Quantitative analysis of dinuclear manganese(II) EPR spectra
Quantitative analysis of dinuclear manganese(II) EPR spectra
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DOI：
10.1016/j.jmr.2003.07.001
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发表时间：
2003-11-01
影响因子：
2.2
通讯作者：
Hendrich, MP
中科院分区：
文献类型：
--
作者：
Golombek, AP;Hendrich, MP
本文提出了一种定量分析双核Mn（II）配合物EPR谱的方法。本文研究了配合物[（Me（3）TACN）（2）Mn（II）（2）（mu-OAc）（3）] BPh_4（1）（Me（3）TACN=N，N '，N”-trimethyl-1，4，7-triazacyclononanane; OAc=acetate（1-）; BPh_4 = tetraphenylborate（1-））在X-和Q-波段的EPR谱，在微波场的垂直和平行极化下，以及在温度变化（2-50 K）下的EPR谱。复合物1是反铁磁耦合的二聚体，其显示来自所有激发的自旋流形的信号，S = 1至5。的光谱进行了模拟与对角化的全自旋哈密顿，其中包括塞曼和零场分裂的个别锰网站内的二聚体，交换和偶极耦合之间的两个锰网站的二聚体，和核超精细耦合为每个锰离子。模拟了所有自旋流形的所有可能跃迁，并根据计算出的每个跃迁的概率确定了强度。此外，所有的共振的非均匀加宽的定量预测使用的线形模型的基础上D-和r-应变。随着温度从2K升高，双核Mn（II）的11线超精细图案特征首次从S = 3流形观察到。D-和R-应变是决定超精细图案将被解析的主要加宽效应。一个单一的独特的参数集被发现模拟所有的温度，微波频率和微波模式产生的所有光谱。模拟是定量的，允许第一次直接从EPR光谱的物种浓度的测定。因此，这项工作描述了第一种方法的定量表征模型配合物和蛋白质中的双核锰中心的EPR谱。测定了配合物Ⅰ的交换偶合参数J（J = -1.5 +/-0.3cm（-1）; H-ex = -2JS（1）（.）S-2），并发现与先前的磁化测定一致。交换收缩现象被认为是微不足道的1。(C)2003年爱思唯尔公司All rights reserved.
A quantitative method for the analysis of EPR spectra from dinuclear Mn(II) complexes is presented. The complex [(Me(3)TACN)(2)Mn(II)(2)(mu-OAc)(3)]BPh4 (1) (Me(3)TACN=N, N',N"-trimethyl-1,4,7-triazacyclononane; OAc=acetate(1-); BPh4 = tetraphenylborate(1-)) was studied with EPR spectroscopy at X- and Q-band frequencies, for both perpendicular and parallel polarizations of the microwave field, and with variable temperature (2-50 K). Complex 1 is an antiferromagnetically coupled dimer which shows signals from all excited spin manifolds, S = 1 to 5. The spectra were simulated with diagonalization of the full spin Hamiltonian which includes the Zeeman and zero-field splittings of the individual manganese sites within the dimer, the exchange and dipolar coupling between the two manganese sites of the dimer, and the nuclear hyperfine coupling for each manganese ion. All possible transitions for all spin manifolds were simulated, with the intensities determined from the calculated probability of each transition. In addition, the non-uniform broadening of all resonances was quantitatively predicted using a lineshape model based on D- and r-strain. As the temperature is increased from 2 K, an 11-line hyperfine pattern characteristic of dinuclear Mn(II) is first observed from the S = 3 manifold. D- and r-strain are the dominate broadening effects that determine where the hyperfine pattern will be resolved. A single unique parameter set was found to simulate all spectra arising for all temperatures, microwave frequencies, and microwave modes. The simulations are quantitative, allowing for the first time the determination of species concentrations directly from EPR spectra. Thus, this work describes the first method for the quantitative characterization of EPR spectra of dinuclear manganese centers in model complexes and proteins. The exchange coupling parameter J for complex I was determined (J = -1.5 +/- 0.3 cm(-1); H-ex = -2JS(1) (.) S-2) and found to be in agreement with a previous determination from magnetization. The phenomenon of exchange striction was found to be insignificant for 1. (C) 2003 Elsevier Inc. All rights reserved.