Self-assembled structures in organogels of amphiphilic diblock codendrimers

Article abstract of DOI:10.1002/chem.200701731

Amphiphilic diblock codendrimers consisting of dendrons of hydroxyl-containing poly(methallyl dichloride) (PMDC) and long alkyl-containing poly(urethane amide) (PUA) were synthesized in different generations. These codendrimers were found to self-assemble

Full text of DOI:10.1002/chem.200701731

DOI: 10.1002/chem.200701731
Self-Assembled Structures in
Codendrimers
A
Miao Yang,[a] Zijian Zhang,[a] Fei Yuan,[a] Wei Wang,*[a] Sandra Hess,[b]
Karen Lienkamp,[b] Ingo Lieberwirth,[b] and Gerhard Wegner*[b]
Abstract: Amphiphilic diblock coden-
drimers consisting of dendrons of hy-
droxyl-containing poly(methallyl di-
chloride) (PMDC) and long alkyl-con-
taining poly(urethane amide) (PUA)
were synthesized in different genera-
tions. These codendrimers were found
to self-assemble into ribbonlike aggre-
gates in organic solvent and further
formed three-dimensional networks
and behaved macroscopically as gels.
The width of the self-assembled rib-
bons decreases with the generation of
both dendritic blocks. Multiple inter-
molecular hydrogen bonds between
amide and hydroxyl groups were found
to be the main driving force to form
these self-assembled gels.
Keywords: amphiphiles
· dendri-
mers · gels · molecular interactions ·
self-assembly
Introduction
assembly owing to their well-defined architectures and di-
versity in functionalization.[2] It has been demonstrated that
modified dendrons can act as building blocks to induce the
formation of spherical or cylindrical supramolecular ob-
jects.[3] It is interesting to mention that bolaform dendritic
molecules with amphiphilic features assemble in their gel
phase into one-dimensional aggregates, which further devel-
op into cross-linked networks in organic or aqueous
media.[4,5] Meanwhile, nanoribbonlike supramolecular struc-
tures have also been found in gels of dendronized rod–coil
molecules.[6] These works have provided a first indication
that the molecular architecture may be one of the key fac-
tors in the gel formation of dendritic molecules.[7] To design
novel gelators, however, we still need to clarify the impor-
tance of some molecular parameters, such as shape, polarity,
and intermolecular interaction, on the formation of supra-
molecular structures in their gels.
Over recent decades, there has been great interest in explor-
ing novel gel-phase materials particularly because of their
potential applications in cosmetics, food processing, drug de-
livery etc.[1] Normally, gelators form well-defined supra-
molecular structures on several hierarchical levels, first by
molecular recognition followed by anisotropic aggregation
in one or two dimensions and finally, three-dimensional net-
works form that can trap solvents.[1] Therefore, investiga-
tions in this field, particularly in exploring novel gelators,
can fully express the bottom-up concept from designing and
then synthesizing novel gelator molecules to constructing
supramolecular structures mainly through self-assembly.
Dendrimer-based molecules acting as promising candi-
dates have attracted great attention in supramolecular self-
Recently our group has concentrated our efforts on the
self-assembly of diblock codendrimers.[8] They have previ-
ously been shown to provide versatile supramolecular
shapes and architectures when tuning their shape and polari-
ty. In this work we study the effects of molecular architec-
ture, multiple interactions, and the polarity of the block co-
dendrimers on their self-assembly characteristics during gel
formation in organic media. To achieve this goal, a series of
amphiphilic diblock codendrimers was prepared, as shown
in Scheme 1. They contain amide branches for the formation
of multiple hydrogen bonds, hydroxyl groups for hydrophilic
ends, and alkyl chain tails for stabilization of the aggregates
through hydrophobic interactions. Clearly, changing the gen-
[a] M. Yang, Z. Zhang, Dr. F. Yuan, Prof. Dr. W. Wang
The Key Laboratory of Functional Polymer Materials
of the Ministry of Education
Institute of Polymer Chemistry, College of Chemistry
Nankai University, Tianjin 300071 (China)
Fax : (+86)22-234-98126
E-mail: weiwang@nankai.edu.cn
[b] Dr. S. Hess, Dr. K. Lienkamp, Dr. I. Lieberwirth,
Prof. Dr. G. Wegner
Max-Planck-Institute for Polymer Research
Ackermannweg 10, 55128, Mainz (Germany)
Fax : (+49)6131-379-330
E-mail: wegner@mpip-mainz.mpg.de
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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FULL PAPER
Results and Discussion
Synthesis and structural fea-
tures of block codendrimers:
The convergent routes to syn-
thesize dendritic poly(urethane
amide) (PUA)[9] and dendritic
poly(methallyl
dichloride)
(PMDC)[10] were employed to
generate alkyl-group-modified
PUA dendrons and hydroxyl-
group-modified PMDC den-
drons. The final block coden-
drimers were obtained by cou-
pling two monodendrons to-
gether at the focal groups by
using an efficient esterification
reaction (Scheme 1).[11] The
coupling reaction was followed
by catalytic hydrogenolysis to
quantitatively remove the ben-
zylidene (Bz) groups to obtain
codendrimers with exposed hy-
droxyl groups at the PMDC
moiety. The purity and the
structural identity of the coden-
drimers were assessed by
combination of and
a
1H
13C NMR spectroscopies, elec-
trospray ionization time-of-
flight (ESI-TOF) and matrix-as-
sisted laser desorption/ioniza-
tion time-of-flight (MALDI-
TOF) mass spectrometries, and
elemental analysis (see the Sup-
porting Information).
