Aggregation behaviours and bactericidal activities of novel cationic surfactants functionalized with amides and ether groups

Article abstract of DOI:10.1039/c4ra14645j

A series of novel cationic surfactants, N-alkylcaramoylmethyl-N-[2-(2-phenoxyacetamido)-ethyl]-N,N-dimethylammonium chloride, were synthesized and their chemical structures were characterized using ¹H-NMR, ¹³C-NMR, ESI-MS and FT-IR. Their aggregation behaviours in aqueous solution were systematically investigated by surface tension and electrical conductivity methods. It was found that the surfactants have higher surface activity compared with a similar structural surfactant. A series of thermodynamic parameters of aggregation indicate that the aggregation is entropy-driven at the investigated temperatures. In addition, they possess excellent bactericidal activities against the selected strains. This journal is

Full text of DOI:10.1039/c4ra14645j

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Aggregation behaviours and bactericidal activities
of novel cationic surfactants functionalized with
amides and ether groups†
Cite this: RSC Adv., 2015, 5, 27197
a
a
b
Guangzhou Cao, Xiangfeng Guo, Lihua Jia and Xuhua Tianb
*
*
A series of novel cationic surfactants, N-alkylcaramoylmethyl-N-[2-(2-phenoxyacetamido)-ethyl]-N,N-
dimethylammonium chloride, were synthesized and their chemical structures were characterized using 1H-
NMR, 13C-NMR, ESI-MS and FT-IR. Their aggregation behaviours in aqueous solution were systematically
investigated by surface tension and electrical conductivity methods. It was found that the surfactants have
higher surface activity compared with a similar structural surfactant. A series of thermodynamic parameters
of aggregation indicate that the aggregation is entropy-driven at the investigated temperatures. In addition,
they possess excellent bactericidal activities against the selected strains.
Received 16th November 2014
Accepted 9th March 2015
DOI: 10.1039/c4ra14645j
www.rsc.org/advances
pyridinium chloride is correlated directly with the intermolecular
H-bonding for the presence of the amide group,18 and the micel-
Introduction
Cationic surfactants are widely applied in germicides,1–3 emul-
sication,4 foaming,5 detergent,6 drug delivery7,8 and materials
synthesis,9,10 et al. Recently, quaternary ammonium surfactants
containing amide, ether, or other functional groups have been
extensively studied due to several interesting properties such as
low-toxicity or biodegradability.11–13 It was found that the
surfactants with amide functionalization could enhance the
aggregation ability compared with those without an amide
group, and the aggregation properties depend strongly on the
position and number of amide bonds.14 Morpholinium-based
amide-functionalized ionic liquids (ILs) in aqueous medium
showed better surface activity and much lower critical micellar
concentration (CMC) compared to non-functionalized ILs,
which was assigned to the intermolecular H-bonding for the
presence of the amide group along with the relatively greater
hydrophobicity and larger size of the morpholinium head-
group.15 Ether functionalized pyridinium cationic surfactants
displayed lower CMC values compared with that of conven-
tional cationic surfactants without ether bond.16 Bis-(N-(3-alkyl-
amidopropyl)-N,N-dimethyl)-p-phenylene diammonium dichlor-
ide17 at the air–water interface showed higher surface activity,
which resulted from the intramolecules hydrogen bond origi-
nated from the amide group of long alkyl chain, and the
micellization process is entropy-driven at the investigated
temperatures. The high surface activity of 1-(alkylcaramoylmethyl)-
lization process is entropy-driven process in the investigated
temperatures. The micellar properties of benzyl-(2-
acylaminoethyl)-dimethyl-ammonium chloride were explained
for the formation of direct- or water-mediated hydrogen
bonding between the amide groups, plus hydrophobic interac-
tions between its benzyl and the alkyl groups.19
It is well known that N-dodecyl-N-benzyl-N,N-dimethyl ammo-
nium chloride (1227) is a conventional cationic surfactants, and
widely used as bactericide.20 However, it has relatively high CMC,
and the microorganism had the drug-resistance to 1227 for it has
been used for a long-term as medical disinfectants.21 The bacteri-
cidal performance of cationic surfactants with amide and ether
functional groups based on phenol still received little attention.
Herein, we designed and synthesized a series of cationic
surfactants with amide and ether functional groups, namely
N-alkylcaramoylmethyl-N-[2-(2-phenoxyacetamido)-ethyl]-N,N-
dimethylammonium chloride (CnPDA, n ¼ 12, 14, 16), and their
aggregation behaviours were investigated by using the
measurements of surface tension and conductivity, and
compared with that of the similar structural surfactants. The
relationships of the aggregation and the structure were dis-
cussed. The bacterial activities were determined and compared
with that of 1227, which may serve for potential application as a
new sterilizing agent in the future.
Results and discussion
aKey Laboratory of Fine Chemicals of College of Heilongjiang Province, Qiqihar Surface properties of CnPDA
University, Qiqihar 161006, China. E-mail: xfguo@163.com
bCollege of Chemistry and Chemical Engineering, Qiqihar University, Qiqihar 161006,
Surface tension measurements were performed to determine
surface behaviour and CMC of CnPDA in aqueous solutions. The
surface tension versus logarithm of concentration at 298.2 K was
shown in Fig. 1.
China. E-mail: jlh29@163.com
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra14645j
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As shown in Fig. 1, the surface tension decreases sharply the surface activity of CnPDA is superior to that of CnABzMe2Cl.
with increasing concentration and attains a break point in the G and Amin can reect the molecule arrangement of surfactants
region of low surfactant concentrations. The surfactant at the air–water interface. The value of Amin for C12PDA is
concentration to the break point is assumed to be CMC of each slightly larger than that of
C12ABzMe2Cl, meaning the
surfactant. Surface tension method can not only estimate the arrangement of C12PDA molecules is relatively looser compared
CMC values of amphiphilic compounds, but also provide valu- with that of C12ABzMe2Cl at the air–water interface.
able information about the adsorption characteristics at the
Moreover, the CMC values are smaller than that of
air–water interface. So, the saturation adsorption (G) and CnABzMe2Cl with the same alkyl length (Table 1). The main
minimum area (Amin) occupied per surfactant molecule at the difference in the structures between CnPDA and CnABzMe2Cl is
air–water interface were analysed. According to the surface that CnPDA contains two amide groups and one ether group,
tension curves, G can be calculated from the Gibbs eqn (1):
while CnABzMe2Cl only contains one amide group. The intro-
duction of one ether and two amides groups increased the
hydrophilicity, as well as promoted the hydrophobicity due to
the hydrogen bonds of the inter-molecules and intra-molecule.
