Self-assembly of 6-O- and 6′-O-hexadecylsucroses mixture under aqueous conditions

Article abstract of DOI:10.1016/j.carres.2010.10.003

In this paper, we report the self-assembly of 6-O- and 6′-O- hexadecylsucroses mixture under aqueous conditions. The mixture was synthesized by a five-step sequence from sucrose. The SEM image of a sample prepared by drying a dispersion of the mixture in

Full text of DOI:10.1016/j.carres.2010.10.003

Carbohydrate Research 345 (2010) 2718–2722
Contents lists available at ScienceDirect
Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
Note
Self-assembly of 6-O- and 60-O-hexadecylsucroses mixture under
aqueous conditions
⇑
Manami Kanemaru, Shin-ya Kuwahara, Kazuya Yamamoto, Yoshiro Kaneko, Jun-ichi Kadokawa
Department of Chemistry, Biotechnology, and Chemical Engineering, Graduate School of Science and Engineering, Kagoshima University, 1-21-40 Korimoto,
Kagoshima 890-0065, Japan
a r t i c l e i n f o
a b s t r a c t
In this paper, we report the self-assembly of 6-O- and 60-O-hexadecylsucroses mixture under aqueous
conditions. The mixture was synthesized by a five-step sequence from sucrose. The SEM image of a sam-
ple prepared by drying a dispersion of the mixture in water showed nanoparticles with the diameter of
ꢀ50 nm and aggregates that were formed by further assembly of them. The XRD measurement of the
sample exhibited the diffraction pattern assignable to face-centered cubic (FCC) structure and the diam-
eter of a sphere, which took part in the FCC structure, was calculated to be 5.1 nm. This value was rela-
tively close to that observed in the DLS measurement of a dispersion of the mixture in water and
estimated for a spherical micelle based on the molecular sizes of the two sucrose ethers. On the basis
of the above findings, the following self-assembly process of the mixture under aqueous conditions
was proposed. The mixture formed the spherical micelles with the diameter of ꢀ5–7 nm in water. The
micelles regularly organized according to the FCC structure during the drying process from the aqueous
dispersion to construct the nanoparticles with the diameter of ꢀ50 nm. Several numbers of the nanopar-
ticles further assembled to form the aggregates.
Article history:
Received 6 August 2010
Received in revised form 1 October 2010
Accepted 4 October 2010
Available online 27 October 2010
Keywords:
6-O- and 60-O-hexadecylsucroses
Amphiphilic
Self-assembly
Nanoparticle
Face-centered cubic
Spherical micelle
Ó 2010 Elsevier Ltd. All rights reserved.
Amphiphilic molecules, so-called amphiphiles, possess both
hydrophilic and hydrophobic moieties. In aqueous media, the
amphiphiles form self-assembling aggregates with various con-
trolled morphologies, such as spherical micelles, cylindrical
micelles, spherical vesicles, planer bilayers, and tubes.1 The amphi-
philes containing carbohydrates as a hydrophilic part such as gly-
colipids exhibit important in vivo functions in living systems.2
Synthetic carbohydrate-based amphiphiles have been known to
show a large variety of self-assembling morphologies.1,3 For exam-
ple, amphiphiles containing a glucose residue as the hydrophilic
part have formed morphologically-controlled nanotubes.4
On the other hand, synthetic carbohydrate-based amphiphiles
have been used as an emulsifier in food industries.5 One of the
