Hydrogen-bonding interactions between [BMIM][BF4] and acetonitrile

N-octylpyridine hydrogen sulphate ionic liquid for multifunctional fluorescent response in different solvents

Ionic liquids (ILs) have attracted considerable interest in the last two decades owing to their unique fluorescent properties. Herein, N-octylpyridine hydrogen sulphate ([OP]HSO4) was synthesised and characterised using 1H NMR and infrared spectroscopies. In addition, the fluorescence spectra of [OP]HSO4 in water, methanol, ethanol and acetonitrile were studied. In a single solvent, as the concentration of the solvent (methanol, ethanol or acetonitrile) increases, the fluorescence intensity of the IL first increases and then decreases. A similar trend was observed in their mixed solvents with water. Moreover, the fluorescence intensity of [OP]HSO4 decreases with increasing temperature. A fluorescence intensity reduction of only 4.46% for [OP]HSO4 after continuous scanning for 40 cycles under the maximum excitation state was analysed. The lack of photobleaching observed in [OP]HSO4 indicates its good photobleaching resistance.

In Situ Species Analysis of a Lithium-Ion Battery Electrolyte Containing LiTFSI and Propylene Carbonate

In this study, we analyzed the species in a model electrolyte consisting of a lithium salt, lithium bis(trifluoromethane sulfone)imide (LiTFSI), and a widely used neutral solvent propylene carbonate (PC) with excess infrared (IR) spectroscopy, ab initio molecular dynamics simulations (AIMD), and quantum chemical calculations. Complexing species including the charged ones [Li+(PC)4, TFSI-, TFSI-(PC), TFSI-(PC)2, and Li(TFSI)2-] are identified in the electrolyte. Quantum chemical calculations show strong Li+···O(PC) interaction, which suggests that Li+ would transport in the mode of solvation-carriage. However, the interaction energy of each hydrogen bond in TFSI-(PC) is very weak, suggesting that TFSI- would transport in hopping mode. In addition, the concentration dependences of the relative population of the species were also derived, providing a scenario for the dissolving process of the salt in PC. These in-depth studies provide physical insights into the structural and interactive properties of the electrolyte of lithium-ion batteries.

Effect of Mixture Composition on the Photophysics of Indoline Dyes in Imidazolium Ionic Liquid-Molecular Solvent Mixtures: A Femtosecond Transient Absorption Study

We conducted a study on the photophysics of three indoline dyes, D102, D149, and D205, in binary mixtures of ionic liquids (IL) and polar aprotic molecular solvents (MS). Specifically, we examined the behavior of these dyes in IL-MS mixtures containing four different imidazolium-based ILs and three different polar aprotic MSs. Our investigation involved several techniques, including stationary absorption and emission measurements, as well as femtosecond transient absorption (TA) spectroscopy. Through our analysis, we discovered a peculiar behavior of several photophysical properties at low IL mole fractions (0 < XIL < 0.2). Indeed, in this range of mixture composition, the absorption maximum wavelength decreases noticeably, while the emission maximum wavelength and the Stokes shift, expressed in wavenumbers, reach a maximum. while a minimum occurs in the relative quantum yield and the excited state lifetime. These results indicate that the solvation of dye undergoes a large change in this range of mixture composition. We found that, at high ionic liquid content, the excited relaxation times are correlated with the high viscosity, while at low content, it is the polarity of the solvent that influences the behavior of the excited relaxation times. At a mixture composition of around 0.10, the behavior of the photophysical properties of the studied IL-MS mixtures indicates a crossover between situations where the solvation is dominated by that of ions and that dominated by the solvent.

New Local Composition Model for Correlating of the Molar Conductivity of Ionic Liquid-Solvent Systems over the Whole Concentration Range

Considering that traditional electrolyte models are limited to use in the solvent-rich region, the development of new models to describe the molar conductivity (Λm) over the whole concentration range of ionic liquid (IL)-solvent systems is a meaningful study. Based on the idea of local composition and the law of independent ion migration, a new model is proposed in this study and used to successfully correlate the relationship between Λm and composition over the whole concentration range for 18 IL-solvent systems with satisfactory fitting accuracy. Meanwhile, the electrical conductivity (κ) of the systems is estimated using the calculated Λm. Moreover, the strength of anion-cation, anion-solvent, and cation-solvent interactions in the systems is explored by the obtained energy parameters, and the effect of the solvent on the interactions is investigated. The proposed model provides a new method to accurately describe the conductivity property of IL-solvent systems over the whole concentration range.

Spectroscopic and Computational Study of ZnCl2-Methanol Low-Melting-Temperature Mixtures

Alcoholic electrolyte mixtures have wide applications in industries. In this study, a series of mixtures composed of ZnCl2 and methanol (MeOH) with ZnCl2 mol % from 6.7 to 25 were prepared, and their spectral, structural, and thermodynamic properties were studied using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), and density functional theory (DFT) calculations. The DFT-assisted analysis of excess spectra, supported by 2D-correlation spectroscopy, led to the identification of the major constituents of ZnCl2-MeOH mixtures, namely, MeOH monomer, MeOH dimer, and ZnCl2-3MeOH complex, produced after dissociation of MeOH trimer which represents the bulk methanol. The Hirshfeld charge analysis showed that in the competition between the O-H···Cl hydrogen bond (H-bond) and Zn ← O coordination bond to transfer charge in ZnCl2-MeOH complexes, the latter always dominates, making MeOH positively charged. The phase diagram of the binary system showed the presence of V-shaped glass transition temperatures (Tg), characteristic of low-melting mixture solvents (LoMMSs). The present study provides insights into the microscopic properties of the system and sheds light on the understanding of the general principles to prepare deep-eutectic solvents (DESs) or LoMMSs using inorganic salts and alcoholic compounds.

