Inclusion complexes of melatonin and randomly methylated beta-cyclodextrin: spectroscopic study

In this research host-guest complex formation of melatonin (MT) with randomly methylated I3-cyclodextrin (RMI3CD) in aqueous solutions and in solid state has been investigated by differential scanning calorimetry, Fourier transform infrared spectroscopy analysis, fluorescence and ultraviolet-visible absorption spectroscopy and phase solubility measurements. The phase solubility data indicate a linear increase in the solubility of MT with RMPCD pointing to the Higuchi's AL-type phase solubility profile. According to the continuous variation Job's method applied to spectroscopy measurements, a 1:1 stoichiometry has been proposed for the complex formed. Stability constants for the RMPCD/MT inclusion complexes have been calculated by fluorescence spectroscopy using the Benesi-Hildebrand method, while the thermodynamic parameters have been estimated using the Van't Hoff equation. The data obtained indicate that the binding process of RMPCD with MT is exothermic and enthalpy-driven. The superiority of the RMI3CD/MT inclusion complex in photostability has been revealed.