most effective food additives practically used are sucrose fatty acid
esters, which contain a sucrose residue as the hydrophilic part
and long-alkyl fatty acid moieties as the hydrophobic part.6 The
self-assembly properties of sucrose fatty acid esters are changed
depending on the lengths and types of fatty acid chains.7 For
example, a typical decrease of the CMCs was observed for longer
chains and the effect of an unsaturation was also seen. In the case
of palmitic esters, a significant change in the size of the aggregates
was observed depending on the position, whereas no effect was
observed for shorter chains.8 On the basis of the above viewpoints,
we have recently studied the synthesis and self-assembly proper-
ties of new sucrose-based amphiphiles having molecular
structures different from the sucrose fatty acid esters. These inves-
tigations were carried out to reveal fundamental aspects of the
new amphiphiles for future practical applications. In this paper,
we report the self-assembly properties of the 6-O- and 60-O-hex-
adecylsucroses mixture (6-C16-sucrose and 60-C16-sucrose,
respectively) under aqueous conditions, which are new sucrose-
based amphiphiles having the structure of a sucrose residue con-
nected with one C16 alkyl chain via an ether linkage at the 6- or
60-position. Self-assembly studies using sucrose ethers have been
much less reported than those using sucrose esters. For example,
the effect of molecular shape on the liquid crystal properties of
mono-O-(2-hydroxydodecyl)sucroses, which were prepared by
the reaction of sucrose with 1,2-epoxydodecane under alkaline
conditions, has been reported so far.9
The synthesis of a mixture of the two sucrose monoethers was
carried out by five reaction steps from sucrose as outlined in
Scheme 1. The process involved triphenylmethylation (tritylation)
at the 6- or 60-position, benzylation of other free hydroxy groups,
detritylation, etherification at the 6- or 60-position, and debenzyla-
tion.10–12 An overall yield of the final products from sucrose was
10.9%. The structures of the products were determined by the 1H
NMR analysis in CD3OD as shown in Figure 1 to be a 6-C16- and
60-C16-sucroses mixture. The signal assignments are as follows: d
0.80 (t, 3H, CH3, J = 4.6 Hz), 1.30–1.33 (m, 26H, –(CH2)13–CH3),
⇑
Corresponding author. Fax: +81 99 285 3253.
E-mail address: kadokawa@eng.kagoshima-u.ac.jp (J. Kadokawa).
0008-6215/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2010.10.003

M. Kanemaru et al. / Carbohydrate Research 345 (2010) 2718–2722
2719
OTr
OTr
OH
O
OBn
O
HO
BnO
BnO
O
O
HO
HO
OH
BnO
OH
OBn
O
OH
O
OBn
OTr
OH
O
TrCl
OH
OBn
NaH
DMF
BnBr, TBAB
HO
HO
O
HO
OH
pyridine
OH
O
OBn
OH
OH
OBn
OH
O
O
BnO
BnO
HO
HO
O
O
BnO
HO
OH
OBn
OH
O
O
OTr
OBn
OH
O(CH2)15CH3
O
OBn
O
OBn
BnO
BnO
O
BnO
BnO
O
BnO
OBn
BnO
OBn
O
OBn
OBn
O
OBn
conc. HCl
CH2Cl2-acetic acid
OBn
NaH
DMF
CH3 (CH2)15 Br
, TBAB
OBn
OBn
OBn
OBn
O
O
BnO
BnO
BnO
O
O
BnO
BnO
BnO
OBn
HO
OBn
O
O
OH
O(CH2)15CH3
OBn
OBn
O(CH2)15CH3
O
OH
Bu
TBAB =Bu N+ Bu
Bu
Ph
C
Ph
O
HO
Bn =
CH2
Tr =
Ph
HO
OH
OH
O
OH
H2, Pd-C
butanol-methanol-water
Br
6-C16-sucrose
OH
OH
O
HO
HO
O
HO
OH
O
O(CH2)15CH3
OH
6'-C16-sucrose
Scheme 1. Synthesis of 6-O- and 60-O-hexadecylsucroses mixture.
1
Figure 1. H NMR spectrum of 6-O- and 60-O-hexadecylsucroses mixture (CD3OD).
