Studies of interionic interactions of l-serine/l-threonine in aqueous trilithium citrate solutions using density and speeds of sound measurements at different temperatures

- Apparent molar properties of amino acids + aqueous trilithium citrate are discussed.
- Positive values are observed for partial molar volumes and compressibility of transfer.
- Hydration number has been calculated.
- l-Threonine shows more interactions as compared to l-serine.
- Pair-wise interactions are dominant in the mixtures.

Densities and speeds of sound of l-serine and l-threonine in aqueous solutions of trilithium citrate have been measured at T = 288.15, 298.15, 308.15 and 318.15 K and atmospheric pressure. The apparent molar volume (Vϕ), the partial molar volume (Vϕ0) and standard partial molar volumes of transfer (ΔVϕ0) for amino acids from water to aqueous trilithium citrate have been calculated from density data. Group contributions of amino acids to partial molar volume were determined. The limiting apparent molar expansibilities have also been calculated. Partial molar isentropic compression (Kϕ,s) and partial molar isentropic compression of transfer (ΔKϕ,S0) have been calculated from speed of sound data. Hydration number (nH) has also been calculated. The pair and triplet interaction coefficients have been calculated from both the properties. The results have been explained based on competing patterns of interactions of co-solvents and the solute.