Rationally designed helical nanofibers via multiple non-covalent interactions: Fabrication and modulation

Article abstract of DOI:10.1039/b926642a

Building well-defined hierarchical architectures via supramolecular chemistry is one of the challenges in nanotechnology and is crucial to our understanding of biological self-assembly and biological phenomenon. In this work, a well-ordered one-dimensiona

Full text of DOI:10.1039/b926642a

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Rationally designed helical nanofibers via multiple non-covalent
interactions: fabrication and modulation†
Yiyang Lin,a Andong Wang,a Yan Qiao,a Chen Gao,a Markus Drechsler,b Jianpin Ye,c Yun Yana
a
*
and Jianbin Huang
Received 17th December 2009, Accepted 10th February 2010
First published as an Advance Article on the web 18th March 2010
DOI: 10.1039/b926642a
Building well-defined hierarchical architectures via supramolecular chemistry is one of the challenges
in nanotechnology and is crucial to our understanding of biological self-assembly and biological
phenomenon. In this work, a well-ordered one-dimensional (1 D) helix is fabricated with a novel
sugar-based lipid by virtue of multiple non-covalent interactions (i.e. hydrophobic interaction,
aromatic stacking, and hydrogen bond). The robust helical nanostructure is evidenced by negative-
staining TEM, cryo-TEM and circular dichroism (CD). A series of amphiphilic molecules are also
synthesized to explore molecular structure-performance relationship and elucidate intermolecular
forces that contribute to complex architectures. Moreover, the supramolecular nanohelices in this work
are demonstrated to be ‘‘smart nanostructures’’ which can be shaped into spherical micelles, vesicles or
unfolded nanofibers by external stimuli, such as pH, light, and surfactant addition.
forms. For example, Yashima and coworkers have reported the
Introduction
first heterostranded double helix held together by inter-strand
amidinium–carboxylate salt bridges of two complementary
homopolymers.10 This work provides a design rationale for
unique double-stranded helical polymers. An alternative
approach towards double helix is to take advantage of bottom-up
fabrication. In this route, polymer-like or one-dimensional
aggregates formed by molecular self-assembly (i.e. small mole-
cules or polymers) can be jointed in a helical fashion. For
example, Frankel and O’Brien prepared amphiphilic diacetylenic
aldonamides which can self-organize into helical structures in
aqueous solution.11 Yanagawa et al. have found a duplex struc-
ture in the self-assembled solution of a phospholipid–nucleoside
conjugate containing two long alkyl chains and a nucleotidyl
residue.12 Recently, Jinnai and coworkers and Liu and coworkers
have reported the visualization of three-dimensional (3D) double
and triple helical morphology of triblock polymers in the mixed
solvent.13 Besides, supramolecular quadruple helices have also
been discovered in nonpolymeric systems involving sugar–lipid
and peptide amphiphiles.14
The discovery of DNA double helix by Watson and Crick1
provides a natural explanation for information transfer during
the replication of DNA and transcription of DNA into
messenger RNA. This discovery is considered as a milestone in
the 20th century’s life sciences, which has promoted greatly the
biomedical research, the naissance of gene engineering tech-
nology and the development of clinical medicine, and turned into
a great landmark during the life sciences history. Chemically,
DNA is a double-stranded polymer that is twisted into a helix
like a spiral staircase. Each strand is comprised of a sugar-
phosphate backbone and numerous base chemicals attached in
pairs. The four bases that make up the stairs in the spiral stair-
case are adenine (A), thymine (T), cytosine (C) and guanine (G).
The perfect structure of DNA’s complementary double helix is of
significant importance to the storage and transfer of genetic
information.2
Inspired by the functionality and complexity of DNA double
helix, chemists have endeavoured in the artificial creation of
double helical architectures in a controllable manner via supra-
molecular self-assembly. In contrast to a large number of single-
stranded helix by synthetic polymers, oligomers or small
molecules,3–9 only a limited number of double helices are repor-
ted. Two strategies have been described in the literature. One
approach is to join two linear polymer chains into double helix
by virtue of inter-chain affinity, which is similar to the way DNA
Despite the study dedicated to artificial double helices, there
are still some issues that need to be addressed. On one hand, the
structural factors at the molecular level that precisely control the
supramolecular self-assembly of a double helix are still vague.
