High Ionic Liquid Concentrations Research Articles

Deciphering the Role of Anions of Ionic Liquids in Modulating the Structure and Stability of ct-DNA in Aqueous Solutions.

Stabilizing biomolecules under ambient conditions can be extremely beneficial for various biological applications. In this context, the utilization of ionic liquids (ILs) in enhancing the stability and preservation of nucleic acids in aqueous solutions is found to be promising. While the role of the cationic moiety of ILs in the said event has been thoroughly explored, the importance of the anionic moiety in ILs, if any, is rather poorly understood. Herein, we examine the function of anions of ILs in nucleic acid stabilization by examining the stability and structure of calf thymus-DNA (ct-DNA) in the presence of various ILs composed of a common 1-ethyl-3-methylimidazolium cations (Emim+) and different anions, which includes Cl-, Br-, , and by employing various spectroscopic techniques as well as Molecular Dynamics (MD) simulation studies. Analysis of our data suggests that the chemical nature of anions including polarity, basicity, and hydrophilicity become an important factor in the overall DNA-IL interaction event. At lower concentrations, the interplay of intermolecular interaction between the IL anions with their respective cations and the solvent molecules becomes a very crucial factor in inducing their stabilizing effect on ct-DNA. However, at higher concentrations of ILs, the ct-DNA stabilization is additionally governed by specific-ion effect. MD simulation studies have also provided valuable insights into molecular-level understanding of the DNA-IL interaction event. Overall, the present study clearly demonstrated that along with the cationic moiety of ILs, the anions of ILs can play a significant role in deciding the stability of duplex DNA in aqueous solution. The findings of this study are expected to enhance our knowledge on understanding of IL-DNA interactions in a better manner and will be helpful in designing optimized IL systems for nucleic acid based applications.

Structure, aggregation dynamics and crystallization of superfolder green fluorescent protein: Effect of long alkyl chain imidazolium ionic liquids

Green fluorescent protein (GFP) and its variants are widely used in medical and biological research, especially acting as indicators of protein structural integrity, protein-protein interactions and as biosensors. This study employs superfolder GFP (sfGFP) to investigate the impact of varying alkyl chain length of 1-Cn-3-methylimidazolium chloride ionic liquid (IL) series ([Cnmim]Cl, n = 2, 4, 6, 8, 10, 12) on the protein fluorescence, structure, hydration, aggregation dynamics and crystallization behaviour. The results revealed a concentration-dependent decrease in the sfGFP chromophore fluorescence, particularly in long alkyl chain ILs ([C10mim]Cl and [C12mim]Cl). Tryptophan (Trp) fluorescence showed the quenching rate increased with longer alkyl chains indicating a nonpolar interaction between Trp57 and the alkyl chain. Secondary structural changes were observed at the high IL concentration of 1.5 M in [C10mim]Cl and [C12mim]Cl. Small-angle X-ray scattering (SAXS) indicated relatively stable protein sizes, but with IL aggregates present in [C10mim]Cl and [C12mim]Cl solutions. Dynamic light scattering (DLS) data showed increased protein size and aggregation with longer alkyl chain ILs. Notably, ILs and salts, excluding [C2mim]Cl, promoted sfGFP crystallization. This study emphasizes the influence of the cation alkyl chain length and concentration on protein stability and aggregation, providing insights into utilizing IL solvents for protein stabilization and crystallization purposes.

Elucidating the Ionic Liquid-Induced Mixed Inhibition of GH1 β-Glucosidase H0HC94.

