Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2020 Jul 7;5(28):17042–17050. doi: 10.1021/acsomega.0c00294

Study on the Surface Properties and Aggregation Behavior of Quaternary Ammonium Surfactants with Amide Bonds

Liyan Wang 1,*, Jia Yang 1, Xianyou He 1, Ming Zhao 1, Danyang Cheng 1, Aiqi Wang 1, Guangming Yin 1, Bing Zhao 1, Yongzhi Liu 1, Wenbo Wang 1
PMCID: PMC7376569  PMID: 32715189

Abstract

graphic file with name ao0c00294_0011.jpg

A number of techniques, including conductivity, surface tension, dynamic light scattering, transmission electron microscopy, and 1H nuclear magnetic resonance (1H NMR), Fourier transform infrared (FT-IR), and 1H–1H 2D nuclear Overhauser effect spectroscopy (1H–1H 2D NOESY), have been used to investigate the effect of amide bonds on the interfacial and assembly properties of a cationic surfactant, N-anilinoformylmethyl-N-cetyl-N,N-dimethyl ammonium chloride (AMC-C16), in aqueous solutions. The adsorption of AMC-C16 has been found to be much better than that of the conventional cationic surfactant, benzyl cetyldimethylammonium chloride (BAC-16) at the air/water interface and in solution. The surface tension measurements show the presence of two critical aggregation concentrations (CAC1 and CAC2) for AMC-C16. The presence of a strong intermolecular hydrogen bond of AMC-C16 was confirmed by 1H NMR and FT-TR. The molecular interactions of AMC-C16 were detected by 1H–1H 2D NOESY. The results show that the rigid group (phenyl) of AMC-C16 was partially overlapped with its alkyl chain in aqueous solution, and the possible aggregation behavior for AMC-C16 was proposed. The effects of an inorganic salt (NaCl) and an organic salt (C6H5COONa) to the aggregates of AMC-C16 have been discussed.

Introduction

In the past few decades, researchers have conducted numerous studies on surfactant properties and applications because of the self-assembly of surfactant molecules in aqueous solution to form various microstructures.1−6 Surfactants can form a variety of different aggregates in aqueous solution such as vesicles, micelles, nanocrystals, and so forth.7,8 These different aggregates have great application value in mimicking biological membranes and drug delivery.9,10 Encapsulation of a drug into vesicles may favor controlled drug release and lower side effects.11,12 In part, the development of advanced materials can be attributed to molecular self-assembly because the self-assembly can form nanomaterials, and the application of nanomaterials in design and manufacture has attracted considerable attention in recent years.13,14 To form different aggregates types, the relationship between structure and aggregation of surfactants have been studied.

It has been reported that the introduction of an ester group or amide group into the molecular structure of a surfactant can cause a significant change in its surface activity and aggregation behavior.15−18 Compared with the surfactants without amide bonds, the presence of the amide bond in the molecular structure makes it easy to form intermolecular bonding to promote intermolecular aggregation.19−22 Because hydrogen bonds interaction is the driving force for self-assembly of single-chain surfactants to form a double-layer vesicle.23,24 A series of anionic surfactants based on amino acids have been synthesized by Roy and Dey; the surface activity and self-assembly behaviors have been studied in aqueous solution.25−27 The results show that these anionic surfactants stepwise aggregate with two CAC values (CAC1 and CAC2). It has been proved that the special aggregation behavior can be attributed to the intermolecular amide hydrogen bond interaction. In the past few years, some single-chain nicotinic acid-based anionic surfactants were synthesized.7,28 Two CAC values (CAC1 and CAC2) have been obtained by the surface tension of different surfactant concentrations. It was confirmed by Fourier transform infrared (FT-IR) and 1H NMR spectra. The formation of intermolecular hydrogen bonding between the amide bonds plays an important role in the aggregation process. This phenomenon of stepwise aggregation was also observed in the surfactant/polymer system.29 It also has been discovered that the ability of the surfactant aggregation could be improved by enhancing the hydrophobic interactions.30 From the previous review, it has been reported that there are two CAC values or various aggregate types during aggregation in some anionic surfactants or surfactant/polymer systems. However, this phenomenon rarely occurs in single-chain cationic surfactant systems without any additives.

As we all know, the different salt types have different influence on the surfactant aggregation process.31 Most inorganic and organic salts reduce the electrostatic interaction between the surfactant head groups by adsorbing on the surface of the aggregates and affect the aggregation of surfactant molecules. Besides reducing electrostatic interaction, the phenyl group of organic salts induce strong hydrophobic interaction by penetrating into aggregates, thereby reducing electrostatic repulsion of the surfactant headgroups more effectively, and it is more favorable for the aggregation of surfactant molecules compared with inorganic salts.31,32

In the present study, AMC-C16 was synthesized according to refs (22) and (33). The adsorption and aggregation behavior of AMC-C16 has been investigated by conductivity, surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM). It has been found that the amide bond can improve the ability of intermolecular aggregation. The novel aspect of this work is AMC-C16 stepwise aggregates with two CAC values (CAC1 and CAC2) with the concentration increase. The intermolecular hydrogen bond and the interaction of the rigid group (phenyl) and the alkyl chain of AMC-C16 have been confirmed by NMR technology. Furthermore, the effect of inorganic and organic salts on the aggregates of AMC-C16 has been studied. This work helps to further understand the effect of amide bonds on the aggregation behavior of single-chain cationic surfactants. The molecular structures of the AMC-C16 and benzyl cetyldimethylammonium chloride (BAC-16) are given in Scheme 1.

Scheme 1. Synthesis Steps of AMC-C16 and BAC-16.

Scheme 1

Open in a new tab

Results and Discussion

Surface Tension Studies

The critical aggregation concentration (CAC) of AMC-C16 and BAC-16 were determined by the surface tension method. The plots of surface tension (γ) versus concentration (C) of AMC-C16 and BAC-16 are shown in Figure 1.

Figure 1.

Figure 1

Open in a new tab

Plot of surface tension (γ) vs concentration (C) of AMC-C16 and BAC-16.

