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Article

Synthesis, Characterization and Application of Novel Cationic Surfactants as Antibacterial Agents

by
Shaban R. M. Sayed
1,*,
Abdelrahman O. Ezzat
2,
Mohamed Taha Yassin
1 and
Ashraf M. M. Abdelbacki
3
1
Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
2
Department of Chemistry, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia
3
Department of Administrative and Social Sciences, College of Applied Studies and Community Service, King Saud University, P.O. Box 22459, Riyadh 11495, Saudi Arabia
*
Author to whom correspondence should be addressed.
Separations 2023, 10(2), 97; https://doi.org/10.3390/separations10020097
Submission received: 28 November 2022 / Revised: 21 January 2023 / Accepted: 25 January 2023 / Published: 1 February 2023
(This article belongs to the Special Issue Isolation and Structure Elucidation of Antibacterial Compound)
Browse Figures
Versions Notes

Abstract

:
It is of great necessity to develop new antimicrobial agents to overcome the accelerated increment in drug-resistant bacteria. The main aim of this work is to manufacture two cationic surfactants, QHETA-9 and QHETA-14, based on quaternary hexamethylenetetramine with long alkyl chains (C-9 and C-14) by simple one-step alkylation reaction. These surfactants were characterized by analytical and statistical data, including FTIR, 1H NMR, 13C NMR and DLS. The antibacterial activities of QHETA-9 and QHETA-14 against some pathogenic bacterial strains were tested using agar disk diffusion method. The results exhibited that QHETA-14 has higher antibacterial activity than that of QHETA-9. It displayed inhibitory zone values for Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis, as Gram-positive bacteria, of 22.7, 21.5 and 25.9 mm, respectively, at 200 μg/disk. Meanwhile, it recorded inhibition zone values of 17.5, 25.2 and 23.8 mm for Escherichia coli, Agrobacterium tumefaciens and Erwinia carotovora, respectively, at 200 μg/disk. As a result, the current investigation verified that the antibacterial properties of QHETA-14 were greater than those of QHETA-9 due to the increase in the length of the alkyl chain. It is clear that QHETA-14 has the potential to be used as an antibacterial agent against bacteria that cause nosocomial infections and food poisoning diseases.

1. Introduction

The exponential rise in bacterial and fungal resistance against antimicrobial agents via genetic mutation(s) or fusion of exogenous genes poses a serious danger to society [1]. For instance, drug-resistant Staphylococcus aureus strains cause more deaths than methicillin-sensitive strains [2]. In this perspective, there is an urgent necessity to find and create novel antibacterial substances that prevent the emergence of resistance development. Since various types of surfactants can interact with the cellular membranes of microorganisms via electrostatic and hydrophobic interactions, they are used as antimicrobial agents in a variety of industries, including the healthcare and food industries [3,4]. Furthermore, surfactants have the ability to be adsorbed at liquid–solid interfaces, forming a protective layer to prevent adhesion of microorganisms [5]. In addition, surfactants are reported to possess potential antiviral activity by inactivating viral spread based on their super hydrophobic characteristics that repel virus-contaminated droplets [6]. Moreover, these compounds possess antibacterial activity through disruption of their lipid membranes, resulting in the induction of bacterial cell death [7]. Domagk [8] recorded the first utilization of cationic surfactants in the field of antibacterial resistance. The use of cationic surfactants at hospitals can lead to reduced infections that can ultimately lead to a decrease in antibiotic usage, which indeed can decrease the development of antibiotic resistance. Over the past few decades, hundreds of new cationic surfactants have been prepared to enhance the antimicrobial efficiency, to minimize surfactant doses and to reduce the selective stimulation of bacteria [9]. Alkyl pyridinium and alkyl trimethylammonium halide surfactants are frequently utilized as antibacterial agents, with priority given to quaternary ammonium compounds (QACs) [10,11,12,13]. Due to the superior characteristics of QACs compared to known antibacterial agents, they are widely used as efficient biocidal agents, as they have excellent environmental stability, lower toxicity, better membrane penetration, higher corrosion inhibition effect and lower skin irritation [14,15,16,17,18]. QACs are positively charged cations and are drawn to negatively charged bacterial proteins of both Gram-positive and Gram-negative bacteria, and can function as all-purpose antimicrobials [19,20]. The objective of the current work is to synthesize new cationic quaternary ammonium surfactants based on hexamethylenetetramine and alkyl bromide with different alkyl chains. They were employed as antibacterial agents against the Gram-positive Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis, and against the Gram-negative Escherichia coli, Agrobacterium tumefaciens and Erwinia carotovora. These surfactants were synthesized by the alkylation of hexamethylenetetramine with nonyl bromide and tetradecyl bromide. The chemical structures of the surfactants were assessed using 1H NMR, 13C NMR and FTIR. In addition, the surface activities, thermodynamic parameters and aggregation characteristics were studied using DLS and DSA. Agar disk diffusion method was used to investigate the antibacterial properties of the produced cationic surfactants.

