Phase Behavior of Aqueous Solutions of Bovine Serum Albumin in the Presence of Dextran, at Rest, and under Shear

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Abstract
The demixing conditions for aqueous solutions of bovine serum albumin (BSA, fraction V) and for joint solutions of BSA plus dextran (DEX, Mw = 2000 kg/mol) were determined by turbidimetric measurements as a function of composition, temperature, and shear rate. Aqueous solutions of BSA phase separate upon heating. Within the region of BSA concentrations between 0.05 and 32 wt %, the demixing temperature, T1, falls from ca. 65 °C to an almost constant value of 45 °C. Adding DEX to the BSA solutions reduces the homogeneous region of the mixture drastically where the amount of DEX required to lower T1 to 25 °C decreases rapidly as the concentration of BSA is raised. Experiments concerning the influences of shear have been performed for the ternary system up to 500 s-1. They demonstrate that the content of dextran determines the sign of the effect. At low DEX concentrations, the mechanical field favors the homogeneous state (shear-induced mixing), whereas the opposite effect (shear-induced demixing) is observed at high DEX concentrations. Possible reasons for this observation are discussed.

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