Analysis of the Statistical Thermodynamic Model for Nonlinear Binary Protein Adsorption Equilibria

Abstract

The statistical thermodynamic (ST) model was used to study nonlinear binary protein adsorption equilibria on an anion exchanger. Single-component and binary protein adsorption isotherms of bovine hemoglobin (Hb) and bovine serum albumin (BSA) on DEAE Spherodex M were determined by batch adsorption experiments in 10 mM Tris-HCl buffer containing a specific NaCl concentration (0.05, 0.10, and 0.15 M) at pH 7.40. The ST model was found to depict the effect of ionic strength on the single-component equilibria well, with model parameters depending on ionic strength. Moreover, the ST model gave acceptable fitting to the binary adsorption data with the fitted single-component model parameters, leading to the estimation of the binary ST model parameter. The effects of ionic strength on the model parameters are reasonably interpreted by the electrostatic and thermodynamic theories. The effective charge of protein in adsorption phase can be separately calculated from the two categories of the model parameters, and the values obtained from the two methods are consistent. The results demonstrate the utility of the ST model for describing nonlinear binary protein adsorption equilibria.

Single and binary adsorption of proteins on ion‐exchange adsorbent: The effectiveness of isothermal models

“…With an increase of salt concentration, both k 11 and k 22 decreased gradually due to the screening effect by co‐ions was strengthened and the electrostatic repulsion of adsorbed protein molecules became weaker. The same tendency was reported previously by Zhou et al . However, k 22 did not follow this pattern as salt concentration increased from 50 to 100 mmol/L.…”

“…Among three isothermal models, values of q BSA were underestimated by SMA model while calculated values of q BSA by ST model were higher than those by other two models. These tendencies in SMA and ST models were also found by previous researches . In order to evaluate the prediction accuracy of isothermal models, values of RSS defined in Eq.…”

“…It may be related to the structural modulation in bHb molecules induced by adsorbent surface and constituents in the buffer . The influence of the structure change of protein molecules to was also discussed previously . All the parameters in Table are used directly in multicomponent models to describe binary adsorption isotherms of BSA and bHb at different experimental conditions.…”

“…Since ion‐exchange adsorption of multicomponent proteins began to be concerned in 1980s , dozens of literature has accumulated on the subject of adsorption equilibria of multiple component proteins . There are many factors influencing ion‐exchange adsorption of multicomponent proteins.…”

“…For example, Lewus et al found that SMA model failed in quantitative description of the binary adsorption studied . Considering the interaction between different proteins in multicomponent adsorption system, Su et al developed a statistical thermodynamic (ST) model for nonlinear multicomponent protein adsorption equilibria on ion‐exchange media and analyzed nonlinear binary protein adsorption equilibria on an anion exchanger in different ionic strength conditions . Besides, Xu et al developed a model based on colloidal energetics to calculate binary adsorption, and found that colloidal model had a marked deviation in describing the adsorption of strong adsorbed protein expressed by a rectangular isotherm .…”