Solution Properties of Alkyl β-D-Maltosides

Article abstract of DOI:10.1002/jsde.12281

Alkyl β-D-maltosides are an important class of sugar-based nonionic surfactants and have been widely studied. Nevertheless, it is still necessary to investigate further their amphiphilic structure-surface property relationships. In this article, we reported a series of properties of synthetic alkyl β-D-maltosides (6a–6i, n = 6–18) including their hydrophilic–lipophilic balance (HLB) number, water solubility, hygroscopicity, moisture-retention capacity, foaming ability, surface tension, thermotropic phase behavior, and skin irritation. Their HLB number and water solubility decreased with increasing alkyl chain length. Hexyl β-D-maltoside exhibited the strongest hygroscopicity and moisture-retention capacity. Decyl β-D-maltoside and dodecyl β-D-maltoside possessed excellent foaming power and foaming stability. Furthermore, the critical micelle concentration (CMC) of alkyl β-D-maltoside (6a–6g, n = 6–14) and their surface tension at CMC decreased with increasing alkyl chain length. At last, alkyl β-D-maltosides (6a–6g) should be considered as safe surfactants by the skin irritation assessment.

Full text of DOI:10.1002/jsde.12281

J Surfact Deterg (2019)
DOI 10.1002/jsde.12281
ORIGINAL ARTICLE
Solution Properties of Alkyl β-D-Maltosides
Zhencao Li1 · Guoyong Chen1 · Langqiu Chen1 · Yanhua Zhang1 · Zhiyong Dai2
Received: 7 December 2017 / Revised: 6 October 2018 / Accepted: 26 February 2019
© 2019 AOCS
Abstract Alkyl β-D-maltosides are an important class of
sugar-based nonionic surfactants and have been widely
studied. Nevertheless, it is still necessary to investigate fur-
ther their amphiphilic structure-surface property relation-
ships. In this article, we reported a series of properties of
synthetic alkyl β-D-maltosides (6a–6i, n = 6–18) including
their hydrophilic–lipophilic balance (HLB) number, water
solubility, hygroscopicity, moisture-retention capacity,
foaming ability, surface tension, thermotropic phase behav-
ior, and skin irritation. Their HLB number and water solu-
bility decreased with increasing alkyl chain length. Hexyl
β-D-maltoside exhibited the strongest hygroscopicity and
moisture-retention capacity. Decyl β-D-maltoside and
dodecyl β-D-maltoside possessed excellent foaming power
and foaming stability. Furthermore, the critical micelle con-
centration (CMC) of alkyl β-D-maltoside (6a–6g,
n = 6–14) and their surface tension at CMC decreased with
increasing alkyl chain length. At last, alkyl β-D-maltosides
(6a–6g) should be considered as safe surfactants by the
skin irritation assessment.
Keywords Nonionic surfactants ꢀ Surface activity ꢀ
Foaming property ꢀ Interfacial science
J Surfact Deterg (2019).
Introduction
Alkyl polyglycosides (APG) are a class of nonionic surfac-
tants, they are derived from sugars and fatty alcohols (Abel
et al., 2011; Aripin et al., 2012; Zhao et al., 2017). Apart from
an excellent performance in terms of surface tension,
foamability, and detergency, APG are environmentally
friendly, biodegradable, and low-toxic surfactants. Thereby,
they can be used for various applications such as drug carriers,
intranasal adjuvants, silk degumming agents, and in oil recov-
ery and sludge anaerobic fermentation (Ahmad et al., 2014;
Faramarzi et al., 2017; Karam et al., 2017; Wang and Zhang,
2017; Wu et al., 2017; Xiao et al., 2017; Zhou et al., 2017).
Alkyl D-maltosides could be prepared using
a
glycochemistry method from the renewable raw materials, D-
maltose and aliphatic alcohols. They could be categorized as
ecologically safe sugar-based surfactants (Ahmad et al.,
2014; Aripin et al., 2012; Karam et al., 2017; Zhao et al.,
2017). From a chemical point of view, alkyl D-maltosides are
stable under neutral and alkaline conditions because they are
comprised of bulkier and rigid sugar headgroups and flexible
alkyl chain tail groups connected via an ether linkage rather
than an ester linkage or an amide linkage (Faramarzi et al.,
2017). Therefore, they have a wide range of applications and
development in food, cosmetic, pharmaceutical industries,
and scientific research (de Foresta et al., 2011; Jastrzebska
et al., 2006; Ni et al., 2011; Pillion et al., 2002; Raman
et al., 2006; Rifkin et al., 2011; Santonicola et al., 2008;
Supporting information Additional supporting information may be
found online in the Supporting Information section at the end of the
article.
* 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 Republic of China
2
Ausnutria Dairy (China) Co. Ltd., Changsha, 410005, Hunan,
People’s Republic of China
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Weber and Benning, 1984; Zhang et al., 1996). They have
been used in drug delivery (Ahmad et al., 2014), thermal sta-
bilization (Ahmad et al., 2014), hydrolytic metabolism
(Weber and Benning, 1984), salt tolerance (Zhang et al.,
1996), formation of higher-ordered structure (Jastrzebska
et al., 2006), co-immunoprecipitation (Lee et al., 2018), and
structure analysis (Ni et al., 2011), as well as therapeutic adju-
vants (Rifkin et al., 2011), permeation enhancers (Pillion
et al., 2002), absorption enhancers (Gradauer et al., 2017),
and membrane protein stabilizers against denaturation (Das
et al., 2017; de Foresta et al., 2011; Jastrzebska et al., 2006;
Klammt et al., 2012; Newby et al., 2009; Raman et al., 2006;
Santonicola et al., 2008; Whorton and MacKinnon, 2013).
However, there are not enough data and messages avail-
able to support effectively the application in the field of life
and material sciences although there are some available
features/parameters including critical micelle concentration
(CMC) (Frotscher et al., 2017; Matsuoka et al., 2017;
Santonicola et al., 2008), sugar headgroup structure (Ehsan
et al., 2016), field-induced phase transition (Hashim et al.,
2017), paracellular permeation (Gradauer et al., 2017), and
cell metabolism (Smułek et al., 2017). The corresponding
fairly accurate and feasible screening should rely heavily
on the empirical evidence, exhaustive trial-and-error pro-
cess and rational thinking, and even intuitive approach.
