Properties of ionic liquid solvents for catalysis

Comparison between Phosphonium Docusate Ionic Liquids and Their Equimolar Mixtures with Alkanes: Temperature-Dependent Viscosity, Glass Transition, and Fragility

In this study, we determined the temperature-dependent viscosities, glass transition temperatures, and fragilities of tetraalkylphosphonium docusate ionic liquids (ILs) and their equimolar mixtures with alkanes to elucidate the effects of the alkyl groups on the phosphonium cation. The target ILs were the docusate salts with tributylheptylphosphonium ([P4447][doc]), tributyltetradecylphosphonium ([P444,14][doc]), butyltrihexylphosphonium ([P4666][doc]), trihexylheptylphosphonium ([P6667][doc]), and trihexyltetradecylphosphonium cations ([P666,14][doc]). The comparable IL/alkane mixtures were equimolar mixtures of IL and alkane with the same carbon numbers of the target ILs: [P4447][doc]/hexane to [P6667][doc]; [P4447][doc]/heptane to [P444,14][doc]; [P444,14][doc]/hexane to [P666,14][doc]; [P4666][doc]/decane to [P666,14][doc]; and [P6667][doc]/heptane to [P666,14][doc]. The viscosities and glass transition temperatures of the neat ILs were higher than those of their respective IL/alkane mixtures. Based on the analysis of temperature-dependent viscosities, including a viscosity value of 1013 mPa·s at the glass transition temperature using the Vogel-Fulcher-Tammann equation, the neat ILs were stronger liquids than the corresponding IL/alkane mixtures. By comparing several combinations of the neat ILs and IL/alkane mixtures, we found that the larger the alkane, the more fragile the mixture.

Advancements in ionic liquid-based corrosion inhibitors for sustainable protection strategies: from experimental to computational insights

The global corrosion cost is estimated to be around 2.5 trillion USD, which is more than 3 % of the global GDP. Against this background, large efforts have been made to find effective corrosion inhibitors. Ionic liquids (ILs) are nowadays regarded as reliable functional materials and one of the most promising classes of anticorrosion agents. Not only are they efficient in preventing corrosion of iron and other metals, but they are also relatively inexpensive, need no solvents, and are non-toxic to humans This review addresses both experimental and theoretical investigations conducted to IL-based corrosion inhibitors (CIs). It covers various ILs used, synthesis methods, and their performance in diverse corrosive environments. Electrochemical techniques like EIS and potentiodynamic polarization, along with computational approaches including quantum chemical calculations and DFT, provide valuable insights into corrosion inhibition mechanisms and the interactions between anticorrosion agents-surfaces. The synergistic combination of experimental and theoretical approaches enhances our understanding of corrosion inhibition, enabling the design and optimization of effective and sustainable corrosion protection strategies. This review consolidates the existing knowledge on ionic liquid-based corrosion inhibitors, highlights the key findings from both experimental and theoretical investigations, and points out possible directions for further studies in this area.

The Application of Green Solvents in the Synthesis of S-Heterocyclic Compounds-A Review

Cyclic organic compounds containing sulfur atoms constitute a large group, and they play an important role in the chemistry of heterocyclic compounds. They are valuable intermediates for the synthesis of other compounds or biologically active compounds themselves. The synthesis of heterocyclic compounds poses a major challenge for organic chemists, especially in the context of applying the principles of "green chemistry". This work is a review of the methods of synthesis of various S-heterocyclic compounds using green solvents such as water, ionic liquids, deep eutectic solvents, glycerol, ethylene glycol, polyethylene glycol, and sabinene. The syntheses of five-, six-, and seven-membered heterocyclic compounds containing a sulfur atom or atoms, as well as those with other heteroatoms and fused-ring systems, are described. It is shown that using green solvents determines the attractiveness of conditions for many reactions; for others, such use constitutes a real compromise between efficiency and mild reaction conditions.

Ionic Liquids in Metal, Photo-, Electro-, and (Bio) Catalysis

Ionic liquids (ILs) have unique physicochemical properties that make them advantageous for catalysis, such as low vapor pressure, non-flammability, high thermal and chemical stabilities, and the ability to enhance the activity and stability of (bio)catalysts. ILs can improve the efficiency, selectivity, and sustainability of bio(transformations) by acting as activators of enzymes, selectively dissolving substrates and products, and reducing toxicity. They can also be recycled and reused multiple times without losing their effectiveness. ILs based on imidazolium cation are preferred for structural organization aspects, with a semiorganized layer surrounding the catalyst. ILs act as a container, providing a confined space that allows modulation of electronic and geometric effects, miscibility of reactants and products, and residence time of species. ILs can stabilize ionic and radical species and control the catalytic activity of dynamic processes. Supported IL phase (SILP) derivatives and polymeric ILs (PILs) are good options for molecular engineering of greener catalytic processes. The major factors governing metal, photo-, electro-, and biocatalysts in ILs are discussed in detail based on the vast literature available over the past two and a half decades. Catalytic reactions, ranging from hydrogenation and cross-coupling to oxidations, promoted by homogeneous and heterogeneous catalysts in both single and multiphase conditions, are extensively reviewed and discussed considering the knowledge accumulated until now.

