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

Thurnauer, Marion C.; Poluektov, Oleg G.; Kothe, G.

doi:10.1007/978-1-4757-4379-1_6

Cited by 18 publications

(26 citation statements)

References 77 publications

(101 reference statements)

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“…This pronounced variation can be used to evaluate the geometry of SCRPs in photosynthetic RCs. 5,22,38,39 From the two-dimensional Q-band experiment, the orientation of the magnetic tensors (g-tensors, dipolar tensor) with respect to a molecular reference system has been obtained. 5 The cofactor orientation of the primary electron donor was then evaluated by analyzing transient X-band ( D 9.5 GHz/350 mT) EPR spectra, extracted from a two-dimensional data set.…”

Section: Three-dimensional Structure Of An Electron Transfer Intermedmentioning

confidence: 99%

“…quantum beats, observed at short delay times after optical excitation; 14 -16 out-of-phase modulation of the electron spin echo (ESE) signal, which is due to dipole-dipole and exchange interactions in the SCRP and allows for distance measurements; 9,17,18 and multiple quantum coherence in photo-induced radical pairs, which allows for direct measurements of coherence decays. Because of current developments and recent availability of TR high-field (HF) EPR, 21,22 the full potential of TR EPR is only now being realized. The enhanced spectral resolution of HF-EPR is providing completely new details of the radical species involved in photosynthetic ET along with their interactions with each other and their protein environments.…”

Section: Introductionmentioning

confidence: 99%

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Structural organization in photosynthetic proteins as studied by high-field EPR of spin-correlated radical pair states

et al. 2005

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We demonstrate the potential of high-field (HF) time-resolved electron paramagnetic resonance (EPR) spectroscopy to reveal unique information about electron transfer processes and the structure of photosynthetic systems. The lineshapes and electron spin polarization (ESP) of spin-correlated radical pair (SCRP) spectra recorded with HF-EPR are very sensitive to the magnetic parameters, interactions, and geometry of the radicals in the pair. This sensitivity facilitates an analysis of more sophisticated models and methods to reveal the important relationship between structural organization and light-induced electron transfer of the photosynthetic proteins. In this review, we report on a new time-resolved HF and multi-frequency EPR approach developed in the Freiburg laboratory in cooperation with the Argonne Photosynthesis group. The method is designed to probe the geometric structure of charge separated states in the photosynthetic membrane. First, we discuss the magneto-orientation of photosynthetic cyanobacteria as revealed by time-resolved HF-EPR of SCRPs. Then, we demonstrate how the three-dimensional structure of the SCRP P700(+)A1 from photosystem I of oxygenic photosynthesis and its arrangement in the membrane is obtained from application of multi-frequency including time-resolved HF-EPR techniques.

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Section: Three-dimensional Structure Of An Electron Transfer Intermedmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structural organization in photosynthetic proteins as studied by high-field EPR of spin-correlated radical pair states

et al. 2005

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“…Although our discussion was concentrated on reaction center proteins of purple bacteria, quantum oscillations of spin-correlated radical pairs are a common feature of systems that undergo efficient photo-induced charge separation. Apparently, these shared characteristics of natural and artificial systems, as revealed through high-time resolution EPR (Kiefer et al 1999;Link et al 2001Link et al , 2005Heinen et al 2002Heinen et al , 2007Thurnauer et al 2004bThurnauer et al , 2006Kothe et al 2008), reflect underlying fundamental structural and energetic requirements for efficient charge separation. Therefore, the quantum oscillation techniques continue to yield new insights into photochemical energy conversion in natural and artificial photosynthetic systems.…”

Section: Discussionmentioning

confidence: 96%

“…Consequently, the amplitude and frequency of the electron spin oscillations vary significantly with B 0 across the powder EPR spectrum. This pronounced variation can be used to evaluate the mutual orientation of the magnetic tensors of the radical pair (Kiefer et al 1999;Link et al 2001Link et al , 2005Heinen et al 2002Heinen et al , 2007Thurnauer et al 2004bThurnauer et al , 2006Kothe et al 2008).…”

Section: Observation Of Quantum Oscillationsmentioning

confidence: 99%

What you get out of high-time resolution electron paramagnetic resonance: example from photosynthetic bacteria

Kothe

Thurnauer

2009

Photosynth Res

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The primary energy conversion steps of natural photosynthesis proceed via light-induced radical ion pairs as short-lived intermediates. Time-resolved electron paramagnetic resonance (EPR) experiments of photosynthetic reaction centers monitor the key charge separated state between the oxidized primary electron donor and reduced quinone acceptor, e.g., P(+)(865)Q(-)(A) of purple photosynthetic bacteria. The time-resolved EPR spectra of P(+)(865)Q(-)(A) are indicative of a spin-correlated radical pair that is created from the excited singlet state of P(865) in an ultra-fast photochemical reaction. Importantly, the spin-correlated radical pair nature of the charge separated state is a common feature of all photosynthetic reaction centers, which gives rise to several interesting spin phenomena such as quantum oscillations, observed at short delay times after optical excitation. In this review, we describe details of the quantum oscillation phenomenon and present a complete analysis of the data obtained from the charge separated state of purple bacteria, P(+)(865)Q(-)(A). The analysis and simulation of the quantum oscillations yield the three-dimensional structure of P(+)(865)Q(-)(A) in the photosynthetic membrane on a nanosecond time scale after light-induced charge separation. Comparison with crystallographic data reveals that the position of Q(-)(A) is essentially the same as in the X-ray structure. However, the head group of Q(-)(A) has undergone a 60° rotation in the ring plane relative to its orientation in the crystal structure. The results are discussed within the framework of the previously suggested conformational gating mechanism for electron transfer from Q(-)(A) to the secondary quinone acceptor Q(B).

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“…(14) (Rohrer et al 1996;Weber et al 1998) information such as H-bond directions and their changes in functional proteins at work. 95-GHz PELDOR on the spin-correlated radical pair P þ 865 Q À A Light-induced transient radical pairs in photosynthetic reactions centers of plants and bacteria have been in the focus of numerous spectroscopic investigations over the past decades (Weber 2000;Thurnauer et al 2004). In particular, the charge-separated radical pair P þ 865 Q À A in bacterial RCs from Rb.…”

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confidence: 99%

High-field EPR

Savitsky

Möbius

2009

Photosynth Res

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Among the numerous spectroscopic techniques utilized in photosynthesis research, high-field/high-frequency EPR and its pulse extensions ESE, ENDOR, ESEEM, and PELDOR play an important role in the endeavor to understand, on the basis of structure and dynamics data, dominant factors that control specificity and efficiency of light-induced electron- and proton-transfer processes in primary photosynthesis. Short-lived transient intermediates of the photocycle can be characterized by high-field EPR techniques, and detailed structural information can be obtained even from disordered sample preparations. The chapter describes how multifrequency high-field EPR methodology, in conjunction with mutation strategies for site-specific isotope or spin labeling and with the support of modern quantum-chemical computation methods for data interpretation, is capable of providing new insights into the photosynthetic transfer processes. The information obtained is complementary to that of protein crystallography, solid-state NMR and laser spectroscopy.

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

Cited by 18 publications

References 77 publications

Structural organization in photosynthetic proteins as studied by high-field EPR of spin-correlated radical pair states

Structural organization in photosynthetic proteins as studied by high-field EPR of spin-correlated radical pair states

What you get out of high-time resolution electron paramagnetic resonance: example from photosynthetic bacteria

High-field EPR

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