1.59 (m, 2H, –O–CH2–CH2–), 3.21–4.09 (m, 15H, H-
10,2,3,30,4,40,5,50,6,60, –O–CH2–CH2–), 5.38, 5.41 (2d, 1H, H-1,
J = 2.3 and 2.3 Hz). The mono-etherificated structures of the prod-
ucts were confirmed by the integrated ratio of the signals due to
CH3 of the hexadecyl group to the signals due to H-1 protons of
the glucose residues, which was 3:1. Furthermore, the presence

2720
M. Kanemaru et al. / Carbohydrate Research 345 (2010) 2718–2722
of the hexadecyl group at the 6- or 60-position in the products was
confirmed by an acetylation experiment using acetic anhydride
and pyridine. The 1H NMR spectrum (CDCl3) of the acetylated
derivatives showed that chemical shift of the signals assignable
to the H-6 or H-60 proton was not changed compared with the
spectrum before acetylation, whereas the signals due to the pro-
tons at other positions (besides H-1) were shifted to lower mag-
netic field. This data indicated that 6- or 60-position was
etherificated in the aforementioned products, and accordingly,
was not acetylated. From the integrated ratio of two H1 signals
of the glucose residues, furthermore, the molar ratio of 6-ether to
60-ether in the products was calculated to be 0.625:0.325. Although
separation of these two isomers was attempted by common exper-
imental techniques such as column chromatography, it was not
successful. Therefore, the resulting products were subjected to
the following investigations on the self-assembly under aqueous
conditions.
Figure 2 shows the SEM images of a sample on an aluminum
plate, which was prepared by drying a dispersion of the mixture
in water (1.0 ꢁ 10ꢂ5 mol/L). Nanoparticles with the diameter of
ꢀ50 nm and aggregates, which are formed by further assembly of
the nanoparticles, can be seen. The SEM result suggested that the
6-C16- and 60-C16-sucroses mixture regularly organized during
the drying process from dispersion in water, which we supposed
was caused by controlled assembly of the mixture. To study the
self-assembly process of the mixture in detail, therefore, powder
X-ray diffraction (XRD) and dynamic light-scattering (DLS) mea-
surements were conducted. Figure 3 shows the XRD pattern of
the sample, which has been prepared by the same procedure as
that for the SEM measurement. The diffraction peaks at 2h values
of 2.10, 2.48, 4.02, 4.81, 7.19, and 9.56° are assignable to the
(1 1 1), (2 0 0), (3 1 1/2 2 2), (4 0 0), (6 0 0), and (8 0 0) Bragg reflec-
tions of face-centered cubic (FCC) structure.13 From the XRD pat-
tern, the diameter of a sphere, which took part in the FCC
structure, was calculated to be 5.1 nm. The DLS measurement of
a dispersion of the 6-C16- and 60-C16-sucroses mixture in water
(1.0 ꢁ 10ꢂ5 mol/L) in Figure 4 shows the formation of nanoaggre-
gates with a monomodal profile, and the number average diameter
and polydispersity index were calculated to be 7.1 nm and 0.37,
respectively. The diameter value was relatively close to that of
the sphere in the FCC structure established from the XRD result.
The slight difference in diameter between XRD and DLS is probably
attributable to the sample conditions (wet and dry) in these mea-
surements. To evaluate the primary assembled structure of the
mixture in water, the molecular sizes of 6-C-16- and 60-C16-suc-
roses were calculated using the MM2 method in the CS Chem 3D
program package. Consequently, the molecular sizes in length
including the sucrose and hexadecyl chain moieties for both
Figure 3. XRD pattern of the sample prepared from a dispersion of 6-O- and 60-O-
hexadecylsucroses mixture.
Figure 4. DLS profile of 6-O- and 60-O-hexadecylsucroses mixture in water.
6-C16- and 60-C16-sucroses were calculated as approximately
3.0 nm. Accordingly, when the mixture formed spherical micelles
having the outer hydrophilic sucrose residues and the inner
Figure 2. SEM images of the sample prepared from a dispersion of 6-O- and 60-O-hexadecylsucroses mixture.

M. Kanemaru et al. / Carbohydrate Research 345 (2010) 2718–2722
2721
hydrophobic hexadecyl chains, the diameter of the sphere could be
estimated to be ꢀ6.0 nm based on the above calculation. This value
was in good agreement with that from the XRD and DLS
measurements.
chromatography on silica gel (chloroform–methanol = 20:1) to
give a mixture of 6-O- and 60-O-tritylsucroses (2.19 g, 3.73. mmol)
1
in 39.2% yield. H NMR (CD3OD) d 3.05–4.00 (m, 13H, H-10,
2,3,30,4,40,5,50,6,60), 5.36, 5.43 (2d, 1H, H-1, J = 4.1 and 4.1 Hz),
7.07–7.21 (m, 15H, aromatics).
