N‐Substituted Benzene‐1‐Urea‐3,5‐Biscarboxamide (BUBA): Easily Accessible C 2 ‐Symmetric Monomers for the Construction of Reversible and Chirally Amplified Helical Assemblies
Résumé
Non‐C3‐symmetric supramolecular helices are gaining interest for the design of hierarchical assemblies, for the compartmentalisation or the self‐assembly of polymer chains and for application in asymmetric catalysis. Herein, N‐substituted benzene‐1‐urea‐3,5‐biscarboxamide (BUBA) monomers, which consist of one urea and two carbon‐connected amide functions linked to an aromatic ring, are introduced as an easily accessible class of C2‐symmetric supramolecular synthons. In apolar solvents, BUBA monomers assemble into long helical assemblies by means of hydrogen‐bonding and aromatic interactions, as assessed by several analytical techniques. To probe the influence of the urea function, BUBA and related benzene‐1,3,5‐tricarboxamide (BTA) helical polymers have been compared, in terms of their thermodynamics of formation, stability, reversibility and chiral amplification properties. Similar to BTA, BUBA monomers form long helices reversibly through a highly cooperative mechanism and the helicity of their assemblies is governed by chiral amplification effects. However, precise quantification of their properties reveals that BUBA monomers assemble in a more cooperative manner. Also, chiral amplification operates to a higher extent in BUBA helices, as probed by both sergeants‐and‐soldiers and majority‐rules experiments. Compatibility between urea and amide functions also allows the formation of co‐assemblies that incorporate both BUBA and BTA monomers. Importantly, a small amount of chiral BUBA monomers in these co‐assemblies is sufficient to obtain single‐handed helices; thus paving the way towards the development of functional supramolecular helices.
Domaines
Chimie organiqueOrigine | Fichiers produits par l'(les) auteur(s) |
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