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Ring-through-ring molecular shuttling in a saturated [3]rotaxane


Mechanically interlocked molecules such as rotaxanes and catenanes comprise two or more components whose motion relative to each other can be controlled. A [2]rotaxane molecular shuttle, for example, consists of an axle bearing two recognition sites and a single macrocyclic wheel that can undergo a to-and-fro motion along the axle—shuttling between the recognition sites. The ability of mechanically interlocked molecules to undergo this type of large-amplitude change is the core mechanism behind almost every interlocked molecular switch or machine, including sophisticated mechanical systems such as a molecular elevator and a peptide synthesizer. Here, as a way to expand the scope of dynamics possible at the molecular level, we have developed a molecular shuttling mechanism involving the exchange of rings between two recognition sites in a saturated [3]rotaxane (one with no empty recognition sites). This was accomplished by passing a smaller ring through a larger one, thus achieving ring-through-ring molecular shuttling.

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This work was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada through a Discovery Grant, an Accelerator Supplement and a Canada Research Chair award to S.J.L. S.J.L also acknowledges support from NSERC, the Canadian Foundation for Innovation, the Ontario Innovation Trust and the University of Windsor for the development and maintenance of the X-ray diffraction centre. The authors thank M. Revington and J. Auld for their technical assistance with NMR spectroscopy and electrospray mass spectrometry, respectively.

Author information

S.J.L. supervised the project. K.Z. designed the experiments, performed all the synthetic experiments and all the NMR characterization. K.Z. collected the single-crystal X-ray diffraction data and G.B. solved the X-ray structures. S.J.L. and K.Z. wrote the manuscript with input from G.B.

Competing interests

The authors declare no competing interests.

Correspondence to Kelong Zhu or Stephen J. Loeb.

Supplementary information

Supplementary Information

Supplementary synthesis and characterization details and analysis, Supplementary Figures 1–5

Crystallographic data

CIF for [2]rotaxane compound with embedded structure factor. CCDC number 1576710

Crystallographic data

CIF for [2]rotaxane compound with embedded structure factor. CCDC number 1576711

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Fig. 1: Structural limits to molecular shuttling.
Fig. 2: Synthesis of saturated [3]rotaxane molecular shuttles.
Fig. 3: Structures of rotaxanes determined by single-crystal X-ray diffraction.
Fig. 4: Characterization of rotaxanes by NMR spectroscopy.
Fig. 5: Measuring the physical parameters of ring-through-ring molecular shuttling.