Polymorphism, pseudopolymorphism, and amorphism of peracetylated alpha-, beta-, and gamma-cyclodextrins

Polymorphism, pseudopolymorphism, and amorphism of hexakis(2,3,6-tri-O-acetyl)-alpha-cyclodextrin (TAalphaCyD), heptakis(2,3,6-tri-O-acetyl)-beta-cyclodextrin (TAbetaCyD), and octakis(2,3,6-tri-O-acetyl)-gamma-cyclodextrin (TAgammaCyD) 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 TAalphaCyD, two monotropic anhydrous polymorphs and three pseudopolymorphs (i.e. methanolate, hydrate, and isopropanolate-hydrate) of TAbetaCyD, as well as two monotropic anhydrous polymorphs and isostructural pseudopolymorphs (e.g. hydrate and isopropanolate-hydrate) of TAgammaCyD were isolated and characterized. The amorphous forms of each TACyD were also obtained. Thermal data for desolvation of TAalphaCyD.2H2O and TAbetaCyD.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.