Micelle formation of imidazolium ionic liquids in aqueous solution

Piezoelectric biomaterials with embedded ionic liquids for improved orthopedic interfaces through osseointegration and antibacterial dual characteristics

Orthopedic implant failures, primarily attributed to aseptic loosening and implant site infections, pose significant challenges to patient recovery and lead to revision surgeries. Combining piezoelectric materials with ionic liquids as interfaces for orthopedic implants presents an innovative approach to addressing both issues simultaneously. In this study, films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) incorporated with 1-ethyl-3-methylimidazolium hydrogen sulfate ([Emim][HSO4]) ionic liquid were developed. These films exhibited strong antibacterial properties, effectively reducing biofilm formation, thereby addressing implant-related infections. Furthermore, stem cell-based differentiation assays exposed the potential of the composite materials to induce osteogenesis. Interestingly, our findings also revealed the upregulation of calcium channel expression as a result of electromechanical stimulation, pointing to a mechanistic basis for the observed biological effects. This work highlights the potential of piezoelectric materials with ionic liquids to improve the longevity and biocompatibility of orthopedic implants. Offering dual-functionality for infection prevention and bone integration, these advancements hold significant potential for advancing orthopedic implant technologies and improving patient outcomes.

Exploring the impact of sodium salts on hydrotropic solubilization

Some ionic liquids (ILs) were shown to display a strong ability to enhance the solubility of phenolic compounds through hydrotropy. However, evidence shows that salt ions in hydrotropic aqueous solutions may change the behavior of molecules by promoting possible interactions between the components of the system, thus causing changes in solubility. Herein, we study the impact of sodium salt anions on the hydrotropic dissolution of syringic acid using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) as a hydrotrope, with a focus on dicyanamide Na[N(CN)2] and thiocyanate Na[SCN] salts. Dynamic light scattering, Raman spectroscopy, and nuclear magnetic resonance spectroscopy were used to investigate how the mixture of IL-salts affects the solvation. The results obtained show that [C4mim]Cl is able to increase the solubility of syringic acid 80-fold. Despite their structural similarities, the presence of Na[N(CN)2] or Na[SCN] in an aqueous solution of [C4mim]Cl induced opposite solubility trends. The addition of Na[N(CN)2] promotes a higher ability to solubilize syringic acid than in the corresponding IL system due to a pH buffering effect, resulting in the deprotonation of the solute. The addition of Na[SCN], on the other hand, induces a relative decrease in syringic acid solubilization at higher concentrations of ILs due to the negative contribution of the NaCl formed by anion-exchange. These results emphasise the often overlooked pH contribution provided by ILs for biomolecule solubilisation whilst providing experimental insights into the structure of aqueous solutions of ionic liquids and the role it plays in the formation of IL-salt aggregates.

Biodegradable arginine based steroid-surfactants: Cationic green agents for hydrophobic ion-pairing

The aim of this study was to evaluate the safety and efficacy for hydrophobic ion-pairing of surfactants based on arginine (Arg). The prepared Arg-cholesteryl ester (ACE) and Arg-diosgenyl ester (ADE) were characterized regarding solubility, pKa, critical micellar concentration (CMC), biodegradability as well as membrane- and aquatic toxicity using DOTAP as reference. The ability for hydrophobic ion-pairing was evaluated and the lipophilicity of formed complexes was determined. NMR, FT-IR and MS confirmed successful synthesis of Arg-surfactants. The slightly soluble single-charged Arg-surfactants (pH < pKa₃ (ACE = 10.42 ± 0.52; ADE = 10.38 ± 0.27)) showed CMCs of 27.17 µM for ACE and 35.67 µM for ADE. CMCs of the sparingly soluble double-charged species (pH < pKa₂ (ACE = 5.30 ± 0.20; ADE = 5.55 ± 0.06)) were determined at concentrations of ≥ 250 µM for ACE and ≥ 850 µM for ADE. The enzymatic- and environmental biodegradability was proven by an entire cleavage of Arg-surfactants within 24 h, whereas DOTAP remained stable. Arg-surfactants exhibited lower membrane- (> 2-fold) and aquatic toxicity (> 15-fold) than DOTAP. The complexes formed with Arg-surfactants and insulin showed higher lipophilicity than the DOTAP-complex. According to these results, Arg-surfactants might be a promising safe tool for the delivery of peptide drugs.

