Synthesis and antibacterial activity of novel amido-amine-based cationic gemini surfactants

Article abstract of DOI:10.1007/s11743-012-1406-4

A series of novel cationic gemini surfactants were synthesized from corresponding amido-amines in a single step reaction. The amido-amines were obtained from long chain carboxylic acids and 3-N,N-dimethylamino-1-propyl-amine with excellent isolated yield (up to 95 %). All the synthesized quaternary ammonium compounds (QACs) were further investigated for surface active properties. The critical micelle concentration (CMC) and the effectiveness of surface tension reduction were determined. The surface tension measurements of newly synthesized gemini surfactants showed good water solubility, and low CMC values, had great efficiency in lowering the surface tension and a strong adsorption at the air/water interface than the corresponding monomeric surfactants. Further, the antibacterial activity of the synthesized QACs against both Gram-positive and Gram-negative bacteria was also investigated.

Full text of DOI:10.1007/s11743-012-1406-4

J Surfact Deterg (2013) 16:85–93
DOI 10.1007/s11743-012-1406-4
ORIGINAL ARTICLE
Synthesis and Antibacterial Activity of Novel Amido-Amine-Based
Cationic Gemini Surfactants
Anant K. Ghumare
•
Balu V. Pawar Sunil S. Bhagwat
•
Received: 22 May 2012 / Accepted: 10 September 2012 / Published online: 25 October 2012
Ó AOCS 2012
Abstract A series of novel cationic gemini surfactants
were synthesized from corresponding amido-amines in a
single step reaction. The amido-amines were obtained from
long chain carboxylic acids and 3-N,N-dimethylamino-1-
propyl-amine with excellent isolated yield (up to 95 %). All
the synthesized quaternary ammonium compounds (QACs)
were further investigated for surface active properties. The
critical micelle concentration (CMC) and the effectiveness of
surface tension reduction were determined. The surface ten-
sion measurements of newly synthesized gemini surfactants
showed good water solubility, and low CMC values, had
great efficiency in lowering the surface tension and a strong
adsorption at the air/water interface than the corresponding
monomeric surfactants. Further, the antibacterial activity of
the synthesized QACs against both Gram-positive and Gram-
negative bacteria was also investigated.
compounds remains a significant challenge in synthetic
chemistry. Since increased resistance of pathogenic bacteria
towards the available antibiotics is a worldwide problem
[1–4] the design of new compounds to deal with resistant
bacteria has become one of the important areas of antibac-
terial research. Besides several antibacterial agents, such as
biguanide, phosphonium salts, triazoles, iodine, etc. quater-
nary ammonium compounds (QACs) have been widely used
as antibacterial agents [5, 6]. This is because most biological
surfaces are usually negatively charged and the positively
charged QACs interact strongly with the biological lipid
membranesof bacteria, fungiandothermicroorganisms. This
strong interaction is advantageous when cationic surfactants
are employed as bactericides and for a gene transfection
procedure mediated by cationic lipid vesicles. Several new
types of QACs have been reported to be effective antibacte-
rial agents [6–8]. A conventional surfactant has one lyophilic
and one lyophobic moiety. Gemini surfactants are a class of
surfactants comprised of two lyophilic and two lyophobic
moieties connected at the level of the head groups or very
close to the head groups by a spacer group [9–11].
Keywords Cationic gemini surfactants Á Amido-amine Á
Critical micelle concentration Á Antibacterial agents
Introduction
The unique health and environmental aspects of gemini
surfactants have been studied widely [12–14]. Cationic
gemini surfactants were found to be less toxic and less
persistent in the environment than the conventional qua-
ternary ammonium surfactants [12, 13]. Such surfactants
are in great demand for skin care and cosmetic formula-
tions since they cause lower skin irritation, and fewer
dryness and itching problems [15, 16]. Cationic gemini
surfactants can also act as delivery agents with excellent
potential for use in gene therapy [13–17]. This unique
property of cationic gemini surfactants can be attributed to
their greater ability to bind and condense DNA and rela-
tively low cytotoxicity toward animal cell lines [18–22].
The gemini have also proved useful as anti-corrosive
Development of environmentally benign, efficient and eco-
nomical methods for the synthesis of biologically interesting
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-012-1406-4) contains supplementary
material, which is available to authorized users.
A. K. Ghumare Á B. V. Pawar Á S. S. Bhagwat (&)
Department of Chemical Engineering, Institute of Chemical
Technology (Autonomous), Matunga, Mumbai 400 019, India
e-mail: ss.bhagwat@ictmumbai.edu.in
A. K. Ghumare
e-mail: anantghumare@gmail.com
1
23

8
6
J Surfact Deterg (2013) 16:85–93
Br
Br
detected. As these cations are bischarged, the observation
of [m-2Br]/2 peak, (where m is the mass of the cationic part
of molecule) was in agreement with respective structure.
O
O
H3C
Q
CH3
N
H
N
N
N
H
n
n
Surface Tension Measurement
Fig. 1 The general structure of novel amido-amine-based cationic
gemini surfactants. Wherein n represents methylene group from 6 to
1
6 carbon atoms; Q represents alkyl chain a spacer group of having
The surface tensions of aqueous solutions of the gemini
surfactants were measured with a Kruss K11 tensiometer
using the Wilhelmy plate technique. To obtain the equi-
librium surface tension, sets of measurements were per-
formed until change in the surface tension was less than
0.01 mN/m every 120 s. Measurements were taken at
25 ± 1 °C. The CMC and surface tension at the CMC were
determined from the breakpoint of the surface tension and
the logarithm of the concentration curve. To estimate the
adsorption and aggregation properties of amido-amine-
based gemini surfactants, we use parameters such as C .
(
2
)
3
2 6
CH and (CH ) groups
agents, catalysts in several organic and inorganic reactions
and in herbicides preparations, fabric softeners, asphalt
additives, textile auxiliaries as well as in enhanced oil
recovery, drug entrapment and release, construction of
high-porosity materials etc [20, 21].