Therefore, it is still indispensable to investigate systemati-
cally the water solubility of glycosides, surface activity,
and other properties to acquire the related data that are con-
venient for scientific research and practical applications.
Based on their bigger hydrophilic disaccharide headgroups,
alkyl D-maltosides should have higher water solubility than
that of alkyl D-glucosides with the same alkyl chain length.
Alkyl D-maltosides with a longer alkyl chain length would
improve the surface properties (for example micelle size) to a
certain extent as a class of sugar-based surfactants/detergents
available for the related research and applications (Smułek
et al., 2017). For the α-anomer and β-anomer micelles with
dodecyl group tails, the computed radii of gyration were 20.2
and 25.4 Å, respectively. Meanwhile, their computed (experi-
mental) average thickness of the polar outer layer was
6.7 ꢁ 0.3 Å (5.4 ꢁ 0.1 Å) and 7.3 ꢁ 0.4 Å (6.2 ꢁ 0.1 Å),
respectively. These values were 39.1% (50.9%) and 33.6%
(43.6%) smaller than the calculated length of the maltose in
its extended configuration (ꢂ11.0 Å) owing to the partial
folding of the maltose head. In contrast, their computed
(experimental) surface areas were 60.3–61.1 Å2 (58 Å2) and
55.5–65.1 Å2 (52 Å2), respectively. Furthermore, the micelles
containing the β-anomer had a more pronounced ellipsoidal
shape than those containing the α anomer. In addition, the
β-anomer was a linear conformation not only in its micellar
form but also in its solvent form. It should be more suitable
for the membrane protein studies than the α-anomer because
the α-anomer was in a right-angle bent shape formed between
the maltosyl headgroup and the alkyl tail group. The
α-anomer appears to be more folded and constrained on the
micelle surface, and hence it shows less solubility than the
β-anomer (Abel et al., 2011).
There is some literature on alkyl D-maltosides (Ericsson
et al., 2005; Kocherbitov and Söderman, 2004; Koeltzow
and Urefer, 1984; Vill et al., 1989; von Minden et al.,
2000). They can be prepared with SnCl4 or BF3ꢀEt2O as
Lewis acid catalysts of the condensation reaction, but the
condensation time is rather difficult to control to some
extent and the yield was low for the condensation step as
concurrent decomposition and serious α-anomerization take
place (Aripin et al., 2012). Alkyl β-D-maltoside (Pillon
et al., 2002), deuterated dodecyl β-D-maltoside (d39-DDM)
(Hiruma-Shimizu et al., 2014), and dodecyl β-D-
melibioside (Hutchison et al., 2017) were stereoselectively
prepared by the Koenigs and Knorr procedure with silver car-
bonate or silver triflate (AgOTf) as an expensive promoter in
the coupling reaction. However, the Koenigs and Knorr pro-
cedure usually is uneconomic and/or may easily cause the
accumulation of toxic heavy metal and the related environ-
mental pollution in spite of its fairly high efficiency. Because
the first article on the Schmidt’s glycosylation method was
published in 1980, the glycosyl trichloroacetimidates have
been the most widely used glycosyl donors (Gao et al., 2016;
Kinnaert et al., 2017). Their high popularity would be most
likely due to two points: First, the relative ease of the donor
preparation with the addition of base-catalyzed
trichloroacetonitrile to the anomeric hydroxy group; and sec-
ond, the high anomeric selectivity of subsequent coupling
reactions via an eight-membered cyclic transition state (Chen
and Kong, 2003; Kumar et al., 2011).
Herein, to gain more detailed insights into the structure–
property relationships, we investigate the related surface
properties involving solubility, foaming property, surface
tension, hygroscopicity, moisture retention capacity, ther-
motropic liquid crystalline behavior, and skin irritation of
synthetic alkyl β-D-maltosides (6a–6i, n = 6–18) (Fig. 1)
with the homologous series.
Experimental Section
General Methods and Synthesis
1H NMR spectra were recorded using an Avance 400 spec-
trometer (Bruker Daltonics Inc., Fällanden, Switzerland).
Optical activities were obtained using a Perkin-Elmer
model 341-MC automatic polarimeter (Perkin-Elmer, Inc.,
Waltham, MA). Melting points were measured using an X-
4 digital melting point apparatus (Yuhua instruments Co.,
Ltd, Henan, China). Surface tension was determined using
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OAc
OAc
O
O
AcO
AcO
AcO
AcO
OAc
OAc
CCl3CN
OH
Ac2O
BnNH2
OAc
Maltose
1
OAc
O
OAc
O
AcONa
O
AcO
O
AcO
OAc
3
OAc
2
OAc
OAc
O
O
AcO
AcO
AcO
AcO
OAc
OH
OAc
CH3(CH2)n-1OH
OAc
4
O
OAc
O
O
AcO
O
AcO
O(CH2)n-1CH3
OC(=NH)CCl3
OAc
OAc
5
O
HO
HO
n = 6, 7, 8, 9, 10, 12, 14, 16, 18
a, b, c, d, e, f, g, h,
OH
1'
i
MeONa
OH
O
O
HO
1
O(CH2)n-1CH3
OH
6
Fig. 1 Synthetic route for alkyl β-D-maltosides
W
a DCAT11 Tensiometer (Dataphysics Instruments Ltd, Fil-
derstadt, Germany). Thermotropic liquid crystalline behav-
ior was investigated using a DM-LM-P polarization
microscope (Leica, Wetzlar, Germany) with a Leitz 350 hot
stage. Thermal stability was determined using a TGA Q50
thermogravimetric analyzer (TA Instruments, NewCastle,
DE, USA). All raw materials and solvents were of chemical
grade or analytical grade.
HLB = 20
ð1Þ
W + O
where W is the molecular mass (341.29) of the hydrophilic
sugar headgroup for β-D-maltoside (6a–6i); O is the molec-
ular mass of the lipophilic alkyl group.
Method 2: According to Davies’ group contribution
method (Berger et al., 2005; Zhou et al., 2001), the HLB
number was calculated by Eq. (2):
The detailed synthetic process (Fig. 1) and the related
characterization of alkyl β-D-maltosides (6a–6i, n = 6–18)
were compiled in Appendix S1 (Supporting Information)
according to the published glycosidation procedure (Chen
et al., 2016a, 2016b; Chen and Kong, 2003).
