Solubility of α-amino acids in water under high pressure:: glycine, L-alanine, L-valine, L-leucine, and L-isoleucine

The solubility of glycine, L-alanine, L-valine, L-leucine, and L-isoleucine in water was measured at 298.15 K and pressures up to 400 MPa. The standard deviation of the logarithm of the solubility is 0.001-0.003, equal to or better than the accuracy of atmospheric pressure measurement in the literature (0.001-0.05). A variety of solubility phenomena were observed. The solubility of glycine decreased with increasing pressure, whereas that of L-alanine increased. The L-valine and L-isoleucine have a solubility maximum at around 100 MPa, and L-leucine seems to exhibit a solid-phase phase transition at around 200 MPa. Pressure coefficient of the solubilities at 0.10 MPa is compared with that thermodynamically estimated in reference to aqueous density measurements of glycine and L-alanine at 298.15 K and 0.10 MPa, supporting a reliability of our high-pressure measurements. Published by Elsevier Science B.V.