Temperature effect on the viscosity and heat capacity behaviour of some amino acids in water and aqueous magnesium chloride solutions

Abstract

Viscosities ( η) for solutions of some amino acids (glycine, l-alanine, and l-leucine) in water and in aqueous magnesium chloride (MgCl 2) solutions of various molalities m S ≈ (0.05 to 0.70) mol · kg −1 have been determined at T = (288.15, 298.15, and 308.15) K. The data have been used to calculate viscosity B-coefficients of the amino acids. The hydration numbers of amino acids have been determined from the present and the earlier volumetric data at different temperatures and molalities of MgCl 2. Free energies of activation ( Δ μ 2 ∞ ) for viscous flow of the solution were obtained by applying the transition state theory to the viscosity B-coefficient and volumetric data. The corresponding activation enthalpy ( Δ H 2 ∞ ) and entropy ( Δ S 2 ∞ ) have also been determined. In continuation to our earlier studies apparent molar heat capacities of l-leucine in water and in aqueous MgCl 2 solutions over the temperature range T = (288.15 to 328.15) K have also been determined using high sensitivity micro-differential scanning calorimeter.