Effect of perethylation on the conformation of γ-cyclodextrin: an X-ray diffraction study

Abstract

The X-ray structure of octakis(2,3,6-tri-O-ethyl)-γ-cyclodextrin (perethylated γ-cyclodextrin (CD)), isolated as a trihydrate, is reported. It crystallises in the monoclinic space group C2 with Z = 2. As a result of perethylation, the host molecule, located on a two-fold axis, adopts a conformation that differs from those of permethylated and peracetylated γ-CDs, being divided into two identical halves connected at kink sites. A particular feature of the kink sites is their stabilisation via hydrogen bonding with included water molecules. Significant ‘self-inclusion’ of two fully extended –CH₂OCH₂CH₃ chains from the primary sides of two diad-related glucose residues occurs, leading to considerable steric congestion in the CD cavity.

Keywords:

• cyclodextrin derivatives
• alkylated cyclodextrins
• hydrates
• X-ray structure

Acknowledgements

We thank the University of Cape Town and the National Research Foundation (Pretoria) for financial support.