Kirshenboim Omer, Frenklah Alexander, Kozuch Sebastian
Department of Chemistry, Ben-Gurion University of the Negev Beer-Sheva 841051 Israel
Chem Sci. 2020 Dec 15;12(9):3179-3187. doi: 10.1039/d0sc06295b.
While the influence of intramolecular electric fields is a known feature in enzymes, the use of oriented external electric fields (EEF) to enhance or inhibit molecular reactivity is a promising topic still in its infancy. Herein we will explore computationally the effects that EEF can provoke in simple molecules close to the absolute zero, where quantum tunnelling (QT) is the sole mechanistic option. We studied three exemplary systems, each one with different reactivity features and known QT kinetics: π bond-shifting in pentalene, Cope rearrangement in semibullvalene, and cycloreversion of diazabicyclohexadiene. The kinetics of these cases depend both on the field strength and its direction, usually giving subtle but remarkable changes. However, for the cycloreversion, which suffers large changes on the dipole through the reaction, we also observed striking results. Between the effects caused by the EEF on the QT we observed an inversion of the Arrhenius equation, deactivation of the molecular fluxionality, and stabilization or instantaneous decomposition of the system. All these effects may well be achieved, literally, at the flick of a switch.
虽然分子内电场的影响在酶中是一个已知特征，但利用定向外部电场（EEF）来增强或抑制分子反应性仍是一个尚处起步阶段的有前景的课题。在此，我们将通过计算探索EEF在接近绝对零度的简单分子中可能引发的效应，在这种情况下量子隧穿（QT）是唯一的反应机制选择。我们研究了三个示例性体系，每个体系都具有不同的反应特征和已知的QT动力学：并五苯中的π键迁移、半篮烷中的科浦重排以及二氮杂双环己二烯的环化逆转。这些情况的动力学既取决于场强及其方向，通常会产生细微但显著的变化。然而，对于在反应过程中偶极矩会发生大幅变化的环化逆转，我们也观察到了惊人的结果。在EEF对QT所造成的影响中，我们观察到了阿仑尼乌斯方程的反转、分子流动性的失活以及体系的稳定或瞬间分解。实际上，所有这些效应都可能在轻按开关之际实现。