In the present work, we have synthesized amido-amine-
based cationic gemini surfactants (compound 8-3-8 to
1
8-6-18) with excellent yields. For clarity purpose, the
2
0
nomenclature adopted is described according to alkyl chain
and the spacer group employed; for e.g. 8-3-8, the first and
third digit represents alkyl chain length while the second
digit denotes the spacer group. All these newly synthesized
compounds were screened for their antibacterial activities
against both Gram-positive and Gram-negative bacterial
strains using agar well diffusion method and were com-
pared with conventional reference standards like cetyl-
trimetylammonium bromide (CTAB). The surface activity
of these molecules was also studied. The general structure
of newly synthesized gemini surfactants is represented in
Fig. 1.
Here, C20 represents the surfactant concentration required
to reduce the surface tension of water by 20 mN/m.
Synthesis and Spectroscopic Data of Amido-Amine
(1a to 1e), RCONH (CH ) N (CH )
2
3
3 2
The 3-N-N-dimethylamino-1-propyl amine (0.7 mmol) was
added slowly to carboxylic acid (0.5 mmol) in toluene,
under dry, under inert atmosphere of nitrogen, in absence
of light. The progress of reaction was monitored with TLC
analysis and water formed during the reaction was mea-
sured using dean-stark trap apparatus. The desired product
was formed after 16–18 h and was further purified either by
fractional distillation (1a to 1c) or recrystallization with
anhydrous acetone (Id to Ie). All the synthesized com-
Experimental Section
1
13
pounds were well characterized with FT-IR, H- and C-
NMR analysis.
Materials
The chemicals 1,3 dibromopropane, 1,6 dibromohexane
were purchased from Sigma Aldrich Pvt. Ltd, India while
C H CONH (CH ) N (CH ) (1a)
7
15
2 3
3 2
3
-N,N-dimethylamino-1-propyl-amine, acetone, diethyl
Colorless, viscous liquid, Yield = 71 %. FT-IR (KBr pel-
-
let) cm = 3280 (N–H, secondary amide), 1635 (amide I
1
ether, hexane and various other solvents used were pur-
chased from M/s S.D. Fine chemicals Pvt. Ltd, India with
the highest purity available and were used without any
further treatment. The synthesized cationic gemini surfac-
tants with three and six methylene spacer groups were
confirmed by using FT-IR (Perkin-Elmer), Mass (APCI),
1
band), 1545 (amide II band). ( H-NMR-300 MHz, TMS,
CD OD) d ppm: 0.86 (t, J = 6.9 Hz, 3H), 1.27 (m, 8H),
3
1.56–1.65 (m, 4H), 2.13 (t, J = 7.8 Hz, 2H), 2.21 (s, 6H)
2.35 (t, J = 6.6 Hz, 2H), 3.32 (m, 2H), 6.92 (br, 1H).
1
13
H, and C NMR (Varian Mercury plus 300 MHz). In the
13
H- and C-NMR spectral data chemical shifts are repor-
C H CONH ((CH ) N (CH ) (1b)
9
19
2 3
3 2
1
ted in parts per million (ppm) relative to the central peak of
the solvent or TMS as an internal standard and coupling
constants (J values) are given in Hertz (Hz). The mass
spectra of ‘‘gemini’’ surfactants were recorded on an
LC/MS (Thermo Fischer Finnigan mass spectrometer) with
atmosphere pressure chemical ionization (positive mode).
In this case, only the cationic part of the molecule was
Colorless, viscous liquid, b.p. 179–181 °C (1.5 mm-Hg),
-1
Yield = 75 %; FT-IR-(KBr pellet) cm = 3239 (N–H
secondary amide), 1645 (amide I band), 1554 (amide II
1
band). H NMR-300 (MHz, TMS, CD OD) d ppm: 0.86
3
(t, J = 6.6 Hz, 3H), 1.25 (m, 12H; 1.56–1.66: m, 4H), 2.13
(t, J = 7.8 Hz, 2H), 2.22 (s, 6H), 2.36 (t, J = 6.3 Hz, 2H),
3.31 (m, 2H), 6.91 (br, 1H).
1
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J Surfact Deterg (2013) 16:85–93
87
1
(amide I band), 1545 (amide II band), H NMR (300 MHz,
C H CONH (CH ) N (CH ) (1c)
3 2
1
1
23
2 3
TMS, CD OD) d ppm: 0.86 (t, J = 6.9 Hz, 3H), 1.27 (m,
3
White, waxy solid; m.p. 32–33 °C; b.p. 208–211 °C
8H), 1.56–1.65 (m, 4H), 2.13 (t, J = 7.8 Hz, 2H), 2.21 (s,
6H), 2.35 (t, J = 6.6 Hz, 2H, 3.32 (m, 2H), 6.92 (br, 1H).
-1
(
3.5 mm-Hg), Yield = 89 %; FT-IR-(KBr pellet) cm
=
3
440 (N–H secondary amide), 1641 (amide I band), 1550
1
(
amide II band). H NMR (300 MHz, TMS, CD OD) d ppm:
C H CONH (CH ) N (CH ) (C H ) (10-Monomer)
9
3
19
2 3
3 2
2 5
0.90 (t, J = 6.6 Hz, 3H), 1.25 (m, 16H), 1.60–1.68 (m, 4H),
2.15 (t, J = 7.26 Hz, 2H), 2.24 (s, 6H), 2.38 (t, J = 6.63 Hz,
2H), 3.28 (pent, J = 5.98 Hz, 2H), 7.25 (br, 1H).
Colorless viscous liquid, Yield = 75 %; FTIR-(KBr pellet)
-
1
cm = 3239 (N–H secondary amide), 1645 (amide I
1
band), 1554 (amide II band). H NMR (300 MHz, TMS,
C H CONH (CH ) N (CH ) (1d)
3 2
CD OD) d ppm: 0.86 (t, J = 6.6 Hz, 3H), 1.25 (m, 12H),
1
3
27
2 3
3
1.56–1.66 (m, 4H), 2.13 (t, J = 7.8 Hz, 2H), 2.22 (s, 6H),
2.36 (t, J = 6.3 Hz, 2H), 3.31 (m, 2H), 6.91 (br, 1H).
