MACROCYCLIC ARTIFICIAL RECEPTORS - MOLECULAR RECOGNITION ABILITY IN AQUEOUS-SOLUTION AND BILAYER-MEMBRANES

Four types of functionalized cyclophanes were prepared and their molecular recognition behavior was discussed in view of their efficiency as artificial receptors in aqueous solution and bilayer membranes. A cyclophane host bearing four L-aspartate moieties (type 1) exhibits pH-responsive molecular recognition toward various aromatic guests in aqueous media. Cage-type macrocycles, each providing a three-dimensionally extended hydrophobic cavity (type 2), are capable of incorporating guest molecules in aqueous solution through the induced-fit or the lock-and-key mechanism, depending on rigidity of their molecular frameworks. Octopus cyclophanes having eight flexible hydrocarbon branches (type 3) exercise the induced-fit binding and are superior to steroid cyclophanes bearing four rigid steroid moieties (type 4) as regards molecular recognition in aqueous media. Anionic and hydrophobic guests are effectively incorporated into the hydrophobic cavities provided by the cationic hosts of type 3 and type 4, that are embedded in bilayer membranes formed with an anionic peptide lipid; the guest-binding site being subjected to change by the structural nature of guest molecules.