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Motion Capture and Manipulation of a Single Synthetic Molecular Rotor by Optical Microscopy

Authors

  • Dr. Tomohiro Ikeda,

    1. Department of Applied Chemistry, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)
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  • Takahiro Tsukahara,

    1. Department of Applied Chemistry, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)
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  • Prof. Ryota Iino,

    1. Okazaki Institute for Integrative Bioscience, Institute for Molecular Science, National Institutes of Natural Sciences, Higashiyama, Myodaijicho, Okazaki, Aichi 444-8787 (Japan)
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  • Prof. Masayuki Takeuchi,

    1. Organic Materials Group, Polymer Materials Unit, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan)
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  • Prof. Hiroyuki Noji

    Corresponding author
    1. Department of Applied Chemistry, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)
    2. Core Research for Evolutional Science and Technology (Japan), Science and Technology Agency, Sanban-cho, Chiyoda-ku, Tokyo 102-0075 (Japan)
    • Department of Applied Chemistry, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)

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  • This work was supported by CREST (Core Research for Evolutional Science and Technology) of the Japan Science and Technology Agency and Grant-in-Aids for Scientific Research (18074005 to H.N., 24651167 to R.I., and 21108010 to M.T.) from the Ministry of Education, Science, Sports, and Culture of Japan.

Abstract

Single-molecule imaging and manipulation with optical microscopy have become essential methods for studying biomolecular machines; however, only few efforts have been directed towards synthetic molecular machines. Single-molecule optical microscopy was now applied to a synthetic molecular rotor, a double-decker porphyrin (DD). By attaching a magnetic bead (ca. 200 nm) to the DD, its rotational dynamics were captured with a time resolution of 0.5 ms. DD showed rotational diffusion with 90° steps, which is consistent with its four-fold structural symmetry. Kinetic analysis revealed the first-order kinetics of the 90° step with a rate constant of 2.8 s−1. The barrier height of the rotational potential was estimated to be greater than 7.4 kJ mol−1 at 298 K. The DD was also forcibly rotated with magnetic tweezers, and again, four stable pausing angles that are separated by 90° were observed. These results demonstrate the potency of single-molecule optical microscopy for the elucidation of elementary properties of synthetic molecular machines.

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