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X-ray Structures Answer Old Riddles Relevant to
Today's Nuclear-Waste Treatment

Structures Sometimes in the progress of forefront research, one gets two answers for the price of one. Based on X-ray structures recently determined at ORNL, it now appears that phenolic extractants known for four decades and recently discovered calixarene-crown extractants share features that confer extremely high selectivity for cesium. Both types of extractants have been examined intensively for use in nuclear-waste cleanup, but it had not been understood that they possess the same ability to bond to alkali metal cations through the pi-cloud of a benzene ring. In the case of calixarene-crowns, the pi-bonding takes place in a preorganized molecular cavity, whereas simple 2-benzylphenols apparently self-assemble about the cation. With a better structural understanding of these compounds, the ORNL Chemical Separations Group aided by calculations performed by Ben Hay at PNNL is designing new modifications that may lead to yet higher selectivity. If you'd like to learn more about this work, please have a look at some of our recent papers such as: J. C. Bryan, L. H. Delmau, B. P. Hay, J. B. Nicholas, L. M. Rogers, R. D. Rogers, and B. A. Moyer, "Cesium Recognition by Supramolecular Assemblies of 2-Benzylphenols with 2-Benzyl-phenolate." Struct. Chem. 10, 187-203 (1999) and R. A. Sachleben, A. Urvoas, J. C. Bryan, T. J. Haverlock, B. P. Hay, and B. A. Moyer, "Dideoxygenated Calix[4]arene Crown-6 Ethers Exhibit Enhanced Selectivity for Cesium over Potassium and Rubidium," J. Chem. Soc., Chem. Commun. 1751-1752 (1999).

This research was sponsored by the Division of Chemical Sciences, Office of Basic Energy Sciences, U. S. Department of Energy, under contract number DE-AC05-96OR22464 with Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corp.

Chemical Separations Group R & D Projects

Provided by Oak Ridge National Laboratory's Chemical Sciences Division
Rev:   October 20, 2005