Synthesis and Properties of Alkyl β-d-Galactopyranoside

Article abstract of DOI:10.1007/s11743-016-1865-0

A series of alkyl β-d-galactopyranosides were prepared by the trichloroacetimidate method with d-galactose and alcohols with different chain lengths as raw materials. Their solubility, surface tension, emulsification, foaming, wettability, thermotropic liquid crystalline properties, and thermal stability were investigated. Alkyl β-d-galactopyranosides are soluble in water and ethanol, and the solubility decreases with increasing alkyl chain length. Decyl β-d-galactopyranoside was insoluble in water, but soluble in ethanol. Dissolution of alkyl β-d-galactopyranoside in water is an endothermic process with dissolution enthalpies greater than zero. Nonyl β-d-galactopyranoside had an excellent emulsifying?property, better foaming ability and the best foam stability. The CMC values of alkyl β-d-galactopyranosides decrease with increasing of alkyl chain length. Alkyl β-d-galactopyranosides are thermally stable up to 270?°C. Alkyl β-d-galactopyranosides show the distinctive optical texture of a thermotropic liquid crystal smectic A type phase. Decyl β-d-galactopyranoside showed the strongest wettability.

Full text of DOI:10.1007/s11743-016-1865-0

J Surfact Deterg
DOI 10.1007/s11743-016-1865-0
ORIGINAL ARTICLE
Synthesis and Properties of Alkyl b-D-Galactopyranoside
Guoyong Chen1 Zhencao Li1 Langqiu Chen1 Shanwei Ji1 Wangzhen Shen1
•
•
•
•
Received: 26 November 2015 / Accepted: 4 August 2016
Ó AOCS 2016
Abstract A series of alkyl b-D-galactopyranosides were
prepared by the trichloroacetimidate method with D-
galactose and alcohols with different chain lengths as raw
materials. Their solubility, surface tension, emulsification,
foaming, wettability, thermotropic liquid crystalline prop-
erties, and thermal stability were investigated. Alkyl b-D-
galactopyranosides are soluble in water and ethanol, and
the solubility decreases with increasing alkyl chain length.
Decyl b-D-galactopyranoside was insoluble in water, but
soluble in ethanol. Dissolution of alkyl b-D-galactopyra-
noside in water is an endothermic process with dissolution
enthalpies greater than zero. Nonyl b-D-galactopyranoside
had an excellent emulsifying property, better foaming
ability and the best foam stability. The CMC values of
alkyl b-D-galactopyranosides decrease with increasing of
alkyl chain length. Alkyl b-D-galactopyranosides are ther-
mally stable up to 270 °C. Alkyl b-D-galactopyranosides
show the distinctive optical texture of a thermotropic liquid
crystal smectic A type phase. Decyl b-D-galactopyranoside
showed the strongest wettability.
Introduction
With increasing concerns regarding environmental protec-
tion, much attention has been paid to environmentally
friendly surfactants. The research and development of vari-
ous green surfactants has become a hot topic [1–3]. Con-
sequently, environmentally friendly surfactants are an
attractive alternative to those that can potentially damage
our environment. Among the various types of surfactants,
alkyl glycosides or/and alkyl polyglycosides are becoming
more and more attractive for commercial use because of
their excellent properties such as high surface activity,
excellent biodegradability, as well as antimicrobial activity
[4, 5]. Moreover, they are low toxicity and readily obtained
from renewable resources including sugars and alcohols [6].
Sugar-based surfactants contain two parts: the
hydrophobic part, which can be an alcohol and the
hydrophilic glycosyl moiety, which can be a monosac-
charide, disaccharide, oligosaccharide, or polysaccharide
[4, 7, 8]. They have a very wide application field, not only
as the surfactants for detergents and emulsifiers, but also in
food applications [4, 9–15]. In addition, they can also be
used as drug carriers due to their peculiar physicochemical
behavior including insensitivity to variations in tempera-
ture and salinity, which is very important in drug devel-
opment. Alkyl galactosides as sugar-based surfactants
possesses potential benefits in pharmaceutical develop-
ment, and can be used to formulate conventional and
advanced drug delivery systems, often being used as a
substitute for conventional surfactants [16]. It is notewor-
thy that galactoside has special pharmaceutical value
because of its high affinity towards the liver, specifically in
the binding of hepatocytes [17]. Large scale industrial
manufacture of glycoside surfactants has only recently
become possible using different alcohols and a large
Keywords Non-ionic surfactants Á Synthesis Á Interfacial
science Á Surface activity
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-016-1865-0) contains supplementary
material, which is available to authorized users.
& Langqiu Chen
chengood2003@263.net
1
College of Chemistry, Key Laboratory of Environmentally
Friendly Chemistry and Application of Ministry of
Education, Xiangtan University, Xiangtan 411105, Hunan,
People’s Republic of China
123

J Surfact Deterg
number of carbohydrates such as glucose, galactose, mal-
tose, dextrose, starch, cellulose and so on.
SmecticA* 107.0 °C Iso Liq, in respective [21]. In fact,
researchers had studied transition temperature which was
affected by factors such as variation of sugar ring, alkyl
chain length, H-bond, polymorphism of crystal phases and/
or thermotropic liquid crystals, miscibility of different
glycosides.
We believe that well-defined alkyl glycosides are nec-
essary for basic scientific research in surface activity,
thermal stability, molecular biology thermotropic liquid
crystalline properties, and for practical and broader appli-
cation in food, cosmetic products and pharmaceuticals
[6, 18, 19]. Therefore, additional research is required to
explore the stereoselective synthesis and physico-chemical
properties of alkyl glycosides due to the potential
polyfunctionality.
Xu researched the chemical synthesis, thermostability,
and cytotoxicity of hydrocarbon (–C6H13 to –C16H33) and
fluorocarbon (–(CH2)2C6F13) alkyl b-D-xylopyranoside
surfactants [22]. The structure–property relationships for
the alkyl b-D-glycosides such as solubility, CMC value,
emulsifying, foaming, wettability, thermotropic liquid
crystalline property, and thermal stability are generally
affected by various factors such as sugar ring (furanoside
or pyranoside, anomeric configuration), type (normal,
branched, complex, substituted) and size of aliphatic chain,
temperature, and so on. Some influences are regular, but
others are relatively optional owing to complexity of
influence of various factors.
