Hexadecyl-β-D-glucopyranoside: A liquid crystal with surfactant properties for stabilization of microemulsions

Article abstract of DOI:10.1080/15421406.2015.1047280

Lyotropic liquid crystals (LLC) having amphiphilic properties are promising materials as co-surfactants in emulsion formulations. A carbohydrate lyotropic liquid crystal, hexadecyl-β-D-glucopyranoside, was synthesized by linking D-glucose to cetyl alcohol via acetylated glucoside and its ability to stabilize microemulsions was investigated. The synthesized compound was characterized by using Nuclear Magnetic Resonance Spectroscopy (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). Both acetylated and deacetylated compounds were found to exhibit thermotropic and lyotropic liquid crystal behavior. The critical micelle concentration (CMC) value of 1.53 × 10^-5mol dm^-3 obtained for hexadecyl-β-D-glucopyranoside from both UV-visible spectroscopic and turbidity methods suggests its non-ionic surfactant properties. Calculated HLB value of 8.86 indicates that it is suitable for making self-emulsifying oils and water in oil (W/O) emulsions. By introducing optimum amount of 0.05 wt% of newly synthesized hexadecyl-β-D-glucopyranoside as a co-surfactant, macro emulsions formulated with olive oil, water and non-ionic lipophilic surfactant sorbitan monostearate (Span 80) was successfully converted into microemulsions.

Full text of DOI:10.1080/15421406.2015.1047280

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Hexadecyl-β-D-Glucopyranoside: A Liquid
Crystal with Surfactant Properties for
Stabilization of Microemulsions
a
b
E. P. N. Premarathne , D. N. Karunaratne & A. D. L. Chandani
b
Perera
a
Postgraduate Institute of Science, University of Peradeniya,
Peradeniya, Sri Lanka
b
Department of Chemistry, Faculty of Science, University of
Peradeniya, Peradeniya, Sri Lanka
Published online: 06 Jul 2015.
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To cite this article: E. P. N. Premarathne, D. N. Karunaratne & A. D. L. Chandani Perera
2015) Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal with Surfactant Properties for
Stabilization of Microemulsions, Molecular Crystals and Liquid Crystals, 613:1, 23-38, DOI:
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Mol. Cryst. Liq. Cryst., Vol. 613: pp. 23–38, 2015
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2015.1047280
Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
with Surfactant Properties for Stabilization
of Microemulsions
1
2
E. P. N. PREMARATHNE, D. N. KARUNARATNE,
2,*
AND A. D. L. CHANDANI PERERA
1Postgraduate Institute of Science, University of Peradeniya, Peradeniya, Sri
Lanka
2
Department of Chemistry, Faculty of Science, University of Peradeniya,
Peradeniya, Sri Lanka
Lyotropic liquid crystals (LLC) having amphiphilic properties are promising materials
as co-surfactants in emulsion formulations. A carbohydrate lyotropic liquid crystal,
hexadecyl-β-D-glucopyranoside, was synthesized by linking D-glucose to cetyl alcohol
via acetylated glucoside and its ability to stabilize microemulsions was investigated. The
synthesized compound was characterized by using Nuclear Magnetic Resonance Spec-
troscopy (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). Both acetylated
and deacetylated compounds were found to exhibit thermotropic and lyotropic liquid
−
5
crystal behavior. The critical micelle concentration (CMC) value of 1.53 × 10 mol
−3
dm obtained for hexadecyl-β-D-glucopyranoside from both UV-visible spectroscopic
and turbidity methods suggests its non-ionic surfactant properties. Calculated HLB
value of 8.86 indicates that it is suitable for making self-emulsifying oils and water in
oil (W/O) emulsions. By introducing optimum amount of 0.05 wt% of newly synthesized
hexadecyl-β-D-glucopyranoside as a co-surfactant, macro emulsions formulated with
olive oil, water and non-ionic lipophilic surfactant sorbitan monostearate (Span 80)
was successfully converted into microemulsions.
Introduction
Currently, “sugar-based surfactants” such as alkyl (poly) glycosides and sucrose fatty acid
esters are being manufactured, [1] and play important roles in the surfactant & detergent
industry. The industrial interest of these surfactants lie in the fact that they can be synthe-
sized from renewable resources, for example glucose from starch and fatty alcohol from
vegetable oils. In addition to the functionality and environmental compatibility, glycolipid
bio-surfactants are directly produced by microbial processes from renewable resources.
Thus, they have a great potential as “environmentally advanced surfactants” as well as
sugar-based surfactants [2]. The selection of a surfactant should be based on its application
because the solubility of the surfactant within the system affects its performance. The HLB
(Hydrophilic Lipophilic Balance) value, the relationship between the hydrophilic portion
∗
Address correspondence to Chandani Perera, Department of Chemistry, Faculty of Science,
University of Peradeniya, Peradeniya, Sri Lanka. E-mail: chandanip2000@yahoo.com
Color versions of one or more of the figures in the article can be found online at
www.tandfonline.com/gmcl.
[755]/23