It can be conclude for CnPDA that the contribution of the
hydrophobicity is stronger than the hydrophilicity by the two
amides and one ether groups to the formation of micelles.14,18
The adsorption efficiency can be characterized by the value
of logarithm of the surfactant concentration C20 at which the
surface tension of water is reduced by 20 mN mꢀ1 (pC20). The
larger the pC20 value, the greater the tendency of the surfactant
to adsorb at the air–water interface.28,29 The values of pC20 show
an increasing tendency with increasing the length of hydro-
carbon chain, which are 3.9, 4.6 and 4.9, respectively (Table 1).
The pC20 values of CnPDA are somewhat larger than that of
CnABzMe2Cl with the same alkyl chain length.19 It discloses that
the adsorption efficiency of CnPDA is stronger than that of
CnABzMe2Cl at the air–water interface.
ꢀ
ꢁ
1
vg
G ¼ ꢀ
(1)
2:303nRT v log C
T
where R is the gas constant; T is the absolute temperature; C is
the surfactant concentration; g is the surface tension in mN
m
ꢀ1; G is the saturation adsorbed amount in mmol mꢀ2; n is the
number of ions that originate in solution by dissociation of the
surfactant and whose concentration changes at the surface with
the change of the bulk solution concentration, for a non-ionic
surfactant, n ¼ 1; for an ionic surfactant where the surfactant
ion and the counterion are univalent, n ¼ 2;22 n is taken as 2 in
this paper. Gibbs equation has been generally used for calcu-
lation G and Amin values, but the limitation for the calculation of
area per molecule of surfactant through Gibbs adsorption
equation has been questioned by various researchers,23–25 for
the presence of very small amount of impurities in cationic
surfactants in recent reports. Thomas et al.26 suggested that the
only solution to this problem is to nd a good model for activity
behaviour in sub-micellar region. However, there is not a
minimum near the breaking point, indicating that the surface
chemical impurities could be ignored in this case. Nevertheless,
the best way to verify the purity of samples is to employ other
techniques such as neutron reection.26,27
For a homologous series of amphiphiles, CMC follows the
empirical Stauff–Klevens rule, which accords with the following
eqn (3):30
log CMC ¼ A ꢀ BN
(3)
where CMC is the critical micelle concentration of CnPDA; N is the
number of carbon atoms of the hydrophobic chains; A and B are
empirical constants reecting the free energy changes involved in
transferring the hydrophilic group and a methylene unit of
hydrophobic group from the aqueous phase to the micelle phase.31
The effect of the hydrophobic chain lengths of CnPDA and Cn-
ABzMe2Cl on their CMC values at 298.2 K are shown in Fig. 2.
These plots exhibit a linear decrease in the CMC with the
increase of hydrophobic chain length. The B values of CnPDA
and CnABzMe2Cl are 0.308 and 0.333, respectively, which are
both close to 0.3 of conventional ionic surfactants.31 Whereas
the value of A of CnPDA is smaller than that of CnABzMe2Cl,
indicating that the ability to form micelles of CnPDA is superior
to that of CnABzMe2Cl in aqueous solutions. It may result from
that the hydrogen bonds of the inter-molecules and intra-
molecule by the two amides and one ether groups, and the
phenyl group at the end of larger hydrophilic group of CnPDA
may fold back toward the micellar core. Both of them have
benecial effect on the formation of micelles of CnPDA.
The minimum area occupied by each CnPDA molecule (Amin
at air–water interface was evaluated by the eqn (2):
)
1
Amin
¼
(2)
GNA
where NA is Avogadro's number and Amin is in nm2. The value of
G and Amin are listed in Table 1. It can be found the gCMC of
CnPDA are smaller than that of CnABzMe2Cl,19 indicating that
Thermodynamic of micellization
In order to investigate the aggregation behaviours of CnPDA in
Fig. 1 Curves on surface tension versus log concentration of CnPDA in
aqueous solution.
aqueous solutions, the electrical conductivity (l) was measured
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Table 1 Surface properties of CnPDA determined by surface tension in aqueous solution at 298.2 K
CMC (mmol Lꢀ1
)
gCMC (mN mꢀ1
)
pC20
G (mmol mꢀ2
)
Amin (nm2)
C12PDA
C14PDA
0.815 ꢁ 0.045
0.206 ꢁ 0.014
0.0461 ꢁ 0.0029
5.8
1.3
0.27
35.8 ꢁ 0.1
37.8 ꢁ 0.1
39.8 ꢁ 0.1
39.6
39.9
42.2
3.9 ꢁ 0.2
4.6 ꢁ 0.2
4.9 ꢁ 0.2
0.20
0.39
0.95
1.92 ꢁ 0.02
1.45 ꢁ 0.02
1.88 ꢁ 0.03
2.02
2.10
2.27
0.86 ꢁ 0.01
1.14 ꢁ 0.02
0.88 ꢁ 0.02
0.82
0.79
0.73
C
16PDA
C
12ABzMe2Cl19
C14ABzMe2Cl19
C16ABzMe2Cl19
A comprehension of the specic binding of counterions to
micelles is a prerequisite for an understanding of micellization
of all kinds of aggregation in aqueous solutions. The degrees of
dissociation (a) of CnPDA micelles in water were obtained using
Evans' eqn (4), which considers that the mobility of micelles is
nonzero.33
!
a2
ꢀ
ꢀ
1000S2 ¼
ð1000S1 ꢀ lCl Þ þ alCl
(4)
2
3
ꢀ
Nagg
where S1 and S2 are the values of Dl/DC below and above the
CMC, respectively; lClꢀ is the equivalent conductivity of the
chloride ion at innite dilution, the values of lClꢀ derived from
the literature;34 the values of Nagg were determined by steady-
state uorescence measurements (Table 2). The relationship
of the degree of counterion binding (b) to micelles and a is as
eqn (5):
Fig. 2 Relationship between log CMC and the hydrocarbon chain
length of CnPDA at 298.2 K.
at 298.2, 303.2, 308.2, 313.2 and 318.2 K, respectively, as plotted
in Fig. 3. There are two linear fragments in the typical curve, and
the steep change of the slope is assigned to the CMC of CnPDA.
