Unravelling ionic liquid solvent effects for a non-polar Cope rearrangement reaction

The impact of ionic liquids (ILs) on polar reactions is well recognised, however the impact of ILs on non-polar reactions is less well understood or explored. Pericyclic Cope rearrangements are highly concerted, exhibit minimal charge localisation and pass through an uncharged but well-defined transition state, and thus provide a good mechanism for exploring the impact of IL polarizability on chemical reactivity. Recently, a 10× rate enhancement has been observed for the Cope rearrangement of 3-phenyl-1,5-hexadiene in the IL 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4C1im][NTf2] compared to benzene. In this work we undertake a DFT based computational study (B3LYP-D3BJ/6-311+G(d,p) and M06-2X-D3/6-311+G(d,p)) of the Cope rearrangement of 3-phenyl-1,5-hexadiene and 3-propyl-hexa-1,5-diene in molecular solvents (acetonitrile, benzene and ethanol) and the IL [C4C1im][NTf2] using the SMD solvation model. The impact of benzene and [C4C1im][NTf2] on the Cope rearrangement of 3-phenyl-1,5-hexadiene is studied in more detail and we provide insight into the reason for the rate enhancement in an IL. The volume of activation is evaluated and the potential impact of 'solvent pressure' is discussed. We identify two potential mechanisms for volume effects to contribute to the rate enhancement. Solvent association energies are evaluated at the DLNPO-CCSD(T) level. Specific solvent interactions are explored through atomic partial charge, molecular orbital and bond critical point analysis, as well as via non-colvalent interaction (NCI) plots, electrostatic potential (ESP) differences and density difference Δρ(r) plots. We find that the cation and anion together form an extensive van der Waals pocket in-which the transition state (TS) sits. Electron density within the TS is anisotropically polarised via a 'push-pull' effect due to the dual cation-anion nature of the IL, stabilising the TS relative to benzene. We also provide experimental evidence that these effects are generalisable to other ILs. Overall, our aim is to provide a deeper moleuclar level understanding of the impact of ILs on non-polar reactions.

Understanding the effects of targeted modifications on the 1 : 2 Choline And GEranate structure

1 : 2 Choline-and-geranate (CAGE) is an ionic liquid (IL) widely studied for its biomedical applications. However, both its industrial-scale preparation and its long-term storage are problematic so finding more suitable candidates which retain its advantageous properties is crucial. As a first step towards this we have conducted a targeted modification study to understand the effects of specific functional groups on the properties of CAGE. 1 : 2 Choline-and-octanoate and 1 : 2 butyltrimethylammonium-and-octanoate were synthesised and their thermal and rheological properties examined in comparison to those of CAGE. Using differential scanning calorimetry and polarising microscopy, the model compound was found to be an isotropic liquid, while the analogues were room-temperature liquid-crystals which transition to isotropic liquids upon heating. Dynamic mechanical analysis showed that the thermal behaviour of the studied systems was even more complex, with the ILs also undergoing a thermally-activated relaxation process. Furthermore, we have used electron paramagnetic resonance (EPR) spectroscopy, along with a variety of spin probes with different functional groups, in order to understand the chemical environment experienced by solutes in each system. The EPR spectra indicate that the radicals experience two distinct environments (polar and nonpolar) in the liquid-crystalline phase, but only one average environment in the isotropic phase. The liquid-crystalline phase experiments also showed that the relative populations of the two domains depend on the nature of the solutes, with polar or strongly hydrogen-bonding solutes preferring the polar domain. For charged solutes, the EPR spectra showed line-broadening, suggesting that their ionic nature leads to complex, unresolved interactions.

Room temperature ionic liquids with two symmetric ions

Room temperature ionic liquids typically contain asymmetric organic cations. The asymmetry is thought to enhance disorder, thereby providing an entropic counter-balance to the strong, enthalpic, ionic interactions, and leading, therefore, to lower melting points. Unfortunately, the synthesis and purification of such asymmetric cations is typically more demanding. Here we introduce novel room temperature ionic liquids in which both cation and anion are formally symmetric. The chemical basis for this unprecedented behaviour is the incorporation of ether-containing side chains - which increase the configurational entropy - in the cation. Molecular dynamics simulations indicate that the ether-containing side chains transiently sample curled configurations. Our results contradict the long-standing paradigm that at least one asymmetric ion is required for ionic liquids to be molten at room temperature, and hence open up new and simpler design pathways for these remarkable materials.

