WorldWideScience
 
 
1

Remote interfacial electron transfer from supramolecular sensitizers  

Energy Technology Data Exchange (ETDEWEB)

There has been intense research in light-to-electrical energy conversion with ruthenium(II) polypyridyl charge transfer sensitizers anchored to wide bandgap semiconductors such as TiO{sub 2}. In an effort to achieve improved molecular control of sensitizer orientation the authors turned to bimetallic coordination compounds based on rhenium and ruthenium where the facial geometry of the Re center holds a Ru sensitizer proximate to the TiO{sub 2} surface. In this communication, the authors report the photophysical and photoelectrochemical properties of two Re-Ru linkage isomers in solution and the same isomers anchored to nanostructured TiO{sub 2} films. The results demonstrate rapid efficient interfacial electron transfer and a remarkably high light-to-electrical energy conversion even though the sensitizer is remote to the semiconductor-bound ligand.

Argazzi, R.; Bignozzi, C.A. [Dipartimento di Chimica dell`Universita, Ferrara (Italy); Heimer, T.A.; Meyer, G.J. [Johns Hopkins Univ., Baltimore, MD (United States)

1997-01-01

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

2003-12-30

3

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

4

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

5

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

6

Interfacial electrochemical electron transfer in biology â?? 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

7

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

Science.gov (United States)

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

Peter, Laurence

2009-11-17

8

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

9

Surface-junction effects on interfacial electron transfer between bis(terpyridine)iron(II) and hydrogen-terminated silicon(111) electrode.  

Science.gov (United States)

Interfacial electron transfer at bis(tpy)–iron(II) complexes (tpy=2,2’:6’,2’’-terpyridine) on Si(111) electrodes was investigated by using four types of surfaceanchor terpyridine ligands. Despite the greater distance, electron transfer between the bis(tpy)–iron(II) unit and the electrode is accelerated in surface-anchor ligands with an additional phenylene group. PMID:24677418

Maeda, Hiroaki; Sakamoto, Ryota; Nishihara, Hiroshi

2014-03-01

10

Rate of Interfacial Electron Transfer through the 1,2,3-Triazole Linkage  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The rate of electron transfer is measured to two ferrocene and one iron tetraphenylporphyrin redox species coupled through terminal acetylenes to azide-terminated thiol monolayers by the Cu(I)-catalyzed azide–alkyne cycloaddition (a Sharpless “click” reaction) to form the 1,2,3-triazole linkage. The high yield, chemoselectivity, convenience, and broad applicability of this triazole formation reaction make such a modular assembly strategy very attractive. Electron-transfer rate constants...

Devaraj, Neal K.; Decreau, Richard A.; Ebina, Wataru; Collman, James P.; Chidsey, Christopher E. D.

2006-01-01

11

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

12

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

13

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

14

Alkaline-resistant titanium dioxide thin film displaying visible-light-induced superhydrophilicity initiated by interfacial electron transfer.  

Science.gov (United States)

We synthesized a three-layer-type photocatalytic structure (TiO2/Cu(II)SiO2/SiO2), consisting of TiO2 on Cu(II)-grafted SiO2, which was deposited on a SiO2-coated glass substrate, and investigated its visible-light absorption and hydrophilic properties. Water contact angle measurements revealed visible-light-induced superhydrophilicity at the film surface that was initiated by interfacial electron transfer (IFET) at the interface of TiO2 and Cu(II)SiO2. Monitoring the oxidation state of Pb(2+) ions confirmed that the IFET-initiated holes diffused to the TiO2 surface, where they likely contributed to the hydrophilic conversion. We also demonstrated that layer-structured TiO2/Cu(II)SiO2/SiO2 was stable under alkaline conditions. Thus, we successfully synthesized alkaline-resistant TiO2 that displays visible-light-induced superhydrophilicity. PMID:23527699

Taguchi, Tsuyoshi; Ni, Lei; Irie, Hiroshi

2013-04-16

15

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

16

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

17

Interfacial Hydration, Dynamics and Electron Transfer: Multi-Scale ET Modeling of the Transient [Myoglobin, Cytochrome b5] Complex  

Science.gov (United States)

Formation of a transient [myoglobin (Mb), cytochrome b5 (cyt b5)] complex is required for the reductive repair of inactive ferri-Mb to its functional ferro-Mb state. The [Mb, cyt b5] complex exhibits dynamic docking (DD), with its cyt b5 partner in rapid exchange at multiple sites on the Mb surface. A triple mutant (Mb(3M)) was designed as part of efforts to shift the electron-transfer process to the simple docking (SD) regime, in which reactive binding occurs at a restricted, reactive region on the Mb surface that dominates the docked ensemble.1 An electrostatically-guided Brownian dynamics (BD) docking protocol was used to generate an initial ensemble of reactive configurations of the complex between unrelaxed partners. This ensemble samples a broad and diverse array of heme-heme distances and orientations. These configurations seeded all-atom constrained molecular dynamics simulations (MD) to generate relaxed complexes for the calculation of electron tunneling matrix elements (TDA) through tunneling-pathway analysis. This procedure for generating an ensemble of relaxed complexes combines the ability of BD calculations to sample the large variety of available conformations and interprotein distances, with the ability of MD to generate the atomic level information, especially regarding the structure of water molecules at the protein-protein interface, that defines electron-tunneling pathways. We used the calculated TDA values to compute ET rates for the [Mb(wt), cyt b5] complex and for the complex with a mutant that has a binding free energy strengthened by three D/E ? K charge-reversal mutations, [Mb(3M), cyt b5]. The calculated rate constants are in agreement with the measured values, and the mutant complex ensemble has many more geometries with higher TDA values than does the wild-type Mb complex. Interestingly, water plays a double role in this electron-transfer system, lowering the tunneling barrier as well as inducing protein interface remodeling that screens the repulsion between the negatively-charged proprionates of the two hemes.

Keinan, Shahar; Nocek, Judith M.; Beratan, David N.; Hoffman, Brian M.

2012-01-01

18

Interfacial transfer in annular dispersed flow  

International Nuclear Information System (INIS)

The interfacial drag, droplet entrainment, droplet deposition and droplet-size distributions are important for detailed mechanistic modeling of annular dispersed two-phase flow. In view of this, recently developed correlations for these parameters are presented and discussed in this paper. The onset of droplet entrainment significantly alters the mechanisms of mass, momentum, and energy transfer between the film and gas core flow as well as the transfer between the two-phase mixture and the wall. By assuming the roll wave entrainment mechanism, the correlations for the amount of entrained droplet as well as for the droplet-size distribution have been obtained from a simple model in collaboration with a large number of data. Then the rate equations for entrainment and deposition have been developed. The drag correlations relevant to the droplet transfer is also presented. The comparison of the correlations to various data show satisfactory agreement

1982-09-03

19

Interfacial Electron Transfer Dynamics in a Solar Cell Organic Dye Anchored to Semiconductor Particle and Aluminum-Doped Mesoporous Materials  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We report on femto- to nanosecond emission studies of the interaction of an organic dye (TPC1) for solar cells, of (electron-donor)-(pi-spacer)-(electron-acceptor) structure, with different semiconductor particles and aluminum-doped MCM-41 silicate mesoporous material, in a dichloromethane (DCM) suspension. We used ZnO, ZrO2, and Al2O3 nanoparticles employed in dye-sensitized solar cells as active electron collection materials or insulating layers. Steady-state absorption and emission spectra...

Martin, Cristina; Ziolek, Marcin; Marchena, Maria; Douhal, Abderrazzak

2011-01-01

20

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

 
 
 
 
21

Influence of surface adsorption on the interfacial electron transfer of flavin adenine dinucleotide and glucose oxidase at carbon nanotube and nitrogen-doped carbon nanotube electrodes.  

Science.gov (United States)

The adsorption of flavin adenine dinucleotide (FAD) and glucose oxidase (GOx) onto carbon nanotube (CNT) and nitrogen-doped CNT (N-CNT) electrodes was investigated and found to obey Langmuir adsorption isotherm characteristics. The amount adsorbed and adsorption maximum are dependent on exposure time, the concentration of adsorbate, and the ionic strength of the solution. The formal potentials measured for FAD and GOx are identical, indicating that the observed electroactivity is from FAD, the redox reaction center of GOx. When glucose is added to GOx adsorbed onto CNT/N-CNT electrodes, direct electron transfer (DET) from enzyme-active FAD is not observed. However, efficient mediated electron transfer (MET) occurs if an appropriate electron mediator is placed in solution, or the natural electron mediator oxygen is used, indicating that GOx is adsorbed and active on CNT/N-CNT electrodes. The observed surface-confined redox reaction at both CNT and N-CNT electrodes is from FAD that either specifically adsorbs from solution or adsorbs from the holoprotein subsequently inactivating the enzyme. The splitting of cathodic and anodic peak potentials as a function of scan rate provides a way to measure the heterogeneous electron-transfer rate constant (k(s)) using Laviron's method. However, the measured k(s) was found to be under ohmic control, not under the kinetic control of an electron-transfer reaction, suggesting that k(s) for FAD on CNTs is faster than the measured value of 7.6 s(-1). PMID:23289639

Goran, Jacob M; Mantilla, Sandra M; Stevenson, Keith J

2013-02-01

22

Electron donor-acceptor distance dependence of the dynamics of light-induced interfacial charge transfer in the dye-sensitization of nanocrystalline oxide semiconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The effect of electronic and nuclear factors on the dynamics of dye-to-semiconductor electron transfer was studied employing RuII(terpy)(NCS)3 sensitizers grafted onto transparent films made of titanium dioxide nanoparticles. Various approaches were strived to understand the dependence of the kinetics of charge injection and recombination processes upon the distance separating the dye molecules and the redox active surface. A series of bridged sensitizers containing p- phenylene spacers of va...

Wenger, Bernard; Bauer, Christophe; Nazeeruddin, Mohammad K.; Comte, Pascal; Zakeeruddin, Shaik M.; Gratzel, Michael; Moser, Jacques-e

2006-01-01

23

Interfacial electron-transfer equilibria and flat-band potentials of ?-Fe2O3 and TiO2 colloids studied by pulse radiolysis  

International Nuclear Information System (INIS)

The kinetics and equilibria of electron transfer between methylviologen cation radicals and ?-Fe2O3 or TiO2 colloidal particles were studied with the pulse-radiolysis technique. The rates of electron transfer to both colloids are lower than those predicted for a diffusion-controlled reaction. For higher pHs (TiO2, pH > 2; ?-Fe2O3, pH > 9) the established equilibrium MV+ in equilibrium MV2+ + (e-)/sub coll/ is strongly influenced by the MV2+ concentration and pH. The MV+ equilibrium concentration can be exploited to derive the flat-band potential of the semiconductor colloids. The method for determining the flat-band potential of the particles is independent of whether the injected electrons are free or trapped, and whether the electrons raise the bulk Fermi level toward the conduction band or just produce a space charge. The flat-band potentials for both colloids appear to be somewhat more negative (-0.1 to -0.2 V) than the corresponding single-crystal electrodes. Also, the flat-band potentials become slightly more negative with increasing radiation dose (initial MV+ concentration). The effect of absorbed radiation dose is explained by the corresponding changes in the ratio of oxidized to reduced forms of the redox couple, which in turn changes the adsorbed ionic charge on the semiconductor surface. For colloidal particles of TiO2 stabilized by poly(vinyl alcohol) (PVA), the flat-band potentials were almost the same as those for PVA-free TiO2 sols. The decrease of particle diameter from 800 to 70 A does not affect the value of the flat-band potentials for TiO2 and ?-Fe2O3 colloids. 28 references, 9 figures

1984-09-13

24

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 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)

2012-06-24

25

Interfacial compatibility of polymer-based structures in electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Interfacial compatibility of dissimilar materials was investigated to achieve a better understanding of interfacial adhesion in metal/polymer/metal systems. Surface modifications of polymers were applied to improve the adhesion. The modified surfaces were characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements accompanied by surface free energy evaluations. The pull-off test was employed to asses...

Turunen, Markus P. K.

2004-01-01

26

Interfacial transfer in annular dispersed flow. [PWR; BWR  

Energy Technology Data Exchange (ETDEWEB)

The interfacial drag, droplet entrainment, droplet deposition and droplet-size distributions are important for detailed mechanistic modeling of annular dispersed two-phase flow. In view of this, recently developed correlations for these parameters are presented and discussed in this paper. The onset of droplet entrainment significantly alters the mechanisms of mass, momentum, and energy transfer between the film and gas core flow as well as the transfer between the two-phase mixture and the wall. By assuming the roll wave entrainment mechanism, the correlations for the amount of entrained droplet as well as for the droplet-size distribution have been obtained from a simple model in collaboration with a large number of data. Then the rate equations for entrainment and deposition have been developed. The drag correlations relevant to the droplet transfer is also presented. The comparison of the correlations to various data show satisfactory agreement.

Ishii, M.; Kataoka, I.

1982-01-01

27

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

28

A Summary of Interfacial Heat Transfer Models and Correlations  

Energy Technology Data Exchange (ETDEWEB)

A long term project has been launched in October 2006 to develop a plant safety analysis code. 5 organizations are joining together for the harmonious coworking to build up the code. In this project, KAERI takes the charge of the building up the physical models and correlations about the transport phenomena. The momentum and energy transfer terms as well as the mass are surveyed from the RELAP5/MOD3, RELAP5-3D, CATHARE, and TRAC-M does. Also the recent papers are surveyed. Among these resources, most of the CATHARE models are based on their own experiment and test results. Thus, the CATHARE models are only used as the comparison purposes. In this paper, a summary of the models and the correlations about the interfacial heat transfer are represented. These surveyed models and correlations will be tested numerically and one correlation is selected finally.

Bae, Sung Won; Cho, Hyung Kyu; Lee, Young Jin; Kim, Hee Chul; Jung, Young Jong; Kim, K. D. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2007-10-15

29

Interfacial heat transfer between bubble agitated immiscible liquid layers  

International Nuclear Information System (INIS)

In a postulated severe light water reactor (LWR) accident, the interaction of corium with the concrete reactor cavity is an important part of the accident analysis. The immiscible metallic and oxidic phases will be separated into two layers due to the large density difference. The interfacial heat transfer between these immiscible layers is important in characterizing the corium/concrete interaction. In this paper, the data on the surface renewal mechanism for heat transfer between bubble agitated immiscible liquid layers is reviewed. A modified version of Szekely's correlation is proposed. The predictions of the new correlation compare favorably with the experimental data of water/mercury and oil/wood's metal. A simple model based on the hydrodynamic stability of a liquid jet is proposed to model the conditions for bubble induced entrainment. The proposed model can predict the published experimental observation of entrainment in an oil/water system and not in a water/mercury system. By applying the model to corium/concrete interaction, it is concluded that the bubble induced entrainment would not occur in corium/concrete interaction

1986-03-01

30

Quantification of interfacial segregation by analytical electron microscopy  

CERN Document Server

The quantification of interfacial segregation by spatial difference and one-dimensional profiling is presented in general where special attention is given to the random and systematic uncertainties. The method is demonstrated for an example of Al-Al sub 2 O sub 3 interfaces in a metal-ceramic composite material investigated by energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy in a dedicated scanning transmission electron microscope. The variation of segregation measured at different interfaces by both methods is within the uncertainties, indicating a constant segregation level and interfacial phase formation. The most important random uncertainty is the counting statistics of the impurity signal whereas the specimen thickness introduces systematic uncertainties (via k factor and effective scan width). The latter could be significantly reduced when the specimen thickness is determined explicitly. (orig.)

Muellejans, H

2003-01-01

31

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

32

Boosting the efficiency of quantum dot sensitized solar cells through modulation of interfacial charge transfer.  

Science.gov (United States)

The demand for clean energy will require the design of nanostructure-based light-harvesting assemblies for the conversion of solar energy into chemical energy (solar fuels) and electrical energy (solar cells). Semiconductor nanocrystals serve as the building blocks for designing next generation solar cells, and metal chalcogenides (e.g., CdS, CdSe, PbS, and PbSe) are particularly useful for harnessing size-dependent optical and electronic properties in these nanostructures. This Account focuses on photoinduced electron transfer processes in quantum dot sensitized solar cells (QDSCs) and discusses strategies to overcome the limitations of various interfacial electron transfer processes. The heterojunction of two semiconductor nanocrystals with matched band energies (e.g., TiO(2) and CdSe) facilitates charge separation. The rate at which these separated charge carriers are driven toward opposing electrodes is a major factor that dictates the overall photocurrent generation efficiency. The hole transfer at the semiconductor remains a major bottleneck in QDSCs. For example, the rate constant for hole transfer is 2-3 orders of magnitude lower than the electron injection from excited CdSe into oxide (e.g., TiO(2)) semiconductor. Disparity between the electron and hole scavenging rate leads to further accumulation of holes within the CdSe QD and increases the rate of electron-hole recombination. To overcome the losses due to charge recombination processes at the interface, researchers need to accelerate electron and hole transport. The power conversion efficiency for liquid junction and solid state quantum dot solar cells, which is in the range of 5-6%, represents a significant advance toward effective utilization of nanomaterials for solar cells. The design of new semiconductor architectures could address many of the issues related to modulation of various charge transfer steps. With the resolution of those problems, the efficiencies of QDSCs could approach those of dye sensitized solar cells (DSSC) and organic photovoltaics. PMID:22493938

Kamat, Prashant V

2012-11-20

33

The role of interfacial films in the mass transfer of naphthalene from creosotes to water  

Science.gov (United States)

Viscous, semi-rigid interfacial films that are formed at the interface of certain multi-component non-aqueous phase liquid (NAPLs) and water can significantly reduce the rates of mass transfer of solutes. Creosote-water systems were investigated for their ability to form interfacial films. The effects of these films on the creosote-water partition and on mass transfer of a representative solute, naphthalene, were investigated in a series of experiments. The area-independent mass transfer coefficient of naphthalene contained in creosote decreased by 30% over a 1-week period in systems containing creosote and water. Further aging for up to 21 days did not result in significant additional decreases in the mass transfer coefficient. The creosote-water partition coefficient, however, did not change with extended contact. The presence of viscous interfacial films in creosote-water systems was demonstrated in pendant drop tests. These interfacial films most likely caused the reduction in solute mass transfer coefficients by providing significant resistance to the diffusion of solutes through the interfacial film. Results from mass transfer experiments conducted under different system conditions suggested that hindered diffusion of naphthalene through the bulk creosote phase, changes in composition of creosote as a result of extended dissolution, or changes in creosote-water interfacial area did not contribute to the decrease in naphthalene mass transfer coefficient.

Alshafie, Mohammed; Ghoshal, Subhasis

2004-10-01

34

Mass transfer during the period of drop formation in presence of interfacial instability  

Energy Technology Data Exchange (ETDEWEB)

The authors propose to find a functional relationship that describes experimental kinetic data on mass transfer during the period of drop formation in presence of interfacial instability. They conduct their experiments in a thermostated glass column where the disperse phase is fed by a micropump through a movable capillary. They conclude that spontaneous interfacial convection has an enormous influence on the end effect. The degree of increase of the amount of substance transferred depends on the intensity of the interfacial convection arising during extraction of acids in various systems.

Shatokhin, V.I.; Ermakov, A.A.; Maksimenko, M.Z.

1985-04-20

35

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. PMID:23862967

Matyushov, Dmitry V

2013-07-14

36

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

37

Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Interfacial Phenomena  

Science.gov (United States)

Experiments have been carried out to study the rates of mass transfer between liquid silicon and CaO-SiO2 slag with impeller stirring at 1823 K (1550 °C). The occurrence of transient interfacial phenomena related to the mass transfer of calcium has been observed; the evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here, it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal recoalesces. The incidental transfer of calcium very likely promotes the transfer of boron by increasing the interfacial area. Mechanical mixing appears to be an extremely effective means to increase the reaction rate of boron extraction and could feasibly be implemented in the industrial slag refining of silicon to improve reaction rates.

White, Jesse F.; Sichen, Du

2013-12-01

38

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

2003-11-15

39

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

CERN Multimedia

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

40

First-principles study of electronic properties of interfacial atoms in metal-metal contact electrification  

International Nuclear Information System (INIS)

The mechanism of contact electrification between metals was studied using the first-principles method, taking the Ag-Fe contact as an example. Charge population, charge density difference, the orbitals and densities of states (DOS) were calculated to study the electronic properties of the contacting interfacial atoms. Based on the calculation, the amount of contact charge was obtained. The investigation revealed that the electrons near Fermi levels with higher energies transfer between the outermost orbitals (s orbitals for Ag and d orbitals for Fe). Meanwhile, polarized covalent bonds form between the d electrons in the deep energy states. These two effects together lead to an increase of charge magnitude at the interface. Also, the electrons responsible for electrification can be determined by their energies and orbitals. (atomic and molecular physics)

2013-05-01

 
 
 
 
41

Implementation of a new interfacial mass and energy transfer model in RETRAN-3D  

International Nuclear Information System (INIS)

The RETRAN-3D MOD002.0 best estimate code includes a five-equation flow field model developed to deal with situations in which thermodynamic non-equilibrium phenomena are important. Several applications of this model to depressurization and pressurization transients showed serious convergence problems. An analysis of the causes for the numerical instabilities identified the models for interfacial heat and mass transfer as the source of the problems. A new interfacial mass and energy transfer model has thus been developed and implemented in RETRAN-3D. The heat transfer for each phase is equal to the product of the interfacial area density, a heat transfer coefficient and the temperature difference between the interface at saturation and the bulk temperature of the respective phase. However, in the context of RETRAN-3D, the vapor remains saturated in a two-phase volume, and no vapor heat transfer is thus calculated. The values of interfacial area density and heat transfer coefficient are obtained based on correlations appropriate for different flow regimes. A flow regime map, based on the work of Taitel and Dukler, with void fraction and mixture mass flux as map coordinates, is used to identify the flow regime present in a given volume. The new model has performed well when assessed against data from four experimental facilities covering depressurization, condensation and steady state void distribution. The results also demonstrate the viability of the approach followed to develop the new model for a five-equation based code. (author)

1999-01-01

42

Intramolecular electron transfer rates  

Science.gov (United States)

The initial goals of this project were: (1) to construct pulsed-accelerated-flow and pulsed-laser (transient absorbance) instruments for intramolecular electron-transfer rate measurements, (2) to design and synthesize appropriate molecules and perform such measurements, (3) to develop further an electrochemical method for gauging site-to-site electronic coupling, and (4) to apply time-dependent Raman scattering theory to the problem of inner-shell reorganization in charge-transfer reactions. Although all four goals were met, we also found it necessary to pursue studies in some unforeseen directions. For example, early on we discovered that medium effects (aggregation and ion pairing) could play a very large, and previously unrecognized, role in some optical intervalence reactions. Given the importance of the effects to the areas above, we chose to map them in a fairly complete fashion. Also, in anticipation of possible renewal we initiated studies in a new area: bimolecular photoredox kinetics in supercritical media. Finally, in a small project carried out largely by undergraduates we examined solvent tuning effects upon lifetimes of photo-excited ruthenium am(m)ine bipyridine complexes. The key new findings and other highlights of these studies are outlined.

Hupp, Joseph T.

43

Study on heat transfer and interfacial stability in supersonic steam injector  

International Nuclear Information System (INIS)

Supersonic steam injector is one of the most possible devices for Next-generation nuclear systems to achieve more simplified system and to enhance the safety and credibility of the systems. Supersonic steam injector has dual functions that are passive jet pump and high efficient heat exchanger. In order to design the supersonic steam injector, it is important to clarify the heat transfer and flow behavior of high-speed water jet in supersonic steam flow. However, thermal-hydraulic behaviors in the steam injector including the interfacial heat transfer behavior due to the direct contact condensation and interfacial stability of water jet are not clarified in detail yet. The purpose of the present study is to investigate the interfacial heat transfer behavior of high-speed water jet. The interface of water jet is observed by using high-speed video camera. From the observation results obtained, wave propagation on the interface is identified. The velocity of the wave propagation is estimated from the visual information. Radial distribution of the pressure and the temperature in the supersonic steam injector are also measured experimentally in order to investigate the dynamic behavior and the heat transfer due to the condensation. From the results, the interaction between the interfacial dynamic behavior and the heat transfer due to the condensation are discussed. (author)

2008-11-24

44

Single Molecule Electron Transfer Process of Ruthenium Complexes.  

Energy Technology Data Exchange (ETDEWEB)

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

Hu, Dehong; Lu, H PETER.

2006-03-01

45

Electron transfer at nickel electrode  

International Nuclear Information System (INIS)

There is considerable contemporary interest in the electron transfer reaction. at active (transition) metal electrodes. this work reports the electrochemical behavior of potassium ferrocyanide at nickel electrode in aqueous potassium nitrate solution. Potassium ferrocyanide is frequently employed to probe one-electron transfer reactions at solid, electrodes. It was found that the voltammetric oxidation of ferrocyanide at nickel is a simple electron transfer reaction. Normal pulse voltammetry revealed similar behavior. (author)

2009-01-01

46

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

47

Effect of interfacial transfer and wall heat transfer constitutive correlations in a model of PWR ECC bypass  

International Nuclear Information System (INIS)

The Emergency Core Cooling (ECC) bypass/refill process in a PWR downcomer, following a postulated large rupture of a cold leg pipe (LOCA), is of particular importance for the PWR thermal-hydraulic safety. In the unlikely event of such accident, due to reactor vessel rapid depressurization and blowdown at the break, coolant flashing and voiding of the reactor core occurs. To prevent fuel assembly overheating, the ECC subcooled water is injected into the reactor vessel. However, instead of penetrating the lower plenum, the ECC water, driven by the steam, flows azimuthally around the core barrel, bypasses through the downcomer and gets expelled out at the break. Mathematical modeling of such complex thermal-hydraulic phenomenon is accompanied with a difficult task of selecting an appropriate set of constitutive correlations. In this paper, using two-dimensional transient diabatic two-phase model of lower plenum ECC refilling and downcomer bypass flow, numerical calculations are performed to study the effect of interphase mass and momentum transfer, and wall heat transfer on lower plenum refilling initiation and rate. The results confirm that the interfacial momentum transfer by interfacial friction has dominant influence on the transient, and that the model is specially sensitive to annular interfacial friction correlation. Considerable difference in refilling predictions was obtained when various annular interfacial friction correlations were assessed in the model. It has been confirmed that with the Popov-Rohatgi correlation, the model refilling predictions are in very good agreement with the experimental data

1988-12-12

48

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

49

Co-extraction during reactive extraction of phenylalanine using Aliquat 336: interfacial mass transfer.  

Science.gov (United States)

Reactive liquid-liquid extraction can be used to separate hydrophilic fermentation products that would not otherwise partition into nonpolar solvents. However, during extraction of the target solute other compounds present in the extraction medium will also react with the ion exchange reagent and are thus co-extracted. In this study the effect of co-extraction on the interfacial flux of the target solute phenylalanine has been investigated for reactive extraction using Aliquat 336. The effect of co-extracting compounds has been included in a new interfacial flux balance, and experimental results reveal that the interfacial concentrations are equal to the final equilibrium conditions of the system. Using this information a simple mass transfer model has been developed from which film mass transfer coefficients may be determined. Co-extraction of other compounds present in the feed was found to reduce the interfacial flux of the target solute by reducing the driving force. Co-extraction did not affect the value of the film mass transfer coefficient, and therefore, co-extraction does not effect the transport properties of the solute to the interface. Extraction from a multicomponent fermentation broth resulted in a reduced flux, which arises from a reduction in the driving force caused by high levels of co-extraction. Furthermore, the flux was also reduced as the result of a mass transfer resistance caused by soluble surface-active compounds present in the fermentation broth adsorbing to the interface. The biomass associated with the fermentation broth was also found to reduce the solute flux, and it is believed that this is due to blockage of the interfacial area. PMID:12675589

Pursell, Mark R; Mendes-Tatsis, M Alcina; Stuckey, David C

2003-01-01

50

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

1980-10-12

51

Comparison of the self-exchange and interfacial charge-transfer rate constants for methyl- versus tert-butyl-substituted Os(III) polypyridyl complexes.  

Science.gov (United States)

Differences in the self-exchange and interfacial electron-transfer rate constants have been evaluated for a relatively unhindered Os(III/II) redox system, osmium(III/II) tris(4,4'-di-methyl-2,2'-bipyridyl), [Os(Me2bpy)3]3+/2+, relative to those of a relatively hindered system, osmium(III/II) tris(4,4'-di-tert-butyl-2,2'-bipyridyl), [Os(t-Bu2bpy)3]3+/2+. In contrast to the predicted increase in rate constant by a factor of 2-3 due to the difference in reorganization energy of the two complexes, introduction of the tert-butyl functionality decreased the self-exchange rate constant, as measured by NMR line-broadening techniques, by a factor of approximately 50 as compared to that of the analogous methyl-substituted osmium complex. Steady-state current density versus potential measurements, in conjunction with differential capacitance versus potential measurements, were used to compare the interfacial electron-transfer rate constants at n-type ZnO electrodes of [Os(t-Bu2bpy)3]3+/2+ and [Os(Me2bpy)3]3+/2+. The interfacial electron-transfer rate constant for the reduction of [Os(t-Bu2bpy)3]3+ was 100 times smaller than that for [Os(Me2bpy)3]3+. The results indicate that the tert-butyl group can act as a spacer on an outer-sphere redox couple and significantly decrease the electronic coupling of the electron-transfer reaction in both self-exchange and interfacial electron-transfer processes. PMID:17166001

Hamann, Thomas W; Brunschwig, Bruce S; Lewis, Nathan S

2006-12-21

52

Proton-Coupled Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Weinberg, Dave; Gagliardi, Christopher J.; Hull, Jonathan F; Murphy, Christine Fecenko; Kent, Caleb A.; Westlake, Brittany C.; Paul, Amit; Ess, Daniel H; McCafferty, Dewey Granville; Meyer, Thomas J

2012-01-01

53

Coherent electron transfer in polyacetylene  

Science.gov (United States)

We examine, using mixed classical-quantum electron-ion dynamics, electron transfer in a donor-acceptor-like molecular junction system based on polyacetylene. We identify two qualitatively-different transfer regimes: hopping and tunnelling. We discuss the criteria for achieving each one and for minimising inelastic scattering and decoherence arising from the coupling to the ions, and we connect our main results to quantities derived from electron dynamics involving simpler, three-state model systems. We identify the requirements to have near-ballistic transfer.

