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1

Photoinduced intermolecular electron transfer in complex liquids: Experiment and theory  

Science.gov (United States)

Photoinduced intermolecular electron transfer between Rhodamine 3B and N,N-dimethylaniline has been studied in a series of seven liquids: acetonitrile, ethanol, propylene glycol, and mixtures of ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol. In each liquid, the donor and acceptors have different diffusion constants and experience distinct dielectric properties. Ps time-dependent fluorescence measurements and steady-state fluorescence yield measurements were made and analyzed using a detailed statistical mechanical theory that includes a distance-dependent Marcus rate constant, diffusion with the hydrodynamic effect, and solvent structure. All solvent-dependent parameters necessary for calculations were measured, including dielectric constants, diffusion constants, and redox potentials, leaving the electronic coupling unknown. Taking the distance-dependence of the coupling to be ?=1 Å-1, data were fit to a single parameter, the coupling matrix element at contact, J0. The theory is able to reproduce both the functional form of the time-dependence and the concentration-dependence of the data in all seven liquids by fitting only J0. Despite the substantial differences in the properties of the experimental systems studied, fits to the data are very good and the values for J0 are very similar for all solvents.

Tavernier, H. L.; Kalashnikov, M. M.; Fayer, M. D.

2000-12-01

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

3

Electron dynamics and intermolecular energy transfer in aqueous solutions studied by X-ray electron spectroscopy  

Science.gov (United States)

X-ray photoelectron spectroscopy measurements from a vacuum liquid microjet are performed to investigate the electronic structure of aqueous solutions. Here, focus is on the excited-state dynamics of chloride and hydroxide anions in water, following core-level excitation. A series of Cl^-(aq) charge-transfer-to-solvent (CTTS) states, and their ultrafast relaxation, on the time scale of the core hole, is identified from the occurrence of spectator Auger decay. Resonant oxygen 1s excitation of aqueous hydroxide, in contrast, leads to non-local decay, involving energy transfer into a neighboring water molecule. This channel is argued to arise from the weak hydrogen donor bond of OH^-(aq), and thus identifies a special transient hydration configuration, which can explain hydroxide's unusual and fast transport in water. Analogous measurements from pure water point to a similar relaxation channel, which is concluded from a strong isotope effect. The characteristic resonance spectral features are considerably stronger for H2O(aq) than for D2O(aq). As for OH^-(aq) the results can be understood in terms of energy transfer from the excited water molecule to a neighbor water molecule.

Winter, Bernd

2009-03-01

4

Photoinduced intermolecular electron transfer and off-resonance Raman characteristics of Rhodamine 101/N,N-diethylaniline  

International Nuclear Information System (INIS)

Highlights: • Mechanism of PIET reaction process for the Rh101+/DEA system is investigated. • The significant geometrical changes of the charge–transfer complex are explained. • Forward Electron transfer from DEA to Rh101+? occurs with lifetime of 425–560 fs. • Backward electron transfer occurs with a time constant of 46.16–51.40 ps. • Intramolecular vibrational relaxation occurs with lifetime of 2.77–5.39 ps. - Abstract: The ultrafast photoinduced intermolecular electron transfer (PIET) reaction of Rhodamine 101 (Rh101+) in N,N-diethylaniline (DEA) was investigated using off-resonance Raman, femtosecond time-resolved multiplex transient grating (TG) and transient absorption (TA) spectroscopies. The Raman spectra indicate that the C=C stretching vibration of the chromophore aromatic ring is more sensitive to ET compared with the C-C stretching mode. The ultrafast photoinduced intermolecular forward ET (FET) from DEA to Rh101+? occurs on a time scale of ?FET = 425–560 fs. The backward ET (BET) occurs in the inverted region with a time constant of ?BET = 46.16–51.40 ps. The intramolecular vibrational relaxation (IVR) process occurs on the excited state potential energy surface with the time constant of ?IVR = 2.77–5.39 ps

5

Inner reorganization limiting electron transfer controlled hydrogen bonding: intra- vs. intermolecular effects.  

Science.gov (United States)

In this work, experimental evidence of the influence of the electron transfer kinetics during electron transfer controlled hydrogen bonding between anion radicals of metronidazole and ornidazole, derivatives of 5-nitro-imidazole, and 1,3-diethylurea as the hydrogen bond donor, is presented. Analysis of the variations of voltammetric EpIcvs. log?KB[DH], where KB is the binding constant, allowed us to determine the values of the binding constant and also the electron transfer rate k, confirmed by experiments obtained at different scan rates. Electronic structure calculations at the BHandHLYP/6-311++G(2d,2p) level for metronidazole, including the solvent effect by the Cramer/Truhlar model, suggested that the minimum energy conformer is stabilized by intramolecular hydrogen bonding. In this structure, the inner reorganization energy, ?i,j, contributes significantly (0.5 eV) to the total reorganization energy of electron transfer, thus leading to a diminishment of the experimental k. PMID:24653999

Martínez-González, Eduardo; Frontana, Carlos

2014-05-01

6

Intermolecular photoinduced electron-transfer processes between C{sub 60} and aniline derivatives in benzonitrile  

Energy Technology Data Exchange (ETDEWEB)

The quenching behavior of the triplets of C{sub 60} by various aniline derivatives (1a-d and 2a-e) was investigated by means of laser flash photolysis in benzonitrile at 293K. Electron transfer process was proposed to be the main mechanism because of the direct detection of radical ions of aniline derivatives and C{sub 60} in time-resolved transient absorption spectra. The quenching rate constants (k{sub q}) of {sup 3}C{sub 60}* by different substrates determined at 740nm approach or reach the diffusion-controlled limit. DFT method was employed to calculate the unknown oxidation potentials of substrates in solution. With these E{sub ox} values, free energy changes ({delta}G) were obtained through Rehm-Weller equation. Dependence of observed quenching rate constants on the free energy changes further indicates the photoinduced reactions between {sup 3}C{sub 60}* and substrates proceed through an electron transfer mechanism. Obtained k{sub q} values for the aniline derivatives are impacted obviously by ground-state configurations and the kinds substituents quantified by Hammett {sigma} constant. Good correlation between logk{sub q} and {sigma} values conforms to the empirical Hammett equation. A more negative {rho} value (-3.356) was gained for anilines (2a-e) than that of N,N-dimethylanilines (1a-d) (-1.382), which suggests a more susceptible reactivity for the former substrates. Charge density distribution of reaction center ''N'' originated from quantum calculation supports this suggestion. In addition, a relationship between quenching rate constants and solvent viscosity was gained from C{sub 60}/dimethyl-p-toluidine system in altered mixtures of acetonitrile and toluene.

Pan Yang [Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China)]. E-mail: panyang@ustc.edu; Tang Wenjian [Department of Chemistry, University of Science and Technology of China, Hefei 230026 (China); Yu Tangqin [Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Wang Jinting [Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China); Fu Yao [Department of Chemistry, University of Science and Technology of China, Hefei 230026 (China); Wang Guanwu [Department of Chemistry, University of Science and Technology of China, Hefei 230026 (China); Yu Shuqin [Department of Chemical Physics, University of Science and Technology of China, Hefei 230026 (China)]. E-mail: sqyu@ustc.edu.cn

2007-10-15

7

Electronic transitions and intermolecular forces  

International Nuclear Information System (INIS)

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.)

8

Potassium ion controlled switching of intra- to intermolecular electron transfer in crown ether appended free-base porphyrin-fullerene donor-acceptor systems.  

Science.gov (United States)

Photoinduced electron transfer in intramolecularly interacting free-base porphyrin bearing one or four 18-crown-6 ether units at different positions of the porphyrin macrocycle periphery and pristine fullerene was investigated in polar benzonitrile and nonpolar o-dichlorobenzene and toluene solvents. Owing to the presence of two modes of binding, stable dyads were obtained in which the binding constants, K, were found to range between 4.2 x 10(3) and 10.4 x 10(3) M(-1) from fluorescence quenching data depending upon the location and number of crown ether entities on the porphyrin macrocycle and the solvent. Computational studies using the B3LYP/3-21G() method were employed to arrive at the geometry and electronic structure of the intramolecular dyads. The energetics of the redox states of the dyads were established from cyclic voltammetric studies. Under the intramolecular conditions, both the steady-state and time-resolved emission studies revealed efficient quenching of the singlet excited free-base porphyrin in these dyads, and the measured rates of charge separation, k(CS), were found to be in the 10(8)-10(9) s(-1) range. Nanosecond transient absorption studies were performed to characterize the electron-transfer products and to evaluate the charge-recombination rates. Shifting of the electron-transfer pathway from the intra- to intermolecular route was achieved by complexing potassium ions to the crown ether cavity(ies) in benzonitrile. This cation complexation weakened the intramolecular interactions between fullerene and the crown ether appended free-base porphyrin supramolecules, and under these conditions, intermolecular type interactions were mainly observed. Reversible inter- to intramolecular electron transfer was also accomplished by extracting the potassium ions of the complex with the addition of 18-crown-6. The present study nicely demonstrates the application of supramolecular methodology to control the excited-state electron-transfer path in donor-acceptor dyads. PMID:16571036

D'Souza, Francis; Chitta, Raghu; Gadde, Suresh; Zandler, Melvin E; McCarty, Amy L; Sandanayaka, Atula S D; Araki, Yasuyaki; Ito, Osamu

2006-04-01

9

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

10

Chemical Exchange Saturation Transfer by Intermolecular Double Quantum Coherence  

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A number of contrast enhancement effects based on the use of intermolecular multiple-quantum coherences, or distant dipolar field effects are known. This phenomenon is based on the dependence on the m-th power of the initial magnetization (where m is the coherence order used). In this article we describe the contrast enhancement based on chemical exchange saturation transfer and NOE, which is achieved by the use of intermolecular double-quantum coherences (iDQC). The method was validated usin...

Ling, Wen; Eliav, Uzi; Navon, Gil; Jerschow, Alexej

2008-01-01

11

Intra- and intermolecular energy transfer in H2+OH collisions  

International Nuclear Information System (INIS)

We have used the method of quasiclassical dynamics to investigate intra- and intermolecular energy transfer in H2+OH collisions. Energy transfer has been investigated as function of translational temperature, rotational energy, and vibrational energy. The energy transfer mechanism is complex with ten types of energy transfer possible, and evidence was found for all types. There is much more exchange between the translational degree of freedom and the H2 vibrational degree of freedom than there is between translation and OH vibration. Translational energy is transferred to the rotational degrees of freedom of each molecule, and this occurs more readily for OH than H2. Both molecules exhibited intramolecular energy transfer from vibration to rotation, and this was a major pathway for vibrational deactivation. Evidence was also found for the intermolecular transfer of energy from vibration to the rotational and vibrational degrees of freedom of the other molecule

12

Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions  

Energy Technology Data Exchange (ETDEWEB)

A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 77/sup 0/K. Good agreement between the model and the experimental kinetic results was obtained.

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

1982-04-15

13

Effects of competition for charge capture from the matrix on intermolecular electron-tunneling reactions  

International Nuclear Information System (INIS)

A general method is presented for correcting for the direct capture of matrix charges by the acceptor in an intermolecular electron-transfer reaction in a rigid medium. The method is based on a two-step electron-tunneling model that takes into account the correlation between matrix charge capture and intermolecular electron transfer. As an experimental test of the method, electron transfer from the anion of cinnamaldehyde to neutral pryomellitic dianhydride was studied in 2-methyltetrahydrofuran glass at 770K. Good agreement between the model and the experimental kinetic results was obtained

14

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.

Takeshi Sugahara

2012-05-01

15

Sequence-specific electron injection into DNA from an intermolecular electron donor.  

Science.gov (United States)

Electron transfer in DNA has been intensively studied to elucidate its biological roles and for applications in bottom-up DNA nanotechnology. Recently, mechanisms of electron transfer to DNA have been investigated; however, most of the systems designed are intramolecular. Here, we synthesized pyrene-conjugated pyrrole-imidazole polyamides (PPIs) to achieve sequence-specific electron injection into DNA in an intermolecular fashion. Electron injection from PPIs into DNA was detected using 5-bromouracil as an electron acceptor. Twelve different 5-bromouracil-containing oligomers were synthesized to examine the electron-injection ability of PPI. Product analysis demonstrated that the electron transfer from PPIs was localized in a range of 8 bp from the binding site of the PPIs. These results demonstrate that PPIs can be a useful tool for sequence-specific electron injection. PMID:23439569

Morinaga, Hironobu; Takenaka, Tomohiro; Hashiya, Fumitaka; Kizaki, Seiichiro; Hashiya, Kaori; Bando, Toshikazu; Sugiyama, Hiroshi

2013-04-01

16

Substrate binding-dissociation and intermolecular electron transfer in cytochrome c oxidase are driven by energy-dependent conformational changes in the enzyme and substrate.  

Science.gov (United States)

Reduction of O? by cytochrome c oxidase (COX) is critical to the cellular production of adenosine-5'-triphosphate; COX obtains the four electrons required for this process from ferrocytochrome c. The COX-cytochrome c enzyme-substrate complex is stabilized by electrostatic interactions via carboxylates on COX and lysines on cytochrome c. Conformational changes are believed to play a role in ferrocytochrome c oxidation and release and in rapid intramolecular transfer of electrons within COX, but the details are unclear. To gather specific information about the extent and relevance of conformational changes, we performed bioinformatics studies using the published structures of both proteins. For both proteins, we studied the surface accessibility and energy, as a function of the proteins' oxidation state. The residues of reduced cytochrome c showed greater surface accessibility and were at a higher energy than those of the oxidized cytochrome c. Also, most residues of the core subunits (I, II, and III) of COX showed low accessibility, ?35%, and compared to the oxidized subunits, the reduced subunits had higher energies. We concluded that substrate binding and dissociation is modulated by specific redox-dependent conformational changes. We further conclude that high energy and structural relaxation of reduced cytochrome c and core COX subunits drive their rapid electron transfer. PMID:23586831

Ashe, Damian; Alleyne, Trevor; Sampson, Valerie

2012-01-01

17

Mechanistic studies of photoinduced intramolecular and intermolecular electron transfer processes in RuPt-centred photo-hydrogen-evolving molecular devices.  

Science.gov (United States)

The photoinduced electron transfer properties of two photo-hydrogen-evolving molecular devices (PHEMDs) [(bpy)2Ru(II)(phen-NHCO-bpy-R)Pt(II)Cl2](2+) (i.e., condensation products of [Ru(bpy)2(5-amino-phen)](2+) and (4-carboxy-4?-R-bpy)PtCl2; bpy = 2,2?-bipyridine, phen = 1,10-phenanthroline; RuPt-COOH for R = COOH and RuPt-CN for R = CN) were investigated. RuPt-CN demonstrates higher photocatalytic performance relative to RuPt-COOH arising from a larger driving force for the intramolecular photoinduced electron transfer (PET) associated with a stronger electron-withdrawing effect of R (?GPET = ?0.43 eV for RuPt-CN and ?0.16 eV for RuPt-COOH). This is the first study on PET events using ultrafast spectroscopy. Dramatic enhancement is achieved in the rate of PET in RuPt-CN (1.78 × 1010 s(?1)) relative to RuPt-COOH (3.1 × 109 s(?1)). For each system, the presence of three different conformers giving rise to three different PET rates is evidenced, which are also discussed with the DFT results. Formation of a charge-separated (CS) state [(bpy)2Ru(III)(phen-NHCO-bpy(??)-R)Pt(II)Cl2](2+) in the sub-picosecond time regime and recombination in the picosecond time regime are characterized spectrophotometrically. The CS-state formation was found to compete with reductive quenching of the triplet excited state by EDTA whose dianionic form ion-pairs with dicationic RuPt-COOH. Thus, a key intermediate [(bpy)2Ru(II)(phen-NHCO-bpy(??)-R)Pt(II)Cl2](+) (i.e., the one-electron-reduced species) prior to the H2 formation was found to be formed either via reduction of the CS state by EDTA or via formation of [(bpy)2Ru(II)(phen(??)-NHCO-bpy-R)Pt(II)Cl2](+) by reductive quenching of the triplet excited state. More importantly, it is also shown that some of the conformers in solution possess a CS lifetime sufficiently long to drive hydrogen evolution from water. PMID:24316670

Suneesh, Chettiyam Veettil; Balan, Bijitha; Ozawa, Hironobu; Nakamura, Yuki; Katayama, Tetsuro; Muramatsu, Masayasu; Nagasawa, Yutaka; Miyasaka, Hiroshi; Sakai, Ken

2014-01-28

18

The study of intermolecular energy transfers in electronic energy quenching for molecular collisions N{sub 2}-N{sub 2}, N{sub 2}-O{sub 2}, O{sub 2}-O{sub 2}  

Energy Technology Data Exchange (ETDEWEB)

Contributions of intermolecular electron energy transfers in the electronic quenching are calculated for molecular collisions N{sub 2}(A{sup 3}{sigma}{sub u}{sup +}, W{sup 3}{delta}{sub u})+N{sub 2}(X{sup 1}{sigma}{sub g}{sup +}, v=0), N{sub 2}(A{sup 3}{sigma}{sub u}{sup +})+N{sub 2}(X{sup 1}{sigma}{sub g}{sup +}, v{>=}0), N{sub 2}(A{sup 3}{sigma}{sub u}{sup +})+O{sub 2}(X{sup 3}{sigma}{sub g}{sup -}, v=0-2), O{sub 2}(a{sup 1}{delta}{sub g}, b{sup 1}{sigma}{sub g}{sup +})+O{sub 2}(X{sup 3}{sigma}{sub g}{sup -}, v=0-2). The calculation has allowed one to estimate the product branching ratios. It is shown that there is a dependence of the calculated rate coefficients on the vibrational excitation of N{sub 2}(X{sup 1}{sigma}{sub g}{sup +}) and O{sub 2}(X{sup 3}{sigma}{sub g}{sup -}) molecules. In many cases, the calculated rate coefficients have a good agreement with available experimental data. (orig.)

Kirillov, A.S. [Kola Science Centre RAS, Apatity (Russian Federation). Polar Geophysical Inst.

2008-07-01

19

Electronic Structure Theory for Radicaloid Systems and Intermolecular Interactions  

Science.gov (United States)

A radical molecule contains one or more electrons that are unpaired. A radicaloid may be defined as a molecule in which there are that are partially unpaired. As a result, the electronic structure of the radicaloid can be quite complicated for a variety of reasons. For a singlet biradicaloid, the singlet and triplet wavefunction can be quite close energetically which can lead to problems when trying to describe the system with a single determinant. The simplest solution to this problem is to allow the wavefunction to break spin-symmetry in order to get a lower energy. Unfortunately this action can lead to wavefunctions that are no longer eigenfunctions of the operator. In the second chapter we investigate a distannyne which has a biradicaloid resonance structure. By examining the orbital Hessian, it is discovered that the spin-symmetric solution is a saddle-point in wavefunction space and is structurally different than the spin-polarized solution. We then increase the complexity of the model system and see that the spin-symmetric solution is only a minimum for the exact experimental system and not for a simplified model system in which bulky organic substituents are replaced by simpler phenyl groups. Therefore, the breaking of spin-symmetry is absolutely critical in the small model systems and the full substituents play a non-trivial role. However, the breaking of the spin-symmetry can have consequences for physical quantities when correlated methods are used. At the point of spin polarization or unrestriction the orbital Hessian will have one eigenvalue which is zero. Since the relaxed density matrix in correlated methods like Second-Order Mo ller-Plesset theory (MP2) depend on the inverse of the Hessian, at the unrestriction point this quantity will be undefined. Some unphysical artifacts are identified as a direct consequence of this fact. First, discontinuities in first order molecular properties such as the dipole moment are seen at the geometries associated with unrestriction. Second, the relaxed density matrix itself fails to be N-representable, with natural orbital occupation numbers less than zero and greater than one. Therefore, it is desirable to use a method that is not dependent on the inverse of the Hessian like orbital optimized MP2 (O2). Another system which requires the use of orbital optimization is a neutral soliton on a polyacetylene chain. In this system, the Hartree-Fock reference suffers from severe spin-polarization making the wavefunction physically unreasonable unless a very sophisticated treatment of electron correlation is used to correct this problem. Originally, it was found that computationally expensive methods like CCSD(T) and CASSCF could adequately describe small model chain but not the full system. The O2 method is found to be an dramatic improvement over traditional MP2 which can be feasibly applied to polyenyl chains long enough to characterize the soliton. It is also discovered that density functionals are generally inadequate in describing the half-width of the soliton. Finally, the last chapter takes a slightly different perspective and focuses on the addition of correlation energy to a successful energy decomposition analysis based on absolutely localized molecular orbitals. It is discovered that the resulting new method can adequately describe systems with dispersive intermolecular interactions and large amounts of charge transfer. This scheme is then applied to the water dimer systems and it is found that all of the intermolecular interactions similar in size with the electrostatic interaction being the largest and the dispersive interaction being the smallest. This method is also contrasted with other EDA schemes.

Kurlancheek, Westin

20

Photo-induced intermolecular charge transfer in porphyrin complexes  

CERN Document Server

Optical excitation of the sequential supermolecule H_2P-ZnP-Q induces an electron transfer from the free-base porphyrin (H_2P) to the quinone (Q) via the zinc porphyrin (ZnP). This process is modeled by equations of motion for the reduced density matrix which are solved numerically and approximately analytically. These two solutions agree very well in a great region of parameter space. It is shown that for the majority of solvents the electron transfer occurs with the superexchange mechanism.

Schreiber, M; Kleinekathöfer, U; Schreiber, Michael; Kilin, Dmitry; Kleinekathoefer, Ulrich

2000-01-01

 
 
 
 
21

Photoinduced coupled twisted intramolecular charge transfer and excited-state proton transfer via intermolecular hydrogen bonding: A DFT/TD-DFT study  

Science.gov (United States)

We discuss theoretically the geometric and electronic structure properties of the thiazolidinedione derivative A and its hydrogen-bonded complex in dimethylformamide (DMF) solution in the S0 and S1 states. To gain insight into the photoinduced coupled excited-state proton transfer (ESPT) and twisted intramolecular charge transfer (TICT) associated with intermolecular hydrogen bonding, the potential energy profiles are provided along the Osbnd H bond and the twisted angle. It is predicted that TICT in S1 can facilitate ESPT initiated by intermolecular hydrogen-bond strengthening in the S1 state. The coupling of ESPT and TICT is energetically preferable.

Wang, Dandan; Lü, Rui; Yuan, Minghu; Chen, Junsheng; Feng, Liqiang; Fu, Aiping; Tian, Fenghui; Varandas, António J. C.; Chu, Tianshu

2014-08-01

22

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

Science.gov (United States)

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. PMID:23712461

Wang, Yi; Li, Minjie; Zhang, Yumo; Yang, Jin; Zhu, Shaoyin; Sheng, Lan; Wang, Xudong; Yang, Bing; Zhang, Sean Xiao-An

2013-07-28

23

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

24

Formation of an intermolecular charge-transfer compound in UHV codeposited tetramethoxypyrene and tetracyanoquinodimethane  

DEFF Research Database (Denmark)

Ultrahigh vacuum (UHV)-deposited films of the mixed phase of tetramethoxypyrene and tetracyanoquinodimethane (TMP -TCNQ ) on gold have been studied using ultraviolet photoelectron spectroscopy (UPS), x-ray diffraction (XRD), infrared (IR) spectroscopy, and scanning tunneling spectroscopy (STS). The formation of an intermolecular charge-transfer (CT) compound is evident from the appearance of new reflexes in XRD (d =0.894nm and d =0.677nm). A softening of the CN stretching vibration (redshift by 7 cm?-1) of TCNQ is visible in the IR spectra, being indicative of a CT on the order of 0.3e from TMP to TCNQ in the complex. Characteristic shifts in the electronic level positions occur in UPS and STS that are in reasonable agreement with the prediction of density-functional theory (DFT) calculations (GAUSSIAN03 with hybrid functional B3LYP). STS reveals a highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of the CT complex of about 1.25 eV being much smaller than the gaps (>3.0eV) of the pure moieties. The electron-injection and hole-injection barriers are 0.3 eV and 0.5 eV, respectively. Systematic differences in the positions of the HOMOs determined by UPS and STS are discussed in terms of the different information content of the two methods. © 2010 The American Physical Society.

