Aggregation behavior and antimicrobial activity of ester-functionalized imidazolium- and pyridinium-based ionic liquids in aqueous solution

Exploring the Properties of Unilamellar Vesicle Bilayers Formed by Ionic Liquid Surfactants for Future Applications in Nanomedicine

Two ionic liquids (ILs) with amphiphilic properties composed of 1-butyl-3-methylimidazolium dioctylsulfosuccinate (bmim-AOT) and 1-hexyl-3-methylimidazolium dioctylsulfosuccinate (hmim-AOT) form unilamellar vesicles spontaneously simply by dissolving the IL-like surfactant in water. These novel vesicles were characterized using two different and highly sensitive fluorescent probes: 6-propionyl-2-(dimethylaminonaphthalene) (PRODAN) and trans-4-[4-(dimethylamino)-styryl]-1-methylpyridinium iodide (HC). These fluorescent probes provide information about the physicochemical properties of the bilayer, such as micropolarity, microviscosity, and electron-donor capacity. In addition, the biocompatibility of these vesicles with the blood medium was evaluated, and their toxicity was determined using Dictyostelium discoideum amoebas. First, using PRODAN and HC, it was found that the bilayer composition and the chemical structure of the ions at the interface produced differences between both amphiphiles, making the vesicles different. Thus, the bilayer of hmim-AOT vesicles is less polar, more rigid, and has a lower electron-donor capacity than those made by bmim-AOT. Finally, the results obtained from the hemolysis studies and the growth behavior of unicellular amoebas, particularly utilizing the D. discoideum assay, showed that both vesicular systems do not produce toxic effects up to a concentration of 0.02 mg/mL. This elegant assay, devoid of animal usage, highlights the potential of these newly organized systems for the delivery of drugs and bioactive molecules of different polarities.

Techniques for recovery and recycling of ionic liquids: A review

Due to beneficial properties like non-flammability, thermal stability, low melting point and low vapor pressure, ionic liquids (ILs) have gained great interest from engineers and researchers in the past decades to replace conventional solvents. The superior characteristics of ILs make them promising for applications in fields as wide-ranging as pharmaceuticals, foods, nanoparticles synthesis, catalysis, electrochemistry and so on. To alleviate the high cost and environmental impact of ILs, various technologies have been reported to recover and purify the used ILs, as well as recycling the ILs. The aim of this article is to overview the state-of-the-art research on the recovery and recycling technologies for ILs including membrane technology, distillation, extraction, aqueous two-phase system (ATPS) and adsorption. In addition, challenges and future perspectives on ILs recovery are discussed. This review is expected to provide valuable insights for developing effective and environmentally friendly recovery methods for ILs.

Interaction and antibacterial activity of ciprofloxacin with choline based ionic liquid and CTAB: A comparative spectroscopic study

In this study, the complexation of potential chemo-therapeutic antibacterial drug, ciprofloxacin (CIP) with varying concentrations of surface active compounds (SACs) i.e., (N-(2-hydroxyethyl)-N,N-dimethyl-1-dodecanaminium bromide (12Cho.Br) and cetyltrimethylammonium bromide (CTAB) has been studied. Multispectroscopic techniques were exploited to carry out the study. The higher binding constant (Kb) value for CIP-CTAB than CIP-12Cho.Br obtained from fluorescence data revealed stronger binding of CTAB than 12Cho.Br, owing to the stronger hydrophobic-hydrophobic interaction betweeen CIP and CTAB compared to CIP and 12Cho.Br. The time resolve fluorescence decay shows changes in average lifetime (τavg) with the increasing concentration of 12Cho.Br and CTAB. The changes in τavg suggests that complex formation is taking place between CIP and 12Cho.Br / CTAB. Further, the formation of micelles by 12Cho.Br / CTAB and the effect of alkyl chain length was studied by dynamic light scattering (DLS) and zeta potential to confirm the drug complexation with 12Cho.Br and CTAB. The antibacterial activity has been performed for CIP and 12Cho.Br and CTAB. It was observed that in presence of lower concentrations of 12Cho.Br/ CTAB, the activity of the drug increased. The activity was also found cationic alkyl chain length dependent. Moreover, in-vitro cytotoxicity of CIP and its combinations with 12Cho.Br and CTAB was performed using MTT assay on HEK293 (Human embryonic kidney cells).

