Models of the cytochromes:: Crystal structures and EPR spectral characterization of low-spin bis-imidazole complexes of (OETPP)FeIII having intermediate ligand plane dihedral angles
Models of the cytochromes:: Crystal structures and EPR spectral characterization of low-spin bis-imidazole complexes of (OETPP)FeIII having intermediate ligand plane dihedral angles
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DOI：
10.1021/ic060283h
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发表时间：
2006-07-10
影响因子：
4.6
通讯作者：
Walker, F. Ann
中科院分区：
文献类型：
--
作者：
Yatsunyk, Liliya A.;Dawson, Alice;Walker, F. Ann
报道了具有两种咪唑、n -苄基咪唑和n -甲基咪唑轴向配体的八乙基四苯基卟啉铁（III）的制备、EPR光谱和晶体结构，[(OETPP)Fe(HLm)2]Cl、[(OETPP)Fe(N-Bzlm)(2)]-Cl和[(OETPP)Fe(N-Melm)(2)]Cl。尽管轴向配体大小变化很大，但所有配合物的单位细胞参数都非常相似；每个结构都有相同的基本基序，由扩展的卟啉框架形成的大空隙（由有序或无序的轴向配体和无序溶剂填充），这使得不同大小的配体可以适应相同的细胞尺寸。每个卟啉核呈鞍状构象，纵杆δ c - β纵杆= 1.13-1.15埃。轴向配体平面之间的二面角δ phi远不是理想的平行或垂直：[(OETPP)Fe(Hlm)(2)]Cl（分子1和2）为30.1度，57.2度，[(OETPP)Fe(N-Bzlm)(2)]Cl为56.8度，[(OETPP)Fe(N-Melm)(2)]Cl为16.0度，44.6度，59.6度和88.1度，其中轴向配体无序。在本研究的配合物中，最大的“平行”角为56.8度的轴向配体δ phi（观察到的正菱形或II型EPR信号（N-Bzlm, g = 3.08, 2.19, 1.31）），最小的“垂直”角为57.2度（观察到的“大g（max）”或I型EPR信号（Hlm, g(max) = 3.24））。从本研究的结果可以看出，I型和II型复合物的最大g的大小是连续变化的，两者之间没有间断。虽然EPR信号类型的转换，从II型到I型，在本研究中似乎非常明显，但这可能是人为的，基于有限的例子数量和（OETPP）Fe-III配合物所需的鞍形失真。然而，通过比较几个二面角接近60度的蛋白和II型EPR光谱，我们可以得出EPR信号类型的转换发生在57度+/- 3-5度附近。
The preparation, EPR spectra, and crystal structures of octaethyltetraphenylporphyrinatoiron(III) having two imidazole, N-benzylimidazole, and N-methylimidazole axial ligands are reported, [(OETPP)Fe(HLm)2]Cl, [(OETPP)Fe(N-Bzlm)(2)]-Cl, and [(OETPP)Fe(N-Melm)(2)]Cl. Despite large variation in axial ligand size, the unit cell parameters for all complexes are very similar; each structure has the same basic motif, with large voids formed by the extended porphyrin framework ( filled by ordered or disordered axial ligands and disordered solvent), which allows differently sized ligands to fit within the same cell dimensions. Each porphyrin core adopts a saddled conformation with vertical bar Delta C-beta vertical bar = 1.13-1.15 angstrom. The dihedral angles between axial ligand planes, Delta phi, are far from being either ideal parallel or perpendicular: 30.1 degrees, 57.2 degrees for [(OETPP)Fe(Hlm)(2)]Cl (molecules 1 and 2), 56.8 for [(OETPP)Fe(N-Bzlm)(2)]Cl, and 16.0 degrees, 44.6 degrees, 59.6 degrees, and 88.1 degrees for [(OETPP)Fe(N-Melm)(2)]Cl, which has disordered axial ligands. Among the complexes of this study, an axial ligand Delta phi of 56.8 degrees is found to be the largest "parallel" angle (as defined by the observation of a normal rhombic or Type II EPR signal (N-Bzlm, g = 3.08, 2.19, 1.31)), while 57.2 degrees is found to be the smallest "perpendicular" Delta phi (as defined by the observation of a "large g(max)" or Type I EPR signal (Hlm, g(max) = 3.24)). From the results of this study, it is clear that the size of the largest g for Types I and II complexes varies continuously, with no break between the two. While the switch in EPR signal type, from Type II to Type I, appears to be very sharp in this study, this may be somewhat artificial based upon limited numbers of examples and the required saddle distortion of the (OETPP)Fe-III complexes. However, in comparison to several proteins with dihedral angles near 60 degrees and Type II EPR spectra, we may conclude that the switch in EPR signal type occurs near 57 degrees +/- 3-5 degrees.