Phase behavior of α-amino acids in multicomponent aqueous alkanol solutions

A model describing the partitioning behavior of α-amino acids in systems containing water and partially miscible alkanols is presented. It incorporates a relationship expressing the solubilities of amino acids in miscible aqueous alkanol solutions and makes use of the phase behavior of the solute-free solvent system and the solubilities of amino acids in the pure solvent components. The solubilities of several amino acids in aqueous ethanol and isomeric propanol solutions and their partition coefficients in the 1-butanol + water system were taken from the literature and could successfully be described with a single, amino acid specific, ternary interaction parameter. It is demonstrated that this parameter is related to well-established hydrophobicity scales for amino acid side-chain moieties. Without additional parameters the partition coefficients of amino acids in 1-octanol/water were predicted from the model and compare well with literature values. The extension of the model to multicomponent solvent systems is straightforward and was demonstrated for the case of the ternary solvent system water + ethanol + 1-butanol.