Structure and biological behaviors of some metallo cationic surfactants

Article abstract of DOI:10.1007/s11743-013-1483-z

In this study, different cationic surfactants were prepared by esterification with bromoacetic acid of different fatty alcohols, i.e., dodecyl, tetradecyl and hexadecyl species. The products were then reacted with diphenyl amine, and the resulting tertiary amines were quaternized with benzyl chloride to produce a series of quaternary ammonium salts. The metallocationic surfactants were prepared by complexing the cationic surfactants with nickel and copper chlorides. Surface tension of these surfactants were investigated at different temperatures. The surface parameters including critical micelle concentration (CMC), maximum surface excess (Γ _max), minimum surface area (A _min), efficiency (PC₂₀) and effectiveness (π _CMC) were studied. The thermodynamic parameters such as the free energy of micellization (δ G_mic^°) and adsorption (δ G_ads^°), enthalpy (δ H _m^°), (δ H_ads^°) and entropy (δ S_m), (δ S_ads^°) were calculated. FTIR spectra and ¹H-NMR spectra were obtained to confirm the compound structures and purity. In addition, the antimicrobial activities were determined via the inhibition zone diameter of the prepared compounds, which were measured against six strains of a representative group of microorganisms. The results indicate that these metallocationic surfactants exhibit good surface properties and good biological activity on a broad spectrum of microorganisms.

Full text of DOI:10.1007/s11743-013-1483-z

J Surfact Deterg (2013) 16:709–715
DOI 10.1007/s11743-013-1483-z
ORIGINAL ARTICLE
Structure and Biological Behaviors of Some Metallo Cationic
Surfactants
Ahmed I. Adawy Mnal M. Khowdiary
•
Received: 23 October 2012 / Accepted: 10 April 2013 / Published online: 27 April 2013
Ó AOCS 2013
Abstract In this study, different cationic surfactants were
prepared by esterification with bromoacetic acid of differ-
ent fatty alcohols, i.e., dodecyl, tetradecyl and hexadecyl
species. The products were then reacted with diphenyl
amine, and the resulting tertiary amines were quaternized
with benzyl chloride to produce a series of quaternary
ammonium salts. The metallocationic surfactants were
prepared by complexing the cationic surfactants with
nickel and copper chlorides. Surface tension of these sur-
factants were investigated at different temperatures. The
surface parameters including critical micelle concentration
Keywords Cationic surfactants ꢁ Surface parameters ꢁ
Biological activity
Introduction
Cationic surfactants offer some additional advantages over
other classes of surfactants [1–4]. Besides their surface
activity, these substances show antibacterial properties and
are used as cationic softeners, lubricants, retarding agents
and antistatic agents.
(
CMC), maximum surface excess (Cmax), minimum surface
Quaternary salt species are well known compounds and
have been examined for their surface and solution behavior
using a variety of methods [5–14].
area (Amin), efficiency (PC ) and effectiveness (pCMC
were studied. The thermodynamic parameters such as the
)
20
ꢀ
mic
free energy of micellization (DG ) and adsorption
Micelle formation of a surfactant in solution is induced
by the hydrophobic interaction between hydrocarbon parts
of the surfactant molecules balanced by their hydration and
electrostatic repulsive effects [15].
ꢀ
ꢀ
ꢀ
ꢀ
(
(
DG ), enthalpy (DH ), (DH ) and entropy (DS ),
ads m ads m
ꢀ
ads
1
DS ) were calculated. FTIR spectra and H-NMR spectra
were obtained to confirm the compound structures and
purity. In addition, the antimicrobial activities were
determined via the inhibition zone diameter of the prepared
compounds, which were measured against six strains of a
representative group of microorganisms. The results indi-
cate that these metallocationic surfactants exhibit good
surface properties and good biological activity on a broad
spectrum of microorganisms.
The metal–surfactant complex is a special type of sur-
factant, where a coordination complex (containing a central
metal ion with surrounding ligands coordinated to the
metal) acts as the surfactant (Scheme 1).
In these surfactants, the metal complex entity containing
the central metal ion with its primary coordination sphere,
acts as the head group and the hydrophobic entity of one or
more ligands acts as the tail part. Surfactant metal complexes
are expected to provide a wide range of interesting phenomena
on aggregation in aqueous solution due to variations in charge
numbers, size and extent of hydrophobicity through combina-
tion of the central metal and ligands [16]. The biological active
compounds generally become more bacteriostatic and carci-
nostatic upon chelation with metal ions [17].
Electronic supplementary material The online version of this
article (doi:10.1007/s11743-013-1483-z) contains supplementary
material, which is available to authorized users.
