Department of Chemistry and Stanford University, Stanford, CA, USA.
The PULSE Institute, Stanford University, Stanford, CA, USA.
Nat Chem. 2020 Mar;12(3):302-309. doi: 10.1038/s41557-019-0396-5. Epub 2020 Jan 6.
Force can induce remarkable non-destructive transformations along a polymer, but we have a limited understanding of the energy transduction and product distribution in tandem mechanochemical reactions. Ladderanes consist of multiple fused cyclobutane rings and have recently been used as monomeric motifs to develop polymers that drastically change their properties in response to force. Here we show that [4]-ladderane always exhibits 'all-or-none' cascade mechanoactivations and the same stereochemical distribution of the generated dienes under various conditions and within different polymer backbones. Transition state theory fails to capture the reaction kinetics and explain the observed stereochemical distributions. Ab initio steered molecular dynamics reveals unique non-equilibrium dynamic effects: energy transduction from the first cycloreversion substantially accelerates the second cycloreversion, and bifurcation on the force-modified potential energy surface leads to the product distributions. Our findings illustrate the rich chemistry in closely coupled multi-mechanophores and an exciting potential for effective energy transduction in tandem mechanochemical reactions.
力可以在聚合物上诱导显著的非破坏性转变，但我们对串联机械化学反应中的能量传递和产物分布的理解有限。梯烷由多个融合的环丁烷环组成，最近被用作单体基序来开发聚合物，这些聚合物在受到力的作用时会剧烈改变其性质。在这里，我们表明[4]-梯烷在各种条件下和不同聚合物主链内总是表现出“全有或全无”级联机械激活，以及生成的二烯的相同立体化学分布。过渡态理论无法捕捉反应动力学并解释观察到的立体化学分布。从头算导向分子动力学揭示了独特的非平衡动力学效应：第一个环重排的能量传递大大加速了第二个环重排，而在力修饰的势能面上的分岔导致了产物分布。我们的研究结果说明了紧密偶联的多机械受体中的丰富化学，并为串联机械化学反应中的有效能量传递提供了令人兴奋的潜力。
