Effect of temperature on volumetric and viscosity properties of some α-amino acids in aqueous calcium chloride solutions

Abstract

Densities and viscosities for solutions of some α-amino acids in aqueous calcium chloride (3.0 mol kg −1) have been determined at 278.15, 288.15, 298.15 and 308.15 K. These data have been used to calculate apparent molar volumes and viscosity B-coefficients of the amino acids. The standard partial molar volumes, V° 2, φ , and hydration numbers of the amino acids have been determined at different temperatures. Free energies of activation, Δ μ° 2 ≠, for viscous flow of the solutions were obtained by application of the transition-state theory to the B-coefficient data, and the corresponding activation enthalpy Δ H° 2 ≠ and entropy Δ S° 2 ≠ were also given. It has been shown that V° 2, φ , B-coefficients and the free energies of activation vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids, and they were split into contributions from the zwitterionic end group (NH 3 +, COO −) and the methylene groups of the amino acids. The volumetric data have been interpreted in terms of the hydration of the hydrophobic and hydrophilic parts of the amino acids. From the viscosity data, structural effects of the amino acids in the solutions have been discussed.