Cholesterol-based low-molecular mass gelators towards smart ionogels

Article abstract of DOI:10.1039/c2sm26332g

Ionic liquids are solvents of future. One of the promising methods to boost their uses is to solidify them in a physical way but with little interruption of their properties. It is therefore of interest to create gels of ionic liquids by using low-molecular mass compounds as gelators (LMMGs). Herein, we report a number of ionic liquid gels (ionogels) of which specially designed and synthesized cholesteryl derivatives were employed as gelators. The ionogels as obtained are thermo-reversible. In particular, the one with 1-butyl-3- methylimidazolium tetrafluoroborate (IL2) as solvent and a cholesteryl derivative containing a d-phenylalanine residue (1D) as a gelator is very stable both in neutral and acidic mediums as demonstrated by a yield stress of 76 Pa for a self-standing cylinder of the ionogel. Furthermore, the ionogel can be easily converted into a hydrogel via simple replacement of the solvent with water in situ. More interestingly, the conversion is reversible, a phenomenon never reported before. At the same time, the critical gelation concentration (CGC) of 1D for IL2 is only 0.06%, w/w, which is almost the lowest value reported for ionogels till now, and falls into the category of super-gelator . Magnetization of the ionogel has been realized by introduction of micro-/nano-Fe₃O₄ particles. As expected, the magnetic gel as obtained is responding to external magnetic field. Specifically, it changes into fluid with the presence of a magnetic field exceeding certain strength, and retains to gel upon removing the magnetic field and with a treatment of sonication and heating-cooling cycle. SEM and TEM observations revealed the continuous fibrous network structures of the molecules of the gelator in the ionogels. To the best of our knowledge, this is the first report on ionogels possessing stimulus-responsive properties, good mechanical strength, and super-gelation talent.

Full text of DOI:10.1039/c2sm26332g

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PAPER
Cholesterol-based low-molecular mass gelators towards smart ionogels†
a
Junlin Yan, Jing Liu, Ping Jing, Chengkun Xu, Jiamin Wu, Di Gao and Yu Fang
a
a
b
b
b
a
*
*
Received 8th June 2012, Accepted 5th September 2012
DOI: 10.1039/c2sm26332g
Ionic liquids are solvents of future. One of the promising methods to boost their uses is to solidify
them in a physical way but with little interruption of their properties. It is therefore of interest to
create gels of ionic liquids by using low-molecular mass compounds as gelators (LMMGs). Herein,
we report a number of ionic liquid gels (ionogels) of which specially designed and synthesized
cholesteryl derivatives were employed as gelators. The ionogels as obtained are thermo-reversible. In
particular, the one with 1-butyl-3-methylimidazolium tetrafluoroborate (IL2) as solvent and a
cholesteryl derivative containing a D-phenylalanine residue (1D) as a gelator is very stable both in
neutral and acidic mediums as demonstrated by a yield stress of 76 Pa for a self-standing cylinder of
the ionogel. Furthermore, the ionogel can be easily converted into a hydrogel via simple replacement
of the solvent with water in situ. More interestingly, the conversion is reversible, a phenomenon
never reported before. At the same time, the critical gelation concentration (CGC) of 1D for IL2 is
only 0.06%, w/w, which is almost the lowest value reported for ionogels till now, and falls into the
category of ‘‘super-gelator’’. Magnetization of the ionogel has been realized by introduction of
micro-/nano-Fe3O4 particles. As expected, the magnetic gel as obtained is responding to external
magnetic field. Specifically, it changes into fluid with the presence of a magnetic field exceeding
certain strength, and retains to gel upon removing the magnetic field and with a treatment of
sonication and heating–cooling cycle. SEM and TEM observations revealed the continuous fibrous
network structures of the molecules of the gelator in the ionogels. To the best of our knowledge, this
is the first report on ionogels possessing stimulus-responsive properties, good mechanical strength,
and super-gelation talent.
of ILs and those of the supramolecular gels.8–14 It is believed
that this combination must boost the practical applications
of ILs.
Introduction
Ionic liquids (ILs) are regarded as ‘‘solvents of future’’,
‘‘designed solvents’’ and ‘‘green solvents’’ due to their high
ionic conductivity, wide electrochemical window, negligible
vapor pressure, nonflammable character, great thermal, and
chemical stability. These characteristics have endowed them
with a broad range of applications in science, technology and
industry.1–7 Recently, ILs gels (ionogels), in particular supra-
molecular ionogels, of which the gelator networks are formed
and maintained by non-covalent interactions, have attracted
great interest due to their combination of both the advantage
Up to now, gelators employed for the gelation of ionic
liquids consist of micro-/nano-particles, polymers, and low-
molecular mass gelators (LMMGs).13–18 Micro-/nano-particle
based ionogels are versatile hosts for catalysts and luminescent
materials.19–22 In particular, ionogels with carbon nanotubes as
gelators have been used as electrodes in double-layer capacitors
or actuators due to their great electro-activity and ionic
conductivity.23 The primary interest for polymer-based ionogels
is their potential applications in electrochemical devices.24–31 In
fact, the performances of perfluorinated polymer ionogels in
actuators, gate dielectrics and thin-film transistors have been
investigated recently.32–34 Compared with the polymer or inor-
ganic micro-/nano-particle based ionogels, LMMGs-based
ionogels have attracted increasing attention during the past few
years due to versatility of the gelators in design and synthesis.
