Quantum chemical approach to the assignment of iron-catecholate vibrations and isotopic substitution shifts
Quantum chemical approach to the assignment of iron-catecholate vibrations and isotopic substitution shifts
复制标题
DOI：
10.1021/ja953409a
复制
发表时间：
1996-04-03
影响因子：
15
通讯作者：
MichaudSoret, I
中科院分区：
文献类型：
--
作者：
Ohrstrom, L;MichaudSoret, I
在本次通讯中，我们报告了使用量子化学模型计算来分配儿茶酚铁振动并获得同位素位移的定量预测。这项研究将展示这种新方法如何提高振动光谱学的潜力，1-3 尤其是共振拉曼技术，4-7 在金属蛋白研究中的潜力。对儿茶酚和[Fe（儿茶酚酸盐）] 2- 进行了全面的几何优化和振动分析，并利用后者获得了 16/18O、54/57Fe 和 1/2H 同位素取代位移。它们成功地与实验模式匹配（图 1）6，并允许对观察到的条带进行更精确的分配。这些计算的巨大兴趣源于使用儿茶酚盐型配体作为非血红素铁蛋白的光谱探针。 8-16 然而，即使使用同位素标记，金属儿茶酚酸盐振动频率的分配也并不简单。特别是 CdO 和 FesO 振动的性质以及螯合振动模式的存在受到质疑。 6 虽然原则上可以在对光谱进行完整的正常坐标分析后预测同位素位移，但这并不总是可能的。然后，人们通常必须依靠双原子谐振子（DHO）来粗略估计位移，但该模型有明显的缺点，因为它无法考虑振动的真实性质。 1 游离儿茶酚的密度泛函理论 (DFT) 计算 17 给出的几何形状 18 和频率与实验数据非常吻合，正如根据相关苯氧基系统的最新结果所预期的那样。 19, 20 文献中关于实验光谱中的振动模式没有完全一致，21, 22，我们能够验证和澄清所提出的分配（参见支持信息）。为了模拟铁-儿茶酚盐键合，我们使用 [Fe-(儿茶酚盐)] 2-。 23 该模型满足以下标准：(1) 它允许在相对先进的理论水平上进行快速频率评估。(2) 儿茶酚盐保持其原始氧化态。(3) 优化的几何结构相当接近 Fe (III)-儿茶酚盐络合物的观测参数。 24 (4) 儿茶酚的总体分析
In this communication we report the use of quantum chemical model calculations to assign iron-catecholate vibrations and to get quantitative predictions of the isotopic shifts. This study will show how such a new approach may increase the potential of vibrational spectroscopy, 1-3 especially the resonance Raman technique, 4-7 in studies of metalloproteins. Full geometry optimizations and vibrational analyses were performed for catechol and [Fe (catecholate)] 2-, and with the latter, the 16/18O, 54/57Fe, and 1/2H isotopic substitution shifts were obtained. They were successfully matched to the experimental pattern (Figure 1) 6 and allowed more precise assignments of the observed bands. The great interest in these calculations stems from the use of catecholate type ligands as spectroscopic probes for non-heme iron proteins. 8-16 However, the assignment of the metal-catecholate vibrational frequencies is not straightforward, even with isotopic labeling. Particularly the nature of the CdO and FesO vibrations and the existence of a chelate vibration mode have been questioned. 6 Although the isotopic shifts can, in principle, be predicted after a complete normal coordinate analysis of the spectrum, this is not always possible. Then one often has to rely on the diatomic harmonic oscillator (DHO) for a rough estimation of the shifts, but this model has obvious shortcomings since it cannot take into account the true nature of the vibrations. 1 Density functional theory (DFT) calculations17 on free catechol gave a geometry18 and frequencies in good agreement with experimental data, as expected in view of recent results on related phenoxy systems. 19, 20 There is no complete consensus in the literature on the vibration modes in the experimental spectra, 21, 22 and we were able to verify and clarify the proposed assignments (see supporting information). To model the iron-catecholate bonding we used [Fe-(catecholate)] 2-. 23 This model fulfills the following criteria:(1) It allows for fast frequency evaluation on a relatively advanced theoretical level.(2) The catecholate remains in its original oxidation state.(3) The optimized geometry comes reasonably close to observed parameters for Fe (III)-catecholate complexes. 24 (4) The population analysis of the catecholate