HLB = 7 + ΣðHÞ−ΣðLÞ
where H is the group contributions for the hydrophilic por-
tions in the molecule, L is the contribution from the lipo-
philic portions in β-D-maltoside (6a–6i).
ð2Þ
Method 3: According to the empirical relationship
HLB = 60H/(H + 2) from 1H NMR technology (Ben-et
and Tartarsky, 1972; Zheng et al., 2007; Zhou and Cui,
2001), H is the ratio of the hydrogen atom numbers (includ-
ing OH, CH, and CH2 in the sugar ring, and OCH2 in the
alkoxy chain) to total hydrogen atom numbers. Therefore,
the HLB number of β-D-maltoside (6a–6i) was obtained
by Eq. (3):
Thermal Stability
Thermogravimetric analysis (TGA) curve was recorded for
alkyl β-D-maltoside (6a–6i) under a nitrogen atmosphere at
a heating rate of 20 ꢃC min−1
.
Thermotropic Phase Behavior
1380
HLB =
ð3Þ
Thermotropic liquid crystalline behavior was studied using
polarization microscopy (POM) according to the literature
(Chen et al., 2016a).
4n + 67
where n is the number of carbon atoms in the alkyl chain of
β-D-maltoside (6a–6i).
Method 4: The HLB number was calculated by Eq. (4)
based on the small revision of Eq. (3):
Hydrophilic–Lipophilic Balance (HLB) Number
1380
2
+ 4:9 × 10−2ðn−6Þ−3:5 × 10−4ðn−18Þ
The HLB number was calculated using the following
methods.
Method 1: According to Griffin’s method (Ji et al.,
2017), the HLB number of β-D-maltoside (6a–6i) was cal-
culated by Eq. (1):
HLB =
3:4n + 65:5
ð4Þ
where n is the carbon atom numbers of the alkyl chain in
β-D-maltoside (6a–6i).
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Table 1 1H NMR data of anomeric protons of alkyl β-D-maltosides
Method 5: Because H = 23/(2n + 22), the HLB number
was calculated as shown in Eq. (5) below:
D-maltoside
solvent
H-1 δ (d/s, J1,2
)
H-10 δ (d/s, J1,2
)
49:110H 0:046 0:797
6a
6b
6c
6d
6e
6f
D2O
D2O
D2O
D2O
D2O
D2O
D2O
4.48 (d, 8.0 Hz) 5.42 (d, 3.6 Hz)
4.45 (d, 7.9 Hz) 5.40 (d, 3.0 Hz)
4.45 (d, 7.9 Hz) 5.39 (d, 2.8 Hz)
4.40 (d, 7.6 Hz) 5.36 (d, 2.8 Hz)
4.39 (d, 7.1 Hz) 5.36 (s)
HLB =
−
+
−1:127
ð5Þ
H2
H + 1:391
H
where H was the same as H in Eq. (3).
Solubility
4.37 (d, 6.4 Hz) 5.35 (s)
6g
6h
6i
4.35 (d, 4.1 Hz) 5.33 (d, 1.0 Hz)
According to the literature method (Chen et al., 2016a; Ji
DMSO-d6/D2O 4.16 (d, 7.7 Hz) 5.03 (d, 3.4 Hz)
DMSO-d6 4.14 (d, 7.7 Hz) 5.00 (d, 3.0 Hz)
et al., 2017), the solubility of alkyl β-D-maltoside (6a–6i)
ꢃ
was determined at 25 C in water, ethanol, and ethyl ace-
tate, respectively.
Results and Discussion
Hygroscopicity and Moisture-Retention
Structure Confirmation
According to the literature method (Chen et al.,
2017; Shen et al., 2018), the hygroscopicity capacity
and the moisture-retention capacity were determined
using the weight method in relative humidity
(RH) 81% or RH 43% at 25 ꢃC. The results of
moisture-retention capacity were compared with the
capacity of glycerol.
1H NMR data of synthetic alkyl β-D-maltosides (6a–6i)
are shown in Appendix S1. As shown in Table 1, the
chemical shifts (the coupling constant) of anomeric pro-
tons of alkyl β-D-maltosides (6a–6g) are 5.33–5.42 ppm
(J1,2 ≤ 3.6 Hz) for H-10 and 4.35–4.48 ppm (J1,2
4.1–8.0 Hz) in D2O for H-1. Meanwhile, the chemical
shifts (the coupling constant) of β-D-maltoside (6h) are
5.03 ppm (J1,2 = 3.4 Hz) for H-10 and 4.16 ppm
(J1,2 = 7.7 Hz) for H-1 in dimethyl sulfoxide-d6/
deuterium oxide (DMSO-d6/D2O). Furthermore, the
chemical shifts (the coupling constant) of β-D-maltoside
(6i) are 5.00 ppm (J1,2 = 3.0 Hz) for H-10 and 4.14 ppm
(J1,2 = 7.7 Hz) for H-1 in DMSO-d6. All data indicate
that the newly formed glycosyl bond (6a–6i) is in a
1,2-trans β-configuration because the configuration is the
1,2-trans β-anomer as 4 Hz < J1,2 ≤ 8 Hz and the config-
uration is the 1,2-cis α-anomer as J1,2 < 4 Hz (Aripin
et al., 2012; Boyd et al., 2000; Chen and Kong, 2003;
Hiruma-Shimizu et al., 2014).
Foaming Properties
Foaming properties were investigated using the published
method (Li et al., 2016; Poole, 1989; Zhou et al., 2017).
0.25% (mass fraction) β-D-maltoside (6a–6g) aqueous
solutions were prepared at 25 ꢃC and then the aqueous
solutions (10 mL) were transferred into the graduated cyl-
inder (100 mL) with a plug. The solutions were followed
by vigorous shaking for 1 min and the volume of the pro-
duced foam was recorded. The disappearance rate (ν) of the
foams was calculated according to Eq. (6) and their stabil-
ity was assessed:
À
Á
ðH0 −H5Þ
60 × 5
ν =
mLs−1
ð6Þ
Thermal Stability
where H0 was the initial volume of the foam that was pro-
duced at the end of shaking, H5 was the volume of the foam
retained at 5 min after shaking.
TGA is an important and useful method in investigating
the pyrolysis behavior and assessing thermal stability.