Ionic Liquids as Biocompatible Antibacterial Agents: A Case Study on Structure-Related Bioactivity on Escherichia coli

The potential of ionic liquids (ILs) to be used as antimicrobial agents for biomedical applications has been hindered by the fact that most of them are cytotoxic toward mammalian cells. Understanding the mechanism of bacterial and mammalian cellular damage of ILs is key to their safety design. In this work, we evaluate the antimicrobial activity and mode of action of several ILs with varying anions and cations toward the clinically relevant Gram-negative Escherichia coli. Langmuir monolayer technique was used to evaluate if the IL's mode of action was related to the bacterial cell membrane interaction for an effective E. coli killing. 1-Decyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide [DMIM][TFSI] and trihexyltetradecyl phosphonium bis(trifluoromethylsulfonyl) imide [P_6,6,6,14][TFSI] were surface-active and induced bacterial cell lysis, through a membrane-disruption phenomenon on bacteria, in a mechanism that was clearly related to the long alkyl chains of the cation. 1-Ethyl-3-methylimidazolium hydrogen sulfate [EMIM][HSO₄] was highly antimicrobial toward E. coli and found suitable for biological applications since it was harmless to mammalian cells at most of the tested concentrations. The results suggest that the imidazolium cation of the ILs is mostly responsible not only for their antimicrobial activity but also for their cytotoxicity, and the inclusion of different anions may tailor the ILs' biocompatibility without losing the capacity to kill bacteria, as is the case of [EMIM][HSO₄]. Importantly, this IL was found to be highly antimicrobial even when incorporated in a polymeric matrix.

Ionic Liquid-Based Polymer Nanocomposites for Sensors, Energy, Biomedicine, and Environmental Applications: Roadmap to the Future

Current interest toward ionic liquids (ILs) stems from some of their novel characteristics, like low vapor pressure, thermal stability, and nonflammability, integrated through high ionic conductivity and broad range of electrochemical strength. Nowadays, ionic liquids represent a new category of chemical-based compounds for developing superior and multifunctional substances with potential in several fields. ILs can be used in solvents such as salt electrolyte and additional materials. By adding functional physiochemical characteristics, a variety of IL-based electrolytes can also be used for energy storage purposes. It is hoped that the present review will supply guidance for future research focused on IL-based polymer nanocomposites electrolytes for sensors, high performance, biomedicine, and environmental applications. Additionally, a comprehensive overview about the polymer-based composites' ILs components, including a classification of the types of polymer matrix available is provided in this review. More focus is placed upon ILs-based polymeric nanocomposites used in multiple applications such as electrochemical biosensors, energy-related materials, biomedicine, actuators, environmental, and the aviation and aerospace industries. At last, existing challenges and prospects in this field are discussed and concluding remarks are provided.

Removal of Perfluorooctanoic Acid from Water Using a Hydrophobic Ionic Liquid Selected Using the Conductor-like Screening Model for Realistic Solvents

The conductor-like screening model for realistic solvents was used to identify ionic liquids (ILs) to efficiently extract perfluorooctanoic acid (PFOA). The infinite dilution chemical potentials of PFOA in 14 000 ILs were calculated and used as descriptors of the chemical affinities between the ILs and PFOA. Trihexyltetradecylphosphonium pivalate ([P6,6,6,14][Piv]) was found to be a good IL for extracting PFOA because it gave a well-balanced combination of a strong chemical attraction for PFOA and useful physicochemical properties. The results of experiments indicated that [P6,6,6,14][Piv] could remove >99.9% of the PFOA in an aqueous solution. However, problematic emulsification of IL in the aqueous phase occurred at PFOA/IL molar ratios <1.9-2.1, and this limited the PFOA removal rate to 80-91%. The ability of the used IL to extract PFOA was found to be partially regenerated by washing the IL with 1% NaOH, and the IL could be reused to extract PFOA with a removal rate decreased by ∼10% in each cycle.

Interaction of ionic liquids with human serum albumin in the view of bioconcentration: a preliminary study

Bioaccumulation potential is critical in PBT and risk assessment of chemicals. However, for ionic liquids (ILs), this aspect remains neglected. It is especially important to fill this gap, because for this group of compounds, existing data confirm their risk of being environmentally persistent and toxicity. Moreover, considering preliminary reports on the interactions of ILs with lipids, it may be assumed that ILs have a higher potential for bioaccumulation than indicated by previous estimations built upon octanol–water partition coefficients. Moreover, the bioconcentration of ionizable chemical compounds may also be strongly related to plasma protein contents. Therefore, in this work, the affinity of a set of imidazolium cations and organic anions, and their combination to human serum albumin (HSA) was determined. The obtained results reveal that both cations and anions can be strongly bound to HSA, and blood proteins might play an important role in overall bioaccumulation. Furthermore, it was observed that HSA binding properties towards IL cations depend on the hydrophobicity of cations. The obtained data also provide indication that cation–anion interaction may affect ILs ions affinity to HSA.

