Molecular assembly of C2-symmetric Bis-(2S)-2-methyldodecanoylamides of α,ω-alkylidenediamines into coiled coil and twisted ribbon aggregates

Article abstract of DOI:10.1021/ja035085t

A series of 10 didodecanoylamides of α,Ω-alkylidenediamines bridged by a straight carbon chain varying in length from 0 to 9 carbons was examined as possible gelator molecules of organic liquids to gain information on the relationships between the spacial arrangement of two amide groups in a molecule and their effects on the microscopic structures of the gel. The structural characteristics of these amides are parallel and antiparallel arrangements of two amide carbonyl groups, which depend on the even and odd numbers of a bridging zigzag carbon chain. The linear alkyl chain moieties and a center carbon chain of diamides intermolecularly interact with each other within the van der Waals contact. Two amide moieties of an even number carbon chain diamide intermolecularly interact with each other by using two pairs of hydrogen bonds with two other molecules in a plane, which formed ribbonlike self-complementarily assembled aggregates. On the other hand, a diamide of an odd number carbon chain forms four independent hydrogen bonds with four other molecules not in a plane, which assembled into woven aggregates. Asymmetric introduction of a methyl group at the α-position of the amide groups successfully twists the two side chain van der Waals cores of the chiral diamides in the fixed direction, giving helically twisted ribbon and coiled coil aggregates. The helically twisted ribbon and coiled coil aggregates of these chiral diamides were directly observed by CD, SEM, and TEM, providing a basis for the design of a sophisticated small molecular gelator of a tailor-made shape.

Full text of DOI:10.1021/ja035085t

Published on Web 09/12/2003
Molecular Assembly of C2-Symmetric
Bis-(2S)-2-methyldodecanoylamides of
r,ω-Alkylidenediamines into Coiled Coil and Twisted Ribbon
Aggregates
Takaaki Sumiyoshi, Katsumi Nishimura, Minoru Nakano, Tetsuro Handa,
Yoshihisa Miwa, and Kiyoshi Tomioka*
Contribution from the Graduate School of Pharmaceutical Sciences, Kyoto UniVersity, Yoshida,
Sakyo-ku, Kyoto 606-8501, Japan
Received March 10, 2003; E-mail: tomioka@pharm.kyoto-u.ac.jp
Abstract: A series of 10 didodecanoylamides of R,ω-alkylidenediamines bridged by a straight carbon chain
varying in length from 0 to 9 carbons was examined as possible gelator molecules of organic liquids to
gain information on the relationships between the spacial arrangement of two amide groups in a molecule
and their effects on the microscopic structures of the gel. The structural characteristics of these amides
are parallel and antiparallel arrangements of two amide carbonyl groups, which depend on the even and
odd numbers of a bridging zigzag carbon chain. The linear alkyl chain moieties and a center carbon chain
of diamides intermolecularly interact with each other within the van der Waals contact. Two amide moieties
of an even number carbon chain diamide intermolecularly interact with each other by using two pairs of
hydrogen bonds with two other molecules in a plane, which formed ribbonlike self-complementarily
assembled aggregates. On the other hand, a diamide of an odd number carbon chain forms four independent
hydrogen bonds with four other molecules not in a plane, which assembled into woven aggregates.
Asymmetric introduction of a methyl group at the R-position of the amide groups successfully twists the
two side chain van der Waals cores of the chiral diamides in the fixed direction, giving helically twisted
ribbon and coiled coil aggregates. The helically twisted ribbon and coiled coil aggregates of these chiral
diamides were directly observed by CD, SEM, and TEM, providing a basis for the design of a sophisticated
small molecular gelator of a tailor-made shape.
Introduction
Some small organic molecules self-complementarily assemble
into microscopic structures through specific hydrogen bonding,7
Gelation by small quantities of a polymer1 has been known
for several centuries.2 Recently, many low molecular weight
compounds have been reported as effective gelators for organic
liquids and have renewed interest in the determining factors
for self-complementary assembly.3-5 The correlation of the
properties to the chemical structure of gelators has been
proposed from detailed spectroscopic and diffraction studies.6
van der Waals interaction,8 and π-π stacking,9 which are
assignable origins responsible for the gelation of organic liquids.3
Tailor-made shapes, especially helical aggregates of these
gelators, are of recent interest and are classified into helical
fibers including coiled coil, twisted ribbon, and helical ribbon.
