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Force Distribution Analysis of Mechanochemically Reactive Dimethylcyclobutene

Authors

  • Dr. Wenjin Li,

    1. CAS-MPG Partner Institute and Key Laboratory for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences (P.R. China)
    2. Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Goettingen (Germany)
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  • Prof. Scott A. Edwards,

    1. College of Physics and Technology, Shenzhen University, 3688 Nanhai Ave, Shenzhen 518060, Guangdong (P.R. China)
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  • Prof. Lanyuan Lu,

    1. Division of Structural and Computational Biology, School of Biological Sciences, Nanyang Technological University (Singapore)
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  • Dr. Tomas Kubar,

    1. Institute for Physical Chemistry, Karlsruhe Institute of Technology (Germany)
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  • Sandeep P. Patil,

    1. Heidelberg Institute for Theoretical Studies, Heidelberg (Germany)
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  • Prof. Helmut Grubmüller,

    1. Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Goettingen (Germany)
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  • Dr. Gerrit Groenhof,

    Corresponding author
    1. Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Goettingen (Germany)
    2. Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland)
    • Department of Theoretical and Computational Biophysics, Max-Planck-Institute for Biophysical Chemistry, Goettingen (Germany)
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  • Dr. Frauke Gräter

    Corresponding author
    1. CAS-MPG Partner Institute and Key Laboratory for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences (P.R. China)
    2. Heidelberg Institute for Theoretical Studies, Heidelberg (Germany)
    • CAS-MPG Partner Institute and Key Laboratory for Computational Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences (P.R. China)
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Abstract

Internal molecular forces can guide chemical reactions, yet are not straightforwardly accessible within a quantum mechanical description of the reacting molecules. Here, we present a force-matching force distribution analysis (FM-FDA) to analyze internal forces in molecules. We simulated the ring opening of trans-3,4-dimethylcyclobutene (tDCB) with on-the-fly semiempirical molecular dynamics. The self-consistent density functional tight binding (SCC-DFTB) method accurately described the force-dependent ring-opening kinetics of tDCB, showing quantitative agreement with both experimental and computational data at higher levels. Mechanical force was applied in two different ways, namely, externally by a constant pulling force and internally by embedding tDCB within a strained macrocycle-containing stiff stilbene. We analyzed the distribution of tDCB internal forces in the two different cases by FM-FDA and found that external force gave rise to a symmetric force distribution in the cyclobutene ring, which also scaled linearly with the external force, indicating that the force distribution was uniquely determined by the symmetric architecture of tDCB. In contrast, internal forces due to stiff stilbene resulted in an asymmetric force distribution within tDCB, which indicated a different geometry of force application and supported the important role of linkers in the mechanochemical reactivity of tDCB. In addition, three coordinates were identified through which the distributed forces contributed most to rate acceleration. These coordinates are mostly parallel to the coordinate connecting the two CH3 termini of tDCB. Our results confirm previous observations that the linker outside of the reactive moiety, such as a stretched polymer or a macrocycle, affects its mechanochemical reactivity. We expect FM-FDA to be of wide use to understand and quantitatively predict mechanochemical reactivity, including the challenging cases of systems within strained macrocycles.

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