Allosteric Modulation of Substrate Binding within a Tetracationic Molecular Receptor

The synthesis and recognition phenomena
of a tetra­cationic
molecular receptor that possesses a nanometer-sized molecular cavity
are described. The host–guest properties of the molecular receptor
can be tuned and modulated allo­sterically, where the association
of a hetero­tropic effector at the periphery of the molecule
serves to modulate its affinity for the globular, electron-rich guest
that resides within its molecular cavity. This stimuli-responsive
host–guest behavior was observed in both the solution phase
and the crystalline solid state, and can be reversed with high fidelity
by sequestration of the effector molecule.