ALBERT

Description: Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding. Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth's crust and found in natural and synthetic oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored, but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between Fe(II)5 and Fe(III)5; the Fe(III)5 state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Okamura, Masaya -- Kondo, Mio -- Kuga, Reiko -- Kurashige, Yuki -- Yanai, Takeshi -- Hayami, Shinya -- Praneeth, Vijayendran K K -- Yoshida, Masaki -- Yoneda, Ko -- Kawata, Satoshi -- Masaoka, Shigeyuki -- England -- Nature. 2016 Feb 25;530(7591):465-8. doi: 10.1038/nature16529. Epub 2016 Feb 10.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Life and Coordination-Complex Molecular Science, Institute for Molecular Science, Higashiyama 5-1, Myodaiji, Okazaki, Aichi 444-8787, Japan. ; SOKENDAI (The Graduate University for Advanced Studies), Shonan Village, Hayama, Kanagawa 240-0193, Japan. ; Research Center of Integrative Molecular Systems, Institute for Molecular Science, Nishigo-naka 38, Myodaiji, Okazaki, Aichi 444-8585, Japan. ; Advanced Catalytic Transformation Program for Carbon Utilization (ACT-C), Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan. ; Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Nishigo-naka 38, Myodaiji, Okazaki, Aichi 444-8585, Japan. ; Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan. ; Department of Chemistry, Graduate School of Science and Technology, Kumamoto University, Kurokami 2-39-1, Kumamoto 860-8555, Japan. ; Department of Chemistry and Applied Chemistry, Graduate School of Science and Engineering, Saga University, Honjo-machi 1, Saga, 840-8502, Japan. ; Department of Chemistry, Faculty of Science, Fukuoka University, Nanakuma, Jonan-ku 8-19-1, Fukuoka 814-0180, Japan.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26863188" target="_blank"〉PubMed〈/a〉

Description: The river mouth of Kitagawa Brook is normally stagnant because it is easily closed by sand and gravel transported by littoral currents of Biwa Lake, Japan. A new urban area exists in the basin and sewerage works were constructed in the early 1990s, so contaminated water with a bad odour had flowed into the brook before the sewerage works. To reduce the smell, the river mouth was excavated to narrow the channel in the early 1980s. Thus, river-bed sediment after this excavation only occurs at the river mouth. From the upper 24 cm of a sediment core, we found 19 strata of leaves which were supplied from deciduous trees in autumn. We also found several gravel layers which were supplied from the lake during severe storms. The combination of veins and gravel layers were reconstructed for about 20 years of sediment records with an error of two to three years.