Induction of one-handed helix sense in achiral poly(N-propargylamides)

Article abstract of DOI:10.1021/ma030324i

Achiral N-propargylamides, i.e., N-propargyl-3-methylbutanamide (1), N-propargyl-2-ethylbutanamide (2), and N-propargyl-3,3-dimethylbutanamide (3), were polymerized with (nbd)Rh⁺[η⁶-C₆H₅B- (C₆H₅)] to afford polymers with moderate molecular weights (M_n = 6000-22000) in good yields. The ¹H NMR and UV-vis spectra demonstrated that the polymers, poly(1)-poly(3), have stereoregular structures (cis = 100%) and equally populated right- and left-handed helical conformation. A predominant helix sense was induced in these polymers by the addition of chiral alcohols or amine, which was confirmed by CD and UV-vis spectroscopies. ¹H NMR and CD spectroscopic studies strongly suggested that the poly(N-propargylamides) interacted with the chiral alcohols by hydrogen bonding at the amide groups of the polymer side chain. Chiral terpenes could also induce single-handed helical conformation. It is likely that hydrophobic interaction led to the one-handed helical conformation in the case of the chiral terpenes because the addition of n-hexane decreased the CD signal.

Full text of DOI:10.1021/ma030324i

Macromolecules 2003, 36, 8603-8608
8603
Articles
Induction of One-Handed Helix Sense in Achiral
Poly(N-propargylamides)
J u n ich i Ta bei, Ryoji Nom u r a , F u m io Sa n d a , a n d Tosh io Ma su d a *
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Kyoto 606-8501, J apan
Received J une 12, 2003; Revised Manuscript Received September 16, 2003
ABSTRACT: Achiral N-propargylamides, i.e., N-propargyl-3-methylbutanamide (1), N-propargyl-2-
+
6
ethylbutanamide (2), and N-propargyl-3,3-dimethylbutanamide (3), were polymerized with (nbd)Rh [η -
C
6
H
5
B-(C ] to afford polymers with moderate molecular weights (M ) 6000-22 000) in good yields.
6
H
5
)
3
n
1
The H NMR and UV-vis spectra demonstrated that the polymers, poly(1)-poly(3), have stereoregular
structures (cis ) 100%) and equally populated right- and left-handed helical conformation. A predominant
helix sense was induced in these polymers by the addition of chiral alcohols or amine, which was confirmed
1
by CD and UV-vis spectroscopies. H NMR and CD spectroscopic studies strongly suggested that the
poly(N-propargylamides) interacted with the chiral alcohols by hydrogen bonding at the amide groups of
the polymer side chain. Chiral terpenes could also induce single-handed helical conformation. It is likely
that hydrophobic interaction led to the one-handed helical conformation in the case of the chiral terpenes
because the addition of n-hexane decreased the CD signal.
In tr od u ction
chiral molecules as the third types of helical polymers.
For instance, Yashima et al. have induced helical
structure in a polymer carrying acid groups in the side
Helix is the most common secondary structure of
1
2
synthetic and biopolymers, which prefers a one-handed
left- or right-handed) screw sense when chiral moieties
1
3
chain by complexation with chiral amines. Green et
al. have observed Cotton effects based on an excess
helicity of poly(hexylisocyanate) in chiral chloroalkane
(
are incorporated into the main or side chain. Helical
polymers attract particular interest because a wide
variety of characteristic features and applications are
1
4
solvents. Inai et al. have reported that a chiral
carboxylic acid acts on the N-terminal amino group of
achiral oligopeptides to predominantly induce a one-
3
expected such as molecular recognition (separation,
4
catalysts, sensory functions, etc.), molecular scaffold
1
5
handed screw sense. Moore and co-workers have found
that chiral monoterpenes can induce an excess helicity
in m-phenyleneethynylene oligomers by binding in the
hydrophobic tubular cavity of the oligomer.16 In this
way, achiral receptors (hosts) can recognize chiral guests
through hydrophilic and/or hydrophobic interactions.