Deciphering the ionic liquid (IL) tolerance of glycoside hydrolases (GHs) to improve their hydrolysis efficiency for fermentable sugar synthesis in the "one-pot" process has long been a hurdle for researchers. In this work, we employed experimental and theoretical approaches to investigate the 1-ethyl-3-methylimidazolium acetate ([C2C1im][MeCO2])-induced inhibition of GH1 β-glucosidase (H0HC94) from Agrobacterium tumefaciens 5A. At 10-15% [C2C1im][MeCO2] concentration, H0HC94 experiences competitive inhibition (R2 = 0.97, alpha = 2.8). As the IL content increased to 20-25%, the inhibition pattern shifted to mixed-type inhibition (R2 = 0.98, alpha = 3.4). These findings were further confirmed through characteristic inhibition plots using Lineweaver-Burk plots. Atomistic molecular dynamics simulations conducted with 0% [C2C1im][MeCO2], 10% [C2C1im][MeCO2], and 25% [C2C1im][MeCO2] revealed the accumulation of [C2C1im]+ at the negatively charged active site of H0HC94 in 10% [C2C1im][MeCO2], supporting the occurrence of competitive inhibition at lower IL concentrations. At higher IL concentrations, the cations and anions bound to the secondary binding sites (SBSs) of H0HC94, leading to a tertiary conformational change, as captured by the principal component analysis based on the free-energy landscape and protein structure networks. The altered conformation of H0HC94 affected the interaction with [C2C1im][MeCO2], which could possibly shift the inhibition from competitive to more mixed-type (competitive + noncompetitive) inhibition, as observed in the experiments. For the first time, we report a combined experimental and theoretical insight behind the mixed inhibition of a GH1 β-glucosidase. Our findings indicated the role of SBS in IL-induced inhibition, which could aid in developing more IL-tolerant β-glucosidases for biorefinery applications.

Examining the Electrochemical Properties of Hybrid Aqueous/Ionic Liquid Solid Polymer Electrolytes through the Lens of Composition‐Function Relationships

AbstractSolid polymer electrolytes (SPEs) have the potential to meet evolving Li‐ion battery demands, but for these electrolytes to satisfy growing power and energy density requirements, both transport properties and electrochemical stability must be improved. Unfortunately, improvement in one of these properties often comes at the expense of the other. To this end, a “hybrid aqueous/ionic liquid” SPE (HAILSPE) which incorporates triethylsulfonium‐TFSI (S2,2,2) or N‐methyl‐N‐propylpyrrolidinium‐TFSI (Pyr1,3) ionic liquid (IL) alongside H2O and LiTFSI salt to simultaneously improve transport and electrochemical stability is studied. This work focuses on the impact of HAILSPE composition on electrochemical performance. Analysis shows that an increase in LiTFSI content results in decreased ionic mobility, while increasing IL and water content can offset its impact. pfg‐NMR results reveal that preferential lithium‐ion transport is present in HAILSPE systems. Higher IL concentrations are correlated with an increased degree of passivation against H2O reduction. Compared to the Pyr1,3 systems, the S2,2,2 systems exhibit a stronger degree of passivation due to the formation of a multicomponent interphase layer, including LiF, Li2CO3, Li2S, and Li3N. The results herein demonstrate the superior electrochemical stability of the S2,2,2 systems compared to Pyr1,3 and provide a path toward further enhancement of HAILSPE performance via composition optimization.

The molecular nature of the eliminating azeotropy of dimethyl carbonate–ethanol system by ionic liquid entrainer

Ionic liquids (ILs) have unique physicochemical features, such as insignificant vapour pressure, which make ILs excellent entrainers in extractive distillation to separate the azeotrope. For better utilization of the IL entrainer in extractive distillation, the microstructure properties of dimethyl carbonate (DMC)–ethanol azeotrope mixtures, before and after the separation breaking of the azeotrope by IL, were studied by Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations with focus on the vibrational region of the ethanol hydroxyl group. Excess spectroscopy followed by two-dimensional correlation spectroscopy (2D-COS) was performed on the original IR spectra to extract the microstructural features of different mixtures step by step. Different sizes of ethanol self-aggregations, DMC–ethanol interaction complex and different IL–ethanol interaction complexes were identified in different mixtures. Specifically, the DMC–ethanol interaction complex existed in both the DMC–ethanol and IL–DMC–ethanol systems at lower IL concentrations (x(IL) < 0.125) while broken out by IL at higher IL concentrations (x(IL) > 0.125). The intrinsic cause of the azeotrope breaking by the 1-hexyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl imide ([HMIM][Tf2N]) entrainer was revealed to be the disappearance of the DMC–ethanol interaction complex by the IL at higher IL concentrations. The hydrogen-bonds between DMC/IL and ethanol were also identified and confirmed in the DMC–ethanol and different IL–ethanol interaction complexes. Both the oxygen atom and the hydrogen atom in the hydroxyl group of ethanol participated in the hydrogen-bond, which confirmed the sensitivity of the hydroxyl group vibrational region. The hydrogen-bonds are weak strength, closed shells and electrostatic dominant interactions.

