Aliphatic-alcohol-induced opaque-to-transparent transformation and application of solubility theory in a bis-dipeptide-based supramolecular gel

Article abstract of DOI:10.1002/cplu.201700206

A bis-dipeptide supramolecular gelator (DMPV) is prepared, based on l-valine moieties having a pyridinyl group and a long fatty diamine. It is found that the gelator can immobilize organic/water binary mixed solvents, and gel-to-gel transitions with unprecedented opaque-to-transparent transformations are observed upon using aliphatic alcohols such as methanol, ethanol, 1-propyl alcohol, and isopropanol as the organic components. Morphological investigations indicate that a reassembly process occurs, and microstructure evolutions from agglomerates to nanofibers are observed. Opaque and transparent assemblies can interconvert, and respond and restore under mechanical force and pH stimuli. Moreover, Hansen and Flory-Huggins parameters are used to investigate the effect of the solvent on the gelation performance of DMPV. This may facilitate the structure and solvent optimizations and aid the development of advanced gel systems.

Full text of DOI:10.1002/cplu.201700206

Accepted Article
Title: Aliphatic alcohols induced opaque to transparent transformation
and application of solubility theory in a bis-dipeptide based
supramolecular gel
Authors: Tingting Xiao, Xiaoyang Zhang, Jiazhi Yang, and Yong Yang
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemPlusChem 10.1002/cplu.201700206
Link to VoR: http://dx.doi.org/10.1002/cplu.201700206
A Journal of
www.chempluschem.org

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
Aliphatic alcohols induced opaque to transparent transformation and
application of solubility theory in a bis-dipeptide based supramolecular
gel
Tingting Xiao, Xiaoyang Zhang, Jiazhi Yang, Yong Yang*
Dedication
Abstract: Gel-to-gel phase transformations under external stimuli, which are visible to the naked eye, have great
application potentials in the field of sensors and specific recognitions. Herein, a bis-dipeptide supramolecular gelator
(DMPV) was prepared base on L-valine moieties having pyridinyl group and a long fatty diamine. It was found that the
gelator could immobilize organic/water binary mixed solvents, and gel-to-gel transitions with unprecedented opaque to
transparent transformations were observed when aliphatic alcohols, such as methanol, ethanol, 1-propyl alcohol and
isopropanol were used as the organic components. Morphological investigations indicated a re-assembly process was
occurred, and microstructure evolutions from agglomerates to nanofibers were observed. Opaque and transparent
assemblies could interconvert and respectively respond and restore under mechanical force and pH stimuli. Moreover,
Hansen and Flory–Huggins parameters were used to investigate the effect of solvent on the gelation performance of
DMPV. This would facilitate the structure and solvent optimizations and improve developing of advanced gel systems.
hich could be distinguished by naked-eyes are of great
value.[7,8] It is not only essential for the study of dynamic
properties for supramolecular assemblies, but also useful
in developing of advanced sensors. [9,10] Among all of the
variations, the gel-to-gel transitions brought in volume and
color changes attracted a great deal of attentions recently.
Liu et al developed a hydrogel composed of the dendron
gelator based on L-glutamic acid and positively charged
azobenzene derivative. The system showed obvious
volume variations with shrinking and swelling upon
photoirradiation.[11] Mallia and co-workers synthesized a
series of organogelators constituted with long alkyl chain,
hydroxyl and secondary amine. The gelators assembled
into fibrillar networks in CCl4 and exhibited temperature
induced gel-to-gel phase transitions with opaque-
transparent changes in the appearance.[12] Banerjee’s group
reported a time-dependent changes from transparent to
turbid of a peptide derived gel.[13] All of the above
macroscopic changes are on behalf of the dynamic and
metastable state properties of supramolecular systems.
However, to the best our knowledge, the gel-to-gel
transformations with visible macroscopic appearance
reported so far are either temperature-induced or time-
dependent, and the examples induced by specific
chemicals are rare.
Introduction
Phase transformation is a general physical phenomenon
presented in materials, it is induced by the variation of
intermolecular interactions and distance, molecular
assembly mode and thermal movements. This process is
ordinarily accompanied by energy absorption and release,
which make the phase change materials have huge
application potentials in the field of energy storage,
temperature control and smart device.[1] Nowadays,
supramolecular gels constructed by low molecular weight
gelators (LMWGs) have attracted great attention for
researchers. These solid-like soft materials are formed by
the assembly of small molecules through noncovalent
interactions, and reversible phase transformations such as
sol-to-crystal, sol-to-gel and gel-to-gel transitions under
the stimuli of mechanical stress,[2] ultrasound,[3] light,[4]
electric or magnetic fields[5] are thus more easily take place.
In contrast to polymer gels, the supramolecular assemblies
are more suitable for specific recognition and controlled
release.[6]
Various phase transformations under external stimuli w-
In addition, with the imperative requirement of modern
smart devices and biomedical engineering, many
supramolecular gels based on natural organics usually
could not meet the demand over special situations.
Therefore, novel molecules which have excellent gelation
Tingting Xiao, Xiaoyang Zhang, Prof. Jiazhi Yang, Prof. Yong Yang
Key Laboratory of Soft Chemistry and Functional Materials, Ministry of
Education, Nanjing University of Science and Technology, Nanjing 210094, P R
China. E-mail address: yw6729@163.com
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
facilitates the formation of noncovalent intermolecular
interactions, which conducted the supramolecular self-
assemblies. Therefore L-valine was selected as the
building block, and bis-dipeptide structure was prepared.