Kimizuka and co-workers reported the first LMMG-based
ionogel of which a glycolipid derivative was employed as a
gelator and an ether-containing ionic liquid as a solvent.35
Shinkai et al. succeeded in physical gelation of both imidazo-
lium and pyridinium types of ionic liquids by using some
aKey Laboratory of Applied Surface and Colloid Chemistry of Ministry of
Education, School of Chemistry and Chemical Engineering, Shaanxi
Normal University, Xi’an, P. R. China, 710062. E-mail: yfang@snnu.
edu.cn; Fax: +86-29-85310097; Tel: +86-29-85310081
bDepartment of Chemical and Petroleum Engineering, University of
Pittsburgh, Pittsburgh, Pennsylvania, USA, 15261. E-mail: gaod@pitt.
edu; Fax: +1 412-624-9639; Tel: +1 412-624-8488
† Electronic supplementary information (ESI) available: Synthetic
schemes of compounds, rheological properties and gel-to-sol transition
temperature of 1D/IL2 ionogel, FTIR spectra of 1D and 1D/IL2
ionogel, optical images of magnetic ionogel and 13C NMR spectra of
compounds. See DOI: 10.1039/c2sm26332g
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cholesteryl derivatives as gelators and some non-ILs solvents as
co-solvents.36 Recently, a number of ionogels has been devel-
oped by taking amino acid derivatives,15,37 sorbitol deriva-
tives,38 compounds containing urea structure,39 organometallic
compounds,40 and ionic compounds as gelators.41 Albeit these
ionogels possess the characteristics of supramolecular gels, their
mechanical strength, stimulus-responsive and acid/alkali resis-
tance properties are far from that required for practical uses.
Therefore, creating stimulus-responsive, super-stable ionogels
sill remains a big challenge.
Results and discussion
Gelation behaviours and properties
The gelation behaviours of compounds 1–4 (Scheme 1) are
summarized in Table 1. Reference to the table, it is seen that
among the 84 combinations (ILs-cholesteryl derivatives), only 8
of them are gels. However, some of the cholesteryl derivatives gel
some of the ILs efficiently. More exactly, the gelator containing
D-phenylalanine residue (1D) is the most effective gelator, which
can gel four imidazolium salts with different alkyls and anions
(IL2, IL3, IL4 and IL11; Scheme 1), and one methyl-
morpholinium salt (IL12). While compound 1L, which was
obtained by simple replacing the D-phenylalanine residue in 1D
with L-phenylalanine, gels only one ionic liquid (IL12). More-
over, replacing the phenyl group in 1D and 1L with methyl group
(2D, 2L) eliminated their gelation property completely. However,
compound 3, which contains neither phenyl group nor methyl
group, can gel two of the ILs under test (IL11 and IL14).
Compound 4, with no amino acid residue in the structure, could
not gel any of the selected ILs.
Cholesteryl derivatives are one kind of the most important
and powerful LMMGs for organic solvents.12,42 And in
particular, supramolecular gels of unusual properties, including
phase-selective gelation at room temperature, gel emulsion and
gel film formation, and super-gelation etc., have been success-
fully developed by employing the compounds as LMMGs
during the last few years.42–49 However, gelation of ILs with
cholesteryl derivatives has been widely neglected, and in fact
there has been only one report which is relevant to the gelation
of ILs by cholesteryl derivatives till now.36 It is of this reason
that gelation of ILs by some simple but specially designed
cholesteryl derivatives have been investigated. The gelators
have been designed by considering the following points and are
composed of one cholesteryl structure and two hydroxyl
groups.
From the above gelation results, it may be concluded that a
subtle variation in the structures of the cholesteryl derivatives
results in substantial change in the gelation properties of the
compounds, a common phenomenon in supramolecular gels.47
For example, the replacement of aromatic amino acids by a
aliphatic residues clarified the importance of aromatic rings in
ionogelation, a result similar to that reported by Das and co-
workers.15 In addition, the configurations of the amino acid
residues are also important in the gelation. As revealed already,
the compounds containing amino acid residues of D configura-
tion is more effective in gelation than those containing amino
acid residues of L configuration, in particular for the ones with
phenylalanine as the amino acid residue. Upon further inspection
of the results shown in the table, it is also seen that the gelation
(1) ILs possess superior dissolving ability to commonly
found low-molecular mass organic compounds, and this brings
difficulties to the search of effective LMMGs for them.
Considering the versatility of cholesterol-based LMMGs in the
gelation of a variety of solvents, and the highly polar nature of
ILs, it was decided to combine a cholesteryl structure, which
possesses typical hydrophobic property, with hydrophilic
structures.
