Novel polymer nanowires with triple hydrogen-bonding sites fabricated by metallogel template polymerization and their adsorption of thymidine

Article abstract of DOI:10.1039/c0sm00857e

Novel polymer nanowires with triple hydrogen-bonding sites have been prepared by a one-pot procedure based on metallogel template polymerization, which was carried out in an Ag(i)-coordinated organogel with benzoyl peroxide (BPO) as initiator. The product

Full text of DOI:10.1039/c0sm00857e

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/softmatter | Soft Matter
Novel polymer nanowires with triple hydrogen-bonding sites fabricated by
metallogel template polymerization and their adsorption of thymidine†
*
Botian Li, Liming Tang, Lu Qiang and Kai Chen
Received 25th August 2010, Accepted 19th October 2010
DOI: 10.1039/c0sm00857e
Novel polymer nanowires with triple hydrogen-bonding sites have been prepared by a one-pot
procedure based on metallogel template polymerization, which was carried out in an Ag(I)-coordinated
organogel with benzoyl peroxide (BPO) as initiator. The product has been characterized using infrared
spectroscopy, scanning electron microscopy and transmission electron microscopy. The experimental
results reveal that the gel fiber is a crucial template for polymerization. Due to the degradation of the
template in the polymerization, nanofibers of metallogel were transcribed to polymer nanowires.
Polymer nanowires synthesized by this method contain triple hydrogen-bonding sites introduced by the
monomer diacryloyl-2,6-diaminopyridine (DADAP); they are used as adsorbing agents for the ‘uptake’
of thymidine from dilute THF solution. The efficient adsorbing performance and reusable properties
will render them ideal candidates for applications relating to biological adsorption.
recognition.20;21 Compared to single hydrogen bonding groups,
Introduction
the incorporation of multiple acceptor and donor units signifi-
cantly enhances the strength of a hydrogen-bonding interac-
tion.17 Some reports have integrated multiple hydrogen-bonding
interactions into nanoparticles by surface modification, and
studied the capability of reversibly attaching polymers to solid
surfaces. For example, Vancso et al. investigated the self-
complementary molecular assembly between Au nanoparticles
modified with quadruple hydrogen-bonding and pyrimidinone
moieties,22 while Rotello and co-workers used Au nanoparticles
and polymers functionalized with complementary hydrogen
bonding groups such as thymine and triazine to form extended
nanoparticle aggregates.23 In those studies, however, the proce-
dures of synthesis were always complicated, which restricted the
application of multiple hydrogen-bonding interaction in these
systems. Also, organic polymer nanostructures with multiple
hydrogen-bonding sites are limited or undeveloped.
In the past several years, polymer nanowires and nanotubes have
attracted considerable attention, since their one-dimensional
morphology and structural versatility impart to them great
application potential in different areas, such as electronic devices,1
separations,2 drug delivery,3 and catalyst supports.4 Generally,
polymer nanowires can be fabricated by a self-assembly process5;6
or by template polymerization. Template-assisted synthesis is an
efficient, controllable, and conventional route to achieve well-
shaped nanowires. Several kinds of materials have been designed
as ‘hard templates’, for example, porous polycarbonate films,7
porous alumina8;9 and silver nanowires.10 However, the removal
of the templates is tedious when these hard templates are used.
Supramolecular gels consisting of nanofiber networks have
been developed as ‘soft templates’ to fabricate a variety of
inorganic nanotubes;11–13 in these gel templates, organic fibrous
structures could be transcribed to inorganic hollow tubes after ‘in
situ’ polymerization and calcination. Besides inorganics, organic
polymer structure have also been achieved using metallogel
templates,14 although these gels just acted as inverse templates in
monomeric solvents for producing porous polymers, their utility
for template fabrication was revealed. Owing to their excellent
heat-stable properties and facile preparation procedure,15 these
gels display potential applications as templates for polymer
nanowires. Recently, our group has developed a silver metallogel
based on which we managed to fabricate polymer nanotubes.16
Heat-initiated polymerization took place on the gel fibers, the
original gel fibers were successively easily removed by using
excess ammonia, resulting in polymer nanotubes.
