Volumetric properties, structural effects, and hydration of amino acids in aqueous salt solutions

Abstract

The dependence of the standard partial volumes of glycine, α-alanine, and serine on the ionic strength of aqueous sodium chloride and sulfate solutions is modeled by the extended Masson equation: {ie534-1}. The error of less than 0.2 cm3/mol is a result of using five values of the A and B parameters: the two values of A are determined by the type of salt and the three values of B by the type of amino acid. A new variation of the additive-group approach is proposed for {ie534-2}. The partial volumes of the CH3 group (α-alanine) and the CH2 group (serine) are found not to depend on the salt concentration. The partial volume of the CH2 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.