Solubility of Amino Acids in Pure Solvent Systems

The effects of various solvents and pH on the solubilities of glycine, L-alanine, L-valine, L-phenylalanine, and DL-amino-octanoic acid were studied in a series of pure aqueous and alcoholic solutions. The aqueous solubility was found to be inversely proportional to the size of the nonpolar portion of the molecule. A low nonaqueous solubility seemed to be due to a dominance of the amino acid by the charged L-amino carboxylic acid portion of the molecule. In aqueous and alcoholic solutions, an isoelectric band of minimum solubility was formed. A distinct increase in solubility proportional to the addition of acid or base was seen as the pH exceeded the limits of the isoelectric band. In the alcoholic solvent systems studied, the addition of either acid or base produced a greater divergence from the isoelectric pH than would be seen in a pure aqueous system.