A NEW METHOD FOR OBTAINING ISOTOPIC FRACTIONATION DATA AT MULTIPLE SITES IN RAPIDLY EXCHANGING SYSTEMS
A NEW METHOD FOR OBTAINING ISOTOPIC FRACTIONATION DATA AT MULTIPLE SITES IN RAPIDLY EXCHANGING SYSTEMS
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DOI：
10.1021/ja00295a017
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发表时间：
1985-01-01
影响因子：
15
通讯作者：
SAUNDERS, M
中科院分区：
文献类型：
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作者：
JARRET, RM;SAUNDERS, M
结论OEC的S2态EPR信号是由多个顺磁位点相互作用产生的。然而，我们的温度依赖性数据不能占一个简单的锰二聚体模型，除非这样的二聚体产生的低自旋形式的锰的铁磁交换耦合。如上所述，低自旋Mn络合物是罕见的，并且不太可能存在于OEC中。一个更合理的模型的物种产生的S2状态EPR信号是一个反铁磁交换耦合Mn（III）-Mn（IV）二聚体是铁磁交换耦合到另一个网站，i= 1。这个第二位可能是低自旋Mn（III）、低自旋Fe（IV），甚至是第二个Mn二聚体。我们将S2状态EPR信号分配给热填充的s= y2状态。因此，如果我们对数据的解释是正确的，那么在低温下应该可以观察到来自s= 3/2基态的EPR信号。该信号预期是各向异性的，因此难以检测。本实验室目前的工作是利用铁磁交换耦合方案来精确模拟三个S2态的EPR谱，并试图观察来自OEC的S2态的s= 3/2基态的EPR信号。我们感谢AW Rutherford博士寄给我们他关于PSII膜中EPR信号方向的手稿的预印本。这项工作得到了美国农业部（83-CRCR-1-1318）、美国国立卫生研究院（1-R 01-GM 32715 -01）、研究公司、石油研究基金（由美国化学学会管理）的捐助者、卡米尔和亨利德雷福斯基金会以及芝加哥社区信托/塞尔学者计划的支持。
Conclusions The data presented in this paper show that the S2 state EPR signals from the OEC arise from the interaction of more than one paramagnetic site. However, our temperature dependence data cannot be accounted for by a simple Mn dimer model, unless such a dimer arises from a ferromagnetic exchange coupling of low-spin forms of Mn. As noted above, low-spin Mn complexes are rare and not likely to be present in the OEC. A more reasonable model for the species giving rise to the S2 state EPR signal isone in which an antiferromagnetically exchange coupled Mn (III)-Mn (IV) dimer is ferromagnetically exchange coupled to another site with i= 1. This second sitecould possibly be low-spin Mn (III), low-spin Fe (IV), or even a second Mn dimer. We assign the S2 state EPR signal to a thermally populated s= y2 state. Therefore, if our interpretation of the data is correct, an EPR signal from the s= 3/2 ground state should be observable at low temperature. This signal is expected to be anisotropic and, therefore, difficult to detect. Current efforts in this laboratory are directed at using the ferromagnetic exchange coupling scheme to accurately simulate the three S2 state EPR spectra and at-tempting to observe EPR signals from the s= 3/2 ground state of the S2 state of the OEC.Acknowledgment. We thank Dr. AW Rutherford for sending us a preprint of his manuscript on the orientation of EPR signals in PSII membranes. This work was supported by the United States Department of Agriculture (83-CRCR-1-1318), National Institutes of Health (1-R01-GM32715-01), Research Corporation, the donors of the Petroleum Research Fund, administered by the American Chemical Society, The Camille and Henry Dreyfus Foundation, and the Chicago Community Trust/Searle Scholars Program.