Synthesis, Surface Activity, and Antimicrobial Efficacy of Hydrogenated Cardanol-Derived Positively Charged Asymmetric Gemini Surfactants

Article abstract of DOI:10.1002/jsde.12324

Nine different hydrogenated cardanol-based quaternary ammonium compounds including one conventional single-tale single-head surfactant, one bicephalic single-tale double-head surfactant, and seven asymmetric Gemini surfactants were synthetized using a sim

Full text of DOI:10.1002/jsde.12324

J Surfact Deterg (2019)
DOI 10.1002/jsde.12324
ORIGINAL ARTICLE
Synthesis, Surface Activity, and Antimicrobial Efficacy
of Hydrogenated Cardanol-Derived Positively Charged
Asymmetric Gemini Surfactants
1
1
1
2
1,3
4
4
Mengen Huang · Jingyi Ma · Xunshen Wu · Min Zhao · Limin Wang · Fei Che · Hui Qian
Received: 29 November 2018 / Accepted: 3 May 2019
©
2019 AOCS
Abstract Nine different hydrogenated cardanol-based qua-
ternary ammonium compounds including one conventional
single-tale single-head surfactant, one bicephalic single-tale
double-head surfactant, and seven asymmetric Gemini surfac-
tants were synthetized using a simple process with high
J Surfact Deterg (2019).
Introduction
1
yields. Their structures were characterized using H NMR,
Humankind has been utilizing fossil fuel resources in the
fields of energy production and synthesis of petroleum-
originated products for centuries (Danner and Braun,
1999). Because the total amount of petroleum feedstock is
limited and chemicals originated from fossil fuels cannot
be degradable, many academic and industrial groups have
begun to investigate renewable resources as potential alter-
natives. To date, research in the categories of plant-based
resources and animal-based resources such as polysaccha-
rides, lignin, tannins, vegetable oils, and proteins has gener-
ated a vast library of sustainable materials (Ragauskas
et al., 2006).
13
C NMR, and high-resolution mass spectral studies. Their
surface active properties were evaluated by the wilhelmy plate
ꢀ
method at 25 C and physical parameters like CMC, γCMC
,
πCMC, C , τCMC, and A
were calculated. The Krafft tem-
20
min
perature values of C-BP-1, C-BP-4, and C-BP-6 are lower
ꢀ
than 0 C, suggesting high-potential industrial application. All
synthesized compounds but C-BP-F exhibit great antimicro-
bial ability against Gram-positive bacteria (S. aureus [ATCC
2
5923] and C. glutamicum [ATCC 13032]) while inadequate
antimicrobial ability against Gram negative strains (E. coli
ATCC 25922] and P. aeruginosa [ATCC 27853]).
[
Among the investigated biorenewable resources, cashew
nut shell liquid (CNSL) has attracted the attention of many
research groups owing to its straightforward isolation process
promising high yields and versatile derivatization possibili-
ties. CNSL is a by-product originating from the cashew nut
Keywords Cardanol ꢁ Quaternary ammonium compound
Gemini surfactant ꢁ Antimicrobial agent
ꢁ
*
Limin Wang
wanglimin@ecust.edu.cn
(
Anacardium occidentale L.) processing industry (Voirin
et al., 2014). Its annual production has reached approximately
50,000 metric tons in 2011 and it was promised that it will
reach 600,000 metric tons in the near future (Attanasi et al.,
006; Balachandran et al., 2013). CNSL locates in the
brown-colored mesocarp of the unprocessed nut, accounts for
8–27% of the total unshelled nut weight, and can be
1
Key Laboratory for Advanced Materials, Institute of Fine
Chemicals, School of Chemistry and Molecular Engineering, East
China University of Science and Technology, 130 Meilong Road,
Shanghai, 200237, P. R. China
4
2
2
3
4
School of Chemistry and Molecular Engineering, East China
University of Science and Technology, 130 Meilong Road,
Shanghai, 200237, P. R. China
1
extracted from the mesoscarp via diverse processes like
mechanical extraction, solvent extraction, hot oil bath, etc.
(Balachandran et al., 2013). The compositions of CNSL
mainly depend on the extraction method adopted. And, it
generally contains cardanol, cardol, anacardic acid, 2-methyl
Key Laboratory of Organofluorine Chemistry, Shanghai Institute
of Organic Chemistry, The Chinese Academy of Sciences, 345
Lingling Road, Shanghai, 200032, P. R. China
Shanghai Bronkow Chemical Co., Ltd., Chuangtong Road 88,
Jinshan District, Shanghai, 201512, China
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Fig. 1 Chemical structure of CNSL compositions
cardol, and polymeric materials with their structures shown
in Fig. 1. During the subsequent process of double vacuum
distillation (at 3–4 mm torr), thermal decarboxylation occurs
(Atta et al., 2018; Tyman and Bruce, 2003, 2004), and cat-
ionic amphiphilic compounds (Bhadani et al., 2011; Ezzat
et al., 2017; Wang et al., 2016).
Gemini surfactant is a special class of amphiphile having
two polar heads as well as two hydrophobic chains together
in one molecule. The linker or spacer connecting two sur-
factant monomers usually exists between two polar heads
or at the location of alkyl chain, which is very near to the
hydrophilic heads (Mondal et al., 2015; Sharma and Ilies,
under heating and cardanol is collected at a boiling point of
ꢀ
2
20 ꢂ 15 C as a transparent yellowish liquid (Anilkumar,
2017). Cardanol is a mixture of four meta-alkyl phenols dif-
fering in the degree of unsaturation of the meta-alkyl chain.