Psiachos, D.

2014-06-01

54

Interfacial equilibrium and mass transfer from liquid CO2 disks through hydrate films  

International Nuclear Information System (INIS)

Dissolution behavior of CO2 in water is a key factor in the ocean sequestration of CO2 in deep sea. Studies have been reported on the mass transfer of CO2 into water through interfacial hydrate layer in convective conditions. Coupled with convective flows, such studies provide limited information on the mass transfer resistance at the interface. In the present study, liquid CO2 was injected into stagnant water to form disks at the center of a disk-like void in a deep sea condition (278 K, 20.0 MPa) and the decreasing radii of disks were photographed with a digital camera. The radius change of the CO2 disk was compared with moving boundary numerical solutions for diffusive dissolutions. The water side of the interfacial hydrate layer was found in equilibrium with aqueous phase and the slower dissolution in hydrate forming conditions is due to the decreased solubility. These findings are in accordance with previous studies in convective conditions.

2010-04-01

55

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

1992-04-01

56

Interfacial energies of aqueous mixtures and porous coverings for enhancing pool boiling heat transfer  

Energy Technology Data Exchange (ETDEWEB)

The interfacial energies effects on pool boiling were measured for combinations of aqueous ethanol mixtures and cationic surfactants. The mixture with 16% ethanol by weight had the lowest contact angle (associated to the highest wettability) and produced the highest convective heat transfer coefficient, h, among the aqueous ethanol mixtures. The surfactant sodium-lauryl-sulfate added at 100 ppm (its calculated critical micelle concentration CMC) to the 16% ethanol aqueous mixture produced an additional increment of the wettability of the mixture and of the h values; other concentrations of the surfactant reduced de contact angle and h values. The effect of these interfacial energies represents a mass-transfer contribution to pool boiling and the proposal of mixture effects both as increased spreadability and as micelle states. Several randomly constructed porous coverings, contributing to the breakage of vapor slugs around the heater, were tested; produced the highest h values for average pore diameters of 0.5 mm, and covering thickness of 0.972 mm. The synergistic effect on h of the interfacial energies of mixtures at their critical micelle concentration, and porous coverings was measured. Therefore, the independent driving forces combined in this study for increasing pool boiling heat transfer are (a) spreadability of the liquid on the solid; (b) the bubble's size reduction, achieved by micelle states; and (c) the bubble's breakage, induced by the porous coverings, for vapor flow not under pressure drop control. (author)

Melendez, Elva [CIICAp, Universidad Autonoma del Estado de Morelos, 62210 (Mexico); Reyes, Rene [Departamento de Ingenieria Quimica y Alimentos, Universidad de las Americas Puebla, Santa Catarina Martir Cholula, Puebla 72820 (Mexico)

2006-08-15

57

Characterization of interfacially electronic structures of gold-magnetite heterostructures using X-ray absorption spectroscopy.  

Science.gov (United States)

Gold-magnetite heterostructures are novel nanomaterials which can rapidly catalyze the reduction reaction of nitroaromatics. In this study, the interfacially structural and electronic properties of various morphologies of Au-Fe3O4 heterostructures were systematically investigated using X-ray absorbance spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The effect of change in electronic structure and charge transfer on electrochemically catalytic activity of Au-Fe3O4 heterostructures was further evaluated by oxygen reduction reaction (ORR). The shifts in binding energy of Au4f and Fe2p peaks in XPS spectra indicate the charge transfer between the Au and Fe3O4 nanoparticles. The increase in d-hole population of Au seeds after the conjugation with iron oxides follows the order flower-like Au-Fe3O4 (FLNPs)>dumbbell-like Au-Fe3O4 (DBNPs)>Au seeds. In addition, the Fe(2+) valence state increases in Au-Fe3O4 heterostructures, which provides evidence to support the hypothesis of charge transfer between Au and Fe3O4 nanoparticles. The theoretical simulation of Au L3-edge XAS further confirms the production of Au-Fe and Au-O bonds at the interface of Au/Fe3O4 and the epitaxial linkage relationship between Au and Fe3O4 nanoparticles. In addition, the electron deficient of Au seeds increases upon increasing Fe3O4 nanoparticles on a single Au seed, and subsequently decreases the catalytic activity of Au in the Au-Fe3O4 heterostructures. The catalytic activity of Au-Fe3O4 toward ORR follows the order Au seeds>Au-Fe3O4 DBNPs>Au-Fe3O4 FLNPs, which is positively correlated to the extent of electronic deficiency of Au in Au-Fe3O4 heterostructures. PMID:24407694

Lin, Fang-hsin; Doong, Ruey-an

2014-03-01

58

The role of interfacial heat and mechanical energy transfers in a liquid-metal MHD generator  

International Nuclear Information System (INIS)

A brief description of the two-phase liquid-metal MHD power generation cycle and its advantages is provided. The importance of good interfacial liquid to gas heat transfer is discussed, and data confirming that satisfactory heat transfer is indeed achieved in an experimental generator are presented. An expression for the effect of the velocity difference between the gas and the liquid on generator performance is derived. An equivalent turbine efficiency is defined to characterize the generator as part of a heat engine and related to experimental data. (author)

1979-01-01

59

Manifestations of sequential electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Thurnauer, M.C.; Tang, J.

1996-05-01

60

Mass transfer rate through liquid membranes: interfacial chemical reactions and diffusion as simultaneous permeability controlling factors  

International Nuclear Information System (INIS)

Equations describing the permeability of a liquid membrane to metal cations have been derived taking into account aqueous diffusion, membrane diffusion, and interfacial chemical reactions as simultaneous permeability controlling factors. Diffusion and chemical reactions have been coupled by a simple model analogous to the one previously described by us to represent liquid-liquid extraction kinetics. The derived equations, which make use of experimentally determined interfacial reaction mechanisms, qualitatively fit unexplained literature data regarding Cu2+ transfer through liquid membranes. Their use to predict and optimize membrane permeability in practical separation processes by setting the appropriate concentration of the membrane carrier [LIX 64 (General Mills), a commercial ?-hydroxy-oxime] and the pH of the aqueous copper feed solution is briefly discussed. 4 figures

1981-01-01

 
 
 
 
61

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

62

Interfacial Area and Interfacial Transfer in Two-Phase Flow Systems (Volume III. Chapters 11-14)  

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

63

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

64

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

65

Ultrafast proton-coupled electron transfer in heterogenous photocatalysis  

Science.gov (United States)

At metal-oxide/protic-solvent interfaces, partially hydrated or "wet electron" states represent the lowest energy pathway for electron transfer. Here we study the photoinduced charge transfer at the H IIO/TiO II(110) interface by means of timeresolved two-photon photoemission spectroscopy and electronic structure theory. At ~1 monolayer coverage of H IIO on partially hydroxylated TiO II surfaces we find an unoccupied electronic state 2.4+/-0.1 eV above the Fermi level. Density functional theory shows this to be a two-dimensional "wet electron" state, which is distinct from hydrated electrons observed on water-covered metal surfaces. The decay of electrons from the wet electron state by the resonant charge transfer to the conduction band of TiO II occurs in 100 fs range above 1 ML CH 3OH coverage. Significantly, a pronounced deuterium isotope effect (CH 3OD) indicates a strong correlation between the interfacial electron transfer and the motion of protons in the molecular overlayer.

Zhao, Jin; Onda, Ken; Li, Bin; Petek, Hrvoje

2006-09-01

66

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)

1965-10-01

67

Interfacial exclusion pressure determines the ability of apolipoprotein A-IV truncation mutants to activate cholesterol ester transfer protein.  

Science.gov (United States)

We used a panel of recombinant human apolipoprotein (apo) A-IV truncation mutants, in which pairs of 22-mer alpha-helices were sequentially deleted along the primary sequence, to examine the impact of protein structure and interfacial activity on the ability of apoA-IV to activate cholesterol ester transfer protein. Circular dichroism and fluorescence spectroscopy revealed that the secondary structure, conformation, and molecular stability of recombinant human apoA-IV were identical to the native protein. However, deletion of any of the alpha-helical domains in apoA-IV disrupted its tertiary structure and impaired its molecular stability. Surprisingly, determination of the water/phospholipid interfacial exclusion pressure of the apoA-IV truncation mutants revealed that, for most, deletion of amphipathic alpha-helical domains increased their affinity for phospholipid monolayers. All of the truncation mutants activated the transfer of fluorescent-labeled cholesterol esters between high and low density lipoproteins at a rate higher than native apoA-IV. There was a strong positive correlation (r = 0.790, p = 0.002) between the rate constant for cholesterol ester transfer and interfacial exclusion pressure. We conclude that molecular interfacial exclusion pressure, rather than specific helical domains, determines the degree to which apoA-IV, and likely other apolipoproteins, facilitate cholesterol ester transfer protein-mediated lipid exchange. PMID:11940599

Weinberg, Richard B; Anderson, Rachel A; Cook, Victoria R; Emmanuel, Florence; Denèfle, Patrice; Tall, Alan R; Steinmetz, Armin

2002-06-14

68

Relationship between casting distortion, mold filling, and interfacial heat transfer. Annual technical report, September 1997 - September 1998  

Energy Technology Data Exchange (ETDEWEB)

In the third year of this program, the final castings necessary to evaluate the effect of casting orientation and gating in silica sand lost foam were poured and measured using a CMM machine. Interfacial heat transfer and gap formation measurements continued. However, significant problems were encountered in making accurate measurements. No consistent evidence of gap formation was found in aluminum sand casting. Initial analysis yields heat transfer values below those previously reported in the literature. The program in continuing.

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

1998-10-22

69

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

70

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.

2011-01-01

71

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

72

Interfacial reactions between Sn-based solders and common metallisations used in electronics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

During their lifetimes the electrical interconnections of portable electronic devices are subjected to high thermal, mechanical, chemical, and electrical loadings, and therefore the metallurgical compatibility between solder alloys and component pad metallisations has become ever more essential from the point of view of interconnection reliability. For this reason, the mechanisms of interfacial reactions are studied in this thesis by making use of thermodynamic calculations together with diff...

2006-01-01

73

Heteroepitaxial metallo-phthalocyanine (MPc, M = cobalt, nickel, copper) thin films on gold: Atomic and interfacial electronic structures  

Science.gov (United States)

Organic semiconductors have become a hot topic for research within the past few years. This work describes research into a family of organic semiconductors known as metallo-phthalocyanine (MPc) in which the electronic and optical properties can be easily tuned by the systematic modification of the metal cations and ligands. More specifically, thin films of CoPc, NiPc, and CuPc have been evaporated onto a "5 x 20" reconstructed Au(001) substrate and have been investigated by employing low energy electron diffraction and ultraviolet photoelectron spectroscopy. Low energy electron diffraction reveals that thin films of CuPc and NiPc are highly ordered with a square unit cell aligned along the substrate and axes. In addition, deposition of CuPc onto the Au(001) substrate when at room temperature and elevated temperatures reveal that the square unit cell is larger when the substrate is heated. On the other hand, CoPc thin films are not well ordered as evidenced by multiple rotationally equivalent square domains, which are separated by 16°. Even more interesting is that the contrast between NiPc and CoPc on Au(001) is further found in the interfacial electronic structure. Ultraviolet photoelectron spectroscopy studies of the interfacial layers of NiPc deposited on the reconstructed gold substrate indicate that NiPc physisorbs on the gold surface as verified by a uniform molecular orbital (MO) shift. However, similar studies of the interfacial layers of CoPc depict an interaction between the CoPc 13a1g MO and the Au surface suggesting a charge transfer between the two. In addition to the research into MPc thin films, this work also describes the development of a Low Energy Electron Diffraction Intensity versus Voltage (LEED-IV) system for the Laboratory for Surface Analysis and Modification. This development involved the merging of various hardware and software systems by means of LabVIEW environment. Characterization of the system performance was carried out through the use of a MoS2 sample with known LEED-IV characteristics. The results of the system characterization revealed that the fully operational and ready to be applied to other samples.

Ellis, Trinity S.

2005-12-01

74

Effect of binder polymer structures used in composite cathodes on interfacial charge transfer processes in lithium polymer batteries  

International Nuclear Information System (INIS)

The effect of binder polymer structures used in composite cathodes on the interfacial charge transfer processes in lithium polymer batteries (LPB) has been studied in detail. A cross-linked comb-copolymer, consisting of ethylene oxide (EO), 2-(2-methoxyethoxy)ethyl glycidyl ether (MEEGE), and allyl glycidyl ether (AGE), was used as a solid polymer electrolyte (SPE). LiCoO2 composite cathodes were fabricated using binder comb-copolymers, consisting of EO and MEEGE with different compositions. Ionic conductivity of the SPE, and the interfacial charge transfer processes between the SPE and metallic lithium and between the SPE and the composite cathode at several cathode potentials versus Li/Li+, were electrochemically explored. With increasing MEEGE composition in the binder copolymers, the interfacial resistances between the SPE and the composite cathode appreciably decreased. As the result, discharge capacity of the LPB also enhanced with increasing the MEEGE composition. The introduction of the branched-side-chains to the polymer backbone to the binder polymers for the composite cathodes caused to facilitate the interfacial charge transport processes, while the introduction had also been found to be very effective in terms of the enhancement of ionic conductivity of SPE

2004-11-30

75

Molecular Basis for Directional Electron Transfer*  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Biological macromolecules involved in electron transfer reactions display chains of closely packed redox cofactors when long distances must be bridged. This is a consequence of the need to maintain a rate of transfer compatible with metabolic activity in the framework of the exponential decay of electron tunneling with distance. In this work intermolecular electron transfer was studied in kinetic experiments performed with the small tetraheme cytochrome from Shewanella oneidensis MR-1 and fro...

Paquete, Catarina M.; Saraiva, Ivo H.; Calc?ada, Eduardo; Louro, Ricardo O.

2010-01-01

76

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

77

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

78

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)

2011-04-01

79

Exocellular electron transfer in anaerobic microbial communities  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Exocellular electron transfer plays an important role in anaerobic microbial communities that degrade organic matter. Interspecies hydrogen transfer between microorganisms is the driving force for complete biodegradation in methanogenic environments. Many organic compounds are degraded by obligatory syntrophic consortia of proton-reducing acetogenic bacteria and hydrogen-consuming methanogenic archaea. Anaerobic microorganisms that use insoluble electron acceptors for growth, such as iron- an...

Stams, A. J. M.; Bok, F. A. M.; Plugge, C. M.; Eekert, M. H. A.; Dolfing, J.; Schraa, G.

2006-01-01

80

Strong interfacial dipole formation with thermal evaporation of lithium cobalt oxide for efficient electron injections  

Science.gov (United States)

We investigated the electronic structures at the interface of Al/lithium cobalt oxide (LiCoO2)/tris(8-hydoxyquinoline) aluminum (Alq3) to elucidate the origin of the electron injection enhancement with the insertion of the LiCoO2 layer in organic light-emitting devices using in situ photoelectron spectroscopy experiments. We discovered that LiCoO2 was decomposed into lithium oxide (Li2O) by thermal evaporation, and only Li2O was deposited on the desired substrate. Li2O forms a strong interfacial dipole, which reduces the surface potential on Alq3 due to its extremely low work function. As a result, the electron injection barrier was dramatically decreased by the Li2O layer. Furthermore, there is no strong chemical interaction at the interface of Al/Li2O/Alq3; hence, this would contribute to extend the device lifetime.

Lee, Hyunbok; Park, Soohyung; Lee, Jeihyun; Lee, Younjoo; Shin, Dongguen; Jeong, Kwangho; Yi, Yeonjin

2013-01-01

 
 
 
 
81

Dynamics of electron transfer in amine photooxidation  

Energy Technology Data Exchange (ETDEWEB)

Studies were initiated utilizing picosecond (ps) absorption spectroscopy, to directly monitor the dynamics of electron transfer from 1,4-diazabicyclo(2.2.2)octane (Dabco) to the excited states of benzophenone and fluorenone. These two systems were chosen because of their contrasting photochemistry. The quantum yield for photoreduction of benzophenone in polar solvents is generally greater than 0.1, while that of fluorenone is zero. In polar solvents, the proposed mechanism dictates that an electron is transferred to the excited singlet state fluorenone, which then back-transfers the electron, regenerating ground-state fluorenone and amine. Photolysis of benzophenone in the presence of an amine transfers an electron to an excited triplet state, forming an ion pair that is stable relative to diffusional separation. The results of this study verify this proposal.

Peters, K.S.; Freilich, S.C.; Schaeffer, C.G.

1980-08-13

82

Electronic Funds Transfer and Monetary Policy.  

Science.gov (United States)

A comprehensive analysis of the institutions, the instruments, and the channels of influence of monetary policy in the national economy is presented. It includes an examination of major points of impact of electronic funds transfer on monetary policy base...

1976-01-01

83

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

1988-08-15

84

Nuclear reorganization barriers to electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-01-01

85

Electron Transfer for Large Molecules through Delocalization  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-01-01

86

Ultrafast electron transfer, recombination and spin dynamics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The quenching of excited singlet methylene blue (1MB+*) by N,N-dimethylaminomethylferrocene (FcN) in acetonitrile at room temperature has been studied using femtosecond pump-probe absorption spectroscopy. At high FcN concentration static quenching via an intermolecular electron transfer mechanism constitutes the predominating decay channel for 1MB+*. The time constants of the large amplitude components for the forward electron transfer from FcN donor to 1MB+* and the subsequent recombination ...

Gilch, Peter; Po?llinger-dammer, Florian; Steiner, Ulrich; Michel-beyerle, Maria Elisabeth

1997-01-01

87

Electron paramagnetic resonance of photocatalytic reaction which involve electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Transient radicals generated under photocatalytic reactions in a polar solvent and their electronically spinned polarization were discussed under UV irradiation by using EPR and N2 gas pulse laser time-divided EPR. The reaction is a reaction of electron transfer from such amines as DABCO or electron donor molecules of SO3{sup -} to such electron accepting compounds as 1,4-benzoquinone and maleic anhydride under the presence of photocatalysts (triple photosensitizers) such as benzophenone and xanthone (XT). Spin polarized cation radicals of DABCO and radical anions of XT were detected in association with one electron transfer. A triple mechanism lies in the spinned polarization of both radicals, and transient XT in the triple state begin the electron transfer reaction. Photo-excited XT acts as a photocatalyst in one electron transfer reaction, the triple XT turns into an electron accepting body, and the transient anion radicals of XT become the electron donor. The XT(S) acts as a photocatalyst in the inter-molecular electron transfer from amine (D) to quinone (A). Its reaction is expressed by the following formula: D + S{sup *} + A{yields}D{sup dot +}+S+A{sup dot -} (where S{sup *} denotes a photo-excited state). 53 refs., 21 figs., 3 tabs.

Kaise, M. [National Institute of Materials and Chemical Research, Tsukuba (Japan)

1995-10-13

88

Implications of the detailed fluctuation theorem for the sources of irreversibility in interfacial charge transfer processes  

International Nuclear Information System (INIS)

We investigate from basic principles of nonequilibrium statistical mechanics the general reasons why electron transfer across an interface is associated with irreversible elements (resistances) in equivalent circuit modeling. We apply the detailed fluctuation theorem [C. Jarzynski, J. Stat. Phys. 98, 77 (2000)] to a simple model of an interface between two different materials. The elementary transition rates are interpreted in terms of the evolution of a microstate, and obey a ratio that is related to the heat absorbed from the phonon bath while promoting an electron to a higher energy level. The amount of irreversibility (the entropy production), and also the macroscopic current density, can be both obtained with the additional constraint that the system belongs in a particular mesostate, determined by the distribution of chemical and electrostatic potential

2005-11-01

89

Implications of the detailed fluctuation theorem for the sources of irreversibility in interfacial charge transfer processes.  

Science.gov (United States)

We investigate from basic principles of nonequilibrium statistical mechanics the general reasons why electron transfer across an interface is associated with irreversible elements (resistances) in equivalent circuit modeling. We apply the detailed fluctuation theorem [C. Jarzynski, J. Stat. Phys. 98, 77 (2000)] to a simple model of an interface between two different materials. The elementary transition rates are interpreted in terms of the evolution of a microstate, and obey a ratio that is related to the heat absorbed from the phonon bath while promoting an electron to a higher energy level. The amount of irreversibility (the entropy production), and also the macroscopic current density, can be both obtained with the additional constraint that the system belongs in a particular mesostate, determined by the distribution of chemical and electrostatic potential. PMID:16383696

Bisquert, Juan

2005-11-01

90

Photocatalytic activity and interfacial carrier transfer of Ag-TiO{sub 2} nanoparticle films  

Energy Technology Data Exchange (ETDEWEB)

The electrodes of Ag-TiO{sub 2} with different Ag content are prepared by a modified sol-gel method. The photochemical properties of Ag-TiO{sub 2} with different Ag content are characterized by surface photovoltage spectroscopy (SPS). The results show that the SPS intensity decreased with increasing Ag contents. This demonstrates that the doping Ag plays the roles trapping photoinduced electrons, which inhibiting the recombination of photoinduced electrons and holes. The photoelectrochemical properties of Ag-TiO{sub 2} electrodes with different Ag content are performed by electrochemical impedance spectroscopy (EIS) under high-pressure mercury lamp (160 W) illuminating, and photocatalytic degradation of RhB are studied at the same time. The experimental results indicate that the process of charge transfer is a controlled-step of photocatalytic reaction. The SPS intensity and the electrical impedance values of EIS equivalent circuits are contrary to photocatalytic degradation ratio of RhB.

Xin Baifu [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Ren Zhiyu [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Hu Haiyuan [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Zhang Xiangyu [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Dong Chunlei [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Shi Keying [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Jing Liqiang [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China); Fu Honggang [Laboratory of Physical Chemistry, School of Chemistry and Materials Science, Heilongjiang University, Xue Fu Road No. 74, Nan-gang, Harbin 150080 (China)]. E-mail: fuhg@vip.sina.com

2005-12-15

91

Electron transfer to continuum states  

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-12-31

92

Heat Transfer Augmentation for Electronic Cooling  

Directory of Open Access Journals (Sweden)

Full Text Available Problem statement: The performance of electronic devices has been improving along with the rapid technology development. Cooling of electronic systems is consequently essential in controlling the component temperature and avoiding any hot spot. The study aims to review the present electronic cooling methods which are widely used in electronic devices. Approach: There are several methods to cool down the electronics components such as the pin-fin heat sink, confined jet impingement, heat pipe, micro heat sink and so on. Results: The cooling techniques can obviously increase heat transfer rate. Nonetheless, for active and passive cooling methods the pressure drop could extremely rise, when the heat transfer rate is increased. Conclusion: When the cooling techniques are used, it is clearly seen that the heat transfer increases with pressure drop. To avoid excessive expense due to high pressure drop, optimization method is required to obtain optimum cost and cooling rate.

Suabsakul Gururatana

2012-01-01

93

Medium effects in photoinduced electron transfer reactions  

International Nuclear Information System (INIS)

The transfer of an electron between two molecules is a fundamental chemical process of great significance in biochemistry as well as in general chemistry. Electron transfer reactions can be induced by the absorption of light - as in photosynthesis - so that one of the molecules reacts through an electronically excited state; a net storage of chemical energy may then take place. When electron transfer involves molecules in condensed phase, the role of the liquid or solid medium must be considered. In the first place, a polar solvent may promote electron transfer through the stabilization of ion pairs and the separation of ions; but if the polar solvent must reorganize prior to the reaction, then an activation barrier will exist against electron transfer in polar solvents. This article gives a citical review of this field, with some novel ideas concerning the role of the medium (liquid solvent or solid matrix) in the overall energy balance of electron transfer, in the kinetics of the reaction, and in the further process of charge separation. It is suggested in particular that no dielectric screening by a polar solvent can exist when ions are formed in direct contact; and that the extensive reorganization of the solvent prior to electron transfer is so unlikely as to be discounted. In these respects the model presented in this article diverges from the commonly accepted model of Weller and of Marcus and Hush. In the Conclusion section some areas of particular importance for further research in this field are outlined. (author) 28 refs., 20 figs., 2 tabs

1988-01-01

94

Electron transfer processes in disordered media  

Energy Technology Data Exchange (ETDEWEB)

The paper reviews a broad range of approaches to the chemical dynamics in condensed phase systems. We analyze the problem of thermal electron transfer in disordered media (proteins) and discuss the interplay of quantum tunneling effects, electronic non-adiabaticity, friction and conformational changes on kinetic rate of the process. (author). 113 refs, 8 figs.

Gudowska-Nowak, E. [Dept. of Statistical Physics, Inst. of Physics, Jagiellonian Univ., Cracow (Poland)

1995-09-01

95

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

96

Integral encounter theory of strong electron transfer  

International Nuclear Information System (INIS)

The integral encounter theory (IET) has been extended to the reactions limited by diffusion along the reaction coordinate to the level crossing points where either thermal or hot electron transfer occurs. IET describes the bimolecular ionization of the instantaneously excited electron donor D* followed by the hot geminate backward transfer which precedes the ion pair equilibration and its subsequent thermal recombination. We demonstrate that the fraction of ion pairs which avoids the hot recombination is much smaller than their initial number when the electron tunneling is strong

2005-03-22

97

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

International Nuclear Information System (INIS)

The interface between electron transfer proteins such as cytochromes and solid phase mineral oxides is central to the activity of dissimilatory-metal reducing bacteria. A combination of potential-based molecular dynamics simulations and ab initio electronic structure calculations are used in the framework of Marcus' electron transfer theory to compute elementary electron transfer rates from a well-defined cytochrome model, namely the small tetraheme cytochrome (STC) from Shewanella oneidensis, to surfaces of the iron oxide mineral hematite (a-Fe2O3). Room temperature molecular dynamics simulations show that an isolated STC molecule favors surface attachment via direct contact of hemes I and IV at the poles of the elongated axis, with electron transfer distances as small as 9 Angstroms. The cytochrome remains attached to the mineral surface in the presence of water and shows limited surface diffusion at the interface. Ab initio electronic coupling matrix element (VAB) calculations of configurations excised from the molecular dynamics simulations reveal VAB values ranging from 1 to 20 cm-1, consistent with nonadiabaticity. Using these results, together with experimental data on the redox potential of hematite and hemes in relevant cytochromes and calculations of the reorganization energy from cluster models, we estimate the rate of electron transfer across this model interface to range from 1 to 1000 s-1 for the most exothermic driving force considered in this work, and from 0.01 to 20 s-1 for the most endothermic. This fairly large range of electron transfer rates highlights the sensitivity of the rate upon the electronic coupling matrix element, which is in turn dependent on the fluctuations of the heme configuration at the interface. We characterize this dependence using an idealized bis-imidazole heme to compute from first principles the VAB variation due to porphyrin ring orientation, electron transfer distance, and mineral surface termination. The electronic matrix element and consequently the rate of electron transfer are found to be sensitive to all parameters considered. This work indicates that biomolecularly similar solvent-exposed bis-histidine hemes in outer-membrane cytochromes such as MtrC or OmcA are likely to have an affinity for the oxide surface in water governing the approach and interfacial conformation and, if allowed sufficient conformational freedom, will achieve distances and configurations required for direct interfacial electron transfer.

2007-08-02

98

Superexchange coupling mechanisms for electron transfer processes  

Science.gov (United States)

Electron transfer matrix elements for electron exchange between various pairs of transition metal complexes in close contact have been calculated and analyzed for a variety of approach geometries for the two reactants. The coupling between the nominal metal ion donor/acceptor sites is achieved by superexchange of the hole type arising from ligand-to-metal charge transfer (LMCT), the dominant ligand-field interaction for the electron-donor ligands considered (H sub 2 O, NH sub 3, the cyclopentadienide anion). The pronounced variations of H sub if with geometry are not correlated with the separation distance of the metal ions (between which the direct overlap is negligible) and span the range from non-adiabatic to strongly adiabatic electronic coupling. The values for metallocene/metallocinium redox pairs bracket recently reported experimental values. Analysis of the results using the method of corresponding orbitals demonstrates the validity of an effective 1-electron model for the electron transfer process to within about 10 percent for the class of systems considered. A higher-order superexchange mechanism was encountered for the Co(NH sub 3) sub 6 (2+/3+) exchange process, in which the LMCT-driven hole-transport mechanism couples excited local states of the metal ions, which in turn are connected to the corresponding ground states by spin-orbit mixing. This mechanism yields on electronic transmission factor within two orders of magnitude of unity.

Newton, M. D.

99

Femtosecond spectroscopic studies of photoinduced electron transfer in MDMO-PPV:ZnO hybrid bulk heterojunctions  

International Nuclear Information System (INIS)

The photophysics of charge carriers (polaron) in MDMO-PPV:ZnO hybrid bulk heterojunction is studied at 80 K by femtosecond transient absorption spectroscopy. A short-lived positive polaron is observed in the blend phase in MDMO-PPV:ZnO blend films with a weight ratio of 1:1 and 1:2. Further increase of ZnO weight ratio results in a significant quenching of the polaron absorption. The results are discussed in the concept that both pristine polymer and MDMO-PPV:ZnO blend phases coexist in the blend films. It is concluded that a polaron is photogenerated within the excitation laser pulse (<100 fs) and electron transfer efficiency is highest in blend films 1:1 and 1:2. Lack of the interfacial area and faster back electron transfer process are discussed to be responsible for the quenching of the electron transfer efficiency in blend film 1:3

2005-07-25

100

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

1981-06-12

 
 
 
 
101

Electron transfer in dinucleoside phosphate anions  

International Nuclear Information System (INIS)

The electron transfer reaction within various dinucleoside phosphate radical anions has been investigated by ESR spectroscopy and pulse radiolysis. In the ESR work electrons are produced by photolysis of K4Fe(CN)6 in a 12 M LiCl glass at 770K. Upon photobleaching the electrons react with the dinucleoside phosphate to form the anion radical. The anions of the four DNA nucleosides were also produced and their ESR spectra were appropriately weighted and summed by computer to simulate the spectra found for the dinucleoside phosphate anions. From the analysis the relative amounts of each of the nucleoside anions in the dinucleoside phosphate anion were determined. Evidence suggests the electron affinity of the pyrimidine bases are greater than the purine bases; however, the results are not sufficient to distinguish between the individual purine or pyrimidine. When dinucleoside phosphate anions containing thymidine are warmed, protonation occurs only on thymine to produce the well known ''thymyl'' spectrum. Pulse radiolysis experiments on individual nucleotides (TMP, dAMP), mixtures of these nucleotides and the dinucleoside phosphate, TdA, in aqueous solution at room temperature show that in the TdA anion electron transfer occurs from adenine to thymine, whereas no electron transfer is found for mixtures of individual nucleotides. Protonation is found to occur only on thymine in the TdA anion in agreement with the ESR results

1976-02-12

102

Electron Transfer at Sensitized Semiconductor Electrodes.  