People are still incapable of rationalizing the creation of a self-
assembled double helix and the supramolecular fabrication of
double helices are still rare. Therefore more efforts are needed to
reveal molecular structure–performance relationships in double
helix systems. On the other hand, one of the advantages in
supramolecular chemistry is to build molecular assemblies in
a controllable fashion.15 These supramolecular structures are
held together by relatively weak non-covalent interactions and
thus might be easily reconfigurable into a variety of morphol-
ogies by external stimuli. Such smart stimuli-responsive supra-
molecular assemblies are attractive for potential applications in
aBeijing National Laboratory for Molecular Sciences (BNLMS), College
of Chemistry and Molecular Engineering, Peking University, Beijing,
100871, China. E-mail: jbhuang@pku.edu.cn.; Fax: +86-10-62751708;
Tel: +86-10-62753557
bElektronenmikroskopie Labor, University of Bayreuth, Germany
cCAS Key Laboratory of Photochemistry, Institute of Chemistry, Chinese
Academy of Sciences, Beijing, 100080, People’s Republic of China
† Electronic Supplementary Information (ESI) available: TEM images,
DLS and CD result. See DOI: 10.1039/b926642a/
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nanotechnology. Yet few works have focused on the morpho-
logical modulation or stimuli-response of a supramolecular
double helix.
(3) Synthesis of C4AG:16 In a flask equipped with a reflux
condenser, N-methyl glucamine (9.99 g, 49 mmol) was incubated
with 4-butyl-40-(oxy-2,3-epoxypropyl) azobenzene (10.9 g,
ꢀ
Herein, we have designed a functional amphiphile bearing
a sugar moiety, azobenzene group and butyl chain. In a self-
assembled manner, the amphiphile can organize readily into one-
dimensional intertwined double helices which were composed of
‘‘polymer-like’’ aggregates or nanofibers in aqueous solution.
The self-assembled double helical structures were demonstrated
to be stable with respect to dilution, heat, urea or organic solvent.
A series of amphiphiles were synthesized to reveal the relation-
ship between molecular structure and self-assembly properties.
Meanwhile intermolecular forces that contributed to the
formation of one-dimensional double helix were suggested.
Morphological modulation of the double helix was realized by
external stimuli including pH, light and surfactant addition.
49 mmol) in 50 ml methanol and 0.01 ml water at 70 C. The
reaction was finished within 24 h. After cooling, the product was
precipitated from methanol solution. The product was further
recrystallized from methanol for three times. The yield was
higher than 90%. 1H NMR (400 MHz, CDCl3): 0.95 (t, 3H), 1.39
(m, 2H), 1.64 (m, 2H), 2.40 (d, 3H), 2.66 (m, 6H), 3.63 (m, 3H),
3.78 (m, 2H), 3.89 (m, 2H), 4.12 (m, 2H), 7.08 (d, 2H), 7.31
(d, 2H), 7.77 (d, 2H), 7.88 (d, 2H); elemental analysis calcd (%)
for C26H39N3O7: C 61.76, N 8.31, H 7.77; found: C 61.59, N 8.28,
H 7.77.
Cryo-TEM image
A small drop of sample was placed on a 400 mesh copper grid,
and a thin film was produced by blotting off the redundant liquid
with filter paper. This thin film was then quickly dipped into
liquid ethane, which was cooled by liquid nitrogen. Observation
Experimental section
Materials
ꢀ
of the cryo-sample was carried out at ꢁ183 C.
Sodium dodecylbenzene sulfonate, sodium dodecylbenzene
sulfonate and other surfactants were bought from Acros
Organics Co. The other reagents are of analytical purity. All the
reagents and solvent were used as received.
Negative-staining TEM
TEM micrographs were obtained with a JEM-100CXII trans-
mission electron microscope (working voltage of 80–100 kV) by
the negative-staining method with uranyl acetate solution (1%)
as the staining agent. One drop of the solution was placed onto
a carbon Formvar-coated copper grid (230 mesh). Filter paper
was employed to suck away the excess liquid. Then one drop of
the staining agent was placed onto the copper grid. The excess
liquid was also sucked away by filter paper.
Amphiphile synthesis
The amphiphiles C10G, C12G and C14G were synthesized
according to the literature.16 The synthesis of amphiphile C4AG
is given as below. The other sugar-based amphiphiles are
synthesized in a similar way.
