ABSTRACT
In 1957, Pedersen reported the synthesis of crown ether,1 a cyclic oligoether that can selectively form an inclusion complex with a cationic ion in relation to its ring size.2 Since the discovery of crown ether, many cyclic molecules have been studied, for instance, cyclodextrin,3 cyclophane,4 and calixarene.5 These studies contributed to the establishment of the new field of host-guest chemistry. Host-guest chemistry has now become an important part of a more general concept known as supramolecular chemistry.6
