Unified Theory on Rates for Electron Transfer Mediated by a Midway Molecule, Bridging between Superexchange and Sequential Processes

Sumi, and Hitoshi; Kakitani, Toshiaki

doi:10.1021/jp010018b

Cited by 55 publications

(118 citation statements)

References 48 publications

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“…It reflects the tendency toward a temperature dependence of the rate, but agrees poorly with experimental data [12,16]. Significantly better results are achieved within phonon theory [14,15], but a large number of parameters are used in such a theory.…”

supporting

confidence: 52%

“…Other approaches based on phonon theory are described in [14,15]. The relations obtained in [14,15] contain many parameters, which is inconvenient in analysis of the experiment and raises doubts about the unambiguous determination of their values.…”

mentioning

confidence: 99%

“…In (15), Ω g(e) is specified by the potential (9). Equation (13) describes the temperature dependence of the modulation (dynamic) broadening of the spectra for both absorption (θ = θ g ) and equilibrium emission (θ = θ e ).…”

mentioning

confidence: 99%

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Model for primary electron transfer and coupling of electronic states at reaction centers of purple bacteria

Pavlovich

2006

J Appl Spectrosc

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A detailed derivation is presented for relations making it possible to describe the effect of temperature on the halfwidth of the P960 and P870 absorption bands and also on the electron transfer (ET) rate at reaction centers (RCs) of the purple bacteria Rps. viridis and Rb. sphaeroides. Primary electron transfer is considered as a resonant nonradiative transition between P * and P + B L − states (where P is a special pair, B L is an additional bacteriochlorophyll in the L branch of the reaction center). It has been shown that the vibrational h α mode with frequency 130-150 cm -1 controls primary electron transfer. It has been found that the matrix element of the electronic transition between the states P * and P + B L − is equal to 12.7 ± 0.9 and 12.0 ± 1.2 cm -1 for Rps.viridis and Rb. sphaeroides respectively. The mechanism is discussed for electron transport from P * and B L and then to bacteriopheophytin H L .Introduction. In bacterial photosynthesis, we can isolate two fundamentally important steps in conversion of solar energy (see, for example, [1][2][3][4][5][6][7][8]). The first step involves absorption of light by light-harvesting antennas LH2 and LH1 followed by transfer of excitation energy to the reaction center. The second step involves electron transport processes in the reaction center. In turn, it includes primary electron transfer from a special pair (P), which is a dimer of bacteriochlorophyll a or b (BChl) to bacteriopheophytin (H) with participation of additional BChl (B), and also secondary electron transfer from bacteriopheophytin to ubiquinone. As a result, rather stable charge separation occurs in the membrane, which controls the sequence of dark electrochemical processes.It is important that in the native forms of the reaction centers, the efficiency of charge separation reaches 100% [9]. For comparison, we note that the best types of semiconductor solar cells provide an efficiency <20% [10]. So persistent efforts have been applied to designing "molecular devices" which under artificial conditions would reproduce the highly efficient processes of conversion of excitation energy to electrical energy, like what occurs in bacterial photosynthesis. Specialists working in the field of storage and conversion of solar energy are especially interested in photosynthesis problems [6,8,11].The task of this work is narrower. It involves refining the theory of the effect of temperature on the spectra and rate of electron transfer (ET), and also developing a method for determining the matrix element for an electronic transition with electron transfer to the reaction center of purple bacteria.Theory of activationless electron transfer. The well-known theory of Bixon and Jortner [12] is based on ideas concerning the effect of polar modes in complex biological systems on the electron transfer rate k ET . According to [12]:

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confidence: 52%

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confidence: 99%

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Model for primary electron transfer and coupling of electronic states at reaction centers of purple bacteria

Pavlovich

2006

J Appl Spectrosc

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“…5,6 The resulting bestfit reorganization energies for primary charge separation have evolved over the years from very low magnitudes ≈0.06-0.1 eV in earlier studies [7][8][9] to 0.19 eV later on, 10 and to a noticeably larger magnitude of 0.35 eV in more recent fits. 11 The situation with the available database of electron-transfer reorganization parameters has improved in the recent decade with the widespread of numerical simulations of biological systems.…”

