Dimeric capsules with a nanoscale cavity for [60]fullerene encapsulation

Article abstract of DOI:10.1002/chem.200701767

The acid-assisted and guest-induced formation of superstructures was achieved by the addition of haloacetic acids to a toluene solution of the resorcin[4]arene derivatives 1 and [60]fullerenes. The formation of dimeric superstructures that encapsulated a nanosized guest molecule was observed when appropriate acids, such as haloacetic acids, and suitable guest molecules, such as [60]fullerenes, were coadded to a toluene solution of cavitand 1 that has four pyridine units, whereas a complicated equilibrium between several species was detected without [60]fullerenes, and the formation of discrete superstructures was not monitored in the absence of haloacetic acids. The spectroscopic data indicate that the formed [60]fullerene-encapsulated complexes have the structure of 2. These complexes are self-assembled through pyridinium-anion-pyridinium interactions and by π-π and van der Waals interactions. The rate of decomplexation of 2 is estimated to be 3.1 s ^-1 from a 2D exchange NMR spectrum. The [60]fullerene encapsulation process can be controlled by modifying the amounts of acids used, changing the temperature of the system, altering the ratio of acid/base, and even through varying the solvent polarity. Moreover, the fluorescence spectra show bandnarrowing spectral changes and a retardation of the relaxation characteristics of isolated and isotropic [60]fullerenes, which indicates that the environmental change around [60]fullerene is induced upon its encapsulation.

Full text of DOI:10.1002/chem.200701767

FULL PAPER
DOI: 10.1002/chem.200701767
Dimeric Capsules with a Nanoscale Cavity for [60]Fullerene Encapsulation
Seong Jin Park,[a, c] Oh-Hoon Kwon,[a, d] Kyung-Sik Lee,[a] Kentaro Yamaguchi,[b]
Du-Jeon Jang,*[a] and Jong-In Hong*[a]
Abstract: The acid-assisted and guest-
induced formation of superstructures
was achieved by the addition of halo-
acetic acids to a toluene solution of the
[60]fullerenes, and the formation of dis-
crete superstructures was not moni-
tored in the absence of haloacetic
acids. The spectroscopic data indicate
that the formed [60]fullerene-encapsu-
lated complexes have the structure of
2. These complexes are self-assembled
through pyridinium–anion–pyridinium
interactions and by p–p and van der
Waals interactions. The rate of decom-
plexation of 2 is estimated to be 3.1 sÀ1
from a 2D exchange NMR spectrum.
The [60]fullerene encapsulation process
can be controlled by modifying the
amounts of acids used, changing the
temperature of the system, altering the
ratio of acid/base, and even through
varying the solvent polarity. Moreover,
the fluorescence spectra show band-
narrowing spectral changes and a retar-
dation of the relaxation characteristics
of isolated and isotropic [60]fullerenes,
which indicates that the environmental
change around [60]fullerene is induced
upon its encapsulation.
resorcin[4]arene derivatives
1
and
[60]fullerenes. The formation of dimer-
ic superstructures that encapsulated a
nanosized guest molecule was observed
when appropriate acids, such as halo-
acetic acids, and suitable guest mole-
cules, such as [60]fullerenes, were co-
added to a toluene solution of cavitand
1 that has four pyridine units, whereas
Keywords: cavitands · fullerenes ·
hydrogen bonds · self-assembly ·
supramolecular chemistry
a
complicated equilibrium between
several species was detected without
Introduction
the field of host–guest chemistry and construction of novel
nanostructures. To date, studies on such complex formation
have been mainly based on inclusion phenomena with dish-
or cup-shaped hosts, such as azacrown ethers,[1] cyclodex-
trins,[2] cyclotriveratrylenes,[3] calix[n]arenes,[4] and homooxa-
calix[3]arenes.[5] Porphyrins and metalloporphyrins have also
been studied and some outstanding examples have been re-
ported.[6] There are, however, only a few examples that
show the encapsulation phenomena of [60]fullerene within
the cavity of the capsulelike host. This is mainly due to the
fact that with covalently linked macromolecules it is very
difficult to encapsulate such a large guest without any strong
driving forces for inclusion, since the hosts must have a
window large enough for a guest to enter but which can also
serve as an exit door. This limitation, however, can be over-
come if noncovalently linked macromolecules are employed,
which are usually formed by making use of hydrogen bonds
and/or metal–ligand interactions. The construction of self-as-
sembled cage molecules utilizing these interactions has at-
tracted widespread interest and considerable progress has
been achieved. Recently, Claessens and Torres reported
[60]fullerene encapsulation phenomena in an M3L2 sub-
phthalocyanine cage.[7,8] Shinkai and co-workers showed the
Supramolecular complexation involving nanosized, electron-
deficient fullerenes has generated a great deal of interest in
[a]Dr. S. J. Park, Dr. O.-H. Kwon, K.-S. Lee, Prof. Dr. D.-J. Jang,
Prof. Dr. J.-I. Hong
Department of Chemistry, College of Natural Sciences
Seoul National University, Seoul 151-747 (Korea)
Fax : (+82)2-889-1568
E-mail: djjang@snu.ac.kr
jihong@snu.ac.kr
[b]Prof. Dr. K. Yamaguchi