Multifunctional molecularly imprinted nanozymes with improved enrichment and specificity for organic and inorganic trace compounds

Although nanozymes exhibit properties superior to those of natural enzymes and conventional engineered enzymes, the development of highly specific nanozymes remains a challenge. New yolk-shell Fe3O4 molecularly imprinted (MIP@void@Fe3O4) nanozymes with peroxidase-like activity were developed by modelling the substrate channels of natural enzymes through molecular imprinting techniques and interfacial affinity modifications in this study. To establish a platform technology for the adsorption and determination of inorganic and organic contaminants, lead ion (Pb2+) and diazinon (DIZ), respectively, were selected as imprinting templates, and a hollow mesoporous shell was synthesized. The as-prepared MIP@void@Fe3O4 nanozymes, characterized using TEM, HRTEM, SEM, FT-IR, TGA, VSM and XPS, not only affirmed the successful fabrication of a magnetic nanoparticle with a unique hollow core-shell structure but also facilitated an exploration of the interfacial bonding mechanisms between Fe3O4 and other shell layers. The enrichment of the MIP@void@Fe3O4 nanozymes due to imprinting was approximately 5 times higher than the local substrate concentration and contributed to the increased activity. Based on selective and competitive recognition experiments, the synthesized nanozymes could selectively recognize organic and inorganic targets with the lowest detection limits (LOD) of 6.6 × 10-9 ppm for Pb2+ and 5.13 × 10-11 M for DIZ. Therefore, the proposed biosensor is expected to be a potent tool for trace pollutant detection, which provides a rational design for more advanced and subtle methods to bridge the activity gap between natural enzymes and nanozymes.

Electrolyte design combining fluoro- with cyano-substitution solvents for anode-free Li metal batteries

Fluoro-substitution solvents have achieved great success in electrolyte engineering for high-energy lithium metal batteries, which, however, is beset by low solvating power, thermal and chemical instability, and possible battery swelling. Instead, we herein introduce cyanogen as the electron-withdrawing group to enhance the oxidative stability of ether solvents, in which cyanogen and ether oxygen form the chelating structure with Li+ not notably undermining the solvating power. Cyano-group strongly bonds with transition metals (TMs) of NCM811 cathode to attenuate the catalytic reactivity of TMs toward bulk electrolytes. Besides, a stable and uniform cathode-electrolyte interphase (CEI) inhibits the violent oxidation decomposition of electrolytes and guarantees the structural integrity of the NCM811 cathode. Also, a N-containing and LiF-rich solid-electrolyte interphase (SEI) in our electrolyte facilitates fast Li+ migration and dense Li deposition. Accordingly, our electrolyte enables a stable cycle of Li metal anode with Coulombic efficiency of 98.4% within 100 cycles. 81.8% capacity of 4.3 V NCM811 cathode remains after 200 cycles. Anode-free pouch cells with a capacity of 125 mAh maintain 76% capacity after 100 cycles, corresponding to an energy density of 397.5 Wh kg-1.

The azeotropy eliminating mechanism of ethyl acetate-acetonitrile system via ionic liquid entrainer: A combination of FTIR and DFT study

Ionic liquids (ILs) are good candidates for azeotropy separation. Knowledge of the microstructure properties of azeotrope - IL mixtures is important because they could reveal the molecular intrinsic cause of the elimination of azeotropy and represent the basis for the practical process. In this work, the microstructures of ethyl acetate-acetonitrile azeotrope mixtures and a representative IL, 1‑butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N], which could eliminate the azeotropy of the ethyl acetate-acetonitrile system, were studied by Fourier transform infrared spectroscopy with the assistance of quantum chemical calculations and excess spectra. The C≡N stretching vibrational region of acetonitrile was closely examined. The interaction complexes of ethyl acetate-acetonitrile and ion cluster/ion pair/ion - acetonitrile were identified. Weak strength hydrogen-bonds with electrostatically dominant and closed-shell interaction properties were found in these complexes. The interactions between [BMIM][Tf2N] and acetonitrile were stronger than those between ethyl acetate and acetonitrile, which caused the addition of IL to easily destroy the ethyl acetate-acetonitrile interaction complex. The interactions between [BMIM][Tf2N] and acetonitrile were stronger than those between [BMIM][Tf2N] and ethyl acetate, which would influence the relative volatility of ethyl acetate and acetonitrile in the azeotrope system. When x(IL) was larger than 0.027, all the interaction complexes between acetonitrile and ethyl acetate were completely broken apart, and the azeotrope was eliminated.

Chemical Scissors Tailored Nano-Tellurium with High-Entropy Morphology for Efficient Foam-Hydrogel-Based Solar Photothermal Evaporators

The development of tellurium (Te)-based semiconductor nanomaterials for efficient light-to-heat conversion may offer an effective means of harvesting sunlight to address global energy concerns. However, the nanosized Te (nano-Te) materials reported to date suffer from a series of drawbacks, including limited light absorption and a lack of surface structures. Herein, we report the preparation of nano-Te by electrochemical exfoliation using an electrolyzable room-temperature ionic liquid. Anions, cations, and their corresponding electrolytic products acting as chemical scissors can precisely intercalate and functionalize bulk Te. The resulting nano-Te has high morphological entropy, rich surface functional groups, and broad light absorption. We also constructed foam hydrogels based on poly (vinyl alcohol)/nano-Te, which achieved an evaporation rate and energy efficiency of 4.11 kg m-2 h-1 and 128%, respectively, under 1 sun irradiation. Furthermore, the evaporation rate was maintained in the range 2.5-3.0 kg m-2 h-1 outdoors under 0.5-1.0 sun, providing highly efficient evaporation under low light conditions.

