Chul-Woong Cho

Environmental fate and toxicity of ionic liquids: a review.

Ionic liquids (ILs) are organic salts with low melting point that are being considered as green replacements for industrial volatile organic compounds. The reputation of these solvents as environmental friendly chemicals is based primarily on their negligible vapor pressure. Nonetheless, the solubility of ILs in water and a number of literature documenting toxicity of ILs to aquatic organisms highlight a real cause for concern. The knowledge of ILs behavior in the terrestrial environment, which includes microbial degradation, sorption and desorption, is equally important since both soil and aquatic milieu are possible recipients of IL contamination. This article reviews the achievements and current status of environmental risk assessment of ILs, and hopefully provides insights into this research frontier.

Cinnamon zeylanicum bark extract and powder mediated green synthesis of nano-crystalline silver particles and its bactericidal activity

The exploitation of various plant materials for the biosynthesis of nanoparticles is considered a green technology as it does not involve any harmful chemicals. The present study reports the synthesis of silver (Ag) nanoparticles from silver precursor using the bark extract and powder of novel Cinnamon zeylanicum. Water-soluble organics present in the plant materials were mainly responsible for the reduction of silver ions to nano-sized Ag particles. TEM and XRD results confirmed the presence of nano-crystalline Ag particles. The pH played a major role in size control of the particles. Bark extract produced more Ag nanoparticles than the powder did, which was attributed to the large availability of the reducing agents in the extract. Zeta potential studies showed that the surface charge of the formed nanoparticles was highly negative. The EC(50) value of the synthesized nanoparticles against Escherichia coli BL-21 strain was 11+/-1.72 mg/L. Thus C. zeylanicum bark extract and powder are a good bio-resource/biomaterial for the synthesis of Ag nanoparticles with antimicrobial activity.

Influence of anions on the toxic effects of ionic liquids to a phytoplankton Selenastrum capricornutum

Investigations on the influence of anions of ionic liquids, with respect to toxicity and ecotoxicity, have been reported; however, no consistent conclusion has been drawn. The aim of this study was to elucidate the influence of the anionic component, using the alga Selenastrum capricornutum, by assessing the toxicity of various anions associated with imidazolium-based ionic liquids as well as alkali salts. Additionally, the hydrolysis of fluoride-containing ionic liquids, i.e., 1-butyl-3-methylimidazolium [BMIM], incorporated with tetrafluoroborate, hexafluorophosphate and hexafluoroantimonate, was also estimated. The results obtained revealed that imidazolium-based ionic liquids were more toxic than their corresponding alkali salts. In both cases, SbF6– and PF6– were identified as the most toxic anions. In general, Selenastrum capricornutum was sensitive to the anion moieties in the order: SbF6– > PF6– > BF4– > CF3SO3– > C8H17OSO3– > Br– ≈ Cl–. With regard to the hydrolytic effect, [BMIM][SbF6] generated a greater amount of fluoride compared with [BMIM][BF4], but no fluoride formation occurred with the hexafluorophosphate.

Alkyl-chain length effects of imidazolium and pyridinium ionic liquids on photosynthetic response of Pseudokirchneriella subcapitata

The toxicities of imidazolium- and pyridinium-based ionic liquids with various alkyl-chain lengths were investigated on the photosynthetic activity of the alga Pseudokirchneriella subcapitata. Our results show that an imidazolium compound with four carbons in the alkyl chain was the least toxic salt, and should be preferred over pyridinium entity.

Biodegradability of 27 pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium ionic liquid cations under aerobic conditions

The chemical and thermal stability of ionic liquids (ILs) makes them interesting for a large variety of applications in nearly all areas of the chemical industry. However, this stability is often reflected in their recalcitrance towards biodegradation, which comes with the risk of persistence when they are released into the environment. In this study we carried out a systematic investigation of the biodegradability of pyrrolidinium, morpholinium, piperidinium, imidazolium and pyridinium-based IL cations substituted with different alkyl or functionalised side chains and using halide counterions. We examined their primary degradability by specific analysis and/or their ultimate biodegradability using biochemical oxygen demand tests according to OECD guideline 301F. Biological transformation products were investigated using mass spectrometry. A comparison of the biodegradation potential of these ILs shows that for all five head groups, representatives can be found that are readily or inherently biodegradable, thus permitting the structural design of ILs with a reduced environmental hazard.

Ionic liquids: predictions of physicochemical properties with experimental and/or DFT-calculated LFER parameters to understand molecular interactions in solution.

In this article, we present evolutionary models to predict the octanol-water partition coefficients (log P), water solubilities, and critical micelle concentrations (CMCs) of ionic liquids (ILs), as well as the anionic activity coefficients and hydrophobicities in pure water and octanol-water. They are based on a polyparameter linear free energy relationship (LFER) using measured and/or DFT-calculated LFER parameters: hydrogen-bonding acidity (A), hydrogen-bonding basicity (B), polarizability/dipolarity (S), excess molar refraction (E), and McGowan volume (V) of IL ions. With both calculated or experimental LFER descriptors of IL ions, the physicochemical parameters were predicted with an errors of 0.182-0.217 for the octanol-water partition coefficient and 0.131-0.166 logarithmic units for the water solubility. Because experimentally determined solute parameters of anions are not currently available, the CMC, anionic activity coefficient, and hydrophobicity were predicted with quantum-chemical methods with R(2) values of at least 0.99, as well as errors below 0.168 logarithmic units. These new approaches will facilitate the assessment of the technical applicability and environmental fate of ionic compounds even before their synthesis.

