Critical Role of Deep Hydrogen Tunneling to Accelerate the Antioxidant Reaction of Ubiquinol and Vitamin E
Critical Role of Deep Hydrogen Tunneling to Accelerate the Antioxidant Reaction of Ubiquinol and Vitamin E
复制标题
深层氢隧道加速泛醇和维生素 E 抗氧化反应的关键作用
DOI：
10.1021/jp410263f
复制
发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Taichi Inagaki and Takeshi Yamamoto
中科院分区：
文献类型：
--
作者：
Q. Han;S. Mihara;K. Hashimoto;T. Fujino;Taichi Inagaki and Takeshi Yamamoto
在生物膜中，多种抗氧化剂起抑制氧化损伤的作用。维生素E和泛醇是最重要的脂溶性抗氧化剂，它们直接捕获脂质过氧化自由基或协同泛醇再生维生素E自由基。本文利用变分过渡态理论和多维隧穿修正来研究后一种再生反应。结果表明，该体系通过明显的给体和受体重排形成致密的H键配合物，使得H转移的势垒相当窄，隧穿效应非常大，传输系数为>4000。与实验结果一致，发现阿伦尼乌斯活化能非常小（~ 1 kcal/mol），这里用穿过势垒的平均隧穿能来解释。在电子结构方面，我们证明了目前的反应是通过质子耦合电子转移（PCET）机制进行的，并表明PCET的特性也有助于通过锐化势垒来产生大的隧道效应。最后，对相关反应进行了系统比较，指出量子隧穿可以显著提高生物膜的抗氧化防御效率。
In biomembranes a variety of antioxidants work to suppress oxidative damage. Vitamin E and ubiquinol are among the most important lipid-soluble antioxidants, which trap lipid peroxyl radicals directly or work cooperatively in the regeneration of vitamin E radicals by ubiquinol. Here, we investigate the latter regeneration reaction by using variational transition-state theory with multidimensional tunneling corrections. The result shows that the system forms a compact H-bonded complex by significantly rearranging the donor and acceptor moieties, which leads to a rather narrow potential barrier for H transfer and a very large tunneling effect with a transmission coefficient >4000. In accord with experiment, the Arrhenius activation energy is found to be very small (∼1 kcal/mol), which is interpreted here in terms of mean tunneling energy through the barrier. Regarding the electronic structure, we demonstrate that the present reaction proceeds via a proton-coupled electron transfer (PCET) mechanism and suggest that the PCET character also contributes to the large tunneling effect by sharpening the potential barrier. Finally, a systematic comparison is made among relevant reactions and it is indicated that the antioxidant defense of biomembranes may benefit rather significantly from quantum tunneling to enhance the reaction efficiency.