Effect of Sodium Acetate and Magnesium Acetate on the Solution Behavior of Some Amino Acids in Water at 298.15 K: A Compressibility Approach

Abstract

Apparent molar adiabatic compressibility, K 2,φ,S, of glycine, DL-α-alanine, DL-α-amino-n-butyric acid, L-leucine and L-phenylalanine in water and in (0.5, 1.0, 2.0, 4.0, 5.5 mol kg−1) aqueous sodium acetate and in (0.5, 1.0, 1.5, 2.0 mol kg−1) aqueous magnesium acetate solutions has been determined from sound velocity, u, measurements at 298.15 K. The partial molar adiabatic compressibilities at infinite dilution, K 0 2,S, obtained from K 2,φ,S data have been used to calculate the corresponding partial molar adiabatic compressibilities of transfer at infinite dilution, Δt K 0 2,S, from water to aqueous sodium acetate and magnesium acetate (cosolutes) solutions. The Δt K 0 2,S values are positive for the studied amino acids in case of both the cosolutes and the values increase with the increase of the concentrations of both the cosolutes. The trends of Δt K 0 2,S have been rationalized in terms of the hydration of hydrophilic and hydrophobic parts of the amino acids studied. The interaction coefficients and hydration number, n H, have also been calculated and are discussed in terms of the dehydration effect of sodium acetate and magnesium acetate upon the amino acids in solutions. Attempt has been made to correlate these results with the earlier reported volumetric and viscometric studies for the same systems.