Effects of Ionic Liquids on the Nucleofugality of Bromide

The nucleofugality of bromide was measured in solvent mixtures containing ionic liquids. The solvolysis rate constants of the bromides of well-defined electrofuges were determined in mixtures containing different proportions of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide in ethanol. Temperature-dependent kinetic studies allowed an explanation of the observed solvent effects in different mixtures in terms of interactions in solution. Using the solvolysis data, the nucleofugality of bromide in these systems was determined. Likewise, nucleofugality data for bromide were determined in mixtures containing high proportions of seven further ionic liquids. These data allowed quantification of the effects of both varying the amount of ionic liquid and the nature of ionic liquid components on the nucleofugality of bromide. Importantly, ionic liquid mixtures were shown to affect the nucleofugality in a manner similar to chloride, providing a method for predicting the effects of ionic liquids on other electrofuges. Further, the ionic liquids were shown to move the transition state earlier along the reaction coordinate, meaning that there is less charge development in the transition state.

Recent Trends in the Petasis Reaction: A Review of Novel Catalytic Synthetic Approaches with Applications of the Petasis Reaction

The Petasis reaction, also called the Petasis Borono-Mannich reaction, is a multicomponent reaction that couples a carbonyl derivative, an amine and boronic acids to yield substituted amines. The reaction proceeds efficiently in the presence or absence of a specific catalyst and solvent. By employing this reaction, a diverse range of chiral derivatives can easily be obtained, including α-amino acids. A broad substrate scope, high yields, distinct functional group tolerance and the availability of diverse catalytic systems constitute key features of this reaction. In this review article, attention has been drawn toward the recently reported methodologies for executing the Petasis reaction to produce structurally simple to complex aryl/allyl amino scaffolds.

Wettability and Surface Tension of Imidazolium, Ammonium, and Phosphonium Bis(fluorosulfonyl)amide Ionic Liquids: Comparison between Pentyl, Ethoxyethyl, and Ethylthioethyl Groups

This study particularly compares the surface tensions and contact angles for molten bis(fluorosulfonyl)amide salts of imidazolium, ammonium, and phosphonium cations with the pentyl, ethoxyethyl, or ethylthioethyl group. The examined substrate plates for contact angle measurements include silicate glass, platinum, copper, graphene, and polytetrafluoroethylene (PTFE). In addition, quantum chemistry calculations were performed to obtain the optimized structures of the cations and anions of the ionic liquids (ILs) that were studied here along with some typical anions and their dipole moments, mean polarizabilities, and charge distributions. All ILs showed the same order of contact angles with respect to the substrates: PTFE > graphene ≈ copper ≈ platinum > silicate glass. By comparing the three functional groups, i.e., pentyl, ethoxyethyl, and ethylthioethyl, the ILs with the ethylthioethyl group featured a higher work of adhesion than the respective ILs with the pentyl or ethoxyethyl group. The values of the surface tensions of the ILs followed the same trend for the three functional groups. Based on the Fowkes theory, it was found that the larger surface tensions of the ILs with the ethylthioethyl group compared with pentyl and ethoxyethyl groups were because of the increase in both dispersive and nondispersive components. The quantum chemistry calculations of the ions showed a larger dipole moment and mean polarizability for the cations with the ethylthioethyl group as compared with the pentyl and ethoxyethyl groups. This is consistent with the analysis results of the surface tensions based on the Fowkes theory. By comparing other anions, the dispersive component of the surface tension of the ILs with bis(fluorosulfonyl)amide was large, which is attributed to the small dipole moment of the anion.

Biochemical interaction of human hemoglobin with ionic liquids of noscapinoids: Spectroscopic and computational approach

In this work, we have developed noscapine based ionic liquids i.e., Noscapine (MeNOS) and 9-Bromonoscapine (MeBrNOS) as cation supported with bis(trifluoromethylsulfonyl)amide (NTf₂^-) as anion. We have reported the mechanism of binding interaction between noscapine based ILs and human hemoglobin (Hb) using various spectroscopic and computational techniques. The corresponding thermodynamics studies showed that the binding is exothermic in nature and major forces responsible for binding are Van der waals and hydrogen bonding interaction. The fluorescence spectra showed that the intensity of Hb decreases in the presence of [MeNOS]NTf₂ and [MeBrNOS]NTf₂ both shows static quenching. The secondary structural changes in Hb were observed and calculated by using CD spectroscopy. Molecular docking studies revealed that both the ILs show strong binding in β1 fragment of the tetrameric structure of Hb, but the binding of [MeNOS]NTf₂ is relatively stronger than [MeBrNOS]NTf₂ and the results are supported by MD simulations.

