Transient electron spin resonance spectroscopy of the carotenoid triplet state in Rhodopseudomonas Sphaeroides wild type

McGann, William J.; Frank, Harry A.

doi:10.1016/0009-2614(85)85521-4

Cited by 31 publications

(35 citation statements)

References 21 publications

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“…These studies have usually been performed using the steady-state technique [5][6][7]. The time-resolved EPR technique has been employed only in the investigation of the triplet-state of the carotenoid molecule contained in the Rhodobacter sphaeroides reaction center, [9] and recently in the investigation of the polyene triplet state of two carotenopyropheophorbide dyads [8].…”

Section: Lntroductionmentioning

confidence: 99%

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

Carbonera

Valentin

Agostini³

et al. 1997

Appl. Magn. Reson.

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A series of carotenoporphyrin dyads, in which the carotenoid is covalently linked to a tetraarylporphyrin at the ortho, meta or para position of one of the meso aromatic rings, has been studied using Time-Resolved Electron Paramagnetic Resonance (TREPR) spectroscopy. In parallel, an investigation has been carried, on two different photosynthetic antenna systems, the B800-B850 complex of R, acidophila and the LHCII complex of higher organisms. The initial spin polarization of the carotenoid triplet-state, populated indirectly by laser excitation, has been detected. It has been demonstrated that the initial polarization is not a characteristic property of the carotenoid triplet-state, as previously stated, but depends on the donor-acceptor mutual orientation. The triplet energy transfer to the carotenoid from a chlorophyll or porphyrin triplet state is discussed on the basis of the observed spin polarizatio

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Section: Lntroductionmentioning

confidence: 99%

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

Carbonera

Valentin

Agostini³

et al. 1997

Appl. Magn. Reson.

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“…In addition, natural reaction centers whose electron-transfer pathways have been blocked by reduction or removal of quinone electron acceptor moieties demonstrate charge recombination to yield chlorophyll and carotenoid triplet states whose spin polarization reflects that of their singletborn radical pair precursor. [7][8][9][10][11] This phenomenon has not been observed in systems containing visible-absorbing pigments related to those found in photosynthetic reaction centers, although it has been detected in a UV-absorbing molecular triad based on aromatic imide chromophores. 12,13 Most of the reaction center models of this type have employed quinones, porphyrins, or aromatic imides as electron acceptor moieties.…”

Section: Introductionmentioning

confidence: 99%

EPR Investigation of Photoinduced Radical Pair Formation and Decay to a Triplet State in a Carotene−Porphyrin−Fullerene Triad

et al. 1998

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The photochemistry of a molecular triad consisting of a porphyrin (P) covalently linked to a carotenoid polyene (C) and a fullerene derivative (C 60 ) has been studied at 20 K by time-resolved EPR spectroscopy following laser excitation. Excitation of the porphyrin moiety yields C-1 P-C 60 , which decays by photoinduced electron transfer to yield C-P •+ -C 60 •-. This state rapidly evolves into a final charge-separated state C •+ -P-C 60 •-, whose spin-polarized EPR signal was observed and simulated. There is a weak exchange interaction between the electrons in the radical pair (J ) 1.2 G). The C •+ -P-C 60 •state decays to give the carotenoid triplet in high yield with a time constant of 1.2 µs. The spin polarization of 3 C-P-C 60 is characteristic of a triplet formed by charge recombination of a singlet-derived radical pair. The kinetics of the decay of 3 C-P-C 60 to the ground state were also determined. The photoinduced electron transfer from an excited singlet state at low temperature and the high yield of charge recombination to a spin-polarized triplet mimic similar processes observed in photosynthetic reaction centers.

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“…sphaeroides R-26.1 the triplet state 3 P 865 was studied, for the other three systems the triplet states of 3 P 865 and 3 Car. Carotenoids protect the photosynthetic apparatus from photo-induced damage by either trapping chlorophyll triplet states or quenching the excited singlet state of molecular oxygen (27). Spectroscopic and kinetic parameters are already available for carotenoids in bacterial reaction centers from earlier studies (28)(29)(30).…”

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confidence: 99%

Low-Temperature Pulsed EPR Study at 34 GHz of the Triplet States of the Primary Electron Donor P₈₆₅and the Carotenoid in Native and Mutant Bacterial Reaction Centers ofRhodobacter sphaeroides

et al. 2007

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The photosynthetic charge separation in bacterial reaction centers occurs predominantly along one of two nearly symmetric branches of cofactors. Low-temperature EPR spectra of the triplet states of the chlorophyll and carotenoid pigments in the reaction center of Rhodobacter sphaeroides R-26.1, 2.4.1 and two double-mutants GD(M203)/AW(M260) and LH(M214)/AW(M260) have been recorded at 34 GHz to investigate the relative activities of the "A" and "B" branches. The triplet states are found to derive from radical pair and intersystem crossing mechanisms, and the rates of formation are anisotropic. The former mechanism is operative for Rb. sphaeroides R-26.1, 2.4.1, and mutant GD(M203)/AW(M260) and indicates that A-branch charge separation proceeds at temperatures down to 10 K. The latter mechanism, derived from the spin polarization and operative for mutant LH(M214)/AW(M260), indicates that no long-lived radical pairs are formed upon direct excitation of the primary donor and that virtually no charge separation at the B-branch occurs at low temperatures. When the temperature is raised above 30 K, B-branch charge separation is observed, which is at most 1% of A-branch charge separation. B-branch radical pair formation can be induced at 10 K with low yield by direct excitation of the bacteriopheophytin of the B-branch at 590 nm. The formation of a carotenoid triplet state is observed. The rate of formation depends on the orientation of the reaction center in the magnetic field and is caused by a magnetic field dependence of the oscillation frequency by which the singlet and triplet radical pair precursor states interchange. Combination of these findings with literature data provides strong evidence that the thermally activated transfer step on the B-branch occurs between the primary donor, P865, and the accessory bacteriochlorophyll, whereas this step is barrierless down to 10 K along the A-branch.

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Transient electron spin resonance spectroscopy of the carotenoid triplet state in Rhodopseudomonas Sphaeroides wild type

Cited by 31 publications

References 21 publications

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

EPR Investigation of Photoinduced Radical Pair Formation and Decay to a Triplet State in a Carotene−Porphyrin−Fullerene Triad

Low-Temperature Pulsed EPR Study at 34 GHz of the Triplet States of the Primary Electron Donor P₈₆₅and the Carotenoid in Native and Mutant Bacterial Reaction Centers ofRhodobacter sphaeroides

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Transient electron spin resonance spectroscopy of the carotenoid triplet state in Rhodopseudomonas Sphaeroides wild type

Cited by 31 publications

References 21 publications

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

Energy transfer and spin polarization of the carotenoid triplet state in synthetic carotenoporphyrin dyads and in natural antenna complexes

EPR Investigation of Photoinduced Radical Pair Formation and Decay to a Triplet State in a Carotene−Porphyrin−Fullerene Triad

Low-Temperature Pulsed EPR Study at 34 GHz of the Triplet States of the Primary Electron Donor P865and the Carotenoid in Native and Mutant Bacterial Reaction Centers ofRhodobacter sphaeroides

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Low-Temperature Pulsed EPR Study at 34 GHz of the Triplet States of the Primary Electron Donor P₈₆₅and the Carotenoid in Native and Mutant Bacterial Reaction Centers ofRhodobacter sphaeroides