Self-assembly of novel cholesterol derivative based on hydrogen bond

Article abstract of DOI:10.1016/j.molstruc.2011.08.032

In this paper, a novel cholesterol derivative was found that it can form regular arrangement with millimeter size when we investigated the synthesis of new cholesterol monomer. The quite interesting thing is that the arrangement can form on common glass sheet after the sample is heating above its melting point and then cooling to room temperature. This is different from most reported regular arrangements formed in solutions. According to the single crystal results of the sample, we believe that the arrangement formed in solid state can be attributed to hydrogen bonding formed between molecular and Van der Waals force among molecular.

Full text of DOI:10.1016/j.molstruc.2011.08.032

Journal of Molecular Structure 1005 (2011) 107–112
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Self-assembly of novel cholesterol derivative based on hydrogen bond
⇑
Yun-long Yu, Hai-yan Du, Jun-hua Zhang
State Key Laboratory of Polymer Materials Engineering of China, Sichuan University, Chengdu, Sichuan Province 610065, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 June 2011
Received in revised form 16 August 2011
Accepted 16 August 2011
Available online 16 September 2011
In this paper, a novel cholesterol derivative was found that it can form regular arrangement with milli-
meter size when we investigated the synthesis of new cholesterol monomer. The quite interesting thing
is that the arrangement can form on common glass sheet after the sample is heating above its melting
point and then cooling to room temperature. This is different from most reported regular arrangements
formed in solutions. According to the single crystal results of the sample, we believe that the arrangement
formed in solid state can be attributed to hydrogen bonding formed between molecular and van der
Waals force among molecular.
Keywords:
Cholesterol derivatives
Hydrogen bonding
Regular arrangement
Ó 2011 Elsevier B.V. All rights reserved.
1
. Introduction
Self-assembly behavior is one common phenomenon in nature.
work have been done based on C3AOH, seldom work [15,16] based
on C5@C6. There are many researchers who are interested in the
cholesterol derivatives in the world, such as Mallia, Ikeda, Kasi,
Zhu groups [17–24]. But in Zhu’ group, they have done majority
work relating to cholic acid and investigated the self-assembly of
cholic acid derivatives because the derivatives always still have
amphiphilic properties.
The small or macro-molecules could aggregate into new or special
structures with various functions under a certain conditions [1]. In
recent years, study on self-assembly has been attracted broad inter-
ests because of the possibility of forming millimeter- [2] or nano-
meter-scale [3] materials with certain well-organized structure
In our group, we have ever synthesized new type of cholesterol
derivatives on C6 position [15,16], the hydroxyl groups on C3 posi-
tion was etherification protected. As a continuation of the research
work, this time we still designed to synthesize derivatives on C6
position but the hydroxyl group was esterification protected. We
found that one of the derivatives has an interesting well-organized
structure on common glass substrates when we investigated cho-
lesterol derivatives on POM. And another interesting thing is the
self-organized process is different from the common methods re-
ported, putting a little amount solid sample between two glass
substrates and then heating the solid sample above its melting
temperature and then cooling the sample to room temperature,
well-organized structures appeared.
[
3], morphology [4] and functions [5]. Self-assembly behavior is
mainly driven by non-covalent interactions, such as hydrogen
bond, van der Waals force, interaction [6]. In addition, the
p–p
hydrogen bond, one kind of moderate intensity and directionality
force, has more favorable molecular orientation than charge inter-
actions and van der Waals force.
Usually these kinds of molecules suitable for assembling well-
ordered arrangements and structures have functional groups such
as hydroxyl, carboxyl, and amine among these groups non-covalent
interactions can be formed in solution or in solid state. In most
cases, the preparation methods are firstly dissolving the sample in
suitable solvent and then casting them on ordered substrates, espe-
cially on metals (e.g. Si, Cu, Ag and Au) [7–10] or graphite [11–13].
Obviously, the ordered surface is helpful for the assembly process,
seldom reports [14] have been mentioned forming ordered arrays
on the surface of sheet glass.
2
. Experimental section
2.1. Materials
Cholesterol can be obtained from organism, and it belongs to
the family of steroid compounds. There are two functional groups
in cholesterol structure, hydroxyl on C3 position (C3AOH) and
double bond between C5 and C6 (C5@C6). However, many research
Cholesterol, acetic anhydride, dicyclohexylcarbodiimide (DCC),
pyridine, 3-chloroperoxybenzoic acid (m-CPBA), dichloromethane,
-methacrylic acid, hydroquinone were all purchased from
a
GuangHua Chemical Co. of China and used as received. Tetrahydro-
furan (THF, analytical reagent; GuangHua chemical reagents) was
purified through standard methods.
⇑
Corresponding author. Fax: +86 028 85402465.
E-mail address: zhangjh@scu.edu.cn (J.-h. Zhang).
0
022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.08.032

