X-ray absorption spectroscopy to analyze nuclear geometry and electronic structure of biological metal centers - Potential and questions examined with special focus on the tetra-nuclear manganese complex of oxygenic photosynthesis
X-ray absorption spectroscopy to analyze nuclear geometry and electronic structure of biological metal centers - Potential and questions examined with special focus on the tetra-nuclear manganese complex of oxygenic photosynthesis
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DOI：
10.1007/s00216-003-1982-2
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发表时间：
2003-07-01
影响因子：
4.3
通讯作者：
Haumann, M
中科院分区：
文献类型：
--
作者：
Dau, H;Liebisch, P;Haumann, M
X射线吸收光谱（XAS）已成为金属酶催化中心过渡金属元素特异性分析的重要工具。在本研究中的信息内容的X-射线光谱相对于核的几何形状，特别是，蛋白质结合的金属离子的电子结构进行了探索，使用锰络合物的光系统II（PSIII）作为模型系统。EXAFS范围携带关于配体的数量和距离以及配体供体功能的化学类型的直接信息。对于第一球配体和第二球金属（在多核配合物中），精确距离的测定大多是简单的，而配位数的测定显然需要更多的努力。EXAFS部分以PSII光谱数据集的示例性讨论开始，重点是协调数问题。随后，线性二色EXAFS光谱的方法进行了介绍，它是如何EXAFS数据导致PSII的四锰络合物的原子分辨率模型。在XANES部分中，考虑了以下方面：（1）通过与一系列模型化合物的比较，评估用于确定金属氧化态的替代方法。(2)通过比较多次散射计算和分子轨道计算，对XANES谱的分子轨道解释进行了探讨。(3)的XANES光谱的氧化态依赖的根本原因进行了探索。此外，现代XANES理论的潜力证明了第一次模拟的PSII锰络合物的XANES光谱中的二色性。
X-ray absorption spectroscopy (XAS) has become a prominent tool for the element-specific analysis of transition metals at the catalytic center of metalloenzymes. In the present study the information content of X-ray spectra with respect to the nuclear geometry and, in particular, to the electronic structure of the protein-bound metal ions is explored using the manganese complex of photosystem II (PSIII) as a model system. The EXAFS range carries direct information on the number and distances of ligands as well as on the chemical type of the ligand donor function. For first-sphere ligands and second-sphere metals (in multinuclear complexes), the determination of precise distances is mostly straightforward, whereas the determination of coordination numbers clearly requires more effort. The EXAFS section starts with an exemplifying discussion of a PSII spectrum data set with focus on the coordination number problem. Subsequently, the method of linear dichroism EXAFS spectroscopy is introduced and it is shown how the EXAFS data leads to an atomic resolution model for the tetra-manganese complex of PSII. In the XANES section the following aspects are considered: (1) Alternative approaches are evaluated for determination of the metal-oxidation state by comparison with a series of model compounds. (2) The interpretation of XANES spectra in terms of molecular orbitals (MOs) is approached by comparative multiple-scattering calculations and MO calculations. (3) The underlying reasons for the oxidation-state dependence of the XANES spectra are explored. Furthermore, the potential of modern XANES theory is demonstrated by presenting first simulations of the dichroism in the XANES spectra of the PSII manganese complex.