Synergistic antimicrobial activity of N-methyl substituted pyrrolidinium-based ionic liquids and melittin against Gram-positive and Gram-negative bacteria

Morpholinium-based Ionic Liquids as Potent Antibiofilm and Sensitizing Agents for the Control of Pseudomonas aeruginosa

Rising antimicrobial resistance is a critical threat to worldwide public health. To address the increasing antibiotic tolerance, diverse antimicrobial agents are examined for their ability to decrease bacterial resistance. One of the most relevant and persistent human pathogens is Pseudomonas aeruginosa. Our study investigates the anti-biofilm and sensitizing activity of 12 morpholinium-based ionic liquids with herbicidal anions on four clinically relevant P. aeruginosa strains. Among all tested compounds, four ionic liquids prevented biofilm formation at sub-minimum inhibitory concentrations for all investigated strains. For the first time, we established a hormetic effect on biofilm formation for P. aeruginosa strains subjected to an ionic liquid treatment. Interestingly, while ionic liquids with 4,4-didecylmorpholinium [Dec2Mor]+ are more efficient against planktonic bacteria, 4-decyl-4-ethylmorpholinium [DecEtMor]+ showed more potent inhibition of biofilm formation. Ionic liquids with 4,4-didecylmorpholinium ([Dec2Mor]+) cations even induced biofilm formation by strain 39016 at high concentrations due to flocculation. Morpholinium-based ionic liquids were also shown to enhance the efficacy of commonly used antibiotics from different chemical groups. We demonstrate that this synergy is associated with the mode of action of the antibiotics.

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).

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.

Ionic Liquids in Pharmaceutical and Biomedical Applications: A Review

The unique properties of ionic liquids (ILs), such as structural tunability, good solubility, chemical/thermal stability, favorable biocompatibility, and simplicity of preparation, have led to a wide range of applications in the pharmaceutical and biomedical fields. ILs can not only speed up the chemical reaction process, improve the yield, and reduce environmental pollution but also improve many problems in the field of medicine, such as the poor drug solubility, product crystal instability, poor biological activity, and low drug delivery efficiency. This paper presents a systematic and concise analysis of the recent advancements and further applications of ILs in the pharmaceutical field from the aspects of drug synthesis, drug analysis, drug solubilization, and drug crystal engineering. Additionally, it explores the biomedical field, covering aspects such as drug carriers, stabilization of proteins, antimicrobials, and bioactive ionic liquids.

Improved Antibacterial Activity of Peptide Nisin with Pyrrole-Based Ionic Liquids Having Bis(trifluoromethylsulfonyl)imide as a Counterion: A Synergistic Approach to Combat Bacterial Infections

Bacterial resistance against antimicrobial drugs is a forthcoming threat to the prevention and treatment of developing bacterial infections. Hence, the development of new antimicrobial therapy or therapeutic drugs is desperately needed. A combination of antibiotics exhibits synergistic antibacterial effects. As the combination approach of antibiotics has always shown better results against pathogens compared to monotherapy with an antibiotic, we focused on creating a new combination that may reduce the chances of strains attaining resistance, consequently lowering the toxicity factor associated with the consumption of high amounts of antibiotics. Nisin, a food preservative and potential antibiotic, shows antibacterial activity against Gram-positive strains. Since the past decade, ionic liquids (ILs) have proven to be an important class of potential antibacterial agents. In our study, we studied the effect of pyrrolidinium-based ILs and arrived at a noncovalent conjugate formed by combining nisin with ILs. The conjugates were tested against a couple of clinically relevant microorganisms, namely, Escherichia coli and Staphylococcus aureus. We reached a novel discovery that the combination of sodium/iodide symporter (NIS) and IL exhibited inhibitory effects against Gram-negative bacteria, which was not observed with NIS alone. The results showed remarkable improvement in the minimum inhibitory concentration (MIC) value of NIS in the presence of ILs targeted against both microorganisms. Further, flow cytometry and confocal microscopy results revealed the membrane disruption efficiency of the best combination obtained, leading to cell death. Additionally, the complexation of nisin and ILs was studied using various techniques, such as surface tension, dynamic light scattering, absorption spectroscopy, and molecular docking.

Imidazolium-Based Ionic Liquid-Assisted Silver Nanoparticles and Their Antibacterial Activity: Experimental and Density Functional Theory Studies

The exclusive properties of ionic liquids (ILs) offer various opportunities to develop advanced materials with appreciable therapeutic applications. Imidazolium-based ILs have been frequently used as reaction media and stabilizers for the development and surface functionalization of noble metal nanoparticles (NPs). This study reports the citrate-mediated reduction of silver ions in three different ILs, that is, 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM][MS]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM][OTf]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]). The resulting Ag-ILs NPs were characterized using many analytical techniques, including UV-visible spectroscopy, dynamic light scattering (DLS), scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction (XRD). DLS and XRD characterization revealed the negatively charged Ag-[EMIM][MS] NPs, Ag-[BMIM][OTf] NPs, and Ag-[BMIM][TFSI] NPs with mean hydrodynamic sizes of 278, 316, and 279 nm, respectively, and a face-centered cubic structure. These hybrid nanomaterials were subjected to in vitro antibacterial screening against three bacterial strains. The Ag-[BMIM][OTf] NPs exhibited significant activities against Escherichia coli, Staphylococcus aureus, and Enterobacter cloacae. The lowest inhibition concentration of 62.5 μg/mL was recorded against E. coli using Ag-[EMIM][MS] and Ag-[BMIM][OTf] NPs. Further, the density functional theory calculations carried out on the computed Ag-ILs in the gas phase and water showed relatively stable systems. Ag-[BMIM][TFSI] exhibited the lowest Gibbs free energy change of -34.41 kcal/mol. The value of the global electrophilicity index (ω = 0.1865 eV) for the Ag-[BMIM][OTf] correlated with its good antibacterial activity.

