Supramolecular hydrogels based on glycoamphiphiles: Effect of the disaccharide polar head

Article abstract of DOI:10.1021/cm301509v

Supramolecular hydrogelators based on amphiphilic glycolipids have been prepared by clicking different sugar polar heads to a hydrophobic linear chain by copper(I)-catalyzed azide-alkyne [3 + 2] cycloaddition. The influence of the sugar polar head on the gelation properties in water has been studied, and the liquid crystalline properties of the amphiphilic materials have also been characterized. Stable hydrogels at room temperature have been obtained and the fibrillar supramolecular structures formed by the self-assembly have been studied by different microscopic techniques on the dried gel (xerogel) and hydrated conditions in order to characterize the micro- and nanostructures. Self-assembly gives rise to supramolecular ribbons with a torsion that is related to a chiral supramolecular arrangement of amphiphiles. The formation of an opposite helical arrangement of the ribbons has been found to depend on the sugar polar head. This fact was confirmed by circular dichroism (CD).

Full text of DOI:10.1021/cm301509v

Article
pubs.acs.org/cm
Supramolecular Hydrogels Based on Glycoamphiphiles: Effect of the
Disaccharide Polar Head
María J. Clemente,† Pilar Romero,† Jose L. Serrano,§ Juliette Fitremann,*,‡ and Luis Oriol*,†
́
†Instituto de Ciencia de Materiales de Aragon
́
(ICMA), Universidad de Zaragoza-CSIC, Dpt. Química Organ
Ciencias, Pedro Cerbuna 12, 50009 Zaragoza, Spain
‡Laboratoire des IMRCP, UMR CNRS 5623, Bat
́
. 2r1, Universite Paul Sabatier, 118 route de Narbonne, F-31062 Toulouse Cedex 9,
́
ica, Facultad de
̂
France
§Instituto de Nanociencia de Aragon
50009 Zaragoza, Spain
́ ́
, Universidad de Zaragoza, Dpt. Química Organica, Facultad de Ciencias, Pedro Cerbuna 12,
S
* Supporting Information
ABSTRACT: Supramolecular hydrogelators based on amphiphilic
glycolipids have been prepared by clicking different sugar polar heads
to a hydrophobic linear chain by copper(I)-catalyzed azide−alkyne [3
+ 2] cycloaddition. The influence of the sugar polar head on the
gelation properties in water has been studied, and the liquid
crystalline properties of the amphiphilic materials have also been
characterized. Stable hydrogels at room temperature have been
obtained and the fibrillar supramolecular structures formed by the
self-assembly have been studied by different microscopic techniques
on the dried gel (xerogel) and hydrated conditions in order to
characterize the micro- and nanostructures. Self-assembly gives rise to supramolecular ribbons with a torsion that is related to a
chiral supramolecular arrangement of amphiphiles. The formation of an opposite helical arrangement of the ribbons has been
found to depend on the sugar polar head. This fact was confirmed by circular dichroism (CD).
KEYWORDS: supramolecular hydrogels, glycolipids, self-assembly, twisted ribbons, click chemistry
single-head amphiphiles8 and bolaamphiphiles9 were subse-
INTRODUCTION
■
quently described. These compounds were reported to have the
ability to gelify in a mixture of water and alcohol or, in some
cases, in water alone. Carbohydrates are hydrophilic building
blocks that are able to form multiple H-bonds due to the
presence of hydroxyl groups, which also favor solubilization in
water. Cyclic forms of carbohydrates provide more stable gels10
because they have directional hydroxyl groups that support
cooperative networks that have a self-assembled fibrous
structure. Stability and gel properties are strongly dependent
on the molecular structure of the gelator. The polar head of
glyco-hydrogelators can be based on monosaccharides11 and, to
a lesser extent, on disaccharides.12 The linker unit between
hydrophilic and hydrophobic parts also plays a relevant role in
the self-assembly. In this way, it has been reported that the
presence of amide groups or the incorporation of π−π stacked
rings also contribute to the cooperative interactions of glyco-
amphiphiles.1,8b,9b
Amphiphilic molecules with a sugar polar head and a fatty
hydrophobic chain can act as supramolecular hydrogelators.
Supramolecular hydrogels are based on low molecular weight
amphiphilic gelators that form a cross-linked network by self-
aggregation, and this three-dimensional (3D) structure can trap
water as solvent.1 Self-assembly in supramolecular gels2 occurs
through a combination of noncovalent interactions such as H-
bonding, π−π stacking, donor−acceptor interactions, solvo-
phobic forces, and van der Waals interactions. Taking into
account the reversibility of these interactions, supramolecular
gels are different from macromolecular gels because they can be
cycled between free-flowing liquids and nonflowing materials
by different stimuli, usually temperature, but depending on the
gelator structure, the reversibility can be triggered by other
stimuli like pH or irradiation.3
Supramolecular hydrogels are soft materials that have
possible technological applications, mainly as smart materials
or biomaterials. For instance, these substances have recently
been described as platforms for tissue engineering and as drug
delivery systems.4 Amphihilic hydrogels based on carbohydrates
have been reported as sensors5 and as a means for cell
encapsulation.6
Glycolipids, due to the polar asymmetry of their structure,
exhibit microsegregated regions and can consequently show
liquid crystal (LC) phases.13 Thermotropic LC phases were
Received: May 16, 2012
The first examples of glyco-amphiphiles as hydrogelators
Revised: September 17, 2012
were found in noncyclic glycosyl derivatives.7 Conventional
© XXXX American Chemical Society
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Figure 1. Chemical structure and nomenclature of the glycolipids.
first observed in alkyl glucopyranosides, and these compounds
are known to form lamellar smectic phases.14 Other
mesophases, such as cubic or columnar phases, have also
been reported for this sort of compound.15 Most of the
mesogenic glycolipids are based on monosaccharides,14,16 and
examples that bear a disaccharide headgroup remain relatively
rare.15,17
Scheme 1. Synthesis of Cell-Tz-C16 and Lact-Tz-C16
In a previous study, we obtained a thermotropic maltose-
based hydrogelator, Malt-Tz-C16 (see Figure 1), which contains
a palmitic fatty chain.18 This compound was prepared by
copper(I)-catalyzed azide−alkyne [3 + 2] cycloaddition of
maltosylazide and an aliphatic derivative. This click reaction19
provides a satisfactory synthetic pathway to link parts with
different polarity. The resulting triazole unit can afford a rigid
fragment that impairs the free rotation of the amphiphile tail
and favors the directional self-assembly in one dimension to
build fibers. Moreover, this ring gives additional π−π stacking,
and its dipole moment increases the hydrophilicity of the
amphiphile, thus aiding the gelation process more specifically in
water.1,20
To better understand how the structure affects gel properties,
in this work, we prepared two new hydrogelators based on a
disaccharide. In these compounds, the stereochemistry of the
sugar polar head is different to that in the maltose derivative
(Figure 1). Cellobiose was selected as the sugar polar head
because it has a β (1→4) connection between two glucoses
instead of the α (1→4) connection of maltose. In the case of
the lactose derivative, a galactose unit is located at the end of
the polar head instead of glucose. In 3D, these disaccharides
with different stereochemistries also adopt preferential
conformations21 that can induce different packing of the
corresponding low molecular mass amphiphiles.22 The differ-
ences in the liquid crystalline and gel-forming properties of
these compounds have been analyzed. Aggregation, self-
assembly, and the supramolecular gel structure were charac-
terized by nuclear magnetic resonance (NMR), scanning
electron microscopy (SEM), transmission electron microscopy
(TEM), cryo-TEM, environmental scanning electron micros-
copy (ESEM), atomic force microscopy (AFM), and circular
dichroism (CD).
cycloaddition using a disaccharide azide and N-propargylpalmi-
tamide.