Microwave Encounters Ionic Liquid: Synergistic Mechanism, Synthesis and Emerging Applications

Progress in microwave (MW) energy application technology has stimulated remarkable advances in manufacturing and high-quality applications of ionic liquids (ILs) that are generally used as novel media in chemical engineering. This Review focuses on an emerging technology via the combination of MW energy and the usage of ILs, termed microwave-assisted ionic liquid (MAIL) technology. In comparison to conventional routes that rely on heat transfer through media, the contactless and unique MW heating exploits the electromagnetic wave-ions interactions to deliver energy to IL molecules, accelerating the process of material synthesis, catalytic reactions, and so on. In addition to the inherent advantages of ILs, including outstanding solubility, and well-tuned thermophysical properties, MAIL technology has exhibited great potential in process intensification to meet the requirement of efficient, economic chemical production. Here we start with an introduction to principles of MW heating, highlighting fundamental mechanisms of MW induced process intensification based on ILs. Next, the synergies of MW energy and ILs employed in materials synthesis, as well as their merits, are documented. The emerging applications of MAIL technologies are summarized in the next sections, involving tumor therapy, organic catalysis, separations, and bioconversions. Finally, the current challenges and future opportunities of this emerging technology are discussed.

Development of Cholinium-Based API Ionic Liquids with Enhanced Drug Solubility: Biological Evaluation and Interfacial Properties

We report an efficient sustainable two-step anion exchange synthetic procedure for the preparation of choline API ionic liquids (Cho-API-ILs) that contain active pharmaceutical ingredients (APIs) as anions combined with choline-based cations. We have evaluated the in vitro cytotoxicity for the synthesized compounds using three different cells lines, namely, HEK293 (normal kidney cell line), SW480, and HCT 116 (colon carcinoma cells). The solubility of APIs and Cho-API-ILs was evaluated in water/buffer solutions and was found higher for Cho-API-ILs. Further, we have investigated the antimicrobial potential of the pure APIs, ILs, and Cho-API-ILs against clinically relevant microorganisms, and the results demonstrated the promise of Cho-API-ILs as potent antimicrobial agents to treat bacterial infections. Moreover, the aggregation and adsorption properties of the Cho-API-ILs were observed by using a surface tension technique. The aggregation behavior of these Cho-API-ILs was further supported by conductivity and pyrene probe fluorescence. The thermodynamics of aggregation for Cho-API-ILs has been assessed from the temperature dependence of surface tension. The micellar size and their stability have been studied by dynamic light scattering, transmission electron microscopy, and zeta potential. Therefore, the duality in the nature of Cho-API-ILs has been explored with the upgradation of their physical, chemical, and biopharmaceutical properties, which enhance the opportunities for advances in pharmaceutical sciences.

Surface-Active Ionic Liquids and Surface-Active Quaternary Ammonium Salts from Synthesis, Characterization to Antimicrobial Properties

The present work provides new evidence of the ongoing potential of surface-active ionic liquids (SAILs) and surface-active quaternary ammonium salts (surface-active QASs). To achieve this, a series of compounds were synthesized with a yield of ≥85%, and their thermal analyses were studied. Additionally, antimicrobial activity against both human pathogenic and soil microorganisms was investigated. Subsequently, their surface properties were explored with the aim of utilizing SAILs and surface-active QASs as alternatives to commercial amphiphilic compounds. Finally, we analyzed the wettability of the leaves' surface of plants occurring in agricultural fields at different temperatures (from 5 to 25 °C) and the model plant membrane of leaves. Our results show that the synthesized compounds exhibit higher activity than their commercial analogues such as, i.e., didecyldimethylammonium chloride (DDAC) and dodecyltrimethylammonium bromide (C12TAB), for which the CMC values are 2 mM and 15 mM. The effectiveness of the antimicrobial properties of synthesized compounds relies on their hydrophobic nature accompanied by a cut-off effect. Moreover, the best wettability of the leaves' surface was observed at 25 °C. Our research has yielded valuable insights into the potential effectiveness of SAILs and surface-active QASs as versatile compounds, offering a promising alternative to established antimicrobials and crop protection agents, all the while preserving substantial surface activity.

Purposefully Designed Surfactants for Facile and Controllable Gold Colloidal Nanocrystal Synthesis

Three new cationic surfactants-N-cetyl-bis(2-dimethylaminoethyl)ether bromide (CBDEB), N-dodecyl-bis(2-dimethylaminoethyl)ether bromide (DBDEB), and N-hexyl-bis(2-dimethylaminoethyl)ether bromide (HBDEB)-have been designed herein using a simple and tailorable synthesis route. CBDEB and DBDEB, the 16- and 12-carbon chain surfactants, demonstrate facile, rapid, and controllable aqueous syntheses of gold nanoparticles (AuNPs) as dual-action reducing and capping agents. The synthesis strategy, using only surfactant and HAuCl4 salt, and 4 min of heating at 80 °C, results in spherical AuNPs (average diameters of 13.4 ± 3.8 nm for CBDEB and 12.0 ± 3.8 nm for DBDEB). Microwave irradiation was also investigated as a heating method and produces AuNPs in as little as 30 s. Control over the size and shape of AuNPs was proven to be feasible (toward populations of Euclidean shapes) by appropriately tuning reaction parameters, such as the molar ratio of surfactant to Au3+, temperature, incorporation of a time delay before heating, or shape control agents, such as Cu2+. Frustratingly, the cytotoxicity of CBDEB is similar to that of cetyltrimethylammonium bromide (CTAB), a popular 16-carbon chain cationic surfactant. Notably, while the shorter HBDEB (6-carbon chain) does not produce AuNPs under the applied conditions, it does appear to improve cell viability upon cytotoxicity evaluation and may be favorable as a new biological surfactant.