Solovyeva, Vita

2010-01-01

25

Keto-enol tautomerization and intermolecular proton transfer in photoionized cyclopentanone dimer in the gas phase  

Science.gov (United States)

Time-of-flight mass spectra of cyclopentanone and its clusters cooled in a supersonic jet expansion have been measured following 4-, 3-, and 2-photon ionizations by the 2nd, 3rd, and 4th harmonic wavelengths, respectively, of a Q-switched Nd:YAG laser. The mass spectra reveal signatures of energetically favored keto to enol tautomerization of the molecular ion leading to intermolecular proton transfer, and this observation is found sharply dependent on the ionization wavelengths used. Electronic structure calculation predicts that in spite of the energetic preference, keto-enol conversion barrier of isolated molecular ion is high. However, the barrier is significantly reduced in a CH⋯O hydrogen-bonded dimer of the molecule. The transition states associated with tautomeric conversion of both cyclopentanone monomer and dimer cations have been identified by means of intrinsic reaction co-ordinate calculation. In a supersonic jet expansion, although a weakly bound dimer is readily generated, the corresponding cation and also the protonated counterpart are observed only for ionization by 532 nm. For other two ionization wavelengths, these species do not register in the mass spectra, where the competing reaction channels via ?-cleavage of the ring become dominant. In contrast to the report of a recent study, we notice that the intact molecular ion largely survives fragmentations when ionized from the 2-photon resonant 3p Rydberg state as intermediate using nanosecond laser pulses, and the corresponding resonant 3-photon ionization spectrum has been recorded probing the intact molecular ion.

Ghosh, Arup K.; Chatterjee, Piyali; Chakraborty, Tapas

2014-07-01

26

Intermolecular and intramolecular charge transfer in polymethylphenylsilane/C60 films  

Science.gov (United States)

The influence of C60 on fluorescence spectra, UV-visible spectra and photoconductivity of polymethylphenylsilane (PMPS) has been studied. The results show that the photoconductivity of PMPS doped with C60 increases by one order of magnitude. The fluorescence and UV-visible analyses indicate that an intermolecular charge-transfer complex of PMPS and C60 may be formed. Compared with C60-doped PMPS, the C60-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

2004-09-01

27

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

28

Intermolecular and intramolecular charge transfer in polymethylphenylsilane/C60 films  

International Nuclear Information System (INIS)

The influence of C60 on fluorescence spectra, UV-visible spectra and photoconductivity of polymethylphenylsilane (PMPS) has been studied. The results show that the photoconductivity of PMPS doped with C60 increases by one order of magnitude. The fluorescence and UV-visible analyses indicate that an intermolecular charge-transfer complex of PMPS and C60 may be formed. Compared with C60-doped PMPS, the C60-linked PMPS displays higher photoconductivity than expected, which may come from the intramolecular charge-transfer process

29

Supramolecular patterns controlled by electron interference and direct intermolecular interactions.  

Science.gov (United States)

Whereas all 230 three-dimensional space groups occur in organic crystals, out of only 17 plane groups some highly symmetric ones such as p31m have not yet been observed in two-dimensional (2D) crystals of organic molecules. Here a kagome network with p31m symmetry is reported for cobalt phthalocyanine on Cu(111). This unusual structure results from substrate-induced reduction of molecular symmetry and substrate-mediated interaction via quantum interference of surface electrons. These interactions provide additional control over the symmetry of 2D crystals of phthalocyanines and lead to a variety of other symmetries in self-assembled arrays. PMID:19594153

Wang, Yongfeng; Ge, Xin; Manzano, Carlos; Kröger, Jörg; Berndt, Richard; Hofer, Werner A; Tang, Hao; Cerda, Jorge

2009-08-01

30

The electronic structure and the ferromagnetic intermolecular interactions in the crystal of TEMPO radicals  

International Nuclear Information System (INIS)

Based on the generalized gradient approximation, full potential linearized augmented plane wave (FP-LAPW) calculations have been performed to study the electronic band structure and the intermolecular ferromagnetic (FM) interactions for the two TEMPO radicals 4-Benzylideneamino-2,2,6,6-tetramethylpiperidin-1-oxyl (1) and 4-(2-naphtylmethyleneamino)-2,2,6,6-tetramethylpiperidin-1-oxyl (2). The total and the partial density of states and the atomic spin magnetic moments are calculated and discussed. The calculation revealed that the two TEMPO radicals have the intermolecular FM interactions, and the spontaneous magnetic moment is 1.0 ? B per molecule of each crystal, which is in good agreement with the experimental value. It is found that the unpaired electrons in these compounds are localized in a molecular orbital constituted primarily of ?* (NO) orbital, and the main contribution of the spin magnetic moment comes from the NO-free radical. The origin of FM is also studied in detail

31

On the Reaction Mechanism of the Complete Intermolecular O2 Transfer between Mononuclear Nickel and Manganese Complexes with Macrocyclic Ligands.  

Science.gov (United States)

The recently described intermolecular O2 transfer between the side-on Ni-O2 complex [(12-TMC)Ni-O2 ](+) and the manganese complex [(14-TMC)Mn](2+) , where 12-TMC and 14-TMC are 12- and 14-membered macrocyclic ligands, 12-TMC=1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane and 14-TMC=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, is studied by means of DFT methods. B3LYP calculations including long-range corrections and solvent effects are performed to elucidate the mechanism. The potential energy surfaces (PESs) compatible with different electronic states of the reactants have been analyzed. The calculations confirm a two-step reaction, with a first rate-determining bimolecular step and predict the exothermic character of the global process. The relative stability of the products and the reverse barrier are in line with the fact that no reverse reaction is experimentally observed. An intermediate with a ?-?(1) :?(1) -O2 coordination and two transition states are identified on the triplet PES, slightly below the corresponding stationary points of the quintet PES, suggesting an intersystem crossing before the first transition state. The calculated activation parameters and the relative energies of the two transition sates and the products are in very good agreement with the experimental data. The calculations suggest that a superoxide anion is transferred during the reaction. PMID:25179780

Zapata-Rivera, Jhon; Caballol, Rosa; Calzado, Carmen J; Liakos, Dimitrios G; Neese, Frank

2014-10-01

32

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

33

Electron transfer control in soluble methane monooxygenase.  

Science.gov (United States)

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

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

2014-07-01

34

Sensitivity analysis of rotational energy transfer processes to the intermolecular potential  

International Nuclear Information System (INIS)

This paper considers the sensitivity of rotational energy transfer processes to the variation of parameters within an assumed model intermolecular potential. The following cross sections are considered here: integral state to state, pressure broadening, effective diffusion and viscosity, and final state summed integral cross sections. In order to simplify the calculation of cross sections, attention is restricted to the scattering of an atom and linear rigid rotor. Furthermore, the collision dynamics are approximated by using the infinite order sudden (IOS) method. It is shown that use of the IOS method allows for the very simple generation of first order sensitivity coefficients (i.e., the partial derivative of cross sections with respect to potential parameters). Particular attention is focused upon the sensitivities of different cross sections and combinations of cross sections to the various parameters. The first order sensitivities are also used to derive new coefficients which describe how the potential parameters correlate given a limited set of cross section measurements. These coefficients are shown to be particularly important in determining the degree to which a set of measurements is able to define various parameters of the assumed potential

35

Intermolecular hydrogen transfer catalyzed by a flavodehydrogenase, bakers' yeast flavocytochrome b2  

International Nuclear Information System (INIS)

Bakers yeast flavocytochrome b2 is a flavin-dependent L-2-hydroxy acid dehydrogenase which also exhibits transhydrogenase activity. When a reaction takes place between [2-3H]lactate and a halogenopyruvate, tritium is found in water and at the halogenolactate C2 position. When the halogenopyruvate undergoes halide ion elimination, tritium is also found at the C3 position of the resulting pyruvate. The amount tau of this intermolecular tritium transfer depends on the initial keto acid-acceptor concentration. At infinite acceptor concentration, extrapolation yields a maximal transfer of 97 +/- 11%. This indicates that the hydroxy acid-derived hydrogen resides transiently on enzyme monoprotic heteroatoms and that exchange with bulk solvent occurs only at the level of free reduced enzyme. Using a minimal kinetic scheme, the rate constant for hydrogen exchange between Ered and solvent is calculated to be on the order of 10(2) M-1 S-1, which leads to an estimated pK approximately equal to 15 for the ionization of the substrate-derived proton while on the enzyme. It is suggested that this hydrogen could be shared between the active site base and Flred N5 anion. It is furthermore shown that some tritium is incorporated into the products when the transhydrogenation is carried out in tritiated water. Finally, with [2-2H]lactate-reduced enzyme, a deuterium isotope effect is observed on the rate of bromopyruvate disappearance. Extrapolation to infinite bromopyruvate concentration yields DV = 4.4. An apparent inverse isotope effect is determined for bromide ion elimination. These results strengthen the idea that oxidoreduction and elimination pathways involve a common carbanionic intermediate

36

Nonadiabatic anharmonic electron transfer  

International Nuclear Information System (INIS)

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

37

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

38

Electron transfer to sulfides:  

International Nuclear Information System (INIS)

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

39

Role of Intermolecular Separation in Nanoscale Patterning C60 Films by Local Injection of Electrons from Scanning Tunneling Microscope Tip  

Science.gov (United States)

A systematic study on the polymerization and decomposition of C60 molecules induced by electron injection from scanning tunneling microscope (STM) tips has revealed that increasing intermolecular separation in the lateral directions with respect to the surface reduces both polymerization and decomposition reaction efficiencies and suppresses the spreading effect of polymerization from the electron injection point, down to ˜2 nm under a good condition. This is understood by considering that the wider lateral intermolecular separation and hence the smaller intermolecular spacing vertical to the surface lead to a suppression of electron spreading parallel to the surface but its enhancement normal to the surface, resulting in the small localization of molecular reactions on the surface.

Nakamura, Yoshiaki; Mera, Yutaka; Maeda, Koji

2005-10-01

40

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

2007-08-01

 
 
 
 
41

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.

42

Intramolecular electron transfer in bipyridinium disulfides.  

Science.gov (United States)

Reductive cleavage of disulfide bonds is an important step in many biological and chemical processes. Whether cleavage occurs stepwise or concertedly with electron transfer is of interest. Also of interest is whether the disulfide bond is reduced directly by intermolecular electron transfer from an external reducing agent or mediated intramolecularly by internal electron transfer from another redox-active moiety elsewhere within the molecule. The electrochemical reductions of 4,4'-bipyridyl-3,3'-disulfide (1) and the di-N-methylated derivative (2(2+)) have been studied in acetonitrile. Simulations of the cyclic voltammograms in combination with DFT (density functional theory) computations provide a consistent model of the reductive processes. Compound 1 undergoes reduction directly at the disulfide moiety with a substantially more negative potential for the first electron than for the second electron, resulting in an overall two-electron reduction and rapid cleavage of the S-S bond to form the dithiolate. In contrast, compound 2(2+) is reduced at less negative potential than 1 and at the dimethyl bipyridinium moiety rather than at the disulfide moiety. Most interesting, the second reduction of the bipyridinium moiety results in a fast and reversible intramolecular two-electron transfer to reduce the disulfide moiety and form the dithiolate. Thus, the redox-active bipyridinium moiety provides a low energy pathway for reductive cleavage of the S-S bond that avoids the highly negative potential for the first direct electron reduction. Following the intramolecular two-electron transfer and cleavage of the S-S bond the bipyridinium undergoes two additional reversible reductions at more negative potentials. PMID:24528295

Hall, Gabriel B; Kottani, Rudresha; Felton, Greg A N; Yamamoto, Takuhei; Evans, Dennis H; Glass, Richard S; Lichtenberger, Dennis L

2014-03-12

43

Determination of stepsize parameters for intermolecular vibrational energy transfer: Progress report, May 1, 1987-April 30, 1988  

International Nuclear Information System (INIS)

Intermolecular vibrational energy transfer for highly excited polyatomic molecules is involved in any mechanism in which excitation energy is required (pyrolysis) or in which energy must be removed from a hot source (cooling). The average energy removed per collision, , is a useful quantity to compare efficiency for energy transfer. The objectives of this work are: to determine the dependence of on excitation energy and on the molecular complexity (number of vibrational modes) of substrate and deactivator; to assess the importance of intermolecular attractions (complex formation) on vibrational energy transfer; to obtain detailed information on the energy distribution after collision and to evaluate the importance of on high-temperature unimolecular reactions. This information will be obtained by monitoring the time dependence of the infrared emission, ultraviolet absorption, refractive index and pressure. The results from these complementary techniques will be benchmarked with values from previous studies on the relaxation of chemically activated alkyl and fluoroalkyl radicals. Trajectory calculations simulating energy transfer are being performed for ''generic'' substrate/deactivator pairs to provide additional details and insight on the important parameters. Model calculations are also being performed to determine the feasibility of obtaining information from experimental data for high-temperature unimolecular reactions

44

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 SciELO Brazil | Language: Portuguese Abstract in portuguese [...] 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 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.

2007-08-01

45

Intramolecular Electron Scattering and Electron Transfer Following Autoionization in Dissociating Molecules  

Science.gov (United States)

Resonant Auger decay of core-excited molecules during ultrafast dissociation leads to a Doppler shift of the emitted electrons depending on the direction of the electron emission relative to the dissociation axis. We have investigated this process by angle-resolved electron-fragment ion coincidence spectroscopy. Electron energy spectra for selected emission angles for the electron relative to the molecular axis reveal the occurrence of intermolecular electron scattering and electron transfer following the primary emission. These processes amount to approximately 25% of the resonant atomic Auger intensity emitted in the studied transition.

Kugeler, O.; Prümper, G.; Hentges, R.; Viefhaus, J.; Rolles, D.; Becker, U.; Marburger, S.; Hergenhahn, U.

2004-07-01

46

Intermolecular interactions and charge transfer transitions in aromatic hydrocarbon-tetracyanoethylene complexes.  

Science.gov (United States)

A comprehensive theoretical study of the electronically excited states in complexes between tetracyanoethylene (TCNE) and three aromatic electron donors, benzene, naphthalene and anthracene, was performed with a focus on charge transfer (CT) transitions. The results show that the algebraic diagrammatic construction method to second order (ADC(2)) provides excellent possibilities for reliable calculations of CT states. Significant improvements in the accuracy of the computed transition energies are obtained by using the scaled opposite-spin (SOS) variant of ADC(2). Solvent effects were examined on the basis of the conductor-like screening model (COSMO) which has been implemented recently in the ADC(2) method. The dielectric constant and the refractive index of dichloromethane have been chosen in the COSMO calculations to compare with experimental solvatochromic effects. The computation of optimized ground state geometries and enthalpies of formation has been performed at the second-order Møller-Plesset perturbation theory (MP2) level. By comparison with experimental data and with high-level coupled-cluster methods including explicitly correlated (F12) wave functions, the importance of the SOS approach is demonstrated for the ground state as well. In the benzene-TCNE complex, the two lowest electronic excitations are of CT character whereas in the naphthalene and anthracene TCNE complexes three low-lying CT states are observed. As expected, they are strongly stabilized by the solvent. Geometry optimization in the lowest excited state allowed the calculation of fluorescence transitions. Solvent effects lead to a zero gap between S1 and S0 for the anthracene-TCNE complex. Therefore, in the series of benzene-TCNE to anthracene a change from a radiative to a nonradiative decay mechanism to the ground state is to be expected. PMID:25156236

Aquino, Adélia A J; Borges, Itamar; Nieman, Reed; Köhn, Andreas; Lischka, Hans

2014-10-14

47

Electron transfer: Lower tunnel barriers  

Science.gov (United States)

A better understanding of electron transfer through molecules could provide the basis for many technological breakthroughs. Now, the rate of electron transfer has been enhanced in a family of molecules by making them more rigid, and this phenomenon may be explained by the loss of electronic energy to vibrations.

Miller, John R.

2014-10-01

48

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

49

Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: The case of Euglena gracilis  

International Nuclear Information System (INIS)

In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A498, non fluorescent and B462, fluorescent. Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A498 becomes B462), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B462 form acts as donor for the non-fluorescent A498 form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.

50

Complete Relaxation and Conformational Exchange Matrix (CORCEMA) Analysis of Intermolecular Saturation Transfer Effects in Reversibly Forming Ligand-Receptor Complexes  

Science.gov (United States)

A couple of recent applications of intermolecular NOE (INOE) experiments as applied to biomolecular systems involve the (i) saturation transfer difference NMR (STD-NMR) method and (ii) the intermolecular cross-saturation NMR (ICS-NMR) experiment. STD-NMR is a promising tool for rapid screening of a large library of compounds to identify bioactive ligands binding to a target protein. Additionally, it is also useful in mapping the binding epitopes presented by a bioactive ligand to its target protein. In this latter application, the STD-NMR technique is essentially similar to the ICS-NMR experiment, which is used to map protein-protein or protein-nucleic acid contact surfaces in complexes. In this work, we present a complete relaxation and conformational exchange matrix (CORCEMA) theory (H. N. B. Moseley et al., J. Magn. Reson. B108, 243-261 (1995)) applicable for these two closely related experiments. As in our previous work, we show that when exchange is fast on the relaxation rate scale, a simplified CORCEMA theory can be formulated using a generalized average relaxation rate matrix. Its range of validity is established by comparing its predictions with those of the exact CORCEMA theory which is valid for all exchange rates. Using some ideal model systems we have analyzed the factors that influence the ligand proton intensity changes when the resonances from some protons on the receptor protein are saturated. The results show that the intensity changes in the ligand signals in an intermolecular NOE experiment are very much dependent upon: (1) the saturation time, (2) the location of the saturated receptor protons with respect to the ligand protons, (3) the conformation of the ligand-receptor interface, (4) the rotational correlation times for the molecular species, (5) the kinetics of the reversibly forming complex, and (6) the ligand/receptor ratio. As an example of a typical application of the STD-NMR experiment we have also simulated the STD effects for a hypothetical trisaccharide bound to a protein. The CORCEMA theory for INOE and the associated algorithm are useful in a quantitative interpretation of the intensity changes in the ligand in both the STD-NMR and ICS-NMR, provided the identity of the receptor protons experiencing direct RF saturation is known. The formalism presented here is likely to be useful in the design of bioactive ligands to a specific target protein and in the quantitative mapping of binding epitopes and interfaces between molecules in complexes.

Jayalakshmi, V.; Krishna, N. Rama

2002-03-01

51

Direct observation of radical intermediates during electron transfer between DNA and a ternary copper complex  

International Nuclear Information System (INIS)

The photoinduced electron transfer (PET) reaction within a ternary copper complex [Cu(phen)(Htrp)]+ (Htrp: L-tryptophanato; phen: 1,10-phenanthroline) (1) and in presence of DNA has been studied in homogeneous buffer medium and in reverse micelles. An intramolecular electron transfer occurs within the photoexcited complex (1) from tryptophan to phen. The copper complex can displace ethidium bromide from DNA backbone and on photoexcitation can oxidize DNA in a deoxygenated environment due to intermolecular electron transfer, although the intramolecular electron transfer is thermodynamically favorable. A prominent magnetic field effect (MFE) has been found even in homogeneous aqueous medium for the triplet born radicals both in case of intra and intermolecular electron transfer reactions. In case of intramolecular electron transfer the observation of MFE is similar to that of linked donor-acceptor system. However the observation of MFE for the intermolecular electron transfer between non-covalently bound complex-DNA systems is rather rare. Some non-covalent weak interaction, e.g. hydrophobic interaction between the phen ligand and DNA base pairs and electrostatic force of attraction between [Cu(phen)(Htrp)]+ complex and DNA may lead to partial intercalation of the copper complex within DNA that is responsible for such a rare observation. - Research Highlights: ? On photoexcitation intra-molecular electron transfer occurs from tryptophan (Htrp) to phenanthroline (phen) within [Cu(phen)(Htrp)]ClO4. ? In presence of CT DNA a ground state complex is formed between CT DNA and ternary copper compound. ? On photoexcitation of the complex an intermolecular electron transfer occurs from DNA base to phen instead of Htrp. ? Magnetic field effect has been used to detect the triplet born radical ions in solution and in reverse micelles.

52

Direct observation of radical intermediates during electron transfer between DNA and a ternary copper complex  

Energy Technology Data Exchange (ETDEWEB)

The photoinduced electron transfer (PET) reaction within a ternary copper complex [Cu(phen)(Htrp)]{sup +} (Htrp: L-tryptophanato; phen: 1,10-phenanthroline) (1) and in presence of DNA has been studied in homogeneous buffer medium and in reverse micelles. An intramolecular electron transfer occurs within the photoexcited complex (1) from tryptophan to phen. The copper complex can displace ethidium bromide from DNA backbone and on photoexcitation can oxidize DNA in a deoxygenated environment due to intermolecular electron transfer, although the intramolecular electron transfer is thermodynamically favorable. A prominent magnetic field effect (MFE) has been found even in homogeneous aqueous medium for the triplet born radicals both in case of intra and intermolecular electron transfer reactions. In case of intramolecular electron transfer the observation of MFE is similar to that of linked donor-acceptor system. However the observation of MFE for the intermolecular electron transfer between non-covalently bound complex-DNA systems is rather rare. Some non-covalent weak interaction, e.g. hydrophobic interaction between the phen ligand and DNA base pairs and electrostatic force of attraction between [Cu(phen)(Htrp)]{sup +} complex and DNA may lead to partial intercalation of the copper complex within DNA that is responsible for such a rare observation. - Research Highlights: On photoexcitation intra-molecular electron transfer occurs from tryptophan (Htrp) to phenanthroline (phen) within [Cu(phen)(Htrp)]ClO{sub 4}. In presence of CT DNA a ground state complex is formed between CT DNA and ternary copper compound. On photoexcitation of the complex an intermolecular electron transfer occurs from DNA base to phen instead of Htrp. Magnetic field effect has been used to detect the triplet born radical ions in solution and in reverse micelles.

Dey, Debarati [Department of Chemistry and Environment, Heritage Institute of Technology, Chowbaga Road, Anandapur, P.O. East Kolkata Township, Kolkata-700107 (India); Basu, Samita, E-mail: samita.basu@saha.ac.i [Chemical Sciences Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700 064 (India)

2011-04-15

53

Intermolecular interactions and charge transfer in the 2:1 tetrathiafulvalene bromanil complex, (TTF)2-BA  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The crystal structure of the 2:1 charge-transfer complex of tetrathiafulvalene [2,2′-bis(1,3-dithiolylidene)] and bromanil (tetrabromo-1,4-benzoquinone) [(TTF)2-BA, (C6H4S4)2-C6Br4O2] has been determined by X-ray diffraction at room temperature, 100 and 25 K. No structural phase transition occurs in the temperature range studied. The crystal is made of TTF-BA-TTF sandwich trimers. A charge-transfer estimation between donor and acceptor (0.2 e) molecules is proposed in comparison to the ...

Garci?a-ordun?a, P.

2011-01-01

54

Electron transfer in pnicogen bonds.  

Science.gov (United States)

As a new type of noncovalent interactions, pnicogen bond between a VA group element (N, P, and As) and an electron donor (Lewis base) has grabbed attention in recent several years. Here we employ the block-localized wave function (BLW) based energy decomposition scheme to probe the bonding nature in a series of substituted phosphines X(n)PH(3-n) complexed with ammonia. As the BLW method can derive the optimal monomer orbitals in a complex with the electron transfer among monomers quenched, we can effectively examine the HOMO-LUMO interaction in these pnicogen bonding systems. Among various energy components, electron transfer energy together with the polarization energy dominates the pnicogen bonding energy. Although usually it is assumed that the electron transfer from ammonia to substituted phosphines occurs in the form of n ? ?*(XP) hyperconjugative interaction, we identify a kind of new pathway when X = NO2 and CN, i.e., n ? d?*, which results from the interaction between the ? orbital of cyano or nitro substituent and d orbitals on P. But still this picture of electron transfer using a single pair of orbitals is greatly simplified, as the electron density difference (EDD) maps corresponding to the overall electron transfer processes show the accumulation of electron density on the P side opposite to the X-P bond, with insignificant or even negligible gain of electron density on the substituent group side. Thus, the EDD maps tend to support the concept of ?-hole in pnicogen bonds. PMID:24588109

Guan, Liangyu; Mo, Yirong

2014-10-01

55

Dynamical aspects of intermolecular proton transfer in liquid water and low-density amorphous ices  

Science.gov (United States)

The microscopic dynamics of an excess proton in water and in low-density amorphous ices has been studied by means of a series of molecular dynamics simulations. Interaction of water with the proton species was modelled using a multistate empirical valence bond Hamiltonian model. The analysis of the effects of low temperatures on proton diffusion and transfer rates has been considered for a temperature range between 100 and 298 K at the constant density of 1 g cm-3. We observed a marked slowdown of proton transfer rates at low temperatures, but some episodes are still seen at 100 K. In a similar fashion, mobility of the lone proton gets significantly reduced when temperature decreases below 273 K. The proton transfer in low-density amorphous ice is an activated process with energy barriers between 1-10 kJ/mol depending of the temperature range considered and eventually showing Arrhenius-like behavior. Spectroscopic data indicated the survival of both Zundel and Eigen structures along the whole temperature range, revealed by significant spectral frequency shifts.

