Structural and physicochemical characterization of the inclusion complexes of cyclomaltooligosaccharides (cyclodextrins) with melatonin Original Research Article

The stoichiometry, geometry, stability, and solubility of the inclusion complexes of melatonin (MLT) with native cyclomaltooligosaccharides (α-, β- or γ-cyclodextrins, CDs) are determined experimentally by high-resolution NMR spectroscopy, calorimetric and solubility measurements, and mass spectrometry. The observed differences are discussed in terms of molecular recognition expression of the host–guest (h–g) interactions within the hydrophobic CDs cavities of different size. The 1:1 h–g stoichiometry in water solution prevails at low CD concentrations; the trend to form higher order associations is observed at increasing CD concentrations. The stability order β-CD>γ-CD>α-CD for the complexes in water solution and β-CD>α-CD>γ-CD for the protonated or alkali-cationated complexes in the gas phase are rationalized on the grounds of the structural data from NMR spectroscopy and of the thermodynamic parameters from calorimetric measurements.