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1

Photosensitized electron transfer reactions in organized interfacial systems  

Energy Technology Data Exchange (ETDEWEB)

The separation of photoproducts formed in photosensitized electron transfer reactions is essential for efficient energy conversion and storage. The organization of the components involved in the photoinduced process in interfacial systems leads to efficient compartmentalization of the products. Several interfacial systems, e.g., lipid bilayer membranes (vesicles), water-in-oil microemulsions and a solid SiO/sub 2/ colloidal interface, were designed to accomplish this goal. An electron transfer across a lipid bilayer membrane leading to the separation of the photoproducts at opposite sides of the membrane is facilitated by establishing a transmembrane potential and organizing the cotransport of cations with specific carriers. Colloidal SiO/sub 2/ particles provide a charged interface that interacts with charged photoproducts. By designing a system that results in oppositely charged photoproducts, a retardation of recombination by the charged interface can be produced. The photosensitized reduction of a neutral acceptor by positively charged sensitizers is described. The reactions are substantially enhanced in the SiO/sub 2/ colloid compared with in the homogeneous phase. The effect of the SiO/sub 2/ interface is attributed to a high surface potential that results in the separation of the intermediate photoproducts. The quantum yields of the photosensitized reactions are correlated with the interfacial surface potential and the electrical effects of other charged interfaces such as micelles are compared with those of SiO/sub 2/. The possible utilization of the energy stored in the stabilized photoproducts in further chemical reactions is discussed. Special attention is given to the photodecomposition of water.

Calvin, M.; Willner, I.; Laane, C.; Otvos, W.

1981-01-01

2

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

Directory of Open Access Journals (Sweden)

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

C. A. Bignozzi; M. Alebbi; E. Costa; C. J. Kleverlaan; R. Argazzi; G. J. Meyer

1999-01-01

3

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

UK PubMed Central (United Kingdom)

We have used hafnium metallocene compounds as cathode interfacial layers for organic solar cells [OSCs]. A metallocene compound consists of a transition metal and two cyclopentadienyl ligands coordinated in a sandwich structure. For the fabrication of the OSCs, poly[3,4-ethylenedioxythiophene]:poly(styrene sulfonate), poly(3-hexylthiophene-2,5-diyl) + 66-phenyl C61 butyric acid methyl ester, bis-(ethylcyclopentadienyl)hafnium(IV) dichloride, and aluminum were deposited as a hole transport layer, an active layer, a cathode interfacial layer, and a cathode, respectively. The hafnium metallocene compound cathode interfacial layer improved the performance of OSCs compared to that of OSCs without the interfacial layer. The current density-voltage characteristics of OSCs with an interfacial layer thickness of 0.7 nm and of those without an interfacial layer showed power conversion efficiency [PCE] values of 2.96% and 2.34%, respectively, under an illumination condition of 100 mW/cm2 (AM 1.5). It is thought that a cathode interfacial layer of an appropriate thickness enhances the electron transfer between the active layer and the cathode, and thus increases the PCE of the OSCs.

Park K; Oh S; Jung D; Chae H; Kim H; Boo JH

2012-01-01

4

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

Energy Technology Data Exchange (ETDEWEB)

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 multilayers studied were fabricated by magnetron sputtering and consist of bilayers from 1.9 mn to 3.3 mn. X-ray diffraction, cross-section TEM and plan-view TEM show the Cu layers to have a BCC structure Cu in contrast to its equilibrium FCC structure. 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 confirm the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr.

Bello, A.F.; Van Buuren, T.; Kepesis, J.E.; Barbee, T.W., Jr.

1998-04-01

5

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

Energy Technology Data Exchange (ETDEWEB)

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 support the presence of charge transfer and indicate that it is localized to the first two interfacial layers in both Cu and Cr.

Barbee, T W; Bello, A F; Klepeis, J E; Van Buuren, T

1999-07-01

6

Long-range interfacial electron transfer of metalloproteins based on molecular wiring assemblies.  

Science.gov (United States)

We address some physical features associated with long-range interfacial electron transfer (ET) of metalloproteins in both electrochemical and electrochemical scanning tunneling microscopy (ECSTM) configurations, which offer a brief foundation for understanding of the ET mechanisms. These features are illustrated experimentally by new developments of two systems with the blue copper protein azurin and enzyme nitrite reductase as model metalloproteins. Azurin and nitrite reductase were assembled on Au(111) surfaces by molecular wiring to establish effective electronic coupling between the redox centers in the proteins and the electrode surface for ET and biological electrocatalysis. With such assemblies, interfacial ET proceeds through chemically defined and well oriented sites and parallels biological ET. In the case of azurin, the ET properties can be characterized comprehensively and even down to the single-molecule level with direct observation of redox-gated electron tunnelling resonance. Molecular wiring using a pi-conjugated thiol is suitable for assembling monolayers of the enzyme with catalytic activity well-retained. The catalytic mechanism involves multiple-ET steps including both intramolecular and interfacial processes. Interestingly, ET appears to exhibit a substrate-gated pattern observed preliminarily in both voltammetry and ECSTM. PMID:16512372

Chi, Qijin; Zhang, Jingdong; Jensen, Palle S; Christensen, Hans E M; Ulstrup, Jens

2006-01-01

7

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

8

Interfacial electrochemical electron transfer in biology - towards the level of the single molecule.  

UK PubMed Central (United Kingdom)

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 J; Chi Q; Hansen AG; Jensen PS; Salvatore P; Ulstrup J

2012-03-01

9

Interfacial electrochemical electron transfer in biology - towards the level of the single molecule.  

Science.gov (United States)

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. PMID:22024483

Zhang, Jingdong; Chi, Qijin; Hansen, Allan G; Jensen, Palle S; Salvatore, Princia; Ulstrup, Jens

2011-10-20

10

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

UK PubMed Central (United Kingdom)

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.

Bauer C; Teuscher J; Brauer JC; Punzi A; Marchioro A; Ghadiri E; De Jonghe J; Wielopolski M; Banerji N; Moser JE

2011-01-01

11

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

12

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

UK PubMed Central (United Kingdom)

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

Peter L

2009-11-01

13

Dependence of the direct electron transfer activity and adsorption kinetics of cytochrome c on interfacial charge properties.  

Science.gov (United States)

With the advantages of in situ analysis and high surface sensitivity, surface-enhanced infrared absorption spectroscopy in attenuated total reflection mode (ATR-SEIRAS) combined with electrochemical methods has been employed to examine the interfacial direct electron transfer activity and adsorption kinetics of cytochrome c (cyt c). This work presents data on cyt c adsorption onto negatively charged mercaptohexanoic acid (MHA) and positively charged 6-amino-1-hexanethiol (MHN) self-assembled monolayers (SAMs) on gold nanofilm surfaces. The adsorbed cyt c displays a higher apparent electron transfer rate constant (33.5 ± 2.4 s(-1)) and apparent binding rate constant (73.1 ± 5.2 M(-1) s(-1)) at the MHA SAMs surface than those on the MHN SAMs surface. The results demonstrate that the surface charge density determines the protein adsorption kinetics, while the surface charge character determines the conformation and orientation of proteins assembled which in turn affects the direct electron transfer activity. PMID:23912152

Wang, Gui-Xia; Wang, Min; Wu, Zeng-Qiang; Bao, Wen-Jing; Zhou, Yue; Xia, Xing-Hua

2013-10-01

14

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 dete...

Bauer, Christophe; Teuscher, Joël; Brauer, Jan Cornelius; Punzi, Angela; Marchioro, Arianna; Ghadiri, Elham; De Jonghe, Jelissa

15

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 dete...

Bauer, C; Teuscher, J; Brauer, JC; Punzi, A; Marchioro, A; Ghadiri, E

16

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

17

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

18

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

UK PubMed Central (United Kingdom)

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

Taguchi T; Ni L; Irie H

2013-04-01

19

Interfacial electrochemical electron transfer processes in bacterial biofilm environments on Au(111).  

UK PubMed Central (United Kingdom)

We have studied Streptococcus mutans (S. mutans) biofilm 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(NH(3))(6)](3+/2+), [Co(terpy)(2)](3+/2+), terpy = 2,2',2''-terpyridine) or negative ([Fe(CN)(6)](3-/4-), [IrCl(6)](3-/4-)) electrostatic charge. [Co(NH(3))(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(NH(3))(6)](3+/2+) and the homologous compound [Co(NH(3))(6)](3+/2+) were the only probe compounds to effect growth inhibition. On the other hand, cyclic voltammetry (CV) of both [Ru(NH(3))(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 [IrCl(6)](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 treatment of the biofilm covered Au(111)-electrode surface partly restores planar diffusion CV of [Fe(CN)(6)](3-/4-) and [IrCl(6)](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 Y; Zhang J; Ulstrup J

2010-06-01

20

Interfacial electrochemical electron transfer processes in bacterial biofilm environments on Au(111).  

Science.gov (United States)

We have studied Streptococcus mutans (S. mutans) biofilm 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(NH(3))(6)](3+/2+), [Co(terpy)(2)](3+/2+), terpy = 2,2',2''-terpyridine) or negative ([Fe(CN)(6)](3-/4-), [IrCl(6)](3-/4-)) electrostatic charge. [Co(NH(3))(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(NH(3))(6)](3+/2+) and the homologous compound [Co(NH(3))(6)](3+/2+) were the only probe compounds to effect growth inhibition. On the other hand, cyclic voltammetry (CV) of both [Ru(NH(3))(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 [IrCl(6)](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 treatment of the biofilm covered Au(111)-electrode surface partly restores planar diffusion CV of [Fe(CN)(6)](3-/4-) and [IrCl(6)](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. PMID:20334394

Hu, Yifan; Zhang, Jingdong; Ulstrup, Jens

2010-06-01

 
 
 
 
21

Orientational control over nitrite reductase on modified gold electrode and its effects on the interfacial electron transfer.  

UK PubMed Central (United Kingdom)

Recently, studies have been reported in which fluorescently labeled redox proteins have been studied with a combination of spectroscopy and electrochemistry. In order to understand the effect of the dye on the protein-electrode interaction, voltammetry and surface analysis have been performed on protein films of dye-labeled and unlabeled forms of a cysteine-surface variant (L93C) and the wild type (wt) of the copper containing nitrite reductase (NiR) from Alcaligenes faecalis S6. The protein has been adsorbed onto gold electrodes modified with self-assembled monolayers (SAMs) made up of 6-mercaptohexanol (6-OH) and mixtures of various octanethiols. Electrochemical and surface-analytical techniques were utilized to explore the influence of the SAM composition on wt and L93C NiR enzyme activity and the orientation of the enzyme molecules with respect to the electrode/SAM. The unlabeled L93C NiR enzyme is only electroactive on mixed SAMs composed of positive 8-aminooctanethiol (8-NH(2)) and 8-mercaptooctanol (8-OH). No enzymatic activity is observed on SAMs consisting of pure 6-OH, 8-OH, or pure 8-NH(2). Modification of L93C NiR with the ATTO 565 dye resulted in enzymatic activity on SAMs of 6-OH, but not on SAMs of 8-OH. Quartz crystal microbalance with dissipation measurements show that well-ordered and rigid protein films (single orientation of the protein) are formed when NiR is electroactive. By contrast, electrode-NiR combinations for which no electrochemical activity is observed still have NiR adsorbed on the surfaces, but a less-structured and water-rich film is formed. For the unlabeled L93C NiR, bilayer formation is observed, suggesting that the Cys93 residue is orientated away from the surface and able to form disulfide bridges to a second layer of L93C NiR. The results indicate that interfacial electron transfer is only possible if the negatively charged surface patch surrounding the electron-entry site of NiR is directed toward the electrode. This can be achieved either by introducing positive charges in the SAM or, when the SAM does not carry a charge, by labeling the enzyme with an ATTO 565 dye, which has some hydrophobic character, close to the electron entry site of the NiR.

Krzemi?ski L; Cronin S; Ndamba L; Canters GW; Aartsma TJ; Evans SD; Jeuken LJ

2011-11-01

22

Orientational control over nitrite reductase on modified gold electrode and its effects on the interfacial electron transfer.  

Science.gov (United States)

Recently, studies have been reported in which fluorescently labeled redox proteins have been studied with a combination of spectroscopy and electrochemistry. In order to understand the effect of the dye on the protein-electrode interaction, voltammetry and surface analysis have been performed on protein films of dye-labeled and unlabeled forms of a cysteine-surface variant (L93C) and the wild type (wt) of the copper containing nitrite reductase (NiR) from Alcaligenes faecalis S6. The protein has been adsorbed onto gold electrodes modified with self-assembled monolayers (SAMs) made up of 6-mercaptohexanol (6-OH) and mixtures of various octanethiols. Electrochemical and surface-analytical techniques were utilized to explore the influence of the SAM composition on wt and L93C NiR enzyme activity and the orientation of the enzyme molecules with respect to the electrode/SAM. The unlabeled L93C NiR enzyme is only electroactive on mixed SAMs composed of positive 8-aminooctanethiol (8-NH(2)) and 8-mercaptooctanol (8-OH). No enzymatic activity is observed on SAMs consisting of pure 6-OH, 8-OH, or pure 8-NH(2). Modification of L93C NiR with the ATTO 565 dye resulted in enzymatic activity on SAMs of 6-OH, but not on SAMs of 8-OH. Quartz crystal microbalance with dissipation measurements show that well-ordered and rigid protein films (single orientation of the protein) are formed when NiR is electroactive. By contrast, electrode-NiR combinations for which no electrochemical activity is observed still have NiR adsorbed on the surfaces, but a less-structured and water-rich film is formed. For the unlabeled L93C NiR, bilayer formation is observed, suggesting that the Cys93 residue is orientated away from the surface and able to form disulfide bridges to a second layer of L93C NiR. The results indicate that interfacial electron transfer is only possible if the negatively charged surface patch surrounding the electron-entry site of NiR is directed toward the electrode. This can be achieved either by introducing positive charges in the SAM or, when the SAM does not carry a charge, by labeling the enzyme with an ATTO 565 dye, which has some hydrophobic character, close to the electron entry site of the NiR. PMID:21939276

Krzemi?ski, Lukasz; Cronin, Samuel; Ndamba, Lionel; Canters, Gerard W; Aartsma, Thijs J; Evans, Stephen D; Jeuken, Lars J C

2011-10-10

23

Interfacial stress transfer in graphene oxide nanocomposites.  

UK PubMed Central (United Kingdom)

Raman spectroscopy has been used for the first time to monitor interfacial stress transfer in poly(vinyl alcohol) nanocomposites reinforced with graphene oxide (GO). The graphene oxide nanocomposites were prepared by a simple mixing method and casting from aqueous solution. They were characterized using scanning electron microscopy, X-ray diffraction, and polarized Raman spectroscopy and their mechanical properties determined by tensile testing and dynamic mechanical thermal analysis. It was found that GO was fully exfoliated during the nanocomposite preparation process and that the GO nanoplatelets tended align in the plane of the films. The stiffness and yield stress of the nanocomposites were found to increase with GO loading but the extension to failure decreased. It was shown that the Raman D band at ~1335 cm(-1) downshifted as the nanocomposites were strained as a result of the interfacial stress transfer between the polymer matrix and GO reinforcement. From knowledge of the Grüneisen parameter for graphene, it was possible to estimate the effective Young's modulus of the GO from the Raman D band shift rate per unit strain to be of the order of 120 GPa. A similar value of effective modulus was found from the tensile mechanical data using the "rule of mixtures" that decreased with GO loading. The accepted value of Young's modulus for GO is in excess of 200 GPa and it is suggested that the lower effective Young's modulus values determined may be due to a combination of finite flake dimensions, waviness and wrinkles, aggregation, and misalignment of the GO flakes.

Li Z; Young RJ; Kinloch IA

2013-01-01

24

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1982-01-01

25

Interfacial charge transfer absorption: Application to metal-molecule assemblies  

International Nuclear Information System (INIS)

[en] Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features, but has been only rarely observed experimentally. Interfacial charge transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here, we utilize a previously published model [C. Creutz, B.S. Brunschwig, N. Sutin, J. Phys. Chem. B 109 (2005) 10251] to predict IFCTA spectra of metal-molecule assemblies and compare the literature observations to these predictions. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that IFCTA is not detectable. However, few experiments designed to detect IFCTA have been done. We suggest approaches to optimizing the conditions for observing the process

2006-05-09

26

Hydrated interfacial ions and electrons.  

UK PubMed Central (United Kingdom)

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

Abel B

2013-01-01

27

Autonomous Control of Interfacial Electron Transfer and the Activation of DNA Machines by an Oscillatory pH System.  

UK PubMed Central (United Kingdom)

An oscillatory pH system is implemented to drive oscillatory pH-switchable DNA machines and to control pH-stimulated electron transfer at electrode surfaces. The oscillatory pH system drives the autonomous opening and closure of DNA tweezers and activates a DNA pendulum by the pH-stimulated formation and dissociation of i-motif structures. Also, a sequence-programmed nucleic acid monolayer-functionalized electrode undergoes autonomous oscillatory pH transitions between random coil and i-motif configurations, leading to the control of electron transfer at electrode surfaces.

Qi XJ; Lu CH; Liu X; Shimron S; Yang HH; Willner I

2013-10-01

28

Autonomous Control of Interfacial Electron Transfer and the Activation of DNA Machines by an Oscillatory pH System.  

UK PubMed Central (United Kingdom)

A pH oscillatory system is implemented to drive oscillatory pH-switchable DNA machines and to control pH-stimulated electron transfer at electrode surfaces. The oscillatory pH system drives the autonomous opening and closure of DNA tweezers and activates a DNA pendulum by the pH-stimulated formation and dissociation of i-motif structures. Also, a sequence-programmed nucleic acid monolayer-functionalized electrode undergoes autonomous pH oscillatory transitions between random coil and i-motif configurations, leading to the control of electron transfer at electrode surfaces.

Qi XJ; Lu CH; Liu X; Shimron S; Yang H; Willner I

2013-08-01

29

Interfacial bond-breaking electron transfer in mixed water-ethylene glycol solutions: reorganization energy and interplay between different solvent modes.  

UK PubMed Central (United Kingdom)

We explore solvent dynamics effects in interfacial bond breaking electron transfer in terms of a multimode approach and make an attempt to interpret challenging recent experimental results (the nonmonotonous behavior of the rate constant of electroreduction of S2O8(2-) from mixed water-EG solutions when increasing the EG fraction; see Zagrebin, P.A. et al. J. Phys. Chem. B 2010, 114, 311). The exact expansion of the solvent correlation function (calculated using experimental dielectric spectra) in a series predicts the splitting of solvent coordinate in three independent modes characterized by different relaxation times. This makes it possible to construct a 5D free-energy surface along three solvent coordinates and one intramolecular degree of freedom describing first electron transfer at the reduction of a peroxodisulphate anion. Classical molecular dynamics simulations were performed to study the solvation of a peroxodisulphate anion (S2O8(2-)) in oxidized and reduced states in pure water and ethylene glycol (EG) as well as mixed H2O-EG solutions. The solvent reorganization energy of the first electron-transfer step at the reduction of S2O8(2-) was calculated for several compositions of the mixed solution. This quantity was found to be significantly asymmetric. (The reorganization energies of reduction and oxidation differ from each other.) The averaged reorganization energy slightly increases with increasing the EG content in solution. This finding clearly indicates that for the reaction under study the static solvent effect no longer competes with solvent dynamics. Brownian dynamics simulations were performed to calculate the electron-transfer rate constants as a function of the solvent composition. The results of the simulations explain the experimental data, at least qualitatively.

Ismailova O; Berezin AS; Probst M; Nazmutdinov RR

2013-07-01

30

Approach to interfacial and intramolecular electron transfer of the diheme protein cytochrome c4 assembled on Au(111) surfaces.  

UK PubMed Central (United Kingdom)

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 c(4) 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 Q; Zhang J; Arslan T; Borg L; Pedersen GW; Christensen HE; Nazmudtinov RR; Ulstrup J

2010-04-01

31

Approach to interfacial and intramolecular electron transfer of the diheme protein cytochrome c4 assembled on Au(111) surfaces.  

Science.gov (United States)

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 c(4) 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. PMID:20359200

Chi, Qijin; Zhang, Jingdong; Arslan, Taner; Borg, Lotte; Pedersen, Gert W; Christensen, Hans E M; Nazmudtinov, Renat R; Ulstrup, Jens

2010-04-29

32

Interfacial transfer in annular dispersed flow  

International Nuclear Information System (INIS)

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

1982-09-03

33

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

34

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

2012-09-06

35

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

UK PubMed Central (United Kingdom)

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.

Achey D; Ardo S; Meyer GJ

2012-09-01

36

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

International Nuclear Information System (INIS)

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

2010-01-01

37

Photosensitized electron transfer processes in SiO/sub 2/ colloids and sodium lauryl sulfate micellar sytems: correlation of quantum yields with interfacial surface potentials  

Energy Technology Data Exchange (ETDEWEB)

The effectiveness of negatively charged colloidal SiO/sub 2/ particles in controlling photosensitized electron transfer reactions has been studied and compared with that of the negatively charged sodium lauryl sulfate (NaLauSO/sub 4/) micellar system. In particular, the photosensitized reduction of the zwitterionic electron acceptor propylviologen sulfonate (PVS/sup 0/) with tris(2,2'-bi-pyridinium)ruthenium(II) (Ru(bipy)/sub 3//sup 2 +/) as the sensitizer and triethanolamine as the electron donor is found to have a quantum yield of 0.033 for formation of the radical anion (PVS) in the SiO/sub 2/ colloid compared with 0.005 in the homogeneous system and 0.0086 in a NaLauSO/sub 4/ micellar solution. The higher quantum yields obtained with the SiO/sub 2/ colloidal system are attributed to substantial stabilization against back reaction of the intermediate photoproducts - i.e., Ru(bipy)/sub 3//sup 3 +/ and PVS/sup -/ - by electrostatic repulsion of the reduced electron acceptor from the negatively charged particle surface. The binding properties of the SiO/sub 2/ particles and NaLauSO/sub 4/ micelles were investigated by flow dialysis. The results show that the sensitizer binds to both interfaces and that the SiO/sub 2/ interface is characterized by much higher surface potential than the micellar interface. The effect of ionic strength on the surface potential was estimated from the Gouy-Chapman theory, and the measured quantum yields of photosensitized electron transfer were correlated shows that the quantum yield is not affected by surface potentials smaller than approx. = -40 mV. At larger potentials, the quantum yield increases rapidly. These results indicate that the surface potential is the dominant factor in the quantum yield improvement for PVS/sup 0/ reduction.

Laane, C. (Agricultural Univ., Wageningen, Netherlands); Willner, I.; Otvos, J.W.; Calvin, M.

1981-10-01

38

Multidimensional mechanistic modeling of interfacial heat and mass transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Shaver, D. R.; Antal, S. P.; Podowski, M. Z. [Center for Multiphase Research, Rensselaer Polytechnic Inst., Troy, NY (United States)

2012-07-01

39

The role of interfacial charge transfer-type interactions in the decay of plasmon excitations in metal nanoparticles.  

UK PubMed Central (United Kingdom)

This perspective describes the influence of interfacial charge transfer-type interactions on the optical spectra and hot electron cooling processes in plasmonic nanoparticles (NPs), and ongoing work to optimize these interactions for charge extraction from the plasmon or hot electron state. The manuscript focuses on interfaces of metal NPs with organic molecules and with semiconductors. Charge extraction from multi-electron excited states has applications in photodetection, sensing, and conversion of solar energy to electricity and fuels.

Aruda KO; Tagliazucchi M; Sweeney CM; Hannah DC; Weiss EA

2013-05-01

40

Interfacial heat transfer in countercurrent flows of steam and water  

International Nuclear Information System (INIS)

[en] A study was conducted to examine the departure from equilibrium conditions with respect to direct contact condensation. A simple analytical model, which used an equilibrium factor, K, was derived. The model was structured to represent the physical dimensions of a nuclear reactor downcomer annulus, water subcooling, wall temperature, and water flow rate. In a two step process the model was first used to isolate the average interfacial heat transfer coefficient from vertical countercurrent steam/water data of Cook et al., with the aid of a Stanton number correlation. In the second step the model was assessed by regeneration of measured steam flow rates in the experiments by Cook et al., and an additional experiment of Kim. This report documents the analytical model, the derived Stanton number correlation, and the comparison of the calculated and measured steam flow rates by which the accuracy of the model was assessed

1987-01-01

 
 
 
 
41

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.

2005-09-15

42

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1999-09-30

43

Ultrafast interfacial charge transfer dynamics in dye-sensitized and quantum dot solar cell  

Science.gov (United States)

Dye sensitized solar cell (DSSC) appeared to be one of the good discovery for the solution of energy problem. We have been involved in studying ultrafast interfacial electron transfer dynamics in DSSC using femtosecond laser spectroscopy. However it has been realized that it is very difficult to design and develop higher efficient one, due to thermodynamic limitation. Again in DSSC most of the absorbed photon energy is lost as heat within the cell, which apart from decreasing the efficiency also destabilizes the device. It has been realized that quantum dot solar cell (QDSC) are the best bet where the sensitizer dye molecules can be replaced by suitable quantum dot (QD) materials in solar cell. The quantum-confinement effect in semiconductors modifies their electronic structure, which is a very important aspect of these materials. For photovoltaic applications, a long-lived charge separation remains one of the most essential criteria. One of the problems in using QDs for photovoltaic applications is their fast charge recombination caused by nonradiative Auger processes, which occur predominantly at lower particle sizes due to an increase in the Coulomb interaction between electrons and holes. Various approaches, such as the use of metal-semiconductor composites, semiconductor-polymer composite, and semiconductor core-shell heterostructures, have been attempted to minimize the fast recombination between electrons and holes. To make higher efficient solar devices it has been realised that it is very important to understand charge carrier and electron transfer dynamics in QD and QD sensitized semiconductor nanostructured materials. In the present talk, we are going to discuss on recent works on ultrafast electron transfer dynamics in dye-sensitized TiO2 nanoparticles/film [1-12] and charge (electron/hole) transfer dynamics in quantum dot core-shell nano-structured materials [13-17].

Ghosh, Hirendra N.

2013-02-01

44

Nonadiabatic anharmonic electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-03-28

45

Nonadiabatic anharmonic electron transfer  

Science.gov (United States)

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

Schmidt, P. P.

2013-03-01

46

Protein electron transfer: Dynamics and statistics.  

UK PubMed Central (United Kingdom)

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 DV

2013-07-01

47

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

48

Study on heat transfer and interfacial stability in supersonic steam injector  

International Nuclear Information System (INIS)

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

2008-01-01

49

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

UK PubMed Central (United Kingdom)

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

Pursell MR; Mendes-Tatsis MA; Stuckey DC

2003-03-01

50

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

Science.gov (United States)

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

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

51

Core-concrete molten pool dynamics and interfacial heat transfer  

International Nuclear Information System (INIS)

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

1980-10-12

52

Vibrational promotion of electron transfer.  

UK PubMed Central (United Kingdom)

By using laser methods to prepare specific quantum states of gas-phase nitric oxide molecules, we examined the role of vibrational motion in electron transfer to a molecule from a metal surface free from the complicating influence of solvation effects. The signature of the electron transfer process is a highly efficient multiquantum vibrational relaxation event, where the nitrogen oxide loses hundreds of kilojoules per mole of energy on a subpicosecond time scale. These results cannot be explained simply on the basis of Franck-Condon factors. The large-amplitude vibrational motion associated with molecules in high vibrational states strongly modulates the energetic driving force of the electron transfer reaction. These results show the importance of molecular vibration in promoting electron transfer reactions, a class of chemistry important to molecular electronics devices, solar energy conversion, and many biological processes.

Huang Y; Rettner CT; Auerbach DJ; Wodtke AM

2000-10-01

53

Simultaneous spectroscopic and topographic near-field imaging of TiO2 single surface states and interfacial electronic coupling.  

