Unique Separation Behavior of a C60 Fullerene-Bonded Silica Monolith Prepared by an Effective Thermal Coupling Agent

Article abstract of DOI:10.1002/chem.201503898

Herein, we report a newly developed C₆₀ fullerene-bonded silica monolith in a capillary with unique retention behavior due to the structure of C₆₀ fullerene. N-Hydroxysuccinimide (NHS)-conjugated C₆₀ fullerene was successfully synthesized by a thermal coupling agent, perfluorophenyl azide (PFPA), and assigned by spectroscopic analyses. Then, NHS-PFPA-C₆₀ fullerene was attached onto the surface of a silica monolith in a capillary. The capillary provided specific separation ability for polycyclic aromatic hydrocarbons in liquid chromatography by an effective π-π interaction. Furthermore, corannulene, which has a hemispherical structure, was selectively retained in the capillary based on the specific structural recognition due to the spherical C₆₀ fullerene. This is the first report revealing the spherical recognition ability by C₆₀ fullerene in liquid chromatographic separation. Spherical recognition: A C₆₀ fullerene-bonded silica monolithic medium was prepared by using a thermal coupling agent conjugated with C₆₀ fullerene. The C₆₀ fullerene-bonded monolith prepared in a capillary showed a very strong π-π interaction in liquid chromatography. Also, the hemispherical molecule corannulene was dramatically retained in the C₆₀ fullerene-bonded monolith by the unique molecular recognition based on a buckyball (see figure).

Full text of DOI:10.1002/chem.201503898

DOI: 10.1002/chem.201503898
Communication
&
Liquid Chromatography
Unique Separation Behavior of a C60 Fullerene-Bonded Silica
Monolith Prepared by an Effective Thermal Coupling Agent
Takuya Kubo,*[a] Yoshiki Murakami,[a] Madoka Tsuzuki,[a] Hiroshi Kobayashi,[b] Toyohiro Naito,[a]
Tomoharu Sano,[c] Mingdi Yan,[d] and Koji Otsuka[a]
action due to the strong van der Waals force,[7] it is expected
Abstract: Herein, we report a newly developed C60 fuller-
that nanocarbon materials show significantly high p–p interac-
ene-bonded silica monolith in a capillary with unique re-
tion effect. For example, the polarizability of C60 fullerene was
tention behavior due to the structure of C60 fullerene. N-
previously estimated to be 84.0 to 85.4”10À40 JÀ1 C2 m2, which
Hydroxysuccinimide (NHS)-conjugated C60 fullerene was
is much higher than that of other PAHs.[8]
successfully synthesized by a thermal coupling agent, per-
Therefore, some researchers reported new separation media
fluorophenyl azide (PFPA), and assigned by spectroscopic
using nanocarbon materials. In one of the reports, graphene
analyses. Then, NHS-PFPA-C60 fullerene was attached onto
oxide was employed for capillary chromatography or capillary
the surface of a silica monolith in a capillary. The capillary
electrochromatography, and then PAHs were effectively sepa-
provided specific separation ability for polycyclic aromatic
rated in these media.[9] However, in these approaches, nonspe-
hydrocarbons in liquid chromatography by an effective p–
cific interactions based on the introduced functional groups
p interaction. Furthermore, corannulene, which has a hemi-
were revealed, so that another method without any oxidation
spherical structure, was selectively retained in the capillary
process is required. Additionally, although C60 fullerene was
based on the specific structural recognition due to the
also utilized as a separation medium in liquid chromatography
spherical C60 fullerene. This is the first report revealing the
(LC), and an effective separation was observed, a complicated
spherical recognition ability by C60 fullerene in liquid chro-
synthesis by Grignard reaction was necessary.[10] On the other
matographic separation.
