Linder Douglas P, Rodgers Kenton R
Department of Chemistry, Biochemistry, and Molecular Biology, North Dakota State University, Fargo, North Dakota 58105-5516, USA.
Inorg Chem. 2005 Nov 14;44(23):8259-64. doi: 10.1021/ic0504745.
A recent report of the structural and vibrational properties of heme-bound HNO in myoglobin, MbHNO, revealed a long Fe-N(HNO) bond with the hydrogen atom bonded to the coordinated N atom. The Fe-N(H)-O moiety was reported to exhibit an unusually high Fe-N(HNO) stretching frequency relative to those of the corresponding [FeNO]6 and [FeNO]7 porphyrinates, despite the Fe-N(HNO) bond being longer than either of its Fe-N(NO) counterparts. Herein, we present results from density functional theory calculations of an active site model of MbHNO that support the previous assignment and clarify this seemingly contradictory result. The results are consistent with the experimental evidence for a ground-state Fe-N(H)-O structure having a long Fe-N(HNO) bond and a uniquely high nu(Fe)(-)(N(HNO)) frequency. This high frequency is the result of the correspondingly low reduced mass of the normal mode, which is largely attributable to significant motion of the N-bound hydrogen atom. Additionally, the calculations show the Fe-N(H)O bonding in this complex to be remarkably insensitive to whether the HNO and ImH ligand planes are parallel or perpendicular. This is attributed to insensitivities of the Fe-L(axial) characters of molecular orbitals to the relative HNO and ImH orientation in both the parallel and perpendicular conformers.
最近一篇关于肌红蛋白中血红素结合的HNO（MbHNO）的结构和振动性质的报告显示，铁与N（HNO）之间存在长键，氢原子与配位的N原子相连。据报道，尽管Fe-N（HNO）键比相应的[FeNO]6和[FeNO]7卟啉酸盐中的Fe-N（NO）键更长，但Fe-N（H）-O部分相对于它们表现出异常高的Fe-N（HNO）伸缩频率。在此，我们展示了对MbHNO活性位点模型进行密度泛函理论计算的结果，这些结果支持了先前的归属并澄清了这一看似矛盾的结果。这些结果与基态Fe-N（H）-O结构具有长Fe-N（HNO）键和独特的高ν（Fe）-（N（HNO））频率的实验证据一致。这种高频是正常模式相应低折合质量的结果，这在很大程度上归因于与N相连的氢原子的显著运动。此外，计算表明该配合物中Fe-N（H）O键对HNO和咪唑配体平面是平行还是垂直非常不敏感。这归因于分子轨道的Fe-L（轴向）特征对平行和垂直构象中HNO和咪唑相对取向不敏感。
