Design, synthesis and cation-binding properties of novel adamantane- and 2-oxaadamantane-containing crown ethers

The synthesis of a series of adamantane- and 2-oxaadamantane-functionalized crown ethers 1-7 is described. Alkali metal picrate extraction profiles ha ve been determined for these novel ionophores. The ability of crown ethers 1-7 to extract the alkali metal picrates was compared with that of benzo-15 -crown-5 and 18-crown-6. Also, Na+- and K+-transport, the ability of ionoph ores 1-3 to transport Na+- and K+ across a bulk liquid membrane was measure d. The results of alkali metal cation extraction experiments showed that th e complexation properties of crown ethers 1 and 2 are comparable to that of benzo-15-crown-5 and 18-crown-6, respectively. Crown ether 3 showed enhanc ed extractability for all cations but lower selectivity compared to 18-crow n-6. However, adamantano-crown ethers 4-7 showed almost negligible extracti on capability toward any of the alkali cations. The observed differences am ong the complexation abilities of the ionophores 1-3 and 4-7 are rationaliz ed on the basis of the results of a molecular modeling study of their corre sponding K+ complexes. (C) 2001 Elsevier Science Ltd. All rights reserved.