24/[756]
E. P. N. Premarathne et al.
and the lipophilic portion of the surfactant is an indicator for the prediction of solubility
of non-ionic surfactants. Thus, the behavior of the surfactant can be expressed by the HLB
value. Surfactants with higher HLB values form oil in water emulsions (O/W) because they
are more likely to dissolve in water. Emulsifying agents with lower HLB values are suitable
for water in oil emulsions (W/O) [3–6]. The HLB value for non-ionic surfactant can be
calculated as follows.
ꢀ
ꢁ
Molecular weight of water loving portion
Total molecular weight of the surfactant
HLB value =
(1)
5
Most surfactant materials show liquid crystalline properties.
Microemulsion systems are defined as thermodynamically stable systems which con-
tain water and oil microstructures due to existence of surfactant film at the oil water interface
[7]. Depending on the dispersed phase, microemulsions can be categorized as W/O (Water
in oil) and O/W (Oil in water) emulsions. Basic components in a microemulsion system
are oil, water, emulsifying agent (surfactant) and more frequently co-surfactant which can
be a long chain alcohol, fatty acid, glycolipids etc. [6].
Micellar solution is the simplest form of self-assembled system. It is a single phase,
homogeneous and amphiphilic system. Spontaneous organization of amphiphiles is quite
interesting because they inherently consist of both polar and nonpolar characteristics.
Continuous addition of amphiphiles into the aqueous solution leads to formation of micelles
at a specific concentration in the system. This specific concentration is called “Critical
Micelle Concentration” (CMC) [4]. According to Gibbs adsorption isotherms when the
concentration of the amphiphiles is increased in the region before the CMC point, the
surface tension of the solution is decreased. Even if the concentration of the amphiphiles is
increased the surface tension of the solution remained constant in the region after the CMC
point [5]. Iodine complex based method and turbidity method were carried out to observe
the CMC value of synthesized glycolipid [3].
The aim of this research is to investigate a carbohydrate lyotropic liquid crystal having
surfactant properties and stabilize its ability to form microemulsions and stabilize unstable
macro emulsions. The influence of different polar and non-polar solvent systems on the
self-assembly of hexadecyl-β-D-glucopyranoside was extensively studied by observing
liquid crystalline textures. Thermotropic behavior of the synthesized compound was also
studied. Ternary phase diagrams were constructed for olive oil/water/Span 80 systems at
◦
7
0 C and room temperature by observing the morphology. In the study, some compositions
of macroemulsions and unstable emulsions with phase separation were selected from the
constructed ternary phase diagrams. Span 80 (nonionic surfactant) was used for the study
and the amount of the surfactant was maintained below 10% in the formulations to avoid
skin irritation [7,8]. Newly synthesized hexadecyl-β-D-glucopyranoside was introduced as
a co-surfactant. Macro emulsions and unstable emulsions could be successfully converted
into microemulsions by introducing 0.05 wt% of the compound.
Materials and Methods
Materials
All chemicals used were purchased from BDH Chemicals Ltd. All solvents were distilled
prior to use.