Tahat, Amani; Martí, Jordi

2014-05-01

56

Intermolecular energy transfer from UO22+ to Eu3+ in solutions  

International Nuclear Information System (INIS)

The quenching constants for the UO22+ ion fluorescence by the Eu3+ ion in H2O, D2O, potassium formate and acetic acid media were determined by measuring the decrease in intensity of the 5050 A fluorescence peak and the lifetime of the UO22+ ion fluorescence. The energy transferred to the Eu3+ ion was found to be a small fraction of the energy lost by the UO22+ ion by the non-radiative processes. The variations of the quenching constants of the UO22+ ion and the fluorescence lifetimes were determined for different concentrations of potassium formate and acetic acid. These results indicate that the UO22+ ion forms inner sphere complexes with the two ligands mentioned

57

Intramolecular photo-switching and intermolecular energy transfer as primary photoevents in photoreceptive processes: The case of Euglena gracilis  

Energy Technology Data Exchange (ETDEWEB)

In this paper we report the results of measurements performed by FLIM on the photoreceptor of Euglenagracilis. This organelle consists of optically bistable proteins, characterized by two thermally stable isomeric forms: A{sub 498,} non fluorescent and B{sub 462}, fluorescent. Our data indicate that the primary photoevent of Euglena photoreception upon photon absorption consists of two contemporaneous different phenomena: an intramolecular photo-switch (i.e., A{sub 498} becomes B{sub 462}), and a intermolecular and unidirectional Forster-type energy transfer. During the FRET process, the fluorescent B{sub 462} form acts as donor for the non-fluorescent A{sub 498} form of the protein nearby, which acts as acceptor. We hypothesize that in nature these phenomena follow each other with a domino progression along the orderly organized and closely packed proteins in the photoreceptor layer(s), modulating the isomeric composition of the photoreceptive protein pool. This mechanism guarantees that few photons are sufficient to produce a signal detectable by the cell.

Mercatelli, Raffaella; Quercioli, Franco [Istituto Sistemi Complessi, CNR, Via Madonna del Piano 10, 50019 Sesto Fiorentino (Italy); Barsanti, Laura; Evangelista, Valter [Istituto di Biofisica, CNR, Via Moruzzi 1, 56124 Pisa (Italy); Coltelli, Primo [ISTI, CNR, Via Moruzzi 1, 56124 Pisa (Italy); Passarelli, Vincenzo; Frassanito, Anna Maria [Istituto di Biofisica, CNR, Via Moruzzi 1, 56124 Pisa (Italy); Gualtieri, Paolo, E-mail: paolo.gualtieri@pi.ibf.cnr.it [Istituto di Biofisica, CNR, Via Moruzzi 1, 56124 Pisa (Italy)

2009-07-24

58

Intermolecular charge transfer and vibrational analysis of hydrogen bonding in acetazolamide  

Science.gov (United States)

In the present work the structural and spectral characteristics of acetazolamide have been studied by methods of infrared, Raman spectroscopy and quantum chemistry. Electrostatic potential surface, optimized geometry, harmonic vibrational frequencies, infrared intensities and activities of Raman scattering were calculated by density functional theory (DFT) employing B3LYP with complete relaxation in the potential energy surface using 6-311++G(d,p) basis set. Based on these results, we have discussed the correlation between the vibrational modes and the structure of the dimers of acetazolamide. The calculated vibrational spectra of three dimers of acetazolamide have been compared with observed spectra, and the assignment of observed bands was carried out using potential energy distribution. The observed spectra agree well with the values computed from the DFT. A comparison of observed and calculated vibrational spectra clearly shows the effect of hydrogen bonding. The frequency shifts observed for the different dimers are in accord with the hydrogen bonding in acetazolamide. Natural bond orbital (NBO) analyses reflect the charge transfer interaction in the individual hydrogen bond units and the stability of different dimers of acetazolamide.

Chaturvedi, Deepika; Gupta, Vineet; Tandon, Poonam; Sharma, Anamika; Baraldi, C.; Gamberini, M. C.

2012-12-01

59

Probing intermolecular protein-protein interactions in the calcium-sensing receptor homodimer using bioluminescence resonance energy transfer (BRET)  

DEFF Research Database (Denmark)

The calcium-sensing receptor (CaR) belongs to family C of the G-protein coupled receptor superfamily. The receptor is believed to exist as a homodimer due to covalent and non-covalent interactions between the two amino terminal domains (ATDs). It is well established that agonist binding to family C receptors takes place at the ATD and that this causes the ATD dimer to twist. However, very little is known about the translation of the ATD dimer twist into G-protein coupling to the 7 transmembrane moieties (7TMs) of these receptor dimers. In this study we have attempted to delineate the agonist-induced intermolecular movements in the CaR homodimer using the new bioluminescence resonance energy transfer technique, BRET2, which is based on the transference of energy from Renilla luciferase (Rluc) to the green fluorescent protein mutant GFP2. We tagged CaR with Rluc and GFP2 at different intracellular locations. Stable and highly receptor-specific BRET signals were obtained in tsA cells transfected with Rluc- and GFP2-tagged CaRs under basal conditions, indicating that CaR is constitutively dimerized. However, the signals were not enhanced by the presence of agonist. These results could indicate that at least parts of the two 7TMs of the CaR homodimer are in close proximity in the inactivated state of the receptor and do not move much relative to one another upon agonist activation. However, we cannot exclude the possibility that the BRET technology is unable to register putative conformational changes in the CaR homodimer induced by agonist binding because of the bulk sizes of the Rluc and GFP2 molecules.

Jensen, Anders A.; Hansen, Jakob L

2002-01-01

60

Mismatched Hartmann-Hahn conditions cause proton-mediated intermolecular magnetization transfer between dilute low-spin nuclei in NMR of static solids.  

Science.gov (United States)

Mismatched Hartmann-Hahn conditions between the protons and dilute spins (such as 15N) are found to cause intermolecular magnetization transfer between the low-gamma nuclei over long distances. This transfer is purely proton mediated and occurs even in the absence of direct 15N-15N couplings. This has been demonstrated experimentally using a static single crystal of n-acetyl Leucine with intermolecular distances between the 15N nuclei exceeding 6.5 A. A quantum-mechanical explanation of this phenomenon is given based on the average-Hamiltonian theory which was confirmed by detailed numerical many-spin simulations. The theory and experiment presented in the present paper may help in the development of solid-state NMR methods for studying interhelical contacts in membrane proteins, as well as for their spectral assignment. PMID:18680251

Nevzorov, Alexander A

2008-08-27

 
 
 
 
61

Bright white-light emission from a novel donor-acceptor organic molecule in the solid state via intermolecular charge transfer.  

Science.gov (United States)

Bright white-light emission was obtained from a novel pyridinium molecule by aggregation. Photophysical, single-crystal structural, and computational studies demonstrated that an additional low-energy emission was generated by the excitation of a new intermolecular charge-transfer (CT) band at the ground state that cooperates with the non-quenched high-energy monomer emission to produce white light. PMID:25376300

Jin, Xu-Hui; Chen, Cheng; Ren, Cai-Xia; Cai, Li-Xuan; Zhang, Jie

2014-11-20

62

The "excited state C-C bond cleavage-luminescence" phenomenon of a biphenyl-substituted methylenecyclopropane triggered by intermolecular energy transfer from triplet benzophenone.  

Science.gov (United States)

Existence of the "excited state C-C bond cleavage-luminescence" phenomenon was demonstrated by utilizing intermolecular energy transfer from the excited-triplet benzophenone to 2,2-di(4-biphenylyl)-1-methylenecyclopropane (3). An excellent linear relationship between the intensity of the excitation laser light and that of luminescence clearly shows that formation of the corresponding excited trimethylenemethane biradical (3)4??* proceeds via a one-photon route. PMID:25267075

Matsui, Yasunori; Kido, Taiki; Ohta, Eisuke; Ikeda, Hiroshi

2014-11-21

63

Explosives sensing by using electron-rich supramolecular polymers: role of intermolecular hydrogen bonding in significant enhancement of sensitivity.  

Science.gov (United States)

We demonstrate here that supramolecular interactions enhance the sensitivity towards detection of electron-deficient nitro-aromatic compounds (NACs) over discrete analogues. NACs are the most commonly used explosive ingredients and are common constituents of many unexploded landmines used during World War?II. In this study, we have synthesised a series of pyrene-based polycarboxylic acids along with their corresponding discrete esters. Due to the electron richness and the fluorescent behaviour of the pyrene moiety, all the compounds act as sensors for electron-deficient NACs through a fluorescence quenching mechanism. A Stern-Volmer quenching constant determination revealed that the carboxylic acids are more sensitive than the corresponding esters towards NACs in solution. The high sensitivity of the acids was attributed to supramolecular polymer formation through hydrogen bonding in the case of the acids, and the enhancement mechanism is based on an exciton energy migration upon excitation along the hydrogen-bond backbone. The presence of intermolecular hydrogen bonding in the acids in solution was established by solvent-dependent fluorescence studies and dynamic light scattering (DLS) experiments. In addition, the importance of intermolecular hydrogen bonds in solid-state sensing was further explored by scanning tunnelling microscopy (STM) experiments at the liquid-solid interface, in which structures of self-assembled monolayer of the acids and the corresponding esters were compared. The sensitivity tests revealed that these supramolecular sensors can even detect picric acid and trinitrotoluene in solution at levels as low as parts per trillion (ppt), which is much below the recommended permissible level of these constituents in drinking water. PMID:25187022

Gole, Bappaditya; Song, Wentao; Lackinger, Markus; Mukherjee, Partha Sarathi

2014-10-13

64

Electron Transfer to Vinylaromatic Polymers  

International Nuclear Information System (INIS)

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

65

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.

66

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

Science.gov (United States)

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 acid (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. PMID:23002723

Ascione, Laura; Pezzella, Alessandro; Ambrogi, Veronica; Carfagna, Cosimo; d'Ischia, Marco

2013-01-01

67

Electron transfer switching in supramolecular porphyrin-fullerene conjugates held by alkylammonium cation-crown ether binding.  

Science.gov (United States)

Reversible switching between intra- to intermolecular electron transfer paths has been accomplished by adding and extracting potassium ions to the supramolecular porphyrin-fullerene conjugates formed by complexing porphyrin functionalized with a benzo-18-crown-6 entity and fullerene functionalized with an alkylammonium cation entity. PMID:17047856

Sandanayaka, Atula S D; Araki, Yasuyaki; Ito, Osamu; Chitta, Raghu; Gadde, Suresh; D'Souza, Francis

2006-11-01

68

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

Energy Technology Data Exchange (ETDEWEB)

The induced oxidation of N-phosphomethionine (NDM) in aqueous solution initiated by {center_dot}OH and Br{sub 2} {center_dot}{sup -}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)

Chu Gaosheng; Du Zhiwen; Ge Xuewu; Zhang Zhicheng; Zhang Manwei [Department of Applied Chemistry, Univ. of Science and Technology of China, Hefei (China); Yao Side [Laboratory of Radiation Chemistry, Academia Sinica, Shanghai Institute of Nuclear Research, Shanghai (China)

2000-03-01

69

Unveiling the details of electron transfer in multicenter redox proteins.  

Science.gov (United States)

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

Paquete, Catarina M; Louro, Ricardo O

2014-01-21

70

Effects of electron coupling to intra- and inter-molecular vibrational modes on the transport properties of single crystal organic semiconductors  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electron coupling to intra- and inter-molecular vibrational modes is investigated in models appropriate to single crystal organic semiconductors, such as oligoacenes. Focus is on spectral and transport properties of these systems beyond perturbative approaches. The interplay between different couplings strongly affects the temperature band renormalization that is the result of a subtle equilibrium between opposite tendencies: band narrowing due to interaction with local mode...

Perroni, C. A.; Ramaglia, V. Marigliano; Cataudella, V.

2011-01-01

71

Contribution of hydrogen bonding to charge-transfer induced surface-enhanced Raman scattering of an intermolecular system comprising p-aminothiophenol and benzoic acid.  

Science.gov (United States)

We investigated the influence of hydrogen bonds (H-bonds) on the intermolecular interactions of a system comprising p-aminothiophenol (PATP) and benzoic acid (BA) using surface-enhanced Raman scattering (SERS) for the first time. In this system, H-bonds form through intermolecular interactions between the -NH2 and -COOH groups and promote the charge-transfer (CT) transition from the Ag substrate to the adsorbed PATP molecules. Accordingly, the intensities of the non-totally symmetric vibrations (the b2-type bands) of PATP are influenced through the Herzberg-Teller contribution. This is clearly a BA concentration-dependent phenomenon. This behaviour can be attributed to an increase in the degree of conjugation of the system, which facilitates the CT process in the system with H-bonds. Furthermore, temperature-dependent SERS experiments and their two-dimensional (2D) correlation analysis confirmed that the formation of H-bonds facilitated the CT transition between the adsorbed molecules and substrate. The degree of CT was reduced by H-bond breakage that occurred with increasing temperature. An additional SERS experiment involving substituted BA molecules yielded similar conclusions. PMID:24407189

Wang, Yue; Ji, Wei; Yu, Zhi; Li, Ran; Wang, Xu; Song, Wei; Ruan, Weidong; Zhao, Bing; Ozaki, Yukihiro

2014-02-21

72

Flavin Electron Shuttles Dominate Extracellular Electron Transfer by Shewanella oneidensis  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Kotloski, Nicholas J.; Gralnick, Jeffrey A.

2013-01-01

73

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

Science.gov (United States)

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

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

2012-04-25

74

Density matrix based microscopic theory of molecule metal-nanoparticle interactions: Linear absorbance and plasmon enhancement of intermolecular excitation energy transfer  

Science.gov (United States)

A microscopic theory of interacting molecule metal-nanoparticle (MNP) systems is presented and used to compute absorption spectra and the plasmon enhancement of intermolecular excitation energy transfer (EET). The approach is based on a nonperturbative consideration of the Coulomb coupling matrix elements responsible for EET between the molecules and the MNP. In this way, the need to determine the local fields induced by surface plasmon excitations of the MNP is removed, but the whole description is restricted to distances among the interacting species less than the wavelength of absorbed photons. Based on a density matrix theory, the approach accounts for the vibrational level structure of the molecules, intramolecular vibrational energy redistribution (IVR), and plasmon damping. Numerical results for linear absorbance spectra and EET dynamics are offered. In this respect the importance of energy dissipation in the MNP due to rapid surface plasmon decay is emphasized.

Kyas, Gerold; May, Volkhard

2011-01-01

75

Direct observation of the intermolecular triplet-triplet energy transfer from UV-A absorber 4- tert -butyl-4?-methoxydibenzoylmethane to UV-B absorber octyl methoxycinnamate  

Science.gov (United States)

Triplet energy transfer (TET) is an important photostabilization process for organic UV absorbers, such as 4- tert-butyl-4'-methoxydibenzoylmethane (BM-DBM) and octyl methoxycinnamate (OMC). To characterize interactions between UV absorbers as TET the interactions between BM-DBM and OMC have been studied through measurements of EPR and time-resolved phosphorescence spectra. The EPR Bmin signals and the phosphorescence of OMC were observed through the selective excitation of BM-DBM at 365 nm in EtOH at 77 K. These results indicate that the intermolecular TET occurs from BM-DBM to OMC. This is the first report of the experimental evidence of the TET between the organic UV absorbers.

Kikuchi, Azusa; Yagi, Mikio

2011-09-01

76

Effects of inter-molecular charge-transfer excitons on the external quantum efficiency of zinc-porphyrin/C{sub 60} heterojunction photovoltaic cells  

Energy Technology Data Exchange (ETDEWEB)

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)/C{sub 60}/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.

Ryuzaki, Sou; Kai, Toshihiro; Onoe, Jun [Department of Nuclear Engineering, Tokyo Institute of Technology, Tokyo 152-8550 (Japan); Toda, Yasunori; Adachi, Satoru, E-mail: jonoe@nr.titech.ac.jp [Department of Applied Physics, Hokkaido University, Sapporo, Hokkaido 060-8628 (Japan)

2011-04-13

77

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.

78

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

Science.gov (United States)

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.

Ryuzaki, Sou; Kai, Toshihiro; Toda, Yasunori; Adachi, Satoru; Onoe, Jun

2011-04-01

79

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.

M. Tachiya

2008-10-01

80

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

Science.gov (United States)

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

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

2012-12-18

 
 
 
 
81

Computer simulation of electron transfer in molecular electronic devices  

Energy Technology Data Exchange (ETDEWEB)

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

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

2005-12-15

82

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

CERN Document Server

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

83

Intermolecular photoinduced electron-transfer processes between C60 and aniline derivatives in benzonitrile  

International Nuclear Information System (INIS)

ibution of reaction center ''N'' originated from quantum calculation supports this suggestion. In addition, a relationship between quenching rate constants and solvent viscosity was gained from C60/dimethyl-p-toluidine system in altered mixtures of acetonitrile and toluene

84

Nuclear reorganization barriers to electron transfer  

International Nuclear Information System (INIS)

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

85

Hierarchical control of electron-transfer  

DEFF Research Database (Denmark)

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

Jensen, Peter Ruhdal

1997-01-01

86

Electron transfer induced fragmentation of acetic acid  

Science.gov (United States)

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

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

2014-04-01

87

Photon-induced electron transfer transitions of the solvated electrons  

Energy Technology Data Exchange (ETDEWEB)

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

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

1978-09-15

88

A perspective of biological supramolecular electron transfer.  

Science.gov (United States)

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

Ramasarma, T

1999-12-01

89

Influence of Mg(2+) on the guanine-cytosine tautomeric equilibrium: simulations of the induced intermolecular proton transfer.  

Science.gov (United States)

Metallic ions are essential for stabilizing the nucleic acid structure, and are also involved in the majority of RNA and DNA biological functions. However, at large concentrations metals may play an opposite role by promoting alterations in the genetic code (mutagenicity). To contribute to the understanding of this effect, theoretical tools are used to investigate the influence of the magnesium dication on the guanine-cytosine (GC) base pair structure and stability. To this end, a fully hydrated Mg(2+) cation is inserted in two models: an isolated GC base pair, and a more realistic DNA model corresponding to a hydrated double-stranded trimer. Calculations performed with a hybrid ONIOM approach reveal that the Mg(2+) cation coordination to the GC base pair alters drastically the natural tautomeric equilibria in DNA by promoting single proton transfer. Nevertheless, the generated rare tautomer will have a limited impact on the total spontaneous mutation due to the low back-reaction barrier allowing a quick return to the canonical form. Additionally, it is demonstrated that the major effects of biological environment arise from the hydration and stacking influence, whereas the impact of phosphate groups is minor. PMID:21954005

Cerón-Carrasco, José P; Jacquemin, Denis

2011-10-01

90

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)

91

Protein electron transfer: Dynamics and statistics  

Science.gov (United States)

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

Matyushov, Dmitry V.

2013-07-01

92

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

93

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

94

Electron transfer in weakly interacting systems  

International Nuclear Information System (INIS)

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

95

Cycloreversion of ?-lactams via photoinduced electron transfer.  

Science.gov (United States)

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

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

2014-10-01

96

75 FR 51707 - Electronic Funds Transfer of Depository Taxes  

Science.gov (United States)

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

2010-08-23

97

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

98

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

99

Effects of the higher electron correlation correction on the calculated intermolecular interaction energies of benzene and naphthalene dimers: comparison between MP2 and CCSD(T) calculations  

Science.gov (United States)

Intermolecular interaction energies of parallel and T-shape benzene dimers and parallel naphthalene dimer were calculated with MP2, MP3, MP4(SDQ), MP4(SDTQ), CCSD and CCSD(T) electron correlation corrections using several basis sets. The MP2 calculations considerably overestimated the attraction compared to the CCSD(T) ones. The MP2 correlation interaction energies, the differences between the HF and MP2 interaction energies, were 21-38% larger than the corresponding CCSD(T) ones. The MP4(SDQ) and CCSD calculations substantially underestimated the attraction compared to MP4(SDTQ) and CCSD(T), which indicated the importance of triple excitation. The estimated CCSD(T) interaction energies of the three dimers with reasonably large basis sets were -1.74, -2.50 and -5.69 kcal/mol, respectively.

Tsuzuki, Seiji; Uchimaru, Tadafumi; Matsumura, Kazunari; Mikami, Masuhiro; Tanabe, Kazutoshi

2000-03-01

100

Experimental and database-transferred electron-density analysis and evaluation of electrostatic forces in coumarin-102 dye.  

Science.gov (United States)

The electron-density distribution of a new crystal form of coumarin-102, a laser dye, has been investigated using the Hansen-Coppens multipolar atom model. The charge density was refined versus high-resolution X-ray diffraction data collected at 100?K and was also constructed by transferring the charge density from the Experimental Library of Multipolar Atom Model (ELMAM2). The topology of the refined charge density has been analysed within the Bader `Atoms In Molecules' theory framework. Deformation electron-density peak heights and topological features indicate that the chromen-2-one ring system has a delocalized ?-electron cloud in resonance with the N (amino) atom. The molecular electrostatic potential was estimated from both experimental and transferred multipolar models; it reveals an asymmetric character of the charge distribution across the molecule. This polarization effect is due to a substantial charge delocalization within the molecule. The molecular dipole moments derived from the experimental and transferred multipolar models are also compared with the liquid and gas-phase dipole moments. The substantial molecular dipole moment enhancements observed in the crystal environment originate from the crystal field and from intermolecular charge transfer induced and controlled by C-H···O and C-H···N intermolecular hydrogen bonds. The atomic forces were integrated over the atomic basins and compared for the two electron-density models. PMID:23165601

Bibila Mayaya Bisseyou, Yvon; Bouhmaida, Nouhza; Guillot, Benoit; Lecomte, Claude; Lugan, Noel; Ghermani, Noureddine; Jelsch, Christian

2012-12-01

 
 
 
 
101

Interatomic and intermolecular coulombic decay: The early years  

International Nuclear Information System (INIS)

Research highlights: ? Autoionization in weakly bonded systems can involve energy transfer between sites. ? These channels have been termed intermolecular coulombic decay (ICD). ? Here, I review the experimental research on ICD from its discovery until 2010. - Abstract: Autoionization is an important pathway for the relaxation of electronically excited states. In weakly bonded matter, efficient autoionization channels have been found, in which not only the initially excited state, but also neighbouring atoms or molecules take part. Since their theoretical prediction in 1997 these processes are known as interatomic or intermolecular coulombic decay (ICD). The author summarizes the experimental research on ICD up to the presence. Experiments on inner valence ICD in rare gas clusters, on cascade ICD after Auger decay and on ICD of satellite states are explicitly discussed. First experiments on water clusters and on solutes will be reviewed. An outlook on other non-local autoionization processes and on future directions of ICD research closes the article.

102

Theory of intermolecular forces  

CERN Document Server

Theory of Intermolecular Forces deals with the exposition of the principles and techniques of the theory of intermolecular forces. The text focuses on the basic theory and surveys other aspects, with particular attention to relevant experiments. The initial chapters introduce the reader to the history of intermolecular forces. Succeeding chapters present topics on short, intermediate, and long range atomic interactions; properties of Coulomb interactions; shape-dependent forces between molecules; and physical adsorption. The book will be of good use to experts and students of quantum mechanics

Margenau, H; Ter Haar, D

1971-01-01

103

Electron transfer theory revisit: Quantum solvation effect  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2006-01-01

104

Monitoring molecule dynamics by free electron transfer  

International Nuclear Information System (INIS)

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

105

Promoting interspecies electron transfer with biochar  

DEFF Research Database (Denmark)

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

Chen, Shanshan; Rotaru, Amelia-Elena

2014-01-01

106

Promoting Interspecies Electron Transfer with Biochar  

Science.gov (United States)

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

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

2014-01-01

107

Promoting interspecies electron transfer with biochar.  

