Aqueous Ionic Liquid Research Articles

Zinc Chemistries of Hybrid Electrolytes in Zinc Metal Batteries: From Solvent Structure to Interfaces.

Along with the booming research on zinc metal batteries (ZMBs) in recent years, operational issues originated from inferior interfacial reversibility have become inevitable. Presently, single-component electrolytes represented by aqueous solution, "water-in-salt," solid, eutectic, ionic liquids, hydrogel, or organic solvent system are hard to undertake independently the task of guiding the practical application of ZMBs due to their specific limitations. The hybrid electrolytes modulate microscopic interaction mode between Zn2+ and other ions/molecules, integrating vantage of respective electrolyte systems. They even demonstrate original Zn2+ mobility pattern or interfacial chemistries mechanism distinct from single-component electrolytes, providing considerable opportunities for solving electromigration and interfacial problems in ZMBs. Therefore, it is urgent to comprehensively summarize the zinc chemistries principles, characteristics, and applications of various hybrid electrolytes employed in ZMBs. This review begins with elucidating the chemical bonding mode of Zn2+ and interfacial physicochemical theory, and then systematically elaborates the microscopic solvent structure, Zn2+ migration forms, physicochemical properties, and the zinc chemistries mechanisms at the anode/cathode interfaces in each type of hybrid electrolytes. Among of which, the scotoma and amelioration strategies for the current hybrid electrolytes are actively exposited, expecting to provide referenceable insights for further progress of future high-quality ZMBs.

Binary imidazolium based aqueous ionic liquid droplet on a rough surface: a molecular dynamics study

Ionic liquids (ILs) have garnered immense attention due to their tunable physicochemical properties. In this study, we delve into the wetting behaviour and interfacial properties of aqueous binary IL mixtures containing [EMIM] [BF4] and [HMIM] [BF4] on both smooth and rough graphite surfaces. Employing classical molecular dynamics simulations, we systematically explored the effects of IL concentration and surface morphology on wetting phenomena. To ensure the equilibrium of the systems, we began by calculating the interaction energies between the components. Subsequently, contact angles were computed, shedding light on the wetting characteristics of the aqueous binary IL mixtures. We meticulously examined the density profiles of the IL systems from the substrate to unravel the dominance of one IL over the other, exploiting the hydrophilic nature of [EMIM] [BF4] and the hydrophobic nature of [HMIM] [BF4]. A comprehensive analysis of hydrogen bond distribution allowed us to discern the intricate nature of these aqueous binary IL droplets. We probed the changes in intermolecular forces within the aqueous IL solution by investigating surface tensions. The tunability of these ILs emerges as a significant aspect of our study, paving the way for their tailored application in engineering and scientific domains. Schematic diagram showing the density distribution of hydrophilic and hydrophobic ILs ([EMIM] [BF4] and [HMIM] [BF4]) in water and also the hydrogen bond (HB) distribution of anion ([BF4]−) water inside the droplet on a pillared surface with a surface fraction ( f ) of 0.4 and pillar height of H = 4 .

Choline Oxidase and Choline Ionic Liquids in Biocatalytic Heme Peroxidase Cascades

Choline oxidase from Alcaligenes sp. (ChOx) is used to generate hydrogen peroxide in situ from choline‐based ionic liquids (ILs) to fuel peroxidase‐mediated biocatalysis, while mitigating oxidative degradation of the heme‐dependent enzymes. Horseradish peroxidase (HRP) and chloroperoxidase from Caldariomyces fumago (CPO), in combination with the ChOx, are evaluated in enzymatic cascades for the ability of the biocatalytic systems to withstand elevated concentrations of different choline additives in oxidative and halogenative enzymatic assays. The findings are applied in various synthetic scenarios to produce important oxygen‐ and nitrogen‐containing heterocycles, using choline ILs in a dual‐purpose fashion, as a substrate‐solubilizing component in the reaction medium as well as the source for hydrogen peroxide. The ChOx/HRP couple is used to induce intramolecular cyclizations of hydroxamic acids and hydroxycarbamates in a nitroso‐ene‐type pathway with choline dihydrogen phosphate as IL additive. The ChOx/CPO cascade successfully mediates brominative cyclizations of α‐allenic alcohols, while amphiphilic surfactants are employed to turn the aqueous choline propionate IL media into a colloidal suspension. ChOx/CPO partnering is also evaluated in an oxygenative rearrangement of 1‐furylethanol with choline acetate IL. The results show the wide potential of choline oxidase for hydrogen peroxide‐driven biocatalysis with both aqueous and micellar choline ionic liquid solutions.

