Applications of Powder X-Ray Diffraction to Inclusion Complexes of Cyclodextrins

In the past three decades, powder X-ray diffraction (PXRD) analysis was widely used in the characterization of cyclodextrins (CDs) and their inclusion complexes. In this paper, representative PXRD spectra of all kinds of CD complexes reported in these years were reviewed. First of all, after comparing XRD spectra of CD hydrates, we found that some of water molecules crystallized in a crystal form played an important role in constructing a three-dimension structure. Next, differences and similarities in PXRD spectra of the inclusion complexes formed by CDs with organic compounds, polymers and transition metal coordination compounds were evaluated systematically. According to the results, the geometric differences in spatial structures of CD supramolecules were associated with the different intermolecular interactions due to different inclusion behaviors between CDs and guests. Finally, several influence factors for the PXRD spectra of CD complexes were summarized.