Journal of Nuclear and Radiochemical Sciences, Vol. 8, No. 2, pp. 105-107, 2007

Synthesis of Endohedral 133Xe-Fullerenol by Using Higher Fullerene
S. Watanabe,* T. Katabuchi, N. S. Ishioka, and S. Matsuhashi
Quantum Beam Science Directorate, Japan Atomic Energy Agency, Takasaki, Gunma 370-1292, Japan
Received: October 20, 2006; In Final Form: April 3, 2007
Hydrophilic endohedral 133Xe-fullerenols [133Xe@C76 (OH) x and 133Xe@C84 (OH) x] were synthesized from hydrophobic endohedral 133Xe-fullerenes. The yields were found to depend on the solubility of endohedral 133Xe-fullerenols in o-dichlorobenzene and water phases, reflecting the number of OH groups of the product. The endohedral
133
Xe-fullerenols stored in 0.9% NaCl solution at 20 °C were stable enough for the use in nuclear medicine.

Hydroxylation process

1. Introduction
Endohedral fullerenes encapsulating a radionuclide within
the fullerene cage are of current interest as radiopharmaceuticals for therapy and diagnosis.1–6 To realize these medical purposes, hydrophilic fullerene derivatives, which allow in vivo
investigations, have to be synthesized. We synthesized hydrophilic endohedral 133 Xe-fullerenols [133 Xe@C 60 (OH) x and133
Xe@C70 (OH) x] 7 which would be applied to the therapy ofbone cancer, because 133Xe emits β rays with the maximum
energy of 0.346 MeV and fullerenol is concentrated in bone
tissues.
For therapeutic purposes, the separation of endohedral 133Xefullerenes from empty fullerenes is necessary, because theendohedral 133Xe-fullerene derivatives not containing empty
fullerenes could effectively concentrate in target tissues. In theprevious work, however, we did not succeed in separating
133
Xe@C60 from C60 and 133Xe@C70 from C70.8,9 Recently, we
produced endohedral higher 133Xe-fullerenes such as 133Xe@C76
and 133Xe@C84 by implantation of 133Xe ions into C76 and C84
fullerene targets. It was easy to separate endohedral higher
133
Xe-fullerenes from empty fullerenes by the high performanceliquid chromatography (HPLC).10 The present work aims at
the synthesis of hydrophilic endohedral 133 Xe-fullerenols[133Xe@C76 (OH) x and 133Xe@C84 (OH) x] from the endohedral
higher 133Xe-fullerenes (133Xe@C76 and 133Xe@C84). To obtain
optimum conditions of the synthesis, yields of the endohedral
133
Xe-fullerenols are examined as a function of reaction time ofhydroxylation of carbon atoms in the fullerene cage. In addition, the extraction behavior of the endohedral 133Xe-fullerenols
from o-dichlorobenzene to water phases are investigated.
2. Experimental
2.1. Production of endohedral higher 133Xe-fullerenes.
The endohedral higher 133 Xe-fullerenes (133 Xe@C 76 and133
Xe@C84) were synthesized in a manner as described in detailin our previous paper.8 Fullerene targets for ion implantation
were prepared by vacuum evaporation of fullerenes (C76 or C84)
on Ni foil. Xenon-133 ions were implanted into the targets with
an isotope separator (Takasaki Institute, JAEA) at an acceleration energy of 30 keV. After the ion implantation, the fullerenes on the target foil were dissolved in o-dichlorobenzene.
The solution was filtered through a membrane filter of 0.2 µm
in pore size (Millipore, JGWP) to remove insoluble materials.
The filtrate was purified by HPLC with a Cosmosil Buckyprep*Corresponding author. E-mail: watanabe.satoshi@jaea.go.jp.
Fax: +81-27-346-9688.

Extraction process

o-dichlorobenzene

133Xe@C

133Xe@Cwater

shaking

76

KOH

1 min

KOH

precipitate

shaking

76(OH)x

water

1 min

precipitate

TBAH

TBAH
133Xe@C

76(OH)x

133Xe@C

76(OH)xo-dichlorobenzene

Figure 1. A Schematic diagram of a synthetic procedure for133
Xe@C76 (OH) x. The same procedure was also used for 133Xe@C60(OH) x, 133Xe@C70 (OH) x, and 133Xe@C84 (OH) x.

