Pleasingly, we found that SSA 1 remained active in our K + /Cl -co-transport assay when added from either a 5 mM stock solution made up in H2O/ EtOH (95:5) or 100% H2O, with some reduction in the observed activity compared to DMSO (Figure ). We performed Hill plot analyses to quantify the transport efficiency of SSA 1 when added using a DMSO, H2O/ EtOH (95:5) and H2O delivery solution, and the results are shown in Table . Based on our calculated EC50 values, we established that SSA 1 was approximately twice as active when delivered from a DMSO stock solution compared to an aqueous or partially aqueous stock solution. Nonetheless, the retention of transport activity using an aqueous delivery vehicle represents a step change in the development of deliverable ionophores. We also found that the observed values for n, the Hill coefficient, were close to 1 in each case. This could be interpreted as evidence to support a unimolecular transport process; however, we note the potential for Hill plot analyses to be complicated by the formation of stable, aggregate species as described by Matile, since stable supramolecules can be misinterpreted as monomers. Given the extensive data on the dimerisation and aggregation of SSAs under a wide range of conditions, 15a, 15b we do not believe that these values offer firm proof of a 1:1 SSA: cation transport process. Table Summary of M+ co-transport results for SSA 1 and anionophore 4.