Binding interactions of bisbenzimidazolyl derivatives with cyclohexanocucurbit[6]uril

Abstract

The binding properties of cyclohexanocucurbit[6]uril (Cy6Q[6]) host toward three 1,w-bisbenzimidazolyl derivatives (guests 1–3, with alkyl chain of different lengths as linker) have been analyzed by 1H NMR spectroscopy and isothermal titration calorimetry (ITC) in aqueous solution and X-ray crystallography in solid state. The 1H NMR spectroscopy reveal that all guests can form 1:1 and 1:2 inclusion complexes with Cy6Q[6] macrocyles residing over benzoimidazole groups. The actual binding ratios or modes depend on the amounts of the host. Interestingly, the encapsulation and release of the guests can be controlled through the pH values of the solution. ITC data show that the binding process of host Cy6Q[6] with gusts 1–3 is driven by enthalpy, which benefits from hydrophobic effects and host–guest interactions. X-ray diffraction analysis provide unambiguous evidence that the benzoimidazole group of the guests 1 and 2 can be encapsulated into the Cy6Q[6] cavity, forming 1:1 host–guest inclusion complexes. The formation of these 1:1 binary inclusion complexes is attributed to the cooperativity of ion–dipole interaction, van der Waals interaction, C–H···π interaction, and hydrogen-bonding interaction. Binding interactions of 1,ω-bisbenzimidazolyl derivatives (guests) with cyclohexanocucurbit[6]uril (Cy6Q[6]) both in aqueous solution and solid state have been investigated by various tools. The results reveal that all guests can form 1:1 or 1:2 inclusion complexes with Cy6Q[6] residing over benzoimidazole groups of the guests.