Lyotropic Aqueous 2-Picolinium Ionic Liquid Crystals and Their Shear-Induced Foams.

1-Dodecyl-2-methylpyridinium bromide ([C12-2-Pic][Br]) and 1-hexadecyl-2-methylpyridinium bromide ([C16-2-Pic][Br]) are two ionic liquid crystals presenting thermotropic smectic phases above 80 °C. Aiming to take advantage of the liquid crystalline properties at lower temperatures, lyotropic aqueous systems were prepared from these two organic salts. Both systems were characterized by polarized optical microscopy (POM), X-ray powder diffraction (XRD), and fast field cycling nuclear magnetic resonance (FFC-NMR) relaxometry to assess their texture, phase structure, and molecular dynamics, respectively. The mesomorphic behavior was induced at room temperature. Moreover, the lyotropic [C12-2-Pic][Br]aq revealed a smectic phase with higher separation between layers, different from the lamellar phases found in the thermotropic system (S1 and SA), which is thermally stable up to 50 °C. Furthermore, the surfactant nature of the ionic liquids diluted solutions investigated in this work allowed the formation of foams. It was found that the precursor solutions of the lyotropic dilutions with the longest alkyl chain ([C16-2-Pic][Br]aq) originated liquid foams with more stable structures than those of [C12-2-Pic][Br]aq.

Competitive Effects of Anions on Protein Solvation by Aqueous Ionic Liquids.

The present study utilizes molecular dynamics simulations to examine how different anions compete for protein solvation in aqueous solutions of ionic liquids (ILs). Ubiquitin is used as model protein and studied in IL mixtures sharing the same cation, 1-ethyl-3-methylimidazolium (EMIM), and two different anions in the same solution, from combinations of dicyanamide (DCA), chloride (Cl), nitrate (NO3), and tetrafluoroborate (BF4). Our findings reveal that specific interactions between anions and the protein are paramount in IL solvation, but that combinations of anions are not additive. For example, DCA exhibits a remarkable ability to form hydrogen bonds with the protein, resulting in a significantly stronger preferential binding to the protein than other anions. However, the combination of DCA with NO3, which also forms hydrogen bonds with the protein, results in a smaller preferential solvation of the protein than the combination of DCA with chloride ions, which are weaker binders. Thus, combining anions with varying affinities for the protein surface modulates the overall ion accumulation through nonadditive mechanisms, highlighting the importance of the understanding of competition for specific interaction sites, cooperative binding, bulk-solution affinity, and overall charge compensations, on the overall solvation capacity of the solution. Such knowledge may allow for the design of novel IL-based processes in biotechnology and material science, where fine-tuning protein solvation is crucial for optimizing performance and functionality.

Aqueous Ionic Liquid Mixtures as Minimal Models of Lipid Bilayer Membranes.

We introduce aqueous ionic liquid (IL) mixtures, specifically mixtures of 1-butyl-3-imidazoliumtetrafluoroborate (BMImBF4), with water as a minimal model of lipid bilayer membranes. Imidazolium-based ILs are known to form clustered nanoscale structures in which local inhomogeneities, micellar or lamellar structures, are formed to shield hydrophobic parts of the cation from the polar cosolvent (water). To investigate these nanostructures, dynamic light scattering (DLS) on samples with different mixing ratios of water and BMImBF4 was performed. At mixing ratios of 50% and 45% (v/v), small and homogeneous nanostructures can indeed be detected. To test whether, in particular, these stable nanostructures in aqueous mixtures may mimic the effects of phospholipid bilayer membranes, we further investigated their interaction with myelin basic protein (MBP), a peripheral, intrinsically disordered membrane protein of the myelin sheath. Using dynamic light scattering (DLS), continuous wave (CW) and pulse electron paramagnetic resonance (EPR), and small-angle X-ray scattering (SAXS) on recombinantly produced, "healthy" charge variants rmC1WT and double cysteine variant C1S17CH85C, we find that the size and the shape of the determined nanostructures in an optimum mixture offer model membranes in which the protein exhibits native behavior. SAXS measurements illuminate the size and shape of the nanostructures and indicate IL-rich "beads" clipped together by functional MBP, one of the in vivo roles of the protein in the myelin sheath. All the gathered data combined indicate that the 50% and 45% aqueous IL mixtures can be described as offering minimal models of a lipid mono- or bilayer that allow native processing and potential study of at least peripheral membrane proteins like MBP.

