title: Two different charge separation pathways in photosystem II.
abstract: Charge separation is an essential step in the conversion of solar energy into chemical energy in photosynthesis. To investigate this process, we performed transient absorption experiments at 77 K with various excitation conditions on the isolated Photosystem II reaction center preparations from spinach. The results have been analyzed by global and target analysis and demonstrate that at least two different excited states, (Chl(D1)Phe(D1))* and (P(D1)P(D2)Chl(D1))*, give rise to two different pathways for ultrafast charge separation. We propose that the disorder produced by slow protein motions causes energetic differentiation among reaction center complexes, leading to different charge separation pathways. Because of the low temperature, two excitation energy trap states are also present, generating charge-separated states on long time scales. We conclude that these slow trap states are the same as the excited states that lead to ultrafast charge separation, indicating that at 77 K charge separation can be either activation-less and fast or activated and slow.
authors.affiliation: Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands. eli@few.vu.nl
authors.forename: Elisabet
authors.initials: E
authors.lastname: Romero
authors.forename: Ivo H M
authors.initials: IH
authors.lastname: van Stokkum
authors.forename: Vladimir I
authors.initials: VI
authors.lastname: Novoderezhkin
authors.forename: Jan P
authors.initials: JP
authors.lastname: Dekker
authors.forename: Rienk
authors.initials: R
authors.lastname: van Grondelle
mesh_terms: D003198:Computer Simulation; D004734:Energy Metabolism / Q000502:physiology; D004735:Energy Transfer / Q000502:physiology; D008027:Light; D008954:Models, Biological; D008956:Models, Chemical; D008958:Models, Molecular; D010777:Photochemistry; D010788:Photosynthesis / Q000502:physiology*; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D018724:Spinacia oleracea / Q000737:chemistry / Q000378:metabolism / Q000502:physiology
chemical_list: D045332:Photosystem II Protein Complex