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

Chemical Modification of Bacterial Cellulose for the Development of an Antibacterial Wound Dressing

Bacterial cellulose is a bacterially derived polymer with great potential for application in wound healing due to its innate properties such as high biocompatibility and biodegradability. In addition to this, it is naturally biosynthesized by bacteria as a hydrogel, which makes it an optimal substrate for the treatment of dry wounds, where additional moisture is required to facilitate the healing process. However, this polymer lacks antibacterial properties. As bacterial infections are becoming increasingly common and difficult to treat due to antimicrobial resistance, it is of crucial importance to develop strategies for the modification of cellulose to ensure protection against bacterial contamination. In this study, a green-chemistry approach was proposed for the functionalization of cellulose to introduce antibacterial functional groups. Two different active agents, namely glycidyl trimethylammonium chloride and glycidyl hexadecyl ether, were used for the covalent derivatization of the hydroxyl groups of glucose through a heterogeneous reaction in basic aqueous conditions. The modified material was chemically and mechanically characterized by solid-state techniques and rheological measurements. A biological assessment was then carried out both using bacterial cells and human keratinocytes. It was observed that the functionalization performed induced a reduction of approximately half of the bacterial population within 24 h of direct contact with Staphylococcus aureus subsp. aureus Rosenbach 6538PTM and Escherichia coli (Migula) Castellani and Chalmers ATCC® 8739TM (respectively, a reduction of 53% and 43% in the cell number was registered for the two strains). In parallel, cytotoxicity studies performed on keratinocytes (HaCaT cell line) showed cell viability in the range of 90 to 100% for up to 6 days of direct contact with both unmodified and modified samples. The morphology of the cells was also visually evaluated, and no significant difference was noted as compared to the control. Finally, the in vitro scratch assay evidenced good wound closure rates in the presence of the samples, with complete coverage of the scratched area after 5 days for both the modified cellulose and the positive control (i.e., keratinocytes growth medium). Overall, the modified hydrogel showed promising features, confirming its potential as an alternative substrate to develop a sustainable, antibacterial and biocompatible wound dressing.

Phosphonium-ammonium-based di-cationic ionic liquids as antibacterial over the ESKAPE group

Emergence of antibioresistance is currently a major threat of public health worldwide. Hence there is an urge need of finding new antibacterial material. Herein, we report a simple and eco-friendly method to synthesize homo and heterodicationic ionic liquids based on quaternary phosphonium and ammonium salt. In order to investigate the structure activity relationship (SAR) we measured the MICs of a series of 16 derivatives with structural variations (nature of cations and counter-ions, size of linker and alkyl side chains as well as structural symmetry) over a range of Gram-positive and Gram-negative bacterial strains from the ESKAPE group. Some of the tested structures exhibit high antimicrobial activities (MIC = 0.5 mg/L) and are active over a wide range of bacteria from Gram-positive to Gram-negative. Overall, these results reveal the strong potential of di-cationic derivatives as antibacterial agents and the determination of activities from structural features gives decisive information for future synthesis of such di-cationic structures for biocidal purpose.

Recycling Old Antibiotics with Ionic Liquids

Antibiotics are considered one of the great "miracles" of the 20th century. Now in the 21st century in the post-antibiotic era, the miracle is turning into a nightmare, due to the growing problem of the resistance of microorganisms to classic antimicrobials and the non-investment by the pharmaceutical industry in new antimicrobial agents. Unfortunately, the current COVID-19 pandemic has demonstrated the global risks associated with uncontrolled infections and the various forms of impact that such a pandemic may have on the economy and on social habits besides the associated morbidity and mortality. Therefore, there is an urgent need to recycle classic antibiotics, as is the case in the use of ionic liquids (ILs) based on antibiotics. Thus, the aim of the present review is to summarize the data on ILs, mainly those with antimicrobial action and especially against resistant strains. The main conclusions of this article are that ILs are flexible due to their ability to modulate cations and anions as a salt, making it possible to combine the properties of both and multiplying the activity of separate cations and anions. Also, these compounds have low cost methods of production, which makes it highly attractive to explore them, especially as antimicrobial agents and against resistant strains. ILs may further be combined with other therapeutic strategies, such as phage or lysine therapy, enhancing the therapeutic arsenal needed to fight this worldwide problem of antibacterial resistance. Thus, the use of ILs as antibiotics by themselves or together with phage therapy and lysine therapy are promising alternatives against pathogenic microorganisms, and may have the possibility to be used in new ways in order to restrain uncontrolled infections.

