Supramolecular polymerization of C3-symmetric organogelators: Cooperativity, solvent, and gelation relationship

Article abstract of DOI:10.1002/chem.201202584

A systematic study of the influence of solvent and the size of C ₃-symmetric discotics on their supramolecular polymerization mechanism is presented. The cooperativity of the self-assembly of the reported compounds is directly related to their gelation ability. The two series of C₃-symmetric discotics investigated herein are based on benzene-1,3,5-tricarboxamides (BTAs) and oligo(phenylene ethynylene)-based tricarboxamides (OPE-TAs) that are peripherally decorated with achiral (1 a and 2 a) or chiral N-(2-aminoethyl)-3,4,5-trialkoxybenzamide units (1 b and 2 b). The supramolecular polymerization of compounds 1 a,b and 2 a,b has been exhaustively investigated in a number of solvents and by using various techniques: variable-temperature circular dichroism (VT-CD) spectroscopy, concentration-dependent ¹H NMR spectroscopy, and isothermal titration calorimetry (ITC). The supramolecular polymerization mechanism of compounds 2 is highly cooperative in solvents such as methylcyclohexane and toluene and is isodesmic in CHCl₃. Unexpectedly, chiral compound 1 b is practically CD-silent, in contrast with previously reported BTAs. ITC measurements in CHCl₃ demonstrated that the supramolecular polymerization of BTA 1 a is isodesmic. These results confirm the strong influence of the π-surface of the central aromatic core of the studied discotic and the branched nature of the peripheral side chains on the supramolecular polymerization. The gelation ability of these organogelators is negated in CHCl₃, in which the supramolecular polymerization mechanism is isodesmic. We C₃ kings: The influence of solvent, the size of the discotics, the π surface of the aromatic core, the nature of the side chains, and the gelation ability of the organogelators 1 and 2 on their supramolecular polymerization mechanism is presented (see figure). Copyright

Full text of DOI:10.1002/chem.201202584

FULL PAPER
DOI: 10.1002/chem.201202584
Supramolecular Polymerization of C3-Symmetric Organogelators:
Cooperativity, Solvent, and Gelation Relationship
Fꢀtima Aparicio, Fꢀtima Garcꢁa, and Luis Sꢀnchez*[a]
In memory of Christian G. Claessens
Abstract: A systematic study of the in-
1a,b and 2a,b has been exhaustively in-
vestigated in a number of solvents and
by using various techniques: variable-
temperature circular dichroism (VT-
CD) spectroscopy, concentration-de-
pendent 1H NMR spectroscopy, and
isothermal titration calorimetry (ITC).
The supramolecular polymerization
mechanism of compounds 2 is highly
cooperative in solvents such as methyl-
cyclohexane and toluene and is isodes-
mic in CHCl3. Unexpectedly, chiral
compound 1b is practically CD-silent,
fluence of solvent and the size of C3-
symmetric discotics on their supramo-
lecular polymerization mechanism is
presented. The cooperativity of the
self-assembly of the reported com-
in contrast with previously reported
BTAs. ITC measurements in CHCl3
demonstrated that the supramolecular
polymerization of BTA 1a is isodesmic.
These results confirm the strong influ-
ence of the p-surface of the central ar-
omatic core of the studied discotic and
the branched nature of the peripheral
side chains on the supramolecular poly-
merization. The gelation ability of
these organogelators is negated in
CHCl3, in which the supramolecular
polymerization mechanism is isodes-
mic.
pounds is directly related to their ge
tion ability. The two series of C3-sym-
metric discotics investigated herein are
based on benzene-1,3,5-tricarbox-
ACHTUNGTRENNUNGamides (BTAs) and oligo(phenylene
ACHTUNGERTNlNUNG a-
ACHTUNGTRENNUNG
ethynylene)-based
tricarboxamides
ꢀ
(OPE TAs) that are peripherally deco-
rated with achiral (1a and 2a) or chiral
N-(2-aminoethyl)-3,4,5-trialkoxybenz-
Keywords: cooperative effects
·
gels · self-assembly · polymeriza-
tion · supramolecular chemistry
ACHTUNGTRENNUNGamide units (1b and 2b). The supramo-
lecular polymerization of compounds
Introduction
the self-assembled fibrillar structures through weak non-co-
valent forces is possible and the resulting bundles produce
low-molecular-weight gels (LMWGs). Such LMWGs are
constituted by interconnected microscale 3D networks that
span the entire sample and are able to immobilize the sol-
vent.[7] The solid-like properties of LMWGs, even though
they are mainly constituted by a liquid component, and the
systematic variation of the gelator structure prompt the ap-
plication of these organized structures in an ample reper-
toire of applications, such as drug-delivery systems, biomate-
rials, electronic devices, and as templates for nanostruc-
tures.[8]
Cooperativity expresses the appearance of properties in a
complex system that are not exhibited by the individual
components.[1] The concept of cooperativity, as exemplified
in biological processes such as the folding of biopolymers,[2]
the binding of oxygen by hemoglobin,[3] and the aggregation
of amyloid peptides,[4] is closely related to other concepts,
such as molecular recognition and supramolecular self-as-
sembly. The aggregation of amyloid peptides[4] is also con-
sidered to be an example of biological cooperative supramo-
lecular polymerization. In supramolecular polymerization,
relatively small and simple molecules self-assemble hier-
archically to produce columnar, 1D organized structures
under dilute conditions.[5] In addition, the decoration of
these small molecules with stereogenic centers generates
helical supramolecular polymers.[6] Further interaction of
Even though the gelation phenomenon is a complex proc-
ess, it is possible to determine some basic rules that enable
the design of efficient and functional organogelators:
1) non-covalent unidirectional interactions should be present
to direct 1D self-assembly; 2) crystallization should be
avoided by controlling the fiber–solvent interfacial energy;
and 3) efficient fiber cross-linking should be induced to
favor the formation of a 3D network.[9] This first rule allows
a consideration of the formation of a LMWG as an example
of supramolecular polymerization in which bundles of single
fibers, which are constituted by supramolecular polymers,
form a gel.[5] A number of reports have correlated the for-
mation of gels with different solvent parameters, such as di-
[a] F. Aparicio, F. Garcꢀa, Prof. Dr. L. Sꢁnchez
Departamento de Quꢀmica Orgꢁnica
Facultad de Ciencias Quꢀmicas
Ciudad Universitaria s/n. 28040 Madrid (Spain)
Fax : (+34)913944103
E-mail: lusamar@quim.ucm.es
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202584.
