Understanding the origin of metal-sulfur vibrations in an oxo-molybdenurn dithiolene complex: Relevance to sulfite oxidase
Understanding the origin of metal-sulfur vibrations in an oxo-molybdenurn dithiolene complex: Relevance to sulfite oxidase
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DOI：
10.1021/ic0506815
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发表时间：
2006-02-06
影响因子：
4.6
通讯作者：
Enemark, JH
中科院分区：
文献类型：
--
作者：
Inscore, FE;Knottenbelt, SZ;Enemark, JH
用X射线结晶学和共振拉曼光谱进一步表征了(Tp*)MoO(Qdt)(Tp*是氢三(3，5-二甲基-1-吡唑基)硼酸盐，Qdt是2，3-喹恶啉二硫杂环戊烯)，它代表了一个重要的基准氧钼单二硫杂环戊烯模型体系，与各种吡喃喋呤钼酶的活性中心有关，包括亚硫酸盐氧化酶。化合物(Tp*)MoO(Qdt)属于三斜空间群，P_1($)，其中a=98424(7)埃，b=11.2323(8)埃，c=11.9408(8)埃，α=92.7560β=98.9530(10)度，伽马=92.7560(10)度。(TP*)MoO(Qdt)分子具有扭曲的六配位几何特征，与具有单一配位二硫杂环戊烯配体的氧钼(V)体系不同。(Tp*)MoO(Qdt)的第一配位球键长度和角度与(Tp*)MoO(Bdt)(Bdt为1，2-苯二硫烯)的相应结构参数非常相似。在(TP*)MoO(QdT)和(TP*)MoO(BdT)之间观察到的相对较小的内球结构变化强烈地表明，几何效应不是这两个氧钼(V)二硫烯电子结构差异的主要原因。因此，在两个分子之间观察到的还原电势和第一电离能的巨大差异似乎主要来自于它们各自硫给体的有效核电荷的差异。然而，二硫杂环的非平面性暗示了对Mo-S键的微扰，这是由折叠角定义的。这种在MoS_2和S-C=C-S平面之间观察到的角变形((TP~*)MoO(QdT)中的角畸变角为29.5度；(TP~*)MoO(BdT)中的角失真为21.3度)，可能通过控制S p-Mod轨道重叠的程度来影响这些氧钼二硫杂环体系的电子结构。在酶中，折叠角度可以被吡喃喋呤动态调节，从而起到与蛋白质构象变化相关的振动能量的换能器的作用，通过折叠角度的变化直接到达活性部位。在原子转移和电子转移过程中，这一过程可以有效地调节活性中心的电荷再分布。RR谱在348和407 cm(-1)处有谱带。通过对模型[(NH_3)(3)MoO(Qdt)](1+)简正波的频率分析，用Gaussian03程序将这些谱带归属为五元Mo-Ditholene核结构的Mo-S混合模振动。拉曼光谱还为(Tp*)MoO(Qdt)和相关的氧钼二硫烯化合物中的面内拟奇异二硫烯S-Mod(Xy)共价键相互作用提供了额外的证据，这对涉及吡喃喋呤二硫烯的亚硫酸盐氧化酶中活性中心的电子转移再生具有重要意义。
X-ray crystallography and resonance Raman (rR) spectroscopy have been used to further characterize (Tp*)MoO(qdt) (Tp* is hydrotris(3,5-dimethyl-1-pyrazolyl)borate and qdt is 2,3-quinoxalinedithiolene), which represents an important benchmark oxomolybdenum mono-dithiolene model system relevant to various pyranopterin Mo enzyme active sites, including sulfite oxidase. The compound (Tp*)MoO(qdt) crystallizes in the triclinic space group, P1 ($) over bar, where a = 9 8424 (7) angstrom, b = 11.2323 (8) angstrom, c = 11.9408 (8) angstrom, alpha = 92.7560 beta = 98.9530 (10)degrees, and gamma = 104.1680 (10)degrees. The (Tp*)MoO(qdt) molecule exhibits the distorted six-coordinate geometry characteristic of related oxo-Mo(V) systems possessing a single coordinated dithiolene ligand. The first coordination sphere bond lengths and angles in (Tp*)MoO(qdt) are very similar to the corresponding structural parameters for (Tp*)MoO(bdt) (bdt is 1,2-benzenedithiolene). The relatively small inner-sphere structural variations observed between (Tp*)MoO(qdt) and (Tp*)MoO(bdt) strongly suggest that geometric effects are not a major contributor to the significant electronic structural differences reported for these two oxo-Mo(V) dithiolenes. Therefore, the large differences observed in the reduction potential and first ionization energy between the two molecules appear to derive primarily from differences in the effective nuclear charges of their respective sulfur donors. However, a subtle perturbation to Mo-S bonding is implied by the nonplanarity of the dithiolene chelate ring, which is defined by the fold angle. This angular distortion (theta = 29.5 degrees in (Tp*)MoO(qdt); 21.3 degrees in (Tp*)MoO(bdt)) observed between the MoS2 and S-C=C-S planes may contribute to the electronic structure of these oxo-Mo dithiolene systems by controlling the extent of S p-Mo d orbital overlap. In enzymes, the fold angle may be dynamically modulated by the pyranopterin, thereby functioning as a transducer of vibrational energy associated with protein conformational changes directly to the active site via changes in the fold angle. This process could effectively mediate charge redistribution at the active site during the course of atom- and electron-transfer processes. The rR spectrum shows bands at 348 and 407 cm(-1). From frequency analysis of the normal modes of the model, [(NH3)(3)MoO(qdt)](1+), using the Gaussian03 suite of programs, these bands are assigned as mixed-mode Mo-S vibrations of the five-membered Mo-ditholene core structure. Raman spectroscopy has also provided additional evidence for an in-plane pseudo-sigma dithiolene S-Mo d(xy) covalent bonding interaction in (Tp*)MoO(qdt) and related oxo-Mo-dithiolenes that has implications for electron-transfer regeneration of the active site in sulfite oxidase involving the pyranopterin dithiolene.