The Nature of the Short Oxygen–Oxygen Distance in the Mn4CaO6 Complex of Photosystem II Crystals,The Journal of Physical Chemistry Letters

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The Nature of the Short Oxygen–Oxygen Distance in the Mn4CaO6 Complex of Photosystem II Crystals
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2020-11-19 , DOI: 10.1021/acs.jpclett.0c02868
Manoj Mandal ₁ , Keisuke Saito _{1,

2} , Hiroshi Ishikita _{1,

2}

Affiliation

The O···O distance for a typical H-bond is ∼2.8 Å, whereas the radiation-damage-free structures of photosystem II (PSII), obtained using the X-ray free electron laser (XFEL), shows remarkably short O···O distances of ∼2 Å in the oxygen-evolving Mn₄CaO_5/6 complex. Herein, we report the protonation/oxidation states of the short O···O atoms in the XFEL structures using a quantum mechanical/molecular mechanical approach. The O5···O6 distance of 1.9 Å is reproduced only when O6 is an unprotonated O radical (O^•–) with Mn(IV)₃Mn(III), i.e., the S₃ state. The potential energy profile shows a barrier-less energy minimum region when O5···O6 = 1.90–2.05 Å (O^•– ↓) or 2.05–2.20 Å (O^•– ↑). Formation of such a short O5···O6 distance is not possible when O6 is OH^– with Mn(IV)₄. In the case in which the O5···O6 distance is 1.9 Å, it seems likely that the O radical species exists in the oxygen-evolving complex of the XFEL-S₃ crystals.

中文翻译：

光系统II晶体Mn ₄ CaO ₆络合物中短氧-氧距离的性质

典型的H键的O··O距离约为2.8Å，而使用X射线自由电子激光（XFEL）获得的光系统II（PSII）的无辐射破坏结构显示出非常短的O ·放氧的Mn ₄ CaO _5/6络合物的O距离约为2Å 。本文中，我们使用量子力学/分子力学方法报告了XFEL结构中短O···O原子的质子化/氧化态。仅当O6是带有Mn（IV）₃ Mn（III）（即S ₃状态）的非质子化的O自由基（O ^•–）时，才会复制1.9的O5···O6距离。当O5···O6 = 1.90–2.05Å（O ^•– ↓）或2.05–2.20Å（O^•– ↑）。当O6为OH ^–和Mn（IV）₄时，不可能形成如此短的O5···O6距离。在O5···O6距离为1.9的情况下，似乎X自由基-X ₃晶体的析氧复合物中存在O自由基。

更新日期：2020-12-03

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