A. I. Adawy (&) ꢁ M. M. Khowdiary
The aim of this paper was to prepare some of metallo-
cationic surfactants and determine their surface and ther-
modynamic properties and evaluate them as biocides.
Petrochemicals Department, Egyptian Petroleum Research
Institute, Nasr City, Cairo, Egypt
e-mail: chem_ahmedadawy@yahoo.ca
1
23

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J Surfact Deterg (2013) 16:709–715
Scheme 1 Preparation of
metallocationic surfactants
n = 10 (I:Id), 12 (II:IId), and 14
CH CH CH OH
3
2
2
BrCH COOH
2
n
BrCH COOCH CH CH
2
2
2
3
n
I, II and III
(
III:IIId)
N
H
N
CH COOCH CH CH3
2
2
2
n
Cl
Ia, IIa and IIIa
Cl
N
2
CH COOCH CH2 CH3
2
2
n
Ib, IIb and IIIb
CuCl .2H O
2
2
NiCl2
1+
1
+
N
2-
2-
N
CuCl .2H O
4
2
NiCl4
CH COOCH CH CH3
2
2
2
n
CH2COOCH2 CH2 CH3
n
2
2
Id, IId and IIId
Ic, IIc and IIIc
Experimental Procedures
3. The quaternary ammonium compounds (Ib, IIb and
IIIb) were synthesized by refluxing tertiary amines (Ia,
IIa and IIIa) (1 mol) with benzyl chloride (1 mol) for
Materials
90 h in benzene. The solid product was filtered and
The chemicals used in this study were of pure grade from
Aldrich and were used without further purification. The
solvents used were of pure grade too.
recrystallized from benzene to obtain the cationic
surfactant named alkyl acetate benzyl diphenyl ammo-
nium salt.
4.
Syntheses of metal complexes (metallosurfactants) were
carried out by refluxing 2 mol of cationic surfactants Ib,
Synthesis
IIb and IIIb once with 1 mol of nickel chloride (NiCl ) in
2
benzene for 4 h to obtain metal complexes Ic, IIc and
IIIc, respectively. The same was repeated with 1 mol of
copper chloride (CuCl ꢁ2H O) in benzene for 4 h to
1
.
.
As shown in Scheme (1), the syntheses of compounds
I, II and III) were carried out by refluxing different
(
2
2
fatty alcohols, i.e., dodecyl, tetradecyl and hexadecyl
alcohol (1 mol) with bromoacetic acid (1 mol) in a
Dien Shtark system in xylene.
obtain metal complexes Id, IId and IIId. The reaction
mixtures were left to cool then filtered.
2
The syntheses of compounds (Ia, IIa and IIIa) were
realized by refluxing ester compounds (I, II and III)
Structural Confirmations of the Prepared Compounds
(1 mol) with diphenyl amine (1 mol) for 6 h in
benzene. The reaction mixtures were left to cool then
filtered.
The chemical structure of the synthesized compounds was
characterized by the following analysis.
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J Surfact Deterg (2013) 16:709–715
711
1
6
The FTIR spectra were obtained using ATI Mattsonm
A
¼ 10 =CmaxNA
where N is the Avogadro’s number 6.023 9 10 ;
TM
TM
min
Infinity series , Bench top 961 controlled by Win First
2
3
V2.01 software. (Egyptian Petroleum Research Institute).
1
On the other hand H-NMR was measured in DMSO-d by
A
Thermodynamic Parameters of Micellization and
Adsorption The thermodynamic parameters of adsorption
and micellization of the synthesized cationic surfactants
were calculated according to Gibb’s adsorption equations
6
1
Spect Varian, GEMINI 200 ( H 200 MHz). (Micro Ana-
lytical Center, National Research Center).
Evaluation Methods of Surface Active Properties
Surface Tension
as follows [20]:
ꢀ
DG ¼ RTlnðCMCÞ
DG ¼ DG ꢂ 6:023 ꢃ 10 ꢃ pCMC ꢃ A
mic
ꢀ
ads
ꢀ
ꢂ1
mic
À
min
ꢀ
Á
Surface tensions of the prepared compounds solutions
were measured using a Du-Nouy Tensiometer (Kr u¨ ss
type 6). The surface tensions of different concentrations
DSmic ¼ ꢂd DG =DT
mic
À
ꢀ
ads
Á
DSads ¼ ꢂd DG =DT
-
2
-5
over a range of 4 9 10
to 1.9 9 10 mol/l at dif-
ꢀ
DHmic ¼ DG
DHads ¼ DG þ T DSads
þ T DSmic
mic
ferent temperatures (35, 45, 55 and 65 °C) were
measured.
