Polymorphism, pseudopolymorphism, and amorphism of peracetylated α-, β-, and γ-cyclodextrins

Polymorphism, pseudopolymorphism, and amorphism of hexakis(2,3,6-tri-O-acetyl)-α-cyclodextrin (TAαCyD), heptakis(2,3,6-tri-O-acetyl)-β-cyclodextrin (TAβCyD), and octakis(2,3,6-tri-O-acetyl)-γ-cyclodextrin (TAγCyD) were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powder X-ray diffractometry (XRPD), Fourier transform infrared spectroscopy (FTIR) and optical microscopy. An anhydrous and a bi-hydrate crystalline forms of TAαCyD, two monotropic anhydrous polymorphs and three pseudopolymorphs (i.e. methanolate, hydrate, and isopropanolate-hydrate) of TAβCyD, as well as two monotropic anhydrous polymorphs and isostructural pseudopolymorphs (e.g. hydrate and isopropanolate-hydrate) of TAγCyD were isolated and characterized. The amorphous forms of each TACyD were also obtained. Thermal data for desolvation of TAαCyD·2H2O and TAβCyD·CH3OH were reconciled with their crystal packing features. Melting temperatures and enthalpies of the crystalline forms of each TACyD can be referred to for possible solid-state interactions with drugs.