Fluoride binding of achiral oligoamide foldamers produces polar and chiral crystal structures and induces exceptional symmetry breaking of the bulk sample.

A series of aromatic oligoamide foldamers with two or three pyridine-2,6-dicarboxamide units as their main folding motifs and varying aromatic building blocks as linkers have been synthetized to study the effects of the structural variation on the folding properties and conformational stability. Crystallographic studies showed that in the solid state the central linker unit either elongates the helices and more open S-shaped conformations, compresses the helices to more compact conformations, or acts as a rigid spacer separating the pyridine-2,6-dicarboxamide units, which for their part add the predictability of the conformational properties. Multidimensional NMR studies showed that, even in solution, foldamers show conformational stability and folded conformations comparable to the solid-state structures.

The anion-binding properties of three closelyrelated oligoamide foldamers were studied using NMR spectroscopy,isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1 HNMR spectra of the foldamers in [D 6 ]acetones olution revealed partial preorganization by intramolecular hydrogen bonding,w hichc reates a suitable cavity for anion binding.T he limited size of the cavity,h owever,e nabled efficient bindingb yt he inner amide protons only for the chloride anion resulting in the formation of at hermodynamically stable 1:1c omplex. All 1:1 chloride complexes displayed as ignificant favourable contri-bution of the entropyt erm. Most likely,t his is duet ot he release of ordereds olvent molecules solvatingt he free foldamer and the anion to the bulk solution upon complex formation. The introduction of electron-withdrawing substituents in foldamers 2 and 3 had only as light effect on the thermodynamic constants for chloride binding compared to the parentr eceptor.R emarkably,t he binding of chloride to foldamer 3 not only produced the expected 1:1c omplex but also open aggregates with 1:2( host:anion) stoichiometry.[c] Prof. P. Ballester Catalan Institution for Research and Advanced Studies (ICREA) Passeig LluísC ompanys 23, 08010 Barcelona (Spain)Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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