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首页> 外文会议>Fifth International Manuel M.Baizer Symposium in Honor of Professor Jean Michel Saveant at the 201st Meeting of the Electrochemical Society Centennial Meeting May 12-17, 2002 Philadelphia, PA, USA >SINGLE TWO-ELECTRON TRANSFERS IN THE ELECTROCHEMICAL OXIDATION AND REDUCTION OF CAROTENOIDS
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SINGLE TWO-ELECTRON TRANSFERS IN THE ELECTROCHEMICAL OXIDATION AND REDUCTION OF CAROTENOIDS

机译：电化学氧化和还原类胡萝卜素中的单电子转移

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摘要

Cyclic voltammetry experiments revealed the inversion of the standard potentials of the 1st and 2nd electron transfers in the oxidation of β-carotene (1) and 15,15′-didehydro-β-carotene (2) (but not in their reduction) as well as in the reduction of canthaxanthin (3) (but not in its oxidation). The factors that control standard potential inversion in these systems, and more generally in symmetrical molecules containing polyconjugated chains, were investigated by B3LYP calculations. Two main interconnected effects play in favor of potential inversion. One is the localization of the charges in the di-ion towards the ends of the molecule, thus minimizing coulombic repulsion. This effect is enhanced by solvation of the di-ion providing its additional stabilization. Localization of the charges in the di-ion is favored by the presence of electron-accepting terminal groups for reductions and of hole-accepting terminal groups for oxidations. The second effect is the delocalization of the charge in the radical ion over the whole molecular framework, which is also disfavoring its stabilization by solvation.
机译：循环伏安法实验表明，在β-胡萝卜素（1）和15,15'-二氢-β-胡萝卜素（2）的氧化中，第一和第二电子转移的标准电势也发生了反转（但没有还原）像角黄素（3）的还原一样（但不氧化）。通过B3LYP计算研究了在这些系统中，更普遍地在包含多共轭链的对称分子中控制标准电势反转的因素。两个主要的相互联系的效应有助于潜在的倒置。一种是使二价离子中的电荷朝向分子末端定位，从而使库仑排斥最小化。通过离子化提供额外的稳定性，可以增强这种效果。通过存在用于还原的电子接受端基和用于氧化的空穴接受端基，有利于电荷在二价离子中的定位。第二个作用是使自由基离子在整个分子框架上发生离域化，这也不利于其通过溶剂化作用的稳定性。

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