Effect of magnesium acetate on the volumetric and transport behavior of some amino acids in aqueous solutions at 298.15 K

Abstract

Densities, ρ, and viscosities, η, of glycine, dl-α-alanine, dl-α-amino- n-butyric acid, l-leucine and l-phenylalanine in 0.5, 1.0, 1.5 and 2.0 m B of aqueous magnesium acetate solutions at 298.15 K have been measured as a function of concentration of amino acids using vibrating tube-digital densimeter and Ubbelohde capillary type viscometer, respectively. The apparent molar volumes, V ϕ , and relative viscosities, η r, of amino acids have been derived. The partial molar volume at infinite dilution, V 2 0 , and viscosity B-coefficient obtained from these data have been used to calculate the corresponding transfer parameters, Δ t V 0, and Δ t B, for the studied amino acids from water to aqueous magnesium acetate solutions. The activation free energies, Δ μ 2 0 ≠ , for the viscous flow of solutions have been obtained by application of the transition-state theory to the viscosity B-coefficient data. The interaction coefficients and hydration number, n H, of amino acids in aqueous solutions have also been calculated to see the effect of magnesium acetate on the hydration of amino acids. The contribution of the zwitterionic end groups ( NH 3 + , COO −) and (CH 2) group of the amino acids to V 2 0 , viscosity B-coefficient and Δ μ 2 0 ≠ have been calculated. These results have been rationalized in terms of the hydration of hydrophilic and hydrophobic parts of amino acids.