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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >~(15)N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem Ⅱ
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~(15)N photochemically induced dynamic nuclear polarization magic-angle spinning NMR analysis of the electron donor of photosystem Ⅱ

机译：〜（15）N光化学诱导的动态光电子诱导的动态核极化魔角旋转NMR分析Ⅱ

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摘要

In natural photosynthesis, the two photosystems that operate in series to drive electron transport from water to carbon dioxide are quite similar in structure and function, but operate at widely different potentials. In both systems photochemistry begins by photo-oxidation of a chlorophyll a, but that in photosystem Ⅱ (PS2) has a 0.7 eV higher midpoint potential than that in photosystem Ⅰ (PS1), so their electronic structures must be very different. Using reaction centers from ~(15)N-labeled spinach, these electronic structures are compared by their photochemically induced dynamic nuclear polarization (photo-CIDNP) in magic-angle spinning (MAS) NMR measurements. The results show that the electron spin distribution in PS1, apart from its known delocalization over 2 chlorophyll molecules, reveals no marked disturbance, whereas the pattern of electron spin density distribution in PS2 is inverted in the oxidized radical state. A model for the donor of PS2 is presented explaining the inversion of electron spin density based on a tilt of the axial histidine toward pyrrole ring Ⅳ causing π-π overlap of both aromatic systems.
机译：在自然光合作用中，两个串联运行以驱动电子从水向二氧化碳传输的光系统在结构和功能上都非常相似，但在很大的不同电势下运行。在这两个系统中，光化学都是通过叶绿素a的光氧化开始的，但是光化学Ⅱ（PS2）的中点电势比光化学Ⅰ（PS1）的中点电势高0.7 eV，因此它们的电子结构必须非常不同。使用〜（15）N标记的菠菜的反应中心，通过电子化学诱导的动态核极化（photo-CIDNP）在魔角旋转（MAS）NMR测量中比较了这些电子结构。结果表明，PS1中的电子自旋分布除已知的在2个叶绿素分子上的离域外，没有显示明显的扰动，而PS2中的电子自旋密度分布的模式在氧化自由基状态下反转。提出了一种PS2供体的模型，该模型解释了基于轴向组氨酸向吡咯环Ⅳ倾斜而引起两个芳族系统π-π重叠的电子自旋密度的反转。

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