NMR Study on the Inclusion Complexes of β-Cyclodextrin with Isoflavones

The structure of the inclusion complexes of beta-cyclodextrin (beta-CD) with daidzein and daidzin in D2O were investigated using NMR spectroscopy. For the beta-CD and daidzein system, two types of 1: 1 complexes were formed with the daidzein deeply inserted into the CD cavity with different orientations. For the beta-CD/daidzin system, a 1: 1 complex was formed with the flavonoid part of daidzin entering the CD cavity from the wide rim. The inclusion complexes determined by NMR were constructed using molecular docking. Furthermore, the mixture of puerarin, daidzein and daidzin, which are the major isoflavonoid components present in Radix puerariae, was analyzed by diffusion-ordered spectroscopy (DOSY) alone and upon addition of beta-CD in order to mimic chromatographic conditions and compare their binding affinities.