Science.gov (United States)

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

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

2014-01-01

108

Variation of geometries and electron properties along proton transfer in strong hydrogen-bond complexes  

Science.gov (United States)

Proton transfer in hydrogen-bond systems formed by 4-methylimidazole in both neutral and protonated cationic forms and by acetate anion are studied by means of MP2/6-311++G(d,p) ab initio calculations. These two complexes model the histidine (neutral and protonated)-aspartate diad present in the active sites of enzymes the catalytic mechanism of which involves the formation of strong hydrogen bonds. We investigate the evolution of geometries, natural bond orbital populations of bonds and electron lone pairs, topological descriptors of the electron density, and spatial distributions of the electron localization function along the process N-H ⋯O?N⋯H⋯O?N⋯H-O, which represents the stages of the H-transfer. Except for a sudden change in the population of electron lone pairs in N and O at the middle N...H...O stage, all the properties analyzed show a smooth continuous behavior along the covalent ? hydrogen bond transit inherent to the transfer, without any discontinuity that could identify a formation or breaking of the hydrogen bond. This way, the distinction between covalent or hydrogen-bonding features is associated to subtle electron rearrangement at the intermolecular space.

Pacios, L. F.; Gálvez, O.; Gómez, P. C.

2005-06-01

109

Education and solar conversion. Demonstrating electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

1998-07-23

110

Long-Range Electron Transfer and Electronic Transport Through Macromolecules  

CERN Document Server

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

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

2002-01-01

111

Photoinduced Electron Transfer within a Zinc Porphyrin-Cyclobis(paraquat-p-phenylene) Donor-Acceptor Dyad.  

Science.gov (United States)

Understanding the mechanism of efficient photoinduced electron-transfer processes is essential for developing molecular systems for artificial photosynthesis. Towards this goal, we describe the synthesis of a donor-acceptor dyad comprising a zinc porphyrin donor and a tetracationic cyclobis(paraquat-p-phenylene) (CBPQT(4+) ) acceptor. The X-ray crystal structure of the dyad reveals the formation of a dimeric motif through the intermolecular coordination between the triazole nitrogen and the central Zn metal of two adjacent units of the dyad. Photoinduced electron transfer within the dyad in MeCN was investigated by femtosecond and nanosecond transient absorption spectroscopy, as well as by transient EPR spectroscopy. Photoexcitation of the dyad produced a weakly coupled ZnP(+.) -CBPQT(3+.) spin-correlated radical-ion pair having a ?=146?ns lifetime and a spin-spin exchange interaction of only 0.23?mT. The long radical-ion-pair lifetime results from weak donor-acceptor electronic coupling as a consequence of having nine bonds between the donor and the acceptor, and the reduction in reorganization energy for electron transfer caused by charge dispersal over both paraquat units within CBPQT(3+.) . PMID:25258209

Fathalla, Maher; Barnes, Jonathan C; Young, Ryan M; Hartlieb, Karel J; Dyar, Scott M; Eaton, Samuel W; Sarjeant, Amy A; Co, Dick T; Wasielewski, Michael R; Stoddart, J Fraser

2014-11-01

112

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

113

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

114

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

2013-08-22

115

Mediated Electron Transfer at Redox Active Monolayers  

Directory of Open Access Journals (Sweden)

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

Michael E.G. Lyons

2001-12-01

116

Intermolecular Contrast in Atomic Force Microscopy Images without Intermolecular Bonds  

Science.gov (United States)

Intermolecular features in atomic force microscopy images of organic molecules have been ascribed to intermolecular bonds. A recent theoretical study [P. Hapala et al., Phys. Rev. B 90, 085421 (2014)] showed that these features can also be explained by the flexibility of molecule-terminated tips. We probe this effect by carrying out atomic force microscopy experiments on a model system that contains regions where intermolecular bonds should and should not exist between close-by molecules. Intermolecular features are observed in both regions, demonstrating that intermolecular contrast cannot be directly interpreted as intermolecular bonds.

Hämäläinen, Sampsa K.; van der Heijden, Nadine; van der Lit, Joost; den Hartog, Stephan; Liljeroth, Peter; Swart, Ingmar

2014-10-01

117

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

118

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

2010-01-01

119

Quantum tunneling resonant electron transfer process in Lorentzian plasmas  

Science.gov (United States)

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

Hong, Woo-Pyo; Jung, Young-Dae

2014-08-01

120

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.)

 
 
 
 
121

Activation entropy of electron transfer reactions  

CERN Document Server

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

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

2005-01-01

122

Electron transfer reactions of organometallic compounds  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Zavarine, Igor S.

1998-01-01

123

GPU-accelerated computation of electron transfer.  

Science.gov (United States)

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

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

2012-11-01

124

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; Christensen, Hans Erik MØlager

2009-01-01

125

Single-element Electron-transfer Optical Detector System  

Science.gov (United States)

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

Jordan, Jeffrey D. (Inventor)

2004-01-01

126

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

127

Intramolecular electron transfer on the vibrational timescale in mixed valence ruthenium clusters  

International Nuclear Information System (INIS)

The thermodynamic stability of the mixed valence (one electron reduced) state between linked Ru3 units was studied by means of electrochemical methods for the series of the ligand-bridged triruthenium cluster dimer, [Ru3(?3-O)(?-CH3CO2)6(CO)(L)(?-BL)Ru3(?3-O)(?-CH3CO2)6(CO)(L)] (BL = 1,4 pyrazine: L = 4-dimethylaminopyridine (dmap) (1a), pyridine (py) (1b), 4-cyanopyridine (cpy) (1c), 1-azabicyclo[2.2.2]octane (1d); BL = 4,4'-bipyridine: L= dmap (2a), py(2b), cpy (2c); BL 2,7-diazapyrene; L = dmap (3a); BL = 1,4-diazabicyclo[2.2.2]octane: L = dmap (4a), py(4b), cpy (4c). The mixed valence states undergoing rapid intermolecular electron transfers were observed by IR spectro-electrochemistry. By simulating dynamical effects on the observed ?(CO) absorption band shapes, the rate constants ke for electron transfer in the mixed valence states of 1a, 1b, 1c and 1d were estimated to be 9x1011 s-1 (at room temperature (rt)), 5x1011 s-1 (at rt), ca. 1x1011 s-1 (at rt), and 1x1012 s-1 (at -18 oC), respectively. Possible applications of this approach to asymmetric mixed valence systems were discussed. (author)

128

Oxide/Electrolyte interface: Electron transfer phenomena  

Directory of Open Access Journals (Sweden)

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

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

Fernández-Ibáñez, P.

2000-08-01

129

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads  

Energy Technology Data Exchange (ETDEWEB)

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

NONE

1993-03-01

130

Quantum coherent contributions in biological electron transfer  

CERN Document Server

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

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

2011-01-01

131

REFINEMENT OF THE OH A2(SIGMA+)(V=0)+AR INTERMOLECULAR POTENTIAL-ENERGY SURFACE  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Several intermolecular vibrational levels of the excited electronic state of OH-Ar correlating with OH A 2?+(v=0)+Ar have been characterized by laser-induced fluorescence and hole-burning experiments. The OH-Ar levels identified include the lowest intermolecular level, an intermolecular bending level with a lower degree of stretching excitation than previously observed, and intermolecular levels with two quanta of bending excitation. The intensities of electronic transitions to these levels ...

Lester, M.; Loomis, R.; Giancarlo, L.; Berry, M.; Chakravarty, C.; Clary, D.

1993-01-01

132

Photoinduced Electron-transfer Reaction of Pentafluoroiodobenzene with Alkenes  

Directory of Open Access Journals (Sweden)

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

Qing-Yun Chen

1997-01-01

133

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

Science.gov (United States)

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

2012-07-10

134

Electron Transfer in Porphyrin Complexes in Different Solvents  

CERN Document Server

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

Kilin, D S; Schreiber, M

2000-01-01

135

Computational Approach to Electron Charge Transfer Reactions  

DEFF Research Database (Denmark)

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

Jónsson, Elvar Örn

2013-01-01

136

Intermolecular correlation in a new approximation scheme  

International Nuclear Information System (INIS)

It is demonstrated for a spin-free, nonrelativistic, complete molecular Hamiltonian that there is an optimal solution to the separation of electronic and nuclear motions. The adiabatic approximation is obtained as a special limiting case. A fruitful interpretation of intermolecular correlation results from the assumption that such correlation involves the degeneracy of a molecular-energy state of one molecule with that of another chemical species, e.g., cubane and cyclooctatetraene. As a consequence, rigorous relations are establiehed for the influence of nodal patterns of the electronic functions on intermolecular correlation. Also derived are stringent symmetry rules which both electronic and nuclear functions involved in the correlation must obey. Throughout the treatment is a many-electron one. 10 references

137

Electron transfer in proteins : in search of preferential pathways  

DEFF Research Database (Denmark)

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

Farver, O; Pecht, I

1991-01-01

138

The distance and temperature dependence of electron-transfer rates  

Energy Technology Data Exchange (ETDEWEB)

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

Sutin, N.

1987-01-01

139

Shewanella secretes flavins that mediate extracellular electron transfer  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2008-01-01

140

Momentum transfer to small particles by aloof electron beams  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Abajo, F. J. Garcia

2007-01-01

 
 
 
 
141

Momentum transfer to small particles by aloof electron beams  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Abajo, F. J. Garcia

2004-01-01

142

Effect of laser intensity on the determination of intermolecular electron transfer rate constants - Observation of Marcus inverted region in photoinduced back electron transfer reactions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The light intensity and concentration dependence of the photoproduct yield are investigated in a monophotonic process. The relationship of the photoproduct yield with the laser intensity and the complex concentration for a monophotonic process is derived under laser flash photolysis. The relationship is confirmed experimentally in a monophotonic process, i.e., triplet-triplet transition for a Cu(I) complex Cu6(DMNSN?)6 (DMNSN?=4,6-dimethylpyrimidine-2-thiolate). At low light intensity, th...

Weng, Yx; Chan, Kc; Tzeng, Bc; Che, Cm

1998-01-01

143

76 FR 29901 - Electronic Fund Transfers  

Science.gov (United States)

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

2011-05-23

144

A molecular shift register based on electron transfer  

Science.gov (United States)

An electronic shift-register memory at the molecular level is described. The memory elements are based on a chain of electron-transfer molecules and the information is shifted by photoinduced electron-transfer reactions. This device integrates designed electronic molecules onto a very large scale integrated (silicon microelectronic) substrate, providing an example of a 'molecular electronic device' that could actually be made. The design requirements for such a device and possible synthetic strategies are discussed. Devices along these lines should have lower energy usage and enhanced storage density.

Hopfield, J. J.; Onuchic, Josenelson; Beratan, David N.

1988-01-01

145

Golden rule kinetics of transfer reactions in condensed phase: The microscopic model of electron transfer reactions in disordered solid matrices  

Energy Technology Data Exchange (ETDEWEB)

The algorithm for a theoretical calculation of transfer reaction rates for light quantum particles (i.e., the electron and H-atom transfers) in non-polar solid matrices is formulated and justified. The mechanism postulated involves a local mode (an either intra- or inter-molecular one) serving as a mediator which accomplishes the energy exchange between the reacting high-frequency quantum mode and the phonon modes belonging to the environment. This approach uses as a background the Fermi golden rule beyond the usually applied spin-boson approximation. The dynamical treatment rests on the one-dimensional version of the standard quantum relaxation equation for the reduced density matrix, which describes the frequency fluctuation spectrum for the local mode under consideration. The temperature dependence of a reaction rate is controlled by the dimensionless parameter ?{sub 0}=??{sub 0}/k{sub B}T where ?{sub 0} is the frequency of the local mode and T is the temperature. The realization of the computational scheme is different for the high/intermediate (?{sub 0} < 1 ? 3) and for low (?{sub 0}? 1) temperature ranges. For the first (quasi-classical) kinetic regime, the Redfield approximation to the solution of the relaxation equation proved to be sufficient and efficient in practical applications. The study of the essentially quantum-mechanical low-temperature kinetic regime in its asymptotic limit requires the implementation of the exact relaxation equation. The coherent mechanism providing a non-vanishing reaction rate has been revealed when T? 0. An accurate computational methodology for the cross-over kinetic regime needs a further elaboration. The original model of the hopping mechanism for electronic conduction in photosensitive organic materials is considered, based on the above techniques. The electron transfer (ET) in active centers of such systems proceeds via local intra- and intermolecular modes. The active modes, as a rule, operate beyond the kinetic regimes, which are usually postulated in the existing theories of the ET. Our alternative dynamic ET model for local modes immersed in the continuum harmonic medium is formulated for both classical and quantum regimes, and accounts explicitly for the mode/medium interaction. The kinetics of the energy exchange between the local ET subsystem and the surrounding environment essentially determine the total ET rate. The efficient computer code for rate computations is elaborated on. The computations are available for a wide range of system parameters, such as the temperature, external field, local mode frequency, and characteristics of mode/medium interaction. The relation of the present approach to the Marcus ET theory and to the quantum-statistical reaction rate theory [V. G. Levich and R. R. Dogonadze, Dokl. Akad. Nauk SSSR, Ser. Fiz. Khim. 124, 213 (1959); J. Ulstrup, Charge Transfer in Condensed Media (Springer, Berlin, 1979); M. Bixon and J. Jortner, Adv. Chem. Phys. 106, 35 (1999)] underlying it is discussed and illustrated by the results of computations for practically important target systems.

Basilevsky, M. V.; Mitina, E. A. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); Odinokov, A. V. [Photochemistry Center, Russian Academy of Sciences, 7a, Novatorov ul., Moscow (Russian Federation); National Research Nuclear University “MEPhI,” 31, Kashirskoye shosse, Moscow (Russian Federation); Titov, S. V. [Karpov Institute of Physical Chemistry, 3-1/12, Building 6, Obuha pereulok, Moscow (Russian Federation)

2013-12-21

146

Dissociative electron attachment and charge transfer in condensed matter  

International Nuclear Information System (INIS)

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

147

Dissociative electron attachment and charge transfer in condensed matter  

Energy Technology Data Exchange (ETDEWEB)

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

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

2003-09-01

148

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

149

Electron transfer in SmHfCo alloys  

International Nuclear Information System (INIS)

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

150

Theory of electron transfer and ionization  

International Nuclear Information System (INIS)

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

151

Theory of electron transfer and ionization  

Energy Technology Data Exchange (ETDEWEB)

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

Becker, R. L.

1979-01-01

152

Proton-coupled electron transfer with photoexcited metal complexes.  

Science.gov (United States)

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

Wenger, Oliver S

2013-07-16

153

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 (? 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 the 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 the transient absorption band due to the benzene dimer radical cation was accelerated by the addition of TEAF·4HF. The observed rate constant increased with increasing concentration of TEAF·4HF. The rate constant of the electrophilic addition of 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

2013-10-17

154

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

Energy Technology Data Exchange (ETDEWEB)

Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, 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 ground state of the complex: a charge delocalization of about 10{sup ?2} electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], 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 visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

Haverkate, Lucas A.; Mulder, Fokko M. [Reactor Institute Delft, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629JB Delft (Netherlands); Zbiri, Mohamed, E-mail: zbiri@ill.fr; Johnson, Mark R. [Institut Laue Langevin, 38042 Grenoble Cedex 9 (France); Carter, Elizabeth [Vibrational Spectroscopy Facility, School of Chemistry, The University of Sydney, NSW 2008 (Australia); Kotlewski, Arek; Picken, S. [ChemE-NSM, Faculty of Chemistry, Delft University of Technology, 2628BL/136 Delft (Netherlands); Kearley, Gordon J. [Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 (Australia)

2014-01-07

155

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

International Nuclear Information System (INIS)

Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, 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 ground state of the complex: a charge delocalization of about 10?2 electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements [L. A. Haverkate, M. Zbiri, M. R. Johnson, B. Deme, H. J. M. de Groot, F. Lefeber, A. Kotlewski, S. J. Picken, F. M. Mulder, and G. J. Kearley, J. Phys. Chem. B 116, 13098 (2012)], 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 visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems

156

Chirped pulse control of long range electron transfer  

International Nuclear Information System (INIS)

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

157

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

Science.gov (United States)

We have made use of classical dynamics trajectory simultions and ab initio electronic structure calculations to estimate the cross sections with which electrons are attached (in electron capture dissociation (ECD)) or transferred (in electron transfer dissociation (ETD)) to a model system that contained both an S-S bond that is cleaved and a -NH(3)(+) positively charged site. We used a Landau-Zener-Stueckelberg curve-crossing approximation to estimate the ETD rates for electron transfer from a CH(3)(-) anion to the -NH(3)(+) Rydberg orbital or the S-S sigma* orbital. We draw conclusions about ECD from our ETD results and from known experimental electron-attachment cross sections for cations and sigma-bonds. We predict the cross section for ETD at the positive site of our model compound to be an order of magnitude larger than that for transfer to the Coulomb-stabilized S-S bond site. We also predict that, in ECD, the cross section for electron capture at the positive site will be up to 3 orders of magnitude larger than that for capture at the S-S bond site. These results seem to suggest that attachment to such positive sites should dominate in producing S-S bond cleavage in our compound. However, we also note that cleavage induced by capture at the positive site will be diminished by an amount that is related to the distance from the positive site to the S-S bond. This dimunition can render cleavage through Coulomb-assisted S-S sigma* attachment competitive for our model compound. Implications for ECD and ETD of peptides and proteins in which SS or N-C(alpha) bonds are cleaved are also discussed, and we explain that such events are most likely susceptible to Coulomb-assisted attachment, because the S-S sigma* and C=O pi* orbitals are the lowest-lying antibonding orbitals in most peptides and proteins. PMID:16833914

Anusiewicz, Iwona; Berdys-Kochanska, Joanna; Simons, Jack

2005-07-01

158

Intermolecular dynamics of hexamethylenetetramine  

International Nuclear Information System (INIS)

The technique of coherent inelastic neutron scattering has been used to measure the dispersion curves of intermolecular modes propagating along various high symmetry directions in the organic molecular crystal deuterated hexamethylenetetramine, at 100 and 298 K. The results are analysed in terms of phenomenological models involving interactions between supposedly rigid molecules. Interactions with both first and second nearest-neighbour molecules are found to be necessary for an adequate description. A simplified five-parameter model, which assumes centrosymmetric molecules, provides almost as good a fit to the results as that given by a generalized twelve-parameter model. Group theory shows that the effects of assuming centrosymmetry may be significant in the [??0] or ? direction. Assuming that the replacement of deuterium by hydrogen does not change the intermolecular forces, the frequency distribution of function and the heat capacity of hydrogenous hexamethylenetetramine are calculated. The agreement between the computed and measured heat capacities is good. The frequency distribution function shows many obvious critical points and other singular features. The existence of logarithmically infinite singularities in this function is investigated. The elastic constants computed from the force models show discrepancies from those measured ultrasonically, and these discrepancies are thought to be significant. The long wavelength optical librational frequency measureh optical librational frequency measured in the present work differs considerably from that deduced from optical measurements, and an explanation of this apparent discrepancy is suggested. The 2% hydrogen content in the specimen results in the presence of hydrogenous 'defect' molecules, and the effects of these on the normal vibrations of the host lattice are shown to be very small. (author)

159

Microbial interspecies electron transfer via electric currents through conductive minerals  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In anaerobic biota, reducing equivalents (electrons) are transferred between different species of microbes [interspecies electron transfer (IET)], establishing the basis of cooperative behaviors and community functions. IET mechanisms described so far are based on diffusion of redox chemical species and/or direct contact in cell aggregates. Here, we show another possibility that IET also occurs via electric currents through natural conductive minerals. Our investigation revealed that electric...

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2012-01-01

160

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

Science.gov (United States)

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

2010-04-01

 
 
 
 
161

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

Science.gov (United States)

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

2010-04-01

162

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

Science.gov (United States)

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

2010-04-01

163

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

Science.gov (United States)

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

2010-04-01

164

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

Science.gov (United States)

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

2010-04-01

165

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

Science.gov (United States)

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

2010-04-01

166

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

Science.gov (United States)

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

2010-04-01

167

Desensitization of metastable intermolecular composites  

Science.gov (United States)

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

168

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

169

Intramolecular photoinduced electron-transfer in azobenzene-perylene diimide  

International Nuclear Information System (INIS)

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

170

Radiative and nonradioactive electron transfer in donor-acceptor phenanthrimidazoles.  

Science.gov (United States)

Photoinduced electron transfer in a series of naphthyl substituted phenanthrimidazoles has been studied in solutions. The intramolecular charge transfer (CT) leads to a large Stokes shift and large dipole moment in the fluorescent state. Solvatochromic effects on the spectral position and profile of the stationary fluorescence spectra clearly indicate the CT character of the emitting singlet states of all the compounds studied. An analysis of the CT fluorescence lead to the quantities relevant for the electron transfer in the Marcus inverted region. PMID:25194432

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

2014-11-01

171

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

172

Accelerated Electron Transfer between Metal Complexes Mediated by DNA  

Science.gov (United States)

DNA-mediated long-range electron transfer from photoexcited 1,10-phenanthroline complexes of ruthenium, Ru(phen)32+, to isostructural complexes of cobalt(III), rhodium(III), and chromium(III) bound along the helical strand. The efficiency of transfer depended upon binding mode and driving force. For a given donor-acceptor pair, surface-bound complexes showed greater rate enhancements than those that were intercalatively bound. Even in rigid glycerol at 253 K, the rates for donor-acceptor pairs bound to DNA remained enhanced. For the series of acceptors, the greatest enhancement in electron-transfer rate was found with chromium, the acceptor of intermediate driving force. The DNA polymer appears to provide an efficient intervening medium to couple donor and acceptor metal complexes for electron transfer.

Purugganan, Michael D.; Kumar, Challa V.; Turro, Nicholas J.; Barton, Jacqueline K.

1988-09-01

173

Reactions of electron transfer with participation of porphyrins  

International Nuclear Information System (INIS)

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

174

Electron transfer in the Hf1Co6 magnetic alloy  

International Nuclear Information System (INIS)

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

175

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

Science.gov (United States)

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

Goun, Alexei A.

176

Quantum interferences and electron transfer in photosystem I.  

Science.gov (United States)

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

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

2013-07-25

177

Hydrogen diffusion and radiationless electron transfer in metal hydrides  

International Nuclear Information System (INIS)

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

178

Electronic energy transfer in actinyl crystals  

International Nuclear Information System (INIS)

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

179

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

Science.gov (United States)

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

Kosman, Daniel J

2008-03-01

180

Intra- and intermolecular vibrational energy transfer in tungsten carbonyl complexes W(CO)5(X) (X=CO, CS, CH3CN, and CD3CN)  

Science.gov (United States)

Vibrational energy relaxation of degenerate CO stretches of four tungsten carbonyl complexes, W(CO)6, W(CO)5(CS), W(CO)5(CH3CN), and W(CO)5(CD3CN), is observed in nine alkane solutions by subpicosecond time-resolved infrared (IR) pump-probe spectroscopy. Between 0 and 10 ps after the vibrational excitation, the bleaching signal of the ground-state IR absorption band shows anisotropy. Decay of the anisotropic component corresponds either to the rotational diffusion of the molecule or to the intramolecular vibrational energy transfer among the degenerate CO stretch modes. The time constant of the anisotropy decay, ?aniso, shows distinct solvent dependence. By comparing the results for the T1u CO stretch of W(CO)6 and the A1 CO stretch of W(CO)5(CS), the time constant of the rotational diffusion, ?r, and the time constant of the intramolecular energy transfer among the three degenerate vibrational modes, ?e, are determined as 12 and 8 ps, respectively. The ?aniso value increases as the number of carbon atoms in the alkane solvent increases. After 10 ps, the recovery of the bleaching becomes isotropic. The isotropic decay represents the vibrational population relaxation, from v=1 to v=0. In heptane, the time constant for the isotropic decay, ?1, for W(CO)5(CS) and W(CO)6 was 140 ps. The ?1 for the two acetonitrile-substituted complexes, however, shows a smaller value of 80 ps. The vibrational energy relaxation of W(CO)5(CH3CN) and W(CO)5(CD3CN) is accelerated by the intramolecular energy redistribution from the CO ligand to the acetonitrile ligand. In the nine alkane solutions, the ?1 value of W(CO)6 ranges between 124 and 158 ps, showing the apparent V-shaped solvent dependence with its minimum in decane, while the ?1 value shows little solvent dependence for W(CO)5(CH3CN) and W(CO)5(CD3CN).

Banno, Motohiro; Iwata, Koichi; Hamaguchi, Hiro-O.