Section: Introductionmentioning

confidence: 95%

Energetics of Bacterial Photosynthesis

LeBard

Matyushov

2009

J. Phys. Chem. B

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We report the results of extensive numerical simulations and theoretical calculations of electronic transitions in the reaction center of Rhodobacter sphaeroides photosynthetic bacterium. The energetics and kinetics of five electronic transitions related to the kinetic scheme of primary charge separation have been analyzed and compared to experimental observations. Nonergodic formulation of the reaction kinetics is required for the calculation of the rates due to a severe breakdown of the system ergodicity on the time scale of primary charge separation, with the consequent inapplicability of the standard canonical prescription to calculate the activation barrier. Common to all reactions studied is a significant excess of the charge-transfer reorganization energy from the width of the energy gap fluctuations over that from the Stokes shift of the transition. This property of the hydrated proteins, breaking the linear response of the thermal bath, allows the reaction center to significantly reduce the reaction free energy of near-activationless electron hops and thus raise the overall energetic efficiency of the biological charge-transfer chain. The increase of the rate of primary charge separation with cooling is explained in terms of the temperature variation of induction solvation, which dominates the average donor-acceptor energy gap for all electronic transitions in the reaction center. It is also suggested that the experimentally observed break in the Arrhenius slope of the primary recombination rate, occurring near the temperature of the dynamical transition in proteins, can be traced back to a significant drop of the solvent reorganization energy close to that temperature.

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“…20 In complex molecular structures like proteins and DNA two distinct mechanisms of charge separation: (i) two-center donor-acceptor, unistep, superexchange-induced charge transfer (the "transition" from off-resonance), and (ii) long-range multistep charge transport (the "transition" from resonance) have also been introduced to the interpretation of CT pathways connecting the donor and the acceptor sites. 14,[21][22][23][24][25] The two mechanisms have received theoretical treatments in several papers, 14,16,20,[26][27][28][29][30][31] and several molecules have been constructed to provide insight into the different mechanisms. 39 and ΔE BD is the energy gap between the electronic origins of D ＋ B -A and the DBA manifolds (the energy difference between the tunneling energy and the molecular orbital energy of the bridge).…”

Section: Introductionmentioning

confidence: 99%

Intramolecular Charge Transfer of Carotene‐porphyrin‐fullerene Triad: Sequential or Superexchange Cechanism

Sun

Yue-Hui

et al. 2008

Chin. J. Chem.

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As an excellent artificial photosynthetic reaction center, the carotene (C)-porphyrin (P)-fullerene (F) triad was extensively investigated experimentally. To reveal the mechanism of the intramolecular charge transfer (ICT) on the mimic of photosynthetic solar energy conversion (such as singlet energy transfer between pigments, and photoinduced electron transfer from excited singlet states to give long-lived charge-separated states), the ICT mechanisms of C-P-F triad on the exciton were theoretically studied with quantum chemical methods as well as the 2D and 3D real space analysis approaches. The results of quantum chemical methods reveal that the excited states are the ICT states, since the densities of HOMO are localized in the carotene or porphyrin unit, and the densities of LUMO are localized in the fullerene unit. Furthermore, the excited states should be the intramolecular superexchange charge transfer (ISCT) states for the orbital transition from the HOMO whose densities are localized in the carotene to the LUMO whose densities are localized in the fullerene unit. The 3D charge difference densities can clearly show that some excited states are ISCT excited states, since the electron and hole are resident in the fullerene and carotene units, respectively. From the results of the electron-hole coherence of the 2D transition density matrix, not only 3D results are supported, but also the delocalization size on the exciton can be observed. These phenomena were further interpreted with non-linear optical effect. The large changes of the linear and non-linear polarizabilities on the exciton result in the charge separate states, and if their changes are large enough, the ICT mechanism can become the ISCT on the exciton.

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Unified Theory on Rates for Electron Transfer Mediated by a Midway Molecule, Bridging between Superexchange and Sequential Processes

Cited by 55 publications

References 48 publications

Model for primary electron transfer and coupling of electronic states at reaction centers of purple bacteria

Model for primary electron transfer and coupling of electronic states at reaction centers of purple bacteria

Energetics of Bacterial Photosynthesis

Intramolecular Charge Transfer of Carotene‐porphyrin‐fullerene Triad: Sequential or Superexchange Cechanism

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