Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, San Rafael Atlixco 186, Col. Vicentina, Iztapalapa, C. P. 09340, México D. F., México.
J Phys Chem B. 2012 Jan 26;116(3):1200-8. doi: 10.1021/jp211172f. Epub 2012 Jan 13.
The free radical scavenging activity of capsaicin (CAP), which is the pungent component of hot chili peppers, has been studied in aqueous and lipid solutions, using the density functional theory. Different mechanisms of reaction have been considered: single electron transfer (SET), hydrogen transfer (HT), and radical adduct formation (RAF). Rate constants and branching ratios of the different channels of reaction are provided, as well as an interpretation of the UV-vis spectra. CAP is predicted to react faster in aqueous solution than in nonpolar media with oxygenated free radicals, and it was found to be a more efficient scavenger than melatonin and caffeine. It was also found that while SET does not contribute to the overall reactivity of CAP toward (•)OOH, (•)OOCH(3), and (•)OCH(3) radicals, it might be important for the reactions with more electrophilic radicals such as (•)OH, (•)OCCl(3), and (•)OOCCl(3). The main process, responsible for the peroxyl scavenging activity of CAP, was found to be the HT from the OH phenolic group. For the reaction with (•)OCH(3), on the other hand, the HT from allylic sites are predicted to be the main channels of reaction. In this particular case a wider product distribution is predicted. This supports the role of the reacting free radical on the preponderant mechanism of action of free radical scavengers.
用密度泛函理论研究了辣椒素（CAP）的清除自由基活性，CAP 是辛辣红辣椒的刺激性成分，在水相和油相溶液中都进行了研究。考虑了不同的反应机制：单电子转移（SET）、氢转移（HT）和自由基加合物形成（RAF）。提供了不同反应通道的速率常数和分支比，以及对紫外可见光谱的解释。预测 CAP 在水相溶液中比在含氧化自由基的非极性介质中反应更快，并且它被发现比褪黑素和咖啡因更有效地清除自由基。还发现，虽然 SET 不会影响 CAP 与（•）OOH、（•）OOCH（3）和（•）OCH（3）自由基的总反应性，但它可能对更亲电自由基如（•）OH、（•）OCCl（3）和（•）OOCCl（3）的反应很重要。对于 CAP 的过氧自由基清除活性，主要过程被发现是来自 OH 酚基团的 HT。另一方面，对于与（•）OCH（3）的反应，预测 HT 从烯丙基位点是主要的反应通道。在这种特殊情况下，预测会有更广泛的产物分布。这支持了反应自由基在自由基清除剂的主要作用机制中的作用。