Dynamics in Quaternary Ionic Liquids with Non-Flexible Anions: Insights from Mechanical Spectroscopy

The present work investigates how mechanical properties and ion dynamics in ionic liquids (ILs) can be affected by ILs' design while considering possible relationships between different mechanical and transport properties. Specifically, we study mechanical properties of quaternary ionic liquids with rigid anions by means of Dynamical Mechanical Analysis (DMA). We are able to relate the DMA results to the rheological and transport properties provided by viscosity, conductivity, and diffusion coefficient measurements. A good agreement is found in the temperature dependence of different variables described by the Vogel-Fulcher-Tammann model. In particular, the mechanical spectra of all the measured liquids showed the occurrence of a relaxation, for which the analysis suggested its attribution to a diffusive process, which becomes evident when the ion dynamics are not affected by the fast structural reorganization of flexible anions on a local level.

A Horizon Scan to Support Chemical Pollution-Related Policymaking for Sustainable and Climate-Resilient Economies

While chemicals are vital to modern society through materials, agriculture, textiles, new technology, medicines, and consumer goods, their use is not without risks. Unfortunately, our resources seem inadequate to address the breadth of chemical challenges to the environment and human health. Therefore, it is important we use our intelligence and knowledge wisely to prepare for what lies ahead. The present study used a Delphi-style approach to horizon-scan future chemical threats that need to be considered in the setting of chemicals and environmental policy, which involved a multidisciplinary, multisectoral, and multinational panel of 25 scientists and practitioners (mainly from the United Kingdom, Europe, and other industrialized nations) in a three-stage process. Fifteen issues were shortlisted (from a nominated list of 48), considered by the panel to hold global relevance. The issues span from the need for new chemical manufacturing (including transitioning to non-fossil-fuel feedstocks); challenges from novel materials, food imports, landfills, and tire wear; and opportunities from artificial intelligence, greater data transparency, and the weight-of-evidence approach. The 15 issues can be divided into three classes: new perspectives on historic but insufficiently appreciated chemicals/issues, new or relatively new products and their associated industries, and thinking through approaches we can use to meet these challenges. Chemicals are one threat among many that influence the environment and human health, and interlinkages with wider issues such as climate change and how we mitigate these were clear in this exercise. The horizon scan highlights the value of thinking broadly and consulting widely, considering systems approaches to ensure that interventions appreciate synergies and avoid harmful trade-offs in other areas. We recommend further collaboration between researchers, industry, regulators, and policymakers to perform horizon scanning to inform policymaking, to develop our ability to meet these challenges, and especially to extend the approach to consider also concerns from countries with developing economies. Environ Toxicol Chem 2023;00:1-17. © 2023 Crown copyright and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article is published with the permission of the Controller of HMSO and the King's Printer for Scotland.

Physical properties and nanostructuring of long-chained homobaric imidazolium ionic liquids

Understanding the structure-property relationship and nanoscopic behaviour of ionic liquids is of utmost importance for their potential applications. Focusing these studies on sets of homobaric ionic liquids could provide important insight into the effects of specific chemical groups on the overall interaction profile, bringing researchers one step closer to succesfully designing ionic liquids which are tailor-made for specific applications. This work focuses on ionic liquids with 12 total carbons on their side chains, studying both their bulk physical properties (such as densities and viscosities) and their nanostructuring. The results reveal that by keeping the total number of carbons constant, but arranging them differently around the imidazolium ring, either in a linear or in a branched-chain formation, can result in compounds with quite distinct properties. Some of those (such as diffusivity) appear to be more sensitive to symmetry variations, while others (such as density) are not significantly affected. X-ray scattering is used in order to get a clearer understanding of the nanostructuring of the studied compounds and to investigate to what extent the observed macroscopic properties are directly linked to the nanoscale ordering.