Faculty of Pharmaceutical Sciences at Kagawa Campus
Tokushima Bunri University
Shido, Sanuki-city, Kagawa 769-2193 (Japan)
[c]Dr. S. J. Park
Current address: Department of Medicinal Chemistry
Research Center, Dong-A Pharmaceutical Company
Yongin 446-905 (Korea)
[d]Dr. O.-H. Kwon
Current address: Laboratory for Molecular Sciences
Arthur Amos Noyes Laboratory of Chemical Physics
California Institute of Technology
Pasadena, CA 91125 (USA)
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
Chem. Eur. J. 2008, 14, 5353 – 5359
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
5353

same phenomena in a homooxacalix[3]arene-based dimeric
capsule constructed by PdII–pyridine interactions.[7,8]
We have extensively investigated resorcin[4]arene deriva-
tives 1 (Scheme 1) that have four pyridine units as pendent
sisted formation of capsules by the simple addition of acids
1
1
was investigated by H NMR spectroscopy. The H NMR ti-
tration spectra, however, show the existence of a complicat-
ed equilibrium between several species when trifluoroacetic
acid (TFA) is added to
a
[D8]toluene solution of 1a.[11,12]
It was anticipated that suitable
guest(s) might induce the for-
mation of guest-encapsulated
superstructures. From CPK and
computer-aided modeling it was
expected that large and spheri-
cal guests, such as [60]fullerene,
would be suitable for the cavity
of
a dimeric supramolecular
capsule formed through pyri-
dine–pyridinium or pyridinium–
anion–pyridinium interactions
(Figure 1).[13]
The interaction between cavi-
tand 1 and [60]fullerene with-
out additional acids was investi-
gated by UV/Vis titration in
Scheme 1. Formation of [60]fullerene-encapsulated superstructures.
groups for the construction of metal-induced superstructures
by using cis-protected square-planar MII ions (M=Pd, Pt).
We have demonstrated how metal-induced self-assembly
can be tuned by subtle changes in the solvent system: an in-
terclipped supramolecular capsule (composed of two units
of cavitand 1 and four metal ions) is formed as a sole adduct
in chloroform/methanol,[9a] an intraclipped supramolecular
bowl (composed of one cavitand 1 and two metal ions) is
formed exclusively in an aqueous phase,[9b] and a capsule
and a bowl coexist in a dynamic manner in nitromethane.[9c]
Herein, we describe the utilization of the pendent pyri-
dine units of cavitand 1 as bases instead of ligands and the
formation of [60]fullerene-encapsulated superstructures,
which take advantage of the cooperative function of a suita-
ble guest and appropriate acids (Scheme 1). To the best of
knowledge, this is the first example in which hydrogen-
bonded cage molecules encapsulate a fullerene and appro-
priately designed macromolecules with basic pendent moiet-
ies lead to supramolecular nanocavities by the simple addi-
tion of acids.
Figure 1. Computer-aided models of the [60]fullerene-encapsulated com-
plexes based on pyridine–pyridinium interactions (left) and pyridinium–
anion–pyridinium interactions (right) (MacroModel 7.0).
toluene. No significant change in the absorption spectrum
was observed (see Figure S2 in the Supporting Information),
which indicates that without acid assistance there is little in-
teraction of cavitand 1 with [60]fullerene.[14]
The concept of acid-assisted and guest-induced formation
1
of a superstructure was first validated by H NMR spectros-
Results and Discussion
copy (Figure 2). When 1a and two equivalents of [60]fuller-
ene were dissolved in [D8]toluene, no evidence of any inter-
action between 1a and [60]fullerene was observed (Fig-
ure 2b), which is consistent with the UV/Vis measurements.
However, as an increasing amount of TFA was added, a new
set of peaks appeared which became the sole product when
four equivalents of TFA were added (Figure 2e).[15]
Similar results were observed with trichloroacetic acid but
not with acetic acid. Presumably this is due to the small
DpKa value between pyridine and acetic acid, since the
Design strategy and 1H NMR spectroscopy: Resorcin[4]ar-
ene derivatives 1 prepared from the corresponding tetrol
cavitand[10] were first utilized as ligands for the construction
of metal-induced dimeric capsules.[9] Due to the availability
of the pyridine units of cavitand 1 as bases, acid-assisted for-
mation of dimeric capsules would be possible by charged hy-
drogen-bonding interactions, such as pyridine–pyridinium
and pyridinium–anion–pyridinium interactions. The acid-as-
5354
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5353 – 5359

[60]Fullerene Encapsulation
FULL PAPER
[60]fullerene is about 3:1, which means that all [60]ful-
lerenes are encapsulated in the dimeric capsule considering
that four equivalents of [60]fullerene are added to each di-
meric capsule. The 2:1 stoichiometry between 1a and
1
[60]fullerene is also observed by 13C and H NMR spectros-
copy carried out with the gradual addition of 1a·4TFA (the
latter number refers to the number of equivalents used) to
the [D8]toluene solution of 13C-enriched [60]fullerene
(Figure 4). When two equivalents of 1a·4TFA were added,
1
Figure 2. Portion of the H NMR spectra with gradual addition of TFA to
a [D8]toluene solution of 1a·2C60 (300 MHz, 300 K). a) 1a; b) 1a·2C60
;
c) 1a·2C60 +1 equiv TFA; d) 1a·2C60 +2 equiv TFA; e) 1a·2C60 +4 equiv
TFA.
