VOLUMETRIC PROPERTIES, STRUCTURAL EFFECTS, AND HYDRATION OF AMINO ACIDS IN AQUEOUS SALT SOLUTIONS
V. P. Korolev
G. A. Krestov Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo
korolev@isuct.ru
Keywords: partial volume, amino acid, aqueous salt solutions, group contributions, hydration numbers
Abstract
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: V0 = Vw0 + AI0,5 + BI. The error of less than 0.2 cm3/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 ΔV0 = V0 - Vw0. The partial volumes of the СН3 group (a-alanine) and the СН2 group (serine) are found not to depend on the salt concentration. The partial volume of the СН2 group of glycine grows with concentration. The structural characteristics of the hydrated complexes of the NH3+ and COO- groups are calculated: the hydration numbers, the molar volumes of water inside and outside the hydration sphere, and the intrinsic volume of NH3+ in COO- in solution. Given the same ionic strength, the aqueous sodium sulfate solution produces a somewhat stronger dehydration of the charged groups.
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