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1

Frontier orbital symmetry control of intermolecular electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

Stevens, B.

1991-09-01

2

Electrochemical study of the intermolecular electron transfer to Pseudomonas aeruginosa cytochrome cd1 nitrite reductase  

International Nuclear Information System (INIS)

The kinetics of electron transfer reaction between cytochrome cd1 nitrite reductase (NiR) from Pseudomonas aeruginosa and various physiological/non physiological redox partners was investigated using cyclic voltammetry at the pyrolytic graphite electrode. While NiR did not exchange electron with the electrode, cytochrome c551 and azurin, both from Ps. aeruginosa, behaved as fast electrochemical systems. The intermolecular electron transfers between NiR and cytochrome c551 or azurin as electron shuttles, in the presence of nitrite, were studied. Second order rate constants of 2x106 and 1.4x105 M-1 s-1 are calculated for cytochrome c551 and azurin, respectively. The dependence of the second-order rate constant on ionic strength and pH is discussed. Finally, the effect of the global charge of the electron shuttles was explored using differently charged species (proteins or small ions). The experimental results suggest involvement of polar interactions as well as of hydrophobic contacts in the protein recognition prior to the intermolecular electron transfer. As the cross-reaction between Ps. nautica cytochrome c552 and Ps. aeruginosa NiR was shown to be as efficient as the catalytic reaction involving the physiological partners, it is concluded to a 'pseudo-specificity' in the recognition between NiR and the electron donor.

2003-04-05

3

Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies.  

UK PubMed Central (United Kingdom)

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications.

Lemmetyinen H; Tkachenko NV; Efimov A; Niemi M

2011-01-01

4

Photoinduced intra- and intermolecular electron transfer in solutions and in solid organized molecular assemblies.  

Science.gov (United States)

The present paper highlights results of a systematic study of photoinduced electron transfer, where the fundamental aspects of the photochemistry occurring in solutions and in artificially or self-assembled molecular systems are combined and compared. In photochemical electron transfer (ET) reactions in solutions the electron donor, D, and acceptor, A, have to be or to diffuse to a short distance, which requires a high concentration of quencher molecules and/or long lifetimes of the excited donor or acceptor, which cannot always be arranged. The problem can partly be avoided by linking the donor and acceptor moieties covalently by a single bond, molecular chain or chains, or rigid bridge, forming D-A dyads. The covalent combination of porphyrin or phthalocyanine donors with an efficient electron acceptor, e.g. fullerene, has a two-fold effect on the electron transfer properties. Firstly, the electronic systems of the D-A pair result in a formation of an exciplex intermediate upon excitation both in solutions and in solid phases. The formation of the exciplex accelerates the ET rate, which was found to be as fast as >10(12) s(-1). Secondly, the total reorganization energy can be as small as 0.3 eV, even in polar solvents, which allows nanosecond lifetimes for the charge separated (CS) state. Molecular assemblies can form solid heterogeneous, but organized systems, e.g. molecular layers. This results in more complex charge separation and recombination dynamics. A distinct feature of the ET in organized assemblies is intermolecular interactions, which open a possibility for a charge migration both in the acceptor and in the donor layers, after the primary intramolecular exciplex formation and charge separation in the D-A dyad. The intramolecular ET is fast (35 ps) and efficient, but the formed interlayer CS states have lifetimes in microsecond or even second time domain. This is an important result considering possible applications. PMID:21031207

Lemmetyinen, Helge; Tkachenko, Nikolai V; Efimov, Alexander; Niemi, Marja

2010-10-29

5

Effect of donor orientation on ultrafast intermolecular electron transfer in coumarin-amine systems  

International Nuclear Information System (INIS)

Effect of donor amine orientation on nondiffusive ultrafast intermolecular electron transfer (ET) reactions in coumarin-amine systems has been investigated using femtosecond fluorescence upconversion measurements. Intermolecular ET from different aromatic and aliphatic amines used as donor solvents to the excited coumarin-151 (C151) acceptor occurs with ultrafast rates such that the shortest fluorescence lifetime component (?1) is the measure of the fastest ET rate (?1=?ETfast=(kETfast)-1), assigned to the C151-amine contact pairs in which amine donors are properly oriented with respect to C151 to maximize the acceptor-donor electronic coupling (Vel). It is interestingly observed that as the amine solvents are diluted by suitable diluents (either keeping solvent dielectric constant similar or with increasing dielectric constant), the ?1 remains almost in the similar range as long as the amine dilution does not cross a certain critical limit, which in terms of the amine mole fraction (xA) is found to be ?0.4 for aromatic amines and ?0.8 for aliphatic amines. Beyond these dilutions in the two respective cases of the amine systems, the ?1 values are seen to increase very sharply. The large difference in the critical xA values involving aromatic and aliphatic amine donors has been rationalized in terms of the largely different orientational restrictions for the ET reactions as imposed by the aliphatic (n-type) and aromatic (?-type) nature of the amine donors [A. K. Satpati et al., J. Mol. Struct. 878, 84 (2008)]. Since the highest occupied molecular orbital (HOMO) of the n-type aliphatic amines is mostly centralized at the amino nitrogen, only some specific orientations of these amines with respect to the close-contact acceptor dye [also of ?-character; A. K. Satpati et al., J. Mol. Struct. 878, 84 (2008) and E. W. Castner et al., J. Phys. Chem. A 104, 2869 (2000)] can give suitable Vel and thus ultrafast ET reaction. In contrary, the HOMO of the ?-type aromatic amines is largely distributed throughout the whole molecule and thus most of the orientations of these amines can give significant Vel for ultrafast ET reactions with close-contact C151 dyes.

2008-09-21

6

Intermolecular electron transfer promoted by directional donor-acceptor attractions in self-assembled diketopyrrolopyrrole-thiophene films.  

UK PubMed Central (United Kingdom)

The photophysics of a symmetric triad consisting of two bithiophene (BT) units covalently linked to a central diketopyrrolopyrrole unit (DPP) has been investigated both in dichloromethane and in the thin film. The DPP-BT film exhibits a red-shifted low-energy absorption band compared to its solution, which is indicative of efficient ?-? interactions in the solid-state phase. The steady-state and time-resolved fluorescence results revealed that the photoluminescence was subjected to severe emission quenching when DPP-BT changes from its solution phase to its film form. Further femtosecond transient absorption studies clarified that rapid intermolecular electron transfer accounts for the considerable fluorescence quenching event. The structural characterization of DPP-BT nanobelts, based on GIXRD and SAED patterns, suggested that the composite may be self-assembled into a slipped face-to-face configuration in the film, providing compact interlayer D-A interactions. As a result, intermolecular electron transfer is promoted by the favorable donor-acceptor attractions between the adjacent molecules. Moreover, this packing configuration provides a moderate channel for charge transportation. The hole mobility, which was measured based on a single-belt field-effect transistor, was found to be around 0.07 cm(2) V(-1) s(-1). Our observation reveals the role of spatial orientation in photophysical processes and the consequential semiconductor performance, providing guidance for the development and self-assembly of new opto-electronic molecules.

Liu H; Jia H; Wang L; Wu Y; Zhan C; Fu H; Yao J

2012-11-01

7

Intermolecular electron transfer promoted by directional donor-acceptor attractions in self-assembled diketopyrrolopyrrole-thiophene films.  

Science.gov (United States)

The photophysics of a symmetric triad consisting of two bithiophene (BT) units covalently linked to a central diketopyrrolopyrrole unit (DPP) has been investigated both in dichloromethane and in the thin film. The DPP-BT film exhibits a red-shifted low-energy absorption band compared to its solution, which is indicative of efficient ?-? interactions in the solid-state phase. The steady-state and time-resolved fluorescence results revealed that the photoluminescence was subjected to severe emission quenching when DPP-BT changes from its solution phase to its film form. Further femtosecond transient absorption studies clarified that rapid intermolecular electron transfer accounts for the considerable fluorescence quenching event. The structural characterization of DPP-BT nanobelts, based on GIXRD and SAED patterns, suggested that the composite may be self-assembled into a slipped face-to-face configuration in the film, providing compact interlayer D-A interactions. As a result, intermolecular electron transfer is promoted by the favorable donor-acceptor attractions between the adjacent molecules. Moreover, this packing configuration provides a moderate channel for charge transportation. The hole mobility, which was measured based on a single-belt field-effect transistor, was found to be around 0.07 cm(2) V(-1) s(-1). Our observation reveals the role of spatial orientation in photophysical processes and the consequential semiconductor performance, providing guidance for the development and self-assembly of new opto-electronic molecules. PMID:22951990

Liu, Huiying; Jia, Hui; Wang, Lanfen; Wu, Yishi; Zhan, Chuanlang; Fu, Hongbing; Yao, Jiannian

2012-11-01

8

Studies on intra-supramolecular and intermolecular electron-transfer processes between zinc naphthalocyanine and imidazole-appended fullerene.  

UK PubMed Central (United Kingdom)

Spectroscopic, computational, redox, and photochemical behavior of a self-assembled donor-acceptor dyad formed by axial coordination of zinc naphthalocyanine, ZnNc, and fulleropyrrolidine bearing an imidazole coordinating ligand (2-(4'-imidazolylphenyl)-fulleropyrrolidine, C60Im) was investigated in noncoordinating solvents, toluene and o-dichlorobenzene, and the results were compared to the intermolecular electron transfer processes in a coordinating solvent, benzonitrile. The optical absorption and ab initio B3 LYP/3-21G(*) computational studies revealed self-assembled supramolecular 1:1 dyad formation between the ZnNc and C60Im entities. In the optimized structure, the HOMO was found to be entirely located on the ZnNc entity while the LUMO was found to be entirely on the fullerene entity. Cyclic voltammetry studies of the dyad exhibited a total of seven one-electron redox processes in o-dichlorobenzene, with 0.1 M tetrabutylammonium perchlorate. The excited-state electron-transfer processes were monitored by both optical-emission and transient-absorption techniques. Direct evidence for the radical-ion-pair (C60Im.-:ZnNC.+) formation was obtained from picosecond transient-absorption spectral studies, which indicated charge separation from the singlet-excited ZnNc to the C60Im moiety. The calculated rates of charge separation and charge recombination were 1.4 x 10(10) s-1 and 5.3 x 10(7) s-1 in toluene and 8.9 x 10(9) s-1 and 9.2 x 10(7) s-1 in o-dichlorobenzene, respectively. In benzonitrile, intermolecular electron transfer from the excited triplet state of ZnNc to C60Im occurs and the second-order rate constant (kqtriplet) for this quenching process was 5.3 x 10(8)M-1s-1.

el-Khouly ME; Rogers LM; Zandler ME; Suresh G; Fujitsuka M; Ito O; D'Souza F

2003-04-01

9

Intermolecular charge transfer involving tryptophan, tyrosine and three electron-bonded intermediates derived from methionine  

International Nuclear Information System (INIS)

[en] Oxidation processes of radiation-generated three-electron-bonded intermediates derived from methionine Met2:S therefore + S: and Met:S therefore plus: (X=Cl, Br) were through reaction with tryptophan and tyrosine, using the optical pulse radiolysis method. Bimolecular rate constants have been measured for the reactions Met2:S therefore S: with TrpH(k=3.8 x 108 dm3 mol-1 s 1 and k=4.9 x 108 dm3 mol-1 s-1 at pH 1 and 4.3, respectively) and Met2[S therefore + S] with tyrosine, k=3.8 x 107 dm3 mol-1 s-1. Rate constants for intermolecular transformation of Met[S Br] and Met[S Cl] into TrpH+ or Trp were also estimated. They varied from 4.7 x 108 dm3 mol-1 s-1 (bromide species) to 1.0 x 109 dm3 mol-1 s-1 (chloride species). It has also been established that azide radicals N 6- anion radicals, N3 in contrast to dihalide radicals (X 2- anion radicals) do not form transients of Met[S therefore plus] (X=N3)-type. However, oxidation of N3- by Met2[S therefore + S] occurs with a bimolecular rate constant of 2.8 x 108 dm3 mol-1 s-1. These results are discussed in the light of some equilibria which have been proposed earlier for methionine-halide systems. (author)

1986-01-01

10

Intermolecular charge transfer involving tryptophan, tyrosine and three electron-bonded intermediates derived from methionine.  

UK PubMed Central (United Kingdom)

Oxidation processes of radiation-generated three-electron-bonded intermediates derived from methionine Met2[S+...S] and Met[S...X] (X=Cl,Br) were investigated through reaction with tryptophan and tyrosine, using the optical pulse radiolysis method. Bimolecular rate constants have been measured for the reactions Met2[S+...S] with TrpH(k=3.8 x 10(8) dm3 mol-1 s-1 and k = 4.9 X 10(8) dm3 mol-1 s-1 at at ph 1 and 4.3, respectively) and Met2[S+...S] with tyrosine, k=3.8 x 10(7) dm3 mol-1 s-1. Rate constants for intermolecular transformation of Met[S...Br] and Met[S...Cl] into TrpH+. or Trp. were also estimated. They varied from 4.7 X 10(8) dm3 mol-1 s-1 (bromide species) to 1.0 X 10(9)dm3 mol-1 s-1 (chloride species). It has also been established azide radicals N-6, N.3 in contrast to dihalide radicals (X-2) do not form transients of Met[S...X] (X = N3)-type. However, oxidation of N-3 by Met2[S+...S] occurs with a bimolecular rate constant of 2.8 X 10(8) dm3 mol-1 s-1. These results are discussed in the light of some equilibria which have been proposed earlier for methionine-halide systems.

Bobrowski K; Lubis R

1986-12-01

11

Photochemistry on surfaces. 2. Intermolecular electron transfer on colloidal alumina-coated silica particles  

Energy Technology Data Exchange (ETDEWEB)

Reductive quenching of two photoexcited ruthenium(II) complexes by an anionic electron donor, 2,2{prime}-azinobis(3-ethyl-benzothiazoline-6-sulfonate) (ABTS{sup 2{minus}}), in aqueous solution was examined by laser flash photolysis before and after adding positively charged colloidal (250-{angstrom} diameter) alumina-coated silica particles. The kinetics and quantum yields of electron transfer with an anionic sensitizer, RuL{sub 3}{sup 4{minus}} (L = bathophenanthroline disulfonate), and a cationic one, Ru(bpy){sub 3}{sup 2+} (bpy = 2,2{prime}-bipyridine), were compared. Coadsorption of ABTS{sup 2{minus}} and RuL{sub 3}{sup 4{minus}} by the particles greatly enhanced the rate of quenching such that only the reaction occurring on the surfaces of the particles was observed. Electron transfer from ABTS{sup 2{minus}} to RuL{sub 3}{sup 4-*} occurred by a static (nondiffusional) process, and the quenching efficiency was maximal when there was close to monolayer coverage of the reactants on the particles. Ru(bpy){sub 3}{sup 2+} was not adsorbed by the particles and served as a luminescent probe for the determination of the binding capacity of the particles for ABTS{sup 2{minus}}.

Kamat, P.V.; Ford, W.E. (Univ. of Notre Dame, IN (USA))

1989-02-23

12

Electronic transitions and intermolecular forces  

International Nuclear Information System (INIS)

[en] This thesis describes two different subjects - electronic transitions and intermolecular forces - that are related mainly by the following observation: The wavenumber at which an electronic transition in an atom or molecule occurs, depends on the environment of that atom or molecule. This implies, for instance, that when a molecule becomes solvated its absorption spectrum may be shifted either to the blue or to the red side of the original gasphase spectrum. In part I attention is paid to the experimental aspects of VUV spectroscopy, both in the gasphase and in the condensed phase. In part II a series of papers are presented, dealing with the calculation of intermolecular forces (and some related topics) both for the ground state and for the excited state interactions, using different non-empirical methods. The calculations provide, among other results, a semiquantitative interpretation of the spectral blue shifts encountered in our experiments. (Auth.)

1981-01-01

13

Barrier-Free Intermolecular Proton Transfer Induced by Excess Electron Attachment to the Complex of Alanine with Uracil  

Energy Technology Data Exchange (ETDEWEB)

The photoelectron spectrum of the uracil-alanine anionic complex (UA)- has been recorded with 2.540 eV photons. This spectrum reveals a broad feature with a maximum between 1.6-2.1 eV. The vertical electron detachment energy is too large to be attributed to an (UA)- anionic complex in which an intact uracil anion is solvated by alanine, or vice versa. The neutral and anionic complexes of uracil and alanine were studied at the B3LYP and second order Moeller-Plesset level of theory with 6-31++G** basis sets. The neutral complexes form cyclic hydrogen bonds and the three most stable neutral complexes are bound by 0.72, 0.61 and 0.57 eV. The electron hole in complexes of uracil with alaninie is localized on uracil, but the formation of a complex with alanine strongly modulates the vertical ionization energy of uracil. The theoretical results indicate that the excess electron in (UA)- occupies a p* orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT) from the carboxylic group of alanine to the O8 atom of uracil. As a result, the four most stable structures of the uracil-alanine anionic complex can be characterized as the neutral radical of hydrogenated uracil solvated by the anion of deprotonated alanine. Our current results for the anionic complex of uracil with alanine are similar to our previous results for the anion of uracil with glycine [Eur. Phys. J. D 20, 431 (2002)], and together they indicate that the BFPT process is not very sensitive to the nature of the amino acid's hydrophobic residual group. The BFPT to the O8 atom of uracil may be relevant to the damage suffered by nucleic acid bases due to exposure to low energy electrons.

Dabkowska, Iwona; Rak, Janusz; Gutowski, Maciej S.; Nilles, J.M.; Stokes, Sarah; Bowen, Kit H.

2004-04-01

14

Barrier-free intermolecular proton transfer induced by excess electron attachment to the complex of alanine with uracil.  

UK PubMed Central (United Kingdom)

The photoelectron spectrum of the uracil-alanine anionic complex (UA)(-) has been recorded with 2.540 eV photons. This spectrum reveals a broad feature with a maximum between 1.6 and 2.1 eV. The vertical electron detachment energy is too large to be attributed to an (UA)(-) anionic complex in which an intact uracil anion is solvated by alanine, or vice versa. The neutral and anionic complexes of uracil and alanine were studied at the B3LYP and second-order Møller-Plesset level of theory with 6-31++G(*) (*) basis sets. The neutral complexes form cyclic hydrogen bonds and the three most stable neutral complexes are bound by 0.72, 0.61, and 0.57 eV. The electron hole in complexes of uracil with alanine is localized on uracil, but the formation of a complex with alanine strongly modulates the vertical ionization energy of uracil. The theoretical results indicate that the excess electron in (UA)(-) occupies a pi(*) orbital localized on uracil. The excess electron attachment to the complex can induce a barrier-free proton transfer (BFPT) from the carboxylic group of alanine to the O8 atom of uracil. As a result, the four most stable structures of the uracil-alanine anionic complex can be characterized as a neutral radical of hydrogenated uracil solvated by a deprotonated alanine. Our current results for the anionic complex of uracil with alanine are similar to our previous results for the anion of uracil with glycine, and together they indicate that the BFPT process is not very sensitive to the nature of the amino acid's hydrophobic residual group. The BFPT to the O8 atom of uracil may be relevant to the damage suffered by nucleic acid bases due to exposure to low energy electrons.

Dabkowska I; Rak J; Gutowski M; Nilles JM; Stokes ST; Bowen KH

2004-04-01

15

Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(1S) + H2(B 1?/sub u/+)  

International Nuclear Information System (INIS)

To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H2(B 1?/sub u/+) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H2(B 1?/sub u/+). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H2(E,F 1?/sub g/+) and with He + H2(X 1?/sub g/+) and cause a local maximum and a deep minimum in the He + H2(B 1?/sub u/+) PES, respectively. The crossing with He + H2(X 1?/sub g/+) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H2(B 1?/sub u/+) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs.

1986-01-01

16

Intermolecular Hydrogen Transfer in Isobutane Hydrate  

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Full Text Available Electron spin resonance (ESR) spectra of butyl radicals induced with ?-ray irradiation in the simple isobutane (2-methylpropane) hydrate (prepared with deuterated water) were investigated. Isothermal annealing results of the ?-ray-irradiated isobutane hydrate reveal that the isobutyl radical in a large cage withdraws a hydrogen atom from the isobutane molecule through shared hexagonal-faces of adjacent large cages. During this “hydrogen picking” process, the isobutyl radical is apparently transformed into a tert-butyl radical, while the sum of isobutyl and tert-butyl radicals remains constant. The apparent transformation from isobutyl to tert-butyl radicals is an irreversible first-order reaction and the activation energy was estimated to be 35 ± 3 kJ/mol, which was in agreement with the activation energy (39 ± 5 kJ/mol) of hydrogen picking in the ?-ray-irradiated propane hydrate with deuterated water.

