The Cationophore Coupled Assay (Cl -and F -): The tetralactam series was then tested using the cationophore coupled transport assay for their ability to perform electroneutral H + /Cl -(or OH -/Cl -antiport) co-transport and electrogenic Cl -selective transport. Synthetic LUVs were produced in the same manner as the Cl -/NO3 -exchange assay, except the internal solution contained KCl (300 mM) and the external solution contained potassium gluconate (K-Gluc, 300 mM) with both solutions buffered to pH 7.2 using 4-(2-hydroxyethyl)-1piperazineethanesulfonic acid (HEPES, 10 mM). Transport was initiated when the transporters were added to the assay system as DMSO solutions and ended when the vesicles were lysed with detergent after 300 s. A baseline was obtained by adding the transporters to a system of untreated vesicles. When the transporters were tested for their ability to perform electrogenic transport, the vesicles were treated with the ionophore valinomycin (Vln, Figure , a), a strict K + uniporter. Alternatively, when the series was tested for the ability to transport Cl -via an electroneutral H + /Cl -(or OH -/Cl -) co-transport pathway, the vesicles were treated with the ionophore monensin (Mon, Figure ), an H + /K + exchanger. For further assay details, see the experimental procedures section, or for more information on experimental data and associated spectra, see Figure -S115 in the ESI.