Antimicrobial Activity and SAR Study of New Gemini Imidazolium-Based Chlorides

Antimicrobial Activity Classification of Imidazolium Derivatives Predicted by Artificial Neural Networks

PURPOSE

This study assesses the Multilayer Perceptron (MLP) neural network, complemented by other Machine Learning techniques (CART, PCA), in predicting the antimicrobial activity of 140 newly designed imidazolium chlorides against Klebsiella pneumoniae before synthesis. Emphasis is on leveraging molecular properties for predictive analysis.

METHODS

Classification and regression decision trees (CART) identified the top 200 predictive molecular descriptors. Principal Component Analysis (PCA) reduced these descriptors to 5 components, retaining 99.57% of raw data information. Antimicrobial activity, categorized as high or low, was based on experimentally proven minimal inhibitory concentration (MIC), with a cut-point at MIC = 0.856 mol/L. A 12-fold cross-validation trained the MLP (architecture 5-12-2 with 5 Principal Components).

RESULTS

The MLP exhibited commendable performance, achieving almost 90% correct classifications across learning, validation, and test sets, outperforming models without PCA dimension reduction. Key metrics, including accuracy (0.907), sensitivity (0.905), specificity (0.909), and precision (0.891), were notably high. These results highlight the MLP model's efficacy with PCA as a high-quality classifier for determining antimicrobial activity.

CONCLUSIONS

The study concludes that the MLP neural network, along with CART and PCA, is a robust tool for predicting the antimicrobial activity class of imidazolium chlorides against Klebsiella pneumoniae. CART and PCA, used in this study, allowed input variable reduction without significant information loss. High classification accuracy and associated metrics affirm the method's potential utility in pre-synthesis assessments, offering valuable insights for antimicrobial compound design.

Surface-Enhanced Raman Scattering (SERS) in Combination with PCA and PLS-DA for the Evaluation of Antibacterial Activity of 1-Isopentyl-3-pentyl-1H-imidazole-3-ium Bromide against Bacillus subtilis

In the current study, surface-enhanced Raman scattering (SERS) was performed to evaluate the antibacterial activity of lab-synthesized drug (1-isopentyl-3-pentyl-1H-imidazole-3-ium bromide salt) and commercial drug tinidazole againstBacillus subtilis. The changes in SERS spectral features were studied for unexposed bacillus and exposed one with various dosages of drug synthesized in the lab (1-isopentyl-3-pentyl-1H-imidazole-3-ium bromide salt), and SERS bands were assigned associated with the drug-induced biochemical alterations in bacteria. Multivariate data analysis tools including principal component analysis (PCA) and partial least-squares discriminant analysis (PLS-DA) have been utilized to analyze the antibacterial activity of the imidazole derivative (lab drug). PCA was employed in differentiating all the SERS spectral data sets associated with the various doses of the lab-synthesized drug. There is clear discrimination among the spectral data sets of a bacterial strain treated with different concentrations of the drug, which are analyzed by PLS-DA with 86% area under the curve in receiver operating curve (ROC), 99% sensitivity, 100% accuracy, and 98% specificity. Various dominant spectral features are observed with a gradual increase in the different concentrations of the applied drug including 715, 850, 1002, 1132, 1237, 1396, 1416, and 1453 cm-1, which indicate the possible biochemical changes caused in bacteria during the antibacterial activity of the lab-synthesized drug. Overall, the findings show that imidazole and imidazolium compounds generated from tinidazole with various alkyl lengths in the amide substitution can be effective antibacterial agents with low cytotoxicity in humans, and these results indicate the efficiency of SERS in pharmaceuticals and biomedical applications.

Efficient Antibacterial Dimeric Nitro Imidazolium Type of Ionic Liquids from a Simple Synthetic Approach

Synthesis of dimeric nitro-substituted imidazolium salts under the conventional/solvent-free method is reported. The solvent-free method is more important than the conventional one because of its shorter reaction time, higher yield from easily available starting material, environmental safety, and so forth. Counter anion exchange is carried out using inorganic salt, which is dissolved in deionized water at room temperature. In antibacterial studies, dimeric nitro-substituted imidazolium cations with bromide counter anions showed excellent inhibition against E. coli and P. aeruginosa bacteria. These experimental results were further supported by molecular docking studies. All the compounds (3-6) (a-d) showed excellent antibacterial activity than the standard drugs (gentamycin, nalidixic acid, oflaxacin, ciproflaxacin, and amikacin). Molecular docking studies showed strong hydrogen bonding, polar and hydrophobic interactions between the dimeric imidazolium salts, and Escherichia coli/Pseudomonas aeruginosa/Proteus vulgaris/Staphylococcus aureus receptors.