The synthesis of the disaccharide azides was performed using
the corresponding peracetylated sugar as the starting material.
Peracetylated lactose (1) was synthesized using sodium acetate
and acetic anhydride, and peracetylated cellobiose was
purchased. Glycosyl azides (2, 3) were synthesized stereo-
selectively employing the general procedure described by
Paulsen23 (Scheme 1). Glycosyl azides can react through a 1,3-
RESULTS AND DISCUSSION
■
Synthesis of Materials. Glycoamphiphiles were synthe-
sized by click coupling of the disaccharide polar head and the
aliphatic chain, as shown in Scheme 1. The connecting group is
a triazole ring bearing a neighboring amide group. The triazole
ring was formed by a copper(I)-catalyzed azide−alkyne [3 + 2]
B
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Figure 2. (a) OAc-Cell-Tz-C16 and Cell-Tz-C16 chemical structure, (b) 1H NMR spectrum of OAc-Cell-Tz-C16 with CDCl3 as solvent at 25 °C, (c)
1H NMR spectrum of Cell-Tz-C16 with MeOD as solvent at 50 °C.
dipolar cycloaddition with N-propargylpalmitamide (4). The
click reaction was carried out in DMF using CuBr and N-
pentamethyldiethylenetriamine (PMDETA) to give the desired
product. All of the protected derivatives were deacetylated at
room temperature according to Zemplens conditions (MeONa
́
and Amberlyst IR120 in anhydrous MeOH) to give the final
product in almost quantitative yield.
The peracetylated precursors and the glycoamphiphiles were
fully characterized by 1H and 13C NMR, infrared (IR) and mass
1
spectrometry. The H NMR spectra of OAc-Cell-Tz-C16 and
Cell-Tz-C16 are shown as representative examples in Figure 2b
1
and c (see the Supporting Information, SI1, for the H NMR
spectra of analogs OAc-Lact-Tz-C16 and Lact-Tz-C16).
Bidimensional NMR experiments (COSY, TOCSY, NOESY,
HSQC, and HMBC) were performed to corroborate the
chemical structure of the glycolipids. It can be seen in Figure 3
that all of the sugar protons of OAc-Cell-Tz-C16 can be
assigned, and these assignments are supported, for example, by
TOCSY experiments. By means of correlations of a whole spin
system, protons from one cycle of the sugar can be
distinguished from the protons of the second cycle.
Figure 3. TOCSY spectrum of OAc-Cell-Tz-C16 with CDCl3 as
solvent at 25 °C and 60 ms of mixing time.
Liquid Crystalline Properties. Carbohydrate amphiphiles
have the ability to self-assemble and undergo microphase
segregation due to hydrophobic interactions of aliphatic chains
and the extensive hydrogen-bonding network formed by the
C
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polar carbohydrate heads, thus giving rise to mesomorphic
properties. The behavior of these compounds and the phase
transition temperatures are dependent on the nature of the
carbohydrate moiety, the length of the hydrophobic alkyl chain
and the type of linker between the two parts.
The mesomorphic properties of the synthesized amphiphilic
glycolipids and the peracetylated precursors were studied by
polarized light microscopy and differential scanning calorimetry
(DSC). Thermogravimetry of samples previously dried and
immediately analyzed showed that weight loss, due to a massive
thermal decomposition process, is observed at temperatures
above 275 °C (see the Supporting Information, SI2).
The peracetylated precursors were studied by polarized
optical microscopy (POM) as a function of temperature, and
mesomorphic behavior was not observed. OAc-Cell-Tz-C16
melts directly from a crystalline state to an isotropic liquid at
175 °C. Nevertheless, in the DSC study of OAc-Lact-Tz-C16,
crystallization was not observed on cooling the molten state
and a glassy material was obtained. DSC traces corresponding
to the second or subsequent scans only exhibit a glass transition
at 52 °C (see Table 1).
was observed for Cell-Tz-C16 and Lact-Tz-C16 although the
mesophase appeared at higher temperatures, around 160 and
150 °C, respectively. Textures were analogous to those
observed for Malt-Tz-C16. On heating samples up to 250 °C,
peaks corresponding to decomposition were observed at
around 170−175 °C, before isotropization.
Smectic A phase for Cell-Tz-C16 and Lact-Tz-C16 was
confirmed by X-ray diffraction (XRD). As an example, see the
Supporting Information SI5 for Cell-Tz-C16. The lamellar
spacing was measured close to 47 Å, which indicates an
interdigitated bilayer.
Gel Properties. The solubility and gelation ability of the
amphiphilic glycolipids were examined in different solvents by
dissolving 5 mg of compound in about 0.1−1 mL of the solvent
(i.e., 0.5−5 wt %). The results are summarized in Table 2.
Table 2. Solubility and Gelation Properties of Glycolipids in
a
Different Solvents, after Heating and Cooling to RT
solvent
hexane
Cell-Tz-C16
Lact-Tz-C16
Malt-Tz-C16
I
I
I
ethyl acetate
tetrahydrofuran
dichloromethane
acetone
I
I
I
I
I
S
I
Table 1. Thermal Transitions of the Synthesized Glycolipids
I
I
a
Determined by DSC (10 °C·min−1)
I
I
I
methanol
P
P
S
cmpd.
thermal transition (°C) [ΔH kJ/mol]
b
c
c
b
water
G
G
G
OAc-Cell-Tz-C16
OAc-Lact-Tz-C16
Cell-Tz-C16
Cr
g
175 [37.7]
52
I
I
b
dimethylsulfoxide
S
S
S
a
c
I = insoluble, P = precipitate, S = solution, G = gel. Results for Malt-
Tz-C16 included as a reference and data taken from ref 18. Gels are
formed at 0.5 wt %. Gels are formed at 1 wt %.
Cr
Cr
159 [1.9]
SA
SA
b
c
Lact-Tz-C16
147[1.5]
c
c
Malt-Tz-C16
Cr 31 [2.0] Cr′ 49 [6.2] SA
a
b
Results of Malt-Tz-C16 taken from ref 18. The heating scans were
c
carried out up to 200 °C. Data from the second heating scan. The
heating scans were carried out up to 165 °C to avoid decomposition.
Data from the second cycle scan. Decomposition was observed in the
third heating scan carried out up to 250 °C. Decomposition
temperatures are around 170−175 °C. Cr = crystal, I = isotropic
phase, SA = smectic A phase, g = glassy state.
Glycoamphiphiles are not soluble at room temperature (RT) in
the selected solvents except for DMSO. However, in some of
the selected solvents, the glycolipids eventually dissolved on
heating. The solution was then cooled to RT, and a solution, a
precipitate, or a gel was observed depending on the solvent.
