A self-assembled ionophore with remarkable Cs+ selectivity
A self-assembled ionophore with remarkable Cs+ selectivity
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DOI：
10.1021/ja970248x
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发表时间：
1997-06-04
影响因子：
15
通讯作者：
Marlow, AL
中科院分区：
文献类型：
--
作者：
Davis, JT;Tirumala, SK;Marlow, AL
Nuclear waste management requires methods for radionuclide separation, and a major component of the waste is 137Cs. 1, 2 Due to its 30 year half-life, most of the 137Cs produced during the nuclear age still exists. Methods for 137Cs+ separation include precipitation as phosphotungstate salts, ion exchange chromatography, and extraction by ionophores. 3 Highly selective ionophores are required to separate 137Cs+, since Na+ and K+ concentrations in nuclear waste are much greater than that of 137Cs+. 3 Selective coordination of Cs+(r) 1.67 Å) in the presence of Na+(r) 0.97 Å) and K+(r) 1.33 Å) is challenging. Because of their flexibility, crown ethers often have only modest Cs+ selectivities. 4 More promising results have been obtained with rigid macrocycles, 5 particularly the calix [4] arenecrowns. 6-8 While the Cs+ selectivities of the calixarenecrowns are impressive, cation and ionophore recovery may prove difficult due to the stability of the ionophore-Cs+ complex.An alternative ionophore design uses hydrogen bonds to build self-assembled structures that coordinate ions. 9-11 Cation binding affinity and selectivity may be achieved through cooperative assembly of the host. We have focused on 5′-(tert-butyldimethylsilyl)-2′, 3′-O-isopropylidene isoguanosine (isoG) 1. IsoG 1 self-associates in organic solvents to form a stable tetramer,(isoG) 4 2 (Scheme 1). 11, 12 Tetramer 2, with four oxygens in its central cavity, has a high affinity for cations. Isopropylidene 1 coordinates K+ to form (isoG) 8-K+ 3, with a binding constant rivaling that of 18-c-6 derivatives. 11b We