ꢀ
ads
Antimicrobial Activity of the Prepared Compounds
Surface Parameters of the Prepared Compounds
The antimicrobial activities of the prepared metallocationic
surfactants were measured individually against a wide range
of microorganisms previously isolated in the Biotechnology
Lab. in the Egyptian Petroleum Research Institute (EPRI)
from different oil polluted environments using a dose equal
to 5 mg/ml by the diffusion agar technique.
Critical Micelle Concentration (CMC) The values of the
critical micelle concentration of the prepared compounds
were determined using the surface tension technique. The
surface tension measurements were plotted against the
corresponding concentration in a log scale, and the break
point was taken as the CMC.
The microorganisms included gram-positive bacteria
Effectiveness (pCMC) pCMC is the difference between the
(
Bacillus pumilus and Micrococcus luteus), gram-negative
bacteria (Pseudomonas aeruginosa and Sarcina lutea), yeast
Candida albicans) and fungi (Penicillium chrysogenum).
surface tension of the pure water (c ) and the surface ten-
o
sion of the surfactant solution (c) at the critical micelle
concentration.
(
pCMC ¼ c ꢂ c
o
CMC
Results and Discussion
Efficiency (PC ) Efficiency (PC ) is determined as the
2
0
20
concentration (mol/l) of the surfactant solutions capable to
reduce the surface tension by 20 mN/m.
Chemical Structure
Maximum Surface Excess Cmax The values of the max-
imum surface excess Cmax calculated from surface or
interfacial data by the use of Gibbs equation [18].
The chemical structure of the prepared cationic surfactants
1
was confirmed by FTIR and H-NMR spectra.
C
max
¼ ꢂ1=2:303nRT ðoc=ologCÞT
FTIR Spectra
2
where Cmax is the maximum surface excess in mol/cm , n
is the number of solute species whose concentration at the
interface changes with change in the value of C and equal
to 2 for conventional ionic surfactants, R the universal gas
The FTIR spectra of the synthesized compounds showed
-
the following absorption bands at 1,732.75–1,740.8 cm
1
-
for the C=O ester group, 2,853–2,857.25 cm for the CH2
1
7
-1 -1
-1
?
constant 8.31 9 10 ergs mol
temperature (273.2 °C), C the surfactant concentration,
qc/qlogC) the slope of the plot surface tension vs. -log C
K
, T the absolute
group and 2,925.87–2,918.97 cm for the N group, see
Figs. (S1–S6) in the supplementary material. The FTIR
spectra confirmed the expected functional groups in the
synthesized cationic surfactants.
(
T
curve just below CMC at constant temperature.
Minimum Surface Area (Amin) The area per molecule at
the interface provides information on the degree of packing
and the orientation of the adsorbed surfactant molecule.
The average area (in square angstrom) occupied by each
molecule adsorbed on the interface [19] is given by:
1
H-NMR Spectra
1
H-NMR spectra of synthesized complexes showed signals
at: d = 0.89 ppm (t, 3H, CH ), 1.39 ppm (s, 2H, CH ),
3
2
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J Surfact Deterg (2013) 16:709–715
1
.29 ppm (q, nH, CH ), 4.13 ppm (t, 2H, CH ), 4.21 ppm
2
surface tension (c) of surfactant solutions versus their bulk
concentrations in mol/l in a log scale at 35, 45, 55 and
65 °C. The CMC values are listed in Tables 1, 2, 3, and 4
showing a decrease in the CMC with increasing alkyl chain
length.
2
(
s, 2H, CH ), 4.4 ppm (s, 2H, CH ) and 7.25 ppm (d, 1H,
2 2
CH phenyl), where n = 18, 22 or 26 for complexes Id, IId
and IIId, respectively, see Figs. (S7–S12) in the supple-
1
mentary material. The data of the H-NMR spectra con-
firmed the expected hydrogen proton distribution in the
synthesized complexes. All the synthesized complexes had
approximately the same values.
The CMC also decreases as the temperature increases
probably due to a decrease in the hydration of the hydro-
philic group, which favors micellization. On the other
hand, the rise in temperature causes disruption of the
Surface Properties
Surface Tension
4
65
5 °C
Ic
The surface tension was measured for aqueous solutions of
the prepared metallocationic surfactant with different
Id
60
55
IIc
IId
IIIc
IIId
-
5
concentrations (4 9 0.01 to 1.9 9 10 mol/l) and at dif-
ferent temperatures (35, 45, 55 and 65 °C). The data are
represented in surface tension-concentration curves as
shown in Figs. 1, 2, 3, 4. It is clear that surface tension
decreases by increasing the concentration of the metallo-
cationic complexes, due to increasing the migration of the
surfactant molecules from the bulk to the interface of the
solution. The figures also show that the surface tension
values decrease as the temperature increase from 35 to
5
4
4
3
0
5
0
5
-
5
-4
-3
-2
-1
0
log C, C Mole/liter
Fig. 2 Surface tension versus log Concentration of complexes at
5 °C
4
6
5 °C.
