Stability and Exchange Properties of Through-ring Cyclodextrin Complexes. Effects of Chain Length in Polymethylene Bis[1-pyridinium] as Guest Molecules

On the basis of 1H NMR spectra, polymethylene bis(1-pyridinium) and α-CD were concluded to afford a rotaxane-type complex. Signals due to the originally equivalent pair of protons in the polymethylene- and pyridinium groups were split into a pair of distinct signals on the complexation. Free energy of activation for the site-exchange in the complex increased with the number of methylene groups (n = 8–12) and reached an asymptotic value (ca. 72 kJ/mol).