As shown in Table 2, the CMC values determined from the
conductivity measurements were close to that of derived from
surface tension at 298.2 K. Plots of CMC versus hydrocarbon
chain length for CnPDA at various temperatures are shown in
Fig. 4. It can be seen the CMC values of CnPDA increase slightly
with the rise of temperature. In the rst place, the hydration
degree of the ionic headgroup domain decreases with a rise of
temperature, which leads to an increasing hydrophobicity of the
surfactant. Moreover, with an increasing temperature the
breakdown of the structured water surrounding the hydro-
phobic domain can occur. This is unfavourable to surfactant
aggregation, as the low entropy of the structured water is the key
driving force of the self-association process.32
b ¼ 1 ꢀ a
(5)
The values are listed in Table 2. In the present systems of
CnPDA (Fig. 5), b decreases with the increase of the investigated
temperature for CnPDA. For an increase of the temperature can
speed the thermal motion of the ions and molecules, which
makes the counterions dissociate easier from the electrostatic
bondage of the micelles,35,36 in other words, the micelle becomes
loose. The loose micelle structure decreases the adsorption
ability to counterions and induces the smaller b value.32
In addition, b decreases with the aggregates as alkyl chain
length increases also suggests that counter ions bind loosely.37
Similar observations have been made in the case of conventional
ammonium-cationic surfactants, where an increase in the alkyl
Fig. 3 Plots of specific conductivity versus the concentration of C12PDA (A), C14PDA (B) and C16PDA (C) aqueous solution at different
temperatures (C298.2 K, :303.2 K, +308.2 K, -313.2 K, ;318.2 K).
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Table 2 Values of CMC, b determined by electrical conductivity measurement and Nagg derived from steady-state fluorescence quenching
measurements of CnPDA
298.2 ꢁ 0.1 K
303.2 ꢁ 0.1 K
308.2 ꢁ 0.1 K
313.2 ꢁ 0.1 K
318.2 ꢁ 0.1 K
C
12PDA
CMC (mmol Lꢀ1
b
)
)
)
1.30 ꢁ 0.02
0.855 ꢁ 0.017
67 ꢁ 6
1.31 ꢁ 0.02
0.854 ꢁ 0.017
62 ꢁ 6
1.32 ꢁ 0.02
0.850 ꢁ 0.017
60 ꢁ 6
1.33 ꢁ 0.02
0.847 ꢁ 0.016
58 ꢁ 5
1.35 ꢁ 0.02
0.841 ꢁ 0.016
55 ꢁ 5
Nagg
C14PDA
CMC (mmol Lꢀ1
0.318 ꢁ 0.006
0.771 ꢁ 0.015
36 ꢁ 2
0.320 ꢁ 0.006
0.768 ꢁ 0.015
35 ꢁ 2
0.323 ꢁ 0.006
0.765 ꢁ 0.015
34 ꢁ 2
0.328 ꢁ 0.006
0.760 ꢁ 0.015
33 ꢁ 2
0.333 ꢁ 0.006
0.753 ꢁ 0.015
31 ꢁ 2
b
Nagg
C16PDA
CMC (mmol Lꢀ1
0.0650 ꢁ 0.0013
0.683 ꢁ 0.013
10 ꢁ 1
0.0669 ꢁ 0.0013
0.682 ꢁ 0.013
10 ꢁ 1
0.0678 ꢁ 0.0013
0.677 ꢁ 0.013
10 ꢁ 1
0.0685 ꢁ 0.0013
0.668 ꢁ 0.013
9 ꢁ 1
0.0712 ꢁ 0.0014
0.664 ꢁ 0.013
9 ꢁ 1
b
Nagg
the parameters of micellization were calculated according to the
mass action model using the following equation:39,40
DGꢂm ¼ RT(1 + b)ln XCMC
(6)
(7)
ꢂ
ꢃ ꢄ
v DGmꢂ
T
DHmꢂ
¼
vð1=TÞ
DHmꢂ ꢀ DGmꢂ
DSmꢂ
¼
(8)
T
where XCMC is the CMC in mole fraction; and b is the degree of
counter ion binding; following eqn (7), the gures of DGꢂm/T
versus 1/T for the solutions of CnPDA were obtained (not given). A
second order polynomial was tted to the data points, and the
values of DHꢂm were calculated from the slopes of tangential lines
at temperatures corresponding to experimental data points.
These parameters are listed in Table 3. Plots of Gibbs free energy
(DGꢂm), enthalpy (DHmꢂ ), and entropy (ꢀTDSꢂm) of micellization
versus the temperature are shown in Fig. 6. It is observed that the
values of DGꢂm become more negative from ꢀ49.0 to ꢀ56.9 kJ
molꢀ1 with the increase of hydrophobic chain length; and the
values of DGꢂm for C12PDA decreased from ꢀ49.0 to ꢀ51.7 kJ
molꢀ1 with the increase of temperature (Table 3). The negative of
DGꢂm suggests that CnPDA have great ability to form micelles in
aqueous solution; and with the increase of chain length, CnPDA
are more likely to form micelles due to the increase of the
hydrophobic interactions between the alkyl chains, which is in
consistent with the changes of the CMC. It is obviously that the
DHꢂm value decreases with the rise of temperature for CnPDA with
the same alkyl chains length (Fig. 6). In a typical run, the values of
DHꢂm for C12PDA decrease from ꢀ1.63 to ꢀ15.0 kJ molꢀ1 as the
temperature increase from 298.2 to 318.2 K. During the micelli-
zation process the variation of enthalpy mainly includes two
opposing aspects for the surfactants. One is the removal of
water molecules from around the monomeric hydrocarbon
chain, and this process is endothermic; another is the
transfer of the hydrocarbon chain from the water to the oil-
like interior of the micelle, and the transfer process is
exothermic.41 Obviously, the latter is dominant factor as
concluded from the experimental results.
