An amphiphilic pillar[5]arene: Synthesis, controllable self-assembly in water, and application in calcein release and TNT adsorption

Article abstract of DOI:10.1021/ja3076617

An amphiphilic pillar[5]arene was made. It could self-assemble to form vesicles and multiwalled microtubes in water. Dynamic light scattering, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, and UV-vis and FTIR spectroscopy were employed to characterize its self-assembly process and the resultant assemblies. The vesicles could encapsulate calcein within their interiors under neutral conditions and release it in response to a decrease in pH. The microtubes, which have primary amine groups on their surfaces, could adsorb TNT through donor-acceptor interactions.

Full text of DOI:10.1021/ja3076617

Communication
pubs.acs.org/JACS
An Amphiphilic Pillar[5]arene: Synthesis, Controllable Self-Assembly
in Water, and Application in Calcein Release and TNT Adsorption
Yong Yao, Min Xue, Jianzhuang Chen, Mingming Zhang, and Feihe Huang*
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Chemistry, Zhejiang University, Hangzhou
310027, P. R. China
S
* Supporting Information
between two functionalizable rims.7 Their repeating units are
ABSTRACT: An amphiphilic pillar[5]arene was made. It
could self-assemble to form vesicles and multiwalled
microtubes in water. Dynamic light scattering, trans-
mission electron microscopy, scanning electron micros-
copy, atomic force microscopy, and UV−vis and FTIR
spectroscopy were employed to characterize its self-
assembly process and the resultant assemblies. The vesicles
could encapsulate calcein within their interiors under
neutral conditions and release it in response to a decrease
in pH. The microtubes, which have primary amine groups
on their surfaces, could adsorb TNT through donor−
acceptor interactions.
connected by methylene bridges at the para positions, forming a
unique rigid pillar architecture that differs from the basket-
shaped structure of meta-bridged calixarenes. They can easily be
chemically modified, making them promising candidates for
applications in nanomaterials, molecular recognition, ion
transport, supramolecular polymers, and so on.7 However, to
the best of our knowledge, amphiphilic pillar[n]arenes have not
been explored to date. Herein we report the synthesis of the first
amphiphilic pillar[5]arene, its controllable self-assembly in
water, and its application in calcein release and TNT adsorption.
Amphiphilic pillar[5]arene 1 was designed to contain five
amino groups as the hydrophilic head and five alkyl chains as the
hydrophobic tail (Scheme 1) to endow the aggregates with
mphiphiles are a class of fascinating molecules bearing both
Scheme 1. Syntheses of Amphiphilic Pillar[5]arene 1 and Its
Monomeric Analogue 4
1
Ahydrophilic and hydrophobic groups.
When they are
dispersed in water, their hydrophilic components preferentially
interact with the aqueous phase while their hydrophobic portions
tend to reside in the air or in the nonpolar solvent or to gather
together in order to decrease the free energy of the hydrophilic−
hydrophobic interface.2 Therefore, the amphiphiles can
spontaneously aggregate to form different assemblies depending
on the repelling and coordinating forces between the hydrophilic
and hydrophobic parts of the component molecules and the
surrounding medium.2e Inspired by this, scientists have devoted
considerable efforts to the design and fabrication of artificial
supramolecular structures from the self-assembly of amphiphiles
for their wide application in chemistry, biology, and materials
science.3 Although various linear amphiphiles such as surfactants
and amphiphilic block copolymers that can self-assemble into
zero-dimensional (0D) or one-dimensional (1D) structures have
been prepared,4 macrocyclic amphiphiles have rarely been made
and employed in the fabrication of supramolecular structures.