The solubility of DMPV was investigated in detail. It is
completely insoluble in water and only soluble in polar
organic solvents including DMF, DMSO, 1,4-dioxane, etc.
It could not form gel as a gelator in a single solvent.
Therefore, the gelation propensity of DMPV was initially
investigated in polar organic solvents by adding different
proportions of pure water. A weighted sample of DMPV
(0.01g) was mixed with an organic solvent in a septum-
capped vial and stirred until the solid was fully dissolved.
Figure 1. Formation of gels and gel-to-gel transitions of DMPV at CGC.
V(organic solvent)/V(H2O)=1/2.
properties need to be prepared. The structure design and
investigation on solvent effect are fundamental. Despite
the cognition of the importance of hydrogen bonding, π-π
stacking, coordination and hydrophobic interactions for
gelation, selection of the solvent system should be tried
repeatedly.[14,15] Several solubility theories have thus been
proposed for the prediction of gel performance of a gelator
and reduction of tedious attempts, such as Hansen
solubility parameters, Hildebrand solubility parameters,
Kamlet-Taft parameters, etc.[16,17] In the article, we report
a gel-to-gel transition with interesting opaque to
transparent transformation. The gelator was prepared
based on L-valine and a long fatty diamine. It was found
that gel could not be formed by the gelator in a single
organic solvent. However, when amounts of water was
Scheme 1. Synthetic route for the gelators.
By introducing a certain amount of water, gels could be
introduced, the gelation process occurred instantaneously formed immediately. If no flow was observed when
without time delay. In particular, a macroscopic phase inverting the vial, the gelation and a stable gel were
denoted. All of the systems exhibited an opaque
appearance, and the obtained gels of DMPV were stable
for several months at room temperature (Figure 2). The
gelation test (Table S1) indicated that the constitution of
mixed solvents are crucial to the formation of gel. The
solvents could not be immobilized when the volume
fraction of water was less than 50%. Meanwhile, if the
volume fraction of water exceeded 90%, precipitation was
obtained instead of the gel. In particular, the water content
of 50% contributed to the fastest gelation behavior and the
best stability, thus the following detailed investigations on
the gel was conducted based on this composition. The
gelation behaviors of DMPV were studied by the standard
heating-cooling method. The systems were heated in an oil
bath, and all of the formed gels could be transformed into
sol upon heating. Subsequently, the sample vial was
cooled down to room temperature, and the aggregation
state was then assessed. To our surprise, the gel in the
mixture of ethanol and water transformed to a transparent
transformation was observed when aliphatic alcohols were
used as the organic solvent. Moreover, Hansen parameters
and Flory–Huggins parameters were tentatively used for
the prediction of gel performance of the gelator. The
utilization of empirical equation provided a strategy for
solvent screening and improved the progress for practical
application of the gel.
Results and Discussion
Gelation studies
The synthesis procedure of this bis-dipeptide gelator is
shown in Scheme 1. DMPV was designed inspired by
peptide gels which have been investigated in many
researches. Chiral functional groups have been
demonstrated a key factor in the construction of
supramolecular gels. Helical structure induced by the
chiral centre makes the molecules orderly packed, it
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
status, whereas another mixtures were all recovered to the relationship between structural details and the gelation
original opaque appearance. The critical concentrations behavior of this type of gelator, we synthesized a similar
(CGCs) and Tgel of DMPV depended on the solvents were bis-dipeptide compound (DMBV) using benzaldehyde
listed in Table S2 and S3. Inspired by the phenomenon instead of 4-pyridine carboxaldehyde. Interestingly,
presented above in ethanol/H2O, methanol, isopropanol DMBV could form the gel in a sole organic solvent. While
and n-butyl alcohol were also used for investigation, heated upon Tgel and water was added, it could not gel
considering the intersolubility of aliphatic and aromatic again and the precipitation was observed. This result
alcohols with water. Interestingly, all of these gel systems indicates that the nitrogen atom of pyridine plays a key role
exhibited the opaque-to-transparent transitions as in the
mixture of ethanol/H2O (Figure S3). DMPV based gels
displayed specific discrimination capacity for aliphatic
alcohols. To the best of our knowledge, the changes
between transparent and opaque in the gel-based soft
materials reported so far are either time-dependent[13] or
temperature-induced.[18] However, this gel-to-gel
transformation in our case occurs based on specific
chemical environment, and the aliphatic alcohols triggered
transformation happened immediately without time delay.
Figure 2. Photographs of DMPV at different mixed solvents (v/v =1/2) a) 1,4-
dioxane/H2O, b) DMF/H2O, c) DMSO/H2O, d) acetonitrile/H2O, e) 1-propyl
alcohol/ H2O, f) isopropanol/H2O, g) methanol/H2O, h) ethanol/H2O.
This would be potential for developing a sensor for prompt
and facile selective recognitions. To analyze the
Figure 3. SEM images of assembles obtained before heating/cooling process in different mixed solvents (v/v =1/2) at the CGC: a) 1,4-dioxane/H2O, b) acetonitrile/H2O,
c) DMF/H2O, d) DMSO/H2O, e) methanol/H2O, f) ethanol/H2O, g) 1-propyl alcohol/ H2O, h) isopropanol/H2O. Upon heating/cooling process: i) 1,4-dioxane/H2O, j)
acetonitrile/H2O, k) DMF/H2O, l) DMSO/H2O,. m) methanol/H2O, n) ethanol/H2O, o) 1-propyl alcohol/ H2O, p) isopropanol/H2O.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
aggregates occurred as the gel went to transparent, which
presented interconnected networks consisted of well-
defined nanofibers with the diameter between 50-100 nm
and several micrometers in length. These observations are
in accordance with the SEM images. The achievement of
a stable transparent gel over the progress indicates the
formation of new aggregates that have no scattering effect
to the visible light. POM was also used for demonstration
of this gel-to-gel transformations, and bright region was
existed in both of the gel states. It indicated the formation
of anisotropic architectures, and DMPV self-assembled
into some organized structures could be confirmed.
