Calcium Manganese Oxides as Oxygen Evolution Catalysts: O2 Formation Pathways Indicated by 18O-Labelling Studies

Authors

  • Dr. Dmitriy Shevela,

    1. Department of Chemistry, Umeå University, Linnaeus Väg 6 (KBC huset), 90187 Umeå (Sweden), Fax: (+46) 90-786-5293
    2. Current address: Center for Organelle Research (CORE), University of Stavanger, Kristine Bonnevis vei 22, 4036 Stavanger (Norway)
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  • Sergey Koroidov,

    1. Department of Chemistry, Umeå University, Linnaeus Väg 6 (KBC huset), 90187 Umeå (Sweden), Fax: (+46) 90-786-5293
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  • Dr. M. Mahdi Najafpour,

    1. Institute for Advanced Studies in Basic Sciences (IASBS), P. O. Box 45195-1159, 45195 Zanjan (Iran)
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  • Prof. Dr. Johannes Messinger,

    Corresponding author
    1. Department of Chemistry, Umeå University, Linnaeus Väg 6 (KBC huset), 90187 Umeå (Sweden), Fax: (+46) 90-786-5293
    • Department of Chemistry, Umeå University, Linnaeus Väg 6 (KBC huset), 90187 Umeå (Sweden), Fax: (+46) 90-786-5293
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  • Dr. Philipp Kurz

    Corresponding author
    1. Institute for Inorganic Chemistry, Christian-Albrechts-University Kiel, Max-Eyth-Strasse 2, 24118 Kiel (Germany), Fax: (+49)431-880-1520
    • Institute for Inorganic Chemistry, Christian-Albrechts-University Kiel, Max-Eyth-Strasse 2, 24118 Kiel (Germany), Fax: (+49)431-880-1520
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Abstract

Oxygen evolution catalysed by calcium manganese and manganese-only oxides was studied in 18O-enriched water. Using membrane-inlet mass spectrometry, we monitored the formation of the different O2 isotopologues 16O2, 16O18O and 18O2 in such reactions simultaneously with good time resolution. From the analysis of the data, we conclude that entirely different pathways of dioxygen formation catalysis exist for reactions involving hydrogen peroxide (H2O2), hydrogen persulfate (HSO5) or single-electron oxidants such as CeIV and [RuIII(bipy)3]3+. Like the studied oxide catalysts, the active sites of manganese catalase and the oxygen-evolving complex (OEC) of photosystem II (PSII) consist of μ-oxido manganese or μ-oxido calcium manganese sites. The studied processes show very similar 18O-labelling behaviour to the natural enzymes and are therefore interesting model systems for in vivo oxygen formation by manganese metalloenzymes such as PSII.

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