The thermal stability of alkyl β-D-maltoside was
achieved by TGA at a rate of 20 ꢃC min−1 under a
nitrogen atmosphere as described in the Appendix S1
(Fig. S3). Alkyl β-D-maltosides (6a–6i) were found to
show typically a first-order pyrolysis behavior. The
related data are shown in Table 2. All β-D-maltosides
decomposed above 220 ꢃC, indicating that they had
excellent thermal stability mainly owing to the intramo-
lecular and multiple intermolecular H-bonding interac-
tions of their headgroup.
Surface Tension
The surface tension (γ) of alkyl β-D-maltoside (6a–6g)
aqueous solution was assessed using the literature method
with the Wilhelmy vertical plate technique at constant tem-
perature (25 ꢃC). The related details are shown in Appendix
S1 (Chen et al., 2016a; Shen et al., 2018; Zhang
et al., 1996).
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Table 2 TGA data of alkyl β-D-maltosides
Table 3 Phase transition temperatures of alkyl β-D-maltosides
D-
Initial
Temperature at
Last
Total
maltoside
R
Tlc/oC
Tiso/oC
ΔT/oC
maltoside decomposition maximum thermal degradation weight
6a
6b
6c
n-C6H13
n-C7H15
n-C8H17
—
—
—
—
—
temperature
(ꢃC)
decomposition
velocity (ꢃC)
temperature loss
(ꢃC)
(%)
—
86.2
(54a; 89–103b)
83.2
118.0
(122.7a; 125b)
124.7
31.8
6a
6b
6c
6d
6e
6f
232.2
235.0
228.8
241.8
262.8
244.0
258.3
263.5
250.2
354.7
363.2
359.3
368.3
336.0
329.6
340.9
357.5
347.1
405.8
403.5
409.2
409.4
422.1
403.1
409.8
413.0
409.0
88.7
92.4
94.8
87.5
93.5
89.1
90.3
92.7
90.1
6d
6e
n-C9H19
41.5
50.1
n-C10H21
86.4
126.5
(205.9a;
(58a; 96–100b; 86c)
207–208b;
156–159c)
241.0
6f
n-C12H25
n-C14H29
94.5
(95–105b;
76–76.5c; 102d;
65e; 102f)
97.4
146.5
150.9
(245b; 125–127c;
244d; 244e;
245f)
6g
6h
6i
6g
248.3
(107f)
(264f)
6h
6i
n-C16H33
n-C18H37
98.9
259.0
160.1
160.4
100.2
260.6
(76–91c; 106f)
(188–210c; 274f)
Thermotropic Phase Behavior
a
Kocherbitov and Söderman, 2004.
Boyd et al., 2000.
For the glycosides that are composed of one aliphatic chain
and one sugar group, lamellar smectic A or A* (chiral
smectic A, SA*) phases (Boyd et al., 2000; Calderer, 2001;
Goodby et al., 2007; Yelamaggad et al., 2005), depending
on their stereochemistry, should lead to a microphase segre-
gation between the carbohydrate moieties and the aliphatic
chains. The SA* phase exhibits characteristic defect tex-
tures that were observed using a polarizing microscope
(Goodby et al., 2007). Accordingly, alkyl β-D-maltosides
(6c–6i) show only SA* phases in their pure state. However,
hexyl β-D-maltoside (6a) and heptyl β-D-maltoside (6b)
did not show distinctive A* phases because both glycosides
perhaps had shorter alkyl chains so as to do not effectively
form distinctive SA* phases. The thermotropic phase
behavior of β-D-maltosides (6c–6i) was characterized by
polarizing microscopy and the data are shown in the
Appendix S1 (Fig. S2).
The double melting transition temperatures of alkyl D-
maltosides (6a–6i) are summarized in Table 3. D-
maltosides (6c–6i) possessed sharp melting temperatures
(Tlc, transition temperature from the crystallized solid into
a liquid crystal) and sharp clearing temperatures (Tiso,
transition temperature from a liquid crystal into an isotro-
pic liquid). The mesophase temperature ranges (ΔT = Tiso
– Tlc) of alkyl D-maltosides (6c–6g) increased with
increasing the alkyl chain length. For hexadecyl D-
maltoside (6h) and octadecyl D-maltoside (6i), their
mesophase temperature ranges were near each other
because they had almost the same Tlc and Tiso values and
reached a plateau where there would be an optimal bal-
ance between the hydrophilic part and hydrophobic part
of the liquid crystal.
b
c
d
e
f
Koeltzow and Urefer, 1984.
Vill et al., 1989.
Ericsson et al., 2005.
von Minden et al., 2000.
reported in the literature (Boyd et al., 2000; Ericsson et al.,
2005). Many researchers (Boyd et al., 2000; Ericsson et al.,
2005; Kocherbitov and Söderman, 2004; Koeltzow and
Urefer, 1984; Vill et al., 1989; von Minden et al., 2000;
Wang and Zhang, 2017) found similar data on D-
maltosides (Table 3). However, Bonicelli et al. (1998)
obserꢃved that decyl D-maltoside (6e) had a pretransition at
78.6 C and a solid–liquid crystal phase transition at 96.5
ꢃC. Finally, the mesophase behavior of maltosides is yet not
fully understood in spite of a large amount of experimental
data. Instead, there is no doubt that other techniques such
as differential scanning calorimeter, X-ray diffraction,
TGA, small-angle X-ray scattering, wide-angle X-ray scat-
tering, deuterium NMR, fourier transform infrared spectros-
copy, and small-angle neutron scattering should be used to
elucidate their complex mesophase information in the
future.
HLB Number, Partition Coefficient, and Solubility
The HLB number, as an empirical parameter that was intro-
duced by William C. Griffin in 1949, was originally devel-
oped as a scale to classify the relative effectiveness of
nonionic surfactants at forming stable emulsions at room
temperature. To date, it is one of the most significant prop-
erties of a surfactant.