1
08
Y.-l. Yu et al. / Journal of Molecular Structure 1005 (2011) 107–112
2
.2. Instruments
1H NMR (400 MHz, CDCl
3
): d (ppm) = 5.37 (s, 1H, 6-H), 4.62
);
IR (KBr pellet, cm ): 2942.9–2867.2 (ACH
1667.6 (AC@C), 1244.7, 1032.0 (CAOAC).
(
s, 1H, 3-H), 2.01 (m, 3H, ACH
3
À1
FTIR spectra were measured on a FT-IR (Nicolet) spectrophotom-
2
A), 1735.7 (AC@O),
1
eter. Proton nuclear magnetic resonance ( H NMR) spectra were re-
corded on a BrukerARMx-400 operating at 400 MHz in deuterated
chloroform. Differential scanning calorimetry (DSC) was carried
out on a thermal analysis (TA) DSC-Q30 with a liquid nitrogen cool-
ing system. The samples were heated from room temperature to
Elem. Anal. Calcd. for C29
81.12%; H, 11.20%.
48 2
H O : C, 81.25%; H, 11.29%. Found: C,
2
.3.2. Synthesis of 5,6-oxy-cholesteryl acetate (2)
Compound 2 was prepared according to the literature proce-
dure [25]. Cholesteryl acetate (8.57 g, 0.02 mol), m-CPBA (4.14 g,
.024 mol), CH Cl (60 ml) were added to a 150 ml round-bottom
1
75 °C, at a heating rate of 10 °C/min, followed by cooling at the
same rate. The crystal structure was obtained on CAD4SDP-44M/
H four-circle single crystal diffractometer made by Enraf–Nonius
Company of Holland. A polarizing optical microscope (POM)
equipped with a hot stage was used to observe phase transition
temperatures and optical textures for the monomer. Elemental
analysis was carried out using an Italian CARLO ERBA 1106 Elemen-
tal analyzer, which simultaneously detects C, H, N, percentage.
0
2
2
flask with flap loosely capped, and then stirred for 24 h at room
temperature. After removing the white precipitate, the filtrate
was washed by saturated sodium bicarbonate and sodium chloride
solution several times, sequentially, and purified from methanol at
last. The yield was 79%.
1
H NMR (400 MHz, CDCl
3
): d (ppm) = 5.02 (s, 1H, 6-H), 4.85
);
2
.3. Synthesis process
(s, 1H, 3-H), 2.2 (m, 3H, ACH
3
À1
IR (KBr pellet, cm ): 2952.4–2868.8 (ACH
1240.9, 1039.4 (CAOAC).
2
A), 1732.7 (AC@O),
The final cholesteryl derivatives were synthesized starting from
cholesterol. The hydroxyl group of cholesterol was initially pro-
tected by esterifying with acetic anhydride, and then the double
bond in cholesterol skeleton was epoxided. Finally the epoxy group
was opened using methacrylic acid. The synthesis route is shown
in Scheme 1.
Elem. Anal. Calcd. for C29
78.35%; H, 10.97%.
48 3
H O : C, 78.33%; H, 10.88%. Found: C,
2
.3.3. Synthesis of 5-hydroxyl, 6-methacrylate-cholesteryl acetate (3)
Compound 2 (3 g, 6.7 mmol) and 1 mg hydroquinone was dis-
solved in 15 ml -methacrylic acid without any catalysts. The reac-
a
2
.3.1. Synthesis of cholesteryl acetate (1)
In a typical experiment, cholesterol (30 g, 0.08 mol), acetic
tion was carried out at 80 °C for 48 h under nitrogen atmosphere.
The mixture was dissolved in acetic ether followed by washing
using saturated sodium bicarbonate and sodium chloride solution
several times, sequentially. The organic layer was dried by magne-
sium sulfate anhydrous for 12 h, obtaining the crude product after
removing the solvent under reduced pressure. And then the prod-
uct was purified by silica gel column chromatography with the
mixture of mineral ether and acetic ether (8:1). Yield: 58%.
anhydride (15 ml), DCC (8 g, 0.04 mol), and a few drops of pyridine
were added to fleshly distilled THF (100 ml) and the reaction mix-
ture was refluxed for 72 h under N atmosphere. Then the white
2
precipitate was removed by filtration and the filtrate was evapo-
rated, the crude product was recrystallized twice from ethanol,
obtaining product 1 with yield of 90.2%.
O
O
O
CH Cl
2
2
H
DCC
H
m-CPBA
H
H
H
H
H
H
H
HO
CH COO
3
CH COO
3
1
O
2
O
OH
H
8
0 °C
H
H
CH COO
3
OH
3
O
O
Scheme 1. The synthesis route of novel cholesterol derivate monomer.

