Thermodynamic Study of Amino Acids in an Aqueous Solution of Calcium Acetate at T = 283.15–308.15 K and Pressure P = 0.1 MPa: A Volumetric Approach

Abstract

In the present work, densities (ρ) of glycine, l-alanine, aminobutyric acid, l-valine, and l-leucine in an aqueous solution of calcium acetate (0.2005; 0.5998; 0.9000; 1.1978; and 1.5991) mol kg–1 have been measured at T = 293.15–308.15 K and pressure P = 0.1 MPa. The infinite dilution apparent molar volumes (V φ 0) and standard volumes of transfer (Δtr V φ 0) vary linearly with those of carbon atoms in the alkyl chain of the amino acids. The contributions of the nonpolar groups to the value of V φ 0 increase with the size of the alkyl chain of amino acids and decrease with the concentration increase of calcium acetate. The group-contribution of charged end groups (NH3 +, COO–) is larger than that corresponding to alkyl chains. The standard transfer volumes (Δtr V φ 0) for all amino acids are positive and increase with the calcium acetate concentrations and decrease with temperature, except for l-valine and l-leucine. Volumetric interaction coefficients of amino acids have been determined using the McMillan–Mayer equation. Calcium acetate shows a strong dehydration effect on amino acids over the entire concentration range. All results show a preferential solvation phenomenon in the mixture due to electrostatic interactions at the first layer solvation between the charged groups of amino acids and the inorganic salt.