Solvation behavior of dipeptides of alanine in aqueous solutions of antibacterial drug ampicillin at different temperatures

The interactions of L-Alanyl-L-alanine (Ala-Ala), L-Alanyl-L-valine (Ala-Val), L-Alanyl-L-leucine (Ala-Leu) with drug ampicillin (AMP) as a function of temperature have been investigated by combination of volumetric and acoustic methods. Densities and speeds of sound of dipeptides of alanine in aqueous solutions of ampicillin have been measured at T = (305.15, 310.15 and 315.15) K and atmospheric pressure. The apparent molar volume (Vϕ), the partial molar volume (Vϕ0) and standard partial molar volumes of transfer (ΔVϕ0) for glycine and its dipeptides from water to aqueous ampicillin solutions have been calculated from density data. Partial molar adiabatic compressibility (κϕ,s) and partial molar adiabatic compressibility of transfer image have been calculated from speed of sound data. The pair and triplet interaction coefficient have been calculated from both the properties. The results have been explained based on competing patterns of interactions of co-solvents and the solute.