Hydration and Solvation Effect of Glycine and Glycylglycine Molecules with β-Cyclodextrin in Aqueous Media. A Thermodynamic Characteristic of Interaction

Abstract

Abstract The densities, ρ and viscosities, η have been measured for DL- glycine (Gly) and glycylglycine (Gly-Gly) in aqueous β cyclodextrin, (β-CD) at temperature 298.15, 303.15, 308.15, 313.15 and 318.15 K. Interaction between macrocyclic β-CD and amino acids was studied by two independent technique: density and viscosity. The two different intensive properties are used to obtain various thermodynamic characteristics of the material behavior. Using the measured density data the apparent molar volumes, Vϕ , partial molar volume at infinite dilution, V ϕ ο , $V_\phi ^o,$ experimental slope, SV , isobaric expansibility, ϕ E 0 , $\phi _E^0,$ and the partial molar volume of transfer at infinite dilution, Δ V ϕ ( t r ) ο $\Delta V_{\phi (tr)}^o$ have been obtained. Moreover, the Falkenhagen’s theoretical coefficient, A, Jones-Dole coefficient, B, free energies of activation of viscous flow per mole of solvent, Δ μ 1 ο # $\Delta \mu _1^{o\# }$ and per mole of solute, Δ μ 2 ο # , $\Delta \mu _2^{o\# },$ enthalpy, ΔHo # and entropy, ΔSo # of activation of viscous flow have been evaluated by using viscosity data. The negative value of transfer volume for Gly and Gly-Gly in aqueous β-CD suggests that the hydrophobic-hydrophilic and hydrophobic-hydrophobic interactions are predominating over ionic-hydrophilic and hydrophilic-hydrophilic interactions. The results indicate the formation of a stable complexation between the β-CD cavity and structural hydration effect of amino acids on the thermodynamic of their interactions in solutions.