Transformation of microstructure and phase of disodium guanosine 5″-monophosphate: Thermodynamic perspectives

Microstructure and phase transformation of disodium guanosine 5′-monophosphate (5′-GMPNa₂) are extremely important for controlling the process and understanding the mechanism of crystallization. In this work, the thermodynamic properties of polymorphous 5′-GMPNa₂ especially the solubility were studied, the solubility results show that 5′-GMPNa₂ is more soluble in ethanol–water (E–W) than in isopropanol–water (I–W). The amorphous form of 5′-GMPNa₂ is more soluble than the crystalline form at the same mole fraction and temperature. Meanwhile, the crystalline forms and morphologies of the residual solids were characterized by PXRD and SEM. The results indicate that solid forms of 5′-GMPNa₂ transformed spontaneously from amorphous to crystalline when the ethanol proportion is ≥ 20%. In addition, increasing the pH facilitates the dissolution of 5′-GMPNa₂ and helps to maintain the crystalline form. The associated Gibbs free energy values were calculated to verify the trend of transformation from amorphous to crystalline 5′-GMPNa₂. These results should help to guide the industrial crystallization process and to obtain the crystalline form of 5′-GMPNa₂.