Fluorinated Bambusurils as Highly Effective and Selective Transmembrane Cl-/HCO3- Antiporters

The exchange of chloride and bicarbonate across lipid bilayers is an important biological process. Synthetic molecules can act as mobile carriers for these anions, although most show little selectivity. Here we report on three bambus[6] uril macrocycles functionalized with fluorinated benzyl groups, which are able to exchange Cl- and HCO3- efficiently. Remarkably, rates for Cl-/NO3- exchange are two orders of magnitude lower. The higher rates of a Cl-/HCO3- transport can be explained by the ability of the bambusurils to complex Cl- and HCO3- simultaneously, facilitating their exchange at the bilayer interface. Furthermore, the exceptionally high affinity and selectivity of these systems for NO3- appear to contribute to the poor Cl-/NO3- exchange. This work not only demonstrates the importance of anion binding characteristics on anion transport but also the potential relevance of bambusurils for anion transport applications considering the high rate observed for Cl-/HCO3- exchange.