Synthesis and mesomorphism study of novel carbohydrate-derived liquid crystals containing glucosyl and chenodiolyl residues

Article abstract of DOI:10.1246/cl.2007.938

Synthesis of carbohydrate-derived liquid crystals by assembling D-(+)-glucose with mesogenic units containing chenodiolyl moieties and a flexible spacer is reported for first time and the thermal properties and liquid-crystalline behavior were carefully s

Full text of DOI:10.1246/cl.2007.938

938
Chemistry Letters Vol.36, No.7 (2007)
Synthesis and Mesomorphism Study of Novel Carbohydrate-derived
Liquid Crystals Containing Glucosyl and Chenodiolyl Residues
Wenqiang Xiao,1 Baoyan Zhang,ꢀ1 and Yuehua Cong2
1The Research Centre for Molecular Science and Engineering, Northeastern University,
Shenyang 110004, P. R. China
2School of Chemistry, Cardiff University, Cardiff, U.K.
(Received April 10, 2007; CL-070384)
Synthesis of carbohydrate-derived liquid crystals by
pounds GCnDB were shown in Scheme 1. The compound R
was transformed into its acid chloride and reacted with cheno-
deoxycholic acid to give compound I. Chenodeoxycholic acid
derivative I was then transformed into acid chloride and reacted
with anhydrous D-(+)-glucose in chloroform and pyridine under
reflux for 36 h to give the crude product. The crude product was
purified and recrystallized from ethanol. The detailed synthetic
approach is described in supplementary material,8 and the de-
sired representative compound GC4DB was carefully identified
assembling D-(+)-glucose with mesogenic units containing
chenodiolyl moieties and a flexible spacer is reported for first
time and the thermal properties and liquid-crystalline behavior
were carefully studied.
Carbohydrates are a new yet very promising source for liq-
uid crystals synthesis. Not only because they could form various
types mesomorphous materials, also because they are the very
common core structure of glycolipids, which are important
biological macromolecules exhibiting liquid-crystalline behav-
ior.1–5 Sugar systems containing cholesteryl residues6,7 which
show perfect liquid crystal textures, have been reported previ-
ously. Chenodeoxycholic acid has a similar molecular structure
to cholesterol. In marked contrast to the extensive studies of
carbohydrate-derived liquid crystals containing cholesteryl de-
rivatives, carbohydrate-derived liquid crystals containing cheno-
deoxycholic acid were far less investigated. In order to gain
more understanding and explore the possibility to apply cheno-
deoxycholic acid and carbohydrate compounds to form novel
liquid-crystalline materials, we designed and synthesized a ser-
ies of liquid crystals using glucose as the chiral core structure,
mesogenic units containing chenodiolyl moieties. Those meso-
genic moieties are introduced to the five hydroxy groups of
glucose by direct esterfication. The obtained liquid crystals
are termed as GCnDB, (Glucose-chenodiol-n-diacid-biphenyl,
n denotes the number of methylene in diacid).
1
by H NMR, 13C NMR, element analysis, and IR.9
The FT-IR of representative GC4DB showed characteristic
bands at 1748 and 1729 cmꢁ1 which correspond to two C=O
stretching representing Ar–OOCR, Ar–COOR, respectively,
1605 cmꢁ1 due to aromatic C=C stretching, and 1254 cmꢁ1
due to C–O–C stretching. The 1H NMR spectra of GC4DB
showed a series of multiple peaks at ꢀ 0.93–4.01, 7.14–8.15,
1.31, 1.58–4.09, and 4.11–6.66 corresponding to chenodiolyl,
aromatic, methyl, methylene, and glucosyl groups, respectively.
The concrete 13C NMR spectra of glucose derivative GC4DB
showed six peaks at ꢀ 62.41, 69.10, 69.23, 70.66, 72.32, 91.21,
these peaks indicated the existence of chiral core structure
glucose; the typical five carbonyl carbon peaks at ꢀ 174.12,
172.75, 172.42, 172.22, 171.72 were the characteristic peaks
to indicate the perfect substitution on glucose. So the target
compound GC4DB was obtained.
The thermal properties of GCnDB series were studied by
differential scanning calorimetry (DSC) and summarized in
Table 1. The representative DSC thermogram of GC4DB was
shown in Figure 1 (Netzsch DSC 204, equipped with a liquid
nitrogen cooling system. Scan rate: 10 ꢂC/min). The DSC curves
of GC4DB indicated that it did not crystallize during cooling
from the isotropic melt. Furthermore, it was quite stable and
Chemical structures and synthetic route of the target com-
OH
O
SOCl2/DMF
Chenodiol
R
R1O
CHCl3/Pyridine
OR1
OR1
OR1
(I)
DSC/(mW/mg)
0.6
exo
0.5
0.4
0.3
0.2
OR1
OR1
OR1
O
O
OR1
O
O
O
D-glucose
SOCl2/DMF
O
(A)
O
0.1
O
O
O
CHCl3/Pyridine
0.0
O
-0.1
(B)
-0.2
R1O
R1O
R1O
R1O
-0.3
-0.4
GCnDB
O
C
C2H5O
O
O
OOC(CH2) COOH
R:
n
50
100
150
200
250
Temperature/°C
O
C
C H O
OOC(CH2) CO
R1:
2
5
n = 0, 4, 8
n
Figure 1. DSC thermograms of liquid crystal GC4DB. A: first
heating; B: first cooling.
Scheme 1. Synthetic route of GCnDB series.
Copyright Ó 2007 The Chemical Society of Japan

