WorldWideScience
1

Theory of plasmon enhanced interfacial electron transfer  

Science.gov (United States)

A particular attempt to improve the efficiency of a dye sensitized solar cell is it's decoration with metal nano-particles (MNP). The MNP-plasmon induced enhancement of the local field enlarges the photoexcitation of the dyes and a subsequent improvement of the charge separation efficiency may result. In a recent work (2014 J. Phys. Chem. C 118 2812) we presented a theory of plasmon enhanced interfacial electron transfer for perylene attached to a TiO2 surface and placed in the proximity of a spherical MNP. These earlier studies are generalized here to the coupling of to up to four MNPs and to the use of somewhat altered molecular parameters. If the MNPs are placed close to each other strong hybridization of plasmon excitations appears and a broad resonance to which molecular excitations are coupled is formed. To investigate this situation the whole charge injection dynamics is described in the framework of the density matrix theory. The approach accounts for optical excitation of the dye coupled to the MNPs and considers subsequent electron injection into the rutile TiO2-cluster. Using a tight-binding model for the TiO2-system with about 105 atoms the electron motion in the cluster is described. We again consider short optical excitation which causes an intermediate steady state with a time-independent overall probability to have the electron injected into the cluster. This probability is used to introduce an enhancement factor which rates the influence of the MNP. Values larger than 500 are obtained.

Wang, Luxia; May, Volkhard

2015-04-01

2

Probing Inhomogeneous Vibrational Reorganization Energy Barriers of Interfacial Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2005-09-01

3

Interfacial Electron Transfer into Functionalized Crystalline Polyoxotitanate Nanoclusters  

OpenAIRE

Interfacial electron transfer (IET) between a chromophore and a semi-conductor nanoparticle is one of the key processes in a dye sensitized solar cell. Theoretical simulations of the electron transfer in polyoxotitanate nanoclusters Ti17O24(OPri)20 (Ti17) functionalized with four para-nitrophenyl acetylacetone (NPA-H) adsorbates, of which the atomic structure has been fully established by X-ray diffraction measurements, are presented. Complementary experimental information showing IET has bee...

Snoeberger, Robert C.; Young, Karin J.; Tang, Jiji; Allen, Laura J.; Crabtree, Robert H.; Brudvig, Gary W.; Coppens, Philip; Batista, Victor S.; Benedict, Jason B.

2012-01-01

4

Single-molecule kinetics of interfacial electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Measurements of single-molecule chemical reaction kinetics are demonstrated for interfacial electron transfer from excited cresyl violet molecules to the conduction band of indium tin oxide (ITO) or energetically accessible surface electronic states under ambient conditions by using a far-field fluorescence microscope. In this system, each single molecule exhibits a single-exponential electron transfer kinetics. A wide distribution of site-specific electron transfer rates is observed for many single cresyl violet molecules examined. This work reveals that the physical origin of multiexponential kinetics of electron transfer in this system is the inhomogeneity of molecular interactions on the semiconductor surface of ITO. We illustrate that the single-molecule experiments provide detailed information not obtainable from experiments conducted on large ensembles of molecules. Single-molecule kinetics is particularly useful in understanding multiexponential behavior of chemical reactions in heterogeneous systems. 42 refs., 4 figs.

Lu, H.P.; Xie, X.S. [Pacific Northwest National Lab., Richland, WA (United States)

1997-04-10

5

Intermittent Single-Molecule Interfacial Electron Transfer Dynamics  

International Nuclear Information System (INIS)

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

6

Intermittent Single-Molecule Interfacial Electron Transfer Dynamics  

Energy Technology Data Exchange (ETDEWEB)

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

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

2004-08-04

7

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

8

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

9

Intermittent Single-molecule Interfacial Electron Transfer Dynamics in Dye-TiO2 Nanoparticle systems  

Science.gov (United States)

Photosensitized interfacial electron transfer dynamics of single molecules of Coumarin 343 (C343) and Cresyl Violet (CV+) acetate dyes adsorbed at TiO2 nanoparticle (NP)-polymer and TiO2 NP-electrolyte interfaces are studied using single-molecule photon-stamping fluorescence spectroscopy. Fluorescence intensity trajectories of individual dye molecules adsorbed at a TiO2 NP-polymer interface in air showed intermittent 'on' and 'off' (blinking) fluorescence in sub-second to second time scales, which are well distinguished from blinking due to intersystem crossing to dark triplet state. Autocorrelation analyses of the intensity trajectories showed non-exponential fluctuation dynamics for the single molecules, and the average rates are of 5 s-1 for both the C343-TiO2 and CV+-TiO2 systems. We attribute the fluorescence intensity fluctuation to the intermittency of the single-molecule interfacial electron transfer reactivity and dynamics.

Biju, Vasudevanpillai; Micic, Miodrag; Hu, Dehong; Lu, H. Peter

2004-03-01

10

Effect of size quantization on interfacial electron transfer dynamics in TiO{sub 2} nanoparticles  

Energy Technology Data Exchange (ETDEWEB)

Interfacial electron transfer dynamics was carried out in alizarin sensitized TiO{sub 2} nanoparticles with quantum size using femtosecond transient absorption (TA) spectroscopy. The TiO{sub 2} nanoparticles have been synthesized by arrested precipitation method. Electron injection dynamics were found to be multi-exponential with time constants of 100 fs, 17 ps and 50 ps. This observation was explained on the basis discreteness of the conduction band levels due to finite size effect. The back electron transfer (BET) dynamics found to be very slow as compared to the bulk system. The result gives us direct proof of non-adiabatic electron transfer reaction in a strong binding dye like alizarin.

Ghosh, Hirendra N. [Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay, Mumbai (India); Max-Born Institute for Nonlinear and Short Pulse Spectroscopy, Berlin (Germany)

2008-07-01

11

Interfacial electronic charge transfer and density of states in short period Cu/Cr multilayers; TOPICAL  

International Nuclear Information System (INIS)

Nanometer period metallic multilayers are ideal structures to investigate electronic phenomena at interfaces between metal films since interfacial atoms comprise a large atomic fraction of the samples. The Cu/Cr binary pair is especially suited to study the interfaces in metals since these elements are mutually insoluble, thus eliminating mixing effects and compound formation and the lattice mismatch is very small. This allows the fabrication of high structural quality Cu/Cr multilayers that have a structure which can be approximated in calculations based on idealized atomic arrangements. The electronic structure of the Cu and the Cr layers in several samples of thin Cu/Cr multilayers were studied using x-ray absorption spectroscopy (XAS). Total electron yield was measured and used to study the white lines at the Cu L(sub 2) and L(sub 3) absorption edges. The white lines at the Cu absorption edges are strongly related to the unoccupied d-orbitals and are used to calculate the amount of charge transfer between the Cr and Cu atoms in interfaces. Analysis of the Cu white lines show a charge transfer of 0.026 electrons/interfacial Cu atom to the interfacial Cr atoms. In the Cu XAS spectra we also observe a van Hove singularity between the L(sub 2) and L(sub 3) absorption edges as expected from the structural analysis. The absorption spectra are compared to partial density of states obtained from a full-potential linear muffin-tin orbital calculation. The calculations supporbital calculation. The calculations support the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr

12

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

International Nuclear Information System (INIS)

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

13

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

14

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

15

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

DEFF Research Database (Denmark)

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

Zhang, Jingdong; Chi, Qijin

2012-01-01

16

Spectroscopic evidence for interfacial Fe(II)-Fe(III) electron transfer in a clay mineral.  

Science.gov (United States)

Interfacial electron transfer has been shown to occur between sorbed Fe(II) and structural Fe(III) in Fe oxides, but it is unknown whether a similar reaction occurs between sorbed Fe(II) and Fe(III)-bearing clay minerals. Here, we used the isotopic specificity of (57)Fe Mo?ssbauer spectroscopy to demonstrate electron transfer between sorbed Fe(II) and structural Fe(III) in an Fe-bearing smectite clay mineral (NAu-2, nontronite). Mo?ssbauer spectra of NAu-2 reacted with aqueous (56)Fe(II) (which is invisible to (57)Fe Mo?ssbauer spectroscopy) showed direct evidence for reduction of NAu-2 by sorbed Fe(II). Mo?ssbauer spectra using aqueous (57)Fe(II) showed that sorbed Fe(II) is oxidized upon sorption to the clay and pXRD patterns indicate that the oxidation product is lepidocrocite. Spectra collected at different temperatures indicate that reduction of structural Fe(III) by sorbed Fe(II) induces electron delocalization in the clay structure. Our results also imply that interpretation of room temperature and 77 K Mo?ssbauer spectra may significantly underestimate the amount of Fe(II) in Fe-bearing clays. These findings provide compelling evidence for abiotic reduction of Fe-bearing clay minerals by sorbed Fe(II), and require us to reframe our conceptual model for interpreting biological reduction of clay minerals, as well as contaminant reduction by reduced clays. PMID:21138293

Schaefer, Michael V; Gorski, Christopher A; Scherer, Michelle M

2011-01-15

17

Ultrafast interfacial electron transfer from the excited state of anchored molecules into a semiconductor  

Science.gov (United States)

Ultrafast heterogeneous electron transfer (HET) from the excited singlet state of the large organic chromophore perylene into the inorganic semiconductor rutile TiO 2 was investigated with femtosecond time-resolved two-photon photoemission (TR-2PPE). The strength of the electronic interaction between the chromophore and the semiconductor was varied by inserting different anchor/bridge groups that functioned either as electronic wire or electronic tunnelling barrier. Both anchor groups, i.e. carboxylic and phosphonic acid, formed strong chemical bonds at the TiO 2 surface. The perylene chromophore with the different anchor/bridge groups was adsorbed from solution in a dedicated ultra-high-vacuum (UHV) chamber. The adsorption geometry of the chromophore perylene was determined from angle and polarization dependent two-photon photoemission (2PPE) signals and was found to be very different for the two different anchor/bridge groups. The measured adsorption geometries are compatible with recent DFT (density functional theory) calculations by P. Persson and co-workers [M. Nilsing, S. Lunell, P. Persson, L. Ojamäe, Phosphonic acid adsorption at the TiO 2 anatase (1 0 1) surface investigated by periodic hybrid HF-DFT computations, Surf. Sci. 582 (2005) 49-60]. Two different processes contributed to the TR-2PPE transients, firstly electron transfer from the chromophore to the electronic acceptor states on the surface and secondly escape of the electrons from the surface into the bulk of the semiconductor. The latter escape process was measured separately by making the interfacial electron injection process instantaneous when the chromophore catechol was employed in place of the perylene compounds. The thus measured electron escape behavior was governed by the same time constants that have recently been predicted by Prezhdo and coworkers from time dependent DFT calculations [W.R. Duncan, W.M. Stier, O.V. Prezhdo, Ab initio nonadiabatic molecular dynamics of the ultrafast electron injection across the Alizarin-TiO 2 interface, J. Am. Chem. Soc. 127 (2005) 7941-7951]. The HET times derived from the 2PPE transients showed very good agreement with HET times measured via transient absorption (TA) on anatase TiO 2 layers. The measured energy distribution of the 2PPE signals for the injected electrons suggests that a high density of electronic acceptor states is operative in both systems and is spread over an at least 1 eV wide energy range. The acceptor states are tentatively identified with surface states created through the formation of chemical bonds between the anchor groups of the organic molecules and surface atoms of the semiconductor.

Gundlach, L.; Ernstorfer, R.; Willig, F.

18

Dynamics and mechanisms of interfacial photoinduced electron transfer processes of third generation photovoltaics and photocatalysis.  

Science.gov (United States)

Photoinduced electron transfer (PET) across molecular/bulk interfaces has gained attention only recently and is still poorly understood. These interfaces offer an excellent case study, pertinent to a variety of photovoltaic systems, photo- and electrochemistry, molecular electronics, analytical detection, photography, and quantum confinement devices. They play in particular a key role in the emerging fields of third-generation photovoltaic energy converters and artificial photosynthetic systems aimed at the production of solar fuels, creating a need for a better understanding and theoretical treatment of the dynamics and mechanisms of interfacial PET processes. We aim to achieve a fundamental understanding of these phenomena by designing experiments that can be used to test and alter modern theory and computational modeling. One example illustrating recent investigations into the details of the ultrafast processes that form the basis for photoinduced charge separation at a molecular/bulk interface relevant to dye-sensitized solar cells is briefly presented here: Kinetics of interfacial PET and charge recombination processes were measured by fs and ns transient spectroscopy in a heterogeneous donor-bridge-acceptor (D-B-A) system, where D is a Ru(II)(terpyridyl-PO3)(NCS)3 complex, B an oligo-p-phenylene bridge, and A nanocrystalline TiO2. The forward ET reaction was found to be faster than vibrational relaxation of the vibronic excited state of the donor. Instead, the back ET occurred on the micros time scale and involved fully thermalized species. The D-A distance dependence of the electron transfer rate was studied by varying the number of p-phenylene units contained in the bridge moiety. The remarkably low damping factor beta = 0.16 angstroms(-1) observed for the ultrafast charge injection from the dye excited state into the conduction band of TiO2 is attributed to the coupling of electron tunneling with nonequilibrium vibrations redistributed on the bridge, giving rise to polaronic transport of charges from the donor ligand to the acceptor solid oxide surface. PMID:22026184

Bauer, Christophe; Teuscher, Joël; Brauer, Jan C; Punzi, Angela; Marchioro, Arianna; Ghadiri, Elham; De Jonghe, Jelissa; Wielopolski, Mateusz; Banerji, Natalie; Moser, Jacques E

2011-01-01

19

Linker dependence of interfacial electron transfer rates in Fe(II)-polypyridine sensitized solar cells  

Science.gov (United States)

Dye-sensitized solar cells (DSSCs) convert solar energy to electricity employing dye molecules attached to a semiconductor surface. Some of the most efficient DSSCs use Ru-based chromophores. Fe-based dyes represent a cheaper and more environmentally friendly alternative to these expensive and toxic dyes. The photoactive state of Fe-based chromophores responsible for charge-separation at the dye-semiconductor interface is, however, deactivated on a sub-picosecond time scale via the intersystem crossing (ISC) into a manifold of low-lying photo-inactive quintet states. Therefore, development of Fe-based dyes capable of fast interfacial electron transfer (IET) leading to efficient charge separation on a time scale competitive with the ISC events is important. This work investigates how linker groups anchoring a prototypical Fe-based dye [Fe(bpy-L)2(CN)2] (bpy = 2,2?-bipyridine, L = linker group) onto the TiO2 semiconductor surface influence the IET rates in the dye–semiconductor assemblies. Linker groups investigated include carboxylic acid, phosphonic acid, hydroxamate, catechol, and acetylacetonate. We employ time-dependent density functional theory (TD-DFT) to obtain absorption spectra of [Fe(bpy-L)2(CN)2] with each linker, and quantum dynamics simulations to investigate the IET rates between the dye and the (101) TiO2 anatase surface. For all attachments, TD-DFT calculations show similar absorption spectra with two main bands corresponding to the metal-to-ligand charge transfer transitions. The quantum dynamics simulations predict that the utilization of the hydroxamate linker instead of the commonly used carboxylic acid linker will lead to a more efficient IET and better photon-to-current conversion efficiencies in Fe(II)-polypyridine sensitized solar cells.

Bowman, David N.; Mukherjee, Sriparna; Barnes, Lyndsay J.; Jakubikova, Elena

2015-04-01

20

Linker dependence of interfacial electron transfer rates in Fe(II)-polypyridine sensitized solar cells.  

Science.gov (United States)

Dye-sensitized solar cells (DSSCs) convert solar energy to electricity employing dye molecules attached to a semiconductor surface. Some of the most efficient DSSCs use Ru-based chromophores. Fe-based dyes represent a cheaper and more environmentally friendly alternative to these expensive and toxic dyes. The photoactive state of Fe-based chromophores responsible for charge-separation at the dye-semiconductor interface is, however, deactivated on a sub-picosecond time scale via the intersystem crossing (ISC) into a manifold of low-lying photo-inactive quintet states. Therefore, development of Fe-based dyes capable of fast interfacial electron transfer (IET) leading to efficient charge separation on a time scale competitive with the ISC events is important. This work investigates how linker groups anchoring a prototypical Fe-based dye [Fe(bpy-L)2(CN)2] (bpy = 2,2'-bipyridine, L = linker group) onto the TiO2 semiconductor surface influence the IET rates in the dye-semiconductor assemblies. Linker groups investigated include carboxylic acid, phosphonic acid, hydroxamate, catechol, and acetylacetonate. We employ time-dependent density functional theory (TD-DFT) to obtain absorption spectra of [Fe(bpy-L)2(CN)2] with each linker, and quantum dynamics simulations to investigate the IET rates between the dye and the (101) TiO2 anatase surface. For all attachments, TD-DFT calculations show similar absorption spectra with two main bands corresponding to the metal-to-ligand charge transfer transitions. The quantum dynamics simulations predict that the utilization of the hydroxamate linker instead of the commonly used carboxylic acid linker will lead to a more efficient IET and better photon-to-current conversion efficiencies in Fe(II)-polypyridine sensitized solar cells. PMID:25767105

Bowman, David N; Mukherjee, Sriparna; Barnes, Lyndsay J; Jakubikova, Elena

2015-04-10

21

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

22

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

OpenAIRE

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

23

Photoelectrochemistry in colloidal systems: Interfacial electron transfer between colloidal TiO/sub 2/ and thionine in acetonitrile  

Energy Technology Data Exchange (ETDEWEB)

When adsorbed on a colloidal TiO/sub 2/ semiconductor suspension, the thiazine dye thionine exhibited a red shift in its absorption and emission spectra. The apparent association constant for the association of TiO/sub 2/ colloid and thionine in acetonitrile was determined to be 2.75 x 10/sup 5/ M/sup -1/. Reversible photoelectrochemical reduction of thionine was observed when the colloidal TiO/sub 2/ suspension in acetonitrile containing thionine was subjected to band gap illumination (lambda < 380 nm). The interfacial electron transfer between colloidal TiO/sub 2/ and thionine in acetonitrile was investigated by means of steady state photolysis and nanosecond laser flash photolysis techniques. The quantum yield for the photoelectrochemical reduction of thionine to semithionine was determined to be 0.1. The dependence of the photoelectrochemical production of semithionine on thionine concentration, the acidity of the medium and the intensity of excitation was examined.

Kamat, P.V.

1985-04-01

24

Molecular monolayers and interfacial electron transfer of pseudomonas aeruginosa azurin on Au(111)  

DEFF Research Database (Denmark)

We provide a comprehensive approach to the formation and characterization of molecular monolayers of the blue copper protein Pseudomonas aeruginosa azurin on Au(111) in aqueous ammonium acetate solution. Main issues are adsorption patterns, reductive desorption, properties of the double layer, and long-range electrochemical electron transfer between the electrode and the copper center. Voltammetry, electrochemical impedance spectroscopy (EIS), in situ scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS) have been employed to disclose features of these issues. Zn-substituted azurin, cystine, and 1-butanethiol are investigated for comparison. Cyclic voltammetric and capacitance measurements show qualitatiVely that azurin is adsorbed at submicromolar concentrations over a broad potential range. The characteristics of reductive desorption suggest that azurin is adsorbed via its disulfide group to form a monolayer. The adsorption of this protein on Au(111) via a gold-sulfur binding mode is further supported by XPS measurements. In situ STM images with molecular resolution have been recorded and show a dense monolayer organization of adsorbed azurin molecules. Direct electron transfer (ET) between the copper atom of adsorbed azurin and the electrode has been revealed by differential pulse voltammetry. The rate constant is estimated from electrochemical impedance spectroscopy and shows that ET is compatible with a long-range ET mode such as that anticipated by theoretical frames. The results constitute the first case of an electrochemically functional redox protein monolayer at single-crystal metal electrodes.

Chi, Qijin; Zhang, Jingdong

2000-01-01

25

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

26

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

27

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

28

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

Science.gov (United States)

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

Rowley, John G.

29

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

30

Photosensitization of nanoparticulate TiO2 using a Re(I)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain.  

Science.gov (United States)

We have synthesized a new photoactive rhenium(i)-complex having a pendant catechol functionality [Re(CO)(3)Cl(L)] (1) (L is 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) for studying the dynamics of the interfacial electron transfer between nanoparticulate TiO(2) and the photoexcited states of this Re(i)-complex using femtosecond transient absorption spectroscopy. Our steady state absorption studies revealed that complex 1 can bind strongly to TiO(2) surfaces through the catechol functionality with the formation of a charge transfer (CT) complex, which has been confirmed by the appearance of a new red-shifted CT band. The longer wavelength absorption band for 1, bound to TiO(2) through the proposed catecholate functionality, could also be explained based on the DFT calculations. Dynamics of the interfacial electron transfer between 1 and TiO(2) nanoparticles was investigated by studying kinetics at various wavelengths in the visible and near infrared regions. Electron injection into the conduction band of the nanoparticulate TiO(2) was confirmed by detection of the conduction band electron in TiO(2) ([e(-)](TiO(2)(CB))) and the cation radical of the adsorbed dye (1?(+)) in real time as monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (kinetics of 1?(+) and . PMID:22549294

Kar, Prasenjit; Banerjee, Tanmay; Verma, Sandeep; Sen, Anik; Das, Amitava; Ganguly, Bishwajit; Ghosh, Hirendra N

2012-06-14

31

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-06-15

32

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

33

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

DEFF Research Database (Denmark)

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

Chi, Qijin; Zhang, Jingdong

2010-01-01

34

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

35

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

International Nuclear Information System (INIS)

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

36

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

Science.gov (United States)

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

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

2012-09-17

37

Heat transfer in turbulent falling liquid films with interfacial shear  

International Nuclear Information System (INIS)

The modeling of turbulent liquid films has been the target of extensive research for the last six decades. However, an in-depth review of the existing works shows that the following questions need to be resolved: Which turbulence model is the most reliable for predictions of heat transfer in turbulent falling liquid films? What are the effects of the interfacial shear, and how do these different turbulence models affect the predictions of heat transfer in the given problems? The main purpose of this paper is to present an improved heat transfer prediction model for turbulent falling liquid films with or without interfacial shear. The present model is partly based on Yih and Liu's unified approach and Mudawwar and El-Masri's semiempirical turbulence models. The results from the examination of the effects of turbulence models and the interfacial shear on the heat transfer are also presented

38

Investigation and assessment of interfacial area/interfacial heat and mass transfer correlations in SPACE code  

Energy Technology Data Exchange (ETDEWEB)

SPACE, which is a safety analysis code for nuclear power plants, has been developed to analyze the multidimensional, two-component and three-field flow. This code can be applied to safety analysis for approval which is thermal-hydraulic analysis to support the nuclear power station design, establishment of accident ease strategy, development of operating guide line, experiment plan and analysis. To do so, SPACE code has the interfacial area and interfacial heat and mass transfer to predict the physical phenomenon occurring at the interface between two different phases. In this report, the physical correlation models are explained and their performance is assessed against several SET

Kim, Jung Woo; Kim, Kyung Doo; Bae, Sung Won; Lee, Young Jin

2010-06-15

39

Hybrid graphene and graphitic carbon nitride nanocomposite: gap opening, electron-hole puddle, interfacial charge transfer, and enhanced visible light response.  

Science.gov (United States)

Opening up a band gap and finding a suitable substrate material are two big challenges for building graphene-based nanodevices. Using state-of-the-art hybrid density functional theory incorporating long-range dispersion corrections, we investigate the interface between optically active graphitic carbon nitride (g-C(3)N(4)) and electronically active graphene. We find an inhomogeneous planar substrate (g-C(3)N(4)) promotes electron-rich and hole-rich regions, i.e., forming a well-defined electron-hole puddle, on the supported graphene layer. The composite displays significant charge transfer from graphene to the g-C(3)N(4) substrate, which alters the electronic properties of both components. In particular, the strong electronic coupling at the graphene/g-C(3)N(4) interface opens a 70 meV gap in g-C(3)N(4)-supported graphene, a feature that can potentially allow overcoming the graphene's band gap hurdle in constructing field effect transistors. Additionally, the 2-D planar structure of g-C(3)N(4) is free of dangling bonds, providing an ideal substrate for graphene to sit on. Furthermore, when compared to a pure g-C(3)N(4) monolayer, the hybrid graphene/g-C(3)N(4) complex displays an enhanced optical absorption in the visible region, a promising feature for novel photovoltaic and photocatalytic applications. PMID:22339061

Du, Aijun; Sanvito, Stefano; Li, Zhen; Wang, Dawei; Jiao, Yan; Liao, Ting; Sun, Qiao; Ng, Yun Hau; Zhu, Zhonghua; Amal, Rose; Smith, Sean C

2012-03-01

40

Investigations on interfacial dynamics with ultrafast electron diffraction  

Science.gov (United States)

An ultrafast electron diffractive voltammetry (UEDV) technique is introduced, extended from ultrafast electron diffraction, to investigate the ultrafast charge transport dynamics at interfaces and in nanostructures. Rooted in Coulomb-induced refraction, formalisms are presented to quantitatively deduce the transient surface voltages (TSVs), caused by photoinduced charge redistributions at interfaces, and are applied to examine a prototypical Si/SiO2 interface, known to be susceptible to photoinduced interfacial charging The ultrafast time resolution and high sensitivity to surface charges of this electron diffractive approach allows direct elucidation of the transient effects of photoinduced hot electron transport at nanometer (˜2 nm) interfaces. Two distinctive regimes are uncovered, characterized by the time scales associated with charge separation. At the low fluence regime, the charge transfer is described by a thermally-mediated process with linear dependence on the excitation fluence. Theoretical analysis of the transient thermal properties of the carriers show that it is well-described by a direct tunneling of the laser heated electrons through the dielectric oxide layer to surface states. At higher fluences, a coherent multiphoton absorption process is invoked to directly inject electrons into the conduction band of SiO2, leading to a more efficient surface charge accumulation. A quadratic fluence dependence on this coherent, 3-photon lead electron injection is characterized by the rapid dephasing of the intermediately generated hot electrons from 2-photon absorption, limiting the yield of the consecutive 1-photon absorption by free carriers. The TSV formalism is extended beyond the simple slab geometry associated with planar surfaces (Si/SiO2), to interfaces with arbitrary geometrical features, by imposing a corrective scheme to the slab model. The validity of this treatment is demonstrated in an investigation of the charge transfer dynamics at a metal nanoparticle/self-assembled monolayer (SAM)/semiconductor interconnected structure, allowing for the elucidation of the photo-initiated charging processes (forward and backward) through the SAM, by monitoring the deflection of the associated Bragg peaks in conjunction with the UEDV extended formalism to interpret the surface voltage. The design, calibration, and implementation of a molecular beam doser (MBD), capable of layer-by-layer coverage is also presented, with preliminary investigations on interfacial ice. With the development of UEDV and implementation of the MBD, continued investigations of charge transfer in more complex interfaces can be explored, such as those pertinent to novel solar-cell device technology, as their quantum efficiencies are usually strongly dependent on an interfacial charge transfer process. As UEDV is inherently capable of probing charge and atomic motion simultaneously, systems that exhibit phenomena that are attributable to strong coupling of the atomic and electronic degrees of freedom are of particular interest for future investigations with UEDV, such as optically induced electronic phase transitions and colossal field switching in functional oxides.

Murdick, Ryan A.

