Synthesis, physiochemical property and antimicrobial activity of novel quaternary ammonium salts

Synthesis and broad-spectrum biocidal effect of novel gemini quaternary ammonium compounds

Since the discovery of antimicrobial agents, the misuse of antibiotics has led to the emergence of bacterial strains resistant to both antibiotics and common disinfectants like quaternary ammonium compounds (QACs). A new class, 'gemini' QACs, which contain two polar heads, has shown promise. Octenidine (OCT), a representative of this group, is effective against resistant microorganisms but has limitations such as low solubility and high cytotoxicity. In this study, we developed 16 novel OCT derivatives. These compounds were subjected to in silico screening to predict their membrane permeation. Testing against nosocomial bacterial strains (G+ and G-) and their biofilms revealed that most compounds were highly effective against G+ bacteria, while compounds 7, 8, and 10-12 were effective against G- bacteria. Notably, compounds 6-8 were significantly more effective than OCT and BAC standards across the bacterial panel. Compound 12 stood out due to its low cytotoxicity and broad-spectrum antimicrobial activity, comparable to OCT. It also demonstrated impressive antifungal activity. Compound 1 was highly selective to fungi and four times more effective than OCT without its cytotoxicity. Several compounds, including 4, 6, 8, 9, 10, and 12, showed strong virucidal activity against murine cytomegalovirus and herpes simplex virus 1. In conclusion, these gemini QACs, especially compound 12, offer a promising alternative to current disinfectants, addressing emerging resistances with their enhanced antimicrobial, antifungal, and virucidal properties.

Anti-adhesive, anti-biofilm and fungicidal action of newly synthesized gemini quaternary ammonium salts

Newly synthesized gemini quaternary ammonium salts (QAS) with different counterions (bromide, hydrogen chloride, methylcarbonate, acetate, lactate), chain lengths (C12, C14, C16) and methylene linker (3xCH2) were tested. Dihydrochlorides and dibromides with 12 carbon atoms in hydrophobic chains were characterized by the highest biological activity against planktonic forms of yeast and yeast-like fungi. The tested gemini surfactants also inhibited the production of filaments by C. albicans. Moreover, they reduced the adhesion of C. albicans cells to the surfaces of stainless steel, silicone and glass, and slightly to polystyrene. In particular, the gemini compounds with 16-carbon alkyl chains were most effective against biofilms. It was also found that the tested surfactants were not cytotoxic to yeast cells. Moreover, dimethylcarbonate (2xC12MeCO3G3) did not cause hemolysis of sheep erythrocytes. Dihydrochlorides, dilactate and diacetate showed no mutagenic potential.

Advances in the Synthesis of Biologically Active Quaternary Ammonium Compounds

This review provides a comprehensive overview of recent advancements in the design and synthesis of biologically active quaternary ammonium compounds (QACs). The covered scope extends beyond commonly reviewed antimicrobial derivatives to include synthetic agents with antifungal, anticancer, and antiviral properties. Additionally, this review highlights examples of quaternary ammonium compounds exhibiting activity against protozoa and herbicidal effects, as well as analgesic and anesthetic derivatives. The article also embraces the quaternary-ammonium-containing cholinesterase inhibitors and muscle relaxants. QACs, marked by their inherent permanent charge, also find widespread usage across diverse domains such as fabric softeners, hair conditioners, detergents, and disinfectants. The effectiveness of QACs hinges greatly on finding the right equilibrium between hydrophilicity and lipophilicity. The ideal length of the alkyl chain varies according to the unique structure of each QAC and its biological settings. It is expected that this review will provide comprehensive data for medicinal and industrial chemists to design and develop novel QAC-based products.

Tetraalkylammonium salts (TAS) in solar energy applications - A review on in vitro and in vivo toxicity

Tetraalkylammonium salt (TAS) is an organic salt widely employed as a precursor, additive or electrolyte in solar cell applications, such as perovskite or dye-sensitized solar cells. Notably, Perovskite solar cells (PSCs) have garnered acclaim for their exceptional efficiency. However, PSCs have been associated with environmental and health concerns due to the presence of lead (Pb) content, the use of hazardous solvents, and the incorporation of TAS in their fabrication processes, which significantly contributes to environmental and human health toxicity. As a response, there is a growing trend towards transitioning to safer and biobased materials in PSC fabrication to address these concerns. However, the potential health hazards associated with TAS necessitate a thorough evaluation, considering the widespread use of this substance. Nevertheless, the overexploitation of TAS could potentially increase the disposal of TAS in the ecosystem, thus, posing a major health risk and severe pollution. Therefore, this review article presents a comprehensive discussion on the in vitro and in vivo toxicity assays of TAS as a potential material in solar energy applications, including cytotoxicity, genotoxicity, in vivo dermal, and systemic toxicity. In addition, this review emphasizes the toxicity of TAS compounds, particularly the linear tetraalkyl chain structures, and summarizes essential findings from past studies as a point of reference for the development of non-toxic and environmentally friendly TAS derivatives in future studies. The effects of the TAS alkyl chain length, polar head and hydrophobicity, cation and anion, and other properties are also included in this review.

