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The molar volume and compressibility of (glycylglycine + CuCl2) in aqueous ethanol mixtures have been obtained at four different temperatures T = (288.15 to 318.15) K from ultrasonic velocity and density measurements. Excess molar volumes were found to be negative throughout the composition range indicating notable changes in hydrogen bonding and electrostatic interactions. Using the Prigogine–Flory–Patterson theory, quantitative estimation of different contributions, i.e. interactional, free volume, and P∗ effect to VE have been obtained. The molar isentropic compressibility has been computed using the ultrasonic velocity and excess volume data. The trends in κ S E are affected by the size of the molecule leading to negative contributions. In order to compare the theoretical values of ultrasonic velocity, the equations of Nomoto and Junjie were used and found to predict the experimental data very well.

The excess molar volumes ( V E ), viscosity deviations (Δ η ), deviations in isentropic compressibility (Δ κ S ) and excess molar refractivity (Δ R m E ) for {(glycylglycine + ZnCl 2 ) 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 V E values. The positive Δ η values indicate a structure breaking effect of aqueous glycylglycine–ZnCl 2 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 Δ κ S 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 Δ R m E values. Finally, the results have lead to a good understanding of the thermodynamics properties of the studied liquid mixture.

Ultrasonic velocity ( u ), density ( ρ ), and viscosity ( η ) have been measured for glycylglycine and CoCl 2 in aqueous and aqueous ethanol systems at T = (288.15 to 318.15) K. Using the experimental values, the adiabatic compressibility ( κ s ), molar hydration number ( n H ), apparent molar compressibility ( K S Φ ), apparent molar volume ( V Φ ), limiting apparent molar compressibility ( K S ϕ 0 ), limiting apparent molar volume ( V ϕ 0 ), their constants ( S K , S V ), viscosity coefficients of A and B parameters of Jones–Dole equation, relative viscosity ( η r ), and excess Gibbs free energy of activation ( ΔG ∗E Δ G ∗ E ) were calculated and the results of all these parameters have been discussed in terms of solute–solvent and solute–solute interactions.