Braiding, branching and chiral amplification of nanofibres in supramolecular gels

Abstract

Helical nanofibres play key roles in many biological processes. Entanglements between helices can aid gelation by producing thick, interconnected fibres, but the details of this process are poorly understood. Here, we describe the assembly of an achiral oligo(urea) peptidomimetic compound into supramolecular helices. Aggregation of adjacent helices leads to the formation of fibrils, which further intertwine to produce high-fidelity braids with periodic crossing patterns. A braid theory analysis suggests that braiding is governed by rigid topological constraints, and that branching occurs due to crossing defects in the developing braids. Mixed-chirality helices assemble into relatively complex, odd-stranded braids, but can also form helical bundles by undergoing inversions of chirality. The oligo(urea) assemblies are also highly sensitive to chiral amplification, proposed to occur through a majority-rules mechanism, whereby trace chiral materials can promote the formation of gels containing only homochiral helices.

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Fig. 1: SEM micrographs and rheological properties of oligo(urea) aggregates from DMF.
Fig. 2: Observed and simulated geometry of twisted ribbons in gels of 2.
Fig. 3: SEM images illustrating branching of gel fibres due to braiding defects.
Fig. 4: SEM micrographs of braid topologies observed in gels of 2.
Fig. 5: Chiral amplification of oligo(urea) fibrils.

Data availability

All the underlying research data are available from https://doi.org/10.15128/r2cz30ps655 in accordance with the UK Research Councils’ open data policy, and from the corresponding authors upon reasonable request.

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Acknowledgements

The authors thank the Engineering and Physical Sciences Research Council for funding this work via a Doctoral Training Studentship awarded to C.D.J. and the Leverhulme Trust for supporting K.E.H. via the Scientific Properties of Complex Knots (SPOCK) Research Programme Grant. The authors also thank L. Bowen, B. Mendis and S. Boothroyd for their assistance in obtaining electron microscopy images and rheological data.

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C.D.J., H.T.D.S. and K.L. performed the synthesis of new compounds. R.L.T. and H.T.D.S. carried out the AFM measurements. K.E.H. and C.D.J. analysed the braid topologies. C.D.J. completed the remaining experimental studies. J.W.S. was responsible for overall project concept, direction and coordination. C.D.J. and J.W.S. wrote the manuscript.

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Correspondence to Jonathan W. Steed.

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Supplementary Information

Details of the synthesis, experimental procedures, compound characterization, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, powder X-ray diffraction, rheometry, braiding and chiral amplification information, a description of braid theory, molecular dynamics details and the MD topology file.

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Jones, C.D., Simmons, H.T.D., Horner, K.E. et al. Braiding, branching and chiral amplification of nanofibres in supramolecular gels. Nat. Chem. 11, 375–381 (2019). https://doi.org/10.1038/s41557-019-0222-0

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