Ab initio molecular dynamics study of hydroxyl positioning in butanediol and its impact on deep eutectic solvent structure

Electrolytes play a crucial role in enhancing the performance of energy storage devices, including batteries and supercapacitors. However, traditional electrolytes, such as aqueous solutions, organic solvents, and ionic liquids, exhibit inherent limitations and challenges. Deep eutectic solvents have recently emerged as promising alternatives due to their environmentally friendly nature and favorable properties. Despite their widespread applications in various domains, their potential as electrolytes remains relatively underexplored. This study investigates three distinct types of deep eutectic solvents derived from different isomers of butanediols combined with choline chloride. Ab initio molecular dynamics simulations are employed to analyze the microstructure of these deep eutectic solvents, focusing on non-covalent electrostatic interactions, hydrogen bonding patterns, and vibrational spectra. The results reveal significant differences in the structural configuration of hydrogen bond acceptors and hydrogen bond donors and their interactions within the deep eutectic solvents. Specifically, the positioning of functional groups in hydrogen bond donors significantly impacts the hydrogen bonding network and the interaction with monoatomic ions. Moreover, the vibrational spectra analysis highlights the existence of hydrogen bonds involving stretching modes of the OH group, as evidenced by redshift deviations. Overall, this study provides valuable insights into the unique features of deep eutectic solvents as potential electrolytes for energy storage applications. The comprehensive analysis of their microstructure and vibrational properties enhances our understanding of deep eutectic solvent utilization and opens avenues for further research in sustainable energy storage.

Standard partial molar volumes of single aqueous ions composing ionic liquids. Measurement and evaluation of temperature dependent values. Parsing and LSER correlation with molecular descriptors based on DFT/COSMO approach

The densities of highly dilute aqueous solutions (m < 0.2 mol·kg−1) of 50 common ionic liquids (ILs) or related salts were accurately measured at seven equidistant temperatures in the range of (288.15 to 318.15) K and ambient pressure. The examined set of ILs/salts composed of 31 ions was judiciously selected to cover wide ranges of ion sizes and chemical structures and allow reliable evaluation of ionic contributions. The data were duly analyzed to infer related thermodynamic properties and information on the behavior of these systems on a molecular level. Appropriate means of mathematical statistics were used to estimate data uncertainties, assign weights to data correlations, and judge the significance of the results obtained. The standard partial molar volumes V¯∞ of the ILs/salts at infinite dilution were evaluated through fitting the concentration dependence of respective apparent molar volumes to Redlich-Meyer equation and their temperature dependence was correlated to quadratic polynomial. The data presented were compared whenever possible with those available in the literature; good agreement was often found, although some data from the literature were also considerably dispersed or in error. Standard partial molar volumes of ILs/salts obeying ionic additivity were split by least-squares optimization into temperature-dependent single-ion values based on the Conway-Millero extrathermodynamic assumption. The ionic additivity of BV parameter was also identified. Its magnitude for anions is typically greater than that for cations, supporting the fact that an anion dominates the volumetric behavior of aqueous ILs. As the BV,anion and the second temperature derivative ∂2V¯anion∞/∂T2 were found to correlate, the two solute’s water structure making/breaking ability indicators appear to speak consistently. Enhanced values of standard partial molar expansion were observed for both strongly kosmotropic and chaotropic anions and a plausible explanation of this phenomenon was suggested. To correlate and analyze the effect of ionic structure on V¯ion,298∞, Linear Solvation Energy Relationship (LSER) methodology with the recently proposed four quantum chemistry computed descriptors based on DFT/COSMO approach was employed providing excellent fit (SD = 2.48 cm3·mol−1, R2 = 0.9996).

