Energetic analysis of the liquid–liquid equilibrium of systems containing polyethylene glycol (4000 g.mol−1 or 6000 g.mol−1) and salts (Na2SO4 or Na3C6H5O7) at different temperatures and their application in the bovine serum albumin and α-lactalbumin partitioning

Abstract

This work aims to determine the interaction parameters and the energetic analysis of the aqueous two-phase systems (ATPS) composed of polyethylene glycol (PEG 4000 g.mol−1 or PEG 6000 g.mol−1), salt (Na2SO4 or Na3C6H5O7) and water at different temperatures T = (293.2, 298.2, 303.2 and 308.2) K. Partition assays of bovine serum albumin (BSA) and α-lactalbumin in the different systems studied were also performed in order to demonstrate the application of the two-phase aqueous systems studied. The temperature had no effect on the ATPS phase equilibrium compositions while the polymer molar mass had an influence, presenting a greater biphasic region in the systems formed by PEG 6000. The systems composed by Na2SO4 showed greater biphasic region. The salting-out capacity and the effective excluded volume (EEV) of the systems were also determined. It was observed that the salting-out effect was greater in the systems composed of Na2SO4. The EEV was higher in the systems formed by PEG 6000 for both salts. In addition, the equilibrium data of the systems were thermodynamically modelled using UNIFAC model and it was found that the water-salt interaction was greater than the water-PEG interaction, thus proving the higher water concentration in the systems bottom phase. It was also verified that the UNIFAC model presented low values of the global deviations (2.970%), being considered adequate to predict the new parameters of interaction between the contribution groups of the studied systems. This study shows that the values found in thermodynamic modelling can be used to predict other systems that have these same contribution groups evaluated. It was also found that α-lactalbumin and BSA migrated preferentially to the bottom phase in most systems. It was observed lower kp in the systems formed by Na2SO4. Such behavior may be related due to the greater interaction of α-lactalbumin and BSA with the bottom phase of the system formed by Na2SO4. For the systems formed by sodium citrate, the partition coefficient for α-lactalbumin and BSA increased with the increase in the molar mass of the polymer (4000 to 6000). The salt type effect had more effect on the partition than the polymer molar mass, but both influenced.