2. Materials and Methods

2.1. Materials

Hexamethylenetetramine (HETA) (Sigma Aldrich/Merck, St. Louis, MO, USA), 1-Bromotetradecane, 1-Bromononane (Fluka AG) and Tetrahydrofuran (THF) solvent were purchased from Sinopharm Chemical Reagent Corporation, Shanghai, PR China). All chemicals in this study were used without further purification.

2.2. Synthesis Strategy

Treatment of hexamethylenetetramine dissolved in THF with different alkyl (1-Bromononane and 1-Bromotetradecane) bromides produced QHETA-9 and QHETA-14, respectively, as shown in Scheme 1.
1-Bromononane (20 mmol, 4.14 g) and 1-Bromotetradecane (20 mmol, 5.54 g) were reacted separately with hexamethylenetetramine (20 mmol, 2.8 g), under reflux in THF solvent. First, hexamethylenetetramine was dissolved in 100 mL of hot THF and then treated with alkyl bromide in a 250 mL flask equipped with a condenser and continuously stirred at 500 rpm for 12 h under reflux condition. At the end of the reaction, the reaction mixture was cooled down and the white precipitate of the quaternized ammonium salt was filtered off. The formed products were washed twice with acetone and recrystallized three times from ethanol and left at room temperature for drying until constant weight was achieved.

2.3. Characterization of QHETA-9 and QHETA-14

The chemical structures of surfactants were characterized utilizing 1H NMR and 13C NMR (NMR; Bruker AVANCE DRX-500 MHz spectrometer) with ethanol-d6 as the solvent. The aqueous micelle size and the zeta potential at the critical micelle concentration (cmc) of the surfactant were investigated by Zetasizer Nano (Malvern Instrument Ltd., Malvern, UK) at 25 °C. The surface activity of the surfactant in distilled water was measured by a drop shape analyzer (DSA-100).
QHETA-9: white powder; Rf: 0.26 (petroleum ether/ethyl acetate/methanol, 3:1:1); yield (83%); m.p. 190–192°C; IR (KBr) ν/cm−1: 3447 (OH), 2924, 2854 (CH-aliphatic), 1466 (CH-bending), 1273, 1246 (C-N); 1H NMR (500 MHz, ethanol-d6) δH: 0.84 (t, 3H, CH3), 1.26–1.34 (m, 12H, CH2), 1.68–1.75 (m, 2H, CH2), 2.93 (t, 2H, CH2N), 4.57–4.67 (m, 6H, N-CH2-N), 5.20–5.23 (m, 6H, N-CH2-N+); 13C NMR (125 MHz, ethanol-d6) δC: 14.24 (CH3), 20.64, 23.30, 27.54, 29.75, 29.91, 30.15, 32.56 (7 × CH2), 42.93 (CH2N+), 79.43, 81.03 (N-CH2-N & N-CH2-N+); m/z: 346.17 [M+, C15H31BrN4].
QHETA-14: white powder; Rf: 0.41 (petroleum ether/ethyl acetate/methanol, 3:1:1); yield (79%); m.p. 194–196°C; IR (KBr) ν/cm−1: 3431 (OH), 2920, 2851 (CH-aliphatic), 1463 (CH-bending), 1274, 1247 (C-N); 1H NMR (500 MHz, ethanol-d6) δH: 0.85 (t, 3H, CH3), 1.25–1.40 (m, 22H, CH2), 1.67–1.79 (m, 2H, CH2), 2.92 (t, 2H, CH2N), 4.56–4.67 (m, 6H, N-CH2-N), 5.21–5.22 (m, 6H, N-CH2-N+); 13C NMR (125 MHz, ethanol-d6) δC: 14.25 (CH3), 20.61, 23.31, 27.54, 29.47, 29.75, 30.06, 30.19, 30.25, 30.33, 30.35, 30.39, 32.65 (12 × CH2), 42.93 (CH2N+), 79.45, 81.05 (N-CH2-N & N-CH2-N+); m/z: 416.25 [M+, C20H41BrN4].

