Penn chemists make first molecular binding measurement radon

Penn chemists make first molecular binding measurement of radon

2:02 PM, 30th July 2011
Penn chemists make first molecular binding measurement of radon
A rendering of a water-soluable cryptophane molecule binding a xenon atom.

PHILADELPHIA, US: Even in trace quantities, the radioactive gas radon is very dangerous; it is second only to cigarette smoking as a cause of lung cancer deaths in the United States. The expense and precautions necessary to study it safely have limited research into its properties. Now, University of Pennsylvania chemists have for the first time measured how well radon binds to a molecule, paving the way for future research on it and other noble gasses.  

The research was led by Associate Professor, Ivan J Dmochowski, along with Undergraduate, Vagelos, Scholar, David R Jacobson and Graduate students, Najat S Khan and Yubin Bai of the Department of Chemistry in Penn’s School of Arts and Sciences. Because radon is so difficult to generate and handle safely, the Penn team collaborated with researchers at the National Institute of Standards and Technology who have experience in that area.

Their work was published in the journal Proceedings of the National Academy of Sciences.

Dmochowski’s research group has long studied how xenon, a gas chemically similar to radon, interacts with the organic molecule cryptophane. With its cage-like structure, different kinds of cryptophane excel at binding even the non-reactive noble gasses. “We predicted that radon would bind slightly better than xenon, as xenon under-fills the cavity in the cryptophane and radon is a little bit larger,” said Dmochowski.

“Other researchers made previous measurements of radon’s interaction with bulk materials, like charcoal or ice,” said Jacobson. “But this is the first measurement of radon binding to a discrete molecule.”

The team didn’t measure individual radon atoms but rather a solution of radon and a new water-soluble cryptophane. The cryptophane was synthesized for the first time in their lab, but acquiring an appreciable amount of radon was a bigger challenge.   

At the core of the method are capsules of another radioactive element, radium, which were developed by NIST, Researcher and Co-author, Ronald Collé. The team placed the capsules into sealed vials of water. As the radium decayed, the gaseous radon leached out. Less free radon gas indicates that the element was binding to the cryptophane. To measure exactly how much radon was bound, the team used a process known as liquid scintillation.

“Now that we have a robust method for measuring radon binding to discrete entities, we could apply it to things like proteins found in the lungs,” said Dmochowski. “If you know radon’s affinity for those proteins, you have a better idea of the concentration and timescale over which it will be dangerous.”

Better radon-binders could be also used to extract the dangerous element from groundwater. The same principle could be used to harvest xenon from the atmosphere. Xenon is relatively safe and has a wide range of medical and industrial uses.  

Ryan Fitzgerald and Lizbeth Laureano-Pérez of NIST also contributed to the research. Their work was supported by the Department of Defense, the National Institutes of Health and the National Science Foundation.

(C) University of Pennsylvania News

 

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