Densities, Partial Molar Volumes, and Heat Capacities of Glycine, l-Alanine, and l-Leucine in Aqueous Magnesium Chloride Solutions at Different Temperatures

Abstract

The apparent molar volumes (V 2, φ) have been determined for glycine, l-alanine, and l-leucine in water and in aqueous magnesium chloride solutions with concentrations ≈ (0.05 to 0.80) mol·kg-1 by measuring the densities at (288.15, 298.15, and 308.15) K. The apparent molar heat capacities (C p2, φ) have also been determined for glycine and l-alanine in aqueous magnesium chloride solutions with concentrations ≈ (0.05 to 0.40) mol·kg-1 by measuring heat capacities in the temperature range (298.15 to 328.15) K. These properties show a peculiar dependence upon the concentration of magnesium chloride. The standard partial molar volumes at infinite dilution ( ) obtained from these data have been used to calculate the partial molar volumes of transfer of amino acids from water to aqueous magnesium chloride solutions at infinite dilution (Δt ), which are positive for the presently studied amino acids at all temperatures and concentrations. The partial molar expansibilities (∂ /∂T) P at infinite dilution and the (∂2 /∂T 2) P values have also been determined from the data at various concentrations of the salt. The volumetric interaction parameters have been calculated from Δt data. The results have been discussed in terms of various interactions operating in these systems.

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

“…2. In all cases, our data are in good agreement with the data from Lark et al [7] at low salt molality, supporting the consistency of the partial molar expansion in pure water presented above. In fact, for the systems containing MgCl 2 the data available in the open literature show big differences.…”

“…The partial molar expansions calculated in this work are in high accordance to those measured by Mota et al [1] and Martins et al [2]. The same approach was applied to the data published by Martins et al [2], Yan et al [10], Shen et al [11], and Banipal et al [12], for DL-alanine and Lark et al [7], for L-alanine, allowing the comparison in Fig. 1a.…”

“…1a. A very good agreement is observed between the information found in the works by Martins et al [2], Lark et al [7], and Shen et al [11], but in conflict with the study published by Yan et al [10], that indicates an opposite change of the partial molar expansion with temperature. The same happens using the data published by Pal and Kumar [8,14], but with such different magnitude, that no information is presented in Fig.…”

“…The dramatic salting-in effects on the solubility of amino acids induced by magnesium chloride [6] prompted us to include this salt in our amino acid partial molar volumes studies, which are also supported by the large differences found in the partial molar volumes at infinite dilution of glycine or L-alanine, in the presence of such salt, published by different researchers [7,8].…”

“…b L-Threonine (open diamond) this work; (X) Mota et al [1]; (open circle) Hakin et al [16]; (open square) Cabani et al [13]; (closed circle) Mizuguchi et al [17]. c L-Valine (open diamond) this work; (closed circle) Banipal et al [12]; (open square) Cabani et al [13]; (open circle) Kikuchi et al [18] [7]; (open square) Pal and Kumar [14] Volumetric interactions of a series of a-amino acids in aqueous magnesium chloride solutions… previously reported that the dehydration is usually more pronounced in the presence of more hydrated anions, which is the case of sulfate when compared to chloride [2]. Even if the dehydration is not always directly related to solubility salting-in or salting-out phenomena, these results are also consistent with the higher salting-in character of MgCl 2 on alanine and valine solubilities, while for alanine (NH 4 ) 2-SO 4 induces a mixed behavior and to valine an evident salting-out.…”