Partial molar volumes of l-serine and l-threonine in aqueous ammonium sulfate solutions at (278.15, 288.15, 298.15, and 308.15) K

In this study, the partial molar volumes of L-serine and L-threonine in aqueous solutions of ammonium sulfate at (0.0, 0.1, 0.3, 0.7, and 1.0) mol.kg(-1) are reported between 278.15 and 308.15 K. Transfer volumes and hydration numbers were obtained, which are larger in L-serine than in L-threonine. Dehydration of the amino acids is observed, rising with the temperature and salt molality. The data suggest that interactions between ions and charged/hydrophilic groups are predominant, and by applying the McMillan and Mayer formalism, it was concluded that they are mainly pair wise. The combination of the data presented in this study with solubility and molecular dynamics data suggests a stronger interaction of the ammonium cation with the zwitterionic centers of the amino acids when compared to the interactions of those centers with the sulfate anion.

Understanding the cation specific effects on the aqueous solubility of amino acids: from mono to polyvalent cations

The interactions established by mono and polyvalent cations in natural media have important implications on the structure formation, function and physico-chemical behavior of biomolecules, playing therefore a critical role in biochemical processes. In order to further elucidate the molecular phenomena behind the cation specific effects in biological environments, and clarify the influence of the charge of the ions, solubility measurements and molecular dynamics simulations were performed for aqueous solutions of three amino acids (alanine, valine and isoleucine), in the presence of a series of inorganic salts comprising mono-, di- and trivalent cations (LiCl, Li2SO4, K2SO4, CaCl2, AlCl3 and Al-2(SO4)(3)). The evidence gathered indicates that the mechanism by which (salting-in inducing) polyvalent cations affect the solubility of amino acids in aqueous solutions is different from that of monovalent cations. A consistent and refined molecular description of the effect of the cation on the solubility of amino acids based on specific interactions of the cations with the negatively charged moieties of the biomolecules is here proposed.

Volumetric interactions of a series of α-amino acids in aqueous magnesium chloride solutions at 278.15, 288.15, 298.15, and 308.15 K

In this work, the partial molar volumes of glycine, l-alanine, l-valine, l-serine, and l-threonine in aqueous solutions of magnesium chloride at 0.0, 0.1, 0.3, 0.7, and 1.0 molal are addressed between 278.15 and 308.15 K. Volumes of transfer were obtained, following the rank serine > glycine a parts per thousand threonine > alanine > valine. Differently, the hydration numbers follow the sequence serine > valine > alanine > threonine > glycine, and dehydration of the amino acids is observed, rising the temperature or salt molality. The data suggest that interactions are mainly pairwise, between the ions and charged/hydrophilic groups of the amino acids. Within the Friedman and Krishnan formalism, a group-contribution scheme has been successfully applied to the pairwise volumetric interaction coefficient. Finally, the dehydration effect of MgCl2 on glycine, alanine, and serine has been predicted applying empirical correlations developed before, showing satisfactory results.