Handedness inversion of chiral amphiphilic molecular assemblies evidenced by supramolecular chiral imprinting in mesoporous silica assemblies

Article abstract of DOI:10.1002/chem.201102146

Antipodal twisted helical ribbons with lamellar bilayer structure were obtained by self-assembly of chiral amphiphilic molecules in water and water/ethanol. The handedness inversion of the molecular arrangement in these antipodal helical ribbons was inves

Full text of DOI:10.1002/chem.201102146

FULL PAPER
DOI: 10.1002/chem.201102146
Handedness Inversion of Chiral Amphiphilic Molecular Assemblies
Evidenced by Supramolecular Chiral Imprinting in Mesoporous Silica
Assemblies
Junjie Xie, Huibin Qiu, and Shunai Che*[a]
Abstract: Antipodal twisted helical rib-
bons with lamellar bilayer structure
were obtained by self-assembly of
chiral amphiphilic molecules in water
and water/ethanol. The handedness in-
version of the molecular arrangement
in these antipodal helical ribbons was
investigated by using chiroptical spec-
troscopy and molecular probes in their
antipodal mesoporous silica assemblies
synthesized through pairing interaction
between the head group of the chiral
amphiphilic molecules and a co-struc-
ture-directing agent. The supramolec-
ular chirality is imprinted in the pore
surface through the organic group of
the co-structure-directing agent. The
mirror-image diffuse-reflectance circu-
lar dichroism spectra of the conjugated
discotic probing molecule introduced
into their supramolecular chiral im-
printed mesoporous silica demonstrat-
ed the origin of inverse chirality from
the antipodal helical stacking of the
molecules.
Keywords: chirality · imprinting ·
mesoporous materials · sol–gel pro-
cesses · supramolecular chemistry
Introduction
We have now succeeded in demonstrating molecular
stacking in antipodal helical molecular assemblies through
their silica mineralization. Left- and right-handed organic
helical ribbons were obtained by cooling solutions of
sodium d-12-hydroxystearate (d-HS-Na) in pure water and
ethanol/water, respectively. To collect information on the in-
ternal structure, especially the packing mode of the mole-
cules, the rigid mesoporous silica assemblies were prepared
on the basis of cooperative self-assembly of d-HS-Na and
silica precursors. Our conceptual method was to build pair-
ing electrostatic interactions between the anionic head
group of d-HS-Na and a cationic co-structure directing
agent (CSDA), namely, N-trimethoxysilylpropyl-N,N,N-tri-
methylammonium chloride (TMAPS).[11] The silane side of
TMAPS is co-condensed with another silica source, such as
tetraethoxysilane (TEOS), to form the silica wall, and finally
the silica mesostructure can be formed. Due to the pairing
effect between TMAPS and d-HS-Na, the chirality of the
d-HS-Na packing mode was accurately memorized by the
helical arrangement of quaternary ammonium groups on the
mesoporous wall, which is regarded as supramolecular chiral
imprinting after extensive extraction.[12] Chiral arrangements
of conjugated probe molecule introduced into mesopores
can be induced by supramolecular chirality imprinted in
mesoporous silica through electrostatic interaction, which
can be readily estimated by chiroptical spectroscopy (see
Supporting Information, Figure S1).
Chirality exists widely in nature and is expressed hierarchi-
cally in many materials. Generally, the chirality of a supra-
molecular entity is controlled specifically by the chirality of
its molecular building blocks.[1]
Nevertheless, the chiral sense towards formation of helical
structures changes with chemical or physical stimulations.
