Synthesis and structure-property relationships of amphiphilic organogelators

Article abstract of DOI:10.1002/chem.200601154

A series of low-molecular-weight amphiphilic molecules was synthesized and investigated for their ability to gel organic solvents. These amphiphilic molecules are composed of a head-group moiety capable of forming intermolecular associations through hydro

Full text of DOI:10.1002/chem.200601154

FULL PAPER
DOI: 10.1002/chem.200601154
Synthesis and Structure–Property Relationships of Amphiphilic
Organogelators
Nils Mohmeyer and Hans-Werner Schmidt*[a]
Abstract: A series of low-molecular-
weight amphiphilic molecules was syn-
thesized and investigated for their abil-
ity to gel organic solvents. These am-
phiphilic molecules are composed of a
head-group moiety capable of forming
intermolecular associations through hy-
drogen bonds and n-alkyl chains of var-
ious lengths. This paper describes the
continuation of recently published
work, in which this class of gelators
was presented for the first time. Here,
the focus addresses systematically three
different structural variations of the
solvents. The aim was to establish
structure–property relationships and to
provide organogelators capable of
forming gels at low concentrations with
adjustable sol–gel transition tempera-
tures and good optical quality. For
some individual compounds of the
series this property profile was ach-
ieved. For the investigated solvents,
with particular compounds, sol–gel
transition temperatures above 1008C
with a reasonable concentration of ge-
lator are obtainable.
head-group moiety: 1) the rigidity,
2) the type and strength of the hydro-
gen-bond-forming units, and 3) the re-
duction of the intermolecular interac-
tion by incorporating a lateral substitu-
ent. The gelation behavior was investi-
gated in p-xylene and in several polar
Keywords: amphiphiles · gels · self-
assembly · sol–gel processes · supra-
molecular chemistry
Introduction
ordination-bond formation, dipole–dipole interactions, and/
or hydrogen bonds. Intensive effort has been expended to
understand the structure–property relationships to tailor or-
ganogelators; however, until now it has not been possible to
predict in advance if a new molecule will gel an organic sol-
vent or not. Therefore, in recent years, many researchers
have attempted to find new efficient gelators, resulting in
the discovery of a variety of small molecules. A selection of
some representatives includes 1,3:2,4-di-O-benzylidene-d-
sorbitol (DBS),[17–19] 2,3-bis-n-decyloxyanthracene,[20,21] cho-
lesterol derivatives,[22–24] fluorinated or bolaform amides,[25,26]
symmetrical dialkylamides,[27] symmetrical mono- and bisur-
eas,[8,28–30] nonsymmetrical bisureas,[31] and N-n-octyl-d-glu-
conamide.[32,33] Recently, we added to this selection a class
of amphiphilic molecules consisting of a head moiety capa-
ble of forming intermolecular hydrogen bonds and a hydro-
phobic long alkyl chain.[34] In more detail, the investigated
molecules consist of three different structural units: an
apolar terminal cyclohexyl group, a hydrogen-bond-forming
segment based on p-phenylenediamines with amide and
urea groups, and a long alkyl chain with more than eight
carbon atoms. The para linkage used provides the rigidity of
the head-group moiety.[34]
Organogelators are low-molecular-weight organic molecules
that are capable of growing from homogeneous solution
into fine fibrillar dendritic structures within the organic sol-
vent. These fibrillar structures build a continuous three-di-
mensional network resulting in a macroscopic gel formation.
The field of organogelators has attracted interest due to in-
dustrial applications in many areas such as cosmetics, poly-
mers, and soft condensed matter with advanced func-
tions.[1–16] The process of these self-assembly-type gelators is
driven by specific noncovalent intermolecular interactions.
The physical gels formed are therefore thermoreversible. By
heating above the sol–gel transition temperature the gelator
is completely dissolved and upon cooling to room tempera-
ture, the three-dimensional network and thus the gel will be
obtained. The intermolecular interactions are typically gen-
erated by electrostatic interactions, p–p stacking, metal-co-
[a]Dr. N. Mohmeyer, Prof. Dr. H.-W. Schmidt
Macromolecular Chemistry I
Bayreuther Institut für Makromolekülforschung (BIMF) and
Bayreuther Zentrum für Grenzflächen und Kolloide (BZKG)
University Bayreuth, 95440 Bayreuth (Germany)
Fax : (+49)921-55-3206
Continuing from this work, we now expand the class of
amphiphilic gelators by different structural variations of the
head-group moiety. With this intention, the rigidity of the
E-mail: hans-werner.schmidt@uni-bayreuth.de
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head group will be reduced by a meta substitution (i). The
type and strength of the hydrogen-bond-forming units will
be varied (ii) and finally, the intermolecular interaction will
also be reduced by the use of a lateral substituent R (iii).
Furthermore, combinations of these approaches will be in-
vestigated.
tuted amide-/urea-functionalized derivatives 7a–c, the meta-
substituted derivatives 8a–c, and also the methyl-functional-
ized derivatives 9a–c (para) and 10a–c (meta).
Structure–property relationships with respect to gelation
ability: In general, gelation ability, efficiency, and gel prop-
erties change dramatically with small structural variations in
the gelator molecule and depend also on the solvent used.
The gelation ability was investigated in p-xylene as apolar
hydrocarbon and in valeronitrile, g-butyrolactone, and 3-me-
thoxypropionitrile as polar solvents. The latter are of special
interest due to their potential application in quasi-solid-state
dye-sensitized solar cells.[36]
To efficiently screen the principle gelation ability, mix-
tures of these compounds at 1 wt% in the given solvents
were heated until the solid was, if possible, completely dis-
solved. The homogenous solutions were cooled slowly to
room temperature and gelation was observed visually. Gela-
tion was considered to have occurred when a gel state that
exhibited no gravitational flow over a period of several
hours was obtained. This process was repeated several
times, demonstrating the thermoreversibility of the gelation
and dissolution process.
The aim is to investigate the influence of these structural
variations and by this, to establish structure–property rela-
tionships with respect to the formation of gels, to adjust sol–
gel transition temperatures and mechanical strength, and to
improve the optical quality, all at the lowest possible gelator
concentration. We focused on the apolar solvent p-xylene
and on polar solvents such as g-butyrolactone, valeronitrile,
and especially 3-methoxypropionitrile with respect to their
application possibilities in dye-sensitized solar cells.[5,19,35,36]
For a better understanding of the structure–property rela-
tionships, Figure 1 illustrates the marginal chemical modifi-
cations of the compounds conducted and Table 1 summariz-
es the results of the screening experiments. The following
discussion begins with the series of para-substituted rigid bi-
samides 3a–c[34] and is structured in comparative sets con-
sisting in each case of two series of three compounds. Firstly,
the reduction of the rigidity of the head-group moiety is dis-
cussed. The modification from the rigid para-bisamides 3a–c
to the kinked meta-bisamides 4a–c changes the gelation
ability dramatically. The para-substituted bisamides 3a–c gel
p-xylene with a minimum required gelator concentration of
between 1.1 and 1.5 wt%. All meta-bisamides 4a–c are solu-
ble in p-xylene at elevated temperatures, precipitate upon
cooling, and do not form gels. In the polar solvents, valero-
nitrile, g-butyrolactone, and 3-methoxypropionitrile, all
para-bisamides 3a–c precipitate with one exception. Com-
pound 3c is able to gel g-butyrolactone at an interestingly
low concentration of only 0.5 wt%. In contrast to this, most
of the meta-bisamides 4a–c are highly soluble and stay in so-
lution. The second variation is the replacement of the amide
group next to the alkyl chain by a urea group yielding the
amide-/urea-functionalized derivatives 7a–c.[34] All three
compounds gel p-xylene at a much lower required gelator
concentration relative to 3a–c. A remarkable improvement
of the gelation ability was observed for the polar solvents.