(2) To improve the adaptiveness of the final cholesteryl
derivatives in the formation of self-assembled network struc-
tures, the hydrophilic part of the compounds to be prepared
should be flexible and possess a variety of hydrogen bonding
formation sites. It was considered that only in this way the
strength of the inter-molecular association of the cholesteryl
derivatives could be strong enough to counter their dissolution
when they are introduced into ILs, and a balance between the
dissolution and precipitation, which is a necessity for formation
of supramolecular gels, may be established. Accordingly, two
hydroxyl groups were introduced at the end of the hydrophilic
part of the cholesteryl derivatives.
(3) Different amino acid residues were chosen as a spacer to
offer both hydrogen bond formation sites and variation in
structures to check if a small difference in the side groups of the
hydrophilic part could significantly affect the gelation behavior
of the compounds in the selected ILs as found in the gelation of
common organic solvents.48
We are lucky to find that some of them are super-effective to
gelate the selected ILs. More interestingly, the ionogels as
developed possess
a number of superior properties, for
example, good mechanical strength, stimulus-responsive prop-
erties, and super gelation talent (CGC, 0.06%, w/w). To the
best of our knowledge, this is the first report on an ionogel
with multiple exceptional properties. This paper reports the
details.
Scheme 1 The chemical structures of cholesteryl-based gelators and
ionic liquids tested.
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Table 1 Gelation behaviors of compounds 1–4 in ILsa
Solvent
1D
1L
2D
2L
3
4
IL1
IL2
IL3
IL4
IL5
IL6
IL7
IL8
P
G(0.06)
G(2.0)
G(1.3)
I
P
P
P
P
P
I
P
P
P
P
P
P
P
I
P
P
I
P
P
P
P
I
P
P
I
P
P
P
P
I
P
P
I
P
I
P
P
P
P
P
I
P
P
IL9
P
P
S
P
P
P
P
I
P
P
P
P
P
I
P
P
P
P
P
P
I
P
P
IL10
IL11
IL12b
IL13
IL14
I
G(2.0)
I
P
G(2.5)
G(1.5)
G(0.8)
P
P
G(1.0)
P
P
P
a
b
G ¼ gel, S ¼ soluble, P ¼ precipitation, I ¼ insoluble. The gel was
formed with water (10%, v/w), the number in bracket is the CGC of
the system (%, w/w).
Fig. 1 Static compression strain vs. stress curve of a cylinder ionogel of
1D/IL2 at 10 mg mLꢀ1 and its rheological behaviors (left inset), the
cylinder ionogel before (a) and after (b) compression (right inset).
behaviours of the compounds are not only dependent upon their
own structures, but also upon the fine structures of the ILs under
study, a result entirely different from other amino acid-based
gelators for ILs.37 For example, 1D gels either IL2 or IL3, but not
IL1, of which the only difference is the length of alkyl side chain
in the imidizolium cation. Beside the substitute alkyl, the anion
can also tune the gelation behaviors. For instance, 1D gels IL2,
but not IL9 and IL11, which contain the same cation but
different anions.
result because of the expectation that the ionogel should be
sensitive to the presence of protons due to existence of a tertiary
amine structure in the gelator. More surprisingly, although the
gelator, 1D, cannot gel water directly through a regular heating–
cooling cycle, a hydrogel of 1D can be prepared by replacing IL2
in 1D/IL2 ionogel with water (Fig. 2d). It is to be noted that the
transformation can be reversed and the process can be repeated
for several times, an observation never reported before.
Effect of external magnetic field upon the magnetic ionogel
Gel stability studies
Inspired by the reports that inorganic micro-/nano-particle based
ionogels are versatile hosts for functional components, such as
As shown in Table 1, among the cholesteryl derivatives, 1D is the
most effective gelator both according to the number of ILs gelled
and the critical gelation concentration (CGC) values (cf. Table 1)
if compared to those of the relevant compounds. Particularly, the
CGC of 1D in IL2 is only 0.06% (w/w), which is almost the lowest
value reported for ionogels till now,40 and falls into the category
of ‘‘super-gelator’’ (CGC < 0.1%, w/w).42 Furthermore, the 1D/
IL2 gel is transparent provided the gelator concentration is lower
than 0.1% (w/w). More interestingly, a self-standing gel could be
prepared by simple injecting a hot solution of 1D in IL2 into a
cylinder mold and then cooling to room temperature (inset (a) in
Fig. 1). The critical pressure to break the self-standing gel (10 mg
mLꢀ1) is 76 Pa (Fig. 1), a value determined by using a dynamic
mechanical analyzer (DMA) on a compress model. This excep-
tional mechanical character was confirmed by the result from
rheological property measurements. Firstly, the value of the yield
stress of the 1D/IL2 ionogel (10 mg mLꢀ1) is 630 Pa (left inset in
Fig. 1), which is much greater than those of other cholesterol-
based physical gels reported till now.37 Secondly, the storage
modulus (G0) of 1D/IL2 ionogel (10 mg mLꢀ1) exhibits week
dependence on frequency sweep (Fig. S1, ESI†), indicating the
good tolerance of the gel to external forces.