Realizing Nanolime Aqueous Dispersion via Ionic Liquid Surface Modification to Consolidate Stone Relics

After decades of research in the conservation of cultural heritage, nanolime (NL) has emerged as a potential alternative inorganic material to the frequently used organic materials. However, its poor kinetic stability in water has been a major challenge that restricted its penetration depth through cultural relics and resulted in unsatisfactory conservation outcomes. Here, for the first time, we realize NL water dispersion by modification of ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate) via a sample aqueous solution deposit method. Our findings indicate that the cation of the ionic liquid (IL) binds strongly to the surface of NL particles (IL-NL) by forming hydrogen bonds with Ca(OH)₂ facets. The absorption of IL causes an unexpected significant alteration in the morphology of NL particles and results in a drastic reduction in NL's size. More importantly, this absorption endows NL excellent kinetic stability dispersed into water and implements NL water dispersion, which makes a breakthrough in terms of extreme poor kinetic stability of as-synthesized NL and commercial NL in water. The mechanism driving IL-NL water dispersion is explained by Stern theory. In the context of consolidating weathered stone, the presence of IL may delay carbonation of NL but the penetration depth of IL-NL through stone samples is three times deeper than that of as-synthesized and commercial NLs. Additionally, the consolidation strength of IL-NL is similar to that of as-synthesized NL and commercial NL. Moreover, IL-NL has no significant impact on the permeability, pore size, and microstructure of consolidated stone relics. Our research contributes to the field of NL-related materials and will enhance the dissemination and utilization of NL-based materials in the preservation of water-insensitive cultural heritage.

Long-Lived Weak Ion Pairs in Ionic Liquids: An Insight from All-Atom Molecular Dynamics Simulations

The microstructure and local dynamics of ions in room-temperature ionic liquids (RTILs) have drawn a lot of attention due to their extensive potential applications in numerous fields. It is well-known that the widely used definitions of ion pairs (IPs) cannot reflect the full picture of RTILs. In this study, we find a universal residence time (τ_MR), which is regardless of the number of counterions in the first solvation shell in RTILs. Inspired by this, we propose a weak IP (WIP) model from a spatiotemporal perspective and demonstrate that the WIPs are long-lived and that their lifetimes obey a log-normal distribution, which is different from the literature. In addition, the electrostatic interactions are the main factors in the formation of WIPs, and the reorientations of ions are vital to the ruptures of WIPs. This research provides a new perspective for understanding the microstructural and dynamical properties of RTILs.

A New Inert Natural Deep Eutectic Solvent (NADES) as a Reaction Medium for Food-Grade Maillard-Type Model Reactions

Sustainability, low toxicity, and high solute potential are the fundamental reasons for focusing green chemistry on natural deep eutectic solvents (NADES). The application of NADES ranges from organic chemistry to the agricultural sector and the food industry. In the food industry, the desired food quality can be achieved by the extraction of small molecules, macromolecules, and even heavy metals. The compound yield in Maillard-type model reactions can also be increased using NADES. To extend the so-called "kitchen-type chemistry" field, an inert, food-grade NADES system based on sucrose/D-sorbitol was developed, characterized, and examined for its ability as a reaction medium by evaluating its temperature and pH stability. Reaction boundary conditions were determined at 100 °C for three hours with a pH range of 3.7-9.0. As proof of principle, two Maillard-type model reactions were implemented to generate the taste-modulating compounds N²-(1-carboxyethyl)guanosine 5'-monophosphate) (161.8 µmol/mmol) and N²-(furfuryl thiomethyl)guanosine 5'-monophosphate (95.7 µmol/g). Since the yields of both compounds are higher than their respective taste-modulating thresholds, the newly developed NADES is well-suited for these types of "kitchen-type chemistry" and, therefore, a potential solvent candidate for a wide range of applications in the food industry.

Study on the hydrophobicity of [Bmim]2[CuCl4] by two-dimensional correlation spectroscopy

By dissolving copper chloride in [Bmim]Cl (1-butyl-3-methylimidazolium chloride), chloride ions can coordinate with copper ions and form [CuCl₄]^2-, thereby inducing the solution being hydrophobic. In the present work, hydrogen bonds between [Bmim]⁺ and anions are analyzed and discussed by two-dimensional correlation spectroscopy. Time-dependent attenuated total reflection spectroscopy (ATR-FTIR) is introduced to monitor the hygroscopic process of [Bmim]₂[CuCl₄] and [Bmim]Cl in situ. Hygroscopic capacity and rate of [Bmim]₂[CuCl₄] shrink compared with [Bmim]Cl. The change of water molecular clusters has been studied by second-derivative spectra in the hygroscopic process. The behaviors of water molecular in the two ionic liquids are also distinctive.

Effect of Oil on Cellulose Dissolution in the Ionic Liquid 1-Butyl-3-methyl Imidazolium Acetate

While ionic liquids (ILs) are well known to be excellent solvents for cellulose, the exact mechanism of dissolution has been a much disputed topic in recent years and is still not completely clear. In this work, we add to the current understanding and highlight the importance of hydrophobic interactions, through studying cellulose dissolution in mixtures of 1-butyl-3-methyl imidazolium acetate (BmimAc) and medium-chain triglyceride (MCT) oil. We demonstrate that the order in which constituents are mixed together plays a key role, through nuclear magnetic resonance (NMR) spectroscopic analysis. When small quantities of MCT oil (0.25-1 wt %) were introduced to BmimAc before cellulose, the effect on BmimAc chemical shift values was much more significant compared to when the cellulose was dissolved first, followed by oil addition. Rheological analysis also showed small differences in the viscosities of oil-cellulose-BmimAc solutions, depending on the order the constituents were added. On the other hand, no such order effect on the NMR results was observed when cellulose was replaced with cellobiose, suggesting that this observation is unique to the macromolecule. We propose that a cellulose-oil interaction develops but only when the cellulose structure has a sufficient degree of order and not when the cellulose is molecularly dispersed, since the hydrophobic cellulose plane is no longer intact. In all cases, cellulose-BmimAc-oil solutions were stable for at least 4 months. To our knowledge, this is the first work that investigates the effect of oil addition on the dissolving capacity of BmimAc and highlights the need for further re-evaluation of accepted mechanisms for cellulose dissolution in ILs.