White, waxy solid; m.p. 48–49 °C; b.p. 194–196 °C
-
1
(
0.5 mm-Hg), Yield = 65 %; FT-IR-(KBr pellet) cm
=
3
445 (N–H secondary amide), 1646 (amide I band), 1556
1
Typical Procedure and Spectroscopic Data
of Synthesized Amido-Amine-Based
Cationic Gemini Surfactants
(
amide II band). H NMR (300 MHz, TMS, CD OD) d
3
ppm: 0.90 (t, J = 7.0 Hz, 3H), 1.30 (m, 22H), 1.60
(
(
m, 2H), 2.11–2.22 (m, 4H), 2.28 (m, 2H), 3.30 (s, 6H), 8.0
1
3
br, 1H). C NMR (300 MHz, TMS, CD OD) d ppm:
Octanoic acid [3-({3-[3-Octanoylamino-propyl)-dimethyl-
amino}-dimethylamino)-propyl]-amide Dibromide (8-3-8)
3
1
4.30 (1C), 22.89 (1C), 25.90 (1C), 26.55 (1C),
2
9.90–30.18 (2C), 30.40–30.50 (2C), 32.55 (1C), 34.10
(
1C), 35.50 (1C), 36.70–36.85 (2C), 37.0 (2C), 43.70 (2C),
1.70 (1C), 174.90 (1C).
The reaction was carried out under dry, oxygen free, nitrogen
conditions. The 1,3 dibromopropane (25 mmol, 5.025 g) in
dry acetone (35 mL) was added dropwise to octanoic acid
(3-dimethyl amino-propyl)-amide (50 mmol, 11.4 g) in dry
acetone (60 mL). The resultingreaction mixturewas refluxed
for 65 h. A white precipitate was formed, filtered and further
recrystallized with diethyl ether (Yield 76 %).
6
C H CONH (CH ) N (CH ) (1e)
3 2
1
7
35
2 3
-
1
White solid; m.p. 66–68 °C; FT-IR-(KBr pellet) cm
3
=
245 (N–H secondary amide), 1645 (amide I band), 1545
1
amide II band). Yield = 80 %. H NMR (300 MHz, TMS,
(
-
FT-IR-(KBr Pellet) cm = 3459 (N–H, Secondary
1
CD OD) d ppm: 0.94 (t, J = 7.0 Hz, 3H), 1.37 (m, 28H),
3
1
.65 (m, 2H), 2.11–2.30 (m, 6H), 2.28 (m, 2H), 3.30
1
Amine), 1639 (Amide I Band), 1560 (Amide II Band)
3
(
s, 6H), 8.0 (br, 1H). C NMR (300 MHz, TMS, CD OD)
3
d ppm: 14.30 (1C), 22.89 (1C), 25.90 (1C), 26.55 (1C),
9.90–30.18 (2C), 30.40–30.50 (2C), 32.55 (1C), 34.10
1C), 35.50 (1C), 36.77–36.41 (4C), 37.2 (4C), 43.70 (2C),
1.70 (1C), 174.90 (1C).
Ms (positive) theoretical: 287.10; observed: 286.27.
1
2
H NMR (300 MHz, TMS, CD OD) d ppm: 0.96
3
(
(t, J = 6.6 Hz, 6H), 1.20 (m, 4H), 1.35 (m, 14H), 1.62
(t, J = 6.9 Hz, 4H), 2.22 (t, J = 7.7 Hz, 4H), 2.35 (m,
6
2
H), 3.15–3.19 (m, 18H), 3.30 (m, 8H), 8.1 (s, 2H).
1
3
Synthesis and Spectroscopic Data of Amido-Amine-
Based Corresponding Monomer 8 to 18-Monomer,
RCONH (CH ) N (CH ) (C H )
C NMR (300 MHz, TMS, CD OD) d ppm: 14.99
3
(2C), 15.99 (1C), 23.88 (2C), 24.11 (1C), 24.48 (1C),
2
3
3 2
2 5
26.37–26.50 (2C), 30.79 (2C), 30.58 (2C), 33.35 (2C),
35.30 (2C), 44.11 (2C), 57.08 (4C), 62.14 (1C), 62.46 (1C),
The reactions were carried out under dry, oxygen free
nitrogen conditions. Ethyl bromide (1.25 mmol) in dry
acetone was added drop wise to amido-amine (1 mmol) in
acetone. The mixture was refluxed for 35–40 h and the
progress of reaction was examined by TLC. The products
were purified either by fractional distillation or recrystal-
lization from anhydrous acetone.
64.5 (2C), 177.07–176.99 (2C).
Decanoic acid [3-({3-[3-Decanoylamino-propyl)-
dimethyl-amino}-dimethylamino)-propyl]-amide
Dibromide (10-3-10)
The 1,3 di-bromopropane (25 mmol, 5.025 g) in dry ace-
tone (30 mL) was added dropwise to decanoic acid
(3-dimethyl amino-propyl)-amide, (50 mmol, 12.85 g) in
dry acetone (70 mL). The mixture was refluxed for 72 h. A
white precipitate was filtered and was recrystallized using
diethyl ether, (Yield 75 %).
C H CONH (CH ) N (CH ) (C H ) (8-Monomer)
7
15
2 3
3 2
2 5
Brown color, viscous liquid, Yield = 71 %; FTIR-IR (KBr
-
1
pellet) cm = 3280 (N–H, secondary amide), 1635
1
23

8
8
J Surfact Deterg (2013) 16:85–93
-
FT-IR-(KBr pellet) cm = 3452 (nN–H, secondary
1
(t, J = 7.3 Hz, 4H), 2.77 (m, 2H), 3.0–3.25 (m, 12H), 3.40
(s, 12H), 8.10 (s, 2H).
amine), 1640 (amide I band), 1550 (amide II band).
