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

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 (Δ t ), 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 Δ t data. The results have been discussed in terms of various interactions operating in these systems.