The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a fifteen-month research fellowship by Dr. Patricia J. Melfi to work with Dr. Luigi Fabbrizzi at the University of Pavia in Italy.
Preferential removal of certain anions in the presence of a number of other species is a major challenge in the field of environmental and supramolecular chemistry. For example, selective removal of sulfate from the nitrate-rich byproducts of the nuclear fuel cycle is essential in the storage of radioactive waste. Elevated levels of anions in drinking water have also been linked to a number of diseases. As the sensing and removal of these anions must occur in the presence of a number of other species; a selective anion receptor is essential. In answer to this problem, an immense number of organic scaffolds have been introduced into the literature in the hopes of increasing the general knowledge of anion coordination. It is now largely accepted that higher anion selectivity may be achieved by the careful design and synthesis of a rigid receptor cavity tailored for the recognition of specific anions of a given geometry. The goal of this project is the synthesis of a new class of anion receptors which combine a somewhat rigid backbone of a metalated cyclam (1,4,8,11-tetraazacyclotetradecane) with ureas. It is hypothesized that careful placement of two or four urea pendant arms around the cyclam macrocycle will result in a cavity able to selectively coordinate specific anions. The size and shape of the cavity can then be quickly altered or 'tuned' for a different anion through coordination of a different metal cation. In addition to the conformation change induced by the cation, the proposed anion receptors will involve a cation-anion pair. In the field of anion recognition, selectivity based on an ion-pair is still relatively young but shows immense potential. With the addition of a cation into an organic receptor, anion binding strength and selectivity can be increased through both electrostatic interactions (from the presence of the electropositive cation) and / or allosteric effects (the receptor is conformationally altered with the addition of a cation). Anion binding and selectivity will be studied by UV-visible and 1H NMR spectroscopy.