To be specific, it contains 3-(pentadecyl)-phenol (5%), 3-(8Z-
pentadecenyl)-phenol (49%), 3-(8Z,11Z-pentadecadienyl)-
phenol (17%), and 3-(8Z,11Z,14-pentadecatrienyl)-phenol
2
014). Presenting unique surface-active properties like
lower critical micelle concentrations (CMC), Gemini sur-
factant has been an interest in the surfactant area for more
than 30 years (Menger and Keiper, 2000; Monger and Lit-
tau, 1991). Meanwhile, quaternary ammonium compound
(29%).
As shown in Fig. 2, in the structure of cardanol locates a
reactive phenolic –OH group, meta-alkyl chain with differ-
ent numbers of cis double bonds and an aromatic ring.
Bearing these three active sites in one molecule, cardanol
serves as a promising starting molecule allowing for chemi-
cal modification to obtain a vast library of functional
chemicals. And, because it is relatively difficult to synthe-
size phenol with a side long alkyl chain at the meta posi-
tion, cardanol could be adopted as a natural phenol-based
monomer with a meta-substituted alkyl chain for further
functionalization. Research focusing on the derivatization
of cardanol has successfully converted this scaffold into
various functional chemicals such as antioxidants (Amorati
et al., 2011), fluorescent markers (Braga et al., 2017), ther-
mosets (Nguyen et al., 2017), flame retardants (Amarnath
et al., 2017), electrodes (Molji et al., 2017), etc. The meta-
substituted long alkyl chain with odd-numbered carbon
atoms has brought cardanol with intrinsic hydrophobicity
and amphiphilicity. And, various types of derivatization on
the phenolic –OH group or aromatic ring have contributed
to a vast library of cardanol-based anionic surfactants
(QAC) is an important class of antiseptics, exhibiting
antibacterial ability via first being electrostatically attracted
to the negatively charged cell membrane of bacteria and
second leading to the disruption of cell membrane, leakage
of cytoplasm, and death of the microorganism (Tischer
et al., 2012).
While many research studies in the field of cardanol-
derived surfactants have been published, cardanol-based
asymmetric Gemini cationic surfactants with a rigid linker
group and their use as antimicrobial agents have never been
published before. In this work, hydrogenated cardanol has
been successfully converted into a series of positively
charged asymmetric Gemini surfactants with their structures
1
13
confirmed using H NMR, C NMR, and high-resolution
mass spectral studies. The surface-active properties were
evaluated with physical parameters like CMC, γCMC (surface
tension at CMC), ΠCMC (surface pressure), C20 (adsorption
efficiency), τCMC (maximum surface excess concentration),
and Amin (minimum surface area per molecule) being calcu-
lated and compared with other published Gemini cationic
surfactants. The Krafft temperature was measured. The
antibacterial efficacy of this series of compounds was
assessed on two strains of Gram-positive bacteria (S. aureus
and C. glutamicum) and two strains of Gram-negative bacte-
ria (E. coli and P. aeruginosa) with minimum inhibitory
concentration (MIC) values measured. It was suggested that
four water soluble QAC, C-BP, C-BP-1, C-BP-4, and C-BP-
(Ahire and Bhagwat, 2017; Bruce et al., 2009; Castro Dan-
tas et al., 2008; Kattimuttathu et al., 2011; Peungjitton
et al., 2008; Scorzza et al., 2009), nonionic surfactants
6
, exhibited excellent surface-active ability with CMC values
−1
lower than 15 μmol L . Meanwhile, all QAC but C-BP-F
exhibit great antimicrobial ability toward Gram-positive
S. aureus and C. glutamicum with corresponding MIC
−1
Fig. 2 Chemical structure of cardanol
values lower than 64 μg mL .
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Experimental Section
Materials and Characterization Methods
cardanol was added into a 50 mL flask containing 20 mL
of acetone and mixed to obtain a clear and brownish solu-
tion. The hydrogenated cardanol solution was slowly
dripped into the 500 mL round-bottom flask containing
(E)-1,4-dibromobut-2-ene dissolved in acetone and the
All reagents and solvents were of analytical grade and were
purchased commercially. All solvents were used as received
ꢀ
mixture was then heated to 56 C. After 24 h of reaction,
the mixture was cooled to room temperature and filtrated
1
unless otherwise mentioned. The H NMR (400 MHz,
13
TMS) and C NMR (100 MHz, TMS) spectra were
obtained using a Bruker AM-500 spectrometer with
J values being listed in Hertz. Melting point values were
measured using a SGW X-4 melting point apparatus sup-
plied by Shanghai Precision & Scientific Instrument
Co. Ltd. (Anting District, Shanghai, China) with all data
uncorrected. The high-resolution mass spectra were mea-
sured on a Micromass GTC spectrometer.
to remove the solid K CO . Meanwhile, the obtained liq-
2
3
uid was subjected to column chromatography on silica gel
eluted with pure petroleum ether to yield the intermediate
product C-Br. Second, into a reaction tube, C-Br 0.43 g
0
(1 mmol), 4,4 -bipyridine 0.78 g (5 mmol), and DMF
ꢀ
were added. The reaction mixture was heated to 80 C for
22 h. After completion of the reaction, the mixture was
cooled to room temperature followed by dropwise addi-
tion of diethyl ether. White solid (the targeting product C-
BP) was noticed, filtrated, and finally recrystallized from
MeOH/EA (1:10, by vol).