1
3
Ms (positive): theoretical: 553.73; observed: 553.4.
1
C NMR (300 MHz, TMS, CD OD) d ppm: 14.99
3
H NMR (300 MHz, TMS, CD OD) d ppm: 0.86 (t,
(2C), 17.15 (1C), 22.19 (2C), 24.13–24.71 (2C), 26.35
(2C), 27.37 (2C), 27.80 (2C), 30.86 (6C), 31.71 (6C),
33.41–34.30 (2C), 35.90–37.50 (2C), 41.00 (2C),
44.12–44.74 (2C), 54.37–55.04 (2C), 63.46 (2C), 66.13
(2C), 177.42 (2C).
3
J = 6.30 Hz, 6H), 1.25–1.35 (m, 24H), 1.60 (m, 4H), 2.10
(
m, 4H), 2.35 (t, J = 6.75 Hz, 4H), 2.85 (m, 2H),
.15–3.19 (m, 12H), 3.25–3.45 (s, 12H), 8.17 (s, 2H).
3
1
3
C
NMR (300 MHz, TMS, CD OD)
d
6.14–16.22 (2C), 19.60 (1C), 24.90–25.05 (2C), 26.80
ppm:
3
1
(
2C), 28.08 (2C), 28.25 (2C), 31.48–31.60 (2C),
Octadecanoic Acid [3-({3-[3Octadecanoylamino-propyl)-
dimethyl-amino}-dimethyl-amino)-propyl]-amide
Dibromide (18-3-18)
3
3
1
1.82–31.92 (2C), 32.03–32.14 (2C), 34.16–34.40 (2C),
8.66 (2C), 45.33 (2C), 54.11 (4C), 62.72 (2C), 63.76 (2C),
78.18–178.76 (2C).
The 1,3 dibromopropane (25 mmol, 5.025 g) in dry
acetone (40 mL) was added dropwise to octadecanoic acid
(3-dimethyl amino-propyl)-amide, (50 mmol, 19.3 g) in
dry acetone (80 mL) under dry, oxygen free, nitrogen
conditions. The mixture was refluxed for 71 h. A white
precipitate was filtered and recrystallized with diethyl ether
(Yield 60 %).
Dodecanoic Acid [3-({3-[3-Dodecanoylamino-propyl)-
dimethyl-amino}-dimethylamino)-propyl]-amide
Dibromide (12-3-12)
The 1,3 dibromopropane (25 mmol, 5.025 g) in dry ace-
tone (35 mL) was added dropwise to dodecanoic acid (3-
dimethyl amino-propyl)-amide, (50 mmol, 14.25 g) in dry
acetone (60 mL) under dry, oxygen free, nitrogen condi-
tions. The mixture was refluxed for 65 h. A white precip-
itate was filtered and recrystallized with diethyl ether,
-
1
FT-IR-(KBr pellet) cm = 3458 (N–H, secondary
amine), 1640 (amide I band), 1552 (amide II band). Ms
(positive): Expected. M/z: 407; observed: 406.38.
1
H NMR (300 MHz, TMS, CD OD) d ppm: 0.96 (t,
3
(
Yield 74 %).
FT-IR-(KBr pellet) cm = 3443 (N–H, secondary
J = 6.9 Hz, 6H), 1.20–1.40 (m, 56H), 1.65 (m, 4H), 2.1
(m, 4H), 2.30 (t, J = 7.1 Hz, 4H), 2.90 (m, 2H), 3.15 (m,
4H), 3.40 (s, 12H), 3.50 (m, 8H), 8.10 (s, 2H).
-
1
amine), 1640 (amide I band), 1550 (amide II band).
1
3
Ms (positive): theoretical: 651.29; observed: 652.0.
1
C NMR (300 MHz, TMS, CD OD) d ppm: 15.066
3
H NMR (300 MHz, TMS, CD OD) d ppm: 0.90 (t,
(3C), 24.25 (2C), 24.51 (2C), 27.52 (2C), 27.97 (2C), 30.84
(2C), 30.99 (2C), 31.32 (16C), 33.58 (2C), 37.62 (2C),
38.56 (2C), 45.36 (2C), 52.34 (4C), 62.17 (2C), 64.50 (2C),
176.82–177.048 (2C).
3
J = 6.6 Hz, 6H), 1.20–1.40 (m, 36H), 1.65 (m, 4H), 2.35
(
t, J = 7.3 Hz, 4H), 2.87 (m, 2H), 3.05–3.20 (m, 12H),
.35 (s, 12H), 7.80 (s, 2H).
3
13
C NMR (300 MHz, TMS, CD OD) d ppm: 16.23
3
(
(
(
2C), 19.62 (1C), 25.09 (4C), 27.05 (2C), 28.30 (2C), 31.96
2C), 32.06 (2C), 32.40 (4C), 34.47 (4C), 38.70 (2C), 45.52
2C), 54.15 (4C), 62.74 (2C), 63.78 (2C), 178.07 (2C).
Octanoic acid [3-({6-[(3-Octanoylamino-propyl)-dimethyl-
amino]-hexyl}-dimethyl-amino)-propyl]-amide Dibromide
(8-6-8)
Tetradecanoic Acid [3-({3-[3Tetradecanoylamino-propyl)-
dimethyl-amino}-dimethyl-amino)-propyl]-amide
Dibromide (14-3-14)
The reaction was carried out under dry, oxygen free,
nitrogen conditions. The 1,6 dibromohexane (25 mmol,
5.025 g) in dry acetone (30 mL) was added dropwise to
octanoic acid (3-dimethyl amino-propyl)-amide, (50 mmol,
9.42 g) in dry acetone (60 mL).The mixture was refluxed
for 60 h. A white precipitate was filtered and recrystallized
using diethyl ether, (Yield 71 %).