UK PubMed Central (United Kingdom)

We have probed single surface states and the involved interfacial charge transfer coupling on the TiO(2) surface using confocal as well as tip-enhanced near-field topographic-spectroscopic imaging analysis on a niobium-doped rutile TiO(2)(110) surface. The confocal images excited with a radially polarized donut mode render ring-shaped excitation patterns typical for quantum systems with two perpendicular transition dipole moments. The tip-enhanced near-field optical images of single surface states are visualized by the strong exciton plasmon-polariton coupling localized at the subdomain boundaries with a spatial resolution of ?15 nm (far beyond the optical diffraction limit). We suggest that the abundant surface states in the doped TiO(2) generate excitons under laser excitation which are strongly coupled to the surface plasmon-polaritons of the Au tip. Moreover, the interfacial electronic molecule-substrate coupling has been characterized by probing the molecule-perturbed surface states distribution and the associated specific Raman vibrational modes. The imaging and characterization of the surface states and their distributions on TiO(2) surfaces at nanoscale are critically relevant to a deep understanding of interfacial electron transfer dynamics and energetics involving in solar energy conversion, photocatalysis, and mechanistic understanding of surface-enhanced Raman scattering spectroscopy.

Sevinc PC; Wang X; Wang Y; Zhang D; Meixner AJ; Lu HP

2011-04-01

54

Simultaneous spectroscopic and topographic near-field imaging of TiO2 single surface states and interfacial electronic coupling.  

Science.gov (United States)

We have probed single surface states and the involved interfacial charge transfer coupling on the TiO(2) surface using confocal as well as tip-enhanced near-field topographic-spectroscopic imaging analysis on a niobium-doped rutile TiO(2)(110) surface. The confocal images excited with a radially polarized donut mode render ring-shaped excitation patterns typical for quantum systems with two perpendicular transition dipole moments. The tip-enhanced near-field optical images of single surface states are visualized by the strong exciton plasmon-polariton coupling localized at the subdomain boundaries with a spatial resolution of ?15 nm (far beyond the optical diffraction limit). We suggest that the abundant surface states in the doped TiO(2) generate excitons under laser excitation which are strongly coupled to the surface plasmon-polaritons of the Au tip. Moreover, the interfacial electronic molecule-substrate coupling has been characterized by probing the molecule-perturbed surface states distribution and the associated specific Raman vibrational modes. The imaging and characterization of the surface states and their distributions on TiO(2) surfaces at nanoscale are critically relevant to a deep understanding of interfacial electron transfer dynamics and energetics involving in solar energy conversion, photocatalysis, and mechanistic understanding of surface-enhanced Raman scattering spectroscopy. PMID:21375338

Sevinc, Papatya C; Wang, Xiao; Wang, Yuanmin; Zhang, Dai; Meixner, Alfred J; Lu, H Peter

2011-03-04

55

Role of surface stoichiometry on the interfacial electron behavior at Ni/TiO2(0 0 1) interfaces  

International Nuclear Information System (INIS)

Highlights: ? Surface stoichiometry affects the interfacial charge re-distribution. ? Separation of electron–hole pairs depends on surface stoichiometry. ? Oxidization state of Ni depends on the initial conditions of the TiO2 surface. ? Insulator-to-metal transition affects the binding energies. - Abstract: The interfacial properties of Ni clusters grown on the stoichiometric and reduced rutile TiO2(0 0 1) surfaces were investigated by means of X-ray photoelectron spectroscopy (XPS). The binding energies (BE's) of elements from both overlayers and substrates were found to be affected by the formation of interfacial dipole. Regardless of the TiO2 surface stoichiometry, the Ni 2p3/2 BE's move monotonically toward lower value with the increase of Ni thickness due to the cluster size effect. However, the Ni 2p3/2 BE shift is much smaller on reduced TiO2(0 0 1) surfaces compared to that on the annealed stoichiometric surface. For stoichiometric and lightly reduced TiO2 surfaces, O 1s BE's exhibit an unexpected upward shift with increasing Ni thickness below 2 ?, and then downward shift to lower BE's when the Ni thickness increases further. This opposite tendency is attributed to the insulator-to-metal transition. On heavily reduced surface, only monotonically downward shift of the O 1s BE's was observed with the increase of Ni thickness. The different behaviors are well elucidated by collective contributions of interfacial charge transfer and image charge effect.

2012-04-16

56

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2006-08-15

57

Interfacial polarization and internal electron tunneling effect on dielectric properties of multilayer polymer films  

Science.gov (United States)

Due to large contrasts in dielectric constant and volumetric conductivity, Maxwell-Wagner-Sillars interfacial polarization is observed in poly(vinylidene fluoride) (PVDF) based multilayer films. This interfacial polarization is helpful to enhance the breakdown strength of multilayer films, because they serve as electron traps to prevent hot electron thermal runaway. In this study, the relationship between volumetric resistivity and internal electron tunneling in polysulfone (PSF)/(PVDF) multilayer film is reported. In general, resistivity decreases with decreasing the thickness of the insulating PSF layer. This is attributed to the internal electron tunneling in thin PSF layers. As a result, the electron-hole neutralization via the PSF layer decreases the interfacial polarization in the PVDF layer, resulting in a lower volumetric resistivity.

Tseng, Jung-Kai; Zhou, Zheng; Mackey, Matt; Carr, Joel; Baer, Eric; Zhu, Lei

2013-03-01

58

Interfacial charge-transfer switch: ruthenium-dppz compounds anchored to nanocrystalline TiO2.  

Science.gov (United States)

The compound Ru(bpy)2(dppz-R)(PF6)2, where bpy is 2,2'-bipyridine and dppz-R is 11-(diethoxyphosphorylmethyl)dipyrido[3,2-a:2',3'-c]phenazine, was prepared and anchored to mesoporous nanocrystalline (anatase) TiO2 thin films as a probe of the effects of interfacial water on excited-state charge transfer processes at semiconductor interfaces. In nitrogen-saturated fluid acetonitrile, the Ru(bpy)2(dppz-R)(PF6)2 compound was found to be highly photoluminescent. Water was found to quench the excited state by a mechanism adequately described by the Perrin model, from which the radius of quenching was abstracted, 75 +/- 2 A. The Ru(bpy)2(dppz-R)(PF6)2 compounds were found to bind to the TiO2 thin films in high surface coverages, 5 x 10(-8) mol cm(-2). When these films were immersed in acetonitrile, long-lived excited states (tau = 825 ns) that were quenched by the addition of water were observed. About 30% of the excited states could not be quenched by water. Efficient electron injection, phi(inj) = 0.8, was observed after light excitation of Ru(bpy)2(dppz-R)/TiO2 in a 0.1 M LiClO4/acetonitrile solution. The addition of large concentrations of water, >0.5 M, was found to decrease the injection yield to phi(inj) = 0.3. PMID:16841970

Delgadillo, Alvaro; Arias, Mauricio; Leiva, Ana Maria; Loeb, Bárbara; Meyer, Gerald J

2006-07-24

59

Gap formation and interfacial heat transfer in alloy 718 investment castings  

Energy Technology Data Exchange (ETDEWEB)

Investment casting foundries increasingly rely on numerical simulations of their casting processes to enhance quality and reduce costs. An important aspect of numerical simulations is the interfacial heat transfer between the solidifying metal and the mold. The contact conductance varies during solidification as the mold expands and the metal shrinks, leading to the formation of a gap and significantly reduced contact conductance. Very little data are available for the estimation of contact conductance, especially for the superalloys used in the aerospace industry. This work reports on experimental and numerical results for the determination of contact conductance for an axi-symmetric casting of alloy 718. The heat transfer code TOPAZ2D in conjunction with Beck`s method was used for the numerical simulation of this inverse heat transfer problem. The effects of variation of mold properties and thermocouple locations on contact conductance are considered. A relationship between the varying interfacial heat transfer and the formation of gaps is also examined and compared to actual measured values determined by X-ray radiography.

Sahai, V.; Overfelt, R.A. [Auburn Univ., AL (United States). Space Power Inst.

1995-12-31

60

Interfacial area and interfacial transfer in two-phase flow systems. Annual technical progress report, 1991--1992  

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. (DLC)

Kojasoy, G.

1992-08-01

 
 
 
 
61

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

62

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

63

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-12-31

64

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

65

Problems of back electron transfer in electron transfer sensitization  

Energy Technology Data Exchange (ETDEWEB)

The problems of back electron transfer in electron transfer sensitization were discussed and methods of preventing back electron transfer to improve the quantum efficiency of charge separation in homogeneous systems were proposed. Although complete quenching of an excited sensitizer by an electron donor or acceptor is not difficult, chemical yields of oxidized or reduced species are in general low. The importance of the coulombic effect was demonstrated for benzophenone/leuco crystal violet, pyrene/methylviologen (MV/sup 2 +/)/ethylenediaminetetraacetic acid and phenothiazine/viologen analogue systems. Then the discussion was extended to the quenching of Ru(bpy)/sub 3/sup(2+*) (bpy=2,2'-bipyridine) by organic acceptors and donors in acetonitrile. The magnitude of the quenching constant ksub(q) as a function of exoergicity could be explainable by the Rehm-Weller equation in both cases: ..delta..H/sup + +/ is apparently negative for oxidative quenching (RuL/sub 3/sup(2+*)+A->RuL/sub 3//sup 3 +/+A/sup -/); in contrast, for reductive quenching (RuL/sub 3/sup(2+*)+D->RuL/sub 3//sup +/+D/sup +/) ..delta..H/sup + +/ is normal and controls ksub(q). A detailed kinetic mechanistic study leads to the conclusion that the attraction between RuL/sub 3//sup 3 +/ and A/sup -/ in oxidative quenching brings about back electron transfer to the excited state, and the charge separation yield is found to be lower than that for reductive quenching as would be expected.

Tazuke, Shigeo; Kitamura, Noboru; Kawanishi, Yuji

1985-05-01

66

A model of the interfacial heat-transfer coefficient during unidirectional solidification of an aluminum alloy  

Energy Technology Data Exchange (ETDEWEB)

A model is presented for the prediction of the interfacial heat-transfer coefficient during the unidirectional solidification vertically upward of an Al-7 wt pct Si alloy cast onto a water cooled copper chill. It has been experimentally determined that the casting surfaces were convex toward the chill, probably due to the deformation of the initial solidified skin of the casting. The model was, therefore, based upon a determination of the (macroscopic) nominal contact area between the respective rough surfaces and, within this region, the actual (microscopic) contact between the casting and the chill surfaces. The model produced approximate agreement with both experimentally determined values of the heat-transfer coefficient and the measured curvature of the casting surface and showed a reasonable agreement with measured temperatures in the casting and the chill also. A common experimental technique for the experimental determination of the heat-transfer coefficient involves the assumption of one-dimensional heat transfer only. An implication of the approach adopted in this model is that the heat transfer in the region of the casting-chill interface may be two-dimensional, and the subsequent error in the experimentally determined values is discussed.

Griffiths, W.D.

2000-04-01

67

A mathematical model for interfacial charge transfer at the semiconductor-dye-electrolyte interface of a dye-sensitised solar cell  

Energy Technology Data Exchange (ETDEWEB)

A mathematical model for the interfacial charge transfer within dye-sensitised solar cells (DSC) is presented for the semiconductor-dye-electrolyte interface. The model explicitly accounts for each reaction at the interface involving dye molecules, electrolyte species and adsorbed electrons associated with the conduction band surface states of the semiconductor. Additionally, the model accounts for photoelectron injection via singlet and triplet excited dye states. The governing equations can be used to describe the total current produced by the DSC under illuminated and non-illuminated conditions, at steady state. Regular perturbation methods are applied to the model equations to obtain closed form analytic approximations, resulting in approximate solutions that negate the need for numerical solution of the model system. All parameter values associated with the model are obtained from the literature and from experimental data. The presented numerical results and analytic approximations compare favourably to experimental data, capturing the interfacial characteristics of current versus voltage curves of the DSC. (author)

Penny, Melissa; Farrell, Troy [School of Mathematical Sciences, Queensland University of Technology, Brisbane, Qld. 4001 (Australia); Please, Colin [School of Mathematics, University of Southampton, Southampton SO17 1BJ (United Kingdom)

2008-01-15

68

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

69

Separate Effect Test Assessment about Interfacial Heat Transfer Model and Correlations in SPACE Code  

International Nuclear Information System (INIS)

The development of Safety and Performance Analysis CodE (SPACE) has been in the second period, in which the main goal is a validation. The source terms that are related to the models and correlations are continuously modified in view of the smoothness and robustness after the first stage development. In addition, the solution quality is the next purpose in the second development period. In the second stage, it is focused to assess the physical models and correlations of SPACE code by using the well known SET problems. For the successful SET assessment procedure, a problem selection process has been performed with the leading of KEPRI. KEPRI has listed suitable SET problems according to the individual assessment purpose. The interfacial heat transfer has 3 topic problems to validate: I) MIT ST4, II) Super Moby Dick, III) GE Level Swell. First topic is about the pressurizing condensation. Others are about the choking and flashing

2010-01-01

70

Separate Effect Test Assessment about Interfacial Heat Transfer Model and Correlations in SPACE Code  

Energy Technology Data Exchange (ETDEWEB)

The development of Safety and Performance Analysis CodE (SPACE) has been in the second period, in which the main goal is a validation. The source terms that are related to the models and correlations are continuously modified in view of the smoothness and robustness after the first stage development. In addition, the solution quality is the next purpose in the second development period. In the second stage, it is focused to assess the physical models and correlations of SPACE code by using the well known SET problems. For the successful SET assessment procedure, a problem selection process has been performed with the leading of KEPRI. KEPRI has listed suitable SET problems according to the individual assessment purpose. The interfacial heat transfer has 3 topic problems to validate: I) MIT ST4, II) Super Moby Dick, III) GE Level Swell. First topic is about the pressurizing condensation. Others are about the choking and flashing

Bae, Sung Won; Lee, Seung Wook; Kim, Kyung Du [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

2010-10-15

71

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

UK PubMed Central (United Kingdom)

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 CO(2) to CO. A remarkable selectivity for CO(2) over H(+) was observed by stopped-flow UV-vis spectroscopy of [Re(bipy-tBu)(CO)(3)](-1). The reaction with CO(2) 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 d(z)(2), which is believed to determine selectivity by favoring CO(2) (? + ?) 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 -CO(2) 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 JM; Benson EE; Kumar B; Grice KA; Seu CS; Miller AJ; Mayer JM; Kubiak CP

2012-09-01

72

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

73

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

Science.gov (United States)

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 CO(2) to CO. A remarkable selectivity for CO(2) over H(+) was observed by stopped-flow UV-vis spectroscopy of [Re(bipy-tBu)(CO)(3)](-1). The reaction with CO(2) 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 d(z)(2), which is believed to determine selectivity by favoring CO(2) (? + ?) 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 -CO(2) 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. PMID:22652573

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

2012-05-31

74

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-10-15

75

Environmental Effects on Photoinduced Electron Transfer Reactions.  

Science.gov (United States)

Photoinduced electron transfer reactions between an electronically excited photosensitizer molecule and a reversible electron acceptor capable of hydrogen production were studied to determine the possible utility of these reactions in solar energy convers...

T. E. Casti

1985-01-01

76

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-10-22

77

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

78

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

79

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

UK PubMed Central (United Kingdom)

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.

Yoon SM; Lou SJ; Loser S; Smith J; Chen LX; Facchetti A; Marks T

2012-12-01

80

Light induced electron transfer of metal complexes  

International Nuclear Information System (INIS)

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

1992-01-01

 
 
 
 
81

Coupled electron transfers in artificial photosynthesis.  

Science.gov (United States)

Light-induced charge separation in molecular assemblies has been widely investigated in the context of artificial photosynthesis. Important progress has been made in the fundamental understanding of electron and energy transfer and in stabilizing charge separation by multi-step electron transfer. In the Swedish Consortium for Artificial Photosynthesis, we build on principles from the natural enzyme photosystem II and Fe-hydrogenases. An important theme in this biomimetic effort is that of coupled electron-transfer reactions, which have so far received only little attention. (i) Each absorbed photon leads to charge separation on a single-electron level only, while catalytic water splitting and hydrogen production are multi-electron processes; thus there is the need for controlling accumulative electron transfer on molecular components. (ii) Water splitting and proton reduction at the potential catalysts necessarily require the management of proton release and/or uptake. Far from being just a stoichiometric requirement, this controls the electron transfer processes by proton-coupled electron transfer (PCET). (iii) Redox-active links between the photosensitizers and the catalysts are required to rectify the accumulative electron-transfer reactions, and will often be the starting points of PCET. PMID:17954432

Hammarström, Leif; Styring, Stenbjörn

2008-03-27

82

Electron transfer reactions in condensed phases  

Energy Technology Data Exchange (ETDEWEB)

Despite the multitude of formalisms, there is general agreement that the crux of the electron transfer problem is the change in equilibrium nuclear configurations that occurs when a molecule or ion gains or loses an electron. In recent developments attention has been focused on the dynamics of these nuclear configuration changes, and, in addition, on the electronic factors, determining the electron transfer rate. In parallel with these theoretical developments there have been a large number of experimental studies. These studies have not only elucidated the factors determining electron transfer rates, but have in many cases directly tested the theories and suggested modifications to the theories where appropriate. It is impossible in an article such as this to cover the entire area of electron transfer reactions. Instead the authors shall concentrate on those aspects of the problem in which they are particularly interested. Steady-state schemes for the diffusion, activation, and electron transfer steps in bimolecular reactions are discussed first. This is followed by a description in terms of Born-Oppenheimer states and surfaces and a discussion of the classical, semiclassical, and quantum mechanical formalisms. Recent experimental studies bearing on the questions raised are presented in the final section. Throughout the discussion to localized or trapped systems is restricted, specifically to systems in which the electronic interaction of the initial and final states is sufficiently small so that the electron transfer can be described in terms of the electronic properties of the unperturbed reactants and products.

Newton, M.D.; Sutin, N.

1984-01-01

83

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.

1997-01-01

84

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

2012-12-03

85

Electron-transfer reactions of excited states  

Energy Technology Data Exchange (ETDEWEB)

Powerful models exist for the prediction and analysis of excited state outer-sphere electron transfer reactivity. Important parameters in these models are the driving force for the electron transfer and the electron exchange rate of the excited state couple. The driving force for excited state electron transfer is determined by the reduction potentials of the excited state and of its reaction partner, and the reduction potential of the excited state can be estimated from its excitation energy and the corresponding ground state reduction potential or from the free energy dependence of its reactions with characterized couples. The electron exchange rate of the excited state couple can be estimated from analogies with ground state exchanges or from the rates of its reactions with characterized reaction partners. The free energy dependences of quenching and back reactions are determined by the competition of elementary electron transfer steps and diffusional processes. Detailed analyses of these dependences can provide nearly unique information about the individual electron transfer steps - information that is crucial to the understanding of the factors determining quenching rates in particular systems and to the manipulation of photochemical yields. The relations between ground state and excited state electron transfer reactions of transition metal complexes, particularly of the polypyridine complexes, are discussed.

Sutin, N.; Creutz, C.

1983-10-01

86

Electron transfer rates for asymmetric reactions  

CERN Document Server

We use a numerically exact real-time path integral Monte Carlo scheme to compute electron transfer dynamics between two redox sites within a spin-boson approach. The case of asymmetric reactions is studied in detail in the least understood crossover region between nonadiabatic and adiabatic electron transfer. At intermediate-to-high temperature, we find good agreement with standard Marcus theory, provided dynamical recrossing effects are captured. The agreement with our data is practically perfect when temperature renormalization is allowed. At low temperature we find peculiar electron transfer kinetics in strongly asymmetric systems, characterized by rapid transient dynamics and backflow to the donor.

Mühlbacher, L

2004-01-01

87

Multistep electron transfer processes on dye co-sensitized nanocrystalline TiO2 films.  

UK PubMed Central (United Kingdom)

We report a method for achieving multilayer co-sensitization of nanocrystalline TiO2 films. The method is based upon an aluminum isopropoxide treatment of the monosensitized film prior to deposition of a second sensitizer. Appropriate selection of sensitizer dyes allows vectorial, multistep, electron transfer processes, resulting in a suppression of interfacial charge recombination and a significantly improved photovoltaic device performance relative to single-layer co-sensitization devices.

Clifford JN; Palomares E; Nazeeruddin MK; Thampi R; Grätzel M; Durrant JR

2004-05-01

88

Nuclear reorganization barriers to electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-01-01

89

Vectorial electron transfer in spatially ordered arrays  

Energy Technology Data Exchange (ETDEWEB)

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

Fox, M.A.

1993-02-01

90

Dynamics of electron transfer in amine photooxidation  

Energy Technology Data Exchange (ETDEWEB)

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

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

1980-08-13

91

Hierarchical control of electron-transfer  

DEFF Research Database (Denmark)

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

Westerhoff, Hans V.; Jensen, Peter Ruhdal

1997-01-01

92

Photoinduced electron transfer reactions through dendrimer architecture  

Energy Technology Data Exchange (ETDEWEB)

Herein we report the first photoreactive dendritic metalloporphyrin having noncovalently assembled electron-acceptor molecules on the exterior surface and describe a long-range photoinduced electron transfer through dendrimer architecture. Here, water-soluble dendritic zinc porphyrins with two different numbers of generations ([KO{sub 2}C]{sub 2(n+1)}LnPZn, n = 2, 4) were newly synthesized. In conclusion the long-range photoinduced electron transfer through an aryl ether dendrimer framework was demonstrated for a water-soluble dendritic zinc porphyrin bearing noncovalently assembled electron-acceptor molecules on the exterior surface. 14 refs., 2 figs., 1 tab.

Sadamoto, Reiko; Tomioka, Nobuyuki; Aida, Takuzo [Univ. of Tokyo (Japan)

1996-04-24

93

Long-range electron transfer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Recent investigations have shed much light on the nuclear and electronic factors that control the rates of long-range electron tunneling through molecules in aqueous and organic glasses as well as through bonds in donor–bridge–acceptor complexes. Couplings through covalent and hydrogen bonds are muc...

Gray, Harry B.; Winkler, Jay R.

94

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

95

Determination of the interfacial heat transfer coefficient h in unidirectional heat flow by Beck`s non linear estimation procedure  

Energy Technology Data Exchange (ETDEWEB)

In the numerical simulation of casting solidification, the thermal behavior of the casting/mold interface is characterized by the interfacial heat transfer coefficient, `h`. The determination of h is difficult as it involves the solution of the Inverse Heat Conduction Problem (IHCP). One of the satisfactory solution procedures for solving the IHCP is the Beck`s non linear estimation procedure. In this work, this procedure has been used successfully by the authors for the determination of h in steady state unidirectional heat flow.

Krishnan, M. [Regional Engineering Coll., Tamil Nadu (India). Dept. of Metallurgical Engineering; Sharma, D.G.R. [Indian Inst. of Tech., Tamil Nadu (India). Dept. of Metallurgical Engineering

1996-03-01

96

Single Molecule Spectroscopy of Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Michael Holman; Ling Zang; Ruchuan Liu; David M. Adams

2009-10-20

97

Decoupling Interfacial Reactions between Plasmas and Liquids: Charge Transfer vs Plasma Neutral Reactions.  

UK PubMed Central (United Kingdom)

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.

Rumbach P; Witzke M; Sankaran RM; Go DB

2013-10-01

98

Interfacial ultramorphology evaluation of resin luting cements to dentin: A correlative scanning electron microscopy and transmission electron microscopy analysis.  

UK PubMed Central (United Kingdom)

The objective of this study was to analyze the dentin-resin cements interfacial ultramorphologies using two different methods: scanning (SEM) and transmission electron microscopy (TEM). Four commercial products were evaluated: two conventional cementing system (RelyX ARC/Adper™ Scotchbond™ Multi-Purpose Plus, 3M ESPE and Clearfil Esthetic Cement/DC Bond, Kuraray) and two self-adhesive resin cements (RelyX Unicem, 3M ESPE and Clearfil SA Cement, Kuraray). Prepolymerized resin disks (Sinfony, 3M ESPE) were cemented on oclusal dentin surfaces of 24 third human molars, simulating the indirect restorations. After 24 h, teeth were sectioned into 0.9-mm thick slabs and processed for microscopy analyses (SEM or TEM/ n = 3). Qualitative characterization of dentin-resin cement interface was performed. Hybrid layer formation with long and dense resin tags was observed only for RelyX ARC cementing system. Clearfil Esthetic Cement/DC Bond system revealed few and short resin tags formation, whereas no hybridization and resin tags were detected for self-adhesive resin cements. Some interfacial regions exhibited that the self-adhesive resin cements were not bonded to dentin, presenting bubbles or voids at the interfaces. In conclusion, TEM and SEM bonding interface analyses showed ultramorphological variations among resin cements, which are directly related to dental bonding strategies used for each resin cement tested. Microsc. Res. Tech., 2013. © 2013 Wiley Periodicals, Inc.

Aguiar TR; Vermelho PM; André CB; Giannini M

2013-09-01

99

Bioinspired electron-transfer systems and applications  

International Nuclear Information System (INIS)

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

2006-01-01

100

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1991-12-01

 
 
 
 
101

Kinetic selectivity of interfacial processes  

Energy Technology Data Exchange (ETDEWEB)

Exciton dissociation and electron transfer (ET) processes are being investigated at solid-solid interfaces between highly-ordered films of liquid crystal porphyrin and redox polymers. Both species possess (approximately) discrete electronic energy levels; thus, theory predicts that interfacial ET reactions will be governed by the Franck-Condon overlap, in contrast to the more usual case where one side of the interface possesses a continuum of energy levels. This overlap may be employed to kinetically select for a desired reaction (forward ET) while inhibiting undesired reactions (hole transfer, recombination). Evidence for kinetic selectivity is observed: in systems where a thermodynamic treatment predicts a maximum photovoltage of +450 mV, the observed value is {minus}1015 mV, demonstrating the dominant nature of the interfacial effects. The efficiency and polarity of exciton dissociation can be controlled by varying the formal potential of the redox polymer.

Gregg, B.A.; Kim, Y.I. [National Renewable Energy Laboratory, Golden, CO (United States)

1993-12-31

102

Toward exceeding the Shockley-Queisser limit: photoinduced interfacial charge transfer processes that store energy in excess of the equilibrated excited state.  

Science.gov (United States)

Nanocrystalline (anatase), mesoporous TiO2 thin films were functionalized with [Ru(bpy)2(deebq)](PF6)2, [Ru(bq)2(deeb)](PF6)2, [Ru(deebq)2(bpy)](PF6)2, [Ru(bpy)(deebq)(NCS)2], or [Os(bpy)2(deebq)](PF6)2, where bpy is 2,2'-bipyridine, bq is 2,2'-biquinoline, and deeb and deebq are 4,4'-diethylester derivatives. These compounds bind to the nanocrystalline TiO2 films in their carboxylate forms with limiting surface coverages of 8 (+/- 2) x 10(-8) mol/cm2. Electrochemical measurements show that the first reduction of these compounds (-0.70 V vs SCE) occurs prior to TiO2 reduction. Steady state illumination in the presence of the sacrificial electron donor triethylamine leads to the appearance of the reduced sensitizer. The thermally equilibrated metal-to-ligand charge-transfer excited state and the reduced form of these compounds do not inject electrons into TiO2. Nanosecond transient absorption measurements demonstrate the formation of an extremely long-lived charge separated state based on equal concentrations of the reduced and oxidized compounds. The results are consistent with a mechanism of ultrafast excited-state injection into TiO2 followed by interfacial electron transfer to a ground-state compound. The quantum yield for this process was found to increase with excitation energy, a behavior attributed to stronger overlap between the excited sensitizer and the semiconductor acceptor states. For example, the quantum yields for [Os(bpy)2(dcbq)]/TiO2 were phi(417 nm) = 0.18 +/- 0.02, phi(532.5 nm) = 0.08 +/- 0.02, and phi(683 nm) = 0.05 +/- 0.01. Electron transfer to yield ground-state products occurs by lateral intermolecular charge transfer. The driving force for charge recombination was in excess of that stored in the photoluminescent excited state. Chronoabsorption measurements indicate that ligand-based intermolecular electron transfer was an order of magnitude faster than metal-centered intermolecular hole transfer. Charge recombination was quantified with the Kohlrausch-Williams-Watts model. PMID:16787088

Hoertz, Paul G; Staniszewski, Aaron; Marton, Andras; Higgins, Gerard T; Incarvito, Christopher D; Rheingold, Arnold L; Meyer, Gerald J

2006-06-28

103

Enhanced electron transfer in Penning gases  

Energy Technology Data Exchange (ETDEWEB)

We present the discovery of the enhanced transfer of electrons produced in avalanches through metal grids in Penning gas mixtures. Measurements are presented showing the enhancement which is particularly dramatic at very low transfer fields. With electric fields on either side of the grid in the ratio of 0.015 the transfer ratio is 0.11, representing an increase of a factor of 7 over that predicted and observed in a conventional gas by Bunemann et al. (1949). We propose a model for this phenomenon and we show that both a uniform electric field and the Penning effect are necessary for this transfer to occur. We also identify a possible reason why other workers have not obtained similar results in Penning mixtures. The application of this 'Penning transfer' to a position sensitive X-ray detector (the Penning Gas Imager or PGI) is discussed.

