Terrestrial ecotoxicity of short aliphatic protic ionic liquids

Synthesis of films based on chitosan and protic ionic liquids to be used as wound dressing on the oral mucosa

Oral mucosal ulcerations expose connective tissue to different pathogens and this can progress to systemic infection. This study aimed to synthesize environmentally-friendly films with chitosan and protic ionic liquids, possessing mucoadhesive properties, activity against opportunistic microorganisms, enhanced malleability and mechanical resistance to be used as a wound dressing on the oral mucosa. Therefore, films with chitosan and 10, 35, and 50 % (wt/wt) of 2-hydroxy diethylammonium lactate, salicylate, and maleate protic ionic liquids were synthesized. Thickness measurements and mechanical properties analysis were performed. In addition, oral mucoadhesion, antimicrobial activity, and cytotoxicity properties were investigated. Results showed that the addition of 35wt% and 50wt% of all kinds of protic ionic liquids tested presented significant improvements in film thickness and mechanical properties. Films based on chitosan and the protic ionic liquid 2-hydroxy diethylammonium salicylate at percentages of 35 and 50wt% exhibited superior mucoadhesive properties, antimicrobial activity on opportunistic microorganisms and an improvement in their flexibility after immersion in synthetic saliva. Cytotoxicity results suggest that all kinds of chitosan/protic ionic liquids films tested are safe for intra-oral use. Therefore, the results of this study indicate that these materials could be good candidates for efficient and environmentally-friendly wound dressing films on the oral mucosa.

Toxicity of oleate-based amino protic ionic liquids towards Escherichia coli, Danio rerio embryos and human skin cells

Protic ionic liquids (PILs) have been widely employed with the label of "green solvents'' in different sectors of technology and industry. The studied PILs are promising for corrosion inhibition and lubrication applications in industry. Industrial use of the PILs can transform them in wastes, due to accidental spill or drag in water due to washing, that can reach water bodies. In addition, the handling of the product by the workers can expose them to accidental contact. Thus, the aim of this work is to evaluate the toxicity of PILs 2-hydroxyethylammonium oleate (2-HEAOl), N-methyl-2-hydroxyethylammonium oleate (m-2HEAOl) and bis-2-hydroxyethylammonium oleate (BHEAOl) towards Escherichia coli, zebrafish embryos, model organisms that can be present in water, and human skin cells. This is the first work reporting toxicity results for these PILs, which constitutes its novelty. Results showed that the studied PILs did not inhibit E. coli bacterial growth but could cause human skin cells death at the concentrations of use. LC₅₀ values for zebrafish eggs were 40.21 mg/L for 2HEAOl, 12.92 mg/L for BHEAOl and 32.74 mg/L for m-2HEAOl, with sublethal effects at lower concentrations, such as hatching retarding, low heart rate and absence of free swimming.

Toward the Proactive Design of Sustainable Chemicals: Ionic Liquids as a Prime Example

The tailorable and often unique properties of ionic liquids (ILs) drive their implementation into a broad variety of seminal technologies. The modular design of ILs allows in this context a proactive selection of structures that favor environmental sustainability─ideally without compromising their technological performance. To achieve this objective, the whole life cycle must be taken into account and various aspects considered simultaneously. In this review, we discuss how the structural design of ILs affects their environmental impacts throughout all stages of their life cycles and scrutinize the available data in order to point out knowledge gaps that need further research activities. The design of more sustainable ILs starts with the selection of the most beneficial precursors and synthesis routes, takes their technical properties and application specific performance into due account, and considers its environmental fate particularly in terms of their (eco)toxicity, biotic and abiotic degradability, mobility, and bioaccumulation potential. Special emphasis is placed on reported structure-activity relationships and suggested mechanisms on a molecular level that might rationalize the empirically found design criteria.