2007-05-01

 
 
 
 
181

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

Science.gov (United States)

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

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

2014-10-01

182

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

Science.gov (United States)

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

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

2014-10-01

183

Plugging in or going wireless: strategies for interspecies electron transfer  

Science.gov (United States)

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

Shrestha, Pravin Malla; Rotaru, Amelia-Elena

2014-01-01

184

Plugging in or Going Wireless: Strategies for Interspecies Electron Transfer  

Directory of Open Access Journals (Sweden)

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

PravinMallaShrestha

2014-05-01

185

Plugging in or Going Wireless : Strategies for Interspecies Electron Transfer  

DEFF Research Database (Denmark)

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

Shrestha, Pravin; Rotaru, Amelia-Elena

2014-01-01

186

Theory of reversible electron transfer reactions in a condensed phase  

Science.gov (United States)

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

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

2010-07-01

187

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

Science.gov (United States)

Photosystem?1 (PS1) triggers the most energetic light-induced charge-separation step in nature and the in vivo electron-transfer rates approach 50?e(-) ?s(-1) ?PS1(-1). Photoelectrochemical devices based on this building block have to date underperformed with respect to their semiconductor counterparts or to natural photosynthesis in terms of electron-transfer rates. We present a rational design of a redox hydrogel film to contact PS1 to an electrode for photocurrent generation. We exploit the pH-dependent properties of a poly(vinyl)imidazole Os(bispyridine)2Cl polymer to tune the redox hydrogel film for maximum electron-transfer rates under optimal conditions for PS1 activity. The PS1-containing redox hydrogel film displays electron-transfer rates of up to 335±14?e(-) ?s(-1) ?PS1(-1), which considerably exceeds the rates observed in natural photosynthesis or in other semiartificial systems. Under O2 supersaturation, photocurrents of 322±19??A?cm(-2) were achieved. The photocurrents are only limited by mass transport of the terminal electron acceptor (O2). This implies that even higher electron-transfer rates may be achieved with PS1-based systems in general. PMID:25066901

Kothe, Tim; Pöller, Sascha; Zhao, Fangyuan; Fortgang, Philippe; Rögner, Matthias; Schuhmann, Wolfgang; Plumeré, Nicolas

2014-08-25

188

Electron Delocalization and Charge Transfer in Polypeptide Chains  

Science.gov (United States)

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

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

2009-09-01

189

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

190

Direct interspecies electron transfer between Geobacter metallireducens and Methanosarcina barkeri.  

Science.gov (United States)

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

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

2014-08-01

191

Photocurrent generation by direct electron transfer using photosynthetic reaction centres  

International Nuclear Information System (INIS)

Photosynthetic reaction centres (RCs) convert light into separated charges with nearly perfect quantum efficiency, and have been used to generate photocurrent. Previous work has shown that electron tunnelling rates between redox centres in proteins depend exponentially on the tunnelling distance. In this work the RC from Rhodobacter sphaeroides was genetically modified with the aim of achieving the shortest tunnelling distances yet demonstrated between the RC's electron-accepting P site and underlying graphite and gold electrodes, and between the electron donor Q site and graphite electrodes. Opposite charges are carried to counter electrodes using mobile mediators, as in dye-sensitised solar cells. Native RCs are bound to graphite surfaces through N-(1-pyrene)iodoacetamide. Although the linker's length is only 4 Å, the electron transfer pathway between the Q electron donor site on the RC and the electrode surface is still too large for current to be significant. A mutant version with the electron acceptor P side close to the graphite surface produced currents of 15 nA cm?2 upon illumination. Direct binding of RCs to a gold surface is shown, resulting in currents of 5 nA cm?2. In both cases the current was unaffected by mediator concentration but increased with illumination, suggesting that direct electron transfer was achieved. The engineering of an RC to achieve direct electron transfer will help with long term efforts to demonstrate RC-baong term efforts to demonstrate RC-based photovoltaic devices

192

The role of excited Rydberg States in electron transfer dissociation.  

Science.gov (United States)

Ab initio electronic structure methods are used to estimate the cross sections for electron transfer from donor anions having electron binding energies ranging from 0.001 to 0.6 eV to each of three sites in a model disulfide-linked molecular cation. The three sites are (1) the S-S sigma(*) orbital to which electron attachment is rendered exothermic by Coulomb stabilization from the nearby positive site, (2) the ground Rydberg orbital of the -NH(3)(+) site, and (3) excited Rydberg orbitals of the same -NH(3)(+) site. It is found that attachment to the ground Rydberg orbital has a somewhat higher cross section than attachment to either the sigma orbital or the excited Rydberg orbital. However, it is through attachment either to the sigma(*) orbital or to certain excited Rydberg orbitals that cleavage of the S-S bond is most likely to occur. Attachment to the sigma(*) orbital causes prompt cleavage because the sigma energy surface is repulsive (except at very long range). Attachment to the ground or excited Rydberg state causes the S-S bond to rupture only once a through-bond electron transfer from the Rydberg orbital to the S-S sigma(*) orbital takes place. For the ground Rydberg state, this transfer requires surmounting an approximately 0.4 eV barrier that renders the S-S bond cleavage rate slow. However, for the excited Rydberg state, the intramolecular electron transfer has a much smaller barrier and is prompt. PMID:16599533

Sobczyk, Monika; Simons, Jack

2006-04-13

193

Light-driven microbial dissimilatory electron transfer to hematite.  

Science.gov (United States)

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

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

2014-10-01

194

Phonon-mediated path-interference in electronic energy transfer.  

Science.gov (United States)

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

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

2012-01-14

195

Intermolecular Forces: A Jigsaw Activity  

Science.gov (United States)

This jigsaw activity is designed as a cooperative learning activity used to introduce the idea of intermolecular forces. Intermolecular forces are the types of attractive forces that occur between molecules in a solid, liquid, or gas. Each force causes different physical properties of matter. Each member of the group will become an expert on one type of force and then teach the rest of the group.

Edu., Boise S.

2011-09-20

196

Heavy particle interference and diffraction in fast electron transfer collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Gudmundsson, Magnus

2011-01-01

197

Multi-Element Electron-Transfer Optical Detector System  

Science.gov (United States)

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

Jordan, Jeffrey D. (Inventor)

2004-01-01

198

Probing electron transfer dynamics of pyranine with reduced graphene oxide.  

Science.gov (United States)

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

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

2014-10-14

199

Electron transfer dynamics: Zusman equation versus exact theory  

International Nuclear Information System (INIS)

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

200

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

 
 
 
 
201

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

202

Vibrational coherence in electron transfer: The tetracyanoethylene-pyrene complex  

Science.gov (United States)

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

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

1996-08-01

203

Auger-assisted electron transfer from photoexcited semiconductor quantum dots.  

Science.gov (United States)

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

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

2014-03-12

204

Theoretical aspects of electron transfer reactions of complex molecules  

DEFF Research Database (Denmark)

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

Ulstrup, Jens

2001-01-01

205

Photoinduced Electron Transfer in a Charge-Transfer Complex Formed between Corannulene and Li(+)@C60 by Concave-Convex ?-? Interactions.  

Science.gov (United States)

A charge-transfer (CT) complex was formed between corannulene (C20H10) and lithium ion-encapsulated [60]fullerene (Li(+)@C60) with the binding constant KG = 1.9 × 10 M(-1) by concave-convex ?-? CT interactions in benzonitrile at 298 K, exhibiting a broad CT absorption extended to the NIR region. Femotosecond laser excitation of the C20H10/Li(+)@C60 CT complex resulted in the singlet charge-separated (CS) state, (1)(C20H10(•+)/Li(+)@C60(•-)), which decayed with the lifetime of 1.4 ns. Nanosecond laser excitation of Li(+)@C60 resulted in intermolecular electron transfer (ET) from C20H10 to the triplet excited state of Li(+)@C60 [(3)(Li(+)@C60)*] to produce the triplet CS state (3)(C20H10(•+)/Li(+)@C60(•-)). The distance between two electron spins in the triplet CS state was estimated to be 10 Å from the zero-field splitting pattern observed by EPR measurements at 4 K. The triplet CS state decayed to the ground state via intramolecular back electron transfer (BET). The CS lifetime was determined to be 240 ?s in benzonitrile at 298 K. The temperature dependence of the rate constant of BET afforded the reorganization energy (? = 1.04 eV) and the electronic coupling term (V = 0.0080 cm(-1)). The long lifetime of triplet CS state results from the spin-forbidden BET process and a small V value. PMID:25166343

Yamada, Mihoko; Ohkubo, Kei; Shionoya, Mitsuhiko; Fukuzumi, Shunichi

2014-09-24

206

Conformational dependence of electron transfer across de novo designed metalloproteins.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

1996-01-01

207

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

208

Theory of electron transfer and molecular state in DNA  

Science.gov (United States)

In this thesis, a mechanism for long-range electron transfer in DNA and a systematic search for high conductance DNA are developed. DNA is well known for containing the genetic code of all living species. On the other hand, there are some experimental indications that DNA can mediate effectively long-range electron transfer leading to the concept of chemistry at a distance. This can be important for DNA damage and healing. In the first part of the thesis, a possible mechanism for long-range electron transfer is introduced. The weak distance dependent electron transfer was experimentally observed using transition metal intercalators for donor and acceptor. In our model calculations, the transfer is mediated by the molecular analogue of a Kondo bound state well known from solid state physics of mixed-valence rare-earth compounds. We believe this is quite realistic, since localized d orbitals of the transition metal ions could function as an Anderson impurity embedded in a reservoir of rather delocalized molecular orbitals of the intercalator ligands and DNA pi orbitals. The effective Anderson model is solved with a physically intuitive variational ansatz as well as with the essentially exact DMRG method. The electronic transition matrix element, which is important because it contains the donor-acceptor distance dependence, is obtained with the Mulliken-Hush algorithm as well as from Born-Oppenheimer potential energy surfaces. Our possible explanation of long-range electron transfer is put in context to other more conventional mechanisms which also could lead to similar behavior. Another important issue of DNA is its possible use for nano-technology. Although DNA's mechanical properties are excellent, the question whether it can be conducting and be used for nano-wires is highly controversial. Experimentally, DNA shows conducting, semi-conducting and insulating properties. Motivated by these wide ranging experimental results on the conductivity of DNA, we have embarked on a theoretical effort to ascertain what conditions might induce such remarkable behavior. We use a combination of an ab initio density functional theory method and a parameterized Huckel-Slater-Koster model. Our focus here is to examine whether any likely DNA structures or environments can yield reduced activation gaps to conduction or enhanced electronic overlaps. In particular, we study a hypothetical stretched ribbon structure, A-, and B-form DNA, and the effects of counterions and humidity. Unlike solids, DNA and other molecules are considered soft condensed matter. Hence, we study the influence of vibrations upon the electronic structure of DNA. We calculate parameters for charge transfer rates between adjacent bases. We find good agreement between our estimated rates and recent experimental data assuming that torsional vibrations limit the charge transfer most significantly.

Endres, Robert Gunter

2002-09-01

209

Energy and electron transfer processes in polymethine dyes  

International Nuclear Information System (INIS)

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

210

Quality assurance and data collection -- Electronic Data Transfer  

International Nuclear Information System (INIS)

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

211

Electron-transfer processes in fast ion-atom collisions  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

Støchkel, Kristian

2005-01-01

212

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

213

Resonant Auger decay driving intermolecular Coulombic decay in molecular dimers  

Science.gov (United States)

In 1997, it was predicted that an electronically excited atom or molecule placed in a loosely bound chemical system (such as a hydrogen-bonded or van-der-Waals-bonded cluster) could efficiently decay by transferring its excess energy to a neighbouring species that would then emit a low-energy electron. This intermolecular Coulombic decay (ICD) process has since been shown to be a common phenomenon, raising questions about its role in DNA damage induced by ionizing radiation, in which low-energy electrons are known to play an important part. It was recently suggested that ICD can be triggered efficiently and site-selectively by resonantly core-exciting a target atom, which then transforms through Auger decay into an ionic species with sufficiently high excitation energy to permit ICD to occur. Here we show experimentally that resonant Auger decay can indeed trigger ICD in dimers of both molecular nitrogen and carbon monoxide. By using ion and electron momentum spectroscopy to measure simultaneously the charged species created in the resonant-Auger-driven ICD cascade, we find that ICD occurs in less time than the 20femtoseconds it would take for individual molecules to undergo dissociation. Our experimental confirmation of this process and its efficiency may trigger renewed efforts to develop resonant X-ray excitation schemes for more localized and targeted cancer radiation therapy.

Trinter, F.; Schöffler, M. S.; Kim, H.-K.; Sturm, F. P.; Cole, K.; Neumann, N.; Vredenborg, A.; Williams, J.; Bocharova, I.; Guillemin, R.; Simon, M.; Belkacem, A.; Landers, A. L.; Weber, Th.; Schmidt-Böcking, H.; Dörner, R.; Jahnke, T.

2014-01-01

214

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

215

Electron transfer kinetics on mono- and multilayer graphene.  

Science.gov (United States)

Understanding of the electrochemical properties of graphene, especially the electron transfer kinetics of a redox reaction between the graphene surface and a molecule, in comparison to graphite or other carbon-based materials, is essential for its potential in energy conversion and storage to be realized. Here we use voltammetric determination of the electron transfer rate for three redox mediators, ferricyanide, hexaammineruthenium, and hexachloroiridate (Fe(CN)6(3-), Ru(NH3)6(3+), and IrCl6(2-), respectively), to measure the reactivity of graphene samples prepared by mechanical exfoliation of natural graphite. Electron transfer rates are measured for varied number of graphene layers (1 to ca. 1000 layers) using microscopic droplets. The basal planes of mono- and multilayer graphene, supported on an insulating Si/SiO2 substrate, exhibit significant electron transfer activity and changes in kinetics are observed for all three mediators. No significant trend in kinetics with flake thickness is discernible for each mediator; however, a large variation in kinetics is observed across the basal plane of the same flakes, indicating that local surface conditions affect the electrochemical performance. This is confirmed by in situ graphite exfoliation, which reveals significant deterioration of initially, near-reversible kinetics for Ru(NH3)6(3+) when comparing the atmosphere-aged and freshly exfoliated graphite surfaces. PMID:25290250

Velický, Mat?j; Bradley, Dan F; Cooper, Adam J; Hill, Ernie W; Kinloch, Ian A; Mishchenko, Artem; Novoselov, Konstantin S; Patten, Hollie V; Toth, Peter S; Valota, Anna T; Worrall, Stephen D; Dryfe, Robert A W

2014-10-28

216

Theoretical studies of electron transfer through dendrimeric architecture  

Science.gov (United States)

We have analyzed the steady-state electron transfer rate through a bridge of dendrimeric architecture. The difference between the linear chain and the dendrimeric architecture has also been demonstrated with steady-state rate as a main observable in the coherent and incoherent regimes of interactions. It is shown that generally the rate of electron transfer in dendrimeric architecture is faster than the rate associated with their linear chain counterpart with similar kind of bonding connectivities. The rate depends upon the size of the molecule, core branching, and the nature of the coupling among the different nodes on the dendrimer molecule. Depending upon the nature of the donor and acceptor, phenomenological dephasing coefficient due to environment and the geometry of the dendrimeric architecture, the modification of electron transfer rate has been studied. In the regime of fully coherent interactions where all quantum effects are considered the rate shows a multiple inversion due to the dendrimer architecture which is neither available in the regime of incoherent interaction nor in the linear chain case in similar condition. We have discussed about the applicability of our model in metal-molecule-metal junction, photoinduced electron transfer process, and molecular conductor.

Rana, Dipankar; Gangopadhyay, Gautam

2006-01-01

217

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

Energy Technology Data Exchange (ETDEWEB)

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

Lian, Tianquan

2014-04-22

218

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2013-01-01

219

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

Energy Technology Data Exchange (ETDEWEB)

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

1990-02-14

220

Multicopper oxidases : intramolecular electron transfer and O2 reduction  

DEFF Research Database (Denmark)

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

Wherland, Scot; Farver, Ole

2014-01-01

 
 
 
 
221

Protein dynamics modulated electron transfer kinetics in early stage photosynthesis  

Science.gov (United States)

A recent experiment has probed the electron transfer kinetics in the early stage of photosynthesis in Rhodobacter sphaeroides for the reaction center of wild type and different mutants [Science 316, 747 (2007)]. By monitoring the changes in the transient absorption of the donor-acceptor pair at 280 and 930 nm, both of which show non-exponential temporal decay, the experiment has provided a strong evidence that the initial electron transfer kinetics is modulated by the dynamics of protein backbone. In this work, we present a model where the electron transfer kinetics of the donor-acceptor pair is described along the reaction coordinate associated with the distance fluctuations in a protein backbone. The stochastic evolution of the reaction coordinate is described in terms of a non-Markovian generalized Langevin equation with a memory kernel and Gaussian colored noise, both of which are completely described in terms of the microscopics of the protein normal modes. This model provides excellent fits to the transient absorption signals at 280 and 930 nm associated with protein distance fluctuations and protein dynamics modulated electron transfer reaction, respectively. In contrast to previous models, the present work explains the microscopic origins of the non-exponential decay of the transient absorption curve at 280 nm in terms of multiple time scales of relaxation of the protein normal modes. Dynamic disorder in the reaction pathway due to protein conformational fluctuations which occur on time scales slower than or comparable to the electron transfer kinetics explains the microscopic origin of the non-exponential nature of the transient absorption decay at 930 nm. The theoretical estimates for the relative driving force for five different mutants are in close agreement with the experimental estimates obtained using electrochemical measurements.

Kundu, Prasanta; Dua, Arti

2013-01-01

222

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

223

Charge transfer and electron emission in ion-surface interactions  

International Nuclear Information System (INIS)

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

224

Mechanism of electron transfer processes photoinduced by lumazine.  

Science.gov (United States)

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

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

2012-02-01

225

Single electron transfer in thermally annealed nanoparticle dropcast thick films  

Science.gov (United States)

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

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

2009-01-01

226

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

DEFF Research Database (Denmark)

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

Solov'yov, Ilia; Chang, Po-Yao

2012-01-01

227

Photoinduced electron-transfer reactions of aryl glycosides  

Energy Technology Data Exchange (ETDEWEB)

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

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

1983-01-01

228

Intermolecular vibrational energy exchange directly probed with ultrafast two dimensional infrared spectroscopy  

Science.gov (United States)

Ultrafast two dimensional infrared (2D IR) spectroscopy has been applied to probe the intermolecular vibrational energy exchange between two model molecules, benzonitrile and acetonitrile-d3. The vibrational energy exchange between these two molecules is manifested through the growth of cross peaks in their 2D IR spectra. In experiments, their nitrile groups (CN) are not involved in the energy exchange but serve as reporters of the process. Our experiments demonstrate that intermolecular vibrational energy transfer can be directly probed with the 2D IR method. Results also show that the mode specific energy transfer can be important in intermolecular vibrational energy transfers.

Bian, Hongtao; Zhao, Wei; Zheng, Junrong

2009-09-01

229

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

Science.gov (United States)

The ab initio theoretical approach to calculations of molecular electron transfer rate and molecular junction conductance is presented. The implemented approach is founded on Landauer formalism coupled to electron propagator theory (Green-Keldysh functions formalism) of solving the Dyson equation for molecular junction. The electron transfer rate calculation algorithm implementing quantum chemistry computational software output is proposed. The conductance through a single molecular orbital is found to be equal to a quantum of conductance, 2e2/h. The existence of the maximal value of electron transfer rate through a single molecular orbital is proposed, (?2/4h)?L?RF, whose order-of-magnitude estimate is 1011-1013 s-1.

Kletsov, Aleksey A.

2014-09-01

230

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

Science.gov (United States)

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

Eisenmayer, Thomas J; Buda, Francesco

2014-10-20

231

Theoretical investigation of electronic excitation energy transfer in bichromophoric assemblies.  

Science.gov (United States)

Electronic excitation energy transfer (EET) rates in rylene diimide dyads are calculated using second-order approximate coupled-cluster theory and time-dependent density functional theory. We investigate the dependence of the EET rates on the interchromophoric distance and the relative orientation and show that Forster theory works quantitatively only for donor-acceptor separations larger than roughly 5 nm. For smaller distances the EET rates are over- or underestimated by Forster theory depending on the respective orientation of the transition dipole moments of the chromophores. In addition to the direct transfer rates we consider bridge-mediated transfer originating from oligophenylene units placed between the chromophores. We find that the polarizability of the bridge significantly enhances the effective interaction. We compare our calculations to single molecule experiments on two types of dyads and find reasonable agreement between theory and experiment. PMID:18298155

Fückel, Burkhard; Köhn, Andreas; Harding, Michael E; Diezemann, Gregor; Hinze, Gerald; Basché, Thomas; Gauss, Jürgen

2008-02-21

232

Electron transfer to Ar2+ from rare-gas atoms  

International Nuclear Information System (INIS)

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

233

Large scale oil lease automation and electronic custody transfer  

International Nuclear Information System (INIS)

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

234

Photophysical and electron transfer studies of a stable carbocation  

Science.gov (United States)

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

Dileesh, S.; Gopidas, K. R.

2000-11-01

235

Molecular model for aqueous ferrous--ferric electron transfer  

Energy Technology Data Exchange (ETDEWEB)

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

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

1988-09-01

236

Intermittent Single-Molecule Interfacial Electron Transfer Dynamics  

International Nuclear Information System (INIS)

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

237

Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2011-01-01

238

Electrochemical studies on small electron transfer proteins using membrane electrodes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2003-01-01

239

Marcus wins nobel prize in chemistry for electron transfer theory  

International Nuclear Information System (INIS)

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

240

Low activation barriers characterize intramolecular electron transfer in ascorbate oxidase  

DEFF Research Database (Denmark)

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

Farver, O; Pecht, I

1992-01-01

 
 
 
 
241

Photoinduced electron transfer in singly labeled thiouredopyrenetrisulfonate azurin derivatives  

DEFF Research Database (Denmark)

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

Borovok, N; Kotlyar, A B

1999-01-01

242

The electron transfer system of syntrophically grown Desulfovibrio vulgaris  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-05-01

243

The Electron Transfer System of Syntrophically Grown Desulfovibrio vulgaris  

Energy Technology Data Exchange (ETDEWEB)

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

PBD; ENIGMA; GTL; VIMSS; Walker, Christopher B.; He, Zhili; Yang, Zamin K.; Ringbauer Jr., Joseph A.; He, Qiang; Zhou, Jizhong; Voordouw, Gerrit; Wall, Judy D.; Arkin, Adam P.; Hazen, Terry C.; Stolyar, Sergey; Stahl, David A.

2009-06-22

244

Electron transfer reactions within zeolites: Radical cation from benzonorbornadiene  

Energy Technology Data Exchange (ETDEWEB)

Zeolites are being used as solid acid catalysts in a number of commercial processes. Occasionally zeolites are also reported to perform as electron transfer agents. Recently, we observed that radical cations of certain olefins and thiophene oligomers can be generated spontaneously within ZSM-5 zeolites. We noticed that these radical cations generated from diphenyl polyenes and thiophene oligomers were remarkably stable (at room temperature) within ZSM-5 and can be characterized spectroscopically at leisure. We have initiated a program on electron transfer processes within large pore zeolites. The basis of this approach is that once a cation radical is generated within a large pore zeolite, it will have sufficient room to undergo a molecular transformation. Our aim is to identify a condition under which electron transfer can be routinely and reliably carried out within large pore zeolites such as faujasites. To our great surprise, when benzonorbornadiene A and a number of olefins were included in divalent cation exchanged faujasites. they were transformed into products very quickly (<15 min). This observation allowed us to explore the use of zeolites as oxidants. Results of our studies on benzonorbornadiene are presented in this communication. 16 refs., 1 fig.

Pitchumani, K.; Ramamurthy, V. [Tulane Univ., New Orleans, LA (United States); Corbin, D.R. [The Du Pont Company, Wilmington, DE (United States)

1996-08-28

245

Nanoparticle facilitated extracellular electron transfer in microbial fuel cells.  

