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

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.本研究采用核磁共振氢谱法（1H NMR spectroscopy）、基质辅助激光解吸电离飞行时间质谱（MALDI-TOF mass spectrometry）、X射线晶体衍射法以及等温滴定量热法（isothermal titration calorimetry, ITC），对水溶液与固态环境中，对称α,α′,δ,δ′-四甲基六元瓜环（symmetrical α,α′,δ,δ′-tetramethylcucurbit[6]uril, TMeQ[6]）与一系列烷基二铵离子之间的结合相互作用展开了探究。其核磁共振氢谱结果表明，实际结合行为会随烷基链长度的不同发生变化。单晶X射线衍射分析显示，客体分子1,2-乙二铵离子位于TMeQ[6]的端口外侧，而其余四种烷基二铵客体可被容纳于TMeQ[6]的空腔内，形成1:1型包结配合物。尤为重要的是，长链烷基二铵离子（1,8-辛二铵与1,10-癸二铵）在结合进入TMeQ[6]空腔后会呈现扭曲构象。此外，等温滴定量热实验结果表明，烷基二铵客体与TMeQ[6]的络合过程主要由焓驱动，该过程的热力学优势源自离子-偶极相互作用。