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.

Discovery of Novel Dimeric Pyridinium Bromide Analogues Inhibits Cancer Cell Growth by Activating Caspases and Downregulating Bcl-2 Protein

Flexible dimeric substituted pyridinium bromides with primary and tertiary amines are prepared by conventional and solvent-free methods. The formation of compounds 2 and 4 is much easier than that of compounds 1 and 3 because of the benzyl carbon which is more electropositive than the primary alkyl carbon. The newly synthesized dimeric pyridinium compounds are optimized using DFT and B3LYP 6-31 g(d,p). The in vitro antiproliferative activity is studied in lung (A549) and breast cancer cell lines (MDA-MB 231). Among the four compounds, 1,1'-(1,3-phenylene bis(methylene)bis 2-aminopyridinium bromide 4 showed potent anticancer activity when compared to the standard drug 5-fluorouracil. 1,1'-(1,3-Phenylene bis(methylene)bis 2-aminopyridinium bromide 4 is not toxic to normal cell lines 3T3-L1 and MRC-5 cell lines. Also, 1,1'-(1,3-phenylene bis(methylene)bis 2-aminopyridinium bromide 4-induced apoptosis in cancer cell lines is examined using AO/EB and Hoechst staining, which is further supported by cell cycle analysis. Western blot analysis showed that 1,1'-(1,3-phenylene bis(methylene)bis 2-aminopyridinium bromide 4 induces apoptosis through the extrinsic apoptotic pathway by upregulating caspase 3 and caspase 9. This compound also downregulates intrinsic apoptotic proteins, including Bcl-2, Bcl-x, and Bad. From the present study results, it is confirmed that 1,1'-(1,3-phenylene bis(methylene)bis 2-aminopyridinium bromide 4 has potent anticancer activity when compared to other compounds.

Collagen-PVA Films Plasticized with Choline Acetate Ionic Liquid for Sustained Drug Release: UV Shielding, Mechanical, Antioxidant, and Antibacterial Properties

Collagen and poly(vinyl alcohol) films as topical drug delivery systems were developed by plasticization with glycerol and different concentrations of choline acetate ([Cho]Ac) ionic liquid (IL). The results showed that [Cho]Ac improved the performance of the materials and can serve as an alternative to synthetic plasticizers such as glycerol. Ciprofloxacin (CIP) was used as a model drug to study its release behavior. Ready-to-use films were characterized for their optical opacity, solubility, swelling, mechanical properties, water contact angle, surface morphology, surface roughness, antioxidant, and antimicrobial activities. Moreover, X-ray diffraction and Fourier Transform Infrared (FTIR) studies were carried out for molecular characterization of the films. [Cho]Ac used as a plasticizing agent showed excellent antioxidant properties, mechanical strength, and UV shielding properties. Further, [Cho]Ac improves the roughness and decreases the solubility of films. The in vitro release behavior of CIP was investigated at physiological pH (7.4), and the results showed that CIP was released in a more controlled manner due to the incorporation of [Cho]Ac into the films' matrix, while the films constructed with glycerol exhibited burst release of CIP. Moreover, the films loaded with CIP showed excellent antibacterial activity against Gram-negative (Escherichia coli) as well as Gram-positive (Staphylococcus aureus) bacteria. This study provides insight into the use of choline-based ILs as plasticizing agents for the fabrication of protein-polymer composite films for wound dressing and many other applications.

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.

Melittin-Based Nano-Delivery Systems for Cancer Therapy

Melittin (MEL) is a 26-amino acid polypeptide with a variety of pharmacological and toxicological effects, which include strong surface activity on cell lipid membranes, hemolytic activity, and potential anti-tumor properties. However, the clinical application of melittin is restricted due to its severe hemolytic activity. Different nanocarrier systems have been developed to achieve stable loading, side effects shielding, and tumor-targeted delivery, such as liposomes, cationic polymers, lipodisks, etc. In addition, MEL can be modified on nano drugs as a non-selective cytolytic peptide to enhance cellular uptake and endosomal/lysosomal escape. In this review, we discuss recent advances in MEL’s nano-delivery systems and MEL-modified nano drug carriers for cancer therapy.

The Emerging Role of Ionic Liquid-Based Approaches for Enhanced Skin Permeation of Bioactive Molecules: A Snapshot of the Past Couple of Years

Topical and transdermal delivery systems are of undeniable significance and ubiquity in healthcare, to facilitate the delivery of active pharmaceutical ingredients, respectively, onto or across the skin to enter systemic circulation. From ancient ointments and potions to modern micro/nanotechnological devices, a variety of approaches has been explored over the ages to improve the skin permeation of diverse medicines and cosmetics. Amongst the latest investigational dermal permeation enhancers, ionic liquids have been gaining momentum, and recent years have been prolific in this regard. As such, this review offers an outline of current methods for enhancing percutaneous permeation, highlighting selected reports where ionic liquid-based approaches have been investigated for this purpose. Future perspectives on use of ionic liquids for topical delivery of bioactive peptides are also presented.