Here, compounds 7b and 7c gel all selected polar solvents
at a very low concentration. The introduction of a lateral
methyl substituent on the aromatic ring in the 2-position
next to the amide group also has slight influence on the ge-
lation ability. In comparison to the bisamides 3a–c, the mol-
ecules 5b and 5c gel p-xylene at concentrations of below
0.5 wt%. This variation is the most interesting one due to
the immense influence on the thermal and optical properties
Results and Discussion
Synthesis: The synthetic route to the eight different series
(each with three compounds) of amphiphilic bisamides and
amide-/urea-functionalized derivatives is shown in
Scheme 1. In the first step, cyclohexanecarboxylic acid chlo-
ride was allowed to react with the four different nitro-
group-containing aromatic amines 1a–d in dry N-methyl-2-
pyrrolidone (NMP) and pyridine. These amines were select-
ed to introduce different structural variations in the head-
group moiety. 4-Nitroaniline 1a was selected to obtain a
linear and rigid moiety and 3-nitroaniline 1b to introduce a
kink within the head group. Two other nitroaniline deriva-
tives 1c–d were chosen to reduce the intermolecular interac-
tions by a lateral methyl substituent. The four resulting nitro
compounds were reduced in the second step with hydrogen,
by using palladium on activated carbon as catalyst, to the
corresponding amine derivatives 2a–d. These four amines
were reacted with octanoyl chloride, tetradecanoyl chloride,
and octadecanoyl chloride to obtain the para-bisamides 3a–
c, the meta-bisamides 4a–c, and the methyl-substituted de-
rivatives 5a–c (para) and 6a–c (meta). To introduce a urea
group instead of the second amide group, the amino com-
pounds 2a–d were reacted with isocyanates of different
chain lengths (-C8, -C14, and -C18) to obtain the para-substi-
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Amphiphilic Organogelators
FULL PAPER
series of the amide-/urea-func-
tionalized
derivatives
7a–c
versus 8a–c. The rigid deriva-
tives 7b and 7c show good gela-
tion ability in all four solvents
investigated,
whereas
the
kinked derivatives 8b and 8c
precipitate upon cooling. Com-
parison of the amide-/urea-func-
tionalized derivatives 9a–c and
10a–c reveals that the gelation
ability decreases by introduction
of the kink. The compounds
10a–c are in most cases insolu-
ble or precipitate. The differ-
ence in the gelation ability of
the methyl-substituted deriva-
tives 5a–c and 6a–c is only mar-
ginal. In apolar solvents the
kinked derivatives 6a–c exhibit
the better gelation behavior;
however, in polar solvents the
rigid derivatives are more effi-
cient.
With respect to the next
structural variation—the re-
placement of one amide group
by a urea group—the gelation
ability changes non-uniformly
within the four comparative
sets. Within the two sets of the
rigid head-group moieties the
gelation capability is increased
from both bisamide series 3a–c
and 5a–c to the amide-/urea-
functionalized derivatives 7a–c
and 9a–c. However, the kinked
bisamides 4a–c and 6a–c com-
pared to the kinked amide-/
urea-functionalized derivatives
8a–c and 10a–c show only slight
changes with no clear tendency.
The introduction of the later-
al methyl substituent improves
the gelation behavior within the
two comparative sets with
kinked head-group moieties.
Compared to the series 4a–c
and 8a–c without methyl sub-
stituents, the methyl-substituted
Scheme 1. Synthesis of the asymmetrically substituted phenylenediamine-based bisamide derivatives 3a–c,
4a–c, 5a–c, and 6a–c and the amide-/urea-functionalized derivatives 7a–c, 8a–c, 9a–c, and 10a–c. a) NMP, pyr-
idine, 808C, 2 h; b) Pd/C, H2, THF/MeOH, 3.5 bar, 408C, 24 h; c) aliphatic acid chloride, NMP, pyridine, 808C,
2 h; d) aliphatic isocyanate, THF, reflux, 2 h.
of the gel systems, which will be discussed later. The deriva-
tives 5b and 5c are also able to gel valeronitrile at concen-
trations of 0.5 and 0.75 wt%, respectively.
derivatives 6a–c and 10a–c exhibit an enhanced tendency to
form gels. Within the sets of compounds with rigid head
groups the gelation ability is qualitatively similar.
In this section, the structural modification from a rigid to
a kinked head-group moiety will be discussed. As men-
tioned above, from compounds 3a–c to 4a–c, the gelation
ability decreases. The same trend was observed for the
All these results support that a well-balanced system of ri-
gidity, intermolecular interactions driven by amide or urea
units, and a slight packing disruption by the lateral methyl
substituent can be balanced to obtain gels at low gelator
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H.-W. Schmidt and N. Mohmeyer
concentration. In general within
this systematic study, the
change from the rigid to the
kinked compounds does not im-
prove the gelation ability.
More-favorable
structural
changes are the replacement of
one amide group by a urea
group and the introduction of a
lateral methyl substituent. Fi-
nally, the variation in the length
of the alkyl chain shows
a
minor effect relative to the
other variations reported here.
Following these more-qualita-
tive investigations, the next sec-
tion discusses the concentration
dependence on selected com-
pounds.
Gelproperties as a function of
concentration: p-xylene
In this section, the gelation
properties in p-xylene are dis-
cussed in particular as a func-
tion of the gelator concentra-
tion. For selected compounds,
the thermal and optical proper-
ties are presented.
Figure 1. Schematic representation of synthesized amphiphilic compounds ordered by their structural variation.
Starting series: 3a–c. Change in x axis direction: introduction of a lateral methyl group at the head-group
moiety; change in y axis direction: reduction of rigidity by introducing a kink due to meta linkage at the head-
group moiety; change in z axis direction: variation in the type and strength of the intermolecular interactions
by replacing an amide group by a urea group.
