Carrier-mediated transport of amino acids through bulk liquid membranes

A novel carrier, the N-methyl, N-dodecyl-ephedrinium ion, was studied for the selective transport of some aromatic amino acids [phenylalanine (Phe), histidine (His) and tryptophan (Trp)] through bulk liquid membranes. Investigations of the main parameters limiting the aided transport of the amino acids were carried out. Transport rates that resulted were affected by the amino acid lipophilicity, the pH variations of feed and receiving solutions, the concentration, and the nature of countertransport ions. Further results indicate that the carrier can interact with amino acids by ion pairing and nonionic interactions. Membrane selectivity showed to be strictly related to kinetics of the amino acid release at the membrane/receiving interface, and its results were satisfactory when the receiving solution was kept in acidic conditions. In these conditions, when a mixture of the three amino acids was used as the feed solution, the transport rate of phenylalanine was over three times higher with respect to tryptophan, while the transport of histidine was almost completely damped down.