Mechanism of Water Delivery to the Active Site of Photosystem II along the S2 to S3 Transition

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• 作者：Matteo Capone ; Daniele Narzi ; Daniele Bovi ; Leonardo Guidoni
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：February 4, 2016
• 年：2016
• 卷：7
• 期：3
• 页码：592-596
• 全文大小：376K
• ISSN：1948-7185

文摘

The two water molecules serving as substrate for the oxygen evolution in Photosystem II are already bound in the S₂ state of the Kok–Joliot’s cycle. Nevertheless, an additional water molecule is supposed to bind the cluster during the transition between the S₂ and S₃ states, which has been recently revealed to have the Mn₄CaO₅ catalytic cluster arranged in an open cubane fashion. In this Letter, by means of ab initio calculations, we investigated the possible pathways for the binding of the upcoming water molecule. Upon the four different possibilities checked in our calculations, the binding of the crystallographic water molecule, originally located nearby the Cl^– binding site, showed the lowest activation energy barrier. Our findings therefore support the view in which the W2 hydroxyl group and the O5 oxygen act as substrates for the oxygen evolution. Within this framework the role of the open and closed Mn₄CaO₅ conformers is clarified as well as the exact mechanistic events occurring along the S₂ to S₃ transition.