Such an optical observation of the so-called double melt-
ing points in amphiphilic sugar-based surfactants was also
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Table 4 HLB number and water solubility (g per 100 g) of alkyl D-maltoside
D-maltoside
6a, C6
6b, C7
6c, C8
6d, C9
6e, C10
6f, C12
6g, C14
6h, C16
6i, C18
HLB number (by Eq. (1))
HLB number (by Eq. (2))
HLB number (by Eq. (3))
HLB number (by Eq. (4))
HLB number (by Eq. (5))
Difference (Eq(1)-Eq(3))
Difference (Eq(1)-Eq(4))
Difference (Eq(1)-Eq(5))
logP
16.01
16.95
15.16
16.01
16.02
0.85
15.50
16.48
14.53
15.46
15.46
0.97
15.02
16.00
13.94
14.95
14.95
1.08
14.57
15.53
13.40
14.48
14.48
1.17
14.14
15.05
12.90
14.04
14.05
1.24
13.37
14.10
12.00
13.26
13.27
1.37
12.67
13.15
11.22
12.59
12.59
1.45
12.04
12.20
10.53
12.00
12.00
1.51
11.48
11.25
9.93
11.48
11.48
1.55
0
0
0.04
0.07
0.09
0.10
0.11
0.08
0.04
−0.01
−1.68
69.31
0.04
0.07
0.09
0.09
0.10
0.08
0.04
0
−1.24
55.06
−0.85
38.36
−0.43
33.17
−0.01
15.23
0.82
1.66
2.49
3.33
0
Water solubility
7.04
0.78
0.0012
There are several methods including obtaining the
HLB number (Ben-et and Tartarsky, 1972; Berger et al.,
2005; Ji et al., 2017; Zheng et al., 2007; Zhou et al.,
2001; Zhou and Cui, 2001). Table 4 and Fig. 2 show the
HLB numbers from Eq. (1), Eq. (2), and Eq. (3), respec-
tively. HLB numbers decrease with increasing alkyl chain
length in the range of C6–C18. However, the HLB num-
ber (by Eq. (3)) was smaller than the HLB numbers
(by Eq. (1) and by Eq. (2)) for the same alkyl chain
length.
In Table 4 and Fig. 2, the HLB numbers in Eq. (3) are very
far away from the values calculated from Eq. (1). When
Eq. (4) is applied, diiferences are reduced (Table 4). Note that
HLB numbers in both Eq. (3) and Eq. (4) are a function of
alkyl chain length (n) in β-D-maltoside (6a–6i)).
the sugar headgroup at a high chemical shift (δ ≥ 4.0 ppm)
(Ben-et and Tartarsky, 1972). For any mixture of alkyl D-
maltoside (n = 6–18) with different alkyl chain lengths and
ratios, the corresponding HLB number should be readily
achieved with DMSO-d6 as a deuterated solvent in 1H
NMR experiment.
In fact, some hydrogen atoms (including CH and CH2 in
the sugar ring, and the OCH2 part of OCH2(CH2)n-2CH3 in
the alkoxy group) were just in the range of δ = 2.9–5.5 ppm
in spite of a lower chemical shift (δ < 2.5 ppm) for (CH2)n-
2CH3) of OCH2(CH2)n-2CH3 in various deuterated solvents
such as D2O, DMSO-d6, and DMSO-d6/D2O (Zheng et al.,
2007). Therefore, Eq. (5) indeed provided effective access to
obtain the HLB number from the molecular structure and/or
the data of the related 1H NMR spectrum.
Next, we expected to obtain further information directly
from the related 1H NMR spectra and/or the molecular
structures. For β-D-maltoside (6a–6i), we found relation-
ships between the chemical shift (δ) and the alkyl chain
length (n) as follows: (i) δ < 2.50 ppm for the (CH2)n-
2CH3) part of OCH2(CH2)n-2CH3; (ii) δ > 2.50 ppm for
both OH, CH, and CH2 in the sugar ring and the OCH2 part
of OCH2(CH2)n-2CH3 in the alkoxy group. In the 1H NMR
spectrum, the related integrated values of the hydrogen
atom were counted as 23 for δ > 2.50 ppm in β-D-
maltoside (6a–6i). Therefore, H = 23/(2n + 22) where H is
the ratio of particular hydrogen atom numbers (including
OH, CH, and CH2 in the sugar ring, and OCH2 in the alk-
oxy chain) to the total hydrogen atom numbers in β-D-
maltoside (6a–6i). Finally, Eq. (5) was readily obtained
from H = 23/(2n + 22) and Eq. (4) because the H values
can be actually obtained from the related the 1H NMR
spectra and/or the molecular structures.
Figure 3 shows the solubility of alkyl β-D-maltosides
(6a–6i) at 25 ꢃC in water, ethanol, and ethyl acetate, respec-
tively. The maltosyl headgroup of alkyl β-D-maltoside not
only has strong intermolecular hydrogen bonds (inter-HB) in
water, which increases water solubility, but also has strong
and rather stable intramolecular hydrogen bonds (intra-HB)
1
Herein, DMSO-d6 was used as the H NMR deuterated
solvent because of the chemical shifts (δ, ppm) (5.49 (1H),
5.45 (1H), 5.06 (1H), 4.90 (2H), 4.51 (1H), and 4.46 (1H))
of all OH in octadecyl β-D-maltoside (6i). As an example,
it can be just discovered near the chemical shifts (δ, ppm)
(4.14 (H-1) and 5.00(H-10) of both anomeric hydrogens of
Fig. 2 HLB numbers of alkyl β-D-maltosides
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that may somewhat weaken the inter-HB. The alkyl chain
tail group is a hydrophobic group and, therefore, has an
opposite effect on water solubility. As shown in Fig. 3 and
Table 4, water solubility decreased rapidly with increasing
alkyl chain length. Finally, two of the β-D-maltosides, (6h
(n = 16) and 6i (n = 18)), were water insoluble.
In contrast, the solubility in ethanol, at first, increased
with increasing alkyl chain length for n ≤ 10, then reached
the maximum value for n = 10 and subsequently decreased
with increasing alkyl chain length for n > 10. Nonetheless,
all β-D-maltoside (6a–6i) did not dissolve in ethyl acetate
for n = 6–18.
In this sense, the HLB numbers from Eq. (4) and Eq. (5)
should also be reasonable. Table 4 shows that the
maltosides (6a–6g) are water-soluble and their HLB num-
bers are bigger than 12.50, whereas the maltosides (6h and
6i) have poor water solubility and their HLB numbers are
within the range of 11.5–12. In fact, hexadecyl β-D-
maltoside (6h, n = 16) is almost water insoluble (only
0.0012 g per 100 g (water), a value that is smaller than the
common threshold (0.1 g per 100 g (water)). Octadecyl
β-D-maltoside (6i, n = 18) is completely insoluble in water.