Sol–gel transition temperature:
An important property of orga-
nogelators is the sol–gel transi-
tion temperature (Tgel). This
thermoreversible transition de-
pends mainly on the concentra-
tion of the gelator and the type
of solvent used. The sol–gel
transition temperature defines
the application range and proc-
essing temperature of organo-
gels. Tgel was determined by the
dropping-ball method.[30]
As generally observed, the
sol–gel transition temperature
decreases as the gelator concen-
tration decreases. However, the
concentration range in which
the organogelator forms stable
gels differs as the chemical
structure and type of organic
solvent varies. Above a certain
concentration, the gelator is not
completely soluble. This is also
limited by the boiling point of
the solvent. Below a certain
Table 1. Comparison of gelation abilities of the synthesized amphiphilic compounds in different solvents at a
concentration of 1 wt%. For gel formation at room temperature, the minimum required concentration in wt%
is given in parentheses; gel: formation of stable gel; insol.: compound is not completely soluble at the boiling
temperature of the solvent; ppt.: compound precipitates upon cooling; sol.: compound stays in solution after
cooling.
Compound
p-Xylene
Valeronitrile
g-Butyrolactone
3-Methoxypropionitrile
3a
3b
3c
4a
4b
4c
gel (1.1)
gel (1.5)
gel (1.5)
ppt.
ppt.
ppt.
ppt.
ppt.
ppt.
sol.
sol.
sol.
ppt.
ppt.
gel (0.5)
sol.
sol.
ppt.
ppt.
ppt.
sol.
ppt.
ppt.
ppt.
5a
5b
5c
6a
6b
6c
7a
7b
7c
8a
8b
8c
ppt.
ppt.
ppt.
gel (1.0)
ppt.
ppt.
ppt.
ppt.
ppt.
gel (1.0)
gel (0.75)
sol.
ppt.
ppt.
ppt.
ppt.
ppt.
ppt.
ppt.
gel (0.25)
gel (0.25)
sol.
ppt.
ppt.
gel (0.5)
gel (0.25)
gel (0.25)
gel (0.25)
gel (0.5)
gel (0.3)
gel (0.25)
gel (0.2)
ppt.
gel (0.5)
gel (0.75)
ppt.
gel (2.0)
ppt.
gel (0.5)
gel (0.25)
gel (0.05)
sol.
ppt.
ppt.
ppt.
ppt.
ppt.
ppt.
9a
9b
9c
10a
10b
10c
insol.
gel (0.25)
gel (0.75)
gel (1.5)
insol.
gel (1.5)
gel (0.5)
gel (0.75)
gel (1.0)
ppt.
ppt.
ppt.
gel (0.75)
gel (0.5)
gel (0.75)
insol.
ppt.
gel (0.25)
gel (0.25)
insol.
insol.
gel (0.25)
ppt.
ppt.
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Amphiphilic Organogelators
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concentration, the concentration is too low to form a three-
dimensional network. Only a viscosity increase is observed.
Figure 2 displays the influence of the gelator concentration
on the sol–gel transition temperatures within the concentra-
tion range of 0.25 to 3.0 wt%. Figure 2, top, compares the
influence of the type of hydrogen-bonding units in the head-
group moiety (bisamide or amide/urea). Bisamide 5b exhib-
its sol–gel transition temperatures from 86 to 1028C within
the concentration range of 0.5 to 2.5 wt%. Below 0.5 wt%
5b is not able to from a stable gel, whereas above 2.5 wt%
the compound is not completely soluble in boiling p-xylene.
In contrast, the sol–gel transition temperatures with the cor-
responding amide-/urea-functionalized derivative 9b are
about 20–308C higher. This increase was also observed in
the comparison of 6c and the amide-/urea-functionalized de-
rivatives 10c. However, 10c shows lower solubility in boiling
p-xylene than the three other compounds. Compound 10c is
only completely soluble up to a concentration of 1.0 wt%
with a Tgel of 1378C, which is 408C higher than that of the
corresponding bisamide 6c. This solubility is limited by the
boiling point of p-xylene at 1388C. The general tendency
that p-xylene gels with the amide-/urea-functionalized deriv-
atives (9b and 10c) show higher Tgel values than the corre-
sponding bisamides (5b and 6c) is attributed to an addition-
al hydrogen bond formed by the second nitrogen at the urea
group in contrast to the amide group.
Figure 2, middle, shows the influence of structural modifi-
cation from a rigid to a kinked head-group moiety on Tgel.
This will also be discussed by means of four compounds, all
with a lateral methyl substituent. The gelation behavior of
compound 5b with the rigid head-group moiety was dis-
cussed above and features only moderate Tgel values. In
comparison, the corresponding derivative 6b with the
kinked head-group moiety induces, at concentrations of be-
tween 0.5 and 2.5 wt%, Tgel values 10–208C higher than
those for compound 5b. This result was also observed in the
comparison of derivatives 9c and 10c, although it was not
expected. From the geometrical point of view, the intermo-
lecular interactions of the para-linked rigid derivatives 5b
and 9c should be stronger than the ones for the kinked, flex-
ible meta-linked compounds 6b and 10c. In para-linked
head-group moieties the molecular packing should be easier
and the intermolecular interactions stronger, leading to
more-stable supramolecular aggregates. However, the con-
trary was the case.
In the case of the introduction of the lateral methyl sub-
stituent (Figure 2, bottom), an unexpected behavior was also
observed. The two bisamides 3c and 5c show nearly the
same Tgel values. However, compound 5c forms stable gels
over the entire concentration range investigated, whereas
compound 3c forms stable gels only within a limited concen-
tration range of between 1.75 and 2.5 wt%. Below this con-
centration, only highly viscous solutions were obtained and
above 2.5 wt%, the compound is not completely soluble.
The same trend was observed with the amide-/urea-function-
alized derivatives 7b and 9b. Here too, the derivative with
the lateral methyl substituent forms gels over the entire con-
centration range. In addition, the sol–gel transition tempera-
ture of 9b is substantially higher than that of 7b. For exam-
ple, at a concentration of 0.5 wt%, compound 7b exhibits a
sol–gel transition temperature of 858C, whereas the Tgel
value for compound 9b is 998C.
Figure 2. Sol–gel transition temperature as a function of the gelator con-
centration of several compounds in p-xylene. The influence of the differ-
ent structural variations of the compounds is illustrated. Top: comparison
of hydrogen-bonding units (amide or urea); middle: comparison of the
position at the aromatic ring (para or meta); bottom: comparison of the
substitution in the 2-position (with or without methyl group).
Details of the intermolecular interaction can be investi-
gated by FTIR spectroscopy. The characteristic IR vibra-
À
tions of amide and urea groups are the C N stretching,
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H.-W. Schmidt and N. Mohmeyer
À
N H stretching and bending vibration, and more important-
caused by the C=O stretching vibration of the urea group in
its hydrogen-bridged form. The second signal at 1652 cmÀ1
corresponds to the amide group, also in its associated form.
The spectra of gels with compound 7b appear different. The
strongest signal is at 1635 cmÀ1 and is, as in the case above,
also related to the hydrogen-bonded C=O stretching vibra-
tion of hydrogen-bonded urea groups. A clear difference
was observed for the amide groups. The spectra show a
signal at 1681 cmÀ1, which we allocate to the presence of
free nonassociated amide groups. This is further supported
by the missing C=O stretching vibration of associated amide
groups, which are barely visible at about 1655 cmÀ1. This
confirms that the organogelator 9b has a better packing and
stronger intermolecular interaction of the head-group
moiety, despite the lateral methyl substituent. This means a
twist of the phenyl out of the amide/urea planes with less
hindrance. As the hydrogen bonding is apparent, it is rea-
sonable to suggest that a conformational effect that enforces
hydrogen bonding in the case of the compound with the ad-
ditional methyl group 9b is operating. Consequently, the
sol–gel transition temperatures are, relative to compound
7b, higher (Figure 2, bottom).