This is particularly important in living systems for
detection and assignment of one of a pair of enantio-
meric drugs, which often show completely different
activities.
function for chromophores, and ordered molecular align-
ment in the solid-phase-like liquid-crystalline materi-
als.5
Synthetic helical polymers are classified into two
categories. One is stable helical polymers such as poly-
6
7
(
triphenylmethyl methacrylate), poly(chloral), and
8
poly(isocyanides), which have bulky, sterically demand-
ing pendant groups and eventually rigid polymer chain.
This type of polymer is synthesized by asymmetric
polymerization (helix-sense-selective polymerization),
and the screw sense of their main chain is kinetically
determined. The other one is thermodynamically in-
Rhodium-based complexes are excellent catalysts for
stereospecific polymerization of various monosubsti-
tuted acetylenes to give high-molecular-weight cis-
9
duced helical polymers like poly(silanes), poly(isocy-
1
0
11
17
anates), and poly(acetylenes), whose polymer chain
is not so rigid compared to the former, and helix
inversion frequently occurs. Screw sense excess is
sometimes observed in copolymers from achiral and only
a small amount of chiral monomers. Control of the screw
sense of helical polymers by external stimuli such as
transoidal poly(acetylenes). We have recently reported
that N-propargylamides polymerize with Rh catalysts,
and the resulting stereoregular polymers take the
helical conformation, which is stabilized by intramo-
lecular hydrogen bonds between the pendant amide
1
8
groups like R-helical polypeptides. The present work
deals with helix induction of poly(N-propargylamides),
i.e., poly(N-propargyl-3-methylbutanamide) [poly(1)],
poly(N-propargyl-2-ethylbutanamide) [poly(2)], and poly-
pH,1 light, temperature, and solvent
2a
12b
12c
12d
has been
widely studied. Furthermore, much attention has been
paid to helical polymers induced by interaction with
(N-propargyl-3,3-dimethylbutanamide) [poly(3)], with
chiral alcohols, amine and monoterpenes (4-15), and
investigation of the interaction between the polymers
*
Corresponding author: Tel +81-75-753-5613; Fax +81-75-753-
5
908; e-mail masuda@adv.polym.kyoto-u.ac.jp.
1
0.1021/ma030324i CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/21/2003

8
604 Tabei et al.
Macromolecules, Vol. 36, No. 23, 2003
Ta ble 1. P olym er iza tion of 1-3a
Sch em e 1
b
Mnc
Mw/Mnc
cis contentd (%)
monomer
yield (%)
1
2
3
82
63
76
19 000
22 000
6 000
1.93
1.99
1.26
100
100
100
a
+
Polymerized with (nbd)Rh [(C6H5)B-(C6H5)3] in THF at 30 °C
+
b
for 1 h. [M]0 ) 2.0 M, [Rh ] ) 20 mM. Hexane-insoluble part.
c
d
Estimated by GPC (eluent CHCl3, PSt calibration). Determined
1
by H NMR measurement.
silica gel (eluent: hexane/AcOEt ) 2/1, v/v). Yield 37%; mp
6
1
2-63 °C. IR (KBr): 3270 (νH-C≡), 2963, 2172 (νC≡C), 1638,
-1 1
545, 1514, 1238, 763 cm
CH , t, 2H, J ) 7.20 Hz), 1.41-1.56 (CH(CH
H), 1.56-1.64 (CH(CH CH , m, 2H), 1.88-1.99 (CH(CH
.
H NMR (CDCl
3
) δ: 0.87 (CH-
(CH
2
3
)
2
2
CH , m,
3 2
)
2
CH
CCH
2
3
)
2
2
3
-
)
3
)
2
, m,1H), 2.21 (HC≡C, d, 1H, J ) 2.44 Hz), 4.06 (CHd
, d, 2H, J ) 2.44 Hz), 5.83 (NH, s, 1H). 13C NMR (CDCl
2
δ: 11.77, 25.42, 28.79, 50.93, 71.21, 79.72, 175.51. Anal. Calcd
for C 15NO: C, 70.55; H, 9.87; N, 9.14. Found: C, 70.33; H,
.64; N, 9.12.
