Model of the Oxygen Evolving Complex Which Is Highly Predisposed to O–O Bond Formation,The Journal of Physical Chemistry Letters

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Model of the Oxygen Evolving Complex Which Is Highly Predisposed to O–O Bond Formation
The Journal of Physical Chemistry Letters ( IF 4.8 ) Pub Date : 2018-06-04 00:00:00 , DOI: 10.1021/acs.jpclett.8b00800
Yulia Pushkar ₁ , Katherine M. Davis ₂ , Mark C. Palenik ₃

Affiliation

Light-driven water oxidation is a fundamental reaction in the biosphere. The Mn₄Ca cluster of photosystem II cycles through five redox states termed S₀–S₄, after which oxygen is evolved. Critically, the timing of O–O bond formation within the Kok cycle remains unknown. By combining recent crystallographic, spectroscopic, and DFT results, we demonstrate an atomistic S₃ state model with the possibility of a low barrier to O–O bond formation prior to the final oxidation step. Furthermore, the associated one electron oxidized S₄ state does not provide more advantages in terms of spin alignment or the energy of O–O bond formation. We propose that a high energy peroxide isoform of the S₃ state can preferentially be oxidized by Tyr_z^ox in the course of final electron transfer leading to O₂ evolution. Such a mechanism may explain the peculiar kinetic behavior of O₂ evolution as well as serve as an evolutionary adaptation to avoid release of the harmful peroxides.

中文翻译：

高度倾向于O–O键形成的析氧复合物模型

光驱动的水氧化是生物圈中的基本反应。光系统II的Mn ₄ Ca团簇循环通过五个称为S ₀ –S _4的氧化还原状态，然后释放出氧气。至关重要的是，在Kok循环中O-O键形成的时机仍然未知。通过结合最新的晶体学，光谱学和DFT结果，我们证明了原子态S ₃状态模型，并且在最终氧化步骤之前，对O-O键形成的势垒可能较低。此外，在自旋对准或O-O键形成的能量方面，一个相关的电子被氧化的S ₄状态没有提供更多的优势。我们提出S _3的高能过氧化物同工型在最终的电子转移过程中，优先地被Tyr _z^ox氧化态，导致O ₂析出。这种机制可以解释O ₂析出的特殊动力学行为，并可以作为进化适应措施，避免有害过氧化物的释放。

更新日期：2018-06-04

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