From compounds 1 to 4, the
chemical structure, molecular
architecture, and functional
groups are gradually altered by
changing the generation of the
dendritic blocks. Among com-
pounds 1, 2, and 3, the PUA
block remains in the second
generation and has two amides
and four urethanes, whereas the
PMDC block increases its gen-
eration from the first to the
third. Therefore, the number of
hydroxyl groups in the periph-
ery of the PMDC block increas-
es from two to eight. Most im-
portant is that this increase
Scheme 1. Schematic structures of diblock codendrimers of PUA and PMDC dendrons with different genera-
tions.
eration of the two dendritic blocks independently can adjust
their sizes, shapes, and intermolecular interactions. In this
way the impact of these factors on self-assemblies can be
properly investigated.
should augment the polarity, so that these codendrimers are
amphiphilic. In compound 4, the third generation PUA
block was coupled with a third generation PMDC block.
The clear difference from the other three compounds is the
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3331

W. Wang, G. Wegner et al.
presence of the six amide and eight urethane groups in the
PUA block, so the ability of forming inter- or intramolecular
hydrogen bonds should be greatly boosted.
Formation and properties of organic gels: The codendrimers
were found to form transparent gels in toluene or benzene.
It is well-known that gel formation is a kinetically controlled
process following a nucleation-growth feature.[12] When solu-
tions of the codendrimers in toluene were cooled from 708C
to an ambient temperature, a limited number of nuclei were
created, so a mixture of clear solution with large gel flakes
was observed. When the solutions were cooled abruptly by
using dry ice/acetone (ꢀ788C) and then allowed to stand at
an ambient temperature, however, the whole solution
became immobile and transparent after one day, which indi-
cated the formation of complete gels. This is because rapid
cooling creates a great number of nuclei distributing homo-
geneously through the entire solution. Further growth facili-
tates the formation of a homogeneous gel.[13] The minimum
gel concentrations, cmin, at which all of the solution became
immobile after gelation, are used to describe the gelation
ability. From cmin we can obtain the value of the number of
trapped solvent molecules per codendrimer molecule (TSM/
CM). The cmin and TSM/CM values of the four codendrimers
investigated are listed in Table 1. The results show that the
Figure 1. SEM image of the ribbonlike structures found in a solution of 3
in toluene at a concentration of 0.1 gLꢀ1. The scale bar is 200 nm.
intermolecular interactions of the dendritic architectures.
Therefore, cmin means the formation of a complete 3D net-
work of supramolecular structures, rather than mere self-as-
sembly. Interestingly, the solutions of the benzylidene-pro-
tected codendrimers did not form gels under the same con-
ditions, which again indicates that the polarities created by
the hydroxyl groups in the PMDC periphery are essential
for gelation.
Multiple intermolecular interactions: FTIR spectra of 3 in
the solid state, the gel phase and the sol phase (fresh solu-
tion in toluene) are shown in Figure 2 (arrows indicate the
peaks studied). It can be seen that the differences between
the spectra for the gel phase and solid state are insignificant.
Table 1. Summary of results from cmin measurements, SAXS experiments,
and molecular modeling.
Mw
cmin
TSM/
CM[a]
Molecular
dimension[b]
[nm]
Interlamellar
spacing[c]
[nm]
ꢀ
[gmolꢀ1
]
[gLꢀ1
]
However, the bands at n˜ =1721 (C=O stretching), 1524 (N
ꢀ1
ꢀ
ꢀ
H bending), 1250 (C N stretching), and 3330 cm (N H
stretching) are shifted to 1686, 1553, 1290, and 3319 cmꢀ1,
respectively, after gelation from solution, which indicates
that upon gelation the amide or urethane groups become
1
2
3
4
1834
2024
2405
4331
9.6
8.2
7.0
4.2
1800
2320
3230
9700
4.5
4.9
5.4
6.4
9.1
8.5
9.6
–
[a] Number of trapped solvent molecules per codendrimer molecule.
[b] Estimated from molecular modeling. [c] Obtained by SAXS experi-
ments on slowly dried gels.
value of cmin decreases, whereas TSM/CM increases from co-
dendrimers 1 to 4, which indicates that the gel-forming abili-
ty increases when increasing the generation of the PUA and
PMDC blocks. This further illustrates that increasing the po-
larity by raising the number of hydroxyl groups on the
PMDC block and enhancing interactions through the incor-
poration of more amide groups in the PUA block can im-
prove the gel-forming ability of the codendrimers.
