The chloride binding capability of the macrocyclic transporters were determined by 1 H NMR titrations in d6-acetone with 2.5% (v/v) D2O, with the anion added as the tetrabutylammonium (TBA) salt. Anion binding led to perturbation of the chemical shift of the phenylic proton ortho to the iodotriazoles, which could be fitted to a 1:1 binding isotherm using the Bindfit software. Vesicle transport assays. 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) LUVs in a solution buffered to a pH of 7 in NaCl with HEPES were prepared to contain the pH-responsive fluorophore 8-hydroxypyrene-1,3,6-trisulfonate in their lumen. A pH gradient was applied across the membrane by addition of a pulse of sodium hydroxide, followed by addition of the carrier as a DMSO solution (<0.5 % v/v). The ability of the anionophore to dissipate the pH gradient by transmembrane OH -/Cl -exchange was determined by recording the change in the HPTS emission, Irel (λem=510 nm), with time following excitation at λex=405/465 nm. Excess Triton X100 detergent was added at the end of the experiment to lyse the vesicles for calibration. The transporter concentration dependence could be established from the corresponding end-point activities immediately prior to lysis.