Abstract
Transferring structural information from the nanoscale to the macroscale is a promising strategy for developing adaptive and dynamic materials. Here we demonstrate that the knotting and unknotting of a molecular strand can be used to control, and even invert, the handedness of a helical organization within a liquid crystal. An oligodentate tris(2,6-pyridinedicarboxamide) strand with six point-chiral centres folds into an overhand knot of single handedness upon coordination to lanthanide ions, both in isotropic solutions and in liquid crystals. In achiral liquid crystals, dopant knotted and unknotted strands induce supramolecular helical organizations of opposite handedness, with dynamic switching achievable through in situ knotting and unknotting events. Tying the molecular knot transmits information regarding asymmetry across length scales, from Euclidean point chirality (constitutional chirality) via molecular entanglement (conformation) to liquid-crystal (centimetre-scale) chirality. The magnitude of the effect induced by the tying of the molecular knots is similar to that famously used to rotate a glass rod on the surface of a liquid crystal by synthetic molecular motors.
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Data availability
The data that support the findings of this study are available within the paper and its Supplementary Information, or are available from the Mendeley data repository (https://bit.ly/3e5chOf) under https://doi.org/10.17632/dw93cmxxs4.2.
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Acknowledgements
We thank the Engineering and Physical Sciences Research Council (EPSRC; EP/P027067/1), the Dutch Research Council (Projectruimte, 13PR3105), the European Research Council (ERC Consolidator Grant to N.K., 772564; ERC Advanced Grant to D.A.L., 786630) and the Marie Skłodowska-Curie Actions of the European Union (Individual Postdoctoral Fellowship to F.S., EC 746993) for funding, the University of Manchester Mass Spectrometry Service Centre for high-resolution mass spectrometry and the COST Action CA17139, EUTOPIA, for networking costs. D.A.L. is a Royal Society Research Professor.
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F.S. and L.P. planned and carried out the synthetic work. F.L. and A.R. designed and performed the liquid crystal experiments. D.A.L. and N.K. directed the research. All authors contributed to the analysis of the results and the writing of the manuscript.
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Extended data
Extended Data Fig. 1 Effect of strand and knot doping in different liquid crystalline hosts.
a, Molecular structures of ZLI-1083 and 5CB which form liquid crystalline phases. b, Table summarizing HTP values for strand 1–3 and knots Λ-Lu1–Λ-Lu3 in ZLI-1083 and 5CB. c, Polarized optical micrograph images (Grandjean-Cano lines and θ-cell measurements) highlighting the chiral helical organization induced by strands 1–3 and corresponding knots in different liquid crystalline hosts. The dashed line shows the rubbing direction of the top substrate. The red arrow shows the rotation of disclination line. Scale bars corresponds to 200 μm. d, CD spectra on ligands 1 (d) and 2 (e) in different solvent mixtures (0.025 mM, 298 K), highlighting how the chiral expressions change with decreasing polarity. Normalized for absorbance.
Extended Data Fig. 2 Probing the effect of the knotted conformation with macrocyclic strands.
a, Treatment of macrocycle 5 with Lu(OTf)3 does not produce a trefoil knot due to topological restrictions, nor does this operation invert macroscopic chirality in liquid crystals. Conditions: Lu(OTf)3, MeCN, 80 °C, 24 h. b, CD spectra of the mixture obtained upon complexation of 5 with Lu(OTf)3 (purple trace, MeCN, 298 K) overlaid with reference knot spectrum belonging to Λ-Lu1 (green trace, MeCN, 298 K). Normalized for absorbance. c, d, Polarized optical image of θ-cell filled with ZLI-1083 nematic host doped with 0.1 wt% of 5 after complexation with Lu(OTf)3 (c) and after decomplexation with tetramethylammonium fluoride (d). Notice that handedness of the chiral nematic liquid crystal is not modified. Thickness of the θ-cell is 50 µm. Scale bars correspond to 200 μm.
Supplementary information
Supplementary Information
General experimental information, synthetic procedures, Supplementary Figs. 1–27, Schemes 1–10, Spectra 1–28 and Table 1.
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Katsonis, N., Lancia, F., Leigh, D.A. et al. Knotting a molecular strand can invert macroscopic effects of chirality. Nat. Chem. 12, 939–944 (2020). https://doi.org/10.1038/s41557-020-0517-1
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DOI: https://doi.org/10.1038/s41557-020-0517-1