41

Interfacial compatibility of polymer-based structures in electronics  

OpenAIRE

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

42

ELECTRON TRANSFER MECHANISM AT THE SOLID-LIQUID INTERFACE OF PHYLLOSILICATES  

Science.gov (United States)

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

43

Interfacial stress transfer in a graphene nanosheet toughened hydroxyapatite composite  

Science.gov (United States)

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

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

2014-10-01

44

Electron transfer: classical approaches and new frontiers  

Science.gov (United States)

Electron transfer, under conditions of weak interaction and a medium acting as a passive thermal bath, is very well understood. When electron transfer is accompanied by transient chemical bonding, such as in interfacial coordination electrochemical mechanisms, strong interaction and molecular selectivity are involved. These mechanisms, which take advantage of "passive self-organization," cannot yet be properly described theoretically, but they show substantial experimental promise for energy conversion and catalysis. The biggest challenge for the future, however, may be dynamic, self-organized electron transfer. As with other energy fluxes, a suitable positive feedback mechanism, through an active molecular environment, can lead to a (transient) decrease of entropy equivalent to an increase of molecular electronic order for the activated complex. A resulting substantial increase in the rate of electron transfer and the possibility of cooperative transfer of several electrons (without intermediates) can be deduced from phenomenological theory. The need to extend our present knowledge may be derived from the observation that chemical syntheses and fuel utilization in industry typically require high temperatures (where catalysis is less relevant), whereas corresponding processes in biological systems are catalyzed at environmental conditions. This article therefore focuses on interfacial or membrane-bound electron transfer and investigates an aspect that nature has developed to a high degree of perfection: self-organization. PMID:9506932

Tributsch; Pohlmann

1998-03-20

45

Study of Interfacial Mass Transfer on Vapor Bubbles in Microgravity  

Directory of Open Access Journals (Sweden)

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

Johannes Straub

2005-03-01

46

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

Science.gov (United States)

This work reports on an investigation into interfacial charge transfer in CH3NH3PbI3 perovskite solar cells by using anatase TiO2 nanocuboids enclosed by active {100} and {001} facets. The devices show 6.0 and 8.0% power conversion efficiency with and without hole-transport material. Transient photovoltage/photocurrent decay and charge extraction, as well as impedance spectroscopy measurements, reveal that carbon materials are effective counter electrodes in perovskite solar cells. The photogenerated charges are observed to be stored in mesoporous TiO2 film under illumination and in the CH3NH3PbI3 layer in the dark. The use of 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene (spiro-MeOTAD) as a hole-transport material accelerates interfacial charge recombination between the photogenerated electrons and holes. PMID:25213607

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

2014-11-01

47

Actively Enhanced Boiling Heat Transfer using Acoustic Interfacial Actuation  

Science.gov (United States)

Acoustic actuation is used to enhance boiling heat transfer on a submerged surface by controlling the formation and evolution of vapor bubbles and inhibiting instabilities that lead to film boiling and critical heat flux. The receptivity of a vapor bubble that forms at a prescribed nucleation site to acoustic interfacial excitation and to acoustically induced Bjerknes body forces is investigated on a surface-embedded hot spot with emphasis on the acoustic effects on nucleation, growth, contact-line motion, condensation, and detachment. The investigation also considers arrays of vapor bubbles that form on a prescribed grid of surface-engineered nucleation sites and the interactions between adjacent vapor bubbles. It is shown that acoustic actuation enables dissipation of higher heat fluxes at a given surface temperature, and a significant delay of the critical heat flux with reduction of the vapor mass above the surface. Supported by ONR.

Boziuk, Thomas R.; Smith, Marc K.; Glezer, Ari

2010-11-01

48

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

49

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

International Nuclear Information System (INIS)

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

50

Mass transfer and interfacial properties in two-phase microchannel flows  

International Nuclear Information System (INIS)

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

51

Defect-driven interfacial electronic structures at an organic/metal-oxide semiconductor heterojunction.  

Science.gov (United States)

The electronic structure of the hybrid interface between ZnO and the prototypical organic semiconductor PTCDI is investigated via a combination of ultraviolet and X-ray photoelectron spectroscopy (UPS/XPS) and density functional theory (DFT) calculations. The interfacial electronic interactions lead to a large interface dipole due to substantial charge transfer from ZnO to 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which can be properly described only when accounting for surface defects that confer ZnO its n-type properties. PMID:24830796

Winget, Paul; Schirra, Laura K; Cornil, David; Li, Hong; Coropceanu, Veaceslav; Ndione, Paul F; Sigdel, Ajaya K; Ginley, David S; Berry, Joseph J; Shim, Jaewon; Kim, Hyungchui; Kippelen, Bernard; Brédas, Jean-Luc; Monti, Oliver L A

2014-07-16

52

SIMULTANEOUS MEASUREMENT OF INTERFACIAL AREA DISTRIBUTION AND MASS TRANSFER COEFFICIENTS IN BUBBLE COLUMN  

Directory of Open Access Journals (Sweden)

Full Text Available In this study, simultaneous measurement of interfacial area distribution and mass transfer coefficients in a bubble column for two-phase dispersed system of air-water is conducted. The time-averaged interfacial area (a distribution was measured by using ultrasonic computed tomography (UCT, the volumetric liquid mass transfer coefficient (kLa is measured by dynamic method, and hence, the liquid side mass transfer coefficient (kL was calculated from the kLa and a. The UCT results show that the higher interfacial area around the center of the column and the lower one near the column wall. The experimental results of interfacial area are in a good agreement with the results obtained by the reported correlation and the results obtained by the physical method. A good agreement is also obtained between the experimental results of liquid side mass transfer coefficient and those by the reported correlation.

MUHAMMAD DANI SUPARDAN

2012-06-01

53

Interfacial electronic states of tetracene deposited on Si(111)  

Science.gov (United States)

The interfacial electronic states of tetracene on Si(111) 7×7 substrate were studied by using ultraviolet photoelectron spectroscopy (UPS). After deposition of tetracene on the Si(111) 7×7 surface, the features originating from the tetracene molecule appear at 1.55, 3.36, 6.78, 9.24, and 10.76 eV below the Fermi level; they shift in binding energy with increasing organic film coverage. From the UPS measurements, the work function of the sample surface was found to decrease with increasing molecular coverage in the submonolayer range suggesting that an interfacial dipole is formed. A density functional theory calculation had also been carried out to determine the favorable adsorption structure. The molecule near the top of a center adatom with the longer molecular axis along the [11¯0] azimuth is the most favorable.

Guan, Dandan; Mao, Hongying; Chen, Meiliang; Dou, Weidong; Song, Fei; Zhang, Hanjie; Li, Haiyang; He, Pimo; Chen, Hongzheng; Bao, Shining

2009-05-01

54

Insights on interfacial charge transfer across P3HT/fullerene photovoltaic heterojunction from Ab initio calculations.  

Science.gov (United States)

The interfacial charge-transfer mechanism of the P3HT/fullerene photovoltaic heterojunction is elucidated using density functional theory calculations. Our findings indicate that an efficient adiabatic electron transfer is highly probable due to the presence of an extended electronic state that has a significant probability distribution across the interface in the lowest excited state. Furthermore, efficient exciton dissociation is possible because this bridging state has significant overlap with near-degenerate unoccupied states that are localized on the fullerene. PMID:17547466

Kanai, Yosuke; Grossman, Jeffrey C

2007-07-01

55

Lead-iodide nanowire perovskite with methylviologen showing interfacial charge-transfer absorption: a DFT analysis.  

Science.gov (United States)

Methylviologen lead-iodide perovskite (MVPb2I6) is a self-assembled one-dimensional (1-D) material consisting of lead-iodide nanowires and intervening organic electron-accepting molecules, methylviologen (MV(2+)). MVPb2I6 characteristically shows optical interfacial charge-transfer (ICT) transitions from the lead-iodide nanowire to MV(2+) in the visible region and unique ambipolar photoconductivity, in which electrons are transported through the three-dimensional (3-D) organic network and holes along the 1-D lead-iodide nanowire. In this work, we theoretically study the electronic band-structure and photocarrier properties of MVPb2I6 by density functional theory (DFT) calculations. Our results clearly confirm the experimentally reported type-II band alignment, whose valence band mainly consists of 5p (I) orbitals of the lead-iodide nanowires and the conduction band of the lowest unoccupied molecular orbital of MV(2+). The DFT calculation also reveals weak charge-transfer interactions between the lead-iodide nanowires and MV(2+). In addition, the electronic distributions of the valence and conduction bands indicate the 3-D transport of electrons and 1-D transport of holes, supporting the reported experimental result. PMID:25050419

Fujisawa, Jun-ichi; Giorgi, Giacomo

2014-09-01

56

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

57

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

58

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

CERN Document Server

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

Bhardwaj, Rajneesh; Attinger, Daniel

2010-01-01

59

Electron transfer in biology  

Science.gov (United States)

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

Williams, R. J. P.

60

SIMULTANEOUS MEASUREMENT OF INTERFACIAL AREA DISTRIBUTION AND MASS TRANSFER COEFFICIENTS IN BUBBLE COLUMN  

OpenAIRE

In this study, simultaneous measurement of interfacial area distribution and mass transfer coefficients in a bubble column for two-phase dispersed system of air-water is conducted. The time-averaged interfacial area (a) distribution was measured by using ultrasonic computed tomography (UCT), the volumetric liquid mass transfer coefficient (kLa) is measured by dynamic method, and hence, the liquid side mass transfer coefficient (kL) was calculated from the kLa and a. The UCT results show that ...

MUHAMMAD DANI SUPARDAN

2012-01-01

61

Advances in electron transfer chemistry  

CERN Document Server

Advances in Electron Transfer Chemistry, Volume 3 presents studies that discuss findings in the various aspects of electron chemistry. The book is comprised of four chapters; each chapter reviews a work that tackles an issue in electron transfer chemistry. Chapter 1 discusses the photoinduced electron transfer in flexible biaryl donor-acceptor molecules. Chapter 2 tackles light-induced electron transfer in inorganic systems in homogeneous and heterogeneous phases. The book also covers internal geometry relaxation effects on electron transfer rates of amino-centered systems. The sequential elec

Mariano, Patrick S

1993-01-01

62

Interfacial Electron Transfer Dynamics for [Ru(bpy)2((4,4?-PO3H2)2bpy)]2+ Sensitized TiO2 in a Dye-Sensitized Photoelectrosynthesis Cell: Factors Influencing Efficiency and Dynamics  

Energy Technology Data Exchange (ETDEWEB)

Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [(Ru(bpy){sub 2}(4,4?-(PO{sub 3}H{sub 2}){sub 2}bpy)]{sup 2+} attached to TiO{sub 2} nanoparticle films, TiO{sub 2}?Ru{sup II}, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H{sub 2} production. In these experiments, laser flash excitation of TiO{sub 2}?Ru{sup II} and rapid injection lead to TiO{sub 2}(e?)?Ru{sup III} with subsequent TiO{sub 2}(e?)?Ru{sup III} ? TiO{sub 2}?Ru{sup II} back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA{sup 4?}) as irreversible electron transfer donors. With added TEOA or EDTA{sup 4?}, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H{sub 2} production in the photoelectrosynthesis cell. Reduction of TiO{sub 2}(e?)?Ru{sup III} by both TEOA and EDTA{sup 4?} occurs with k{sub D} ? 10{sup 6} M{sup ?1} s{sup ?1}. EDTA{sup 4?} is a more efficient scavenger by a factor of ?3 because of a more favorable partition equilibrium between the film and the external solution. Its increased scavenger efficiency appears in incident photon-to-current conversion efficiency (IPCE) measurements, in electron collection efficiencies (?{sub coll}), and in photocurrent measurements with H{sub 2} production. Evaluation of electron collection efficiencies by transient current measurements gave ?{sub coll} ? 24% for TEOA and ? 70% for EDTA{sup 4?}. The dynamics of back electron transfer are minimized, and collection efficiencies, photocurrents, and hydrogen production are maximized by application of a positive applied bias consistent with the results of I?V measurements. A pH dependent plateau is reached at ?0 V at pH = 4.5 (EDTA{sup 4?}) and at ? ?0.4 V at pH 6.7 (TEOA). The difference is qualitatively consistent with the influence of pH on electron population in trap states below the conduction band and the role they play in back electron transfer. The excitation dependence of IPCE measurements matches the spectrum of TiO{sub 2}?Ru{sup II} with IPCE values ?3 times higher for EDTA{sup 4?} than for TEOA as noted above. Absorbed photon-to-current efficiency (APCE) values are light-intensity dependent because of the effect of multiple injection events and the influence of increasing trap site electron densities on back electron transfer. The key to efficient H{sub 2} production is minimizing back electron transfer. Application of a sufficiently positive potential relative to E{sub CB} for TiO{sub 2} accelerates loss of electrons from the film in competition with back electron transfer allowing for H{sub 2} production with efficiencies approaching 14.7% under steady-state irradiation.

Song, Wenjing; Brennaman, Kyle M; Concepcion, Javier J; Jurss, Jonah W.; Hoertz, Paul G; Luo, Hanlin; Chen, Chuncheng; Hanson, Kenneth G.; Meyer, Thomas J.

2011-01-01

63

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)

64

Interfacial and thin film chemistry in electron device fabrication  

Science.gov (United States)

Progress on the Columbia URI program on 'Interfacial and Thin Film Chemistry in Electron Device Fabrication' is reported for the 1986-1991 period. Three broad areas of research included MBE Growth and Devices, Laser Surface Interactions, and Fundamentals of Processing Gas/Surface Interactions. Research in the area of MBE Growth and Devices included Heterostructures Grown by Molecular Beam Epitaxy by Professor Wen Wang and Interface Chemical Modification of Metal on Superconductor-Semiconductor Systems by Professor Ed Yang. Research in the area of Laser Surface Interactions included Laser-Surface Interactions and In Situ Diagnostics of Surface Chemistry During Electronic Processing by Professor Richard Osgood, Jr.; In Situ Optical Diagnostics of Semiconductors Prepared by Laser Chemical Processing and Other Novel Methods by Professor Irving Herman; and Ultrafast Optoelectronic Measurements of Surfaces and Interfaces by Professor David Auston. Research in Fundamentals of Processing Gas/Surface Interactions included Quantum State-Resolved Studies of Gas/Surface Chemical Reactions by Professor George Flynn and Photochemical and Photophysical Probes of Interfaces by Professor Nicholas Turro. Research results of Columbia's Principal Investigators supported by ONR/URI were published in nearly 200 scholarly articles which are listed in this report.

Auston, D.; Flynn, G.; Herman, I.; Osgood, R.; Turro, N.

1992-01-01

65

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 hrelations 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

66

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

67

75 FR 31665 - Electronic Fund Transfers  

Science.gov (United States)

...responsibilities of participants in electronic fund transfer systems. An...one consent form (or in the course of obtaining opt-ins through...205 Consumer protection, Electronic fund transfers, Federal Reserve...as follows: PART 205--ELECTRONIC FUND TRANSFERS...

2010-06-04

68

A layer-by-layer ZnO nanoparticle-PbS quantum dot self-assembly platform for ultrafast interfacial electron injection.  

Science.gov (United States)

Absorbent layers of semiconductor quantum dots (QDs) are now used as material platforms for low-cost, high-performance solar cells. The semiconductor metal oxide nanoparticles as an acceptor layer have become an integral part of the next generation solar cell. To achieve sufficient electron transfer and subsequently high conversion efficiency in these solar cells, however, energy-level alignment and interfacial contact between the donor and the acceptor units are needed. Here, the layer-by-layer (LbL) technique is used to assemble ZnO nanoparticles (NPs), providing adequate PbS QD uptake to achieve greater interfacial contact compared with traditional sputtering methods. Electron injection at the PbS QD and ZnO NP interface is investigated using broadband transient absorption spectroscopy with 120 femtosecond temporal resolution. The results indicate that electron injection from photoexcited PbS QDs to ZnO NPs occurs on a time scale of a few hundred femtoseconds. This observation is supported by the interfacial electronic-energy alignment between the donor and acceptor moieties. Finally, due to the combination of large interfacial contact and ultrafast electron injection, this proposed platform of assembled thin films holds promise for a variety of solar cell architectures and other settings that principally rely on interfacial contact, such as photocatalysis. PMID:25163799

Eita, Mohamed; Usman, Anwar; El-Ballouli, Ala'a O; Alarousu, Erkki; Bakr, Osman M; Mohammed, Omar F

2015-01-01

69

Charge transfer through interfacial water inside an STM junction  

International Nuclear Information System (INIS)

Charge transfer through thin layers of water between an STM tip and an Au surface has been investigated by using a scanning tunneling microscopy (STM) technique at a relative humidity of 95%. The plateau currents were found to appear at separations larger than several A where the current decay stops. The polarity dependence of the electrochemical currents was not observed with STM junction between an Au tip and an Au surface, which was observed with STM junction between a Pt/Ir tip and an Au surface. The plateau currents at H2O saturation were measured to be 10-20% higher than those at D2O saturation at bias voltages above |0.4| V. The results were rationalized in terms of the electrochemical currents originating mostly from the processes of OH- (OD-) or H2O (D2O) on the positive surface with different conductivity between H2O and D2O

70

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

71

Near-infrared fluorescent single walled carbon nanotube-chitosan composite: Interfacial strain transfer efficiency assessment  

Science.gov (United States)

Effective load transfer at the single walled carbon nanotube (SWCNT)-polymer interface is most desirable for mechanically reinforced polymer composites. Versatile layer-by-layer assembly technique achieved dispersion and uniform distribution of sodium carboxymethylcellulose (CMC)-solubilized SWCNTs within the polymer matrix. Electrostatic interaction between positively charged chitosan and negatively charged CMC facilitates design of an optically active biocompatible nanocomposite. Interfacial strain transfer efficiency of SWCNT-chitosan nanocomposite was assessed via SWCNT Raman and photoluminescence band shifts under uniaxial strain. Photoluminescence peak shift rates of individual semiconducting SWCNTs were investigated and compared with tight binding model calculations.

Mol Menamparambath, Mini; Arabale, Girish; Nikolaev, Pavel; Baik, Seunghyun; Arepalli, Sivaram

2013-04-01

72

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

73

Advances in electron transfer chemistry  

CERN Document Server

Advances in Electron Transfer Chemistry, Volume 4 presents the reaction mechanisms involving the movement of single electrons. This book discusses the electron transfer reactions in organic, biochemical, organometallic, and excited state systems. Organized into four chapters, this volume begins with an overview of the photochemical behavior of two classes of sulfonium salt derivatives. This text then examines the parameters that control the efficiencies for radical ion pair formation. Other chapters consider the progress in the development of parameters that control the dynamics and reaction p

Mariano, Patrick S

1995-01-01

74

Effect of interfacial wavy motion on film boiling heat transfer from isothermal downward-facing hemispheres  

International Nuclear Information System (INIS)

Film boiling heat transfer coefficients for a downward-facing hemispherical surface are measured from the quenching tests in Downward-Boiling Experiment Laminar Transition Apparatus (DELTA). Two test sections are made of copper to maintain low Biot numbers. The outer diameters of the hemispheres are 120 and 294 mm, respectively. The thickness of all the test sections is 30 mm. The effect of diameter on film boiling heat transfer is quantified utilizing results obtained from the test sections. The measured data are compared with the numerical predictions from laminar film boiling analysis. The measured heat transfer coefficients are found to be greater than those predicted by the conventional laminar flow theory on account of the interfacial wavy motion incurred by the Helmholtz instability. Incorporation of the wavy motion model considerably improves the agreement between the experimental and numerical results in terms of heat transfer coefficient. In addition, the film boiling was visualized using a digital camera

75

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

76

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

Energy Technology Data Exchange (ETDEWEB)

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 Cu/sup 2 +/ 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 ..beta..-hydroxy-oxime) and the pH of the aqueous copper feed solution is briefly discussed. 4 figures.

Danesi, P.R. (Argonne National Lab., IL); Horwitz, E.P.; Vandegrift, G.F.; Chiarizia, R.

1981-01-01

77

Turbulence structure and prediction of interfacial heat and mass transfer in wavy-stratified flow  

Energy Technology Data Exchange (ETDEWEB)

Interfacial transport of mass and heat in gas-liquid systems is encountered in many industries and involved in a wide variety of equipment and processes such as heat exchangers, boilers, steam condensers, cooling towers, gas absorbers, and chemical reactors. The turbulence structure of the liquid phase near a wavy gas-liquid interface in stratified flow was experimentally investigated in a 50 mm (H) x 100 mm (W) rectangular duct. The characteristic parameters of the organized motion under the liquid waves such as the frequency of appearance and length scale were estimated by using the variable-interval time-averaging and the photochromic dye activation techniques. These characteristics were used in a hybrid surface renewal-eddy cell model to predict the interfacial heat- and mass-transfer coefficients in stratified two-phase flow. The predictions for cocurrent and countercurrent flows agreed reasonably well with experimental data available in the literature.

Lorencez, C.; Nasr-Esfahany, M.; Kawaji, M. [Univ. of Toronto, Ontario (Canada). Dept. of Chemical Engineering and Applied Chemistry

1997-06-01

78

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-03-15

79

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-03-15

80

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

81

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

82

Direct correlation of charge transfer absorption with molecular donor:acceptor interfacial area via photothermal deflection spectroscopy  

KAUST Repository

We show that the Charge Transfer (CT) absorption signal in bulk-heterojunction (BHJ) solar cell blends, measured by photothermal deflection spectroscopy (PDS), is directly proportional to the density of molecular donor/acceptor interfaces. Since the optical transitions from ground state to the interfacial CT state are weakly allowed at photon energies below the optical gap of both donor and acceptor, we can exploit the use of this sensitive linear absorption spectroscopy for such quantification. Moreover, we determine the absolute molar extinction coefficient of the CT transition for an archetypical polymer-fullerene interface. The latter is ~100 times lower than the extinction coefficient of the donor chromophore involved, allowing us to experimentally estimate the transition dipole moment (0.3 D) and the electronic coupling between ground state and CT state to be on the order of 30 meV.

Vandewal, Koen

2015-04-09

83

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.

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

2012-06-01

84

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

85

Polar solvation and electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

1993-04-13

86

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

Science.gov (United States)

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

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

2014-02-01

87

Electron-transfer organic and bioorganic photochemistry  

International Nuclear Information System (INIS)

A review is given of the literature on electron transfer in organic and bioorganic photochemistry mainly from 1985 to April 1988. Topics covered include the theory and kinetics of electron transfer, the dynamic and chemical behaviour of the geminate ion-radical pair, the effects of salts on photoinduced electron-transfer reactions, the photorepair of UV-damaged DNA and cyclobutane-ring splitting by photoinduced electron transfer, model compounds of NAD(P)+/NAD(P)H, deazoflavin and flavin and two-electron photoredox reactions and the application of photoinduced electron transfer reactions to organic synthesis. (U.K.)

88

"Butterfly effect" in CuO/graphene composite nanosheets: a small interfacial adjustment triggers big changes in electronic structure and Li-ion storage performance.  

Science.gov (United States)

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

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

2014-10-01

89

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-09-25

90

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

Science.gov (United States)

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

Sun, Zhizhong; Zhang, Xuezhi; Hu, Henry; Niu, Xiaoping

2012-01-01

91

Microstructure Simulation of Al-Cu Alloy Based on Inverse Identified Interfacial Heat Transfer Coefficient  

Science.gov (United States)

The interfacial heat transfer coefficient (IHTC) is taken as one of the most important factors affecting the accuracy of the simulation. In the present paper, the IHTC variation with temperature was obtained by an inverse heat conduction method. Then, a 3D cellular automaton-finite element method was adopted to predict the microstructure of an Al-Cu alloy based on the identified IHTC. It was found that the IHTC was of prime importance for the precise simulation of solidification microstructure, especially in the grains distribution. In addition, the simulated results using the IHTC variation with temperature were found to exhibit a better agreement with the experimental results than those using the constant value.

Bu, X. B.; Li, L. X.; Zhang, L. Q.; Zhu, B. W.; Xu, R.; Wang, S. P.

2013-09-01

92

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

International Nuclear Information System (INIS)

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

93

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

International Nuclear Information System (INIS)

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

94

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

Science.gov (United States)

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

Cao, Yongyou; Guo, Zhipeng; Xiong, Shoumei

2012-07-01

95

Quantum Plasmonics: Electron transfer processes  

Science.gov (United States)

Plasmon energies can be tuned across the spectrum by simply changing the geometrical shape of a nanostructure. Plasmons can efficiently capture incident light and focus it to nanometer sized hotspots which can enhance electronic and vibrational excitations in nearby structures.[1] Another important but still relatively unexplored property of plasmons, is that they can be efficient sources of hot energetic electrons which can transfer into nearby structures and induce a variety of processes. This process is a quantum mechanical effect: the decay of plasmon quanta into electron-hole pairs. I will discuss how plasmon induced hot electrons can be used in various applications: such as to induce chemical reactions in molecules physisorbed on a nanoparticle surface;[2] to inject electrons directly into the conduction band of a nearby substrate;[3] and to induce local doping of a nearby graphene sheet.[4] References [1] N.J. Halas et al., Adv. Mat. 24(2012)4842 [2] R. Huschka et al., JACS 133(2011)12247; S. Mukherjee et al. TBP 2012 [3] M. W. Knight et al., Science 332(2011)702, Z.Y. Fang et al., NL 12(2012)3808 [4] Z.Y. Fang et al., ACS Nano 6(2012)10.1021/nn304028b

Nordlander, Peter

2013-03-01

96

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

International Nuclear Information System (INIS)

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

97

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

98

Interfacial adhesion in metal/polymer systems for electronics  

OpenAIRE

The effects of the different surface modification methods on the adhesion of electroless and sputter-deposited metals to dielectric polymers were investigated. The adhesion of Cu and Cr/Cu metallizations to the epoxies, liquid crystalline polymer and inorganic-organic hybrid polymer was measured with the newly developed pull test method. The microstructure and chemical state of the surfaces were characterized with the help of X-ray photoelectron spectroscopy (XPS), scanning electron microscop...

Ge, Jun

2003-01-01

99

Interfacial electron transfer dynamics of photosensitized zinc oxide nanoclusters  

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-06-01

100

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

101

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

Science.gov (United States)

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

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

2014-09-01

102

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

Science.gov (United States)

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.

Wang, Hai-Dong; Ma, Wei-Gang; Guo, Zeng-Yuan; Zhang, Xing; Wang, Wei

2011-04-01

103

Molecular Basis for Directional Electron Transfer*  

OpenAIRE

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

104

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

105

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

106

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-09-25

107

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

International Nuclear Information System (INIS)

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

108

Proceedings of the conference on electron and ion transfer in condensed media. Theoretical physics for reaction kinetics  

International Nuclear Information System (INIS)

The book includes 23 papers presented at the conference on ''Electron and Ion Transfer in Condensed Media. Theoretical Physics for Reaction Kinetics'' held in Trieste (Italy) between 15-19 July 1996. The papers are grouped in six chapters: Introduction (2 papers), The Liquid Environment of Charge Transfer: Structure and Dynamics (5 papers), Fundamental of Elementary Act of Electron and Ion Transfer (4 papers), Interfacial Charge Transfer, Electrochemistry, in situ STM (5 papers), Ion Conductors (2 papers) and ''Organized'' Charge Transfer (5 papers). A separate abstract was prepared for each paper

109

Intramolecular electron transfer in the inverted region  

Energy Technology Data Exchange (ETDEWEB)

In 1960 Marcus predicted that rate constants for electron transfer should decrease with -{Delta}G in the inverted region. In the inverted region, -{Delta}G > {lambda}, where {lambda} is the reorganization energy and {Delta}G the free energy loss associated with the electron transfer. Experimental verification of this prediction has been difficult to obtain but has been found by pulse radiolysis in rigid organic glasses, by Closs, Miller, and co-workers in unsymmetrical, linked organics, in accounting for separation yields in photoinduced electron transfer, and by light-induced electron transfer in linked porphyrin-quinone systems. The authors report here the first examples based on transition-metal complexes and, as predicted theoretically, that there is a clear relationship between electron transfer in the inverted region and nonradiative decay in a closely related family of excited states.

Chen, Pingyun; Duesing, R.; Tapolsky, G.; Meyer, T.J. (Univ. of North Carolina, Chapel Hill (USA))

1989-10-11

110

Manipulating NiFe/AlOx interfacial chemistry for the spin-polarized electrons transport  

International Nuclear Information System (INIS)

Through vacuum annealing, interfacial chemical composition of sputter-deposited AlOx/NiFe/AlOx can be controlled for electron transport manipulation. Chemical status change at the NiFe/AlOx interface was quantified by X-ray photoelectron spectroscopy and correlated to the structure and electron transport properties of the heterostructure. It is found that elemental Al existed in the insulting AlOx after annealing at intermediate temperature can improve the AlOx/NiFe interface and thus favor the electronic transport. Annealing at higher temperature will result in native AlOx formation and degrade transport properties due to the NiFe/AlOx interfaces deterioration caused by significant difference in thermal expansion coefficients of the two materials.

111

Fluorinated copper phthalocyanine nanowires for enhancing interfacial electron transport in organic solar cells.  

