Theoretical and experimental studies of the inclusion phenomena of β-cyclodextrin with organic amines

The inclusion complexations of beta-cycloclextrin (beta-CD) with ethylenediamine 1 and its three analogs, diethylenetriamine 2, triethylamine 3 and ethylene diaminetetraacetic acid 4 were examined by means of both experimental measurements and theoretical calculations. From the polarimetric method, it was found that beta-CD could form 1/1 host-guest inclusion complexes with these guests, and the formation constants (K) of the inclusion complexes have also been determined in aqueous solution at 298.2 K. Semiempirical PM3 calculations were carried out to assess the intermolecular binding, ability of beta-CD to a series of short chain aliphatic amines such as guests 1-7, cyclic aliphatic amines 8-11, and aromatic amines 12-13. The interaction processes between beta-CD and the guests were reported, and the complexation differences of beta-CD with these guests also discussed. The energy contribution from deformation energy or hydrate energy to interaction energy in the inclusion systems was found to be quite small. The stability of beta-CD inclusion complexes depended on the size fit between the host and guest. For beta-CD complexes of guests 1-4, the order of the K values from the polarimetric measurements is in good accordance with that of the absolute values of the complexation energies from PM3 calculations.