Molecular simulation of poly(VDF-HFP) copolymer with imidazolium-based ionic liquid as an effective medium for biogas separation

The embedding of ionic liquids (ILs) into the polymer membrane matrix affects the morphology and properties of the material. Due to the unique nature of ILs, including high thermal stability and the ability to selectively absorb various gases, polymer-IL systems generally exhibit improved separation properties. In this work, the CO2/CH4 separation properties of poly (vinylidene fluoride-co-hexafluoropropylene)) (poly (VDF-HFP)) with different amounts of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([EMIM] [TFSI]) were simulated by classical molecular dynamics (MD). MD simulations were performed using the GROMACS program with an AMBER force field for various polymer chain lengths (8, 10 and 12 mer) and different IL concentrations (0, 20, 40, 60 and 80 wt%) in the polymer. While the increased affinity of CO2 for the membrane containing a high concentration of IL was observed, the effect of IL on the affinity of CH4 was found to be negligible. A benefit of understanding the mechanism of gas absorption in polymeric-IL systems and revealing the interactions of gas molecules with IL and polymer molecules at the molecular level indicates the potential of MD simulation for understanding processes in membrane gas separations.

Spatial confinement and ion exchange synergetic strategy for highly selective removal of metal ions from the spinning solution containing ionic liquids

The accumulation of metal ions (Na+, K+, Ca2+, Mg2+, Fe3+, Cu2+ and Zn2+) in the coagulating and water baths generated during the spinning process using ionic liquids (ILs) as solvent seriously affects the strength and textile performance of regenerated cellulose fibers, and make a huge challenge for the recycling and reuse of ILs. In this work, a spatial confinement and ion exchange synergetic strategy was adopted and the molecular sieves with proper pore size and exchangeable structural metal ions were used. Batch adsorption demonstrated the superior removal efficiency and high selectivity of the 10X molecular sieve towards different metal ions. As a result, the highest removal ratios of 82.7%, 95.2%, 93.5%, 97.3%, 99.1% were achieved for K+, Ca2+, Mg2+, Cu2+ and Zn2+, respectively, and that for IL (1-ethyl-3-methylimidazolium diethyl phosphate, [Emim]Dep) was below 0.6%. Moreover, the adsorbed 10X could be facilely eluted and reused by the HCl solution. The fixed-bed experiments found that the 40.2 BV [Emim]Dep solution could be entirely purified at a contact time of 10 min, further indicating its favorable removal efficiency and long-term application perspective. All these results confirmed that this commercial and cost-effective molecular sieve could be used in the efficient separation of trace metal ions from the aqueous solutions with high IL concentration produced during the cellulose spinning process.

Effect of choline-based ionic liquids on thermodynamic and transport properties of aqueous diphenhydramine hydrochloric acid solutions

In this work, to investigate a possible interactions between diphenhydramine hydrochloric acid [DPH-HCl] and two ionic liquids (ILs) (choline bi-tartrate [Ch][bit] and choline lactate [Ch][Lac]) the isopiestic measurements were carried out on the aqueous systems containing (choline bi-tartrate + diphenhydramine hydrochloric acid) and (choline lactate + diphenhydramine hydrochloric acid) and the corresponding binary solutions at 298.15 K. The obtained experimental water activity data were fitted to the generalized polynomial equation from which activity coefficients of the drug and ionic liquids were calculated. The negative deviation of water isoactivity lines from the semi-ideal solution and positive transfer Gibbs energy values calculated from activity coefficients of ternary and binary solutions indicate that there are unfavorable interactions between both of ILs and the drug.Density, speed of sound and viscosity of the above ternary and binary solutions have also been measured at T=(288.15 to 318.15 K) from which respectively apparent molar volume, apparent molar compressibility, viscosity B-coefficient values and the corresponding transfer values from binary to ternary solutions have been calculated. The negative transfer molar volumes imply unfavorable interactions between both of ILs and the drug which is consistent with the isopiestic results. These data were also used to obtain some information on the effect of temperature and concentration of ionic liquids on the ILs-drug interactions. The more negative transfer molar volume at higher concentrations of ILs indicates that these interactions are more weakened by increasing of both of ionic liquids concentrations.

