To confirm that the observed pH gradient dissipation in these experiments occurs via the postulated Cl -transport mechanism, we performed experiments in which the Cl -ion was replaced with the bulky and hydrophilic gluconate anion, which cannot typically be transported (Figure ). Inactivity in this assay revealed that the observed pH dissipation is not due to the possible cation-dependent H + /Na + antiport mechanism and confirms the integrity of the LUV membranes to non-specific ion or HPTS leakage in the presence of the macrocycles. A mobile carrier mechanism was confirmed by performing transport experiments in 1,2-dipalmitoyl-sn-glycero-3phosphocholine (DPPC) lipid vesicles at both 25 and 45 °C, below and above the gel-liquid phase transition temperature of 41°C, respectively (Figure ). Inactivity in the gel phase and restoration of transport in the liquid phase of the lipid is indicative of the expected carrier mechanism, in contrast to the phase-independent behaviour typically observed for membranespanning channels. 49