Effect of l-serine and l-threonine on volumetric and acoustic behaviour of aqueous metformin hydrochloride solutions at T = (305.15, 310.15 and 315.15) K

• Densities and speeds of sound of amino acids in aqueous metformin hydrochloride.
• Transfer volume decrease with the increase in size of alkyl side chain of amino acids.
• (Ion + hydrophilic) and (hydrophilic + hydrophilic) interactions are present.
• Pair-wise interactions are dominant in the mixtures.

The interactions of l-serine and l-threonine with drug metformin hydrochloride (Metformin-HCl) as a function of temperature have been investigated by combination of volumetric and acoustic methods. Densities and speeds of sound of l-serine and l-threonine in (0.00, 0.03, 0.045, 0.06 and 0.09) mol · kg−1 aqueous solutions of Metformin-HCl have been measured at T = (305.15, 310.15 and 315.15) K and experimental pressure p = 0.1 MPa. The apparent molar volume VϕVϕ, the partial molar volume Vϕ°Vϕ° and standard partial molar volumes of transfer ΔVϕ°ΔVϕ° for l-serine and l-threonine from water to aqueous Metformin-HCl solutions have been calculated from density data. Partial molar isentropic compression Kϕ,sKϕ,s and partial molar isentropic compression of transfer ΔKϕ,s°ΔKϕ,s° have been calculated from speed of sound data. The pair and triplet interaction coefficient have also been calculated. The results have been explained based on competing patterns of interactions of co-solvents and the solute.