Chemistry Letters Vol.36, No.7 (2007)
939
tion.8 No peak appeared in SAXS and broad peaks occurred
Table 1. Phase-transition temperatures and specific rotation
of GCnDB
ꢂ
˚
at 2ꢂ ꢄ 20 (d ꢄ 4:5 A) in WAXD. The broad peaks indicated
20
that the GCnDB series were almost amorphous.
GCnDB
(n)
½ꢁꢃ589
Tm(/ꢂC)a Ti(/ꢂC)a ꢀT(/ꢂC)a Ta(/ꢂC)a
In conclusion, a series of novel glucose-derived liquid crys-
tals GCnDB series were designed and synthesized. They demon-
strate wide mesogenic region and high thermal stabilities, which
could lead to potential applications. These compounds do not
crystallize on cooling. The length of spacer group plays an
important role to the SROT and melting point. The fingerprint
textures were observed, which were typical characteristic of
chiral nematic LC phase.
(c 0.34, in CHCl3)
0
4
8
203.3
175.3
170.1
235.0
237.0
234.0
31.7
61.7
63.9
252.0
255.0
251.0
ꢁ10:3
ꢁ23:9
ꢁ49:5
aTm: Temperature of melting point. Ti: Isotropic transition temperature.
Ta: Temperature at which 5% weight loss occurred. ꢀT ¼ Ti ꢁ Tm:
20
Mesogenic region. ½ꢁꢃ589: Specific rotation.
The authors are grateful to National Natural Science
Fundamental Committee of China and HI-Tech Research and
development program (863) of China for financial support of
this work.
References and Notes
(a)
(b)
(c)
1
D. F. Ewing, M. Glew, J. W. Goodby, J. A. Haley, S. M.
Kelly, B. U. Komanschek, P. Letellier, G. Mackenzie,
G. H. Mehl, J. Mater. Chem. 1998, 8, 871.
Figure 2. Optical textures of GCnDB series. (a) GC0DB, on
heating to 205 ꢂC. (b) GC4DB, on heating to 190 ꢂC. (c)
GC8DB, on heating to 200 ꢂC.
2
3
4
5
6
7
8
D. F. Ewing, J. W. Goodby, J. A. Haley, S. M. Kelly, P.
Letellier, G. Mackenzie, Liq. Cryst. 1997, 23, 759.
H. Kuttenreich, H. J. Hinz, R. D. Koynova, B. G. Tenchov,
Chem. Phys. Lipids 1993, 66, 55.
R. N. A. H. Lewis, D. A. Mannock, R. N. McElhaney,
P. T. T. Wong, H. H. Mantsch, Biochemistry 1990, 29, 8933.
K. Yoshimoto, K. Tahara, S. Suzuki, K. Sasaki, Y.
Nishikawa, Y. Tsuda, Chem. Pharm. Bull. 1979, 27, 2661.
S. Seo, Y. Tomita, K. Tori, Y. Yoshimura, J. Am. Chem. Soc.
1978, 100, 3331.
P. Allevi, M. Anastasia, P. Ciuffreda, A. Fiecchi, A. Scala,
Chem. Phys. Lipids 1990, 53, 219.
Supporting Information is available: The synthetic route of
GC4DB; the Synthesis and experimental details; the molecu-
lar structure of GC4DB and the X-ray diffraction patterns of
quenched GCnDB series.
no sharp melting peak was observed when it was reheated. This
phenomenon is often observed with a small molecular weight
polymer, but GC4DB is not a polymer. A similar phenomenon
is observed in GCnDB series. The observations indicate that
the crystallization of these molecules is hindered owing to steric
effect.10
As summarized in Table 1, the GCnDB series all showed
the enantiotropic behavior, the wide mesogenic region with their
high clearing points. On heating, the melting points of GCnDB
series decreased from 203.3, 175.3, to 170.1 ꢂC with GCnDB
