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

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2010-04-01

329

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

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2010-04-01

330

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

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2010-04-01

331

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

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2010-04-01

332

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

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2010-04-01

333

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

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2010-04-01

334

Electron-transfer reactions of tryptophan and tyrosine derivatives  

International Nuclear Information System (INIS)

Oxidation of tryptophan, tyrosine, and derivatives by oxidizing radicals was studied by pulse radiolysis in aqueous solutions at 20 0C. Rate constants for the oxidation of tryptophan derivatives with .N3 and Br2-. radicals vary from 8 x 108 to 4.8 and 109 M-1 s-1 and oxidation goes to completion; no pH dependence was observed. Oxidation rate constants for tyrosine derivatives increase upon deprotonation of the phenolic residue at higher pH. Redox potentials for the indolyl and phenoxyl radicals were derived from the measured equilibrium constants by using p-methoxyphenol (E/sub 7.5/ = 0.6 and E13 = 0.4 V), bisulfite (E3 = 0.84 V), and guanosine (E7 = 0.91 V) redox couples as reference systems. Redox potentials of tryptophan derivatives were found to be in dependent on the nature of the side chain and higher than the redox potentials of tryptophan derivatives. Electron transfer from tyrosine to tryptophyl radical was found to be slow in neutral media and is suggested to proceed via multiple steps, one of which is proton transfer from tyrosine to tryptophyl radical followed by electron transfer. 26 references, 2 figures, 4 tables

335

Reduced density matrix hybrid approach: Application to electronic energy transfer  

International Nuclear Information System (INIS)

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

336

Hetero-cycloreversions mediated by photoinduced electron transfer.  

Science.gov (United States)

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

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

2014-04-15

337

First principle study of the electronic structure of Sr2FeMoO6/SrTiO3 multilayers with and without interfacial Fe deficiency  

Science.gov (United States)

We investigate the electronic structure of Sr2FeMoO6/SrTiO3 (SFMO/STO) multilayers using the ab initio Full Potential Linearized Augmented Plane Wave method in order to study their properties within the GGA and GGA+U methods. We examin more especially the role of the interface on the magnetic and transport properties of these multilayers taking into account a possible Fe deficiency at the interface and we show that bulk behaviour is rapidly recovered due to the strong localization of the interfacial perturbation. For perfect interfaces, the whole structure is found half-metallic within the GGA+U method; the situation being ambiguous within the GGA method where SFMO is at the limit of being half-metallic depending on the structural deformation induced by the STO layer. This leads us to the conclusion that such a system could be used as injection electrode and tunnel barrier in magnetic tunnel junctions with a fully spin polarized injected current. For Fe deficient interfaces, we show that the interfacial densities of states are nearly unpolarized showing that this kind of imperfection has potentially a strong impact on the properties of the multilayers.

Stoeffler, D.

2008-03-01

338

Modeling biofilms with dual extracellular electron transfer mechanisms.  

Science.gov (United States)

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

339

Modeling biofilms with dual extracellular electron transfer mechanisms  

Energy Technology Data Exchange (ETDEWEB)

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

340

Microbial interspecies electron transfer via electric currents through conductive minerals.  

Science.gov (United States)

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

 
 
 
 
341

Reaction of radicals with benzoquinone. Addition or electron-transfer?  

International Nuclear Information System (INIS)

Complete text of publication follows. Although radical reactions involving quinones have been intensely studied in the past, there are some points deserving attention. Considering reactions of radicals of different structure, there are three possible pathways, depending on the redox potential of the radical: addition of the radical to benzoquinone, oxidation as well as the reduction of the benzoquinone by one-electrone transfer. In the case of addition and/or reduction in aqueous solution the real correlation of these processes is hard to distinguish because of the semiquinone radical - radical anion equilibrium. Therefore we report about pulse radiolysis studies on the reactions of different radical types (alkyl-, hydroxyalkyl-, alkoxyl-, peroxyl-, etc.) with benzoquinone in non-polar solvents, such as n-butylchloride, cyclohexane etc.. Radical addition resulted in substituted semiquinone radicals, whereas electron transfer reduction generated the semiquinone radical anions. Concerning radicals with outstanding oxidation properties (e.g. n-butylchloride radical cation), one-electron oxidation of benzoquinone leads to the benzoquinone radical-cation as a first observable intermediate, followed by the reaction of these species with a nucleophile. The final product of this reaction is also a substituted semiquinone - as well as in the case of direct radical addition, which makes the analysis of the reaction mechanism more complex. Although all mentioned quinone transients exhibited quite similar optical absorption behavior, we were able to identify them and to establish the reaction mechanisms

342

Single Electron Transfer Living Radical Polymerization via a New Initiator  

Science.gov (United States)

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

343

Scanning electron microscopy in nematode-induced giant transfer cells.  

