Interaction between lysozyme and humic acid in layer-by-layer assemblies: effects of pH and ionic strength

Area of Science:

• Environmental Chemistry
• Biomolecular Interactions
• Materials Science

Background:

• Understanding protein-organic matter interactions is crucial for environmental processes and biomaterial development.
• Lysozyme (LSZ) and humic acids (PAHA) are model compounds representing proteins and soluble organic matter.

Purpose of the Study:

• To investigate the layer-by-layer assembly of LSZ and PAHA in both solid-surface (2-D) and solution (3-D) systems.
• To elucidate the influence of pH and ionic strength on the stability, composition, and interactions within these assemblies.

Main Methods:

• Layer-by-layer assembly technique applied to a silica surface and in solution.
• Alternating adsorption of LSZ and PAHA solutions.
• Analysis of adsorbed amounts, mass ratios, and K+ incorporation under varying pH and ionic strength (KCl concentration).

Main Results:

• At pH 5, LSZ-PAHA layers are stable, with adsorption decreasing as ionic strength increases.
• Higher pH (6-8) and moderate ionic strength lead to LSZ solubilization and complex desorption, influenced by PAHA's charge.
• High ionic strength (400 mmol L(-1) KCl) screens electrostatic interactions, preventing layer erosion.
• In solution, the PAHA/LSZ mass ratio depends on the order of addition, affecting complex formation and charge neutralization.

Conclusions:

• The assembly of LSZ and PAHA is highly sensitive to solution conditions, particularly pH and ionic strength.
• Electrostatic interactions govern the stability and composition of LSZ-PAHA assemblies, with potential for complex solubilization and desorption.
• The findings provide insights into protein-humic substance interactions relevant to environmental and material science applications.