Galano Annia
Instituto Mexicano del Petróleo, Eje Central Lázaro Cárdenas 152, 007730 México DF, México.
J Phys Chem B. 2007 Nov 8;111(44):12898-908. doi: 10.1021/jp074358u. Epub 2007 Oct 17.
The relative antioxidant efficiency, expressed as electron donating capability, of a large series of carotenoids has been studied using density functional theory. Their reactivity toward nine different radicals has been modeled as well as the electron transfer between pairs of carotenoids, one of which is present as a radical cation. The influence of the solvent polarity has also been studied. Torulene was found to be the most easily oxidized carotenoid, followed by lycopene. This higher reactivity is proposed in the present work for the first time, and the potential implications of such a finding are discussed. Since torulene has not been previously studied, compared to other carotenoids in terms of oxidation potentials, further experimental studies are suggested in order to confirm or reject this prediction. Ionization potential seems to be a magnitude calculable at low computational cost that correctly predicts the relative ease of oxidation in a series of carotenoids. The nuclear reorganization energy associated with electron-transfer reactions has been calculated in a very simple but apparently efficient way that allows computation of free energy barriers and relative rate constants in good agreement with the experimental values. In addition, an additive correction is proposed to include the effect of increasing the size of basis sets on the energies of Car(n) --> Car(n-1)(*+) processes. The general agreement between different calculated magnitudes and the corresponding available experimental data supports the predictions from this work.
利用密度泛函理论研究了一系列类胡萝卜素以给电子能力表示的相对抗氧化效率。模拟了它们对九种不同自由基的反应活性以及类胡萝卜素对之间的电子转移，其中一对中的一个以自由基阳离子形式存在。还研究了溶剂极性的影响。发现辣椒玉红素是最易氧化的类胡萝卜素，其次是番茄红素。本工作首次提出了这种较高的反应活性，并讨论了这一发现的潜在影响。由于之前尚未对辣椒玉红素与其他类胡萝卜素的氧化电位进行比较研究，因此建议进一步开展实验研究以证实或否定这一预测。电离电位似乎是一种可以以较低计算成本计算的量，它能正确预测一系列类胡萝卜素的相对氧化难易程度。以一种非常简单但显然有效的方式计算了与电子转移反应相关的核重组能，从而能够计算出自由能垒和相对速率常数，且与实验值吻合良好。此外，还提出了一种加性校正，以纳入基组大小增加对Car(n) --> Car(n - 1)(*+)过程能量的影响。不同计算量与相应现有实验数据之间的总体一致性支持了本工作的预测。