Science.gov (United States)

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

344

Advances in Enhanced Boiling Heat Transfer From Electronic Components  

Science.gov (United States)

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

345

Suppression of electron transfer to dioxygen by charge transfer and electron transfer complexes in the FAD-dependent reductase component of toluene dioxygenase.  

Science.gov (United States)

The three-component toluene dioxygenase system consists of an FAD-containing reductase, a Rieske-type [2Fe-2S] ferredoxin, and a Rieske-type dioxygenase. The task of the FAD-containing reductase is to shuttle electrons from NADH to the ferredoxin, a reaction the enzyme has to catalyze in the presence of dioxygen. We investigated the kinetics of the reductase in the reductive and oxidative half-reaction and detected a stable charge transfer complex between the reduced reductase and NAD(+) at the end of the reductive half-reaction, which is substantially less reactive toward dioxygen than the reduced reductase in the absence of NAD(+). A plausible reason for the low reactivity toward dioxygen is revealed by the crystal structure of the complex between NAD(+) and reduced reductase, which shows that the nicotinamide ring and the protein matrix shield the reactive C4a position of the isoalloxazine ring and force the tricycle into an atypical planar conformation, both factors disfavoring the reaction of the reduced flavin with dioxygen. A rapid electron transfer from the charge transfer complex to electron acceptors further reduces the risk of unwanted side reactions, and the crystal structure of a complex between the reductase and its cognate ferredoxin shows a short distance between the electron-donating and -accepting cofactors. Attraction between the two proteins is likely mediated by opposite charges at one large patch of the complex interface. The stability, specificity, and reactivity of the observed charge transfer and electron transfer complexes are thought to prevent the reaction of reductase(TOL) with dioxygen and thus present a solution toward conflicting requirements. PMID:22992736

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

2012-11-01

346

Electron-phonon heat transfer in monolayer and bilayer graphene  

Science.gov (United States)

We calculate the heat transfer between electrons to acoustic and optical phonons in monolayer and bilayer graphene (MLG and BLG) within the quasiequilibrium approximation. For acoustic phonons, we show how the temperature-power laws of the electron-phonon heat current for BLG differ from those previously derived for MLG and note that the high-temperature (neutral-regime) power laws for MLG and BLG are also different, with a weaker dependence on the electronic temperature in the latter. In the general case we evaluate the heat current numerically. We suggest that a measurement of the heat current could be used for an experimental determination of the electron-acoustic-phonon coupling constants, which are not accurately known. However, in a typical experiment heat dissipation by electrons at very low temperatures is dominated by diffusion and we estimate the crossover temperature at which acoustic-phonon coupling takes over in a sample with Joule heating. At even higher temperatures optical phonons begin to dominate. We study some examples of potentially relevant types of optical modes, including, in particular, the intrinsic in-plane modes and additionally the remote surface phonons of a possible dielectric substrate.

Viljas, J. K.; Heikkilä, T. T.

2010-06-01

347

Transcriptomic and genetic analysis of direct interspecies electron transfer  

DEFF Research Database (Denmark)

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

Shrestha, Pravin Malla; Rotaru, Amelia-Elena

2013-01-01

348

Transcriptomic and genetic analysis of direct interspecies electron transfer.  

Science.gov (United States)

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

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

2013-04-01

349

Local operator partitioning of electronic energy for electronic energy transfer: An efficient algorithm  

CERN Document Server

An efficient computational algorithm to implement a local operator approach to partitioning electronic energy in general molecular systems is presented. This approach, which rigorously defines the electronic energy on any subsystem within a molecule, gives a precise meaning to the subsystem ground and excited electronic energies, which is crucial for investigating electronic energy transfer from first principles. We apply the technique to the $9-$(($1-$naphthyl)$-$methyl)-anthracene (A1N) molecule by partitioning A1N into anthracenyl and CH$_2-$naphthyl groups as subsystems, and examine their electronic energies and populations for several excited states using Configuration Interaction Singles method. The implemented approach shows a wide variety of different behaviors amongst these excited electronic states.