Toxicity of ionic liquids in marine and freshwater microorganisms and invertebrates: state of the art

The variety of applications and expected growth in ionic liquid production are raising concerns about the release of these compounds into aquatic systems. Up to date, 103 studies have provided ecotoxicological data regarding the exposure effects of Ionic Liquids towards aquatic microorganisms and invertebrate species: 61 were devoted to freshwater species (n = 28), while marine species (n = 12) were mentioned in 42. The aim of this review, by gathering published studies on ionic liquids and model aquatic organisms, was to present the toxic effects described in distinct species and to understand which are the main factors influencing the toxicity of some ionic liquids. In accordance with the most recognized pattern, freshwater species were featured in a higher number of publications than marine ones. After literature analysis, algal species were the most represented organisms in aquatic toxicity assessments. Among tested compounds, the imidazolium cations in combination with long alkyl-chain anions, showed to be the most toxic one. In analytical terms, it is not straightforward to find the undissociated compound in a natural compartment, as ionic liquids are composed of ionic components, easily subjected to dissociation. Given the aforementioned, the present review paper points out the need of increasing the number of organisms being assessed in ionic liquids toxicity assays, in order to start defining monitoring procedures. Moreover, such would allow a better understanding of ionic liquids contamination status and, also, the opportunity to remark the effectiveness of new in silico methods for the ecotoxicity assessment of this kind of substances.

Sequence-specific eDNA extraction using hydrophobic magnetic ionic liquids attached with oligonucleotide strand

Isolation of high-purity nucleic acids, especially sequence-specific DNA, from complex samples is critical to the downstream nucleic acid analysis. In this work, an oligonucleotide strand-attached magnetic ionic liquid (OSMIL) was designed and prepared for DNA extraction. The attached oligonucleotide strand has a sequence complementary to that of a specific DNA to be extracted. The OSMIL has good hydrophobicity and magnetic response properties. At the extraction temperature, OSMIL was in a liquid state, which was favorable for maximizing the adsorption of DNA; while at the separation temperature, OSMIL was in a solid state (with an average particle size of 897 nm) and could be attracted by an external magnet in 3s, which was favorable for the separation and recovery of DNA. The sequence-specific DNA extraction process with OSMIL is simple and fast. After extraction, the DNA-enriched OSMILs were quickly attracted and separated by an external magnetic field. The extracted DNA was evaluated by a NanoDrop (wavelength detection at 260-280 nm) and the OSMIL can be recycled and reused. The enrichment factor was 0.81. Through single-factor experimental analysis, the effects of OSMIL extraction volume, thermal excitation temperature, thermal excitation time, pH, and other factors on the DNA extraction process were systematically investigated. The RSD of repeatability experiment was 1.19% (n = 3), showing the method has good repeatability. The extraction method presented here has been shown to extract DNA with specific sequences from mixtures containing DNA of different sequences and from mixtures containing proteins, respectively. In addition, the OSMIL has been applied to extract target environmental DNA with specific sequences from different water environments with high extraction efficiency. In the long run, OSMIL has great potential for identifying existing organisms in environmental samples or exploring unknown organisms.

Physical Properties and Low-Frequency Polarizability Anisotropy and Dipole Responses of Phosphonium Bis(fluorosulfonyl)amide Ionic Liquids with Pentyl, Ethoxyethyl, or 2-(Ethylthio)ethyl Group

This study compared the physical properties, e.g., glass transition temperature, melting point, viscosity, density, surface tension, and electrical conductivity, and the low-frequency spectra under 200 cm^-1 of three synthesized ionic liquids (ILs), triethylpentylphosphonium bis(fluorosulfonyl)amide ([P₂₂₂₅][NF₂]), ethoxyethyltriethylphosphonium bis(fluorosulfonyl)amide ([P_222(2O2)][NF₂]), and triethyl[2-(ethylthio)ethyl]phosphonium bis(fluorosulfonyl)amide ([P_222(2S2)][NF₂]), at various temperatures using femtosecond Raman-induced Kerr effect spectroscopy (fs-RIKES) and terahertz time-domain spectroscopy (THz-TDS). The [P_222(2S2)][NF₂] had the highest viscosity and glass transition temperature, whereas the [P_222(2O2)][NF₂] had the lowest. Among the three ILs, the [P_222(2S2)][NF₂] had the highest density and surface tension, and the [P_222(2O2)][NF₂] had the highest electrical conductivity. The RIKES and THz-TDS spectral line shapes for the three ILs varied significantly. For the [P₂₂₂₅][NF₂], molecular dynamics simulations successfully reproduced the line shapes of the experimental spectra and indicated that the RIKES spectrum was mainly due to the cation and cross-term and their rotational motions, whereas the THz-TDS spectrum was mainly due to the anion and its translational motion. This shows that it is desirable to utilize both fs-RIKES and THz-TDS methods to reveal molecular motions at the low-frequency domain. The [P_222(2S2)][NF₂] had higher frequency peaks and broader bands in the low-frequency spectra via fs-RIKES and THz-TDS than those for the [P₂₂₂₅][NF₂] and [P_222(2O2)][NF₂].

