Effect of choline carboxylate ionic liquids on biological membranes

Choline chloride-based deep eutectic solvent as an inhibitor of metalloproteases (collagenase and elastase) in cosmetic formulation

Green chemistry and engineering are potential alternatives for achieving higher sustainability and lower generation of hazardous compounds in chemical product design, production, and use. Deep Eutectic Solvents (DES) are characterized as green solvents and have become increasingly attractive due to their characteristic design solvents. In this work, two DES (choline chloride (ChCl)/glycerol and ChCl/Urea), aqueous solutions of the DES-forming components, and green tea extracts obtained with DES were used as anti-ageing active in cosmetic products using in vitro tests to inhibit extracellular matrix metalloproteases (such as collagenase and elastase). Finally, the stability of the formulations with DES as a cosmetic active was also evaluated. The results showed that DES based on ChCl/Urea and ChCl/glycerol exhibited remarkable inhibition values of collagenase (91.1 and 92.7%, respectively) and elastase (49.8 and 45.7%, respectively). However, pure urea displayed better inhibition values (66%) for elastase, possibly due to its direct contribution to intramolecular hydrogen bonds. ChCl/glycerol showed remarkable stability in the average cube diameter values, which may indicate no change in the conformation of the micellar structure of the cosmetic formulation. Moreover, the formulation containing this DES remained stable at room temperature. Given the remarkable results, DES can be applied in cosmetic products for anti-ageing purposes.

Advances Brought by Hydrophilic Ionic Liquids in Fields Involving Pharmaceuticals

The negligible volatility and high tunable nature of ionic liquids (ILs) have been the main drivers of their investigation in a wide diversity of fields, among which is their application in areas involving pharmaceuticals. Although most literature dealing with ILs is still majorly devoted to hydrophobic ILs, evidence on the potential of hydrophilic ILs have been increasingly provided in the past decade, viz., ILs with improved therapeutic efficiency and bioavailability, ILs with the ability to increase drugs' aqueous solubility, ILs with enhanced extraction performance for pharmaceuticals when employed in biphasic systems and other techniques, and ILs displaying low eco/cyto/toxicity and beneficial biological activities. Given their relevance, it is here overviewed the applications of hydrophilic ILs in fields involving pharmaceuticals, particularly focusing on achievements and advances witnessed during the last decade. The application of hydrophilic ILs within fields involving pharmaceuticals is here critically discussed according to four categories: (i) to improve pharmaceuticals solubility, envisioning improved bioavailability; (ii) as IL-based drug delivery systems; (iii) as pretreatment techniques to improve analytical methods performance dealing with pharmaceuticals, and (iv) in the recovery and purification of pharmaceuticals using IL-based systems. Key factors in the selection of appropriate ILs are identified. Insights and perspectives to bring renewed and effective solutions involving ILs able to compete with current commercial technologies are finally provided.

Phase Behavior of Aqueous Biphasic Systems with Choline Alkanoate Ionic Liquids and Phosphate Solutions: The Influence of pH

Aqueous biphasic systems (ABS) composed of the choline alkanoate ionic liquids (ILs) choline acetate [Cho][OAc], choline propanoate [Cho][Pro], choline butyrate [Cho][But], and choline hexanoate [Cho][Hex], mixed with K3PO4 solutions at pH 7.2 and 14.5, were prepared and their phase diagrams were compared. The ability to form ABS with alkaline K3PO4 solutions decreased in the order [Cho][OAc] ≈ [Cho][Pro] > [Cho][But] > [Cho][Hex], while with neutral K3PO4 solutions, [Cho][OAc] could not form an ABS, and the other three ILs performed similarly. All of the biphasic regions of the ABS decreased with the increase in pH. 1H-NMR data indicated anion exchange between phases in ABS at neutral pH. The ABS at neutral pH were evaluated to extract the triazine herbicides simazine, cyanazine, and atrazine, and the ABS formed by [Cho][Pro] and the pH 7.2 K3PO4 solution has shown extraction recoveries higher than 90%.

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.

Novel ammonium dichloroacetates with enhanced herbicidal activity for weed control

Dichloroacetic acid (DCA) exhibits great potential as an herbicide (nontoxic, easily biodegradable), but its application in agriculture has scarcely been investigated. Since DCA readily undergoes photolysis when exposed to natural light or UV irradiation, there is a large activity loss in controlling weeds. To improve the activity of DCA, we proposed the transformation of DCA into an ionic salt form by using an herbicidal ionic liquids (HILs) strategy. Herein, fifteen novel ammonium dichloroacetates were designed and achieved for the first time. When compared to the anionic precursor DCA, three salts with longer alkyl chains ranging from dodecyl to hexadecyl chains were found to enhance not only the post emergence herbicidal activity but also the rates of activity against some broadleaf weeds under greenhouse conditions. The enhancement was due to the synergistic effect of structural factors, such as the surface activity, solubility and stability arising from their ionic nature. In addition, IL 13 possesses a low phytotoxicity to cotton plants with a favorable selectivity index above 2. This study will be useful for the design of new, high-performance herbicidal formulations.

