229 research outputs found
MAGNETIC FIELD EFFECT ON TRIPLETS AND RADICAL IONS IN REACTION CENTERS OF PHOTOSYNTHETIC BACTERIA
Time-resolved magnetic field effect on triplet formation in photosynthetic reaction centers of rhodopseudomonas sphaeroides R-26
Recombination dynamics in bacterial photosynthetic reaction centers
The time dependence of magnetic field effects on light absorption by triplet-state and radical ions in quinone-depleted reaction centers of Rhodopseudomonas sphaeroides strain R-26 has been investigated. Measurements on the time scale of the hyperfine interaction in the radical pair [(BChl)2+. ...BPh-.)] provided kinetic data characterizing the recombination process. The results have been interpreted in terms of a recently proposed model that assumes an intermediate electron acceptor (close site) between the bacteriochlorophyll "special pair" (BChl)2 and the bacteriopheophytin BPh (distant site). Recombination is assumed to proceed through this intermediate acceptor. The experiments led to effective recombination rates for the singlet and triplet channel: k(Seff) = 3.9 . 107 s-1 and k(Teff) = 7.4 . 10(8) s-1. These correspond to recombination rates ks = 1 . 10(1) s-1 and kT = 7.1 . 10(11) s-1 in the close configuration. The upper bound of the effective spin dephasing rate k2eff approximately equal to 1 . 10(9) s-1 is identical with the rate of the electron hopping between the distant site of zero spin exchange interaction and the close site of large interaction. Interpretation of data for the case of direct recombination yields the recombination rates, spin dephasing rate, and exchange interaction in a straightforward way
Determination of QA-content in bacterial reaction centers: an indispensable requirement for quantifying B-branch charge separation
AbstractWe have been able to determine the occupancy of the quinone site at the A-branch (QA) of a reaction center preparation with an accuracy of 2%. This is achieved by accumulating the P+Q−A state after multiple actinic excitation and monitoring the extent of the 30 ms ground state bleaching. This bleaching is corrected for deviations from complete saturation due to competing charge separation to the B-branch. On the other hand, knowledge of the QA content is indispensable for determining the yield of B-branch charge separation from nanosecond transients associated with the recombination of P+H−B, which have to be corrected for the nanosecond signal originating from P+H−A of RCs having lost QA
Time-resolved measurements of fluorescence from reaction centres of Rhodopseudomonas viridis and the effect of menaquinone reduction
AbstractThe kinetics of the fluorescence emitted by the ‘special pair’ of bacteriochlorophyll b molecules in reaction centres from Rhodopseudomonas viridis was recorded in the near infrared, with a time resolution of 1 ns. In nonreduced reaction centres two decay components were resolved with lifetimes of <0.5 and 2.5 ns. Upon reduction of the menaquinone electron acceptor three decay components were detected with lifetimes of < 0.5, 2.5 and 15ns
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