Schwarz, H.E.; Thornton, J.; Mason, I.M. (University Coll., London (UK). Mullard Space Science Lab.)

1984-08-15

104

Enhanced electron transfer in Penning gases  

International Nuclear Information System (INIS)

We present the discovery of the enhanced transfer of electrons produced in avalanches through metal grids in Penning gas mixtures. Measurements are presented showing the enhancement which is particularly dramatic at very low transfer fields. With electric fields on either side of the grid in the ratio of 0.015 the transfer ratio is 0.11, representing an increase of a factor of 7 over that predicted and observed in a conventional gas by Bunemann et al. (1949). We propose a model for this phenomenon and we show that both a uniform electric field and the Penning effect are necessary for this transfer to occur. We also identify a possible reason why other workers have not obtained similar results in Penning mixtures. The application of this 'Penning transfer' to a position sensitive X-ray detector (the Penning Gas Imager or PGI) is discussed. (orig.).

1984-01-01

105

Electron transfer in weakly interacting systems  

International Nuclear Information System (INIS)

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

1981-06-12

106

Electron transfer in weakly interacting systems  

Energy Technology Data Exchange (ETDEWEB)

A recently proposed semiclassical model, in which an electronic transmission coefficient and a nuclear tunneling factor are introduced as corrections to the classical activated-complex expression, is described. The nuclear tunneling corrections are shown to be important only at low temperatures or when the electron transfer is very exothermic. By contrast, corrections for nonadiabaticity may be significant for most outer-sphere reactions of metal complexes. The rate constants for the Fe(H/sub 2/O)/sub 6//sup 2 +/-Fe(H/sub 2/O)/sub 6//sup 3 +/, Ru(NH/sub 3/)/sub 6//sup 2 +/-Ru(NH/sub 3/)/sub 6//sup 3 +/ and Ru(bpy)/sub 3//sup 2 +/-Ru(bpy)/sub 3//sup 3 +/ electron exchange reactions predicted by the semiclassical model are in very good agreement with the observed values. The implications of the model for optically-induced electron transfer in mixed-valence systems are noted.

Sutin, N.; Brunschwig, B.S.

1981-01-01

107

Solvent gating of intramolecular electron transfer  

Energy Technology Data Exchange (ETDEWEB)

The rates for ionic photodissociation of malachite green leucocyanide to form cyanide ion and a malachite green carbonium ion were measured as a function of solvent and temperature. The observed rates in mixtures of polar and nonpolar solvents all had an activation energy of about 1 kcal/mol for a wide range of dielectric constants. This dissociative intramolecular electron transfer (DIET) is unusual because it is the first example where solvent configurational entropy changes are required to enable a large amplitude molecular distortion leading to a nonadiabatic electron transfer and ionic dissociation. This solvent gated intramolecular electron-transfer mechanism is supported by analysis of the preexponential and activation energy trends in dipolar aprotic solven mixtures and alcohol solvents. The large amplitude motion is not separately measurable due to the slow gating rates, but viscosity effects on both the preexponential and the activation energy are analyzed to demonstrate consistency with a barrierless diffusion model having a structural dependence on electron-transfer rate. The rate has an inverse dependence on viscosity raised to the 0.53 power. 36 refs., 6 figs., 4 tabs.

Miller, R.M. (California State Univ., Chico, CA (United States)); Spears, K.G.; Gong, J.H.; Wach, M. (Northwestern Univ., Evanston, IL (United States))

1994-02-03

108

Photoinduced electron transfer reaction in zeolite cages  

Energy Technology Data Exchange (ETDEWEB)

Research continued on photochemically induced electron transfer in zeolites. Reactions and synthesis of Ru(bpy){sub 3}{sup 2+} are discussed. Also, the intercalation properties of LiAl{sub 2}(OH){sub 6}{sup +}-X{sup {minus}} are being pursued. 5 figs. (CBS)

Dutta, P.K.

1990-01-01

109

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1990-10-20

110

A Study Looking the Electronic Funds Transfer  

Directory of Open Access Journals (Sweden)

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

Codruta POENAR

2008-01-01

111

Electron transfer between cytochrome c and porphyrins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electron transfer between cytochrome c and several water-soluble porphyrins (ZnTPPS, ZnTMPyP, ZnTPPC, H2TPPS, and H2TMPyP where TPPS is tetrakis(sulfonatophenyl)porphyrin, TMPyP is tetrakis(N-methylpyridyl)porphyrin, and TPPC is tetrakis(carboxyphenyl)porphyrin) has been studied by the method of...

Cho, KC; Che, CM; Ng, KM; Choy, CL

112

Electron transfer between azurin and metalloporphyrins  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electron-transfer reactions between azurin and the triplet as well as the radicals of several water-soluble metalloporphyrins (ZnTPPS, ZnTPPC, and ZnTMPyP where TPPS is tetrakis(sulfonatophenyl)porphyrin, TPPC is tetrakis(carboxyphenyl)porphyrin, and TMPyP is tetrakis(N-methylpyridyl)porphyrin) ...

Cho, KC; Che, CM; Ng, KM; Choy, CL

113

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1999-06-04

114

Electron reactions and electron transfer reactions catalyzed by micellar systems  

International Nuclear Information System (INIS)

[en] The kinetics of the reaction of hydrated electrons with pyrene, pyrene butyric acid, and pyrene sulfonic acid (PSA) have been investigated in aqueous solutions of cetyltrimethylammonium bromide (CTAB). With all three solubilizates the formation of the electron adduct (P-) occurs very rapidly with rate constants greater than 1011 M-1.sec-1. These abnormally high rate constants are shown to be due to fast trapping of e-/sub aq/ in the positive potential field of the middle and subsequent efficient penetration of electrons into the micellar interior. A similar enhancement was observed for electron transfer reactions between CO2- and solutes solubilized in or on the micelle. For example CO2- readily transfers an electron to pyrene sulfonic acid on the surface of the micelle. This reaction does not occur in homogeneous solution but is catalyzed by the positive electrostatic surface potential. Addition of electrolyte drastically reduces the rate of e-/sub aq/ and CO2- with solubilizates. The Debye-Hueckel theory of electrolytes was invoked to elucidate the role of the charged micellar interface in facilitating the penetration of the electron into the micelle and promoting the electron transfer reaction on the surface. Ion distributions were calculated via solution of a Poisson--Boltzmann equation, generalized to take into account the probable change of the microscopic dielectric constant in the vicinity of the micellar interface

1975-03-01

115

Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.  

UK PubMed Central (United Kingdom)

The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors.

Qiao PF; Mou S; Chuang SL

2012-01-01

116

Electronic band structures and optical properties of type-II superlattice photodetectors with interfacial effect.  

Science.gov (United States)

The electronic band structures and optical properties of type-II superlattice (T2SL) photodetectors in the mid-infrared (IR) range are investigated. We formulate a rigorous band structure model using the 8-band k · p method to include the conduction and valence band mixing. After solving the 8 × 8 Hamiltonian and deriving explicitly the new momentum matrix elements in terms of envelope functions, optical transition rates are obtained through the Fermi's golden rule under various doping and injection conditions. Optical measurements on T2SL photodetectors are compared with our model and show good agreement. Our modeling results of quantum structures connect directly to the device-level design and simulation. The predicted doping effect is readily applicable to the optimization of photodetectors. We further include interfacial (IF) layers to study the significance of their effect. Optical properties of T2SLs are expected to have a large tunable range by controlling the thickness and material composition of the IF layers. Our model provides an efficient tool for the designs of novel photodetectors. PMID:22330471

Qiao, Peng-Fei; Mou, Shin; Chuang, Shun Lien

2012-01-30

117

Enhanced photosensitized activity of a BiOCl-Bi2WO6 heterojunction by effective interfacial charge transfer.  

UK PubMed Central (United Kingdom)

A BiOCl-Bi2WO6 heterojunction with a chemically bonded interface was synthesized via a facile one-step solvothermal method. A series of characterization techniques (XRD, XPS, TEM, SEM, EDS etc.) confirmed the existence of a BiOCl-Bi2WO6 interface. The heterojunction yielded a higher photodegradation rate of Rhodamine B under visible light irradiation compared to its individual components. Theoretical studies based on density functional theory calculations indicated that the enhanced photosensitized degradation activity could be attributed to the favorable band offsets across the BiI-O-BiII bonded interface, leading to efficient interfacial charge carrier transfer. Our results reveal the photosensitized mechanism of BiOCl-Bi2WO6 heterojunctions and demonstrate their practical use as visible-light-driven photocatalytic materials.

Yang W; Ma B; Wang W; Wen Y; Zeng D; Shan B

2013-10-01

118

Enhanced photosensitized activity of a BiOCl-Bi2WO6 heterojunction by effective interfacial charge transfer.  

Science.gov (United States)

A BiOCl-Bi2WO6 heterojunction with a chemically bonded interface was synthesized via a facile one-step solvothermal method. A series of characterization techniques (XRD, XPS, TEM, SEM, EDS etc.) confirmed the existence of a BiOCl-Bi2WO6 interface. The heterojunction yielded a higher photodegradation rate of Rhodamine B under visible light irradiation compared to its individual components. Theoretical studies based on density functional theory calculations indicated that the enhanced photosensitized degradation activity could be attributed to the favorable band offsets across the BiI-O-BiII bonded interface, leading to efficient interfacial charge carrier transfer. Our results reveal the photosensitized mechanism of BiOCl-Bi2WO6 heterojunctions and demonstrate their practical use as visible-light-driven photocatalytic materials. PMID:24121901

Yang, Wenjuan; Ma, Bo; Wang, Weichao; Wen, Yanwei; Zeng, Dawen; Shan, Bin

2013-10-23

119

Comparison of interfacial heat transfer coefficient estimated by two different techniques during solidification of cylindrical aluminum alloy casting  

Energy Technology Data Exchange (ETDEWEB)

The interfacial heat transfer coefficient (IHTC) is necessary for accurate simulation of the casting process. In this study, a cylindrical geometry is selected for the determination of the IHTC between aluminum alloy casting and the surrounding sand mold. The mold surface heat flux and temperature are estimated by two inverse heat conduction techniques, namely Beck's algorithm and control volume technique. The instantaneous cast and mold temperatures are measured experimentally and these values are used in the theoretical investigations. In the control volume technique, partial differential heat conduction equation is reduced to ordinary differential equations in time, which are then solved sequentially. In Beck's method, solution algorithm is developed under the function specification method to solve the inverse heat conduction equations. The IHTC was determined from the surface heat flux and the mold surface temperature by both the techniques and the results are compared. (orig.)

Rajaraman, R. [Anna University, B. S. Abdur Rahman Crescent Engineering College, Chennai (India); Velraj, R. [Anna University, College of Engineering Guindy, Chennai (India)

2008-07-15

120

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

Energy Technology Data Exchange (ETDEWEB)

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

Sutin, N.

1982-09-01

 
 
 
 
121

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

International Nuclear Information System (INIS)

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

1982-01-01

122

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

UK PubMed Central (United Kingdom)

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

Uddin MS; Hidajat K; Lim B; Ching C

1990-01-01

123

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

124

Imidazole facilitates electron transfer from organic reductants.  

UK PubMed Central (United Kingdom)

In cyclic voltammetry studies at pH 8, imidazole facilitates oxidation of organic compounds that normally lose hydrogen atoms. High concentrations of imidazole shift the oxidizing wave of ascorbic acid, 2,3-dimethoxy-5-methyl-1,4-hydroquinone, and the vitamin E analogue Trolox toward lower potentials. By contrast, imidazole has no effect on the cyclic voltammogram of methyl viologen, which undergoes electron rather than hydrogen-atom transfer. The effect of imidazole is observed at pH 8.0 but only to a lesser extent at pH 5.5 indicating that imidazole must be unprotonated to facilitate oxidation. Digital simulation shows that these results are consistent with a mechanism in which imidazole acts as a proton acceptor permitting concerted proton/electron transfer by the organic reductant.

Kipp BH; Faraj C; Li G; Njus D

2004-08-01

125

Imidazole facilitates electron transfer from organic reductants.  

Science.gov (United States)

In cyclic voltammetry studies at pH 8, imidazole facilitates oxidation of organic compounds that normally lose hydrogen atoms. High concentrations of imidazole shift the oxidizing wave of ascorbic acid, 2,3-dimethoxy-5-methyl-1,4-hydroquinone, and the vitamin E analogue Trolox toward lower potentials. By contrast, imidazole has no effect on the cyclic voltammogram of methyl viologen, which undergoes electron rather than hydrogen-atom transfer. The effect of imidazole is observed at pH 8.0 but only to a lesser extent at pH 5.5 indicating that imidazole must be unprotonated to facilitate oxidation. Digital simulation shows that these results are consistent with a mechanism in which imidazole acts as a proton acceptor permitting concerted proton/electron transfer by the organic reductant. PMID:15219240

Kipp, Brian H; Faraj, Chadi; Li, Guoliang; Njus, David

2004-08-01

126

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

Directory of Open Access Journals (Sweden)

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

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

2007-01-01

127

Environmental effects on photoinduced electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

Photoinduced electron transfer reactions between an electronically excited photosensitizer molecule and a reversible electron acceptor capable of hydrogen production were studied to determine the possible utility of these reactions in solar energy conversion systems. The influence of charged macromolecules on the forward and back electron-transfer reaction between oppositely charged initial photoproducts, the photosensitizer zinc tetra(4-N-methyl pyridinium) porphyrin (ZnP/sup +4/) and the neutral electron acceptor, propyl viologen sulfonate (PVS/sup 0/), has been investigated using continuous photolysis and flash photolysis techniques. Flash photolysis experiments have been performed to study the effect of anionic polyelectrolyte poly(styrene sulfonate) (PSS) on the photoreaction between ZnP/sup +4/ and PVS/sup 0/. These experiments show that all bimolecular rate constants involving PSS-bound ZnP/sup +4/ are decreased by a factor for 40-100. A kinetic model has been developed that describes the transient absorbance behavior of ZnP/sup +4//PVS/sup 0//colloidal silica photolysis systems in which scavenging of PVS/sup -/ by residual O/sub 2/ occurs. Flash photolysis experiments confirmed that alumina-modified silica particles are significantly more effective than unmodified silica sols in neutral pH media at decreasing the rate of back-reaction between ZnP/sup +4/ and PVS/sup -/. 25 refs., 32 figs., 5 tabs.

Casti, T.E.

1985-12-01

128

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 are presented as well as a discussion of the typical product areas (e.g. photographic papers, release papers, magnetic media) using this high speed transfer technology.

1984-01-01

129

Interaction of interfacial convection and mass transfer effects in the system CO{sub 2}-water  

Energy Technology Data Exchange (ETDEWEB)

The mass transfer of the system CO{sub 2}-water was measured up to a pressure of 360 bar at a temperature of 25 deg C and the results were compared to empirical predictions. The influence of a surfactant on the mass transfer was investigated. A Schlieren method and a three-mode magnetic suspension balance connected to an optical cell were used to analyse the mass transfer. A good simulation of the experimental values was achieved by linear superposition of free convection and Marangoni convection. The surfactant enforces the Marangoni convection while the solubility of CO{sub 2} stayed unaffected. (Author)

Arendt, B.; Dittmar, D.; Eggers, R. [Technical Univ. Hamburg-Harburg, Dept. of Thermal Separation Processes, Hamburg (Germany)

2004-08-01

130

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

Science.gov (United States)

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

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

1990-01-01

131

Electron transfer dissociation of peptide anions.  

Science.gov (United States)

Ion/ion reactions of multiply deprotonated peptide anions with xenon radical cations result in electron abstraction to generate charge-reduced peptide anions containing a free-radical site. Peptide backbone cleavage then occurs by hydrogen radical abstraction from a backbone amide N to facilitate cleavage of the adjacent C-C bond, thereby producing a- and x-type product ions. Introduction of free-radical sites to multiply charged peptides allows access to new fragmentation pathways that are otherwise too costly (e.g., lowers activation energies). Further, ion/ion chemistry, namely electron transfer reactions, presents a rapid and efficient means of generating odd-electron multiply charged peptides; these reactions can be used for studying gas-phase chemistries and for peptide sequence analysis. PMID:15907703

Coon, Joshua J; Shabanowitz, Jeffrey; Hunt, Donald F; Syka, John E P

2005-04-14

132

Electron transfer dissociation of peptide anions.  

UK PubMed Central (United Kingdom)

Ion/ion reactions of multiply deprotonated peptide anions with xenon radical cations result in electron abstraction to generate charge-reduced peptide anions containing a free-radical site. Peptide backbone cleavage then occurs by hydrogen radical abstraction from a backbone amide N to facilitate cleavage of the adjacent C-C bond, thereby producing a- and x-type product ions. Introduction of free-radical sites to multiply charged peptides allows access to new fragmentation pathways that are otherwise too costly (e.g., lowers activation energies). Further, ion/ion chemistry, namely electron transfer reactions, presents a rapid and efficient means of generating odd-electron multiply charged peptides; these reactions can be used for studying gas-phase chemistries and for peptide sequence analysis.

Coon JJ; Shabanowitz J; Hunt DF; Syka JE

2005-06-01

133

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

CERN Document Server

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

Li, J C; Szulczewski, G J

2005-01-01

134

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

Energy Technology Data Exchange (ETDEWEB)

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

Benjamin, A.S.

1980-01-01

135

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

Science.gov (United States)

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

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

2012-03-01

136

Photoinduced electron transfer reactions in zeolite cages  

Energy Technology Data Exchange (ETDEWEB)

This report summarizes work in the two areas of zeolites and layered double hydroxides. Results of studies on structural aspects of Ru(bpy)[sub 3][sup 2+]-zeolite Y are summarized. Photoinduced electron transfer between entrapped Ru(bpy)[sub 3][sup 2+] and methylviologen (MV) in neighboring supercages was examined. Benzylviologen was also used. Since molecules larger than 13 [angstrom] cannot be accomodated in zeolite cages, the layered double metal hydroxides (LDH) LiAl[sub 2](OH)[sub 6][sup +]X[sup [minus

Dutta, P.K.

1992-01-01

137

Mixed Valent Sites in Biological Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-05-26

138

Transmembrane electron transfer catalyzed by phospholipid-linked manganese porphyrins  

Energy Technology Data Exchange (ETDEWEB)

Synthetic models can be very helpful in studying the effect of distance and orientation in electron transfer reactions in biological membrane processes such as occur in photosynthesis and mitochondria. To provide a model for the electron transfer where porphyrin pigments play the key role, the preparation of porphyrin derivatives that are capable of light-induced intra- or intermolecular electron transfer was reported. However, there has been little study of ground-state electron transfer between porphyrin complexes to provide insight into the effect of distance and orientation in the electron transfer so that a vectorial electron transfer system may be constructed in the biological membrane. We now report transmembrane electron transfer catalyzed by manganese complexes of bilayer-active phospholipid-linked porphyrins 1, PE-C{sub n}-MnTTP (n = 0, 5, 11) (Scheme I), which can be easily immersed into the lipid bilayer. The synthetic procedures leading are described.

Nango, Mamoru; Mizusawa, Atsushi; Miyake, Takenori; Yoshinaga, Junji (Univ. of Osaka Prefecture (Japan))

1990-02-14

139

Photoinduced electron transfer in ordered polymers  

Energy Technology Data Exchange (ETDEWEB)

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

Jones, G. II.

1993-01-01

140

Photochemical electron transfer reactions of tirapazamine.  

UK PubMed Central (United Kingdom)

The absorption and fluorescence spectra of 3-aminobenzo-1,2,4-triazine di-N-oxide (tirapazamine) have been recorded and exhibit a dependence on solvent that correlates with the Dimroth ET30 parameter. Time-dependent density functional theory calculations reveal that the transition of tirapazamine in the visible region is pi-->pi* in nature. The fluorescence lifetime is 98+/-2 ps in water. The fluorescence quantum yield is approximately 0.002 in water. The fluorescence of tirapazamine is efficiently quenched by electron donors via an electron-transfer process. Linear Stern-Volmer fluorescence quenching plots are observed with sodium azide, potassium thiocyanate, guanosine monophosphate and tryptophan (Trp) methyl ester hydrochloride. Guanosine monophosphate, tyrosine (Tyr) methyl ester hydrochloride and Trp methyl ester hydrochloride appear to quench the fluorescence at a rate greater than diffusion control implying that these substrates complex with tirapazamine in its ground state. This complexation was detected by absorption spectroscopy.

Poole JS; Hadad CM; Platz MS; Fredin ZP; Pickard L; Guerrero EL; Kessler M; Chowdhury G; Kotandeniya D; Gates KS

2002-04-01

 
 
 
 
141

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

2001-01-01

142

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.

2010-01-01

143

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

144

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; XIONG Shou-mei

2007-01-01

145

Radiationsless transfer of electron excitation during vibrational relaxation  

International Nuclear Information System (INIS)

[en] The hot transfer of electronic excitation during the vibrarional relaxation in the excited electronic state of the donor is studied theoretically for strong vibronic interactions. The theory is applied to inter- and intra-centre transfer. The Weber effect is explained. The role of hot transfer in photosynthesis, in intra-centre luminescence depolarisation and in oher processes is discussed

1974-01-01

146

Electron transfer in gas surface collisions  

International Nuclear Information System (INIS)

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

1983-01-01

147

Electronic and Nuclear Factors in Charge and Excitation Transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Piotr Piotrowiak

2004-09-28

148

Exploring fast electron transfer processes by magnetic fields.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photoinduced electron transfer generates radical pairs which recombine with 10(-9)10(-8)s by electron back-transfer to either singlet or triplet products. The product distribution determined by the spin motion of the unpaired electrons in the radical pairs is affected by external magnetic fields. Th...

Schulten, K; Weller, A

149

Activation entropy of electron transfer reactions  

CERN Multimedia

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

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

2005-01-01

150

Nanocantilever signal transduction by electron transfer.  

UK PubMed Central (United Kingdom)

Microfabricated cantilever beams promise to bring about a revolution in the field of chemical, physical, and biological sensor development. The resonance frequency of a microfabricated cantilever shifts sensitively because of mass loading from molecular adsorption. The minimum detectable adsorbed mass on a cantilever sensor can be increased by orders of magnitude by changing the dimensions of the device; smaller and thicker cantilevers offer higher resonance frequency and therefore better mass detection sensitivity. Here we describe micromachined silicon cantilevers that are 0.5 to 4 microns in length, fabricated with the use of a focused ion beam (FIB). In addition, we demonstrate a technique for detection of the cantilever resonance frequency that is based on electron transfer.

Datskos PG; Thundat T

2002-06-01

151

GPU-accelerated computation of electron transfer.  

Science.gov (United States)

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

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

2012-07-30

152

GPU-accelerated computation of electron transfer.  

UK PubMed Central (United Kingdom)

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

Höfinger S; Acocella A; Pop SC; Narumi T; Yasuoka K; Beu T; Zerbetto F

2012-11-01

153

Nanoparticles: toxicity, radicals, electron transfer, and antioxidants.  

UK PubMed Central (United Kingdom)

In recent years, nanoparticles have received increasing attention in research and technology, including a variety of practical applications. The bioactivity appears to be related to the small particle size, in addition to inherent chemical activity as electron transfer (ET) agents, generators of reactive oxygen species (ROS) with subsequent oxidative stress (OS), and as antioxidants (AOs). The mechanism of toxicity, therapeutic action, and AO property is addressed based on the ET-ROS-OS approach. There are several main classes of ET functionalities, namely, quinones (or phenolic precursors), metal compounds, aromatic nitro compounds (or reduction products), and imine or iminium species. Most of the nanospecies fall within the metal category. Cell signaling is also discussed. This review discusses recent developments based on ET-ROS-OS-AO framework.

Kovacic P; Somanathan R

2013-01-01

154

Analytical model for rates of electron attachment and intramolecular electron transfer in electron transfer dissociation mass spectrometry.  

UK PubMed Central (United Kingdom)

A new physical model is put forth to allow the prediction of electron transfer rates and distances for (i) intramolecular transfer from an n > or = 3 Rydberg orbital on a positive site to a disulfide or amide bond site and (ii) intermolecular transfer from an anion donor to an n > or = 3 Rydberg orbital of a positively charged polypeptide. Although ab initio methods have proven capable of handling such electron transfer events when the Rydberg orbital has principal quantum number n = 3, they have proven to be incapable of handling Rydberg states having quantum number n > 3, so having a new tool capable of handling n > 3 Rydberg states is important. The model (i) focuses on each Rydberg orbital's large peak of high amplitude, (ii) approximates the electron density within this peak as constant within a radial shell characterized by a radius and thickness T both of which depend on the quantum number n, and (iii) assumes that strong coupling (either with an orbital of an anion donor or to a disulfide sigma* or a backbone amide pi* orbital) occurs when the valence orbital penetrates fully within the radial shell of the Rydberg orbital. These assumptions permit a derivation of the ratios of rates of electron transfer for n > 3 to those for n = 3. Combining these ratios with ab initio rates for n = 3 allows one to make rate predictions for inter- and intramolecular electron transfer involving Rydberg orbitals appropriate to the electron transfer dissociation process. One important prediction of this model is that the combination of large-penetration and Landau-Zener surface-crossing conditions places very severe limitations on which Rydberg levels can initially be populated in electron transfer dissociation. Another prediction is that a Rydberg orbital of a given principal quantum number n has a limited range of distances over which it can transfer an electron; sigma* or pi* orbitals either too far from or too close to a given Rydberg orbital cannot accept an electron from that orbital.

Simons J

2010-05-01

155

Electron transfer mechanism of cytochrome c at the oil/water interface as a biomembrane model.  

UK PubMed Central (United Kingdom)

The electron transfer (ET) between cytochrome c (Cyt c) in water (W) and 1,1'-dimethylferrocene (DiMFc) in 1,2-dichloroethane (DCE) was studied. The cyclic voltammograms obtained for the interfacial ET under various conditions could be well reproduced by digital simulation based on the ion-transfer (IT) mechanism, in which the ET process occurs not at the DCE/W interface but in the W phase nearest the interface. In this mechanism, the current signal is due to the IT of DiMFc(+) as the reaction product. On the other hand, the measurement of the double-layer capacity showed that Cyt c is adsorbed at the DCE/W interface. However, the contribution from the adsorbed proteins to the overall ET is considered to be small because of the thicker reaction layer in the IT mechanism. These findings would offer a useful suggestion for the behaviors of Cyt c in vivo.

Imai Y; Sugihara T; Osakai T

2012-01-01

156

Electron transfer mechanism of cytochrome c at the oil/water interface as a biomembrane model.  

Science.gov (United States)

The electron transfer (ET) between cytochrome c (Cyt c) in water (W) and 1,1'-dimethylferrocene (DiMFc) in 1,2-dichloroethane (DCE) was studied. The cyclic voltammograms obtained for the interfacial ET under various conditions could be well reproduced by digital simulation based on the ion-transfer (IT) mechanism, in which the ET process occurs not at the DCE/W interface but in the W phase nearest the interface. In this mechanism, the current signal is due to the IT of DiMFc(+) as the reaction product. On the other hand, the measurement of the double-layer capacity showed that Cyt c is adsorbed at the DCE/W interface. However, the contribution from the adsorbed proteins to the overall ET is considered to be small because of the thicker reaction layer in the IT mechanism. These findings would offer a useful suggestion for the behaviors of Cyt c in vivo. PMID:22166053

Imai, Yoko; Sugihara, Takayasu; Osakai, Toshiyuki

2011-12-28

157

Internal electron transfer within mitochondrial succinate-cytochrome C reductase  

International Nuclear Information System (INIS)

Internal electron transfer within succinate-cytochrome C reductase from pigeon breast muscle mitochondria was followed by the pulse radiolytic technique. The electron equivalent is transferred from an unknown donor to b type cytochrome(s), in a first order process with a rate constant of: 660 +- 150s-1. This process might be the rate determining step of electron transfer in mitochondria, since it is similar in rate to the turnover number of the mitochondrial respiratory chain

1978-12-29

158

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.