It is clear from Figure 1 that there are two break points (CAC1 and CAC2) for AMC-C16 but one break (CAC1) for BAC-16. For AMC-C16, the CAC was given by the first break; the second break may be due to the onset of secondary aggregation. To confirm whether the second breakpoint was caused by impurities, the purity of AMC-C16 was verified by 1H NMR spectrum and liquid chromatography–mass spectrometry (LC–MS) spectrum (Figures S1 and S2), and there was no minimum value near the breakpoint. This indicates that AMC-C16 may form two different morphologies of aggregates within the concentration range studied. It has been reported that two break points are caused by post-micellar aggregation.7,24−27,34 The post-micellar aggregation in AMC-C16 may be due to the presence of amide bonds in the AMC-C16 molecular structure. It is easy to form intermolecular bonding to promote intermolecular aggregation.21,22

The CAC values obtained are listed in Table 1. It is clear that AMC-C16 has lower CAC1 value than BAC-16. The introduction of the amide group in the surfactant molecular structure leads to a further reduction in the CAC value.16,17,35 It shows that the micellization is more favorable for AMC-C16. As listed in Table 1, the γCAC value of AMC-C16 is lower than that of BAC-16. This indicates that AMC-C16 has good surface activity.

Table 1. Surface Properties of AMC-C16 and BAC-16 in Aqueous Solution at 25 °C Obtained by Different Techniques.

surfactant CAC1 (mM) CAC2 (mM) γCAC (mN·m–1) πCAC (mN·m–1) Γmax (μmol·m–2) Amin (nm2) pC20 β ΔGagg° (kJ·mol–1) ΔGads° (kJ·mol–1)
AMC-C16 0.10 1.44 37.5 (CAC1) 34.52 2.04 0.82 4.62 0.54 –30.49 –47.38
      32.4 (CAC2)              
BAC-16 0.43   40.5 31.55 1.49 1.11 3.87 0.44 –27.51 –44.38
  0.40a   39.6a   1.46a 1.14a 4.13a      
Open in a new tab
a

The data of corresponding surfactant BAC-16 reported in ref (23).

Furthermore, the surface excess concentration (Γmax) and the area occupied (Amin) by a single surfactant molecule at the air/water interface at the interface are crucial to the interpretation of the surface activities of surfactants.36 The values of Γmax and Amin were calculated by the Gibbs adsorption equations.37 The Gibbs adsorption eqs 1 and 2 are given as follows

graphic file with name ao0c00294_m001.jpg 1
graphic file with name ao0c00294_m002.jpg 2

where dγ/dlog C is the maximum slope before CAC, R = 8.314 J·mol–1·K–1, T = 298.15 K, NA is Avogadro’s number, and n = 2 for the monovalent ionic surfactant.38

The effectiveness of surface tension decrease (πCAC) and the adsorption efficiency (pC20) is calculated as the following eqs 3 and 4

graphic file with name ao0c00294_m003.jpg 3
graphic file with name ao0c00294_m004.jpg 4

where γ0 is the surface tension of pure water and γCAC is the surface tension of the solution at CAC. C20 is the surfactant concentration needed to reduce the surface tension of pure water by 20.0 mN/m. The values of πCAC, pC20, Γmax, and Amin are listed in Table 1.

It can be seen that the pC20 value of AMC-C16 is larger than the pC20 value of BAC-16, which indicates that AMC-C16 is superior to BAC-16 in the adsorption efficiency. The values of Γmax and Amin reflect the adsorption and arrangement of the molecules at the air/water interface, respectively. It is worth noting that the value of Amin for AMC-C16 is lower than that for BAC-16; thus, large aggregates may form in the case of AMC-C16. This can be attributed to the intermolecular amide hydrogen bond interactions, which cause the surfactant molecules to pack tightly. The standard free energy of aggregation per mole of surfactant (ΔGagg°) and the Gibbs free energy of adsorption (ΔGads) were calculated by the eqs 5 and 6(16,39)

graphic file with name ao0c00294_m005.jpg 5
graphic file with name ao0c00294_m006.jpg 6

where R is the gas constant, T is the temperature (K), β = 1 – α. The degree of counterion dissociation (α) was given by the ratio of the slopes of the κ versus C curve above and below CAC (Figure S3). The counterion binding parameter (β) gives the average number of counterions per surfactant ion in the micelle and can be estimated from the ratio of the slopes.16 The values of β, ΔGagg°, and ΔGads are listed in Table 1. The larger the negative values of ΔGads°, the more favorable is the aggregate formation in aqueous solution compared with ΔGagg.

DLS Studies

To obtain the size distribution of aggregates, DLS was carried out on the aqueous solution of AMC-C16 and BAC-16. The sizes and distributions of the aggregates are shown in Figure 2.

Figure 2.

Figure 2

Open in a new tab

Size distribution of the aggregates in aqueous solution [(a) AMC-C16, (b) BAC-16].

It is clear from Figure 2 that there are two size-distributions in the concentration of 6 mM (4 times the CAC2) of AMC-C16, and the average hydrodynamic diameter (Dh) of the aggregates is about 5 and 119 nm, respectively. However, there was only one size-distribution, about 60 nm, in the concentration of 1.74 mM (4 times the CMC) of BAC-16.

From the DLS measurement results, the molecules of AMC-C16 form different aggregate types in aqueous solution. It has been reported that the amide group in the surfactant molecular structure, because it is prone to form intermolecular hydrogen bonds, promotes molecular aggregation and forms different aggregate types.7,21,23 The size distribution at 5 nm corresponds to micelles.18,40 There was one obvious peak with an average apparent hydrodynamic radius of 100 nm, reflecting the typical size of a big aggregate,41,42 which is well consistent with the result of TEM observations.

Morphological Study by TEM Observations

To visually observe the morphology of the aggregates, TEM test was performed on the solution of AMC-C16. The TEM pictures of AMC-C16 solution are shown in Figure 3.

Figure 3.

Figure 3

Open in a new tab

TEM micrographs of the aggregates for AMC-C16 in aqueous solution [(a,b) 6 mM].

At 6 mM (4 times the CAC2), different sizes of vesicles are observed. The sizes of large vesicles are in the range 20–100 nm, Figure 3a,b (marked by arrows). These results are consistent with the DLS measurements.