Fig. 4 Plots of CMC versus hydrocarbon chain length of CnPDA at
298.2 K (C), 303.2 K (:), 308.2 K (+), 313.2 K (-) and 318.2 K (;).
chain length leads to a decrease in the CMC along with a decrease
in b as a consequence of an increase in the area per head group of
the surfactant ion at the surface of the micelle.38 For CnPDA, the
decrease of b is attributed to the exibility provided by the long
alkyl chain in the vicinity of the amides and ether groups, which
increases the availability of the amides and ether groups to water,
leading to high hydration in the head group region, the increased
extent of hydration results in a decrease of b.38
For the availability of the thermodynamic parameters of
micellization at various temperatures can give valuable insight
into the principles which govern the formation of micelles, so
The temperature dependence of DCꢂp,m manifests itself in
large negative values of the change in heat capacity (DCꢂp,m),
Fig. 5 Plots of the degree of counterion dissociation versus the
temperature for C12PDA (-), C14PDA (C) and C16PDA (:).
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Table 3 Values of thermodynamic parameters from the electric conductivity measurements for CnPDA aqueous solution
T (K)
DGꢂm (kJ molꢀ1
)
DHꢂm (kJ molꢀ1
)
ꢀTDSꢂm (kJ molꢀ1
)
DCpꢂ,m (kJ molꢀ1 Kꢀ1
)
C12PDA
298.2 ꢁ 0.1
303.2 ꢁ 0.1
308.2 ꢁ 0.1
313.2 ꢁ 0.1
318.2 ꢁ 0.1
298.2 ꢁ 0.1
303.2 ꢁ 0.1
308.2 ꢁ 0.1
313.2 ꢁ 0.1
318.2 ꢁ 0.1
298.2 ꢁ 0.1
303.2 ꢁ 0.1
308.2 ꢁ 0.1
313.2 ꢁ 0.1
318.2 ꢁ 0.1
ꢀ49.0 ꢁ 0.9
ꢀ49.7 ꢁ 0.9
ꢀ50.4 ꢁ 1.0
ꢀ51.1 ꢁ 1.0
ꢀ51.7 ꢁ 1.0
ꢀ53.0 ꢁ 1.0
ꢀ53.7 ꢁ 1.0
ꢀ54.5 ꢁ 1.0
ꢀ55.1 ꢁ 1.1
ꢀ55.7 ꢁ 1.1
ꢀ56.9 ꢁ 1.1
ꢀ57.7 ꢁ 1.1
ꢀ58.4 ꢁ 1.1
ꢀ59.1 ꢁ 1.1
ꢀ59.8 ꢁ 1.2
ꢀ1.63 ꢁ 0.03
ꢀ5.16 ꢁ 0.10
ꢀ8.56 ꢁ 0.17
ꢀ11.8 ꢁ 0.2
ꢀ47.3 ꢁ 0.9
ꢀ44.6 ꢁ 0.9
ꢀ41.9 ꢁ 0.8
ꢀ39.2 ꢁ 0.8
ꢀ36.6 ꢁ 0.7
ꢀ49.6 ꢁ 1.0
ꢀ46.1 ꢁ 0.9
ꢀ42.6 ꢁ 0.9
ꢀ39.2 ꢁ 0.8
ꢀ35.9 ꢁ 0.7
ꢀ49.1 ꢁ 1.0
ꢀ45.4 ꢁ 0.9
ꢀ41.9 ꢁ 0.9
ꢀ38.3 ꢁ 0.8
ꢀ34.9 ꢁ 0.7
ꢀ0.701 ꢁ 0.014
ꢀ0.679 ꢁ 0.013
ꢀ0.657 ꢁ 0.013
ꢀ0.635 ꢁ 0.012
ꢀ0.613 ꢁ 0.012
ꢀ0.810 ꢁ 0.016
ꢀ0.786 ꢁ 0.015
ꢀ0.762 ꢁ 0.015
ꢀ0.738 ꢁ 0.014
ꢀ0.714 ꢁ 0.014
ꢀ0.927 ꢁ 0.019
ꢀ0.900 ꢁ 0.018
ꢀ0.873 ꢁ 0.017
ꢀ0.846 ꢁ 0.017
ꢀ0.819 ꢁ 0.016
ꢀ15.0 ꢁ 0.3
C
14PDA
16PDA
ꢀ3.37 ꢁ 0.06
ꢀ7.68 ꢁ 0.15
ꢀ11.85 ꢁ 0.23
ꢀ15.89 ꢁ 0.31
ꢀ19.81 ꢁ 0.38
ꢀ7.85 ꢁ 0.16
ꢀ12.3 ꢁ 0.2
C
ꢀ16.59 ꢁ 0.3
ꢀ20.76 ꢁ 0.4
ꢀ24.79 ꢁ 0.5
which is the unique feature of all processes related to the could be attributed to the basis of “melting” of the “iceberg
hydrophobic effect, and it was calculated from eqn (9):42
structure” of water molecules surrounding hydrophobic moie-
ties.47 The extensive hydrogen bonding in water gradually breaks
down with increasing temperature, causing the importance of the
entropic term of hydrophobic hydration to decrease and the
dispersion interactions to become increasingly dominant.48,49
Furthermore, that the entropy term DTSꢂm played the dominant
role in DGꢂm (Fig. 6), in other words, the micellization of CnPDA
was entropy-driven in the investigated temperatures range.
