Preparation, Characterization and Water Solubility of Inclusion Complexes of Daidzein with Amino-modified β-Cyclodextrins

To improve the water solubility of daidzein, solid inclusion complexes of daidzein with two amino. modified beta-cyclodextrins (ACDs), i.e., mono-6-amino-6-deoxy-beta-cyclodextrin (NCD) and mono-6-ethylenediamino-6-deoxy-beta-cyclodextrin (ENCD), were prepared by the saturated solution method in water under the preparation conditions as follows: the ratio of daidzein/ACD was 3:1 and the stirring time was 72 h (83% and 67% yields, respectively). The formation of two inclusion complexes was confirmed by x-ray diffractometry (XRD) and themogravimetric (TG) analysis. The inclusion stoichiometry of the inclusion complexes was 1:1 from the Job plot and their complexation stability constants (KS) were 899.2 and 203.8 L/mol from fluorescence titration, respectively. After formation of inclusion complexes with NCD and ENCD, the water solubility of daidzein was dramatically raised from 8. 31 mu g/mL to 15. 2 and 13. 2 mg/mL at 25 degrees C, increasing by 1800-fold and 1500-fold.