Parallel β-sheet as a novel template for polymerization of diacetylene

Article abstract of DOI:10.1246/cl.2005.116

The peptide having diacetylene at its side group formed parallel β-sheet structure in crystalline solid, and solid-state polymerization of the diacetylene groups successfully occurred by UV irradiation or heating of the crystal. Copyright

Full text of DOI:10.1246/cl.2005.116

116
Chemistry Letters Vol.34, No.1 (2005)
Parallel ꢀ-sheet as a Novel Template for Polymerization of Diacetylene
Takeshi Mori,ꢀ Kenji Shimoyama, Youichi Fukawa, Keiji Minagawa, and Masami Tanakay
Department of Chemical Science and Technology, Faculty of Engineering, The University of Tokushima,
Tokushima 770-8506
yFaculty of Pharmaceutical Science, Tokushima Bunri University, Tokushima 770-8514
(Received November 8, 2004; CL-041326)
The peptide having diacetylene at its side group formed
(a) parallel -sheet
(b) anti-parallel -sheet
β
β
parallel ꢀ-sheet structure in crystalline solid, and solid-state
polymerization of the diacetylene groups successfully occurred
by UV irradiation or heating of the crystal.
O
C
R
C
H
H
N
R
C
H
O
H
H
C
R
H
C
R
H
C
R
H
C
R
C
N
N
H
C
O
N
C
H
O
O
O
ca. 5 A
ca. 5 A
R
C
H
O
C
H
N
R
C
H
O
R
C
H
H
H
C
R
H
C
R
H
C
R
C
N
N
H
C
O
N
C
O
O
H
O
Diacetylenes undergo radical polymerization in assemblies
such as single-crystal, vesicle, monolayer, Langmuir–Blodgett
film, and liquid crystal.1–4 The polymerization is induced by
heating or irradiation of UV, ꢁ- and X-ray. The polydiacetylenes
thus obtained are ꢂ-conjugated polymer so that they have re-
ceived much attention as conductive and non-linear optical ma-
terials.1–4 A necessary condition for the solid-state polymeriza-
tion of diacetylenes is that the diacetylene groups are spaced
ca. 5 A
ca. 5 A
O
C
R
C
H
H
N
R
C
H
O
H
H
C
R
H
C
R
H
C
R
H
C
R
C
N
N
H
C
O
N
C
H
O
Figure 1. Structural models of parallel (a) and anti-parallel (b)
ꢀ-sheets.
C=O stretching vibrations of the amide groups coupled to the in-
plane N–H bending and C–N stretching modes,7 is useful for an
analysis of secondary structure of peptide. It is known that both
the parallel and anti-parallel ꢀ-sheet structures show absorption
ꢁ
1a
ꢀ
at ca. 5 A with a 45 -declination angle.
5 A
R
R
R
R
R
R
polym.
at around 1630 cmꢂ1 as amide I band, whereas anti-parallel ꢀ-
45
sheet has an additional weak absorption at around 1690 cmꢂ1
.
8
R'
R'
R'
R'
R'
R'
Figure 3 shows the IR spectra of the both crystals in amide I
and II regions. 1 and 2 have maximum absorption at 1640 and
1637 cmꢂ1, respectively, and 2 has weak absorption at 1682
cmꢂ1. These spectral patters show that 1 and 2 form parallel
and anti-parallel ꢀ-sheets in the crystalline solid, respectively.
So far, the crystal structures of some N-acetyl-L-amino acid
methylamides have been determined, and the both parallel and
anti-parallel ꢀ-sheet structures have been found depending on
the kind of amino acids.9 Because N-acetyl-L-phenylalanine-N-
methylamide, which has a similar structure of 1 except for
having no alkyl ether substitunent at p-position, forms ideal
parallel ꢀ-sheet structure,9 the compound 1 would also form that
structure.
So far, many diacetylene derivatives have been synthesized
for the crystalline-state polymerization.1a,2 Most of them have
symmetric structure, and have aromatic groups and urethane
bonds at both sides so that an aromatic stacking interaction
and a hydrogen bonding can space the diacetylene group with
1a,2
ꢀ
5-A distance.
We assumed that the parallel and anti-parallel
ꢀ-sheet structures which are one of the secondary structures of
peptide are worth paying attention because, in these structures,
hydrogen bonding arises between the amide bonds of the peptide
ꢀ
chains to arrange them with a distance of ca. 5 A as shown in
Figure 1.5 Because, in the parallel ꢀ-sheet structure, a distance
ꢀ
between side groups (R) is also ca. 5 A (Figure 1a), the structure
will be applicable to template for polymerization of diacetylene
when diacetylene group is introduced in the side group of pep-
tide. On the other hand, in the anti-parallel ꢀ-sheet structure,
two different distances appear alternatingly (Figure 1b) and both
of them will not suit for the polymerization of diacetylene.
To confirm the applicability of parallel ꢀ-sheet motif to the
polymerization of diacetylene, in this study, we synthesized pep-
tides with amide groups at both N- and C-termini (Figure 2; 1
and 2) and investigated their reactivity in solid-state. Figure 2
shows the polymerization scheme of 1 or 2 aimed in this study.
The compounds 1 and 2 were synthesized from Boc-L-Tyr-OH
and Boc-L-Thr-OH, respectively, by six-step reactions.6 Al-
though 1 and 2 were crystallized from methanol to obtain nee-
dle-like pale yellow crystals, the size of the crystals was not
large enough to conduct a single-crystal X-ray crystallographic
analysis. Thus, we measured FT-IR spectrum to obtain informa-
tion about the arrangement of the molecules in the crystals. The
amide I band (1600–1700 cmꢂ1), which represents primarily the
Then, we applied UV light (high pressure mercury lamp) to
the crystals to polymerize the diacetylene group. Figure 4a
shows UV–vis reflection spectrum of crystal 1 obtained after
6-h UV irradiation. There was absorption maximum at 590 nm
Figure 2. Chemical structures of peptides 1 and 2 (above)
and schematic representation of polymerization of the peptide
(below).
Copyright Ó 2005 The Chemical Society of Japan