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[757]/25
Instrumentation
◦
FTIR spectroscopic analysis was done at 25 C using infrared spectrophotometer (IR-
PRESTISE -21,SHIMADZU) with pure KBr as the blank. Melting points of the synthe-
sized products were measured using melting point apparatus (SMP1, Stuart Scientific, UK).
Proton NMR spectroscopy was carried out using 300 MHz Varian VTR-300 spectrometer.
Turbidity of solutions was measured using a digital nephlo-turbidity meter (2100 P/ HACH)
in nephelometric turbidity units (NTU). The polarized light optical micrographs were taken
with a polarized light microscope (Euromex, Holland) at room temperature. Silverson
SL2 Laboratory Emulsifier was used for the formulation of emulsions. Centrifuge model
(SIGMA -3 30 KS, Germany) was used for centrifuge purposes. Refractive indices were
measured using a refractometer (HILGER WATTS, England).The conductivity measure-
◦
ments were performed with a conductivity meter (WPA CM 3J Linton, Cambridge) at 25 C.
X-ray analysis was done using the X-ray diffractometer D-5000 (Siemens, Germany); 2θ
◦
◦
◦
◦
range from 2.0 to 20.0 at 1.5406 A wavelength with a scan rate of 0.0001 / min and step
size of 7 S.
Synthesis of Penta-O-Acetyl-β-D-Glucopyranoside
Anhydrous finely powdered sodium acetate (33.0 mmol) was added to acetic anhydride
(
27.7 mmol) contained in a 100 ml round bottom flask. The flask was fitted with a reflux
◦
water condenser and heated on a water bath at 90 C; which was the optimized temperature
for the reaction. After sodium acetate was completely dissolved, finely powdered D-glucose
(27.0 mmol) was added and heated for 3 hours. The mixture was poured into ice water
with ice cubes, stirred vigorously and allowed to stand for 20 min at room temperature.
The solid obtained was filtered and recrystallized from methylated spirit. The experimental
yield was 47.26%.
−
1
FTIR data for penta-O-acetyl-β-D-glucopyranoside (3000–2900 cm – (-CH2,CH
−1
−1
−1
bending), 1790 cm –(Carbonyl group), 1490 cm –(-C-O stretching), 2850-3000 cm
−
–
(aliphatic C-H Stretching),1350-1480 cm 1 –(-C-H Bending)).
◦
The melting point of penta-O-acetyl-β-D-glucopyranoside was 125–130 C.
Synthesis of (Hexadecyl-2,3,4,6-Tetra-O-Acetyl-β-D-Glucopyranoside)
Penta-O-acetyl-β-D-glucopyranoside (2.24 mmol) and cetyl alcohol (3.00 mmol) were
dissolved in dichloromethane (50.00 ml) and boron trifluoride diethyl etherate (3.50 mmol)
was added to it via a syringe. This was stirred under nitrogen atmosphere and the system was
◦
sealed. After that, the reaction mixture was stirred at 0 C for 2 h and allowed to slowly warm
to ambient temperature. Formation of product was monitored by thin layer chromatography.
The reaction mixture was diluted with chloroform (150.0 ml) and washed with saturated
sodium bicarbonate solution (50.00 ml) followed by two portions of deionized water. Then,
the organic layer was separated and dried over anhydrous sodium sulfate, filtered, and
the solvent was removed under reduced pressure. The residue was purified by column
chromatography on silica gel with hexane and ethyl acetate as (3:1) eluent. The solid
◦
product was obtained with a yield of 49.06%.M.p 277-281 C
FTIR data for hexadecyl-2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside 1350-
− −1 −1
1
1
1
480 cm –(-C-H bending), 1790 cm –(carbonyl), 1460 cm –(-C-O stretching),
−1
−1
−1
225 cm –(-C-H stretching), 1110 cm –(-C-C bending), 1050-1250 cm –(C-O
stretching)).

26/[758]
E. P. N. Premarathne et al.
Deacetylation of Hexadecyl-2,3,4,6-Tetra-O-Acetyl-β-D-Glucopyranoside
The crude hexadecyl-2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside (10.0 mg) was added to
a 100 ml round bottom flask. Sodium methoxide in methanol (15.00 ml) was added and
purged with nitrogen gas, and stirred in a closed environment for 6 hours. The excess
solvents were removed under reduced pressure. The final product was obtained with the
◦
yield of 69.59% by series of recrystallization with acetone. M.p 279–285 C
−1
FTIR data for hexadecyl-β-D-glucopyranoside (3600-3400 cm –(-OH group), 2900
−
1
−
1
–
2850 cm –(aliphatic a symmetric -C-H stretching), 900 cm –(out of plane -C-H
−1
−1
bending),1350–1480 cm –(Aliphatic -C-H Stretching), 1350-1480 cm –(-C-H Bend-
−1
ing), 1790 cm –(carbonyl group)).
Detailed characterization of hexadecyl-β-D- glucopyranoside was carried out by H1-
NMR.
1
H NMR (300 MHz, D2O): δ/ppm 0.88 (t, 3H, H-16’), 1.24–1.30 (m, 26H, 13×CH2,
H-3’ to H15’), 1.57 (m, 2H, H-2’), 3.48 (dt, 1H, H-1’a), 3.89 (dt, 1H, H-1’b), 3.93 (t, 1H,
H-5), 4.16 (d, 2H, H-6a and H-6b), 4.48 (d, 1H, H-1), 5.03 (dd, 1H, H-3), 5.18 (dd, 1H,
H-2), 5.38 (dd, 1H, H-4).
Thermotropic and Lyotropic Liquid Crystaline Properties
Thermotropic liquid crystalline properties of hexadecyl-β-D- glucopyranoside was ob-
served by polarized light microscope after heating to isotropic phase and while cooling
down to room temperature. Lyotropic liquid crystaline properties of the final product,
hexadecyl-β-D- glucopyranoside, was observed under polarized light microscope by using
different polar and non-polar solvents such as, acetone, dichloromethane, ethyl acetate,
methanol, ethanol and water with different concentration (Table 1). Optical Microscopic
images were taken for the deacetylated final product, hexadecyl-β-D-glucopyranoside.
Measurement of CMC
(
a) UV- Absorption Spectroscopy
−3
An aqueous stock solution (0.025 mol dm ) of hexadecyl-β-D-glucopyranoside
was prepared. Saturated aqueous solution of iodine (2.50 ml) was placed in
Table 1. Concentrations of the prepared lyotropic liquid crystal samples with different
solvents
Sample Name
Concentration (%wt)
LW1
LW2
LW3
LW4
LW5
LW6
LM
LE
LEA
LA
70.69
55.71
65.82
72.59
46.00
39.13
68.35
69.20
72.19
70.40