Naohiro Kobayashi; Takashi Minami; Atsushi Tani; Mikio Nakagoshi; Takeshi Sugahara; Kei Takeya; Kazunari Ohgaki

2012-01-01

17

Intermolecular proton transfer in anionic complexes of uracil with alcohols  

Energy Technology Data Exchange (ETDEWEB)

A series of eighteen alcohols (ROH) has been designed with an enthalpy of deprotonation (HDP) in a range of 13.8-16.3 eV. The effects of excess electron attachment to the binary alcohol-uracil (ROH…U) complexes have been studied at the density functional level with a B3LYP exchange-correlation functional and at the second order Møller-Plesset perturbation theory level. The photoelectron spectra of anionic complexes of uracil with three alcohols (ethanol, 2,2,3,3,3-pentafluoroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol) have been measured with 2.54 eV photons. For ROHs with deprotonation enthalpies larger than 14.8 eV only the ROH...U- minimum exists on the potential energy surface of the anionic complex. For alcohols with deprotonation enthalpies in a range of 14.3-14.8 eV two minima might exist on the anionic potential energy surface, which correspond to the RO-…HU. and ROH...U- structures. For ROHs with deprotonation enthalpies smaller than 14.3 eV, the excess electron attachment to the ROH…U complex always induces a barrier-free proton transfer from the hydroxyl group of ROH to the O8 atom of U, with the product being RO-…HU.. A driving force for the intermolecular proton transfer is to stabilize the excess negative charge localized on a ?* orbital of uracil. Therefore, these complexes with proton transferred to the anionic uracil are characterized by larger values of electron vertical detachment energy (VDE). The values of VDE for anionic complexes span a range from 1.0 to 2.3 eV and roughly correlate with the acidity of alcohols. However, there is a gap of ~0.5 eV in the values of VDE, which separates the two families, ROH...U- and RO-…HU., of anionic complexes. The energy of stabilization for the anionic complexes spans a range from 0.6 to 1.7 eV and roughly correlates with the acidity of alcohols. The measured photoelectron spectra are in good agreement with the theoretical predictions.

Haranczyk, Maciej; Rak, Janusz; Gutowski, Maciej S.; Radisic, Dunja; Stokes, Sarah T.; Bowen, Kit H.

2005-07-14

18

Intermolecular proton transfer in anionic complexes of uracil with alcohols  

International Nuclear Information System (INIS)

A series of eighteen alcohols (ROH) has been designed with an enthalpy of deprotonation (HDP) in a range of 13.8-16.3 eV. The effects of excess electron attachment to the binary alcohol-uracil (ROH...U) complexes have been studied at the density functional level with a B3LYP exchange-correlation functional and at the second order Moeller-Plesset perturbation theory level. The photoelectron spectra of anionic complexes of uracil with three alcohols (ethanol, 2,2,3,3,3-pentafluoroethanol and 1,1,1,3,3,3-hexafluoro-2-propanol) have been measured with 2.54 eV photons. For ROHs with deprotonation enthalpies larger than 14.8 eV only the ROH...U- minimum exists on the potential energy surface of the anionic complex. For alcohols with deprotonation enthalpies in a range of 14.3-14.8 eV two minima might exist on the anionic potential energy surface, which correspond to the RO-...HU. and ROH...U- structures. For ROHs with deprotonation enthalpies smaller than 14.3 eV, the excess electron attachment to the ROH...U complex always induces a barrier-free proton transfer from the hydroxyl group of ROH to the O8 atom of U, with the product being RO-...HU.. A driving force for the intermolecular proton transfer is to stabilize the excess negative charge localized on a orbital of uracil. Therefore, these complexes with proton transferred to the anionic uracil are characterized by larger values of electron vertical detachment energy (VDE). The values of VDE for anionic complexes span a range from 1.0 to 2.3 eV and roughly correlate with the acidity of alcohols. However, there is a gap of ?0.5 eV in the values of VDE, which separates the two families, ROH...U- and RO-...HU., of anionic complexes. The energy of stabilization for the anionic complexes spans a range from 0.6 to 1.7 eV and roughly correlates with the acidity of alcohols. The measured photoelectron spectra are in good agreement with the theoretical predictions

2005-07-14

19

Intermolecular electron transfer between coumarin dyes and aromatic amines in Triton-X-100 micellar solutions: Evidence for Marcus inverted region  

International Nuclear Information System (INIS)

Photoinduced electron transfer (ET) between coumarin dyes and aromatic amines has been investigated in Triton-X-100 micellar solutions and the results have been compared with those observed earlier in homogeneous medium. Significant static quenching of the coumarin fluorescence due to the presence of high concentration of amines around the coumarin fluorophore in the micelles has been observed in steady-state fluorescence studies. Time-resolved studies with nanosecond resolutions mostly show the dynamic part of the quenching for the excited coumarin dyes by the amine quenchers. A correlation of the quenching rate constants, estimated from the time-resolved measurements, with the free energy changes (?G0) of the ET reactions shows the typical bell shaped curve as predicted by Marcus outer-sphere ET theory. The inversion in the ET rates for the present systems occurs at an exergonicity (-?G0) of ?0.7-0.8 eV, which is unusually low considering the polarity of the Palisade layer of the micelles where the reactants reside. Present results have been rationalized on the basis of the two dimensional ET model assuming that the solvent relaxation in micellar media is much slower than the rate of the ET process. Detailed analysis of the experimental data shows that the diffusional model of the bimolecular quenching kinetics is not applicable for the ET reactions in the micellar solutions. In the present systems, the reactions can be better visualized as equivalent to intramolecular electron transfer processes, with statistical distribution of the donors and acceptors in the micelles. A low electron coupling (Vel) parameter is estimated from the correlation of the experimentally observed and the theoretically calculated ET rates, which indicates that the average donor-acceptor separation in the micellar ET reactions is substantially larger than for the donor-acceptor contact distance. Comparison of the Vel values in the micellar solution and in the donor-acceptor close contact suggests that there is an intervention of a surfactant chain between the interacting donor and acceptor in the micellar ET reaction.

2004-02-08

20

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

 
 
 
 
21

Density-functional based determination of intermolecular charge transfer properties for large-scale morphologies.  

UK PubMed Central (United Kingdom)

Theoretical studies of charge transport in organic conducting systems pose a unique challenge since they must describe both extremely short-ranged and fast processes (charge tunneling) and extremely long-ranged and slow ones (molecular ordering). The description of the mobility of electrons and holes in the hopping regime relies on the determination of intermolecular hopping rates in large-scale morphologies. Using Marcus theory these rates can be calculated from intermolecular transfer integrals and on-site energies. Here we present a detailed computational study on the accuracy and efficiency of density-functional theory based approaches to the determination of intermolecular transfer integrals. First, it is demonstrated how these can be obtained from quantum-chemistry calculations by forming the expectation value of a dimer Fock operator with frontier orbitals of two neighboring monomers based on a projective approach. We then consider the prototypical example of one pair out of a larger morphology of tris(8-hydroxyquinolinato)aluminium (Alq(3)) and study the influence of computational parameters, e.g. the choice of basis sets, exchange-correlation functional, and convergence criteria, on the calculated transfer integrals. The respective results are compared in order to derive an optimal strategy for future simulations based on the full morphology.

Baumeier B; Kirkpatrick J; Andrienko D

2010-09-01

22

Determination of stepsize parameters for intermolecular vibrational energy transfer  

Energy Technology Data Exchange (ETDEWEB)

Intermolecular energy transfer of highly excited polyatomic molecules plays an important role in many complex chemical systems: combustion, high temperature and atmospheric chemistry. By monitoring the relaxation of internal energy we have observed trends in the collisional efficiency ({beta}) for energy transfer as a function of the substrate's excitation energy and the complexities of substrate and deactivator. For a given substrate {beta} increases as the deactivator's mass increase to {approximately}30 amu and then exhibits a nearly constant value; this is due to a mass mismatch between the atoms of the colliders. In a homologous series of substrate molecules (C{sub 3}{minus}C{sub 8}) {beta} decreases as the number of atoms in the substrate increases; replacing F with H increases {beta}. All substrates, except for CF{sub 2}Cl{sub 2} and CF{sub 2}HCl below 10,000 cm{sup {minus}1}, exhibited that {beta} is independent of energy, i.e. <{Delta}E>{sub all} is linear with energy. The results are interpreted with a simple model which considers that {beta} is a function of the ocillators energy and its vibrational frequency. Limitations of current approximations used in high temperature unimolecular reactions were evaluated and better approximations were developed. The importance of energy transfer in product yields was observed for the photoactivation of perfluorocyclopropene and the photoproduction of difluoroethyne. 3 refs., 18 figs., 4 tabs.

Tardy, D.C.

1992-03-01

23

Intermolecular proton transfer induced by excess electron attachment to adenine(formic acid){sub n} (n = 2, 3) hydrogen-bonded complexes  

Energy Technology Data Exchange (ETDEWEB)

The propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA){sub 2,3} complexes span a range of 0.8-1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A-FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed.

Mazurkiewicz, Kamil; Haranczyk, Maciej; Storoniak, Piotr [University of Gdansk, Faculty of Chemistry, Sobieskiego 18, 80-952 Gdansk (Poland); Gutowski, Maciej [University of Gdansk, Faculty of Chemistry, Sobieskiego 18, 80-952 Gdansk (Poland); Chemistry-School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom); Rak, Janusz [University of Gdansk, Faculty of Chemistry, Sobieskiego 18, 80-952 Gdansk (Poland)], E-mail: janusz@chem.univ.gda.pl; Radisic, Dunja; Eustis, Soren N.; Wang, Di [Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218 (United States); Bowen, Kit H. [Department of Chemistry, Johns Hopkins University, Baltimore, MD 21218 (United States)], E-mail: kbowen@jhu.edu

2007-12-06

24

Intermolecular proton transfer induced by excess electron attachment to adenine(formic acid)n (n = 2, 3) hydrogen-bonded complexes  

Energy Technology Data Exchange (ETDEWEB)

The research described in this product was performed in part in the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. The propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA)2,3 complexes span a range of 0.8–1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A–FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed.

Mazurkiewicz, Kamil; Haranczyk, Maciej; Storoniak, Piotr; Gutowski, Maciej S.; Rak, Janusz; Radisic, Dunja; Eustis, Soren; Wang, Di; Bowen, Kit H.

2007-12-06

25

Intermolecular proton transfer induced by excess electron attachment to adenine(formic acid)n (n = 2, 3) hydrogen-bonded complexes  

International Nuclear Information System (INIS)

[en] The propensity of the neutral complexes between both adenine and 9-methyladenine (A/MA) with formic acid (FA) in 1:2 and 1:3 stoichiometries to bind an excess electron was studied using photoelectron spectroscopy and quantum chemistry computational methods. Although an isolated canonical adenine does not support bound valence anions, solvation by one formic acid molecule stabilizes the excess electron on adenine. The adiabatic electron affinities of the A/MA(FA)2,3 complexes span a range of 0.8-1.23 eV indicating that the anions of 1:2 and 1:3 stoichiometries are substantially more stable than the anionic A-FA dimer (EA = 0.67 eV), which we studied previously and an attachment of electron triggers double-BFPT, confirmed at the MPW1K level of theory, in all the considered systems. Hence, the simultaneous involvement of several molecules capable of forming cyclic hydrogen bonds with adenine remarkably increases its ability to bind an excess electron. The calculated vertical detachment energies for the most stable anions correspond well with those obtained using photoelectron spectroscopy. The possible biological significance of our findings is briefly discussed

2007-12-06

26

Chemistry of binuclear bridge complexes of platinum metals. 4. Quantum-chemical interpretation of electron spectra and simulation of intermolecular electron transfer in mixed-valent complexes [(NH3)5Ru-L-Ru(NH3)5]5+  

International Nuclear Information System (INIS)

The referral of electron spectra of binuclear mixed-valent complexes [(NH3)5Ru-L-Ru(NH3)5]5+ (L - pyrazine, pyrimidine, 4,4'-bipyridine and bis(4-pyridyl)acetylene) is given in the framework of semiempirical CINDO+CI method. Dynamics of intramolecular electron transfer from Ru(2) to Ru(3) is considered.

1997-01-01

27

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

28

Intra- and intermolecular proton transfer in methyl-2-hydroxynicotinate  

International Nuclear Information System (INIS)

[en] Spectral characteristics of methyl 2-hydroxynicotinate (MEHNA) have been studied using absorption, fluorescence excitation and fluorescence spectroscopy, as well as, using single photon counting nanosecond spectrofluorimeter. MEHNA is present as enol in less polar solvents and keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to phototautomer, formed by excited state intramolecular proton transfer (ESIPT), whereas fluorescence is only observed from keto form in polar solvents. In aqueous and polar solvents monocation (MC) is formed by protonating the exo carbonyl oxygen atom in the ground state (S0) and in the first excited singlet state (S1), MC is obtained by protonating carbonyl oxygen atom of the ester. It is formed by ESIPT from exo carbonyl proton to carbonyl oxygen atom of the ester. Dication is formed by protonating both the oxygen atoms. Two kinds of monoanions formed by deprotonating phenolic proton or >N-H proton of keto suggest the presence of enol and keto in aqueous solution. In cyclohexane MC is formed by protonating carbonyl oxygen in both S0 and S1 states. The electronic structure calculations were performed on each species using semi-empirical quantum mechanical AM1 method and density functional theory B3LYP with 6-31G** basis set using Gaussian 98 program, along with potential energy mapping, to characterize the particular species

2004-01-01

29

Intra- and intermolecular proton transfer in methyl-2-hydroxynicotinate  

Energy Technology Data Exchange (ETDEWEB)

Spectral characteristics of methyl 2-hydroxynicotinate (MEHNA) have been studied using absorption, fluorescence excitation and fluorescence spectroscopy, as well as, using single photon counting nanosecond spectrofluorimeter. MEHNA is present as enol in less polar solvents and keto in polar media. In non-polar solvents, large Stokes shifted fluorescence band is assigned to phototautomer, formed by excited state intramolecular proton transfer (ESIPT), whereas fluorescence is only observed from keto form in polar solvents. In aqueous and polar solvents monocation (MC) is formed by protonating the exo carbonyl oxygen atom in the ground state (S{sub 0}) and in the first excited singlet state (S{sub 1}), MC is obtained by protonating carbonyl oxygen atom of the ester. It is formed by ESIPT from exo carbonyl proton to carbonyl oxygen atom of the ester. Dication is formed by protonating both the oxygen atoms. Two kinds of monoanions formed by deprotonating phenolic proton or >N-H proton of keto suggest the presence of enol and keto in aqueous solution. In cyclohexane MC is formed by protonating carbonyl oxygen in both S{sub 0} and S{sub 1} states. The electronic structure calculations were performed on each species using semi-empirical quantum mechanical AM1 method and density functional theory B3LYP with 6-31G** basis set using Gaussian 98 program, along with potential energy mapping, to characterize the particular species.

Balamurali, M.M.; Dogra, S.K. E-mail: skdogra@iitk.ac.in

2004-11-01

30

Production of low kinetic energy electrons and energetic ion pairs by Intermolecular Coulombic Decay.  

UK PubMed Central (United Kingdom)

PURPOSE: The paper gives an introduction into Interatomic and Intermolecular Coulombic Decay (ICD). ICD is an autoionization process, which contrary to Auger decay involves neighbouring sites of the initial vacancy as an integral part of the decay transition. As a result of ICD, slow electrons are produced which generally are known to be active in radiation damage. The author summarizes the properties of ICD and reviews a number of important experiments performed in recent years. MATERIALS AND METHODS: Intermolecular Coulombic Decay can generally take place in weakly bonded aggregates in the presence of ionizing particles or ionizing radiation. Examples collected here mostly use soft X-rays produced by synchrotron radiation to ionize, and use rare-gas clusters, water clusters or solutes in a liquid jet to observe ICD after irradiation. RESULTS: Intermolecular Coulombic Decay is initiated by single ionization into an excited state. The subsequent relaxation proceeds via an ultra-fast energy transfer to a neighbouring site, where a second ionization occurs. Secondary electrons from ICD have clearly been identified in numerous systems. ICD can take place after primary ionization, as the second step of a decay cascade which also involves Auger decay, or after resonant excitation with an energy which exceeds the ionization potential of the system. CONCLUSIONS: ICD is expected to play a role whenever particles or radiation with photon energies above the ionization energies for inner valence electrons are present in weakly bonded matter, e.g., biological tissue. The process produces at the same time a slow electron and two charged atomic or molecular fragments, which will lead to structural changes around the ionized site.

Hergenhahn U

2012-12-01

31

Stress acidulated amphoteric molecules and mechanochromism via reversible intermolecular proton transfer.  

UK PubMed Central (United Kingdom)

Stress has been proved to acidulate amphoteric molecules and promote an intermolecular proton transfer, which results in a significant absorption and emission change. The stress acidulated amphoteric molecules open a new avenue for developing mechanochromic materials and anticipate many broad applications such as stress/pressure sensors and rewritable media.

Wang Y; Li M; Zhang Y; Yang J; Zhu S; Sheng L; Wang X; Yang B; Zhang SX

2013-07-01

32

Effect of the electronic structure of quinoline and its derivatives on the capacity for intermolecular interactions  

Energy Technology Data Exchange (ETDEWEB)

Calculations of the ground and excited states of quinoline and its 20H-, 70H-, 7NH2-, 7N(CH3)2-, and 7N(C2H5)2- substituted derivatives were undertaken by the INDO method, and the effect of intramolecular proton transfer (IPT) on their electronic structure was studied. The proton-accepting capacity of the compounds for intermolecular interactions was estimated by the molecular electrostatic potential method. It was shown that the proton-accepting capacity with respect to intermolecular interactions increases during the tautomeric transformation of the enolic form of 2-OH-quinoline to its keto form. The change in the basicity of the two forms of the molecules is affected by the orbital nature, and the multiplicity of the state is also important for the keto form. Substitution by electron-donating groups leads to increase in the proton-accepting capacity of both forms of the compounds in the S0, S/sub */, and T/sub */ states.

Privalova, N.Yu.; Sokolova, I.V.

1985-05-01

33

Intermolecular thermoelectric-like effects in molecular nano electronic systems  

International Nuclear Information System (INIS)

[en] Intramolecular thermoelectric-like coefficients are introduced and computed of a single molecule nano electronic system. Values of the electronic Intramolecular thermoelectric-like coefficients are calculated based on the density and energy transfers between different parts of the molecule using quantum theory of atoms in molecule. Since, Joule and Peltier heating are even (symmetrical) and odd (antisymmetric) functions of the external bias, it is possible to divide Intramolecular thermoelectric-like coefficients into two components, symmetrical and antisymmetrical Intramolecular thermoelectric-like coefficients, which describe the intramolecular Joule-like and Peltier-like effects, respectively. In addition, a semiclassical temperature model is presented to describe intramolecular temperature mapping (intramolecular energy distributions) in molecular nano electronic systems.

2012-01-01

34

Description of cross peaks induced by intermolecular vibrational energy transfer in two-dimensional infrared spectroscopy  

CERN Document Server

In the present work, the analytical description of an intermolecular vibrational energy transfer, analyzed by two dimensional infrared spectroscopy, is established. The energy transfer process takes place between the dark combination states of low frequency modes pertaining to different molecules. The appearance of the cross peaks results from coherent transfer between these combination states and an optically active state of the acceptor molecule. Such a process has recently been observed experimentally between the nitrile groups of acetonitrile-d3 and benzonitrile molecules. This molecular system will be used as a model for the simulations of their two-dimensional infrared spectra. The dependence of the cross-peak growth, which is a signature of the intermolecular energy transfer, will be discussed in detail as a function of the molecular dynamical constants.

Villaeys, Albert A

2013-01-01

35

Long range intermolecular forces in change-of-phase heat transfer  

Energy Technology Data Exchange (ETDEWEB)

The variation of long range intermolecular forces near interfaces profoundly affects the performance of change-of-phase heat exchangers. Starting with the fundamental electromagnetic force between molecules (dielectric properties), the effects of shape, temperature and concentration on the heat transfer characteristics and stability of thin films and larger systems are reviewed. A judicious selection of literature gives a consistent set of models of particular use in heat transfer. Examples of experimental verification in this rapidly developing field are also presented.

Wayner, P.C. Jr.

1999-07-01

36

Intra- and intermolecular charge transfer: twin themes and simultaneous competing transitions involving ferrocenes.  