2.4. Screening of Antibacterial Activity of QHETA-9 and QHETA-14 against the Tested Pathogens

To assay their antimicrobial effectiveness, QHETA-9 and QHETA-14 were screened for their antibacterial activity against the tested bacterial pathogens. Disk diffusion assay was utilized to investigate the antibacterial activity of these compounds against bacterial strains of Staphylococcus aureus, MRSA and Enterococcus faecalis as Gram-positive bacteria, and against E. coli, A. tumefaciens and E. carotovora as Gram-negative bacteria. The tested bacteria were grown on nutrient broth medium (3.0 g beef extract, 5.0 g/L peptone and a final pH of 6.8 ± 0.2; Sigma-Aldrich, Steinheim, Germany) at 30 °C ± 2 °C for 48 h. After this, the bacterial cultures were homogeneously swapped onto individual plates by using sterile cotton swabs. Sterile filter paper discs (9 mm in diameter) were loaded with 200 μg of QHETA-9 and QHETA-14 solutions and placed on the top of the NA plates (peptone 5g, sodium chloride 5 g, peptone 1.5 g, yeast extract 1.5 g, agar 15 g/ L with a final pH 7.4 ± 0.2). However, negative control disks loaded with distilled H2O were used as negative control, and Norfloxacin disks (10 μg) were used as positive control.

2.5. Determination of Minimum Inhibitory Concentration of QHETA-9 and QHETA-14

The antibacterial efficacies of QHETA-9 and QHETA-14 were investigated against six harmful bacterial strains, including Staphylococcus aureus (S. aureus), methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis (E. carotovora) as Gram-positive bacteria and against Escherichia coli (E. coli), Agrobacterium tumefaciens (A. tumefaciens) and Erwinia carotovora (E. carotovora) as Gram-negative bacteria, using agar disk diffusion method. All the organisms were gathered at the Botany and Microbiology Department, King Saud University, Riyadh, Saudi Arabia. Sterile filter paper discs (9 mm in diameter) were loaded with 12.5, 25, 50, 100, and 200 μg of QHETA-9 and QHETA-14 solutions, separately, and placed on the top of seeded NA plates as previously described. By using a Vernier caliper and recording the existence of inhibitory zones in relation to the concentrations of QHETA-9 and QHETA-14, the plates were incubated at 37 °C for 48 h. The lowest doses of both antibacterial agents were determined to be the minimum inhibitory concentrations (MICs). Minimum bactericidal concentration (MBC) was determined by performing streaking from MIC concentration and the two other subsequent concentrations of E. coli and S. aureus plates onto freshly prepared nutrient agar plates. After that, the plates were incubated for 48 h at 37 °C, and the lowest concentration demonstrating no bacterial growth was recorded as the MBC.

2.6. Statistical Analysis

GraphPad Prism 8 was used to statistically analyze the study data using one-way analysis of variance and Tukey’s test. All experiments were conducted in triplicate, and data were presented as mean ± standard error.

