Supramolecular self-assemblies of inverted cucurbit[7]uril with biogenic amines

The interactions between inverted cucurbit[7]uril (iQ[7]) and six biogenic amines, namely tyramine (TA), 2-phenylethylamine (PEA), histamine (HI), tryptamine (TR), spermine (SPM), and spermidine (SPD), were studied through 1H nuclear magnetic resonance (NMR) spectroscopy, UV/vis absorption spectroscopy, fluorescence spectroscopy, isothermal titration calorimetry (ITC), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). The results showed that iQ[7] exhibits binding affinity towards five of these biogenic amines, with the exception of HI, and that the host–guest binding sites differ depending on the structure of the biogenic amine. For the aromatic amines (TA and PEA), the phenyl groups are completely encapsulated within iQ[7]; for the heterocyclic aromatic amine TR, there is deep inclusion of its indole group in the cavity of iQ[7]; for the fatty amines (SPM and SPD), the central alkyl chain is bound within the central cavity of iQ[7].