In this paper, we focused on the template fabrication of
polymer nanowires with triple hydrogen-bonding sites on the
surface by a one-pot procedure. The resulting polymer nanowires
were confirmed by TEM and SEM analysis and their adsorption
properties in thymidine THF solution were detected by a UV-Vis
spectrometer. Thanks to the hydrogen-bonding interactions and
huge specific surface area, the product is capable of ‘uptaking’
thymidine molecules from dilute solution effectively. That makes
the polymer nanowires excellent sorbents for specific biological
molecules. To the best of our knowledge, this is the first example
of novel polymer nanowires with triple hydrogen-bonding sites
prepared using metallogel nanofibers as the template. This simple
approach might be extended to synthesize some other polymer
nanostructures bearing multiple hydrogen-bonding sites.
Multiple hydrogen-bonding interactions, which are the most
important noncovalent forces in biological systems,17 have been
widely employed in copolymer self-assembly,18;19 surface
Experimental
Laboratory of Advanced Materials, Department of Chemical Engineering,
Tsinghua University, Beijing, 100084, P. R. China. E-mail: tanglm@mail.
tsinghua.edu.cn; Fax: (+86) 10-6278-0304
Materials
Tetrahydrofuran (THF, Tianjin Chemical Reagents) was freshly
distilled from sodium prior to use; dichloromethane was refluxed
† Electronic supplementary information (ESI) available: Experimental
details and additional images. See DOI: 10.1039/c0sm00857e
This journal is ª The Royal Society of Chemistry 2011
Soft Matter, 2011, 7, 963–969 | 963

View Article Online
with calcium hydride and distilled before use. Benzoyl peroxide
(BPO) and 2,6-diaminopyridine were purchased from Beijing
Chemicals and purified by recrystallization using methanol.
Benzene-1,3,5-tricarbonyl trichloride, 3-hydroxyl pyridine and
acryloyl chloride purchased from Alfa Aesar were used as
received. Other solvents and reagents, including AgNO3,
deionized water, ethanol, pyridine and so on were used without
further purification.
Characterization
1H NMR spectra were obtained on a JEOL JNM-ECA300
spectrometer. Fourier-transform infrared (FT-IR) spectroscopy
experiments were performed using a Nicolet 560 instrument.
Field emission scanning electron microscopy (SEM) measure-
ments were carried out with a JEOL FESEM 6704F electron
microscope operating at an accelerating voltage of 20 kV by drop
casting the sample dispersed in ethanol on a silicon slice.
Transmission electron microscopy (TEM) images were obtained
on a JEOL J2010 transmission electron microscope with an
accelerating voltage of 200 kV by drop casting the sample
dispersion on copper grids coated with carbon film. Electron
dispersive X-ray spectroscopy (EDS) was performed on JEOL
J2010 with an Oxford spectrometer. The mechanical properties
of samples were investigated using a Physica MCR300 rheo-
meter. The rate of guest molecule adsorption was measured by
placing 100 mg of polymer nanowires in thymidine THF solution
(100 mg Lꢁ1). The absorbance spectrum of the solution was
recorded with a UV757CRT spectrophotometer, and the char-
acteristic absorbance of thymidine at 267 nm was used to
monitor its concentration.
Synthesis of tripyridin-3-yl benzene-1,3,5-tricarboxylate (ligand
L)
Firstly, 2.86 g (30 mmol) 3-hydroxyl pyridine and 3.2 g pyridine
(40 mmol) was dissolved in 30 mL dehydrated dichloromethane.
2.65 g (10 mmol) benzene-1,3,5-tricarbonyl trichloride dissolved
in another 30 mL of dehydrated dichloromethane was dropped
into the solution in 1 h at room temperature. After addition, the
solution was refluxed at 45 ꢀC for 15 h. After that, 20 mL
deionized water was added to the resulting solution after cooling,
and the aqueous phase was extracted twice with dichloro-
methane. After evaporation of dichloromethane at reduced
pressure, the remaining white solid was recrystallized using
ethanol to give 3.42 g product (78% yield).