[16]
degree of proton transfer is a function of DpKa. The pyri-
dinium proton of the complex is observed at d=19.77 ppm
(see Figure S5 in the Supporting Information) and the peak-
intensity ratio of the pyridinium proton of the complex to
the pyridineꢁs a proton is about 1:2, which indicates that all
pyridines are protonated. It is also noteworthy that Hb un-
dergoes a more downfield shift than Ha (d=1.1 and 0.8 ppm
for Hb and Ha, respectively) when the complex is formed.
This means that Hb is closer to the encapsulated electron-de-
ficient [60]fullerene than Ha.
1
Figure 4. Portion of the 13C and H NMR spectra with gradual addition of
1a·4TFA to
a
[D8]toluene solution of 13C-enriched [60]fullerene
(300 MHz, 300 K): a) 0, b) 0.5, c) 1.0, d) 1.5, e) 2, and f) 2.5 equiv. The
peak from the encapsulated [60]fullerene is indicated by and that from
*
*
.
the free [60]fullerene by
1H and 13C NMR spectroscopy with 13C-enriched [60]fuller-
ene: The cooperation of acid and guest for the construction
of the supramolecular capsule was also confirmed by
13C NMR spectroscopy (Figure 3). In the 13C NMR spectra
the 13C resonance from free [60]fullerene disappeared with-
out the appearance of any additional peak in the H NMR
1
spectra (Figure 4e). Further augmentation of 1a·4TFA,
1
however, caused the appearance of H NMR spectroscopic
peaks from nonencapsulated material (Figure 4f). These
findings mean that [60]fullerene is strongly wrapped in the
supramolecular capsule composed of two 1a molecules.
We can obtain more information from the 13C NMR spec-
tra (Figures 3 and 4); the observed peak separation implies
that the complexation–decomplexation exchange rate is
slower than the timescale of the 13C NMR spectroscopic
measurements. According to Cramꢁs studies on molecular
containers, the rate of guest liberation from a hemicarcerand
is known to be related not only to the size of the guest mol-
ecules but also to their rigidity and shape.[18] As might be ex-
pected from the rigidity, spherical shape, and complementa-
ry size of [60]fullerene, the exchange rate was observed to
be slower than the 13C NMR timescale. Notably, the
[60]fullerene within complex 2a gives a single 13C signal.
This means that [60]fullerene within the supramolecular
cavity still rotates at a speed faster than the 13C NMR spec-
troscopic timescale.
Figure 3. Portion of the 13C NMR spectra with gradual addition of TFA
(125 MHz, [D8]toluene, 300 K). a) C60; b) 1a·2C60; c) 1a·2C60 +4 equiv
TFA. A signal at d=137.7 ppm from C7D8 is marked with an asterisk.
with 13C-enriched [60]fullerene, a new peak appeared at a
higher magnetic field (d=142.36 ppm) than the peak for
free [60]fullerene (d=143.57 ppm) only when TFA was
added to the [D8]toluene solution of 1a and [60]fullerene.[17]
This peak can be assigned to the encapsulated [60]fullerene,
and the peak-intensity ratio of free to encapsulated
Structure elucidation: The guest-induced and acid-assisted
formation of the dimeric capsule complex might utilize
charged hydrogen bonds, such as pyridine–pyridinium and
pyridinium–anion–pyridinium interactions (Figure 1).
A
Chem. Eur. J. 2008, 14, 5353 – 5359
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5355

J.-I. Hong, D.-J. Jang et al.
great deal of effort has been made to determine which inter-
actions are the sources of the supramolecular structure.
Countless trials to obtain a suitable crystal for X-ray crystal-
lography were in vain. The crystals obtained from slow dif-
fusion of a toluene solution of 1b·C60·4TFA were too unsta-
ble to handle because they were too brittle and decomposed
rapidly when exposed to air. Mass spectrometers equipped
with soft-ionization apparatus are broadly used for the char-
acterization of supramolecular structures. Mass spectromet-
ric evidence for the [60]fullerene-encapsulated superstruc-
tures, however, has not been obtained even from soft-ioniza-
tion methods, such as matrix-assisted laser desorption/ioni-
zation mass spectrometry (MALDI-MS) and cold-spray ion-
ization mass spectrometry (CSI-MS).[19] In the case of
MALDI-MS, the addition of a somewhat polar matrix might
cause the destruction of the supramolecular complex, and in
CSI-MS the solvent, toluene, does not have sufficient ioniza-
tion ability; the addition of polar solvent to promote ioniza-
tion resulted in decomplexation.
Figure 5. Downfield region of the 1H–1H EXSY spectrum (600 MHz,
298 K, 1a·C60·2TFA concentration=2.0 mm, [D8]toluene, mixing time
0.6 s).