hand, phenyl azide, which provide nitrene by a photo and/or
thermal action,[11] is one of the suitable interface to react with
carbon materials.[12] Additionally, the phenyl azide substituted
Nanocarbon materials, such as fullerenes, graphene, and
carbon nanotubes, have specific properties, such as high spe-
cific surface area, physical strength, and conductivity.[1] There-
fore, a variety of applications had been carried out for elec-
tronic materials,[2] reinforced materials,[3] medicals,[4] and
others.[5] As another possibility of nanocarbon materials, the ef-
fective separations of polycyclic aromatic hydrocarbons (PAHs)
and halogenated aromatic compounds based on the p–p in-
teraction are attractive for new applications.[6] In general, the
London dispersion leading to the p–p interaction is dependent
on the polarizability among compounds, so that aromatic com-
pounds provided relatively higher interaction. Especially be-
cause PAHs with large p conjugations allow higher p–p inter-
with fluorine effectively reacted with nanocarbon materials
through the suppression of side-reactions due to an increase
of an activation energy introduced by the electron-withdraw-
ing character of the four fluorine atoms, which leads to the
chemoselective reaction by a nitrene.[13] In recent years, Yan
and co-workers reported perfluorophenyl azide (PFPA). PFPA is
attractive for semi-click type reaction with carbon materials
and a number of applications by immobilization of graphene
or C60 fullerene were described.[14] In our previous study, the
polymer-based PFPA derivative allowed the immobilization of
graphene flakes on the silicon wafer[15] and a protein microar-
ray by immobilization of sugars.[16] Furthermore, C60 fullerene
was immobilized onto the capillary inner wall through PFPA
derivatives and the open tubular capillary provided the effec-
tive separation of PAHs.[17]
[a] Dr. T. Kubo, Y. Murakami, M. Tsuzuki, Dr. T. Naito, Prof. Dr. K. Otsuka
Department of Material Chemistry, Graduate School of Engineering
Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510 (Japan)
E-mail: kubo@anchem.mc.kyoto-u.ac.jp
Herein, we aim to develop a new separation medium for LC
with a C60 fullerene-conjugated PFPA using a silica monolithic
capillary, which provides the high-separation efficiency in LC.
The separation selectivity based on the p–p interaction for
PAHs using the capillary was evaluated in detail. Also, the spe-
cific spherical recognition due to the bonded C60 fullerene is
discussed.
[b] H. Kobayashi
Shinwa Chemical Industries Ltd. 50-2 Kagekatsu-cho
Fushimi-ku, Kyoto 612-8307 (Japan)
[c] Dr. T. Sano
Center for Environmental Measurement and Analysis, National Institute for
Environmental Studies, Onogawa 16-2, Tsukuba, Ibaraki 305-8506 (Japan)
To obtain an active agent for immobilization of C60 fullerene,
N-hydroxysuccinimide (NHS)-introduced PFPA conjugated with
C60 fullerene was successfully synthesized as shown in
Scheme 1. Although the synthesis of NHS-PFPA-C60 fullerene
was previously reported,[18] the detailed spectroscopic data
[d] Prof. Dr. M. Yan
Department of Chemistry, University of Massachusetts Lowell
One University Ave., Lowell, MA 01854 (USA)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201503898.
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Scheme 1. Synthesis of N-hydroxysuccinimide-introduced PFPA conjugated
with C60 fullerene (NHS-PFPA-C60 fullerene). (1) Methyl pentafluorobenzoate;
(2) PFPA-CO2CH3; (3) PFPA-COOH; (4) PFPA-NHS; and (5) NHS-PFPA-C60 fuller-
ene.
was not completed. Herein, the purification was optimized,
and a few characteristic data including FTIR, 13C NMR, FABMS,
and elemental analysis of NHS-PFPA-C60 fullerene was summar-
ized (see Figures S1 to S3 and Table S1 in the Supporting Infor-
mation). These results clearly showed the isolation of an objec-
tive compound. In brief, the FTIR spectra corresponded to the
structures of all the intermediates, FABMS showed the exis-
tence of C60 fullerene-based on the isotope peaks and the
parent ion, 13C NMR analysis provided the clear aromatic peaks
containing C60 fullerene and NHS moiety.