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.

Stable and Oriented Liquid Crystal Droplets Stabilized by Imidazolium Ionic Liquids

Liquid crystals represent a fascinating intermediate state of matter, with dynamic yet organized molecular features and untapped opportunities in sensing. Several works report the use of liquid crystal droplets formed by microfluidics and stabilized by surfactants such as sodium dodecyl sulfate (SDS). In this work, we explore, for the first time, the potential of surface-active ionic liquids of the imidazolium family as surfactants to generate in high yield, stable and oriented liquid crystal droplets. Our results show that [C₁₂MIM][Cl], in particular, yields stable, uniform and monodisperse droplets (diameter 74 ± 6 µm; PDI = 8%) with the liquid crystal in a radial configuration, even when compared with the standard SDS surfactant. These findings reveal an additional application for ionic liquids in the field of soft matter.

Importance of Conjugation of the Bile Salt on the Mechanism of Lipolysis

We aim to advance the discussion on the significance of the conjugation of bile salts (BS) in our organism. We hypothesize that conjugation influences the rate of lipolysis. Since the rate of lipolysis is a compound parameter, we compare the effect of conjugation on four surface parameters, which contribute to the rate. Since deconjugation is due to gut microbiota, we hypothesize that microbiota may affect the rate of lipolysis. A meta-analysis of literature data of critical micelle concentration, β, aggregation number, and molar solubilization ratio has been performed for the first time. In addition, critical micelle concentration (CMC), interfacial tension, and lipolysis rate measurements were performed. It was found that the unconjugated BS in mixed micelles increases the antagonism between the BS, therefore, increasing the CMC. This correlated with the effect of unconjugated BS on the solubilization capacity of mixed micelles. The collected literature information indicates that the role of the BS and its conjugation in our organism is a key factor influencing the functioning of our organism, where too high levels of unconjugated BS may lead to malabsorption of fat-soluble nutrients. The experimental lipolysis results irrevocably showed that conjugation is a significant factor influencing the rate.

Ionic Liquid-Based Materials for Biomedical Applications

Ionic liquids (ILs) have been extensively explored and implemented in different areas, ranging from sensors and actuators to the biomedical field. The increasing attention devoted to ILs centers on their unique properties and possible combination of different cations and anions, allowing the development of materials with specific functionalities and requirements for applications. Particularly for biomedical applications, ILs have been used for biomaterials preparation, improving dissolution and processability, and have been combined with natural and synthetic polymer matrixes to develop IL-polymer hybrid materials to be employed in different fields of the biomedical area. This review focus on recent advances concerning the role of ILs in the development of biomaterials and their combination with natural and synthetic polymers for different biomedical areas, including drug delivery, cancer therapy, tissue engineering, antimicrobial and antifungal agents, and biosensing.

The Hydrotropic Effect of Ionic Liquids in Water-in-Salt Electrolytes*

Water-in-salt electrolytes have successfully expanded the electrochemical stability window of aqueous electrolytes beyond 2 V. Further improvements in stability can be achieved by partially substituting water with either classical organic solvents or ionic liquids. Here, we study ternary electrolytes composed of LiTFSI, water, and imidazolium ionic liquids. We find that the LiTFSI solubility strongly increases from 21 mol kg^-1 in water to up to 60 mol kg^-1 in the presence of ionic liquid. The solution structure is investigated with Raman and NMR spectroscopy and the enhanced LiTFSI solubility is found to originate from a hydrotropic effect of the ionic liquids. The increased reductive stability of the ternary electrolytes enables stable cycling of an aqueous lithium-ion battery with an energy density of 150 Wh kg^-1 on the active material level based on commercially relevant Li₄ Ti₅ O₁₂ and LiNi_0.8 Mn_0.1 Co_0.1 O₂ electrode materials.

Surfing the Third Wave of Ionic Liquids: A Brief Review on the Role of Surface-Active Ionic Liquids in Drug Development and Delivery

The relevance of ionic liquids (ILs) is now well established in many fields, as their unique properties make them appealing as 1) greener alternatives to organic solvents (first-generation ILs), 2) tunable task-specific materials (second-generation ILs), and 3) multifunctional players in life and pharmaceutical sciences (third-generation ILs). This third wave of ILs encompasses a wide range of compounds, from bioactive molecules with single or even dual therapeutic action, to potential ingredient molecules for drug formulation and transport systems. In this context, the focus of this review is the emergent role of surface-active ionic liquids (SAILs) in drug development and delivery.