Interestingly, below cmin the solution becomes partially im-
mobile and consists of the solvent and gel blocks down to a
concentration of 0.1 gLꢀ1 (much lower than cmin =7.0 gLꢀ1
for compound 3). Below a concentration of 0.1 gLꢀ1, a ho-
mogeneous solution is formed. At a concentration of
0.1 gLꢀ1, codendrimer 3 can form ribbonlike objects (as
shown in Figure 1) like those formed at concentrations
above cmin. This means that over a wide concentration range
the codendrimer molecules self-assemble to form aggregates
rather than stay molecularly dispersed owing to the multiple
Figure 2. FTIR spectra of 3 in the solid state, the gel-phase and the sol-
phase. The solvent is toluene.
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Amphiphilic Diblock Codendrimers
FULL PAPER
strongly hydrogen bonded.[9d,14] Most important to note is
ꢀ
that the C N stretching bands at 1250 (in solution) and
1290 cmꢀ1 (in the gel phase) have a trans formation of the
amide and urethane groups, which indicates the formation
of intermolecular hydrogen bonds after gelation. Thus, the
IR data clearly indicates that the intermolecular hydrogen
bonds between amides and urethanes are a key contribution
to gelation.
A broad absorption of the wet gel from 3120 to 3680 cmꢀ1
indicates the existence of multiple interactions between the
hydroxyl groups on the PMDC blocks, which may be anoth-
er key factor in assisting gel formation of the codendrimers.
We can now understand why the solutions of the benzyli-
dene-protected codendrimers did not form gels under the
same conditions: owing to their lack of amphiphilicity, there
is no driving force to bring them together. Furthermore, the
ꢀ
IR spectra in Figure 2 show that the C H stretching and
rocking bands are shifted from 2924, 2855, and 1139 cmꢀ1 to
2916, 2849 and 1151 cmꢀ1, respectively, after gelation. This
result provides evidence to indicate the formation of a
denser packing of the alkyl chains in the gel phase, which is
the third factor for assisting gel formation and the stabiliza-
tion of the supramolecular structure.
Figure 3. TEM images of dried gels of 1 (A), 2 (B), 3 (C), and 4 (D). The
solvent used was toluene and the scale bars are 500 nm.
As discussed in the previous subsection, the gel-forming
ability is improved with increasing the numbers of amide or
urethane groups in the PUA blocks and the hydroxyl groups
in the PMDC blocks. Our IR studies have provided evi-
dence at the molecular level to verify that the strong inter-
actions, particularly the multiple hydrogen bonds between
the PUA blocks in adjacent codendrimers, are the key for
forming a stable gel phase. Therefore, it is also understanda-
ble that a change in these interactions will affect the gel-
forming ability, as indicated in Table 1.
Supramolecular structures: It is well-known that gels de-
rived from low molecular mass gelators are supramolecular
compounds, which means that the small gelator molecules
assemble one- or two-dimensional aggregates at first that
further entangle to form self-assembled aggregate networks
through a combination of noncovalent interactions.[1] In this
work we used transmission electron microscopy (TEM),
scanning electron microscopy (SEM), and small-angle X-ray
scattering (SAXS) to investigate the self-assembled struc-
tures of the codendrimers in the gel phase. The TEM
images in Figure 3 show networks of one-dimensional aggre-
gates existing in the gels. The aggregates of compounds 1
and 2 show ribbonlike morphologies that occasionally fuse
and intertwine. The aggregates of compounds 3 and 4 show
fully cross-linked networks from which we know that the
network of 4 is better developed than that of 3. This is evi-
dence on the nanometer scale to reveal why the gel-forming
ability of the codendrimers is improved with increasing the
generation of both dendrons. SEM images obtained at a
higher magnification in Figure 4 evidently show the ribbon-
like aggregates. The ribbon widths are approximately
100 nm for 1, 80 nm for 2, 50 nm for 3, and 30 nm for 4. This
width decrease with the increasing generation further sug-
Figure 4. SEM images of dried gels of 1 (A), 2 (B), 3 (C), and 4 (D). The
solvent used was toluene and the scale bars are 200 nm.
gests that codendrimers composed of higher-generation den-
drons need fewer molecules to construct ribbons with the
same ability to build up the three-dimensional network. Un-
ambiguously, this is because increasing the generation of the
dendron blocks will result in an increase in the numbers of
hydroxyl, amide, and urethane groups in the codendrimers
that lead to a higher molecular polarity and stronger inter-
actions. These improvements further promote a highly or-
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3333

W. Wang, G. Wegner et al.
dered arrangement of codendrimers in supramolecular
structures. Therefore, the gel-forming ability of codendrim-
ers is enhanced, which exhibits a lowering of the cmin on the
macroscopic level.
SAXS experiments provide further details of the ribbon-
like structures of aggregates 1 to 3 as shown in Figure 5.
SAXS patterns of slowly concentrated gels from 1 to 3
same lamellar structure compared to a slowly concentrated
gel.
