Electron paramagnetic resonance and Mössbauer spectroscopy and density functional theory analysis of a high-spin Fe(IV)-oxo complex.
Electron paramagnetic resonance and Mössbauer spectroscopy and density functional theory analysis of a high-spin Fe(IV)-oxo complex.
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DOI：
10.1021/ja303224p
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发表时间：
2012-06-13
影响因子：
15
通讯作者：
Hendrich, Michael P.
中科院分区：
文献类型：
--
作者：
Gupta, Rupal;Lacy, David C.;Bominaar, Emile L.;Borovik, A. S.;Hendrich, Michael P.
在非血红素铁酶中，具有动力学活性的氧化剂是一种高自旋的FeIV-oxo物种，它的特性不如血红素体系中的中间自旋物种。本工作利用穆斯堡尔谱和双频/双模电子顺磁共振光谱对结构相似的[FeIVH3buea(O)]-，[FeIIIH3buea(O)]2-和[FeIH3buea(OH)]-(H3buea=tris[(N‘-tert-butylureaylato)-N-ethylene]aminato))进行了详细的表征。[FeIVH3buea(O)]-配合物具有由C3对称配体施加的高自旋(S=2)构型。[FeIVH3buea(O)]-络合物的EPR波谱是第一个记录在案的来自FeIV-oxo络合物的EPR信号的例子，展示了用EPR波谱检测和定量FeIV物种的能力。定量模拟可以确定零场参数D=+4.7 cm-1和物种浓度。零场参数的密度泛函理论计算结果与实验值吻合较好，表明对D值的主要贡献来自于在1.2 eV激发的S=1电子组态基态的自旋-轨道耦合。17O同位素浓缩实验测定了[FeIVH3buea(O)]-的超精细常数170Az=10 MHz，[FeIIIH3buea(OH)]-的170Ay=8 MHz，170Az=12 MHz。由实验值求出了各向同性超精细常数(170Aiso=-16.8 MHz)，以定量测定[FeIVH3buea(O)]-中Fe-OxO键的自旋极化(ρp=0.56)。这是第一次对非血红素络合物进行实验测定，表明铁-氧键具有显著的共价性。高场穆斯堡尔谱给出了[FeIVH3buea(O)]-络合物的~(57)Fe Adip张量为(+5.6，+5.3，-10.9)MHz，Aiso=-25.9 MHz，密度泛函理论计算结果与该络合物的核参数相吻合。
The kinetically competent oxidant in non-heme iron enzymes is a high-spin FeIV-oxo species, which are not as well characterized as the intermediate-spin species of heme systems. The present work gives a detailed characterization of the structurally similar [FeIVH3buea(O)]-, [FeIIIH3buea(O)]2- and [FeIIIH3buea(OH)]- (H3buea = tris[(N'-tert-butylureaylato)-N-ethylene]aminato) complexes using Mössbauer and dual-frequency/dual-mode electron paramagnetic resonance (EPR) spectroscopies. The [FeIVH3buea(O)]- complex has a high-spin (S = 2) configuration imposed from the C3-symmetric ligand. EPR spectroscopy of the [FeIVH3buea(O)]- complex is the first documented example of an EPR signal from an FeIV-oxo complex, demonstrating the ability to detect and quantify FeIV species with EPR spectroscopy. Quantitative simulations allowed determination of the zero-field parameter, D = +4.7 cm-1, and the species concentration. Density functional theory calculations of the zero-field parameter are found to be in agreement with the experimental value and indicate the major contribution to the D-value is from spin–orbit coupling of the ground state with an excited S = 1 electronic configuration at 1.2 eV. 17O isotope enrichment experiments allowed a determination of the hyperfine constant 170Az = 10 MHz for [FeIVH3buea(O)]- and 170Ay = 8 MHz, 170Az = 12 MHz for [FeIIIH3buea(OH)]-. The isotropic hyperfine constant (170Aiso = -16.8 MHz) was derived from the experimental value to allow a quantitative determination of the spin polarization (ρp = 0.56) of the oxo p-orbitals of the Fe-oxo bond in [FeIVH3buea(O)]-. This is the first experimental determination for non-heme complexes, and indicates significant covalency in the Fe-oxo bond. High-field Mössbauer spectroscopy gave an 57Fe Adip tensor of (+5.6, +5.3, -10.9) MHz and Aiso = -25.9 MHz for the [FeIVH3buea(O)]- complex, and DFT calculations are in agreement with the nuclear parameters of the complex.
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