Effect of temperature on viscosity properties of some α-amino acids in aqueous urea solutions Original Research Article

Viscosities for solutions of glycine, dl-α-alanine, dl-α-amino-n-butyric acid, dl-valine, dl-leucine and l-serine in 5 mol kg−1 aqueous urea have been determined at 278.15, 288.15, 298.15 and 308.15 K. The viscosity B-coefficients for the amino acids in the aqueous urea solution have been calculated at different temperatures. The effect of temperature on the B-coefficients is discussed on the basis of the Feakins equation. The contribution of solute to the activation parameters (Δμ20≠, ΔH20≠, ΔS20≠) for viscous flow of the solution have been calculated, together with the Gibbs energy, enthalpy and entropy of transfer for the amino acids from the ground-state solvent to the hypothetical viscous transition state solvent. The contributions of the charged end group (NH3+, COO−) and CH2 groups of the amino acids to B-coefficient and Δμ20≠ have been also estimated using the linear correlations between B-coefficient or Δμ20≠ and the number of carbon atoms in the alkyl chains of the amino acids. All the activation parameters are discussed in terms of the solutesolvent interactions in the ground and transition states.