Insights into structure-property relationships in ionic liquids using cyclic perfluoroalkylsulfonylimides

Room temperature ionic liquids of cyclic sulfonimide anions ncPFSI (ring size: n = 4-6) with the cations [EMIm]⁺ (1-ethyl-3-methylimidazolium), [BMIm]⁺ (1-butyl-3-methylimidazolium) and [BMPL]⁺ (BMPL = 1-butyl-1-methylpyrrolidinium) have been synthesized. Their solid-state structures have been elucidated by single-crystal X-ray diffraction and their physicochemical properties (thermal behaviour and stability, dynamic viscosity and specific conductivity) have been assessed. In addition, the ion diffusion was studied by pulsed field gradient stimulated echo (PFGSTE) NMR spectroscopy. The decisive influence of the ring size of the cyclic sulfonimide anions on the physicochemical properties of the ILs has been revealed. All ILs show different properties compared to those of the non-cyclic TFSI anion. While these differences are especially distinct for ILs with the very rigid 6cPFSI anion, the 5-membered ring anion 5cPFSI was found to result in ILs with relatively similar properties. The difference between the properties of the TFSI anion and the cyclic sulfonimide anions has been rationalized by the rigidity (conformational lock) of the cyclic sulfonimide anions. The comparison of selected IL properties was augmented by MD simulations. These highlight the importance of π⁺-π⁺ interactions between pairs of [EMIm]⁺ cations in the liquid phase. The π⁺-π⁺ interactions are evident for the solid state from the molecular structures of the [EMIm]⁺-ILs with the three cyclic imide anions determined by single-crystal X-ray diffraction.

Anion and ether group influence in protic guanidinium ionic liquids

Ionic liquids are attractive liquid materials for many advanced applications. For targeted design, in-depth knowledge about their structure-property-relations is urgently needed. We prepared a set of novel protic ionic liquids (PILs) with a guanidinium cation with either an ether or alkyl side chain and different anions. While being a promising cation class, the available data is insufficient to guide design. We measured thermal and transport properties, nuclear magnetic resonance (NMR) spectra as well as liquid and crystalline structures supported by ab initio computations and were able to obtain a detailed insight into the influence of the anion and the ether substitution on the physical and spectroscopic properties. For the PILs, hydrogen bonding is the main interaction between cation and anion and the H-bond strength is inversely related to the proton affinity of the constituting acid and correlated to the increase of ¹H and ¹⁵N chemical shifts. Using anions from acids with lower proton affinity leads to proton localization on the cation as evident from NMR spectra and self-diffusion coefficients. In contrast, proton exchange was evident in ionic liquids with triflate and trifluoroacetate anions. Using imide-type anions and ether side groups decreases glass transitions as well as fragility, and accelerated dynamics significantly. In case of the ether guanidinium ionic liquids, the conformation of the side chain adopts a curled structure as the result of dispersion interactions, while the alkyl chains prefer a linear arrangement.

Molecular Dynamics of Ionic Liquids from Fast-Field Cycling NMR and Molecular Dynamics Simulations

Understanding the connection between the molecular structure of ionic liquids and their properties is of paramount importance for practical applications. However, this connection can only be established if a broad range of physicochemical properties on different length and time scales is already available. Even then, the interpretation of the results often remains ambiguous due to the natural limits of experimental approaches. Here we use fast-field cycling (FFC) to access both translational and rotational dynamics of ionic liquids. These combined with a comprehensive physicochemical characterization and MD simulations provide a toolkit to give insight into the mechanisms of molecular mechanics. The FFC results are consistent with the computer simulation and conventional physicochemical approaches. We show that curling of the side chains around the positively charged cationic core is essential for the properties of ether-functionalized ionic liquids, and we demonstrate that neither geometry nor polarity alone are sufficient to explain the macroscopic properties.