1977-11-05

159

[Group transfer and electron transfer reactions of organometallic complexes]: Summary of research accomplished in 1993  

Energy Technology Data Exchange (ETDEWEB)

In the past year the research on mechanisms of electron transfer processes between organometallic complexes has continued to progress with emphasis on two electron processes and on reactions of organometallic radicals. This summary will highlight the research on: (1) halide transfer reactions, (2) alkyl and acyl transfer reactions and (3) reactions of seventeen-electron organometallic complexes. At this point some conclusions on the transfer of hydrogen, halogen and methyl as the cation, radical and anion can be made. For each group, transfer as the cation is more facile. For hydrogen, transfer as the hydride is considerably slower, but H{center_dot} transfers nearly as rapidly as H{sup +}. Methyl could be transferred as CH{sub 3}{sup +} or CH{sub 3}{sup {minus}}, but not as the radical. Halogens transfer readily as X{sup +}, more slowly as X{center_dot} and not at all as X{sup {minus}}.

1993-12-31

160

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

UK PubMed Central (United Kingdom)

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

Perraud O; Tommasino JB; Robert V; Albela B; Khrouz L; Bonneviot L; Dutasta JP; Martinez A

2013-02-01

 
 
 
 
161

Single and Accumulative Electron Transfer – Prerequisites for Artificial Photosynthesis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Photoinduced electron transfer is involved in a number of photochemical and photobiological processes. One example of this is photosynthesis, where the absorption of sunlight leads to the formation of charge-separated states by electron transfer. The redox equivalents built up by successive photoabs...

Karlsson, Susanne

162

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

163

The reaction of trimethylamine dehydrogenase with electron transferring flavoprotein.  

Science.gov (United States)

The kinetics of electron transfer between trimethylamine dehydrogenase (TMADH) and its physiological acceptor, electron transferring flavoprotein (ETF), has been studied by static and stopped-flow absorbance measurements. The results demonstrate that reducing equivalents are transferred from TMADH to ETF solely through the 4Fe/4S center of the former. The intrinsic limiting rate constant (klim) and dissociation constant (Kd) for electron transfer from the reduced 4Fe/4S center of TMADH to ETF are about 172 s-1 and 10 microM, respectively. The reoxidation of fully reduced TMADH with an excess of ETF is markedly biphasic, indicating that partial oxidation of the iron-sulfur center in 1-electron reduced enzyme significantly reduces the rate of electron transfer out of the enzyme in these forms. The interaction of the two unpaired electron spins of flavin semiquinone and reduced 4Fe/4S center in 2-electron reduced TMADH, on the other hand, does not significantly slow down the electron transfer from the 4Fe/4S center to ETF. From a comparison of the limiting rate constants for the oxidative and reductive half-reactions, we conclude that electron transfer from TMADH to ETF is not rate-limiting during steady-state turnover. The overall kinetics of the oxidative half-reaction are not significantly affected by high salt concentrations, indicating that electrostatic forces are not involved in the formation and decay of reduced TMADH-oxidized ETF complex. PMID:7592591

Huang, L; Rohlfs, R J; Hille, R

1995-10-13

164

The distance and temperature dependence of electron-transfer rates  

International Nuclear Information System (INIS)

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

1987-01-01

165

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

International Nuclear Information System (INIS)

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

2010-05-28

166

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

Science.gov (United States)

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

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

2013-03-01

167

Cytochrome c folding triggered by electron transfer.  

UK PubMed Central (United Kingdom)

BACKGROUND: Experimental and theoretical studies of protein folding suggest that the free-energy change associated with the folding process is a primary factor in determining folding rates. We have recently developed a photochemical electron-transfer-triggering method to study protein-folding kinetics over a wide range of folding free energies. Here, we have used this technique to investigate the relationship between folding rate and free-energy change using cytochromes c from horse (h-cyt c) and yeast (y-cyt c), which have similar backbone folds but different amino-acid sequences and, consequently, distinct folding energies. RESULTS: The folding free energies for oxidized and reduced h-cyt c and y-cyt c are linear functions of the denaturant (guanidine hydrochloride) concentration, but the concentration required to unfold half of the protein is 1.5 M lower for y-cyt c. We measured the folding rates of reduced h-cyt c and y-cyt c over a range of guanidine hydrochloride concentrations at two temperatures. When driving forces are matched at the appropriate denaturant concentrations, the two homologs have comparable folding rates. The activation free energies for folding h-cyt c and y-cyt c are linearly dependent on the folding free energies. The slopes of these lines are similar (approximately 0.4) for the two proteins, suggesting an early transition state along the folding reaction coordinate. CONCLUSIONS: The free-energy relationships found for h-cyt c and y-cyt c folding kinetics imply that the height of the barrier to folding depends upon the relative stabilities of the unfolded and folded states. The striking correspondence in rate/free-energy profiles for h-cyt c and y-cyt c suggests that, despite low sequence homology, they follow similar folding pathways.

Mines GA; Pascher T; Lee SC; Winkler JR; Gray HB

1996-06-01

168

Interfacial and sub-interfacial fracture  

Energy Technology Data Exchange (ETDEWEB)

Crack nucleation and growth near or at interfaces, rather than in the bulk, is a serious problem in industrial components. Length scales range from nanostructures in electronic components to explosion cladded macro-components in nuclear reactors. The crystallographic incompatibility of an interface impedes slip across it. Consequently, the interfacial region reaches an advanced stage of hardening as compared with the bulk material. Therefore, internal stresses are higher at interfaces. Elastic incompatibility at interfaces or triple point junctions lead to stress concentration, which magnify the remotely applied service load. Under these conditions of high internal stresses, badly bonded interfaces de-cohere and hence lead to fracture. Interfacial and sub-interfacial fracture is easier than in the bulk. The following examples given pertain to all length scales: (1) high resolution microscopy of silicon bi-crystals; (2) measurements of crack resistance curves of interfacial and sub-interfacial cracks in austenite-ferrite, ferrite-copper and ferrite-aluminum compounds; (3) fracture strength of concrete-concrete and concrete-stone interfaces.

Kirchner, H.O.K. [Universite Paris-Sud, Orsay (France)

1995-12-31

169

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

Science.gov (United States)

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

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

2013-10-01

170

Coincidence spectroscopy of continuum electron transfer in heavy ion collisions  

International Nuclear Information System (INIS)

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

1979-09-07

171

Electron transfer and decay processes of highly charged iodine ions  

International Nuclear Information System (INIS)

In the present experimental work we have investigated multi-electron transfer processes in Iq+ (q=10, 15, 20 and 25) + Ne, Ar, Kr and Xe collisions at 1.5q keV energy. The branching ratios between Auger and radiative decay channels have been measured in decay processes of multiply excited states formed by multi-electron transfer collisions. It has been shown that, in all the multi-electron transfer processes investigated, the Auger decays are far dominant over the radiative decay processes and the branching ratios are clearly characterized by the average principal quantum number of the initial excited states of projectile ions. We could express the branching ratios in high Rydberg states formed in multi-electron transfer processes by using the decay probability of one Auger electron emission. (author)

2005-01-01

172

Ultrafast Charge Transfer Visualized by Two-Dimensional Electronic Spectroscopy  

Directory of Open Access Journals (Sweden)

Full Text Available Two-dimensional electronic spectroscopy (2D-ES) is used to investigate ultrafast excited-state dynamics in a lutetium bisphthalocyanine dimer. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the electronic 2D spectra. The combination of density matrix propagation and quantum chemical calculations results in a molecular view of the charge transfer dynamics and highlights the role of the counter-ion in providing an energetic perturbation which promotes charge transfer across the complex.

Bixner O.; Christensson N.; Hauer J.; Milota F.; Man?al T.; Lukeš V.; Kauffmann H. F.

2013-01-01

173

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1980-07-01

174

Electron acceptor dependence of electron shuttle secretion and extracellular electron transfer by Shewanella oneidensis MR-1.  

Science.gov (United States)

Shewanella oneidensis MR-1 is an extensively studied dissimilatory metal-reducing bacterium with a great potential for bioremediation and electricity generation. It secretes flavins as electron shuttles which play an important role in extracellular electron transfer. However, the influence of various environmental factors on the secretion of flavins is largely unknown. Here, the effects of electron acceptors, including fumarate, ferrihydrite, Fe(III)-nitrilotriacetic acid (NTA), nitrate and trimethylamine oxide (TMAO), on the secretion of flavins were investigated. The level of riboflavin and riboflavin-5'-phosphate (FMN) secreted by S. oneidensis MR-1 varied considerably with different electron acceptors. While nitrate and ferrihydrite suppressed the secretion of flavins in relative to fumarate, Fe(III)-NTA and TMAO promoted such a secretion and greatly enhanced ferrihydrite reduction and electricity generation. This work clearly demonstrates that electron acceptors could considerably affect the secretion of flavins and consequent microbial EET. Such impacts of electron acceptors in the environment deserve more attention. PMID:23558182

Wu, Chao; Cheng, Yuan-Yuan; Li, Bing-Bing; Li, Wen-Wei; Li, Dao-Bo; Yu, Han-Qing

2013-03-14

175

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

176

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

177

Proton-coupled electron transfer with photoexcited metal complexes.  

UK PubMed Central (United Kingdom)

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.

Wenger OS

2013-07-01

178

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

2013-02-13

179

A tubular view of electron transfer in azurin  

Energy Technology Data Exchange (ETDEWEB)

A new theoretical approach emphasizes tubes (tightly grouped families of pathways) for electron transfer and looks for interaction between these families rather than focussing on individual paths. in some cases, for a given donor D and acceptor A, the electron transfer can be thought of as pathway-like wherein the protein bridge can be physically reduced to a tube without changing the overall coupling. In other cases, the transfer is characterized by multiple tubes which can interfere with one another, and a single path assumption will fail to identify all of the structural elements which control the coupling. Reducing the protein to only the relevant parts (tubes) that mediate the tunneling matrix element is a useful tool for understanding electron transfer in biological medium. An example is carried out on blue copper protein azurin that plays an important role as an electron carrier in biological systems. (N.T.).

Regan, J.J.; Onuchic, J.N. [California Univ., San Diego, La Jolla, CA (United States). Dept. of Physics

1996-12-31

180

75 FR 52485 - Electronic Funds Transfer of Depository Taxes; Correction  

Science.gov (United States)

...relating to Federal tax deposits (FTDs) by Electronic Funds Transfer (EFT). FOR FURTHER INFORMATION CONTACT: Michael E. Hara, (202) 622-4910 (not a toll-free number). SUPPLEMENTARY INFORMATION: Background The correction notice that is...

2010-08-26

 
 
 
 
181

Electron energy transfer rates for vibrational excitation of N2.  

Energy Technology Data Exchange (ETDEWEB)

The calculation of the electron density and electron temperature distribution in our ionosphere (from {approx} 150-600 km) requires a knowledge of the various heating, cooling and energy flow processes that occur. The energy transfer from electrons to neutral gases and ions is one of the dominant electron cooling processes in the ionosphere, and the role of vibrationally excited N2 in this is particularly significant.

Campbell, L. (Laurence); Cartwright, D. C. (David C.); Tuebner, P. J. O.; Brunger, M. J. (Michael J.)

2003-01-01

182

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

International Nuclear Information System (INIS)

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

2013-01-01

183

Analysis of transmission efficiency of SSRF electron beam transfer lines  

International Nuclear Information System (INIS)

[en] In this article, the main factors which influence transmission efficiency of the SSRF electron beam transfer lines are described, including physical requirements for magnet system, vacuum system, beam diagnostic system, trajectory correction system, etc. The dynamic simulation calculation and transmission efficiency analysis of the SSRF electron beam transfer lines are presented, and the studies show that the design purpose of efficient beam transmission and injection will be achieved. (authors)

2006-01-01

184

Heavy particle interference and diffraction in fast electron transfer collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This thesis presents experimental results from the synchrotron cooler and storage ring CRYRING on charge transfer processes in fast electron transfer collisions using high-resolution cold target recoil-ion momentum spectroscopy. The main focus of these studies was to investigate a key concept of qua...

Gudmundsson, Magnus

185

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2010-04-30

186

Theory of electron transfer by solitons  

Energy Technology Data Exchange (ETDEWEB)

The effect of strong electron-phonon interaction on the electron motion in a molecular chain formed by molecules with constant electric dipole moments is analyzed. The properties of three-dimensional solitons (polarons) in ion crystals, taking into account the optical-phonon dispersion without employing the perturbation theory relative to ion kinetic energy, are discussed.

Davydov, A.S.

1980-01-01

187

Interfacial and Network Characteristics of Silicon Nanoparticle Layers Used in Printed Electronics  

Science.gov (United States)

In printed electronics the use of semiconducting silicon nanoparticles allows more than the simple printing of conductive materials. It gives the possibility of fabricating robust and inexpensive, active and reactive components like temperature sensors which are shown as an example. In our approach high quality silicon nanoparticles with stable, essentially oxide-free surfaces are used to replace the pigment in water-based graphic inks, which on curing have unique semiconducting properties, arising from the transport of charge through a percolation network of crystalline silicon nanoparticles. In this study scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were employed to investigate the mesoscale structure of the particle network and, more importantly the structure of the interface between particles. An intimate contact between lattice planes of different particles was observed, without the presence of an intervening oxide layer.

Männl, Ulrich; Chuvilin, Andrey; Magunje, Batsirai; Jonah, Emmanuel Ohieku; Härting, Margit; Britton, David Thomas

2013-05-01

188

Electron and proton transfer in chemistry and biology  

International Nuclear Information System (INIS)

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

1992-01-01

189

Alternative ground states enable pathway switching in biological electron transfer.  

Science.gov (United States)

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

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

2012-10-10

190

Electron-transfer processes in fast ion-atom collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The subject of this thesis is experimental studies of electron-transfer processes in ion-atom collisions at velocities significantly higher than typical orbital velocities of electrons in bound states of atoms or molecules. The experimental technique applied combines the high beam intensity of heavy...

Støchkel, Kristian

191

Alternative ground states enable pathway switching in biological electron transfer.  

UK PubMed Central (United Kingdom)

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

Abriata LA; Álvarez-Paggi D; Ledesma GN; Blackburn NJ; Vila AJ; Murgida DH

2012-10-01

192

Electron transfer between cytochrome c and metalloporphyrins at high exothermicities  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The electron-transfer rates between cytochrome c and the anion radical of two metalloporphyrins ZnTPPS and ZnTPPC (?E for the reaction is 1.42eV) have been measured by laser flash spectroscopy. The anion radicals were produced by reaction of the porphyrins with hydrated electrons which resulted from...

Cho, KC; Ng, KM; Choy, CL; Che, CM

193

Interfacial Rheology  

CERN Document Server

This is the first book on interfacial rheology and aims to describe both its history as well as the current, most frequently used experimental techniques for studying dilational and shear rheology of layers at liquid/gas and liquid/liquid interfaces. The book opens with a chapter on the fundamentals of interfacial rheology. All (16) contributions include the theoretical basis for the presented methodologies and experimental examples are given.

Miller, R

2009-01-01

194

A tetrastable naphthalenediimide: anion induced charge transfer, single and double electron transfer for combinational logic gates.  

UK PubMed Central (United Kingdom)

Herein we demonstrate the formation of the first tetrastable naphthalenediimide (NDI, 1a) molecule having multiple distinctly readable outputs. Differential response of 1a to fluoride anions induces intramolecular charge transfer (ICT), single/double electron transfer (SET/DET) leading to a set of combinational logic gates for the first time with a NDI moiety.

Ajayakumar MR; Hundal G; Mukhopadhyay P

2013-09-01

195

Nuclear interlevel transfer driven by electronic transitions  

International Nuclear Information System (INIS)

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

1985-01-01

196

Quantum interferences and electron transfer in photosystem I.  

UK PubMed Central (United Kingdom)

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

Renaud N; Powell D; Zarea M; Movaghar B; Wasielewski MR; Ratner MA

2013-07-01

197

Quantum interferences and electron transfer in photosystem I.  

Science.gov (United States)

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

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

2012-11-15

198

Intramolecular electron transfer and dehalogenation of nitroaromatic anion radicals  

International Nuclear Information System (INIS)

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

1983-02-09

199

Intramolecular electron transfer and dehalogenation of nitroaromatic anion radicals  

Energy Technology Data Exchange (ETDEWEB)

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

Bays, J.P. (St. Mary' s College, Notre Dame, IN); Blumer, S.T.; Baral-Tosh, S.; Behar, D.; Neta, P.

1983-02-09

200

Studies of impulsive vibrational influence on ultrafast electronic excitation transfer.  

Science.gov (United States)

We investigated electronic energy-transfer dynamics in three model dimers within which coherent intramonomer nuclear motion had been induced by impulsive Raman excitation using an optimized, electronically preresonant control pulse. Calculations of the donor-survival probability, the ultrafast pump-probe signal, and the pump-probe difference signal are presented for dithia-anthracenophane and homodimers of 2-difluoromethylanthracene and 2-trifluoromethylanthracene. Survival probabilities and signals, along with phase-space analyses, elucidated the mechanisms, extent, and spectroscopic manifestations of external vibrational or torsional control over electronic excitation transfer. PMID:22236325

Biggs, Jason D; Cina, Jeffrey A

2012-02-10

 
 
 
 
201

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

202

Electronic energy transfer: vibrational control and nonlinear wavepacket interferometry  

CERN Multimedia

The time-development of photoexcitations in molecular aggregates exhibits specific dynamics of electronic states and vibrational wavefunction. We discuss the dynamical formation of entanglement between electronic and vibrational degrees of freedom in molecular aggregates with theory of electronic energy transfer and the method of vibronic 2D wavepackets [Cina, Kilin, Humble, J. Chem. Phys. 118, 46 (2003)]. The vibronic dynamics is also described by applying Jaynes-Cummings model to the electronic energy transfer [Kilin, Pereverzev, Prezhdo, J. Chem. Phys. 120, 11209 (2004);math-ph/0403023]. Following the ultrafast excitation of donor[chem-ph/9411004] the population of acceptor rises by small portions per each vibrational period, oscillates force and back between donor and acceptor with later damping and partial revivals of this oscillation. The transfer rate gets larger as donor wavepacket approaches the acceptor equilibrium configuration, which is possible at specific energy differences of donor and acceptor...

Kilin, D S; Prezhdo, O V; Kilin, Dmitri S.; Cina, Jeffrey A.; Prezhdo, Oleg V.

2004-01-01

203

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

2009-06-08

204

Optomechanical and crystallization phenomena visualized with 4D electron microscopy: interfacial carbon nanotubes on silicon nitride.  

UK PubMed Central (United Kingdom)

With ultrafast electron microscopy (UEM), we report observation of the nanoscopic crystallization of amorphous silicon nitride, and the ultrashort optomechanical motion of the crystalline silicon nitride at the interface of an adhering carbon nanotube network. The in situ static crystallization of the silicon nitride occurs only in the presence of an adhering nanotube network, thus indicating their mediating role in reaching temperatures close to 1000 degrees C when exposed to a train of laser pulses. Under such condition, 4D visualization of the optomechanical motion of the specimen was followed by quantifying the change in diffraction contrast of crystalline silicon nitride, to which the nanotube network is bonded. The direction of the motion was established from a tilt series correlating the change in displacement with both the tilt angle and the response time. Correlation of nanoscopic motion with the picosecond atomic-scale dynamics suggests that electronic processes initiated in the nanotubes are responsible for the initial ultrafast optomechanical motion. The time scales accessible to UEM are 12 orders of magnitude shorter than those traditionally used to study the optomechanical motion of carbon nanotube networks, thus allowing for distinctions between the different electronic and thermal mechanisms to be made.

Flannigan DJ; Zewail AH

2010-05-01

205

Optomechanical and crystallization phenomena visualized with 4D electron microscopy: interfacial carbon nanotubes on silicon nitride.  

Science.gov (United States)

With ultrafast electron microscopy (UEM), we report observation of the nanoscopic crystallization of amorphous silicon nitride, and the ultrashort optomechanical motion of the crystalline silicon nitride at the interface of an adhering carbon nanotube network. The in situ static crystallization of the silicon nitride occurs only in the presence of an adhering nanotube network, thus indicating their mediating role in reaching temperatures close to 1000 degrees C when exposed to a train of laser pulses. Under such condition, 4D visualization of the optomechanical motion of the specimen was followed by quantifying the change in diffraction contrast of crystalline silicon nitride, to which the nanotube network is bonded. The direction of the motion was established from a tilt series correlating the change in displacement with both the tilt angle and the response time. Correlation of nanoscopic motion with the picosecond atomic-scale dynamics suggests that electronic processes initiated in the nanotubes are responsible for the initial ultrafast optomechanical motion. The time scales accessible to UEM are 12 orders of magnitude shorter than those traditionally used to study the optomechanical motion of carbon nanotube networks, thus allowing for distinctions between the different electronic and thermal mechanisms to be made. PMID:20377202

Flannigan, David J; Zewail, Ahmed H

2010-05-12

206

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

207

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

208

Modification of interfacial electronic structure as a function of organic overlayer stereochemistry  

Science.gov (United States)

Hydrogen bonding interactions involving molecular chiral centers control the organizational structure at the tartaric acid/Ag(111) interface. Specifically, for enantiopure tartaric acid films, a single molecule basis adsorbs with the molecular axis orientated parallel to the surface plane. Conversely, a paired basis unit composed of opposite enantiomers adsorbs with the combined molecular axis perpendicular to the surface plane for racemic tartaric acid films. Here, the unique electronic structure of each interface will be discussed. Scanning tunneling spectroscopy results give quantitative shifts of the Ag(111) Shockley-type surface state (67 meV below the Fermi level) of 881 meV and 55 meV for enantiopure and racemic films, respectively. Density functional theory computations have also been carried out in support of the experimental results. The respective energetic shifts will be discussed in terms of a modified surface potential, film polarizability, and work function changes.

Santagata, N. M.; Andrews, K. M.; Calzolari, A.; Buongiorno Nardelli, M.; Pearl, T.

2010-03-01

209

Interfacial reactions of glasses for biomedical application by scanning transmission electron microscopy and microanalysis.  

Science.gov (United States)

Short-term physico-chemical reactions at the interface between bioactive glass particles and biological fluids are studied for three glasses with different bioactive properties; these glasses are in the SiO(2)-Na(2)O-CaO-P(2)O(5)-K(2)O-Al(2)O(3)-MgO system. Our aim is to show the difference between the mechanisms of their surface reactions. The relation between the composition and the bioactive properties of these glasses is also discussed. The elemental analysis is performed at the submicrometer scale by scanning transmission electron microscopy associated with energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. After different immersion times (ranging from 0 to 96 h) of bioactive glass particles in a simulated biological solution, results show the formation of different surface layers at the glass periphery in the case of two bioactive glasses (A9 and BVA). For the third glass (BVH) we do not observe any surface layer formation or any modification of the glass composition. For the two other glasses (A9 and BVA), we observe the presence of different layers: an already observed (Si, O, Al) rich layer at the periphery, a previously demonstrated thin (Si, O) layer formed on top of the (Si, O, Al) layer and a (Ca, P) layer. We determine the different steps of the mechanisms of the surface reactions, which appear to be similar in these glasses, and compare the physico-chemical reactions and kinetics using the different immersion times. The A9 glass permits the observation of all important steps of the surface reactions which lead to bioactivity. This study shows the important relationship between composition and bioactivity which can determine the medical applicability of the glass. PMID:16701894

Banchet, V; Michel, J; Jallot, E; Wortham, L; Bouthors, S; Laurent-Maquin, D; Balossier, G

2006-03-24

210

Electron Transfer Between Colloidal ZnO Nanocrystals  

Energy Technology Data Exchange (ETDEWEB)

Colloidal ZnO nanocrystals capped with dodecylamine and dissolved in toluene can be charged photochemically to give stable solutions in which electrons are present in the conduction bands of the nanocrystals. These conduction-band electrons are readily monitored by EPR spectroscopy, with g* values that correlate with the nanocrystal sizes. Mixing a solution of charged small nanocrystals (e{sub CB}{sup -}:ZnO-S) with a solution of uncharged large nanocrystals (ZnO-L) caused changes in the EPR spectrum indicative of quantitative electron transfer from small to large nanocrystals. EPR spectra of the reverse reaction, e{sub CB}{sup -}:ZnO-L + ZnO-S, showed that electrons do not transfer from large to small nanocrystals. Stopped-flow kinetics studies monitoring the change in the UV bandedge absorption showed that reactions of 50 {micro}M nanocrystals were complete within the 5 ms mixing time of the instrument. Similar results were obtained for the reaction of charged nanocrystals with methyl viologen (MV{sup 2+}). These and related results indicate that the electron-transfer reactions of these colloidal nanocrystals are quantitative and very rapid, despite the presence of {approx}1.5 nm long dodecylamine capping ligands. These soluble ZnO nanocrystals are thus well-defined redox reagents suitable for studies of electron transfer involving semiconductor nanostructures.

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

2011-03-30

211

Photochemical electron transfer in liquid/liquid solvent systems  

Energy Technology Data Exchange (ETDEWEB)

A photoinduced charge transfer at the water/1,2-dichloroethane and water/benzonitrile interfaces was studied, using the photoredox couple ruthenium-trisbipyridine complex, Ru(byp){sub 3}{sup 2+}, dissolved in the organic phase and methyl viologen, MV{sup 2+}, in the aqueous phase. It was concluded that the photocurrent observed can be ascribed to an electron transfer between the excited ruthenium complex and methyl viologen.

Marecek, V.; De Armond, A.H.; De Armond, M.K. (New Mexico State Univ., Las Cruces (USA))

1989-03-29

212

Electron transfer between superoxide ion and in ?,?-unsaturated ketone  

International Nuclear Information System (INIS)

In order to study the single electron transfer between the superoxide ion and an ?,?-unsaturated ketone, cis-2,2,6,6-tetramethylhept-4-en-3-one was chosen as a molecule with appropriate reactivity criteria and without acidic protons. The stereochemistry of recovered starting material and product at low extents of reaction was examined. The reaction process of superoxide rapidly and reversibly transferring to olefin to produce a ketyl radical anion in a cage with O2 is proposed.

1984-01-01

213

Electron microscopic study on interfacial characterization of electroless Ni-W-P plating on aluminium alloy  

International Nuclear Information System (INIS)

The interface between electroless plating Ni-W-P deposit and aluminium alloy (Al) matrix at different temperature heated for 1 h was studied using transmission electron microscope. The results show that the interface between as-deposited Ni-W-P deposit and Al matrix is clear. There are no crack and cavity. The bonding of Ni-W-P deposit and Al matrix is in good condition. The Ni-W-P plating is nanocrystalline phase (5-6 nm) in diameter. After being heated at 200 deg. C for 1 h, the interface of Ni-W-P deposit and Al matrix is clear, without the appearance of the diffusion layer. There exist a diffusion layer and educts of intermetallic compounds of nickle and aluminium such as Al3Ni, Al3Ni2, NiAl, Ni5Al3 and so on between Ni-W-P deposit and Al matrix after being heated at 400 deg. C for 1 h.

2007-03-30

214

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

UK PubMed Central (United Kingdom)

In this paper we discuss the newly synthesized binuclear species [Cu2(L(PY18))2(?1,1-N3)2(N3)2] () and [Cu2(L(PY18))2(?1,3-SCN)2(NCS)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 and ?1,3-bridged (end-to-end, 2117 cm(-1)) thiocyanate groups in . Anion-to-copper LMCT electronic processes at 390 and 440 nm for and at 415 nm for 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, and 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.

Verani CN; Shanmugam R; Xavier FR; Allard MM; Kpogo KK

2013-07-01

215

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.

2007-04-20

216

Reactant-product quantum coherence in electron transfer reactions.  

