The Cl -/NO3 -Exchange Assay: Tetralactams 1a-4c were tested for their ability to transport anions across the lipid bilayer using the ion-sensitive electrode (ISE) based Cl -/NO3 -exchange assay. The assay was performed using synthetic large unilamellar vesicles (200 nm) formed from 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (POPC), prepared according to literature methods. The vesicles contained an internal solution of NaCl (489 mM) suspended in an external solution of NaNO3 (489 mM), with both solutions being buffered to pH 7.2 with a sodium phosphate salt buffer (5 mM) (Figure , a). Anion transport was initiated at t = 0 s by adding each tetralactam as DMSO solution, and the subsequent Cl -efflux was recorded using the ISE (Figure ). The 100% Cl -efflux value required for data calibration was obtained by lysing the vesicles with detergent at t = 300 s and collecting a further 120 s of data before the collection was stopped at t = 420 s. For information regarding experimental methods, see the experimental procedures section, or for information on the fitted experimental data, including errors and associated spectra, see Table and Figure -S90 in the ESI.