Mechanism and thermodynamics of ion selectivity in aqueous solutions of 18-crown-6 ether: A molecular dynamics study
- Pacific Northwest Lab., Richland, WA (United States)
Extensive classical molecular dynamics simulations are performed to examine the mechanism and thermodynamics for ion selectivity in aqueous solutions of 18-crown-6 ether. The free energy profiles or potential of mean force (pmf) for M+: 18-crown-6 (M+ = K+, Na+, Rb+, Cs+) complexation are computed via the free energy perturbation method. Counterion effects are considered and all long-range interactions are computed via the Ewald summation method. This is the first study of ion selectivity in aqueous solutions using the prof approach. The resultant pmfs indicate that free-energy minima for the K+ and Na+ ions are located at the crown ether center-of-mass. Potassium is selected over sodium because of the free energy penalty associated with displacing water molecules from sodium as it approaches the crown ether. This leads to a substantial increase in the activation free energy and a decrease in the binding free energy for Na+: 18-crown-6 complexation as compared to K+: 18-crown-6. The selection of potassium over rubidium and cesium is due to the cation-size relative to the crown-ether cavity. The calculated binding free energies follow the sequence K+ > Rb+ > Cs+ > Na+, which is in accordance with experimental measurements.
- OSTI ID:
- 126852
- Report Number(s):
- CONF-950402-; TRN: 95:006086-0896
- Resource Relation:
- Conference: 209. American Chemical Society (ACS) national meeting, Anaheim, CA (United States), 2-6 Apr 1995; Other Information: PBD: 1995; Related Information: Is Part Of 209th ACS national meeting; PB: 2088 p.
- Country of Publication:
- United States
- Language:
- English
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