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Aggregation behavior of sodium fusidate in aqueous solution
A Coello1, F Meijide, E Rodríguez Núñez
1Universidade de Santiago, Campus de Lugo, Facultade de Ciencias, Departamentos de Química Física e Física Aplicada, Spain.
Journal of Pharmaceutical Sciences
|June 1, 1994
Summary
Sodium fusidate acts as a strong electrolyte at low concentrations but self-aggregates at higher concentrations. This aggregation behavior, particularly the formation of trimers, involves specific counterion interactions and follows a leveling-off monomer concentration curve.
Area of Science:
- Physical Chemistry
- Solution Chemistry
- Colloid Science
Background:
- Sodium fusidate exhibits complex behavior in aqueous solutions.
- Understanding its aggregation is crucial for pharmaceutical applications.
Purpose of the Study:
- To analyze the aggregation behavior of sodium fusidate in aqueous solutions.
- To determine the monomer concentration and aggregation number.
- To investigate the role of counterions in aggregate stability.
Main Methods:
- Freezing point depression measurements.
- Potentiometric sodium ion (pNa) measurements.
- Hydrodynamic radii determination.
- Comparison with similar surfactant systems.
Main Results:
- Sodium fusidate behaves as a 1:1 electrolyte below 0.011 mol kg(-1).
- Self-aggregation occurs at higher concentrations, supporting a leveling-off monomer concentration hypothesis.
- Aggregation number increases from 2 to 3 below 0.08 mol kg(-1), stabilizing thereafter.
- Trimers involve one Na+ counterion, shielding carboxylate group repulsion.
Conclusions:
- The study elucidates the aggregation mechanism of sodium fusidate.
- A disklike model with specific counterion shielding is proposed for trimers.
- Formation equilibrium constants and ion transfer energetics were determined.