Preparation, Characterization, and Formulation Optimization of Ionic-Liquid-in-Water Nanoemulsions toward Systemic Delivery of Amphotericin B

Amphotericin B (AmB) is an antifungal agent that poses a challenge for intravenous drug delivery due to its hydrophobicity and severe side effects that are attributed to the self-aggregation of AmB in aqueous solution. To overcome this problem, we have rationally designed an ionic-liquid-in-water nanoemulsion drug delivery system that harnesses the unique properties of ionic liquids. The complex drug AmB serves as a model pharmaceutical agent to demonstrate the robustness of ionic-liquid-in-water nanoemulsions. High concentrations of AmB were solubilized in a new hydrophobic dicholinium-based ionic liquid. The absorption spectrum of AmB in an ionic liquid mixture and prepared nanoemulsion indicates AmB solubilization in the monomeric form. The hydrophobic ionic liquid exhibits high in vivo biocompatibility with zebrafish. The hemolytic activity of the AmB nanoemulsion was negligible, yet it maintained antifungal activity against Candida albicans. The preliminary results presented in this Communication indicate that ionic-liquid-in-water nanoemulsions may allow for the delivery of a variety of pharmaceuticals intravenously, broadening the scope of ionic liquids in the pharmaceutical sciences.

Influence of Carboxylate Anions on Phase Behavior of Choline Ionic Liquid Mixtures

Mixing ionic liquids is a suitable strategy to tailor properties, e.g., to reduce melting points. The present study aims to widen the application range of low-toxic choline-based ionic liquids by studying eight binary phase diagrams of six different choline carboxylates. Five of them show eutectic points with melting points dropping by 13 to 45 °C. The eutectic mixtures of choline acetate and choline 2-methylbutarate were found to melt at 45 °C, which represents a remarkable melting point depression compared to the pure compounds with melting points of 81 (choline acetate) and 90 °C (choline 2-methylbutarate), respectively. Besides melting points, the thermal stabilities of the choline salt mixtures were investigated to define the thermal operation range for potential practical applications of these mixtures. Typical decomposition temperatures were found between 165 and 207 °C, with choline lactate exhibiting the highest thermal stability.

Interactions of Ionic Liquids and Spirocyclic Compounds with Liposome Model Membranes. A Steady-State Fluorescence Anisotropy Study

Understanding the toxicity of ionic liquids (ILs) is crucial in the search of greener chemicals. By comparing in vivo toxicity and in vitro interactions determined between compounds and biomimetic lipid membranes, more detailed toxicity vs. structure relation can be obtained. However, determining the interactions between non-surface-active compounds and liposomes has been a challenging task. Organisational changes induced by ILs and IL-like spirocyclic compounds within 1,6-diphenyl-1,3,5-hexatriene-doped biomimetic liposomes was studied by steady-state fluorescence anisotropy technique. The extent of organisational changes detected within the liposome bilayers were compared to the toxicity of the compounds determined using Vibrio Fischeri bacteria. Four liposome compositions made of pure 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocoline (POPC) and mixtures of POPC, 1-palmitoyl-2-oleyl-sn-glycero-3-phosphoserine (POPS), and cholesterol (Chol) were tested as biomimetic models. Changes observed within the POPC/POPS/Chol 55:20:25 bilayers correlated the best with the toxicity results: ten out of twelve compounds followed the trend of increasing bilayer disorder - increasing toxicity. The study suggests that the toxicity of non-surface-active compounds is dependent on their ability to diffuse into the bilayers. The extent of bilayer's organisational changes correlates rather well with the toxicity of the compounds. Highly sensitive technique, such as fluorescence anisotropy measurements, is needed for detecting subtle changes within the bilayer structures.