Solvents and Stabilization in Ionic Liquid Films

We report the interfacial structures and chemical environments of ionic liquid films as a function of dilution with molecular solvents and over a range of film thicknesses (a few micrometers). Data from spectroscopic ellipsometry and infrared spectroscopy measurements show differences between films comprised of neat ionic liquids, as well as films comprised of ionic liquids diluted with two molecular solvents (water and acetonitrile). While the water-diluted IL films follow thickness trends predicted by the Landau-Levich model, neat IL and IL/MeCN films deviate significantly from predicted behaviors. Specifically, these film thicknesses are far greater than the predicted values, suggesting enhanced intermolecular interactions or other non-Newtonian behaviors not captured by the theory. We correlate film thicknesses with trends in the infrared intensity profiles across film thicknesses and IL-solvent dilution conditions and interpret the changes from expected behaviors as varying amounts of the film volume existing in isotropic (bulk) vs anisotropic (interfacial) states. The hydrogen bonding network of water-diluted ionic liquids is implicated in the agreement of this system with the Landau-Levich model's thickness predictions.

Hydrogen bonds-triggered differential extraction efficiencies for bifenthrin by three polymeric ionic liquids with varying anions based on FT-IR spectroscopy

Herein, we fabricated three imidazolium-based polymeric ionic liquids (PILs) with different anions (P[VEIM]BF4, P[VEIM]PF6 and P[VEIM]Br), and analyzed their differential extraction efficiencies for bifenthrin through H-bonding induced effects. Three PILs all presented an irregular block structure with rough surface and lower specific-surface area (SSA, 11.2-18.7 m2 g-1) than carbon-based nanomaterials. They formed hydrogen bonds with free-water molecules in the lattice of PILs, including C2,4,5-H⋯O-H, Br⋯H-O-H⋯Br, O-H⋯Br, C2,4,5-H⋯F-P, P-F⋯H-O-H⋯F-P, C2,4,5-H⋯F-B and B-F⋯H-O-H⋯F-B. After extraction, the O-H stretching-vibration peak was prominently intensified, whereas the C-H bond varied slightly concomitant with reduced B-F and P-F vibration. Theoretically, the C-H vibration should become more intense in the C4,5-H⋯H2O and C2-H⋯H2O bonds after extraction in contrast to before extraction. These contrary spectral changes demonstrated that the hydrogen bonds between cations in the PILs and free-water molecules were broken after extraction, yielding the H-bonding occurrence between bifenthrin and H-O-H in the lattice. As a time indicator for the free-water binding and releasing process, the highest slope for the plot of I t /I 0 against time implied that the shortest time was required for P[VEIM]PF6 to reach an adsorption equilibrium. Overall, the strong hydrophobicity, small SSA and electrostatic-repulsion force for P[VEIM]PF6 are all not conducive to its efficient adsorption. Beyond our anticipation, P[VEIM]PF6 provided the highest extraction recovery for bifenthrin up to 92.4% among three PILs. Therefore, these data lead us to posit that the above high efficiency results from the strongest H-bonding effect between P[VEIM]PF6 and bifenthrin. These findings promote our deep understanding of PILs-triggered differential efficiency through a H-bonding induced effect.

Generalized Excess Spectroscopy

With a clear enhancement of the apparent resolution of experimentally determined spectra, excess spectroscopy has been developed as a powerful tool to study solution structures and molecular interactions. In the standard procedure of the method, excess spectra are calculated based on the ideal spectra constructed using two pure compounds. This limits the applications of the method when the pure compounds are unstable or their physical state is different from that of the mixtures. To overcome the problem or to extend the application, we propose generalized excess spectroscopy in this work, where the ideal spectrum is evaluated from the spectra of reference mixtures. After deducing the working equations, we performed digital simulation and then applied the novel approach to a binary system consisting of tert-butanol and carbon tetrachloride. Both results illustrated the feasibility and universality of the method.

The effect of dilution on induced free charge density gradients in room temperature ionic liquids

We report on changes in the magnitude and length scale of the induced free charge density gradient, ρ_f, in three imidazolium room temperature ionic liquids (RTILs) with dilution by methanol and acetonitrile. Using depth- and time-resolved fluorescence measurements of cresyl violet rotational diffusion, we find that ρ_f persists in RTILs to varying degrees depending on RTIL and diluent identity, and in all cases the functional form of ρ_f is not a smooth monotonic diminution in either magnitude or persistence length with increasing diluent, but a stepwise collapse. This finding is consistent with changes in the bulk RTIL as a function of dilution seen using rotational diffusion measurements that show the rotating entity in bulk RTILs exhibits a larger effective hydrodynamic volume than would be expected based on bulk viscosity data for the diluted RTILs. This excess hydrodynamic volume can be understood in the context of aggregation of RTIL ion pairs in the diluted RTIL system. The size of the aggregates is seen to depend on RTIL identity and diluent, and in all cases aggregate size increases with increasing dilution. This finding is consistent with the ρ_f dependence on dilution data. The collapse of ρ_f is seen to correlate with the onset of RTIL ion pair dimer formation, a condition that may facilitate dissociated RTIL ion mobility in the binary system.

The Composition of Saturated Vapor over 1-Butyl-3-methylimidazolium Tetrafluoroborate Ionic Liquid: A Multi-Technique Study of the Vaporization Process

A multi-technique approach based on Knudsen effusion mass spectrometry, gas phase chromatography, mass spectrometry, NMR and IR spectroscopy, thermal analysis, and quantum-chemical calculations was used to study the evaporation of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF₄). The saturated vapor over BMImBF₄ was shown to have a complex composition which consisted of the neutral ion pairs (NIPs) [BMIm⁺][BF₄^-], imidazole-2-ylidene C₈N₂H₁₄BF₃, 1-methylimidazole C₄N₂H₆, 1-butene C₄H₈, hydrogen fluoride HF, and boron trifluoride BF₃. The vapor composition strongly depends on the evaporation conditions, shifting from congruent evaporation in the form of NIP under Langmuir conditions (open surface) to primary evaporation in the form of decomposition products under equilibrium conditions (Knudsen cell). Decomposition into imidazole-2-ylidene and HF is preferred. The vapor composition of BMImBF₄ is temperature-depended as well: the fraction ratio of [BMIm⁺][BF₄^-] NIPs to decomposition products decreased by about a factor of three in the temperature range from 450 K to 510 K.

