Leu Bogdan M, Zgierski Marek Z, Wyllie Graeme R A, Scheidt W Robert, Sturhahn Wolfgang, Alp E Ercan, Durbin Stephen M, Sage J Timothy
Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts, USA.
J Am Chem Soc. 2004 Apr 7;126(13):4211-27. doi: 10.1021/ja038526h.
We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of the Fe atom in porphyrins designed to model heme protein active sites. Nuclear resonance vibrational spectroscopy (NRVS) yields frequencies, amplitudes, and directions for 57Fe vibrations in a series of ferrous nitrosyl porphyrins, which provide a benchmark for evaluation of quantum chemical vibrational calculations. Detailed normal mode predictions result from DFT calculations on ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), its cation [Fe(TPP)(NO)]+, and ferrous nitrosyl porphine Fe(P)(NO). Differing functionals lead to significant variability in the predicted Fe-NO bond length and frequency for Fe(TPP)(NO). Otherwise, quantitative comparison of calculated and measured Fe dynamics on an absolute scale reveals good overall agreement, suggesting that DFT calculations provide a reliable guide to the character of observed Fe vibrational modes. These include a series of modes involving Fe motion in the plane of the porphyrin, which are rarely identified using infrared and Raman spectroscopies. The NO binding geometry breaks the four-fold symmetry of the Fe environment, and the resulting frequency splittings of the in-plane modes predicted for Fe(TPP)(NO) agree with observations. In contrast to expectations of a simple three-body model, mode energy remains localized on the FeNO fragment for only two modes, an N-O stretch and a mode with mixed Fe-NO stretch and FeNO bend character. Bending of the FeNO unit also contributes to several of the in-plane modes, but no primary FeNO bending mode is identified for Fe(TPP)(NO). Vibrations associated with hindered rotation of the NO and heme doming are predicted at low frequencies, where Fe motion perpendicular to the heme is identified experimentally at 73 and 128 cm-1. Identification of the latter two modes is a crucial first step toward quantifying the reactive energetics of Fe porphyrins and heme proteins.
我们采用定量实验和理论方法来表征卟啉中铁原子的振动动力学，这些卟啉旨在模拟血红素蛋白活性位点。核共振振动光谱（NRVS）给出了一系列亚铁亚硝酰卟啉中57Fe振动的频率、振幅和方向，为评估量子化学振动计算提供了基准。详细的简正模式预测来自对亚铁亚硝酰四苯基卟啉Fe(TPP)(NO)、其阳离子[Fe(TPP)(NO)]+以及亚铁亚硝酰卟吩Fe(P)(NO)的密度泛函理论（DFT）计算。不同的泛函导致Fe(TPP)(NO)预测的Fe-NO键长和频率有显著差异。否则，在绝对尺度上对计算和测量的Fe动力学进行定量比较，总体上显示出良好的一致性，这表明DFT计算为观察到的Fe振动模式的特征提供了可靠的指导。这些模式包括一系列涉及卟啉平面内Fe运动的模式，而这些模式很少能用红外和拉曼光谱识别。NO的配位几何结构打破了Fe环境的四重对称性，并且预测的Fe(TPP)(NO)平面内模式的频率分裂与观察结果一致。与简单三体模型的预期相反，模式能量仅在两种模式中局域在FeNO片段上，一种是N-O伸缩振动，另一种是具有Fe-NO伸缩和FeNO弯曲混合特征的模式。FeNO单元的弯曲也对几种平面内模式有贡献，但对于Fe(TPP)(NO)未识别出主要的FeNO弯曲模式。预测了与NO受阻旋转和血红素穹顶化相关的低频振动，其中垂直于血红素的Fe运动在实验中被确定为73和128 cm-1。识别后两种模式是量化铁卟啉和血红素蛋白反应能量学的关键的第一步。
