Protein adsorption at the air–water: when the charge sign matters

Proteins adsorb from aqueous solutions to the air–water interface, and lower the interfacial tension. Due to their acidic and/or basic groups, their net charge varies with pH, depending on their isoelectric point. Coulombic effects make the adsorption process and the properties of the adsorption layer sensitive to the net charge. Upon evaporation of the protein solution, the water flow across the interface results in advection, i.e. protein transport towards the interface, which may also affect adsorption.

Neutron reflectometry and ellipsometry show that when lysozyme or ovalbumin adsorbs at the air–water interface, it is necessary to combine a positive protein net charge and the presence of advection to obtain multilayers. When these conditions are not both fulfilled, stationary monolayers are observed. We tried to simulate the experimental results using a model involving advection, which tends to accumulate protein at the interface, and diffusion, which opposes to accumulation and tend to flatten the concentration gradient. This model cannot reproduce at the same time the shape and dimensions of spatial and temporal concentration gradients.

Both a positive charge and an evaporation flux are required for the formation of multilayers at air-water interfaces

This work suggests that intermolecular interactions depending on the sign of the protein net charge should be considered to explain the properties of adsorption layers.

Collaborations

• IPR, Institute of Physics of Rennes
• LLB, Laboratoire Léon Brillouin
• TBI, Toulouse Biotechnology Institute
• Laboratoire Colloïdes et Matériaux Divisés
• Laboratoire Interdisciplinaire de Physique

Read more

Pasquier, C., Pezennec, S., Bouchoux, A., Cabane, B., Lechevalier, V., Le Floch-Fouéré, C., Paboeuf, G., Pasco, M., Dollet, B., Lee, L.-T. & Beaufils, S. (2021) Protein Transport upon Advection at the Air/Water Interface: When Charge Matters. Langmuir 37, 12278–12289. https://dx.doi.org/10.1021/acs.langmuir.1c01591. https://hal.inrae.fr/hal-03375385

Contacts

• Stéphane Pezennec