For instance, right-handed B-DNA converts to the left-
handed Z form at high salt conditions.[2] Besides, a variety
of spontaneous helical superstructures, such as chiral poly-
mers, foldamers, helical liquid crystals, and amphiphile self-
assemblies adopt inverse bistable chiral senses according to
the solvent, temperature, and light.[3,4,5,6] Self-assemblies of
d-12-hydroxystearic acid
ACHTUNGTRENNUNG(d-HSA) and its alkali metal salts show opposite chiral
senses, which can be switched by a series of n-aliphatic alco-
hols.[7] On the other hand, the handedness of silica replicas
of chiral amphiphilic molecular assemblies occasionally
varied with the preparation conditions.[8] Although
handednessACHTUNGTRENNUNGinversion phenomena have been intensively in-
vestigated and several investigations were performed on the
origin of handedness inversion, very limited evidence was
obtained for the origin at the molecular level.[6b,9,10]
[a] J. Xie, H. Qiu, Prof. S. Che
School of Chemistry and Chemical Engineering
State Key Laboratory of Metal Matrix Composites
Key Laboratory for Thin Film and
Microfabrication Technology of the Ministry of Education
800 Dongchuan Road, Shanghai, 200240 (P.R. China)
Fax : (+86)21-5474-5365
Results and Discussion
Antipodal assembly of d-HS-Na: Organic lipids were pre-
pared and their morphology and structure were character-
ized, in order to provide evidence for the templating effect
E-mail: chesa@sjtu.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102146.
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of the amphiphilic molecules in their silica replicas. Samples
were synthesized from d-HS-Na (Figure 1A) in pure water
and in ethanol/water (1/4, v/v) with addition of equivalent
NaOH. The solutions were cooled from 353 K to room tem-
perature (ca. 293 K), and white organic gels were formed,
which were separated by centrifugation and freeze-dried.
Figure 2. XRD pattern of samples shown in Figure 1a (black line) and b
(gray line).
Figure 3. DRCD and DRUV spectra of samples shown in Figure 1a
(black line) and b (gray line).
Figure 1. Molecular structure of d-HS-Na (A), SEM images (B), and
TEM images (C) of the d-HS-Na assemblies formed in pure water (a)
and ethanol/water solutions (b).
Corresponding antipodal mesoporous silica assemblies: The
corresponding helical silica assemblies were prepared by a
sol–gel process,[13–15] which was carried out by adding
TMAPS and TEOS to the above cooled lipid solutions. The
mixture was stirred for 5 min and then the reaction was al-
lowed continued at room temperature under static condi-
tions for 2 d, and the reaction mixture subsequently aged at
353 K for 1 d. White powders were obtained by centrifuga-
tion and dried. To obtain chiral supramolecular imprinted
mesoporous helical silica functionalized with quaternary am-
monium groups, the as-made samples were extracted by
heating to reflux in 10% ethanolic HCl solution for 1 d.
meso-Tetrakis(4-sulfonatophenyl)porphyrin (TSPP), a conju-
gated guest molecular probe, was loaded into the extracted
helical mesoporous silica ribbons as described previously.[12]
Figure 4 shows the SEM and TEM images of the as-made
mesoporous silicas. The sample obtained from the left-
handed twisted organic gel was consisted of exclusively left-
handed coiled ribbons with adhering double layers with the
same thickness of about 40 nm (Figure 4a1; see also Sup-
porting Information, Figure S4). Interestingly, with well-
maintained handedness, the original twisted character of the
organic aggregates was converted to loosely coiled helical
ribbons with larger width of about 450 nm (Figure 4a1).
Figure 1B and C show SEM and TEM images of these
samples, which are composed uniformly of single left- (a)
and right-handed (b) twisted ribbons with width of about
250 nm, thickness of about 40 nm, and pitch length of about
2.0 mm (for the purity, see Figure S2 in the Supporting Infor-
mation).
Small-angle XRD patterns revealed a set of evenly spaced
peaks in the region of 2q=1–88 with a d spacing of 4.76 nm
(Figure 2), indicating a typical periodic lamellar structure of
the d-HS-Na bilayers. As shown in Figure 3, the left-handed
twisted assembly formed without addition of ethanol exhib-
ited a negative Cotton effect in the region below 250 nm,
while the right-handed product obtained in ethanolic/aque-
ous solution showed a mirror-image diffuse-reflectance cir-
cular dichroism (DRCD) spectrum. The CD spectra of
monomeric species in solution were silent in the whole
region detected (see Supporting Information, Figure S3),
probably because the carboxylate group of d-HS-Na is not
directly connected with the chiral carbon center through a
covalent bond. Therefore, these CD signals are assigned to
the chiral or helical arrays of carboxylate groups on the anti-
podal helical surface of chiral assemblies.