Recent developments in membrane targeting antifungal agents to mitigate antifungal resistance

Fungal infections cause severe and life-threatening complications especially in immunocompromised individuals. Antifungals targeting cellular machinery and cell membranes including azoles are used in clinical practice to manage topical to systemic fungal infections. However, continuous exposure to clinically used antifungal agents in managing the fungal infections results in the development of multi-drug resistance via adapting different kinds of intrinsic and extrinsic mechanisms. The unique chemical composition of fungal membranes presents attractive targets for antifungal drug discovery as it is difficult for fungal cells to modify the membrane targets for emergence of drug resistance. Here, we discussed available antifungal drugs with their detailed mechanism of action and described different antifungal resistance mechanisms. We further emphasized structure-activity relationship studies of membrane-targeting antifungal agents, and classified membrane-targeting antifungal agents on the basis of their core scaffold with detailed pharmacological properties. This review aims to pique the interest of potential researchers who could explore this interesting and intricate fungal realm.

Surface charge regulation of imidazolium salts/starch/carboxymethyl cellulose ternary polymer blend films for controlling antimicrobial performance and hydrophobicity

Starch (SR)/carboxymethyl cellulose (CMC) based antimicrobial films have been widely applied in packaging field. As a high-effect antimicrobial agent, the surface charge of imidazolium salt plays an important effect on antimicrobial performances of starch/carboxymethyl cellulose. Here in, the surface charge of dodecyl imidazolium bromide salt was regulated via thiol-ene reaction. Furthermore, antibacterial films were prepared by mixing imidazolium salts with SR/CMC via solution casting method. Under the optimized ratio of CMC to SR, the antibacterial activity for as-prepared ternary polymer blend films was enhanced with the increasing of surface charge of imidazolium salt. The sample of ADSC-01 film with highest surface charge showed best antibacterial properties for E. coli and S. aureus with the inhibition zone of 3.20 cm and 3.00 cm, respectively. In addition, hydrophobic property exhibited similar positive correlation with the surface charge. Therefore, this work provides a new route to regulate the antibacterial activity of bio-based ternary polymer blend films in the packaging.

Cholinium-Based Ionic Liquids as Promising Antimicrobial Agents in Pharmaceutical Applications: Surface Activity, Antibacterial Activity and Ecotoxicological Profile

Cholinium-based ionic liquids are compounds increasingly studied in pharmaceutics and biomedicine to enhance bioavailability in drug delivery systems and as bioactive ingredients in pharmaceutical formulations. However, their potential as antimicrobial agents has scarcely been investigated. Herein, we explored the antimicrobial activity of a series of surface-active cholinium-based ionic liquids (Chol-ILs). For this purpose, Chol-ILs with alkyl chains of 10-16 carbon atoms were synthesized and their self-assembly in aqueous medium was investigated. Subsequently, their antimicrobial activity against a panel of clinically relevant bacteria and their ability to eradicate MRSA and P. aeruginosa PAO1 biofilms was evaluated. Finally, we analyzed the ecotoxicological profile of Chol-ILs in terms of susceptibility to aerobic biodegradation and acute aquatic toxicity against D. magna and V. fisheri. Our results reveal that cholinium-based ILs with alkyl chain lengths ≥12 C show a broad spectrum of antibacterial activity. Their antimicrobial efficacy depends on their hydrophobicity, with the C₁₄-C₁₆ homologs being the most effective compounds. These ILs exhibit antimicrobial activity similar to that of imidazolium ILs and quaternary ammonium antiseptics. Moreover, the longer alkyl chain Chol-ILs are able to eradicate established biofilms at concentrations as low as 16-32 µg/mL. The biodegradation rate of cholinium-based ILs decreases with alkyl chain elongation. Our results reinforce the suitability of Chol-ILs as promising multifunctional compounds for application in pharmaceutical and biomedical formulation.