Science.gov (United States)

Electron transfer from the excited state of sensitizing dyes to the conduction band of semiconductors has been studied through photoelectrochemical techniques. Two systems were analyzed in detail: rhodamine B on ZnO and rose bengal on TiO sub 2 . Prior to...

M. T. Spitler

1977-01-01

103

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

104

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

105

Nuclear, electronic, and frequency factors in electron-transfer reactions  

International Nuclear Information System (INIS)

The crux of the problem is the fact that the equilibrium configuration of a species changes when it loses an electron. Configuration changes of organometallic metal complexes involve the metal-ligand and intra-ligand bond lengths and angles as well as changes in vibrations and rotation of surrounding solvent dipoles. Discussion indicates that rate constants can be expressed as a product of a nuclear, an electronic, and a frequency factor. Good agreement with measured rate constants is obtained in the normal free-energy region. Understanding of electron transfer rates in highly exothermic regions remains uncertain. 75 references, 2 figures, 2 tables

1982-01-01

106

Finite difference method for computer study of the interfacial heat transfer coefficient during rapid solidification of spherical samples on a metallic substrate  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper a numerical model will be adopted to analyze the heat transfer process during rapid solidification of a spherical sample placed on a metallic substrate cooled by water. The interfacial heat transfer coefficient between the sample and the substrate will be evaluated by matching model calculations with the surface temperature history recorded by a digital camera during solidification of a sample melted in an Arc-image furnace. .

Nikoli? Z.S.; Yoshimura M.; Araki S.; Fujiwara T.

2007-01-01

107

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

108

Reaction coordinates for electron transfer reactions  

International Nuclear Information System (INIS)

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

2008-12-07

109

Electron transfer in silver telluride melt  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer in silver telluride melt was studied experimentally at different temperatures. The method used to study electron transfer and thermodiffusion is based on Onsager's theory and consists of measuring the electrodiffusion potential which varies as a function of time in the system formed by the liquid semiconductor and the neutral metallic electrodes. The effective charges and the average coefficients of diffusion of silver ions were calculated and the ionic component of the total electrical conductivity of Ag/sub 2/Te melt was evaluated. It was observed that the indicated characteristics vary systematically in the series of silver chalcogenides with anionic substitution. The negative temperature coefficient of electrical conductivity in silver sulfide and silver selenide melts was explained.

Glazov, V.M.; Burkhanov, A.S.

1987-06-01

110

Custody transfer enhanced by electronic billing system  

Energy Technology Data Exchange (ETDEWEB)

Transcontinental Gas Pipe Line (TGPL) Corp. engineers have developed an electronic billing system for custody transfer that can reduce the cost of doing business and improve the accuracy of transfer measurements. The system accurately measures gas flow and quality, transmits gas data to a central facility, provides a capability to review the collected data, prepares bills based upon these data, and reduces staffing associated with the data collection and billing process. On-line flow computers are keys to this electronic billing system. These computers, referred to as remote terminal units (RTU's), are currently in service at TGPL at more than 30 locations with 30 more locations due to be on-line within 6 months and an additional 40 locations due within 15 months. These RTU's will be obtaining gas data from metering stations located in New York, New Jersey, Pennsylvania, Maryland, Virginia, North Carolina, Georgia, Louisiana, and Texas.

Knox, R.M.

1986-10-20

111

Activation entropy of electron transfer reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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...

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

2005-01-01

112

Interfacial mass transfer in extraction of amino acid by ALIQUAT 336 in organic phase.  

Science.gov (United States)

Reactive extraction of L-phenylalanine from alkaline aqueous solution into xylene in the presence of tri-octyl-methyl-ammonium chloride (ALIQUAT 336) as complexing agent was studied using a stirred transfer cell. The study investigated the effects of carrier concentration and temperature on mass transfer rates. Transfer rate across the interface in the presence of surfactant molecules was also studied. A two-film model was proposed by considering film mass transfer resistances at the aqueous and organic phases. The model predicted adequately the experimental time-concentration data at different carrier concentrations and temperatures. The model was modified to take into account the presence of surfactant in the organic phase. PMID:1366697

Uddin, M S; Hidajat, K; Lim, B; Ching, C

1990-01-01

113

Direct contact heat exchange interfacial phenomena for liquid metal reactors : Part I - heat transfer  

International Nuclear Information System (INIS)

Experiments on direct-contact heat exchange between molten metal and water for steam production were conducted. These experiments involved the injection of water into molten lead-bismuth eutectic for heat transfer measurements in a 1-D geometry. Based on the initial results of the experiments, the effects of the water flow rate and the molten metal superheat (temperature difference between molten metal and saturated water) on the volumetric heat transfer coefficient were discussed

2002-04-14

114

75 FR 51707 - Electronic Funds Transfer of Depository Taxes  

Science.gov (United States)

...Electronic Funds Transfer of Depository Taxes AGENCY: Internal Revenue Service (IRS...proposed regulations relating to Federal tax deposits (FTDs) by Electronic Funds Transfer...contains proposed amendments to the Income Tax Regulations (26 CFR part 1), the...

2010-08-23

115

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

Science.gov (United States)

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

2011-01-06

116

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

117

Frontier orbital symmetry control of intermolecular electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Research continued on the study of intermolecular electron transfer. This report discusses the following topics: fluorescence quenching by electron transfer and the modification of quenching dynamics by solvent properties and net free energy change; transient absorption measurements following selective excitation of 1:1 EDA complex isomers; selective quenching of dual fluorescence from linked EDA systems; electron-transfer sensitized cycloreversion of rubrene endoperoxide; and vibronic modification of adiabatic requirements for intermolecular electron transfer. (CBS)

Stevens, B.

1990-11-01

118

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

119

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

120

In situ high-resolution transmission electron microscopy study of interfacial reactions of Cu thin films on amorphous silicon  

Science.gov (United States)

Interfacial reactions of Cu with amorphous silicon (a-Si) in the Cu/a-Si/glass system are studied by in situ high-resolution transmission electron microscopy at 550 °C. Various Cu silicides, such as ?-Cu3Si, Cu15Si4, and Cu5Si, and Cu particles are observed. The formation of the Cu particles can be attributed to a heating effect from electron beam irradiation. Around the Cu silicides, crystallization of a-Si occurs. Around the Cu particles, however, crystallization does not occur. Crystallization appears to be enhanced by Cu dissolved in a-Si.

Lee, Sung Bo; Choi, Duck-Kyun; Phillipp, Fritz; Jeon, Kyung-Sook; Kim, Chang Kyung

2006-02-01

 
 
 
 
121

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

122

Photon-to-electron quantum information transfer  

Science.gov (United States)

Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, preparation and read-out of the electron spin state must be spin coherent, but both the traditional preparation and read-out of the spin state are projective to up/down spin states, which do not have spin coherence. We have recently demonstrated that the polarization coherence of light can be coherently transferred to the spin coherence of electrons in a semiconductor. We have also developed a new scheme named tomographic Kerr rotation (TKR) by generalizing the traditional KR to directly readout the spin coherence of optically prepared electrons without the need for the spin dynamics, which allows the spin projection measurement in an arbitrary set of basis states. These demonstrations were performed using g-factor-controlled semiconductor quantum wells with precessing and nonprecessing electrons. The developed scheme offers a tool for performing basis-independent preparation and read-out of a spin quantum state in a solid. These results encourage us to make a quantum media converter between flying photon qubits and stationary electron spin qubits in semiconductors.

Kosaka, Hideo

2011-05-01

123

Marcus' contributions to electron-transfer theory  

Energy Technology Data Exchange (ETDEWEB)

The contributions of R.A. Marcus to the development of electron-transfer theory are reviewed. Marcus was one of the first to postulate that electron transfer depended upon nuclear configuration changes. He later developed a parallel formalism for electron-transfer and redox reactions at an electrode.

Sutin, N.

1986-07-31

124

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

125

A time-resolved study of electron transfer mechanisms: Beyond outer-sphere electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Of the primary objectives of our research has been to understand some of the fundamental mechanistic issues underlying electron transfer reactions. We have designed molecular systems to provide information on several aspects of charge transfer reactions, including the role of protons in long-distance electron transfer, bimolecular donor-acceptor pair reactivity at high driving forces, and excited state multielectron transformations. In our systems a photon can initiate the reaction by placing the molecules in an excited electronic state, which permits the reactant and product concentrations to be monitored as a function of time. These dynamic measurements are conducted by exciting the molecules with a short light pulse, and following the progress of the reaction by optical methods, such as transient absorption spectroscopy and emission lifetime. Electron transfer reactions through a proton interface have been conducted by the design of hydrogen-bonded donor-acceptor pairs, where the donor, a carboxylic acid derivative of a Zn-substituted porphyrin, transfer an electron to several aromatic acceptors from its excited state. The charge separation and subsequent charge recombination rates have been determined utilizing picosecond transient absorption spectroscopy, for protiated and deuterated donors and acceptors. A slight attenuation in the rates is observed. The transient absorption technique has also been utilized to characterize the excited states that lead to two-electron reactivity in quadrupoly-bonded inorganic complexes of the type M{sub 2}Cl{sub 4}(L){sub n}, where M = molybdenum or tungsten and L = monodentate or bidentate phosphine ligands. It was observed that the reactions do not proceed directly from an excited electronic state, but from a conformationally-distorted intermediate formed following light excitation. The distorted intermediate is believed to possess favorable characteristics that permit the observed two-electron oxidative-addition reactions.

Turro, C.

1992-12-31

126

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

127

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

128

Interfacial nonradiative energy transfer in responsive core-shell hydrogel nanoparticles.  

Science.gov (United States)

Fluorescently labeled core-shell latex particles composed mainly of the thermoresponsive polymer poly-N-isopropylacrylamide (p-NIPAm) have been synthesized such that an energy transfer donor (phenanthrene) and an energy transfer acceptor (anthracene) are covalently localized in the core and shell, respectively. When the thermally induced particle deswelling is interrogated by photon correlation spectroscopy (PCS), a continuous (non-first order) phase transition is observed. Conversely, when the nonradiative energy transfer (NRET) efficiency is used to probe the collapse of these same particles, the phase transition event is observed to occur over a much smaller temperature range and approaches first-order (discontinuous) behavior. Furthermore, core-shell particles with differing shell thicknesses display identical phase transition temperatures when PCS is used to monitor the transition, while NRET measurements show a clear increase in collapse temperature as the shell thickness is increased. These apparently contradictory results are discussed in terms of a radial phase coexistence that exists in the microgel particles, which arises from a similarly radial inhomogeneity in the cross-linker concentration. The prospects for the NRET technique as a molecular-scale probe of nanostructured microgels are also discussed. PMID:11516270

Gan, D; Lyon, L A

2001-08-29

129

Photoinduced electron transfer in model systems of photosynthesis.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Hofstra, U.

1988-01-01

130

Particle Morphology and Interfacial Energy Transfer in CdSe/CdS Nanocrystals  

Science.gov (United States)

CdSe/CdS core-shell nanocrystal heterostructures are unique systems to study nanoscale energy migration. We perform single-particle excitation spectroscopy at low temperatures by monitoring both the luminescence intensity and energy of the core as a function of optical excitation energy in three different heterostructure shapes: spherical particles, rods, and tetrapods. In the tetrapod and rod structures, the shapes of the PLE spectra fall into one of two classes while the spherical particles all exhibit one universal form, which we attribute to the general shape and quantum confinement symmetry of the CdS shell. We confirm this assignment by correlated single particle SEM and PLE measurements. By resolving the core emission energy as a function of excitation energy, we identify two distinct exciton species in the tetrapods indicating the presence of a barrier that prevents charge transfer across the heterostructure interface [1]. [4pt] [1] Borys et al., Science (in press)

Borys, Nicholas; Walter, Manfred; Huang, Jing; Talapin, Dmitri; Lupton, John

2011-03-01

131

Devices which transfer electrons one-by-one  

International Nuclear Information System (INIS)

An introduction is given to the field of single-electron devices, which are electronic circuits across which electrons may be transferred one by one. Experiments are described on the single-junction box and the four-junction box, devices in which electrons were transferred to a metallic island and their presence detected using a single-electron electrometer. The single-junction box, the simpler of the two devices, allows one to control the thermally-averaged number of excess electrons on the metallic island, whereas with the four-junction box one can actually control the transfer of individual electrons. (author) 11 refs.; 5 figs

1992-02-01

132

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.)

1983-01-01

133

Electron transfer at sensitized semiconductor electrodes  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer from the excited state of sensitizing dyes to the conduction band of semiconductors has been studied through photoelectrochemical techniques. Two systems were analyzed in detail: rhodamine B on ZnO and rose bengal on TiO/sub 2/. Prior to electrochemical experimentation, the adsorption characteristics of these dyes were investigated using ZnO, ZnS, and TiO/sub 2/ single crystals as substrates. Absorbance measurements of the adsorbed dye were taken as a function of the solution concentration of the dye. Adsorption isotherms heats of adsorption were also established; they were similar to literature data reported for adsorption of these dyes on powdered substrates. Using the absorbance data, the quantum efficiency for photoinjection of electrons from rhodamine B into a ZnO electrode was determined to be 2.7 x 10/sup -2/. This value was independent of the dye surface concentration down to 50% coverage of the electrode. With the assumption that not all of the rhodamine B adsorbed on the electrode has the same rate of electron injection, a kinetic model for the time decay of the photocurrent was developed; data were analyzed according to this theory. A rate constant for photoreduction of the adsorbed dye was determined for the reducing agents. 86 references.

Spitler, M.T.

1977-03-01

134

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

Science.gov (United States)

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.

Gangineni, R. B.; Bellouard, C.; Duluard, A.; Negulescu, B.; Baraduc, C.; Gaudin, G.; Tiusan, C.

2014-05-01

135

Activation entropy of electron transfer reactions  

CERN Multimedia

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

136

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...

1998-01-01

137

Electronic and Nuclear Factors in Charge and Excitation Transfer  

Energy Technology Data Exchange (ETDEWEB)

We report the and/or state of several subprojects of our DOE sponsored research on Electronic and Nuclear Factors in Electron and Excitation Transfer: (1) Construction of an ultrafast Ti:sapphire amplifier. (2) Mediation of electronic interactions in host-guest molecules. (3) Theoretical models of electrolytes in weakly polar media. (4) Symmetry effects in intramolecular excitation transfer.

Piotr Piotrowiak

2004-09-28

138

Fabrication of a stable, switchable An/SAM-Au electrode with tunable electron transfer and excellent electrochemical properties  

International Nuclear Information System (INIS)

This paper describes the electrochemical properties, such as electrode reactivity, and interfacial capacitance of an anthracene/self-assembled monolayer (An/SAM) Au electrode prepared through controllable immersion of the dodecanethiol (C12SH) SAM-Au electrode in a THF solution of anthracene (An). The C12SH SAM almost totally blocks heterogeneous electron transfer between the bare Au electrode and Fe(CN)63-/4- in solution, but adsorption of the An molecules onto the SAM-Au electrode restores electron transfer. The prepared An/SAM-Au electrode possesses good reactivity without a remarkable barrier to heterogeneous electron transfer. On the other hand, the electroactive form of the An/SAM-Au electrode can be converted back to the non-electroactive form by immersing the electrode into pure THF

2008-10-15

139

Fabrication of a stable, switchable An/SAM-Au electrode with tunable electron transfer and excellent electrochemical properties  

Energy Technology Data Exchange (ETDEWEB)

This paper describes the electrochemical properties, such as electrode reactivity, and interfacial capacitance of an anthracene/self-assembled monolayer (An/SAM) Au electrode prepared through controllable immersion of the dodecanethiol (C{sub 12}SH) SAM-Au electrode in a THF solution of anthracene (An). The C{sub 12}SH SAM almost totally blocks heterogeneous electron transfer between the bare Au electrode and Fe(CN){sub 6}{sup 3-/4-} in solution, but adsorption of the An molecules onto the SAM-Au electrode restores electron transfer. The prepared An/SAM-Au electrode possesses good reactivity without a remarkable barrier to heterogeneous electron transfer. On the other hand, the electroactive form of the An/SAM-Au electrode can be converted back to the non-electroactive form by immersing the electrode into pure THF. (author)

Raoof, Jahan-Bakhsh; Ojani, Reza; Rashid-Nadimi, Sahar [Electroanalytical Chemistry Research Laboratory, Department of Analytical Chemistry, Faculty of Chemistry, Mazandaran University, 3rd Kilometer of Air Force Road, Postal Code: 47416-95447, Babolsar (Iran)

2008-10-15

140

Single and Accumulative Electron Transfer – Prerequisites for Artificial Photosynthesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photoinduced electron transfer is involved in a number of photochemical and photobiological processes. One example of this is photosynthesis, where the absorption of sunlight leads to the formation of charge-separated states by electron transfer. The redox equivalents built up by successive photoabsorption and electron transfer is further used for the oxidation of water and reduction of carbon dioxide to sugars. The work presented in this thesis is part of an interdisciplinary effort aiming a...

2010-01-01

 
 
 
 
141

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

Science.gov (United States)

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

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

2013-02-01

142

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

143

Interfacial energy level bending in a crystalline p/p-type organic heterostructure  

International Nuclear Information System (INIS)

A conduction channel was observed at the heterointerface of the crystalline p-type organic films copper phthalocyanine (CuPc) and 2,5-bis(4-biphenylyl) bithiophene (BP2T). Energy level bending at the interface is confirmed by photoemission spectroscopy, which verifies a charge transfer between CuPc and BP2T. This provides a further route to utilize interfacial electronic properties in functional devices and also documents the importance of reconsidering the interfacial electronic structure of organic heterostructures.

2011-05-16

144

Activation entropy of electron transfer reactions  

International Nuclear Information System (INIS)

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 continuum models is not supported by the microscopic theory. Also, the reorganization and overall solvation entropies are substantially larger in the microscopic theory compared to continuum models

2006-05-09

145

Photoinduced Electron-transfer Reaction of Pentafluoroiodobenzene with Alkenes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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.

Ping Cao; Zheng-Yu Long; Qing-Yun Chen

1997-01-01

146

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

147

Long-distance electron transfer from a triplet excited state  

Science.gov (United States)

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

Murtagh, James; Thomas, J. Kerry

148

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 �rn

2013-01-01

149

Particle size and interfacial effects on thermo-physical and heat transfer characteristics of water-based ?-SiC nanofluids  

International Nuclear Information System (INIS)

The effect of average particle sizes on basic macroscopic properties and heat transfer performance of ?-SiC/water nanofluids was investigated. The average particle sizes, calculated from the specific surface area of nanoparticles, were varied from 16 to 90 nm. Nanofluids with larger particles of the same material and volume concentration provide higher thermal conductivity and lower viscosity increases than those with smaller particles because of the smaller solid/liquid interfacial area of larger particles. It was also demonstrated that the viscosity of water-based nanofluids can be significantly decreased by pH of the suspension independently from the thermal conductivity. Heat transfer coefficients were measured and compared to the performance of base fluids as well as to nanofluids reported in the literature. Criteria for evaluation of the heat transfer performance of nanofluids are discussed and optimum directions in nanofluid development are suggested.

2010-05-28

150

Electron transfer reactions between excited atoms and molecules  

International Nuclear Information System (INIS)

Electron transfer reactions have been extensively studied for atoms in ground state colliding with molecules. On the contrary, few experiments have been performed for atoms excited above the first resonance states and it has been supposed by some authors that above a given degree of excitation, electron transfer becomes negligeable. By using a simple Landau-Zener model and a LCAO calculation of the coupling matrix element between ionic and covalent states for excited atoms and molecules with small electron affinities, we conclude that there is no limit to the electron transfer, in agreement with the experimental observation of ion pair formation for Rydberg atoms colliding with given molecules such as SF6

1984-01-01

151

The distance and temperature dependence of electron-transfer rates  

International Nuclear Information System (INIS)

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

1987-04-05

152

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

Science.gov (United States)

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

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

2013-03-01

153

Electron Transfer Dissociation of iTRAQ Labeled Peptide Ions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Triply and doubly charged iTRAQ (isobaric tagging for relative and absolute quantitation) labeled peptide cations from a tryptic peptide mixture of bovine carbonic anhydrase II were subjected to electron transfer ion/ion reactions to investigate the effect of charge bearing modifications associated with iTRAQ on the fragmentation pattern. It was noted that electron transfer dissociation (ETD) of triply charged or activated ETD (ETD + supplemental collisional activation of intact electron tran...

Han, Hongling; Pappin, Darryl J.; Ross, Philip L.; Mcluckey, Scott A.

2008-01-01

154

Heat Transfer Augmentation for Electronic Cooling  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Problem statement: The performance of electronic devices has been improving along with the rapid technology development. Cooling of electronic systems is consequently essential in controlling the component temperature and avoiding any hot spot. The study aims to review the present electronic cooling methods which are widely used in electronic devices. Approach: There are several methods to cool down the electronics components such as the pin-fin heat sink, confined jet impingeme...

Suabsakul Gururatana

2012-01-01

155

Quinone methide generation via photoinduced electron transfer.  

Science.gov (United States)

Photochemical activation of water-soluble 1,8-naphthalimide derivatives (NIs) as alkylating agents has been achieved by irradiation at 310 and 355 nm in aqueous acetonitrile. Reactivity in aqueous and neat acetonitrile has been extensively investigated by laser flash photolysis (LFP) at 355 nm, as well as by steady-state preparative irradiation at 310 nm in the presence of water, amines, thiols, and ethyl vinyl ether. Product distribution analysis revealed fairly efficient benzylation of the amines, hydration reaction, and 2-ethoxychromane generation, in the presence of ethyl vinyl ether, resulting from a [4 + 2] cycloaddition onto a transient quinone methide. Remarkably, we found that the reactivity was dramatically suppressed under the presence of oxygen and radical scavengers, such as thiols, which was usually associated with side product formation. In order to unravel the mechanism responsible for the photoreactivity of these NI-based molecules, a detailed LFP study has been carried out with the aim to characterize the transient species involved. LFP data suggest a photoinduced electron transfer (PET) involving the NI triplet excited state (?(max) 470 nm) of the NI core and the tethered quinone methide precursor (QMP) generating a radical ions pair NI(•-) (?(max) 410 nm) and QMP(•+). The latter underwent fast deprotonation to generate a detectable phenoxyl radical (?(max) 390 and 700 nm), which was efficiently reduced by the radical anion NI(•-), generating detectable QM. The mechanism proposed has been validated through a LFP investigation at 355 nm exploiting an intermolecular reaction between the photo-oxidant N-pentylnaphthalimide (NI-P) and a quaternary ammonium salt of a Mannich base as QMP (2a), in both neat and aqueous acetonitrile. Remarkably, these experiments revealed the generation of the model o-QM (?(max) 400 nm) as a long living transient mediated by the same reactivity pathway. Negligible QM generation has been observed under the very same conditions by irradiation of the QMP in the absence of the NI. Owing to the NIs redox and recognition properties, these results represent the first step toward new molecular devices capable of both biological target recognition and photoreleasing of QMs as alkylating species, under physiological conditions. PMID:21425810

Percivalle, Claudia; La Rosa, Andrea; Verga, Daniela; Doria, Filippo; Mella, Mariella; Palumbo, Manlio; Di Antonio, Marco; Freccero, Mauro

2011-05-01

156

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

1979-04-07

157

REFLECTIONS ON THE TWO-STATE ELECTRON TRANSFER MODEL.  

Energy Technology Data Exchange (ETDEWEB)

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

Brunschwig, B.S.

2000-01-12

158

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

2004-12-06

159

Chirped pulse control of long range electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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 {pi}-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.

Fainberg, B.D. [Department of Exact Sciences, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102 (Israel) and Raymond and Beverly Sackler Faculty of Exact Sciences, School of Chemistry, Tel-Aviv University, Tel-Aviv 69978 (Israel)]. E-mail: fainberg@hait.ac.il; Gorbunov, V.A. [Department of Exact Sciences, Holon Academic Institute of Technology, 52 Golomb Street, Holon 58102 (Israel); Lin, S.H. [Institute of Atomic and Molecular Science, Academia Sinica, P.O. Box 23-166, Taipei 106, Taiwan ROC (China)

2004-12-06

160

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 Eu_3"+ 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, Eu_3"+, 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

1982-01-01

 
 
 
 
161

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

162

A self-doping, O{sub 2}-stable, n-type interfacial layer for organic electronics  

Energy Technology Data Exchange (ETDEWEB)

Solid films of a water-soluble dicationic perylene diimide salt, perylene bis(2-ethyltrimethylammonium hydroxide imide), Petma{sup +}OH{sup -}, are strongly doped n-type by dehydration and reversibly de-doped by hydration. The hydrated films consist almost entirely of the neutral perylene diimide, PDI, while the dehydrated films contain {proportional_to}50% PDI anions. The conductivity increases by five orders of magnitude upon dehydration, probably limited by film roughness, while the work function decreases by 0.74 V, consistent with an n-type doping density increase of {proportional_to}12 orders of magnitude. Remarkably, the PDI anions are stable in dry air up to 120 C. The work function of the doped film, {phi} (3.96 V vs. vacuum), is unusually negative for an O{sub 2}-stable contact. Petma{sup +}OH{sup -} is also characterized as an interfacial layer, IFL, in two different types of organic photovoltaic cells. Results are comparable to state of the art cesium carbonate IFLs, but may improve if film morphology can be better controlled. The films are stable and reversible over many months in air and light. The mechanism of this unusual self-doping process may involve the change in relative potentials of the ions in the film caused by their deshielding and compaction as water is removed, leading to charge transfer when dry. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Reilly, Thomas H. III; Hains, Alexander W.; Chen, Hsiang-Yu; Gregg, Brian A. [National Renewable Energy Laboratory, Golden, CO (United States)

2012-04-15

163

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

164

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.

2010-03-15

165

Photoinduced electron transfer from DABCO to trans-nitrostilbenes  

Science.gov (United States)

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

Görner, Helmut; Schulte-Frohlinde, Dietrich

166

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

2010-03-25

167

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

Energy Technology Data Exchange (ETDEWEB)

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

Stevens, B.

1997-07-01

168

Distorted wave calculations for double electron transfer  

International Nuclear Information System (INIS)

The resonant double electron capture by alpha particles in helium targets is studied, at intermediate and high collision energies, using the Continuum Distorted Wave - Eikonal Initial State (CDW-EIS) model. Differential and total cross sections for capture into the He (1 s2) final state are calculated in the framework of an Independent Electron Approximation (IEA). Theoretical results are compared with the experimental data available at present for capture into any final state of helium. (author)

1991-08-04

169

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

1990-09-19

170

Nuclear interlevel transfer driven by electronic transitions  

International Nuclear Information System (INIS)

We show how a gamma-ray laser might be made by optically exciting a transfer of population from a long-lived isomer to an energetically adjacent short-lived state of the same nucleus. We compare the advantages of using transitions of high multipolarity versus transitions of low multi-polarity. Preliminary numerical investigations of the mechanism show it to be somewhat favorable. 35 refs., 4 figs

1985-05-21

171

Interfacial and bulk electronic properties of complex oxides and buried interfaces probed by HAXPES  

Energy Technology Data Exchange (ETDEWEB)

Highlights: ? Analysis of well screened satellites and electron screening in complex oxides ? Identification of DOS electronic character in LSMO ? Analysis of s-states contribution in organic spintronics systems. -- Abstract: Designing, understanding and controlling the properties of engineered and functional materials, based on oxides and buried interfaces, is one of the most flourishing research fields and one of the major challenges faced by contemporary solid state science and technology. Often, a reliable spectroscopic analysis of such systems is hindered by surface effects, as structural distortion, stoichiometry changes, strong reactivity to external agent and major atomic and/or electronic reconstruction to name but a few. Hard X-Ray PhotoEmission Spectroscopy (HAXPES) is a powerful technique to overcome such limitations, allowing to monitor truly bulk sensitive properties. We report selected HAXPES results for manganese-based oxides, both in films and crystal forms, and for buried metal–organic interfaces, with the aim of highlighting some of the important features such technique brings in the analysis of electronic properties of the solids.

Borgatti, F. [CNR – Istituto per lo Studio dei Materiali Nanostrutturati (ISMN),Via Piero Gobetti 101, 40129 Bologna (Italy); Offi, F. [CNISM and Dipartimento di Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Rome (Italy); Torelli, P. [CNR, Istituto Officina dei Materiali (IOM), Lab. TASC, in Area Science Park, S.S. 14 km 163.5, I-34149 Trieste (Italy); Monaco, G. [European Synchrotron Radiation Facility, BP 220, 38043 Grenoble (France); Panaccione, G., E-mail: panaccioneg@elettra.trieste.it [CNR, Istituto Officina dei Materiali (IOM), Lab. TASC, in Area Science Park, S.S. 14 km 163.5, I-34149 Trieste (Italy)

2013-10-15

172

Interfacial and bulk electronic properties of complex oxides and buried interfaces probed by HAXPES  

International Nuclear Information System (INIS)

Highlights: ? Analysis of well screened satellites and electron screening in complex oxides ? Identification of DOS electronic character in LSMO ? Analysis of s-states contribution in organic spintronics systems. -- Abstract: Designing, understanding and controlling the properties of engineered and functional materials, based on oxides and buried interfaces, is one of the most flourishing research fields and one of the major challenges faced by contemporary solid state science and technology. Often, a reliable spectroscopic analysis of such systems is hindered by surface effects, as structural distortion, stoichiometry changes, strong reactivity to external agent and major atomic and/or electronic reconstruction to name but a few. Hard X-Ray PhotoEmission Spectroscopy (HAXPES) is a powerful technique to overcome such limitations, allowing to monitor truly bulk sensitive properties. We report selected HAXPES results for manganese-based oxides, both in films and crystal forms, and for buried metal–organic interfaces, with the aim of highlighting some of the important features such technique brings in the analysis of electronic properties of the solids

2013-10-01

173

Photoinduced electron transfer from a conducting polymer to buckminsterfullerene  

Energy Technology Data Exchange (ETDEWEB)

Evidence for photoinduced electron transfer form the excited state of a conducting polymer onto buckminsterfullerene, C{sub 60}, is reported. After photo-excitation of the conjugated polymer with light of energy greater than the {pi}-{pi} gap, an electron transfer to the C{sub 60} molecule is initiated. Photoinduced optical absorption studies demonstrate a different excitation spectrum for the composite as compared to the separate components, consistent with photo-excited charge transfer. A photoinduced electron spin resonance signal exhibits signatures of both the conducting polymer cation and the C{sub 60} anion. Because the photoluminescence in the conducting polymer is quenched by interaction with C{sub 60}, the data imply that charge transfer form the excited state occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures. 34 refs., 4 figs.

