ArticleFluorinated Bambusurils as Highly Effective and Selective Transmembrane Cl À /HCO 3 À Antiporters Synthetic anion receptors can be used to transport ions across membranes. In this work, bambusuril macrocycles are demonstrated to be very efficient in exchanging chloride and bicarbonate ions, whereas exchange with nitrate is much slower. This is explained by the anion binding properties of the receptor. The high rates of transport by these bambusurils and mechanistic insight provided here represent an advancement toward the future therapeutic applications of synthetic anion carriers.

Driving forces of anion binding in water in contrast to nonpolar environments are of high interest because of their relevance to biology and medicine. Here we report a neutral bambusuril macrocycle (1), soluble in both water and nonpolar solvents due to decoration with 12 polyethylene glycol-based substituents. The new bambusuril has the highest affinity for I in pure water ever reported for a synthetic macrocycle relying on hydrogen bonding interactions rather than metal coordination or Coulombic forces. Isothermal titration calorimetry (ITC) experiments in nine different solvents, ranging from polar water to nonpolar carbon tetrachloride, provided insight into the forces responsible for halide binding by bambusurils. The different importance of anion solvation and solvent expulsion from the cavity of the macrocycle in various solvents is illustrated by the fact that halide binding in water and chloroform is exclusively driven by favorable enthalpy with an entropic penalty, while in alcohols and nonpolar solvents, both favorable enthalpy and entropy contribute to anion encapsulation. DFT calculations and correlation of thermodynamic data with the solvent Swain acity parameter further underscore the importance of solvent effects on anion binding by bambusurils.

Bambusurils are recently developed neutral anion receptors that show a high affinity towards many inorganic anions, not only in organic solvents but also in water. However, the number of water-soluble bambusurils and also those bearing functional groups is very limited. In this paper we report the synthesis of four-and six-membered bambusurils containing eight and twelve nitro groups. All the nitro groups on the bambusuril portals could be transformed into amino functions,

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