AHCTUNGTRENNUNG
electric constant,[10a] the ET(30) parameter,[10b] the Hildebrand
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solubility parameter,[10c] the Hansen solubility pa
eters,[10d] the Kamlet–Taft parameters,[10e] and thermodynam-
N
temperature circular dichroism (VT-CD) spectroscopy, con-
centration-dependent H NMR spectroscopy, and isothermal
1
N
ic dissolution parameters.[10f] These reports have demonstrat-
ed the relevance of solvent–solute interactions in the gelati-
on phenomenon but they have not investigated the influence
of these solvent–solute interactions on the solute–solute in-
teractions. These latter interactions are responsible for the
formation of supramolecular polymers that bundle to form
the gel. Importantly, the morphology and properties of su-
pramolecular polymers can be directly related to the mecha-
nism, either isodesmic or cooperative,[5,11] describing the
growth of these supramolecular structures from their mono-
meric component upon changing the concentration or tem-
perature. To reinforce the above-mentioned set of rules, a
challenging task in the field of supramolecular gels and pol-
ymers involves the investigation of the relationships be-
tween the supramolecular polymerization mechanism and
the gelation ability of relatively simple organogelators. A
titration calorimetry (ITC). These ITC measurements in
CHCl3 demonstrate that the supramolecular polymerization
ꢀ
mechanism of both BTAs (1) and OPE TAs (2) is isodes-
mic. Decreasing the polarity of the solvent produces a dras-
tic change in the self-assembly mechanism and VT-CD ex-
periments indicate that the supramolecular polymerization
of the larger-sized discotics is cooperative. We also tested
the gelation ability of the organogelators in the solvents that
were utilized for the cooperativity studies. A direct correla-
tion between the supramolecular polymerization mecha-
nism—and, therefore, solute–solute interactions—and ge
AHCTUNGTREGUNtNN ion ability can be extracted from these studies.
ACHTUNGTRENNUNGla-
Results and Discussion
number of organogelators have been reported to self-assem-
Synthesis: The preparation of C3-symmetric organogelators
1a,b and 2a,b started with the synthesis of previously re-
ported N-(2-aminoethyl)-3,4,5-trialkoxybenzamide units that
were decorated with either achiral dodecyl chains (3a) or
chiral 3,7-dimethyloctyl chains (3b).[14] These units were
readily synthesized from methyl 3,4,5-trihydroxybenzoate,
dodecyl bromide or (S)-3,7-dimethyloctan-1-ol, and
ethyleneACTHNGUTRENNUdG iamine in three steps. The resulting N-(2-amino-
ethyl)-3,4,5-trialkoxybenzamides (3) were reacted with tri-
mesic acid to yield BTAs 1a and 1b in 56% and 65% yield,
19]
ble cooperatively,[12a,b,
but only ones that were based on
functionalized l-lysine dimers have been correlated to the
level of cooperativity.[12c]
Herein, we report on the self-assembly features of a series
of C3-symmetric organogelators based on the benzene-1,3,5-
tricarboxamide (BTA) skeleton (1, Figure 1) and oligo-
ꢀ
(phenylene ethynylene)-based tricarboxamides (OPE TAs,
respectively (Scheme 1). Palladium-catalyzed threefold So-
[15]
ꢀ
nogashira C C cross-coupling between iodo-derivatives 4,
which were prepared by reacting the corresponding benz-
AHCTUNGTREGaNNUN mide (3a or 3b) with 4-iodobenzoic acid, and 1,3,5-triethy-
nylbenzene (5)[16] afforded OPE TAs 2a and 2b in 37%
and 20% yield, respectively (Scheme 1). All of these report-
ed compounds were characterized by NMR and FTIR spec-
troscopy and by HRMS (see the Supporting Information).
Compounds 1c[17a] and 2c[18] were prepared according to lit-
erature procedures and were used as reference compounds.
ꢀ
ꢀ
IR spectroscopy: The self-assembly of BTAs and OPE TAs
proceeds through the formation of an intermolecular triple
ꢀ
array of H bonds between the N H and C=O moieties, thus
giving rise to a three-fold helical arrangement of the discot-
ics.[17,18] The formation and relative strength of the H bonds
can be monitored by FTIR spectroscopy. The FTIR spectra
Figure 1. Chemical structures of the C3-symmetric BTAs (1) and triangu-
ꢀ
lar-shaped OPE TAs (2).
of compounds 1a,b and 2a,b, as well as the spectra of BTA
[18]
1c[17a] and OPE TA 2c for comparison are shown in Fig-
ꢀ
ꢀ
2, Figure 1) that are peripherally decorated with achiral (1a
and 2a) or chiral 3,4,5-trialkyloxy-N-ethylenbenzamide units
(1b and 2b). The discotics reported herein (1a,b and 2a,b)
are equipped with three 3,4,5-trialkoxybenzamide moieties,
which have been reported to have an unfavorable effect on
self-assembly,[13] but with six amide functional groups in the
peripheral arms that can enhance the self-assembly features
of these compounds. The supramolecular polymerization of
ure S1 in the Supporting Information. The diagnostic N H
and amide I stretches and the amide II bend of compounds
1a–1c and 2a–2c are collected in Table 1.[19]
ꢀ
Taking BTA 1c as a reference, the N H and amide I
stretching bands and the amide II bending bands of com-
pounds 1a,b and 2a,b appear at intermediate wavenumbers
(see Table 1 and Figure S1 in the Supporting Information)
between the tightly H-bonded helices and completely un-
bound amide functional groups (e.g., 3240 cmꢀ1 and
ꢀ
both BTA and OPE TA organogelators in solution were in-
[19]
3450 cmꢀ1 for the N H stretch, respectively).
These
ꢀ
vestigated by using different techniques, that is, variable-
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Supramolecular Polymerization of C3-Symmetric Organogelators
FULL PAPER
by considering the formation of dimers that subsequently
interact to form a tri
ACHTUNGTRNEdNUNG imensional network, as in trimeth-
yl-1,3,5-benzene-tri
AHCTUNGTRENNUNG
Supramolecular polymerization in solution: Herein, we
investigated the influence of the solvent on the supramo-
lecular polymerization mechanism of these organogela-
tors by evaluating the influence of the solvent on the re-
action. The aggregation of BTAs that were endowed
with chiral peripheral chains was extensively investigated
in alkane solvents by VT-CD experiments. The operation
of helical H-bonding arrangements in apolar solvents in-
duces a highly cooperative supramolecular polymeriza-
tion for this kind of C3-symmetric discotics. The prefer-
red helical organization of previously reported chiral
BTAs at a concentration of about 10ꢀ5 m was justified by
the presence of a bisignated Cotton effect, which was ob-
served in their corresponding CD spectra.[17b,c,21] First,
we studied the supramolecular polymerization mecha-
ꢀ
nism of chiral BTA 1b and chiral OPE TA 2b by VT-
CD spectroscopy. Unexpectedly, the CD spectra of com-
pound 1b in methylcyclohexane (MCH) exhibited no di-
chroic response at a concentration of 1ꢃ10ꢀ5 m and it
was only possible to detect a very weak and noisy di-
chroic signal on increasing the concentration to 1ꢃ10ꢀ4
m
(see Figure S2 in the Supporting Information). This lack
of a dichroic response implies that BTA 1b is not organ-
ized into columnar stacks with a preferred helical sense,
in good agreement with that observed in the above-men-
tioned FTIR studies.