3. Results and Discussion

3.1. Characterization of QHETA

The structures of the synthesized QHETA derivatives were determined based on the respective spectroscopic analyses, as shown in Figures S1–S5. For instance, the IR spectrum of QHETA-9 (Figure S1a) exhibited six absorption bands at ν 3447, 2924, 2854, 1466, 1273 and 1246 cm−1, indicating the existence of the quaternary ammonium salt, the stretching aliphatic CH, bending CH and stretching C-N functionality. In addition, the 1H NMR of the assigned structure (Figure S2) displayed triplet signal at δH = 0.84 ppm for methyl group, and two multiplets at δH = 4.57–4.67 and 5.20–5.23 ppm, corresponding to (N-CH2-N and N-CH2-N+) protons. Moreover, the spectrum exhibited three signals correlated to methylene protons of the long alkyl chain, as follows: two multiplets at δH = 1.26–1.34 and 1.68–1.75 ppm and a triplet at δH = 2.93 ppm. Further, the 13C NMR spectrum of QHETA-9 (Figure S3) disclosed one spectral line at δC = 14.24 due to methyl carbons, and eight spectral lines at δC = 20.64, 23.30, 27.54, 29.75, 29.91, 30.15, 32.56 and 42.93 ppm due to the methylene carbons of the long alkyl chain. In addition, the N-CH2-N and N-CH2-N+ groups displayed two spectral lines at δC = 79.43 and 81.03 ppm.

3.2. Solubility and Surface Activity of QHETA-9 and QHETA-14 Surfactants at 25 °C

Surface activity is one of the most characteristic properties of cationic surfactants. Hence, different aqueous concentrations of QHETA-9 and QHETA-14 were examined to determine the surface tension, cmc and the adsorption properties at the air–water interface. The cmc values of QHETA-9 and QHETA-14 were determined from the abrupt changes in curves calculated by plotting the surface tension (ST) against concentration isotherms at 25 °C (Figure 1).
The cmc (mol. L−1) and ST (γcac; mN.m−1) data of QHETA-14 and QHETA-9 surfactants are given in Table 1. The cmc value for QHETA-9 was higher than that for QHETA-14 because of the longer aliphatic chain in the latter that lowered its aqueous solubility, while the surface tension value at cmc for QHETA-9 was less than that for QHETA-14 [21]. Moreover, the relative solubility number (RSN) of the prepared surfactants was measured as mentioned in a previous work [22], and obtained results are tabulated in Table 1. RSN measurement is an alternative practical method to hydrophilic–lipophilic balance (HLB) [22], and according to its value, the solubility of the surfactant in water can be predicted. If the RSN value is less than 13, the surfactant is considered insoluble in water; the surfactant is considered as water-dispersed at low concentrations if the RSN value is between 13 and 17. The solubility of surfactant in water is verified by an RSN value greater than 17. In this respect, both QHETA-9 and QHETA-14 are water-soluble, as their RSN values are 21 and 17, respectively; the higher value of solubility for QHETA-9 is due to its alkyl chain length being lower than that of QHETA-14.
The values of the two parameters, maximum excess surface concentration (Γmax) and average minimum surface area per molecule (Amin), were utilized to study the adsorption of QHETA-9 and QHETA-14 at air-water interface. The values of Γmax and Amin were determined using Gibbs adsorption isotherm equations [23]. The Amin value declined with the increased length of the alkyl chain (Table 1), as the longer the alkyl chains, the tighter the monolayers are at the air–water interface [24].
Charged surfactants have a strong potential to interact with bacteria by electrostatically binding onto their negatively charged surface and, as a consequence, disrupt the membrane continuity and the metabolic processes occurring on the bacterial inner membrane [25]. The micelle charges of the surfactants were studied using zeta potential measurements, as depicted in Figure S6, and the results, listed in Table 1, confirm that QHETA-9 and QHETA-14 have positive charges on their micelle surfaces that can facilitate their attraction to bacterial membranes. The zeta potential values for QHETA-9 and QHETA-14 were 18.33 ± 2 and 21.2 ± 3, respectively, which indicate the formation of stable micelles in the water, as particles with a ζ-potential less than −15 mV or more than 15 mV are expected to be stable from electrostatic considerations [26].
The micelle particle sizes of both QHETA-9 and QHETA-14 in their aqueous solutions were measured, as displayed in Figure S7. The aggregates’ hydrodynamic diameter (Dh; nm) and PDI values increased with increasing hydrophobic chain length, indicating that QHETA-14 formed larger aggregates than QHETA-9.