UK PubMed Central (United Kingdom)

We investigate the physical meaning of quantum superposition states between reactants and products in electron transfer reactions. We show that such superpositions are strongly suppressed and, to leading orders of perturbation theory, do not pertain in electron transfer reactions. This is because of the intermediate manifold of states separating the reactants from the products. We provide an intuitive description of these considerations with Feynman diagrams. We also discuss the relation of such quantum coherences to understanding the fundamental quantum dynamics of spin-selective radical-ion-pair reactions.

Kominis IK

2012-08-01

217

Spin-Transfer Torque and Electron-Magnon Scattering  

CERN Multimedia

According to the spin-torque model, current-driven magnetic dynamics in ferromagnetic multilayers is determined by the transfer of electron spin perpendicular to the layers' magnetizations. By separating the largest contributions to the magnetic dynamics, we demonstrate that the dominant effect of spin-torque is rather due to the electron spin parallel to the field. We show that this effect can be equivalently described as stimulated current-driven excitation of spin-waves, and discuss four specifically quantum-mechanical aspects of spin-transfer, not described by the spin-torque.

Urazhdin, S

2004-01-01

218

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

219

Study of the interfacial reactions between a bioactive apatite-mullite glass-ceramic coating and titanium substrates using high angle annular dark field transmission electron microscopy.  

UK PubMed Central (United Kingdom)

Glass of generic composition SiO(2) . Al(2)O(3) . P(2)O(5) . CaO . CaF(2) will crystallise predominantly to apatite and mullite upon heat-treatment. Such ceramics are bioactive, osseoconductive, and have a high resistance to fracture. As a result, they are under investigation for use as biomedical device coatings, and in particular for orthopaedic implants. Previous work has shown that the material can be successfully enamelled to titanium with an interfacial reaction zone produced during heat treatment. The present study uses high angle annular dark field transmission electron microscopy (HAADF-TEM) to conduct a detailed examination of this region. Results show evidence of complex interfacial reactions following the diffusion of titanium into an intermediate layer and the production of titanium silicides and titanium phosphides. These results confirm previously hypothesised mechanisms for the bonding of silicate bioceramics with titanium alloys.

Stanton KT; O'Flynn KP; Nakahara S; Vanhumbeeck JF; Delucca JM; Hooghan B

2009-04-01

220

Intramolecular electron transfer in nitrite reductase studied by pulse radiolysis  

International Nuclear Information System (INIS)

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

1995-01-01

 
 
 
 
221

Intramolecular electron transfer in nitrite reductase studied by pulse radiolysis  

Energy Technology Data Exchange (ETDEWEB)

We report the evidence for the electron-transfer reaction between two copper sites in nitrite reductase from Achromobacter cycloclastes IAM 1013 by pulse radiolysis. Type 1 Cu sites in native (type 1 Cu : type 2 Cu = 1 : 0.5) and type 2 Cu-depleted (T2D) nitrite reductase are reduced with N-methylnicotinamide radical generated by the hydrated electron. The reductions of the coppers in the both enzymes give second-order rate constants of (3.4 - 3.5) x 10{sup 8} M{sup -1}s{sup -1}. In the case of the native enzyme, moreover, the recovery of the absorbance of reduced type 1 Cu is observed (about 35 %). This finding suggests the intramolecular electron transfer from type 1 Cu to type 2 Cu, because T2D nitrite reductase does not show the recovery of the absorption band at all. The electron-transfer occurs with an observed first order rate constant of 1400 s{sup -1}. The incomplete electron transfer from type 1 Cu to type 2 Cu are due to the difference between the redox potential of two Cu sites. (author).

Kobayashi, K.; Tagawa, S. [Osaka Univ., Ibaraki (Japan). Inst. of Scientific and Industrial Research; Kouzuma, T.; Deligeer; Yamaguchi, K.; Nakamura, N.; Suzuki, S.; Shidara, S.

1995-03-01

222

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

2013-01-09

223

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.)

1980-01-01

224

Quantum Mechanical Hysteresis and the Electron Transfer Problem  

CERN Multimedia

We study a simple quantum mechanical symmetric donor-acceptor model for electron transfer (ET) with coupling to internal deformations. The model contains several basic properties found in biological ET in enzymes and photosynthetic centers; it produces tunnelling with hysteresis thus providing a simple explanation for the slowness of the reversed rate and the near 100% efficiency of ET in many biological systems. The model also provides a conceptual framework for the development of molecular electronics memory elements based on electrostatic architectures.

Etchegoin, P G

2004-01-01

225

Exothermic rate restrictions on electron transfer in a rigid medium  

International Nuclear Information System (INIS)

Many highly exothermic (2--3 eV) electron transfer reactions are shown to be slower than moderately exothermic reactions by factors as large as 105. The decrease occurs in a regular way with increasing exothermicity, tending to confirm theoretical predictions of Franck--Condon restrictions on strongly exothermic electron transfer reactions. Deviations from the above trends occur if the reaction product, a molecular anion, has a low-lying electronic excited state into which the reaction may occur with more moderate vibrational exothermicity. Then greatly enhanced rates are found. The rates are enhanced to a lesser extent for acceptors likely to undergo configurational changes upon accepting an electron. These effects are found in measurements of rates of electron tunneling reactions between trapped electrons and 48 organic electron acceptors in rigid 2-methyltetrahydrofuran glass at 77 K. Electron tunneling rates were observed from 10-6 to 102 s. Measured tunneling distances were 15--40 A. In most cases the observed kinetic decay curves are well simulated by a theory in which the only variable parameter is the effective Franck--Condon factor (F), which is a constant characteristic of the acceptor. For the various acceptors F ranges from 1 to 10-5, and scales the reaction rate at each distance. However in reactions of small vibration exothermicity, the Franck--Condon factors are expected to be very sensitive to small changes in reaction exothermicity caused by relaxations of trapped electrons, which deepen their trap depths with time and, possibly, a dispersion of trap depths. These effects cause F to change with time leading to changes in the shapes of the decay curves. The relationship between the shapes of the decay curves, Franck--Condon factors, and exothermicity allows a semiquantitative interpretation of the present results and much of the earlier tunneling data on electron transfer

1979-12-01

226

Accumulative electron transfer: multiple charge separation in artificial photosynthesis.  

UK PubMed Central (United Kingdom)

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.

Karlsson S; Boixel J; Pellegrin Y; Blart E; Becker HC; Odobel F; Hammarström L

2012-01-01

227

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

228

Magnetic resonance studies of photo-induced electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

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

van Willigen, H.

1992-11-01

229

Fluctuations in biological and bioinspired electron-transfer reactions.  

UK PubMed Central (United Kingdom)

Central to theories of electron transfer (ET) is the idea that nuclear motion generates a transition state that enables electron flow to proceed, but nuclear motion also induces fluctuations in the donor-acceptor (DA) electronic coupling that is the rate-limiting parameter for nonadiabatic ET. The interplay between the DA energy gap and DA coupling fluctuations is particularly noteworthy in biological ET, where flexible protein and mobile water bridges take center stage. Here, we discuss the critical timescales at play for ET reactions in fluctuating media, highlighting issues of the Condon approximation, average medium versus fluctuation-controlled electron tunneling, gated and solvent relaxation controlled electron transfer, and the influence of inelastic tunneling on electronic coupling pathway interferences. Taken together, one may use this framework to establish principles to describe how macromolecular structure and structural fluctuations influence ET reactions. This framework deepens our understanding of ET chemistry in fluctuating media. Moreover, it provides a unifying perspective for biophysical charge-transfer processes and helps to frame new questions associated with energy harvesting and transduction in fluctuating media.

Skourtis SS; Waldeck DH; Beratan DN

2010-01-01

230

Energy and photoinduced electron transfer in porphyrin-fullerene dyads  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-09-26

231

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads. Technical progress report, 1989  

Energy Technology Data Exchange (ETDEWEB)

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

1989-04-12

232

Photoinduced electron transfer reactions of rose bengal and selected electron donors  

Energy Technology Data Exchange (ETDEWEB)

The photoinduced electron transfer reactions of the triplet state of rose bengal (RB) and several electron donors were investigated by the complementary techniques of steady state and time-resolved electron paramagnetic resonance (EPR) and laser flash photolysis (LFP). The yield of radicals varied with the light fluence rate, RB concentration and, in particular, the electron donor used. Thus for L-dopa (dopa, dihydroxyphenylalanine) only 10% of RB anion radical (RB[sup [minus

Sarna, T.; Zajac, J. (Jagiellonian Univ., Krakow (Poland). Dept. of Biophysics); Bowman, M.K. (Argonne National Lab., IL (United States). Chemistry Div.); Truscott, T.G. (Univ. of Keele (United Kingdom). Dept. of Chemistry)

1991-01-01

233

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

UK PubMed Central (United Kingdom)

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 < r(d) < 10 microm) and on the potential-determining ion concentration in the oil phase. The interfacial ET 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.

Nakatani K; Uchino M; Suzuki S; Negishi T; Osakai T

2009-02-01

234

Proton-Coupled Electron Transfer from Hydrogen-Bonded Phenols  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Proton-coupled electron transfer (PCET) is one of the elementary reactions occurring in many chemical and biological systems, such as photosystem II where the oxidation of tyrosine (TyrZ) is coupled to deprotonation of the phenolic proton. This reaction is here modelled by the...

Irebo, Tania

235

Energy transfer from ions to electrons and the Coulomb logarithm  

International Nuclear Information System (INIS)

Application of Chandrasekhar's stellar approach to plasmas reveals the importance of nondominant terms in both the energy transfer from ions to electrons and the form of the Coulomb logarithm. Curves illustrate the role of dominant and nondominant terms in the neighborhood of v/sub e/ approximately v/sub i/

1977-01-01

236

Fast electron transfer processes in cytochrome C and related metalloproteins.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Various free radicals formed on pulse radiolysis of aqueous solutions have been used to investigate the mechanisms of reduction of cytochrome(III) c by inter- and intramolecular electron transfer. The rapid formation of free radicals (t less than 1 mus) and their high reactivity with cytochrome (k a...

Simic, M G; Taub, I A

237

Electron transfer reactions from aromatic carbonyl triplets to paraquat dication  

Energy Technology Data Exchange (ETDEWEB)

The rate constants for electron transfer reactions from several aromatic carbonyl triplets to paraquat dication leading to the formation of paraquat radical ion have been measured by nanosecond laser flash photolysis and are found to be in the range, 1 - 9 x 10/sup 9/ M/sup -1/s/sup -1/.

Das, P.K.

1981-01-01

238

Electron transfer and ionic displacements at the origin of the 2D electron gas at the LAO/STO interface: direct measurements with atomic-column spatial resolution.  

UK PubMed Central (United Kingdom)

Using state-of-the-art, aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy with atomic-scale spatial resolution, experimental evidence for an intrinsic electronic reconstruction at the LAO/STO interface is shown. Simultaneous measurements of interfacial electron density and system polarization are crucial for establishing the highly debated origin of the 2D electron gas.

Cantoni C; Gazquez J; Miletto Granozio F; Oxley MP; Varela M; Lupini AR; Pennycook SJ; Aruta C; di Uccio US; Perna P; Maccariello D

2012-08-01

239

Ion and electron velocity distributions within flux transfer events  

Energy Technology Data Exchange (ETDEWEB)

The detailed nature of the thermal and suprathermal ion and electron distributions within magnetic flux transfer events (FTEs) is examined. Examples of both magnetosheath FTEs and magnetospheric FTEs are discussed. The detailed distributions confirm that FTEs contain a mixture of magnetosheath and magnetospheric plasmas. To lowest order, the distributions are consistent with a simple superposition of the two interpenetrating populations, with no strong interactions between them. To first order, some interesting differences appear, especially in the electron distributions, suggesting that considerable pitch angle scattering and some electron energy diffusion are also occurring. These observations should provide a useful test of analytical and numerical studies of interpenetrating plasmas. copyright American Geophysical Union 1987

Thomsen, M.F.; Stansberry, J.A.; Bame, S.J.; Fuselier, S.A.; Gosling, J.T.

1987-11-01

240

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

Directory of Open Access Journals (Sweden)

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

Manoranjan Reddy,; Vanka Amit,; SSV Prasad

2011-01-01

 
 
 
 
241

Charge transfer and electron backdonation in metallofullerenes encapsulating NSc3  

International Nuclear Information System (INIS)

[en] Orbital interaction analysis is employed to understand the complex charge transfer mechanism operative in endohedral metallofullerenes of composition NSc3-C n (n = 68, 78). This phenomenon combines substantial electron transfer from the core to the cage with electron backdonation, involving the interaction between the occupied orbitals of the negatively charged cage and the unoccupied d orbitals of the positively charged core. This electron backdonation differs fundamentally from conventional orbital hybridization, which takes place primarily between the HOMO of the metal core and the LUMO of the fullerene cage. These findings imply the pronounced stability of NSc3-C n (n = 68, 78), especially for NSc3 encapsulated in the non-IPR C68 enclosure, as experimentally established

2006-11-21

242

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

International Nuclear Information System (INIS)

The fundamental processes of electron transfer, ionization, and excitation in ion-atom collisions are being studied. These collision processes are treated in the context of simple one- or two-electron systems in order to provide unambiguous results and reveal more clearly the collisional mechanisms. As outlined in the original proposal, three coupled-state calculations are being carried out over the present three-year period: a Sturmian-pseudostate study of ionization in collisions between protons and the hydrogenic ions He+, Li2+, Be3+, ...; a triple-center, atomic-state study of ionization in collisions between ? particles and H(ls) atoms and between protons and He+(ls) ions; and an atomic-state study of electron transfer and excitation in collisions between protons and neutral He atoms. 12 refs

1987-01-01

243

Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved?  

UK PubMed Central (United Kingdom)

This review illuminates extracellular electron transfer mechanisms that may be involved in microbial bioelectrochemical systems with biocathodes. Microbially-catalyzed cathodes are evolving for new bioprocessing applications for waste(water) treatment, carbon dioxide fixation, chemical product formation, or bioremediation. Extracellular electron transfer processes in biological anodes, were the electrode serves as electron acceptor, have been widely studied. However, for biological cathodes the question remains: what are the biochemical mechanisms for the extracellular electron transfer from a cathode (electron donor) to a microorganism? This question was approached by not only analysing the literature on biocathodes, but also by investigating known extracellular microbial oxidation reactions in environmental processes. Here, it is predicted that in direct electron transfer reactions, c-type cytochromes often together with hydrogenases play a critical role and that, in mediated electron transfer reactions, natural redox mediators, such as PQQ, will be involved in the bioelectrochemical reaction. These mechanisms are very similar to processes at the bioanode, but the components operate at different redox potentials. The biocatalyzed cathode reactions, thereby, are not necessarily energy conserving for the microorganism.

Rosenbaum M; Aulenta F; Villano M; Angenent LT

2011-01-01

244

Cathodes as electron donors for microbial metabolism: which extracellular electron transfer mechanisms are involved?  

Science.gov (United States)

This review illuminates extracellular electron transfer mechanisms that may be involved in microbial bioelectrochemical systems with biocathodes. Microbially-catalyzed cathodes are evolving for new bioprocessing applications for waste(water) treatment, carbon dioxide fixation, chemical product formation, or bioremediation. Extracellular electron transfer processes in biological anodes, were the electrode serves as electron acceptor, have been widely studied. However, for biological cathodes the question remains: what are the biochemical mechanisms for the extracellular electron transfer from a cathode (electron donor) to a microorganism? This question was approached by not only analysing the literature on biocathodes, but also by investigating known extracellular microbial oxidation reactions in environmental processes. Here, it is predicted that in direct electron transfer reactions, c-type cytochromes often together with hydrogenases play a critical role and that, in mediated electron transfer reactions, natural redox mediators, such as PQQ, will be involved in the bioelectrochemical reaction. These mechanisms are very similar to processes at the bioanode, but the components operate at different redox potentials. The biocatalyzed cathode reactions, thereby, are not necessarily energy conserving for the microorganism. PMID:20688515

Rosenbaum, Miriam; Aulenta, Federico; Villano, Marianna; Angenent, Largus T

2010-08-04

245

A device for measuring spin selectivity in electron transfer.  

UK PubMed Central (United Kingdom)

A new type of device is presented that allows direct measurement of spin selectivity in charge transfer processes occurring in adsorbed molecules. The new device provides direct information about the nature of the charge being transferred (electrons or holes) and on spin selectivity, if it exists. Here the device is applied for establishing the spin-dependent electron transfer through double-stranded DNA and its variation with the length of the oligomer. The DNA is self-assembled on a silver substrate and is measured under ambient conditions. The device is based on monitoring the electric potential between a ferromagnetic Ni layer and a silver layer, on top of which the DNA is self-assembled. When a dye molecule, attached to the DNA, is photoexcited, a charge transfer between the dye and the silver substrate takes place, resulting in a change in the electric potential between the Ni and the silver. If the charge transfer is spin selective, the electric potential measured depends on the direction of magnetization of the Ni.

Senthil Kumar K; Kantor-Uriel N; Mathew SP; Guliamov R; Naaman R

2013-10-01

246

Electron transfer by excited benzoquinone anions: slow rates for two-electron transitions.  

UK PubMed Central (United Kingdom)

Electron transfer (ET) rate constants from the lowest excited state of the radical anion of benzoquinone, BQ(-•)*, were measured in THF solution. Rate constants for bimolecular electron transfer reactions typically reach the diffusion-controlled limit when the free-energy change, ?G°, reaches -0.3 eV. The rate constants for ET from BQ(-•)* are one-to-two decades smaller at this energy and do not reach the diffusion-controlled limit until -?G° is 1.5-2.0 eV. The rates are so slow probably because a second electron must also undergo a transition to make use of the energy of the excited state. Similarly, ET, from solvated electrons to neutral BQ to form the lowest excited state, is slow, while fast ET is observed at a higher excited state, which can be populated in a transition involving only one electron. A simple picture based on perturbation theory can roughly account for the control of electron transfer by the need for transition of a second electron. The picture also explains how extra driving force (-?G°) can restore fast rates of electron transfer.

Zamadar M; Cook AR; Lewandowska-Andralojc A; Holroyd R; Jiang Y; Bikalis J; Miller JR

2013-09-01

247

Energy transfer between electrons and ions in dense displacement cascades  

International Nuclear Information System (INIS)

A theory of the energy exchange between valence electrons and ions in the dense displacement cascades in metals is proposed. It is shown that the theory based on the relaxation of the nonequilibrium electron-ion system gives a common basis for the electronic stopping power of slow ions due to valence electrons and for the energy transfer via an electron-phonon interaction. It is found that the energy loss owing to the electron-phonon interaction bears a close relationship to the electronic stopping power, but it is greatly enhanced because of the emergence of phonon excitations and band structure. The corresponding cooling rates of the thermalizing cascade are several times greater in metals with a strong electron-ion interaction than in metals with a weak interaction. A similar conclusion holds in the intermediate region, where the ions in the thermalizing cascade are essentially free to move but band-structure effects persist. However, conduction electrons play a role in the cooling of the cascade only if the dynamics of the ions gives rise to phonons.

1993-01-01

248

Energy transfer between electrons and ions in dense displacement cascades  

Energy Technology Data Exchange (ETDEWEB)

A theory of the energy exchange between valence electrons and ions in the dense displacement cascades in metals is proposed. It is shown that the theory based on the relaxation of the nonequilibrium electron-ion system gives a common basis for the electronic stopping power of slow ions due to valence electrons and for the energy transfer via an electron-phonon interaction. It is found that the energy loss owing to the electron-phonon interaction bears a close relationship to the electronic stopping power, but it is greatly enhanced because of the emergence of phonon excitations and band structure. The corresponding cooling rates of the thermalizing cascade are several times greater in metals with a strong electron-ion interaction than in metals with a weak interaction. A similar conclusion holds in the intermediate region, where the ions in the thermalizing cascade are essentially free to move but band-structure effects persist. However, conduction electrons play a role in the cooling of the cascade only if the dynamics of the ions gives rise to phonons.

Koponen, I. (Department of Physics, University of Helsinki, Siltavuorenpenger 20 D, SF-00170 Helsinki (Finland))

1993-06-01

249

Electron transfer around photosystem I in cyanobacterial heterocyst membranes  

Energy Technology Data Exchange (ETDEWEB)

Cyanobacteria are unique among the prokaryotes in possessing a higher plant-type of photosynthesis, with two photosystems linked in series. The heterocyst is a specialized cell type occurring in some filamentous strains at a frequency of 5 to 10%, and is the site of N/sub 2/-fixation under aerobic conditions. During differentiation of the heterocyst, the O/sub 2/-evolving PSII is lost and cyclic electron transfer around PSI predominates. The absence of PSII reaction centres and the diminished levels of accessory pigments give membranes isolated from heterocysts excellent properties for spectroscopic studies. Soluble components such as plastocyanin, cytochrome c-553 and PSI acceptors, washed from the membranes during isolation, may be selectively reconstituted. Additionally, the presence of an endogenous uptake hydrogenase which can be utilized experimentally to reduce the plastoquinone pool and the electron transfer chain, make heterocyst membranes a useful system in which to study cyclic electron flow. This paper reports an initial flash spectroscopic characterization of the electron transfer chain and speculates on the potential of the system.

Hawkesford, M.J.; Houchins, J.P.; Hind, G.

1983-01-01

250

Electronic energy transfer: vibrational control and nonlinear wavepacket interferometry  

Science.gov (United States)

The time-development of photoexcitations in molecular aggregates exhibits specific dynamics of electronic states and vibrational wavefunction. We discuss the dynamical formation of entanglement between electronic and vibrational degrees of freedom in molecular aggregates with theory of electronic energy transfer and the method of vibronic 2D wavepackets [ J. Chem. Phys. 118, 46 (2003); quant-ph/0412219]. The vibronic dynamics is also described by applying Jaynes-Cummings model to the electronic energy transfer [J. Chem. Phys. 120, 11209 (2004); math-ph/0403023]. Following the ultrafast excitation of donor [ J. Phys. Chem 99, 2568 (1995); chem-ph/9411004] the population of acceptor rises by small portions per each vibrational period, oscillates force and back between donor and acceptor with later damping and partial revivals of this oscillation. The transfer rate gets larger as donor wavepacket approaches the acceptor equilibrium configuration, which is possible at specific energy differences of donor and acceptor and at maximal amount of the vibrational motion along the line that links donor and acceptor equilibria positions. The four-pulse phase-locked nonlinear wavepacket 2D interferograms reflect the shape of the relevant 2D vibronic wavepackets and have maxima at longer delay between excitation pulses for dimers with equal donor-acceptor energy difference compare to dimers with activationless energy configuration [Cina, Fleming, J. Phys. Chem. A. 108, 11196 (2004)].

Prezhdo, Oleg V.; Cina, Jeffrey A.; Kilin, Dmitri S.

2005-04-01

251

Unveiling the Details of Electron Transfer in Multicenter Redox Proteins.  

UK PubMed Central (United Kingdom)

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

Paquete CM; Louro RO

2013-08-01

252

Electron transfer and redox metalloenzyme catalysis at the single-molecule level  

DEFF Research Database (Denmark)

Voltammetry based on single-crystal, atomically-planar metal electrodes is novel in bioelectrochemistry. Together with in situ scanning tunneling microscopy (STM) directly in aqueous buffer, single-crystal voltammetry has disclosed new detail in molecular adsorption and interfacial electron transfer (ET). Image interpretation requires, however, theoretical support, as STM represents both electronic and topographic features. Molecules with accessible redox levels offer other insight into electron tunneling mechanisms, addressed in detail for ET metalloproteins. We present here in situ STM of the blue redox metalloenzyme copper nitrite reductase (Achromobacter xylosoxidans, AxCuNiR) on Au(111) electrode surfaces modified by a self-assembled cysteamine monolayer. AxCuNiR displays strong nitrite reduction waves in this environment. AxCuNiR/cysteamine/ Au(111) surfaces were imaged at KNO2 concentrations where most of the enzyme is in the enzyme-substrate bound state. Molecular resolution for both cysteamine/Au(111) and AxCuNiR/cysteamine/ Au(111) electrode surfaces was achieved. The enzyme coverage is about 1.5 x 10(-13) Mol cm(-2), which is low compared with an ideal close-packed monolayer. The adlayer behaves as an assembly of individual molecules, reflected in distributions of molecular appearance, although a number of molecules do show the triangular shape of the trimeric AxCuNiR structure. The apparent average molecular height is about 11 Angstrom. This suggests that details of electronic structures and larger assemblies are needed to disentangle enzyme mechanisms at the single-molecule level.

Hansen, Allan Glargaard; Zhang, Jingdong

2004-01-01

253

Structures of protein-protein complexes involved in electron transfer.  

UK PubMed Central (United Kingdom)

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.

Antonyuk SV; Han C; Eady RR; Hasnain SS

2013-04-01

254

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

2013-03-27

255

Atomic-orbital expansion representation of electron transfer in two-electron systems  

International Nuclear Information System (INIS)

[en] Election transfer in two electron ion-atom collision systems is examined using united-atom orbitals (AO+) basic sets. The Hamiltonian is the sum of H0 (i), the Hamiltonian of electron i with respect to the two nuclei (or atomic cores), and the electron-electron interaction. With the electron wavefunction expanded in the AO+ basis sets, with the Hamiltonian and with a curved-line inter-nuclear trajectory, the time-dependent Schroedinger equation is solved within the basis space without further approximations. 8 refs., 1 fig

1985-01-01

256

Distance dependence of photochemical electron transfer across peptide spacers  

Energy Technology Data Exchange (ETDEWEB)

The distance dependence of the rate and activation parameters for photoinduced electron transfer (ET) across a series of L-proline peptide spacers has been determined in compounds 0-2. In 0-2, the d{pi}(Re){yields}{pi}{sup *}(bpy) metal-to-ligand charge-transfer (MLCT) excited state is quenched by intramolecular ET from the aromatic amine. The rate for ET (k{sub et}) was determined by comparing the MLCT emission lifetimes of 0-2 with the lifetimes of appropriate model complexes. The kinetic results are consistent with a nonadiabatic mechanism for ET in which the variation of k{sub et} with distance results mainly from a decrease in electronic coupling with increased donor-acceptor separation.

Schanze, K.S.; Cabana, L.A. (Univ. of Florida, Gainesville (USA))

1990-04-05

257

SF4: electron affinity determination by charge-transfer reactions  

Science.gov (United States)

A selected-ion flow drift tube was used to conduct an extensive study of the negative ion/molecule reaction of SF4 and SF-4. Thirteen reactions proceed by electron transfer. Data from these reactions, and information from systems that do not react at all, are used to determine the electron affinity of SF4, EA(SF4) = 1.5 ± 0.2 eV. Additional thermochemical data are used to determine the fluoride affinity of SF3, D(SF3-F-) = 1.8 ± 0.3 eV.

Viggiano, A. A.; Miller, Thomas M.; Stevens Miller, Amy E.; Morris, Robert A.; van Doren, Jane M.; Paulson, John F.

1991-11-01

258

Electronic structure charge transfer excitations, and high temperature superconductivity  

International Nuclear Information System (INIS)

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

1988-01-01

259

Free radical scavenging by natural polyphenols: atom versus electron transfer.  

UK PubMed Central (United Kingdom)

Polyphenols (synthetically modified or directly provided by human diet) scavenge free radicals by H-atom transfer and may thus decrease noxious effects due to oxidative stress. Free radical scavenging by polyphenols has been widely theoretically studied from the thermodynamic point of view whereas the kinetic point of view has been much less addressed. The present study describes kinetic-based structure-activity relationship for quercetin. This compound is very characteristic of the wide flavonoid subclass of polyphenols. H-atom transfer is a mechanism based on either atom or electron transfer. This is analyzed here by quantum chemical calculations, which support the knowledge acquired from experimental studies. The competition between the different processes is discussed in terms of the nature of the prereaction complexes, the pH, the formation of activated-deprotonated forms, and the atom- and electron-transfer efficiency. The role of the catechol moiety and the 3-OH group of quercetin as scavengers of different types of free radicals (CH3OO(•), CH3O(•), (•)OH, and (•)CH2OH) is rationalized. Identifying the exact mechanism and accurately evaluating kinetics is of fundamental importance to understand antioxidant behavior in physiological environments.

