title: How Does Solvation Affect the Binding of Hydrophilic Amino Saccharides to Cucurbit[7]uril with Exceptional Anomeric Selectivity?
abstract: Cucurbit[7]uril (CB[7]) is known to bind strongly to hydrophilic amino saccharide guests with exceptional α-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 α 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 β-anomer complexes over their α 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 α anomers is recovered. The α 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 β 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.
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.
authors.forename: Jianping
authors.initials: J
authors.lastname: Wang
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.|Department of Chemistry, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.
authors.forename: Yoonjung
authors.initials: Y
authors.lastname: Jang
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.
authors.forename: Jayshree K
authors.initials: JK
authors.lastname: Khedkar
authors.affiliation: Division of Advanced Materials Science, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.
authors.forename: Jin Young
authors.initials: JY
authors.lastname: Koo
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.
authors.forename: Yonghwi
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea.
authors.forename: Chang Jun
authors.initials: CJ
authors.lastname: Lee
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea. ymrhee@postech.ac.kr.|Department of Chemistry, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea. ymrhee@postech.ac.kr.
authors.forename: Young Min
authors.initials: YM
authors.lastname: Rhee
authors.affiliation: Center for Self-assembly and Complexity, Institute for Basic Science (IBS), 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea. kkim@postech.ac.kr.|Department of Chemistry, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea. kkim@postech.ac.kr.|Division of Advanced Materials Science, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, 37673, Republic of Korea. kkim@postech.ac.kr.
authors.forename: Kimoon
authors.initials: K
authors.lastname: Kim
keywords: anomeric selectivity; host-guest systems; molecular dynamics; solvent effects; supramolecular chemistry