Cation transfer across a hydrogel/organic phase: Effect of cation size, hydrophobicity and acid–base properties

The transfers of tetraethylammonium (TEA+) and protonated triflupromazine (HTFP+) through a hydrogel/liquid interface (g/o) and a liquid/liquid interface (w/o) were compared using cyclic voltammetry. After the two phases were put in contact, the behavior of each molecule was analyzed at different pH values and at different time points. The gel induces hydrophobic and electrostatic interactions with TEA+ and HTFP+, shifting the peak potentials to more positive values. The diffusion coefficients, D, in both phases (g and w) at different pH values were calculated. In the case of TEA+, the D value remains constant in both systems. However, the D value of HTFP+ is lower in the gel phase than in the liquid phase.HTFP+ is transferred from the aqueous phase to the organic phase via a direct mechanism that involves coupled acid–base and partition processes. At the g/o interface, the coupled chemical reactions of HTFP+ were inhibited by the drug/gel interaction. The results demonstrate that the g/o system could be used as a model to study the controlled release of charged drugs.