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

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 mB 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, Vϕ, and relative viscosities, ηr, of amino acids have been derived. The partial molar volume at infinite dilution, V20, and viscosity B-coefficient obtained from these data have been used to calculate the corresponding transfer parameters, ΔtV0, and ΔtB  , for the studied amino acids from water to aqueous magnesium acetate solutions. The activation free energies, Δμ20≠, 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, nH, 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 (NH3+, COO−) and (CH2) group of the amino acids to V20, viscosity B  -coefficient and Δμ20≠ have been calculated. These results have been rationalized in terms of the hydration of hydrophilic and hydrophobic parts of amino acids.