Immobilization of natural lipid biomembranes and their interactions with choline carboxylates. A nanoplasmonic sensing study

The cell membrane is mainly composed of lipid bilayers with inserted proteins and carbohydrates. Lipid bilayers made of purified or synthetic lipids are widely used for estimating the effect of target compounds on cell membranes. However, the composition of such biomimetic membranes is much simpler than the composition of biological membranes. Interactions between compounds and simple composition biomimetic membranes might not demonstrate the effect of target compounds as precisely as membranes with compositions close to real organisms. Therefore, the aim of our study is to construct biomimetic membrane closely mimicking the state of natural membranes. Liposomes were prepared from lipids extracted from L-α-phosphatidylcholine, Escherichia coli, yeast (Saccharomyces cerevisiae) and bovine liver cells through agitation and sonication. They were immobilized onto silicon dioxide (SiO₂) sensor surfaces using N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer with calcium chloride. The biomimetic membranes were successfully immobilized onto the SiO₂ sensor surface and detected by nanoplasmonic sensing. The immobilized membranes were exposed to choline carboxylates. The membrane disruption effect was, as expected, more pronounced with increasing carbohydrate chain length of the carboxylates. The results correlated with the toxicity values determined using Vibrio fischeri bacteria. The yeast extracted lipid membranes had the strongest response to introduction of choline laurate while the bovine liver lipid extracted liposomes were the most sensitive towards the shorter choline carboxylates. This implies that the composition of the cell membrane plays a crucial role upon interaction with choline carboxylates, and underlines the necessity of testing membrane systems of different origin to obtain an overall image of such interactions.

Simple lysis of bacterial cells for DNA-based diagnostics using hydrophilic ionic liquids

The extraction of nucleic acids from microorganisms for subsequent molecular diagnostic applications is still a tedious and time-consuming procedure. We developed a method for the rapid preparation of genomic DNA from bacteria based on hydrophilic ionic liquids (ILs). First, we tested eight ILs in different buffer systems for their inhibitory effects on quantitative PCR. The cell lysis potential of different IL/buffer combinations was assessed by application on Enterococcus faecalis as a model organism for Gram-positive bacteria. The two best ILs, choline hexanoate and 1-ethyl-3-methylimidazolium acetate, were compared with the reference enzymatic method and two commercial DNA extraction kits. All methods were evaluated on four Gram-positive and four Gram-negative bacterial species that are highly relevant for environmental, food, or clinical diagnostics. In comparison to the reference method, extraction yields of the IL-based procedure were within one order of magnitude for most of the strains. The final protocol for DNA extraction using the two ILs is very low-cost, avoids the use of hazardous chemicals and can be performed in five minutes on a simple heating block. This makes the method ideal for high sample throughput and offers the opportunity for DNA extraction from bacteria in resource-limited settings or even in the field.

Correlating Lipid Membrane Permeabilities of Imidazolium Ionic Liquids with their Cytotoxicities on Yeast, Bacterial, and Mammalian Cells

Alkyl-imidazolium chloride ionic liquids (ILs) have been broadly studied for biochemical and biomedical technologies. They can permeabilize lipid bilayer membranes and have cytotoxic effects, which makes them targets for drug delivery biomaterials. We assessed the lipid-membrane permeabilities of ILs with increasing alkyl chain lengths from ethyl to octyl groups on large unilamellar vesicles using a trapped-fluorophore fluorescence lifetime-based leakage experiment. Only the most hydrophobic IL, with the octyl chain, permeabilizes vesicles, and the concentration required for permeabilization corresponds to its critical micelle concentration. To correlate the model vesicle studies with biological cells, we quantified the IL permeabilities and cytotoxicities on different cell lines including bacterial, yeast, and ovine blood cells. The IL permeabilities on vesicles strongly correlate with permeabilities and minimum inhibitory concentrations on biological cells. Despite exhibiting a broad range of lipid compositions, the ILs appear to have similar effects on the vesicles and cell membranes.

Biocompatible ionic liquids: fundamental behaviours and applications

The bio- and eco-friendly nature of biocompatible ionic liquids contributes to their widespread use in a wide range of fields.

Extraction and recovery processes for cynaropicrin from Cynara cardunculus L. using aqueous solutions of surface-active ionic liquids

Due to the wide range of relevant biological activities and high commercial value of cynaropicrin, and aiming at developing cost-effective processes, aqueous solutions of ionic liquids (ILs) were investigated for the extraction and recovery of cynaropicrin from the leaves of Cynara cardunculus L. Both cationic (1-alkyl-3-methylimidazolium chloride) and anionic (cholinium carboxylate) surface-active ILs were investigated, as well as a wide range of conventional surfactants and molecular organic solvents, allowing us to conclude that aqueous solutions of cationic surface-active ILs display a better performance for the extraction of cynaropicrin. Operational conditions were optimized, leading to a cynaropicrin extraction yield of 3.73 wt%. The recycling of both the biomass and the solvent were further investigated to appraise the extraction media saturation and to achieve a higher cynaropicrin extraction yield (6.47 wt%). Finally, it was demonstrated that 65 wt% of the extracted cynaropicrin can be efficiently recovered by precipitation from the IL aqueous extract through the addition of water as anti-solvent, allowing us to put forward both the extraction and recovery processes of the target value-added compound from biomass followed by solvent recycling. This approach opens the door to the development of more sustainable processes using aqueous solutions of ILs instead of the volatile organic solvents commonly used in biomass processing.

