Effect of sodium caproate on the volumetric and viscometric properties of glycine, dl-α-alanine, and dl-α-amino-<f>n</f>-butyric acid in aqueous solutions

The apparent molar volumes (<f>Vm,2</f>) and relative viscosities (<f>ηr</f>) at <f>T</f>=(298.15 and 308.15) K have been obtained for glycine, dl-α-alanine, and dl-α-amino-butyric acid in aqueous sodium caproate solutions from measurements of density and the flow time. The standard partial molar volumes (<f>V∘m,2</f>), standard volumes of transfer (<f>ΔtV∘</f>), the viscosity <f>B</f>-coefficients, and the activation thermodynamic quantities (<f>Δμ2∘≠</f> and <f>ΔS2∘≠</f>) of viscous flow have been calculated for the amino acids. It is shown that the standard partial molar volumes, viscosity <f>B</f>-coefficients, and activation free energies for viscous flow increase with increasing number of carbon atoms in the alkyl chain of the amino acids. An increase in <f>V∘m,2</f> and <f>ΔtV∘</f> with increasing electrolyte concentrations have been explained due to the interactions of sodium caproate with the charged center of zwitterions for the amino acids. A comparison of the <f>V∘m,2</f> values for glycine, dl-α-alanine, and dl-α-aminon-<f>n</f>-butyric acid in different aqueous salts solutions showed that carboxylate ions have stronger interactions with amino acid than chloride, thiocyanate, and nitrate ions. Results of viscosity are discussed in terms of changes in solvent structure. [Copyright &y& Elsevier]