The scattering peaks in Figure 5 are relatively broad. Ac-
cording to the Scherrerꢁs theory the broad scattering peaks
imply only limited numbers of lamellae of compounds 1 to 3
stacked together to form the ribbons.[16] For compound 4,
our scattering study does not show any scattering signals re-
quired for structural determination. Possibly, the numbers of
the lamellae contained in the ribbons are less than those of
the other three codendrimers and may be the reason why 4
shows the best gel-phase forming ability of the four com-
pounds.
A possible model for ribbon formation: On the basis of our
experimental results, we suggest the simple model shown in
Figure 6 to rationalize the formation of ribbonlike structures
of the codendrimers. The possible steps are as follows: The
hydrogen bonds between hydroxyl groups on the periphery
of the PMDC blocks bring the two codendrimers together
to form a unit with an interdigitated layer structure. The hy-
drogen bonds inside the PUA blocks bring the units togeth-
er to form supramolecules with a ribbonlike structure.
During the process, the hydrogen bonds in the trans amide
and urethane groups result in a face-to-face arrangement be-
tween adjacent and fan-shaped PUA blocks. This is the key
factor that causes the dominating growth of the ribbons
along the direction perpendicular to the PUA face.
Figure 5. SAXS plots of slowly dried gels of 1 to 3. The solvent used was
toluene.
showed
a lamellar structure
with interlayer spacings of 9.1,
8.5, and 9.6 nm, respectively.
Considering the molecular di-
[15]
mensions (see Table 1), a lay-
ered packing of pairs of mole-
cules can be assumed. For com-
pound 1 the interlayer spacing
is twice that of molecular
length, which indicates bilay-
ered packing. For compounds 2
and 3, a dense packing of the
segment of the PMDC blocks
probably requires an interdigi-
tation of adjacent molecules to
avoid free volume.[8a] This is the
reason why the interlayer spac-
ing is slightly smaller than twice
that of the molecular length of
2 and 3. To ensure that the
Figure 6. A possible model for ribbon formation of the codendrimers.
slowly concentrated gel main-
tained the true structure of the
wet gel, freeze-drying was used for the gel in benzene. After
freeze-drying, the gel remained a cross-linked network of as-
semblies that had a macroscopically cottonlike appearance.
SAXS results of the freeze-dried gel showed almost the
Conclusion
In summary, a series of amphiphilic diblock codendrimers
consisting of PUA and PMDC blocks have been synthe-
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Amphiphilic Diblock Codendrimers
FULL PAPER
wtsample
sized. These novel codendrimers were found to self-assem-
ble into ribbonlike aggregates in toluene that could further
produce three-dimensional networks behaving macroscopi-
cally as gels. Our experimental studies have clearly demon-
strated that adjusting the generation of two individual den-
drons in the codendrimers can alter the molecular architec-
ture, the polarity ability, and the molecular interactions.
One important conclusion is that the high polarity and the
multiple molecular interactions, particularly the hydrogen
bonds between amide and hydroxyl groups can enhance the
gel-forming ability. Our work thus demonstrates that by
taking control over molecular parameters of low molecular
mass gelators we can control their self-assembly characteris-
tics. Thus, amphiphilic codendritic building blocks provide a
new strategy for the rational design of supramolecularly
structured functional materials.
cmin
¼
ð1Þ
wtsoln
lðmlÞꢀ
1toluene
The final cmin value was an average from three measurements.
Synthesis of codendrimers C16-PUA-b-PMDC(OH)
16g2g1_(OH)2 (1): Compound (5) (112.5 mg, 0.0585 mmol) was dissolved
in methanol/CH2Cl2 (1:1, 20 mL) and Pd/C (10%, 12 mg) was added. The
apparatus for catalytic hydrogenolysis was cooled by using liquid N2, the
air was evacuated, and it was filled with H2. The reaction was stirred at
RTfor 5 h. After the reaction was complete, the catalyst was filtered in a
glass filter and carefully washed with CH2Cl2. The filtrate was evaporated
to give 1 as a white powder (102 mg, 95%). 1H NMR (700 MHz, CDCl3)
d=0.88 (t, J=7.1 Hz, 12H; CH3), 1.11 (s, 3H; CH3 (PMDCOH)), 1.25 (s,
104H; (CH2)13), 1.58 (m, 8H; CH2CH2OCO), 1.66–1.86 (m, 12H;
CH2CONHCH2CH2CH2NCOCH2),
NCOCH2CH2CO), 3.07–3.37 (m, 24H; CONHCH2CH2CH2NCO), 3.57
(s, 4H; CH2OH (PMDCOH)), 3.98–4.06 (m, 8H; CH2CH2OCO), 4.17 (s,
2.54–2.70
(m,
12H;
2H; CH2O(PMDCOH)), 5.24, 5.32, 5.41, 5.50 ppm (s, 1H; NHCO);
R
13C NMR (62.9 MHz, CDCl3): d=14.1, 17.0, 22.7, 25.9, 27.1, 27.85, 27.92,
28.1, 28.4, 28.9, 29.1, 29.3, 29.6, 29.7, 30.9, 31.0, 31.9, 36.6, 37.0, 37.9, 38.3,
40.7, 45.3, 65.0, 65.1, 67.0, 156.95, 157.00, 157.1, 171.8, 172.5, 172.8, 173.0,
173.9 ppm; MALDI-TOF MS: m/z: 1872 [M+K]+; elemental analysis
calcd (%) for C103H197N9O17: C 67.46, H 10.83, N 6.87; found: C 67.50, H
10.88, N 6.70.