Di Meo F; Lemaur V; Cornil J; Lazzaroni R; Duroux JL; Olivier Y; Trouillas P

2013-03-01

260

Electrogenerated chemiluminescence and interfacial charge transfer dynamics of poly(3-hexylthiophene-2,5-diyl) (P3HT)-TiO2 nanoparticle thin film.  

UK PubMed Central (United Kingdom)

We present electrogenerated chemiluminescence (ECL) and photoluminescence (PL) characteristics of poly(3-hexylthiophene-2,5-diyl) (P3HT) thin films incorporated with monodisperse TiO(2) nanoparticles prepared using a hydrothermal reaction in the presence of oleylamine and oleic acid. The ECL turn-on potential decreases in the presence of TiO(2) nanocrystals, accompanied with an increase in ECL intensity. Only a minor ECL quantum efficiency decrease is obtained in the presence of <40 wt% TiO(2), indicating the formation of an effective interpenetrating network of TiO(2) and disordering of polymer packing to allow the ECL coreactant to transport through the film for efficient electroluminescence. In contrast, PL quenching increases with the weight percentage of TiO(2) and significant PL quenching is obtained when the P3HT film contains up to 80 wt% TiO(2) due to charge transfer. Polaron absorption after the photoinduced charge separation in the presence of 80 wt% TiO(2) nanoparticles is significantly enhanced with longer-lived lifetimes of >1000 ps in contrast to the neat P3HT film. The absorption of polarons created at the P3HT-TiO(2) interface is found to increase with the P3HT-TiO(2) interfacial area per unit volume.

Geng H; Hill CM; Pan S; Huang L

2013-03-01

 
 
 
 
261

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).  

Science.gov (United States)

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 120s Ta and Ag in the presence of N2 and O2 led to the faster E. coli inactivation by a TaON/Ag sample within ?40min 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 Ag(0), 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. PMID:23867967

Rtimi, S; Sanjines, R; Pulgarin, C; Houas, A; Lavanchy, J-C; Kiwi, J

2013-06-15

262

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).  

UK PubMed Central (United Kingdom)

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 120s Ta and Ag in the presence of N2 and O2 led to the faster E. coli inactivation by a TaON/Ag sample within ?40min 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 Ag(0), 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.

Rtimi S; Sanjines R; Pulgarin C; Houas A; Lavanchy JC; Kiwi J

2013-09-01

263

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

CERN Document Server

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

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

2005-01-01

264

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

Scientific Electronic Library Online (English)

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

Velasco, Jaime González

2007-01-01

265

Effect of long-distance electron transfer on chemiluminescence efficiencies  

Energy Technology Data Exchange (ETDEWEB)

The electrogenerated chemiluminescence (ecl) of Mo/sub 6/Cl/sub 14//sup 2 -/ with three series of structurally and electronically related electroactive organic compounds in acetonitrile has been investigated. The yields for the formation of the electronically excited Mo/sub 6/Cl/sub 14//sup -/ ion produced by the electron-transfer reaction of Mo/sub 6/Cl/sub 14//sup 3 -/ with aromatic amine radical cations (A+) and by the reaction of Mo/sub 6/Cl/sub 14//sup -/ with nitroaromatic radical anions (D/sup -/) and pyridinium radicals (D) have been measured over a wide potential range by simply varying the reduction potential of the electroactive organic reagent. The dependence of the formation yield of Mo/sub 6/Cl/sub 14//sup 2 -/*, phi/sub es/, on the driving force of the annihilation reaction is similar for the three series, phi/sub es/ is immeasurable (< 10/sup -6/) for reactions with free energies positive of a threshold value. Over a narrow free energy range just negative of threshold, phi/sub es/ rapidly increases. And with increasing exergonicity of the electron-transfer reaction, phi/sub es/ asymptotically approaches a limiting value less than unity (phi/sub es//sup lim/(Mo/sub 6/Cl/sub 14//sup -//D/sup -/) = 0.013 +/- 0.001; phi/sub es//sup lim/(Mo/sub 6/Cl/sub 14//sup -//D) = 0.079 +/- 0.008; phi/sub es//sup lim/(Mo/sub 6/Cl/sub 14//sup 3 -//A/sup +/) = 0.132 +/- 0.006). Analysis of these excited-state production yields by Marcus theory suggests that unit efficiencies for excited-state production are circumvented by long-distance electron transfer.

Mussell, R.D.; Nocera, D.G.

1988-04-27

266

Rapid long range intramolecular electron transfer within a steroid molecule with two electron binding groups  

Energy Technology Data Exchange (ETDEWEB)

Intramolecular electron transfer has been observed to have occurred in less than 100 ns in a steroid molecule having two distinct electron binding groups separated by distances distributed from 7--11 A. Experiments were carried out in organic glasses at 77 K with pulse radiolysis techniques to create trapped electrons which were captured by a group on one end of the steroid molecule. Although one of the groups, benzoate, is held to the steroid spacer by a flexible linkage, the rigidity of the glassy matrices prevented movement to alter the initial distance. Interestingly, no effects of distance were seen: all ET processes appeared to have occurred much faster than our 100 ns time resolution, consistent with measurements of the rate of intermolecular electron transfer between the same functional groups in random solutions. Solvation energetics, on the other hand, had a remarkable influence on the extent and direction of electron transfer. A change in solvent polarity was observed to reverse the direction of electron transfer. Evidence was obtained for a distribution of solvation environments for ions in glasses which may be as broad as 0.15 eV.

Huddleston, R.K.; Miller, J.R.

1983-12-01

267

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-10-22

268

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

Science.gov (United States)

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

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

2008-09-25

269

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

International Nuclear Information System (INIS)

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

2008-10-22

270

On the hopping efficiency of nanoparticles in the electron transfer across self-assembled monolayers.  

Science.gov (United States)

Redox reactions of solvated molecular species at gold-electrode surfaces modified by electrochemically inactive self-assembled molecular monolayers (SAMs) are found to be activated by introducing Au nanoparticles (NPs) covalently bound to the SAM to form a reactive Au-alkanedithiol-NP-molecule hybrid entity. The NP appears to relay long-range electron transfer (ET) so that the rate of the redox reaction may be as efficient as directly on a bare Au electrode, even though the ET distance is increased by several nanometers. In this study, we have employed a fast redox reaction of surface-confined 6-(ferrocenyl) hexanethiol molecules and NPs of Au, Pt and Pd to address the dependence of the rate of ET through the hybrid on the particular NP metal. Cyclic voltammograms show an increasing difference in the peak-to-peak separation for NPs in the order Auinterfacial electrochemical ET theory, combined with a simplified two-step view of the NP coupling to the electrode and the molecule, this observation is referred to the density of electronic states of the NPs, reflected in a broadening of the molecular electron/NP bridge group levels and energy-gap differences between the Fermi levels of the different metals. PMID:23401384

Liu, Feng; Khan, Kamran; Liang, Jing-Hong; Yan, Jia-Wei; Wu, De-Yin; Mao, Bing-Wei; Jensen, Palle Skovhus; Zhang, Jingdong; Ulstrup, Jens

2013-02-07

271

On the hopping efficiency of nanoparticles in the electron transfer across self-assembled monolayers.  

UK PubMed Central (United Kingdom)

Redox reactions of solvated molecular species at gold-electrode surfaces modified by electrochemically inactive self-assembled molecular monolayers (SAMs) are found to be activated by introducing Au nanoparticles (NPs) covalently bound to the SAM to form a reactive Au-alkanedithiol-NP-molecule hybrid entity. The NP appears to relay long-range electron transfer (ET) so that the rate of the redox reaction may be as efficient as directly on a bare Au electrode, even though the ET distance is increased by several nanometers. In this study, we have employed a fast redox reaction of surface-confined 6-(ferrocenyl) hexanethiol molecules and NPs of Au, Pt and Pd to address the dependence of the rate of ET through the hybrid on the particular NP metal. Cyclic voltammograms show an increasing difference in the peak-to-peak separation for NPs in the order Auinterfacial electrochemical ET theory, combined with a simplified two-step view of the NP coupling to the electrode and the molecule, this observation is referred to the density of electronic states of the NPs, reflected in a broadening of the molecular electron/NP bridge group levels and energy-gap differences between the Fermi levels of the different metals.

Liu F; Khan K; Liang JH; Yan JW; Wu DY; Mao BW; Jensen PS; Zhang J; Ulstrup J

2013-04-01

272

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 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.

2003-05-14

273

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1997-07-01

274

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-06-08

275

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

Science.gov (United States)

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

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

2012-02-01

276

A nonadiabatic and nonlinear theory for electron transfer  

Science.gov (United States)

We propose a general theory both non adiabatic and nonlinear which extends those used for the standard theory of electron transfer (ET) in chemistry but also becomes equivalent to it far from the inversion point. In the vicinity of the inversion point, the model parameters may be finely tuned such that large amplitude electronic oscillations between the donor and an extrasite, associated with large amplitude and collective phonon oscillations at the same frequency, are spontaneously generated (coherent electron phonon oscillator or CEPO). This extrasite is not a true acceptor but could play the role of a catalyst because by the CEPO it may trigger irreversible and ultrafast ET at low temperature toward a third site which is a real acceptor (while in the absence of catalyst, ET cannot occur). Such a trimer system may be regulated by small perturbations and behaves as a molecular transistor. We illustrate this idea by explicit numerical simulations on trimer models of the type donor-catalyst-acceptor. We discuss the relevance of our approach for understanding the ultrafast electron transfer experimentally observed in biosystems such as the photosynthetic reaction center.

Aubry, Serge

2008-03-01

277

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

278

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads. Technical progress report  

Energy Technology Data Exchange (ETDEWEB)

This research project involves the design, synthesis and study of molecules which mimic many of the important aspects of photosynthetic electron and energy transfer. The knowledge gained from the study of synthetic model systems which abstract features of the natural photosynthetic apparatus can be used to design artificial photosynthetic systems which employ the basic physics and chemistry of photosynthesis to help meet mankind`s energy needs. More specifically, the proposed models are designed to mimic the following aspects of natural photosynthetic multistep electron transfer: electron donation from a tetrapyrrole excited singlet state, electron transfer between tetrapyrroles, electron transfer from tetrapyrroles to quinones, and electron transfer between quinones with different redox properties.

Gust, J.D. Jr.; Moore, T.A.

1988-04-12

279

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 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

1992-01-01

280

Ion and electron velocity distributions within flux transfer events  

International Nuclear Information System (INIS)

[en] The detailed nature of the thermal and suprathermal ion and electron distributions within magnetic flux transfer events (FTEs) is examined. Examples of both magnetosheath FTEs and magnetospheric FTEs are discussed. The detailed distributions confirm that FTEs contain a mixture of magnetosheath and magnetospheric plasmas. To lowest order, the distributions are consistent with a simple superposition of the two interpenetrating populations, with no strong interactions between them. To first order, some interesting differences appear, especially in the electron distributions, suggesting that considerable pitch angle scattering and some electron energy diffusion are also occurring. These observations should provide a useful test of analytical and numerical studies of interpenetrating plasmas. copyright American Geophysical Union 1987

1987-11-01

 
 
 
 
281

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-04-01

282

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

International Nuclear Information System (INIS)

We study for electron-impact excitation of ions with two valence electrons (Be2+, C2+ and Si2+) from the ground state to the first 1P0 state using the R-matrix method. The integral cross sections and polarization degree for this transition of each ion are obtained. The differential cross sections and angular momentum transfer are also shown at a few energies in the non-resonant region. The present angular momentum transfer for Be2+ and C2+ at small scattering angles has positive values, while it is negative for Si2+.

2009-04-01

283

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 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.

1979-01-01

284

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.

2009-04-01

285

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

UK PubMed Central (United Kingdom)

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

Choi H; Santra PK; Kamat PV

2012-06-01

286

Dynamic Control of Electron Transfers in Diflavin Reductases  

Directory of Open Access Journals (Sweden)

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

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

2012-01-01

287

Front-end electron transfer dissociation: a new ionization source.  

UK PubMed Central (United Kingdom)

Electron transfer dissociation (ETD), a technique that provides efficient fragmentation while depositing little energy into vibrational modes, has been widely integrated into proteomics workflows. Current implementations of this technique, as well as other ion-ion reactions like proton transfer, involve sophisticated hardware, lack robustness, and place severe design limitations on the instruments to which they are attached. Described herein is a novel, electrical discharge-based reagent ion source that is located in the first differentially pumped region of the mass spectrometer. The reagent source was found to produce intense reagent ion signals over extended periods of time while having no measurable impact on precursor ion signal. Further, the source is simple to construct and enables implementation of ETD on any instrument without modification to footprint. Finally, in the context of hybrid mass spectrometers, relocation of the reagent ion source to the front of the mass spectrometer enables new approaches to gas phase interrogation of intact proteins.

Earley L; Anderson LC; Bai DL; Mullen C; Syka JE; English AM; Dunyach JJ; Stafford GC Jr; Shabanowitz J; Hunt DF; Compton PD

2013-09-01

288

Quantum theory for free energies of electron transfer  

Energy Technology Data Exchange (ETDEWEB)

We consider the problem of electron transfer between two symmetric redox states for cases in which the interstate coupling can be strong and the coupled harmonic bath can be nonadiabatic. We utilize an adiabatic bath coupled to the charge transfer species as a reference system and treat the solvation effects of nonzero frequency Fourier modes approximately, yielding an analytical theory for the activation free energy in terms of the spectral density of the bath. The theory is exact for both slow and fast bath modes. For small interstate coupling, the theory agrees with the golden rule result. We test the theory's accuracy at large couplings in the intermediate frequency regime by comparison with Monte Carlo simulation.

Gehlen, J.N.; Chandler, D. (Department of Chemistry, University of California at Berkeley, Berkeley, California 94720 (United States))

1992-10-01

289

Front-end electron transfer dissociation: a new ionization source.  

Science.gov (United States)

Electron transfer dissociation (ETD), a technique that provides efficient fragmentation while depositing little energy into vibrational modes, has been widely integrated into proteomics workflows. Current implementations of this technique, as well as other ion-ion reactions like proton transfer, involve sophisticated hardware, lack robustness, and place severe design limitations on the instruments to which they are attached. Described herein is a novel, electrical discharge-based reagent ion source that is located in the first differentially pumped region of the mass spectrometer. The reagent source was found to produce intense reagent ion signals over extended periods of time while having no measurable impact on precursor ion signal. Further, the source is simple to construct and enables implementation of ETD on any instrument without modification to footprint. Finally, in the context of hybrid mass spectrometers, relocation of the reagent ion source to the front of the mass spectrometer enables new approaches to gas phase interrogation of intact proteins. PMID:23909443

Earley, Lee; Anderson, Lissa C; Bai, Dina L; Mullen, Christopher; Syka, John E P; English, A Michelle; Dunyach, Jean-Jacques; Stafford, George C; Shabanowitz, Jeffrey; Hunt, Donald F; Compton, Philip D

2013-08-19

290

Covalent electron transfer chemistry of graphene with diazonium salts.  

UK PubMed Central (United Kingdom)

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.

Paulus GL; Wang QH; Strano MS

2013-01-01

291

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.

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

2013-01-01

292

Light induced electron transfer reactions of metal complexes  

International Nuclear Information System (INIS)

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

1980-07-19

293

Photoinduced electron transfer from phycoerythrin to colloidal metal semiconductor nanoparticles.  

UK PubMed Central (United Kingdom)

Phycoerythrin is a water soluble pigment which absorbs in the visible region at 563 nm. The interaction of phycoerythrin with colloidal metal semiconductors was studied by absorption, FT-IR and fluorescence spectroscopy. Phycoerythrin adsorbed strongly on the surface of TiO(2) nanoparticles, the apparent association constant for the association between colloidal metal-TiO(2) nanoparticles and phycoerythrin was determined from fluorescence quenching data. The free energy change (DeltaG(et)) for electron transfer process has been calculated by applying Rehm-Weller equation.

Kathiravan A; Chandramohan M; Renganathan R; Sekar S

2009-04-01

294

Importance of Charge Transfer Excitations in DNA Electron Spectrum:  

Science.gov (United States)

Electron spectra of DNA model compounds, adenosine-thymidine and guanosine-cytidine nucleoside base pairs, as well as the relevant homogeneous stacked base pair steps in A-DNA and B-DNA conformations, were investigated using ZINDO semiempirical quantum-chemical method. This work confirms that, in DNA with intact Watson-Crick hydrogen bonding and base stacking, the highest occupied molecular orbitals (HOMO) are residing on purine base residues, whereas the lowest unoccupied molecular orbitals (LUMO) — on pyrimidine base residues. In general, the present results are satisfactorily comparable with the available experimental data. The role of charge transfer excitations in the polymer DNA 260 nm spectral band is discussed.

Starikov, E. B.

295

Preliminary estimate of heavy ion electron-transfer cross sections  

International Nuclear Information System (INIS)

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

1978-09-26

296

Artificial Photosynthesis: From Nanosecond Electron Transfer to Catalytic Water Oxidation.  

UK PubMed Central (United Kingdom)

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.

Kärkäs MD; Johnston EV; Verho O; Akermark B

2013-08-01

297

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

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

Sutin, N.; Creutz, C.

1980-01-01

298

Light induced electron transfer reactions of metal complexes  

Energy Technology Data Exchange (ETDEWEB)

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

Sutin, N; Creutz, C

1980-01-01

299

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.

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

2011-01-01

300

Controlled single electron transfer between Si:P quantum dots  

CERN Document Server

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

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

2005-01-01

 
 
 
 
301

Biochemical Mechanisms Controlling Terminal Electron Transfer in Geobacter sulfurreducens  

Science.gov (United States)

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

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

2009-04-01

302

Electronic Energy Transfer: Localized Operator Partitioning of Electronic Energy in Composite Quantum Systems  

CERN Multimedia

A Hamiltonian based approach using spatially localized projection operators is introduced to give precise meaning to the chemically intuitive idea of the electronic energy on a quantum subsystem. This definition facilitates the study of electronic energy transfer in arbitrarily coupled quantum systems. In particular, the decomposition scheme can be applied to molecular components that are strongly interacting (with significant orbital overlap) as well as to isolated fragments. The result leads to the proper electronic energy at all internuclear distances, including the case of separated fragments, and reduces to the well-known Forster and Dexter results in their respective limits. Numerical calculations of coherent energy and charge transfer dynamics in simple model systems are presented and the effect of collisionally induced decoherence is examined.

Khan, Yaser R

2012-01-01

303

An electron transfer dependent membrane potential in chromaffin-vesicle ghosts.  

UK PubMed Central (United Kingdom)

Adrenal medullary chromaffin-vesicle membranes contain a transmembrane electron carrier that may provide reducing equivalents for intravesicular dopamine beta-hydroxylase in vivo. This electron transfer system can generate a membrane potential (inside positive) across resealed chromaffin-vesicle membranes (ghosts) by passing electrons from an internal electron donor to an external electron acceptor. Both ascorbic acid and isoascorbic acid are suitable electron donors. As an electron acceptor, ferricyanide elicits a transient increase in membrane potential at physiological temperatures. A stable membrane potential can be produced by coupling the chromaffin-vesicle electron-transfer system to cytochrome oxidase by using cytochrome c. The membrane potential is generated by transferring electrons from the internal electron donor to cytochrome c. Cytochrome c is then reoxidized by cytochrome oxidase. In this coupled system, the rate of electron transfer can be measured as the rate of oxygen consumption. The chromaffin-vesicle electron-transfer system reduces cytochrome c relatively slowly, but the rate is greatly accelerated by low concentrations of ferrocyanide. Accordingly, stable electron transfer dependent membrane potentials require cytochrome c, oxygen, and ferrocyanide. They are abolished by the cytochrome oxidase inhibitor cyanide. This membrane potential drives reserpine-sensitive norepinephrine transport, confirming the location of the electron-transfer system in the chromaffin-vesicle membrane. This also demonstrates the potential usefulness of the electron transfer driven membrane potential for studying energy-linked processes in this membrane.

Harnadek GJ; Callahan RE; Barone AR; Njus D

1985-01-01

304

Between a Rock and a Hard Place: Geomicrobial Electron Transfer  

Energy Technology Data Exchange (ETDEWEB)

The success of microbial life on Earth can largely be attributed to their collective ability to squeeze energy from a broad range of electron donor and acceptor couples including many where the electrochemical potential between the couples is marginally favorable (i.e, small ?G). Many of the redox couples that microbiologists employ to cultivate their favorite organism(s) involve compounds that are relatively water soluble, such as glucose and O2, and can readily diffuse to and from cells. In contrast, many organic and inorganic substrates, either electron donors or acceptors, exist as solids that are poorly soluble or insoluble. Certain heterotrophic microorganisms have overcome this problem by secreting enzymes outside the cell that can break down insoluble polymers, such as chitin and cellulose, to soluble subunits that are readily accessed by cells. Over the past few decades an increasing number of microorganisms have been isolated and studied that are capable of utilizing transition metal ions such as Fe and Mn as electron acceptors or donors. In their most oxidized form Fe(III) and Mn(IV) exist predominantly as metal oxides of varying morphology and composition but have in common low solubility in neutral pH environments and in the absence of complexing ligands. What clever mechanisms have microorganisms evolved to facilitate electron transfer to and from metal ions that are sequestered in minerals?

Fredrickson, Jim K.

2005-03-10

305

Electromagnetic field generation by ATP-induced reverse electron transfer.  

UK PubMed Central (United Kingdom)

This paper describes a mechanism to explain low-level light emission in biology. A biological analog of the electrical circuitry, modeled on the parallel plate capacitor, traversed by a helical structure, required to generate electromagnetic radiation in the optical spectral range, is described. The charge carrier required for the emissions is determined to be an accelerating electron driven by an ATP-induced reverse electron transfer. The radial velocity component, the emission trajectory, of the moving charges traversing helical protein structures in a cyclotron-type mechanism is proposed to be imposed by the ferromagnetic field components of the iron in the iron-sulfur proteins. The redox systems NADH, riboflavin, and chlorophyll were examined with their long-wavelength absorption maxima determining the energetic parameters for the calculations. Potentials calculated from the axial velocity components for the riboflavin and NADH systems were found to equal the standard redox potentials of these systems as measured electrochemically and enzymatically. The mechanics for the three systems determined the magnetic moments, the angular momenta, and the orbital magnetic fluxes to be adiabatic invariant parameters. The De Broglie dual wave-particle equation, the fundamental equation of wave mechanics, and the key idea of quantum mechanics, establishes the wavelengths for accelerating electrons which, divided into a given radial velocity, gives its respective emission frequency. Electrons propelled through helical structures, traversed by biologically available electric and magnetic fields, make accessible to the internal environment the optical spectral frequency range that the solar spectrum provides to the external environment.

Steele RH

2003-03-01

306

Spatial Resolution and Information Transfer in Scanning Transmission Electron Microscopy  

Energy Technology Data Exchange (ETDEWEB)

The relation between image resolution and information transfer is explored. It is shown that the existence of higher frequency transfer in the image is just a necessary but not sufficient condition for the achievement of higher resolution. Adopting a two-point resolution criterion, we suggest that a 10% contrast level between two features in an image should be used as a practical definition of resolution. In the context of scanning transmission electron microscopy, it is shown that the channeling effect does not have a direct connection with image resolution because sharp channeling peaks do not move with the scanning probe. Through a quantitative comparison between experimental image and simulation, a Fourier-space approach is proposed to estimate defocus and sample thickness. The effective atom size in Z-contrast imaging depends on the annular detector's inner angle. Therefore, an optimum angle exists for the highest resolution as a trade-off between reduced atom size and reduced signal with limited information transfer due to noise.

Peng, Yiping [ORNL; Oxley, Mark P [ORNL; Lupini, Andrew R [ORNL; Chisholm, Matthew F [ORNL; Pennycook, Stephen J [ORNL

2008-01-01

307

Wireless transfer of sensor data into electronic health records.  

Science.gov (United States)

The purpose of this study is to explore how wireless transfer of sensor data can be implemented in existing Electronic Health Record (EHR) systems. Blood glucose data from people with diabetes Type 1 has been selected as the case.As proof of concept, a prototype for sending blood glucose measurements into an EHR system was developed for the DIPS EHR system. For the prototype to be transferable to a general setting, care was taken not to introduce any additional workload for the diabetes nurses or the diabetes Type 1 patients. In the prototype, the transfer of blood glucose data is automatic and invisible to the user, and the data is presented to the nurses within the existing DIPS laboratory module.To determine whether deployment of such a system would present any risks or hazards to patients (medical or financial), a risk analysis was performed. The analysis indicates that storing blood glucose values in the patient's EHR does not represent any significantly increased risks for the diabetes patient.The study shows that existing EHR systems are well suited to receive sensor data. The three main EHR systems in Norwegian hospitals are all supported with application programming interfaces (APIs), enabling external vendors to add modules. These APIs are sufficient to implement modules for receiving sensor data. However, none of the systems currently have commercially available modules for receiving such data. PMID:16160281

Walseth, Ole Anders; Arsand, Eirik; Sund, Torbjørn; Skipenes, Eva

2005-01-01

308

Wireless transfer of sensor data into electronic health records.  

UK PubMed Central (United Kingdom)

The purpose of this study is to explore how wireless transfer of sensor data can be implemented in existing Electronic Health Record (EHR) systems. Blood glucose data from people with diabetes Type 1 has been selected as the case.As proof of concept, a prototype for sending blood glucose measurements into an EHR system was developed for the DIPS EHR system. For the prototype to be transferable to a general setting, care was taken not to introduce any additional workload for the diabetes nurses or the diabetes Type 1 patients. In the prototype, the transfer of blood glucose data is automatic and invisible to the user, and the data is presented to the nurses within the existing DIPS laboratory module.To determine whether deployment of such a system would present any risks or hazards to patients (medical or financial), a risk analysis was performed. The analysis indicates that storing blood glucose values in the patient's EHR does not represent any significantly increased risks for the diabetes patient.The study shows that existing EHR systems are well suited to receive sensor data. The three main EHR systems in Norwegian hospitals are all supported with application programming interfaces (APIs), enabling external vendors to add modules. These APIs are sufficient to implement modules for receiving sensor data. However, none of the systems currently have commercially available modules for receiving such data.

Walseth OA; Arsand E; Sund T; Skipenes E

2005-01-01

309

Photoinduced Electron Transfer Modeling to Simulate Flavoprotein Fluorescence Decay.  

UK PubMed Central (United Kingdom)

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

Nunthaboot N; Lugsanangarm K; Nueangaudom A; Pianwanit S; Kokpol S; Tanaka F

2014-01-01

310

ELECTRONIC FUNDS TRANSFER: EXPLORING THE DIFFICULTIES OF SECURITY  

Directory of Open Access Journals (Sweden)

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

MPAKWANA ANNASTACIA MTHEMBU

2010-01-01

311

Photoinduced electron transfer modeling to simulate flavoprotein fluorescence decay.  

Science.gov (United States)

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

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

2014-01-01

312

Photoinduced electron transfer modeling to simulate flavoprotein fluorescence decay.  

UK PubMed Central (United Kingdom)

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

Nunthaboot N; Lugsanangarm K; Nueangaudom A; Pianwanit S; Kokpol S; Tanaka F

2014-01-01

313

Hydrogen Transfer between Sulfuric Acid and Hydroxyl Radical in the Gas Phase: Competition among Hydrogen Atom Transfer, Proton-Coupled Electron-Transfer, and Double Proton Transfer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

9 pages, 2 tables, 1 scheme. , In an attempt to assess the potential role of the hydroxyl radical in the atmospheric degradation of sulfuric acid, the hydrogen transfer between H2SO4 and HO• in the gas phase has been investigated by means of DFT and quantum-mechanical electronic-structure calculations,...