ꢀ
ꢁ
vHmꢂ
DCpꢂ;m
¼
(9)
vT
T
As shown in Table 3, that all DCꢂp,m are negative, which is cor-
responding with the transfer of the surfactant molecules from
their hydrophobically hydrated (ordered) state in the aqueous
pseudo-phase to a more labile, water-free micellarꢂinterior.42–44 For
C12PDA, C14PDA, and C16PDA, the values of DCp,m equal ꢀ701,
ꢀ810, and ꢀ921 J molꢀ1 Kꢀ1 with increase of alkyl chain at 298.2
K, respectively, these are more negative than those of CnABzMe2Cl
with the same alkyl chain at 298.2 K, respectively. According to the
literature,45,46 the change in DCpꢂ,m is a linear function of the
hydrophobic surface that ꢂis not exposed to water in the micelle.
For C12PDA at 298.2 K, DCp,m ¼ ꢀ701 J molꢀ1 Kꢀ1, indicating that
ꢃ21 hydrogen atoms are not in contact with water in the micelle,
corresponding to the terminal methyl plus nine methylene groups.
Additional, the phenyl group at the end of larger hydrophilic group
couldꢂfold back toward the micellar core,42 which may contribute
to DCp,m The results indicate the effect of temperature on micellar
property is inuenced dominantly by the hydrophobic groups.
Enthalpy–entropy compensation was observed for CnPDA,
causing the change in DGmꢂ to be very small. The value of DSꢂm for
CnPDA decreased with increasing temperature (Table 3), which
Aggregation number (Nagg
)
The steady-state uorescence quenching measurements using
pyrene as the uorescent probe and diphenyl ketone as the
quencher have been utilized to gain information about Nagg of
micelles in CnPDA solutions using the following eqn (10):15
NaggCq
lnðI0=IÞ ¼
(10)
ðCt ꢀ CMCÞ
where Cq, Ct are the molar concentrations of the quencher,
diphenyl ketone, and total concentration of CnPDA, respec-
tively, while I and I0 are the uorescence intensities of pyrene
uorescence at 376 nm in the presence and absence of
quencher, respectively. Pyrene emission spectra versus the
concentration of quencher for C12PDA (A), C14PDA (B) and
C
16PDA (C) are given in the ESI.†
Fig. 6 Variation of DGꢂm (-), DHmꢂ (C), and ꢀTDSꢂm (:) with the temperatures for C12PDA (A), C14PDA (B) and C16PDA (C) in aqueous solutions.
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Table 4 Minimum bactericidal concentration of CnPDA and 1227
MBC (mg mLꢀ1
When the concentrations of quencher ranged from 0.01 to
0.25 mmol Lꢀ1, there is a good linear relationship of ln(I0/I) versus
Cq (Fig. 7). Thus the mean Nagg can be determined from the slope
of the curve using the CMC value derived from conductivity
measurements. The obtained Nagg is shown in Table 2. The Nagg
decreases with the increase of the alkyl chain length and that of
the temperature. It implies that the compactness of micelles
decreased with the increase in alkyl chain length or the increase
of temperature, which led to formation of loose micelles having
less number of monomers.15,32
)
Bacterial strains
1227
C12PDA
C14PDA
C16PDA
Staphylococcus aureus
Streptococcus
Salmonella
97.6
195.3
48.8
24.4
97.6
97.6
48.8
24.4
24.4
24.4
24.4
48.8
48.8
97.6
24.4
Escherichia coli
195.3
were carried out on an Agilent 6310 ESI-Ion Trop Mass spec-
trometer of Santa Clara, CA, USA; the melting points of CnPDA
were determined using a Tektronix X-6 micro melting point
apparatus of Beijing Taike, China; surface tension was tested on a
Bactericidal activities
Staphylococcus aureus, Streptococcus, Salmonella and Escherichia
coli are the representative of gram-positive bacteria and gram-
negative bacteria and widely exists in our living environment,
could cause a serious infection of living body. Therefore, it is
important to study a kind of effective fungicide. The bactericidal
activities of CnPDA and 1227 show good activities against
studied strains as shown in Table 4.
¨
K100 Processor Tensiometer, Germany Kruss Company; conduc-
tivity was measured on DDS-307A conductivity analyzer with a cell
constant of 1 cmꢀ1, Shanghai Precision & Scientic Instrument
Company; steady-state uorescence spectra were recorded on
Hitachi F-4500 Fluorescence Spectrometer.
It can be found the introduction ether and amide functional
groups to the surfactant promoted signicantly the bactericidal
activity. The bactericidal activity of CnPDA was superior to that
of 1227; the bactericidal activities of C14PDA is the best for
CnPDA, it may be due to the optimum hydrophilic–lipophilic
balance of C14PDA resulting in the preferential adsorption at
the bacterial cell wall to disrupt the bacterial cell membrane.50
Synthesis
The synthetic routes of CnPDA were shown in Scheme 1.
A mixture of N-alkyl-2-chloroacetamide and N0-(2-phenoxy-
acetyl)-N,N-dimethylethylenediamine (mole ratio 1.1 : 1) was
dissolved in isopropanol (30 mL), and the solution was reuxed
for 18 h. Aer evaporation of solvent under reduced pressure,
the residue was puried three times by recrystallization from
chloroform and petroleum ether to give pure product as a white
solid. The target products were donated as CnPDA, where n
represents the carbon number of alkyl chain, n ¼ 12, 14 or 16,
respectively. All the synthesized surfactants were characterized
by 1H-NMR, 13C/DEPT-NMR, ESI-MS and FT-IR, and provided in
the ESI.† The spectral data of CnPDA are given bꢂelow.