Monomer 3 was prepared in a similar way from 3,3-
dimethylbutanoic acid. Yield 59%; mp 37-38 °C. IR (KBr):
9
H
9
-
1
3
298 (νH-C≡), 2963, 2153 (νC≡C), 1634, 1543, 1262, 669 cm
.
1
H NMR (CDCl
3
) δ: 1.02 (CH
, s, 2H), 2.21 (HC≡C, d, 1H, J ) 2.46 Hz), 4.05 (CHd
, d, 2H, J ) 2.46 Hz), 6.24 (NH, s, 1H). 13C NMR (CDCl
)
3
2 3 3 2
C(CH ) , s, 9H), 2.09 (CH C-
(CH
3
)
3
CCH
2
δ: 28.85, 29.69, 30.95, 50.03, 71.29, 79.74, 171.46. Anal. Calcd
for C 15NO: C, 70.55; H, 9.87; N, 9.14. Found: C, 70.49; H,
.62; N, 9.21.
P olym er iza tion P r oced u r e. A THF solution of a monomer
9
H
9
1
with the chiral compounds by means of CD and H NMR
spectroscopies (Scheme 1).
+
6
([M] ) 2.0 M) was added to a THF solution of (nbd)Rh [η -
0
+
6 5 6 5 3 0
C H B-(C H ) ] ([M] /[Rh ] ) 100) under dry nitrogen, and the
solution was kept at 30 °C for 1 h. The reaction mixture was
poured into a large amount of hexane to precipitate a polymer.
The resulting polymer was separated by filtration and dried
under reduced pressure.
Exp er im en ta l Section
Mea su r em en ts. Melting points (mp) were measured with
a Yanaco micromelting point apparatus. Elemental analyses
were conducted at the Kyoto University Elemental Analysis
Sp ectr oscop ic Da ta of P olym er s. Poly(2): IR (KBr):
1
13
Center. NMR ( H: 400 MHz; C: 100 MHz) spectra were
recorded on a J EOL EX-400 spectrometer. IR spectra were
obtained with a Shimadzu FTIR-8100 spectrophotometer.
-1 1
3
0
2
288, 2963, 1649, 1546, 1228, 1115 cm . H NMR (CDCl
.65-1.22 (CH(CH CH ), 1.22-1.79 (CH(CH CH ), 1.79-
.38 (CH(CH CH ), 3.54-4.68 (CHdCCH ), 5.82-6.38 (CHd
3
) δ:
2
3
)
2
2
3 2
)
2
3
)
2
2
Number-average molecular weights (M
distributions (M /M ) of polymers were estimated by GPC
Shodex KF-850L columns) eluted with chloroform by use of a
n
) and molecular weight
C), 7.72-8.48 (NH). Poly(3): IR (KBr): 3306, 2955, 1655, 1546,
-1
1
w
n
1
1
(
236, 758 cm . H NMR (CDCl
) δ: 0.99-1.41 (CH
2 3 3
C(CH ) ),
3
(
.41-1.75 (CH C(CH ), 3.58-4.44 (CHdCCH
2
3
)
3
2
), 5.88-6.22
polystyrene calibration. UV-vis spectra were recorded on a
J ASCO V-500 spectrophotometer. CD spectra were recorded
on a J ASCO V-530 spectropolarimeter. Unless otherwise
specified, UV-vis and CD spectra were measured at a polymer
concentration of 5.0 mM with respect to repeat unit and a
CHdC), 7.58-7.91 (NH).
Resu lts a n d Discu ssion
P olym er iza tion . We have previously demonstrated
1
8b
chiral compound concentration of 1.0 M in CHCl
0 °C.
