Evidence for covalent binding between copper ions and cyclodextrin cavity: a vibrational circular dichroism study

Vibrational absorption and circular dichroism (VCD) spectra were obtained for parent cyclodextrins, hydroxyl deuterated α-cyclodextrin, cyclodextrin–copper complexes, and for the cyclodextrin inclusion complexes with Methyl Orange, methyloxirane, 1-propanol, and substituted cyclohexanones, in the solution phase. Changes in the VCD spectra, reflecting perturbations of cyclodextrin cavity, were found in the case of an inclusion complex with Methyl Orange, but for the remaining inclusion complexes measurable changes in VCD were not found. Significant changes observed in the VCD spectra of cyclodextrin–copper complexes suggest that the covalent binding of copper ions to the hydroxyl groups of cyclodextrin is involved.