46
CHUANSHENG WANG et al.
EXPERIMENTAL
recorded on a Nicolet Nexus 470. FT–IR spectrosꢀ
copy was performed in a spectroscopic cell with a CaF2
window and 50ꢀ
spacers operating at a 2 cm–1 resoꢀ
lution with 32 scans for solution and the KBr method
for gel states. Xꢀray diffraction pattern was performed
Lꢀphenylalanine ethyl ester hydrochloride, carꢀ
μm
bobenzoxy chloride (Cbz–Cl),
ꢀtetradecanoyl chloride, ꢀhexadecanoyl chloride,
ꢀoctadecanoyl chloride were purchased from Yangꢀ
nꢀdodecanoyl chloride
n
n
n
using a Bruker D8 ADVANCE instrument using Cu
radiation from 0.5° to 40° (2 ) in steps of 0.05°. The
K
α
zhou Baosheng Biochemical Co., Ltd and used as
received. Hydrazine hydrate was obtained form Tianꢀ
jin Bodi Chemical Co., Ltd. The other chemicals were
of the highest commercial grade available and used
without further purification. All solvents used in the
syntheses were purified, dried, or freshly distilled as
required.
θ
preparation of sample was similar to that of the SEM
samples.
RESULTS AND DISCUSSION
The gelation ability of Lꢀphenylalanine dihyꢀ
drazide derivatives with different length of the alkyl
chains were examined in various organic solvents. As
summarized in table, all of the three compounds were
able to form organic solvents into stable organogels in
a wide range, such as vegetable oils, aromatic solvents,
The synthetic routes for organogelators 1–3 were
shown above and the detailed synthetic method is
described below. The preparation of gel concludes
three steps. Lꢀphenylalanine methyl ester hydrochloꢀ
ride (25 mmol) was dissolved in 100 ml of saturated
solution of NaHCO3 at room temperature, and then
carbobenzoxy chloride (Cbz–Cl) (25 mmol) was
added dropwise to the solution. The mixture was
stirred at room temperature for 16 h. The solution was
extracted by ether. The organic layer was washed with
alcohols, esters, pꢀdioxane and tetrachloromethane,
indicating that Lꢀphenylalanine dihydrazide derivaꢀ
tives acts as versatile gelators of various organic solꢀ
vents. The critical gelation concentration (CGC) was
studied by dissolving a small amount (0.1–3.0 wt %) of
compound in 2 ml of the desired solvent under heatꢀ
ing. Upon cooling to ambient temperatures, the comꢀ
plete volume of the respective solvent was immobilized
and a gel was formed. The gelation was confirmed by
the inverted test tube method [16]. These gels are staꢀ
ble toward shaking and they are also stable for a few
weeks at room temperature (25°C). It can be seen that
water thoroughly, and dried over anhydrous MgSO4
.
After filtration, the solvent was removed under
reduced pressure to afford Cbz–L–Phe–OMe as a
colorless and transparent oily liquid.
A mixture of Cbz–L–Phe–OMe (20 mmol) and
hydrazine hydrate (60 mmol) in methanol (100 ml)
was stirred for 16 h under reflux, the solvent was
removed under reduced pressure. The residue was disꢀ
solved in chloroform. The solution was washed with
saturated brine thoroughly, and dried over anhydrous
MgSO4. After filtration, the solvent was removed
under reduced pressure to afford Cbz–L–Phe–
hydrazide as a white solid.
To a solution of Cbz–L–Phe–Hz (10 mmol) in
chloroform (200 ml), the corresponding alkanoyl
chloride (10 mmol) was added. The reaction mixture
was stirred for 6 h at room temperature followed by the
removal of the solvent under reduced pressure to
3
showed the best gelation ability among these comꢀ
pounds in most solvents. However, this type of gelators
can not gelatinize DMF, DMSO, methanol and ethaꢀ
nol, maybe the strong polarity destroys the hydrogen
bonding interaction between amideꢀamide groups. In
addition, Lꢀphenylalanine dihydrazide derivatives did
not dissolve at all in some aliphatic or lower polarity
solvents, such as ether, nꢀhexane, acetone, cyclohexꢀ
ane and hexane, even after prolonged heating at the
temperature to the boiling point of the solvents. Genꢀ
erally, the gelation ability of the gelator is related to the
interaction between gelator and solvent molecules,
governed by molecular polarity and the respective
structural factors. So it also implied that some relaꢀ
tionship exists among polarity, aromaticity, and gelaꢀ
tion ability, although the gel stability is directly proꢀ
portional to the concentration of gelator [1].
afford
obtained after recrystallizing with methanol for three
times. Characterization (Compound ): FT–IR (KBr,
, cm–1): 3285, 3225 (N–H), 3062 (ArH), 1698 (C=O,
urethane), 1676, 1604 (C=O, amide I), 1544 (N–H,
1–4 as a white solid. The final products were
3
ν
1
amide II). H NMR (DMSO, 600 MHz): 10.10 (s,
δ
1H), 9.81 (s, 1H), 7.60 (d, 1H), 7.22 (m, 10H), 4.93 (s,
2H), 4.31 (m, 1H), 3.02 (dd, 1H), 2.77 (dd, 1H), 2.12 (t,
2H), 1.51 (m, 2H), 1.23 (s, 24H), 0.85 (t, 3H).
Molecular selfꢀassembly at the micro level can be
observed using scanning electron microscopy (SEM).
This technique provides a comparative visual techꢀ
nique to assess the impact of the spacer unit on the
LCꢀMS: m/z .
574.8 [M + Na]+
Scanning electron microscopy (SEM) images of mode of selfꢀassembly [17]. Figure 1 shows SEM
the xerogel were obtained using a JEOL JSMꢀ6360LV images of xerogel of obtained from chlorobenzene,
scanning electron microscope. The accelerating voltꢀ ꢀhexanol and benzene. Obviously, the solvents much
age was 10 kV. The heated solution spread on a glass influenced the morphology of gelator aggregates. As
plate was allowed to cool to room temperature. After shown in Fig. 1a, the molecules spontaneously selfꢀ
3
n
3
freezeꢀdrying with liquid nitrogen, the xerogel was assembled into entangling thick fibrous aggregates
subjected to SEM observation. Fourier transform through nonꢀcovalent interactions and further form
infrared (FT–IR) spectra measurements were random threeꢀdimensional networks. However, the
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 1 2012