Sarciftci, N.S.; Smilowitz, L.; Heeger, A.J. [Univ. of California, Santa Barbara, CA (United States)] [and others

1992-11-27

174

Small reorganization energies of photoinduced electron transfer between spherical fullerenes.  

Science.gov (United States)

Rate constants of photoinduced electron transfer between spherical fullerenes were determined using triscandium nitride encapsulated C80 fullerene (Sc3N@C80) as an electron donor and the triplet excited state of lithium ion-encapsulated C60 fullerene (Li(+)@C60) as an electron acceptor in polar and less polar solvents by laser flash photolysis measurements. Upon nanosecond laser excitation at 355 nm of a benzonitrile (PhCN) solution of Li(+)@C60 and Sc3N@C80, electron transfer from Sc3N@C80 to the triplet excited state [(3)(Li(+)@C60)*] occurred to produce Sc3N@C80(•+) and Li(+)@C60(•-) (?(max) = 1035 nm). The rates of the photoinduced electron transfer were monitored by the decay of absorption at ?(max) = 750 nm due to (3)(Li(+)@C60)*. The second-order rate constant of electron transfer from Sc3N@C80 to (3)(Li(+)@C60)* was determined to be k(et) = 1.5 × 10(9) M(-1) s(-1) from dependence of decay rate constant of (3)(Li(+)@C60)* on the Sc3N@C80 concentration. The rate constant of back electron transfer from Li(+)@C60(•-) to Sc3N@C80(•+) was also determined to be k(bet) = 1.9 × 10(9) M(-1) s(-1), which is close to be the diffusion limited value in PhCN. Similarly, the rate constants of photoinduced electron transfer from C60 to (3)(Li(+)@C60)* and from Sc3N@C80 to (3)C60* were determined together with the back electron-transfer reactions. The driving force dependence of log k(et) and log k(bet) was well fitted by using the Marcus theory of outer-sphere electron transfer, in which the internal (bond) reorganization energy (?i) was estimated by DFT calculations and the solvent reorganization energy (?s) was calculated by the Marcus equation. When PhCN was replaced by o-dichlorobenzene (o-DCB), the ? value was decreased because of the smaller solvation changes of highly spherical fullerenes upon electron transfer in a less polar solvent. PMID:23862971

Kawashima, Yuki; Ohkubo, Kei; Fukuzumi, Shunichi

2013-08-01

175

Mechanistic study of direct electron transfer in bilirubin oxidase  

International Nuclear Information System (INIS)

The mechanism of direct electron transfer in multicopper oxidases is not well understood. In this work, the mechanism of oxygen reduction in Bilirubin oxidase (BOD) is analyzed using a rotating ring-disc electrode (RRDE). The glassy carbon disc potential was swept from 0.8 V to 0 V while the platinum ring potential was held at 0.8 V, resulting currents were measured. Minimal hydrogen peroxide evolution from BOD is detected on the Pt ring, independent of rotation rate. The electron transfer rate constant, ket, is calculated to be 1.14 × 10?3 cm/s. The number of electrons transferred per molecule of oxygen is calculated to be 3.92 electrons using Koutecky–Levich equation and 3.7 ± 0.2 electrons using mass/charge balance which corresponds to 7.5 ± 5% of oxygen reduction via the 2 electron pathway with a hydrogen peroxide intermediate. The 4 electron transfer mechanism is preferred because it is more efficient than the two electron mechanism.

2012-02-01

176

Interfacial tension phenomenon and mass transfer process in the reservoir brine-CO2 system at high pressures and elevated temperatures. Paper no. IGEC-1-090  

International Nuclear Information System (INIS)

In this paper, an experimental technique is developed to study the dynamic interfacial tension (IFT) phenomenon and the mass transfer process in a reservoir brine-CO2 system at high pressures and elevated temperatures, based on the axisymmetric drop shape analysis (ADSA) for the pendant drop case. More specifically, the dynamic IFT between the reservoir brine and CO2 is measured under different pressures at two constant temperatures. It is found that the dynamic IFT gradually reduces to a constant value, which is referred to as the equilibrium IFT. The equilibrium IFT decreases as the pressure increases, whereas it increases as the temperature increases. It is also found that there exists two-way mass transfer between the brine phase and CO2. This two-way mass transfer results in the so-called brine swelling effect, shrinking effect and the reservoir brine-CO2 interface disappearance. The brine swelling effect is observed at all the pressures and temperatures tested, while the brine shrinking effect occurs only at high pressures and a lower temperature (T=27oC). Furthermore, at an elevated temperature (T=58oC), no pendant brine drop can be observed in CO2 phase at P. 12.238 MPa. The observed two-way mass transfer between the reservoir brine and CO2 phase may significantly affect accurate determination of the maximum sequestrable CO2 in a depleted reservoir or in a saline aquifer. (author)

2005-06-12

177

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.

178

[Electrochemical measurement of intraprorein and interprotein electron transfer].  

Science.gov (United States)

Intramolecular and intermolecular direct (unmediated) electron transfer was studied by means of electrochemical techniques in flavohemoprotein cytochrome P450 BM3 (CYP102A1 from Bacillius megaterium) and between cytochrome b5 and cytochrome c. Flavohemoprotein cytochrome P450 BM3 was immobilized on a screen printed graphite electrode, modified with a biocompatible nanocomposite material based on the didodecyldimethylammonium bromide DDAB and gold nanoparticles. Analytical characterictics of DDAB/Au/P450 BM3 electrodes were studied with cyclic voltammetry and square wave voltammetry. It was shown that intramolecular electron transfer was realized between diflavin (FAD/FMN) and heme domain of CYP102A1. An electron transport chain of flavohemoprotein P450 BM3 immobilized at nanostructued electrode is realized as: electrode --> FAD --> FMN --> heme. Electron transfer occurs inside the protein, and it is an evidence of functional interaction between diflavin and heme domains. The effect of a substrate (lauric acid) or inhibitors (metyrapone or imidazole) binding on the electrochemical parameters of flavohemoprotein P450 BM3 was also studied. Interprotein electron transfer was analyzed between cytochrome b5 and cytochrome c. Electrochemical analysis revealed that electron transfer takes place in protein-protein complexes with participants possessing different redox potentials. PMID:24159813

Shumiantseva, V V; Bulko, T V; Lisitsina, V B; Urlakher, V B; Kuzikov, A B; Suprun, E V; Archakov, A I

2013-01-01

179

Intramolecular electron transfer and dehalogenation of nitroaromatic anion radicals  

International Nuclear Information System (INIS)

A series of nitroaromatic compounds, containing Cl, Br, or tosyl groups at various positions, were synthesized and studied by pulse radiolysis in aqueous alcohol solutions. One-electron reduction of the compounds produces the anion radicals which then undergo an intramolecular electron transfer and eliminate X- (Cl-, Br-, or TsO-). The rates of X- elimination vary over six orders of magnitude and are affected by the C-X bond dissociation energies, the size and nature of the group bridging the X with the ? system, and the relative positions of these groups. Intramolecular electron transfer through space is also demonstrated

1983-02-09

180

Electron transfer reactions in microporous solids  

Energy Technology Data Exchange (ETDEWEB)

Basic thrust the research program involves use of microporous solids (zeolites, clays, layered and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. Purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H[sub 2] and I[sub 3][sup [minus

Mallouk, T.E.

1993-01-01

 
 
 
 
181

CRADA Final Report for CRADA No. ORNL99-0544, Interfacial Properties of Electron Beam Cured Composites  

Energy Technology Data Exchange (ETDEWEB)

Electron beam (EB) curing is a technology that promises, in certain applications, to deliver lower cost and higher performance polymer matrix composite (PMC) structures compared to conventional thermal curing processes. PMCs enhance performance by making products lighter, stronger, more durable, and less energy demanding. They are essential in weight- and performance-dominated applications. Affordable PMCs can enhance US economic prosperity and national security. US industry expects rapid implementation of electron beam cured composites in aircraft and aerospace applications as satisfactory properties are demonstrated, and implementation in lower performance applications will likely follow thereafter. In fact, at this time and partly because of discoveries made in this project, field demonstrations are underway that may result in the first fielded applications of electron beam cured composites. Serious obstacles preventing the widespread use of electron beam cured PMCs in many applications are their relatively poor interfacial properties and resin toughness. The composite shear strength and resin toughness of electron beam cured carbon fiber reinforced epoxy composites were about 25% and 50% lower, respectively, than those of thermally cured composites of similar formulations. The essential purpose of this project was to improve the mechanical properties of electron beam cured, carbon fiber reinforced epoxy composites, with a specific focus on composite shear properties for high performance aerospace applications. Many partners, sponsors, and subcontractors participated in this project. There were four government sponsors from three federal agencies, with the US Department of Energy (DOE) being the principal sponsor. The project was executed by Oak Ridge National Laboratory (ORNL), NASA and Department of Defense (DOD) participants, eleven private CRADA partners, and two subcontractors. A list of key project contacts is provided in Appendix A. In order to properly manage the large project team and properly address the various technical tasks, the CRADA team was organized into integrated project teams (IPT's) with each team focused on specific research areas. Early in the project, the end user partners developed ''exit criteria'', recorded in Appendix B, against which the project's success was to be judged. The project team made several important discoveries. A number of fiber coatings or treatments were developed that improved fiber-matrix adhesion by 40% or more, according to microdebond testing. The effects of dose-time and temperature-time profiles during the cure were investigated, and it was determined that fiber-matrix adhesion is relatively insensitive to the irradiation procedure, but can be elevated appreciably by thermal postcuring. Electron beam curable resin properties were improved substantially, with 80% increase in electron beam 798 resin toughness, and {approx}25% and 50% improvement, respectively, in ultimate tensile strength and ultimate tensile strain vs. earlier generation electron beam curable resins. Additionally, a new resin electron beam 800E was developed with generally good properties, and a very notable 120% improvement in transverse composite tensile strength vs. earlier generation electron beam cured carbon fiber reinforced epoxies. Chemical kinetics studies showed that reaction pathways can be affected by the irradiation parameters, although no consequential effects on material properties have been noted to date. Preliminary thermal kinetics models were developed to predict degree of cure vs. irradiation and thermal parameters. These models are continually being refined and validated. Despite the aforementioned impressive accomplishments, the project team did not fully realize the project objectives. The best methods for improving adhesion were combined with the improved electron beam 3K resin to make prepreg and uni-directional test laminates from which composite properties could be determined. Nevertheless, only minor improvements in the composite shear strengt

Janke, C.J.

2005-10-17

182

Electron transfer reactions between excited atoms and molecules  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer reactions have been extensively studied for atoms in ground state colliding with molecules. On the contrary, few experiments have been performed for atoms excited above the first resonance states and it has been supposed by some authors that above a given degree of excitation, electron transfer becomes negligeable. By using a simple Landau-Zener model and a LCAO calculation of the coupling matrix element between ionic and covalent states for excited atoms and molecules with small electron affinities, we conclude that there is no limit to the electron transfer, in agreement with the experimental observation of ion pair formation for Rydberg atoms colliding with given molecules such as SF/sub 6/.

Astruc, J.P.; Barbe, R.; Schermann, J.P. (Laboratoire de Physique des Lasers, 93 - Villetaneuse (France))

1984-01-01

183

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)

1982-10-10

184

Electron transfer from nucleobase electron adducts to 5-bromouracil: a radiation chemical study  

International Nuclear Information System (INIS)

Electron transfer to 5-bromouracil from their nucleobase electron adducts and their protonated forms has been studied by product analysis. When an electron is transferred to 5-bromouracil, the ensuing 5-bromouracil radical anion rapidly loses a bromide ion. The uracilyl radical thus formed reacts with added t-butanol, yielding uracil. From the uracil yields measured as a function of (N)/(5-BrU) after ?-radiolysis of Ar-saturated solutions it is concluded that the hetero atom protonated forms transfer electron quantitatively to 5-bromouracil. (author). 3 refs., 1 fig

1996-01-01

185

Effect of proton transfer on the electronic coupling in DNA  

International Nuclear Information System (INIS)

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

2006-06-20

186

Measuring electron and hole transfer in core/shell nanoheterostructures.  

Science.gov (United States)

Using femtosecond transient absorption and time-resolved photoluminescence spectroscopy, we studied the electron versus hole dynamics in photoexcited quasi-type-II heterostructured nanocrystals with fixed CdTe core radii and varying CdSe shell coverage. By choosing the pump wavelength in resonance with the core or the shell states, respectively, we were able to measure the excited electron and hole dynamics selectively. Both, the core- and the shell-excited CdTe/CdSe nanocrystals showed the same spectral emission and photoluminescence lifetimes, indicating that ultrafast electron and hole transfer across the core/shell interface resulted in the identical long-lived charge transfer state. Both charge carriers have subpicosecond transfer rates through the interface, but the subsequent relaxation rates of the hole (?(dec) ? 800 ps) and electron (?(avg) ? 8 ps) are extremely different. On the basis of the presented transient absorption measurements and fitting of the steady-state spectra, we find that the electron transfer occurs in the Marcus inverted region and mixing between the CdTe exciton and charge transfer states takes place and therefore needs to be considered in the analysis. PMID:21671650

Chuang, Chi-Hung; Doane, Tennyson L; Lo, Shun S; Scholes, Gregory D; Burda, Clemens

2011-07-26

187

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

188

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.

Rotaru, Amelia-Elena

2014-01-01

189

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

190

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

2013-09-15

191

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)  

Energy Technology Data Exchange (ETDEWEB)

Highlights: • Design, preparation, testing and characterization of uniform sputtered films. • Interfacial charge transfer from the Ag{sub 2}O (cb) to the lower laying Ta{sub 2}O{sub 5} (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 N{sub 2} and O{sub 2} 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 Ta{sub 2}O{sub 5} and Ag-species. The shifts observed for the XPS peaks have been assigned to AgO to Ag{sub 2}O and Ag{sup 0}, and are a function of the applied sputtering times. The mechanism of interfacial charge transfer (IFCT) from the Ag{sub 2}O conduction band (cb) to the lower laying Ta{sub 2}O{sub 5} (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.

Rtimi, S., E-mail: sami.rtimi@epfl.ch [Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-GPAO, Station 6, CH-1015 Lausanne (Switzerland); UR Catalyse/Matériaux pour l‘Environnement et les Procédés (URCMEP), Faculté des Sciences de Gabès, Université de Gabès, 6072 Gabès (Tunisia); Sanjines, R. [Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-IPMC-LNNME, Bat PH, Station 3, CH1015 Lausanne (Switzerland); Pulgarin, C., E-mail: cesar.pulgarin@epfl.ch [Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-GPAO, Station 6, CH-1015 Lausanne (Switzerland); Houas, A. [UR Catalyse/Matériaux pour l‘Environnement et les Procédés (URCMEP), Faculté des Sciences de Gabès, Université de Gabès, 6072 Gabès (Tunisia); Lavanchy, J.-C. [Université de Lausanne, IMG, Centre d’Analyse Minérale, Bat Anthropole, CH-1015 Lausanne (Switzerland); Kiwi, J. [Ecole Polytechnique Fédérale de Lausanne, EPFL-SB-ISIC-LPI, Bat Chimie, Station 6, CH1015 Lausanne (Switzerland)

2013-09-15

192

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

Energy Technology Data Exchange (ETDEWEB)

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

1992-12-31

193

[Electron transfer, ionization, and excitation in atomic collisions  

International Nuclear Information System (INIS)

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

1992-01-01

194

Optical and interfacial electronic properties of diamond-like carbon films  

Science.gov (United States)

Hard, semitransparent carbon films were prepared on oriented polished crystal wafers of silicon, indium phosphide and gallium arsenide, as well as on KBr and quartz. Properties of the films were determined using IR and visible absorption spectrocopy, ellipsometry, conductance-capacitance spectroscopy and alpha particle-proton recoil spectroscopy. Preparation techniques include RF plasma decomposition of methane (and other hydrocarbons), ion beam sputtering, and dual-ion-beam sputter deposition. Optical energy band gaps as large as 2.7 eV and extinction coefficients lower than 0.1 at long wavelengths are found. Electronic state densities at the interface with silicon as low as 10 to the 10th states/eV sq cm per were found.

Woollam, J. A.; Natarajan, V.; Lamb, J.; Khan, A. A.; Bu-Abbud, G.; Banks, B.; Pouch, J.; Gulino, D. A.; Domitz, S.; Liu, D. C.

1984-01-01

195

Sub-Thermal Electron Transfer in Semiconductor Quantum Structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate non-equilibrium charge transfer processes by performing high-resolution transport spectroscopy. Unprecedented spectral resolution is obtained by using electrostatically defined quantum dots for energy-selective emission and detection which furthermore offers a high degree of tunability of relevant experimental parameters. Strikingly, we observe that the spectral width of elastically transferred electrons can be substantially smaller than the thermal energy $k_...

Ro?ssler, Clemens; Burkhard, Simon; Kra?henmann, Tobias; Ro?o?sli, Marc; Ma?rki, Peter; Basset, Julien; Ihn, Thomas; Ensslin, Klaus; Reichl, Christian; Wegscheider, Werner

2014-01-01

196

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?...

2011-01-01

197

Gaussian fluctuations and linear response in an electron transfer protein  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In response to charge separation or transfer, polar liquids respond in a simple linear fashion. A similar linear response for proteins might be expected from the central limit theorem and is postulated in widely used theories of protein electrostatics, including the Marcus electron transfer theory and dielectric continuum theories. Although these theories are supported by a variety of experimental data, the exact validity of a linear protein dielectric response has been difficult to determine...

2002-01-01

198

Influence of interfacial reaction upon atomic diffusion studied by in situ Auger electron spectroscopy  

Science.gov (United States)

Pd reaction on Si(001) substrate was studied under ultra-high vacuum using in situ real time Auger electron spectroscopy (AES). Comparison with in situ real time X-ray diffraction measurements performed on the same samples showed that the AES intensity variations observed during isothermal annealing give information concerning the kinetics of three consecutive phenomena: i) Pd2Si growth, ii) Pd dissolution in Pd2Si, and iii) Si surface segregation on Pd2Si. The kinetics related to these three phenomena allowed to determine, in the same samples, the average effective atomic diffusion during growth, and the Si and Pd self-diffusion after growth in Pd2Si. Atomic transport during growth was found to be several orders of magnitude faster than Si and Pd diffusion after growth under the same experimental conditions. This effect is assumed to be related to point-defect injection in the Pd2Si layer during growth, due to Pd–Si reaction at Pd/Pd2Si and Pd2Si/Si interfaces.

Portavoce, A.; Hoummada, K.; Dahlem, F.

2014-06-01

199

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

200

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

 
 
 
 
201

High-pressure effects on intramolecular electron transfer compounds  

International Nuclear Information System (INIS)

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

2002-11-11

202

High-pressure effects on intramolecular electron transfer compounds  

Energy Technology Data Exchange (ETDEWEB)

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 Liming [Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080 (China); Zhong Bo [Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080 (China); Li Hong [Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080 (China); Zhang Baowen [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100101 (China); Li Yi [Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100101 (China); Yang Guoqiang [Laboratory of Photochemistry, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080 (China)

2002-11-11

203

A role for excreted quinones in extracellular electron transfer  

Science.gov (United States)

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

Newman, Dianne K.; Kolter, Roberto

2000-05-01

204

Intramolecular electron transfer in nitrite reductase studied by pulse radiolysis  

International Nuclear Information System (INIS)

We report the evidence for the electron-transfer reaction between two copper sites in nitrite reductase from Achromobacter cycloclastes IAM 1013 by pulse radiolysis. Type 1 Cu sites in native (type 1 Cu : type 2 Cu = 1 : 0.5) and type 2 Cu-depleted (T2D) nitrite reductase are reduced with N-methylnicotinamide radical generated by the hydrated electron. The reductions of the coppers in the both enzymes give second-order rate constants of (3.4 - 3.5) x 108 M-1s-1. In the case of the native enzyme, moreover, the recovery of the absorbance of reduced type 1 Cu is observed (about 35 %). This finding suggests the intramolecular electron transfer from type 1 Cu to type 2 Cu, because T2D nitrite reductase does not show the recovery of the absorption band at all. The electron-transfer occurs with an observed first order rate constant of 1400 s-1. The incomplete electron transfer from type 1 Cu to type 2 Cu are due to the difference between the redox potential of two Cu sites. (author)

1995-03-01

205

Energy and electron transfer processes in polymethine dyes  

Science.gov (United States)

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 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 Förster energy transfer radius calculated from the time-resolved data exceeds the value received from the overlap integral by 15%, indicating deviation from a normal Förster 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.

Feller, Karl-Heinz; Gadonas, Roaldas

1996-04-01

206

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

207

Role of direct microbial electron transfer in corrosion of steels  

Digital Repository Infrastructure Vision for European Research (DRIVER)

It has recently been discovered that many microbial species have the capacity to connect their metabolism to solid electrodes, directly exchanging electrons with them through membrane-bound redox compounds,nevertheless such a direct electron transfer pathway has been evoked rarely in the domain of microbial corrosion. Here was evidenced for the first time that the bacterium Geobacter sulfurreducens is able to increase the free potential of 304 L stainless steel up to 443 mV in only a few hour...

2009-01-01

208

Resonant optical electron transfer in one-dimensional multiwell structures  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider coherent single-electron dynamics in the one-dimensional nanostructure under resonant electromagnetic pulse. The structure is composed of two deep quantum wells positioned at the edges of structure and separated by a sequence of shallow internal wells. We show that complete electron transfer between the states localized in the edge wells through one of excited delocalized states can take place at discrete set of times provided that the pulse frequency matches one...

Tsukanov, A. V.

2008-01-01

209

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

210

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

211

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

2013-01-01

212

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

Directory of Open Access Journals (Sweden)

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

Nibbering Erik T. J.

2013-03-01

213

Electronic structure charge transfer excitations, and high temperature superconductivity  

International Nuclear Information System (INIS)

The high precision local density electronic band structure results (for YBa2Cu3O7, YBa2Cu3O6, and GdBa2Cu3O7) lead to the possibly important role of charge transfer excitations as the mechanism of high Tc superconductivity. They explain the coexistence of magnetism and superconductivity in the high Tc rare-earth superconductors

1988-01-01

214

Electronic Structure, Charge Transfer Excitations and High Temperature Superconductivity.  

Science.gov (United States)

High precision local density electronic band structure results (for YBa sub 2 Cu sub 3 O sub 7 , YBa sub 2 Cu sub 3 O sub 6 and GdBa sub 2 Cu sub 3 O sub 7 ) lead to the possibly important role of charge transfer excitations as the mechanism of high T/sub...

A. J. Freeman J. Yu S. Massidda D. D. Koelling

1987-01-01

215

77 FR 30923 - Electronic Fund Transfers (Regulation E)  

Science.gov (United States)

...3170-AA22 Electronic Fund Transfers (Regulation E) AGENCY: Bureau of Consumer Financial Protection...issue a proposal to extend the Regulation E protections to GPR cards. Your comments...cards'' such as payroll cards, Regulation E generally does not apply to GPR cards....

2012-05-24

216

D Simulation for Maximizing Electron Transfer Efficiency in Thick GEMS  

Science.gov (United States)

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

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

2012-08-01

217

Reduced density matrix hybrid approach: Application to electronic energy transfer  

CERN Document Server

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 t...

Berkelbach, Timothy C; Reichman, David R

2011-01-01

218

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

219

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

220

Electron solvation in water clusters following charge transfer from iodide  

International Nuclear Information System (INIS)

The dynamics following charge transfer to solvent from iodide to a water cluster are studied using time-resolved photoelectron imaging of I-(H2O)n and I-(D2O)n clusters with n?28. The results show spontaneous conversion, on a time scale of ?1 ps, from water cluster anions with surface-bound electrons to structures in which the excess electron is more strongly bound and possibly more internalized within the solvent network. The resulting dynamics provide valuable insight into the electron solvation dynamics in water clusters and the relative stabilities between recently observed isomers of water cluster anions

2005-12-15

 
 
 
 
221

Electron solvation in water clusters following charge transfer from iodide.  

Science.gov (United States)

The dynamics following charge transfer to solvent from iodide to a water cluster are studied using time-resolved photoelectron imaging of I-(H2O)n and I-(D2O)n clusters with n< or =28. The results show spontaneous conversion, on a time scale of approximately 1 ps, from water cluster anions with surface-bound electrons to structures in which the excess electron is more strongly bound and possibly more internalized within the solvent network. The resulting dynamics provide valuable insight into the electron solvation dynamics in water clusters and the relative stabilities between recently observed isomers of water cluster anions. PMID:16392904

Verlet, Jan R R; Kammrath, Aster; Griffin, Graham B; Neumark, Daniel M

2005-12-15

222

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

223

Inclusive electron - nucleus scattering at large momentum transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

1999-03-01

224

Electron Transfer in DNA through magnetic bound states  

CERN Document Server

Electron transfer (ET) via quantum mechanical tunneling between well separated donor (D) and acceptor (A) complexes is part of such biological processes as respiration, photosynthesis, and possibly DNA repair or damage. Data and theory for ET in proteins give a typical tunneling length of 0.1 nm. In contrast, fluorescence quenching in DNA at D/A distances of 4 nm or more suggests ET with tunneling lengths of order 1 nm. We show how such long ranged ET can be mediated by rapidly forming magnetic Kondo bound states (KS) arising from: (1) strong electron interactions and magnetic moments on D and/or A complexes satisfying suitable energy requirements, and (2) "quantum deconfinement" of electrons through extended bridge molecular orbitals. Realistic long range Coulomb interaction strengths between bridge electrons and localized D/A charges modestly enhance these ET rates.

Cox, D L; Pati, S K

2000-01-01

225

Radiative electron transfer in planar donor acceptor quinoxaline derivatives  

Science.gov (United States)

Synthetic and spectral studies have been performed for a family of electron donor-acceptor (D-A) quinoxaline derivatives possessing an aromatic amine as an electron donor. A photophysical behaviour of the compounds with an internal degree of freedom for internal D-A rotation and their rigid analogues with a fixed planar conformation appears to be very similar. Electronic transition dipole moments related to the charge-transfer (CT) absorption and fluorescence are determined by both the direct interactions between the 1CT and ground states and by the contributions from the locally excited configurations. The radiative properties of the D-A systems under study can be explained in terms of the simple model which assumes that the electronic coupling elements are mainly determined by the interactions between the atoms forming the A-D bond.

Czerwieniec, Rafa?; Herbich, Jerzy; Kapturkiewicz, Andrzej; Nowacki, Jacek

2000-08-01

226

Intramolecular Electron Transfer in Phenoxylate and Catecholate based Molecular Systems  

Digital Repository Infrastructure Vision for European Research (DRIVER)

La Tesi "Intramolecular Electron Transfer in Phenoxylate and Catecholate Based Molecular Systems" es situa entre el camp de la química inorgànica i la química física. L'objectiu principal és l'estudi dels diversos mecanismes de transferència electrònica intramolecular (TEI), degut al seu interès en camps emergents com l'electrònica molecular. Els complexes de valència-mixte (VM) formats per un lligand orgànic electro-actiu i un ió metàl·lic amb almenys dos estats d'oxida...

2008-01-01

227

Intramolecular electron transfer in phenoxylate and catecholate based molecular systems/  

Digital Repository Infrastructure Vision for European Research (DRIVER)

La Tesi "Intramolecular Electron Transfer in Phenoxylate and Catecholate Based Molecular Systems" es situa entre el camp de la química inorgànica i la química física. L'objectiu principal és l'estudi dels diversos mecanismes de transferència electrònica intramolecular (TEI), degut al seu interès en camps emergents com l'electrònica molecular. Els complexes de valència-mixte (VM) formats per un lligand orgànic electro-actiu i un ió metàl·lic amb almenys dos estats d'oxida...

2009-01-01

228

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

229

Dimers of Azurin as model systems for electron transfer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis describes the investigation of crosslinked complexes of the blue copper protein azurin by means of spectroscopic techniques such as Uv-Vis and NMR as well as by X-ray crystallography. These non-physiological dimers serve as model systems for interprotein electron transfer (ET) and allow the investigation of various parameters that can influence the ET dynamics. By site-directed mutagenesis several mutant complexes have been created with tunable properties and/or high rates of elec...

Jongh, Thyra Estrid

2006-01-01

230

Marcus wins nobel prize in chemistry for electron transfer theory  

Energy Technology Data Exchange (ETDEWEB)

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.

Levi, B.G.

1993-01-01

231

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 ...

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

2011-01-01

232

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

1993-01-01

233

Reorganization Energy for Internal Electron Transfer in Multicopper Oxidases.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have calculated the reorganization energy for the intramolecular electron transfer between the reduced type 1 copper site and the peroxy intermediate of the trinuclear cluster in the multicopper oxidase CueO. The calculations are performed at the combined quantum mechanics and molecular mechanics (QM/MM) level, based on molecular dynamics simulations with tailored potentials for the two copper sites. We obtain a reorganization energy of 91-133 kJ/mol, depending on the theoretical treatment...