Optical and morphological properties: For applications,
the optical properties of organogels are of special interest.
The goal is the preparation of transparent gels with excel-
lent clarity and haze. These properties are thickness depen-
dent and can be measured by using standardized equip-
ment.[40] Most sensitive is the haze value, which is attributed
to scattering above an angle larger than 2.58. The haze value
varies from 100% for a highly scattering opaque material to
0% for a clear liquid, such as water. For the measurements,
a homogeneous solution of the gelator in p-xylene at elevat-
ed temperatures was carefully filled in a disc-shaped quartz
cell with a diameter of 18 mm and a thickness of 10 mm.
After cooling to room temperature at a cooling rate of
58CminÀ1, the gels were maintained at room temperature
for 24 h before performing the measurement. Figure 4 shows
ly, the C=O stretching vibration. These vibrations appear at
different wavenumbers for free or hydrogen-bonded amide
and urea groups, respectively. In addition, the strength of
the hydrogen bonds shifts the location of the vibrations in
À
the spectra. The amide I (C=O stretching) and amide II (C
N stretching and N H bending) vibrations are located be-
À
tween 1500 and 1700 cmÀ1. In this discussion we focus on
the shift of the C=O stretching vibration. For amide groups,
free C=O stretching vibrations are located at around
1685 cmÀ1, whereas associated hydrogen-bonded C=O
stretching vibrations are located at around 1660 cmÀ1.[37] In
the case of urea groups, the free C=O stretching vibration is
located between 1680 and 1690 cmÀ1, and the associated hy-
drogen-bonded C=O stretching vibration is located between
1630 and 1655 cmÀ1.[38,39]
Figure 3 shows FTIR spectra of p-xylene gels with deriva-
tive 9b (top) with the lateral methyl substituent in the head-
group moiety, and the corresponding derivative 7b (bottom)
without methyl substituent, at three different concentrations
(0.25, 0.5, and 0.75 wt%). The IR spectra of the gels with
compound 9b for different concentrations showed two sig-
nals with the same proportion. The signal at 1630 cmÀ1 is
Figure 3. Sections of the IR spectra of p-xylene gels comprising different
concentrations of 9b (top) and 7b (bottom) measured at room tempera-
ture showing the differences in the amide I vibration.
Figure 4. Optical properties of p-xylene gels comprising different concen-
&
*
trations of 7b ( ) and 9b ( ). The haze values were measured by using a
disc-shaped quartz cell with a thickness of 10 mm.
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Amphiphilic Organogelators
FULL PAPER
the haze values of the p-xylene gels for compounds 7b and
9b as a function of the concentration. At all concentrations,
the haze values of the p-xylene gels comprising the deriva-
tive 9b are lower than for derivative 7b. In both cases the
haze values increase as gelator concentration increases, most
probably due to an increase in size of the fibrillar nanostruc-
tures. The best haze value of 25% was observed with com-
pound 9b at a concentration of 0.25 wt%. At the same con-
centration, 7b had a haze value of 30%.
To understand the difference in the optical properties be-
tween the p-xylene gels, transmission electron microscopy
(TEM) and scanning electron microscopy (SEM) were car-
ried out. The samples for TEM were prepared by forming
the gel on a grid and slowly evaporating the solvent at room
temperature under vacuum. Figure 5, top and middle, dis-
play the TEM images of the three-dimensional-network
structures formed from a 0.5-wt% gel of compounds 7b and
9b. The amide-/urea-functionalized derivative 7b without
the methyl substituent forms long fibrils with diameters of
between 100 and 200 nm. In comparison, the TEM image of
the network system of compound 9b with the lateral methyl
substituent reveals thinner and more-uniform fibrillar struc-
tures with an average thickness of about 50 nm. This obser-
vation is in agreement with the results of the optical meas-
urements, in which the gels based on compound 9b exhibit
lower haze values. The three-dimensional-network structure
can also be visualized by SEM after removal of the p-xylene
with supercritical carbon dioxide (sc-CO2). Figure 5, bottom,
shows the network structure of 9b for a sample prepared
from a gel with a gelator concentration of 1.0 wt%.
Gel properties as function of concentration: polar solvents
In this section we briefly review the gelation capability in
the two polar solvents, valeronitrile and 3-methoxypropioni-
trile. For this, the best candidates, the two bisamides 5b, 6b
and the two amide-/urea-functionalized derivatives 7b and
9b, were selected.
Figure 6, top, compares the influence of the type of hydro-
gen-bonding units in the head-group moiety (bisamide or
amide/urea) on the sol–gel transition temperature (Tgel) in
valeronitrile. It was found, similar to the p-xylene gels
(Figure 2, top), that the sol–gel transition temperatures with
the amide/urea compound 9b are higher than with the bisa-
mide 5b. In both cases, the Tgel values of the valeronitrile
gels are lower than the corresponding p-xylene gels. For ex-
ample, at a concentration of 1.0 wt% compound 5b reveals
a Tgel of 908C in p-xylene, but of 648C in valeronitrile.
The influence on the Tgel of a kink in the head-group
moiety was investigated by using the rigid derivative 5b and
the kinked derivative 6b. As shown in Figure 6, middle, the
same trend as in p-xylene gels was observed for the valero-
nitrile gel. Here too, the sol–gel transition temperatures are
lower. The rigid derivative 5b causes lower Tgel values of va-
leronitrile gels than does the kinked derivative 6b. The
same was observed in p-xylene gels (Figure 2, middle). No-
tably, compound 5b had a broad gel-formation range (0.5 to
3.0 wt%), whereas compound 6b forms gels at concentra-
tions of between 2.0 and 3.0 wt%.
The results of introducing the lateral methyl substituent
are shown in Figure 6, bottom, and are discussed for the sol-
vent 3-methoxypropionitrile, whereby the same tendency
was also found with valeronitrile. The amide-/urea-function-
alized derivative 9b with a lateral methyl substituent and
the derivative 7b without a methyl substituent were select-
ed. The Tgel values of 3-methoxypropionitrile over the entire
concentration range are about 108C higher for compound
9b with the methyl substituent than for compound 7b. The
same behavior was observed in p-xylene gels (Figure 2,
bottom).
In conclusion, this comparison demonstrates that for both
solvent systems, the nonpolar p-xylene and the polar sol-
vents (valeronitrile and 3-methoxypropionitrile), the same
underlying self-assembly principle is present and the differ-
ence depends mainly on the solubility of the organogelator.
Figure 5. Electron microscopy images of network structures. Top: TEM
image of 7b after evaporation of p-xylene (initial gelator concentration:
0.5 wt%); middle: TEM image of 9b (0.5 wt%) after evaporation of p-
xylene; bottom: SEM image of 9b (1 wt%) after removal of p-xylene
with sc-CO2.
