Mechanisms of amino acid partitioning in cationic reversed micelles

The aim of this work is to discuss the mechanisms involved in amino acid solubilization in cationic reversed micelles. A simple mechanism was assumed in which the amino acid solubilization is mediated by an ion exchange process between the amino acid and the surfactant counter ion neglecting the effect of the reversed micellar structure. Based on this mechanism a simple model to predict equilibrium was developed and applied to the solubilization of amino acids with different structures. It was found that solubilization of hydrophilic and slightly hydrophobic amino acids can be described by an ion-exchange mechanism and the amino acid equilibrium concentration can be determined for different experimental conditions using this model. However, solubilization of hydrophobic amino acids can not be described by a simple ion-exchange model. In this case hydrophobic contributions play an important role in amino acid solubilization and must be considered in the overall solubilization process. This hydrophobic contribution was evaluated by determination of an interfacial partition coefficient. The overall amino acid extraction was determined using distribution coefficients of all the amino acid forms and considering their dependence on ionic strength.