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Polyoxometalates (POMs) are discrete metal-oxo anions of early transition-metals in high oxidation states (e.g. W VI , Mo VI

Tyrosinases, bifunctional metalloenzymes, catalyze the oxidation of monophenols and o-diphenols to o-quinones, the precursor compounds of the brown-coloured pigment melanin. In eukaryotic organisms, tyrosinases are expressed as latent zymogens that have to be proteolytically cleaved in order to form highly active enzymes. This activation mechanism, known as the tyrosinase maturation process, has scientific and industrial significance with respect to biochemical and technical applications of the enzyme. Here, not only the first crystal structure of the mushroom tyrosinase abPPO4 is presented in its active form (Ser2-Ser383) and in its 21 kDa heavier latent form (Ser2-Thr545), but furthermore the simultaneous presence of both forms within one single-crystal structure is shown. This allows for a simple approach to investigate the transition between these two forms. Isoform abPPO4 was isolated and extensively purified from the natural source (Agaricus bisporus), which contains a total of six polyphenol oxidases (PPOs). The enzyme formed crystals (diffracting to a resolution of 2.76 Å ) owing to the employment of the 6-tungstotellurate (VI)

The functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi-redox Mn(III)/Mn(IV) manifold that evolves through five electronic states (S(i), where i=0-4). The synthetic model system of this catalytic cycle and of its S0→S4 intermediates is the expected turning point for artificial photosynthesis. The tetramanganese-substituted tungstosilicate [Mn(III)3Mn(IV)O3(CH3COO)3(A-α-SiW9O34)](6-)(Mn4POM) offers an unprecedented mimicry of the natural system in its reduced S0 state; it features a hybrid organic-inorganic coordination sphere and is anchored on a polyoxotungstate. Evidence for its photosynthetic properties when combined with [Ru(bpy)3](2+) and S2O8(2-) is obtained by nanosecond laser flash photolysis; its S0→S1 transition within milliseconds and multiple-hole-accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7%.

Affordable energy storage is crucial for a variety of technologies. One option is sodium ion batteries (NIBs) for which, however, suitable anode materials are still a problem. We report on the application of a promising new class of materials, polyoxometallates (POMs), as an anode in NIBs. Specifically Na 6 [V 10 O 28 ]•16H 2 O has been synthesized and characterized. Galvanostatic tests revealed a reversible capacity of approximately 276 mA h g-1 with an average discharge potential of 0.4 V, as well as a high cycling stability. The underlying mechanism was rationalized to be an insertion of Na + in between the [V 10 O 28 ] 6-•anions rather than an intercalation into a crystal structure; the accompanying reduction of + to + was confirmed by X-Ray Photoelectron Spectroscopy. Finally, a working full-cell setup is presented with the POM as the anode, substantiating the claim that Na 6 [V 10 O 28 ]•16H 2 O is a promising option for future high-performing sodium ion batteries.