Mangiferin/β-cyclodextrin complex: determination of the Inclusion constant in aqueous solution by Higuchi–Connors method and molecular absorption and photoluminescence UV spectroscopies at pH 3.4

The purpose of this paper was to determine the inclusion constant of the complex formed between mangiferin and β -cyclodextrin (βCD) at pH 3.4, by Higuchi–Connors and absorption and fluorescence spectroscopies methods, as well as to elucidate whether mangiferin molecule enters to the cavity of βCD by the glucosidic or by the xanthone end of the molecule, using computational chemistry calculations of density functional theory (DFT). The phase-solubility diagram showed that H 4 MGF was included in the cavity of βCD to form a complex with the stoichiometric ratio 1:1 (H 4 MGF/βCD) with the inclusion constant: K 1:1 = 344 ± 32 (logK 1:1 = 2.54 ± 0.04) at pH 3.4. The inclusion constant obtained using the program SQUAD by the fitting of absorption and fluorescence spectra is in good agreement with that value. Finally, the DFT calculations have shown that mangiferin molecule enters by its xanthone group—to the cavity—through the wider rim of the βCD molecule.