The reaction was carried out under dry, oxygen free,
nitrogen conditions. The 1,3 dibromopropane (25 mmol,
5
.025 g) in dry acetone (40 mL) was added dropwise to
tetradecanoic acid (3-dimethyl amino-propyl)-amide,
50 mmol, 15.65 g) in dry acetone (70 mL) and was
-
1
FT-IR-(KBr pellet) cm = 3459 (N–H, secondary
amine), 1645 (amide I band), 1551 (amide II band). Ms
(positive): Expected. M/z: (M-2Br)/2 ? 1 = 271.36;
(
refluxed for 70 h. The white precipitate was formed, fil-
tered and recrystallized with diethyl ether, (Yield 78 %).
observed: 271.33.
1
-
1
FT-IR-(KBr pellet) cm = 3447 (N–H, secondary
H NMR (300 MHz, TMS, CD OD) d ppm: 0.94
3
amine), 1647 (amide I band), 1549 (amide II band). Ms
(t, J = 6.9 Hz, 6H), 1.30 (m, 16H), 1.45 (m, 4H), 1.60
(p, J = 7.3 Hz, 4H), 1.82 (m, 4H), 2.0 (m, 4H), 2.21
(t, J = 7.6 Hz, 4H), 3.15 (s, 12H), 3.25 (m, 4H), 3.35
(m, 8H), 8.17 (s, 2H).
(
positive): theoretical: 372; observed: 371.27.
1
H NMR (300 MHz, TMS, CD OD) d ppm: 0.88
3
(
t, J = 6.8 Hz, 6H); 1.25–1.45 (m, 44H), 1.67 (m, 4H), 2.2
1
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J Surfact Deterg (2013) 16:85–93
89
1
3
C NMR (300 MHz, TMS, CD OD) d ppm: 14.94
Tetradecanoic Acid [3-({6-[(3-Tetradecanoylamino-
propyl)-dimethyl-amino]-hexyl}-dimethyl-amino)-propyl]-
amide Dibromide (14-6-14)
3
(
(
(
2C), 23.67 (2C), 24.12 (2C), 24.46 (2C), 27.04 (2C), 27.40
2C), 30.57–30.77 (4C), 33.31 (2C), 37.62 (2C), 37.70
2C), 51.97 (4C), 63.77 (2C), 65.857 (2C), 176.98 (2C).
The 1,6 dibromohexane (25 mmol, 5.025 g) in dry acetone
(35 mL) was added dropwise to tetradecanoic acid
(3-dimethyl amino-propyl)-amide, (50 mmol, 12.84 g) in
dry acetone (60 mL). The mixture was refluxed for 65 h. A
white precipitate was filtered and recrystallized using die-
thyl ether, (Yield 80 %).
Decanoic Acid [3-({6-[(3-Decanoylamino-propyl)-
dimethyl-amino]-hexyl}-dimethyl-amino)-propyl]-amide
Dibromide (10-6-10)
The 1,6 dibromohexane (25 mmol, 5.025 g) in dry acetone
-
1
(
35 mL) was added dropwise to decanoic acid (3-dimethyl
amino-propyl)-amide, (50 mmol, 10.54 g) in dry acetone
70 mL) reaction was carried out under dry, oxygen free
FT-IR-(KBr pellet) cm = 3438 (N–H, secondary
1
amine), 1650 (amide I band), 1549 (amide II band). H
(
NMR (300 MHz, TMS, CD OD) d ppm: 0.90 (t,
3
nitrogen conditions. The mixture was refluxed for 63 h. A
white precipitate was formed, filtered and recrystallized
with diethyl ether, (Yield 65 %).
J = 6.9 Hz, 6H), 1.35 (m, 44H), 1.62 (m, 4H), 1.90 (m,
8H), 2.30–2.57 (m, 4H), 2.95 (t, J = 7.7 Hz, 4H), 3.15 (m,
1
4H), 3.35 (m, 4H), 3.50 (s, 12H), 7.80 (s, 2H). C NMR
3
-
1
FT-IR-(KBr pellet) cm = 3460 (N–H, secondary
(300 MHz, TMS, CD OD) d ppm: 15.01 (2C), 22.20 (2C),
3
amine), 1641 (amide I band), 1549 (amide II band). Ms
24.13–24.34 (2C), 24.54–24.71 (2C), 26.35–26.50 (2C),
27.33–27.44 (2C), 27.58–27.79 (2C), 28.70–28.83 (2C),
30.70 (2C), 30.86 (2C), 31.17 (2C), 33.46–33.99 (2C),
34.17–34.26 (2C), 34.80–35.33 (2C), 35.46–35.93 (2C),
37.57–38.63 (2C), 40.92 (2C), 46.09 (4C), 62.80–63.43
(2C), 66.10–67.57 (2C), 175.53 (2C).
(
positive): Expected. m/z—(M-2Br)/2 = 321.4; observed—
20.20.
3
1
H NMR (300 MHz, TMS, CD OD) d ppm: 0.90
3
(
t, J = 6.9 Hz, 6H), 1.30 (m, 24H), 1.5(m, 4H), 1.60(m, 4H);
.80 (m, 4H); 2.0 (p, J = 7.6 Hz, 4H); 2.20 (t, J = 7.7 Hz,
1
4
H), 3.15 (s, 12H), 3.22 (m, 4H), 3.35 (m, 8H), 7.78 (s, 2H).
13
C NMR (300 MHz, TMS, CD OD) d ppm: 15.03
Octadecanoic Acid [3-({6-[(3-Octadecanoylamino-
propyl)-dimethyl-amino]-hexyl}-dimethyl-amino)-propyl]-
amide Dibromide (18-6-18)
3
(
(
(
2C), 23.69 (2C), 24.21 (2C), 24.50 (2C), 27.05 (2C), 27.45
2C), 30.09 (4C), 30.97 (2C), 31.00 (2C), 33.51 (2C), 37.68
2C), 37.75 (2C), 52.02 (4C), 63.80 (2C), 65.88 (2C),
1
76.97 (2C).
