Johannes Messinger - Water-Splitting by Photosystem II and Bio-Inspired Catalysts

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Photosystem II (PSII) is a unique, specialized protein complex that uses light energy to oxidize water, resulting in the release of molecular oxygen into the atmosphere. PSII performs this reaction within a functional unit known as the water-oxidizing complex (WOC) or the oxygen-evolving complex (OEC). The WOC consists of an inorganic manganese-oxygen-calcium core (Mn4OxCa complex) surrounded by a functionally important ligand sphere. Understanding the structure of the WOC and its water-splitting mechanism is not only of academic interest, but is also important for the development of artificial water-splitting catalysts, for which the WOC often serves as a blueprint.
Messinger_Johannes_portrait

Structural model of the water-splitting Mn4OxCa cluster in photosystem II as derived by single crystal EXAFS spectroscopy and DFT-based modeling. Purple spheres: Mn ions, red spheres: oxygen atoms, green sphere: Ca, grey spheres: hydrogen. The letters label the four Mn ions, while the numbers indicate discussed binding sites and modes for the two substrate ‘water’ molecules.

Although crystal structures are available for PSII, the detailed structure of the WOC cannot be discerned from them, because of specific radiation damage to the Mn4OxCa cluster. We are therefore trying to derive the structure of the water- splitting complex of photosystem II by a combination of biophysical techniques, such as magnetic resonance (EPR, NMR), X-ray spectroscopy, time-resolved mass spectrometry, electrochemistry and quantum mechanical calculations. These experiments are performed within a network of local and international collaborations. Special emphasis is given to the question of how substrate water is coordinated to the Mn4OxCa cluster. Comparative studies on Mn model complexes and genetically modified photosystem II complexes are carried out to guide data interpretation.
In a new second line of experiments, artificial water-splitting and hydrogen-producing catalysts are being studied under various experimental conditions with an electrochemical cell that is directly coupled to a membrane-inlet mass spectrometer. These activity studies will help our understanding of the water-splitting mechanisms and capacities of such artificial catalysts, which is crucial for their improvement. The ultimate goal is the construction of an ‘artificial leaf’ that uses sunlight to split water into O₂ and H₂

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Key publications

Messinger J, Badger M, Wydrzynski T (1995) Detection of one slowly exchanging substrate water molecule in the S3 state of photosystem II. Proc. Natl. Acad. Sci. USA 92: 3209- 3213

Messinger J, Nugent JH, Evans MCW (1997) Detection of an EPR multiline signal for the S0* state in photosystem II. Biochemistry 36: 11055-11060

Yano J, Kern J, Sauer KH, Latimer M, Pushkar Y, Biesiadka J, Loll B, Saenger W, Messinger J, Zouni A, Yachandra VK (2006) Where water is oxidized to dioxygen: Structure of the Mn4Ca cluster in photosystem II. Science 314: 821-825

Kulik, LV, Epel B, Lubitz W, Messinger J (2007) Electronic structure of the Mn4OxCa cluster in the S0 and S2 states of the oxygen-evolving complex of photosystem II based on pulse 55Mn-ENDOR and EPR spectroscopy. J. Am. Chem. Soc. 129: 13421-13435

Lubitz W, Reijerse EJ, Messinger J (2008) Solar water- splitting into H2 and O2: design principles of photosystem II and hydrogenases. Energy Environ. Sci. 1: 15-31

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May 2013

Sunday, May 19, 2013
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