Copolymers functionalized with quaternary ammonium compounds under template chain exhibit simultaneously efficient bactericidal and flocculation properties: Characterization, performance and mechanism

In this work, novel multifunctional cationic template copolymers with flocculation and sterilization capabilities were synthesized using a low-pressure ultraviolet (LP-UV) template polymerization method for the removal of kaolin and Escherichia coli (E. coli) from water. The influence of template agents on the structural performance of the copolymers was evaluated through characterization, which showed that template copolymer TPADM possesses a higher cationic charge density and a more complex rough surface, contributing to better flocculation performance than that of the non-template copolymer CPADM. Under optimal experimental conditions, TPADM-1 exhibited removal rates of 98.45% for kaolin and 99% for E. coli (OD600 =0.04), marginally outperforming the non-template copolymer. Simultaneously, TPADM-1 produced good adaptability to kaolin and E. coli wastewater in terms of wide pH, speculating that charge neutralization, adsorption bridging, patching, and sweeping simultaneously dominate the flocculation mechanism. Interestingly, SEM and 3D-EEM analysis confirm that the sterilization of E. coli occurs through two distinct functions: initially adsorption followed by subsequent cell membrane rupture and leakage of cellular contents, ultimately leading to cell death. This research further confirms the feasibility of the designed novel multifunctional copolymers for achieving simultaneous disinfection and turbidity removal, demonstrating practical applicability in real water treatment processes.

Quaternary ammonium salts for water treatment with balanced rate of sterilization and degradation

The growing number of infections caused by drug-resistant bacteria which arise from the overuse of antibiotics has severely affected the normal operation of human society. The high antibacterial activity of QAS makes it promising as an alternative to antibiotics, but it suffers from secondary pollution due to its non-degradation. Here we have synthesized a class of gemini quaternary ammonium salts (GQAS) with different carbon chain lengths containing ester groups by using facile methylation reaction. Quaternary ammonium groups contribute to insert negatively charged bacterial membranes, resulting in membrane damage and bacteria death. Compared with conventional single-chain QAS, except for the more efficient antibacterial efficiency attribute to the presence of the second carbon chain, GQAS with alterable antibacterial properties can minimize the possibility of bacterial resistance and reduce the accumulation of GQAS in the environment through the introduction of degradable ester groups. GQAS is completely superior to the commercial bactericide benzalkonium chloride (BAC) in both antibacterial activity and degrade performance, which can be used as a more environmentally friendly bactericide.

Efficacy of Novel Quaternary Ammonium and Phosphonium Salts Differing in Cation Type and Alkyl Chain Length against Antibiotic-Resistant Staphylococcus aureus

Antibacterial resistance poses a critical public health threat, challenging the prevention and treatment of bacterial infections. The search for innovative antibacterial agents has spurred significant interest in quaternary heteronium salts (QHSs), such as quaternary ammonium and phosphonium compounds as potential candidates. In this study, a library of 49 structurally related QHSs was synthesized, varying the cation type and alkyl chain length. Their antibacterial activities against Staphylococcus aureus, including antibiotic-resistant strains, were evaluated by determining minimum inhibitory/bactericidal concentrations (MIC/MBC) ≤ 64 µg/mL. Structure-activity relationship analyses highlighted alkyl-triphenylphosphonium and alkyl-methylimidazolium salts as the most effective against S. aureus CECT 976. The length of the alkyl side chain significantly influenced the antibacterial activity, with optimal chain lengths observed between C10 and C14. Dose-response relationships were assessed for selected QHSs, showing dose-dependent antibacterial activity following a non-linear pattern. Survival curves indicated effective eradication of S. aureus CECT 976 by QHSs at low concentrations, particularly compounds 1e, 3e, and 5e. Moreover, in vitro human cellular data indicated that compounds 2e, 4e, and 5e showed favourable safety profiles at concentrations ≤ 2 µg/mL. These findings highlight the potential of these QHSs as effective agents against susceptible and resistant bacterial strains, providing valuable insights for the rational design of bioactive QHSs.