Ma ter ia ls. Solvents were distilled by usual methods prior
to use. Propargylamine (Aldrich), 2-ethylbutanoic acid (Wako),
,3-dimethylbutanoic acid (Wako), thionyl chloride (Wako),
3
solution at
that most poly(N-propargylamides) having â-
or
1
8c
2
R-branched pendant amide groups, no matter whether
chiral or achiral, take the helical conformation. Thus,
we decided to employ poly(N-propargylamides), poly(1)-
poly(3), as the candidate polymers for induction of one-
handed helices in the present study. Polymerization of
3
pyridine (Wako), L-(-)-menthol (4, Wako), (S)-(-)-1-phenyle-
thanol (5, Azmax), (S)-(-)-1-phenylethylamine (6, Wako), (S)-
+
6
1
(
-3 was carried out using with (nbd)Rh [η -C6H5B-
C6H5)3] as a catalyst in THF. The results of the
(
+)-2-butanol (7, Tokyo Kasei), (S)-(-)-2-methyl-1-butanol (8,
Tokyo Kasei), (S)-(+)-3-methyl-1-pentanol (9, Tokyo Kasei),
polymerization are listed in Table 1. Polymers with
moderate molecular weights (Mn ) 6000-22 000) were
obtained in 63-82% yields. All of the polymers displayed
unimodal GPC chromatograms, which means that the
polymerization proceeded through a single propagating
(
(
S)-(+)-4-methyl-1-hexanol (10, Tokyo Kasei), (S)-(+)-2-octanol
11, Azmax), R-pinene (12, Wako), â-pinene (13, Wako),
D-limonene (14, Nakarai), and (S)-(+)-citronellyl bromide (15,
+
6
17a
Aldrich) were used as received. (nbd)Rh [η -C
6
H
5
6 5 3
B-(C H ) ]
1
8b
and monomer 1 were prepared according to the literature.
1
Syn th esis of Mon om er s 2 a n d 3. Monomer 2 was pre-
pared as follows: Thionyl chloride (150 g, 0.39 mol) was added
to 2-ethylbutanoic acid (10 g, 0.11 mol), and the reaction
mixture was heated with refluxing for 3 h. The excessive
thionyl chloride was distilled off, and the resulting acyl
species. The H NMR spectra of the resulting polymers,
poly(1)-poly(3), showed a signal assignable to cis-
olefinic proton in the main chain around 6 ppm. The
cis contents of poly(1)-poly(3) were all estimated to be
1
00% by comparison of the cis-olefinic proton signal with
2
chloride was add to an Et O solution of propargylamine (22.7
other proton signals. All the polymers exhibited UV-
vis absorption at 390 nm, which indicates that they take
helical conformation as expected.
mL, 0.33 mol) and pyridine (26.9 mL, 0.33 mol) at 0 °C. The
solution was stirred at room temperature for 24 h. After the
formed white precipitate was filtered off, the solution was
1
8
In d u ction of On e-Ha n d ed Helix in P olym er .
washed with aqueous HCl and saturated aqueous NaHCO
dried over MgSO , and concentrated by rotary evaporation.
Monomer 2 was purified by flash column chromatography on
3
,
Poly(1) is populated by right- and left-handed helical
4
1
8b
conformations equally in CHCl3 solution. When 4 was

Macromolecules, Vol. 36, No. 23, 2003
Achiral Poly(N-propargylamides) 8605
F igu r e 2. 1H NMR spectra of (a) 4, (b) 4 and poly(1) ([repeat
F igu r e 1. (a) CD and (b) UV-vis spectra of poly(1) ([repeat
unit] ) 0.10, 0.25, 0.5, and 5.0 mM) in the presence of 4 (100
unit] ) 50 mM) measuered in CDCl3 at room temperature,
mM) measured in CHCl
3
at 20 °C. (c) Titration curves of poly-
at 20
and (c) after the addition of D O to the sample (b).