ꢀ
Scheme 1. Synthesis of C3-symmetric BTAs (1) and OPE TAs (2).
Similarly to BTAs, we have recently reported on the
cooperative supramolecular polymerization of triangu-
Table 1. Selected vibrations in the structures of BTAs 1a–1c and
[18]
ꢀ
lar-shaped OPE TAs in diluted MCH solutions.
Unlike
ꢀ
OPE TAs 2a–2c at room temperature.
ꢀ
compound 1b, the CD spectrum of chiral OPE TA 2b at a
concentration of 1ꢃ10ꢀ5 m in MCH exhibits an intense bisig-
nated Cotton effect, with positive and negative waves at 280
and 303 nm, respectively, which are diagnostic of the aggre-
gation of compound 2b into left-handed helical structures.[22]
These CD features contrast with those reported previously
Compound
nNꢀ
namide I
namide II
[cmꢀ1
H
[cmꢀ1
]
E
]
N
]
1a
1b
1c
2a
2b
2c
3306
3310
3240
3283
3283
3286
1645
1643
1638
1633
1635
1635
1580
1579
1559
1579
1578
1579
ꢀ
for one chiral congener of OPE TA 2c, in which the sign of
the Cotton effect was opposite and more intense (see the
Figure S3, compound S1 in the Supporting Information).[18b]
These experimental findings have recently been observed
for referable N-centered OPE-based discotics and have
been ascribed to the influence of the amide connectivity on
the spatial distribution of the sterogenic centers.[23] Upon
heating the sample at 908C for 1 h, the intensity of the bis-
values indicate a lesser degree of helical organization of the
aggregates, especially in BTAs 1a,b. The crystal structure of
N,N’,N’’-tris(2-methACHTUNGTRENNUNGoxyethyl)benzene-1,3,5-tricarboxamide
demonstrates that the self-assembly of this kind of discotics
is directed by a triple helical network of hydrogen bonds in
which the adjacent BTA molecules are rotated through
608.[20] By applying this supramolecular organization to com-
pounds 1a and 1b, one must consider that the outer amide
functionalities of one molecule would be quite far apart to
form intermolecular, helical H-bonds with the amides of an
adjacent molecule that is placed on top of it. Therefore, the
FTIR data suggest that both amide functional groups do
form H bonds but do not form a helical structure. The su-
pramolecular interactions of BTAs 1a,b could be justified
AHCTUNGTREGiNNNU gnated dichroic signal of compound 2b diminishes, but does
not disappear (see Figure S4). This dichroic behavior was
also found in a more-dilute solution of compound 2b in
MCH (5ꢃ10ꢀ6 m), which implies that this compound exhibits
a very strong tendency to aggregate in this apolar solvent
(see Figure S4). Only by lowering the concentration of com-
pound 2b to 2.5ꢃ10ꢀ6 m is it possible to cancel the dichroic
response upon heating the sample at 908C (Figure 2a). The
cooling curve that was obtained under these conditions was
non-sigmoidal, thus indicating a cooperative aggregation
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L. Sꢁnchez et al.
performed VT-CD experiments in this solvent (Figure 2b).
The higher polarity of toluene compared to MCH results in
a
smaller—but clearly visible—dichroic response at
1ꢃ10ꢀ5 m. In addition, heating this solution at 908C com-
pletely cancels the dichroic signal. As in MCH, the cooling
curve in toluene was non-sigmoidal (Figure 2b, inset), which
demonstrates that the supramolecular polymerization of
compound 2b in toluene is also cooperative. Under these
conditions, by applying Equations (1) and (2), he and Ka
values of ꢀ64 kJmolꢀ1 and 0.00022, respectively, were calcu-
lated. The lower Te value in this solvent (305 K) in compari-
son to that in MCH (358 K) is indicative of the lower stabili-
ty of the aggregates that are formed from compound 2b in
MCH, despite the fourfold-higher concentration. To eluci-
date the supramolecular polymerization mechanism in all of
the solvents in which we have performed gelation studies,
the CD spectra of compound 2b in CHCl3 and EtOAc were
recorded. Unfortunately, no dichroic signal was visible in
their corresponding CD spectra. Most probably, the high po-
larity of these solvents weakens the H-bonding interactions
between the amide functional groups, thus cancelling the di-
chroic response at this concentration.
To complete our investigation of the influence of solvent
on the supramolecular polymerization mechanism and, in
turn, on the gelation ability of the reported organogelators,
we performed concentration-dependent 1H NMR spectro-
scopy and ITC experiments with compounds 1a,b and 2a,b
in CHCl3. These compounds are highly soluble in CHCl3,
which allows us to use concentrated solutions without ob-
serving gelation (Figure 3 and Figures S5–S7 in the Support-
ing Information). Unfortunately, the gelation features of the
reported discotics in other solvents, such as toluene, MCH,
and EtOAc, impede the realization of the corresponding
concentration-dependent 1H NMR spectroscopy and ITC
studies.
Figure 2. CD spectra of compound 2b: a) 2.5ꢃ10ꢀ6 m in MCH and b) 1ꢃ
10ꢀ5 m in toluene. Insets depict the cooling curves of compound 2b from
363 to 288 K at intervals of 0.5 Kminꢀ1; the dark gray and light gray lines
are the fits for the elongation and nucleation processes, respectively.
1
Concentration-dependent H NMR experiments in CDCl3
show that the self-association of these organogelators occurs
ꢀ
ꢀ
with monomeric OPE TA 2b, which starts to self-assemble
through p p and hydrogen-bonding interactions, as demon-
strated by the changes of the chemical shifts of the different
at high temperatures (Figure 2a, inset). By fitting the tem-
perature-dependent CD-intensity data with the Van der
Schoot nucleation-elongation model, as defined by Equa-
tions (1) and (2), it is possible to attain relevant thermo-
ACHTUNGTRENNUNGdynamic parameters, such as the enthalpy released during
elongation (he), the temperature at which the nucleation
regime changes into elongation (Te), and the degree of coop-
erativity expressed by Ka.[24] The calculated he, Te, and Ka
values for compound 2b in MCH are ꢀ67 kJmolꢀ1, 358 K,
and 0.0023, respectively.
ꢀhe
ꢀn ¼ ꢀSAT ð1 ꢀ exp½
ðT ꢀ TeÞꢁÞ
ð1Þ
ð2Þ
RTe2
he
ꢀn ¼ Ka1=3 exp½ð2=3Kaꢀ1=3 ꢀ 1Þ
ðT ꢀ TeÞꢁ
RTe2
Figure 3. Partial concentration-dependent 1H NMR spectra of compound
Despite the optical features of toluene that impede re-
cording a complete CD spectrum of compound 2b, we also
2a (300 MHz, CDCl3, 298 K).