Experimental
Materials and instruments
All of the solvents were of analytical grade and were dried prior to
use. 1227 was purchased from Aladdin and used as received; pyr-
ene and diphenyl ketone were purchased from Sigma-Aldrich and
used aer recrystallization from ethanol; the synthetic procedure
and characterization data of the intermediate compound, namely,
ethyl phenoxyacetate and N0-(2-phenoxyacetyl)-N,N-dimethylethy-
lenediamine, are provided in ESI.† Millipore water was used in all
experiments. FT-IR spectra of the compounds were measured by
C12PDA. C12PDA yield: 82%. M.P.: 89.0–89.5 C. FT-IR (KBr
pellet) v cmꢀ1: 3444 (N–H, amide), 2917 (–CH3), 2847 (–CH2–),
1683 (C]O, amide), 1061 (Ar-O–R, ether), 890–669 (C–H,
aromatic hydrocarbon); 1H-NMR (600 MHz, CDCl3): d ppm 9.24
(d, J ¼ 4.8 Hz, 1H, C6H5OCH2 CONH), 8.69 (s, 1H, N(CH3)2-
CH2CONH), 6.97–7.30 (m, 5H, C6H5OCH2CONH), 4.55 (s, 2H,
C6H5OCH2CONH), 4.53 (s, 2H, N(CH3)2CH2CONH), 3.93 (d, J ¼
4.8 Hz, 2H, CONH CH2CH2N), 3.74 (t, J ¼ 4.8 Hz, 2H,
CONHCH2CH2N), 3.36 (s, 6H, N(CH3)2CH2CONH), 3.21–3.24
(m, 2H, CONHCH2CH2(CH2)9CH3), 1.53–1.58 (m, 2H,
CONHCH2CH2(CH2)9CH3), 1.24–1.29 (br s, 18H, CONHCH2-
CH2(CH2)9CH3), 0.88 (t, J ¼ 7.2 Hz, 3H, CONHCH2CH2(CH2)9-
CH3); 13C/DEPT-NMR (150 MHz, CDCl3): d ppm 169.83 (–CONH–),
1
Nicolet Avatar-370; H-NMR and 13C-NMR spectra were recorded
on a Bruker AV-600 spectrometer with chemical shis recorded as
ppm in CDCl3, TMS as internal standard; mass spectral analyses
Fig. 7 Variation of ln(I0/I) versus the concentration of quencher at
298.2 K (the correlation factors of R2 > 0.994).
Scheme 1 Synthetic route of CnPDA.
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162.47 (–CONH–R), 157.27 (Benzene ring carbon directly attached datum is an average of ve individual points, with an accuracy
to –O–CH2–), 129.63 (Benzene ring carbons directly attached to of ꢁ0.1 mN mꢀ1. The samples were equilibrated in the
–CH–O–CH2–), 121.97 (Benzene ring carbons directly attached to measuring vessel for 15 min to minimize the dri due to
–CH–CH–O–CH2–), 114.81 (Benzene ring carbons directly adsorption kinetics. All the measurements were repeated at
attached to –CH–CH–CH–O–CH2–), 66.93 (–O–CH2–CONH–), 65.31 least twice.
(–N+–CH2–CONH–), 62.71 (–CH2–CH2–N+–), 52.81 (–N+–(CH3)2),
Electrical conductivity. The electrical conductivity method
39.90 (–CONH–CH2–R), 34.08 (–CONH–CH2–CH2–N+–), 31.87 was employed to determine the CMC of CnPDA at the investi-
(–CH2CH2CH3), 27.02–29.60 (chain –CH2–), 22.64 (–CH2–CH3), gated temperatures. Millipore water (specic conductivity of
14.08 (–CH3); ESI-MS (m/z): [M ꢀ Cl]+ 483.89.
0.68 ms cmꢀ1 at 298.2 K) was used to prepare the solutions for all
C14PDA. C14PDA yield: 74%. M.P.: 92.5–93.5 ꢂC. FT-IR (KBr the surfactants, and the uncertainty of the measurements was
pellet) v cmꢀ1: 3444 (N–H, amide), 2913 (–CH3), 2847 (–CH2–), within ꢁ2%. For the measurement of CMC, adequate quantities
1683 (C]O, amide), 1078 (Ar-O–R, ether), 882–662 (C–H, of the concentrated solution were added in order to change the
1
aromatic hydrocarbon); H-NMR (600 MHz, CDCl3): d ppm 9.23 surfactant concentration from concentrations well below the
(d, J ¼ 4.8 Hz, 1H, C6H5OCH2CONH), 8.68 (t, J ¼ 5.1 Hz, 1H, critical micelle concentration to up to at least three times the
N(CH3)2CH2CONH), 6.99–7.29 (m, 5H, C6H5OCH2CONH), 4.55 (s, CMC.
2H, C6H5OCH2CONH), 4.53 (s, 2H, N(CH3)2CH2CONH), 3.93 (d, J ¼
Steady-state uorescence. Pyrene was chosen as the uo-
4.8 Hz, 2H, CONH CH2CH2N), 3.74 (t, J ¼ 5.1 Hz, 2H, CONHCH2- rescent probe in the measurement of steady-state uorescence
CH2N), 3.36 (s, 6H, N(CH3)2CH2CONH), 3.21–3.24 (m, 2H, spectra. The pyrene-surfactant binary solution was dispersed
CONHCH2CH2(CH2)11CH3), 1.53–1.58 (m, 2H, CONHCH2CH2- with ultrasound and kept overnight. The emission wavelength
(CH2)11CH3), 1.24–1.29 (br s, 22H, CONHCH2CH2 (CH2)11CH3), ranged from 350 nm to 500 nm, and the excitation wavelength
0.88 (t, J ¼ 6.9 Hz, 3H, CONHCH2CH2(CH2)11CH3); 13C/DEPT-NMR was focused at 335 nm. Excitation and emission slits were xed
(150 MHz, CDCl3): d ppm 169.88 (–CONH–), 162.50 (–CONH–R), at 2.5 and 2.5 nm, respectively. The scan rate was selected at 240
157.31 (Benzene ring carbon directly attached to –O–CH2–), nm minꢀ1. The temperature was kept 298.2 K using a water-ow
129.67 (Benzene ring carbons directly attached to –CH–O–CH2–), thermostat connected to the cell compartment. The concen-
122.01 (Benzene ring carbons directly attached to tration of pyrene was 1.0 ꢄ 10ꢀ6 mol Lꢀ1 for each solution. In all
–CH–CH–O–CH2–), 114.85 (Benzene ring carbons directly attached cases, the concentration of surfactant was used above CMC. A
to –CH–CH–CH–O–CH2–), 66.96 (–O–CH2–CONH–), 65.36 pyrene uorescence quenching experiment was performed to
(–N+–CH2–CONH–), 62.75 (–CH2–CH2–N+–), 52.86 (–N+–(CH3)2), obtain the aggregation number of the micelles (Nagg) using
39.95 (–CONH–CH2–R), 34.12 (–CONH–CH2–CH2–N+–), 31.92 diphenyl ketone as the quencher. The pyrene solution was
(–CH2CH2CH3), 27.06–29.70 (chain –CH2–), 22.69 (–CH2–CH3), added to the individual and mixed micellar solutions of
14.13 (–CH3); ESI-MS (m/z): [M ꢀ Cl]+ 511.92.