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[759]/27
stoppered calibrated centrifuged tubes (15 ml). Varying amounts from the stock
solution of hexadecyl-β-D-glucopyranoside were added to each falcon tube and
the final volume was made up to 10.00 ml by adding distilled water so as to make a
−
5
series of standard solutions in the concentration range of (0.250 – 6.00) × 10 mol
−3
dm [9]. The absorbance spectrum of each solution was measured at 298 K.
The absorbance at selected wavelengths of maximum absorbance 351.2 nm and
288.6 nm were recorded and used in the calculation.
(b) Turbidity measurements
From the prepared stock solution of hexadecyl-β-D-glucopyranoside in (a) above,
−
5
−3
a series of solutions in the concentration range of (0.250 – 5.00) × 10 mol dm
was prepared by adding varying amounts from the stock solution and making the
final volume up to 10.00 ml with distilled water. Then, turbidity of each solution
was measured at 298 K using a digital nephlo-turbidity meter.
Preparation of Unstable Microemulsion Systems
Microemulsion systems consisting of olive oil, water and surfactant (Span 80) were formu-
◦
lated at room temperature and 70 C. The ingredients were thoroughly mixed at 2500 rpm
in an emulsifier until they appeared to be homogeneous. Morphologies were observed soon
after preparation, after 1 hour, two hours, one day and two weeks of preparation. Ternary
phase diagrams were constructed based on the morphologies of emulsions observed two
weeks after preparation (Fig. 1). Three compositions of macro emulsions and phase sepa-
◦
rated unstable emulsions were selected from the phase diagram constructed at 70 C (Fig.
1(b)), and newly synthesized compound was introduced (Table 2). The physical stability
was assessed by observing morphology of emulsions and thermodynamic stability was
determined as described below. The optimum amounts of hexadecyl-β-D-glucopyranoside
necessary for converting macro emulsions and phase separated unstable emulsions to mi-
croemulsions were determined.
Assessment of Thermodynamic Stability of Microemulsions. Microemulsions formed by
addition of hexadecyl-β-D-glucopyranoside were subjected to the following thermody-
namic stability tests.
◦
Figure 1. Phase diagram constructed for the emulsion system (a) at Room temperature (b) at 70 C.

28/[760]

