Comparison of the manganese cluster in oxygen-evolving photosystem II with distorted cubane manganese compounds through X-ray absorption spectroscopy
Comparison of the manganese cluster in oxygen-evolving photosystem II with distorted cubane manganese compounds through X-ray absorption spectroscopy
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DOI：
10.1021/ic991003j
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发表时间：
1999-12-27
影响因子：
4.6
通讯作者：
Yachandra, VK
中科院分区：
文献类型：
--
作者：
Cinco, RM;Rompel, A;Yachandra, VK
X-射线吸收光谱被用来评估光系统II(PS II)中的放氧络合物(OEC)与一类含有扭曲的立方烷[Mn4O3X]核的合成锰络合物(X=苯甲酸盐、乙酸酯、甲醇、氢氧化物、叠氮、氟化物、氯或溴)之间的相似程度。这些[Mn-4(Mu(3)-O)(3)(Mu(3)-X)]立方烷具有C-3nu对称性，除了X=苯甲酸盐物种外，X=苯甲酸酯物种的对称性稍强，只有C-S对称性。此外，本研究还包括了在三个锰上含有三个或六个末端氯配体的Mn4O3Cl络合物。氧配合物的MnK边X射线吸收近边结构(XANES)开始类似于PS II(S-1态)谱的一般特征，尽管二阶导数与PS II中的不同。这些锰化合物的扩展X射线吸收精细结构(EXAFS)也显示出表面上与PS II的相似之处，但对物相和幅度的仔细观察显示出重大的差异。最明显的区别是PS Il EXAFS的傅里叶变换(FT)比来自扭曲立方体的FT更小。对Mn EXAFS谱的曲线拟合验证了已知的Mn立方体的核心结构，并表明临界的2.7和3.3埃的Mn-Mn距离数与在OEC中观察到的不同。EXAFS方法检测到随着X在这一系列中的变化，核心结构发生了微小的变化，并用于排除C-3Nu对称性的扭曲立方体作为OEC的Mn催化簇的拓扑模型。相反，该方法表明，为了与PS II中的锰团簇相似，需要对古巴骨架进行更大的扭曲，改变锰-锰距离的比例。
X-ray absorption spectroscopy has been employed to assess the degree of similarity between the oxygen-evolving complex (OEC) in photosystem II (PS II) and a family of synthetic manganese complexes containing the distorted cubane [Mn4O3X] core (X = benzoate, acetate, methoxide, hydroxide, azide, fluoride, chloride, or bromide). These [Mn-4(mu(3)-O)(3)(mu(3)-X)] cubanes possess C-3 nu symmetry except for the X = benzoate species, which is slightly more distorted with only C-s symmetry. In addition, Mn4O3Cl complexes containing three or six terminal Cl ligands at three of the Mn were included in this study. The Mn K-edge X-ray absorption near edge structure (XANES) from the oxygen-ligated complexes begin to resemble general features of the PS II (S-1 state) spectrum, although the second derivatives are distinct from those in PS II. The extended X-ray absorption fine structure (EXAFS) of these Mn compounds also displays superficial resemblance to that of PS II, but major differences emerge on closer examination of the phases and amplitudes. The most obvious distinction is the smaller magnitude of the Fourier transform (FT) of the PS Il EXAFS compared to the FTs from the distorted cubanes. Curve fitting of the Mn EXAFS spectra verifies the known core structures of the Mn cubanes, and shows that the number of the crucial 2.7 and 3.3 Angstrom Mn-Mn distances differs from that observed in the OEC. The EXAFS method detects small changes in the core structures as X is varied in this series, and serves to exclude the distorted cubane of C-3 nu symmetry as a topological model for the Mn catalytic cluster of the OEC. Instead, the method shows that even more distortion of the cubans framework, altering the ratio of the Mn-Mn distances, is required to resemble the Mn cluster in PS II.