A comprehensive experimental and theoretical investigation of the transmembrane chloride transport promoted by four series of squaramide derivatives, with different degrees of fluorination, number of convergent N-H binding units and conformational shapes, is reported. The experimental chloride binding and transport abilities of these small synthetic molecules in liposomes were rationalised with quantum descriptors and molecular dynamics simulations in POPC bilayers. The tripodal tren-based compounds, with three squaramide binding motifs, have high chloride affinity, isolating the anion from water molecules within the membrane model and preventing its release to the aqueous phase, in agreement with the absence of experimental transport activity. In contrast, the symmetrical mono-squaramides, with moderate chloride binding affinity, are able to bind and release chloride either in the aqueous phase or at the membrane interface level, in line with experimentally observed high transport activity. The PMF profiles associated with the diffusion of these free transporters and their chloride complexes across phospholipid bilayers show that the assisted chloride translocation is thermodynamically favoured.

Tetraureido‐dihomooxacalix[4]arenes (tert‐butyl 4a and phenyl 4b) were synthesised and obtained in a partial cone conformation in solution and in the solid state, as confirmed by NMR and X‐ray diffraction studies. Their complexation ability towards halides, pseudo‐halides and oxoanions was assessed by 1H NMR and UV/Vis titrations. Structural and energetic insights of phenylurea 4b complexes were also obtained using molecular dynamics (MD) simulations. The binding data showed that the association constants are strongly dependent on the nature of the substituent (alkyl/aryl) at the urea unit. tert‐Butyl urea 4a is a much weaker receptor than phenylurea 4b, and showed association constants that decrease with decreasing of anion basicity. Phenylurea 4b is a highly efficient anion receptor, exhibiting a remarkable binding ability towards BzO– ion (log Kass = 4.81). In comparison to the phenylurea analogue bearing a butyl spacer and a cone conformation, receptor 4b containing a shorter spacer (three carbon atoms) and a partial cone conformation is more pre‐organized, displaying a strong enhancement of its binding efficiency. MD simulations have shown that the anions are preferentially bound to the urea moieties of the macrocycle lower rim, in agreement with the ROESY spectrum carried out with phenylurea 4b and BzO– anion.

The anion-bindinga nd transport properties of an extensive library of thiophene-based molecules are reported. Seventeen bis-urea positional isomers, with different binding conformationsa nd lipophilicities, have been synthesized by appending a-o rb-thiopheneo ra-, b-, or g-benzo[b]thiophene moieties to an ortho-phenylenediamine central core, yielding six subsets of positional isomers. Through 1 HNMR, X-ray crystallography, molecular modelling,a nd anion efflux studies, it is demonstrated that the most active transporters adopt ap re-organized binding conformation capable of pro-moting the recognition of chloride, using urea and CÀH bindingg roups in ac ooperative fashion.A dditional large unilamellar vesicle-based assays, carriedo ut under electroneutral and electrogenic conditions, together with N-methyld-glucamine chloride assays,h ave indicated that anion efflux occurs mainly through an H + /Cl À symportm echanism. On the other hand, the most efficient anion transporter displays cytotoxicity against tumor cell lines, while having no effects on acystic fibrosis cell line.