1
13C and H NMR spectroscopic studies revealed evidence
for the formation of the [60]fullerene-encapsulated complex
through pyridinium–anion–pyridinium interactions: 1) four
equivalents of acid are required for the formation of the di-
meric capsule structure, 2) all the pyridine moieties of 1 are
protonated, and 3) the 2:1 stoichiometry between 1a and
[60]fullerene is observed. Therefore, the above data suggest
that the [60]fullerene-encapsulated complex would be
formed not through pyridine–pyridinium interactions but
through pyridinium–anion–pyridinium interactions.[20,21]
1H–1H exchange spectroscopy (EXSY) and the rate of guest
release: The transfer of spin polarization from the [60]fuller-
ene-encapsulated complex 2a to its debris was observed in a
1H–1H EXSY experiment (Figure 5).[22] Intense exchange
cross-peaks between the pyridine a protons of the com-
plexed and dissociated material are obtained. The rate con-
stant, estimated on the basis of the integration of the cross-
peaks, was 3.1 sÀ1. The free energy of activation (DG°) was
calculated by the Eyring equation to be 16.8 kcalmolÀ1.
Figure 6. Portion of temperature-dependent 1H NMR spectra of
[D8]toluene solution of 1a·2C60·2TFA. a) 300, b) 313, c) 323, d) 333 K,
and e) return to 300 K. The peaks from the fullerene-encapsulated capsu-
a
*
.
les are indicated by
Decomplexation phenomena were also observed by the
addition of relatively polar solvents, such as [D]chloroform,
[D2]dichloromethane, and [D3]acetonitrile. This may be par-
tially due to a decrease in the solubility of the complex or
[60]fullerene and partially to diminution of pyridinium–
anion–pyridinium interactions.[23] Moreover, the [60]fuller-
ene encapsulation process can be controlled through the ad-
dition of a base (Figure 7). The addition of triethylamine
(TEA) to a [D8]toluene solution of 1a·2C60·4TFA destroyed
the acid-assisted formation of the [60]fullerene-encapsulated
superstructure; the gradual addition of TEA caused the de-
struction of 2a and complete destruction was achieved when
four equivalents of TEA were added. Subsequent addition
of four equivalents of TFA restored the original complex.
1H NMR spectroscopy with varying temperatures, solvent
polarities, and TEA/TFA ratios: It is well-known that inter-
molecular non-bonding interactions are so labile that exter-
nal stimuli affect the formation of non-bonded complexes.
To validate this concept in our system, temperature-depen-
dent 1H NMR spectroscopy was carried out with
a
[D8]toluene solution of 1a·2C60·2TFA from 300 to 333 K
(Figure 6). As the temperature increases, the intensity of the
peaks assigned to 2a decreases. Moreover, these peaks com-
pletely disappear at 333 K. When the temperature returns to
300 K, the original peaks are restored. This phenomenon im-
plies that the [60]fullerene-encapsulated complex 2a is dis-
assembled with increasing temperature owing to attenuation
of the assembling forces, such as triple-ion interactions, p–p
interactions, and van der Waals interactions, and that the en-
capsulation of [60]fullerene is a reversible process since re-
assembly occurs with decreasing temperature.
UV/Vis–fluorescence spectroscopy: The symmetrically for-
bidden lowest-absorption band at 540 nm of [60]fullerene
appears weakly in solution due to a reduction in local sym-
5356
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5353 – 5359

[60]Fullerene Encapsulation
FULL PAPER
Figure 7. Portion of the 1H NMR spectra with gradual addition of TEA
to a [D8]toluene solution of 1a·2C60·4TFA (300 MHz, 296 K). a) 0, b) 1,
c) 2, d) 3, and e) 4 equiv TEA; f) 4 equiv TEA then 4 equiv TFA.
metry resulting from solute–solvent interactions. Addition
of 1a·4TFA) to the toluene solution of [60]fullerene led to
an increase in the absorption band at 440 nm and a decrease
at 540 nm, characteristic of complexation (see Figure S7 in
the Supporting Information). The decrease of the forbidden
transition band at 540 nm can be attributed to suppressed
solute–solvent interactions, which implies that the guest,
[60]fullerene, is encapsulated by the host complex and parti-
ally isolated from solvent molecules.
The [60]fullerene encapsulation phenomenon was also
clearly seen in the fluorescence spectra (Figure 8a). Bare
[60]fullerene in toluene showed a typical fluorescence spec-
trum around 700 nm, which matched very well with reported
cases.[24] However, the addition of 21a·8TFA led to a band-
narrowing spectral change. The change of the environment,
mainly polarity, around [60]fullerene upon its encapsulation
is presumed to cause the spectral change. Of note is that
such a phenomenon was observed only with the co-addition
of 1a and TFA; the addition of 1a or TFA alone did not
affect the fluorescence spectrum of [60]fullerene.
