Water-soluble hexakis-imidazolium cages: synthesis and selective binding of sodium urate

Three hexakis-imidazolium-incorporated molecular cages o-, m- and p-HiCages have been prepared through the condensation of 1,3,5-tri(imidazolyl)benzene and o-, m- or p-xylylene dibromide. The new hexacationic molecular cages are highly water-soluble. It is demonstrated that among various purines, m- and p-HiCages have the ability to bind uric acid selectively in water. The binding constants of their complexes with uric acid are determined by isothermal titration calorimetric experiments to be (5.86 ± 0.30) × 104 M−1 and (2.61 ± 0.06) × 104 M−1, and the structures of both complexes are confirmed by X-ray diffraction analysis. These imidazolium-derived molecular cages exhibit low cytotoxicity and hemolysis rates, providing the possibility for subsequent biological applications.