Special Mixing Behavior of Chelate-based Ionic Liquid with Methanol

Compared to the general ionic liquids (ILs), a significant deviation of the binary mixtures of 1-decyl-3-methylimidazolium tri(hexafluoroacetylaceto)-copper(II) ([C₁₀ mim][Cu(hfacac)₃ ]) with methanol was found, indicating the way methanol interacts with ILs might be governed by the special structure of the chelating anion. IR results showed that the v (C2-H) of 1-decyl-3-methylimidazolium hexafluoroacetylacetonate ([C₁₀ mim][hfacac]) blue-shifted more significantly than that of [C₁₀ mim][Cu(hfacac)₃ ], meanwhile the v (C=O) red-shifted in [C₁₀ mim][Cu(hfacac)₃ ], which is contrast with that in [C₁₀ mim][hfacac]. Two-dimensional correlation analysis of the FTIR spectra indicated that the chelating cavity has little effect on the sequence of the ILs sites that interact with methanol. Combined with small angle X-ray scattering (SAXS) results, the picture of mixing processes in these two systems were proposed. Methanol interacts directly with the anion followed by the cation in [C₁₀ mim][hfacac], while methanol preferentially enters the chelating cavity and enhances the packing effect in the [C₁₀ mim][Cu(hfacac)₃ ] system.

Insights into the Structure and Dynamics of Imidazolium Ionic Liquid and Tetraethylene Glycol Dimethyl Ether Cosolvent Mixtures: A Molecular Dynamics Approach

In this work, the effect of molecular cosolvents tetraethylene glycol dimethyl ether (TEGDME) on the structure and versatile nature of mixtures of these compounds with imidazolium-based ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) is analyzed and discussed at a molecular level by means of all-atom molecular dynamics (MD) simulations. In the whole concentration range of the binary mixtures, the structures and properties evolution was studied by means of systematic molecular dynamics simulations of the fraction of hydrogen bonds, the radial and spatial distribution functions for the various molecular ions and molecular species in the system, together with the snapshots visualization of equilibrated simulation boxes with a color-coding scheme and the rotational dynamics of coumarin 153 (C153) in the binary mixtures. The goal of the work is to provide a molecular-level understanding of significant improvement of ionic conductivity and self-diffusion with the presence of TEGDME as a cosolvent, which causes an enhancement to the ion translational motion and fluidity in the [bmim][PF₆] ionic liquids (ILs). Under a mixture concentration change, the microstructure changes of [bmim][PF₆] with the TEGDME molar fraction (X_TEG) above 0.50 show a slight difference from that of neat [bmim][PF₆] IL and concentrated [bmim][PF₆]/TEGDME mixture in terms of the radial and spatial distribution functions. The relative diffusivities of solvent molecules to cations as a function of concentration were found to depend on the solvent but not on the anion. A TEGDME increase is found to be advantageous to the dissipation of the polar regions as well as the nonpolar regions in the [bmim][PF₆] ionic liquids. These conclusions are consistent with the experimental results, which verified that the unique, complex, and versatile nature of [bmim][PF₆]/TEGDME mixture can be correctly modeled and discussed at a molecular level using MD simulation data.

Tracking the Micro-Heterogeneity and Hydrogen-Bonding Interactions in Hydroxyl-Functionalized Ionic Liquid Solutions: A Combined Experimental and Computational Study

Ionic liquids (ILs) are an important class of media that are usually used in combination with polar solvents to reduce costs and tune their physicochemical properties. In this regard, it is essential to understand the influence of adding solvents on the properties of ILs. In this work, the micro-heterogeneity and H-bonding interactions between a hydroxyl-functionalized IL, [HOEmim][TFSI], and acetonitrile (ACN) were investigated by attenuated total reflection Fourier transform infrared spectroscopy and molecular simulations. All studied IL-ACN mixtures were found to deviate from the ideal mixtures. The degree of deviations reaches the maximum at about x(ACN)=0.7 with the presence of both homogeneous clusters of pure IL/ACN and heterogeneous clusters of IL-ACN. With the addition of ACN to IL, the mixtures undergo the transformation from "ACN solvated in [HOEmim][TFSI]" to "[HOEmim][TFSI] solvated in ACN". It is found that the newly formed H-bonding interactions between the IL and ACN is the main factor that contributes to the red shifts of O-H, C₂ -H, C_4,5 -H, and C_alkyl -H of [HOEmim]⁺ cation, and the blue shifts of C-D, C≡N of ACN, and C-F, S=O of [TFSI]^- anion. These in-depth studies on the mixtures of hydroxyl-functionalized IL and acetonitrile would help to understand the micro-heterogeneity and H-bonding interactions of miscible solutions and shed light on exploring their applications.

Substrate–Solvent Crosstalk—Effects on Reaction Kinetics and Product Selectivity in Olefin Oxidation Catalysis

In this work, we explored how solvents can affect olefin oxidation reactions catalyzed by MCM-bpy-Mo catalysts and whether their control can be made with those players. The results of this study demonstrated that polar and apolar aprotic solvents modulated the reactions in different ways. Experimental data showed that acetonitrile (aprotic polar) could largely hinder the reaction rate, whereas toluene (aprotic apolar) did not. In both cases, product selectivity at isoconversion was not affected. Further insights were obtained by means of neutron diffraction experiments, which confirmed the kinetic data and allowed for the proposal of a model based on substrate–solvent crosstalk by means of hydrogen bonding. In addition, the model was also validated in the ring-opening reaction (overoxidation) of styrene oxide to benzaldehyde, which progressed when toluene was the solvent (reaching 31% styrene oxide conversion) but was strongly hindered when acetonitrile was used instead (reaching only 7% conversion) due to the establishment of H-bonds in the latter. Although this model was confirmed and validated for olefin oxidation reactions, it can be envisaged that it may also be applied to other catalytic reaction systems where reaction control is critical, thereby widening its use.