Chem. Eur. J. 2007, 13, 4499 – 4509
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4505

H.-W. Schmidt and N. Mohmeyer
tors. Common to all these studies is a careful balance of mo-
lecular symmetry/asymmetry, hydrogen-bonding moieties,
and units that provide the necessary solubility.
The present study of a particular set of amphiphilic asym-
metrical molecules and experiments revealed that within
this class of organogelators, the gelation capability, that is,
the sol–gel transition temperature at low concentrations,
and the optical properties of the resulting gels are improved
by introducing a lateral methyl group at the hydrogen-bond-
ing moiety. This improvement is visible in rigid para-linked
as well as in kinked meta-linked head-groups. This phenom-
enon may be more general and transferable to the symmet-
rically designed organogelators.
The structure–property relationships established and de-
scribed here can also be utilized to accelerate the discovery
of efficient gelators for other solvents, for example, highly
viscous materials or ionic liquids, with different solubility
behavior, that is, polarity and boiling point.
In summary, this work is a further step towards establish-
ing general structure–property relationships and supports a
universally valid understanding of the gelation phenomenon.
ExperimentalSection
Materials and methods: Solvents for synthesis were purified and dried as
necessary according to standard procedures. The amines and isocyanates
used were obtained from Aldrich and Fluka and were used as received.
Solvents for gelation tests were obtained from Merck–Suchardt and
Fluka and were used as received. 1H NMR spectra were recorded at
room temperature by using a Bruker AC 250 instrument. Mass spectra
were recorded by using the Mass Spectrometer VARIAN MAT CH-7 in-
strument (direct probe inlet, electron impact ionization) at the Central
Analytic Laboratories of the University of Bayreuth. Elemental analysis
was carried out by using an EA 3000 instrument (HEKAtech) at the De-
partment of Chemical Engineering (Prof. A. Jess) of the University of
Bayreuth.
Generalsynthetic route to substituted aminophenylamides 2a—d : The
different amines (1a–d) (0.1 mol) were dissolved in dry N-methyl-2-pyr-
rolidone (150 mL) and dry pyridine (20 mL), and approximately 0.05 g of
dried LiCl was added. The cyclohexanecarboxylic acid chloride (0.1 mol)
was added and the mixture was stirred for 2 h at 808C. After cooling to
room temperature, the mixture was precipitated in ice water (500 mL).
The mixture was filtered (glass filter G3) to retrieve the solid, which was
washed with water and dried. The resulting products were purified by re-
crystallization from methanol. Yields after recrystallization varied from
70 to 90%. The obtained nitro compounds were dissolved in a mixture of
THF (200 mL) and methanol (40 mL), to which Pd/C (1 g; 10 wt% Pd on
activated carbon) was added. This mixture was stirred in an autoclave for
24 h at 408C with H2 pressure of 3.5 bar. The colorless mixture was fil-
tered (Alox N) and the solvents were evaporated. Subsequently, the ob-
tained solid was purified by performing column chromatography on silica
gel (1:1 hexane/EtOAc) to yield the white amino compounds 2a–d. The
1H NMR data of the individual compounds are given below.
Figure 6. Sol–gel transition temperature as a function of the gelator con-
centration of several compounds in valeronitrile and 3-methoxypropioni-
trile. The influence of the different structural variations of the com-
pounds is illustrated. Top: comparison of hydrogen-bonding units (amide
or urea); middle: comparison of the position at the aromatic ring (para
or meta); bottom: comparison of the substitution in the 2-position (with
or without methyl group).
Cyclohexanecarboxylic acid(4-aminophenyl)amide (2a): 1H NMR
([D6]DMSO, 250 MHz): d=1.51 (m, 10H), 2.24 (m, 1H), 4.75 (s, 2H),
5.83 (s, 1H), 6.67 (d, J=8.7 Hz, 2H), 7.05 ppm (m, J=8.7 Hz, 2H).
Conclusion
Cyclohexanecarboxylic acid(3-aminophenyl)amide (2b): 1H NMR
([D6]DMSO, 250 MHz): d=1.31 (m, 5H), 1.71 (m, 5H), 2.27 (s, 1H), 4.97
(s, 2H), 6.20 (d, J=8.8 Hz, 1H), 6.66 (m, J=8.8 Hz, 1H), 6.88 (m, 2H),
9.43 ppm (s, 1H).
To date, prediction of gelation capability and efficiency has
been nearly impossible. As reported in comparable studies,
for example, those of Feringa and co-workers,[8,30] basic
structure–property relationships with new molecules have to
be established in order to optimize and tailor organogela-
Cyclohexanecarboxylic
acid
A
C
(2c):
1H NMR ([D6]DMSO, 250 MHz): d=1.44 (m, 10H), 1.98 (s, 3H), 2.26 (s,
4506
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Chem. Eur. J. 2007, 13, 4499 – 4509

Amphiphilic Organogelators
FULL PAPER
1H), 4.85 (s, 2H), 6.33 (m, 2H), 6.79 (d, J=8.2 Hz, 1H), 8.79 ppm (s,
1H).
amino compound 2c (1.16 g, 5.0 mmol) and octadecoyl chloride (1.82 g,
6 mmol). The product was purified by recrystallization from acetone.
Yield 1.46 g of a white powder (58%, 2.9 mmol): m.p. 1858C; Rf =0.64
(1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz): d=0.87
(t, J=7.0 Hz, 3H), 1.25 (m, 32H), 1.76 (m, 3H), 1.91 (m, 2H), 2.07 (m,
2H), 2.23 (s, 3H), 2.29 (m, 1H), 2.54 (t, J=7.6 Hz, 2H), 7.29 ppm (m,
3H); MS: m/z (%): 498 (52) [M+]; elemental analysis calcd (%) for
C32H54N2O2 (498.79): C 77.06, H 10.91, N 5.62; found: C 76.46, H 10.86,
N 5.68.
Cyclohexanecarboxylic
acid
N
(2-methyl)phenyl]amide
(2d):
The syntheses of compounds 3a–c are described in our previous work.[34]
Cyclohexanecarboxylic acid(3-octoylaminophenyl)amide (4a): The amino
compound 2b (1.2 g, 6.0 mmol) was dissolved in 50 mL NMP and dry
pyridine (15 mL), and approximately 0.05 g of dried LiCl was added. The
octoyl chloride (1.2 mL, 7 mmol) was added and the mixture was stirred
for 2 h at 808C. After cooling to room temperature, the mixture was pre-
cipitated in ice water (1000 mL). The mixture was filtered (glass filter
G3) to retrieve the solid, which was washed with water and dried. The
crude product was suspended in boiling hexane, and THF was added
dropwise to obtain a clear solution. For crystallization, the solution was
stored at 48C for 12 h to retrieve a white solid. Yield 0.91 g of a white
powder (44%, 2.6 mmol): m.p. 1278C; Rf =0.34 (1:1 hexane/THF);
1H NMR ([D6]DMSO, 250 MHz): d=0.86 (t, J=7.0 Hz, 3H), 1.26 (m,
15H), 1.57 (m, 3H), 1.76 (m, 4H), 2.27 (m, 3H), 7.22 (m, 3H), 7.92 (s,
1H), 9.76 (s, 1H), 9.80 ppm (s, 1H); MS: m/z (%): 344 (24) [M+]; ele-
mental analysis calcd (%) for C21H32N2O2 (344.25): C 73.22, H 9.36, N
8.13; found: C 73.28, H 9.31, N 8.11.