column of 4.6 mm i.d. × 250 mm long. The purified solution
was used to synthesize endohedral 133Xe-fullerenols.
2.2. Synthesis of endohedral higher 133Xe-fullerenols.
Hydroxylation of endohedral higher 133 Xe-fullerenes to133
Xe@C 76 (OH) x and 133Xe@C84 (OH) x was carried out in amanner as described in our previous paper.7 The method comprises two processes: hydroxylation and extraction (Figure 1).
In the hydroxylation process, o-dichlorobenzene solution
containing 133Xe@C76 or 133Xe@C84 was shaken for 1 min with
14 M KOH solution containing tetrabutylammonium hydroxide(TBAH, 40% in water) in a polypropylene centrifuge tube.
After shaking, the mixture was centrifuged (9000 rpm, 5 min)to form three fractions of o-dichlorobenzene phase, KOH
phase, and precipitate in between the o-dichlorobenzene and
KOH phases. The o-dichlorobenzene and KOH phases wereseparately transferred into another polypropylene centrifuge
tube, and evacuated in a vacuum desiccator to release gaseous133
Xe from the solution. The 133Xe radioactivity in each fraction of the o-dichlorobenzene phase, the KOH phase, and theprecipitate remaining in the centrifuge tube was measured by
γ-ray spectrometry with a germanium detector.
In the extraction process, water was added to the o-dichlorobenzene containing hydroxylated products, and then the mixture was shaken for 1 min to extract 133Xe@C 76 (OH) x and133
Xe@C84 (OH) x into the water phase. After centrifugation,
each fraction was evacuated in a vacuum desiccator to releasegaseous 133Xe. The radioactivity of 133Xe in each fraction wasmeasured by γ-ray spectrometry.
3. Results and Discussion
Yields of endohedral 133Xe-fullerenols calculated as a percentage of the 133Xe radioactivity extracted into the water phaseagainst the initial 133Xe radioactivity of endohedral higher
133
Xe-fullerenes are summarized in Table 1, together with thoseof 133Xe@C60 (OH) x and 133Xe@C70 (OH) x.7 Here listed are the© 2007 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 10/19/2007

106 J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007

Watanabe

Fullerene species

Yield /%

C60
C70
C76
C84

43
18
21
11

100
Partial yield/ %TABLE 1: Yields of endohedral 133Xe-fullerenols throughhydroxylation for 1 min and extraction for 1 min

50
C60
C70
C76
C84

30

60
40
20 Hydroxylation process

o-dichlorobenzene phase

0

(a)

5
10
15
Reaction time/min

20

100 Hydroxylation process

20
10
0
0

80

0

5
10
15
Reaction time/min

20

Figure 2. Yields of endohedral 133Xe-fullerenols as a function ofreaction time of hydroxylation. The extraction time is fixed to 1 min.

yields obtained at 1 min extraction after hydroxylation for 1
min. The yield decreases with increasing number of carbon
atoms in a fullerene, although slight disorder is seen between
133
Xe@C 70 (OH) x and 133Xe@C 76 (OH) x . The yields should
depend on the number of hydroxyl groups of endohedral 133Xefullerenols synthesized here.
To obtain optimum conditions, the yields of the endohedral
133
Xe-fullerenols were examined as a function of reaction timeof hydroxylation from 1 to 15 min, the extraction time being
fixed to 1 min. As shown in Figure 2, the yield of 133Xe@C60(OH) x decreases monotonically with an increase of the reaction
time, whereas the yields of 133Xe@C70 (OH) x, 133Xe@C76 (OH) x,
and 133Xe@C84 (OH) x increase up to 7 min and then decrease.
Here, it is to be noted that the sum of distribution of 133Xe in
the organic (o-dichlorobenzene) phase and precipitate in thehydroxylation process were almost constant, and higher than
90% irrespective of the reaction time of hydroxylation. The
distribution of 133Xe in the aqueous (KOH) phase was about
5%. The endohedral 133Xe-fullerenols once produced in theorganic phase did not migrate to the aqueous phase, suggestingthat the fullerenols synthesized here should be insoluble in 14
M KOH solution. The gaseous 133Xe released from endohedral
133
Xe-fullerenes was about 5% or lower in the present work.
Changes in the distribution of 133Xe in the organic phase andprecipitate in the hydroxylation process are shown in Figures
3(a) and 3(b) as a function of the reaction time of hydroxylation. As shown in Figure 3(a), the distributions of 133Xe as
133
Xe@C70 (OH) x, 133Xe@C76 (OH) x, and 133Xe@C84(OH) x in theorganic phase are as high as 90% at short reaction time but
decrease after 7 min. On the contrary, the distributions of 133Xein the precipitate increase after 7 min as shown in Figure 3(b).
The fact suggests that endohedral higher 133Xe-fullerenols once
produced should change to the precipitating species at longer
time of hydroxylation. The precipitating species might be ahydrophilic endohedral fullerenols insoluble in o-dichlorobenzene with a large number of hydroxyl groups.
To get an insight into the extraction process, we observed