Experimental Section
16g2g2_(OH)4 (2): Compound 6 (762 mg, 0.346 mmol) was dissolved in
methanol/CH2Cl2 (1:1, 40 mL) and Pd/C (10%, 76 mg) was added. Com-
pound 16g2g2_Bz2 was deprotected according to the general procedure
for the removal of the Bz groups to give 2 as a white powder (690 mg,
98%). 1H NMR (700 MHz, CDCl3): d=0.80 (s, 6H; CH3 (PMDCOH)),
0.88 (t, J=7.0 Hz, 12H; CH3), 1.25(s, 104H; (CH2)13), 1.59 (m, 8H,
CH2CH2OCO), 1.64–1.86 (m, 12H; CH2CONHCH2CH2CH2NCOCH2),
2.23 (m, 1H; CH2CHCH2 (PMDCOH)), 2.53–2.68 (m, 12H;
NCOCH2CH2CO), 3.06–3.40 (m, 24H; CONHCH2CH2CH2NCO), 3.40–
3.62 (m, 16H; OCH2 (PMDCOH)), 3.98–4.06 (m, 8H; CH2CH2OCO),
4.18 (d, J=5.8 Hz, 2H; COOCH2CH (PMDCOH)), 5.29, 5.35 5.47,
5.51 ppm (s, 1H; NHCO); 13C NMR (62.9 MHz, CDCl3): d=14.1, 17.1,
22.7, 25.8, 27.0, 27.9, 28.5, 29.0, 29.1, 29.58, 29.64, 29.7, 30.88, 30.93, 31.9,
36.8, 37.9, 38.3, 39.3, 41.0, 42.8, 45.3, 50.8, 62.7, 65.0, 65.1, 67.5, 67.6, 75.3,
157.0, 157.1, 171.6, 172.4, 172.7, 172.9, 173.4 ppm; MALDI-TOF MS: m/
z: 2062 [M+K]+; elemental analysis calcd (%) for C112H215N9O21: C
66.46, H 10.71, N 6.23; found: C 66.44, H 10.65, N 6.32.
Materials: All reagents and solvents were purchased from major chemi-
cal suppliers and used without further purification unless otherwise
noted. Dry THF and dry CH2Cl2 (water content of less than 50 ppm)
were purchased from Acros.
Characterization methods of chemical structures: The purity and the
structural identity of the products were assessed by a combination of
TLC, 1H and 13C NMR spectroscopies, ESI-TOF and MALDI-TOF mass
spectrometries, and elemental analysis.
TLC was carried out on silica gel coated aluminum plates (0.25 mm silica
gel with F254 indicator, MACHEREY-NAGEL, Germany). 1H
(250 MHz) and 13C NMR (62.9 MHz) spectra were recorded in CDCl3 or
[D8]THF by using a Brucker Spectrospin 250 spectrometer and 700 MHz
1H NMR spectra were recorded in CDCl3 by using a Brucker Ultrashield
700 spectrometer. All d values are given in ppm relative to tetramethylsi-
lane. MALDI-TOF mass spectrometry was recorded by using a Bruker
Reflex II-TOF spectrometer equipped with a 337 nm nitrogen laser. The
samples for MALDI-TOF measurements were prepared with a dithranol
matrix and potassium salt by using CH2Cl2 as solvent. Elemental analysis
was performed by using an Elemental Vario MICRO CURE instrument.
16g2g3_(OH)8 (3): Compound 7 (529 mg, 0.192 mmol) was dissolved in
methanol/CH2Cl2 (1:1, 30 mL) and Pd/C (10%, 53 mg) was added.
16g2g3_Bz4 was deprotected according to the general procedure for the
removal of the Bz groups to give 3 as a white powder (456 mg, 99%).