Ionic liquids as potentially new antifungal agents against Alternaria species

The fungal genus Alternaria Nees 1816 includes the most prevalent pathogenic species that can cause crop diseases such as blight, black spot, and dark leaf spot. In accordance with the aim of developing modern sustainable approaches in agriculture for the replacement of synthetic and toxic substances with environmentally friendly alternatives, the objective of this study was to examine the in vitro antifungal activities of 18 newly synthesized ionic liquids (ILs) against three Alternaria strains: A. padwickii, A. dauci and A. linicola. The antifungal activities of the ILs were estimated via a microdilution method to establish minimal inhibitory concentration (MIC) and minimal fungicidal concentration (MFC) values. The results confirmed that 17 of the 18 ILs showed strain specificity, including good antifungal activity toward Alternaria strains, with MIC and MFC values in the range of 0.04 to 0.43 mol dm-3. The strongest antifungal effects toward all analyzed Alternaria strains were displayed by the compounds with long alkyl chains: [omim][Cl] (MIC/MFC: 0.042 mol dm-3), [dmim][Cl] (MIC/MFC: 0.043 mol dm-3), [ddmim][Cl] (MIC/MFC: 0.053 mol dm-3), [ddTSC][Br] (MIC/MFC: 0.053 mol dm-3), and [Allyl-mim][Cl] (MIC/MFC: 0.054 mol dm-3). The introduction of oxygen as a hydroxyl group resulted in less-pronounced toxicity towards Alternaria compared to the introduction of an ether group, while the contribution of the hydroxyl group was shown to be a more determining factor than the prolongation of the side-chain, resulting in overall fungicidal activity decrease. Our results indicate the possibility that the most effective ILs ([Allyl-mim][Cl], [omim][Cl], [dmim][Cl], [ddmim][Cl], [bTSC][Br], [hTSC][Br], [oTSC][Br], [dTSC][Br], and [ddTSC][Br]) could be applied to the control of plant diseases caused by Alternaria species, based on their potential as an environmentally friendly crop protection approach. Since salts based on TSC cations are significantly cheaper to synthesize, stable under mild conditions, and environmentally friendly after degradation, thiosemicarbazidium-based ILs can be a suitable replacement for commercially available imidazolium ILs.

Correlation between lipophilicity of newly synthesized ionic liquids and selected Fusarium genus growth rate

The purpose of the present study was to examine the effectiveness of 23 different synthesized ionic liquids (ILs) on Fusarium culmorum and Fusarium oxysporum growth rate. The strategy of IL synthesis was a structural modification of ionic liquids through changing the polarity of imidazolium and pycolinium cations and replacing halide anions with well known antifungal anions (cinnamate, caffeate and mandelate). The findings clearly suggest that the type of alkyl chain on the cation is the most determining factor for IL toxicity. In order to examine how IL structure affects their toxicity towards Fusarium genus, lipophilic descriptor A log P is calculated from density functional theory and correlated with Fusarium growth rate. All these results demonstrate the high level of the interdependency of lipophilicity and toxicity for investigated ILs towards the Fusarium genus. The data collected in this research suggest that the inhibitory influence of ILs is more pronounced in the case of F. oxysporum.

Cytotoxic effect of protic ionic liquids in HepG2 and HaCat human cells: in vitro and in silico studies

Protic ionic liquids (PILs) are innovative chemical compounds, which due to their peculiar nature and amazing physico-chemical properties, have been studied as potential sustainable solvents in many areas of modern science, such as in the industrial fields of textile dyeing, pharmaceuticals, biotechnology, energy and many others. Due to their more than probable large-scale use in a short space of time, a wider analysis in terms of ecotoxicity and biological safety to humans has been attracting significant attention, once many ionic liquids were found to be "a little less than green compounds" towards cells and living organisms. The aim of this study is to investigate the cytotoxicity of 13 recently synthesized PILs, as well as to reinforce knowledge in terms of key thermodynamic magnitudes. All the studied compounds were tested for their in vitro toxic activities on two human cell lines (normal keratinocytes HaCaT and hepatocytes HepG2). In addition, due to the enormous number of possible combinations of anions and cations that can form ionic liquids, a group contribution QSAR model has been tested in order to predict their cytotoxicity. The estimated and experimental values were adequately correlated (correlation coefficient R 2 = 0.9260). The experimental obtained results showed their remarkable low toxicity for the studied in vitro systems.

Evaluation of the impact of different alkyl length and type of substituent in imidazolium ionic liquids on cucumber germination, growth and oxidative stress

In this work, the effect on cucumber growth of seven different imidazolium-based ionic liquids, namely 1-(2-oxybutyl)-3-methylimidazolium chloride, [C₂OC₂mIm][Cl]; 1-(2-oxypropyl)-3-methylimidazolium chloride, [C₁OC₂mIm][Cl]; 1-(3-hydroxypropyl)-3-ethylimidazolium chloride, [OHC₃eIm][Cl]; 1-(3-hydroxypropyl)-3-methylimidazolium chloride, [OHC₃mIm][Cl]; 1-(2-hydroxyethyl)-3-methylimidazolium chloride, [OHC₂mIm][Cl], 1-butyl-3-methylimidazolium chloride, [bmim][Cl] and imidazolium chloride, [Im][Cl], were examined. The influence of polarity of the alkyl side chain of the imidazolium cation on the reduction of the ionic liquid's toxicity is investigated. For all investigated seedlings, significant reduction of biomass was noted, with the incoherent influence of the ionic liquid (IL) concentration. The total inhibition of germination was shown at the highest used concentration for some of the used ionic liquids. Although investigated ILs affected root and shoot growth of cucumber, the effect on stress marker (MDA) as well as biosynthesis of chlorophyll and carotenoids was negligible. The data collected in this research suggest that tuning of the lipophilicity of imidazolium cations by the introduction of polar groups in the side alkyl chain does not have pronounced effect on cucumber, as it was shown for other plant species.