Insight into the structure-antibacterial activity of amino cation-based and acetate anion-based ionic liquids from computational interactions with the POPC phospholipid bilayer

Investigations relevant to ionic liquids (ILs) as antibacterial agents have drawn considerable attention. However, the high cost and potential toxicity of ILs have severely limited their extensive applications, which has motivated researchers to design inexpensive and health-benign ILs. In this work, the interactions between the hydrated zwitterionic phospholipid (POPC) bilayer and a series of hypothetical amino cation-based and acetate anion-based ILs with different counterparts were investigated using molecular dynamics (MD) simulations to predict their antibacterial abilities. The cations of the ILs were found to insert into the lipid bilayer spontaneously, especially amino cations. Reorientation of the inserted imidazolium-based cations was observed, while the inserted amino cations showed no obvious reorientation phenomena, probably because of the strong charge interactions between the positive NH₃ groups of the amino cation and the negative PO₄ groups of the lipid bilayer. Due to their strong affinity with water, acetate-based anions disperse better in water solution, which weakens the insertion of the cations into the lipid bilayer to some extent. The structure and dynamic properties of the lipid bilayer, such as electrostatic potential, local ordering, area per lipid, volume per lipid, bilayer thickness, and lateral diffusion, are significantly influenced by the insertion of the cations, which results in disorder of the lipid bilayer and further disruption of the activity of the cell membrane. The insights into the relationship between the structures of ILs and their antibacterial activity in this work will provide a good reference for the screening and design of less expensive, safer, and greener IL candidates as antibacterial agents.

Hemocompatible magnetic particles with broad-spectrum bacteria capture capability for blood purification

Pathogen capture and removal from whole blood is a new strategy for extracorporeal blood purification, especially in initial treatment of sepsis before pathogen identification. Herein, hemocompatible magnetic particles with broad-spectrum bacteria capture capability were proposed for pathogen removal from whole blood, omitting the necessity of pathogen identification. Firstly, we designed and synthesized a new kind of imidazolium-based ionic liquid with good antibacterial activity, and polydopamine coating was utilized as a hemocompatible platform to immobilize ionic liquids on Fe₃O₄ nanoparticles, forming the hemocompatible magnetic particles (Fe₃O₄@PDA-IL). The magnetic particles exhibited good hemocompatibility and performed well in the removal of various species of clinically significant pathogens from human whole blood, including S. aureus, E. coli, and the hard-to-treat bacteria of P. aeruginosa and Methicillin-resistant S. aureus, which are the most common pathogens in bloodstream infections. Besides, the Fe₃O₄@PDA-IL particles were also capable to remove bacterial endotoxins from blood, inhibiting further aggravation of sepsis. Overall, we demonstrated the application of hemocompatible magnetic particles in the removal of pathogens and bacterial endotoxins from whole blood via electrostatic and hydrophobic interactions, without significant effects on blood cells or the activation of coagulation and complement, addressing the feasibility of using imidazolium-based ionic liquids for bacteria capture and removal from whole blood. It would contribute to the development of magnetic separation-based approaches to remove bacteria and bacterial endotoxin for extracorporeal blood purification, especially in initial sepsis therapy before pathogen identification.

Ionic Liquid-Functionalized Multiwalled Carbon Nanotube-Based Hydrophobic Coatings for Robust Antibacterial Applications

In recent years, the biomimetic superhydrophobic coatings have received tremendous attention, owing to their potential in fabricating self-cleaning surfaces, in environmental applications. Consequently, extensive research has been devoted to create a superhydrophobic surface using the oxidized derivatives of CNTs and graphene. Thus, the design and development of a self-cleaning/superhydrophobic surface with good biocompatibility are an effective approach to deal with the bacterial infections related to biomedical devices used in hospitals. In this context, herein, we have developed the material based on ionic liquid (IL)-functionalized multiwalled carbon nanotubes (MWCNTs) for hydrophobic coatings, which was fully characterized with various techniques such as Fourier transform infrared, powder X-ray diffraction, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. We have evaluated the synthesized ILs for their antibacterial potential against the pathogenic bacterial strains such as Gram-positive (Staphylococcus aureus and methicillin-resistant S. aureus) and Gram-negative (Escherichia coli) bacterial strains. Further, atomic force and scanning electron microscopic studies have been performed to investigate the morphological changes to unravel the mechanism of action, whereas DNA binding study indicates the binding of IL-1d@MWCNT with DNA (K_a = 2.390 × 10⁴ M^-1). Furthermore, the developed material (IL-1d@MWCNT) is coated onto the surface of polyvinyl chloride (PVC) and evaluated for hydrophobicity through water contact angle measurements and possesses long-term antibacterial efficiency against both under-investigating pathogenic strains. For the biocompatibility assay, the obtained coated PVC material has also been evaluated for its cytotoxicity, and results reveal no toxicity against viable cells. These all results are taken together, indicating that by coating with the developed material IL-1d@MWCNT, a robust self-sterilizing surface has achieved, which helps in maintaining a bacteria-free surface.

