Radicals and Radical Pairs in Photosynthesis

Angerhofer, Alexander; Bittl, Robert

doi:10.1111/j.1751-1097.1996.tb02989.x

Cited by 73 publications

(52 citation statements)

References 367 publications

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“…The decay time of 35ms corresponds to a well-known lifetime constant of the charge separated pair in the bacterial RC proteins (Snyder and Thumauer. 1993;Angerhofer and Bittl. 1996).…”

Section: Relaxation Decay Of the Electron Spin-polarization As A Toolmentioning

confidence: 96%

“…When monitored by time-resolved EPR, the spectrum of P+Q· exhibits strong electron spin-polarization (ESP), which indicates that P+Q· is a so-called spin-correlated radical pair. Time-resolved EPR spectroscopy is a unique technique to observe the ESP pattern and has been extensively used to study the P+Q· pair in purple bacteria and photosystem I and II (pS I and PS II) of plants (Thurnauer and Norris, 1980;Snyder and Thurnauer, 1993;Angerhofer and Bittl, 1996;Link et ai., 2001). Importantly, the ESP is sensitive to the magnetic resonance parameters and magnetic interactions between photochemically oxidized and reduced species.…”

Section: Photoinduced Charge Separation In the Photosynthetic Systemsmentioning

confidence: 99%

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Time-Resolved High-Frequency and Multifrequency EPR Studies of Spin-Correlated Radical Pairs in Photosynthetic Reaction Center Proteins

Thurnauer

Poluektov

Kothe

2004

Very High Frequency (VHF) ESR/EPR

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Abstract:In this chapter we demonstrate the potential of high-frequency and multifrequency time-resolved electron paramagnetic resonance (EPR) to reveal unique information on the electron-transfer processes in the photosynthetic systems, where spectra exhibit spin-polarization phenomena. A precise determination of the magnetic resonance parameters of the radicals in the spin-correlated radical pairs with highfrequency EPR facilitates an analysis of more sophisticated models and methods, such as sequential electron transfer spin-polarization and quantum beats oscillations. These approaches help to describe dynamics, structure and electron transfer pathways in the photosynthetic proteins. In the first part of the manuscript we concentrate on the study of the dynamics of the sequential electron-transfer in deuterated photosynthetic bacterial reaction center proteins. High-frequency EPR spectroscopy reveals the influence of the relationship between structure and dynamics on the rate of charge separation. In the second part of the chapter we demonstrate how the three-dimensional structure of the electron intermediates in green plant photosystem I can be determined by high time-resolution multifrequency and high-frequency EPR techniques.

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“…The decay time of 35ms corresponds to a well-known lifetime constant of the charge separated pair in the bacterial RC proteins (Snyder and Thumauer. 1993;Angerhofer and Bittl. 1996).…”

Section: Relaxation Decay Of the Electron Spin-polarization As A Toolmentioning

confidence: 96%

Section: Photoinduced Charge Separation In the Photosynthetic Systemsmentioning

confidence: 99%

Time-Resolved High-Frequency and Multifrequency EPR Studies of Spin-Correlated Radical Pairs in Photosynthetic Reaction Center Proteins

Thurnauer

Poluektov

Kothe

2004

Very High Frequency (VHF) ESR/EPR

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show abstract

“…Time resolved EPR is well-suited for characterizing systems such as this because, apart from providing unambiguous proof that a light-induced electron transfer takes place, it also yields information about the structure of the chargeseparated state and the coupling between the unpaired electrons. In addition, the fast electron transfer leads to the nonadiabatic generation of consecutive weakly coupled spin pairs which exhibit interesting phenomena such as spin polarization, quantum beats, and nuclear modulations (see [4] for a review). These effects contain information about the spin dynamics of the system and can be used to deduce the nature of the precursor states which are too shortlived to be observed directly.…”

Section: Introductionmentioning

confidence: 99%

Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ

et al. 1997

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Abstraet. The donor-acceptor complex, 2-tetraalkylphenylenediamine-zinc porphyrin-2-naphthoquinone (TAPD-ZnP-NQ), is studied using transient EPR at K-band (24 GHz). Spin polarized spectra of the radical pair TAPD+'NQ -" and of the triplet state TAPD-3ZnP-NQ are observed simultaneously following light exeitation of the complex at 30 K in ~ozen solutions 2-methyl-tetrahydrofuran and the liquid crystal BDH E7. In the liquid crystal, the complex is partially ordered and the spectra depend on the orientation of the sample with respect to the magnetic field. The orientational distribution function is obtained independently by simulating the spectra of the triplet state and assuming that the principal axes of the order matrix coincide with those of the inertia tensor as has been found for solutes in nematie phases. The spectra of TAPD+'NQ -" are analyzed on the basis of the coupled correlated radical pair (CCRP) model using ah estimate of the geometry based on the X-ray crystal structures of the components and the independently obtained orientational distribution function. It is shown that the experimental speetra are eonsistent with the assumed geometry and that the exchange coupling, J, is approximately 0.1 mT. This value is at least two orders of magnitude larger than that found in the analogous radical pair P+'Q-" in photosynthetic reaction centres. This difference is rationalized in terms of different mechanisms for the exchange coupling.

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“…Information about the electronic structure of the triplet state has also been obtained by other methods, as reviewed in [7,8]. As an example zero-field EPR [7] or singlet-triplet absorption difference spectra have been investigated [9].…”

Section: Introductionmentioning

confidence: 99%

“…As an example zero-field EPR [7] or singlet-triplet absorption difference spectra have been investigated [9].…”

Section: Introductionmentioning

confidence: 99%

ENDOR on the triplet state of the primary electron donor in the photosynthetic bacteriumRhodobacter sphaeroides — One step forward in a still unfinished story

et al. 1997

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The electronic structure of the primary electron donor (D) of the photosynthetic bacterium Rhodobacter sphaeroides is investigated by ENDOR in the photoinduced triplet state of D. Hyperfine (hi') splittings of the triplet state measured on frozen solutions are given and compared to the results obtained earlier (Lendzian F., van Willigen H., Sastry S., M6bius K., Scheer H., Feick R.: Chem. Phys. Lett. 118, 145 (1985)). The hf splittings found are consistent with a model of ma asymmetric spin density distribution over the two baeteriochlorophyll moleeules which constitute D, suggesting a mirror image symmetry of HOMO and LUMO coefficients. This could be relevant for electron transfer, in particular tmidirectionality in the reaction center (RC). The first triplet state ENDOR experiments on single crystals of RC's are also reported.

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Radicals and Radical Pairs in Photosynthesis

Cited by 73 publications

References 367 publications

Time-Resolved High-Frequency and Multifrequency EPR Studies of Spin-Correlated Radical Pairs in Photosynthetic Reaction Center Proteins

Time-Resolved High-Frequency and Multifrequency EPR Studies of Spin-Correlated Radical Pairs in Photosynthetic Reaction Center Proteins

Separation of the exchange and dipolar contributions to the spin-spin coupling in the donor-acceptor complex TAPD-ZnP-NQ

ENDOR on the triplet state of the primary electron donor in the photosynthetic bacteriumRhodobacter sphaeroides — One step forward in a still unfinished story

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