1H NMR (300 MHz, [D6]DMSO, TMS, d (ppm)): 9.04 (s, 3H,
aryl H), 8.60 (d, 3H, 2-pyridyl H), 8.55 (d, 3H, 6-pyridyl H), 7.86
(d, 3H, 4-pyridyl H), 7.61 (d*d, 3H, 5-pyridyl H).
FT-IR (KBr, cmꢁ1): 3076, 3061 (aryl and pyridyl C–H), 1732
(CO, strong), 1577, 1473, 1424 (aryl, pyridyl C]C and pyridyl
C]N).
Results and disscusion
In our work, we attempted to achieve functional polymer nanowires
with triple hydrogen-bonding sites via metallogel template poly-
merization. The metallogel utilized in experiments denotes an
organogel in which a metal ion is included to induce gelation.24
According to the studies by Xu’s group,25 crosslinking of multi-
dentate ligands by transitional metal ions can form 3D networks
responsible for gelation. Herein we synthesized ligand L,
a compound with three pyridyl groups, and found that a L/Ag+
complex can gelate THF solventbyforming crosslinking nanofibers.
The triple hydrogen-bonding interaction is introduced by the
monomer DADAP, which could be considered as a kind of DAD
Synthesis of diacryloyl-2,6-diaminopyridine (DADAP)
To an aqueous solution (60 mL) of 2.29 g (21 mmol) 2,6-dia-
minopyridine and 1.68 g (42 mmol) NaOH, 4.43 g (49 mmol)
acryloyl chloride dissolved in 10 mL dichloromethane was added
slowly over 15 min. The round-bottomed flask was cooled in an
ice-water bath and stirred for 2 h. After removal of solvent in
organic layer by rotary evaporation, the yellow solid was filtered
and purified by column chromatography using ethyl acetate as
eluent to give 2.98 g product (66% yield).
(donor–acceptor–donor) monomer with
group.26 The synthesis routes of both ligand and monomer are
a diaminopyridine
facile and suitable for large-scale production.
Synthesis of polymer nanowires
1H NMR (300 MHz, CDCl3, TMS, d (ppm)): 8.00 (d, 2H, 3-
pyridyl H), 7.74 (t, 1H, 4-pyridyl H), 6.47 (d, 2H, 3-acryloyl cis
H), 6.24 (d, 2H, 2-acryloyl H), 5.82 (d, 2H, 3-acryloyl trans H),
4.28 (s, b, 2H, amide H).
FT-IR (KBr, cmꢁ1): 3327 (N–H stretch), 3033, 2984 (pyridyl
and acryloyl C–H), 1679 (C]O stretch), 1592, 1450 (pyridyl
C]C and pyridyl C]N).
The preparation procedure is illustrated in Scheme 1. In the first
step, a metallogel was prepared by injecting AgNO3 solution into
ligand solution, while the monomer DADAP and the initiator
BPO were also mixed simultaneously. The gel was rapidly
produced in 10 s, and formation of gel was confirmed by the
inverted-test-tube method.27
ꢀ
Afterwards, the gel was treated at 65 C for 10 h to carry out
the radical polymerization of DADAP. Poly(diacryloyl-2,6-dia-
minopyridine) (PDADAP) was synthesized on the template gel
fiber, giving polymer nanowires as a white gel. After polymeri-
zation, excess ammonia was added to remove the remaining
metallogel template; the products were finally obtained after
filtration and drying in a vacuum.
Synthesis of polymer nanowires
In a typical process, 30 mg (0.068 mmol) of ligand L and 30 mg
DADAP was dissolved in 1.5 g THF in a vial, then a 1.5 g THF
solution of AgNO3 (18 mg, 0.106 mmol) and BPO (3 mg) was
injected. A gel (1.6 wt%) was produced in 10 s, and subsequently
kept at 65 ꢀC for 10 h. After polymerization, excess ammonia was
added. The white solid was collected by filtration, washed
repeatedly with deionized water (20ꢀmL) and ethanol (20 mL) for
three times, and finally dried at 40 C in vacuum.