Hygroscopicity
The octanol–water partition coefficient value (logP) of
alkyl β-D-maltoside (6a–6i) was calculated by
ChemBiodraw (Ultra 14.0), as shown in Table 4.
The hygroscopicities of alkyl β-D-maltoside (6a–6i) were
determined with different humidity (RH43 and RH81%) at
25 ꢃC. The results are shown in Fig. 4. The experiments show
that the hygroscopicity (Rh) value increases with time, but
decreases with increasing alkyl chain length. The Rh value
reaches a maximum value at 48 h. The Rh value at RH43%
was bigger than that at RH81%. The Rh value of dodecyl β-D-
maltoside (6f) reaches 14.8% (RH81%) and 23.2% (RH43%),
respectively, at 48 h mainly attributed to the intermolecular H-
bonding network of its polyhydroxy group in water.
HLB numbers and the logP values of alkyl β-D-
maltosides (6a–6g) were within the range of 12.67–16.01
(Eq. (1)) and − 1.68–1.66, respectively (Table 4), which
illustrate that they have stronger hydrophilicity and could
be used to stabilize O/W emulsions. However, the HLB
numbers and the logP values of alkyl β-D-maltosides (6h
and 6i) were in the range of 11.48–12.04 (Eq. (1)) and
2.49–3.33, respectively. Such glycosides are considered to
have weaker hydrophilicity although they should perhaps
have the ability to stabilize O/W emulsions to some extent
because their HLB number was bigger than 10.
Moisture-Retention Capacity
The literature (Berger et al., 2005) indicates that
surfactants with HLB numbers between 10 and 20 are
water-soluble and generally form stable, oil-in-water (O/W)
emulsions, whereas surfactants with HLB numbers below
10 are oil-soluble and generally form water-in-oil (W/O)
emulsion. Thus, the nonionic amphiphilic surfactants, β-D-
maltosides (6a–6i), probably are, therefore, suitable as
O/W emulsifiers because their HLB numbers are in the
range of 10–17.
β-D-maltosides (6a–6e) and glycerol were selected to
investigate their moisture-retention capacity (Rm), and the
results are shown in Fig. 5. Rm values of glycerol decrease
with the time, and also decreased faster at RH81% than that
at RH43%. The decreasing tendency of Rm values of D-
maltosides (6a–6e) is similar to that of glycerol at RH43%
and at RH81%. The Rm value of D-maltoside (6a–6e)
decreases with increasing alkyl chain length. The Rm values
of D-maltosides (6a–6e) at RH81% are smaller and
decrease faster than at RH43%.
Foaming Properties
The foaming behavior of alkyl β-D-ꢃmaltoside (6a–6g)
aqueous solutions was evaluated at 25 C, and the results
are presented in Fig. 6. The initial foam volume (H0)
increases with the alkyl chain length for n ≤ 9. Nonyl β-D-
maltoside (6d, n = 9) shows the strongest foaming power
(H0). However, the H0 value subsequently decreased with
increasing alkyl chain length for n > 9. The volume (H5) of
the foam retained at 5 min after shaking was high, for
n = 9–12, but decreased for n < 9 and n > 12. The disap-
pearance rate (ν) of the foam decreased with increasing
alkyl chain length for 6 ≤ n ≤ 14. The smaller the disap-
pearance rate (ν) of foam, the higher the foam stability. The
disappearance rate (ν) was almost equal to zero for
tetradecyl β-D-maltoside (6g, n = 14), meaning high foam
Fig. 3 Solubility of maltosides in ethyl acetate, ethanol, and water
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Fig. 4 Hygroscopicity (Rh) of D-maltosides (a) RH = 43%; (b) RH = 81%
Fig. 5 Moisture-retention capacity (Rm) of D-maltosides and glycerol (a) RH = 43% (left); (b) RH = 81% (right)
stability. In a practical way, nonyl β-D-maltoside (6d,
n = 9), decyl β-D-maltoside (6e, n = 10), and dodecyl β-D-
maltoside (6f, n = 12) should be considered as good
foaming agents as they showed the highest foaming power
and better stability.
Table 5 also shows the surface excess concentration
(Γmax) and the minimum area (Amin) data. The Γmax value
of alkyl β-D-maltoside (6a–6g) decreases slowly with
increasing alkyl chain length. Amin values increase slightly
with increasing alkyl chain length. Indeed, the longer the
hydrophobic alkyl chain length, the bigger Amin, and the
Surface Tension
smaller Γmax.
Furthermore, the values of effectiveness (πCMC) were
obtained with Eq. (S5) in Appendix S1 and are listed in
Table 5. The πCMC value increases with increasing hydro-
phobic chain length. Accordingly, the πCMC value is the
highest (38.16 mN m−1) for tetradecyl β-D-maltoside (6g),
and, therefore, it shows the best ability to decrease surface
tension.
Figure 7 shows the relationship between the surface tension
(γ) of alkyl β-D-maltoside (6a–6g) and the logarithm of the
concentration (C). The corresponding CMC and γCMC
(surface tension at CMC) obtained from Fig.7 are presented
in Table 5.
CMC and γCMC values decrease with increasing alkyl
chain length. Accordingly, tetradecyl β-D-maltoside (6g)
shows the lowest CMC and γCMC values.
In addition, Table 5 also provides the efficiency (pC20) data
obtained from Eq. (S6) in Appendix S1. The pC20 value of
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length; For n = 9 and 10, the CMC values of maltosides
are greater than the CAC values of glucosides with the
same alkyl chain length. All surface tension values at the
CMC (γCMC) of alkyl maltoside are greater than surface
tension values at the CAC (γCAC) value of glucoside with
the same alkyl chain length. The Amin value of maltoside
increases with increasing alkyl chain length, but the
change of the Amin value of alkyl glucoside shows no defi-
nite trend with increasing alkyl chain length.
Acute Skin Irritation
Alkyl β-D-maltosides (6a–6g) were tested for acute skin irri-
tation including erythema, edema at 1, 24, and 48 h on mice.
The corresponding stimulating effects on the local skin
were summarized according to the scoring system (i.e., the
experimental mean score 0–0.4 was classified as the non-
irritation reaction, 0.5–1.9 was light stimulation, 2.0–5.9
was moderate stimulation, and 6.0–8.0 was strong stimula-
tion) (British Standard Institution, 2010; General Adminis-
tration of Quality Supervision, Inspection and Quarantine
of P.R.C., 2000). The experimental results are shown in
Appendix S1 (Table S1). The total scores were as low as
0.1, which is classified as the nonirritation reaction. There-
fore, alkyl β-D-maltosides (6a–6g) produce no skin irrita-
tion, and they should be considered as safe sugar-based
surfactants.
