Host-guest interactions in an inverted cucurbit[7]uril with α,ω-alkyldiammonium guestsElectronic supplementary information (ESI) available: Titration 1H NMR spectra and ITC for iQ[7]-guest (1-6) and Q[7]-guest (1-6). See DOI: 10.1039/c5ra13339d

Host-guest interactions in an aqueous solution of an inverted cucurbit[7]uril (iQ[7]) with α,ω-alkyldiammonium guests (H 3 N(CH 2 ) x NH 3 Cl 2 , x = 2, 4, 6, 8, 10, and 12 named 1-6 ) were investigated by nuclear magnetic resonance (NMR) and isothermal titration calorimetry (ITC). 1 H NMR spectroscopy revealed that all alkyldiammonium cations are involved in interactions with iQ[7] that fall into three groups. Averaged signals of free and bound guests with shorter alkyl chains including 1-3 indicate a higher binding and unbinding exchange ratio, within the time scale of the NMR experiments. Averaged signals for the guest 1 compound exhibited a downfield shift indicative of a dominant portal interaction between 1 and iQ[7], in contrast to guest 2 and 3 compounds that exhibited an upfield shift. Averaged signals of guests with longer alkyl chains such as 4-6 displayed a lower binding and unbinding exchange ratio on the NMR time scale. The occurrence of upfield shifts for all guests except 1 indicate a dominant inclusion interaction between the guests and iQ[7]. ITC experiments showed that the thermodynamics of complexation of the alkyldiammonium guests with iQ[7] were both enthalpically and entropically driven. Interestingly, complexation was predominantly entropically driven for the first guest group, with the exception of guest 3 , but was enthalpically driven for the third guest group. Host-guest interactions of the more conventional cucurbit[7]uril (Q[7]) with these α,ω-alkyldiammonium guests were also investigated under the same conditions for comparison. Host-guest interactions in an aqueous solution of an inverted cucurbit[7]uril (iQ[7]) with α,ω-alkyldiammonium guests (H 3 N(CH 2 ) x NH 3 Cl 2 , x = 2, 4, 6, 8, 10, and 12 named 1-6 ) were investigated by nuclear magnetic resonance (NMR) and isothermal titration calorimetry (ITC).