Hunting the “Invisible” Elements

Hunting the “Invisible” Elements

Author: Susanne Poth

Understanding the basic chemical properties of astatine is a major challenge: It is mostly produced in cyclotrons, and since it has only short-lived isotopes, experimental investigations are led at ultra-trace concentrations and so the Pourbaix diagram (or EH-pH diagram) remains unfinished. A Pourbaix diagram gives information on behavior of a system as the pH and potential vary. However, there is increasing interest in astatine, especially astatine-221 (221At) radionuclide, for use in nuclear medicine.

It is generally assumed that astatide (At) is the predominant astatine species in basic aqueous media. Nicolas Galland and Gilles Montavo, Université de Nantes, France, and co-workers questioned this assumption in non-complexing and non-reductive aqueous solutions and combined chromatography, competition experiments, and quantum mechanical calculations to prove it. Contrary to what is usually believed, they found that At is a minor species at pH = 11. Rather, they identified the AtO(OH)2 species as the one that predominates in non-complexing and non-reductive basic aqueous solutions.

Beyond being a fundamental steps towards the completion of the Pourbaix diagram of astatine, this new information is of interest for the development of 211At radiolabeling protocols.


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