Nagesh, Jayashree; Brumer, Paul

2013-01-01

350

Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber  

Directory of Open Access Journals (Sweden)

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

Tanya M. Monro

2011-10-01

351

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

Science.gov (United States)

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

352

Parton models of high momentum transfer electron-nuclear scattering  

International Nuclear Information System (INIS)

High-energy electron-nuclear scattering processes are discussed from the point of view of a parton model description. The light-cone formalism is introduced in a schematic presentation emphasizing: (i) the connection to relativistic dynamics, (ii) the phenomenological construction of the far off-shell components of wave functions, and (iii) asymptotic scaling laws. A survey is made of some of the recent calculations based on a nucleon constituent parton model and their comparison with data for momentum transfers Q22. A prospective discussion is also made on multiquark nuclear components and the quark parton model in QCD

353

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

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

354

Preliminary estimate of heavy ion electron-transfer cross sections  

International Nuclear Information System (INIS)

Preliminary estimates of cross sections for the electron transfer process Ba+ + Ba+ ? Ba + Ba++ are reported for the energy range 100 to 300 keV. The relative motion of the heavy ions' nuclei can be treated as a classical motion along straight line trajectories. The molecular states of Ba2++ are first obtained as functions of internuclear separation, treating the nuclei as stationary point charges. Then, the time-dependent Schroedinger equation is solved for the moving nuclei, using these molecular states as a basis

355

Large momentum transfer electron scattering from few-nucleon systems  

International Nuclear Information System (INIS)

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

356

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

International Nuclear Information System (INIS)

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

357

Ag-mediated charge transfer from electron-doped SrTiO 3 to CO and NO: A first-principles study  

Science.gov (United States)

Ag-mediated charge transfer from electron-doped SrTiO 3 to molecules CO and NO has been studied through the first-principles calculations based on density functional theory (DFT). Evaluation of Fukui functions indicates that Ag atom on SrTiO 3 (001) surface is presented as an active reduction and oxidation site. It shows that Ag prefers to mediate the charge transfer from electronically excited SrTiO 3 to target species. It illustrates that electron initially transfers from electron-doped SrTiO 3 to Ag, i.e., Ag is negatively charged. Interfacial charge transfer induces dipole moment and changes the surface work function. SrO-termination of SrTiO 3 (001) surface has weak activity to CO and NO while CO and NO can be strongly adsorbed on the negatively charged Ag atom. Negatively charged Ag donates its charge to the molecules. Charge occupies the molecule ? 2p* orbital, which is responsible for the activation of the molecular bonds. Evidence that deposited metals on photocatalyst surface can efficiently separate the photogenerated electron-hole pairs has been addressed in this study.

Wei, Wei; Dai, Ying; Guo, Meng; Niu, Chengwang; Huang, Baibiao

2011-07-01

358

Gated electron transfer of yeast iso-1 cytochrome c on self-assembled monolayer-coated electrodes.  

Science.gov (United States)

Iso-1 yeast cytochrome c (YCC) was adsorbed on Ag electrodes coated with self-assembled monolayers (SAMs) consisting either of 11-mercaptoundecanoic acid (MUA) or of 1:1 mixtures of MUA and either 11-mercaptoundecanol (MU) or 7-mercaptoheptanol (MH). The redox potentials and the apparent rate constants for the interfacial redox process as well as for the protein reorientation were determined by stationary surface-enhanced resonance Raman (SERR) and time-resolved SERR spectroscopy, respectively. For YCC immobilized on MUA and MUA/MU at pH 7.0 and 6.0, the negative shifts of the redox potentials with respect to that for the protein in solution can be rationalized in terms of the potential of the zero-charge determined by impedance measurements. The apparent electron transfer rate constants of YCC on MUA/MU and MU/MH at pH 6.0 were determined to be 8 and 18 s(-1), respectively. A decrease of the relaxations constants by a factor of ca. 2 was found for pH 7.0, and a comparable low value was determined for a pure MUA even at pH 6.0. In each system, the rate constant for protein reorientation was found to be the same as that for the electron transfer, implying that protein reorientation is the rate limiting step for the interfacial redox process. This gating step is distinctly slower than that for horse heart cytochrome c (HHCC) observed previously under similar conditions (Murgida, D. H.; Hildebrandt, P. J. Am. Chem. Soc. 2001, 123, 4062-4068). The different rate constants of protein reorientation for both proteins and the variations of the rate constants for the different SAMs and pH are attributed to the electric field dependence of the free energy of activation which is assumed to be proportional to the product of the electric field strength and the molecular dipole moment of the protein. The latter quantity is determined by molecular dynamics simulations and electrostatic calculations to be more than 2 times larger for YCC than for HHCC. Moreover, the dipole moment vector and the heme plane constitute an angle of ca. 10 and 45 degrees in YCC and HHCC, respectively. The different magnitudes and directions of the dipole moments as well as the different electric field strengths at the various SAM/protein interfaces allow for a qualitative description of the protein-, SAM-, and electrode-specific kinetics of the interfacial redox processes studied in this and previous works. PMID:18975895

