The calculated Hill coefficients of n ≈ 1 showed that the tested tetralactams transported Cl -in an approximate 1:1 host:guest stoichiometry, in line with both the 1:1 host:guest binding stoichiometry observed during binding studies (Table ) and the 1:1 host:guest single crystal X-ray structures of 2c and 3a (Figure and). The EC50 values demonstrated that the three transporters with the highest transport activity contain the 4,5-difluorophenylene-linker (3c > 2c > 4c). These findings agree with the observed 1 H-NMR binding trends, where the same compounds had the highest binding constants of their respective sub-series. Tetralactams 2a, 3a, and 4c obtained EC50 values of 0.036, 0.096, and 0.015 mol%, respectively (Table ), representing a moderate level of transport activity.