Moreover, agglomerate and fibrillar textures could be
differentiated between Figure 4b and Figure 4d, which
consistent with the SEM and TEM analyses and further
declared the different assemble processes.
in gel formation of DMPV under mixed solvents and phase
transformations.
Morphological analysis
Macroscopic changes are the reflection of microstructure
evolutions, the above phenomenon indicates a reversible
change in the structure of the supramolecular aggregates
between the opaque and transparent gels. To gain insight
into the mechanisms of gelation and phase transformation,
the morphological details of the samples were firstly
investigated by scanning electron microscopy (SEM). As
displayed in Figure 3, the gels obtained in the mixed
solvents of 1,4-dioxane/H2O, acetonitrile/H2O, DMF/H2O
and DMSO/H2O exhibited crumpled appearances.
Whereas, the assemblies in methanol/H2O, ethanol/H2O,
1-propyl alcohol/H2O and isopropanol/H2O presented the
agglomerate structures under the same scales. Their
opaque properties might be resulted from the large sizes of
the aggregates. Upon heating and cooling process, gels in
1,4-dioxane/H2O, acetonitrile/H2O, DMF/H2O and
DMSO/H2O displayed nearly the same morphologies.
Therefore, the macroscopic features did not change, they
remained opaque. It is worth noting that, fibrous structures
were obtained in the mixture of aliphatic alcohols and
water. DMPV re-assembled into interconnected 3D
networks and a gel-to-gel phase transitions occurred. The
variation of microstructures brought about the changes in
the reflection of visible light, the transparent appearance
was thus formed. However, the opaque gel both in original
and reformed situations displayed agglomeration state
over a large scale. This could explain the reason for their
remaining opaque appearances.
Spectral analysis
FT-IR was also used to identify the structure variations of
opaque to transparency for the gels assembled in aliphatic
alcohols/H2O mixture. As shown in Figure 5a, the original
synthesized DMPV exhibited significant absorptions at
3280 cm-1, 2961 cm-1,1631 cm-1,1338 cm-1 and 1225 cm-1,
which corresponded to the N-H stretching, alkyl stretching,
C=O stretching (amide I), N-H bending (amide II) and C-
N stretching (amide III) vibrations, respectively. After the
self-assembly in the mixture of ethanol and water, the
bands corresponding to N-H and C=O stretching
vibrations at 3280 cm-1 and 1631 cm-1 red-shifted to lower
frequencies both in the opaque and transparent gels. It
signified that hydrogen bondings played a key role in the
assembly process. It is worth noting that, the transparent
gel obtained in aliphatic alcohols/H2O binary mixture red-
shifted further compared with the opaque one. FT-IR
spectra of the xerogels obtained from methanol/H2O, 1-
propyl alcohol/H2O and isopropanol/H2O are showed in
Figure S4, and they all exhibited the same trends of the
red-shift. These observations indicate a more ordered
hydrogen-bond networks in the fibrous structure, which
could only be constructed favored by aliphatic alcohols.
To gain further insight into the structures, X-ray powder
diffraction investigations were carried out and displayed in
Figure 5b. The powdery sample exhibited nearly no
obvious diffractions, which demonstrated an amorphous
structure. After the assembly, the opaque xerogel exhibited
an intense peak at 19.2°, implying the formation of ordered
molecular packings in this self-assembled system. For the
transparent xerogel re-assembled in ethanol/H2O,
prominent reflections were observed at 2θ of 19.2° and
22.4°, which corresponded to d-spacing of 4.6701 Å and
3.8696 Å. The appearance of new sharper peaks for
transparent gel indicates that there is an obvious
transformation from one gel phase to the other gel state,
more orderly regions were formed by gelator molecules.
Figure 4. (a, b) TEM and POM images of the opaque xerogel of DMPV obtained
from ethanol/H2O (v/v=1/2). (c, d) TEM and POM images of the transparent
xerogel of DMPV obtained from ethanol/H2O (v/v=1/2).
Transmission electron microscopy (TEM) and polarized
optical microscope (POM) analyses are further performed
for the investigation of transformations between opaque
and transparency in the gel obtained from ethanol/H2O. As
it can be seen, TEM image for the opaque xerogel
demonstrated random aggregates of DMPV. Upon
heating/cooling process, re-self assemble to small and thin
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
These analyses were in accordance with the microscopic opaque gel, it was destroyed and changed to sol. In contrast
morphology observations. The presence of one peak at to the opaque gel, it should be noting that the average
almost same position (around 19.2°) for both opaque and storage modulus increased (G′ > 104 Pa), and it was one
transparent xerogels suggests the similar ordered packings order of magnitude higher than the loss modulus (G″) over
for them. The d spacing of 4.6701 Å could be assigned to the entire range of stresses (0.1%~100%) for the
the distance between adjacent peptide strands, indicating transparent gel. Dynamic frequency sweep (DFS)
the formation of hydrogen bondings.[19] Notably, a experiments were also performed and the results were
characteristic peak with d spacing of 3.8696 Å arised for exhibited in Figure 6c. G′ and G″ displayed a slight
the transparent xerogel. This could be assigned to the dependence upon the frequency, which signified a good
distance between adjacent layers, which contributed to the tolerance of both opaque and transparent gels against
formation of nanofibers.[20] Based on the morphology, 1H external force. Moreover, the transparent gel showed an
NMR, FT-IR, and XRD investigations, the molecular almost four fold increase in the storage modulus value (G′)
packings of transparent gel is proposed in Figure 5d.
compared with the opaque one, which signified an
appreciable difference in the mechanical properties for
them. The transparent gel with fibrillar textures possessed
better mechanical strength than the opaque gel with
agglomerate structure. However, the dissipation factors of
tan δ (G″/ G′) for both opaque gel and transparent gel are
0.14 and 0.18 respectively, there is not much difference of
tan δ values.