Malt-Tz-C16 was studied previously, and it forms a gel in
water at a minimum concentration of 1 wt % in the absence of
other organic solvents.18 Changes in the sugar polar head to
cellobiose and lactose gives compounds Cell-Tz-C16 and Lact-
Tz-C16, and these also form gels in water (Figure 4). Maltose
and lactose derivatives both gel at a minimum concentration of
1 wt %, while the cellobiose derivative gels at a minimum
concentration of 0.5 wt %. To solubilize the glycolipids in
The final glycolipids Cell-Tz-C16 and Lact-Tz-C16, as with the
previously reported Malt-Tz-C16, exhibited birefringent textures
associated with thermotropic liquid crystalline behavior. The
poorly defined birefringent textures of the viscous mesophase
(see the Supporting Information, SI3) precluded unambiguous
assignment of the mesophase. According to previous results
obtained on maltose derivatives, it can be postulated that this
mesophase is lamellar. Samples become brown due to a clear
decomposition at temperatures around 250 °C.
A DSC study of the glycolipids was performed by heating the
compounds to 165 °C in the first and second scans (see the
Supporting Information, SI4), before decomposition in the
third scan, in order to minimize thermal decomposition of the
samples, which was observed in this technique around 170−175
°C. In the third scan, the sample was heated to 260 °C. Under
these conditions, the second and third scans were reproducible
and the transition data are gathered in Table 1.
Malt-Tz-C16 was previously characterized and exhibits a peak
corresponding to the melting transition at around 50 °C. Above
this temperature, the sample is highly viscous, and at
temperatures above approximately 90 °C, the sample becomes
more fluid and can be clearly characterized as liquid crystalline
according to the optical observations. The decomposition
temperature was detected at around 175 °C. Similar behavior
Figure 4. Hydrogel of Cell-Tz-C16 (0.5 wt %) and Lact-Tz-C16 (1 wt
%).
D
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Figure 5. 1H NMR spectra in DMSO-d6 at 25 °C upon addition of water, (a) 3.4 mg of Lact-Tz-C16 in 0.40 mL DMSO-d6, (b) addition of 0.04 mL
H2O, (c) addition of 0.08 mL H2O, (d) addition of 0.12 mL H2O, (e) addition of 0.16 mL H2O, (f) addition of 0.18 mL H2O.
water, solutions have to be heated to 90−100 °C and the
hydrogel is obtained by cooling. In all cases, the gels are
thermoreversible and stable at RT. The sol state can be
achieved again by reheating. Thus, the septum-capped test tube
was heated in a heating block and the gel−sol transition occurs
for Cell-Tz-C16 at 95 °C and for Lact-Tz-C16 at 85 °C.
ring and an amide group, both of which could be responsible
for the molecular aggregation and formation of the supra-
molecular gel. In an effort to confirm the participation of these
groups in the supramolecular assembly, the variation of the
chemical shift (Δδ) was studied in NMR experiments by
adding water to a DMSO solution of the glycolipids. A singlet
corresponding to the H of the triazole ring is located at 8.04
ppm, and the signal corresponding to the NH group is located
at around 8.27 ppm for both compounds in DMSO-d6, as can
To better establish the exact temperature of gel−sol
transitions, hydrogels were studied by DSC (under a nitrogen
atmosphere, 10 °C min−1). A hydrogel of Cell-Tz-C16 (0.5 wt
%) shows a broad endothermic peak at around 90 °C (see the
Supporting Information, SI6), which is consistent with the
results obtained on heating the samples in a heating block and
corresponds to the gel−sol transition. A thermal peak was not
observed in the cooling scan, however, and in the second and
third heating scans, the peak at around 90 °C was again
observed, thus confirming the reversibility of this transition. In
the case of Lact-Tz-C16, peaks corresponding to the sol−gel
transition were not detected by DSC (under the same
conditions). In the case of Malt-Tz-C16, it was reported that
the gel−sol transition occurs by DSC at around 65 °C.18 NMR
experiments also provide information about gel−sol transitions.
On progressive heating of a gel sample in D2O, the spectrum
was fully resolved once the corresponding sol (clear solution) is
obtained. For Cell-Tz-C16 (0.5 wt % D2O) was fully resolved at
around 95 °C and for Lact-Tz-C16 (1 wt % D2O) was fully
resolved at around 80 °C (see the Supporting Information, SI7
and SI8, respectively). Consequently, Cell-Tz-C16 and Lact-Tz-
C16 present a gel state with a higher temperature range. As one
would expect, the nature of the sugar polar head, and especially
the nature of the glycosidic linkage between the two units (α
1→4 for maltose, β 1→4 for cellobiose and lactose), influences
the stability of the supramolecular network that supports the
gels, a conclusion based on the differences in the gel−sol
temperature as well as differences in the gel concentration.
Two of the driving forces that can promote gel formation are
π−π stacking of aromatic rings and H-bonding. The structure
of the synthesized glycoamphiphiles contains a 1,2,3-triazole
1
be seen in Figure 5 for Lact-Tz-C16 (the analogous H NMR
region for Cell-Tz-C16 can be found in the Supporting
Information, SI9). The addition of water to the sample led to
shielding of the signal due to the H of the triazole ring, a
change that indicates the contribution of π−π stacking to the
aggregation.24 Moreover, a simultaneous deshielding of the NH
signal was also observed, and this can be assigned to self-
assembly through hydrogen bonding.24b The Δδmax value for
the H of the triazole is 0.068 ppm, and Δδmax for NH is 0.097
ppm on a sample of 3.4 mg of Lact-Tz-C16 in 0.40 mL DMSO-
d6 when 0.16 mL of water (40%) was added. The signals did
not shift anymore, and a gel-like structure, suspended in the
solvent, is formed when additional water was added in both
cases.
The influence of amide groups in the design of hydrogelators
is well-known, but the presence of the triazole as the linking
unit of the hydrophobic and hydrophilic parts of the
synthesized glycoamphiphiles also seem to play an important
role. Indeed, the triazole ring is a rigid fragment of the
amphiphile structure that can promote the formation of
aggregates. Furthermore, its dipole moment also increases the
hydrophilicity, thus ensuring appropriate solubility in water,
which in turn facilitates the preparation of hydrogels.
Microscopic Gel Characterization. The self-assembled
microstructures of the xerogels derived from Cell-Tz-C16 and
Lact-Tz-C16 were studied by SEM and TEM. Additional
experiments were performed by ESEM and cryo-TEM in order
to better understand the swollen structure in water. AFM
E
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Figure 6. (a) FESEM image of Cell-Tz-C16 (0.5 wt % water) xerogel, (b) FESEM image of Lact-Tz-C16 (1 wt % water) xerogel, (c) FESEM image of
a single ribbon of Cell-Tz-C16 (0.5 wt % water) xerogel. (d) FESEM image of a single ribbon of Lact-Tz-C16 (1 wt % water) xerogel. The samples
were coated with platinum.
measurements were also performed in order to obtain
topological information on the structure.
the case of Cell-Tz-C16, flat ribbons are observed while Lact-Tz-
C16 shows a rough brain-like structure (Figure 8). Smaller fibers
are detected as the gels are progressively dried. This technique
also allows holes in the structure to be viewed (these are easily
observed in Cell-Tz-C16 in comparison with Lact-Tz-C16, see
Figures 8b and d). Significant changes were not observed on
studying the same field of view in the samples while
progressively decreasing the humidity. This fact shows that
the supramolecular 3D network remains very similar when
water is removed (see the Supporting Information, SI10).
Cryo-TEM experiments were carried out directly on
hydrogels vitrified in liquid ethane. The ribbons resulting
from the self-assembly of the amphiphiles were also detected by
this technique in both samples. A cryo-TEM microphotograph
of the Cell-Tz-C16 gel is shown in Figure 9 (for Lact-Tz-C16
cryo-TEM results, see the Supporting Information, SI11). On
studying the twisted part of the ribbon, it can be seen that the
cross sections of the ribbon show alternate dark and bright
regions (as can be seen in the zoom of Figure 9) with a
thickness of these regions of about 2 and 2.5 nm, respectively.
