Homo-and heterotypic pentameric cyclophanes exhibiting fascinating host-guest binding properties

Abstract

Tetraaza[2.2.1.2.2.1]paracyclophane (L) and tetraaza[6.1.6.1]paracyclophane (S), which have larger and smaller cavities, respectively, were utilized to develop cationic cyclophane (CP) pentamers as water-soluble hosts. Homotypic CP pentamer L5, in which five Ls are linked in a divergent fashion, as well as heterotypic CP pentamer hetero5 consisting of one L and four Ss were synthesized. L5 and hetero5 exhibited fascinating molecular recognition in guest-binding toward stocky guests such as 1-pyrenebutyric acid (PBA) and perylene-3,9-dicarboxylic acid (PeDA), and elongated guests such as 6-ptoluidinonaphthalene-2-sulfonate (TNS) and 4-N,N-dimethylamino-azobenzene-4'-sulfonyl derivative (CDab). That is, L5 potently captured PBA and PeDA, with binding constants in the order 10⁶ M^-1 , whereas hetero5 potently captured not only PBA but also TNS and CDab. The guest-binding ability of L5 and hetero5 to preferred guests was significantly improved compared to the corresponding monocyclic CPs L1 and S1, which reflects an increase in the local concentration of the macrocycles. Furthermore, both PBA and CDab molecules were simultaneously and efficiently incorporated into the macrocycles of hetero5, which was confirmed by fluorescence spectroscopy.