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A single synthetic small molecule that generates force against a load

Nature Nanotechnology volume 6, pages 553–557 (2011)Cite this article

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Abstract

Some biomolecules are able to generate directional forces by rectifying random thermal motions. This allows these molecular machines to perform mechanical tasks such as intracellular cargo transport or muscle contraction1 in plants and animals. Although some artificial molecular machines have been synthesized2,3,4 and used collectively to perform mechanical tasks5,6,7, so far there have been no direct measurements of mechanical processes at the single-molecule level. Here we report measurements of the mechanical work performed by a synthetic molecule less than 5 nm long. We show that biased Brownian motion of the sub-molecular components in a hydrogen-bonded [2]rotaxane8—a molecular ring threaded onto a molecular axle—can be harnessed to generate significant directional forces. We used the cantilever of an atomic force microscope to apply a mechanical load to the ring during single-molecule pulling–relaxing cycles. The ring was pulled along the axle, away from the thermodynamically favoured binding site, and was then found to travel back to this site against an external load of 30 pN. Using fluctuation theorems, we were able to relate measurements of the work done at the level of individual rotaxane molecules to the free-energy change as previously determined from ensemble measurements. The results show that individual rotaxanes can generate directional forces of similar magnitude to those generated by natural molecular machines.

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Figure 1: Chemical structure of the rotaxane-based molecule shuttle.
Figure 2: Single-molecule force spectroscopy of the rotaxane.
Figure 3: Experimental AFM pulling curves.
Figure 4: Pulling–relaxing cycles for the rotaxane–PEO molecule.

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Acknowledgements

This research was funded by the Fonds de la Recherche Scientifique-Fonds National pour la Recherche Scientifique (FRS-FRNS; Fonds de la Recherche Fondamentale Collective 2.4.512.07 and Mandat d'Impulsion Scientifique F.4.501.08 to A-S.D.), the Politique Scientifique Fédérale (BELSPO; IUAP VI/27), the European Research Council and the Engineering and Physical Sciences Research Council. C-A.F. is a Research Associate of the FRS-FNRS.

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Authors and Affiliations

  1. Department of Chemistry, University of Liège, B6a Sart-Tilman, Liège, 4000, Belgium

    Perrine Lussis, Tiziana Svaldo-Lanero & Anne-Sophie Duwez

  2. School of Chemistry, University of Edinburgh, The King's Buildings, West Mains Road, Edinburgh, EH9 3JJ, UK

    Andrea Bertocco & David A. Leigh

  3. Institute of Condensed Matter and Nanosciences (IMCN), Place Louis Pasteur 1, Université catholique de Louvain, Belgium

    Charles-André Fustin

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  1. Perrine Lussis
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Contributions

P.L. and T.S-L. performed the AFM experiments and analysed the data. A.B. carried out the rotaxane synthesis and characterization studies. C-A.F. participated in rotaxane synthesis. A-S.D., C-A.F. and D.A.L. designed the experiments and prepared the manuscript.

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Correspondence to David A. Leigh or Anne-Sophie Duwez.

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Lussis, P., Svaldo-Lanero, T., Bertocco, A. et al. A single synthetic small molecule that generates force against a load. Nature Nanotech 6, 553–557 (2011). https://doi.org/10.1038/nnano.2011.132

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