Figure 6. Dynamic strain sweep (DSS) plots of (a) opaque and (b) transparent
DMPV gels. (c)Dynamic frequency sweep (DFS) experiments at constant strain
of 0.1%. The DMPV gels were prepared at the CGC, ethanol/H2O (v/v=1/2).
Figure 5. (a) FT-IR spectra and (b) XRD patterns of the pristine DMPV, the
opaque and transparent DMPV xerogels obtained from ethanol/H2O (v/v=1/2). (c)
Hydrogen bondings of DMPV. (d) Proposed molecular packings of DMPV.
Multistimuli-responsive study
As a soft material, multi-responsive and self-healing
characteristic
are
fundamental
properties
for
Thixotropic and rheological studies
supramolecular gels, which are vital to their smart
applications. The response to thixotropic force of the gel
was examined by the shaking and resting tests. As
displayed in Figure 7, the opaque and transparent gels
transformed into turbid liquids through vigorous shaking
by hand. After resting for a few seconds, they quickly
restored to self-supported gels. Meanwhile, chemical
stimuli was performed by the addition of acid and base.
When hydrochloric acid was added, both of the gels
transformed into transparent liquids due to disruption of
the hydrogen bondings. The solutions would quickly
restore to the original gel after adding an equivalent
To demonstrate the strength of the gels before and after the
gel-to-gel
transitions,
oscillatory
rheological
measurements were conducted. As depicted in Figure 6,
from the strain sweep profiles, the average storage
modulus (G′ > 103 Pa) was one order of magnitude higher
than the loss modulus (G″) for opaque gel assembled in
ethanol/H2O. This confirmed the formation of stable
supramolecular gel and its dominant elastic property. The
average storage modulus decreased intensely and became
less than the loss modulus upon 10% of the stress for the
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
amount of ammonia into the system. It was worth noting expected, this binary mixed solvents were gelled by
that, both of the opaque and transparent gels could recover DMPV. By virtue of the above model, a lot of tedious
to their original states, DMPV based gels exhibited well attempts on different solvents could be avoided, the
features mentioned above suffered from both physical and progress on morphology and performance siftings for
chemical stimuli.
application are largely shortened.
Figure 7. Reversible gel–sol transitions of the opaque (a) and transparent (b)
DMPV gels triggered by mechanical and pH stimuli.
Figure 8. The calculated Flory–Huggins parameters of DMPV and solvents in the
gelation test. S: solution, black squares; G: gelation, red circles; P: precipitation,
blue triangles.
Solubility theory application
Conclusions
The formation of a gel is the results of gelator–solvent and
gelator–gelator interactions.[21] To predict the range of
solvents which are likely to be gelled by this bis-dipeptide
gelator of DMPV, and facilitate the further investigation
and application of the gelator, Hansen and Flory–Huggins
parameters were both used for clarification of the
relationship between the structure of DMPV and different
solvents. Unfortunately, as shown in Figure S5, the
gelation behaviors of our compound toward the tested
solvents were not in accordance with the Hansen
parameter analysis based on δd, δp and δh. It was not
suitable for the DMPV gelator. So the Flory–Huggins
parameter of χ was alternatively used. Generally, χ is
estimated from the Hildebrand solubility parameters as
follows,
In conclusion, we designed an L-valine derived bis-
dipeptide gelator of DMPV and investigated its gelling
behaviors, self-assembled nanostructures and stimuli-
responsiveness. The gelation was induced by addition of
water into the organic solutions of DMPV, and the
resultant supramolecular gels exhibited an unprecedented
opaque to transparent transformations when aliphatic
alcohols were used as the organic components. Evolutions
of the assembled status from agglomerates to nanofibers
by the stimulation of aliphatic alcohols were observed.
Whereas, the crumpled morphologies remained upon
heating/cooling process in another binary mixed solvents.
The opaque and transparent assemblies could respectively
respond and restore under both of the chemical and
physical stimuli. Meanwhile, Flory–Huggins parameters
were successfully used to predict the gelling performance
of DMPV in untested solvents, it would considerably
improve the schedules involved during the identification
of a suitable gel system for a particular field, and the
further solvent screening and application for special
recognition of chemicals are in progress.