3.3. Screening of Antibacterial Activity of QHETA-9 and QHETA-14

The antibacterial activities of QHETA-9 and QHETA-14 were screened against the bacterial strains of interest. The findings revealed that E. faecalis was the most sensitive strain to QHETA-14, demonstrating a relative zone diameter of 24.54 ± 0.08 mm. However, Erwinia demonstrated the highest susceptibility to QHETA-. Interestingly, QHETA-14 revealed a higher antibacterial activity against S. aureus, MRSA, A. tumefaciens and E. carotovora strains compared to norfloxacin antibiotic (Table 2 and Figure S8). Collectively, QHETA-14 demonstrated a higher antibacterial activity against the tested strains compared to QHETA-9, and this could be attributed to the increase in the alkyl chain length.

3.4. Minimum Inhibitory and Bactericidal Concentrations (MIC and MBC) of QHETA-9 and QHETA-14

The tested pathogenic bacterial strains showed variable susceptibilities to QHETA-9 and QHETA-14, as shown in Figure 2 and Figure 3 as well as Table 3. QHETA-14 recorded the strongest antibacterial effects towards S. aureus, methicillin-resistant (MRSA) and E. faecalis with zone diameters of 22.7, 21.5 and 25.9 mm, respectively, at a concentration of 200 µg/disk. The lowest minimal inhibitory concentration (MIC) for QHETA-14 as an antibacterial agent towards Gram-positive bacteria was 12.5 µg/disk, with zone diameters of 12.5, 14.7 and 14.3 mm for S. aureus, MRSA and E. faecalis, respectively. In addition, the tested Gram-negative strains were more affected by QHETA-14, with maximum inhibition zone diameters of 17.5, 25.2 and 23.8 mm for E. coli, A. tumefaciens and E. carotovora, respectively, at a concentration of 200 µg/disk.
The MIC for QHETA-14 was 25 µg/disk with zone diameters of 10.0, 18.2 and 16.7 mm for E. coli, A. tumefaciens and E. carotovora, respectively. The minimum bactericidal concentrations (MBCs) against S. aureus and E. coli bacteria were discovered to be 50 and 100 µg/disk, respectively. In contrast, only the large concentration of QHETA-9 (200 µg/disk) recorded antibacterial efficacy against the tested bacterial strains, with inhibition zone diameters varying from 10 to 14 mm. Additionally, QHETA-9 exhibited antibacterial activity only at the concentration of 200 µg/disk against the tested bacterial strains expect E. coli and E. faecalis strains. The difference in microbial susceptibility to QHETA-14 and QHETA-9 may be varied due to the length of the alkyl chain. Nosocomial bacterial infections are considered to be of great concern due to the high morbidity and mortality rate resulting from the high incidence of antimicrobial resistance [27]. In this regard, QHETA-14 exhibited antibacterial efficiency against S. aureus, which is considered the main cause of bacterial infections among hospitalized patients, as reported by previous studies [28], and against A. tumefaciens and E. carotovora, which are some of the most devastating plant pathogenic bacteria. Furthermore, methicillin-resistant S. aureus (MRSA) was reported as one of the main etiological agents of nosocomial infections, contributing to approximately 30% of infections occurring during hospital admission [29]. The solution of QHETA-14 exhibited anti-MRSA activity, demonstrating inhibition zones with all concentrations starting at the 12.5 µg/disk. Our findings were in accordance with those of Domagk and Kawabata [10,19]. Furthermore, A. tumefaciens exhibited the highest sensitivity to QHETA-14 with concentrations starting from 25 µg/disk [20]. Our findings showed that the examined bacterial strains had different sensitivity levels to the investigated compounds; consequently, QHETA-14 was the compound with the highest level of activity against S. aureus, MRSA, E. faecalis, E. coli, A. tumefaciens and E. carotovora.
QHETA-14 demonstrated strong antibacterial activity at a low concentration of 200 µg/disk, exhibiting inhibition zones with diameters of 22.75 and 17.45 mm. These outcomes were superior to those of an earlier study that evaluated the antibacterial activity of mono-quaternary ammonium compounds towards S. aureus and E. coli strains, recording inhibition zone widths of 22.4 and 24.1 mm, respectively, at a high concentration of 500 µg/mL— 2.5 times higher than the concentration used in the current study [30]. Another investigation revealed the antibacterial efficacy of mono-QACs against S. aureus, recording inhibition zone widths of 14.3 mm at the concentration of 500 µg/mL, which was substantially greater than the concentration employed in the current study [31]. When compared to earlier reports, QHETA-14 collectively displayed potent antibacterial activity against the pathogenic bacterial strains, indicating the potential for using these materials to create effective antibacterial agents against various human and plant-pathogenic bacterial strains.

