Why did nature choose manganese to make oxygen?
Why did nature choose manganese to make oxygen?
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DOI：
10.1098/rstb.2007.2223
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发表时间：
2008-03-27
影响因子：
6.3
通讯作者：
Armstrong, Fraser A.
中科院分区：
文献类型：
--
作者：
Armstrong, Fraser A.
本文讨论了锰在催化水生成分子氧中的作用。锰是一种丰富的元素。就其固有性质而言，与其他d区元素相比，Mn具有特别丰富的氧化还原化学，具有几种氧化态。最稳定状态的Mn 2+的行为类似于第2族元素-它是移动的，弱络合，容易被细胞吸收，在简单的水介质中氧化还原不活跃。只有在合适的配体存在下，Mn 2+才会被氧化，因此它为氧释放中心（OEC）提供了一个简单的结构单元。中间氧化态Mn（III）和Mn（IV）被O-2-强烈络合并形成稳健的混合价多氧簇，其中Mn（IV）/Mn（III）比率可以升高，一次一个电子，积累氧化电位和容量。OEC是Mn 4CaOx簇，其在高于IV的电势下经历P680（+）的连续氧化，最终达到包括一个Mn（V）或Mn（IV）-氧基自由基的超氧化水平。后者是强有力的氧化，并提供了关键的“动力冲程”，以产生一个O-O键。这留下了一个中心仍然富含Mn（IV），确保快速后续通过O-2。
This paper discusses the suitability of manganese for its function in catalysing the formation of molecular oxygen from water. Manganese is an abundant element. In terms of its inherent properties, Mn has a particularly rich redox chemistry compared with other d-block elements, with several oxidizing states accessible. The most stable-state Mn2+ behaves like a Group 2 element-it is mobile, weakly complexing, easily taken up by cells and redox-inactive in simple aqueous media. Only in the presence of suitable ligands does Mn2+ become oxidized, so it provides an uncomplicated building unit for the oxygen-evolving centre (OEC). The intermediate oxidation states Mn( III) and Mn(IV) are strongly complexed by O-2-and form robust mixed-valence poly-oxo clusters in which the Mn(IV)/Mn(III) ratio can be elevated, one electron at a time, accumulating oxidizing potential and capacity. The OEC is a Mn4CaOx cluster that undergoes sequential oxidations by P680(+) at potentials above 1 V, ultimately to a super-oxidized level that includes one Mn( V) or a Mn(IV)-oxyl radical. The latter is powerfully oxidizing and provides the crucial 'power stroke' necessary to generate an O-O bond. This leaves a centre still rich in Mn(IV), ensuring a rapid follow-through to O-2.