Mechanical gating of a mechanochemical reaction cascade.

Junpeng Wang,Tatiana B Kouznetsova,Roman Boulatov,Stephen L Craig

doi:10.1038/ncomms13433

Junpeng Wang, Tatiana B Kouznetsova + Show 2 more

Open Access

https://doi.org/10.1038/ncomms13433

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Journal: Nature communications	Publication Date: Nov 16, 2016
Citations: 114	License type: CC BY 4.0

Affiliation: Duke University, University of Liverpool

Abstract

Covalent polymer mechanochemistry offers promising opportunities for the control and engineering of reactivity. To date, covalent mechanochemistry has largely been limited to individual reactions, but it also presents potential for intricate reaction systems and feedback loops. Here we report a molecular architecture, in which a cyclobutane mechanophore functions as a gate to regulate the activation of a second mechanophore, dichlorocyclopropane, resulting in a mechanochemical cascade reaction. Single-molecule force spectroscopy, pulsed ultrasonication experiments and DFT-level calculations support gating and indicate that extra force of >0.5 nN needs to be applied to a polymer of gated gDCC than of free gDCC for the mechanochemical isomerization gDCC to proceed at equal rate. The gating concept provides a mechanism by which to regulate stress-responsive behaviours, such as load-strengthening and mechanochromism, in future materials designs.

Highlights

Covalent polymer mechanochemistry offers promising opportunities for the control and engineering of reactivity
This inversion is a result of the sequential loading of the scissile bonds enforced by the fused-ring architecture of DCTCU: the applied force is coupled to only one scissile bond at a time, which must dissociate before another scissile bond is loaded
When stretching force of 1 nN is applied to DCTCU, the calculated activation free energy for dissociation of the outer C–C bond of the cyclobutane moiety (TS1f, blue) is reduced to 32.5 kcal mol À 1 compared with 51.7 kcal mol À 1 and 41.7 kcal mol À 1 for dissociation of the bridgehead bonds of the cyclobutane and cis-gDCC moieties, respectively, which are uncoupled from the applied force

Summary

Introduction

Covalent polymer mechanochemistry offers promising opportunities for the control and engineering of reactivity. Covalent polymer mechanochemistry[1,2,3,4,5] has been extensively explored in recent years for a variety of purposes, including biasing reaction pathways[6,7,8,9], trapping transition states and intermediates[10,11], catalysis[12,13,14,15], release of small molecules and protons[16,17,18], stress reporting[19,20,21,22], stress strengthening[22,23,24] and soft devices[25,26] These efforts are largely facilitated by the fact that, unlike other energy sources, mechanical force is directional and regulated by local molecular structure. Quantum-chemical calculations confirm that the difference reflects the additional force needed to open the cyclobutane core, that is, that the mechanochemical kinetics of cis-gDCC isomerization is controlled by that of cyclobutane dissociation rather than the intrinsic mechanochemistry of cis-gDCC

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