Another meaningful character of 1D/IL2 ionogel is its stability
both in neutral and acidic mediums. The ionogel looks like a
fresh one after sealed in a vial for one year at room temperature
(Fig. 2c). Additionally, it was found that 1D/IL2 ionogel (0.5%,
w/v) keeps its gel state for at least one week after addition of 100
mL of hydrochloric acid (36%, Fig. 2e). This is a rather surprising
Fig. 2 The phase behavior of 1D/IL2 (0.5%, w/v) at different conditions.
(a) gelator 1D; (b) IL2; (c) ionogel; (d) hydrogel; (e) gel under HCl
atmosphere; (f) magnetic gel containing Fe3O4; and (g) magnetic gel
under external magnetic field.
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catalysts, luminescent compounds and conductive components,
the inclusive property of 1D/IL2 gel was specially studied. It was
found gratifyingly that the ionogel under study is an ideal host
for micro-/nano-particles (ꢁ50 nm or ꢁ5 mm) of Fe3O4 (Fig. S3,
ESI†), which possesses typical paramagnetic property. The
loading of the particles (ꢁ50 nm) can be as high as 30% (w/w,
Fig. 2f). Presence of an external magnetic field (Neodymium–
Iron–Boron Magnet, maximum pull 18.3 kg, McMaster-Carr)
shows little effect upon the macroscopic property of the ionogel
provided the loading content of the magnetic particles is less than
12% (w/w). However, the gel changes into fluid instantly upon
imposing it within the magnetic field when the loading density of
the magnetic particles extends 20% (w/w, Fig. 2g), a result of
breakage of the gel networks which must be caused by the
magnetic field oriented movement of the particles doped in the
gel (Fig. S3f, ESI†). As expected, the gel-state can be easily
recovered by simple sonication of the system and then by a
treatment of heating–cooling cycle. Furthermore, these processes
can be repeated for many times, a typical and rarely found
magnetorheological fluids (Fig. 2g).46
concentration of the gelator reaches to 0.1% (w/v) as examined
by TEM measurement (Fig. 3h).
Mechanism of the gelation
It is well known that for a physical gel, the main reason for the
existence of it is the formation of 3D networks, which are results
of aggregation of the gelator molecules in the gel. The driving
forces behind the aggregation can be various non-covalent
interactions. In particular, for the present systems, intermolec-
ular hydrogen bonding may play a crucial role considering the
structures of the gelators. Accordingly, the FTIR spectra of 1D
in CDCl3 and that of 1D/IL2 xerogel were recorded and the
results are shown in Fig. S4 (ESI†). It is shown that in solution
state 1D shows a broad band at 3400 cmꢀ1 owing to the coupling
of the stretching vibration of O–H with that of the N–H, and two
sharp bands at 1646 cmꢀ1 and 1541 cmꢀ1 which can be assigned
to the stretching vibration of C]O and the bending vibration of
N–H, respectively. However, with the aggregation of 1D, the
band splits into 3536 cmꢀ1 and 3321 cmꢀ1, and the stretching
vibration of C]O and the bending vibration of N–H shift to
1667 cmꢀ1 and 1569 cmꢀ1, respectively, direct evidences for the
existence of hydrogen bonds in the xerogel. This tentative
conclusion is further supported by the result from 1H NMR
measurements. Fig. 4 shows the temperature- and concentration-
Morphology studies
Scanning electron microscopy observations were conducted to
investigate the network morphologies of some of the ionogels.
For this purpose, their xerogels were prepared by extracting the
ILs from the ionogels with water, and then freezing–dried under
vacuum. Reference to the images (Fig. 3a–d), it was revealed that
the xerogels are characterized by continuous fibrous network
structures no matter what nature of the solvent is. To reveal the
formation process of the gel networks, concentration-dependent
SEM images of the 1D/IL2 xerogels were also taken (Fig. 3e–g).
With reference to the figures, it is clearly seen that the fibrous
structure becomes thinner with decreasing the gelator concen-
tration in the ionogel. For example, the width of the continuous
fiber decreases from 2 mm (1%, w/v) to less than 200 nm (0.2%,
w/v). Moreover, the width decreases to 50 nm when the
1
dependent H NMR spectra of 1D in CDCl3. It is clearly seen
that at 293 K, the amide proton exhibits a 1H NMR signal at d ¼
7.68 ppm. However, the signal shifts to d ¼ 7.61 ppm and d ¼
7.53 ppm at 303 K and 313 K, respectively (Fig. 4, up). With
increase of the concentration of 1D, the signal of the amide
proton significantly shifts to downfield (Fig. 4, down), a definite
evidence of intermolecular hydrogen bonding formation. Similar
to that of amide proton, the signal of hydroxyl protons at about
3.5 ppm shifts to up field along with increasing temperature
(Fig. 4, up). However, unlike amide proton, the hydroxyl proton
is not sensitive to the variation in concentration (Fig. 4, down),
suggesting that the hydroxyl protons may encounter
Fig. 3 SEM images of the xerogels of 1D/IL2 (a), 1D/IL4 (b), 1D/IL12 (c), and 1 L/IL12 (d) (2.5%, w/v); concentration-dependent SEM images of 1D/
IL2 xerogels at 1%, w/v (e), 0.5%, w/v (f), and 0.2%, w/v (g), TEM image of 1D/IL2 ionogel at 0.1%, w/v (h).
