Formation, Structure and Thermal Degradation of the Supramolecular Complex between <em>&beta;</em>-Cyclodextrin and 18-Crown-6

Abstract

The formation of a 1:1 supramolecular complex between β-cyclodextrin (β-CD) and 18crown-6 (18C6) by simply mixing them was confirmed by elemental analysis, 1 H nuclear magnetic resonance (1 H NMR) and electrospray ionization mass spectrometry. The probable interaction sites between these species were determined by two-dimensional rotating frame nuclear Overhauser effect spectroscopy (ROESY), which showed that 18C6 tended to be located on the narrow end of the cavity of β-CD. Also, the degradation process including the degree of degradation and the degradation products of the complex was carefully compared with those of β-CD and 18C6 through thermogravimetric analysis and gas chromatography coupled to time-of-flight mass spectrometry. The experimental data indicated that the presence of 18C6 resulted in an earlier degradation of β-CD. Furthermore, the relative abundance of larger fragments from the degradation process of the two components was reduced drastically because of an intermolecular interaction. These results strongly indicate that a supramolecular complex can be constructed using the flexible macrocyclic molecule 18C6 as a guest and the rigid macrocyclic molecule β-CD as the host via molecular assembly between them.