Confinement of nucleic acid bases and related compounds using tetra-p-sulfonatocalix[4]arene

Supramolecular complexes of tetra-p-sulfonatocalix[4]arene and guanine, cytosine, benzimidazole, and 2-hydroxybenzimidazole have been isolated in the solid state, and their structures have been elucidated using single-crystal X-ray diffraction data, as have 2-hydroxybenzimidazole complexes and complexes with large cations tetraphenylphosphonium (Ph₄P⁺) and triethylbenzylammonium (Et₃BzN⁺). These large cations disrupt the usual bilayer arrangement of the sulfonated calixarenes, as can benzimadole itself, and a combination of guanine and cytosine, in the absence of the large cations. Some of the structures show a "molecular capsule" type arrangement with two calixarenes arranged with their cavities directed toward each other, effectively shrouding two nucleic acid bases.