Concyclic CH-\u03c0 arrays for single-axis rotations of a bowl in a tube

Taisuke Matsuno,Masahiro Fujita,Hiroyuki Isobe,Kengo Fukunaga,Sota Sato

doi:10.1038/s41467-018-06270-6

Taisuke Matsuno, Masahiro Fujita + Show 3 more

Open Access

https://doi.org/10.1038/s41467-018-06270-6

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Abstract

The hydrogen bond is undoubtedly one of the most important non-covalent interactions. Among the several types of the hydrogen bonds, the CH–π interaction is a relatively new notion that is being recognised in chemistry and biology. Although the CH–π hydrogen bond and conventional hydrogen bonds share common features such as directionality, this weak interaction has played a secondary role in molecular recognition. In this study, we have devised a host–guest complex that is assembled solely by the CH–π hydrogen bonds. Multivalent interactions of a bowl-shaped hydrocarbon with its peripheral hydrogen atoms are made possible via CH–π hydrogen bonds by adopting a tubular hydrocarbon as a host for their enthalpy-driven complexation. Concyclic arrays of weak hydrogen bonds further allow dynamic rotational motions of the guest in the host. Solid-state analysis with crystallographic and spectroscopic methods reveal a single-axis rotation of the bowl in the tube.

Highlights

Among the various types of hydrogen bonds1, the CH–π interaction is uniquely characterised by its weak bonding governed largely by dispersion forces2,3
The CH–π hydrogen bond normally plays a secondary role in molecular recognition, reinforcement with other interactions such as hydrophobic effects has allowed this weak force to encapsulate non-polar hydrocarbon guests in capsule-like hosts without freezing their dynamic motions
This study demonstrates that when embedded in elaborate molecular designs, the directional CH–π hydrogen bonds can assemble tight supramolecular complexes with motional dynamics

Summary

Introduction

Among the various types of hydrogen bonds, the CH–π interaction is uniquely characterised by its weak bonding governed largely by dispersion forces. The CH–π hydrogen bond normally plays a secondary role in molecular recognition, reinforcement with other interactions such as hydrophobic effects has allowed this weak force to encapsulate non-polar hydrocarbon guests in capsule-like hosts without freezing their dynamic motions. Despite the tightened host–guest association in polar media, for instance, the CH–π hydrogen bonds permitted tumbling motions of the guests in the host. Solution phase studies with the aid of theoretical results reveal the fundamental association behaviours, and solid-state crystallography and spectroscopy reveal the unique dynamics. Solution phase analyses in non-polar media disclose a tight association of a 1:1 complex, which is driven by a large association enthalpy of –7 kcal mol–1. This study demonstrates that when embedded in elaborate molecular designs, the directional CH–π hydrogen bonds can assemble tight supramolecular complexes with motional dynamics

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