Supramolecular Structure of β-Cyclodextrin and Poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) Inclusion Complexes

Abstract

Supramolecular crystals were prepared via self-assembly of a series of inclusion complexes of β-cyclodextrin (β-CD) with poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-b-PPO-b-PEO) block copolymer. In this study, two PEO-b-PPO-b-PEO copolymers were used with different molecular weights for the PEO blocks. On the basis of two-dimensional (2D) wide-angle X-ray diffraction (WAXD) and selected area electron diffraction (SAED) experiments, the supramolecular crystal structure was determined to be a monoclinic lattice with a = 1.910 nm, b = 2.426 nm, c = 1.568 nm, and β = 111°f or both inclusion complex systems. Each crystal unit cell contained four inclusion complexes. The space group was identified to be C 2 symmetry based on the relationship among diffraction spot intensity and systematic extinctions. With the help of computer simulations of the supramolecular structure, the packing of inclusion complexes in the crystal lattice could be achieved. The simulated 2D WAXD fiber patterns and SAED patterns agreed well with the experimental results. Observations of the morphology in transmission electron microscopy combined with the [001] zone SAED patterns indicated that the supramolecular crystals are lozenge-shaped, bound by four (110) planes. Furthermore, the tethered PEO blocks were found to crystallize, and the c-axis of the PEO crystals was nearly parallel to the lamellar surface normal of the supramolecular crystals. The existence of PEO crystals resulted in additional proof that β-CDs are only selectively threaded onto the PPO blocks when forming the inclusion complexes. These PEO crystals acted as locks to prevent the dethreading of the β-CDs from the complexes and physically stabilized the supramolecular structure.

Self-assembly Polyrotaxanes Nanoparticles as Carriers for Anticancer Drug Methotrexate Delivery

“…Early papers have reported polyrotaxane nanoparticles as drug carriers, however, the selfassembly of polyrotaxane nanoparticles were driven by the crystallization of polyrotaxanes [12][13][14], whose compact architectures hindered the loading of anticancer drugs. In our previous work, we reported a new strategy, small π-π conjugated molecules such as coumarin derivative and cinnamic acid were immobilized on the terminal groups of PEG chains to prepare amphiphiles [15,16], α-cyclodextrins (α-CDs) were threaded in the amphiphiles and the polyrotaxanes self-assembled into nanoparticles.…”

Non-covalent hydrogels of cyclodextrins and poloxamines for the controlled release of proteins

“…According to the literature, these precipitates are formed by the inclusion of the PPO blocks inside the β-CD cavities producing a polypseudorotaxane type structure (Harada, 1998) yielding self-associated structures such as nanoplatelets (Perry et al, 2011, Tsai et al, 2010.…”

Self-Assembled Supramolecular Gels of Reverse Poloxamers and Cyclodextrins

“…This can be very useful for some applications such as drug release resulting from a complete erosion of the matrix. Recently, some studies have demonstrated the self-organization of Pluronic/natural β-CD systems in crystalline domains [21][22][23][24] . These studies prove that a complex with a certain crystalline order is obtained when combining PEO-PPO-PEO block copolymers with β-CD.…”