Corrosion inhibition mechanism of imidazole ionic liquids with high temperature in 20% HCl solution

BACKGROUND

This paper focuses on the chemical and physical adsorption of 1-hexyl-2,3-dimethyl imidazolium bromide (HDMIMBr), 1-decyl-2,3-dimethyl imidazolium bromide (DDMIMBr), and 1-hexadecyl-2,3-dimethyl imidazolium bromide (C16DMIMBr) on the surface of mild steel at high temperature in order to explore the mechanism of a corrosion inhibitor in a complex environment.

METHODS

Gravimetric, scanning electron microscope, X-ray photoelectron spectroscopy, and electrochemical tests explored the corrosion inhibition performance from the experimental level. Quantum chemical calculations and molecular dynamics simulations reveal the corrosion inhibition mechanism from the molecular scale.

RESULTS

The results show that the longer the alkyl chain of the three corrosion inhibitors studied, the better the corrosion inhibition performance. This is due to the hydrophobic effect of the long alkyl chain, which has its own synergistic effect and then self-assembles to form an adsorption film with a multilayer structure.

CONCLUSION

This dense adsorption film makes corrosion inhibitors a good application prospect in complex corrosive environments.

Understanding X-ray Photoelectron Spectra of Ionic Liquids: Experiments and Simulations of 1-Butyl-3-methylimidazolium Thiocyanate

We demonstrate a combined experimental and computational approach to probe the electronic structure and atomic environment of an ionic liquid, based on core level binding energies. The 1-butyl-3-methylimidazolium thiocyanate [C₄C₁Im][SCN] ionic liquid was studied using ab initio molecular dynamics, and results were compared against previously published and new experimental X-ray photoelectron spectroscopy (XPS) data. The long-held assumption that initial-state effects in XPS dominate the measured binding energies is proven correct, which validates the established premise that the ground state electronic structure of the ionic liquid can be inferred directly from XPS measurements. A regression model based upon site electrostatic potentials and intramolecular bond lengths is shown to account accurately for variations in core-level binding energies within the ionic liquid, demonstrating the important effect of long-range interactions on the core levels and throwing into question the validity of traditional single ion pair ionic liquid calculations for interpreting XPS data.

Rapidly Photocurable Solid-State Poly(ionic liquid) Ionogels For Thermally Robust and Flexible Electrochromic Devices

Formation of ionogels through in situ polymerization can effectively improve electrolyte processability; however, the curing process has been slow and oxygen-sensitive. Considering the low oxygen solubility of poly(ionic liquid)s (PILs), in situ polymerized ionogels are designed to realize excellent electrolytes. Herein, two in situ polymerized ionogels (PIL A & PIL B) are formulated, and they can be rapidly photocured within a minute. The ionogels are highly transparent, stretchable, and exhibit excellent physicochemical stability, including thermal, electrochemical, and air stability, allowing them to perform in various conditions. Benefitting from these properties, two high-performance electrochromic devices (ECDs) are assembled, with iron-centered coordination polymer (FeCP) and tungsten oxide (P-WO₃ ) electrochromic materials, achieving high color contrast (45.2% and 56.4%), fast response time (1.5/1.9 and 1.7/6.4 s), and excellent cycling endurance (>90% retention over 3000 cycles). Attributed to the thermal robustness of the ionogels, the ECDs can also be operated over a wide temperature range (-20 to 100 °C). With the use of deformable substrates (e.g., ultrathin ITO glass), curved electrochromic eye protector and flexible electrochromic displays are realized, highlighting their potential use in futuristic wearables.

Free N-heterocyclic carbenes from Brønsted acidic ionic liquids: Direct detection by electrospray ionization mass spectrometry

RATIONALE

The occurrence of N-heterocyclic carbenes in imidazolium-based ionic liquids has long been discussed, but no spectroscopic evidence has been reported yet due to their transient nature. The insertion of an ionizable acid group into the cation scaffold of an ionic liquid which acts as a charge tag allows for the direct detection of free carbenes by mass spectrometry.