Y.-l. Yu et al. / Journal of Molecular Structure 1005 (2011) 107–112
109
20
40
60
80
100
120
140
160
180
T/°C
Fig. 1. The DSC heating and cooling curves of compound 3.
Fig. 3. SEM images of compound 3 obtained by cooling melting sample to room
temperature.
À1
tion peak of CH
2
@CHA was found at about 1636 cm . All the re-
sults above indicated that the monomer synthesized was the one
we expected. Structurally, it is difficult to introduce large groups
into the C5 position due to the steric hindrance and the methacry-
late group should be connected to C6 position. The corresponding
characterization was shown in the following content.
3.2. DSC curve analysis
It is well known that cholesterol esters and hydrocholesterol
[
27] usually have liquid crystalline properties. In our experiment
a question occurred in our mind that whether the final monomer
starting from cholesterol ester has liquid crystalline property or
not. Thermal behavior of compound 3 was characterized by DSC
at a rate of 10 °C/min. The heating curve shown in Fig. 1 reveals
that there is only a melting peak, and no other thermal transition
peaks are detected. Moreover, no corresponding peak presents dur-
ing cooling process. During the second heating and the second
cooling, there are not any peaks observed. However, if the com-
pound 3 was given enough time under room temperature, it began
to crystallize again, and the melting could be observed again in the
process of heating. In addition, we found that if the temperature
was heated above 200 °C, polymerization of the monomer oc-
curred. That is because the powder after being heated above
Fig. 2. The POM image after the compound 3 cooling from melting state to room
temperature.
1H NMR (400 MHz, CDCl
3
): d (ppm) = 5.62, 6.13 (s, 2H,@CH
2
),
5
2
.31 (s, 1H, 6-H), 4.78 (s, 1H, 3-H), 2.2 (m, 3H, ACH
IR (KBr pellet, cm ): 3474.9 (AOH), 3101.7 (AC@CH
869.5 (ACH A), 1737.0 (AC@O), 1636.1 (AC@C), 1241.7, 1025.2
2
3
);
À1
2
), 2941.8–
2
00 °C cannot be completely dissolved in ethyl acetate.
(
CAOAC).
Elem. Anal. Calcd. for C33
4.55%; H, 10.28%.
54 5
H O : C, 74.67%; H, 10.25%. Found: C,
3.3. POM and SEM results
7
The melting and cooling process of compound 3 was also ob-
3
. Results and discussion
served by POM. The monomer melting takes place after being
heated to about 153 °C, and then it is isotropic liquid. What inter-
esting is some ordered stripes were observed when the melted
sample was cooled to room temperature, as shown in Fig. 2. The
most prominent features are the ordered domains, which consist
of parallel stripes, the distance between the adjacent two stripes
3.1. Synthesis of monomers
In cholesterol structure there is a hydroxyl group on C3 position
and a double bond between C5 and C6 position. The hydroxyl group
of C3 position initially was esterified by acetic anhydride [26]. Then
ranges from 11 to 16 lm. Besides, we found this area was colorful
the double bond between C5 and C6 position was oxidized to epoxy
on the surface of glass sheets. It is known that cholesteric phase ex-
hibit iridescent colors if the helical pitch or reflected wavelength
coincides with the wavelength of visible light. Even though the
two glass sheets are separated from each other, the well-defined
stripes still obviously present on glass sheets.
1
and the epoxy group was opened by using methacrylic acid.
H
NMR results show that there exists obvious double bond displace-
ment in compound 3, suggesting the ring-opening reaction was
successful. Moreover, in the FTIR spectra, the characteristic absorp-

