Theory of proton-coupled electron transfer in energy conversion processes.
Theory of proton-coupled electron transfer in energy conversion processes.
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DOI：
10.1021/ar9001284
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发表时间：
2009-12-21
影响因子：
18.3
通讯作者：
Hammes-Schiffer, Sharon
中科院分区：
文献类型：
--
作者：
Hammes-Schiffer, Sharon
质子耦合电子转移(PCET)反应在包括光合作用和呼吸作用在内的广泛的能量转换过程中起着至关重要的作用。这些反应也构成了许多类型的太阳能燃料电池和电化学装置的基础。PCET理论的最新进展使预测体系性质对反应速率的影响成为可能。这些预测可能会指导设计更高效的能源生产催化剂，包括基于人工光合作用和太阳能转换的催化剂。本文总结了理论上预测的PCET速率与体系性质的关系，并说明了调节化学体系中反应速率的可能方法。在过去的十年里，关于PCET反应的一般理论公式已经发展起来。在这个理论中，PCET反应是用反应物和产物电子-质子振动态之间的非绝热跃迁来描述的。对于均相和电化学PCET反应，在各种定义好的极限下，导出了一系列非绝热速率常数的表达式。最近，这一理论已经扩展到包括溶剂动力学的影响和描述超快界面PCET。对速率常数表达式的分析提供了对PCET基本物理原理的洞察，并使得能够预测速率对系统物理性质的依赖关系。此外，动力学同位素效应，即氢和氢的速率之比，提供了一个有用的机械探测器。通常情况下，PCET速率会随着电子耦合和温度的升高而增加，随着总重组能和平衡质子给体-受体距离的减小而减小。随着驱动力变得更负，速率常数预计会增加，而不是在反转区域表现出翻转行为，因为与低自由能垒和相对较大的振动耦合相关的激发振动产物态变得容易获得。文献中对实验观察到的PCET反应的pH依赖性的物理基础进行了辩论。当质子受体是缓冲物种时，pH依赖可能源于缓冲液的质子化平衡。它也可能是由于相互竞争的协调和顺序的PCET反应途径的动力学复杂性造成的。在电化学PCET中，非均匀速率常数和电流密度强烈地依赖于过电位。电子转移时平衡质子给体-受主距离的变化可能导致Tafel图的不对称性和转移系数偏离零过电势下一半的标准值。将这一理论应用到实验研究的系统中，说明了可以用来调整PCET速率的方法。例如，可以通过改变pH或使用不同的缓冲物种作为质子受体来调节速率。这一比率也可以通过生物体系中的定点突变或化学修饰来调节，这些化学修饰改变了化学体系中氧化还原物种上的取代基。了解这些变化对PCET速率的影响可能有助于加强能量转换过程的实验工作。
Proton-coupled electron transfer (PCET) reactions play an essential role in a broad range of energy conversion processes, including photosynthesis and respiration. These reactions also form the basis of many types of solar fuel cells and electrochemical devices. Recent advances in the theory of PCET enable the prediction of the impact of system properties on the reaction rates. These predictions may guide the design of more efficient catalysts for energy production, including those based on artificial photosynthesis and solar energy conversion. This Account summarizes the theoretically predicted dependence of PCET rates on system properties and illustrates potential approaches for tuning the reaction rates in chemical systems. A general theoretical formulation for PCET reactions has been developed over the past decade. In this theory, PCET reactions are described in terms of nonadiabatic transitions between the reactant and product electron-proton vibronic states. A series of nonadiabatic rate constant expressions for both homogeneous and electrochemical PCET reactions have been derived in various well-defined limits. Recently this theory has been extended to include the effects of solvent dynamics and to describe ultrafast interfacial PCET. Analysis of the rate constant expressions provides insight into the underlying physical principles of PCET and enables the prediction of the dependence of the rates on the physical properties of the system. Moreover, the kinetic isotope effect, which is the ratio of the rates for hydrogen and deuterium, provides a useful mechanistic probe. Typically the PCET rate will increase as the electronic coupling and temperature increase and as the total reorganization energy and equilibrium proton donor-acceptor distance decrease. The rate constant is predicted to increase as the driving force becomes more negative, rather than exhibit turnover behavior in the inverted region, because excited vibronic product states associated with low free energy barriers and relatively large vibronic couplings become accessible. The physical basis for the experimentally observed pH dependence of PCET reactions has been debated in the literature. When the proton acceptor is a buffer species, the pH dependence may arise from the protonation equilibrium of the buffer. It could also arise from kinetic complexity of competing concerted and sequential PCET reaction pathways. In electrochemical PCET, the heterogeneous rate constants and current densities depend strongly on the overpotential. The change in equilibrium proton donor-acceptor distance upon electron transfer may lead to asymmetries in the Tafel plots and deviations of the transfer coefficient from the standard value of one-half at zero overpotential. Applications of this theory to experimentally studied systems illustrate approaches that can be utilized to tune the PCET rate. For example, the rate can be tuned by changing the pH or using different buffer species as proton acceptors. The rate can also be tuned with site-specific mutagenesis in biological systems or chemical modifications that vary the substituents on the redox species in chemical systems. Understanding the impact of these changes on the PCET rate may assist experimental efforts to enhance energy conversion processes.
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影响因子：
15
作者：
Cape, JL;Bowman, MK;Kramer, DM
通讯作者：
Kramer, DM
影响因子：
--
作者：
MARCUS, RA
通讯作者：
MARCUS, RA
DOI：
10.1073/pnas.0710643105
发表时间：
2008-01-29
影响因子：
11.1
作者：
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通讯作者：
Klinman, Judith P.
影响因子：
2.9
作者：
Costentin, Cyrille;Robert, Marc;Teillout, Anne-Lucie
通讯作者：
Teillout, Anne-Lucie
影响因子：
15
作者：
Irebo, Tania;Reece, Steven Y.;Hammarstrom, Leif
通讯作者：
Hammarstrom, Leif