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Supramolecular Polymerization of C3-Symmetric Organogelators
FULL PAPER
resonances. Thus, all of the aromatic signals for the central
aromatic units shift upfield upon increasing the concentra-
tion (as exemplified by proton Ha, Scheme 1). In contrast,
the resonance of the proton that corresponds to the trialkox-
ybenzamide units (Hb) experiences an opposite effect and
shifts downfield with increasing concentration. This effect
can be reasonably attributed to the electron-donating char-
acter of the alkoxy chains.
The self-assembly of compounds 1a,b and 2a,b is also vi-
sualized by the shift of the two anisochronous amide groups
(Hc and Hd, Scheme 1). The inner and outer amide function-
alities appear at different chemical shifts and both are de-
shielded upon increasing the concentration (see Figures S5–
S7 in the Supporting Information). However, the aggrega-
tion behavior of BTAs 1a,b differ considerably to that of
ꢀ
OPE TAs 2a,b. All of the protons of compounds 1a,b
appear very broad in their corresponding concentration-de-
1
pendent H NMR spectra. The progressive broadening and
slight shielding of these signals upon increasing the concen-
tration could be indicative of the formation of aggregates
(Figure 3).[25]
To accurately calculate the binding constant of the supra-
molecular polymerization of discotics of class 1 and 2, ITC
measurements were performed in CHCl3 (see Figure 4 and
Figures S7–S9 in the Supporting Information). This techni-
que is widely used in biochemistry and supramolecular
chemistry to describe interacting systems,[26] but examples in
which ITC data are used to investigate the formation of su-
pramolecular polymers remain scarce.[27] To determine the
self-assembly mechanism by ITC experiments, a concentrat-
ed solution of the supramolecular polymer is injected into a
cell that contains the pure solvent. The first injection of the
studied solution results in a low-enough concentration to
detect the corresponding dissociation, which is characterized
by endothermic enthalpograms. Very recently, Arnaud and
Bouteiller reported a mathematical model that allows the
binding constants and also the molar enthalpies of associa-
tion for a supramolecular polymerization mechanism to be
extracted from concentration-dependent ITC experiments,
as shown in Equation (3),[27a] where Q(i) is the heat ex-
Figure 4. a) Heat effect produced by injecting aliquots (6 mL) of different
solutions of compound 1a in CHCl3 at 258C. b) Enthalpograms of differ-
ent solutions of compound 1a in CHCl3 versus concentration (normalized
by the final cell concentration, T=258C). The curves are fits that were
obtained from Equation (3).
ꢀ
ꢁ
3
3
ðcs1Þ
cs0½cc1ðiÞꢁ
QðiÞ ¼ ꢀDHK2KVi
2 ꢀ
2
ð1 ꢀ Kcs1Þ
cc0ðiÞ½1 ꢀ cc1ðiÞꢁ
ð3Þ
ꢀ
ꢁ
ðcs1Þ
cs0½cc1ðiÞꢁ
2
2
s
c
changed, c0 and c0 (i) are the starting concentrations of the
ꢀDH2K2Vi
ꢀ
1 ꢀ Kcs1
cc0ðiÞ½1 ꢀ cc1ðiÞꢁ
s
aggregate in the syringe and in the cell, respectively, c1 and
c
c1 (i) are the monomer concentrations in the syringe and in
the cell, respectively, and Vi is the volume injected. Equa-
tion (3) contains four unknown parameters, that is, the en-
thalpies that are associated to the elongation regime (DH)
and the dimerization process (DH2) and the binding con-
stants that correspond to these two processes (K and K2, re-
spectively). In an isodesmic process, DH=DH2 and K=K2,
whereas, if DH>DH2 and K>K2, the self-assembly is coop-
erative.[5,10] Only very few self-assembly processes with
DH<DH2 and K<K2 and, hence, anticooperativity, have
been reported.[28]
The heat-flow curves that were obtained upon injecting
different solutions of achiral organogelator 1a in CHCl3 into
pure CHCl3 at 258C are shown in Figure 4a. Diluting the
solutions of compound 1a prompts the dissociation of the
H-bonding arrays between the amide groups, thus gener-
AHCTUNGTREGaNNNU ting endothermic heat-flow curves. The intensity of the
upward peaks gradually decreases until the concentration of
compound 1a inside the cell reaches the dissociation limit.
The integration of these peaks at each investigated concen-
tration affords the enthalpograms shown in Figure 4b. A
simulACTHNURGTENNtUG aACHUTNGTERNNUGneous fitting of the ITC data for the different solu-
tions of compound 1a to the isodesmic model gave a value
for K of 496mꢀ1 (Table 2).
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L. Sꢁnchez et al.
Table 2. Thermodynamic parameters that were determined by fitting the
ITC data for solutions of compounds 1a, 1c, 2a, and 2c in CHCl3 at
258C.
Compound
K
A
DH
[kJmolꢀ1
Concentration
[mm]
[mꢀ1
]
G
]
1a
1c
2a
2c
496
3
388
13
ꢀ5.64
80, 44, 33, 22
ꢀ12.88
ꢀ8.07
ꢀ8.15
124, 100, 80, 60, 40
53, 35, 20, 15, 10
78, 52, 39, 18
Similar to compound 1a, ITC experiments with BTA 1c
under the same conditions exhibited an isodesmic surpamo-
lecular polymerization mechanism but with a lower binding
constant (Table 2 and Figure S7 in the the Supporting Infor-
mation). The presence of aromatic peripheral groups on the
benzenetricarboxamide unit in compounds 1a,b increases
the p surface, thus increasing the corresponding binding con-
stant. The exothermic character of the supramolecular poly-
merization of compounds 1 and 2 is visualized by the endo-
thermic enthalpograms that were obtained from ITC meas-
urements with compounds 2a and 2c in CHCl3. The calcu-
lated K values for compounds 2a and 2c are 388 and 13mꢀ1,
respectively, which were obtained by performing a global fit-
ting of the ITC data to an isodesmic mechanism (Table 2
and Figures S8 and S9 in the Supporting Information).
Unfortunately, the high concentration that was required
to perform the ITC measurements impeded an elucidation
of the supramolecular polymerization mechanism of the re-
ported discotics in less-polar solvents, such as EtOAc, tol-
uene, and MCH, because stable gels were formed in these
solvents. However, the studies reported herein demonstrate
the strong influence of: 1) the nature of the solvent; 2) the
p-surface of the central aromatic core of the studied discot-
ic; and 3) the branched nature of the peripheral side-chains
on the supramolecular polymerization.
Figure 5. Amplification of chirality experiments for achiral compound 2a
upon mixing with chiral compound 2b (298 K, MCH, total concentration
2.5ꢃ10ꢀ6 m).
high dilution conditions. These findings suggest the strong
dependence of this amplification-of-chirality phenomenon
with the number of amide functional groups, which allow a
higher number of non-covalent interactions, and also with
the presence of a larger number of chiral peripheral chains
in the chiral sergeants.
