Desolvation kinetics of sulfameter solvates

Area of Science:

• Solid-state chemistry
• Pharmaceutical sciences
• Crystallography

Background:

• Solvates are common in pharmaceutical solids, and their physical stability is crucial for drug formulation.
• Understanding solvate stability informs the development of effective and stable pharmaceutical products.

Purpose of the Study:

• To investigate the solid-state stability of five structurally related sulfameter (5-methoxysulfadiazine) solvates.
• To analyze the kinetics of the desolvation reaction using thermogravimetric analysis (TGA).

Main Methods:

• Thermogravimetric analysis (TGA) was employed for both isothermal and nonisothermal desolvation kinetic studies.
• Isothermal analysis used conventional model-fitting, while nonisothermal analysis utilized a complementary method.
• Kinetic parameters (model, pre-exponential factor A, and activation energy E(a)) were calculated and compared.

Main Results:

• A direct relationship was found between desolvation activation energy (from isothermal data) and solvent molecule size; larger solvents exhibited higher activation energies.
• The best-fitting solid-state reaction model correlated with single crystal structural features, specifically solvent molecules occupying unit cell cavities.
• Significant discrepancies were observed in kinetic parameters obtained from isothermal versus nonisothermal methods.

Conclusions:

• The crystal structure and solvent size significantly influence the solid-state stability and desolvation kinetics of sulfameter solvates.
• Kinetic parameters derived from isothermal desolvation studies cannot be directly extrapolated to nonisothermal conditions, and vice versa.