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Single crystals of mechanically entwined helical covalent polymers

Abstract

Double helical conformation of polymer chains is widely observed in biomacromolecules and plays an essential role in exerting their biological functions, such as molecular recognition and information storage. It has remained challenging, however, to prepare synthetic helical polymers, and those that exist have mainly been limited to single-stranded polymers or short oligomeric double helices. Here, we report the synthesis of covalent helical polymers, with a high molecular weight, from the achiral monomer hexahydroxytriphenylene through to spiroborate formation. Polymerization and crystallization occurred simultaneously under solvothermal conditions to form single crystals of the resulting helical covalent polymers. Characterization by single-crystal X-ray diffraction showed that each crystal consisted of pairs of mechanically entwined polymers. No strong non-covalent interactions were observed between the two helical polymers that formed a pair; instead, each strand interacted with neighbouring pairs through hydrogen bonding. Each individual crystal was made up of helical polymers of the same handedness, but the crystallization process produced a racemic conglomerate, with equal amounts of right-handed and left-handed crystals.

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Fig. 1: The helical covalent polymer.
Fig. 2: Single-crystal structures of 1 showing a double helical conformation.
Fig. 3: The HCP helical chirality and PXRD patterns.
Fig. 4: The HCP morphology and mechanical properties.

Data availability

Experimental data and characterization data are provided in the Supplementary Information. Crystallographic data for the two crystals of 1 (tentatively assigned to right-handed) reported in this Article have been deposited at the Cambridge Crystallographic Data Centre, under deposition numbers CCDC 2017159 (HCP crystal 1) and 2034057 (HCP crystal 2). Copies of the data can be obtained free of charge via https://www.ccdc.cam.ac.uk/structures/.

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Acknowledgements

We thank V. Ferguson and A. Tomaschke for the nano-indentation tests, D. Gin for the assistance with the PXRD facility, B. Lama for the solid-state NMR measurements and X. Tang for circular dichroism measurements. We thank the University of Colorado Boulder for funding support. Y.C. acknowledges support from the National Science Foundation of China (91856204) and Key Project of Basic Research of Shanghai (18JC1413200). W.G. is supported by the China Postdoctoral Science Foundation (2019M661482). Z.Z. and T.J. are sponsored by the Shanghai Pujiang Talent Plan (no. 20PJ1414100) and the National Natural Science Foundation of China (62005198). X.C. is supported by the National Natural Science Foundation of China (no. 61925504). This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility, under contract no. DE-AC02-05CH11231.

Author information

Authors and Affiliations

Authors

Contributions

Y.H., Y.J. and W.Z. conceived the idea and led the project. Y.H., H.C. and J.W. conducted the synthesis and crystal growth. W.G., Y.C. and S.J.T. carried out single-crystal study and structure refinement. Z.Z., T.J. and X.C. performed the AFM test and infrared scattering scanning nearfield optical microscopy measurements. Y.J. and W.Z. wrote the manuscript with help from Y.H. and Y.C. All authors discussed and revised the manuscript.

Corresponding author

Correspondence to Wei Zhang.

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The authors declare no competing interests.

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Peer review information Nature Chemistry thanks the anonymous reviewers for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–13, Discussion and Tables 1–5.

Supplementary Data 1

Crystallographic data of the helical covalent polymer, crystal 1; CCDC 2017159.

Supplementary Data 2

Crystallographic data of the helical covalent polymer, crystal 2; CCDC 2034057.

Supplementary Data 3

Source data for Supplementary Fig. 7.

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Hu, Y., Teat, S.J., Gong, W. et al. Single crystals of mechanically entwined helical covalent polymers. Nat. Chem. 13, 660–665 (2021). https://doi.org/10.1038/s41557-021-00686-2

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