Volumetric and Viscometric Behaviour of some Amino Acids and their Group Contributions in Aqueous Tetramethylammonium Bromide at Different Temperatures

Abstract

Densities, ρ and viscosities, η for L-serine, L-threonine, L-glutamine, L-lysine, L-arginine and L-histidine (0.05–0.25 m) in 0.20 m aqueous tetramethylammonium bromide were determined at 298.15, 303.15, 308.15, and 313.15 K. The density data was used to compute apparent molar volume, φ_v. The partial molar volume, φ_v⁰, at infinite dilution and experimental slope, S_v^*were obtained from Masson´s equation and interpreted in terms of solute-solvent and solute-solute interactions, respectively. The φ_v⁰ values are found to vary with temperature as a power series of temperature. The structure-making/-breaking ability of solute were discussed using Hepler´s criterion. The partial molar volumes of transfer, φ_v⁰_(tr) of amino acid from aqueous to aqueous tetramethylammonium bromide solution were interpretedin the light of cosphere overlap model. The viscosity data was utilized to determine A- and B-coefficients of viscosity, free energy of activation of viscous flow, Δμ₁⁰* and Δμ₂⁰*, per mole of solvent and solute, respectively, and ΔH^* and ΔS^*were also evaluated. The linear variation of φ_v⁰ and B-coefficient with the number of carbon atoms in the alkyl chain of amino acids was utilized to determine the respective contributions of (NH₃⁺, COO^–) and CH₂ groups to φ_v⁰ and B-coefficient, respectively.