Antimicrobial and Cytotoxic Activity of Novel Imidazolium-Based Ionic Liquids

In this study, a series of 10 novel 1-methyl-3-octyloxymethylimidazolium derivatives carrying various anionic moieties (4-hydroxybenzenesulfonate, benzenesulfonate, carvacroloxyacetate, chloride, formate, propionate, thymoloxyacetate, vanillinoxyacetate, eugenoloxyacetate and trimethylacetate) were synthesized. Compounds were tested for their antimicrobial activity against six microbe strains (Staph-ylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, Enterococcus faecalis, and Candida albicans), cytotoxic activity against the mouse melanoma cell line (B16 F10), and surface active properties. All synthesized compounds exhibited antimicrobial activity (expressed as minimum inhibitory concentration; in range of 0.10–27.82 mM/L), especially against Gram-positive bacteria and fungi. In addition, all compounds demonstrated cytotoxicity on B16 F10 cells (IC50 values 0.0101–0.0197 mM/L). Surface properties defined as CMC values, ranged from 0.72 to 32.35 mmol L-1. The obtained results provide an insight into the promising activity of a novel group of quaternary imidazolium derivatives having ionic liquid properties. The most potent compounds, containing a thymoloxyacetate and eugenoloxyacetate moiety, could be candidates for new antimicrobial agents or surfactants.

Structure-Activity Relationships of the Imidazolium Compounds as Antibacterials of Staphylococcus aureus and Pseudomonas aeruginosa

This paper presents the results of structure-activity relationship (SAR) studies of 140 3,3'-(α,ω-dioxaalkan)bis(1-alkylimidazolium) chlorides. In the SAR analysis, the dominance-based rough set approach (DRSA) was used. For analyzed compounds, minimum inhibitory concentration (MIC) against strains of Staphylococcus aureus and Pseudomonas aeruginosa was determined. In order to perform the SAR analysis, a tabular information system was formed, in which tested compounds were described by means of condition attributes, characterizing the structure (substructure parameters and molecular descriptors) and their surface properties, and a decision attribute, classifying compounds with respect to values of MIC. DRSA allows to induce decision rules from data describing the compounds in terms of condition and decision attributes, and to rank condition attributes with respect to relevance using a Bayesian confirmation measure. Decision rules present the most important relationships between structure and surface properties of the compounds on one hand, and their antibacterial activity on the other hand. They also indicate directions of synthesizing more efficient antibacterial compounds. Moreover, the analysis showed differences in the application of various parameters for Gram-positive and Gram-negative strains, respectively.

Imidazole and Imidazolium Antibacterial Drugs Derived from Amino Acids

The antibacterial activity of imidazole and imidazolium salts is highly dependent upon their lipophilicity, which can be tuned through the introduction of different hydrophobic substituents on the nitrogen atoms of the imidazole or imidazolium ring of the molecule. Taking this into consideration, we have synthesized and characterized a series of imidazole and imidazolium salts derived from L-valine and L-phenylalanine containing different hydrophobic groups and tested their antibacterial activity against two model bacterial strains, Gram-negative E. coli and Gram-positive B. subtilis. Importantly, the results demonstrate that the minimum bactericidal concentration (MBC) of these derivatives can be tuned to fall close to the cytotoxicity values in eukaryotic cell lines. The MBC value of one of these compounds toward B. subtilis was found to be lower than the IC₅₀ cytotoxicity value for the control cell line, HEK-293. Furthermore, the aggregation behavior of these compounds has been studied in pure water, in cell culture media, and in mixtures thereof, in order to determine if the compounds formed self-assembled aggregates at their bioactive concentrations with the aim of determining whether the monomeric species were in fact responsible for the observed antibacterial activity. Overall, these results indicate that imidazole and imidazolium compounds derived from L-valine and L-phenylalanine—with different alkyl lengths in the amide substitution—can serve as potent antibacterial agents with low cytotoxicity to human cell lines.

The structure - Activity correlation in the family of dicationic imidazolium surfactants: Antimicrobial properties and cytotoxic effect

BACKGROUND

The development of new effective microbicide surfactants and the search for the structure-biological activity relationship is an important and promising problem. Surfactants containing imidazolium fragment attract attention of researchers in the field of chemotherapy, because these compounds often exhibit high antimicrobial activity. The aim of this work is to identify the newly synthesized surfactants from the viewpoint of their potential usefulness in pharmacology and medicine. For this purpose, a detailed study of antimicrobial, hemolytic and cytotoxic activity of dicationic alkylimidazolium surfactants of the m-s-m (Im) series with a variable length of a hydrocarbon tail (m = 10, 12) and a spacer fragment (s = 2, 3, 4) was carried out.

METHODS

Aggregation of surfactants in solutions was estimated by tensiometry and conductivity. Antimicrobial activity was determined by the serial dilution technique. Cytotoxic effects of the test compounds on human cancer and normal cells were estimated by means of the multifunctional Cytell Cell Imaging system. Cell Apoptosis Analysis was made by flow cytometry.

