Host–guest Complex of a Water-soluble Cucurbit[6]uril Derivative with the Hydrochloride Salt of 3-amino-5-phenylpyrazole

Abstract

Interaction between tetramethylcucurbit[6]uril and 3-amino-5-phenylpyrazole hydrochloride in aqueous solution has been investigated by using ¹H NMR spectroscopy, electronic absorption spectroscopy and fluorescence spectroscopy, as well as by a single crystal X-ray diffraction determination. The ¹H NMR spectra analysis established a basic interaction model in which an inclusion complex with a host:guest ratio of 1:1 forms, in which the host selectively binds the phenyl moiety of the guest. Absorption spectrophotometric and fluorescence spectroscopic analysis in aqueous solution defined the stability of the host–guest inclusion complexes quantitatively as 6.8 × 10⁵ mol^− 1 L at pH 2.6; the interaction is pH dependent, decreasing as pH rises. The single crystal X-ray structure of the isolated inclusion complex shows the phenyl moiety of the guest inserted into the host cavity, which supports particularly the ¹H NMR spectroscopic study in solution. In the crystal structure of the inclusion complex, the host–guest interaction involves both inter- and intra-complex hydrogen bonding, forming 2:2 dimers that stack in one dimension as supramolecular tubes.

Keywords:

• Host–guest complex
• sym-Tetramethyl-cucurbit[6]uril
• 3-amino-5-phenylpyrazole
• ¹H NMR spectroscopy
• Binding constant
• Single crystal X-ray structure

Acknowledgements

Support of the National Natural Science Foundation of China (NSFC; No. 20662003), the International Collaborative Project Fund of Chinese Ministry of Science and Technology (Grant No. 2003DF000030), the “Chun-Hui” Fund of Chinese Ministry of Education (Grant No. Z2005-1-52011), the Science and Technology Fund of Guizhou Province (Grant No. J-2005-2012) and the Governor Foundation of Guizhou Province, P. R. China, are gratefully acknowledged.