Scheme 2. Schematic image of the modification with C60 fullerene onto the
surface of a silica monolith.
the mesopore. On the other hand, the absolute C% was
almost the same level as an authentic octadecylsilyl bonded
silica (C18) column, so that we considered the prepared capilla-
ry column was acceptable for the evaluation in LC separations.
The chromatographic separations were carried out with sev-
eral PAHs as test solutes (see Figure S4 in the Supporting Infor-
mation). As was expected, when we employed methanol as
a mobile phase, the retentions of PAHs were clearly observed,
and the retention factor, k, of triphenylene was reached at 8.60
(see Eq. (1) and Figure S5a in the Supporting Information):
Then, the NHS-PFPA-C60 fullerene was modified onto silica
monolith. It is known that the silica monolithic materials pro-
vide high separation efficiency in LC and capillary electrophor-
eses, and the monolith can be easily modified with silane cou-
pling due to the silanol groups on the pore surface of the
monolith.[19] Herein, we employed a silica monolithic capillary,
which had relatively smaller domain size and allowed higher
separation efficiency,[20] as a platform for immobilization of C60
fullerene. Schematic image of the immobilization of C60 fuller-
ene is described in Scheme 2. To obtain a simple reaction with
NHS moiety, amino groups were introduced into the surface of
the silica monolith using 3-aminopropyltrimethoxysilane
(APTMS) in advance. Then, the synthesized compound, NHS-
PFPA-C60 fullerene was reacted with the monolithic capillary.
Herein, the bulk-type monolith was also prepared by the same
procedures and modified with NHS-PFPA-C60 fullerene to be
characterized by the elemental analysis. The results are sum-
marized in Table S2 in the Supporting Information. As we ex-
pected, C60 fullerene was effectively immobilized by the
method according to the significant increase of C% in C60 full-
erene-bonded monolith. The density of the immobilized amino
groups or C60 fullerene was also estimated as shown in
Table S3 in the Supporting Information. Brunauer–Emmett–
Teller (BET) analysis showed the specific surface area of the
monolith at 463 m2 gÀ1, and the density of C60 fullerene was es-
timated at 0.21 mmolmÀ2. Only the amino groups of 11.5%
were reacted with NHS-PFPA-C60 fullerene, because the amino
groups were modified at not only the surface of macropore,
but also mesopore. Therefore, it was assumed that the bulky
compound, NHS-PFPA-C60 fullerene, could not be reached to
k ¼ ðtRÀt0Þ=t0
ð1Þ
in which tR is elution time of a solute R and t0 is elution time
of nonretained solute (acetone).
Additionally, we examined the reproducibility of the prepara-
tion of the C60 fullerene-bonded monolith (n=4). Then, the
value of the relative standard deviation (RSD) for k of tripheny-
lene was 4.3%, so we considered the reproducibility of the
preparation procedures to be acceptable.
Interestingly, if n-hexane is utilized as a mobile phase, in
which the hydrophobic interaction does not occur for the re-
tention toward any solutes, the baseline separation of PAHs is
achieved even when naphthalene is also separated by the
strong interaction with the C60 fullerene-bonded monolith (Fig-
ure S5b in the Supporting Information). These results clearly
suggested that relatively strong p–p interaction contributed
for the retention of PAHs. To examine the relative strength of
p–p interaction in C60 fullerene bonded monolith, a comparison
of chromatographic evaluations was carried out with the com-
mercially available columns including C18 column and pNAPꢁ,
which provides specific retention based on the p–p interaction
due to the bonded naphthalene moiety. The relation between
the retention factors and octanol/water partition coefficient,
Pow, of each PAH or alkylbenzene was examined with the re-
sults by the columns (see Figure S6 in the Supporting Informa-
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tion). The plots of logarithm Pow against logarithm k provided
the date of higher p–p interaction strength in C60 fullerene-
bonded monolith. In brief, although the slopes for the plots in
C18 column was similar toward all the solutes and the slight
selectivity for PAHs was observed in pNAPꢁ column, the slope
for PAHs in the C60 fullerene-bonded monolith was dramatical-
ly higher (see Table S4 in the Supporting Information). Conse-
quently, we supposed that the C60 fullerene-bonded monolith
had a potential for a separation medium based on the p–p in-
teraction as main separation driving force.
