A new aromatic amino acid based organogel for oil spill recovery

Article abstract of DOI:10.1039/c2jm30711a

An aromatic amino acid (phenylglycine) based amphiphile with amide and ester groups and a long fatty acyl chain has been found to form organogels selectively in the fuel hydrocarbon solvents including hexane, heptane, cyclohexane, diesel, kerosene and pump-oil at room temperature. Organogels have been well characterized morphologically by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Morphological studies of these xerogels have revealed the presence of fascinating right-handed twisted nanoribbons (in n-heptane and n-octane). Involvement of different non-covalent interactions among the gelator molecules within the gel matrix has been studied using FT-IR and XRD. The organogel in diesel is mechanically stable with high yield stress (177.8 Pa) and storage modulus (>10⁴ Pa) values, as has been evidenced from the rheological studies. Interestingly, this gelator compound exhibits phase selective gelation properties and the phase selective gelation occurs efficiently and quickly (within 90 s), in oil-water mixtures and the gelator molecule can be recovered and reused several times easily, indicating its applicability in oil spill cleaning.

Full text of DOI:10.1039/c2jm30711a

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PAPER
A new aromatic amino acid based organogel for oil spill recovery†
*
Shibaji Basak, Jayanta Nanda and Arindam Banerjee
Received 6th February 2012, Accepted 6th April 2012
DOI: 10.1039/c2jm30711a
An aromatic amino acid (phenylglycine) based amphiphile with amide and ester groups and a long fatty
acyl chain has been found to form organogels selectively in the fuel hydrocarbon solvents including
hexane, heptane, cyclohexane, diesel, kerosene and pump-oil at room temperature. Organogels have
been well characterized morphologically by field emission scanning electron microscopy (FE-SEM) and
atomic force microscopy (AFM). Morphological studies of these xerogels have revealed the presence of
fascinating right-handed twisted nanoribbons (in n-heptane and n-octane). Involvement of different
non-covalent interactions among the gelator molecules within the gel matrix has been studied using FT-
IR and XRD. The organogel in diesel is mechanically stable with high yield stress (177.8 Pa) and
storage modulus (>104 Pa) values, as has been evidenced from the rheological studies. Interestingly, this
gelator compound exhibits phase selective gelation properties and the phase selective gelation occurs
efficiently and quickly (within 90 s), in oil–water mixtures and the gelator molecule can be recovered
and reused several times easily, indicating its applicability in oil spill cleaning.
dispersants,19 sorbents20 and solidifiers.21 Dispersants emulsify
Introduction
the oil and sorbents are solid powders, which absorb the oil from
the oil–water mixture. Sometimes, these materials are toxic to
marine life. On the other hand, solidifiers can be polymers, which
convert the oil to a solid or semi-solid like state. However, the
recovery of the oil from that solid is really difficult.
Phase selective gelation22 of organic solvents (oil) from oil–
water mixtures can be an excellent way for oil spill recovery.
