Biodegradability of imidazolium and pyridinium ionic liquids by an activated sludge microbial community

Quaternary ammonium salts for water treatment with balanced rate of sterilization and degradation

The growing number of infections caused by drug-resistant bacteria which arise from the overuse of antibiotics has severely affected the normal operation of human society. The high antibacterial activity of QAS makes it promising as an alternative to antibiotics, but it suffers from secondary pollution due to its non-degradation. Here we have synthesized a class of gemini quaternary ammonium salts (GQAS) with different carbon chain lengths containing ester groups by using facile methylation reaction. Quaternary ammonium groups contribute to insert negatively charged bacterial membranes, resulting in membrane damage and bacteria death. Compared with conventional single-chain QAS, except for the more efficient antibacterial efficiency attribute to the presence of the second carbon chain, GQAS with alterable antibacterial properties can minimize the possibility of bacterial resistance and reduce the accumulation of GQAS in the environment through the introduction of degradable ester groups. GQAS is completely superior to the commercial bactericide benzalkonium chloride (BAC) in both antibacterial activity and degrade performance, which can be used as a more environmentally friendly bactericide.

Insights into the quantitative structure-activity relationship for ionic liquids: a bibliometric mapping analysis

Environmental protection and sustainability is the development goal that countries all over the world are pursuing. Ionic liquids (ILs), as a new type of green material, have a great application prospect. And the quantitative structure-activity relationship (QSAR) is significant for the research of ILs. To better understand the role played by QSAR in the research of ILs, 4139 literatures published in the WOS database from 2002 to 2022 were used for bibliometric analysis, and different types of knowledge maps were mapped to obtain the current status and trends of IL research applied QSAR. The distribution pattern of the literature output chronology, country, institution, author cooperation, and major source journals can be obtained through the research of the distribution of literature. Through core literature, dual-map overlays, and evolutionary path analysis, the research knowledge base was obtained mainly including ionic liquid toxicological properties research, environmental protection and sustainability, ionic liquid design, and mild steel corrosion inhibition; through the co-occurrence and evolution of keywords, the current research hotspots are basic properties of ILs, corrosion inhibition of mild steel, the effect of toxicity on the environment, QSAR modeling methods, solvent application of ILs, and drug design.

Comprehensive Ecotoxicity Studies on Quaternary Ammonium Salts Synthesized from Vitamin B3 Supported by QSAR Calculations

Lately, ionic forms (namely, quaternary ammonium salts, QASs) of nicotinamide, widely known as vitamin B₃, are gaining popularity in the sectors developing novel pharmaceuticals and agrochemicals. However, the direct influence of these unique QASs on the development of various terrestrial plants, as well as other organisms, remains unknown. Therefore, three compounds comprising short, medium, and long alkyl chains in N-alkylnicotinamide were selected for phytotoxicity analyses, which were conducted on representative dicotyledonous (white mustard) and monocotyledonous (sorghum) plants. The study allowed the determination of the impact of compounds on the germination capacity as well as on the development of roots and stems of the tested plants. Interestingly, independently of the length of the alkyl chain or plant species, all QASs were established as non-phytotoxic. In addition, QSAR simulations, performed using the EPI Suite™ program pack, allowed the determination of the products' potential toxicity toward fish, green algae, and daphnids along with the susceptibility to biodegradation. The obtained nicotinamide derivative with the shortest chain (butyl) can be considered practically non-toxic according to GHS criteria, whereas salts with medium (decyl) and longest (hexadecyl) substituent were included in the 'acute II' toxicity class. These findings were supported by the results of the toxicity tests performed on the model aquatic plant Lemna minor. It should be stressed that all synthesized salts exhibit not only a lack of potential for bioaccumulation but also lower toxicity than their fully synthetic analogs.

Quaternary Ammonium Salts: Insights into Synthesis and New Directions in Antibacterial Applications

The overuse of antibiotics has led to the emergence of a large number of antibiotic-resistant genes in bacteria, and increasing evidence indicates that a fungicide with an antibacterial mechanism different from that of antibiotics is needed. Quaternary ammonium salts (QASs) are a biparental substance with good antibacterial properties that kills bacteria through simple electrostatic adsorption and insertion into cell membranes/altering of cell membrane permeability. Therefore, the probability of bacteria developing drug resistance is greatly reduced. In this review, we focus on the synthesis and application of single-chain QASs, double-chain QASs, heterocyclic QASs, and gemini QASs (GQASs). Some possible structure-function relationships of QASs are also summarized. As such, we hope this review will provide insight for researchers to explore more applications of QASs in the field of antimicrobials with the aim of developing systems for clinical applications.

Role of Fungi in Biodegradation of Imidazolium Ionic Liquids by Activated Sewage Sludge

Ionic liquids (ILs), due to their specific properties, can play the role of persistent water contaminants. Fungi manifest the ability to decompose hardy degradable compounds, showing potential in the biodegradation of ILs, which has been studied extensively on sewage sludge; however, attention was drawn mainly to bacterial and not fungal species. The aim of the research was to determine the significance of fungi in ILs' biodegradation to extend the knowledge and possibly point out ways of increasing their role in this process. The research included: the isolation and genetic identification of fungal strains potentially capable of [OMIM][Cl], [BMIM][Cl], [OMIM][Tf₂N], and [BMIM][Tf₂N] degradation, adjustment of the ILs concentration for biodegradability test by MICs determination and choosing strains with the highest biological robustness; inoculum adaptation tests, and finally primary biodegradation by OECD 301F test. The study, conducted for 2 mM [OMIM][Cl] as a tested substance and consortium of microorganisms as inoculum, resulted in an average 64.93% biodegradation rate within a 28-day testing period. For the individual fungal strain (Candida tropicalis), the maximum of only 4.89% biodegradation rate was reached in 10 days, then inhibited. Insight into the role of fungi in the biodegradation of ILs was obtained, enabling the creation of a complex overview of ILs toxicity and the possibilities of its biological use. However, only an inoculum consisting of a consortium of microorganisms enriched with a selected strain of fungi was able to decompose the IL, in contrast to that consisting only of an individual fungal strain.

