Interactions of Bovine Serum Albumin Molecules in an Aqueous Sodium Sulfate Solution Determined by an Osmotic Pressure Method

Abstract

In this work, the interactions of aqueous bovine serum albumin (BSA) solutions at four pH values (4.5, 4.8, 5.4, and 7.4), and at three sodium sulfate (Na2SO4) concentrations (0.15, 0.50, and 1.00 mol·L−1), was investigated through the use of osmotic pressure measurements. The osmotic second virial coefficients of BSA were determined from the osmotic pressure data. According to the molecular thermodynamic model, as described in the literature (Moon et al. in Fluid Phase Equilib 168:229–239, 2000), the electrostatic repulsion potential, attractive dispersion potential and the ion-excluded-volume potential were calculated. The dependencies of the three potentials on the solution pH and on the ionic strength are discussed. We compared the potentials of BSA molecules in an aqueous sodium sulfate solution with the potentials in aqueous ammonium sulfate [(NH4)2SO4] and sodium chloride (NaCl) solutions. The order of the potential values in the aqueous solutions with the different salts was also discussed.