The reaction was carried out under dry, oxygen free, nitrogen
conditions. The 1,6 dibromohexane (25 mmol, 5.025 g) in
dry acetone (35 mL) was added dropwise to octadecanoic
acid (3-dimethyl amino-propyl)-amide, (50 mmol, 15.83 g)
in dry acetone (60 mL). The mixture was refluxed for 70 h. A
white precipitate obtained was filtered and recrystallized
using diethyl ether, (Yield 61 %).
Dodecanoic Acid [3-({6-[(3-Dodecanoylamino-propyl)-
dimethyl-amino]-hexyl}-dimethyl-amino)-propyl]-amide
Dibromide (12-6-12)
The reaction was carried out under dry, oxygen free,
nitrogen conditions. The 1,6 dibromohexane (25 mmol,
-
1
FT-IR-(KBr pellet) cm = 3461 (N–H, secondary
1
amine), 1640 (amide I band), 1553 (amide II band). H
5
.025 g) in dry acetone (40 mL) was added dropwise to
dodecanoic acid (3-dimethyl amino-propyl)-amide,
50 mmol, 11.85 g) in dry acetone (80 mL). The mixture
NMR (300 MHz, TMS, CD OD) d ppm: 0.90 (t,
3
(
J = 6.9 Hz, 6H), 1.30 (m, 60H), 1.50 (m, 4H), 1.60 (m,
4H), 1.80 (m, 4H), 2.0 (m, 4H), 2.20 (t, J = 7.5 Hz, 4H),
3.15 (s, 12H), 3.30 (m, 8H), 7.80 (s, 2H).
was refluxed for 68 h. A white precipitate was formed,
filtered and recrystallized with diethyl ether, (Yield 72 %).
-
1
FT-IR-(KBr pellet) cm = 3460 (nN–H, secondary
13
C NMR (300 MHz, TMS, CD OD) d ppm: 13.06 (2C),
3
amine), 1645 (amide I band), 1550 (amide II band). Ms
21.83 (2C), 22.34 (2C), 22.70 (2C), 25.30 (2C), 25.58 (2C),
29.09–29.27(6C), 29.40 (18C), 31.68 (2C), 35.80 (2C), 35.91
(2C), 52.07 (4C), 61.93 (2C), 64.01 (2C), 175.34, (2C).
(
positive): Expected m/z (M-2Br) = 653; observed = 655.
1
H NMR (300 MHz, TMS, CDCl ) d ppm: 0.86 (t,
3
J = 6.9 Hz, 6H), 1.25 (m, 32H), 1.45–1.65 (m, 8H),
1
.90–2.1 (m, 8H), 2.25 (t, J = 7.3 Hz, 4H), 3.0–3.35 (m,
Antibacterial Activity
1
H), 3.50 (s, 12H), 3.75 (m, 8H), 7.8 (s, 2H), C NMR
3
4
(
300 MHz, TMS, CDCl ) d ppm: 14.11 (2C), 22.66 (2C),
The microbial strains namely, Escherichia coli (ATCC-
8739), Bacillus subtilis (ATCC-10702), Staphylococcus
aureus (ATCC-6538), Pseudomonas aeruginosa (ATCC-
8027) were used to investigate the antibacterial activity for
various synthesized gemini compounds using the agar well
3
2
2
3
1
3.09 (2C), 24.85 (2C), 25.88 (2C), 29.34 (2C), 29.47 (2C),
9.56 (6C), 29.63 (2C), 29.69 (2C), 31.89 (4C),
6.14–36.41 (2C), 51.20 (4C), 62.53 (2C), 64.76 (2C),
74.44 (2C).
1
23

9
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J Surfact Deterg (2013) 16:85–93
diffusion method. The bacterial strains were suspended in
0 mL sterile nutrient broth and were incubated on an orbital
shaker at 180 rpm at 37 °C, 18–24 h for bacterial strains. The
microorganisms were diluted to obtain 10 –10 colony
forming unit (cfu/mL) and the suspensions were added to a
flask containing sterile molten nutrient agar (NA, 250
amido-amine was reacted with ethyl bromide under reflux
conditions for 35–40 h under an inert atmosphere. Dry
acetone was used as the solvent. The desired products were
obtained with moderate yield (Table 1, entries 1–5).
2
6
7
Synthesis of Amido-Amine-Based Gemini Surfactants
1
2 mL). The sterile molten agar (NA, 12 mL), was poured
into sterile petri dishes (9 cm in diameter). The agar was
allowed to solidify forming a basal layer. The bacterial strain
inoculated molten agar (seed layer of 8 mL) was poured on to
the basal layer and allowed to solidify at a lower temperature
The amido-amines were further reacted with dibromo
propane and dibromo hexane in order to obtain cationic
gemini surfactants with propyl and hexyl spacer groups
respectively, (Fig. 2; Table 1, entries 6–15). The reaction
was carried out under reflux conditions and an inert
atmosphere. Dry acetone was used as solvent to facilitate
the reaction. Overall, the gemini surfactants were synthe-
sized with moderate to good yields (Table 1).
8
–10 °C. Four equidistant wells (8 mm in diameter) were cut
from the agar with the aid of a sterile cork borer. The 100-lL
samples with a concentration of 1 mg/mL (1,000 ppm) dis-
solved in methanol as a solvent were then put into the wells in
triplicate. The microorganisms were inoculated at 37 °C,
1
8–24 h for bacterial strains. At the end of the incubation
Surface Active Properties of All the Newly Synthesized
Compounds
period, all the plates were examined for the appearance of any
zone of growth inhibition and the diameters of these zones
were measured in millimeters. All the tests were performed in
triplicate and the results were presented as an average. CTAB
was used as standard cationic surfactants. The control/blank
test was also performed, to investigate the effect of methanol
on microbial growth. The values obtained for methanol were
subtracted from the test samples to obtain the accurate inhi-
bition zone values. The observed data on the antibacterial
activity of the gemini compounds and control are summa-
rized in Table 3 of the main manuscript.