On the basis of the above analytical results and calculations, the
following self-assembly process of the 6-C16- and 60-C16-sucroses
mixture under aqueous conditions is proposed (Fig. 5). The mixture
first forms spherical micelles with the diameter of ꢀ5–7 nm in
water. The micelles regularly organize according to the FCC struc-
ture during drying process to construct the nanoparticles with the
diameter of ꢀ50 nm.14 Several numbers of nanoparticles further
assemble to form the aggregates as seen in the SEM image (Fig. 2).
In conclusion, this study investigated the characteristics of the
self-assembly of a mixture of 6-O- and 60-O-hexadecylsucroes
under aqueous conditions. The mixture was synthesized in the
overall yield of 10.9% via five-step sequence from sucrose. On the
basis of the analytical results and calculations, the following self-
assembly process of the mixture under aqueous condition was
proposed. The mixture formed spherical micelles with the diame-
ter of ꢀ5–7 nm in water, which then regularly organized according
to the FCC structure during drying process from the aqueous dis-
persion to construct the nanoparticles with the diameter of
ꢀ50 nm. Several numbers of the nanoparticles further assembled
to form the aggregates. This study revealed fundamental aspects
of sucrose ethers as new amphiphiles for future practical applica-
tions. The separation of 6-O- and 60-O-hexadecylsucroses and their
own self-assembly properties are now in progress.
Under argon, to a dispersion of NaH (2.68 g, 44.6 mmol) in DMF
(25.0 mL) was added a solution of a mixture of 6-O- and 60-O-trityl-
sucroses (1.50 g, 2.55 mmol) at room temperature and the mixture
was stirred at that temperature for 30 min. After a solution of tet-
rabutylammonium bromide (small amount) in DMF and benzyl
bromide (3.20 mL, 26.8 mmol) were added to the mixture, the
reaction was conducted at room temperature for 24 h. The reaction
was stopped by addition of methanol to the reaction mixture. After
the resulting mixture was concentrated and diluted with chloro-
form, the solution was washed with water, dried over anhydrous
Na2SO4, filtered, and evaporated. The residue was recrystallized
from methanol–acetone (1:0.075) to give a mixture of 10,2,3,30,4,
4,60-hepta-O-benzyl-6-O-trityl- and 10,2,3,30,4,4,6-hepta-O-benzyl-
60-O-tritylsucroses (2.88 g, 2.36 mmol) in 92.6% yield. 1H NMR
(CDCl3) d 2.88–4.13 (m, 13H, H-10,2,3,30,4,40,5,50,6,60), 4.26–4.87
(m, 14H, CH2-Ph), 5.89, 5.96 (2d, 1H, H-1, J = 3.6 and 3.6 Hz),
6.82–7.51 (m, 50H, aromatics).
To a solution of the above products (5.67 g, 4.66 mmol) in ice-
cold dichloromethane–acetic acid (2:1, 22.8 mL) was added drop-
wise a small amount of concd HCl. After the reaction was carried
out at that temperature for 1.5 h, the reaction mixture was diluted
with dichloromethane, neutralized with saturated aq, NaHCO3
washed with water, dried over anhydrous Na2SO4, filtered, and
evaporated. The residue was subjected to column chromatography
on silica gel (ethyl acetate–hexane 1:10) to give a mixture of
10,2,3,30,4,4,60-hepta-O-benzyl- and 10,2,3,30,4,4,6-hepta-O-benzyl-
sucroses (2.67 g, 2.74 mmol) in 58.9% yield. 1H NMR (CDCl3) d
3.21–4.15 (m, 13H, H-10,2,3,30,4,40,5,50,6,60), 4.24–4.90 (m, 14H,
CH2-Ph), 5.53, 5.77 (2d, 1H, H-1, J = 3.7 and 3.7 Hz), 7.09–7.35 (m,
35H, aromatics).
1. Experimental
1.1. Materials
All reagents were available commercially and used without fur-
ther purification. DMF was purified by distillation over calcium hy-
dride. Other solvents were used as received.
