Volumetric, viscometric and refractive index behaviour of amino acids in aqueous glycerol at different temperatures

摘要

Densities, ρ, viscosities, η, and refractive indices, n_D, of solutions of some amino acids (glycine, DL-alanine, DL-α-amino-n-butyric acid, L-valine and L-leucine) in the concentration range 0.02 to 0.10 m in 5% (v/v) aqueous glycerol were determined at 298.15, 303.15, 308.15 and 313.15 K. These experimental data were used to calculate the apparent molar volumes, φ_v, the infinite dilution apparent molar volumes, φ_v~0, the partial molar volumes of transfer, φ_v~0_((tr)), of the amino acids from aqueous to aqueous glycerol solution, as well as the viscosity A and B coefficients of the Jones-Dole equation of the amino acids. The free energies of activation of viscous flow, Δμ_1~(0#) and Δμ_2~(0#) per mole of solvent and solute, respectively, were obtained by application of the transition-state theory to the B coefficient data and the corresponding activation enthalpy, ΔH~*, and entropy, ΔS~*, were also determined. The φ_v~0, B coefficients and Δμ_2~(0#) were found to vary linearly with increasing number of carbon atoms in the alkyl chain of the amino acids, and they were split into contributions from the zwitterionic end groups (NH_3~+, COO~-) and methylene (CH_2) groups of the amino acids. The experimental values of the refractive indices, n_D, were used to calculate the molar refractive indices, R_D, of the amino acids + aqueous glycerol ternary mixtures. The results were interpreted in the light of the solute-solvent and solute-solute interactions in the mixed solvents.