Creation of Double Silica Nanotubes by Using Crown-Appended Cholesterol Nanotubes

Article abstract of DOI:10.1002/chem.200305008

New crown-appended cholesterol-based organogelators 1-3, which have one or two cholesterol skeletons as a chiral aggregate-forming site, two amino groups as an acidic proton binding site, and one crown moiety as a cation binding site, were synthesized, an

Full text of DOI:10.1002/chem.200305008

FULL PAPER
Creation of Double Silica Nanotubes by Using Crown-Appended
Cholesterol Nanotubes
Jong Hwa Jung,*[a, b] Seok-Hoon Lee,[a] Jong Shin Yoo,[a] Kaname Yoshida,[b]
Toshimi Shimizu,[b] and Seiji Shinkai*[c]
Abstract: New crown-appended choles-
terol-based organogelators 1 3, which
have one or two cholesterol skeletons as
a chiral aggregate-forming site, two
amino groups as an acidic proton bind-
ing site, and one crown moiety as a
cation binding site, were synthesized,
and the gelation ability was evaluated in
organic solvents. These gelators could
gelatinize several organic solvents under
1.0 wt%, indicating that 1 3 act as a
versatile gelator of various organic sol-
vents. We observed CD spectra of the
propionic acid gels 2 and 3, bearing only
one cholesterol, moiety exhibit a nega-
tive sign for the first Cotton effect,
strongly suggesting that the dipole mo-
ments of the azobenzene chromophores
orient into the anticlockwise direction.
The TEM images of the 1‡acetic acid
gel resulted in the helical ribbon and
tubular structures. Sol-gel polyconden-
sation of tetraethoxysilane (TEOS) was
carried out with 1 3 as templates in the
gel phase. The silica obtained from the
1‡acetic acid gel showed the helical
ribbon with 200 1700 nm width and the
tubular structure of the silica with con-
stant about 560 nm outer diameter. As
far as can be recognized, all the helicity
possesses a right-handed helical motif.
Since the exciton coupling band of the
organogel also shows P (right-handed)
helicity, we consider that a microscopic
helicity is reflected by a macroscopic
helicity. On the other hand, the tubular
structure of the silica obtained from the
organogels 2 and 3 is somewhat different
from that prepared from the organogel
1. The careful examination of SEM and
TEM pictures revealed that the tube
wall of the silica features a roll-paper-
like multilayer structure. Thus, this pa-
per demonstrates successful and rare
examples for precise transcription of gel
superstructures into inorganic silica ma-
terials.
acetic acid or propionic acid gels of 1
3
to characterize the aggregation mode in
the organogel system. In the CD spec-
trum of the acetic acid gel 1, the positive
sign for the first Cotton effect indicates
that the dipole moments of azobenzene
chromophores tend to orient into the
clockwise direction. On the other hand,
Keywords: crown compounds
¥
double-layered tubes ¥ gels ¥ helical
structures ¥ silicates ¥ sol-gel proc-
esses
correspond to these organic assemblies, one potential ap-
proach is to transcribe them to produce inorganic replicas,
thus mimicking biomineralization processes. Amphiphilic
molecules, for example, exhibit one of the richest polymor-
phism of structures and mesophases.[1] Among these, vesi-
cles,[2] ultra-thin membranes,[3] and others[4] have been utilized
as templates to create nano-sized inorganic materials.[5] In
order to ™design∫ the sizes and shapes of such materials (as
organic compounds and assemblies can be ™designed∫), it is
essential to explore and elucidate the transcription mecha-
nisms of various organic precursors.
Introduction
Both in natural and artificial systems, the self-assembly of
organic building blocks give rise to supramolecular structures
of various sizes, shapes, chemical compositions, and functions.
