Theoretical study of ion/macrocycle interactions using both hybrid quantum mechanical-molecular mechanical and ab initio methods

Synthetic macrocycles have drawn much experimental and theoretical interest since Pederson first synthesized the crown-ether 18-crown-6 (18c6) in 1967. Crown-ethers show a remarkable range of specificity for a wide variety of cations that depends, in part, on the size of the ether, the type of donor atoms (e.g. oxygen, nitrogen, sulfur), and the polarity of the solvent. Crown-ethers and related macrocycles are of particular interest to research efforts in chemical separations applied to environmental remediation. For example, at the Hanford nuclear facility {sup 9O}Sr{sup 2+} and {sup 137}Cs{sup +} are two major generators of heat which complicate the disposal of nuclear waste. One example of the use of crown-ethers for radionuclide separation is the Strontium Extraction (SREX) process which uses di-t-butylcyclohexano-18-crown-6 for recovering {sup 9O}Sr{sup 2+} from acidic solution. A more thorough understanding of fundamental interactions of cation/crown-ether solution chemistry may provide the basis for rational design of new ligands useful in the separation of these and other radionuclides from radionuclide-containing waste streams at hazardous waste storage facilities. There is also a growing interest in the use of crown-ethers, cryptands, and other ligands for use in chemical sensors. Specifically, fluoroionophores, which consisting of a fluorophore (e.g. dye-molecule) linked to an ionophore (e.g. crown-ether), exhibit measurable changes in the photophysical properties of the fluorophore upon ion binding by the ionophore. Fluoroionophores would be useful for monitoring ground-water aquifers and industrial effluent streams for low-levels of hazardous radionuclides and other toxic metals