(1) 4-Butyl-40-hydroxyl azobenzene: 14.9 g 4-butylaniline was
dissolved in 200 mL water and 25 mL concentrated hydrochloric
acid. The solution was cooled to 5 ꢀC in an ice bath and reacted
with 15 mL aqueous sodium nitrite (6.67 M) at 5 ꢀC for 1 h. The
resulting diazonium solution was then added to a solution con-
taining 9.4 g phenol, 4 g sodium ꢀhydroxide, 10 g of sodium
carbonate, and 100 mL water at 0 C for 2 h. The product was
collected by filtration, dried in vacuum, and purified by recrys-
UV-vis absorbance
UV-vis absorbance measurements of solution were carried out
on the spectrophotometer (Cary 1E, Varian Australia PTY Ltd.)
equipped with a thermostated cell holder. The UV-vis measure-
ꢀ
ment was all carried out at 30 C.
1
tallization in hexane. The yield was 65%. H NMR (400 MHz,
Dynamic light scattering
CDCl3): 0.94 (t, 3H), 1.40 (m, 2H), 1.65 (m, 2H), 2.68 (t, 2H),
6.93 (d, 2H), 7.29 (d, 2H), 7.80 (d, 2H), 7.87 (d, 2H). elemental
analysis calcd (%) for C16H18N2O: C 75.56, H 7.13, N 11.01;
found: C 75.55, H 7.30, N 11.08.
To prepare dust-free solutions for light scattering measurements,
the solutions were filtered through a 0.20 mm membrane filter of
hydrophilic PVDF into light scattering cells before the
measurements. The light scattering cells had been rinsed with
distilled acetone to ensure a dust-free condition before use. DLS
was performed with a spectrometer (ALV-5000/E/WIN Multiple
Tau Digital Correlator) and a Spectra-Physics 2017 200 mW Ar
laser (514.5 nm wavelength). The scattering angle was 90ꢀ, and
the intensity autocorrelation functions were analyzed by using
the methods of Contin.
(2) 4-Butyl-40-(oxy-2,3-epoxypropyl) azobenzene:20 4-butyl-40-
hydroxyl azobenzene (11.31 g, 50.0 mmol) was dissolved in
100 ml of 90% ethanol and sodium hydroxide (2.06 g, 50.0 mmol).
Epichlorohydrin (9.34 g, 100 mmol) was slowly added dropwise
into the solution at 60 ꢀC. After the mixture refluxed for 2 h, the
solvent was removed under reduced pressure. The residue was
dissolved in 100 ml of chloroform and sodium chloride was
removed by filtration. The filtrate was dried under vacuum and
the product was purified by column chromatography using 2%
(v/v) ethyl acetate–chloroform as the eluent. The yield was 70%.
1H NMR (400 MHz, CDCl3): 0.95 (t, 3H), 1.38 (m, 2H), 1.63
(m, 2H), 2.68 (t, 2H), 2.80 (dd, H), 2.94 (dd, H), 3.41 (m, H), 4.02
(dd, H), 4.31 (dd, H), 7.02 (d, 2H), 7.30 (d, 2H), 7.83 (d, 2H), 7.91
(d, 2H); elemental analysis calcd (%) for C19H22N2O2: C 73.52, H
7.14, N 9.03; found: C 73.72, H 7.17, N 9.01.
Photoisomeric experiment
For light-triggered trans/cis transition, solution samples were
irradiated with 365 nm UV light from a Spectroline FC-100F
fan-cooled, long wave UV lamp. The power of the mercury arc
lamp is 100 W. Samples were placed in a quartz tube, and irra-
diation was done for a specific duration. For cis/trans transition,
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irradiation by visible light was performed using a 200 W incan-
descent light bulb (> 440 nm).
When elevated to 75 ꢀC, C4AG can be soluble in aqueous
solution. After slowly cooled to room temperature, this solution
became bluish and viscous. As the sample concentration was
increased to a threshold value, elastic hydrogel can be obtained.
This hydrogel can be characterized by up-side-down test (Fig. 1a)
and dynamic rheological measurement. From Fig. 1b, it can be
seen that the storage modulus (G0) can reach to 103 Pa, which was
remarkably larger than that of loss modulus (G00). The micro-
structures formed in C4AG solution was characterized by
cryo-TEM and negative-staining TEM. Large amount of one-
dimensional nanofibers were observed in cryo-TEM image,
which can be as long as several micrometres (Fig. S1, ESI†). The
entanglement of nanofibers was believed to be responsible for
solution viscosity enhancement and hydrogel formation. The
enlarged cryo-TEM image in Fig. 2a illustrated the existence of
double helices with 12–16 nm in width and approximate 25 nm in
pitch. Negative-staining TEM also provided evidence of double
helix formation (Fig. 2b and 2c).