METHODS

Three different Brønsted acidic ionic liquids were synthesized: 1-methyl-3-carboxymethylimidazolium chloride (MAICl), 1-methyl-3-carboxymethylimidazolium acetate (MAIAc) and the corresponding 2-(3-methyl-1H-imidazol-3-ium-1-yl)acetate zwitterion (MAI - H). The speciation of these compounds was then analysed by electrospray ionization ion-trap mass spectrometry in the negative ion mode.

RESULTS

The C2-H deprotonation of the imidazolium cation leading to the formation of the corresponding carbene is highly affected by the basic properties of the counter-anion. In the case of MAICl and MAI - H ionic liquids, no charged species corresponding to the free N-heterocyclic carbene was detected. On the contrary, in the presence of a sufficiently basic anion, such as acetate of MAIAc ionic liquid, an intense signal related to the free carbenic species was observed without the addition of an external base.

CONCLUSIONS

In situ formation of free N-heterocyclic carbenes from Brønsted acidic ionic liquids was demonstrated, highlighting the crucial role of anion basicity in promoting the C2-H proton abstraction from imidazolium cations with a carboxylic side chain.

Analysis of the effect of 1-Allyl-3-Methylimidazolium chloride on thermodynamic stability, folding kinetics, and motional dynamics of horse cytochrome c

1-allyl-3-methylimidazolium chloride (AMIMCl) acts as a potential green solvent for proteins. The present work provides a possible pathway by which the structural, kinetic, thermodynamic, and folding properties of horse cytochrome c (cyt c) are affected in green aqueous-AMIMCl systems. Analysis of the effect of AMIMCl on thermodynamic stability, refolding/unfolding kinetics, and motional dynamics of cyt c provided important information, (i) AMIMCl decreases the thermodynamic stability of reduced cyt c and also strengthens the guanidinium chloride (GdmCl)-mediated decrease in thermodynamic stability of protein, (ii) AMIMCl reduces the thermal-fluctuation of Met80-containing omega-loop of natively-folded compact state of carbonmonoxycytochrome c (MCO-state) due to polyfunctional interactions between the AMIM⁺ and different groups of protein, (iii) AMIMCl shifts the kinetic chevron plot, ln k_obs[GdmCl] to the lower concentration of GdmCl, (iv) AMIMCl shifts the refolding and unfolding limps to vertically downwards and upwards, respectively, and (v) AMIMCl reducing the unfolding free energy estimated by both thermodynamic and kinetic analysis.

Thermodynamics and In-Plane Viscoelasticity of Anionic Phospholipid Membranes Modulated by an Ionic Liquid

This article presents the effects of an imidazolium-based ionic liquid (IL) on the thermodynamics and in-plane viscoelastic properties of model membranes of anionic phospholipids. The negative Zeta potential of multilamellar vesicles of 14 carbon lipid 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DMPG) is observed to reduce due to the presence of few mole % of an IL 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]). The effect was found to be stronger on enhancing the chain length of the lipid. The surface pressure-area isotherms of lipid monolayer formed at air-water interface are modified by the IL reducing the effective area per molecule. Further, the equilibrium elasticity of the film is altered depending upon the thermodynamic phase of the lipids. While the presence of the IL in the DMPG lipid makes it ordered in the gel phase by reducing the entropy, the effect is opposite in the fluid phase. The in-plane viscoelastic parameters of the lipid film is quantified by dilation rheology using the oscillatory barriers of a Langmuir trough. Even though the low chain lipid DMPG does not show any effect of IL on its storage and loss moduli, the longer chain lipids exhibit a prominent effect in the liquid extended (LE) phase. Further, the dynamic response of the lipid film is found to be distinctly different in the liquid condensed (LC) phase from that of the LE phase.

Effects of Dicationic Imidazolium-Based Ionic Liquid Coatings on Oral Osseointegration of Titanium Implants: A Biocompatibility Study in Multiple Rat Demographics