The gelator compounds bearing R-amino acids,10 glucose,11
cyclohexanediamine,12 and vancomycin13 have been claimed to
form helical fibers, those bearing chirally branched alkyl chains
(1) Guenet, G.-M. ThermoreVersible Gelation of Polymers and Biopolymers;
Academic Press: London, 1992.
(2) (a) Flory, P. J. Faraday Discuss. Chem. Soc. 1974, 57, 7-18. (b) Tanaka,
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1997, 327-328. (c) Hanabusa, K.; Maekawa, Y.; Kimura, M.; Shirai, H.
Tetrahedron Lett. 1999, 40, 2385-2388. (d) Kimura, T.; Yamashita, T.;
Koumoto, K.; Shinkai, S. Tetrahedron Lett. 1999, 40, 6631-6634. (e)
Bhattacharya, S.; Acharya, S. N. G. Chem. Mater. 1999, 11, 3121-3132.
(f) Nakashima, T.; Kimizuka, N. AdV. Mater. 2003, 14, 1113-1116. (g)
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2263-2266. (c) Abdallah, D. J.; Weiss, R. G. AdV. Mater. 2000, 12, 1237-
1247.
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Y.; McPherson, G. L. J. Am. Chem. Soc. 1994, 116, 9464-9470. (b) Placin,
F.; Colomes, M.; Desvergne, J.-P. Tetrahedron Lett. 1997, 38, 2665-2668.
(c) Terech, P.; Allegraud, J.-J.; Garner, C. M. Langmuir 1998, 14, 3991-
3998. (d) Garner, C. M.; Terech, P.; Allegraud, J.-J.; Mistrot, B.; Nguyen,
P.; de Geyer, A.; Rivera, D. J. Chem. Soc., Faraday Trans. 1998, 94, 2173-
2179.
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B. L. Chem.-Eur. J. 1995, 9, 594-597. (b) Keller, U.; Muellen, K.; De
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J.; Melendez, R.; Geib, S. J.; Hamilton, A. D. Tetrahedron Lett. 1998, 39,
7447-7450.
(6) Fuhrhop, J. H.; Koening, J. Membranes and Molecular Assemblies: the
synkinetic approach; Royal Society of Chemistry: Cambridge, 1994.
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Abdallah, D. J.; Weiss, R. G. Chem. Mater. 1999, 11, 2907-2911. (c)
Abdallah, D. J.; Weiss, R. G. Chem. Mater. 2000, 12, 406-413.
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2001, 123, 5148-5149. (d) Ajayaghosh, A.; George, S. J.; Praveen, V.
Angew. Chem., Int. Ed. 2003, 42, 332-335.
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A R T I C L E S
Sumiyoshi et al.
on the π-π stacking cores14 form coiled coil, those bearing
tartrate, gluconate, malate,15 and gluconamide16 form twisted
ribbon, and those bearing cholesterol17 form helical ribbon
aggregates. Of these modificators, chiral acceptor/donors of
hydrogen bonds are impressive in dominant use as chiral cores,
except for, for example, the approaches of Nolte,14b Shinkai,17
and Maitra14a to helical coiled coil and ribbon aggregates by
the use of chiral aliphatic tails as a chiral modificator on a crown
ether and pyrene cores. For the sophisticated design of the
specific shape and its application to materials, however, it is
still necessary to understand the fundamental role of hydrogen
bonding and van der Waals interaction cores of gelator
molecules. Especially, it seems reasonable and important to gain
information on the relationships between the spacial arrangement
of two amide groups in a molecule and their effects on
microscopic structures. A series of didodecanoylamides of R,ω-
alkylidenediamines bridged by a straight carbon chain varying
in length from 0 to 9 carbons were examined as possible gelator
molecules. These amides self-complementarily assembled into
microscopic woven and ribbon structures through hydrogen
bonding and van der Waals interactions.18 The SEM visible
shape of the aggregate structures depends on the even and odd
numbers of the bridging carbon chain of R,ω-alkylidenedi-
amines. Further deductive logic led us to the assumption that
introduction of chirality to the van der Waals interaction core
of the diamides twists the ribbon and woven structures to the
corresponding helically twisted ribbon and coiled coil ag-
gregates. We describe herein these approaches in detail.