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[761]/29
Centrifuge Stress Test. Microemulsion systems were centrifuged at 6,000 rpm for 30 min
and then examined for phase separation [10].
Freeze–Thaw Cycle Stress Test. Microemulsions were subjected to a total of three complete
◦
◦
freeze–thaw cycles, each cycle consisting of 24 h at 25 C followed by 24 h at −5 C [11].
Characterization of Microemulsions
Conductivity Measurements
In order to assess both the microemulsion type and stability, conductivity measurements
were performed using a conductivity meter. The measurements were performed in triplicate.
All measurements were performed immediately after preparation and 14 days after storage
at room temperature
Refractive Index
The refractive indices of microemulsion formulations were determined using a refractome-
ter.
Results and Discussion
◦
In order to obtain a maximum β glycoside, the reaction was carried out at 0 C. The β-
1
configuration of purified hexadecyl-β-D-glucopyranoside was confirmed by H NMR. In
the deacetylation step of hexadecyl-2,3,4,6-tetra-O-acetyl-β-D- glucopyranoside, stirring
time was increased up to 48 hours. This resulted in a significant increase in the final yield
of hexadecyl-β-D-glucopyranoside.
Study of the Lyotropic and Thermotropic Liquid Crystalline Properties of
hexadecyl-β-D-glucopyranoside
After linking the D-glucose moiety and the lipophilic part (hexadecane) through a glycosyl
linkage, the molecule becomes amphiphilic comprising a hydrophilic head group and
hydrophobic hydrocarbon chain. Therefore sequences of hydrophilic and lipophilic layers
are formed due to these microscopic separations. These generated layers have showed the
same geometry as the Smectic A phase. The ‘micro-phase separation’ and the ‘Closest
Packing’ are the two basic concepts which correspond to the mesophase behavior of the
liquid crystal. If the molecule is a simple-shaped mesogenic compound, there is a high
possibility to form a ‘Closest Packing’ structure because, rod-like molecules tends to pack
in an ordered way (liquid crystal phase) rather than in a random way (isotropic phase) [23].
Anisotropic shape of the molecule is the major factor which stabilizes thermotropic
LC mesophases. The molecules are self-organized to form thermotropic LC mesophases as
a function of temperature. The different texture patterns were observed under the polarized
light microscope while changing the temperature (thermotropic liquid crystalline properties;
Fig. 2) and with different solvent types and the concentrations (lyotropic liquid crystalline
properties; Fig. 3). Molecules have high rotational and translational entropy above their
melting points and also convert into isotropic state.
Upon heating the hexadecyl-β-D-glucopyranoside to isotropic liquid and cooling back
to room temperature, fan-like texture pattern was observed (Fig. 4a) under crossed polarizers

30/[762]
E. P. N. Premarathne et al.
Figure 2. Thermotropic LC textures for deacetylated product. Magnification 400; crossed.
in a polarized light microscope with water as the solvent at lower concentration (Table 1).
The Periodic stripe domains appeared on the fan like texture at high concentrations (Table 1)
of deacetylated compound, while increasing the concentration 55.71% wt to 72.59% wt
(Fig. 4b and 4c). As the amount of the solvent increased, the Periodic stripe domains were
broadened (Fig. 4d and 4e). This effect may be due to loosely packing arrangements low
concentration of the compound. The molecules which contain long alkyl chains tend to
organize in a hexagonal pattern. According to the XRD data for the compound in the water
◦
matrix, a single intense peak can be found in the small angle region, at 2θ = 2.60 with a
◦
d-spacing of 34.20 A (Fig. 5a). An intense peak and two smaller peaks (three reflection
◦
◦
peaks) can be seen in the small angle region (2θ = 2 -10 ,) which is a required observation
for columnar hexagonal phases [24,25]. Thus, it can be concluded that the compound
shows columnar hexagonal phases with water as the solvent. Also the molecular length
calculated from Gaussian modelling (a simple molecular modelling package), was around
◦
2
5.094 A and the d-spacing is greater than 1 and less than 2 times the molecular length.
Therefore, molecules may exist in bilayers forming a head-to-head molecular packing in
two dimensions (Fig. 6a) [24,25].
Similarly, upon cooling, small fan like texture pattern Characteristic for Smectic A
phase was observed with methanol and ethanol (Fig. 3b–3c). According to the XRD data
for the compound in the ethanol matrix, a single intense peak can be found in the small
◦
◦
angle region, at 2θ = 2.81 with a d-spacing of 31.58 A (Fig. 5b) which is characteristic
for smectic phases. Here also the calculated from Gaussian modelling (a simple molecular
modelling package), molecular length was around 25.094 A and the d-spacing is greater
◦
than 1 and less than 2 times the molecular length. Therefore, molecules may exist in bilayers
forming a head-to-head molecular packing in two dimensions (Fig. 6b) [24,25].
However, this compound also showed typical Schlieren texture patterns with non-polar
solvents such as acetone and ethyl acetate. In ethyl acetate, a characteristic “threading”
texture pattern was observed throughout the colored regions, corresponding to molecular
◦
domains which are aligned with one of the optical polarizers (Fig. 3d, e) at 42 C to room
temperature. Even this texture contains thread like structure; it also exhibits two- and four-
fold brushes. Smectic Schlieren textures exhibit only four-fold brushes, and therefore, this
texture may be related to the typical behavior for nematics or smectic (Fig. 3d). In the
corresponding XRD data for the compound in the ethyl acetate matrix intense peak was
◦
observed at 2θ = 3.24 in the small angle region (Fig. 5c) corresponding to d-spacing of
◦
◦
2
7.21 A . This value is almost similar to the calculated molecular length, 25.094 A at its
most stable conformation in the model. Therefore it can be concluded that molecules may