Compound 2b is also CD-active in toluene, but the left-
handed helical structures are less stable in this solvent, as
demonstrates by the Te value that was calculated from the
corresponding VT-CD studies. Finally, we performed “ser-
geants-and-soldiers” experiments by mixing 1ꢃ10ꢀ5 m solu-
tions of compounds 2a and 2b in toluene. The amplifica-
tion-of-chirality effect in more-polar toluene is inferred
from the nonlinear trend that is exhibited by the dichroic re-
sponse of a mixture of both achiral compound 2a and chiral
compound 2b (see Figure S10 in the Supporting Informa-
tion). This higher polarity confirms that, upon adding about
20% of chiral sergeant 2b, it is possible to achieve maxi-
mum handedness. The amount of chiral compound 2b that
is added to reach the maximum value of the dichroic re-
sponse is about twofold higher than that determined in less-
polar MCH.
Amplification of chirality: CD studies that were performed
ꢀ
with OPE TA 2b demonstrated the self-assembly of this
compound into left-handed helical structures in MCH and
toluene. We have recently reported on the amplification of
chirality of compound 2c upon performing “sergeants-and-
soldiers”[29] experiments with chiral congeners.[18] In these
experiments, the helicity of a racemic mixture of both M
and P enantiomers of compound 2c (the soldiers) is biased
by the addition of about 20% of the chiral units (the ser-
geants). Considering the extraordinarily high aggregation
tendency of compound 2b in MCH, we performed “ser-
geants-and-soldiers” experiments by mixing this chiral
Gelation behavior and morphological studies: The LMWGs
presented herein were designed to hierarchically self-assem-
ble into columnar aggregates that can bundle into thick fila-
ments and immobilize the solvent molecules. The structural
ꢀ
difference between BTAs 1a,b and OPE TAs 2a,b is the
ꢀ
OPE TA with racemic compound 2a under very high dilu-
larger aromatic central core in these latter compounds,
which enabled us to perform a systematic study of the influ-
ence of chemical structure on the gelation ability of C3-sym-
metric discotics in different solvents (Table 3). The critical
gel concentration was estimated by performing simple and
reproducible test-tube-inversion assays and the maximum
concentration in these gelation experiments was
200 mgmLꢀ1.[30]
tion conditions (total concentration: 2.5ꢃ10ꢀ6 m). The addi-
tion of increasing amounts of chiral compound 2b into a so-
ACHTUNGTRENNUNGluACHTUNGTRENNUNGtion of achiral compound 2a, whilst keeping the total con-
centration constant and heating above the Te value, leads to
a chiroptical response that increases non-linearly (Figure 5).
The maximum handedness is obtained upon adding a small-
er amount of chiral sergeant 2b (around 10%), despite the
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Supramolecular Polymerization of C3-Symmetric Organogelators
FULL PAPER
Table 3. Gelation behavior of compounds 1a,b and 2a,b in different sol-
vents. The critical gelation concentration [mgmLꢀ1] is given in parenthe-
ses.[a]
(those in which the studied compounds are insoluble), and
S solvents (those in which the studied compounds are com-
pletely soluble). Very recently, this method was successfully
utilized to predict the solvents in which a determined gela-
tor would form a gel.[33] In our case, the gelification domain
is located in the right-bottom part of the Tea plot and those
solvent whose Teas parameters lie in this domain should
form their corresponding organogels.
Solvent
1a
1b
2a
2b
EtOH
CHCl3
EtOAc
toluene
MCH
I
S
I
I
S
I
S
S
S
S
S
G (4)
G (10)
G (20)
G (4)
G (60)
G (80)
G (20)
S
S
The morphology of the aggregates that constituted the
gels was analyzed by atomic force microscopy (AFM) of
dilute solutions in toluene that were deposited onto a
HOPG surface. The AFM images that were obtained upon
drop-casting a 1ꢃ10ꢀ5 m solution of achiral BTA 1a showed
wire-like structures, which bundled together to form small
domains of fibrillar structures (see Figure S11 in the Sup-
porting Information). The small size of these fibrillar struc-
tures is indicative of the weak tendency of compound 1a to
self-assemble under such dilute conditions. BTA 1b exhibits
a weaker trend to form fibrillar structures, which could be
related to the weaker interactions of the branched alkyl
chains of compound 1b in comparison to the straight alkyl
chains of compound 1a. Thus, after several attempts to de-
posit the sample by drop-casting or by spin-coating, we
could not obtain AFM images that showed organized struc-
tures from chiral BTA 1b. However, Figure 7a,b, and Fig-
[a] I: Insoluble, S: Soluble, G: stable gel.
The data collected in Table 3 show that the presence of
stereogenic centers in the LMWG notably retards the gela-
AHCTUNGTRENNUNG
ACHTUNGTRENNUNGtion ability, with the exception of compound 2b, which is
able to gelate EtOAc at a concentration of 20 mgmLꢀ1
(Figure 6). The less-efficient interdigitation of the peripheral
side-chains could justify these findings (see below). The ge-
ꢀ
lation of the solvent by OPE TAs 2a,b, with a bigger p sur-
face than BTAs 1a,b, requires a larger amount of the orga-
nogelator to constitute the gel, which is diagnostic of the sig-
nificance of the size of the central aromatic core on the ge-
lation ability.
Figure 6. a) Optical images of organogels that were formed from BTAs
ꢀ
1a,b and OPE TAs 2a,b in EtOAc. b) Teas plot of the solubility pa
G
Figure 7. AFM images of dilute solutions (1ꢃ10ꢀ5 m in toluene) of com-
pounds 1b (a,b) and 2a (c,d) on highly oriented pyrolytic graphite
(HOPG). The z scales in (a)–(d) are 10, 7, 75, and 12 nm, respectively.
Inset in (b) shows the height profile along the black line.
eters of compounds 1a and 2a and the solvents in the gelation test (~ I,
^ S, * G). The dotted line shows the gelation domain.
The gelation data that were extracted from discotics 1 and
2, together with Teas parameters fd, fp, and fh (which express
the dispersion, polar, and hydrogen-bonding component of a
solvent, respectively)[31,32] of the utilized solvents, allowed
the elaboration of a Teas plot, in which the solvents were
grouped into G solvents (those that form gels), I solvents
ure S12 in the Supporting Information show AFM images of
chiral BTA 1b that was deposited onto HOPG from a
1ꢃ10ꢀ5 m solution in toluene, followed by toluene vapor ex-
posure at about 258C for 12 h.[34] These AFM images
showed well-defined, long and thin bundles of chiral fibers,
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L. Sꢁnchez et al.
and the mixture was stirred at RT for 14 h. The organic layer was washed
with 1m HCl, 1m NaHCO3, and water and dried over MgSO4. After
evaporation of the solvent, the residue was purified by column chroma-
tography on silica gel (CHCl3/MeOH, 98:2), thereby affording compound
1a as a white solid (0.14 g, 56%). 1H NMR (300 MHz, CDCl3, 258C,
TMS): d=7.90 (br s, 6H, Hb+e), 7.78 (br s, 3H; Ha), 7.09 (s, 6H; Hf), 3.92
the height of which was about 3 nm, which fit with the calcu-
lated diameter of the discotic molecule (Figure 7b, inset).