The model shown in Figure 9 is proposed to explain the
assembly of amphiphiles into ribbons and the resulting layered
structure of the cross-section. This layered structure of the
cross-section of ribbons is formed by alternating hydrophilic
parts, consisting of a bilayer of sugar polar heads, and
hydrophobic parts of interdigitated aliphatic domains. In fact,
the theoretical length of the hydrophobic part is about 25 Å
(18.5 Å for the palmitic chain and 6.6 Å for amide and triazole
ring), which is in accordance with the thickness of the bright
motives of around 2.5 nm. In the same way the theoretical
length of the disaccharide is around 10 Å. The thickness of the
dark motive is around 2 nm, which is in accordance with a
disaccharide bilayer.
Field emission scanning electron microscopy (FESEM)
measurements on the xerogel obtained from Cell-Tz-C16 (0.5
wt % gel in water) show a supramolecular fibrillar network
formed by bundles of ribbons with a width ranging from
around 50 to 400 nm, and a length of several micrometers
(Figure 6a). Similar ribbons are also observed for Lact-Tz-C16
(1.0 wt % gel in water), with a width ranging around 40 to 150
nm and a length of several μm (Figure 6b). This physical
network of ribbons is responsible for the immobilization of
water in hydrogels.
When single ribbons are observed, torsion can be detected in
the structure. Cell-Tz-C16 ribbons exhibit a right-handed twist,
as can be seen in Figure 6c, while the torsion in Lact-Tz-C16
ribbons leads to a left-handed twist (Figure 6d).
For TEM measurements, gel samples were first diluted down
to 0.05 or 0.1 wt % and negatively stained with uranyl acetate.
Microphotographs of the physical network and a close up of the
ribbon are shown in Figure 7. Upon dilution, TEM micro-
photographs also display a physical network of twisted ribbons
that have a width of around 60 to 150 nm for Cell-Tz-C16 (see
Figure 7a). In Lact-Tz-C16, the ribbons seem to have a more
regular width of around 40 nm (see Figure 7b). On careful
observation of a single ribbon of Cell-Tz-C16 (see Figure 7c), a
right-handed twist is detected. In the single ribbon of Lact-Tz-
C16 (see Figure 7d), a left-handed twist can be observed. The
space between two torsions (pitch) seems to be approximately
regular within a single ribbon but differs from one fiber to
another, especially as the width changes.
ESEM and Cryo-TEM experiments were also carried out in
order to better understand the structure without drying the gel.
ESEM measurements on the gels provide an insight into the
micrometer structure under wet environmental conditions. In
F
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Figure 7. (a) TEM image of Cell-Tz-C16 (0.05 wt %), (b) TEM image of Lact-Tz-C16 (0.1 wt % water), (c) TEM image of a single ribbon of Cell-
Tz-C16 (0.05 wt % water) with a right handed twist, (d) TEM image of a single ribbon of Lact-Tz-C16 (0.1 wt % water) with a left handed twist.
TEM images were taken on samples that were dried and negatively stained with uranyl acetate (1 wt % water).
AFM measurements were performed on a drop of the gel
placed onto graphite and subsequently dried with air. It can be
observed in Figure 10 that the samples have opposite twisted
ribbons in hydrogels from Cell-Tz-C16 and Lact-Tz-C16a
situation in accordance with the results obtained by electron
microscopy. As an example, for a single ribbon of Cell-Tz-C16,
the profiles of two different zones are represented in Figure
10d. The widths for the two profiles are around 125 nm. A
height of 42 nm was determined at the highest point (profile 1,
black) and 26 nm at the torsion (profile 2, red).
Circular Dichroism Measurements. The twisted ribbons
detected in gels are a consequence of a chiral supramolecular
arrangement of self-assembled amphiphiles. The opposite
handedness of the ribbons, as observed by the different
microscopic techniques, seems to be consequence of an
opposite supramolecular chirality. In an attempt to confirm
this opposite supramolecular chirality, circular dichroism (CD)
measurements were carried out on the gels and the results are
represented in Figure 11.
The λmax value for a hydrogel of Cell-Tz-C16 at minimum
gelator concentration (0.5 wt %) in the UV absorption
spectrum appears at around 230 nm and this absorption can
be assigned to the triazole group. The hydrogel of this
compound (0.5 wt %), when placed between two quartz discs,
exhibited a positive Cotton effect, for which the θmax value
appeared to be slightly displaced from the λmax in the UV
spectrum to 240 nm (please see the Supporting Information,
SI12, for similar figure at concentration of Cell-Tz-C16 gel at 1
wt %). For the hydrogel derived from Lact-Tz-C16 at minimum
gelator concentration (1 wt %), the λmax (due to the triazole
group) appears at 227 nm, but in this case, the Cotton effect
was negative. The θmin value appeared to be displaced from the
λmax in the UV spectrum to 237 nm. For this compound, the
values and signal of the Cotton effect matched those obtained
for an aqueous gel of Malt-Tz-C16 at 1 wt %. It was confirmed
that the contribution of the linear dichroism (LD) to the CD
spectrum is negligible by comparing several CD spectra
recorded at different angles around the incident light beam.
The opposite CD signals can be attributed to an opposite
chiral supramolecular arrangement of the molecules, a structure
that is the origin of the opposite handeness observed in the
ribbons. This fact shows that the stereochemical arrangement
of only one hydroxyl group (equatorial OH-4 in Cell-Tz-C16 vs
axial OH-4 in Lact-Tz-C16), or the arrangement of the
glycosidic bond (β 1→4 in Cell-Tz-C16 vs α 1→4 in Malt-
Tz-C16), has a significant effect on the preferential con-
formation21 and the self-assembly and supramolecular organ-
ization22 of these molecules.
CONCLUSIONS
■
New amphiphiles based on disaccharides as polar head groups
have been synthesized, and their liquid crystalline and gel-
forming properties have been investigated. Glycolipids were
prepared by a copper(I)-catalyzed azide−alkyne [3 + 2]
G
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Figure 8. (a) ESEM image of Cell-Tz-C16 (0.5 wt % water) 99.9% humidity, 3.0 °C, 759 Pa, (b) ESEM image of Cell-Tz-C16 (0.5 wt % water) 20%
humidity, 3.0 °C, 152 Pa, (c) ESEM image of Lact-Tz-C16 (1 wt % water) 99.9% humidity, 3.0 °C, 759 Pa, (d) ESEM image of Lact-Tz-C16 (1 wt %
water) 20.0% humidity, 3.0 °C, 152 Pa.
= 8.7 Hz, H2′β), 5.10 (dd, 1H, J1,2 = 7.8 Hz, J2,3 = 10.5 Hz, H2β), 5.23
(dd, 1H, J2′,3′ = 8.7 Hz, J3′,4′ = 9.3 Hz, H3′β), 5.34 (dd, 1H, J3,4 = 3.4
Hz, J4,5 = 1.1 Hz, H4β), 5.66 (d, 1H, J1′,2′ = 8.2 Hz, H1′β). (1α) 1.96 (s,
3H), 2.00 (s, 3H), 2.05 (s, 3H), 2.05 (s, 3H) 2.06 (s, 3H), 2.12 (s,
3H), 2.15 (s, 3H), 2,17 (s, 3H) CH3COO ×8, 3,78−3.90 (m,
2H, H4′α, H5α), 3.97 (m, 1H, H5′α), 4.05−4.18 (m, 2H, H6aα, H6bα),
4.12−4.18 (m, 1H, H6′aα), 4.43−4.51 (m, 2H, H6′bα, H1α), 4.94−
4.97 (m, 1H, H3α), 5.00 (dd, 1H, J1′,2′ = 3.7 Hz, J2′,3′ = 10.5 Hz, H2′α),
5.10−5.14 (m, 1H, H2α), 5.34−5.37 (m, 1H, H4α,), 5.45 (dd, 1H,
cycloaddition to link a cellobiose or lactose to a palmitoyl
derivative bearing an alkyne group.