Infrared spectroscopy
The polymer nanowires are investigated by FT-IR spectroscopy.
In Fig. 1, the FT-IR spectra of the monomer DADAP (a) and
964 | Soft Matter, 2011, 7, 963–969
This journal is ª The Royal Society of Chemistry 2011

View Article Online
Scheme 1 Illustration of the procedure for fabrication of polymer nanowires.
polymer nanowires (b) both show the characteristic vibrations of
pyridyl amide. The broad peak at 3278 cmꢁ1 is ascribed to the
typical N–H stretching vibration, and the absorptions at
1583 cmꢁ1, 1449 cmꢁ1 are assigned as fundamental vibrations of
pyridine rings, peaks at 1693 cmꢁ1, 1519 cmꢁ1, 1287 cmꢁ1 are
attributed to band I, band II, band III of amide absorption
respectively. The spectrum of the monomer (Fig. 1a) exhibits
unsaturated C–H stretching absorption at 3025 cmꢁ1. After
polymerization, alkyl absorptions arise at 2923 cmꢁ1, 2849 cmꢁ1
(Fig. 1b), and all of the peaks become broader.
In order to investigate the template effect for polymerization
and the fabrication mechanism, we monitored the polymeri-
zation process in different stages via TEM observation. Fig. 3
gives the morphology changes of polymer nanowires with shell/
core structure: In the early stage (Fig. 3A), the polymer formed
a thin layer on the surface of the gel nanofibers; in the middle
stage (Fig. 3B–C), more and more DADAP monomers were
polymerized and the polymer layer (as indicated by arrow a)
became thicker and thicker, meanwhile the dark nanofiber core
denoted by arrow b got thinner. In Fig. 3D, we cannot find gel
fiber in the core of the sample which was obtained after 24 h
polymerization; this means that the template gel fibers were
destroyed during polymerization. We also performed another
polymerization experiment without a gel template, and found
that almost no polymer was produced at the same concentration
of DADAP (1 wt%).
Morphology characterization
Ligand L can be dissolved in polar solvent such as THF and
ethanol; its tripodal structure is designed to ‘‘catch’’ silver ions in
order to build a coordination polymer,28;29 the 3D network
structure of which could be employed to gelate a solvent. In this
work, the fibrillar networks of the metallogel (1.6 wt%) is used as
a template to fabricate polymer nanowires. As shown in Fig. 2,
the diameters of gel nanofibers are about 30–50 nm, and the
average diameter is 40 nm.
According to the results of our experiments, a possible
mechanism can be proposed as depicted in Fig. 4. Because of
coordination between the pyridyl group of DADAP and the
silver ions constituting the metallogel, the monomer was adsor-
bed on to the closest surface of gel the fibers, where heat-initiated
Fig. 1 IR spectra of (a) DADAP and (b) polymer nanowires.
This journal is ª The Royal Society of Chemistry 2011
Fig. 2 TEM image of metallogel nanofibers as template.
Soft Matter, 2011, 7, 963–969 | 965

View Article Online
Fig. 3 TEM images of PDADAP nanowires after (A) 4 h; (B) 10 h; (C) 16 h; and (D) 24 h polymerization.
polymerization took place; gel fibers acted as the template in this
process. The polymer layer was thickened as polymerization time
was prolonged. Simultaneously, metallogel fibers were eroded by
polymer from the surface, causing degradation of the template.
At last, the whole gel fiber was replaced by a polymer nanowire.
This destruction process could be ascribed to the pyridyl groups
of the polymer, which were inclined to coordinate with the silver
ions of template gel. Prolonging the reaction time (24 h) resulted
in solid nanowires instead of hollow nanotubes. Since the
template degraded spontaneously in polymerization, we may
describe the mechanism as ‘self-degraded template polymeriza-
tion’.
interconnected. Lengths of the nanowires can reach tens of
micrometres and their uniform diameter is 50 nm, consistent with
the result from the TEM image shown in Fig. 3D.
