Model proton-coupled electron transfer reactions in solution: Predictions of rates, mechanisms, and kinetic isotope effects
Model proton-coupled electron transfer reactions in solution: Predictions of rates, mechanisms, and kinetic isotope effects
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DOI：
10.1021/jp001967s
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发表时间：
2000-10-19
影响因子：
2.9
通讯作者：
Hammes-Schiffer, S
中科院分区：
文献类型：
--
作者：
Decornez, H;Hammes-Schiffer, S
本文对模型系统进行了全面的理论研究，旨在预测溶质和溶剂性质对质子耦合电子转移 (PCET) 反应的速率、机制和动力学同位素效应的影响。这些研究基于多态连续体理论，其中用多态价键模型描述溶质，将溶剂表示为介电连续体，并用量子力学处理活性电子和转移质子。该理论公式能够描述一系列机制，包括单电子转移和电子和质子同时转移的顺序或协同 EPT 机制。随着（I）电子供体-受体距离减小，（2）质子供体-受体距离减小，（3）质子转移反应变得更加放热，（4）电子转移反应变得更加吸热（在正常马库斯区域），（5）温度降低，（6）溶剂极性降低，以及（7）电子供体和受体的尺寸增加，EPT机制的概率预计会增加。相对于这些性质，预计速率将以类似的方式增加，不同之处在于速率将随着温度升高以及电子转移反应在正常马库斯区域中变得更加放热而增加。随着 EPT 机制概率的增加以及反应物和产物质子振动波函数之间的定位和距离的增加，预计动力学同位素效应也会增加。由于转移的电子和质子之间的强耦合，可以观察到异常强的动力学同位素效应。这些理论研究阐明了 PCET 反应的基本原理，并提供了可以通过实验测试的预测。
This paper presents a comprehensive theoretical study of model systems directed at predicting the effects of solute and solvent properties on the rates, mechanisms, and kinetic isotope effects for proton-coupled electron transfer (PCET) reactions. These studies are based on a multistate continuum theory in which the solute is described with a multistate valence bond model, the solvent is represented as a dielectric continuum, and the active electrons and transferring protons are treated quantum mechanically. This theoretical formulation is capable of describing a range of mechanisms, including single electron transfer and sequential or concerted EPT mechanisms in which both an electron and a proton are transferred. The probability of the EPT mechanism is predicted to increase as (I) the electron donor-acceptor distance is decreased, (2) the proton donor-acceptor distance is decreased, (3) the proton transfer reaction becomes more exothermic, (4) the electron transfer reaction becomes more endothermic (in the normal Marcus region), (5) the temperature decreases, (6) the solvent polarity decreases, and (7) the size of the electron donor and acceptor increases. The rates are predicted to increase with respect to these properties in a similar manner, with the exception that the rates will increase as the temperature increases and as the electron transfer reaction becomes more exothermic in the normal Marcus region. The kinetic isotope effects are predicted to increase as the probability of the EPT mechanism increases and as the localization and the distance between the reactant and product proton vibrational wave functions increase. Unusually strong kinetic isotope effects may be observed due to strong coupling between the transferring electron and proton. These theoretical studies elucidate the fundamental principles of PCET reactions and provide predictions that can be tested experimentally.