Studies of volumetric and activity behaviors of binary and ternary aqueous solutions containing β-cyclodextrin and glucose

Abstract

Osmotic vapor pressure and density measurements have been carried-out for binary aqueous solutions of glucose and ternary aqueous solutions containing glucose and a fixed concentration of β-cyclodextrin (β-CD) [0.01262molkg−1] using techniques of vapor pressure osmometer and digital densitometer at 298.15K. The measured water activities were used to estimate the activity coefficients and free energy changes in the binary system. The activity data of binary aqueous glucose solutions are further used to obtain the hydration number of glucose. The free energy change shows that at low concentration glucose forms almost an ideal solution in water. In ternary solutions the activity coefficient and transfer free energies of β-CD and glucose are studied as a function of concentration of glucose. Using earlier reported data for binary aqueous β-CD system and these newly studied systems, transfer free energies of β-CD from aqueous to aqueous glucose solutions are determined. These results are further subjected to McMillan–Mayer theory of solutions which yield the value of thermodynamic equilibrium constant (K) for β-CD:glucose complex in aqueous solutions after evaluation of salting constant and pair and triplet interaction parameters. It has been found that log K values are positive and high. These results are discussed in terms of hydrogen bonding, replacement of water molecules from β-CD cavity and solute–solute association equilibria involving pair and triplet interactions.