Alkyl glycoside surfactant molecules in aqueous or oil
media are affected by two forces. One is the intermolecular
repulsion forces between the hydrophobic alkyl chain and
water or between their hydrophilic glycosyl components
and oil. Another is the intermolecular attraction forces
between their hydrophilic glycosyl components and water
or between their hydrophobic alkyl chain and oil. The
competition between the opposite intermolecular forces
regulates the properties involving solubility, surface ten-
sion, emulsification, foaming, wettability, and so on.
Many scientists have carried out a variety of investiga-
tions since the first alkyl glucoside was synthesized and
identified by Emil Fischer. As a kind of nonionic surfac-
tant, alkyl glucosides are electrolyte tolerant to the various
levels of naturally occurring hard water. The alkyl chain
length has a far stronger influence on the critical micelle
concentration (CMC) than the number of glycosyl units in
the head group. The CMC values of octyl, decyl and
dodecyl b-D-glucoside were found to be 25, 2.2 and
0.19 mmol L-1 at 25 °C, respectively [4]. However, Castro
reported that the CMC values of octyl and dodecyl b-D-
glucoside were 10 and 2.3 mmol L-1 at 25 °C [12].
Yakimchuk reported that the initial foam height of hexyl
and octyl glucoside were 2 and 4 mm at 0.5 g L-1 and
20 °C by the Ross-Miles method, respectively [13].
Hashim studied sugar stereochemistry (epimers and
anomers), for example b-glucosides and a-galactosides,
and collected the data for thermotropic phases and transi-
tion temperatures of aGal-C8 (Cr * 40 °C, SA95 4 °C
Iso), aGlc-C8 (Cr69 °C, SA116 °C Iso), bGal-C8 (Cr96 °C,
SA127 °C Iso) and bGlc-C8 (Cr69 °C, SA107 °C Iso), and
pointed out that thermotropic (dry state) phase was perhaps
the smectic A (SA) for the glycosides composed of simple
sugar and single alkyl chain [20]. Thermotropic mesophase
of octyl b-D-glucopyranoside was found as a texture of
Smectic A* phase, and the thermotropic data of octyl b-D-
glucopyranoside, octyl a-D-glucopyranoside, octyl b-D-
galactofuranoside, decyl b-D-galactofuranoside, and decyl
a-D-galactofuranoside were Cryst 67.1 °C SmecticA*
106.4 °C Iso Liq, Cryst 72.3 °C SmecticA* 116.3 °C Iso
Liq, Cryst 96.0 °C SmecticA* 128.5 °C Iso Liq, Cryst
98.0 °C SmecticA* 155.0 °C Iso Liq, and Cryst 62.4 °C
A variety of methods for synthesis of alkyl glycosides
have been reported [23, 24], such as the Koenigs-Knorr
method and modification thereof, the Fischer glycosylation
method and the trichloroacetimidate method. The Koenigs-
Knorr method is a kind of mature method involving an SN2
substitution at the anomeric carbon and proceeds stereos-
electively with inversion of configuration. The method has
been widely employed to prepare 1,2-trans-glycoside. In
general, the catalysts or/and promoters are very expensive
or highly poisonous heavy metal salts, for example the
former is silver salt and the latter is mercury salt, and the
poisonous heavy metal salts would inevitably cause serious
environment pollution [25, 26].
The greatest disadvantage of the Fischer glycosylation
method is that the reaction products contain a complex
mixture of a- and b-anomers dominated by pyranoside via
kinetically favored furanoside, since the glycosylation is an
equilibrium reaction. Another is the formation of randomly
linked glycoside oligomers owing to the polyfunctionality
of the carbohydrate. Therefore, individual glycoside com-
ponent is often difficult to isolate from the mixture of the
Fischer glycosylation [4, 27].
The transglycosidation method (also called two-stage
transacetalization method) may have the shortcoming since
the composition and quality of the product are severely
affected by catalyst, residual lower alcohol and the raw
material carbohydrate, overreaction, degradation of gly-
coside, polymerization, and exact control of reaction time
[28]. The trichloroacetimidate method can as well be used
to synthesize a single configuration of 1,2-trans-glycosides
with high selectivities, mainly b-anomers for glucose and
galactose [27, 29].
The aim of this paper was to prepare a series of alkyl
b-D-galactopyranosides with different alkyl chain lengths
123

J Surfact Deterg
Solubility Properties
and investigate their properties as surfactants. We first
synthesized alkyl b-D-galactopyranosides by the
trichloroacetimidate method involving five steps: acety-
lation, deacetylation at the position of C1, conversion to
trichloroacetimidate, coupling with alcohol and depro-
tection (Fig. 1). Next, we investigated their properties in
order to obtain the data of their solubility, surface
activity, thermotropic liquid crystalline property, and
thermal stability based on previous literature
[20, 28–38].
Methods for determining the solubility of the prepared
alkyl b-D-galactopyranosides in water, ethyl acetate and
ethanol at room temperature (25 °C) were described by Li
[30]. A certain amount of the glycoside was accurately
weighed. Then the glycoside and a certain amount of sol-
vent that was accurately measured and put into a test cup
that was put on a shaking table. According to the situation
of dissolution after 1 h, a small amount of solvent was
added and the test cup was shaken further until the gly-
coside had dissolved completely. The solubility of the
glycosides at 15, 20 and 30 °C was determined using the
same method as described above.
Experimental Section
General Methods and Synthesis of Alkyl b-D-
galactopyranosides
Dissolution Enthalpy and Entropy
1H-NMR spectra were recorded using an Avance 400
spectrometer (Bruker) for solutions in CDCl3 or D2O.