EDS analysis of the selected region of nanowires in Fig. 6A
presents the peaks of silver ions, proving that silver metallogel
fibers are still existent in the core of the nanowire. The small
black particles scattered throughout the fiber should be silver
nanoparticles; they were produced from reducing reaction of
silver ions. In contrast, after removal of template nanofiber core,
the silver peaks disappear (Fig. 6B).
Ammonia treatment can quickly remove the metallogel
template and it seems that the polymer obtained in the middle
stage should form nanotubes with the addition of excess
ammonia. However, most of them are nanowires—only a small
part of product exhibits a hollow structure (Fig. 7) with a narrow
The SEM image of the sample of polymer nanowires reveals
a network structure in Fig. 5. Similar to the original gel fibers,
the networks of polymer nanowires are branched and
Fig. 4 Template fabrication mechanism of polymer nanowires.
966 | Soft Matter, 2011, 7, 963–969
Fig. 5 SEM image of polymer nanowires.
This journal is ª The Royal Society of Chemistry 2011

View Article Online
template nanofibers were removed, these nanowires might
collapse quickly, and the minority of them with larger interspaces
remained nanotubes. If the polymer layer is too weak to support
the tube structure, nanotubes will be squashed into ribbons.
Mechanical properties
In the experiment, we found that the Ag(I) metallogel formed by
mixing solutions of silver ions and ligands interestingly exhibits
pronounced thixotropic behavior. Shaking or sonication could
destroy the fragile gel, resulting in a free-flowing liquid which
reformed into a white gel upon standing for several hours. The
reversible gel–sol transformation of the metallogel has been
reported before as a gel mechano-responsive property.30 After
polymerization of DADAP, the product was obtained as a gel
which could not be destroyed by shaking or sonication, indi-
cating the formation of a polymer gel. We can take the white gel
out of the vial (Fig. 8A), and it exhibits excellent self-supporting
ability. In the saturated gel, networks of polymer nanowires
trapped lots of solvent molecules. When dried in air for 3 days,
the polymer gel shrinks severely because of the volatilization of
the solvent, as shown in Fig. 8B.
The mechanical properties were measured by rheometer. In
Fig. 9, curves of the storage modulus (G0) and the loss modulus
(G00) against frequency are presented. Obviously, the polymer gel
displays a higher strength (G0 of the polymer gel is about 25 000
Pa, 20 times that of the metallogel, while G00 is more than 10 times
larger). In contrast to the metallogel, the polymer gel shows
typical elastic behavior, and is strong enough to be used as
a specific adsorbing material.
Adsorption of thymidine
To functionalize polymer nanowires prepared by metallogel
template fabrication, we introduce hydrogen bonding recogni-
tion on the surface of nanowires. Our design is based on the use
of a biologically inspired, well-defined, triple hydrogen-bonding
motif formed by the complex between thymine and 2,6-
diacyldiaminopyridine moieties shown in Fig. 10. This motif
provides a robust recognition unit with binding characteristics
that are well known in solution.31;32 The polymer nanowires with
triple hydrogen-bonding sites can be utilized for adsorption in
solution.
Fig. 6 EDS of a single nanowire obtained after 10 h polymerization: (A)
with template; (B) after removal of the metallogel template.
The polymer nanowires have been tested for adsorbing
thymidine, a kind of biologically important nucleoside, from
Fig. 7 Polymer nanotubes obtained after removal of the template.
inner diameter, and sometimes a ribbon structure could also be
seen (denoted by the white arrow). These results could be
ascribed to the flexible mechanical properties of PDADAP; when
Fig. 8 Macroscopic images of polymer gel: (A) the sample saturated by
THF; (B) dried sample.