The molecular behavior of pyridinium/imidazolium based ionic liquids and toluene binary systems

Imidazolium and pyridinium-based ionic liquids (ILs) have attracted increasing attention in the extraction of aromatic VOCs. However, fundamental studies on the mechanism of capturing aromatic VOCs have been less reported. In this work, the interactions between two ILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) and N-butylpyridinium bis(trifluoromethylsulfonyl)imide (BpyTFSI), and toluene (C₆H₅CH₃), were investigated by using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), excess infrared spectroscopy, hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy and quantum chemical calculations. Some conclusions were obtained as follows: (1) H atoms on EMIMTFSI/BpyTFSI were located above or below the benzene ring and were mainly formed as C2-Hπ bonds and C2,6-Hπ bonds with C₆H₅CH₃, respectively. C-Hπ bonds played a significant role in capturing aromatic compounds. (2) Upon adding C₆H₅CH₃, the two IL-C₆H₅CH₃ system's interaction strength was as follows: EMIMTFSI-C₆H₅CH₃ > BpyTFSI-C₆H₅CH₃. (3) Since C₆H₅CH₃ was unable to disrupt the interactions between cations and anions of ion pairs in the two studied IL-C₆H₅CH₃ systems, only ion cluster-C₆H₅CH₃ and ion pair-C₆H₅CH₃ complexes were observed. This work may provide theoretical insights into the separation mechanism for capturing VOCs.

Research for improvement on the extract efficiency of lignans in traditional Chinese medicines by hybrid ionic liquids: As a case of Suhuang antitussive capsule

Recently, efficient extraction of natural products from traditional Chinese medicines (TCMs) by green solvents is deemed an essential area of green technology and attracts extensive attentions. In this work, a green protocol for simultaneous ultrasonic-extraction of the native compounds with different polarities of TCMs by using a hybrid ionic liquids (HILs)-water system was reported for the first time. As a case study, three superior ILs (1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), and 1-allyl-3-methylimidazolium chloride ([AMIM]Cl)) were chosen as the compositions of the HILs system, and the TCMs Suhuang antitussive capsule (SH) containing different-polarity lignans was selected. Primarily, an ultra-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry (UPLC-QqQ-MS/MS) method in the multiple reaction monitoring (MRM) mode was established for qualitative and quantitative analysis of 18 lignans. After majorization by uniform design experiment, the HILs prepared with [AMIM]Cl, [EMIM][BF4], and [EMIM][OAc] at a volume ratio of 1:5:5 could simultaneously extract multi-polarity lignans compared to single IL. Subsequently, the conditions of ultrasonic extraction employing with HILs and traditional organic solvent were optimized by the response surface methodology, respectively. The results indicated that the extract efficiency of the HILs system for target compounds was significantly improved compared with the traditional organic solvent-extraction, i.e. the content of total lignans in ethanol system was up to 47 mg/g, while that in the HILs system was up to 69 mg/g, with an increasing of 47%. Additionally, ¹H-NMR and ¹³C-NMR spectra were used to characterize the hydrogen-bond interactions in the HILs-lignan mixtures. Extraction with the HILs in TCMs is a new application schema of ILs, which not only avoids the use of volatile toxic organic solvents, but also shows the potential to be comprehensively applied for the extraction of bioactive compounds from TCMs.

The Structures of ZnCl2-Ethanol Mixtures, a Spectroscopic and Quantum Chemical Calculation Study

We report in this article the structural properties, spectral behavior and heterogeneity of ZnCl₂-ethanol (EtOH) mixtures in a wide-composition range (1:3 to 1:14 in molar ratios), using ATR-FTIR spectroscopy and quantum chemical calculations. To improve the resolution of the initial IR spectra, excess spectroscopy and two-dimensional correlation spectroscopy were employed. The transformation process was suggested to be from EtOH trimer and EtOH tetramer to EtOH monomer, EtOH dimer and ZnCl₂-3EtOH complex upon mixing. The theoretical findings showed that increasing the content of EtOH was accompanied with the flow of negative charge to ZnCl₂. This led to reinforcement of the Zn←O coordination bonds, increase of the ionic character of Zn‒Cl bond and weakening and even dissociation of the Zn‒Cl bond. It was found that in some of the ZnCl₂-EtOH complexes optimized at the gas phase or under the solvent effect, there existed hydroxyls with a very special interactive array in the form of Cl‒Zn⁺←O‒H^…Cl^-, which incredibly red-shifted to wavenumbers <3000 cm^-1. This in-depth study shows the physical insights of the respective electrolyte alcoholic solutions, particularly the solvation process of the salt, help to rationalize the reported experimental results, and may shed light on understanding the properties of the deep eutectic solvents formed from ZnCl₂ and an alcohol.

A novel strategy to reduce the viscosity of cellulose-ionic liquid solution assisted by transition metal ions

The high viscosity of ionic liquids, even at relatively high temperatures, can greatly affect the production of cellulose fibers through the wet-spinning process. The high viscosity mainly by due to the hydrogen bond interaction between the cations and anions of ionic liquids. It is possible to reduce the viscosity by modulating the hydrogen bond interaction. In the present work, copper chloride (CuCl₂) was dissolved in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl)-cellulose solution, followed by the formation of a complex with the chloride anions by converting it to [CuCl₄]^2- anion. Through this strategy, the extrusion velocity of the solution improved, and the produced fibers obtained smoother surfaces and shrunken diameters.

