MOLECULAR RECOGNITION BY MACROCYCLIC RECEPTORS HAVING MULTIPLE HYDROPHOBIC BRANCHES IN A SYNTHETIC BILAYER-MEMBRANE

Hybrid molecular assemblies were prepared in combinations of a synthetic peptide lipid, involving an L-alanine residue interposed between an anionic head group and a hydrophobic double-chain segment, with cationic macrocyclic hosts, a steroid cyclophane bearing four rigid steroid moieties and octopus cyclophanes having eight flexible hydrocarbon branches. On addition of the cyclophanes to multi-walled bilayer membranes composed of the anionic lipid, thermodynamic parameters (DELTAH and DELTAS) associated with the phase transition between the gel and liquid-crystalline states were subjected to changes that are consistent with the formation of the hybrid assemblies. Anionic fluorescent guests, 8-anilinonaphthalene-1-sulphonate and 6-p-toluidinonaphthalene-2-sulphonate, were effectively incorporated into the hydrophobic cavities provided by the cationic cyclophanes embedded in the bilayer membrane through hydrophobic and electrostatic interactions. The guest-binding modes of the hybrid assemblies are classified into two types; a guest is included in the proximity of the hydrogen-belt domain of the bilayer membrane in one mode, and a guest is incorporated into the hydrophobic bilayer domain composed of double hydrocarbon chains of the lipid in another.