Synergistic activity between colistin and the ionic liquids 1-methyl-3-dodecylimidazolium bromide, 1-dodecyl-1-methylpyrrolidinium bromide, or 1-dodecyl-1-methylpiperidinium bromide against Gram-negative bacteria

OBJECTIVES

Ionic liquids have shown potential for applications as antimicrobials. Their antimicrobial activity has been shown to be higher against Gram-positive than Gram-negative bacteria, suggesting a protective role for the outer membrane of Gram-negative microorganisms. Colistin is a last-resort antibiotic often used for treating infections caused by multi-drug resistant Gram-negative bacteria. Colistin interacts with the bacterial lipopolysaccharide, thus altering the structure and increasing the permeability of the outer membrane. The aim of this study was to investigate the interaction between colistin and the ionic liquids 1-methyl-3-dodecylimidazolium bromide, 1-dodecyl-1-methylpyrrolidinium bromide, and 1-dodecyl-1-methylpiperidinium bromide against Gram-negative bacteria of clinical importance such as Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii.

METHODS

The interaction between colistin and ionic liquids against Gram-negative bacteria was evaluated by the checkerboard assay. Bacterial killing assays against P. aeruginosa were carried out to assess whether the synergistic combinations were bactericidal.

RESULTS

The results of checkerboard assays showed that all three ionic liquids interacted synergistically with colistin against K. pneumoniae, P. aeruginosa, and A. baumannii but not against E. coli, which was more sensitive to all three ionic liquids compared with the other tested species. The synergistic combinations showed no haemolytic activity. Bacterial killing assays showed that the synergistic effect between colistin and each one of the three tested ionic liquids against P. aeruginosa was bactericidal.

CONCLUSION

Overall, the results obtained suggest that colistin and ionic liquids might be used in combination for possible applications to combat infections caused by multi-drug resistant Gram-negative bacteria.

Polyanionic Composite Membranes Based on Bacterial Cellulose and Amino Acid for Antimicrobial Application

Ideal wound dressing materials should be active components in the healing process. Bacterial cellulose (BC) has attracted a great deal of attention as novel wound dressing materials; however, it has no intrinsic antimicrobial activity. To explore the practical application values of BC and develop novel wound dressing materials, a series of composite membranes based on BC and polymeric ionic liquids (BC/PILs, composed of BC, and PILs formed by choline and different amino acids) with antimicrobial activity were synthesized by an ex situ method. The physicochemical and antimicrobial properties and biocompatibility of these membranes were systematically investigated. The results indicated that BC/PIL membranes with excellent properties could be obtained by adjusting the concentration and type of PILs. Several kinds of BC/PIL membranes exhibited good biocompatibility and high antimicrobial activity against Gram-positive and Gram-negative bacteria and fungus. The anionic PILs played important roles in the antimicrobial activity of BC/PIL membranes. The obtained membranes provided a novel promising candidate for wound dressing materials.

Uptake and accumulation of imidazolium ionic liquids in rice seedlings: Impacts of alkyl chain length

The uptake and accumulation of three imidazolium ionic liquids with different alkyl chain lengths ([C₂min]Br, [C₄min]Br, [C₈min]Br) in rice seedlings were investigated. All three different ILs were primarily accumulated in roots, while only a little amount of ILs were translocated and accumulated in stems and leaves. Accumulation and transportation of ILs in rice depend on the concentration and the alkyl chain length of ILs. ILs contents in the roots, stems and leaves decreased as ILs alkyl chain length increased. Growth inhibition results showed that the toxic effects of ILs on rice growth depends on the alkyl chain length: [C₈min]Br >[C₄min]Br >[C₂min]Br. As markers of defense and phytotoxicity, the plant antioxidant enzymes and biochemical stress responses were also assessed. All different ILs significantly increased malondialdehyde (MDA), catalase (CAT), peroxidase (POD) and dismutase (SOD) activities in rice tissue. Compared to the control group, the contents of chlorophyll a reduced by 59.56%, 62.28% and 69.74% after addition of [C₂min]Br, [C₄min]Br, and [C₈min]Br, respectively. This study provides important information for a better understanding on the uptake and accumulation of imidazolium ILs by agricultural plants.