In order to develop novel inorganic materials that closely
[a] Dr. J. H. Jung, Dr. S.-H. Lee, Dr. J. S. Yoo
Nano Material Team, Korea Basic Science Institute (KBSI)
52 Yeoeun-dong, Yusung-gu, Daejeon, 305-333 (Korea)
Fax : (‡82)42-865-3419
E-mail: jonghwa@kbsi.re.kr
[b] Dr. J. H. Jung, Dr. K. Yoshida, Prof. Dr. T. Shimizu
Nanoarchitectonics Research Center (NARC)
National Institute of Advanced Industrial Science and
Technology (AIST)
Recently, numerous thermoreversible physical gels formed
with low-molecular-weight organic molecules have been
10]
reported.[6
The interest shown lies in the numerous
Tsukuba Central 5, 1-1-1 Higashi, Tsukuba
Ibaraki 305-8565 (Japan)
potential applications envisaged for these materials, such as
hardeners of solvents, drug delivery systems, membranes, and
sensors. Very recently, organogels were applied as novel
media to produce various structures of the silica such as
[c] Prof. Dr. S. Shinkai
Department of Chemistry and Biochemistry
Graduate School of Engineering, Kyushu University
Fukuoka 812-8581 (Japan)
e]
linear,[11a,b] lamellar,[11c and helical fibers,[11f] and spheri-
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DOI: 10.1002/chem.200305008
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J. H. Jung, S. Shinkai et al.
FULL PAPER
cal[11g] structures by sol-gel polycondensation. These results
indicate that the superstructures formed in organogels are
useful as templates to create various silica structures. One
particularly interesting class of gelators, crown-appended
cholesterol-based gelators, frequently resulted in various
novel structures such as the fibrous, lamellar,[11d] vesicular,[11g]
and multilayered tubular[11c] structures.
Results and Discussion
Characterization of organogel superstructures by circular
dichroism (CD), SEM, and TEM: Compounds 1 3 were
synthesized according to the method reported previously
(Scheme 1).[11c] The gelation ability of compounds 1 3 was
The groups of Kunitake and Schnur
found that certain amphiphiles can
form the tubular structure through the
helical ribbon structure in aqueous
solution.[1, 12] They possess a polar head
group and suitable chiral hydrophobic
groups to form stable aggregates. On
the other hand, certain gemini-type
gelators which consist of two compo-
nents, gave helical ribbon structures in
aqueous and organic solvents;[13] how-
ever, the formation mechanism of the
tubular structure was not confirmed in
these gel systems. It thus occurred to us
that judging from the versatility of
crown-appended cholesterol-based ge-
lators,[11d,e,g] one might be able to find
both structures, growing from the twist-
ed ribbon to the tubule (as suggested by
Kunitake et al.[12] for the aqueous sol-
ution system). In addition, superstruc-
tures created from these gelators might
be useful as templates for the tran-
scription into the silica structures.
Scheme 1. Reagents and conditions of crown-appended cholesterol gelators 1 3. a) Dibromobutane,
KOH, ethanol; b) cholesterol, DCC, DMAP, dichloromethane; c) PdC, H2, dimethylacetamide
anhyrate; d) Na2CO3, n-butyronitrile.
With these objects in mind, we have
designed compounds 1 3, which have
one or two cholesterol skeletons as a
chiral aggregate-forming site, two ami-
no groups as an acidic proton binding site, and one crown
moiety as a cationic binding site. We have studied the
influence of the crown size induced into the amphiphiles by
circular dichroism (CD), SEM, and TEM, and evaluated their
sol-gel transcription into the silica structures. We have found
that 1 3 not only gelate various organic solvents under 1.0
wt%, but enable us to observe both the helical ribbon and
tubule structures. In addition, 1 acts as a template for sol-gel
polycondensation of TEOS to produce the novel ™helical
ribbon∫ silica and the ™double-layered tubular∫ silica, where-
as 2 and 3 induce only the ™roll-paper-like multilayered
tubular∫ structure of silica. Also, we could synthesize various
morphologies of silica, such as double-layer, helical, and
vesicular structures, by changing the sol-gel reaction temper-
ature using the organogel 1. To the best of our knowledge the
influence of of changes in the sol gel reaction temperature
on the silica morphologies and the growth mechanism from
the helical ribbon of an organogel into the tube has not yet
been reported. To the best of our knowledge, these are the
first examples not only for the morphology control of the
silica in the self-assembled superstructure system, but also for
the growth mechanism from the helical ribbon of an organic
self-assembly into the tubular structure through sol-gel tran-
scription.
estimated in various organic solvents. As summarized in
Table 1, they can gelate acetic acid, propionic acid, acetoni-
trile, 1-hexanol, DMSO, and/or DMF under 1.0 wt%, indicat-
ing that they act as a versatile gelator of various organic
solvents.