The compounds synthesized exhibit a mesomorphic lamellar
fluid state and are able to gel in pure water. These hydrogels are
stable at room temperature, and the gel−sol transition is
thermoreversible. The minimum concentrations to form a gel
are 1 or 0.5 wt % for lactose or cellobiose compounds,
respectively. The resulting self-assembled fibrillar network was
studied by different microscopic techniques, either in the
xerogel state by TEM, FESEM, and AFM or in a wet
environment by cryo-TEM and ESEM. Twisted ribbons were
observed, and the supramolecular chirality was supported by
the observation of a CD effect. The opposite direction of the
torsion and sense of the CD signal were found to depend on
the sugar polar head. This study has led to a deeper insight into
the supramolecular organization of hydrogels based on low
molecular weight sugar amphiphiles.
J
2′,3′ = 10.5 Hz, J3′,4′ = 9.3 Hz, H3′α), 6.24 (d, 1H, J1′,2′ = 3.7 Hz, H1′α).
13C NMR (125 MHz, CDCl3, 25 °C, δ ppm): (1β) 20.7, 20.7, 20.8,
20.9, 20.9, 21.0 CH3CO ×8, 61.0, 61.9 C6β, C6′β, 66.7 C4β, 69.1
C2β, 70.6 C2′β, 70.9, 71.7, C5β, C3β, 72.8 C3′β, 73.6 C5′β, 75.8 C4′β,
91.7 C1′β, 101.6 C1β, 169.0, 169.2 C2OCO, C1′OCO,
169.7, 169.8 C2′OCO, C3′OCO, 170.2, 170.3, 170.5,
170.5 C3OCO, C4OCO, C6OCO, C6′O
CO. (1α) 20.8, 21.1, 20,7, 21,1 CH3CO ×8, 60.9, 61.6, C6α, C6′α,
69.3, 69.8, 71.1, 75.9, CXα 69.5 C3′α, 70.8 C5′α, 89.1 C1′α, 101.3 C1α,
169.1, 169.3, 170.1 CH3OCO, other C cannot be assigned.
MALDI-TOF MS (DIT+NaTFA): 701.2 [M + Na]+.
EXPERIMENTAL SECTION
■
IR (KBr, cm−1): 3481, 2983, 1754, 1371, 1219, 1048, 898, 601.
Synthesis of Hepta-O-acetyl-β-lactosyl Azide (2) and Hepta-
O-acetyl-β-cellobiosyl Azide (3). Trimethylsilyl azide (1.1 mL, 8.36
mmol) and tin tetrachloride (350 μL, 2.99 mmol) were added, at room
temperature and under argon, to a solution of lactose octaacetate (1)
or cellobiose octaacetate (4.01 g, 5.92 mmol) in dry CH2Cl2 (15 mL).
The reaction mixture was stirred at room temperature, and the
reaction was monitored by TLC (1:1 hexane/ethyl acetate). After 24
h, CH2Cl2 was added and the solution was washed with saturated
Na2CO3 and twice with water. The organic layer was dried over
MgSO4, filtered, and evaporated under reduced pressure. The product
D-lactose monohydrate and cellobiose octaacetate were purchased
from Aldrich and were used without previous purification. Lactose
octaacetate25 (1) and N-propargyl palmitoylamide (4)18 were
synthesized according to a previously described procedure.
Octa-O-acetyl-β-lactose C28H38O19 (1). 1H NMR (500 MHz,
CDCl3, 25 °C, δ ppm): (1β) 1.96 (s, 3H), 2.02 (s, 3H), 2.03 (s, 3H),
2.04 (s, 3H) 2.06 (s, 3H), 2.09 (s, 3H), 2.11 (s, 3H), 2,15 (s, 3H)
CH3COO ×8, 3.75 (ddd, 1H, J5′,6′b = 2.0 Hz, J5′,6′a = 4.8 Hz,
J
4′,5′ = 9.8 Hz, H5′β), 3.81 − 3.88 (m, 2H, H5β, H4′β), 4.04−4.16 (m,
3H, H6aβ, H6bβ, H6′aβ), 4.41−4.49 (m, 2H, H6′bβ, H1β), 4.94 (dd,
1H, J3,4 = 3.4 Hz, J2,3 = 10.5 Hz, H3β), 5.04 (dd, 1H, J1′,2′ = 8.2 Hz, J2′,3′
H
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Figure 9. Cryo-TEM image of Cell-Tz-C16 0.5 wt % water gel (top) and model proposed for molecular arrangement (bottom): Ribbons formed by
alternating hydrophobic sugar regions and interdigitated hydrophobic regions. A close up of the cross-section of the ribbon is shown on the right
corner (see the model for this cross-section).
Figure 10. AFM microphotographs of hydrogels (a) Cell-Tz-C16 (0.5 wt %), (b) single ribbon of Cell-Tz-C16 (0.5 wt %), (c) single ribbons of Lact-
Tz-C16 (1 wt %), (d) profiles of two different zones of a single ribbon of Cell-Tz-C16 (0.5 wt %).
I
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169.2 C2OCO, 169.4 C4OCO, 169.6 C2′O
CO, 169.8 C3′OCO, 170.3, 170.4, 170.6 C3OCO,
C6OCO, C6′OCO.
MALDI-TOF MS (DIT+NaTFA): 684.0 [M + Na]+.
IR (KBr, cm−1): 3474, 2954, 2879, 2121, 1748, 1371, 1238, 1066,
1046, 904, 600.
N-Propargylpalmitoylamide C19H35NO (4). 1H NMR (300
MHz, CDCl3, 25 °C, δ ppm): 0.87 (t, 3H, J = 6,5 Hz, CH2CH3),
1.20−1.40 (m, 24H, CH2(CH2)12−), 1.59−1.64 (m, 2H, 
CH2(CH2)12), 2.18 (t, 2H, J = 7,5 Hz, COCH2), 2.22 (t,
1H, J = 2,4 Hz, HCC), 4.05 (dd, 2H, JCH2,CCH = 2,5 Hz, JCH2,NH
= 5,0 Hz, CCH2NH), 5.63 (s, 1H, NH).
13C NMR (75 MHz, CDCl3, 25 °C, δ ppm): 14.1 CH2CH3,
25.6 CH2(CH2)12, 22.7, 29.2, 29.3, 29.3, 29.4, 29.5, 29.6, 29.7,
29.7, 31.9 (CH2)12, CCH2NH, 36.5 CO
CH2(CH2)13, 71.5 HCC, 79.7 HCCCH2, 172.7 NH
COCH2.
Micro-TOF MS: 294.2773 [M+H]+ calcd 293.2713; 316.2612 [M
+Na]+, calcd 316.2611.
IR (KBr, cm−1): 3292, 3073, 2955, 2918, 2848, 1639, 1553, 1472,
1462, 1275, 729, 719, 689, 666, 631, 570.