Anglada Rull, Josep M; Olivella, Santiago; Solé, Albert

314

Interfacial microstructure and defect analysis in Cu(In,Ga)Se([sub]2)-based multilayered film by analytical transmission electron microscopy and focused ion beam  

International Nuclear Information System (INIS)

Interfacial microstructures of Cu(In,Ga)Se2(CIGS)-based multilayered film are closely characterized by TEM (transmission electron microscopy), SEM (scanning electron microscopy) and FIB (focused ion beam). A cross-sectional TEM, energy dispersive X-ray spectroscopy and energy-filtered TEM reveal that a pronounced Cu diffusion occurs across the interface of the CdS/CIGS, which leads to a large amount of Cu rich in the CdS layer and a Cu-deficient sub-surface in the CIGS layer as well as a rough interfacial structure. TEM studies further reveal that the interface microstructures in the multilayered film are dissimilar, both ZnO/CdS and CdS/CIGS interfaces are strongly bonded whereas the CIGS/Mo interface is weakly bonded and interface separation occasionally occurs. Mo back contact layer shows a well adhesion to glass substrate. Detailed observation on defects in the CIGS-based multilayered film is carried out by 3D (3-dimensional) FIB and SEM techniques. Sequential 2D (2-demensional) cross-sectioning shows that dominant growth-defects in the CIGS and top SiO2 layers are micro-scale crack, appearing as diversified morphologies. The micro-scale crack in the CIGS layer is possibly released by propagating into the adjacent layer while the crack in the SiO2 layer is relieved usually by forming a small particle behind. It is noted that in the multilayered film the interface frequently acts as crack initiation sites due to distinct thermal expansion coefficients.

2009-06-01

315

Charge transfer emission in coumarin 343 sensitized TiO{sub 2} nanoparticle: A direct measurement of back electron transfer  

Energy Technology Data Exchange (ETDEWEB)

Electron injection and back electron transfer dynamics in coumarin 343 (C-343) adsorbed on TiO{sub 2} nanoparticles are studied by picosecond transient absorption and time-resolved fluorescence spectroscopy. The direct detection of electrons in the nanoparticles and the parent cation are monitored using picosecond transient absorption spectroscopy, and the corresponding dynamics of the adsorbate are monitored by time-resolved absorption spectra of the cation radical of C-343 in the visible region. When the electron returns from the nanoparticles to the present cation, a low quantum yield red-shifted charge transfer emission is observed. Measuring the charge transfer emission lifetimes by a picosecond time-resolved fluorimeter, the author gets an exact rate of back electron transfer reaction from the nanoparticle to the parent cation.

Ghosh, H.N.

1999-11-25

316

Alternative mitochondrial electron transfer as a novel strategy for neuroprotection.  

UK PubMed Central (United Kingdom)

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

Wen Y; Li W; Poteet EC; Xie L; Tan C; Yan LJ; Ju X; Liu R; Qian H; Marvin MA; Goldberg MS; She H; Mao Z; Simpkins JW; Yang SH

2011-05-01

317

One-dimensional electron systems, DNA electron conduction and proton transfer  

Science.gov (United States)

Structural fluctuations, such as phonons and proton motion in hydrogen bonding play an important role in charge conduction of biopolymers. Different from the phonons which are oscillatory motions in a single-minimum potential, the proton can tunnel form one side of a hydrogen bond to another in a double-minimum potential just as a particle moving in a two-level system. This proton transfer reaction is especially important in double-stranded DNA since the cause of tautomeric base pair by proton transfer could induce genetic mutation in DNA, as pointed out by Watson and Crick. In the stacking base pairs of DNA, since the pi electrons can be transferred across the base pairs, the proton transfer and the electron conduction in DNA can be affected by each other. Although until now the nature of DNA electronic ground state is still a controversy, due to the low dimensionality of DNA, we can investigate the motions of the protons and charges in DNA by considering various one-dimensional electron systems with the effects of structural fluctuations. Three models are proposed for the possibly different charge conductions in DNA. For the model of conductors, the coupling between electrons and protons can stablize the excited state of proton transfer in the hydrogen bond and make it more likely. The DNA sequences with strong electron-proton coupling or a good electrical conduction may result in genetic mutations. In the Mott insulator, the soliton created from the Umklapp process can delocalize the proton in a hydrogen bond and be stabilized by the effects of two-level system and acoustical phonons. For the model of the band insulator, we found that the charge trapped by either the hydrogen bonds or phonons can form a polaron. The polaron diffusion in the continuous media can correspond to the multiple-step hopping mechanism in the discrete model and derive the reaction rate of the long-range charge transfer in DNA. The result in the optical case is in agreement with the experimental results.

Chang, Chun-Min

2002-01-01

318

Hydrogen transfer between sulfuric acid and hydroxyl radical in the gas phase: competition among hydrogen atom transfer, proton-coupled electron-transfer, and double proton transfer.  

Science.gov (United States)

In an attempt to assess the potential role of the hydroxyl radical in the atmospheric degradation of sulfuric acid, the hydrogen transfer between H2SO4 and HO* in the gas phase has been investigated by means of DFT and quantum-mechanical electronic-structure calculations, as well as classical transition state theory computations. The first step of the H2SO4 + HO* reaction is the barrierless formation of a prereactive hydrogen-bonded complex (Cr1) lying 8.1 kcal mol(-1) below the sum of the (298 K) enthalpies of the reactants. After forming Cr1, a single hydrogen transfer from H2SO4 to HO* and a degenerate double hydrogen-exchange between H2SO4 and HO* may occur. The single hydrogen transfer, yielding HSO4* and H2O, can take place through three different transition structures, the two lowest energy ones (TS1 and TS2) corresponding to a proton-coupled electron-transfer mechanism, whereas the higher energy one (TS3) is associated with a hydrogen atom transfer mechanism. The double hydrogen-exchange, affording products identical to reactants, takes place through a transition structure (TS4) involving a double proton-transfer mechanism and is predicted to be the dominant pathway. A rate constant of 1.50 x 10(-14) cm(3) molecule(-1) s(-1) at 298 K is obtained for the overall reaction H2SO4 + HO*. The single hydrogen transfer through TS1, TS2, and TS3 contributes to the overall rate constant at 298 K with a 43.4%. It is concluded that the single hydrogen transfer from H2SO4 to HO* yielding HSO4* and H2O might well be a significant sink for gaseous sulfuric acid in the atmosphere. PMID:16451034

Anglada, Josep M; Olivella, Santiago; Solé, Albert

2006-02-01

319

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

320

Distance Dependent Electron Transfer at TiO2 Interfaces Sensitized with Phenylene Ethynylene Bridged Ru(II)-Isothiocyanate Compounds.  

Science.gov (United States)

Excess electrons present in semiconductor nanocrystallites generate a significant electric field, yet the role this field plays in molecular charge transfer processes remains poorly understood. Three ruthenium bipyridyl cis-Ru(bpy)(LL)(NCS)2 compounds, where LL is a 4-substituted bpy, with zero, one, or two phenylene ethynylene bridge units, were anchored to mesoporous nanocrystalline TiO2 thin films to specifically quantify interfacial charge transfer with chromophores designed to be set at variable distances from the surface. Injection of electrons into TiO2 resulted in a blue shift of the metal-to-ligand charge transfer absorption consistent with an underlying Stark effect. The electroabsorption data were used to quantify the electric field experienced by the compounds that decreased from 0.85 to 0.22 MV/cm as the number of OPE spacers increased from 0 to 2. Charge recombination on the 10(-8)-10(-5) s time scale correlated with the magnitude of the electric field with an apparent attenuation factor ? = 0.12 Å(-1). Slow components to charge recombination observed on the 10(-4)-10(-1) s time scale that were unaffected by temperature, irradiance, or the bridge units present on the molecular sensitizer were attributed to electron tunneling between TiO2 acceptor states. The photocurrent efficiencies of solar cells based on these compounds decreased markedly when the bridge units were present on the sensitizer. Iodine was found to form adducts with all three compounds, K = 1.8 ± 0.2 × 10(4) M(-1), but only significantly lowered the excited state injection yield for those that possessed the bridge units. PMID:23692179

Johansson, Patrik G; Kopecky, Andrew; Galoppini, Elena; Meyer, Gerald J

2013-05-21

 
 
 
 
321

Distance Dependent Electron Transfer at TiO2 Interfaces Sensitized with Phenylene Ethynylene Bridged Ru(II)-Isothiocyanate Compounds.  

UK PubMed Central (United Kingdom)

Excess electrons present in semiconductor nanocrystallites generate a significant electric field, yet the role this field plays in molecular charge transfer processes remains poorly understood. Three ruthenium bipyridyl cis-Ru(bpy)(LL)(NCS)2 compounds, where LL is a 4-substituted bpy, with zero, one, or two phenylene ethynylene bridge units, were anchored to mesoporous nanocrystalline TiO2 thin films to specifically quantify interfacial charge transfer with chromophores designed to be set at variable distances from the surface. Injection of electrons into TiO2 resulted in a blue shift of the metal-to-ligand charge transfer absorption consistent with an underlying Stark effect. The electroabsorption data were used to quantify the electric field experienced by the compounds that decreased from 0.85 to 0.22 MV/cm as the number of OPE spacers increased from 0 to 2. Charge recombination on the 10(-8)-10(-5) s time scale correlated with the magnitude of the electric field with an apparent attenuation factor ? = 0.12 Å(-1). Slow components to charge recombination observed on the 10(-4)-10(-1) s time scale that were unaffected by temperature, irradiance, or the bridge units present on the molecular sensitizer were attributed to electron tunneling between TiO2 acceptor states. The photocurrent efficiencies of solar cells based on these compounds decreased markedly when the bridge units were present on the sensitizer. Iodine was found to form adducts with all three compounds, K = 1.8 ± 0.2 × 10(4) M(-1), but only significantly lowered the excited state injection yield for those that possessed the bridge units.

Johansson PG; Kopecky A; Galoppini E; Meyer GJ

2013-05-01

322

A semiclassical theory of electron transfer reactions in Condon approximation and beyond  

DEFF Research Database (Denmark)

The effect of the modulation of the electronic wave functions by configurational fluctuations of the molecular environment on the kinetic parameters of electron transfer reactions is discussed. A self-consistent algorithm for the calculation of the potential profile along the reaction coordinate of adiabatic electron transfer reactions is elaborated. A new formula for the transition probability of non-adiabatic electron transfer reactions is obtained in an improved Condon approximation A regular method for the calculation of non-Condon corrections is suggested. The importance of these effects for some specific biological and electrochemical electron transfer systems is discussed.

Kuznetsov, A. M.; Sokolov, V. V.

2001-01-01

323

Coupled proton and electron transfer reactions in cytochrome oxidase.  

Science.gov (United States)

Cytochrome oxidase catalyzes the four-electron reduction of O2 to water and conserves the substantial free energy of the reaction in the form of a protonmotive force. For each electron, two full charges are translocated across the membrane, resulting in a voltage. One of the mechanisms to generate the charge separation in cytochrome oxidase is via a proton pump. A single reaction cycle can be monitored over the course of about 1 msec using absorption spectroscopy, revealing distinct intermediates. Thus, the reaction cycle can be studied as a series of steps. Each of the reaction steps in the catalytic cycle involves a sequence of coupled electron and proton transfer reaction, where protons are either consumed in the chemistry of water formation or pumped across the membrane. The pumping mechanism requires consideration of both the thermodynamics of the various species but also the favored kinetic pathways that assure proton pumping is unidirectional. Hence, a knowledge of transition states and transiently, poorly populated intermediates is likely to be important to understand the mechanism of the pump. PMID:14766393

Gennis, Robert B

2004-01-01

324

Dissociative electron capture of halocarbon caused by the internal electron transfer from water trimer anion.  

Science.gov (United States)

Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF(2)Cl(2) molecule and a water trimer anion e(-)(H(2)O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H(2)O)(3)-CF(2)Cl(2), was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF(2)Cl(2) as a function of time. Immediately, the Cl(-) ion was dissociated from CF(2)Cl(2)(-) adsorbed on the water cluster. The reaction was schematically expressed by e(-)(H(2)O)(3)-CF(2)Cl(2)-->[(H(2)O)(3)-->-CF(2)CL(2)](-) --> (H(2O)(3) + CF(2)CL + CI(-) (I) where [(H(2)O)(3)-CF(2)Cl(2)](-) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF(2)Cl(2). The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF(2)Cl(2) and CF(2)Cl(2)-(H(2)O)(3), i.e. e(-) + CF(2)Cl(2), and e(-) + CF(2)Cl(2)-(H(2)O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310]. PMID:18404226

Tachikawa, Hiroto

2008-03-03

325

Dissociative electron capture of halocarbon caused by the internal electron transfer from water trimer anion.  

UK PubMed Central (United Kingdom)

Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF(2)Cl(2) molecule and a water trimer anion e(-)(H(2)O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H(2)O)(3)-CF(2)Cl(2), was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF(2)Cl(2) as a function of time. Immediately, the Cl(-) ion was dissociated from CF(2)Cl(2)(-) adsorbed on the water cluster. The reaction was schematically expressed by e(-)(H(2)O)(3)-CF(2)Cl(2)-->[(H(2)O)(3)-->-CF(2)CL(2)](-) --> (H(2O)(3) + CF(2)CL + CI(-) (I) where [(H(2)O)(3)-CF(2)Cl(2)](-) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF(2)Cl(2). The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF(2)Cl(2) and CF(2)Cl(2)-(H(2)O)(3), i.e. e(-) + CF(2)Cl(2), and e(-) + CF(2)Cl(2)-(H(2)O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310].

Tachikawa H

2008-04-01

326

An approach to long-range electron transfer mechanisms in metalloproteins: in situ scanning tunneling microscopy with submolecular resolution.  

Science.gov (United States)

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins. PMID:9990032

Friis, E P; Andersen, J E; Kharkats, Y I; Kuznetsov, A M; Nichols, R J; Zhang, J D; Ulstrup, J

1999-02-16

327

The rate of the electron-ion heat transfer in swift heavy particle tracks in metals  

Energy Technology Data Exchange (ETDEWEB)

A model of the heat transfer from the excited electron gas to the ionic framework in tracks formed by swift heavy particles in metals is discussed. The model allows to predict the rate of the electron-to-ion heat transfer in tracks in the broad range of electron temperatures, both above and below the Fermi energy. (orig.).

Volkov, A.E. [Kurchatov Inst. (RKI), Moscow (Russian Federation); Borodin, V.A. [Kurchatov Inst. (RKI), Moscow (Russian Federation)

1996-02-01

328

78 FR 49365 - Electronic Fund Transfers (Regulation E); Correction  

Science.gov (United States)

...Protection Act (Dodd-Frank Act) regarding remittance transfers. This rule makes a clarificatory...consumerfinance.gov/regulations/final-remittance-rule-amendment-regulation-e...Transfer Act's provisions regarding remittance transfers and the official...

2013-08-14

329

77 FR 6310 - Electronic Fund Transfers (Regulation E)  

Science.gov (United States)

...for each transfer described above would create information overload for consumers. Subsequent Advance Transfers Under...for each transfer described above would create information overload for consumers. The Timing and Accuracy...

2012-02-07

330

Structural studies of photoinduced intramolecular electron transfer in cyclopentadienylnickelnitrosyl  

Energy Technology Data Exchange (ETDEWEB)

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

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

1994-03-01

331

Photoinduced electron transfer reaction in polymer-surfactant aggregates: Photoinduced electron transfer between N,N-dimethylaniline and 7-amino coumarin dyes  

International Nuclear Information System (INIS)

Photoinduced electron transfer between coumarin dyes and N,N-dimethylaniline has been investigated by using steady state and picosecond time resolved fluorescence spectroscopy in sodium dodecyl sulphate (SDS) micelles and PVP-polyvinyl pyrrolidone (SDS) polymer-surfactant aggregates. A slower rate of electron transfer is observed in PVP-SDS aggregates than in polymer-free SDS micelles. A Marcus type inversion is observed in the correlation of free energy change in comparison with the electron transfer rate. The careful investigation reveals that C-151 deviates from the normal Marcus inverted region compared to its analogs C-152 and C-481 due to slower rotational relaxation and smaller translational diffusion coefficient.

2008-05-28

332

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

International Nuclear Information System (INIS)

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

2008-06-02

333

Theory of Proton-Coupled Electron Transfer in Energy Conversion Processes  

Science.gov (United States)

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

Hammes-Schiffer, Sharon

2010-01-01

334

Chlorophyll-quinone photochemical electron transfer in liposomes  

Energy Technology Data Exchange (ETDEWEB)

The study described involves the reduction of electron acceptors (quinones) by photoexcited Chloroplasts (Chl). Chl a (from spinach) is incorporated into phosphatidylcholine (either synthetic or from hen egg yolks) liposomes suspended in 10 mM phosphate buffer (pH 7.0). The quinones are either present during liposome formation or added later, depending upon their water solubility. The measurement technique employed is laser flash photolysis. A pulsed nitrogen laser pumps a dye laser, which delivers a short light flash (10 ns) to the sample at a wavelength (655-660 nm) within an absorption band of Chl. This raises Chl to an excited singlet level, which can rapidly cross to the lowest excited triple level (/sup 3/Chl). From this state Chl can transfer an electron to acceptors such as quinones, resulting in the formation of the Chl cation radical (Chl./sup +/) and the semiquinone anion radical (Q./sup +/). Transient absorbance changes ocurring within the sample cell are monitored and can be attributed to processes such as excited state quenching (of /sup 3/Chl by Q) and radical product formation and decay. (JMT)

Hurley, J.K.; Castelli, F.; Tollin, G.

1981-09-01

335

Electron scattering off simple atoms for large momentum transfer collisions  

Science.gov (United States)

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.Pacs3434.80.Bm34.80.DpKeywordsAtomsCollisionsHydrogenHeliumLarge momentum transferReferencesS.GeltmanM.B.HidalgoJ. Phys.B419711299J.GauJ.MacekPhys. Rev. A101974522F.W.ByronC.J.JoachainJr.J. Phys. B81975L284E.J.KelseyPhys. Rev. A14197656D.EimerlPhys. Rev. A1419762061I.BrayD.A.KonovalovI.E.McCarthyPhys. Rev. A4419915586Private Communication from I. Bray (2006). The data used is actually of incident electron energy of 499.5 eV and are dependent on the frozen core approximation used for helium. The results are nearly identical to those ofD.V.FursaI.BrayPhys. Rev. A5219951279D.C.CartwrightG.CsanakS.TrajmarD.F.RegisterPhys. Rev. A4519921602S.TrajmarD.F.RegisterD.C.CartwrightG.CsanakJ. Phys. B2519924889J.F.WilliamsJ. Phys. B819752191M.P.ScottP.G.BurkeJ. Phys. B261993L191F.T.ChanC.H.ChangM.LieberY.-K.KimPhys. Rev. A1719781869Note that in general one should use an integrating factor to avoid divergent behavior in separating these two terms and integrating them separately. We do this for elastic scattering. SeeL.I.SchiffQuantum Mechanics3rd ed.1968McGraw-HillNew York Cityp. 333H.A.BetheE.E.SalpeterOne- and Two-Electron Atoms1957Springer-VerlagBerlinp. 83E.J.KelseyJ.MacekJ. Math. Phys.1719761182R.H.DalitzProc. R. Soc. A2061951509P.G.BurkePotential Scattering in Atomic Physics1st ed.1977Plenum PressNew YorkChap. 8, p. 108I.BrayD.V.FursaA.S.KheifetsA.T.StelbovicsJ. Phys. B352002R117R146My search of the literature has not shown any articles on this atomic collision. However, it is difficult to believe that a transition which when performed by radio frequency photons was so important to physics history has not been considered by someone as a possible deexcitation that could be done or has been done by electron scattering.See Ref. [11] p. 107.E.J.KelseyPhys. Rev. A151977647MitioInokutiRev. Mod. Phys.431971297This argument is similar to one in Ref. [2] p. 57.See Ref. [10] p. 141.I.S. Gradshteyn, I.M. Ryzhik, Y.V. Geronimus, M. Yu Tseytlin, Table of Integrals, Series, and Products, 4th ed., in: A. Jeffrey (Ed.), vol. 1, Academic Press, New York, 1965, Chap. 3, p. 294.This is at best a ballpark estimate.Eq. is correct independent of the choice of Z in the hydrogen-like wave functions as long as all the hydrogen-like wave functions have the same value. One could, for example, set Z equal to ZG to allow the ground state wave function be the familiar Hylleraas helium ground state wave function (Eq. ).

Kelsey, Edward J.

2007-08-01

336

Electronic structure and proton transfer in ground-state hexafluoroacetylacetone.  

Science.gov (United States)

The ground electronic state (X(1)A(1)) of hexafluoroacetylacetone (HFAA) has been subjected to synergistic experimental and theoretical investigations designed to resolve controversies surrounding the nature of intramolecular hydrogen bonding for the enol tautomer. Cryogenic (93K) X-ray diffraction studies were conducted on single HFAA crystals grown in situ by means of the zone-melting technique, with the resulting electron density maps affording clear evidence for distinguishable O(1)-H and H...O(2) bonds that span an interoxygen distance of 2.680 +/- 0.003 A. Such laboratory findings have been corroborated by a variety of quantum chemical methods including Hartree-Fock (HF), density functional [DFT (B3LYP)], Møller-Plesset perturbation (MPn), and coupled cluster [CCSD, CCSD(T)] treatments built upon extensive sets of correlation-consistent basis functions. Geometry optimizations performed at the CCSD(T)/aug-cc-pVDZ level of theory predict an asymmetric (C(s)) equilibrium configuration characterized by an O...O donor-acceptor separation of 2.628 A. Similar analyses of the transition state for proton transfer reveal a symmetric (C(2v)) structure that presents a potential barrier of 21.29 kJ/mol (1779.7 cm(-1)) height. The emerging computational description of HFAA is in reasonable accord with crystallographic measurements and suggests a weakening of hydrogen-bond strength relative to that of the analogous acetylacetone molecule. PMID:20507165

Chatterjee, Chandrima; Incarvito, Christopher D; Burns, Lori A; Vaccaro, Patrick H

2010-06-24

337

Ultrafast Photoinduced Electron Transfer in Viologen-Linked BODIPY Dyes.  

UK PubMed Central (United Kingdom)

New boron-dipyrromethene (BODIPY) dyes linked to viologen are prepared and their photophysical and electrochemical properties are investigated. Both synthesized molecules have similar electronic absorption spectra with the absorption maximum localized at 517 and 501?nm for dye?1 and dye?2, respectively. They exhibit well-defined redox behavior, highlighting the presence of BODIPY and viologen subunits, with little perturbation of the redox potential of both subunits with respect to the parent compounds. Both dyes are heavily quenched by photoinduced electron transfer from the BODIPY to the viologen subunit. The transient absorption technique demonstrates that dye?2 forms the viologen radical within a timeframe of 7.1?ps, and that the charge-separated species has a lifetime of 59?ps. Sustained irradiation of dye?2 in the presence of a tertiary amine allows for the accumulation of BODIPY-methyl-4,4'-bipyridinium (BODIPY-MV(+) ), as observed by its characteristic absorption at 396 and 603?nm. However, dye?2 does not generate catalytic amounts of hydrogen under standard conditions.

Frath D; Yarnell JE; Ulrich G; Castellano FN; Ziessel R

2013-08-01

338

Electron transfer dissociation of multiply protonated and fixed charge disulfide linked polypeptides  

Science.gov (United States)

Multiply protonated disulfide linked peptides and fixed charged analogs have been subjected to electron transfer ion/ion reactions to examine the role of excess protons in inducing cleavage of the disulfide bond in electron transfer dissociation. Systems in which all of the excess charge was due to fixed charge sites (i.e., quaternary ammonium groups) showed somewhat more disulfide bond cleavage than the fully protonated species. This observation argues against a major role for a mechanism that requires hydrogen transfer to the disulfide bond as a prerequisite for its cleavage. Interestingly, species with mixed cation sites (one or more excess protons and one or more fixed charge side chains) showed lower propensities for disulfide bond cleavage than either the corresponding fully protonated or fully derivatized species. This observation is not likely to be accounted for by direct electron transfer to a Coulomb stabilized disulfide bond because the identities of the charge bearing sites are not expected to play a significant role in the degree of stabilization. The results appear to be best rationalized on the basis of the [`]through bond electron transfer' mechanism of Simons et al., in conjunction with rate limiting intramolecular electron transfer(s) between charge bearing sites. Intramolecular electron transfer between charge sites can play a role in mediating electron movement from the site of initial electron capture to the site from which an electron is transferred to the disulfide anti-bonding orbital.

Gunawardena, Harsha P.; Gorenstein, Lev; Erickson, David E.; Xia, Yu; McLuckey, Scott A.

2007-09-01

339

Formation of fuel via photochemical electron transfer. Progress report, February 1, 1982-January 31, 1983  

Energy Technology Data Exchange (ETDEWEB)

Current research is devoted to photo-induced electron transfer reactions which have particular relevance to the generation of fuels or useful chemicals, potentially using sunlight as a radiation source. Results from the following studies are given: a comparison of electron transfer yield as a function of charge type in ruthenium (II) complexes and methyl viologen analogs; ionic photodissociation of visible absorbing CT complexes of methyl viologen (MV/sup 2 +/); dioethers as electron transfer agents; simulated temperature dependence of quantum yields for photoreactions involving energy or electron transfer; and effects of ultra-high magnetic fields on intramicellar radical pair dynamics in amphiphilic media.

Jones, G. II

1983-01-25

340

Reorganization energy of electron transfer processes in ionic fluids: a molecular Debye-Huckel approach.  

UK PubMed Central (United Kingdom)

The reorganization energy of electron transfer processes in ionic fluids is studied under the linear response approximation using a molecule Debye-Hückel theory. Reorganization energies of some model reactants of electron transfer reactions in molten salts are obtained from molecular simulations and a molecule Debye-Hückel approach. Good agreements between simulation results and the results from our theoretical calculations using the same model Hamiltonian are found. Applications of our theory to electron transfer reactions in room temperature ionic liquids further demonstrate that our theoretical approach presents a reliable and accurate methodology for the estimation of reorganization energies of electron transfer reactions in ionic fluids.

Xiao T; Song X

2013-03-01

 
 
 
 
341

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

Energy Technology Data Exchange (ETDEWEB)

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){sub 6}{sup 3-} as an anionic redox probe molecule. The surface pK{sub 1/2} 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){sub 6}{sup 3-} with repeated alternation of pH values to investigate the electrostatic interaction of the protonated or deprotonated imidazole with Fe(CN){sub 6}{sup 3-} and (2) in the acidic or basic electrolyte containing Ru(NH{sub 3}){sub 6}{sup 3+} 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){sub 6}{sup 3-} and concluded that the adsorbed Fe(CN){sub 6}{sup 3-} catalyzed the electron transfer of both Fe(CN){sub 6}{sup 3-} itself and cationic Ru(NH{sub 3}){sub 6}{sup 3+}.

Hwang, Seongpil [Department of Chemistry and School of Molecular Science (BK21), KAIST, Daejeon 305-701 (Korea, Republic of); Lee, Bang Sook [Division of Nano Science (BK21), Ewha Womans University, 11-1 Daehyun-Dong, Seodaemun-Gu, Seoul 120-750 (Korea, Republic of); Chi, Young Shik [Department of Chemistry and School of Molecular Science (BK21), KAIST, Daejeon 305-701 (Korea, Republic of); Kwak, Juhyoun [Department of Chemistry and School of Molecular Science (BK21), KAIST, Daejeon 305-701 (Korea, Republic of)], E-mail: Juhyoun_Kwak@kaist.ac.kr; Choi, Insung S. [Department of Chemistry and School of Molecular Science (BK21), KAIST, Daejeon 305-701 (Korea, Republic of); Lee, Sang-gi [Division of Nano Science (BK21), Ewha Womans University, 11-1 Daehyun-Dong, Seodaemun-Gu, Seoul 120-750 (Korea, Republic of)

2008-01-01

342

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+.

2008-01-01

343

Photodriven heterogeneous charge transfer with transition-metal compounds anchored to TiO2 semiconductor surfaces.  

UK PubMed Central (United Kingdom)

A critical review of light-driven interfacial charge-transfer reactions of transition-metal compounds anchored to mesoporous, nanocrystalline TiO2 (anatase) thin films is described. The review highlights molecular insights into metal-to-ligand charge transfer (MLCT) excited states, mechanisms of interfacial charge separation, inter- and intra-molecular electron transfer, and interfacial charge-recombination processes that have been garnered through various spectroscopic and electrochemical techniques. The relevance of these processes to optimization of solar-energy-conversion efficiencies is discussed (483 references).

Ardo S; Meyer GJ

2009-01-01

344

Photodriven heterogeneous charge transfer with transition-metal compounds anchored to TiO2 semiconductor surfaces.  