Dicationic imidazolium-based ionic liquids with amino acid anions, such as IonL-phenylalanine (IonL-Phe), have been proposed as a multifunctional coating for titanium (Ti) dental implants. However, there has been no evaluation of the biocompatibility of these Ti coatings in the oral environment. This study aims to evaluate the effects of IonL-Phe on early healing and osseointegration of Ti in multiple rat demographics. IonL-Phe-coated and uncoated Ti screws were implanted into four demographic groups of rats to represent biological variations that could affect healing: young males (YMs) and females (YFs), ovariectomized (OVXFs) females, and old males (OMs). Samples underwent histopathological and histomorphometric analysis to evaluate healing at 7 and 30 days around IonL-coated and uncoated Ti. The real-time quantitative polymerase chain reaction was also conducted at the 2- and 7-day YM groups to evaluate molecular dynamics of healing while the IonL-Phe was present on the surface. IonL-coated and uncoated implants demonstrated similar histological signs of healing, while coated samples’ differential gene expression of immunological and bone markers was compared with uncoated implants at 2 and 7 days in YMs. While YMs presented suitable osseointegration for both uncoated and IonL-Phe-coated groups, decreased success rate in other demographics resulted from lack of supporting bone in YFs and poor bone quality in OVXFs and OMs. Overall, it was found that IonL-coated samples had increased bone-to-implant contact across all demographic groups. IonL-Phe coating led to successful osseointegration across all animal demographics and presented the potential to prevent failures in scenarios known to be challenged by bacteria.

1,3 Dialkylated Imidazolium Ionic Liquid Causes Interdigitated Domains in a Phospholipid Membrane

Amphiphilic imidazolium-based ionic liquids (ILs) have proven their efficacy in altering the membrane integrity and dynamics. The present article investigates the phase-separated domains in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane induced by 1,3 dialkylated imidazolium IL. Isotherm measurements on DPPC monolayers formed at the air-water interface have shown a decrease in the mean molecular area with the addition of this IL. The positive value of the excess Gibbs free energy of mixing indicates an unfavorable mixing of the IL into the lipid. This leads to IL-induced phase-separated domains in the multilayer of the lipid confirmed by the occurrence of two sets of equidistance peaks in the X-ray reflectivity data. The electron density profile along the surface normal obtained by the swelling method shows the bilayer thickness of the newly formed IL-rich phase to be substantially lower (∼34 Å) than the DPPC phase (∼45.8 Å). This IL-rich phase has been confirmed to be interdigitated, showing an enhanced electron density in the tail region due to the overlapping hydrocarbon chains. Differential scanning calorimetry measurements showed that the incorporation of IL enhances the fluidity of the lipid bilayer. Therefore, the study indicates the formation of an interdigitated phase with a lower order compared to the gel phase in the DPPC membrane supplemented with the IL.

Recent Progress of Fluorescence Sensors for Histamine in Foods

Biological amines are organic nitrogen compounds that can be produced by the decomposition of spoiled food. As an important biological amine, histamine has played an important role in food safety. Many methods have been used to detect histamine in foods. Compared with traditional analysis methods, fluorescence sensors as an adaptable detection tool for histamine in foods have the advantages of low cost, convenience, less operation, high sensitivity, and good visibility. In terms of food safety, fluorescence sensors have shown great utilization potential. In this review, we will introduce the applications and development of fluorescence sensors in food safety based on various types of materials. The performance and effectiveness of the fluorescence sensors are discussed in detail regarding their structure, luminescence mechanism, and recognition mechanism. This review may contribute to the exploration of the application of fluorescence sensors in food-related work.

Mixed chloridometallate(ii) ionic liquids with tunable color and optical response for potential ammonia sensors

Eight d-metal-containing N-butylpyridinium-based ionic liquids (ILs) were synthesized, characterized, and investigated for their optical properties.

Effects of Ionic Liquids on the Nucleofugality of Chloride

The nucleofugality of chloride has been measured in solvent mixtures containing ionic liquids for the first time, allowing reactivity in these solvents to be put in context with molecular solvents. Using well-described electrofuges, solvolysis rate constants were determined in mixtures containing different proportions of ethanol and the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide; the different solvent effects observed as the mixture changed could be explained using interactions of the ionic liquid with species along the reaction coordinate, determined using temperature dependent kinetic studies. The solvolysis data allowed determination of the nucleofugality of chloride in these mixtures, which varied with the proportion of salt in the reaction mixture, demonstrating quantitatively the importance of the amount of ionic liquid in the reaction mixture in determining reaction outcome. Nucleofugality data for chloride were determined in seven further ionic liquids, with the reactivity shown to vary over more than an order of magnitude. This outcome illustrates that the components of the ionic liquid are critical in determining reaction outcome. Overall, this work quantitatively extends the understanding of solvent effects in ionic liquids and demonstrates the potential for such information to be used to rationally select an ionic liquid to control reaction outcome.