Science.gov (United States)

Electronic absorption spectra of ferrocene, ferrocenecarboxylaldehyde, butylferrocene, and 1,1'-diacetylferrocene in pure organic polar and non-polar solvents, pure halocarbon solvents and in several hexane-halocarbon solvent mixtures have been recorded. The investigated ferrocenes have shown several intra-molecular electronic transitions of the types pi-pi*, n-pi*, and d-d*. On using protonic solvents (HA) each of the ferocenes (Fc) acquires a proton exported from the solvent to form a complex with the formula [FcH](+)[A](-). However, on using halocarbon solvents each of the ferrocenes has shown an intermolecular charge-transfer-to-solvent (CTTS) which is characterized by the appearance of new absorption spectral band(s) for each ferrocene-halocarbon solvent interaction. Formation constants (K(CT)) and molar absorption coefficients (epsilon(CT)) of these interactions have been determined and discussed. The study has indicated that the observed different transitions are dependent upon the number and nature of the substituents involved in the ferrocenes. PMID:19733114

Rabie, Usama M

2009-08-12

37

Intra- and intermolecular charge transfer: twin themes and simultaneous competing transitions involving ferrocenes.  

UK PubMed Central (United Kingdom)

Electronic absorption spectra of ferrocene, ferrocenecarboxylaldehyde, butylferrocene, and 1,1'-diacetylferrocene in pure organic polar and non-polar solvents, pure halocarbon solvents and in several hexane-halocarbon solvent mixtures have been recorded. The investigated ferrocenes have shown several intra-molecular electronic transitions of the types pi-pi*, n-pi*, and d-d*. On using protonic solvents (HA) each of the ferocenes (Fc) acquires a proton exported from the solvent to form a complex with the formula [FcH](+)[A](-). However, on using halocarbon solvents each of the ferrocenes has shown an intermolecular charge-transfer-to-solvent (CTTS) which is characterized by the appearance of new absorption spectral band(s) for each ferrocene-halocarbon solvent interaction. Formation constants (K(CT)) and molar absorption coefficients (epsilon(CT)) of these interactions have been determined and discussed. The study has indicated that the observed different transitions are dependent upon the number and nature of the substituents involved in the ferrocenes.

Rabie UM

2009-10-01

38

Intermolecular and intramolecular charge transfer in polymethylphenylsilane/C{sub 60} films  

Energy Technology Data Exchange (ETDEWEB)

The influence of C{sub 60} on fluorescence spectra, UV-visible spectra and photoconductivity of polymethylphenylsilane (PMPS) has been studied. The results show that the photoconductivity of PMPS doped with C{sub 60} increases by one order of magnitude. The fluorescence and UV-visible analyses indicate that an intermolecular charge-transfer complex of PMPS and C{sub 60} may be formed. Compared with C{sub 60}-doped PMPS, the C{sub 60}-linked PMPS displays higher photoconductivity than expected, which may come from the intramolecular charge-transfer process.

Shen Yue; Zhang Jiancheng; Gu Feng; Huang Pingping; Xia Yiben [School of Materials Science and Engineering, Shanghai University, Shanghai 201800 (China)

2004-09-21

39

Intermolecular forces in phase-change heat transfer: 1998 Kern award review  

Energy Technology Data Exchange (ETDEWEB)

The variation of long-range intermolecular forces near interfaces profoundly affects the performance of change-of-phase heat exchangers. Starting with the fundamental electromagnetic force between molecules (dielectric properties), the effects of shape (Kelvin effect), temperature (Clapeyron effect) and concentration on the heat-transfer characteristics of thin films and larger systems are reviewed and connected. A judicious selection of literature gives a consistent set of models of particular use in heat transfer. Examples of experimental verification of these interfacial models in this rapidly developing field are also presented.

Wayner, P.C. Jr.

1999-10-01

40

Vibronic spectra of perylene bisimide oligomers: effects of intermolecular charge-transfer excitation and conformational flexibility.  

UK PubMed Central (United Kingdom)

We have recently presented a theoretical study on the temperature-dependent absorption and photoluminescence spectroscopy of rubrene multichromophores by combining the time-dependent long-range-corrected density functional theory with the Frenkel exciton model (Gao; et al. J. Phys. Chem. A2009, 113, 12847). The spectra of rubrene multichromophores up to heptamers have been calculated and the effects of exciton-phonon coupling and temperature on the photophysical properties of both H- and J-aggregated oligomers were addressed. However, in that work the contribution of intermolecular charge-transfer excitons (CTEs) to vibronic spectra was not addressed. Here we take into account the effect of CTEs for the absorption and emission spectra of the aggregated perylene bisimide (PBI) oligomers in order to have a quantitative explanation to the experimental absorption and emission spectra of the PBI dyes. The role of intermolecular CTEs is discussed for different intermolecular orientations and distances. The simulations demonstrate that the contribution of CTEs becomes significant when the intermolecular distance is less than 4.5 Å for the ?-? stacked PBI aggregates, and the mixed exciton model is prerequisite to explain the experimentally observed red-shift of the absorption spectra in this case. The large Stokes shift of the emission spectra can be reproduced by our model, and it is induced by the asymmetric nature of the lowest excitonic state of the H-aggregated oligomers. The experimentally observed broad emission bands come from two species with different conformations. As for J-aggregated PBI oligomers, the interactions of FEs induce the red-shift and the increase of the relative intensity of 0-0 peak of the absorption spectra with more aggregated units.

Gao F; Zhao Y; Liang W

2011-03-01

 
 
 
 
41

Vibronic spectra of perylene bisimide oligomers: effects of intermolecular charge-transfer excitation and conformational flexibility.  

Science.gov (United States)

We have recently presented a theoretical study on the temperature-dependent absorption and photoluminescence spectroscopy of rubrene multichromophores by combining the time-dependent long-range-corrected density functional theory with the Frenkel exciton model (Gao; et al. J. Phys. Chem. A2009, 113, 12847). The spectra of rubrene multichromophores up to heptamers have been calculated and the effects of exciton-phonon coupling and temperature on the photophysical properties of both H- and J-aggregated oligomers were addressed. However, in that work the contribution of intermolecular charge-transfer excitons (CTEs) to vibronic spectra was not addressed. Here we take into account the effect of CTEs for the absorption and emission spectra of the aggregated perylene bisimide (PBI) oligomers in order to have a quantitative explanation to the experimental absorption and emission spectra of the PBI dyes. The role of intermolecular CTEs is discussed for different intermolecular orientations and distances. The simulations demonstrate that the contribution of CTEs becomes significant when the intermolecular distance is less than 4.5 Å for the ?-? stacked PBI aggregates, and the mixed exciton model is prerequisite to explain the experimentally observed red-shift of the absorption spectra in this case. The large Stokes shift of the emission spectra can be reproduced by our model, and it is induced by the asymmetric nature of the lowest excitonic state of the H-aggregated oligomers. The experimentally observed broad emission bands come from two species with different conformations. As for J-aggregated PBI oligomers, the interactions of FEs induce the red-shift and the increase of the relative intensity of 0-0 peak of the absorption spectra with more aggregated units. PMID:21384839

Gao, Fang; Zhao, Yi; Liang, WanZhen

2011-03-08

42

Rhodium-catalyzed intermolecular [2 + 2] cycloaddition of terminal alkynes with electron-deficient alkenes.  

UK PubMed Central (United Kingdom)

The first catalytic intermolecular [2 + 2] cycloaddition of terminal alkynes with electron-deficient alkenes is reported. The reaction proceeds with an 8-quinolinolato rhodium/phosphine catalyst system to give cyclobutenes from various substrates having polar functional groups in high yields with complete regioselectivity.

Sakai K; Kochi T; Kakiuchi F

2013-03-01

43

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

44

Magneto-Dielectric Effects Induced by Optically-Generated Intermolecular Charge-Transfer States in Organic Semiconducting Materials.  

UK PubMed Central (United Kingdom)

Traditionally, magneto-dielectric effects have been developed by combining ferroelectric and magnetic materials. Here, we show a magneto-dielectric effect from optically-generated intermolecular charge-transfer states in an organic semiconducting donor:acceptor (PVK:TCNB) system. We observe in magnetic field effects of photoluminescence that a magnetic field can change singlet/triplet population ratio in intermolecular charge-transfer states. Furthermore, our theoretical analysis and experimental evidence indicate that the singlets and triplets in charge-transfer states have stronger and weaker electrical polarizations, respectively. Therefore, the observed magneto-dielectric effect can be attributed to magnetically-dependent singlet/triplet ratio in intermolecular charge-transfer states. In principle, a magneto-dielectric effect can be generated through two different channels based on magneto-polarization and magneto-current effects when the singlet/triplet ratio in intermolecular charge-transfer states is changed by a magnetic field. We find, from the simulation of dielectric effects, that magneto-polarization and magneto-current effects play primary and secondary roles in the generation of magneto-dielectric effect.

Zang H; Yan L; Li M; He L; Gai Z; Ivanov I; Wang M; Chiang L; Urbas A; Hu B

2013-01-01

45

Structure and Intermolecular Vibrations of Perylene- trans-1,2-Dichloroethene, a Weak Charge-Transfer Complex.  

UK PubMed Central (United Kingdom)

The vibronic spectra of strong charge-transfer complexes are often congested or diffuse and therefore difficult to analyze. We present the spectra of the pi-stacked complex perylene-trans-1,2-dichloroethene, which is in the limit of weak charge transfer, the electronic excitation remaining largely confined to the perylene moiety. The complex is formed in a supersonic jet and its S_0 <-> S_1 spectra are investigated by two-color resonant two-photon ionization (2C-R2PI) and fluorescence spectroscopies. Under optimized conditions, vibrationally cold (T_{vib} ~ 9 K) and well resolved spectra are obtained. These are dominated by vibrational progressions in the "hindered-rotation" R_c intermolecular vibration with very low frequencies of 11 cm-1 (S_0) and 13 cm-1 (S_1). The intermolecular T_z stretch and the R_a and R_b bend vibrations are also observed. The normally symmetry-forbidden intramolecular 1a_u "twisting" vibration of perylene also appears, showing that the pi-stacking interaction deforms the perylene moiety, lowering its local symmetry from D_{2h} to D_2. We calculate the structure and vibrations of this complex using six different density functional theory (DFT) methods (CAM-B3LYP, BH\\&HLYP, B97-D3, omegaB97X-D, M06 and M06-2X) and compare the results to those calculated by correlated wave-function methods (SCS-MP2 and SCS-CC2). The structures and vibrational frequencies predicted with the CAM-B3LYP and BH\\&HLYP methods disagree with the other calculations and with experiment. The other four DFT and the ab initio methods all predict a pi-stacked "centered" structure with nearly co-planar perylene and dichloroethene moieties and intermolecular binding energies of D_e=-20.8 to -26.1 kcal/mol. The 0_0^0 band of the S_0\\rightarrow S_1 transition is red-shifted by delta nu= -301 cm-1 relative to that of perylene, implying that the D_e increases by 3.6 kJ/mol or ~15\\% upon electronic excitation. The intermolecular vibrational frequencies are assigned to the calculated R_c, T_z, R_a and R_b vibrations by comparing to the observed/calculated frequencies and S_0\\leftrightarrow S_1 Franck-Condon factors. Of the three DFT methods tested, the hybrid-meta-GGA functional M06-2X shows the best agreement with the experimental electronic transition energies, spectral shifts and vibronic spectra, closely followed by the omegaB97X-D functional, while the M06 functional gives inferior results.

Balmer FA; Ottiger P; Pfaffen C; Leutwyler S

2013-09-01

46

Theoretical study of intermolecular energy transfer involving electronically excited molecules: He(/sup 1/S) + H/sub 2/(B /sup 1/. sigma. /sub u//sup +/). [Solution for coupled channel equations  

Energy Technology Data Exchange (ETDEWEB)

To further understanding of gas phase collision dynamics involving electronically-excited molecules, a fully quantum mechanical study of He + H/sub 2/(B /sup 1/..sigma../sub u//sup +/) was undertaken. Iterative natural orbital configuration interaction (CI) calculations were performed to obtain the interaction potential between He and H/sub 2/(B /sup 1/..sigma../sub u//sup +/). The potential energy surface (PES) is highly anisotropic and has a van der Waals well of about 0.03 eV for C/sub 2v/ approach. Avoided PES crossings occur with He + H/sub 2/(E,F /sup 1/..sigma../sub g//sup +/) and with He + H/sub 2/(X /sup 1/..sigma../sub g//sup +/) and cause a local maximum and a deep minimum in the He + H/sub 2/(B /sup 1/..sigma../sub u//sup +/) PES, respectively. The crossing with He + H/sub 2/(X /sup 1/..sigma../sub g//sup +/) provides a mechanism for fluorescence quenching. The computed CI energies were combined with previous multi-reference double excitation CI calculations and fit with analytic functions for convenience in scattering calculations. Accurate dipole polarizabilities and quadrupole moment of H/sub 2/(B /sup 1/..sigma../sub u//sup +/) were computed for use in the multipole expansion, which is the analytic form of the long-range PES. 129 refs., 28 figs., 35 tabs.

Grimes, R.M.

1986-11-01

47

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

48

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

49

Intermolecular diatomic energies of a hydrogen dimer with non-Born-Oppenheimer nuclear and electron wave packets  

Science.gov (United States)

We have developed an efficient theoretical framework of a non-Born-Oppenheimer (non-BO) nuclear and electron wave packet (NWP and EWP) method and applied it to intra- and intermolecular energies of a hydrogen dimer. The energy surface functions were derived at low computational cost. In contrast with the ordinary BO nuclear quantization on a given energy surface that reduces the effective barrier, non-trivial non-BO interactions between the EWPs and NWPs resulted in increases of intermolecular rotational and translational barriers. A direct comparison demonstrated that the non-BO effect on the intermolecular energy is significant.

Hyeon-Deuk, Kim; Ando, Koji

2012-04-01

50

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

51

A CSOV study of the difference between HF and DFT intermolecular interaction energy values: the importance of the charge transfer contribution.  

UK PubMed Central (United Kingdom)

Intermolecular interaction energy decompositions using the Constrained Space Orbital Variation (CSOV) method are carried out at the Hartree-Fock level on the one hand and using DFT with usual GGA functionals on the other for a number of model complexes to analyze the role of electron correlation in the intermolecular stabilization energy. In addition to the overall stabilization, the results provide information on the variation, with respect to the computational level, of the different contributions to the interaction energy. The complexes studied are the water linear dimer, the N-methylformamide dimer, the nucleic acid base pairs, the benzene-methane and benzene-N2 van der Waals complexes, [Cu+ -(ImH)3]2, where "ImH" stands for the Imidazole ligand, and ImH-Zn++. The variation of the frozen core energy (the sum of the intermolecular electrostatic energy and the Pauli repulsion energy) calculated from the unperturbed orbitals of the interacting entities indicates that the intramolecular correlation contributions can be stabilizing as well as destabilizing, and that general trends can be derived from the results obtained using usual density functionals. The most important difference between the values obtained from HF and DFT computations concerns the charge transfer contribution, which, in most cases, undergoes the largest increase. The physical meaning of these results is discussed. The present work gives reference calculations that might be used to parametrize new correlated molecular mechanics potentials.

Piquemal JP; Marquez A; Parisel O; Giessner-Prettre C

2005-07-01

52

A CSOV study of the difference between HF and DFT intermolecular interaction energy values: the importance of the charge transfer contribution.  

Science.gov (United States)

Intermolecular interaction energy decompositions using the Constrained Space Orbital Variation (CSOV) method are carried out at the Hartree-Fock level on the one hand and using DFT with usual GGA functionals on the other for a number of model complexes to analyze the role of electron correlation in the intermolecular stabilization energy. In addition to the overall stabilization, the results provide information on the variation, with respect to the computational level, of the different contributions to the interaction energy. The complexes studied are the water linear dimer, the N-methylformamide dimer, the nucleic acid base pairs, the benzene-methane and benzene-N2 van der Waals complexes, [Cu+ -(ImH)3]2, where "ImH" stands for the Imidazole ligand, and ImH-Zn++. The variation of the frozen core energy (the sum of the intermolecular electrostatic energy and the Pauli repulsion energy) calculated from the unperturbed orbitals of the interacting entities indicates that the intramolecular correlation contributions can be stabilizing as well as destabilizing, and that general trends can be derived from the results obtained using usual density functionals. The most important difference between the values obtained from HF and DFT computations concerns the charge transfer contribution, which, in most cases, undergoes the largest increase. The physical meaning of these results is discussed. The present work gives reference calculations that might be used to parametrize new correlated molecular mechanics potentials. PMID:15898112

Piquemal, Jean-Philip; Marquez, Antonio; Parisel, Olivier; Giessner-Prettre, Claude

2005-07-30

53

The inclusion of electron correlation in intermolecular potentials: Applications to the formamide dimer and liquid formamide  

DEFF Research Database (Denmark)

A test of the quality of the electrostatic properties and polarizabilities used in the nonempirical molecular orbital (NEMO) potential is carried out for formamide by calculating the molecular dipole moment and polarizability at the second-order Moller-Plesset (MP2) level of theory. The molecular dipole moment is 11% lower at the MP2 level than at the Hartree-Fock (HF) level, whereas the isotropic part of the polarizability is increased by 36% by adding electron correlation and using a considerably larger basis set. The atomic charges, dipole moments and polarizabilities obtained at the HF level are rescaled to get the correct molecular properties at the MP2 level. The potential minimum for the cyclic dimer of formamide is -17.50 kcal/mol with the MP2-scaled properties and is significantly lower than other potentials give. Two intermolecular potentials are constructed and used in subsequent molecular dynamics simulations: one with the regular NEMO potential and the other with the rescaled MP2 properties. A damping of the electrostatic field at short intermolecular distances is included in the present NEMO model. The average energies for liquid formamide are lower for the MP2-scaled model and are in good agreement with experimental results. The lowering of the simulation energy for the MP2-scaled potential indicates the strong dispersive interactions in liquid formamide.

Brdarski, S.; Åstrand, P.-O.

2000-01-01

54

Relação entre transferência de carga e as interações intermoleculares em complexos de hidrogênio heterocíclicos Relationship between charge transfer and intermolecular interactions in heterocyclic hydrogen-bonded complexes  

Directory of Open Access Journals (Sweden)

Full Text Available Hydrogen-bonded complexes formed by the interaction of the heterocyclic molecules C2H4O and C2H5N with HF, HCN, HNC and C2H2 have been studied using density functional theory. The hydrogen bond strength has been analyzed through electron density charge transfer from the proton acceptor to the proton donor. The density charge transfer has been estimated using different methods such as Mulliken population analysis, CHELPG, GAPT and AIM. It has been shown that AIM-estimated charge transfer correlates very well with the hydrogen bond energy and the infrared bathochromic effect of the proton donor stretching frequencies.

Boaz G. Oliveira; Regiane C. M. U. de Araújo

2007-01-01

55

Reversible electron-induced cis-trans isomerization mediated by intermolecular interactions  

International Nuclear Information System (INIS)

Reversible isomerization processes are rarely found when organic molecular switches are adsorbed on metal surfaces. One obstacle is the large energy difference of the isomeric forms, since usually the most planar conformer has the largest adsorption energy. In the example of an imine derivative, we show a strategy for also stabilizing the non-planar isomer by intermolecular bonding to its neighbors. Tunneling electrons from the tip of a scanning tunneling microscope can then be used to induce reversible switching between the trans and cis-like state. Supported by model force-field calculations, we illustrate that the most probable cause of the enhanced stability of the three-dimensional cis state at specific adsorption sites is the electrostatic interaction with N sites of the neighboring molecule.

2012-10-03

56

Identification of molecular crystals capable of undergoing an acyl-transfer reaction based on intermolecular interactions in the crystal lattice.  

UK PubMed Central (United Kingdom)

Investigation of the intermolecular acyl-transfer reactivity in molecular crystals of myo-inositol orthoester derivatives and its correlation with crystal structures enabled us to identify the essential parameters to support efficient acyl-transfer reactions in crystals: 1)?the favorable geometry of the nucleophile (?OH) and the electrophile (C?O) and 2)?the molecular assembly, reinforced by C?H???? interactions, which supports a domino-type reaction in crystals. These parameters were used to identify another reactive crystal through a data-mining study of the Cambridge Structural Database. A 2:1 co-crystal of 2,3-naphthalene diol and its di-p-methylbenzoate was selected as a potentially reactive crystal and its reactivity was tested by heating the co-crystals in the presence of solid sodium carbonate. A facile intermolecular p-toluoyl group transfer was observed as predicted. The successful identification of reactive crystals opens up a new method for the detection of molecular crystals capable of exhibiting acyl-transfer reactivity.

