Inclusion complexes of chain molecules with cycloamyloses -: III.: Molecular dynamics simulations of polyrotaxanes formed by poly(propyleneglycol) and β-cyclodextrins

Molecular dynamics simulations were performed in vacuo on "channel type" polyrotaxanes composed of beta-cyclodextrins (beta CDs) threaded onto isotactic and syndiotactic poly(propylene glycol) (PPG). In the most stable complex, the beta CDs form a close-packed structure from one end of the PPG chain to the other. Non-bonded van der Waals interactions between beta CD and PPG are the main source of stabilization of the complex. Head-to-head and rail-to-tail orientation of successive beta CDs in the complex is more favorable than a head-to-tail orientation, due to intermolecular hydrogen bonding between head-to-head beta CD units. beta CDs in polyrotaxanes adopt a more rigid and symmetrical macroring conformation than does an isolated beta CD. Formation of the polyrotaxane is accompanied by an increase in the number of trans stales at the bonds in the backbone of PPG. For this reason, the PPG chain in the polyrotaxane is much more extended than the unperturbed chain.