Computational Analysis of Switchable Catenanes
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The first synthesis of a catenane was reported in the 1960s. Since then, the chemistry of topologically nontrivial macromolecular systems such as knots, catenanes, and rotaxanes has attracted considerable attention. With the surge of interest in nanoscience since 1990, this attention has focused on their promise for the fabrication of molecular devices. The design, synthesis, and characterization of nanodevices and molecular devices are now grand challenges to the scientific and engineering communities. Consequently, reports of novel catenanes are appearing with increased frequency.
Catenanes form a subset of a special class of topologically complex host/guest complexes where the host and guest components are chemically independent but mechanically interlocked with each other. Catenanes are an entirely different class of mechanically interlocked molecules from their close relatives—the rotaxanes. In particular, a catenane is a complex comprising two (or more) macrocyclic rings interlocked like adjacent links of a chain. The two (or more) macrocycles are not linked covalently to each other; rather, their dissociation is prevented only mechanically. The associated co-conformations are stabilized by intercomponent noncovalent interactions, and interconversion among these co-conformations requires the circumrotation of the macrocycle rings. In a switchable catenane, the relative populations of these co-conformations are controllable reversibly by an external stimulus such as complexation/decomplexation by metal ions, protonation/deprotonation, or oxidation/reduction process. Like the rotaxane systems discussed in the accompanying entry entitled “Computational Analysis of Switchable Rotaxanes,” switchable catenanes have recently become the subject of intense interest because of their potential to form components of nanodevices and molecular devices.