Melting points were determined with a X-4 digital melting
point apparatus (Dura Labs). Thermal stability was deter-
mined with a TGA Q50 thermogravimetric analyzer (TA
Instruments). The liquid crystal properties were determined
with a DM-LM-P polarization microscope (Leica). Surface
tension was determined with DP-A precision digital pres-
sure thermometer (Nanjing Sangli electronic equipment
factory). Thin-layer chromatography (TLC) was performed
on silica gel HF254 with detection by charring with a
mixture of 30 % (v/v) sulfuric acid and methanol. The
purity of all raw materials are analytical pure or chemical
pure.
Using the same method described by Li [31], the solubility
of the glycosides (6a–6d) was measured at temperatures of
15–30 °C, the solubility (xA) and the temperature (T) were
correlated using the Eq. 1:
B
ln xA ¼ A þ
ð1Þ
T
where A and B represent fitting parameters obtained from least
squares fitting of the experimental data and T is the tempera-
ture in Kelvin. xA represents the saturated solubility of gly-
coside in mole fraction units obtained from Eq. 2 where mA
and mB represent the mass of solute and solvent, respectively.
mA=MA
xA ¼
ð2Þ
mA=MA þ mB=MB
The detailed synthesis and characterization of alkyl b-D-
galactopyranosides are shown in Supplementary
Information.
The Dissolution Enthalpy (DsolH) and Dissolution
Entropy (DsolS) Can Be Calculated as Follows
Fig. 1 Synthetic scheme for alkyl b-D-galactopyranoside
123

J Surfact Deterg
ꢀ
ꢁ
linear fitting of the front section below CMC value in the
isotherm surface tension curve, the slope (dc/dlnC) was
estimated. The surface excess concentration (Cmax) of
single layer saturated adsorption, i.e., the maximum surface
excess, could be calculated by the Gibbs Eq. 9, where R is
the universal gas constant (8.314 9 10-3 kJ mol-1 K-1), T
is the temperature (K) and n = 1 since the glycosides are
nonionic surfactants. Thus the minimum cross-sectional
d ln xA
dT
DsolH ¼ RT2
ð3Þ
ð4Þ
p
ꢀ
ꢁ
d ln xA
dT
DsolS ¼ RT
p
The Eqs. 3 and 4 are deduced by the Gibbs–Duhem
equation. The following Eqs. 5 and 6 are the simplified
form from Eqs. 3 and 4.
2
˚
area (packing area, Amin, in A ) per glycoside could be
DsolH ¼ ÀRB
DsolS ¼ ÀRB=T
where B ¼ ÀT2
ð5Þ
ð6Þ
calculated by the Eq. 10, where N0 is the Avogadro
number.
ꢂ
ꢃ
c ¼ KDP
Cmax ¼ À
ð8Þ
ð9Þ
d ln xA
dT
:
p
1
dc
nRT d ln C
Á
Emulsifying Properties
1
Amin
¼
ð10Þ
Using the same method described by Liu [38], a 0.1 %
aqueous solution of the glycoside was first prepared. At
25 °C, 20 mL of the solution and 20 mL of rapeseed oil or
toluene were added to a measuring cylinder with a plug
and vigorously shaken to mix. The emulsifying property
was determined by the volume of emulsion (VER or VET) or
the clear aqueous phase (Vwr or Vwt) separating from the
emulsion after 1 h.
N0Cmax
The effectiveness (pCMC) represents the surface pressure
at the CMC and is calculated by the difference between the
surface tension of bidistilled water (c0) and that of the
glycoside solution (cCMC) at the CMC as dscribed in by
Eq. 11 [35].
pCMC ¼ c0 À cCMC
ð11Þ
The standard free energy of micellization (DGmic) and
adsorption (DGads) of individual glycoside could be cal-
culated using Eq. 12 [35] and Eq. 13 [36], respectively.
Foaming Properties
Using the same method described by Patist [32] and Liu
[38], a 0.1 % aqueous solution of the glycoside was first
prepared. At 25 °C, 10 mL of the solution was added into a
100 mL measuring cylinder with a plug. The foamability
was evaluated by the initial foam height (H0) after the
solution was vigorously shaken for 1 min. After 5 min, the
foam height (H5) of the solution was also recorded. The
foam stability was evaluated by the disappearance rate (t)
of bubble as Eq. 7.
DGmic ¼ RT lnðCMCÞ
ð12Þ
ð13Þ
pCMC
DGads ¼ DGmic
À
:
Cmax
Thermal Stability
The thermograms were obtained for the glycosides
(3–5 mg) by a TGA (thermal gravity analysis) at a heating
rate of 20 °C per min, using nitrogen as the shielding gas.
v ¼ ðH0 À H5Þ=t ðmm=sÞ
ð7Þ
Thermotropic Phase Behavior
Interfacial Properties
Using the same method described by Hashim [20], the
thermotropic liquid crystalline phases of the galactopyra-
nosides were observed by a OPM (optical polarizing
microscope) at a heating rate of 3 °C per min. The phase
transition temperatures were recorded during the course of
heating, the changes were subsequently investigated at a
cooling rate of 3 °C per min.
The maximum bubble pressure method (MBPM) was used
to study the surface tension of the glycoside in water at 25
and 35 °C [33, 34]. A series of different concentrations of
the glycoside were prepared. The excess pressure value
(DP) of the different solutions at 25 and 35 °C was mea-
sured, and the equilibrium surface tension (c) of the gly-
cosides in water was calculated at different concentration
using the Laplace Eq. 8. K is a constant obtained using the
bidistilled water as reference solution. The isotherm curve
of the c versus the concentration (C) of the solution was
drawn, thus obtaining the critical micelle concentration
(CMC) and the surface tension (cCMC). According to the
Wettability
Using the same method described by Li [37], a 0.1 %
aqueous solution of the galactopyranoside was first
123

J Surfact Deterg
prepared. Then the sinking time of a canvas disc (U35 mm,
HG/T2575-94) in the solution was measured at 35, 45 and
55 °C.