Synthesis, Characterization, Biological Evaluation, and In Silico Studies of Imidazolium-, Pyridinium-, and Ammonium-Based Ionic Liquids Containing n-Butyl Side Chains

Ionic liquids (ILs) have emerged as active pharmaceutical ingredients because of their excellent antibacterial and biological activities. Herein, we used the green-chemistry-synthesis procedure, also known as the metathesis method, to develop three series of ionic liquids using 1-methyl-3-butyl imidazolium, butyl pyridinium, and diethyldibutylammonium as cations, and bromide (Br⁻), methanesulfonate (CH₃SO₃⁻), bis(trifluoromethanesulfonyl)imide (NTf₂⁻), dichloroacetate (CHCl₂CO₂⁻), tetrafluoroborate (BF₄⁻), and hydrogen sulfate (HSO₄⁻) as anions. Spectroscopic methods were used to validate the structures of the lab-synthesized ILs. We performed an agar well diffusion assay by using pathogenic bacteria that cause various infections (Escherichia coli; Enterobacter aerogenes; Klebsiella pneumoniae; Proteus vulgaris; Pseudomonas aeruginosa; Streptococcus pneumoniae; Streptococcus pyogenes) to scrutinize the in vitro antibacterial activity of the ILs. It was established that the nature and unique combination of the cations and anions were responsible for the antibacterial activity of the ILs. Among the tested ionic liquids, the imidazolium cation and NTf₂⁻ and HSO₄⁻ anions exhibited the highest antibacterial activity. The antibacterial potential was further investigated by in silico studies, and it was observed that bis(trifluoromethanesulfonyl)imide (NTf₂⁻) containing imidazolium and pyridinium ionic liquids showed the maximum inhibition against the targeted bacterial strains and could be utilized in antibiotics. These antibacterial activities float the ILs as a promising alternative to the existing antibiotics and antiseptics.

Inventory of biodegradation data of ionic liquids

Ionic liquids (ILs) are increasingly of interest for environmentally open applications. Therefore, completely mineralising ILs are highly desirable. We reviewed the current state of knowledge on ILs' environmental biodegradability and identified research needs. Literature data were evaluated as for applied standard methods (e.g. OECD, ISO, APHA) for biodegradation of ILs in order to get an overview on the validity of the test results received and ILs' biodegradability. 109 studies were evaluated. The ILs were categorised based on the cation's core structure. The biodegradation data was classified according to a traffic light system (red: 0-19% degradation, amber: 20-59% degradation, green: ≥ 60% degradation). Not all studies could be assessed for compliance with the test guidelines due to missing test parameters. Moreover, no study discussed all validation criteria as defined by the test guidelines. Consequently, the reliability and quality of the existing biodegradation data is restrained. With regard to the different cations classified for ≥ 60% biodegradability, phosphonium ILs are the least biodegradable, followed by imidazolium ones. The most ILs that were biodegradable are cholinium ILs. The results indicate the need for more and qualitatively better testing according to standard methods including application and reporting of all validation criteria in order to get reliable data that enables the comparison of the test data and a comprehensive understanding of ILs' biodegradability. Moreover, reliable data allows the selection of sufficiently environmentally biodegradable ILs if an introduction into the environment during use cannot be excluded.

Thermal, chemical, electrochemical, radiolytic and biological stability of ionic liquids and deep eutectic solvents

Ionic liquids (ILs) and deep eutectic solvents (DESs) are regarded as two kinds of novel solvents with high tunability and they exist in liquid-state for a wide range of temperature....

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.

Use of Ionic Liquid Pretreated and Fermented Sugarcane Bagasse as an Adsorbent for Congo Red Removal

A large amount of industrial wastewater containing pollutants including toxic dyes needs to be processed prior to its discharge into the environment. Biological materials such as sugarcane bagasse (SB) have been reported for their role as adsorbents to remove the dyes from water. In this study, the residue SB after fermentation was utilized for the dye removal. A combined pretreatment of NaOH and methyltrioctylammonium chloride was given to SB for lignin removal, and the pretreated SB was utilized for cellulase production from Bacillus aestuarii UE25. The strain produced 118 IU mL^-1 of endoglucanse and 70 IU mL^-1 of β-glucosidase. Scanning electron microscopy and FTIR spectra showed lignin and cellulose removal in fermented SB. This residue was utilized for the adsorption of an azo dye, congo red (CR). The thermodynamic, isotherm and kinetics studies for the adsorption of CR revealed distinct adsorption features of SB. Untreated SB followed Langmuir isotherm, whereas pretreated SB and fermented SB obeyed the Freundlich isotherm model. The pseudo-second-order model fitted well for the studied adsorbents. The results of thermodynamic studies revealed spontaneous adsorption with negative standard free energy values. Untreated SB showed a 90.36% removal tendency at 303.15 K temperature, whereas the adsorbents comprised of pretreated and fermented SB removed about 98.35% and 97.70%, respectively. The study provided a strategy to utilize SB for cellulase production and its use as an adsorbent for toxic dyes removal.

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.

