Berlin 2001 – scientific programme
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CPP: Chemische Physik und Polymerphysik
CPP 17: Poster: Spectroscopy and Single Particle Spectroscopy of Molecular Systems, Photoprocesses, Biological Systems
CPP 17.23: Poster
Tuesday, April 3, 2001, 12:30–15:00, AT1
Spin–Correlated Radical Pairs in Photosynthetic Reaction Centers: The Influence of Spin Labels on Transient and Pulsed EPR Spectra — •Stephan G. Zech1, Kev M. Salikhov2, and Dietmar Stehlik1 — 1Fachbereich Physik, Freie Universität Berlin, Germany — 2Kazan Physical Technical Institut, Kazan, Russian Federation
Time–resolved (TR) EPR spectroscopy proved to be a powerful tool to study light induced radical pairs (RPs) which take part in the primary process of photosynthetic charge separation. The improved X–ray structure of Photosystem I (PS I) reveals two pseudo–C2 symmetrically arranged branches of cofactors. This raises the question whether electron transfer (ET) proceeds unidirectionally along one branch or whether both branches are active.
One possibility to address this question of directionality is to introduce a third electron spin into the system in terms of a cysteine based spin label. In this contribution, the influence of such a third spin on cw– and pulsed EPR experiments on spin–correlated RPs is investigated. As revealed by numerical simulations of a three–spin system, the additional spin–spin interactions between the RP partners and the spin label give rise to specific changes in the TR–EPR spectra of the RP state P700•+A1•−. Furthermore, the modulation of the out–of–phase electron spin echo is expected to be even more sensitive to the presence of additional spin–spin couplings. Implications for the directionality of ET in PS I are discussed.