To characterize the aggregation mode in the organogel
phase, we observed CD spectra of acetic acid and propionic
acid gels of 1 3. In the CD spectrum of acetic acid gel 1, the
Table 1. The gelation ability of 1 3 in organic solvents.[a]
1
2
3
methanol
ethanol
I
I
I
I
I
I
1-butanol
1-hexanol
DMSO
G
G
G
G
G
G
G
G
S
P
G
G
G
P
G
I
I
S
S
P
G
G
G
P
DMF
acetic acid
propionic acidG
acetone
acetonitrile
chloroform
tetrahydrofuran
I
I
S
S
S
[a] Gelatorˆ 1.0 wt%; G ˆ stable gel formed at room temperature; S ˆ
solution; I ˆ insoluble, P ˆ precipitation.
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Double Silica Nanotubes
5307 5313
lqˆ0 value appears at 353 nm, which is consistent with the
absorption maximum at lmax ˆ 353 nm. One can thus assign
the CD spectrum to the exciton coupling band, although it is
somewhat asymmetric (Figure 1). It is known that azoben-
zene-appended cholesterol gelators with natural (S)
Figure 2. SEM (a) and TEM (b) pictures of the xerogel 1 prepared from
acetic acid, and SEM pictures of the xerogels 2 (c) and 3 (d) prepared from
propionic acid.
structure into at tube is very difficult due to an extremely fast
growing rate.
Figure 1. CD spectra of the organogels a) 1, b) 2, and c) 3.
To the best of our knowledge, it is very a rare example for
the direct observation of the growing process of these
superstructures by self-assembly. Most of organic tubes
reported so far are produced in aqueous solution, and not in
gel systems. In particular, the structure of 1 is quite different
from those of sugar amphiphiles, previously reported by our
group, which have long aliphatic groups.[14] These amphiphiles
were transformed from the helical ribbon structure (its
presence is assumed) into the tubular structure with 10
100 nm of diameters in aqueous solution by heating, whereas
1 can form both the helical ribbon structure and the tubular
structure with approximately 520 nm out diameter.
The organogels 2 and 3 featured the tubular-like structures
with 45 75 nm wall thickness and 170 390 nm inside tube
diameter as shown in Figure 2c and d. Very careful examina-
tion of these pictures reveals that the wall consists of a
multilayer-like structure. These results indicate that the
balance between the hydrophilicity and the hydrophobicity
in amphiphiles is of importance to develop the tubular
structure through the helical ribbon structure.
C-3 configuration tend to give a positive sign for the first
Cotton effect (Figure 1a), indicating that the dipole moments
of azobenzene chromophores tend to orient into the clockwise
direction.[11e,f] In contrast, gels 2 and 3 bearing only one or two
cholesterol moiety exhibit a negative sign for the first Cotton
effect (Figure 1b and c), indicating that the dipole moments of
the azobenzene chromophores orient into the anticlockwise
direction. In all cases, it was confirmed that the contribution
of linear dichroism (LD) to the true CD spectra is negligible.
These CD data support the view that the aggregation mode of
1 is somewhat different from those of 2 and 3. It is undoubted
that the organogels of 2 and 3 are formed by both intermo-
lecular cholesterol cholesterol and azobenzene azoben-
zene interactions; the former interaction in the central
columnar aggregate and the latter in the side chain aggregate
around the central column. On the other hand, in the
organogel compound 1 may adopt a folded conformation to
enjoy efficient intramolecular cholesterol cholesterol and
azobenzene azobenzene interactions; this may be the origin
of the positive sign for the first Cotton effect.
To obtain visual insights into the aggregation mode, we
observed the xerogel structures of organogels 1 3 by TEM
and SEM. Figure 2 shows a TEM and SEM pictures of the
xerogels 1 3 obtained from acetic acid or propionic acid.
Very interestingly, the xerogel 1 mainly consists of the tubular
structures with about 520 nm outer diameter, but also
contains the helical ribbon with 1700 nm pitch (Figure 2a
and b). In addition, the SEM picture of the xerogel 1 also
reveals the characteristic right-handed helical ribbon struc-
ture. These results indicate that the structure of the organogel
process involves several metastable intermediate structures,
namely, the linear ribbon, the helical ribbon, and the tubule.