surfactants. The quencher was added progressively and the
C16PDA. C16PDA yield: 81%. M.P.: 95.2–95.7 ꢂC. FT-IR (KBr intensity was recorded for data analysis.
pellet) v cmꢀ1: 3444 (N–H, amide), 2917 (–CH3), 2851 (–CH2–),
Bactericidal activity. The minimum bactericidal concentra-
1683 (C]O, amide), 1078 (Ar-O–R, ether), 882–665 (C–H, tions (MBC) of CnPDA were tested against Staphylococcus aureus,
aromatic hydrocarbon), cmꢀ1; 1H-NMR (600 MHz, CDCl3): d ppm Streptococcus, Salmonella and Escherichia coli, by the broth
9.26 (s, 1H, C6H5OCH2CONH), 8.68 (s, 1H, N(CH3)2CH2CONH), dilution method according to Chinese standard GB15981-1995.
6.99–7.30 (m, 5H, C6H5OCH2CONH), 4.54 (s, 2H, C6H5O CH2- Stock solutions were made by serially diluting CnPDA using
CONH), 4.53 (s, 2H, N(CH3)2CH2CONH), 3.94 (d, J ¼ 2.4 Hz, 2H, autoclaved Millipore water. Bacteria to be tested were grown for
CONHCH2CH2N), 3.73 (s, 2H, CONHCH2CH2N), 3.36 (s, 6H, 6 h in a suitable media and contained ꢃ109 cfu mLꢀ1 (deter-
N(CH3)2CH2CONH), 3.22–3.24 (m, 2H, CONHCH2CH2(CH2)13- mined by the spread plating method), which was then diluted to
CH3), 1.54–1.57 (m, 2H, CONHCH2CH2(CH2)13 CH3), 1.24–1.29 105 cfu mLꢀ1 using nutrient media. The concentration of the
(br s, 26H, CONHCH2CH2(CH2)13CH3), 0.88 (t, J ¼ 6.9 Hz, 3H, surfactant with sterilizing rate over 99.9% was picked up as
CONH CH2CH2(CH2)13CH3); 13C/DEPT-NMR (150 MHz, CDCl3): d minimum bactericidal concentration (MBC). Each concentra-
ppm 169.90 (–CONH–), 162.48 (–CONH–R), 157.30 (Benzene ring tion had triplicate values, the whole experiment was done at
carbon directly attached to –O–CH2–), 129.67 (Benzene ring least twice, and the MBC value was determined by taking the
carbons directly attached to –CH–O–CH2–), 122.01 (Benzene ring average of triplicate values for each concentration.
carbons directly attached to –CH–CH–O–CH2–), 114.85 (Benzene
ring carbons directly attached to –CH–CH–CH–O–CH2–), 66.96
Conclusions
(–O–CH2–CONH–), 65.43 (–N+–CH2–CONH–), 62.73 (–CH2–CH2–
N+–), 52.89 (–N+–(CH3)2), 39.96 (–CONH–CH2–R), 34.14 (–CONH– A series of novel cationic surfactants of the N-alkylcaramoylmethyl-
CH2–CH2–N+–), 31.93 (–CH2CH2CH3), 27.07–29.71 (chain –CH2–), N-[2-(2-phenoxyacetamido)-ethyl]-N,N-dimethylammonium chlo-
22.70 (–CH2–CH3), 14.13 (–CH3); ESI-MS (m/z): [M ꢀ Cl]+ 539.95. ride with amides and ether groups (CnPDA, n ¼ 12, 14, 16) were
successfully synthesized. CnPDA possess lower critical micelle
concentration and stronger ability to forming micelle in aqueous
solution compared with that of CnABzMe2Cl. The process of
Measurements
Equilibrium surface tension. Surface tension measurements micellization of CnPDA is entropy-driven in the temperature
were performed with the ring method at 298.2 ꢁ 0.1 K. Each range of 298.2 K to 318.2 K. The bactericidal activity of CnPDA is
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better than that of 1227 against the studied strains. In conclu- 21 M. Tandukar, S. Oh, U. Tezel, K. T. Konstantinidis and
sion, CnPDA have good advantages both in the surface proper- S. G. Pavlostathis, Environ. Sci. Technol., 2013, 47, 9730–9738.
ties and the antimicrobial activities, and they would serve for 22 R. Zana, Adv. Colloid Interface Sci., 2002, 97, 205–253.
potential application as a new sterilizing agent in the future.
23 F. M. Menger, L. Shi and S. A. A. Rizvi, J. Am. Chem. Soc.,
2009, 131, 10380–10381.
24 P. X. Li, Z. X. Li, H. H. Shen, R. K. Thomas, J. Penfold and
J. R. Lu, Langmuir, 2013, 29, 9324–9334.
25 H. Xu, P. X. Li, K. Ma, R. K. Thomas, J. Penfold and J. R. Lu,
Langmuir, 2013, 29, 9335–9351.
26 P. X. Li, R. K. Thomas and J. Penfold, Langmuir, 2014, 30,
6739–6747.
27 J. Eastoe, S. Nave, A. Downer, A. Paul, A. Rankin, K. Tribe and
J. Penfold, Langmuir, 2000, 16, 4511–4518.
28 W. Qiao, H. Peng, Y. Zhu and H. Cai, Colloids Surf., A, 2012,
405, 45–50.
29 L. Zhi, Q. Li, Y. Li and Y. Song, Colloids Surf., A, 2013, 436,
684–692.
Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (21176125), the Natural Science Foundation of
Heilongjiang Province (B201114, B201314), and the Science
Research Project of the Ministry of Education of Heilongjiang
Province of China (2012TD012, 12511Z030, JX201210).