Figure 1. Self-complementarily assembling molecule.
Figure 2. Bridging methylene chain number-dependent parallel and
antiparallel two-amide groups and two types of assembly structures of
diamides 1.
These diamides 1 are classified into two categories with
regard to the length of the carbon chain: one is the diamide 1
bearing a bridging carbon chain of 0 or an even number (n)
(the left structure in Figure 2), and the other 1 bears a carbon
chain of an odd number (the right structure in Figure 2). The
zigzag arrangement of the carbon chain of even number directs
the two amide carbonyl groups of 1 antiparallel (the opposite
direction), while those of the carbon chain of the odd number
are parallel (the same direction). Consequently, a diamide
molecule 1 of an even number carbon chain forms two pairs of
hydrogen bonds with two other molecules in a plane. On the
other hand, 1 of an odd number carbon chain forms four
independent hydrogen bonds with four other molecules not in
a plane. Furthermore, the linear alkyl chain moieties (R1) and
a center carbon chain of diamide 1 intermolecularly interact
with each other within van der Waals contact. These analyses
predict the ribbon and woven shapes of self-complementarily
assembled structures of even and odd number diamides 1.
Design of Self-Complementarily Assembling, Small,
and Linear Diamide Molecules
The small and linear gelator molecule is constituted from three
parts of van der Waals interaction cores, of which the center
core is bridged by two hydrogen bonding cores, satisfying C2-
symmetric character for analytical simplification (Figure 1).
Each core provides intermolecular hydrogen bonding and van
der Waals interactions suitable for the self-complementary
assembly of these structures. The diamides 1 of R,ω-alkylidene-
diamines bridged by a straight carbon chain varying in length
from 0 to 9 carbons are the chemical structure corresponding
to the image shown in Figure 1 (Figure 2).
(11) (a) Friggeri, A.; Gronwald, O.; van Bommel, K. J. C.; Shinkai, S.;
Reinhoudt, D. N. J. Am. Chem. Soc. 2002, 124, 10754-10758. (b)
Kobayashi, H.; Friggeri, A.; Koumoto, K.; Amaike, M.; Shinkai, S.;
Reinhoudt, D. N. Org. Lett. 2002, 4, 1423-1426.
(12) (a) Hanabusa, K.; Yamada, M.; Kimura, M.; Shirai, H. Angew. Chem., Int.
Ed. Engl. 1996, 35, 1949-1951. (b) Jung, J. H.; Ono, Y.; Shinkai, S. Chem.-
Eur. J. 2000, 6, 4552-4556. (c) van Esch, J.; Schoonbeck, F.; de Loos,
M.; Koojiman, H.; Spek, A. L.; Kellogg, R. M.; Feringa, B. L. Chem.-Eur.
J. 1999, 5, 937-950.
Gelation by Achiral Diamides 2 and 3
The didodecanoyl amides 2 (1 of n ) 0 or even number)
and 3 (1 of n ) odd number) were prepared by acylation of
alkylidenediamines under standard conditions (Figure 3). Gel
formation of 2 and 3 with organic liquids was determined by
the method “stable to inversion of the container”.19 A mixture
of a crystalline diamide and an organic liquid in a container
was heated to a solution and was then cooled back to room
temperature. Benzene, toluene, mesitylene, pyridine, ethyl
acetate, and acetonitrile20 were suitable organic liquids in
forming opaque and reversible gels. The minimum concentration
of 2 and 3 for gelation of mesitylene ranged from 1 to over 50
(13) Xing, B.; Yu, C.-W.; Chow, K.-H.; Ho, P.-L.; Fu, D.; Xu, B. J. Am. Chem.
Soc. 2002, 124, 14846-14847.
(14) (a) Maitra, U.; Potluri, V. K.; Sangeetha, N. M.; Babu, P.; Raju, A. R.
Tetrahedron: Asymmetry 2001, 12, 477-480. (b) Engelkamp, H.; Middle-
beek, S.; Nolte, R. J. M. Science 1999, 284, 785-788.
(15) (a) Oda, R.; Huc, I.; Candau, S. J. Angew. Chem., Int. Ed. 1998, 37, 2689-
2691. (b) Oda, R.; Huc, I.; Schmutz, M.; Candau, S. J.; MacKintosh, F. C.