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Handedness Inversion of Chiral Molecular Assemblies
FULL PAPER
images (Figure 4b2 and b3) confirmed the existence of less
ordered mesoporous channels in the silica ribbon wall.
Nitrogen adsorption/desorption isotherms of the extracted
left- and right-handed mesoporous silica ribbons showed
similar type IV curves, with similar average pore diameters
of about 3.7 nm, BET surface areas of 289 and 276 m2 gÀ1,
and pore volume of 713 and 599 cm3 gÀ1, respectively
(Figure 5). The chiral amphiphile d-HS-Na was completely
Figure 5. N2 adsorption/desorption isotherms (left) and pore size distribu-
*
*
tions (right) of extracted samples shown in Figure 4a ( ) and b ( ).
removed by extensive extraction with an HCl/EtOH solu-
tion, and the quaternary ammonium groups rested on the
silica wall, as shown by 13C CP/MAS NMR spectra (see Sup-
porting Information, Figure S6).
As shown in Figure 6, the as-made and extracted helical
silica assemblies revealed comparable DRCD spectra, which
appeared to be mirror images for the left- and right-handed
samples. The left-handed samples revealed a strong negative
Cotton effect in the region below 230 nm, while the right-
handed samples show a strong positive Cotton effect, which
Figure 4. SEM (a1 and b1) and TEM images (a2 and b2) of the as-made
mesoporous silicas derived from the left-and right-handed organic assem-
blies in Figure 1 and corresponding TEM images of the cross sections (a3
and b3).
Such morphological transformation between twisted and
coiled helical ribbons is found widely in chiral assemblies[16]
and in this case would be induced by the addition of silica
precursors.[17] TEM images (Figure 4a2) revealed that the
inner ordered mesoporous channels are oriented parallel to
the rim of the helical ribbon. Meanwhile, high-resolution
TEM images of the cross-section (Figure 4a3) showed that
the mesoporous channels are unambiguously stacked in a
two-dimensional (2D) hexagonal mesostructure with a unit-
cell parameter of about 7.5 nm, which was confirmed by
XRD analysis (see Supporting Information, Figure S5). This
result indicates that the lipid lamellar structure was trans-
formed into 2D hexagonal mesostructure during silica min-
eralization while maintaining the handedness.
On the other hand, the sol–gel process performed on the
right-handed d-HS-Na ribbons with addition of ethanol
completely gave rise to right-handed twisted silica ribbons
(Figure 4 b1; see also Figure S4 in the Supporting Informa-
tion), which consisted of double sheets with the same thick-
ness of about 40 nm and a width of about 400 nm. TEM
Figure 6. DRCD and DRUV spectra of the as-made (c) and extracted
(g) left-handed (black lines) and right-handed (gray lines) helical
mesoporous silica assemblies.
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S. Che et al.
may be interpreted in terms of the supramolecular helical
stacking of d-HS-Na and the helical silica frameworks. Nev-
ertheless, it is difficulty to resolve the packing modes of
these chiral assemblies.
Supramolecular chiral imprinting: During the CSDA-pro-
moted sol–gel process, the primary supramolecular structure
of the rodlike micelles can be precisely memorized by the
array of quaternary ammonium groups of TMAPS as an im-
printing due to the pairing effect of electrostatic interac-
tion.[11] This feature provides access to studying the molecu-
lar stacking of d-HS-Na in the rodlike micelles and further
inspires a deep insight to the bilayer structure. To detect
these imprintings, conjugated discotic molecules (e.g.,
TSPP) were introduced into the extracted helical mesopo-
rous silica ribbons. Similar to what was observed in chiral
mesoporous silica–TSPP complexes, the left- and right-
handed mesoporous silica ribbon–TSPP complexes revealed
a pair of mirror-image DRCD spectra with a strong exiton
couplet in the Soret band of TSPP and four weak Cotton ef-
fects corresponding to the Q bands (Figure 7), which indi-
cates that TSPP was inversely helically stacked in the meso-
porous channels due to helical
Figure 7. DRCD and DRUV spectra of TSPP loaded into the extracted
left- (black lines) and right-handed (gray lines) helical mesoporous silica
assemblies.
