Influence of conformation on the EPR spectrum of 5,5-dimethyl-1-hydroperoxy-1-pyrrolidinyloxyl: A spin trapped adduct of superoxide
Influence of conformation on the EPR spectrum of 5,5-dimethyl-1-hydroperoxy-1-pyrrolidinyloxyl: A spin trapped adduct of superoxide
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DOI：
10.1021/jo0354894
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发表时间：
2004-02-20
影响因子：
3.6
通讯作者：
MacKerell, AD
中科院分区：
文献类型：
--
作者：
Rosen, GM;Beselman, A;MacKerell, AD
自旋捕获是一种用于表征短寿命自由基的技术，包括使用硝酮或亚硝基化合物来“捕获”不稳定的自由基作为可以通过EPR光谱表征的长寿命氨基氧基。所得到的aminoxyl表现出超精细分裂常数是依赖于自旋陷阱和自由基。2，2-二甲基-5-羟基-1-吡咯烷氧基（DMPO-OH）和2，2-二甲基-5-氢过氧-1-吡咯烷氧基就是这种情况（DMPO-OOH），其超精细分裂常数分别为A（N）= A（H）= 14.9 G和A（N）= 14.3 G，A（H）（β）= 11.7 G和A（H）（γ）= 1.25 G，已经被用来证明HO的产生。和O-2（.-）。然而，迄今为止，DMPO-OOH中明显的Ally超精细分裂的来源尚不清楚。我们考虑三种可能的解释来解释DMPO-OOH的独特EPR谱。第一种是γ-分裂来自DMPO-OOH的碳3或碳4上的一个氢原子。二是γ劈裂起源于DMPO-OOH的氢原子。第三是DMPO-R的构象性质在从DMPO-OH到DMPO-OOH时发生变化。实验和理论化学方法以及EPR光谱建模被用来调查这些假设可以解释DMPO-OOH的不对称EPR谱。从这些研究中，它表明，DMPO-OOH的12线EPR谱的结果不是从任何邻近的氢，但从DMPO-OOH的额外的构象。因此，1.25 G超精细分裂，这已被指定为γ分裂，实际上是从两个单独的EPR光谱与DMPO-OOH的不同构象。
Spin trapping, a technique used to characterize short-lived free radicals, consists of using a nitrone or nitroso compound to "trap" an unstable free radical as a long-lived aminoxyl that can be characterized by EPR spectroscopy. The resultant aminoxyl exhibits hyperfine splitting constants that are dependent on the spin trap and the free radical. Such is the case with 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO-OH) and 2,2-dimethyl-5-hydroperoxy-1-pyrrodinyloxyl (DMPO-OOH) whose hyperfine splitting constants, A(N) = A(H) = 14.9 G and A(N) = 14.3 G, A(H)(beta) = 11.7 G, and A(H)(gamma) = 1.25 G, respectively, have been used to demonstrate the generation of HO. and O-2(.-). However, to date, the source of the apparent Ally hyperfine splitting in DMPO-OOH is not known. We consider three possible explanations to account for the unique EPR spectrum of DMPO-OOH. The first is that the gamma-splitting arises from one of the hydrogen atoms at either carbon 3 or carbon 4 of DMPO-OOH. The second is that the gamma-splitting originates from the hydrogen atom of DMPO-OOH. The third is that the conformational properties of DMPO-R change upon going from DMPO-OH to DMPO-OOH. Experimental and theoretical chemical approaches as well as EPR spectral modeling were used to investigate which of these hypotheses may explain the asymmetric EPR spectrum of DMPO-OOH. From these studies it is shown that the 12-line EPR spectrum of DMPO-OOH results not from any proximal hydrogen, but from additional conformers of DMPO-OOH. Thus, the 1.25 G hyperfine splitting, which has been assigned as a gamma-splitting, is actually from two individual EPR spectra associated with different conformers of DMPO-OOH.