2
(
°
1) ([repeat unit] ) 5.0 mM) with 4, 5, 6, and 8 in CHCl
3
C.
[
polymer] ) 5.0 mM, [chiral alcohol]/[polymer] ) 200
as the optimal one below.
1
added to a CHCl3 solution of poly(1), an intense CD peak
H NMR Sp ectr oscop ic Stu d ies on th e Com p lex-
2
1
(
(
[θ]max ) 10 000 deg cm /dmol) appeared around 390 nm
a tion of P oly(1) w ith 4. The H NMR spectra of 4 were
Figure 1a). This means that poly(1) interacted with 4
measured in CHCl3 in the absence and presence of poly-
(1) to examine their interaction (Figure 2). The peak
around 1.3 ppm showed a downfield shift and broadened
when an equivalent amount of poly(1) was added to a
solution of 4 (Figure 2b) ([poly(1)] ) [4] ) 50 mM in
CDCl3). When a few drops of D2O was added to the
sample of Figure 2b, this peak disappeared (Figure 2c).
This result implies that the peak is assignable to the
hydroxy proton of 4. It seems that the mobility of the
hydroxy proton of 4 was restricted due to the formation
of hydrogen bonding between the hydroxy and amide
groups in the presence of poly(1).
and transformed into one-handed helical conformation.
Then, CD spectra of poly(1) were measured in CHCl3
at various polymer concentrations in the presence of 4
(
c ) 100 mM). The intensities of the Cotton effect were
2
almost constant ([θ]max ) 8000-10 000 deg cm /dmol)
irrespective of the concentration of poly(1) in the range
from 0.1 to 5.0 mM. This result indicates that the
magnitude of CD signal does not depend on polymer
concentration in this range. The apparent efficiency of
one-handed helix induction increases with raising the
polymer concentration. For example, [4]/[poly(1)] is as
high as 1000 when the concentration of the polymer is
We have previously demonstrated that poly(1) un-
dergoes a helix to random coil transition by adding a
polar solvent such as methanol because polar solvents
destroy intramolecular hydrogen bonding between the
amide groups, which stabilizes the helical structure of
0
.1 mM, while [4]/[poly(1)] is no more than 20 when the
concentration of the polymer is 5.0 mM, and in the
meantime the magnitude of CD signal is almost the
same. Next, CD measurement was conducted with fixing
the concentration of poly(1) at 5.0 mM. As shown in
Figure 1b, the incremental addition of 4 to a solution of
poly(1) resulted in the increase and virtual saturation
1
8a
poly(N-propargylamides). In the present study, poly-
(1) did not undergo the helix-coil transition upon the
addition of 4. We therefore added several primary
alcohols (methanol, ethanol, propanol, and butanol) to
a CHCl3 solution of poly(1) (5.0 mM) and examined the
2
of CD signal ([θ]max ) 60 000 deg cm /dmol) at [4]/[poly-
(1)] ) 200. We therefore decided to use the condition of

8
606 Tabei et al.
Macromolecules, Vol. 36, No. 23, 2003
F igu r e 4. (a) CD spectra and (b) UV-vis spectra of poly(1)
(
3
[repeat unit] ) 5.0 mM) measured in CHCl in the presence
F igu r e 3. CD and UV-vis spectra of poly(1) ([repeat uint] )
.0 mM) in the presence of 7-11 ([alcohol]/[poly(1)] ) 200)
measured in CHCl at 20 °C.
of 4 (1.0 M) at 0, 20, 35, 40, 45, and 50 °C.