Synthesis of Acetylated Glycolipids OAc-Lact-Tz- C16 and
OAc- Cell-Tz-C16. Propargyl derivative 4 (0.44 g, 1.50 mmol), azide
derivative 2 or 3 (1.00 g, 1.51 mmol), copper(I) bromide (46.6 mg,
0.32 mol), and N-pentamethyldiethylenetriamine (PMDETA) (65 μL,
0.31 mmol) were dissolved in anhydrous dimethylformamide (10 mL)
under argon atmosphere. The mixture was stirred at room temperature
for 2 days. The reaction was monitored by TLC with hexane/ethyl
acetate 1:1 as eluent. The catalyst was then removed by filtration, and
the solvent was removed under reduced pressure. The reaction was
poured into 150 mL of water. The aqueous phase was extracted three
times, each with 200 mL of hexane/ethyl acetate 1:1. The organic
phase was dried with anhydrous MgSO4. The solution was filtered, and
the solvent was removed under reduced pressure. The resulting white
solid was purified by flash chromatography using initially dichloro-
methane/ethyl acetate 1:1 and then increasing the polarity. A white
solid was obtained (1.17 g, 81% of OAc-Lact-Tz-C16) (1.14 g, 80% of
OAc-Cell-Tz-C16).
Figure 11. CD (top) and UV−vis (bottom) spectra of hydrogels
derived from Cell-Tz-C16, (0.5 wt %), solid line, and Lact-Tz-C16 (1 wt
%), dashed line.
was purified by flash chromatography using hexane/ethyl acetate 1:1.
A white solid was obtained (3.19 g, 82%).
Hepta-O-acetyl-β-lactosyl Azide C26H35N3O17 (2). 1H NMR
(400 MHz, CDCl3, 25 °C, δ ppm): 1.96 (s, 3H), 2.04 (s, 3H), 2.04 (s,
3H), 2.06 (s, 3H), 2.06 (s, 3H), 2.13 (s, 3H), 2.14 (s, 3H) CH3
COO ×7, 3.70 (ddd, 1H, J5′,6′b = 5.1 Hz, J5′,6′a = 2.2 Hz, J4′,5′ = 9.9
Hz, H5′), 3.81 (dd, 1H, J3′,4′ = 9.1 Hz, J4′,5′ = 9.9 Hz, H4′), 3.87 (ddd,
1H, J5,6b = 7.3 Hz, J5,6a = 7.3 Hz, J5,4 = 0.9 Hz, H5), 4.05−4.14 (m, 3H,
H6a, H6b,H6′b), 4.47−4.52 (m, 2H, H1, H6′a), 4.62 (d, 1H, J1′,2′ = 8.8
Hz, H1′, 4.85 (dd, 1H, J1′,2′ = 8.8 Hz, J2′,3′ = 9.3 Hz, H2′), 4.95 (dd,
1
OAc-Lact-Tz-C16 C45H70N4O18. H NMR (400 MHz, CDCl3, 25
°C, δ ppm): 0.87 (t, 3H, J = 6.8 Hz, (CH2)12CH3), 1.20−1.36 (m,
24H, (CH2)12), 1.56−1.65 (m, 2H, COCH2 
CH2(CH2)12), 1.86 (s, 3H), 1.97 (s, 3H), 2.05 (s, 3H), 2.06 (s,
3H), 2.08 (s, 3H), 2.11(s, 3H), 2.16 (s, 3H) CH3COO ×7, 2.18
(t, 2H, J = 7.3 Hz, COCH2CH2), 3.85−3.99 (m, 3H, H4′,H5,
H5′), 4.05−4.19 (m, 3H, H6a, H6b, H6′a), 4.42−4.57 (m, 4H, C
CH2NH, H1, H6′b), 4.97 (dd, 1H, J2,3 = 10.4 Hz, J3,4 = 3.5 Hz, H3),
5.12 (dd, 1H, J1,2 = 7.9 Hz, J2,3 = 10.4 Hz, H2), 5.33−5.44 (m, 3H,
H2′, H3′, H4), 5.78 (d, 1H, J1′,2′ = 9.2 Hz, H1′), 6.11 (t, 1H, J = 5.3
Hz, CH2NHCO), 7.71 (s, 1H, NCHCCH2 triazole).
13C NMR (100 MHz, CDCl3, 25 °C, δ ppm): 14.2 (CH2)12
CH3, 20.3, 20.6, 20.7, 20.8, 20.9 CH3COO ×7, 22.8 CH2
CH2CH2)12, 25.7 COCH2CH2(CH2)12, 29.4, 29.5, 29.5,
29.6, 29.7, 29.8, 29.8, 32.1, (CH2)12, 34.9 CCH2NH, 36.7
COCH2CH2, 60.9, 61.8 C6, C6′, 66.7 C4, 69.1 C2, 70.7, 70.9,
71.0, 72.5, 75.5, 75.9, C2′, C3′, C4′, C5′, C3, C5, 85.6 C1′, 101.2 C1,
120.8 CH triazole, 145.5 C triazole, 169.2, 169.2, 169.6, 170.2, 170.2,
170.3, 170.5 CH3COO, 173.4 NHCOCH2.
1H, J3,4 = 3.5 Hz, J2,3 = 10.5 Hz, H3), 5.10 (dd, 1H, J1,2 = 7.9 Hz, J2,3
=
10.5 Hz, H2), 5.20 (dd,1H, J2′,3′ = 9.3 Hz, J3′,4′ = 9.1 Hz, H3′), 5.34
(dd, 1H, J3,4 = 3.5 Hz, J4,5 = 0.9 Hz, H4).
13C NMR (100 MHz, CDCl3, 25 °C, δ ppm): 20.6, 20.7, 20.7, 20.7
20.8, 20.9 CH3CO ×7, 60.9 C6, 61.8 C6′, 66.7 C4, 69.2 C2, 70.8,
71.0, 71.1 C3, C5, C2′, 72.6 C3′, 74.9 C5′, 75.9 C4′, 87.8 C1′, 101.2
C1, 169.2 C2OCO, 169.6 C2′OCO, 169.7 C3′O
CO, 170.1, 170.2 C3OCO, C4OCO, 170.4, 170.5
C6OCO, C6′OCO.
MALDI-TOF MS (DIT+NaTFA): 684.3 [M + Na]+.
IR (KBr, cm−1): 3481, 2983, 2122, 1753, 1372, 1230, 1057, 899,
602.
Hepta-O-acetyl-β-cellobiosyl Azide C26H35N3O17 (3). 1H NMR
(400 MHz, CDCl3, 25 °C, δ ppm): 1.98 (s, 3H), 2.00 (s, 3H), 2.02 (s,
3H), 2.03 (s, 3H), 2.06 (s,3H), 2.08 (s, 3H), 2.14 (s,3H) CH3CO
O ×7, 3.61−3.73 (m, 2H, H5, H5′), 3.79 (dd, 1H, J3′,4′ = 9.0 Hz,
J4′,5′ = 9.9 Hz, H4′), 4.03 (dd, 1H, J5,6a = 2.3 Hz, J6a,6b = 12.9 Hz, H6a),
4.11 (dd, 1H, J5′,6′a = 4.9 Hz, J6′a,6′b = 12.2 Hz, H6′a), 4.37 (dd, 1H,
J5,6b = 4.5 Hz, J6a,6b = 12.9 Hz, H6b), 4.48−4.56 (m, 2H, H1, H6′b),
MALDI-TOF MS (DIT+NaTFA): 977.4 [M + Na]+.