However, observation of the growing step for helical ribbon
Influences on sol gel transcription temperature: To tran-
scribe the superstructure formed in the organogel into the
silica structure, we carried out sol gel polycondensation of
TEOS using 1 3 in the acetic acid or propionic acid gel phase
according to the method described previously.[11] We observed
SEM and TEM pictures of the silica obtained from 1 3 after
calcination. Figure 3 shows the TEM pictures: the silica
obtained from acetic acid gel 1 possesses the helical ribbon
structure with various width (450 1500 nm) of ribbon and the
tubular structure of the silica with a constant outer diameter
of about 560 nm. As far as can be recognized, all the helicity
possesses a right-handed (P) helical motif. Since the exciton-
coupling band of the organogel also shows P helicity, we
consider that a microscopic helicity is reflected by a macro-
scopic helicity. These results indicate that the novel helical
Chem. Eur. J. 2003, 9, 5307 5313
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J. H. Jung, S. Shinkai et al.
FULL PAPER
Figure 3. TEM pictures (a, b, c, and d) of the silica obtained from the
1‡acetic acid gel after calcinations.
ribbon structure and the tubular structure of the organogel 1
have successfully been transcribed into the silica structures.
Also, these findings strongly suggest that the organic tube
formed by self-assembly was produced with the growth of
width of the helical ribbon and constant pitch angle as shown
in Figure 4b, rather than by the mechanism in Figure 4a; also
Figure 5. SEM or TEM pictures a) of the silica obtained from the 1‡acetic
acid gel by method A, b) and c) by method B, and d) by method C after
calcination.
In the absence of heating after TEOS and water addition
(Method B), the silica resulted in the tubular structure with
600 nm outer diameter, 340 nm inner diameter, and 90
100 nm spaces (Figure 5b and c); however, no helical ribbon
structure was observed. This result consistently supports the
view that the organic tube is made up of the multi-layered
packing structure. Also, this strongly confirms the aforemen-
tioned assumption that the silica particles are adsorbed onto
both the surface and the inner of tubular structure of the
organogel 1 obtained through several metastable intermedi-
ate structures.
In method C, the silica gave the vesicular structure with
30 50 nm diameters by sol gel polycondensation at a
temperature above the sol gel phase-transition temperature
of organogel 1 (Figure 5d). This result suggests that the self-
assembled superstructure of organogel 1 exists as the vesicle
at temperatures above the sol gel phase-transition temper-
ature. In addition, these findings indicate that a variety of
superstructural silica materials, such as vesicular and tubular
structures, can be created at different temperatures of sol gel
polycondensation by using the organic tube as a template.
Figure 6 displays SEM pictures of the silica obtained from
propionic acid gels 2 and 3 after calcination. The tubular
structure of the silica obtained from the organogels 2 and 3 is
somewhat different from that prepared from the organogel 1.
Very interestingly, the tube wall of the silica features a roll-
paper-like multilayer structure, as shown by careful examina-
tion of SEM and TEM measurements. Also, the helical ribbon
structure of the silica was not obtained by this method.
We now propose the mechanism for the formation of both
spherical structures and the co-existence of helical ribbons
and double tubes with 8 9 nm and 90 100 nm spaces as
shown in Figure 7. In case of Method A, oligomeric silica
particles are adsorbed onto the surface of the helical ribbon,
to give a tubular structure with 8 9 nm thickness, before
complete growth into the tube (Figure 7a); this leads to a
mixture of the helical ribbon and double layered tubes with
Figure 4. Representation for tubular formation mechanisms of the 1 ‡
acetic acid gel; a) tube formed by changing of pitch angle, b) tube formed
with the growth in width of the helical ribbon.
the growth of organic tube was fixed by absorption of rigid
silica particles (Figure 4b). This mechanism is quite different
from observed for natural cholesterol tube by Chung et al.,[16]
which had two different pitch angles. In addition, it was
confirmed by high-magnification TEM that the silica consists
of double layers with an interlayer distance of 8 9 nm
(Figure 5a). The size of the space between layers of the silica
obtained by Method A (see Experimental Section) suggests
that helical ribbon and tubular structures of the incipient
organogel 1 are encapsulated in the silica particles. In
addition, these results indicate that TEOS (or oligomeric
silica particles) was adsorbed onto both surfaces of the tubules
with 8 9 nm thickness. Therefore, the tubular silica possesses
two hollow cavities. The smaller hollow with 8 9 nm layers
was created by organogel template, whereas the larger hollow,
with inner diameters of approximately 480 nm, was created by
the growth of the helical ribbon.
