Probing the influence of local coordination environment on the properties of Fe-type nitrile hydratase model complexes
Probing the influence of local coordination environment on the properties of Fe-type nitrile hydratase model complexes
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DOI：
10.1021/ic001271d
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发表时间：
2001-03-26
影响因子：
4.6
通讯作者：
Kovacs, JA
中科院分区：
文献类型：
--
作者：
Jackson, HL;Shoner, SC;Kovacs, JA
本文报道了一系列四种结构相关的顺式二硫纶配位Fe（III）配合物[Fe-III（DITpy）（2）]Cl（1）、[Fe-III（DITIm）（2）]-Cl（2）、[Fe-III（ADIT）（2）]Cl（3）和[Fe-III（AMIT）（2）]Cl（4）。3的结构表征以及3和4的光谱性质先前已报道。i、2和4的晶体数据如下：1 . 3 H（2）O在正交空间群Pca 2（1）中结晶，其中n = 19.800（4）埃，B = 18.450（4）埃，c = 14.800（3）埃，Z = 8。2.1/2 EtOH·1/2 H（2）O在单斜晶系空间群C-c中结晶，a = 24.792（4），B = 14.364（3）埃，c = 17.527（3）埃，β = 124.91（2）度，Z = 8。4在棒上的三斜空间群P（1）中结晶，其中a = 8.0152（6）埃，B = 10.0221（8）埃，c = 11.8384（10）埃，α = 73.360（3）度，β = 71.451（5）度，γ = 72.856（4）度和Z = 2。配合物1-4共享共同的S2 N4配位环境，其由两个顺式硫醇盐、两个反式亚胺和两个顺式末端氮供体组成：N-末端=吡啶（1）、咪唑（2）和伯胺（3和4）。晶体学确定的平均Fe-S键距在1-4范围从2.196到2.232埃，并且是低自旋Fe（III）-硫醇盐络合物的特征。低自旋S = 1/2基态的EPR和磁化率测量证实。这些配合物的电子光谱的特征在于宽吸收带中心附近类似于700 nm，这是与配体到金属的电荷转移（CT）带一致。通过循环伏安法测量进一步表征络合物;并且所有络合物都具有高度负的Fe（III）/Fe（II）氧化还原对（类似于-IV vs SCE，饱和甘汞电极），表明烷基硫醇盐供体在稳定Fe（III）中心方面是有效的。氧化还原;耦合和可见光谱中的700 nm波段显示依赖于溶剂的位移，这取决于溶剂的氢键能力。这些结果与含铁腈水合酶的活性位点的影响进行了讨论。
A series of four structurally related cis-dithiolate-ligated Fe(III) complexes, [Fe-III(DITpy)(2)]Cl (1), [Fe-III(DITIm)(2)]-Cl (2), [Fe-III(ADIT)(2)]Cl (3), and [Fe-III(AMIT)(2)]Cl (4), are described. The structural characterization of 3 as well as the spectroscopic properties of 3 and 4 has been previously reported. Crystal data for i, 2, and 4 are as follows: 1 . 3H(2)O crystallizes in the orthorhombic space group Pca2(1) with n = 19.800(4) Angstrom, b = 18.450(4) Angstrom, c = 14.800(3) Angstrom, and Z = 8. 2 .1/2EtOH .1/2H(2)O crystallizes in the monoclinic space group C-c with a = 24.792(4) at b = 14.364(3) Angstrom, c = 17.527(3) Angstrom, beta = 124.91(2)degrees, and Z = 8. 4 crystallizes in the triclinic space group P (1) over bar with a = 8.0152(6) Angstrom, b = 10.0221(8) Angstrom, c = 11.8384(10) Angstrom, alpha = 73.360(3)degrees, beta = 71.451(5)degrees, gamma = 72.856(4)degrees and Z = 2. Complexes 1-4 share a common S2N4 coordination environment that consists of two cis-thiolates, two trans-imines, and two cis-terminal nitrogen donors: N-term = pyridine (1), imidazole (2), and primary amine (3 and 4). The crystallographically determined mean Fe-S bond distances in 1-4 range from 2.196 to 2.232 Angstrom and are characteristic of low-spin Fe(III)-thiolate complexes. The low-spin S = 1/2 ground state was confirmed by both EPR and magnetic susceptibility measurements. The electronic spectra of these complexes are characterized by broad absorption bands centered near similar to 700 nm that are consistent with ligand-to-metal charge-transfer (CT) bands. The complexes were further characterized by cyclic voltammetry measurements; and all possess highly negative Fe(III)/Fe(II) redox couples (similar to -1 V vs SCE, saturated calomel electrode) indicating that alkyl thiolate donors are effective at stabilizing Fe(III) centers. Both the redox; couple and the 700 nm band in the visible spectra show solvent-dependent shifts that are dependent upon the H-bonding ability of the solvent. The implications of these results with respect to the active site of the iron-containing nitrile hydratases are also discussed.