χ12=V1 (δ2-δ1)2/RT
(1)
where δ1, δ2 and V1 are denoted as Hilderbrand solubility
parameters of the solvent and gelator, the solvent molar
volume, respectively. The Hilderbrand solubility
parameters of bis-dipeptide gelator can be calculated
according to the Fedors group contribution method (Table
S5). The values of Flory–Huggins parameter of the gelator
in each solvent were calculated as described above (Table
S6) and plotted in Figure 8. It showed a strong correlation
between the solvent and χ. The stable gel would form in
the range from 2.15 to 3.17 for χ, whereas the sol and
precipitation would generate in a range less than 1.63 and
more than 3.81. It should be noting that, the mixture of sol
and gel was existed between 1.63 and 2.15. The gelation
was a metastable state between the dissolution and
precipitation. From the above point of view, if an untested
solvent lies in the gelation domain, it would be gelled by
DMPV. In order to test the hypothesis, we carried out the
gelation test for DMPV in untested solvents of
acetonitrile/H2O (1:1 v/v), which possessed a χ of 1.72. As
Experimental Section
Materials and instruments
L-valine, 1-ethyl-3-(3dimethyllaminopropyl)carbodiimide
hydrochloride (EDC.HCl), pyridine-4-carboxaldehyde,
Benzaldehyde, 1-Hydroxybenzotriazole (HOBt) and
triethylamine were purchased from Aladdin. Methanol and
all of the other solvents were all the products of Shanghai
Chemical Reagent Company and distilled prior to use.
Other chemicals were used as received without further
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
purification. FT-IR spectra were obtained on a Bruker DMSO, ppm): δ 7.63~7.786 (t, J1=5.5Hz, J2=6Hz, 2H), δ
Tensor 27 FT-IR spectrometer using KBr pellets. 1H NMR 3.347 (s, 2H), δ 3.008~3.077 (m, 4H), δ 2.867~2.878 (d,
spectra measurements were recorded on a Bruker J=5.5Hz, 2H), δ 1.80~1.851 (m, 2H), δ 1.585 (s, 4H), δ
AVANCE 500 MHz NMR spectrometer. X-ray diffraction 1.366~1.392 (t, J1=6.5Hz, J2=6.5Hz, 4H), δ 1.232 (s, 16H),
(XRD) measurements were recorded using a Brucker D8 δ 0.763~0.855 (dd, J1=6.5Hz, J2=6.5Hz, 12H).
Advance diffractometer equipped with a Cu target tube
Preparation of dodecamethylene-1,12-bis(N-(N-(4-
and a graphite monochromator. Morphologies of the
pyridylmethyl-L-valyl))-L-valine)(DMPV)
xerogels were investigated by scanning electron
microscopy (FEI Quanta 250F). Transmission electron Dodecamethylene-1,12-bis(N-L-valine) (1.99g, 0.005mol)
microscopy (TEM) images were recorded by a FEI Tecnai and N-(4-Pyridylmethyl)-L-valine (2.184g, 0.0105mol)
20 microscope. Polarizing optical microscopy (POM) of were dissolved in DMF (120 mL). Then EDC·HCl (2.865g,
RX50OMRT was used for visual observations at 25℃. 0.015mol) and HOBT (2.057g, 0.015mol) were added.
Rheology measurements were used by Anton Paar MCR- The reaction mixture was stirred at 50℃ for 12 h. After
102 rheometer.
poured into 0.5% of Na2CO3 aqueous solution (1L). The
collected precipitate was recrystallized from
CH3OH/CH2Cl2 (1:10, v/v) to obtain the pure products.
Preparation of N-4-Pyridylmethyl-L-valine (PV)
PV was prepared according to literatures[22,23] with some FT-IR (KBr, cm-1): ν(NH), 3215; ν(CH), 3012; ν(CH),
modification. To an aqueous solution (20 mL) of L-valine 2987; ν(C=C), 1723; ν(C=O), 1690; ν(N-H), 1580;
(2g, 17mmol) and Na2CO3 (0.92g, 8.5 mmol), Pyridine-4- ν(C=N), 1430; ν(C-N), 1292. 1H-NMR (500MHz, DMSO,
carboxaldehyde (1.84g, 17 mmol) in MeOH (15 mL) was ppm): δ 8.471~8.480 (d, J=4.5Hz, 4H), δ 7.974~7.979 (m,
dropped slowly. The solution was stirred for 5 h at room 4H), δ 7.321~7.330 (d, J=5.5Hz, 4H), δ 4.147~4.179 (t,
temperature and cooled in an ice bath. Then NaBH4 (0.76g, J1=8Hz,J2=8Hz,
2H),
δ
3.456~3.728
(dd,
20.4mmol) was added. The mixture was stirred for another J1=14.5Hz,J2=15Hz 4H), δ 2.982~3.089 (m, 4H), δ
12 h, and 36% hydrochloric acid was used to adjust the 2.771~2.782 (d, J=6Hz, 2H), δ 2.536~2.610 (brs, 2H), δ
basic (pH~11) system to acerbic (pH~5-6). The mixture 1.766~1.940 (m, 4H), δ 1.350~1.361 (brs,4H), δ
was stirred further for 2h and subsequently evaporated to 1.194~1.233 (brs, 16H), δ 0.832~0.914 (m, 24H).
dryness. The resultant solid was extracted with hot and dry
Preparation of dodecamethylene-1,12-bis (N-(N-
EtOH, and the filtrate was evaporated to obtain the white
(phenylmethyl-L-valyl))-L-valine (DMBV)
powdery PV. FT-IR (KBr, cm-1): ν(N-H), 3385; ν(O-H),
1
3255; ν(C=O), 1690; ν(C=N), 1430. H-NMR (500MHz, Dodecamethylene-1,12-bis
(N-(N-(phenylmethyl-L-
D2O, ppm): δ 8.446~8.455 (d, J=4.5Hz, 2H), δ valyl))-L-valine (DMBV) was synthesized in the similar
7.324~7.334 (d, J=5Hz, 2H), δ 3.546~3.858 (dd, J1=15Hz, way with the DMPV using benzaldehyde instead of
J2=14.5Hz, 2H), δ 2.782~2.793(d, J=5.5Hz, 1H), δ pyridine-4-carboxaldehyde. FT-IR (KBr, cm-1): ν(NH),
1.847~1.930 (m,1H), δ 0.859~0.884 (t, J1=6Hz,J2=6.5Hz, 3282; ν(CH), 3012; ν(CH), 2987; ν(C=C), 1723; ν(C=O),
1
6H).