Exploration of diverse interactions of nonionic poly(vinylpyrrolidone) (PVP) and anionic sodium carboxymethylcellulose (NaCMC) polymers in aqueous imidazolium-based surface active ionic liquid solutions

The binding interactions in complex formation between surface active ionic liquids (SAILs) and polymers (nonionic or anionic) are gaining attention because of their potential applications in novel materials. Therefore, the use of a variety of measurements is required for a better understanding of the interactions involved in polymer/SAIL formation. Here, we have investigated the interactions of nonionic poly(vinylpyrrolidone) (PVP) and anionic sodium carboxymethylcellulose (NaCMC) polymers with SAIL 1-tetradecyl-3-methylimidazolium chloride [C14mim][Cl] in aqueous solution using different measurements such as conductivity, surface tension, fluorescence spectroscopy, dynamic light scattering (DLS) and rheometric measurements. The surface tension, conductivity and fluorescence profiles for SAIL-NaCMC systems provide distinct breakpoints that correspond to four different aggregation states: the concentration at which SAIL monomers begin to attach to the polymer chain (C1), the critical aggregation concentration C2 (cac), the saturation concentration (CS) and the critical micelle concentration (cmc). In the case of SAIL-PVP systems, the surface tension and fluorescence profiles confer three transition states: C2 (cac), CS and cmc and only two transition states have been observed in conductivity curves. The cooperative binding of SAIL to the NaCMC/PVP chain at the solution interface was analyzed by calculating various thermodynamic and interfacial parameters. Strong complexation was observed between NaCMC-SAIL molecules compared to PVP-SAIL systems at the air-solution surface. This is due to the non-ionic character of the PVP chain, which shows weak interactions with SAIL in comparison to NaCMC. Furthermore, DLS and fluorescence measurements were used to investigate the interactions between SAIL and polymers.

Studies on wetting behaviour of pure and aqueous protic ionic liquids (PIL) solutions on different surfaces: ILphobicity to ILphilicity

In this study, the wetting behaviour of pure protic ionic liquids (PILs) and their mixture with water was studied at ambient conditions. Ethanolammonium acetate [EAAc], ethanolammonium butyrate [EABu], and ethanolammonium hexanoate [EAHx] were used as PILs for the wetting studies on various surfaces. The contact angle and wetting area of pure and mixed PIL solutions were determined on superhydrophobic, hydrophilic, and total wetting surfaces. Smaller alkyl chain PIL, ethanolammonium acetate (EAAc) displayed the highest contact angle (CA) of 141° on superhydrophobic surfaces. On hydrophilic polycarbonate (PC), shorter anionic chain PILs demonstrated CA < 90°, showing the ILphilic behaviour, and the variation of CA was PIL anionic chain length dependent. Total wetting glass exhibited the lowest CA for [EAAc], which increased with the PIL anionic chain. A binary mixture of PIL with water demonstrated unique wetting behaviour on the total wetting surface. The aqueous drops of EAHx exhibited a dynamic contact line on the glass surface, showing the greatest expansion in wetting area compared to drops of aqueous EAAc or aqueous EABu. This occurrence could be ascribed to the substantial decrease in water surface tension induced by the hydrophobic hexanoate anion, potentially leading to improved spreading characteristics.

Exploration of Solvation Consequences of Nicotinic Acid (Vitamin B3) Prevailing in Two Significant Aqueous Ionic Liquid Solutions by Physicochemical and Computational Studies

Exploration of Solvation Consequences of Nicotinic Acid (Vitamin B3) Prevailing in Two Significant Aqueous Ionic Liquid Solutions by Physicochemical and Computational Studies

Toward Greater DNA Stability by Leveraging the Proton-Donating Ability of Protic Ionic Liquids.