2011-01-01

234

Intramolecular electron transfer in single-site-mutated azurins  

DEFF Research Database (Denmark)

Single-site mutants of the blue, single-copper protein, azurin, from Pseudomonas aeruginosa were reduced by CO2- radicals in pulse radiolysis experiments. The single disulfide group was reduced directly by CO2- with rates similar to those of the native protein [Farver, O., & Pecht, I. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 6968-6972]. The RSSR- radical produced in the above reaction was reoxidized in a slower intramolecular electron-transfer process (30-70 s-1 at 298 K) concomitant with a further reduction of the Cu(II) ion. The temperature dependence of the latter rates was determined and used to derive information on the possible effects of the mutations. The substitution of residue Phe114, situated on the opposite side of Cu relative to the disulfide, by Ala resulted in a rate increase by a factor of almost 2. By assuming that this effect is only due to an increase in driving force, lambda = 135 kJ mol-1 for the reorganization energy was derived. When Trp48, situated midway between the donor and the acceptor, was replaced by Leu or Met, only a small change in the rate of intramolecular electron transfer was observed, indicating that the aromatic residue in this position is apparently only marginally involved in electron transfer in wild-type azurin. Pathway calculations also suggest that a longer, through-backbone path is more efficient than the shorter one involving Trp48. The former pathway yields an exponential decay factor, beta, of 6.6 nm-1. Another mutation, raising the electron-transfer driving force, was produced by changing the Cu ligand Met121 to Leu, which increases the reduction potential by 100 mV.(ABSTRACT TRUNCATED AT 250 WORDS)

Farver, O; Skov, L K

1993-01-01

235

Mitochondrial copper(I) transfer from Cox17 to Sco1 is coupled to electron transfer.  

Science.gov (United States)

The human protein Cox17 contains three pairs of cysteines. In the mitochondrial intermembrane space (IMS) it exists in a partially oxidized form with two S-S bonds and two reduced cysteines (HCox17(2S-S)). HCox17(2S-S) is involved in copper transfer to the human cochaperones Sco1 and Cox11, which are implicated in the assembly of cytochrome c oxidase. We show here that Cu(I)HCox17(2S-S), i.e., the copper-loaded form of the protein, can transfer simultaneously copper(I) and two electrons to the human cochaperone Sco1 (HSco1) in the oxidized state, i.e., with its metal-binding cysteines forming a disulfide bond. The result is Cu(I)HSco1 and the fully oxidized apoHCox17(3S-S), which can be then reduced by glutathione to apoHCox17(2S-S). The HSco1/HCox17(2S-S) redox reaction is thermodynamically driven by copper transfer. These reactions may occur in vivo because HSco1 can be found in the partially oxidized state within the IMS, consistent with the variable redox properties of the latter compartment. The electron transfer-coupled metallation of HSco1 can be a mechanism within the IMS for an efficient specific transfer of the metal to proteins, where metal-binding thiols are oxidized. The same reaction of copper-electron-coupled transfer does not occur with the human homolog of Sco1, HSco2, for kinetic reasons that may be ascribed to the lack of a specific metal-bridged protein-protein complex, which is instead observed in the Cu(I)HCox17(2S-S)/HSco1 interaction. PMID:18458339

Banci, Lucia; Bertini, Ivano; Ciofi-Baffoni, Simone; Hadjiloi, Theodoros; Martinelli, Manuele; Palumaa, Peep

2008-05-13

236

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

237

Interfacial heat transfer in the thin liquid film region near triple contact line of a cylindrical fiber  

Energy Technology Data Exchange (ETDEWEB)

Simulating a porous surface that is partially saturated with a liquid, a two-dimensional meniscus attaching two adjacent cylinders with the same diameters is studied under heating and convective conditions. Convective heat transfer in the fluid above the meniscus and within the liquid are simulated separately using finite element codes. A scheme of iterative coupling between two fluid regime is developed to allow the update of meniscus shape under dynamic conditions. The modified Young-Laplace equation for the meniscus profile is used for the main meniscus region. A thin film model using the disjoint pressure concept is derived to couple the heat transfer between three phases near the interline. The analysis is limited to the stable meniscus profiles only. The preliminary analysis is performed to characterize the geometry of the transition region of a thin liquid film under isothermal and zero shear stress conditions. The sensitivity of the specific transition region length, based on the static meniscus contour, and the effect of the disjoint pressure on the results are discussed.

Tao, Y.X.; Byrd, L.; Palli, R.M.

1997-07-01

238

Electron transfer to covalently immobilized Keggin polyoxotungstates on gold.  

Science.gov (United States)

Spontaneously adsorbed monolayers have been formed on gold electrodes using a Keggin polyoxotungstate with covalently attached alkanethiol linkers of two different lengths. Films of both polyoxotungstates show two well-defined reduction processes associated with the polyoxotungstate centers where the ionic liquid, [BMIM][BF4], acts as supporting electrolyte. The surface coverages are both less than that expected for a close-packed monolayer. For the short and long linkers, the voltammetric response can be described in terms of the Butler-Volmer response involving a surface confined species using standard heterogeneous electron transfer rate constants of 170 and 140 s(-1) for the first reduction and 150 and 100 s(-1) for the second reduction processes, respectively. The rate of electron transfer to a solution phase redox probe, ferrocyanide, is significantly more sensitive to the length of the linker than the rate of electron transfer to the tungstate centers. This behavior probably arises due to potential-induced changes in the film structure. PMID:24670101

Yaqub, Mustansara; Walsh, James J; Keyes, Tia E; Proust, Anna; Rinfray, Corentin; Izzet, Guillaume; McCormac, Timothy; Forster, Robert J

2014-04-22

239

Interspecies Electron Transfer during Propionate and Butyrate Degradation in Mesophilic, Granular Sludge  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Granules from a mesophilic upflow anaerobic sludge blanket reactor were disintegrated, and bacteria utilizing only hydrogen or formate or both hydrogen and formate were added to investigate the role of interspecies electron transfer during degradation of propionate and butyrate. The data indicate that the major electron transfer occurred via interspecies hydrogen transfer, while interspecies formate transfer may not be essential for interspecies electron transfer in this system during degrada...

Schmidt, J. E.; Ahring, B. K.

1995-01-01

240

Combined spectroscopic characterization of electron transfer at hybrid CuPcF16/GaAs semiconductor interfaces  

International Nuclear Information System (INIS)

We characterize photoinduced charge injection at the interface between a fluorinated copper phthalocyanine (CuPcF16) film deposited over a GaAs(100) wafer by means of pump-probe spectroscopy combined with ultraviolet photoemission spectroscopy (UPS) and electromodulated transmission spectroscopy. UPS characterization of the hybrid interface demonstrates that the CuPcF16 's lowest unoccupied molecular level (LUMO) is almost aligned with the GaAs conduction band. Upon photoexcitation of the hybrid interface with 150 fs pulses we observe an efficient photoinduced electron transfer from CuPcF16 to GaAs. The evolution of interfacial CuPcF16 charges appear to be strongly influenced by energy level alignment at the GaAs/CuPcF16 heterojunction.

2008-10-22

 
 
 
 
241

Combined spectroscopic characterization of electron transfer at hybrid CuPcF{sub 16}/GaAs semiconductor interfaces  

Energy Technology Data Exchange (ETDEWEB)

We characterize photoinduced charge injection at the interface between a fluorinated copper phthalocyanine (CuPcF{sub 16}) film deposited over a GaAs(100) wafer by means of pump-probe spectroscopy combined with ultraviolet photoemission spectroscopy (UPS) and electromodulated transmission spectroscopy. UPS characterization of the hybrid interface demonstrates that the CuPcF{sub 16} 's lowest unoccupied molecular level (LUMO) is almost aligned with the GaAs conduction band. Upon photoexcitation of the hybrid interface with 150 fs pulses we observe an efficient photoinduced electron transfer from CuPcF{sub 16} to GaAs. The evolution of interfacial CuPcF{sub 16} charges appear to be strongly influenced by energy level alignment at the GaAs/CuPcF{sub 16} heterojunction.

Cabanillas-Gonzalez, Juan; Egelhaaf, Hans-Joachim; Lanzani, Guglielmo [IFN-CNR, Dipartimento di Fisica, ULTRAS-INFM, Politecnico di Milano, Milano 20133 (Italy); Brambilla, Alberto; Sessi, Paolo; Duo, Lamberto; Finazzi, Marco; Ciccacci, Franco [CNISM and Dipartimento di Fisica, Politecnico di Milano, piazza Leonardo da Vinci 32, Milano 20133 (Italy)], E-mail: juan.cabanillas@polimi.it

2008-10-22

242

Combined spectroscopic characterization of electron transfer at hybrid CuPcF16/GaAs semiconductor interfaces  

Science.gov (United States)

We characterize photoinduced charge injection at the interface between a fluorinated copper phthalocyanine (CuPcF16) film deposited over a GaAs(100) wafer by means of pump-probe spectroscopy combined with ultraviolet photoemission spectroscopy (UPS) and electromodulated transmission spectroscopy. UPS characterization of the hybrid interface demonstrates that the CuPcF16 's lowest unoccupied molecular level (LUMO) is almost aligned with the GaAs conduction band. Upon photoexcitation of the hybrid interface with 150 fs pulses we observe an efficient photoinduced electron transfer from CuPcF16 to GaAs. The evolution of interfacial CuPcF16 charges appear to be strongly influenced by energy level alignment at the GaAs/CuPcF16 heterojunction.

Cabanillas-Gonzalez, Juan; Egelhaaf, Hans-Joachim; Brambilla, Alberto; Sessi, Paolo; Duò, Lamberto; Finazzi, Marco; Ciccacci, Franco; Lanzani, Guglielmo

2008-10-01

243

Combined spectroscopic characterization of electron transfer at hybrid CuPcF(16)/GaAs semiconductor interfaces.  

Science.gov (United States)

We characterize photoinduced charge injection at the interface between a fluorinated copper phthalocyanine (CuPcF(16)) film deposited over a GaAs(100) wafer by means of pump-probe spectroscopy combined with ultraviolet photoemission spectroscopy (UPS) and electromodulated transmission spectroscopy. UPS characterization of the hybrid interface demonstrates that the CuPcF(16) 's lowest unoccupied molecular level (LUMO) is almost aligned with the GaAs conduction band. Upon photoexcitation of the hybrid interface with 150 fs pulses we observe an efficient photoinduced electron transfer from CuPcF(16) to GaAs. The evolution of interfacial CuPcF(16) charges appear to be strongly influenced by energy level alignment at the GaAs/CuPcF(16) heterojunction. PMID:21832670

Cabanillas-Gonzalez, Juan; Egelhaaf, Hans-Joachim; Brambilla, Alberto; Sessi, Paolo; Duò, Lamberto; Finazzi, Marco; Ciccacci, Franco; Lanzani, Guglielmo

2008-10-22

244

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 orientation

1991-10-17

245

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

1987-10-21

246

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

Energy Technology Data Exchange (ETDEWEB)

Phosphite and hypophosphite coordinate to cobalt(III) in (NH/sub 3/)/sub 5/Co/sup III/ through oxygen, rather than through phosphorus. The resulting complexes undergo electron-transfer reactions with Ru(NH/sub 3/)/sub 6//sup 2 +/ much more slowly than with Eu/sup 2 +/ or V/sup 2 +/, indicating that the latter two reactants preferentially utilize ligand bridging. Reductions with Cr/sup 2 +/ 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 23/sup 0/C) 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 Co/sup 2 +/ in an induced electron-transfer process. The yield of Co/sup 2 +/ 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 (NH/sub 3/)/sub 5/Co(H/sub 2/O)/sup 3 +/ and H/sub 2/PO/sub 2//sup -/ appears to be catalyzed specifically by OH/sup -/. Deuterium-labeling experiments disclose a solvent isotope effect. Reaction mechanisms are suggested for all the observed results. 54 references, 5 tables.

Linn, D.E. Jr.; Gould, E.S.

1987-10-21

247

Electron Transfer Reactions in Colloidal Quantum Dot-Ligand Complexes  

Science.gov (United States)

This thesis describes a quantitative analysis of the chemical composition of colloidal II-VI quantum dot (QD)-ligand complexes and transient absorption experiments analyzing the rates of electron transfer reactions in these complexes functionalized with redox active ligands. Chemical analysis reveals that phosphonate impurities in the surfactants used to synthesize CdSe QDs are the dominant ligands on the surface of the QDs, and these phosphonate impurities cause size-dependent Cd-enrichment of the QD surface. A study of the adsorption equilibrium of solution-phase CdS quantum dots and acid-derivatized viologen ligands (V2+) reveals that the structure of the surfaces of the QDs depends on the concentration of the QDs. A new model based on the Langmuir isotherm that treats both the number of adsorbed ligands per QD and the number of available binding sites per QD as binomially-distributed quantities is described. Transient absorption spectroscopy of solution-phase mixtures of colloidal CdS QDs and V2+ indicates electron transfer occurs from the conduction band of the QD to the LUMO of V2+. The rate constant for photoinduced electron transfer (PET) is independent of the number of methylene groups in the alkyl chain on the acid-derivatized viologen. The insensitivity of the electron transfer rate constant to the length of the functional groups on the viologen suggests a van der Waals (vdW) pathway for PET, where the electron bypasses the alkylcarboxylate and tunnels through the orbitals of the QD and of the bipyridinium core. The rate of PET from colloidal CdSe quantum dots (QDs) to oxo-centered triruthenium clusters (Ru 3O) depends on the structure of the chemical headgroup by which the Ru3O clusters adsorb to the QDs. Complexes comprising QDs and Ru 3O clusters adsorbed through a pyridine-4-carboxylic acid ligand have a PET rate constant of (4.9 ± 0.9)×109 s -1 whereas complexes comprising QDs and Ru3O clusters adsorbed through a 4-mercaptopyridine ligand have an intrinsic PET rate constant of (36 ± 7)×109 s-1. The difference in the observed rates of PET for the two complexes is attributed to a difference in donor-acceptor electronic coupling.

Morris-Cohen, Adam Joshua

248

Enhancement of electrochemical ion/electron-transfer reaction at solid|liquid interface by polymer coating on solid surface  

International Nuclear Information System (INIS)

Controlling the ion/electron-transfer reaction at the electrode|electrolyte (solid/liquid) interface is a necessary and vitally important point for improving the operation of various electrochemical devices. In this paper, we propose a polymer coating technique which enhances the Li+ ion-transfer reaction at the LiCoO2|electrolyte interface, and confirm the effects of the polymer coating by cyclic voltammetry (CV) and AC impedance techniques. The results from the experiments indicated that the application of an F-introduced polymer on the LiCoO2 (LCO) surface decreased the activation barrier for Li+ ion transfer. Besides the electrochemical studies, the present computational results indicated that the Li+ exchange process between two states, which are both solved with ethylene carbonate (EC) and coordinated with an F-introduced polymer, might occur due to the close energy levels of Li+ stability. Accordingly, we inferred that the transition state of this exchange process promotes the observed decrease in activation energy for the interfacial Li+-transfer reaction

2008-11-30

249

Enhancement of electrochemical ion/electron-transfer reaction at solid|liquid interface by polymer coating on solid surface  

Energy Technology Data Exchange (ETDEWEB)

Controlling the ion/electron-transfer reaction at the electrode|electrolyte (solid/liquid) interface is a necessary and vitally important point for improving the operation of various electrochemical devices. In this paper, we propose a polymer coating technique which enhances the Li{sup +} ion-transfer reaction at the LiCoO{sub 2}|electrolyte interface, and confirm the effects of the polymer coating by cyclic voltammetry (CV) and AC impedance techniques. The results from the experiments indicated that the application of an F-introduced polymer on the LiCoO{sub 2} (LCO) surface decreased the activation barrier for Li{sup +} ion transfer. Besides the electrochemical studies, the present computational results indicated that the Li{sup +} exchange process between two states, which are both solved with ethylene carbonate (EC) and coordinated with an F-introduced polymer, might occur due to the close energy levels of Li{sup +} stability. Accordingly, we inferred that the transition state of this exchange process promotes the observed decrease in activation energy for the interfacial Li{sup +}-transfer reaction.

Kaneko, Mayumi [Zeon Corporation, R and D Center, 1-2-1 Yako, Kawasaki, Kanagawa 210-9507 (Japan); Department of Applied Chemistry, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552 (Japan); Nakayama, Masanobu [Department of Applied Chemistry, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552 (Japan); Wakizaka, Yasuhiro [Zeon Corporation, R and D Center, 1-2-1 Yako, Kawasaki, Kanagawa 210-9507 (Japan); Kanamura, Kiyoshi [Department of Applied Chemistry, Tokyo Metropolitan University, 1-1 Minami-ohsawa, Hachioji, Tokyo 192-0397 (Japan); Wakihara, Masataka [Zeon Corporation, R and D Center, 1-2-1 Yako, Kawasaki, Kanagawa 210-9507 (Japan)

2008-11-30

250

Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy  

International Nuclear Information System (INIS)

Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D0), surface coverage (?R), and monolayer thickness (di) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density (?DNA) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: ?DNA (dsS-DNA/Au) > ?DNA (MCH/dsS-DNA/Au) > ?DNA (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

2009-06-08

251

Immobilization, hybridization, and oxidation of synthetic DNA on gold surface: Electron transfer investigated by electrochemistry and scanning tunneling microscopy  

Energy Technology Data Exchange (ETDEWEB)

Fundamental understanding of interfacial electron transfer (ET) among electrolyte/DNA/solid-surface will facilitate the design for electrical detection of DNA molecules. In this report, the electron transfer characteristics of synthetic DNA (sequence from pathogenic Cryptosporidium parvum) self-assembled on a gold surface was electrochemically studied. The effects of immobilization order on the interface ET related parameters such as diffusion coefficient (D{sub 0}), surface coverage ({theta}{sub R}), and monolayer thickness (d{sub i}) were determined by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). DNA surface density ({Gamma}{sub DNA}) was determined by the integration of the charge of the electro-oxidation current peaks during the initial cyclic voltammetry scans. It was found that the DNA surface densities at different modifications followed the order: {Gamma}{sub DNA} (dsS-DNA/Au) > {Gamma}{sub DNA} (MCH/dsS-DNA/Au) > {Gamma}{sub DNA} (dsS-DNA/MCH/Au). It was also revealed that the electro-oxidation of the DNA modified gold surface would involve the oxidation of nucleotides (guanine and adenine) with a 5.51 electron transfer mechanism and the oxidative desorption of DNA and MCH molecules by a 3 electron transfer mechanism. STM topography and current image analysis indicated that the surface conductivity after each surface modification followed the order: dsS-DNA/Au < MCH/dsS-DNA/Au < oxidized MCH/dsS-DNA/Au < Hoechst/oxidized MCH/dsS-DNA/Au. The results from this study suggested a combination of variations in immobilization order may provide an alternative approach for the optimization of DNA hybridization and the further development for electrical detection of DNA.

McEwen, Gerald D.; Chen Fan [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States); Zhou Anhong, E-mail: Anhong.Zhou@usu.edu [Biological Engineering Program, Department of Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322-4105 (United States)

2009-06-08

252

Electron transfer mechanism and photochemistry of ferrioxalate induced by excitation in the charge transfer band.  

Science.gov (United States)

The photoredox reaction of ferrioxalate after 266/267 nm excitation in the charge transfer band has been studied by means of ultrafast extended X-ray absorption fine structure (EXAFS) analysis, optical transient spectroscopy, and quantum chemistry calculations. The Fe-O bond length changes combined with the transient spectra and kinetics have been measured and in combination with ultrahigh frequency density functional theory (UHF/DFT) calculations are used to determine the photochemical mechanism for the Fe(III) to Fe(II) redox reaction. The present data and the results obtained with 266/267 nm excitations strongly suggest that the primary reaction is the dissociation of the Fe-O bond before intramolecular electron transfer occurs. Low quantum yield electron photodetachment from ferrioxalate has also been observed. PMID:18284192

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

2008-03-17

253

Electrochemical study of a reconstituted photosynthetic electron-transfer chain.  

Science.gov (United States)

A multi-enzyme electron-transfer chain involving solubilized photosystem I (PSI) as photocatalytic unit, cytochrome c6 and ferredoxin as electron carriers and ferredoxin/NADPH oxidoreductase (FNR) as electron acceptor was reconstituted in an electrochemical cell and studied by cyclic voltammetry. The working gold electrodes were modified to react selectively with cytochrome c6. Quantitative analysis of the photocatalytic current under continuous illumination allowed the determination of the values kon and koff for the ferredoxin/PSI interaction. An efficient recycling system for NADPH was established, and the dissociation constant of the oxidized ferredoxin/semiquinone FNR complex was extracted by modeling the catalytic efficiency of the chain as a function of ferredoxin concentration. The value determined hereby is consistent with a shift of -50 to -100 mV of the reduction potential of ferredoxin when complexed with FNR. PMID:17602558

Fourmond, Vincent; Lagoutte, Bernard; Sétif, Pierre; Leibl, Winfried; Demaille, Christophe

2007-07-25

254

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

1987-09-07

255

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

256

Electron and hydrogen transfer in small hydrogen fluoride anion clusters.  

Science.gov (United States)

A new stable structure has been found for the anion clusters of hydrogen fluoride. The ab initio method was used to optimize the structures of the (HF)(3)(-), (HF)(4)(-), (HF)(5)(-), and (HF)(6)(-) anion clusters with an excess "solvated" electron. Instead of the well-known "zig-zag" (HF)(n)(-) structure, a new form, (HF)(n-1)F(-)···H, was found with lower energy. In this new form, the terminal hydrogen atom in the (HF)(n)(-) chain is separated from the other part of the cluster and the inner hydrogens transfer along the hydrogen bonds toward the outside fluoride. The negative charge also transfers from the terminal HF molecule of the chain to the center fluoride atoms. The (HF)(n)(-) clusters for n = 4, 5, and 6 have not yet been observed experimentally. These results should assist in the search for these systems and also provide a possible way to study the proton and electron transfer in some large hydrogen bonding systems. PMID:21854014

Bai, Xin; Ning, Ming; Brown, Richard E

2011-09-29

257

Reduced density matrix hybrid approach: Application to electronic energy transfer  

Science.gov (United States)

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

Berkelbach, Timothy C.; Markland, Thomas E.; Reichman, David R.

2012-02-01

258

Interfacial reactions between titanium and borate glass  

Energy Technology Data Exchange (ETDEWEB)

Interfacial reactions between melts of several borate glasses and titanium have been investigated by analytical scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS). A thin titanium boride interfacial layer is detected by XPS after short (30 minutes) thermal treatments. ASEM analyses after longer thermal treatments (8--120 hours) reveal boron-rich interfacial layers and boride precipitates in the Ti side of the interface.

Brow, R.K. [Sandia National Labs., Albuquerque, NM (United States); Saha, S.K.; Goldstein, J.I. [Lehigh Univ., Bethlehem, PA (United States). Dept. of Materials Science

1992-12-31

259

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

260

Photoinduced electron transfer from dialkyl nitroxides to halogenated solvents  

Energy Technology Data Exchange (ETDEWEB)

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

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

1990-02-02

 
 
 
 
261

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

262

A stochastic reorganizational bath model for electronic energy transfer  

CERN Document Server

The fluctuations of optical gap induced by the environment play crucial roles in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker model, in which the energy-gap fluctuation is approximated as a white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to take the thermal fluctuation of excitation energies into account. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equ...

Fujita, Takatoshi; Aspuru-Guzik, Alan

2014-01-01

263

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

264

Synchronized energy and electron transfer processes in covalently linked CdSe-squaraine dye-TiO2 light harvesting assembly.  

Science.gov (United States)

Manipulation of energy and electron transfer processes in a light harvesting assembly is an important criterion to mimic natural photosynthesis. We have now succeeded in sequentially assembling CdSe quantum dot (QD) and squaraine dye (SQSH) on TiO(2) film and couple energy and electron transfer processes to generate photocurrent in a hybrid solar cell. When attached separately, both CdSe QDs and SQSH inject electrons into TiO(2) under visible-near-IR irradiation. However, CdSe QD if linked to TiO(2) with SQSH linker participates in an energy transfer process. The hybrid solar cells prepared with squaraine dye as a linker between CdSe QD and TiO(2) exhibited power conversion efficiency of 3.65% and good stability during illumination with global AM 1.5 solar condition. Transient absorption spectroscopy measurements provided further insight into the energy transfer between excited CdSe QD and SQSH (rate constant of 6.7 × 10(10) s(-1)) and interfacial electron transfer between excited SQSH and TiO(2) (rate constant of 1.2 × 10(11) s(-1)). The synergy of covalently linked semiconductor quantum dots and near-IR absorbing squaraine dye provides new opportunities to harvest photons from selective regions of the solar spectrum in an efficient manner. PMID:22658983

Choi, Hyunbong; Santra, Pralay K; Kamat, Prashant V

2012-06-26

265

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

266

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

267

Quantum simulation of nuclear rearrangement in electron transfer reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A quantum simulation scheme based on the path integral molecular dynamics technique has been used to calculate the effective activation energies associated with nuclear rearrangement in the electron transfer reactions Co(NH3)62+ + Co(NH3)63+ ? Co(NH3)63+ + Co(NH3)62+ and Ru(NH3)62+ + Ru(NH3)63+ ? Ru(NH3)63+ + Ru(NH3)62+. Even with a simple Hamiltonian and short time dynamic simulations, the results are in satisfactory agreement with other theoretical calculations. This simulation approach...

1989-01-01

268

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

269

Electron transfer and protein dynamics in the photosynthetic reaction center.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We have measured the kinetics of electron transfer (ET) from the primary quinone (Q(A)) to the special pair (P) of the reaction center (RC) complex from Rhodobacter sphaeroides as a function of temperature (5-300 K), illumination protocol (cooled in the dark and under illumination from 110, 160, 180, and 280 K), and warming rate (1.3 and 13 mK/s). The nonexponential kinetics are interpreted with a quantum-mechanical ET model (Fermi's golden rule and the spin-boson model), in which heterogenei...

Mcmahon, B. H.; Mu?ller, J. D.; Wraight, C. A.; Nienhaus, G. U.

1998-01-01

270

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 (Q"2 > 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 Q"2 is given

1979-01-01

271

Photoinduced electron transfer based ion sensing within an optical fiber.  

Science.gov (United States)

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. PMID:22163712

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

2011-01-01

272

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

273

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 Ba_2"+"+ 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

1978-09-26

274

Effect of electron transfer on contact fusion kinetics  

International Nuclear Information System (INIS)

The effect of electric current on the kinetics of contact fusion (CF) is investigated. It is revealed that electric current can not only retard or accelerate CF in the diffusion regime at constant temperature T, but it can result in the process of ''contact crysllization''. CF may be used to study electron transfer in liquid solutions of eutectic systems. The results obtained may be applied in problems of the so-called contact-reactive soldering. In-Bi, Pb-Bi and Cd-Bi systems were used for investigations

1983-01-01

275

Light induced electron transfer reactions of metal complexes  

International Nuclear Information System (INIS)

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

1980-07-19

276

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

277

Multiple electron transfer in slow Ne9+-Ne collisions  

International Nuclear Information System (INIS)

Multielectron transfer probabilities in 90-keV Ne9+-Ne collisions have been measured with respect to the projectile scattering angle ? in a range between ?=12 and 75 mrad. The projectile final charge state was determined in coincidence with the target-ion final charge state using a time-of-flight technique. For ?>45 mrad, projectile and target undergo a complete equilibration of their atomic shells (including the K shell) leading to the excitation of both collision partners and the autoionization of three electrons on average. A comparison of the measured final charge-state distributions of projectile and target with those obtained in a former experiment with the system 90-keV Ne7+-Ne [H. Schmidt-Boecking et al., Phys. Rev. A 37, 4640 (1989)] leads to the conclusion that L- and K-shell charge transfer can be treated as independent processes. Interference structure in the K-K vacancy-transfer probabilities has been observed in the final charge-state probabilities of the ''heavy-ion''--atom system

1992-11-01

278

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

279

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

280

Charge transfer and electronic relaxation in ion-surface scattering  

International Nuclear Information System (INIS)

The purpose of this work is to investigate theoretically a widely studied process at the gas-surface interface, namely the transfer of one electron from a surface to an impinging ion and the subsequent electronic relaxation of the possibly excited neutralized atom. The theoretical techniques used are reviewed in Chapter 1, where the concepts of density matrix theory and field theory strictly related to the rest of the work are presented. The necessity of using a density matrix to describe the quantum state of a system that interacts with another unobserved system, is stressed in Chapter 1.A. In Chapter 1.B., after reviewing how the quantization procedure is performed for both a classical particle and a classical field, second quantization is presented as the quantum theory that correctly describes a system of many particles whose total number is not conserved. In Chapter 2, second quantization techniques are applied to ion-neutralization at surfaces. The experimental and theoretical state of the art is reviewed in Chapter 2.A., while in Chapter 2.B. is presented a perturbative treatment of the Fano-Anderson effective potential to model the charge transfer process. The theory is applied to proton neutralization at alkali-halide surfaces, which are systems for which the perturbative expansion converges quickly. The qualitative behavior of the calculated dependence of the neutralization probability on the ion collision velocity is found to be in agreement with experimental measurements

1985-01-01

 
 
 
 
281

Promoting direct interspecies electron transfer with activated carbon  

DEFF Research Database (Denmark)

Granular activated carbon (GAC) is added to methanogenic digesters to enhance conversion of wastes to methane, but the mechanism(s) for GACâ??s stimulatory effect are poorly understood. GAC has high electrical conductivity and thus it was hypothesized that one mechanism for GAC stimulation of methanogenesis might be to facilitate direct interspecies electron transfer (DIET) between bacteria and methanogens. Metabolism was substantially accelerated when GAC was added to co-cultures of Geobacter metallireducens and Geobacter sulfurreducens grown under conditions previously shown to require DIET. Cells were attached to GAC, but did not aggregate as they do when making biological electrical connections between cells. Studies with a series of gene deletion mutants eliminated the possibility that GAC promoted electron exchange via interspecies hydrogen or formate transfer and demonstrated that DIET in the presence of GAC did not require the electrically conductive pili and associated c-type cytochrome involved in biological interspecies electrical connections. GAC also greatly stimulated ethanol metabolism and methane production in co-cultures of G. metallireducens and Methanosarcina barkeri. Cells were attached to GAC, but not closely aggregated, suggesting little opportunity for biological electrical contacts between the species. GAC also enhanced methane production in samples from a methanogenic digester in which Methanosaeta were the predominant methanogens. The results demonstrate that GAC can promote DIET and suggest that stimulation of metabolism in methanogenic digesters can be attributed, at least in part, to the high conductivity of GAC providing better interspecies electrical connections than those that can be forged biologically.

