Magnetic-field-induced orientation of photosynthetic reaction centers as revealed by time-resolved W-band EPR of spin-correlated radical paris: Development of a molecular model

Autor: Sandra L. Schlesselman, Thomas Berthold, Diego Frezzato, Oleg G. Poluektov, Ernst Ohmes, U. Heinen, Gerd Kothe, Giorgio J. Moro, J. R. Golecki, Marion C. Thurnauer
Rok vydání: 2004
Předmět:
Zdroj: Applied Magnetic Resonance. 26:99-115
ISSN: 1613-7507
0937-9347
DOI: 10.1007/bf03166565
Popis: Spin-correlated radical pairs are the short-lived intermediates of the primary energy conversion steps of photosynthesis. In this paper, we develop a comprehensive model for the spin-polarized electron paramagnetic resonance (EPR) spectra of these systems. Particular emphasis is given to a proper treatment of the alignment of the photosynthetic bacteria by the field of the EPR spectormeter. The model is employed to analyze time-resolved W-band (94 GHz) EPR spectra of the secondary radical pair P 700 + A 1 − in photosystem I formed by photoexcitation of the deuterated and15N-substituted cyanobacteriumSynechococcus lividus. Computer simulations of the angular-dependent EPR spectra of P700/+A1/− provide values for the order parameter of the cyanobacterial cells and for the orientation of the membrane normal in a molecular reference system. The order parameter from EPR compares favorably with corresponding data from electron microscopy obtained for theS. lividus cells under similar experimental conditions. It is shown that high-field EPR of a magnetically aligned sample in combination with the study of quantum beat oscillations represents a powerful structural tool for the short-lived radical pair intermediates of photosynthesis.
Databáze: OpenAIRE
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