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 <sup>0</sup> = V <sub>w</sub> <sup>0</sup> + AI <sup>0,5 </sup>+ BI. The error of less than 0.2 cm <sup>3</sup>/mol is a result of using five values of the <i>А</i> and <i>В</i> parameters: the two values of <i>А</i> are determined by the type of salt and the three values of <i>В</i> by the type of amino acid. A new variation of the additive-group approach is proposed for Δ <i>V</i> <sup>0</sup> = <i>V</i> <sup>0</sup> - <i>V</i> <sub>w</sub> <sup>0</sup>. The partial volumes of the СН <sub>3</sub> group (a-alanine) and the СН <sub>2</sub> group (serine) are found not to depend on the salt concentration. The partial volume of the СН <sub>2</sub> group of glycine grows with concentration. The structural characteristics of the hydrated complexes of the NH <sub>3</sub> <sup>+</sup> and COO <sup>-</sup> groups are calculated: the hydration numbers, the molar volumes of water inside and outside the hydration sphere, and the intrinsic volume of NH <sub>3</sub> <sup>+</sup> in COO <sup>-</sup> in solution. Given the same ionic strength, the aqueous sodium sulfate solution produces a somewhat stronger dehydration of the charged groups.