ꢀ
AFM images of achiral OPE TA 2a indicated the stron-
ger tendency of this compound to self-assemble into fibrillar
structures, which subsequently bundled into thick filaments.
Figure 7c shows a tangle of fibers, which is present even at
high dilution (1ꢃ10ꢀ5 m in toluene). These fibers are consti-
tuted by helical nanofibers (Figure 7d and Figure S13 in the
Supporting Information) and the fibrillar aggregates that
were formed by achiral compound 2a were stable, even at
higher dilution levels. Figure S14 in the Supporting Informa-
tion shows the fibrillar structures that were seen upon drop-
casting a 5ꢃ10ꢀ6 m solution of compound 2a in toluene onto
HOPG.
ACTHNUTRGNEUNG
(t, 3J(H,H)=6.5 Hz, 6H; Hg’), 3.88 (t, 3J (H,H)=6.0 Hz, 12H; Hg), 3.49
(br s, 6H; Hc), 3.45 (br s, 6H; Hd), 1.69 (m. 18H; Hh), 1.43 (m, 6H; Hiꢄ),
1.38 (m, 12H; Hi), 1.25 (br s, 48H; Hj’–q’), 1.24 (br s, 96H; Hj–q), 0.87 ppm
3
(t, J
N
168.6, 166.8, 153.1, 141.2, 134.8, 128. 9, 106.0, 73.6, 69.4, 40.8, 40.6, 32.1,
30.5, 29.9, 29.8, 29.6, 29.5, 29.3, 26.2, 22.8, 14.2 ppm; FTIR (neat): n˜ =720,
1118, 1231, 1293, 1338, 1379, 1432, 1463, 1497, 1542, 1580, 1646, 2855,
2924, 3310 cmꢀ1; HRMS (MALDI-TOF): m/z calcd for C144H252N6O15
:
2307.9157 [M]+; found: 2307.9141.
N1,N3,N5-Tris(2-(3,4,5-tris((S)-3,7-dimethyloctyloxy)benzamido)-ethyl)-
benzene-1,3,5-tricarboxamide (1b): Trimesic acid (0.03 g, 0.15 mmol) was
dissolved in dry THF (2 mL) and the solution was cooled to 08C. 1-
Ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (0.09 g,
0.47 mmol) and 4-dimethylaminopyridine (0.06 g, 0.47 mmol) were added
to the solution of trimesic acid under an argon atmosphere. The mixture
was cooled to 08C and stirred for 15 min. Next, compound 3b (0.30 g,
0.47 mmol) was added portionwise and the mixture was stirred at RT for
16 h. The organic layer was washed with 1m HCl, 1m NaHCO3, and
water and dried over MgSO4. After evaporation of the solvent, the resi-
due was purified by column chromatography on silica gel (CHCl3/MeOH,
98:2), thereby affording compound 1b as a white solid (0.20 g, 65%).
1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.90 (br s, 3H; Hb), 7.84 (s,
3H; Ha), 7.74 (br s, 3H; He) 7.13 (s, 6H; Hf), 3.95 (m, 18H; Hg), 3.46
Conclusion
The supramolecular polymerization mechanism of two
series of C3-symmetric discotics has been exhaustively stud-
ied. The first series consists of BTA-like compounds that are
decorated with peripheral 3,4,5-trialkyloxy-N-ethylenbenz-
ACHTUNGTRENNUNGamide units. The self-assembly of these discotics (1) was in-
vestigated by ITC in CHCl3, which demonstrated the isodes-
mic character of the supramolecular polymerization of these
(br s, 12H; Hc,d), 1.78 (m, 9H; Hi), 1.64 (br s, 9H; Hn), 1.49 (m, 18H;
3
Hh), 1.37–1.01 (br s, 54H; Hk–m), 0.89 (d, J
0.80 (br s, 18H; Hj), 0.85 (d, J
AHCTUNGTRENNUNG
(H,H)=6.5 Hz, 9H; Hj’), 0.87–
discotics in CHCl3, with values for the binding constant of
3
3
ꢀ1
ACHTUNGRTENN(NUG H,H)=6.6 Hz, 18H; Ho’), 0.84 ppm (d, J-
ꢀ
about 496m . The second series consists of OPE TAs dis-
(H,H)=6.6 Hz, 36H; Ho); 13C NMR (75Mz, CDCl3, 258C, TMS): d=
cotics that are also endowed with 3,4,5-tris
ethylen
A
168.6, 166.8, 153.0, 141.1, 134.8, 128. 8, 128.3, 105.8, 71.7, 67.4, 40.9, 40.5,
39.4, 39.3, 37.6, 37.4, 36.4, 29.8, 29.7, 28.0, 24.8, 22.7, 22.6, 19.5, 19.4 ppm;
FTIR (neat): n˜ =763, 862, 994, 1114, 1230, 1290, 1335, 1377, 1430, 1465,
1496, 1541, 1580, 1644, 2872, 2926, 2954, 3311 cmꢀ1; HRMS (ESI-FT):
benzamide groups. The larger p-surface of these dis-
cotics allows a more-accurate study of the aggregation
ꢀ
mechanism. Thus, chiral OPE TA 2b self-assembles cooper-
m/z calcd for C126H217N6NaO15
:
2077.62490 [M+H+Na]+; found:
atively in apolar MCH or toluene, with Ka values of 0.0023
and 0.00022, respectively, as established in the correspond-
ing VT-CD experiments. ITC experiments for compounds 2
in CHCl3 demonstrate that these compounds follow an iso-
desmic mechanism with a calculated K value of around
388mꢀ1 for self-assembly. These studies confirm the strong
influence of: 1) the nature of the solvent; 2) the p-surface of
the central aromatic core of the studied discotic; and 3) the
branched nature the peripheral side-chains on the supramo-
lecular polymerization and, consequently, the gelation abili-
ty. Thus, this gelation ability notably decreases in CHCl3, in
which the supramolecular polymerization is isodesmic.
Therefore, these studies underpin the self-assembly features
of organogelators in solution with their ability to generate
LMWGs.
2077.62531.