1690; ν(N-H), 1580; ν(C-N), 1292. H-NMR (500MHz,
DMSO, ppm): δ 7.917~8.048 (m, 4H), δ 7.201~7.324 (m,
10H), δ 4.174~4.207 (t, J1=7.5Hz, J2=9Hz, 2H), δ
3.432~3.690 (dd, J1=13Hz, J2=13Hz, 4H), δ 3.040~3.076
Preparation of dodecamethylene-1,12-bis(N-L-valine)
(DM)
The compound DM was prepared following a modified (m, 4H), δ 2.791~2.802 (d, J=5.5Hz, 2H), δ 2.307 (brs,
literature procedure.[24] L-Valine (5.85g, 0.05mol), KOH 2H) ,δ 1.775~1.936 (m, 4H) ,δ 1.362~1.375 (brs, 4H), δ
(2.8g, 0.05mol) and ethyl 3-oxobutanoate (7.0mL, 1.191~1.209 (brs,16H) , δ 0.831~0.995 (m, 24H).
0.055mol) were dissolved in isopropyl acetate (100mL).
The mixture was heated to reflux for 2h and isopropyl
acetate (200mL) was added. The solution was cooled to
12℃ in an ice bath. Pivaloylchloride (12.3, 0.05mol) was
added and the reaction mixture was stirred for 1h. Then
1,12-diaminododecane (4.55g, 0.023mol) was added to the
solution and stirred at room temperature for 30 min. Water
(300mL) was added to the reaction mixture and the pH was
adjusted to 1-2 by addition of HCL. The aqueous phase
was separated and washed with isopropyl acetate. The pH
was adjusted to 10-11 by addition of NaOH solution. The
solution was cooled to 0℃ and the precipitate was filtered
off, washed with cold isopropyl acetate and dried at 60℃
Acknowledgements
This work was financially supported by the National
Natural Science Foundation of China (51303083), the
Natural Science Foundation of Jiangsu Province
(BK20130759), the Fundamental Research Funds for the
Central Universities (30917011310) and Priority
Academic Program Development of Jiangsu Higher
Education Institutions (PAPD).
Keywords: bis-dipeptide • L-valine • opaque to transparent
in vacuum. FT-IR (KBr, cm-1): ν(N-H), 3281; ν(C-H), transformations • aliphatic alcohols • Flory–Huggins parameters
1
3092; 2921; 2851; ν(C=O), 1632. H-NMR (500MHz,
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
[1] a) S. Chen, H. He, G. Tang, B. Wu, M. Ma, Y. Shi, X.
Wang, RSC Adv. 2015, 5, 101437-101443; b) D. Wu, W.
Wen, S. Chen, H. Zhang, J. Mater. Chem A. 2015, 3, 2589-
2600; c) Z. Zhang, X. Fang, Energy Convers. Manage.
2006, 47, 303-310; d) X. Wang, E. Lu, W. Lin, Energy
Convers. Manage. 2000, 41, 135-144.
Commun. 2009, 310-312; d) V. K. Praveen, C. Ranjith, E.
Bandini, A. Ajayaghosh, N. Armaroli, Chem. Soc. Rev.
2014, 43, 4222-4242; e) S. Ogi, V. Stepanenko, K.
Sugiyasu, M. Takeuchi, F. Wìrthner, J. Am. Chem. Soc.
2015, 137, 3300-3307; f) D. M. Zurcher, Y. J. Adhia, J. D.
Romero, A. J. McNeil, Chem. Commun. 2014, 50, 7813-
7816.
[2] a) B. R. Adhikari, D. Kim, J. H. Bae, J. Yeon, K. C.
Roshan, S. K.Kang, E. H. Lee, Cryst. Growth Des. 2016
,
[8] a) S. Mahesh, R .Thirumalai, Yagai S, A. Kitamura , A.
Ajayaghosh, Chem. Commun. 2009, 5984-5986; b)
Y .Zhang, B .Zhang, Y .Kuang, Y. Gao, J. Shi, X .X.
Zhang , B. Xu, J. Am. Chem. Soc. 2013, 135, 5008-5011;
c) Z. Sun, Z. Li, Y. He, R. Shen, L. Deng, M. Yang, Y.
Liang, Y. Zhang, J. Am. Chem. Soc. 2013, 135, 13379.
[9] a) E. Busseron, Y. Ruff, E. Moulin, N. Giuseppone,
Nanoscale. 2013, 5, 7098-7140; b) Q. Lin, Q. P. Yang,
B .Sun, Y. P. Fu, X. Zhu, T. B. Wei, Y. M. Zhang, Mater.
Lett. 2014, 137, 444-446; c) X. L. Dong, H. Wang, F. Fang,
X. Li , Y. J. Yang, Electrochim. Acta. 2010, 55, 2275-2279;
[10] a) X. Wang, T. He, L. Yang, H. Wu, R. Zhang, Z. Zhang,
R. Shen, J. Xiang, Y. Zhang, C. Wei, Nanoscale 2016, 8,
6479-6483; b)Y. Zhang, S. Li, M. Ma, M. Yang, Y. Wang,
A. Hao , P. Xing, New J. Chem. 2016, 40, 5568-5576; c)
K. M. Galler, L. Aulisa, K. R. Regan, R. N. D'Souza, J. D.
Hartgerink, J. Am. Chem. Soc. 2010, 132, 3217-3223.