Nature 1999, 399, 566-569.
(16) (a) Fuhrhop, J.-H.; Schnieder, P.; Rosenberg, J.; Boekema, E. J. Am. Chem.
Soc. 1987, 109, 3387-3390. (b) Hafkamp, R. J. H.; Kokke, B. P. A.; Danke,
I. M.; Geurts, H. P. M.; Rowan, A. E.; Feiters, M. C.; Nolte, R. J. M. J.
Chem. Soc., Chem. Commun. 1997, 545-546. (c) Hafkamp, R. J. H.;
Feiters, M. C.; Nolte, R. J. M. J. Org. Chem. 1999, 64, 412-426.
(17) (a) Jung, J. H.; Kobayashi, H.; Masuda, M.; Shimizu, T.; Shinkai, S. J.
Am. Chem. Soc. 2001, 123, 8785-8789. (b) Murata, K.; Aoki, M.; Suzuki,
T.; Harada, T.; Kawabata, H.; Komori, T.; Ohseto, F.; Ueda, K.; Shinkai,
S. J. Am. Chem. Soc. 1994, 116, 6664-6676.
(19) Menger, F. M.; Caran, K. L. J. Am. Chem. Soc. 2000, 122, 11679-11691.
(20) Although gelation of ethyl acetate and acetonitrile was not clear in a smaller
container (7 mm diameter), these gelated in a bigger container (15 mm
diameter).
(18) Tomioka, K.; Sumiyoshi, T.; Narui, S.; Nagaoka, Y.; Iida, A.; Miwa, Y.;
Taga, T.; Nakano, M.; Handa, T. J. Am. Chem. Soc. 2001, 123, 11817-
11818.
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Molecular Assembly of Bis-(2S)-2-methyldodecanoylamides
A R T I C L E S
Figure 4. Self-complementarily assembling molecule with a twisted van
der Waals interaction core.
Figure 3. Achiral and chiral diamides 2-5.
Table 1. Minimum Concentration (mg/mL) of Diamides 2 (n ) 0
or Even Number) and 3 (n ) Odd Number) for Gelation of Organic
Liquid (p, Precipitation; i, Insoluble)
Figure 5. Twist of ribbon (a) and woven (b) aggregates of 2 and 3 into
twisted ribbon and coiled coil aggregates of 4 and 5.
2, 3/n
0
1
2
3
4
5
6
7
8
9
hexane
i
i
4
1
benzenea
20
14
5
3
25
14
p
8
3
40 13 50
29 10 33
4
1
>100
mesitylenea
methyl oleate 21 20
soy bean oil
AcOEt
MeCN
58
20 22
16 14
52
48 24
19 34 23 28 22
19 16 28 15 27 22 24 17
37 25 15 19 53 15 34 15
27
5
a Minimum concentration of 2 and 3 quoted from ref 18.
Figure 6. Bisecting conformations A and ent-A of achiral diamide 3
(m ) 1) and B of chiral diamide 5.
mg/mL (Table 1). Although hexane was a liquid that did not
afford a gel, long aliphatic oils bearing alkyl chains, for example,
soy bean oil (a mixture of triglycerides of fatty acids) and methyl
oleate, were successfully converted to gel.
The gelation power of 2 and 3 is not linearly correlated with
the length of the carbon chain (n in 1). The even and odd
numbers of the carbon chain of 2 and 3 are decisive for the
gelation. For gelation of mesitylene by 2, the longer the carbon
chain is, the poorer the efficiency is. In contrast, 3 is generally
highly capable of gelating mesitylene with less than 10 mg. A
similar tendency was observed for gelation of long aliphatic
chain esters and other liquids; that is, 3 (n ) odd number) is
superior to 2.