Treatment of copper converter slag with deep eutectic solvent as green chemical

Industrial copper slag is among the most important wastes to be evaluated in terms of containing valuable metals and the amount of waste approaching 30 million tons per year. Therefore, in this study, it was aimed to propose a feasible route for copper and zinc recovery from copper converter slag (CCS) by using choline chloride (ChCl) based deep eutectic solvent which is applied on this type of slag for the first time. During the leaching experiments with the pure ChCl-2urea mixture, temperature (25-95 °C), leaching duration (2-72 h), and pulp density (1/10-1/40 g/mL) were selected as the parameters to be investigated for Cu and Zn extraction. After the experimental results, the optimized conditions for the ChCl-2urea leaching process, which gave 89.9% Cu and 65.3% Zn extraction was found at 48 h, 95 °C, 1/20 g/mL pulp density with 600 rpm stirring speed. It is noted that the iron dissolution ratio is very low (max. 4.7%) under the selected conditions. At the end of the iron cementation stage, the total recovery efficiency as a pure metallic copper was 63%. The calculated activation energy for the dissolution of the copper and zinc from CCS is 8.86 kJ mol^-1 and 14.48 kJ mol^-1, respectively.

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.

Cellulose extraction from methyltrioctylammonium chloride pretreated sugarcane bagasse and its application

Cellulose, the most abundant feedstock of chemicals and energy is extracted from various agro-industrial wastes, such as sugarcane bagasse (SB). Pretreatment of SB with ionic liquids improves extraction of cellulose, yet the use of ionic liquid is hindered by its high cost. In this study, cellulose was extracted from SB pretreated with methyltrioctylammonium chloride under relatively mild conditions. The extracted cellulose from pretreated SB (PTB) and untreated SB (UTB) was characterized by scanning electron microscopy and FTIR. Fermentation of cellulose extracted from PTB by a thermophilic bacterium, Bacillus aestuarii UE25, yielded 245.16% higher titers of cellulase than cellulose extracted from UTB. The recyclability of the IL was assessed to make the pretreatment process cost effective and was monitored through TLC and FTIR. The results of this research demonstrated the potential of ionic liquid pretreated SB for cellulose extraction and for its subsequent utilization in thermostable cellulase production.

Extraction of lignin and quantitative sugar release from biomass using efficient and cost-effective pyridinium protic ionic liquids

Lignocellulosic biomass is enormously abundant around the globe. It bears huge potential for renewable products as its components can be converted to many useful products via cheaper processes. Recently, the component of biomass that has attracted enormous attention is lignin owing to its several aromatic or phenolic constituents. The utilization of lignin, however, is hindered by its troublesome separation mainly due to the difficult nature of the lignocellulosic biomass. Protic ionic liquids have great potential for extraction of lignin from the lignocellulosic biomass to make it viable for various transformations. In this study, protic ionic liquids comprising a pyridinium cation and a dihydrogen phosphate anion (H₂PO₄⁻) were prepared and used for lignin extraction and subsequent saccharification of the cellulose pulp. The ILs exhibited appreciably high lignin yields (optimum 73%) under mild conditions (100 °C) and shorter time (2 h). Fairly good sugar (glucose) yields (77%) verify effective delignification. The analysis of ILs and biomass was accomplished by H-NMR, FT-IR, SEM, HSQC and GPC.

Lignocellulosic biomass is enormously abundant around the globe. It bears huge potential for renewable products as its components can be converted to many useful products via cheaper processes.

Renal injury and hepatic effects from the methylimidazolium ionic liquid M8OI in mouse

The ionic liquid 1-octyl-3-methylimidazolium (M8OI) has been found in the environment and identified as a hazard for triggering the liver disease primary biliary cholangitis (PBC). Given limited toxicity data for M8OI and other structurally-related ionic liquids, target organs for M8OI toxicity were examined. Adult male C57Bl6 mice were acutely exposed to 0-10 mg/kg body weight M8OI via 2 intraperitoneal injections (time zero and 18 h) and effects examined at 24 h. At termination, tissue histopathology, serum and urinary endpoints were examined. No overt pathological changes were observed in the heart and brain. In contrast, focal and mild to multifocal and moderate degeneration with a general trend for an increase in severity with increased dose was observed in the kidney. These changes were accompanied by a dose-dependent increased expression of Kim1 in kidney tissue, marked elevations in urinary Kim1 protein and a dose-dependent increase in serum creatinine. Hepatic changes were limited to a significant dose-dependent loss of hepatic glycogen and a mild but significant increase in portal tract inflammatory recruitment and/or fibroblastic proliferation accompanied by a focal fibrotic change. Cultured mouse tissue slices reflected these in vivo effects in that dose-dependent injury was observed in kidney slices but not in the liver. Kidney slices accumulated higher levels of M8OI than liver slices (e.g. at 10 μM, greater than 4 fold) and liver slices where markedly more active in the metabolism of M8OI. These data indicate that the kidney is a target organ for the toxic effects of M8OI accompanied by mild cholangiopathic changes in the liver after intraperitoneal administration.

Ionic Liquids Toxicity-Benefits and Threats

Ionic liquids (ILs) are solvents with salt structures. Typically, they contain organic cations (ammonium, imidazolium, pyridinium, piperidinium or pyrrolidinium), and halogen, fluorinated or organic anions. While ILs are considered to be environmentally-friendly compounds, only a few reasons support this claim. This is because of high thermal stability, and negligible pressure at room temperature which makes them non-volatile, therefore preventing the release of ILs into the atmosphere. The expansion of the range of applications of ILs in many chemical industry fields has led to a growing threat of contamination of the aquatic and terrestrial environments by these compounds. As the possibility of the release of ILs into the environment s grow systematically, there is an increasing and urgent obligation to determine their toxic and antimicrobial influence on the environment. Many bioassays were carried out to evaluate the (eco)toxicity and biodegradability of ILs. Most of them have questioned their "green" features as ILs turned out to be toxic towards organisms from varied trophic levels. Therefore, there is a need for a new biodegradable, less toxic "greener" ILs. This review presents the potential risks to the environment linked to the application of ILs. These are the following: cytotoxicity evaluated by the use of human cells, toxicity manifesting in aqueous and terrestrial environments. The studies proving the relation between structures versus toxicity for ILs with special emphasis on directions suitable for designing safer ILs synthesized from renewable sources are also presented. The representants of a new generation of easily biodegradable ILs derivatives of amino acids, sugars, choline, and bicyclic monoterpene moiety are collected. Some benefits of using ILs in medicine, agriculture, and the bio-processing industry are also presented.