Cytotoxicity and Antibacterial Efficacy of Betaine- and Choline-Substituted Polymers

Cationic charge has been widely used to increase polymer adsorption and flocculation of dispersions or to provide antimicrobial activity. In this work, cationization of hydroxyethyl cellulose (HEC) and polyvinyl alcohol (PVA) was achieved by covalently coupling betaine hydrochloride and choline chloride to the polymer backbones through carbonyl diimidazole (CDI) activation. Two approaches for activation were investigated. CDI in excess was used to activate the polymers' hydroxyls followed by carbonate formation with choline chloride, or CDI was used to activate betaine hydrochloride, followed by ester formation with the polymers' hydroxyls. The first approach led to a more significant cross-linking of PVA, but not of HEC, and the second approach successfully formed ester bonds. Cationic, nitrogen-bearing materials with varying degrees of substitution were obtained in moderate to high yields. These materials were analyzed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, polyelectrolyte titration, and kaolin flocculation. Their dose-dependent effect on the growth of Staphylococcus aureus and Pseudomonas aeruginosa, and L929 mouse fibroblasts, was investigated. Significant differences were found between the choline- and betaine-containing polymers, and especially, the choline carbonate esters of HEC strongly inhibited the growth of S. aureus in vitro but were also cytotoxic to fibroblasts. Fibroblast cytotoxicity was also observed for betaine esters of PVA but not for those of HEC. The materials could potentially be used as antimicrobial agents for instance by coating surfaces, but more investigations into the interaction between cells and polysaccharides are necessary to clarify why and how bacterial and human cells are inhibited or killed by these derivatives, especially those containing choline.

Multicationic Quaternary Ammonium Compounds: A Framework for Combating Bacterial Resistance

During previous stages of research, high biocidal activity toward microorganism archival strains has been used as the main indicator in the development of new antiseptic formulations. Although this factor remains one of the most important characteristics of biocide efficiency, the scale of antimicrobial resistance spread causes serious concern. Therefore, focus shifts toward the development of formulations with a stable effect even in the case of prolonged contact with pathogens. Here, we introduce an original isocyanuric acid alkylation method with the use of available alkyl dichlorides, which opened access to a wide panel of multi-QACs with alkyl chains of various lengths between the nitrogen atoms of triazine and pyridine cycles. We used a complex approach for the resulting series of 17 compounds, including their antibiofilm properties, bacterial tolerance development, and antimicrobial activity toward multiresistant pathogenic strains. As a result of these efforts, available compounds have shown higher levels of antibacterial activity against ESKAPE pathogens than widely used commercial QACs. Hit compounds possessed high activity toward clinical bacterial strains and have also demonstrated a long-term biocidal effect without significant development of microorganism tolerance. The overall results indicated a high level of antibacterial activity and the broad application prospects of multi-QACs based on isocyanuric acid against multiresistant bacterial strains.

Quaternary Ammonium Salts: Insights into Synthesis and New Directions in Antibacterial Applications

The overuse of antibiotics has led to the emergence of a large number of antibiotic-resistant genes in bacteria, and increasing evidence indicates that a fungicide with an antibacterial mechanism different from that of antibiotics is needed. Quaternary ammonium salts (QASs) are a biparental substance with good antibacterial properties that kills bacteria through simple electrostatic adsorption and insertion into cell membranes/altering of cell membrane permeability. Therefore, the probability of bacteria developing drug resistance is greatly reduced. In this review, we focus on the synthesis and application of single-chain QASs, double-chain QASs, heterocyclic QASs, and gemini QASs (GQASs). Some possible structure-function relationships of QASs are also summarized. As such, we hope this review will provide insight for researchers to explore more applications of QASs in the field of antimicrobials with the aim of developing systems for clinical applications.

The effectiveness of newly synthesized quaternary ammonium salts differing in chain length and type of counterion against priority human pathogens

Quaternary ammonium salts (QAS) commonly occur as active substances in disinfectants. QAS have the important property of coating abiotic surfaces, which prevents adhesion of microorganisms, thus inhibiting biofilm formation. In this study, a group of nine monomeric QAS, differing in the structure and length of the aliphatic chain (C12, C14, C16) and the counterion (methylcarbonate, acetate, bromide), were investigated. The study included an analysis of their action against planktonic forms as well as bacterial biofilms. The compounds were tested for their anti-adhesion properties on stainless steel, polystyrene, silicone and glass surfaces. Moreover, mutagenicity analysis and evaluation of hemolytic properties were performed. It was found that compounds with 16-carbon hydrophobic chains were the most promising against both planktonic forms and biofilms. Tested surfactants (C12, C14, C16) showed anti-adhesion activity but it was dependent on the type of the surface and strain used. The tested compounds at MIC concentrations did not cause hemolysis of sheep blood cells. The type of counterion was not as significant for the activity of the compound as the length of the hydrophobic aliphatic chain.

