An ab initio study of the selective binding of alkali and alkaline earth metal cations for crown ethers
- Pacific Northwest Lab., Richland, WA (United States)
Crown ethers are a class of macrocyclic polyether that are known to preferentially bind certain cations in potentially complex mixtures of other cations. They are being considered as candidates for separating radioactive cesium ({sup 137}Cs) and strontium ({sup 90}Sr) from the high level waste tanks on the Hanford Nuclear Reservation. We present the results of RHF and MP2 calculations on a variety of crown ethers, including 18-crown-6, which is known to prefer potassium in polar solvents. Gas phase calculations show that 18-crown-6 most strongly binds lithium, but our results indicate that potassium selectivity is recovered with the inclusion of even a small number of waters of hydration in the calculations. A variety of Gaussian basis sets (3-21G, 6-31+G* and correlation consistent) were employed in an effort to derive convergence estimates for the binding enthalpies. The only available experimental values, obtained from FT-ICR experiments by A.R. Katritzky et al., Rapid Comm. Mass Spect., 6, 25 (1992), are over 30 kcal/mol smaller than our best estimate for K+/18-crown-6.
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 214666
- Report Number(s):
- CONF-950801--
- Country of Publication:
- United States
- Language:
- English
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