DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals •HO2 and •O2- by caffeic acid phenethyl ester and some of its derivatives
DFT study of the effect of solvent on the H-atom transfer involved in the scavenging of the free radicals •HO2 and •O2- by caffeic acid phenethyl ester and some of its derivatives
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DOI：
10.1007/s00894-014-2509-9
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发表时间：
2014-11-01
影响因子：
2.2
通讯作者：
Motapon, Ousmanou
中科院分区：
文献类型：
--
作者：
Holtomo, Olivier;Nsangou, Mama;Motapon, Ousmanou
研究了咖啡酸苯乙酯(CAPE)、3-甲基-2-丁烯基咖啡酸酯(MBC)、苯甲酸咖啡酸酯(BC)、3-羟基肉桂酸苯乙酯(P3HC)和苯基-4-羟基肉桂酸乙酯(P4HC)与所选自由基(HO2)的H原子转移。这种转移可以以三种不同的方式进行：协同质子耦合电子转移(CPCET)，先电子转移后质子转移(ET-PT)，以及质子转移后电子转移(PT-ET)。在极性介质中，后者有时与序贯质子损失电子转移(SPLET)竞争。分析CAPE及其衍生物与共反应物种反应的热力学描述符--特别是反应自由能、CPCET机制的活化势垒及其速率常数--似乎是研究感兴趣的H原子转移的最现实的方法。这些分析是通过DFT计算进行的，这与从实验研究(IC50)和CBS计算获得的数据很好地吻合。在整个工作中使用了CPCM溶剂化模型，而用作参考的SMD模型仅用于CAPE。分析得出的主要结论是，SPLET是控制酚酸与(HO2)-H-中心点反应的机理，PT-ET是控制酚类化合物与O-中心点(2)-反应的机理。在CPCET过程的动力学研究中，随着溶剂极性的增加，反应速率常数减小，反应速度变慢。
H-atom transfer from caffeic acid phenethyl ester (CAPE), MBC (3-methyl-2-butenyl caffeate), BC (benzoic caffeate), P3HC (phenethyl-3-hydroxycinnamate), and P4HC (phenethyl-4-hydroxycinnamate) to the selected free radicals (HO2)-H-center dot and O-center dot(2)- was studied. Such a transfer can proceed in three different ways: concerted proton-coupled electron transfer (CPCET), electron transfer followed by proton transfer (ET-PT), and proton transfer followed by electron transfer (PT-ET). The latter pathway is sometimes competitive with SPLET (sequential proton loss electron transfer) in polar media. Analyzing the thermodynamic descriptors of the reactions of CAPE and its derivatives with co-reactive species-in particular, the free energies of reactions, the activation barrier to the CPCET mechanism, and their rate constants-appears to be the most realistic method of investigating the H-atom transfers of interest. These analyses were performed via DFT calculations, which agree well with the data acquired from experimental studies (IC50) and from CBS calculations. The CPCM solvation model was used throughout the work, while the SMD model-employed as a reference-was used only for CAPE. The main conclusion drawn from the analysis was that SPLET is the mechanism that governs the reaction of phenolic acids with (HO2)-H-center dot, while PT-ET governs the reaction of phenols with O-center dot(2)-. In kinetic investigations of the CPCET process, the rate constant decreases as the solvent polarity increases, so the reaction velocity slows down.