Self-organization of amide dendrons with focal dipeptide units

Article abstract of DOI:10.1039/c1sm06008b

Dendron-dipeptide conjugates were synthesized to investigate their self-assembly characteristics not only in the aqueous phase but also in organic media. In the aqueous phase, the self-organized structure of 2G-PhePhe and 2G-GlyGly was influenced predominantly by the self-assembly characteristics of the amide dendron unit to exhibit vesicular structures. For 1G-PhePhe and 1G-GlyGly, however, the role of the focal dipeptide unit became important to show donut-like assemblies and rod-like structures, respectively. In HFIP/H ₂O (1:100 v/v), 2G-PhePhe and 1G-PhePhe exhibited donut-like structures, while 2G-GlyGly and 1G-GlyGly formed rod-like structures. The secondary structures of the dendron-peptide conjugates were remarkably influenced by the dendron unit. The circular dichroism (CD) spectra showed that 1G-PhePhe in H₂O adopted the β-sheet structure. On increasing the generation of the dendron unit, on the other hand, 2G-PhePhe did not adopt the β-sheet structure but exhibited random structures. In addition, the curvature of the assembled structure of the dendron-peptide conjugates was affected by the dendron unit. In organic media such as toluene, all the dendron-dipeptide conjugates formed fibrous structures which could induce thermoreversible gel formation. Therefore, the modulation of the dendritic moiety and the focal peptide unit provided an opportunity to produce diverse self-organized structures in various conditions.

Full text of DOI:10.1039/c1sm06008b

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PAPER
Self-organization of amide dendrons with focal dipeptide units†
a
Jeonghun Lee, Joung Min Kim, Mikyoung Yun, Chiyoung Park, Junwon Park, Keun Hyeung Lee
b
a
a
b
b
*
a
*
and Chulhee Kim
Received 31st May 2011, Accepted 12th July 2011
DOI: 10.1039/c1sm06008b
Dendron–dipeptide conjugates were synthesized to investigate their self-assembly characteristics not
only in the aqueous phase but also in organic media. In the aqueous phase, the self-organized structure
of 2G-PhePhe and 2G-GlyGly was influenced predominantly by the self-assembly characteristics of the
amide dendron unit to exhibit vesicular structures. For 1G-PhePhe and 1G-GlyGly, however, the role
of the focal dipeptide unit became important to show donut-like assemblies and rod-like structures,
respectively. In HFIP/H2O (1 : 100 v/v), 2G-PhePhe and 1G-PhePhe exhibited donut-like structures,
while 2G-GlyGly and 1G-GlyGly formed rod-like structures. The secondary structures of the dendron–
peptide conjugates were remarkably influenced by the dendron unit. The circular dichroism (CD)
spectra showed that 1G-PhePhe in H2O adopted the b-sheet structure. On increasing the generation of
the dendron unit, on the other hand, 2G-PhePhe did not adopt the b-sheet structure but exhibited
random structures. In addition, the curvature of the assembled structure of the dendron–peptide
conjugates was affected by the dendron unit. In organic media such as toluene, all the dendron–
dipeptide conjugates formed fibrous structures which could induce thermoreversible gel formation.
Therefore, the modulation of the dendritic moiety and the focal peptide unit provided an opportunity
to produce diverse self-organized structures in various conditions.
phase.14,17–19 In addition, incorporation of peptide units at the
focal point of the benzyl ether dendrons induced formation of
supramolecular assemblies. For example, Aida et al. reported the
formation of gigantic fibers from benzyl ether dendrons with the
focal Tyr-Ala dipeptide unit in organic media.6 Self-assembled
helical pores from the amphiphilic benzyl ether dendron with the
Tyr-Ala dipeptide core were reported by Percec et al., which
provided a hydrophobic transmembrane channel with proton
transport properties.5
Introduction
The tuning of nanoarchitectures by self-organization of diverse
building blocks has been of great interest in many areas of
nanoscience.1–4 One of the key issues in this subject is the rational
design of molecularly programmed building blocks which can
self-organize into functional architectures in various conditions.
