Layered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashion
Layered manganese oxides for water-oxidation: alkaline earth cations influence catalytic activity in a photosystem II-like fashion
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DOI：
10.1039/c2sc20226c
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发表时间：
2012-01-01
期刊：
影响因子：
8.4
通讯作者：
Kurz, Philipp
中科院分区：
文献类型：
--
作者：
Wiechen, Mathias;Zaharieva, Ivelina;Kurz, Philipp
在光驱动水裂解成H-2和O-2的反应序列中，水氧化是一个关键的反应步骤。在体内，这一过程在一种称为光系统II （PSII）的光酶中由一个m-氧化sCaMn(4)簇，即氧进化复合物（OEC）催化。众所周知，如果Ca2+从OEC结构中去除，OEC实际上是不活跃的。Ca2+和Sr2+离子的加入均可恢复活性。我们最近介绍了birnite矿物家族的层状钙锰氧化物作为OEC的功能合成模型化合物。在这里，我们展示了层状锰氧化物的合成，我们改变了层间阳离子，制备了一系列含K， Ca， Sr和mg的碳酸盐。使用x射线吸收光谱（XAS）确定了这些材料中的结构基序，表明所有材料具有相似的原子结构，尽管它们的元素组成不同。通过水氧化实验来阐明结构-反应性关系。这些实验表明，氧化物（如oec）需要在其结构中存在钙才能达到最大的催化活性。作为OEC的另一个相似之处，Sr2+是仲阳离子的“次优选择”。因此，这些结果支持了Ca2+在生物水氧化中起重要催化作用的机制建议。此外，它们为开发用于人工光合作用的合成锰基水氧化催化剂提供了有价值的线索。
In reaction sequences for light driven water-splitting into H-2 and O-2, water-oxidation is a crucial reaction step. In vivo, the process is catalysed within a photoenzyme called photosystem II (PSII) by a m-oxido sCaMn(4) cluster, the oxygen-evolving complex (OEC). The OEC is known to be virtually inactive if Ca2+ is removed from its structure. Activity can be restored not only by the addition of Ca2+ but also Sr2+ ions. We have recently introduced layered calcium manganese oxides of the birnessite mineral family as functional synthetic model compounds for the OEC. Here, we present the syntheses of layered manganese oxides where we varied the interlayer cations, preparing a series of K-, Ca-, Sr- and Mg-containing birnessites. Structural motifs within these materials were determined using X-ray absorption spectroscopy (XAS) showing that all materials have similar atomic structures despite their different elemental compositions. Water-oxidation experiments were carried out to elucidate structure-reactivity relations. These experiments demonstrated that the oxides-like the OEC-require the presence of calcium in their structures to reach maximum catalytic activity. As another similarity to the OEC, Sr2+ is the "second best choice" for the secondary cation. The results thus support mechanistic proposals which involve an important catalytic role for Ca2+ in biological water-oxidation. Additionally, they offer valuable hints for the development of synthetic, manganese-based water-oxidation catalysts for artificial photosynthesis.