The macrocycles can locate hydrophilic and hydrophobic chains
to the respective sides. This can promote their self-assembly into
various well-defined architectures. Moreover, in view of the rich
research results on the host−guest chemistry of macrocycles,5
the use of macrocyclic amphiphiles in the fabrication of
multidimensional and hierarchical self-assemblies is important
since it may provide interesting new topological structures based
on the self-selectivity of host−guest interactions and novel
functions due to the environmental responsiveness of host−
guest interactions.6
enhanced stability and a pH-responsive character. To prepare 1
(Scheme 1), the nonsymmetric monomer 3 was first synthesized
[Scheme S2 in the Supporting Information (SI)]. Next,
condensation of 3 with boron trifluoride etherate as the catalyst
in CH2ClCH2Cl afforded the four constitutional isomers 2a−2d
(Scheme S3),7h among which 2a is the one having all five ester
functional groups on the same side, as confirmed by its crystal
structure (Scheme 1). At last, compound 1 was obtained by
refluxing a solution of 2a and 1,2-ethanediamine in ethanol.
As a new class of supramolecular hosts, pillar[n]arenes,
especially pillar[5]arenes, are useful and interesting macrocyclic
compounds that present a hydrophobic core sandwiched
Received: August 2, 2012
Published: September 11, 2012
© 2012 American Chemical Society
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When amphiphilic pillar[5]arene 1 was dissolved in water, the
water surface tension (γ) as a function of the concentration of 1
(C) was measured to determine its critical micelle concentration
(CMC) in water (Figure S14 in the SI).2e,6b There were two
linear segments in the γ versus C curve and a sudden reduction in
the slope, implying that the CMC is ∼1.5 × 10−4 M. The
aggregation behavior of 1 in water was then investigated using
dynamic light scattering (DLS), scanning electron microscopy
(SEM), and transmission electron microscopy (TEM). The DLS
experiment was performed with a 2.0 × 10−4 M aqueous solution
of 1 over a scattering angle range of 90°. 1 showed aggregation
behavior with a narrow size distribution, indicating well-
equilibrated structures. The average hydrodynamic radius (RH)
of 1 was observed to be ∼200 nm (Figure 1a), which greatly
within their interiors under neutral conditions and release the
guest molecules in response to a decrease in pH. This stimuli-
responsive nanocapsule might have potential applications in
selective drug delivery in tissues having a lower pH, such as
infected tissues and tumor tissues.4 With this in mind, calcein as a
model hydrophilic guest was encapsulated in the vesicles. Release
of calcein from the interiors of the vesicles was accompanied by
an increase in fluorescence emission as the free calcein in solution
was dequenched. As shown in Figure S17b, no leakage of
entrapped calcein was observed over a period of 1 day, indicating
that these vesicles were stable toward leakage. However,
exposure of the calcein-loaded vesicles to a pH 4 environment
resulted in rapid and complete release of the encapsulated
calcein. This result can be explained by considering a pH-
triggered vesicle-to-micelle transition. The decrease in pH results
in the quaternization of the amine groups. This increases the
surface area of the hydrophilic headgroup, triggering the collapse
of the vesicular structure into a micellar structure with
concomitant release of the encapsulated calcein (Figure 2).4
Figure 2. Schematic representation of a pH-triggered vesicle-to-micelle
transition of the aggregates of 1 and the subsequent release of
encapsulated calcein.
Additionally, floccules were observed in solution after 2 weeks
(Figure S18b), and the floccules were found to become
consistently larger and darker as the incubation time increased.
The aggregation behavior of 1 in water as a function of aging time
was investigated by UV−vis spectroscopy (Figure S18a). The
characteristic peak at ∼290 nm, which is due to the absorbance of
1, decreased because of the decreasing concentration of free 1 in
solution caused by the formation of floccules. For comparison,
the noncyclic monomeric analogue 4 was synthesized (Scheme
1) and allowed to self-assemble in water under the same
experimental conditions. However, no floccules formed even
after 4 months, indicating that the pillar[5]arene frame plays a
significant role in the self-assembly process of 1.