5
3
center was short like in 7, 8, and 11. On the other hand,
the CD signs were minus when the chiral center was
away from the hydroxy group as in 9 and 10. Thus, this
polymer-chiral compound system did not obey the odd-
even rule, and further the bulkiness of alkyl group did
not affect the intensity of CD signal (7 vs 11). The same
CD sign (+) was induced by the chiral alcohols 5, 7, 8,
and 11 and amine 6 with S-configurated chiral R-carbon
of the OH or NH2 group. Comparison of 5, 6, 7, and 11
leads to a conclusion that the CD sign is decided by the
absolute configuration of the chiral center when the
distance between chiral center and polar functional
group is constant.
secondary structure by UV-vis spectroscopy.19 While
a UV-vis absorption peak of helical poly(N-propargy-
lamide) appears around 390 nm, the UV-vis absorption
should appear around 320 nm when it takes a random
coil structure. In the cases of methanol and ethanol, the
helix-coil transition occurred when the alcohol content
exceeded only 5 and 14 vol %, respectively. On the other
hand, the transition hardly took place with propanol and
butanol, even when 35 vol % of alcohol was added. These
results suggest that the helix-coil transition is de-
pressed by steric repulsion between the alkyl group of
the alcohol and polymer side chain.
Tem p er a tu r e Effect on th e In d u ction of On e-
Ha n d ed Helix. Poly(1) undergoes the helix-coil tran-
sition by thermal stimuli, which can be detected by UV-
Rela tion sh ip betw een th e Cotton Effect a n d th e
Str u ctu r e of Ch ir a l Com p ou n d s. Titration of poly-
(1) was carried out by using chiral alcohols 5, 8, and
1
8b
vis absorption shift from 390 to 320 nm. We therefore
investigated the temperature effect on the helical
conformation induced by the chiral compounds. Figure
amine 6 (Figure 1b). J ust like 4, the intensity of CD
signal increased with increasing amount of these chiral
alcohols and amine. When [5 or 8]/[poly(1)] was 200, the
4
depicts the CD and UV-vis spectra of poly(1) in the
presence of 4 measured in CHCl3 ([poly(1) ) 5.0 mM,
poly(1)]/[4] ) 200]) at various temperatures. Both the
CD signals became saturated at the intensities of [θ]max
2
)
20 000 and 18 000 deg cm /dmol, respectively, about
[
one-third that of 4. In the case of 6, which has the same
structure as of 5 except for the amino group, we needed
UV-vis absorption and CD signal around 390 nm
gradually decreased in intensity upon heating and
completely disappeared at 50 °C. This means that the
induced helical structure of poly(1) transforms into a
random coil structure upon heating.
to add 500 equiv of 6 to poly(1) to achieve saturation
2
(
[θ]max ) 20 000 deg cm /dmol). The helical structure
collapsed when [6]/[poly(1)] was 600, presumably be-
cause of the excessive addition of the polar compound.
The magnitude of the induced Cotton effect, i.e., the
efficiency of one-handed helix induction, depended on
the structure of alcohol or amine and the kind of polar
functional group. For instance, the chiral alcohols could
inducethe Cotton effect more efficiently than the cor-
responding amine, presumably because the hydroxy
group can form hydrogen bonding more strongly than
amino group with the amide group of poly(1). Further,
the shape of chiral compounds also influenced the CD
magnitude.
Effect of th e Sid e Ch a in Str u ctu r e. We examined
the helix induction of other poly(N-propargylamides) in
CHCl3 to check the variation of efficiency with the
structure of polymer pendant group (Figure 5). The CD
intensity of poly(2) and poly(3) increased with increasing
concentration of 4, but the sensitivities of poly(2) and
poly(3) were lower than that of poly(1), presumably
because poly(2) and poly(3) have bulky pendant groups,
which weaken the interaction between the amide groups
and 4 (Figure 5a).
CD spectra of poly(1) were measured in the presence
of various alcohols 7-11 with the same absolute con-
figuration (Figure 3). The CD signs were plus when the
distance between the hydroxy group and the chiral
It is known that hydrophobic interaction also plays
an important role in chiral recognition between achiral
1
4,16
and chiral compounds.