Viscosity of Surfactant Solution

The formation of different vesicles is normally manifested by the increase of bulk viscosity of the surfactant solution.28,43−46 Therefore, the relative viscosity of different concentrations of the aqueous solution of AMC-C16 was measured. The variation of relative viscosity is shown in Figure 4.

Figure 4.

Figure 4

Open in a new tab

Plot of relative viscosity vs concentration of AMC-C16 in aqueous solution.

As shown in Figure 4, the viscosity increased nonlinearly as the concentration of AMC-C16 increased. Especially, the solution viscosity of AMC-C16 relative to water increases very rapidly when the concentration is more than CAC2. Therefore, the micelles may exist in solution of AMC-C16 when the concentration exceeds CAC2.47 The results of the viscosity measurements are consistent with the DLS measurements.

Intermolecular Hydrogen Bonding

To explain intermolecular hydrogen bonding interactions, the NMR technique was applied. The 1H NMR spectra of AMC-C16 in DMSO-d6 and DMSO-d6 + H2O are shown in Figure 5.

Figure 5.

Figure 5

Open in a new tab

1H NMR spectra of AMC-C16 [(a) DMSO-d6, (b) DMSO-d6 + 10 μL H2O, (c) DMSO-d6 + 30 μL H2O].

It can be clearly observed from Figure 5 that as the amount of H2O increases, the chemical shift of the amide proton (H4) shifts to high field. The results show that there are strong intermolecular hydrogen bonds between AMC-C16 and water molecules.

To further verify the existence of intermolecular hydrogen bonds, FT-IR spectra were used to record the change of amide stretching frequency of AMC-C16, under conditions of dryness and the presence of water (Figures S4–S6). The NH-stretching frequency, amide I band, and amide II band of the CONH linkage appeared at higher frequency (3198, 1698, 1564 cm–1) under conditions of dryness, but transferred to a lower frequency (3169, 1691, 1546 cm–1) in the presence of water. This result further confirmed that the hydrogen atom and oxygen atom of amide bond with water molecules could form the intermolecular hydrogen bond.

We speculated that the rigid group (phenyl) bends around the amide bond. It has been reported in the literature that such a bend will make the amide bond more favorable for the formation of intermolecular hydrogen bonds with water molecules during the formation of aggregates, therefore leading to greater hydration of the cationic headgroup region.22 In addition, with the concentration of the solution increasing, the rigid group (phenyl) hydrophobic interactions become strong enough to promote the bending around the flexible amide bond. Kamboj et al.20 reported a cationic surfactant which contains an amide bond and morpholine ring near the headgroup. The morpholine ring coils back toward the interior of the micelle when cetyl is a hydrophobic chain. Moreover, Zhai et al.30 reported a cationic surfactant containing a large rigid group and a flexible alkyl chain. The alkyl chain of the product was partially overlapped with its non-planar rigid structure in aqueous solution, and the possible aggregation process for the product was proposed.

Study of Aggregation Behavior

In order to understand the formation process of the AMC-C16 aggregates, 1H–1H 2D NOESY was used to detect the molecular interactions of AMC-C16 in aqueous solution. The 1H–1H 2D NOESY spectra of AMC-C16 are shown in Figure 6.

Figure 6.

Figure 6

Open in a new tab

1H–1H 2D NOESY spectra of AMC-C16 in D2O.

As can be seen from Figure 6, the proton of phenyl (H1, H2, and H3) shows strong correlations with the protons on the flexible alkyl (H7-10) (marked with rounded rectangles). Usually, if the distance between protons is less than 5 Å, the cross-peak signals will appear in the 1H–1H 2D NOESY spectrum.31,48,49 The amide proton (H4) has shown correlations with the protons on the flexible alkyl (H7–10) (marked with rectangles). Also, the protons on methylene (H5) have shown weak correlations with the proton of phenyl (H2 and H3). This indicates that the hydrophobic chains are close to the rigid group (phenyl) in AMC-C16 aggregates.

Salt Effect on AMC-C16 Aggregation

It is well known that the presence of salts has a very significant effect on the aggregation of ionic surfactants. The surface tension curves of AMC-C16 at different concentrations of NaCl and C6H5COONa are presented in Figure 7. The CAC values obtained from Figure 7 were plotted against the different concentrations of salts, as shown in Figure S7.

Figure 7.

Figure 7

Open in a new tab

Plot of surface tension (γ) vs concentration (C) of AMC-C16 at different salt concentrations: (a) NaCl, (b) C6H5COONa.

As shown in Figures 7 and S7, as the concentration of inorganic salt (NaCl) and organic salt (C6H5COONa) increases, the values of CAC and γCAC decrease. The addition of salts in the aqueous solution of AMC-C16 can effectively promote the aggregation and adsorption at the interface of AMC-C16. This is because the addition of salts can effectively reduce the electrostatic repulsion between the surfactant headgroups.

It was worth noting that the first platform of the curve becomes shorter and eventually disappears as the salt concentration increases (Figure 7). Because the concentration of AMC-C16 increases, the hydrophobic and the amide bonds effect of the rigid group (phenyl) should promote aggregation and molecular conformational changes.18,31,50 Hence, the secondary aggregation is much more sensitive to ionic strength.

Additionally, at the same concentration of salts, compared with the addition of the inorganic salt (NaCl), the organic salt (C6H5COONa) can be more effective in pushing the second turning point toward the first turning point. This means that the aggregates of AMC-C16 change significantly with the addition of salts.

Furthermore, the changes of AMC-C16 aggregates in the presence of different salts were studied by the DLS technique. The concentrations of AMC-C16 are 0.3 mM (between CAC1 and CAC2) and 6 mM (>CAC2), the concentration of the salts is different. It is 2.5–15 mM for NaCl and 2–17 mM for C6H5COONa. The size distributions of the aggregates of AMC-C16 at different salt concentrations are shown in Figures 8 and 9.

Figure 8.

Figure 8

Open in a new tab

Size distribution of the aggregates for 0.3 mM AMC-C16 at different salt concentrations: (a) NaCl, (b) C6H5COONa.

Figure 9.

