Electrolyte Effects on the Amino Acid Solubility in Water: Solubilities of Glycine, l-Leucine, l-Phenylalanine, and l-Aspartic Acid in Salt Solutions of (Na+, K+, NH4+)/(Cl–, NO3–)

Abstract

The solubilities of glycine, l-leucine, l-phenylalanine, and l-aspartic acid in aqueous solutions of the salts composed by combining Na+, K+, and NH4+ cations and Cl– and NO3– anions were measured up to 2.0 salt molality at 298.2 K by the analytical gravimetric method. Using these data along with a review of literature information, encompassing all amino acids for which solubility is available in the studied aqueous electrolyte solutions, allowed us to interpret the effect of the functional groups of amino acids on their solubility. The four amino acids studied here showed higher solubility in aqueous solutions of salts with the nitrate anion. Except for l-aspartic acid with a polar side chain, amino acids with apolar side chains presented the highest salting-in effect in aqueous salt solutions with NH4+. The cations Na+ and K+ did not seem to establish relevant interactions with the amino acids and had little impact on their aqueous solubility.