Models of the cytochromes b. 8. Two-dimensional nuclear Overhauser and exchange spectroscopy studies of paramagnetic "cavity" type (tetraphenylporphinato)iron(III) complexes of planar ligands
Models of the cytochromes b. 8. Two-dimensional nuclear Overhauser and exchange spectroscopy studies of paramagnetic "cavity" type (tetraphenylporphinato)iron(III) complexes of planar ligands
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细胞色素模型 B.
DOI：
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发表时间：
1991
期刊：
影响因子：
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通讯作者：
U. Simonis
中科院分区：
文献类型：
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作者：
F. Walker;U. Simonis
通过 NOESY（核欧沃豪瑟和交换光谱）实验在 CD2C12 中研究了氯化（四均三基卟啉）铁（III）氯化物的顺磁性双-2-甲基咪唑配合物，具有短 TI 和 T 弛豫时间，作为温度（-29、-54、-74 °C）的函数。在 -29 和 -29 和 -74 °C 下获得的二维（2-D）图谱。 -54°C 显示了由于化学交换和核奥弗豪瑟效应 (NOE) 造成的交叉峰，而在 -74°C 获得的图仅显示 NOE 交叉峰。 NOE 互相关与位于内消旋碳原子上方或附近的 2-MeImH 配体一致，而不是位于卟啉氮上，如 Nakamura 和 Groves 先前建议的（四面体） 1988, 44, 3225）。对于轴向配体的这种取向，2-甲基咪唑（2-MeImH）配体的甲基和卟啉苯环的基团之间的非键合相互作用产生强烈褶皱的卟啉核，其具有两个彼此成直角的长方形“空腔”，一个在卟啉环平面上方，一个在卟啉环平面下方， 其将“受阻”轴向配体保持在介观位置上方的垂直平面中。由于轴向配体的旋转而不是轴向配体交换，化学交换交叉峰指示特定类型的所有共振的相互转换。这一解释得到了以下事实的证实：在任何研究的温度下，自由和协调的 2-MelmH 共振之间都没有观察到交叉峰。 2-MeImH配体的旋转需要交替的苯环随着配体旋转而上下“拍打”。吡咯-H 质子之间的耦合模式与根据居里图的外推截距所预期的耦合模式一致。
The paramagnetic bis-2-methylimidazole complex of (tetramesitylporphinato)iron(III) chloride, with short TI and T, relaxation times, was investigated in CD2C12 by NOESY (nuclear Overhauser and exchange spectroscopy) experiments as a function of temperature (-29, -54, -74 "C). The two-dimensional (2-D) maps obtained at -29 and -54 "C revealed cross peaks due to both chemical exchange and the nuclear Overhauser effect (NOE), while the map obtained at -74 "C showed only NOE cross peaks. The NOE cross correlations are consistent with the 2-MeImH ligands being positioned over or near the meso carbon atoms, rather than over the porphyrin nitrogens, as previously suggested by Nakamura and Groves (Tetrahedron 1988, 44, 3225). The nonbonded interactions between the methyl groups of the 2-methylimidazole (2-MeImH) ligands and the mesityl groups of the porphyrin phenyl rings for this orientation of the axial ligands produce a strongly ruffled porphyrin core having two oblong "cavities" at right angles to each other, one above and one below the plane of the porphyrin ring, which hold the "hindered" axial ligands in perpendicular planes over the meso positions. The chemical exchange cross peaks are indicative of interconversion of all resonances of a particular type, due to rotation of the axial ligands rather than axial ligand exchange. This interpretation is confirmed by the fact that there are no cross peaks observed between free and coordinated 2-MelmH resonances at any of the temperatures investigated. Rotation of the 2-MeImH ligands requires that alternate phenyl rings "flap" up and down as the ligands rotate. The coupling pattern between the pyrrole-H protons is consistent with that expected on the basis of the extrapolated intercepts of the Curie plot.