Synthesis and Aggregation of Novel Sugar-Based Gemini Surfactant with a N, N′-Acetylethylenediamine Spacer in Aqueous Solution

Article abstract of DOI:10.1002/jsde.12424

A novel sugar-based Gemini surfactant with a N,N′-acetylethylenediamine spacer (N,N′ (N-dodecyl-2-D-glucosaminyl acetyl) ethylenediamine, Glu(12)-(AA)-Glu(12)), was synthesized with D-(+)-Glucono-1,5-lactone as starting material in three steps. The surfactant's structure was confirmed using ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry (ESI-MS). The aggregation behavior of Glu(12)-(AA)-Glu(12) in aqueous solution at pH 4.0, 7.0, and 10.0 was investigated by surface tension, dynamic light scattering (DLS), and cryogenic transmission electron microscopic (Cryo-TEM) measurements. The surface tension measurement shows that the critical micelle concentration (CMC) of Glu(12)-(AA)-Glu(12) is at the concentration level of 10^?5 mol·L^?1 at 25 °C, which is significantly lower than that of corresponding monomeric sugar-based surfactants. Compared with such sugar-based Gemini surfactants with similar hydrophilic spacers, Glu(12)-(AA)-Glu(12) demonstrated similar or slightly lower surface activity. The CMC value of Glu(12)-(AA)-Glu(12) underwent a slight decrease with the increase of pH. DLS and Cryo-TEM measurements reveal that Glu(12)-(AA)-Glu(12) forms micelles at acidic pH (pH 4.0) and the micelles are transformed into vesicles at neutral or high pH (pH 7.0, 10.0). The microstructural transformation of Glu(12)-(AA)-Glu(12) aggregates is related to the protonation state of its two tertiary amines in the head groups versus pH.

Full text of DOI:10.1002/jsde.12424

J Surfact Deterg (2020)
DOI 10.1002/jsde.12424
ORIGINAL ARTICLE
Synthesis and Aggregation of Novel Sugar-Based Gemini
Surfactant with a N, N0-Acetylethylenediamine Spacer in
Aqueous Solution
Ruijuan Wang1 · Ruihua WanYan1 · Shuo Yang1 · Dong Wang2 · Zhigang Yin1
Received: 3 January 2020 / Revised: 4 May 2020 / Accepted: 4 May 2020
© 2020 AOCS
Abstract A novel sugar-based Gemini surfactant with a
N,N0-acetylethylenediamine spacer (N,N0 (N-dodecyl-2-D-
glucosaminyl acetyl) ethylenediamine, Glu(12)-(AA)-Glu
(12)), was synthesized with D-(+)-Glucono-1,5-lactone as
starting material in three steps. The surfactant’s structure
(12) underwent a slight decrease with the increase of
pH. DLS and Cryo-TEM measurements reveal that Glu
(12)-(AA)-Glu(12) forms micelles at acidic pH (pH 4.0)
and the micelles are transformed into vesicles at neutral or
high pH (pH 7.0, 10.0). The microstructural transformation
of Glu(12)-(AA)-Glu(12) aggregates is related to the pro-
tonation state of its two tertiary amines in the head groups
versus pH.
1
was confirmed using H and 13C nuclear magnetic reso-
nance (NMR) spectroscopy and electrospray ionization
mass spectrometry (ESI-MS). The aggregation behavior of
Glu(12)-(AA)-Glu(12) in aqueous solution at pH 4.0, 7.0,
and 10.0 was investigated by surface tension, dynamic light
scattering (DLS), and cryogenic transmission electron
microscopic (Cryo-TEM) measurements. The surface ten-
sion measurement shows that the critical micelle concentra-
tion (CMC) of Glu(12)-(AA)-Glu(12) is at the
concentration level of 10−5 molꢀL−1 at 25 ꢁC, which is sig-
nificantly lower than that of corresponding monomeric
sugar-based surfactants. Compared with such sugar-based
Gemini surfactants with similar hydrophilic spacers, Glu
(12)-(AA)-Glu(12) demonstrated similar or slightly lower
surface activity. The CMC value of Glu(12)-(AA)-Glu
Keywords Sugar-based gemini surfactant ꢀ pH ꢀ Surface
tension ꢀ DLS ꢀ Cryo-TEM
J Surfact Deterg (2020).