Synthesis of silver nanoparticles colloids in imidazolium halide ionic liquids and their antibacterial activities for gram-positive and gram-negative bacteria

Four 1-butyl-3-methylimidazolium halide ionic liquids were synthesized via metathesis and anion exchange reactions. Silver nanoparticles (AgNPs) colloids were synthesized in four ionic liquids in the pressurized reactor by reduction of silver nitrate with hydrogen gas, without adding solvents or stabilizing agents. Antibacterial activities of base ionic liquids and AgNPs colloids in ionic liquids were reviewed by well-diffusion method for gram-positive Bacillus cereus (NCIM-2155) and gram-negative Escherichia coli (NCIM-2931) bacteria. Antibacterial activities of ionic liquids and AgNPs colloids in ionic liquids were observed to be controlled by ionic liquids anions and AgNPs particle size. The 1-butyl-3-methylimidazolium iodide ionic liquid exhibited higher antibacterial activities among the studied ionic liquids. Further, the presence of AgNPs in 1-butyl-3-methylimidazolium iodide, ionic liquid enhanced its antibacterial activity for Bacillus cereus and Escherichia coli bacteria.

Influence of the interfacial molecular structures of quaternary ammonium-type poly(ionic liquid) brushes on their antibacterial properties

Alkyl chains of C4 are more active in killing bacteria than C16 due to their orderly extension toward PBS solution.

Imidazolium-based ionic polyurethanes with high toughness, tunable healing efficiency and antibacterial activities

Ionic polyurethanes (PUs) with high toughness, fast self-healing ability, antibacterial activity and shape memory behaviors are synthesized.

Polyvinylidene fluoride-Hyaluronic acid wound dressing comprised of ionic liquids for controlled drug delivery and dual therapeutic behavior

To improve the efficacy of transdermal drug delivery systems, the physical and chemical properties of drugs need to be optimized to better penetrate into the stratum corneum and to better diffuse into the epidermis and dermis layers. Accordingly, dual-biological function ionic liquids composed of active pharmaceutical ingredients were synthesized, comprising both analgesic and anti-inflammatory properties, by combining a cation derived from lidocaine and anions derived from hydrophobic nonsteroidal anti-inflammatory drugs. Active pharmaceutical ingredient ionic liquids (API-ILs) were characterized through nuclear magnetic resonance, cytotoxicity assay, and water solubility assay. All properties were compared with those of the original drugs. By converting the analgesic and anti-inflammatory drugs into dual-function API-ILs, their water solubility increased up to 470-fold, without affecting their cytotoxic profile. These API-ILs were incorporated into a bilayer wound dressing composed of a hydrophobic polyvinylidene fluoride (PVDF) membrane to act as a drug reservoir and a biocompatible hyaluronic acid (HA) layer. The prepared bilayer wound dressing was characterized in terms of mechanical properties, membrane drug uptake and drug release behavior, and application in transdermal delivery, demonstrating to have desirable mechanical properties and improved release of API-ILs. The assessment of anti-inflammatory activity through the inhibition of LPS-induced production of nitric oxide and prostaglandin E2 by macrophages revealed that the prepared membranes containing API-ILs are as effective as those with the original drugs. Cell adhesion of fibroblasts on membrane surfaces and cell viability assay confirmed improved the viability and adhesion of fibroblasts on PVDF/HA membranes. Finally, wound healing assay performed with fibroblasts showed that the bilayer membranes containing dual-function API-ILs are not detrimental to wound healing, while displaying increased and controlled drug delivery and dual therapeutic behavior. STATEMENT OF SIGNIFICANCE: This work shows the preparation and characterization of bilayer wound dressings comprising dual-biological function active pharmaceutical ingredients based on ionic liquids with improved and controlled drug release and dual therapeutic efficiency. By converting analgesic and anti-inflammatory drugs into ionic liquids, their water solubility increases up to 470-fold. The prepared bilayer wound dressing membranes have desirable mechanical properties and improved release of drugs. The prepared membranes comprising ionic liquids display anti-inflammatory activity as effective as those with the original drugs. Cell adhesion of fibroblasts on membrane surfaces and cell viability assays show improved viability and adhesion of fibroblasts on PVDF/HA membranes, being thus of high relevance as effective transdermal drug delivery systems.

In situ synthesis of biocompatible imidazolium salt hydrogels with antimicrobial activity

Infection with antibiotic-resistant bacteria is becoming a significant public health risk. In this study, we synthesized a series of imidazolium salt (IMS)-containing polymers and hydrogels and tested their antimicrobial properties against both gram-positive (Staphylococcus aureus and MRSA) and gram-negative (Escherichia coli and PA01) bacteria. IMSs were either grafted as side chains or functionalized in the main chain of linear polymers, which demonstrated antimicrobial properties with minimum inhibitory concentrations as low as 2 μg/mL. Similarly, the optimized IMS-containing hydrogel effectively killed MRSA with a 96.1% killing efficiency and inhibited the growth of PA01. These hydrogels also demonstrated high performance in terms of mechanical property (compressive strength >2 MPa) and were noncytotoxic toward human dermal fibroblasts. STATEMENT OF SIGNIFICANCE: A series of polyimidazolium hydrogels were fabricated with acrylamide monomer and poly(ethylene glycol) dimethacrylate by thermal-initiated polymerization. These hydrogels completely killed methicillin-resistant Staphylococcus aureus and inhibited the growth of Pseudomonas aeruginosa. More importantly, these hydrogels demonstrated adequate mechanical property and biocompatibility. These antimicrobial hydrogels have the potential as biomaterials for preventing infections associated with multidrug-resistant bacteria.