Deoxyribonucleic acid (DNA) stability is a prerequisite in many applications, ranging from DNA-based vaccines and data storage to gene therapy. However, the strategies to enhance DNA stability are limited, and the underlying mechanisms are poorly understood. Ionic liquids (ILs), molten salts of organic cations and organic/inorganic anions, are showing tremendous prospects in myriads of applications. With a judicious choice of constituent ions, the protic nature of ILs can be tuned. In this work, we investigate the relative stability of full-length genomic DNA in aqueous IL solutions of increasing protic nature. Our experimental measurements show that the protic ionic liquids (PILs) enhance the DNA melting temperature significantly while unaltering its native B-conformation. Molecular dynamics simulations and quantum mechanical calculation results suggest that the intramolecular Watson-Crick H-bonding in DNA remains unaffected and, in addition, the PILs induce stronger H-bonding networks in solution through their ability to make multiple intermolecular H-bonds with the nucleobases and among its constituent ions, thus aiding greater DNA stability. The detailed understanding obtained from this study could bring about the much-awaited breakthrough in improved DNA stability for its sustained use in the aforesaid applications!

Degradation of imidazolium-based ionic liquids by UV photolysis and pulsed corona discharge: The effect of persulfates addition

Ionic liquids (ILs) are salts with exceptional properties important for future development, although potentially hazardous for humans and aquatic life due to their high aqueous solubility and toxicity. Biodegradation of ILs depends on the anion nature and cation structure: many ILs are not readily degraded during conventional wastewater treatment, thus requiring alternative cost-effective and energy-efficient solutions. In this research, the degradation of aqueous imidazolium-based ILs by pulsed corona discharge (PCD) and UV photolysis combined with persulfates was studied, using peroxymonosulfate (PMS) and peroxydisulfate (PDS) as extrinsic oxidants. 1-Ethyl-3-methylimidazolium chloride ([Emim][Cl]), 1-methyl-3-octylimidazolium chloride ([Omim][Cl]), and 1-ethyl-3-methylimidazolium bromide ([Emim][Br]) were chosen as imidazolium-based ILs with different alkyl chain lengths and anions in oxidation experiments under variable operation factors - pH, concentrations of persulfates, pulse repetition frequency in PCD. Pulsed corona discharge has previously shown high energy efficiency in the degradation of micropollutants but has not yet been applied to ionic liquids. The experimental results showed the ability of PCD, PCD/oxidant and UV/oxidant combinations to completely degrade the ILs with the degradation rates in descending order [Emim][Cl] > [Omim][Cl] > [Emim][Br], indicating an impact of both the alkyl chain length and the type of anion on the oxidation rate. The strong activation of persulfates was observed in UV/oxidant combinations, whereas PCD demonstrated the effect of persulfates addition between slight acceleration and moderate deceleration of oxidation dependent on the concentration of extrinsic oxidants. The addition of the sulfate radicals’ scavenger, however, showed the presence of those in all combinations indicating a certain replacement of PCD-generated reactive oxygen species with secondary reactants formed from persulfates. The unassisted PCD and UV/PDS combination demonstrated similar energy efficiencies of about 54 and 26 mmol kWh−1 for [Emim][Cl] and [Emim][Br] degradation, respectively, while for [Omim][Cl] the UV/PDS combination showed energy efficiency 1.42 times higher than unassisted PCD.

Efficient Extraction of Sericin Protein from Mulberry and Non‐Mulberry Silk Fibers: Utilizing Aqueous Ionic Liquid Solutions as Green Solvents

AbstractProtein extraction from silk is a unique area of research and the foremost need is the efficient extraction of the silk proteins namely fibroin and sericin from the silk fibres, which is conventionally done using chemicals. In this work, we show that Ionic liquids (ILs) can be employed as a green and alternative method for degumming sericin from both mulberry (B. mori) and non‐mulberry (A. assamensis and P. ricini) silk. Six different ILs with varying tail lengths were studied for their degumming efficiencies. The interaction between silk proteins and IL ions involves a complex ionic disruption of hydrogen bonds, non‐polar interactions, and electrostatic effects. We have found that 1‐Butyl‐3‐methylimidazolium chloride (BMIM.Cl), 1‐ethyl‐3‐methylimidazolium tetrafluoroborate (EMIM.BF4) and Tetraethylammonium bromide (TEAB) bring in higher weight loss % in silk fibres compared to other ILs, indicating that it can be used in better sericin removal without significant damage to the silk fibre. TEAB emerged as a potential candidate for sericin extraction due to its promotion of protein destabilization. Additionally, no drastic changes in the structure of the extracted silk protein sericin were observed, as evident from the FTIR spectra and SEM images. This work highlights for the first time, the use of ILs for extraction of non‐mulberry silk sericin and also proves that ILs can be a potential green solvent for sericin extraction.