The structural properties of a ZnCl2-ethylene glycol binary system and the peculiarities at the eutectic composition

ATR-FTIR spectroscopy was performed on a series of ZnCl2-ethylene glycol (EG) mixtures with a wide-range of compositions (1 : 1.5-1 : 14 in molar ratios), involving the stable ZnCl2-4EG deep-eutectic solvent (DES) composition, to explore the spectral variations, structural heterogeneity, and hydrogen bonding (H-bonding) properties. To enhance the resolution of the spectra, excess absorption and two-dimensional correlation spectroscopies were employed. In the initial IR spectra, a quasi-isosbestic point was identified, signaling that the major disturbance on EG microstructures by adding ZnCl2 is to form a distinct complex. Further analysis uncovered the main transformation process to be from the EG tetramer to the ZnCl2-4EG complex. It was also found that as the EG content increases, negative charge increasingly transfers to ZnCl2, resulting in the strengthening of the Zn ← O coordination bonds and the weakening and finally dissociation of Zn-Cl bonds. Regarding the ZnCl2-4EG DES, several incomparable specificities were observed. It was found that ZnCl2 destructed the H-bonding network of pure EG to the largest extent, resulting in the highest production of the dimer and trimer of EG. Moreover, in comparison with other compositions, the ZnCl2-4EG DES showed abrupt increases in the negative charge of the salt, the length of the Zn-Cl bond, and the strength of the Zn ← O coordination bond. All these imply the strongest intermolecular interactions and the highest solvation of ZnCl2 in EG at the eutectic composition compared to those of other mixtures, resulting in a super-stable liquid mixture. The work provides physical insights into the structural and interactive properties of deep-eutectic solvents.

Multi-Interactions in Ionic Liquids for Natural Product Extraction

Natural products with a variety of pharmacological effects are important sources for commercial drugs, and it is very crucial to develop effective techniques to selectively extract and isolate bioactive natural components from the plants against the background of sustainable development. Ionic liquids (ILs) are a kind of designable material with unique physicochemical properties, including good thermal stability, negligible vapor pressure, good solvation ability, etc. ILs have already been used in pharmaceuticals for extraction, purification, drug delivery, etc. It has been reported that multi-interactions, like hydrogen bonding, hydrophobic interactions, play important roles in the extraction of bioactive components from the plants. In this review, recent progress in the understanding of scientific essence of hydrogen bonding, the special interaction, in ILs was summarized. The extraction of various natural products, one important area in pharmaceutical, by conventional and functional ILs as well as the specific roles of multi-interactions in this process were also reviewed. Moreover, problems existing in bioactive compound extraction by ILs and the future developing trends of this area are given, which might be helpful for scientists, especially beginners, in this field.

Computational NMR Study of Ion Pairing of 1-Decyl-3-methyl-imidazolium Chloride in Molecular Solvents

The 1H NMR spectra of 10-5 mole fraction solutions of 1-decyl-3-methyl-imidazolium chloride ionic liquid in water, acetonitrile, and dichloromethane have been measured. The chemical shift of the proton at position 2 in the imidazolium ring of 1-decyl-3-methyl-imidazolium (H2) is rather different for all three samples, reflecting the shifting equilibrium between the contact pairs and free fully solvated ions. Classical molecular dynamics simulations of the 1-decyl-3-methyl-imidazolium chloride contact ion pair as well as of free ions in water, acetonitrile, and dichloromethane have been conducted, and the quantum mechanics/molecular mechanics methods have been applied to predict NMR chemical shifts for the H2 proton. The chemical shift of the H2 proton was found to be primarily modulated by hydrogen bonding with the chloride anion, while the influence of the solvents-though differing in polarity and capabilities for hydrogen bonding-is less important. By comparing experimental and computational results, we deduce that complete disruption of the ionic liquid into free ions takes place in an aqueous solution. Around 23% of contact ion pairs were found to persist in acetonitrile. Ion-pair breaking into free ions was predicted not to occur in dichloromethane.

Ion Dissociation in Ionic Liquids and Ionic Liquid Solutions

The extent to which cations and anions in ionic liquids (ILs) and ionic liquid solutions are dissociated is of both fundamental scientific interest and practical importance because ion dissociation has been shown to impact viscosity, density, surface tension, volatility, solubility, chemical reactivity, and many other important chemical and physical properties. When mixed with solvents, ionic liquids provide the unique opportunity to investigate ion dissociation from infinite dilution in the solvent to a completely solvent-free state, even at ambient conditions. The most common way to estimate ion dissociation in ILs and IL solutions is by comparing the molar conductivity determined from ionic conductivity measurements such as electrochemical impedance spectroscopy (EIS) (which measure the movement of only the charged, i.e., dissociated, ions) with the molar conductivity calculated from ion diffusivities measured by pulse field gradient nuclear magnetic resonance spectroscopy (PFG-NMR, which gives movement of all of the ions). Because the NMR measurements are time-consuming, the number of ILs and IL solutions investigated by this method is relatively limited. We have shown that use of the Stokes-Einstein equation with estimates of the effective ion Stokes radii allows ion dissociation to be calculated from easily measured density, viscosity, and ionic conductivity data (ρ, η, λ), which is readily available in the literature for a much larger number of pure ILs and IL solutions. Therefore, in this review, we present values of ion dissociation for ILs and IL solutions (aqueous and nonaqueous) determined by both the traditional molar conductivity/PFG-NMR method and the ρ, η, λ method. We explore the effect of cation and anion alkyl chain length, structure, and interaction motifs of the cation and anion, temperature, and the strength of the solvent in IL solutions.

Is the Fourier Transform Infrared Free-OH Band of t-Butanol Only from Free OHs? Case Studies on the Binary Systems of the Alcohol with CCl4 and CHCl3

Attenuated total reflection-Fourier transform infrared spectroscopy and quantum chemical calculations were performed on tert-butyl alcohol (t-BuOH) and its binary solutions with CCl₄ and CHCl₃. The study was focused on the free-OH stretching bands. Two resolution-enhancing methods, excess spectroscopy and two-dimensional correlation spectroscopy, were employed to examine the structural heterogeneity and search for the detailed contributors to the free-OH bands. Unexpectedly, CCl₄ was found not to be an inert solvent and, similar to CHCl₃, formed hydrogen/halogen bonds (H-/X-bond) with t-BuOH. It was observed that the free-OH band in the t-BuOH-CHCl₃ system is larger and more red-shifted than that in the t-BuOH-CCl₄ system, indicating the stronger intermolecular interactions in the former system. Furthermore, in the t-BuOH-CHCl₃ system, the H-bonds are stronger than the X-bonds, while in the t-BuOH-CCl₄ system, both interactions are similar in strength. To assign the free-OH bands, it was found that they are not only from the free OH of the t-BuOH monomer, but they are also contributed by the quasi-free OH with the oxygen bonded to H or Cl and even the weakly H-bonded OH of t-BuOH molecules. Finally, all the identified species increased simultaneously via cosolvent addition, suggestive of the destabilization of the highly associated t-BuOH clusters.

