Abstract View
The Exploration of Halogen Chemistry on Buckyballs for Understanding Homologues of 211Astatine
Category: Other Halogen Radionuclide Chemistry
Authors:
Elizabeth Schnorrenberg1,2, Shayden Fritz1,2, Marcus Le1,2, Federica Pisaneschi3, Lauren McIntosh1, Sherry J. Yennello1,2
1 Cyclotron Institute, Texas A&M University, College Station, TX USA; 2 Department of Chemistry, Texas A&M University, College Station, TX USA; 3 Institute of Molecular Medicine, UT Health Houston, Houston, TX USA
Objective: Astatine-211 (211At) is an alpha emitter with a short half-life, 7.21 hours, being studied for its possible use in targeted alpha therapy. There are no stable isotopes of astatine, leaving limited availability to understand its chemistry, so the ability to find a homologue for its chemical properties is imperative. Astatine is in group 17 of the periodic table, and is hence considered a halogen. Iodine is just above astatine in the chain of halogens, and the most likely surrogate for studying the chemistry of astatine. The astatine-carbon bond has been a particular interest of study, where astatine has strong interactions with sp2 hybridized carbons. The ability to find a more stable astatine-carbon bond would help in the design of future radiopharmaceuticals. Fullerene rings, also known as buckyballs, are completely sp2 hybridized carbon compounds. Since there is known favorability of astatine bonds towards sp2 carbons, it is hypothesized that the interaction of astatine with a fully sp2 carbon complex would help stabilize the astatine-carbon bond. Studying and fully characterizing the interaction of iodine with C60 fullerene rings, which are completely sp2 hybridized, could shed light on astatine’s interactions. Comparing the reactivity of iodine versus that of astatine with C60 can also give insight into the utility of iodine as a homologue for future studies.
Methods: I2, in excess, and C60 were dissolved in toluene. The solution was heated at 95oC and mixed for 24 hours. The solution was then run on a reverse phase HPLC column (Waters Spherisorb ODS2) at 350 ± 20nm, in a 9:1 Methanol:Toluene mobile phase. The HPLC chromatogram was compared to HPLCs of standards (unreacted C60 and I2).
Results: The I2 reacted with the C60, as the peaks shifted in the HPLC diagrams (fig 1). The pure C60 peaks and I2 peak had retention times of 34 seconds, 49 seconds, and 1 minute 56 seconds, respectively (fig 1a&b). In an excess of iodine, there was a 12% ROI overlap between the C60 and I2 peaks, with a retention time of 1 minute 40 seconds. There was still a pure I2 peak within the HPLC, which was expected as there was excess I2 to begin with, but no pure C60 peak, indicating that the C60 reacted in full. The reacted ROI contains approximately 4.83µg I2 and 18µg C60.
Conclusions: From these preliminary data, iodine seems to react with the C60 structure. Crystals are currently growing for chemical characterization, XRD and SEM of the iodine and fullerene reaction product. After complete characterization is done, the experiment will be repeated with 125I and with 211At for studies of its halogen characteristics, to determine if fullerene is a suitable building block for a stable astatine-carbon bond, with the potential to be incorporated in radiopharmaceuticals.
Figure 1. (A) HPLC chromatograph of unreacted I2;(B) HPLC chromatograph of unreacted C60;(C) HPLC chromatograph of heated C60 and I2 solution.