Growth Performance and Antioxidative Response of Chlorella pyrenoidesa, Dunaliella salina, and Anabaena cylindrica to Four Kinds of Ionic Liquids

Ionic liquids are widely used for lipid and pigment extractions from microalgae. It is possible that ionic liquids are discharged into environments. The evaluation of growth performance and antioxidative response of ionic liquids to microalgae is helpful to explore the stress regulation mechanism and investigate possible environmental risk. Ionic liquids induce production of reactive oxygen species (ROS) to microalgae. These oxidative stresses are possible from cations, anions, and salinity. In this study, the growth inhibitions of [BMIM]Br, [BMIM]Cl, [EMIM]Cl, and [EMIM]EtOSO3 to Anabaena cylindrica, Chlorella pyrenoidesa, and Dunaliella salina were evaluated. It was interesting that Br- and two kinds of cations, [BMIM] and [EMIM], had significant effects on growth inhibitions of these microalgae. IC50 values of these ionic liquids for A. cylindrica, C. pyrenoidesa, and D. salina were also estimated based on the results of growth inhibitions. It was proved that [EMIM]Cl is relatively harmless to C. pyrenoidesa and D. salina, and [EMIM]EtOSO3 is relatively or practically harmless to C. pyrenoidesa. [BMIM]Br and [BMIM]Cl are practically harmless to A. cylindrica and C. pyrenoidesa, and relatively harmless to D. salina. More than 0.8 g/L [EMIM]EtOSO3 led to bleaching of both A. cylindrica and D. salina at 48 h which was shown that the anion, EtOSO3-, had higher inhibition to A. cylindrica and D. salina than Cl-. In addition, high concentration of ionic liquids led to reductions of chlorophyll content in these three kinds of microalgae, increase of ROS levels and malondialdehyde contents for most of the cases. High concentration of ionic liquids also increased the activities of superoxide dismutase in three kinds of microalgae. There were positive correlations between ROS levels or MDA content, and inhibitions ratios of these ionic liquids to microalgae except [EMIM]Cl to A. cylindrica. These antioxidant enzymes were beneficial for reducing the ROS induced by ionic liquids.

In-situ penetration of ionic liquids during surface densification of Scots pine

Abstract The moisture-induced recovery of compressed wood is one of the major problems of wood densification technology. Achieving a cost-efficient surface densification process without the need for additional resins to eliminate the set-recovery may lead to an increase in value of low-density wood species. A previous study has shown that a pre-treatment with ionic liquids (ILs) can nearly eliminate the set-recovery. It was however observed that during the pre-treatment process the IL did not penetrate sufficiently deep into the wood to explain the achieved reduction in set-recovery. Based on these findings, the hypothesis was posed that further penetration of the IL into the wood occurs during the densification stage as a consequence of the applied heat and pressure. Thermo-gravimetric analysis (TGA) and gas-chromatography mass-selective-detection (GC-MSD) showed that the depth of penetration of the IL was greater after the densification process than before. Digital image correlation (DIC) showed that in regions with a high IL concentration, there was almost no set-recovery, and it gradually increased with a decrease in the IL concentration, as observed with TGA and GC-MSD analysis.