Synthesis of new water-soluble ionic liquids and their antibacterial profile against gram-positive and gram-negative bacteria

A series of imidazolium bromide salts (NIM-Br 1a, 1b and 1c) bearing different lengths of alkyl chains were synthesized and theirin vitro antibacterial activities were determined by measuring the minimum inhibitory concentration (MIC) values for Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Enterococcus faecalis. In addition, these imidazolium derivatives were also evaluated against biofilm produced by these bacterial strains. All compounds were found to be effective against Gram-positive and Gram-negative bacteria, and also more effective on the S. aureus biofilm production than the others.

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.

Responsive Ionogel Surface with Renewable Antibiofouling Properties

The synthesis of ionogels with a responsive, self-replenishing surface for combating biofouling is described. Ionogels are prepared by infiltrating poly(vinylidene fluoride-co-hexafluoropropylene) with binary mixtures of ionic liquids (IL): 1-octadecyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([C₁₈ C₁ im][NTf₂ ], melting point T_m = 55 °C) and 1-hexyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([C₆ C₁ im][NTf₂ ], T_m = -9 °C). The IL mixtures release spontaneously from the gel matrix and eventually crystallize on the surface. This leads to self-replenishment of the surface of ionogels even after mechanical damage. The incorporation of [C₆ C₁ im][NTf₂ ] provides the antimicrobial efficacy of ionogels while the crystals of [C₁₈ C₁ im][NTf₂ ] serve as a skeleton maintaining [C₆ C₁ im][NTf₂ ] on the surface. By heating, the ionogel surface transforms from solid to liquid-infused state-the removal of biofilms/bacteria developed under a long time of colonization is facilitated. The antimicrobial efficacy is maintained even after several cycles of biofilm formation and detachment. This work provides an opportunity to apply ionogels as functional coatings with renewable antibiofouling properties.

Fluorescent Imidazolium-Type Poly(ionic liquid)s for Bacterial Imaging and Biofilm Inhibition

Fluorescent imidazolium-type poly(ionic liquid)s (PIL)s were synthesized by anion exchange of bromide (Br^-) in poly(3-butyl-1-vinylimidazolium bromide) (PIL-Br) with a fluorescent anion, namely, 3-(4-(1,2,2-triphenylvinyl)phenoxy)propane-1-sulfonate (TPESO₃^-). Such an anion exchange provided antibacterial PILs with aggregation-induced emission (AIE) properties that simultaneously kill and image bacteria. These fluorescence and antibacterial properties could be regulated by controlling the Br^-/TPESO₃^- ratio. The fluorescence intensity increases as this ratio increases, while the antibacterial property exhibits an opposite trend. Moreover, the AIE-type PILs are useful for fluorescently imaging dead bacteria (macroscopically and microscopically) and could effectively inhibit biofilm growth. This study provided a convenient method to obtain fluorescent PILs with adjustable antibacterial and imaging properties.

Self-assembled systems based on novel hydroxyethylated imidazolium-containing amphiphiles: Interaction with DNA decamer, protein and lipid

The study on aggregation capacity of novel imidazolium-containing amphiphiles of 1-(2-hydroxyethyl)alkylimidazolium bromide series and their interaction with bio-objects (DNA decamer, bovine serum albumin, phospholipid) was performed. It was revealed that introduction of hydroxyethyl moiety into the surfactant molecule resulted in 1.5-2-fold decrease of critical micelle concentration. These modified amphiphiles quantitatively bind DNA decamer due to intercalation and hydrophobic interactions with lipoplex formation. The evaluation of membranotropic properties of these surfactants exhibited that initiation of disordering and compression of the model cell wall consisting of dipalmitoyl phosphocholine (regulation of permeability for various compounds) could be achieved by variation of the length of hydrophobic tail of imidazolium-containing amphiphiles. Transition from individual surfactants solutions to their mixtures with protein (bovine serum albumin) is accompanied by 8-fold decrease of aggregation thresholds and characterized by the presence of two critical points. The binding of components of surfactant/BSA binary systems took place through tryptophan amino acid residue of peptide macromolecule.