Retardation of the relaxation of [60]fullerene at the
lowest excited singlet state (S1) was also observed (Fig-
ure 8b). The lifetime of [60]fullerene at S1 was measured to
be (1.19Æ0.02) ns in a toluene solution, and was hardly af-
fected by the variation of the solvent.[25] When [60]fullerene
forms the complex 2a, a 6% elongation of the lifetime
((1.26Æ0.02) ns) was observed. Although it shows a small
elongation of the lifetime at S1, this finding clearly indicates
the great reduction of nonradiative relaxation channels,
other than the very efficient intersystem crossing to the trip-
let state (FT ꢀ0.96),[26] by solute–solvent interactions to the
ground state.
Figure 8. a) Fluorescence spectra of [60]fullerene, C60·21a, C60·8TFA, and
C60·21a·8TFA in toluene. Samples were excited at 330 nm. b) Fluores-
*
*
cence kinetic profiles of [60]fullerene ( ) and C60·21a·8TFA ( ), excited
at 532 nm and monitored above 660 nm, in toluene. Fitted curves (c)
are also shown.
have four pyridine units, and [60]fullerenes. The formation
of the superstructures was demonstrated by 1H NMR,
13C NMR, and UV/Vis–fluorescence spectroscopies. The
[60]fullerene encapsulation process can be controlled
through changing the temperature, adding an acid/base, and
even through varying the solvent polarity. Moreover, the
fluorescence spectra of the encapsulated [60]fullerenes show
band-narrowing spectral changes and a retardation of the re-
laxation characteristics of isolated and isotropic [60]ful-
lerenes. This study proposes a new strategy by which the
simple addition of acids to appropriately designed macromo-
lecules with basic pendent moieties leads to supramolecular
nanocavities capable of encapsulating large molecules, such
as [60]fullerene.
Conclusion
Experimental Section
We have shown the formation of [60]fullerene-encapsulated
superstructures 2 by the addition of an appropriate acid to a
toluene solution of the resorcin[4]arene derivatives 1, which
General: All chemicals were of reagent grade and were used without fur-
ther purification. [60]Fullerene (99.5%) was obtained from Southern
Chemical Group (USA) and 13C-enriched [60]fullerene (13C content: 10–
Chem. Eur. J. 2008, 14, 5353 – 5359
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5357

J.-I. Hong, D.-J. Jang et al.
15%) was purchased from MER Corporation (USA). NMR spectra were
recorded on either a Bruker Avance DPX-300 or a Bruker Avance 600
spectrometer. Chemical shifts are given in parts per million by using the
residual resonances of deuterated solvents (d=7.27 ppm for chloroform;
d=7.00 ppm for toluene) as an internal reference. The rates of chemical
exchange were measured by using EXSY by integrating the peaks of 2D
NOESY. Molecular modeling was performed on a Silicon Graphics O2
machine with a MacroModel 7.0 program. Fast atom bombardment mass
spectrometry (FAB-MS) data were obtained on a JEOL JMS-AX505WA
mass spectrometer with m-nitrobenzyl alcohol as matrix. CSI-MS data
were obtained on a four-sector (BE/BE) tandem mass spectrometer
(JEOL, JMS-700T) equipped with a CSI source. UV/Vis spectra were re-
corded on a Beckman DU650 spectrophotometer. Fluorescence spectra
were obtained by using a homemade fluorimeter composed of a 75 W Xe
lamp (Acton Research, XS 432), 0.15 and 0.30 m monochromators
(Acton Research, Spectrapro 150 and 300), and a photomultiplier tube
(Acton Research, PD438). Fluorescence spectra were not corrected for
the spectral sensitivity of the fluorimeter. Pulses (532 nm) of 25 ps dura-
tion from an actively and passively mode-locked Nd:YAG laser (Quantel,
YG 701) were employed to excite the samples. The fluorescence wave-
length was selected by using an appropriate combination of filters. Fluo-
rescence kinetic profiles were detected with a 10 ps streak camera (Ha-
mamatsu, C2830) attached to a CCD (Princeton Instruments, RTE-128-
H). Fluorescence kinetic constants were extracted by fitting a measured
kinetic profile to a computer-simulated kinetic curve convoluted with the
temporal response function (ꢀ50 ps) iteratively. Unless specified other-
Acknowledgements
Support for this work in the form of a grant from the MOCIE (grant
no. 10022945) is gratefully acknowledged. This research was also support-
ed in part by the Seoul R&BD Program. S.J.P., O.-H.K., and K.-S.L.
thank the Ministry of Education & Human Resources Development for
the award of BK 21 fellowships. We thank Dr. Hae-Kap Cheong at KBSI
for helpful advice.
[1]F. Diederich, J. Effing, U. Jonas, L. Jullien, T. Plesnivy, H. Ringsdorf,
C. Thilgen, D. Weinstein, Angew. Chem. 1992, 104, 1683–1686;
Angew. Chem. Int. Ed. Engl. 1992, 31, 1599–1602.
