Supramolecular Self-assembly of Symmetric Dicyclohexanocucurbit[6]uril and Nicotinic Hydrazide

Cucurbit[n]uril (Q[n]) is a relatively new supramolecular macrocyclic compound, which has a unique structure comprised of a hydrophobic cavity with intermediate potential, two carbonyl portals with negative potential, and an outer surface with positive potential. Cyclohexyl-substituted Q[n]s have also attracted a lot of attention as the first member of the Q[n] family that can be dissolved in organic solvents and water. In this paper, the interaction modes between the symmetric dicyclohexanocucurbit[6]uril (CyH(2)Q[6]) as a host and nicotinic hydrazide (NH) as a guest were investigated by nuclear magnetic resonance spectroscopy (H-1 NMR), isothermal titration calorimetry (ITC), matrix assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry, and single-crystal X-ray diffraction. The H-1 NMR spectrum results showed that the proton peaks shift to the downfield, indicating that NH is located at the portal of CyH(2)Q[6]. ITC experiment results showed that the binding constant (K-a) of NH@CyH(2)Q[6] is (1.019 +/- 0.118)x10(3) L.mol(-1), the host-guest binding ratio is 0.954 +/- 0.013, and the enthalpy value is Delta H=(-48.21 +/- 0.35) kJ.mol(-1) and entropy value T Delta S=(-31.04 +/- 0.52) kJ.mol(-1). The MALDI-TOF mass spectrum also showed that the molecular ion peak m/z is 1242.4542 (theoretical value: 1242.1603), which is attributed to [CyH(2)Q[6]center dot HNH](+). These experimental results showed that CyH(2)Q[6] formed a stable 1: 1 exclusion complex with NH in an aqueous solution. In addition, the host CyH(2)Q[6], ZnCl2 and the guest NH were added to HCl aqueous solution, and the complex single-crystal structure was obtained by evaporation and standing. The single-crystal structure of the complex showed that there are ion-dipole interactions and hydrogen bonds between the carbonyl oxygen of CyH(2)Q[6] and NH, and there are ion-dipole interactions between the outer surface of CyH(2)Q[6] and [ZnCl4](2-). These weak interactions are the driving forces of the multi-dimensional and multi-level supramolecular framework formed by the complex.

Automated summary

This study investigated the interaction modes between cyclohexyl-substituted Q[n] and nicotinic hydrazide, and confirmed the formation of a stable 1:1 exclusion complex in an aqueous solution.