The effect of imidazolium based ionic liquids on wheat and barley germination and growth: Influence of length and oxygen functionalization of alkyl side chain

In this work five different imidazolium based ionic liquids, namely: 1-(2-oxybutyl)-3-methylimidazolium chloride, [C₂OC₂mIm][Cl]; 1-(2-oxypropyl)-3-methylimidazolium chloride, [C₁OC₂mIm][Cl]; 1-(3-hydroxypropyl)-3-ethylimidazolium chloride, [OHC₃eIm][Cl]; 1-(3-hydroxypropyl)-3-methylimidazolium chloride, [OHC₃mIm][Cl]; 1-(2-hydroxyethyl)-3-methylimidazolium chloride, [OHC₂mIm][Cl], together with commercial 1-butyl-3-methylimidazolium chloride, [bmim][Cl] and synthesized protic imidazolium chloride, [Im][Cl], were prepared and their toxicity examined towards wheat and barley germination and growth. Introduction of the polar groups (in the form of hydroxyde and/or ether group) in the alkyl side chain of the imidazolium cation and their influence on the reduction of the ionic liquid's toxicity is demonstrated. The results indicate that toxicity of oxygen functionalized ILs is significantly lower against wheat comparing to non-functionalized analogues. In the case of barley, influence on germination follow the same trend as in the case of wheat, but for seedlings growth different trend is observed with more pronounced toxicity of ether functionalized ILs. From these results it was also shown that alkylation in the position N-3 atom of the imidazole significantly reduces toxicity of cation.

New insight into the environmental impact of two imidazolium ionic liquids. Effects on seed germination and soil microbial activity

The next generation of ionic liquids must be synthetized taking into account structures that guarantee the suitable properties for a defined application as well as ecological data. Thus, searching of the right methodologies to know, quickly and efficiently, the ecological effects of these compounds is a preliminary task. The effects of two imidazolium based ionic liquids with different anions, 1-butyl-3-methylimidazolium tetrafluoroborate, [C₄C₁Im][BF₄], and 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C₃C₁Im][NTf₂], on seedling emergence of six tree species and on the microbial behaviour of two soils were determined in this work. Results showed that the highest doses of both ionic liquids caused the total inhibition of germination for almost all the species studied and that the seeds are more sensitive to the presence of these compounds than soil microbial activity. Nevertheless, signals of stress and death are observed from the results of heat released by microorganisms after the addition of the highest doses of both ionic liquids. The novelty of this work resides in the enlargement of knowledge of toxicity of ILs on complex organisms such as arboreal species and microbial activity of soils studied for the first time through a microcalorimetric technique.

Environmental Impact of Ionic Liquids: Recent Advances in (Eco)toxicology and (Bio)degradability

This Review aims to integrate the most recent and pertinent data available on the (bio)degradability and toxicity of ionic liquids for global and critical analysis and on the conscious use of these compounds on a large scale thereafter. The integrated data will enable focus on the recognition of toxicophores and on the way the community has been dealing with them, with the aim to obtain greener and safer ionic liquids. Also, an update of the most recent biotic and abiotic methods developed to overcome some of these challenging issues will be presented. The review structure aims to present a potential sequence of events that can occur upon discharging ionic liquids into the environment and the potential long-term consequences.

Phase Behavior and Physical Properties of New Biobased Ionic Liquid Crystals

Protic ionic liquids (PILs) have emerged as promising compounds and attracted the interest of the industry and the academy community, due to their easy preparation and unique properties. In the context of green chemistry, the use of biocompounds, such as fatty acids, for their synthesis could disclose a possible alternative way to produce ILs with a low or nontoxic effect and, consequently, expanding their applicability in biobased processes or in the development of bioproducts. This work addressed efforts to a better comprehension of the complex solid-[liquid crystal]-liquid thermodynamic equilibrium of 20 new PILs synthesized by using fatty acids commonly found in vegetable oils, as well as their rheological profile and self-assembling ability. The work revealed that their phase equilibrium and physical properties are significantly impacted by the structure of the ions used for their synthesis. The use of unsaturated fatty acids and bis(2-hydroxyethyl)ammonium for the synthesis of these biobased ILs led to a drastic decreasing of their melting temperatures. Also, the longest alkyl chain fatty acids promoted higher self-assembling and more stable mesophases. Besides their sustainable appeal, the marked high viscosity, non-Newtonian profile, and very low critical micellar concentration values of the PIL crystals here disclosed make them interesting renewable compounds with potential applications as emulsifiers, stabilizers, thickeners, or biolubricants.

