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.