Finally, since some resorcin [4]arenes are known to bind alkali metal cations, we were interested to see if there is any influence of cations on the transport activity of 2. To verify this, we compared the results of the lucigenin assays using cesium salts instead of sodium salts. The results were the same within the experimental error (see SI), indicating that alkali metal cations are unlikely to play any significant role in the Cl -/NO3 -exchange process. This is in agreement with the aforementioned lack of activity in the Na + transport experiment performed in a sodium gluconate medium (see SI).