Cation–anion interaction-directed formation of functional vesicles and their biological application for nucleus-specific imaging

A strategy for the construction of counterion-induced vesicles in aqueous media has been described. Furthermore, the imidazolium salt with an AIE fluorophore exhibits highly specific nucleus imaging in the living cells.

Enhanced dissolution of ibuprofen using ionic liquids as catanionic hydrotropes

Ionic liquids as powerful hydrotropes for ibuprofen, where both cation and anion may contribute to the hydrotropic mechanism in a synergistic manner.

Aggregation behaviour of biocompatible choline carboxylate ionic liquids and their interactions with biomolecules through experimental and theoretical investigations

The self-assembly of long-chain choline carboxylates accompanied by their interaction with BSA protein were investigated with focus on environmental sustainability.

Surface-Active Ionic Liquid Cholinium Dodecylbenzenesulfonate: Self-Assembling Behavior and Interaction with Cellulase

The conventional sodium dodecylbenzenesulfonate (NaDBS) has been converted into an efficient and nontoxic anionic surface-active ionic liquid, cholinium dodecylbenzenesulfonate (Cho[DBS]). We have investigated its self-assembling behavior, interaction with the enzyme cellulase, and ecotoxicity. The surface-active properties at the air-liquid interface and the aggregation behavior of Cho[DBS] in water have been determined using tensiometry, isothermal titration calorimetry (ITC), conductometry, and dynamic light scattering (DLS). The enzyme activity was observed using dinitro salicylic acid analysis. The enhanced enzyme activity was explained through active-site exfoliation and structural constancy of cellulase in the micellar medium using the results from fluorescence, circular dichroism, DLS, and ITC. The nontoxic nature was confirmed by toxicity analysis on the freshwater microalgae Scenedesmus sp.

Synergistic effects of polymyxin and ionic liquids on lipid vesicle membrane stability and aggregation

Ionic liquids (ILs) have been investigated for potential antibacterial and antibiotic applications due to their ability to destabilize and permeabilize the lipid bilayers in cell membranes. Bacterial assays have shown that combining ILs with antibiotics can provide a synergistic enhancement of their antibacterial activities. We have characterized the mechanism by which the conventional ILs 1-butyl-3-methylimidazolium chloride (BMICl) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF₄) enhance the lipid membrane permeabilization of the well-known antibiotic polymyxin B (PMB). We studied the sizes and membrane permeabilities of multilamellar and unilamellar lipid bilayer vesicles in the presence of ILs alone in aqueous solution, PMB alone, and ILs combined together with PMB. Light scattering-based experiments show that vesicle sizes dramatically increase when ILs are combined with PMB, which suggests that the materials combine to synergistically enhance lipid membrane disruption leading to vesicle aggregation. Lipid bilayer leakage experiments using tris (2,2'-bipyridyl) ruthenium (II) (Ru(bpy)₃²⁺) trapped in lipid vesicles, in which the trapped Ru(bpy)₃²⁺ fluorescence lifetime increases when it leaks out of the vesicle, show that combining BMIBF₄ and PMB together permeabilize the membrane significantly more than with PMB or the IL alone. This demonstrates that ILs can assist in antibiotic permeabilization of lipid bilayers which could explain the increased antibiotic activities in the presence of ILs in solution.

An Experimental and Molecular Dynamics Study of Red Fluorescent Protein mCherry in Novel Aqueous Amino Acid Ionic Liquids

The search for biocompatible ionic liquids (ILs) with novel biochemical and biomedical applications has recently gained greater attention. In this report, we characterize the effects of two novel amino acid-based aqueous ILs composed of tetramethylguanidinium (TMG) and amino acids on the structure and stability of a widely used red fluorescent protein (mCherry). Our experimental data shows that while the aspartic acid-based IL (TMGAsp) has effects similar to previously studied conventional ILs (BMIBF4, EMIAc, and TMGAc), the alanine-based IL (TMGAla) has a much stronger destabilization effect on the protein structure. Addition of 0.30 M TMGAla to mCherry decreases the unfolding temperature from 83 to 60 °C. Even at 25 °C, TMGAla results in a blue shift of the mCherry absorbance and fluorescence peaks and an increased Stokes shift. Molecular dynamics simulations show that the chromophore conformation and its interaction with mCherry with TMGAla are changed relative to those with TMGAsp or in the absence of ILs. Protein-ILs contact analysis indicates that the mCherry-Asp interactions are hydrophilic but the (fewer) mCherry-Ala interactions are more hydrophobic and may modulate the TMG interaction with the protein. Hence, the anion hydrophobicity may explain the special TMGAla destabilization of mCherry.