creased head surface area of d-HS-Na induced by the ad-
sorption and condensation of silica precursors on both surfa-
ces of the organic lipid forces lamellar bilayers to adopt a
rodlike micellar structure with higher curvature.[17] From the
characterization data of the left-handed ribbon, it could be
inferred that the twisted lipid ribbons orderly accumulated
imprinting on the pore walls.
Consequently, the rodlike mi-
cellar stacks of d-HS-Na de-
rived from the lamellar struc-
ture is thought to be in antipo-
dal helical conformations in
the left- and right-handed silica
materials.
Evolution of molecular stack-
ing during phase deformation
from lamellar bilayers to rod-
like micelles: As described
above, the left- and right-
handed mesoporous silica rib-
bons replicated the antipodal
helical d-HS-Na lipid assem-
blies, while the initial lamellar
bilayers were transformed into
rodlike micelles with helical
profile and well-preserved
handedness. It can be deduced
from the twisted ribbonlike
morphology and the lamellar
bilayer structure that the origi-
nal organic gel is constructed
by screwing the single slice of
d-HS-Na assemblies layer by
layer along the central axis of
the helix, which is left-handed
Scheme 1. Illustration of chiral transcription from lamellar bilayers to rodlike micelles through phase deforma-
tion. a1) and b1) Lamellar bilayers of left- and right-handed d-HS-Na helical ribbons. a2) and b2) Phase evolu-
tion from lamellar bilayers to rodlike micelles in the sol–gel process. a3) and b3) Helical rodlike micelles of
d-HS-Na formed after condensation of silicates. a4) and b4) Helical arrangement of the quaternary ammonium
groups remaining on the surface of mesopore after extraction.
in water and becomes antipo-
dal in the presence of ethanol
(Scheme 1a1 and b1). During
the sol–gel process, the in-
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Handedness Inversion of Chiral Molecular Assemblies
FULL PAPER
The white powder was separated with a centrifuge and dried in air at
313 K.
multiple bilayers (approximately eight bilayers, calculated
by the thickness of the ribbons and d spacing of its lamellar
structure) were reassembled to 2D hexagonal columnar
mesostructure with two layers. To minimize the overall
energy and satisfy the dynamics, helical rodlike micelles are
progressively formed with increasing crossing angles of
neighboring molecules which retain the original chiral sense.
Such phase deformation occurs discretely in well-bounded
regions, for example, in lines along with the helical ribbon,
as shown in Scheme 1a2 and b2, which favors the formation
of ordered rodlike mesoporous channels in the silica repli-
cas. Consequently, the helical molecular stacking becomes
distinct in the rodlike micelles after phase deformation
(Scheme 1a3 and 1b3) and can be estimated through its im-
printing (Scheme 1a4 and b4). Meanwhile, eight bilayers
were separated into two adhering sheets with hexagonal or
disordered structure, the reason for which is not clear. The
formation of micelles and their arrangement would be dis-
torted by ethanol and result in the mesophase transforma-
tion from right-handed lamellar structure to disordered
mesostructure. Further investigation is in progress on the
stimulating effects of ethanol on the inverse helical molecu-
lar stacking of d-HS-Na and the control of mesostructure or-
deredness during the sol–gel process.
Loading TSPP into the extracted mesoporous silica: Typically, TSPP
(5 mg) was dissolved in ion-exchanged water (5 mL) and the pH value
was adjusted to about 7.40 by addition of a certain amount of 0.1m
NaOH aqueous solution. The extracted mesoporous silica powder
(50 mg) was then dispersed in the above solution with stirring in 30 min
at room temperature. The red powder was separated by centrifugation
and dried in air at 313 K.