Bhattacharya and co-workers first reported the phase selective
gelator (PSG) by an alanine-based amphiphile that gel organic
solvents in presence of water.22a There are several other reports
regarding phase selective gelator molecules. However, they have
some limitations to use in real situations, because, phase selective
gelation can only be achieved after a heating–cooling cycle to
immobilize the oil from oil–water mixture.22a,e
Low molecular weight gels1 (LMWGs) are an important class of
soft materials owing to their many interesting properties such as
structure directing agents,2a stabilization of organic photo-
chromatic material,2b in situ formation and stabilization of
nanoparticles,2c light harvesting materials,2d dental composite
carriers,2e preparing dye sensitized solar cells2f and others.2g–l
However, research and development of functional organogels3–16
still remains a challenging task. Oil spills are a serious problem to
mankind. An oil spill is a release of liquid petroleum oil into the
environment, which creates environmental hazards. In recent
decades, the world has faced several accidents regarding the
marine oil spill, which brings about an irrecoverable damage to
environment especially to marine life.17 So, there is a great need
to develop techniques for managing this type of pollution. In this
context, a commonly used process available to clean up an oil
spill is known as bioremediation,18 in which microorganisms are
used for the cleaning up procedure. In the bioremediation
process, hydrocarbons are degraded to carbon dioxide and water
by the help of bacteria and it takes nearly 28 days for 98%
conversion. Other materials available in oil spill recovery are
The ideal PSG for oil spill treatment in real situation must
fulfil some requirements such as: (a) gelation of the oil phase
selectively and efficiently, (b) instant gelation at room tempera-
ture, (c) the gelator can be easily synthesized from cheap starting
materials, (d) easy recovery of the oil from the gel phase mate-
rials, (e) the gelator should be recyclable for reuse.23 Several
research groups have also reported the phase selective gelation by
using a change in the pH of the medium22b or by mechanical
shaking22c or sonication.22d Another way to achieve phase selec-
tive gelation at room temperature is by adding a gelator
compound (dissolved in a co-solvent) into the oil–water mixture
and it is a quite feasible process in real situation for oil spill
recovery. John and co-workers recently demonstrated a model
study regarding oil spill treatment by using sugar amphiphiles.23
These gelators gel the oil part selectively from an oil–water
mixture and ethanolic solution of gelators is required for
Department of Biological Chemistry, Indian Association for the Cultivation
of Science, Jadavpur, Kolkata-700 032, India. E-mail: bcab@iacs.res.in;
arindamkol1966@gmail.com; Fax: +91-332473-2805; Tel: +91-332473-
4971
1
† Electronic supplementary information (ESI) available: H NMR, 13C
NMR, HRMS of the synthesized amino acid based amphiphiles, the
FE-SEM images in the higher concentration, wide angle XRD in gel
state, model of self-assembly, tand vs. oscillatory stress of the
amphiphile P1 and a picture of phase selective gelation in a beaker. See
DOI: 10.1039/c2jm30711a
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gelation. But, it took much more time to become a stiff gel. So,
there is a genuine need for the discovery and development of
gelator that can phase selectively gel fuel oils instantly. The
molecules with long fatty acyl chain, hydrogen bonding func-
tionality including amide and ester groups and aromatic residue
can be self-assembled nicely utilizing various non-covalent
interactions including van der Waals interaction, hydrogen
bonding and aromatic–aromatic interactions to form a three
dimensional network structure with lots of interstitial cavities
occupied by solvent molecules to form gel. Herein, we report
a simple amino acid phenylglycine based amphiphilic new gelator
molecule P1 (Scheme 1) which selectively, efficiently and
instantly can immobilize the fuel oils from the oil–water mixture.
The gelator acts as a phase selective, thermo-reversible organo-
gelator, which selectively gelate the oil phase in the oil–water
mixture and satisfy all the above mentioned requirements and are
promising for oil spill treatment.
Fig. 1 (a) n-Heptane gel in an inverted gel vial. (b) Inverted gel vial
showing typical phase selective gelation exposing gelled heptane layer and
intact water layer.
the gelator molecules by competing with the hydrogen bonding
sites. However, in this case the gel formation ability of the
amphiphilic gelator P1 remains undisturbed and the organogel is
stable over months in the presence of water (data not shown).
