VOLUMETRIC PROPERTIES, STRUCTURAL EFFECTS, AND HYDRATION OF AMINO ACIDS IN AQUEOUS SALT SOLUTIONS
The dependence of the standard partial volumes of glycine, a-alanine, and serine on the ionic strength of aqueous sodium chloride and sulfate solutions is modeled by the extended Masson equation: V 0 = V w 0 + AI 0,5 + BI. The error of less than 0.2 cm 3/mol is a result of using five values of the А and В parameters: the two values of А are determined by the type of salt and the three values of В by the type of amino acid. A new variation of the additive-group approach is proposed for Δ V 0 = V 0 - V w 0. The partial volumes of the СН 3 group (a-alanine) and the СН 2 group (serine) are found not to depend on the salt concentration. The partial volume of the СН 2 group of glycine grows with concentration. The structural characteristics of the hydrated complexes of the NH 3 + and COO - groups are calculated: the hydration numbers, the molar volumes of water inside and outside the hydration sphere, and the intrinsic volume of NH 3 + in COO - in solution. Given the same ionic strength, the aqueous sodium sulfate solution produces a somewhat stronger dehydration of the charged groups.