Figure 9

Open in a new tab

Size distribution of the aggregates for 6 mM AMC-C16 at different salt concentrations: (a) NaCl, (b) C6H5COONa.

As the concentration of inorganic salts (NaCl) increases, there are two types of aggregates, spherical micelles (8 nm) and small-size vesicles (about 75–112 nm) in solution (Figure 8a). However, as the concentration of the organic salt (C6H5COONa) increases, only one type of aggregate exists in the solution, which may be large vesicles (about 130 nm) (Figure 8b).

Furthermore, from Figure S8, with the addition of salt, the solution state of AMC-C16 is obviously different. The solution of AMC-C16 is always a clear solution as the concentration of NaCl increases. However, the solution of AMC-C16 turns into a colloidal solution when the concentration of C6H5COONa is more than 5 mM. This indicates that increase in the concentration of C6H5COONa is beneficial to stabilize the vesicles. This unexpected observation could be attributed to the different interactions between NaCl and C6H5COONa with AMC-C16.

NaCl affects the aggregation of surfactant only by reducing the electrostatic repulsion between the surfactant headgroup by adsorption on the surface of the aggregates. However, the aromatic counterions affect the micellization of surfactants both electrostatically as well as hydrophobically because of the C6H5COO– anion’s greater tendency of penetrating the head group region of the surfactant aggregates and reducing the electrostatic repulsion among the surfactant headgroups.31,47 Therefore, the C6H5COO– anion shows more pronounced stabilization of the vesicles and is more beneficial to aggregation of the surfactant molecules. Therefore, the organic salt stabilizes the vesicles.

From Figure 9, when the concentration of AMC-C16 is 6 mM (>CAC2), as the concentration of inorganic salts (NaCl) increases, the vesicle peak gradually becomes smaller (Figure 9a). Also, when the concentration of organic salts (C6H5COONa) is above 2 mM, only one type of aggregate exists in the solution, which may be large vesicles (about 20–500 nm) (Figure 9b). These results imply that the addition of proper salts can effectively adjust the structure of the surfactant aggregates. It is helpful in understanding the effect of both inorganic and organic salts on the aggregation behavior of surfactants. This phenomenon was also previously reported.51,52

Conclusions

The effects of the amide bond on the adsorption and aggregation behavior of AMC-C16 have been investigated in aqueous solution by various techniques. The presence of the amide bond, prone to hydrogen bonds, has been found to favor the AMC-C16 molecular adsorption or aggregation in the interface or aqueous solution. This can be attributed to the presence of the hydrogen bond, which can counterbalance effectively the electrostatic repulsion of the AMC-C16 molecular headgroup. The introduction of the amide bond leads to AMC-C16 with higher surface activity and enhanced tendency to form aggregates above the CAC having hydrodynamic diameters in the range 0.88–119 nm compared to BAC-16 and to earlier reported cationic surfactants.15,16,22,53,54 Surface tension measurements at different concentrations indicate stepwise aggregate of AMC-C16 and thus produce two critical aggregation concentration (CAC1 and CAC2). With the concentration increasing, the vesicles were formed by AMC-C16 at suitable concentrations without any additives, which have been confirmed by TEM. In addition, the rigid group (phenyl) bends into the hydrophobic region when vesicles are formed as revealed by 1H–1H 2D NOESY experiments. The AMC-C16 may have potential application value in the pharmaceutical industry as a drug-delivery vehicle.

Experimental Section

Instruments and Material

All reagents were of analytical grade, were commercially available, and used as received without further purification. Melting points (mp) were determined using an MPA100 Optimelt Automated Melting Point System, Stanford Research Systems Company, U.S.A. FT-IR was recorded using Frontier type infrared spectrometer, PerkinElmer Corp., U.S.A. 1H NMR was recorded by using Avance 600 superconducting NMR, Bruker Company, Switzerland. Mass spectra were recorded on a Waters Xevo UPLC/G2-QT instrument, Agilent Company, U.S.A. Conductivity was measured on Alvarez DDS-307 conductivity analyzer, Shanghai Precision and Scientific Instrument Company. Surface tensions were determined on a K100 tension meter, Krüss Company, Germany. DLS measurements were performed on a Malvern Autosizer, Malvern, U.K.. TEM image was obtained with an H-7650, Hitachi Instruments Company. Relative viscosities were measured in thermostatted Ubbelohde viscometers, Shanghai Huake Labware Co. All samples were prepared using Milli-Q water (18.25 MΩ·cm). All measurements were carried out at room temperature (25.0 ± 0.1 °C).

Synthesis and Characterization

Scheme 1 shows the synthesis steps of AMC-C16 and BAC-16.

Synthesis and Characterization of Chloroacetanilide

Chloroacetanilide was synthesized. The solution of chloroacetyl chloride (45 mmol) in acetone (15 mL) was slowly dropped into the solution of aniline (30 mmol) and K2CO3 (24 mmol) in acetone (45 mL) under cooling with an ice-water bath; then, the mixture was stirred under nitrogen for 2.5 h. Acetone was evaporated off under reduced pressure (525–675 mmHg) at 40–45 °C. The oily liquid crude product was obtained, and distilled water (50 mL) was added. The precipitate formed was filtered and washed with distilled water (20 mL × 5). Then, recrystallization from anhydrous ethanol gave pure chloroacetanilide as a white solid (77% yield).

1H NMR (600 MHz, CDCl3): δ 8.23 (s, 1H, NH), 7.56 (d, 2H, J = 8.4 Hz, PhH), 7.36 (t, 2H, J = 7.8 Hz, PhH), 7.18 (t, 1H, J = 7.2 Hz, PhH), and 4.20 (s, 2H, O=C–CH2).

Synthesis and Characterization of N-Anilinoformylmethyl-N-cetyl-N,N-dimethyl Ammoniumchloride (AMC-C16)

The AMC-C16 was synthesized. A mixture of chloroacetanilide (9.1 mmol), N,N-dimethyl-N-hexadec-ylamine (10.9 mmol), and acetonitrile (40 mL) was heated to 80 °C for 5 h. Acetonitrile was evaporated off under reduced pressure at room temperature to obtain the crude product. The crude product was purified by recrystallization from ethyl acetate for at least 4 to 6 times till the purity of the compound was confirmed by thin liquid chromatography (TLC). A white solid powder of AMC-C16 was obtained with a yield of 94%.