Results and discussion
Following our interest in the self-assembled nanohelix, we have
synthesized a sugar-based amphiphile, denoted as C4AG. The
details of synthetic process were described in the Experimental
Section. The novel amphiphile consisted of three parts: azo-
benzene group, sugar moiety and butyl tail (Chart 1). The
hydrophilic sugar headgroup is known to improve the molecular
solubility and also generate multiple intermolecular hydrogen
bonds. Azobenzene group was chosen because of its planar
aromatic structure which may direct one-dimensional molecular
packing. Meanwhile, the incorporation of azobenzene is antici-
pated to impart light-activity to self-assembled systems. Addi-
tionally, terminal butyl chain is a good balance for hydrophobic
interaction and molecular flexibility. It is worthwhile that sugar–
lipids have recently become research focus owing to their
biocompatibility, low toxicity, etc. In this report, we have utilized
a ring-opening reactions of epoxides with N-methylglucamine to
give high yield product.16
To investigate helicity of self-assemblies at molecular level,
circular dichroism spectroscopy was performed. As Fig. 3a
shows, the double helix solution exhibited strong CD signal with
a negative Cotton effect (ꢂ 340 nm) followed by a positive
Cotton effect (ꢂ 290 nm), indicating that dipole moments
orientate in an anticlockwise in the aggregates.17 This micro-
scopic helicity was reflected in the mesoscopic helicity observable
under TEM. The intense CD signal revealed strong interaction
between azobenzene rings. In a control experiment, no notable
CD signal in methanol solution was found, in which the
amphiphile will not aggregate (Fig. 3a). It is therefore believed
that dichroic signals should not be attributed to molecular
chirality but to the supramolecular chirality, which originated
from the chiral packing of amphiphiles inside self-assembled
aggregates.
Chart 1 Molecular structure of novel sugar–lipid amphiphile C4AG
(blue part represents hydrophobic group and the red represents hydro-
philic group).
The stability of self-assembled double helix was also studied
with respect to dilution, heating, and additives (i.e. urea and
organic solvent). First, it is found that double helical nanofibers
can be observed even when the sample was diluted to low
concentrations (Fig. 4). The CD result (not shown here) shows
that a Cotton effect can be intense at low concentration of 10ꢁ4
mol Lꢁ1, indicating a notable stability of molecular architectures.
Second, it is demonstrated that helical nanostructures can exist at
the temperature of 50 ꢀC (Fig. S2, ESI†). At higher temperatures,
the helical nanostructures can be well-dispersed which gives a less
bluish and viscous solution. At lower temperature, helical
nanofibers tend to aggregate leading to strongly turbid solution
Fig. 1 (a) Macroscopic appearance of self-assembled hydrogel at 20 mM
C4AG. (b) Frequency sweep of elastic hydrogel with 20 mM C4AG.
Fig. 2 Double-stranded helix in aqueous solution: (a) cryo-TEM and
(b) negative-staining TEM image. (c) Enlarged picture of red line zone in
Fig. 2b, which shows left-handed helicity of double helix. The black dot in
Fig. 2a is due to the formation of ice crystal during vitrification process.
Scale bar in Fig. 2c represents 50 nm.
Fig. 3 (a) CD spectra of C4AG solution in water (light grey) and in
methanol (dark grey). (b) CD spectra of C4AG solution in water: in the
presence of urea (light grey) and absence of urea (black).
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amphiphiles without azobenzene groups (Chart 2a). Helical
nanofibers can not be observed in these systems when the azo-
benzene group is replaced by a saturated aliphatic chain. It is
therefore suggested that p–p stacking of azobenzene groups was
indispensable for the formation of one-dimensional helix.
Second, when the sugar head was replaced by other hydrophilic
group (i. e. quarter-amino, carboxyl, or glycol), the amphiphilies
would self-organize into global micelles or vesicles but not one-
dimensional architectures (Chart 2b). This is because sugar
group can generate multiple site hydrogen-bonds, which can
promote close packing of amphiphiles and simultaneously guild
the orientation of molecules within aggregates. The existence of
hydrogen-bonding interactions is demonstrated by FT-IR
(Fig. S3, ESI†). Finally, we have demonstrated that butyl chain
in C4AG amphiphile was essential for the 1 D nanostructure.
