Characterization of some mesogenic alkyl 1-thioglycosides

Article abstract of DOI:10.1139/v02-157

A series of dodecyl 1-thio-β-D-glycosides has been synthesized and characterized (DSC, NMR, CP MAS, X-ray diffraction) as possible new marking materials with liquid-crystalline properties. These compounds undergo solid to liquid crystal phase transitions at various temperatures, which depend on the nature of the carbohydrate part of the structure. Their liquid-crystalline phases show extreme shear thinning behaviour.

Full text of DOI:10.1139/v02-157

1162
Characte rization of s ome me s oge nic alkyl
1-thioglycos ide s
B. He nris s a t, G.K. Ha m e r, M.G. Ta ylor, a nd R.H. Ma rc he s s a ult
Abstract: A series of dodecyl 1-thio-β -D-glycosides has been synthesized and characterized (DSC, NMR, CP MAS, X-
ray diffraction) as possible new marking materials with liquid-crystalline properties. These compounds undergo solid to
liquid crystal phase transitions at various temperatures, which depend on the nature of the carbohydrate part of the
structure. Their liquid-crystalline phases show extreme shear thinning behaviour.
Key words: liquid crystal, powder X-ray diffraction, phase transition, thioglycoside, solid-state NMR, marking material
Résumé : On a effectué la synthèse et on a caractérisé (DSC, RMN, CP MAS, diffraction des rayons X) une série de
1-thio-β -D-glycosides de dodécyle, de nouveaux marqueurs potentiels ayant des propriétés de cristaux liquides. Ces
composés subissent des transitions de solide à cristal liquide à diverses températures qui dépendent de la nature de la
portion hydrate de carbone de la structure. Leurs phases cristal liquide présentent un comportement extrême de
fluidisation par cisaillement.
Mots clés : cristal liquide, diffraction de rayons X par des poudres, transition de phase, thioglycoside, RMN à l’état
solide, marqueur.
[Traduit par la Rédaction] Henrissat et al. 1165
Introduc tion
62.5 MHz, respectively, on a Bruker AM 250 spectrometer.
Chemical shifts are given with respect to external tetra-
methylsilane. Differential scanning calorimetry was carried
out with a PerkinElmer DSC-2C calorimeter on 12 mg sam-
ples sealed in aluminum capsules. The heating and cooling
rates were 20°C min–1. Powder X-ray diagrams were ob-
tained in a Warhus flat-film camera by using Ni-filtered
Cu Kα radiation on the sample loaded in 0.5-mm capillary
tubes.
Alkyl glycosides have been shown to be thermotropic
mesogens when the alkyl chain ranges from heptyl upwards
(1). Because of the great variety of possible carbohydrates,
alkyl chain length, type of linkage and its position of attach-
ment to the sugar molecule, it has been predicted that several
million carbohydrate liquid crystals could be obtained (2). A
few of these amphiphilic carbohydrates have found biochem-
ical applications as non-ionic detergents for membrane pro-
tein extraction (3). As part of a research program concerned
with the evaluation of their liquid-crystalline phase as poten-
tial materials with advanced properties, we report here
synthesis and the characterization of some dodecyl 1-
thioglycosides.
Solid-state 13C NMR
High resolution 13C NMR spectra were acquired at
50.3 MHz with a Bruker CXP 200 instrument. Cross-
polarization (CP) was performed with Hartmann–Hahn
matched radio-frequency fields of about 60 Hz. Spectra were
collected with a 1 ms contact time and 6 s recycle delay over
a sweep width of 10 kHz. Magic-angle spinning (MAS) at
about 2.5 kHz was achieved in a probe from Doty Scientific.
A small chip of linear polyethylene (NBS Standard Refer-
ence Material 1475) was added to the samples to provide a
chemical shift reference at 32.9 ppm (4) with respect to
tetramethylsilane. The spectrum of the liquid-crystalline
phase was not recorded because cross-polarization was inef-
fective due to high molecular mobility. Furthermore, the
Expe rim e nta l
General methods
Solutions were evaporated below 45°C under diminished
pressure. TLC was performed on silica gel F254 (Aldrich),
eluent was ethyl acetate – hexane (1:2, v/v) and detection
was done with 5% sulfuric acid in ethanol followed by heat-
1
ing. The H and 13C NMR spectra were recorded at 250 and
Received 4 December 2001. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 4 September 2002.
Dedicated to the memory of Professor Raymond U. Lemieux.
B. Henrissat,1 G.K. Hamer,2 M.G. Taylor and R.H. Marchessault.3,4 Xerox Research Centre of Canada, 2660 Speakman Drive,
Mississauga, ON L5K 2L1, Canada.
1Present address: AFMB-CNRS, 31 Chemin Joseph Aiguier, 13402, Marseille CEDEX 20, France.
2Present address: Unit 1 2280 South Milway, Mississauga, ON L5L 2P4, Canada.
3Present address: Department of Chemistry, McGill University, 3420 University St., Montreal, QC H3A 2A7, Canada.
4Corresponding author (e-mail: Robert.marchessault@mcgill.ca).
Can. J. Chem. 80: 1162–1165 (2002)
DOI: 10.1139/V02-157
© 2002 NRC Canada