A comparative study on the design and application of new nano benzimidazolium gemini ionic liquids for curing interfacial properties of the crude oil-water system

Gemini surface active ionic liquids (GSAILs) are considered a new prosperous class of ionic liquids and recognized as high performance materials. The present study explores the capabilities of the newly synthesized GSAILs, constructed from two benzimidazole rings attached via a four or a six carbon spacer, namely [C₄benzim-C_n-benzimC₄][Br₂], n = 4 and 6. The products were characterized with FT-IR, NMR, XRD, TGA, DTG and SEM methods and were used in curing interfacial properties of the crude oil-water system. The interfacial tension (IFT) was reduced to about 64 and 71% under critical micelle concentrations (CMCs) of 0.028 and 0.025 mol dm^-3 at 298.2 K for n = 4 and 6 GSAILs, respectively. Temperature significantly assisted this effect. Both the GSAILs could transfer the wettability of the solid surface from oil-wet to water-wet. Further, stable oil/water emulsions were produced, having emulsion indices of 74.2 and 77.3% for n = 4 and 6 GSAILs, respectively. Compared to homologous imidazolium GSAILs, the benzimidazolium products revealed better performance in the sense of exhibiting desired effects on the investigated interfacial properties. These can be attributed to the stronger hydrophobicity of the benzimidazolium rings as well as better spreading of the molecular charges. The Frumkin isotherm could exactly reproduce the IFT data, leading to precise determination of the important adsorption and thermodynamic parameters.

Construction of Graphene Quantum Dot-based Dissolving Microneedle Patches for the Treatment of Bacterial Keratitis

Bacterial keratitis (BK) is an ophthalmic infection caused by bacteria and poses a risk of blindness. Numerous drugs have been used to treat BK, the majority suffered from limited effect owing to their backward antimicrobial and delivery efficacy. Herein, we evaluated the antibacterial effect of a cationic carbon-based nanomaterial, i.e., imidazole-modified graphene quantum dots (IMZ-GQDs), which exhibits disinfection rates of >90% against three typical Gram-positive strains within 3 h owing to the loss of membrane integrity and decline in membrane potential. For ocular application, we further developed IMZ-GQDs-loaded dissolving microneedle patches (IMZ-GQDs MNs) via a typical two-step micromolding method. IMZ-GQDs MNs showed sufficient dissolution and penetration for intrastromal delivery in vitro and successfully overcome the rabbit corneal epithelial layer in vivo. The excellent biocompatibility of IMZ-GQDs MNs was demonstrated both in cell and animal models, and they exhibited low cytotoxicity, low invasiveness and low ocular irritation. The topical application of IMZ-GQDs MNs has the benefits of both high antibacterial activity and effective drug delivery, thereby leading to the resolution of Staphylococcus aureus-induced BK in rabbits in 7 days. Therefore, IMZ-GQDs MNs is a promising approach for BK treatment, which is safe and efficient.

Comparative study of the hydrogen bonding interactions between ester-functionalized/non-functionalized imidazolium-based ionic liquids and DMSO

There have been some studies on the microscopic properties of ester-functionalized ionic liquids (ILs), but the microscopic properties of their mixtures with co-solvents have seldom been reported. In practical applications, ILs are usually used together with co-solvents. Therefore, it is very important to study the microstructure of ester-functionalized ILs and co-solvents. In this work, the hydrogen bonding interactions between ester-functionalized IL 1-acetoxyethyl-3-methylimidazolium tetrafluoroborate (AOEMIMBF₄) and DMSO were studied using spectroscopic methods and quantum chemical calculations. Non-functionalized IL 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄) and DMSO were used for comparison. The results indicate that (1) by adding DMSO, the hydrogen bonding interactions of ν(C2-H) were enhanced, and DMSO could form hydrogen bonds with anions and cations simultaneously. (2) The incorporation of an ester group could enhance the hydrogen bonding interactions. (3) Both the stretching vibration of C2-H and CO indicated changes in the microscopic structure: AOEMIMBF₄ ion clusters first interacted with DMSO, then broke into AOEMIMBF₄-DMSO complexes and finally existed as [AOEMIM]⁺/[BF₄]^--DMSO complexes.

Cationic Surfactants Based on Arginine-Phenylalanine and Arginine-Tryptophan: Synthesis, Aggregation Behavior, Antimicrobial Activity, and Biodegradation

Cationic surfactants have great potential as drug vehicles and for use in gene therapy (cationic vesicles made from cationic surfactants can encapsulate RNA or DNA for cellular transfer). They can also be used as antimicrobial and antifungal agents to treat human infections. In an era of increasing antimicrobial resistance, the development of new biocompatible surfactants suitable for application as antimicrobial agents is of high interest. In this work, a library of amino acid-based surfactants was synthesized, characterized and tested for antimicrobial activity. The head group architecture (number and type of amino acids, density of cationic charge, ionic character) and the hydrophobic moiety (alkyl chain length and position of the hydrophobic group) were systematically modified, and the effect on the surfactant biological and aggregation behavior was studied. Thus, the pKa values, micellization process, antimicrobial efficiency and biodegradability were evaluated. The critical micelle concentration values of the surfactants depended on their hydrophobic character, but changes in the polar head as well as the position and length of the alkyl chain also significantly affected activity against some of the tested microorganisms. Moreover, biodegradability was closely related to the hydrophobic character of the surfactant and attachment of the alkyl chain to the polar head. The structure-activity relationships established here may open perspectives for the design of effective biodegradable antimicrobial materials that can overcome emerging resistance.

