X. Ge, Q. Lei, S. Wu et al.
Journal of Molecular Liquids 342 (2021) 117464
composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine,
di-n-hexadecyldimethylammonium bromide, and n-dodecyl-b-
glucoside [39]. In 2016, Movahedi et al. reported an Fe-cysteine
biocatalyst in a vesicular aqueous solution in which sodium dode-
cyl sulfate and dodecyltrimethylammonium bromide (SDS/DTAB)
were mixed [40]. Nevertheless, compared with micellar catalysis,
vesicular catalysis in water has received less attention [41,42].
Moreover, although ionic surfactants can be induced to enable
the spontaneous formation of vesicles, such surfactant systems
are generally complicated. In 2017, we reported a temperature-
induced micelle-to-vesicle transition with a single pseudogemini
surfactant [43]. However, it is still unknown whether it is possible
to develop a vesicular catalytic system in water by aggregate tran-
sition in a single surfactant aqueous solution.
Sugar, composed of polyhydric hydrophilic structures, can be
attached to a hydrophobic chain to produce a surface-active sub-
stance [44,45]. Due to their eco-friendliness, renewable nature,
and biodegradable characteristics, sugar-based surfactants have
attracted significant attention and play an important role in cos-
metics, pharmaceuticals, biochemistry, and gene transfection [46-
aggregation of the surfactant in aqueous solution, the conductivi-
ties of C11D12 at different temperatures (25 °C, 35 °C, 45 °C, and
55 °C) were examined. The specific calculation formula is based
on a previously reported method [67] and the results are shown
in Fig. 2 and Table 1. The CMC was obtained by conductivity
0
m
method at 25 °C. The
DG
value of C11
D12 is negative at 25–
5
5 °C. Therefore, the formation of C11
D
12 micelles is a thermody-
namic spontaneous process. In addition, the negative value of
0
D
H
indicates that the micellization process is exothermic. The
m
0
0
value of T
DS
is greater than the absolute value of
D
H , which
m
m
indicates that the micellization process is entropy-driven. Taking
these data into account, the micellization of C11
namic, spontaneous, and exothermic process.
D12 is a thermody-
The phase behavior of the C11
D12 aqueous solution was studied
at a fixed concentration of 1 mM. The turbidity of the C11
D
12 aque-
ous solution was determined by the absorbance at 600 nm using a
UV–vis spectrophotometer (UV-2700). The break point in the
absorbance was determined to be 41.2 °C, indicating that aggregate
transition takes place at this temperature. The effect of tempera-
ture on the aggregates of the 1 mM C11D12 aqueous solution was
5
0]. Recently, a series of novel sugar-based surfactants were
examined and the results are summarized in Fig. 3. When the tem-
perature was controlled at 39 °C, the average diameter of aggre-
gates in the homogenous and transparent solution was 8.5 nm.
When the temperature was increased to 40 °C, aggregates with a
diameter of 263.6 nm were gradually formed and the solution
turned pale blue, a characteristic feature of solutions containing
vesicles. Increasing the temperature to 45 °C resulted in the disap-
pearance of 8.2 nm aggregates, and only 113.4 nm diameter aggre-
gates were formed. At this temperature, the solution became
cloudy and turbid. These results provide preliminary evidence for
a micelle-to-vesicle transition. Moreover, the temperature of the
break point is defined as the temperature of self-assembly transi-
tion from micelle to vesicle (TMVT). To further elucidate the
designed and synthesized [45,51-59]. Interestingly, a transition of
aggregates was not observed in these sugar-based surfactants
[
51,60-62]. In our previous work [63], pseudogemini surfactants
were constructed using N-dodecyl glucosamine (and N-dodecyl
lactosamine) and dicarboxylic acid (HOOC(CH n-2COOH, n = 3, 4,
, 6, 8) in aqueous solution via non-covalent bonds. The influence
2
)
5
of spacer group length on their physicochemical properties was
studied without the occurrence of coacervation. In this work, a
micelle-to-vesicle transition was observed in an aqueous solution
of a sugar-based pseudogemini surfactant (C11D12, Fig. 1) non-
covalently constructed with N-dodecylglucosamine (D12Ga) and
undecanedioic acid. The size and morphology of aggregate transi-
tion was studied by changing the temperature. Furthermore, the
microstructures of the 1 mM C11D12 aqueous solution at 39 °C
aggregates generated by
11
C D12 were applied in a copper-
and 45 °C, the morphology of the aggregates was studied by
cryo-TEM (Fig. 3c, d). The aggregates at 39 °C are spherical micelles
with an average diameter of 8.5 nm, while at 45 °C, vesicles with
an average diameter of 122.8 nm are present. This verifies that
the transition of aggregates from spherical micelles to vesicles is
induced by increasing the temperature. Moreover, further increas-
ing temperature causes a decrease in vesicle size. The vesicles at
catalyzed C-S coupling reaction in water, exhibiting superb cat-
alytic performance.
2
. Results and discussion
2.1. Aggregate transition in C11D12 aqueous solution
1
00 °C are about 24 nm in diameter and 4 nm in wall thickness,
Critical micelle concentration (CMC) is an important character-
istic of surfactants [64-66]. As shown in Fig. S1, the CMC value of
the sugar-based pseudogemini surfactant C11 12 was determined
to be 0.56 mM. The surface tension decreases sharply when
increasing the concentration of C11 12 aqueous solution until a
D
D
break point appears. Furthermore, above the CMC, the value of
the surface tension is almost constant. It is clear that the sugar-
based pseudogemini surfactant C11D12 was successfully synthe-
sized by the in-situ neutralization reaction of N-dodecyl glucosy-
lamine and undecanedioic acid in water. To investigate the
Fig. 2. Dependence of the electroconductivity (j) of C11D12 aqueous solution on
Fig. 1. Chemical structure of sugar-based pseudogemini surfactant (C11D12).
surfactant concentration (c) at different temperatures.
2