1H NMR (700 MHz, CDCl3): d=0.81 (s, 12H; CH3 (PMDCOH)), 0.88 (t,
J=7.1 Hz, 12H; CH3), 1.25(s, 104H; (CH2)13), 1.58 (m, 8H,
CH2CH2OCO), 1.64–1.86 (m, 12H; CH2CONHCH2CH2CH2NCOCH2),
2.14 (m, 2H; CH2CHCH2 (PMDCOH)), 2.21 (m, 1H; CH2CHCH2
(PMDCOH)), 2.52–2.70 (m, 12H; NCOCH2CH2CO), 3.06–3.40 (m, 24H;
CONHCH2CH2CH2NCO), 3.40–3.52 (m, 24H; OCH2 (PMDCOH)),
3.56–3.62 (m, J=10.9 Hz, 16H; OCH2 (PMDCOH)), 3.98–4.04 (m, 8H;
CH2CH2OCO), 4.10 (d, J=5.5 Hz, 2H; COOCH2CH (PMDCOH)),
5.32, 5.40, 5.46, 5.50 ppm (s, 1H; NHCO); 13C NMR (62.9 MHz, CDCl3):
d=14.1, 17.2, 22.7, 25.9, 28.0, 28.6, 29.1, 29.4, 29.65, 29.69, 30.9, 31.9, 36.8,
38.0, 38.3, 39.2, 40.0, 40.9, 42.9, 45.3, 50.8, 62.9, 65.0, 67.6, 69.1, 69.7, 70.2,
75.9, 157.0, 157.1, 171.7, 172.6, 172.7, 173.0, 173.4 ppm; MALDI-TOF
Characterization methods of microstructure and properties of gels: IR
spectra were recorded by using a Bio-rad FTS 6000 FT-IR spectrometer
with a germanium attenuated total reflectance (ATR) accessory. TEM
observations were performed by using a transmission electron micro-
scope (Philips EM420) operated under 120 kV. The samples were pre-
pared by putting the gels on carbon film-coated copper grids. SEM obser-
vations were performed by using a LEO 1530 Gemini instrument with an
acceleration voltage of 0.5 kV and inlens mode. The gel was transferred
to a silica wafer and dried under vacuum before measurements were
taken. SAXS experiments were performed by using a Bruker AXS
NANOSTAR instrument with a monochromatic X-ray beam and a two-
dimensional detector for scattering intensity recording. The distance be-
tween the samples and the detector was 1080 mm. The plots of intensity
versus the scattering wave vector (q), which is calculated from q=4p/
MS: m/z: 2442 [M+K]+; elemental analysis calcd (%) for C130H251N9O29
:
C 64.94, H 10.52, N 6.24; found: C 64.75, H 10.59, N 5.18.
lsin(q/2) in which q is the scattering angle and l=1.54 Š for the X-ray
beam, were produced by integrating the two-dimensional scattering pat-
terns.
A
16g3g3_(OH)8 (4): Compound 8 (142 mg, 0.0303 mmol) was dissolved in
methanol/CH2Cl2 (1:1, 15 mL) and Pd/C (10%, 15 mg) was added. Com-
pound 16g3g3_Bz4 was deprotected according to the general procedure
for the removal of the Bz groups to give 4 as a white powder (127 mg,
97%). 1H NMR (700 MHz, CDCl3): d=0.81 (s, 12H; CH3 (PMDCOH)),
0.88 (t, J=7.0 Hz, 24H; CH3), 1.26(s, 208H; (CH2)13), 1.59 (m, 16H;
CH2CH2OCO), 1.72–2.06 (m, 28H; CH2CONHCH2CH2CH2NCOCH2),
2.14 (m, 2H; CH2CHCH2 (PMDCOH)), 2.21 (m, 1H; CH2CHCH2
The cmin values were measured as follows: The solutions consisting of co-
dendrimer 1 to 4 (wtsample: 8, 7, 6, and 3 mg, respectively) and of toluene
(1 mL) were prepared as gels. After gelation the lower part of the solu-
tion was immobile and the upper part was fluid solvent, which was sepa-
rated and weighed (wtsoln). Then cmin was calculated by using Equa-
tion (1):
(PMDCOH)), 2.65 (m, 4H; COCH2CH2CO(center)), 3.10–3.25 (m, 24H;
A
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3335

W. Wang, G. Wegner et al.
COCH2CH2CO) 3.30–3.70 (m, 96H; CONHCH2CH2CH2NCO
G
(PMDCOH)), 3.98–4.04 (brd, J=11.5 Hz, 16H; CH2CH2OCO
G
CHCH2O(8H), PMDCOH)), 4.10 (d, J=5.9 Hz, 2H; COOCH2CH
AHCTREUNG
OCH2 (PMDCOH)), 4.03 (m, 16H; CH2CH2OCO), 4.14 ppm (d, J=
5.6 Hz, 2H; COOCH2CH (PMDCOH)); 13C NMR (62.9 MHz, CDCl3):
d=14.1, 17.2, 22.7, 25.9, 28.0, 29.1, 29.3, 29.6, 29.7, 30.8, 31.9, 36.8, 38.0,
38.4, 40.0, 41.0, 45.4, 65.1, 67.4, 69.1, 69.7, 70.1, 72.9, 75.7, 157.0, 157.1,
172.8, 172.9, 173.1, 173.2 ppm; MALDI-TOF MS: m/z: 4369 [M+K]+; el-
emental analysis calcd (%) for C266H471N21O45: C 66.00, H 10.59, N 6.79;
found: C 66.12, H 10.56, N 6.87.