[11] F. Xie, L. Qin, M. Liu, Chem. Commun. 2016, 52, 930-
933.
[12] V. A. Mallia, P. D. Butler, B. Sarkar, K. T. Holman, R. G.
Weiss, J. Am. Chem. Soc. 2011, 133, 15045-15054.
[13] A. Baral, S. Basak, K. Basu, A. Dehsorkhi, I. W. Hamley,
A. Banerjee, Soft Matter. 2015, 11, 4944-4951.
[14] a) T. Tazawa, S. Yagai, Y. Kikkawa, T. Karatsu, A.
Kitamura , A. Ajayaghosh, Chem. Commun. 2010, 46,
1076-1078; b) A. Pramanik, A. Paikar, K. Majiand
D .Haldar, RSC Adv. 2016, 6, 59851-59857; c) S. K.
Pathak, B. Pradhan, R. K. Gupta, M. Gupta, S. K. Pal ,A.
S. Achalkumar, J. Mater. Chem. C. 2016, 4, 6546-6561;
[15] a) L. Niu, J. Song, J. Li, N. Tao, M. Lu , K. Fan, Soft
Matter. 2013, 9, 7780-7786; b) D. C. Zhong, L. Q. Liao,
16, 7198-7204; b) Y. Wang, L. Tang, J. Yu, Cryst. Growth
Des. 2008, 8, 884-889; c) L. E. Buerkle, S. J. Rowan,
Chem. Soc. Rev. 2012, 41, 6089-6102; d) A. Gasnier, G.
Royal, P. Terech, Langmuir. 2009, 25, 8751-8762; e) Z.
Qi, C. Schalley, Acc. Chem. Res. 2014, 47, 2222-2233; f)
L. Fang, H. Zhang, Z. Li, Y. Zhang, Y. Zhang, H. Zhang,
Macromolecules. 2013, 46, 7650-7660.
[3] a) R. Liang, Z. Luo, G. Pu, W. Wu, S. Shi, J. Yu, Z. Zhang,
H. Chen, X. Li, RSC Adv. 2016, 6, 76093-76098; b) X.
Pang, X. Yu, H. Lan, X. Ge, Y. Li, X. Zhen, T. Yi, ACS
Appl. Mat. Interfaces. 2015, 7, 13569-13577; c) X .Wu, Y.
Li, C. Lin, X. Hu, L. Wang, Chem. Commun. 2015, 51,
6832-6835; d) S. Datta, S. Bhattacharya, Chem. Eur. J.
2016, 22, 7524-7532; e) S. Liu, Y. Luo, G. Liang,
Nanoscale .2016, 8, 766-769; f) D. Bardelang, F. Camerel,
J. Margeson, D. Leek, M. Schmutz, M. Zaman, K. Yu, D.
Soldatov, R. Ziessel, C. Ratcliffe, J. Ripmeester, J. Am.
Chem. Soc. 2008, 130, 3313-3315; g) J. Wu, T. Yi, Q. Xia,
Y. Zhou, F. Liu, J. Dong, T. Shu, F. Li, C. Huang, Chem.
Eur. J. 2009, 15, 6234-6243; h) J. Malicka, A. Sandeep, F.
Monti, E. Bandini, M. Gazzano, C. Ranjith, V. Praveen, A.
Ajayaghosh, N. Armaroli, Chem. Eur. J. 2013, 19, 12991-
13001.
[4] a) S. Bhattacharjee, B. Maiti, S. Bhattacharya, Nanoscale.
2016, 8, 11224-11233; b) G. Cravotto, P. Cintas, Chem.
Soc. Rev. 2009, 38, 2684-2697; c) M. D. Segarra-Maset,
V. J. Nebot, J. F. Miravet , B. Escuder, Chem. Soc. Rev.
2013, 42, 7086–7098; d) Y. Y. Li, J. A. Liu, G. Y. Du, H.
Yan, H. Y. Wang, H. C. Zhang, W. An, W. J. Zhao, T. Sun,
F. E. Xin, L. Kong, Y. M. Li, A. Y. Hao , J. C. Hao, J.
Phys. Chem. B .2010, 114, 10321-10326; e) S. Yagai, T.
Iwashima, K. Kishikawa, S. Nakahara, T. Karatsu, A.
Kitamura, Chem. Eur. J. 2006, 12, 3984-3994; f) Y. Su, J.
Liu, Y. Jiang, C. Chen, Chem. Eur. J. 2011, 17, 2435-2441;
g) R. Du, J. Wu, L. Chen, H.Huang, X. Zhang, J. Zhang,
Small. 2014, 10, 1387-1393.
K. J. Wang, H. J. Liu, X. Z. Luo, Soft Matter. 2015
,
11 ,6386-6392; c) L. Zhang, X. F. Wang, T. Y. Wang, M.
H. Liu, Small. 2015, 11, 1025-1038; d) W. Miao, D. Yang ,
M. Liu, Chem. Eur. J. 2015, 21, 7562-7570.
[16] a) M. Raynal, L. Bouteiller, Chem. Commun. 2011, 47,
8271-8273; b) A .F .M. Barton ,Chem. Rev. 1975, 75, 731-
753; c) J. Bonnet, G. Suissa, M. Raynal, L. Bouteiller, Soft
Matter. 2014, 10, 3154-3160; d) A .R. Hirst, D. K .Smith,
Langmuir. 2004, 20, 10851-10857;
[17] a) W. Edwards, C. A. Lagadec, D. K. Smith, Soft Matter.