Elucidating the effect of the ionic liquid type and alkyl chain length on the stability of ionic liquid-iron porphyrin complexes

The present study is motivated by the long-term objective of understanding how ionic liquids are biodegraded by cytochrome P450, which contains iron porphyrin (FeP) serving as the catalytic center. To this end, the current study is designed to elucidate the impact of types and conformations of ionic liquids on the binding energy with FeP, the key interactions that stabilize the ionic liquid-FeP complex, and how the electron uptake ability of FeP is altered in the presence of ionic liquids. Four classes of ionic liquids are considered: 1-alkyl-3-methylimidazolium, 1-alkyl-pyridinium, 1-alkylsulfonium, and N-methyl-N-alkylpyrrolidinium. The influence of linear alkyl chains of ethyl, butyl, hexyl, octyl, and decyl is examined on the favorable binding modes with FeP, considering two widely different conformations: tail up and tail down with respect to FeP. Electronic structure calculations are performed at the M06 level of theory with the 6-31G(d,p) basis set for C, H, and N atoms, while the Lanl2DZ basis set is employed for Fe. Donor-acceptor interactions contributing to the binding of ionic liquids to FeP are unraveled through the natural bond orbital analysis. The results from this study indicate that the binding energies are dependent not only on the class of ionic liquids but also on the conformations presented to FeP. The propensity of FeP to acquire an electron is significantly enhanced in the presence of ionic liquid cations, irrespective of the type and the alkyl chain length.

A study into the species sensitivity of green algae towards imidazolium-based ionic liquids using flow cytometry

The sensitivity of individual organisms towards toxic agents is an important indicator of environmental pollution. However, organism-specific quantification of sensitivity towards pollutants remains a challenge. In this study, we determined the sensitivity of Chlorella vulgaris (C. vulgaris) and Scenedesmus quadricauda (S. quadricauda) towards three ionic liquids (ILs), 1-alkyl-3-methyl-imidazolium chlorides [C_nmim][Cl] (n = 4,6,8). We kept all external parameters constant to identify the biotic parameters responsible for discrepancies in species sensitivity, and used flow cytometry to determine four conventional endpoints to characterise cell viability and cell vitality. Our results demonstrate that after exposure to the ILs, cell proliferation was inhibited in both species. At the same time, the cell size, complexity and membrane permeability of both algae also increased. However, while Chl a synthesis by S. quadricauda was inhibited, that of C. vulgaris was enhanced. S. quadricauda has evolved a metabolic defense that can counteract the decreased esterase activity that has been shown to occur in the presence of ILs. While it is likely that S. quadricauda was less sensitive than C. vulgaris to the ILs because of this metabolic defense, this alga may also exhibit better membrane resistance towards ILs.

Utilization of methyltrioctylammonium chloride as new ionic liquid in pretreatment of sugarcane bagasse for production of cellulase by novel thermophilic bacteria

Fermentation of carbohydrates present in lignocellulosic (LC) biomass is facilitated by lignin removal, which is usually achieved by adopting various pretreatment methods to provide the enzymes proper access to their respective substrates. Pretreatment using ionic liquid (IL) is relatively recent advancement and considered as mild and green process. ILs can dissolve extensive quantities of biomass and depolymerize the cellulose. In this context, an abundantly available LC biomass, sugarcane bagasse (SB), was pretreated using alkali or with an IL, methyltrioctylammonium chloride, and was used for cellulase production from thermophilic bacteria. In all, 26 indigenously isolated thermophilic bacterial strains were quantitatively screened for cellulase production. 16S rDNA sequences of the promising isolates UE10 and UE27 revealed relatedness with Brevibacillus borstelensis, while the strain UE1 belonged to Aneurinibacillus thermoaerophilus. Cellulase production was compared by utilizing alkali pretreated and IL pretreated SB and the later was found more appropriate. UE1, UE10 and UE27 yielded 22.2, 22.18 and 33.3 IU mL^-1 of endoglucanase, respectively, by fermenting IL pretreated SB. The changes in SB structure after pretreatment were evaluated by scanning electron microscopy. This study demonstrated the potential of novel thermophilic bacterial strains to utilize IL pretreated SB for production of industrially important enzyme, cellulase.

Disentanglement of the chemical, physical, and biological processes aids the development of quantitative structure-biodegradation relationships for aerobic wastewater treatment

Attenuation of organic compounds in sewage treatment plants (STPs) is affected by a complex interplay between chemical (e.g. ionization, hydrolysis), physical (e.g. sorption, volatilization), and biological (e.g. biodegradation, microbial acclimation) processes. These effects should be accounted for individually, in order to develop predictive cheminformatics tools for STPs. Using measured data from 70 STPs in the Netherlands for 69 chemicals (pharmaceuticals, herbicides, etc.), we highlighted the influences of 1) chemical ionization, 2) sorption to sludge, and 3) acclimation of the microbial consortia on the primary removal of chemicals. We used semi-empirical corrections for each of these influences to deduce biodegradation rate constants upon which quantitative structure-biodegradation relationships (QSBRs) were developed. As shown by a global QSBR, biodegradation in STPs generally relates to structural complexity, size, energetics, and charge distribution. Statistics of the global QSBR were reasonable, being R²_training=0.69 (training set of 51 compounds) and R²_validation=0.50 (validation set of 18 compounds). Class-specific QSBRs utilized electronic properties potentially relating to rate-limiting enzymatic steps. For class-specific QSBRs, values of R² of in between 0.7 and 0.8 were obtained. With caution, environmental risk assessment methodologies may apply these models to estimate biodegradation rates for 'data-poor' compounds. The approach also highlights 'meta data' on STP operational parameters needed to develop QSBRs of better predictability in the future.