Notes and references
´
1 L. Perez, A. Pinazo, R. Pons and M. Infante, Adv. Colloid
Interface Sci., 2014, 205, 134–155.
30 I. J. Lin, J. Phys. Chem., 1972, 76, 2019–2023.
2 L. Tavano, M. R. Infante, M. A. Riya, A. Pinazo, 31 N. Li, S. Zhang and L. Zheng, Phys. Chem. Chem. Phys., 2008,
M. P. Vinardell, M. Mitjans and L. Perez, So Matter, 2013,
10, 4375–4377.
9, 306–319.
32 Q. Zhang, X. Wang, X. Wei and J. Liu, J. Chem. Eng. Data,
2013, 58, 807–813.
3 Z. Zhao, X. Guo, L. Jia and Y. Liu, RSC Adv., 2014, 4, 56918–
56925.
33 H. C. Evans, J. Chem. Soc., 1956, 579–586.
¨
4 X. Yan, W. Xu, R. Sao, L. Tang and Y. Ji, Colloids Surf., A, 34 N. C. Li and W. Brull, J. Am. Chem. Soc., 1942, 64, 1635–1637.
2014, 443, 60–65.
5 L. A. D'Agostino and S. A. Mabury, Environ. Sci. Technol.,
2013, 48, 121–129.
6 P. Bharmoria, M. J. Mehta, I. Pancha and A. Kumar, J. Phys.
Chem. B, 2014, 118, 9890–9899.
7 E. Lepeltier, C. Bourgaux and P. Couvreur, Adv. Drug Delivery
Rev., 2014, 71, 86–97.
35 S. Zhang, J. Yu, J. Wu, W. Tong, Q. Lei and W. J. Fang, J.
Chem. Eng. Data, 2014, 59, 2891–2900.
36 J. Tan, D. Ma, S. Feng and C. Zhang, Colloids Surf., A, 2013,
417, 146–153.
37 V. Chauhan, R. Kamboj, S. P. S. Rana, T. Kaur, G. Kaur,
S. Singh and T. S. Kang, J. Colloid Interface Sci., 2015, 446,
263–271.
8 C. Tourne-Peteilh, B. Coasne, M. In, D. Brevet, 38 M. J. Rosen, Surfactants and Interfacial Phenomena, Wiley,
J. M. Devoisselle, A. Vioux and L. Viau, Langmuir, 2014, 30,
1229–1238.
New York, 2nd edn, 1989.
39 R. Zana, Langmuir, 1996, 12, 1208–1211.
9 L. Jiang, M. Deng, Y. Wang, D. Liang, Y. Yan and J. Huang, J. 40 N. Li, S. Zhang, L. Zheng and T. Inoue, Langmuir, 2009, 25,
Phys. Chem. B, 2001, 13, 7498–7504.
10473–10482.
10 H. Fan, B. Li, Y. Yan, J. Huang and W. Kang, So Matter, 41 M. S. Ramadan, D. F. Evans and R. Lumry, J. Phys. Chem.,
2014, 10, 4506–4512. 1983, 87, 4538–4543.
11 V. Chauhan, S. Singh, R. Mishra and G. Kaur, J. Colloid 42 S. Shimizu, P. A. R. Pires and O. A. El Seoud, Langmuir, 2004,
Interface Sci., 2014, 436, 122–131. 20, 9551–9559.
12 V. Chauhan, S. Singh, R. Kamboj, R. Mishra and G. Kaur, 43 S. Paula, W. Sues, J. Tuchtenhagen and A. Blume, J. Phys.
Colloid Polym. Sci., 2014, 292, 467–476.
Chem., 1995, 99, 11742–11751.
13 M. T. Garcia, I. Ribosa, L. Perez, A. Manresa and F. Comelles, 44 A. Chatterjee, S. P. Moulik, S. K. Sanyal, B. K. Mishra and
Colloids Surf., B, 2014, 123, 318–325.
P. M. Puri, J. Phys. Chem. B, 2001, 105, 12823–12831.
14 J. Hoque, S. Gonuguntla, V. Yarlagadda, D. S. Uppu, 45 S. J. Gill and I. Wadso, Proc. Natl. Acad. Sci. U. S. A., 1976, 73,
¨
P. Kumar and J. Haldar, Phys. Chem. Chem. Phys., 2014, 16,
11279–11288.
15 R. Kamboj, P. Bharmoria, V. Chauhan, S. Singh, A. Kumar,
V. S. Mithu and T. S. Kang, Langmuir, 2014, 3, 9920–9930.
16 V. Chauhan, S. Singh, R. Kamboj, R. Mishra and G. Kaur, J.
Colloid Interface Sci., 2014, 417, 385–395.
2955–2958.
46 T. Mehrian, A. De Keizer, A. J. Korteweg and J. Lyklema,
Colloids Surf., A, 1993, 71, 255–267.
47 H. S. Frank and M. W. Evans, J. Chem. Phys., 1945, 13, 507–
532.
48 C. Tanford, The Hydrophobic Effect: Formation of Micelles and
Biological Membranes, Wiley, New York, 2nd edn, 1980.
17 D. Hu, X. Guo and L. Jia, J. Surfactants Deterg., 2013, 16, 913–919.
18 Z. Feng, X. Guo, L. Jia and Y. Zhang, Res. Chem. Intermed., 49 W. Blokzijl and J. B. F. N. Engberts, Angew. Chem., Int. Ed.,
2013, DOI: 10.1007/s11164-013-1492-6. 1993, 32, 1545–1579.
19 S. Shimizu and O. A. El Seoud, Langmuir, 2003, 19, 238–243. 50 S. Kanjilal, S. Sunitha, P. S. Reddy, K. P. Kumar, U. S. Murty
20 P. H. Mc Cay, A. A. Ocampo-Sosa, G. T. A. Fleming and
and R. B. Prasad, Eur. J. Lipid Sci. Technol., 2009, 111, 941–
G. T. Fleming, Microbiology, 2010, 156, 30–38.
948.
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