What is it about?

Rotaxanes are made by a ring-type molecule and an axle-type molecule bearing bulky groups (stoppers) at both extremities, so that the molecular ring and axle components are mechanically interlocked. These species are interesting for the construction of molecular machines, because the interaction between the components can be modulated by external signals, e.g. light. In this way, stimuli-controlled movements of the molecular components can be achieved. However, how an axle exits from a ring (dethreading process) is still an open question at molecular level. For this reason, we modeled the dethreading of rotaxanes formed by a dialkylammonium axle and a crown ether ring. Our results explain the reasons for the significant differences in the thermodynamic and kinetic behaviour of two rotaxanes which govern the functionality of such light-powered molecular devices.

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Why is it important?

For the first time, we elucidate the interactions between the molecular components which control the dethreading process at the molecular level. Different escape mechanisms are revealed for two different configurations of the axle: while the former undergoes a one-step process, the dethreading of the latter proceeds through a transition state and an intermediate structure.


Our study shed light, at the atomistic scale level, on the reason why the disassembling process in the two rotaxanes is different. The elliptic shape of the opening of the ring is capable of recognizing two different configurations of the terminal azobenzene group of the axle in the dethreading process. This insight may open the way to the construction of light-powered molecular pumps.

Gloria Tabacchi
university of insubria

Read the Original

This page is a summary of: Dethreading of a Photoactive Azobenzene-Containing Molecular Axle from a Crown Ether Ring: A Computational Investigation, ChemPhysChem, March 2016, Wiley,
DOI: 10.1002/cphc.201501160.
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