Feng, Jiu-Ju; Murgida, Daniel H; Kuhlmann, Uwe; Utesch, Tillmann; Mroginski, Maria Andrea; Hildebrandt, Peter; Weidinger, Inez M

2008-11-27

359

Hydride transfer from NADH analogues to a nonheme manganese(iv)-oxo complex via rate-determining electron transfer.  

Science.gov (United States)

Hydride transfer from NADH analogues to a nonheme Mn(iv)-oxo complex, [(Bn-TPEN)Mn(IV)(O)](2+), proceeds via a rate-determining electron transfer step with no deuterium kinetic isotope effect (KIE = 1.0 ± 0.1); a charge-transfer complex formed between the Mn(IV)(O) complex and NADH analogues is involved in the hydride transfer reaction. PMID:25220234

Yoon, Heejung; Lee, Yong-Min; Nam, Wonwoo; Fukuzumi, Shunichi

2014-09-30

360

Controlled single electron transfer between Si:P quantum dots  

CERN Document Server

The Kane Si:P quantum computer scheme requires the positioning of single phosphorus atoms in silicon, registered to surface control gates with high precision, together with an ability to readout a single spin or charge. Here we present an experimental demonstration of gate-controlled transfer of single electrons between two buried Si:P quantum dots, each containing ~600 phosphorus atoms, with non-invasive detection using rf single electron transistors (SETs). These results open the way to a new class of precision-doped quantum dots in silicon. Combined with a novel single ion implantation process that enables dots to be configured with just one P atom, a path is provided towards physical realization of Si:P qubits.

Bühler, T M; Ferguson, A J; Dzurak, A S; Hudson, F E; Reilly, D J; Hamilton, A R; Clark, R G; Jamieson, D N; Yang, C; Pakes, C I; Prawer, S

2005-01-01

 
 
 
 
361

Biochemical Mechanisms Controlling Terminal Electron Transfer in Geobacter sulfurreducens  

Science.gov (United States)

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

362

Charge amplification and transfer processes in the gas electron multiplier  

International Nuclear Information System (INIS)

We report the results of systematic investigations on the operating properties of detectors based on the gas electron multiplier (GEM). The dependence of gain and charge collection efficiency on the external fields has been studied in a range of values for the hole diameter and pitch. The collection efficiency of ionization electrons into the multiplier, after an initial increase, reaches a plateau extending to higher values of drift field the larger the GEM voltage and its optical transparency. The effective gain, fraction of electrons collected by an electrode following the multiplier, increases almost linearly with the collection field, until entering a steeper parallel plate multiplication regime. The maximum effective gain attainable increases with the reduction in the hole diameter, stabilizing to a constant value at a diameter approximately corresponding to the foil thickness. Charge transfer properties appear to depend only on ratios of fields outside and within the channels, with no interaction between the external fields. With proper design, GEM detectors can be optimized to satisfy a wide range of experimental requirements: tracking of minimum ionizing particles, good electron collection with small distortions in high magnetic fields, improved multi-track resolution and strong ion feedback suppression in large volume and time-projection chambers

363

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

Science.gov (United States)

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

364

Electron transfer across ?-helical peptide monolayers: importance of interchain coupling.  

Science.gov (United States)

Four helical peptides with the general formula (Boc)-Cys-(S-Acm)-(Ala-Leu)(n)-NH-(CH(2))(2)-SH (n = 4-7) were synthesized and further used for the preparation of self-assembled monolayers (SAMs) on gold substrates. The electron-transfer behavior of these systems was probed using current-sensing atomic force microscopy (CS-AFM). It was found that the electron transmission through SAMs of helical peptides trapped between an AFM conductive tip and a gold substrate occurs very efficiently and that the distance dependence obeys the exponential trend with a decay constant of 4.6 nm(-1). This result indicates that the tunneling mechanism is operative in this case. Conductance measurements under mechanical stress show that peptide-mediated electron transmission occurs with the possible contribution of intermolecular electron tunneling between adjacent helices. It was also demonstrated that an external electric field applied between metallic contacts can affect the structure of the peptide SAM by changing its thickness. This explains the asymmetry of the current-voltage response of metal-monolayer-metal junction. PMID:23181704