(PMDCOH)), 5.39 (s, 4H; CHPh), 5.27, 5.33, 5.46, 5.50, 6.98, 7.04 (s, 1H;
NHCO), 7.34 (m, 12H; Ph), 7.46 ppm (m, 8H; Ph); 13C NMR (62.9 MHz,
CDCl3): d=14.1, 17.6, 22.7, 25.9, 27.1, 27.6, 27.9, 28.9, 29.08, 29.10, 29.4,
29.65, 29.70, 30.9, 31.9, 34.6, 37.9, 38.3, 39.3, 40.5, 42.6, 45.0, 63.3, 64.9,
65.1, 69.1, 69.8, 73.3, 73.6, 101.7, 126.1, 128.2, 128.8, 138.4, 156.9, 157.0,
171.4, 172.3, 172.4, 172.6, 173.4 ppm; MALDI-TOF MS: m/z: 2780
[M+Na]+, 2796 [M+K]+; elemental analysis calcd (%) for C158H267N9O29
:
16g2g1_Bz (5): PUA 16g2_COOH (500 mg, 0.289 mmol), PMDC(OH)
g1-ol (72 mg, 0.347 mmol, 1.2 equiv), 4-(dimethylamino) pyridinium p-tol-
uenesulfonate (DPTS) (85 mg, 0.289 mmol) and dry CH2Cl2 (10 mL)
were mixed in a dry Schlenk tube (25 mL). After the reaction tube was
flushed with argon, N,N’-dicyclohexylcarbodiimide (DCC) (89.4 mg,
0.434 mmol, 1.5 equiv) was added. The reaction was allowed to stir at RT
for 36 h under argon. Once the reaction was complete, the DCC-urethane
was filtered off in a glass filter and washed with CH2Cl2. The crude prod-
uct was purified by column chromatography on silica gel, eluting with
ethyl acetate gradually increasing to 20:80 methanol/ethyl acetate to give
5 as a white powder (478 mg, 86%). 1H NMR (700 MHz, CDCl3): d=
0.82 (s, 3H; CH3 (PMDCOH)), 0.88 (t, J=7.1 Hz, 12H; CH3), 1.25 (s,
104H; (CH2)13), 1.58 (m, 8H; CH2CH2OCO), 1.64–1.84 (m, 12H;
C 68.84, H 9.76, N 4.75; found: C 68.70, H 9.84, N 4.73.
16g3g3_Bz4 (8): PUA 16g3-COOH (300 mg 0.082 mmol), PMDC(OH)
g3-ol (103 mg, 0.098 mmol, 1.2 equiv), DPTS (24 mg, 0.082 mmol), and
DCC (33.8 mg, 0.164 mmol) were allowed to react according to the gen-
eral esterification procedure in dry CH2Cl2 (2 mL) for 24 h (monitored
by TLC). The crude product was purified by column chromatography on
silica gel, eluting with CH2Cl2/ethyl acetate/methanol (7/1/1.6) to give 8
as a white powder (352 mg, 92%). 1H NMR (700 MHz, CDCl3): d=0.78
(s, 12H; CH3 (PMDCOH)), 0.88 (t, J=7.1 Hz, 24H; CH3), 1.26(s, 208H;
(CH2)13), 1.59 (m, 16H; CH2CH2OCO), 1.66–1.96 (m, 28H;
CH2CONHCH2CH2CH2NCOCH2),
2.18
(m,
3H;
CH2CHCH2
(PMDCOH)), 2.52–2.80 (m, 28H; COCH2CH2CO), 3.06–3.44 (m, 56H;
CONHCH2CH2CH2NCO), 3.44–3.64 (m, 40H; OCH2 (PMDCOH)),
3.98–4.04 (m, 16H; CH2CH2OCO), 4.12 (d, J=5.9 Hz, 2H; COOCH2CH
(PMDCOH)), 5.28 (s, 4H; CHPh), 5.46 (s, 4H; NHCO), 7.34 (m, 12H;
Ph), 7.46 ppm (m, 8H; Ph); 13C NMR (62.9 MHz, CDCl3): d=14.1, 17.6,
22.7, 25.8, 28.0, 29.1, 29.3, 29.6, 29.7, 30.9, 31.9, 34.5, 36.8, 37.9, 38.3, 40.5,
42.6, 45.1, 63.3, 64.9, 65.1, 69.1, 69.8, 73.3, 73.5, 74.1, 101.7, 126.1, 128.2,
128.8, 138.4, 157.0, 157.1, 171.3, 172.4, 172.5, 172.8, 173.2, 173.4 ppm;
MALDI-TOF MS: m/z: 4722 [M+K]+; elemental analysis calcd (%) for
C266H471N21O45: C 68.21, H 10.14, N 6.28; found: C 68.14, H 10.04, N 6.22.
CH2CONHCH2CH2CH2NCOCH2),
2.52–2.72
(m,
12H;
NCOCH2CH2CO), 3.07–3.37 (m, 24H; CONHCH2CH2CH2NCO), 3.66
(d, J=11.8 Hz, 2H; CH2O (PMDCOH)), 3.98–4.06 (m, 10H;
CH2CH2OCO
A
ACHTREUNG
NHCO), 7.34 (m, 3H; Ph), 7.46 ppm (m, 2H; Ph); 13C NMR (62.9 MHz,
CDCl3): d=14.1, 17.1, 22.7, 25.8, 27.1, 27.6, 27.9, 28.0, 28.5, 28.9, 29.1,
29.4, 29.6, 29.7, 30.9, 31.9, 33.8, 36.7, 37.8, 38.2, 42.5, 45.0, 64.9, 65.1, 66.7,
73.3, 101.9, 126.1, 128.3, 129.0, 138.0, 156.9, 157.1, 171.4, 172.3, 172.5,
172.7, 173.5 ppm; MALDI-TOF MS: m/z: 1960 [M+K]+; elemental anal-
ysis calcd (%) for C110H201N9O17: C 68.75, H 10.54, N 6.56; found: C
68.80, H 10.43, N 6.61.