Under argon, to a dispersion of NaH (0.95 g, 15.9 mmol) in DMF
(30.0 mL) was added a solution of the above products (5.14 g,
5.29 mmol) in DMF (50.0 mL) and the mixture was stirred at that
temperature for 50 min. After a solution of tetrabutylammonium
bromide (small amount) in DMF and 1-bromohexadecane
(4.85 mL, 15.9 mmol) were added to the mixture, the reaction
was conducted at 80 °C for 24 h. The reaction was stopped by the
addition of methanol to the reaction mixture. After the resulting
mixture was concentrated and diluted with chloroform, the
solution was washed with water, dried over anhydrous Na2SO4,
1.2. Synthesis of 6-O- and 60-O-hexadecylsucroses mixture10-12
Under argon, to a dispersion of sucrose (3.42 g, 10.0 mmol) in
pyridine (20.0 mL) was added triphenylmethyl chloride (4.18 g,
15.0 mmol) at room temperature and the mixture was stirred for
20 h at that temperature. After the reaction mixture was concen-
trated and diluted with chloroform, the solution was successively
washed with 10% HCl aq and water, dried over anhydrous Na2SO4,
filtered, and evaporated. The residue was subjected to column
Figure 5. Plausible self-assembly process of 6-O- and 60-O-hexadecylsucroses mixture under aqueous condition mixture.

2722
M. Kanemaru et al. / Carbohydrate Research 345 (2010) 2718–2722
filtered, and evaporated. The residue was subjected to chromatog-
raphy on silica gel (ethyl acetate–hexane 1:50) to give a mixture of
10,2,3,30,4,4,60-hepta-O-benzyl-6-O-hexadecyl- and 10,2,3,30,4,4,6-
hepta-O-benzyl-60-O-hexadecylsucroses (4.88 g, 4.07 mmol) in
77.0%. 1H NMR (DMSO-d6 containing a small amount of D2O) d
0.83 (t, 3H, CH3, J = 6.8 Hz), 1.22–1.25 (m, 26H, –(CH2)13–CH3),
1.54 (m, 2H, –O–CH2–CH2–), 3.14–4.12 (m, 15H, H-
10,2,3,30,4,40,5,50,6,60, –O–CH2–CH2–), 4.40–4.88 (m, 14H, CH2-Ph),
5.61, 5.64 (2d, 1H, H-1, J = 3.2 and 3.7 Hz), 7.22–7.34 (m, 35H,
aromatics).
scope. XRD measurements were conducted using a PANalytical
X’Pert Pro MPD with Ni-filtered CuK radiation (k = 0.15418 nm).
DLS measurements were conducted using FPAR-1000 (Otsuka Elec-
a
tronics Co., Ltd).
References
1. Shimizu, T.; Masuda, M.; Minakawa, H. Chem. Rev. 2005, 105, 1401–1443.
2. (a) Corti, M.; Cantù, L.; Brocca, P.; Favero, E. D. Curr. Opin. Colloid Interface Sci.
2007, 12, 148–154; (b) Kitamoto, D.; Morita, T.; Fukuoka, T.; Konishi, M.; Imura,
T. Curr. Opin. Colloid Interface Sci. 2009, 14, 315–328.
To a solution of the above products (0.21 g, 0.18 mmol) in a
mixed solvent of butanol, methanol, and water (10:1:0.25) was
added 10% palladium on carbon (0.04 g) and the mixture was
stirred at 38 °C for 168 h under a hydrogen atmosphere. After
the reaction mixture was filtered and the filtrate was evaporated,
the residue was subjected to column chromatography on silica
gel (chloroform–methanol 10:1) to give a mixture of 6-O- and 60-
O-hexadecylsucroses (0.066 g, 0.116 mmol) in 66.1% yield. 1H
NMR (CD3OD) d 0.80 (t, 3H, CH3, J = 4.6 Hz), d 1.30–1.33 (m, 26H,
–(CH2)13–CH3), 1.59 (m, 2H, –O–CH2–CH2–), 3.21–4.09 (m, 15H,
H-10,2,3, 30,4,40,5,50,6,60, –O–CH2–CH2–), 5.38, 5.41 (2d, 1H, H-1,
J = 2.3 and 2.3 Hz).