Cyclohexanecarboxylic acid[3-octoylaminoACHTREU(NG 2-methyl)phenyl]amide (6a):
This compound was prepared as described for 4a, starting from amino
compound 2d (1.16 g, 5.0 mmol) and octoyl chloride (1.03 mL, 6 mmol).
The product was purified by recrystallization from THF. Yield 1.30 g of a
white powder (73%, 3.6 mmol): m.p. 2108C; Rf =0.50 (1:1 hexane/THF);
1H NMR ([D6]DMSO, 250 MHz): d=0.86 (t, J=7.0 Hz, 3H), 1.28 (m,
15H), 1.58 (m, 2H), 1.78 (m, 2H), 1.98 (s, 3H), 2.29 (m, 3H), 7.09 (s,
3H), 9.19 (s, 1H), 9.28 ppm (s, 1H); MS: m/z (%): 358 (64) [M+]; ele-
mental analysis calcd (%) for C22H34N2O2 (358.52): C 73.70, H 9.56, N
7.81; found: C 73.82, H 9.69, N 7.73.
Cyclohexanecarboxylic acid[3-tetradecoylaminoACTHRE(UNG 2-methyl)phenyl]amide
(6b): This compound was prepared as described for 4a, starting from
amino compound 2d (1.16 g, 5.0 mmol) and tetradecoyl chloride
(1.63 mL, 6 mmol). The product was purified by recrystallization from
THF. Yield 1.96 g of a white powder (86%, 4.4 mmol): m.p. 2028C; Rf =
0.54 (1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz): d=
0.87 (t, J=7.0 Hz, 3H), 1.28 (m, 27H), 1.81 (m, 2H), 1.90 (m, 2H), 2.10
(m, 4H), 2.63 (m, 2H), 7.27 ppm (m, 3H); MS: m/z (%): 442 (78) [M+];
elemental analysis calcd (%) for C28H46N2O2 (442.68): C 75.97, H 10.47,
N 6.33; found: C 75.70, H 10.63, N 6.31.
Cyclohexanecarboxylic acid(3-tetradecoylaminophenyl)amide (4b): This
compound was prepared as described for 4a, starting from amino com-
pound 2b (1.2 g, 6.0 mmol) and tetradecoyl chloride (1.97 mL, 7 mmol).
The product was purified by recrystallization from methanol/water 10:1.
Yield 1.55 g of a white powder (60%, 3.6 mmol): m.p. 1348C; Rf =0.36
(1:1 hexane/THF); 1H NMR ([D6]DMSO, 250 MHz): d=0.85 (t, J=
7.1 Hz, 3H), 1.23 (m, 25H), 1.56 (m, 3H), 1.76 (m, 4H), 2.27 (m, 3H),
7.20 (m, 3H), 7.92 (s, 1H), 9.76 (s, 1H), 9.80 ppm (s, 1H); MS: m/z (%):
428 (39) [M+]; elemental analysis calcd (%) for C27H44N2O2 (428.34): C
75.65, H 10.35, N 6.54; found: C 76.38, H 10.31, N 6.45.
Cyclohexanecarboxylic acid[3-octadecoylaminoACTHRE(UNG 2-methyl)phenyl]amide
(6c): This compound was prepared as described for 4a, starting from
amino compound 2d (1.16 g, 5.0 mmol) and octadecoyl chloride (1.82 g,
6 mmol). The product was purified by recrystallization from DMF. Yield
1.84 g of a white powder (74%, 3.7 mmol): m.p. 1998C; Rf =0.58 (1:1
hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz): d=0.87 (t,
J=6.8 Hz, 3H), 1.28 (m, 35H), 1.81 (m, 2H), 1.92 (m, 2H), 2.12 (m,
4H), 2.63 (m, 2H), 7.27 ppm (m, 3H); MS: m/z (%): 498 (91) [M+]; ele-
mental analysis calcd (%) for C32H54N2O2 (498.79): C 77.06, H 10.91, N
5.62; found: C 77.05, H 11.07, N 5.73.
Cyclohexanecarboxylic acid(3-octadecoylaminophenyl)amide (4c): This
compound was prepared as described for 4a, starting from amino com-
pound 2b (1.09 g, 5.0 mmol) and octadecoyl chloride (1.82 g, 6 mmol).
The product was purified by recrystallization from methanol/water 10:1.
Yield 1.8 g of a white powder (74%, 3.7 mmol): m.p. 1168C; Rf =0.38
(1:1 hexane/THF); 1H NMR ([D6]DMSO, 250 MHz): d=0.85 (t, J=
7.1 Hz, 3H), 1.23 (m, 33H), 1.57 (m, 3H), 1.76 (m, 4H), 2.27 (m, 3H),
7.19 (m, 3H), 7.92 (s, 1H), 9.76 (s, 1H), 9.80 ppm (s, 1H); MS: m/z (%):
484 (48) [M+]; elemental analysis calcd (%) for C31H52N2O2 (484.4): C
76.81, H 10.81, N 5.78; found: C 76.88, H 10.91, N 5.71.
The syntheses of compounds 7a–c are described in our previous work.[34]
Cyclohexanecarboxylic acid[3-(3-octylureido)phenyl]amide (8a): A solu-
tion of amino compound 2b (1.07 g, 5.0 mmol) in THF (50 mL) was
added to a solution of octylisocyanate (0.93 mL, 6.0 mmol) in THF
(15 mL). The reaction mixture was refluxed for 2 h. After cooling to
room temperature, the mixture was added to methanol (80 mL) and
evaporated to the halfway point. The precipitation began while cooling
to room temperature. After 2 h, the mixture was filtered (glass filter G3)
to retrieve the solid, which was washed with water and dried. The prod-
uct was purified by recrystallization from methanol. Yield 1.56 g of a
white powder (84%, 4.2 mmol); m.p. 1598C; Rf =0.52 (1:1 hexane/THF);
1H NMR (5:1 CDCl3/CF3COOD, 250 MHz): d=0.89 (t, J=7.0 Hz, 3H),
1.46 (m, 17H), 1.91 (m, 5H), 2.44 (m, 1H), 3.35 (t, J=7.4 Hz, 2H), 7.16
(m, 1H), 7.42 ppm (m, 3H); MS: m/z (%): 373 (28) [M+]; elemental
analysis calcd (%) for C22H35N3O2 (373.54): C 70.74, H 9.44, N 11.25;
found: C 70.43, H 9.58, N 11.26.