Antiviral capacity of polypropylene/(1-Hexadecyl) trimethyl-ammonium bromide composites against COVID-19

During the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, scientists from different areas are looking for alternatives to fight it. SARS-CoV-2, the cause of the infectious respiratory disease COVID-19, is mainly transmitted through direct or indirect contact with infected respiratory droplets. The integrity of the virus structure is crucial for its viability to attack human cells. Quaternary ammonium salts are characterized by having antiviral capabilities which alter or destroy the structure of the viral capsid. In this work, polypropylene (PP)/(1-Hexadecyl) trimethyl-ammonium bromide (CTAB) composites have been prepared in order to create an antiviral material. The composites were melt processed and blown to produce thin films. The CTAB content on the antiviral effect was evaluated using antibodies and serum from infected patients with the SARS-CoV-2 virus. In addition, the mechanical and thermal properties of blown films were investigated, and CTAB release kinetics from the films was followed by UV-Vis. The results indicate that the virus tends to remain less on the polymer surface by increasing the amount of CTAB in the PP matrix.

Sheet-like Janus hemostatic dressings with synergistic effects of cardanol hemostasis and quaternary ammonium salt antibacterial action

It is of utmost importance that bleeding should be stopped and infection be prevented in people with trauma. In this study, an anisotropic Janus mesoporous silica nanosheet (MSNS) with different functional groups was designed and prepared. In order to endow both sides of the MSNS with independent fast hemostasis and effective antibacterial action, the MSNS was modified with cardanol (CA) and 2,3-epoxypropyltrimethylammonium (GTA). The addition of CA significantly improved the hemostatic property of the MSNS. In a SD rat femoral artery injury model, the hemostatic time of CA-MSNS-GTA was 47% shorter than that of the MSNS, attributed to the sealing of the hydrophobic alkyl side chain and the adhesion of phenolic hydroxyl groups in CA. CA-MSNS-GTA could form a three-dimensional network with fibrin to further accelerate the coagulation process. This Janus material exhibited excellent antibacterial effects (∼90%) against Gram-positive bacteria (S. pneumoniae) and Gram-negative bacteria (E. coli) due to the presence of GTA. The cytotoxicity test showed that CA-MSNS-GTA exhibited biosafety, which provided safety guarantee for clinical applications in the future. This Janus dressing with different functions on two opposite sides provides synergetic multifunctional effects during wound healing.

Design, synthesis, and insecticidal and fungicidal activities of quaternary ammonium salt derivatives of a triazolyphenyl isoxazoline insecticide

BACKGROUND

Insect pests seriously decrease the yield and quality of agricultural crops. Resistance to commonly used insecticides is increasingly undermining their effectiveness, and therefore the development of agents with novel modes of action is desirable. Isoxazolines are a new class of insecticides that act on γ-aminobutyric acid (GABA) gated chloride channels. In this work, we used the highly active 4-triazolyphenyl isoxazoline DP-9 as a parent structure to design and synthesize a series of quaternary ammonium salt (QAS) derivatives, and we systematically evaluated their insecticidal and antifungal activities.

RESULTS

Many of the synthesized QASs exhibit insecticidal activities equivalent to or higher than that of DP-9. In particular, compounds I-31 (93%, 0.00005 mg/L) and I-34 (80%, 0.00001 mg/L) showed insecticidal activities against diamondback moth larvae that were 2-10 times higher than those of fluralaner (70%, 0.0001 mg/L) and DP-9 (80%, 0.0001 mg/L), in addition to showing excellent activities against oriental armyworm, fall armyworm, cotton bollworm, corn borer, and mosquito larvae. Furthermore, all of the synthesized compounds also showed broad-spectrum fungicidal activities.

CONCLUSION

The insecticidal activities of QAS derivatives of DP-9 were the same as or better than the activity of DP-9. Compounds I-31 and I-34 showed better insecticidal activities against diamondback moth larvae than fluralaner and DP-9, and thus are promising new candidates for insecticide research.

Quaternary Phosphonium Compounds: An Examination of Non-Nitrogenous Cationic Amphiphiles That Evade Disinfectant Resistance

Quaternary ammonium compounds (QACs) serve as mainstays in the formulation of disinfectants and antiseptics. However, an over-reliance and misuse of our limited QAC arsenal has driven the development and spread of resistance to these compounds, as well as co-resistance to common antibiotics. Extensive use of these compounds throughout the COVID-19 pandemic thus raises concern for the accelerated proliferation of antimicrobial resistance and demands for next-generation antimicrobials with divergent architectures that may evade resistance. To this end, we endeavored to expand beyond canonical ammonium scaffolds and examine quaternary phosphonium compounds (QPCs). Accordingly, a synthetic and biological investigation into a library of novel QPCs unveiled biscationic QPCs to be effective antimicrobial scaffolds with improved broad-spectrum activities compared to commercial QACs. Notably, a subset of these compounds was found to be less effective against a known QAC-resistant strain of MRSA. Bioinformatic analysis revealed the unique presence of a family of small multiresistant transporter proteins, hypothesized to enable efflux-mediated resistance to QACs and QPCs. Further investigation of this resistance mechanism through efflux-pump inhibition and membrane depolarization assays illustrated the superior ability of P6P-10,10 to perturb the cell membrane and exert the observed broad-spectrum potency compared to its commercial counterparts. Collectively, this work highlights the promise of biscationic phosphonium compounds as next-generation disinfectant molecules with potent bioactivities, thereby laying the foundation for future studies into the synthesis and biological investigation of this nascent antimicrobial class.

