Characterization of the high-resolution ESR spectra of superoxide radical adducts of 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO).: Analysis of conformational exchange
Characterization of the high-resolution ESR spectra of superoxide radical adducts of 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO).: Analysis of conformational exchange
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DOI：
10.1080/10715760500155688
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发表时间：
2005-08-01
影响因子：
3.3
通讯作者：
Mason, RP
中科院分区：
文献类型：
--
作者：
Dikalov, S;Jiang, JJ;Mason, RP
研究表明，自旋捕获剂5-（二乙氧基磷酰基）-5-甲基-1-吡咯啉N-氧化物（DEPMPO）能与超氧自由基形成稳定的自由基加合物。然而，DEPMPO自由基加合物的非对映异构体的存在和superhyperfine结构的外观复杂的ESR谱的解释。DEPMPO/（OOH）-O中心点的ESR谱中的超超精细结构是构象交换的结果。对DEPMPO/（OOH）-O-中心点及其结构类似物DMPO/（OOH）-O-中心点的ESR谱随温度变化的分析表明，这两种ESR谱都含有两种构象间相互转化的交换效应。计算机模拟计算的构象寿命的顺序为0.1 μ s的DMPO/（OOH）-O-中心点在室温下。DEPMPO/（OOH）-O-中心点的ESR谱的温度依赖性表明超超精细结构不依赖于构象交换。我们现在已经发现，六线ESR谱与superhyperfine结构应被分配到DEPMPO超氧化物衍生的分解产物。因此，先前分配给DEPMPO/（OOH）-O-中心点的ESR谱不仅包含DEPMPO/（OOH）-O-中心点的两种非对映体，而且还包含分解产物，并且这些谱应模拟为四种物质的组合：第一非对映体的两种构象异构体、第二非对映体的一种构象异构体和超氧化物衍生的分解产物。四个物种的存在已被支持的ESR光谱的温度依赖性，亲核合成的自由基加合物，和同位素取代实验。显然，为了正确解释DEPMPO对超氧自由基的自旋捕获，必须仔细考虑二级自由基加合物的形成。
It has been previously reported that the spin trap 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO) can form stable radical adducts with superoxide radical. However, the presence of diastereomers of DEPMPO radical adducts and the appearance of superhyperfine structure complicates the interpretation of the ESR spectra. It has been suggested that the superhyperfine structure in the ESR spectrum of DEPMPO/(OOH)-O-center dot is a result of conformational exchange between conformers. The analysis of the temperature dependence of the ESR spectrum of DEPMPO/(OOH)-O-center dot and of its structural analog DMPO/(OOH)-O-center dot have demonstrated that both ESR spectra contain exchange effects resulting from conversion between two conformers. Computer simulation calculates a conformer lifetime on the order of 0.1 mu s for DMPO/(OOH)-O-center dot at room temperature. However, temperature dependence of the ESR spectrum of DEPMPO/(OOH)-O-center dot suggests that superhyperfine structure does not depend on the conformational exchange. We have now found that the six-line ESR spectrum with superhyperfine structure should be assigned to a DEPMPO-superoxide-derived decomposition product. Therefore, ESR spectra previously assigned to DEPMPO/(OOH)-O-center dot contain not only the two diastereomers of DEPMPO/(OOH)-O-center dot but also the decomposition product, and these spectra should be simulated as a combination of four species: two conformers of the first diastereomer, one conformer of the second diastereomer and the superoxide-derived decomposition product. The presence of four species has been supported by the temperature dependence of the ESR spectra, nucleophilic synthesis of radical adducts, and isotopic substitution experiments. It is clear that to correctly interpret DEPMPO spin trapping of superoxide radicals, one must carefully consider formation of secondary radical adducts.