Please do not adjust margins phenylenediamine-based transporter has a EC50 value of 0.0015 mol% in the Cl -/NO3 -exchange assay. Measurable activity was observed for compound 3 at transporter to lipid loadings as low as 1:500000 transporter:lipid ratio (2 nM in the aqueous suspension, or 0.0002 mol%), as shown in Figure . A Hill coefficient of close to n = 1 was determined for receptors 3 and 4, indicating that these compounds transport Cl -in a 1:1 host:guest stoichiometry. The Hill coefficient for the other compounds (5, 8-10) was determined to be n ≥ 2, suggesting a higher stoichiometry is required to facilitate transport. The distorted binding site present in bis-thiourea compounds 8-10 may leave a bound chloride anion too exposed to the lipid bilayer interior. A requirement of at least two bis-thiourea molecules to successfully shield the negative charge is another potential explanation for the poorer transport activity displayed by the bis-thiourea compounds in this assay compared to their bis-urea analogues. The rates of chloride efflux achieved by receptors 4, 5 and 8-10 were calculated from the efflux plots at a transporter loading of 0.05 mol%, to offer comparison across the series, and are shown in Table . The high activity of compound 3 in the Cl -/NO3 -exchange assay allowed the determination of the maximum transport rate to be calculated at a lower transporter loading of 0.01 mol%. The transport rate values of compounds 3-4 and 8-9 were obtained by fitting the respective efflux plots to an exponential decay function and calculating the initial rate. The trend in rates for these compounds is concordant with the calculated EC50 values, and the rate of transport facilitated by compound 3 was significantly higher than the other compounds tested even at a lower loading. The efflux plots at 0.05 mol% loading of the para-SF5 compounds 5 and 10 were sigmoidal in shape and were therefore fit to a Boltzmann sigmoidal curve. The maximum rate of transport calculated for these compounds occurs in the middle of the experiment, rather than at the beginning. The slow initial rate of transport exhibited by the para-SF5 receptors is reflective of their poor solubility, suggesting that delivery of the transporter and its partition into the lipid bilayer may be the rate-limiting step of the transport process.