Origin of ργ/T scaling of primary and secondary conductivity relaxation times in mixture of water with protic ionic liquid.

Murali et al. [J. Phys. Chem. Lett., 2024, 15, 3376-3382] made ambient and high pressure dielectric measurements of a supercooled aqueous mixture of an acidic ionic liquid to find the presence of the primary (σ) conductivity relaxation together with the secondary (ν) conductivity relaxation originating from the water clusters confined by the cations and anions with relaxation times τσ and τν respectively. From the isothermal and isobaric conductivity relaxation data found on varying thermodynamic conditions (i.e. T and P) at constant τσ are the invariance of (i) the frequency dispersion or the Kohlrausch function exponent (1 - n) of the primary conductivity relaxation, and (ii) the ratio of the primary and secondary conductivity times, τσ/τν. This co-invariance of τσ, τν, and (1 - n) at constant τσ was observed before in non-aqueous ionic liquids, but it is found for the first time in aqueous ionic liquids. The new data together with PVT measurements enable Murali et al. to show additionally that both τσ and τν are functions of ργ/T with a single exponent γ = 0.58. The Coupling model is the only theory predicting the co-invariance of τσ, τν, and (1 - n) as well as the ργ/T scaling of both τσ and τν. It is applied herein to address and explain the data of the ionic liquid-water mixture.

Structure-dependent CO2 reduction on molybdenite (MoS2) electrocatalysts.

Scanning electrochemical cell microscopy (SECCM) is employed to directly identify the structure-dependent electrochemical CO2 reduction reaction (eCO2RR) activity of molybdenite (MoS2) electrocatalysts in an aqueous imidazolium-based aprotic ionic liquid electrolyte. Nanoscale defects, where the edge plane (EP) is exposed, are directly targeted, revealing heightened overall activity (eCO2RR + the competing hydrogen evolution reaction, HER) over the relatively inactive basal plane (BP). In addition, certain types of defects (e.g., step edges) only exhibit heightened activity under a CO2 atmosphere (i.e., compared to N2), indirectly confirming higher selectivity at these surface sites. Overall, this work will guide the bottom-up design of earth-abundant electrocatalysts for use in large-scale CO2 electrolysis.

Ion-combination specific effects driving the enzymatic activity of halophilic alcohol dehydrogenase 2 from Haloferax volcanii in aqueous ionic liquid solvent mixtures.

Biocatalysis in ionic liquids enables novel routes for bioprocessing. Enzymes derived from extremophiles promise greater stability and activity under ionic liquid (IL) influence. Here, we probe the enzyme alcohol dehydrogenase 2 from the halophilic archaeon Haloferax volcanii in thirteen different ion combinations for relative activity and analyse the results against molecular dynamics (MD) simulations of the same IL systems. We probe the ionic liquid property space based on ion polarizability and molecular electrostatic potential. Using the radial distribution functions, survival probabilities and spatial distribution functions of ions, we show that cooperative ion-ion interactions determine ion-protein interactions, and specifically, strong ion-ion interactions equate to higher enzymatic activity if neither of the ions interact strongly with the protein surface. We further demonstrate a tendency for cations interacting with the protein surface to be least detrimental to enzymatic activity if they show a low polarizability when combined with small hydrophilic anions. We also find that the IL ion influence is not mitigated by the surplus of negatively charged residues of the halophilic enzyme. This is shown by free energy landscape analysis in root mean square deviation and distance variation plots of active site gating residues (Trp43 and His273) demonstrating no protection of specific structural elements relevant to preserving enzymatic activity. On the other hand, we observe a general effect across all IL systems that a tight binding of water at acidic residues is preferentially interrupted at these residues through the increased presence of potassium ions. Overall, this study demonstrates a co-ion interaction dependent influence on allosteric surface residues controlling the active/inactive conformation of halophilic alcohol dehydrogenase 2 and the necessity to engineer ionic liquid systems for enzymes that rely on the integrity of functional surface residues regardless of their halophilicity or thermophilicity for use in bioprocessing.