Liu, Fanghua; Rotaru, Amelia-Elena

2012-01-01

282

Low temperature free energy relations for electron transfer reactions  

International Nuclear Information System (INIS)

Using the multiphonon theory of electron transfer reactions we present calculations and simple expressions for the rate of electron transfer between molecules in a medium as a function of the free energy changes, especially in the exothermic region. We include effects of the medium modes as well as higher frequency modes which are allowed to change during the reaction. We find that there are activated as well as nonactivated regions depending on the free energy change and the temperature. The rate in the so called ''anomalous'' (or nonactivated) region decreases much more slowly with free energy than it does in the activated region. In fact, the logorithm of the rate depends roughly linearly on the free energy change in that region. Fortunately the rate is most dependent on the frequency of the high energy modes and less on the coupling strength about which we know the least. In addition we have studied uses of frequency averaging to reproduce the results of a multimode case

1982-09-01

283

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

284

Highly-effective photocatalytic properties and interfacial transfer efficiencies of charge carriers for the novel Ag?CO?/AgX heterojunctions achieved by surface modification.  

Science.gov (United States)

Novel Ag2CO3/AgX heterojunctions are achieved from the surface modification of Ag2CO3 with AgX (X = Cl, Br and I) nanoparticles by a facile and efficient ion-exchange method, which distinctly enhances the degradation activity for typical RhB, MB, and MO dyes compared with Ag2CO3. The formation of the heterostructure is evidenced by XRD, SEM, EDS, XPS and UV-vis DRS analyses, which indicates the bonding interaction between Ag2CO3 and AgX reduces the potential transfer barrier of charge carriers on their interface and extends visible light harvesting at 480-640 nm. Photocurrent responses and PL spectra demonstrate the Ag2CO3/AgX heterojunctions can effectively separate electron-hole pairs and suppress their recombination. The dye sensitization effect indicates that the effective electronic injection from RhB to the heterojunction is in favor of improving the photocatalytic ability. The possible transferred and separated behavior of electron-hole pairs and photocatalytic mechanisms are illustrated in detail. PMID:24691642

Dong, Hongjun; Chen, Gang; Sun, Jingxue; Feng, Yujie; Li, Chunmei; Xiong, Guihong; Lv, Chade

2014-05-21

285

Collisional electron transfer to photoexcited acceptor radical anions  

DEFF Research Database (Denmark)

In this article, we show that photoexcitation of radical anions facilitates electron transfer from sodium atoms in femtosecond encounters. Thus, excitation of 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and fluorinated TCNQ (TCNQ-F(4)) anions to the second optically active state at 478 nm led to increases in the yields of dianions of about 20% and 10%, respectively. Photoexcitation with a nanosecond-long laser pulse was done a few microseconds before the ions entered the sodium collision cell so that none of the ions would be in any of the initially reached doublet-excited states. We suggest an explanation for the higher electron capture cross section based on the formation of long-lived quartet state anions. Excitation of TCNQ anions within the lowest-energy absorption band, where there are no accessible quartet states, led instead to a lower yield of dianions. There are at least three explanations for the lower dianion yields: (1) Depletion of the monoanion beam due to photodetachment after the absorption ofminimum two photons; (2) Formation of short-lived vibrationally excited dianions that decay by electron autodetachment prior to identification; and (3) Lower electron capture cross sections of vibrationally excited monoanions. Similar losses in dianion signal can occur at 478 nm so the actual yield of dianions at this wavelength due to the population of quartet states is therefore greater than that observed. Our methodology devises a more efficient route for the production of molecular dianions, and at the same time it may provide information on long-lived electronic states.

Wyer, Jean Ann; Støchkel, Kristian

2012-01-01

286

Cluster PEACE observations of electrons during magnetospheric flux transfer events  

Directory of Open Access Journals (Sweden)

Full Text Available During the first quarter of 2001 the apogees of the Cluster spacecraft quartet precessed through midday local times. This provides the first opportunity for 4 spacecraft studies of the bow shock, magnetosheath and the dayside magnetopause current layer and boundary layers. In this paper, we present observations of electrons in the energy range ~ 10 eV–26 keV made by the Plasma Electron And Current Experiment (PEACE located just inside the magnetopause boundary, together with supporting observations by the Flux Gate Magnetometer (FGM. During these observations, the spacecraft have separations of ~ 600 km. This scale size is of the order or less than the typical size of flux transfer events (FTEs, which are expected to be observed following bursts of reconnection on the dayside magnetopause. We study, in detail, the 3-D configuration of electron populations observed around a series of enhancements of magnetosheath-like electrons which were observed within the magnetosphere on 2 February 2001. We find that individual spacecraft observe magnetic field and electron signatures that are consistent with previous observations of magnetospheric FTEs. However, the differences in the signatures between spacecraft indicate that these FTEs have substructure on the scale of the spacecraft separation. We use these differences and the timings of the 4 spacecraft observations to infer the motions of the electron populations and thus the configuration of these substructures. We find that these FTEs are moving from noon towards dusk. The inferred size and speed of motion across the magnetopause, in one example, is ~ 0.8 RE and ~ 70 km s-1 respectively. In addition, we observe a delay in and an extended duration of the signature at the spacecraft furthest from the magnetopause. We discuss the implications of these 4 spacecraft observations for the structure of these FTEs. We suggest that these may include a compression of the closed flux tubes ahead of the FTE, which causes density and field strength enhancements; a circulation of open flux tubes within the FTE itself, which accounts for the delay in the arrival of the magnetosheath electron populations at locations deepest within the magnetosphere; and a possible trapping of magnetospheric electrons on the most recently opened flux tubes within the FTE.

Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind - magnetosphere interactions

C. J. Owen

287

Electron transfer rates and equilibrium within cytochrome c oxidase  

DEFF Research Database (Denmark)

Intramolecular electron transfer (ET) between the CuA center and heme a in bovine cytochrome c oxidase was investigated by pulse radiolysis. CuA, the initial electron acceptor, was reduced by 1-methyl nicotinamide radicals in a diffusion-controlled reaction, as monitored by absorption changes at 830 nm. After the initial reduction phase, the 830 nm absorption was partially restored, corresponding to reoxidation of the CuA center. Concomitantly, the absorption at 445 nm and 605 nm increased, indicating reduction of heme a. The rate constants for heme a reduction and CuA reoxidation were identical within experimental error and independent of the enzyme concentration. This demonstrates that a fast intramolecular electron equilibration is taking place between CuA and heme a. The rate constants for CuA --> heme a ET and the reverse (heme a --> CuA) process were found to be 13 000 s-1 and 3700 s-1, respectively, at 25 degrees C and pH 7.4. This corresponds to an equilibrium constant of 3.4 under these conditions. Thermodynamic and activation parameters of the ET reactions were determined. The significance of these results, particularly the observed low activation barriers, are discussed within the framework of the known three-dimensional structure, ET pathways and reorganization energies.

Farver, O; Einarsdóttir, O

2000-01-01

288

Radiolytic and electron-transfer reactions in supercritical CO2  

International Nuclear Information System (INIS)

Using supercritical fluids as solvents is useful for both practical and theoretical reasons. It has been proposed to use supercritical CO2 as a solvent for synthesis because it eliminates the air pollution arising from other solvents. The properties of supercritical fluids can be easily varied with only modest changes in temperature and density, so they provide a way of testing theories of chemical reactions. It has also been proposed to use supercritical fluids for the treatment of hazardous mixed waste. For these reasons the authors have studied the production of radiolytic species in supercritical CO2 and have measured their reactivity as a function of density. They have shown that the C2O4+ is formed. They also have shown that the electron transfer reactions of dimethylaniline to C2O4+ and CO2(e-) to benzoquinone are diffusion controlled over a considerable density range

1999-03-13

289

Reorganization energy of electron transfer at the solvent glass transition  

CERN Document Server

We present a molecular-dynamics study of the solvent reorganization energy of electron transfer in supercooled water. We observe a sharp decrease of the reorganization energy at a temperature identified as the temperature of structural arrest due to cage effect as discussed by the mode coupling theory. Both the heat capacity and dielectric susceptibility of the pure water show sharp drops at about the same temperature. This temperature also marks the onset of the enhancement of translational diffusion relative to rotational relaxation signaling the break-down of the Stokes-Einstein relation. The change in the reorganization energy at the transition temperature reflects the dynamical arrest of the slow, collective relaxation of the solvent related to Debye relaxation of the solvent dipolar polarization.

Ghorai, P K; Ghorai, Pradip K.; Matyushov, Dmitry V.

2005-01-01

290

Electron transfer flavoprotein deficiency: Functional and molecular aspects.  

DEFF Research Database (Denmark)

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a recessively inherited metabolic disorder that can be due to a deficiency of electron transfer flavoprotein (ETF) or its dehydrogenase (ETF-ubiquinone oxidoreductase). ETF is a mitochondrial matrix protein consisting of alpha- (30kDa) and beta- (28kDa) subunits encoded by the ETFA and ETFB genes, respectively. In the present study, we have analysed tissue samples from 16 unrelated patients with ETF deficiency, and we report the results of ETF activity, Western blot analysis and mutation analysis. The ETF assay provides a reliable diagnostic tool to confirm ETF deficiency in patients suspected to suffer from MADD. Activity ranged from less than 1 to 16% of controls with the most severely affected patients disclosing the lowest activity values. The majority of patients had mutations in the ETFA gene while only two of them harboured mutations in the ETFB gene. Nine novel disease-causing ETF mutations are reported.

Schiff, M; Froissart, R

2006-01-01

291

Facile direct electron transfer in glucose oxidase modified electrodes  

International Nuclear Information System (INIS)

Glucose oxidase (GOx) is widely used in the glucose biosensor industry. However, mediatorless direct electron transfer (DET) from GOx to electrode surfaces is very slow. Recently, mediatorless DET has been reported via the incorporation of nanomaterials such as carbon nanotubes and nanoparticles in the modification of electrodes. Here we report GOx electrodes showing DET without the need for any nanomaterials. The enzyme after immobilization with poly-L-lysine (PLL) and Nafion retains the biocatalytic activities and oxidizes glucose efficiently. The amperometric response of Nafion-PLL-GOx modified electrode is linearly proportional to the concentration of glucose up to 10 mM with a sensitivity of 0.75 ?A/mM at a low detection potential (-0.460 V vs. Ag/AgCl). The methodology developed in this study will have impact on glucose biosensors and biofuel cells and may potentially simplify enzyme immobilization in other biosensing systems.

2009-07-15

292

Facile direct electron transfer in glucose oxidase modified electrodes  

Energy Technology Data Exchange (ETDEWEB)

Glucose oxidase (GOx) is widely used in the glucose biosensor industry. However, mediatorless direct electron transfer (DET) from GOx to electrode surfaces is very slow. Recently, mediatorless DET has been reported via the incorporation of nanomaterials such as carbon nanotubes and nanoparticles in the modification of electrodes. Here we report GOx electrodes showing DET without the need for any nanomaterials. The enzyme after immobilization with poly-L-lysine (PLL) and Nafion retains the biocatalytic activities and oxidizes glucose efficiently. The amperometric response of Nafion-PLL-GOx modified electrode is linearly proportional to the concentration of glucose up to 10 mM with a sensitivity of 0.75 {mu}A/mM at a low detection potential (-0.460 V vs. Ag/AgCl). The methodology developed in this study will have impact on glucose biosensors and biofuel cells and may potentially simplify enzyme immobilization in other biosensing systems.

Wang Dan [Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701 (United States); Chen Liwei [Department of Chemistry and Biochemistry, Ohio University, Athens, OH 45701 (United States); Suzhou Institute of Nano Tech and Nano Bionics, Chinese Academy of Sciences, 398 Ruoshui Road, Suzhou Industrial Park, Suzhou, Jiangsu 215125 (China)], E-mail: lwchen2008@sinano.ac.cn

2009-07-15

293

A stochastic reorganizational bath model for electronic energy transfer.  

Science.gov (United States)

Environmentally induced fluctuations of the optical gap play a crucial role in electronic energy transfer dynamics. One of the simplest approaches to incorporate such fluctuations in energy transfer dynamics is the well known Haken-Strobl-Reineker (HSR) model, in which the energy-gap fluctuation is approximated as white noise. Recently, several groups have employed molecular dynamics simulations and excited-state calculations in conjunction to account for excitation energies' thermal fluctuations. On the other hand, since the original work of HSR, many groups have employed stochastic models to simulate the same transfer dynamics. Here, we discuss a rigorous connection between the stochastic and the atomistic bath models. If the phonon bath is treated classically, time evolution of the exciton-phonon system can be described by Ehrenfest dynamics. To establish the relationship between the stochastic and atomistic bath models, we employ a projection operator technique to derive the generalized Langevin equations for the energy-gap fluctuations. The stochastic bath model can be obtained as an approximation of the atomistic Ehrenfest equations via the generalized Langevin approach. Based on this connection, we propose a novel scheme to take account of reorganization effects within the framework of stochastic models. The proposed scheme provides a better description of the population dynamics especially in the regime of strong exciton-phonon coupling. Finally, we discuss the effect of the bath reorganization in the absorption and fluorescence spectra of ideal J-aggregates in terms of the Stokes shifts. We find a simple expression that relates the reorganization contribution to the Stokes shifts - the reorganization shift - to the ideal or non-ideal exciton delocalization in a J-aggregate. The reorganization shift can be described by three parameters: the monomer reorganization energy, the relaxation time of the optical gap, and the exciton delocalization length. This simple relationship allows one to understand the physical origin of the Stokes shifts in molecular aggregates. PMID:24985614

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

2014-06-28

294

The Golden Rule. Application for fun and profit in electron transfer, energy transfer, and excited-state decay.  

Science.gov (United States)

Time-dependent perturbation theory and application of the Golden Rule have been shown to be quantitatively applicable to electron transfer in the inverted region, energy transfer, and excited-state decay based on spectroscopic measurements on d?(6) polypyridyl complexes of Ru(II), Os(II), and Re(I). PMID:22842806

Ito, Akitaka; Meyer, Thomas J

2012-10-28

295

Analyses of donor-acceptor distance-dependent rates of photo-induced electron transfer in flavoproteins with three kinds of electron transfer theories  

International Nuclear Information System (INIS)

Reported donor-acceptor distance-dependent rates of photo-induced electron transfer from tryptophan (Trp), tyrosine (Tyr), and benzoate (Bz) to the excited isoalloxazine in ten flavoprotein systems were analyzed with three kinds of electron transfer theories by Marcus, by Bixon and Jortner, and also by Kakitani, Yoshimori, and Mataga. Average donor-acceptor distances that were obtained from X-ray structures of flavoproteins were used for the analysis, rather than the edge-to-edge distance. The observed photo-induced electron transfer rates were best reproduced by the Kakitani, Yoshimori, and Mataga theory

2008-06-02

296

Analyses of donor-acceptor distance-dependent rates of photo-induced electron transfer in flavoproteins with three kinds of electron transfer theories  

Energy Technology Data Exchange (ETDEWEB)

Reported donor-acceptor distance-dependent rates of photo-induced electron transfer from tryptophan (Trp), tyrosine (Tyr), and benzoate (Bz) to the excited isoalloxazine in ten flavoprotein systems were analyzed with three kinds of electron transfer theories by Marcus, by Bixon and Jortner, and also by Kakitani, Yoshimori, and Mataga. Average donor-acceptor distances that were obtained from X-ray structures of flavoproteins were used for the analysis, rather than the edge-to-edge distance. The observed photo-induced electron transfer rates were best reproduced by the Kakitani, Yoshimori, and Mataga theory.

Tanaka, Fumio [SC1-413, Department of Chemistry, Faculty of Science, Mahasarakham University, Mahasarakham 44150 (Thailand)], E-mail: fukoh2003@yahoo.com; Rujkorakarn, Rong [Department of Physics, Faculty of Science, Khon Kaen University, Khon Kaen 40002 (Thailand); Chosrowjan, Haik; Taniguchi, Seiji; Mataga, Noboru [Institute for Laser Technology, Utsubo-Hommachi 1-8-4, Nishiku, Osaka 550-0004 (Japan)

2008-06-02

297

Modulating electron transfer properties of gold nanoparticles for efficient biosensing.  

Science.gov (United States)

Present study concerns modulating the electron transfer properties of gold nanoparticles through amino acid induced coupling among them. In addition to conductivity, the amino functionalization of the nanoparticles results in enhanced activity and operational stability of the biosensor fabricated using the same. Nanoparticles synthesized using amino acid as reducing agent (average diameter-20 nm), incorporate the natural coupling property of amino acids and are seen to align in a chain-like arrangement. The coupling of the individual nanoparticles to form chain like structure was confirmed by both absorption spectroscopy as well as transmission electron microscopy. The glucose biosensor developed by adsorption of glucose oxidase (GOx) enzyme onto these coupled gold nanoparticles showed enhanced efficiency as compared to the one with glucose oxidase immobilized onto gold nanoparticles synthesized using the conventional method (trisodium citrate as reducing agent). The fabricated biosensor demonstrated a wide linear concentration range from 1 ?M-5mM and a high sensitivity of 47.2 ?A mM(-1) cm(-2). Also, an enhanced selectivity to glucose was observed with negligible interference in the physiological range, from easily oxidizable biospecies, e.g. uric acid and ascorbic acid. Furthermore, the electrochemical biosensor has excellent long term stability- retaining greater than 85% of the biosensor activity up to 60 days. PMID:22608576

Sharma, Shikha; Gupta, Nidhi; Srivastava, Sudha

2012-01-01

298

Ions interacting with planar aromatic molecules: Modeling electron transfer reactions  

Science.gov (United States)

We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C14H10, coronene C24H12, or circumcoronene C54H18. These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

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

2013-02-01

299

Ions interacting with planar aromatic molecules: Modeling electron transfer reactions  

International Nuclear Information System (INIS)

We present theoretical absolute charge exchange cross sections for multiply charged cations interacting with the Polycyclic Aromatic Hydrocarbon (PAH) molecules pyrene C14H10, coronene C24H12, or circumcoronene C54H18. These planar, nearly circular, PAHs are modelled as conducting, infinitely thin, and perfectly circular discs, which are randomly oriented with respect to straight line ion trajectories. We present the analytical solution for the potential energy surface experienced by an electron in the field of such a charged disc and a point-charge at an arbitrary position. The location and height of the corresponding potential energy barrier from this simple model are in close agreement with those from much more computationally demanding Density Functional Theory (DFT) calculations in a number of test cases. The model results compare favourably with available experimental data on single- and multiple electron transfer reactions and we demonstrate that it is important to include the orientation dependent polarizabilities of the molecules (model discs) in particular for the larger PAHs. PAH ionization energy sequences from DFT are tabulated and used as model inputs. Absolute cross sections for the ionization of PAH molecules, and PAH ionization energies such as the ones presented here may be useful when considering the roles of PAHs and their ions in, e.g., interstellar chemistry, stellar atmospheres, and in related photoabsorption and photoemission spectroscopies.

2013-02-07

300

Ions interacting with planar aromatic molecules: Modeling electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

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

Forsberg, B. O.; Alexander, J. D.; Chen, T.; Pettersson, A. T.; Gatchell, M.; Cederquist, H.; Zettergren, H. [Department of Physics, Stockholm University, SE-106 91 Stockholm (Sweden)

2013-02-07

 
 
 
 
301

Calculation of electron transfer reorganization energies using the finite difference Poisson-Boltzmann model.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

1998-01-01

302

Theory of Electron-Transfer Reactions and of Related Phenomena  

International Nuclear Information System (INIS)

Data on electronexchange reactions have provided insight into factors influencing rates of electron-transfer reactions in solution. The present paper has the twofold purpose of discussing some of these factors and of describing applications of these exchange data and theory to other phenomena. The reaction rate depends upon the extent of reorganization of bond lengths (angles) in the reactants and of solvent reorientation outside them. The reorganization is facilitated or hindered in a comparatively simple way by a favorable or unfavorable standard free energy of reaction. The rate depends, too, on coulombic and other interactions, as evidenced perhaps by certain salt effects, though probably only by a few orders of magni - tude typically. The observed variation of rates of some 15 orders of magnitude is best attributed primarily to differences in the vibrational reorganization term, a factor calculable from bond lengths and force constants when known. A remaining factor, non-adiabaticity, is at present of uncertain importance. Arrhenius frequency factors in chemical and electrochemical exchange rate constants would provide the most direct information, but can be complicated or even dwarfed by solvent reordering effects in the coulombic interaction. Available data are few. They provide examples where a non-adiabatic effect is minor. There appear to be no known examples where it is major (Fe2+ - Fe3+, could be a candidate but its mechanism is apparently uncertain). Reorganization in reactants and in solvent occurs in a variety of related phenomena, and related concepts will be applied to treat them. In turn, chemical exchange data have useful applications to the latter. These areas include electrochemical exchange reactions, chemiluminescent electron-transfer reactions (between positive and negative aromatic ions, for example), and redox reactions of the solvated electron. An explanation for the chemiluminescent reactions will be based on the possible ''inverse ?F°'' effect, discussed several years ago by the author. A related phenomenon involving solvent 'orientation strain' occurs in light absorption or emission by polar solutes in polar solvents, and the theoretical approach used by the author for treating it is closely related to that used for the exchange reactions. (author)

1965-10-01

303

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

Science.gov (United States)

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

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

2014-03-21

304

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

Science.gov (United States)

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

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

2014-05-01

305

Direct electron transfer from glucose oxidase immobilized on a nano-porous glassy carbon electrode  

International Nuclear Information System (INIS)

Highlights: ? A direct electron transfer reaction of glucose oxidase was observed on the surface of a nano-porous glassy carbon electrode. ? A pair of well-defined and reversible redox peaks was observed at the formal potential of approximately -0.439 V. ? The apparent electron transfer rate constant was measured to be 5.27 s-1. ? A mechanism for the observed direct electron transfer reaction was proposed, which consists of a two-electron and a two-proton transfer. - Abstract: A pair of well-defined and reversible redox peaks was observed for the direct electron transfer (DET) reaction of an immobilized glucose oxidase (GOx) on the surface of a nano-porous glassy carbon electrode at the formal potential (Eo') of -0.439 V versus Ag/AgCl/saturated KCl. The electron transfer rate constant (ks) was calculated to be 5.27 s-1. The dependence of Eo' on pH indicated that the direct electron transfer of the GOx was a two-electron transfer process, coupled with two-proton transfer. The results clearly demonstrate that the nano-porous glassy carbon electrode is a cost-effective and ready-to-use scaffold for the fabrication of a glucose biosensor.

2011-11-30

306

Direct electron transfer from glucose oxidase immobilized on a nano-porous glassy carbon electrode  

Energy Technology Data Exchange (ETDEWEB)

Highlights: > A direct electron transfer reaction of glucose oxidase was observed on the surface of a nano-porous glassy carbon electrode. > A pair of well-defined and reversible redox peaks was observed at the formal potential of approximately -0.439 V. > The apparent electron transfer rate constant was measured to be 5.27 s{sup -1}. > A mechanism for the observed direct electron transfer reaction was proposed, which consists of a two-electron and a two-proton transfer. - Abstract: A pair of well-defined and reversible redox peaks was observed for the direct electron transfer (DET) reaction of an immobilized glucose oxidase (GOx) on the surface of a nano-porous glassy carbon electrode at the formal potential (E{sup o}') of -0.439 V versus Ag/AgCl/saturated KCl. The electron transfer rate constant (k{sub s}) was calculated to be 5.27 s{sup -1}. The dependence of E{sup o}' on pH indicated that the direct electron transfer of the GOx was a two-electron transfer process, coupled with two-proton transfer. The results clearly demonstrate that the nano-porous glassy carbon electrode is a cost-effective and ready-to-use scaffold for the fabrication of a glucose biosensor.

Haghighi, Behzad, E-mail: haghighi@iasbs.ac.ir [Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Gava Zang, Zanjan (Iran, Islamic Republic of); Tabrizi, Mahmoud Amouzadeh [Department of Chemistry, Institute for Advanced Studies in Basic Sciences, P.O. Box 45195-1159, Gava Zang, Zanjan (Iran, Islamic Republic of)

2011-11-30

307

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

Science.gov (United States)

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

Samarukha, I A

2014-01-01

308

Electron transfer reactions of macrocyclic compounds of cobalt  

Energy Technology Data Exchange (ETDEWEB)

The kinetics and mechanisms of reduction of H/sub 2/O/sub 2/, Br/sub 2/, and I/sub 2/ by various macrocyclic tetraaza complexes of cobalt(II), including Vitamin B/sub 12r/, were studied. The synthetic macrocycles studied were all 14-membered rings which varied in the degree of unsaturation,substitution of methyl groups on the periphery of the ring, and substitution within the ring itself. Scavenging experiments demonstrated that the reductions of H/sub 2/O/sub 2/ produce free hydroxyl radicals only in the case of Co((14)ane)/sup 2 +/ but with none of the others. In the latter instances apparently H/sub 2/O/sub 2/ simultaneously oxidizes the metal center and the ligand. The reductions of Br/sub 2/ and I/sub 2/ produce an aquohalocobalt(III) product for all reductants (except B/sub 12r/ + Br/sub 2/, which was complicated by bromination of the corrin ring). The mechanism of halogen reduction was found to involve rate-limiting inner-sphere electron transfer from cobalt to halogen to produce a dihalide anion coordinated to the cobalt center. This intermediate subsequently decomposes in rapid reactions to halocobalt(III) and halogen atom species or reacts with another cobalt(II) center to give two molecules of halocobalt(III). The reductions of halomethylcobaloximes and related compounds and diamminecobaloxime by Cr/sup 2 +/ were also studied. The reaction was found to be biphasic in all cases with the reaction products being halomethane (for the halomethylcobaloximes), Co/sup 2 +/ (in less than 100 percent yield), a Cr(III)-dimethylglyoxime species, a small amount of free dmgH/sub 2/, and a highly-charged species containing both cobalt and chromium. The first-stage reaction occurs with a stoichiometry of 1:1 producing an intermediate with an absorption maximum at 460 nm for all starting reagents. The results were interpreted in terms of inner-sphere coordination of the cobaloxime to the Cr(II) and electron transfer through the oxime N-O bond.

Heckman, R.A.

1978-08-01

309

Proton transfer dynamics at the membrane/water interface: dependence on the fixed and mobile pH buffers, on the size and form of membrane particles, and on the interfacial potential barrier.  

Science.gov (United States)

Crossing the membrane/water interface is an indispensable step in the transmembrane proton transfer. Elsewhere we have shown that the low dielectric permittivity of the surface water gives rise to a potential barrier for ions, so that the surface pH can deviate from that in the bulk water at steady operation of proton pumps. Here we addressed the retardation in the pulsed proton transfer across the interface as observed when light-triggered membrane proton pumps ejected or captured protons. By solving the system of diffusion equations we analyzed how the proton relaxation depends on the concentration of mobile pH buffers, on the surface buffer capacity, on the form and size of membrane particles, and on the height of the potential barrier. The fit of experimental data on proton relaxation in chromatophore vesicles from phototropic bacteria and in bacteriorhodopsin-containing membranes yielded estimates for the interfacial potential barrier for H(+)/OH(-) ions of approximately 120 meV. We analyzed published data on the acceleration of proton equilibration by anionic pH buffers and found that the height of the interfacial barrier correlated with their electric charge ranging from 90 to 120 meV for the singly charged species to >360 meV for the tetra-charged pyranine. PMID:14747306

Cherepanov, Dmitry A; Junge, Wolfgang; Mulkidjanian, Armen Y

2004-02-01

310

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

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

311

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

Science.gov (United States)

Studies on Acidithiobacillus ferrooxidans accepting electrons from Fe(II) have previously focused on cytochrome c. However, we have discovered that, besides cytochrome c, type IV pili (Tfp) can transfer electrons. Here, we report conduction by Tfp of A. ferrooxidans analyzed with a conducting-probe atomic force microscope (AFM). The results indicate that the Tfp of A. ferrooxidans are highly conductive. The genome sequence of A. ferrooxidans ATCC 23270 contains two genes, pilV and pilW, which code for pilin domain proteins with the conserved amino acids characteristic of Tfp. Multiple alignment analysis of the PilV and PilW (pilin) proteins indicated that pilV is the adhesin gene while pilW codes for the major protein element of Tfp. The likely function of Tfp is to complete the circuit between the cell surface and Fe(II) oxides. These results indicate that Tfp of A. ferrooxidans might serve as biological nanowires transferring electrons from the surface of Fe(II) oxides to the cell surface. PMID:23440740

Li, Yongquan; Li, Hongyu

2014-03-01

312

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

Science.gov (United States)

A scanning electrochemical microscope (SECM) was used to arrange two microelectrodes face-to-face separated by a micrometric gap. Polyaniline (PANI) was deposited electrochemically from the SECM tip side until it bridged the two electrodes. The junctions obtained were characterized by following the current through the PANI as a function of its electrochemical potential measured versus a reference electrode acting as a gate electrode in a solid-state transistor. PANI nanojunctions showed conductances below 100 nS in the oxidized state, indicating control of the charge transport within the whole micrometric gap by a limited number of PANI wires. The SECM configuration makes it possible to observe in the same experiment and in the same current range the electron-transfer and electron-transport processes. These two phenomena are distinguished here and characterized by following the variation of the current with the bias voltage and the scan rate. The electron-transfer current changes with the scan rate, while the charge-transport current varies with the bias voltage. Finally, despite the initially micrometric gap, a junction where the conductance is controlled by a single oligoaniline strand is achieved. PMID:23331168

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

2013-02-13

313

Intermolecular interactions in electron transfer through stretched helical peptides.  