Characterization: XRD patterns were recorded by using a Rigaku D/
Max 2000 powder diffractometer equipped with CuKa radiation. The mor-
phologies of all samples were observed by using a JEOL JSM-7401F mi-
croscope at 1.0 kV. TEM observation was performed by using a JEOL
JEM-2100 microscope operated at 200 kV. UV and DRUV spectra were
taken by using
a Shimadzu UV-2450 spectropolarimeter fitted with
DRUV apparatus. CD and DRCD spectra were taken by using a JASCO
J-815 spectropolarimeter fitted with DRCD apparatus. The N2 adsorp-
tion/desorption isotherms were obtained at 77 K by using a Quantach-
rome NOVA 4200E surface area and pore-size analyzer. Solid-state 13C
CP/MAS NMR spectra were collected by using an Oxford AS400 NMR
spectrometer at 100 MHz and a sample spinning frequency of 3 kHz.
Acknowledgements
This work was supported by the National Natural Science Foundation of
China (grant no. 20890121) and the 973 project (2009CB930403).
Conclusion
[1] a) J. R. Schnur, Science 1993, 262, 1669; b) J. H. Fuhrhop, W. Hel-
frich, Chem. Rev. 1993, 93, 1565; c) F. J. M. Hoeben, P. Jonkheijm,
E. W. Meijer, A. P. H. J. Schenning, Chem. Rev. 2005, 105, 1491;
d) T. Shimizu, M. Masuda, H, Minamikawa, Chem. Rev. 2005, 105,
1401.
[2] F. M. Pohl, T. M. Jovin, J. Mol. Biol. 1972, 67, 375.
[3] a) S. Sakurai, K. Okoshi, J. Kumaki, E. Yashima, J. Am. Chem. Soc.
2006, 128, 5650; b) K. Maeda, H. Mochizuki, M. Watanabe, E. Ya-
shima, J. Am. Chem. Soc. 2006, 128, 7639; c) E. Yashima, K. Maeda,
Y. Furusho, Acc. Chem. Res. 2008, 41, 1166; d) T. Fukushima, K.
Tsuchihara, Macromolecules 2009, 42, 5453.
The handedness inversion of d-HS-Na helical ribbons and
their mesoporous silica replicas has been investigated in
depth by evolving the supramolecular chiral imprinting tech-
nology. The utilization of CSDA enables a precise study on
the molecular stacking of helical lamellar bilayers by ampli-
fying, immobilizing, and developing the original chirality.
The methodology developed in this work is applicable to a
variety of chiral assemblies, for both fundamental investiga-
tions and applications.[18]
[4] N. Delsuc, T. Kawanami, J. Lefeuvre, A. Shundo, H. Ihara, M. Taka-
fuji, I. Huc, ChemPhysChem 2008, 9, 1882.
[5] a) M. Muto, H. Suzuki, S. K. Lee, S. Kang, M. Tokita, J. Watanabe,
J. Phys. Chem. B 2008, 112, 15521; b) J. Barberꢁ, L. Giorgini, F.
Paris, E. Salatelli, R. M. Tejedor, L. Angiolini, Chem. Eur. J. 2008,
14, 11209.
Experimental Section
[6] a) J. J. D. de Jong, L. N. Lucas, R. M. Kellog, J. van Esch and B. L.
Feringa, Science 2004, 304, 278; b) Y. Huang, J. Hu, W. Kuang, Z.
Wei, C. F. J. Faul, Chem. Commun. 2011, 47, 5554.
Materials: d-HSA and TEOS were purchased from TCI, and TMAPS
(50% in methanol) from Azmax. Ethanol and NaOH were purchased
from Shanghai Chemical Company. All chemicals were used without fur-
ther purification.
[7] a) T. Tachibana, H. Kambara, J. Am. Chem. Soc. 1965, 87, 3015;
b) T. Tachibana, H. Kambara, Bull. Chem. Soc. Jpn. 1969, 42, 3422;
c) T. Tachibana, H. Takeno, Bull. Chem. Soc. Jpn. 1970, 43, 2418.