Recently, dendritic building blocks were reported to exhibit
unique self-assembly behavior toward well-defined supramolec-
ular structures to provide unusual functional performances.5–12
For example, amide dendrons exhibited unusual self-organiza-
tion behavior in various conditions such as solid state, organic
media, aqueous phase, and solid–liquid interface.13–20 They self-
organized into lamellar or columnar arrays in organic media.13–17
Dendron dimers and dendronized polymers are also unique
building blocks involved in construction of nano-
architectures.7,8,15–17 In addition, the amide dendrons with the
appropriate focal moieties formed supramolecular assemblies
such as vesicles, rods, and cylindrical micelles in the aqueous
Peptides have emerged as valuable building blocks because
they have unique self-assembly characteristics to form supra-
molecular structures with biofunctions.21–23 Peptides can spon-
taneously associate to form nanotubes, nanospheres, nanofibrils,
nanotapes, and other ordered nanostructures.3,4,24–26 Particu-
larly, diphenylalanine (Phe-Phe, FF), a key structural motif in
the formation of amyloid fibers by Alzheimer’s b-amyloid
polypeptide,27 self-organizes into a robust nanotube structure in
aqueous media with a trace of 1,1,1,3,3,3-hexafluoroisopropanol
(HFIP).24 In addition, the structural modification of the dipep-
tide unit induces a drastic change in self-assembled supramo-
lecular structures. For example, when a thiol is introduced at the
diphenylalanine unit, spherical nanoparticles are formed instead
of nanotubes.28 Therefore, modification of dipeptides with other
self-assembly motifs would provide a useful route to induce
formation of diverse supramolecular architectures.
aDepartment of Polymer Science and Engineering, Inha University,
Incheon, 402-751, Korea. E-mail: chk@inha.ac.kr; Fax: +82-32-865-
5178; Tel: +82-32-860-7487
bDepartment of Chemistry, Inha University, Incheon, 402-751, Korea.
E-mail: leekh@inha.ac.kr; Fax: +82-32-867-5604; Tel: +82-32-860-7674
† Electronic supplementary information (ESI) available: MALDI-TOF
mass spectra of dendron–peptide conjugates and SAXS result. See
DOI: 10.1039/c1sm06008b
The focal peptide unit of the dendritic building blocks can be
utilized not only to trigger self-assembly processes but also to
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provide unusual functions. Therefore, we reasoned that the
conjugation of dipeptides at the focal point of the amide den-
drons, 1G and 2G, would provide an opportunity for the amide
dendron–dipeptide conjugates to self-assemble in a synergistic or
competitive manner.
1522.17, obsd 1522.80; 1G-PhePhe [M + Na]+ calcd 911.64, obsd
911.73; 2G-PhePhe [M + Na]+ calcd 1703.27, obsd 1701.92).
Loading of Nile red into the vesicular membrane
A mixture of an aqueous vesicular solution of the dendrons
(30 mM) with n-hexane solution of Nile red (30 mM) was soni-
cated for an hour and equilibrated overnight. After filtration of
the aqueous phase through a Millipore hydrophilic filter (cellu-
lose acetate membrane filter, pore size ¼ 0.45 mm), confocal laser
scanning microscopy (CLSM) images were obtained by using the
LSM 510 Meta (Carl Zeiss, Jena, Germany).
In this report, we introduced dipeptides such as Phe-Phe or
Gly-Gly at the focal point of the amide dendrons (1G and 2G) to
prepare 1G-PhePhe, 2G-PhePhe, 1G-GlyGly, and 2G-GlyGly,
respectively. The effect of the dendron and dipeptide moieties in
the self-assembly of the amide dendron–dipeptide conjugates was
investigated not only in the aqueous phase but also in organic
media.
Dynamic light scattering
Experimental section
Dynamic light scattering (DLS) measurements were performed
using a Brookhaven BI-200SM goniometer and a BI-9000AT
digital autocorrelator. All the measurements were carried out at
room temperature. The scattered light of a He–Ne laser
(Research Electro-optics, 35 mW) operated at 632.8 nm was
measured at an angle of 90ꢀ and collected on an autocorrelator.
The sample solutions were purified through a Millipore syringe
filter (pore size ¼ 0.45 mm). The hydrodynamic diameters (d) of
vesicles were calculated using the Stokes–Einstein equation
d ¼ kBT/3phD, where kB is the Boltzmann constant, T is the
absolute temperature, h is the solvent viscosity, and D is the
diffusion coefficient.