Tamboli MI; Krishnaswamy S; Gonnade RG; Shashidhar MS

2013-09-01

57

Relação entre transferência de carga e as interações intermoleculares em complexos de hidrogênio heterocíclicos/ Relationship between charge transfer and intermolecular interactions in heterocyclic hydrogen-bonded complexes  

Scientific Electronic Library Online (English)

Full Text Available Abstract in english Hydrogen-bonded complexes formed by the interaction of the heterocyclic molecules C2H4O and C2H5N with HF, HCN, HNC and C2H2 have been studied using density functional theory. The hydrogen bond strength has been analyzed through electron density charge transfer from the proton acceptor to the proton donor. The density charge transfer has been estimated using different methods such as Mulliken population analysis, CHELPG, GAPT and AIM. It has been shown that AIM-estimated (more) charge transfer correlates very well with the hydrogen bond energy and the infrared bathochromic effect of the proton donor stretching frequencies.

Oliveira, Boaz G.; Araújo, Regiane C. M. U. de

2007-08-01

58

Role of Intramolecular and Intermolecular Hydrogen Bonding in Both Singlet and Triplet Excited States of Aminofluorenones on Internal Conversion, Intersystem Crossing, and Twisted Intramolecular Charge Transfer  

Science.gov (United States)

Time-dependent density functional theory method was performed to investigate the intramolecular and intermolecular hydrogen bonding in both the singlet and triplet electronic excited states of aminofluorenones AF, MAF, and DMAF in alcoholic solutions as well as their important roles on the excited-state photophysical processes of these aminofluorenones, such as internal conversion, intersystem crossing (ISC), twisted intramolecular charge transfer (TICT), and so forth. The intramolecular hydrogen bond C?O···H-N can be formed between the carbonyl group and amino group for the isolated AF and MAF. However, no intramolecular hydrogen bond for DMAF can be formed. At the same time, the most stable conformation of DMAF is out-of-plane structure, where the two dihedral angles formed between dimethyl groups and fluorenone plane are 163.1° and 41.74°, respectively. The formation of intramolecular hydrogen bond for AF and MAF is tightly associated with the intersystem crossing of these aminofluorenones. Furthermore, the ISC process can be dominantly determined by the change of intramolecular hydrogen bond between S1 and T1 states of aminofluorenones. Since the change of hydrogen bond between S1 and T1 states of AF is stronger than that of MAF, the rate of ISC process for AF is faster than that for MAF. Moreover, the rate constant of the ISC process of DMAF is nearly close to zero because of the absence of intramolecular hydrogen bond. On the other hand, the intermolecular hydrogen bond C?O···H-O can be also formed between all aminofluorenones and alcoholic solvents. The internal conversion process from S1 to S0 state of these aminofluorenones is facilitated by the intermolecular hydrogen bond strengthening in the electronic excited state of aminofluorenones because of the decrease of energy gap between S1 and S0 states. At the same time, the change of intermolecular hydrogen bond between S1 and T1 states for AF is much stronger than that for MAF, which may also contribute to the faster ISC process for AF than that for MAF in the same solvents. The TICT process plays an important role in the deactivation of the photoexcited DMAF, since the TICT process along the twisted dihedral angle is nearly barrierless in the S1 state of DMAF. However, the TICT cannot take place for AF and MAF because of the presence of the intramolecular hydrogen bond.

Zhao, Guang-Jiu; Han, Ke-Li

2009-05-01

59

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

60

Model building of a protein-protein complexed structure using saturation transfer and residual dipolar coupling without paired intermolecular NOE  

Energy Technology Data Exchange (ETDEWEB)

For understanding the precise mechanisms of molecular recognition of proteins, three-dimensional structural analyses of the protein-protein complexes are essential. For this purpose, a new method to reveal complex structures was developed with the assistance of saturation transfer (SAT) and residual dipolar coupling (RDC) by heteronuclear NMR experiments, without any paired intermolecular NOE information. The SAT and RDC experiments provide the information of the interfacial residues and the relative orientations of the two protein molecules, respectively. Docking simulation was then made to reconstruct a complex conformation, which satisfies the SAT and RDC data. The method was applied to the CAD-ICAD complex structure, which was previously determined by the NOE-distance geometry method. The quality of the current model was evaluated.Abbreviations: ASA - accessible surface area; HSQC - heteronuclear single quantum correlation; MD - molecular dynamics; NOE - nuclear Overhauser effect; TROSY - Transverse-Relaxation Optimized Spectroscopy.

Matsuda, Tomoki [Riken Genome Science Center (Japan); Ikegami, Takahisa; Nakajima, Nobuyuki [Osaka University, Institute for Protein Research (Japan); Yamazaki, Toshio [RIKEN Genome Science Center (Japan); Nakamura, Haruki [Osaka University, Institute for Protein Research (Japan)], E-mail: harukin@protein.osaka-u.ac.jp

2004-07-15

 
 
 
 
61

Model building of a protein-protein complexed structure using saturation transfer and residual dipolar coupling without paired intermolecular NOE  

International Nuclear Information System (INIS)

For understanding the precise mechanisms of molecular recognition of proteins, three-dimensional structural analyses of the protein-protein complexes are essential. For this purpose, a new method to reveal complex structures was developed with the assistance of saturation transfer (SAT) and residual dipolar coupling (RDC) by heteronuclear NMR experiments, without any paired intermolecular NOE information. The SAT and RDC experiments provide the information of the interfacial residues and the relative orientations of the two protein molecules, respectively. Docking simulation was then made to reconstruct a complex conformation, which satisfies the SAT and RDC data. The method was applied to the CAD-ICAD complex structure, which was previously determined by the NOE-distance geometry method. The quality of the current model was evaluated.Abbreviations: ASA - accessible surface area; HSQC - heteronuclear single quantum correlation; MD - molecular dynamics; NOE - nuclear Overhauser effect; TROSY - Transverse-Relaxation Optimized Spectroscopy

2004-01-01

62

Chemistry of binuclear bridge complexes of platinum metals. 5. Intermolecular electron transfer in mixed-valent complexes [(NH3)5Ru-py-(C2H2)n-py-Ru(NH3)5]5+ with extended bridge ligands  

International Nuclear Information System (INIS)

[en] Energies and intensities of spectral transitions in [(NH3)5Ru-py-(C2H2)n-py-Ru(NH3)5]5+ complexes are calculated in the framework of quantum-chemical procedure developed and approved earlier. Structure-dynamic approach is suggested for considering the process of intramolecular electron transfer; which is based on the solution of nonstationary Shroedinger equation in the basis of multi-electron functions describing different structural nodes of Ru(2) -> pyridyl -> (C2H2)n -> pyridyl -> Ru(3) electron-transport chain

1997-01-01

63

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

64

Determination of stepsize parameters for intermolecular vibrational energy transfer. Final report, May 1, 1987--December 31, 1991  

Energy Technology Data Exchange (ETDEWEB)

Intermolecular energy transfer of highly excited polyatomic molecules plays an important role in many complex chemical systems: combustion, high temperature and atmospheric chemistry. By monitoring the relaxation of internal energy we have observed trends in the collisional efficiency ({beta}) for energy transfer as a function of the substrate`s excitation energy and the complexities of substrate and deactivator. For a given substrate {beta} increases as the deactivator`s mass increase to {approximately}30 amu and then exhibits a nearly constant value; this is due to a mass mismatch between the atoms of the colliders. In a homologous series of substrate molecules (C{sub 3}{minus}C{sub 8}) {beta} decreases as the number of atoms in the substrate increases; replacing F with H increases {beta}. All substrates, except for CF{sub 2}Cl{sub 2} and CF{sub 2}HCl below 10,000 cm{sup {minus}1}, exhibited that {beta} is independent of energy, i.e. <{Delta}E>{sub all} is linear with energy. The results are interpreted with a simple model which considers that {beta} is a function of the ocillators energy and its vibrational frequency. Limitations of current approximations used in high temperature unimolecular reactions were evaluated and better approximations were developed. The importance of energy transfer in product yields was observed for the photoactivation of perfluorocyclopropene and the photoproduction of difluoroethyne. 3 refs., 18 figs., 4 tabs.

Tardy, D.C.

1992-03-01

65

Polar solvation and electron transfer. Annual progress report, July 1, 1992--June 30, 1993  

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

66

MOLECULAR PACKING AND NPT-MOLECULAR DYNAMICS INVESTIGATION OF THE TRANSFERABILITY OF THE RDX INTERMOLECULAR POTENTIAL TO 2,4,6,8,1O,12- HEXANITROHEXAAZAISOWURTZITANE (HNIW)  

Science.gov (United States)

We have explored the degree to which an intermolecular potential for the explosive hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX) is transferable for predictions of crystal structures (within the approximation of rigid molecules) of a similar chemical system,in this case, polymo...

67

Intermolecular Visible-Light Photoredox Atom-Transfer Radical [3+2]-Cyclization of 2-(Iodomethyl)cyclopropane-1,1-dicarboxylate with Alkenes and Alkynes.  

UK PubMed Central (United Kingdom)

Radical chemistry! A visible-light-promoted, tin/boron-free intermolecular [3+2] atom-transfer radical cyclization reaction was developed by using iridium polyphenylpridinyl complex as the sensitizer. 2-(Iodomethyl)cyclopropane-1,1-dicarboxylate reacted with various alkenes and alkynes to form cyclopentane and cyclopentene derivatives.

Gu X; Li X; Qu Y; Yang Q; Li P; Yao Y

2013-07-01

68

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

69

Rhodium-Catalyzed Acyl-Transfer Reaction between Benzyl Ketones and Thioesters: Synthesis of Unsymmetric Ketones by Ketone CO-C Bond Cleavage and Intermolecular Rearrangement.  

UK PubMed Central (United Kingdom)

In the presence of catalytic amounts of RhH(CO)(PPh(3))(3) and 1,2-bis(diphenylphosphino)benzene (dppBz), acyl groups were transferred between benzyl ketones and thioesters/aryl esters. The rhodium complex catalyzed the cleavage of ketone CO-C bonds and intermolecular rearrangement giving unsymmetric ketones. The acyl-transfer reaction also occurred with 1-(p-chlorophenyl)-3-(p-cyanophenyl)propane-2-one giving unsymmetric ketones.

Arisawa M; Kuwajima M; Toriyama F; Li G; Yamaguchi M

2012-07-01

70

Sequential photooxidation of a Pt(II) (diimine)cysteamine complex: intermolecular oxygen atom transfer versus sulfinate formation.  

Science.gov (United States)

The thiolato complex [platinum(II) (bipyridine)(N,S-aminoethanethiolate)](+)Ch(-) (1) undergoes sequential reactions with singlet oxygen to initially form the corresponding sulfenato complex [platinum(II) (bipyridine)(N,S(?O)-aminoethansulfenate)](+) (2) followed by a much slower reaction to the corresponding sulfinato complex. In contrast with many platinum dithiolato complexes, 1 does not produce any singlet oxygen, but its rate constant for singlet oxygen removal (k(T)) is quite large (3.2 × 10(7) M(-1) s(-1)) and chemical reaction accounts for ca. 25% of the value of k(T). The behavior of 1 is strikingly different from that of the complex platinum(II) (bipyridine)(1,2-benzenditholate) (4). The latter complex reacts with (1)O(2) (either from an external sensitizer or via a self-sensitized pathway) to form a sulfinato complex. These two very different reactivity pathways imply different mechanistic pathways: The reaction of 1 with (1)O(2) must involve O-O bond cleavage and intermolecular oxygen atom transfer, while the reactive intermediate in complex 4 collapses intramolecularly to the sulfinato moiety. PMID:23356398

Zhang, Dong; Bin, Ye; Tallorin, Lorillee; Tse, Florence; Hernandez, Blanca; Mathias, Errol V; Stewart, Timothy; Bau, Robert; Selke, Matthias

2013-01-28

71

Sequential photooxidation of a Pt(II) (diimine)cysteamine complex: intermolecular oxygen atom transfer versus sulfinate formation.  

UK PubMed Central (United Kingdom)

The thiolato complex [platinum(II) (bipyridine)(N,S-aminoethanethiolate)](+)Ch(-) (1) undergoes sequential reactions with singlet oxygen to initially form the corresponding sulfenato complex [platinum(II) (bipyridine)(N,S(?O)-aminoethansulfenate)](+) (2) followed by a much slower reaction to the corresponding sulfinato complex. In contrast with many platinum dithiolato complexes, 1 does not produce any singlet oxygen, but its rate constant for singlet oxygen removal (k(T)) is quite large (3.2 × 10(7) M(-1) s(-1)) and chemical reaction accounts for ca. 25% of the value of k(T). The behavior of 1 is strikingly different from that of the complex platinum(II) (bipyridine)(1,2-benzenditholate) (4). The latter complex reacts with (1)O(2) (either from an external sensitizer or via a self-sensitized pathway) to form a sulfinato complex. These two very different reactivity pathways imply different mechanistic pathways: The reaction of 1 with (1)O(2) must involve O-O bond cleavage and intermolecular oxygen atom transfer, while the reactive intermediate in complex 4 collapses intramolecularly to the sulfinato moiety.

Zhang D; Bin Y; Tallorin L; Tse F; Hernandez B; Mathias EV; Stewart T; Bau R; Selke M

2013-02-01

72

Contra-thermodynamic behavior in intermolecular hydrogen transfer of alkylperoxy radicals.  

Science.gov (United States)

Quantum chemical investigation of bimolecular hydrogen transfer involving alkylperoxy radicals, a key reaction family in the free-radical oxidation of hydrocarbons, was performed to establish structure-reactivity relationships. Eight different reactions were investigated featuring four different alkane substrates (methane, ethane, propane and isobutane) and two different alkylperoxy radicals (methylperoxy and iso-propylperoxy). Including forward and reverse pairs, sixteen different activation energies and enthalpies of reaction were used to formulate structure-reactivity relationships to describe this chemistry. We observed that the enthalpy of formation of loosely bound intermediate states has a strong inverse correlation with the overall heat of reaction and that this results in unique contra-thermodynamic behavior such that more exothermic reactions have higher activation barriers. A new structure-reactivity relationship was proposed that fits the calculated data extremely well: E(A)=E(o)+alphaDeltaH(rxn) where alpha=-0.10 for DeltaH(rxn)0 and E(o)=3.05 kcal mol(-1). PMID:17680581

Pfaendtner, Jim; Broadbelt, Linda J

2007-09-17

73

Contra-thermodynamic behavior in intermolecular hydrogen transfer of alkylperoxy radicals.  

UK PubMed Central (United Kingdom)

Quantum chemical investigation of bimolecular hydrogen transfer involving alkylperoxy radicals, a key reaction family in the free-radical oxidation of hydrocarbons, was performed to establish structure-reactivity relationships. Eight different reactions were investigated featuring four different alkane substrates (methane, ethane, propane and isobutane) and two different alkylperoxy radicals (methylperoxy and iso-propylperoxy). Including forward and reverse pairs, sixteen different activation energies and enthalpies of reaction were used to formulate structure-reactivity relationships to describe this chemistry. We observed that the enthalpy of formation of loosely bound intermediate states has a strong inverse correlation with the overall heat of reaction and that this results in unique contra-thermodynamic behavior such that more exothermic reactions have higher activation barriers. A new structure-reactivity relationship was proposed that fits the calculated data extremely well: E(A)=E(o)+alphaDeltaH(rxn) where alpha=-0.10 for DeltaH(rxn)<0, and alpha=1.10 for DeltaH(rxn)>0 and E(o)=3.05 kcal mol(-1).

Pfaendtner J; Broadbelt LJ

2007-09-01

74

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

75

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

76

Spectroscopic study on the intermolecular double proton transfer in 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine with acid  

Energy Technology Data Exchange (ETDEWEB)

With 2,4,6-trichloro-1,3,5-triazine as starting material, a functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated by UV-vis absorption and fluorescence emission. It is found that both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer, resulting in amino-imino tautomerization emission in excited state. - Highlights: Black-Right-Pointing-Pointer A functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Black-Right-Pointing-Pointer Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated. Black-Right-Pointing-Pointer Both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer. Black-Right-Pointing-Pointer Amino-imino tautomerization emission in excited state are proposed.

Li Zongyao [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Research Institute of Henan Coal and Chemical Industry Group, Zhengzhou 450046 (China); Li Chunli [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Zhao Chunmei [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Institute for Functional Nanomaterials, Huanghe Science and Technology College, Zhengzhou 450000 (China); Wu Wei [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Wang Hua, E-mail: hwang@henu.edu.cn [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China)

2012-10-15

77

Spectroscopic study on the intermolecular double proton transfer in 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine with acid  

International Nuclear Information System (INIS)

With 2,4,6-trichloro-1,3,5-triazine as starting material, a functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated by UV–vis absorption and fluorescence emission. It is found that both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer, resulting in amino–imino tautomerization emission in excited state. - Highlights: ? A functionalized triazine derivative, 4-(naphthalen-1-yl)-6-octyl-1,3,5-triazin-2-amine (NOTA) was synthesized in 14% yield through three steps: Kumada cross-coupling, Suzuki coupling and amination. ? Intermolecular double proton transfer of NOTA with acetic acid (HOAc) and trifluoroacetic acid (TFA) in chloroform was investigated. ? Both NOTA/HOAc and NOTA/TFA undergo excited state double proton transfer. ? Amino–imino tautomerization emission in excited state are proposed.

2012-01-01

78

Study on the oxidation and electron transfer of N-phosphoamino acids and their peptide derivatives  

International Nuclear Information System (INIS)

[en] The induced oxidation of N-phosphomethionine (NDM) in aqueous solution initiated by ·OH and Br2 ·-bar radicals etc., intermolecular electron transfer involving NDM and tryptophan(TrpH) and intramolecular electron transfer within N-phosphodipeptide derivatives (NDM-TrpOMe and NDT-MetOMe) have been investigated by using the technique of pulse radiolysis. A series of kinetic parameters have been determined and the related mechanisms have been deduced. Structurally, the effect of N-phosphoryl group on the oxidation and ET has been discussed. (author)

2000-01-01

79

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

80

Calculation of the electronic spectra of intermolecular complexes of 3-amino-phthalimide using a modified Huckel method of molecular orbitals  

International Nuclear Information System (INIS)

Using intermolecular complexes of 3-amino-phthalimide as an example, the calculation of its electronic spectra has shown that in the presence of hydrogen bonds the resonance integrals are distinct from, zero for atoms of donors and acceptors of proton. A theoretical analysis of strained complexes of 3-amino-phthalimide allowed us to clarify the role of hydrogen bonds in the formation of such complexes. Taking the intermolecular peptide hydrogen bond as an example, the influence of solvents on its characteristics is investigated. It is shown that the formation of hydrogen bond with the proton acceptor group of the chelate ring leads to the reduction of the resonance integral and hence to a decrease in the enthalpy of the formation of the intermolecular hydrogen bond. Such a reduction is much more pronounced for the formation of hydrogen bonds with acceptor donor groups as compared to proton donor groups. (authors)

2006-01-01

 
 
 
 
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

Crystal structure of pyrogallol-phloroglucinol transhydroxylase, an Mo enzyme capable of intermolecular hydroxyl transfer between phenols.  

Science.gov (United States)

The Mo enzyme transhydroxylase from the anaerobic microorganism Pelobacter acidigallici catalyzes the conversion of pyrogallol to phloroglucinol. Such trihydroxybenzenes and their derivatives represent important building blocks of plant polymers. None of the transferred hydroxyl groups originates from water during transhydroxylation; instead a cosubstrate, such as 1,2,3,5-tetrahydroxybenzene, is used in a reaction without apparent electron transfer. Here, we report on the crystal structure of the enzyme in the reduced Mo(IV) state, which we solved by single anomalous-diffraction technique. It represents the largest structure (1,149 amino acid residues per molecule, 12 independent molecules per unit cell), which has been solved so far by single anomalous-diffraction technique. Tranhydroxylase is a heterodimer, with the active Mo-molybdopterin guanine dinucleotide (MGD)(2) site in the alpha-subunit, and three [4Fe-4S] centers in the beta-subunit. The latter subunit carries a seven-stranded, mainly antiparallel beta-barrel domain. We propose a scheme for the transhydroxylation reaction based on 3D structures of complexes of the enzyme with various polyphenols serving either as substrate or inhibitor. PMID:15284442

Messerschmidt, Albrecht; Niessen, Holger; Abt, Dietmar; Einsle, Oliver; Schink, Bernhard; Kroneck, Peter M H

2004-07-29

84

Crystal structure of pyrogallol-phloroglucinol transhydroxylase, an Mo enzyme capable of intermolecular hydroxyl transfer between phenols.  

