Solid-State 55Mn NMR Spectroscopy of bis(μ-oxo)dimanganese(IV) [Mn2O2(salpn)2], a Model for the Oxygen Evolving Complex in Photosystem II
Given the obvious global energy needs, it has become imperative to develop a catalytic process for converting water to molecular oxygen and protons. Many have sought to understand the details of photosynthesis and in particular the water splitting reaction to help in the development of the appropriate catalysis.1-3 While the scientific community has made great strides towards this goal, it has fallen short at the critical stage of the determination of the structure associated with the oxygen evolving complex (OEC) within photosystem II (PSII).4,5 Despite the existence of x-ray structures of PSII,6-8 the best data we have for the structure of the OEC comes from models derived from EPR and EXAFS measurements.9-14 This experimental situation has led to collaborations with theoreticians to enable the development of models for the structure of the OEC where the experimental observables (EXAFS and magnetic resonance parameters) serve as constraints to the theoretical calculations. Of particular interest to this study is the observation of the S1 state of the Kok cycle15 where the core of the OEC can be described as a tetranuclear manganese cluster composed of Mn4OxCa. The simplest model for the OEC can be thought of as two Mn-pairs and a Ca2+ where each Mn-pair is antiferromagnetically coupled to its partner. We utilize the term "pair" to describe the Mn atoms within the OEC with the same oxidation state, which for the S1 state is (Mn2(III, III) and Mn2(IV, IV)).16 It is unclear as to the degree of interaction between the pairs as well as the role of the Ca2+. At cryogenic temperatures the S1 state of the OEC is diamagnetic and in principle amenable to solid-state NMR experiments.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1002166
- Report Number(s):
- PNNL-SA-72469; JACSAT; 39732; 400412000; TRN: US1100486
- Journal Information:
- Journal of the American Chemical Society, 132(47):16727-16729, Vol. 132, Issue 47; ISSN 0002-7863
- Country of Publication:
- United States
- Language:
- English
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Tetranuclear manganese-oxo complex with a 2. 7- angstrom Mn hor ellipsis Mn separation and intramolecular H sub 2 O hor ellipsis (. mu. -O) hydrogen-bonded contacts: (Mn sub 4 O sub 2 (TPHPN) sub 2 (H sub 2 O) sub 2 (CF sub 3 SO sub 3 ) sub 2 )(CF sub 3 SO sub 3 ) sub 3. Possible mode for binding of water at the active site of the oxygen-evolving complex in photosystem II
Related Subjects
ATOMS
CATALYSIS
CRYOGENICS
MAGNETIC RESONANCE
MANGANESE
OXYGEN
PHOTOSYNTHESIS
PROTONS
SPECTROSCOPY
VALENCE
WATER
ORDER REGULAR APPROXIMATION
DENSITY-FUNCTIONAL THEORY
PHOTOSYNTHETIC MN4CA CLUSTER
TRANSITION-METAL-COMPLEXES
COUPLING-CONSTANTS
WATER OXIDATION
ZINC PROTEINS
MN CLUSTER
EXCHANGE
DIMERS
Environmental Molecular Sciences Laboratory