Kinetics and thermodynamics of the inclusion of ionene-6,10 in alpha-cyclodextrin in an aqueous solution

The kinetics of the inclusion of ionene-6,10 (3b) dibromide and of its monomeric model, 1,10-bis(trimethylammonium)decane (5) diiodide, by alpha-cyclodextrin (1a) were investigated by H-1 NMR spectroscopy in an aqueous solution. The inclusion of the monomer 5 is unusually slow and shows a high activation energy, E-a = 63 kJ mol(-1), which was attributed to a high steric hindrance for the threading caused by the terminal trimethylammonium groups. Microcalorimetric titration of 5 with 1a revealed a stability constant, K-S = 1540 M-1, of the inclusion compound. Because of its high kinetic stability, 5.1a was termed a rotaxane. The inclusion of the ionene polymer by cr-cyclodextrin takes days, months, or even years depending on the temperature. The kinetics could be described quantitatively by a Monte Carlo type of computer simulation of a consecutive hopping process of the rings along the polymer chain. The rate constants and activation energies for the polymer 3b were found to be similar to those for the monomer 5. A very high occupation of the polymer 3b (95% of the repeat units) was reached by the thermally induced threading of la. The resulting supramolecular structure of one polymer chain and about 65 rings was termed a polyrotaxane, as it can be isolated by GPC or dialysis.