In silico modelling for predicting the cationic hydrophobicity and cytotoxicity of ionic liquids towards the Leukemia rat cell line, Vibrio fischeri and Scenedesmus vacuolatus based on molecular interaction potentials of ions

In this study we present prediction models for estimating in silico the cationic hydrophobicity and the cytotoxicity (log [1/EC50]) of ionic liquids (ILs) towards the Leukemia rat cell line (IPC-81), the marine bacterium Vibrio fischeri and the limnic green algae Scenedesmus vacuolatus using linear free energy relationship (LFER) descriptors computed by COSMO calculations. The LFER descriptors used for the prediction model (i.e. excess molar refraction (E), dipolarity/polarizability (S), hydrogen-bonding acidity (A), hydrogen-bonding basicity (B) and McGowan volume (V)) were calculated using sub-descriptors (sig2, sig3, HBD3, HBA4, MR, and volume) derived from COSMO–RS, COSMO and OBPROP. With the combination of two solute descriptors (B, V) of the cation we were able to predict cationic hydrophobicity values (log ko ) with r 2 = 0.987 and standard error (SE) = 0.139 log units. By using the calculated log k o values, we were able to deduce a linear toxicity prediction model. In the second prediction study for the cytotoxicity of ILs, analysis of descriptor sensitivity helped us to determine that the McGowan volume (V) terms of the cation was the most important predictor of cytotoxicity and to simplify prediction models for cytotoxicity of ILs towards the IPC-81 (r 2 of 0.778, SE of 0.450 log units), Vibrio fischeri (r 2 of 0.762, SE of 0.529 log units) and Scenedesmus vacuolatus (r 2 of 0.776, SE of 0.825 log units). The robustness and predictivity of the two models for IPC-81 and Vibrio fischeri were checked by comparing the calculated SE and r 2 (coefficient of determination) values of the test set.

Biodegradability of fluoroorganic and cyano-based ionic liquid anions under aerobic and anaerobic conditions

The present study deals with the primary biodegradability of ionic liquids in order to obtain a greater insight into their fate under different environmental conditions. The focus was thereby on the biodegradation potential of ionic liquid anions when undergoing aerobic and anaerobic biological waste water treatment. Five technologically relevant fluoroorganic and cyano-based ionic liquid anions were investigated as alkaline salts (Li (CF3SO2)2N, K (C2F5)3PF3 and Na N(CN)2, K C(CN)3, K B(CN)4 respectively). Their biodegradability was determined in activated sludge over a period of around 60 days by specific analysis of the anion using ion chromatography. Additionally, the antimicrobial activity of the test compounds towards the activated sludge organisms was tested in inhibition studies. Because of the technologically desirable chemical, thermal and electrochemical stability of these anions, their biodegradability is questioned. The results seem to support the hypothesis: although the concentrations used did not inhibit the inoculum, none of these anions could be biodegraded under either aerobic or denitrifying conditions. The present paper provides information concerning the biodegradability of ionic liquids in waste water treatment plants and gives a first systematic view of the aerobic and anaerobic biodegradability of fluoroorganic and cyano-based ionic liquid anions and therefore supports further hazard assessment.

Effect of imidazolium‐based ionic liquids on the photosynthetic activity and growth rate of Selenastrum capricornutum

Ionic liquids (ILs) are low-melting organic salts that are being researched intensively as possible environmentally friendly replacements for volatile organic solvents. Despite their nonmeasurable vapor pressure, some quantities of ILs soon will be present in effluent discharges because solubility of ILs in water is small, but far from negligible. Therefore, it is important to understand how ILs will influence aquatic ecosystems. In the present study, the toxic effects of imidazolium-based ILs (1-butyl-3-methylim-idazolium cation associated with bromide [BMIM][Br] and tetrafluoroborate [BMIM][BF4]) to the freshwater green alga Selenastrum capricornutum were investigated. Two approaches were followed to quantify toxicity of these compounds: Analyses of photosynthetic activity and cell proliferation. The obtained data showed that the relative declines of growth rates generally were more pronounced than those of photosynthetic activity. The ecotoxicity of a range of common organic solvents also was examined. It was revealed that both imidazolium-based ILs studied were some orders of magnitude more toxic than methanol, isopropanol, and dimethylformamide. In addition, with respect to IL incorporating perfluorinated anion, EC50 values (concentrations which lead to a 50% reduction of the exposed organisms relative to control) of the previously prepared stock solution were significantly lower compared to those of the freshly made one. This might be due to hydrolytic effects of [BMIM][BF4] leading to fluoride formation, which was confirmed by ion chromatography analysis. This indicates that, after ILs are discharged into the aqueous system, they can become more toxic than expected by laboratory data with fresh ILs.

Structural effects of ionic liquids on microalgal growth inhibition and microbial degradation

In the present study, we investigated structural effects of various ionic liquids (ILs) on microalgal growth inhibition and microbial biodegradability. For this, we tested pyridinium- and pyrrolidinium-based ILs with various alkyl chain lengths and bromide anion, and compared the toxicological effects with log EC50 values of imidazolium-based IL with the same alkyl chains and anion from literature. Comparing determined EC50 values of cationic moieties with the same alkyl chain length, pyridinium-based ILs were found to be slightly more toxic towards the freshwater green alga, Pseudokirchneriella subcapitata, than a series of pyrrolidinium and imidazolium except to 1-octyl-3-methylimidazolium bromide. Concerning the biodegradation study of 12 ILs using the activated sludge microorganisms, the results showed that the pyridinium derivatives except to 1-propyl-3-methylpyridinium cation were degraded. Whereas in case of imidazolium- and pyrrolidinium-based compounds, only n-hexyl and n-octyl substituted cations were fully degraded but no significant biodegradation was observed for the short chains (three and four alkyl chains).