UK PubMed Central (United Kingdom)

The Mo enzyme transhydroxylase from the anaerobic microorganism Pelobacter acidigallici catalyzes the conversion of pyrogallol to phloroglucinol. Such trihydroxybenzenes and their derivatives represent important building blocks of plant polymers. None of the transferred hydroxyl groups originates from water during transhydroxylation; instead a cosubstrate, such as 1,2,3,5-tetrahydroxybenzene, is used in a reaction without apparent electron transfer. Here, we report on the crystal structure of the enzyme in the reduced Mo(IV) state, which we solved by single anomalous-diffraction technique. It represents the largest structure (1,149 amino acid residues per molecule, 12 independent molecules per unit cell), which has been solved so far by single anomalous-diffraction technique. Tranhydroxylase is a heterodimer, with the active Mo-molybdopterin guanine dinucleotide (MGD)(2) site in the alpha-subunit, and three [4Fe-4S] centers in the beta-subunit. The latter subunit carries a seven-stranded, mainly antiparallel beta-barrel domain. We propose a scheme for the transhydroxylation reaction based on 3D structures of complexes of the enzyme with various polyphenols serving either as substrate or inhibitor.

Messerschmidt A; Niessen H; Abt D; Einsle O; Schink B; Kroneck PM

2004-08-01

85

Intermolecular ?-electron perturbations generate extrinsic visible contributions to eumelanin black chromophore in model polymers with interrupted interring conjugation.  

UK PubMed Central (United Kingdom)

The key structural factors underlying the unique black chromophore of eumelanin biopolymers have so far defied elucidation. Capitalizing on the ability of 1% polyvinylalcohol (PVA) to prevent pigment precipitation during melanogenesis in vitro, we have investigated the visible chromophore properties of soluble eumelanin-like polymers produced by biomimetic oxidation of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic (DHICA) in 1% PVA-containing buffer at pH 7. Upon dilution DHI-eumelanin solutions exhibited almost linear visible absorbance changes, whereas DHICA-eumelanin displayed a remarkable deviation from linearity in simple buffer, but not in PVA-containing buffer. It is suggested that in DHICA polymers, exhibiting repeated interruptions of interring conjugation due to lack of planar conformations, the black chromophore is not due to an overlap of static entities defined intrinsically by the conjugation length across the carbon frame, but results largely from aggregation-related intermolecular perturbations of the ?-electron systems which are extrinsic in character.

Ascione L; Pezzella A; Ambrogi V; Carfagna C; d'Ischia M

2013-03-01

86

Valence anions in complexes of adenine and 9-methyladenine with formic acid: stabilization by intermolecular proton transfer.  

Science.gov (United States)

Photoelectron spectra of adenine-formic acid (AFA(-)) and 9-methyladenine-formic acid (MAFA(-)) anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9-methyladenine and formic acid were also studied computationally at the B3LYP, second-order Møller-Plesset, and coupled-cluster levels of theory with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds, and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both AFA(-) and MAFA(-) occupies a pi* orbital localized on adenine/9-methyladenine, and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA(-) and MAFA(-), respectively. The attachment of the excess electron to the complexes induces a barrier-free proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-methyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine (9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low-energy electrons. PMID:17263404

Mazurkiewicz, Kamil; Hara?czyk, Maciej; Gutowski, Maciej; Rak, Janusz; Radisic, Dunja; Eustis, Soren N; Wang, Di; Bowen, Kit H

2007-02-01

87

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

88

Two-Dimensional Free Energy Surfaces for Electron Transfer Reactions in Solution  

Directory of Open Access Journals (Sweden)

Full Text Available Change in intermolecular distance between electron donor (D) and acceptor (A) can induce intermolecular electron transfer (ET) even in nonpolar solvent, where solvent orientational polarization is absent. This was shown by making simple calculations of the energies of the initial and final states of ET. In the case of polar solvent, the free energies are functions of both D-A distance and solvent orientational polarization. On the basis of 2-dimensional free energy surfaces, the relation of Marcus ET and exciplex formation is discussed. The transient effect in fluorescence quenching was measured for several D-A pairs in a nonpolar solvent. The results were analyzed by assuming a distance dependence of the ET rate that is consistent with the above model.

Shigeo Murata; Maged El-Kemary; M. Tachiya

2008-01-01

89

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

90

Photoinduced electron-transfer chemistry of the bielectrophoric N-phthaloyl derivatives of the amino acids tyrosine, histidine and tryptophan  

Directory of Open Access Journals (Sweden)

Full Text Available The photochemistry of phthalimide derivatives of the electron-rich amino acids tyrosine, histidine and tryptophan 8–10 was studied with respect to photoinduced electron-transfer (PET) induced decarboxylation and Norrish II bond cleavage. Whereas exclusive photodecarboxylation of the tyrosine substrate 8 was observed, the histidine compound 9 resulted in a mixture of histamine and preferential Norrish cleavage. The tryptophan derivative 10 is photochemically inert and shows preferential decarboxylation only when induced by intermolecular PET.

Axel G. Griesbeck; Jörg Neudörfl; Alan de Kiff

2011-01-01

91

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

92

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

93

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

94

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

95

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

96

Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex  

CERN Multimedia

Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics within the CT complex, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the groundstate of the complex: a charge delocalization of about 10-2 electron from the HAT6 core to TNF is deduced from both Raman and NMR measurements, implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visi...

Haverkate, Lucas; Johnson, Mark; Carter, Elisabeth; Kotlewski, Arek; Picken, Stephen; Mulder, Fokko; Kearley, Gordon

2013-01-01

97

Valence anions in complexes of adenine and 9-methyladenine with formic acid - stabilization by intermolecular proton transfer  

Energy Technology Data Exchange (ETDEWEB)

The photoelectron spectra of the adenine-formic acid (AFA)- and 9-methyladenine-formic acid (MAFA)- anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and anionic complexes of adenine/9- methyladenine and formic acid were also studied computationally at the B3LYP, second order Møller-Plesset and coupled clusters levels of theory, with the 6-31++G** and aug-cc-pVDZ basis sets. The neutral complexes form cyclic hydrogen bonds and the most stable dimers are bound by 17.7 and 16.0 kcal/mol for AFA and MAFA, respectively. The theoretical results indicate that the excess electron in both (AFA)- and (MAFA)- occupies a p* orbital localized on adenine/9-methyladenine and the adiabatic stability of the most stable anions amounts to 0.67 and 0.54 eV for AFA- and MAFA-, respectively. The excess electron attachment to the complexes induces a barrierfree proton transfer (BFPT) from the carboxylic group of formic acid to a N atom of adenine or 9-mathyladenine. As a result, the most stable structures of the anionic complexes can be characterized as neutral radicals of hydrogenated adenine(9-methyladenine) solvated by a deprotonated formic acid. The BFPT to the N atoms of adenine may be biologically relevant because some of these sites are not involved in the Watson-Crick pairing scheme and are easily accessible in the cellular environment. We suggest that valence anions of purines might be as important as those of pyrimidines in the process of DNA damage by low energy electrons. The calculations were performed at the Academic Computer Center in Gda?sk (TASK) and at the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy's Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory, which is operated by Battelle for the US Department of Energy. The MSCF resources were available through a Computational Grand Challenge Application grant.

Mazurkiewicz, Kamil; Haranczyk, Maciej; Gutowski, Maciej S.; Rak, Janusz; Radisic, Dunja; Eustis, Soren; Wang, Di; Bowen, Kit H.

2007-02-07

98

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.

99

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

100

Effects of inter-molecular charge-transfer excitons on the external quantum efficiency of zinc-porphyrin/C60 heterojunction photovoltaic cells  

International Nuclear Information System (INIS)

We have examined the structural effects of zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic heterojunction photovoltaic (OPV) cells [ITO/Zn(OEP)/C60/Al], and investigated what exactly causes the improvement of EQE. When the structure of the Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of around 35% for previously reported OPV cells using buffer materials (Peumans and Forrest 2001 Appl. Phys. Lett. 79 126). The crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge-transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE of the photoabsorption band under illumination due to the IMCT excitons.

2011-04-13

 
 
 
 
101

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

102

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

103

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

104

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

105

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

106

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

107

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

108

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

109

Effect of surface-plasmon polaritons on spontaneous emission and intermolecular energy-transfer rates in multilayered geometries  

International Nuclear Information System (INIS)

We use a Green's tensor method to investigate the spontaneous emission rate of a molecule and the energy-transfer rate between molecules placed in two types of layered geometries: a slab geometry and a planar waveguide. We focus especially on the role played by surface-plasmon polaritons in modifying the spontaneous emission and energy-transfer rates as compared to free space. In the presence of more than one interface, the surface-plasmon polariton modes split into several branches, and each branch can contribute significantly to modifying the electromagnetic properties of atoms and molecules. Enhancements of several orders of magnitude both in the spontaneous emission rate of a molecule and the energy-transfer rate between molecules are obtained and, by tuning the parameters of the geometry, one has the ability to control the range and magnitude of these enhancements. For the energy-transfer rate interference effects between contributions of different plasmon-polariton branches are observed as oscillations in the distance dependence of this rate.

2011-01-01

110

Effect of surface-plasmon polaritons on spontaneous emission and intermolecular energy-transfer rates in multilayered geometries  

Energy Technology Data Exchange (ETDEWEB)

We use a Green's tensor method to investigate the spontaneous emission rate of a molecule and the energy-transfer rate between molecules placed in two types of layered geometries: a slab geometry and a planar waveguide. We focus especially on the role played by surface-plasmon polaritons in modifying the spontaneous emission and energy-transfer rates as compared to free space. In the presence of more than one interface, the surface-plasmon polariton modes split into several branches, and each branch can contribute significantly to modifying the electromagnetic properties of atoms and molecules. Enhancements of several orders of magnitude both in the spontaneous emission rate of a molecule and the energy-transfer rate between molecules are obtained and, by tuning the parameters of the geometry, one has the ability to control the range and magnitude of these enhancements. For the energy-transfer rate interference effects between contributions of different plasmon-polariton branches are observed as oscillations in the distance dependence of this rate.

Marocico, C. A.; Knoester, J. [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747 AG Groningen (Netherlands)

2011-11-15

111

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

112

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

113

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

114

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

115

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

116

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

117

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

118

Solvent reorganization energies measured by an electron transfer reaction in supercritical ethane.  

Energy Technology Data Exchange (ETDEWEB)

The intermolecular electron transfer reaction between a biphenyl anion and pyrene in supercritical ethane was studied using pulse radiolysis. Second-order electron transfer rates were found to be of the order of 10{sup 11} M{sup {minus}1} s{sup {minus}1}. The rate constants appear to be approximately constant over the pressure range 55-133 bar. Two possibilities are discussed that could explain the present results: solvent clustering; or a dependence of the solvent reorganization energy on pressure. Reorganization energies E{sub r} of non-polar supercritical ethane were estimated from the observed rate constant using the modified Marcus equation. E{sub r} may be larger than normally expected for non-polar solvents because of density fluctuations.

Feng, W.; Jonah, C. D.; Sawamura, S.; Takahashi, K.

1997-04-14

119

Photocatalytic Monofluorination of Benzene by Fluoride via Photoinduced Electron Transfer with 3-Cyano-1-methylquinolinium.  

Science.gov (United States)

The photocatalytic fluorination of benzene occurs under photoirradiation of an oxygen-saturated acetonitrile (MeCN) of the 3-cyano-1-methylquinolinium ion (QuCN(+)) containing benzene and tetraethylammonium fluoride tetrahydrofluoride (TEAF·4HF) with a xenon lamp (500 W) attached to a colored-glass filter (? fluoride to the benzene radical cation was determined to be 9.4 × 10(9) M(-1) s(-1). Thus, the photocatalytic reaction is initiated by intermolecular photoinduced electron transfer from benzene to the single excited state of QuCN(+). The benzene radical cation formed by photoinduced electron transfer reacts with the fluoride anion to yield the F-adducted radical. However, QuCN(•) can reduce O2 to O2(•-), and this is followed by the protonation of O2(•-) to afford HO2(•). The hydrogen abstraction of HO2(•) from the F-adduct radical affords fluorobenzene and H2O2 as the final products. PMID:24050618

Ohkubo, Kei; Fujimoto, Atsushi; Fukuzumi, Shunichi

2013-10-03

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

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

123

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

124

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

125

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

126

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

127

New Type of Dual Solid-State Thermochromism: Modulation of Intramolecular Charge Transfer by Intermolecular ?-? Interactions, Kinetic Trapping of the Aci-Nitro Group, and Reversible Molecular Locking  

Science.gov (United States)

When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10-7-10-6 s-1 for BDB2 to about 0.1 s-1 in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened ?-? interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered by intramolecular proton transfer of one amino proton to the nitro group, whereupon an aci-nitro form is thermally populated. Contrary to the numerous examples of solid thermochromic molecules based on either pericyclic reactions or keto-enol tautomerism, this system appears to be the first organic thermochromic family where the thermochromic change appears as an effect of intermolecular ?-? interactions and thermal intramolecular proton transfer to aromatic nitro group.

Naumov, Pan?e; Lee, Sang Cheol; Ishizawa, Nobuo; Jeong, Young Gyu; Chung, Ihn Hee; Fukuzumi, Shunichi

2009-09-01

128

Model for the charge-transfer probability in helium nanodroplets following electron-impact ionization  

International Nuclear Information System (INIS)

A theoretical model has been developed to describe the probability of charge transfer from helium cations to dopant molecules inside helium nanodroplets following electron-impact ionization. The location of the initial charge site inside helium nanodroplets subject to electron impact has been investigated and is found to play an important role in understanding the ionization of dopants inside helium droplets. The model is consistent with a charge migration process in small helium droplets that is strongly directed by intermolecular forces originating from the dopant, whereas for large droplets (tens of thousands of helium atoms and larger) the charge migration increasingly takes on the character of a random walk. This suggests a clear droplet size limit for the use of electron-impact mass spectrometry for detecting molecules in helium droplets.

2007-01-01

129

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

130

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

131

Electron transfer mechanism in organometallic molecules studied by subpicosecond extended X-ray absorption fine structure spectroscopy.  

UK PubMed Central (United Kingdom)

The mechanism responsible for the redox reaction of [Co(III)(en)3]Ac3 to Co(II) complex has been determined to be intramolecular electron transfer. It was measured in real time by means of subpicosecond extended X-ray absorption fine structure spectra, EXAFS, and optical experiments and supported by density functional theory calculations. The proposed mechanism is based on histograms of bond length changes of the transient structures measured as a function of time, with subpicosecond time and sub-Angstrom resolution and femtosecond transient spectra and kinetics after excitation with a 267 nm femtosecond pulse. Even though four Fe and Co complexes were excited in the charge transfer band and the photoinduced redox reaction proceeds with similar high redox quantum yield, the dominant electron operating mechanism differs: intramolecular for amine metal complexes and intermolecular for oxalate metal complexes. The ligand orientation degree of freedom and counterion effect are proposed to provide tentative explanation for the electron transfer mechanism.

Chen WK; Chen J; Rentzepis PM

2013-04-01

132

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

133

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

134

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

135

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

136

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

137

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

138

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

139

A retarded coupling approach to intermolecular interactions  

International Nuclear Information System (INIS)

[en] A wide range of physical phenomena such as optical binding and resonance energy transfer involve electronic coupling between adjacent molecules. A quantum electrodynamical description of these intermolecular interactions reveals the presence of retardation effects. The clarity of the procedure associated with the construction of the quantum amplitudes and the precision of the ensuing results for observable energies and rates are widely acknowledged. However, the length and complexity of the derivations involved in such quantum electrodynamical descriptions increase rapidly with the order of the process under study. Whether through the use of time-ordering approaches, or the more expedient state-sequence method, time-consuming calculations cannot usually be bypassed. A simple and succinct method is now presented, which provides for a direct and still entirely rigorous determination of the quantum electrodynamical amplitudes for processes of arbitrarily high order. Using the approach, new results for optical binding in two- and three-particle systems are secured and discussed.

2009-04-28

140

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

 
 
 
 
141

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

142

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

143

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

144

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

145

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

146

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

147

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

148

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

149

Direct observation of photodriven intermolecular hole transfer across TiO2 nanocrystallites: lateral self-exchange reactions and catalyst oxidation.  

Science.gov (United States)

Photoselection of Ru(II)-polypyridyl sensitizers with polarized pulsed-light excitation, when anchored to TiO(2) nanocrystallites interconnected in a mesoporous thin film, results in an anisotropic distribution of excited sensitizers. Under conditions where excited-state sensitizers efficiently inject electrons into TiO(2), the resulting oxidized sensitizers exhibit an initial anisotropy in their absorption difference spectra. Over the course of the charge-separated lifetime for many sensitizers, the transient absorption anisotropy signal decays to nearly zero indicative of lateral self-exchange hole-transfer reactions at the interface. When a cobalt metalloporphyrin catalyst was coanchored to the sensitized nanocrystalline TiO(2) film, excited-state injection was followed by lateral hole transfer to oxidize the surface-bound catalyst. PMID:20565127

Ardo, Shane; Meyer, Gerald J

2010-07-14

150

Direct observation of photodriven intermolecular hole transfer across TiO2 nanocrystallites: lateral self-exchange reactions and catalyst oxidation.  

UK PubMed Central (United Kingdom)

Photoselection of Ru(II)-polypyridyl sensitizers with polarized pulsed-light excitation, when anchored to TiO(2) nanocrystallites interconnected in a mesoporous thin film, results in an anisotropic distribution of excited sensitizers. Under conditions where excited-state sensitizers efficiently inject electrons into TiO(2), the resulting oxidized sensitizers exhibit an initial anisotropy in their absorption difference spectra. Over the course of the charge-separated lifetime for many sensitizers, the transient absorption anisotropy signal decays to nearly zero indicative of lateral self-exchange hole-transfer reactions at the interface. When a cobalt metalloporphyrin catalyst was coanchored to the sensitized nanocrystalline TiO(2) film, excited-state injection was followed by lateral hole transfer to oxidize the surface-bound catalyst.

Ardo S; Meyer GJ

2010-07-01

151

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

152

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

153

[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

154

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

155

Electron transfer patterns of the di-heme protein cytochrome c(4) from Pseudomonas stutzeri  

DEFF Research Database (Denmark)

We report kinetic data for the two-step electron transfer (ET) oxidation and reduction of the two-domain di-heme redox protein Pseudomonas stutzeri cytochrome (cyt) c(4) by [Co(bipy)(3)](2- 3-) (bipy = 2,2'-bipyridine). Following earlier reports, the data accord with both bi- and tri-exponential kinetics. A complete kinetic scheme includes both "cooperative" intermolecular ET between each heme group and the external reaction partner, and intramolecular ET between the two heme groups. A now data analysis scheme shows unequivocally that two-ET oxidation and reduction of P. stutzeri cyt c(4) is entirely dominated by intermolecular ET between the heme groups and the external reaction partner in the ms time range, with virtually no contribution from intramolecular interheme ET in this time range. This is in striking contrast to two-ET electrochemical oxidation or reduction of P. stutzeri cyt c(4) for which fast, ms to sub-ms intramolecular interheme ET is a crucial step. The rate constant dependence on the solventviscosity has disclosed strong coupling to both a (set of) frictionally damped solvent/protein nuclear modes and intramolecular friction-less "ballistic" modes, indicative of notable protein structural mobility in the overall two-ET process. We suggest that conformational protein mobility blocks intramolecular interheme ET in bulk homogeneous solution but triggers opening of this gated ET channel in the electrochemical environment or in the membrane environment of natural respiratory cyt c(4) function.

Raffalt, Anders Christer; Schmidt, L.

2009-01-01

156

Electron transfer patterns of the di-heme protein cytochrome c(4) from Pseudomonas stutzeri.  

Science.gov (United States)

We report kinetic data for the two-step electron transfer (ET) oxidation and reduction of the two-domain di-heme redox protein Pseudomonas stutzeri cytochrome (cyt) c(4) by [Co(bipy)(3)](2+/3+) (bipy=2,2'-bipyridine). Following earlier reports, the data accord with both bi- and tri-exponential kinetics. A complete kinetic scheme includes both "cooperative"intermolecular ET between each heme group and the external reaction partner, and intramolecular ET between the two heme groups. A new data analysis scheme shows unequivocally that two-ET oxidation and reduction of P. stutzeri cyt c(4) is entirely dominated by intermolecular ET between the heme groups and the external reaction partner in the ms time range, with virtually no contribution from intramolecular interheme ET in this time range. This is in striking contrast to two-ET electrochemical oxidation or reduction of P. stutzeri cyt c(4) for which fast, ms to sub-ms intramolecular interheme ET is a crucial step. The rate constant dependence on the solvent viscosity has disclosed strong coupling to both a (set of) frictionally damped solvent/protein nuclear modes and intramolecular friction-less "ballistic" modes, indicative of notable protein structural mobility in the overall two-ET process. We suggest that conformational protein mobility blocks intramolecular interheme ET in bulk homogeneous solution but triggers opening of this gated ET channel in the electrochemical environment or in the membrane environment of natural respiratory cyt c(4) function. PMID:19217165

Raffalt, Anders C; Schmidt, Lars; Christensen, Hans E M; Chi, Qijin; Ulstrup, Jens

2009-01-21

157

Electron transfer patterns of the di-heme protein cytochrome c(4) from Pseudomonas stutzeri.  