Organic Synthesis
The synthetic route for target compounds is illustrated in
Scheme 1. Nine hydrogenated cardanol-derived QAC were
obtained with their chemical structures listed in Fig. 3.
C-Br
1
Yield in 54%, as a yellow liquid, H NMR (400 MHz,
Synthesis of Cardanol-Derived Conventional Cationic
Surfactant (C-BP)
CDCl ): δ 7.15–7.19 (m, 1H), 6.69–6.79 (m, 3H),
5.95–6.10 (m, 2H), 4.52–4.53 (d, J = 4.0 Hz, 2H),
3
3
.97–3.98 (d, J = 4.0 Hz, 2H), 2.54–2.58 (t, J = 8.0 Hz,
Two steps are required to obtain C-BP. First, into a
2H), 1.58–1.61 (m, 2H), 1.25–1.30 (m, 24H), and
0.87–0.89 (t, J = 4.0 Hz, 3H); C NMR (101 MHz,
13
500 mL round-bottom flask, (E)-1,4-dibromobut-2-ene
2.83 g (60 mmol), anhydrous K CO 16.58 g
1
CDCl ): δ 153.15, 139.48, 125.07, 123.95, 123.87, 116.04,
2
3
3
(
120 mmol), and 100 mL of acetone were added. Agita-
tion was started to fully dissolve (E)-1,4-dibromobut-
-ene. Meanwhile, 6.09 g (20 mmol) of hydrogenated
109.73, 106.33, 61.88, 30.81, 26.46, 26.17, 24.19, 24.33,
24.17, 17.5, and 8.93. HRMS (ESI-TOF) m/z: [M + H]
+ Calcd for C H BrO 437.2419; Found 437.2418.
2
25 42
Scheme 1 Synthetic routes for the target hydrogenated cardanol-based quaternary ammonium compounds
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Fig. 3 Chemical structure of hydrogenated cardanol-based quaternary ammonium compounds
C-BP
P. C. Minbiole’s group, two efficient routes of synthesizing
BP-1 and BP-R were adopted with minor modifications
(Grenier et al., 2012). Briefly, to obtain BP-1, 4,4 -
ꢀ
1
0
Yield in 87%, as a pale white solid, m.p. 61.6–64.9 C, H
NMR (400 MHz, CD OD): δ 9.08–9.10 (d, J = 8.0 Hz, 2H),
bipyridine 3.12 g (20 mmol) and CH I (1.5 mL, 24 mmol)
3
3
8.83–8.84 (d, J = 4.0 Hz, 2H), 8.52–8.53 (d, J = 4.0 Hz,
2H), 7.98–8.00 (d, J = 8.0 Hz, 2H), 7.14–7.18 (m, 1H),
6.72–6.77 (m, 3H), 6.20–6.39 (m, 2H), 5.35–5.36
were, respectively, dissolved in dichlormethane (DCM).
0
The DCM solution of CH I was added dropwise into 4,4 -
3
ꢀ
bipyridine, followed by heating to 40 C and reacting for
(
2
d, J = 4.0 Hz, 2H), 4.65–4.66 (d, J = 4.0 Hz, 2H),
an hour. After cooling to room temperature, yellow precipi-
tate was observed, filtrated, and recrystallized from MeOH
to obtain the intermediate compound BP-1. To obtain BP-
.53–2.57 (t, J = 8.0 Hz, 2H), 1.55–1.59 (m, 2H), 1.27–1.30
13
(
(
m, 24H), and 0.87–0.91 (t, J = 8.0 Hz, 3H); C NMR
0
101 MHz, CD OD): δ 159.75, 151.84, 150.96, 145.87,
R, 4,4 -bipyridine 2.34 g (15 mmol), corresponding alkyl
3
1
1
3
43.62, 137.06, 130.34, 127.20, 124.78, 123.58, 122.43,
15.97, 112.79, 110.11, 67.77, 63.43, 36.94, 33.08, 32.65,
0.77, 30.48, 30.34, 23.74, and 14.44. HRMS (ESI-TOF) m/z:
halide (3 mmol) and anhydrous acetonitrile were added into
a reaction tube pretreated with water removal and argon
filling. The mixture was maintained at 82 C for 18 h. After
cooling to room temperature, noticeable solid was precipi-
tated out, filtrated and recrystallized from MeOH/EA (1:10,
by vol) as intermediate compound BP-R. Finally, into a dry
reaction tube pre-installed with an argon atmosphere, C-Br
ꢀ
+
[M-Br] Calcd for C H N O 513.3839; Found 513.3837.
35 49 2
Synthesis of Cardanol-Derived Bicephalic and Gemini
Cationic Surfactants (C-BP-R)
0
.525 g (1.2 mmol) and corresponding BP-1 or BP-R
ꢀ
Three subsequent steps are required to obtain a series of
nine C-BP-R. First, C-Br was synthesized as mentioned
above. Second, in accordance to work published by Kevin
(1 mmol) were added. After reacting at 82 C for 18 h, tar-
get compounds were precipitated, filtrated, and washed
with anhydrous acetonitrile (15 mL × 3).
