The anion transport activity of acridinone-based bis-(thio)urea receptors 1-10 was investigated using the Cl -/NO3 -exchange assay (Figure ). Large unilamellar vesicles (200 nm) were prepared with a NaCl internal solution (487 mM) buffered to pH 7.2 with sodium phosphate salts (5 mM). The vesicles were subsequently suspended in a NaNO3 external solution (487 mM) buffered to pH 7.2 following a similar method. Receptors were