C60 fullerene-bonded monolith and pNAPꢁ column. However,
when we utilized corannulene as a solute, the retention in the
C60 fullerene-bonded monolith was significantly high, whereas
that in pNAPꢁ column was much below the correlation line. As
was reported by several groups, corannulene is one of specific
molecules and has hemispherical structure as a part of C60 full-
erene.[21] Therefore, we anticipated that the specific molecular
recognition based on the bonded C60 fullerene was contribut-
ed to the higher retention of corannulene, while the retention
was decreased in the pNAPꢁ column because of the non-
planar structure of corannulene. To confirm the retention selec-
tivity, the separation of the mixture of corannulene and coro-
nene, which has completely planar structure and strongly re-
tained by the p–p interaction, was demonstrated. As shown in
Figure 2a, coronene was more retained than corannulene
based on the difference of the p–p interaction in the pNAPꢁ
column, as we expected. On the other hand, when we used
the C60 fullerene-bonded monolith with the same mobile
For further understanding about the p–p interaction in C60
fullerene-bonded monolith, another quantitative approach by
an LC evaluation was carried out. Figure 1 shows the correla-
tion between the numbers of p electrons in each PAH and its
retention factor in the LC evaluation. The evaluation was per-
formed with the C60 fullerene-bonded monolith and pNAPꢁ
column using n-hexane/chloroform as the mobile phases. As
shown in these figures, the correlation between the number of
p electrons and retention factor was close to linear in both the
Figure 2. Separation of coronene and corannulene in LC evaluation. (a) LC
system Prominence (Shimadzu Co.), column pNAPꢁ (Nacalai Tesque), mobile
phase n-hexane/chloroform 9:1, flow rate 0.1 mLminÀ1, detection UV
l=254 nm; (b) pump DiNa S (KYA Technologies), detector CE 2070 (JASCO);
column C60 fullerene-bonded monolithic capillary (100 mm I.D., effective
length 20.0 cm), mobile phase n-hexane/chloroform 1:1, flow rate
1000 nLminÀ1, detection UV l=254 nm; solutes 0.5 mm coronene, corannu-
lene/mobile phase.
Figure 1. Retention factors in LC evaluation and p electrons of PAHs. Condi-
tions: (a) column pNAPꢁ (Nacalai Tesque), mobile phase n-hexane, 408C;
(b) column C60 fullerene-bonded monolithic capillary (100 mm I.D., effective
length 20.0 cm), mobile phase n-hexane/chloroform 7:3, 408C.
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phase condition as the pNAPꢁ column, the elution of corannu-
lene was not confirmed until 2 h operation because of the sig-
nificantly higher retention. Then, we employed another mobile
phase containing higher ratio of chloroform, which has higher
elution power compared to n-hexane in this chromatographic
condition. As a result, the elution order among coronene and
corannulene was inversed; in fact, the elution of corannulene
was later than coronene. According to the data, we concluded
that the C60 fullerene-bonded monolith had specific spherical
molecular recognition due to the buckyball structure of C60
fullerene.
[2] a) W. A. De Heer, A. Chatelain, D. Ugarte, Science 1995, 270, 1179; b) S. J.
Tans, A. R. Verschueren, C. Dekker, Nature 1998, 393, 49.
[3] M. Popov, M. Kyotani, R. Nemanich, Y. Koga, Phys. Rev. B 2002, 65,
033408.
