Due to the low aqueous solubility of the series, transporter concentrations of 0.05 mol% were required to obtain initial rate constants (kini, s -1 , Table ), which were calculated using Equations 2-4. Even at a reduced concentration, the naphthalenesubstituted transporters (1-4b) were relatively inactive, with 1b and 4b slowly precipitating out of solution. The electroneutral transport character (ENC) was calculated for each transporter. The ENC factors describe how well a compound can perform H + /Cl -co-transport over Cl -uniport and are calculated by dividing the kini transport rate obtained from Mon-treated vesicles by the rate obtained from Vln-treated vesicles (Table ). An ENC factor value > 1.0 is indicative of higher electroneutral transport activity.