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C-BP-1
C-BP-8
ꢀ
1
ꢀ
Yield in 82%, as a red solid, m.p. 194.8–197.7 C, H
Yield in 85%, as a pale yellow solid, m.p. 200.8–202.4 C,
1
NMR (400 MHz, CD OD): δ 9.25–9.27 (d, J = 8.0 Hz,
H NMR (400 MHz, CD OD): δ 9.29–9.30 (d, J = 4.0 Hz,
3
3
2
7
5
2
H), 9.19–9.21 (d, J = 8.0 Hz, 2H), 8.66–8.70 (m, 4H),
.14–7.18 (m, 1H), 6.73–6.77 (m, 3H), 6.23–6.45 (m, 2H),
.43–5.45 (d, J = 8.0 Hz, 2H), 4.66–4.67 (d, J = 4.0 Hz,
H), 4.54 (s, 3H), 2.54–2.57 (t, J = 6.0 Hz, 2H), 1.55–1.62
2H), 9.25–9.27 (d, J = 8.0 Hz, 2H), 8.69–8.71 (m, 4H),
7.14–7.18 (m, 1H), 6.73–6.78 (m, 3H), 6.23–6.44 (m, 2H),
5.43–5.45 (d, J = 8.0 Hz, 2H), 4.74–4.77 (t, J = 6.0 Hz,
2H), 4.66–4.67 (d, J = 4.0 Hz, 2H), 2.54–2.57 (t,
J = 6.0 Hz, 2H), 2.06–2.13 (m, 2H), 1.55–1.62 (m, 2H),
(m, 2H), 1.28–1.31 (m, 24H), and 0.88–0.91 (t, J = 6.0 Hz,
13
13
3
1
1
3
H); C NMR (101 MHz, CD OD): δ 159.78, 150.97,
1.28–1.44 (m, 34H), and 0.88–0.92 (m, 6H); C NMR
3
45.87, 137.51, 130.37, 128.39, 128.04, 124.46, 122.41,
16.01, 112.74, 67.82, 63.94, 36.97, 33.10, 32.69, 30.79,
0.50, 30.39, 23.77, and 14.49. HRMS (ESI-TOF) m/z:
(101 MHz, CD OD): δ 159.77, 151.69, 145.88, 137.49,
3
130.35, 128.38, 124.45, 122.43, 121.63, 115.99, 112.71,
67.78, 63.96, 63.36, 36.95, 33.09, 32.90, 32.66, 32.61,
30.76, 30.48, 30.36, 30.14, 27.26, 23.75, 23.68, 14.46, and
2+
[M-Br-I]
Calcd for C H N O 264.2034; Found
36 52 2
2+
264.2029.
14.41. HRMS (ESI-TOF) m/z: [M-2Br]
Calcd for
C H N O 313.2582; Found 313.2589.
43 66 2
C-BP-4
C-BP-10
ꢀ
Yield in 91%, as a pale yellow solid, m.p. 201.3–203.7 C,
1
ꢀ
H NMR (400 MHz, CD OD): δ 9.29–9.30 (d, J = 4.0 Hz,
Yield in 89%, as a pale yellow solid, m.p. 201.2–203.5 C,
3
1
2H), 9.25–9.27 (d, J = 8.0 Hz, 2H), 8.69–8.71 (m, 4H),
7.14–7.18 (m, 1H), 6.73–6.78 (m, 3H), 6.23–6.44 (m, 2H),
5.43–5.45 (d, J = 8.0 Hz, 2H), 4.74–4.78 (t, J = 8.0 Hz,
2H), 4.66–4.67 (d, J = 4.0 Hz, 2H), 2.54–2.58 (t,
H NMR (400 MHz, CD OD): δ 9.29–9.30 (d, J = 4.0 Hz,
3
2H), 9.25–9.27 (d, J = 8.0 Hz, 2H), 8.69–8.71 (m, 4H),
7.14–7.18 (m, 1H), 6.73–6.77 (m, 3H), 6.23–6.45 (m, 2H),
5.43–5.45 (d, J = 8.0 Hz, 2H), 4.74–4.77 (t, J = 6.0 Hz,
2H), 4.66–4.67 (d, J = 4.0 Hz, 2H), 2.54–2.57 (t,
J = 8.0 Hz, 2H), 2.04–2.12 (m, 2H), 1.55–1.62 (m, 2H),
1
0
.28–1.31 (m, 24H), 1.02–1.06 (t, J = 8.0 Hz, 3H), and
.88–0.91 (t, J = 6.0 Hz, 3H); C NMR (101 MHz,
J = 6.0 Hz, 2H), 2.06–2.13 (m, 2H), 1.53–1.61 (m, 2H),
1
3
13
1.27–1.44 (m, 38H), and 0.87–0.91 (t, J = 8.0 Hz, 6H);
C
CD OD): δ 159.77, 151.69, 145.88, 137.49, 130.35,
NMR (101 MHz, CD OD): δ 159.77, 151.27, 145.87,
3
3
1
6
2
28.38, 124.44, 122.43, 121.36, 115.98, 112.71, 67.78,
3.96, 63.12, 36.95, 34.50, 32.67, 30.76, 30.48, 30.36,
3.75, 20.50, 14.46, and 13.79. HRMS (ESI-TOF) m/z:
137.49, 130.35, 128.39, 124.46, 122.42, 121.42, 116.00,
112.71, 67.79, 63.95, 63.37, 36.96, 33.09, 33.05, 32.67,
32.61, 30.77, 30.62, 30.55, 30.42, 30.18, 27.27, 23.71, and
2+
2+
[M-2Br]
Calcd for C H N O 285.2269; Found
14.44. HRMS (ESI-TOF) m/z: [M-2Br]
Calcd for
3
9 58 2
285.2271.
