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Biasing reaction pathways with mechanical force


During the course of chemical reactions, reactant molecules need to surmount an energy barrier to allow their transformation into products. The energy needed for this process is usually provided by heat, light, pressure or electrical potential, which act either by changing the distribution of the reactants on their ground-state potential energy surface or by moving them onto an excited-state potential energy surface and thereby facilitate movement over the energy barrier. A fundamentally different way of initiating or accelerating a reaction is the use of force to deform reacting molecules along a specific direction of the reaction coordinate. Mechanical force has indeed been shown to activate covalent bonds in polymers, but the usual result is chain scission1. Here we show that mechanically sensitive chemical groups make it possible to harness the mechanical forces generated when exposing polymer solutions to ultrasound2, and that this allows us to accelerate rearrangement reactions and bias reaction pathways to yield products not obtainable from purely thermal or light-induced reactions. We find that when placed within long polymer strands, the trans and cis isomers of a 1,2-disubstituted benzocyclobutene undergo an ultrasound-induced electrocyclic ring opening in a formally conrotatory and formally disrotatory process, respectively, that yield identical products. This contrasts with reaction initiation by light or heat alone3, in which case the isomers follow mutually exclusive pathways to different products. Mechanical forces associated with ultrasound can thus clearly alter the shape of potential energy surfaces4 so that otherwise forbidden or slow processes proceed under mild conditions, with the directionally specific nature of mechanical forces providing a reaction control that is fundamentally different from that achieved by adjusting chemical or physical parameters. Because rearrangement in our system occurs before chain scission, the effect we describe might allow the development of materials that are activated by mechanical stress fields.

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Figure 1: Electrocyclic ring opening of benzocyclobutenes.
Figure 2: Preparation and reaction of mechanosensitive polymers.
Figure 3: Reaction of the mechanosensitive polymers.
Figure 4: Comparison of reaction products and pathways for trans and cis benzocyclobutenes induced by ultrasound and by heating.


  1. 1

    Beyer, M. K. & Clausen-Schaumann, H. Mechanochemistry: The mechanical activation of covalent bonds. Chem. Rev. 105, 2921–2948 (2005)

    CAS  Article  Google Scholar 

  2. 2

    Basedow, A. M. & Ebert, K. H. Ultrasonic degradation of polymers in solution. Adv. Polym. Sci. 22, 83–148 (1977)

    CAS  Article  Google Scholar 

  3. 3

    Woodward, R. B. & Hoffmann, R. The conservation of orbital symmetry. Angew. Chem. Int. Edn Engl. 8, 781–853 (1969)

    CAS  Article  Google Scholar 

  4. 4

    Evans, E. Probing the relation between force-lifetime and chemistry in single molecular bonds. Annu. Rev. Biophys. Biomol. Struct. 30, 105–128 (2001)

    CAS  Article  Google Scholar 

  5. 5

    Beyer, M. K. The mechanical strength of a covalent bond calculated by density functional theory. J. Chem. Phys. 112, 7307–7312 (2000)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Roth, W. R., Rekowski, V., Börner, S. & Quast, M. Die disrotative cyclobuten-ringöffnung. Liebigs Ann. Chem. 409–430 (1996)

  7. 7

    Boffa, L. S. & Novak, B. M. “Link-functionalized” polymers: an unusual macromolecular architecture through bifunctional initiation. Macromolecules 30, 3494–3506 (1997)

    ADS  CAS  Article  Google Scholar 

  8. 8

    Nguyen, T. Q. & Kausch, H.-H. Mechanochemical degradation in transient elongational flow. Adv. Polym. Sci. 100, 73–182 (1992)

    Article  Google Scholar 

  9. 9

    Berkowski, K. L., Potisek, S. L., Hickenboth, C. R. & Moore, J. S. Ultrasound-induced site-specific cleavage of azo-functionalized poly(ethylene glycol). Macromolecules 38, 8975–8978 (2005)

    ADS  CAS  Article  Google Scholar 

  10. 10

    Reddy, P. Y., Kondo, S., Fujita, S. & Toru, T. Efficient synthesis of fluorophore-linked maleimide derivatives. Synthesis 999–1002 (1998)

  11. 11

    Price, G. J. The use of ultrasound for the controlled degradation of polymer solutions. Adv. Sonochem. 1, 231–287 (1990)

    CAS  Google Scholar 

  12. 12

    Arnold, B. J., Sammes, P. G. & Wallace, T. W. Photochemical reactions. Part IV. Thermal generation of photoenols and their derivatives from disubstituted 1,2-dihydrobenzocyclobutenes. J. Chem. Soc. Perkin Trans. I 415 (1974)

  13. 13

    Suslick, K. S., Goodale, J. W., Schubert, P. F. & Wang, H. H. Sonochemistry and sonocatalysis of metal carbonyls. J. Am. Chem. Soc. 105, 5781–5785 (1983)

    CAS  Article  Google Scholar 

  14. 14

    Graessley, W. W. Polymer chain dimensions and the dependence of viscoelastic properties on concentration, molecular weight and solvent power. Polymer 21, 258–262 (1980)

    CAS  Article  Google Scholar 

  15. 15

    Rodd, L. E., Scott, T. P., Boger, D. V., Cooper-White, J. J. & McKinley, G. H. The inertio-elastic planar entry flow of low-viscosity elastic fluids in micro-fabricated geometries. J. Non-Newtonian Fluid Mech. 129, 1–22 (2005)

    CAS  Article  Google Scholar 

  16. 16

    Kersey, F. R., Yount, W. C. & Craig, S. L. Single-molecule force spectroscopy of bimolecular reactions: system homology in the mechanical activation of ligand substitution reactions. J. Am. Chem. Soc. 128, 3886–3887 (2006)

    CAS  Article  Google Scholar 

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We thank T. Martínez, K. Suslick and P. Beak for discussions. This work was supported by grants from the Air Force Office of Scientific Research and The Petroleum Research Fund.

Author Contributions J.S.M. conceived the BCB experiment. C.R.H. performed all experiments and initial computational analyses. J.B. performed the final computational analysis. S.R. Wilson performed the crystallography. N.R.S., S.R. White and J.S.M. directed the research and all authors wrote the manuscript.

The atomic coordinates for cis-1,2-bis[(3-carboxypropanoyl)oxy]-1,2-dihydrobenzocyclobutene 2 (accession number 628670), N-(1-pyrene)-2,3-naphthimide (accession number 628377), and 4,9-diacetoxy-2-(1-pyrenyl)-(3aR,4c,9c,9ac)-3a,4,9,9a-tetrahydro-benzo[f]isoindole-1,3-dione 6 (accession number 628671) have been deposited in the Cambridge Crystal Structure Database.

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Correspondence to Jeffrey S. Moore.

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Supplementary Information

This file contains Supplementary Figures 1-10 with Legends, Supplementary discussion and additional references. The file contains all of the supporting information including results of computational studies, results of all control experiments, procedures for the synthesis and characterization of all new compounds reported in the manuscript, representative GPC traces of ultrasound experiments, and 13C NMR spectra of all new reported compounds. (PDF 1266 kb)

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Hickenboth, C., Moore, J., White, S. et al. Biasing reaction pathways with mechanical force. Nature 446, 423–427 (2007).

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