The binding behaviours between cyclopentanocucurbit[6]uril and three amino acids.

Siyuan Cheng,Xinan Yang,Liantong Wei,Weiwei Zhao,Peihua Ma,Zhu Tao,Ye Meng

doi:10.1098/rsos.202120

Abstract

Binding behaviours between cyclopentanocucurbit[6]uril (CyP6Q[6]) and three amino acids have been investigated by means of X-ray crystallography, proton nuclear magnetic resonance spectroscopy and isothermal titration calorimetry. The results showed that CyP6Q[6] forms a 1 : 2 inclusion complex with glycine, but 1 : 1 complexes with both leucine and lysine. Whereas the carboxyl group of glycine can enter the interior of the cavity of CyP6Q[6], only the alkyl chains of leucine and lysine can enter this cavity. Interestingly, leucine can adopt two different self-assembly modes upon its interaction with cucurbituril, depending on the external conditions, whereas glycine and lysine do not exhibit such behaviour.

Highlights

Cucurbit[n]urils (n = 5–8, 10, 14) are macrocyclic compounds with an inner hydrophobic cavity and two portals rimmed by polar carbonyl oxygen atoms, formed by multiple glycoluril monomers doubly bridged by methylene units [1,2,3]
An oak ridge thermal-ellipsoid plot program (ORTEP) representation of the asymmetric unit is shown in the electronic supplementary material, figure S1
Glycine is bound slightly differently in the two phases; a 1 : 2 inclusion complex is formed in each case, the methylene units have different locations

Summary

Introduction

Cucurbit[n]urils (n = 5–8, 10, 14) are macrocyclic compounds with an inner hydrophobic cavity and two portals rimmed by polar carbonyl oxygen atoms, formed by multiple glycoluril monomers doubly bridged by methylene units [1,2,3]. As fourth-generation supramolecular hosts following crown ethers, cyclodextrins and calix[n]arenes, their high-affinity hydrophobic cavities have propelled their host–guest chemistry into the mainstream, making it a ‘hot spot’ in cucurbituril chemistry. Because the hydrophobic cavities of cucurbiturils readily form stable inclusion complexes or rotaxane analogues, molecular capsules and other supramolecular structures incorporating various organic small molecules [4,5,6,7], especially in aqueous systems, cucurbituril host–guest chemistry has played a significant role in the fields of drug delivery, chemical sensors and cucurbituril supramolecular self-assembly materials [8,9,10].

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Results

Conclusion