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Double Silica Nanotubes
5307 5313
tube. Also, this silica morphology is clearly different between
1 and 3: compound 1 gave the tubular and the helical ribbon
structures, whereas 3 gave the roll-paper-like structure.[11c]
This implies that growth mechanism for tubular structure of
the self-assembled 1 is quite different from that of 3. The self-
assembled 1 spontaneously grows up from vesicle to the
helical ribbon to the tubular structure, whereas the compound
3 self-assembles into the roll-paper-like structure. In addition,
these two different morphologies of the self-assembly are
accurately reflected into the silica structures by the sol gel
method.
Conclusion
The present paper has demonstrated that the organogelators
1
3, bearing different crown-ring size, such as dibenzo[30]-
crown-10 and dibenzo[24]crown-8, create the novel helical
and/or tubular structures in organic solvents. The organogel
morphology is clearly different between 1, and 2 and 3;
compound 1 gave the tubular structure from the helical
ribbon, whereas organogelators 2 and 3 formed the paper-like
tubular structures. Also, the tubular structure of organogel 1 is
formed from the growth in the ribbon width and with constant
diameter. Sol gel polycondensation of TEOS in the presence
of the helical structure of 1 leads to the formation of the
helical ribbon and double-layered tubular structures of silica
in the gel phase. This is a very rare example of chiral inorganic
materials. The helical ribbon structures of silica are created
with aid of hydrogen-bonding as well as electrostatic inter-
actions. On the other hand, the organogel 1 also produced the
vesicular structure of the silica at temperatures above the
sol gel phase-transition temperature. The organogels 2 and 3
induced the tubular structures of silica. The results clearly
indicate the versatility of the template method by using
organogels for the creation of various silica structures.
Figure 6. SEM pictures of the silica obtained from the 2‡propionic acid
gel (a and b) and the 3‡propionic acid gel (c).
In general, organic materials are capable of constructing a
variety of supramolecular structures that reflect their own
molecular shape, whereas ™shape design∫ is very difficult from
inorganic materials. The present findings suggest, as also
suggested by a few other research groups, that various novel
assembly structures created by weak intermolecular forces
can be imprinted as permanent structures in inorganic
materials. The present study clearly demonstrates that the
organogel system is one of the most suitable molecular
assemblies for this transcription. We believe that the silica
structures presented here, with the unique higher-order
morphology, are still very useful as unique catalysts for
asymmetric syntheses without chiral organic ligands.[17]
Figure 7. Schematic representation of sol gel transcription of the organo-
gel 1: i) template, ii) sol gel polycondensation, iii) before calcination, and
iv) after calcination (SEM and TEM images in Figures 2, 3, and 5).
Experimental Section
Apparatus for spectroscopy measurements: 1H and 13C NMR spectra were
measured on a Bruker ARX 300 apparatus. IR spectra were obtained in
KBr pellets using a Shimadzu FT-IR 8100 spectrometer, and MS spectra
were obtained by a Hitachi M-250 mass spectrometer.
8
9 nm spaces between layers. In contrast, in case of
Method B, silica particles are adsorbed onto the surface of
the tubular structure with 90 100 nm wall thickness of acetic
acid gel 1 (Figure 7b); this gave only the double-layered silica
TEM and SEM observations: For transmission electron microscopy
(TEM), a piece of the gel was placed on a carbon-coated copper grid
(400 mesh) and removed after 1 min, leaving some small patches of the gel
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J. H. Jung, S. Shinkai et al.
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on the grid. After specimens had been dried at low pressure, its was stained
with 10 ꢀ 15 mL drops of uranyl acetate (2.0 wt%aqueous solution). Then,
this was dried for 1 h at low pressure. The specimen was examined with an
Hitachi H-7100 microscope, with an accelerating voltage of 75 100 kVand
a 16 nm working distance. Scanning electron microscopy (SEM) was
performed on a Hitachi S-4500 microscope. The silica was coated with
palladium platinum and observed by 5- 15 kV of the accelerating voltage
and the emission current of 10mA.
temperature. The reaction mixture was filtered to remove PdC, and the
filtrate was evaporated in vacuo to dryness. The residue was purified by a
silica gel column chromatography eluting with methanol/chloroform (1:9 v/
v) to give 7 as brown solid (0.10 g, 84%yield). M.p. 68 71 8C; 1H NMR
(300 MHz, CDCl3): d ˆ 3.48 (brs, 4H), 3.68 (brs, 8H), 3.74 (brs, 8H), 3.84
(brd, J ˆ 12.4 Hz, 8H), 4.08 (brs, 8H), 6.21 (dd, J ˆ 8.4, 2.5 Hz, 2H), 6.29
(brs, 2H), 6.88 ppm (d, J ˆ 8.4 Hz, 2H); IR (KBr): nÄ3350, 3007, 2985, 1521,
‡
1504, 1340, 1205 cmÀ1; MS(SIMS): m/z: 557.2 [M‡2 H] ; elemental analysis
calcd (%) for C29H42N2O10: C 59.78, H 7.96, N 4.81; found: C 60.02, H 7.90,
N 4.53.
