Abstract
Effect of sodium tetraborate (borax, Na_2B_4O_7) on the thermal properties and protein secondary structure of a freeze-dried pharmaceutical formulation model was studied. Addition of sodium tetraborate raised frozen solution T_g' (glass transition temperature of maximally freeze-concentrated solutes) and freeze-dried solid T_g (glass transition temperature) of bovine serum albumin and disaccharide (sucrose, trehalose) combinations, indicating borate-saccharide complex formation. Sodium tetraborate reduced structure-stabilizing effect of sucrose and trehalose against lyophilization-induced structural perturbation to some extent. The borate-saccharide complex should improve protein storage stability in dispense of decreased structure-stabilization during the freeze-drying process.
