Schizophyllan can act as a one-dimensional host to construct poly(diacetylene) nanofibers

Article abstract of DOI:10.1246/cl.2005.40

Schizophyllan binds 1,4-bis(p-amidophenyl)butadiyne and acts as a one-dimensional host to produce fibrous polydiacetylene assemblies through UV-irradiation. Copyright

Full text of DOI:10.1246/cl.2005.40

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Chemistry Letters Vol.34, No.1 (2005)
Schizophyllan Can Act as a One-dimensional Host to Construct Poly(diacetylene) Nanofibers
Teruaki Hasegawa, Shuichi Haraguchi, Munenori Numata, Tomohisa Fujisawa, Chun Li,
Kenji Kaneko, Kazuo Sakurai,y and Seiji Shinkai
Graduate School of Engineering, Kyushu University, Hakozaki, 6-10-1, Fukuoka 812-8581
yDepartment of Chemical Processes and Environments, Faculty of Environmental Engineering,
The University of Kitakyushu, Hibikino, 1-1, Wakamatsu-ku, Kitakyushu, Fukuoka 808-0135
(Received October 4, 2004; CL-041172)
Schizophyllan binds 1,4-bis(p-amidophenyl)butadiyne and
acts as a one-dimensional host to produce fibrous polydiacety-
lene assemblies through UV-irradiation.
ꢀ-Conjugated polymers (poly(acetylene)s, poly(diacety-
lene)s, poly(phenylenethynylene)s, etc.) have received increas-
ing interests because of their potential utility as conductive wires
in nanoscale electric circuits of comming age.1 Especially, pol-
y(diacetylene)s are of quite interest, since it is readily produced
through UV-irradiations without any additives such as catalysts.
However, simple polymerization of the corresponding mono-
mers usually results in amorphous, morphologically uninterest-
ing polymer aggregates. It is therefore strongly desired to estab-
lish easy and general strategies to construct their morphological-
ly controlled assemblies, e.g., fibrous ones, in which individual
polymers are aligned in a parallel fasion. Such fibers are expect-
ed to have an excellent conductivity through the long axis and
should be therefore useful as molecular wires. Many reseach
groups have placed their intense researh efforts on producing
such fibrous assemblies of poly(diacetylene)s, mainly utilizing
rod-like self-assemblies of the amphiphilic monomers.2
Figure 1. Schematic illustration of our concept to use SPG as a
1-D host to construct poly(diacetylene) nanofibers.
ꢀ-conjugated polymers through UV-irradiation (Figure 1).
A DMSO solution containing s-SPG (Mw ¼ 150 kDa) and 1
was diluted with water to regenerate a t-SPG helical structure
([H2O] ¼ 70 v/v %). Although 1 was hardly soluble by itself
in this solution system, the resultant slightly-turbid solution
showed a clear circular dichroism (CD) spectrum, in which a
negative CD exciton-coupling (260–600 nm) assignable to an
absorption band of 1 was observed (Figure 2a). Together with
the fact that SPG or 1 themselves gave no CD signal at this
wavelength region, this negative CD exciton coupling is indica-
tive of twisted conformations or packings of 1 arising from the
strong interaction with SPG.
Schizophyllan (SPG, Chart 1a) is a ꢁ-1,3-glucan having a ꢁ-
1,6-glucoside-appendage at every three repeating units. The
most interesting features of SPG include a reversible transition
between a triple-straded helix (t-SPG) in water and a single-
stranded random coil (s-SPG) in dimethylsulfoxide (DMSO).3
Recently, we found that SPG interacts with various hydrophobic
polymers (single-walled carbon nanotube,4 polyaniline,5 etc.) by
mixing s-SPG (in DMSO) with these polymers (in water) to form
unique macromolecular complexes, in which the hydrophobic
polymers are encapsulated within a tubular hollow constructed
by the helical superstructure of SPG. We expected, therefore,
that SPG would accommodate not only aforementioned poly-
mers but also small hydrophobic monomers and would act as a
‘‘one-dimensional (1-D) host’’ to produce fibrous polymer as-
semblies. Herein, we report one of such examples that SPG ac-
commodates amido-functionalized 1,4-diphenylbutadiyne (1,6
Chart 1b) to produce nanofibers composed of the corresponding
To clarify the detailed mechanism of the interaction, we car-
ried out some referential experiments as follows. 1) DMSO con-
tents of the resultant solution have a critical impact on the CD
spectrum (Figure 2b). The CD signal was observed only under
water-rich conditions ([H2O] ¼ 60{99 v/v %), suggesting that
not hydrogen-bonding but hydrophobic interactions play major
roles for the complexation. 2) Furthermore, no or negligibly
weak CD signal is observed in our referential experiments using