Synthesis and Antimicrobial Evaluation of Bis-morpholine Triazine Quaternary Ammonium Salts

Efficient, environmentally and economically sustainable, and nontoxic antibacterial products are of global relevance in the fight against microorganism contamination. In this work, an easy and straightforward method for the synthesis of bis-morpholino triazine quaternary ammonium salts (bis-mTQAS) is reported, starting from 2,4,6-trichloro-1,3,5-triazine or 2,4-dichloro-6-methoxy-1,3,5-triazine and various N-alkylmorpholines. Bis-mTQAS were tested as antimicrobials against Gram-negative and Gram-positive bacterial strains. The best-performing bis-mTQAS were found to achieve total disinfection against Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922 at 50 and 400 μg/mL, respectively. Distinctively, bis-mTQAS with the highest antimicrobial efficiency had lowest cytotoxicity.

Study of Ground State Interactions of Enantiopure Chiral Quaternary Ammonium Salts and Amides, Nitroalkanes, Nitroalkenes, Esters, Heterocycles, Ketones and Fluoroamides

Chiral phase-transfer catalysis provides high level of enantiocontrol, however no experimental data showed the interaction of catalysts and substrates. 1 H NMR titration was carried out on Cinchona and Maruoka ammonium bromides vs. nitro, carbonyl, heterocycles, and N-F containing compounds. It was found that neutral organic species and quaternary ammonium salts interacted via an ensemble of catalyst + N-C-H and (sp2 )C-H, specific for each substrate studied. The correspondent BArF salts interacted with carbonyls via a diverse set of + N-C-H and (sp2 )C-H compared to bromides. This data suggests that BArF ammonium salts may display a different enantioselectivity profile. Although not providing quantitative data for the affinity constants, the data reported proofs that chiral ammonium salts coordinate with substrates, prior to transition state, through specific C-H positions in their structures, providing a new rational to rationalize the origin of enantioselectivity in their catalyses.

Antimicrobial Activity of 1,3,4-Oxadiazole Derivatives

The worldwide development of antimicrobial resistance forces scientists to search for new compounds to which microbes would be sensitive. Many new structures contain the 1,3,4-oxadiazole ring, which have shown various antimicrobial activity, e.g., antibacterial, antitubercular, antifungal, antiprotozoal and antiviral. In many publications, the activity of new compounds exceeds the activity of already known antibiotics and other antimicrobial agents, so their potential as new drugs is very promising. The review of active antimicrobial 1,3,4-oxadiazole derivatives is based on the literature from 2015 to 2021.

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Quaternary ammonium compounds (QACs) belong to a well-known class of cationic biocides with a broad spectrum of antimicrobial activity. They are used as essential components in surfactants, personal hygiene products, cosmetics, softeners, dyes, biological dyes, antiseptics, and disinfectants. Simple but varied in their structure, QACs are divided into several subclasses: Mono-, bis-, multi-, and poly-derivatives. Since the beginning of the 20th century, a significant amount of work has been dedicated to the advancement of this class of biocides. Thus, more than 700 articles on QACs were published only in 2020, according to the modern literature. The structural variability and diverse biological activity of ionic liquids (ILs) make them highly prospective for developing new types of biocides. QACs and ILs bear a common key element in the molecular structure-quaternary positively charged nitrogen atoms within a cyclic or acyclic structural framework. The state-of-the-art research level and paramount demand in modern society recall the rapid development of a new generation of tunable antimicrobials. This review focuses on the main QACs exhibiting antimicrobial and antifungal properties, commercial products based on QACs, and the latest discoveries in QACs and ILs connected with biocide development.

The mode of antibacterial action of quaternary N-benzylimidazole salts against emerging opportunistic pathogens

Quaternary ammonium compounds (QACs) are antimicrobial agents displaying a broad spectrum of activity due to their mechanism of action targeting the bacterial membrane. The emergence of bacterial resistance to QACs, especially in times of pandemics, requires the continuous search for new and potent QACs structures. Here we report the synthesis and biological evaluation of QACs based on imidazole derivative, N-benzylimidazole. The antimicrobial activity was tested against a range of pathogenic bacteria and fungi, both ATCC and clinical isolates, showing varying activities ranging in minimal inhibitory concentrations (MICs) from as low as 7 ng/mL. The most promising compound, N-tetradecyl derivative (BnI-14), proved to be very potent against bacterial biofilms, even at sub-MIC doses, suggesting interference with the bacterial growth and/or division process. The BnI-14 treatment induces bacterial membrane disruption, as observed by fluorescence spectroscopy and atomic force microscopy and it also binds to DNA indicating that bacterial membrane might not be the only cellular target of QACs. Most importantly, BnI-14 exhibits low toxicity to healthy human cell lines, suggesting that N-benzylimidazolium-based QACs may be promising new antimicrobial agents.