C H N O 327.2738; Found 327.2732.
4
5 70 2
C-BP-6
C-BP-12
ꢀ
ꢀ
Yield in 88%, as a pale yellow solid, m.p. 200.4–202.1 C,
Yield in 79%, as a pale yellow solid, m.p. 200.3–203.1 C,
1
1
H NMR (400 MHz, CD OD): δ 9.28–9.30 (d, J = 8.0 Hz,
H NMR (400 MHz, CD OD): δ 9.28–9.30 (d, J = 8.0 Hz,
3
3
2H), 9.25–9.27 (d, J = 8.0 Hz, 2H), 8.69–8.70 (m, 4H),
7.14–7.18 (m, 1H), 6.73–6.78 (m, 3H), 6.23–6.44 (m, 2H),
5.43–5.44 (d, J = 4.0 Hz, 2H), 4.74–4.77 (t, J = 6.0 Hz,
2H), 4.66–4.67 (d, J = 4.0 Hz, 2H), 2.54–2.58 (t,
2H), 9.25–9.27 (d, J = 8.0 Hz, 2H), 8.68–8.71 (m, 4H),
7.14–7.18 (m, 1H), 6.73–6.78 (m, 3H), 6.24–6.43 (m, 2H),
5.43–5.45 (d, J = 8.0 Hz, 2H), 4.73–4.77 (t, J = 8.0 Hz,
2H), 4.66–4.67 (d, J = 4.0 Hz, 2H), 2.54–2.57 (t,
J = 8.0 Hz, 2H), 2.06–2.13 (m, 2H), 1.55–1.62 (m, 2H),
J = 6.0 Hz, 2H), 2.06–2.13 (m, 2H), 1.55–1.62 (m, 2H),
1
3
13
1.28–1.47 (m, 30H), 0.88–0.95 (m, 6H);
C NMR
1.28–1.44 (m, 42H), and 0.87–0.91 (t, J = 8.0 Hz, 6H);
C
(
101 MHz, CD OD): δ 159.77, 151.69, 145.88, 137.49,
NMR (101 MHz, CD OD): δ 159.77, 151.29, 145.88,
3
3
1
6
3
30.35, 128.37, 124.44, 122.43, 121.20, 115.98, 112.70,
7.77, 63.97, 63.34, 36.95, 33.09, 32.66, 32.56, 30.76,
0.48, 30.36, 26.93, 23.75, 23.52, 14.45, 14.28. HRMS
137.49, 130.35, 129.85, 124.45, 122.43, 115.96, 112.70,
67.78, 63.96, 63.37, 36.95, 33.08, 32.67, 32.61, 30.76,
30.48, 30.36, 30.18, 27.27, 23.75, and 14.45. HRMS (ESI-
2
+
2+
(ESI-TOF) m/z: [M-2Br]
Calcd for C H N O
TOF) m/z: [M-2Br] Calcd for C H N O 341.2895;
4
1
62
2
47 74 2
299.2426; Found 299.2419.
Found 341.2908.
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C-BP-14
ꢀ
Yield in 83%, as a pale yellow solid, m.p. 201.1–203.5 C,
1
H NMR (400 MHz, CD OD): δ 9.28–9.30 (d, J = 8.0 Hz,
3
2H), 9.25–9.27 (d, J = 8.0 Hz, 2H), 8.69–8.71 (m, 4H),
7.14–7.18 (m, 1H), 6.73–6.77 (m, 3H), 6.23–6.44 (m, 2H),
5.43–5.45 (d, J = 8.0 Hz, 2H), 4.74–4.77 (t, J = 6.0 Hz,
2H), 4.66–4.67 (d, J = 4.0 Hz, 2H), 2.53–2.57 (t,
J = 8.0 Hz, 2H), 2.06–2.13 (m, 2H), 1.55–1.62 (m, 2H),
13
1.28–1.44 (m, 46H), and 0.87–0.91 (t, J = 8.0 Hz, 6H);
C
NMR (101 MHz, CD OD): δ 159.77, 151.27, 145.87,
3
1
1
3
37.48, 130.35, 128.39, 124.46, 122.42, 121.42, 116.00,
12.70, 67.78, 63.95, 63.36, 36.96, 33.09, 32.68, 32.62,
0.78, 30.37, 30.19, 27.27, 23.76, and 14.46. HRMS (ESI-
2
+
TOF) m/z: [M-2Br] Calcd for C H N O 355.3052;
4
9 78 2
Found 355.3042.
