Mechanical Synthesis

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Science  09 Jul 2004:
Vol. 305, Issue 5681, pp. 149
DOI: 10.1126/science.305.5681.149c

Rotaxanes consist of one or more ring-shaped molecules that are positioned around a thread or linear segment that is capped by bulky end groups, much like beads on an abacus. Despite their importance in the design of molecular machines, for example, they are difficult to make, as one typically needs to slip the thread through the ring and then cap the ends before the ring slips off. Most synthetic methods rely upon building recognition units into both the thread and the ring so that they stick together, which has limited the number of molecules that can be made.

Hannam et al. have come up with a more general synthesis route that should make it easier to incorporate functional compounds such as dyes, chromophores, or catalysts into the ring component, without regard for the chemistry of the thread. The authors initially built the stoppered thread so that at one end it contained a macrocycle template around which the ring could be assembled. The key was to include a gating element to the macrocycle template that would restrict translation of the ring. After the ring was completed, the gate was removed, and the ring pushed onto the thread. The gate was then put back into place, and finally, both it and the template were replaced by a second stopper. — MSL

Angew. Chem. Int. Ed. 43, 3260 (2004).

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