The Adjusted HPTS Transport Selectivity Assay Recently, Talukdar and co-workers reported on a series of benzimidazolyl hydrazone H + /Cl -co-transporters which were shown to be the most active synthetic transporters studied to date, with one compound returning an EC50 of 0.000022 mol%. However, the transport properties of the series were investigated using an adjusted HPTS transport selectivity assay where a single excitation wavelength (450 nm) was used to excite the HPTS probe with an emission wavelength of 510 nm instead of a dual excitation wavelength. Other adjustments included the use of 100 nm L-α-phosphatidylcholine (EYPC) vesicles, buffered to pH 7.2, compared to the HPTS assay conditions above, which used 200 nm POPC vesicles buffered to pH 7.0. Due to these differences in experimental methods, anionophores 2c and 3c were tested using the conditions in the adjusted HPTS assay (Figure ). For further information and fitted experimental spectra, see Figure -S165 in the ESI.