Volumetric study of α-amino acids and their group contributions in aqueous solutions of cetyltrimethylammonium bromide at different temperatures

Abstract

Apparent molar volume, Vϕ and apparent molar isentropic compression, κS,ϕ of glycine (Gly), L-alanine (Ala), and L-valine (Val) in binary aqueous solutions of 4·10−4 and 12·10−4m (molkg−1) cetyltrimethylammonium bromide (CTAB) have been determined at 298.15, 303.15, 308.15, and 313.15K from density and ultrasonic speed measurements. Apparent molar volumes at infinite dilution, Vϕ0 apparent molar isentropic compressions at infinite dilution, κS,ϕ0 and the experimental slopes (Sv*andSk*) were obtained from Masson's equation. These values are used for calculating the number of water molecules hydrated, nH to the amino acids. The structure-making/-breaking ability of solutes was discussed using Hepler's criterion. Transfer volumes, ΔtrVϕ0 at infinite dilution from aqueous to aqueous CTAB solutions have been calculated and were interpreted in terms of solute–cosolute interactions on the basis of cosphere overlap model. Group contributions of amino acids to the partial molar volume were determined. The obtained data were discussed in the light of various interactions operating in ternary systems of amino acids, water and CTAB.