Science.gov (United States)

The helical peptide Cys-Ala-Lys-(Glu-Ala-Ala-Ala-Lys)(2)-Ala-NH-(CH(2))(2)-SH has been organized forming a self-assembled monolayer on gold (0.602 peptides per nm(2)), its conductance behavior under stretching conditions being studied using scanning tunnelling microscopy and current sensing atomic force microscopy. The helical conformation of the peptide has been found to play a fundamental role in the conductance. Moreover, variation of the current upon molecular stretching indicates that peptides can be significantly elongated before the conductance drops to zero, the critical elongation being 1.22 ± 0.47 nm. Molecular dynamics simulations of a single peptide in the free state and of a variable number of peptides tethered to a gold surface (i.e. densities ranging from 0.026 to 1.295 peptides per nm(2)) have indicated that the helical conformation is intrinsically favored in solvated environments while in desolvated environments it is retained because of the fundamental role played by peptide-peptide intermolecular interactions. The structure obtained for the system with 24 tethered peptides, with a density of 0.634 peptides per nm(2) closest to the experimental one, is in excellent agreement with experimental observations. On the other hand, simulations in which a single molecule is submitted to different compression and stretching processes while the rest remain in the equilibrium have been used to mimic the variation of the tip-substrate distance in experimental measures. Results allowed us to identify the existence, and in some cases coexistence, of intermolecular and intramolecular ionic ladders, suggesting that peptide-mediated electron transfer occurs through the hopping mechanism. Finally, quantum mechanical calculations have been used to investigate the variation of the electronic structure upon compression and stretching deformations. PMID:22735160

López-Pérez, Daniel E; Revilla-López, Guillermo; Jacquemin, Denis; Zanuy, David; Palys, Barbara; Sek, Slawomir; Alemán, Carlos

2012-08-01

314

Electron Doping by Charge Transfer at LaFeO 3 /Sm 2 CuO 4 Epitaxial Interfaces  

Energy Technology Data Exchange (ETDEWEB)

The breakdown of the lattice translational invariance symmetry that occurs at complex oxide interfaces may profoundly modify their electronic structure, leading to interfacial states with properties drastically different from those of the superlattice individual components. The appearance of a conducting two dimensional (2D) electron gas at the interface between two insulating oxides and induced magnetism in a non-magnetic material are just two among many fascinating examples. [ 1 8 ] One of the key factors underlying novel properties is the modifi cation of the doping and orbital occupancy near those interfaces, which may result from charge transfer processes. [ 3 , 9 11 ] If materials used in heterostructures have different work functions, a non-equilibrium situation will be created at the interface and charge will be transferred until the chemical potential levels off. [ 12 ] The use of such phenomena to modify doping in heterostructures has been proposed theoretically as a new route to avoid the quenched disorder that inevitably accompanies the chemical doping. At the interface between a Mott insulating parent compound of the high critical temperature superconductor (HTSC) family and a suitable material that would act as the charge donor, electron doped phases could be stabilized which would eventually turn metallic and perhaps superconducting. [ 12 , 13 ] Such charge transfer processes have been observed at interfaces involving copper oxides such as La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7 , [ 14 ] La 2 x Sr x CuO 4 /La 2 CuO 4 [ 15 ] and SrTi 1 x Nb x O 3 / Sm 2 CuO 4 . [ 16 ] While a novel 2D superconducting state was found at the La 2-x Sr x CuO 4 /La 2 CuO 4 interface, [ 17 ] the effect of doping by charge transfer could not be examined in the other two cases due to the detrimental effect on the YBa 2 Cu 3 O 7 superconductivity of the spin polarized electrons from La 0.7 Ca 0.3 MnO 3 in one case and due to the conducting nature of the SrTi 1 x Nb x O 3 in the other case, which obscures changes in the conducting properties of the interface layer. In this paper, the structural and

Bruno, Flavio Y. [Universidad Complutense, Spain; Schmidt, R [Universidad Complutense de Madrid, Spain; Varela, Maria [UCM, Dept Fis Aplicada 3, Madrid, Spain; Garcia-Barriocanal, Javier [Universidad Complutense, Spain; Rivera-Calzada, Alberto [Universidad Complutense, Spain; Cuellar, F. [Universidad Complutense de Madrid, Spain; Leon, Carlos [Universidad Complutense de Madrid, Spain; Thakur, P. [European Synchrotron Radiation Facility (ESRF); Cezar, J. C. [European Synchrotron Radiation Facility (ESRF); Brookes, N. B. [European Synchrotron Radiation Facility (ESRF); Garcia-Hernandez, M [Instituto de Ciencia de Materiales de Madrid (ICMM); Dagotto, Elbio R [ORNL; Pennycook, Stephen J [ORNL; Santamaria, J. [Universidad Complutense, Spain

2013-01-01

315

Electron transfer across ?-helical peptides: Potential influence of molecular dynamics  

Science.gov (United States)

Three hydrophobic leucine-rich peptides Fc18L, Ac18L and 18LAc were prepared. These peptides are equipped with a cystein sulfhydryl group which enables the formation of thin films on gold surfaces. Using these peptides, two types of films of ?-helical peptides have been prepared, in which the redox-active peptide Fc18L is diluted by Ac18L ( SAM1) or by a mixture of Ac18L and 18LAc ( SAM2). In SAM1, the dipole moments of the peptides are aligned in the same direction, whereas in SAM2, they are opposite. Reflection absorption infrared spectroscopy (RAIRS) revealed that the peptides are more vertically oriented in SAM2 compared to those in SAM1. The interaction among the macroscopic helix dipoles gives tighter packing of the peptides in SAM2. Importantly, the electron transfer properties in the two films are significantly different, which is rationalized by differences in the molecular dynamics of the two films.

Mandal, Himadri S.; Kraatz, Heinz-Bernhard

2006-07-01

316

Electron transfer across ?-helical peptides: Potential influence of molecular dynamics  

International Nuclear Information System (INIS)

Three hydrophobic leucine-rich peptides Fc18L, Ac18L and 18LAc were prepared. These peptides are equipped with a cystein sulfhydryl group which enables the formation of thin films on gold surfaces. Using these peptides, two types of films of ?-helical peptides have been prepared, in which the redox-active peptide Fc18L is diluted by Ac18L (SAM1) or by a mixture of Ac18L and 18LAc (SAM2). In SAM1, the dipole moments of the peptides are aligned in the same direction, whereas in SAM2, they are opposite. Reflection absorption infrared spectroscopy (RAIRS) revealed that the peptides are more vertically oriented in SAM2 compared to those in SAM1. The interaction among the macroscopic helix dipoles gives tighter packing of the peptides in SAM2. Importantly, the electron transfer properties in the two films are significantly different, which is rationalized by differences in the molecular dynamics of the two films

2006-07-11

317

Oxidation of ascorbate anion by electron transfer to phenoxyl radicals  

International Nuclear Information System (INIS)

Most phenoxyl radicals rapidly oxidize ascorbate anion (rate constants from 4 to 20 x 108 M-1 sec-1) by a simple electron transfer process. The product radical anion is relatively unreactive and has a well-characterized absorption at 360 nm where it has an extinction coefficient of 3300 M-1 cm-1. In the case of a phenoxyl radical produced by OH attack on phenol, oxidation appears to be quantitative. Ascorbate is oxidized only slowly or not at all by less reactive radicals, such as the alcohol radicals, para-semiquinones, or the phenyl radical. Ascorbate can, therefore, be used to selectively remove phenoxyl radicals from many mixed radical systems. Because ascorbate radical anion absorbs only weakly above 390 nm, where phenoxyl and para-semiquinone radicals absorb more strongly, ascorbate can be used to examine the oxidation of substrates in cases where phenoxyl and semiquinone radicals are produced simultaneously. This application is illustrated by a study of the attack of OH at the fluorine position of para-fluorophenol. A second illustrative example is provided by a study of the tertiary oxidation of ascorbate following reduction of the bromophenols by e/sub aq/-. It is shown, in agreement with previous optical and ESR studies, that phenoxyl radicals are produced by rapid protonation of the hydroxyphenyl radical anion in the case of the ortho- and para-isomers but not in the case of the meta-isomer

1977-01-01

318

Electron transfer of peroxidase assemblies at tailored nanocarbon electrodes  

International Nuclear Information System (INIS)

In bioelectrochemistry, the catalytic function of redox enzymes depends largely upon the nature of the working electrode material. One major example of this phenomenon is the improvement of biogenic analyte detection at graphitic carbon with increased edge plane character in the graphene lattice. In our laboratories, we have found that the edge plane character of carbon nanotubes (CNTs) prepared using chemical vapor deposition (CVD) can be tuned via selective doping with nitrogen, termed N-CNTs. In this report, we extend these studies to investigate the influence of N-doping of nanocarbons on the electron transfer of horseradish peroxidase (HRP) using spectrophotometric enzyme activity assays and electrochemical measurements. Our findings demonstrate that HRP adsorption at N-CNTs increases by a factor of two relative to that of nondoped CNTs, with surface coverages, ?m, of 75 ± 4 and 33 ± 5 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) U/mg, respectively. Surprisingly, however, only ?40% of the HRP adsorbed at N-CNTs is electroactive, as assessed by voltammetry of the HRP Fe2+/3+ redox response. By contrast, HRP adsorbed at nondoped CNTs is nearly 100% electroactive, suggesting that the nature of the HRP adsorption (e.g., electrostatic, van der Waals) and geometric factors of heme orientation affect the biocatalytic performance. We also describe studies that utilize the properties of both nondoped CNTs and N-CNTs with adsorbed HRP for unmediated, quantitative H2O2 sensing

2008-10-01

319

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1999-01-21

320

Effects of the electron irradiation energy on synthesis of gold nanoparticles using gas-liquid interfacial plasma  

Science.gov (United States)

Structure controlled gold nanoparticles (AuNPs) are synthesized at the surface of the ionic liquid by the plasma irradiation under the strong magnetic field. The AuNPs are easily synthesized in the region where the edge of the plasma is irradiated, while hardly synthesized in the region where the core plasma is irradiated. In the plasma edge region, high energy electrons collide with neutral gas and the diffused low energy electrons generate the AuNPs by reducing Au ions of the gold chloride. On the other hand, in the core plasma region, the irradiated high energy electrons can dissociate the ionic liquid and generate the new compounds with oxidation effect, which inhibit the synthesis of the AuNPs.

Takahashi, S.; Kaneko, T.

2014-06-01

 
 
 
 
321

Axisymmetric interfacial condensation model  

Energy Technology Data Exchange (ETDEWEB)

This paper employs a simple axisymmetric model to study interfacial condensation. Numerical results show the effects of interfacial forces, subcooling of the liquid, superheating of the vapor, and the presence of a noncondensable gas in the vapor. While pressure and shear stress play an important role in determining the flow fields, and hence interfacial mass and energy transport, interfacial mass fluxes do not. Subcooling of the liquid is the dominant mechanism in determining the interfacial condensation rate. While superheating of the vapor is insignificant, except near the critical point, a noncondensable gas in the vapor greatly reduces condensation.

Gerner, F.M.; Tien, C.L. (Univ. of California, Berkeley (United States))

1989-05-01

322

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

Science.gov (United States)

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

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

2014-05-01

323

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

Energy Technology Data Exchange (ETDEWEB)

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

Tang, Jau

1994-02-01

324

Coherent phonons in CdSe quantum dots triggered by ultrafast electron transfer  

Directory of Open Access Journals (Sweden)

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

Wachtveitl J.

2013-03-01

325

Linker-free layer-by-layer self-assembly of gold nanoparticle multilayer films for direct electron transfer of horseradish peroxidase and H2O2 detection  

International Nuclear Information System (INIS)

Highlights: ? Gold nanoparticle (AuNP) multilayer films were fabricated via a linker-free layer-by-layer assembly. ? Direct electron transfer of horseradish peroxidase (HRP) absorbed on as-prepared AuNP multilayer films was enhanced. ? The optimized HRP/AuNP multilayer film had a relatively rapid response and satisfactory selectivity for H2O2 detection. - Abstract: Au nanoparticle (AuNP) multilayer films were fabricated by combining interfacial assembly and layer-by-layer assembly. The key point is that the procedure does not require assistance of organic linker molecules, thus providing a suitable platform for the modification of biological molecules. Direct electron transfer can easily take place between a glassy carbon electrode and horseradish peroxidase (HRP) molecules adsorbed on AuNP films. The current density of direct electron transfer was closely related to the layer number, m, and reached a maximum value for m = 4. The optimized HRP/AuNP multilayer film had a relatively rapid response and satisfactory selectivity for H2O2 detection. The linear range and the detection limit were 9.8 x 10-6 to 6 x 10-3 mol/L and ?4.9 x 10-6 mol/L (S/N = 3), respectively.

2011-08-01

326

Electron-phonon energy transfer in hot-carrier solar cells  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Hot-carrier solar cells may yield very high efficiency if the heat transfer from electrons to phonons is low enough. In this paper we calculate this heat transfer for the two inelastic mechanisms known to limit the electric conductivity: the multi-valley scattering in non-polar semiconductors and the coupling of electrons to longitudinal optical phonons in polar semiconductors. Heat transfer is ruled by matrix elements deduced from electric conductivity measurements. The cell power extracted ...

Luque Lo?pez, Antonio; Marti? Vega, Antonio

2010-01-01

327

Proton coupled electron transfer and redox active tyrosines in Photosystem II  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this article, progress in understanding proton coupled electron transfer (PCET) in photosystem II is reviewed. Changes in acidity/basicity may accompany oxidation/reduction reactions in biological catalysis. Alterations in the proton transfer pathway can then be used to alter the rates of the electron transfer reactions. Studies of the bioenergetic complexes have played a central role in advancing our understanding of PCET. Because oxidation of the tyrosine results in deprotonation of the ...

Barry, Bridgette A.

2011-01-01

328

Transfer of entanglement from electrons to photons by optical selection rules  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The entanglement transfer from electrons localized in a pair of quantum dots to circularly polarized photons is governed by optical selection rules, enforced by conservation of angular momentum. We point out that the transfer can not be achieved by means of unitary evolution unless the angular momentum of the two initial qubit states differs by 2 units. In particular, for spin-entangled electrons the difference in angular momentum is 1 unit -- so the transfer fails. Neverthe...

Titov, M.; Trauzettel, B.; Michaelis, B.; Beenakker, C. W. J.

2005-01-01

329

Selective electron transfer between the quantum dots under the resonant pulse  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The coherent quantum dynamics of an electron in the quantum-dot ring structure under the resonant electromagnetic pulse is studied theoretically. A possibility of the selective electron transfer between any two dots is demonstrated. The transfer probability as a function of the pulse and dot parameters is calculated. It is shown that this probability can be close to unity. The factors lowering the transfer probability in real systems are discussed. The results obtained may b...

Tsukanov, A. V.; Openov, L. A.

2004-01-01

330

Photoinduced bimolecular electron transfer kinetics in small unilamellar vesicles  

International Nuclear Information System (INIS)

Photoinduced electron transfer (ET) from N,N-dimethylaniline to some coumarin derivatives has been studied in small unilamellar vesicles (SUVs) of the phospholipid, DL-?-dimyristoyl-phosphatidylcholine, using steady-state and time-resolved fluorescence quenching, both below and above the phase transition temperature of the vesicles. The primary interest was to examine whether Marcus inversion [H. Sumi and R. A. Marcus, J. Chem. Phys. 84, 4894 (1986)] could be observed for the present ET systems in these organized assemblies. The influence of the topology of SUVs on the photophysical properties of the reactants and consequently on their ET kinetics has also been investigated. Absorption and fluorescence spectral data of the coumarins in SUVs and the variation of their fluorescence decays with temperature indicate that the dyes are localized in the bilayer of the SUVs. Time-resolved area normalized emission spectra analysis, however, reveals that the dyes are distributed in two different microenvironments in the SUVs, which we attribute to the two leaflets of the bilayer, one toward bulk water and the other toward the inner water pool. The microenvironments in the two leaflets are, however, not indicated to be that significantly different. Time-resolved anisotropy decays were biexponential for all the dyes in SUVs, and this has been interpreted in terms of the compound motion model according to which the dye molecules can experience a fast wobbling-in-cone type of motion as well as a slow overall rotating motion of the cone containing the molecule. The expected bimolecular diffusion-controlled rates in SUVs, as estimated by comparing the microviscosities in SUVs (determined from rotational correlation times) and that in acetonitrile solution, are much slower than the observed fluorescence quenching rates, suggesting that reactant diffusion (translational) does not play any role in the quenching kinetics in the present systems. Accordingly, clear inversions are observed in the correlation of the fluorescence quenching rate constants kq with the free energy change, ?G0 of the reactions. However, the coumarin dyes, C152 and C481 (cf. Scheme 1), show unusually high kq values and high activation barriers, which is not expected from Marcus ET theory. This unusual behavior is explained on the basis of participation of the twisted intramolecular charge transfer states of these two dyes in the ET kinetics

2007-11-21

331

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

Science.gov (United States)

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

Chen, Shengli; Liu, Yuwen; Chen, Junxiang

2014-07-01

332

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

International Nuclear Information System (INIS)

Electron transfer (ET) reactions are one of the most important processes in chemistry and biology. Because of the quantum nature of the processes and the complicated roles of the solvent, theoretical study of ET processes is challenging. To simulate ET processes at the electronic level, we have developed an efficient density functional theory (DFT) quantum mechanical (QM)/molecular mechanical (MM) approach that uses the fractional number of electrons as the order parameter to calculate the redox free energy of ET reactions in solution. We applied this method to study the ET reactions of the aqueous metal complexes Fe(H2O)62+/3+ and Ru(H2O)62+/3+. The calculated oxidation potentials, 5.82 eV for Fe(II/III) and 5.14 eV for Ru(II/III), agree well with the experimental data, 5.50 and 4.96 eV, for iron and ruthenium, respectively. Furthermore, we have constructed the diabatic free energy surfaces from histogram analysis based on the molecular dynamics trajectories. The resulting reorganization energy and the diabatic activation energy also show good agreement with experimental data. Our calculations show that using the fractional number of electrons (FNE) as the order parameter in the thermodynamic integration process leads to efficient sampling and validate the ab initio QM/MM approach in the calculation of redox free energies

2008-03-28

333

Transverse dispersion and interfacial dephasing effects on the shape and amplitude of the ballistic-electron-emission spectroscopy of nanographenes.  

Science.gov (United States)

We investigate charge transport across metal-molecule-metal junctions, i.e. hexagonal and triangular nanographene molecular layers sandwiched between Pt and Pd thin films, as measured by ballistic-electron-emission spectroscopy (BEEM). The measured shape of current-voltage curves cannot be explained in the framework of existing BEEM theories of bulk inorganic semiconductors. We develop a tight-binding model for the BEEM process and propose that the energetic dispersion of molecular layers and the dephasing effect due to the interface states account for the anomalous BEEM current-voltage behavior and play an important role in determining the shape of the curve. The electron-phonon scattering can also affect the shape of current-voltage curves. PMID:22634547

Wang, Xue-Feng; Chandrasekhar, Natarajan; Su, Haibin

2012-06-27

334

Interfacial Al segregation limiting electron mobility at the inverted interface of AlGaAs/GaAs quantum well  

International Nuclear Information System (INIS)

Low-temperature mobility spectrum of two-dimensional electron gas (2DEG) at the inverted interface of AlGaAs/GaAs quantum well has been evaluated theoretically taking into account nonabrupt composition profile due to segregation of Al atoms into the well. In this approach, the Al content profile at the inverted interface has been considered as exponential decay function, and transport mobility components were calculated in the Lindhard's framework and flat interface approximation. It was found that alloy scattering due to segregated Al atoms can be significant, and even limits electron mobility at high 2DEG densities. The segregation decay length is evaluated from comparing experimental mobility spectrum with theory. (paper)

2012-10-01

335

MnO2-filled multiwalled carbon nanotube/polyaniline nanocomposites with enhanced interfacial interaction and electronic properties  

International Nuclear Information System (INIS)

This paper reports the synthesis and characterization of new ternary nanocomposites combining polyaniline (PANI), multiwalled carbon nanotubes (MWCNTs) and manganese dioxide (MnO2). MnO2 was successfully incorporated within the MWCNTs. In situ polymerization of aniline in the presence of MWCNTs-MnO2 was carried out to form PANI/MWCNT-MnO2 nanocomposites, which were characterized by UV-visible and Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy with energy-dispersive X-ray analysis, and transmission electron microscopy, as well as electrical conductivity measurements. The PANI/MWCNT-MnO2 nanocomposites showed enhanced electrical conductivity compared to neat PANI and PANI/MWCNTs without MnO2 addition.

2009-09-01

336

Transverse dispersion and interfacial dephasing effects on the shape and amplitude of the ballistic-electron-emission spectroscopy of nanographenes  

International Nuclear Information System (INIS)

We investigate charge transport across metal-molecule-metal junctions, i.e. hexagonal and triangular nanographene molecular layers sandwiched between Pt and Pd thin films, as measured by ballistic-electron-emission spectroscopy (BEEM). The measured shape of current-voltage curves cannot be explained in the framework of existing BEEM theories of bulk inorganic semiconductors. We develop a tight-binding model for the BEEM process and propose that the energetic dispersion of molecular layers and the dephasing effect due to the interface states account for the anomalous BEEM current-voltage behavior and play an important role in determining the shape of the curve. The electron-phonon scattering can also affect the shape of current-voltage curves. (paper)

2012-06-27

337

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

International Nuclear Information System (INIS)

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

2006-05-01

338

Vibrational coherence in electron transfer: an exactly solvable model  

Energy Technology Data Exchange (ETDEWEB)

The exact solution for a transition probability in vibrationally modulated electron transfer is found by employing three independent methods based on: (a) a path integral technique, (b) direct diagonalization of the Hamiltonian by a unitary transformation, and (c) Keldysh-Green's function techniques. We also consider a solution in the noninteracting blip approximation (NIBA). The comparative analysis reveals that the NIBA is valid at longer times, small reorganization energy, high temperatures, and for small transition matrix elements, {delta}{sub 0}, while at large {delta}{sub 0} the NIBA provides relaxation rates as much as twice greater. When {delta}{sub 0}=0, the NIBA transition probability difference oscillates in time with the frequency {approx}{radical}(E{sub r}kT/(h/2{pi})) exhibiting incorrect behavior. At low temperatures, the exact solution yields power-law evolution. The NIBA solution exhibits incorrect behavior at small values of {delta}{sub 0}. At larger transition matrix elements, the NIBA practically yields a correct description, i.e. the decay in accordance with the exact solution while the coherent oscillations reveal some phase shift at longer times. An important case of several mode modulation is also studied. The Fourier analysis of the transition probability provides useful information of the vibrational couplings and frequencies. In general, the Fourier spectrum of the transition probability is the sum of the contributions from the harmonics with the frequencies vertical bar {delta}{sub 0}+{sigma}{sub i=0}{sup n}({+-})k{sub i}{omega}{sub i} vertical bar (k{sub i}=0,1,2,3,...), where {omega}{sub i} is a modulating frequency. Thus, a generally used assumption about coincidence of coherence and vibrational frequencies appears to be incorrect.

Creechley, Jaremy; Dahnovsky, Yuri

2004-01-26

339

EZINE – a way of electronic transfer for specific information?  

Directory of Open Access Journals (Sweden)

Full Text Available The transfer of information is essential to any society. The channels through which the information is transferred and the support used for memorize it represents essential elements which can determine the speed of transfer, the quality of information at the reception point and the cost also. This work paper presents a way that can be used in specialized information transfer: the "ezine" concept. This concept is presented together with its advantages, a few practical aspects and a case study about the effects and the costs that can be reached if we used it.

Daniela DANCIULESCU

2006-01-01

340

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-03-01

 
 
 
 
341

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

Distance-dependent energy transfer occurs from the Metal-to-Ligand Charge Transfer (MLCT) excited state to an anthracene-acrylate derivative (Acr-An) incorporated into the polymer network of a semirigid poly(ethyleneglycol)dimethacrylate monolith. Following excitation, to Acr-An triplet energy transfer occurs followed by long-range, Acr-3An—Acr-An ? Acr-An—Acr-3An, energy migration. With methyl viologen dication (MV2+) added as a trap, Acr-3An + MV2+ ? Acr-An+ + MV+ electron...

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

2012-01-01

342

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

CERN Document Server

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

Vanevic, M; Belzig, W; Vanevic, Mihajlo; Nazarov, Yuli V.; Belzig, Wolfgang

2007-01-01

343

Structural, dynamic, and energetic aspects of long-range electron transfer in photosynthetic reaction centers  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Intramolecular electron transfer within proteins plays an essential role in biological energy transduction. Electron donor and acceptor cofactors are bound in the protein matrix at specific locations, and protein–cofactor interactions as well as protein conformational changes can markedly influence the electron transfer rates. To assess these effects, we have investigated charge recombination from the primary quinone acceptor to the special pair bacteriochlorophyll dimer in wild-type reacti...

2004-01-01

344

Quantum Dynamical Approach to Electron Transfers in DNA-Molecular Nanowires  

International Nuclear Information System (INIS)

We numerically investigate electron transfers in nanowires which consist of deoxyribonucleic acid (DNA) molecules (up to five base pairs for double-strands and seven bases for single-strands) by quantum dynamical calculations. DNA molecules are applied to organic nanodevices and the performance depends on electronic transfer properties. Combining quantum chemical molecular-orbital calculations and stochastic mechanics, we provide an analyzing method of quantum dynamical electron motions. From one-electron wavefunctions or molecular orbitals, we calculate some dynamical properties, such as mean-square displacement and self-diffusion coefficients relating with electron mobility. Our calculation suggests that the electron transfers through the double-strands of GC base pairs while the electrons are localized in the double-strands of AT base pairs nor the single-strands of G bases

2007-04-01

345

Quantum Dynamical Approach to Electron Transfers in DNA-Molecular Nanowires  

Energy Technology Data Exchange (ETDEWEB)

We numerically investigate electron transfers in nanowires which consist of deoxyribonucleic acid (DNA) molecules (up to five base pairs for double-strands and seven bases for single-strands) by quantum dynamical calculations. DNA molecules are applied to organic nanodevices and the performance depends on electronic transfer properties. Combining quantum chemical molecular-orbital calculations and stochastic mechanics, we provide an analyzing method of quantum dynamical electron motions. From one-electron wavefunctions or molecular orbitals, we calculate some dynamical properties, such as mean-square displacement and self-diffusion coefficients relating with electron mobility. Our calculation suggests that the electron transfers through the double-strands of GC base pairs while the electrons are localized in the double-strands of AT base pairs nor the single-strands of G bases.

Sakamoto, S; Ohmachi, Y; Tomiya, M [Department of Materials and Life Science, Seikei University, Musashino, Tokyo 180-8633 (Japan)

2007-04-15

346

Electron transfer flavoprotein domain II orientation monitored using double electron-electron resonance between an enzymatically reduced, native FAD cofactor, and spin labels  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Human electron transfer flavoprotein (ETF) is a soluble mitochondrial heterodimeric flavoprotein that links fatty acid ?-oxidation to the main respiratory chain. The crystal structure of human ETF bound to medium chain acyl-CoA dehydrogenase indicates that the flavin adenine dinucleotide (FAD) domain (?II) is mobile, which permits more rapid electron transfer with donors and acceptors by providing closer access to the flavin and allows ETF to accept electrons from at least 10 different flav...

2011-01-01

347

Poly(N-isopropylacrylamide) brushes grafted from cellulose nanocrystals via surface-initiated single-electron transfer living radical polymerization.  

Science.gov (United States)

Cellulose nanocrystals (CNCs) or nanowhiskers produced from sulfuric acid hydrolysis of ramie fibers were used as substrates for surface chemical functionalization with thermoresponsive macromolecules. The CNCs were grafted with poly(N-isopropylacrylamide) brushes via surface-initiated single-electron transfer living radical polymerization (SI-SET-LRP) under various conditions at room temperature. The grafting process was confirmed via Fourier transform IR spectroscopy and X-ray photoelectron spectroscopy and the different molecular masses of the grafts were quantified and found to depend on the initiator and monomer concentrations used. No observable damage occurred to the CNCs after grafting, as determined by X-ray diffraction. Size exclusion chromatography analyses of polymer chains cleaved from the cellulose nanocrystals indicated that a higher degree of polymerization was achieved by increasing initiator or monomer loading, most likely caused by local heterogeneities yielding higher rates of polymerization. It is expected that suspension stability, interfacial interactions, friction, and other properties of grafted CNCs can be controlled by changes in temperature and provide a unique platform for further development of stimuli-responsive nanomaterials. PMID:20843063

Zoppe, Justin O; Habibi, Youssef; Rojas, Orlando J; Venditti, Richard A; Johansson, Leena-Sisko; Efimenko, Kirill; Osterberg, Monika; Laine, Janne

2010-10-11

348

Ligand and Tetrathiometalate Effects in Induced Internal Electron Transfer Reactions.  

Science.gov (United States)

New rhenium sulfide complexes, [Re(IV)(2)(&mgr;-S)(2)(&mgr;-S(2))(&mgr;-S(2)COR)(S(2)COR)(2)](-) and [Re(IV)(2)(&mgr;-S)(2)(S(2)COR)(4)], and a new tungsten sulfide complex, [WS(S(2))(S(2)CC(6)H(5))(2)], have been synthesized and isolated via induced internal redox reactions involving the appropriate tetrathiometalate and 1,1-dithiolate disulfide. The red complex [Re(IV)(2)(&mgr;-S)(2)(&mgr;-S(2))(&mgr;-S(2)COR)(S(2)COR)(2)](-), 1, was isolated from the reaction of dialkylxanthogen disulfide, [(ROCS(2))(2)], and tetraethylammonium tetrathioperrhenate, [Et(4)N][Re(VII)S(4)]. Crystal structure analysis of 1 reveals an edge-sharing (&mgr;-S)(2) bioctahedron containing both bridging disulfide and xanthate ligands. This reaction is compared to the known reaction between tetraalkylthiuram disulfide, [(R(2)NCS(2))(2)], and [Et(4)N][ReS(4)], which produces the green complex [Re(IV)(2)(&mgr;-S)(2)(S(2)CNR(2))(4)]. The corresponding green alkyl xanthate analogue, [Re(IV)(2)(&mgr;-S)(2)(S(2)COR)(4)], 2, was synthesized by a simple redox reaction between rhenium pentachloride, ReCl(5), and potassium alkyl xanthate, [K(S(2)COR)]. Comparing 1 with other known [ReS(4)](-)/1,1-dithiolate disulfide reaction products, such as [Re(IV)(2)(&mgr;-S)(2)(S(2)CNR(2))(4)] and [Re(III)(S(2)CC(6)H(5))(S(3)CC(6)H(5))(2)], shows a correlation between the electron-donating ability of the ligand and the nature of the reaction product. Reactions of [Et(4)N](2)[Mo(VI)S(4)], [Et(4)N][Re(VII)S(4)], or [Et(4)N](2)[W(VI)S(4)] with dithiobenzoate disulfide, [(S(2)CC(6)H(5))(2)], reveal a correlation between the ligand-to-metal charge transfer energy band (LMCT(1)) of the tetrathiometalate and the reaction product. The known purple complex [Mo(IV)(S(2)CC(6)H(5))(4)] and two new green complexes, [Re(III)(S(2)CC(6)H(5))(S(3)CC(6)H(5))(2)] (recently communicated) and [W(VI)S(S(2))(S(2)CC(6)H(5))(2)], were isolated from related reactions. PMID:11670869

McConnachie, C. A.; Stiefel, E. I.