Gelation test of organic fluids: The gelator and the solvent were put in a
septum-capped test tube and heated in an oil bath until the solid was
dissolved. The solution was cooled to room temperature. If the stable gel
was observed at this stage, it was classified as G in Table 1.
Dinitrodibenzo[24]crown-8 (9): This compound was prepared as described
above for 8. 1H NMR (300 MHz, CDCl3): d ˆ 3.60 (brs, 8H), 3.73 (brs,
8H), 4.15 (brs, 8H), 6.80 (d, J ˆ 8.2 Hz, 2H), 7.73 (s, 2H), 7.79 ppm (d, J ˆ
8.2 Hz, 2H); IR (KBr): nÄ ˆ 3005, 2987, 1508, 1210 cmÀ1; MS(SIMS): m/z:
Sol-gel polycondensation of TEOS
Method A: Compounds 1 3 (6.63 Â 10À3 mol) were dissolved in acetic acid
or propionic acid (200 mg) by heating. The gel sample was cooled to room
temperature. TEOS (20 mg) and water (6.0 mg) were then added to gel
sample. The reaction mixture was then reheated until it became homoge-
neous, and then it was placed at room temperature for 2 14 days.
Method B: Compound 1 (6.63 Â 10À3 mol) was dissolved in acetic acid
(200 mg) by heating. The gel sample was cooled to room temperature.
TEOS (20 mg) and water (6.0 mg) were the added to gel sample. Without
the heating process, this reaction mixture was placed at room temperature
for 2 14 days.
‡
538.5 [M‡2H] ; elemental analysis calcd (%) for C24H30N2O12: C 53.53, H
5.62, N 5.20; found: C 54.02, H 5.65, N 5.25.
Diaminodibenzo[24]crown-8 (10): This compound was prepared as descri-
bed above for 7. 1H NMR (300 MHz, CDCl3): d ˆ 3.53 (brs, 8H), 3.63 (brs,
8H), 4.15 (brs, 8H), 6.21 (dd, J ˆ 8.4, 2.5 Hz, 2H), 6.29 (brs, 2H), 6.88 ppm
(d, J ˆ 8.4 Hz, 2H); IR (KBr): nÄ ˆ 3350, 3007, 2985, 1521, 1504, 1340,
‡
1205 cmÀ1; MS(SIMS): m/z: 478.5 [M‡2H] ; elemental analysis calcd (%)
for C24H34N2O8: C 60.24, H 7.16, N 5.85; found: C 60.05, H 7.15, N 5.80.
4-[Bis(diaminodibenzo[30]crown-10-butoxy]-4'-[(cholesteyloxy)carbony-
Method C: Compound 1 (6.63 Â 10À3 mol) was dissolved in acetic acid
(200 mg) by heating. The gel sample was cooled to room temperature.
TEOS (20 mg) and water (6.0 mg) were then added to gel sample. The
reaction mixture was then reheated until it became homogeneous, and then
it was maintained at 808C for 2 days. The products obtained by three
methods were calcinated at 2008C for 2 h, 5008C for 2 h under a nitrogen
atmosphere, and then kept at 5008C under aerobic conditions for 4 h to
remove the gelators. The silica thus obtained was colorless.
