The Targeted Alpha Therapy research group in Gothenburg, Sweden (www.tat.gu.se) has been working with the rare nuclide astatine-211 for over 20 years. After cyclotron production astatine is recovered using dry distillation and many of the early ears was spend trying to stop the astatine from “disappearing”, ending up in the wrong place of the experimental set-up and, once in the right place, taking on a suitable chemical form. Serendipity and hard-earned experience finally resulted in successful and efficient recoveries, revealing chloroform to be the almost ideal solvent for astatine. Ironically enough this toxic carcinogen has been in the service of medicine, including oncology, ever since the mid 1800’s as an anesthetic, and still seem to have an important role to play in the future. This as astatine dissolved in chloroform can be evaporated to dryness without any loss of activity, allowing all sorts of different chemistry to be performed with starting point in the dry residue. “But what form is your astatine in then?” one especially obnoxious colleague asked me at a conference, and later, the same person asked the exact same thing at another meeting, and truth be told, we had no idea, other than it worked fine! So, I therefore decided to embark on the journey to try and elucidate the chemistry of astatine in chloroform.
Astatine-211 is perhaps the most promising nuclide candidate for Targeted Alpha Therapy of disseminated cancer with a curative intent. This is due to its beneficial physical properties such as suitable half-life and short decay chain without toxic daughters, compared to many other alpha particle emitting options. However, what is less beneficial with astatine is the chemistry, which is much less well-known than that of most other elements in nuclear medicine. This is because no long-lived or stable isotopes exists to enable standard chemical investigations. This very fact, that astatine-211 is a short-lived (t1/2=7.21 h) alpha particle emitter that is intended for therapeutic use, requiring high activity preparations, is something that we have decided to take into account in our investigations, i.e. that radiolysis severely affects the chemical behavior. This makes experimental conditions much more complicated and the interpretation of results notably challenging but, that’s research …
Because of this I would like to call our work applied basic investigations, and although we have come a long way with the present study, employing a number of different experimental techniques in combination with theoretical models, much work still remain before the chemistry of astatine has been elucidated!
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