Regulation of Surface Charge by Biological Osmolytes
| Autor: | Roy Govrin, Shani Tcherner, Itai Schlesinger, Uri Sivan |
|---|---|
| Rok vydání: | 2017 |
| Předmět: |
0301 basic medicine
Cation binding Inorganic chemistry General Chemistry 010402 general chemistry Photochemistry 01 natural sciences Biochemistry Small molecule Catalysis 0104 chemical sciences 03 medical and health sciences chemistry.chemical_compound Silanol 030104 developmental biology Colloid and Surface Chemistry Deprotonation chemistry Osmolyte Glycerol Urea Surface charge |
| Zdroj: | Journal of the American Chemical Society. 139:15013-15021 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | Osmolytes, small molecules synthesized by all organisms, play a crucial role in tuning protein stability and function under variable external conditions. Despite their electrical neutrality, osmolyte action is entwined with that of cellular salts and protons in a mechanism only partially understood. To elucidate this mechanism, we utilize an ultrahigh-resolution frequency modulation-AFM for measuring the effect of two biological osmolytes, urea and glycerol, on the surface charge of silica, an archetype protic surface with a pK value similar to that of acidic amino acids. We find that addition of urea, a known protein destabilizer, enhances silica's surface charge by more than 50%, an effect equivalent to a 4-unit increase of pH. Conversely, addition of glycerol, a protein stabilizer, practically neutralizes the silica surface, an effect equivalent to 2-units' reduction of pH. Simultaneous measurements of the interfacial liquid viscosity indicate that urea accumulates extensively near the silica surface, while glycerol depletes there. Comparison between the measured surface charge and Gouy-Chapman-Stern model for the silica surface shows that the modification of surface charge is 4 times too large to be explained by the change in dielectric constant upon addition of urea or glycerol. The model hence leads to the conclusion that surface charge is chiefly governed by the effect of osmolytes on the surface reaction constants, namely, on silanol deprotonation and on cation binding. These findings highlight the unexpectedly large effect that neutral osmolytes may have on surface charging and Coulomb interactions. |
| Databáze: | OpenAIRE |
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