l]azobenzene) (1):
A mixture of compound 4 (0.24 g, 0.32 mmol),
compound (0.085 g, 0.15 mmol), and sodium carbonate (0.317 g,
7
3.00 mmol) in dry n-butyronitrile (30 mL) was refluxed for 72 h. The
solution was filtered after cooling and the filtrate was evaporated in vacuo
to dryness. The residue was purified by aluminum oxide column chroma-
tography eluting with ethanol/chloroform (1:30 v/v) to give the desired
product as yellow solid (20%yield). M.p. 168.2 168.7 8C; 1H NMR
(300 MHz, CDCl3): d ˆ 0.70 (s, 6H), 0.87 (d, J ˆ 6.6 Hz, 12H), 0.92 2.06
(m, 70H), 2.48 (d, J ˆ 6.4 Hz, 4H), 3.16 (t, J ˆ 6.4 Hz, 4H), 3.43 (brs, 2H),
3.51 3.79 (m, 16H), 3.83 3.92 (m, 8H), 4.08 (brs, 8H), 4.78 4.93 (m,
2H), 5.44 (d, J ˆ 3.9 Hz, 2H), 6.17 (dd, J ˆ 2.4 Hz, 4H), 6.22 (brs, 2H), 6.27
(d, J ˆ 2.4 Hz, 2H), 6.75 (dd, J ˆ 9.1 Hz, 4H), 7.01 (d, J ˆ 8.4 Hz, 4H), 7.90
(d, J ˆ 8.4 Hz, 4H), 7.94 (d, J ˆ 8.7 Hz, 4H), 8.17 ppm (d, J ˆ 8.4 Hz, 4H);
IR (KBr): nÄ ˆ 3350, 3007, 2987, 1600, 1585, 1500, 1220 cmÀ1; MS(SIMS):
4-(Hydroxyphenyl)azobenzoic acid (4) and 4-(n-bromobutoxylphenyl)-
azobenzoic acid (5): These compounds were prepared as described
[11g]
previously.[11c]
,
4-n-bromobutoxyl-4'-[(cholesteryloxy)carbonyl]azobenzene (6): Com-
pound 5 (0.7 g, 1.86 mmol) and cholesterol (0.718 g, 2.23 mmol) were
dissolved in dichloromethane (20 mL) under a nitrogen atmosphere. The
solution was maintained at 08C by an ice bath. Dicyclohexylcarbodiimide
(DCC, 0.383 g, 1.86 mmol) and dimethylaminopyridine (DMAP) (0.022 g,
0.186 mmol) were then added, and the reaction mixture was stirred for 4 h
at 08C. The reaction mixture was filtered, and the filtrate was washed with
acidic and basic aqueous solutions (50 mL each). The organic layer was
evaporated to dryness. The residue was purified by a silica-gel column
chromatography eluting with THF/n-hexane (1:6 v/v) to give compound 6
‡
m/z: 1898.6 [M‡2H] ; elemental analysis calcd (%) for C116H162N6O16: C
73.46, H 8.61, N 4.43; found: C 72.71, H 8.73, N 4.45.
4-(Diaminodibenzo[30]crown-10-butoxy)-4'-[(cholesteyloxy)carbonyl]-
azobenzene (2): This compound was prepared as described above for 1.
Yellow solid (25%yield; M.p. 159.5 160.2 8C; 1H NMR (300 MHz,
CDCl3): d ˆ 0.70 (s, 6H), 0.87 (d, J ˆ 6.6 Hz, 12H), 0.92 2.06 (m, 70H),
2.48 (d, J ˆ 6.4 Hz, 4H), 3.16 (t, J ˆ 6.4 Hz, 4H), 3.43 (brs, 2H), 3.51 3.79
(m, 16H), 3.83 3.92 (m, 8H), 4.08 (brs, 8H), 4.78 4.93 (m, 2H), 5.44 (d,
J ˆ 4.0 Hz, 2H), 6.17 (dd, J ˆ 2.6 Hz, 4H), 6.22 (brs, 2H), 6.27 (d, J ˆ
2.6 Hz, 2H), 6.75 (dd, J ˆ 9.1 Hz, 4H), 7.01 (d, J ˆ 8.4 Hz, 4H), 7.90 (d,
J ˆ 8.4 Hz, 4H), 7.94 (d, J ˆ 8.7 Hz, 4H), 8.17 ppm (d, J ˆ 8.4 Hz, 4H); IR
(KBr): nÄ ˆ 3355, 3007, 2983, 1600, 1585, 1500, 1220 cmÀ1; MS(SIMS): m/z:
1
in 26%yield as yellow solid. M.p. 141.5 8C; H NMR (300 MHz, CDCl3):
d ˆ 8.17 (d, J ˆ 9.0 Hz, 2H), 7.72 (d, J ˆ 9.0 Hz, 2H), 7.90 (d, J ˆ 9.0 Hz,
2H), 7.10 (d, J ˆ 9.0 Hz, 2H), 5.45 (d, J ˆ 6.3 Hz, 1H), 5.02 4.88 (m, 1H),
41 (t, J ˆ 6.3 Hz, 2H), 3.52 (t, J ˆ 6.2 Hz, 2H), 2.49 (d, J ˆ 6.2 Hz, 2H),
2.28 0.94 (m, 35H), 0.88 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d ˆ
165.1, 161.88, 155.20, 146.98, 139.9, 130.2, 125.18, 122.84, 122.28, 114.72,
67.22, 66.67, 56.67, 56.11, 50.01, 42.30, 39.71, 39.50, 38.20, 37.01, 36.64, 36.17,
35.79, 33.32, 31.92, 31.86, 29.3, 28.32, 28.01, 27.88, 27.78, 24.28, 23.82, 22.83,
22.56, 21.04, 19.38, 19.38, 18.71, 11.86 ppm; IR (KBr): nÄ ˆ 3005, 1722, 1603,
‡
1231.78 [M‡2H] ; elemental analysis calcd (%) for C72H102N4O13: C 70.22,
H 8.35, N 4.55; found: C 70.52, H 8.21, N 4.50.
