Lymar Sergei V, Khairutdinov Rafail F, Hurst James K
Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA.
Inorg Chem. 2003 Aug 25;42(17):5259-66. doi: 10.1021/ic030104l.
Peroxynitrite decay in weakly alkaline media occurs by two concurrent sets of pathways which are distinguished by their reaction products. One set leads to net isomerization to NO(3)(-) and the other set to net decomposition to O(2) plus NO(2)(-). At sufficiently high peroxynitrite concentrations, the decay half-time becomes concentration-independent and approaches a limiting value predicted by a mechanism in which reaction is initiated by unimolecular homolysis of the peroxo O-O bond, i.e., the following reaction: ONOOH --> ()OH + ()NO(2). This dynamical behavior excludes alternative postulated mechanisms that ascribe decomposition to bond rearrangement within bimolecular adducts. Nitrate and nitrite product distributions measured at very low peroxynitrite concentrations also correspond to predictions of the homolysis model, contrary to a recent report from another laboratory. Additionally, (1) the rate constant for the reaction ONOO(-) --> ()NO + ()O(2)(-), which is critical to the kinetic model, has been confirmed, (2) the apparent volume of activation for ONOOH decay (DeltaV() = 9.7 +/- 1.4 cm(3)/mol) has been shown to be independent of the concentration of added nitrite and identical to most other reported values, and (3) complex patterns of inhibition of O(2) formation by radical scavengers, which are impossible to rationalize by alternative proposed reaction schemes, are shown to be quantitatively in accord with the homolysis model. These observations resolve major disputes over experimental data existing in the literature; despite extensive investigation of these reactions, no verifiable experimental evidence has been advanced that contradicts the homolysis model.
过氧亚硝酸根在弱碱性介质中的衰变通过两组同时发生的途径进行，这两组途径由其反应产物区分。一组导致净异构化为硝酸根离子（NO₃⁻），另一组导致净分解为氧气（O₂）加亚硝酸根离子（NO₂⁻）。在足够高的过氧亚硝酸根浓度下，衰变半衰期变得与浓度无关，并接近由过氧O - O键单分子均裂引发反应的机制所预测的极限值，即以下反应：ONOOH → (·)OH + (·)NO₂。这种动力学行为排除了将分解归因于双分子加合物内键重排的其他假定机制。与另一个实验室最近的报告相反，在非常低的过氧亚硝酸根浓度下测量的硝酸盐和亚硝酸盐产物分布也与均裂模型的预测相符。此外，（1）对动力学模型至关重要的反应ONOO⁻ → (·)NO + (·)O₂⁻的速率常数已得到证实，（2）过氧亚硝酸（ONOOH）衰变的表观活化体积（ΔVₐ = 9.7 ± 1.4 cm³/mol）已被证明与添加的亚硝酸盐浓度无关，并且与大多数其他报道的值相同，以及（3）自由基清除剂对氧气形成的复杂抑制模式，这是其他提出的反应方案无法合理解释的，但已证明在定量上与均裂模型一致。这些观察结果解决了文献中存在的关于实验数据的主要争议；尽管对这些反应进行了广泛研究，但尚未提出与均裂模型相矛盾的可验证实验证据。
