Micellar extraction of amino acids using chiral hydrophobic selectors.: A comparison with chromatographic procedures

In this work we study the micellar extraction of two amino acids, namely tryptophan and tyrosine, using N-n-dodecyl-L-proline (1) and trans-N-n-dodecyl-4-hydroxy-L-proline (2) as hydrophobic chiral selectors with copper(II) ions. In the first part of our study the solubilities of the two selectors 1 and 2 and their ability to form micelles are examined. Quantum mechanical calculations are performed to access their Gibbs solvation energies in order to explain their different behaviours. Micellar extraction is then studied using both selectors solubilised in non-ionic micelles. The results obtained are discussed and comparisons made with the data reported in the literature for similar selectors deposited onto an octadecyl silylated stationary phase in chromatographic procedures or solubilised in a real biphasic system in solvent extraction experiments.