RESULTS

The test compounds show high antimicrobial activity against a wide range of test microorganisms and do not possess high hemolytic activity. Importantly, some of them display a bactericidal activity comparable to ciprofloxacin fluoroquinolone antibiotic against Gram-positive bacteria, including methicillin-resistant strains of S. aureus (MRSA). The cytotoxicity of the compounds against normal and tumor human cell lines has been tested as well, with cytotoxic effect and selectivity strongly controlled by structural factor and kind of cell line. Superior results were revealed for compound 10-4-10 (Im) in the case of HuTu 80 cell line (duodenal adenocarcinoma), for which IC₅₀ value at the level of doxorubicin and a markedly higher selectivity index (SI 7.5) were demonstrated. Flow cytometry assay shows apoptosis-inducing effect of this compound on HuTu 80 cells, through significant changes in the potential of mitochondrial membrane.

MAJOR CONCLUSIONS

Antibacterial properties are shown to be controlled by alkyl chain length, with the highest activity demonstrated by surfactants with decyl tail, with the length of the spacer fragment showing practically no effect. The results indicate that the mechanism of cytotoxic effect of the compounds can be associated with the induction of apoptosis via the mitochondrial pathway.

GENERAL SIGNIFICANCE

Selectivity against pathogenic microorganisms and low toxicity against eukaryotic cells allow considering dicationic imidazolium surfactants as new effective antimicrobial agents. At the same time, high selectivity against some cancer cell lines indicates the prospect of their using as components of new anticancer drugs.

Aggregation-induced emission-based ionic liquids for bacterial killing, imaging, cell labeling, and bacterial detection in blood cells

A series of aggregation-induced emission (AIE)-based imidazolium-type ionic liquids (ILs) were designed and synthesized for bacterial killing and imaging, cell labeling, and bacterial detection in blood cells. The AIE-based ILs showed antibacterial activities against both Escherichia coli and Staphylococcus aureus. The carbon chain length of substitution at the N3 position of the imidazolium cations highly affects the antibacterial properties of ILs. Owing to their AIE characteristics, the ILs could selectively capture fluorescence image of dead bacteria while killing the bacteria. The fluorescence intensity varied with the concentration of bacteria, indicating that AIE-based ILs has potential as an antibacterial material and an efficient probe for bacterial viability assay. In addition, the synthesized AIE-based ILs exhibit relatively low cytotoxicity and hemolysis rate and therefore potential for cell labeling, as well as bacterial detection in blood cells. STATEMENT OF SIGNIFICANCE: Bacteria are ubiquitous, especially the pathogenic bacteria, which pose a serious threat to human health. There is an urgent need for materials with efficient antibacterial properties and biocompatibility and without causing drug resistance. In this work, we synthesized a series of aggregation-induced emission (AIE)-doped imidazolium type ionic liquids (ILs) with multifunction potential of bacterial killing and imaging, cell labeling, and detection of bacteria from blood cells. The synthesized AIE-based ILs can image dead bacteria at the same time of killing these bacteria, which can avoid the fluorescent dyeing process. Simultaneously, the fluorescent imaging of dead bacteria can be distinguished by the naked eye, and the fluorescence intensity from the AIE-based ILs varied with the concentration of bacteria. In addition, the AIE-based ILs exhibit relatively low cytotoxicity and hemolysis rate and therefore potential for cell labeling as well as detection of bacteria from red blood cell suspension.

Synthesis and Antibacterial Evaluation of Bis-thiazolium, Bis-imidazolium, and Bis-triazolium Derivatives

Given the worldwide spread of bacterial drug resistance, there is an urgent need to develop new compounds that exhibit potent antibacterial activity and that are unimpaired by this phenomenon. Quaternary ammonium compounds have been used for many years as disinfectants, but recent advances have shown that polycationic derivatives exhibit much stronger activity and are less prone to bacterial resistance than commonly used monocationic compounds. In this sense, we prepared three series of new bis-cationic compounds: bis-thiazoliums, bis-imidazoliums, and bis-1,2,4-triazoliums. If some compounds of the first series showed fair antibacterial activity, most of those belonging to the two other series were highly potent, with minimum inhibitory concentrations close to 1 μg mL^-1 . Some of them also exhibited low toxicity toward eukaryotic MRC-5 lung fibroblasts, and we showed that this toxicity is clearly correlated with clogP. Finally, four selected compounds were found to exhibit a clear bactericidal effect.

