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A hydrogen-bonding receptor that binds cationic monosaccharides with high affinity in methanol
S I Tamaru1, M Yamamoto, S Shinkai
1Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University, Fukuoka, Japan.
Chemistry (Weinheim an Der Bergstrasse, Germany)
|February 2, 2002
Summary
This study demonstrates a novel dicarboxylate host effectively binds cationic monosaccharides in methanol through electrostatic and hydrogen-bonding interactions, forming strong noncovalent complexes for potential saccharide recognition systems.
Area of Science:
- Supramolecular Chemistry
- Host-Guest Chemistry
- Carbohydrate Recognition
Background:
- Saccharide recognition in protic solvents is challenging due to strong solvation.
- Developing selective host molecules for saccharides remains a key goal in supramolecular chemistry.
Purpose of the Study:
- To investigate the binding of cationic monosaccharides by a dicarboxylate host in methanol.
- To elucidate the binding interactions and complex formation stoichiometry.
- To explore the potential for developing saccharide recognition systems.
Main Methods:
- Circular Dichroism (CD) spectroscopy to detect complex formation and binding modes.
- Molar ratio and Job plots to determine complex stoichiometry.
- 1H NMR spectroscopy and molecular mechanics calculations to analyze binding interactions.
- Competition experiments to validate the proposed binding model.
Main Results:
- High affinity binding (K1 = 8.0 x 10(4)-2.0 x 10(5) M(-1)) of cationic monosaccharides (D-glucosamine HCl, D-galactosamine-HCl, D-mannosamine-HCl) by the dicarboxylate host in methanol.
- CD spectroscopy revealed a positive exciton-coupling band, indicating multiple point interactions and recognition.
- Complex formation is driven by electrostatic interactions between the guest's ammonium group and the host's carboxylate, with secondary hydrogen bonding.
- 1:1 pseudo-cyclic complexes form at low guest concentrations, transitioning to 1:2 acyclic complexes at higher concentrations.
- The study reports exceptionally strong saccharide complexes formed via noncovalent interactions in a protic solvent.
Conclusions:
- The dicarboxylate host effectively recognizes cationic monosaccharides in methanol, overcoming challenges associated with protic solvents.
- The binding mechanism involves a combination of electrostatic and hydrogen-bonding interactions, with defined stoichiometry.
- These findings represent a significant advancement towards designing sophisticated saccharide recognition systems for potential applications.