Solution structure of the inclusion complexes between cyclodextrins and dialkylamines: An NMR study

Interaction between chemically modified cyclodextrins (CDs) and benzyl(tert-butyl)amine (1), tert-butyl(methyl)amine (2) and benzyl(methyl)amine (3) has been investigated by NMR spectroscopy. The experimental results revealed that the complexation-induced shifts for the reported amines were more pronounced for the carbon atoms than for the protons. These shift variations were successfully exploited for determining the association constants with heptakis(2,6-O-dimethyl)-beta -CD, which were found to be 295, 119 and 101 M-1 for 1, 2 and 3, respectively. Features of the geometries of the amine/DM-beta -CD complexes were deduced by measuring the NOE intermolecular interactions between host and guest protons. These data made it possible to elucidate fully the nature of the amine/CD complexes and provided information complementary to that previously obtained by EPR spectroscopy on the complexation of the closely related nitroxide/CD paramagnetic complexes.