2011, 7, 110-117; b) S. J. Liu, W. Yu, C. X. Zhou, Soft
Matter. 2013, 9, 864-874; c) Y. Lan, M. G. Corradini, R.
G. Weiss, S. R. Raghavan , M. A. Rogers, Chem. Soc. Rev.
2015, 44, 6035–6058; d) R. Lu, J. Hu, C. L. Liu, H. X. Gao,
Y. Ju, Soft Matter. 2012, 8, 9576-9580.
[5] a) X. L. Zhang, C. M. Dong, W. Y. Huang, H. M. Wang,
L. Wang, D. Ding, H. Zhou, J. F. Long, T. L. Wang, Z. M.
Yang, Nanoscale. 2015, 7, 16666-16670; b) K. Fan, J.
Song, J. Li, X. Guan, N. Tao, C. Tong, H. Shen , L. Niu,
J. Mater. Chem. C. 2013, 1, 7479-7482; c) M. Yoshio, Y.
Shiko, Y. Tochigi, Y. Nishikawa, T. Kato, J. Am. Chem.
Soc. 2009, 131, 6763-6767; d) C. Wang, Q. Chen, F. Sun,
D. Zhang, G. Zhang, Y. Huang, R. Zhao, D. Zhu, J. Am.
Chem. Soc. 2010, 132, 3092-3096.
[6] a) Y. Osada, A. R. Khokhlov, Polymer Gels and Networks;
Marcel Dekker: New York, 2002; b) S.k. Ahn, R. M. Kasi,
S.C. Kim, N. Sharma, Y. Zhou, Soft Matter. 2008, 4, 1151-
1157; c) N. M. Sangeetha, U. Maitra, Chem. Soc. Rev.
2005, 34, 821-836; d) A. R. Hirst, B. Escuder, J. F.
Miravet, D. K. Smith, Angew. Chem. 2008, 120, 8122-
8139; e) D. Diaz. Diaz, D. Kuhbeck, R. J. Koopmans,
Chem. Soc. Rev. 2011, 40, 427-448; f) X. M. Li, J. Y. Li,
Y. A. Gao, Y. Kuang, J. F. Shi, B. Xu, J. Am. Chem. Soc.
2010, 132, 17707-17709.
[18] S. Saha, J. Bachl, T. Kundu, D. D. Diaz , R. Banerjee,
Chem. Commun. 2014, 50, 7032-7035.
[19] B. Escuder , J. F. Miravet, Langmuir. 2006, 22, 7793-7797.
[20] Z. Guo, R. Gong, Y. Jiang , X. Wan, Soft Matter. 2015, 11,
6118-6124.
[21] a) K. Ramesh, S. Bhowmik, U. Maitra, J. Indian Chem.
Soc. 2011, 88, 1903-1915; b) J. Gao, S. Wu and M. A.
Rogers, J. Mater. Chem. 2012, 22, 12651-12658; c) A.
Aggeli, M. Bell, N. Boden, J. N. Keen, P. F. Knowles, T.
C. B. McLeish, M. Pitkeathly, S. E. Radford, Nature. 1997
386, 259-262; d) P. L. Zhu, X. H. Yan, Y. Su, Y. Yang, J.
B. Li, Chem. Eur. J. 2010, 16, 3176-3183.
,
[7] a) P. Bairi, B. Roy, A. K. Nandi, J. Mater. Chem. 2011
,
21, 11747-11749; b) B. Bai, X. Mao, J. Wei, Z. Wei, H.
Wang, M. Li, Sens. Actuators B. 2015, 211, 268-274; c) J.
P. Hong, M. C. Um, S. R. Nam, J. I. Hong, S. Lee, Chem.
[22] S. Saha, J. Bachl, T. Kundu, D. D. Díaz, R. Banerjee,
Chem. Commun. 2014, 50, 3004-3006.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
[23] X. Wang, T. He, L. Yang, H. Wu, R. Zhang, Z. Zhang, R.
Shen, J. Xiang, Y. Zhang, C. Wei, Nanoscale. 2016, 8,
6479.
[24] M. Suzuki, S. Owa, M. Yumoto, M. Kimura, H. Shirai, K.
Hanabusa, Tetrahedron Lett. 2004, 45, 5399-5402.
This article is protected by copyright. All rights reserved.

10.1002/cplu.201700206
ChemPlusChem
FULL PAPER
FULL PAPER
Supramolecular Chemistry
Tingting Xiao, Xiaoyang Zhang,
Jiazhi Yang, Yong Yang*
Page No. – Page No.
Aliphatic
opaque
alcohols
to
induced
transparent
transformation and application
of solubility theory in a bis-
dipeptide based supramolecular
gel
Opaque to transparent transformation of the bis-dipeptide based supramolecular gel occurred when aliphatic alcohols
were used as the component of organic/H2O binary mixed solvents for gelation. This would be potential for developing
a sensor for prompt and facile selective recognitions. A re-assembly process with microstructure evolutions from
agglomerates to nanofibers was observed during this gel-to-gel phase transition. Moreover, solubility theory of Flory–
Huggins parameter was successfully used for the prediction of gelling performance of this gelator, it would improve the
progress of system screening for practical applications.
This article is protected by copyright. All rights reserved.