AI Article Synopsis
- Researchers investigated the mechanochemical cycloreversion of cyclobutane through ultrasound experiments, but the forces needed for this process were unclear.
- They developed tailored macrocycles with an ethylene glycol chain to facilitate the assignment of ruptured bonds during atomic force microscopy (AFM) experiments.
- The study found that cycloreversion occurs at forces greater than 1.7 nN, with length changes of the stretched polymer correlating well with calculated values using the external force explicitly included (EFEI) method.
Article Abstract
Mechanochemical cycloreversion of cyclobutane is known from ultrasound experiments. It is, however, not clear which forces are required to induce the cycloreversion. In atomic force microscopy (AFM) experiments, on the other hand, it is notoriously difficult to assign the ruptured bond. We have solved this problem through the synthesis of tailored macrocycles, in which the cyclobutane mechanophore is bypassed by an ethylene glycol chain of specific length. This macrocycle is covalently anchored between a glass substrate and an AFM cantilever by polyethylene glycol linkers. Upon mechanical stretching of the macrocycle, cycloreversion occurs, which is identified by a defined length increase of the stretched polymer. The measured length change agrees with the value calculated with the external force explicitly included (EFEI) method. By using two different lengths for the ethylene glycol safety line, the assignment becomes unambiguous. Mechanochemical cycloreversion of cyclobutane is observed at forces above 1.7 nN.
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