Soft Matter
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respectively (Scheme 1), were purchased from Chengjie Chemical
Co. Ltd. (Shanghai, China) and used without further purification.
Gelation test was conducted by adding a certain amount of
gelator in 1 mL ILs under a heating–cooling cycle. IL12 is liq-
uefied by adding 10% of water (H2O/IL ¼ 1 : 10, v/v) in it before
the test as it is a solid at room temperature. The transformation
of the ionogel into a hydrogel was performed by immersing the
ionogel in water for four weeks, and during that period water was
refreshed three times a day. The reverse process was conducted in
an open vial, in which the hydrogel was covered by IL2 and the
water was evaporated naturally. The mechanical strength test of
the gel was performed by using a dynamic mechanical analyzer
(Q800DMA, TA Instrument, USA) at a compression model on
25 ꢂC. For mechanical strength test, a self-standing cylinder of an
ionogel (1.2 cm in diameter and 0.6 cm in height) was prepared
by injecting the hot solution of a gelator in IL2 into a stainless
hollow cylinder mold, cooling slowly to room temperature and
keeping overnight. Rheological experiments were performed on a
stress-controlled rheometer (TA Instruments AR-G2) equipped
with a parallel plate (20 mm diameter). SEM images of the
xerogel were taken on a Quanta 200 SEM (Philips-FEI). The
accelerating voltage was 20 kV, and the emission was 10 mA.
The xerogel was prepared by freezing the obtained hydrogels in
liquid nitrogen followed by frozen drying. For TEM measure-
ment (JEOL JEM-2100), carbon-meshed copper grid was dipped
twice into the above mentioned ‘‘hydrogel’’ and dried at room
temperature. The FTIR spectra of the solution and gel samples
were recorded in a transmission mode by a Bruker Equinox 55
infrared spectrometer. The gel sample for measurement was
prepared by coating it on a KBr slice as a smooth gel film and
Fig. 4 Partial 1H NMR spectra of 1D in CDCl3: up, temperature
dependence at a concentration of 12% (w/v); down, concentration (w/v)
dependence at 25 ꢂC.
intra-molecular hydrogen bonding. Considering the main inter-
actions between the gelator molecules, and the network structure
of the assembly in ionogel as discussed above, the gelation
process could be described as following. At the beginning, the
molecules of the gelator aggregate into fibrils at a molecular level
via intermolecular hydrogen bonding and van der Walls inter-
action, a widely recognized interaction among cholesteryl
moieties, then the fibrils pile up to thicker fibers and networked
structures, and finally, the solvent was confined due to interface
tension and capillary force within the system.
1
then freeze-drying it. H and 13C NMR spectra were recorded
with Bruker AV 600 (600 MHz) NMR spectrometer.
General procedures for preparation of the gelators
General procedures for synthesis of the cholesterol-based
compounds are schematically shown in Scheme S1 (ESI†). Step
(a): a mixture of the hydrochloride salt of an amino acid
derivative of cholesterol (2.5 mmol), which was prepared and
characterized according to the procedures reported before,50
and triethylamine (5 mmol) in 50 mL dry benzene was refluxed
for 4 h and cooled to room temperature. Then 10 mL dry
benzene containing 2.5 mmoꢂl of acryloyl chloride was added
dropwise to the solution at 0 C under stirring. The system was
left to react for another 2 h after finishing the dropping
process. After filtration and evaporation of the solvent, the
residue was re-crystallized from cyclohexane to give the desired
intermediate as white crystals.
Experimental section
Materials and methods
All chemicals were bought from Sinopharm Chemical Reagent
Co. Ltd., Shanghai, China. The solvents were purified according
to the standard methods. Fourteen ILs, which are 1-alkyl-3-
methylimidazolium tetrafluoroborate ([CnImC1]BF4, IL1 (n ¼ 2),
IL2 (n ¼ 4), IL3 (n ¼ 6)), 1-hydroxyethyl-3-methylimidazolium
tetrafluoroborate (IL4), 1-carboxymethyl-3-methylimidazolium
tetrafluoroborate (IL5), 1-butyl-2,3-methylimidazolium tetra-
fluoroborate (IL6), butylpyridinium tetrafluoroborate (IL7), 1-
butyl-1-methylmorpholinium tetrafluoroborate (IL8), 1-butyl-3-
methylimidazolium iodine (IL9), 1-butyl-3-methylimidazolium
hexafluorophosphate (IL10), 1-butyl-3-methylimidazolium bis-
(trifluoromethylsulfony)imide (IL11), 1-butyl-1-methylmorph-
olinium iodine (IL12), 1-butyl-1-methylpyrazolidinium bis(tri-
Step (b): the above intermediate (3.5 mmol) and diethanol-
amine (5.2 mmol) were dissolved in 10 mL CHCl3 and the
solution as prepared was stirred for 7 days at room temperature.