Results and Discussion
Solubility Properties
The solubilities of alkyl b-D-galactopyranoside (6a–6e) in
water, ethanol and ethyl acetate at 25 °C are shown in
Fig. 2. The solubilities in water and ethanol all decrease
with increasing alkyl chain length. The solubility in ethyl
acetate first increased with increasing alkyl chain length for
6 B n B 8 until a maximum value [1.05/100 g for 6c
(n = 8)] was reached, and subsequently, decreased with
increasing alkyl chain length for 8 \ n B 10. The solu-
bility in ethanol is obviously higher than that in water or
ethyl acetate for n = 6–10. The solubility in water is very
low, 0.11/100 g for 6d, and 0.05/100 g for 6e. The latter is
considered to be insoluble as its solubility was less than
0.1 g per 100 g of water. The solubility of decyl b-D-
galactopyranoside (6e, n = 10) in ethyl acetate was also
very small, 0.14/100 g.
Fig. 3 Solubility of alkyl b-D-galactopyranoside in water at different
temperature
15–30 °C. The solubilities of hexyl galactoside (6a) and
heptyl galactoside (6b) were rather large and the difference
of their solubility (lnxA) was small, but the solubilities
(lnxA) of octyl galactopyranoside (6c) and nonyl galac-
topyranoside (6d) were obviously decreasing with increase
of alkyl chain length. The parameters A and B in Eq. (1)
obtained from Fig. 3 are shown in Table 1. The dissolution
enthalpy (DsolH) calculated from Eq. 5 is shown in
Table 1. Since DsolH [ 0, the dissolution process of alkyl
b-D-galactopyranoside (6a–6d) in water is an endothermic
process and the solubility became larger with increasing
temperature.
Dissolution Enthalpy and Entropy
The dissolution enthalpy (DsolH) and dissolution entropy
(DsolS) were only investigated for 6a–6d (n = 6–9) in
water at 15, 20, 25 and 30 °C since 6e (n = 10) is insoluble
in water.
The dissolution entropy (DsolS) obtained from Eq. (6)
decreased linearly with increases in temperature as shown
in Fig. 4. The DsolS value of hexyl b-D-galactopyranoside
(6a) was the lowest. The DsolS values of heptyl galac-
topyranoside (6b) and octyl galactopyranoside (6c) were
increasing in turn. The DsolS value of nonyl b-D-galac-
topyranoside (6d) reached the highest. As described by
Kocherbitov [35], the phase transition is driven by enthalpy
and entropy changes. Since DsolH and DsolS were both
positive, the dissolution process is driven by entropy.
The relationship between the solubility (lnxA) in water
and temperature of alkyl b-D-galactopyranosides (6a–6d) is
shown in Fig. 3. The solubility (lnxA) decreases with the
increase in the reciprocal of temperature (1/T) for each
galactopyranoside (6a–6d) over the temperature range of
Emulsification and Foaming Properties
The emulsification and foaming properties were only
investigated for alkyl b-D-galactopyranoside (6a–6d)
(n = 6–9) since the solubility of 6e (n = 10) in water was
quite low. The emulsification properties are shown in
Fig. 5. Hexyl b-D-galactopyranoside (6a) showed poor
emulsification properties for both toluene and rapeseed oil
as the aqueous phase and the organic phase returned to
their original volumes (Vwt = Vwr = 20 mL) after 1 h. For
toluene, alkyl b-D-galactopyranosides (6b–6d) exhibited
improved emulsification properties as the alkyl chain
length increases. Nonyl b-D-galactopyranoside (6d)
Fig. 2 Solubility of alkyl b-D-galactopyranoside in water, ethanol
and ethyl acetate
123

J Surfact Deterg
Table 1 Parameters of Eq. 1 and dissolution enthalpies DsolH for
different solutions
Glycoside
A
B
D
solH (KJÁmol-1
)
6a
6b
6c
6d
6.78
-3826.05
31.81
55.72
84.95
96.29
16.41
26.37
28.87
-6701.61
-10217.18
-11581.63
Fig. 6 Foaming ability of alkyl b-D-galactopyranoside
The foam properties are shown in Fig. 6. Hexyl b-D-
galactopyranoside (6a) showed the weakest foaming ability
(H0 = 4.0 mm). Heptyl b-D-galactopyranoside (6b) was
slightly stronger than 6a. Octyl b-D-galactopyranoside (6c)
had the strongest foaming ability (H0 = 33.0 mm). Nonyl
b-D-galactopyranoside (6d) was down slightly to
H0 = 25.0 mm. The foam height (H5) of the alkyl b-D-
galactopyranoside (6a–6d) after 5 min increased with alkyl
chain length. For nonyl b-D-galactopyranoside (6d), its
H5 = 22.0 mm, rather near the foaming height
(H0 = 25.0 mm). The foaming ability of octyl b-D-galac-
Fig. 4 Dissolution entropy of alkyl b-D-galactopyranoside (6a–6d) at
different temperature
topyranoside
(6c,
n = 8)
was
the
strongest
(H0 = 33.0 mm), but the disappearance rate of the bubble
was maximum, t = 0.05 mm/s, suggesting that the foam
stability was the worst. The foaming ability of nonyl b-D-
galactopyranoside (6d, n = 9) was the stronger
(H0 = 25.0 mm), but the disappearance rate of the bubble
was the smallest, t = 0.01 mm s-1, suggesting that the
foam stability was the best. Overall, nonyl b-D-galactopy-
ranoside (6d, n = 9) was considered as excellent emulsi-
fying property, better foaming ability and the finest foam
stability.
Fig. 5 Emulsifiability of alkyl b-D-galactopyranoside
Interfacial Properties
At low concentrations in water, alkyl glycoside molecules
adsorb at the air/water interface and reduce the surface
tension by the hydrophobic effect. The hydrophobic alkyl
chains orientate towards air with the glycosyl head group in
the water phase. In general, the lower the surface tension,
the higher the surface activity. Because hexyl b-D-galac-
topyranoside (6a) displayed the worst emulsification and
foaming properties, we did not measure its surface activity.