Science.gov (United States)

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

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

2014-11-12

246

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

Science.gov (United States)

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

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

2014-05-19

247

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

248

Computational studies on intermolecular interactions in solvation  

Science.gov (United States)

This thesis presents the results of computational studies of intermolecular interactions in various contexts. We first investigated the relation between solute-solvent intermolecular interactions and local density augmentation in supercritical solvation. The phenomenon of interest is the excess density that exists in the neighborhood of an attractive solute in a supercritical solvent in the vicinity of the critical point. In Chapter 2, we examined the ability of various measures of the strength of solute-solvent interactions, calculated from all-atom potential functions, to correlate the extent of local density augmentation in both experimental and model solvents. The Gibbs Ensemble Monte Carlo (GEMC) method enables us to calculate phase equilibrium in pure substances and mixtures. It provides a convenient way to test and develop model potentials. In Chapter 3 we present some methodological aspects of such calculations, the issues related to approach to critical points and finite-size effects and applications to simple fluids. Chapter 4 then describes a simplified 2-site potential model for simulating supercritical fluoroform. The GEMC method was used to simulate the vapor-liquid coexistence curve of the model fluid and the dynamic properties were studied by performing NVT molecular dynamics (MD) simulations. The results show that despite its simplicity, this model is able to reproduce many important properties of supercritical fluoroform, making it useful in molecular simulations of supercritical solvation. In the above two studies, the intermolecular interactions are described by a sum of pair-wise additive Lennard-Jones + Coulomb terms. The standard Lorentz-Berthelot combining rules (geometric mean rule for well depth and arithmetic mean rule for collision diameter) are commonly applied to account for the unlike pair Lennard-Jones parameters. In Chapter 5, we examined the applicability of the combining rules for modeling alkane-perfluoroalkane interactions. It was found that the geometric combining rule fails to predict the "weaker-than-expected" alkane-perfluoroalkane interactions, as illustrated by the systematic disagreements with experiment in the case of cross second pressure viral coefficients, gas solubilities, and liquid-liquid mixing properties. In Chapter 6, this study was extended to the investigation on combining rules and potential functions by looking extensively at the limit of accuracy of using some 2-parameter potential functions with some combining rules to represent a wide range of nonpolar interactions by fitting to experimental 2nd pressure virial coefficients. Overall, no pairing of potential function and any combining rules were found to represent simultaneously the intermolecular interactions within the provided experimental uncertainties for the range of molecules involved in the study. The limit of accuracy of representing the interactions using transferable parameters was found to be approximately 10--15%.

Song, Weiping

249

Electron transfer between ? and ? haem groups in haemoglobin  

International Nuclear Information System (INIS)

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

250

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

Science.gov (United States)

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

2010-10-01

251

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

Science.gov (United States)

... A person that provides an electronic fund transfer service to...1) and (2), from two business days to four business days after the consumer learns...and this part with respect to electronic fund transfers initiated...

2010-01-01

252

Effects of molecular orientation on electron-transfer collisions  

International Nuclear Information System (INIS)

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

253

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

254

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

International Nuclear Information System (INIS)

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

255

Charge amplification and transfer processes in the gas electron multiplier  

CERN Document Server

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

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

1999-01-01

256

Effects of electrostatic interactions on electron transfer reactions  

International Nuclear Information System (INIS)

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

257

Noise-assisted quantum electron transfer in photosynthetic complexes  

CERN Document Server

Electron transfer (ET) between primary electron donors and acceptors is modeled in the photosystem II reaction center (RC). Our model includes (i) two discrete energy levels associated with donor and acceptor, interacting through a dipole-type matrix element and (ii) two continuum manifolds of electron energy levels ("sinks"), which interact directly with the donor and acceptor. Namely, two discrete energy levels of the donor and acceptor are embedded in their independent sinks through the corresponding interaction matrix elements. We also introduce classical (external) noise which acts simultaneously on the donor and acceptor (collective interaction). We derive a closed system of integro-differential equations which describes the non-Markovian quantum dynamics of the ET. A region of parameters is found in which the ET dynamics can be simplified, and described by coupled ordinary differential equations. Using these simplified equations, both sharp and flat redox potentials are analyzed. We analytically and nu...

Nesterov, Alexander I; Martínez, José Manuel Sánchez; Sayre, Richard T

2013-01-01

258

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

International Nuclear Information System (INIS)

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

259

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

Science.gov (United States)

Terrestrial plants contain ~70% hemicellulose and cellulose that are a significant renewable bioresource with potential as an alternative to petroleum feedstock for carbon-based fuels. The efficient and selective deconstruction of carbohydrates to their basic components, carbon monoxide and hydrogen, so called synthesis gas, is an important key step towards the realization of this potential, because the formation of liquid hydrocarbon fuels from synthesis gas are known technologies. Here we show that by using a polyoxometalate as an electron transfer-oxygen transfer catalyst, carbon monoxide is formed by cleavage of all the carbon-carbon bonds through dehydration of initially formed formic acid. In this oxidation-reduction reaction, the hydrogen atoms are stored on the polyoxometalate as protons and electrons, and can be electrochemically released from the polyoxometalate as hydrogen. Together, synthesis gas is formed. In a hydrogen economy scenario, this method can also be used to convert carbon monoxide to hydrogen. PMID:25082188

Sarma, Bidyut Bikash; Neumann, Ronny

2014-01-01

260

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

 
 
 
 
261

Concerted proton-electron transfers: electrochemical and related approaches.  

Science.gov (United States)

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

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

2010-07-20

262

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

Science.gov (United States)

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

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

2014-06-20

263

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

Science.gov (United States)

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

2010-04-01

264

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

Science.gov (United States)

... false Payment of tax by electronic fund transfer. 26.112a...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...112a Payment of tax by electronic fund transfer. (a) General...bank in making payment by electronic fund transfer...

2010-04-01

265

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

Science.gov (United States)

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

2010-04-01

266

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

Science.gov (United States)

... false Payment of tax by electronic fund transfer. 24.272...ALCOHOL AND TOBACCO TAX AND TRADE BUREAU, DEPARTMENT OF THE...272 Payment of tax by electronic fund transfer. (a) General...institution in making payment by electronic fund transfer (EFT)...

2010-04-01

267

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

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...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

268

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

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...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

269

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

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...institution to make an electronic fund transfer in the...later than the close of business on the last day for...institution to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

270

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

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...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

271

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

Science.gov (United States)

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund Transfer....

2010-04-01

272

Electron-transfer reactions of tryptophan and tyrosine derivatives  

International Nuclear Information System (INIS)

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

273

Reduced density matrix hybrid approach: Application to electronic energy transfer  

International Nuclear Information System (INIS)

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

274

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

275

Phenomena induced by intermolecular interactions  

International Nuclear Information System (INIS)

This is concerned with recent experimental and theoretical work dealing with phenomena created by the transient dipoles and polarizabilities produced by intermolecular interactions. The former produce absorption from the microwave to the optical regions of the spectrum and the latter produce Rayleigh and Raman scattering; such absorption and scattering would be absent without collisions. Static properties, such as dielectric constant, refractive index, and Kerr effect, also exhibit the effects of induced dipoles and polarizabilities

276

Hetero-cycloreversions mediated by photoinduced electron transfer.  

Science.gov (United States)

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

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

2014-04-15

277

Modeling biofilms with dual extracellular electron transfer mechanisms.  

Science.gov (United States)

Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as terminal electron acceptors for their metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce the requisite components for both mechanisms. In this study, a generic model is presented that incorporates the diffusion- and the conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to S. oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found in the literature. Our simulation results show that (1) biofilms having both mechanisms available, especially if they can interact, may have a metabolic advantage over biofilms that can use only a single mechanism; (2) the thickness of G. sulfurreducens biofilms is likely not limited by conductivity; (3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and (4) the local biofilm potential and redox potential are two distinct parameters and cannot be assumed to have identical values. Finally, we determined that simulated cyclic and squarewave voltammetry based on our model are currently not capable of determining the specific percentages of extracellular electron transfer mechanisms in a biofilm. The developed model will be a critical tool for designing experiments to explain EET mechanisms. PMID:24113651

Renslow, Ryan; Babauta, Jerome; Kuprat, Andrew; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim; Beyenal, Haluk

2013-11-28

278

Modeling biofilms with dual extracellular electron transfer mechanisms  

Energy Technology Data Exchange (ETDEWEB)

Electrochemically active biofilms have a unique form of respiration in which they utilize solid external materials as their terminal electron acceptor for metabolism. Currently, two primary mechanisms have been identified for long-range extracellular electron transfer (EET): a diffusion- and a conduction-based mechanism. Evidence in the literature suggests that some biofilms, particularly Shewanella oneidensis, produce components requisite for both mechanisms. In this study, a generic model is presented that incorporates both diffusion- and conduction-based mechanisms and allows electrochemically active biofilms to utilize both simultaneously. The model was applied to Shewanella oneidensis and Geobacter sulfurreducens biofilms using experimentally generated data found the literature. Our simulation results showed that 1) biofilms having both mechanisms available, especially if they can interact, may have metabolic advantage over biofilms that can use only a single mechanism; 2) the thickness of Geobacter sulfurreducens biofilms is likely not limited by conductivity; 3) accurate intrabiofilm diffusion coefficient values are critical for current generation predictions; and 4) the local biofilm potential and redox potential are two distinct measurements and cannot be assumed to have identical values. Finally, we determined that cyclic and squarewave voltammetry are currently not good tools to determine the specific percentage of extracellular electron transfer mechanisms used by biofilms. The developed model will be a critical tool in designing experiments to explain EET mechanisms.

Renslow, Ryan S.; Babauta, Jerome T.; Kuprat, Andrew P.; Schenk, Jim; Ivory, Cornelius; Fredrickson, Jim K.; Beyenal, Haluk

2013-11-28

279

Microbial interspecies electron transfer via electric currents through conductive minerals.  

Science.gov (United States)

In anaerobic biota, reducing equivalents (electrons) are transferred between different species of microbes [interspecies electron transfer (IET)], establishing the basis of cooperative behaviors and community functions. IET mechanisms described so far are based on diffusion of redox chemical species and/or direct contact in cell aggregates. Here, we show another possibility that IET also occurs via electric currents through natural conductive minerals. Our investigation revealed that electrically conductive magnetite nanoparticles facilitated IET from Geobacter sulfurreducens to Thiobacillus denitrificans, accomplishing acetate oxidation coupled to nitrate reduction. This two-species cooperative catabolism also occurred, albeit one order of magnitude slower, in the presence of Fe ions that worked as diffusive redox species. Semiconductive and insulating iron-oxide nanoparticles did not accelerate the cooperative catabolism. Our results suggest that microbes use conductive mineral particles as conduits of electrons, resulting in efficient IET and cooperative catabolism. Furthermore, such natural mineral conduits are considered to provide ecological advantages for users, because their investments in IET can be reduced. Given that conductive minerals are ubiquitously and abundantly present in nature, electric interactions between microbes and conductive minerals may contribute greatly to the coupling of biogeochemical reactions. PMID:22665802

Kato, Souichiro; Hashimoto, Kazuhito; Watanabe, Kazuya

2012-06-19

280

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

International Nuclear Information System (INIS)

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

 
 
 
 
281

Single Electron Transfer Living Radical Polymerization via a New Initiator  

Science.gov (United States)

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

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

2014-08-01

282

Scanning electron microscopy in nematode-induced giant transfer cells.  

Science.gov (United States)

A study of giant cells induced by the root-knot nematode, Meloidogyne incognita, in roots of Impatiens balsamina was made by scanning electron microscopy. The cytoplasmic contents of giant cells were removed by a procedure based on KOH digestion, to reveal inner wall structure. Wall ingrowths typical of transfer cells are present in giant cells from six days onwards after induction. They develop on walls adjacent to vascular tissues, and their distribution and development was examined. Pit fields contianing plasmodesmata become elaborated in walls between giant cells, but pit fields are lost between giant cells and cells outside them. The distribution of plasmodesmata in pit fields suggests that de novo formation of plasmodesmata occurs in walls between giant cells. Various aspects of giant cell formation and function are discussed and wall ingrowth development is compared in giant cells and normal transfer cells. PMID:1001022

Jones, M G; Dropkin, V H

1976-01-01

283

Advances in Enhanced Boiling Heat Transfer From Electronic Components  

Science.gov (United States)

This paper reviews recent advances in enhancing boiling heat transfer from electronic components immersed in dielectric liquids by use of surface microstructures. The microstructures developed include rough surfaces produced by sanding, vapor blasting hard particles, sputtering of SiO2 followed by wet etching of the surface, chemical vapor deposition of SiO2 film etc., laser-drilled cavities, a brush-like structure (dendritic structure), reentrant and micro-reentrant cavities, microfins, and porous structures fabricated by alumina particle spraying and painting of silver flakes, diamond particles, aluminum particles and copper particles. Heat sink studs with drilled holes, microfins, multi-layered micro-channels and pores, and pin fins with and without microporous coating have also been developed. The height of microstructure ranges from 0 to 12mm. The primary issues discussed are the mitigation of temperature overshoot at boiling incipience, enhancement of nucleate boiling heat transfer and increasing the critical heat flux.

Honda, Hiroshi; Wei, Jinjia

284

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

Science.gov (United States)

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

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

2012-11-01

285

Electron-phonon heat transfer in monolayer and bilayer graphene  

Science.gov (United States)

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

Viljas, J. K.; Heikkilä, T. T.

2010-06-01

286

Coherent wavepacket motion in an ultrafast electron transfer system monitored by femtosecond degenerate four-wave-mixing and pump-probe spectroscopy  

Science.gov (United States)

Coherent nuclear wavepacket motions were monitored by three types of femtosecond time-resolved spectroscopy, namely, transient absorption measurement utilizing white-light supercontinuum (WC-TA), degenerate four-wave-mixing (DFWM), and pump-probe (PP) measurements, for an ultrafast intermolecular electron transfer (ET) system with a dye molecule, oxazine 1 (Ox1), dissolved in an electron donating solvent, N,N-dimethylaniline (DMA). Vibrational frequencies of the wavepacket motion in the excited and in the ground states were 560-562 and 567-569 cm-1, respectively, with only a few frequency difference of 5-9 cm-1, which were clearly distinguishable by the highly accurate measurements. In DMA, the excited state wavepacket motion declined with time constant of 160-240 fs which is somewhat longer than that of the ultrafast ET; 60-80 fs.

Nagasawa, Yutaka; Yoneda, Yusuke; Nambu, Shohei; Muramatsu, Masayasu; Takeuchi, Eisuke; Tsumori, Hiroki; Morikawa, Soichiro; Katayama, Tetsuro; Miyasaka, Hiroshi

2014-10-01

287

Transcriptomic and genetic analysis of direct interspecies electron transfer  

DEFF Research Database (Denmark)

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

Shrestha, Pravin Malla; Rotaru, Amelia-Elena

2013-01-01

288

Transcriptomic and genetic analysis of direct interspecies electron transfer.  

Science.gov (United States)

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

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

2013-04-01

289

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

CERN Document Server

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

Nagesh, Jayashree; Brumer, Paul

2013-01-01

290

Photoinduced Electron Transfer Based Ion Sensing within an Optical Fiber  

Directory of Open Access Journals (Sweden)

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

Tanya M. Monro

2011-10-01

291

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

Science.gov (United States)

Human society faces a fundamental challenge as energy consumption is projected to increase due to population and economic growth as fossil fuel resources decrease. Therefore the transition to alternative and sustainable energy sources is of the utmost importance. The conversion of solar energy into chemical energy, by splitting H2O to generate molecular O2 and H2, could contribute to solving the global energy problem. Developing such a system will require the combination of several complicated processes, such as light-harvesting, charge separation, electron transfer, H2O oxidation, and reduction of the generated protons. The primary processes of charge separation and catalysis, which occur in the natural photosynthetic machinery, provide us with an excellent blueprint for the design of such systems. This Account describes our efforts to construct supramolecular assemblies capable of carrying out photoinduced electron transfer and to develop artificial water oxidation catalysts (WOCs). Early work in our group focused on linking a ruthenium chromophore to a manganese-based oxidation catalyst. When we incorporated a tyrosine unit into these supramolecular assemblies, we could observe fast intramolecular electron transfer from the manganese centers, via the tyrosine moiety, to the photooxidized ruthenium center, which clearly resembles the processes occurring in the natural system. Although we demonstrated multi-electron transfer in our artificial systems, the bottleneck proved to be the stability of the WOCs. Researchers have developed a number of WOCs, but the majority can only catalyze H2O oxidation in the presence of strong oxidants such as Ce(IV), which is difficult to generate photochemically. By contrast, illumination of ruthenium(II) photosensitizers in the presence of a sacrificial acceptor generates [Ru(bpy)3](3+)-type oxidants. Their oxidation potentials are significantly lower than that of Ce(IV), but our group recently showed that incorporating negatively charged groups into the ligand backbone could decrease the oxidation potential of the catalysts and, at the same time, decrease the potential for H2O oxidation. This permitted us to develop both ruthenium- and manganese-based WOCs that can operate under neutral conditions, driven by the mild oxidant [Ru(bpy)3](3+). Many hurdles to the development of viable systems for the production of solar fuels remain. However, the combination of important features from the natural photosynthetic machinery and novel artificial components adds insights into the complicated catalytic processes that are involved in splitting H2O. PMID:23957573

Kärkäs, Markus D; Johnston, Eric V; Verho, Oscar; Akermark, Björn

2014-01-21

292

Parton models of high momentum transfer electron-nuclear scattering  

International Nuclear Information System (INIS)

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

293

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

294

Preliminary estimate of heavy ion electron-transfer cross sections  

International Nuclear Information System (INIS)

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

295

Large momentum transfer electron scattering from few-nucleon systems  

International Nuclear Information System (INIS)

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

296

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

International Nuclear Information System (INIS)

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

297

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

Science.gov (United States)

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

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

2014-09-30

298

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

299

Intermolecular Diels-Alder reactions of brominated masked o-benzoquinones with electron-deficient dienophiles. A detour method to synthesize bicyclo[2.2.2]octenones from 2-methoxyphenols.  

Science.gov (United States)

Intermolecular Diels-Alder reactions of masked o-benzoquinones, i.e., 6,6-dimethoxy-2,4-cyclohexadienones 5-7 and 21-24 generated from 2-methoxyphenols 1-3 and 17-20, respectively, with electron-deficient dienophiles leading to highly functionalized bicyclo[2.2.2]octenones are described. The masked o-benzoquinones (MOBs) 5-7 underwent Diels-Alder cycloadditions with methyl acrylate, methyl methacrylate, and methyl vinyl ketone to provide bicyclo[2.2.2]octenones 13a-c to 15a-c (direct method) in low to moderate yields with the concomitant formation of considerable amounts of dimers 9-11. To retard dimerization and to improve the yields of the requisite bicyclo[2.2.2]octenones, a detour method comprised of sequential bromination of 2-methoxyphenols 1-4, oxidation and Diels-Alder reaction, and debromination has been developed. The oxidation of bromophenols 17-20 produced MOBs 21-24 which are stable enough to be isolated. The MOBs 21-24 underwent cycloaddition with electron-deficient dienophiles in a very efficient manner to afford the corresponding cycloadducts 25a-c to 28a-c in good to high yields without self-dimerization. When the cycloadducts 25a-c to 28a-c were treated with either Bu(3)SnH/AIBN or tributylammonium formate-palladium reagent, the corresponding debrominated products 13a-cto 16a-c were obtained in high to excellent yields. In general, the cycloadducts 13a-c to 15a-c were obtained in 20-40% higher yields via the detour method than those via the direct method. In both routes, the Diels-Alder reactions proceeded in a highly regio- and stereoselective manner to furnish a single cycloadduct in each case. PMID:12201772

Lai, Chien-Hsun; Shen, Yi-Ling; Wang, Min-Nen; Kameswara Rao, N S; Liao, Chun-Chen

2002-09-01

300

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

 
 
 
 
301

Charge amplification and transfer processes in the gas electron multiplier  

International Nuclear Information System (INIS)

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

302

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

Science.gov (United States)

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

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

2014-10-20

303

Determination of the electronics transfer function for current transient measurements  

CERN Document Server

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

Scharf, Christian

2014-01-01

304

Electron-transfer functionality of synthetic coiled-coil metalloproteins  

Scientific Electronic Library Online (English)

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

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

1516-15-01

305

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

306

ELECTRONIC FUNDS TRANSFER: EXPLORING THE DIFFICULTIES OF SECURITY  

Directory of Open Access Journals (Sweden)

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

MPAKWANA ANNASTACIA MTHEMBU

2010-10-01

307

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

Science.gov (United States)

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

2010-01-01

308

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

Science.gov (United States)

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

Shinkarev, Vladimir P; Wraight, Colin A

2007-04-17

309

ATP-induced electron transfer by redox-selective partner recognition  

Science.gov (United States)

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

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

2014-08-01

310

Transfer printing methods for the fabrication of flexible organic electronics  

Science.gov (United States)

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

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

2007-01-01

311

Control of electron acceptor ability with ligands (L) in photoinduced electron transfer from zinc porphyrin or zinc phthalocyanine to [Ru3(mu3-O)(mu-CH3COO)6L3]+.  

Science.gov (United States)

Photoinduced electron-transfer processes from the excited triplet states of zinc tetraphenylporphyrin (3ZnTPP*) or zinc tetra-tert-butylphthalocyanine (3ZnTBPc*) to oxo-acetato-bridged triruthenium clusters [Ru3(mu3-O)(mu-CH3CO2)6(L)3]+ have been confirmed by nanosecond laser flash photolysis in the visible and near-IR regions. The rise of the transient absorption spectra of the radical cations of ZnTPP and ZnTBPc and the reduced form of the oxo-acetato-bridged triruthenium cluster ([Ru3(mu3-O)(mu-CH3CO2)6(L)3]0) were observed with the concomitant decays of 3ZnTPP* or 3ZnTBPc*. The evaluated rate constants (kET) and quantum yields (PhiET) for electron-transfer were increased with the order of electron-withdrawing ability of the ligands (L) coordinated to the Ru atoms, 4-cyanopyridine > triphenylphosphine > pyridine > 4-(dimethylamino)pyridine, which is the order of promoting the electron-accepting ability of [Ru3(mu3-O)(mu-CH3CO2)6(L)3]+. The PhiET values for 3ZnTPP* were lower than those for 3ZnTBPc*, suggesting the presence of competitive processes such as energy transfer process from 3ZnTPP* to the triplet states of [Ru3(mu3-O)(mu-CH3COO)6(L)3]+. For the back electron-transfer process, second-order kinetics indicates that the radical cations of ZnTPP or ZnTBPc and [Ru3(mu3-O)(mu-CH3COO)6(L)3]0 return to the original system after solvation in polar solvents at a diffusion controlled limit without side reactions, providing reversible photosensitizing intermolecular electron-transfer systems. PMID:15733001

Itou, Mitsunari; Otake, Midoriko; Araki, Yasuyuki; Ito, Osamu; Kido, Hiroaki

2005-03-01

312

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

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

2009-01-01

313

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

Science.gov (United States)

Density Functional Theory and Time-Dependent Density Functional Theory calculations have been carried out on a recently synthesized amino-corrole and a corrole-azafullerene dyad which exhibits photoinduced electron transfer (PET). Good agreement of the theoretical results with experiment is obtained regarding the absorption and emission spectra of the corrole, the absorption spectra of the corrole-azafullerene dyad and the transient anionic and cationic radicals of azafullerene and corrole respectively. Application of Mulliken's theory for charge-transfer states yields the excitation energy of the charge-separated state of the dyad very close to the S1 excitation of amino-corrole, consistent with a PET process.