It was expected that the surface tension values of the
5
5 °C
cationic complexes (Ic, Id, IIc, IId, IIIc and IIId) would be
lower than for the parent cationic surfactants (Ib, IIb and
IIIb). This is the result of the increase in the hydrophobicity
of these complexes in comparison to the parent cationics,
which is due to the presence of two ligands coordinated to
the metal ion [21], i.e., an increase in the non polar part.
Consequently, the water/surfactant molecules’ interactions
decrease, which force them to the air–water interface [22]
with a surface tension decrease.
6
0
Ic
Id
55
50
IIc
IId
IIIc
IIId 45
4
0
5
3
-
5
-4
-3
-2
-1
0
log C, C Mole/liter
The Critical Micelle Concentration (CMC)
Fig. 3 Surface tension versus log Concentration of complexes at
5 °C
5
Critical micelle concentration values of the prepared met-
allocationic surfactants were determined by plotting the
6
5 °C
3
5°C
6
5
0
6
6
5
0
Ic
Ic
Id
5
Id
IIc
IId
IIIc
IIId
50
IIc 55
IId
4
5
5
4
4
3
0
5
0
5
IIIc
IIId
40
35
30
-5
-4
-3
-2
-1
0
-5
-4
-3
-2
-1
0
log C, C Mole/liter
log C, C Mole/liter
Fig. 1 Surface tension versus log Concentration of complexes at
5 °C
Fig. 4 Surface tension versus log Concentration of complexes at
65 °C
3
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J Surfact Deterg (2013) 16:709–715
713
Table 1 Surface properties of
the synthesized metallocationic
surfactants at 35 °C
-3
-4
-11
2
Surfactant
CMC 9 10
mol/l
,
p
CMC
mN/m
,
Pc20 9 10
mol/l
,
C
mol/cm
max 9 10
,
Amin, nm
2
Ic
1.59
1.66
1.4
1.41
1.1
1
22
13
3.3
5
Id
23.3
24.2
25.6
31.27
30.27
11.5
7.5
11
3.14
3.25
3.7
5.3
5.1
4.5
4.7
5.9
IIc
IId
IIIc
IIId
2.1
1.3
3.55
2.83
Table 2 Surface properties of
the synthesized metallocationic
surfactants at 45 °C
-3
-4
-11
2
Surfactant
CMC 9 10
mol/l
,
p
CMC
mN/m
,
Pc20 9 10
mol/l
,
C
mol/cm
max 9 10
,
Amin, nm
2
Ic
1.46
1.53
1.25
1.1
26.7
25.12
26.25
26.3
33.5
32.6
11.7
6.2
4.2
4.9
1.4
0.9
4.4
3.8
4.2
4.5
4.6
4.3
6.1
Id
3.94
3.67
3.57
3.78
2.74
IIc
IId
IIIc
IIId
0.81
0.72
Table 3 Surface properties of
the synthesized metallocationic
surfactants at 55 °C
-3
-4
-11
2
Surfactant
CMC 9 10
mol/l
,
p
CMC
mN/m
,
Pc20 9 10
mol/l
,
C
mol/cm
max 9 10
,
Amin, nm
2
Ic
1.32
1.4
27.74
27
10
4
4.1
4
Id
3.82
3.98
3.74
3.47
2.65
4.3
4.2
4.4
4.8
6.2
IIc
IId
IIIc
IIId
0.73
0.79
0.52
0.5
28.47
28.05
34.1
32
1.9
3.6
0.8
0.3
Table 4 Surface properties of
the synthesized metallocationic
surfactants at 65 °C
-3
-4
-11
2
Surfactant
CMC 9 10
mol/l
,
p
CMC
,
mN/m
Pc20 9 10
mol/l
,
C
mol/cm
max 9 10
,
Amin, nm
2
Ic
1
28.35
27.85
30.14
29.56
33.67
32.9
2.9
2.2
1.4
1
4
4.1
4.1
3.8
4
Id
1.1
4
IIc
IId
IIIc
IIId
0.63
0.67
0.32
0.33
4.37
4.12
3.67
2.57
0.4
0.1
4.5
6.4
structured water surrounding the hydrophobic group, an
effect that disfavors micellization. The relative magnitude
of these two opposing effects, determines whether the
CMC increases or decreases over a particular temperature
range. Data in the Tables 1, 2, 3, and 4 reveal that in this
case the CMC decreases upon rising the temperature, i.e.,
the micellization is enhanced.
