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Title: Energetics of the S 2 state spin isomers of the oxygen-evolving complex of Photosystem II

Here, the S 2 redox intermediate of the oxygen-evolving complex in Photosystem II is present as two spin isomers. The S = 1/2 isomer gives rise to a multiline EPR signal at g = 2, while the S = 5/2 isomer exhibits a broad EPR signal at g = 4.1. The electronic structures of these isomers are known, but their role in the catalytic cycle of water oxidation remains unclear. We show that formation of the S = 1/2 state from the S = 5/2 state is exergonic at temperatures above 160 K. However, the S = 1/2 isomer decays to S 1 more slowly than the S = 5/2 isomer. These differences support the hypotheses that the S 3 state is formed via the S 2 state S = 5/2 isomer and that the stabilized S 2 state S = 1/2 isomer plays a role in minimizing S 2Q A- decay in light-limiting conditions.
Authors:
 [1] ;  [2] ;  [3] ;  [3] ;  [3]
  1. Yale Univ., New Haven, CT (United States); Louisiana State Univ., Baton Rouge, LA (United States)
  2. Yale Univ., New Haven, CT (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
  3. Yale Univ., New Haven, CT (United States)
Publication Date:
Grant/Contract Number:
FG02-05ER15646
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
Additional Journal Information:
Journal Name: Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry; Journal ID: ISSN 1520-6106
Publisher:
American Chemical Society
Research Org:
Yale Univ., New Haven, CT (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 59 BASIC BIOLOGICAL SCIENCES
OSTI Identifier:
1339161