(Eco)toxicity and biodegradability of protic ionic liquids

Ionic liquids (ILs) are often claimed to be "environmentally friendly" compounds however, the knowledge of their potential toxicity towards different organisms and trophic levels is still limited, in particular when protic ionic liquids (PILs) are addressed. This study aims to evaluate the toxicity against various microorganisms and the biodegradability of four PILs namely, N-methyl-2-hydroxyethylammonium acetate, m-2-HEAA; N-methyl-2-hydroxyethylammonium propionate, m-2-HEAPr; N-methyl-2-hydroxyethylammonium butyrate, m-2-HEAB; and N-methyl-2-hydroxyethylammonium pentanoate, m-2-HEAP. The antimicrobial activity was determined against the two bacteria, Sthaplylococcus aureus ATCC-6533 and Escherichia coli CCT-0355; the yeast Candida albicans ATCC-76645; and the fungi Fusarium sp. LM03. The toxicity of all PILs was tested against the aquatic luminescent marine bacterium Vibrio fischeri using the Microtox(®) test. The impact of the PILs was also studied regarding their effect on lettuce seeds (Lactuta sativa). The biodegradability of these PILs was evaluated using the ratio between the biochemical oxygen demand (BOD) and the chemical oxygen demand (COD). The results show that, in general, the elongation of the alkyl chain tends to increase the negative impact of the PILs towards the organisms and biological systems under study. According to these results, m-2-HEAA and m-2-HEAP are the less and most toxic PILs studied in this work, respectively. Additionally, all the PILs have demonstrated low biodegradability.

A comparative study of the terrestrial ecotoxicity of selected protic and aprotic ionic liquids

Ionic liquids (ILs) are a fairly new and very promising group of compounds with a vast variety of possible structures and uses. They are considered to be potentially "green", but their impact on the environment tends to be neglected or not studied enough, especially when it comes to terrestrial ecotoxicity, where there are very few studies performed to date. This work presents a comparative study of the terrestrial ecotoxicity of selected representatives of two ILs groups: a new family of protic ILs (derived from aliphatic amines and organic acids) and some frequently used aprotic ILs (substituted imidazolium and piridinium chlorides). Toxicity of the ILs towards three terrestrial plant species (Allium cepa, Lolium perenne and Raphanus sativus) and soil microorganisms involved in carbon and nitrogen transformation was analyzed. Protic ILs have shown no toxic effect in most of the tests performed. The EC50 values for aprotic ILs are various orders of magnitude lower than the ones for protic ILs in all of the tests. The most toxic ILs are the most complex ones in both of the analyzed groups. Protic ILs seem to have a potential for biodegradation in soil, while aprotic ILs exhibit inhibitory effects towards the carbon transforming microbiota. These findings indicate that protic ILs can be considered as less toxic and safer for the terrestrial environment than the aprotic ILs.

Imidiazolium based ionic liquids: effects of different anions and alkyl chains lengths on the barley seedlings

We studied the effects of five imidiazolium based ionic liquids with different anions and length of alkyl chains linked to imidazolium ring on the early development of barley (Hordeum vulgare). The inhibitory effect depends on the ionic liquids concentration and chemical structure, whereby the most toxic one was [C10mim][Br], followed by [C7mim][Br], [C4mim][Br], [C4mim][CH3CO2] and [C4mim][BF4]. Both anion and cation structures affected the toxicity of ionic liquid indicating that selection of more biocompatible anions such as [CH3CO2] does not necessarily indicate lower toxicity. Alternation in the extent of oxidative stress and antioxidant enzymes activities were found in barley plants due to ionic liquid treatments. When seedlings were exposed to higher concentrations of ionic liquids, antioxidant system could not effectively remove reactive oxidative species, leading to lipid peroxidation and damage of the photosynthetic system. However, overall data indicated that the performance of barley seedling was improved when all measured enzymes involved in scavenging of reactive oxygen species (ROS) were increased with special emphasis on GPX activities. Since there are no studies about ionic liquid (IL) toxicity in plants, that simultaneously evaluates the antioxidative enzyme system in response to different ILs, this work is valuable for gaining knowledge about the protection mechanism of plants from oxidative stress caused by IL exposure.