FT-IR (KBr pellet) ν (cm–1): 3198 (N–H stretching, amino), 3037 (C–H stretching, benzene ring), 2920 (C–H stretching, methyl), 2851 (C–H stretching, methylene), 1698 (O=C stretching, carbonyl), 1605, 1500, 1446 (skeleton stretching vibration, benzene ring), and 722 (alkyl chain bending, methylene). 1H NMR (600 MHz, CDCl3): 11.73 (s, 1H, NH), 7.80 (d, 2H, J = 8.4 Hz, PhH), 7.31 (t, 2H, J = 7.5 Hz, PhH), 7.13 (t, 1H, J = 7.2 Hz, PhH), 4.88 (s, 2H, CH2–N+), 3.62 (t, 2H, J = 8.4 Hz, N+–CH2CH2−), 3.42 (s, 6H, N+–CH3), 1.81 (q, 2H, N+–CH2CH2−), 1.25–1.35 (m, 26H, −CH2(CH2)13–CH3), and 0.88 (t, 3H, J = 6.6 Hz, CH3). ESI-MS (positive ions) m/z: calcd, 403.3683 for [M – Cl]+; found, 403.3676. mp: 131.5–134.6 °C.

Synthesis and Characterization of Benzylcetyl Dimethylammonium Chloride (BAC-16)

A mixture of benzyl chloride (30 mmol), N,N-dimethyl-N-hexadecylamine (36 mmol), and acetonitrile (50 mL) was heated to 80 °C for 5.5 h. Acetonitrile was evaporated off under reduced pressure at room temperature to obtain the crude product. The crude product was purified by recrystallization from ethyl acetate and acetone for at least 4 to 6 times till the purity of the compound was confirmed by TLC. A white solid powder of BAC-16 was obtained with a yield of 86%.

FT-IR (KBr pellet) ν (cm–1): 3008 (C–H stretching, benzene ring), 2922 (C–H stretching, methyl), 2853 (C–H stretching, methylene), 1616, 1472, 1456 (skeleton stretching vibration, benzene ring), and 723 (alkyl chain bending, methylene). 1H NMR (600 MHz, CDCl3): δ 7.65 (d, 2H, J = 7.2 Hz, PhH), 7.45–7.49 (m, 3H, PhH), 5.02 (s, 2H, CH2–N+), 3.49 (t, 2H, J = 8.4 Hz, N+–CH2CH2−), 3.31 (s, 6H, N+–CH3), 1.81 (br s, 2H, N+–CH2CH2−), 1.26–1.35 (m, 26H, −CH2(CH2)13–CH3), and 0.88 (t, 3H, J = 6.9 Hz, CH3). ESI-MS (positive ions) m/z: calcd, 360.3625 for [M – Cl]+; found, 360.3615. mp: 58–60 °C.

Conductivity

The conductivities of the solutions of AMC-C16 and BAC-16 were determined by using a digital conductivity meter at 25 °C. The solutions were thermostated at 25.0 ± 0.1 °C using a thermostatic bath during the measurements. The conductivity values of the solutions of different concentrations were tested by a dilution method.4 The measurements were repeated 3 times.

Surface Tension

Surface tension was determined using a Krüss K100 automatic tensiometer by the Du Nouy ring method at 25.0 ± 0.1 °C. The temperature of the solution was strictly controlled during the measurement. The surface tension values of the solution of different concentrations were tested by a dilution method. The instrument was calibrated using Milli-Q water before every experiment began and the standard deviation was kept within ±0.1 mN/m. The measurements were repeated 3 times.

Dynamic Light Scattering

DLS measurements were performed using a Malvern Autosizer light scattering apparatus at a scattering angle of 90°. The sample solution was filtrated through a membrane filter with a pore size of 0.45 μm just before the measurements. The samples were thermally equilibrated for 10 min at 25 °C before measurement. The measurements were repeated 3 times.

Transmission Electron Microscopy

Transmission electron microscopy was performed with an H-7650 operating at 100 kV. The solution of the surfactant needs to equilibrate for 12 h before performing the transmission electron microscopic measurements. Freshly prepared phosphotungstic acid solution (2%) was used as a staining agent. One drop of the solution was placed on a carbon formvar-coated copper grid (200 mesh), and the excess solution was removed with a filter paper to obtain a thin liquid film on the copper grid. Subsequently, a staining agent was dropped on the liquid film for 2 min, and the excess liquid was removed with a filter paper. The prepared samples were dried in air and tested.

Relative Viscosity

The Ubbelohde viscometer was used to measure the relative viscosities of the surfactant solution. The viscosity of Milli-Q water was used as the control. The solutions were heated at 25.0 °C using a thermostatic bath during the measurements. The measurements were repeated 3 times and averaged.

NMR Measurement

1H NMR spectra were recorded on a 600 MHz Bruker Avance NMR spectrometer at room temperature of 25.0 ± 0.1 °C. DMSO-d6 (99.9%) and CDCl3 (99.9%) were used to prepare the stock solution of the cationic surfactants. About 1 mL of the solution was transferred to a 5 mm NMR tube for each measurement. TMS is an internal standard on a Bruker AV 600 MHz. The signal assignment of the proton of surfactant molecules was measured by 1H–1H 2D NOESY using D2O as the solvent.

Acknowledgments

This work was financially supported by the Qiqihar University Graduate Innovation Fund Grants of China (YJSCX2018-ZD07), the Natural Science Foundation of Heilongjiang Province of China (LH2019B021), the Scientific Research Project of Heilongjiang Province Department of Education of China (no. 135409303), the Special Subject of Plant Food Processing Technology of Scientific Research Project of Heilongjiang Province Department of Education of China (no. YSTSXK201848), the National Natural Science Foundation of China (no. 21978140).

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c00294.

