Supramolecular interactions between ethylene-bridged oligoureas: nanorings and chains formed by cooperative positive allostery

David P. Tilly*, Matej Žabka, Inigo Vitorica-Yrezabal, Hazel A. Sparkes, Natalie Pridmore, Jonathan Clayden

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

4 Citations (Scopus)
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Abstract

Ethylene-bridged oligoureas are dynamic foldamers in which the polarity of a coherent chain of intramolecular hydrogen bonds may be controlled by intra- or intermolecular interactions with hydrogen-bond donors or acceptors. In this paper, we describe the way that supramolecular interactions between ethylene-bridged oligoureas bearing a 3,5-bis(trifluoromethyl)phenylurea (BTMP) terminus leads to higher-order structures both in the crystalline state and in solution. The oligoureas self-assemble by head-to-tail hydrogen bonding interactions to form either supramolecular ‘nanorings’ with cyclic hydrogen bond chain directionality, or supramolecular helical chains of hydrogen bonds. The self-assembly process features a cascade of cooperative positive allostery, in which each intermolecular hydrogen bond formation at the BTMP terminus switches the native hydrogen bond chain directionality of monomers, favouring further assembly. Monomers with a benzyl urea terminus self-assemble into nanorings, whereas monomers with a N-ethyl urea terminus form helical chains. In the crystal state, parallel helices have identical handedness and polarity, whereas antiparallel helices have opposite handedness. The overall dipole moment of crystals is zero due to the antiparallel arrangements of local dipoles in the crystal packing. Supramolecular interactions in solution were also examined by VT and DOSY NMR spectroscopy, up to the point of crystal formation. The size of higher aggregates in dichloromethane was estimated by their hydrodynamic radius. The relative orientation of the monomers within the aggregates, determined by 2D ROESY NMR, was the same as in the crystals, where syn-orientations lead to the formation of rings and anti-orientations result in chains. Overall, the switch of hydrogen bond polarity propagates intermolecularly in crystal and solution states, constituting an example of intermolecular communication within supramolecular polymers.

Original languageEnglish
Pages (from-to)13153-13159
Number of pages7
JournalChemical Science
Volume13
Issue number44
DOIs
Publication statusPublished - 25 Oct 2022

Bibliographical note

Funding Information:
This work was carried out using the computational facilities of the Advanced Computing Research Centre, University of Bristol - http://www.bristol.ac.uk/acrc/ . We acknowledge funding from the European Research Council through Advanced Grant 883786 (DOGMATRON), the EPSRC, and the European Commission through a Marie Sklodowska Curie fellowship (REFOLDAMER) to D. P. T. We acknowledge Diamond Light Source for the time allocated (cy23480).

Funding Information:
This work was carried out using the computational facilities of the Advanced Computing Research Centre, University of Bristol - http://www.bristol.ac.uk/acrc/. We acknowledge funding from the European Research Council through Advanced Grant 883786 (DOGMATRON), the EPSRC, and the European Commission through a Marie Sklodowska Curie fellowship (REFOLDAMER) to D. P. T. We acknowledge Diamond Light Source for the time allocated (cy23480).

Publisher Copyright:
© 2022 The Royal Society of Chemistry.

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