Introduction
Gemini surfactants (Menger and Littau, 1991) are com-
posed of two amphiphilic molecules connected by a spacer
through chemical bonds at or near the head groups, which
not only enhances the hydrophobic interaction between
hydrophobic groups but also weakens the electrostatic
repulsion between head groups due to the restriction of the
spacer, so they have many remarkable features over
corresponding traditional single-chain surfactants, such as
higher surface activity, richer self-aggregated behavior, and
greater molecular structure controllability. (Fan et al., 2016;
Zana, 2002; Zana and Talmon, 1993). Therefore, design
and preparation of Gemini surfactants with novel structure
and further characterization of their unique properties have
attracted much attention in recent years.
Supporting information Additional supporting information may be
found online in the Supporting Information section at the end of the
article.
* Ruijuan Wang
wangruijuan@iccas.ac.cn
* Zhigang Yin
yinck@zzuli.edu.cn
1
School of Material and Chemical Engineering, Zhengzhou
University of Light Industry, Zhengzhou, Henan 450002,
People’s Republic of China
Recently, as the world population has demonstrated
increased concern for environmental pollution and the
potential shortage of petrochemical resources in the future,
2
Centre for Bioengineering and Biotechnology, China University
of Petroleum (East China), Qingdao, 266580, People’s Republic
of China
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the development of novel bio-based surfactants with high
surface activity has gained interest. Sugar-based Gemini
surfactants, a typical representative, are prepared based on
natural renewable sugars (mono-, di- and polysaccharides)
and sugar derivatives (e.g., glycolactones, glycoacids, and
glycoamines), which combine utilization of renewable
biomass resources of sugar-based surfactant with the high
surface activity of Gemini surfactant. Now, some novel
structured sugar-based Gemini surfactants have been syn-
thesized, such as those formed from alkyl glycosides
(Castro et al., 1997; Castro et al., 1999; Castro
et al., 2006; Mariano et al., 2000), alkyl sugar (acyl)
amines (Gan et al., 2018; Gan et al., 2019; Johnsson
et al., 2003a; Laska et al., 2006; Sakai et al., 2008;
Tomokazu et al., 2013; Wagenaar and Engberts, 2007;
Warwel et al., 2004; Warwel and Brüse, 2004), and sugar-
based spacers (Menger and Mbadugha, 2001). Among the
cited studies, the synthesis and study of alkyl sugar (acyl)
amine Gemini surfactants has received the most attention.
Since this category of Gemini surfactants contains two
pH-sensitive tertiary nitrogens in their head groups that
can be protonated or deprotonated, a pH-dependent aggre-
gation behavior is expected. Some literatures have
reported that the aggregate microstructural transition of
alkyl sugar (acyl) amine Gemini surfactants from vesicle
(or double-layer -based structure) to rod-like and spherical
micelle (monolayer-based) can be successfully realized by
lowering the solution pH from neutral to acidic (Fielden
et al., 2001; Johnsson et al., 2003a, b; Johnsson and
Engberts, 2004). Moreover, alkyl sugar (acyl) amine Gem-
ini surfactants are nontoxic, biocompatible, and biode-
gradable, so they can be used as an ideal delivery vehicle
for gene transfection and drug delivery. (Fielden
et al., 2001; Zana, 2002; Zana and Talmon, 1993). This
inspires us to design and synthesize novel sugar-based
Gemini surfactants and investigate their aggregation
behavior.
