The challenge of flavonoid/cyclodextrin complexation in a complex matrix of the quercetin, luteolin, and 3-O-methylquercetin

The complexation of herbal constituents with cyclodextrin has been a useful tool to improve their aqueous solubility. However, the simultaneous complexation of these compounds still lacks detailed studies. The present study investigated the multicomplexation of quercetin (QCT), luteolin (LUT), and 3-O-methylquercetin (3OMQ) with (2-hydroxypropyl)-beta-cyclodextrin (HP beta CD), when they are simultaneously contained in a flavonoid-enriched fraction (FEF) of Achyrocline satureioides. The phase-solubility diagram revealed a linear correlation between the flavonoids solubility and the HP beta CD concentration, demonstrating the formation of complexes with a 1:1 stoichiometric ratio, which was confirmed by ESI-MS. Negative Delta G(0) values indicated that complexation was spontaneous. Flavonoids/HP beta CD interactions were evidenced by FT-IR, DSC, SEM, and 1D and 2D NMR. The last one showed the formation of inclusion complexes by insertion of the B-ring of the flavonoids into the cavity of HP beta CD. Unexpectedly, the FEF/HP beta CD complex showed a radical scavenger potential lower than the FEF. The HPLC analysis revealed that the complex contained different flavonoid ratio than the fraction. Thus, the antioxidant capacity of the samples was demonstrated to be related to the ratio among the flavonoids, rather than to the total flavonoids. These new findings are very useful for developing herbal cyclodextrin-based products from A. satureioides or other herbal products.

Automated summary

This study investigated the multicomplexation of flavonoids with cyclodextrin and confirmed the formation of complexes with a 1:1 stoichiometric ratio. The research also found that the complex exhibited lower antioxidant capacity compared to the non-complexed flavonoids, and the flavonoid ratio in the complex was different from the original fraction. These findings are valuable for the development of cyclodextrin-based herbal products.