Supramolecular rotaxane shuttles

A rotaxane is a supramolecular system composed of a macrocyclic and a dumbbellshaped component. The macrocycle encircles the linear rod-like portion of the dumbbell-shaped component and is trapped mechanically around it by two bulky stoppers. Thus, the two components cannot dissociate, but the ring component can shuttle along the axis component (Fig. 15). 

This opposite solvent polarity dependence is generally observed for solvophobically versus electrostatically driven complexation processes see, for instance, the recent study by Mizutani et al. This general phenomena is used to create a wide variety of supramolecular devices, such as molecular shuttles based on rotaxanes as well as other so-called. molecular machines. ... 

Upon snpramolecnlar complexation, neutral hydrophobic orgauic compounds and hydrophilic metal cations usually show entirely different, often opposite, solvent polarity dependencies. Snch contrasting behavior is very generally observed when one compares the solvophobically versus electrostatically driven complexation for detailed discussion, see, for example, the study by Mizutani et al This difference in solvation property is exploited as a conventional tool for creating a vast variety of supramolecular architectures and devices, including rotaxane-based molecular shuttles and other so-called molecular machines. " ... 

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