Henrissat et al.
1163
1
Table 1. H NMR data for ring protons of 1-thio-β-D-glycosides 4, 9, 14, and 15.
Compound
Chemical shifts (ppm) and coupling constants (Hz)
H-1
H-2
H-3
H-4
H-5
H-6a
H-6b
4
4.48
d
5.23
t
5.09
t
5.03
t
3.71
m
4.25
dd
4.14
dd
(J1,2 = 10.0)
(J2,3 = 10.0)
(J3,4 = 10.0)
(J4,5 = 10.0)
(J5,6a = 5.0)
(J6a,6b = 12.0)
(J5,6b = 2.5)
9
4.48
5.24
5.05
5.43
3.93
d
t
dd
dd
dt
(J1,2 = 10.0)
(J2,3 = 10.0)
(J3,4 = 4.0)
(J4,5 = 1.0)
(J5,6a = 8.0)
H-2
H-3
H-4
H-5a
H-5b
H-1
14
15
4.51
d
(J1,2 = 10.0)
5.28
t
(J2,3 = 10.0)
4.97
t
(J3,4 = 10.0)
4.95
m
(J4,5a = 10.0)
4.23
dd
(J5a,5b = 13.0)
3.38
dd
(J4,5b = 6.0)
4.24
3.04
3.18
3.34
3.78
3.08
d
t
t
m
dd
dd
(J1,2 = 10.0)
(J2,3 = 10.0)
(J3,4 = 10.0)
(J4,5a = 10.0)
(J5a,5b = 12.0)
(J4,5b = 6.0)
Notes: For each compound: 1st line, chemical shift; 2nd line, multiplicity; 3rd line, coupling constant (in parenthesis). d= doublet; t = triplet; dd =
doublet of doublets; m = multiplet.
sample flowed under the rapid spinning conditions, leading
to imbalance in the rotor and to magic angle spinning insta-
bilities.
scope equipped with a heating stage. Upon heating, all sam-
ples undergo melting to a birefringent liquid characteristic of
a liquid-crystalline phase. When further heating is applied,
they change to isotropic fluids and loose their birefringence.
Upon cooling, the reverse succession of events is observed,
i.e., the appearance of a liquid-crystalline phase and then, at
lower temperatures, crystallization to a solid. The melting
behavior of 5, 10, and 15 was examined by differential scan-
ning calorimetry. A typical thermogram is shown in Fig. 1.
The transition temperatures of the three dodecyl 1-thio-
glycosides 5, 10, and 15 are reported in Table 2. It is inter-
esting to note that the crystal – liquid crystal transitions
(K2-LC) occur at significantly higher temperatures on heat-
ing than on cooling. Also, while 1-thio-glycosides 10 and 15
both exhibit crystal-to-crystal transitions (K1-K2), glycoside
5 does not. It is possible that such a transition also occurs
for the latter compound, but at a temperature lower than
ambient.
Syntheses
Syntheses of the 2-thiopseudourea derivatives 2, 7, and 12
from the corresponding glycosyl bromides 1, 6, and 11 were
done as previously described (5). S-alkylation was adapted
from a classical procedure (6). In a typical experiment, the
2-thiopseudourea derivative (40 g) and potassium carbonate
(70 g) in water (60 mL) are stirred with dichloromethane at
room temperature, the extract is concentrated, and the resi-
due is alkylated with an appropriate alkyl halide (75 mL).
De-O-acetylation was effected with sodium methoxide in
methanol.
Re s ults a nd dis c us s ion
A solid-state 13C NMR study was done with dodecyl 1-
thio-β-D-xylopyranoside 15 because the two transitions of
Tetra-O-acetyl-α -D-glucopyranosyl bromide (7) 1 was
converted into 2-S-(tetra-O-acetyl-β-D-glucopyranosyl)-2-
thiopseudourea hydrobromide 2 according to standard proce-
dures (5). 2,3,4,6-Tetra-O-acetyl-1-thio-β-D-glucopyranose 3
was generated from 2 and was S-alkylated in situ with 1-
bromododecane in the presence of potassium carbonate (6).
Treatment of the resulting dodecyl 2,3,4,6-tetra-O-acetyl-1-
thio-β-D-glucopyranoside 4 with a catalytic amount of so-
dium methoxide gave the expected dodecyl 1-thio-β-D-
glucopyranoside 5. An identical synthetic route was fol-
lowed for the synthesis of dodecyl 1-thio-β-D-galacto- 10
and -xylo-pyranoside 15 starting, respectively, from tetra-O-
acetyl-α -D-galactopyranosyl bromide (8) 6 and tri-O-acetyl-
α -D-xylopyranosyl bromide (9) 11.
1H NMR (e.g., Table 1) has been used to characterize the
stereochemistry of the synthetic intermediates 4, 9, and 14
as well as of the final products 5, 10, and 15. The anomeric
β configuration is unambiguously confirmed by the large
coupling constants JH-1,H-2 of about 10 Hz (Table 1).
The three dodecyl 1-thioglycosides 5, 10, and 15 have
been examined under polarized light with an optical micro-
© 2002 NRC Canada