Ionic Systems and Nanomaterials as Antiseptic and Disinfectant Agents for Surface Applications: A Review

Antiseptics and disinfectants are extensively used for a variety of topical and hard-surface applications. A wide variety of biocides as active chemical agents is found in these products, including alcohols, phenols, iodine, and chlorine. Many of these active agents demonstrate broad-spectrum antimicrobial activity; however, the mode of action of these agents is not well-documented. This review is focused on several examples of ionic systems based on ionic surfactants and ionic liquids as well as nanomaterials and nanoparticles acting as antiseptics and disinfectants for surfaces. It is important to note that many of these biocides may be used singly or in combination in a variety of products, which vary considerably in activity against microorganisms. Antimicrobial activity can be influenced by several factors such as formulation effects, presence of an organic load, synergy, temperature, dilution, and test method. The most promissory compounds based on ionic systems and nanomaterials published in mainly the last decade is chronologically reported in this review.

Scrutinizing Self-Assembly, Surface Activity and Aggregation Behavior of Mixtures of Imidazolium Based Ionic Liquids and Surfactants: A Comprehensive Review

The desire of improving various processes like enhanced oil recovery (EOR), water treatment technologies, biomass extraction, organic synthesis, carbon capture etc. in which conventional surfactants have been traditionally utilized; prompted various researchers to explore the self-assembly and aggregation behavior of different kinds of surface-active molecules. Ionic liquids (ILs) with long alkyl chain present in their structure constitute the advantageous properties of surfactant and ILs, hence termed as surface-active ionic liquids (SAILs). The addition of ILs and SAILs significantly influence the surface-activity and aggregation behavior of industrially useful conventional surfactants. After a brief review of ILs, SAILs and surfactants, the prime focus is made on analyzing the self-assembly of SAILs and the mixed micellization behavior of conventional surfactants with different ILs.

Synergic effects of ultrasound and ionic liquids on fluconazole emulsion

The aim of this work was to evaluate the influence of US on the properties of the fluconazole emulsions prepared using imidazolium-based ILs ([C_n C₁im]Br). The effects of the preparation method (mechanical stirring or US), US amplitude, alkyl chain length (of [C₁₂C₁im]Br or [C₁₆C₁im]Br), and IL concentration on the physicochemical properties were evaluated. Properties such as droplet size, span index, morphology, viscosity encapsulation efficiency, and drug release profile were determined. The results showed that US-prepared emulsions had a smaller droplet size and smaller polydispersity (Span) than those prepared by mechanical stirring. Additionally, the results showed that emulsions prepared with [C₁₆C₁im]Br and US had spherical shapes and increased stability compared to emulsions prepared by MS, and also depended on the IL concentration. The emulsion prepared by US at 40% amplitude had increased encapsulation efficiency. US provided a decrease in the viscosity of emulsions containing [C₁₂C₁im]Br; however, in general, all emulsions had viscosity close to that of water. Emulsions containing [C₁₆C₁im]Br had the lowest viscosities of all the emulsions. The emulsions containing the IL [C₁₆C₁im]Br had more controlled release and a lower cumulative percentage of drug release. The IL concentration required to prepare these emulsions was lower than the amount of conventional surfactant required, which highlights the potential synergic effects of ILs and US in preparing emulsions of hydrophobic drugs.

Ionic liquids as environmental hazards - Crucial data in view of future PBT and PMT assessment

Ionic liquids (ILs) constitute a large group of chemical compounds. They have gained much attention among scientists and industry due to their unique properties. Due to the fact that ILs are purely ionic compounds, there is the possibility to design an enormous number of cation and anion combinations, making them designer solvents. Thus it also creates the possibility of producing more environmentally benign solvents. However, significant drawbacks related mainly to their toxicity and persistence have already been noticed. Furthermore the interest in these compounds is constantly growing and their impact on the environment should be defined. More and more ILs are produced or imported in the amount higher than 10 tonnes per year and the group of ILs registered in REACH is still expanding. Thus for an increasing number of compounds, it will be necessary to perform a PBT and PMT assessment using the criteria described in REACH. Therefore the data collected in this work thoroughly sort out the information on the toxicity, bioconcentration/bioaccumulation, biodegradation and mobility of ILs in the context of PBT and PMT assessment.