The phase selective gelation is very efficient in various above-
mentioned solvents and oils. The uniqueness of this study is that
this new gelator molecule can phase selectively gelate fuel-oils in
presence of water relatively very quickly (within 90 s). These gels
are stable over months, indicating their high stability. The
thermal stability of the gel in different organic solvents has been
measured by determining the gel melting temperature (Tgel) at
MGC. It has been performed by heating organogels in a ther-
mostat controlled water bath at a heating rate of 1 ꢀC/5 min until
it has melted. The Tgel values (at MGC) of the gels prepared in
various hydrocarbon solvents and oils have been found to be
Results and discussion
Gelation ability and thermal stability
The aromatic amino acid phenylglycine based amphiphile P1
forms a supramolecular gel in various aliphatic hydrocarbons
(hexane, heptane, octane, cyclohexane and methylcyclohexane)
including diesel, kerosene, and pump oil efficiently and instantly
(Fig. 1). The gelation ability of new gelator has been summarized
in Table 1. Interestingly, this amphiphile P1 can selectively gel
only aliphatic hydrocarbons, but not aromatic hydrocarbons
including benzene, toluene and others. From Table 1, it has been
found that the minimum gelation concentrations (MGC) of P1 in
different solvents are ranging from 0.5 to 2.0% (w/v). We are
curious to know whether there is any structural effect on P1 in
gelation. The side chain of the gelator molecule has been changed
from phenylglycine (P1) to phenylalanine (P2) and alanine (P3)
separately keeping the long alkyl chain and other functionalities
intact (Scheme 1). These modifications have been done to address
the question of whether these two molecules, P2 and P3, can form
gel under similar conditions or not. It is interesting to note that
P2 and P3 cannot form any kind of gel, not only in fuel solvents
including hydrocarbons, diesel and others, but also in other
tested solvents including benzene, toluene, ethanol, hexanol
under similar conditions. In P2, an additional –CH2 group in the
side chain brings flexibility and in P3, the aromatic group is
absent. The lack of flexibility and the presence of aromatic group
in side chain may be the important factor for gelation in this
study. Interestingly, P1 has been found to act as a PSG, which
can selectively gel the oil part of an oil–water mixture keeping the
water part intact (Fig. 1b). Presence of water molecules in
the organogel medium can disrupt the self-assembly process of
ꢀ
ranging from 38–50 C (Table 1). The calculated error range in
gel melting temperature (Tgel) determination has been found to
be ꢁ1 ꢀC. These organogels have been found to be thermo-
reversible in nature in various hydrocarbon solvents. Differential
scanning calorimetry (DSC) experiments have been carried out
to scrutinize the thermo-reversibility of the gel (Fig. 2).
Table 1 The gelation ability of amphiphile P1 in various organic
solvents and hydrocarbons
Solvents
Statea
MGC (% w/v)
Tgel at MGC (ꢀC)
n-Hexane
n-Heptane
n-Octane
Petroliumbenzine
Isooctane
Cyclohexane
Methylcyclohexane
Benzene
Chlorobenzene
1,2-Dichlorobenzene
Toluene
Chloroform
Methanol
Ethanol
n-Hexanol
Ethyl acetate
Kerosine
G
G
G
G
G
G
G
S
S
S
S
S
S
S
S
S
G
G
G
1.07
0.63
0.51
1.16
1.23
2.02
2.06
—
—
—
—
—
—
—
—
—
1.55
1.03
1.47
38
41
42
49
47
45
46
—
—
—
—
—
—
—
—
—
50
46
47
Diesel
Pump oil
a
Scheme 1 Chemical structures and the one step synthetic procedure of
amphiphiles P1, P2 and P3.
G ¼ Gel, S ¼ Solution.
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It has been observed from Fig. 2 that the gel material in n-
heptane has shown an endotherm on heating and an exotherm on
cooling. The temperature difference between the endotherm and
the exotherm is in the range of 20 ꢀC, which indicates the
hysteresis. This is a characteristic feature of first order phase
transition.24
Morphological study
Morphological features of these organogels have been investi-
gated using field emission scanning electron microscopy (FE-
SEM) and atomic force microscopy (AFM) studies. Both studies
in Fig. 3 indicate the formation of one dimensional twisted
ribbon25 network structures in xerogel state obtained from P1
gels. FE-SEM images of the organogels have been presented in
the Fig. 3a–b in n-heptane and n-octane solvents respectively and
twisted ribbons have been observed in both solvents. In relatively
higher concentration, an interwoven three dimensional network
structure (ESI, Fig. S10†) has been obtained from the assembly
of these nanoribbons and the network structure might be
responsible for entrapment of large volumes of organic solvents.