Design, synthesis, and biodistribution studies of new analogues of marine alkaloids: Potent in vitro and in vivo fungicidal agents against Candida spp

Invasive candidiasis, such as intra-abdominal candidiasis (IAC), is a significant cause of morbidity and mortality worldwide. IAC is still poorly understood, and its treatment represents a challenge for public health. In this study, we showed the in vitro anti-Candida activity of four alkaloid synthetic derivatives and their antifungal potential in a murine model of IAC. The biological effects of alkaloids were evaluated against Candida spp. through the determination of the minimum inhibitory concentration (MIC). For the alkaloids that showed antifungal activity, the fungicidal concentration, time-kill curve, synergism with azoles and polyenes, phenotypic effects, and the effect against virulence factors were also determined. The most active alkaloids were selected for in vivo assays. The compounds 6a and 6b were active against C. albicans, C. glabrata, and C. tropicalis (MIC 7.8 μg/mL) and showed promising antifungal activity against C. krusei (MIC 3.9 μg/mL). The compound 6a presented a potent fungicidal effect in vitro, eliminating the yeast C. albicans after 8 h of incubation at MIC. An important in vitro synergistic effect with ketoconazole was observed for these two alkaloids. They also induced the lysis of fungal cells by binding to the ergosterol of the membrane. Besides that, 6a and 6b were able to reduce yeast-to-hyphal transition in C. albicans, as well as inhibit the biofilm formation of this pathogen. In the in vivo assay, the compound 6a did not show acute toxicity and was mainly absorbed by the liver, spleen, and lung after a parenteral administration. Also, this analogue significantly reduced the fungal load of C. albicans on the kidney and spleen of animals with IAC. Therefore, these results showed that the compound 6a is a potent anti-Candida agent in vitro and in vivo.

Evaluation of Antibacterial Activity of Three Quaternary Ammonium Disinfectants on Different Germs Isolated from the Hospital Environment

BACKGROUND

The microbiological risk of the hospital environment, including inert surfaces, medical devices, and equipment, represents a real problem.

OBJECTIVE

This study is aimed at demonstrating and assessing the antibacterial activity of three synthetic disinfectants classified as quaternary ammoniums on different bacterial strains (Gram-negative and Gram-positive like Escherichia coli, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus) isolated from the hospital environment. The reference strains included Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 29213, and Pseudomonas aeruginosa ATCC 27853 used as negative control strains.

METHOD

Three quaternary ammonium disinfectants were tested: DDN9® (0.5%) which contains didecylmethylpolyoxyethylammonium propionate as an active substance, spray (0.4%) containing quaternary ammonium compounds, and Phagosurf ND® (0.4%) with didecyldimethylammonium chloride. Their effect was evaluated using the disk diffusion technique and the broth dilution methods, allowing the Minimum Inhibitory Concentration (MIC) and then the Minimum Bactericidal Concentration (MBC).

RESULT

Only the growth of Gram-positive bacteria and some strains of Gram-negative bacteria were inhibited by the three synthetic disinfectants. NDD9® demonstrated an antibacterial effect only against the Gram-positive strains (S. aureus and S. aureus ATCC 29213) with a MIC of 0.25 mg/ml. The disinfectant spray showed effect against all four strains including E. coli (9), S. aureus, E. coli ATCC 25922, and P. aeruginosa ATCC 27853 with an inhibitory concentration of 4 mg/ml, while the growth of S. aureus ATCC 29213 was inhibited at 2 mg/ml. The third disinfectant, Phagosurf ND®, inhibited only the growth of S. aureus ATCC 29213 at a MIC of 4 mg/ml.

CONCLUSION

This study is the first here in Morocco to evaluate the bacterial activity of products intended for the control of the healthcare environment. The results obtained on the three disinfectants tested reveal an ineffectiveness against some isolated strains from the hospital environment.

Metallocene QACs: The Incorporation of Ferrocene Moieties into monoQAC and bisQAC Structures

Inspired by the incorporation of metallocene functionalities into a variety of bioactive structures, particularly antimicrobial peptides, we endeavored to broaden the structural variety of quaternary ammonium compounds (QACs) by the incorporation of the ferrocene moiety. Accordingly, 23 ferrocene-containing mono- and bisQACs were prepared in high yields and tested for activity against a variety of bacteria, including Gram-negative strains and a panel of clinically isolated MRSA strains. Ferrocene QACs were shown to be effective antiseptics with some displaying single-digit micromolar activity against all bacteria tested, demonstrating yet another step in the expansion of structural variety of antiseptic QACs.