Fig. 4 Surface tension isotherms of compounds C-BP, C-BP-1, C-
BP-4, and C-BP-6 at 25 C
ꢀ
C-BP-F
Krafft Temperature
ꢀ
1
Yield in 81%, as a red solid, m.p. 247.6–249.7 C, H
NMR (400 MHz, CD OD): δ 9.42–9.43 (d, J = 4.0 Hz,
The Krafft temperature was determined in accordance with
the method reported before (Scorzza et al., 2009). In brief,
solutions of tested compound in the concentration of 1%
3
2H), 9.26–9.28 (d, J = 8.0 Hz, 2H), 8.75–8.77 (d,
J = 8.0 Hz, 2H), 7.14–7.18 (m, 1H), 6.73–6.78 (m, 3H),
ꢀ
6
4
2
1
.24–6.45 (m, 2H), 5.43–5.45 (d, J = 8.0 Hz, 2H),
.66–4.67 (d, J = 4.0 Hz, 2H), 3.18–3.27(m, 2H),
.54–2.58 (t, J = 8.0 Hz, 2H), 1.55–1.62 (m, 2H),
.28–1.31 (m, 24H), and 0.88–0.91 (t, J = 4.0 Hz, 3H);
(mass percent) were prepared and heated to 90 C with agi-
tation to obtain a transparent liquid. Upon cooling, the tem-
perature at which turbidity first occurred was marked down
as its Krafft temperature. Each sample was tested at least
three times with the final results being listed in Table 1.
1
3
C NMR (101 MHz, CD OD): δ 159.76, 151.40,
3
1
1
6
2
45.58, 142.64, 130.35, 128.59, 126.55, 124.39, 122.43,
20.68, 118.70, 118.63, 115.98, 112.69, 111.53, 67.76,
3.96, 62.83, 36.96, 33.09, 32.68, 30.77, 30.49, 30.37,
4.55, 23.76, and 14.46. HRMS (ESI-TOF) m/z: [M-I-
Antimicrobial Activity
The antibacterial efficacy of the reported nine QAC was
evaluated on two Gram positive strains (S. aureus ATCC
2
+
Br]
Calcd for C H F N O 380.2002; Found
41 53 9 2
3
80.1995.
2
5923 and C. glutamicum ATCC 13032) as well as two
Gram negative strains (E. coli ATCC 25922 and
P. aeruginosa ATCC 27853). To measure MIC values, the
broth microdilution method was performed according to
the standard protocol (Matthew et al, 2009). In brief, over-
night bacterial cultures of the four mentioned strains were
grown in Mueller-Hinton Broth, followed by dilution to
Surface Tension Measurements
Tensiometry method was adopted to evaluate the surface-
active properties of the synthesized compounds. The sur-
face tension values were acquired on an automatic tensi-
ometer (JK99B, Shanghai Zhongchen Digital Technic
Apparatus Co., Ltd., Putuo District, Shanghai, China) at
6
−1
approximately 10 cfu mL , which was comfirmed by
optical density (OD) measurement at 600 nm. For water-
2
98.15 K based on the Wilhelmy plate method (Ahire and
Bhagwat, 2017). The testing solutions were aged over-
night prior to measurement. Before each round of mea-
surement, the platinum plate was scrubbed with absolute
ethyl alcohol and distilled water, followed with heating on
the alcohol lamp to remove potential residuals. The sur-
face tension value at each concentration was measured
three times with its mean value as well as SD being listed
in Fig. 4.
Table 1 Krafft temperature of hydrogenated cardanol-derived quater-
nary ammonium compounds
ꢀ
Compound
Krafft point ( C)
C-BP
3.5
<0
<0
<0
C-BP-1
C-BP-4
C-BP-6
J Surfact Deterg (2019)

J Surfact Deterg
Table 2 MIC values of hydrogenated cardanol-derived quaternary ammonium compounds toward four testing bacterial strains
Compound
MIC (μg mL−1) (μmol L−1
)
S. aureus ATCC 25923
C. glutamicum ATCC 13032
E. coli ATCC 25922
P. aeruginosa ATCC 27853
C-BP
64 (108)
64 (87)
32 (54)
32 (44)
32 (44)
8 (11)
>128 (>216)
>128 (>174)
>128 (>176)
>128 (>169)
>128 (>163)
>128 (>158)
>128 (>152)
>128 (>147)
>128 (>132)
>128 (>216)
>128 (>174)
>128 (>176)
>128 (>169)
>128 (>163)
>128 (>158)
>128 (>152)
>128 (>147)
>128 (>132)
C-BP-1
C-BP-4
C-BP-6
C-BP-8
C-BP-10
C-BP-12
C-BP-14
C-BP-F
32 (44)
16 (21)
16 (20)
8 (10)
16 (20)
8 (9.8)
8 (9.5)
8 (9.5)
8 (9.2)
8 (9.2)
>128 (>132)
>128 (>132)
1
soluble compounds (C-BP, C-BP-1, C-BP-4, and C-BP-6),
each one was dissolved in 10 mL sterile water reaching a
concentration of 1280 μg mL . For the other five slightly
water-soluble compounds, each one was first dissolved in
at 5.43–5.45 ppm in H NMR and peaks at 63.90 ppm in
13
C NMR. Meanwhile, high-resolution mass spectrum
−
1
results suggested a minor difference lower than 0.001
between molecular ion peaks shown in the spectra and
molecular ion weight calculated using ChemDraw, further
confirming the validity of the synthesized structures
(Ning, 2011).