  • 1H NMR spectrum, LC–MS spectrum, conductivity, FT-IR spectra, CAC values, and physical appearance (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c00294_si_001.pdf (390.5KB, pdf)

References

  1. Israelachvili J. N.Thermodynamic and geometric aspects of amphiphile aggregation into micelles, vesicles and bilayers, and the interactions between them. In Physics of Amphiphiles: Micelles, Vesicles and Microemulsions; Degiorgio V., Corti M., Eds.; North-Holland: Amsterdam, The Netherlands, 1985; pp 24–58 [Google Scholar]
  2. Seddon J. M.; Templer R. H.. Polymorphism of lipid-water systems. In Handbook of Biological Physics; Lipowsky R., Sackmann E., Eds.; Elsevier: Amsterdam, The Netherlands, 1995, pp 97–160. [Google Scholar]
  3. Lasic D. D.Applications of liposomes. In Handbook of Biological Physics; Lipowsky R., Sackmann E., Eds.; Elsevier: Amsterdam, The Netherlands, 1995, pp 491–519. [Google Scholar]
  4. Goodchild I.; Collier L.; Millar S. L.; Prokeš I.; Lord J. C. D.; Butts C. P.; Bowers J.; Webster J. R. P.; Heenan R. K. Structural studies of the phase, aggregation and surface behaviour of 1-alkyl-3-methylimidazolium halide + water mixtures. Colloids Interface Sci. 2007, 307, 455–468. 10.1016/j.jcis.2006.11.034. [DOI] [PubMed] [Google Scholar]
  5. Lin Y.; Qiao Y.; Cheng X.; Yan Y.; Li Z.; Huang J. Hydrotropic Salt Promotes Anionic Surfactant Self-assembly into Vesicles and Ultralong Fibers. Colloids Interface Sci. 2012, 369, 238–244. 10.1016/j.jcis.2011.11.067. [DOI] [PubMed] [Google Scholar]
  6. Song B.; Hu Y.; Song Y.; Zhao J. Alkyl Chain Length-Dependent Viscoelastic Properties in Aqueous Wormlike Micellar Solutions of Anionic Gemini Surfactants with an Azobenzene Spacer. J. Colloid Interface Sci. 2010, 341, 94–100. 10.1016/j.jcis.2009.09.023. [DOI] [PubMed] [Google Scholar]
  7. Gao Y.; Li N.; Li X.; Zhang S.; Zheng L.; Bai X.; Yu L. Microstructures of Micellar Aggregations Formed within 1-Butyl-3-methylimidazolium Type Ionic Liquids. J. Phys. Chem. B 2009, 113, 123–130. 10.1021/jp809166f. [DOI] [PubMed] [Google Scholar]
  8. Hao J.; Liu W.; Xu G.; Zheng L. Vesicles from Salt-Free Cationic and Anionic Surfactant Solutions. Langmuir 2003, 19, 10635–10640. 10.1021/la030065q. [DOI] [Google Scholar]
  9. Liu Y.; Tan T.; Wang B.; Zhai R.; Song X.; Li E.; Wang H.; Yan H. Fabrication of CdS Films with Superhydrophobicity by the Microwave Assisted Chemical Bath Deposition. J. Colloid Interface Sci. 2008, 320, 540–547. 10.1016/j.jcis.2007.10.066. [DOI] [PubMed] [Google Scholar]
  10. Pal T.; Sahu K. Anomalous Variation of Excited-State Proton Transfer Dynamics inside a Triblock Copolymer-Cationic Surfactant Mixed Micelle. J. Phys. Chem. B 2019, 123, 8559–8568. 10.1021/acs.jpcb.9b06575. [DOI] [PubMed] [Google Scholar]
  11. Rajput S. M.; Kumar S.; Aswal V. K.; El Seoud O. A.; Malek N. I.; Kailasa S. K. Drug-Induced Micelle-to-Vesicle Transition of a Cationic Gemini Surfactant: Potential Applications in Drug Delivery. Chemphyschem 2018, 19, 865–872. 10.1002/cphc.201701134. [DOI] [PubMed] [Google Scholar]
  12. Guchhait A.; Pal A. J. Correlation between Photoinduced Electron Transfer and Photovoltaic Characteristics in Solar Cells Based on Hybrid Core–Shell Nanoparticles. J. Phys. Chem. C 2010, 114, 19294–19298. 10.1021/jp108256t. [DOI] [Google Scholar]
  13. Ai S.; Lu G.; He Q.; Li J. Highly Flexible Polyelectrolyte Nanotubes. Chem. Soc. 2003, 125, 11140–11141. 10.1021/ja0356378. [DOI] [PubMed] [Google Scholar]
  14. Matsui H.; Douberly G. E. Organization of Peptide Nanotubes into Macroscopic Bundles. Langmuir 2001, 17, 7918–7922. 10.1021/la010910+. [DOI] [Google Scholar]
  15. Bhadani A.; Singh S.; Kamboj R.; Chauhan V. Synthesis and Self Aggregation Properties of Ester-Functionalized Heterocyclic Pyrrolidinium Surfactants. Ind. Eng. Chem. Res. 2013, 291, 2289–2297. 10.1007/s00396-013-2971-4. [DOI] [Google Scholar]
  16. Kamboj R.; Bharmoria P.; Chauhan V.; Singh G.; Kumar A.; Singh S.; Kang T. S. Effect of cationic head group on micellization behavior of new amide-functionalized surface active ionic liquids. Phys. Chem. Chem. Phys. 2014, 16, 26040–26050. 10.1039/c4cp04054f. [DOI] [PubMed] [Google Scholar]
  17. Garcia M. T.; Ribosa I.; Perez L.; Manresa A.; Comelles F. Self-assembly and Antimicrobial Activity of Long-chain Amide-Functionalized Ionic Liquids in Aqueous Solution. Colloids Surf., B 2014, 123, 318–325. 10.1016/j.colsurfb.2014.09.033. [DOI] [PubMed] [Google Scholar]
