Volumetric properties of aqueous solutions of amino acids from the singular to critical temperature

The partial volume -V ₂ ⁰ of amino acids in aqueous solution is assumed to be zero for T = 227 K (singular temperature) and T= T _c (critical temperature). The literature data for -V ₂ ⁰(T) of ten amino acids at 278–328 K are reproduced by the two-parameter equation with a standard deviation of 0.06–0.16 cm³/mol. Only for asparagine and tryptophan the standard deviation exceeds 0.3 cm³/mol. In the case of glycine and alanine, the relation -V ₂ ⁰(T) in the high temperature range is obtained. -V ₂ ⁰ is divided into contributions (?-H ₂ ⁰/?p) _T and —T·(?-S ₂ ⁰/?p) _T . Their dependence on the temperature and amino acid nature is discussed. Positive values of ?-C ₂ ⁰/?p) _T characterize amino acids as water structure breakers; however, the differentiation of compounds by this feature is not successful. The behavior of amino acids in aqueous solutions is compared with the behavior of urea.