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[763]/31
Figure 3. Lyotropic LC textures for deacetylated product with (a) water (LW
1
), (b) methanol (LM),
(c) ethanol (LE), (d) ethyl acetate (LEA), (e) acetone (LA), (f) after evaporation of water: Magnifica-
tion 400; crossed. Concentrations–Table 1
exist in monolayer with loosely packed Smectic arrangement because the molecules which
contain long alkyl chains, tend to organize in the layers in a loosely packed arrangement to
form smectic phases (Fig. 6c) [24,25].
Spherulite texture of the crystalline phase was observed after evaporation of water.
Measurement of CMC
Depending on the concentration of the amphiphiles, proportion of molecules present at the
surface or as micelles in the bulk of the solvent is changed. At low concentration, molecules

32/[764]
E. P. N. Premarathne et al.
Figure 4. Lyotropic LC textures for deacetylated product with water; (a) low concentration (LW
b) and (c) High concentration (LW , LW ), (d) and (e) higher dilution regions (LW , LW ), (f) after
evaporation of water: Magnification 400; crossed. Concentrations–Table 1
2
),
(
3
4
5
6
Figure 5. XRD patterns for lyotropic liquid crystal with different solvents; (a) water, (b) ethanol,
◦
(
c) ethyl acetate: Step time 4 s at 25 C.

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[765]/33
Figure 6. Molecular packing with different solvents (a) water, (b) ethanol, (c) ethyl acetate.
tend to arrange on the surface. At higher concentration levels the surface becomes crowded
and excess molecules will arrange into micelles. At a critical concentration of surfactant
the solvent surface becomes completely loaded such that any further tiny additions undergo
spontaneous self-association into ordered structures called micelles. That concentration is
called the Critical Micelle Concentration (CMC). This is an important fundamental property
which affects most of bulk physical properties.
Usually to determine CMC of surfactants some physicochemical parameters such
as conductometry, tensiometry, fluorescence emission spectroscopy, calorimetry, kinetic
approaches, light scattering, NMR spectroscopy and cyclic voltametry are used [13–19].
CMC of hexadecyl-β-D-glucopyranoside was studied using two different methods.
(a) UV-Visible Spectrometric Studies
The UV-Visible spectrophotometric studies were conducted to determine the CMC of
the synthesized glucoside using donor-acceptor complex formation of Iodine-surfactant
molecules. Due to formation of donor-acceptor complex, the spectral absorbance at max-
imum absorbance wave length (λmax) is reduced. The formation of the complex is mainly
due to the fact that nonionic surfactants have the ability to perform as iodophores or I2
carriers without destroying the surfactant properties [9]. Saturated I2 solutions absorb at
3
51.2 nm and 288.6 nm. Figure 7 shows the plot of absorbance Vs concentration of glu-
−5
coside at 351.2 nm and 288.6 nm. It shows sharp distinct break point at 1.55 × 10 mol
−3
−5
−3
dm and 1.53 × 10 mol dm for 288.6 nm and 351.2 nm respectively.

34/[766]
E. P. N. Premarathne et al.
Figure 7. Absorbance Vs Concentration plot at two maximum absorbance wave lengths, concentra-
◦
tion related to the distinct break point is the CMC value at 27 C.
(
b) Turbidity Measurements
◦
The intensities of a transmitted and diffused monochromatic light at 90 by the solution
are measured and its ratio in Nephlo turbidity units (NTU) is taken as the turbidity. The
turbidity changes with concentration in such a way that the change before and after the
critical point results in a break point which is the CMC [17,18].
The prepared series of aqueous solutions of surfactant with concentration in the range
−
5
−3
of (0.25 – 5.0) × 10 mol dm , shows significant turbidity in the measurable linear range
of the instrument. A plot of turbidity Vs concentration (Fig. 8) showed a distinct break
−
5
−3
point at 0.98 × 10 mol dm in the plot which corresponds to the CMC value. The CMC
Figure 8. Turbidity Vs concentration of surfactant solution, concentration corresponding to the
◦
distinct break point is the CMC value at 27 C.

