Inclusion Mechanism and Heat Stability of the Complex of 4'-Hydroxychalcone and Hydroxypropyl-β-Cyclodextrin

Purpose: To study the inclusion mechanism and heat stability of the complex formed between 4'- hydroxychalcone and hydroxypropyl-β-cyclodextrin (HP-β-CD)
Methods: The inclusion mechanism of the complex of 4'-hydroxychalcone and HP-β-CD was investigated by phase solubility method. The physicochemical properties of the complex were evaluated by Fourier transform infrared spectroscopy (FT-IR) and x-ray diffractometry (XRD) while the heat stability of the complex was measured by thermogravimetric/differential scanning calorimetry (TG/DSC).
Results: The stability constants of the complexes were higher than those of β-CD at all temperatures. For the formation of the complex, Gibbs energy (-16.87 KJ/mol at 20 °C) was negative, and positive entropy (31.15 KJ/mol) along with a slightly positive enthalpic change (163.89 J/mol) was also found. IR and XRD analysis showed that the physical phase of 4-hydroxylchalcone was changed and completely dispersed in HP-β-CD while TG/DSC data indicate that the starting decomposition temperature of 4'- hydroxychalcone (200 °C) was significantly enhanced to 397 °C due to the formation of inclusion complex with HP-β-CD in the solid state.
Conclusion: The stability constant of HP-β-CD for 4'-hydroxychalcone is higher than that of β-CD. The inclusion is a spontaneous process, driven by hydrophobic forces. The heat stability of 4’- hydroxychalcone is significantly enhanced by complexing with HP-β-CD.

Keywords
4'-Hydroxychalcone; Hydroxypropyl-β-cyclodextrin; Inclusion complex; Phase solubility; Thermogravimetry; Differential scanning calorimetry