Surface tension isotherms for the alkyl b-D-
reached the lowest value (Vwt = 13.5 mL). For rapeseed
oil, the alkyl b-D-galactopyranosides (6b–6d) exhibited a
similar trend with emulsification properties improving with
increase in alkyl chain length. Nonyl b-D-galactopyra-
noside (6d) again reached the lowest value (Vwr = 15.0 -
mL). These results suggest that nonyl b-D-
galactopyranoside (6d, n = 9) interacts stronger with
rapeseed oil through the longer alkyl chain of the glycoside
itself.
123

J Surfact Deterg
galactopyranosides (6b–6e) by the maximum bubble
pressure method at 25 and 35 °C are shown in Fig. 7.
Figure 7 shows that alkyl b-D-galactopyranosides (6b–
6e) could efficiently decrease the surface tension at 25 and
35 °C. The critical micelle concentration (CMC) of the
galactopyranosides (6b–6e) decreases with increasing alkyl
chain length. Meanwhile, the CMC values are higher at
25 °C than at 35 °C for same glycoside.
The cCMC values are roughly the same at 25 and 35 °C
for the same glycoside. Linear fitting of the pre-micellar
data was performed, and the -dc/dlnC at 25 °C was cal-
culated (11.72–10.57 mol m-2), which was smaller than
the slope at 35 °C (13.04–12.21 mol m-2). The slope was
substituted into the Gibbs equation to obtain the surface
excess concentration values (Cmax) given in Table 2. The
values increase with alkyl chain length at both
temperatures.
The higher the effectiveness of surface tension reduction
at the CMC (pCMC), the stronger the surface activity. The
pCMC values at 25 °C are larger than the values at 35 °C for
the same glycoside, but the values first increased rapidly
and then decreased slightly with increasing alkyl chain
length. The effectiveness of decyl galactopyranoside (6e)
was the highest at 25 and 35 °C suggesting it had the
maximum surface activity.
The efficiency of surface tension reduction (pC20) is
given by the -logC required to reduce the surface tension
of the solvent by 20 mN/m [35]. The larger the pC20 value,
the stronger the ability to decrease surface tension. The
pC20 value at 25 °C are larger than that at 35 °C for same
glycoside, and increase with increasing alkyl chain length
of the glycoside.
C
max values at 25 °C are smaller than the value at 35 °C for
same glycoside, and decreases with increasing alkyl chain
length.
The negative value of the standard free energy of
micellization (DGmic) and adsorption (DGads) of individual
glycoside at 25 and 35 °C imply that micelle (perhaps
including vesicle formation) and surface excess formation
are thermodynamically favored for alkyl glycosides (6b–
6e). The absolute values of DGmic and DGads at 25 °C are
larger than the values at 35 °C for same glycoside, and
increase with increasing alkyl chain length. Since the alkyl
chain of the glycoside is hydrophobic, both adsorption and
aggregation are entropy driven process. As a result, the
longer the alkyl chain, the greater the entropic gain.
Comparing DGmic and DGads, the DGads values are larger
than that of DGmic and the tendency is stronger for the
glycoside being adsorbed to the air–water interface rather
than forming micelles.
The minimum cross-sectional area (Amin) per surfactant
molecule, i.e., the minimum surface area per alkyl gly-
coside (6b–6e) at the air/water interface at 25 °C was lar-
ger than the area at 35 °C for same glycoside. The Amin
Thermal Stability
The thermal decompistion of alkyl galactopyranosides was
measured by thermogravmetric analysis. Figure 8 and
Table 3 show the weight loss as a function of temperature.
The temperature ranges of decomposition of alkyl b-D-
galactopyranosides (6a–6e) were 274.3–360.1 °C,
300.6–340.5 °C, 284.1–320.1 °C, 303.0–344.7 °C and
294.2–326.4 °C in sequence. The rate of weight loss
reached their maximum at 316.3, 327.7, 314.4, 333.4 and
321.1 °C. These results suggest that the maximum thermal
temperature is below 270 °C.
Thermotropic Liquid Crystalline Properties
The cell membranes of living systems contain vast
resources of liquid crystals which are often related to
normal physiological function, plant defense, microbial
infection and the occurrence of disease [21]. Alkyl b-D-
galactopyranosides are monoalkylated galactosides. Sakya
Fig. 7 Relationship between surface tension vs concentration of
alkyl b-D-galactopyranoside (6b–6e) at 25 °C (up) and 35 °C (down)
123

J Surfact Deterg
Table 2 Adsorption parameter at 25 and 35 °C
Glycoside
T
°C
CMC
mmol L-1
cCMC
pCMC
dc/dlnC
Umax
Amin
A
pC20
DGmic
DGads
2
˚
mN m-1
mN m-1
910-6 mol m-2
KJ mol-1
KJ mol-1
6b
6c
6d
6e
25
35
25
35
25
35
25
35
17.54
28.72
16.23
21.11
3.21
39.0
39.2
31.0
32.0
32.0
34.4
30.0
31.2
32.97
31.18
40.97
38.38
39.97
35.98
41.97
39.18
-11.72
-13.04
-11.26
-12.92
-10.69
-12.76
-10.57
-12.21
4.73
5.26
4.54
5.21
4.31
5.12
4.26
4.93
35.12
31.58
36.59
31.87
38.54
32.27
38.99
33.71
2.22
1.90
2.62
2.31
3.30
2.79
3.85
3.26
-10.02
-8.80
-16.99
-14.73
-19.23
-16.93
-23.50
-19.99
-26.97
-23.23
-10.21
-9.56
-14.23
-12.97
-17.12
-15.28
5.34
1.00
2.10
in Figs. 9, 10 and Table 4. Alkyl b-D-galactopyranosides
(6a–6e) show thermotropic liquid crystallinity upon heat-
ing. b-D-Galactopyranosides (6b–6e) has a distinctively
optical texture (a smectic A type phase) [21]. Alkyl b-D-
galactopyranosides (6a–6e) possessed sharp melting points
(mp, a transition from a solid state to a liquid crystal phase)
and sharp clearing points (Cp, a change from the liquid
crystal phase into a liquid state), and the mesophase tem-
perature ranges (DT = Cp -mp) rose gradually with
increasing alkyl chain length [22].