Science.gov (United States)

Zinc oxide is a promising candidate as an interfacial layer (IFL) in inverted organic photovoltaic (OPV) cells due to the n-type semiconducting properties as well as chemical and environmental stability. Such ZnO layers collect electrons at the transparent electrode, typically indium tin oxide (ITO). However, the significant resistivity of ZnO IFLs and an energetic mismatch between the ZnO and the ITO layers hinder optimum charge collection. Here we report that inserting nanoscopic copper hexadecafluorophthalocyanine (F(16)CuPc) layers, as thin films or nanowires, between the ITO anode and the ZnO IFL increases OPV performance by enhancing interfacial electron transport. In inverted P3HT:PC(61)BM cells, insertion of F(16)CuPc nanowires increases the short circuit current density (J(sc)) versus cells with only ZnO layers, yielding an enhanced power conversion efficiency (PCE) of ?3.6% vs ?3.0% for a control without the nanowire layer. Similar effects are observed for inverted PTB7:PC(71)BM cells where the PCE is increased from 8.1% to 8.6%. X-ray scattering, optical, and electrical measurements indicate that the performance enhancement is ascribable to both favorable alignment of the nanowire ?-? stacking axes parallel to the photocurrent flow and to the increased interfacial layer-active layer contact area. These findings identify a promising strategy to enhance inverted OPV performance by inserting anisotropic nanostructures with ?-? stacking aligned in the photocurrent flow direction. PMID:23181741

Yoon, Seok Min; Lou, Sylvia J; Loser, Stephen; Smith, Jeremy; Chen, Lin X; Facchetti, Antonio; Marks, Tobin J; Marks, Tobin

2012-12-12

112

Effects of turbulence on interfacial heat transfer: a priori test and filters evaluation  

International Nuclear Information System (INIS)

Full text of publication follows: Many applications involving multiphase flows (for instance: spray formation, oil transportation, sea aerosol formation,...) induce very high Reynolds numbers. In these turbulent regimes, non-linear effects mainly drive the behavior of such flows. Consequently, Direct Numerical Simulation (DNS) calculations have to entail a number of freedom degrees proportional to the third power of the Reynolds number to correctly describe the flow behavior. This extremely hard restraint makes it impossible to use DNS for industrial applications. However, the turbulent behavior of the flow is expected to widely favor the energy transfers through the interface and then to have a major effect on the energy balance of the flows. Until now, the great majority of numerical calculations for multiphase turbulent flows use RANS (Reynolds Averaged Navier-Stokes) and LES (Large-Eddy Simulation) modeling in order to add energy dissipation to the molecular diffusion terms. However, no theoretical or experimental justifications have been proposed. The impact of the local and instantaneous multiphase topology of the flow on the turbulent characteristics has never been carefully studied, and the modeling (RANS or LES) is mainly based on analytical considerations which needs additional terms when considering interfaces and turbulence. The Direct Numerical Simulation (DNS) calculation is used in this work to provide information for LES and RANS modeling thanks to a pon for LES and RANS modeling thanks to a priori tests. To correctly handle the challenging modeling process of the energy transfers, the final paper proposes a mathematical formalism of the filtered system of multiphase one-fluid equations, including the filtered energy equation. A general formulation for LES or RANS calculation is provided. Different filtering processes are discussed focusing on the concept of extensive (a.k.a. on the extensive variables) or intensive (a.k.a. on the intensive variables) filtering. Thus, this theoretical background is illustrated with two non-isothermal turbulent interfacial problems: a two-dimensional air bubble in water interacting with contra-rotative vortices using the Trio U calculation code and the water-oil phase separation in a square box submitted to a temperature gradient using Aquilon CFD library. These test cases exhibit for example the increase of energy transfers at the interface, for example when a bubble plunged into a temperature gradient is impacted by two vortices. The different sub-grid terms to close in the case of under-resolved (RANS or LES) calculations are identified and compared. Different definitions of the filtering are used and are shown to provide drastically different results. The present work highlights the modeling issues and the choice of the balance equations to solve. It is demonstrated that the order of magnitude of the sub-grid scale terms arising in the equations can vary from a factor of 100 depending on the filtering chosen and that neglecting the sub-grid scale terms leads to a widely over-estimated heat transfer at the interface. (authors)

113

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

114

Advances in electron transfer chemistry, v.6  

CERN Document Server

It is clear that electron transfer chemisty is now one of the most active areas of chemical study. Advances in Electron Transfer Chemistry has been designed to allow scientists who are developing new knowledge in this rapidly expanding area to describe their most recent research findings. This volume will serve those interested in learning about current breakthroughs in this rapidly expanding area of chemical research.

Mariano, PS

1999-01-01

115

Oxidation of freestanding silicon nanocrystals probed with electron spin resonance of interfacial dangling bonds  

Science.gov (United States)

The oxidation of freestanding silicon nanocrystals (Si-NCs) passivated with Si-H bonds has been investigated for a wide range of oxidation times (from a few minutes to several months) by means of electron spin resonance (ESR) of dangling bonds (DBs) naturally incorporated at the interface between the NC core and the developing oxide shell. These measurements are complemented with surface chemistry analysis from Fourier transform infrared spectroscopy. Two surface phenomena with initiation time thresholds of 15 min and 30 h are inferred from the dependence of ESR spectra on oxidation time. The first initiates before oxidation of surface Si-Si bonds and destruction of the NC hydrogen termination takes place (induction period) and results in a decrease of the DB density and a localization of the DB orbital at the central Si atom. Within the Cabrera-Mott oxidation mechanism, we associate this process with the formation of intermediate interfacial configurations, resulting from surface adsorption of water and oxygen molecules. The second surface phenomenon leads to a steep increase of the defect density and correlates with the formation of surface Si-O-Si bridges, lending experimental support to theoretically proposed mechanisms for interfacial defect formation involving the emission of Si interstitials at the interface between crystalline Si and the growing oxide.

Pereira, R. N.; Rowe, D. J.; Anthony, R. J.; Kortshagen, U.

2011-04-01

116

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

117

Low Temperature Electronic Transport and Electron Transfer through Organic Macromolecules  

OpenAIRE

It is shown that at low temperatures and moderate electron dephasing the electron transmission function reveales a structure containing information about donor/acceptor sites effectively participating in the electron transfer (ET) processes and primary pathways of electrons tunneling through molecular bridges in macromolecules. This important information can be obtained as a result of analysis of experimental low temperature current-voltage characteristics for chosen molecules.

Zimbovskaya, Natalya A.

2002-01-01

118

Pseudospin Transfer Torques in Semiconductor Electron Bilayers  

OpenAIRE

We use self-consistent quantum transport theory to investigate the influence of electron-electron interactions on interlayer transport in semiconductor electron bilayers in the absence of an external magnetic field. We conclude that, even though spontaneous pseudospin order does not occur at zero field, interaction-enhanced quasiparticle tunneling amplitudes and pseudospin transfer torques do alter tunneling I-V characteristics, and can lead to time-dependent response to a d...

Kim, Youngseok; Macdonald, Allan H.; Gilbert, Matthew J.

2012-01-01

119

Single Molecule Spectroscopy of Electron Transfer  

International Nuclear Information System (INIS)

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

120

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

Science.gov (United States)

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

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

2013-11-01

121

Bioinspired electron-transfer systems and applications  

International Nuclear Information System (INIS)

Bioinspired electron-transfer systems including artificial photosynthesis and respiration are presented herein together with some of their applications. First, multi-step electron-transfer systems composed of electron donor-acceptor ensembles have been developed, mimicking functions of the photosynthetic reaction center. However, a significant amount of energy is lost during the multi-step electron-transfer processes. Then, as an alternative to conventional charge-separation functional molecular models based on multi-step long-range electron transfer within redox cascades, simple donor-acceptor dyads have been developed to attain along-lived and high energy charge-separated state without significant loss of excitation energy, by fine control of the redox potentials and of the geometry of donor-acceptor dyads that have small reorganization energies of electron transfer. Such simple molecular dyads, capable of fast charge separation but extremely slow charge recombination, have significant advantages with regard to synthetic feasibility, providing a variety of applications including construction of organic solar cells and development of efficient photo-catalytic systems for the solar energy conversion. An efficient four-electron reduction of dioxygen to water by one-electron reductants such as ferrocene derivatives as well as by an NADH analog has also been achieved as a respiration model by using a cofacial dicobalt porphyrin that can form the ?-peroxo Co(III)-O2hat can form the ?-peroxo Co(III)-O2Co(III) complex. The catalytic mechanism of the four-electron reduction of dioxygen has been clarified based on the detailed kinetic study and the detection of the intermediate. (author)

122

Interfacial spin-filter assisted spin transfer torque effect in Co/BeO/Co magnetic tunnel junction  

Science.gov (United States)

The first-principles calculation is employed to demonstrate the spin-selective transport properties and the non-collinear spin-transfer torque (STT) effect in the newly proposed Co/BeO/Co magnetic tunnel junction. The subtle spin-polarized charge transfer solely at O/Co interface gives rise to the interfacial spin-filter (ISF) effect, which can be simulated within the tight binding model to verify the general expression of STT. This allows us to predict the asymmetric bias behavior of non-collinear STT directly via the interplay between the first-principles calculated spin current densities in collinear magnetic configurations. We believe that the ISF effect, introduced by the combination between wurtzite-BeO barrier and the fcc-Co electrode, may open a new and promising route in semiconductor-based spintronics applications.

Tang, Y.-H.; Chu, F.-C.

2015-03-01

123

Promoting Knowledge Transfer with Electronic Note Taking  

Science.gov (United States)

We investigated the differences between (a) copying and pasting text versus typed note-taking methods of constructing study notes simultaneously with (b) vertically scaffolded versus horizontally scaffold notes on knowledge transfer. Forty-seven undergraduate educational psychology students participated. Materials included 2 electronic

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

2005-01-01

124

Quantum effects in biological electron transfer.  

Czech Academy of Sciences Publication Activity Database

Ro?. 14, ?. 17 (2012), s. 5902-5918. ISSN 1463-9076 Institutional research plan: CEZ:AV0Z40550506 Keywords : electron transfer * tunnelling * decoherence * semi-classical molecular dynamics * density functional theory Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 3.829, year: 2012

de la Lande, A.; Babcock, N. S.; ?ezá?, Jan; Levy, B.; Sanders, B. C.; Salahub, D.

2012-01-01

125

Femtosecond events in the free electron transfer  

Energy Technology Data Exchange (ETDEWEB)

The ion-molecule reaction between solvent parent radical cations and hetero group-substituted aromatics in non-polar media shows a characteristic product distribution, which depends strongly on the mobility of the substituent. This electron transfer phenomenon seems to reflect femtodynamics of the donor molecule, which is appearing in the nanosecond time range.

Brede, Ortwin [Interdisciplinary Group Time-Resolved Spectroscopy, University of Leipzig (Germany)]. E-mail: brede@mpgag.uni-leipzig.de; Naumov, Sergej [Institute of Surface Modification, Leipzig (Germany)

2007-08-15

126

Monitoring molecule dynamics by free electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Molecular oscillations take place in the time range of some 10-100 fs. In asymmetric molecules, accompanied with rotation and necking motions of molecule parts changes of the electron distribution of the molecular orbitals occur. In phenols the rotation motion of the C-OH bond with a frequency around 10{sup 13} Hz causes dramatical electron motions in the molecule. These motions could be monitored with an extremely rapid chemical reaction (free electron transfer) which results in product characteristics for the assumed different borderline structures of the phenol molecule.

Brede, O. E-mail: brede@mpgag.uni-leipzig.de; Naumov, S.; Hermann, R

2003-06-01

127

Interfacial tension-hindered phase transfer of polystyrene-b-poly(ethylene oxide) polymersomes from a hydrophobic ionic liquid to water.  

Science.gov (United States)

We examine the phase transfer of polystyrene-b-poly(ethylene oxide) (PS-PEO) polymersomes from a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), into water. The dependence of the phase transfer on the molecular weight and PEO volume fraction (fPEO) of the PS-PEO polymersomes was systematically studied by varying the molecular weight of PS (10,000-27,000 g/mol) as well as by varying the volume fraction of PEO (fPEO) between 0.1 and 0.3. We demonstrate a general boundary for the phase transfer in terms of a reduced tethering density for PEO (?PEO), which is independent of the molecular weight of the hydrophobic PS. The reduced PEO tethering density was controlled by changing the polymersome size (i.e., increased polymersome sizes increase ?PEO), confirming that it is the driving force in the transfer of PS-PEO polymersomes at room temperature. The phase transfer dependence on ?PEO was also analyzed in terms of the free energy of polymersomes in the biphasic system. The quality of the aqueous phase, which affects the interfacial tension of the PS membrane, influenced the phase transfer. We systematically reduced the interfacial tension by adding a water-selective solvent, THF, which has a similar effect to increasing ?PEO. The results indicate that the interfacial tension between the membrane and water plays an important role in the phase transfer with the corona and that the phase transfer can be controlled either by the dimensions of the polymersomes or by the suitability of the solvent for the membrane. The interfacial tension-hindered phase transfer of polymersomes in the biphasic water-[EMIM][TFSI] system will inform the design of temperature-sensitive and reversible nanoreactors and the separation of polydisperse particles according to size by tuning the quality of the solvent. PMID:25555164

So, Soonyong; Lodge, Timothy P

2015-01-13

128

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

DEFF Research Database (Denmark)

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

Gilbert, Benjamin; Katz, Jordan E.

2013-01-01

129

Estimates of electronic coupling for excess electron transfer in DNA  

Science.gov (United States)

Electronic coupling Vda is one of the key parameters that determine the rate of charge transfer through DNA. While there have been several computational studies of Vda for hole transfer, estimates of electronic couplings for excess electron transfer (ET) in DNA remain unavailable. In the paper, an efficient strategy is established for calculating the ET matrix elements between base pairs in a ? stack. Two approaches are considered. First, we employ the diabatic-state (DS) method in which donor and acceptor are represented with radical anions of the canonical base pairs adenine-thymine (AT) and guanine-cytosine (GC). In this approach, similar values of Vda are obtained with the standard 6-31G* and extended 6-31++G** basis sets. Second, the electronic couplings are derived from lowest unoccupied molecular orbitals (LUMOs) of neutral systems by using the generalized Mulliken-Hush or fragment charge methods. Because the radical-anion states of AT and GC are well reproduced by LUMOs of the neutral base pairs calculated without diffuse functions, the estimated values of Vda are in good agreement with the couplings obtained for radical-anion states using the DS method. However, when the calculation of a neutral stack is carried out with diffuse functions, LUMOs of the system exhibit the dipole-bound character and cannot be used for estimating electronic couplings. Our calculations suggest that the ET matrix elements Vda for models containing intrastrand thymine and cytosine bases are essentially larger than the couplings in complexes with interstrand pyrimidine bases. The matrix elements for excess electron transfer are found to be considerably smaller than the corresponding values for hole transfer and to be very responsive to structural changes in a DNA stack.

Voityuk, Alexander A.

2005-07-01

130

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

OpenAIRE

We investigate the charge-transfer interfaces between metal and redox arylamine molecular films through studying the current-voltage characteristics of single-layer organic diodes with the aid of anode interfacial engineering method. The diode turn-on voltage is shown to be highly sensitive to the arylamine/metal charge-transfer interfaces and thus can serve as a probe in detecting such organic/metal interfaces. We show that the diode electrical performance could be tuned th...

Li, J. C.; Blackstock, S. C.; Szulczewski, G. J.

2005-01-01

131

An investigation of the effects of interfacial shear between the gas and turbulent falling liquid film on the heat transfer coefficient  

International Nuclear Information System (INIS)

An improved method is presented for the prediction of heat transfer coefficients in turbulent falling liquid films with or without interfacial shear for both heating or condensation. A modified Mudawwar and El-Masri's semiempirical turbulence model, particularly to extend its use for the turbulent falling film with high interfacial shear, is used to replace the eddy viscosity model incorporated in the unified approach proposed by Yih and Liu. The liquid film thickness and asymptotic heat transfer coefficients against the film Reynolds number for wide range of interfacial shear predicted by both present and existing methods are compared with experimental data. The results show that, in general, predictions of the modified model agree more closely with experimental data than that of existing models. Comparisons of the predictions of the present model with that of existing models and the experimental data show that agreement is fairly good and consistent. A brief summary of the results are as follows: (1) As opposed to the previous model, present model utilizes a continuous linear variation of eddy viscosity near the interfacial surface. For freely falling liquid film, the present model reduce to the Mudawwar and El-Masri's model. (2) The curves of the present model for the heat transfer coefficients with liquid film Reynolds number have positive slopes in turbulent regime while the curves obtained by other models have negative slopes particularly for condensation. (3) The two criteria for transition from laminar to turbulent film flow, one for low interfacial shear and the other for high interfacial shear, respectively are shown to give the best agreement with the data for the present method

132

Electron transfer reactions in microporous solids  

Science.gov (United States)

The research program involves the use of microporous solids (zeolites, clays, layered, and tunnel structure oxide semiconductors) as organizing media for artificial photosynthetic systems. The purpose of the microporous solid is twofold. First, it induces spatial organization of photoactive and electroactive components (sensitizers, semiconductor particles, electron relays, and catalysts) at the solid-solution interface, enhancing the quantum efficiency of charge separation and separating physically the ultimate electron donor and acceptor in the electron transport chain. Second, since the microcrystalline solid admits only molecules of a certain charge and size, it is possible to achieve permanent charge separation by sieving chemical photoproducts (e.g., H2 and I3(-), or H2 and O2) from each other. Spectroscopic and electrochemical methods are used to study the kinetics of electron transfer reactions in these hybrid molecular/solid state assemblies.

Mallouk, T. E.

1993-01-01

133

Electron transfer in branched expanded pyridinium molecules.  

Czech Academy of Sciences Publication Activity Database

Aveiro : DEMAC - Universidade de Aveiro , 2014. s. 99-99. [Meeting of the Portuguese Electrochemical Society /19./. Iberian Meeting of Electrochemistry /16./. 30.06.2014-02.07.2014, Aveiro ] R&D Projects: GA ?R(CZ) GA14-05180S Grant ostatní: Rada Programu interní porpory projekt? mezinárodní spolupráce AV ?R M200401202 Institutional support: RVO:61388955 Keywords : electron transfer * electrochemistry * pyridinium Subject RIV: CG - Electrochemistry

Hromadová, Magdaléna; Lachmanová, Št?pánka; Pospíšil, Lubomír; Fortage, J.; Dupeyre, G.; Perruchot, Ch.; Lainé, P. P.

134

Promoting Interspecies Electron Transfer with Biochar  

OpenAIRE

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...

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

2014-01-01

135

Resonant electron transfer between quantum dots  

OpenAIRE

An interaction of electromagnetic field with a nanostructure composed of two quantum dots is studied theoretically. An effect of a resonant electron transfer between the localized low-lying states of quantum dots is predicted. A necessary condition for such an effect is the existence of an excited bound state whose energy lies close to the top of the barrier separating the quantum dots. This effect may be used to realize the reversible quantum logic gate NOT if the superposi...

Openov, Leonid A.

1999-01-01

136

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

137

Kinetic ion thermometers for electron transfer dissociation.  

Science.gov (United States)

Peptide fragment ions of the z-type were used as kinetic ion thermometers to gauge the internal energy of peptide cation-radicals produced by electron transfer in the gas-phase. Electron transfer dissociation (ETD)-produced z2 ions containing the leucine residue, z2(Leu-Lys) and z2(Leu-Arg), were found to undergo spontaneous dissociation by loss of C3H7 that was monitored by time-resolved kinetic measurements on the time scale of the linear ion trap mass spectrometer. Kinetic modeling of the dissociations, including collisional cooling and product loss by neutralization, provided unimolecular rate constants for dissociation that were converted to the z ion internal energies using RRKM theory. The internal energy of z2(Leu-Lys) and z2(Leu-Arg) fragment ions was found to decrease with the increasing size of the precursor peptide ion, indicating vibrational energy partitioning between the ion and neutral fragments and ergodic behavior. The experimentally determined excitation in the peptide cation-radicals upon electron transfer (285-327 kJ mol(-1)) was found to be lower than that theoretically calculated from the reaction exothermicity. The reasons for this missing energy are discussed. PMID:25594857

Pepin, Robert; Ture?ek, František

2015-02-19

138

Bulk heterojunction solar cells with large open-circuit voltage: electron transfer with small donor-acceptor energy offset  

Energy Technology Data Exchange (ETDEWEB)

Photoinduced electron transfer is observed in polymer bulk heterojunction solar cells with very small interfacial energy offset. The results imply that open circuit voltage values close to the band gap of the semiconducting polymer should be possible for polymer bulk heterojunction solar cells just as for inorganic solar cells. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Gong, Xiong; Tong, Minghong; Brunetti, Fulvio G.; Seo, Junghwa; Sun, Yanming; Moses, Daniel; Wudl, Fred; Heeger, Alan J. [Center for Polymers and Organic Solids, University of California Santa Barbara, Santa Barbara, CA 93106 (United States)

2011-05-24

139

Transfer coating by electron initiated polymerization  

International Nuclear Information System (INIS)

The high speed and depth of cure possible with electron initiated monomer/oligomer coating systems provide many new opportunities for approaches to product finishing. Moreover, the use of transfer or cast coating using films or metallic surfaces offers the ability to precisely control the surface topology of liquid film surfaces during polymerization. Transfer coating such as with textiles has been a commercial process for many years and the synergistic addition of EB technology permits the manufacture of unusual new products. One of these, the casting paper used in the manufacture of vinyl and urethane fabrics, is the first EB application to use a drum surface for pattern replication in the coating. In this case the coated paper is cured against, and then released from, an engraved drum surface. Recent developments in the use of plastic films for transfer have been applied to the manufacture of transfer metallized and coated paper and paperboard products for packaging. Details of these and related processes will be presented as well as a discussion of the typical product areas using this high speed transfer technology. (author)

140

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

141

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

142

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

143

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

144

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

145

Proton transfer across a liquid/liquid interface facilitated by phospholipid interfacial films.  

Czech Academy of Sciences Publication Activity Database

Ústí nad Labem : BEST servis, 2010 - (Navrátil, T.; Barek, J.), s. 70-72 ISBN 978-80-254-6710-7. [Modern Electroanalytical Methods /30./. Jet?ichovice (CZ), 24.05.2010-28.05.2010] R&D Projects: GA AV ?R IAA400400806; GA MŠk(CZ) LC06063 Institutional research plan: CEZ:AV0Z40400503 Keywords : liquid-liquid interface * proton transfer * phospholipid layers Subject RIV: CF - Physical ; Theoretical Chemistry

Holub, Karel; Jänchenová, Hana; Štulík, Karel; Mare?ek, Vladimír

146

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

Directory of Open Access Journals (Sweden)

Full Text Available The high pressure die casting (HPDC process is one of the fastest growing and most efficient methods for the production of complex shape castings of magnesium and aluminum alloys in today’s manufacturing industry.In this study, a high pressure die casting experiment using AZ91D magnesium alloy was conducted, and the temperature profiles inside the die were Measured. By using a computer program based on solving the inverse heat problem, the metal/die interfacial heat transfer coefficient (IHTC was calculated and studied. The results show that the IHTC between the metal and die increases right after the liquid metal is brought into the cavity by the plunger,and decreases as the solidification process of the liquid metal proceeds until the liquid metal is completely solidified,when the IHTC tends to be stable. The interfacial heat transfer coefficient shows different characteristics under different casting wall thicknesses and varies with the change of solidification behavior.

GUO Zhi-peng

2007-02-01

147

Interfacial Properties of Monolayer and Bilayer MoS2 Contacts with Metals: Depressed Many-electron Effects  

OpenAIRE

Although many devices based on MoS2 have been fabricated, where MoS2-metal contact plays a critical role, the nature of MoS2-metal contact has not been well established yet. We provide the first comparative study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au) with inclusion of many-electron effects based on a dual interface model. A comparison between the calculated and observed Schottky b...

Zhong, Hongxia; Ni, Zeyuan; Wang, Yangyang; Ye, Meng; Song, Zhigang; Pan, Yuanyuan; Quhe, Ruge; Yang, Jinbo; Yang, Li; Shi, Junjie; Lu, Jing

2015-01-01

148

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

OpenAIRE

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

Guo, Zhi-peng; Xiong, Shou-mei

2007-01-01

149

Electron transfer pathways in microbial oxygen biocathodes  

Energy Technology Data Exchange (ETDEWEB)

The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O{sub 2} reduction by heme compounds. Here we showed that 1 muM of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O{sub 2} reduction to H{sub 2}O{sub 2} with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

Freguia, Stefano, E-mail: stefano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Tsujimura, Seiya, E-mail: seiya@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan); Kano, Kenji, E-mail: kkano@kais.kyoto-u.ac.j [Bio-analytical and Physical Chemistry Laboratory, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto 606-8205 (Japan)

2010-01-01

150

Electron transfer pathways in microbial oxygen biocathodes  

International Nuclear Information System (INIS)

The ability of some bacteria to enhance the rate of cathodic oxygen reduction to water has been recently discovered, opening the way to an entirely renewable and environmentally friendly concept of biocathode. In this study we reveal that several mechanisms may induce catalytic effects by bacteria. These comprise mechanisms that are putatively beneficial to the bacteria as well as mechanisms which are merely side effects, including quinone autoxidation and direct O2 reduction by heme compounds. Here we showed that 1 ?M of ACNQ is able to generate a significant catalytic wave for oxygen reduction, with onset at approximately 0 V vs. SHE. Similarly, adsorption of hemin on a carbon surface catalyses O2 reduction to H2O2 with an onset of +0.2 V vs. SHE. To evaluate the catalytic pathways of live cells on cathodic oxygen reduction, two species of electrochemically active bacteria were selected as pure cultures, namely Acinetobacter calcoaceticus and Shewanella putrefaciens. The former appears to exploit a self-excreted redox compound with redox characteristics matching those of pyrroloquinoline quinone (PQQ) for extracellular electron transfer. The latter appears to utilise outer membrane-bound redox compounds. Interaction of quinones and cytochromes with the membrane-bound electron transfer chain is yet to be proven.

151

Mediated Electron Transfer at Redox Active Monolayers  

Directory of Open Access Journals (Sweden)

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

Michael E.G. Lyons

2001-12-01

152

Transfer line TT70 (electrons from PS to SPS)  

CERN Multimedia

As injectors for LEP, PS and SPS had to be converted to the acceleration of electrons and positrons. So far, only positively charged particles had been transferred from the PS to the SPS, for the negatively charged electrons a new transfer line, TT70, had to be built. Due to the difference in level of the two machines, the transfer line slopes and tilts.

1981-01-01

153

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

154

A test for interfacial effects and stress transfer in ceramic matrix composites  

Science.gov (United States)

The efforts to fabricate single embedded filament specimens of carbon and SiC fibers were unsuccessful largely due to the thermal stresses resulting from differences in thermal coefficient of expansion. Other factors appear to have been involved including embrittlement of the metal substrate by the H2 gas in the chemical vapor deposition flow stream and reaction layers formed between the silicon carbide and the metal substrate. The carbon fiber may have been attacked by the CVD reactant. It is concluded that these differential stresses are so large as to make the embedded fiber test impractical for the study of interphase effects and stress transfer in fiber ceramic matrix systems.

Bascom, Willard D.; Lee, Ilzoo

1988-01-01

155

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

International Nuclear Information System (INIS)

The oxidative half-reaction of electron-transfer flavoprotein (ETF), electron transfer from ETF to electron-transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO), is dependent on complementary surface charges on the two proteins. ETF is the positively charged member of the redox pair. The evidence is based on the pH and ionic strength dependencies of the comproportionation of oxidized ETF and ETF hydroquinone catalyzed by ETF-QO and on the effects of chemical modification of ETF on the comproportionation reaction. Acetylation of one and five epsilon-amino groups of lysyl residues results in 3- and 13-fold increases, respectively, in the K/sub m/ of ETF-QO for ETF but no change in V/sub max/. Amidination, which maintains positive charge at modified loci, has no effect on steady-state kinetic constants. These chemical modifications have no effect on the equilibrium constant for equilibration of ETF redox states. The K/sub m/ of ETF-QO for ETF is pH dependent above pH 8.5, suggesting titration of lysyl residues. The ionic strength dependence of TN/KmETF for the reaction follows the limiting Bronsted equation. The ETF-QO-catalyzed comproportionation reaction exhibits a primary deuterium isotope effect in D2O, perhaps indicating the participation of solvent water in the electron-transfer reaction

156

Manipulating NiFe/AlO{sub x} interfacial chemistry for the spin-polarized electrons transport  

Energy Technology Data Exchange (ETDEWEB)

Through vacuum annealing, interfacial chemical composition of sputter-deposited AlO{sub x}/NiFe/AlO{sub x} can be controlled for electron transport manipulation. Chemical status change at the NiFe/AlO{sub x} interface was quantified by X-ray photoelectron spectroscopy and correlated to the structure and electron transport properties of the heterostructure. It is found that elemental Al existed in the insulting AlO{sub x} after annealing at intermediate temperature can improve the AlO{sub x}/NiFe interface and thus favor the electronic transport. Annealing at higher temperature will result in native AlO{sub x} formation and degrade transport properties due to the NiFe/AlO{sub x} interfaces deterioration caused by significant difference in thermal expansion coefficients of the two materials.