[2]a) Y. Liu, H. Wang, P. Liang, H.-Y. Zhang, Angew. Chem. 2004, 116,
2744–2748; Angew. Chem. Int. Ed. 2004, 43, 2690–2694; b) T. An-
dersson, G. Westman, G. Stenhagen, M. Sundahl, O. Wennerstrçm,
Tetrahedron Lett. 1995, 36, 597–600; c) Z.-i. Yoshida, H. Takekuma,
S.-i. Takekuma, Y. Matsubara, Angew. Chem. 1994, 106, 1658–1660;
Angew. Chem. Int. Ed. Engl. 1994, 33, 1597–1599; d) T. Anderson,
K. Nilsson, M. Sundahl, G. Westman, O. Wennerstrçm, J. Chem.
Soc. Chem. Commun. 1992, 604–606.
[3]a) S. Zhang, A. Palkar, A. Fragoso, P. Prados, J. de Mendoza, L.
Echegoyen, Chem. Mater. 2005, 17, 2063–2068; b) Y. Rio, J.-F. Nier-
engarten, Tetrahedron Lett. 2002, 43, 4321–4324; c) H. Matsubara,
S.-y. Oguri, K. Asano, K. Yamamoto, Chem. Lett. 1999, 431–432;
d) M. J. Hardie, P. D. Godfrey, C. L. Raston, Chem. Eur. J. 1999, 5,
1828–1833; e) J. L. Atwood, M. J. Barnes, M. G. Gardiner, C. L.
Raston, Chem. Commun. 1996, 1449–1450; f) J. W. Steed, P. C.
Junk, J. L. Atwood, M. J. Barnes, C. L. Raston, R. S. Burkhalter, J.
Am. Chem. Soc. 1994, 116, 10346–10347.
[4]a) T. Haino, M. Yanase, C. Fukunaga, Y. Fukazawa, Tetrahedron
2006, 62, 2025–2035; b) S. Zhang, L. Echegoyen, J. Org. Chem.
2005, 70, 9874–9881; c) G.-B. Pan, J.-M. Liu, H.-M. Zhang, L.-J.
Wan, Q.-Y. Zheng, C.-L. Bai, Angew. Chem. 2003, 115, 2853–2857;
Angew. Chem. Int. Ed. 2003, 42, 2747–2751; d) T. Haino, H. Araki,
Y. Yamanaka, Y. Fukazawa, Tetrahedron Lett. 2001, 42, 3203–3206;
e) J. Wang, S. G. Bodige, W. H. Watson, C. D. Gutsche, J. Org.
Chem. 2000, 65, 8260–8263; f) A. Ikeda, M. Yoshimura, S. Shinkai,
Tetrahedron Lett. 1997, 38, 2107–2110; g) C. L. Raston, J. L.
Atwood, P. J. Nichols, I. B. N. Sudria, Chem. Commun. 1996, 2615–
2616; h) J. L. Atwood, G. A. Koutsantonis, C. L. Raston, Nature
1994, 368, 229–231.
[5]a) J. L. Atwood, L. J. Barbour, P. J. Nichols, C. L. Raston, C. A. San-
doval, Chem. Eur. J. 1999, 5, 990–996; b) A. Ikeda, T. Hatano, M.
Kawaguchi, H. Suenaga, S. Shinkai, Chem. Commun. 1999, 1403–
1404; c) K. Tsubaki, K. Tanaka, T. Kinoshita, K. Fuji, Chem.
Commun. 1998, 895–896.
wise, all the fluorescence measurements were carried out with
a
[60]fullerene concentration of 1 mm in toluene with/without two equiva-
lents of 1a and/or eight equivalents of TFA at room temperature.
Synthesis of tetrapyridine-tethered cavitand (1a): A mixture of the corre-
sponding tetrol cavitand (244 mg, 0.2 mmol),[10] K2CO3 (690 mg,
5.0 mmol), and 4-picolyl chloride hydrochloride (328 mg, 2.0 mmol) in
dry DMF (5 mL) was stirred under a nitrogen atmosphere at 608C for
18 h. The solvent was evaporated under vacuum and the residue was dis-
solved in chloroform (50 mL). The solution was washed with water and
brine, then dried (MgSO4) and evaporated to dryness under vacuum.
Silica-gel chromatography with CH2Cl2/CH3OH (15:1) was used to
obtain 1a (yield 238 mg; 75%). 1H NMR (300 MHz, CDCl3): d=8.61 (d,
3J
6.88 (s, 4H; ArH), 5.79 (d, J
(s, 8H; OCH2Py), 4.75 (t, 3J
(H,H)=7.12 Hz, 4H; ArOCHoHiOAr), 2.22 (brm, 8H; CHCH2CH2),
1.4–1.1 (brs, 72H; CH2A (H,H)=6.58 Hz, 12H;
(CH2)9CH3), 0.90 ppm (t, 3J
ACHTREUNG ACHTRENUG
(H,H)=5.89 Hz, 8H; PyHa), 7.32 (d, 3J
2
AHCTREUNG
AHCTREUNG
C
ACHTREUNG
CH2CH3); 13C NMR (75 MHz, CDCl3): d=149.69, 147.97, 147.01, 144.09,
139.07, 121.39, 114.69, 99.45, 73.37, 36.91, 31.92, 29.83, 29.71, 29.40, 27.91,
22.68, 14.11 ppm; FAB-MS: m/z: calcd: 1581.9920; found: 1581.9962
[M+H]+; elemental analysis calcd (%) for C100H132N4O12: C 75.91, H
8.41, N 3.54; found: C 76.04, H 8.66, N 3.38.