Comparative evaluation of antimicrobial activity of different types of ionic liquids

In order to identify most suitable ionic liquids (ILs) for potential applications in infection prevention and control, in the present study we comparatively evaluated the antimicrobial potency and hemolytic activity of 15 ILs, including 11 previously described and four newly synthesized ILs, using standard microbiological procedures against Gram-positive and Gram-negative bacteria. ILs showing the lowest minimum inhibitory concentration (MIC) were tested for their hemolytic activity. Three ILs characterized by low MIC values and low hemolytic activity, namely 1-methyl-3-dodecylimidazolium bromide, 1-dodecyl-1-methylpyrrolidinium bromide, and 1-dodecyl-1-methylpiperidinium bromide were further investigated to determine their minimum bactericidal concentration (MBC), and their ability to inhibit biofilm formation by Staphylococcus aureus or Pseudomonas aeruginosa. Killing kinetics results revealed that both Gram-positive and Gram-negative bacteria are rapidly killed after exposure to MBC of the selected ILs. Furthermore, the selected ILs efficiently inhibited biofilm formation by S. aureus or P. aeruginosa. To our knowledge, this is the first systematic study investigating the antimicrobial potential of different types of ionic liquids using standard microbiological procedures. In the overall, the selected ILs showed low hemolytic and powerful antimicrobial activity, and efficient inhibition of biofilm formation, especially against S. aureus, suggesting their possible application as anti-biofilm agents.

Poly(ionic liquid) Electrolytes for a Switchable Silver Mirror

Imidazolium-type small-molecule ionic liquids (ILs) and their corresponding poly(ionic liquid) (PIL) homopolymers were synthesized and applied to reversible electrochemical mirrors (REMs). The effects of alkyl chain length of the carbon chains at the N3 position and cation charge density (mono- and bis-imidazolium) on the electrochromic properties of Ag-based REMs were investigated by analyzing their electrodeposition and spectral properties. Longer alkyl chains and higher charge densities decreased the size and resulted in a more uniform distribution of Ag nanoparticles. Compared with IL-based liquid electrolytes, the PIL-based gel electrolytes formed smaller and denser electrodeposited metallic Ag nanoparticles because of their higher viscosity. These findings were used to guide fabrication of a 50 cm² mirror dynamic window and flexible display. Because of several unique properties of PILs, the PIL-based REM exhibits fast switching speeds, superb cycling durability, small particle sizes, and uniform electrodeposited Ag nanoparticle films. These results make dynamic windows based on PIL electrolytes promising and competitive alternatives to traditional electrochromic windows.

Rapid and Superior Bacteria Killing of Carbon Quantum Dots/ZnO Decorated Injectable Folic Acid-Conjugated PDA Hydrogel through Dual-Light Triggered ROS and Membrane Permeability

One of the most difficult challenges in the biomedical field is bacterial infection, which causes tremendous harm to human health. In this work, an injectable hydrogel is synthesized through rapid assembly of dopamine (DA) and folic acid (FA) cross-linked by transition metal ions (TMIs, i.e., Zn²⁺ ), which was named as DFT-hydrogel. Both the two carboxyl groups in the FA molecule and catechol in polydopamine (PDA) easily chelates Zn²⁺ to form metal-ligand coordination, thereby allowing this injectable hydrogel to match the shapes of wounds. In addition, PDA in the hydrogel coated around carbon quantum dot-decorated ZnO (C/ZnO) nanoparticles (NPs) to rapidly generate reactive oxygen species (ROS) and heat under illumination with 660 and 808 nm light, endows this hybrid hydrogel with great antibacterial efficacy against Staphylococcus aureus (S. aureus, typical Gram-positive bacteria) and Escherichia coli (E. coli, typical Gram-negative bacteria). The antibacterial efficacy of the prepared DFT-C/ZnO-hydrogel against S. aureus and E. coli under dual-light irradiation is 99.9%. Importantly, the hydrogels release zinc ions over 12 days, resulting in a sustained antimicrobial effect and promoted fibroblast growth. Thus, this hybrid hydrogel exhibits great potential for the reconstruction of bacteria-infected tissues, especially exposed wounds.

