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Neutron diffraction of alpha, beta and gamma cyclodextrins: hydrogen bonding patterns.
B Hingerty1, B Klar, G L Hardgrove
1Health and Safety Research Division, Oak Ridge National Laboratory, TN 37831.
Journal of Biomolecular Structure & Dynamics
|August 1, 1984
Summary
Cyclodextrins, enzyme models, exhibit complex hydrogen bonding. Neutron diffraction reveals their dynamic structures and catalytic mechanisms, offering insights into molecular interactions.
Area of Science:
- Supramolecular Chemistry
- Biophysical Chemistry
- Crystallography
Background:
- Cyclodextrins (CDs) are torus-shaped glucose polymers acting as enzyme models.
- Their unique geometry facilitates host-guest complex formation and catalytic activity.
- CDs catalyze various reactions, including hydrolysis and aromatic substitutions, with rate enhancements up to 400-fold.
Purpose of the Study:
- To elucidate hydrogen bonding in cyclodextrins using neutron diffraction.
- To understand the structural basis of CD catalytic activity and complex formation.
- To investigate the dynamic nature of hydrogen bonds in crystalline CD systems.
Main Methods:
- Neutron diffraction data collection and analysis.
- X-ray diffraction comparison for hydrogen atom positioning.
- Structural characterization of alpha-, beta-, and gamma-cyclodextrins.
Main Results:
- Neutron diffraction unambiguously determined hydrogen atom positions, crucial for understanding hydrogen bonding.
- Alpha-cyclodextrin exhibits two distinct structures ('tense' and 'relaxed') with an 'induced-fit' complexation mechanism.
- Beta- and gamma-cyclodextrins display disordered water structures with unique flip-flop hydrogen bonding (O-H...H-O).
Conclusions:
- Hydrogen bonds are critical in cyclodextrin structure and function.
- Cyclodextrins serve as valuable models for studying enzyme-like catalytic mechanisms.
- Dynamic hydrogen bonding occurs even in the solid state, influencing molecular interactions.