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Extended and Contorted Conformations of Alkanediammonium Ions in Symmetrical α,α′,δ,δ′-Tetramethylcucurbit[6]uril Cavity

Yang, Bo, Zheng, Li-Mei, Gao, Zhong-Zheng, Xiao, Xin, Zhu, Qian-Jiang, Xue, Sai-Feng, Tao, Zhu, Liu, Jing-Xin, Wei, Gang
Journal of organic chemistry 2014 v.79 no.22 pp. 11194-11198
X-ray diffraction, aqueous solutions, calorimetry, chemical reactions, chemical structure, enthalpy, ions, matrix-assisted laser desorption-ionization mass spectrometry, nuclear magnetic resonance spectroscopy, organic chemistry, organic compounds, titration
Binding interactions between symmetrical α,α′,δ,δ′-tetramethylcucurbit[6]uril (TMeQ[6]) and a series of alkyldiammonium ions in aqueous solution and in the solid state were investigated by ¹H NMR spectroscopy, MALDI-TOF mass spectrometry, X-ray crystallography, and isothermal titration calorimetry (ITC). Their ¹H NMR spectra reveal that the actual binding behaviors vary depending upon the alkyl chain length. Their single-crystal X-ray diffraction analyses indicate the guest 1,2-ethanediammonium is located outside of the TMeQ[6] portal, while the other four alkyldiammonium guests can be accommodated in the TMeQ[6] cavity, forming 1:1 inclusion complexes. Most importantly, the long-chain alkyldiammoniums (1,8-octanediammonium and 1,10-decanediammonium) take a contorted conformation when bound within the TMeQ[6] cavity. Additionally, ITC experiments show that the complexation of the alkyldiammonium guests with TMeQ[6] is mainly enthalpy driven, which benefits from ion–dipole interactions.