Study of the host–guest interaction between N,N′-bis[4-(dimethylaminophenyl)methyl]butane-1,4-diamine and the cucuribit[n]urils (n = 6, 7)

The interaction between the cucuribit[n]urils (Q[n]), where n = 6 or 7, and the guest N,N′-bis[4-(dimethylaminophenyl)methyl]butane-1,4-diamine (G) has been studied in aqueous solution by 1H NMR spectroscopy, electronic absorption spectroscopy and Isothermal Titration Calorimetry (ITC). In the case of Q[6], a 1 : 1 host–guest complex is favoured with one end of G initially embedded in the Q[6], although over time (48 h), the Q[6] shuttles along the chain such that it resides over the centre of G. For Q[7], a 2 : 1 host–guest complex is formed with the aromatic groups at each end of G buried in a Q[7] cavity. The molecular structure of the inclusion complex having an overall composition of Q[6]·GH2·2Cl·14H2O has been determined, and clearly shows the insertion of the guest molecule with the host Q[6] and it is localised therein by two N–H⋯O hydrogen bonds.