4-Iodo-(2-(3,4,5-tris(dodecyloxy)benzamido)ethyl)carbamoyl)benzene
(4a): p-Iodobenzoic acid (0.12 g, 0.50 mmol) was dissolved in dry CH2Cl2
(4 mL) and the solution was cooled to 08C. 1-Ethyl-3-(3-dimethylamino-
propyl)carbodiimide hydrochloride (0.09 g, 0.47 mmol) and 4-dimethyla-
minopyridine (0.11 g, 0.56 mmol) were added to the solution of p-iodo-
benzoic acid under an argon atmosphere. The mixture was cooled to 08C
and stirred for 15 min. Next, compound 3a (0.40 g, 0.56 mmol) was added
portionwise and the mixture was stirred at RT for 14 h. The organic layer
was washed with 1m HCl, 1m NaHCO3, and water and dried over
MgSO4. After evaporation of the solvent, compound 4a was obtained
without further purification as a white solid (0.39 g, 78%). 1H NMR
(300 MHz, CDCl3, 258C, TMS): d=7.94 (br s, 1H; Hc), 7.72 (br s, 1H;
Hf), 7.68 (d, 3J
Hb), 3.98 (t, 3J(H,H)=6.5 Hz, 2H; Hh’), 3.90 (t, 3J
Hh), 1.73 (m, 6H; Hi), 1.41 (m, 6H; Hj), 1.25 (br s, 48H; Hk–r), 0.87 ppm
(t, 3J(H,H)=6.9 Hz, 9H; Hs); 13C NMR (75Mz, CDCl3, 258C, TMS): d=
G
ACHTUNGTREN(NGNU H,H)=8.4 Hz, 2H;
E
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
168.9, 168.0, 153.2, 141.2, 137.8, 133.3, 128.9, 105.7, 98.7, 73.6, 69.3, 41.0
32.0, 30.4, 29.8, 29.7, 29.6, 29.5, 29.4, 26.2, 26.1, 22.8, 14.2 ppm; FTIR
(neat): n˜ =676, 721, 844, 1007, 1065, 1122, 1234, 1304, 1345, 1386, 1428,
1467, 1499, 1542, 1584, 1634, 2853, 2922, 3279 cmꢀ1
.
Experimental Section
4-Iodo-(2-(3,4,5-tris((S)-3,7-dimethyloctyloxy)benzamido)ethyl)carba-
moyl)benzene (4b): p-Iodobenzoic acid (0.14 g, 0.58 mmol) was dissolved
in dry CH2Cl2 (6 mL) and the solution was cooled to 08C. 1-Ethyl-3-(3-
dimethylaminopropyl)carbodiimide hydrochloride (0.12 g, 0.64 mmol)
and 4-dimethylaminopyridine (0.08 g, 0.64 mmol) were added to the solu-
tion of p-iodobenzoic acid under an argon atmosphere. The mixture was
cooled to 08C and stirred for 15 min. Next, compound 3b (0.40 g,
0.64 mmol) was added portionwise and the mixture was stirred at RT for
16 h. The organic layer was washed with 1m HCl, 1m NaHCO3, and
N1,N3,N5-Tris(2-(3,4,5-tris(dodecyloxy)benzamido)ethyl)benzene-1,3,5-tri-
carboxamide (1a): Trimesic acid (0.02 g, 0.11 mmol) was dissolved in dry
THF (2 mL) and the solution was cooled to 08C. 1-Ethyl-3-(3-dimethyl-
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(2 mL) and the mixture was added to the solution of trimesic acid under
an argon atmosphere. The mixture was cooled to 08C and stirred for
15 min. Next, compound 3a (0.25 g, 0.35 mmol) was added portionwise
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Supramolecular Polymerization of C3-Symmetric Organogelators
FULL PAPER
water and dried over MgSO4. After evaporation of the solvent, com-
Yꢅlamos, Dr. E. Pꢅrez, and Prof. N. Martꢀn from the UCM. We also
gratefully acknowledge Prof. L. Bouteiller for his helpful discussions on
the ITC results.
pound 4b was obtained without further purification as a white solid
(0.49 g, 97%). 1H NMR (300 MHz, CDCl3, 258C, TMS): d=7.74 (d, 3J-
3
G
N
1H; Hf), 7.01 (s, 2H; Hg), 4.01 (m, 6H; Hh), 3.65 (br s, 4H; Hd,e), 1.84
(m, 3H; Hj), 1.67 (br s, 3H; Ho), 1.52 (m, 6H; Hi), 1.38–1.08 (br s, 18H;
[1] a) C. A. Hunter, H. L. Anderson, Angew. Chem. 2009, 121, 7624–
7636; Angew. Chem. Int. Ed. 2009, 48, 7488–7499; b) J. D. Badjic,
A. Nelson, S. J. Cantrill, W. B. Turnbull, J. F. Stoddart, Acc. Chem.
Res. 2005, 38, 723–732; c) A. Mulder, J. Huskens, D. N. Reinhoudt,
Org. Biomol. Chem. 2004, 2, 3409–3424; d) S. Shinkai, M. Ikeda, A.
Sugasaki, M. Takeuchi, Acc. Chem. Res. 2001, 34, 494–503.
[2] M. F. Q. Perutz, Q. Rev. Biophys. 1989, 22, 139–236.
[3] Biochemistry 6th ed (Eds.: J. M. Berg, J. L. Tymoczko, L. Stryer),
W. H. Freeman, New York, 2007.
[4] E. Terzi, G. Hçlzemann, J. Seelig, J. Mol. Biol. 1995, 252, 633–642.
[5] T. F. A. De Greef, M. M. J. Smulders, M. Wolffs, A. P. H. J. Schen-
ning, R. P. Sijbesma, E. W. Meijer, Chem. Rev. 2009, 109, 5687–
5754.
Hl,m), 0.92 (d, 3J
ACHTUNGTRENNUNG ACHTUNGTRENNUNG
(H,H)=6.4 Hz, 6H; Hk), 0.91 (d, 3J
Hk’), 0.86 ppm (d, 3J
ACHTUNGTRENNUNG
258C, TMS): d=169.1, 168.0, 153.3, 137.9, 133.4, 128.8, 128.7, 105.7, 98.8,
71.9, 67.7, 41.4, 41.0, 39.5, 39.4, 37.6, 37.5, 36.5, 30.0, 29.8, 28.1, 24.9, 22.8,
22.7, 19.7 ppm; FTIR (neat): n˜ =742, 864, 1006, 1116, 1235, 1301, 1342,
1384, 1498, 1548, 1583, 1632, 1733, 2867, 2926, 2954, 3083, 3277 cmꢀ1
.
1,3,5-Tris(2-((4-(2-(3,4,5-tris(dodecyloxy)benzamido)ethyl)carbamoyl)-
phenyl)ethynyl)benzene (2a): Compound 4a (355 mg, 0.37 mmol), com-
pound 5 (17 mg, 0.11 mmol), bis(triphenylphosphine)palladium(II) chlo-
ACHTUNGTRENNUNGride (4 mg, 0.005 mmol), and copper(I) iodide (1 mg, 0.006 mmol) were
dissolved in dry THF (8 mL) and the mixture was subjected to several
vacuum/argon cycles. After that, triethylamine (2 mL) was added and the
reaction mixture was subjected to further vacuum/argon cycles before
being heated at 708C with stirring overnight. After evaporation of the
solvent under reduced pressure, the residue was washed with 1m HCl, ex-
tracted with CH2Cl2, washed with NH4Cl, and dried over MgSO4. After
evaporation of the solvent, the residue was purified by column chroma-
tography on silica gel (CHCl3/MeOH, 100:1), thereby affording com-
[6] A. R. A. Palmans, E. W. Meijer, Angew. Chem. 2007, 119, 9106–
9126; Angew. Chem. Int. Ed. 2007, 46, 8948–8968.
