Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 52 (2019)

Speciation analysis of oxidation states of astatine
extracted into ethanol-water solutions
Y. Shin,∗1 K. Kawasaki,∗1 K. Aoi,∗2 K. Washiyama,∗3 A. Yokoyama,∗2 I. Nishinaka,∗4 S. Yanou,∗5 and H. Haba∗5
The short-path length and high linear energy transfer of α particles are expected to enable targeted alpha therapy for the treatment of tumor. A promising
nuclide among various α emitters is 211 At with a halflife of 7.21 h, which has gained popularity owing to its
appropriate life and possible compounds as a halogen
element. This has been the motivation behind several
preclinical studies on At-chemistry1) However, the successive chemical processes for the general use of Atchemistry has not been well studied. We aim to study
the wet chemistry processes of At that may form a prevailing technology.
In previous studies,2,3) the At-211 radioactivity wasrecovered eﬃciently from an irradiated Bi target in thechemical systems of dodecane and ethanol solution withoxidizing agents such as N-bromosuccinimide (NBS)
and bromine water, which supply Br2 . However, themechanism of solvent extraction was not clariﬁed in thestudy. Here, we performed a thin layer chromatography(TLC) experiment to investigate the oxidation states ofAt species extracted into the system with NBS as wellas bromine water, in reference to a TLC study on Atspecies.4)
The At-211 radioactivity was produced via 209 Bi(α,2n) reaction at the RIKEN AVF cyclotron and delivered
to Kanazawa University. The irradiated Bi target wasdissolved in 2 mL of 6 M HNO3 and diluted with 10 mLof H2 O to prepare a 1 M HNO3 solution, from which
the 211 At nuclide was extracted into the dodecane solvent. Aliquots of the solution were subjected to backextractions into 90% ethanol solution with NBS or Br2
water after 15 min of its addition or without an oxidizing agent. 10 μL from each sample of 211 At (ca. 15 to50 Bq) obtained in the back extractions was spotted on
a TLC plate (Merck Silica gel 60 F254 aluminum sheet,
10 × 2 cm) and developed with 50% ethanol solution for
90 min (7 cm in ﬂow distance). After drying, the platewas exposed to an imaging plate for 10 to 20 min to
perform an image analysis of its radioactivity.
The images of TLC demonstrated in Fig. 1 suggestthat three diﬀerent species were separated. The results of the analysis exhibit that the oxidizing agents ofBr2 water and NBS signiﬁcantly increase the oxidized
species of AtO4 − instead of decreasing the others’ as
∗1
∗2
∗3
∗4
∗5

Institute and College of Science and Engineering, Kanazawa
UniversityGraduate School of Natural Science and Technology,
Kanazawa University
Fukushima Global Medical Science Center, Fukushima Medical Unversity
Quantum Beam Science Research Directorate, National Institutes for Quantum and Radiological Science and TechnologyRIKEN Nishina Center- 204 -compared to the case without an oxidizing agent. This
indicates that such oxidation due to the agents causes
distribution among the species and enhance the distribution ratio of At during extraction. Therefore, theback-extraction favors the oxidized species instead ofAt− .

Fig. 1. Imaging of 211 At radioactivity on thin-layer chromatography for (a) Br2 water, (b) NBS, and (c) no oxidizing agent (see text for detail).

Table 1. Distributions of At chemical species in extractedsolutions.

ChemicalspeciesAt㸫AtO3㸫
AtO4㸫

Br2 waterNBS

No addition

12 %
47 %
41 %

13 %
45 %
42 %

23 %
57 %
20 %

References
1) F. Guérard, J-F. Gestin, M. W. Brechbiel, Cancer Biother. Radiopharm., 28, 1 (2013).
2) E. Maeda, A. Yokoyama, T. Taniguchi, K. Washiyama,
I. Nishinaka, J. Radioanal. Nucl. Chem. 303 (2), 1465
(2015).
3) Y. Shin, K. Kawasaki, N. Yamada, K. Washiyama,
A. Yokoyama, I. Nishinaka, S. Yanou, H. Haba, RIKEN
Accel. Prog. Rep. 51, 228 (2018).
4) I. Nishinaka, K. Hashimoto, H. Suzuki, J. Radioanal.
Nucl. Chem. 318, 897 (2018).