Single-Event Spectroscopy and Unravelling Kinetics of Covalent Domains Based on Cyclobutane Mechanophores.

TitleSingle-Event Spectroscopy and Unravelling Kinetics of Covalent Domains Based on Cyclobutane Mechanophores.
Publication TypeJournal Article
Year of Publication2021
AuthorsBH Bowser, S Wang, TB Kouznetsova, HK Beech, BD Olsen, M Rubinstein, and SL Craig
JournalJournal of the American Chemical Society
Volume143
Start Page5269
Issue13
Pagination5269 - 5276
Date Published04/2021
Abstract

Mechanochemical reactions that lead to an increase in polymer contour length have the potential to serve as covalent synthetic mimics of the mechanical unfolding of noncovalent "stored length" domains in structural proteins. Here we report the force-dependent kinetics of stored length release in a family of covalent domain polymers based on <i>cis</i>-1,2-substituted cyclobutane mechanophores. The stored length is determined by the size (<i>n</i>) of a fused ring in an [<i>n</i>.2.0] bicyclic architecture, and it can be made sufficiently large (>3 nm per event) that individual unravelling events are resolved in both constant-velocity and constant-force single-molecule force spectroscopy (SMFS) experiments. Replacing a methylene in the pulling attachment with a phenyl group drops the force necessary to achieve rate constants of 1 s<sup>-1</sup> from ca. 1970 pN (dialkyl handles) to 630 pN (diaryl handles), and the substituent effect is attributed to a combination of electronic stabilization and mechanical leverage effects. In contrast, the kinetics are negligibly perturbed by changes in the amount of stored length. The independent control of unravelling force and extension holds promise as a probe of molecular behavior in polymer networks and for optimizing the behaviors of materials made from covalent domain polymers.

DOI10.1021/jacs.1c02149
Short TitleJournal of the American Chemical Society