Yeon Hee Cho*, Seung Gul Rha*, Taek Dong Chung, Keunchang Cho,
Hasuck Kim,and Suk-Kyu Chang*
Department of Chemistry, Seoul National University, Seoul 151-742,
Korea
*Department of Chemistry, Chung-Ang University, Seoul 156-756, Korea
A series of bis(crown ether)s based-upon a xanthene-4,5-dicarboxylic
acid skeletonwere prepared and their ionophoric properties toward
alkali metal cations were investigated.Bis(crown ether)s bearing
15-crown-5 and 18-crown-6 moieties exhibited pronouncedextraction
efficiencies toward K+ and Cs+ ions, respectively, and the extraction
constantestimated by solvent extraction studies was as high as 109
for the 2?s+ system.Using UV titration of cesium picrate with 2
in THF, the complex was found to have a structureof completely
encapsulated guest in the host. In transport experiments,
the bis(crown ether)sshowed no significant selectivity pattern compared
with extraction results, again implyingthe strong complexation of
bis(crown ether)s. Ion-selective electrode studies alsodemonstrated
that the selective ionophoric properties of 2 were reminiscent of the
naturalantibiotic valinomycin except for a somewhat slow response.