The single ribbon obtained from n-octane has been found several
micrometers in length with 170–175 nm width (Fig. 3b). The
twisted ribbons obtained from the n-heptane gel have also shown
nearly equal length and width (Fig. 3a). So, the effect of solvent is
not pronounced on nanostructure of ribbons. Similar kind of
morphological features have been noticed using AFM studies in
n-heptane and n-octane solvents (Fig. 3c and 3d). Both of these
microscopy studies (FE-SEM and AFM) clearly indicate that P1
forms a right-handed twisted ribbon structure in the above-
mentioned solvents.
Fig. 3 (a) and (b) FE-SEM images of P1 in n-heptane and n-octane
solvents respectively, (c) and (d) AFM images of P1 in n-heptane and n-
octane solvents respectively (scale bar 1 mm). The inset of c shows a single
ribbon. Both microscopy studies show the right-handed twisted ribbons.
for ester >C]O stretching band have been found in heptane gel.
These data indicate that hydrogen-bonding interaction is playing
a major role in self-association of the gelator molecules to form
the gel.
XRD study
X-ray diffraction (XRD) experiments have been carried out to
obtain information about the molecular packing of self-assem-
bled amphiphile P1 in the gel state. Fig. 5 shows the XRD pattern
of the xerogel prepared from n-octane in small angle and wide
angle regions respectively. In the low angle region (Fig. 5a),
a distinct peak at 2q ¼ 3.1ꢀ has been observed and it corresponds
FT-IR study
FT-IR studies of the gelator amphiphile in solution state as well
as in gel state have been performed to examine whether hydrogen
bond driven aggregation is taking place in gel state. The results of
the FT-IR studies have been plotted in the Fig. 4 in solution as
well as in the gel state. The NH stretching band of P1 in solution
state at 3427 cmꢂ1 has shifted to 3309 cmꢂ1 in heptane gel. The
amide I (amide >C]O stretching) band has appeared at 1682
cmꢂ1 for solution, and it has been shifted to 1649 cmꢂ1 in heptane
gel. Other peaks at 1534 cmꢂ1 for amide II band and at 1740 cmꢂ1
ꢀ
to the d spacing value of 28.31 A (D). This value is smaller than
twice of the calculated molecular length of P1, but larger than the
ꢀ
length of one molecule of P1 (24.3 A). This can arise due to the
intercalation of the alkyl chains of the gelator molecules.
The wide angle XRD pattern (Fig. 5b) of the xerogel shows
periodical diffraction peaks and this indicates that P1 is
Fig. 4 FT-IR spectra of the amphiphilic gelator P1 in n-heptane solvent
Fig. 2 DSC diagram of P1 gel in n-heptane (4.1% w/v).
11660 | J. Mater. Chem., 2012, 22, 11658–11664
at solution and in the gel state.
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applied angular frequency under a constant strain 0.1%. It is
worth mentioning that G0 and G00 respectively symbolize the
ability of the deformed material to restore its original geometry
and tendency of a material to flow. In this study, the storage
modulus (G0) is higher than the loss modulus (G00) and does not
cross to each other throughout the experimental region (Fig. 6a).
This observation suggests the formation of soft solid-like gel
material.27a–c,f This suggests that the gel matrix has good tolerance
towards the external forces.26f Both the storage and loss moduli
are dependent on frequency. The storage modulus of the diesel gel
is in the order of 104 Pa indicating its higher mechanical strength
compared to other previously reported supramolecular gel.27a
In another typical experiment, the storage modulus and loss
modulus have been measured with respect to oscillatory stress in
a oscillatory stress sweep experiment.27d–e It is evident from the
Fig. 6b, the storage modulus is higher than loss modulus initially
and at a certain stress (at 177.83 Pa) the storage modulus and loss
modulus crosses each other. This is called the yield stress. High
storage modulus, high yield stress and low tand value (<0.1 up to
oscillatory stress 13 Pa, see ESI, Fig. S13†) indicate the forma-
tion of a stiff gel material in diesel.