Experimental Section
Materials
Bromoacetyl bromide (97%), dodecylamine (98%), and
D-(+)-Glucono-1, 5-lactone (99%) were purchased from
Shanghai Macklin Biochemical Science and Technology
Co., Ltd (Shanghai, China). Sodium dihydngen phoshate
anhydrous (99%), sodium phosphate dibasic (99%), sodium
tetraborate (≥99%), citric acid (≥99.5%), potassium carbon-
ate (99.5%), sodium carbonate (99%), sodium hydroxide
(99%), and hydrochloric acid (99%), used were of analyti-
cal grade. Triply distilled water was used in all
experiments.
Synthesis
The sugar-based Gemini surfactant of N, N0 (N-dodecyl-
2-D-glucosaminyl acetyl) ethylenediamine (3) was synthe-
sized according to Fig. 1. The melting point of the
intermediates N, N0-bis (2-bromoacetyl) ethylenediamine
(1) and N, N0-bis(2-dodecanoacetyl) ethylenediamine (2)
was measured using a micro-melting point apparatus X-4
(Beijing MAISIQI High-tech Co. Ltd., Beijing, China).
The structures (1)–(3) were characterized by H and 13C
1
NMR (Avance 600, Bruker Corp., Karlsruhe, Germany),
and ESI-MS (Exactive Orbitrap, Thermo Fisher, Waltham,
Mass, America). The spectra are provided in the
Supporting Information.
Synthesis of the Intermediate N, N0-Bis (2-Bromoacetyl)
Ethylenediamine (1)
A solution of ethylenediamine (0.03 mol) in trichloro-
methane (40 mL) inꢁa round-bottom flask of 250 mL was
cooled to around 0 C, and then solutions of bromoacetyl
bromide (0.10 mol) in trichloromethane (30 mL) and potas-
sium carbonate (0.08 mol) in water were added dropwise
with vigorous stirring over a period of 4 h while keeping
In the present work, we synthesized a novel alkyl
sugar (acyl) amine type Gemini surfactant with a N, N0-
acetylethylenediamine spacer (N, N0 (N-dodecyl-2-D-
glucosaminyl acetyl) ethylenediamine, Glu(12)-(AA)-Glu
(12)) (structure (3) of Fig. 1) based on D-(+)-Glucono-1,-
5-lactone. Glu(12)-(AA)-Glu(12) was prepared in three
steps, and the structures of the intermediates and the tar-
ꢁ
the temperature around 0 C. Next, the mixture was stirred
for 12 h at room temperature (around 25 C). Then, the
ꢁ
resulting suspension was heated about 2 h so that the solu-
tion underwent reflux and the resultant two-phase mixture
was separated while hot using a separatory funnel. After
that, the isolated (top) aqueous layer was extracted with hot
trichloromethane and the extract was combined with the
(bottom) organic phase of the separation. Finally, the white
precipitate was filtered out and concentrated in vacuo, and
recrystallized with ethanol, to give the pure intermediate
(1) as white crystals.
1
get product were characterized using H and 13C nuclear
magnetic resonance (NMR) spectroscopy and electrospray
ionization mass spectrometry (ESI-MS). The aggregation
behavior of Glu(12)-(AA)-Glu(12) in aqueous solution at
pH 4.0, 7.0, and 10.0 at 25.0ꢁC was investigated by
using surface tension, dynamic light scattering (DLS),
and cryogenic transmission electron microscopy
(Cryo-TEM).
N, N0-bis (2-bromoacetyl) ethylenediamine (1): white
solid, yield 50.21%. mp. 150.1 ~ 150.3 ꢁC, 1H NMR
(600 MHz, CD3OD,
δ
ppm):
δ
3.35–3.40 (t, 2H,
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Fig 1 Synthetic procedure of Glu(12)-(AA)-Glu(12) (3)
Br CH2 CO NH CH2 ),
Br CH2 CO NH CH2 ).