3.5. Structure–Activity Relationship (SAR) Studies

According to the findings of the antibacterial testing, the structure–activity relationship of the newly synthesized QHETA-9 and QHETA-14 derivatives can be deduced. Cationic quaternary ammonium surfactants can be used as antiseptics due to their efficiency in destroying microorganisms, such as Gram-negative and Gram-positive bacteria. This mechanism is performed by two pathways. First, the surfactant diffuses from the aqueous phase to the cell membranes through an electrostatic interaction between its cationic head and the negatively charged outer membrane. Next, the surfactant’s hydrocarbon chains come into contact with the hydrophobic portion of the inner membrane and have an impact on protein synthesis. The second method involves sealing the surfactant to the cell membrane and creating a micellar pseudo-phase in the aqueous medium concurrently, which interacts with the lipid bilayer of the membrane and causes cell lysis [32,33,34]. The development of the surfactant’s antibacterial properties is accompanied by an increase in the chain length [35,36]; therefore, QHETA-14 demonstrated higher activity than QHETA-9. The cationic surfactants are membrane-active agents which target the cytoplasmic bacterial membrane, inducing bacterial cell death through a number of mechanisms [37]. In detail, these compounds adsorb and penetrate the bacterial cell wall and then impair the cytoplasmic membrane, leading to the discharge of intracellular components. In addition, the cationic surfactants destroy the bacterial nucleic acids and proteins [38]. When combined, these substances cause the membrane to become disorganized, losing its integrity and causing bacterial cell death. When the cationic surfactant interacts with the phospholipid components of the bacterial membrane, the integrity of the membrane is disrupted [39]. Other researchers attributed the antibacterial efficacy of these compounds to their ability to change the surface potential of bacterial cell membranes from negative to positive, resulting in bacterial cell death [40].

4. Conclusions

Two new cationic surfactants based on quaternary hexamethylenetetramine surfactants with C-9 and C-14 alkyl chains (QHETA-9 and QHETA-14) were synthesized and characterized. Their chemical structures, surface activities and antibacterial efficacies against six pathogenic bacterial strains were investigated. The main characteristic difference between the prepared surfactants is the alkyl chain length, which causes the difference in their surface and antimicrobial activities. It was discovered that QHETA-14 had greater antimicrobial efficacy than QHETA-9 against S. aureus, MRSA and E. faecalis as Gram-positive bacteria, and against E. coli, A. tumefaciens and E. carotovora as Gram-negative bacteria. The higher activity of QHETA-14 in comparison to QHETA-9 is due to the longer alkyl chain of QHETA-14. QHETA-14 exhibited large inhibition zones of 24.3 mm and 25.2 mm against A. tumefaciens at 100 μg/disk and 200 μg/disk, respectively. These results indicate that QHETA-14 could be used as a possible antibacterial agent against bacterial pathogens causing nosocomial infections and food poisoning. Additionally, the possibility of using QHETA-14 in the creation of antibacterial coatings for the preservation of seeds is highlighted by its possible antibacterial activity against plant-pathogenic bacterial strains such as Agrobacterium and Erwinia strains. Future cytotoxic investigations, however, should be carried out to guarantee the safety of using this substance as an antibacterial agent on a broad scale.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/separations10020097/s1, Figure S1: FTIR spectra of (a) QHETA-9 and (b) QHETA-14; Figure S2: 1H NMR spectra of QHETA-9. (500 MHz, Ethanol-d6); Figure S3: 13C NMR spectra of QHETA-9 (125 MHz, Ethanol-d6); Figure S4: 1H NMR spectra of QHETA-14. (500 MHz, Ethanol-d6); Figure S5: 13C NMR spectra of QHETA-14 (125 MHz, Ethanol-d6); Figure S6: Zeta potential measurements of (a) QHETA-14 and (b) QHETA-9; Figure S7: Particle size distributions of (a) QHETA-14 and (b) QHETA-9 at their cmc and at 25 °C; Figure S8: Effect of the antibiotic Norfloxacin 10 µg cobncentraion as standered material on bacterial growth of bacteria strains including: S. aureus (1), MRSA (2), E. faecalis (3). A. tumefaciens (4), E. carotovora (5) and E. coli (6).