  18. Zhang Q.; Gao Z.; Xu F.; Tai S.; Liu X.; Mo S.; Niu F. Surface Tension and Aggregation Properties of Novel Cationic Gemini Surfactants with Diethylammonium Headgroups and a Diamido Spacer. Langmuir 2012, 28, 11979–11987. 10.1021/la3011212. [DOI] [PubMed] [Google Scholar]
  19. Hoque J.; Gonuguntla S.; Yarlagadda V.; Aswal V. K.; Haldar J. Effect of Amide Bonds on the Self-assembly of Gemini Surfactants. Phys. Chem. Chem. Phys. 2014, 16, 11279–11288. 10.1039/c3cp55244f. [DOI] [PubMed] [Google Scholar]
  20. Kamboj R.; Bharmoria P.; Chauhan V.; Singh S.; Kumar A.; Mithu V. S.; Kang T. S. Micellization Behavior of Morpholinium-Based Amide-Functionalized Ionic Liquids in Aqueous Media. Langmuir 2014, 30, 9920–9930. 10.1021/la501897e. [DOI] [PubMed] [Google Scholar]
  21. Wang L.; Zhang Y.; Ding L.; Liu J.; Zhao B.; Deng Q.; Yan T. Synthesis and physiochemical properties of novel gemini surfactants with phenyl-1,4-bis(carbamoylmethyl) spacer. RSC Adv. 2015, 5, 74764–74773. 10.1039/c5ra13616d. [DOI] [Google Scholar]
  22. Bordes R.; Tropsch J.; Holmberg K. Role of an Amide Bond for Self-Assembly of Surfactants. Langmuir 2010, 26, 3077–3083. 10.1021/la902979m. [DOI] [PubMed] [Google Scholar]
  23. Khatua D.; Dey J. Fluorescence, Circular Dichroism, Light Scattering, and Microscopic Characterization of Vesicles of Sodium Salts of ThreeN-Acyl Peptides. J. Phys. Chem. B 2007, 111, 124–130. 10.1021/jp065225w. [DOI] [PubMed] [Google Scholar]
  24. Tan J.; Xiong X.; He Z.; Cao F.; Sun D. Aggregation Behavior of Polyether Based Siloxane Surfactants in Aqueous Solutions: Effect of Alkyl Groups and Steric Hindrance. J. Phys. Chem. B 2019, 123, 1390–1399. 10.1021/acs.jpcb.8b10727. [DOI] [PubMed] [Google Scholar]
  25. Roy S.; Dey J. Spontaneously Formed Vesicles of SodiumN-(11-Acrylamidoundecanoyl)-glycinate andl-Alaninate in Water. Langmuir 2005, 21, 10362–10369. 10.1021/la051206m. [DOI] [PubMed] [Google Scholar]
  26. Roy S.; Dey J. Effect of hydrogen-bonding interactions on the self-assembly formation of sodium N-(11-acrylamidoundecanoyl)-l-serinate, l-asparaginate, and l-glutaminate in aqueous solution. J. Colloid Interface Sci. 2007, 307, 229–234. 10.1016/j.jcis.2006.11.014. [DOI] [PubMed] [Google Scholar]
  27. Roy T. G.; Hazari S. K. S.; Dey B. K.; Sutradhar R.; Dey L.; Anowar N.; Tiekink E. R. T. Axial Ligand Substitution in Diastereoisomeric Trans-[Co- (Me814ane)Cl2] Complexes and Their Anti-Fungal Activities. Chem. Soc. Jpn. 2006, 59, 351–362. 10.1080/00958970500344664. [DOI] [Google Scholar]
  28. Roy A.; Maiti M.; Roy S. Spontaneous Formation of Vesicles by Sodium 2-Dodecylnicotinate in Water. Langmuir 2012, 28, 12696–12703. 10.1021/la302484x. [DOI] [PubMed] [Google Scholar]
  29. Wang H.; Guo W.; Zheng C.; Wang D.; Zhan H. Effect of Temperature on Foaming Ability and Foam Stability of Typical Surfactants Used for Foaming Agent. J. Surfactants Deterg. 2017, 20, 615. 10.1007/s11743-017-1953-9. [DOI] [Google Scholar]
  30. Zhai Z.; Yan X.; Song Z.; Shang S.; Rao X. Annular and threadlike wormlike micelles formed by a bio-based surfactant containing an extremely large hydrophobic group. Soft Matter 2018, 14, 499–507. 10.1039/C7SM02163A. [DOI] [PubMed] [Google Scholar]
  31. Yu D.; Huang X.; Deng M.; Lin Y.; Jiang L.; Huang J.; Wang Y. Effects of Inorganic and Organic Salts on Aggregation Behavior of Cationic Gemini Surfactants. J. Phys. Chem. B 2010, 114, 14955–14964. 10.1021/jp106031d. [DOI] [PubMed] [Google Scholar]
  32. Bijma K.; Engberts J. B. F. N. Effect of Counterions on Properties of Micelles Formed by Alkylpyridinium Surfactants. 1. Conductometry and1H-NMR Chemical Shifts. Langmuir 1997, 13, 4843–4849. 10.1021/la970171q. [DOI] [Google Scholar]
  33. He X.; Wang L.; Wu J.; Yang J.; Ma W.; Bai L.; Zhao B.; Song B. The Effects of Amide Bonds and Aromatic Rings on the Surface Properties and Antimicrobial Activity of Cationic Surfactants. J. Surfactants Deterg. 2018, 22, 315–325. 10.1002/jsde.12221. [DOI] [Google Scholar]
  34. Won Y.-Y.; Brannan A. K.; Davis H. T.; Bates F. S. Cryogenic Transmission Electron Microscopy (Cryo-TEM) of Micelles and Vesicles Formed in Water by Poly(ethylene oxide)-Based Block Copolymers. J. Phys. Chem. B 2002, 106, 3354–3364. 10.1021/jp013639d. [DOI] [Google Scholar]
  35. Xin X.; Pang J.; Li W.; Wang Y.; Yuan J.; Xu G. Dispersing Carbon Nanotubes in Aqueous Solutions of Trisiloxane-Based Surfactants Modified by Ethoxy and Propoxy Groups. J. Surfactants Deterg. 2015, 18, 163–170. 10.1007/s11743-014-1636-8. [DOI] [Google Scholar]
