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arXiv · 2105.12387

Toward understanding the S2-S3 transition in the Kok Cycle of Photosystem II: Lessons from Sr-Substituted Structure

Muhamed Amin·Divya Kaur·M. R. Gunner·Gary Brudvig
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Abstract

Understanding the water oxidation mechanism in Photosystem II (PSII) stimulates the design of biomimetic artificial systems that can convert solar energy into hydrogen fuel efficiently. The Sr2+ substituted PSII is active but slower than with the native Ca2+ as an oxygen evolving catalyst. Here, we use Density Functional Theory (DFT) to compare the energetics of the S2 to S3 transition in the Mn4O5Ca2+ and Mn4O5Sr2+ clusters. The calculations show that deprotonation of the water bound to Ca2+ (W3), required for the S2 to S3 transition, is energetically more favorable in Mn4O5Ca2+ than Mn4O5Sr2+. In addition, we have calculated the pKa of the water that bridges Mn4 and the Ca2+/Sr2+ in the S2 using continuum electrostatics. The calculations show that the pKa is higher by 4 pH units in the Mn4O5Sr2+.

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Muhamed Amin, Divya Kaur, M. R. Gunner, Gary Brudvig. 2021-05-26. Toward understanding the S2-S3 transition in the Kok Cycle of Photosystem II: Lessons from Sr-Substituted Structure. https://arxiv.org/abs/2105.12387

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