from GC0DB to GC8DB. This is the result of increased molecu-
lar flexibility with the longer spacer group (n increased from 0 to
8). The results thermal gravimetric analysis (TGA) show that the
temperatures when 5% weight loss occurred (Ta) are all higher
than 250 ꢂC, which reveals the GCnDB series have relative high
thermal stabilities.
1
9
Selected physical data of GC4DB are as follows: H NMR
(300 MHz; CDCl3; Me4Si) ꢀ 1.31 (m, 30H, –CH3), 4.09
(m, 20H, –CH2–O–), 7.14 (d, 20H, J ¼ 5 Hz, –O–Ar–
COO–), 8.15 (d, 20H, J ¼ 1 Hz, –O–Ar–COO–), 7.16–7.64
(m, 80H, –Ar–Ar–), 1.58–2.36 (m, 80H, –OOC–(CH2)4–
COO–), 0.93–4.01 (m, 185H, H–chenodiolyl), 4.11 (d, 2H,
J ¼ 0:67 Hz, CH2–glucosyl), 4.60–6.66 (m, 5H, CH–gluco-
syl); 13C NMR (300 MHz; CDCl3; Me4Si) ꢀ 14.61
(10 ꢅ q), 63.76 (10 ꢅ t), 114.24, 132.27 (40 ꢅ d), 121.82,
163.33, 164.89 (30 ꢅ s), 122.08, 128.08 (80 ꢅ d), 137.89,
150.09, 150.56 (40 ꢅ s), 24.17, 33.80, 33.96 (40 ꢅ d),
172.21, 173.21 (20 ꢅ s), 13.53, 13.36, 19.31 (15 ꢅ q),
20.77, 24.86, 28.03, 29.63, 31.23, 31.24, 31.57, 32.46,
35.81, 40.22 (50 ꢅ t), 34.75, 37.03, 42.64, 45.36, 49.11,
56.10, 71.35, 73.91 (40 ꢅ d), 35.02, 42.47, 174.12, 172.75,
172.42, 172.22, 171.72 (15 ꢅ s), 62.41 (t), 69.10, 69.23,
70.66, 72.32, 91.21 (5 ꢅ d). IR (KBr) ꢃ 2936, 2849, 1748,
1729, 1605, 1254 cmꢁ1. Anal. Calcd for C396H442O81: C,
73.20; H, 19.94%. Found: C, 72.90; H, 19.71%.
Furthermore, the specific rotations (SROT: ½ꢁꢃ58920, a
Perkin-Elmer Polarimeter model 341, temperature: 20 ꢂC, wave-
length: 589 nm) of GCnDB series were measured and summariz-
ed in Table 1. There is a remarkable increase of SROT of
20
GCnDB series from ½ꢁꢃ589 ꢁ 10:3 (c 0.34, in CHCl3) to
20
½ꢁꢃ589 ꢁ 49:5 (c 0.34, in CHCl3) with the flexible spacer chain
extends (n increased from 0 to 8), which is due to the longer
distance between the biphenyl unit and chenodiolyl. The more
freedom the chain has, the less compact the molecular pack is.
The liquid crystal textures of GCnDB series were studied
by polarizing optical microscopy (POM). The representative op-
tical textures of GCnDB series were shown in Figure 2. Typical
chiral nematic fingerprint textures11 were observed in mesogenic
region of GCnDB series and the length of flexible spacer group
did not affect the mesogenic type and texture of GCnDB series.
The quenched samples of GCnDB series were identified by
wide angle X-ray diffraction (WAXD) and small angle X-ray
scattering (SAXS), (XRD measurements are performed using
a nickel-filtered Cu Kꢁ radiation with a DMAX-3A Rigaku
powder diffractometer), and the X-ray diffraction patterns of
quenched GCnDB series were shown in Supporting Informa-
10 D. S. Yao, B. Y. Zhang, Y. H. Li, W. Q. Xiao, Tetrahedron
Lett. 2004, 45, 8953.
11 I. Dierking, in Textures of Liquid Crystals, ed. by I. Dierking,
Wiley–VCH Verlag GmbH & Co. KGaA, Weinheim, 2003,
Chap. 5, pp. 51–70.
Published on the web (Advance View) June 27, 2007; doi:10.1246/cl.2007.938