Size- and shape-sensitive molecular discrimination by cage-type cyclophanes in aqueous media

Abstract

Cage-type cyclophanes, which are constructed with two rigid macrocyclic skeletons, tetraaza[3.3.3]paracyclophane and tetraaza[6.1.6.1]paracyclophane, and four chiral bridging components, strongly bind an anionic fluorescent guest, 8-anilinonaphthalene-1-sulfonate, and give out an efficient motional repression effect on the incorporated guest. The cage-type hosts bearing chiral valine residues furnish more apolar internal cavities for the guest molecule than those bearing chiral alanine residues. On the other hand, binding ability and motional repression by peptide cyclophanes, which were prepared by introducing four amino acid residues into a rigid tetraaza[6.1.6.1]paracyclophane skeleton, are less efficient than the cage-type hosts toward the identical guest. Furthermore, microenvironmental polarity of the internal cavities of peptide cyclophanes is much more polar than that of the cage-type hosts. The cage-type hosts perform size- and shape-sensitive molecular discrimination toward nonionic guests of various bulkiness, such as perylene, pyrene, anthracene, and naphthalene, in aqueous media. In addition, binding constants for the cage-type hosts with 4-(1-pyrene)butanoic acid, are greater than those for the identical hosts with pyrene, due to an intermolecular hydrogen-bonding interaction between the butyric acid moiety of the former guest and the bridging segments of the hosts.