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Crystal form III of beta-cyclodextrin-ethanol inclusion complex: layer-type structure with dimeric motif
Thammarat Aree1, Narongsak Chaichit
1Department of Chemistry, Faculty of Science, Chulalongkorn University, Phyathai Road, Pathumwan, Bangkok 10330, Thailand. thammarat.aree@gmail.com
Carbohydrate Research
|May 21, 2008
Summary
The crystal structure of beta-cyclodextrin (beta-CD)-ethanol complex (form III) reveals a unique triclinic arrangement. Beta-CD dimers encapsulate disordered ethanol molecules, differing from other crystal forms and influenced by acidic conditions.
Area of Science:
- Supramolecular Chemistry
- Crystallography
- Carbohydrate Chemistry
Background:
- Beta-cyclodextrin (beta-CD) is a cyclic oligosaccharide known for its ability to form inclusion complexes with various guest molecules.
- Different crystal forms of beta-CD inclusion complexes exhibit distinct structural arrangements and guest molecule orientations.
- Understanding these structural variations is crucial for controlling complex formation and properties.
Purpose of the Study:
- To elucidate the crystal structure of the beta-cyclodextrin-ethanol inclusion complex, specifically crystal form III.
- To investigate the structural characteristics of beta-CD dimers and the orientation of ethanol guest molecules within the complex.
- To compare the structural features of form III with previously reported forms (I and II) and understand the influence of pH on crystal packing.
Main Methods:
- Single-crystal X-ray diffraction analysis was performed on the beta-cyclodextrin-ethanol inclusion complex (form III).
- Unit cell constants and space group determination (triclinic, P1) were established.
- Detailed structural analysis of beta-cyclodextrin dimer conformation, guest molecule (ethanol) orientation, and hydrogen bonding interactions was conducted.
Main Results:
- Crystal form III of the beta-CD-ethanol complex crystallizes in the triclinic space group P1 with specific unit cell parameters.
- Beta-CD forms dimers with a 'round' conformation, stabilized by intramolecular hydrogen bonds.
- Two disordered ethanol molecules are located within the beta-CD dimer cavity, with distinct orientations and occupancies compared to forms I and II. Form III exhibits a layer-type packing, contrasting with the channel-type packing of form II and herringbone of form I, attributed to moderate acidic conditions.
Conclusions:
- The crystal structure of beta-CD-ethanol inclusion complex form III provides detailed insights into the arrangement of beta-CD dimers and guest molecules.
- The orientation and disorder of ethanol molecules vary significantly across different crystal forms, influenced by the surrounding environment and packing motifs.
- The observed packing modes (layer-type in form III) are linked to the self-aggregation tendencies of beta-CD under specific pH conditions, highlighting the sensitivity of crystal structure to environmental factors.
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