We demonstrate that stable and relatively unreactive "environmentally persistent free radicals (PFRs)" can be readily formed in the post-flame and cool-zone regions of combustion systems and other thermal processes. These resonance-stabilized radicals, including semiquinones, phenoxyls, and cyclopentadienyls, can be formed by the thermal decomposition of molecular precursors including catechols, hydroquinones and phenols. Association with the surfaces of fine particles imparts additional stabilization to these radicals such that they can persist almost indefinitely in the environment. A mechanism of chemisorption and electron transfer from the molecular adsorbate to a redox-active transition metal or other receptor is shown through experiment, and supported by molecular orbital calculations, to result in PFR formation. Both oxygen-centered and carbon-centered PFRs are possible that can significantly affect their environmental and biological reactivity.

中文翻译：

---

持久自由基的形成和稳定。


我们证明，在燃烧系统和其他热过程的火焰后和冷区区域中很容易形成稳定且相对不反应的“环境持久性自由基（PFR）”。这些共振稳定的自由基，包括半醌、苯氧基和环戊二烯基，可以通过包括儿茶酚、氢醌和苯酚在内的分子前体的热分解而形成。与细颗粒​​表面的结合赋予这些自由基额外的稳定性，使得它们可以几乎无限期地存在于环境中。通过实验显示了从分子吸附物到氧化还原活性过渡金属或其他受体的化学吸附和电子转移机制，并得到分子轨道计算的支持，从而导致 PFR 形成。以氧为中心和以碳为中心的 PFR 都可能显着影响其环境和生物反应性。