Figure 1. (a) DLS results at a scattering angle of 90° for the vesicles
formed by 1 (2.0 × 10−4 M) in water. (b) SEM and (c) TEM images of
aggregates of 1 (2.0 × 10−4 M) in water. (d) SEM image of a ruptured
vesicle.
exceeds the corresponding extended molecular length of 1 (∼2
nm), suggesting that these aggregates were vesicular entities
rather than simple micelles. Further evidence for the formation of
vesicles from 1 was provided by TEM experiments. As shown in
Figure 1b, the TEM image revealed an obvious color contrast
between the peripheries and centers of the spheres, characteristic
of the projection images of hollow spheres. The formation of
spherical aggregates from 1 was also confirmed by SEM
experiments (Figure 1c). The resultant micrograph showed
spherical aggregates with diameters of ∼200 nm, consistent with
the results obtained from the above-mentioned DLS and TEM
experiments. Moreover, the wall thickness of the vesicles was ∼4
nm, as observed from a ruptured vesicle (Figure 1d and Figure
S16), indicating that the vesicles had a bilayer wall.
The morphology of the aggregates was examined by SEM
(Figure 3), TEM (Figure S20), and atomic force microscopy
(AFM) (Figure S19). The overview of the aggregates provided
by SEM demonstrated that the floccules were actually micro-
fibers (Figure 3a). AFM and TEM images (Figures S19 and S20)
More importantly, the vesicular structure appeared to
transform into a micellar structure with a decrease in pH. The
effect of pH on the aggregation behavior of 1 was investigated by
DLS measurements. As shown in Figure S15, a decrease in pH
induced a dramatic decrease in the aggregate diameter from 200
nm at pH 7 to 10 nm at pH 3, while the aggregates maintained a
narrow size distribution. This unique aggregation behavior seems
to be due to a transition from a vesicular structure to a micellar
structure (Figure S17a inset). Therefore, one can envision that
the vesicles formed by 1 encapsulate hydrophilic guest molecules
Figure 3. SEM images of the amphiphilic pillar[5]arene 1-based
microfibers: (a) overview of the microfibers; (b) enlarged image of (a).
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and an enlarged SEM image (Figure 3b) of individual microfibers
showed that the average diameter of the microfibers was ∼1.2
μm.
Furthermore, the SEM images of the floccules showed that
some of the microfibers were oblate (Figure S21), suggesting that
the fibers should not be solid. It can be seen from the cross-
section of a microfiber that the microfibers are actually hollow
(Figure 4a and Figure S22). To explore the fine structures of
microtubes. After 4 months, there were no sheetlike or
necklacelike structures, indicating that all of these structures
had been converted to microtubes.
Pillar[5]arene 1 has five hydrophilic amino headgroups, a
hydrophobic pillar[5]arene cavity, and five hydrophobic alkyl
tails, so it can be considered as an amphiphilic molecule. A
possible mechanism for the generation of microtubes is shown in
Figure 5. It is proposed that molecules of 1 initially undergo tail-
Figure 4. (a) SEM image of the cross-section of a microfiber: (b) TEM
image of the cross-section of a microfiber; (c) TEM image of the vertical
section of a microfiber.
these microfibers, an ultrathin slice of a microfiber was observed
by TEM. The results (Figure 4b,c) clearly showed that the
microfibers were in fact microtubes with an exterior diameter of
∼1.2 μm, a thickness of ∼200 nm, and an inner diameter of ∼800
nm.
Figure 5. Schematic illustration of the self-assembly process of
amphiphilic pillar[5]arene 1 into microtubes.
To study the mechanism of the self-assembly process, the
Fourier transform IR spectra of a powder sample of 1 and of the
microtubes self-assembled from 1 were compared (Figure S23).
It was observed that the N−H stretching and carbonyl bands of
the powder were at 3396 and 1676 cm−1, respectively, and shifted
to 3393 and 1671 cm−1, respectively, in the microtubes. The
decrease in the wavenumber suggests an enhancement of the
hydrogen-bonding strength and also shows that stronger and
more ordered hydrogen bonds are formed in the microtubes.6b
In addition, the antisymmetric and symmetric stretching
vibrations of the CH2 alkyl chains in the microtubes were at
2924 and 2854 cm−1, respectively, while the corresponding peaks
for the powder sample were at 2926 and 2856 cm−1. It is well-
known that the symmetric and antisymmetric stretching
vibrations of CH2 can be used as sensitive indicators of the
order of alkyl chains, with increases in the frequencies and band
widths being associated with the increasing numbers of gauche
defects and disorder.8 Therefore, the decrease in wavenumber in
going from the powder to the microtubes suggested an increase
in the number of van der Waals interactions between neighboring
alkyl chains in the microtubes.