1
mL absolute methanol and then diffused in 9 mL sterile
−
1
water reaching 1280 μg mL as well. Accordingly, abso-
lute methanol controls were performed. Each stock solution
was subjected to serial twofold dilution to obtain 11 testing
solutions with concentration ranging from 1280 to
−
1
1
.25 μg mL . In triplicate, 10 μL of each testing solution
Tensiometric Property
and 90 μL of bacterial culture as mentioned above were
pipetted into the corresponding well of a 96-well microtiter
tray. Meanwhile, a growth control group containing no
antimicrobial agent was added. The 96-well trays were kept
The tensiometric property of the synthesized amphiphiles
was evaluated via the surface tension measurements
adopting the Wilhelmy plate method. Among the reported
surfactants, four of them (C-BP, C-BP-1, C-BP-4, and C-
BP-6) exhibited great water solubility. With an increase in
the hydrophobic chain length or the introduction of the
fluorine-substituted side chain, the water solubility of the
corresponding surfactants (C-BP-8, C-BP-10, C-BP-12, C-
BP-14, and C-BP-F) decreased greatly. Thus, only the surface
tension isotherms of four water-soluble surfactants (C-BP, C-
BP-1, C-BP-4, and C-BP-6) are depicted in Fig. 4.
ꢀ
at 37 C in an ambient air incubator for 24 h. The MIC
value was the lowest concentration at which the growth of
bacteria within the well was completely inhibited, indicated
by the phenomena that no turbidity within the well was
observed visually. The MIC data are listed in Table 2.
Results and Discussion
To obtain surface tension isotherm, firstly, the surface
tension value of distilled water was measured as γ . Follow-
0
Surfactant Synthesis and Characterization
ing surface tension data, γ was individually determined after
i
subsequent addition of specific volume of the prepared test-
The synthetic route to obtain C-BP and C-BP-R is clearly
illustrated in Scheme 1. The structural elucidation was con-
ing solutions. It was noticed during the measuring process
that γ gradually decreased until reaching a plateau where
i
1
13
ducted using H NMR, C NMR, and high-resolution
mass spectroscopic studies and all data of spectral charac-
teristics were presented in the Experimental Section. The
formation of C-BP was confirmed by the doublet occurring
further increase of concentration resulted in a minor γi
decrease, resulting in two curve regions in the final surface
tension plots. CMC was determined at the cross point of the
two curve regions (Rosen and Kunjappu, 2012). As shown
in Table 3, the CMC values of C-BP, C-BP-1, C-BP-4, and
1
at 5.35–5.36 ppm in H NMR and characteristic peaks at
13
−1
6
3.43 ppm in C NMR, indicating the quaternarization
C-BP-6 are 0.011, 0.013, 0.010, and 0.005 mmol L ,
reaction that occurred between one nitrogen atom of the
bipyridine ring and the carbon atom of C-Br that was
substituted with Br before the reaction. Similarly, the for-
mation of C-BP-R was confirmed by the doublet appearing
respectively, much lower than commercially available
−1
hexadecyl trimethyl ammonium chloride (16 mmol L )
and other categories of the cationic surfactant (Jurij Lah and
Vesnaver, 2000; Ray et al., 2005; Venable & Nauman,
J Surfact Deterg (2019)

J Surfact Deterg
Table 3 Physical parameters of hydrogenated cardanol-derived asymmetric Gemini cationic surfactants
CMC (mmol L−
1
)
γ
CMC (mN m−1
)
π
CMC (mN m−1
)
C
20 (10−4 mol L−1
)
CMC
C20
τ
max (μmol m−2
)
A
min (nm )
2
Compound
C-BP
0.011
15.64
30.53
32.85
33.28
33.21
34.21
35.25
36.46
24.75
56.36
41.47
39.15
38.72
38.79
37.79
36.75
35.54
47.25
0.021
5.24
1.63
1.02
C-BP-1
C-BP-4
C-BP-6
C-BP-8
C-BP-10
C-BP-12
C-BP-14
C-BP-F
0.013
0.030
4.33
1.03
1.61
0.010
0.029
3.45
0.98
1.69
0.005
0.015
3.21
0.99
1.67
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
/
1
964), and comparable to other cardanol-derived cationic
into the air-water interface. The higher the parameter, the
more the test surfactant prefers to lower the surface tension
of its aqueous solution (Desnoyers, 1992). It was noted in
Table 3 that the CMC/C20 value decreases from C-BP to C-
BP-4, which is in alignment with the fact that C-BP is the
most efficacious one to reduce the surface tension of water.
Furthermore, the maximum surface excess concentration
amphiphiles (Bhadani et al., 2011; Wang et al., 2016). It
was noticed that the bicephalic surfactant C-BP-1 shows a
higher CMC value than the conventional surfactant C-BP.