δ
3.80–3.86 (s, 2H,
CH2 CH2 ), δ 2.51–2.62 (d, 2H, CH3 (CH2)n
− 3
− 3
CH2 CH2 N),
δ
3.21–3.28
(s,
2H,
CH2 NH CH2 CO NH CH2 ), δ 3.38–3.50 (t, 2H,
CH2 NH CH2 CO NH CH2 ), δ 7.52–7.65 (s, 1H,
Synthesis of the Intermediate N, N0-Bis
(2-Dodecanoacetyl) Ethylenediamine (2)
CH2 NH CH2 CO NH CH2 ).
13C
NMR
(600 MHz, CDCl3, δ ppm): 14.13, 22.70, 27.20, 29.37,
29.56, 29.64, 29.65, 29.69, 30.14, 31.93, 39.11, 50.30,
52.54, 172.77. MS-ESI (m/z): calcd, 510.49; found, 511.53
[M + H]+, 256.27 [(M + 2H)/2]+.
The intermediate (1) (0.03 mol) was added to stirred and
heated ethanolic solution of dodecylamine (0.07 mol) in a
round-bottom flask of 250 mL over a period of 48 h under
reflux temperature. Then, the removal of the solvent etha-
nol was conducted by the rotary evaporation, and the
obtained residue was washed with ethanol several times
and filtrated by vacuum, which produced diamine bromate
as white crystalline flakes. Next, excess sodium carbonate
was added to the stirred ethanol solution of diamine bro-
mate for 1 d under reflux. Then, the reaction mixture was
filtrated, and the ethanol evaporated. Finally, the white
solid product, i.e., the intermediate (2), was obtained.
Synthesis of N, N0 (N-dodecyl-2-D-Glucosaminyl Acetyl)
Ethylenediamine (Glu(12)-(AA)-Glu(12)) (3)
A solution of the intermediate (2) (0.05 mol) in methanol
in a round-bottom flask of 100 mL was added to a stirred
and heated methanolic solution of D-(+)-Glucono-1,
5-lactone (0.2 mol). The reaction mixture was stirred for
2 d under reflux. Then, the solvent was removed by evapo-
ration, and the obtained residue was recrystallized several
times from the mixtures of ethanol-acetonitrile, producing
Glu(12)-(AA)-Glu(12) as viscous solid.
N, N0-bis(2-dodecanoacetyl) ethylenediamine (2): white
solid, yield 52.9%. mp. 102.0 ~ 102.2 ꢁC. 1H NMR
(600 MHz, CDCl3,
δ ppm): δ 0.85–0.93 (t, 3H,
CH3 CH2 ),
δ
1.18–1.35 (m, 18H, CH3 (CH2)n
N, N0 (N-dodecyl-2-D-glucosaminyl acetyl) eth-
ylenediamine (3): viscous solid, yield 52.9%. 1H NMR
CH2 ),
2
δ 1.36–1.50 (m, 2H, CH3 (CH2)n
−
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(600 MHz, CDCl3,
δ
ppm):
δ
0.82–0.96 (t, 3H,
Dynamic Light Scattering
CH3 CH2 ),
δ
δ
1.13–1.40 (m, 18H, CH3 (CH2)n
1.48–1.81 (m, 2H, CH3 (CH2)n
CH2 ),
3
The laser light scattering spectrometer (ALV-CGS-3), with
a multi-τ digital time correlater (ALV-7004), was used to
measure the hydration radius (Rh) of the sugar-based Gem-
ini surfactꢁant aggregates at different pHs and at
25.0 ꢂ 0.1 C. A solid-state He−Ne laser, with the output
power of 21 mW and the wavelength of 632.8 nm, was
used as the light source. Before testing, a membrane filter
with the micron aperture of 0.45 μm was used to filter the
newly prepared sugar-based Gemini surfactant solution.
