Rotaxanes and pseudorotaxanes are two different prototypes of molecular machines that have drawn increasing attention in supramolecular chemistry and nanotechnology. Both of them are composed of an axle and a wheel, with the macrocyclic compounds always acting as the wheel component.
Yu Liu, Nankai University, Tianjin, China, and colleagues have constructed a pseudorotaxane, based on an azobenzene-bridged bis-ferrocene as the axle molecule and α-cyclodextrin as the wheel component. Then, the two ferrocene groups in this pseudorotaxane were encapsulated by two cucurbiturils to obtain a pseudorotaxane (pictured). This heteropseudorotaxane displayed high stability towards harsh temperatures and the isomerization of azobenzene, so it can be regarded as a rotaxane.
In this rotaxane, two macrocyclic cucurbituril molecules act not only as the wheel components of the heteropseudorotaxane, but also as its stoppers. This supramolecular stoppering strategy could provide a simpler methodology for the construction of future rotaxanes.
- Insights into the Difference Between Rotaxane and Pseudorotaxane,
He-Lue Sun, Heng-Yi Zhang, Zhen Dai, Xu Han, Yu Liu,
Chem. Asian J. 2016.