Effectiveness (GCMC)
The most efficient surfactant is one that attains the lowest
surface tension at the critical micelle concentration (CMC).
According to the results shown in Tables 1, 2, 3, and 4
increasing the alkyl chain length and the temperature
improves the effectiveness of the complexes due to an
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J Surfact Deterg (2013) 16:709–715
Table 5 The results of the antimicrobial activity of the metallocat-
ionic surfactants against tested microorganisms at 5 mg/ml
there is a greater increase in the negative value of DGads
compared to those of micellization. This suggests a strong
tendency of the molecules to be adsorbed at the interface.
Tested compounds
microorganisms
Ic
Id
IIc
IId
IIIc IIId
Pseudomonas aeruginosa
-ve 13
-ve -ve 12
17
Antimicrobial Activity of the Prepared Compounds
(
Gram -ve)
Sarcina lutea (Gram -ve)
Bacillus pumilus (Gram ?ve) 13
Micrococcus luteus -ve -ve 14
Gram ?ve)
12
-ve -ve 12
12 -ve -ve 14
-ve 19
The cell membrane of microorganisms is composed of
several lipid and protein layers arranged together in spe-
cific arrangement called the bilayer (or multilayer lipo-
protein structure).
18
22
-ve 12
(
Candida albicans (Yeast)
-ve 13
-ve 14
13
16
The presence of the lipids as a building unit in the cell
membrane gives them their hydrophobic character [23].
The hydrophobic chain length has a remarkable influ-
ence on the biological activity on the tested compounds. In
general, increasing the hydrophobic chain length increases
the biological activity of the surfactants.
Penicillium chrysogenum
(
-ve -ve 12
-ve -ve 19
Fungus)
The action mode of such metallocationic biocides (Ic,
Id, IIc, IId, IIIc and IIId) on the bacterial strains is
explained as an electrostatic interaction and a physical
disruption. The electrostatic interaction occurs between the
oppositely charged centers on the cellular membrane and
the positively charged head group of the biocide molecules.
On the other hand, the physical disruption is the result from
the penetration of the hydrophobic chains into the cellular
membrane due to their similarity in chemical nature and
structure.
increase in the hydrophobicity. Complexes (IIIc and IIId)
were found to be the most effective ones at 35 °C, i.e., with
a tension of 31.27 and 30.27 mN/m, respectively. They are
also the most effective at the other temperatures as seen in
Tables 1, 2, 3, and 4.
Efficiency (Pc )
2
0
Efficiency values of the prepared cationic surfactants are
given in Tables 1, 2, 3, and 4. From these data it was
observed that the efficiency decreases when the length of
the alkyl chain and the temperature increase, probably due
to the fast formation of monolayer of surfactant at the
surface.
The interaction between the biocide molecules and the
cellular membrane causes a strong damage in the selective
permeability of these membranes which disturbs the met-
abolic pathway within the cytoplasm.
As shown in Table 5, the synthesized metallocationic
surfactants have moderate activity towards different
microorganisms, except compound IIId which exhibits a
strong activity, probably because it has the longest alkyl
chain length; moreover, it contains a copper ion which has
a higher biological activity than the nickel ion. This is
certainly due to a lower electronegativity and a larger
volume of the copper ion, which increases its molecular
area, hence the effective area of the complex on the cell
membrane will increase too [24].
Maximum Surface Excess (Cmax
)
The values of Cmax are reported in Tables 1, 2, 3, and 4). In
general the maximum surface excess Cmax rises by
increasing the carbon chain length.
Minimum surface area (Amin
)
The minimum area per molecule at the water/air interface
for the prepared surfactants is listed in 1, 2, 3, and 4. The
minimum surface area (Amin) decreases with an increase in
the chain length of the hydrophobic part in the surfactant
molecule.
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Ahmed I. Adawy is a researcher at the Egyptian Petroleum Research
Institute (EPRI), Cairo, Egypt. He was awarded his Ph.D. by Benha
University, Egypt, for his study of surface and biological activity of
some metallocationic surfactants. His research interests are in
surfactants and their applications.
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Mnal M. Khowdiary is a researcher at the Egyptian Petroleum
Research Institute (EPRI), Cairo, Egypt. Her Ph.D. was awarded by
Ain Shams University, Egypt, for her study of surface and biological
activity of some metallocationic surfactants. Her research interests are
in surfactants and their applications.
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