Viscosity B-coefficients of some alpha-amino acids in aqueous guanidine hydrochloride solution from 278.15 to 308.15 K

The relative viscosities of glycine, DL-alpha-alanine, DL-alpha-amino-n-but yric acid, DL-valine, DL-leucine and L-serine in 6 mol . kg(-1) aqueous gua nidine hydrochloride solution have been measured at 278.15, 288.15, 298.15 and 308.15 K. The viscosity B-coefficients for each of the amino acids have been determined and used to probe the changes of water structure when guan idine hydrochloride is added. The corresponding activation free energies (D elta mu(2)(0 not equal)) for viscous flow have been evaluated with the help of the Feakins equation. It has been observed that both B-coefficient and activation free energy vary linearly with increasing number of carbon atoms in the alkyl chains of the amino acids at given temperatures. These linear correlations were used to estimate the contributions of the charged end gr oup (NH3+, COO-) and CH2 groups of the amino acids to B-coefficient and Del ta mu(2)(0 not equal). Based on the data of Delta mu(2)(0 not equal) for th e amino acids and their groups, the contributions of (NH3+, COO-) and CH2 g roups to activation enthalpy (Delta H-2(0 not equal)) and entropy (Delta S- 2(0 not equal)) were also reported. The activation parameters are discussed in terms of the solute-solvent and solvent-solvent interactions in the gro und and transition states.