The final mixture was washed with saturated sodium chloride
solution for six times. The organic layer was collected, dried with
anhydrous MgSO4 and then evaporated to dryness. The final
residue was purified by using a silica gel column to give the
desired compound as a white powder. As a control, another
compound 4 (Scheme S2, ESI†) of similar structure to those
listed in Scheme S1† was also designed and prepared, but in this
case, there is no amino acid residue in the structure.
fluoromethylsulfony)imide
(IL13)
and
1-butyl-1-
methylpiperidinium bis(trifluoromethylsulfony)imide (IL14),
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For 10: mp ¼ 117–118 ꢂC (10D), 153–154 ꢂC (10L); [a]2D5 ꢀ46.6
6.6, 13.9 Hz), 2.64 (t, 4H, CH2, J ¼ 9.7 Hz), 2.54 (d, 2H, CH2, J ¼
13.3 Hz), 2.35 (b, 4H, CH2), 2.02–0.68 (m, 41H, cholesteryl
protons). 13C NMR (600 MHz, CDCl3, TMS) 172.9, 172.4,
139.2, 136.3, 129.3, 128.5, 127.0, 123.0, 76.0, 60.0, 56.9, 56.7,
56.2, 53.5, 51.5, 50.1, 42.3, 39.5, 37.8, 37.0, 36.5, 36.2, 35.8, 34.0,
31.9, 30.4, 28.2, 28.0, 27.5, 24.3, 23.8, 22.8, 22.6, 21.1, 19.3, 18.7,
11.9. FTIR (KBr), nmax/cmꢀ1: 3360 (O–H), 2940 (C–H), 1740,
1640 (C]O). Elemental analysis (%): calcd for C43H68N2O5: C,
74.52; H, 9.89; N, 4.04. Found: C, 74.39; H, 9.80; N, 3.63%. MS
(m/z): calcd for [(M + H)+]: 693.5206, found: 693.5164.
1
(20D) (c ¼ 0.003 CHCl3), ꢀ53.6 (20L) (c ¼ 0.0019 CHCl3); H
NMR (600 MHz, CDCl3, TMS): d ¼ 7.27 (m, 3H, C6H5), 7.12 (d,
2H, C6H5, J ¼ 6.9 Hz), 6.30, 6.27 (dd, 1H, CH2]CH, J ¼ 1.1, 15.6
Hz), 6.10 (q, 1H, CH2]CH, J ¼ 10.3 Hz), 6.03 (d, 1H, NH, J ¼ 7.4
Hz), 5.67 (d, 1H, CH2]CH, J ¼ 10.3 Hz), 5.38 (m, 1H, alkenyl),
4.93 (q, 1H, CH, J ¼ 5.8 Hz), 4.63 (m, 1H, oxycyclohexyl), 3.17 (d,
2H, CH2, J ¼ 5.7 Hz), 2.33–2.21 (b, 2H, CH2), 2.02–0.68 (m, 41H,
cholesteryl protons). 13C NMR (600 MHz, CDCl3, TMS) 171.0,
164.9, 139.2, 135.9, 130.4, 129.5, 128.5, 127.1, 123.0, 75.6, 56.7,
56.2, 53.3, 50.0, 42.3, 39.5, 38.0, 37.9, 36.9, 36.6, 36.2, 35.8, 31.9,
31.8, 28.2, 28.0, 27.7, 24.3, 23.8, 22.8, 22.6, 21.1, 19.3, 18.7, 11.9.
FTIR (KBr), nmax/cmꢀ1: 3300 (N–H), 3040 (C–H), 1740 (C]O).
Elemental analysis (%): calcd for C39H57NO3: C, 79.68; H, 9.77;
N, 2.38. Found: C, 79.52; H, 9.46; N, 2.17%.
For 20: mp ¼ 133–134 ꢂC (20D), 148–149 ꢂC (20L); [a]2D5 ¼ ꢀ8.0
(20D), ꢀ26.1 (20L) (c ¼ 0.003 CHCl3); 1H NMR (600 MHz,
CDCl3, TMS): d ¼ 6.30 (d, 1H, CH2]CH, J ¼ 17.0 Hz), 6.21 (b,
1H, NH), 6.14 (q, 1H, CH2]CH, J ¼ 10.3 Hz), 5.67 (d, 1H,
CH2]CH, J ¼ 10.3 Hz), 5.38 (d, 1H, alkenyl, J ¼ 4.9 Hz), 4.66
(m, 2H, CH and oxycyclohexyl), 2.33 (m, 2H, CH2), 2.02–0.68
(m, 44H, CH3 and cholesteryl protons). 13C NMR (600 MHz,
CDCl3, TMS) 172.6, 164.9, 139.3, 130.6, 126.9, 123.0, 75.4, 56.7,
56.2, 50.0, 48.3, 42.3, 39.5, 38.0, 36.9, 36.6, 36.2, 35.8, 31.9, 31.8,
28.2, 28.0, 27.6, 24.3, 23.9, 22.8, 22.6, 21.1, 19.3, 18.7, 11.9. FTIR
(KBr), nmax/cmꢀ1: 3300 (N–H), 3040 (C–H), 1740 (C]O).
