Peculiarities of free induction and primary spin echo signals for spin-correlated radical pairs

Salikhov, K. M.; Kandrashkin, Yu. E.; Salikhov, A. K.

doi:10.1007/bf03166790

Cited by 114 publications

(121 citation statements)

References 3 publications

Supporting

Mentioning

113

Contrasting

Order By: Relevance

“…Recently, ESE experiments have been used to determine the distance between P700 ϩ and A 1 Ϫ in native PS I (3)(4)(5) and to demonstrate that the distance remains the same for a number of nonnative quinones used in A 1 extraction/substitution experiments (4,29). The ESE of a weakly coupled spin correlated radical pair is phase shifted by 90°compared with that of a single radical and shows deep amplitude modulations as a function of the pulse spacing (30). The modulation frequency is selectively determined by the spin-spin coupling, the dipolar part of which yields the distance between the radicals.…”

Section: Fig 4 Photoaccumulated and Simulated Q-band Cw Epr Spectramentioning

confidence: 99%

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Zybailov¹,

Est²,

Zech³

et al. 2000

Journal of Biological Chemistry

View full text Add to dashboard Cite

Electron paramagnetic resonance (EPR) and electronnuclear double resonance studies of the photosystem (PS) I quinone acceptor, A 1 , in phylloquinone biosynthetic pathway mutants are described. Room temperature continuous wave EPR measurements at X-band of whole cells of menA and menB interruption mutants show a transient reduction and oxidation of an organic radical with a g-value and anisotropy characteristic of a quinone. In PS I complexes, the continuous wave EPR spectrum of the photoaccumulated Q ؊ radical, measured at Q-band, and the electron spin-polarized transient EPR spectra of the radical pair P700 ؉ Q ؊ , measured at X-, Q-, and W-bands, show three prominent features: (i) Q ؊ has a larger g-anisotropy than native phylloquinone, (ii) Q ؊ does not display the prominent methyl hyperfine couplings attributed to the 2-methyl group of phylloquinone, and (iii) the orientation of Q ؊ in the A 1 site as derived from the spin polarization is that of native phylloquinone in the wild type. Electron spin echo modulation experiments on P700 ؉ Q ؊ show that the dipolar coupling in the radical pair is the same as in native PS I, i.e. the distance between P700؉ and Q ؊ (25.3 ؎ 0.3 Å) is the same as between P700 ؉ and A 1 ؊ in the wild type. Pulsed electron-nuclear double resonance studies show two sets of resolved spectral features with nearly axially symmetric hyperfine couplings. They are tentatively assigned to the two methyl groups of the recruited plastoquinone-9, and their difference indicates a strong inequivalence among the two groups when in the A 1 site. These results show that Q (i) functions in accepting an electron from A 0 ؊ and in passing the electron forward to the iron-sulfur clusters, (ii) occupies the A 1 site with an orientation similar to that of phylloquinone in the wild type, and (iii) has spectroscopic properties consistent with its identity as plastoquinone-9.Light-induced charge separation in all well characterized photosynthetic reaction centers (RCs) 1 proceeds via a common multistep electron transfer process to a stabilized, charge-separated radical pair state P ϩ Q Ϫ consisting of an oxidized (bacterio)chlorophyll donor and a reduced quinone acceptor (whether the green sulfur bacterial RC and the heliobacterial RC contain a quinone acceptor is still controversial). Two types of RCs can be distinguished according to the electron acceptors and electron transfer pathways subsequent to the first quinone acceptor. A series of iron-sulfur clusters with electron transfer essentially perpendicular to the membrane characterize Type I RCs (PS I, green sulfur bacteria, and heliobacteria), whereas a second quinone acceptor Q B and electron transfer parallel to the membrane from the first quinone acceptor Q A characterize Type II RCs (PS II and the RC of purple bacteria). The first quinone is therefore the interface either between electron transfer involving organic cofactors and electron transfer involving iron-sulfur clusters (Type I) or between pure electron transfer and coupled electron/proton tr...

show abstract

Section: Fig 4 Photoaccumulated and Simulated Q-band Cw Epr Spectramentioning

confidence: 99%

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Zybailov¹,

Est²,

Zech³

et al. 2000

Journal of Biological Chemistry

View full text Add to dashboard Cite

show abstract

“…In their theoretical study, Salikhov et al [6] applied a ( 7~/ 2 )~--~-( 7~)~ mw pulse sequence following at time t after an initial laser pulse. The observed echo amplitude S depends (i) on the delay time t between laser pulse and the first mw pulse, (ii) on the mw pulse spacing r and (iii) on the detection time T after the second mw pulse.…”

Section: Theorymentioning

confidence: 99%

“…The observed echo amplitude S depends (i) on the delay time t between laser pulse and the first mw pulse, (ii) on the mw pulse spacing r and (iii) on the detection time T after the second mw pulse. As shown in [6], the dependence of the echo amplitude on the time t is governed by the frequency Q which is the singlet-triplet oscillation or quantum-beat frequency of the RP [13]. Several transient EPR studies of spin-polarized RPs demonstrated that due to the fast damping caused by hyperfine couplings, this frequency is visible only for approx.…”

Section: Theorymentioning

confidence: 99%

“…Therefore, for a large delay time t the dependence of S on f can be neglected. Assuming a detection at T = T after the second mw pulse, the expression for the echo intensity S given in [6] reduces to:…”

Section: Theorymentioning

confidence: 99%

“…For the analysis of the experimental spectra, the model of the correlated coupled RP (CCRP) [4, 51 has successfully been applied. In a theoretical study, Salikhov et al investigated the particular effects of pulsed EPR spectroscopy applied to spin-polarized RPs [6]. For a two-pulse microwave (mw) excitation sequence following a laser pulse, a phase-shifted electron spin echo (ESE) showing a deep envelope modulation (ESEEM) as a function of the delay time between the two mw pulses was predicted.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Pulsed EPR experiments on radical pairs in photosynthesis: Comparison of the donor‐acceptor distances in photosystem I and bacterial reaction centers

Zech

Lubitz

Bittl

1996

Ber Bunsenges Phys Chem

View full text Add to dashboard Cite

Pulsed EPR spectroscopy is applied to the radical pairs P&Q, in bacterial reaction centers of Rhodobacter sphaeroides R-26 and P;&, ' in photosystem I from Synechococcus elongatus. For both radical pairs an outof-phase echo was observed showing a deep modulation as a function of the spacing between the two microwave pulses. From the modulation frequency the dipolar and isotropic couplings between the radical pair spins were derived. For the bacterial reaction centers a dipolar coupling of D = -121 FT was obtained, resulting in a distance of about 28.4 A between the electron spins of the radical pair. This value is in good agreement with the distance derived from the x-ray structure of Rhodobacter sphaeroides R-26. From the faster modulation in the PS I sample we obtained a dipolar coupling of D = -170 wT, indicating a distance of 25.4 A between the primary donor P,oo and the acceptor quinone A , . For both radical pairs, only a small isotropic coupling of J = 1 pT, consistent with transient EPR spectra, was found.

show abstract

Computational Modeling and Least‐Squares Fittingof EPR Spectra

Stoll

2014

Multifrequency Electron Paramagnetic Resonance

View full text Add to dashboard Cite

Peculiarities of free induction and primary spin echo signals for spin-correlated radical pairs

Cited by 114 publications

References 3 publications

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I

Pulsed EPR experiments on radical pairs in photosynthesis: Comparison of the donor‐acceptor distances in photosystem I and bacterial reaction centers

Computational Modeling and Least‐Squares Fittingof EPR Spectra

Contact Info

Product

Resources

About