Adsorption Motifs and Molecular Orientation at the Ionic Liquid/Noble Metal Interface: [C2C1Im][NTf2] on Pt(111)

In solid catalysts with ionic liquid layers (SCILLs), ionic liquid (IL) thin films are used to modify the activity and selectivity of catalytic materials. In this work, we investigated the adsorption behavior of the IL 1-ethyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide [C₂C₁Im][NTf₂] on Pt(111) by combining experimental and theoretical studies. Under ultrahigh vacuum (UHV) conditions, the IL was deposited onto a Pt(111) single crystal surface by physical vapor deposition (PVD) at different surface temperatures (200, 300, and 400 K). The adsorption process was monitored by in situ infrared reflection absorption spectroscopy (IRAS). Complementary to the IRAS studies, we performed density functional theory (DFT) calculations and analyzed the adsorption motifs and orientation of the IL ions. In total, we calculated four different systems: (a) [C₂C₁Im]⁺ and [NTf₂]^- ions in the gas phase; [NTf₂]^- anions in (b) small (4 × 4) and (c) large (6 × 6) Pt(111) supercells; and (d) a complete ion pair of [C₂C₁Im][NTf₂] in a (6 × 6) Pt(111) supercell. Based on DFT, we simulated IR spectra and compared them to the experimental data. Our results suggest that the binding motif and orientation of the IL is strongly dependent on the actual IL coverage. In the monolayer (ML), [NTf₂]^- interacts strongly with the metal surface and adopts a specific orientation in which it interacts with the Pt surface via the SO₂ groups. Also the [C₂C₁Im]⁺ cations adopt a preferential orientation up to coverages of 1 ML. Upon transition to the multilayer region, the specific orientation of the ions is gradually lost.

Guanidinium Hydrophobic Magnetic Ionic Liquid-Based Dispersive Droplet Extraction for the Selective Extraction of DNA

Six hydrophobic magnetic guanidinium ionic liquids (HMILs) were designed and prepared for the extraction of DNA. The physical and thermal properties of the HMILs were characterized using vibrating sample magnetometry, density meter, rotational rheometer, Karl Fischer moisture, Fourier transform infrared spectrometry, and thermogravimetric analysis. Single-stranded DNA and duplex DNA extracted by HMILs can be rapidly collected by a magnet. Three assisted extraction methods, including vortex extraction, mechanical shaking extraction, and ultrasonic extraction, were introduced to extract DNA with HMILs and the extraction efficiencies were evaluated using NanoDrop. Influencing factors of the DNA extraction were comprehensively evaluated, involving the HMIL volume, extraction time, pH, and extraction temperature. The HMIL-based extraction method can well extract DNA from complex matrices and Escherichia coli cell lysates.

Effect of Bulky Anion around the Dication on the Electronic Structure and Normal Frequencies in 1,3-Bis(3-methylimidazolium-1-yl)propane Bis(trifluoromethanesulfonyl)imide Ionic Liquid

A manifestation of hydrogen bonding between the dication and anions attributed to their relative position of the anions around the cation can influence both the conformational equilibrium and the physical properties of ionic liquids. With this view, we studied the electronic structure and normal frequencies using density functional theory calculations to analyze the hydrogen-bonding interactions in dicationic ionic liquids. The conformers are distinguished based on the hydrogen-bonding sites of the cation and anion. The weak hydrogen bonding between the dication and anions in dication ionic liquids can lead to greater conformational equilibrium compared to the monocation system. Consequences of these interactions for the vibrational spectrum are analyzed to provide an insight into the conformational equilibrium in dicationic ionic liquids at the molecular level.

Lanthanide-Doped Luminescent Nanophosphors via Ionic Liquids

Lanthanide (Ln3+) ion(s)-doped or rare-earth ion(s)-doped nanomaterials have been considered a very important class of nanophosphors for various photonic and biophotonic applications. Unlike semiconductors and organic-based luminescent particles, the optical properties of Ln3+-doped nanophosphors are independent of the size of the nanoparticles. However, by varying the crystal phase, morphology, and lattice strain of the host materials along with making core-shell structure, the relaxation dynamics of dopant Ln3+ ions can be effectively tuned. Interestingly, a judicious choice of dopant ions leads to unparallel photophysical dynamics, such as quantum cutting, upconversion, and energy transfer. Recently, ionic liquids (ILs) have drawn tremendous attention in the field of nanomaterials synthesis due to their unique properties like negligible vapor pressure, nonflammability, and, most importantly, tunability; thus, they are often called "green" and "designer" solvents. This review article provides a critical overview of the latest developments in the ILs-assisted synthesis of rare-earth-doped nanomaterials and their subsequent photonic/biophotonic applications, such as energy-efficient lighting and solar cell applications, photodynamic therapy, and in vivo and in vitro bioimaging. This article will emphasize how luminescence dynamics of dopant rare-earth ions can be tuned by changing the basic properties of the host materials like crystal phase, morphology, and lattice strain, which can be eventually tuned by various properties of ILs such as cation/anion combination, alkyl chain length, and viscosity. Last but not least, different aspects of ILs like their ability to act as templating agents, solvents, and reaction partners and sometimes their "three-in-one" use in nanomaterials synthesis are highlighted along with various photoluminescence mechanisms of Ln3+ ion like up- and downconversion (UC and DC).