[4] N. W. S. Kam, M. O’Connell, J. A. Wisdom, H. Dai, Proc. Natl. Acad. Sci.
USA 2005, 102, 11600.
[5] a) X. Wang, S. Tao, B. Xing, Environ. Sci. Technol. 2009, 43, 6214; b) I. Vel-
zeboer, C. Kwadijk, A. Koelmans, Environ. Sci. Technol. 2014, 48, 4869.
[6] a) F. Tournus, S. Latil, M. Heggie, J.-C. Charlier, Phys. Rev. B 2005, 72,
075431; b) M. Cao, A. Fu, Z. Wang, J. Liu, N. Kong, X. Zong, H. Liu, J. J.
Gooding, J. Phys. Chem. C 2014, 118, 2650.
[7] C. D. Zeinalipour-Yazdi, D. P. Pullman, J. Phys. Chem. B 2006, 110, 24260.
[8] a) M. Pederson, A. Quong, J. Broughton, J. Feldman, Comput. Mater. Sci.
1994, 2, 536; b) H. Steger, J. Holzapfel, A. Hielscher, W. Kamke, I. Hertel,
Chem. Phys. Lett. 1995, 234, 455.
In conclusion, we have successfully synthesized a C60 fuller-
ene-conjugated compound, which can be reacted with an
amino group via a NHS moiety, by coupling with the thermal
active agent, PFPA. The synthesized compound was isolated
and characterized by a few spectroscopic analyses. Additional-
ly, NHS-PFPA-C60 fullerene was effectively modified on the sur-
face of a silica monolith via coupling with an amino group. Ac-
cording to LC evaluations using the C60 fullerene-bonded mon-
olithic capillary, the specific separation for PAHs based on the
effective p–p interaction was achieved. Although n-hexane
was employed as a mobile phase in LC, PAHs were also com-
pletely separated by the strong p–p interaction. Furthermore,
the C60 fullerene-bonded monolith allowed the unique molecu-
lar recognition based on the spherical structure of C60 fuller-
ene. In brief, a hemispherical molecule or corannulene was se-
lectively retained on the C60 fullerene-bonded monolith. We
believe that the results shown herein are the description of
the direct interaction between corannulene and C60 fullerene-
based on their spherical structure. The concept of the immobi-
lization technique can be used for the other carbon materials,
and the C60 fullerene-bonded monolith will be utilized as a spe-
cific separation compound due to the spherical structure.
[9] a) S. Stankovich, D. A. Dikin, R. D. Piner, K. A. Kohlhaas, A. Kleinhammes,
Y. Jia, Y. Wu, S. T. Nguyen, R. S. Ruoff, Carbon 2007, 45, 1558; b) D. R.
Dreyer, S. Park, C. W. Bielawski, R. S. Ruoff, Chem. Soc. Rev. 2010, 39,
228; c) Q. Qu, C. Gu, X. Hu, Anal. Chem. 2012, 84, 8880.
[10] a) H. Nagashima, H. Terasaki, E. Kimura, K. Nakajima, K. Itoh, J. Org.
Chem. 1994, 59, 1246; b) K. Jinno, K. Tanabe, Y. Saito, H. Nagashima, An-
alyst 1997, 122, 787; c) Y. Saito, H. Ohta, K. Jinno, Anal. Chem. 2004, 76,
266A.
[11] a) M. S. Platz, Acc. Chem. Res. 1995, 28, 487; b) N. Gritsan, M. Platz,
Chem. Rev. 2006, 106, 3844.
[12] a) M. Prato, Q. C. Li, F. Wudl, V. Lucchini, J. Am. Chem. Soc. 1993, 115,
1148; b) W. T. Borden, N. P. Gritsan, C. M. Hadad, W. L. Karney, C. R. Kem-
nitz, M. S. Platz, Acc. Chem. Res. 2000, 33, 765; c) M. Holzinger, J. Abra-
ham, P. Whelan, R. Graupner, L. Ley, F. Hennrich, M. Kappes, A. Hirsch, J.
