Experiments designed to test discrepancies in theoretical computational chemistry have turned up a barely two-angstrom difference that may lead to a new approach to locate and remove dangerous toxins such as perchlorate and nitrates from the environment.
The research targets toxic groundwater contaminants that contain negatively charged ions known as anions (a-NI-ens), which are historically difficult to remove. Perchlorate, a rocket fuel additive recently linked to thyroid deficiency in women, has contaminated more than 450 wells in California alone. Nitrate contamination, which results mainly from the use of nitrogen fertilizer, is a leading cause of shutdowns of wells and public water supplies in the United States.
"There is a need for improved materials that are effective at removing anions from the environment," said Darren W. Johnson, a University of Oregon chemist and co-principal investigator of a study appearing online Dec. 13 ahead of regular publication in the Journal of the American Chemical Society. "A current leading strategy is anion exchange, which uses a polymeric resin to exchange an anion for one thats not a problem." (Two other currently used methods aimed at anions are biochemical denitrification and reverse osmosis.)
In the new study, led by UO doctoral student Orion B. Berryman, researchers focused on anion-pi interaction, in which a negatively charged species is attracted to a neutral electron-deficient aromatic ring, which could be incorporated into a specifically designed receptor.
Anion-pi interactions have been the focus of recent theoretical work, in which electronic structure calculations predicted that anion binding between halides and electron-deficient aromatic rings will occur over the center of a ring. However, the lab experiments on crystalline material found that the binding occurs as much as 2 angstroms, or 0.2 nanometers from the center.