EXTRACTION OF AMINO-ACIDS TO MICROEMULSION

The mechanism of amino acid extraction to AOT/n-heptane microemulsion was elucidated from the experimental data on the amino acid distribution between aqueous and microemulsion phases and on the fluorescence spectra for tryptophan. The hydrophilic amino acids such as glycine are taken up in the water pools of the microemulsion globules. The amino acids with hydrophobic side chains, such as tryptophan, are mainly incorporated in the interfacial zone of the globule. The localization of the amino acid in the microemulsion is affected by the electric charge states and the hydrophobicity of amino acids. The partition coefficient of amino acid J in charged state i between the above two phases, i.e., D(J)i, is given by the sum of the contribution of the water pool D(J)iWP and that of the interfacial zone D(J)iML. The D(J)+/-ML for zwitterionic amino acids is related to hydrophobicity indexes proposed by Nozaki-Tanford and Yunger et al. The electrostatic effect is evaluated from the D(J)+ML/D(J)+/-ML value for cationic amino acid and from the D(J)-ML/D(J) +/- ML value for the anionic one. Tryptophan acts as cosurfactant when its loading to the microemulsion phase is high.