LI+ ION-SELECTIVE BINDING AND TRANSPORT-PROPERTIES OF 12-MEMBERED RING LARIAT ETHERS - EXPERIMENTAL AND COMPUTATIONAL STUDIES ON CROWN RING SIDEARM COOPERATIVITY

A variety of lariat ethers were prepared in which amine, ether, ester, amide, nitrile, and pyridine moieties were attached as cation-ligating sidearms to azacrown rings. Among them, amine-armed aza-12-crown-4 compounds specifically accommodated a Li+ cation in a three dimensional fashion and clearly distinguished it from other metal cations. FAB-MS and Li-7/C-13 NMR binding and liquid membrane transport studies confirmed that amine-armed aza-12-crown-4s formed stable and encapsulated Li+ complexes suitable for specific recognition and transport, while other aza-12-crown-4 derivatives exhibited Naf ion selectivity. Using the density functional method, stabilization energies were estimated for some lariat ether-metal complexes. Since this nonempirical calculation offered results consistent with several experimental observations, combined studies of lariat ether chemistry and computer calculation may provide a new and interesting approach to the design of a specific cation receptor.