Insights on the DNA Stability in Aqueous Solutions of Ionic Liquids

Deoxyribonucleic acid (DNA) carries the genetic information essential for the growth and functioning of living organisms, playing a significant role in life sciences research. However, the long-term storage and preservation of DNA, while ensuring its bioactivity, are still current challenges to overcome. In this work, aqueous solutions of ionic liquids (ILs) were investigated as potential preservation media for double stranded (dsDNA). A screening of several ILs, by combining the cholinium, tetrabutylammonium, tetrabutylphosphonium, and 1-ethyl-3-methylimidazolium, cations with the anions bromide, chloride, dihydrogen phosphate, acetate, and glycolate, was carried out in order to gather fundamental knowledge on the molecular features of ILs that improve the dsDNA stability. Different IL concentrations and the pH effect were also addressed. Circular dichroism (CD) spectroscopy was used to evaluate the conformational structure and stability of dsDNA. IL-DNA interactions were appraised by UV-Vis absorption spectrophotometry and 31P nuclear magnetic resonance (NMR) spectroscopy. The results obtained demonstrate that pH has a significant effect towards the dsDNA stability. Amongst the ILs investigated, cholinium-based ILs are the most promising class of ILs to preserve the dsDNA structure, in which electrostatic interactions between the cholinium cation and the DNA phosphate groups play a significant role as demonstrated by the 31P NMR data, being more relevant at higher IL concentrations. On the other hand, the denaturation of dsDNA mainly occurs with ILs composed of more hydrophobic cations and able to establish dispersive interactions with the nucleobases environment. Furthermore, the IL anion has a weaker impact when compared to the IL cation effect to interact with DNA molecules. The experimental data of this work provide relevant fundamental knowledge for the application of ILs in the preservation of nucleic acids, being of high relevance in the biotechnology field.

Impact of ionic liquid on lithium ion battery with a solid poly(ionic liquid) pentablock terpolymer as electrolyte and separator

In this study, the physical, transport, mechanical, morphological, and electrochemical properties of a ternary blend solid polymer electrolyte (SPE) (poly(ionic liquid) (PIL) multiblock polymer, lithium salt, and ionic liquid (IL)) were systematically investigated as a function of IL concentration. With increasing IL concentration, the conductive volume increases along with the polymer chain segmental mobility. This facilitates high ionic conductivity, while the mechanical modulus exhibits a percolation threshold. Surprisingly, at higher IL concentrations, there is a reduction in the lithium cation mobility as evidenced by pulsed-field gradient nuclear magnetic resonance, which coincides with an increased overpotential evidenced by lithium metal stripping and plating. Stable lithium ion battery cycling durability (over 100 cycles at room temperature) is demonstrated with the ternary blend SPE as the electrolyte and separator. This work provides valuable insights into the design of new SPEs with both high ionic conductivity and improved battery stability.

Solubility and aggregation of soy protein isolate induced by different ionic liquids with the assistance of ultrasound

The aim of this study was to evaluate the effects of ionic liquids (ILs) and ultrasound on the solubility and aggregation behavior of soy protein isolate (SPI). A variety of ILs were tested. Results showed that changes in cation or anion altered the physicochemical properties of ionic liquids, which in turn influenced the solubility of SPI. High concentration of ILs resulted in the formation of insoluble aggregates, which lead to the decrease of solubility. In most of the cases, ultrasound pretreatment had a considerable impact on the solubility and aggregation of SPI. The solubility of SPI processed by combination of 1 mg/mL 1-butyl-2,3-dimethyl imidazolium chloride ([BDMIM]Cl) and ultrasound changed remarkably compared with single ultrasound and single [BDMIM]Cl processing, which was increased by 71.8% compared with that of control (P < .05). Changes in particle size, intrinsic fluorescence spectra and free sulfhydryl (SH) groups indicated that the structure of SPI refolded and reaggregated after the ultrasound and ILs pretreatments. Combined ultrasound and 1 mg/mL [BDMIM]Cl pretreatment showed a synergistic effect on changing the SPI microstructure. In conclusion, ultrasound-assisted ILs could be an effective modification method for the globular proteins.

