Hessenauer-Ilicheva Natalya, Franke Alicja, Meyer Dominik, Woggon Wolf-D, van Eldik Rudi
Inorganic Chemistry, Department of Chemistry and Pharmacy, Egerlandstrasse 1, 91058 Erlangen, Germany.
Chemistry. 2009;15(12):2941-59. doi: 10.1002/chem.200801423.
Two new models for cytochrome P450 in which the thiolate axial ligand is replaced by a RSO(3)(-) group, form oxo-iron(IV) porphyrin pi-cation radicals as sole oxidation products in "peroxo shunt" reactions independent of the nature of the employed solvent (polar or non-polar) and electronic nature of the porphyrin rings. Although the properties of the solvent and push-pull effects from the porphyrin rings do not affect the mode of the O-O bond cleavage (heterolytic or homolytic) in these models, they strongly affect the rate and mechanism of each reaction step leading to the formation of the high-valent iron intermediates. This article reports the results of mechanistic studies involving the measurements of the rate of oxo-iron(IV) porphyrin pi-cation radical formation from the enzyme mimics of P450 for different oxidant concentration, temperature and pressure in selected organic solvents. Extraction of the appropriate rate constants and activation parameters for the reactions studied enable a detailed discussion of the effects of solvent and electronic nature of the porphyrin rings on the position of the first pre-equilibrium involving formation of the acylperoxo-iron(III) porphyrin intermediate, as well as on the rate of heterolytic O-O bond cleavage leading to the formation of the high-valent iron species. Furthermore, an unusual effect of solvent on the kinetics of oxo-iron(IV) porphyrin pi-cation radical formation in methanol is demonstrated and discussed in the present work.
在两种新的细胞色素P450模型中，硫醇盐轴向配体被RSO(3)(-)基团取代，在“过氧分流”反应中形成氧代铁(IV)卟啉π-阳离子自由基作为唯一的氧化产物，该反应与所用溶剂的性质（极性或非极性）以及卟啉环的电子性质无关。尽管溶剂的性质和卟啉环的推挽效应不会影响这些模型中O-O键的断裂方式（异裂或均裂），但它们会强烈影响导致高价铁中间体形成的每个反应步骤的速率和机理。本文报道了机理研究的结果，该研究涉及在选定的有机溶剂中，测量不同氧化剂浓度、温度和压力下，P450酶模拟物形成氧代铁(IV)卟啉π-阳离子自由基的速率。对所研究反应提取合适的速率常数和活化参数，能够详细讨论溶剂和卟啉环的电子性质对涉及酰基过氧铁(III)卟啉中间体形成的第一个预平衡位置的影响，以及对导致高价铁物种形成的异裂O-O键断裂速率的影响。此外，本文还展示并讨论了溶剂对甲醇中氧代铁(IV)卟啉π-阳离子自由基形成动力学的异常影响。
