Protein diffusiophoresis and salt osmotic diffusion in aqueous solutions

Area of Science:

• Physical Chemistry
• Biophysical Chemistry
• Solution Thermodynamics

Background:

• Solute diffusion can be influenced by the concentration gradients of other solutes, a phenomenon termed cross-diffusion.
• Understanding cross-diffusion in complex systems like protein-salt-water mixtures is crucial for various scientific and technological applications.

Purpose of the Study:

• To experimentally investigate and quantify cross-diffusion coefficients in a ternary lysozyme-NaCl-water system.
• To characterize protein diffusiophoresis and protein-salt interactions, providing insights into thermodynamic and transport phenomena.

Main Methods:

• Utilized Rayleigh interferometry to measure cross-diffusion coefficients in the lysozyme-NaCl-water system at 25 °C and pH 4.5.
• Analyzed experimental data to determine protein-salt interactions and protein diffusiophoresis as a function of concentration.

Main Results:

• Measured cross-diffusion coefficients related to salt osmotic diffusion and protein diffusiophoresis.
• Extracted a negative Stefan-Maxwell diffusion coefficient for protein-salt interactions, explained by protein hydration effects.
• Quantitatively examined protein diffusiophoresis, enabling accurate estimation of lysozyme electrophoretic mobility.

Conclusions:

• This study provides the first experimental characterization of protein diffusiophoresis and reports a protein-salt Stefan-Maxwell diffusion coefficient.
• Findings enhance the understanding of concentration gradient effects in protein-salt systems, relevant to mass-transfer technologies and biological transport.