The effect of buffer concentration on the dynamic/equilibrium surface tension of bovine serum albumin solution

The effect of phosphate buffer (Na₂HPO₄ and NaH₂PO₄) concentration on the dynamic and equilibrium surface tension (ST) of bovine serum albumin (BSA) solutions was examined in this study. A pendant bubble tensiometer was utilized for measuring the ST relaxation of BSA solutions in varying buffer concentration (0, 0.01–300 mM). The data showed: (i) an initial increase in buffer concentration (C_buff < 0.3 mM) resulted in a slower ST relaxation and a notable rise in the equilibrium ST; (ii) a further rise in buffer concentration (C_buff > 0.3 mM) resulted in a faster ST relaxation and a progressive decrease in the equilibrium ST; and (iii) despite an increase in BSA concentration from 2 to 15 (10⁻¹⁰ mol/cm³), the dynamic ST of BSA solutions always relaxed the slowest at C_buff = 0.3 mM. The equilibrium ST of BSA solutions in 10 and 44 mM buffer [C = 0.1–15 (10⁻¹⁰ mol/cm³)] was also obtained and the data confirmed the near-constant equilibrium ST of purely aqueous BSA solutions [Le et al., J.Mol.Liq (2022) 118305] to not be an anomalous behavior but, observable irrespective of the solvent formulation.