Fig. 6 Foaming ability of alkyl D-maltosides
hexyl β-D-maltoside (6a) was only 2.14 mol L−1, suggesting
that its efficiency was the lowest. The pC20 value increased
gradually with increasing alkyl chain length, so that the effi-
ciency of tetradecyl β-D-maltoside (6g) should be the highest.
The standard free energy of micellization (ΔGmic) and
the standard free energy of adsorption (ΔGads) values of D-
maltosides (6a–6g) are negative as shown in Table 5. Their
ΔGmic and the ΔGads values became gradually more nega-
tive with increasing alkyl chain length. Because the alkyl
chains of the D-maltosides are hydrophobic, the entropic
effect is the most important contribution to the overall
Gibbs free energy of aggregation. Because ΔGads values
are more negative than ΔGmic for the same alkyl chain,
adsorption at the air/water interface appears to be more
favorable than the micellization in solution.
Conclusion
Ogawa’s group (Ogawa et al., 2013) investigated the
surface activities of a series of alkyl β-glucopyranosides
(n = 5–10) (Table6). For n = 6–8, the CMC values of
maltosides are smaller than the critical aggregation con-
centration values of glucosides with the same alkyl chain
Alkyl β-D-maltosides (6a–6i, n = 6–18) are nonionic
amphiphilic disaccharide-based surfactants. To validate
their potential application, their structure–property relation-
ships were investigated. Their calculated HLB number and
water solubility at 25 ꢃC decrease with increasing alkyl
chain length. Their hygroscopicity and moisture retention
capacity also decrease gradually with increasing alkyl chain
length. Hexyl β-D-maltoside (6a) and heptyl β-D-maltoside
(6b) have good moisture retention capacity. Decyl β-D-
maltoside (6e) and dodecyl β-D-maltoside (6f) have
outstanding foaming power and foaming stability. Alkyl
β-D-maltosides (6a–6g) have excellent surface activity.
The CMC, γCMC, and the Γmax values decrease monoto-
nously with increasing alkyl chain length. Amin, πCMC, and
the pC20 values increase gradually with alkyl chain length.
ΔGmic and ΔGads become more negative with increasing
alkyl chain length. Furthermore, the ΔGads values are more
negative than ΔGmic for the same alkyl chain length. Con-
cerning thermotropic behavior, a distinctive thermotropic
A* phase for β-D-maltoside (6c–6i) was found. The melt-
ing temperature, the clearing temperature, and the
Fig. 7 Surface tension of aqueous alkyl D-maltoside solution
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Table 5 Adsorption parameters of alkyl D-maltoside
D-maltoside
CMC
γCMC
Γmax × 1010
Amin
πCMC
pC20
ΔGmic
ΔGads
(mol L−1
)
(mN m−1
)
(mol cm−2
)
(Å2)
(mN m−1
)
(mol L−1
)
(kJ mol−1
)
(kJ mol−1
)
6a
6b
6c
6d
6e
6f
2.86 × 10−2
1.16 × 10−2
6.18 × 10−3
5.26 × 10−3
2.91 × 10−3
2.00 × 10−4
2.66 × 10−5
41.15
37.34
37.15
37.08
36.26
35.28
34.44
3.43
3.36
3.18
2.99
2.74
2.50
2.30
48.36
49.39
52.24
55.56
60.63
66.45
72.23
31.45
35.26
35.45
35.52
36.34
37.32
38.16
2.14
2.74
3.06
3.20
3.59
4.98
5.97
−8.66
−10.86
−12.39
−12.79
−14.23
−20.75
−25.67
−17.83
−21.35
−23.54
−24.67
−27.49
−35.68
−42.26
6g
Table 6 Adsorption parameters of alkyl β-D-maltoside and alkyl β-D-glucopyranoside
β-D-glucoside
(n)
CAC
γCAC
Amin
β-D-maltoside
CMC
γCMC
Amin
(mol L−1
)
(mN m−1
)
(Å2)
(n)
(mol L−1
)
(mN m−1
)
(Å2)
C5Glc (n = 5)
C6Glc (n = 6)
C7Glc (n = 7)
C8Glc (n = 8)
C9Glc (n = 9)
5.316 × 10−1
2.322 × 10−1
5.93 × 10−2
1.46 × 10−2
5.0 × 10−3
38.1
34.4
32.0
29.6
29.0
28.0
63.2
49.4
45.0
47.9
44.3
48.4
6a (n = 6)
6b (n = 7)
6c (n = 8)
6d (n = 9)
6e (n = 10)
6f (n = 12)
6g (n = 14)
2.86 × 10−2
1.16 × 10−2
6.18 × 10−3
5.26 × 10−3
2.91 × 10−3
2.00 × 10−4
2.66 × 10−5
41.15
37.34
37.15
37.08
36.26
35.28
34.44
48.36
49.39
52.24
55.56
60.63
66.45
72.23
C
10Glc (n = 10)
1.3 × 10−3
micelles in water: Influence of the headgroup conformation and
force field parameters. Journal of Physical Chemistry B, 115:
487–499.
mesophase temperature ranges of D-maltosides (6c–6g)
increase with alkyl chain length.
Overall, this study showed that the alkyl β-D-maltosides
(6a–6i, n = 6–18) obtained are safe, amphiphilic, and sur-
face active. Because their maltosyl headgroup is bigger
than the glucosyl headgroup of alkyl D-glucopyranoside,
their solubilities are higher than that of alkyl D-
glucopyranosides with the same alkyl chain length. The
experimental results are expected to provide the scientific
basis and are useful reference. The obtained products are
expected to have potential applications in a wide variety of
fields, as detergents, fine chemicals, cosmetics, food addi-
tives, and pharmaceutical products, as well as in biochemis-
try research and supramolecular research.
Ahmad, N., Ramsch, R., Llinàs, M., Solans, C., Hashim, R., &
Tajuddin, H. A. (2014) Influence of nonionic branched-chain alkyl
glycosides on a model nano-emulsion for drug delivery systems.
Colloids and Surfaces B: Biointerfaces, 115:267–274.