Durably Antibacterial and Bacterially Antiadhesive Cotton Fabrics Coated by Cationic Fluorinated Polymers

Considerable attention has been devoted to producing antibacterial fabrics due to their very wide applications in medicine, hygiene, hospital, etc. However, the poor antibacterial durability and bad bacterial antiadhesion capacity of most existing antibacterial fabrics limit their applications. In this work, a series of antibacterial and polymeric quaternary ammonium monomers with different alkyl chain length were successfully synthesized to copolymerize with fluorine-containing and other acrylic monomers to generate cationic fluorinated polymer emulsions and durably antibacterial and bacterially antiadhesive cotton fabrics. The relation between antibacterial constituent and its antibacterial activity was investigated. The study indicated that the alkyl chain length and contents of the antibacterial monomers, as well as the add-on percentage of polymer greatly influenced the antibacterial activities of the fabrics. In addition, it was found that incorporation of fluorine component into the polymer greatly enhanced the antibacterial activity and bacterial antiadhesion of the treated fabrics due to the low surface energy induced hydrophobicity. Finally, antibacterial and antiadhesive models of action of the obtained fabrics were illustrated.

Advances in the synthesis, molecular architectures and potential applications of gemini surfactants

Gemini surfactants have been the subject of intensive scrutiny by virtue of their unique combination of physical and chemical properties and being used in ordinary household objects to multifarious industrial processes. In this review, we summarize the recent developments of gemini surfactants, highlighting the classification of gemini surfactants based on the variation in headgroup polarity, flexibility/rigidity of spacer, hydrophobic alkyl chain and counterion along with potential applications of gemini surfactants, depicting the truly remarkable journey of gemini surfactants that has just come of age. We have focused on those objectives which will act as suitable candidates to take the field forward. The preceding information will permit us to estimate the effect of structural variation on the aggregation behavior of gemini surfactants for nanoscience and biological applications like antimicrobial, anti-fungal agent, better gene and drug delivery agent with low cytotoxicity and biodegradability, which makes them more advantageous for a number of technological processes and hence reduces the impact of these gemini surfactants on the environment.

Structure-Antibacterial Activity Relationships of Imidazolium-Type Ionic Liquid Monomers, Poly(ionic liquids) and Poly(ionic liquid) Membranes: Effect of Alkyl Chain Length and Cations

The structure-antibacterial activity relationship between the small molecular compounds and polymers are still elusive. Here, imidazolium-type ionic liquid (IL) monomers and their corresponding poly(ionic liquids) (PILs) and poly(ionic liquid) membranes were synthesized. The effect of chemical structure, including carbon chain length of substitution at the N3 position and charge density of cations (mono- or bis-imidazolium) on the antimicrobial activities against both Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was investigated by determination of minimum inhibitory concentration (MIC). The antibacterial activities of both ILs and PILs were improved with the increase of the alkyl chain length and higher charge density (bis-cations) of imidazolium cations. Moreover, PILs exhibited lower MIC values relative to the IL monomers. However, the antibacterial activities of PIL membranes showed no correlation to those of their analogous small molecule IL monomers and PILs, which increased with the charge density (bis-cations) while decreasing with the increase of alkyl chain length. The results indicated that antibacterial property studies on small molecules and homopolymers may not provide a solid basis for evaluating that in corresponding polymer membranes.

Structural diversity, physicochemical properties and application of imidazolium surfactants: Recent advances

The current review covers recent advances on development and investigation of cationic surfactants containing imidazolium headgroup, which are being extensively investigated for their self-aggregation properties and are currently being utilized in various conventional and non-conventional application areas. These surfactants are being used as: soft template for synthesis of mesoporous/microporous materials, drug and gene delivery agent, stabilizing agent for nanoparticles, dispersants for single/multi walled carbon nanotubes, antimicrobial and antifungal agent, viscosity modifiers, preparing nanocomposite materials, stabilizing microemulsions, corrosion inhibitors and catalyst for organic reactions. Recently several structural derivatives of these surfactants have been developed having many interesting physicochemical properties and they have demonstrated enormous potential in the area of nanotechnology, material science and biomedical science.

Prediction of antifungal activity of gemini imidazolium compounds

The progress of antimicrobial therapy contributes to the development of strains of fungi resistant to antimicrobial drugs. Since cationic surfactants have been described as good antifungals, we present a SAR study of a novel homologous series of 140 bis-quaternary imidazolium chlorides and analyze them with respect to their biological activity against Candida albicans as one of the major opportunistic pathogens causing a wide spectrum of diseases in human beings. We characterize a set of features of these compounds, concerning their structure, molecular descriptors, and surface active properties. SAR study was conducted with the help of the Dominance-Based Rough Set Approach (DRSA), which involves identification of relevant features and relevant combinations of features being in strong relationship with a high antifungal activity of the compounds. The SAR study shows, moreover, that the antifungal activity is dependent on the type of substituents and their position at the chloride moiety, as well as on the surface active properties of the compounds. We also show that molecular descriptors MlogP, HOMO-LUMO gap, total structure connectivity index, and Wiener index may be useful in prediction of antifungal activity of new chemical compounds.