Oil spill recovery
The gelation ability of P1, selectively in hydrocarbon solvents and
in oils, efficiently and instantly, at room temperature has attracted
us to use P1 as a phase selective gelator for oil spill cleaning. The
gelator amphiphile P1 shows the phase selective gelation of the oil
phase in the presence of water in an oil–water mixture within 90 s.
Instant gelation is required for oil spill recovery and to avoid the
Fig. 5 XRD diffraction pattern of the xerogel obtained from n-octane
solvent: (a) in low angle (1ꢀ–5ꢀ) and (b) wide angle (5ꢀ–30ꢀ) regions.
self-assembled into an ordered structure. Periodic peaks at 6.55ꢀ
(D/2), 9.36ꢀ (D/3), 12.45ꢀ (D/4), 15.58ꢀ (D/5), 18.82ꢀ (D/6) and
21.75ꢀ (D/7) indicate the existence of one dimensional lamellar
structure in the gel state.26a The peak at 2q ¼ 19.85 (d ¼ 4.44 A)
ꢀ
ꢀ
corresponds to hydrogen bonding distance of gelator moleculeꢀs
ꢀ
ꢀ
in the gel state. The peaks at 2q ¼ 22.62 (d ¼ 3.9 A) and 11.18
ꢀ
(d ¼ 7.88 A) can correspond to the packing distance between
long alkyl chains of gelator molecules.26b Another peak at 23.65ꢀ
ꢀ
with a d spacing value of 3.7 A can correspond to p–p stacking
distance of the aromatic phenyl ring of the gelator molecules.26c
According to the XRD data, it can be assumed that the helical
ribbons consist of repeating layered structural units and it is
evidenced by the periodic peaks obtained from the wide angle
XRD data. The exact reason(s) for the formation of helical
ribbons still remains to be unclear. It is assumed that the
amphiphilic gelator molecules undergo self-association to form
lamellar assembly, which further self-assemble using various
non-covalent interactions and the presence of chiral phenyl-
glycine moiety may assist the formation of the helical ribbon
structure. A probable self-assembling model is presented in
Fig. S12 (see ESI†).
Rheology study
The study of the mechanical strength of these gels is important to
find its utility. These gels have been subjected to rheological
analysis to study their viscoelastic properties. For rheological
study, gels have been prepared in diesel in 2.0% (w/v). An angular
frequency sweep experiment has been performed. In a typical
frequency sweep experiment, the variation of storage modulus
(G0) and loss modulus (G00) has been monitored as a function of
Fig. 6 Dynamic rheology of diesel gel contained 2.0% (w/v) gelator (a)
frequency sweep and (b) oscillatory stress sweep experiment at 25 ꢀC.
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spreading of oil over river- or sea-water. The merits of our gelator
amphiphile are instant phase selective gelation at room tempera-
ture and the reusability of the gelator compound. The phase
selective gelation test has been performed in several solvents
including diesel and pump oil and the phase selectivity was found
with much efficiency. Phase selectivity at room temperature has
been achieved by adding the ethanolic solution of gelator into the
oil–water mixture. The gelator P1 is highly soluble in ethanol at
room temperature and it cannot gelate the ethanolic solution,
even at higher concentrations. It has been observed in this study
that diesel gel has been efficiently formed by using the gelator P1 in
the presence of a small amount of ethanol. Although the presence
of a small amount of ethanol can change the solvation properties
of entire liquid system, the gelation efficiency of P1 has not been
apparently affected.
formation of gel phase material. By simply heating, gel to solu-
tion transition can be performed. Gel (diesel gel) can be scooped
from the glass vial and it can be subjected to distillation. The
water can also be syringed out from the vial and the gel can be
subjected to distillation. However, the gel phase separation from
the water is more preferable to recover of the oil part due to its
practical use. The scooped gel has been taken in a round bottom
flask (Fig. 7d) and then it has been vacuum distilled (Fig. 7e). The
ꢀ
gel melts at 47 C and the diesel is subsequently distilled off in
a round bottom flask. Thus, oil can be collected almost quanti-
tatively. The residue found in round bottom flask has been
characterized by mass spectrometry and the gelator P1 is found
to be intact for further use.
