Steroid cyclophane as a versatile artificial receptor. Molecular recognition in water, at air–Water interface, and in lipid bilayer membrane

Abstract Steroid cyclophanes, having four steroidal moieties on a tetraazaparacyclophane skeleton, were designed and synthesized as a structural and functional hybrid of the macrocyclic hosts and the bile acid aggregates. The steroid cyclophanes exhibited molecular recognition behavior environmentally sensitive in various media. In aqueous solution, the host provided a three-dimensionally extended hydrophobic and chiral cavity for aromatic molecules with large binging constants and marked guest specificity. At the air–water interface, a steroid cyclophane bearing four cholate moieties performed a unique and drastic cavity conversion depending on the surface pressure, and the resulting monolayer assembly acted as an effective piezoluminescent molecular device. The steroid cyclophane embedded in lipid bilayer membrane behaved as an artificial cell-surface receptor, and the characteristic of the molecular recognition in aqueous solution was basically maintained even in the lipid membrane. When an enzyme was non-covalently fixed on the molecular assembly in the presence of copper(II) ions as a signal transmitter between the receptor and the enzyme, the signal transduction behavior in which a response of the molecular recognition of a signaling ligand by the steroid cyclophane was transmitted to an effector enzyme was observed.