During the measurements, the scattering angle was con-
trolled at 90ꢁ. The distribution of the diffusion coefficient
(D) was obtained by analyzing the autocorrelation function
from the scattering data via the Contin method (Antony
et al., 1998). Finally, the Stokes−Einstein equation was
used to calculate the hydrodynamic radius of Rh: Rh = kT/
(6πηD), where k is the Boltzmann constant, T the absolute
temperature, and η the solvent viscosity.
−
CH2 CH2 ), δ 3.53–4.60 (m, 16H, CH3 (CH2)n
− 3
− 3
CH2 CH2 N,
CH2 NH CO CH2
,
protons
from sugar moieties).
Measurements
Surface Tension Measurement
The Krüss K100 tensiometer (Hamburg, Germany) was
used to measure the surface tension of the sugar-based
Gemini surfactant solution at different pHs controlled
by using pH buffers which are formed by disodium
hydrogen phosphate and citric acid, disodium hydrogen
phosphate and sodium dihydrogen phosphate, and borax
and sodium hydroxide, respectively; and a Haake DC30
thermostatic bath (Karlsruhe, Germany) was used ꢁ to
control the temperature of all samples at 25.0 ꢂ 0.1 C.
During every test, the titration of the original Gemini
surfactant solution was continuously carried out to
obtain surfactant at a desired concentration range, and
the surface tension of the surfactant solution at each
concentration point was obtained by averaging three
measured values.
Cryogenic Transmission Electron Microscopy
The microstructure of the sugar-based Gemini surfactant
aggregates at different pHs was measured by Cryo-TEM.
Samples with a volume of 3–5 μL was dropped onto the
freshly carbon-coated holey TEM grids through a liquid
gun, and the redundant sample from the carbon-coated
holey TEM grids was removed by using a filter paper to
absorb the redundant samples, leaving only a very thin
layer of liquid sample on the carbon-coated holey TEM
grids. Then, they were quickly put into liquid ethane at
about 90 K to complete the rapid freezing of samples. Next,
the carbon-coated holey TEM grids with the prepared fro-
zen hydrated specimens were tranꢁsferred from liquid ethane
to liquid nitrogen at about −196 C for storage. After that,
they were taken out from the liquid nitrogen reservoir and
imaged through an FEI Tecnai 20 electron microscope
(Hillsboro, Oregon, America) with the filament of LaB6,
which was operated at accelerating voltage of 200 kV with
the low-dose mode about 2000 eꢀnm−2. Finally, images
were recorded on Kodak SO163 films, and further they
were digitized using Nikon (Tokyo, Japan) 9000 with a
scanning step of 2000 dpi, which is corresponding to
2.54 Å/pixel.
The parameter C20, i.e., the surfactant concentration that
reduces the surface tension of water by 20 mNꢀm−1, was
used to characterize the efficiency of surfactant for reduc-
tion of surface tension.
70
pH=4.0
pH=7.0
pH=10.0
60
50
40
30
20
Results and Discussion
0.01
0.1
1
Surface Tension Measurement
C (mM)
Fig. 2 shows the variation of the surface tension (γ) of Glu
(12)-(AA)-Glu(12) in aqueous solution with the surfactant
Fig 2 Variation of surface tension as a function of Glu(12)-(AA)-Glu
(12) concentration at different pHs and at 25.0 ꢁC
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ꢁ
concentration at different pHs and at 25.0 C. At pHs of
7.0 and 10.0, at low surfactant concentration, the surface
tension values decrease linearly with surfactant concentra-
tion (log scale), and then the surface tension remains con-
stant. The occurrence of the transition is due to the
saturation of surfactant molecules adsorbing onto the air-
water interface, leading to the formation of micelles
(i.e., the critical micelle concentration, or CMC). However,
at pH 4.0, there are two transition points. According to the
reported literatures, the transition at lower concentration is
attributed to the formation of premicelles, and the transition
at higher concentration to the formation of micelles by
Zana (2002); Piekarski et al. (2011); Łudzik et al. (2014).