After synthesis of the novel surfactants, we further inves-
tigated their surface active properties (Fig. 2 and Table 2).
The amido-amine-based gemini surfactants and the corre-
sponding monomeric surfactants at 10 % concentration
exhibited good water solubility at 25 °C. Critical micelle
concentration (CMC) values, surface tension at CMC
(cCMC) and C20 are summarized in Table 2. In general,
CMC represents the concentration at which the surfactant
begins to aggregate into micelles. C20 is defined as the
surfactant concentration at which the surface tension of the
solution is less than the pure solvent (water) by 20 mN/m
(Fig. 3). The CMC, cCMC and C20 value was determined for
the synthesized cationic gemini surfactants and the exam-
ple of 18-3-18 is mentioned herewith representing a model
surfactant for the present study.
Results and Discussion
Synthesis of Amido-Amine
The carboxylic acids (C , C , C , C , C ) were reacted
18
It is anticipated that the gemini surfactants have a lower
CMC than the corresponding monomeric surfactants. The
increase in hydrocarbon chain length from 8 to 12 results in
a decrease in CMC for the both monomeric as well as
gemini surfactants. However, this trend was not observed
in the case of gemini surfactants with chain lengths from 14
to 18. The observation was anticipated as the cohesion of
the two hydrophobic chains appeared to be stronger when
the hydrophobic chain length ‘n’ is more than 14. Similar
results were reported in the literature for cyanuric chloride-
based gemini surfactants [23]. Moreover, it was observed
that the C20 decreases with an increasing hydrophobic
portion of the QACs as shown in Table 2.
8
10
12
14
with stoichiometric excess (20 %) of 3-N,N-dimethyl-
amino-1-propyl amine in presence of toluene to synthesize
corresponding amido-amines quantitatively (Fig. 2,
comp.1a–1e). These amido-amines were then used as
precursors for the synthesis of gemini surfactants. The
reaction was performed for 16–18 h and was monitored by
measuring the water formed during the reaction. The
amido-amine products were confirmed using spectroscopic
analyses which were in good agreement with those repor-
ted in the literature [22]. In the present methodology, an
excess amount of amine was found to be necessary for
completion of the reaction within 16–18 h.
Synthesis of Amido-Amine-Based Monomeric
Surfactants
Antibacterial Activity of All the Newly Synthesized
Compounds
A one-step methodology was applied for the synthesis of
amido-amine-based monomeric surfactants (Fig. 2). The
The antibacterial activity of all the synthesized QACs and
the monomeric surfactants was assessed (Table 3). Stock
1
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J Surfact Deterg (2013) 16:85–93
91
Fig. 2 The synthesis route of a
series of amido-amine-based
cationic gemini and monomeric
surfactants
O
O
N, N dimethyl propyl
, 3 diamine
1
H C
3
H C
3
Toluene, reflux,
16-18 h, N2
N
H
N
OH
n
n
1a-1e
Amido-amine
Ethyl bromide
dry acetone,
reflux, N
5-40 h
Br
N
2
,
Dibromo alkane
dry acetone, reflux
0-80 h, N2
3
C H
2
5
6
NH
Br
Br
O
O
O
H C
3
Q
CH
3
N
H
N
N
N
H
n
n
n
H C
3
8
to 18-Monomers
8-3-8 to 18-6-18
Cationic Gemini Surfactants
Cationic Monomeric Surfactants
Table 1 Physical data and
yield of synthesized compounds
a
Entry
Comp name
Molecular formula
Mol Wt
n
Q
Yield (%)
1
2
3
4
5
6
7
8
9
8-Monomer
10-Monomer
12-Monomer
14-Monomer
18-Monomer
8-3-8
C
C
C
C
C
C
C
C
C
C
C
C
15
17
19
21
25
29
33
37
41
49
32
36
H
H
H
H
H
H
H
H
H
H
H
H
33
37
41
45
53
62
70
78
86
N
N
N
N
N
N
N
N
N
2
2
2
2
2
4
4
4
OBr
OBr
OBr
OBr
OBr
355
363
391
419
475
658
714
770
826
938
700
756
812
868
980
6
8
–
71
75
78
73
80
76
75
74
78
60
71
65
72
80
61
–
10
12
16
6
–
–
–
2
O Br
2
O Br
2
O Br
2
O Br
2
2
2
2
(CH
(CH
(CH
(CH
(CH
(CH
(CH
2
2
2
2
2
2
2
)
)
)
)
)
)
)
3
3
3
3
3
6
6
10-3-10
8
12-3-12
10
12
16
6
14-3-14
4
1
1
0
1
18-3-18
102
N
4 2 2
O Br
8-6-8
68
N
4
O
2
Br
Br
2
2
2
The entries 1–5 are monomeric
surfactants while entries 6–15
are gemini surfactants
12
13
14
10-6-10
76
N
O
4 2
8
12-6-12
C H N O Br
4
0
84
4
2
10
12
16
2 6
(CH )
n methylene groups, Q spacer
group
14-6-14
C H N O Br
4
2 6
(CH )
4
92
4
2
2
1
5
18-6-18
C
H
52 108
N
4 2
O Br
2
2 6
(CH )
a
Isolated yield
solutions of the surfactants were prepared in methanol and
used for investigation of the antibacterial activity. Each
experiment was performed in triplicate and the average
values are reported (for more details please refer to the
supplementary material). The control test was performed,
to investigate the effect of methanol on microbial growth.
The values obtained for methanol were subtracted from the
test samples to obtain the accurate inhibition zone values.