Zhao, Chong-Jun [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Sun, Li [Department of Mechanical Engineering and Texas Center for Superconductivity (TcSUH), University of Houston, Houston, Texas 77204 (United States); Ding, Lei [School of Materials and Chemical Engineering, Hainan University, Haikou 570228 (China); Li, Jian-Wei; Zhang, Jing-Yan; Cao, Yi [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China); Yu, Guang-Hua, E-mail: ghyu@mater.ustb.edu.cn [Department of Materials Physics and Chemistry, University of Science and Technology Beijing, Beijing 100083 (China)

2013-10-15

157

Path integral approach to non-relativistic electron charge transfer  

Energy Technology Data Exchange (ETDEWEB)

A path integral approach has been generalized for the non-relativistic electron charge transfer processes. The charge transfer - the capture of an electron by an ion passing another atom, or more generally the problem of rearrangement collisions - is formulated in terms of influence functionals. It has been shown that the electron charge transfer process can be treated either as an electron transition problem or as ion and atom elastic scattering in the effective potential field. The first-order Born approximation for the electron charge transfer reaction cross section has been reproduced to prove the adequacy of the path integral approach for this problem. (author)

Laskin, N. [IsoTrace Laboratory, University of Toronto, Toronto, ON (Canada)]. E-mail: nlaskin@rocketmail.com; Tomski, I. [IsoTrace Laboratory, University of Toronto, Toronto, ON (Canada)

2001-11-28

158

Interfacial wicking dynamics and its impact on critical heat flux of boiling heat transfer  

Science.gov (United States)

Morphologically driven dynamic wickability is essential for determining the hydrodynamic status of solid-liquid interface. We demonstrate that the dynamic wicking can play an integral role in supplying and propagating liquid through the interface, and govern the critical heat flux (CHF) against surface dry-out during boiling heat transfer. For the quantitative control of wicking, we manipulate the characteristic lengths of hexagonally arranged nanopillars within sub-micron range through nanosphere lithography combined with top-down metal-assisted chemical etching. Strong hemi-wicking over the manipulated interface (i.e., wicking coefficients) of 1.28 mm/s0.5 leads to 164% improvement of CHF compared to no wicking. As a theoretical guideline, our wickability-CHF model can make a perfect agreement with improved CHF, which cannot be predicted by the classic models pertaining to just wettability and roughness effects, independently.

Kim, Beom Seok; Lee, Hwanseong; Shin, Sangwoo; Choi, Geehong; Cho, Hyung Hee

2014-11-01

159

77 FR 6310 - Electronic Fund Transfers (Regulation E)  

Science.gov (United States)

...CFPB-2011-0009] RIN 3170-AA15 Electronic Fund Transfers (Regulation...Regulation E, which implements the Electronic Fund Transfer Act, and the...respect to the phrase ``normal course of business'' in the definition...the following methods: Electronic:...

2012-02-07

160

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.)

161

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

162

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

International Nuclear Information System (INIS)

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

163

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2014-05-05

164

Activation entropy of electron transfer reactions  

CERN Document Server

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

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

2005-01-01

165

Direct electron transfer based enzymatic fuel cells  

International Nuclear Information System (INIS)

In this mini-review we briefly describe some historical developments made in the field of enzymatic fuel cells (FCs), discussing important design considerations taken when constructing mediator-, cofactor-, and membrane-less biological FCs (BFCs). Since the topic is rather extensive, only BFCs utilizing direct electron transfer (DET) reactions on both the anodic and cathodic sides are considered. Moreover, the performance of mostly glucose/oxygen biodevices is analyzed and compared. We also present some unpublished results on mediator-, cofactor-, and membrane-less glucose/oxygen BFCs recently designed in our group and tested in different human physiological fluids, such as blood, plasma, saliva, and tears. Finally, further perspectives for BFC applications are highlighted.

166

Electron transfer behavior of monolayer protected nanoclusters and nanowires of silver and gold.  

Science.gov (United States)

Understanding the electron transfer behavior of nanometer sized, both metallic and semiconducting particles and wires is important due to the fundamental interest in size and shape dependent electronic properties and also because of its applications in nano-electronic devices like single electron transistors and molecular switches. Monolayer protected nanoclusters enable one simple and elegant method of synthesis of these types of metallic and semiconducting materials using interfacial chemistry as has been successfully used in several applications ranging from catalysis to molecular electronics. The success of this type of nanostructured materials is due in part to the well known protecting/stabilizing action of the ligands (also known as surface passivating/capping agents), which facilitate the synthesis and processing of these hydrophobic colloids in solution form. The present article discusses the electron transfer behavior of silver nanowires and nanoparticles with varied sizes. In particular, we have investigated the electrochemical properties of silver nanowires (diameter 70 nm, length several micrometers) and compared with the behavior of similar relatively larger sized nanoparticles (size 40 nm). A critical analysis of the redox behavior of silver nanowires and nanoparticles is presented in aqueous medium under various electrolytic conditions along with a comparison of analogous properties of smaller sized (2-7 nm) silver and gold nanoclusters. PMID:17252790

Sharma, Jadab; Vivek, J P; Vijayamohanan, Kunjukrishna P

2006-11-01

167

Plugging in or Going Wireless: Strategies for Interspecies Electron Transfer  

OpenAIRE

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 whi...

PravinMallaShrestha; Amelia-ElenaRotaru

2014-01-01

168

Electron transfer reactions of metal complexes in solution  

International Nuclear Information System (INIS)

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

169

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

Science.gov (United States)

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

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

2014-03-01

170

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

Energy Technology Data Exchange (ETDEWEB)

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

Fox, M.A.

1997-01-01

171

Influence of the electron–phonon interfacial conductance on the thermal transport at metal/dielectric interfaces  

Science.gov (United States)

Thermal boundary conductance at a metal-dielectric interface is a quantity of prime importance for heat management at the nanoscale. While the boundary conductance is usually ascribed to the coupling between metal phonons and dielectric phonons, in this work we examine the influence of a direct coupling between the metal electrons and the dielectric phonons. The effect of electron–phonon processes is generally believed to be resistive and tends to decrease the overall thermal boundary conductance as compared to the phonon–phonon conductance ?p. Here, we find that the effect of a direct electron-phonon interfacial coupling ?e is to enhance the effective thermal conductance between the metal and the dielectric. Resistive effects turn out to be important only for thin films of metals that have a low electron–phonon coupling strength. Two approaches are explored to reach these conclusions. First, we present an analytical solution of the two-temperature model to compute the effective conductance which accounts for all the relevant energy channels, as a function of ?e, ?p and the electron–phonon coupling factor G. Second, we use numerical resolution to examine the influence of ?e on two realistic cases: a gold film on silicon or silica substrates. We point out the implications for the interpretation of time-resolved thermoreflectance experiments.

Lombard, J.; Detcheverry, F.; Merabia, S.

2015-01-01

172

Transcriptomic and Genetic Analysis of Direct Interspecies Electron Transfer  

OpenAIRE

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 wa...

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

2013-01-01

173

Computer Simulation of Electron Transfer at Hematite Surfaces  

International Nuclear Information System (INIS)

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

174

Mechanism of Intermolecular Electron Transfer in Bionanostructures  

Science.gov (United States)

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

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

175

Quantum coherent contributions in biological electron transfer  

CERN Document Server

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

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

2011-01-01

176

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

Directory of Open Access Journals (Sweden)

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

Ulrich J. Krull

2011-06-01

177

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

178

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1993-02-22

179

Computational Approach to Electron Charge Transfer Reactions  

DEFF Research Database (Denmark)

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

Jónsson, Elvar Örn

2013-01-01

180

Shewanella secretes flavins that mediate extracellular electron transfer  

OpenAIRE

Bacteria able to transfer electrons to metals are key agents in biogeochemical metal cycling, subsurface bioremediation, and corrosion processes. More recently, these bacteria have gained attention as the transfer of electrons from the cell surface to conductive materials can be used in multiple applications. In this work, we adapted electrochemical techniques to probe intact biofilms of Shewanella oneidensis MR-1 and Shewanella sp. MR-4 grown by using a poised electrode as an electron acc...

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

2008-01-01

181

Electrostatic influence on energetics of electron transfer reactions.  

OpenAIRE

Electron transfer chains in biological systems must operate efficiently to satisfy metabolic energetic requirements. The component proteins in these chains are expected to exhibit characteristic structural features that facilitate electron transfer to the appropriate donor and acceptor proteins. A survey of soluble one-electron carrier proteins indicates a significant tendency for lower potential proteins to be more negatively charged than higher potential proteins. Consideration of the elect...

Rees, D. C.

1985-01-01

182

Electron Transfer Dissociation of iTRAQ Labeled Peptide Ions  

OpenAIRE

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

183

Hierarchical assembly of ultrathin hexagonal SnS2 nanosheets onto electrospun TiO2 nanofibers: enhanced photocatalytic activity based on photoinduced interfacial charge transfer.  

Science.gov (United States)

Well-designed hierarchical nanostructures with one dimensional (1D) TiO(2) nanofibers (120-350 nm in diameter and several micrometers in length) and ultrathin hexagonal SnS(2) nanosheets (40-70 nm in lateral size and 4-8 nm in thickness) were successfully synthesized by combining the electrospinning technique (for TiO(2) nanofibers) and a hydrothermal growth method (for SnS(2) nanosheets). The single-crystalline SnS(2) nanosheets with a 2D layered structure were uniformly grown onto the electrospun TiO(2) nanofibers consisted of either anatase (A) phase or anatase-rutile (AR) mixed phase TiO(2) nanoparticles. The definite heterojunction interface between SnS(2) nanosheets and TiO(2) (A or R) nanoparticles were investigated by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). Moreover, the as-prepared SnS(2)/TiO(2) hierarchical nanostructures as nanoheterojunction photocatalysts exhibited excellent UV and visible light photocatalytic activities for the degradation of organic dyes (rhodamine B and methyl orange) and phenols (4-nitrophenol), remarkably superior to the TiO(2) nanofibers and the SnS(2) nanosheets, mainly owing to the photoinduced interfacial charge transfer based on the photosynergistic effect of the SnS(2)/TiO(2) heterojunction. Significantly, the SnS(2)/TiO(2) (AR) hierarchical nanostructures as the tricomponent heterojunction system possessed stronger photocatalytic activity than the bicomponent heterojunction system of SnS(2)/TiO(2) (A) hierarchical nanostructures or TiO(2) (AR) nanofibers, which was discussed in terms of the three-way photosynergistic effect between SnS(2), TiO(2) (A) and TiO(2) (R) component in the SnS(2)/TiO(2) (AR) heterojunction resulting in the high separation efficiency of photoinduced electron-hole pairs, as evidenced by photoluminescence (PL) and surface photovoltage spectra (SPS). PMID:23202888

Zhang, Zhenyi; Shao, Changlu; Li, Xinghua; Sun, Yangyang; Zhang, Mingyi; Mu, Jingbo; Zhang, Peng; Guo, Zengcai; Liu, Yichun

2013-01-21

184

Inelastic electron scattering at low momentum transfer  

International Nuclear Information System (INIS)

Recent advances of high energy resolution (?E approx. 30 keV FWHM) inelastic electron scattering at low momentum transfer (q -1) using selected experimental data from the Darmstadt electron linear accelerator are discussed. Strong emphasis is given to a comparison of the data with theoretical nuclear model predictions. Of the low multipolarity electric transitions investigated, as examples only E1 transitions to unnatural parity states in 11B and E2 transitions of the very fragmented isoscalar quadrupole giant resonance in 208Pb are considered. In 11B the role of the Os hole in the configuration of the 1/2+, 3/2+ and 5/2+ states is quantitatively determined via an interference mechanism in the transition probability. By comparison of the high resolution data with RPA calculations the E2 EWSR in 208Pb is found to be much less exhausted than anticipated from previous medium energy resolution (e,e) and hadron scattering experiments. In the case of M1 transitions it is shown that the simplest idealized independent particle shell-model prediction breaks down badly. In 28Si, ground-state correlations influence largely the detected M1 strength and such ground-state correlations are also responsible for the occurence of a strong M1 transition to a state at Ex = 10.319 MeV in 40Ca. In 90Zr only about 10% of the theoretically expected M1 strength is he theoretically expected M1 strength is seen in (e,e) and in 140Ce and 208Pb none (detection limit 1-2 ?2K). In the case of 208Pb high resolution spectra exist now up to an excitation energy of Ex = approx. 12MeV. The continuous decrease of the M1 strength with mass number is corroborated by the behaviour of strong but very fragmented M2 transitions which are detected in 28Si, 90Zr, 140Ce and 208Pb concentrated at an excitation energy E x approx. 44A-1/3MeV. In 90Zr, the distribution of spacings and widths of the many J? = 2 states are consistent with a Wigner and Porter-Thomas distribution, respectively. (orig.) 891 KBE/orig. 892 ARA

185

Charge-Transfer State Dynamics Following Hole and Electron Transfer in Organic Photovoltaic Devices  

OpenAIRE

The formation of bound electron-hole pairs, also called charge-transfer (CT) states, in organic-based photovoltaic devices is one of the dominant loss mechanisms hindering performance. While CT state dynamics following electron transfer from donor to acceptor have been widely studied, there is not much known about the dynamics of bound CT states produced by hole transfer from the acceptor to the donor. In this letter, we compare the dynamics of CT states formed in the differ...

Bakulin, Artem A.; Dimitrov, Stoichko D.; Rao, Akshay; Chow, Philip C. Y.; Nielsen, Christian B.; Schroeder, Bob C.; Mcculloch, Iain; Bakker, Huib J.; Durrant, James R.; Friend, Richard H.

2013-01-01

186

Mechanism for electron transfer in fast ion-atomic collisions.  

Science.gov (United States)

We discuss a mechanism for electron capture in fast ion-atom collisions which has not been considered so far. Similarly as in the radiative capture, where the electron transfer occurs due to photon emission, within the mechanism under consideration the electron capture takes place due to the emission of an additional electron. This first-order capture mechanism leads to the so-called transfer ionization and has a number of interesting features; in particular, in the target frame it results in electron emission mainly into the backward semisphere. PMID:19113481

Najjari, A B Voitkiv B; Ullrich, J

2008-11-28

187

Morphology, interfacial electronic structure, and optical properties of oligothiophenes grown on ZnSe(100) by molecular beam deposition  

Science.gov (United States)

We report on the growth of two types of oligothiophenes, ? -sexithiophene and a substituted terthiophene, on c(2×2) reconstructed ZnSe(100) surfaces by molecular beam deposition. The study is aimed at a deeper understanding of the structural and electronic properties of organic/ inorganic semiconductor interfaces. The structure and morphology of the organic adlayer from submonolayer up to several monolayer coverage were characterized by atomic force microscopy. The interfacial electronic structure and the optical properties were investigated by photoemission and photoluminescence spectroscopy, respectively. The results reveal that the organic adlayer is bonded by van der Waals forces to the ZnSe(100) c(2×2) surface. The electronic structure and the optical properties of the two materials forming the interface remain unperturbed, indicating that surface passivation, which is found indispensable when using other covalent inorganic semiconductor surfaces such as GaAs as substrates for organic thin films, is not required to allow for an ordered growth of the organic adlayer on ZnSe(100) .

Blumstengel, S.; Koch, N.; Duhm, S.; Glowatzky, H.; Johnson, R. L.; Xu, C.; Yassar, A.; Rabe, J. P.; Henneberger, F.

2006-04-01

188

Stochastic mechanical approach to electron transfer in acene molecules  

Energy Technology Data Exchange (ETDEWEB)

By using stochastic mechanical simulations, we numerically investigate electron transfers in oligoacenes (anthracene, tetracene and pentacene). These {pi}-conjugated oligomers are applied to organic devices and the performance depends on the electronic transfer properties. From quantum mechanical or quantum chemical calculations, estimation of the transport properties have been so far discussed via transfer integrals. Stochastic mechanics provide the quantum motion of electrons from the wave functions. From the analysis of the quantum motion of electrons, we calculate some dynamical properties, such as mean-square displacement relating with the mobility and the electron transfer rate between two anthracenes. Our dynamical approach is efficient and practical and especially important for analysis of molecular or nanoscale devices.

Sakamoto, Shoichi; Tomiya, Mitsuyoshi

2004-10-01

189

Final Report: Vibrational Dynamics in Photoinduced Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Kenneth G. Spears

2006-04-19

190

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

191

Spin-polarized electron transfer in ferromagnet/C60 interfaces  

Science.gov (United States)

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

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

2014-09-01

192

Electronic structure and vibrational mode study of nafion membrane interfacial water interactions.  

Science.gov (United States)

The structural, energetic, and mid-infrared spectral properties of water clusters interacting with a model perfluorosulfonate (Nafion) ionomer segment have been investigated by means of quantum chemical calculations. Density functional theory calculations were conducted to model interfacial water condensed in pores and channels of Nafion and helped shedding light on the structural and vibrational properties of hydrated Nafion membranes. The computational models consisted of a sodium counterion, the Nafion ionomer, and a cluster of water molecules positioned in three different regions of the ionomer. The orientations of the water molecules in the vicinity of the ionomer were examined to understand the appearance of O-H stretching bands that deviated from the typical bulk water values as well as the appearance of multiple free O-H stretching bands. The calculations revealed insights into the structure, orientation, and energetics of Nafion and water clusters in and around the membrane interface; the results show that hydrogen atoms at the water-ionomer interface hydrogen bond to the hydrophilic sulfonate group as well as to the hydrophobic fluorinated backbone. PMID:25412259

Kabrane, Joseph; Aquino, Adelia J A

2015-03-01

193

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

194

Proton-coupled electron transfer with photoexcited metal complexes.  

Science.gov (United States)

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

Wenger, Oliver S

2013-07-16

195

77 FR 24667 - TANF Assistance and Electronic Benefit Transfer Transactions; Request for Public Comment  

Science.gov (United States)

...to prevent electronic benefit transfer transactions...gambling casinos, or other gaming establishments, and...used in any electronic benefit transfer transaction...gambling casino, or gaming establishment; or any...defines an electronic benefit transfer...

2012-04-25

196

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

197

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

198

Electron-Transfer Acceleration Investigated by Time Resolved Infrared Spectroscopy.  

Czech Academy of Sciences Publication Activity Database

Ro?. 48, ?. 3 (2015), s. 868-876. ISSN 0001-4842 Institutional support: RVO:61388955 Keywords : electron transfer * infrared spectroscopy Subject RIV: CG - Electrochemistry Impact factor: 24.348, year: 2013

Vl?ek Jr., Antonín; Kvapilová, Hana; Towrie, M.; Záliš, Stanislav

2015-01-01

199

Length-Dependence of Electron Transfer in Conjugated Molecular Wires  

Science.gov (United States)

The electron transfer (ET) properties of ?-electron conjugated molecular wires consisting of polyene chain, [>C=CVDA decreases exponentially with increase in the length of the molecular wire. However, in contrast with the rigid ?-bonded molecular wires, the decay constant, ?, for the conjugated systems exhibits three different regimes over the calculated length. This is attributed to the delocalized nature of the electrons along molecular length that facilitates retention of the electron coupling even at large separations between the donor and acceptor centers.

Karna, Shashi; Mallick, Govind; Pandey, Ravindra

2007-03-01

200

Adiabatic transfer of net electron polarization to nuclear polarization  

OpenAIRE

A new type of spin chemical experiment is suggested which utilizes adiabatic reversion of a low magnetic Bo field for an efficient transfer of net electron spin polarization, as arising from some CIDEP mechanism, to the nuclear polarization of radicals. After trapping the radicals in diamagnetic products and transferring the sample to a NMR probe, the adiabatic polarization transfer effect can be measured as induced CIDNP, as in the recently established SNP method. The optimum conditions conc...

Lukzen, Nikita N.; Steiner, Ulrich

1995-01-01

201

Initial experience with a electronic CT image transfer system.  

OpenAIRE

An electronic image transfer system for computed tomographic images links the CT scanner in Altnagelvin Hospital, Londonderry with the regional neuroradiology department in the Royal Victoria Hospital, Belfast. In the first 13 months of operation, scans of 100 patients were transferred; 49 scans were taken in acute neurosurgical emergencies, and 51 were non-acute sent for a specialist neuroradiological opinion. Potentially hazardous inter-hospital transfer was avoided in 21 cases of acute neu...

Bell, K. E.; Loughrey, C.; Morrison, C. M.

1994-01-01

202

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

203

Single-molecule electron transfer reactions in nanomaterials  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-07-26

204

Thermodynamics of electron transfer in Escherichia coli cytochrome bo3  

OpenAIRE

The proton translocation mechanism of the Escherichia coli cytochrome bo3 complex is intimately tied to the electron transfers within the enzyme. Herein we evaluate two models of proton translocation in this enzyme, a cytochrome c oxidase-type ion-pump and a Q-cycle mechanism, on the basis of the thermodynamics of electron transfer. We conclude that from a thermodynamic standpoint, a Q-cycle is the more favorable mechanism for proton translocation and is likely occ...

Schultz, Brian E.; Chan, Sunney I.

1998-01-01

205

Single Molecule Electron Transfer Dynamics in Complex Environments  

International Nuclear Information System (INIS)

We propose a new theoretical approach to study the kinetics of the electron transfer (ET) under the dynamical influence of the complex environments with the first passage times (FPT) of the reaction events. By measuring the mean and high order moments of FPT and their ratios, the full kinetics of ET, especially the dynamical transitions across different temperature zones, is revealed. The potential applications of the current results to single molecule electron transfer are discussed

206

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.

207

Improved heterogeneous electron transfer kinetics of fluorinated graphene derivatives  

Science.gov (United States)

Though graphitic carbons are commercially available for various electrochemical processes, their performance is limited in terms of various electrochemical activities. Recent experiments on layered carbon materials, such as graphene, demonstrated an augmented performance of these systems in all electrochemical activities due to their unique electronic properties, enhanced surface area, structure and chemical stabilities. Moreover, flexibility in controlling electronic, as well as electrochemical activities by heteroatom doping brings further leverage in their practical use. Here, we study the electron transfer kinetics of fluorinated graphene derivatives, known as fluorinated graphene oxide (FGO) and its reduced form, RFGO. Enhanced electron transfer kinetics (heterogeneous electron transfer (HET)) is observed from these fluorinated systems in comparison to their undoped systems such as graphene oxide (GO) and reduced GO. A detailed study has been conducted using standard redox probes and biomolecules revealing the enhanced electro-catalytic activities of FGO and RFGO, and electron transfer rates are simulated theoretically. This study reveals that fluorine not only induces defects in graphitic lattice leading to an enhanced HET process but also can modify the electronic structure of graphene surface.Though graphitic carbons are commercially available for various electrochemical processes, their performance is limited in terms of various electrochemical activities. Recent experiments on layered carbon materials, such as graphene, demonstrated an augmented performance of these systems in all electrochemical activities due to their unique electronic properties, enhanced surface area, structure and chemical stabilities. Moreover, flexibility in controlling electronic, as well as electrochemical activities by heteroatom doping brings further leverage in their practical use. Here, we study the electron transfer kinetics of fluorinated graphene derivatives, known as fluorinated graphene oxide (FGO) and its reduced form, RFGO. Enhanced electron transfer kinetics (heterogeneous electron transfer (HET)) is observed from these fluorinated systems in comparison to their undoped systems such as graphene oxide (GO) and reduced GO. A detailed study has been conducted using standard redox probes and biomolecules revealing the enhanced electro-catalytic activities of FGO and RFGO, and electron transfer rates are simulated theoretically. This study reveals that fluorine not only induces defects in graphitic lattice leading to an enhanced HET process but also can modify the electronic structure of graphene surface. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr02563f

Boopathi, Sidhureddy; Narayanan, Tharangattu N.; Senthil Kumar, Shanmugam

2014-08-01

208

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

Science.gov (United States)

The photo-induced electron transfer between Coumarin dyes and aromatic amines has been investigated using steady state and time-resolved fluorescence quenching studies. We have observed a Marcus type inversion in the electron transfer rate in correlation of quenching constant to the free energy change occurred during reaction. To justify the "inverted region" obtained in the correlation of quenching constant versus free energy curve, we have performed anisotropy measurement and estimated the several diffusional parameters. The translational diffusion coefficients exhibit a similar picture like electron transfer rate constant when it is plotted against free energy. Thus we argued that the diffusion has played an important role in the electron transfer kinetics.

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

2006-03-01

209

Electron Transfer in Ferritin as Probed by Muon Spin Relaxation  

Science.gov (United States)

Electron-transfer processes play a vital role in many biological phenomena, from energy storage to photosynthesis. Positive muons allow such transfer processes in macromolecules, such as proteins, to be probed on a microscopic level. We have used this probe via muon spin relaxation (?SR) to investigate electron-transfer processes in ferritin; the normal iron storage protein. Data collected at finite fields is well described using the Risch-Kehr model at all measured temperatures with inter and intra-chain diffusion rates of 109 and 1011 rad s-1 being determined respectively. The results are compared to similar measurements on other proteins.

Telling, Mark T. F.; Kilcoyne, Susan H.

210

Electron transfer in pendant-group and molecularly doped polymers  

Science.gov (United States)

Utilizing the molecular-ion model previously constructed to describe photoemission and ultraviolet absorption in pendant-group polymers, we derive an expression for the probability of electron transfer between a molecular ion and a neutral molecular species embedded in a frequency-dependent dielectric medium described by the (nonlocal) longitudinal dielectric response function ?(q-->,?). The medium is taken to exhibit three branches of its longitudinal polarization excitation spectrum defined by ?(q-->,?(q-->))=0: a low-frequency branch corresponding to intermolecular motions, an infrared branch corresponding to molecular vibrational modes, and a high-frequency branch corresponding to valence-electron excitations. In addition, the linear coupling of the electron to the intramolecular modes of the initial and final molecular ions is incorporated into the model. The electron-transfer probability is evaluated as a function of the spacing, R, between the molecular-ion sites and the energy difference between the intitial and final molecular-ion states. Utilizing parameters in ?(q-->,?) typical of pendant-group polymers (e.g., polystyrene, polyvinylpyridine) or the matrices utilized in molecularly doped polymers films (e.g., polycarbonates), we find that the electron-transfer process is activated and that the low-frequency dielectric relaxations characteristic of these polymers create this activation. Explicit expressions for the activation energies are derived and evaluated numerically for poly(2-vinylypyridine): a material for which a model of ?(q-->,?) is available in the literature. The valence-electron excitations do not influence the electron-transfer activation energies, but both the intramolecular and longitudinal-polarization vibrational modes increase these activation energies above the values predicted using the low-frequency relaxations alone. The energies, ??n, of many of these vibrational modes are, however, larger than thermal energies, kT. Consequently, the predicted electron-transfer activation energies are smaller than those given by traditional semiclassical models of electron transfer. Moreover, these activation energies also depend explicitly on the spacing, R, between the two sites. This R dependence is evaluated for both classical and quantum-mechanical models of the change densities on the molecular ions. Our analysis predicts, therefore, the complete spacing and temperature dependence of the electron-transfer probabilities as functions of the intramolecular molecular-ion vibrational frequencies and electron-vibration coupling constants, and of the frequency and spatial dependence of the dielectric response of the medium in which these ions are embedded. This prediction permits the identification of scaling laws relating both the activation energies and electron-transfer prefactors to molecular and dielectric observables: an identification which provides valuable guidance in the molecular design of efficient electronic transport media.

Duke, C. B.; Meyer, R. J.

1981-03-01

211

Reaction of radicals with benzoquinone--addition or electron transfer?  

Energy Technology Data Exchange (ETDEWEB)

Pulse radiolysis studies are reported on reactions of radicals of different electronic structure (chloroalkyl-, {alpha}-, {beta}-hydroxyalkyl-) with benzoquinone and its methyl-substituted derivatives in non-polar surroundings. Hence, radical addition onto the quinones resulted in substituted semiquinone radicals, whereas electron transfer reduction generated semiquinone radical anions, which could be clearly identified in cyclohexane solution.

Maroz, A.; Brede, O. E-mail: brede@mpgag.uni-leipzig.de

2003-06-01

212

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.

