Structurally unique novel ionophores of penta-crown ethers were successfully synthesized. Diaza-18-crown-6 was designed as the parent crown ring. The penta-crown ethers were prepared by the reaction of 1,3,5-triacryloylhexahydro-1,3,5-triazine (TAHTA) with diaza 18-crown-6 followed by a Michael reaction. The binding interactions of the newly synthesized penta-crown ethers with alkali metal cations were examined; the results indicate that the new penta-crown ethers can bind alkali cations of different sizes.Crown ethers have attracted significant attention from various fields since they were first introduced by Pedersen in 1967. 1 During the last two decades, considerable research interest has been devoted to the design of multisite crown ethers, in particular the construction of multisite molecular receptor molecules capable of binding two or more guest metal cations. [2][3][4][5] The crown ether moiety is one of the most popular host compounds in host-guest chemistry field, which has shown a remarkable ability to form strong complexes with alkali metal, alkaline metal, and organic cations. Metal cations exactly fitting the size of the crown ether unit form a host/guest 1:1 complex; when the cation size exceeds that of the crown cavity the cation can only partially fit and, as a result, can be accommodated by two crowns forming a host/guest 2:1 sandwich complex, 6-14 such as the 'butterfly crown ethers'. [11][12][13][14] The 'bis-crown effect' occurs when two crown ether rings in one molecule bind a cation in a sandwich-type structure; it enables the molecules to bind a cation that is larger than the ideal size for particular crown ether unit. [15][16][17][18][19] This is due to the bridge effect of the metal cations with the two crown rings. The formation of sandwich complexes is strongly favored when the crowns are linked by a spacer. In this case, the selectivity towards large cations is increased. 8,10,20 The 'bis-crown effect' can be applied to synthetic methodology and medical chemistry when constructing new organic and inorganic molecular receptors.We reported 21,22 the synthesis of unique structural trisand tetra-crown ethers, novel host compounds which contain multisite crown rings are of great interest, they can form host/guest 1:n (n ≥ 3) complexes. Herein, we report the design, synthesis, and characterization of a new type of ionophores of penta-crown ethers. The structures of the newly synthesized penta-crown ethers are outlined in Figure 1. To our knowledge, there have been few reports of compounds containing five crown ether rings. The binding interactions of the penta-crown ethers with alkali metal cations were examined. From the results, we found that the newly synthesized ionophores of penta-crown ethers had the ability to complex with alkali metal cations of various sizes such as Na + , K + , and Cs + . The new pentacrown ionophores lead to original applications for the preparation of new types of host-guest complexes. The properties can be applied in different areas, such as synthetic, medicin...
