Thermodynamic Study of Amino Acids in an Aqueous Solution of Calcium Acetate atT= 283.15-308.15 K and PressureP= 0.1 MPa: A Volumetric Approach

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^-1have been measured atT= 293.15-308.15 K and pressureP= 0.1 MPa. The infinite dilution apparent molar volumes (V_φ⁰) and standard volumes of transfer (Δ_trV_φ⁰) vary linearly with those of carbon atoms in the alkyl chain of the amino acids. The contributions of the nonpolar groups to the value ofV_φ⁰increase 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 (Δ_trV_φ⁰) for all amino acids are positive and increase with the calcium acetate concentrations and decrease with temperature, except forl-valine andl-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.