Temperature of Maximum Density for Binary Aqueous Solutions of Five Amino Acids

Density in the temperature interval of 273.65–283.15 K has been experimentally determined for aqueous solutions of l-tyrosine, l-tryptophan, l-histidine, l-phenylalanine, and l-proline. These data have allowed the temperature of maximum density (TMD) to be obtained as a function of amino acid concentration. All systems present a TMD depression against concentration, which was quantified through the Despretz constant. Compared with other compounds, the studied amino acids show a medium effect over TMD, with Despretz constants ranging from −9.85 K·mol–1·kg for proline to −16.6 K·mol–1·kg for tyrosine. The partial molar volume has also been calculated from density values to perform a thermodynamic consistency test between them and TMD data, yielding satisfactory results.