UK PubMed Central (United Kingdom)

We report kinetic data for the two-step electron transfer (ET) oxidation and reduction of the two-domain di-heme redox protein Pseudomonas stutzeri cytochrome (cyt) c(4) by [Co(bipy)(3)](2+/3+) (bipy=2,2'-bipyridine). Following earlier reports, the data accord with both bi- and tri-exponential kinetics. A complete kinetic scheme includes both "cooperative"intermolecular ET between each heme group and the external reaction partner, and intramolecular ET between the two heme groups. A new data analysis scheme shows unequivocally that two-ET oxidation and reduction of P. stutzeri cyt c(4) is entirely dominated by intermolecular ET between the heme groups and the external reaction partner in the ms time range, with virtually no contribution from intramolecular interheme ET in this time range. This is in striking contrast to two-ET electrochemical oxidation or reduction of P. stutzeri cyt c(4) for which fast, ms to sub-ms intramolecular interheme ET is a crucial step. The rate constant dependence on the solvent viscosity has disclosed strong coupling to both a (set of) frictionally damped solvent/protein nuclear modes and intramolecular friction-less "ballistic" modes, indicative of notable protein structural mobility in the overall two-ET process. We suggest that conformational protein mobility blocks intramolecular interheme ET in bulk homogeneous solution but triggers opening of this gated ET channel in the electrochemical environment or in the membrane environment of natural respiratory cyt c(4) function.

Raffalt AC; Schmidt L; Christensen HE; Chi Q; Ulstrup J

2009-05-01

158

Excited-state intermolecular proton transfer reactions of 7-azaindole(MeOH)(n) (n = 1-3) clusters in the gas phase: on-the-fly dynamics simulation.  

UK PubMed Central (United Kingdom)

Ultrafast excited-state intermolecular proton transfer (PT) reactions in 7-azaindole(methanol)(n) (n = 1-3) [7AI(MeOH)(n=1-3)] complexes were performed using dynamics simulations. These complexes were first optimized at the RI-ADC(2)/SVP-SV(P) level in the gas phase. The ground-state structures with the lowest energy were also investigated and presented. On-the-fly dynamics simulations for the first-excited state were employed to investigate reaction mechanisms and time evolution of PT processes. The PT characteristics of the reactions were confirmed by the nonexistence of crossings between S(??*) and S(??*) states. Excited-state dynamics results for all complexes exhibit excited-state multiple-proton transfer (ESmultiPT) reactions via methanol molecules along an intermolecular hydrogen-bonded network. In particular, the two methanol molecules of a 7AI(MeOH)(2) cluster assist the excited-state triple-proton transfer (ESTPT) reaction effectively with highest probability of PT.

Daengngern R; Kungwan N; Wolschann P; Aquino AJ; Lischka H; Barbatti M

2011-12-01

159

Intermolecular Forces (Netorials)  

Science.gov (United States)

Intermolecular Forces: this is a resource in the collection "Netorials". In this resource there is a review of Lewis structures, molecular geometry, electronegativity, or molecular polarity. After that, you can learn about the forces of attraction that exist between molecules. This module explores London forces and dipole-dipole forces (including hydrogen bonds). The Netorials cover selected topics in first-year chemistry including: Chemical Reactions, Stoichiometry, Thermodynamics, Intermolecular Forces, Acids & Bases, Biomolecules, and Electrochemistry.

160

Electron-gas plus damped-dispersion model for intermolecular forces: the rare-gas and H2-He, H2-Ne, and H2-Ar potentials  

International Nuclear Information System (INIS)

The modified Gordon-Kim (MGK) electron-gas model for the calculation of the short-range repulsive interactions between closed-shell atoms and molecules is used with a damped-dispersion term of a form suggested by Hepburn et al. to calculate the intermolecular potentials between the rare-gas atoms and H2-He, H2-Ne, and H2-Ar. The damping function for the dispersion energies is found by comparison with the experimental Ar-Ar potential and is then used without change for all other interactions. Except for interactions involving Ne atoms, the results for the atom-atom interactions are uniformly quite good, with an average deviation from experiment in the position of the minimum (neglecting those involving Ne atoms) of only 0.7%. Both the radical V0(r) and anisotropic V2(r) terms of the atom-molecule results are compared with experiment. The calculated V0(r) potentials for He-H2 and Ar-H2 show close agreement with experiment, though the V2 terms are less well determined. All interactions involving Ne atoms are too repulsive. The errors in the potentials involving Ne atoms are attributed to errors in the treatment of the exchange energy in the MGK model. 29 references, 11 figures, 5 tables

1984-09-13

 
 
 
 
161

Effects of Aromatic Trifluoromethylation, Fluorination, and Methylation on Intermolecular ?-? Interactions.  

Science.gov (United States)

Marcus theory states that the rate of charge transfer is directly proportional to the amount of intermolecular orbital overlap. Theoretically optimizing the electronic coupling through the orientation and distance which both can increase the frontier orbital overlap between molecules is an attractive route to potentially provide theoretical insight for discovering new high performance semiconductor materials. To investigate how these parameters qualitatively affect charge transfer of model systems, unconstrained dimer optimizations with MP2 and dispersion-corrected DFT methods were used to probe the ?-? interactions of methylated, fluorinated, and trifluoromethylated benzene, pyridine, and bipyridine dimers. These systems can serve as simplified models representing weak noncovalent interactions in organic semiconductor materials. Enhanced intermolecular interaction energies, reduced ?-? distances, and more favorable cofacial orientations were found with the trifluoromethylated dimers compared to fluorinated and methylated dimers studied. Similar effects were found with donor-acceptor pairs that represent organic p-n heterojunction systems. These enhanced ?-? interactions are likely caused by increased molecular quadrupole moment and dispersion interaction associated with trifluoromethylation. This computational study illustrates the strong potential of trifluoromethylation and, possibly perfluoroalkylation of acenes and heteroacenes, leading qualitatively to enhanced electron transfer through better ?-? stacked structures, making them viable candidates for use as n-type organic semiconductor materials. The findings also provide insight for fundamental interactions between drug molecules that include fluorinated and trimethylfluorinated aromatics binding to protein receptors. PMID:23906416

Mottishaw, Jeffery D; Sun, Haoran

2013-08-02

162

Effects of Aromatic Trifluoromethylation, Fluorination, and Methylation on Intermolecular ?-? Interactions.  

UK PubMed Central (United Kingdom)

Marcus theory states that the rate of charge transfer is directly proportional to the amount of intermolecular orbital overlap. Theoretically optimizing the electronic coupling through the orientation and distance which both can increase the frontier orbital overlap between molecules is an attractive route to potentially provide theoretical insight for discovering new high performance semiconductor materials. To investigate how these parameters qualitatively affect charge transfer of model systems, unconstrained dimer optimizations with MP2 and dispersion-corrected DFT methods were used to probe the ?-? interactions of methylated, fluorinated, and trifluoromethylated benzene, pyridine, and bipyridine dimers. These systems can serve as simplified models representing weak noncovalent interactions in organic semiconductor materials. Enhanced intermolecular interaction energies, reduced ?-? distances, and more favorable cofacial orientations were found with the trifluoromethylated dimers compared to fluorinated and methylated dimers studied. Similar effects were found with donor-acceptor pairs that represent organic p-n heterojunction systems. These enhanced ?-? interactions are likely caused by increased molecular quadrupole moment and dispersion interaction associated with trifluoromethylation. This computational study illustrates the strong potential of trifluoromethylation and, possibly perfluoroalkylation of acenes and heteroacenes, leading qualitatively to enhanced electron transfer through better ?-? stacked structures, making them viable candidates for use as n-type organic semiconductor materials. The findings also provide insight for fundamental interactions between drug molecules that include fluorinated and trimethylfluorinated aromatics binding to protein receptors.

Mottishaw JD; Sun H

2013-08-01

163

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

164

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

165

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

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

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

169

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

170

Intermolecular and surface forces  

CERN Document Server

This reference describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition.· starts fr

Israelachvili, Jacob N

2011-01-01

171

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

172

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

173

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

174

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

175

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

176

Electronic excitation in the benzonitrile dimer: The intermolecular structure in the S0 and S1 state determined by rotationally resolved electronic spectroscopy  

Science.gov (United States)

The rotationally resolved UV spectrum of the electronic origin of the benzonitrile dimer has been measured and analyzed using a genetic algorithm based fitting strategy. For the electronic ground state, a C2h symmetric structure is found in which the permanent dipole moments of the benzonitrile monomers are aligned anti-parallel. The orientation of the transition dipole moment could be shown to be parallel to the orientation in the monomer moiety. The distance between the two monomer moieties decreases slightly upon electronic excitation and the symmetry of the benzonitrile dimer changes from C2h in the electronic ground state to Cs in the electronically excited state. This break of symmetry is probably caused by the local excitation of only one benzonitrile moiety in the cluster due to the weak electronic coupling between the cluster moieties.

Schmitt, Michael; Böhm, Marcel; Ratzer, Christian; Siegert, Swen; Beek, Marloes Van; Meerts, W. Leo

2006-08-01

177

Intermolecular forces - hybrid calculations  

International Nuclear Information System (INIS)

The available theoretical methods for the calculation of molecular interactions can be divided into three categories: 1) 'a priori' methods, 2) semi-empirical methods and 3) hybrid methods. The author presents the modification of a previously introduced hybrid method which is useful to predict intermolecular forces with precision comparable to that obtained from experimental information

1980-02-15

178

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

179

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

180

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

 
 
 
 
181

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

182

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

183

Photocatalytic Monofluorination of Benzene by Fluoride via Photoinduced Electron Transfer with 3-Cyano-1-Methylquinolinium.  

UK PubMed Central (United Kingdom)

Photocatalytic fluorination of benzene occurs under photoirradiation of an oxygen-saturated acetonitrile (MeCN) of 3-cyano-1-methylquinolinium ion (QuCN+) containing benzene and tetraethylammonium fluoride tetrahydrofluoride (TEAF•4HF) with a xenon lamp (500 W) attached with a color glass filter (? < 290 nm) to yield fluorobenzene and hydrogen peroxide. The quantum yield of formation of fluorobenzene was 6%. Nanosecond laser flash photolysis measurements were performed to elucidate the mechanistic details for photocatalytic fluorination. Transient absorption spectra taken after the nanosecond laser excitation at 355 nm of a degassed MeCN solution of QuCN+ and benzene exhibited absorption bands due to QuCN• (?max = 500 nm) and benzene dimer radical cation (?max = 900 nm), which were generated by photoinduced electron transfer from benzene to the singlet excited state of QuCN+. The decay rate of transient absorption band due to benzene dimer radical cation was accelerated by addition of TEAF•4HF. The observed rate constant increased with increasing the concentration of TEAF•4HF. The rate constant of the electrophilic addition of fluoride to benzene radical cation was determined to be 9.4 × 109 M-1 s-1. Thus, the photocatalytic reaction is initiated by intermolecular photoinduced electron transfer from benzene to the single exited state of QuCN+. Benzene radical cation formed by photoinduced electron transfer reacts with fluoride anion to yield the F-adducted radical. On the other hand, QuCN• can reduce O2 to O2•- and this is followed by protonation of O2•- to afford HO2•. The hydrogen abstraction of HO2• from F-adduct radical affords fluorobenzene and H2O2 as the final products.

Ohkubo K; Fujimoto A; Fukuzumi S

2013-09-01

184

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

185

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

186

Intermolecular forces for hydrogen, nitrogen and acetylene  

International Nuclear Information System (INIS)

Orientation-dependent intermolecular potentials for H2, N2, and C2H2 have been determined on the basis of electron charge density contours, octopolar induction in the dispersion force, electrostatic quadrupolar interaction, and the observed second virial coefficients. The recently settled structure of low-temperature solid acetylene has been discussed. (Auth.)

1977-05-01

187

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

188

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

189

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

190

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

191

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

192

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

193

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

194

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

195

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

196

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

197

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

198

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

199

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

200

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

 
 
 
 
201

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

202

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

203

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

204

Naphthalenedicarboxamides as fluorescent probes of inter- and intramolecular electron transfer in single strand, hairpin, and duplex DNA  

Energy Technology Data Exchange (ETDEWEB)

The 2,6-naphthalenedicarboxamide chromophore has been investigated as a fluorescent probe for DNA hairpin and duplex formation and DNA electron transfer. The high fluorescence quantum yield and long singlet lifetime of this chromophore make it an attractive candidate for these studies. The kinetics of intermolecular quenching of a naphthalenedicarboxamide by nucleosides is dependent upon the nucleoside oxidation potential and solvent. Bis(oligonucleotide) conjugates containing naphthalene linkers have been prepared by means of conventional phosphoramidite chemistry. The base-sequence dependence of the naphthalene fluorescence intensity and decay times in both single-strand and hairpin conjugates indicates that singlet naphthalene is quenched by neighboring dA more efficiently than by dT, in accord with an electron-transfer quenching mechanism. These data are analyzed by means of a three-state model which includes a nonemissive dark state. Duplexes formed between complementary naphthalene-linked oligonucleotides display naphthalene excimer emission. The base-sequence dependence of the excimer emission quantum yields indicates that the excimer is not quenched by neighboring dA but that distance-dependent electron-transfer quenching by dG may occur. Quenching serves to protect the naphthalene chromophore from photobleaching in both single strand and duplex structures.

Lewis, F.D.; Zhang, Y.; Liu, X.; Xu, N.; Letsinger, R.L. [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry

1999-04-01

205

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

206

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

207

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

208

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

209

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

210

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

211

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

212

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

213

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

214

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

215

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

216

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

217

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

218

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

219

Electron transfer rate of redox ion controlled by electrostatic interaction with 4-aminothiophenol monolayer on gold electrode; 4-aminothiophenol tanbunshimaku denkyoku tono seiden sogo sayo wo riyoshita redox ion no denshi ido sokudo no seigyo  

Energy Technology Data Exchange (ETDEWEB)

In order to clarify the influence of inter-molecular interaction between 4-aminothiophenol (ATP) monolayer and organic redox ion on the electron transfer rate at the electrode, the electron transfer rate constant of redox ion and the influence on the concentration on the electrode surface were examined using ac frequency response. For the experiments, the modified electrode and electron transfer in the interface of electrode/solution was evaluated by means of cyclic voltammetry and ac impedance spectroscopy. As a result, it was found that the protonated ATP electrode with positive electric charge accelerated the concentration of anionic redox ion on the electrode surface. Capacity and resistance of the membrane obtained from the ac frequency response in the high frequency range can be used for the evaluation of modification including the adsorption of redox ion on the electrode surface. The interface electron transfer rate was affected by the inter-molecular static interaction as well as by the electron transfer distance. 11 refs., 8 figs., 4 tabs.

Yamaguchi, T.; Takahashi, K.; Komura, T. [Kanazawa University, Ishikawa (Japan). Faculty of Engineering

1998-09-05

220

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

 
 
 
 
221

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

222

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

223

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

224

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

225

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

226

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

227

Correlated ab initio investigations on the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O2(-)(X2?g)-HF(X1?+) complex.  

Science.gov (United States)

This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O(2)(-)(X(2)?(g))-HF(X(1)?(+)) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2-5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and C(s) symmetry along the A" surface of the complex, whereas the A' surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-D(e)) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and D(e) value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C(2v) symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm(-1). The calculated harmonic oscillator vibrational frequencies showed that the H-F stretch vibrational transition in the complex is redshifted by 2564 cm(-1) and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the O(2)(-)-HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer. PMID:23298038

Fawzy, Wafaa M; Elsayed, Mahmoud; Zhang, Yuchen

2013-01-01

228

Correlated ab initio investigations on the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O2(-)(X2?g)-HF(X1?+) complex.  

UK PubMed Central (United Kingdom)

This work reports the first highly correlated ab initio study of the intermolecular and intramolecular potential energy surfaces in the ground electronic state of the O(2)(-)(X(2)?(g))-HF(X(1)?(+)) complex. Accurate electronic structure calculations were performed using the coupled cluster method including single and double excitations with addition of the perturbative triples correction [CCSD(T)] with the Dunning's correlation consistent basis sets aug-cc-pVnZ, n = 2-5. Also, the explicitly correlated CCSD(T)-F12a level of theory was employed with the AVnZ basis as well as the Peterson and co-workers VnZ-F12 basis sets with n = 2 and 3. Results of all levels of calculations predicted two equivalent minimum energy structures of planar geometry and C(s) symmetry along the A" surface of the complex, whereas the A' surface is repulsive. Values of the geometrical parameters and the counterpoise corrected dissociation energies (Cp-D(e)) that were calculated using the CCSD(T)-F12a/VnZ-F12 level of theory are in excellent agreement with those obtained from the CCSD(T)/aug-cc-pV5Z calculations. The minimum energy structure is characterized by a very short hydrogen bond of length of 1.328 Å, with elongation of the HF bond distance in the complex by 0.133 Å, and D(e) value of 32.313 Kcal/mol. Mulliken atomic charges showed that 65% of the negative charge is localized on the hydrogen bonded end of the superoxide radical and the HF unit becomes considerably polarized in the complex. These results suggest that the hydrogen bond is an incipient ionic bond. Exploration of the potential energy surface confirmed the identified minimum and provided support for vibrationally induced intramolecular proton transfer within the complex. The T-shaped geometry that possesses C(2v) symmetry presents a saddle point on the top of the barrier to the in-plane bending of the hydrogen above and below the axis that connects centers of masses of the monomers. The height of this barrier is 7.257 Kcal/mol, which is higher in energy than the hydrogen bending frequency by 909.2 cm(-1). The calculated harmonic oscillator vibrational frequencies showed that the H-F stretch vibrational transition in the complex is redshifted by 2564 cm(-1) and gained significant intensity (by at least a factor of 30) with respect to the transition in the HF monomer. These results make the O(2)(-)-HF complex an excellent prototype for infrared spectroscopic investigations on open-shell complexes with vibrationally induced proton transfer.

Fawzy WM; Elsayed M; Zhang Y

2013-01-01

229

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

230

Kinetics and mechanisms of photoinduced electron-transfer reaction of zinc myoglobin  

International Nuclear Information System (INIS)

Photoinduced electron transfer (ET) between zinc myoglobin (ZnPPMb) and a variety of quenchers, such as hexacyanoferrate(III)([Fe(CN)6]3-) and hexaammineruthenium(III)(Ru(NH3)6]3+ ions, cationic viologens, copper(II) protein (stellacyanin), and metmyoglobins, has been studied in aqueous degassed solutions. The excited triplet state of ZnPPMb(*ZnPPMb) was quenched by [Fe(CN)6]3- in a self-associated complex. Both quenching rate constant and formation constant of the self-associated complex decrease with increasing ionic strengths. The thermal backward ET reaction for this system was not observed; it is most likely that the backward ET step is much faster than the quenching reaction. All of the cationic quenchers examined in this work did not form a self-associated complex with *ZnPPMb, and the intermolecular quenching occurred. The thermal backward ET reaction was observed for these cationic quenchers. Not only photoinduced ET but also thermal backward ET reactions were insensitive to the driving force of the reactions, suggesting that the reactions are controlled by conformational changes in ZnPPMb. The quenching rate constants increase with increasing ionic strength for the cationic quenchers. The effects of poly-L-lysine hydrochloride, sodium poly-L-glutamate, and sodium cyclo-hexaphosphate were also examined. The active site of the *ZnPPMb toward both anionic and cationic quenchers is assumed to be the positively charged site near the heme pocket. (author).