Chemistry Letters Vol.34, No.1 (2005)
117
1637
no acid of 1 will be applicable to the stabilization of protein con-
formation by cross-linking reaction (polymerization) among the
amino acids incorporated in a parallel ꢀ-sheet region of a pro-
tein. Moreover, if we apply the system for polypeptide, we can
obtain nano-composite material which is composed of polypep-
tide and polydiacetylene.
(b) 2
1682
1640
(a) 1
We are grateful to Professor T. Moriga and Dr. K. Murai for
measurements of reflection spectra and XRD, and Dr. T. Hirano
for critical reading of the manuscript. This work was partly
supported by the Sasakawa Scientific Research Grant from
The Japan Science Society.
1800
1700
1600
1500
1400
wavenumber /cm-1
Figure 3. FT-IR spectra of amide I and II regions of crystals of
1 (a) and 2 (b).
with a shoulder at 555 nm, and this corresponds to typical ab-
sorption spectrum of the polydiacetylene crystal.1a On the other
hand, UV–vis spectrum of 2 did not change after UV irradiation,
and thus the polymerization of 2 did not proceed. The difference
in polymerization reactivities of 1 and 2 should result from the
difference in the crystal structures of the peptides.
References and Notes
1
a) V. Enkelmann, Adv. Polym. Sci., 63, 91 (1984). b) H. Oikawa, T.
Korenaga, S. Okada, and H. Nakanishi, Polymer, 40, 5993 (1999).
c) B. G. Kim, S. Kim, J. Seo, N.-K. Oh, W.-C. Zin, and S. Y. Park,
Chem. Commun., 2003, 2306. d) J. Nagasawa, M. Kudo, S.
Hayashi, and N. Tamaoki, Langmuir, 20, 7907 (2004). e) B. Tieke,
G. Lieser, and G. Wegner, J. Polym. Sci., Polym. Chem. Ed., 17,
1631 (1979). f) D. Day and J. B. Lando, Macromolecules, 13,
1478 (1980). g) T. Kuo and D. F. O’Brien, J. Am. Chem. Soc.,
110, 7571 (1988). h) A. Matsumoto, A. Matsumoto, T. Kunisue,
A. Tanaka, N. Tohnai, K. Sada, and M. Miyata, Chem. Lett., 33,
96 (2004).
The polymerization of 1 also proceeded by incubating the
crystal at 150 ꢁC in N2 atmosphere. After 72-h incubation, ab-
sorption resulting from diacetylene group (2254 cmꢂ1) almost
disappeared, indicating the almost complete conversion of diac-
etylene groups. The powder X-ray diffraction pattern of poly-
merized 1 was different from that of monomer crystal and the
diffraction peaks of the polymerized 1 were as sharp as that of
the monomer crystal (data not shown). These facts prove that
polymerization reaction of 1 proceeds via a crystal-to-crystal
process. The polymerized 1 is insoluble for common organic sol-
vents except for trifluoroacetic acid and dichloroacetic acid
(DCA). These solvents are known as good solvents for peptide
because of their strong hydrogen bonding ability to peptide
amide bond. Thus, the limited solubility of the polymerized 1 in-
dicates that there is a strong hydrogen bonding interaction
among the monomeric units of the polydiacetylene along the
polymer strand as illustrated in Figure 2.
The polydiacetylene solution shows solvatochromism
(Figure 4b). In the yellow colored DCA solution, there was an
absorption maximum at 470 nm. When the non-solvent (metha-
nol) content was 40 vol %, the absorption maximum red-shifted
to 540 nm and a shoulder appeared at 500 nm, and then the color