213

Heat transfer between adsorbate and laser-heated hot electrons  

Energy Technology Data Exchange (ETDEWEB)

Strong short laser pulses can give rise to a strong increase in the electronic temperature at metal surfaces. Energy transfer from the hot electrons to adsorbed molecules may result in adsorbate reactions, e.g. desorption or diffusion. We point out the limitations of an often used equation to describe the heat transfer process in terms of a friction coupling. We propose a simple theory for the energy transfer between the adsorbate and hot electrons using a newly introduced heat transfer coefficient, which depends on the adsorbate temperature. We calculate the transient adsorbate temperature and the reaction yield for a Morse potential as a function of the laser fluency. The results are compared to those obtained using a conventional heat transfer equation with temperature-independent friction. It is found that our equation of energy (heat) transfer gives a significantly lower adsorbate peak temperature, which results in a large modification of the reaction yield. We also consider the heat transfer between different vibrational modes excited by hot electrons. This mode coupling provides indirect heating of the vibrational temperature in addition to the direct heating by hot electrons. The formula of heat transfer through linear mode-mode coupling of two harmonic oscillators is applied to the recent time-resolved study of carbon monoxide and atomic oxygen hopping on an ultrafast laser-heated Pt(111) surface. It is found that the maximum temperature of the frustrated translation mode can reach high temperatures for hopping, even when direct friction coupling to the hot electrons is not strong enough.

Ueba, H [Graduate School of Science and Engineering, University of Toyama, Toyama (Japan); Persson, B N J [IFF, FZ-Juelich, Postfach 1913, 52425 Juelich (Germany)], E-mail: ueba@eng.u-toyama.ac.jp

2008-06-04

214

[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

215

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-12-03

216

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

Science.gov (United States)

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

Cheng, Hsin-Ming; Hsieh, Wen-Feng

2010-12-01

217

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

International Nuclear Information System (INIS)

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

218

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

219

Optical Spectroscopy of the Bulk and Interfacial Hydrated Electron from Ab Initio Calculations.  

Czech Academy of Sciences Publication Activity Database

Ro?. 118, ?. 35 (2014), s. 7507-7515. ISSN 1089-5639 R&D Projects: GA ?R GBP208/12/G016 Institutional support: RVO:61388963 Keywords : hydrated electron * optical spectrum * ab initio molecular dynamics Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.775, year: 2013

Uhlig, Frank; Herbert, J. M.; Coons, M. P.; Jungwirth, Pavel

2014-01-01

220

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

221

Electronic energy transfer on a vibronically coupled quantum aggregate  

Science.gov (United States)

We examine the transfer of electronic excitation (an exciton) along a chain of electronically coupled monomers possessing internal vibronic structure and which also interact with degrees of freedom of the surrounding environment. Using a combination of analytical and numerical methods, we calculate the time evolution operator or time-dependent Green's function of the system and thereby isolate the physical parameters influencing the electronic excitation transport. Quite generally, we show that coupling to vibrations slows down and inhibits migration of electronic excitation due to dephasing effects on the coherent transfer present without vibrations. In particular, coupling to a continuous spectrum of environment states leads to a complete halting of transfer, i.e., a trapping of the exciton.

Roden, Jan; Schulz, Georg; Eisfeld, Alexander; Briggs, John

2009-07-01

222

Effect of proton transfer on the electronic coupling in DNA  

Science.gov (United States)

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

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

2006-06-01

223

Efficient light-to-current conversion by organic-inorganic interfacial charge-transfer transitions in TiO2 chemically adsorbed with 2-anthroic acid  

Science.gov (United States)

Organic-inorganic interfacial charge-transfer (ICT) transitions provide the concepts that organic-inorganic interfaces serve as a field for light absorption and charge separation directly occurs without energy loss. Here, we report efficient light-to-current conversion due to the ICT transitions in TiO2 chemically adsorbed with 2-anthroic acid. The incident photon-to-current conversion efficiency (IPCE) surpasses 85%, showing the significant improvement as compared to the reported results. Density functional analysis shows that the ICT absorption arises from strong d?-?* interactions at the inorganic-organic interface. In addition, we examined the density of states (DOS) of unoccupied surface states on TiO2 from the absorption and IPCE spectra.

Fujisawa, Jun-ichi; Nagata, Morio

2015-01-01

224

Theory of reversible electron transfer reactions in a condensed phase.  

Science.gov (United States)

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

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

2010-07-01

225

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

226

Plugging in or going wireless: strategies for interspecies electron transfer  

Science.gov (United States)

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

Shrestha, Pravin Malla; Rotaru, Amelia-Elena

2014-01-01

227

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

228

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

Directory of Open Access Journals (Sweden)

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

Itamar Willner

2006-04-01

229

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

Science.gov (United States)

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

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

2014-10-01

230

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

Science.gov (United States)

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

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

2014-10-01

231

Effect of superheat, mold, and casting materials on the metal/mold interfacial heat transfer during solidification in graphite-lined permanent molds  

Science.gov (United States)

Heat transfer during the solidification of an Al-Cu-Si alloy (LM4) and commercial pure tin in single steel, graphite, and graphite-lined metallic (composite) molds was investigated. Experiments were carried out at three different superheats. In the case of composite molds, the effect of the thickness of the graphite lining and the outer wall on heat transfer was studied. Temperatures at known locations inside the mold and casting were used to solve the Fourier heat conduction equation inversely to yield the casting/mold interfacial heat flux transients. Increased melt superheats and higher thermal conductivity of the mold material led to an increase in the peak heat flux at the metal/mold interface. Factorial experiments indicated that the mold material had a significant effect on the peak heat flux at the 5% level of significance. The ratio of graphite lining to outer steel wall and superheat had a significant effect on the peak heat flux in significance range varying between 5 and 25%. A heat flux model was proposed to estimate the maximum heat flux transients at different superheat levels of 25 to 75 °C for any metal/mold combinations having a thermal diffusivity ratio (? R) varying between 0.25 and 6.96. The heat flow models could be used to estimate interfacial heat flux transients from the thermophysical properties of the mold and cast materials and the melt superheat. Metallographic analysis indicated finer microstructures for castings poured at increased melt superheats and cast in high-thermal diffusivity molds.

Prabhu, K. Narayan; Suresha, K. M.

2004-10-01

232

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

233

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

234

Vectorial electron transfer in spatially ordered arrays  

Energy Technology Data Exchange (ETDEWEB)

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

Fox, M.A.

1992-01-01

235

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

Science.gov (United States)

...CFPB-2012-0050] RIN 3170-AA33 Electronic Fund Transfers (Regulation...Regulation E, which implements the Electronic Fund Transfer Act (EFTA...remittance transfers in the normal course of business, and...

2013-01-29

236

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

Energy Technology Data Exchange (ETDEWEB)

The focus of the work described in this report is on single electron transfer reactions of excited states which culminate in the formation of stable or metastable even electron species. For the most part the studies have involved even electron organic substrates which are thus converted photochemically to odd electron species and then at some stage reconvert to even electron products. These reactions generally fall into two rather different categories. In one set of studies we have examined reactions in which the metastable reagents generated by single electron transfer quenching of an excited state undergo novel fragmentation reactions, chiefly involving C-C bond cleavage. These reactions often culminate in novel and potentially useful chemical reactions and frequently have the potential for leading to new chemical products otherwise unaffordable by conventional reaction paths. In a rather different investigation we have also studied reactions in which single electron transfer quenching of an excited state is followed by subsequent reactions which lead reversibly to metastable two electron products which, often stable in themselves, can nonetheless be reacted with each other or with other reagents to regenerate the starting materials with release of energy. 66 refs., 9 figs., 1 tab.

Whitten, D.G.

1991-10-01

237

Direct interspecies electron transfer between Geobacter metallireducens and Methanosarcina barkeri.  

Science.gov (United States)

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

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

2014-08-01

238

Light-driven microbial dissimilatory electron transfer to hematite.  

Science.gov (United States)

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

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

2014-11-14

239

Photoinduced interfacial electron transfer and lateral charge transport in molecular donor–acceptor photovoltaic systems  

OpenAIRE

Nanostructured liquid|solid and solid|solid bulk heterojunctions designed for the conversion of solar energy offer ideal models for the investigation of light-induced ET dynamics at surfaces. Despite significant study of processes leading to charge generation in third-generation solar cells, a conclusive picture of the photophysics of these photovoltaic converters is still missing. More specifically searched is the link between the molecular structure of the interface and the kinetics of surf...

Punzi, Angela; Brauer, Jan C.; Marchioro, Arianna; Ghadiri, Elham; Jonghe, Jelissa; Moser, Jacques-e

2011-01-01

240

Heavy particle interference and diffraction in fast electron transfer collisions  

OpenAIRE

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

Gudmundsson, Magnus

2011-01-01

241

Electron transfer in proteins: theory, applications and future perspectives.  

Science.gov (United States)

The study of electron transfer (ET) by means of computational techniques has experienced a great development in the last few decades. In particular, understanding the atomic details of its mechanism in complex biological systems is currently possible with a large range of different in silico modelling tools. We review here some theories and representative major contributions to this development. We also underline some of our group's main inputs, focusing on long range and protein-protein electron transfer, and analyse future perspectives. At the end of the article, we emphasize the importance of the basic electron transfer knowledge in the frame of medical and bioengineering applications: mitochondrial therapeutic targets, bioengineering for clean energy, and biosensors. PMID:23936901

Saen-Oon, Suwipa; Lucas, Maria Fatima; Guallar, Victor

2013-10-01

242

Electron transfer in ion interactions with chlorine covered silver surfaces  

International Nuclear Information System (INIS)

The effect of chemical environment on the neutralisation of ions with adsorbate covered surfaces was investigated on the example of H+ and rare gas ion scattering on chlorine covered Ag. Changes in coverage from the submonolayer chemisorption to chloride nucleation stage, strongly affect electron transfer. In the case of H+, Ne+ and Ar+ these changes induce an ''unusual'' non-linear, oscillating, coverage dependence of electron transfer probabilities, due to modifications in the surface electronic structure. In case of the more highly bound He, we assign the observed changes to modifications in quasi-resonant charge transfer rates involving the Cl 3s core level, because of the core level shifts induced by changes in chemical environment

243

Electron transfer, ionization, and excitation atomic collisions  

International Nuclear Information System (INIS)

Basic atomic-collision processes at intermediate and high energies are being studied theoretically at Penn State by Alston and Winter. In the high velocity regime, single-electron capture is treated using a high order multiple-scattering approach; extensive comparison with experiment and analysis of mechanisms have been made. Fitting the calculated amplitude with a simple analytic form, the asymptotic velocity dependence of the cross section is obtained. The effect on the capture amplitude of altering the inner part of the internuclear potential has also been explored. In the intermediate velocity regime, earlier work on collisions between protons and hydrogenic-ion targets using a coupled-state approach is being extended to the two-electron helium target. 29 refs

244

Monitoring sequential electron transfer with EPR  

International Nuclear Information System (INIS)

A completely general model which treats electron spin polarization (ESP) found in a system in which radical pairs with different magnetic interactions are formed sequentially has been described. This treatment has been applied specifically to the ESP found in the bacterial reaction center. Test cases show clearly how parameters such as structure, lifetime, and magnetic interactions within the successive radical pairs affect the ESP, and demonstrate that previous treatments of this problem have been incomplete. The photosynthetic bacterial reaction center protein is an ideal system for testing the general model of ESP. The radical pair which exhibits ESP, P870+Q- (P870+ is the oxidized, primary electron donor, a bacteriochlorophyll special pair and Q- is the reduced, primary quinone acceptor) is formed via sequential electron transport through the intermediary radical pair P870+I- (I- is the reduced, intermediary electron acceptor, a bacteriopheophytin). In addition, it is possible to experimentally vary most of the important parameters, such as the lifetime of the intermediary radical pair and the magnetic interactions in each pair. It has been shown how selective isotopic substitution (1H or 2H) on P870, I and Q affects the ESP of the EPR spectrum of P870+Q-, observed at two different microwave/sup>, observed at two different microwave frequencies, in Fe2+-depleted bacterial reaction centers of Rhodobacter sphaeroides R26. Thus, the relative magnitudes of the magnetic properties (nuclear hyperfine and g-factor differences) which influence ESP development were varied. The results support the general model of ESP in that they suggest that the P870+Q- radical pair interactions are the dominant source of ESP production in 2H bacterial reaction centers

245

Electron transfer statistics and thermal fluctuations in molecular junctions.  

Science.gov (United States)

We derive analytical expressions for probability distribution function (PDF) for electron transport in a simple model of quantum junction in presence of thermal fluctuations. Our approach is based on the large deviation theory combined with the generating function method. For large number of electrons transferred, the PDF is found to decay exponentially in the tails with different rates due to applied bias. This asymmetry in the PDF is related to the fluctuation theorem. Statistics of fluctuations are analyzed in terms of the Fano factor. Thermal fluctuations play a quantitative role in determining the statistics of electron transfer; they tend to suppress the average current while enhancing the fluctuations in particle transfer. This gives rise to both bunching and antibunching phenomena as determined by the Fano factor. The thermal fluctuations and shot noise compete with each other and determine the net (effective) statistics of particle transfer. Exact analytical expression is obtained for delay time distribution. The optimal values of the delay time between successive electron transfers can be lowered below the corresponding shot noise values by tuning the thermal effects. PMID:25725711

Goswami, Himangshu Prabal; Harbola, Upendra

2015-02-28

246

Dynamics of combined electron- and proton transfer at metal electrodes  

International Nuclear Information System (INIS)

A model for combined electrochemical electron- and proton transfer is proposed, which is based on a second-quantized model Hamiltonian. It allows the calculation of potential energy surfaces for the reactions, which typically show four minima corresponding to the four system states. For the case of adiabatic transitions, reaction rates are obtained from stochastic dynamics simulations. Non-adiabatic proton transfer is examined in greater detail, and the path of the transferring proton is followed explicitly. In addition, the dependence of the reaction rate on the solvent friction and on the characteristics of the proton potential is investigated

247

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

248

Electron Transfer Dissociation Mass Spectrometry of Hemoglobin on Clinical Samples  

Science.gov (United States)

A mass spectrometry-based assay combining the specificity of selected reaction monitoring and the protein ion activation capabilities of electron transfer dissociation was developed and employed for the rapid identification of hemoglobin variants from whole blood without previous proteolytic cleavage. The analysis was performed in a robust ion trap mass spectrometer operating at nominal mass accuracy and resolution. Subtle differences in globin sequences, resulting with mass shifts of about one Da, can be unambiguously identified. These results suggest that mass spectrometry analysis of entire proteins using electron transfer dissociation can be employed on clinical samples in a workflow compatible with diagnostic applications.

Coelho Graça, Didia; Lescuyer, Pierre; Clerici, Lorella; Tsybin, Yury O.; Hartmer, Ralf; Meyer, Markus; Samii, Kaveh; Hochstrasser, Denis F.; Scherl, Alexander

2012-10-01

249

High-pressure effects on intramolecular electron transfer compounds  

CERN Document Server

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

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

2002-01-01

250

Electronic and interfacial behavior of gemini metallosurfactants with copper(II)/pseudohalide cascade cores.  

Science.gov (United States)

In this paper we discuss the newly synthesized binuclear species [Cu2(L(PY18))2(?1,1-N3)2(N3)2] (1) and [Cu2(L(PY18))2(?1,3-SCN)2(NCS)2] (2), as obtained from the monometallic precursor [Cu(L(PY18))Br2]. These gemini metallosurfactants incorporate metal/anion cascade cores and are investigated by experimental and theoretical methods. Diagnostic IR stretches support the presence of ?1,1-bridged (end-on, 2075 cm(-1)) azide groups in 1 and ?1,3-bridged (end-to-end, 2117 cm(-1)) thiocyanate groups in 2. Anion-to-copper LMCT electronic processes at 390 and 440 nm for 1 and at 415 nm for 2 reinforce the nature of the metal/anion cascade cores. Both species are redox-active, magnetically uncoupled due to poor orbital overlap, and robust in the presence of strongly coordinating solvents. At the air-water interface, 1 and 2 yield Langmuir films with high collapse pressures of ca. 60 mN m(-1). Domain formation is considerably less extensive than that observed for the related monometallic precursor and the average molecular areas are in good agreement with their modeled molecular size. The resulting Langmuir-Blodgett films are isolated on silica substrates and investigated using IR-reflectance/absorbance spectroscopy. PMID:23877838

Verani, Cláudio N; Shanmugam, Rama; Xavier, Fernando R; Allard, Marco M; Kpogo, Kenneth Kwame

2013-11-21

251

Photonic modulation of electron transfer with switchable phase inversion.  

Science.gov (United States)

Photochromes may be reversibly photoisomerized between two metastable states and their properties can influence, and be influenced by, other chromophores in the same molecule through energy or electron transfer. In the photochemically active molecular tetrad described here, a porphyrin has been covalently linked to a fullerene electron acceptor, a quinoline-derived dihydroindolizine photochrome, and a dithienylethene photochrome. The porphyrin first excited singlet state undergoes photoinduced electron transfer to the fullerene to generate a charge-separated state. The quantum yield of charge separation is modulated by the two photochromes: one isomer of each quenches the porphyrin excited state, reducing the quantum yield of electron transfer to near zero. Interestingly, when the molecule is illuminated with white light, the quantum yield decreases as the white light intensity is increased, generating an out-of-phase response of the quantum yield to white light. However, when the same experiment is performed in the presence of additional, steady-state UV illumination, a phase inversion occurs. The quantum yield of electron transfer now increases with increasing white light intensity. Such effects illustrate emergent complexity in a relatively simple system and could find applications in molecular logic, photochemical labeling and drug delivery, and photoprotection for artificial photosynthetic molecules. The photochemistry leading to this behavior is discussed. PMID:23259536

Frey, Julien; Kodis, Gerdenis; Straight, Stephen D; Moore, Thomas A; Moore, Ana L; Gust, Devens

2013-01-24

252

Long-distance photoinitiated electron transfer through polyene molecular wires  

International Nuclear Information System (INIS)

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

253

Role of the electronic properties of azurin active site in the electron-transfer process  

Science.gov (United States)

Electron transfer proteins, such as azurin (a blue copper protein), are promising candidates for the implementation of biomolecular nanoelectronic devices. To understand the details of electron transfer in redox active azurin molecules, we performed plane-wave pseudo-potential density functional theory (DFT) calculations of the protein active site in the two possible oxidation states Cu(I) and Cu(II). The ab initio results are used to discuss how the electronic spectrum and wavefunctions may mediate the shuttling of electrons through the copper ion. We find that the Cu-ligand hybridization is very similar in the two charge states of the metal center, but the energy spectrum changes substantially. This result might indicate important effects of electronic correlations in the redox activity and consequent electron transfer through the Cu site.

Corni, Stefano; de Rienzo, Francesca; di Felice, Rosa; Molinari, Elisa

254

Solvent structure and hydrodynamic effects in photoinduced electron transfer  

International Nuclear Information System (INIS)

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

255

Quality assurance and data collection -- Electronic Data Transfer  

International Nuclear Information System (INIS)

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

256

Multi-electron transfer to and from organic molecules  

OpenAIRE

Herein, the influence of protonation and adsorption upon the redox and electrocatalysis of quinone species - specifically anthraquinone derivatives – is investigated.Through the comparison of the measured rate constants of one-electron reductions of a family of quinones in acetonitrile at both graphite and gold electrodes, it was confirmed that the redox potential indirectly influences the rate of electron transfer in a manner consistent with the potential-dependence of the density of...

Batchelor-mcauley, Christopher; Compton, Richard Guy

2012-01-01

257

Resonant optical electron transfer in one-dimensional multiwell structures  

OpenAIRE

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

258

Light-Induced Dynamics in Photosystem I Electron Transfer  

OpenAIRE

Protein dynamics are likely to play important, regulatory roles in many aspects of photosynthetic electron transfer, but a detailed description of these coupled protein conformational changes has been unavailable. In oxygenic photosynthesis, photosystem I catalyzes the light-driven oxidation of plastocyanin or cytochrome c and the reduction of ferredoxin. A chlorophyll (chl) a/a? heterodimer, P700, is the secondary electron donor, and the two P700 chl, are designated PA and PB. We used spec...

Bender, Shana L.; Barry, Bridgette A.

2008-01-01

259

Inelastic electron photon scattering at moderate four momentum transfers  

International Nuclear Information System (INIS)

We present new high statistics data on hadron production in photon photon reactions. The data are analyzed in terms of an electron photon scattering formalism. The dependence of the total cross section on Q2, the four momentum transfer squared of the scattered electron, and on the mass W of the hadronic system is investigated. The data are compared to predictions from Vector Dominance and the quark model. (orig.)

260

Solvation dynamics and solvent-controlled electron transfer  

International Nuclear Information System (INIS)

This paper discusses traditional descriptions of outer sphere electron transfer (ET) in polar solvents which rest on the implicit assumption that either the microscopic electronic process, rather than the dielectric relaxation, constitutes the rate determining step, or the solvation occurs fast enough, so that the orientational part of solvent polarization is in equilibrium with the charge distribution at any time instant. Solvation kinetics are considered

261

Carboxylate Shifts Steer Interquinone Electron Transfer in Photosynthesis*  

OpenAIRE

Understanding the mechanisms of electron transfer (ET) in photosynthetic reaction centers (RCs) may inspire novel catalysts for sunlight-driven fuel production. The electron exit pathway of type II RCs comprises two quinone molecules working in series and in between a non-heme iron atom with a carboxyl ligand (bicarbonate in photosystem II (PSII), glutamate in bacterial RCs). For decades, the functional role of the iron has remained enigmatic. We tracked the iron site using microsecond-resolu...

Chernev, Petko; Zaharieva, Ivelina; Dau, Holger; Haumann, Michael

2010-01-01

262

Accumulative electron transfer: multiple charge separation in artificial photosynthesis.  

Science.gov (United States)

To achieve artificial photosynthesis it is necessary to couple the single-electron event of photoinduced charge separation with the multi-electron reactions of fuel formation and water splitting. Therefore, several rounds of light-induced charge separation are required to accumulate enough redox equivalents at the catalytic sites for the target chemistry to occur, without any sacrificial donors or acceptors other than the catalytic substrates. Herein, we discuss the challenges of such accumulative electron transfer in molecular systems. We present a series of closely related systems base on a Ru(II)-polypyridine photosensitizer with appended triaryl-amine or oligo-triaryl-amine donors, linked to nanoporous TiO2 as the acceptor. One of the systems, based on dye 4, shows efficient accumulative electron transfer in high overall yield resulting in the formation of a two-electron charge-separated state upon successive excitation by two photons. In contrast, the other systems do not show accumulative electron transfer because of different competing reactions. This illustrates the difficulties in designing successful systems for this still largely unexplored type of reaction scheme. PMID:22470977

Karlsson, Susanne; Boixel, Julien; Pellegrin, Yann; Blart, Errol; Becker, Hans-Christian; Odobel, Fabrice; Hammarström, Leif

2012-01-01

263

Electron transfer between exogenous electron donors and reaction center of photosystem 2.  

Science.gov (United States)

Transfer of electrons between artificial electron donors diphenylcarbazide (DPC) and hydroxylamine (NH2OH) and reaction center of manganese-depleted photosystem 2 (PS2) complexes was studied using the direct electrometrical method. For the first time it was shown that reduction of redox-active amino acid tyrosine Y(Z)(.) by DPC is coupled with generation of transmembrane electric potential difference (DeltaPsi). The amplitude of this phase comprised ~17% of that of the DeltaPsi phase due to electron transfer between Y(Z) and the primary quinone acceptor Q(A). This phase is associated with vectorial intraprotein electron transfer between the DPC binding site on the protein-water interface and the tyrosine Y(Z)(.). The slowing of DeltaPsi decay in the presence of NH2OH indicates effective electron transfer between the artificial electron donor and reaction center of PS2. It is suggested that NH2OH is able to diffuse through channels with diameter of 2.0-3.0 A visible in PS2 structure and leading from the protein-water interface to the Mn(4)Ca cluster binding site with the concomitant electron donation to Y(Z)(.). Because the dielectrically-weighted distance between the NH2OH binding site and Y(Z)(.) is not determined, the transfer of electrons from NH2OH to Y(Z)(.) could be either electrically silent or contribute negligibly to the observed electrogenicity in comparison with hydrophobic donors. PMID:20632936

Mamedov, M D; Kurashov, V N; Petrova, I O; Zaspa, A A; Semenov, A Yu

2010-05-01

264

Electron Correlation and Charge Transfer Instability in Bilayered Two Dimensional Electron Gas  

OpenAIRE

We prove that the predicted charge transfer state in symmetric bilayers of two dimensional electron gases is always unstable at zero bias voltage, due to interlayer correlation and/or tunneling. This is most easily seen by resorting to a pseudospin formalism and considering coherent states obtained from the charge transfer state through rotations of the pseudospins. Evidently, the charge transfer state is stabilized by a sufficiently strong gate voltage, as found in recent e...

Conti, Sergio; Senatore, Gaetano

1996-01-01

265

Electronic excitation energy transfer between quasi-zero-dimensional systems.  

Czech Academy of Sciences Publication Activity Database

Ostrava : Tanger, 2013. ISBN 978-80-87294-44-4. [International Conference NANOCON 2013 /5./. Brno (CZ), 16.10.2013-18.10.2013] R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism

Král, Karel; Menšík, Miroslav

266

Cluster transfer matrix method for the single electron box  

OpenAIRE

With the newly developed cluster transfer matrix method, we calculate the average electron number n vs nx (the polarization charge) for varying junction conductance and its first derivative at nx=0 for finite temperatures, and demonstrate that the new method is as powerful as the Monte Carlo and renormalization group methods.

Chung, S. G.

1999-01-01

267

CORRELATING ELECTRONIC AND VIBRATIONAL MOTIONS IN CHARGE TRANSFER SYSTEMS  

Energy Technology Data Exchange (ETDEWEB)

The goal of this research program was to measure coupled electronic and nuclear motions during photoinduced charge transfer processes in transition metal complexes by developing and using novel femtosecond spectroscopies. The scientific highlights and the resulting scientific publications from the DOE supported work are outlined in the technical report.

Khalil, Munira

2014-06-27

268

Heterogeneous electron transfer of pesticides. Current trends and applications.  

Czech Academy of Sciences Publication Activity Database

Kerala : Transworld Research Network, 2008 - (Colombini, M.; Tassi, L.), s. 43-76 ISBN 978-81-7895-343-4 R&D Projects: GA AV ?R IAA400400505; GA MŠk LC510; GA MŠk OC 140 Institutional research plan: CEZ:AV0Z40400503 Keywords : heterogeneous electron transfer * pesticides * redox reactions Subject RIV: CF - Physical ; Theoretical Chemistry

Sokolová, Romana; Hromadová, Magdaléna; Pospíšil, Lubomír

269

Ion and Electron Transfer Reactions at Metal-Solution Interfaces  

Science.gov (United States)

An extension of the Anderson-Newns model is used as a unifying framework for both ion and electron transfer reactions on metal electrodes. The model allows the construction of effective free-energy surfaces as functions of a generalized solvent coordinate and of the reactant's separation from the surface. For electron transfer reactions the reaction coordinate is mainly in the direction of the solvent coordinate; for ion transfer the partial loss of the solvation sheath and the accompanying solvent displacement is the rate-determining step, and the reaction coordinate is mainly determined by the separation from the metal surface. Explicit results are presented for the adsorption of an iodide ion on Pt(100), for the deposition of Zn^2+ on Hg, and for the Fe^2+/Fe^3+ reaction. The reaction rates can be calculated from these surfaces with the aid of Kramers theory.

Schmickler, Wolfgang

1997-03-01

270

Shewanella secretes flavins that mediate extracellular electron transfer.  

