A Cucurbituril Derivative That Exhibits Cation-Modulated Self-Assembly

Cucurbiturils are the most potent artificial receptors known for many organic molecules in water. However, little is known about their supramolecular chemistry in organic solvents. Here we present a new cucurbituril derivative, 1, and investigate its supramolecular properties in methanol. The macrocycle resembles a five-membered cucurbituril in which four glycoluril units are replaced with propanediurea. Macrocycle 1 can bind to one cation such as potassium or anilinium via each of its opposed portals. The stability of these complexes in methanol at nanomolar concentrations exceeds that of complexes between metal cations and crown ethers. Moreover, macrocycle 1 forms a self-assembled tetrameric aggregate in the solid state and in methanol. The tetramer is stabilized by the addition of up to 1 equiv of a cation but is fully disassembled in the presence of 2 equiv of the cation. Cations can thus be used to tune the aggregation of 1 in solution.