Toxicity and inhibition assessment of ionic liquids by activated sludge

Toxicity of 13 ionic liquids (ILs) corresponding to different families were studied by inhibition respiration assays (15 min) using activated sludge. Toxicity increased as increasing the number of carbons in the alkyl-chain of imidazolium-based ILs, with EC₅₀ values from 4.19 to 0.17 for 1-ethyl-3-methylimidazolium chloride ([Emim][Cl]) and 1-octyl-3-methylimidazolium chloride ([Omim][Cl]), respectively. An increase in toxicity was observed for aromatic-based ILs (pyridinium- and imidazolium-based ILs) due to the hydrophobic character of the head groups in comparison with linear structures as phosphonium and ammonium cations. Among to the anions studied fixing [Emim]⁺ as cation, [HSO₄]^- and [NTf₂]^- presented low EC₅₀ values (0.34 mM and 1.69 mM, respectively) while [Cl]^- and [EtSO₄]^- were considered harmless anions due to the hydrophilic character of chloride and the organic nature of [EtSO₄]^-. ILs toxicity/inhibition was determined by adding a biodegradable compound and measuring the sludge response after being in contact with the ILs for at least 15 h. The exposure of sewage sludge to ILs for more than 15 min used in short inhibition assays caused more toxic effect on microorganisms, even for [Choline][NTf₂], previously defined as practically harmless (EC₅₀ = 2.79 mM). Biodegradability assays confirmed the biodegradable nature of choline cation, related with TOC conversion of 40%, only due to cation consumption. No oxygen consumption or even lysis of microbial cells was observed for Tetrabutylammonium bis(trifluoromethylsulfonyl)imide and for 1-Ethyl-3-methylimidazolium hydrogensulphate due to the presence of anions previously defined as hazardous ([NTf₂]^- and [HSO₄]^-), maintaining their recalcitrant character to sewage systems.

Moderate halophilic bacteria, but not extreme halophilic archaea can alleviate the toxicity of short-alkyl side chain imidazolium-based ionic liquids

Imidazolium-based ionic liquids (IL) with short-alkyl side chain such as 1-ethyl-3-methyl-imidazolium chloride ([Emim]Cl) and 1-butyl-3-methyl-imidazolium chloride ([Bmim]Cl) has immense application potential including in lignocellulosic bioenergy production. But they are toxic to most microorganisms, and those isolated from different environments as IL-tolerant have salt tolerance capabilities. This study evaluates the relationship between salt and [Emim]Cl tolerance of microorganisms using different salinity sediments (2-19%) and brines (35%) of India's largest inland hypersaline lake, Sambhar in Rajasthan as the model system. While samples with 2% and 35% salinities do not yield any [Emim]Cl (100 mM) tolerant colonies, others have 6-50% colonies tolerant to the IL. Similar trend was observed with 50 mM [Bmim]Cl. Moderate halophilic isolates of genera Halomonas and Bacillus (growth in 0.7-3.0 M NaCl) isolated from the sediments could grow in as high as 375 mM [Emim]Cl, or 125 mM [Bmim]Cl facilitated by higher synthesis, and uptake of organic osmolytes; and up to 1.7-fold increased activity of active efflux pumps. [Bmim]Cl was more toxic than [Emim]Cl in all performed experiments. [Emim]Cl-adapted cells could trounce IL-induced stress. Interestingly, enrichment with 100 mM [Emim]Cl resulted in increase of IL-tolerant colonies in all sediments including the one with 2% salinity. However, the salt saturated brines (35%) do not yield any such colony even after repeated incubations. Extreme halophilic archaea, Natronomonas (growth in 3.0-4.0 M NaCl) isolated from such brines, were exceedingly sensitive to even 5 mM [Emim]Cl, or 1 mM [Bmim]Cl. Two additional extremophilic archaea, namely Haloferax and Haladaptatus were also sensitive to the tested ILs. Archaeal sensitivity is possibly due to the competitive interaction of [Emim]⁺ with their acidic proteome (15.4-17.5% aspartic and glutamic acids, against 10.7-12.9% in bacteria) that they maintain to stabilize the high amount of K⁺ ion accumulated by salt-in strategy. Thus, general salt adaptation strategies of moderate halophilic bacteria help them to restrain toxicity of these ILs, but extremophilic archaea are highly sensitive and demands meticulous use of these solvents to prevent environmental contamination.

The interaction between ionic liquids (ILs) and an enriched ammonia oxidising bacteria (AOB) culture

Ionic liquids (ILs) have attracted attention in recent years due to their "greener" properties compared to conventional organic solvents. However, they may still pose a risk to the environment as their toxicity is not fully understood. Bioremediation of such ILs can be an economically and environmentally friendly approach. Therefore, this study aims to examine the interaction of three ILs (1-dodecylpyridnium chloride [DPy]⁺Cl, 1-Butyl-3-methylimidazolium chloride [BMIm]⁺Cl, and 1-Carbamoylmethyl pyridinium chloride [CMPy]⁺Cl) at different concentrations with an enriched ammonia oxidising bacteria (AOB) culture, and investigate their effects on the ammonia oxidation rate (AOR) as well as their removal and transformation. The results indicated that the longer chain IL [DPy]⁺Cl had a negative effect on the AOR while [BMIm]⁺Cl and [CMPy]⁺Cl enhanced the AOR. However, the IL removal rates displayed the opposite results as [DPy]⁺Cl was observed with the highest removal. It was found that biosorption played a major role in [DPy]⁺Cl removal. Biotransformation products for each IL were identified and their pathways were proposed. This study demonstrated that although longer chain ILs have a greater degree of removal, and they are also more toxic to AOB at higher concentration.

