Experimental and density functional theoretical investigations of linkage isomerism in six-coordinate {FeNO}6 iron porphyrins with axial nitrosyl and nitro ligands
Experimental and density functional theoretical investigations of linkage isomerism in six-coordinate {FeNO}6 iron porphyrins with axial nitrosyl and nitro ligands
复制标题
DOI：
10.1021/ja0567891
复制
发表时间：
2006-02-15
影响因子：
15
通讯作者：
Bagley, KA
中科院分区：
文献类型：
--
作者：
Novozhilova, IV;Coppens, P;Bagley, KA
NO和亚硝酸盐的生物活性的一个关键组成部分涉及它们与血红素蛋白中的铁中心的配位。在11 K下照射（330 <λ < 500 nm）亚硝酰基-硝基化合物（TPP）Fe（NO）（NO2）（TPP =四苯基卟啉根二价阴离子）导致与硝基-亚硝酰基和亚硝酰基-异亚硝酰基键合异构现象相关的IR光谱的变化。在200 K下仅得到硝基-至-亚硝酰基键合异构体，表明异亚硝酰基键合异构体比亚硝酰基键合异构体更不稳定。DFT计算揭示了（卟吩）Fe（NO）（NO2）的两种基态构象，它们的相对轴向配体取向不同（即，GS平行于和GS垂直于）。在两种构象中，对于这种形式上的{FeNO}（6）化合物，FeNO基团是弯曲的（GS平行于156.4度，GS垂直于159.8度）。亚硝酰-硝基异构体（卟吩）Fe（NO）（ONO）的三种构象（MSall，MSa垂直于，MSa（L））和异亚硝酰-硝基异构体（卟吩）Fe（ON）（NO 2）的两种构象（MSb 11和MSb垂直于），以及双键异构体（卟吩）Fe（ON）（ONO）的三种构象（MSc平行于，MSc垂直于，MSCL）。10种优化的几何构型中只有2种含有近线性的FeNO（MSa（L））和FeON（MSCL）键。基态和异构体结构的能量按GS < MSa < MSb <Me的顺序增加.计算了所有键合异构体的振动频率，并分析了（卟吩）Fe（NO）（NO2）的理论气相吸收光谱，得到了键合异构化的电子跃迁信息.实验和理论的红外光谱的比较并没有提供证据的双键异构体的存在（TPP）Fe（NO）（NO2）。
A critical component of the biological activity of NO and nitrite involves their coordination to the iron center in heme proteins. Irradiation (330 < lambda < 500 nm) of the nitrosyl-nitro compound (TPP)Fe(NO)(NO2) (TPP = tetraphenylporphyrinato dianion) at 11 K results in changes in the IR spectrum associated with both nitro-to-nitrito and nitrosyl-to-isonitrosyl linkage isomerism. Only the nitro-to-nitrito linkage isomer is obtained at 200 K, indicating that the isonitrosyl linkage isomer is less stable than the nitrito linkage isomer. DFT calculations reveal two ground-state conformations of (porphine)Fe(NO)(NO2) that differ in the relative axial ligand orientations (i.e., GS parallel to and GS-perpendicular to). In both conformations, the FeNO group is bent (156.4 degrees for GS parallel to, 159.8 degrees for GS perpendicular to) for this formally {FeNO}(6) compound. Three conformations of the nitrosyl-nitrito isomer (porphine)Fe(NO)(ONO) (MSall, MSa perpendicular to, and MSa(L)) and two conformations of the isonitrosyl-nitro isomer (porphine)Fe(ON)(NO2) (MSbll and MSb perpendicular to) are identified, as are three conformations of the double-linkage isomer (porphine)Fe(ON)(ONO) (MSc parallel to, MSc perpendicular to, MSCL). Only 2 of the 10 optimized geometries contain near-linear FeNO (MSa(L)) and FeON (MSCL) bonds. The energies of the ground-state and isomeric structures increase in the order GS < MSa < MSb < Me. Vibrational frequencies for all of the linkage isomers have been calculated, and the theoretical gas-phase absorption spectrum of (porphine)Fe(NO)(NO2) has been analyzed to obtain information on the electronic transitions responsible for the linkage isomerization. Comparison of the experimental and theoretical IR spectra does not provide evidence for the existence of a double linkage isomer of (TPP)Fe(NO)(NO2).