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.