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[767]/35
Figure 9. Unstable Emulsion system (a) E-MA, (b) E-MB, (c) E-MC without adding LLC
value thus obtained from turbidity measurement is slightly lower than that obtained from
−5
−3
the UV method (1.55 × 10 mol dm ) but they are in the same order.
The HLB value of the surfactant provides an idea about the lowest interfacial tension
between oil phase and water phase. It indicates several physicochemical parameters and
behaviors of the surfactant. The HLB value of synthesized glycolipid, hexadecyl-β-D-
glucopyranoside calculated using Equation (1), was 8.86. This HLB value suggests that
the synthesized glycolipid is suitable for making self-emulsifying oils and as a water in oil
emulsifier.
Figure 10. Microemulsion system (a) E-MALC, (b) E-MBLC, (c) E-MCLC with LLC

36/[768]
E. P. N. Premarathne et al.
Table 3. Parameters for the selected microemulsion systems
−6
Emulsion number
Conductivity(× 10 )/ S
pH value
Refractive index
E-MALC
E-MBLC
E-MCLC
1.753
1.718
1.723
6.9
7.2
7.2
1.4610
1.4590
1.4640
Construction of Ternary Phase Diagrams
A phase diagram for a particular binary or ternary system depicts the relationship among
the phase components of the system and the phase behavior of the formulation. Since the
free energy requirement for the formation of the emulsion system is very small, therefore,
the morphologies at stable states should be observed very carefully [24]. In this study,
olive oil was selected as the oil phase and Span 80 was chosen as the surfactant (S). Two
separate pseudo ternary phase diagrams were constructed for the same system of oil, water
◦
and Span 80 at room temperature and 70 C. Figure 1(a) is the ternary phase diagram
for emulsions formulated at room temperature. It clearly shows four types of emulsions;
microemulsions, macro emulsions, phase-separated emulsions and cloudy emulsions. On
◦
heating to 70 C (Fig. 1(b)), the microemulsion region was expanded significantly narrowing
phase-separated and macro emulsion regions.
Stabilization of Unstable Emulsion Systems with LLC
The compositions of macro emulsions and unstable emulsions with phase separation se-
lected for our study are shown in Table 2. Upon inclusion of glycolipid, hexadecyl-β-
D-glucopyranoside (LLC) to the unstable macro emulsion systems a distinct change to
microemulsions was observed (Figs. 9, 10).
By introducing minimum amount of 0.05 wt% of newly synthesized LLC material,
hexadecyl-β-D-glucopyranoside, as a co-surfactant, unstable macro emulsions were suc-
cessfully converted to transparent micro emulsions and the stability was increased. Mor-
phologies were observed through naked eye.
Characterization of Microemulsion Systems
In order to characterize the selected stabilized microemulsion systems given in Table 2,
pH values, refractive indices and conductivity measurements were carried out. Table 3
summarizes the measured parameters. The refractive index values of the three stabilized
emulsions were 1.46. The observed refractive index value of 1.46 for all three stabilized
microemulsions is in the range expected for transparent isotropic systems [25].
The conductivity values of the stabilized microemulsions are in the range of
−
6
(
1.753–1.718) × 10 S. Generally, all formulations are low viscous and the measurements
were performed in triplicate. All measurements were performed after 14 days storage at
room temperature.

