Axial ligation modes in iron(III) Porphyrins. Models for the oxidized reaction states of cytochrome P-450 enzymes and the molecular structure of iron(III) protoporphyrin IX dimethyl ester p-nitrobenzenethiolate.
Axial ligation modes in iron(III) Porphyrins. Models for the oxidized reaction states of cytochrome P-450 enzymes and the molecular structure of iron(III) protoporphyrin IX dimethyl ester p-nitrobenzenethiolate.
复制标题
铁(III)卟啉的轴向连接模式。
DOI：
10.1021/ja00425a008
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发表时间：
1976
影响因子：
15
通讯作者：
R. H. Holm
中科院分区：
文献类型：
--
作者：
S. Tang;S. Koch;G. Papaefthymiou;S. Foner;R. Frankel;J. Ibers;R. H. Holm
Cytochrome P-450 monooxygenaseenzymes contain a protoporphyrin IX prosthetic groupand exhibit five reac-tion states, in each of whichthe nature of axial ligation to Fe (II, III) is uncertain. The occurrence of sulfur coordination has been a matter of active speculation. The two oxidized states, ox-P-450 (resting, low spin) and ox-P-450-S (substrate bound, high spin), contain Fe (III) with apparentsix and five coordination, respectively. In an attempt to develop experimental criteria for identifying axial ligands in iron (IIl) porphyrins, the series of complexes Fe (P) L (high spin) and Fe (P) LL'(low spin), P= octaethylporphyrin, protoporphyrin IX dimethyl ester (PPIXDME) dianions, havebeen isolated and generated in situ, respectively, and subjected to detailed physical studies. Axial ligands L and U include a variety of oxygen, sulfur, and nitro-gen donors intended to model possible protein side chain coordination. Isolable Fe (P) SR complexes were obtained with R= aryl. The crystal structure of Fe (PPIXDME)(SC6H4-;>-N02) has been determined by x-raydiffraction techniques utilizing 6320 observations collected by counter methods. The compound crystallizes in space group Cf-PI with two molecules in a cell of dimensions a= 13.585 (6), b= 14.016 (2), c= 13.297 (2) Á, a= 110.83 (2), ß= 119.74 (2), and= 62.60 (2). The observed density of 1.35 (2) g cm-3 compares favorablywith the calculated density of 1.378 g cm-3. Refinement of an anisotropic model (497 variables) by full-matrix least-squares methods leads to a conventional R index (on F2) of 0.126 for the 6320 observations and to a conventional R index (on F) of 0.071 for the3225 observations having F0> 3a (F0). The mol-ecule exhibits near square pyramidal geometry with an Fe-S distance of 2.324 (2) Á and Fe-N distances ranging from 2.042 (5) to 2.081 (5) and averaging to 2.064 Á. The ironatom is 0.448 Á above the mean plane of the porphyrin core, which is nearly planar (mean deviation from the mean plane is 0.038 Á) but exhibits a slight ruffling that corresponds roughly to an S4 distortion. Although the mean dimensions within the porphyrin agree well with previouslyreported values, there is a perceptible alternation in the lengths of the Cb-Ca bonds around the peripheryof the porphyrin as well as an alternation of the Ca-Cm bonds such that there occurs a long-short-long-short... sequence of Cb-Ca, Ca-Cm, Cm-Ca, Ca-Cb bonds. The phe-nyl ring makes a dihedral angle of 11.1 with the porphyrin plane, and is situated away from the bulky propionic ester substituents. Extensive compilations of results are presented and include (i) electronic spectral data,(ii) principal gvalues evaluated from EPR spectra,(iii) Mossbauer parameters,(iv) effective magneticmoment values and crystal field parameters obtained from field dependent (< 60 kOe) magnetizationdata. Of the species Fe (P) L (L=