[8] a) Y. Chen, Y. Guo, H. Zhao, L. Bi, X. Pei, B. Li, Y. Yang, Nano-
technology 2008, 19, 355603; b) Y. Li, H. Wang, L. Wang, F. Zhou,
Y. Chen, B. Li, Y. Yang, Nanotechnology 2011, 22,135605.
[9] K. Murata, M. Aoki, T. Suzuki, T. Harada, H. Kawabata, T. Komori,
F. Ohseto, K. Ueda, S. Shinkai, J. Am. Chem. Soc. 1994, 116, 6664–
6676.
[10] P. Duan, Y. Li, L. Li, J. Deng, M. Liu, J. Phys. Chem. B 2011, 115,
3322.
[11] a) S. Che, A. E. Garcia-Bennett, T. Yokoi, K. Sakamoto, H. Kunie-
da, O. Terasaki, T. Tatsumi, Nat. Mater. 2003, 2, 801; b) S. Che, Z.
Liu, T. Ohsuna, K. Sakamoto, O. Terasaki, T. Tatsumi, Nature 2004,
429, 281.
Synthesis of organic lipids and mesoporous silica replicas: In a typical
synthesis, d-HSA (0.3 g, 1.0 mmol) and 1.0m NaOH (1.0 g) aqueous solu-
tion were added to a 100 mL glass beaker containing deionized water
(29.0 g) alone or with additional ethanol (6.6 g). The beaker was sealed
with PE cling wrap and kept at 353 K with stirring for 30 min for com-
pletely dissolve the mixture and then cooled to room temperature (ca.
293 K) in water, which led to formation of a white precipitate. For char-
acterization of organic assemblies, the precipitate was separated by cen-
trifugation and freeze-dried. The sol–gel process was carried out by
adding TMAPS (50% in MeOH, 0.26 g, 0.5 mmol) and TEOS (1.20 g,
5.8 mmol) to the above mixture with stirring for 5 min, left under static
conditions for 2 d, and then subjected to aging treatment at 353 K for
1 d. The product was obtained by centrifugation and freeze-dried. The
d-HS-Na molecules were removed by exhaustive solid–liquid extraction
overnight by heating to reflux in 10% ethanolic HCl solution for 1 d.
[12] H. Qiu, Y. Inoue, S. Che, Angew. Chem. 2009, 121, 3115; Angew.
Chem. Int. Ed. 2009, 48, 3069.
Chem. Eur. J. 2012, 18, 2559 – 2564
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2563

S. Che et al.
[13] a) Y. Ono, K. Nakashima, M. Sano, Y. Kanekiyo, K. Inoue, J. Hojo,
S. Shinkai, Chem. Commun. 1998, 1477; b) Y. Ono, Y. Kanekiyo, K.
Inoue, J. Hojo, S. Shinkai, Chem. Lett. 1999, 28, 1119; c) K. J. C. van
Bommel, A. Friggeri, S. Shinkai, Angew. Chem. 2003, 115, 1010;
Angew. Chem. Int. Ed. 2003, 42, 980.
[16] a) E. T. Pashuck and S. I. Stupp, J. Am. Chem. Soc. 2010, 132, 8819;
b) L. Ziserman, H.-Y. Lee, S. R. Raghavan, A. Mor, D. Danino, J.
Am. Chem. Soc. 2011, 133, 2511.
[17] H. Jin, H. Qiu, Y. Sakamoto, P. Shu, O. Terasaki, S. Che, Chem. Eur.
J. 2008, 14, 6413.
[14] A. M. Seddon, H. M. Patel, S. L. Burkett, S. Mann, Angew. Chem.
2002, 114, 3114; Angew. Chem. Int. Ed. 2002, 41, 2988.
[18] H. Goto, J. Mater. Chem. 2009, 19, 4914.
[15] a) Y. Yang, M. Suzuki, S. Owa, H. Shirai, K. Hanabusa, Chem.
Commun. 2005, 4462; b) Y. Yang, M. Suzuki, H. Fukui, H. Hirofusa,
K. Hanabusa, Chem.Mater. 2006, 18, 1324.
Received: July 13, 2011
Published online: January 20, 2012
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