Host-guest interactions of hemicucurbiturils with aminophenols

The host-guest interactions between hemicucurbit[6 and 12]urils and o-, m-, and p-aminophenols have been investigated by means of H-1 NMR spectrometry, fluorescence emission spectroscopy, and isothermal titration calorimetry. The H-1 NMR spectra suggest that the interaction could involve hydrogen bonding between the hydroxyl groups of the guests and the carbonyl groups of the hemicucurbiturils. The fluorescence emissions of the guests are enhanced upon addition of increasing amounts of hemicucurbiturils, with a slight blue-shift of the emission peaks. Moreover, the linearity of emission intensity responses of the guests to the HemiQs concentration shows different slopes depending on the structure of the hemicucurbituril. Thermodynamic data have been obtained by isothermal titration calorimetry, and the results indicate 1:1 host-guest interactions between the hemicucurbiturils and aminophenols. All of the interaction systems have similar stabilities and approximately equal association constants, and the negative enthalpy change upon the addition of the hemicucurbiturils is the driving force of the host-guest interaction. Formation of interaction complexes of aminophenols with hemicucurbit[6 and 12] in organic solvent have been investigated.