This was attributed to the increased hydrophilicity induced
by the introduction of a second head group, which is in
alignment with the finding of Kevin L. Caran’s group’s
work of biscationic bicephalic (double-headed) amphiphiles
exhibiting higher CMC values owing to increased water sol-
ubility (Roszak et al., 2009). Both Gemini surfactants C-
BP-4 (0.010 mM) and C-BP-6 (0.005 mM) have lower
CMC values compared with the conventional surfactant C-
BP (0.011 mM), because in the structure of Gemini surfac-
tant C-BP-R locates a rigid bipyridine spacer to covalently
connect the head groups of two surfactant monomers, func-
tioning against the electrostatic repulsion between head
groups of two surfactant monomers when forming micelles,
thus helping two hydrophobic chains within a Gemini sur-
factant to pack tightly, facilitating the formation of micelle
and leading to a lower CMC value (Menger and Keiper,
−
2
τmax (μmol m ) as well as the minimum surface area per
2
molecule Amin (nm ) were calculated via the Gibb’s
adsorption isotherm equation (Rosen and Kunjappu, 2012):
ꢀ
ꢁ
1
023
−1
∂γ
τmax
=
=
ð2Þ
NA × Amin nRT ∂lnC
T
where N denotes Avogadro’s number, R means universal
A
gas constant, T is the absolute temperature, C indicates the
surfactant concentration, and (∂γ/∂lnC) is the premicellar
T
slope in the surface tension isotherm (Chauhan et al.,
2
015). n was set as 2 for C-BP and 3 for the rest of the
compounds based on the number of species formed after
the dissolution of the test surfactant (Ahire and Bhagwat,
2000; Sharma and Ilies, 2014). After elongation of the side
2
017). CMC, γCMC, πCMC, C , CMC/C , τmax, and Amin
20 20
alkyl chain, surfactant exhibits larger intermolecular hydro-
phobic interaction, leading to tight packing and decreased
CMC values (Shukla and Tyagi, 2006). The surface tension
at CMC was designated as γCMC. And the surface pressure
πCMC indicating the effectiveness of surface tension reduc-
tion was calculated by the following equation (Rosen and
Kunjappu, 2012).
values are listed in Table 3.
Antimicrobial Activity
MIC value signifies the smallest concentration of the test
compound above which the visible growth of a bacterium is
inhibited (Matthew et al, 2009). The lower the MIC value,
the better the antimicrobial efficacy. In this study, the MIC
values of nine synthesized quaternary ammonium salts
against two Gram positive strains (S. aureus and
C. glutamicum) as well as two Gram negative strains
(E. coli and P. aeruginosa) were measured. And the results
are listed in Table 2. During measurement, for slightly
water-soluble C-BP-8, C-BP-10, C-BP-12, C-BP-14, and C-
BP-F, each one was firstly dissolved in 1 mL absolute meth-
anol and then diffused in 9 mL sterile water to get testing
solutions. Therefore, absolute methanol controls were
πCMC = γ −γ
ð1Þ
0
CMC
Meanwhile, C20 indicating the concentration of the test
amphiphile needed to reduce the surface tension of pure
water by 20 mN m− was also determined, standing for the
adsorption efficiency of the test surfactant. The values of
1
−
1
πCMC were 56.36, 41.47, 39.15, and 38.72 mN m for C-
BP, C-BP-1, C-BP-4, and C-BP-6, respectively. The
decrease of πCMC could be well explained by CMC/C20
analysis. CMC/C20 is a comparison parameter showing the
preference of the test surfactant to form micelle or adsorb
J Surfact Deterg (2019)

J Surfact Deterg
conducted. It was found that four bacterial strains could
grow pretty well under the highest absolute methanol testing
(Jurij Lah and Vesnaver, 2000; Ray et al., 2005; Venable &
Nauman, 1964). The Krafft temperature of C-BP-1, C-BP-
4, and C-BP-6 was lower than 0 C, suggesting high-
potential industrial applications. All synthesized com-
pounds but C-BP-F exhibit great antimicrobial ability
against Gram-positive bacteria (S. aureus and
C. glutamicum) while inadequate antimicrobial ability
against Gram negative strains (E. coli and P. aeruginosa).
−1
ꢀ
concentration of 128 μg mL , suggesting that methanol
would not interfere with the MIC testing results. It was
found that this series of compounds have great antimicrobial
activity toward Gram-positive S. aureus and C. glutamicum
while inadequate antimicrobial activity against two test
Gram-negative strains. After the introduction of fluorine-
substituted side chain, C-BP-F exhibits poor antimicrobial
ability toward all four testing stains. When comparing the
conventional surfactant C-BP with the bicephalic surfactant
C-BP-1, it was found that the introduction of a second head
group decreased the MIC value against S. aureus from
Acknowledgements This research was financially supported by the
National Nature Science Foundation of China (21772039, 21272069),
the Fundamental Research Funds for the Central Universities, and
Key Laboratory of Organofluorine Chemistry, Shanghai Institute of
Organic Chemistry, Chinese Academy of Sciences.
1
−1
1
08 μmol L− (C-BP) to 87 μmol L (C-BP-1) and the
−1
Conflict of Interest The authors declare that they have no conflict
MIC value against C. glutamicum from 54 μmol L (C-
BP) to 44 μmol L− (C-BP-1). The introduction of a second
cationic head group helps to strengthen the electrostatic
interaction between the cationic amphiphile and the anionic
bacterial cell surface, leading to a better antimicrobial effi-
cacy and a lower MIC value (Forman et al., 2016; Jayanta
Haldar and Bhattachary, 2005). With the elongation of the
long carbon chain R group on C-BP-R, the corresponding
MIC value against two Gram-positive strains both gradually
decreases. It was caused by the enhanced interaction
between the prolonged lipophilic chain of the test surfactant
and the hydrophobic sector of the membrane bilayer, which
contributes to disrupt the integrity of the cell envelope and
consequently leads to the breakage of the cell membrane,
leakage of cytoplasm, and finally death of the bacterial cell
1
of interest.
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