other polysaccharides (amylose, pullulan, and dextran), also sup-
porting our assumption that hydrogen bondings are not main
driving force for the interaction (Figure 2a). 3) Finally, when
we mixed t-SPG (in water) with 1 (in DMSO), the resultant solu-
tion gave no CD signal, indicating that the structural transition
from s-SPG to t-SPG is essential for the interaction. This last
finding is of quite interest since it implies that 1 locates inside
the helical structure of renascent t-SPG (if 1 interacts with the
outer surface, the structural transition is unnecessary for the
interaction), although we can not exclude a possibility that 1
locates at grooves of the helical structure of SPG.
UV-irradiation using a high pressure Hg lamp induced a
gradual color change of the solution containing SPG/1 complex
from colorless to pale blue (It is visibly detectable as shown in
our graphical abstract).9 The UV–vis spectrum of the resultant
solution shows an absorption band at around 720 nm which is
characteristic of poly(diacetylene)s with extremely long ꢀ-con-
jugated length and/or tight interstranded packings.8,9 UV-medi-
ated polymerization of 1 was also confirmed by Raman spectra
Chart 1. Chemical structures of (a) SPG and (b) 1.
Copyright ꢀ 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.1 (2005)
41
Figure 2. (a) CD spectra of 1 in the presence of SPG, amylose,
dextran, or pullulan, and (b) CD spectra of 1 in the presence of
SPG under various aqueous DMSO solutions with different wa-
ter contents: d ¼ 1:0 cm, 20 ꢁC, [H2O] ¼ 70 v/v %, [1] ¼ 25
mg mLꢀ1, [SPG] ¼ 25 mg mLꢀ1, 24 h after sample preparation.
(Figure 3b), in which SPG/1 complex shows a clear peak at
2000 cmꢀ1 assignable to poly(diacetylene)s (–CH=CH– strech-
ing vibration) after 16-h UV irradiation.9 On the contrary, no
such Raman peak appeared without SPG. Together with the fact
that UV-mediated polymerization of diacetylenes proceeds in a
topochemical manner, these data suggest that SPG accommo-
dates 1 to align them in a packing suitable for such topochemical
polymerization.10 It should be noted that p-amido-functionalities
of 1 are essential for the UV-mediated polymerization. 1,4-Di-
phenylbutadiyne with SPG showed a CD spectrum with much
small intensity (ca. 1/4 times in comparison to that of 1) and
no UV-mediated polymerization was induced. We assume that
the p-amido-functionalities should form supporting hydrogen
bonds with SPG and/or neigboring monomers to orientate the
monomers in the suitable packing for the polymerization.
Transmittance electron microscopic (TEM) observations
showed that the resultant SPG/poly(1)s complex has a fibrous
structure (Figure 4a) with diameters ranging from 2 to 20 nm.
On the other hand, no such fibrous assembly was observed with-
out SPG (data not shown). We also confirmed that neither carbo-
hydrate-based surfactant (dodecyl-ꢁ-D-glucoside) nor other sin-
gle-stranded polysaccharides (amylose, dextran, pullulan, etc.)
can produce such nanofibers (Figures 4b and 4c, respectively).
These data clearly emphasize an advantage of SPG as a 1-D host
to produce the nanofibers. Energy dispersive X-ray (EDX) spec-
troscopic analysis of the nanofibers also showed a large amount
of oxygen, suggesting that SPG still coexists around poly(1)
nanofibers (Figure 4d).
Figure 4. TEM images of poly(1)s in the presence of (a) SPG,
(b) dodecyl-ꢁ-D-glucoside, or (c) amylose and (d) EDX spec-
trum of the nanofiber.
fibrous assemblies of the corresponding polymers through
UV irradiation, in which SPG acts as a 1-D host. Our research
efforts are now focused on the assessment of the conductivity
through these fibers.
This work was supported by the Japan Science and
Technology Corporation (SORST Program). We also thank
Taito Co., Japan, for providing the native schizophyllan.
References and Notes
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3
4
In conclusion, p-amido-functionalized 1,4-diphenylbuta-
diyne (1) can be polymerized in the presence of SPG to produce
5
6
M. Numata, T. Hasegawa, T. Fujisawa, K. Sakurai, and S.
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Amido-functionalized 1,4-diphenylbutadiyne (1) was synthe-
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7
Photomediated polymerization of 1 was carried out by using
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Figure 3. (a) UV–vis spectra of 1 in the presence of SPG before
8
9
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Published on the web (Advance View) January 5, 2005; DOI 10.1246/cl.2005.40