Excess and deviation properties of {(glycylglycine + ZnCl2) in aqueous methanol} mixtures

The excess molar volumes (VE), viscosity deviations (Δη), deviations in isentropic compressibility (ΔκS) and excess molar refractivity (ΔRmE) for {(glycylglycine + ZnCl2) in aqueous methanol} mixture have been calculated from the experimental values. The bridging water molecules bend the chains into stable open ring structures together with intermolecular hydrogen bonding and interstitial accommodation leading to negative VE values. The positive Δη values indicate a structure breaking effect of aqueous glycylglycine–ZnCl2 upon contact with methanol molecules. It is also noted that chelation of zinc to glycylglycinate is through carboxylic group and not the amino group. The negative ΔκS values suggest the formation of an open ring structure lowering the entropy of the solution. Due to weak interaction between solute and solvent, the molecular structure of individual molecule does not change significantly and leads to negative ΔRmE values. Finally, the results have lead to a good understanding of the thermodynamics properties of the studied liquid mixture.

Research highlights
► Excess and Deviation Properties of glycylgycine+ZnCl2 aqueous methanol solutions.
► The bridging water molecules bend the chains into stable open ring structures.
► A structure breaking effect of aqueous glycylglycine-ZnCl2 was noted.
► Chelation of zinc to glycylglycine is through carboxylic group and not amino group.