The values of CMC, C20, and the surface tension at the
CMC (γCMC) for Glu(12)-(AA)-Glu(12) at pH 10.0, 7.0,
and 4.0 are listed in Table 1. The table indicates that the
pH=10.0
pH=7.0
pH=4.0
0.1
1
10
100
(nm)
1000
10000
R
h
CMC values are at the concentration level of 10−5 molꢀL−1
,
Fig 3 Distributions of the hydrodynamic radius Rh of Glu(12)-(AA)-
Glu(12) at different pHs and at 25.0 ꢁC
which is about one order of magnitude smaller than the
CMC of the traditional single-chain sugar-based surfactant
with the same carbon chain length (Burczyk et al., 2001).
Compared with such sugar-based Gemini surfactants with
similar hydrophilic spacers, Glu(12)-(AA)-Glu(12) demon-
strates similar or slightly lower surface activity (Warwel
et al., 2004; Warwel and Brüse, 2004). Moreover, with an
increase of pH, the CMC of Glu(12)-(AA)-Glu(12) slightly
decreases. This trend is closely related to the relationship
between pH and the degree of protonation for tertiary
amine nitrogen atoms of the head groups. Increased pH
causes the tertiary amine nitrogen atoms to be
deprotonated, thereby weakening the electrostatic repulsion
between the head groups and leading to a slight decrease
of CMC.
As shown in Fig. 3, at pH 4.0, two different of aggre-
gates with different hydrodynamic radius (Rh) of 2.82 nm
and 109.59 nm, are formed in aqueous solution. The
smaller-sized accounted for the larger proportion, indicat-
ing that Glu(12)-(AA)-Glu(12) mainly forms micellar struc-
ture at pH 4.0. At pH 7.0, the two aggregates possessed Rh
of 19.25 nm and 138.66 nm, and the larger aggregate was
present at a larger proportion. The results reveal that the
microstructure of Glu(12)-(AA)-Glu(12) aggregate varies
with pH. Accordingly, as shown in Fig. 4, the Cryo-TEM
images show that the system forms vesicular structured
aggregates at pH 7.0. At pH 10.0, the system mainly forms
larger-sized aggregates, with Rh 93.76 nm, and the Cryo-
TEM images show that the system also forms vesicles in
aqueous solution (Figs. 3 and 4).
DLS and Cryo-TEM Measurements
Glu(12)-(AA)-Glu(12) has two pH sensitive tertiary
nitrogens in its hydrophilic head groups which can be pro-
tonated or deprotonated; therefore, pH has a major impact
on its microstructure. As discussed above, increased pH
caused the tertiary amine nitrogen atoms to be
deprotonated, thereby weakening the electrostatic repulsion
between the head groups. This results in the enlargement of
the interfacial head group area (a0) of the surfactant mole-
cules. According to the critical packing parameter theory,
Glu(12)-(AA)-Glu(12) tends to form micelles at low pH
(pH 4.0) and forms vesicles at higher pH (pH 7.0, 10.0) in
the system. Previous research literatures have reported that
the aggregate microstructures of alkyl sugar (acyl) amine
Gemini surfactants with aliphatic spacers of varying length
To understand the microstructure of Glu(12)-(AA)-Glu
(12) at different pHs in the solution above, DLS and Cryo-
TEM measurements were carried out to characterize the
size and morphology of the aggregates. Fig. 3 displays the
distributions of the hydrodynamic radius (Rh) of Glu(12)-
(AA)-Glu(12) aggregates at different pHs from DLS, and
the corresponding Cryo-TEM micrographs of Glu(12)-
(AA)-Glu(12) aggregates at different pHs are shown
in Fig. 4.