Effect of amino acid on the surface adsorption and micellar properties of surface active ILs varying in cationic head groups

The interfacial along with bulk characteristics of the aqueous solutions of ILs with dissimilar cationic head group viz. 1-dodecyl-3-methylimidazolium bromide ([C₁₂mim][Br]), and N-dodecyl-N-methylmorpholinium bromide ([Mor_1,12][Br]) in the absence and the presence of an amino acid L-Methionine as an external additive have been examined by electrical conductivity, UV-Visible, surface tension, and DLS measurements. The CMC values, and the lowest maximum surface excess concentration (Г_max) achieved from all three techniques, and surface tension measurements respectively displayed more surface activity of the [C₁₂mim][Br] than the [Mor_1,12][Br]. Also, the morpholinium head group is less hazardous than imidazolium, it can be utilised to design ILs that are greener, mainly in combination with polar, small, and non-toxic side chains and anions.

Ionic Liquids: Emerging Antimicrobial Agents

Antimicrobial resistance has become a serious threat to global health. New antimicrobials are thus urgently needed. Ionic liquids (ILs), salts consisting of organic cations and anions with melting points less than 100°C, have been recently found to be promising in antimicrobial field as they may disrupt the bacterial wall and membrane and consequently lead to cell leakage and death. Different types of antimicrobial ILs are introduced in the review, including cationic, polymeric, and anionic ILs. Being the main type of the antimicrobial ILs, the review focuses on the structure and the antimicrobial mechanisms of cationic ILs. The quantitative structure-activity relationship (QSAR) models of the cationic ILs are also included. Increase in alkyl chain length and lipophilicity is beneficial to increase the antimicrobial effects of cationic ILs. Polymeric ILs are homopolymers of monomer ILs or copolymers of ILs and other monomers. They have great potential in the field of antibiotics as they provide stronger antimicrobial effects than the sum of the monomer ILs. Anionic ILs are composed of existing anionic antibiotics and organic cations, being capable to enhance the solubility and bioavailability of the original form. Nonetheless, the medical application of antimicrobial ILs is limited by the toxicity. The structural optimization aided by QSAR model and combination with existing antibiotics may provide a solution to this problem and expand the application range of ILs in antimicrobial field.

A comparative evaluation of antibacterial activities of imidazolium-, pyridinium-, and phosphonium-based ionic liquids containing octyl side chains

Antibacterial activity is an essential property of ionic liquids. In this work, a comprehensive study has been performed on the antibacterial activity of ionic liquids to be utilized for further research and applications. Eighteen ionic liquids viz. Octyl Imidazolium, octyl Pyridinium, quaternary phosphonium-based cations containing bromide, sodium methane sulphonates, bis(trifluoromethane sulfonyl) imide, dichloroacetate, tetrafluoroborate, hydrogen sulfate were prepared and characterized with the help of different spectroscopic techniques. All these samples of ionic liquids were tested for their antibacterial activity against the most commonly occurring bacteria in the environment, i.e., Enterobacter aerogenes (E. aerogenes), Proteus vulgaris (P. vulgaris), Klebsiella pneumoniae (K. pneumoniae), Pseudomonas aeruginosa (P. aeruginosa), Escherichia coli (E. coli), and Streptococcus pyogenes (S. pyogenes). Most of the ionic liquids show good antibacterial properties, and imidazolium-based ionic liquids were even more antibacterial as compared to positive control. It was observed that a unique combination of cation and anion is essential to achieve desired antibacterial properties. The mechanism of antibacterial activity was further investigated using density functional theory calculations. A good correlation was found between experimental and theoretical studies.

Micellization and thermodynamics study of ester functionalized picoline-based ionic liquid surfactants in water

A novel series of picoline-based ionic liquid surfactants, N-alkyoxycarbonyl-3-picoline bromides [C _n Empy][Br] (n = 10, 12, 14), have been synthesized. The thermal stability, aggregation behavior and surface activity of the synthetic ionic liquid surfactants were investigated systematically though a series of methods, such as thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), tensiometry and conductivity. The thermodynamics of micellization of the ionic liquid surfactants solution were studied by using the conductivity method in the temperature range 278.15-318.15 K. The surface activity parameters and thermodynamics parameters were derived, respectively. The enthalpy-entropy compensation effect was further discussed by using relative thermodynamics parameters. It was found that the [C _n Empy][Br] have moderate surface activity, and their critical micelle concentration (CMC) decreased with the ester-functionalized chain length and exhibited a U-shape with temperature. The calculation results of the thermodynamic parameters showed that the micellization processes of [C _n Empy][Br] were spontaneous, endothermic at low temperature and exothermic at higher temperature.

