I&EC 68 |
| Tatiana G. Levitskaia1, Bruce Moyer2, Viktor N. Pastushok3, Jonathan L. Sessler4, and Thomas Vercouter3. (1) Radiochemical Processing Laboratory, Pacific Northwest National Laboratory, Richland, WA 99352, (2) Oak Ridge National Laboratory, (3) Chemical Sciences Division, Oak Ridge National Laboratory, Bldg. 4500S, P.O. Box 2008, Oak Ridge, TN 37831-6119, (4) Department of Chemistry and Biochemistry, University of Texas, Austin, TX 7812-1167 |
| Liquid-liquid ion-pair extraction separations of inorganic salts from aqueous matrices commonly employ host-guest chemistry. In this overview, fundamental principles that control anion selectivity and extractability are discussed using examples from our research on crown ethers and calixcrowns. Bias selectivity in favor of large charge-diffuse anions is a solvation-based effect, which is sustained in the liquid-liquid distribution systems. It is rarely recognized that electrostatic forces can be exploited to modify this solvation bias selectivity. The relationship between anion selectivity and ion-pairing effects will be discussed in regard to the structure of the cation receptor and its cationic complex. One of the most powerful tools to control anion selectivity is the application of an anion host. Combined utilization of cation and anion receptors in a dual-host extraction system synergistically favors extraction of small anions. Structurally non-preorganized hydrogen-bond donor receptors for anions, namely lipophilic sulfonamides and hydroxy compounds, exhibit linear anti-Hofmeister synergism. In contrast, fluorinated calix[4]pyrroles discriminate in anion binding, and thus, in transport of halide anions across liquid-liquid boundary. |
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Molecular Hosts for Anion Binding (sponsored by Separation Science & Technology Subdivision)
1:30 PM-4:55 PM, Monday, March 29, 2004 Marriott -- Orange County 1, Oral
Division of Industrial and Engineering Chemistry |