Flexibility is the key to tuning the transport properties of fluorinated imide-based ionic liquids

Ionic liquids are becoming increasingly popular for practical applications such as biomass processing and lithium-ion batteries. However, identifying ionic liquids with optimal properties for specific applications by trial and error is extremely inefficient since there are a vast number of potential candidate ions. Here we combine experimental and computational techniques to determine how the interplay of fluorination, flexibility and mass affects the transport properties of ionic liquids with the popular imide anion. We observe that fluorination and flexibility have a large impact on properties such as viscosity, whereas the influence of mass is negligible. Using targeted modifications, we show that conformational flexibility provides a significant contribution to the success of fluorination as a design element. Contrary to conventional wisdom, fluorination by itself is thus not a guarantor for beneficial properties such as low viscosity.

Effect of the cation structure on the properties of homobaric imidazolium ionic liquids

In this work we investigate the structure-property relationships in a series of alkylimidazolium ionic liquids with almost identical molecular weight. Using a combination of theoretical calculations and experimental measurements, we have shown that re-arranging the alkyl side chain or adding functional groups results in quite distinct features in the resultant ILs. The synthesised ILs, although structurally very similar, cover a wide spectrum of properties ranging from highly fluid, glass forming liquids to high melting point crystalline salts. Theoretical ab initio calculations provide insight on minimum energy orientations for the cations, which then are compared to experimental X-ray crystallography measurements to extract information on hydrogen bonding and to verify our understanding of the studied structures. Molecular dynamics simulations of the simplest (core) ionic liquids are used in order to help us interpret our experimental results and understand better why methylation of C² position of the imidazolium ring results in ILs with such different properties compared to their non-methylated analogues.

Pressing matter: why are ionic liquids so viscous?

Room temperature ionic liquids are considered to have huge potential for practical applications such as batteries. However, their high viscosity presents a significant challenge to their use changing from niche to ubiquitous. The modelling and prediction of viscosity in ionic liquids is the subject of an ongoing debate involving two competing hypotheses: molecular and local mechanisms versus collective and long-range mechanisms. To distinguish between these two theories, we compared an ionic liquid with its uncharged, isoelectronic, isostructural molecular mimic. We measured the viscosity of the molecular mimic at high pressure to emulate the high densities in ionic liquids, which result from the Coulomb interactions in the latter. We were thus able to reveal that the relative contributions of coulombic compaction and the charge network interactions are of similar magnitude. We therefore suggest that the optimisation of the viscosity in room temperature ionic liquids must follow a dual approach.

Non-traditional solvent effects in organic reactions

This special cross-journal collection of Organic and Biomolecular Chemistry (OBC) and Physical Chemistry Chemical Physics (PCCP) is dedicated to non-traditional solvent effects in organic reactions.

Curled cation structures accelerate the dynamics of ionic liquids

Ionic liquids are modern liquid materials with potential and actual implementation in many advanced technologies. They combine many favourable and modifiable properties but have a major inherent drawback compared to molecular liquids - slower dynamics. In previous studies we found that the dynamics of ionic liquids are significantly accelerated by the introduction of multiple ether side chains into the cations. However, the origin of the improved transport properties, whether as a result of the altered cation conformation or due to the absence of nanostructuring within the liquid as a result of the higher polarity of the ether chains, remained to be clarified. Therefore, we prepared two novel sets of methylammonium based ionic liquids; one set with three ether substituents and another set with three butyl side chains, in order to compare their dynamic properties and liquid structures. Using a range of anions, we show that the dynamics of the ether-substituted cations are systematically and distinctly accelerated. Liquefaction temperatures are lowered and fragilities increased, while at the same time cation-anion distances are slightly larger for the alkylated samples. Furthermore, pronounced liquid nanostructures were not observed. Molecular dynamics simulations demonstrate that the origin of the altered properties of the ether substituted ionic liquids is primarily due to a curled ether chain conformation, in contrast to the alkylated cations where the alkyl chains retain a linear conformation. Thus, the observed structure-property relations can be explained by changes in the geometric shape of the cations, rather than by the absence of a liquid nanostructure. Application of quantum chemical calculations to a simplified model system revealed that intramolecular hydrogen-bonding is responsible for approximately half of the stabilisation of the curled ether-cations, whereas the other half stems from non-specific long-range interactions. These findings give more detailed insights into the structure-property relations of ionic liquids and will guide the development of ionic liquids that do not suffer from slow dynamics.