Materials
1,10-Carbonyldiimidazole (CDI), lauric acid, trifluoroacetic acid
(TFA), diethyl ether, N,N-dimethylformamide (DMF) and
piperidine 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) obtained
from Aldrich were used as received. N,N0-Diisopropylcarbodii-
mide (DIPC) and 1-hydroxybenzotriazole (HOBt) were obtained
from BeadTech. Fmoc protected amino acids were obtained
from Nova Biochem and PAL Resin was obtained from
Advanced Chemtech. N-(3-Aminopropyl)-propanediamine and
triethylamine (TEA) obtained from Aldrich were purified by
vacuum distillation under calcium hydride. Succinic anhydride
(Aldrich) was recrystallized from n-hexane/acetone (2 : 8 v/v). All
the solvents were purified using published procedures.29
Transmission electron microscopy
Transmission electron microscopy (TEM) was performed using
a Philips CM 200 operated at an acceleration voltage of 80 kV.
For the preparation of TEM samples, a drop of sample solution
was placed onto a 300-mesh copper grid coated with carbon.
About 2 min after deposition, the grid was tapped with a filter
paper to remove surface water and air-dried. The grid was
stained using uranyl acetate (2 wt%) and dried again. The TEM
sample of 1G-GlyGly in toluene was prepared by dropping the
supernatant onto a TEM grid after precipitation and then dried.
The other gels were directly transferred to the TEM grids and
dried.
Syntheses of 1G and 2G
Amide dendrons with the first and second generations (1G and
2G) were synthesized as described previously.13
Conjugation of dendrons with peptides
All dendron–peptide conjugates and resin-bound peptides were
synthesized using Fmoc-chemistry by solid phase peptide
synthesis. The coupling reaction of amino acids was performed
using 3 molar excess of the corresponding Fmoc amino acid and
coupling reagents (DIPC and HOBt) in DMF within 8 min under
temperature-controlled microwave irradiation (150 W, 85 ꢀC).
The coupling of dendron (1G and 2G) with peptide was per-
formed by applying the following procedure. To the resin-bound
peptide (232 mg. 0.1 mmol), the solution of DIPC (38 mg,
0.3 mmol), HOBt (40 mg, 0.3 mmol) and dendron (0.3 mmol) in
DMF (3 ml) was added. The resulting solution containing resin
was stirred under temperature-controlled microwave irradiation
(85 ꢀC, 150 W) for 8 min. After filtration, the resin was washed 5
times, with DMF and MeOH (4 ml) each time. The coupling
reaction was repeated until no color change was observed in the
ninhydrin test. Deprotection and cleavage were achieved by
treatment with a mixture of TFA/H2O (9.5 : 0.5 v/v) at room
temperature for 3–4 h. After cleavage of the product from resin,
the dendron–dipeptide conjugates were obtained by precipitation
Field emission scanning electron microscopy
Field emission scanning electron microscopy (FE-SEM) was
carried out on a Hitachi S-4300 FE-SEM instrument with a field
emission gun (accelerating voltage ¼ 10–15 kV and pressure
range ¼ 0.8–0.9 Torr). The FE-SEM samples were prepared by
transferring a drop of the sample solution onto a silicon wafer or
an aluminium foil. After deposition for about 5–10 minutes, the
excess water was removed by touching the edge of the substrate
with a filter paper.
Small angle X-ray scattering
Internal structures of the self-assembly were determined by the
high resolution small angle X-ray scattering (SAXS) facility in
the Pohang Accelerator Laboratory (4C1 beam line) utilizing the
synchrotron source. A specially designed sample holder was used
to hold the solution samples including the gels for the X-ray
ꢀ
with acetonitrile at ꢁ20 C. The successful synthesis and purity
of the conjugates were confirmed by MALDI-TOF mass spec-
trometry (Voyager-DE STR, Applied Biosystem). (1G-GlyGly
[M + Na]+ calcd 731.54, obsd 731.81; 2G-GlyGly [M + Na]+ calcd
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ꢀ
scattering measurement. The X-ray wavelength was 1.608 A and
the beam size was 0.3 mm ꢂ 0.3 mm. The sample to detector
distance was 3 metres and was calibrated by a standard sample
(Styrene-Ethylene-Butadiene-Styrene (SEBS)).
Circular dichroism spectrometry
All circular dichroism (CD) spectra were recorded on a JASCO-
810 polarimeter by continuously purging dry N2 gas at 5 l minꢁ1
during data acquisition. Each spectrum was collected from 250
nm to 190 nm in a quartz cuvette with a 1 cm path length at
a response time of 8 s, a scan speed of 50 nm minꢁ1 and a band-
width of 1 nm and averaged over three scans. Then, the intensity
of CD spectra was converted into molar ellipticity.
