An electric molecular motor

Creators: Zhang, Long; Qiu, Yunyan; Liu, Wei-Guang; Chen, Hongliang; Shen, Dengke; Song, Bo; Cai, Kang; Wu, Huang; Jiao, Yang; Feng, Yuanning; Seale, James S. W.; Pezzato, Cristian; Tian, Jia; Tan, Yu; Chen, Xiao-Yang; Guo, Qing-Hui; Stern, Charlotte L.; Philp, Douglas; Astumian, R. Dean; Goddard, William A., III; Stoddart, J. Fraser

Abstract

Macroscopic electric motors continue to have a large impact on almost every aspect of modern society. Consequently, the effort towards developing molecular motors that can be driven by electricity could not be more timely. Here we describe an electric molecular motor based on a [3]catenane, in which two cyclobis(paraquat-p-phenylene)(6) (CBPQT⁴⁺) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop. The constitution of the loop ensures that both rings undergo highly (85%) unidirectional movement under the guidance of a flashing energy ratchet, whereas the interactions between the two rings give rise to a two-dimensional potential energy surface (PES) similar to that shown by FₒF₁ ATP synthase. The unidirectionality is powered by an oscillating voltage or external modulation of the redox potential. Initially, we focused our attention on the homologous [2]catenane, only to find that the kinetic asymmetry was insufficient to support unidirectional movement of the sole ring. Accordingly, we incorporated a second CBPQT⁴⁺ ring to provide further symmetry breaking by interactions between the two mobile rings. This demonstration of electrically driven continual circumrotatory motion of two rings around a loop in a [3]catenane is free from the production of waste products and represents an important step towards surface-bound electric molecular motors.

Additional Information

© The Author(s) 2023. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. We thank Northwestern University (NU) for its support of this research, the Integrated Molecular Structure Education and Research Center (IMSERC) at NU for providing access to equipment for relevant experiments, S. Shafaie for assistance with high-resolution mass spectrometry measurements, Y. Zhang and Y. Wu for help with NMR spectroscopic measurements and C. Cheng for useful discussions. The computational investigations at California Institute of Technology were supported by National Science Foundation grant no. CBET-2005250 (W.-G.L. and W.A.G.). Contributions. J.F.S. directed the project. L.Z. and C.P. conceived the idea for the project. L.Z. designed, synthesized and characterized the compounds. W.-G.L. and W.A.G. performed density functional theory calculations. R.D.A. contributed to theoretical analyses carried out on the mechanism of operation of the electric molecular motor. Y.Q. provided some of the precursors and performed CPE experiments. H.C. contributed to the graphical design used in the figures. D.S. conducted the video recording and contributed to the animation. B.S. carried out electrospray ionization mass spectrometry and travelling-wave ion mobility mass spectrometry measurements and analyses. C.L.S. collected the single-crystal X-ray diffraction data and solved the solid-state structure. K.C., H.W., Y.J., Y.F., J.S.W.S., J.T., Y.T., X.-Y.C., Q.-H.G. and D.P. commented on the data. All the authors participated in evaluating the results. L.Z., R.D.A. and J.F.S. produced numerous drafts of the manuscript and supplementary materials, with input from all authors. Data availability. The data that support the findings of this study are available within the paper and its Supplementary Information files. Crystallographic data for the [3]catenane in its reduced state [3]CMM⁷⁺⁶• can be obtained free of charge from www.ccdc.cam.ac.uk under CCDC deposition number 2168726. The authors declare no competing interests.

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