[6]a) A. Ouchi, K. Tashiro, K. Yamaguchi, T. Tsuchiya, T. Akasaka, T.
Aida, Angew. Chem. 2006, 118, 3622–3626; Angew. Chem. Int. Ed.
2006, 45, 3542–3546; b) M. Shirakawa, N. Fujita, H. Shimakoshi, Y.
Hisaeda, S. Shinkai, Tetrahedron 2006, 62, 2016–2024; c) A. L.
Kieran, S. I. Pascu, T. Jarrosson, J. K. M. Sanders, Chem. Commun.
2005, 1276–1278; d) T. Yamaguchi, N. Ishii, K. Tashiro, T. Aida, J.
Am. Chem. Soc. 2003, 125, 13934–13935; e) D. Sun, F. S. Tham,
C. A. Reed, L. Chaker, P. D. W. Boyd, J. Am. Chem. Soc. 2002, 124,
6604–6612; f) J.-Y. Zheng, K. Tashiro, Y. Hirabayashi, K. Kinbara,
K. Saigo, T. Aida, S. Sakamoto, K. Yamaguchi, Angew. Chem. 2001,
113, 1909–1913; Angew. Chem. Int. Ed. 2001, 40, 1857–1861; g) D.
Sun, F. S. Tham, C. A. Reed, L. Chaker, M. Burgess, P. D. W. Boyd,
J. Am. Chem. Soc. 2000, 122, 10704–10705.
Synthesis of tetrapyridine-tethered cavitand (1b): Prepared by a similar
method to 1a in 70% yield. 1H NMR (300 MHz, CDCl3): d=8.66 (d, 3J
(H,H)=3.34 Hz, 8H; PyHa), 7.44 (d, 3J
ACHTREUNG
(brm, 12H; PhH), 7.18 (d, 3J
ArH), 5.83 (d, 2J
ACHTREUNG
ACHTREUNG
A
ACHTREUNG
6.12 Hz, 4H; ArOCHoHiOAr), 2.70 (brm, 8H; CH2CH2Ph), 2.53 ppm
(brm, 8H; CH2CH2Ph); 13C NMR (75 MHz, CDCl3): d=148.92, 148.23,
147.99, 144.30, 141.50, 138.99, 128.63, 128.40, 126.16, 121.77, 114.66, 99.51,
73.43, 37.07, 34.44, 32.30 ppm; FAB-MS: m/z: calcd: 1381.5538; found:
1381.5527 [M+H]+; elemental analysis calcd (%) for C88H76N4O12: C
76.50, H 5.54, N 4.06; found: C 75.12, H 5.79, N 3.82.
[7]a) C. G. Claessens, T. Torres, Chem. Commun. 2004, 1298–1299;
b) A. Ikeda, H. Udzu, M. Yoshimura, S. Shinkai, Tetrahedron 2000,
56, 1825–1832; c) A. Ikeda, M. Yoshimura, H. Udzu, C. Fukuhara,
S. Shinkai, J. Am. Chem. Soc. 1999, 121, 4296–4297.
Preparation of [60]fullerene-encapsulated capsule (2): Diluted TFA
(4 mmol) in toluene was added to a toluene solution of tetrapyridine-
tethered cavitand 1 (1 mmol) and [60]fullerene (>0.5 mmol) in a vial.
[8]Recently, a British group reported [60f]ullerene encapsulation phe-
nomena in
a resorcin[4]arene-based trimeric/tetrameric complex
constructed by metal–dithiocarbamate interactions: O. D. Fox, J.
Cookson, E. J. S. Wilkinson, M. G. B. Drew, E. J. MacLean, S. J.
Teat, P. D. Beer, J. Am. Chem. Soc. 2006, 128, 6990–7002.
5358
www.chemeurj.org
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2008, 14, 5353 – 5359

[60]Fullerene Encapsulation
FULL PAPER
[9]a) S. J. Park, J.-I. Hong, Chem. Commun. 2001, 1554–1555; b) S. J.
Park, D. M. Shin, S. Sakamoto, K. Yamaguchi, Y. K. Chung, M. S.
Lah, J.-I. Hong, Chem. Commun. 2003, 998–999; c) S. J. Park, D. M.
Shin, S. Sakamoto, K. Yamaguchi, Y. K. Chung, M. S. Lah, J.-I.
Hong, Chem. Eur. J. 2005, 11, 235–241.
[10]J. C. Sherman, C. B. Knobler, D. J. Cram, J. Am. Chem. Soc. 1991,
113, 2194–2204.
[11]The resorcin[4a]reneꢁs chemical shifts are not well fitted to the cal-
culated values based on 1:2 or 1:4 binding modes (see Figure S1 in
the Supporting Information).
113, 2754–2755; c) For a comprehensive review, see: D. J. Cram,
J. M. Cram, Container Molecules and Their Guests, Royal Society of
Chemistry, Cambridge, 1994.