Conclusion
In this study, 20.0 mg P1 has been dissolved in 200 mL ethanol
and added to a 1 mL : 0.8 mL mixture of diesel and water in a glass
vial. In the course of the process, the diesel phase has been con-
verted to gel within 90 s, keeping the water phase intact. Phase
selective gelation process has also been observed with 20.0 mg P1
in a small amount of ethanol (100 mL of ethanol and 900 mL
diesel). This gel is stiff enough to keep its own weight in the
presence of an upper layer occupied by the water in an inverted
glass vial (Fig. 7c). Thus, we can treat the oil spill nearly quanti-
tatively. Interestingly, in this study the phase selective gelation has
not been disturbed in the presence of a saturated salt solution of
NaCl, CaCl2 and acidic or basic water medium and this process
canbescaled-up (Fig. S14†)promising forthe potential real useon
the basis of gelation in the presence of salt solution. This supports
the real use of this gelator molecule for phase selective gelation of
oil phase from the oil–water mixture in the sea or river.
In this study, an aromatic amino acid based new gelator molecule
has been discovered for the phase selective gelation of fuel oil
from the oil–water mixture instantly at room temperature. Other
advantages of our method are (i) the gelator molecules can be
synthesized from cheap starting materials using a single step
reaction, (ii) the gelator molecules can be recycled multiple times
for reuse and (iii) spilled oil can be almost quantitatively recov-
ered from the gel by a simple distillation procedure. This gelator
molecule holds future promise for oil spill recovery treatment.
Experimental section
Materials
L-Phenylalanine, L-alanine, L-phenylglycine and myristic acid
were purchased from Aldrich. HOBt (1-hydroxybenzotriazole),
DCC (N,N0-dicyclohexylcarbodiimide), and all gelling solvents
were purchased from SRL, India.
One important feature in oil spill treatment is to recover the oil
part after its immobilization in gel phase. Non-covalent inter-
actions including hydrogen bonding, van der Waals interaction
and others are weak in nature. They are responsible for the
Methods
Amino acid based amphiphiles were synthesized by conventional
solution phase methodology using racemization free fragment
condensation strategy. The C-terminus was protected as a methyl
ester. Couplings of myristic acid and corresponding methyl ester
of amino acids (Scheme 1) were mediated by DCC/HOBt. All
compounds were purified by column chromatography using
silica gel (100–200 mesh size) as stationary phase and chloroform
and ethyl acetate as eluent. Finally, compounds were charac-
1
terized by H NMR (300 MHz), 13C NMR (75 MHz) and mass
spectrometry.
General procedure for synthesis
Myristic acid (4.56 g, 20 mmol) was placed in 10 mL DMF and
cooled in an ice-water bath. Then the corresponding methyl ester
(H-Phg-OMe/H-Phe-OMe/H-Ala-OMe) was isolated from the
corresponding methyl ester hydrochloride salt (40 mmol) by
neutralization, subsequent extraction with ethyl acetate and
concentrate to 10 mL. Then it was added to the reaction mixture,
followed immediately by DCC (4.12 g, 20 mmol) and HOBt
(3.06 g, 20 mmol). The reaction mixture was stirred for three
days. The reaction mixture was taken in ethyl acetate (60 mL)
and the DCU (N,N0-dicyclohexylurea) was filtered off. The
Fig. 7 Phase selective gelation and recovery of diesel: (a) 200 mL of
ethanol solution of P1, (b) 1 mL water and 0.8 mL diesel mixture, (c)
mixture of (a) and (b) results in phase selective gelation within 90 s, (d)
scooped gel (in several batches) taken in a round bottom flask, (e) the
distillate diesel collected in a round bottom flask.
