Institut für Physiologische Chemie, Universitätsklinikum Essen, Hufelandstr. 55, Essen D-45122, Germany.
Institut für Organische Chemie, Universität Duisburg-Essen, Universitätsstr. 5, Essen D-45117, Germany.
Chem Res Toxicol. 2022 Jul 18;35(7):1135-1145. doi: 10.1021/acs.chemrestox.1c00355. Epub 2022 Jun 28.
The toxicity of peroxynitrite, ONOO, is directed by carbon dioxide via the formation of the corresponding adduct, ONOOCO. Entity ONOOCO is believed to be a highly unstable compound that primarily decomposes to nitrate and carbon dioxide, but it also undergoes fractional homolysis to generate carbonate radical anion, CO, and nitrogen dioxide, NO, in a so-called solvent (radical) cage reaction. Recently, Koppenol et al. reviewed their proposal that ONOOCO is a relatively long-lived intermediate, arguing that "the solvent cage as proposed is physically not realistic". To further address whether ONOOCO could be a long-lived species, bond dissociation enthalpies (BDE) were calculated by the composite reference method (SMD)W1BD. Anion ONOOCO can exist in two conformers, and with predicted gas-phase O-O BDEs of about 10.8 and 9.5 kcal mol, respectively. Therefore, both conformers should have very short lifetimes. The (SMD)W1BD method was also used to evaluate the thermodynamic parameters of interest, revealing that the homolytic decomposition of ONOOCO is the most reasonable pathway. Moreover, previously reported experimental chemically induced dynamic nuclear polarization data also support the intermediacy of the radical cage and the formation of products CO and NO at a total yield of about 70%. Because the solvent radical cage concept for the decay of ONOO in the presence of CO is supported by a variety of spectrometric methods as well as by quantum chemical calculations at high levels of theory, it provides strong evidence against the "out-of-cage" construct. For clarification of the nature of the transient UV/vis absorption(s) between 600 and 700 nm, as observed by Koppenol et al., several experimental approaches are suggested.
过氧亚硝酸盐（ONOO ）的毒性受二氧化碳的影响，形成相应的加合物 ONOOCO。据信，实体 ONOOCO 是一种极不稳定的化合物，主要分解为硝酸盐和二氧化碳，但它也会发生部分同质裂解，生成碳酸根自由基阴离子（CO ）和二氧化氮（NO ），发生所谓的溶剂（自由基）笼反应。最近，Koppenol 等人回顾了他们关于 ONOOCO 是一种相对长寿命中间体的建议，认为“所提出的溶剂笼在物理上是不现实的”。为了进一步研究 ONOOCO 是否可能是一种长寿命物种，通过复合参考方法（SMD）W1BD 计算了键离解焓（BDE）。阴离子 ONOOCO 可以以两种构象存在， 和 ，气相 O-O BDE 分别约为 10.8 和 9.5 kcal/mol。因此，这两种构象都应该具有非常短的寿命。SMD）W1BD 方法还用于评估感兴趣的热力学参数，结果表明，ONOOCO 的均裂分解是最合理的途径。此外，先前报道的实验化学诱导动态核极化数据也支持自由基笼的中间体形成，以及产物 CO 和 NO 的形成，总产率约为 70%。由于存在 CO 时 ONOO 衰减的溶剂自由基笼概念得到了各种光谱方法以及高水平理论的量子化学计算的支持，这为反对“出笼”结构提供了有力证据。为了澄清 Koppenol 等人观察到的 600nm 至 700nm 之间瞬态紫外/可见吸收（s）的性质，提出了几种实验方法。