Ion-induced free energy landscapes of Aβ33–42 peptide dimer in wet ionic liquids

The transitions between α-helix and β-sheet conformation of Aβ33–42 peptide dimer in water and an aqueous solution of three ionic liquids (ILs) at two concentrations are investigated using umbrella sampling-based classical molecular dynamics simulations. The ionic liquids chosen for this study are Ethylammonium Mesylate (EAM), Ethylammonium Nitrate (EAN), and Triethylammonium Mesylate (TEAM). The average psi angle of the peptide backbone was used as the reaction coordinate to explore the free energy pathway of the transition. The secondary structure element values were calculated for peptide dimer along the reaction coordinate to probe the conformational changes during the transition between α-helix and β-sheet conformations. We observe the α-helix conformation as the global minimum at low concentration of EAM and EAN ILs and β-sheet conformation as the global minimum at low concentration of TEAM as well as the high concentration of EAM, EAN, and TEAM ILs. The average numbers of intramolecular and intermolecular hydrogen bonds were calculated for the conformations corresponding to the free-energy minima; these numbers are in correlation with the secondary structure element values. The atom-atom radial distribution functions of cation, anion, and water around amide hydrogen and oxygen atoms of the peptide backbone were calculated to understand the peptide-IL interactions. The solvent-accessible surface area of the peptide was calculated to understand the exposure to the solvent during the transition. Finally, to understand the stability of conformations on the free-energy landscape, we calculated van der Waals and Coulomb interaction energies between peptide-cation, peptide anion, and peptide-water molecules. We find that the TEA cation in TEAM contributes more towards the vdWs and less towards Coulomb interactions with the peptide as compared to EA cation in EAM and EAN ILs, which results in destabilization of α-helix conformation in TEAM ILs.

Characterization and Enzyme Engineering of a Hyperthermophilic Laccase Toward Improving Its Activity in Ionic Liquid

Ionic liquids (ILs) are organic salts molten at room temperature that can be used for a wide variety of applications. Many ILs, such as 1-ethyl-3-methylimidazolium acetate ([C2C1Im][OAc]), have been shown to remove a significant fraction of the complex biopolymer lignin from biomass during pretreatment. Valorizing lignin via biological pathways (e.g. enzymes) holds promise but is limited by the low biocompatibility of many ILs used for pretreatment. The discovery of thermostable enzymes and the application of enzyme engineering techniques have yielded biocatalysts capable of withstanding high concentrations of ILs. Converting lignin from a waste product to value-added chemicals is vital to the success of future cellulosic biorefineries. To that end, we screened the activity of the lignolytic enzyme laccase from a hyperthermophilic bacterium (Thermus thermophilus) in aqueous [C2C1Im][OAc]. Despite the thermophilicity (Topt > 90 oC) of this laccase, significant activity loss (>50%) was observed in only 2% (w/v) [C2C1Im][OAc]. Kinetics studies show that the IL can bind to the free enzyme and the enzyme-substrate complex. Docking simulations suggest that the cation favors binding to a region close to the active site. We then used a rational design strategy to improve the activity of the laccase in [C2C1Im][OAc]. A total of 8 single amino acid mutations were made; however, there were no significant improvements in the activity of the mutants in [C2C1Im][OAc] compared to the wild type. The results of this study shed light on the complex nature of enzyme-IL interactions and the challenges faced when designing a biological lignin valorization strategy.

Cosolvent polarity dependence of solution structure in [BMIM] [PF6] + acetonitrile/1, 4-dioxane/hexane binary mixtures: Insights from composition dependent Voronoi polyhedra analyses, iso-surfaces and radial distribution functions