  36. Zhou L.; Jiang X.; Li Y.; Chen Z.; Hu X. Synthesis and Properties of a Novel Class of Gemini Pyridinium Surfactants. Langmuir 2007, 23, 11404–11408. 10.1021/la701154w. [DOI] [PubMed] [Google Scholar]
  37. Song L. D.; Rosen M. J. Surface Properties, Micellization, and Premicellar Aggregation of Gemini Surfactants with Rigid and Flexible Spacers. Langmuir 1996, 12, 1149–1153. 10.1021/la950508t. [DOI] [Google Scholar]
  38. Alami E.; Levy H.; Zana R.; Skoulios A. Alkanediyl-.alpha.,.omega.-bis(dimethylalkylammonium bromide) surfactants. 2. Structure of the lyotropic mesophases in the presence of water. Langmuir 1993, 9, 940–944. 10.1021/la00028a011. [DOI] [Google Scholar]
  39. Moulik S. P.; Haque M. E.; Jana P. K.; Das A. R. Micellar Properties of Cationic Surfactants in Pure and Mixed States. Phys. Chem. 1996, 100, 701–708. 10.1021/jp9506494. [DOI] [Google Scholar]
  40. Lu T.; Han F.; Mao G.; Lin G.; Huang J.; Huang X.; Wang Y.; Fu H. Effect of Hydrocarbon Parts of the Polar Headgroup on Surfactant Aggregates in Gemini and Bola Surfactant Solutions. Langmuir 2007, 23, 2932–2936. 10.1021/la063435u. [DOI] [PubMed] [Google Scholar]
  41. Pisárčik M.; Polakovicová M.; Devínsky F.; Lacko I. Dynamic Light Scattering, Interfacial Properties, and Conformational Analysis of Biodegradable Quaternary Ammonium Surfactants. Langmuir 2006, 22, 9160–9168. 10.1021/la0613934. [DOI] [PubMed] [Google Scholar]
  42. Aratono M.; Onimaru N.; Yoshikai Y.; Shigehisa M.; Koga I.; Wongwailikhit K.; Ohta A.; Takiue T.; Lhoussaine B.; Strey R.; Takata Y.; Villeneuve M.; Matsubara H. Spontaneous Vesicle Formation of Single Chain and Double Chain Cationic Surfactant Mixtures. J. Phys. Chem. B 2007, 111, 107–115. 10.1021/jp0637328. [DOI] [PubMed] [Google Scholar]
  43. Angelescu D.; Khan A.; Caldararu H. Viscoelastic Properties of Sodium Dodecyl Sulfate with Aluminum Salt in Aqueous Solution. Langmuir 2003, 19, 9155–9161. 10.1021/la034770a. [DOI] [Google Scholar]
  44. Hassan P. A.; Yakhmi J. V. Growth of Cationic Micelles in the Presence of Organic Additives. Langmuir 2000, 16, 7187–7191. 10.1021/la000517o. [DOI] [Google Scholar]
  45. Soltero J. F. A.; Puig J. E.; Manero O. Rheology of the Cetyltrimethylammonium Tosilate–Water System. 2. Linear Viscoelastic Regime. Langmuir 1996, 12, 2654–2662. 10.1021/la950368n. [DOI] [Google Scholar]
  46. Pal O. R.; Gaikar V. G.; Joshi J. V.; Goyal P. S.; Aswal V. K. Small-Angle Neutron Scattering Studies of Mixed Cetyl Trimethylammonium Bromide–Butyl Benzene Sulfonate Solutions. Langmuir 2002, 18, 6764–6768. 10.1021/la0200919. [DOI] [Google Scholar]
  47. Akram M.; Yousuf S.; Sarwar T.; Kabir-ud-Din fnm Micellization and interfacial behavior of 16-E2-16 in presence of inorganic and organic salt counterions. Colloids Surf., A 2014, 441, 281–290. 10.1016/j.colsurfa.2013.09.007. [DOI] [Google Scholar]
  48. Fan Y.; Hou Y.; Xiang J.; Yu D.; Wu C.; Tian M.; Han Y.; Wang Y. Synthesis and aggregation behavior of a hexameric quaternary ammonium surfactant. Langmuir 2011, 27, 10570–10579. 10.1021/la202453c. [DOI] [PubMed] [Google Scholar]
  49. Feng Y.; Chu Z. pH-Tunable Wormlike Micelles Based on an Ultra-Long-Chain “Pseudo” Gemini Surfactant. Soft Matter 2015, 11, 4614–4620. 10.1039/c5sm00677e. [DOI] [PubMed] [Google Scholar]
  50. Fang L.; Tan J.; Zheng Y.; Li H.; Li C.; Feng S. Effect of organic salts on the aggregation behavior of tri-(trimethylsiloxy)silylpropylpyridinium chloride in aqueous solution. Colloids Surf., A 2016, 509, 48–55. 10.1016/j.colsurfa.2016.08.086. [DOI] [Google Scholar]
  51. Claessens M. M. A. E.; Leermakers F. A. M.; Hoekstra F. A.; Cohen Stuart M. A. Entropic Stabilization and Equilibrium Size of Lipid Vesicles. Langmuir 2007, 23, 6315–6320. 10.1021/la0637622. [DOI] [PubMed] [Google Scholar]
  52. Nascimento D. B.; Rapuano R.; Lessa M. M.; Carmona-Ribeiro A. M. Counterion Effects on Properties of Cationic Vesicles. Langmuir 1998, 14, 7387–7391. 10.1021/la980845c. [DOI] [Google Scholar]
  53. Garcia M. T.; Ribosa I.; Perez L.; Manresa A.; Comelles F. Micellization and Antimicrobial Properties of Surface-Active Ionic Liquids Containing Cleavable Carbonate Linkages. Langmuir 2017, 33, 6511–6520. 10.1021/acs.langmuir.7b00505. [DOI] [PubMed] [Google Scholar]
  54. Garcia M. T.; Ribosa I.; Perez L.; Manresa A.; Comelles F. Aggregation Behavior and Antimicrobial Activity of Ester-Functionalized Imidazolium- and Pyridinium-Based Ionic Liquids in Aqueous Solution. Langmuir 2013, 29, 2536–2545. 10.1021/la304752e. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao0c00294_si_001.pdf (390.5KB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES