Phase equilibrium and protein partitioning in aqueous two-phase systems containing ammonium carbamate and block copolymers PEO–PPO–PEO

Abstract

The liquid–liquid equilibrium of aqueous two-phase systems formed by the PEO–PPO–PEO block copolymers F38 or F68 and ammonium carbamate and the partition of the model proteins bovine serum albmin, lysozyme, α-lactalbumin, β-lactoglobulin and γ-globulin in these systems are presented in this paper. Phase diagrams were determined at 4 °C (F38) and 25 °C (F38 and F68); systems containing F68 present a narrow two-phase region, while systems containing F38 have a suitable working region. Partition coefficients, defined as the ratio of protein concentration in the polymer-rich phase to that in the salt-rich phase, were found to vary in the range of 0.1 to 0.8 for bovine serum albumin, 0.5 to 2.0 for lysozyme, 1.0 to 2.5 for α-lactalbumin, 0.1 to 1.0 for β-lactoglobulin and 0.3 to 1.0 for γ-globulin, depending on the polymer chain-size, temperature and tie-line length. The different trends of protein partition coefficients show that high degrees of separation can be achieved, establishing the system F38 and ammonium carbamate as an alternative to be considered when planning the downstream processing of proteins.