Molecular-Thermodynamic Modeling of Mixed Cationic/Anionic Vesicles.

Area of Science:

• Physical Chemistry
• Colloid and Surface Science
• Materials Science

Background:

• Vesicles serve as model cells and are utilized as drug carriers and encapsulating devices.
• Understanding vesicle formation is crucial for their practical applications in various industries.

Purpose of the Study:

• To develop a molecular-thermodynamic theory for predicting the formation and properties of two-component mixed vesicles.
• To elucidate the mechanisms of stabilization in mixed cationic/anionic vesicular systems.
• To investigate the influence of surfactant molecular structure and solution conditions on vesicle characteristics.

Main Methods:

• Calculated the free energy of vesiculation by modeling surfactant-tail packing, headgroup steric repulsions, and electrostatic interactions.
• Employed a mean-field approach for tail conformations and the nonlinear Poisson-Boltzmann equation for charged vesicles.
• Accounted for curvature corrections to interfacial tensions and steric repulsion surfaces.

Main Results:

• The theory accurately predicts vesicle size distribution, surface potentials, and leaflet compositions.
• Demonstrated entropic stabilization in mixed cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) vesicles.
• Predicted a mean vesicle radius of 1200 Å and an outer surface potential of -72 mV for a specific CTAB/SOS mixture, aligning with experimental data.

Conclusions:

• The developed theory provides a fundamental understanding of vesicle formation and stabilization mechanisms.
• It enables prediction of vesicle properties based solely on surfactant molecular structures and solution conditions.
• The theory successfully explains the behavior of mixed cationic/anionic vesicles, including the effect of added salt.