Petsalakis, Ioannis D.; Theodorakopoulos, Giannoula

2014-08-01

314

Interfacial Electron Transfer and Transient Photoconductivity Studied with Terahertz Spectroscopy  

Science.gov (United States)

Terahertz spectroscopy is distinguished from other far infrared and millimeter wave spectroscopies by its inherent phase sensitivity and sub-picosecond time resolution making it a versatile technique to study a wide range of physical phenomena. As THz spectroscopy is still a relatively new field, many aspects of THz generation mechanisms have not been fully examined. Using terahertz emission spectroscopy (TES), THz emission from ZnTe(110) was analyzed and found to be limited by two-photon absorption and free-carrier generation at high excitation fluences. Due to concerns about the continued use of fossil fuels, solar energy has been widely investigated as a promising source of renewable energy. Dye-sensitized solar cells (DSSCs) have been developed as a low-cost alternative to conventional photovoltaic solar cells. To solve the issues of the intermittency and inefficient transport associated with solar energy, researchers are attempting to adapt DSSCs for water oxidation and chemical fuel production. Both device designs incorporate sensitizer molecules covalently bound to metal oxide nanoparticles. The sensitizer, which is comprised of a chromophore and anchoring group, absorbs light and transfers an electron from its excited state to the conduction band of the metal oxide, producing an electric current. Using time-resolved THz spectroscopy (TRTS), an optical pump/THz probe technique, the efficiency and dynamics of electron injection from sensitizers to metal oxides was evaluated as a function of the chromophore, its anchoring group, and the metal oxide identity. Experiments for studying fully functioning DSSCs and water oxidation devices are also described. Bio-inspired pentafluorophenyl porphyrin chromophores have been designed and synthesized for use in photoelectrochemical water oxidation cells. Influences on the efficiency and dynamics of electron injection from the chromophores into TiO2 and SnO2 nanoparticles due to changes in both the central substituent to the porphyrin ring and degree of fluorination of ring substituents were analyzed. Due to the high reduction potentials of these sensitizers, injection into TiO2 was generally not observed. Injection timescales from the porphyrins into SnO2 depended strongly on the identity of the central substituent and were affected by competition with excited-state deactivation processes. The carboxylate anchoring group is commonly used to bind DSSC sensitizers to metal oxide surfaces but is typically not stable under the aqueous and oxidative conditions required for water oxidation. Electron injection efficiency and water stability of several alternative anchoring groups, including phosphonic acid, hydroxamic acid, acerylacetone, and boronic acid, were evaluated. While all of the anchoring groups exhibited water stability superior to carboxylate, the hydroxamate anchor had the best combination of ease of handling and electron injection efficiency. The effects on photoconductivity due to metal oxide morphology and the addition of dopants were also analyzed. Mixtures of anatase and rutile TiO 2 nanoparticles are known to exhibit cooperative effects which increase the efficiency of DSSCs and photocatalysis relative to the pure-phase materials. Through analysis of TRTS measurements, the mechanism of this synergistic effect was found to involve electron transfer from the lower-mobility, higher surface area rutile nanoparticles to anatase particles, resulting in a higher charge collection efficiency. In addition to morphology, doping has been investigated as a means of expanding the spectral range of visible absorption of photocatalysts. Doping ZnO nanowires with manganese(II) was found to significantly decrease the electron mobility, and doping with cobalt(II) increased the timescale for electron trapping. These differences can be understood by considering the changes to the band structure of ZnO effected by the dopants. Preliminary analyses of the solvent and electrolyte dependence on the electron injection rate and efficiency suggest that electron injection can be affected by

Milot, Rebecca Lee

315

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

Science.gov (United States)

We have studied electron transfers (ET) between electron donors and acceptors, taking as illustrative example the case of ET in methionine enkephalin. Recent pulse and gamma radiolysis experiments suggested that an ultrafast ET takes place from the C-terminal tyrosine residue to the N-terminal, oxidized, methionine residue. According to standard theoretical frameworks like the Marcus theory, ET can be decomposed into two successive steps: i) the achievement through thermal fluctuations, of a set of nuclear coordinates associated with degeneracy of the two electronic states, ii) the electron tunneling from the donor molecular orbital to the acceptor molecular orbital. Here, we focus on the analysis of the time-dependent electronic dynamics during the tunneling event. This is done by extending the approaches based on the topological analyses of stationary electronic density and of the electron localization function (ELF) to the time-dependent domain. Furthermore, we analyzed isosurfaces of the divergence of the current density, showing the paths that are followed by the tunneling electron from the donor to the acceptor. We show how these functions can be calculated with constrained density functional theory. Beyond this work, the topological tools used here can open up new opportunities for the electronic description in the time-dependent domain. PMID:25060148

Pilmé, Julien; Luppi, Eleonora; Bergès, Jacqueline; Houée-Lévin, Chantal; de la Lande, Aurélien

2014-08-01

316

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

317

Electron transfer through 3D monolayers on Au25 clusters.  

Science.gov (United States)

The monolayer protecting small gold nanoparticles (monolayer-protected clusters, MPCs) is generally represented as the 3D equivalent of 2D self-assembled monolayers (SAMs) on extended gold surfaces. However, despite the growing relevance of MPCs in important applied areas, such as catalysis and nanomedicine, our knowledge of the structure of 3D SAMs in solution is still extremely limited. We prepared a large series of monodisperse Au25(SCnH2n+1)18 clusters (n=2, 4, 6, 8, 10, 12, 14, 16, 18) and studied how electrons tunnel through these monolayers. Electron transfer results, nicely supported by 1H NMR spectroscopy, IR absorption spectroscopy, and molecular dynamics results, show that there is a critical ligand length marking the transition between short ligands, which form a quite fluid monolayer structure, and longer alkyl chains, which self-organize into bundles. At variance with the truly protecting 2D SAMs, efficient electronic communication of the Au25 core with the outer environment is thus possible even for long alkyl chains. These conclusions provide a different picture of how an ultrasmall gold core talks with the environment through/with its protecting but not-so-shielding monolayer. PMID:24460378

Antonello, Sabrina; Arrigoni, Giorgio; Dainese, Tiziano; De Nardi, Marco; Parisio, Giulia; Perotti, Lorena; René, Alice; Venzo, Alfonso; Maran, Flavio

2014-03-25

318

Carboxylate shifts steer interquinone electron transfer in photosynthesis.  

Science.gov (United States)

Understanding the mechanisms of electron transfer (ET) in photosynthetic reaction centers (RCs) may inspire novel catalysts for sunlight-driven fuel production. The electron exit pathway of type II RCs comprises two quinone molecules working in series and in between a non-heme iron atom with a carboxyl ligand (bicarbonate in photosystem II (PSII), glutamate in bacterial RCs). For decades, the functional role of the iron has remained enigmatic. We tracked the iron site using microsecond-resolution x-ray absorption spectroscopy after laser-flash excitation of PSII. After formation of the reduced primary quinone, Q(A)(-), the x-ray spectral changes revealed a transition (t½ ? 150 ?s) from a bidentate to a monodentate coordination of the bicarbonate at the Fe(II) (carboxylate shift), which reverted concomitantly with the slower ET to the secondary quinone Q(B). A redox change of the iron during the ET was excluded. Density-functional theory calculations corroborated the carboxylate shift both in PSII and bacterial RCs and disclosed underlying changes in electronic configuration. We propose that the iron-carboxyl complex facilitates the first interquinone ET by optimizing charge distribution and hydrogen bonding within the Q(A)FeQ(B) triad for high yield Q(B) reduction. Formation of a specific priming intermediate by nuclear rearrangements, setting the stage for subsequent ET, may be a common motif in reactions of biological redox cofactors. PMID:21169354

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

2011-02-18

319

Path Integral Approach to the Non-Relativistic Electron Charge Transfer  

CERN Document Server

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

Laskin, N

2001-01-01

320

pH-dependent reduction potentials and proton-coupled electron transfer mechanisms in hydrogen-producing nickel molecular electrocatalysts.  

Science.gov (United States)

The nickel-based P2(Ph)N2(Bn) electrocatalysts comprised of a nickel atom and two 1,5-dibenzyl-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane ligands catalyze H2 production in acetonitrile. Recent electrochemical experiments revealed a linear dependence of the Ni(II/I) reduction potential on pH with a slope of 57 mV/pH unit, implicating a proton-coupled electron transfer (PCET) process with the same number of electrons and protons transferred. The combined theoretical and experimental studies herein provide an explanation for this pH dependence in the context of the overall proposed catalytic mechanism. In the proposed mechanisms, the catalytic cycle begins with a series of intermolecular proton transfers from an acid to the pendant amine ligand and electrochemical electron transfers to the nickel center to produce the doubly protonated Ni(0) species, a precursor to H2 evolution. The calculated Ni(II/I) reduction potentials of the doubly protonated species are in excellent agreement with the experimentally observed reduction potential in the presence of strong acid, suggesting that the catalytically active species leading to the peak observed in these cyclic voltammetry (CV) experiments is doubly protonated. The Ni(I/0) reduction potential was found to be slightly more positive than the Ni(II/I) reduction potential, indicating that the Ni(I/0) reduction occurs spontaneously after the Ni(II/I) reduction, as implied by the experimental observation of a single CV peak. These results suggest that the PCET process observed in the CV experiments is a two-electron/two-proton process corresponding to an initial double protonation followed by two reductions. On the basis of the experimental and theoretical data, the complete thermodynamic scheme and the Pourbaix diagram were generated for this catalyst. The Pourbaix diagram, which identifies the most thermodynamically stable species at each reduction potential and pH value, illustrates that this catalyst undergoes different types of PCET processes for various pH ranges. These thermodynamic insights will aid in the design of more effective molecular catalysts for H2 production. PMID:23477912

Horvath, Samantha; Fernandez, Laura E; Appel, Aaron M; Hammes-Schiffer, Sharon

2013-04-01

 
 
 
 
321

Electronic shift register memory based on molecular electron-transfer reactions  

Science.gov (United States)

The design of a shift register memory at the molecular level is described in detail. The memory elements are based on a chain of electron-transfer molecules incorporated on a very large scale integrated (VLSI) substrate, and the information is shifted by photoinduced electron-transfer reactions. The design requirements for such a system are discussed, and several realistic strategies for synthesizing these systems are presented. The immediate advantage of such a hybrid molecular/VLSI device would arise from the possible information storage density. The prospect of considerable savings of energy per bit processed also exists. This molecular shift register memory element design solves the conceptual problems associated with integrating molecular size components with larger (micron) size features on a chip.

Hopfield, J. J.; Onuchic, Jose Nelson; Beratan, David N.

1989-01-01

322

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

Science.gov (United States)

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

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

2014-08-19

323

Bond charges and electronic charge transfer in ternary semiconductors  

International Nuclear Information System (INIS)

By means of a simple molecule-theoretic model of 'linear superposition of two-electron molecules' the bond charges between nearest neighbours and the effective charges of ions are calculated for ternary zinc-blende structure alloys as well as chalcopyrite semiconductors. Taking into account both, the charge transfer among the ions caused by the differences of electronegativities of atoms used and between the bonds created by the internal stress of the lattice a nearly unvaried averaged bond charge amount of the alloy is found, but rather dramatically changed local bond charge parameters in comparison with the respective values of binary compounds used. This fact should influence the noncentral force interaction in such semiconductors. (author)

324

Electron impact single ionization of helium with large energy transfer  

International Nuclear Information System (INIS)

We report triply differential cross section (TDCS) for electron impact single ionization of helium at the incident energy of 729.6 eV for a variety of scattering angles and ejection energies. The calculations are based on two different methods, namely, the Glauber approximation (GA) and the 3C approximation, also called the BBK method. In the GA the effects of post collision interaction have been taken into account by a classical method, whereas the BBK method has been studied with and without exchange. A comparison is made of the present TDCS with the results of other calculations and the experimental data from two different laboratories. For large energy transfer we find a significant contribution from the exchange effect. Both the GA-PCI and the BBK methods show some shifts in the position of binary maxima which are in reasonably good agreement with experiment

325

Reorganization energy of electron transfer at the solvent glass transition  

CERN Document Server

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

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

2005-01-01

326

Facile direct electron transfer in glucose oxidase modified electrodes  

International Nuclear Information System (INIS)

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

327

Electron transfer in systems of well-defined geometry  

Energy Technology Data Exchange (ETDEWEB)

Two mesopyropheophorbide macrocycles can be joined via two covalent linkages to produce a cyclophane. It is possible to insert one or two Mg atoms into the cyclophane. The Qy transitions of the macrocycles are nearly orthogonal. The visible absorption spectrum of the monometal cyclophane is nearly a superposition of the spectra of the monomers. Emission from the monometal cyclophane arises primarily from the red most absorbing chromophore. The excited state difference spectrum shows that both macrocycles are excited. Fluorescence lifetimes of the monometal cyclophane decrease with increasing dielectric strength. Changes in the fluorescence and the triplet yield parallel the shortening of the singlet lifetime. Thus the radiative rate is solvent independent. This is in contrast to what one would expect if the emitting state had charge transfer character. Since the fluorescence lifetime is dependent on dielectric, the nonradiative relaxation from the singlet state is due to formation of a radical pair. The decay rate of the postulated radical pair was monitored by observing the kinetics of ground state repopulation. For the geometry of this cyclophane, electron transfer proceeds relatively slowly (k = 3 x 10/sup 9/ sec/sup -1/) in the forward direction. Modeling calculations indicate that the rate of annihilation of the radical pair may decrease as the solvent dielectric decreases.

Overfield, R.E.; Kaufmann, K.J.; Wasielewski, M.R.

1980-01-01

328

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

Science.gov (United States)

...taxpayer's bank to make an electronic fund transfer in the...later than the close of business on the last day for filing...the bank to effect an electronic fund transfer message...before the close of business on the prescribed last...Payment of Tax by Electronic Fund...

2010-04-01

329

Hierarchical intermolecular interaction models of N-heteroaromatic STM adlayer structures  

Science.gov (United States)

The molecular scale electronic device concept was initiated in 1974 with the semi-quantitative analysis of a hemiquinone molecule. Because of the molecule's electron donor and acceptor properties, and ability to transfer electrons along the pi-network, it was proposed that the molecule could perform as a circuit rectifier. Many investigations of molecular scale systems have occurred since then, in particular, of organic molecules with large, fused ring systems that spontaneously self-organize after deposition onto a substrate. The directionality and molecular specificity of hydrogen bonding differentiates it from the other weak interactions, driving molecules into specific arrangements and enabling spontaneous rearrangement after addition of only a small amount of enthalpic energy. A direct application of molecular recognition through self-assembly has been the design of patterned self-assembled monolayers (SAMs) for the construction of microelectrodes and supramolecular templates. However, the intermolecular interactions that drive ordered structures to form, including molecular chains and large aggregates, has not been well understood. To elucidate a quantitative description of the intermolecular forces of pi network systems of aromatics that control such features as packing density and porosity, two individual model heteroaromatic systems of 9-acridinecarboxylic acid and isonicotinic acid are investigated using both experimental and computational resources. Supported by scanning tunneling microscopy (STM) topographies, x-ray diffraction (XRD) data and x-ray photoelectron (XPS) spectra, this class of N-heteroaromatics adsorbed on Ag (111) serves as a model system to systematically investigate 2-dimensional intermolecular (2-D) interactions and their impact on forming different structural phases of molecular chain domains. To approach an understanding of the dynamics of N-heteroaromatic film growth, an intermolecular interaction model of 1-D single phase chains and clusters is performed. The model considers the anisotropy of the electrostatic force interactions to determine what charge arrangements (dipole, quadrupole, etc.) better characterize the molecular interactions. Furthermore, the competition between phase chain types is shown to be length dependent and in qualitative agreement with the coverage dependent STM structural phase composition.

Evans, Diane

330

Modular electron transfer circuits for synthetic biology: insulation of an engineered biohydrogen pathway.  

Science.gov (United States)

Electron transfer is central to a wide range of essential metabolic pathways, from photosynthesis to fermentation. The evolutionary diversity and conservation of proteins that transfer electrons makes these pathways a valuable platform for engineered metabolic circuits in synthetic biology. Rational engineering of electron transfer pathways containing hydrogenases has the potential to lead to industrial scale production of hydrogen as an alternative source of clean fuel and experimental assays for understanding the complex interactions of multiple electron transfer proteins in vivo. We designed and implemented a synthetic hydrogen metabolism circuit in Escherichia coli that creates an electron transfer pathway both orthogonal to and integrated within existing metabolism. The design of such modular electron transfer circuits allows for facile characterization of in vivo system parameters with applications toward further engineering for alternative energy production. PMID:21468209

Agapakis, Christina M; Silver, Pamela A

2010-01-01

331

Mechanistic insights into hydride-transfer and electron-transfer reactions by a manganese(IV)-oxo porphyrin complex.  

Science.gov (United States)

Hydride transfer from dihydronicotinamide adenine dinucleotide (NADH) analogs to a manganese(IV)-oxo porphyrin complex, (TMP)Mn(IV)(O) [TMP = 5,10,15,20-tetrakis(2,4,6-trimethylphenyl)porphyrin], occurs via disproportionation of (TMP)Mn(IV)(O) to [(TMP)Mn(III)](+) and [(TMP)Mn(V)(O)](+) that acts as the actual hydride acceptor. In contrast, electron transfer from ferrocene derivatives to (TMP)Mn(IV)(O) occurs directly to afford ferricenium ions and (TMP)Mn(III)(OH) products. The disproportionation rate constant of (TMP)Mn(IV)(O) was determined by the dependence of the observed second-order rate constants on concentrations of NADH analogs to be (8.0 +/- 0.6) x 10(6) M(-1) s(-1) in acetonitrile at 298 K. The disproportionation rate constant of (TMP)Mn(IV)(O) in hydride-transfer reactions increases linearly with increasing acid concentration, whereas the rate constant of electron transfer from ferrocene to (TMP)Mn(IV)(O) remains constant irrespective of the acid concentration. The rate constants of electron transfer from a series of ferrocene derivatives to (TMP)Mn(IV)(O) were evaluated in light of the Marcus theory of electron transfer to determine the reorganization energy of electron transfer by the (TMP)Mn(IV)(O) complex. PMID:19888722

Fukuzumi, Shunichi; Fujioka, Naofumi; Kotani, Hiroaki; Ohkubo, Kei; Lee, Yong-Min; Nam, Wonwoo

2009-12-01

332

Ions interacting with planar aromatic molecules: Modeling electron transfer reactions  

Energy Technology Data Exchange (ETDEWEB)

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

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

2013-02-07

333

Human ceruloplasmin. Intramolecular electron transfer kinetics and equilibration  

DEFF Research Database (Denmark)

Pulse radiolytic reduction of disulfide bridges in ceruloplasmin yielding RSSR(-) radicals induces a cascade of intramolecular electron transfer (ET) processes. Based on the three-dimensional structure of ceruloplasmin identification of individual kinetically active disulfide groups and type 1 (T1) copper centers, the following is proposed. The first T1 copper(II) ion to be reduced in ceruloplasmin is the blue copper center of domain 6 (T1A) by ET from RSSR(-) of domain 5. The rate constant is 28 +/- 2 s(-1) at 279 K and pH 7.0. T1A is in close covalent contact with the type 3 copper pair and indeed electron equilibration between T1A and the trinuclear copper center in the domain 1-6 interface takes place with a rate constant of 2.9 +/- 0.6 s(-1). The equilibrium constant is 0.17. Following reduction of T1A Cu(II), another ET process takes place between RSSR(-) and T1B copper(II) of domain 4 with a rate constant of 3.9 +/- 0.8. No reoxidation of T1B Cu(I) could be resolved. It appears that the third T1 center(T1C of domain 2) is not participating in intramolecular ET, as it seems to be in a reduced state in the resting enzyme.

Farver, O; Bendahl, L

1999-01-01

334

Photoinduced electron transfer processes in homogeneous and microheterogeneous solutions  

Science.gov (United States)

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

Whitten, D. G.

1990-10-01

335

Contrasting effects of axial ligands on electron-transfer versus proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes.  

Science.gov (United States)

The effects of axial ligands on electron-transfer and proton-coupled electron-transfer reactions of mononuclear nonheme oxoiron(IV) complexes were investigated by using [Fe(IV)(O)(tmc)(X)](n+) (1-X) with various axial ligands, in which tmc is 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane and X is CH(3)CN (1-NCCH(3)), CF(3)COO(-) (1-OOCCF(3)), or N(3) (-) (1-N(3)), and ferrocene derivatives as electron donors. As the binding strength of the axial ligands increases, the one-electron reduction potentials of 1-X (E(red), V vs. saturated calomel electrode (SCE)) are more negatively shifted by the binding of the more electron-donating axial ligands in the order of 1-NCCH(3) (0.39) > 1-OOCCF(3) (0.13) > 1-N(3) (-0.05 V). Rate constants of electron transfer from ferrocene derivatives to 1-X were analyzed in light of the Marcus theory of electron transfer to determine reorganization energies (lambda) of electron transfer. The lambda values decrease in the order of 1-NCCH(3) (2.37) > 1-OOCCF(3) (2.12) > 1-N(3) (1.97 eV). Thus, the electron-transfer reduction becomes less favorable thermodynamically but more favorable kinetically with increasing donor ability of the axial ligands. The net effect of the axial ligands is the deceleration of the electron-transfer rate in the order of 1-NCCH(3) > 1-OOCCF(3) > 1-N(3). In sharp contrast to this, the rates of the proton-coupled electron-transfer reactions of 1-X are markedly accelerated in the presence of an acid in the opposite order: 1-NCCH(3) < 1-OOCCF(3) < 1-N(3). Such contrasting effects of the axial ligands on the electron-transfer and proton-coupled electron-transfer reactions of nonheme oxoiron(IV) complexes are discussed in light of the counterintuitive reactivity patterns observed in the oxo transfer and hydrogen-atom abstraction reactions by nonheme oxoiron(IV) complexes (Sastri et al. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 19 181-19 186). PMID:19937616

Fukuzumi, Shunichi; Kotani, Hiroaki; Suenobu, Tomoyoshi; Hong, Seungwoo; Lee, Yong-Min; Nam, Wonwoo

2010-01-01

336

Pyrylogens: synthesis, structural, electrochemical, and photophysical characterization of a new class of electron transfer sensitizers.  

Science.gov (United States)

The synthesis and photophysical properties of a new series of dicationic electron transfer sensitizers have been reported. These new materials, pyrylogens, are hybrids of pyrylium cations and Viologen dications. Electron transfer reactions of neutral organic substrates using these new sensitizers generate radical-cation/radical-cation pairs whose repulsive (repellent) interaction is designed to compete with energy wasting return electron transfer (RET) by enhancing diffusive separation and formation of solvent separated ions. PMID:18500798

Clennan, Edward L; Liao, Chen; Ayokosok, Erambo

2008-06-18

337

Proton-coupled electron transfer: the mechanistic underpinning for radical transport and catalysis in biology  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Charge transport and catalysis in enzymes often rely on amino acid radicals as intermediates. The generation and transport of these radicals are synonymous with proton-coupled electron transfer (PCET), which intrinsically is a quantum mechanical effect as both the electron and proton tunnel. The caveat to PCET is that proton transfer (PT) is fundamentally limited to short distances relative to electron transfer (ET). This predicament is resolved in biology by the evolution of enzymes to contr...

Reece, Steven Y.; Hodgkiss, Justin M.; Stubbe, Joanne; Nocera, Daniel G.

2006-01-01

338

Quantitative exploration of electron transfer in a single noncovalent supramolecular assembly.  

Science.gov (United States)

Electron transfer through a noncovalent interaction bears essential relevance to the functions of bottom-up supramolecular assembly. However, rather little knowledge regarding such phenomena at the single-molecule level is currently available. Herein we report the direct quantification of electron-transfer processes for a single noncovalently linked porphyrin-fullerene dyad. Facilitated electron transfer via a charge-transfer interaction in-between was successfully measured by utilizing a fullerene molecular tip. The rectification property of the supramolecular assembly was determined and quantitatively assessed. The present study opens up a way to explore quantitatively the rich electronic properties of supramolecules at the single-molecule level. PMID:23534478

Bui, Phuc T; Nishino, Tomoaki; Yamamoto, Yojiro; Shiigi, Hiroshi

2013-04-10

339

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation  

Energy Technology Data Exchange (ETDEWEB)

Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

Wasielewski, M.R.; Wiederrecht, G.P.; Svec, W.A.

1993-01-01

340

Ultrafast photoinduced electron transfer reactions in supramolecular arrays: Studies of electronic coupling and solvation  

Energy Technology Data Exchange (ETDEWEB)

Research in our laboratory focuses on developing supramolecular arrays that produce long-lived charge separation by limiting the electronic coupling between the separated charges, and on the role of solvation in determining the rates and energetics of photoinitiated electron transfer reactions. Arrays have been developed that closely mimic the electronic coupling that was observed only for long-lived radical pairs produced in photosynthetic glassy solids. A series of 36 fixed-distance donor-acceptor molecules using porphyrin donors, triptycene spacers, and 9 different acceptors has been prepared; these are used to probe the dependence of photoinduced charge separation rates on free energy of reaction as a function of solvent both in liquid and solid solution. Data were obtained on rates of charge separation in dioxane, MTHF, butyronitrile, toluene, chlorobenzene, and benzonitrile.

Wasielewski, M.R.; Wiederrecht, G.P.; Svec, W.A.

1993-05-01

 
 
 
 
341

Desensitization and recovery of metastable intermolecular composites  

Science.gov (United States)

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

342

Light-induced electron transfer vs. energy transfer in molecular thin-film systems  

International Nuclear Information System (INIS)

Quenching of fluoranthene (FA) singlets by tetrabromo-o-benzoquinone (TBBQ) and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) was studied both in xylene solutions and in spin-cast polystyrene (PS) films. Emphasis was placed on time-resolved fluorescence transients resulting from pulsed excitation. Linear Stern-Volmer plots were obtained for quenching in solution and gave diffusion-controlled rate constants, of 1.45 x 1010 M-1 sec-1 and 1.53 x 1010 M-1 sec-1 for TBBQ and TMPD, respectively. TBBQ was found to quench FA singlets in PS over the studied concentration range 12 mM 0 was experimentally determined to be 24.3 A, which is in good agreement with the theoretical value of 23 A calculated from spectral data. Quenching of FA singlets in PS films was found to be independent of FA concentration over a 300 mM to 1200 mM FA concentration range for a constant TBBQ concentration of 24.0 mM. TMPD was only slightly effective as a quencher of FA singlets in PS because it apparently behaves strictly as a contact quencher based on reversible charge transfer. The implications of these results for the design of systems intended to exploit light-induced electron transfer are discussed

343

36 CFR 1235.50 - What specifications and standards for transfer apply to electronic records?  

Science.gov (United States)

...Administration, Electronic/Special Media Records Services Division...Administration, Electronic/Special Media Records Services Division...geospatial data files . Digital spatial data files must be transferred...Records Administration, Special Media Archives Services...

