Electron microscopic observations of inclusion complexes of α-, β-, and γ-cyclodextrins

Inclusion complexes of α-, β-, and γ-cyclodextrins (α-, β-, and γ-CyDs) were prepared with poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), and poly(ethylene adipate) (PEA), respectively. By observing respective inclusion complexes by transmission electron microscopy, it was found that the crystalline complexes grew as follows: (1) α-CyD-PEO complexes formed a hexagonal crystal, (2) β-CyD-PPO complexes crystallized with hexagonal lateral packing of molecular columns with their axes tilted at the basal plane, and (3) γ-CyD-PEA crystallized in a tetragonal form with a super lattice with cell dimensions a=b=13.40 nm, which consisted of sub-cell with cell dimensions a′=b′=1.657 nm. No diffuse scattering was observed in the electron diffraction pattern of complexes of α-CyD-PEO and β-CyD-PPO, because disordering of guest molecules within host channels gave no diffuse scattering as long as host molecules were arrayed in an ordered way. γ-CyD-PEA complexes gave characteristic streaky diffuse scattering along a^* and b^*. Stacking faults occurred in γ-CyD-PEA complexes.