Toxicity of ionic liquids: eco(cyto)activity as complicated, but unavoidable parameter for task-specific optimization

Rapid progress in the field of ionic liquids in recent decades led to the development of many outstanding energy-conversion processes, catalytic systems, synthetic procedures, and important practical applications. Task-specific optimization emerged as a sharpening stone for the fine-tuning of structure of ionic liquids, which resulted in unprecedented efficiency at the molecular level. Ionic-liquid systems showed promising opportunities in the development of green and sustainable technologies; however, the chemical nature of ionic liquids is not intrinsically green. Many ionic liquids were found to be toxic or even highly toxic towards cells and living organisms. In this Review, we show that biological activity and cytotoxicity of ionic liquids dramatically depend on the nature of a biological system. An ionic liquid may be not toxic for particular cells or organisms, but may demonstrate high toxicity towards another target present in the environment. Thus, a careful selection of biological activity data is a must for the correct assessment of chemical technologies involving ionic liquids. In addition to the direct biological activity (immediate response), several indirect effects and aftereffects are of primary importance. The following principal factors were revealed to modulate toxicity of ionic liquids: i) length of an alkyl chain in the cation; ii) degree of functionalization in the side chain of the cation; iii) anion nature; iv) cation nature; and v) mutual influence of anion and cation.

Efficient Sustainable Tool for Monitoring Chemical Reactions and Structure Determination in Ionic Liquids by ESI-MS

An easy and convenient procedure is described for monitoring chemical reactions and characterization of compounds dissolved in ionic liquids using the well-known tandem mass spectrometry (MS/MS) technique. Generation of wastes was avoided by utilizing an easy procedure for analysis of ionic liquid systems without preliminary isolation and purification. The described procedure also decreased the risk of plausible contamination and damage of the ESI-MS hardware and increased sensitivity and accuracy of the measurements. ESI-MS detection in MS/MS mode was shown to be efficient in ionic liquids systems for structural and mechanistic studies, which are rather difficult otherwise. The developed ESI-MS/MS approach was applied to study samples corresponding to peptide systems in ionic liquids and to platform chemical directed biomass conversion in ionic liquids.

(Eco)toxicity and biodegradability of selected protic and aprotic ionic liquids

Ionic liquids (ILs) are a promising group of compounds with a large variety of possible structures and uses. They are considered as a potential "green" replacement for traditional volatile organic solvents, but their impact on the environment is often neglected or not studied enough. In the present study, selected representatives of two ILs groups were analyzed: a new family of protic ILs (derived from aliphatic amines and organic acids) and some frequently used aprotic ILs (substituted imidazolium and piridinium chlorides). The aquatic toxicity (test organisms Vibrio fischeri, Pseudokirchneriella subcapitata and Lemna minor) and biodegradability tests were carried out. The additional tests with enzyme (acetylcholinesterase) and leukemia rat cells (IPC-81) provided more in-depth evaluation of toxicity. In our comparative hazard assessment protic ILs have EC50 values >100 mg L(-1) in all of the tests performed, except in the case of three representatives toward Lemna minor. They also show good biodegradability rates. The EC50 values for aprotic ILs are various orders of magnitude lower than the ones for protic ILs in most of the tests and they show a lower biodegradability potential. These findings indicate that protic ILs can be considered as environmentally safer alternatives for more toxic ILs and organic solvents.

Automated carboxylesterase assay for the evaluation of ionic liquids' human toxicity

Aiming the prediction of ionic liquids' (ILs) human toxicity, an automated carboxylesterase activity assay was developed. The method was implemented on a sequential injection analysis (SIA) system and relied on the hydrolysis of 4-methylumbelliferyl acetate by the enzyme, to produce the fluorescent compound 4-methylumbelliferone (λ(exc)=365 nm; λ(em)=460 nm). The adopted approach was based on activity/inhibition assays in which the reduction of enzyme activity was denoted by a decrease of fluorescence. The activity assays were performed in aqueous media and in the presence of increasing concentrations of seven commercially available ILs and sodium bis(p-nitrophenyl) phosphate, a strong inhibitor of carboxylesterase. The inhibitory effects were quantified by means of the calculation of half maximal inhibitory effective concentration (EC(50)) values that were between 38 and 134 μmol L(-1). This allowed us to perform some considerations about the toxicity of the compounds. The less and more toxic ILs found in this study were emim [Ms] and tbph [Ms], respectively. The developed SIA methodology is robust and exhibits good repeatability in all the tested conditions (rsd<5.0%, n=10). At the same time a reduction of costs was attained by reduced consumption of reagents and minimal effluent production (2 mL per cycle).