Microstructural and Dynamical Heterogeneities in Ionic Liquids

Ionic liquids (ILs) are a special category of molten salts solely composed of ions with varied molecular symmetry and charge delocalization. The versatility in combining varied cation-anion moieties and in functionalizing ions with different atoms and molecular groups contributes to their peculiar interactions ranging from weak isotropic associations to strong, specific, and anisotropic forces. A delicate interplay among intra- and intermolecular interactions facilitates the formation of heterogeneous microstructures and liquid morphologies, which further contributes to their striking dynamical properties. Microstructural and dynamical heterogeneities of ILs lead to their multifaceted properties described by an inherent designer feature, which makes ILs important candidates for novel solvents, electrolytes, and functional materials in academia and industrial applications. Due to a massive number of combinations of ion pairs with ion species having distinct molecular structures and IL mixtures containing varied molecular solvents, a comprehensive understanding of their hierarchical structural and dynamical quantities is of great significance for a rational selection of ILs with appropriate properties and thereafter advancing their macroscopic functionalities in applications. In this review, we comprehensively trace recent advances in understanding delicate interplay of strong and weak interactions that underpin their complex phase behaviors with a particular emphasis on understanding heterogeneous microstructures and dynamics of ILs in bulk liquids, in mixtures with cosolvents, and in interfacial regions.

Theoretical Insight into the Interaction between Chloramphenicol and Functional Monomer (Methacrylic Acid) in Molecularly Imprinted Polymers

Molecular imprinting technology is a promising method for detecting chloramphenicol (CAP), a broad-spectrum antibiotic with potential toxicity to humans, in animal-derived foods. This work aimed to investigate the interactions between the CAP as a template and functional monomers required for synthesizing efficient molecularly imprinted polymers for recognition and isolation of CAP based on density functional theory. The most suitable monomer, methacrylic acid (MAA), was determined based on interaction energies and Gibbs free energy changes. Further, the reaction sites of CAP and MAA was predicted through the frontier molecular orbitals and molecular electrostatic potentials. Atoms in molecules topology analysis and non-covalent interactions reduced density gradient were applied to investigate different types of non-covalent and inter-atomic interactions. The simulation results showed that CAP was the main electron donor, while MAA was the main electron acceptor. Moreover, the CAP–MAA complex simultaneously involved N-H···O and C=O···H double hydrogen bonds, where the strength of the latter was greater than that of the former. The existence of hydrogen bonds was also confirmed by theoretical and experimental hydrogen nuclear magnetic resonance and Fourier transform infrared spectroscopic analyses. This research can act as an important reference for intermolecular interactions and provide strong theoretical guidance regarding CAP in the synthesis of molecularly imprinted polymers.

Hydrogen Bonds with BF4− Anion as a Proton Acceptor

The BF4− anion is characterised by weak Lewis base properties; it is usually classified as a “non-coordinating anion”. The searches through the Cambridge Structural Database (CSD) were performed and it was found that the BF4− anion often occurs in crystal structures and it is involved in numerous intermolecular interactions; hydrogen bonds are the majority of them. The hydrogen bonds involving the BF4− anion as a proton acceptor are closer to linearity with the increase of the strength of interaction that is in line with the tendency known for other hydrogen bonds. However, even for short contacts between the proton and the Lewis base centre, slight deviations from linearity occur. The MP2/aug-cc-pVTZ calculations on the BF4−…HCN complex and on the BF4−…(HCN)4 cluster were also carried out to characterise corresponding C-H…F hydrogen bonds; such interactions often occur in crystal structures.

Influence of Hydration on the Structure and Interactions of Ethaline Deep-Eutectic Solvent: A Spectroscopic and Computational Study

Deep-eutectic solvents (DESs) are regarded as alternative green solvents to ionic liquids. In this work we report the structural properties and hydrogen bonding (H-bonding) interactions of an aqueous DES system. The used DES, ethaline (ETH), is composed of choline chloride and ethylene glycol (EG) in 1 : 2 molar ratio. The investigations were carried out by FTIR spectroscopy combined with quantum chemical calculations. Excess spectroscopy and two-dimensional correlation spectroscopy (2D-COS) were used to explore the data in detail. The results showed that, upon mixing, ETH transforms to EG dimers and trimers and D₂ O clusters transform to various ETH-D₂ O complexes. Theoretical calculations show that water molecules insert between the anion and cation of ETH, break the strong doubly ionic Cl^-… H-O_Ch+ H-bond, share charges of the ions and form H-bond with them, thus modulate the interaction properties of ETH. This study deepens our molecular-level understanding of the system and would shed light on its applications.

Excess spectroscopy and its applications in the study of solution chemistry

Characterization of structural heterogeneity of liquid solutions and the pursuit of its nature have been challenging tasks to solution chemists. In the last decade, an emerging method called excess spectroscopy has found applications in this area. The method, combining the merits of molecular spectroscopy and excess thermodynamic functions, shows the ability to enhance the apparent resolution of spectra, provides abundant information concerning solution structures and intermolecular interactions. In this review, the thinking and mathematics of the method, as well as its developments, are presented first. Then, research progress related to the exploration of the method is thoroughly reviewed. The materials are classified into two parts, small-molecular solutions and ionic liquid solutions. Finally, potential challenges and the perspective for further development of the method are discussed.