Patchy Charge Distribution Affects the pH in Protein Solutions during Dialysis.

Area of Science:

• Biophysical Chemistry
• Protein Chemistry
• Separation Science

Background:

• Dialysis and diafiltration are used for protein purification, relying on buffer pH for product stability.
• Achieving target pH in protein solutions during dialysis is challenging due to pH differences between permeate and retentate.
• Existing models neglect the impact of protein surface charge distribution on pH.

Purpose of the Study:

• To develop a computational model for understanding pH variations in protein solutions during dialysis.
• To investigate the role of patchy distribution of ionizable sites on protein surface charge and pH.
• To improve theoretical predictions for protein dialysis processes.

Main Methods:

• A simple computational model of a colloidal particle with patchy acidic sites was developed.
• Molecular simulations in the Grand-Reaction ensemble were employed.
• Systematic variation of model parameters to analyze acid-base equilibria.

Main Results:

• Interactions between ionizable sites significantly affect nanoparticle charge.
• Patchy distribution of ionizable sites contributes to pH differences between permeate and retentate.
• The effect of patchy distribution is more pronounced when sites are on smaller patches.

Conclusions:

• Protein solutions exhibit similar physics to the model system.
• Accurate prediction of pH during protein dialysis requires accounting for the patchy distribution of ionizable sites.
• This finding is essential for optimizing protein purification processes and preventing product precipitation.