The high and low efficiency of 2 and 3 in gelation was
predictable from the SEM pictures of mesitylene gels.18 The
self-assembled thin and flat ribbonlike structure was observed
for xerogel (mesitylene) of 2 (m ) 3, n ) 6 for 1) in the SEM
photograph as had been predicted in the design stage of the
study (Figure 2). On the contrary, the fine woven structure of
the xerogel of 3 (m ) 4, n ) 9 for 1) was observed. It is also
important to note that the crystal structure of 3 (m ) 1, n ) 3
for 1) indicates self-assembly of one molecule with four other
molecules through hydrogen bonds as had been predicted in
the design stage of the study (Figure 2).18 These characteristics
of the aggregate structures are nicely correlated to the finer
network by 3 rather than by 2.
to twist the side chain arms into the twisted ribbon and helical
coiled coil aggregate structures by the introduction of chirality
on the van der Waals interaction moieties when the hydrogen
bonding cores are preserved as shown in Figure 4. Consequently,
the ribbon and woven structures are capable of being twisted
to the corresponding twisted ribbon and coiled coil aggregate
structures depending on the parallel and antiparallel arrange-
ments (Figure 5).
Because the X-ray crystallographic structure of achiral 3
(m ) 1, n ) 3 for 1) shows a zigzag arrangement of all carbon
chain, except for the bisecting conformations A and ent-A
around two amide groups (Figure 6),18 replacement of R2 ) H
in 2 and 3 with a methyl group (R2 ) CH3) renders molecular
chirality to the diamides and fixes the conformation to B.22 On
the basis of this idea, we prepared and examined a series of 10
C2-symmetric chiral diamides 4 and 5 bridged by a straight
carbon chain varying in length from 0 to 9 carbons (n in 1) in
which two methyl groups were asymmetrically introduced at
the R-positions of amides 2 and 3 (Figure 3).
Synthesis of Chiral Diamides 4 and 5
The nine chiral diamides 4 and 5 (m ) 1-4, n ) 0, 2-9 for
1) were synthesized in high yields by acylation of the diamines
with (2S)-2-methyldodecanoyl chloride23 in ether-water in the
presence of sodium bicarbonate. The diamide 5 (m ) 0, n ) 1
for 1) was prepared by treatment of diaminomethane with the
acid chloride in pyridine-THF. The optically pure chiral acid
Design of Chiral Diamides for Helical Shape Aggregate
The design of a tailor-made helical shape stems from the
above findings that antiparallel (n ) even number) and parallel
(n ) odd number) arrangements of two amide groups, CONH,
of diamides of R,ω-alkylidenediamines 2 and 3 (R ) H) direct
a specific shape formation of the ribbon and woven aggregates
in gelation of organic liquids (Figures 1 and 2).21 It is possible
(21) Shimizu, T.; Masuda, M. J. Am. Chem. Soc. 1997, 119, 2812-2818.
(22) A bisecting conformation B seems not to be dominant and is equilibrated
to the eclipsed cis-confomation, in which molecular chirality is still
maintained.
(23) Morigaki, K.; Dallavalle, S.; Walde, P.; Colonna, S.; Luisi, P. L. J. Am.
Chem. Soc. 1997, 119, 292-301.
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A R T I C L E S
Sumiyoshi et al.
Table 2. Minimum Concentration (mg/mL) of Chiral Diamides 4
and 5 for Gelation of Organic Liquid (p, Precipitation)
4, 5/n
0
1
2
3
4
5
6
7
8
9
hexane
benzene
mesitylene
methyl oleate 15 16
AcOEt
MeCN
13
14 18
15 18
p
3
6
3
7
6
5
p
p
p
14 14 12
7
62
4
10 18
10 15
9
7
11 15 88
11 16 92
32 19 13 16 11 13 14
40 40 20 30 11 21
17 20 19 16 12 14 12
14 15
18
p
8
Figure 8. Melting points (°C) of diamides 2-5.
Figure 7. Minimum concentration (mg/mL) of diamides 2-5 for gelation
Figure 9. Gel-to-sol and sol-to-gel phase transition temperatures of the
mesitylene gels of diamides 2-5 (DSC, °C, 50 mg/mL). (No gelation was
observed for 5 (n ) 3).)
of benzene.
chloride was successfully prepared in quantity by an asymmetric
methylation reaction according to the Evans chiral oxazolidinone
procedure.24
The gel-to-sol and sol-to-gel phase transition temperatures
of the mesitylene gels of 4 and 5, determined by differential
scanning calorimetry (DSC), were lower than those of achiral
diamides 2 and 3 of the corresponding number (n) of the carbon
chain by a factor of 22-40 °C (Figure 9). However, the valley
and top of the gel-to-sol and sol-to-gel phase transition
temperatures were alternately repeated according to the odd and
even numbers of the carbon chain. The high and low melting
points and gel-to-sol and sol-to-gel phase transition temperatures
of 4 and 5 are attributable to the parallel and antiparallel
arrangements of the two amide groups and subsequent structural
differences in the self-complementary assembly as had been
observed with 2 and 3.18 The relatively lower transition points
of 4 and 5 than those of 2 and 3 are due to the unfavorable
steric repulsion by the introduction of the extra methyl groups.
