Supramolecular shuttle

A mechanism based on the double function of the cyclodextrins as supramolecular shuttle and protective agent was proposed (Scheme 11.4), as also described for the hydrogenation of various hydrophobic substrates using (3-cyclodextrin-... 

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). 

In addition to these molecular shuttles, other dynamic supramolecular systems have been reported with the development of molecular trains utilizing catenanes [79], where one catenane ring can continually cycle around another via several stations. Sauvage and co-workers ]80-83] reported electrochemically induced ring gliding in copper catenanes which exploits the differing preferred geometries associated with Cu(I)/Cu(II). 

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. " ... 

The 1 1 complex between the tetracationic cyclophane and tetrathiafulvene (TIT) forms continuous stacks with no hinderance of the central channel by either solvent molecules or the counterions Figure 4). The TTF molecules have their long axis almost perfectly aligned along this crystallographic direction with a separation of 4.9 A between the tertiary alkenic carbon atoms in adjacently located TTF molecules." This supramolecular structural arrangement also demonstrates the potential of the tetracationic cyclophane to form polyrotaxane-like assemblies with suitably linked n-donor compounds. Furthermore, its inclusion inside [BBIPYBIXYCY] illustrates its potential for the production of molecular "shuttles and "switches . 

Supramolecular assemblies of metal complexes are of considerable interest because of their versatile chemistry that can be adapted to produce materials with applications in several areas such as separation, electron transfer, catalysis, magnetic devices, and optical devices. Transition metal complexes with the ability to shuttle between multiple redox states are playing a pivotal role in developing such materials. Moreover, some of these complexes are important in understanding the complex clusters in biological macromolecules. 

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