École Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide, ISIC, FSB-BSP, CH-1015 Lausanne, CH, Switzerland.
Phys Chem Chem Phys. 2014 Jan 28;16(4):1617-31. doi: 10.1039/c3cp53683a.
We present an iron K-edge X-ray absorption study of carboxymyoglobin (MbCO), nitrosylmyoglobin (MbNO), oxymyoglobin (MbO2), cyanomyoglobin (MbCN), aquomet myoglobin (metMb) and unligated myoglobin (deoxyMb) in physiological media. The analysis of the XANES region is performed using the full-multiple scattering formalism, implemented within the MXAN package. This reveals trends within the heme structure, absent from previous crystallographic and X-ray absorption analysis. In particular, the iron-nitrogen bond lengths in the porphyrin ring converge to a common value of about 2 Å, except for deoxyMb whose bigger value is due to the doming of the heme. The trends of the Fe-Nε (His93) bond length is found to be consistent with the effect of ligand binding to the iron, with the exception of MbNO, which is explained in terms of the repulsive trans effect. We derive a high resolution description of the relative geometry of the ligands with respect to the heme and quantify the magnitude of the heme doming in the deoxyMb form. Finally, time-dependent density functional theory is used to simulate the pre-edge spectra and is found to be in good agreement with the experiment. The XAS spectra typically exhibit one pre-edge feature which arises from transitions into the unoccupied dσ and dπ - πligand* orbitals. 1s → dπ transitions contribute weakly for MbO2, metMb and deoxyMb. However, despite this strong Fe d contribution these transitions are found to be dominated by the dipole (1s → 4p) moment due to the low symmetry of the heme environment.
我们呈现了羧基肌红蛋白（MbCO）、亚硝基肌红蛋白（MbNO）、氧合肌红蛋白（MbO2）、氰基肌红蛋白（MbCN）、水合肌红蛋白（metMb）和去氧肌红蛋白（deoxyMb）在生理介质中的铁 K 边 X 射线吸收研究。XANES 区域的分析是使用全多次散射公式，在 MXAN 软件包中实现的。这揭示了在血红素结构中存在的趋势，这是以前的晶体学和 X 射线吸收分析所没有的。特别是，卟啉环中的铁-氮键长度收敛到约 2 Å 的共同值，除了去氧肌红蛋白，其较大的值是由于血红素的拱顶。Fe-Nε（His93）键长的趋势被发现与配体与铁结合的效果一致，除了 MbNO，这可以用反式效应的排斥来解释。我们得出了配体相对于血红素的相对几何形状的高分辨率描述，并量化了去氧肌红蛋白形式中血红素拱顶的程度。最后，使用含时密度泛函理论模拟了预边谱，发现与实验吻合较好。XAS 谱通常表现出一个预边特征，这是由未占据的 dσ和 dπ-π配体*轨道的跃迁引起的。1s→dπ跃迁对 MbO2、metMb 和 deoxyMb 的贡献较弱。然而，尽管铁 d 轨道的贡献很强，但由于血红素环境的低对称性，这些跃迁被发现主要由偶极子（1s→4p）矩主导。