This journal is ª The Royal Society of Chemistry 2011
Soft Matter, 2011, 7, 963–969 | 967

View Article Online
Fig. 12 Mass increase of adsorbed thymidine in polymer nanowires with
Fig. 9 Storage modulus and loss modulus of the polymer gel and the
respect to time.
metallogel at different frequencies.
dilute THF solution (100 mg Lꢁ1). When the dry powder of
polymer nanowires has been submerged in a solution of thymi-
dine, within a few hours it is capable of removing guest molecules
from the organic phase efficiently. It has been observed from the
time-dependent UV-Vis spectra (Fig. 11) that the intensity of the
peak decreases with respect to time, from 1 h to 9 h, and after
24 h it reaches equilibrium. We investigated the mass of thymi-
dine adsorbed in the polymer nanowires as the adsorption time
increased; as shown in Fig. 12, the curve obtained apparently
follows first-order kinetics, similar to most surface adsorption
procedures. Such result suggests the formation of a triple
hydrogen-bonding motif, and the high specific surface area of the
nanowires contributes to the adsorption of guest molecules,
making the polymer nanowires good sorbents for biological
molecules.
Fig. 10 Triple hydrogen-bonding recognition dyad, based on thymine
and 2,6-diacyldiaminopyridine, used in this study.
According to the reversible nature of hydrogen-bonding,
desorption of thymidine will take place when a heated proton
solvent is used. So we treated the polymer nanowires adsorbed
thymidine with 12 h Soxhlet extraction using ethanol as solvent,
then thymidine was removed from sorbents thoroughly. The
polymer nanowires could be regenerated in this way and used as
sorbents repeatedly which is a great advantage for nucleoside-
adsorbing materials.
Conclusions
In conclusion, using a metallogel as a template, we successfully
fabricated polymer nanowires with triple hydrogen-bonding
sites. This approach is very simple and efficient, involving poly-
merization in a gel system at a moderate temperature. Triple
hydrogen-bonding sites are introduced directly by the monomer.
TEM and SEM analyses of the reaction product demonstrate the
morphology of polymer nanowires which duplicate the networks
of nanofibers of template metallogel. The mechanism of the
template polymerization is also illustrated clearly. The polymer
nanowires prepared by this method could be used as adsorbing
agents of biological molecules, such as thymidine, by immersing
in dilute THF solution and the adsorption procedure accords
with first-order kinetics. Adsorbed polymer nanowires could be
Fig. 11 UV-Vis spectra of time-dependent adsorption of thymidine
from THF solution by the application of polymer nanowires.
968 | Soft Matter, 2011, 7, 963–969
This journal is ª The Royal Society of Chemistry 2011

View Article Online
11 S. Kawano, S. Tamaru, N. Fujita and S. Shinkai, Chem.–Eur. J.,
2004, 10, 343–351.
12 J. H. Jung, K. Nakashima and S. Shinkai, Nano Lett., 2001, 1,
145–148.
13 S. Kobayashi, N. Hamasaki, M. Suzuki, M. Kimura, H. Shirai and
K. Hanabusa, J. Am. Chem. Soc., 2002, 124, 6550–6551.
14 Q. Wei and S. L. James, Chem. Commun., 2005, 1555–1556.
15 B. A. Xing, M. F. Choi, Z. Y. Zhou and B. Xu, Langmuir, 2002, 18,
9654–9658.
regenerated by Soxhlet extraction. Our study has introduced
multiple hydrogen-bonding sites into polymer nanowires. Using
this strategy, a variety of functionalized polymer nanowires for
biological application might be prepared under appropriate
conditions.
Acknowledgements
16 K. Chen, L. M. Tang, Y. Xia and Y. J. Wang, Langmuir, 2008, 24,
13838–13841.
17 L. J. Prins, D. N. Reinhoudt and P. Timmerman, Angew. Chem., Int.
Ed., 2001, 40, 2382–2426.
18 U. Drechsler, R. J. Thibault and V. M. Rotello, Macromolecules,
2002, 35, 9621–9623.
The financial support from the National Natural Science
Foundation of China (Nos. 20574041 and 20874055) and Hi-tech
Research and Development Program (863 plan) of China (No.
2009AA062903) is gratefully acknowledged.