1994-01-01

231

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

232

[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

233

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

234

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

235

Desensitization of metastable intermolecular composites  

Energy Technology Data Exchange (ETDEWEB)

A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

Busse, James R. (South Fork, CO); Dye, Robert C. (Los Alamos, NM); Foley, Timothy J. (Los Alamos, NM); Higa, Kelvin T. (Ridgecrest, CA); Jorgensen, Betty S. (Jemez Springs, NM); Sanders, Victor E. (White Rock, NM); Son, Steven F. (Los Alamos, NM)

2011-04-26

236

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

237

The theory of intermolecular forces  

CERN Document Server

The theory of intermolecular forces has advanced very greatly in recent years. It has become possible to carry out accurate calculations of intermolecular forces for molecules of useful size, and to apply the results to important practical applications such as understanding protein structure and function, and predicting the structures of molecular crystals. The Theory of Intermolecular Forces sets out the mathematical techniques that are needed to describe and calculate intermolecular interactions and to handle the more elaborate mathematical models. It describes the methods that are used to calculate them, including recent developments in the use of density functional theory and symmetry-adapted perturbation theory. The use of higher-rank multipole moments to describe electrostatic interactions is explained in both Cartesian and spherical tensor formalism, and methods that avoid the multipole expansion are also discussed. Modern ab initio perturbation theory methods for the calculation of intermolecular inte...

Stone, Anthony J

2013-01-01

238

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

239

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

240

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

 
 
 
 
241

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

242

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

243

Electronic Mechanisms of Intra and Intermolecular J Couplings in Systems with C-H···O Interactions  

Directory of Open Access Journals (Sweden)

Full Text Available Abstract: Correlation effects on the change of 1J(CH) couplings in model systems I:NCH...H2O and II:CH4...H2O as a function of the H...O distance are discussed. RPA and SOPPA results follow a similar trend in system II. In system I RPA values decrease monotonously as the H...O distance decreases, while SOPPA ones exhibit flat maximum near equilibrium. Such different behavior is ascribed to the π-transmitted component. Intermolecular couplings at the equilibrium geometry of I are analyzed by means of the CLOPPA approach. The larger absolute value of 2hJ(CO) compared to 1hJ(HO) is found to arise from contributions involving a vacant LMO localized in the C-H...O moiety.

Claudia G. Giribet; Martin C. Ruiz de Azua; Celia V. Vizioli; Claudio N. Cavasotto

2003-01-01

244

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

245

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

246

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

247

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

248

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

249

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

250

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

251

New type of dual solid-state thermochromism: modulation of intramolecular charge transfer by intermolecular pi-pi interactions, kinetic trapping of the aci-nitro group, and reversible molecular locking.  

Science.gov (United States)

When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10(-7)-10(-6) s(-1) for BDB2 to about 0.1 s(-1) in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened pi-pi interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered by intramolecular proton transfer of one amino proton to the nitro group, whereupon an aci-nitro form is thermally populated. Contrary to the numerous examples of solid thermochromic molecules based on either pericyclic reactions or keto-enol tautomerism, this system appears to be the first organic thermochromic family where the thermochromic change appears as an effect of intermolecular pi-pi interactions and thermal intramolecular proton transfer to aromatic nitro group. PMID:19780605

Naumov, Pance; Lee, Sang Cheol; Ishizawa, Nobuo; Jeong, Young Gyu; Chung, Ihn Hee; Fukuzumi, Shunichi

2009-10-22

252

New type of dual solid-state thermochromism: modulation of intramolecular charge transfer by intermolecular pi-pi interactions, kinetic trapping of the aci-nitro group, and reversible molecular locking.  

UK PubMed Central (United Kingdom)

When heated above room temperature, some crystalline polymorphs of the 1,3-bis(hydroxyalkylamino)-4,6-dinitrobenzenes (BDBn, n = 2-5), bis(hydroxyalkyl) analogues of the intramolecular charge-transfer molecule 1,3-diamino-4,6-dinitrobenzene, exhibit "dual" thermochromism: gradual color change from yellow to orange at lower temperatures, and sharp color change from orange to red at higher temperatures. These two thermochromic changes are related to different solid-state processes. When allowed to cool to room temperature, the yellow color of the thermochromic molecules with different alkyl length (n) is recovered with unexpectedly different kinetics, the order of the respective rate constants ranging from 10(-7)-10(-6) s(-1) for BDB2 to about 0.1 s(-1) in the case of BDB3. The thermochromic mechanism and the reasons behind the different kinetics were clarified on the basis of detailed crystallographic characterization, kinetic thermoanalysis, and spectroscopic study of eight crystalline forms (seven polymorphs and one solvate). It was found that the polymorphism is due to the possibility of "locking" and "unlocking" of the alkyl arms by formation of a strong intramolecular hydrogen bond between the hydroxyl groups at their hydroxyl termini. The locking of BDB2, with shortest alkyl arms, is reversible and it can be controlled thermally; either of the two conformations can be obtained in the solid state by proper thermal treatment. By use of high temperature in situ single crystal X-ray diffraction analysis of BDB3, direct evidence was obtained that the gradual thermochromic change is related to increased distance and weakened pi-pi interactions between the stacked benzene rings: the lattice expands preferably in the stacking direction, causing enhanced oscillator strength and red shift of the absorption edge of the intramolecular charge transfer transition. The second, sharp thermochromic change had been assigned previously to solid-solid phase transition triggered by intramolecular proton transfer of one amino proton to the nitro group, whereupon an aci-nitro form is thermally populated. Contrary to the numerous examples of solid thermochromic molecules based on either pericyclic reactions or keto-enol tautomerism, this system appears to be the first organic thermochromic family where the thermochromic change appears as an effect of intermolecular pi-pi interactions and thermal intramolecular proton transfer to aromatic nitro group.

Naumov P; Lee SC; Ishizawa N; Jeong YG; Chung IH; Fukuzumi S

2009-10-01

253

Interatomic (Intermolecular) Decay Processes in Clusters: Current Status and Outlook  

International Nuclear Information System (INIS)

Since their theoretical prediction a decade ago, interatomic (intermolecular) Coulombic decay (ICD) and related processes have been in the focus of intensive theoretical and experimental research. The spectacular progress in this direction has been stimulated both by the fundamental importance of the new electronic decay phenomena and by the exciting possibility of their practical application, for example in spectroscopy. We review the current status of the research of interatomic (intermolecular) decay phenomena in clusters and discuss some perspectives of this new field.

2007-11-29

254

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

255

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

256

Excess Electron Attachment Induces Barrier-Free Proton Transfer in Anionic Complexes of Thymine and Uracil with Formic Acid  

Energy Technology Data Exchange (ETDEWEB)

The anionic complexes of formic acid with uracil and thymine reveal broad features in photoelectron spectroscopy (PES) experiments with maxima at 1.7 and 1.1 eV, respectively. The results of quantum chemical calculations suggest that electron vertical detachment energies (VDE) of 1.6-1.9 eV correspond to anionic structures in which a proton has been transferred from the carboxylic group of the formic acid to the O8 atom of uracil or thymine. Smaller values of VDE (0.8 to 1.3 eV) correspond to chemically untransformed complexes, in which anionic uracil or thymine interacts through two hydrogen bonds with the carboxylic group of the intact formic acid. The recorded spectra and the results of quantum chemical calculations suggest that both nucleic acid bases undergo barrier-free proton transfer in anionic complexes with formic acid. The difference in experimental spectra of UF- and TF- provides an indication that the methyl group of thymine could make a difference in the intermolecular proton transfer.

Haranczyk, Maciej; Dabkowska, Iwona; Rak, Janusz; Gutowski, Maciej S.; Nilles, J.M.; Stokes, Sarah; Radisic, Dunja; Bowen, Kit H.

2004-06-03

257

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

258

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

259

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

260

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

 
 
 
 
261

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

262

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

263

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

264

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

265

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

266

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

267

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

268

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

269

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

270

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

271

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

272

Intermolecular nitrile oxide transfer in fullerene isoxazolines  

Energy Technology Data Exchange (ETDEWEB)

Mass spectrometric analysis of fullerene derivatives often requires very different conditions and produces very different results than are expected when examining underivatized fullerenes. Frequently, mass spectra of derivatives have relatively small molecular ion peaks and are dominated by fullerene ion peak at high masses. The need for reliable mass spectrometric methods is increasing as new classes of fullerene derivatives are introduced. One such class of derivatives, the fullerene isoxazolines, is examined in this presentation.

Pogue, R.T.; Meier, M.S.; Thomas, C.; Majidi, V. [Univ. of Kentucky, Lexington, KY (United States)

1995-12-31

273

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

274

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

275

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

276

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.

277

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

278

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

279

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

280

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

 
 
 
 
281

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

282

The reorganization energy of electron transfer in nonpolar solvents: Molecular level treatment of the solvent  

International Nuclear Information System (INIS)

The intermolecular electron transfer in a solute pair consisting of pyrene and dimethylaniline is investigated in a nonpolar solvent, n-hexane. The earlier elaborated approach [M. Tachiya, J. Phys Chem. 97, 5911 (1993)] is used; this method provides a physically relevant background for separating inertial and inertialess polarization responses for both nonpolarizable and polarizable molecular level simulations. The molecular-dynamics technique was implemented for obtaining the equilibrium ensemble of solvent configurations. The nonpolar solvent, n-hexane, was treated in terms of OPLS-AA parametrization. Solute Lennard-Jones parameters were taken from the same parametrization. Solute charge distributions of the initial and final states were determined using ab initio level [HF/6-31G(d,p)] quantum-chemical calculations. Configuration analysis was performed explicitly taking into account the anisotropic polarizability of n-hexane. It is shown that the Gaussian law well describes calculated distribution functions of the solvent coordinate, therefore, the rate constant of the ET reaction can be characterized by the reorganization energy. Evaluated values of the reorganization energies are in a range of 0.03-0.11 eV and significant contribution (more then 40% of magnitude) comes from anisotropic polarizability. Investigation of the reorganization energy ? dependence on the solute pair separation distance d revealed unexpected behavior. The dependence has a very sharp peak at the distance d=7 A where solvent molecules are able to penetrate into the intermediate space between the solute pair. The reason for such behavior is clarified. This new effect has a purely molecular origin and cannot be described within conventional continuum solvent models.

2005-12-08

283

The reorganization energy of electron transfer in nonpolar solvents: Molecular level treatment of the solvent  

Science.gov (United States)

The intermolecular electron transfer in a solute pair consisting of pyrene and dimethylaniline is investigated in a nonpolar solvent, n-hexane. The earlier elaborated approach [M. Tachiya, J. Phys Chem. 97, 5911 (1993)] is used; this method provides a physically relevant background for separating inertial and inertialess polarization responses for both nonpolarizable and polarizable molecular level simulations. The molecular-dynamics technique was implemented for obtaining the equilibrium ensemble of solvent configurations. The nonpolar solvent, n-hexane, was treated in terms of OPLS-AA parametrization. Solute Lennard-Jones parameters were taken from the same parametrization. Solute charge distributions of the initial and final states were determined using ab initio level [HF/6-31G(d,p)] quantum-chemical calculations. Configuration analysis was performed explicitly taking into account the anisotropic polarizability of n-hexane. It is shown that the Gaussian law well describes calculated distribution functions of the solvent coordinate, therefore, the rate constant of the ET reaction can be characterized by the reorganization energy. Evaluated values of the reorganization energies are in a range of 0.03-0.11 eV and significant contribution (more then 40% of magnitude) comes from anisotropic polarizability. Investigation of the reorganization energy ? dependence on the solute pair separation distance d revealed unexpected behavior. The dependence has a very sharp peak at the distance d=7 A? where solvent molecules are able to penetrate into the intermediate space between the solute pair. The reason for such behavior is clarified. This new effect has a purely molecular origin and cannot be described within conventional continuum solvent models.

Leontyev, I. V.; Tachiya, M.

2005-12-01

284

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

285

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

286

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

287

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

288

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

289

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

290

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

291

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

292

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

293

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

294

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

295

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

296

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

297

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

298

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

299

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

300

Perturbation analyses of intermolecular interactions.  

Science.gov (United States)

Conformational fluctuations of a protein molecule are important to its function, and it is known that environmental molecules, such as water molecules, ions, and ligand molecules, significantly affect the function by changing the conformational fluctuations. However, it is difficult to systematically understand the role of environmental molecules because intermolecular interactions related to the conformational fluctuations are complicated. To identify important intermolecular interactions with regard to the conformational fluctuations, we develop herein (i) distance-independent and (ii) distance-dependent perturbation analyses of the intermolecular interactions. We show that these perturbation analyses can be realized by performing (i) a principal component analysis using conditional expectations of truncated and shifted intermolecular potential energy terms and (ii) a functional principal component analysis using products of intermolecular forces and conditional cumulative densities. We refer to these analyses as intermolecular perturbation analysis (IPA) and distance-dependent intermolecular perturbation analysis (DIPA), respectively. For comparison of the IPA and the DIPA, we apply them to the alanine dipeptide isomerization in explicit water. Although the first IPA principal components discriminate two states (the ? state and PPII (polyproline II) + ? states) for larger cutoff length, the separation between the PPII state and the ? state is unclear in the second IPA principal components. On the other hand, in the large cutoff value, DIPA eigenvalues converge faster than that for IPA and the top two DIPA principal components clearly identify the three states. By using the DIPA biplot, the contributions of the dipeptide-water interactions to each state are analyzed systematically. Since the DIPA improves the state identification and the convergence rate with retaining distance information, we conclude that the DIPA is a more practical method compared with the IPA. To test the feasibility of the DIPA for larger molecules, we apply the DIPA to the ten-residue chignolin folding in explicit water. The top three principal components identify the four states (native state, two misfolded states, and unfolded state) and their corresponding eigenfunctions identify important chignolin-water interactions to each state. Thus, the DIPA provides the practical method to identify conformational states and their corresponding important intermolecular interactions with distance information. PMID:21929141

Koyama, Yohei M; Kobayashi, Tetsuya J; Ueda, Hiroki R

2011-08-12

 
 
 
 
301

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

302

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

303

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

304

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

305

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

306

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

307

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

308

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

309

Intermolecular Forces: Solids and Liquids  

Science.gov (United States)

General chemistry WebCT exam/quiz questions. The Intermolecular Forces: Solids and Liquids topic covers the forces that exist between atoms and molecules in solids and liquids, and how these affect properties such as boiling point, conductivity, and lattice energy.

2007-09-07

310

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

311

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

312

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

313

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

314

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

315

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

316

"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

317

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

318

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

319

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

320

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

 
 
 
 
321

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

322

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

323

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

324

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

325

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

326

Topological characterisation of intermolecular lithium bonding  

International Nuclear Information System (INIS)

Bader's atoms in molecules topological theory was employed to analyse the B3LYP/6-311++G(3d2f,3p2d) electron distributions of several adducts that contain LiF. The results indicate significant differences between lithium bonding (LB) and hydrogen bonding (HB): (i) in spite of their larger stability, the charge density at the intermolecular critical points of LB complexes is about half of its value in the corresponding HB complexes, suggesting a dominant role of electrostatic interactions in the former; (ii) the Li atom in LB compounds is more shared between the base atom and the attached fluorine than hydrogen in HB complexes; and (iii) the Li atom gains electron charge from the hydrogens in all the complexes here studied, undergoing energetic stabilisation.

2006-08-01

327

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

328

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

329

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

330

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

331

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

332

Electric field effects on photoinduced electron transfer processes of methylene-linked compounds of pyrene and N,N-dimethylaniline in a polymer film  

International Nuclear Information System (INIS)

Time-resolved measurements of the electric-field-induced change in fluorescence intensity have been made for methylene-linked compounds of pyrene and N,N-dimethylaniline (DMA) doped in a polymer film. The lifetime of the fluorescence emitted from the locally excited state of pyrene chromophore becomes shorter in the presence of electric field (F), when the dopant concentration is high. The lifetime of the excipelx fluorescence resulting from the photoinduced electron transfer (PIET) from DMA to the excited state of pyrene chromophore between different molecules also becomes shorter in the presence of F. Based on the simulation of the electric field effect on fluorescence decay, the mechanism of intermolecular PIET between DMA and pyrene chromophore in a polymer film is discussed.

2004-04-01

333

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

334

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

335

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

336

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

337

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

338

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

339

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

340

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

 
 
 
 
341

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

342

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

343

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

344

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

345

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

346

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

347

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

348

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

349

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

350

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

351

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

352

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

353

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

354

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

355

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

356

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

357

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

358

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 undeuterated radical cations. 1 fig., 2 tabs.

Gould, I.R.; Farid, S.

1988-11-09

359

Theory of the transition from sequential to concerted electrochemical proton-electron transfer.  

UK PubMed Central (United Kingdom)

A theory for the calculation of potential energy surfaces of electrochemical proton-coupled electron transfer is considered and parameterized on the basis of thermodynamic relations. The paper discusses the qualitatively different potential energy surfaces predicted by the theory, and their relation to the existence of sequential and concerted proton-electron transfer pathways. The concomitant activation energies for sequential and concerted PET are calculated. The applied overpotential may change the qualitative shape of the PES and therefore the mechanism of the proton-coupled electron transfer reaction.

Koper MT

2013-02-01

360

Electron transfer. 144. Reductions with germanium(II).  

Science.gov (United States)

Solutions 0.2-0.4 M in Ge(II) and 6 M in HCl, generated by reaction of Ge(IV) with H3PO2, are stable for more than 3 weeks and can be diluted 200-fold with dilute HCl to give GeCl3- preparations to be used in redox studies. Kinetic profiles for the reduction of Fe(III) by Ge(II), as catalyzed by Cu(II), implicate the odd-electron intermediate, Ge(III), which is formed from Cu(II) and Ge(II) (k = 30 M-1 s-1 in 0.5 M HCl at 24 degrees C) and which is consumed by reaction with Fe(III) (k = 6 x 10(2) M-1 s-1). A slower direct reaction between Ge(II) and Fe(III) (k = 0.66 M-1 s-1) can be detected in 1.0 M HCl. The reaction of Ge(II) with I3- in 0.01-0.50 M iodide is zero order in oxidant and appears to proceed via a rate-determining heterolysis of a Ge(II)-OH2 species (k = 0.045 s-1) which is subject to H(+)-catalysis. Reductions of IrCl6(2-) and PtCl6(2-) by Ge(II) are strongly Cl(-)-catalyzed. The Ir(IV) reaction proceeds through a pair of 1e- changes, of which the initial conversion to Ge(III) is rate-determining, whereas the Pt(IV) oxidant probably utilizes (at least in part) an inner-sphere PtIV-Cl-GeII bridge in which chlorine is transferred (as Cl+) from oxidant to reductant. The 2e- reagent, Ge(II), like its 5s2 counterpart, In(I), can partake in 1e- transactions, but requires more severe constraints: the coreagent must be more powerfully oxidizing and the reaction medium more halide-rich. PMID:11198868

Babich, O A; Gould, E S

2000-09-01

 
 
 
 
361

Electron transfer. 144. Reductions with germanium(II).  

UK PubMed Central (United Kingdom)

Solutions 0.2-0.4 M in Ge(II) and 6 M in HCl, generated by reaction of Ge(IV) with H3PO2, are stable for more than 3 weeks and can be diluted 200-fold with dilute HCl to give GeCl3- preparations to be used in redox studies. Kinetic profiles for the reduction of Fe(III) by Ge(II), as catalyzed by Cu(II), implicate the odd-electron intermediate, Ge(III), which is formed from Cu(II) and Ge(II) (k = 30 M-1 s-1 in 0.5 M HCl at 24 degrees C) and which is consumed by reaction with Fe(III) (k = 6 x 10(2) M-1 s-1). A slower direct reaction between Ge(II) and Fe(III) (k = 0.66 M-1 s-1) can be detected in 1.0 M HCl. The reaction of Ge(II) with I3- in 0.01-0.50 M iodide is zero order in oxidant and appears to proceed via a rate-determining heterolysis of a Ge(II)-OH2 species (k = 0.045 s-1) which is subject to H(+)-catalysis. Reductions of IrCl6(2-) and PtCl6(2-) by Ge(II) are strongly Cl(-)-catalyzed. The Ir(IV) reaction proceeds through a pair of 1e- changes, of which the initial conversion to Ge(III) is rate-determining, whereas the Pt(IV) oxidant probably utilizes (at least in part) an inner-sphere PtIV-Cl-GeII bridge in which chlorine is transferred (as Cl+) from oxidant to reductant. The 2e- reagent, Ge(II), like its 5s2 counterpart, In(I), can partake in 1e- transactions, but requires more severe constraints: the coreagent must be more powerfully oxidizing and the reaction medium more halide-rich.

Babich OA; Gould ES

2000-09-01

362

Environment assisted electron capture  

CERN Document Server

Electron capture by {\\it isolated} atoms and ions proceeds by photorecombination. In this process a species captures a free electron by emitting a photon which carries away the excess energy. It is shown here that in the presence of an {\\it environment} a competing non-radiative electron capture process can take place due to long range electron correlation. In this interatomic (intermolecular) process the excess energy is transferred to neighboring species. The asymptotic expression for the cross section of this process is derived. We demonstrate by explicit examples that under realizable conditions the cross section of this interatomic process can clearly dominate that of photorecombination.