Elemental analysis (%): calcd for C33H53NO3: C, 77.45; H, 10.44;
N, 2.74. Found: C, 77.08; H, 10.50; N, 3.01%.
For 30: mp ¼ 167–168 ꢂC; [a]D25 ¼ ꢀ40.9 (c ¼ 0.003 CHCl3); 1H
NMR (600 MHz, CDCl3, TMS): d ¼ 6.32 (d, 1H, CH2]CH, J ¼
17.0 Hz), 6.16 (q, 1H, CH2]CH, J ¼ 10.3 Hz), 6.10 (b, 1H, NH),
5.70 (d, 1H, CH2]CH, J ¼ 10.3 Hz), 5.38 (d, 1H, alkenyl, J ¼
4.7 Hz), 4.70 (m, 1H, oxycyclohexyl), 4.10 (d, 2H, CH2, J ¼ 5.0
Hz), 2.34 (d, 2H, CH2, J ¼ 7.0 Hz), 2.03–0.68 (m, 41H, choles-
teryl protons). 13C NMR (300 MHz, CDCl3, TMS) 169.4, 165.5,
139.3, 130.2, 127.2, 123.0, 75.6, 56.7, 56.2, 50.0, 42.3, 41.7, 39.5,
38.0, 36.9, 36.6, 36.2, 35.8, 31.9, 31.8, 28.2, 28.0, 27.7, 24.3, 23.9,
22.8, 22.6, 21.1, 19.3, 18.7, 11.9. FTIR (KBr), nmax/cmꢀ1: 3300
(N–H), 3080, 2950 (C–H), 1750 (C]O). Elemental analysis (%):
calcd for C32H51NO3: C, 77.22; H, 10.33; N, 2.81. Found: C
77.11; H, 10.33; N, 2.51%.
For 40: mp ¼ 125–126 ꢂC; [a]D25 ¼ ꢀ41.2 (c ¼ 0.003 CHCl3); 1H
NMR (600 MHz, CDCl3, TMS): d ¼ 6.40, 6.37 (dd, 1H, CH2]
CH, J ¼ 1.4 Hz, 15.9 Hz), 6.10 (q, 1H, CH, J ¼ 10.4 Hz), 5.80 (dd,
1H, CH2]CH, J ¼ 1.4, 10.4 Hz), 5.38 (d, 1H, alkenyl, J ¼ 4.8 Hz),
4.70 (m, 1H, oxycyclohexyl), 2.36 (d, 2H, CH2, J ¼ 7.1 Hz), 2.02–
0.68 (m, 41H, cholesteryl protons). 13C NMR (600 MHz, CDCl3,
TMS) 165.6, 139.6, 130.2, 129.1, 122.7, 74.1, 56.7, 56.2, 50.1, 42.3,
For 2 (purified by a silica gel column eluting with tetrahy-
drohexane–hexane (3 : 1, v/v)): mp ¼ 119–120 ꢂC (2D), 116–117
1
ꢂC (2L); [a]D25 ¼ ꢀ15.3 (2D), ꢀ49.4 (2L) (c ¼ 0.003 CHCl3); H
NMR (600 MHz, CDCl3, TMS): d ¼ 7.37 (b, 1H, NH), 5.36 (s,
1H, alkenyl), 4.66 (b, 1H, CH), 4.54 (m, 1H, oxycyclohexyl), 3.72
(t, 2H, OH, J ¼ 6.0 Hz), 3.62 (b, 4H, CH2), 2.72 (b, 4H, CH2),
2.60 (b, 2H, CH2), 2.45–2.30 (m, 4H, CH2), 2.02–0.68 (m, 44H,
CH3 and cholesteryl protons). 13C NMR (600 MHz, CDCl3,
TMS) 174.3, 172.4, 139.2, 123.0, 75.7, 59.9, 56.8, 56.7, 56.1, 51.2,
50.0, 48.3, 42.3, 39.5, 37.8, 36.9, 36.6, 36.2, 35.8, 34.1, 31.9, 28.2,
28.0, 27.6, 24.3, 23.8, 22.8, 22.6, 21.0, 19.3, 18.7, 18.0, 11.9. FTIR
(KBr), nmax/cmꢀ1: 3390 (O–H), 2940 (C–H), 1740, 1660 (C]O).
Elemental analysis (%): calcd for C37H64N2O5: C, 72.04; H,
10.46; N, 4.54. Found: C, 71.62; H, 10.45; N, 4.52%. MS (m/z):
calcd for [(M + H)+]: 617.4893, found: 617.4869.