Gelation of Organic Liquids by Chiral Diamides 4 and 5
In addition to liquids such as benzene, mesitylene, ethyl
acetate, and acetonitrile, hexane that was not gelated by achiral
2 and 3 was also a suitable organic liquid in forming opaque
gels by the chiral diamides 4 and 5. The gel was stable and
reversible upon repeated heating and cooling. The minimum
concentration of 4 and 5 for gelation of mesitylene ranged from
3 to 18 mg/mL, except for that it was 92 mg/mL for 5 with
n ) 9 (m ) 4) (Table 2). Although the tendency of the gelation
was equally averaged even in which chiral diamides and liquids
were used, the striking difference from achiral diamides is the
higher efficiency of chiral 4 than the corresponding achiral 2.
Introduction of only two extra methyl groups improved the
efficiency of gelation by 4.
Small-Angle X-ray Scattering of Mesitylene Gels of
The gelating behavior of chiral diamides is not linearly
correlated with the length and the odd and even numbers (n) of
the carbon chain (Figure 7). Unlike the achiral diamides 2 and
3, of which odd and even numbers of the carbon chain are
decisive for the gelation, there is little difference in the ability
of 4 and 5 based on the odd and even numbers, gelating at a
similar concentration, except for 5 (n ) 9).
Diamides 2-5
Bragg reflections were unambiguously observed in the small-
angle X-ray scattering (SAXS) of the mesitylene gels of 2-5.
1
1
1
1
These peaks had a periodicity of /1, /2, /3, and /4 that is
attributed to a lamellar structure, indicating regularly arranged
molecular layers. The d values, which correspond to the
interlayer distance, of the mesitylene gels showed the similar
and alternately repeated top and valley according to the odd
and even numbers of the carbon chain (Figure 10). The top and
valley are reverse to those of the melting points and phase
transition temperatures, indicating that efficiency in both gelation
and molecular self-complementary assembly are directly pro-
portionate to the interlayer distance. It is also interesting to find
that d values of chiral diamides 4 and 5 are shorter than the
achiral 2 and 3 of the corresponding number of the carbon chain
(n), suggesting the winded-molecular structure of 4 and 5 by
the extra methyl group. The helical structure of the aggregates
seems responsible for such smaller d values and molecule
winding.
Thermotropic Behavior of Chiral Diamides
The influence of the extra methyl groups was also observed
in other properties. Melting points of 4 and 5 were lower than
those of the corresponding achiral 2 and 3 by a factor of 12-
36 °C, probably due to the unfavorable intermolecular steric
repulsion by a methyl group (Figure 8). However, the valley
and top of the melting points of achiral and chiral diamides
2-5 were alternately repeated according to the odd and even
numbers of the carbon chain, suggesting the same type of the
molecular packing structure.
(24) Gage, J. R.; Evans, D. A. Org. Synth. 1990, 68, 83-91.
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Molecular Assembly of Bis-(2S)-2-methyldodecanoylamides
A R T I C L E S
Figure 10. The d values of the mesitylene gels of diamides 2-5. No Bragg
reflection was observed for 5 (n )3).
Figure 11. The CD spectra of (a) the hexane gel of 4 (m ) 4, n ) 8, 3.3
mg/mL, 25 °C) and of (b) the hexane gel of 5 (m ) 3, n ) 7, 8.6 mg/mL,
25 °C).
Figure 12. SEM pictures of the mesitylene xerogel of 4 (m ) 4, n ) 8)
((a) twisted ribbon) and 5 (m ) 3, n ) 7) ((b, c) coiled coil). The pictures
(a) and (b) are presented in the same scale. The picture (c) is an 8-fold
expanded picture of (b).
