How Does Solvation Affect the Binding of Hydrophilic Amino Saccharides to Cucurbit[7]uril with Exceptional Anomeric Selectivity?

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Cucurbit[7]uril (CB[7]) is known to bind strongly to hydrophilic amino saccharide guests with exceptional -anomer selectivities under aqueous conditions. Single-crystal X-ray crystallography and computational methods were used to elucidate the reason behind this interesting phenomenon. The crystal structures of protonated galactosamine (GalN) and glucosamine (GluN) complexes confirm the inclusion of anomers inside CB[7] and disclose the details of the host-guest binding. Whereas computed gas-phase structures agree with these crystal structures, gas-phase binding free energies show preferences for the -anomer complexes over their counterparts, in striking contrast to the experimental results under aqueous conditions. However, when the solvation effect is considered, the binding structures drastically change and the preference for the anomers is recovered. The anomers also tend to bind more tightly and leave less space in the CB[7] cavity toward inclusion of only one water molecule, whereas loosely bound anomers leave more space toward accommodating two water molecules, with markedly different hydrogen-bonding natures. Surprisingly, entropy seems to contribute significantly to both anomeric discrimination and binding. This suggests that of all the driving factors for the strong complexation of the hydrophilic amino saccharide guests, water mediation plays a crucial role in the anomer discrimination.
Publisher
WILEY-V C H VERLAG GMBH
Issue Date
2016-10
Language
English
Article Type
Article
Keywords

HIGH-ENERGY WATER; HAMILTONIAN REPLICA-EXCHANGE; HIGH-AFFINITY BINDING; GAS-PHASE; SYNTHETIC RECEPTORS; ATOMIC CHARGES; CARBOHYDRATE-RECOGNITION; SUPRAMOLECULAR CHEMISTRY; NONCOVALENT INTERACTIONS; CUCURBITURIL HOMOLOGS

Citation

CHEMISTRY-A EUROPEAN JOURNAL, v.22, no.44, pp.15791 - 15799

ISSN
0947-6539
DOI
10.1002/chem.201602810
URI
http://hdl.handle.net/10203/225355
Appears in Collection
CH-Journal Papers(저널논문)
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