Direct sol-gel replication of the self-assembled nanostructure modified with H-bond functionalities

Article abstract of DOI:10.1246/cl.2002.1246

The glucopyranoside-based amphiphile 1 formed nanofiber structures with 25-100 nm of diameters and several micrometer lengths in the presence of aminophenyl glucopyranoside 2, and their self-assembled nanostructures were successfully replicated into the s

Full text of DOI:10.1246/cl.2002.1246

1246
Chemistry Letters 2002
Direct Sol-Gel Replication of the Self-assembled Nanostructure Modified with H-bond
Functionalities
Jong Hwa Jungy and Toshimi Shimizuꢀy;yy
yCREST, Japan Science and Technology Corporation (JST), Nanoarchitectonics Research Center, National Institute of Advanced
Industrial Science and Technology (AIST), Tsukuba Central 4, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562
yyNanoarchitectonics Research Center, National Institute of Advanced Industrial Science and Technology (AIST),
Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565
(Received September 3, 2002; CL-020751)
The glucopyranoside-based amphiphile 1 formed nanofiber
structures with 25–100 nm of diameters and several micrometer
lengths in the presence of aminophenyl glucopyranoside 2, and
their self-assembled nanostructures were successfully replicated
into the silica tube by sol-gel polymerization of TEOS.
In the present paper, we report new approach to preparation
of well-defined silica nanotube through direct sol-gel polymer-
ization of tetraethoxysilane (TEOS) in the self-assembly of
compounds 1 + 2.
The aminophenyl glucopyranoside 2 was synthesized from
nitrophenyl glucopyranoside by the reaction with Pd-C and H2
gas in THF. The obtained aminophenyl glucopyranoside was then
treated with olelic acid chloride and triethylamine in THF.
Compound 1 was identified by IR, NMR, Mass spectral evidence
and elemental analysis.
The self-assembly of the matrix amphiphiles 1 and 2 (1 : 1
mol%) occurred rapidly under mild conditions. For example,
compounds 1 and 2 were dissolved in boiling water to give a clear
solution and gradually cooled to room temperature. Fine fiber
structure was obtained within 5 h under ambient conditions.
Figure 1a displays TEM image of the self-assembled 1 in the
presence of 2in aqueous solutions. 1shows typical fiber structures
of 25–100 nm in widths and several micrometers in lengths.
To confirm whether 2 was incorporated into the self-
assembled fiber of 1, we measured 1H NMR spectrum of the
dried solid sample prepared from 1 + 2 in aqueous solution. The
small amount of aminophenyl glucopyranoside 2 (ca. 10 mol%)
was actually incorporated into the self-assembled fiber of 1
(Figure 1b). Therefore, we expect that the amino group of 2
should act as efficient driving force in order to adsorb ‘‘anionic
silica’’ precursor by intermolecular hydrogen-bonding interac-
tion in sol-gel reaction.
Recently, the self-assembled nanostructures of amphiphiles
have been extensively studied and exploited in various fields to
advance potential application.1{4 Despite much effort in the
fields, there are only a few examples for application due to the
unstability of the self-assembled superstructure at certain
temperature.5;6 How can we apply and stabilize the self-
assembled nanostructure of amphilies in water? Probably they
will directly be used as templates for synthesis of various
inorganic materials by sol-gel reaction. Also, they can be
stabilized by sol-gel reaction. The obtained nanostructures
keeping intrinsic superstructure can easily be applicable in
various fields.
On the other hand, a variety of inorganic nanotubes have been
synthesized by only mixing self-assembling molecules with
inorganic precursor, such as organogelators,7;8 surfactants,9
organic crystals,10 and have been actively progressed in
application fields such as catalysis, chromatography, adsorbent,
etc.9d,11
We carried out sol-gel polymerization of TEOS in order to
replicate the self-assembled nanofibers from 1 + 2 into the silica
structure. The experimental procedure is as follows: first, the self-
assembled samples 1 + 2 mixture or 1 (ca. 2–10 mg) was prepared
in water. Second, the self-assembled nanofibers were collected by
centrifuge. Then, TEOS (20.0 mg), water (100 mg) and benzyl-
amine (5.0 mg) were added to self-assembled fiber. The reaction
mixture was stirred for 30 min, and left without stirring at 30 ꢁC
for 10 days. Subsequently, the sample was heated at 200 ꢁC for 2 h
followed by 2 h at 500 ꢁC, both under a nitrogen atmosphere and
then kept at 500 ꢁC under aerobic conditions for 4 h. The
formation process of the silica fiber was observed by scanning
electron microscopy (SEM) and transmission electron micro-
scopy (TEM).
After calcination, the silica obtained from the self-assembly
of glucopyranoside-based amphiphile 1 in the presence of 2
shows the well-defined silica nanotube with outer diameters of
70–150 nm and several micrometers of length (Figure 2a). On the
other hand, the silica obtained from the self-assembly of
amphiphile 1 in the absence of 2 only gave granular structure.
In order to fabricate the inorganic tubular nano-material, we
thus have synthesized compound 1, which, together with
aminophenyl glucopyranoside 2, forms self-assembled fibers
that can be replicated into the silica tube. Generally, the
crystalline self-assembled nanostructures of amphiphiles are
quite different from those of organogels which trap the solvent
within the voids of the network. First, we prepared the self-
assembled nanofiber of amphiphile 1 in the presence of 2 in water.
Second, the obtained nanofiber was used in direct sol-gel reaction
without any structural change. This procedure highly contrasts to
the cases of organogels. For example, the gelator was mixed in
advance together with inorganic precursor, water, and catalyst.
The reaction mixture was heated until clear solution. Therefore,
sol-gel replication was progressed by competitive reaction
between self-assembling formation of gelator and polymerization
of inorganic precursor.
Copyright Ó 2002 The Chemical Society of Japan

Chemistry Letters 2002
1247
Figure 2. (a) SEM and (b) TEM images of the silica tube (after calcination)
obtained through replication of the self-assembly of glucopyranoside-based
amphiphile 1 and its derivative 2.
nanofibers from glucopyranoside-based amphiphile and its
homologue as a template, by direct sol-gel reaction. This silica
tube is created by the intermolecular hydrogen-bonding interac-
tion with the fine fiber structure characterization of the self-
assembly. We believe that this concept will be more generally
applicable to further new silica preparation using various self-
assembled superstructures of amphiphiles as templates.
Figure 1. (a) TEM image of the self-assembled fiber in water prepared
from 1 + 2, and (b) schematic representation of the self-assembled structure
of glucopyranoside-based amphiphile 1 and its derivative 2.
References
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amine moiety of 2 and negatively charged silica precursors.
TEM analysis after removal of 1 + 2 by calcinations enabled
us to further confirm that the self-assembled structure really acted
a template for the formation of the silica structure, showing that
no morphological change took place. TEM image also clearly
shows that the center part of the tubes is light whereas both edges
dark (Figure 2b), confirming the well-defined tubular structure
and the previous existence of the self-assembled fiber inside the
silica fibers. Average inner and outer diameters are 20–100 nm
and 60–150 nm, respectively, making the thickness of the silica
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for the silica tubes is in good agreement with the thickness of the
self-assembled fibers observed independently (Figure 1a). These
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fibers indeed act as a template. We believe that this method is
usable not only to stabilize a variety of the self-assembled
superstructure of amphiphile into permanent structure as
inorganic oxide, but also to preparation of various shapes of
inorganic materials.
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In conclusion, this present paper has demonstrated a new
approach to prepare the silica tube, using self-assembled