Inclusion Complexes of Daidzein with Cyclodextrin-Based Metal–Organic Framework-1 Enhance Its Solubility and Antioxidant Capacity

Daidzein, an aglycone-type isoflavone, is useful in the prevention of atherosclerotic cardiovascular diseases. However, the solubility of daidzein remains relatively low even with pharmaceutical interventions (e.g., γ-cyclodextrin inclusion complex). In the present study, daidzein-cyclodextrin-metal organic framework solid dispersion complexes were prepared by the solvent evaporation method. The physicochemical properties of the complex and its effect on the solubility of daidzein were evaluated. The enhancement effect of a cyclodextrin-metal organic framework on the antioxidant properties of daidzein was verified using a diphenyl-picrylhydrazyl radical scavenging test. Powder X-ray diffraction results showed that the characteristic diffraction peaks of daidzein and cyclodextrin-metal organic framework disappeared and new peaks (2θ = 7.1°, 16.5°) were observed. FT-IR measurements showed that the peak derived from the carbonyl group of daidzein shifted to the lower wavenumber. NOESY 1H-1H NMR showed cross peaks at the proton on the resorcinol side of daidzein and the proton (H-5, H-6) in a cyclodextrin-metal organic framework. Dissolution rate of daidzein at 5 min in distilled water was 0.06% for daidzein alone while the daidzein inclusion complex was about 100%. When fasted state simulated intestinal fluid was used, the dissolution rate of the daidzein complex was about 71% compared with that of daidzein alone (~ 3.0%) at 5 min. The daidzein inclusion complex improved the antioxidant capacity to ~ 1.3 times (17.8 µg/mL) compared to the IC50 of daidzein alone (22.9 µg/mL). Preparations of cyclodextrin-metal organic framework inclusion complexes will be a platform in developing pharmaceutical formulations to enhance the bioavailability and activity of drugs.