Kinetics of solid state stability of glycine derivatives as a model for peptides using differential scanning calorimetry.

Kinetics of solid state stability of seven derivatives of 3,5-disubstituted tetrahydro-2H-1,3,5-thiadiazine-2-thione (THTT) of glycine as a model for amino acids and peptide drugs were studied using differential scanning calorimetry (DSC). Each DSC curve for each derivative showed an endothermic peak followed by an exothermic one, which could be attributed to the melting and decomposition, respectively. The decomposition activation energy of each derivative was calculated using the Augis and Bennet, Kissinger equations and Mahadevan approximation. Also, the melting activation energies as well as the thermodynamic parameter (enthalpy) for the investigated derivatives were evaluated. The relative stability of the derivatives in the solid state according to the calculated values of the decomposition activation energy, frequency factors and half-life for each derivative could be determined.