4-[Bis(diaminodibenzo[24]crown-8-butoxy)-4'-[(cholesteyloxy)carbonyl]-
azobenzene) (3): This compound was prepared as described above for 1.
Yellow solid (32%yield); m.p. 153.2 155.1 8C; 1H NMR (300 MHz,
CDCl3): d ˆ 0.70 (s, 6H), 0.87 (d, J ˆ 6.6 Hz, 12H), 0.92 2.06 (m, 70H),
2.48 (d, J ˆ 6.4 Hz, 4H), 3.16 (t, J ˆ 6.4 Hz, 4H), 3.43 (brs, 2H), 3.51 3.79
(m, 16H), 3.83 3.92 (m, 8H), 4.08 (brs, 8H), 4.78 4.93 (m, 2H), 5.44 (d,
J ˆ 4.0 Hz, 2H), 6.17 (dd, J ˆ 2.5 Hz, 4H), 6.22 (brs, 2H), 6.27 (d, J ˆ
2.5 Hz, 2H), 6.75 (dd, J ˆ 9.2 Hz, 4H), 7.01 (d, J ˆ 8.4 Hz, 4H), 7.90 (d,
J ˆ 8.4 Hz, 4H), 7.94 (d, J ˆ 8.7 Hz, 4H), 8.17 (d, J ˆ 8.4 Hz, 4H); IR (KBr):
nÄ ˆ 3352, 3005, 2982, 1600, 1585, 1500, 1220 cmÀ1; MS(SIMS): m/z: 1820.31
‡
1579, 1500, 1468, 1284, 1116, 1047 cmÀ1; MS(SIMS): m/z: 745 [M‡H] .
Dinitrodibenzo[30]crown-10 (8): HNO3 (60%, 1 mL) was added dropwise
to a stirred solution of dibenzo[30]crown-10 (0.15 g, 0.28 mmol) in acetic
acid (5 mL) and water (1 mL) at 5.08C. The reaction mixture was warmed
to room temperature over a period of 30 min and stirred for an additional
2 h at room temperature. Then, NaOHaq (1.0m) was added to the reaction
mixture until the solution became neutral. The precipitate was filtered off,
to give compound 8 in yield 85.0%as yellow powder. M.p. 133 135 8C;
1H NMR (300 MHz, CDCl3): d ˆ 3.69 (brs, 8H), 3.77 (brs, 8H), 3.93 (brs,
8H), 4.22 (brs, 8H), 6.87 (d, J ˆ 8.4 Hz, 2H), 7.73 (s, 2H), 7.84 ppm (d, J ˆ
8.4 Hz, 2H); IR (KBr): nÄ ˆ 3005, 2987, 1508, 1210 cmÀ1; MS(SIMS): m/z:
‡
[M‡2H] ; elemental analysis calcd (%) for C112H154N6O14: C 74.38, H 8.58,
N 4.65; found: C 73.81, H 8.73, N 4.70.
‡
644.5 [M‡2H] ; elemental analysis calcd (%) for C29H42N2O14: C 54.20, H
6.59, N 4.36; found: C 54.50, H 6.55, N 4.30.
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www.chemeurj.org
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Received: March 31, 2003 [F5008]
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¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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