11662 | J. Mater. Chem., 2012, 22, 11658–11664
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organic layer was washed with 1 M HCl (3 ꢃ 50 mL), brine (2 ꢃ
50 mL), 1 M sodium carbonate (1 ꢃ 50 mL), brine (2 ꢃ 50 mL)
and then dried over anhydrous sodium sulphate and evaporated
in vacuum to yield peptide as a white solid. Purification was done
by silica gel column (100–200 mesh) using chloroform and ethyl
acetate as eluent.
carried out by placing a small amount of sample on a mica foil.
The material was then allowed to dry in air first by slow evap-
oration and then under vacuum at room temperature for a few
hours. Images were taken using an Autoprobe CP Base Unit di
CP-II instrument (model no. AP-0100).
Differential scanning calorimetry (DSC). Thermal behavior of
the gel was studied using a Perkin-Elmer differential scanning
calorimeter (Diamond DSC-7) working under N2 atmosphere.
Gel sample was taken in large volume capsule (LVC) tightly
seaꢀled with an O-ring. Gel samꢀple was then heated from 20 ꢀC to
90 C at the heating rate of 5 C minꢂ1. A cooling run was also
taken after waitiꢀng 10 min at 90 ꢀC and then cooling at a rate of 2
ꢀC minꢂ1 to 20 C. The instrument was calibrated with indium
and cyclohexane.
P1 [CH3(CH2)12CONHCH(Ph)COOMe]. Yield: 5.43 g (14.5
mmol, 72.5%), [a]D ¼ + 91.7 (c 0.44, CHCl3), M.P. 65 ꢀC.
1H NMR (300 MHz, CDCl3, TMS, 25 ꢀC): d 7.35–7.34
(Aromatic Hs, 5H, m), 6.48–6.46 (NH, 1H, d, J ¼ 6.9), 5.60–5.58
(aCH, 1H, d, J ¼ 7.2), 3.72 (–OCH3, 3H, s), 2.25–2.20 (aCH2, 2H,
m), 1.64–1.60 (bCH2, 2H, t, J ¼ 7.0), 1.25 (10CH2, 20H, s), 0.90–
0.85 (–CH3, 3H, t, J ¼ 6.6). 13C NMR (75 MHz, CDCl3, TMS, 25
ꢀC): d 172.6, 171.7, 136.8, 129.1, 128.6, 127.4, 56.4, 52.9, 52.9,
36.5, 32.0, 29.8, 29.7, 29.6, 29.5, 29.4, 29.3, 25.6, 22.8, 14.2. Anal.
Cal. for C23H37NO3 (375.2773): C, 73.56; H, 9.93; N, 3.73; found
C, 73.58; H, 9.95; N, 3.76. HRMS (m/z): 376.2982 [M + H]+,
398.2720 [M + Na]+.
Rheology study. Rheological experiments were done using an
Advanced Rheometer AR 2000 (TA Instruments) by cone and
plate geometry in a peltier plate. The cone diameter was 40 mm,
cone angle 1ꢀ 590 5000, and truncation 56 mm.
P2 [CH3(CH2)12CONHCH(CH2Ph)COOMe]. Yield: 6.08 g
(15.42 mmol, 77.1%), [a]D ¼ + 62.0 (c 0.46, CHCl3), M.P. 54 ꢀC.