Author Contributions

Conceptualization, S.R.M.S. and A.O.E.; methodology, A.M.M.A.; software, M.T.Y.; validation, A.O.E., A.M.M.A. and A.M.M.A.; formal analysis, A.O.E.; investigation, A.M.M.A.; resources, A.O.E.; data curation, O.AE and S.R.M.S.; writing—original draft preparation, A.O.E., S.R.M.S., and M.T.Y.; writing—review and editing, MTY., and A.M.M.A.; visualization, M.T.Y.; supervision, A.M.M.A.; project administration, A.O.E.; funding acquisition, S.R.M.S. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Researchers Supporting Project number (RSPD2023R743), King Saud University, Riyadh, Saudi Arabia.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data presented in this study are available on request from the corresponding author.

Acknowledgments

The authors extend their appreciation to the Researchers Supporting Project number (RSPD2023R743), King Saud University, Riyadh, Saudi Arabia.

Conflicts of Interest

The authors declare no conflict of interest.

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Separations 10 00097 sch001 550
Scheme 1. Preparation of QHETA-9 and QHETA-14.
Scheme 1. Preparation of QHETA-9 and QHETA-14.
Separations 10 00097 sch001
Separations 10 00097 g001 550
Figure 1. Surface tension of QHETA-14 and QHETA-9 in aqueous solution at 25 °C.
Figure 1. Surface tension of QHETA-14 and QHETA-9 in aqueous solution at 25 °C.
Separations 10 00097 g001
Separations 10 00097 g002 550
Figure 2. Effect of different concentrations of QHETA-9 (A) and QHETA-14 (B) on the growth of the Gram-positive bacteria S. aureus (1), MRSA (2) and E. faecalis (3).
Figure 2. Effect of different concentrations of QHETA-9 (A) and QHETA-14 (B) on the growth of the Gram-positive bacteria S. aureus (1), MRSA (2) and E. faecalis (3).
Separations 10 00097 g002
Separations 10 00097 g003 550
Figure 3. Effect of different concentrations for QHETA-9 (A) and QHETA-14 (B) on the growth of the Gram-negative bacteria A. tumefaciens (1), E. carotovora (2) and E. coli (3).
Figure 3. Effect of different concentrations for QHETA-9 (A) and QHETA-14 (B) on the growth of the Gram-negative bacteria A. tumefaciens (1), E. carotovora (2) and E. coli (3).
Separations 10 00097 g003
Table
Table 1. Surface activity properties, cmc, RSN and zeta potentials of QHETA-9 and QHETA-14 surfactants at 25 °C.
Table 1. Surface activity properties, cmc, RSN and zeta potentials of QHETA-9 and QHETA-14 surfactants at 25 °C.
Surface Activity PropertiesQHETA-9QHETA-14
cmc (mM)2.62.35
(−∂γ/∂ ln c)T6.98.26
γcmc (mN/m)47 ± 0.840 ± 0.5
Δγ (mN/m)25 ± 0.832 ± 0.5
Γmax × 10 −6 (mol/m2)2.783.33
Amin (nm2/molecule)0.60.5
RSN2117
Zeta potential (mV)18.33 ± 221.2 ± 3
γcmc: surface tension at critical micelle concentration; Γmax: maximum excess surface concentration; Amin: average minimum surface area per molecule; RSN: relative solubility number.
