Compounds 2c and 3c both achieved greater activity under the conditions of the adjusted assay. The significant change in transport rate between the two studies can be attributed to the absolute rate of anion transport into a vesicle being proportionate to the vesicle surface area. Previously, Davis and co-workers stated that only transporters capable of eliciting high transport activities would produce any significant difference in activity due to liposome size. Tests performed using 2c and 3c indicated a 25% and 41% increase in transport activity, respectively (Table ), compared to the previous HPTS transport selectivity study. Fitting the transport data to the Hill equation (Equation ) resulted in EC50 values of 0.0000070 mol% and 0.000018 mol% for 2c and 3c, respectively. Additionally, the Hill coefficients obtained for 2c and 3c were both n ≈ 1. Tetralactam 2c achieved a 3.1-fold enhancement in transport activity compared to the best benzimidazolyl hydrazone co-transporter, while 3c produced a 1.2-fold increase in H + /Cl -co-transport activity. These comparisons demonstrate that 2c and 3c display the highest H + /Cl -co-transport activities among any natural or synthetic Cl -anionophores tested under the HPTS assay.