PARENT SESSION

Symposium S6A Type II reaction centres: Excited state dynamics and donor side
Thursday September 2nd, 2004 10:20 AM-12:20 PM Room 511D
Chair: Bill Rutherford
Co-Chair: Marilyn Gunner

Charge separation in the photosystem II reaction center revealed with femtosecond midinfrared spectroscopy. Marie Louise Groot^*,1, Natalia Pawlowicz-Wereszczynska¹, Jacques Breton³, Luuk van Wilderen¹, Rienk van Grondelle¹, ¹ Faculty of Sciences, Amsterdam, The Netherlands³ Service de Bioenegetique, Bat. 532, France

ABSTRACT- The photosystem II core complex consists of several individual pigment-protein complexes: core antenna's CP43 and CP47 and D1D2-cytb559 reaction center (RC). In this work we have studied energy transfer and charge separation in the PS II RC with Visible/MidInfraRed pump-probe spectroscopy at room temperature. Spectral changes in C=O absorption bands associated with energy and electron transfer were observed over a wide spectral range between 2200 and 1600 cm^-1. In this region mainly the absorption changes in the C=O stretches of the chromophore and protein (the 9-keto and 10a-ester modes) were probed. The PS II RC pigments were excited with three different wavelengths: at 585 nm (unselectively), 670 nm and 680nm. It was found that after excitation at 680 nm P⁺ state formation occurs partly in 600 fs, most likely to form the state P⁺Chl^-. At the same time part of the RC remains excited. P⁺Pheo^- formation occurs on a time scale of 26 ps; at the same time the excited states disappear. Energy transfer was found to occur on time scales of ∼100-200 fs, 3 ps and 25-30 ps. It was concluded that the initial state of charge separation is P⁺Chl^-.

KEY WORDS: Type II reaction center, Photosystem II, Visible/MidInfraRed pump-probe spectroscopy, Energy/electron transfer