Rational Optimization and Action Mechanism of Novel Imidazole (or Imidazolium)-Labeled 1,3,4-Oxadiazole Thioethers as Promising Antibacterial Agents against Plant Bacterial Diseases

The emergence and widespread occurrence of plant bacterial diseases that cause global production constraints have become major challenges to agriculture worldwide. To promote the discovery and development of new bactericides, imidazole-labeled 1,3,4-oxadiazole thioethers were first fabricated by integrating the crucially bioactive scaffolds of the imidazole motif and 1,3,4-oxadiazole skeleton in a single molecular architecture. Subsequently, a superior antibacterial compound A₆ was gradually discovered possessing excellent competence against plant pathogens Xanthomonas oryzae pv oryzae and Xanthomonas axonopodis pv citri with EC₅₀ values of 0.734 and 1.79 μg/mL, respectively. These values were better than those of commercial agents bismerthiazol (92.6 μg/mL) and thiodiazole copper (77.0 μg/mL). Further modifying the imidazole moiety into the imidazolium scaffold led to the discovery of an array of potent antibacterial compounds providing the corresponding minimum EC₅₀ values of 0.295 and 0.607 μg/mL against the two strains. Moreover, a plausible action mechanism for attacking pathogens was proposed based on the concentration dependence of scanning electron microscopy, transmission electron microscopy, and fluorescence microscopy images. Given the simple molecular structures, easy synthetic procedure, and highly efficient bioactivity, imidazole (or imidazolium)-labeled 1,3,4-oxadiazole thioethers can be further explored and developed as promising indicators for the development of commercial drugs.

Structure-function relationships of nonviral gene vectors: Lessons from antimicrobial polymers

In recent years, substantial advances have been achieved in the design and synthesis of nonviral gene vectors. However, lack of effective and biocompatible vectors still remains a major challenge that hinders their application in clinical settings. In the past decade, there has been a rapid expansion of cationic antimicrobial polymers, due to their potent, rapid, and broad-spectrum biocidal activity against resistant microbes, and biocompatible features. Given that antimicrobial polymers share common features with nonviral gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. Building off these observations, we provide here an overview of the structure-function relationships of polymers for both antimicrobial applications and gene delivery by elaborating some key structural parameters, including functional groups, charge density, hydrophobic/hydrophilic balance, MW, and macromolecular architectures. By borrowing a leaf from antimicrobial agents, great advancement in the development of newer nonviral gene vectors with high transfection efficiency and biocompatibility will be more promising. STATEMENT OF SIGNIFICANCE: The development of gene delivery is still in the preclinical stage for the lack of effective and biocompatible vectors. Given that antimicrobial polymers share common features with gene vectors in various aspects, such as membrane affinity, functional groups, physicochemical characteristics, and unique macromolecular architectures, these polymers may provide us with inspirations to overcome challenges in the design of novel vectors toward more safe and efficient gene delivery in clinic. In this review, we systematically summarized the structure-function relationships of antimicrobial polymers and gene vectors, with which the design of more advanced nonviral gene vectors is anticipated to be further boosted in the future.

Rapid Identification of Bacteria by Membrane-Responsive Aggregation of a Pyrene Derivative

An imidazolium-derived pyrene aggregation was developed to rapidly identify and quantify different bacteria species. When the nonemissive aggregates bound to the anionic bacteria surface, the sensor disassembled to turn on significant fluorescence. At the same time, ratiometric signals between pyrene monomer and excimer emission were controlled by different interactions with various bacteria surfaces. The resulted different fluorescent emission profiles then were obtained as fingerprints for various bacterial species. By converting emission profiles directly into output signals of two channels, fluorescence increase and ratiometric change, a two-dimensional analysis map was generated for bacteria identification. We demonstrated that our sensor rapidly identified 10 species of bacteria and 14 clinical isolated multidrug-resistant bacteria, and we determined their staining properties (Gram-positive or Gram-negative).

Does poly(ionic liquid) modulate the non-covalent interactions of chicken egg white lysozyme? Elucidation of biomolecular interactions between biomolecules and macromolecular solvents

Stabilizing and destabilizing effects of different poly(ionic liquid) (PIL) concentrations on chicken egg white lysozyme as a reason for bimolecular interactions.

Antibacterial activities of N-alkyl imidazolium-based poly(ionic liquid) nanoparticles

N-Alkyl imidazolium-based PIL nanoparticles can effectively kill bacteria through adhering to the bacterial surface and then disrupting the cell membrane.

Facile and Versatile Modification of Cotton Fibers for Persistent Antibacterial Activity and Enhanced Hygroscopicity

