Thermodynamics of Water and Solute Binding to Binary Mixtures of Biopolymers and Lipid

Extents of hydration of binary mixtures of different biopolyrners and lipid in different proportions have been measured in the absence and presence of inorganic salts and urea at a fixed temperature using isopiestic vapour pressure technique. Moles of water adsorbed per kg of mixture at unit water activity have been evaluated by extrapolation method. Standard free energy (ΔG⁰) and enthalpy (ΔH⁰) changes for the mixture in bringing water activity from zero to unity have been evaluated from the experimental data. The extent of excess hydration of different binary mixtures in the presence of excess of neutral salts and urea have been evaluated using the same isopiestic method. In all cases, the moles of water and solute respectively bound in absolute amount to mixtures have been evaluated in the limited range of solute concentrations in the medium. Also, using the integrated form of the Gibbs adsorption equation, standard free energy changes (ΔG⁰) for the solute and the solvent interactions for different types of mixtures have been computed and values have been compared critically.