The enhancement of isoflavones water solubility by complexation with modified cyclodextrins: A spectroscopic investigation with implications in the pharmaceutical analysis

Abstract The improvement of isoflavones bioavailability by complexation with chemically modified cyclodextrins (CyDs) has been exploited to analyse the drug/macrocycle binding affinity by a conventional method with new useful measures. Genistein (Gen) and daidzein (Daidz) were investigated in aqueous medium and in presence an amount of (2-hydroxypropyl)-β-cyclodextrin (HP-β-CyD) at different host/guest molar ratios. The solubility in pure water, ∼3 × 10 −6  M for Gen and ∼10 × 10 −6  M for Daidz, was obtained by distributing the of guest molecule between water and the organic solvent. The stoichiometric ratios and stability constants describing the extent of formation of the complexes have been determined by phase-solubility UV–vis measurements and confirmed by circular dichroism data. These results have implications in the determination of the carrier's capacity for the complexation of the drug in water solution.