Ionic-liquid-based microextraction method for the determination of silver nanoparticles in consumer products

A simple method to determine hazardous silver nanoparticles (AgNPs) based on ionic liquid (IL) dispersive liquid-liquid microextraction and back-extraction is described. This approach involves AgNP stabilization using a cationic surfactant followed by extraction from the sample matrix by means of an IL as an extraction phase. Certain ILs have high affinity for metals, and preliminary experiments showed that those ILs consisting of imidazolium cation efficiently extracted AgNPs in the presence of a cationic surfactant and a chelating agent. Afterward, histamine was used as a dispersing agent to promote phase transfer of differently coated AgNPs from the IL in aqueous solution to be subsequently analyzed by UV-visible spectrometry. The analytical procedure allows AgNPs to be recovered from the sample matrix in an aqueous medium, the enrichment factor being up to 4, preserving both AgNP size and AgNP shape as demonstrated by transmission electron microscopy images and the localized surface plasmon resonance band characteristic of each AgNP. The present method exhibited a linear response for AgNPs in the range from 3 to 20 μg/mL, the limit of detection being 0.15 μg/mL. Method efficiency was assessed in spiked orange juice and face cream, yielding recoveries ranging from 75.7% to 96.6%. The method was evaluated in the presence of other nanointerferents (namely, gold nanoparticles). On the basis of diverse electrophoretic mobilities and surface plasmon resonance bands for metal nanoparticles, capillary electrophoresis was used to prove the lack of interaction of the target AgNPs with gold nanoparticles during the whole protocol; thus, interferents do not affect AgNP determination. As a consequence, the analytical approach described has great potential for the analysis of engineered nanosilver in consumer products. Graphical abstract Simple protocol for the determination of silver nanoparticles (AgNPs) based on dispersive liquid-liquid extraction with a specific short alkyl side chain ionic liquid and their quantitative detection with a UV-visible spectrometer. HMIM•PF₆ 1-hexyl-3-methylimidazolium hexafluorophosphate, NP nanoparticle, SPR surface plasmon resonance.

Toxicity profiling of 24 l-phenylalanine derived ionic liquids based on pyridinium, imidazolium and cholinium cations and varying alkyl chains using rapid screening Vibrio fischeri bioassay

A library of 24 pyridinium-, imidazolium-, and cholinium-based ionic liquids (ILs) with varying alkyl chain from C₂ to C₁₆ was toxicologically profiled using naturally luminescent marine bacteria Vibrio fischeri. The toxicity (30-min EC₅₀) of studied ILs to Vibrio fischeri ranged from 7.82 µM (4.2 mg/L) (PyC₁₂Phe) to 3096 µM (1227 mg/L) (ImidC₂Phe), i.e. from "toxic" (EC₅₀ 1-10 mg/L) to "not harmful" (EC₅₀ > 100 mg/L). Inhibition of the bacterial luminescence upon 30-min exposure to ILs correlated well with bacterial viability (exposure for 4 h). The toxicity of studied ILs was largely driven by the length of the alkyl chain (hydrophobicity) and not the type of cationic part of the IL: starting from C₁₀ all the ILs irrespective of the cationic part proved "toxic". The toxicity of the studied ILs was increasing in parallel to their hydrophobicity up to log K_ow = 1 (C₈-C₁₀) and then levelling up, being consistent with the previously obtained analogous data sets. The "cut-off" effect reported in this study for longer chain length members of the ILs series leads to the "limit" toxicity level for this type of ILs to be ca. 8 mM. Two open-access online tools (www.molinspiration.com and www.vcclab.org) have been applied for the calculation of the K_ow values for the 24 ILs reported in this study and 21 ILs reported in the literature. This lead to plotting two nonlinear monotonic correlations between the values of experimental log (1/EC₅₀) and calculated log K_ow. The limitation of the online tools and an effect of the ILs structure on the "cut-off" effect have been discussed. The challenge of developing low microbial toxicity surface active ILs remains a significant task to overcome. Our results shed light on the new approaches for designing environmentally benign ILs and functional surfactants. As the hydrophobicity of the ILs significantly correlated with the toxicity, the Vibrio fischeri assay could be considered a powerful tool in providing toxicity data for building and evaluating the QSAR toxicity models for ILs.

The role of ammonium oxidising bacteria (AOB) in ionic liquid 1-dodecylpyridinium chloride removal

Ionic liquids (IL) have emerged as the next-generation "green" solvent that can replace traditional organic solvent due to properties such as high thermal stability and no vapour pressure. However, their increased usage inevitably allows them to find their way into the environment. The objective of this study was to evaluate the role of autotrophic ammonia-oxidising bacteria (AOB) in the potential removal of 1-dodecylpyridinium chloride ([DPy]⁺Cl) in both short- and long-term studies. In short-term batch experiments, it was observed that a notable amount of [DPy]⁺ can be removed by the AOB culture with the removal mechanism being biodegradation and absorption, with the latter playing a greater role. It was also found that [DPy]⁺ can be released back into the liquid phase when AOB's preferred substrate, NH₃, was present. In the long-term study, [DPy]⁺Cl was successfully biodegraded and a total of nine transformation products were identified. The biodegradation pathway was also proposed. This study demonstrated that [DPy]⁺Cl can be biological transformed by enriched AOB culture and the accumulation of the by-product did not show long-term negative impact on AOB activities.