For 3 (purified by a silica gel column eluting with tetrahy-
drohexane–cyclohexane, 8 : 1, v/v): mp ¼ 81–82 ꢂC; [a]D25 ¼ ꢀ31.7
(c ¼ 0.003 CHCl3); 1H NMR (600 MHz, CDCl3, TMS): 8.13 (b,
1H, NH), 5.37 (s, 1H, alkenyl), 4.63 (m, 1H, oxycyclohexyl), 3.95
(d, 2H, CH2, J ¼ 4.5 Hz), 3.75 (m, 4H, CH2OH), 3.60 (t, 2H, OH,
J ¼ 5.6 Hz), 3.14 (b, 2H, CH2), 2.93 (q, 2H, CH2, J ¼ 6.7 Hz), 2.61
(s, 4H, CH2), 2.50 (m, 4H, CH2), 2.32 (m, 2H, CH2), 2.02–0.68 (m,
41H, cholesteryl protons). 13C NMR (600 MHz, CDCl3, TMS)
172.4, 170.2, 139.3, 122.9, 75.5, 62.0, 58.1, 56.7, 56.3, 56.2, 50.7,
50.0, 42.3, 39.7, 39.5, 37.9, 36.9, 36.5, 36.2, 35.8, 31.9, 31.8, 28.2,
28.0, 27.6, 24.3, 23.9, 22.8, 22.6, 21.0, 19.3, 18.7, 11.9. FTIR
(KBr), nmax/cmꢀ1: 3390 (O–H), 2940 (C–H), 1740, 1660 (C]O).
Elemental analysis (%): calcd for C35H60N2O5: C, 71.49; H, 10.27;
N, 4.76. Found: C, 71.72; H, 10.37; N, 4.65%. MS (m/z): calcd for
[(M + H)+]: 603.4737, found: 603.4697.
For 4 (purified by a silica gel column eluting with tetrahy-
drofuran–n-hexane, 2 : 1, v/v): mp ¼ 58–59 ꢂC; [a]D25 ꢀ28.4 (c ¼
0.003 CHCl3); 1H NMR (600 MHz, CDCl3, TMS): d ¼ 5.36 (m,
1H, alkenyl), 4.65 (m, 1H, oxycyclohexyl), 3.62 (t, 2H, OH, J ¼
5.2 Hz), 3.52 (m, 2H, CH2), 2.84 (q, 2H, CH2, J ¼ 6.0 Hz), 2.65 (t,
4H, CH2, J ¼ 5.2 Hz), 2.48 (t, 4H, CH2, J ¼ 6.2 Hz), 2.32 (m, 2H,
CH2), 2.02–0.68 (m, 41H, cholesteryl protons). 13C NMR (600
MHz, CDCl3, TMS) 172.3, 139.4, 122.7, 74.3, 59.3, 56.6, 56.1,
56.07, 50.0, 42.2, 39.7, 39.5, 38.0, 36.9, 36.5, 36.2, 35.8, 31.9, 31.8,
28.2, 28.0, 27.7, 24.2, 23.9, 22.8, 22.6, 21.0, 19.3, 18.7, 11.8. FTIR
(KBr), nmax/cmꢀ1: 3410 (O–H), 2940 (C–H), 1730 (C]O);
elemental analysis (%): calcd for C34H59NO4: C, 74.81; H, 10.89;
N, 2.57. Found: C, 74.98; H, 11.16; N, 2.34%. MS (m/z): calcd for
[(M + H)+]: 546.4522, found: 546.4490.
39.8, 39.5, 38.1, 37.0, 36.6, 36.2, 35.8, 31.9, 31.8, 28.2, 28.0, 27.8,
ꢀ1
24.3, 23.9, 22.8, 22.6, 21.1, 19.4, 18.7, 11.9. FTIR(KBr), nmax/cm
:
2940 (C–H), 1720 (C]O). Elemental analysis (%): calcd for
C30H48O2: C, 81.76; H, 10.98. Found: C, 81.91; H 11.06%.
For 1 (purified by a silica gel column eluting with tetrahy-
drohexane–hexane (3 : 1, v/v)): mp ¼ 101–102 ꢂC (1D), 90–91 ꢂC
(1L); [a]2D5 ¼ ꢀ29.6 (1D), ꢀ13.0 (1L) (c ¼ 0.003 CHCl3); 1H
NMR (600 MHz, CDCl3, TMS): d ¼ 7.58 (b, 1H, NH), 7.29 (m,
3H, C6H5), 7.17 (d, 1H, J ¼ 7.3 Hz), 5.38 (b, 1H, alkenyl), 4.82
(q, 1H, CH, J ¼ 4.8 Hz), 4.64 (m, 1H, oxycyclohexyl), 3.64 (t, 2H,
OH, J ¼ 8.5 Hz), 3.52 (b, 4H, CH2), 3.13, 3.10 (dq, 2H, CH2, J ¼
Conclusion
A number of stable and smart ionogels were successfully created
by using specially designed and synthesized cholesteryl
Soft Matter
This journal is ª The Royal Society of Chemistry 2012

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19 K. Lunstroot, K. Driesen, P. Nockemann, K. V. Hecke,
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This work was supported by the Natural Science Foundation of
China (Nos. 91027017, 21273141, 20902055), the 13115 program
of Shaanxi Province (no. 2010 ZDKG-89), Program for
Changjiang Scholars and Innovative Research Team in Univer-
sity (IRT1070), China Scholarship Council and National Science
Foundation of USA (Grant CBET 0967722).
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Soft Matter