Dissolution thermodynamics and polymorphic transformation behaviors of glutathione

Glutathione (GSH) is a bioactive oligopeptide which was widely used in sports, pharmaceutical and food industry. This paper compared the properties of two crystalline forms of GSH (Form α and Form β) in thermodynamics and explored the transformation of corresponding polymorph. The solubility data of GSH were determined by using the dynamic method in binary mixed solvents (methanol + water, ethanol + water, isopropanol + water, ethylene glycol + water) at temperatures ranging from 278.15 to 313.15 K. The solubilities of the two forms both increased with the increasing of mole fraction of water and temperature. The modified Apelblat equation, the CNIBS/R-K model and the Jouyban-Acree model were used to correlate the experimental solubility. The mixing thermodynamic properties of GSH in the binary mixed solvents were calculated by Van't Hoff equation. Form β was supposed to be the stable crystalline form based on the thermodynamics analysis, which corresponded to the solvent-mediated transformation from Form α to Form β.