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Specific cation adsorption on protein-covered particles and its influence on colloidal stability
J A. Molina-Bolívar1, F Galisteo-González, R Hidalgo-Alvarez
1Departamento de Física Aplicada II, Escuela Politécnica, Universidad de Málaga, Campus de El Ejido, 29013, Málaga, Spain
Colloids and Surfaces. B, Biointerfaces
|May 30, 2001
Summary
Protein-coated particles show unexpected stability in high salt solutions, defying DLVO theory. This is explained by a hydration force from cation adsorption, particularly Ca(2+), which reverses zeta-potential and enhances colloidal stability.
Area of Science:
- Colloid and Surface Science
- Physical Chemistry
- Biophysical Chemistry
Background:
- Classical DLVO theory predicts protein-coated particle aggregation at high ionic strength.
- Observed anomalous colloidal stability deviates from DLVO predictions above a critical electrolyte concentration.
Purpose of the Study:
- To investigate the mechanism behind anomalous colloidal stability in protein-coated particles at high ionic strength.
- To provide evidence for a short-range repulsive hydration force due to specific cation adsorption.
Main Methods:
- Measurement of electrophoretic mobilities of protein-carrying latex particles.
- Analysis of particle behavior in varying concentrations of sodium chloride and calcium chloride solutions.
- Application of Ohshima's theoretical treatment for large charged colloidal particles.
Main Results:
- Anomalous colloidal stability observed at high ionic strength, contrary to DLVO predictions.
- Specific adsorption of Ca(2+) ions on protein molecules, leading to zeta-potential sign reversal.
- Increased positive fixed-charge density on proteins due to cation adsorption, dependent on pH.
Conclusions:
- A hydration force, arising from specific hydrated cation adsorption, explains the anomalous colloidal stability.
- Cation adsorption, especially Ca(2+), significantly influences particle surface charge and colloidal behavior.
- The findings support the proposed hydration force mechanism and its role in protein-coated particle interactions.