Analogues for the molybdenum center of sulfite oxidase: oxomolybdenum(V) complexes with three thiolate sulfur donor atoms.
Analogues for the molybdenum center of sulfite oxidase: oxomolybdenum(V) complexes with three thiolate sulfur donor atoms.
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DOI：
10.1021/ic990768o
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发表时间：
2000-02
影响因子：
4.6
通讯作者：
M. Mader;M. Carducci;J. Enemark
中科院分区：
文献类型：
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作者：
M. Mader;M. Carducci;J. Enemark
顺式，反式 -（L - N₂S₂）Mo（V）O（SR）[L - N₂S₂H₂ = N,N' - 二甲基 - N,N' - 双（巯基苯基）乙二胺；R = CH₂Ph，CH₂CH₃和对 - C₆H₄ - Y（Y = CF₃，Cl，Br，F，H，CH₃，CH₂CH₃和OCH₃）]是首批结构特征明确的具有三个硫醇盐供体的单核Mo化合物，正如在亚硫酸氧化酶中的Mo活性位点所呈现的那样。顺式，反式 -（L - N₂S₂）Mo（V）O（SR）化合物（其中R = CH₂Ph，CH₂CH₃，对 - C₆H₄ - OCH₃和对 - C₆H₄ - CF₃）的X射线晶体结构显示，Mo原子周围具有相似的配位几何结构，所有三个硫醇盐硫供体都在赤道平面上。这种配位几何结构使两个相邻的S π轨道平行于Mo = O键，类似于亚硫酸氧化酶中烯 - 二硫醇盐配体的取向；第三个S π轨道位于赤道平面内。从S p到Mo d轨道的电荷转移跃迁发生在约28000 cm⁻¹（ε：4400 - 6900 L mol⁻¹ cm⁻¹）和15500 cm⁻¹（ε：3200 - 4900 L mol⁻¹ cm⁻¹）处。所有顺式，反式 -（L - N₂S₂）Mo（V）O（SR）化合物的EPR参数几乎相同（g₁约为2.022，g₂约为1.963，g₃约为1.956，A₁约为58.4×10⁻⁴ cm⁻¹，A₂约为23.7×10⁻⁴ cm⁻¹，A₃约为22.3×10⁻⁴ cm⁻¹），是由多个硫醇盐供体配位的氧 - Mo（V）中心的典型特征。g和A张量通过围绕重合的g₂和A₂张量元素旋转24°相关联，反映了近似的Cs配位对称性。这些EPR参数比先前具有两个或四个硫醇盐供体的模型化合物更接近模拟亚硫酸氧化酶的低pH形式和黄嘌呤氧化酶的“极快速”物种。顺式，反式 -（L - N₂S₂）Mo（V）O（SR）化合物经历准可逆的单电子还原和不可逆氧化，这对Y基团的哈米特参数σp呈线性依赖。顺式，反式 -（L - N₂S₂）Mo（V）O（SR）化合物为系统研究Mo（V）OS₃中心的电子结构及其对钼酶的影响提供了一个明确的平台。
cis,trans-(L-N2S2)Mo(V)O(SR) [L-N2S2H2 = N,N'-dimethyl-N,N'-bis(mercaptophenyl)ethylenediamine; R = CH2Ph, CH2CH3, and p-C6H4-Y (Y = CF3, Cl, Br, F, H, CH3, CH2CH3, and OCH3)] are the first structurally characterized mononuclear Mo compounds with three thiolate donors, as occurs at the Mo active site in sulfite oxidase. X-ray crystal structures of the cis,trans-(L-N2S2)Mo(V)O(SR) compounds, where R = CH2Ph, CH2CH3, p-C6H4-OCH3, and p-C6H4-CF3, show a similar coordination geometry about the Mo atom with all three sulfur thiolate donors in the equatorial plane. This coordination geometry places two adjacent S ppi orbitals parallel to the Mo=O bond, analogous to the orientation in the ene-dithiolate ligand in sulfite oxidase; the third S ppi orbital lies in the equatorial plane. Charge-transfer transitions from the S p to the Mo d orbitals occur at approximately 28,000 cm(-1) (epsilon: 4,400-6,900 L mol(-1)] cm(-1)) and 15,500 cm(-1) (epsilon: 3,200-4,900 L mol(-1) cm(-1)). The EPR parameters are nearly identical for all the cis,trans-(L-N2S2)Mo(V)O(SR) compounds (g1 approximately 2.022, g2 approximately 1.963, g3 approximately 1.956, Al approximately 58.4 x 10(-4) cm(-1), A2 approximately 23.7 x 10(-4) cm(-1), A3 approximately 22.3 x 10(-4) cm(-1)) and are typical of an oxo-Mo(V) center coordinated by multiple thiolate donors. The g and A tensors are related by a 24 degrees rotation about the coincident g2 and A2 tensor elements, reflecting the approximate Cs coordination symmetry. These EPR parameters more closely mimic those of the low pH form of sulfite oxidase and the "very rapid" species of xanthine oxidase than previous model compounds with two or four thiolate donors. The cis,trans-(L-N2S2)Mo(V)O(SR) compounds undergo a quasi-reversible, one-electron reduction and an irreversible oxidation that show a linear dependence upon the Hammett parameter, sigmap, of the Y group. The cis,trans-(L-N2S2)Mo(V)O(SR) compounds provide a well-defined platform for the systematic investigation of the electronic structures of the Mo(V)OS3 centers and their implications for molybdoenzymes.