Regulation of Surface Charge by Biological Osmolytes

Area of Science:

• Biophysics
• Surface Chemistry
• Molecular Interactions

Background:

• Osmolytes are vital for protein stability and function, interacting with cellular salts and protons through incompletely understood mechanisms.
• Understanding osmolyte-surface interactions is key to explaining cellular responses to environmental changes.

Purpose of the Study:

• To investigate the impact of biological osmolytes (urea and glycerol) on the surface charge of silica, a model protic surface.
• To elucidate the mechanism by which neutral osmolytes influence surface charge and interfacial properties.

Main Methods:

• Utilized ultrahigh-resolution frequency modulation-atomic force microscopy (FM-AFM) to measure silica surface charge.
• Measured interfacial liquid viscosity to assess osmolyte accumulation/depletion near the surface.
• Applied the Gouy-Chapman-Stern model for quantitative analysis.

Main Results:

• Urea (protein destabilizer) increased silica surface charge by over 50% (pH equivalent +4), with significant surface accumulation.
• Glycerol (protein stabilizer) nearly neutralized silica surface charge (pH equivalent -2), with surface depletion.
• Observed surface charge modifications were four times larger than predicted by dielectric constant changes alone.

Conclusions:

• Osmolyte effects on surface reaction constants (silanol deprotonation, cation binding) primarily govern surface charging.
• Neutral osmolytes exert a substantial influence on surface charge and Coulombic interactions.
• Findings challenge existing models and highlight the significant role of osmolytes in biological interfacial phenomena.