Natural fibers with functionalities have attracted considerable attention. However, developing facile and versatile strategies to modify natural fibers is still a challenge. In this study, cotton fibers, the most widely used natural fibers, were partially oxidized by sodium periodate in aqueous solution, to give oxidized cotton fibers containing multiple aldehyde groups on their surface. Then poly(hexamethylene guanidine) was chemically grafted onto the oxidized cotton fibers forming Schiff bases between the terminal amines of poly(hexamethylene guanidine) and the aldehyde groups of oxidized cotton fibers. Finally, carbon-nitrogen double bonds were reduced by sodium cyanoborohydride, to bound poly(hexamethylene guanidine) covalently to the surface of cotton fibers. These functionalized fibers show strong and persistent antibacterial activity: complete inhibition against Escherichia coli and Staphylococcus aureus was maintained even after 1000 consecutive washing in distilled water. On the other hand, cotton fibers with only physically adsorbed poly(hexamethylene guanidine) lost their antibacterial activity entirely after a few washes. According to Cell Counting Kit-8 assay and hemolytic analysis, toxicity did not significantly increase after chemical modification. Attributing to the hydrophilicity of poly(hexamethylene guanidine) coatings, the modified cotton fibers were also more hygroscopic compared to untreated cotton fibers, which can improve the comfort of the fabrics made of modified cotton fibers. This study provides a facile and versatile strategy to prepare modified polysaccharide natural fibers with durable antibacterial activity, biosecurity, and comfortable touch.

Understanding the effect of alkyl chains of gemini cations on the physicochemical and cellular properties of polyurethane micelles

Cationic gemini quaternary ammonium (GQA) has been used as a cell internalization promoter to improve the permeability of the cell membrane and enhance the cellular uptake. However, the effect of the alkyl chain length on the cellular properties of nanocarriers has not been elucidated yet. In this study, we developed a series of polyurethane micelles containing GQAs with various alkyl chain lengths. The alteration of the gemini alkyl chain length was found to change the distribution of GQA surfactants in the micellar structure and affect the surface charge exposure, stability, and the protein absorption properties of nanocarriers. Moreover, we also clarified the role of the alkyl chain length in tumor cell internalization and macrophage uptake of polyurethane micelles. This work provides a new understanding on the effect of the GQA alkyl chain length on the physicochemical and biological properties of nanomedicines, and offers guidance on the rational design of effective drug delivery systems where the issue of functional group exposure at the micellar surface should be considered.

The Use of Liquids Ionic Fluids as Pharmaceutically Active Substances Helpful in Combating Nosocomial Infections Induced by Klebsiella Pneumoniae New Delhi Strain, Acinetobacter Baumannii and Enterococcus Species

This review deals with various microbiological activities of ionic liquids, which constitute the first anti-infective defense against multi-drug-resistant bacteria-with a particular emphasis placed on medicine and pharmacology. The quoted data on the biological activity of ionic liquids including their antimicrobial properties (depending on the type of a cation or an anion) and are discussed in view of possible applications in nosocomial infections. Dedicated attention is given to finding infections with the Klebsiella pneumoniae New Delhi strain, Acinetobacter baumannii, and Enterococcus species, which are responsible for the induction of antibiotic resistance in intensive care units. Diagnosis and treatment using current antibiotics is a significant problem in hospital care, and the relevant burden on the health systems of the European Union member states induces the search for new, effective methods of treatment. Ionic liquids, due to their antibacterial effect, can be considered topical and general medications and may provide the basis for treatment to eliminate the antibiotic resistance phenomenon in the future. At present, the number of infections with resistant pathogens in hospitals and outpatient clinics in the European Union is growing. In 2015⁻2017, a significant incidence of respiratory and bloodstream infections with bacteria resistant to antibiotics from the 3rd generation group of cephalosporins, glycopeptides, and carbapenems were observed. The paper presents examples of synthesized bifunctional salts with at least one pharmaceutically active ion in obtaining a controlled release, controlled delivery, and biological impact on the pathogenic bacteria, viruses and fungi. The ionic liquids obtained in the presented way may find applications in the treatment of wounds and infections.

Chemo-Enzymatic Synthesis of Poly(4-piperidine lactone- b-ω-pentadecalactone) Block Copolymers as Biomaterials with Antibacterial Properties

With increasing troubles in bacterial contamination and antibiotic-resistance, new materials possessing both biocompatibility and antimicrobial efficacy are supposed to be developed for future biomedical application. Herein, we demonstrated a chemo-enzymatic ring opening polymerization (ROP) approach for block copolyester, that is, poly(4-benzyl formate piperidine lactone- b-ω-pentadecalactone) (PNPIL- b-PPDL), in a one-pot two-step process. Afterward, cationic poly(4-piperidine lactone- b-ω-pentadecalactone) (PPIL- b-PPDL) with pendent secondary amino groups was obtained via acidic hydrolysis of PNPIL- b-PPDL. The resulting cationic block copolyester exhibited high antibacterial activity against Gram negative E. coli and Gram positive S. aureus, while showed low toxicity toward NIH-3T3 cells. Moreover, the antibacterial property, cytotoxicity and degradation behavior could be tuned simply by variation of PPIL content. Therefore, we anticipate that such cationic block copolymers could potentially be applied as biomaterials for medicine or implants.