Phase solubility and thermoanalytical studies of the inclusion complex formation between curcumin and hydroxypropyl-β-cyclodextrin in hydroalcoholic solutions

Curcumin (CURC) is endowed with many pharmacological properties, among these anti-inflammatory, antioxidant, antimicrobial, and anticancer activity. Unfortunately, CURC is basically water-insoluble and undergoes a rapid photodegradation, chemical degradation, and metabolism. CURC stability and solubility can be improved by the complexation with cyclodextrins, which are cyclic oligosaccharides with a hydrophilic outer surface and a lipophilic cavity. Thus, in this work, the formation of the inclusion complex between the semisynthetic hydroxypropyl-β-cyclodextrin (HPβCD) and CURC has been studied by means of phase solubility, differential scanning calorimetry and isothermal calorimetry experiments to assess the formation, stoichiometry and affinity constant of the obtained inclusion complexes. The thermodynamics of the complex formation has been studied in different hydroalcoholic solutions and the experiments have been performed at physiological and acidic pH to verify the effect of the ionization state on the efficacy of complex formation. Results show the relevance in the choice of the pH, solvent, and mixing time on the formation of the inclusion complex between active drug(s) and HPβCD.