[19]Only the charged hydrogen-bonded capsule was observed when
CSI-MS was applied with a chloroform solution of 1a·4TFA (see
Figure S6 in the Supporting Information).
[20]The concept of using triple-ion interactions for the construction of
supramolecular architectures was reported whilst we were preparing
this manuscript: G. V. Oshovsky, D. N. Reinhoudt, W. Verboom, J.
Am. Chem. Soc. 2006, 128, 5270–5278.
[12]It was reported that the nonpolar solution of pyridine and trihalo-
acetic acid contains several species: a) Z. Dega-Szafran, M. Grund-
[21]One referee suggested a new model for the complex, in which the
two cavitands are staggered and each of the eight acetate anions
bridges two pyridinium moieties to form a continuous seam around
the equator, since our proposed model would have charges so would
lead to precipitation from toluene. In fact, a cloudy solution was de-
´
wald-Wyspianska, M. Szafran, Spectrochim. ActaPart A 1991, 47,
´
543–550; b) P. Barczyniski, Z. Dega-Szafran, M. Szafran, J. Mol.
Liq. 1987, 33, 101–117; c) E. M. Arnett, B. Chawla, J. Am. Chem.
Soc. 1978, 100, 217–221.
tected when the cavitandꢁs R group was methyl and
a slightly
[13]Molecular modeling was carried out by using MacroModel 7.0: F.
Mohamadi, N. G. J. Richards, W. C. Guida, R. Liskamp, M. Lipton,
C. Caufield, G. Chang, T. Hendrickson, W. C. Still, J. Comput.
Chem. 1990, 11, 440–467.
[14]A wide range of calix[ n]arenes were screened for complexation of
[60]fullerene in toluene and little change was found in the absorp-
tion spectrum of [60]fullerene with the addition of calix[4]arenes
(see ref. [4 f]). This indicates that there is no evidence for complexa-
tion between calix[4]arenes and [60]fullerene in the solution phase,
probably due to small cavities and rigidities. Because resorcin[4]ar-
enes have a similar cavity size and more rigid backbones compared
to calix[4]arenes (see ref. [14]), there is less chance for resorcin[4]ar-
enes to interact with [60]fullerene.
[15]Addition of more than four equivalents of TFA caused decomplexa-
tion. Complete destruction of the capsule structure was observed
when four more equivalents of TFA were added (see Figure S3 in
the Supporting Information). This finding might be explained by
considering that the 2:1 TFA–pyridine complex is the most stable
species when two equivalents of haloacetic acids are added to a non-
polar solution containing pyridine derivatives (see ref. [12]and Fig-
ure S4 in the Supporting Information).
opaque solution was detected at high concentration even when R
was CH2CH2Ph, which implies the formation of charged species.
Moreover, it was found from computer-aided modeling (MacroMo-
del 7.0) that the model suggested by the referee could not be
formed to encapsulate [60]fullerene due to the short length of link-
ers (acetate) and severe strain. There might, however, be an equilib-
rium among several species including our proposed structures and
the structure formed through quadrupole interactions (two acetate
ions are between the two pyridinium moieties on the two cavitands:
pyridinium–two anions–pyridinium interactions).
[22]a) M. Pons, O. Millet, Prog. Nucl. Magn. Reson. Spectrosc. 2001, 38,
267–324; b) C. L. Perrin, T. J. Dwyer, Chem. Rev. 1990, 90, 935–
967; c) E. W. Abel, T. P. J. Coston, K. G. Orrell, V. Sik, D. Stephen-
son, J. Magn. Reson. 1986, 70, 34–53.
[23]The instability of the complex 2 in polar media may be the main
reason for the difficulty in obtaining the mass data.
[24]Y.-P. Sun, P. Wang, N. B. Hamilton, J. Am. Chem. Soc. 1993, 115,
6378–6381.
[25]a) D. Kim, M. Lee, Y. D. Suh, S. K. Kim, J. Am. Chem. Soc. 1992,
114, 4429–4430; b) T. W. Ebbesen, K. Tanigaki, S. Kuroshima,
Chem. Phys. Lett. 1991, 181, 501–504.
[16]a) Z. J. Li, Y. Abramov, J. Bordner, J. Leonard, A. Medek, A. V.
Trask, J. Am. Chem. Soc. 2006, 128, 8199–8210; b) S. L. Johnson,
K. A. Rumon, J. Phys. Chem. 1965, 69, 74–86.
[26]M. Lee, O.-K. Song, J.-C. Seo, D. Kim, Y. D. Suh, S. M. Jin, S. K.
Kim, Chem. Phys. Lett. 1992, 196, 325–329.
[17]TFA itself did not affect the 13C NMR spectrum of free [60]ful-
lerenes.
[18]a) D. J. Cram, R. Jaeger, K. Deshayes, J. Am. Chem. Soc. 1993, 115,
10111–10116; b) M. L. Quan, D. J. Cram, J. Am. Chem. Soc. 1991,
Received: November 9, 2007
Published online: April 22, 2008
Chem. Eur. J. 2008, 14, 5353 – 5359
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5359