Structural characterization of inclusion complexes between cyanidin-3-O-glucoside and β-cyclodextrin.

Inclusion complex formation between the multiple equilibrium forms of cyanidin-3-O-glucoside (cy3glc) and β-cyclodextrin (β-CD) was investigated using a combined approach of NMR spectroscopy and Molecular Dynamics simulation. Diffusion ordered NMR spectroscopy (DOSY) and study of nuclear Overhauser effects (NOE) were used to determine the selective intermolecular interactions and structure of these complexes in aqueous solution. The observed chemical shift displacements of resonance signals of protons from the interior of β-CD cavity and protons belonging to the hemiketal (B) and cis-chalcone forms (Cc), the diffusion measurements using DOSY and the NOE studies have anticipated the formation of an inclusion complex between these two forms and β-CD. The analysis of the NMR spectral data has shown no evidence of internal interaction between β-CD and the flavylium cation (AH(+)) or trans-chalcone (Ct) forms of cy3glc. The hemiketal formed a 1:1 inclusion complex with β-cyclodextrin in which the pyranic C ring is deeply included inside the β-CD cavity while B ring lies on the plane of the wider rim of β-CD. The structure of the complexes was also clarified through a theoretical approach by Molecular Dynamics simulation.