Investigation on a host–guest inclusion system by β-cyclodextrin derivative and its analytical application

The host–guest inclusion system of ethyl substituted β-cyclodextrin (DE-β-CD) with mangiferin (MA) was investigated by fluorescence spectra in solution. The results showed that the MA was encapsulated in the DE-β-CD’s cavity to form a 2:1 stoichiometry host–guest inclusion complex (DE-β-CD/MA) and the inclusion constant (K = 3.04 × 106 L2/mol2) was confirmed by the typical double reciprocal plots. Furthermore, several experimental conditions were optimized in order to obtain the maximum fluorescence signal. In addition, the thermodynamic parameters, Gibbs free energy (ΔG°), enthalpy change (ΔH°) and entropy change (ΔS°) of DE-β-CD/MA were obtained by the Van’t Hoff equation. A spectrofluorimetric method for the determination of MA in solution in the presence of DE-β-CD was developed based on the remarkable enhancement of the fluorescence intensity of MA. The linear range was 2.00 × 10−8–7.00 × 10−6 mol/L and the detection limit was 4.05 × 10−9 mol/L. The proposed method was successfully applied to the analysis of MA in serum with the satisfactory result.

To elucidate a plausible complex structure for the supramolecular complex, we performed the molecular modelling study. The inclusion complex was emulated by entering the guest molecule from the large face of the CD cavity of the DE-β-CD molecule by steps. Subsequently, the energy minimization was carried out for each step without any constraint. Full-geometry optimization was performed, using the molecular mechanics MM+ method followed by the semiempirical AM1 method to obtain the minimum structure.Figure optionsDownload as PowerPoint slide