Preparation, characterization and molecular modeling studies of the inclusion complex of Caffeine with Beta-cyclodextrin

The formation through supramolecular interaction of a host guest inclusion complex of caffeine (CA) with nano-hydrophobic cavity beta-cyclodextrin (beta-CD) is achieved by a physical mixture, a kneading method and a co-precipitation method. The formation of the inclusion complex of CA with beta-CD in solution state is confirmed by UV-visible spectrophotometer, fluorescence spectrophotometer and time-resolved fluorescence spectrophotometer. The stoichiometry of the inclusion complex is 1:1; the imidazole ring and pyrimidine ring of caffeine is deeply entrapped in the beta-cyclodextrin as confirmed by spectral shifts. The Benesi-Hildebrand plot is used to calculate the binding constant of the inclusion complex of CA with beta-CD at room temperature. The Gibbs free energy change of the inclusion complex process is calculated and the process is found to be spontaneous. The thermal stability of the inclusion complex of CA with beta-CD is analyzed using differential scanning calorimetry. The crystal structure modification of a solid inclusion complex is confirmed by scanning electron microscopy image analysis. The formation of the inclusion complex of CA with beta-CD in the solid phase is also confirmed by FT-IR and XRD. The formation of the inclusion complex between CA and beta-CD, as confirmed by molecular docking studies, is in good relationship with the results obtained through different experimental methods. (C) 2015 Published by Elsevier B.V.