19 H. S. Bazzi and H. F. Sleiman, Macromolecules, 2002, 35, 9617–9620.
20 K. Viswanathan, H. Ozhalici, C. L. Elkins, C. Heisey, T. C. Ward and
T. E. Long, Langmuir, 2006, 22, 1099–1105.
Notes and references
21 J. T. Han, D. H. Lee, C. Y. Ryu and K. W. Cho, J. Am. Chem. Soc.,
2004, 126, 4796–4797.
22 S. Zou, Z. H. Zhang, R. Forch, W. Knoll, H. Schonherr and
G. J. Vancso, Langmuir, 2003, 19, 8618–8621.
23 A. K. Boal, M. Gray, F. Ilhan, G. M. Clavier, L. Kapitzky and
V. M. Rotello, Tetrahedron, 2002, 58, 765–770.
24 J. K. H. Hui, Z. Yu and M. J. MacLachlan, Angew. Chem., Int. Ed.,
2007, 46, 7980–7983.
25 B. G. Xing, M. F. Choi and B. Xu, Chem.–Eur. J., 2002, 8, 5028–5032.
26 L. Brunsveld, B. J. B. Folmer, E. W. Meijer and R. P. Sijbesma, Chem.
Rev., 2001, 101, 4071–4097.
1 (a) Il Cho and S. B. Lee, Acc. Chem. Res., 2008, 41, 699–707; (b)
Aleshin, Adv. Mater., 2006, 18, 17–27; (c) H. X. Chang, Y. Yuan,
N. L. Shi and Y. F. Guan, Anal. Chem., 2007, 79, 5111–5115.
2 (a) H. J. Wang, W. H. Zhou, X. F. Yin, Z. X. Zhuang, H. H. Yang
and X. R. Wang, J. Am. Chem. Soc., 2006, 128, 15954–15955; (b)
E. N. Savariar, K. Krishnamoorthy and S. Thayumanavan, Nat.
Nanotechnol., 2008, 3, 112–117.
3 M. R. Abidian, D. H. Kim and D. C. Martin, Adv. Mater., 2006, 18,
405.
4 S. Ko and J. Jang, Angew. Chem., Int. Ed., 2006, 45, 7564–7567.
5 I. W. Hamley, Soft Matter, 2005, 1, 36–43.
27 L. A. Estroff and A. D. Hamilton, Chem. Rev., 2004, 104, 1201–1217.
28 M. Oh and C. A. Mirkin, Angew. Chem., Int. Ed., 2006, 45,
5492–5494.
29 Y. M. Jeon, J. Heo and C. A. Mirkin, J. Am. Chem. Soc., 2007, 129,
7480.
6 T. Shimizu, M. Masuda and H. Minamikawa, Chem. Rev., 2005, 105,
1401–1443.
7 C. Schonenberger, B. M. I. vanderZande, L. G. J. Fokkink,
M. Henny, C. Schmid, M. Kruger, A. Bachtold, R. Huber, H. Birk
and U. Staufer, J. Phys. Chem. B, 1997, 101, 5497–5505.
8 M. Steinhart, R. B. Wehrspohn, U. Gosele and J. H. Wendorff,
Angew. Chem., Int. Ed., 2004, 43, 1334–1344.
30 W. G. Weng, J. B. Beck, A. M. Jamieson and S. J. Rowan, J. Am.
Chem. Soc., 2006, 128, 11663–11672.
31 Z. Li, J. F. Ding, M. Day and Y. Tao, Macromolecules, 2006, 39,
2629–2636.
9 K. J. Lee, J. H. Oh, Y. Kim and J. Jang, Chem. Mater., 2006, 18,
5002–5008.
32 D. J. Duffy, K. Das, S. L. Hsu, J. Penelle, V. M. Rotello and
H. D. Stidham, J. Am. Chem. Soc., 2002, 124, 8290–8296.
10 A. H. Chen, H. X. Xie, H. Q. Wang, H. Y. Li and X. Y. Li, Synth.
Met., 2006, 156, 346–350.
This journal is ª The Royal Society of Chemistry 2011
Soft Matter, 2011, 7, 963–969 | 969