Advancements in the Development of Non-Nitrogen-Based Amphiphilic Antiseptics to Overcome Pathogenic Bacterial Resistance

The prevalence of quaternary ammonium compounds (QACs) as common disinfecting agents for the past century has led bacteria to develop resistance to such compounds. Given the alarming increase in resistant strains, new strategies are required to combat this rise in resistance. Recent efforts to probe and combat bacterial resistance have focused on studies of multiQACs. Relatively unexplored, however, have been changes to the primary atom bearing positive charge in these antiseptics. Here we review the current state of the field of both phosphonium and sulfonium amphiphilic antiseptics, both of which hold promise as novel means to address bacterial resistance.

Synthetic Polymeric Antibacterial Hydrogel for Methicillin-Resistant Staphylococcus aureus-Infected Wound Healing: Nanoantimicrobial Self-Assembly, Drug- and Cytokine-Free Strategy

Antibacterial hydrogels are attracting extensive attention in soft tissue repair and regeneration, including bacteria-infected-wound healing. The abuse of antibiotics leads to drug resistance. Recent developments have demonstrated that the delivery of inorganic bactericidal agents in hydrogels can drive the wound healing process; however, this approach is complicated by external light stimuli, cytotoxicity, nondegradability, and sophisticated fabrication. Herein, an inherent antibacterial, bioresorbable hydrogel was developed by the spontaneous self-aggregation of amphiphilic, oxadiazole-group-decorated quaternary ammonium salts (QAS)-conjugated poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCEC-QAS) micellar nanoantimicrobials for methicillin-resistant Staphylococcus aureus (MRSA)-infected cutaneous wound healing. The PCEC-QAS hydrogel showed a stable gel state within the temperature range of 5-50 °C and antibacterial efficacy against both Gram-negative and -positive bacteria in vitro and in vivo. Additionally, the PCEC-QAS hydrogel facilitated the cell spreading, proliferation, and migration without cytotoxicity. An in vivo degradation and skin defect healing study suggested the PCEC-QAS hydrogel was totally absorbed without local or systemic toxicity and could promote wound repair in the absence of drugs, cytokines, or cells. Significantly, this hydrogel accelerated the regeneration of a MRSA-infected full-thickness impaired skin wound by successfully reconstructing an intact and thick epidermis similar to normal mouse skin. Collectively, a self-assembling PCEC-QAS antibacterial hydrogel is a promising dressing material to promote skin regeneration and prevent bacterial infection without additional drugs, cells, light irradiation, or delivery systems, providing a simple but effective strategy for treating dermal wounds.

The wide-spectrum antimicrobial effect of novel N-alkyl monoquaternary ammonium salts and their mixtures; the QSAR study against bacteria

Quaternary ammonium salts (QASs) have been widely used for disinfection purposes because of their low price, high efficacy and low human toxicity for decades. However, precise mechanisms of action nor the powerful versatile agent against all antimicrobial species are known. In this study we have prepared 43 novel N-alkyl monoquaternary ammonium salts including 7 N,N-dialkyl monoquaternary ammonium salts differing bearing alkyl chain either of 12, 14 or 16 carbons. Together with 15 already published QASs we have studied the antimicrobial efficacy of all water-soluble compounds together with standard benzalkonium salts against Gram-positive (G+) and Gram-negative (G-) bacteria, anaerobic spore-forming Cl. difficile, yeasts, filamentous fungi and enveloped Varicella zoster virus (VZV). To address the mechanism of action, lipophilicity seems to be a key parameter which determines antimicrobial efficacy, however, exceptions are likely to occur and therefore QSAR analysis on the efficacy against G+ and G- bacteria was applied. We showed that antibacterial activity is higher when the molecule is larger, more lipophilic, less polar, and contains fewer oxygen atoms, fewer methyl groups bound to heteroatoms or fewer hydrogen atoms bound to polarized carbon atoms. In addition, from an application point of view, we have formulated mixtures, on the basis of obtained efficiency of individual compounds, in order to receive wide-spectrum agent. All formulated mixtures completely eradicated tested G+ and G- strains, including the multidrug-resistant P. aeruginosa as well as in case of yeasts. However, effect on A. fumigatus, Cl. difficile and VZV the exposition towards mixture resulted in significant reduction only. Finally, 3 out of 4 formulated mixtures were safer than reference commercial agent based on benzalkonium salts only in the skin irritation test using reconstructed human epidermidis.

Further Investigations into Rigidity-Activity Relationships in BisQAC Amphiphilic Antiseptics

Thirty-six biscationic quaternary ammonium compounds were efficiently synthesized in one step to examine the effect of molecular geometry of two-carbon linkers on antimicrobial activity. The synthesized compounds showed strong antimicrobial activity against a panel of both Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). While the linker geometry showed only a modest correlation with antimicrobial activity, several of the synthesized bisQACs are promising potential antiseptics due to good antimicrobial activity (MIC≤2 μM) and their higher therapeutic indices compared to previously reported QACs.