2010-07-01

344

Electron transfer reactions of macrocyclic compounds of cobalt  

Energy Technology Data Exchange (ETDEWEB)

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

Heckman, R.A.

1978-08-01

345

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

346

Measurement of the Charge Transfer Efficiency of Electrons Clocked on Superfluid Helium  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electrons floating on the surface of liquid helium are possible qubits for quantum information processing. Varying electric potentials do not modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This scheme depends upon efficient inter-gate electron transfer and on the absence of electron traps. We will present a measurement of the charge transfer efficiency (CTE) of electrons clocked back and forth ab...

Sabouret, G.; Lyon, S. A.

2006-01-01

347

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

Science.gov (United States)

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

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

2013-02-13

348

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

Science.gov (United States)

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

Li, Yongquan; Li, Hongyu

2014-03-01

349

Modeling of ultrafast electron-transfer processes: Validity of multilevel Redfield theory  

International Nuclear Information System (INIS)

The capability of multilevel Redfield theory to describe ultrafast photoinduced electron-transfer reactions is investigated. Adopting a standard model of photoinduced electron transfer in a condensed-phase environment, we consider electron-transfer reactions in the normal and inverted regimes, as well as for different values of the electron-transfer parameters, such as reorganization energy, electronic coupling, and temperature. Based on the comparison with numerically exact reference results, obtained using the self-consistent hybrid method, we discuss in some detail the advantages and shortcomings of two different versions of Redfield theory, which employ the time-dependent and stationary Redfield tensor, respectively. The results of the study demonstrate that multilevel Redfield theory, if applied in the appropriate parameter regime, is well suited to describe the ultrafast coherent dynamics of photoinduced electron-transfer reactions

350

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.

Nielsen, Jens Ulrik; Ulstrup, Jens

2000-01-01

351

Electron transfer reactions in condensed phase: Effect of reversibility  

Science.gov (United States)

We propose a generalized one-dimensional kinetic equation for multidimensional reversible electron transfer (ET) reaction with a nonequilibrium situation as the initial condition. The rate constant for the forward reversible ET reaction obtained here consists of the rate for the corresponding irreversible ET reaction, and an extra term due to reversibility of the ET process which includes the rates of diffusion dynamics in the reactant and product wells. In order to understand the effect of reversibility, we consider back ET reaction in a system consisting of an electron donor-acceptor pair in a solvent modeled through low frequency solvent collective coordinates (multidimensional) characterized by the orientational polarization and slowly relaxing one-dimensional vibrational mode. We propose here a new generalized polarization energy functional corresponding to the extension of the continuum version for the same, which has opened up the possibility of inclusion of molecular nature of the solvent into the solvent reorganization energy. We then derive an exact expression for the ET rate for this model system. The numerical results calculated by using the proposed one-dimensional approach are shown to be in good agreement with the available experimental results. Non-Marcus free energy gap dependence of the rates observed here for the reversible and irreversible ET reactions are very close to each other in the barrierless region, while for other situations, the rate for the former process is found to be less than the latter. The extra term, which makes the difference between the rate constants for irreversible and reversible ET reactions, is found to be contributed by the diffusion dynamics from both reactant and product wells but the dominating contribution is provided mainly by the product well.

Dhole, Kajal; Jena, Naresh K.; Samanta, Alok; Ghosh, Swapan K.

2012-02-01

352

Synthesis, characterization, photophysics and photochemistry of pyrylogen electron transfer sensitizers.  

Science.gov (United States)

A series of new dicationic sensitizers that are hybrids of pyrylium salts and viologens has been synthesized. The electrochemical and photophysical properties of these "pyrylogen" sensitizers are reported in sufficient detail to allow rationale design of new photoinduced electron transfer reactions. The range of their reduction potentials (+0.37-+0.05 V vs SCE) coupled with their range of singlet (48-63 kcal mol(-1)) and triplet (48-57 kcal mol(-1)) energies demonstrate that they are potent oxidizing agents in both their singlet and triplet excited states, thermodynamically capable of oxidizing substrates with oxidation potentials as high as 3.1 eV. The pyrylogens are synthesized in three steps from readily available starting materials in modest overall 11.4-22.3% yields. These sensitizers have the added advantages that: (1) their radical cations do not react on the CV timescale with oxygen bypassing the need to run reactions under nitrogen or argon and (2) have long wavelength absorptions between 413 and 523 nm well out of the range where competitive absorbance by most substrates would cause a problem. These new sensitizers do react with water requiring special precautions to operate in a dry reaction environment. PMID:24112032

Clennan, Edward L; Liao, Chen

2014-01-01

353

Effects of quantum coherence in metalloprotein electron transfer  

Science.gov (United States)

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, Ross; Goold, John; Heaney, Libby; Farrow, Tristan; Vedral, Vlatko

2012-09-01

354

Oxidation of ascorbate anion by electron transfer to phenoxyl radicals  

International Nuclear Information System (INIS)

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

355

Electron and hole transfer in DNA: the role of tunneling and environment  

International Nuclear Information System (INIS)

Owing to the biological significance of radiation induced DNA damage, electron and hole transfer processes in DNA have attracted considerable interest. Various mechanisms for these processes have been proposed including tunneling and hopping. In our efforts we have investigated electron transfer for DNA in glasses, ices and solids at low temperatures via electron spin resonance (ESR) spectroscopy. Electrons and holes generated by irradiation at 77 K are trapped on DNA and transfer to a randomly interspersed intercalator, mitoxantrone (MX). Monitoring the changes of ESR signals of MX radicals, one electron oxidized guanine (G·+), one-electron reduced cytosine [C(N3)H·], and thymine anion radicals (T·-) with time at 77 K allows for the direct observation of electron and hole transfer. For DNA in aqueous glasses at low temperatures we are able to isolate the tunneling of excess electrons and we report overall distances of travel and the tunneling decay constant, beta. Studies with the duplexes polydAdT·polydAdT and polydIdC·polydIdC randomly intercalated with mitoxantrone (MX) show the excess electron transfer distances to be longer for pdAdT·pdAdT, than for for pdIdC·pdIdC. The beta value for DNA (0.9Angstroms-1) lies intermediate between that for pdAdT·pdAdT (0.75 Angstroms-1) and that for pdIdC·pdIdC (1.4 Angstroms-1). These results suggest that proton transfer from I to C·- forming CH· significantly slows but does not stop electron transfer. Similarly in DNA proton transfer in GC anion radical is not found to prevent electron transfer. Electron and hole transfer processes in frozen solutions (D2O ices) show that electron/hole transfer in polyA·polyU is significantly further than in DNA and transfer distances in polyC·polyG are substantially less than in DNA. These findings confirm our results in aqueous glasses. Our investigations of the effect of hydration, space filling lipid amine cation complexes, and temperature will also be discussed. Our modeling of electron transfer rates and distances of electron transfer in DNA-complexes allow for estimates of the spacing between DNA double stranded helices in each complex. This research was supported by the NIH NCI Grant RO1 CA45424

356

Intermolecular interactions in solid benzene.  

Science.gov (United States)

The lattice dynamics and molecular vibrations of benzene and deuterated benzene crystals are calculated from force constants derived from density-functional theory (DFT) calculations and compared with measured inelastic neutron-scattering spectra. A very small change (0.5%) in lattice parameter is required to obtain real lattice-mode frequencies across the Brillouin zone. There is a strong coupling between wagging and breathing modes away from the zone center. This coupling and sensitivity to cell size arises from two basic interactions. Firstly, comparatively strong interactions that hold the benzene molecules together in layers. These include an intermolecular interaction in which H atoms of one molecule link to the center of the aromatic ring of a neighboring molecule. The layers are held to each other by weaker interactions, which also have components that hold molecules together within a layer. Small changes in the lattice parameters change this second type of interaction and account for the changes to the lattice dynamics. The calculations also reveal a small auxetic effect in that elongation of the crystal along the b axis leads to an increase in internal pressure in the ac plane, that is, elongation in the b direction induces expansion in the a and c directions. PMID:16460192

Kearley, G J; Johnson, M R; Tomkinson, J

2006-01-28

357

Vibrational predissociation of Van der Waals molecules and intermolecular potential energy surfaces  

International Nuclear Information System (INIS)

Spectroscopic experiments yield information about energy transfer processes in van der Waals molecules, for which we do not have reliable guides for geometries. Important properties of the molecules are included in the areas of intermolecular potential energy curves, structure, and energy transfer processes. Vibrational predissociation is more fully explored through experimental studies, a theoretical model, numerical results, momentum gap, and relaxation channels

358

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

Science.gov (United States)

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

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

2014-05-01

359

Electron-transfer photochromism to switch bulk second-order nonlinear optical properties with high contrast.  

Science.gov (United States)

The first bulk electron-transfer photochromic compound with intrinsic second-order nonlinear optical (NLO) photoswitching properties has been synthesized. This system employs an electron-transfer photoactive asymmetric viologen ligand coordinated to a zinc(II) center. PMID:25195919

Li, Pei-Xin; Wang, Ming-Sheng; Zhang, Ming-Jian; Lin, Chen-Sheng; Cai, Li-Zhen; Guo, Sheng-Ping; Guo, Guo-Cong

2014-10-20

360

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

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...the taxpayer's bank to make an electronic fund transfer in the amount of...Account by no later than the close of business on the last day for filing the return...Procedure entitled Payment of Tax by Electronic Fund Transfer. This...

2010-04-01

 
 
 
 
361

Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer–fullerene blends  

Science.gov (United States)

The conversion of photoexcitations into charge carriers in organic solar cells is facilitated by the dissociation of excitons at the donor/acceptor interface. The ultrafast timescale of charge separation demands sophisticated theoretical models and raises questions about the role of coherence in the charge-transfer mechanism. Here, we apply two-dimensional electronic spectroscopy to study the electron transfer process in poly(3-hexylthiophene)/PCBM (P3HT/PCBM) blends. We report dynamics maps showing the pathways of charge transfer that clearly expose the significance of hot electron transfer. During this ultrafast electron transfer, vibrational coherence is directly transferred from the P3HT exciton to the P3HT hole polaron in the crystalline domain. This result reveals that the exciton converts to a hole with a similar spatial extent on a timescale far exceeding other photophysical dynamics including vibrational relaxation.

Song, Yin; Clafton, Scott N.; Pensack, Ryan D.; Kee, Tak W.; Scholes, Gregory D.

2014-09-01

362

Vibrational coherence probes the mechanism of ultrafast electron transfer in polymer-fullerene blends.  

Science.gov (United States)

The conversion of photoexcitations into charge carriers in organic solar cells is facilitated by the dissociation of excitons at the donor/acceptor interface. The ultrafast timescale of charge separation demands sophisticated theoretical models and raises questions about the role of coherence in the charge-transfer mechanism. Here, we apply two-dimensional electronic spectroscopy to study the electron transfer process in poly(3-hexylthiophene)/PCBM (P3HT/PCBM) blends. We report dynamics maps showing the pathways of charge transfer that clearly expose the significance of hot electron transfer. During this ultrafast electron transfer, vibrational coherence is directly transferred from the P3HT exciton to the P3HT hole polaron in the crystalline domain. This result reveals that the exciton converts to a hole with a similar spatial extent on a timescale far exceeding other photophysical dynamics including vibrational relaxation. PMID:25215959

Song, Yin; Clafton, Scott N; Pensack, Ryan D; Kee, Tak W; Scholes, Gregory D

2014-01-01

363

Photochemical reactions of electron-deficient olefins with N,N,N?,N?-tetramethylbenzidine via photoinduced electron-transfer  

Science.gov (United States)

Photoinduced electron transfer reactions of several electron-deficient olefins with N, N, N', N'-tetramethylbenzidine (TMB) in acetonitrile solution have been studied by using laser flash photolysis technique and steady-state fluorescence quenching method. Laser pulse excitation of TMB yields 3TMB* after rapid intersystem crossing from 1TMB*. The triplet which located at 480 nm is found to undergo fast quenching with the electron acceptors fumaronitrile (FN), dimethyl fumarate (DMF), diethyl fumarate (DEF), cinnamonitrile (CN), ?-acetoxyacrylonitrile (AAN), crotononitrile (CrN) and 3-methoxyacrylonitrile (MAN). Substituents binding to olefin molecule own different electron-donating/withdrawing powers, which determine the electron-deficient property (?-cloud density) of olefin molecule as well as control the electron transfer rate constant directly. The detection of ion radical intermediates in the photolysis reactions confirms the proposed electron transfer mechanism, as expected from thermodynamics. The quenching rate constants of triplet TMB by these olefins have been determined at 510 nm to avoid the disturbance of formed TMB cation radical around 475 nm. All the kqT values approach or reach to the diffusion-controlled limit. In addition, fluorescence quenching rate constants kqS have been also obtained by calculating with Stern-Volmer equation. A correlation between experimental electron transfer rate constants and free energy changes has been explained by Marcus theory of adiabatic outer-sphere electron transfer. Disharmonic kq values for CN and CrN in endergonic region may be the disturbance of exciplexs formation.

Pan, Yang; Zhao, Junshu; Ji, Yuanyuan; Yan, Lei; Yu, Shuqin

2006-01-01

364

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

International Nuclear Information System (INIS)

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

365

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

International Nuclear Information System (INIS)

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

366

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

Science.gov (United States)

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

Chen, Shengli; Liu, Yuwen; Chen, Junxiang

2014-08-01

367

Transfer excitation in slow collisions between ions of very high charge and two-electron targets  

International Nuclear Information System (INIS)

We argue that a three-step transfer-excitation (capture and target excitation) mechanism enhances (depletes) the cross section for one- (two-) electron removal from a two-electron target. This mechanism, which becomes very important at high projectile charge (q), is mediated through quasimolecular couplings between diabatic double-capture and transfer-excitation channels, in which the inner of two active electrons is transferred to an excited target state. The inclusion of this process in the extended classical over-barrier model gives excellent agreement with unexplained experimental cross sections for one- and two-electron removal from He in slow collisions with Xe ions of high charge (q?31)

368

SO2-* electron transfer ion/ion reactions with disulfide linked polypeptide ions.  

Science.gov (United States)

Multiply-charged peptide cations comprised of two polypeptide chains (designated A and B) bound via a disulfide linkage have been reacted with SO2-* in an electrodynamic ion trap mass spectrometer. These reactions proceed through both proton transfer (without dissociation) and electron transfer (with and without dissociation). Electron transfer reactions are shown to give rise to cleavage along the peptide backbone, loss of neutral molecules, and cleavage of the cystine bond. Disulfide bond cleavage is the preferred dissociation channel and both Chain A (or B)-S* and Chain A (or B)-SH fragment ions are observed, similar to those observed with electron capture dissociation (ECD) of disulfide-bound peptides. Electron transfer without dissociation produces [M + 2H]+* ions, which appear to be less kinetically stable than the proton transfer [M + H]+ product. When subjected to collision-induced dissociation (CID), the [M + 2H]+* ions fragment to give products that were also observed as dissociation products during the electron transfer reaction. However, not all dissociation channels noted in the electron transfer reaction were observed in the CID of the [M + 2H]+* ions. The charge state of the peptide has a significant effect on both the extent of electron transfer dissociation observed and the variety of dissociation products, with higher charge states giving more of each. PMID:15914021

Chrisman, Paul A; Pitteri, Sharon J; Hogan, Jason M; McLuckey, Scott A

2005-07-01

369

EZINE – a way of electronic transfer for specific information?  

Directory of Open Access Journals (Sweden)

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

Daniela DANCIULESCU

2006-01-01

370

Signal and Charge Transfer Efficiency of Few Electrons Clocked on Microscopic Superfluid Helium Channels  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Electrons floating on the surface of liquid helium are possible spin-qubits for quantum information processing. Varying electric potentials are not expected to modify spin states, which allows their transport on helium using a charge-coupled device (CCD)-like array of underlying gates. This approach depends upon efficient inter-gate transfer of individual electrons. Measurements are presented here of the charge transfer efficiency (CTE) of few electrons clocked back and fort...

Sabouret, G.; Bradbury, F. R.; Shankar, S.; Lyon, S. A.

2007-01-01

371

High throughput electron transfer from carbon dots to chloroplast: a rationale of enhanced photosynthesis  

Science.gov (United States)

A biocompatible amine functionalized fluorescent carbon dots were developed and isolated for gram scale applications. Such carbogenic quantum dots can strongly conjugate over the surface of the chloroplast and due to that strong interaction the former can easily transfer electrons towards the latter by assistance of absorbed light or photons. An exceptionally high electron transfer from carbon dots to the chloroplast can directly effect the whole chain electron transfer pathway in a light reaction of photosynthesis, where electron carriers play an important role in modulating the system. As a result, carbon dots can promote photosynthesis by modulating the electron transfer process as they are capable of fastening the conversion of light energy to the electrical energy and finally to the chemical energy as assimilatory power (ATP and NADPH).A biocompatible amine functionalized fluorescent carbon dots were developed and isolated for gram scale applications. Such carbogenic quantum dots can strongly conjugate over the surface of the chloroplast and due to that strong interaction the former can easily transfer electrons towards the latter by assistance of absorbed light or photons. An exceptionally high electron transfer from carbon dots to the chloroplast can directly effect the whole chain electron transfer pathway in a light reaction of photosynthesis, where electron carriers play an important role in modulating the system. As a result, carbon dots can promote photosynthesis by modulating the electron transfer process as they are capable of fastening the conversion of light energy to the electrical energy and finally to the chemical energy as assimilatory power (ATP and NADPH). Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr06079a

Chandra, Sourov; Pradhan, Saheli; Mitra, Shouvik; Patra, Prasun; Bhattacharya, Ankita; Pramanik, Panchanan; Goswami, Arunava

2014-03-01

372

Coincidence spectroscopy of continuum electron transfer in heavy ion collisions. [Review  

Energy Technology Data Exchange (ETDEWEB)

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. (JFP)

Sellin, I.A.

1979-01-01

373

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

Science.gov (United States)

...operator using the Retailer Electronic Benefit Transfer...must occur within two business days after receipt...interoperable and where electronic benefits are not portable...where out-of-State electronic benefits can be used...shall occur within one business day following...

2010-01-01

374

Transferable pseudoclassical electrons for aufbau of atomic ions.  

Science.gov (United States)

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

Ekesan, Solen; Kale, Seyit; Herzfeld, Judith

2014-06-01

375

Intramolecular electron transfer in heterosubstituted benzene derivatives as probed by dissociative electron attachment.  

Science.gov (United States)

The electron transmission and dissociative electron attachment spectra of the 1-chloroalkyl benzene derivatives, C(6)H(5)(CH(2))(3)Cl and C(6)H(5)(CH(2))(4)Cl, and of the sulfur and silicon derivatives, C(6)H(5)SCH(2)Cl, C(6)H(5)Si(CH(3))(2)CH(2)Cl and C(6)H(5)CH(2)Si(CH(3))(2)CH(2)Cl, are presented for the first time. The relative Cl(-) fragment anion currents generated by electron attachment to the benzene pi* LUMO are measured in the series C(6)H(5)(CH(2))(n)Cl, with n = 1-4, and in the heteroatomic compounds. The Cl(-) yield reflects the rate of intramolecular electron transfer between the pi-system and the remote chlorine atom, which in turn depends on the extent of through-bond coupling between the localized pi* and sigma*(Cl-C) orbitals. In compounds C(6)H(5)(CH(2))(n)Cl the Cl(-) current rapidly decreases with increasing length of the saturated chain. This decrease is significantly attenuated when a carbon atom of the alkyl skeleton is replaced with a third-row heteroatom. This greater ability to promote through-bond coupling between the pi* and sigma*(Cl-C) orbitals is attributed to the sizably lower energy of the empty sigma*(S-C) and sigma*(Si-C) orbitals with respect to the sigma*(C-C) orbitals. In the sulfur derivative the increase of the Cl(-) current is larger than in the silicon analogue. In this case, however, other negative fragments are observed, due to dissociation of the S-C bonds. PMID:12105932

Modelli, Alberto; Venuti, Marco; Szepes, László

2002-07-17

376

Influence of ionic strength on triplet-state natural organic matter loss by energy transfer and electron transfer pathways.  

Science.gov (United States)

Triplet state excited natural organic matter chromophores ((3)NOM*) are important reactive intermediates in indirect photochemical processes, yet the impact of salt concentrations relevant to estuarine and marine environments on (3)NOM* is poorly understood. The formation rates, pseudo-first-order loss rate constants, and steady-state concentration of (3)NOM* were monitored using the sorbate probe method in synthetic matrices with increasing ionic strength (IS) to seawater values using seawater halides or other salts. The steady-state concentration of (3)NOM* approximately doubled at seawater IS, regardless of the salt used, due to a decrease in the (3)NOM* decay rate constant. The electron transfer-mediated degradation of 2,4,6-trimethylphenol (TMP) by (3)NOM* was significantly slowed at higher IS. A model is proposed wherein high IS slows intra-organic matter electron transfer pathways, an important (3)NOM* loss pathway, leading to longer (3)NOM* lifetimes. Although IS did not appear to impact energy transfer pathways directly, the higher (3)NOM* steady-state concentrations promote energy transfer interactions. The observed decrease in decay rate constant, increase in steady-state concentration of (3)NOM* at high IS, and the inhibition of electron transfer pathways should be considered when determining the fate of organic pollutants in estuarine and marine environments. PMID:23952218

Parker, Kimberly M; Pignatello, Joseph J; Mitch, William A

2013-10-01

377

Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.  

Science.gov (United States)

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide. PMID:19197929

Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

2009-01-01

378

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

CERN Document Server

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

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

2011-01-01

379

Electron transfer reactions in electrolyte solutions: effects of ion atmosphere and solvent relaxation  

Science.gov (United States)

A molecular theory of the effects of solution dynamics on the rates of adiabatic outer-sphere electron transfer reactions in electrolyte solutions is presented. The theory correctly includes the dynamics of both ions and solvent molecules through frequency dependent ion and solvent susceptibilities. The rate of electron transfer is calculated by employing the well-known Grote-Hynes theory. The barrier-crossing frequency of electron transfer is found to depend rather strongly on the salt concentration dependent solvent longitudinal relaxation time and on the ionic conductivity. Numerical results are presented for some common aqueous and non-aqueous electrolyte solutions.

Chandra, Amalendu

1996-05-01

380

A reversible photoredox reaction: Electron-transfer photoreduction of. beta. -lapachone by triethylamine  

Energy Technology Data Exchange (ETDEWEB)

Light-induced electron-transfer reactions are being studied as possible energy conversion or storage processes. One such reaction of a light-induced electron-transfer reaction and subsequent electron- and atom-transfer processes, which are at least partially reversible, is reported herein. The specific reaction studied was the photooxidation of triethylamine by excited state o-quinones. The energy stored in the overall process is modest, and the degree of reversibility is limited by the reactivity of the amine oxidation products. 33 refs.

Ci, Xiaohong; Goodman, J.L.; Whitten, D.G. (Univ. of Rochester, NY (USA)); da Silva, R.S.; Nicodem, D.E. (Univ. of Rio de Janeiro (Brazil))

1988-12-07

 
 
 
 
381

Morphology controlled nanostructures self-assembled from phthalocyanine derivatives bearing alkylthio moieties: effect of sulfur-sulfur and metal-ligand coordination on intermolecular stacking.  

Science.gov (United States)

To investigate the effect of sulfur-sulfur and metal-ligand coordination on the molecular structure and morphology of self-assembled nanostructures, metal-free 2,3,9,10,16,17,23,24-octakis(isopropylthio)phthalocyanine H(2)Pc(?-SC(3)H(7))(8) (1) and its copper and lead congeners CuPc(?-SC(3)H(7))(8) (2) and PbPc(?-SC(3)H(7))(8) (3) are synthesized and fabricated into organic nanostructures by a phase-transfer method. The self-assembly properties are investigated by electronic absorption and Fourier transform infrared (FTIR) spectroscopy, transmission electron micro