Gokhberg, Kirill

2009-01-01

363

Atom-atom partitioning of intramolecular and intermolecular Coulomb energy  

Science.gov (United States)

An atom-atom partitioning of the (super)molecular Coulomb energy is proposed on the basis of the topological partitioning of the electron density. Atom-atom contributions to the molecular intra- and intermolecular Coulomb energy are computed exactly, i.e., via a double integration over atomic basins, and by means of the spherical tensor multipole expansion, up to rank L=lA+lB+1=5. The convergence of the multipole expansion is able to reproduce the exact interaction energy with an accuracy of 0.1-2.3 kJ/mol at L=5 for atom pairs, each atom belonging to a different molecule constituting a van der Waals complex, and for nonbonded atom-atom interactions in single molecules. The atom-atom contributions do not show a significant basis set dependence (3%) provided electron correlation and polarization basis functions are included. The proposed atom-atom Coulomb interaction energy can be used both with post-Hartree-Fock wave functions and experimental charge densities in principle. The Coulomb interaction energy between two molecules in a van der Waals complex can be computed by summing the additive atom-atom contributions between the molecules. Our method is able to extract from the supermolecule wave function an estimate of the molecular interaction energy in a complex, without invoking the reference state of free noninteracting molecules. We provide computational details of this method and apply it to (C2H2)2; (HF)2; (H2O)2; butane; 1,3,5-hexatriene; acrolein and urocanic acid, thereby covering a cross section of hydrogen bonds, and covalent bonds with and without charge transfer.

Popelier, P. L. A.; Kosov, D. S.

2001-04-01

364

Proton-coupled electron transfer drives the proton pump of cytochrome c oxidase  

Science.gov (United States)

Electron transfer in cell respiration is coupled to proton translocation across mitochondrial and bacterial membranes, which is a primary event of biological energy transduction. The resulting electrochemical proton gradient is used to power energy-requiring reactions, such as ATP synthesis. Cytochrome c oxidase is a key component of the respiratory chain, which harnesses dioxygen as a sink for electrons and links O2 reduction to proton pumping. Electrons from cytochrome c are transferred sequentially to the O2 reduction site of cytochrome c oxidase via two other metal centres, CuA and haem a, and this is coupled to vectorial proton transfer across the membrane by a hitherto unknown mechanism. On the basis of the kinetics of proton uptake and release on the two aqueous sides of the membrane, it was recently suggested that proton pumping by cytochrome c oxidase is not mechanistically coupled to internal electron transfer. Here we have monitored translocation of electrical charge equivalents as well as electron transfer within cytochrome c oxidase in real time. The results show that electron transfer from haem a to the O2 reduction site initiates the proton pump mechanism by being kinetically linked to an internal vectorial proton transfer. This reaction drives the proton pump and occurs before relaxation steps in which protons are taken up from the aqueous space on one side of the membrane and released on the other.

Belevich, Ilya; Verkhovsky, Michael I.; Wikström, Mårten

2006-04-01

365

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

Science.gov (United States)

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

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

2013-06-06

366

Pulse radiolytic studies of electron transfer processes and applications to solar photochemistry. Progress report  

Energy Technology Data Exchange (ETDEWEB)

The pulse radiolysis technique is applied to the study of electron transfer processes in a variety of chemical systems. Reactive intermediates are produced in solution by electron pulse irradiation and the kinetics of their reactions are followed by time resolved absorption spectrophotometry. Complementary experiments are carried out with excimer laser flash photolysis. These studies are concerned with mechanisms, kinetics, and thermodynamics of reactions of organic and inorganic radicals and unstable oxidation states of metal ions. Reactions are studied in both aqueous and non-aqueous solutions. The studies focus on the unique ability of pulse radiolysis to provide absolute rate constants for reactions of many inorganic radicals and organic peroxyl radicals, species that are key intermediates in many chemical processes. A special concern of this work is the study of electron transfer reactions of metalloporphyrins, which permits evaluation of these molecules as intermediates in solar energy conversion. Metalloporphyrins react with free radicals via electron transfer, involving the ligand or the metal center, or via bonding to the metal, leading to a variety of chemical species whose behavior is also investigated. The highlights of the results during the past three years are summarized below under the following sections: (a) electron transfer reactions of peroxyl radicals, concentrating on the characterization of new peroxyl radicals derived from vinyl, phenyl, other aryl, and pyridyl; (b) solvent effects on electron transfer reactions of inorganic and organic peroxyl radicals, including reactions with porphyrins, and (c) electron transfer and alkylation reactions of metalloporphyrins and other complexes.

Neta, P.

1995-02-01

367

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

Science.gov (United States)

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

Lang, Bernhard; Rosspeintner, Arnulf; Vauthey, Eric

2013-03-01

368

Vectorial electron transfer in spatially ordered arrays. Progress report, January 1992--January 1993  

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

369

Radicals and radical ions as intermediates of electron transfer processes through peptides.  

UK PubMed Central (United Kingdom)

Electron transfer (ET) through peptides and proteins is a key biochemical process, which involves radicals and radical ions as reactive intermediates. We have developed an assay that allows us to study this fundamental chemical reaction.

Giese B; Eckhardt S; Lauz M; Gao J; Wang M

2012-01-01

370

Non-Markovian electron transfer reactions with frequency-dependent friction  

Energy Technology Data Exchange (ETDEWEB)

A modified non-Markovian Zusman equation for electron transfer reactions with frequency-dependent friction is presented. The derivation is based on the spin-boson model with a two-level system coupled to a non-Debye polar solvent bath with frequency-dependent friction. The diffusion constant in the Smoluchowski diffusion operator of the ordinary Zusman equation should be replaced by a convolution of a retarded time-dependent diffusion constant. An analytical expression for the electron transfer rate constant was derived using the Green`s function method. In the adiabatic regime, electron transfer process is generally nonexponential. Because of the time-retardation, initial electron transfer reaction is influenced more by the higher frequency components in the solvent relaxation.

Tang, J.

1993-12-31

371

Single electron transfer-induced cross-coupling reaction of alkenyl halides with aryl Grignard reagents.  

UK PubMed Central (United Kingdom)

Alkenyl halides were found to undergo coupling with aryl Grignard reagents to give the corresponding styrene derivatives in a stereo-retained manner. The cross-coupling reaction is considered to proceed through a single electron transfer mechanism.

Shirakawa E; Watabe R; Murakami T; Hayashi T

2013-06-01

372

Charge transfer in quasi-one-electron systems at 'high' energy  

International Nuclear Information System (INIS)

[en] We have made absolute and relative measurements of differential cross sections for single-electron transfer in collisions between Mg+ (30-150 keV) and Be+ (56.25 keV) ions and He atoms. The behaviour of transfer probability as a function of impact parameter can be understood qualitatively from recent molecular orbital calculations of quasi-one-electron systems. (author)

1988-08-14

373

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

International Nuclear Information System (INIS)

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

1983-12-22

374

Electron transfer experiments and atomic magnetism values. Progress report, February 1, 1975--September 30, 1975  

International Nuclear Information System (INIS)

Progress in the first seven months of this new research is described. A new apparatus was constructed, tested and moved to Oak Ridge National Laboratory for studies using the Penning ion source test facility. Preliminary electron transfer cross section results for N4+, N5+, He2+ and C5+ ions on gases were obtained. Energy loss measurements made to date support expectations that single electron transfer for multiply-charged ions colliding with gas atoms produces excited final state ions

1975-01-01

375

Heterogeneous electron transfer of cytochrome c facilitated by polypyrrole and methylene blue polypyrrole film modified electrodes.  

UK PubMed Central (United Kingdom)

Polypyrrole and methylene blue incorporated polypyrrole thin-film modified electrodes were prepared by the electrochemical polymerization method. These modified electrodes may facilitate heterogeneous electron transfer of cytochrome c with high electrocatalytic activity and good stability. Optical thin-layer spectroelectrochemical techniques were used to determine the characteristics of these electrochemical processes such as formal redox potential (E0), electron transfer number (n), and the apparent rate constant (ks.h0).

Zhang WB; Song SH; Dong SJ

1990-11-01

376

Heterogeneous electron transfer of cytochrome c facilitated by polypyrrole and methylene blue polypyrrole film modified electrodes.  

Science.gov (United States)

Polypyrrole and methylene blue incorporated polypyrrole thin-film modified electrodes were prepared by the electrochemical polymerization method. These modified electrodes may facilitate heterogeneous electron transfer of cytochrome c with high electrocatalytic activity and good stability. Optical thin-layer spectroelectrochemical techniques were used to determine the characteristics of these electrochemical processes such as formal redox potential (E0), electron transfer number (n), and the apparent rate constant (ks.h0). PMID:1963438

Zhang, W B; Song, S H; Dong, S J

1990-11-01

377

Tunneling-induced coherent electron population transfer in an asymmetric quantum well  

CERN Multimedia

We propose an asymmetric double quantum well structure with a common continuum and investigate the effect of resonant tunneling on the control of coherent electron population transfer between the two quantum wells. By numerically solving the motion equations of element moments, the almost complete electron population transfer from initial subband to the target subband could be realized due to the constructive interference via flexibly adjusting the structure parameters.

Cui, Ni; Gong, Shangqing

2009-01-01

378

PROTON AND PROTON-COUPLED ELECTRON TRANSFER WITH PARADIGMS TOWARDS SINGLE-MOLECULE SYSTEMS  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Abstract Proton (PT), H-atom, and proton coupled electron transfer (PCET) are ubiquitously encountered in chemical and biological processes. PT and H-atom transfer can belong to the partially or totally adiabatic limits representing “weak” or “strong” interactions between the donor and accep...

379

Desensitization and recovery of metastable intermolecular composites  

Energy Technology Data Exchange (ETDEWEB)

A method to substantially desensitize a metastable intermolecular composite material to electrostatic discharge and friction comprising mixing the composite material with an organic diluent and removing enough organic diluent from the mixture to form a mixture with a substantially putty-like consistency, as well as a concomitant method of recovering the metastable intermolecular composite material.

Busse, James R. (South Fork, CO); Dye, Robert C. (Los Alamos, NM); Foley, Timothy J. (Los Alamos, NM); Higa, Kelvin T. (Ridgecrest, CA); Jorgensen, Betty S. (Jemez Springs, NM); Sanders, Victor E. (White Rock, NM); Son, Steven F. (Los Alamos, NM)

2010-09-07

380

The Nature of Intermolecular Interactions Between Aromatic Amino Acid Residues  

Energy Technology Data Exchange (ETDEWEB)

The nature of intermolecular interactions between aromatic amino acid residues has been investigated by a combination of molecular dynamics and ab initio methods. The potential energy surface of various interacting pairs, including tryptophan, phenilalanine, and tyrosine, was scanned for determining all the relevant local minima by a combined molecular dynamics and conjugate gradient methodology with the AMBER force field. For each of these minima, single-point correlated ab initio calculations of the binding energy were performed. The agreement between empirical force field and ab initio binding energies of the minimum energy structures is excellent. Aromatic-aromatic interactions can be rationalized on the basis of electrostatic and van der Waals interactions, whereas charge transfer or polarization phenomena are small for all intermolecular complexes and, particularly, for stacked structures.

Gervasio, Francesco; Chelli, Riccardo; Procacci, Piero; Schettino, Vincenzo

2002-05-01

 
 
 
 
381

Kinetics of electron transfer through the respiratory chain.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We show that the rate at which electrons pass through the respiratory chain in mitochondria and respiring prokaryotic cells is described by the product of three terms, one describing electron donation, one acceptance, and a third, the thermodynamic drive. We apply the theory of nonequilibrium thermo...

Jin, Qusheng; Bethke, Craig M

382

Dynamic Control of Electron Transfers in Diflavin Reductases  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 f...

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

383

The Rehm-Weller experiment in view of distant electron transfer.  

UK PubMed Central (United Kingdom)

The driving-force dependence of bimolecular fluorescence quenching by electron transfer in solution, the Rehm-Weller experiment, is revisited. One of the three long-standing unsolved questions about the features of this experiment is carefully analysed here, that is, is there a diffusional plateau? New experimental quenching rates are compiled for a single electron donor, 2,5-bis(dimethylamino)-1,3-benzenedicarbonitrile, and eighteen electron acceptors in acetonitrile. The data are analysed in the framework of differential encounter theory by using an extended version of the Marcus theory to model the intrinsic electron-transfer step. Only by including the hydrodynamic effect and the solvent structure can the experimental findings be well modelled. The diffusional control region, the "plateau", reveals the inherent distance dependence of the reaction, which is shown to be a general feature of electron transfer in solution.

Rosspeintner A; Kattnig DR; Angulo G; Landgraf S; Grampp G

2008-01-01

384

Transfer of single electrons and single cooper pairs in nanojunction circuits  

Energy Technology Data Exchange (ETDEWEB)

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

Devoret, M.H.; Esteve, D.; Urbina, C. [CEA Centre d`Etudes de Saclay, 91 - Gif-sur-Yvette (France). Dept. de Recherche sur l`Etat Condense, les Atomes et les Molecules

1994-12-31

385

Beyond frontier molecular orbital theory: a systematic electron transfer model (ETM) for polar bimolecular organic reactions.  

UK PubMed Central (United Kingdom)

Polar bimolecular reactions often begin as charge-transfer complexes and may proceed with a high degree of electron transfer character. Frontier molecular orbital (FMO) theory is predicated in part on this concept. We have developed an electron transfer model (ETM) in which we systematically transfer one electron between reactants and then use density functional methods to model the resultant radical or radical ion intermediates. Sites of higher reactivity are revealed by a composite spin density map (SDM) of odd electron character on the electron density surface, assuming that a new two-electron bond would occur preferentially at these sites. ETM correctly predicts regio- and stereoselectivity for a broad array of reactions, including Diels-Alder, dipolar and ketene cycloadditions, Birch reduction, many types of nucleophilic additions, and electrophilic addition to aromatic rings and polyenes. Conformational analysis of radical ions is often necessary to predict reaction stereochemistry. The electronic and geometric changes due to one-electron oxidation or reduction parallel the reaction coordinate for electrophilic or nucleophilic addition, respectively. The effect is more dramatic for one-electron reduction.

Cahill KJ; Johnson RP

2013-03-01

386

Intermolecular interactions for hydrocarbons on Wyodak coal  

Energy Technology Data Exchange (ETDEWEB)

Adsorption enthalpies have been measured for hydrocarbons interacting with Wyodak coal surfaces. A different dependence of adsorption enthalpy on electronic polarizability has been found for saturated and for unsaturated hydrocarbons. Adsorption enthalpies for all 1-alkenes studied decreased by the same amount ({approximately}1.2 kcal/mol) when the coal was heated to 200{degrees}C, independent of the alkene`s size. This value (1.2 kcal/mol) represents the strength of the specific interaction between an alkene double bond and a carboxylate or ion-exchange site on the coal. Plots of adsorption enthalpy vs. electronic polarizability are steeper for unsaturated hydrocarbons (alkenes and benzene) than for saturated hydrocarbons (alkanes), demonstrating that alkenes and aromatics experience stronger nonspecific van der Waals forces than those experienced by alkanes. A dispersive surface energy of {approximately}20 mJ/m{sup 2} has been measured for Wyodak coal. This quantity depends on interactions with alkanes only. In contrast, data for unsaturated hydrocarbons demonstrate that components of the Wyodak surface produce complex intermolecular forces on this coal.

Glass, A.S.; Stevenson, D.S. [Univ. of Dayton, OH (United States)

1996-10-01

387

A cytochrome C electron transfer switch modulated by heme ligation and isomerization of a peptidyl-prolyl bond.  

UK PubMed Central (United Kingdom)

Intermolecular electron transfer (ET) between hexaamineruthenium(II), a(6) Ru(2+) , and a K73H/K79A variant of iso-1-cytochrome c, iso-1-Cytc, is used to study conformational ET switches mediated by His73-heme ligation and cis to trans isomerization of the Ile75-Pro76 peptidyl-prolyl bond of iso-1-Cytc. The biomolecular rate constant for ET to the native state of K73H/K79A iso-1-Cytc is ?270 mM(-1) s(-1) near neutral pH. The unimolecular conformational ET switches due to His73-heme ligation and the Ile75-Pro76 peptidyl-prolyl bond gate ET at rate constants of 5 to 10 s(-1) and 0.05 to 0.06 s(-1) . Thus, at 1 mM a(6) Ru(2+) , these conformational ET switches slow electron transfer by about 50- and 5000-fold, respectively. The conformational ET switches are populated between pH 5 and 7, providing a means of modulating ET in this redox protein over several orders of magnitude by simply changing pH. The conformationally-gated ET measurements are analyzed in the context of previous pH jump measurements on the His73-heme alkaline transition of K73H/K79A iso-1-Cytc. The ability to obtain microscopic rate constants with conformationally-gated ET measurements has allowed more precise determination of the pK(a) s of the three ionizable groups that mediate population of the His73-heme ET switch. We have also been able to show that the ionizable group with a pK(a) near 9 stabilizes the His73-heme conformer relative to the native state of iso-1-Cytc and that contrary to the conclusions from our pH jump studies, this ionization does not strongly affect the rate of the Ile75-Pro76 peptidyl-prolyl isomerization. © 2012 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 100: 114-124, 2013.

Bandi S; Bowler BE

2013-04-01

388

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

Energy Technology Data Exchange (ETDEWEB)

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

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

1984-01-01

389

Periodic field control of long range electron transfer in dynamically disordered media  

International Nuclear Information System (INIS)

The control of long-range electron transfer in dynamically disordered media like proteins by periodic fields is studied within a driven spin-boson model. It is assumed that the transferred electron strongly couples to a specific protein vibration and moves through a molecular bridge by virtue of the superexchange mechanism. The bridge should undergo transitions between conducting and non-conducting states resulting from stochastic jumps between the various protein conformations. Considering the equilibrium protein modes in a manner similar to the noninteracting blip approximation, a set of coupled generalized master equations can be derived. They describe the electron transfer averaged with respect to the bridge fluctuations and include the external field nonperturbatively. A detailed analysis is carried out for the case of a fast periodic field resulting in an analytical expression for the effective transfer rate. It is demonstrated that a strong periodic field can invert the direction of the gated electron transfer. Furthermore, a field-induced crossover is discussed between the quasi-adiabatic (gated) regime and the nonadiabatic regime of electron transfer. (author).

1997-01-01

390

Electron transfer of carbonylmetalate radical pairs: femtosecond visible spectroscopy of optically excited ion pairs  

Energy Technology Data Exchange (ETDEWEB)

Charge transfer excitation at 640 nm of the cobaltocenium tetracarbonylcobaltate ion pair, [Cp{sub 2}Co{sup +}{vert_bar}Co(CO){sub 4}{sup -}], was monitored in 1,2- dichloroethane solution by femtosecond transient visible absorption spectroscopy. The absorption prepares a neutral radical pair that can undergo spontaneous back electron transfer, and which shows a double peaked spectrum with features at 760 and 815 nm at 3 ps delay time. Transient decay times of 5.8{+-}0.5 ps were measured by monitoring the decay of Co(CO){sub 4} at 757 nm and 780 nm, and these are assigned to the back electron transfer step. The ET kinetics are consistent with the previously reported rates of electron transfer that were measured for specific vibrational states by picosecond transient IR.

Wen, X.; Spears, K.G. [Northwestern Univ., Evanston, IL (United States). Dept. of Chemistry; Wiederrecht, G.P.; Wasielewski, M.R. [Argonne National Lab., IL (United States)

1997-02-01

391

ESR studies of radiation induced electron transfer between myosin and caffeic acid  

International Nuclear Information System (INIS)

The mechanism of radiation induced electron transfer within a series of binary molecular aggregates, which were composed of myosin and caffeic acid with varied molar ratios (r) of amino acid residues in myosin to caffeic acid, has been studied by resolution of composite ESR spectra recorded at 77 K. A series of spin transfer ratios (RST) defined as the spin concentration ratios of caffeic acid anion radical arising from transfer of captured electron by peptide chain of myosin to that from directly trapping of secondary electrons by caffeic acid were obtained. A series of RST were plotted against r varied from 1:1 to 100:1. A linear relationship between RSt and r demonstrates that RSt increase linearly with decrease of caffeic acid content. The capture of radiation induced secondary electrons depend on the electron affinities of components including electron affinitive amino acid residues and peptide carbonyl of myosin and caffeic acid. The process of electron transfer along peptide chain and trapping on caffeic acid finally has been elucidated based on the comparison of the energies of lowest empty molecular orbital (ELUMO) of the electron affinitive components and reaction rate constants of eaq- with these components respectively using pulse radiolysis techniques

1994-01-01