Hexadecyl-β-D-Glucopyranoside: A Liquid Crystal
[769]/37
Conclusion
Carbohydrate lyotropic liquid crystal, hexadecyl-β-D-glucopyranoside was synthesized
with a maximum yield of 63.47%. The chemical structure, surfactant and liquid crystal
properties were confirmed.
Upon heating the hexadecyl-β-D-glucopyranoside to isotropic temperature and cool-
ing back to room temperature, fan-like texture pattern was observed. The inherent rods
like shape of the molecules favor arrangement as hexagonal array. As observed from XRD
data molecules may exist in bilayers forming a head-to-head molecular packing in two
dimensions. Similarly, upon cooling, small fan like texture pattern characteristic for Smec-
tic A phase was observed with methanol and ethanol. Here also XRD data suggested
that molecules may exist in bilayers forming a head-to-head molecular packing in two
dimensions.
However, this compound also showed typical Schlieren texture patterns with non-polar
solvents such as acetone and ethyl acetate. In ethyl acetate, a characteristic “threading”
texture pattern was observed throughout the colored regions, corresponding to molecular
domains which are aligned with one of the optical polarizers. Even this texture contains
thread like structure; it also exhibits two- and four-fold brushes. Smectic Schlieren textures
exhibit only four-fold brushes, and therefore, this texture relates to smectic phase because
XRD data concluded that molecules may exist in monolayer, molecules with loosely packed
Smectic arrangement in the packing because the molecules which contain long alkyl chains,
tend to organize in loosely packed layers so that form smectic phases.
The CMC for hexadecyl-β-D-glucopyranoside from both UV visible spectroscopic
−5
−4
−3
method and turbidity method was in the region between 10 –10 mol dm which is typi-
cal for nonionicsurfactants. CalculatedHLBvalue8.86indicatesthat synthesizedglycolipid
is suitable for making self emulsifying oils and water in oil emulsions. Hexadecyl-β-D-
glucopyranoside has the ability to transform macro emulsions and unstable emulsions to
microemulsions. By introducing only 0.05 wt% of LLC-hexadecyl-β-D-glucopyranoside
the conversion is affected to produce stable microemulsions. The results strongly sug-
gest that the synthesized glycolipid is suitable for use as co-surfactant to stabilize the
microemulsions.
References
[1] Stubenrauch, C. (2001). Current Opinion in Colloid & Interface Science, 6,16.
[2] Kitamoto, Dai, Morita, Tomotake, Fukuoka, Tokuma, Konishi, Masa-aki, & Imura, Tomohiro.
(2009). Current Opinion in Colloid & Interface Science, 14, 315.
[
3] Maissel, L.I. & Glang, R. (1990). Handbook of Thin Films Technology. McGraw-Hill, New
York.
[
[
[
4] Nesrullajev, A.N., Rustamov, F.A., & Sonin, A.S. (1984). Crystallography (Sov.)., 29, 1133.
5] Quist, P.O., & Furo, B.I. Halle. (1992). Journal of Chemical Physics, 96, 3875.
6] Pillai, V. et al. (1999). In: Hand book of microemulsion science and technology, Kumar, P. &
Mittal, K. L. (Eds.), Chapter 24, Marcel Dekker Inc: New York, Basel.
7] Ekwall, P. (1975). Advanced Liquid Crystal Technologies, 1, 1.
8] Yuan, J. S., & Acosta, E. J. (2005). International Journal of Pharmaceutics, 338 (2009), 63.
9] Bronaugh, R. L., & Maibach, H. I. (2005). Percutaneous absorption: drugs, cosmetics, mecha-
nisms, methodology. 4th ed. Boca Raton: Taylor & Francis.
[
[
[
[
10] Delgado-Charro, M.B., Iglesias-Vilas, G., Blanco-M e´ ndez, J., L o´ pez-Quintela, M.A., Marty, J.,
&
Guy, R.H. (1997). European Journal of Pharmaceutics and Biopharmaceutics, 43, 37.

38/[770]
E. P. N. Premarathne et al.
[
11] Williams, A.C., & Barry, B.W. (1992). Skin absorption enhancers. Critical ReviewsTM in Ther-
apeutic Drug Carrier Systems, 9, 305–353.
[
[
[
[
[
[
12] Fuguest, E., & Rafols, B. (2005). Analytica Chimica Acta., 548, 95.
13] Arai, T. Takasugi, K., & Esumi, K. (1996). Colloids and Surfaces, 119, 81.
14] Paxton, T.R. (1969). Journal of Collide interface Science, 31, 19.
15] Percowski, J., Mayer, J., & Ledakowiez, S. (1995). Colloids Surface, 101, 103.
16] Kato, T., Lwai, M., & Seimiya, T. (1989). Journal of Colloid Interface Science, 130, 439.
17] Ray, G.B., Chakraborty, I., & Moulik, S. P. (2006). Journal of Colloid Interface Science, 294,
2
48.
18] Ghosh, S. K., Khatua, P. K., & Bhattacharya, S. C. (2004). Journal of Colloid Interface Science,
79, 523.
[
2
[
[
19] Thies, M., Poschmann, M., Hinze, U., & Paradies, H. H. (1995). Colloid Surface, 101, 159.
20] Craig, D.Q.M. Barker, S.A. Banning, D. & Booth, S.W. (1995). International Journal of
Pharmaceutics, 114, 103Y110.
[21] Junyaprasert, V.B. Boonme, P. Songkro, S. Krauel, K. & Rades, T. (2007). Journal of Pharma-
ceutical Science, 10 (3), 288.
[
[
[
[
22] Vora B. Khopade A.J. & Jain N.K. (1998). Journal of Control Release, 54, 149.
23] Volkmar, V., & Rauzah, H. (2002). Current Opinion in Colloid and Interface Science, 7, 395.
24] Jeffrey, G. A. (1986). Accounts of Chemical Research, 19, 170.
25] Wingert, L. M., Jeffrey, G. A., Cabaret, D. & Wakselman, M. (1995). Carbohydrate Research,
275, 25.