Tuning the low-temperature phase behavior of aqueous ionic liquids.

Water's anomalous behavior is often explained using a two-liquid model, where two types of water, high-density liquid (HDL) and low-density liquid (LDL), can be separated via a liquid-liquid phase transition (LLPT) at low temperature. Mixtures of water and the ionic liquid hydrazinium trifluoroacetate were suggested to also show an LLPT but with the advantage that there is no rapid ice crystallization hampering its observation. It remains controversial whether these solutions exhibit an LLPT or are instead associated with complex phase separation phenomena. We here show detailed low-temperature calorimetry and diffraction experiments on aqueous solutions containing hydrazinium trifluoroacetate and other similar ionic liquids, all at a solute mole fraction of x = 0.175. Hydrazinium trifluoroacetate, ammonium trifluoroacetate, ethylammonium trifluoroacetate and hydrazinium pentafluoropropionate all boast exothermic transitions unrelated to crystallization as well as remarkable structural changes upon cooling into the glassy state. We propose a model inspired by micelle formation and decomposition in surfactant solutions, which is complemented by MD simulations and allows rationalizing the rich phase behavior of our mixtures during cooling. The fundamental aspect of the model is the hydrophobic nature of fluorinated anions that enables aggregation, which is reversed upon cooling and culminates in the remarkable exothermic first-order transition observed at low temperature. That is, we assign the first-order transition not to an LLPT but to phase-separations similar to the ones when falling below the Krafft temperature. All other solutions merely show simple vitrification behavior. Still, they exhibit distinct differences in liquid fragility, which is decreased continuously with decreasing hydrophobicity of the anions. This might enable the systematic tuning of ionic liquids with the goal of designing aqueous solutions of specific fragility.

Interionic bonding in aqueous phosphonium ionic liquid solutions exhibiting LCST behavior with high phase separation temperatures

Phosphonium-derived ionic liquids have emerged as a powerful class of thermoresponsive materials with sought after Lower Critical Solution Temperature (LCST) phase separation with applications across a broad range of fields. Herein, we report the spectroscopic examination of phosphonium salts bearing the general structure [X][P444n] wherein systematic structural variations were designed to gain a fundamental understanding behind the impact of alkyl chain length, anion size, and effective nuclear charge on their temperature-dependent phase separation behavior. Using variable temperature 1H, 31P, and 19F NMR, the bonding changes which drive LCST phase separation for the assembled thermoresponsive ILs were elucidated. For the first time, spectroscopic evidence revealed a delicate balance between the interdependence of alkyl chain length and anion size on phase separation that formed the basis of new LCST design principles.

The role of hydrogen bonding in solubilizing camptothecin in hydrophilic and hydrophobic ionic liquids

Utilizing ionic liquid (IL)-water mixtures as selective extraction solvents for raw materials from natural sources represents an efficacious approach; however, elucidating the underlying mechanisms inherent in various types of IL-aqueous solutions continues to pose a significant challenge. In this study, molecular dynamics simulations and density functional theory calculations are employed to illuminate the influence of the functional anion within ILs and the water content on the solvation mechanism and phase separation phenomena observed during the extraction of camptothecin (CPT) using aqueous IL solutions. The simulation results show that the anions in ILs preferentially dissolve CPT through hydrogen bonding at low water concentrations. As the water concentration increases, the hydrophobic IL binds more tightly to CPT, enabling the water to self-aggregate. The anions in hydrophilic IL form hydrogen bonds with water instead, further enhancing the dissolution of CPT. This work reveals the mechanism of phase separation and solvation of different types of IL aqueous solutions, which is helpful in developing new drug extraction and purification technologies.