Armed crown ether

The definition of armed crown ether is self-evident and covers all of the crowns containing arms. This definition includes the lariat ethers which are characterized by the presence of binding... 

Each of the various classes of armed crown ethers described above contains a large number of representatives and all of them are permanently enriched by new related derivatives. Several less abundant types of arm-containing crown ethers have been described. 

Double armed crown ethers" were prepared from corresponding di-azacrown ethers (Kryptofix 21, 22, and 23, Merck Japan). Typically, Kryptofix 22 (l,7,10,16-tetraoxa-4,13-diazacyclooctadecane) was condensed with 2-furoyl chloride, and the resultant diamide was reduced by diborane in THF. Recrystallization from CH Cl -hexane gave white crystals 4 Mp, 37-38°C. Elemental analysis Calcd. C 62.54, H 8.11,... 

Crown ethers 2 3 and 6 were similarly obtained. The structures of the prepared "double armed crown ethers" are shown in Figure 1. 

Transport Properties of "Double Armed Crown Ethers"... 

The ring size of the double armed crown ether was an essential factor determining transport properties. We examined furam-bearing crown ethers having 15- to 21-membered rings, As shown in Figure 4, they... 

Recently, l iriat ethers" and gther single armed crown ethers have extensively been investigated. They exhibited interesting cation binding and extracting profiles, based on their three-dimensional coordination geometry. Similar principles should be involved in the present "double armed crown ether" systems. 

As well known, 18-crown-6 type carriers transported NH cation but could not discriminate NH cation from K cation in the transport process. Furan-bearing double armed crown ether 4 also showed high transport efficiencies for both cations and seemed to be non-selective carrier in some sense. 

H.Tsukube, Double Armed Crown Ethers With Specific Cation Transport Ability , J.Chem.Soc.,Chem.Commun., 315 (1984). 

New approaches for development of specific carriers for use in liquid membrane are described (i) computer-aided design of cation-specific carriers and (ii) functionalization of rare earth complexes as anion carriers. A new series of Li(I) and Ag(I) ion-specific carriers are successfully designed using MM2, MNDO and density functional calculations. Computer chemistry provides a rational basis for design and characterization of cation-specific carriers of armed crown ether-and podand-types. Lipophilic lanthanide tris(p-diketonates) are shown to be a new class of membrane carriers. They form 1 1 complexes with anionic guests and mediate transport of amino acid derivatives. Since these complexes exhibit different anion transport properties from those of crown ethers, further applications of rare earth complexes offer promising possibilities in the development of specific anion carriers for liquid membrane systems. 

Figure 5. Armed crown ethers as Li+ ion-specific carriers.

Figure 9. Possible binding modes of armed crown ether.

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