Energetics of the S2 State Spin Isomers of the Oxygen-Evolving Complex of Photosystem II

David J. Vinyard, Sahr Khan, Mikhail Askerka, Victor S. Batista, Gary W. Brudvig

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19 Citations (Scopus)


The S2 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 electron paramagnetic resonance (EPR) signal at g = 2.0, whereas 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 S1 more slowly than the S = 5/2 isomer. These differences support the hypotheses that the S3 state is formed via the S2 state S = 5/2 isomer and that the stabilized S2 state S = 1/2 isomer plays a role in minimizing S2QA- decay under light-limiting conditions.

Original languageEnglish
Pages (from-to)1020-1025
Number of pages6
JournalJournal of Physical Chemistry B
Issue number5
Publication statusPublished - Feb 9 2017

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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