Table 1 CMC values, C20, and the surface tension at CMC (γCMC
)
of Glu(12)-(AA)-Glu(12) at different pHs and at 25.0 ꢁC
pH
CMC (mM)
C20 (mmolꢀL−1
)
γcmc (mNꢀm−1
)
( (CH2)n ) or short ethylene oxide ( (OCH2CH2)n
)
4.0
0.095
0.088
0.073
0.0078
0.0050
0.0180
27.30
33.38
41.69
spacer are transformed from vesicle (or double-layer struc-
ture) to rod-like and spherical micelles with varying the
solution pH from neutral to acid.(Fielden et al., 2001;
7.0
10.0
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Fig 4 Cryo-TEM micrographs of Glu(12)-(AA)-Glu(12) at different pHs values: (a) pH = 7.0, (b) pH = 10.0
Johnsson et al., 2003a, b; Johnsson and Engberts, 2004) In
principle, the nature of the spacer of Gemini surfactant,
such as length, polarity, and flexibility, should have an
obvious influence on its aggregate microstructure. How-
ever, in this article, the microstructure of Glu(12)-(AA)-
Glu(12) aggregates with a different natured spacer shows
similar changes to the reported literature. It reveals that as
to this kind of sugar-based Gemini surfactants, the nature
of the spacer has a little effect on the aggregation process.
The protonation of the two tertiary amine nitrogen atoms in
its head groups plays a crucial role in the formation of
micelles or vesicles.
vesicles is caused by the deprotonation of tertiary amines in
its head groups. In an aqueous environment at physiologi-
cal pH, Glu(12)-(AA)-Glu(12) forms vesicles, which can
be used to encapsulate hydrophilic and hydrophobic drugs,
but it undergoes the phase transition from vesicle to micelle
in the endosomal pH range as a result of an increased pro-
tonation state. Therefore, the transition of Glu(12)-(AA)-
Glu(12) from vesicles to micelles with varying the solution
pH may be applied to drug delivery or gene delivery.
Acknowledgements This work was supported by the Foundation of
Henan Educational Committee (19B150019), Foundation of Henan
Department of Science and Technology (CLY20170165) and the Doc-
toral Research Fund of Zhengzhou University of Light Industry
(2014BSJJ063).
Conclusions
The novel sugar-based Gemini surfactant with a N, N0-
acetylethylenediamine spacer (N, N0 (N-dodecyl-2-D-
glucosaminyl acetyl) ethylenediamine, Glu(12)-(AA)-Glu
(12)) was synthesized and characterized. The aggregation
behavior of Glu(12)-(AA)-Glu(12) in aqueous solution at
pH 4.0, 7.0 and 10.0 was investigated by surface tension,
DLS and Cryo-TEM measurements. The surface tension
result indicates that the CMC values of Glu(12)-(AA)-Glu
(12) at pH 4.0, 7.0 and 10.0 are at the concentration level
of 10−5 molꢀL−1, which shows much higher surface activity
than the corresponding monomeric sugar-based surfactants
and similar or slightly lower surface activity to such kinds
of Gemini surfactants with the same hydrophobic carbon
chain length but similar hydrophilic spacers. The slight
decrease of CMC with the decrease of the solution pH is
mainly driven by the enhancement of the electrostatic
repulsion, caused by the protonation of the tertiary amino
groups in the hydrophilic head groups. The DLS and cryo-
TEM data demonstrate that a structural transformation
occurs with changing the solution pH. At acidic pH
(pH 4.0), the formation of micelles is driven by an
increased electrostatic repulsion, caused by the protonation
of tertiary amines in its head groups. At neutral or higher
pH (pH 7.0 or 10.0), the transformation of micelles into
Supporting information
1H NMR of the intermediate N, N0-bis (2-bromoacetyl) eth-
1
ylenediamine (1), H NMR, 13C NMR and ESI-MS (ESI−)
spectra of the intermediate N, N0-bis(2-dodecanoacetyl)
1
ethylenediamine (2), and H NMR of the target product of
N,N0
(N-dodecyl-2-D-glucosaminyl
acetyl)
eth-
ylenediamine Glu(12)-(AA)-Glu(12) (3). These materials
are available free of charge via the Internet at https://
onlinelibrary.wiley.com.
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