1999-03-01

349

Transferable pseudoclassical electrons for aufbau of atomic ions.  

Science.gov (United States)

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

Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

2014-06-01

350

Interfacial behavior of polymer electrolytes  

Energy Technology Data Exchange (ETDEWEB)

Evidence is presented concerning the effect of surfaces on the segmental motion of PEO-based polymer electrolytes in lithium batteries. For dry systems with no moisture the effect of surfaces of nano-particle fillers is to inhibit the segmental motion and to reduce the lithium ion transport. These effects also occur at the surfaces in composite electrodes that contain considerable quantities of carbon black nano-particles for electronic connection. The problem of reduced polymer mobility is compounded by the generation of salt concentration gradients within the composite electrode. Highly concentrated polymer electrolytes have reduced transport properties due to the increased ionic cross-linking. Combined with the interfacial interactions this leads to the generation of low mobility electrolyte layers within the electrode and to loss of capacity and power capability. It is shown that even with planar lithium metal electrodes the concentration gradients can significantly impact the interfacial impedance. The interfacial impedance of lithium/PEO-LiTFSI cells varies depending upon the time elapsed since current was turned off after polarization. The behavior is consistent with relaxation of the salt concentration gradients and indicates that a portion of the interfacial impedance usually attributed to the SEI layer is due to concentrated salt solutions next to the electrode surfaces that are very resistive. These resistive layers may undergo actual phase changes in a non-uniform manner and the possible role of the reduced mobility polymer layers in dendrite initiation and growth is also explored. It is concluded that PEO and ethylene oxide-based polymers are less than ideal with respect to this interfacial behavior.

Kerr, John; Kerr, John B.; Han, Yong Bong; Liu, Gao; Reeder, Craig; Xie, Jiangbing; Sun, Xiaoguang

2003-06-03

351

Steric effects in photoinduced electron transfer reactions of ruthenium(II) complexes with aromatic amines  

International Nuclear Information System (INIS)

The rate constants (kq) of excited state electron transfer reactions of RuL32+ complexes (L is 4-alkyl-4'-methyl-2, 2'-bipyridyl) with several aromatic amines are sensitive to the size of the ligand and nature of the amine. The variation of kq with the size of the ligand is explained in terms of the change of electron transfer distance and steric effect. The importance of back electron transfer to form *RuL32+ in the endoergic and slightly exoergic regions has been realised. (author). 1 tab., 4 figs., 19 refs

1991-01-01

352

Study of intermediates from transition metal excited-state electron-transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

Conventional and fast-kinetics techniques of photochemistry, photophysics, radiation chemistry, and electrochemistry were used to study the intermediates involved in transition metal excited-state electron-transfer reactions. These intermediates were excited state of Ru(II) and Cr(III) photosensitizers, their reduced forms, and species formed in reactions of redox quenchers and electron-transfer agents. Of particular concern was the back electron-transfer reaction between the geminate pair formed in the redox quenching of the photosensitizers, and the dependence of its rate on solution medium and temperature in competition with transformation and cage escape processes. (DLC)

Hoffman, M.Z.

1992-07-31

353

Electron- and hydride-transfer reactivity of an isolable manganese(V)-oxo complex.  

Science.gov (United States)

The electron-transfer and hydride-transfer properties of an isolated manganese(V)?oxo complex, (TBP8Cz)Mn(V)(O) (1) (TBP8Cz = octa-tert-butylphenylcorrolazinato) were determined by spectroscopic and kinetic methods. The manganese(V)?oxo complex 1 reacts rapidly with a series of ferrocene derivatives ([Fe(C5H4Me)2], [Fe(C5HMe4)2], and ([Fe(C5Me5)2] = Fc*) to give the direct formation of [(TBP8Cz)Mn(III)(OH)]? ([2-OH]?), a two-electron-reduced product. The stoichiometry of these electron-transfer reactions was found to be (Fc derivative)/1 = 2:1 by spectral titration. The rate constants of electron transfer from ferrocene derivatives to 1 at room temperature in benzonitrile were obtained, and the successful application of Marcus theory allowed for the determination of the reorganization energies (?) of electron transfer. The ? values of electron transfer from the ferrocene derivatives to 1 are lower than those reported for a manganese(IV)?oxo porphyrin. The presumed one-electron-reduced intermediate, a Mn(IV) complex, was not observed during the reduction of 1. However, a Mn(IV) complex was successfully generated via one-electron oxidation of the Mn(III) precursor complex 2 to give [(TBP8Cz)Mn(IV)]+ (3). Complex 3 exhibits a characteristic absorption band at ?(max) = 722 nm and an EPR spectrum at 15 K with g(max)? = 4.68, g(mid)? = 3.28, and g(min)? = 1.94, with well-resolved 55Mn hyperfine coupling, indicative of a d3 Mn(IV)S = 3/2 ground state. Although electron transfer from [Fe(C5H4Me)2] to 1 is endergonic (uphill), two-electron reduction of 1 is made possible in the presence of proton donors (e.g., CH3CO2H, CF3CH2OH, and CH3OH). In the case of CH3CO2H, saturation behavior for the rate constants of electron transfer (k(et)) versus acid concentration was observed, providing insight into the critical involvement of H+ in the mechanism of electron transfer. Complex 1 was also shown to be competent to oxidize a series of dihydronicotinamide adenine dinucleotide (NADH) analogues via formal hydride transfer to produce the corresponding NAD+ analogues and [2-OH]?. The logarithms of the observed second-order rate constants of hydride transfer (k(H)) from NADH analogues to 1 are linearly correlated with those of hydride transfer from the same series of NADH analogues to p-chloranil. PMID:21218824

Fukuzumi, Shunichi; Kotani, Hiroaki; Prokop, Katharine A; Goldberg, David P

2011-02-16

354

76 FR 81019 - Electronic Fund Transfers (Regulation E)  

Science.gov (United States)

...or (iii) Held in book-entry form by a...language other than English, provided that the...transfers made on the books of correspondent banks...languages other than English, provided they are available in English upon request....

2011-12-27

355

77 FR 6310 - Electronic Fund Transfers (Regulation E)  

Science.gov (United States)

...just described, and the quantitative and qualitative characteristics of the...this service, and the quantitative and qualitative characteristics of the...these transfers, and the quantitative and qualitative characteristics of...

2012-02-07

356

Detection of single-electron heat transfer statistics  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We consider a quantum dot system whose charge fluctuations are monitored by a quantum point contact allowing for the detection of both charge and transferred heat statistics. Our system consists of two nearby conductors that exchange energy via Coulomb interaction. In interfaces consisting of capacitively coupled quantum dots, energy transfer is discrete and can be measured by charge counting statistics. We investigate gate-dependent deviations away from a charge fluctuation theorem in the pr...

Sa?nchez, Rafael; Bu?ttiker, Markus

2012-01-01

357

Enhanced electron-transfer reactivity of nonheme manganese(IV)-oxo complexes by binding scandium ions.  

Science.gov (United States)

One and two scandium ions (Sc(3+)) are bound strongly to nonheme manganese(IV)-oxo complexes, [(N4Py)Mn(IV)(O)](2+) (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) and [(Bn-TPEN)Mn(IV)(O)](2+) (Bn-TPEN = N-benzyl-N,N',N'-tris(2-pyridylmethyl)-1,2-diaminoethane), to form Mn(IV)(O)-(Sc(3+))1 and Mn(IV)(O)-(Sc(3+))2 complexes, respectively. The binding of Sc(3+) ions to the Mn(IV)(O) complexes was examined by spectroscopic methods as well as by DFT calculations. The one-electron reduction potentials of the Mn(IV)(O) complexes were markedly shifted to a positive direction by binding of Sc(3+) ions. Accordingly, rates of the electron transfer reactions of the Mn(IV)(O) complexes were enhanced as much as 10(7)-fold by binding of two Sc(3+) ions. The driving force dependence of electron transfer from various electron donors to the Mn(IV)(O) and Mn(IV)(O)-(Sc(3+))2 complexes was examined and analyzed in light of the Marcus theory of electron transfer to determine the reorganization energies of electron transfer. The smaller reorganization energies and much more positive reduction potentials of the Mn(IV)(O)-(Sc(3+))2 complexes resulted in remarkable enhancement of the electron-transfer reactivity of the Mn(IV)(O) complexes. Such a dramatic enhancement of the electron-transfer reactivity of the Mn(IV)(O) complexes by binding of Sc(3+) ions resulted in the change of mechanism in the sulfoxidation of thioanisoles by Mn(IV)(O) complexes from a direct oxygen atom transfer pathway without metal ion binding to an electron-transfer pathway with binding of Sc(3+) ions. PMID:23742163

Yoon, Heejung; Lee, Yong-Min; Wu, Xiujuan; Cho, Kyung-Bin; Sarangi, Ritimukta; Nam, Wonwoo; Fukuzumi, Shunichi; Fuhkuzumi, Shunichi

2013-06-19

358

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-06-14

359

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

International Nuclear Information System (INIS)

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

2013-06-14

360

Electron localization function study on intramolecular electron transfer in the QTTFQ and DBTTFI radical anions.  

Science.gov (United States)

The unsymmetrical distribution of the unpaired electron in the ground state of the DBTTFI(•-) radical anion (bi(6-n-butyl-5,7-dioxo-6,7-dihydro-5H-[1,3]dithiolo[4,5-f]isoindole-2-ylidene) is theoretically predicted using the M06-2X/6-31+G(d,p) level of calculations. The results are additionally confirmed by single point calculations at B3LYP/aug-cc-pVTZ, LC-?PBE/aug-cc-pVTZ, and M06-2X/aug-cc-pVTZ levels. DBTTFI, containing the TTF (tetrathiafulvalene) fragment, may be used in the construction of organic microelectronic devices, similarly to the radical anion of QTTFQ. The unsymmetrical distribution of spin density in (QTTFQ)(•-) has been confirmed using M06-2X/aug-cc-pVTZ calculations, with subsequent study using topological analysis of electron localization function (ELF). The reorganization of the chemical bonds during intramolecular electron transfer in (QTTFQ)(•-) and (DBTTFI)(•-) has been analyzed using bonding evolution theory (BET). The reaction path has been simulated by the IRC procedure, and the evolution of valence basins has been described using catastrophe theory. The simple mechanisms: (QTTFQ)(•-): ?-1-3-CC(+)-0: (-•)(QTTFQ) and (DBTTFI)(•-): ?-1-3-[F](4)[F(+)](4)-0: (-•)(DBTTFI), each consisting of three steps, have been observed. Two cusp or 4-fold catastrophes occur immediately after the TS. Our study shows that potential future microelectronic devices, constructed on the basis of the (QTTFQ)(•-) and (DBTTFI)(•-) systems, should exploit the properties of the C?C bond. PMID:22029410

Kalinowski, Jaroslaw; Berski, Slawomir; Gordon, Agnieszka J

2011-11-24

 
 
 
 
361

ElectronTransfer Induced Ring Opening of α-Epoxyketones: Spirodioxolane Formation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Stereospecific formation of spirodioxolanes has been observed on electron transfer induced ring opening of α-epoxyketones by 2,4,6-triphenylpyrylium tetrafluoroborate in the presence of cyclohexanone

2002-01-01

362

Electron Transfer Experiments and Atomic Magnetism Values. Progress Report, February 1, 1975--September 30, 1975.  

Science.gov (United States)

Progress in the first seven months of this new research is described. A new apparatus was constructed, tested and moved to Oak Ridge National Laboratory for studies using the Penning ion source test facility. Preliminary electron transfer cross section re...

J. E. Bayfield V. W. Hughes

1975-01-01

363

Photoinduced electron transfer reactions of ruthenium(II)-complexes containing amino acid with quinones.  

Science.gov (United States)

With the aim of mimicking, at basic level the photoinduced electron transfer process in the reaction center of photosystem II, ruthenium(II)-polypyridyl complexes, carrying amino acids were synthesized and studied their photoinduced electron transfer reactions with quinones by steady state and time resolved measurements. The reaction of quinones with excited state of ruthenium(II)-complexes, I-V in acetonitrile has been studied by luminescence quenching technique and the rate constant, k(q), values are close to the diffusion controlled rate. The detection of the semiquinone anion radical in this system using time-resolved transient absorption spectroscopy confirms the electron transfer nature of the reaction. The semiclassical theory of electron transfer has been successfully applied to the photoluminescence quenching of Ru(II)-complexes with quinones. PMID:24590578

Eswaran, Rajkumar; Kalayar, Swarnalatha; Paulpandian, Muthu Mareeswaran; Seenivasan, Rajagopal

2014-05-01

364

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

Science.gov (United States)

...operation of Electronic Benefit Transfer (EBT) systems for the Food Stamp Program as...October 1, 2002, State agencies must have EBT systems implemented statewide, unless...faces unusual barriers to implementing an EBT system. In general, these rules...

2009-01-01

365

Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

Pascal Rathelot; Vincent Rémusat; Patrice Vanelle

2002-01-01

366

Model-free Investigation of Ultrafast Bimolecular Chemical Reactions: Bimolecular Photo Induced Electron Transfer  

Directory of Open Access Journals (Sweden)

Full Text Available Using photoinduced bimolecular electron transfer reactions as example we demonstrate how diffusion controlled bimolecular chemical reactions can be studied in a model-free manner by quantitatively combining different ultrafast spectroscopical tools.

Rosspeintner Arnulf

2013-03-01

367

Radiation and photo induced electron transfer processes: Exciting possibilities for basic research and applications  

International Nuclear Information System (INIS)

Radiation and/or photo induced electron transfer reaction results in retrievable storage of information, with extensive applications ranging from dosimetry, efficient light conversion molecular devices (LCMD), photo refraction, optical phase conjunction and holography. These areas gives ample new opportunities to conduct basic investigations to elucidate the mechanistic aspects of photo (radiation) induced electron transfer, and to translate the acquired knowledge into making a device. The talk will focus on the investigation by the author on photo induced electron transfer reaction in photorefractive systems and also on the radiation induced electron transfer processes in dosimetric materials. Furthermore, the recent trends in the light conversion molecular devices using rare earth complexes and the fluorescent molecular sensors for cation recognition will be discussed. (author)

2001-01-01

368

Synthesis of 3-Alkenyl-1-azaanthraquinones via Diels-Alder and Electron Transfer Reactions  

Directory of Open Access Journals (Sweden)

Full Text Available A convenient route to 3-alkenyl-1-azaanthraquinones via a hetero Diels-Alder reaction between an azadiene and naphthoquinone, a free radical chlorination and an electron transfer reaction is reported.

Patrice Vanelle

2002-12-01

369

Electron transfer from humic substances to biogenic and abiogenic Fe(III) oxyhydroxide minerals.  

Science.gov (United States)

Microbial humic substance (HS) reduction and subsequent abiotic electron transfer from reduced HS to poorly soluble Fe(III) (oxyhydr)oxides, a process named electron shuttling, significantly increases microbial Fe(III) mineral reduction rates. However, the importance of electron shuttling in nature and notably the electron transfer from HS to biogenic Fe(III) (oxyhydr)oxides have thus far not been determined. In this study, we have quantified the rate and extent of electron transfer from reduced and nonreduced Pahokee Peat humic acids (PPHA) and fresh soil organic matter (SOM) extracts to both synthetic and environmentally relevant biogenic Fe(III) (oxyhydr)oxides. We found that biogenic Fe(III) minerals were reduced faster and to an equal or higher degree than their abiogenic counterparts. Differences were attributed to differences in crystallinity and the association of bacterial biomass with biogenic minerals. Compared to purified PPHA, SOM extract transferred fewer electrons per milligram of carbon and electron transfer was observed only to poorly crystalline ferrihydrite but not to more crystalline goethite. This indicates a difference in redox potential distribution of the redox-active functional groups in extracted SOM relative to the purified PPHA. Our results suggest that HS electron shuttling can also contribute to iron redox processes in environments where biogenic Fe(III) minerals are present. PMID:24400782

Piepenbrock, Annette; Schröder, Christian; Kappler, Andreas

2014-02-01

370

Characterization of interfacial failure in SiC reinforced Si3N4 matrix composite material by both fiber push-out testing and Auger electron spectroscopy  

Science.gov (United States)

AES depth profiling and a fiber push-out test for interfacial shear-strength determination have been used to ascertain the mechanical/chemical properties of the fiber/matrix interface in SiC-reinforced reaction-bonded Si3N4, with attention to the weak point where interfacial failure occurs. In the cases of both composite fracture and fiber push-outs, the interfacial failure occurred either between the two C-rich coatings that are present on the double-coated SiC fibers, or between the inner C-rich coating and the SiC fiber. Interface failure occurs at points of very abrupt concentration changes.

Eldridge, J. I.; Honecy, F. S.

1990-01-01

371

Direct electron transfer of Trametes hirsuta laccase adsorbed at unmodified nanoporous gold electrodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The enzyme Trametes hirsuta laccase undergoes direct electron transfer at unmodified nanoporous gold electrodes, displaying a current density of 28 mu A/cm(2). The response indicates that ThLc was immobilised at the surface of the nanopores in a manner which promoted direct electron transfer, in contrast to the absence of a response at unmodified polycrystalline gold electrodes. The bioelectrocatalytic activity of ThLc modified nanoporous gold electrodes was strongly dependent on the presence...

Salaj-kosla, Urszula; Poeller, Sascha; Schuhmann, Wolfgang; Shleev, Sergey; Magner, Edmond

2013-01-01

372

Person-to-person electronic funds transfers: Recent developments and policy issues  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The paper investigates the reasons why person-to-person electronic funds transfers are still not very common in the United States compared with practices in many other countries. The paper also describes recent enhancements to online and mobile banking that provide account holders with low-cost interfaces to manage person-to-person electronic funds transfers via automated clearing house (ACH). On the theoretical side, the paper characterizes the critical mass levels needed for payment instrum...

Shy, Oz

2010-01-01

373

FinalReport for completed IPP-0110 and 0110A Projects:"High Energy Ion Technology of Interfacial Thin Film Coatings for Electronic, Optical and Industrial Applications"  

Energy Technology Data Exchange (ETDEWEB)

The DOE-supported IPP (Initiatives for Proliferation Prevention) Project, IPP-0110, and its accompanying 'add-on project' IPP-0110A, entitled 'High Energy Ion Technology of Interfacial Thin Film Coatings for Electronic, Optical and Industrial Applications' was a collaborative project involving the Lawrence Berkeley National Laboratory (LBNL) as the U.S. DOE lab; the US surface modification company, Phygen, Inc., as the US private company involved; and the High Current Electronics Institute (HCEI) of the Russian Academy of Sciences, Tomsk, Siberia, Russia, as the NIS Institute involved. Regular scientific research progress meetings were held to which personnel came from all participating partners. The meetings were held mostly at the Phygen facilities in Minneapolis, Minnesota (with Phygen as host) with meetings also held at Tomsk, Russia (HCEI as host), and at Berkeley, California (LBNL as host) In this way, good exposure of all researchers to the various different laboratories involved was attained. This report contains the Final Reports (final deliverables) from the Russian Institute, HCEI. The first part is that for IPP-0110A (the 'main part' of the overall project) and the second part is that for the add-on project IPP-0110A. These reports are detailed, and contain all aspects of all the research carried out. The project was successful in that all deliverables as specified in the proposals were successfully developed, tested, and delivered to Phygen. All of the plasma hardware was designed, made and tested at HCEI, and the performance was excellent. Some of the machine and performance parameters were certainly of 'world class'. The goals and requirements of the IPP Project were well satisfied. I would like to express my gratitude to the DOE IPP program for support of this project throughout its entire duration, and for the unparalleled opportunity thereby provided for all of the diverse participants in the project to join in this collaborative research. The benefits are superb, as measured in quite a number of different ways.

Brown, Ian

2009-09-01

374

Microbial nanowires: a new paradigm for biological electron transfer and bioelectronics.  

Science.gov (United States)

The discovery that Geobacter sulfurreducens can produce protein filaments with metallic-like conductivity, known as microbial nanowires, that facilitate long-range electron transport is a paradigm shift in biological electron transfer and has important implications for biogeochemistry, microbial ecology, and the emerging field of bioelectronics. Although filaments in a wide diversity of microorganisms have been called microbial nanowires, the type IV pili of G. sulfurreducens and G. metallireducens are the only filaments that have been shown to be required for extracellular electron transport to extracellular electron acceptors or for conduction of electrons through biofilms. Studies of G. sulfurreducens pili preparations and intact biofilms under physiologically relevant conditions have provided multiple lines of evidence for metallic-like conduction along the length of pili and for the possibility of pili networks to confer high conductivity within biofilms. This mechanism of electron conduction contrasts with the previously known mechanism for biological electron transfer via electron tunneling or hopping between closely associated molecules, a strategy unlikely to be well adapted for long-range electron transport outside the cell. In addition to promoting electron exchange with abiotic electron acceptors, microbial nanowires have recently been shown to be involved in direct interspecies electron transfer between syntrophic partners. An improved understanding of the mechanisms for metallic-like conductivity in microbial nanowires, as well as engineering microorganisms with desirable catalytic abilities with nanowires, could lead to new applications in microbial electrosynthesis and bioelectronics. PMID:22614997

Malvankar, Nikhil S; Lovley, Derek R

2012-06-01

375

Elastic electron-deuteron scattering at high momentum transfer  

International Nuclear Information System (INIS)

We show that a careful conventional treatment of exchange currents in the calculation of the deuteron form factor 022 is not in contradiction with experiment. It rather shows an overall good agreement. We propose measurements of the deuteron form factor at momentum transfer much higher than q2approx. =100 fm-2 in order to obtain valuable information on the neutron form factor

1976-02-16

376

Transfer of single electrons and single cooper pairs in nanojunction circuits  

International Nuclear Information System (INIS)

Electrons can be made to pass through a circuit one by one, in nanoscale devices based on the combination of the Coulomb interaction between electrons and their passage by quantum tunnelling through an insulating barrier. Under appropriate conditions, when parts of the circuit are superconducting, it is possible to observe a direct manifestation of electron pairing: the transfer of electrons two by two. Single-electron devices provide a new way of measuring the charge quantum, and clarify how electronic signal processing at the molecular level might function. (authors). 59 refs., 10 figs

1994-01-01

377

Ultrafast photoinduced electron transfer in coumarin 343 sensitized TiO2-colloidal solution  

Directory of Open Access Journals (Sweden)

Full Text Available Photoinduced electron transfer from organic dye molecules to semiconductor nanoparticles is the first and most important reaction step for the mechanism in the so called “wet solar cells” [1]. The time scale between the photoexcitation of the dye and the electron injection into the conduction band of the semiconductor colloid varies from a few tens of femtoseconds to nanoseconds, depending on the specific electron transfer parameters of the system, e.g., electronic coupling or free energy values of donor and acceptor molecules [2–10]. We show that visible pump/ white light probe is a very efficient tool to investigate the electron injection reaction allowing to observe simultaneously the relaxation of the excited dye, the injection process of the electron, the cooling of the injected electron and the charge recombination reaction.

Michael Grätzel

1999-01-01

378

An Implementation of Interfacial Transport Equation into the CUPID code  

International Nuclear Information System (INIS)

A component scale thermal hydraulic analysis code, CUPID (Component Unstructured Program for Interfacial Dynamics), is being developed for the analysis of components for a nuclear reactor, such as reactor vessel, steam generator, containment, etc. It adopted a three-dimensional, transient, two phase and three-field model. In order to develop the numerical schemes for the three-field model, various numerical schemes have been examined including the SMAS, semi-implicit ICE, SIMPLE. The governing equations for a 2-phase flow are composed of mass, momentum, and energy conservation equations for each phase. These equation sets are closed by the interfacial transfer rate of mass, momentum, and energy. The interfacial transfer of mass, momentum, and energy occurs through the interfacial area, and this area plays an important role in the transfer rate. The flow regime based correlations are used for calculating the interracial area in the traditional style 2-phase flow model. This is dependent upon the flow regime and is limited to the fully developed 2-phase flow region. Its application to the multi-dimensional 2-phase flow has some limitation because it adopts the measured results of 2-phase flow in the 1-dimensional tube. The interfacial area concentration transport equation had been suggested in order to calculate the interfacial area without the interfacial area correlations. The source terms to close the interfacial area transport equation should be further developed for a wide ranger usage of it. In this study, the one group interfacial area concentration transport equation has been implemented into the CUPID code. This interfacial area concentration transport equation can be used instead of the interfacial area concentration correlations for the bubbly flow region

2009-01-01

379

ARTICLES: Use of electron-excitation energy transfer in dye laser active media  

Science.gov (United States)

A study was made of the spectral luminescence and lasing characteristics of two-component dye mixtures, and of the use of electron-excitation energy transfer to improve the laser emission parameters. A considerable increase in the lasing efficiency was found on exciting Trypaflavine by energy transfer from coumarin dyes. The use of electron-excitation energy transfer enabled the laser emission spectrum to be broadened. It was found that by varying the energy donor and acceptor concentrations one could produce laser emission of constant intensity in the spectral range between the donor and acceptor lasing regions.

Rodchenkova, V. V.; Reva, M. G.; Akimov, A. I.; Uzhinov, Boris M.

1984-01-01

380

Liquid-liquid extraction of uranium from phosphoric acid by di-2-ethyl hexyl phosphoric acid and tri-octyl phosphine oxide: interfacial transfer  

International Nuclear Information System (INIS)

The transfer of hexavalent uranium has been investigated at three different liquid-liquid interfaces [U(VI)-H_3PO_4/HDEHP; U(VI)-H_3PO_4/TOPO; U(VI)-H_3PO_4/HDEHP + TOPO] using the single drop technique. The experimental data are interpreted on the basis of the four theoretical models. The nature of the extractant is shown to have a great influence on the mechanism allowing the transfer of uranium

1985-01-01

 
 
 
 
381

Cluster PEACE observations of electrons during magnetospheric flux transfer events  

Digital Repository Infrastructure Vision for European Research (DRIVER)

During the first quarter of 2001 the apogees of the Cluster spacecraft quartet precessed through midday local times. This provides the first opportunity for 4 spacecraft studies of the bow shock, magnetosheath and the dayside magnetopause current layer and boundary layers. In this paper, we present observations of electrons in the energy range similar to 10 eV-26 keV made by the Plasma Electron And Current Experiment (PEACE) located just inside the magnetopause boundary, together with support...

Owen, C. J.; Fazakerley, A. N.; Carter, P. J.; Coates, A. J.; Krauklis, I. C.; Szita, S.; Taylor, M. G. G. T.; Travnicek, P.; Watson, G.; Wilson, R. J.; Balogh, A.; Dunlop, M. W.

2001-01-01

382

Electron Transfer Between Colloidal ZnO Nanocrystals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Colloidal ZnO nanocrystals, capped with dodecylamine and dissolved in toluene, can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals with a solution of uncharged large nanocrystals, e-CB:ZnO–S + ZnO–L, causes changes in the EPR spectr...

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

2011-01-01

383

Average electron tunneling route of the electron transfer in protein media.  

Science.gov (United States)

We present a new theoretical method to determine and visualize the average tunneling route of the electron transfer (ET) in protein media. In this, we properly took into account the fluctuation of the tunneling currents and the quantum-interference effect. The route was correlated with the electronic factor in the case of ET by the elastic tunneling mechanism. We expanded by the interatomic tunneling currents 's. Incorporating the quantum-interference effect into the mean-square interatomic tunneling currents, denoted as , we could express as a sum of variant Planck's over 2pi(2). Drawing the distribution of on the protein structure, we obtain the map which visually represents which parts of bonds and spaces most significantly contribute to . We applied this method to the ET from the bacteriopheophytin anion to the primary quinone in the bacterial photosynthetic reaction center of Rhodobacter sphaeroides. We obtained 's by a combined method of molecular dynamics simulations and quantum chemical calculations. In calculating , we found that much destructive interference works among the interatomic tunneling currents even after taking the average. We drew the map by a pipe model where atoms a and b are connected by a pipe with width proportional to the magnitude of . We found that two groups of 's, which are mutually coupled with high correlation in each group, have broad pipes and form the average tunneling routes, called Trp route and Met route. Each of the two average tunneling routes is composed of a few major pathways in the Pathways model which are fused at considerable part to each other. We also analyzed the average tunneling route for the ET by the inelastic tunneling mechanism. PMID:18630851

Nishioka, Hirotaka; Kakitani, Toshiaki

2008-08-14

384

Transfer printing of thermoreversible ion gels for flexible electronics.  

Science.gov (United States)

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

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

2013-10-01

385

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

Science.gov (United States)

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

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

2008-10-01

386

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

Science.gov (United States)

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

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

2008-01-01

387

Electron transfer properties of iodine-doped single-walled carbon nanotubes using field effect transistor.  

Science.gov (United States)

Single-walled carbon nanotubes (SWNTs) are known to have a p-type charge transfer character in the atmosphere. The energy state of SWNTs can be modulated by doping with either an electron donor or an acceptor. In this study, iodine molecules are chosen for intercalation to SWNTs to predict the charge transfer tendency between them. Field-effect transistors (FETs) using iodine intercalated SWNTs (I-SWNTs) are fabricated and their electronic properties are investigated to better understand the charge transfer between iodine and SWNTs by changing gate voltages. Under vacuum, I-SWNT FETs exhibit weak n-type character, indicating that electrons are transferred slightly from the iodine to the SWNTs. After exposure to O2 gas, n-type characters are reduced; however, they still retain their original type. PMID:22966660

Park, Taehee; Sim, Kijo; Lee, Jongtaek; Yi, Whikun

2012-07-01