We investigate in this paper, via molecular dynamics simulations, the composition dependent solution structures in the binary mixtures composed of the ionic liquid (IL), 1-butyl-3methyl-imidazolium hexafluorophosphate, ([BMIM] [PF6]), and three different co-solvents of comparable sizes but with differing polarities. These cosolvents are acetonitrile (dipolar), 1,4-dioxane (quadrupolar) and hexane (non-polar). Five different IL mole fractions for the binary mixtures (FIL = 0.90, 0.75, 0.50, 0.25, 0.10) along with the neat solvents have been studied. The cosolvent polarity and concentration dependencies have been assessed through the examination of the composition dependent spatial and radial distribution functions, coordination numbers and the Voronoi polyhedra analyses. The solution structure is found to be dominated by the cosolvent clustering at high IL concentrations, and segregation of the IL into polar and non-polar domains in dilute IL solutions, their extent being strongly dependent upon cosolvent polarity. The aggregation behavior of the IL in the non-polar and dipolar binary mixtures is explained in terms of the Debye screening length (DSL). Such an explanation, however, fails to explain the comparable solubility of 1,4-dioxane in this IL. Isodensity surfaces constructed from the simulated spatial distribution functions show a dramatic cosolvent polarity dependence for the binary solution structure and reflects that microscopic phase segregation is the most pronounced for IL + hexane binary mixtures. The Voronoi polyhedra (VP) analyses indicate broader void and neck distributions upon dilution of the IL by cosolvents, suggesting increased heterogeneity in the solution structure of the binary mixtures. The severe phase segregation observed for [BMIM] [PF6] + hexane mixtures at the low IL concentrations did not allow similar VP analyses for this binary mixture for all the mixture compositions considered.

The effect of ionic liquid on the structure of active site pocket and catalytic activity of a β-glucosidase from Halothermothrix orenii

Abstract Understanding the inhibition of cellulase activity in the presence of ionic liquids (IL) is extremely important towards engineering IL tolerant enzymes for biomass saccharification and subsequent biofuel production. Here we report the all-atom molecular dynamics simulations of a highly active and thermostable GH1 β-glucosidase (EC 3.2.1.21) B8CYA8 from Halothermothrix orenii in the presence of the IL, 1-ethyl-3-methylimidazolium chloride ([EMIM][Cl]). In the presence of IL, we observed a lack of destabilization of the overall protein structure but instead a localized increase in fluctuations of active site pocket residues corresponding to the loop region, gatekeeper region, aglycone binding site, and glycone binding site. The role of specific residues was confirmed by the Principal Component Analysis (PCA) and Chemical Shift Perturbation (CSP) analyses. Since the enzymatic saccharification requires the proper arrangement of catalytic side chains, residue fluctuation within the active site tunnel affects the reaction rate. Indeed, while B8CYA8 exhibits very high IL tolerance, high concentrations of IL inhibit the enzyme, our analyses show that in high concentrations of IL, the IL accumulates at the active site pocket entrance and near the active site catalytic residues to restrict substrate accessibility to the catalytic site and decreases enzyme activity. Unlike the reaction product glucose, the IL does not change the overall tunnel diameter to constrict substrate access. To understand how IL viscosity may affect enzyme behavior, we determined the self-diffusion constant and show that the presence of IL has a significant effect on substrate access to the catalytic site due to the low diffusivity of the substrate in IL. These results highlight the role played by the residues in active site pocket and the IL properties and may guide in the design of better protein and IL pairs for efficient catalysis.

Oxidative stress response and proteomic analysis reveal the mechanisms of toxicity of imidazolium-based ionic liquids against Arabidopsis thaliana

Ionic liquids (ILs) are extensively used in various fields, posing a potential threat in the ecosystem because of their high stability, excellent solubility, and biological toxicity. In this study, the toxicity mechanism of three ILs, 1-octyl-3-methylimidazolium chloride ([C8MIM]Cl), 1-decyl-3-methylimidazolium chloride ([C10MIM]Cl), and 1-dodecyl-3-methylimidazolium chloride ([C12MIM]Cl) on Arabidopsis thaliana were revealed. Reactive oxygen species (ROS) level increased with higher concentration and longer carbon chain length of ILs, which led to the increase of malondialdehyde (MDA) content and antioxidase activity, including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and peroxidase (POD) activities. SOD, CAT, and GPX activities decreased in high ILs concentration due to the excessive ROS. Differentially expressed protein was analyzed based on Gene ontology (GO) and KEGG pathways analysis. 70, 45, 84 up-regulated proteins, and 72, 104, 79 down-regulated proteins were identified in [C8MIM]Cl, [C10MIM]Cl, and [C12MIM]Cl treatment, respectively (fold change ≥ 1.5 with ≥95% confidence). Cellular aldehyde metabolic process, mitochondrial and mitochondrial respiratory chains, glutathione transferase and oxidoreductase activity were enriched as up-regulated proteins as the defense mechanism of A. thaliana to resist external stresses. Chloroplast, photosynthetic membrane and thylakoid, structural constituent of ribosome, and transmembrane transport were enriched as the down-regulated protein. Compared with the control, 8 and 14 KEGG pathways were identified forup-regulated and down-regulated proteins, respectively, in three IL treatments. Metabolic pathways, carbon metabolism, biosynthesis of amino acids, porphyrin and chlorophyll metabolism were significantly down-regulated. The GO terms annotation demonstrated the oxidative stress response and effects on photosynthesis of A. thaliana in ILs treatment from biological process, cellular component, and molecular function categories.