[7] For selected reviews, see: a) P. Terech, R. G. Weiss, Chem. Rev.
1997, 97, 3133–3159; b) J. H. van Esch, B. L. Feringa, Angew. Chem.
2000, 112, 2351–2354; Angew. Chem. Int. Ed. 2000, 39, 2263–2266;
c) M. George, R. G. Weiss, Acc. Chem. Res. 2006, 39, 489–497;
d) M. Sada, N. Takeuchi, M. Fujita, M. Numata, S. Shinkai, Chem.
Soc. Rev. 2007, 36, 415–435; e) A. Ajayaghosh, V. K. Praveen, C. Vi-
jayakumar, Chem. Soc. Rev. 2008, 37, 109–122; f) P. Dastidar,
Chem. Soc. Rev. 2008, 37, 2699–2715; g) M. Llusar, C. Sꢁnchez,
Chem. Mater. 2008, 20, 782–820; h) J. W. Steed, Chem. Soc. Rev.
2010, 39, 3686–3699; i) J. W. Steed, Chem. Commun. 2011, 47, 1379–
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[8] a) A. Ajayaghosh, R. Varghese, V. K. Praveen, S. Mahesh, Angew.
Chem. 2006, 118, 3339–3342; Angew. Chem. Int. Ed. 2006, 45, 3261–
3264; b) S. Yagai, S. Mahesh, Y. Kikkawa, K. Unoike, T. Karatsu, A.
Kitamura, A. Ajayaghosh, Angew. Chem. 2008, 120, 4769–4772;
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malai, S. Yagai, A. Kitamura, A. Ajayaghosh, Chem. Commun.
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Lloyd, N. Clarke, J. A. K. Howard, J. W. Steed, Nat. Chem. 2010, 2,
1037–1043; e) A. Vidyasagar, K. Handore, K. M. Sureshan, Angew.
Chem. 2011, 123, 8171–8174; Angew. Chem. Int. Ed. 2011, 50, 8021–
8024; f) S. S. Babu, S. Prasanthkumar, A. Ajayaghosh, Angew.
Chem. 2012, 124, 1800–1810; Angew. Chem. Int. Ed. 2012, 51, 1766–
1776; g) F. Aparicio, E. Matesanz, L. Sꢁnchez, Chem. Commun.
2012, 48, 5757–5759.
1
pound 2a as an orange solid (106 mg, 37%). H NMR (300 MHz, CDCl3,
3
258C, TMS): d=7.60 (d, J
N
(br s, 3H; Hd/g), 7.35 (br s, 9H; Hb, d/g), 6.97 (s, 6H; Hh), 3.90 (m, 18H;
Hi,i’), 3.62 (br s, 12H; He, f), 1.69 (m, 18H; Hj,j’), 1.38–1.17 (br s, 162H;
Hk,l,k’,l’), 0.79 ppm (m, 27H; Ht,t’); 13C NMR (75Mz, CDCl3, 258C, TMS):
d=169.5, 168.4, 153.5, 141.5, 133.9, 132.1, 129.1, 127.5, 126.5, 124.3, 105.9,
90.4, 90.2, 73.9, 69.6, 41.4, 41.2, 32.3, 30.1, 30.1, 29.9, 29.8, 26.5, 23.1,
14.5 ppm; FTIR (neat): n˜ =672, 723, 761, 853, 962, 1011, 1118, 1232, 1303,
1339, 1382, 1430, 1464, 1498, 1542, 1580, 1636, 1719, 2362, 2854, 2924,
3078, 3293 cmꢀ1; HRMS (MALDI-TOF): m/z calcd for C168H265N6O15
2607.0158 [M+H]+; found: 2607.0166.
:
1,3,5-Tris(2-((4-(2-(3,4,5-tris((S)-3,7-dimethyloctyloxy)benzamido)ethyl)-
carbamoyl)phenyl)ethynyl)benzene (2b): Compound 4b (390 mg,
0.41 mmol), compound 5 (20 mg, 0.13 mmol), bis(triphenylphosphine)pal-
ladium(II) chloride (5 mg, 0.007 mmol), and copper(I) iodide (2 mg,
0.008 mmol) were dissolved in dry THF (10 mL) and the mixture was
subjected to several vacuum/argon cycles. After that, triethylamine
(2 mL) was added and the reaction mixture was subjected to further
vacuum/argon cycles before being heated at 708C with stirring for 48 h.
After evaporation of the solvent under reduced pressure, the residue was
washed with 1m HCl, extracted with CH2Cl2, washed again with NH4Cl,
and dried over MgSO4. After evaporation of the solvent, the residue was
purified by column chromatography on silica gel (CHCl3/MeOH, 100:1),
thereby affording compound 2b as a pale-orange solid (60 mg, 20%).
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U
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6H; Hb), 7.41 (br s, 3H; Hd/g), 7.08 (s, 6H; Hh), 4.03 (m, 18H; Hi,i’), 3.71
(br s, 12H; He,f), 2,05–1.13 (br s, 108H; Hj–p,j’–p’), 0.92 (m, 27H; Hl,l’),
ACHTUNGTRENNUNG
0.86 ppm (d, 3J(H,H)=6.6 Hz, 54H; Hq,q’); 13C NMR (75Mz, CDCl3,
258C, TMS): d=168.8, 168.1, 153.2, 141.2, 134.3, 133.6, 131.7, 128.7,
127.2, 126.1, 105.7, 90.0, 89.8, 71.7, 67.5, 40.9, 40.8, 39.4, 37.6, 37.4, 37.3,
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24.6, 22.7, 22.6, 19.6, 19.6 ppm; FTIR (neat): n˜ =642, 671, 733, 853, 964,
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Received: July 23, 2012
Revised: November 30, 2012
Published online: && &&, 0000
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ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Supramolecular Polymerization of C3-Symmetric Organogelators
FULL PAPER
Organogelators
F. Aparicio, F. Garcꢀa,
L. Sꢁnchez* ...................... &&& — &&&
Supramolecular Polymerization of C3-
Symmetric Organogelators: Coopera-
tivity, Solvent, and Gelation Relation-
ship
We C3 kings: The influence of solvent,
the size of the discotics, the p-surface
of the aromatic core, the nature of the
side chains, and the gelation ability of
the organogelators 1 and 2 on their
supramolecular polymerization mecha-
nism is presented (see figure).
Chem. Eur. J. 2013, 00, 0 – 0
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!