Cationic Imidazolium Amphiphiles Bearing a Methoxyphenyl Fragment: Synthesis, Self-Assembly Behavior, and Antimicrobial Activity

Novel cationic amphiphiles of the 3-alkyl-1-(4-methoxyphenyl)-1H-imidazol-3-ium bromide series bearing methoxyphenyl fragments (MPI-n) have been synthesized. Their aggregation properties in aqueous solutions, solubilization capacity, and hemolytic and antimicrobial activities have been investigated by a number of physicochemical methods. Using tensiometry, conductometry, and fluorescence spectroscopy, it was shown that the MPI-n have lower CMCs than their nonfunctionalized counterparts. The unusual alkyl-chain-length-dependent morphology of aggregates is testified for this homological series. Amphiphiles with 12, 14, and 16 alkyl tails are characterized by the formation of micellar aggregates, while a surfactant with a decyl tail is characterized by the formation of larger aggregates with lower surface curvature. The MPI-10 aggregate morphology was rationalized in terms of the packing parameter consideration and was supported by size measurements and the fluorescence probe techniques, which showed that vesicle-like aggregates in close-packing mode probably occur. MPI-n aggregates have exhibited a high solubilization capacity toward hydrophobic azo dye Orange OT. Importantly, amphiphiles studied showed (i) high bacteriostatic activity at the level of ciprofloxacin; (ii) high bactericidal action against all Gram-positive bacteria, including methicillin-resistant strains; (iii) bactericidal properties against Gram-negative bacteria; and (iv) low hemolytic activity.

Sustainable Synthesis of Ionic Liquid-Functionalized Zinc Oxide Nanosheets (IL@ZnO): Evaluation of Antibacterial Potential Activity for Biomedical Applications

Zinc oxide (ZnO)-derived materials exhibit unique antibacterial, antifungal, and photochemical activities and are widely used in antibacterial formulations. In this work, ZnO nanosheets were prepared by green and cost-effective synthesis via a hydrothermal method, and the prepared ZnO nanosheets were further functionalized with an eco-friendly ionic liquid (IL). Thus, a sustainable approach was established to synthesize ZnO nanosheets. The functionalization of ZnO with the synthesized IL was fully characterized by advanced spectroscopic and microscopic techniques. The prepared ionic liquid-functionalized ZnO (IL@ZnO) showed self-organized layered-sheet arrangements caused by the intercalation of the IL onto the surface of ZnO nanosheets as revealed by scanning electron microscopy (SEM). The design of the IL comprised a carboxylic acid moiety for functionalization onto the surface of ZnO, whereas the hydrophobicity was tuned through the incorporation of a long alkyl chain. The developed IL@ZnO material was also tested against both Gram-positive and Gram-negative pathogenic bacteria for potential antibacterial activity by colony-forming unit (CFU) and minimum inhibitory concentration tests. The results revealed that the IL@ZnO exhibits significant antibacterial activity against tested strains. In particular, potent activity was observed against the Gram-positive skin-specific Staphylococcus aureus bacteria strain. The mechanism of bactericidal activity against bacteria was also explored along with the cytotoxicity toward mammalian cells, which reveals that the IL@ZnO is nontoxic in nature. To utilize the developed material owing to its bactericidal activity for practical applications, the IL@ZnO was fabricated onto the surface of cotton fabric, and its surface morphology was examined by SEM; the activity of IL@ZnO-treated cotton fabric was evaluated by the zone of inhibition assay. Additionally, the IL@ZnO-treated cotton fabric exhibited remarkable stability along with significant hydrophobicity and breathability and thus can be utilized as a biomaterial for biomedical applications, especially in medical masks, for reducing the risk of transmission of infectious diseases.

Mixed Oxime-Functionalized IL/16-s-16 Gemini Surfactants System: Physicochemical Study and Structural Transitions in the Presence of Promethazine as a Potential Chiral Pollutant

The increasing concern about chiral pharmaceutical pollutants is connected to environmental contamination causing both chronic and acute harmful effects on living organisms. The design and application of sustainable surfactants in the remediation of polluted sites require knowledge of partitioning between surfactants and potential pollutants. The interfacial and thermodynamic properties of two gemini surfactants, namely, alkanediyi-α,ω-bis(dimethylhexadecyl ammonium bromide) (16-s-16, where s = 10, 12), were studied in the presence of the inherently biodegradable oxime-functionalized ionic liquid (IL) 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide (4-PyC8) in an aqueous solution using surface tension, conductivity, fluorescence, FTIR and 1H NMR spectroscopic techniques. The conductivity, surface tension and fluorescence measurements indicated that the presence of the IL 4-PyC8 resulted in decreasing CMC and facilitated the aggregation process. The various thermodynamic parameters, interfacial properties, aggregation number and Stern–Volmer constant were also evaluated. The IL 4-PyC8-gemini interactions were studied using DLS, FTIR and NMR spectroscopic techniques. The hydrodynamic diameter of the gemini aggregates in the presence of promethazine (PMZ) as a potential chiral pollutant and the IL 4-PyC8 underwent a transition when the drug was added, from large aggregates (270 nm) to small micelles, which supported the gemini:IL 4-PyC8:promethazine interaction. The structural transitions in the presence of promethazine may be used for designing systems that are responsive to changes in size and shape of the aggregates as an analytical signal for selective detection and binding pollutants.