A review on machine learning algorithms for the ionic liquid chemical space

There are thousands of papers published every year investigating the properties and possible applications of ionic liquids. Industrial use of these exceptional fluids requires adequate understanding of their physical properties, in order to create the ionic liquid that will optimally suit the application. Computational property prediction arose from the urgent need to minimise the time and cost that would be required to experimentally test different combinations of ions. This review discusses the use of machine learning algorithms as property prediction tools for ionic liquids (either as standalone methods or in conjunction with molecular dynamics simulations), presents common problems of training datasets and proposes ways that could lead to more accurate and efficient models.

Observation of the Pockels Effect in Ionic Liquids and Insights into the Length Scale of Potential-Induced Ordering

Ionic liquids (ILs) under electric fields play essential roles in the electrochemical utilization of ILs. Recently, long-range organization of ILs in the vicinity of charged (and even neutral) surfaces has been revealed, but experimental evidence for such an ordering is still limited and its spatial length scale remains controversial. Here, we use confocal Raman microspectroscopy to investigate the effect of an applied electric potential on the IL 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and its analogues in a space-resolved manner. Much to our surprise, the observed Raman difference spectra of the ILs obtained with and without an applied potential exhibit uniform intensity changes independent of vibrational modes of cations and anions, a finding in sharp contrast with the electric field effects on molecular liquids that we have previously observed. We interpret this unexpected finding in terms of the Pockels effect that occurs as a result of a potential-induced ordering of the IL near an IL-electrode interface. The refractive index changes due to the applied potential are estimated using the experimental Raman intensity changes. The results allow us to deduce that the length scale of the ordering in the ILs is tens to hundreds of nanometers, extending more than would be expected for the electrical double layer but not as far as a micrometer scale.

Targeted modifications in ionic liquids - from understanding to design

Ionic liquids are extremely versatile and continue to find new applications in academia as well as industry. This versatility is rooted in the manifold of possible ion types, ion combinations, and ion variations. However, to fully exploit this versatility, it is imperative to understand how the properties of ionic liquids arise from their constituents. In this work, we discuss targeted modifications as a powerful tool to provide understanding and to enable design. A 'targeted modification' is a deliberate change in the structure of an ionic liquid. This includes chemical changes in an experiment as well as changes to the parameterisation in a computer simulation. In any case, such a change must be purposeful to isolate what is of interest, studying, as far as is possible, only one concept at a time. The concepts can then be used as design elements. However, it is often found that several design elements interact with each other - sometimes synergistically, and other times antagonistically. Targeted modifications are a systematic way of navigating these overlaps. We hope this paper shows that understanding ionic liquids requires experimentalists and theoreticians to join forces and provides a tool to tackle the difficult transition from understanding to design.

Mixing divalent ionic liquids: effects of charge and side-chains

We have prepared novel divalent ionic liquids (ILs) based on the bis(trifluoromethylsulfonyl)imide anion where two charged imidazolium groups in the cations are either directly bound to each other or linked by a single atom. We assessed the influence of the side-chain functionality and divalency on their physical properties and on the thermodynamics of mixing. The results indicate that shortening the spacer of a divalent IL reduces its thermal stability and increases its viscosity. Mixtures of divalent and monovalent ILs show small but significant deviations from ideality upon mixing. These deviations appear to depend primarily on the (mis)match of the nature and length of the cation side-chain. The non-ideality imposed by mixing ILs with different side-chains appears to be enhanced by the increase in formal charge of the cations in the mixture.