Further investigation provided us with deeper insight into the
nature of the self-assembly. It was interesting that vesicular
structures appeared to transform into microtubes with increasing
incubation time (Figure S24), suggesting a possible mechanism
for the formation of the microtubes. This observation was very
important since it highlighted the significance of vesicles in the
self-assembly process to form microtubes. Figure S24a shows an
SEM image of the floccules after an incubation time of 2 weeks, in
which a large number of vesicles and several microtubes can be
seen. The number of vesicles decreased when the floccules self-
assembled for 1 month (Figure S24b). Furthermore, when the
incubation time was increased to 2 months, a large number of
microtubes and only a few vesicles were observed (Figure S24c).
Remarkably, almost all of the vesicles were converted to
microtubes after 4 months (Figure S24d). Simultaneously,
some necklacelike and sheetlike structures were also found in the
intermediates (Figure S25). With an increase in the incubation
time, these structures were also gradually converted to
to-tail packing to form bilayer vesicles. Subsequently, some
bilayer vesicles are transformed into necklacelike structures when
they are close to each other, while other bilayer vesicles fuse into
large vesicles, with sheetlike structures being formed by rupture
of these large vesicles. These necklacelike structures then further
fuse into microtubes.6c,e At the same time, the sheetlike
structures could subsequently roll-up via hydrogen-bonding
interactions, which could also lead to the generation of
microtubes (Figure 5).6a,b Taken together, the studies described
above suggested that hydrophobic interactions9 of alkyl chains
provide the driving force for the formation of vesicles.
Furthermore, aromatic stacking10 between the pillar[5]arene
frames and hydrogen-bonding interactions between the amino
groups and acylamino groups contribute to the generation of
microtubes and account for the stability of the resulting
architectures.6d All of these factors lead to the formation of the
microtubular structures, in which the hydrophobic surfaces are
shielded from the polar solvent water whereas the hydrophilic
chains (primary amine groups) are in contact with the aqueous
environment.
2,4,6-Trinitrotoluene (TNT) is a leading example of nitro-
aromatic explosives with significant detrimental effects on the
environment and human health. How to curb TNT is a
challenging mission today.11 The supramolecular microtubes in
the present work can be considered as electron donors because
they contain primary amines on their inner and outer walls.
Therefore, we envisioned that TNT could be adsorbed on the
surfaces of the microtubes through donor−acceptor (D−A)
interactions. A decrease in the characteristic absorbance of TNT
from 0.342 to 0.065 after the microtubes were immersed in an
aqueous solution of TNT confirmed that TNT was indeed
adsorbed by the microtubes (Figure S26). Furthermore, this
characteristic absorbance did not decrease after free 1 or 4 was
added to an aqueous solution of TNT.
In conclusion, the results described here demonstrate that
amphiphilic pillar[5]arene 1 can self-assemble to form well-
defined vesicles under neutral conditions. These vesicles were
observed to transform into small globular micelles at low pH.
This transformation can be used to trigger the controlled release
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Soc. 2011, 133, 2836. (g) Zheng, B.; Wang, F.; Dong, S.; Huang, F.
Chem. Soc. Rev. 2012, 41, 1621. (h) Noujeim, N.; Zhu, K.; Vukotic, V.
N.; Loeb, S. J. Org. Lett. 2012, 14, 2484. (i) Jiang, W.; Nowosinski, K.;
Low, N. L.; Dzyuba, E. V.; Klautzsch, F.; Schafer, A.; Huuskonen, J.;
Rissanen, K.; Schalley, C. A. J. Am. Chem. Soc. 2012, 134, 1860.
(j) Joosten, A.; Trolez, Y.; Collin, J.-P.; Heitz, V.; Sauvage, J.-P. J. Am.