3. (a) Shimizu, T. Macromol. Rapid Commun. 2002, 23, 311–331; (b) Fuhrhop, J.-H.;
Wang, T. Chem. Rev. 2004, 104, 2901–2937.
4. (a) John, G.; Masuda, M.; Okada, Y.; Yase, K.; Shimizu, T. Adv. Mater. 2001, 13,
715–718; (b) John, G.; Jung, J. H.; Minamikawa, H.; Yoshida, K.; Shimizu, T.
Chem. Eur. J. 2002, 8, 5494–5500; (c) Jung, J. H.; John, G.; Yoshida, K.;
Shimizu, T. J. Am. Chem. Soc. 2002, 124, 10674–10675; (d) Kamiya, S.;
Minamikawa, H.; Jung, J. H.; Yang, B.; Masuda, M.; Shimizu, T. Langmuir 2005,
21, 743–750.
5. Kralova, I.; Sjoblom, J. J. Dispersion Sci. Technol. 2009, 30, 1363–1383.
6. (a) Hodate, Y.; Ueno, S.; Yano, J.; Katsuragi, T.; Tezuka, Y.; Tagawa, T.;
Yoshimoto, N.; Sato, K. Colloids Surf., A 1997, 128, 217–224; (b) Awad, T.; Sato,
K. J. Am. Oil Chem. Soc. 2001, 78, 837–842; (c) Katsuragi, T.; Kaneko, N.; Sato, K.
Colloids Surf., B 2001, 20, 229–237; (d) Awad, T.; Sato, K. Colloids Surf., B 2002,
25, 45–53.
7. (a) Molinier, V.; Kouwer, P. J. J.; Fitremann, J.; Bouchu, A.; Mackenzie, G.;
Queneau, Y.; Goodby, J. W. Chem. Eur. J. 2006, 12, 3547–3557; (b) Goodby, J. W.;
Görtz, V.; Cowling, S. J.; Mackenzie, G.; Martin, P.; Plusquellec, D.; Benvegnu, T.;
Boullanger, P.; Lafont, D.; Queneau, Y.; Chambert, S.; Fitremann, J. Chem. Soc.
Rev. 2007, 36, 1971–2035.
1.3. Preparation of samples for SEM and XRD measurements
8. Queneau, Y.; Chambert, S.; Besset, C.; Cheaib, R. Carbohydr. Res. 2008, 343,
1999–2009.
9. Queneau, Y.; Gagnaire, J.; West, J. J.; Mackenzie, G.; Goodby, J. W. J. Mater. Chem.
2001, 11, 2839–2844.
A dispersion of the 6- and 60-C16-sucroses mixture (1.0 ꢁ 10
ꢂ5 mol/L) was placed on an appropriate plate for each measure-
ment and it was left standing under ambient atmosphere until
water was evaporated. Then, the resulting solid sample was sub-
jected to the measurements.
10. Otake, T. Bull. Chem. Soc. Jpn. 1970, 43, 3199–3205.
11. Mach, M.; Jarosz, S.; Listkowski, A. J. Carbohydr. Chem. 2001, 20, 485–493.
12. (a) Sofian, A. S.; Lee, C. K. J. Carbohydr. Chem. 2001, 20, 191–205; (b) Sofian, A. S.
M.; Lee, C. K. J. Carbohydr. Chem. 2003, 22, 185–206.
13. (a) El-Safty, S. A.; Hanaoka, T. Chem. Mater. 2004, 16, 384–400; (b) Tang, J.;
Zhou, X.; Zhao, D.; Lu, G. Q.; Zou, J.; Yu, C. J. Am. Chem. Soc. 2007, 129, 9044–
9048; (c) Liu, X.; Huang, R.; Zhu, J. Chem. Mater. 2008, 20, 192–197.
14. Sathe, B. R.; Shinde, D. B.; Pillai, V. K. J. Phys. Chem. C 2009, 113, 9616–
9622.
1.4. Measurements
1H NMR spectra were recorded on a JEOL ECX400 spectrometer.
SEM images were obtained using Hitachi SU-70 electron micro-