Mixed Oxime-Functionalized IL/16-s-16 Gemini Surfactants System: Physicochemical Study and Structural Transitions in the Presence of Promethazine as a Potential Chiral Pollutant

The increasing concern about chiral pharmaceutical pollutants is connected to environmental contamination causing both chronic and acute harmful effects on living organisms. The design and application of sustainable surfactants in the remediation of polluted sites require knowledge of partitioning between surfactants and potential pollutants. The interfacial and thermodynamic properties of two gemini surfactants, namely, alkanediyi-α,ω-bis(dimethylhexadecyl ammonium bromide) (16-s-16, where s = 10, 12), were studied in the presence of the inherently biodegradable oxime-functionalized ionic liquid (IL) 4-((hydroxyimino)methyl)-1-(2-(octylamino)-2-oxoethyl)pyridin-1-ium bromide (4-PyC8) in an aqueous solution using surface tension, conductivity, fluorescence, FTIR and 1H NMR spectroscopic techniques. The conductivity, surface tension and fluorescence measurements indicated that the presence of the IL 4-PyC8 resulted in decreasing CMC and facilitated the aggregation process. The various thermodynamic parameters, interfacial properties, aggregation number and Stern–Volmer constant were also evaluated. The IL 4-PyC8-gemini interactions were studied using DLS, FTIR and NMR spectroscopic techniques. The hydrodynamic diameter of the gemini aggregates in the presence of promethazine (PMZ) as a potential chiral pollutant and the IL 4-PyC8 underwent a transition when the drug was added, from large aggregates (270 nm) to small micelles, which supported the gemini:IL 4-PyC8:promethazine interaction. The structural transitions in the presence of promethazine may be used for designing systems that are responsive to changes in size and shape of the aggregates as an analytical signal for selective detection and binding pollutants.

Emerging impacts of ionic liquids on eco-environmental safety and human health

Owing to their unique physicochemical properties, ionic liquids (ILs) have been rapidly applied in diverse areas, such as organic synthesis, electrochemistry, analytical chemistry, functional materials, pharmaceutics, and biomedicine. The increase in the production and application of ILs has resulted in their release into aquatic and terrestrial environments. Because of their low vapor pressure, ILs cause very little pollution in the atmosphere compared to organic solvents. However, ILs are highly persistent in aquatic and terrestrial environments due to their stability, and therefore, potentially threaten the safety of eco-environments and human health. Specifically, the environmental translocation and retention of ILs, or their accumulation in organisms, are all related to their physiochemical properties, such as hydrophobicity. Based on results of ecotoxicity, cytotoxicity, and toxicity in mammalian models, the mechanisms involved in IL-induced toxicity include damage of cell membranes and induction of oxidative stress. Recently, artificial intelligence and machine learning techniques have been used in mining and modeling toxicity data to make meaningful predictions. Major future challenges are also discussed. This review will accelerate our understanding of the safety issues of ILs and serve as a guideline for the design of the next generation of ILs.

Review on Amphiphilic Ionic Liquids as New Surfactants: From Fundamentals to Applications

The demand for lowering interfacial tension (IFT) in different processes has persuaded researchers to use stable and resistant surfactants with low environmental impact. For this purpose, surface-active ionic liquids (SAILs) have attracted much attention owing to their good amphiphilic nature and prominent properties like recyclability and high performance under harsh conditions. This review initially explains how the IFT and critical micelle concentration of different systems vary in the presence of different SAILs with a variety of alkyl chain lengths, head groups, and counter anions. Towards this aim, some physicochemical properties of SAILs as well as the corresponding theoretical aspects of adsorption are considered. Then, recent advances in utilizing SAILs for reducing IFT of different chemical systems are surveyed. Relevantly, the role of important operating parameters of temperature, pH, presence of electrolytes, and the chemical nature of involved phases are adequately discussed. Further, an overview of different SAILs applications in stabilization, separation, and in petroleum industries is scrutinized. To allow better judgment, precise comparisons between different types of SAILs and conventional surfactants are provided. Finally, challenges and possible directions of future research on SAILs are highlighted.

