Molecule-Ion Interaction and Its Effect on Electrostatic Interaction in the System of Copper Chloride and β-Cyclodextrin

The present work was devoted to an experimental investigation of the molecule-ion interaction between copper chloride (CuCl2) and beta-cyclodextrin (CD) and its effect on the electrostatic interaction between Cu2+ and Cl- ions. Our results gave an explicit description of the mutual effect between the interactions. First, the molecular arrangement and surface feature of beta-CD experienced a fundamental structural change after interaction with Cu2+ and Cl- ions, which was ascribed to a good separation of Cu2+ from Cl- ions in beta-CD matrix. Second, arguments based on electronic structural analysis provided a direct indication of the change in charge density distributions of Cu2+ and Cl- ions in the presence of beta-CD. Third, the actual occurrence of a second signal in the course of water release at a higher temperature suggested that the Cu2+ ions were trapped in the form of hydrates in the crystal interstice of beta-CD molecules. Fourth, comparison of the mass spectra indicated that the thermal decomposition of beta-CD in the presence of CuCl2 produced a series of interesting molecular ions: C3H2OH+, C4H3OH+, C5H4OH+, and C7H6OH+. We consider that this study is helpful in providing a new approach to the evaluation of the extent of the mutual effect between an inorganic salt and an organic molecule.