Chem. Soc. 2012, 134, 1802. (k) Zheng, X.; Wang, D.; Shuai, Z.; Zhang,
X. J. Phys. Chem. B 2012, 116, 823. (l) Ayme, J.-F.; Beves, J. E.; Leigh, D.
A.; McBurney, R. T.; Rissanen, K.; Schultz, D. J. Am. Chem. Soc. 2012,
134, 9488. (m) Yan, X.; Wang, F.; Zheng, B.; Huang, F. Chem. Soc. Rev.
2012, 41, 6042.
(6) (a) Yan, D.; Zhou, Y.; Hou, J. Science 2004, 303, 65. (b) Sun, Y.;
Yan, C.-G.; Yao, Y.; Han, Y.; Shen, M. Adv. Funct. Mater. 2008, 18, 3981.
(c) Guan, B.; Jiang, M.; Yang, X.; Liang, Q.; Chen, Y. Soft Matter 2008, 4,
1393. (d) Sun, Y.; Yao, Y.; Yan, C.-G.; Han, Y.; Shen, M. ACS Nano
2010, 4, 2129. (e) Liang, Q.; Chen, G.; Guan, B.; Jiang, M. J. Mater.
Chem. 2011, 21, 13262. (f) Zhu, L.; Lu, M.; Zhang, Q.; Qu, D.; Tian, H.
Macromolecules 2011, 44, 4092.
(7) (a) Ogoshi, T.; Kanai, S.; Fujinami, S.; Yamagishi, T. A.; Nakamoto,
Y. J. Am. Chem. Soc. 2008, 130, 5022. (b) Cao, D.; Kou, Y.; Liang, J.;
Chen, Z.; Wang, L.; Meier, H. Angew. Chem., Int. Ed. 2009, 48, 9721.
(c) Zhang, Z.; Xia, B.; Han, C.; Yu, Y.; Huang, F. Org. Lett. 2010, 12,
2385. (d) Han, C.; Ma, F.; Zhang, Z.; Xia, B.; Yu, Y.; Huang, F. Org. Lett.
2010, 12, 4360. (e) Li, C.; Zhao, L.; Li, J.; Ding, X.; Chen, S.; Zhang, Q.;
Yu, Y.; Jia, X. Chem. Commun. 2010, 46, 9016. (f) Zhang, Z.; Yu, G.; Han,
C.; Liu, J.; Ding, X.; Yu, Y.; Huang, F. Org. Lett. 2011, 13, 4818.
(g) Zhang, Z.; Luo, Y.; Chen, J.; Dong, S.; Yu, Y.; Ma, Z.; Huang, F.
Angew. Chem., Int. Ed. 2011, 50, 1397. (h) Zhang, Z.; Luo, Y.; Xia, B.;
Han, C.; Yu, Y.; Chen, X.; Huang, F. Chem. Commun. 2011, 47, 2417.
(i) Strutt, N. L.; Forgan, R. S.; Spruell, J. M.; Botros, Y. Y.; Stoddart, J. F.
J. Am. Chem. Soc. 2011, 133, 5668. (j) Ma, Y.; Ji, X.; Xiang, F.; Chi, X.;
Han, C.; He, J.; Abliz, Z.; Chen, W.; Huang, F. Chem. Commun. 2011, 47,
12340. (k) Si, W.; Chen, L.; Hu, X.-B.; Tang, G.; Chen, Z.; Hou, J.-L.; Li,
Z.-T. Angew. Chem., Int. Ed. 2011, 50, 12564. (l) Li, C.; Chen, S.; Li, J.;
Han, K.; Xu, M.; Hu, B.; Yu, Y.; Jia, X. Chem. Commun. 2011, 47, 11294.
(m) Ma, Y.; Zhang, Z.; Ji, X.; Han, C.; He, J.; Abliz, Z.; Chen, W.; Huang,
F. Eur. J. Org. Chem. 2011, 5331. (n) Cragg, P. J.; Sharma, K. Chem. Soc.
Rev. 2012, 41, 597. (o) Xue, M.; Yang, Y.; Chi, X.; Zhang, Z.; Huang, F.