Sample preparation in the aqueous phase
In a typical procedure, 1 mmol of dendron–peptide was placed
into a 100 ml round bottom flask and dissolved in 3–5 ml of
THF. Doubly distilled water (50 ml) was added slowly into the
flask with gentle stirring. After vigorous stirring for 15 min, THF
was evaporated under reduced pressure. The resulting solution
was filtered with a syringe filter (pore diameter ¼ 0.45 mm).
Sample preparation using a mixed solvent of water and HFIP
Scheme 1 (a) The structure of dendrons (1G and 2G). (b) Synthetic routes
to dendron–peptide conjugates. Conditions: (i) Fmoc-Gly-OH (for 2a and
3a) or Fmoc-Phe-OH (for 2b and 3b), HOBt, DIPC, microwave (150 W, 85
ꢀC), 8 min; (ii) piperidine/DMF (2 : 8 v/v), 15 min, RT; (iii) 1G, HOBt,
DIPC, microwave(150 W, 85 ꢀC), 8 min; (iv) 2G, HOBt, DIPC, microwave
(150 W, 85 ꢀC), 8 min; (v) TFA/H2O (9.5 : 0.5 v/v) 4 h, RT.
As in previous reports,24,27,30 10 ml of doubly distilled water was
poured into the solution of dendron–dipeptides (4.04 mmol) in
HFIP (100 ml) under stirring. The final concentration of den-
dron–dipeptides was 400 mM.
Results and discussion
For 1G–dipeptide conjugates, the self-organization in the
aqueous phase was remarkably influenced by the dipeptide unit
to exhibit assembled structures which are different from those of
2G–dipeptide conjugates. In the case of 1G-PhePhe, a donut-like
toroidal structure was formed as shown in Fig. 2a and b possibly
because the effect of the dendron moiety was decreased
The amide dendron–dipeptide conjugates were prepared by solid
phase synthesis using Fmoc-chemistry as shown in Scheme 1.
The reaction of the amino acids was performed using 3 molar
excess of the corresponding Fmoc amino acid and coupling
reagents (DIPC and HOBt) in DMF within 8 min under
temperature-controlled microwave irradiation. The coupling
reaction of the dendrons to the resin was also performed using 3
molar excess of the amide dendrons and coupling reagents in
DMF within 8 min under microwave irradiation. Each coupling
reaction was repeated until no color was observed in the ninhy-
drin test. Deprotection and cleavage were achieved by treatment
with a mixture of TFA/H2O (9.5 : 0.5 v/v) at room temperature
for 3–4 h. After cleavage of the product from the resin, the
dendron–dipeptide conjugates were obtained by precipitation
ꢀ
with acetonitrile at ꢁ20 C. The successful synthesis and purity
of the conjugates were confirmed by MALDI-TOF mass spec-
trometry (Fig. S1–S4, ESI†).
We investigated the self-assembly characteristics of the den-
dron–peptide conjugates in the aqueous phase by using TEM
and FE-SEM. 2G-PhePhe self-organized into a vesicular struc-
ture in the aqueous phase (20 mM) as shown in Fig. 1a and b with
the average diameter of 375 nm from the DLS experiment
(Fig. 1c). The vesicular organization was further confirmed by
the CLSM image of the hydrophobic dye (Nile red) encapsulated
in the hydrophobic vesicular membrane of 2G-PhePhe as shown
in Fig. 1d.
Fig. 1 TEM (a) and FE-SEM (b) images of 2G-PhePhe in H2O. (c) DLS
data of 2G-PhePhe in H2O (20 mM). (d) CLSM image of 2G-PhePhe in
H2O (20 mM). Nile red was encapsulated in the vesicular membrane of
2G-PhePhe.
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the membrane at the center of the vesicles, as shown in Fig. 3c
and d. When the concentration of 2G-PhePhe in HFIP/H2O
(1 : 100 v/v) reached 400 mM, we observed donut-like toroidal
structures rather than vesicles as shown in Fig. 3e and f. The
presence of HFIP enhances the interaction of the focal dipeptide
unit for 2G-PhePhe to form toroidal micelles.32,33 Because the
PhePhe unit has a powerful driving force to construct stable self-
assembled structures such as nanotubes with a typical diameter
of 80–300 nm and micron length in HFIP/H2O (1 : 100 v/v),24 the
introduction of the PhePhe unit to the amide dendron provides
an opportunity for the construction of these diverse nano-
assemblies of dendrons.