Synergistic interactions of ionic liquids and antimicrobials improve drug efficacy

Combinations of ionic liquids (ILs) with antimicrobial compounds have been shown to produce synergistic activities in model liposomes. In this study, imidazolium chloride-based ILs with alkyl tail length variations are combined with commercially available, small-molecule antimicrobials to examine the potential for combinatorial and synergistic antimicrobial effects on P. aeruginosa, E. coli, S. aureus, and S. cerevisiae. The effects of these treatments in a human cell culture model indicate the cytotoxic limits of ILs paired with antimicrobials. The analysis of these ILs demonstrates that the length of the alkyl chain on the IL molecule is proportional to both antimicrobial activity and cytotoxicity. Moreover, the ILs which exhibit synergy with small-molecule antibiotics appear to be acting in a membrane permeabilizing manner. Collectively, results from these experiments demonstrate an increase in antimicrobial efficacy with specific IL + antimicrobial combinations on microbial cultures while maintaining low cytotoxicity in a mammalian cell culture model.

Unique Orientation of the Solid-Solid Interface at the Janus Particle Boundary Induced by Ionic Liquids

This study reveals the unique role on Janus particles of the solid-solid interface at the boundary in determining particle interactions and assembly. In an aqueous ionic liquid (IL) solution, Janus spheres adopt intriguing orientations with their boundaries pinned on the glass substrate. It was further discovered that the orientation was affected by the particle amphiphilicity as well as the chemical structure and concentration of the IL. Further characterization suggests that the adsorption on the hydrophilic side is due to both an electrostatic interaction and hydrogen bonding, while adsorption on the hydrophobic side is due to hydrophobic attraction. Through the concerted interplay of all these interactions, the amphiphilic boundary may attract an excessive amount of IL cations, which guide the unique orientations of the Janus spheres. The results highlight the importance of the Janus boundary that has not been recognized previously. Adsorption at the solid-solid interfaces may inspire new applications in areas such as separation and catalysis.

Morphological and Interaction Characteristics of Surface-Active Ionic Liquids and Palmitic Acid in Mixed Monolayers

A series of water soluble, surface-active ionic liquids (SAILs), namely, 1-alkyl-3-methyl imidazolium chlorides ([C_n -mim]Cl) and their mixtures with palmitic acid (PA) are investigated in Langmuir monolayers and Langmuir-Blodgett films. It is inferred from the surface pressure-area isotherms that C₁₆ -mim-IL mixes non-ideally with PA and stabilizes the binary mixed films. In addition, the residence of mim-IL at the water surface is enhanced as a function of the increasing alkyl side chain length. Generally, the compressional moduli values decrease upon increasing the content of the mim-ILs over a wide range of compositions. Furthermore, film relaxation measurements indicate that the IL component is selectively excluded from the mixed films upon achieving a certain target pressure. Brewster angle microscope images demonstrate minimal changes on the PA domains in the presence of either C₄ - and C₈ -mim-ILs, whereas presence of the hexadecyl counterpart results in the formation of condensed sheets. Atomic force microscopy imaging of deposited films show the formation of propeller-like aggregates when C₈ - or C₁₆ -mim-IL is present in the mixed films.

Lysine-Based Biodegradable Surfactants: Increasing the Lipophilicity of Insulin by Hydrophobic Ion Paring

AIM

The aim of this study was to evaluate biodegradable cationic surfactants based on lysine.

METHODS

Lysine was esterified with cholesterol, oleyl alcohol and 1-decanol resulting in cholesteryl lysinate (CL), oleyl lysinate (OL) and decyl lysinate (DL). Esters were investigated regarding their log D_{n-octanol/water}, critical micelle concentration (CMC) and biodegradability. Hemolytic potential of CL, OL, DL and the already established hexadecyl lysinate (HL) was determined and complexes with insulin (INS) were formed by hydrophobic ion pairing (HIP). Lipophilic characteristics of ion-pairs were examined by analyzing their log P_{n-butanol/water}.

RESULTS

Successful synthesis of CL, OL and DL was confirmed by IR, NMR and MS. Log D analysis revealed amphiphilic properties for the esters and a CMC of 0.01 mM, 2.0 mM and 6.0 mM was found for CL, OL and DL, respectively. Biodegradability was proven, as over 99% of OL and DL were degraded by isolated enzymes within 30 min and after 3 h 97% of CL was cleaved by membrane bound enzymes. OL as well as DL displayed no hemolytic effect and for CL cytotoxicity was significantly reduced in comparison to HL. INS/CL complex exhibited highest lipophilicity.

CONCLUSION

Cholesterol-amino acid based surfactants seem to be promising agents for HIP.