Science.gov (United States)

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

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

2008-03-11

271

Microstructure, phase transition, and interfacial chemistry of Gd2O3/Si(111) grown by electron-beam physical vapor deposition  

International Nuclear Information System (INIS)

The effects of growth temperature, film thickness, and oxygen flux on the microstructure, phase transition, and interfacial chemistry of gadolinium oxide (Gd2O3) films grown on Si(111) substrates by electron-beam physical vapor deposition were investigated using a combination of transmission electron microscopy (TEM), electron diffraction, scanning TEM, x-ray energy dispersive spectrometry, and electron energy loss spectrometry. The authors find that a low growth temperature (250 °C) and a high oxygen flux (200 sccm) led to a small grain size and a high porosity of the Gd2O3 film. Lowering the oxygen flux to 50 sccm led to reduced film porosity, presumably due to the increased diffusion length of the Gd atoms on the surface. Increasing the growth temperature to 650 °C resulted in a film with large columnar grains and elongated pores at the grain boundaries. Thin films grown at 250 °C consisted of cubic Gd2O3, but thermodynamically less stable monoclinic phase formed as the film thickness increased. Lowering the oxygen flux apparently further promoted the formation of the monoclinic phase. Furthermore, monoclinic phase dominated in the films grown at 650 °C. Such phase transitions may be related to the stress evolution of the films at different temperatures, thicknesses, and oxygen fluxes. Enhanced Gd2O3/Si interfacial reaction was observed as the growth temperature, film thicknas the growth temperature, film thickness, and oxygen flux increased. Moreover, oxygen was found to play a crucial role in the Gd2O3/Si interfacial reaction and the formation of Gd-Si-O interface layers, which proceeded by the reaction of excess oxygen with Si followed by the intermixing of SiOx and Gd2O3.

272

Interfacial energies and surface-tension forces involved in the preparation of thin, flat crystals of biological macromolecules for high-resolution electron microscopy.  

Science.gov (United States)

It is generally agreed that surface-tension forces and the direct interaction between the specimen and either the air-water interface or the water-substrate interface can influence significantly the preparation of biological materials for electron microscopy. Even so, there is relatively little systematic information available that would make it possible to control surface-tension forces and interfacial energies in a quantitative fashion. The main objective in undertaking the present work has been to understand somewhat better the factors that influence the degree of specimen flatness of large, monolayer crystals of biological macromolecules. However, the data obtained in our work should be useful in understanding the preparation of specimens of biological macromolecules in general. Data collection by electron diffraction and electron microscopy at high resolution and high tilt angles requires thin crystals of biological macromolecules that are flat to at least 1 degree, and perhaps less than 0.2 degrees, over areas as large as 1 micron2 or more. In addition to determining empirically by electron diffraction experiments whether sufficiently flat specimens can be prepared on various types of modified or unmodified carbon support films, we have begun to use other techniques to characterize both the surfaces involved and the interaction of our specimen with these surfaces. In the specific case of large, monolayer crystals of bacteriorhodopsin prepared as glucose-embedded specimens on hydrophobic carbon films, it was concluded that the initial interfacial interaction involves adsorption of the specimen to the air-water interface rather than adsorption of the specimen to the substrate. Surface-tension forces at the air-water interface and an apparently repulsive interaction between the specimen and the hydrophobic carbon seem to be major factors influencing the specimen flatness in this case. In the more general case it seems likely that interfacial interactions with either the substrate or the air-water interface can be variously manipulated in the search to find desirable conditions of specimen preparation. PMID:2016735

Glaeser, R M; Zilker, A; Radermacher, M; Gaub, H E; Hartmann, T; Baumeister, W

1991-01-01

273

Electron-transfer reactions at the plasma-liquid interface.  

Science.gov (United States)

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

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

2011-11-01

274

Electron Transfer in Donor-Acceptor Systems: Many-Particle Effects and Influence of Electronic Correlations  

CERN Document Server

We investigate electron transfer processes in donor-acceptor systems with a coupling of the electronic degrees of freedom to a common bosonic bath. The model allows to study many-particle effects and the influence of the local Coulomb interaction U between electrons on donor and acceptor sites. Using the non-perturbative numerical renormalization group approach we find distinct differences between the electron transfer characteristics in the single- and two-particle subspaces. We calculate the critical electron-boson coupling alpha_c as a function of $U$ and show results for density-density correlation functions in the whole parameter space. The possibility of many-particle (bipolaronic) and Coulomb-assisted transfer is discussed.

Tornow, S; Bulla, R; Tornow, Sabine; Tong, Ning-Hua; Bulla, Ralf

2006-01-01

275

Electron scattering off simple atoms for large momentum transfer collisions  

International Nuclear Information System (INIS)

In a previous paper this author examined the Born expansion and isolated those parts of the expansion that contribute most significantly to the scattering amplitude for large momentum transfer collisions in inelastic collisions from the ground state of both hydrogen and helium. It turned out that certain terms where the scattering electron interacts once with the nucleus and once with the other electron dominate. The physical reason is that large momentum transfer collisions require the nucleus to take the bulk of the incident momentum but require an interaction with the one of the bound electrons to change the state of the atom. The arguments are quite general and this paper will extend this analysis by comparing the inelastic results obtained by this method for hydrogen and helium to a close coupling calculation with many intermediate states. Further, we will extend this analysis to the correction to the 1st Born result for elastic electron-hydrogen and electron-helium collisions and provide some results for scattering from the initial metastable states of hydrogen for large momentum transfer collisions. A comparison of the results of this analytic approach will be made to the numerical close coupling approach and experiments where available. The agreement is remarkable

276

Photorelaxation induced by water-chromophore electron transfer.  

Science.gov (United States)

Relaxation of photoexcited chromophores is a key factor determining diverse molecular properties, from luminescence to photostability. Radiationless relaxation usually occurs through state intersections caused by distortions in the nuclear geometry of the chromophore. Using excited-state nonadiabatic dynamics simulations based on algebraic diagrammatic construction, it is shown that this is the case of 9H-adenine in water cluster, but not of 7H-adenine in water cluster. 7H-adenine in water cluster relaxes via a state intersection induced by electron transfer from water to the chromophore. This result reveals an unknown reaction pathway, with implications for the assignment of relaxation mechanisms of exciton relaxation in organic electronics. The observation of photorelaxation of 7H-adenine induced by water-chromophore electron transfer is a proof of principle calling for further computational and experimental investigations to determine how common this effect is. PMID:25010652

Barbatti, Mario

2014-07-23

277

Syntrophic growth via quinone-mediated interspecies electron transfer  

Science.gov (United States)

The mechanisms by which microbial species exchange electrons are of interest because interspecies electron transfer can expand the metabolic capabilities of microbial communities. Previous studies with the humic substance analog anthraquinone-2,6-disulfonate (AQDS) suggested that quinone-mediated interspecies electron transfer (QUIET) is feasible, but it was not determined if sufficient energy is available from QUIET to support the growth of both species. Furthermore, there have been no previous studies on the mechanisms for the oxidation of anthrahydroquinone-2,6-disulfonate (AHQDS). A co-culture of Geobacter metallireducens and G. sulfurreducens metabolized ethanol with the reduction of fumarate much faster in the presence of AQDS, and there was an increase in cell protein. G. sulfurreducens was more abundant, consistent with G. sulfurreducens obtaining electrons from acetate that G. metallireducens produced from ethanol, as well as from AHQDS. Co-cultures initiated with a citrate synthase-deficient strain of G. sulfurreducens that was unable to use acetate as an electron donor also metabolized ethanol with the reduction of fumarate and cell growth, but acetate accumulated over time. G. sulfurreducens and G. metallireducens were equally abundant in these co-cultures reflecting the inability of the citrate synthase-deficient strain of G. sulfurreducens to metabolize acetate. Evaluation of the mechanisms by which G. sulfurreducens accepts electrons from AHQDS demonstrated that a strain deficient in outer-surface c-type cytochromes that are required for AQDS reduction was as effective at QUIET as the wild-type strain. Deletion of additional genes previously implicated in extracellular electron transfer also had no impact on QUIET. These results demonstrate that QUIET can yield sufficient energy to support the growth of both syntrophic partners, but that the mechanisms by which electrons are derived from extracellular hydroquinones require further investigation. PMID:25741332

Smith, Jessica A.; Nevin, Kelly P.; Lovley, Derek R.

2015-01-01

278

Syntrophic growth via quinone-mediated interspecies electron transfer.  

Science.gov (United States)

The mechanisms by which microbial species exchange electrons are of interest because interspecies electron transfer can expand the metabolic capabilities of microbial communities. Previous studies with the humic substance analog anthraquinone-2,6-disulfonate (AQDS) suggested that quinone-mediated interspecies electron transfer (QUIET) is feasible, but it was not determined if sufficient energy is available from QUIET to support the growth of both species. Furthermore, there have been no previous studies on the mechanisms for the oxidation of anthrahydroquinone-2,6-disulfonate (AHQDS). A co-culture of Geobacter metallireducens and G. sulfurreducens metabolized ethanol with the reduction of fumarate much faster in the presence of AQDS, and there was an increase in cell protein. G. sulfurreducens was more abundant, consistent with G. sulfurreducens obtaining electrons from acetate that G. metallireducens produced from ethanol, as well as from AHQDS. Co-cultures initiated with a citrate synthase-deficient strain of G. sulfurreducens that was unable to use acetate as an electron donor also metabolized ethanol with the reduction of fumarate and cell growth, but acetate accumulated over time. G. sulfurreducens and G. metallireducens were equally abundant in these co-cultures reflecting the inability of the citrate synthase-deficient strain of G. sulfurreducens to metabolize acetate. Evaluation of the mechanisms by which G. sulfurreducens accepts electrons from AHQDS demonstrated that a strain deficient in outer-surface c-type cytochromes that are required for AQDS reduction was as effective at QUIET as the wild-type strain. Deletion of additional genes previously implicated in extracellular electron transfer also had no impact on QUIET. These results demonstrate that QUIET can yield sufficient energy to support the growth of both syntrophic partners, but that the mechanisms by which electrons are derived from extracellular hydroquinones require further investigation. PMID:25741332

Smith, Jessica A; Nevin, Kelly P; Lovley, Derek R

2015-01-01

279

Distance dependence of intramolecular electron transfer through rigid hydrocarbon spacers  

International Nuclear Information System (INIS)

The effects of energy, distance and molecular structure on rates of electron transfer between molecules are the subjects of continuing investigations in the authors laboratory. The use of rigid molecular spacers between electron donor and acceptor groups facilitates study of the above questions, and is a promising method to obtain energy storage with directed charge separation. Here they present recent results focusing principally on the effects of distance through rigid hydrocarbon spacers. Through-bond interaction is the dominant source of the electronic coupling which enables electron transfer to occur in a series of molecules of the type D-S-A. Pulse radiolysis measurements used molecules D (donor) = biphenyl and A (acceptor) = naphthalene attached to a series of spacer molecules, S, having 3,4,6,7 or 10 saturated hydrocarbon bonds between the D and A groups. The spacer groups were 1,3-cyclohexane (three bonds), 1,4-cyclohexane (four bonds), 2,7-decalin (six bonds), 2,6-decalin (seven bonds) and 3,16-androstance (ten bonds). They attached electrons to these molecules using Argonne's picosecond Linac and measured electron transfer rates (ET) from 3.5 x 109s-1 across three bonds to 1.5 x 106s-1 across ten bonds. The clearest understanding of the rates is obtained by comparing the electronic-coupling interactions. The electronic interactions decrease regularly with increasing number of bonds, but do not correlate very well of bonds, but do not correlate very well with either edge-to-edge or center-to-center distance

280

Interfacial phenomena in solar materials  

Energy Technology Data Exchange (ETDEWEB)

A short review is provided of the fundamental features of general classes of interfaces and interfacial thermodynamics. The energetics and structures of interfaces are reviewed in the context of applications of current understanding of interfacial phenomena to specific materials in several solar technologies. Overviews are presented for interfacial energetics, compositional and chemical analysis of interfaces, and the structure of interfaces and representative illustrations are provided. Numerous examples of interfacial phenomena pertinent to solar materials interface problems are included, and solar materials interface problems are discussed and summarized in a general way. Problems or concerns are tabulated for interfaces in specific solar systems or components, e.g. reflectors, polymers, absorbers, collectors, photovolatic cells, storage systems and heat transfer materials.

Murr, L.E.

1982-04-01

281

Simulations of charge transfer in Electron Multiplying Charge Coupled Devices  

Science.gov (United States)

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

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

2014-12-01

282

Internal electron transfer in cytochrome c oxidase from Rhodobacter sphaeroides.  

Science.gov (United States)

Absorbance changes following CO dissociation by flash photolysis from mixed-valence aa3 cytochrome oxidase from Rhodobacter sphaeroides have been followed in the Soret and alpha regions. They reflect internal electron transfer in the partially reduced enzyme, and the kinetics of the reactions has been determined. As with the bovine enzyme, three kinetic phases are found with relaxation time constants at neutral pH of about 3 microseconds, 35 microseconds, and 1 ms. The first reaction phase represents electron transfer from cytochrome a3 to cytochrome a, and the extent of this reaction is about 3 times larger compared to the bovine enzyme. The energetics of the reaction has been analyzed on the basis of measurements of its temperature dependence. The reorganization energy is close to 120 kJ mol-1, and it is suggested that this rather high value is the result of changes in solvation at the cytochrome a3-CuB site. The subsequent electron transfer between cytochrome a and CuA, with a time constant of 35 microseconds, is almost activationless and has a very low reorganization energy. The final phase, with a time constant close to 1 ms at neutral pH, represents a further shift in the equilibrium between cytochrome a3 and cytochrome a, and it is limited by proton-transfer reactions. The pKa values of the groups involved are significantly shifted in the bacterial oxidase compared to the bovine one. The total extent of electron transfer in the three backflow reactions has also been determined by a comparison of the CO-recombination rates in the mixed-valence and fully reduced enzymes.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:7893697

Adelroth, P; Brzezinski, P; Malmström, B G

1995-03-01

283

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

DEFF Research Database (Denmark)

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

Solov'yov, Ilia; Chang, Po-Yao

2012-01-01

284

Electron transfer mechanisms of DNA repair by photolyase.  

Science.gov (United States)

Photolyase is a flavin photoenzyme that repairs two DNA base damage products induced by ultraviolet (UV) light: cyclobutane pyrimidine dimers and 6-4 photoproducts. With femtosecond spectroscopy and site-directed mutagenesis, investigators have recently made significant advances in our understanding of UV-damaged DNA repair, and the entire enzymatic dynamics can now be mapped out in real time. For dimer repair, six elementary steps have been characterized, including three electron transfer reactions and two bond-breaking processes, and their reaction times have been determined. A unique electron-tunneling pathway was identified, and the critical residues in modulating the repair function at the active site were determined. The dynamic synergy between the elementary reactions for maintaining high repair efficiency was elucidated, and the biological nature of the flavin active state was uncovered. For 6-4 photoproduct repair, a proton-coupled electron transfer repair mechanism has been revealed. The elucidation of electron transfer mechanisms and two repair photocycles is significant and provides a molecular basis for future practical applications, such as in rational drug design for curing skin cancer. PMID:25830375

Zhong, Dongping

2015-04-01

285

High-efficiency inverted organic solar cells with polyethylene oxide-modified Zn-doped TiO2 as an interfacial electron transport layer  

Science.gov (United States)

High efficiency inverted organic solar cells are fabricated using the PTB7:PC71BM polymer by incorporating Zn-doped TiO2 (ZTO) and 0.05 wt% PEO:ZTO as interfacial electron transport layers. The 0.05 wt% PEO-modified ZTO device shows a significantly increased power conversion efficiency (PCE) of 8.10%, compared to that of the ZTO (7.67%) device.High efficiency inverted organic solar cells are fabricated using the PTB7:PC71BM polymer by incorporating Zn-doped TiO2 (ZTO) and 0.05 wt% PEO:ZTO as interfacial electron transport layers. The 0.05 wt% PEO-modified ZTO device shows a significantly increased power conversion efficiency (PCE) of 8.10%, compared to that of the ZTO (7.67%) device. Electronic supplementary information (ESI) available: Experimental part, UPS spectra, absorption spectra, XPS spectra, J-V characteristics, IPCE spectra, AFM, and PL spectra. See DOI: 10.1039/c4nr02780a

Thambidurai, M.; Kim, Jun Young; Ko, Youngjun; Song, Hyung-Jun; Shin, Hyeonwoo; Song, Jiyun; Lee, Yeonkyung; Muthukumarasamy, N.; Velauthapillai, Dhayalan; Lee, Changhee

2014-07-01

286

Electron transfer, decoherence, and protein dynamics: insights from atomistic simulations.  

Science.gov (United States)

Electron transfer in biological systems drives the processes of life. From cellular respiration to photosynthesis and enzymatic catalysis, electron transfers (ET) are chemical processes on which essential biological functions rely. Over the last 40 years, scientists have sought understanding of how these essential processes function in biology. One important breakthrough was the discovery that Marcus theory (MT) of electron transfer is applicable to biological systems. Chemists have experimentally collected both the reorganization energies (?) and the driving forces (?G°), two parameters of Marcus theory, for a large variety of ET processes in proteins. At the same time, theoretical chemists have developed computational approaches that rely on molecular dynamics and quantum chemistry calculations to access numerical estimates of ? and ?G°. Yet another crucial piece in determining the rate of an electron transfer is the electronic coupling between the initial and final electronic wave functions. This is an important prefactor in the nonadiabatic rate expression, since it reflects the probability that an electron tunnels from the electron donor to the acceptor through the intervening medium. The fact that a protein matrix supports electron tunneling much more efficiently than vacuum is now well documented, both experimentally and theoretically. Meanwhile, many chemists have provided examples of the rich physical chemistry that can be induced by protein dynamics. This Account describes our studies of the dynamical effects on electron tunneling. We present our analysis of two examples of natural biological systems through MD simulations and tunneling pathway analyses. Through these examples, we show that protein dynamics sustain efficient tunneling. Second, we introduce two time scales: ?coh and ?FC. The former characterizes how fast the electronic coupling varies with nuclear vibrations (which cause dephasing). The latter reflects the time taken by the system to leave the crossing region. In the framework of open quantum systems, ?FC is a short time approximation of the characteristic decoherence time of the electronic subsystem in interaction with its nuclear environment. The comparison of the respective values of ?coh and ?FC allows us to probe the occurrence of non-Condon effects. We use ab initio MD simulations to analyze how decoherence appears in several biological cofactors. We conclude that we cannot account for its order of magnitude by considering only the atoms or bonds directly concerned with the transfer. Decoherence results from contributions from all atoms of the system appearing with a time delay that increases with the distance from the primarily concerned atoms or bonds. The delay and magnitude of the contributions depend on the chemical nature of the system. Finally, we present recent developments based on constrained DFT for efficient and accurate evaluations of the electronic coupling in ab initio MD simulations. These are promising methods to study the subtle fluctuations of the electronic coupling and the mechanisms of electronic decoherence in biological systems. PMID:25730126

Narth, Christophe; Gillet, Natacha; Cailliez, Fabien; Lévy, Bernard; de la Lande, Aurélien

2015-04-21

287

Structures of protein-protein complexes involved in electron transfer.  

Science.gov (United States)

Electron transfer reactions are essential for life because they underpin oxidative phosphorylation and photosynthesis, processes leading to the generation of ATP, and are involved in many reactions of intermediary metabolism. Key to these roles is the formation of transient inter-protein electron transfer complexes. The structural basis for the control of specificity between partner proteins is lacking because these weak transient complexes have remained largely intractable for crystallographic studies. Inter-protein electron transfer processes are central to all of the key steps of denitrification, an alternative form of respiration in which bacteria reduce nitrate or nitrite to N2 through the gaseous intermediates nitric oxide (NO) and nitrous oxide (N2O) when oxygen concentrations are limiting. The one-electron reduction of nitrite to NO, a precursor to N2O, is performed by either a haem- or copper-containing nitrite reductase (CuNiR) where they receive an electron from redox partner proteins a cupredoxin or a c-type cytochrome. Here we report the structures of the newly characterized three-domain haem-c-Cu nitrite reductase from Ralstonia pickettii (RpNiR) at 1.01?Å resolution and its M92A and P93A mutants. Very high resolution provides the first view of the atomic detail of the interface between the core trimeric cupredoxin structure of CuNiR and the tethered cytochrome c domain that allows the enzyme to function as an effective self-electron transfer system where the donor and acceptor proteins are fused together by genomic acquisition for functional advantage. Comparison of RpNiR with the binary complex of a CuNiR with a donor protein, AxNiR-cytc551 (ref. 6), and mutagenesis studies provide direct evidence for the importance of a hydrogen-bonded water at the interface in electron transfer. The structure also provides an explanation for the preferential binding of nitrite to the reduced copper ion at the active site in RpNiR, in contrast to other CuNiRs where reductive inactivation occurs, preventing substrate binding. PMID:23535590

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

2013-04-01

288

Real-time simulations of photoinduced coherent charge transfer and proton-coupled electron transfer.  

Science.gov (United States)

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

Eisenmayer, Thomas J; Buda, Francesco

2014-10-20

289

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

OpenAIRE

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 comb...

Bhardwaj, Rajneesh; Longtin, Jon P.; Attinger, Daniel

2010-01-01

290

Electron transfer and projectile excitation in single collisions  

International Nuclear Information System (INIS)

Studies of electron transfer (capture) and projectile excitation together in a single encounter are reviewed. This combined capture and excitation can result from either a correlated or an uncorrelated interaction. The correlated process is referred to as resonant transfer and excitation (RTE), while the uncorrelated process is called nonresonant transfer and excitation (NTE). RTE is analogous to dielectronic recombination (DR) which occurs in the interaction between an ion and a free electron. Experimental and theoretical works leading to establishing the existence of RTE are reviewed as well as considerations relevant to distinguishing RTE from NTE. The dependences of RTE on projectile atomic number (14 ? Z ? 23) for Li-like ions, and on projectile charge state for H-like to Ne-like ions have been measured and compared with theory. The effect of the target electron momentum distribution on RTE has been demonstrated by comparing measurements for H2 and He targets. Measurements of RTE involving L-shell excitation have been conducted and compared with K-shell results. All of the measured RTE cross sections to date for H2 and He targets are in reasonable agreement with calculations based on theoretical DR cross sections averaged over the target electron momentum distribution; however, systematic discrepancies between experiment and theory exist. Additionally, is has been found that RTE can contribute considerably to total single-electron capturerably to total single-electron capture cross sections in the region where RTE is important, accounting for nearly half of the total capture events for calcium ions colliding with H2. (orig.)

291

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

292

Nile blue can photosensitize DNA damage through electron transfer.  

Science.gov (United States)

The mechanism of DNA damage photosensitized by Nile blue (NB) was studied using (32)P-5'-end-labeled DNA fragments. NB bound to the DNA strand was possibly intercalated through an electrostatic interaction. Photoirradiated NB caused DNA cleavage at guanine residues when the DNA fragments were treated with piperidine. Consecutive guanines, the underlined G in 5'-GG and 5'-GGG, were selectively damaged through photoinduced electron transfer. The fluorescence lifetime of NB was decreased by guanine-containing DNA sequence, supporting this mechanism. Single guanines were also slightly damaged by photoexcited NB, and DNA photodamage by NB was slightly enhanced in D2O. These results suggest that the singlet oxygen mechanism also partly contributes to DNA photodamage by NB. DNA damage photosensitized by NB via electron transfer may be an important mechanism in medicinal applications of photosensitizers, such as photodynamic therapy in low oxygen. PMID:24576317

Hirakawa, Kazutaka; Ota, Kazuhiro; Hirayama, Junya; Oikawa, Shinji; Kawanishi, Shosuke

2014-04-21

293

Solvation-induced one-dimensional polarons and electron transfer.  

Science.gov (United States)

When a one-dimensional (1D) semiconductor nanostructure is immersed in a sluggish polar solvent, fluctuations of the medium may result in the appearance of localized electronic levels inside the band gap. An excess charge carrier can occupy such a level and undergo self-localization into a large-radius adiabatic polaron surrounded by a self-consistent medium polarization pattern. Within an appropriately adapted framework of the Marcus theory, we explore the description and qualitative picture of thermally activated electron transfer involving solvation-induced polaroniclike states by considering transfer between small and 1D species as well as between two 1D species. Illustrative calculations are performed for tubular geometries with possible applications to carbon nanotube systems. PMID:20441283

Ussery, G L; Gartstein, Yu N

2010-04-28

294

Solvation-induced one-dimensional polarons and electron transfer  

CERN Document Server

When a one-dimensional (1D) semiconductor nanostructure is immersed in a sluggish polar solvent, fluctuations of the medium may result in the appearance of localized electronic levels inside the band gap. An excess charge carrier can occupy such a level and undergo self-localization into a large-radius adiabatic polaron surrounded by a self-consistent medium polarization pattern. Within an appropriately adapted framework of the Marcus theory, we explore the description and qualitative picture of thermally activated electron transfer involving solvation-induced polaronic-like states by considering transfer between small and 1D species as well as between two 1D species. Illustrative calculations are performed for tubular geometries with possible applications to carbon nanotube systems.

Ussery, G L

2009-01-01

295

Polarization-transfer electron-Zeeman resolved EPR  

Science.gov (United States)

Polarization-transfer electron-Zeeman resolved (EZ) EPR is introduced. In this two-dimensional pulse EPR method, which is based on the stimulated-echo sequence, the magnetic field is changed during the pulse sequence by applying a sinusoidal field of variable amplitude. EZ-EPR can be used to improve the spectral resolution of disordered systems with g anisotropy or to separate overlapping spectra of sites with different g values in single-crystal EPR studies. A theoretical description of the method is given, and model calculations as well as experiments on disordered systems with anisotropic electron Zeeman interactions are presented.

Eichel, Rüdiger-A.; Schweiger, Arthur

2002-05-01

296

Strongly enhanced backward emission of electrons in transfer and ionization.  

Science.gov (United States)

We studied three-dimensional angular distributions and longitudinal momentum spectra of electrons ejected in transfer plus ionization (TI), i.e., the ejection of one and the capture of a second target electron, for ion-helium collisions. We observe a pronounced structure strongly focused opposite to the projectile beam direction, which we associate with a new correlated TI mechanism proposed recently. This process contributes significantly to the total cross sections over a broad range of perturbations ?, even at ? as large as 0.5, where uncorrelated TI mechanisms were thought to be dominant. PMID:22400839

Schulz, M; Wang, X; Gundmundsson, M; Schneider, K; Kelkar, A; Voitkiv, A B; Najjari, B; Schöffler, M; Schmidt, L Ph H; Dörner, R; Ullrich, J; Moshammer, R; Fischer, D

2012-01-27

297

Photoinduced electron transfer from phenanthrimidazole to magnetic nanoparticles.  

Science.gov (United States)

The dynamics of photoinduced electron injection from (E)-1-(4-methoxyphenyl)-2-styryl-1H-phenanthro [9,10-d]imidazole (MPSPI) synthesised using nano TiO2 as catalyst to Fe2O3 nanocrystal has been studied by FT-IR, absorption, fluorescence and lifetime spectroscopic methods. The binding between nanoparticle and MPSPI is confirmed by binding constant and binding site. The distance between MPSPI and nanoparticle as well as the critical energy transfer distance has been obtained. The free energy change (?Get) for electron injection has also been deduced. PMID:25591997

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

2015-01-01

298

Microscopic solvation dynamics and solvent-controlled electron transfer  

Energy Technology Data Exchange (ETDEWEB)

In this paper the authors investigate solvent size effects on solvent-controlled electron transfer (ET) in polar liquids. An interrelationship was established between the solvation time correlation function and the ET rate, which was presented within the first passage time approximation. For the case of activationless ET the ET rate, which is equal to the initial solvation rate, was expressed within the framework of the mean spherical approximation. The theory predicts that the activationless ET times are shorter than the average dipole solvation times, in accord with experimental data for intramolecular ET in electronically excited bianthryl in nonassociated polar solvents.

Rips, I.; Klafter, J.; Jortner, J. (Tel Aviv Univ. (Israel))

1990-11-15

299

Probing concerted proton–electron transfer in phenol–imidazoles  

OpenAIRE

A series of seven substituted 4,6-di-tert-butyl-2-(4,5-diarylimidazolyl)-phenols have been prepared and characterized, along with two related benzimidazole compounds. X-ray crystal structures of all of the compounds show that the phenol and imidazole rings are close to coplanar and are connected by an intramolecular ArOH?N hydrogen bond. One-electron oxidation of these compounds occurs with movement of the phenolic proton to the imidazole base by concerted proton–electron transfer (CPET) ...

