Tsai, C.-C.; Zhang, W.-B.; Wang, C.-L.; Van Horn, R. M.; Graham, M. J.; Huang, J.; Chen, Y.; Guo, M.; Cheng, S. Z. D.* Evidence of formation of site-selective inclusion complexation between β-cyclodextrin and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) copolymers. J. Chem. Phys. 2010, 132, 204903/1-204903/9. [Link] [PDF]
 

 

Abstract
A series of inclusion complexes of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) with β-cyclodextrin (β-CD) was prepared. Their formation, structure, and dynamics were investigated by solution two-dimensional rotating-frame Overhauser effect spectroscopy (2D ROESY) and one-dimensional (1D) and 2D solid-state C13C13NMR. The inclusion complexes between the PEO-b-PPO-b-PEO copolymers and the ββ-CDs were formed in aqueous solution and detected by 2D ROESY. The high efficiency of cross polarization and spin diffusion experiments in C13C13 solid-state NMR showed that the mobility of the PPO blocks dramatically decreases after β-CD complexation, indicating that they are selectively incorporated onto the PPO blocks. The hydrophobic cavities of β-CD restrict the PPO block mobility, which is evidence of the formation of inclusion complexes in the solid state. The 2D wide-line separation NMR experiments suggested that β-CDs only thread onto the PPO blocks while forming the inclusion complexes. The stoichiometry of inclusion complexes was studied using H1H1NMR, and a 3:1 (PO unit to β-CD) was found for all inclusion complexes, which indicated that the number of threaded β-CDs was only dependent on the molecular weight of the PPO blocks. 1D wide angle x-ray diffraction studies demonstrated that the β-CD in the inclusion complex formed a channel-like structure that is different from the pure β-CD crystal structure.