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.