Pawlowski, Jan; Juhaniewicz, Joanna; Tymecka, Dagmara; Sek, Slawomir

2012-12-18

365

Determination of the electronics transfer function for current transient measurements  

CERN Document Server

We describe a straight-forward method for determining the transfer function of the readout of a sensor for the situation in which the current transient of the sensor can be precisely simulated. The method relies on the convolution theorem of Fourier transforms. The specific example is a planar silicon pad diode connected with a 50 $\\Omega $ cable to an amplifier followed by a 5 GS/s sampling oscilloscope. The charge carriers in the sensor were produced by picosecond lasers with light of wavelengths of 675 and 1060 nm. The transfer function is determined from the 1060 nm data with the pad diode biased at 1000 V. It is shown that the simulated sensor response convoluted with this transfer function provides an excellent description of the measured transients for the laser light of both wavelengths, at voltages 50 V above the depletion voltage of about 90 V up to the maximum applied voltage of 1000 V. The method has been developed for the precise measurement of the dependence of the drift velocity of electrons an...

Scharf, Christian

2014-01-01

366

Electron-transfer functionality of synthetic coiled-coil metalloproteins  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in portuguese O campo emergente da engenharia molecular de metaloproteínas visa preparar proteínas artificiais, cujas propriedades podem imitar e talvez até mesmo melhorar várias características encontradas nas metaloenzimas naturais. Este artigo de revisão resume nossos esforços recentes na preparação de metalop [...] roteínas sintéticas, construídas a partir de "coiled-coils" alfa-hélices, e na incorporação de grupos de transferência de elétrons nesses sistemas. Recentemente, concebemos uma cisteína contendo um peptídeo com hélice randômica, o qual forma uma estrutura "coiled-coil" alfa-helicoidal ao se ligar a vários metais. O aduto de CuI pode atuar como agente fotoindutor de transferência de elétrons para receptores exógenos, e transfere elétrons por colisão na região invertida de Marcus para várias aminas de rutênio, as quais atuam como receptores. Especula-se que este resultado inesperado advenha do posicionamento do cofator de CuI no interior da porção hidrofóbica da proteína, o qual proíbe a aproximação entre o doador e o receptor, diminuindo a velocidade de transferência eletrônica daquelas reações termodinamicamente muito favorecidas, para velocidades inferiores à do limite difusional. Abstract in english The emerging field of metalloprotein design seeks to prepare artificial proteins whose properties can mimic, enhance, and perhaps improve upon many features found in natural metalloenzymes. This review summarizes our recent efforts to prepare synthetic metalloproteins built from alpha-helical coiled [...] -coils and to incorporate electron-transfer functionality within these systems. We have recently designed a cysteine-containing random-coil peptide which forms a alpha-helical coiled-coil upon binding various metals. The CuI adduct can serve as photoinduced electron-transfer agent to exogenous acceptors and undergoes collisional electron-transfer in the inverted Marcus region to various ruthenium ammine acceptors. It is speculated that this unexpected result might be due to the positioning of the CuI cofactor within the hydrophobic core of the protein which prohibits close approach between the donor and acceptor to slow the high driving force reaction rates below the diffusion limit.

Michael Y., Ogawa; Jiufeng, Fan; Anna, Fedorova; Jing, Hong; Olesya A., Kharenko; Anna Y., Kornilova; Robin C., Lasey; Fei, Xie.

1516-15-01

367

Photoinduced electron transfer modeling to simulate flavoprotein fluorescence decay.  

Science.gov (United States)

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

368

ELECTRONIC FUNDS TRANSFER: EXPLORING THE DIFFICULTIES OF SECURITY  

Directory of Open Access Journals (Sweden)

Full Text Available Generally the banking laws, regulations and supervision were designed primarily to address the fundamental principle relating to safe and sound business practices by financial institutions. In order to maintain safe and sound business practice it is of outmost importance that customers are protected against losses resulting from inadequate remedies available to them. Banking by its very nature is a high risk business. However, the major risks associated with banking are legal risks, credit interest rates and liquidity. Internet banking has increased some of these risks by creating new ones. Electronic funds transfers are based on technology which by its nature is designed to extend the geographical reach of banks and customers. This kind of a market expansion extend beyond borders, therefore there will be problems which banks will try to avoid like regulation and supervision. Other regulatory and legal risks include, the uncertainty about legal requirements in some countries and jurisdiction ambiguities regarding the responsibilities of different national authorities. Customers and banks may be exposed to legal risks associated with non-compliance with different national laws and regulations including consumer protection laws, record keeping and report requirements. Due to insecurity created by electronic funds transfer, it of importance to analyse measures under South African Law and whether these measures can effectively prevent insecurity and what lessons can be learned from abroad.