The small angle X-ray scattering (SAXS) results of the toroidal
assembly of 2G-PhePhe (400 mM) in HFIP/H2O (1 : 100 v/v)
showed that the membrane of the toroid had a lamellar structure
ꢀ
with an inter-lamellar spacing of 41.3 A (Fig. S5, ESI†).
Fig. 2 TEM (a and c) and FE-SEM (b and d) images of 1G-PhePhe (a
and b) in H2O (20 mM) and (c and d) in HFIP/H2O (1 : 100 v/v, 400 mM).
Considering the dimension of 2G-PhePhe, each lamellar layer is
believed to consist a pair of 2G-PhePhe in which the focal
dipeptide moieties were exposed to the aqueous phase while the
hydrophobic alkyl peripheries of two dendron units were located
at the center of a lamellar layer. In addition, the dimension of the
compared with that of 2G-PhePhe to enhance the dipeptide
interactions such as hydrogen bonding and p–p interaction of
the phenyl moiety, which could promote the formation of
enhanced curvature so that toroidal micelles are formed by the
nucleation and growth mechanism.31 Similarly, 1G-PhePhe in
HFIP/H2O (1 : 100 v/v) also formed a donut shaped assembly as
shown in the TEM and FE-SEM images (Fig. 2c and d).
ꢀ
fully stretched structure of 2G-PhePhe (45 A) suggests that the
focal dipeptide units of the adjacent dendrons overlapped each
other and the alkyl tails were interdigitated with the long
molecular axis tilted in the lamellar layer, as illustrated in Fig. 4.
As a control experiment, we synthesized the dendron–diglycine
conjugates (2G-GlyGly and 1G-GlyGly) instead of dendron–
diphenylalanine. The dipeptide, Gly-Gly, is soluble in the
aqueous phase, which has a different behavior from that of the
dendron conjugates. The TEM and FE-SEM images of
2G-GlyGly in the aqueous phase (Fig. 5a and b) also show that
spherical vesicles were formed with an average diameter of 74 nm
in the DLS experiment. On the other hand, the second generation
amide dendron, 2G, has a capability of organizing diverse focal
moieties into vesicles and other micellar structures.13,16,18 These
results suggest that the second generation amide dendron moiety
played a dominant role in the second generation dendron–
dipeptide conjugates to self-organize into vesicular structures in
the aqueous phase. On the other hand, 1G-GlyGly without
a phenyl moiety for p–p interaction exhibited a rod-like struc-
ture in the aqueous phase as shown in Fig. 5c and d.
When HFIP/H2O was used as the solvent (1 : 100 v/v), 2G-
PhePhe (20 mM) exhibited vesicular structures with a small
amount of umbilicate assembly with an average diameter of
108 nm from the DLS experiment as shown in Fig. 3a and b. On
increasing the concentration of 2G-PhePhe to 200 mM, the
aggregate size was increased and the remarkable development to
a donut-like structure was observed as a result of the collapse of
The self-assembled behavior of dendron–diglycine in
HFIP/H2O (1 : 100 v/v) was also investigated. The TEM and
FE-SEM images of the assembled structure of the dendron–
diglycine conjugates (2G-GlyGly and 1G-GlyGly) in HFIP/H2O
(1 : 100 v/v, 400 mM) are shown in Fig. 5e–h. The 1G-GlyGly
Fig. 3 TEM (a, c, and e) and FE-SEM (b, d, and f) images of 2G-PhePhe
in HFIP/H2O (1 : 100 v/v). The concentration of the solution was 20 mM
(a and b), 200 mM (c and d) and 400 mM (e and f).
Fig. 4 Schematic representation of toroids of 2G-PhePhe in HFIP/H2O
mixed solvent.
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spectra showed that 1G-PhePhe adopted the b-sheet structure in
H2O, and both b-sheet and turn structures in HFIP/H2O.34,35 On
increasing the generation of the dendron unit, on the other hand,
the CD spectra of 2G-PhePhe in H2O or in HFIP/H2O did not
exhibit the characteristic peak of the b-sheet structure. The CD
spectra indicated that 2G-PhePhe in H2O or in HFIP/H2O
adopted random structures with aromatic stacking of PhePhe
units based on the observation of broad positive bands at 200–
230 nm.36 These results indicated that the secondary structure of
the dendron–peptide conjugates was remarkably influenced by
the dendron unit. In addition, the curvature of the assembled
structure of the dendron–peptide conjugates was also affected by
the dendron unit. The volume ratio of the hydrophobic periphery
to the focal PhePhe unit of the dendron–PhePhe conjugates
decreased on decreasing the generation of the dendron unit.