1H NMR (300 MHz, CDCl3, TMS, 25 ꢀC): 7.27–7.04
(Aromatic Hs, 5H, m), 5.90–5.87(NH, 1H, d, J ¼ 7.5), 4.91–4.84
(aCH, 1H, q), 3.70 (–OCH3, 3H, s), 3.16–3.02 (bCH, 2H, m),
2.16–2.11 (aCH2, 2H, t, J ¼ 7.5), 1.57–1.52 (bCH2, 2H, m), 1.22
(10CH2, 20H, m), 0.87–0.82 (CH3, 3H, t, J ¼ 6.4); 13C NMR (75
FT-IR spectroscopy. FT-IR spectroscopy was performed using
Nicolate 380 FT-IR spectrophotometer (Thermo Scientific). All
reported FT-IR spectra were taken using the spectroscopic cell
with CaF2 window in the case of a dilute solution of gelators and
wet gels. During the recording of IR spectra using the CaF2 cell
for the diluted solution of amphiphilic gelator, 100 scans were
performed and the solvent (n-heptane) subtraction technique was
performed.
ꢀ
MHz, CDCl3, TMS, 25 C): d 177.3, 172.8, 172.2, 135.9,134.3,
129.3, 128.6, 127.1, 52.9, 52.3, 37.9, 36.5, 31.9, 29.7, 29.5, 29.4,
29.3, 29.2, 25.6, 24.8, 22.7, 14.1. Anal. Cal. for C24H39NO3
(389.2930): C, 73.99; H, 10.09; N, 3.60; found C, 74.03; H, 10.04;
N, 3.62. HRMS (m/z): 390.2827 [M + H]+, 412.2621 [M + Na]+.
X-ray diffraction study. X-ray diffraction study of the xerogel
was carried out by placing the sample on a glass plate. Experi-
ments were carried out by using an X-ray diffractometer (Bruker
AXS, Model No. D8 Advance). The instrument was operated at
a 40 kV voltages and 40 mA current using Ni-filtered CuKa
radiation and the instrument was calibrated with a standard
Al2O3 (corundum) sample before use. For scan 1ꢀ–5ꢀ, the scin-
tillation counts detector was used with scan speed 2 s and step
size 0.02ꢀ. In another scan 5ꢀ–30ꢀ, the LynxEye super speed
detector was used with scan speed 0.3 s and step size 0.02ꢀ.
P3 [CH3(CH2)12CONHCH(CH3)COOMe]. Yield: 5.5 g (17.57
ꢀ
mmol, 87.8%), [a]D ¼ +17.4 (c 0.47, CHCl3), M.P. 59 C.
1H NMR (300 MHz, CDCl3, TMS, 25 ꢀC): 6.13 (NH, 1H, br),
4.60–4.55 (aCH, 1H, m), 3.72 (–OCH3, 3H, s), 2.20–2.15 (aCH2,
2H, t, J ¼ 7.6), 1.62–1.57 (bCH2, 2H, m), 1.38–1.35 (bCH, 3H, d, J
¼ 7.2), 1.25–1.22 (10CH2, 20H, m), 0.87–0.82 (CH3, 3H, t, J ¼
6.5); 13C NMR (75 MHz, CDCl3, TMS, 25 C, d): 173.8, 172.8,
ꢀ
52.5, 52.5, 47.9, 36.6, 32.0, 29.7, 29.7, 29.6, 29.4, 29.3, 25.7, 22.8,
18.6, 14.2. Anal. Cal. for C18H35NO3 (313.2617): C, 68.97; H,
11.25; N, 4.47; found C, 68.99; H, 11.27; N, 4.45. HRMS (m/z):
314.1449 [M + H]+, 336.1183 [M + Na]+, 352.0808 [M + K]+.
Acknowledgement
S. B. and J. N. thank the CSIR, New Delhi, India, for financial
assistance. We also thank anonymous reviewers for their very
helpful comments. We also thank DST, Govt. of India for
financial support.
Instrumentation
Field emission scanning electron microscopic (FE-SEM) study.
FE-SEM experiments were performed by placing a small portion
of gel samples on a microscope cover glass. Then, these samples
were dried first in air and then in vacuum and coated with
platinum for 90 s at 10 kV voltages and 10 mA current. The
average thickness of the coating layer of platinum was 3 to 4 nm.
After that micrographs were taken by using a Jeol Scanning
Microscope JSM-6700F.
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