On the Influence of the Menthol Moiety on the Transport Properties of a Homologue Series of Functionalized Bis(trifluoromethylsulfonyl)imide Room-Temperature Ionic Liquids: A Quest for the Structure-Property Relationship

This study explores the transport properties of bis(trifluoromethylsulfonyl)imide-based ionic liquids with a naturally derived (1R,2S,5R)-(-)-menthol moiety in the cationic part. In particular, we investigated the dependence of the dynamic viscosity and electrical conductivity as functions of the alkyl chain length. An important finding of this study is that both properties show nonmonotonic behavior with respect to the alkyl chain length. The nonmonotonic dependency is an obstacle for establishing the relationships between the structure and transport properties of homologues. To overcome this difficulty, we recommend fast property screening using a theoretical model that we developed, which allows for efficient viscosity prediction by means of the group contribution method. As demonstrated in this study, the model allows for reliable predictions of viscosity in the studied series with an overall relative deviation of less than 8%.

Rapid relaxation NMR measurements to predict rate coefficients in ionic liquid mixtures. An examination of reaction outcome changes in a homologous series of ionic liquids

A series of ionic liquids based on the 1-alkyl-3-methylimidazolium cations were examined as components of the solvent mixture for a bimolecular substitution process. The effects on both the rate coefficient of the process and the NMR spin-spin relaxation of the solvent components of changing either the alkyl chain length or the amount of ionic liquid in the reaction mixture were determined. At a constant mole fraction, a shorter alkyl chain length resulted in a greater rate coefficient enhancement and a longer relaxation time, with the opposite effects for a longer alkyl chain length. For a given ionic liquid, increasing the proportion of salt in the reaction mixture resulted in a greater rate coefficient and a shorter relaxation time. The microscopic origins of the rate coefficient enhancement were determined and a step change found in the activation parameters on increasing the alkyl chain length from hexyl to octyl, suggesting notable structuring in solution. Across a range of ionic liquids and solvent compositions, the relaxation time from NMR measurements was shown to relate to the reaction rate coefficient. The approach of using fast and simple NMR relaxation measurements to predict reaction outcomes was exemplified using a morpholinium-based ionic liquid.

Task-Specific Ionic Liquids with Lactate Anion Applied to Improve ZnO Dispersibility in the Ethylene-Propylene-Diene Elastomer

Task-specific ionic liquids (TSILs) are ionic liquids with structures and, consequently, properties and behaviors designed for particular applications. In this work, task-specific ILs with alkylammonium or benzalkonium cations and carboxyl groups in the form of lactate anions were used to promote the homogeneous dispersion of the curatives in the elastomer matrix. The reaction of carboxyl groups of TSILs with zinc oxide, which acts as a vulcanization activator, was confirmed. This interaction improved the solubility and dispersibility of zinc oxide particles in the ethylene-propylene-diene (EPDM) monomer matrix, which consequently affected the curing characteristics of rubber compounds. Most importantly, TSILs increased the efficiency of vulcanization by shortening the time, lowering the temperature and increasing the enthalpy of this process, while maintaining safe processing of elastomer composites. EPDM vulcanizates containing TSILs with lactate anion were characterized by satisfactory functional properties.

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.

Charge-Induced Birefringence in a Room-Temperature Ionic Liquid

We have reported previously on the existence of a surface charge-induced free charge density gradient (ρ_f) in room-temperature ionic liquids (RTILs) with a characteristic persistence length of ca. 50 μm [Ma, K. Langmuir 2016, 32, 9507-9512]. The free charge density gradient is related to the dielectric response of the RTIL. We report here on the existence of a surface charge-induced gradient in the RTIL refractive index and quantify the relationship between the index gradient and ρ_f. Because ρ_f is uniaxial, the induced refractive index gradient is manifested as an induced birefringence. The RTIL sample holder has a curved surface such that the RTIL can function as a lens, and ρ_f is controlled by the surface charge density (σ_s) of the (concave) RTIL support. Current passed through an indium-doped tin oxide (ITO) surface layer on the support surface controls σ_s. The far-field image of light passed through the RTIL lens as a function of σ_s is used to measure the charge-induced changes of n in the RTIL. We demonstrate a modulation of the refractive index on the order of 15%, proportional to σ_s. This report places the relationship between ρ_f and RTIL dielectric response on a quantitative footing and suggests the utility of RTILs for electro-optic applications.

Temperature dependent quantum cutting in cubic BaGdF5:Eu3+ nanophosphors

A task-specific ionic liquid (IL) is employed as a structure directing agent for the synthesis of quantum cutting BaGdF₅:Eu³⁺ nanophosphors.