of the solution was red. The color change with increasing meth-
anol content is probably due to revival of hydrogen bonding
among the neighboring monomeric units along the polymer
chain so that the effective conjugation system grows longer.
In conclusion, we succeeded in the application of the paral-
lel ꢀ-sheet motif to the polymerization of diacetylene. The ami-
2
H. Zuilhof, H. M. Barentsen, M. van Dijk, E. J. R. Sudholter, R. J.
¨
O. M. Hoofman, L. D. A. Siebbeles, M. P. de Haas, and J. M.
Warman, ‘‘Supramolecular Photosensitive and Electroactive
Materials,’’ ed. by H. S. Nalwa, Academic Press, San Diego
(2002), Chap. 4, p 339.
3
4
A. Mueller and D. F. O’Brien, Chem. Rev., 102, 727 (2002).
S. Okada, S. Peng, W. Spevak, and D. Charych, Acc. Chem. Res.,
31, 229 (1998).
5
6
L. Pauling and R. B. Corey, Proc. Natl. Acad. Sci. U.S.A., 39, 255
(1953).
1 was synthesized by following procedure. Boc-L-Tyr-OH was re-
acted with propargyl bromide to obtain Boc-O-2,4-octadiyn-1-yl-
L-tyrosine, and the obtained compound was reacted with 1-bro-
mo-1-pentyne to obtain Boc-O-2,4-octadiyn-1-yl-L-tyrosine. The
resulting compound was introduced with acetyl group at N-termi-
nus and methyl amide group at C-terminus, respectively and then 1
was obtained as a light sensitive needle-like white solid. 1H NMR
(400 MHz, CDCl3) ꢃ 0.97 (t, J ¼ 7:3, 3H, CH3CH2), 1.54 (m, 2H,
CH3CH2), 1.96 (s, 3H, COCH3), 2.25 (t, J ¼ 7:1, 2H, CH2), 2.70
(d, J ¼ 4:9, 3H, NHCH3), 2.98 (m, 2H, ꢀ-CH2), 4.59 (m, 1H, ꢄ-
CH), 4.71 (s, 2H, OCH2), 6.30 (q, J ¼ 4:9, 1H, NHCH3), 6.71
(d, J ¼ 8:0, 1H, ꢄ-CHNH), 6.88 (d, J ¼ 8:5, 2Ar-H, m to ꢀ-
CH2), 7.13 (d, J ¼ 8:5, 2Ar-H,
o
to ꢀ-CH2); 13C NMR
(100 MHz, CDCl3) ꢃ 13.4, 21.2, 21.6, 23.1, 26.1, 37.8, 54.9,
56.4, 64.4, 70.1, 72.2, 81.9, 114.9, 129.7, 130.2, 156.4, 170.0,
171.6. 2 was synthesize from Boc-L-Thr-OH by the similar proce-
dure and obtained as a light sensitive white solid. Mp 124 ꢁC; H
1
NMR (400 MHz, CDCl3) ꢃ 0.92 (t, J ¼ 7:3, 3H, CH2CH3), 1.06
(d, J ¼ 6:4, 3H, ꢁ-CH3), 1.50 (m, 2H, CH2CH3), 1.99 (s, 3H,
COCH3), 2.19 (t, J ¼ 6:8, 2H, ꢃCCH2), 2.77 (d, J ¼ 4:9, 3H,
NHCH3), 4.04 (m, 1H, ꢀ-CH), 4.24 (m, 2H, OCH2), 4.42 (m,
1H, ꢄ-CH), 6.48 (d, J ¼ 4:2, 1H, ꢄ-CH2NH), 6.56 (d, J ¼ 6:8,
1H, NHCH3); 13C NMR (100 MHz, CDCl3) ꢃ 13.4, 15.5, 21.2,
21.6, 23.2, 26.3, 56.2, 57.8, 64.4, 71.3, 71.5, 74.6, 81.6, 169.5,
170.2.
W. K. Surewicz and H. H. Mantsch, Biochim. Biophys. Acta, 952,
115 (1988).
a) T. Miyazawa, J. Chem. Phys., 32, 1647 (1960). b) T. Miyazawa
and E. R. Blout, J. Am. Chem. Soc., 83, 712 (1961). c) C. Toniolo,
G. M. Bonora, M. Palumbo, and E. Peggion, Biopolymers, 17, 1713
(1978).
0.5
(a)
(b)
MeOH
(vol%)
0.4
0.3
0.2
0.1
0
50
60
40
30
20
0
30
0, 20
7
8
300 400 500 600
700 800
350
450
550
650
wavelength / nm
wavelength / nm
Figure 4. (a) UV–vis reflection spectrum of polymerized crys-
tal of 1, and (b) UV–vis absorption spectra of polymer 1
(0.03 mg/mL) in dichloroacetic acid/methanol mixed solvents.
9
T. Ashida, I. Tanaka, and T. Yamane, Int. J. Pept. Protein Res., 17,
322 (1981).
Published on the web (Advance View) December 18, 2004; DOI 10.1246/cl.2005.116