MPAKWANA ANNASTACIA MTHEMBU

2010-10-01

369

7 CFR 274.12 - Electronic Benefit Transfer issuance system approval standards.  

Science.gov (United States)

...detailed schedules, and resources needed to implement the pilot...benefits. (i) Verifying electronic transactions flowing to or...operator using the Retailer Electronic Benefit Transfer (EBT...must be able to use their electronic benefits upon...

2010-01-01

370

Intermonomer electron transfer in the bc1 complex dimer is controlled by the energized state and by impaired electron transfer between low and high potential hemes.  

Science.gov (United States)

The cytochrome bc(1) complex (commonly called Complex III) is the central enzyme of respiratory and photosynthetic electron transfer chains. X-ray structures have revealed the bc(1) complex to be a dimer, and show that the distance between low potential (b(L)) and high potential (b(H)) hemes, is similar to the distance between low potential hemes in different monomers. This suggests that electron transfer between monomers should occur at the level of the b(L) hemes. Here, we show that although the rate constant for b(L)-->b(L) electron transfer is substantial, it is slow compared to the forward rate from b(L) to b(H), and the intermonomer transfer only occurs after equilibration within the first monomer. The effective rate of intermonomer transfer is about 2-orders of magnitude slower than the direct intermonomer electron transfer. PMID:17399709

Shinkarev, Vladimir P; Wraight, Colin A

2007-04-17

371

ATP-induced electron transfer by redox-selective partner recognition  

Science.gov (United States)

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

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

2014-08-01

372

Transfer printing methods for the fabrication of flexible organic electronics  

Science.gov (United States)

A transfer printing method for fabricating organic electronics onto flexible substrates has been developed. The method relies primarily on differential adhesion for the transfer of a printable layer from a transfer substrate to a device substrate. The works of adhesion and cohesion for successful printing are discussed and developed for a model organic thin-film transistor device consisting of a polyethylene terephthalate (PET) substrate, gold (Au) gate and source/drain electrodes, a polymethylmethacrylate (PMMA) [or poly(4-vinylphenol)] dielectric layer, and a pentacene (Pn) organic semiconductor layer. The device components are sequentially printed onto the PET device substrate with no mixed processing steps performed on the device substrate. Optimum printing conditions for the Pn layer were determined to be 600psi and 120°C for 3min. A set of devices with a PMMA dielectric layer was measured as a function of channel length and exhibited a contact resistance corrected mobility of 0.237cm2/Vs. This is larger than the mobility measured for a control device consisting of Pn thermally deposited onto the thermally oxidized surface of a silicon substrate (SiO2/Si) with e-beam deposited Au top source/drain contacts. The structure of transfer printed Pn films was also investigated using x-ray diffraction. The basal spacing correlation length for a 50nm Pn film printed at 600psi and 120°C for 3min onto a PMMA surface showed a 35% increase as compared to an unprinted film on a thermally oxidized silicon substrate. The crystalline size was seen to correlate with the mobility as a function of printing conditions.

Hines, D. R.; Ballarotto, V. W.; Williams, E. D.; Shao, Y.; Solin, S. A.

2007-01-01

373

Electrochemical Measurement of Electron Transfer Kinetics by Shewanella oneidensis MR-1*  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Shewanella oneidensis strain MR-1 can respire using carbon electrodes and metal oxyhydroxides as electron acceptors, requiring mechanisms for transferring electrons from the cell interior to surfaces located beyond the cell. Although purified outer membrane cytochromes will reduce both electrodes and metals, S. oneidensis also secretes flavins, which accelerate electron transfer to metals and electrodes. We developed techniques for detecting direct electron transfer by intact cells, using tur...

Baron, Daniel; Labelle, Edward; Coursolle, Dan; Gralnick, Jeffrey A.; Bond, Daniel R.

2009-01-01

374

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

Science.gov (United States)

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

375

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

Science.gov (United States)

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

376

Collisional electron transfer to photoexcited acceptor radical anions  

DEFF Research Database (Denmark)

In this article, we show that photoexcitation of radical anions facilitates electron