Wettability
The wettability of alkyl b-D-galactopyranosides (6a–6e)
solution was investigated at 35, 45 and 55 °C, and the
results are shown in Table 5. Hexyl b-D-galactopyranoside
(6a) and heptyl b-D-galactopyranoside (6b) did not wet the
canvas disc after 12 h indicating that their wetting prop-
erties are the worst. The wettability of alkyl b-D-galac-
topyranoside (6c–6e) solution increased with increasing
alkyl chain length. Decyl b-D-galactopyranoside (6e)
showed the strongest wettability, and the sinking time (also
called wetting time) of canvas disc in the solution fell
within a very short range (52.7–94.3 s) at 35–55 °C. The
wettability was affected by temperature, the higher the
temperature, the shorter the sinking time and the better the
wetting ability.
Fig. 8 TG curve of alkyl b-D-galactopyranoside (6a–6e)
reported that thermotropic phase behavior of seven
monoalkyl glycosides. The data for n-octyl b-D-galac-
topyranoside was 96 °C SAd 127 °C [39]. Monoalkylated
glycosides can exhibit different thermotropic phase
behavior from branched chain glycosides. Hashim men-
tioned that monoalkylated glycosides could only exhibit a
SA (La) phase when heated, however, Guerbet glycosides
could exhibit a variety of phases (Lc, La, HII and QII) [40].
The thermotropic phase behavior of alkyl b-D-galac-
topyranoside (6a–6e) in the heating process was observed
by using the polarization microscope and results are shown
Table 3 TG Parameters of alkyl b-D-galactopyranosides (6a–6e)
Glycoside Temperature of initial
decomposition/°C
Temperature of terminal
decomposition/°C
Temperature of maximum
decomposition rate/°C
Percent of weight
loss/%
6a
6b
6c
6d
6e
274.3
300.6
284.1
303.0
294.2
360.1
340.5
320.1
344.7
326.4
316.3
327.7
314.4
333.4
321.1
93.6
93.6
93.2
96.7
69.7
123

J Surfact Deterg
Fig. 9 Texture of alkyl b-D-galactopyranoside characterized by OPM upon heating (a) and cooling (b)
Table 5 Wettability of alkyl b-D-galactopyranoside (6a–6e) solution
Glycoside
35 °C
45 °C
55 °C
6a
6b
6c
6d
6e
–
–
–
–
–
–
9.30 h
32.4 min
94.3 s
6.56 h
26.3 min
74.3 s
3.50 h
16.5 min
52.7 s
(6a–6e) were prepared by successive five steps including
acetylation, selective deacetylation at the C1 position,
conversion to glycosyl trichloroacetimidate, coupling with
alcohols, and deprotection.
Fig. 10 Phase transition temperature of alkyl b-D-galactopyranoside
(6a–6e)
Their structure–property relationships including solubil-
ity, surface tension, emulsification, foaming, wettability,
thermotropic phase behavior, and thermal stability were
investigated. The solubility of alkyl b-D-galactopyranosides
(6a–6e) in water is lower than in ethanol at 25 °C and sol-
ubilities decreased with increasing alkyl chain length in both
solvents. Alkyl b-D-galactopyranosides (6a–6d) were sol-
uble in water, but decyl b-D-galactopyranosides (6e) was
insoluble in water. The solubility of alkyl b-D-galactopyra-
nosides (6a–6e) in ethyl acetate shows a downward parabola
with nonyl b-D-galactopyranosides (6d) being the most sol-
uble. The dissolution enthalpy and entropy values of alkyl b-
D-galactopyranoside (6a–6d) (n = 6–9) in water at
15–30 °C are larger than zero and increase with increasing
alkyl chain length. Dissolution is an endothermic process and
the solubility became larger with increasing solution tem-
perature. In addition, the dissolution entropy values decrease
linearly with increasing temperature. The alkyl b-D-
Table 4 Phase
galactopyranosides
transition
temperature
of
alkyl
b-D-
Glycoside
R
mp/°C
Cp/°C
DT/°C
6a
6b
6c
6d
6e
n-C6H13
n-C7H15
n-C8H17
n-C9H19
n-C10H21
113.6
96.9
98.9
94.3
93.3
116.7
113.6
131.6
146.2
153.9
3.1
16.7
32.7
51.9
60.6
Conclusion
This paper reports on the synthesis and properties of a
series of n-alkyl b-D-galactopyranosides. With D-galactose
as raw material, a series of n-alkyl b-D-galactopyranosides
123

J Surfact Deterg
¨
2. Cederlund H, Borjesson E (2016) Hot foam for weed control—do
alkyl polyglucoside surfactants used as foaming agents affect the
mobility of organic contaminants in soil? J Hazard Mater
314:312–317
galactopyranoside (6b–6d, n = 7–9) showed moderate
emulsifying and foaming properties, and the volume of the
aqueous phase separated from the emulsion decreased with
increasing alkyl chain length. Nonyl b-D-galactopyranoside
(6d) showed the emulsifying property, foaming ability and
foam stability. Alkyl b-D-galactopyranosides (6b–6e,
n = 7–10) were able to decrease the surface tension of
aqueous solution at 25 and 35 °C. The CMC decreases with
increasing alkyl chain length, and is higher at 25 °C than at
35 °C for the same glycoside. The glycosides (6b–6e) could
migrate more favorably to the interface than remain in the
solution. Alkyl b-D-galactopyranosides (6a–6e, n = 6–10)
were stability below 270 °C. Alkyl b-D-galactopyranoside
(6a–6e, n = 6–10) possess melting points and sharp clearing
points, and their mesophase temperature ranges rose gradu-
ally with increasing alkyl chain length. The b-D-galactopy-
ranosides (6b–6e) had distinctively optical texture of a
thermotropic liquid crystal smectic A type phase. The wet-
tability of aqueous solution was affected by alkyl b-D-
galactopyranoside and temperature. Alkyl b-D-galactopyra-
noside (6c–6e, n = 8–10) show moderate wetting times.