Circular Dichroism of Hexane Gels of Diamides 4 and 5
The CD spectrum (a in Figure 11) of the hexane gel of 4
(m ) 4, n ) 8) at 25 °C exhibited a strong negative peak at
210 nm. The spectrum b of the hexane gel of 5 (m ) 3, n ) 7)
exhibited a positive peak around 210-220 nm and a negative
peak at 201 nm, and a λθ)0 value appeared at 207 nm. These
strong peaks disappeared upon heating and in the trifluoroeth-
anol solution of 4 and 5 (n ) 7, 8) at 25 °C. These results
indicate that the peaks were attributable to the helical aggregates,
not to the chirality of the molecule,12a and that chiral diamides
4 and 5 self-assembled into different structured aggregates,
respectively. The CD spectrum of the hexane gel of 4 (m ) 4,
n ) 8) is similar to that of the twisted ribbon aggregates
observed by Shimizu,25 indicating that 4 (m ) 4, n ) 8) self-
assembled into twisted ribbon aggregates as we designed. The
peaks of hexane gel of 5 (m ) 3, n ) 7) are assigned to the
exciton coupling bands. The positive sign for the first Cotton
effect indicated that the dipole moments are oriented in a
clockwise direction as has been described by Shinkai12b in the
right-handed helical coiled coil aggregates, suggesting the right-
handed coiled coil aggregates of 5 (m ) 3, n ) 7).
Scanning Electron Micrograph (SEM) and
Transmission Electron Micrograph (TEM)
The twisted ribbon aggregates (a in Figure 12) with 2000-
3000 nm widths of 4 (m ) 4, n ) 8) and coiled coil aggregates
(b and c) with 200-300 nm widths of 5 (m ) 3, n ) 7) were
observed by the SEM pictures of the mesitylene xerogels. The
coiled coil aggregates of 5 (m ) 3, n ) 7) are composed of
helical fibers with 50-80 nm widths. The twisted ribbon
aggregates (a in Figure 13) with 2000-3000 nm widths of 4
(m ) 4, n ) 8) and coiled coil aggregates (b and c) with 200-
300 nm widths of 5 (m ) 3, n ) 7) were also clearly observed
Figure 13. TEM pictures of the mesitylene xerogel of 4 (m ) 4, n ) 8)
((a) twisted ribbon) and 5 (m ) 3, n ) 7) ((b, c) coiled coil). The pictures
(a) and (b) are presented in the same scale. The picture (c) is a 3-fold
expanded picture of (b).
by the TEM pictures of the mesitylene xerogels. The twisted
ribbon and coiled coil aggregates have the right-handed helical
structures. The ribbon and woven aggregates of achiral 2 and 3
were twisted by asymmetrically introducing two methyl groups
on van der Waals interaction cores to the twisted ribbon and
coiled coil aggregates of chiral 4 and 5, respectively.18
(25) Jung, J. H.; John, G.; Yoshida, K.; Shimizu, T. J. Am. Chem. Soc. 2002,
124, 10674-10675.
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J. AM. CHEM. SOC. VOL. 125, NO. 40, 2003 12141

A R T I C L E S
Sumiyoshi et al.
Conclusion
in a plane, which forms woven aggregates. Asymmetric
introduction of a methyl group at the R-position of two amide
groups successfully twists the two side chain van der Waals
cores in the fixed direction, giving helically twisted ribbon and
coiled coil aggregates. The shape-controlled self-complementary
assembly of the diamides opens a new way for the design of a
sophisticated small molecular gelator of a tailor-made shape.
The characteristics of didodecanoyl amides of R,ω-alkyli-
denediamines are parallel and antiparallel arrangements of two
amide carbonyl groups, which are dependent on the even and
odd numbers of a bridging zigzag carbon chain. The linear alkyl
chain moieties and a center carbon chain of the diamides
intermolecularly interact with each other within van der Waals
contact. Two amide moieties of an even number carbon chain
diamide interact with each other by using two pairs of hydrogen
bonds with two other molecules in a plane, which forms
ribbonlike self-complementarily assembled aggregates. On the
other hand, a diamide of an odd number carbon chain forms
four independent hydrogen bonds with four other molecules not
Supporting Information Available: Preparation and analyti-
cal data of 4 and 5, and experimental procedures (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
JA035085T
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12142 J. AM. CHEM. SOC. VOL. 125, NO. 40, 2003