Review of the toxic effects of ionic liquids

Interest in ionic liquids (ILs), called green or designer solvents, has been increasing because of their excellent properties such as thermal stability and low vapor pressure; thus, they can replace harmful organic chemicals and help several industrial fields e.g., energy-storage materials production and biomaterial pretreatment. However, the claim that ILs are green solvents should be carefully considered from an environmental perspective. ILs, given their minimal vapor pressure, may not directly cause atmospheric pollution. However, they have the potential to cause adverse effects if leaked into the environment, for instance if they are spilled due to human mistakes or technical errors. To estimate the risks of ILs, numerous ILs have had their toxicity assessed toward several micro- and macro-organisms over the past few decades. Since the toxic effects of ILs depend on the method of estimating toxicity, it is necessary to briefly summarize and comprehensively discuss the biological effects of ILs according to their structure and toxicity testing levels. This can help simplify our understanding of the toxicity of ILs. Therefore, in this review, we discuss the key findings of toxicological information of ILs, collect some toxicity data of ILs to different species, and explain the influence of IL structure on their toxic properties. In the discussion, we estimated two different sensitivity values of toxicity testing levels depending on the experiment condition, which are theoretical magnitudes of the inherent sensitivity of toxicity testing levels in various conditions and their changes in biological response according to the change in IL structure. Finally, some perspectives, future research directions, and limitations to toxicological research of ILs, presented so far, are discussed.

Antimicrobial and Toxicity Evaluation of Imidazolium-Based Dicationic Ionic Liquids with Dicarboxylate Anions

Imidazolium-based dicationic ILs (DILs) presenting antimicrobial activity and relatively low toxicity are highly desirable and are envisioned for use in live tissue to prevent bacterial or fungal infections. In this context, we present here DILs with dicarboxylate anions [C_n(MIM)₂[C_n(MIM)₂][CO₂-(CH₂)_mCO₂], in which n = 4, 6, 8, and 10, and m = 0, 1, 2, 3, 4, and 5. The results showed that DILs with an alkyl chain spacer of ten carbons were active against yeasts and the bacterial strains tested. However, most of the DILs were cytotoxic and toxic at 1 mM. By contrast, DILs with alkyl chains possessing less than ten carbons were active against some specific Candidas and bacteria (mainly S. aureus), and they showed moderate cytotoxicity. The best activity against Gram-positive bacteria was observed for [C₄(MIM)₂][Pim] toward MRSA. For the DILs described herein, their level of toxicity against C. elegans was lower than that of most of the mono- and dicationic IL analogs with other anions. Our results showed that the presence of carboxylate anions reduces the toxicity of DILs compared to DILs containing halide anions, which is particularly significant to the means of designing biologically active compounds in antimicrobial formulations.

Cytotoxicity and Membrane Permeability of Double-Chained 1,3-Dialkylimidazolium Cations in Ionic Liquids

We have evaluated ionic liquids based on double-chained 1-alkyl-3-octylimidazolium cations ([C_nC₈IM]⁺, n = 2, 4, 6, 8, 10, 12) for their cytotoxicity toward various cell lines. The toxicity of ionic liquids was correlated to their ability to partition into and permeabilize phosphocholine (POPC)- or phosphoglycerol (POPG)-based large unilamellar vesicles. Membrane partitioning of ionic liquids was assessed using the ζ-potential measurements, and membrane permeability was determined using fluorescence-based dye leakage assays. Both cytotoxicity and membrane permeability of these ILs were found to increase in a sigmoidal fashion with increasing chain length on the N1 atom (n in [C_nC₈IM]⁺) cations. These results were compared with those for ionic liquids based on single-chained 1-alkyl-3-methylimidazolium cations ([C_n+8C₁IM]⁺), carrying a similar number of carbon atoms but as a single alkyl chain. Our studies show that ionic liquids containing double-chained cations are relatively less cytotoxic and membrane-permeabilizing than the cations bearing a single long alkyl chain.

A computational approach for the screening of potential antiviral compounds against SARS-CoV-2 protease: Ionic liquid vs herbal and natural compounds

The current scenario across the globe shows unprecedented healthcare and an economic crisis due to the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Recently, the World Health Organization (WHO) has declared a pandemic stage worldwide because of the high mortality and morbidity rate caused by novel infection disease. There have been several clinical trials and identification underway to find a treatment of this novel virus. For the treatment of severe infection involves the blocking of the replication of its CoV-2 protein. Hydroxychloroquine and remdesivir has been used on an emergency basis for its treatment. The uncontrolled infection and increasing death rate underline the emergence to develop the antiviral drug. In our study, the blind docking of various classes of compounds including control antiviral drugs (abacavir, acyclovir, quinoline, hydroxyquinoline), antimicrobial drugs (levofloxacin, amoxicillin, cloxacin, ofloxacin), natural compounds (lycorine, saikosaponins, myricetin, amentaflavone), herbal compounds (silymarin, palmatine, curcumin, eugenin) available in Indian Ayurveda was done. Besides, we have also performed the blind docking of various ionic liquids (ILs) such as pyrrolidinium, piperidinium, pyridinium, imidazolium based ILs against CoV-2 protease as they have recently emerged as a potential antimicrobial agent. Further, the pharmacokinetic properties and cytotoxicity of the compounds were determined computationally. The docking results showed successful binding to the active site or near a crucial site. The present computational approach was found helpful to predict the best possible inhibitor of protease and may result in an effective therapeutic agent against COVID-19.