Decyl b-D-galactopyranoside (6e) shows the strongest wet-
tability with a wetting time of 52.7 s at 55 °C.
´
´
´
3. Rıos F, Fernandez-Arteaga A, Lechuga M, Jurado E, Fernandez-
Serrano M (2016) Kinetic study of the anaerobic biodegradation
of alkyl polyglucosides and the influence of their structural
parameters. Environ Sci Pollut Res 23:8286–8293
4. Rybinski WV, Hill K (1998) Alkyl polyglycosides-properties and
applications of a new class of surfactants. Angew Chem Int Edit
37:1328–1345
5. Nagae M, Yamaguchi Y (2014) Three-dimensional structural
aspects of protein–polysaccharide interactions. Int J Mol Sci
15:3768–3783
6. Lundemo P, Adlercreutz P, Karlsson EN (2013) Improved
transferase/hydrolase ratio through rational design of a family 1
b-glucosidase from Thermotoga neapolitana. Appl Environ
Microb 79:3400–3405
7. Svensson D, Ulvenlund S, Adlercreutz P (2009) Enzymatic route
to alkyl glycosides having oligomeric head groups. Green Chem
11:1222–1226
8. Ehsan M, Du Y, Scull NJ, Tikhonova E, Mortensen JS, Loland
CJ, Skiniotis G, Guan L, Byrne B, Kobilka BK, Chae PS (2016)
Highly branched pentasaccharide-bearing amphiphiles for mem-
brane protein studies. J Am Chem Soc 138:3789–3796
9. Rather MY, Ara KZG, Karlsson EN, Adlercreutz P (2015)
Characterization of cyclodextrin glycosyltransferases (CGTases)
and their application for synthesis of alkyl glycosides with oli-
gomeric head group. Process Biochem 50:722–728
Overall, the alkyl chain length was found to affect the
property of galactoside significantly. Alkyl b-D-galac-
topyranosides (6a–6e) with different chain length showed
different solubility in different solvents and their solubili-
ties in water and ethanol both decrease with increasing
alkyl chain length. The longer the alkyl chain, the stronger
emulsifying ability for toluene and rapeseed oil. However,
their foaming property exhibited different trend with
increasing alkyl chain length. Octyl b-D-galactopyrano-
sides (6c) exhibited the best foaming ability, but its
foaming stability was the worst. Generally, nonyl b-D-
galactopyranosides (6d) exhibited the best foaming prop-
erties. The minimum cross-sectional area (Amin) and CMC
value increased with increasing alkyl chain length. The
absolute values of DGads increased with increasing alkyl
chain length, suggesting that the longer the alkyl chain
length, the stronger the adsorption at the air–water inter-
face. Their mesophase temperature ranges rose gradually
and their wettability increased with increasing alkyl chain
length.
¨
10. Mu¨ller MM, Ku¨gler JH, Henkel M, Gerlitzki M, Hormann B,
Pohnlein M, Syldatk C, Hausmann R (2012) Rhamnolipids-next
¨
generation surfactants? J Biotechnol 162:366–380
11. Yang R, Wang Z, Bi Y, Jia J, Zhao X, Liu X, Du W (2015)
Convenient synthesis of alkyl and phenylalkyl b-D-glucopyrano-
sides using facile and novel biocatalysts of plant origin. Ind Crop
Prod 74:918–924
12. Castro MJL, Kovensky J, Cirelli AF (2005) Ecologically safe
alkyl glucoside-based gemini surfactants. Arkivoc 12:253–267
13. Yakimchuk OD, Kotomin AA, Petel’skii MB, Naumov VN
(2004) Cleaning action and surfactant properties of alkyl gluco-
sides. Russ J Appl Chem ? 77:2001–2005
14. Balcerzak AK, Capicciotti CJ, Briard JG, Ben RN (2012)
Designing ice recrystallization inhibitors: from antifreeze
(glyco)proteins to small molecules. RSC Adv 4:42682–44269
15. Smułek W, Zdarta A, Milewska M, Kaczorek E (2016) Alkyl
polyglucosides as cell surface modification factors: influence of
the alkyl chain length. Toxicol Environ Chem 98:13–25
´
´
´
16. Savic S, Tamburic S, Savic MM (2010) From conventional
towards new-natural surfactants in drug delivery systems design:
current status and perspectives. Expert Opin Drug Deliv 7:353–369
17. Aripin NFK, Park JW, Park HJ (2012) Preparation of vesicle drug
carrier from palm oil-and palm kernel oil-based glycosides.
Colloid Surfaces B 95:144–153
´
´
18. Fegyver E, Meszaros R (2014) Fine-tuning the nonequilibrium
behavior of oppositely charged macromolecule/surfactant mix-
tures via the addition of nonionic amphiphiles. Langmuir
30:15114–15126
Acknowledgments We are grateful to the Natural Science Founda-
tion of Hunan Province, China (Grant No. 14JJ2067 and 10JJ6023).