Impact of Surface-Active Guanidinium-, Tetramethylguanidinium-, and Cholinium-Based Ionic Liquids on Vibrio Fischeri Cells and Dipalmitoylphosphatidylcholine Liposomes

We investigated the toxicological effect of seven novel cholinium, guanidinium, and tetramethylguanidinium carboxylate ionic liquids (ILs) from an ecotoxicological point of view. The emphasis was on the potential structure-toxicity dependency of these surface-active ILs in aqueous environment. The median effective concentrations (EC₅₀) were defined for each IL using Vibrio (Aliivibrio) fischeri marine bacteria. Dipalmitoylphosphatidylcholine (DPPC) liposomes were used as biomimetic lipid membranes to study the interactions between the surface-active ILs and the liposomes. The interactions were investigated by following the change in the DPPC phase transition behaviour using differential scanning calorimetry (DSC). Critical micelle concentrations for the ILs were determined to clarify the analysis of the toxicity and the interaction results. Increasing anion alkyl chain length increased the toxicity, whereas branching of the chain decreased the toxicity of the ILs. The toxicity of the ILs in this study was mainly determined by the surface-active anions, while cations induced a minor impact on the toxicity. In the DSC experiments the same trend was observed for all the studied anions, whereas the cations seemed to induce more variable impact on the phase transition behaviour. Toxicity measurements combined with liposome interaction studies can provide a valuable tool for assessing the mechanism of toxicity.

Inhibitory effects of ionic liquids on the lactic dehydrogenase activity

Ionic liquids (ILs) were widely used in scientific and industrial application and have been reported to possess potential toxicity to the environment and human health. The effects of six typical N-methylimidazolium-based ILs ([Cnmim]X, n=4, 6, 8; X=Br(-), Cl(-), BF4(-), CF3SO3(-)) on the lactic dehydrogenase (LDH) activity and the molecular interaction mechanism of ILs and the LDH were investigated with the aid of spectroscopic techniques. Experimental results showed that the LDH activity was inhibited in the presence of ILs. For the ILs with the same anion but different cations, their inhibitory ability on the LDH activity increased with increasing the alkyl chain length on the IL cation. Thermodynamic parameters, enthalpy change (ΔH) and entropy change (ΔS) were obtained by analyzing the fluorescence behavior of LDH with the addition of ILs. Both positive ΔH and ΔS suggested that hydrophobicity was the major driven force in the interaction process as expected.

Influence of chain length and double bond on the aqueous behavior of choline carboxylate soaps

In preceding studies, we demonstrated that choline carboxylates ChC(m) with alkyl chain lengths of m = 12 - 18 are highly water-soluble (for m = 12, soluble up to 93 wt % soap and 0 °C). In addition, choline soaps are featured by an extraordinary lyotropic phase behavior. With decreasing water concentration, the following phases were found: micellar phase (L(1)), discontinuous cubic phase (I(1)' and I(1)"), hexagonal phase (H(1)), bicontinuous cubic phase (V(1)), and lamellar phase (L(α)). The present work is also focused on the lyotropic phase behavior of choline soaps but with shorter alkyl chains or different alkyl chain properties. We have investigated the aqueous phase behavior of choline soaps with C(8) and C(10) chain-lengths (choline octanoate and choline decanoate) and with a C(18) chain-length with a cis-double bond (choline oleate). We found that choline decanoate follows the lyotropic phase behavior of the longer-chain homologues mentioned above. Choline octanoate in water shows no discontinuous cubic phases, but an extended, isotropic micellar solution phase. In addition, choline octanoate is at the limit between a surfactant and a hydrotrope. The double bond in choline oleate leads also to a better solubility in water and a decrease of the solubilization temperature. It also influences the Gaussian curvature of the aggregates which results in a loss of discontinuous cubic phases in the binary phase diagram. The different lyotropic mesophases were identified by the penetration scan technique with polarizing light microscope and visual observations. To clarify the structural behavior small (SAXS) and wide (WAXS) angle X-ray scattering were performed. To further characterize the extended, isotropic micellar solution phase in the binary phase diagram of choline octanoate viscosity and conductivity measurements were also carried out.