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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Iron-57 NMR Chemical Shifts and M#ssbauer Quadrupole Splittings in Metalloporphyrins, Ferrocytochrome c, and Myoglobins: A Density Functional Theory Investigation
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Iron-57 NMR Chemical Shifts and M#ssbauer Quadrupole Splittings in Metalloporphyrins, Ferrocytochrome c, and Myoglobins: A Density Functional Theory Investigation

机译：铁卟啉，铁细胞色素c和肌球蛋白中铁57 NMR的化学位移和M＃ssbauer四极分裂：密度泛函理论研究

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摘要

We have evaluated the ↑(57)Fe nuclear magnetic resonance chemical shielding and M#ssbauer electric field gradient tensors and their orientations for a cytochrome c model compound as well as for isopropyl isocyanide and Carbon monoxy-myoglobin model systems and two simple metalloporphyrins containing bis(pyridine) and bis(trimethylphosphine) ligands, using Kohn-Sham density functional theory. For cytochrome c we used a model Fe(II) porphyrin structure together with a 1-methylimidazole base (to represent His-18) and a dimethyl sulfide molecule (to represent Met-80 in the structure of horse heart ferrocytochrome c), both located at the X-ray coordinates for cyt c Fe(II). For the Mb calculations, we used the coordinates of two recently characterized metalloporphyrins: (i-PrNC)(1-methylimidazole)(5,10,15,20-tetraphenylporphinato)Fe(Ⅱ) and (CO)(1-methylimidazole)(5,10,15,20-tetraphenylporphinato)Fe(II), while literature structures were used for the bis-ligand adducts. We used a "locally dense" basis to evaluate the (57)↑Fe shieldings and electric field gradients at iron and compared them with the measured chemical shifts and M#ssbauer quadrupole splittings, respectively. There is moderately good agreement between theory and experiment for the cytochrome c and Mb (57) ↑Fe chemical shifts and shielding tensors, and very good (0.10 mm s↑(-1) rmsd) agreement for the (57) ↑Fe M#ssbauer quadrupole splittings, using the following basis sets and functional:a Wachters’all electron representation for iron, a 6-311++G(2d) basis for all atoms directly attached to iron, 6-31G↑(*) for the second shell and 3-21G↑(*) bases for the other more distant atoms, together with a B3LYP hybrid exchange-correlation functional. Extensive tests with other functionals and basis set schemes are also reported. The shift and electric field gradient tensor orientations are generally close to obvious molecular symmetry axes, with the skew of the shielding tensor reversing sign on transition from strong to weak ligand fields. The paramagnetic contribution to shielding overwhelmingly dominates overall shielding and the variations seen between weak ligand field (bis(pyridine), cytochrome c) and strong ligand field (CO, PMe↓(3), i-PrNC) systems. Poor accord between theory and experiment is obtained for the ↑(57)Fe chemical shifts when MbCO models having highly distorted X-ray geometries are employed, suggesting that the Fe-C-O is close to the porphyrin normal, both in solution and in the solid state.
机译：我们评估了细胞色素c模型化合物，异丙基异氰化物和一氧化碳-肌红蛋白模型系统以及两个简单的含双卟啉的简单金属卟啉的↑（57）Fe核磁共振化学屏蔽和M＃ssbauer电场梯度张量及其方向使用Kohn-Sham密度泛函理论，确定（吡啶）和双（三甲基膦）配体。对于细胞色素c，我们使用模型Fe（II）卟啉结构以及1-甲基咪唑碱基（代表His-18）和二甲基硫醚分子（代表马心铁细胞色素c的Met-80），两者均位于在cyt c Fe（II）的X射线坐标上。对于Mb计算，我们使用了两个最近表征的金属卟啉的坐标：（i-PrNC）（1-甲基咪唑）（5,10,15,20-四苯基卟啉）Fe（Ⅱ）和（CO）（1-甲基咪唑）（ 5,10,15,20-四苯基卟啉）Fe（II），而文献结构用于双配体加合物。我们使用“局部密集”的基础来评估铁的（57）↑Fe屏蔽和电场梯度，并将它们分别与测得的化学位移和M＃ssbauer四极分裂相比较。对于细胞色素c和Mb（57）↑Fe的化学位移和屏蔽张量，理论和实验之间的一致性适中，对于（57）↑Fe M＃的一致性很好（0.10 mm s↑（-1）rmsd）。 ssbauer四极分裂，使用以下基集和函数：铁的Wachters全电子表示，直接附着于铁的所有原子的6-311 ++ G（2d）基，第二个为6-31G↑（*）壳和其他较远原子的3-21G↑（*）碱基，以及B3LYP杂化交换相关功能。还报告了使用其他功能和基础设置方案的广泛测试。位移和电场梯度张量方向通常接近明显的分子对称轴，在从强配体场过渡到弱配体场时，屏蔽张量的反转符号反转。顺磁对屏蔽的贡献在绝大多数情况下占据了主导地位，在弱配体场（双（吡啶），细胞色素c）和强配体场（CO，PMe↓（3），i-PrNC）系统之间的变化也占主导地位。当使用具有高度扭曲的X射线几何结构的MbCO模型时，对于↑（57）Fe的化学位移，理论和实验之间的一致性差，这表明溶液和固体中的Fe-CO都接近于卟啉正态。州。

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