CTAB was used as a conventional reference antibacte-
rial agent. Excellent antibacterial potency against E. coli
was observed for the monomeric surfactant (Table 3, entry
2) while other gemini surfactants (Table 3, entries 7–15,
except entries 8, 13), and monomeric surfactant (Table 3,
entry 5) had a profound antibacterial activity against
another Gram negative bacteria. i.e. P. aeruginosa. It is
noteworthy that the 14-3-14 gemini surfactant (Table 3,
entry 9) provided the highest activity against P. aerugin-
osa, compared to other gemini surfactants, monomers and
CTAB. A model for various classes of antibacterial agents
suggests that the hydrogen bonding is one of the most
1
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9
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J Surfact Deterg (2013) 16:85–93
Table 2 Surface active properties of all newly synthesized
compounds
Table 3 Results of antibacterial activity tested compounds (the val-
ues of inhibition zone are mentioned on the ‘mm’ scale)
Entry
Compound
name
CMC
(mM/L)
c
CMC
(mN/m)
C
20
Entry Sample ID
Gram-negative
Gram-positive
(mM/L)
E. coli P.
(
B. subtilis S. aureus
(mm)
mm)
aeruginosa (mm)
mm)
1
2
3
4
5
6
7
8
9
8-Monomer
10-Monomer
12-Monomer
14-Monomer
18-Monomer
8-3-8
14.0
1.0
35.94
25.59
39.93
23.14
33.59
22.76
23.07
26.31
29.65
38.90
40.48
32.38
39.50
24.60
41.07
1.78
(
0.016
0.008
0.0069
0.010
0.20
0.034
1.00
0.10
12.5
0.68
0.008
0.060
0.090
2.24
0.80
0.03
0.29
0.46
1
2
8-Monomer
–
–
–
–
–
10
18
10
15
–
12
20
09
16
11
10
13
11
15
10
11
19
–
10-Monomer 16
3
12-Monomer
14-Monomer
18-Monomer
8-3-8
–
–
–
–
–
–
–
–
–
–
–
–
–
11
4
10-3-10
0.0067
0.0011
0.0071
0.012
0.18
5
9
12-3-12
6
–
–
14-3-14
7
10-3-10
12-3-12
14-3-14
18-3-18
8-6-8
10
–
–
1
1
1
1
1
1
0
1
2
3
4
5
18-3-18
8
–
8-6-8
9
19
12
11
12
–
12
–
10-6-10
0.016
0.009
0.0075
0.020
10
11
12
13
12-6-12
10
12
13
15
11
10
14-6-14
10-6-10
12-6-12
14-6-14
18-6-18
CTAB
18-6-18
1
1
1
4
5
6
13
09
–
16
10
–
activity depends on the alkyl chain length. A linear rela-
tionship was observed between alkyl chain length and
antibacterial activity for entries 6–9, 11–14, and 1–4
(except Entry 2) of Table 3. Another structural parameter is
the length of the hydrocarbon spacer between the two
ammonium groups. Table 3 shows that a gemini surfactant
with a six-carbon spacer has a higher activity than the
corresponding three-carbon spacer gemini surfactant.
Fig. 3 The representative plot of cationic gemini 18-3-18 surfactants
Conclusions
important descriptor [22]. The results in Table 3 illustrate
similar trends. Gemini surfactants are more effective anti-
bacterial agents than the corresponding monomers and also
have a wider and more effective spectrum with the
exception of 10-monomer (Table 3, entry 2). Moreover, the
gemini surfactants (Table 3, entries 9, 11–15), and mono-
meric surfactants (Table 3, entries 1–4) possess good
activity against B. subtilis bacteria. Overall, it was
observed that the synthesized gemini surfactants exhibited
higher antibacterial activity against Gram-positive bacteria
than the Gram-negative. This can be explained by different
cell membrane structures of the two bacterial types. The
external layer of the outer membrane of Gram-negative
bacteria is almost entirely composed of lipopolysaccha-
rides and proteins that restrict the entrance of biocides and
amphiphilic compounds and hence are more resistant than
Gram-positive bacteria [24]. In general, the antibacterial
In conclusion, a novel protocol for the synthesis of a series of
amido-amine-based cationic gemini surfactants, containing
propyl and hexyl groups as spacers were developed. The
cationic gemini surfactants revealed a wider and more
effective antibacterial spectrum than those for the commer-
cial standards such as CTAB against both Gram-positive as
well as Gram-negative bacteria. The surface activityof QACs
is higher than those of the corresponding monomers. These
synthesized novel gemini surfactants are believed to have a
profound potential for industrial applications.
Acknowledgments The author (AKG) is greatly thankful to the
UGC (University Grant Commission, India) for providing a fellow-
ship. The authors would also extend their special thanks to Mr. Sharad
Gaikwad and Mr. Chetan Pawar, K. T. H. M. College, Nashik,
Maharashtra, India for carrying out antibacterial activity analysis
during this work.
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J Surfact Deterg (2013) 16:85–93
93
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Author Biographies
Anant K. Ghumare completed his graduation in chemistry (2004)
and his post graduation studies (2006) in organic chemistry at the
University of Pune, India. After a short stay in the industrial sector, he
began his Ph.D. studies in 2007 under the guidance of Prof. S. S.
Bhagwat, at the Institute of Chemical Technology, India. The topic of
his research is synthesis, characterization and applications of cationic
gemini surfactants.
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J (2001) Fate and effect of monoalkyl quaternary ammonium
surfactants in the aquatic environment. J. Environ Pollut
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11:169–175
Balu V. Pawar completed his graduation in chemistry (2004) and his
post graduation studies (2006) in organic chemistry at the University
of Pune, India. After a short stay in the industrial sector, he began his
Ph.D. studies in 2007 under the guidance of Prof. S. S. Bhagwat, at
the Institute of Chemical Technology, India. The topic of his Ph.D.
research is organic transformation in micellar media.
1
1
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Synthesis, aggregation, and biological properties of a new class of
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Talmon Y (2005) Self-aggregation in dimeric arginine-based
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Sunil S. Bhagwat is a professor of chemical engineering in the
Department of Chemical Engineering, at the Institute of Chemical
Technology (ICT), Mumbai, India. He received his Ph.D. from the
University of Bombay (Mumbai), India in 1989. His research interests
are interfacial science and engineering, energy engineering, computer
processes stimulation, micellar catalyzed reactions, gemini surfac-
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