Distribution of 133Xe/ %Yield/ %

40

C60
C70
C76
C84

Precipitate phase

80
60

C60
C70
C76
C84

40
20
0

0

(b)
5
10
15
Reaction time/min

20

Figure 3. (a) Partial yields of endohedral 133Xe-fullerenols obtainedin the o-dichlorobenzene phase in the hydroxylation process as afunction of reaction time of hydroxylation. (b) Distribution of 133Xein precipitate in the hydroxylation process as a function of reaction
time of hydroxylation.

changes in the partial yield that was defined as a percentage ofthe endohedral 133Xe-fullerenols extracted into the water phaserelative to the initial amount of endohedral 133Xe-fullerenols
produced in the o-dichlorobenzene phase through hydroxylation. The partial yields of the endohedral 133Xe-fullerenols
extracted into the water phase are shown in Figure 4(a) as afunction of reaction time of hydroxylation, the extraction time
being fixed to 1 min. As shown in Figure 4(a), the partial
yields of 133Xe@C 70 (OH) x , 133Xe@C 76 (OH) x , and 133Xe@C84(OH) x increase from 20% or less to 40% or more in 7 min andthen become almost constant thereafter. In contrast, the distributions of 133Xe in the water-insoluble precipitate (Figure 4(b))
are as high as 60–75% for the endohedral higher 133Xe-fullerenols synthesized in short-time hydroxylation, and decrease
gradually to smaller values in 7 min. They become almost
constant after 7 min. In this extraction process, the distributions of 133Xe in gaseous phase were about 15% or lower, and in
the organic phase were about 5% or lower.
The increase of the yields of 133Xe@C70 (OH) x , 133Xe@C76(OH) x, and 133Xe@C84(OH) x up to 7 min (Figure 2) is explained
as follows. Endohedral higher 133Xe-fullerenols that are highly
soluble in o-dichlorobenzene are synthesized through hydroxylation up to 7 min (Figure 3(a)). These fullerenols with rather
small number of hydroxyl groups are still hydrophobic andinsoluble in the water phase at the reaction time of 1 min(Figure 4(a)). According to Li et al.,11 fullerenols with lesshydroxyl groups than 10 is insoluble in water. As the reaction
time increases, the hydroxylation proceeds to afford hydrophilic species soluble in water. After 7 min, endohedral 133Xefullerenols with a large number of hydroxyl groups are

J. Nucl. Radiochem. Sci., Vol. 8, No. 2, 2007 107

Synthesis of Endohedral 133Xe-Fullerenol by Using Higher Fullerene
133

Partial yield/ %100
Extraction process
Water phase

80
60
40

C60
C70
C76
C84

20
0

0

100

Distribution of 133Xe/ %

(a)

80

5
10
15
Reaction time/min
Extraction process
Precipitate phase

20

(b)

Acknowledgement. The authors wish to thank Dr. H. Kudoof Tohoku Radiation Science Center for his helpful discussions
and suggestions.

60
40

References
C60
C70
C76
C84

20
0

0

Xe@C70 (OH) x, 133Xe@C76 (OH) x, and 133Xe@C84 (OH) x were43%, 34%, 45%, and 26%, respectively. When we synthesizedthese endohedral 133Xe-fullerenols by using the method of
Cagle et al., 5 the corresponding yields were as low as 1.2%,
2.1%, 12%, and 17%. In addition, most of the encapsulated
133
Xe atoms were found to be released from the fullerene cagein the latter case where it took 12 h for hydroxylation.
For medical applications, the stability of 133Xe@C60 (OH) x,
133
Xe@C70 (OH) x, 133Xe@C76 (OH) x, and 133Xe@C84 (OH) x synthesized here was examined in saline solution. When the endohedral 133Xe-fullerenols were stored in 0.9% NaCl at 20 °C, thedecomposition or release of 133Xe was less than 10% even after
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would be favorable for nuclear medicine. In particular, themedical use of 133Xe@C76 (OH) x and 133Xe@C84(OH) x would behighly promising because 133Xe@C76 and 133Xe@C84 are easily
separated from empty fullerenes (C76 and C84) by HPLC before
the hydroxylation.105
10
15
Reaction time/min

20

Figure 4. (a) Partial yields of endohedral 133Xe-fullerenols extracted
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Xe-fullerenols produced in the o-dichlorobenzene phase throughhydroxylation.

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Xe@C 6 0 (OH) x soluble in o-dichlorobenzene decreased
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