384
Published on the web March 12, 2011
Enantioselective Pervaporation through Membranes from Poly(1,3-phenyleneethynylene)-based
One-handed Helical Foldamer and Unfoldamer
Makoto Inoue,1 Masahiro Teraguchi,*2,3 Toshiki Aoki,1,2,3,4 Takeshi Namikoshi,5 Edy Marwanta,3,4 and Takashi Kaneko3
1Graduate School of Science and Technology, Niigata University, 2-8050 Ikarashi, Niigata 950-2181
2Institute of Science and Technology, Niigata University, 2-8050 Ikarashi, Niigata 950-2181
3Center for Transdisciplinary Research, Niigata University, 2-8050 Ikarashi, Niigata 950-2181
4Venture Business Laboratory, Niigata University, 2-8050 Ikarashi, Niigata 950-2181
5Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090-8507
(Received January 17, 2011; CL-110039; E-mail: teraguti@eng.niigata-u.ac.jp)
We synthesized two kinds of poly(1,3-phenyleneethynyl-
enes), one has (+)-menthoxycarbonyl groups at all repeating
O
O
[PdCl2(PPh3)2]
CuI, PPh3
units and the other has (+)-menthoxycarbonyl groups and n-
dodecyloxy groups alternately. Self-supporting membranes
could be obtained easily by solvent casting. Enantioselective
permeations of the polymers were investigated by pervaporation
of 2-butanol. Enantioselective permeabilities of the membrane
consisting of one-handed helical foldamer and unfoldamer were
clarified.
I
I
n
+
O
THF/ Et3N
O
R
R
O
R =
=
O
PMtMt
PMtODo
OC12H25
Syntheses of optically active helical polymers have attracted
particular interests of polymer scientists due to interesting
technological applications in optical resolution, chiral sensors,
chiroptics, microelectronics, chiral magnets, and so on.1
It is well known that some poly(1,3-phenyleneethynylene)s
can form helical foldamer conformation depending on their side
groups and/or solvent.2-6 These properties are very interesting
and many functions such as molecular recognition,7-10 magnet-
ism,11,12 and reactive sieve13 have been reported.
Scheme 1. Synthesis of chiral poly(1,3-phenyleneethynylenes).
Table 1. Polycondensation results by using [PdCl2(PPh3)2]-
PPh3-CuI (1:4:6)a
b
20 c
¹3 d
Yield Mw
/% /©104
½¡ꢀD
[ª]320 © 10
/deg¢cm2¢dmol
b
Code
Mw/Mn
¹1
/°
PMtMt
72
23.0
17.2
2.20
1.45
91.0
62.0
9.3
3.1
However, to the best of our knowledge, functions of
poly(1,3-phenyleneethynylenes) used as free-standing mem-
brane have been never reported.14 Needless to say, there are
no reports that functions of free-standing membranes consisting
of foldamer and unfoldamer were compared. Enantioselective
permeation by chiral main chains of polymers is a very
interesting subject in polymer science. Herein, we synthesized
two kinds of chiral poly(1,3-phenyleneethynylenes), one has
(+)-menthoxycarbonyl groups at all repeating units and the
other has (+)-menthoxycarbonyl groups and n-dodecyloxy
groups alternately in the repeating units (named PMtMt and
PMtODo, respectively) (Scheme 1). Then we prepared free-
standing membranes consisting of one-handed helical foldamer
and unfoldamer by casting and investigated the enantioselective
permeability of the foldamer and the unfoldamer membranes.
PMtMt was synthesized according to a previous report from
our laboratory.15 PMtODo was newly synthesized to improve
solubility and membrane forming ability.16 The polymerization
data for the polymers used in this paper are summarized in
Table 1. Both polymers were pale yellow solids and soluble in
chloroform, dichloromethane, carbon tetrachloride, THF, tol-
uene, and benzene and insoluble in hexane, diethyl ether,
methanol, and acetone.
PMtODo 50
aPolycondensations were carried out in THF/Et3N for 24 h at
b
r.t.; [M]0,total = 0.125 M, [Pd cat] = 0.025 M. Determined by
GPC correlating polystyrene standard; eluent: THF. cIn
¹1
CHCl3/benzene (volume ratio: 2:8); 0.10 g L
(2.5 © 10¹4 M) at 20 °C.
.
dIn toluene
other hand, no Cotton effects were observed in chloroform
solution because PMtODo exists in extended chain conforma-
tion (unfoldamer) in chloroform.
The CD profile of PMtODo in toluene was similar to that of
PMtMt,15 but the [ª] value of PMtODo in toluene was one third
of that of PMtMt in toluene (Table 1). It was attributed to the
chiral menthyl group, i.e., menthyl group content of PMtODo
was less than that of PMtMt and less contribution of
solvophobic effects by n-dodecyloxy groups as a driving force
for foldamer formation than that of menthoxycarbonyl groups.
To elucidate a one-handed helical conformation in the
membrane state, a thin membrane was prepared on a quartz disc
by spin-coating. A strong Cotton effect was observed in the CD
spectra of PMtODo membrane prepared from toluene solution,
which was similar to that of in solution. On the other hand, no
Cotton effect was observed in the CD spectra of PMtODo
membrane prepared from chloroform solution (Figure 1). These
results were the same in the case of PMtMt previously
reported.15 UV-vis spectra of foldamer and unfoldamer were
PMtODo in toluene displayed intense Cotton effects in
circular dichroism (CD) spectra in the range of 270-360 nm
which are attributable to the backbone. This indicates that
PMtODo in toluene forms one-handed helical foldamer. On the
Chem. Lett. 2011, 40, 384-386
© 2011 The Chemical Society of Japan