Galano Annia, Francisco-Marquez Misaela
Departamento de Química, Universidad Autónoma Metropolitana-Iztapalapa, Iztapalapa, CP 09340 México DF México.
J Phys Chem B. 2009 Aug 13;113(32):11338-45. doi: 10.1021/jp904061q.
The relative free radical scavenging activity of beta-carotene, lycopene, and torulene toward OOH radicals has been studied using density functional theory. Hydrogen atom transfer (HAT) and radical adduct formation (RAF) mechanisms have been considered. All the possible reaction sites have been included in the modeling, and detailed branching ratios are reported for the first time. The reactions of hydrocarbon carotenoids (Car) with peroxyl radicals, in both polar and nonpolar environments, are predicted to proceed via RAF mechanism, with contributions higher than 98% to the overall OOH + Car reactions. Lycopene and torulene were found to be more reactive than beta-carotene. In nonpolar environments the reactivity of the studied carotenoids toward peroxyl radical follows the trend LYC > TOR > BC, whereas in aqueous solutions it is TOR > LYC > BC. OOH adducts are predicted to be formed mainly at the terminal sites of the conjugated polyene chains. The main addition sites were found to be C5 for beta-carotene and lycopene and C30 for torulene. The general agreement between the calculated magnitudes and the available experimental data supports the predictions from this work.
利用密度泛函理论研究了β-胡萝卜素、番茄红素和链孢红素对OOH自由基的相对自由基清除活性。考虑了氢原子转移（HAT）和自由基加合物形成（RAF）机制。建模中纳入了所有可能的反应位点，并首次报告了详细的分支比。预计在极性和非极性环境中，烃类类胡萝卜素（Car）与过氧自由基的反应均通过RAF机制进行，对OOH + Car总反应的贡献高于98%。发现番茄红素和链孢红素比β-胡萝卜素更具反应活性。在非极性环境中，所研究的类胡萝卜素对过氧自由基的反应活性遵循LYC > TOR > BC的趋势，而在水溶液中则为TOR > LYC > BC。预计OOH加合物主要在共轭多烯链的末端位点形成。发现主要的加成位点对于β-胡萝卜素和番茄红素是C5，对于链孢红素是C30。计算值与现有实验数据之间的总体一致性支持了本研究的预测。