Tracing membrane biofouling to the microbial community structure and its metabolic products: An investigation on the three-stage MBR combined with worm reactor process

The biofouling characteristics of an MBR (S-MBR) combined with the worm reactor and a conventional MBR (C-MBR) were analyzed, respectively, over the three-stage (fast-slow-fast) process. Whether it was in the C-MBR or the S-MBR, the species of the active sludge (AS) were similar to that of the cake sludge (CS) in stage 1 (before day 1), the bacterial adsorption and the metabolites attachment contributed to this transmembrane pressure (TMP) rise. In the stage 2, the TMP increasing rate of the C-MBR was eight times more than that of the S-MBR. During this period, a characteristic community colonized the AS and CS of the S-MBR with the microbes, ie Flavobacteria, Firmicutes and Chloroflexi which were responsible for the degradation of extracellular polymeric substances (EPS) and soluble microbial products (SMP). These dominant species caused the slower accumulation of biofouling metabolites in the CS, resulting in the slow rise-related in TMP. Meanwhile, the enrichment of β-proteobacterium and the absence of Mycobacterium and Propionibacterium in AS and CS of the C-MBR were deemed as the main biological factors bringing about the rise-associated in TMP. In the stage 3, the biofilm was matured, and the cake layer was more compacted, which resulted in an abrupt rise in TMP and severe membrane fouling. Additionally, the statistical analysis revealed that a highly correlation between the TMP increasing rate and the content of carbonhydrates in SMP (SMP_c). When the SMP_c content increased slowly, there was a relatively slow biofouling. But, when the SMP_c increasing rate was greater, it led to a more serious membrane fouling with the sudden TMP jump. Additionally, there was also a highly significant correlation coefficient for the TMP rise and the content of carbonhydrates in EPS (EPS_c) and the protein in SMP (SMP_p), rather than the protein in EPS (EPS_p). The cluster analysis showed that the microbes contributing to membrane fouling were more abundant in the C-MBR, while the microbes related to organic compounds degradation were more abundant in the S-MBR. There was significant correlation between the microbes and their metabolites. The SMP_c in conjunction with EPS_c and SMP_p were the main factors accelerating the membrane fouling. It was concluded that a quick rise in SMP_c triggered an abrupt increase in TMP, while the EPS_c and SMP_p caused the sustained increase in TMP.

Removal of imidazolium-based ionic liquid by coupling Fenton and biological oxidation

In this work, we assessed the potential of combining Fenton´s reagent and biological oxidation for removing the imidazolium-based ionic liquid 1-Ethyl-3-methylimidazolium chloride (EmimCl). Fenton-like oxidation was conducted at variable H₂O₂ doses from 20 to 100% the stoichiometric value as calculated from the theoretical chemical oxygen demand (COD). The stoichiometric H₂O₂ dose afforded Total Organic Carbon (TOC) conversion and COD removal of 50 and 62%, respectively. Identifying the reaction by-products formed at low hydrogen peroxide doses allowed a plausible pathway for EmimCl oxidation to be proposed. The effluents from Fenton-like oxidation at substoichiometric H₂O₂ doses were less ecotoxic and more biodegradable than was the parent ionic liquid. The effluent from Fenton-like oxidation with the 60% H₂O₂ dose (TOC conversion ≅ 41%, COD removal ≅ 31%) was subsequently subjected to an effective biological treatment that allowed complete removal of the starting compound, increased its ecotoxicity to a low-moderate level and rendered it acceptably biodegradable. Biological oxidation was performed in 8-h and 12-h cycles in a sequencing batch reactor. Combining Fenton and biological oxidation of EmimCl afforded TOC conversion and COD removal of around 90%.

Reduced ecotoxicity and improved biodegradability of cationic biocides based on ester-functionalized pyridinium ionic liquids

Ester-functionalized pyridinium ionic liquids (ILs), 1-decyloxycarbonylmethylpyridinium chloride (PyrСOOC₁₀-Cl), and 1-dodecyloxycarbonylmethylpyridinium chloride (PyrСOOC₁₂-Cl) have been synthesized and studied for their environmental toxicity. Simple long-chain pyridinium ILs, 1-dodecylpyridinium chloride (PyrC₁₂-Cl), and commercial disinfectant cetylpyridinium chloride (CPC) were used as reference compounds. Both ester-functionalized ILs and CPC showed significantly reduced antibacterial activity compared to PyrC₁₂-Cl. However, ester-functionalized ILs were found to have excellent antifungal activity towards Candida albicans fungus strains, similar to PyrC₁₂-Cl and much higher than for CPC. The molecular docking of ILs in the active site of the known antifungal target N-myristoyltransferase (Nmt) C. albicans has been conducted. The obtained results indicate the possibility of ILs binding into the Nmt pocket. The high stability of the complexes, especially for PyrCOOC₁₀-Cl, is ensured by hydrogen bonding, electrostatic anion-pi interactions, as well as hydrophobic pi-alkyl and alkyl interactions that was confirmed by calculated binding energy values. The acute toxicity studies of ester-functionalized ILs on D. rerio (zebrafish) hydrobiont have shown their dramatically reduced ecotoxicity compared to PyrC₁₂-Cl and CPC. Thus, LD₅₀ values of 15.2 mg/L and 16.8 mg/L were obtained for PyrCOOC₁₀-Cl and PyrCOOC₁₂-Cl, respectively, whereas CPC had LD₅₀ value of 0.018 mg/L. The primary biodegradation test CEC L-33-A93 of ILs indicated an improved biodegradability of ester-functionalized compounds compared to simple long-chain ILs. Based on the obtained results, PyrCOOC₁₀-Cl may be considered as very promising cationic biocide due to the combination of soft antimicrobial activity and reduced ecotoxicity, as well as improved biodegradability.

