Viscosity Analysis of High Concentration Bovine Serum Albumin Aqueous Solutions

ABSTRACTPurposeTo understand the apparent inconsistency between the dilute and high concentration viscosity behavior of bovine serum albumin (BSA).MethodZeta potential and molecular charge on BSA were determined from Electrophoretic mobility measurements. Second virial coefficient (B22) and interaction parameter (kD) obtained from static and dynamic light scattering, respectively, quantified intermolecular interactions. Rheology studies characterized viscoelasticity at high concentration. The dipole moment was calculated using Takashima’s approximation for proton fluctuations over charged residues.ResultsThe effective isoelectric point of BSA was pH 4.95. In dilute solutions (≤ 40 mg/ml), the viscosity was minimal at the pI; at high concentrations, pH 5.0 solutions were most viscous. B22 and kD showed intermolecular attractions at pH 5.0; repulsions dominated at other pHs. The attractive interactions led to a high storage modulus (G′) at pH 5.0.ConclusionIn dilute solutions, the electroviscous effect due to net charge governs the viscosity behavior; at high concentrations, the solution viscosity cannot be justified based on a single parameter. The net interplay of all intermolecular forces dictates viscosity behavior, wherein intermolecular attraction leads to a higher solution viscosity.