1
10
Y.-l. Yu et al. / Journal of Molecular Structure 1005 (2011) 107–112
Fig. 4. The crystal structure of compound 3.
Fig. 5. The hydrogen bond between H (1) and O (3) of two molecules.
In order to identify and repeat the organization of the parallel
3.4. Characterization of X-ray monocrystal diffraction
stripe, samples were sprayed on glass sheet and covered another
empty glass sheet on the sample. Then the sample was heated to
the temperature above its melting point and then cooled down
to room temperature. SEM was employed to characterize the mor-
phology and microstructure. Fig. 3 shows the similar arrangement
as shown in POM results. Pictures of much greater magnification
could be recorded in a certain scope, one can discern the white
and black regions from it. It should be noticed that the same stripes
still could be observed no matter how fast the rate of quenching,
and the observation is repeatable through pressing the glass plate
slightly when melting, and it is repeatable.
In order to study how the stripes form, we focus on the research
of interaction and molecular packing of single crystal. The interac-
tions between molecules revealed in the single crystal may offer
valuable insight into the ordered structures of superamolecule.
Therefore, the single crystal of compound 3 was cultivated from
its acetic ether solution, and clear pictures were obtained through
four-circle single crystal diffractometer. As Fig. 4 shows C3 position
connects with ACH
ACH C (CH ) COO (up). The data of single crystal of 3 is shown as
follows: formula: C33 , formula weight: 530.76, crystal size:
3
COO (up), C5 with AOH (down) and C6 with
3
2
54 5
H O

Y.-l. Yu et al. / Journal of Molecular Structure 1005 (2011) 107–112
111
Fig. 6. Molecular packing and hydrogen bonds (green lines) formed in the single crystal of 3. (A); (B) and (C) are views observed from a, b and c axes respectively. (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
3
0
.36 Â 0.28 Â 0.19 mm , temperature: 296 K, crystal system:
after slowly solvent volatilizing. There are HAbonding interactions
between every two molecules which could form small aggregate as
shown in Fig. 5. Meanwhile, the van der Waals force integrates
these small aggregates into a whole supermolecule which presents
regular arrangement of stripes in a macroscopic view. Maybe that
only happens in ideal environment, however, when the solids were
heated up to the melting point, the molecules desultorily arranged
in the form of isotropic liquid. That is the ideal environment when
the isotropic liquid was cooled at a slow rate. Every two molecules
could be combined together through HAbonding. With further
cooling, van der Waals force plays an important role in accumulat-
ing the small aggregates into the superamolecules. Views from a, b,
c axes of the forming structure are shown in Fig. 6. Thereinto, view
from b explains the regular arrays of rod stripes observed from
POM. The intermolecular packing and assembling forms the
superamolecule ordered structures and they are stable at room
temperature.
monoclinic, space group:
2
C , a: 31.9922 Å, b: 9.9421 Å, c:
3
1
1
0.3358 Å,
.075 mg/mm , F(000): 1168, reflections collected: 7423, final R
= 0.0756, wR = 0.1692.
calc
a: 90°, b: 93.758°, c: 90°, volume: 3280.4 Å , Z: 4, q :
3
indices (all data): R
1
2
As Fig. 5 shows, there is intermolecular hydrogen bond between
every two molecules. Since the group connected on C5 and C6 faces
to the opposite direction, it is feasible to form strong interaction
between two molecules in space. The C@O at C6 position of com-
pound 3 forms hydrogen bond with the OH at C5 position of an-
other molecule of compound 3, at the same time, another
hydrogen bond is formed at the opposite position. The single crys-
tal data show the angle of hydrogen bond is 168.5° which is nearly
80°. In the basis of the above results, we assert the hydrogen bond
plays an important role in the formation of ordered structures of
superamolecular.
Except hydrogen bonding formed between every two molecules,
van der Waals force also plays an important part in forming regular
structure. After purification by silica gel column chromatography,
we got the molecular solids through rotary evaporators. The solids
are crystalline, and all the crystals accumulated together through
van der Waals interactions because of fast dissolvent volatilizing.
While, the single crystal was obtained from its acetic ether solution
1
The present observation is not identical with the general self-
assembly, because it takes place during the melting cooling process
rather than the traditional self-assembly in solution, which is novel
and interesting.
The experiment of forming well-defined arrays is repeatable;
however, the forming ordered domain is not wide enough. The

1
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Y.-l. Yu et al. / Journal of Molecular Structure 1005 (2011) 107–112
next step we will try to increase the effective domain sizes and ex-
plore the mechanism of the formation of parallel stripes. Further-
more, it is necessary to study the effects of various substrates in
the self-assembly process.
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New types of lateral cholesteryl derivates were synthesized.
Through various methods of characterization, the parallel arrays
of rod stripes were observed for hydrogen bond and van der Waals
force. This novel self-assembly behavior occurred in cooling pro-
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simple and repeatable.
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Acknowledgment
This work described in this article was supported by the Na-
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