Insight into conformationally-dependent binding of 1-n-alkyl-3-methylimidazolium cations to porphyrin molecules using quantum mechanical calculations

The first step in the biodegradation of imidazolium-based ionic liquids involves the insertion of the –OH group into the alkyl side chain, and it is believed to be triggered by cytochrome P450. In this work, we investigate the effect of conformations on binding energies of ionic liquid cations to the catalytic center of P450.

Equilibria and correlation of systems involving 1-hexyl-3-methylpyridinium trifluoromethanesulfonate

Ionic liquids are being proposed for the improvement of many refinery-related applications where water and oil coexist. However, the lack of relevant thermodynamic data on equilibrium processes involving water, oil and an ionic liquid is a stumbling block. Phase diagrams of these systems are complex, with many different regions, especially when the ionic liquid is solid at room conditions. This greatly complicates modelling, which is usually neglected or carried out only partially. In this work, for the first time, the simultaneous correlation not only of liquid–liquid and liquid–liquid–liquid but also solid–liquid equilibrium data for ternary systems involving ionic liquids has been carried out. To that end, the ionic liquid 1-hexyl-3-methylpyridinium trifluoromethanesulfonate, with an alkyl chain length that favours nano-segregation, was selected. Phase diagrams with water and different representative oils (octane, toluene and cyclohexane) have been determined at various temperatures and atmospheric pressure. The great capacity of the NRTL model, a powerful tool used in all chemical process simulators, was shown by simultaneously correlating data from all the equilibrium regions. However, adequate equilibrium equations and pivotal strategies were required. Low deviations and a good representation of phase diagrams was achieved. A topological analysis based on the Gibbs common tangent criterion and a stability test allowed validation of the proposed correlation parameters.

The NRTL model is a useful tool to carry out the simultaneous correlation of all different equilibrium regions found in a phase diagram.

Removal of imidazolium- and pyridinium-based ionic liquids by Fenton oxidation

The oxidation of imidazolium (1-hexyl-3-methylimidazolium chloride, HmimCl) and pyridinium (1-butyl-4-methylpyridinium chloride, BmpyrCl) ionic liquids (ILs) by Fenton's reagent has been studied. Complete conversion was achieved for both ILs using the stoichiometric H₂O₂ dose at 70 °C, reaching final TOC conversion values around 45 and 55% for HmimCl and BmpyrCl, respectively. The decrease in hydrogen peroxide dose to substoichiometric concentrations (20-80% stoichiometric dose) caused a decrease in TOC conversion and COD removal and the appearance of hydroxylated oxidation by-products. Working at these substoichiometric H₂O₂ doses allowed the depiction of a possible degradation pathway for the oxidation of both imidazolium and pyridinium ILs. The first step of the oxidation process consisted in the hydroxylation of the ionic liquid by the attack of the ·OH radicals, followed by the ring-opening and the formation of short-chain organic acids, which could be partially oxidized up to CO₂ and H₂O. At H₂O₂ doses near stoichiometric values (80%), the resulting effluents showed non-ecotoxic behaviour and more biodegradable character (BOD₅/COD ratio around 0.38 and 0.58 for HmimCl and BmpyrCl, respectively) due to the formation of short-chain organic acids. Graphical abstract ᅟ.

Insight into the negative impact of ionic liquid: A cytotoxicity mechanism of 1-methyl-3-octylimidazolium bromide

Ionic liquids (ILs) as a green replacement for volatile organic solvents are increasingly used in large-scale commercial applications. A good understanding of the toxic mechanisms and environmental impact of ILs is neede to reduce the risk for human health and the environment. For this purpose, we aimed to evaluate the possible impacts of 1-methyl-3-octylimidazolium bromide ([C₈mim]Br) exposure on human hepatocellular carcinoma (HepG2) cells as to elucidate the cytotoxic mechanism of [C₈mim]Br. Biochemical assays revealed that [C₈mim]Br exposure altered the protein levels of heat shock protein 70 (HSP70) and HSP90, generally inhibiting total antioxidative capacity (T-AOC), depleting heme oxygenase-1 (HO-1) and increasing transcription and activity of inducible nitric oxide synthase (iNOS) in HepG2 cells. These results indicated that [C₈mim]Br may induce biochemical disturbances and cause oxidative stress in HepG2 cells. Moreover, increased phosphorylation of p53, mitochondrial membrane disruption, cyclooxygenase-2 activation, Bcl-2 family protein modulation, cytochrome c and Smac/DIABLO release, and inhibition of apoptosis inhibitory protein-2 (c-IAP2) and survivin were also observed in [C₈mim]Br-treated cells, suggesting that [C₈mim]Br-induced apoptosis might be mediated by the mitochondrial pathway. Further research showed that [C₈mim]Br exposure increased tumour necrosis factor α (TNF-α) transcription and content and promoted the expression of Fas and FasL, indicating that TNF-α and Fas/FasL are involved in the apoptosis induced by [C₈mim]Br. Additionally, [C₈mim]Br cytotoxicity was partly inhibited by N-acetyl-cysteine (NAC), and NAC reversed [C₈mim]Br-mediated mitochondrial dysfunction and blocked apoptotic events by inhibiting the generation of reactive oxygen species (ROS). This work first demonstrated that the ROS-mediated mitochondrial and death receptor-initiated apoptotic pathway is involved in [C₈mim]Br-induced HepG2 cell apoptosis.