Herein we synthesized series of sugar-based amphiphiles with
azobenzene moieties (denoted as C0AG, C2AG, C4AG, and
C6AG), in which the hydrocarbon chain was varied (Chart 3). It
is found that the amphiphiles with longer hydrocarbon chains
(i.e. C4AG and C6AG) can self-assemble into double helical
nanofibers (Fig. 5). However, the amphiphiles with shorter
hydrocarbon chains (i.e. C0AG and C2AG) could not aggregate
into well-ordered structures but only thick precipitates. It is
proposed that rigid molecules such as C0AG and C2AG tend to
closely pack into precipitates owing to p–p stacking. The exis-
tence of butyl or hexyl groups can interfere with close packing
between aromatic groups to avoid precipitate formation.
Fig. 4 Negative-staining TEM image of self-assembled double-stranded
helix in C4AG aqueous solution: (a) 0.1 mM and (b) 10 mM.
with low viscosity. Third, the effect of urea addition was also
examined. It is well known that urea can break hydrogen-bonds
in water which results in proteins being denatured or DNA
double chain melt.18 The self-assembled doubled helix in C4AG
solution seems to be inert to urea addition; even when the
concentration of urea reaches 5 M, double helical fibers can be
still observed. The circular dichroism spectrum gives evidence for
the existence of helical nanostructures in the presence of urea
(Fig. 3b). This implies that hydrogen bonds are not the exclusive
force driving double helix formation. Finally, it is found that the
double helix can survive in the presence of a small amount of
organic solvent such as methanol, ethanol, DMSO and DMF.
In summary, a one-dimensional double helix was fabricated
cooperatively by multiple weak interactions including the
hydrophobic effect, p–p stacking between azobenzene groups
Exploring the driving force for double helix: structure–
performance relationship
In this section, the relationship between molecular structure and
mesoscopic assemblies was discussed and the intermolecular
forces that governed the self-assembled double helix were sug-
gested. The C4AG amphiphile was composed of three main
parts: hydrophilic sugar, planar azobenzene moiety and hydro-
carbon tail. By varying molecular structures, we systematically
investigated the structure–performance relationship in a series of
compounds. First, the effect of the azobenzene group was
considered, which was believed to bring additional p–p stacking
to molecular self-assembly. In order to investigate the role of the
azobenzene group, we have synthesized three analogous
Chart 3 Sugar-based amphiphiles containing an azobenzene moiety
with different lengths of hydrocarbon chain, denoted as C0AG, C2AG,
C4AG and C6AG.
Chart 2 (a) Series of sugar-based amphiphiles without azobenzene
Fig. 5 Negative-staining TEM image of C6AG in an aqueous solution
group; (b) alkyl azobenzene derivatives without sugar groups.
(1 mM).
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ꢀ
trans-form to 5.5 A in cis-form. Likewise, trans-azobenzene has
no dipole moment while the dipole moment of the nonplanar
cis-compound is 3.0 D.19 As shown in Fig. 7, the C4AG molecule
can realize reversible trans/cis transitions triggered by UV or
visible light, leading to remarkable reduction of the CD signal
intensity of the C4AG solution (Fig. 8a). The DLS data clearly
indicated the existence of small particles with 3 nm radius, which
is comparable to the molecular length of C4AG (Fig. 8b). Hence
it is proposed that global micelle was formed in C4AG solution
after UV irradiation. The effect of conformational change in
azobenzene group may involve two aspects. On one hand, the
light-triggered cis-azobenzene can be more hydrophilic than
the trans-form owing to the enhancement of dipole moment. On
the other hand, the existence of cis-azobenzene may restrict close
packing of amphiphiles in the aggregates which is responsible for
CD signal decrease. These two factors ultimately gave birth to
the transition from helical nanofibers to global micelles.
Fig. 6 Representative scheme of double-stranded helix in aqueous
solution.
and hydrogen-bonding of sugar moieties. In particular, hydro-
carbon chains seem to be essential for supramolecular self-
assemblies. Combined with the TEM image, CD spectrum and
the above discussions, we have described a representative scheme
of double helix formation (Fig. 6). Driven by the hydrophobic
effect, p–p interaction and hydrogen bonding, C4AG molecules
can self-assemble into 1 D nanofibers which are analogues to
‘‘rodlike micelles’’. Meanwhile the chiral sugar will not pack
parallel but rather pack at a non-zero twist angle with respect to
their neighbors, leading the whole nanostructure to twist into
a helix. On the other hand, hydrogen bonds arising from sugar
groups between two adjacent strands were thought to provide the
buckling force to join the two cylinders together.