19. Ahmadi S, Achari VM, Nguan H, Hashim R (2014) Atomistic
simulation studies of the a/b-glucoside and galactoside in anhy-
drous bilayers: effect of the anomeric and epimeric configura-
tions. J Mol Model 20:2165
References
20. Hashim R, Mirzadeh SM, Heidelberg T, Minamikawa H,
Yoshiaki T, Sugimura A (2011) A reevaluation of the epimeric
and anomeric relationship of glucosides and galactosides in
thermotropic liquid crystal self-assemblies. Carbohyd Res
346:2948–2956
1. Negm NA, El Farargy AF, Tawfik SM, Abdelnour AM, Hefni
HH, Khowdiary MM (2013) Synthesis, surface and thermody-
namic properties of substituted polytriethanolamine nonionic
surfactants. J Surf Deterg 16:333–342
123

J Surfact Deterg
¨
21. Goodby JW, Gortz V, Cowling SJ, Mackenzie G, Martin P,
Plusquellec D, Benvegnu T, Boullanger P, Lafont D, Queneau Y,
Chambert S, Fitremann J (2007) Thermotropic liquid crystalline
glycolipids. Chem Soc Rev 36:1971–2032
36. Yoshimura T, Sakato A, Tsuchiya K, Ohkubo T, Sakai H, Abe M,
Esumi K (2007) Adsorption and aggregation properties of amino
acid-based N-alkyl cysteine monomeric and N, N0-dialkyl cystine
gemini surfactants. J Colloid Interf Sci 308:466–473
37. Li H, Ge H, Li M, Xu P, Qi J (1996) Synthesis and properties of
octyl polyglucoside. J Zhengzhou Grain Coll 17(4):31–35 (in
Chinese)
38. Liu D, Chen L, Li H, Zeng S, Kuang N, Tian J (2013) Syntheses
and properties of alkyl b-D-glucopyranosides. Chin J Appl Chem
30:1120–1126 (in Chinese)
39. Sakya P, Seddon JM (1997) Thermotropic and lyotropic phase
behaviour of monoalkyl glycosides. Liq Cryst 23:409–424
40. Hashim R, Sugimura A, Minamikawa H, Heidelberg T (2012)
Nature-like synthetic alkyl branched-chain glycolipids: a review
on chemical structure and self-assembly properties. Liq Cryst
39:1–17
22. Xu W, Osei-Prempeh G, Lema C, Oldham ED, Aguilera RJ,
Parkin S, Rankin SE, Knutson BL, Lehmler H-J (2012) Synthesis,
thermal properties, and cytotoxicity evaluation of hydrocarbon
and fluorocarbon alkyl b-D-xylopyranoside surfactants. Carbohyd
Res 349:12–23
23. Kong F, Yang J, Zhen Z, Liang T, Zhu D, Gao R, Xie G (2015)
Gene cloning and molecular characterization of a b-glucosidase
from RUK-10: an effective tool for synthesis of galacto-
oligosaccharide and alkyl galactopyranosides. Chem Res Chin
Univ 31:774–780
24. Chen L, Liu D, Kuang N (2013) Synthesis of 2-chloroethyl
2,3,4,6-tetra-O-acetyl-b-D-glucopyranoside. J Xuzhou Inst Tech-
nol (Nat Sci Ed) 28(4):24–27 (in Chinese)
25. Wimmer Z, Pechova L, Saman D (2004) Koenigs-Knorr syn-
thesis of cycloalkyl glycosides. Molecules 9:902–912
26. Chen L, Lai D, Song Z, Zhao X, Kong F (2006) Strategies on
stereoselective synthesis of oligosaccharides. Chin J Org Chem
26:627–642 (in Chinese)
ˇ
´
Guoyong Chen is a postgraduate student in the College of Chemistry
at Xiangtan University. He obtained his B.E. in polymer materials and
engineering from Ludong University in 2013. His studies involve the
synthesis and application of alkyl glycoside.
27. Bornaghi LF, Poulsen SA (2005) Microwave-accelerated Fischer
glycosylation. Tetrahedron lett 46:3485–3488
28. El-Sukkary MMA, Syed NA, Aiad I, EI-Azab (2008) Synthesis
and characterization of some alkyl polyglycosides surfactants.
J Surfact Deterg 11:129–137
Zhencao Li is a postgraduate student in the College of Chemistry at
Xiangtan University. He obtained his B.Sc. in pharmacy from Jining
Medical University in 2013. His studies involve the synthesis and
application of alkyl glycoside.
29. Chen L, Kong F (2003) Unusual a-glycosylation with galactosyl
donors with a C2 ester capable of neighboring group participa-
tion. Tetrahedron Lett 44:3691–3695
Langqiu Chen received his Ph.D. from the Graduate School of the
Chinese Academy of Sciences (Research Center for Eco-Environ-
mental Science, Academia Sinica) in 2003 and worked in a
postdoctoral position in the Department of Chemistry at Oxford
University. He is a professor in the College of Chemistry at Xiangtan
University. His studies involve the research of carbohydrate chem-
istry, sugar-based surfactants, organic synthesis, pharmaceutical
synthesis and food additives.
30. Li LJ (2007) Study on the determination of PAA solubility and the
extraction technology. Appl Chem Ind 36:547–549 (in Chinese)
31. Li Y, Xu L, Wang F, Jin H, Ren B (2010) Solubilities of cefepime
hydrochloride in water ? (ethanol, 1-propanol, or 2-propanol)
from (278.15 to 308.15) K. J Chem Eng Data 55:4098–4103
32. Patist A, Huibers PDT, Deneka B, Shah DO (1998) Effect of
tetraalkylammonium chlorides on foaming properties of sodium
dodecyl sulfate solutions. Langmuir 14:4471–4474
33. Fainerman VB, Kazakov VN, Lylyk SV, Makievski AV, Miller R
(2004) Dynamic surface tension measurements of surfactant
solutions using the maximum bubble pressure method—limits of
applicability. Colloid Surf A 250:97–102
Shanwei Ji is a postgraduate student in the College of Chemistry at
Xiangtan University. He obtained his B.Sc. in materials chemistry
from Yulin Normal University in 2014. His studies involve the
synthesis and application of alkyl glycoside.
34. Eastoe J, Dalton JS (2000) Dynamic surface tension and
adsorption mechanisms of surfactants at the air-water interface.
Adv Colloid Interfac 85:103–144
35. ZakyMF Badawi AM, Sabbah IE, Ghani RAA, Hendawy ME
(2015) Synthesis, characterization and surface activities of
cationic polysaccharide (Aloe) schiff base surfactants. J Surfact
Deterg 18:455–461
Wangzhen Shen is a postgraduate student in the College of
Chemistry at Xiangtan University. She obtained her B.E. in food
quality and safety from Jishou University in 2014. Her studies involve
the synthesis and application of sugar-based surfactants.
123