Structural Forces in Mixtures of Ionic Liquids with Organic Solvents.

Using molecular dynamics simulations, we study the impact of electrode charging and addition of solvent (acetonitrile, ACN) on structural forces of the BMIM PF6 ionic liquid (IL) confined by surfaces at nanometer separations. We establish relationships between the structural forces and the microscopic structure of the confined liquid. Depending on the structural arrangements of cations and anions across the nanofilm, the load-induced squeeze-out of liquid layers occurs via one-layer or bilayer steps. The cations confined between charged plates orient with their aliphatic chain perpendicular to the surface planes and link two adjacent IL layers. These structures facilitate the squeeze-out of single layers. For both pure IL and IL-ACN mixtures, we observe a strong dependence of nanofilm structure on the surface charge density, which affects the simulated pressure-displacement curves. Addition of solvent to the IL modifies the layering in the confined film. At high electrode charges and high dilution of IL (below 10% molar fraction), the layered structure of the nanofilm is less well defined. We predict a change in the squeeze-out mechanism under pressure, from a discontinuous squeeze-out (for high IL concentrations) to an almost continuous one (for low IL concentrations). Importantly, our simulations show that charged electrodes are coated with ions even at low IL concentrations. These ion-rich layers adjacent to the charged plate surfaces are not squeezed out even under very high normal pressures of ∼5 GPa. Hence, we demonstrate the high performance of IL-solvent mixtures to protect surfaces from wear and to provide lubrication at high loads.

Thermodynamic modeling of ternary systems containing imidazolium-based ionic liquids and acid gases using SRK, Peng-Robinson, CPA and PC-SAFT equations of state

In this study, the cubic and the associative equations of state are applied to model the VLE data of ternary systems containing ionic liquids. In the first section, the simultaneous solubility of CO2 and H2S in the ionic liquids [omim][Tf2N], [omim][PF6] and [bmim][PF6] is modeled and the selective absorption of CO2/H2S is investigated at the temperatures T/K = (303.15 and 343.15) and the pressures P/MPa = (0.1 and 1). According to the obtained results, the percent deviations in pressure were varying between 6.0 and 10.8 for the SRK EoS, 6.0 and 10.6 for the PR EoS, 2.6 and 9.6 for the CPA EoS and 3.4 and 6.1 for the PC-SAFT EoS. Also, percent deviations in vapor phase composition were varying between 3.1 and 4.9 for the SRK EoS, 3.3 and 4.9 for the PR EoS, 3.1 and 7.0 for the CPA EoS and 3.8 and 4.9 for the PC-SAFT EoS. In the selectivity calculations, at high ionic liquid concentrations, the cubic models predict the selectivity drop; while the associative models present increasing trend. In the second section, the CO2 solubility in ethanol and [emim][Tf2N] as well as the mixture of ethanol and [emim][Tf2N] is modeled and the experimental points were tested for thermodynamic consistency. According to the obtained results, the percent deviation in pressure of the ternary systems was 3.9 for the SRK EoS, 3.9 for the PR EoS, 3.8 and 4.0 for the CPA EoS and 3.1 and 3.2 for the PC-SAFT EoS. In the same temperature and pressure, the CO2 solubility decrease when the concentration of ethanol increases, and the proposed models can describe this phase behavior.