Acc. Chem. Res. 2012, 45, 1294. (p) Yao, Y.; Xue, M.; Chi, X.; Ma, Y.; He,
J.; Abliz, Z.; Huang, F. Chem. Commun. 2012, 48, 6505. (q) Nier-
engarten, I.; Guerra, S.; Holler, M.; Nierengarten, J.-F.; Deschenaux, R.
Chem. Commun. 2012, 48, 8072. (r) Yu, G.; Han, C.; Zhang, Z.; Chen, J.;
Yan, X.; Zheng, B.; Liu, S.; Huang, F. J. Am. Chem. Soc. 2012, 134, 8711.
(s) Yu, G.; Zhang, Z.; Han, C.; Xue, M.; Zhou, Q.; Huang, F. Chem.
Commun. 2012, 48, 2958. (t) Ma, Y.; Chi, X.; Yan, X.; Liu, J.; Yao, Y.;
Chen, W.; Hou, J.-L.; Huang, F. Org. Lett. 2012, 14, 1532. (u) Han, C.;
Yu, G.; Zheng, B.; Huang, F. Org. Lett. 2012, 14, 1712. (v) Dong, S.;
Han, C.; Zheng, B.; Zhang, M.; Huang, F. Tetrahedron Lett. 2012, 53,
3668. (w) Guan, Y.; Ni, M.; Hu, X.; Xiao, T.; Xiong, S.; Lin, C.; Wang, L.
Chem. Commun. 2012, 48, 8529. (x) Duan, Q.; Xia, W.; Hu, X.; Ni, M.;
Jiang, J.; Lin, C.; Pan, Y.; Wang, L. Chem. Commun. 2012, 48, 8532.
(y) Zhang, Z.; Han, C.; Yu, G.; Huang, F. Chem. Sci. 2012, 3, 3026.
(z) Yu, G.; Xue, M.; Zhang, Z.; Li, J.; Han, C.; Huang, F. J. Am. Chem.
Soc. 2012, 134, 13248.
of encapsulated calcein. Moreover, these vesicles underwent
further self-assembly to produce microtubes after 4 months, and
the resultant microtubes could adsorb TNT driven by D−A
interactions. However, monomeric molecule 4 could neither
assemble into microtubes nor adsorb TNT under the same
conditions, indicating that the pillar[5]arene frame plays a
significant role in controlling self-assembly of 1 in aqueous
media. In contrast to previous studies that mainly dealt only with
the formation of 0D or 1D morphologies in water,2,3,6 this work
indicates that both 0D and 1D aggregates can be obtained from a
simple building block. It will stimulate further studies on
macrocyclic amphiphiles that can self-assemble to produce
aggregates with potential applications in biological systems and
materials science.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details; NMR spectra; SEM, TEM, and AFM
images; and other supporting materials. This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
fhuang@zju.edu.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (20834004, 91027006, and 21172166), the
Fundamental Research Funds for the Central Universities
(2012QNA3013), the Program for New Century Excellent
Talents in University, and the Zhejiang Provincial Natural
Science Foundation of China (R4100009).
REFERENCES
■
(1) Jiang, Y.; Wang, Y.; Ma, N.; Wang, Z.; Smet, M.; Zhang, X.
Langmuir 2007, 23, 4029.
(2) (a) Lehn, J.-M. Science 2002, 295, 2400. (b) Li, C.; Ge, Z.; Fang, J.;
Liu, S. Macromolecules 2009, 42, 2916. (c) Guo, D.-S.; Wang, K.; Wang,
Y.-X.; Liu, Y. J. Am. Chem. Soc. 2012, 134, 10244. (d) Liu, K.; Yao, Y.;
Liu, Y.; Wang, C.; Li, Z.; Zhang, X. Langmuir 2012, 28, 10697. (e) Wang,
C.; Wang, Z.; Zhang, X. Acc. Chem. Res. 2012, 45, 608. (f) Hu, J.; Wu, T.;
Zhang, G.; Liu, S. J. Am. Chem. Soc. 2012, 134, 7624.
