Rotaxane Chemistry

Amide-linked catenanes and rotaxanes, readily accessible via nonionic template synthesis, are molecules with fascinating topology, but their final breakthrough was only achieved when they became substrates for further chemical derivatiza-tion. A potential reaction site in the catenanes and rotaxanes presented so far is the sulfonamide group, because the proton can be selectively abstracted in the presence of carbon amide groups. Subsequent alkylation offers numerous possibilities of catenane and rotaxane chemistry. 

Because of their wheel and axle structure, much of the interest in rotaxane chemistry is focused on the mechanical movements of the ring around and along the dumbbell-shaped component. Of particularly interest is the possibility to control... 

Two higher homologues of the [2]-rotaxane are represented the [3]-rotaxane and the [4]-rotaxane. Whereas [3]-rotaxanes are relatively common [56-60], this is not the case for the linear [4]-rotaxane [61] and its branched or dendritic analogue [62]. Very important in the recent developments of rotaxane chemistry is the [2]-rotaxane whose dumbbell contains two separated sites for interaction of the threaded macrocycle. In this molecule, the macrocycle may be moved between two sites of the dumbbell, in a degenerate manner, if the sites are identical [63-65], or in a controlled manner, thanks to an external trigger, if the sites are different [28-31]. A chiral [2]-rotaxane, whose chirality arises from the mechanical bonding, is obtained if the macrocycle is oriented (by an appropriate substitution pattern) and the dumbbell made non-symmetrical, for example by attaching two different stoppers [66],... 

These examples of template effects illustrate the close relationship between host-guest and rotaxane chemistry. Appropriate concave host molecules bind convex guests in such a way that they can be equipped with two stoppers that mechanically prevent dissociation of the host-guest complex. Any macrocyclic receptor may thus be suitable for the formation of rotaxanes. 

Although the goal of perfectly functional molecular motors or electronic building blocks has not yet been reached, these examples illustrate how far the development in rotaxane chemistry and the art of controlling it has gone. For the future, we expect the field to shift more to applications, which might be the focus of the next decade. 

Keywords. Rotaxane dendrimers. Host-guest interaction, Recognition, Self-assembly, Supra-molecular chemistry... 

A useful summary of the various and numerous types of rotaxanes, catenanes, and knots can be found in a review of template routes to interlocked molecular structures 468). Inorganic chemistry is centrally involved in the templating involved in self-assembly and in controlled synthesis of such species. 

Keywords Molecular Devices a Molecular Machines a Molecular Wires a Antenna Systems a Molecular Switches a Plug/socket Systems a Pseudorotaxanes a Rotaxanes a Catenanes a Supramolecuiar Chemistry a Photochemistry a Electrochemistry a Luminescence... 

Like the currently popular area, called nanoscience , the field of supramolecular chemistry has rather hazy boundaries. Indeed, both areas now share much common ground in terms of the types of systems that are considered. From the beginning, electrochemistry, which provides a powerful complement to spectroscopic techniques, has played an important role in characterizing such systems and this very useful book goes considerably beyond the volume on this same topic by Kaifer and Gomez-Kaifer that was published about 10 years ago. Some of the classic supramolecular chemistry topics such as rotaxanes, catenanes, host-guest interactions, dendrimers, and self-assembled monolayers remain, but now with important extensions into the realms of fullerenes, carbon nanotubes, and biomolecules, like DNA. 

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