Second, the amino atom in C4AG can be protonated with
addition of acid which imparted pH-sensitivity to C4AG self-
assemblies (Fig. 9). The pKa of C4AG in aqueous solution is 8.9.
It can be noted that the addition of acid can lead to the trans-
formation from helical nanofibers to small micelles, accompa-
nied by the disappearance of Cotton effect (Fig. S4 and S5,
ESI†). It is rationalized that the protonation of amino group can
greatly enhance molecular hydrophilicity and also brings
electrostatic repulsion between amphiphiles, which are not
conducive to higher-ordered self-assemblies.
Third, as we have declared that, double-stranded helix was
held together by attractive interaction of hydrogen bond. It is
hence reasonable that when the repulsive effect was introduced
into the double strands, people can unfold the double helix in
controllable fashion just as the DNA chains melt. Herein, we
have actually succeeded by incorporating ionic surfactant into
a double helix. As Fig. 10a shows, fragmentized unfolded
Morphological modulation of double helix by external
stimuli
As demonstrated above, the supramolecular double helix was
held together by relatively weak non-covalent interactions, which
implied that helical nanostructures might be easily reconfigurable
into a variety of morphologies. In this section, we have modu-
lated the self-assembled organizations by external stimuli
including pH, light irradiation and surfactant addition.
First, the incorporation of an azobenzene moiety can endow
light-activity to the double helix. Azobenzene can undergo
photo-induced isomerism accompanied by large structural
change as reflected in the dipole moment and change in geom-
etry. The isomerization involves a decrease in the distance
ꢀ
between para carbon atoms in azobenzene from about 9.0 A in
Fig. 8 (a) CD spectrum of C4AG molecule in aqueous solution before
and after UV irradiation; (b) dynamic light scattering of C4AG solution
after UV irradiation, which indicates the existence of small micelles.
Fig. 7 (a) UV-vis of C4AG solution before and after UV irradiation;
(b) repeated UV-vis absorbance of C4AG solution, which illustrated the
reversibility of photo-triggered trans/cis transition.
Fig. 9 Structural change of C4AG molecular with addition of acid or base.
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nanofibers can be clearly observed with the addition of sodium
dodecyl sulfonate. This can be rationalized that ionic surfactant
can penetrate into helical aggregate owing to hydrophobic effect
and impart electrostatic repulsion to the adjacent helix which can
result into the unfolding of the double helix. Similar results were
also found by using other ionic surfactants. Further addition of
ionic surfactants can result into the dissociation of nanofibers. In
addition, the double nanohelix can be shaped into global vesicles
with the addition of sodium dodecylbenzene sulfonate (SDBS)
(Fig. 10b). The vesicles exhibit uniform diameter of 40–50 nm. It
is proposed that aromatic group in sodium dodecylbenzene
sulfonate may contribute to vesicle formation.
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Conclusions
In conclusion, a hierarchical self-assembled double helix was
fabricated by a novel amphiphile of glucose-based lipid. The
driving forces for the self-assembled architectures are proposed
to be multiple weak interactions including hydrophobic inter-
action, aromatic stacking and hydrogen bond. In addition,
morphological modulation of supramolecular double helix can
be rationally realized by external stimuli, such as pH, light, and
surfactant addition. Triggered by external inputs, double-strand
helix can be shaped into spherical micelle or vesicle. Meanwhile
we have for the first time realized unfolding double-stranded
helix into single-stranded nanofibers by introducing repulsive
effect into the aggregates. We hope our work can help to
understand helical structures in life (i.e. DNA, protein b-sheet,
etc.) and also the self-assembled complex architectures in nature.
In addition, the supramolecular self-assembled double helix is
anticipated to be exploited to mimic DNA biomineralization to
direct inorganic double-stranded helices synthesis.
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Acknowledgements
This work was supported by National Natural Science Foun-
dation of China (20873001, 20633010 and 50821061) and
National Basic Research Program of China (Grant No.
2007CB936201).
€
€
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2036 | Soft Matter, 2010, 6, 2031–2036
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