Electric field-induced decrease of quantum yield of charge separation in photosynthetic reaction centers

Ogrodnik, A.; Langenbacher, Thomas; Bieser, Gero; Siegl, J.; Eberl, Ulrich; Völk, Martin; Michel‐Beyerle, M. E.

doi:10.1016/0009-2614(92)85044-b

Cited by 18 publications

(8 citation statements)

References 16 publications

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“…39 In the electric field employed here, the quantum yield of P+H-is reduced by approximately 8%, as can be seen from the reduction of the Q, bleaching of P at short delay times (Figure 2 and Table I). This effect is due to an energetic shift of a charge separated state (P' H;, P' B; , or P+Bir,39 with subscripts A and B marking the pigments on the A and B branch, respectively) and, therefore, leads to a selection of RCs with a specific orientation of the dipole moment of this state in the electric field.…”

Section: Discussionmentioning

confidence: 79%

What can be learned from the singlet-triplet splitting of the radical pair P+H- [p = primary donor] in the photosynthetic reaction center: conclusions from electric field effects on the P+H- recombination dynamics

Völk¹,

Haeberle²,

Feick³

et al. 1993

J. Phys. Chem.

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The singlet-triplet splitting J of the radical pair P+H-in the photosynthetic reaction center critically depends on the energy separation between P+H-and the triplet state 3P*. Due to its large dipole moment, the energy of P+H-can be considerably shifted by the application of an external electric field. Following a simple perturbation theoretical approach, such a shift should enlarge J to values which do not allow singlet-triplet-mixing in PH-, thereby inhibiting the triplet recombination channel P+H--c 3P*. In contrast to this prediction, the recombination dynamics of P+H-and the yield of 3P* in reaction centers of Rb. sphaeroides were found to change only slightly in an external electric field. This insensitivity of the recombination dynamics to the energy of P+H-is predicted in an extended theoretical treatment of J taking into account nuclear oscillations. Following the extended treatment, J is much less sensitive to the energy of P+H-. This has important consequences for the discussion of J in the context of primary charge separation and also for the values of J to be expected in reaction centers in which the energetics have been altered by chemical or genetic modifications.

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Section: Discussionmentioning

confidence: 79%

What can be learned from the singlet-triplet splitting of the radical pair P+H- [p = primary donor] in the photosynthetic reaction center: conclusions from electric field effects on the P+H- recombination dynamics

Völk¹,

Haeberle²,

Feick³

et al. 1993

J. Phys. Chem.

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“…As has been discussed extensively in the literature, ,− the field-induced change in the free energy gaps modifies the associated ET rate constants according to the standard ET theory . In the present analysis, the ET rate constants for 1 P*BH → P + B - H ( k 12 ), P + B - H → P + BH - ( k 23 ), and P + BH - → P + BHQ - ( k 34 ) are described in terms of a nonadiabatic expression incorporating the low-frequency medium vibrational modes characterized, for simplicity, by an average frequency ω m and the high-frequency intramolecular vibrational modes characterized by an average frequency ω c : , Here, V denotes the electronic coupling constant between the associated donor and acceptor; S m = λ m /ℏω m , λ m , and ν̄ m = [exp(βℏω m ) − 1] -1 refer to the reorganization energy and thermal population of the medium modes, respectively.…”

Section: Modelmentioning

confidence: 94%

“…A further approach to studying experimentally the energetics associated with the ET reactions in RCs is to modify the kinetics by means of an externally applied electric field. − For RC samples oriented 22 and randomly oriented 24-26 with respect to the applied field, the quantum yields of the charge-separated states, P + H - (in Q-depleted samples) and P + Q - , have proven to be reducible by 10−20% with an electric field of 1 MV/cm. This effect is interesting both from the viewpoint of understanding the ET energetics in RCs and for possible implications for the design of various energy conversion and switching devices.…”

Section: Introductionmentioning

confidence: 99%

“…The reason for this requirement is that k et is larger than the k 10 in Figure by about 2 orders of magnitude. This difficulty is explicitly exhibited in Figure , which shows the electric field dependence of charge-separation quantum yield Y Q for the oriented RC sample 22 at 295 K. In the earlier models, ,, Y Q is evaluated from ( e . g ., eq 2 in ref , eq IV.11 in ref , and a similar expression in ref ) in both the sequential and superexchange ET models, where the rate constants have been calculated using the procedure given in section 2.…”

Section: Introductionmentioning

confidence: 99%

“…This difficulty is explicitly exhibited in Figure , which shows the electric field dependence of charge-separation quantum yield Y Q for the oriented RC sample 22 at 295 K. In the earlier models, ,, Y Q is evaluated from ( e . g ., eq 2 in ref , eq IV.11 in ref , and a similar expression in ref ) in both the sequential and superexchange ET models, where the rate constants have been calculated using the procedure given in section 2.