Anal. calcd for C45H70N4O18: C, 56.59; H, 7.39; N, 5.87. Found: C,
56.88; H, 7.73; N, 5.84.
IR (KBr, cm−1): 3398, 2925, 2854, 1754, 1658, 1371, 1230, 1047,
919, 603.
1
OAc-Cell-Tz-C16 C45H70N4O18. H NMR (400 MHz, CDCl3, 25
°C, δ ppm): 0.87 (t, 3H, J = 6.8 Hz, (CH2)12CH3), 1.19−1.35
(m, 24H, (CH2)12), 1.55−1.65 (m, 2H, COCH2
CH2(CH2)12), 1.86 (s, 3H), 1.98 (s, 3H), 2.01 (s, 3H), 2.03 (s,
3H), 2.04 (s, 3H), 2.10 (s, 3H), 2.11 (s, 3H) CH3COO ×7, 2.17
(t, 2H, J = 7.3 Hz, COCH2CH2), 3.69 (ddd, 1H, J4,5 = 9.6 Hz,
J5,6a = 2.1 Hz, J5,6b = 4.3 Hz,, H5), 3.84−3.98 (m, 2H, H4′, H5′), 4.06
(dd, 1H, J5,6a = 2.1 Hz, J6a,6b = 12.5 Hz, H6a), 4.12 (dd, 1H, J5′,6′a = 4.7
4.61 (d, 1H, J1′,2′ = 8.9 Hz, H1′), 4.86 (dd, 1H, J1′,2′ = 8.9 Hz, J2′,3′
=
8.4 Hz, H2′), 4.92 (dd, 1H, J1,2 = 7.9 Hz, J2,3 = 9.1 Hz, H2), 5.06 (dd,
1H, J3,4 = 9.4 Hz, J4,5 = 9.7 Hz, H4), 5.14 (dd, 1H, J2,3 = 9.1 Hz, J3,4
9.4 Hz, H3), 5.18 (dd,1H, J2′,3′ = 8.4 Hz, J3′,4′ = 9.0 Hz, H3′).
=
13C NMR (100 MHz, CDCl3, 25 °C, δ ppm): 20.6, 20.7, 20.7, 20.8,
20.9 CH3CO ×7, 61.6, 61.7 C6, C6′, 67.8 C4, 71.0 C2′, 71.7 C2,
72.2, 72.3, 73.0, 75.0 C3, C5, C3′, C5′, 76.1 C4′, 87.8 C1′, 100.8 C1,
J
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Hz, J6′a,6′b = 12.2 Hz, H6′a), 4.38 (dd, 1H, J5,6b = 4.3 Hz, J6a,6b = 12.5
Hz, H6b), 4.43−4.53 (m, 3H, H6′b, CCCH2NH), 4.55 (d, 1H,
J1,2 = 8.2 Hz, H1), 4.94 (dd, 1H, J1,2 = 8.2 Hz, J2,3 = 9.4 Hz, H2), 5.07
(dd, 1H, J3,4 = 9.5 Hz, J4,5 = 9.6 Hz, H4), 5.16 (dd, 1H, J2,3 = 9.4 Hz,
J3,4 = 9.5 Hz, H3), 5.33−5.42 (m, 2H, H2′, H3′), 5.73−5.73−5.81 (m,
1H, H1′), 6.11 (t, 1H, J = 5.6 Hz, CH2NHCO), 7.70 (s, 1H,
NCHCCH2 triazole).
Anal. calcd for C31H56N4O11•H2O: C, 54.85; H, 8.61; N, 8.25.
Found: C, 54.94; H, 8.88; N, 8.27.
IR (KBr, cm−1): 3326, 2915, 2848, 1649, 1542, 1468, 1368, 1328,
1247, 1227, 1210, 1095, 1041, 997, 899, 997, 899, 831, 760, 719, 655.
1
Characterization Techniques. H and 13C NMR spectra were
recorded on BRUKER AV-400 or AV-500 spectrometers. IR spectra
were measured on Thermo NICOLET Avatar 360 FT-IR spectropho-
tometer using KBr pellets. Mass Analysis was performed using a
13C NMR (100 MHz, CDCl3, 25 °C, δ ppm): 14.4 (CH2)12
CH3, 20.5, 20.7, 20.8, 21.0, 21.1 CH3COO ×7, 23.0 (CH2)12
, 25.8 COCH2CH2(CH2)12, 29.6, 29.6, 29.7, 29.8, 29.9, 29.9,
30.0, 32.2, (CH2)12, 35.1 CCH2NH, 36.9 COCH2CH2,
61.9 ×2 C6, C6′, 68.0 C4, 70.8 C2′or C3′, 71.9 C2, 72.5, 72.6 C5,
C2′or C3′, 73.2 C3, 76.0 C4′, 76.3 C5′, 85.9 C1′, 100,1 C1, 121.2 CH
triazole, 145.7 C triazole, 169.3 C2′OCO or C3′OCO,
169.4 C2OCO, 169.6 C4OCO, 169.8 C2′O
CO or C3′OCO, 170.4, 170.5 C3OCO, C6′O
CO, 170.8 C6OCO, 173.6 NHCOCH2.
MALDI+/TOF Bruker Microflex system with a DIT + NaFTA matrix
̈
and MicroTOF Bruker equipment for exact mass measurements.
̈
Elemental analysis was performed using a Perkin-Elmer CHN2400
microanalyzer.
The mesogenic behavior was studied by optical microscopy with an
Olympus BH-2 polarizing microscope equipped with a Linkam THMS
hot-stage central processor and a CS196 cooling system. Differential
scanning calorimetry (DSC) was performed using a DSC Q2000 from
TA Instruments with samples sealed in aluminum pans and a scanning
rate of 10 °C/min under a nitrogen atmosphere. Temperatures were
read at the maximum of the transition peaks and glass transition at the
midpoint of the jump of the baseline. Thermogravimetric analysis
(TGA) was performed using a TGA Q5000IR from TA Instruments at
a rate of 10 °C/min under a nitrogen atmosphere. Circular dichroism
was measured using a Jasco J-180 equipment. The CD spectra of the
samples were registered by rotating the sandwich every 60 degrees
around the light beam axis.
FESEM measurements were performed using a Carl Zeiss MERLIN
equipment at the laboratory of the ‘Servicio de Microscopia de la
Universidad de Zaragoza’. The sample was fixed onto glass and coated
with platinum. ESEM measurements were performed using a
QUANTA FEG 250 and TEM measurements were performed using
a TECNAI G2 20 (FEI COMPANY), 200 kV, both at the Laboratory
of Advanced Microscopy (LMA) of the ‘Instituto de Nanociencia de
Aragon’. For TEM sample preparation, a drop of the solution (gel
diluted) was placed on a copper grid and left to dry for 15 min. The
copper grid was then placed again over a drop of 1% uranyl acetate
solution as a negative stain for 30 s and was then left to dry. CryoTEM
measurements were performed on this microscope with a cryo-holder.
AFM measurements were performed using a VEECO MULTI-
MODE 8, mode tapping and tips 20−80 nN/m and υ 300 kHz at
Laboratory of Advanced Microscopy (LMA).
MALDI-TOF MS (DIT+NaTFA): 977.4 [M + Na]+.
Anal. calcd for C45H70N4O18: C, 56.59; H, 7.39; N, 5.87. Found: C,
57.00; H, 7.75; N, 5.93.