Cyclohexanecarboxylic acid[4-octoylaminoACHTREU(NG 2-methyl)phenyl]amide (5a):
This compound was prepared as described for 4a, starting from amino
compound 2c (1.16 g, 5.0 mmol) and octoyl chloride (1.03 mL, 6 mmol).
The product was purified by recrystallization from acetone. Yield 1.38 g
of a white powder (77%, 3.8 mmol): m.p. 2008C; Rf =0.60 (1:1 hexane/
1
THF); H NMR ([D6]DMSO, 250 MHz): d=0.85 (t, J=7.1 Hz, 3H), 1.26
(m, 15H), 1.58 (m, 2H), 1.77 (m, 2H), 2.10 (s, 3H), 2.25 (t, J=7.3 Hz,
2H), 2.35 (m, 1H), 7.15 (d, J=8.7 Hz, 1H), 7.30 (d, J=8.7 Hz, 1H), 7.41
(s, 1H), 9.04 (s, 1H), 9.73 ppm (s, 1H); MS: m/z (%): 358 (43) [M+]; ele-
mental analysis calcd (%) for C22H34N2O2 (358.52): C 73.70, H 9.56, N
7.81; found: C 73.63, H 9.66, N 7.85.
Cyclohexanecarboxylic acid[4-tetradecoylaminoACTHRE(UNG 2-methyl)phenyl]amide
Cyclohexanecarboxylic acid[3-(3-tetradecylureido)phenyl]amide (8b):
This compound was prepared as described for 8a, starting from amino
compound 2b (1.09 g, 5.0 mmol) and tetradecylisocyanate (1.44 g,
6.0 mmol). The product was purified by recrystallization from methanol.
Yield 1.55 g of a white powder (68%, 3.4 mmol); m.p. 1468C; Rf =0.58
(1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz): d=0.87
(t, J=7.0 Hz, 3H), 1.39 (m, 29H), 1.90 (m, 5H), 2.45 (m, 1H), 3.35 (t,
J=7.3 Hz, 2H), 7.17 (m, 1H), 7.42 ppm (m, 3H); MS: m/z (%): 457 (8)
[M+]; elemental analysis calcd (%) for C28H47N3O2 (457.71): C 73.48, H
10.35, N 9.18; found: C 72.99, H 10.67, N 8.72.
(5b): This compound was prepared as described for 4a, starting from
amino compound 2c (1.16 g, 5.0 mmol) and tetradecoyl chloride
(1.63 mL, 6 mmol). The product was purified by recrystallization from
acetone. Yield 1.47 g of a white powder (66%, 3.3 mmol): m.p. 1888C;
Rf =0.62 (1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz):
d=0.87 (t, J=7.0 Hz, 3H), 1.28 (m, 24H), 1.76 (m, 3H), 1.89 (m, 2H),
2.07 (m, 2H), 2.23 (s, 3H), 2.29 (m, 1H), 2.55 (t, J=7.6 Hz, 2H),
7.29 ppm (m, 3H); MS: m/z (%): 442 (100) [M+]; elemental analysis
calcd (%) for C28H46N2O2 (442.68): C 75.97, H 10.47, N 6.33; found: C
75.85, H 10.56, N 6.41.
Cyclohexanecarboxylic acid[3-(3-octadecylureido)phenyl]amide (8c):
This compound was prepared as described for 8a, starting from amino
compound 2b (1.09 g, 5.0 mmol) and octadecylisocyanate (1.77 g,
Cyclohexanecarboxylic acid[4-octadecoylamino
ACHTRE(UNG 2-methyl)phenyl]amide
(5c): This compound was prepared as described for 4a, starting from
Chem. Eur. J. 2007, 13, 4499 – 4509
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4507

H.-W. Schmidt and N. Mohmeyer
6.0 mmol). The product was purified by recrystallization from THF. Yield
2.33 g of a white powder (91%, 4.5 mmol); m.p. 1428C; Rf =0.64 (1:1
hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz): d=0.87 (t,
J=7.0 Hz, 3H), 1.48 (m, 37H), 1.90 (m, 5H), 2.45 (m, 1H), 3.35 (t, J=
7.3 Hz, 2H), 7.17 (m, 1H), 7.44 ppm (m, 3H); MS: m/z (%): 513 (13)
[M+]; elemental analysis calcd (%) for C32H55N3O2 (513.81): C 74.80, H
10.79, N 8.18; found: C 74.59, H 11.20, N 7.62.
527 (18) [M+]; elemental analysis calcd (%) for C33H57N3O2 (527.84): C
75.09, H 10.88, N 7.96; found: C 75.05, H 11.07, N 8.01.
Gelation tests: In a typical gelation test, a weighed amount of the com-
pound was mixed with 2 mL of solvent in a test tube with a screw cap,
and then the mixture was heated until the solid was completely dissolved.
The resulting solution was allowed to cool slowly to room temperature.
Gelation was considered to have occurred when a homogenous substance
that exhibited no gravitational flow was obtained. For the determination
of the sol–gel transition temperature (Tgel) of the gels, the steel-ball
method was used.[30] A steel ball (260 mg) with a diameter of 4.5 mm was
placed on top of the gel and the vial was sealed. The samples were
Cyclohexanecarboxylic
acid[2-methyl-4-(3-octylureido)phenyl]amide
(9a): This compound was prepared as described for 8a, starting from
amino compound 2c (1.16 g, 5.0 mmol) and octylisocyanate (0.93 g,
6.0 mmol). The product was purified by recrystallization from DMF.
Yield 1.29 g of a white powder (67%, 3.3 mmol); m.p. 2318C (decomp) ;
Rf =0.32 (1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz):
d=0.86 (t, J=7.0 Hz, 3H), 1.42 (m, 17H), 1.92 (m, 5H), 2.25 (s, 3H),
2.54 (m, 1H), 3.35 (t, J=7.1 Hz, 2H), 7.14 (m, 2H), 7.40 ppm (d, J=
8.4 Hz, 1H); MS: m/z (%): 387 (46) [M+]; elemental analysis calcd (%)
for C23H37N3O2 (387.57): C 71.28, H 9.62, N 10.84; found: C 71.61, H
9.71, N 10.79.
placed in a heating system that was slowly heated, typically at 58CminÀ1
,
and the temperature was determined by using a temperature sensor that
was dipped in a separate vial containing solvent. The Tgel of the gel was
defined as the temperature at which the steel ball hit the bottom of the
vial.
Electron microscopy: For TEM, a formar/carbon-coated copper grid (300
mesh) was dipped for a very short time (<1 s) in the solution of the gela-
tor in the organic solvent and then laid on a weighing paper to become a
gel. After 1 h, the grid was placed in a round-bottomed flask and dried at
low pressure (<10À2 mbar). The grids were examined under a Zeiss
CEM 902 electron microscope, operating at 80 kV. For SEM, a xerogel
was prepared. Gels (2 mL) of a mixture of 1.0 wt% in p-xylene were pre-
pared in a glass with a diameter of 22 mm. After 24 h at room tempera-
ture, the glass was placed in an autoclave (volume: 1 L; PARR Instru-
ment Co., Frankfurt am Main). The autoclave was annealed at 88C with
a pressure of 56 bar. After an extraction time of 4 h, the CO2 content was
reduced to 10%. This process was repeated twice to ensure the complete
extraction of p-xylene. The autoclave was refilled with CO2 and after 2 h,
the temperature was increased stepwise (28C/10 min) up to 358C to
reach a pressure of 130 bar: the parameters of the supercritical CO2.