2 Simplified calculation for the electric field ( F ext ) dependence of the charge-separation quantum yield Y Q for the oriented RC sample at 295 K on the basis of (a) sequential and (b) superexchange ET models.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Electron Transfer Model for the Electric Field Effect on Quantum Yield of Charge Separation in Bacterial Photosynthetic Reaction Centers

Tanaka

Marcus

1997

J. Phys. Chem. B

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The effect of an electric field on a photoinduced charge separation process is treated theoretically. The system considered is a reaction center (RC) of photosynthetic bacteria, involving an electron transfer (ET) from the electronically excited singlet state of the bacteriochlorophyll dimer (P) to the bacteriopheophytin (H) and quinone (Q). In contrast to formulations which focus only on the forward steps and do not explain the major effect on the quantum yield of P + Q -or, in Q-depleted samples, of P + H -, the present study includes the effect on the back reactions, an effect which we find to be large. The low-frequency medium and highfrequency intramolecular vibrational modes are included in the calculation of the various ET rates. Recent experimental results on the ET energetics, including the estimated effect of static heterogeneity in RCs, are incorporated. The rate equations for the population densities of distinct states are solved for both oriented and randomly oriented (isotropic) RC samples, and the results are compared with experimental data for the field-induced reduction of the quantum yield of formation of charge-separated state P + Q -. A simple (quasiequilibrium) model calculation illustrates the essential features of this analysis of the electric field effect and compares reasonably well with these numerical results of the more detailed model. The question of the electric field effect on the fluorescence quantum yield is also addressed, and a suggestion is made for consistency with the data on the formation of P + Q -.

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The internal conversion rate of the primary donor in reaction centers of Rhodobacter sphaeroides

Müller

Bieser

Hartwich

et al. 1996

Ber Bunsenges Phys Chem

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The most prominent cornerstone of reaction center function is the high quantum yield of transmembrane charge separation approaching unity in the systems studied so far. This feature necessarily implies that the deactivation rate of the excited primary donor 1P* not involving electron transfer is not accessible in native systems. Therefore, reaction centers of Rhodobacter sphaeroides have been modified via thermal exchange of the relevant primary electron acceptor BA. Substitution of BA with 3‐vinyl‐132‐OH‐bacteriochlorophyll increases the lifetime of 1P* from about 2 to 240 ps at 90 K. Transient absorption studies reveal that this increase is due to a decrease of the rate of charge separation. At 90 K this decrease causes a concomitant drop in the quantum yield of charge separation Y to 78% leading to a fast ground state P recovery of 22%. This directly translates into an internal conversion rate from 1P* to the ground state of kIC = (1.1 ns)−1 at 90 K. The corresponding data at 270 K (τF(1P*) = 66 ps; Y = 91%) result in kIC = (750 ps)−1 suggesting a weak thermal activation as usually observed for internal conversion processes. These internal conversion data constitute an important parameter for theoretical modelling of the primary charge separation along both, the active and inactive pigment branches.

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Electric field-induced decrease of quantum yield of charge separation in photosynthetic reaction centers

Cited by 18 publications

References 16 publications

What can be learned from the singlet-triplet splitting of the radical pair P+H- [p = primary donor] in the photosynthetic reaction center: conclusions from electric field effects on the P+H- recombination dynamics

What can be learned from the singlet-triplet splitting of the radical pair P+H- [p = primary donor] in the photosynthetic reaction center: conclusions from electric field effects on the P+H- recombination dynamics

Electron Transfer Model for the Electric Field Effect on Quantum Yield of Charge Separation in Bacterial Photosynthetic Reaction Centers

The internal conversion rate of the primary donor in reaction centers of Rhodobacter sphaeroides

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