(3) (a) Menger, F. M. Angew. Chem., Int. Ed. Engl. 1991, 30, 1086.
(b) Lee, M.; Cho, B.-K.; Zin, W.-C. Chem. Rev. 2001, 101, 3869.
(c) Seeman, N. C. Nature 2003, 421, 427. (d) Zhou, Y.; Yan, D. Angew.
Chem., Int. Ed. 2004, 43, 4896. (e) Hoeben, F. J. M.; Jonkheijm, P.;
Meijer, E. W.; Schenning, A. P. H. J. Chem. Rev. 2005, 105, 1491.
(f) Chen, D. Y.; Jiang, M. Acc. Chem. Res. 2005, 38, 494. (g) Yamamoto,
Y.; Fukushima, T.; Suna, Y.; Ishii, N.; Saeki, A.; Seki, S.; Tagawa, S.;
Taniguchi, M.; Kawai, T.; Aida, T. Science 2006, 314, 1761. (h) Ma, Y. J.;
Dong, W. F.; Hempenius, M. A.; Mohwald, H.; Vancso, G. J. Nat. Mater.
(8) (a) Schnur, J. M. Science 1993, 262, 1669. (b) Hostetler, M. J.;
Stokes, J. J.; Murray, R. W. Langmuir 1996, 12, 3604. (c) Yamada, N.;
Ariga, K.; Naito, M.; Matsubara, K.; Koyama, E. J. Am. Chem. Soc. 1998,
120, 12192. (d) Paramonov, S. E.; Jun, H.-W.; Hartgerink, J. D. J. Am.
Chem. Soc. 2006, 128, 7291.
2006, 5, 724. (i) Zhang, X.; Chen, Z. J.; Wurthner, F. J. Am. Chem. Soc.
̈
2007, 129, 4886. (j) Palmer, L. C.; Stupp, S. I. Acc. Chem. Res. 2008, 41,
1674. (k) Rudick, J. G.; Percec, V. Acc. Chem. Res. 2008, 41, 1641.
(l) Azevedo, H. S.; Velichko, Y. S.; Stupp, S. I. Science 2008, 319, 1812.
(4) Lee, M.; Lee, S.-J.; Jiang, L.-H. J. Am. Chem. Soc. 2004, 126, 12724.
(5) (a) Podkoscielny, D.; Gadde, S.; Kaifer, A. E. J. Am. Chem. Soc.
2009, 131, 12876. (b) Koshkakaryan, G.; Klivansky, L. M.; Cao, D.;
Snauko, M.; Teat, S. J.; Struppe, J. O.; Liu, Y. J. Am. Chem. Soc. 2009, 131,
2078. (c) Zhang, M.; Zhu, K.; Huang, F. Chem. Commun. 2010, 46,
8131. (d) Gu, Z.-Y.; Guo, D.-S.; Sun, M.; Liu, Y. J. Org. Chem. 2010, 75,
3600. (e) Davis, N. K. S.; Thompson, A. L.; Anderson, H. L. J. Am. Chem.
Soc. 2011, 133, 30. (f) Niu, Z.; Huang, F.; Gibson, H. W. J. Am. Chem.
(9) Chandler, D. Nature 2005, 437, 640.
(10) (a) Blau, W. J.; Fleming, A. J. Science 2004, 304, 1457.
(b) Balakrishnan, K.; Datar, A.; Zhang, W.; Yang, X.; Naddo, T.;
Huang, J.; Zuo, J.; Yen, M.; Moore, J. S.; Zang, L. J. Am. Chem. Soc. 2006,
128, 6576. (c) Hamaoui, B. E.; Zhi, L.; Pisula, W.; Kolb, U.; Wu, J.;
Mullen, K. Chem. Commun. 2007, 43, 2384.
̈
(11) Jiang, Y.; Zhao, H.; Zhu, N.; Lin, Y.; Yu, P.; Mao, L. Angew. Chem.,
Int. Ed. 2008, 47, 8601.
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