1164
Can. J. Chem. Vol. 80, 2002
Fig. 1. Differential scanning calorimetry thermogram of dodecyl
1-thio-β-D-xylopyranoside 15. The top and bottom curves corre-
spond to the heating and cooling cycles, respectively. (Endo) and
(Exo) indicate endo- and exo-thermal transitions, respectively.
Fig. 2. Solid-state 13C NMR spectra of dodecyl 1-thio-β-D-
xylopyranoside 15 at 25°C (K1 form) (A) and 90°C (K2 form)
(B).
in this crystal form. It is interesting to note that the X-ray
crystal structure of octyl 1-thio-β-D-xylopyranoside (a lower
homologue of compound 15 but with a shorter alkyl chain)
shows a disordered structure where the carbohydrate moiety
has two orientations with equal occupancy (10). The solid-
state NMR results here show that a disordered structure
could also be valid for dodecyl 1-thio-β-D-xylopyranoside
15. A mixture of crystal polymorphs could also explain the
peak multiplicity observed for 15; however, in such a case
the differential scanning calorimetry thermogram would
show a more complex melting profile. The spectrum of the
higher temperature form (K2), although of lower definition,
also shows peak multiplicity, indicating at least two non-
equivalent environments in the crystal (Fig. 2B).
Table 2. Transition temperatures derived from differential scan-
ning calorimetry.
Transitions (°C)a
Compound
Conditions
K1↔K2
K2↔LC
LC↔ISO
5
60
—
115
50–60
105
88
Heating
Cooling
Heating
Cooling
Heating
Cooling
—
—
88
—
80
—
164
158
171
171
126
121
10
15
aK1↔K2: crystal-to-crystal transition; K2↔LC: crystal-to-liquid crystal
transition (melting point); LC↔ISO: liquid crystal-to-isotropic liquid
transition (clearing point).
The cooling behavior of the 1-thio-glycoside 15 was also
investigated by solid-state NMR. Although it was not possi-
ble to record the spectrum of the material in the liquid crys-
tal form, it was, however, heated in the spectrometer for one
hour at 110°C and then cooled to 27°C. The differential
scanning calorimetry data (Fig. 1 and Table 2) indicated that
on cooling from the liquid-crystalline phase, 15 underwent
only one transition to the intermediate crystal form (K2).
Figure 3A shows the spectrum of the sugar-ring carbons ob-
tained immediately after cooling the material. This spectrum
clearly corresponds to the K2 form as seen by comparison
with the spectrum obtained at 90°C (Fig. 3B). The sample
was allowed to equilibrate at room temperature for 24 h be-
fore another spectrum was acquired at 27°C. In this case
(Fig. 3C), it is seen that the material has returned to the K1
form by comparison with the original room temperature
spectrum (Fig. 3D). It is interesting to note that the same
number of lines is observed as in the original spectrum
(Fig. 2A), but that there are differences in the relative inten-
sities. These intensity variations may originate from a non-
isotropic orientation of the crystals during the thermal transi-
tions, which occurred under high-speed magic angle spinning
conditions in the magnetic field of the NMR spectrometer.
Powder X-ray diffraction diagrams of 15 were recorded to
characterize its crystal-to-crystal transition at 80°C and to
further identify the crystalline form obtained after standing
24 h at room temperature. Table 3 lists the main d spacings
interest (K-K2 and K2-LC) occur at temperatures (80 and
105°C, respectively) compatible with the heating stage of
our spectrometer. Figures 2A and 2B show the solid-state
spectra recorded at 25 and 90°C, i.e., under and above the
K1-K2 transition. In both forms, there are indications of
multiple resonance for individual chemically equivalent car-
bons. This effect is more pronounced in the spectrum of the
K1 form, where obvious splittings are observed for many
resonances, especially for the terminal methyl group at
15 ppm and for the sugar C-1 carbon at 90 ppm. Specific
resonance assignments are difficult since the peak positions
change dramatically in the two forms. The peaks in the 87–
95 ppm region can, however, be assigned with confidence to
the C-1 carbon of the sugar ring. By analogy with the solu-
tion NMR spectrum, the remaining peaks can probably be
assigned in order of decreasing chemical shift: C-3, C-2,
C-4, C-5.
In the K1 form, the resonance assigned to C-1 of com-
pound 15 clearly consists of four lines between 88 and
95 ppm with relative intensities of about 2:2:1:1. A similar
situation is noted for the peaks at 77 and 79 ppm, each of
which has a shoulder. Application of resolution enhancement
shows four lines in this region with relative intensities of
about 1:2:1:2. These observations indicate that there are four
magnetically non-equivalent environments for the sugar ring
© 2002 NRC Canada