IR (KBr, cm−1): 3360, 3073, 2923, 2852, 1750, 1650, 1377, 1228,
1044, 906, 599.
Synthesis of Glycolipids Lact-Tz-C16 and Cell-Tz-C16. The
protected triazole-disaccharide-heptaacetate derivatives (OAc-Lact-Tz-
C16 and OAc-Cell-Tz-C16) (401 mg, 0.42 mmol) were dissolved in 25
mL of anhydrous methanol. Sodium methoxide (160 mg, 2.96 mmol)
was added. The solution was stirred at room temperature until the
reaction was complete (TLC, dichoromethane/ethyl acetate 1:1).
Amberlyst IR 120 (H+ form) was added to exchange sodium ions; the
resin was filtered off. A white solid was obtained (220 mg, 80% for
Lact-Tz-C16) (214 mg, 77% for Cell-Tz-C16).
1
Lact-Tz-C16 C31H56N4O11. H NMR (400 MHz, MeOD, 50 °C, δ
ppm): 0.90 (t, 3H, J = 6.9 Hz, (CH2)12CH3), 1.22−1.40 (m, 24H,
(CH2)12), 1.56−1.66 (m, 2H, CO−CH2CH2(CH2)12), 2.21
(t, 2H, J = 7.3 Hz, COCH2CH2), 3.50 (dd, 1H, J2,3 = 9.7 Hz, J3,4
= 3.3 Hz, H3), 3.59 (dd, 1H, J1,2 = 7.8 Hz, J2,3 = 9.7 Hz, H2), 3.82−
3.86 (m, 1H, H4), 3.60−3.64 (m, 1H), 3.69−3.82 (m, 5H), 3.87−3.91
(m, 2H, H3′,H4′, H5′, H6′a, H6′b, H5, H6a, H6b), 3.95 (dd, 1H, J1′,2′
=
9.2 Hz, J2′,3′ = 8.9 Hz, H2′), 4.42 (d, 1H, J1,2 = 7.8 Hz, H1), 4.44 (s,
1H, CH2NHCO), 5.60 (d, 1H, J1′‑2′ = 9.2 Hz, H1′), 8.02 (s,
1H, CH triazole).
Gelation test: The gelator and the solvent were placed in a septum-
capped test tube. The resulting mixture was heated until a clear
solution was obtained. The solution was cooled to room temperature
and if the tube was turned upside down and the solution did not flow,
the formation of a gel was registered.
13C NMR (100 MHz, MeOD, 50 °C, δ ppm): 14.3 (CH2)12
CH3, 23.6 (CH2)12, 26.8 COCH2CH2(CH2)12, 30.3,
30.3, 30.5, 30.6, 30.7, 32.9, CH2(CH2)12, 35.6 CCH2
NH, 37.0 COCH2CH2, 61.8, 62.6, 76.9, 77.1, 79.6,
80.1,C3′,C4′, C5′,C6′, C5, C6, 70.4 C4, 72.6 C2, 73.8 C2′, 75.0 C3,
89.1 C1′, 105.2 C1, 123.4 CH triazole, 146.4 C triazole, 176.2 NH
COCH2.
ASSOCIATED CONTENT
* Supporting Information
■
S
1H NMR of OAc-Lact-Tz-C16 and Lact-Tz-C16. Thermogravi-
metric analysis of peracetylated precursors and glycolipids.
Microphotograph of Cell-Tz-C16 by POM. DSC curves in the
solid state of Cell-Tz-C16 and Lact-Tz-C16. X-ray patterns of
Cell-Tz-C16. DSC analysis of Cell-Tz-C16 (0.5 wt %) water gel.
1H NMR spectra of Cell-Tz-C16 hydrogel, 0.5 wt % D2O, taken
at different temperatures. 1H NMR spectra of Lact-Tz-C16
MicroTOF MS: 661.4008 [M+ Na]+, calcd: 661.4018.
Anal. calcd for C31H56N4O11•H2O: C, 54.85; H, 8.61; N, 8.25.
Found: C, 55.34; H, 8.96; N, 8.39.
IR (KBr, cm−1): 3328, 2915, 2848, 1649, 1542, 1467, 1416, 1379,
1329, 1247, 1227, 1130, 1089, 1074, 1048, 998, 895, 758, 700, 645.
1
Cell-Tz-C16 C31H56N4O11. H NMR (500 MHz, MeOD, 50 °C, δ
ppm): 0.90 (t, 3H, J = 6.8 Hz, (CH2)12CH3), 1.13−1.45 (m,
24H, (CH2)12CH3), 1.56−1.66 (m, 2H, COCH2
CH2(CH2)12), 2.21 (t, 2H, J = 7.3 Hz, COCH2CH2), 3.27
(dd, 1H, J1,2 = 7.3 Hz, J2,3 = 8.4 Hz, H2), 3.32−3.46 (m, 3H), 3.65−
3.80 (m, 4H), 3.85−3.92 (m, 3H, H3′, H4′, H5′, H6′a, H6′b, H3, H4,
H5, H6a, H6b), 3.95 (dd, 1H, J1′,2′ = 9.8 Hz, J2′,3′ = 7.7 Hz, H2′), 4.45
(m, 2H, CCH2NH), 4.48 (d, 1H, J1,2 = 7.3 Hz, H1), 5.60 (d, 1H,
J1′,2′ = 9.2 Hz, H1′), 8.00 (s, 1H, CH triazole).
1
hydrogel, 1 wt % D2O, taken at different temperatures. H
NMR experiments in DMSO-d6 increasing water concentration
of Cell-Tz-C16. ESEM images of Lact-Tz-C16 (1 wt % water) gel
decreasing humidity. CryoTEM images of Cell-Tz-C16 (0.5 wt
%) water gel and Lact-Tz-C16 (1 wt %) water gel. CD and UV−
vis spectra of hydrogels derived from Cell-Tz-C16 and Lact-Tz-
C16 at 1 wt %. This material is available free of charge via the
Internet at http://pubs.acs.org.
13C NMR (125 MHz, MeOD, 55 °C, δ ppm): 14.3 (CH2)12
CH3, 23.6 (CH2)12, 26.8 COCH2CH2(CH2)12, 30.4, 30.5,
30.7, 32.9 CH2(CH2)12, 35.6 CCH2NH, 37.0 CO
CH2CH2, 61.7, 62.6, 71.5, 76.9, 78.0, 78.2, 79.6, 79.9 C3′,C4′,
C5′,C6′, C3,C4, C5,C6, 73.8 C2′, 75.6 C2, 89.4 C1′, 104.6 C1, 123.4
CH triazole, 146.4 C triazole, 176.3 NHCOCH2.
AUTHOR INFORMATION
Corresponding Author
*E-mail: loriol@unizar.es and fitremann@chimie.ups-tlse.fr.
■
MicroTOF MS: 661.3997 [M+ H]+, calcd: 661.4018.
K
dx.doi.org/10.1021/cm301509v | Chem. Mater. XXXX, XXX, XXX−XXX

Chemistry of Materials
Article
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the Spanish MINECO project
MAT2011-27978-C02-01, Fondo Europeo de Desarrollo
́
Regional (FEDER), and Gobierno de Aragon, and Fondo
Social Europeo is gratefully acknowledged. The authors also
acknowledge ‘Servicio de Microscopia de la Universidad de
Zaragoza’ for FESEM measurements, Laboratory of Advanced
Microscopy (LMA) of the INA (Instituto de Nanociencia de
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