Therefore, the curvature of the assembled membrane of 1G-
PhePhe became higher than that of 2G-PhePhe, which would be
favorable to induce toroidal morphology.37 This tendency was
also observed in the assembled structure of the dendron–GlyGly
conjugates. As shown in Fig. 5, 2G-GlyGly formed a vesicular
organization in H2O. However, 1G-GlyGly exhibited a rod-like
structure in H2O due to the high curvature induced by the
reduced volume fraction of the hydrophobic peripheral moiety.
We also observed the gelation behavior of the dendron–
dipeptides in organic media (1.5 wt%) as summarized in Table 1.
The dendron–peptides formed a gel in organic media such as
toluene, THF and methylene chloride while they were soluble in
chloroform, HFIP, ethanol and DMF. In particular, in toluene,
thermoreversible gels were obtained with 1G-PhePhe, 2G-Phe-
Phe and 2G-GlyGly and their thermal transition temperatures
were 70 ꢀC, 40 ꢀC and 40 ꢀC, respectively. 1G-GlyGly was
partially dispersed in toluene with formation of a precipitate
possibly because the volume ratio of the hydrophilic moiety of
1G-GlyGly including the amide branches and focal GlyGly
moiety is greater than that of the other dendron–peptide
conjugates.
Fig. 5 TEM (a and c) and FE-SEM (b and d) images of 2G-GlyGly (a
and b) and 1G-GlyGly (c and d) in H2O. TEM (e and g) and FE-SEM (f
and h) images of 2G-GlyGly (e and f) and 1G-GlyGly (g and h) in HFIP/
H2O (1 : 100 v/v, 400 mM).
formed a rod-like structure which is similar to that obtained in
water. On the other hand, while 2G-GLyGly formed a vesicular
organization in H2O, 2G-GlyGly exhibited a rod-like structure in
HFIP/H2O (1 : 100 v/v).
The TEM and FE-SEM images in Fig. 7 show the organized
structure of the dendron–peptide conjugates in toluene. All the
dry gels of dendron–peptides showed fibrous or nanoribbon-like
structures with different appearances. The intermolecular
hydrogen bonding between the focal dipeptides would be one of
the driving forces for the supramolecular ordering of the den-
dron–dipeptide conjugates in toluene.6,13 In the dendron–peptide
conjugates, the focal dipeptide units would maintain intermo-
lecular hydrogen bonding between the focal dipeptides, which
allows the dendron dimer to be the primary building block in
The effect of the dendron unit on the assembled structure was
further investigated by using CD as shown in Fig. 6. The CD
Table 1 Gelation of peptide–dendron (1.5 wt%) in organic solvents
Solvent
2G-PhePhe
1G-PhePhe
2G-GlyGly
1G-GlyGly
Toluene
Chloroform
THF
HFIP
MC
Ga
Sc
G
S
G
S
G
S
P
S
G
S
S
G
S
G
S
G
S
S
Pb
S
P
S
P
P
S
Ethanol
DMF
S
a
Gel formation. b Precipitation. c Soluble.
Fig. 6 Circular dichroism spectra of 1G-PhePhe and 2G-PhePhe in H2O
and HFIP/H2O (1 : 100 v/v).
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Acknowledgements
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korea government (MEST)
(no. 2009-0079739).
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Conclusions
In summary, the dendron–PhePhe and dendron–GlyGly conju-
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In the aqueous phase, the self-organized structure of 2G-PhePhe
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assembly characteristics of the amide dendron unit to exhibit
vesicular structures. For 1G-PhePhe and 1G-GlyGly, however,
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donut-like assemblies and rod-like structures, respectively. In
HFIP/H2O (1 : 100 v/v) where PhePhe forms nanotubes, 2G-
PhePhe and 1G-PhePhe exhibited donut-like structures, while
2G-GlyGly and 1G-GlyGly formed rod-like structures. In
organic media such as toluene, all the dendron–dipeptide
conjugates formed fibrous structures which can induce the
formation of thermoreversible gels. Therefore, the modulation of
the dendritic moiety and the focal peptide units provided an
opportunity to produce diverse self-organized structures in
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9026 | Soft Matter, 2011, 7, 9021–9026
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