Dynamics of the Special Pair of Chlorophylls of Photosystem II

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• 作者：Daniele Narzi ; Daniele Bovi ; Pietro De Gaetano ; Leonardo Guidoni
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：January 13, 2016
• 年：2016
• 卷：138
• 期：1
• 页码：257-264
• 全文大小：523K
• ISSN：1520-5126

文摘

Cholophylls are at the basis of the photosynthetic energy conversion mechanisms in algae, plants, and cyanobacteria. In photosystem II, the photoproduced electrons leave a special pair of chlorophylls (namely, P_D1 and P_D2) that becomes cationic. This oxidizing pair [P_D1,P_D2]⁺, in turn, triggers a cascade of oxidative events, eventually leading to water splitting and oxygen evolution. In the present work, using quantum mechanics/molecular mechanics calculations, we investigate the electronic structure and the dynamics of the P_D1P_D2 special pair in both its oxidized and reduced states. In agreement with previously reported static calculations, the symmetry between the two chlorophylls was found to be broken, the positive charge being preferentially located on P_D1. Nevertheless, this study reveals for the first time that large charge fluctuations occur along dynamics, temporarily inverting the charge preference for the two branches. Finally, a vibrational analysis pinpointed that such charge fluctuations are strongly coupled to specific modes of the special pair.