Acknowledgements
16g2g2_Bz2 (6): PUA 16g2_COOH (800 mg, 0.462 mmol), PMDC(OH)
g2-ol (247 mg, 0.508 mmol, 1.1 equiv), DPTS (136 mg, 0.462 mmol), and
DCC (143 mg 0.693 mmol) were allowed to react according to the gener-
al esterification procedure in dry CH2Cl2 (10 mL) for 36 h. The crude
product was purified by column chromatography on silica gel, eluting
with ethyl acetate gradually increasing to 20:80 methanol/ethyl acetate to
give 6 as a white powder (961 mg, 95%). 1H NMR (700 MHz, CDCl3):
d=0.78 (s, 6H; CH3 (PMDCOH)), 0.88 (t, J=7.1 Hz, 12H; CH3), 1.25(s,
104H; (CH2)13), 1.58 (m, 8H; CH2CH2OCO), 1.64–1.84 (m, 12H;
This work was supported by the National Science Foundation of China
(NSFC Grant Nos. 20374030 and 20734001). M.Y. thanks the Internation-
al Max-Planck Research School for supporting his stay in Germany.
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CH2CONHCH2CH2CH2NCOCH2),
(PMDCOH)), 2.49–2.68 (m, 12H; NCOCH2CH2CO), 3.04–3.38 (m, 24H;
CONHCH2CH2CH2NCO), 3.50–3.60 (m, 8H; OCH2C(CH3)CH2O
(PMDCOH)), 3.63 (s, 4H; OCH2C(CH3)CH2O (PMDCOH)), 3.98–4.06
(brd, J=11.7 Hz, 12H; CH2CH2OCO(8H), CHCH2O(4H, PMDCOH)),
2.29
(m,
1H;
CH2CHCH2
AHCTREUNG
AHCTREUNG
AHCTREUNG
4.17 (d, J=6.1 Hz, 2H; COOCH2CH (PMDCOH)), 5.40 (s, 2H; CHPh),
5.26, 5.33 5.48, 5.54, 6.95, 7.04 (s, 1H; NHCO), 7.35 (m, 6H; Ph),
7.46 ppm (m, 4H; Ph); 13C NMR (62.9 MHz, CDCl3): d=14.1, 17.5, 22.7,
25.9, 27.1, 27.6, 27.9, 28.0, 28.9, 29.1, 29.3, 29.6, 29.65, 29.69, 31.0, 31.9,
34.6, 36.7, 37.8, 38.3, 39.5, 42.5, 45.0, 63.3, 65.0, 65.1, 69.4, 73.4, 73.5,
101.7, 126.1, 128.2, 128.9, 138.4, 156.9, 157.1, 171.4, 172.3, 172.4, 172.7,
173.4; MALDI-TOF MS: m/z: 2223 [M+Na]+, 2239 [M+K]+; elemental
analysis calcd (%) for C126H223N9O21: C 68.78, H 10.22, N 5.73; found: C
68.85, H 10.02, N 5.73.
16g2g3_Bz4 (7): PUA 16g2-COOH (600 mg, 0.347 mmol), PMDC(OH)
g3-ol (396 mg, 0.381 mmol, 1.1 equiv), DPTS (102 mg, 0.347 mmol), and
DCC (107 mg, 0.521 mmol) were allowed to react according to the gener-
al esterification procedure in dry CH2Cl2 (10 mL) for 36 h. The crude
product was purified by column chromatography on silica gel, eluting
with ethyl acetate gradually increasing to 20:80 methanol/ethyl acetate to
give 7 as a white powder (890 mg, 93%). 1H NMR (700 MHz, CDCl3):
d=0.77 (s, 12H; CH3 (PMDCOH)), 0.88 (t, J=7.1 Hz, 12H; CH3),
1.25(s, 104H; (CH2)13), 1.58 (m, 8H; CH2CH2OCO), 1.62–1.84 (m, 12H;
CH2CONHCH2CH2CH2NCOCH2),
(PMDCOH)), 2.49–2.66 (m, 12H; NCOCH2CH2CO), 3.04–3.37 (m, 24H;
CONHCH2CH2CH2NCO), 3.37–3.62 (m, 32H; OCH2C(CH3)CH2O
2.18
(m,
3H;
CH2CHCH2
AHCTREUNG
3336
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Chem. Eur. J. 2008, 14, 3330 – 3337

Amphiphilic Diblock Codendrimers
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Received: November 2, 2007
Published online: February 21, 2008
Chem. Eur. J. 2008, 14, 3330 – 3337
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3337