Am. Chem. Soc. 2003, 125, 8566.
[13] R. Poe, K. Schnapp, M. J. Young, J. Grayzar, M. S. Platz, J. Am. Chem. Soc.
1992, 114, 5054.
[14] a) L. H. Liu, M. D. Yan, Nano Lett. 2009, 9, 3375; b) L. H. Liu, M. M. Lerner,
M. D. Yan, Nano Lett. 2010, 10, 3754; c) L. H. Liu, M. D. Yan, Acc. Chem.
Res. 2010, 43, 1434; d) L. H. Liu, M. D. Yan, J. Mater. Chem. 2011, 21,
3273.
[15] T. Kubo, X. Wang, Q. Tong, M. D. Yan, Langmuir 2011, 27, 9372.
[16] Q. Tong, X. Wang, H. Wang, T. Kubo, M. D. Yan, Anal. Chem. 2012, 84,
3049.
[17] T. Kubo, Y. Murakami, Y. Tominaga, T. Naito, K. Sueyoshi, M. Yan, K.
Otsuka, J. Chromatogr. A 2014, 1323, 174.
[18] M. Yan, S. X. Cai, J. F. Keana, J. Org. Chem. 1994, 59, 5951.
[19] a) N. Tanaka, H. Kobayashi, K. Nakanishi, H. Minakuchi, N. Ishizuka, Anal.
Chem. 2001, 73, 420A; b) N. Tanaka, H. Kimura, D. Tokuda, K. Hosoya, T.
Ikegami, N. Ishizuka, H. Minakuchi, K. Nakanishi, Y. Shintani, M. Furuno,
K. Cabrera, Anal. Chem. 2004, 76, 1273; c) K. Nakanishi, N. Tanaka, Acc.
Chem. Res. 2007, 40, 863.
Acknowledgements
This research was partly supported by the Grant-in Aid for Sci-
entific Research (No. 25620111 and 15K13756) from the Japan
Society for the Promotion of Science and an Environment Re-
search and Technology Development Fund (5-1552) from the
Ministry of the Environment, Japan.
[20] T. Hara, H. Kobayashi, T. Ikegami, K. Nakanishi, N. Tanaka, Anal. Chem.
2006, 78, 7632.
[21] a) E. Steiner, P. W. Fowler, L. W. Jenneskens, Angew. Chem. Int. Ed. 2001,
40, 362; Angew. Chem. 2001, 113, 375; b) R. C. Dunbar, J. Phys. Chem. A
2002, 106, 9809; c) A. Sygula, F. R. Fronczek, R. Sygula, P. W. Rabideau,
M. M. Olmstead, J. Am. Chem. Soc. 2007, 129, 3842; d) M. R. Kennedy,
L. A. Burns, C. D. Sherrill, J. Phys. Chem. A 2012, 116, 11920; e) D. Vijay,
H. Sakurai, V. Subramanian, G. N. Sastry, Phys. Chem. Chem. Phys. 2012,
14, 3057; f) J. Li, Y. Liu, Y. Qian, L. Li, L. Xie, J. Shang, T. Yu, M. Yi, W.
Huang, Phys. Chem. Chem. Phys. 2013, 15, 12694.
Keywords: corannulene · fullerenes · pi interactions · silica
monolith · spherical recognition
[1] a) W. Krätschmer, L. D. Lamb, K. Fostiropoulos, D. R. Huffman, Nature
1990, 347, 354; b) S. Iijima, Nature 1991, 354, 56; c) S. Iijima, T. Ichihashi,
Nature 1993, 364, 737; d) F. Schedin, A. Geim, S. Morozov, E. Hill, P.
Blake, M. Katsnelson, K. Novoselov, Nat. Mater. 2007, 6, 652.
Received: September 29, 2015
Published online on October 23, 2015
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