III-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Solvent extraction and speciation of astatine species via thin layer
chromatography
S. Maruyama,∗1 K. Aoi,∗1 Y. Nagai,∗2 K. Washiyama,∗3 A. Yokoyama,∗2,∗4 I. Nishinaka,∗5 Y. Wang,∗4 andH. Haba∗4
The short path length and high linear energy transfer of α particles are expected to enable targeted alphatherapy for the treatment of cancer. A promising nuclide among various α emitters is 211 At with a half-lifeof 7.21 h, which has gained prominence owing to its appropriate half-life for labelling and drug pharmacokinetics and potential to synthesize labelled compounds as ahalogen element. This has motivated several preclinical studies on At chemistry.1) However, the successive
chemical processes for the general use of At chemistry
have not been understood well. One of the diﬃculties in
At chemistry is the coexistence of several At species ina sample. For instance, the species of At− , AtO−
3 , andAtO−
4 are identiﬁed in some solutions via thin layer chromatography (TLC).2) This makes the processes complex,
and the species need to be adjusted by varying the redox
potential, hydrogen ion concentration, and other factors
for appropriate preparation of At solutions.
We aimed to study At species in diisopropyl ether(DIPE) solvent, which was shown to extract cationicspecies of At in a previous study.3) Speciation of At
was performed via TLC similar to the method in Ref. 2)
but in an argon atmosphere, to allow preservation of thespecies during the drying and development time for theTLC.
In this study, 211 At was produced via the 209 Bi(α, 2n)reaction at the RIKEN AVF cyclotron and delivered toKanazawa University. The irradiated Bi target was dissolved in 3 mL of 6 M HNO3 and mixed with an appropriate amount of H2 O to prepare 1 M HNO3 solution,

Fig. 1. TLC chromatogram of At species extracted from 9 M
HCl.
∗1
∗2
∗3
∗4
∗5Graduate School of Natural Science and Technology,
Kanazawa University
Institute and College of Science and Engineering, Kanazawa
University
Fukushima Global Medical Science Center, Fukushima Medical University
RIKEN Nishina Center
Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and Technology

Fig. 2. Distributions of At species extracted to DIPE by TLC
and their extraction ratios.

7 mL of which was used to extract the 211 At nuclide into
7 mL of dodecane solvent.
Aliquots of the dodecane solution were subjected toback extractions into several solutions of various HClconcentrations ranging from 1 M to 9 M. Approximately
0.5 mL of each HCl solution was subject to solvent extraction with 0.5 mL of DIPE. TLC was performed on
10 µL of each DIPE solution to determine the 211 Atspecies.
Figure 1 displays the TLC chromatogram showing anew species at approximately Rf = 0.2, which was notfound in an open air experiment, in addition to the At− ,−AtO−
3 , and AtO4 . Figure 2 demonstrates the compositions of the At species, except for the continuum composition deduced from the TLC chromatograms, in Ref. 2),
and the At extraction rates dependent on the HCl concentration. The new species increases with the increasein the HCl concentration and the extraction rate. Therefore, the species is considered to be a cation of At basedon a previous study.3)
We are in planning on applying the TLC technique toother extraction systems to identify extracted At species
and clarify the mechanism of At extraction. Such information will be useful to construct chemical processes forthe general use of At chemistry.
References

1) F. Guérard, J. -F. Gestin, M. W. Brechbiel, Cancer Biother. Radiopharm. 28, 1 (2013).
2) I. Nishinaka et al., J. Radioanal. Nucl. Chem. 318, 897(2018).
3) T. Taniguchi, Master thesis of Graduate School of NaturalScience and Technology, Kanazawa University (2015).

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