Aripin, N. F. K., Park, J. W., & Park, H. J. (2012) Preparation of vesi-
cle drug carrier from palm oil- and palm kernel oil-based glyco-
sides. Colloids and Surfaces B: Biointerfaces, 95:144–153.
Ben-et, G., & Tartarsky, D. (1972) Application of NMR for the deter-
mination of HLB values of nonionic surfactants. Journal of Ameri-
can Oil Chemistry Society, 49:499–500.
Berger, B. W., García, R. Y., Lenhoff, A. M., Kaler, E. W., &
Robinson, C. R. (2005) Relating surfactant properties to activity
and solubilization of the human adenosine A3 receptor. Biophysical
Journal, 89:452–464.
Bonicelli, M. G., Ceccaroni, G. F., & Mesa, C. L. (1998) Lyotropic
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Acknowledgements This work was supported by the National Nat-
ural Science Foundation of China (Grant No. 21643010), Hunan 2011
Collaborative Innovation Center of Chemical Engineering & Technol-
ogy with Environmental Benignity and Effective Resource Utilization,
and the Natural Science Foundation of Hunan Province, China (Grant
No. 14JJ2067).
Boyd, B. J., Drummond, C. J., Krodkiewska, I., & Grieser, F. (2000)
How chain length, headgroup polymerization, and anomeric config-
uration govern the thermotropic and lyotropic liquid crystalline
phase behavior and the air-water interfacial adsorption of glucose-
based surfactants. Langmuir, 16:7359–7367.
Conflict of Interest The authors declare that they have no conflict
of interest.
British Standard Institution (BSI) (2010) Biological evaluation of
medical devices part 10: Tests for irritation and skin sensitization
(ISO 10993-10:2010). Author. Retrieved from https://www.iso.
org/standard/40884.html.
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Biographies
Zhencao Li is currently a researcher in STA Pharmaceutical Co., Ltd.
He obtained his B.Sc. in pharmacy from Jining Medical University in
2013, his M.Sci. in Chemistry from Xiangtan University. His research
interests focus on sugar-based surfactants, organic synthesis, and
pharmaceutical synthesis.
Wang, F., & Zhang, Y.-Q. (2017) Effects of alkyl polyglycoside
(APG) on Bombyx mori silk degumming and the mechanical prop-
erties of silk fibroin fibre. Materials Science & Engineering C-
Materials for Biological Applications, 74:152–158.
Guoyong Chen is currently a researcher in STA Pharmaceutical Co.,
Ltd. He obtained his B.Eng. in polymer materials and engineering
from Ludong University in 2013, his M.Eng. in chemical engineering
from Xiangtan University. His research interests focus on pharmaceu-
tical synthesis and sugar-based surfactants.
Weber, N., & Benning, H. (1984) Metabolism of orally administered
alkyl β-glycosides in the mouse.Journal of Nutrition, 114:247–254.
Whorton, M. R., & MacKinnon, R. (2013) X-ray structure of the
mammalian GIRK2–βγ G-protein complex. Nature, 498:190–197.
Wu, H., Bao, Y., Wang, X., Zhou, D., & Wu, W. (2017) Alkyl poly-
glycoside, a highly promising adjuvant in intranasal split influenza
vaccines. Human Vaccines & Immunotherapeutics, 13:1279–1287.
Prof. (Dr.) Langqiu Chen is currently a professor in the College of
Chemistry at Xiangtan University. He received his B.Sc. in chemistry
from Xiangtan University (China) in 1984, his M.Eng. in food Engi-
neering from Light Industry Institute of Tianjin (China) in 1990, and
his Ph.D. from the Graduate School of Chinese Academy of Sciences
(Research Center for Eco-Environmental Science, Academia Sinica)
(China) in 2003, respectively. He worked as a guest researcher in
Ryukoku University (Japan), supported by JSPS for 10 months and as
a postdoctoral researcher in the Department of Chemistry at the Uni-
versity of Oxford (United Kingdom) for 1 year. His research interests
focus on carbohydrate chemistry, sugar-based surfactants, organic
synthesis, pharmaceutical synthesis, and food additives.
Xiao, J., Zhao, L., & Shen, Z. (2017) Enhanced sludge anaerobic fer-
mentation using microwave pretreatment combined with
biosurfactant alkyl polyglycoside. RSC Advances, 7:43772–43779.
Yelamaggad, C. V., Mathews, M., Hiremath, U. S., Rao, D. S. S., &
Prasad, S. K. (2005) Self-assembly of chiral mesoionic heterocycles
into smectic phases: A new class of polar liquid crystal. Tetrahe-
dron Letters, 46:2623–2626.
Zhang, L., Somasundaran, P., & Maltesh, C. (1996) Electrolyte effects
on the surface tension and micellization of n-dodecyl β-D-maltoside
solutions. Langmuir, 12:2371–2373.
Zhao, H., Bai, Y., Sun, H., & Li, Y. (2017) Study of the molecular
array behaviours and interfacial activities of green surfactant alkyl
polyglycoside and the mixed systems with other surfactants on oil–
water interface. Molecular Simulation, 43:1107–1115.
Yanhua Zhang has just received her M. Sc. from College of Chemis-
try, Xiangtan University. She obtained her B.Sc. in chemistry from
Hengyang Normal University (China) in 2015. Her research interest
includes the synthesis and aggregation behaviors of sugar-based
surfactants.
Zheng, W., Shen, Y., & Lu, W. (2007) Determination of high purity
soybean lecithin HLB by NMR.Cereals & Oils, 7:39–41 (in Chinese).
Zhou, J., & Cui, Y. (2001) Measurement and calculation of HLB
value of surfactants I. The measurement of HLB value. Speciality
Petrochemicals, 2:11–14 (in Chinese).
Zhiyong Dai is currently a researcher in Ausnutria Dairy (China) Co.
Ltd. He obtained his B.Sc. in Chemistry from Xiangtan University in
1997, his M.Ag. in food processing from Central South University of
Forestry and Technology in 2017. His research interests focus on
sugar, Protein, Animal milk, and food processing technology.
Zhou, J., Cui, Y., & Wu, Y. (2001) Measurement and calculation of
HLB value of surfactants II. The calculation of HLB value. Special-
ity Petrochemicals, 4:38–41 (in Chinese).
J Surfact Deterg (2019)