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

2008-01-01

300

Interfacial Engineering of Molecular Photovoltaics  

Science.gov (United States)

One of the most worthy pursuits in the field of organic solar cells is that of discovering ways to more effectively harvest charge generated by light absorption. The measure of the efficacy of this process is the external quantum efficiency (EQE). It is determined by the efficiency of incident light absorption, exciton diffusion, exciton splitting and charge transfer, and charge collection. Enhanced EQE can be realized by engineering interfaces between materials in the device to allow for smoother charge transfer throughout the extent of the device, which is usually between 10 and 200 nanometers. Improvements in charge transport are vitally important because the photogenerated excitons in electron donating polymers and small molecules typically only diffuse between 5 and 10 nanometers. These excitons must reach the interface between the electron donor and electron acceptor in order to be split so that the resulting electron and hole can be harvested at the cathode and anode, respectively. The aim of much of this dissertation is to describe a method by which the donor-acceptor interfacial area can be augmented using nanoimprint lithography, first with a single donor and then with multiple donors. Nanoimprint lithography is introduced as a simple embossing technique that can create features in a single component donor with dimensions as small as 20 nm. Solution-processable small molecules are of interest for their ease of synthesis and fabrication. I continue the discussion of nanoimprint lithography by offering candidates for a two-component donor combination. A two-component donor can extend the absorption range across a broader portion of the solar spectrum than just one donor to improve energy harvesting. After considering ways of optimizing the donor-acceptor interface, I describe the use of a charge selective layer for better charge transport and collection. When incorporated into a bilayer solar cell and an inverted solar cell, these two molecules markedly improve the energy conversion efficiency.

Shelton, Steven Wade

301

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

International Nuclear Information System (INIS)

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

302

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

303

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

304

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

OpenAIRE

Smell is a vital sense for animals. The mainstream explanation of smell is based on recognition of the odorant molecules through characteristics of their surface, e.g., shape, but certain experiments suggest that such recognition is complemented by recognition of vibrational modes. According to this suggestion an olfactory receptor is activated by electron transfer assisted through odorant vibrational excitation. The hundreds to thousands of different olfactory receptors in an animal recogniz...

Solov’yov, Ilia A.; Chang, Po-yao; Schulten, Klaus

2012-01-01

305

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

306

[Electron transfer, ionization and excitation in atomic collisions  

International Nuclear Information System (INIS)

The research being carried out at Penn State by Winter and Alston addresses the fundamental atomic-collision processes of electron transfer, ionization, and excitation. Winter has focussed attention on intermediate and, more recently, higher collision energies -- proton energies of at least about 50 keV -- for which coupled-state approaches are appropriate. Alston has concentrated on perturbative approaches to symmetric ion-ion/atom collisions at high energies and to asymmetric collisions at intermediate to high energies

307

Structures of Protein-Protein Complexes involved in electron transfer  

OpenAIRE

Electron transfer (ET) reactions are essential for life since they underpin oxidative phosphorylation and photosynthesis, processes leading to the generation of ATP, and are involved in many reactions of intermediary metabolism1. Key to these roles is the formation of transient inter-protein ET complexes. The structural basis for the control of specificity between partner proteins is lacking since these weak transient complexes have remained largely intractable for crystallographic studies2,3...

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

2013-01-01

308

Electron transfer at sensitized TiO/sub 2/ electrodes  

Energy Technology Data Exchange (ETDEWEB)

Electron transfer from the excited state of tetra-iodo, tetra-chloro fluorescein (rose bengal) to the conduction band of TiO/sub 2/ has been studied through photoelectrochemical techniques. The measured transfer rate was correlated with information from absorbance and adsorption measurements of this dye molecule on the (001) surface of the single crystals used as electrodes. The quantum efficiency for the photoinjection of electrons was determined to be 4.0 x 10/sup -3/ independent of the pH of the electrolyte and the dye surface concentration. With these data, an argument is given supporting the existence of excitation transfer among the dye molecules on the surface. A temperature study of the electron transfer efficiency yielded an activation enthalpy of 3.2 +- 0.3 kcal/mole with a pre-exponential factor of 1.0. A heat of adsorption of 7.6 +- 0.5 kcal/mole for this dye on TiO/sub 2/ single crystals was derived from analysis of adsorption isotherms measured at 21.5 and 36.5degreeC. In addition to the photo-oxidation process, a photoreduction was also observed upon cathodic polarization of the semiconductor. Action spectra revealed participation of solution dye molecules in this reaction; the reduction rate is dependent upon oxygen concentration in solution. It was concluded that the oxidized dye in solution accepts an electron from the TiO/sub 2/ to generate this current. This photoreduction was found with triphenylmethane and thiazine dyes as well as with other fluorescein derivatives.

Spitler, M.T.; Calvin, M.

1977-05-15

309

Electron transfer reactions on small CdSe colloids  

International Nuclear Information System (INIS)

Colloidal CdSe particles were investigated by both laser flash photolysis and pulse radiolysis. Electron transfer reactions were observed from each technique. Transient absorption attributed to trapped excess charge and formation of Cd+ and Se- sites was detected during the laser photolysis. Transient absorption was again detected during pulse radiolysis of the aqueous solution. In the latter case the trapped excess charge is reduced to Cd0 in short order

310

41 CFR 102-118.70 - Must my agency make all payments via electronic funds transfer?  

Science.gov (United States)

...agency make all payments via electronic funds transfer? 102-118...agency make all payments via electronic funds transfer? Yes...must make all payments for goods and services via EFT (this includes goods and services ordered...

2010-07-01

311

77 FR 34127 - Financial Management Service; Proposed Collection of Information: Electronic Transfer Account...  

Science.gov (United States)

...Fiscal Service Financial Management Service; Proposed Collection...Electronic Transfer Account (ETA) Financial Agency...Agreement AGENCY: Financial Management Service, Fiscal Service...notice, the Financial Management Service solicits comments...Electronic Transfer Account (ETA) Financial...

2012-06-08

312

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

313

Photoinduced electron transfer pathways in hydrogen-evolving reduced graphene oxide-boosted hybrid nano-bio catalyst.  

Science.gov (United States)

Photocatalytic production of clean hydrogen fuels using water and sunlight has attracted remarkable attention due to the increasing global energy demand. Natural and synthetic dyes can be utilized to sensitize semiconductors for solar energy transformation using visible light. In this study, reduced graphene oxide (rGO) and a membrane protein bacteriorhodopsin (bR) were employed as building modules to harness visible light by a Pt/TiO2 nanocatalyst. Introduction of the rGO boosts the nano-bio catalyst performance that results in hydrogen production rates of approximately 11.24 mmol of H2 (?mol protein)(-1) h(-1). Photoelectrochemical measurements show a 9-fold increase in photocurrent density when TiO2 electrodes were modified with rGO and bR. Electron paramagnetic resonance and transient absorption spectroscopy demonstrate an interfacial charge transfer from the photoexcited rGO to the semiconductor under visible light. PMID:25050831

Wang, Peng; Dimitrijevic, Nada M; Chang, Angela Y; Schaller, Richard D; Liu, Yuzi; Rajh, Tijana; Rozhkova, Elena A

2014-08-26

314

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

315

Nanoparticle facilitated extracellular electron transfer in microbial fuel cells.  

Science.gov (United States)

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

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

2014-11-12

316

Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives  

DEFF Research Database (Denmark)

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

Borovok, N; Kotlyar, A B

1999-01-01

317

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/oxidizedzed 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.

318

Probing the nature of electron transfer in metalloproteins on graphene-family materials as nanobiocatalytic scaffold using electrochemistry  

Science.gov (United States)

Graphene-based nanomaterials have shown great promise not only in nanoelectronics due to ultrahigh electron mobility but also as biocatalytic scaffolds owing to irreversible protein surface adsorption and facilitating direct electron transfer. In this work, we synthesized stable dispersions of graphene using liquid-phase exfoliation approach based on non-covalent interactions between graphene and 1-pyrenesulfonic acid sodium salt (Py-1SO3), 1-pyrenemethylamine salt (Py - Me-NH2) and Pluronic® P-123 surfactant using only water as solvent compatible with biomolecules. The resulting graphene nanoplatelets (Gr_LPE) are characterized by a combination of analytical (microscopy and spectroscopy) techniques revealing mono- to few-layer graphene displaying that the exfoliation efficiency strongly depends upon the type of pyrene-based salts and organic surfactants. Moreover being completely water-based approach, we build robust nanoscaffolds of graphene-family nanomaterials (GFNs) namely, monolayer graphene, Gr_LPE (the one prepared with Pluronic® P-123), graphene oxide (GO) and its reduced form (rGO) on glassy carbon electrode surface with three important metalloproteins include cytochrome c (Cyt c) [for electron transfer], myoglobin (Mb) [for oxygen storage] and horseradish peroxidase (HRP) [for catalyzing the biochemical reaction]. In order to demonstrate the nanobiocatalytical activity of these proteins, we used electrochemical interfacial direct electron transfer (DET) kinetics and attempt to determine the rate constant (kET) using two different analytical approaches namely, linear sweep voltammetry and Laviron's theory. We elucidated that all of the metalloproteins retain their structural integrity (secondary structure) upon forming mixtures with GFNs confirmed through optical and vibrational spectroscopy and biological activity using electrochemistry. Among the GFNs studied, Gr-LPE, GO and rGO support the efficient electrical wiring of the redox centers (with an increase in catalytic efficiency of Cyt c and Mb in the presence of GFNs attributed partially to the surface functional (carboxyl, epoxide and hydroxyl) groups on GO and rGO facilitating rapid charge transfer.

Gupta, Sanju; Irihamye, Aline

2015-03-01

319

Probing the nature of electron transfer in metalloproteins on graphene-family materials as nanobiocatalytic scaffold using electrochemistry  

Directory of Open Access Journals (Sweden)

Full Text Available Graphene-based nanomaterials have shown great promise not only in nanoelectronics due to ultrahigh electron mobility but also as biocatalytic scaffolds owing to irreversible protein surface adsorption and facilitating direct electron transfer. In this work, we synthesized stable dispersions of graphene using liquid-phase exfoliation approach based on non-covalent interactions between graphene and 1-pyrenesulfonic acid sodium salt (Py–1SO3, 1-pyrenemethylamine salt (Py ? Me-NH2 and Pluronic® P-123 surfactant using only water as solvent compatible with biomolecules. The resulting graphene nanoplatelets (Gr_LPE are characterized by a combination of analytical (microscopy and spectroscopy techniques revealing mono- to few-layer graphene displaying that the exfoliation efficiency strongly depends upon the type of pyrene-based salts and organic surfactants. Moreover being completely water-based approach, we build robust nanoscaffolds of graphene-family nanomaterials (GFNs namely, monolayer graphene, Gr_LPE (the one prepared with Pluronic® P-123, graphene oxide (GO and its reduced form (rGO on glassy carbon electrode surface with three important metalloproteins include cytochrome c (Cyt c [for electron transfer], myoglobin (Mb [for oxygen storage] and horseradish peroxidase (HRP [for catalyzing the biochemical reaction]. In order to demonstrate the nanobiocatalytical activity of these proteins, we used electrochemical interfacial direct electron transfer (DET kinetics and attempt to determine the rate constant (kET using two different analytical approaches namely, linear sweep voltammetry and Laviron’s theory. We elucidated that all of the metalloproteins retain their structural integrity (secondary structure upon forming mixtures with GFNs confirmed through optical and vibrational spectroscopy and biological activity using electrochemistry. Among the GFNs studied, Gr-LPE, GO and rGO support the efficient electrical wiring of the redox centers (with an increase in catalytic efficiency of Cyt c and Mb in the presence of GFNs attributed partially to the surface functional (carboxyl, epoxide and hydroxyl groups on GO and rGO facilitating rapid charge transfer.

Sanju Gupta

2015-03-01

320

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

321

Electron transfer behaviour of biological macromolecules towards the single-molecule level  

DEFF Research Database (Denmark)

Redox metalloproteins immobilized on metallic surfaces in contact with aqueous biological media are important in many areas of pure and applied sciences. Redox metalloprotein films are currently being addressed by new approaches where biotechnology including modified and synthetic proteins is combined with state-of-the-art physical electrochemistry with emphasis on single-crystal, atomically planar electrode surfaces, in situ scanning tunnelling microscopy (STM) and other surface techniques. These approaches have brought bioelectrochemistry important steps forward towards the nanoscale and single-molecule levels.We discuss here these advances with reference to two specific redox metalloproteins, the blue single-copper protein Pseudomonas aeruginosa azurin and the single-haem protein Saccharomyces cerevisiae yeast cytochrome c, and a short oligonucleotide. Both proteins can be immobilized on Au(111) by chemisorption via exposed sulfur-containing residues. Voltammetric, interfacial capacitance, x-ray photoelectron spectroscopy and microcantilever sensor data, together with in situ STM with single-molecule resolution, all point to a coherent view of monolayer organization with protein electron transfer (ET) function retained. In situ STM can also address the microscopic mechanisms for electron tunnelling through the biomolecules and offers novel notions such as coherent multi-ET between the substrate and tip via the molecular redox levels. This differs in important respects from electrochemical ET at a single metal/electrolyte interface. Similar data for a short oligonucleotide immobilized on Au(111) show that oligonucleotides can be characterized with comparable detail, with novel perspectives for addressing DNA electronic conduction mechanisms and for biological screening towards the single-molecule level.

Zhang, Jingdong; Grubb, Mikala

2003-01-01

322

Electron transfer behaviour of biological macromolecules towards the single-molecule level  

International Nuclear Information System (INIS)

Redox metalloproteins immobilized on metallic surfaces in contact with aqueous biological media are important in many areas of pure and applied sciences. Redox metalloprotein films are currently being addressed by new approaches where biotechnology including modified and synthetic proteins is combined with state-of-the-art physical electrochemistry with emphasis on single-crystal, atomically planar electrode surfaces, in situ scanning tunnelling microscopy (STM) and other surface techniques. These approaches have brought bioelectrochemistry important steps forward towards the nanoscale and single-molecule levels. We discuss here these advances with reference to two specific redox metalloproteins, the blue single-copper protein Pseudomonas aeruginosa azurin and the single-haem protein Saccharomyces cerevisiae yeast cytochrome c, and a short oligonucleotide. Both proteins can be immobilized on Au(111) by chemisorption via exposed sulfur-containing residues. Voltammetric, interfacial capacitance, x-ray photoelectron spectroscopy and microcantilever sensor data, together with in situ STM with single-molecule resolution, all point to a coherent view of monolayer organization with protein electron transfer (ET) function retained. In situ STM can also address the microscopic mechanisms for electron tunnelling through the biomolecules and offers novel notions such as coherent multi-ET between the substrate and tip via the molecular redox levels. This differs in important respdox levels. This differs in important respects from electrochemical ET at a single metal/electrolyte interface. Similar data for a short oligonucleotide immobilized on Au(111) show that oligonucleotides can be characterized with comparable detail, with novel perspectives for addressing DNA electronic conduction mechanisms and for biological screening towards the single-molecule level

323

Understanding interfacial charge transfer between metallic PEDOT counter electrodes and a cobalt redox shuttle in dye-sensitized solar cells.  

Science.gov (United States)

Conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with iron(III) tris-p-toluenesulfonate (PEDOT:Tos) having metallic conductivity was coated onto fluorine-doped tin oxide (FTO) glass and plain glass substrates and used as a counter electrode (CE) in a dye-sensitized solar cell (DSC) with a [Co(bpy)3](3+/2+) complex redox shuttle. DSCs with PEDOT:Tos/glass CE yielded power conversion efficiencies (PCE) of 6.3%, similar to that of DSCs with platinized FTO glass CE (6.1%). The PEDOT:Tos-based counter electrodes had 5 to 10 times lower charge-transfer resistance than the Pt/FTO CE in DSCs, as analyzed by impedance spectroscopy. More detailed studies in symmetrical CE-CE cells showed that the PEDOT:Tos layers are nanoporous. Not all internal area can be used catalytically under solar cell conditions and effective charge-transfer resistance was similar to that of Pt/FTO. PMID:24410094

Park, Byung-wook; Pazoki, Meysam; Aitola, Kerttu; Jeong, Seunghee; Johansson, Erik M J; Hagfeldt, Anders; Boschloo, Gerrit

2014-02-12

324

Electron and energy transfer in artificial photosynthesis supermolecules  

Science.gov (United States)

Photophysical properties of a variety of organic supermolecules were studied in order to elucidate structural and thermodynamic criteria pertinent to the design of artificial photosynthetic structures and molecular electronic devices. These supermolecules were designed using covalently linked porphyrins, carotenoids, C60 fullerenes, quinones, and aromatic imide chromophores. Time-resolved absorption and fluorescence spectroscopy on a femtosecond to millisecond time scale was used to investigate mechanisms of photoinduced electron transfer, singlet and triplet energy transfer, and radical pair dynamics. Several photophysical processes, previously found only in photosynthetic reaction centers, were observed and characterized for the first time in these artificial systems. Molecular dyads, triads, and a hexad were shown to form long-lived charge separated states with high quantum yields, thus efficiently converting electronic excited state energy into (electro) chemical energy. These systems demonstrate that favorable photophysical properties can be conveniently (and predictably) controlled by changes in the molecular structure and the physical characteristics of the medium, such as the solvent polarity or temperature. Molecules studied in this work could be utilized as components of functional supramolecular assemblies. C60 fullerenes were shown to be preferable electron acceptors in molecular structures intended to function in a non-polar media or at low temperatures. This was attributed to the low intramolecular and solvent reorganization energies for C60 fullerenes. The magnetic field dependence of charge recombination in linked organic biradicals was studied. This effect can be used as the basis for a magnetically controlled molecular optical or optoelectronic switch (AND gate).

Kuciauskas, Darius

1999-12-01

325

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

International Nuclear Information System (INIS)

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

326

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

Science.gov (United States)

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

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

2006-05-01

327

Charge amplification and transfer processes in the gas electron multiplier  

CERN Document Server

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

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

1999-01-01

328

Electron transfer, ionization, and excitation in atomic collisions  

Energy Technology Data Exchange (ETDEWEB)

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

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

1992-01-01

329

Quantum effects in adiabatic electrochemical electron-transfer reactions  

Science.gov (United States)

The role of nuclear tunneling in adiabatic electrochemical electron-transfer reactions is studied by applying the WKB approximation and the Quantum Kramers Theory to the ground-state potential energy surface calculated from an extended Anderson-Newns Hamiltonian. Reorganization of both solvent and ligand modes is considered. In the limit of vanishing electronic coupling analytical formulas are obtained for the temperature dependence of the activation parameters, which are valid over a practically unlimited temperature range. In the limit of high temperature, they are shown to be identical to expression derived from the non-adiabatic Levich-Dogonadze theory. The effect of friction and non-vanishing electronic coupling are studied and both are found to suppress the relative contribution of the nuclear tunneling to the overall reaction rate.

Koper, M. T. M.; Mohr, J.-H.; Schmickler, W.

1997-07-01

330

Electron transfer reactions involving acridine and related compounds  

International Nuclear Information System (INIS)

Acridine is rapidly reduced by e/sub sol/- (k = 3 x 1010 M-1 s-1) and by (CH3)2CO- (k = 3 x 109 M-1 s-1 in water and 1.4 x 109 M-1 s-1 in i-PrOH). Reduction by (CH3)2COH and CO2- is rapid and efficient only when the acridine is protonated (pK/sub a/ = 5.6). With neutral acridine, however, the slow reduction is accompanied by addition of these radicals to acridine. Both forms of acridine are reduced by pyridinyl radicals, although the acid more rapidly than the neutral form. In all these one-electron reductions the anion radical of acridine is produced, which in aqueous and alcoholic solutions undergoes rapid protonation on the nitrogen to form a neutral radical, with a pK/sub a/ apparently above 14. Related heterocyclic compounds, such as 1,10-phenanthroline and phenazine, behave in a similar fashion. The radicals produced by reduction of acridine and other heterocycles can transfer an electron to 9,10-anthraquinone in nonaqueous media or to anthraquinonesulfonate in aqueous solutions (k approx. 109 M-1 s-1). The spectra of the resulting semiquinone radicals were found, in all cases examined, to be identical with those obtained by direct reduction of the quinone under similar conditions without the intermediacy of the heterocycle. This is in contrast w of the heterocycle. This is in contrast with previous findings with a porphyrin-anthraqinone system. It is concluded that, despite the previous suggestion that an intermediate complex is formed upon electron transfer from tetraphenylporphyrin radical to anthraquinone, no such complex appears to be formed in the electron transfer reactions involving acridine and related heterocycles

331

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

332

Electron-transfer reactions of tryptophan and tyrosine derivatives  

International Nuclear Information System (INIS)

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

333

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

International Nuclear Information System (INIS)

We carry out the R-matrix calculations for electron-impact excitations of ions with one valence electron. The integral cross sections and polarization degree are obtained for the excitation process from the ground state to the first 2P0 state of Li2+, B2+ and Al2+ as functions of electron incident energy. The differential cross sections and angular momentum transfer are also shown at non-resonant low-energy points. As for the angular momentum transfer (Lperpendicular) at small scattering angles, they are negative for B2+ and Al2+, while it is positive for Li2+. Thus Lperpendicular of doubly charged ions with one-valence electron is not simple.

334

Ultrafast intramolecular electron transfer from a ferrocene donor moiety to a nile blue acceptor  

Science.gov (United States)

The fastest electron transfer processes between molecular donor/acceptor systems have been observed for solvent to solute type reactions, where the number of solvent molecules participating could be high. This might explain the very short electron transfer times of ?100 fs observed. Here the photo-induced electron transfer in a bridged donor/acceptor system was studied by femtosecond pump-probe spectroscopy with a time resolution of 15 fs. After photoexcitation of the acceptor (nile blue) an electron is transferred from the donor (ferrocene) with a time constant of 90 fs, i.e. close to fastest electron transfer times in the solute/solvent systems.

Baigar, E.; Gilch, P.; Zinth, W.; Stöckl, M.; Härter, P.; von Feilitzsch, T.; Michel-Beyerle, M. E.

2002-01-01

335

Theory of electron transfer in the presence of dissipation  

International Nuclear Information System (INIS)

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

336

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

337

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

338

Single Electron Transfer Living Radical Polymerization via a New Initiator  

Science.gov (United States)

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

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

2014-08-01

339

Covalent electron transfer chemistry of graphene with diazonium salts.  

Science.gov (United States)

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

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

2013-01-15

340

Comparison of dynamical aspects of nonadiabatic electron, proton, and proton-coupled electron transfer reactions  

International Nuclear Information System (INIS)

The dynamical aspects of a model proton-coupled electron transfer (PCET) reaction in solution are analyzed with molecular dynamics simulations. The rate for nonadiabatic PCET is expressed in terms of a time-dependent probability flux correlation function. The impact of the proton donor-acceptor and solvent dynamics on the probability flux is examined. The dynamical behavior of the probability flux correlation function is dominated by a solvent damping term that depends on the energy gap correlation function. The proton donor-acceptor motion does not impact the dynamical behavior of the probability flux correlation function but does influence the magnitude of the rate. The approximations previously invoked for the calculation of PCET rates are tested. The effects of solvent damping on the proton donor-acceptor vibrational motion are found to be negligible, and the short-time solvent approximation, in which only equilibrium fluctuations of the solvent are considered, is determined to be valid for these types of reactions. The analysis of PCET reactions is compared to previous analyses of single electron and proton transfer reactions. The dynamical behavior is qualitatively similar for all three types of reactions, but the time scale of the decay of the probability flux correlation function is significantly longer for single proton transfer than for PCET and single electron transfer due to a smaller solvent reorganization energy for proton transferfor proton transfer

341

Transcriptomic and Genetic Analysis of Direct Interspecies Electron Transfer  

Science.gov (United States)

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

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

2013-01-01

342

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

343

Transcriptomic and genetic analysis of direct interspecies electron transfer.  

Science.gov (United States)

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

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

2013-04-01

344

Interfacial electronic structure and full spectral Hamaker constants of Si3N4 intergranular films from VUV and SR-VEEL spectroscopy  

International Nuclear Information System (INIS)

The interfacial electronic structure, presented as the interband transition strength Jcv(?) of the interatomic bonds, can be determined by Kramers Kronig (KK) analysis of vacuum ultraviolet (VUV) reflectance or spatially resolved valence electron energy loss (SR-VEEL) spectra. For the wetted interfaces in Si3N4, equilibrium thin glass films are formed whose thickness is determined by a force balance between attractive and repulsive force terms KK analysis of Jcv(?) to yield var-epsilon 2(?) for the phases present, permits the direct calculation of the configuration-dependent Hamaker constants for the attractive vdW forces from the interfacial electronic structure. Interband transition strengths and full spectral Hamaker constants for Si3N4samples containing a SiYAlON glass have been determined using SR-VEELS from grains and grain boundaries and compared with results from bulk VUV spectroscopy on separate samples of glass and nitride. The A121Hamaker constant for Si3N4 with glass of the bulk composition is 8 zJ (zJ = 10-21J) from the more established optical method. The EELS method permits the determination of vdW forces based upon actual local compositions and structure, which may differ noticeably from bulk standards. Current results show that full spectral Hamaker constants determined from VUV and SR-VEEL measurements of uniform bulk samples agmeasurements of uniform bulk samples agree, but care must be take in the single scattering and zero loss subtraction corrections, and more work is ongoing in this area. Still the results show that for the grain boundary films present in these polycrystalline Si3N4 samples the glass composition is of lower index of refraction. This can arise from increased oxygen content in determined in situ from the SR-VEELS of a particular grain boundary film. 45 refs

345

Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber  

Directory of Open Access Journals (Sweden)

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

Tanya M. Monro

2011-10-01

346

Long-range intramolecular electron transfer in azurins  

DEFF Research Database (Denmark)

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

Farver, O; Pecht, I

1989-01-01

347

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

348

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

349

Parton models of high momentum transfer electron-nuclear scattering  

International Nuclear Information System (INIS)

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

350

Electronic excitation energy transfer between quasi-zero-dimensional systems.  

Czech Academy of Sciences Publication Activity Database

Tokyo : The Surface Science Society of Japan, 2014, s. 11-17. ISSN 1348-0391. [International Conference on Atomically Controlled Surfaces, Interfaces and Nanostructures /12/ - International Colloquium on Scanning Probe Microscopy /21./. Tsukuba (JP), 04.11.2013-08.11.2013] R&D Projects: GA MŠk LH12236; GA MŠk LH12186 Institutional support: RVO:68378271 ; RVO:61389013 Keywords : quantum dots * energy transfer * electron-phonon interaction Subject RIV: BM - Solid Matter Physics ; Magnetism https://www.jstage.jst.go.jp/result?item1=4&word1=Atomically+Controlled+Surfaces+ AND +kral

Král, Karel; Menšík, Miroslav; Mao, H.

351

Analysis of electron transfer processes across liquid/liquid interfaces: estimation of free energy of activation using diffuse boundary model.  

Science.gov (United States)

The evaluation of the free energy of activation pertaining to the electron-transfer reactions occurring at liquid/liquid interfaces is carried out employing a diffuse boundary model. The interfacial solvation numbers are estimated using a lattice gas model under the quasichemical approximation. The standard reduction potentials of the redox couples, appropriate inner potential differences, dielectric permittivities, as well as the width of the interface are included in the analysis. The methodology is applied to the reaction between [Fe(CN)6](3-/4-) and [Lu(biphthalocyanine)](3+/4+) at water/1,2-dichloroethane interface. The rate-determining step is inferred from the estimated free energy of activation for the constituent processes. The results indicate that the solvent shielding effect and the desolvation of the reactants at the interface play a central role in dictating the free energy of activation. The heterogeneous electron-transfer rate constant is evaluated from the molar reaction volume and the frequency factor. PMID:16430304

Harinipriya, S; Sangaranarayanan, M V

2006-01-31

352

ATP-induced electron transfer by redox-selective partner recognition  

Science.gov (United States)

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

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

2014-08-01

353

The electronic transfer of information and aerospace knowledge diffusion  

Science.gov (United States)

Increasing reliance on and investment in information technology and electronic networking systems presupposes that computing and information technology will play a motor role in the diffusion of aerospace knowledge. Little is known, however, about actual information technology needs, uses, and problems within the aerospace knowledge diffusion process. The authors state that the potential contributions of information technology to increased productivity and competitiveness will be diminished unless empirically derived knowledge regarding the information-seeking behavior of the members of the social system - those who are producing, transferring, and using scientific and technical information - is incorporated into a new technology policy framework. Research into the use of information technology and electronic networks by U.S. aerospace engineers and scientists, collected as part of a research project designed to study aerospace knowledge diffusion, is presented in support of this assertion.

Pinelli, Thomas E.; Bishop, Ann P.; Barclay, Rebecca O.; Kennedy, John M.