Science.gov (United States)

A critical review of light-driven interfacial charge-transfer reactions of transition-metal compounds anchored to mesoporous, nanocrystalline TiO2 (anatase) thin films is described. The review highlights molecular insights into metal-to-ligand charge transfer (MLCT) excited states, mechanisms of interfacial charge separation, inter- and intra-molecular electron transfer, and interfacial charge-recombination processes that have been garnered through various spectroscopic and electrochemical techniques. The relevance of these processes to optimization of solar-energy-conversion efficiencies is discussed (483 references). PMID:19088971

Ardo, Shane; Meyer, Gerald J

2008-12-01

345

Intraprotein electron transfer in inducible nitric oxide synthase holoenzyme.  

UK PubMed Central (United Kingdom)

Intraprotein electron transfer (IET) from flavin mononucleotide (FMN) to heme is essential in NO synthesis by NO synthase (NOS). Our previous laser flash photolysis studies provided a direct determination of the kinetics of the FMN-heme IET in a truncated two-domain construct (oxyFMN) of murine inducible NOS (iNOS), in which only the oxygenase and FMN domains along with the calmodulin (CaM) binding site are present (Feng et al. J. Am. Chem. Soc. 128, 3808-3811, 2006). Here we report the kinetics of the IET in a human iNOS oxyFMN construct, a human iNOS holoenzyme, and a murine iNOS holoenzyme, using CO photolysis in comparative studies on partially reduced NOS and a NOS oxygenase construct that lacks the FMN domain. The IET rate constants for the human and murine iNOS holoenzymes are 34 +/- 5 and 35 +/- 3 s(-1), respectively, thereby providing a direct measurement of this IET between the catalytically significant redox couples of FMN and heme in the iNOS holoenzyme. These values are approximately an order of magnitude smaller than that in the corresponding iNOS oxyFMN construct, suggesting that in the holoenzyme the rate-limiting step in the IET is the conversion of the shielded electron-accepting (input) state to a new electron-donating (output) state. The fact that there is no rapid IET component in the kinetic traces obtained with the iNOS holoenzyme implies that the enzyme remains mainly in the input state. The IET rate constant value for the iNOS holoenzyme is similar to that obtained for a CaM-bound neuronal NOS holoenzyme, suggesting that CaM activation effectively removes the inhibitory effect of the unique autoregulatory insert in neuronal NOS.

Feng C; Dupont AL; Nahm NJ; Spratt DE; Hazzard JT; Weinberg JB; Guillemette JG; Tollin G; Ghosh DK

2009-01-01

346

Orthogonal bis(terpyridine)-Fe(II) metal complex oligomer wires on a tripodal scaffold: rapid electron transport.  

UK PubMed Central (United Kingdom)

The present work reports a tripodal scaffold for bis(terpyridine)-Fe(II) oligomer wires on an Au(111) surface: the tripodal scaffold realised both orthogonality of the oligomer wires, and fast interfacial electron transfer through the oligomer wires.

Sakamoto R; Ohirabaru Y; Matsuoka R; Maeda H; Katagiri S; Nishihara H

2013-08-01

347

Tuning photoinduced intramolecular electron transfer by electron accepting and donating substituents in oxazolones.  

Science.gov (United States)

The solvatochromic and spectral properties of oxazolone derivatives in various solvents were reported. Fluorescence spectra clearly showed positive and negative solvatochromism depending on substituents. The solvatochromic plots and quantum chemical computations at DFT-B3LYP/6-31?+?G(d,p) level were used to assess dipole moment changes between the ground and the first excited singlet-states. The electron accepting nitro substituent at the para-position increased the ?-electron mobility, however, the 3,5-dinitro substituent decreased the ?-electron mobility as a result of inverse accumulation of the electronic density as compared with that of its ground state. Experimental and computational studies proved that the photoinduced intramolecular electron transfer (PIET) is responsible for the observed solvatochromic effects. We demonstrate that PIET can be finely tailored by the position of the electron accepting and donating substituents in the phenyl ring of the oxazolone derivatives. We propose that the photoactive CPO derivatives are new molecular class of conjugated push-pull structures using azlactone moiety as the ?-conjugated linker and may find applications in photovoltaic cells and light emitting diodes. PMID:23494168

Oztürk, Gülsiye; Karab?y?k, Hasan; Aygün, Muhittin; Alp, Serap; Ozçelik, Serdar

2013-03-15

348

Structural and interfacial characteristics of thin (<10 nm) SiO{sub 2} films grown by electron cyclotron resonance plasma oxidation on [100] Si substrates  

Energy Technology Data Exchange (ETDEWEB)

The feasibility of fabricating ultra-thin SiO{sub 2} films on the order of a few nanometer thickness has been demonstrated. SiO{sub 2} thin films of approximately 7 nm thickness have been produced by ion flux-controlled Electron Cyclotron Resonance plasma oxidation at low temperature on [100] Si substrates, in reproducible fashion. Electrical measurements of these films indicate that they have characteristics comparable to those of thermally grown oxides. The thickness of the films was determined by ellipsometry, and further confirmed by cross-sectional High-Resolution Transmission Electron Microscopy. Comparison between the ECR and the thermal oxide films shows that the ECR films are uniform and continuous over at least a few microns in lateral direction, similar to the thermal oxide films grown at comparable thickness. In addition, HRTEM images reveal a thin (1--1.5 nm) crystalline interfacial layer between the ECR film and the [100] substrate. Thinner oxide films of approximately 5 nm thickness have also been attempted, but so far have resulted in nonuniform coverage. Reproducibility at this thickness is difficult to achieve.

Nguyen, T.D.; Carl, D.A.; Hess, D.W.; Lieberman, M.A.; Gronsky, R.

1991-04-01

349

Structural and interfacial characteristics of thin (<10 nm) SiO sub 2 films grown by electron cyclotron resonance plasma oxidation on (100) Si substrates  

Energy Technology Data Exchange (ETDEWEB)

The feasibility of fabricating ultra-thin SiO{sub 2} films on the order of a few nanometer thickness has been demonstrated. SiO{sub 2} thin films of approximately 7 nm thickness have been produced by ion flux-controlled Electron Cyclotron Resonance plasma oxidation at low temperature on (100) Si substrates, in reproducible fashion. Electrical measurements of these films indicate that they have characteristics comparable to those of thermally grown oxides. The thickness of the films was determined by ellipsometry, and further confirmed by cross-sectional High-Resolution Transmission Electron Microscopy. Comparison between the ECR and the thermal oxide films shows that the ECR films are uniform and continuous over at least a few microns in lateral direction, similar to the thermal oxide films grown at comparable thickness. In addition, HRTEM images reveal a thin (1--1.5 nm) crystalline interfacial layer between the ECR film and the (100) substrate. Thinner oxide films of approximately 5 nm thickness have also been attempted, but so far have resulted in nonuniform coverage. Reproducibility at this thickness is difficult to achieve.

Nguyen, T.D.; Carl, D.A.; Hess, D.W.; Lieberman, M.A.; Gronsky, R.

1991-04-01

350

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

Energy Technology Data Exchange (ETDEWEB)

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

1990-02-14

351

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

International Nuclear Information System (INIS)

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

2011-11-30

352

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2011-11-30

353

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

354

Electron transfer process from marine biofilms to graphite electrodes in seawater.  

UK PubMed Central (United Kingdom)

It is known that electron transfer processes exist between microorganisms and electrodes. Many anaerobic bacteria, which can transfer electrons to solid electrodes, had been identified. However, little attention has been paid to the interactions between aerobic biofilms and electrodes. In this study, marine biofilms formation on graphite electrodes was characterized by open circuit potential and field emission scanning electron microscopy. Electron transfer between marine aerobic biofilms and graphite electrodes was investigated primarily by cyclic voltammograms and electrochemical impedance spectroscopy techniques. Herein, we suggest that marine biofilms are a kind of conductive biofilms that can transfer electrons to graphite electrodes under anaerobic and aerobic conditions. Some cytochrome species in bacterial biofilms may play a key role in the electron transfer process.

Xu F; Duan J; Hou B

2010-04-01

355

Synthetic control over photoinduced electron transfer in phosphorescence zinc sensors.  

UK PubMed Central (United Kingdom)

Despite the promising photofunctionalities, phosphorescent probes have been examined only to a limited extent, and the molecular features that provide convenient handles for controlling the phosphorescence response have yet to be identified. We synthesized a series of phosphorescence zinc sensors based on a cyclometalated heteroleptic Ir(III) complex. The sensor construct includes two anionic cyclometalating ligands and a neutral diimine ligand that tethers a di(2-picolyl)amine (DPA) zinc receptor. A series of cyclometalating ligands with a range of electron densities and band gap energies were used to create phosphorescence sensors. The sensor series was characterized by variable-temperature steady-state and transient photoluminescence spectroscopy studies, electrochemical measurements, and quantum chemical calculations based on time-dependent density functional theory. The studies demonstrated that the suppression of nonradiative photoinduced electron transfer (PeT) from DPA to the photoexcited Ir(IV) species provided the underlying mechanism that governed the phosphorescent response to zinc ions. Importantly, the Coulombic barrier, which was located on either the cyclometalating ligand or the diimine ligand, negligibly influenced the PeT process. Phosphorescence modulation by PeT strictly obeyed the Rehm-Weller principle, and the process occurred in the Marcus-normal region. These findings provide important guidelines for improving sensing performance; an efficient phosphorescence sensor should include a cyclometalating ligand with a wide band gap energy and a deep oxidation potential. Finally, the actions of the sensor were demonstrated by visualizing the intracellular zinc ion distribution in HeLa cells using a confocal laser scanning microscope and a photoluminescence lifetime imaging microscope.

Woo H; Cho S; Han Y; Chae WS; Ahn DR; You Y; Nam W

2013-03-01

356

Synthetic control over photoinduced electron transfer in phosphorescence zinc sensors.  

Science.gov (United States)

Despite the promising photofunctionalities, phosphorescent probes have been examined only to a limited extent, and the molecular features that provide convenient handles for controlling the phosphorescence response have yet to be identified. We synthesized a series of phosphorescence zinc sensors based on a cyclometalated heteroleptic Ir(III) complex. The sensor construct includes two anionic cyclometalating ligands and a neutral diimine ligand that tethers a di(2-picolyl)amine (DPA) zinc receptor. A series of cyclometalating ligands with a range of electron densities and band gap energies were used to create phosphorescence sensors. The sensor series was characterized by variable-temperature steady-state and transient photoluminescence spectroscopy studies, electrochemical measurements, and quantum chemical calculations based on time-dependent density functional theory. The studies demonstrated that the suppression of nonradiative photoinduced electron transfer (PeT) from DPA to the photoexcited Ir(IV) species provided the underlying mechanism that governed the phosphorescent response to zinc ions. Importantly, the Coulombic barrier, which was located on either the cyclometalating ligand or the diimine ligand, negligibly influenced the PeT process. Phosphorescence modulation by PeT strictly obeyed the Rehm-Weller principle, and the process occurred in the Marcus-normal region. These findings provide important guidelines for improving sensing performance; an efficient phosphorescence sensor should include a cyclometalating ligand with a wide band gap energy and a deep oxidation potential. Finally, the actions of the sensor were demonstrated by visualizing the intracellular zinc ion distribution in HeLa cells using a confocal laser scanning microscope and a photoluminescence lifetime imaging microscope. PMID:23458333

Woo, Hana; Cho, Somin; Han, Yejee; Chae, Weon-Sik; Ahn, Dae-Ro; You, Youngmin; Nam, Wonwoo

2013-03-13

357

Distance dependence of intramolecular electron-transfer rates: importance of the nuclear factor  

Energy Technology Data Exchange (ETDEWEB)

The conventional assumption that the distance dependence of the rate constant depends only on the electronic factor is questioned. It is shown for polyproline systems that the nuclear factor is larger than the electronic factor. It is shown further, that relative importance of nuclear and electronic factors must be considered when determining the distance dependence of electron transfer rates.

Isied, S.S.; Vassilian, A.; Wishart, J.F.; Creutz, C.; Schwarz, H.A.; Sutin, N.

1988-01-20

358

Theoretical study of photoinduced electron transfer from tetramethylethylene to tetracyanoethylene  

Science.gov (United States)

Using ab initio and density functional calculations, we studied photoexcitation of a charge-balanced electron donor-acceptor (DA) complex comprised of tetracyanoethylene (TCE) and tetramethylethylene (TME). We considered both the TCE-TME stacked conformer and a possible conformer with a solvent molecule (dichloromethane) inserted between TCE and TME. The photoexcitation of the DA complex can directly form a charge transfer (CT) state. Our theoretical investigations show that the CT state can also be produced from the decay of higher excited states. Using the continuum model, we investigated the solvent effects on CT absorption, local excitation, and CT emission in the polar solvent. The equilibrium solvation energies of the ground and excited states of the DA complex were calculated using the self-consistent reaction field method, and then the correction of nonequilibrium solvation energies for the vertical transitions was made. The transition energies (i.e., CT absorption for the DA complexes and CT emission for the contact ion pair complexes) in the polar solvent show redshifts relative to those in the gas phase.

Yi, Hai-Bo; Duan, Xiao-Hui; Lee, Jin Yong; Lee, Han Myoung; Li, Xiang-Yuan; Kim, Kwang S.

2003-11-01

359

Effects of quantum coherence in metalloprotein electron transfer.  

UK PubMed Central (United Kingdom)

Many intramolecular electron transfer (ET) reactions in biology are mediated by metal centers in proteins. This process is commonly described by a model of diffusive hopping according to the semiclassical theories of Marcus and Hopfield. However, recent studies have raised the possibility that nontrivial quantum mechanical effects play a functioning role in certain biomolecular processes. Here, we investigate the potential effects of quantum coherence in biological ET by extending the semiclassical model to allow for the possibility of quantum coherent phenomena using a quantum master equation based on the Holstein Hamiltonian. We test the model on the structurally defined chain of seven iron-sulfur clusters in nicotinamide adenine dinucleotide plus hydrogen:ubiquinone oxidoreductase (complex I), a crucial respiratory enzyme and one of the longest chains of metal centers in biology. Using experimental parameters where possible, we find that, in limited circumstances, a small quantum mechanical contribution can provide a marked increase in the ET rate above the semiclassical diffusive-hopping rate. Under typical biological conditions, our model reduces to well-known diffusive behavior.

Dorner R; Goold J; Heaney L; Farrow T; Vedral V

2012-09-01

360

Electron transfer precedes ATP hydrolysis during nitrogenase catalysis.  

UK PubMed Central (United Kingdom)

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

Duval S; Danyal K; Shaw S; Lytle AK; Dean DR; Hoffman BM; Antony E; Seefeldt LC

2013-09-01

 
 
 
 
361

Distance dependence of electron transfer from liposome-embedded (alkanephosphocholine-porphinato) zinc  

Energy Technology Data Exchange (ETDEWEB)

(Alkanephosphocholine-porphinato)zinc forms a geometrically well-defined bilayer liposome with phospholipid. Electron transfer from the liposome-embedded (porphinato)zincs with different alkyl chain lengths to methylviologen present in the outer bulk solution is measured by laser flash photolysis: the intermolecular electron transfer was observed only when the porphyrin plane is located within 12 A from the surface.

Tsuchida, E.; Kaneko, M.; Nishide, H.; Hoshino, M.

1986-05-22

362

Synthesis and photoinduced electron transfer studies of a tri(phenothiazine)-subphthalocyanine-fullerene pentad.  

UK PubMed Central (United Kingdom)

A novel donor-acceptor pentad featuring subphthalocyanine and fullerene as the primary electron donor and acceptor, and three phenothiazine entities as secondary hole transferring agents, have been newly synthesized and characterized as an photosynthetic reaction center model compound. Occurrences of ultrafast photoinduced electron transfer (PET) and slower charge recombination are witnessed in the pentad from the femtosecond and nanosecond transient absorption studies.

Kc CB; Lim GN; Zandler ME; D'Souza F

2013-09-01

363

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

International Nuclear Information System (INIS)

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

2011-08-01

364

Effect of ultrafast electron transfer on photon echo signal: Decoherence process in electron-donating solvents  

Science.gov (United States)

The effect of ultrafast electron transfer (ET) on the coherent state was investigated by means of three pulse photon echo for an azaporphyrin (AzP) derivative, 2,7,12,17-Tetra- tert-butyl-5,10,15,20-tetraaza-21 H,23 H-porphine, in electron-donating solvents. The peak shift and fwhm of the echo signal substantially decreased in the reactive solvents, indicating that the ultrafast ET affected the coherent state of the chromophore significantly. By integrating the present results in reactive and inert solvents with those previously performed for other systems, the role of the rapid reaction in the decoherence process was discussed from the viewpoints of the strength of the solute-solvent coupling.

Nagasawa, Yutaka; Mukai, Ryusuke; Mori, Kazuya; Muramatsu, Masayasu; Miyasaka, Hiroshi

2009-11-01

365

Bio-batteries and bio-fuel cells: leveraging on electronic charge transfer proteins.  

UK PubMed Central (United Kingdom)

Bio-fuel cells are alternative energy devises based on bio-electrocatalysis of natural substrates by enzymes or microorganisms. Here we review bio-fuel cells and bio-batteries based on the recent literature. In general, the bio-fuel cells are classified based on the type of electron transfer; mediated electron transfer and direct electron transfer or electronic charge transfer (ECT). The ECT of the bio-fuel cells is critically reviewed and a variety of possible applications are considered. The technical challenges of the bio-fuel cells, like bioelectrocatalysis, immobilization of bioelectrocatalysts, protein denaturation etc. are highlighted and future research directions are discussed leveraging on the use of electron charge transfer proteins. In addition, the packaging aspects of the bio-fuel cells are also analyzed and the found that relatively little work has been done in the engineering development of bio-fuel cells.

Kannan AM; Renugopalakrishnan V; Filipek S; Li P; Audette GF; Munukutla L

2009-03-01

366

Application of the density matrix method to the primary electron transfer in photosynthetic reaction centers  

Energy Technology Data Exchange (ETDEWEB)

The ultrafast time evolution of the primary electron transfer processes in photosynthetic reaction centers is theoretically studied by consideration of protein-induced and direct mechanisms in the density matrix method. The effective Liouvillian for the primary electron transfer processes in the pigment molecules is derived by projecting out the variables of the protein subunits. The protein-induced and direct electron transfer mechanisms are considered through the imaginary and real parts of the effective Liouvillian respectively. The model calculations of the population changes in the photosynthetic reaction center of Rhodopseudomonas viridis show that the protein-induced electron transfer mechanism plays an important role in the primary electron transfer processes. The model calculation is carried out without invoking the adiabatic approximation, i.e. stationary approximation of the off-diagonal density matrix elements. (orig.).

Sugawara, M.; Fujimura, Y. (Tohoku Univ., Sendai (Japan). Dept. of Chemistry); Yeh, C.Y.; Lin, S.H. (Arizona State Univ., Tempe (USA). Dept. of Chemistry Arizona State Univ., Tempe, AZ (USA). Center for the Study of Early Events in Photosynthesis)

1990-11-15

367

Direct measurement of the rate of intramolecular electron transfer in a diruthenium mixed-valence complex  

International Nuclear Information System (INIS)

[en] The communication reports the rate of intramolecular electron transfer in the mixed-valence ion (NH3)5Ru/sup II/pzRu/sup III/(edta)+ (pz = pyrazine, edta = ethylenediamine-tetraacetate) which does not exhibit intervalence transfer absorption. The results suggest a revised model for the electron-transfer process in systems in which the activation barriers arise largely from solvent reorganization. 43 references, 1 table

1979-08-29

368

A short comparison of electron and proton transfer processes in biological systems  

International Nuclear Information System (INIS)

[en] The main differences between electron and proton transfers that take place in biological systems are examined. The relation between the distance dependence of the rate constant and the mass of the transferred particle is analyzed in detail. Differences between the two processes have important consequences at the experimental level, which are discussed. The various mechanisms that ensure the coupling between electron and proton transfers are briefly described

2005-01-01

369

Efficiencies of photoinduced electron-transfer reactions: Role of the Marcus inverted region in return electron transfer within geminate radical-ion pairs  

Energy Technology Data Exchange (ETDEWEB)

In photoinduced electron-transfer processes the primary step is conversion of the electronic energy of an excited state into chemical energy retained in the form of a redox (geminate radical-ion) pair (A + D {sup hv}{yields} A{sup {sm bullet}{minus}}/D{sup {sm bullet}+}). In polar solvents, separation of the geminate pair occurs with formation of free radical ions in solution. The quantum yields of product formation, from reactions of either the free ions, or of the geminate pair, are often low, however, due to the return electron transfer reaction (A{sup {sm bullet}{minus}}/D{sup {sm bullet}+} {yields} A + D), an energy-wasting step that competes with the useful reactions of the ion pair. The present study was undertaken to investigate the parameters controlling the rates of these return electron transfer reactions. Quantum yields of free radical ion formation were measured for ion pairs formed upon electron-transfer quenching of the first excited singlet states of cyanoanthracenes by simple aromatic hydrocarbon donors in aceonitrile at room temperature. The free-ion yields are determined by the competition between the rates of separation and return electron transfer.

Gould, I.R.; Ege, D.; Moser, J.E.; Farid, S. (Eastman Kodak Company, Rochester, NY (USA))

1990-05-23

370

Photoinduced electron transfer in fullerene triads bearing pyrene and fluorene  

International Nuclear Information System (INIS)

Photochemical properties of pyrene and fluorene appended fulleropyrrolidine triads (AH1-C60-AH2; AH1=pyrene and fluorene; AH2=naphthalene and phenyl) are reported. Electrochemical studies using cyclic voltammetry technique and DFT calculations at B3LYP/3-21G(*) method revealed that the charge-separated states in pyrene and fluorene appended triads are pyrenedot+-C60dot-AH2 and fluorenedot+-C60dot-AH2, respectively; however, no such charge-separated states could be established for naphthalene and phenyl appended triads. As demonstrated from the time resolved fluorescence, upon excitation of AH moiety in nonpolar solvents, energy transfer predominantly occurred from the singlet excited fluorophore to the C60 moiety, whereas in polar DMF charge-separation also contributed to the fluorescence quenching. Additionally, charge separation also occurred from the singlet excited C60 to the pyrene or fluorene entities of the triads in DMF. The rates and quantum yields of charge separation obtained by time-resolved emission studies were around 109s-1 and 0.9-0.6 for pyrene-C60-AH2 and fluorene-C60-AH2 triads. Nanosecond transient absorption spectral studies performed by using 355nm laser light on the triads, exhibited transient bands corresponding to the C60dot- and pyrenedot+ or fluorenedot+, thus establishing the occurrence of electron transfer in these triads in DMF. The rates of charge recombination obtained by monitoring the decay of the C60dot- were found to be around 106s-1 in DMF which resulted in the lifetimes of the radical ion pairs up to 1000ns indicating charge stabilization in pyrene-C60-AH2 and fluorene-C60-AH2 triads. The formations of long-lived charge-separated states, pyrenedot+-C60d'ot-AH2 and fluorenedot+-C60dot-AH2 in DMF, were rationalized by evaluating the Marcus parameters from the temperature dependence of the charge-recombination rate constants.

2006-06-20

371

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

International Nuclear Information System (INIS)

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

2012-06-27

372

Variable electron transfer pathways in an amphibian cryptochrome: tryptophan versus tyrosine-based radical pairs.  

Science.gov (United States)

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

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

2013-02-19

373

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

UK PubMed Central (United Kingdom)

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

Vanevi? M; Nazarov YV; Belzig W

2007-08-01

374

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

CERN Multimedia

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

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

2007-01-01

375

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

Science.gov (United States)

We find that the statistics of electron transfer in a coherent quantum point contact driven by an arbitrary time-dependent voltage is composed of elementary events of two kinds: unidirectional one-electron transfers determining the average current and bidirectional two-electron processes contributing to the noise only. This result pertains at vanishing temperature while the extended Keldysh-Green's function formalism in use also enables the systematic calculation of the higher-order current correlators at finite temperatures. PMID:17930910

Vanevi?, Mihajlo; Nazarov, Yuli V; Belzig, Wolfgang

2007-08-13

376

Numerical studies of electron transfers in two-dimensional multiple quantum dots  

International Nuclear Information System (INIS)

[en] Quantum dynamical properties of electron transfers through multiple quantum dots (QDs) are numerically investigated. The QDs are modeled as two-dimensional electron systems and the conductive properties are calculated from the time evolution of the electron wavefunctions. In addition, we propose a new technique dealing with the electron-electron correlation and demonstrate the dynamical simulations of the Coulomb blockade as well as the spin blockade

2008-09-30

377

Energy transfer studies of coumarin dyes using electron pulse radiolysis  

International Nuclear Information System (INIS)

Pulse radiolysis studies of the triplets of four 7-amino coumarin laser dyes were carried out in benzene. Energy transfer technique was used to confirm and also to determine the characteristics of these triples. Use of these studies in energy transfer dye lasers is discussed. (author) 8 refs.; 2 figs.; 5 tabs.

1991-01-01

378

Electron transfer through ?-peptides attached to vertically aligned carbon nanotube arrays: a mechanistic transition.  

UK PubMed Central (United Kingdom)

The mechanism of electron transfer in ?-aminoisobutyric (Aib) homoligomers is defined by the extent of secondary structure, rather than just chain length. Helical structures (Aib units ?3) undergo an electron hopping mechanism, while shorter disordered sequences (Aib units <3) undergo an electron superexchange mechanism.

Yu J; Zvarec O; Huang DM; Bissett MA; Scanlon DB; Shapter JG; Abell AD

2012-01-01

379

Long-range intramolecular electron transfer in aromatic radical anions and binuclear transition metal complexes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Intramolecular electron transfer (ET) over distances up to about 10 Å between states in which the electron is localized on donor and acceptor groups by interaction with molecular or external solvent nuclear motion occurs, in particular, in two classes of systems. The excess electron in anionic radic...

Kuznetsov, A. M.; Ulstrup, Jens

380

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

Energy Technology Data Exchange (ETDEWEB)

Cyclic voltammetry (CV), UV/visible absorption spectroscopy, and electrospray mass spectrometry (ES-MS) are used in conjunction to study the mono- and /or dications produced in solution from the reaction of three model compounds ([beta]-carotene, cobalt(II) octaethylporphyrin (Co[sup II]OEP), nickel(II) octaethylporphyrin (Ni[sup II]OEP), in three different solvent/electron-transfer reagent systems (methylene chloride/0.1% trifluoroacetic acid (TFA) (v/v), methylene chloride/0.1% TFA/2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) v/v/200 [mu]M), methylene chloride/0.1% TFA/0.1% antimony pentafluoride (SbF[sub 5]) (v/v/v)). The reactions were carried out on-line with ES-MS by means of flow injection. Correlation of the CV data for these analytes with the ionic species determined to be in the solution on the basis of UV/visible absorption spectra and/or on the basis of the ionic species observed in the gas phase by ES-MS, along with our previously published data on these solvent/reagent systems, allowed an effective oxidation potential range, E, to be assigned to these solvent/reagent systems: methylene chloride/0.1% TFA (v/v), 0.6V [le] E[sub TFA] < 0.7 V; methylene chloride/0.1% TFA/DDQ (v/v/200 [mu]M), 0.8 [le] E[sub TFA/DDQ] < 1.0 V; methylene chloride/0.1% TFA/0.1% SbF[sub 5] (v/v/v), 1.3 [le] E[sub TFA/SbF(5)] < 1.5. 40 refs., 7 figs.

Van Berkel, G.J.; Zhou, F. (Oak Ridge National Lab., TN (United States))

1994-10-15

 
 
 
 
381

Specific deuterium isotope effects on the rates of electron transfer within geminate radical-ion pairs  

Energy Technology Data Exchange (ETDEWEB)

The results of the first systematic study of the effect of isotopic substitution on the rates of electron transfer for reactions in the inverted region are reported. Rates of return electron transfer within germinate radical ion pairs of 9,10-dicyanoanthracene (DCA) and 2,6,9,10-tetracyanoanthracene (TCA) radical ions and radical cations of perdeuteriated methyl-substituted benzene derivatives determined by a previously reported method are tabulated. The free energies of the electron-transfer reactions for both sets of ion pairs have been calculated, and in each case the reactions with deuterated cations was slower than with