Henrissat et al.
1165
Table 3. X-ray d spacings (Å) observed for dodecyl 1-thio-β-D-
Fig. 3. Solid-state 13C NMR spectra of the carbohydrate part of
dodecyl 1-thio-β-D-xylopyranoside 15 after different heat treat-
ments. (A) Spectrum obtained at 27°C immediately after 1 h of
treatment at 110°C; (B) spectrum of the K2 form obtained at
90°C; (C) same as (A) but after 24 h at room temperature; (D)
spectrum of the K1 form (never heated).
xylopranoside 15.
Conditionsa
A
B
C
12.70
7.35
6.54
4.77
4.02
15.60
7.68
5.43
4.60
4.36
4.20
4.10
12.65
7.33
6.56
4.75
4.00
a(A) sample room temperature; (B) same as (A) but after 2 h at 90°C;
(C) same as (B) but after 24 h at room temperature.
line-packing model, for liquid-crystalline alkyl 1-glycosides,
which can be applied to the compounds in this study, is a
hydrogen-bonded layer of carbohydrate moieties with the
alkyl chains pointing outwards in parallel arrangement (2).
The latter are the first to melt, while the hydrogen-bonded
layers resist the thermal motion up to a higher temperature.
Jeffrey (2) predicted a staggering potential for easily avail-
able liquid-crystalline compounds from carbohydrate mole-
cules.
Ac knowle dgm e nt
Dr. Arthur Perlin kindly reviewed the manuscript and pro-
vided helpful comments.
Re fe re nc e s
measured for compound 15 at room temperature (A),
immediately after heating two hours at 90°C (B), and 24 h
later (C). One clearly observes different d spacings after
heating above the transition temperature. After 24 h standing
at room temperature, the material returns to its low tempera-
ture polymorph.
1. G.A. Jeffrey and S. Bhattacharjee. Carbohydr. Res. 115, 53
(1983).
2. G.A. Jeffrey. Acc. Chem. Res. 19, 168 (1986).
3. For example see: C. Baron and T.E. Thompson. Biochim.
Biophys. Acta, 283, 276 (1975); S.L. Wagner and R.D. Gray.
Biochemistry, 24, 3809 (1985); J. Cordoba, M.D. Reboiras,
and M.N. Jones. Int. J. Biol. Macromol. 10, 270 (1988).
4. D.L. VanderHart. J. Chem. Phys. 84, 1196 (1986).
5. D. Horton. Methods Carbohydr. Chem. 2, 433 (1963).
6. M. Cerny and J. Pacak. Chem. Listy, 52, 2090 (1958).
7. R. U. Lemieux. Methods Carbohydr. Chem. 2, 221 (1963).
8. J. Conchie and G.A. Levy. Methods Carbohydr. Chem. 2, 335
(1963).
9. F. Weygand. Methods Carbohydr. Chem. 1, 182 (1962).
10. S. Bhattacharjee and G.A. Jeffrey. Mol. Cryst. Liq. Cryst. 101,
247 (1983).
11. W.M. Schwarz, R.H. Marchessault, L. Alexandru, and B.
Henrissat. U.S. Patent 5 006 170 (1991).
Conc lus ions
This work covers part of an extensive program at Xerox
Corporation on marking materials. The subject herein is de-
scribed as hot-melt inks suitable for ink jet printing. A set of
examples in a United States patent (11) makes use of the re-
search described herein. The carbohydrate chemistry leading
to synthesis of these liquid-crystalline materials is outlined
schematically in the above referenced patent and their char-
acterization was inspired by published data. However, while
this work was in progress a related study by van Doren et al.
(12) appeared, which reminded us of how Jeffrey (2) pio-
neered the field of carbohydrate mesogens. His basic crystal-
12. H.A. van Doren, R. van der Geerst, R.H. Kellogg, and H.
Wynberg. Carbohyd. Res. 194, 71 (1989).
© 2002 NRC Canada