Volumetric, Viscometric and Spectroscopic Properties of Glycylglycine in Citrate and Acetate Buffer Solutions at Different Temperatures

Interactions of proteins with the surrounding solvent play an important role in their conformational stability and unfolding behavior of globular proteins. In order to understand various interactions (H-bonding and electrostatic interactions etc.) between the protein molecules and the solvent, densities (rho) and viscosities (eta) of glycylglycine in water, in aqueous tri-sodium citrate buffer and in aqueous sodium acetate buffer solutions of pH 7.40 were determined at different temperatures, T= (288.15 to 328.15) K and at atmospheric pressure. These data have been used to calculate partial molar volumes (phi(o)(nu)) and relative viscosities (eta(r)). Positive values of phi(o)(nu) and viscosity B-coefficients indicate the presence of strong solute-solvent interactions among the system. Positive transfer volumes show the dominance of ion-dipolar interactions. Further, interaction coefficients, partial molar expansibilities, their second order derivatives, dB/dT and hydration numbers were also calculated. The free energy of activation of viscous flow, (Delta mu(o#)(1)) and (Delta mu(o#)(2)) per mole of the solvent and solute were obtained by applying transition-state theory to viscosity B-coefficient data and the corresponding activation parameters, enthalpy (Delta H-o#) and entropy (Delta S-o#) were also determined. FTIR studies were also carried out for glycylglycine in aqueous and mixed aqueous solutions at pH 7.40 and at room temperature (i.e. T= 298.15 K). Overall, the results have been interpreted in-terms of various competitive interactions among these systems.