The CD induction of poly-
(1)-poly(3) was also observed by the addition of â-pinene

Macromolecules, Vol. 36, No. 23, 2003
Achiral Poly(N-propargylamides) 8607
F igu r e 5. (a) Titration curves of poly(1)-poly(3) ([repeat unit]
F igu r e 6. CD and UV-vis spectra of poly(1) ([repeat unit] )
)
3
5.0 mM) with 4 in CHCl at 20 °C. (b) Titration curves of
5
.0 mM) in the presence of 12-15 measured in CHCl
3
poly(1)-poly(3) ([repeat unit] ) 5.0 mM) with 12 in CHCl
0 °C.
3
at
3
(monoterpene/CHCl ) 1/1, v/v) at 20 °C.
2
(
12), which has no polar group (Figure 5b). We had to
add 12 as much as a half amount of the solvent ([12]/
polymer] ) 3000 equiv) to observe the evident Cotton
[
2
effect ([θ]max ) 10 000 deg cm /dmol). The efficiency of
induction of one-handed helical conformation was simi-
lar among poly(1)-poly(3). Thus, it has been demon-
strated that 12, a nonpolar chiral compound, can also
interact with the present polymers to induce one-handed
helical conformation. CD spectra of poly(1) were also
measured in the presence of other monoterpenes such
as 13-15 (Figure 6). 14 and 15 induced intense CD
signals (one-handed helical structure), whereas 13 did
not. It is noteworthy that the two isomers 12 and 13
exhibited a drastic difference. Prince and co-workers
have reported that m-phenyleneethynylene oligomers
also show a large difference in diastereoselectivity
between 12 and 13.16 They describe that this phenom-
enon is caused by the difference in the association
constants of 12 and 13 and that the magnitude of CD
is roughly proportional to the difference in the associa-
tion constants. We suppose that the difference in our
system is also caused in a similar fashion. There was
no relationship between the absolute configuration of
the monoterpenes and CD signs, which is probably
because the monoterpens have no specific site to interact
with the polymer unlike the case of alcohols or amine.
We further examined the interaction between poly(1)
and monoterpene 12 in hexane/CHCl3 mixed solvents
with various compositions (Figure 7). The Cotton effect
decreased with increasing ratio of hexane and com-
pletely disappeared at hexane/CHCl3 ) 2/3. This result
supports the idea that poly(1) complexes with 12
through hydrophobic interaction; it is likely that hexane
hampered the interaction between poly(1) and 12 and
eventually the generation of helix with one-handed
screw sense.
F igu r e 7. CD and UV-vis spectra of poly(1) ([repeat unit] )
.0 mM) in the presence of 12 measured in CHCl /hexane (â-
pinene/solvent ) 1/1, v/v) at 20 °C.
5
3
Con clu sion . We found by CD and UV-vis spec-
troscopies that the achiral cis-stereoregulated poly(N-
propargylamides), poly(1)-poly(3), can form a one-
handed helical structure upon the addition of the chiral
alcohols or amine 4-11. The intensity of induced CD
depended on the concentration of chiral alcohols and

8
608 Tabei et al.
Macromolecules, Vol. 36, No. 23, 2003
became saturated at around [alcohol] ) 1.0 M. It is
(8) (a) Kamer, P. C. J .; Nolte, R. J . M.; Drenth, W. J . J . Am.
Chem. Soc. 1988, 110, 6818-6825. (b) Deming, T. J .; Novak,
B. M. J . Am. Chem. Soc. 1993, 115, 9101-9111.
1
suggested from H NMR spectroscopic study that the
poly(N-propargylamides) interact with the chiral alco-
hols through hydrogen bonding. The sign of induced CD
was decided by the absolute configuration of the alcohols
and amine with R-chiral carbon atoms. Chiral terpenes
could also induce one-handed helical conformation. It
is inferred that hydrophobic interaction led to the single-
handed helical structure because the addition of n-
hexane decreased the CD signal. On the basis of these
features, poly(N-propargylamides) may find application
to chiral molecular recognition materials in the future
like in the poly(4-carboxyphenylacetylene)/amino acid
system.1
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