Table
Table 2. Screening of antibacterial activity of QHETA-9 and QHETA-14 against the tested bacterial pathogens.
Table 2. Screening of antibacterial activity of QHETA-9 and QHETA-14 against the tested bacterial pathogens.
The Tested StrainsInhibition Zone Diameter (mm)
QHETA-9QHETA-14NorfloxacinNegative Control
S. aureus10.03 ± 0.1621.41 ± 0.3118.92 ± 0.150.00 ± 0.00
MRSA10.53 ± 0.2322.03 ± 0.0621.86 ± 0.110.00 ± 0.00
E. faecalis10.28 ± 0.0224.54 ± 0.0828.05 ± 0.020.00 ± 0.00
A. tumefaciens12.82 ± 0.2224.06 ± 0.0925.91 ± 0.030.00 ± 0.00
E. carotovora13.62 ± 0.2421.57 ± 0.4222.59 ±0.110.00 ± 0.00
E. coli0.00 ± 0.0018.02 ± 0.1327.86 ± 0.060.00 ± 0.00
Table
Table 3. Different minimum inhibitory concentrations of QHETA-9 and QHETA-14 against the tested bacterial pathogens.
Table 3. Different minimum inhibitory concentrations of QHETA-9 and QHETA-14 against the tested bacterial pathogens.
Tested StrainsInhibition Zone Diameter (mm)
12.5 µg/Disk25 µg/Disk50 µg/Disk100 µg/Disk200 µg/Disk
QHETA-9QHETA-14QHETA-9QHETA-14QHETA-9QHETA-14QHETA-9QHETA-14QHETA-9QHETA-14
S. aureus0.00 ± 0.0012.51 ± 0.120.00 ± 0.0016.31± 0.240.00 ± 0.0017.91 ± 0.370.00 ± 0.0020.19 ± 0.4210.43 ± 0.3522.75 ± 0.21
MRSA0.00 ± 0.0014.76 ± 0.360.00 ± 0.0015.83 ± 0.310.00 ± 0.0017.15 ± 0.290.00 ± 0.0019.22 ± 0.1810.65 ± 0.2421.52 ± 0.08
E. faecalis0.00 ± 0.0014.34 ± 0.280.00 ± 0.0016.76 ± 0.170.00 ± 0.0021.34 ± 0.150.00 ± 0.0024.25 ± 02610.39 ± 0.1425.96 ± 0.43
A. tumefaciens0.00 ± 0.0014.38 ± 0.190.00 ± 0.0018.23 ± 0.3811.41 ± 0.2321.26 ± 0.0912.67 ± 0.3824.37 ± 0.3213.71 ± 0.3425.23 ± 0.23
E. carotovora0.00 ± 0.0013.27 ± 0.410.00 ± 0.0016.71 ± 0.2410.83 ± 0.1419.32 ± 0.3613.21 ± 0.2122.53 ± 0.4314.26 ± 0.1923.86 ± 0.51
E. coli0.00 ± 0.000.00 ± 0.000.00 ± 0.0010.15 ± 0.410.00 ± 0.0011.63 ± 0.310.00 ± 0.0015.13 ± 0.170.00 ± 0.0017.54 ± 0.39
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Sayed, S.R.M.; Ezzat, A.O.; Yassin, M.T.; Abdelbacki, A.M.M. Synthesis, Characterization and Application of Novel Cationic Surfactants as Antibacterial Agents. Separations 2023, 10, 97. https://doi.org/10.3390/separations10020097

AMA Style

Sayed SRM, Ezzat AO, Yassin MT, Abdelbacki AMM. Synthesis, Characterization and Application of Novel Cationic Surfactants as Antibacterial Agents. Separations. 2023; 10(2):97. https://doi.org/10.3390/separations10020097

Chicago/Turabian Style

Sayed, Shaban R. M., Abdelrahman O. Ezzat, Mohamed Taha Yassin, and Ashraf M. M. Abdelbacki. 2023. "Synthesis, Characterization and Application of Novel Cationic Surfactants as Antibacterial Agents" Separations 10, no. 2: 97. https://doi.org/10.3390/separations10020097

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