1992-01-01

354

Generalized Holstein model for spin-dependent electron transfer reaction  

CERN Document Server

Some chemical reactions are described by electron transfer (ET) processes. The underlying mechanism could be modeled as a polaron motion in the molecular crystal-the Holstein model. By taking spin degrees of freedom into consideration, we generalize the Holstein model (molecular crystal model) to microscopically describe an ET chemical reaction. In our model, the electron spins in the radical pair simultaneously interact with a magnetic field and their nuclear-spin environments. By virtue of the perturbation approach, we obtain the chemical reaction rates for different initial states. It is discovered that the chemical reaction rate of the triplet state demonstrates its dependence on the direction of the magnetic field while the counterpart of the singlet state does not. This difference is attributed to the explicit dependence of the triplet state on the direction when the axis is rotated. Our model may provide a possible candidate for the microscopic origin of avian compass.

Yang, Li-Ping; Sun, C P

2011-01-01

355

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

Science.gov (United States)

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

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

2015-02-12

356

Picosecond Raman investigation of interligand electron transfer in Ruthenium(II) complexes  

Energy Technology Data Exchange (ETDEWEB)

Interligand electron transfer has been investigated in the excited MLCT electronic states of mixed ligand ruthenium(II) polypyridine complexes containing bipyridine, bipyrimidine, and carboxybipyridine. Two-color picosecond Raman spectroscopy has been used to unambiguously establish the vibrational spectrum corresponding to the ligand-localized MLCT states. With these data direct measurements of electron-transfer dynamics are obtained. It is found that interligand electron transfer is complete on a time scale significantly faster than the 30-ps experimental time resolution.

Yabe, T.; Orman, L.K.; Anderson, D.R.; Yu, Soochang; Xu, Xiaobing; Hopkins, J.B. (Louisiana State Univ., Baton Rouge (USA))

1990-09-06

357

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

Science.gov (United States)

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

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

2014-10-20

358

Charge amplification and transfer processes in the gas electron multiplier  

International Nuclear Information System (INIS)

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

359

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

360

Electron-transfer functionality of synthetic coiled-coil metalloproteins  

Scientific Electronic Library Online (English)

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

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

1516-15-01

361

Coincidence spectroscopy of continuum electron transfer in heavy ion collisions  

International Nuclear Information System (INIS)

This paper is devoted to review on the continuum transfer process of heavy ions. The recent experiments at University of Tennessee revealed that the projectile Z dependence for the electron capture to continuum states (ECC) by bare C6+. O8+ and Si14+ in Ne and Ar appeared to follow a velocity independent power law of Z with the exponent of 2.3. The characteristic asymmetry for ECC in bare ions was observed, and the interesting interpretation was presented. Two experimental efforts to test this conjecture are under way. Core shift Rydberg state Auger structure was seen in the energy spectrum of electrons emitted in the forward direction in the collision of O4+ ion on Ar. By means of examining the final charge state of scattered ions in coincidence with ECC electrons, it was found to be possible to quantitatively examine the relative importance of simultaneous, coincidence bound and continuum state capture channels, as compared to the process of continuum state capture alone. A high degree of the correlation between the processes of multiple electron capture into bound and continuum states at the velocity used is suggested. Efforts to provide an answer for a question raised from this suggestion are under way at University of Tennessee. Coincidence experiments concerning K-ionizing ion-atom collision and multiple electron loss to discrete continuum states were performed with the same apparatus as that used for the studies on ECparatus as that used for the studies on ECC and electron loss to the continuum (ELC). (Kato, T.)

362

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 GAC’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

363

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

364

Long-range electron transfer in biomolecules. Tunneling or hopping?  

Science.gov (United States)

Two competing mechanisms are relevant for long-range electron transfer (ET) in biomolecules: direct electron tunneling between donor (D) and acceptor (A), D ? A, and multistep hopping D ? X ? A, where an electron or an electron hole is transiently localized on intermediate sites X. Which of these mechanisms dominates the ET reaction is determined by the arrangement and electronic properties of the redox centers. For thermal ET, it is shown that single-step tunneling is overcome by hopping when the energy gap E between D and X is smaller than the crossover barrier E(C), E(C) = (?G/2) + (3/4)k(B)T?R(DA), where ?G is the driving force, ? the decay parameter, and R(DA) the donor-acceptor distance. In proteins at T = 300 K, hopping will dominate when E E(C). Thus, one can explore the ET mechanism using three quantities E, ?G, and R(DA). When ?G = 0 and E = 0.5 eV (the difference in redox potentials of D and X is 0.5 V), two-step hopping D ? X ? A will be favored at R(DA) >25 Å. In protein ET chains, the distance between redox cofactors is often smaller than 20 Å, but the gap E between the cofactors and surrounding amino acid residues is larger than 0.5 eV. Therefore, ET in the systems should occur by single-step tunneling D ? A. In the activationless regime (?G ? -?, ? is the reorganization energy) often observed for photoinduced ET, the crossing point energy is determined by E(C) = (2?kT?R(DA))(1/2) - ?. The suggested expressions for the threshold barrier may be useful to predict the ET mechanism in natural and artificial redox systems. PMID:21923189

Voityuk, Alexander A

2011-10-27

365

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

366

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

Science.gov (United States)

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

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

2015-02-10

367

Correlation properties of surface and percolation transfer of electrons  

International Nuclear Information System (INIS)

In this work was received equation, connecting correlatively properties of surface with electrons distribution function. Usually for equilibrium is necessary a large number of collisions. Collisions are 'destroying' correlations. In case rare collisions large importance have correlations and 'memory' effects. Non-Markov's character of emitting particles by surface lead to strongly nonequilibrium condition of 'gas'. Here kinetic equation of diffusive form does not apply. Classical kinetic equation are described only conditions near to equilibrium. This work offers to use ideas anomal diffusion in phase-space. The correlation properties of surface describe by correlations of velocities of emitting electrons: B(t). We offer to use functional equation for probability collision instead of kinetic equation: ?0?0WnoncollF(?) dv = 1 - B(t). This functional allow to consider 'memory' effects. It is important for consideration of electrons and clusters near surfaces. Distribution function become direct connected with correlations. In classical Kubo-Mory theory of transfer is necessary to get nondivergences integral: D ? ?0?B(t). In considering case we can use even 'power function'. It was used 'slow' correlation function as Kohlraush in calculations. The information about kinetics and correlations properties are containing in one functional equation. It was received solution of this equation in form Levy function: F(?) ? 1/?? exp(-1/?). The solution of this form can not be get with help asymptotic methods of kinetic theory. Asymptotics of solution have scale-invariant character F(V) ? 1/V?. This indicate on fractal properties phase-space. (author)

368

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

Science.gov (United States)

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

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

2014-08-19

369

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

370

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

371

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.

372

Interfacial Fermi Loops from Interfacial Symmetries  

Science.gov (United States)

We propose a concept of interfacial symmetries such as interfacial particle-hole symmetry and interfacial time-reversal symmetry, which appear in interfaces between two regions related to each other by particle-hole or time-reversal transformations. These symmetries result in novel dispersion of interface states. In particular, for the interfacial particle-hole symmetry, the gap closes along a loop ("Fermi loop") at the interface. We numerically demonstrate this for the Fu-Kane-Mele tight-binding model. We show that the Fermi loop originates from a sign change of a Pfaffian of a product between the Hamiltonian and a constant matrix.

Takahashi, Ryuji; Murakami, Shuichi

2014-12-01

373

Quantum Dynamics of Electron Transfer from Bacteriochlorophyll to Pheophytin in Bacterial Reaction Centers  

OpenAIRE

Abstract: We extend our previous works on the early electron-transfer steps in bacterial photosynthetic reaction centers to the dynamics of electron transfer from the bacteriochlorophyll anion to pheophytin. The approach employed here takes into account the whole set of normal coordinates of the acceptor and donor groups, in order to reliably account both for shifts and mixing of the normal coordinates and for changes in vibrational frequencies upon electron transfer. It is shown that intramo...

Borrelli, R.; Di Donato, M.; Peluso, A.

2007-01-01

374

Characterization of electron transfer dissociation in the Orbitrap Velos HCD cell.  

OpenAIRE

Electron transfer dissociation (ETD) is commonly employed in ion traps utilizing rf fields that facilitate efficient electron transfer reactions. Here, we explore performing ETD in the HCD collision cell on an Orbitrap Velos instrument by applying a static DC gradient axially to the rods. This gradient enables simultaneous three dimensional, charge sign independent, trapping of cations and anions, initiating electron transfer reactions in the center of the HCD cell where oppositely charged io...

Frese, Ck; Nolting, D.; Altelaar, Af; Griep-raming, J.; Mohammed, S.; Heck, Aj

2013-01-01

375

A stochastic reorganizational bath model for electronic energy transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Fujita, Takatoshi, E-mail: tfujita@fas.harvard.edu, E-mail: aspuru@chemistry.harvard.edu; Huh, Joonsuk; Aspuru-Guzik, Alán, E-mail: tfujita@fas.harvard.edu, E-mail: aspuru@chemistry.harvard.edu [Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138 (United States)

2014-06-28

376

A stochastic reorganizational bath model for electronic energy transfer  

International Nuclear Information System (INIS)

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

377

Strong electronic correlations in superconducting organic charge transfer salts  

CERN Document Server

We review the role of strong electronic correlations in quasi--two-dimensional organic charge transfer salts such as (BEDT-TTF)$_2X$, (BETS)$_2Y$ and $\\beta'$-[Pd(dmit)$_2$]$_2Z$. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerised and is described by a half-filled Hubbard model; the second class is not strongly dimerised and is described by a quarter filled extended Hubbard model. We argue that these models capture the essential physics of these materials. We explore the phase diagram of the half-filled quasi--two-dimensional organic charge transfer salts, focusing on the metallic and superconducting phases. We review work showing that the metallic phase, which has both Fermi liquid and `bad metal' regimes, is described both quantitatively and qualitatively by dynamical mean field theory (DMFT). The phenomenology of the superconducting state is still a matter of contention. We critically review the experimental si...

Powell, B J; Kenzie, Ross H. Mc

2006-01-01

378

Faradaic impedance titration and control of electron transfer of 1-(12-mercaptododecyl)imidazole monolayer on a gold electrode  

International Nuclear Information System (INIS)

In this work, we studied interfacial proton transfer of the self-assembled monolayer (SAM) of 1-(12-mercaptododecyl)imidazole on a gold electrode by faradaic impedance titration method with Fe(CN)63- as an anionic redox probe molecule. The surface pK1/2 was found to be 7.3, which was nearly the same as that of 1-alkylimidazole in solution. We also investigated the electrochemical properties of the SAM-modified electrode by cyclic voltammetry. Cyclic voltammetry was performed (1) in the solution containing Fe(CN)63- with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN)63- and (2) in the acidic or basic electrolyte containing Ru(NH3)63+ as a cationic redox probe to verify the effect of the polarity of a redox probe. We observed the reversible adsorption/desorption of Fe(CN)63- and concluded that the adsorbed Fe(CN)63- catalyzed the electron transfer of both Fe(CN)63- itself and cationic Ru(NH3)63+

379

Kinetic analysis of electron transfer across single water-microdroplet/oil and oil-microdroplet/water interfaces.  

Science.gov (United States)

Using techniques comprising laser trapping, microcapillary injection/manipulation, fluorescence microspectroscopy and electrochemistry of single microdroplets, we kinetically investigated the electron transfer (ET) reaction between decamethylferrocene in tributyl phosphate and hexacyanoferrate(III) in water. In the oil-microdroplet/water system, the overall ET reaction rate significantly depended on the droplet radius (r(d), 0.5 microm reaction rate constant determined in the water-microdroplet (r(d) = 21 microm)/oil system agreed very well with that in the oil-microdroplet (r(d) > 2 microm)/water system. The rate constant values were extremely small in the Gibbs free energy (DeltaG) range of -10 to -25 kJ mol(-1), with DeltaG consisting of the Galvani potential difference between the water and oil phases and the redox potential difference of the solutes. The characteristic ET reaction was discussed in terms of the ion transfer and the ET across the interfacial mixed layer with nanometer-sized thickness. PMID:19212051

Nakatani, Kiyoharu; Uchino, Mitsuharu; Suzuki, Shingo; Negishi, Takayuki; Osakai, Toshiyuki

2009-02-01

380

Dynamic modulation of electron correlation by intramolecular modes in charge transfer compounds  

OpenAIRE

Electron-phonon and electron-electron interactions are in competition in determining the properties of molecular charge transfer conductors and superconductors. The direct influence of phonons on the electron-electron interaction was not before considered and in the present work the coupling of intramolecular modes to electron-electron interaction (U-vib interaction) is investigated.The effect of this coupling on the frequency of the normal modes of a dimer model is obtained...

Meneghetti, M.

1999-01-01

381

Poly (3,4-ethylenedioxythiophene) promotes direct electron transfer at the interface between Shewanella loihica and the anode in a microbial fuel cell  

Science.gov (United States)

Anode modification is an effective method for enhancing extracellular electron transportation and improving the power density of microbial fuel cells (MFCs). In this study, a new conductive polymer called poly (3,4-ethylenedioxythiophene) (PEDOT) is electrochemically polymerized to modify the anode. The surface of the electrochemically polymerized PEDOT layer has a widespread porous structure. Both the anode electrochemical discharge experiment and MFC discharge test demonstrate the improved performance of the PEDOT-modified anode compared with a plain anode. Cyclic voltammetry and electrochemical impedance spectroscopy analyses show that the PEDOT modification increases the availability of redox active sites and reduces the interfacial electron transfer resistance of the anode. Compared with the unmodified anode, the PEDOT anodic modification improves the power density by 43%-140 mW m-2. Possible mechanisms are proposed to help understand the function of the PEDOT-modified anodic layer.

Liu, Xing; Wu, Wenguo; Gu, Zhongze

2015-03-01

382

Electron transfer in peptides: on the formation of silver nanoparticles.  

Science.gov (United States)

Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag(+) ions bound by peptides with histidine as the Ag(+) -binding amino acid and tyrosine as photoinducible electron donor cannot be reduced to Ag nanoparticles (AgNPs) under ET conditions because the peptide prevents the aggregation of Ag atoms to form AgNPs. Only in the presence of chloride ions, which generate AgCl microcrystals in the peptide matrix, does the synthesis of AgNPs occur. The reaction starts with the formation of 100?nm Ag@AgCl/peptide nanocomposites which are cleaved into 15?nm AgNPs. This defined transformation from large nanoparticles into small ones is in contrast to the usually observed Ostwald ripening processes and can be followed in detail by studying time-resolved UV/Vis spectra which exhibit an isosbestic point. PMID:25663127

Kracht, Sonja; Messerer, Matthias; Lang, Matthieu; Eckhardt, Sonja; Lauz, Miriam; Grobéty, Bernard; Fromm, Katharina M; Giese, Bernd

2015-03-01

383

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

Science.gov (United States)

Chemical electron transfer-induced fragmentation of a variety of electron donors was shown to be a quite general process. In previous studies, attention was focused on alpha-Beta aminoalcohols and 1,2-ditertiary amines. In the present year, studies were extended to include pinacols, an richer variety of diamines and amino-ketones. The mechanisms, intermediates involved in these fragmentation reactions, and medium effects were also studied. Studies of pinacols and a variety of diamines show that photooxidative cleavage of 1,2-diheteroatom-containing molecules is a very general process which can occur for several different types of molecules. In order to demonstrate clearly that cation radicals of the heteroatom containing donor can be intermediates in these reactions, the reaction was studied of several different donors with the acceptors, dicyanoanthracene (DCA) and tetracyanoanthracene (TCA) using biphenyl (BP) as a cosensitizer. The second major focus of the work was to look at donors which, undergo reversible redox reactions to give relatively high energy products which are capable of undergoing clean thermal reverse redox reactions but which survive long enough to be potentially useful for other purposes. The reaction explored extensively is the oxidation of tertiary amines to enamines by quinone type molecules such as beta-lapachone. These studies are continued and other reactions are examined which may be more promising in terms of finding a photochemical-thermal redox cycle which can be carried out with little loss of material through competing side reactions.

Whitten, D. G.

1990-10-01

384

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

385

Dynamic modeling of interfacial structures via interfacial area transport equation  

International Nuclear Information System (INIS)

Full text of publication follows:In the current thermal-hydraulic system analysis codes using the two-fluid model, the empirical correlations that are based on the two-phase flow regimes and regime transition criteria are being employed as closure relations for the interfacial transfer terms. Due to its inherent shortcomings, however, such static correlations are inaccurate and present serious problems in the numerical analysis. In view of this, a new dynamic approach employing the interfacial area transport equation has been studied. The interfacial area transport equation dynamically models the two-phase flow regime transitions and predicts continuous change of the interfacial area concentration along the flow field. Hence, when employed in the thermal-hydraulic system analysis codes, it eliminates artificial bifurcations stemming from the use of the static flow regime transition criteria. Therefore, the interfacial area transport equation can make a leapfrog improvement in the current capability of the two-fluid model from both scientific and practical point of view. Accounting for the substantial differences in the transport phenomena of various sizes of bubbles, the two-group interfacial area transport equations have been developed. The group 1 equation describes the transport of small-dispersed bubbles that are either distorted or spherical in shapes, and the group 2 equation describes the transport of large cap, slug or churn-turbulent bubbles. The source and s churn-turbulent bubbles. The source and sink terms in the right hand-side of the transport equations have been established by mechanistically modeling the creation and destruction of bubbles due to major bubble interaction mechanisms. The coalescence mechanisms include the random collision driven by turbulence, and the entrainment of trailing bubbles in the wake region of the preceding bubble. The disintegration mechanisms include the break-up by turbulence impact, shearing-off at the rim of large cap bubbles and the break-up of large cap bubbles due to surface instability. In the present paper, the interfacial area transport equations currently available are reviewed to address the feasibility and reliability of the model. Results from extensive benchmark experiments for the model evaluation are also present. These include the data from adiabatic upward air-water two-phase flow in round tubes of various sizes, from a rectangular duct, and from adiabatic co-current downward air-water two-phase flow in round pipes of two different sizes. Furthermore, some guidelines for the future study on interfacial area transport equation are discussed. (authors)

386

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

Science.gov (United States)

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

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

2014-12-16

387

Photoinduced electron transfer from aliphatic amines to coumarin dyes  

Science.gov (United States)

Electron transfer (ET) interactions of a series of 7-aminocoumarin dyes with aliphatic amine donors have been investigated using steady-state (SS) and time-resolved (TR) fluorescence quenching, picosecond laser flash photolysis (LFP) and pulse radiolysis (PR) techniques. For different coumarin-amine pairs, the estimated quenching constants (kq) from SS and TR fluorescence measurements are found to be similar within the experimental error. That ET from amine donors to excited (S1) coumarin dyes takes place has been established from the LFP and the PR results. For different coumarin-amine pairs, the kq values are seen to correlate well with the free energy changes (?G0) for the ET reactions following Marcus' outer-sphere ET theory. The total reorganization energy (?) estimated from this correlation is seen to be just similar to the solvent reorganization energy (?s). The leveled-off kq value under diffusion-controlled condition (kqDC) appears to be much lower (˜2.5 times) for the present systems compared to the corresponding value obtained for the ET reactions in coumarin-aromatic amine systems. The large difference in the kqDC values with aliphatic and aromatic amines as the electron donors has been rationalized on the basis of the shapes of the highest occupied molecular orbitals (HOMO) of the amine donors. For aliphatic amines, since their HOMOs are largely localized on the amino group, a large orientation factor is involved in the encounter complexes for the ET reaction to take place. With ? like HOMOs, such orientational restriction is just nominal with the aromatic amines as the electron donors. Present ET results under diffusive conditions have also been discussed with a comparison to the ET rates observed under nondiffusive conditions, where the amines are directly used as the solvent donors.

Nad, Sanjukta; Pal, Haridas

2002-01-01

388

Electron transfer in keV-energy 4He++ atomic collisions. I. Single and double electron transfer with He, Ar, H2, and N2  

International Nuclear Information System (INIS)

Single- and double-electron-transfer cross sections have been measured for a 4He++ beam incident on thin He, Ar, H2, and N2 gas targets over the energy range 15--125 keV. Comparison with previous 3He++ experimental results is made at the same incident particle velocity. For He++ collisions with He, we find good agreement with the theory for double electron transfer, but conclude that the single-electron-transfer cross section is far from being understood. Interpretation of the data in terms of simple theoretical ideas indicates that capture into excited states of the He+ ion can be the dominant single-electron-transfer process in some keV-energy He++ atomic collisions

389

Bimolecular processes on silica gel surfaces: energetic factors in determining electron-transfer rates.  

Science.gov (United States)

Triplet state and radical cation formation is observed following laser excitation of anthracene, phenanthrene and naphthalene (and their derivatives) adsorbed on silica gel. Energy- and electron-transfer reactions of these compounds with co-adsorbed azulene have been studied using a time-resolved diffuse reflectance laser flash photolysis technique. Triplet energy transfer from the arene derivative to azulene and electron transfer from azulene to the arene radical cation have been investigated in order to distinguish between diffusional and energetic control in these systems. Energy and electron transfer can be studied independently due to differing absorption properties and energy dependencies of production of the triplet states and radical cations. Transient decay kinetics for both electron and energy transfer have been modelled using two different rate constant distributions: a log Gaussian and a symmetrical Levy stable distribution. The latter model has also been demonstrated to be applicable to the decay of radical cations in the absence of an electron donor, which cannot be adequately described by the Gaussian model. Energy-transfer rates between the arene derivatives and azulene have been found to be close to the diffusion-controlled limit; however, in most cases, the rate of electron transfer is considerably lower. A correlation between the bimolecular rate constant and free energy of electron transfer has been found, indicating a Marcus inverted region. Compounds with bulky substituents show a further reduction in the rate of electron transfer, suggesting that an additional steric factor is involved in this process. PMID:14743281

Worrall, David R; Kirkpatrick, Iain; Williams, Sian L

2004-01-01

390

From charge transfer to electron transfer in halogen-bonded complexes of electrophilic bromocarbons with halide anions.  

Science.gov (United States)

Experimental and computational studies of the halogen-bonded complexes, [R-Br, X(-)], of bromosubstituted electrophiles, R-Br, and halide anions, X(-), revealed that decrease of a gap between the frontier orbitals of interacting species led to reduction of the energy of the optical charge-transfer transition and to increase in the ground-state charge transfer (X(-) ? R-Br) in their associates. These variations were accompanied by weakening of the intramolecular, C-Br, and strengthening of the intermolecular, BrX(-), bonds. In the limit of the strongest electron donor-acceptor pairs, formation of the halogen-bonded complexes was followed by the oxidation of iodide to triiodide, which took place despite the fact that the I(-) ? R-Br electron-transfer step was highly endergonic and the calculated outer-sphere rate constant was negligibly small. However, the calculated barrier for the inner-sphere electron transfer accompanied by the halogen transfer, R-BrI(-) ? R?Br-I(-)?, was nearly 24 kcal mol(-1) lower as compared to that calculated for the outer-sphere process and the rate constant of such reaction was consistent with the experimental kinetics. A dramatic decrease of the electron-transfer barriers (leading to 18-orders of magnitude increase of the rate constant) was related to the strong electronic coupling of the donor and acceptor within the halogen-bonded precursor complex, as well as to the lower solvent reorganization energy and the successor-complex stabilization. PMID:25591991

Rosokha, Sergiy V; Traversa, Alfredo

2015-02-01

391

A new mechanism for electron transfer in fast ion-atomic collisions  

OpenAIRE

We discuss a new mechanism for the electron capture in fast ion-atom collisions. Similarly like in the radiative capture, where the electron transfer occurs due to photon emission, within the mechanism under consideration the electron capture takes place due to the emission of an additional electron. This first order capture process leads to the so called transfer-ionization and has a number of interesting features, in particular, in the target frame it results in the electr...

Voitkiv, A. B.; Najjari, B.; Ullrich, J.

2008-01-01

392

Coherent transfer of light polarization to electron spins in a semiconductor  

OpenAIRE

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

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

2007-01-01

393

Interfacial phenomenon theory  

International Nuclear Information System (INIS)

This book is composed of 8 chapters. It tells what interfacial phenomenon is by showing interfacial energy, characteristic of interface and system of interface from chapter 1. It also introduces interfacial energy and structure theory, molecular structure and orientation theory, and interfacial electricity phenomenon theory in the following 3 chapters. It still goes on by introducing super molecule cluster, disequilibrium dispersion, and surface and film through 3 chapters. And the last chapter is about colloid and application of interface.

394

Overpotential-induced lability of the electronic overlap factor in long-range electrochemical electron transfer: charge and distance dependence  

DEFF Research Database (Denmark)

Long-distance electrochemical electron transfer exhibits approximately exponential dependence on the electron transfer distance. On the basis of a jellium model of the metal surface we show that the slope of the logarithm of the current vs. the transfer distance also depends strongly on the electrode charge. The slope is smaller the more negative the charge density due to enhanced extension of the surface electronic density profile on the solution side, and thereby better electronic overlap with the reacting molecule. The effect is sensitive to the bulk electron density of the metal and the localization of the electronic state at the molecular reactant site. Effects similar to these have been observed experimentally and could be common for electronically light metals.

Kornyshev, A. A.; Kuznetsov, A. M.

2000-01-01

395

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

396

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

397

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

398

Strong electronic correlations in superconducting organic charge transfer salts  

International Nuclear Information System (INIS)

We review the role of strong electronic correlations in quasi-two-dimensional organic charge transfer salts such as (BEDT-TTF)2X (BETS)2Y, and ?'-(Pd(dmit)2)2Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerized and is described by a half-filled Hubbard model; the second class is not strongly dimerized and is described by a quarter-filled extended Hubbard model. We argue that these models capture the essential physics of these materials. We explore the phase diagram of the half-filled quasi-two-dimensional organic charge transfer salts, focusing on the metallic and superconducting phases. We review work showing that the metallic phase, which has both Fermi liquid and 'bad metal' regimes, is described both quantitatively and qualitatively by dynamical mean field theory (DMFT). The phenomenology of the superconducting state is still a matter of contention. We critically review the experimental situation, focusing on the key experimental results that may distinguish between rival theories of superconductivity, particularly probes of the pairing symmetry and measurements of the superfluid stiffness. We then discuss some strongly correlated theories of superconductivity, in particular the resonating valence bond (RVB) theory of superconductivity. We conclude by discussing some of the major challenges currently facing the field. Thesellenges currently facing the field. These include parameterizing minimal models, the evidence for a pseudogap from nuclear magnetic resonance (NMR) experiments, superconductors with low critical temperatures and extremely small superfluid stiffnesses, the possible spin-liquid states in ?-(ET)2Cu2(CN)3 and ?'-[Pd(dmit)2]2Z, and the need for high quality large single crystals. (topical review)

399

Strong electronic correlations in superconducting organic charge transfer salts  

Energy Technology Data Exchange (ETDEWEB)

We review the role of strong electronic correlations in quasi-two-dimensional organic charge transfer salts such as (BEDT-TTF){sub 2}X (BETS){sub 2}Y, and {beta}'-(Pd(dmit){sub 2}){sub 2}Z. We begin by defining minimal models for these materials. It is necessary to identify two classes of material: the first class is strongly dimerized and is described by a half-filled Hubbard model; the second class is not strongly dimerized and is described by a quarter-filled extended Hubbard model. We argue that these models capture the essential physics of these materials. We explore the phase diagram of the half-filled quasi-two-dimensional organic charge transfer salts, focusing on the metallic and superconducting phases. We review work showing that the metallic phase, which has both Fermi liquid and 'bad metal' regimes, is described both quantitatively and qualitatively by dynamical mean field theory (DMFT). The phenomenology of the superconducting state is still a matter of contention. We critically review the experimental situation, focusing on the key experimental results that may distinguish between rival theories of superconductivity, particularly probes of the pairing symmetry and measurements of the superfluid stiffness. We then discuss some strongly correlated theories of superconductivity, in particular the resonating valence bond (RVB) theory of superconductivity. We conclude by discussing some of the major challenges currently facing the field. These include parameterizing minimal models, the evidence for a pseudogap from nuclear magnetic resonance (NMR) experiments, superconductors with low critical temperatures and extremely small superfluid stiffnesses, the possible spin-liquid states in {kappa}-(ET){sub 2}Cu{sub 2}(CN){sub 3} and {beta}'-[Pd(dmit){sub 2}]{sub 2}Z, and the need for high quality large single crystals. (topical review)

Powell, B J; McKenzie, Ross H [Department of Physics, University of Queensland, Brisbane, Queensland 4072 (Australia)

2006-11-15