Compounds 1-3 were tested as Cl -transporters with the commonly used HPTS assay (see SI for details) and 1 and 3 were found to be active at 4 mol%. In contrast, 2 did not show any transport activity, despite its higher affinity for Cl -compared to 3. This confirms that the strength of anion binding in an organic solvent and transport are not necessarily correlated. To study the phosphate transport properties of 1-3 by emission spectroscopy, the phosphate responsive lanthanide probe [Eu.pBOH2] + (Figure ) was encapsulated in large unilamellar vesicles (LUVs, 0.4 mM POPC, ~ 200 nm diameter) at pH 7. This water soluble probe, recently developed by Butler and co-workers, gives a selective emission enhancement in the presence of phosphate, with no response for a range of biological anions including chloride, sulfate, and bicarbonate. The LUVs were prepared in a 100 mM N-methyl-D-glucamine hydrochloride (NMDGH + Cl -) solution buffered at pH 7 with 10 mM HEPES. This solution was used to provide Cl -anions that could participate in a H2PO4 -/Cl -antiport process, while avoiding the potential transport of cations (NMDGH + is a hydrophilic cation that is difficult to transport 33 ).