Diversity-oriented synthesis and antifungal activities of novel pimprinine derivative bearing a 1,3,4-oxadiazole-5-thioether moiety

Based on the strategy of diversity-oriented synthesis and the structures of natural product pimprinine and streptochlorin, two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized under the optimized reaction conditions. Biological assays conducted at Syngenta showed the designed derivatives displayed an altered pattern of biological activity, of which 5h was identified as the most promising compound with strong activity against Pythium dissimile and also a broad antifungal spectrum in primary screening. Further structural optimization of pimprinine and streptochlorin derivatives is well under way, aiming to discover synthetic analogues with improved antifungal activity. Two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized through diversity-oriented synthesis strategy under the optimized conditions. Biological assays showed the designed derivatives exhibited potential activity.

Crystal structure of N 1,N 3-bis(2-hydroxyethyl)-N 1, N 1,N 3,N 3-tetramethylpropane-1,3-diaminium dibromide, C11H28Br2N2O2

C11H28Br2N2O2, triclinic, P1̄ (no. 2), a = 12.0519(11) Å, b = 12.6670(12) Å, c = 12.9161(12) Å, α = 117.088(3)°, β = 92.459(1)°, γ = 108.199(2))°, V = 1627.2(3) Å3, Z = 4, R gt(F) = 0.0645, wR ref(F 2) = 0.1632, T = 298(2) K.

Ionic liquids strongly affect the interaction of bacteria with magnesium oxide and silica nanoparticles

Quaternary ammonium theophylline-based ionic liquids and imidazolium-based ionic liquids, magnesium oxide and silica nanoparticles were used in order to investigate the interaction with Gram negative Escherichia coli and Gram positive Bacillus cereus. The changes of bacterial sensitivity to both nanoparticles (NPs) and ionic liquids (ILs) were examined. In order to assess the impact of ILs on the interaction of nanoparticles with bacteria, respirometric analysis, activity of dehydrogenases, peroxidase analyses as well as scanning and fluorescence microscopy examinations were conducted. The interactions of ILs with nanoparticles based on adsorption and sedimentation tests were also investigated in order to assess how the ILs affect the agglomeration of NPs. It was assumed, as the main hypothesis of the present studies, that the differences in sensitivity of bacteria to combined ILs and NPs can be observed, even if the concentration of both compounds are below the minimum inhibitory concentration (MIC). The results indicated that ILs strongly affected the sensitivity of bacteria to nanoparticles however, the changes of sensitivity depended on the surface characteristics of the nanoparticles. The presence of ILs at non-lethal concentrations caused an increase of bacterial sensitivity to MgO nanoparticles. Notably, the sensitivity of Gram positive bacteria increased significantly when ILs were present. This was an important observation because the toxicity of nanoparticles toward Gram positive bacteria is usually lower than their toxicity toward Gram negative bacteria. Using silica nanoparticles, the presence of ionic liquids caused the adsorption of bacteria onto the surface of nanoparticle agglomerates. In conclusion, two opposing effects have been observed. On the one hand, the toxicity of MgO NPs in the presence of ILs has increased. On the other hand, the presence of silica nanoparticles caused a decreased sensitivity of both types of bacteria toward ILs. Our studies indicate potentially useful processes in many environmantal protection technologies like water treatment where flocculation and disinfection are extremely needed.

Antibacterial performance of polymer quaternary ammonium salt-capped silver nanoparticles on Bacillus subtilis in water

In this study, we prepared polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) and investigated their antimicrobial activities. The antimicrobial effectiveness of PQAS–AgNPs on Bacillus subtilis (B. subtilis), and the effect of dose, pH, chloride ion and humic acid (HA) were studied. It was found that PQAS–AgNPs revealed excellent antimicrobial activity to B. subtilis, compared with polyvinylpyrrolidone-capped silver nanoparticles (PVP-AgNPs), which was the reference antimicrobial material. The positive surface, the antimicrobial activity of PQAS, and the synergistic antibacterial effect between PQAS and AgNPs contributed to the significant antibacterial superiority of PQAS–AgNPs. This study demonstrated that the impact of the dose of the material was positive and the microbiocidal efficacy of PQAS–AgNPs was stronger at lower pH. In addition, the antibacterial performance of PQAS–AgNPs decreased in the presence of Cl⁻ and HA. Finally, in combination with the results of FCM and adenosine triphosphate (ATP) content, it was found that PQAS–AgNPs destroyed the respiratory chain of bacterial cells, reduced the synthesis of ATP, and destroyed the cell wall and cell membrane function.

Polymer quaternary ammonium salt–capped silver nanoparticles (PQAS–AgNPs) were synthesized, and they exhibited significant antibacterial capacity against Bacillus subtilis.