After 10 min, the pressure was reduced to 1 bar over 1 h. The SEM meas-
urements were performed by using a LEO 1530 (FE-REM with Schott-
ky-field-emision cathode) and an in-lens detector.
Cyclohexanecarboxylic
acid[2-methyl-4-(3-tetradecylureido)phenyl]-
ACHTREUNGamide (9b): This compound was prepared as described for 8a, starting
from amino compound 2c (1.16 g, 5.0 mmol) and tetradecylisocyanate
(1.44 g, 6.0 mmol). The product was purified by recrystallization from
DMF. Yield 1.86 g of a white powder (78%, 3.9 mmol); m.p. 2278C
1
(decomp) ; Rf =0.38 (1:1 hexane/THF); H NMR (5:1 CDCl3/CF3COOD,
250 MHz): d=0.87 (t, J=7.0 Hz, 3H), 1.49 (m, 29H), 1.92 (m, 5H), 2.25
(s, 3H), 2.52 (m, 1H), 3.35 (t, J=7.3 Hz, 2H), 7.16 (m, 2H), 7.40 ppm (d,
J=8.4 Hz, 1H); MS: m/z (%): 471 (86) [M+]; elemental analysis calcd
(%) for C29H49N3O2 (471.73): C 73.84, H 10.47, N 8.91; found: C 73.54, H
10.56, N 8.91.
Cyclohexanecarboxylic acid[2-methyl-4-(3-octadecylureido)phenyl]amide
(9c): This compound was prepared as described for 8a, starting from
amino compound 2c (1.16 g, 5.0 mmol) and octadecylisocyanate (1.77 g,
6.0 mmol). The product was purified by recrystallization from DMF.
Yield 2.13 g of a white powder (81%, 4.0 mmol); m.p. 2288C (decomp) ;
Rf =0.44 (1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz):
d=0.87 (t, J=7.0 Hz, 3H), 1.46 (m, 37H), 1.93 (m, 5H), 2.25 (s, 3H),
2.52 (m, 1H), 3.35 (t, J=7.6 Hz, 2H), 7.15 (m, 2H), 7.40 ppm (d, J=
8.4 Hz, 1H); MS: m/z (%): 527 (13) [M+]; elemental analysis calcd (%)
for C33H57N3O2 (527.84): C 75.09, H 10.88, N 7.96; found: C 75.06, H
10.97, N 7.87.
Opticalproperties : The standard optical characteristic “haze” was mea-
sured for the p-xylene gels by using a “Haze-Gard Plus” instrument
(BYK Gardner GmbH, Germany), which conforms to ASTM D-1003. A
homogeneous solution of the gelator in p-xylene at the different concen-
trations was poured into a quartz cell of volume 2 mL, diameter 18 mm,
and thickness 10 mm. After cooling to room temperature at a cooling
rate of 58CminÀ1, the gel was maintained at 258C for 24 h before per-
forming the measurement.
Cyclohexanecarboxylic
acid[2-methyl-3-(3-octylureido)phenyl]amide
(10a): This compound was prepared as described for 8a, starting from
amino compound 2d (1.16 g, 5.0 mmol) and octylisocyanate (0.93 g,
6.0 mmol). The product was purified by recrystallization from DMF.
Yield 1.35 g of a white powder (70%, 3.4 mmol); m.p. 2468C (decomp) ;
Rf =0.46 (1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz):
d=0.78 (t, J=7.0 Hz, 3H), 1.41 (m, 17H), 1.85 (m, 5H), 2.10 (s, 3H),
2.47 (m, 1H), 3.26 (t, J=7.3 Hz, 2H), 7.22 ppm (m, 3H); MS: m/z (%):
387 (42) [M+]; elemental analysis calcd (%) for C23H37N3O2 (387.57): C
71.28, H 9.62, N 10.84; found: C 70.97, H 9.65, N 10.87.
IR spectroscopy: The infrared measurements were performed by using a
BIO-RAD Digilab FTS-40 spectrometer with a NaCl cell of diameter
2 mm. The gelator was dissolved in the p-xylene at elevated temperatures
and then poured into the cell with a syringe through a closable opening.
After cooling to room temperature at a cooling rate of 58CminÀ1, the gel
was maintained at 258C for 24 h before performing the measurement.
Cyclohexanecarboxylic
acid[2-methyl-3-(3-tetradecylureido)phenyl]-
ACHTREUNGamide (10b): This compound was prepared as described for 8a, starting
from amino compound 2d (1.16 g, 5.0 mmol) and tetradecylisocyanate
(1.44 g, 6.0 mmol). The product was purified by recrystallization from
DMF. Yield 1.73 g of a white powder (73%, 3.7 mmol); m.p. 2408C
Acknowledgements
We thank N. Glaser and C. Abetz (BIMF) for the electron microscopy
experiments and B. Brunner (Department of Chemical Engineering,
Prof. A. Jess, University of Bayreuth) for performing the elemental anal-
ysis. We are also indebted to Sandra Ganzleben for her assistance in the
synthesis of several compounds.
1
(decomp) ; Rf =0.51 (1:1 hexane/THF); H NMR (5:1 CDCl3/CF3COOD,
250 MHz): d=0.87 (t, J=7.0 Hz, 3H), 1.47 (m, 29H), 1.92 (m, 5H), 2.19
(s, 3H), 2.53 (m, 1H), 3.34 (t, J=7.3 Hz, 2H), 7.29 ppm (m, 3H); MS: m/
z (%): 471 (17) [M+]; elemental analysis calcd (%) for C29H49N3O2
(471.73): C 73.84, H 10.47, N 8.91; found: C 73.77, H 10.47, N 8.93.
Cyclohexanecarboxylic acid[2-methyl-3-(3-octadecylureido)phenyl]amide
(10c): This compound was prepared as described for 8a, starting from
amino compound 2d (1.16 g, 5.0 mmol) and octadecylisocyanate (1.77 g,
6.0 mmol). The product was purified by recrystallization from DMF.
Yield 2.05 g of a white powder (78%, 3.9 mmol); m.p. 2338C (decomp) ;
Rf =0.56 (1:1 hexane/THF); 1H NMR (5:1 CDCl3/CF3COOD, 250 MHz):
d=0.87 (t, J=7.0 Hz, 3H), 1.48 (m, 37H), 1.92 (m, 5H), 2.19 (s, 3H),
2.55 (m, 1H), 3.34 (t, J=7.3 Hz, 2H), 7.29 ppm (m, 3H); MS: m/z (%):
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Received: August 9, 2006
Revised: January 3, 2007
Published online: March 9, 2007
Chem. Eur. J. 2007, 13, 4499 – 4509
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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