MAS NMR Investigation of Molecular Order in an Ionic Liquid Crystal

The structure and molecular order in the thermotropic ionic liquid crystal (ILC), [choline][geranate(H)octanoate], an analogue of Choline And GEranate (CAGE), which has potential for use as a broad-spectrum antimicrobial and transdermal and oral delivery agent, were investigated by magic-angle spinning (MAS) nuclear magnetic resonance (NMR), polarizing optical microscopy, small-angle X-ray scattering (SAXS), and mass spectrometry. Mass spectrometry and the ¹H NMR chemical shift reveal that CAGE-oct is a dynamic system, with metathesis (the exchange of interacting ions) and hydrogen exchange occurring between hydrogen-bonded/ionic complexes such as [(choline)(geranate)(H)(octanoate)], [(choline)(octanoate)₂(H)], and [(choline)(geranate)₂(H)]. These clusters, which are shown by mass spectrometry to be significantly more stable than expected for typical electrostatic ion clusters, involve hydrogen bonding between the carboxylic acid, carboxylate, and hydroxyl groups, with rapid hydrogen bond breaking and re-formation observed to average the ¹H chemical shifts. The formation of a partial bilayer liquid crystal (LC) phase was identified by SAXS and polarizing optical microscopy at temperatures below ∼293 K. The occurrence of this transition close to room temperature could be utilized as a potential temperature-induced "switch" of the anisotropic properties for particular applications. The presence of an isotropic component of approximately 23% was observed to coexist with the LC phase, as detected by polarizing optical microscopy and quantified by both ¹H-¹³C dipolar-chemical shift correlation (DIPSHIFT) and ¹H double-quantum (DQ) MAS NMR experiments. At temperatures above the LC-to-isotropic transition, intermediate-range order (clustering of polar and nonpolar domains), a feature of many ILs, persists. Site-specific order parameters for the LC phase of CAGE-oct were obtained from the MAS NMR measurement of the partially averaged ¹³C-¹H dipolar couplings (D_CH) by cross-polarization (CP) build-up curves and DIPSHIFT experiments, and ¹H-¹H dipolar couplings (D_HH) by double-quantum (DQ) build-up curves. The corresponding order parameters, S_CH and S_HH, are in the range 0-0.2 and are lower compared to those for smectic (i.e., layered) phases of conventional nonionic liquid crystals, resembling those of lamellar phases formed by lyotropic surfactant-solvent systems.

The effect of structural heterogeneity upon the microviscosity of ionic liquids

The behaviour of two molecular rotors, one charged - 3,3'-diethylthiacarbocyanine iodide (Cy3) and one neutral - 8-[4-decyloxyphenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY-C10), have been studied in various ionic liquids. The fluorescent decay lifetime has been used to elucidate the structure of the immediate region around the rotor. The neutral BODIPY-C10 was found to prefer the non-polar alkyl chain environment, leading to two trends in the lifetime of the dye: one when it was fully partitioned into the non-polar domain, and one when it also sampled polar moieties. The positively charged Cy3 dye showed a complex relationship between the bulk viscosity of the ionic liquid and lifetime of the molecular rotor. This was attributed to a combination of polarity related spectral changes, changes in anion cages around the dye, and temperature dependent fluorescent lifetimes alongside the dependence of the rotor upon the viscosity.

Conformational design concepts for anions in ionic liquids

Interchangeable functional groups for imide ions are investigated computationally, new ILs with low/high viscosity are designed a priori and experimentally characterised.

Ether functionalisation, ion conformation and the optimisation of macroscopic properties in ionic liquids

Ionic liquids are an attractive material class due to their wide liquid range, intrinsic ionic conductivity, and high chemical as well as electrochemical stability. However, the widespread use of ionic liquids is hindered by significantly higher viscosities compared to conventional molecular solvents. In this work, we show how the transport properties of ionic liquids can be altered significantly, even for isostructural ions that have the same backbone. To this end, structure-property relationships have been determined for a set of 16 systematically varied representative ionic liquids. Variations in molecular structure include ammonium vs. phosphonium, ether vs. alkyl side chains, and rigid vs. flexible anions. Ab initio calculations are used to relate molecular structures to the thermal, structural and transport properties of the ionic liquids. We find that the differences in properties of ether and alkyl functionalised ionic liquids are primarily dependent on minimum energy geometries, with the conformational flexibility of ether side chains appearing to be of secondary importance. We also show unprecedented correlations between anion conformational flexibility and transport properties. Critically, increasing fluidity upon consecutive introduction of ether side chains and phosphonium centres into the cation is found to be dependent on whether the anion is flexible or rigid. We demonstrate that targeted design of functional groups based on structure-property relationships can yield ionic liquids of exceptionally high fluidity.

Effect of an external electric field on the dynamics and intramolecular structures of ions in an ionic liquid

Simulations of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in an external electric field have been performed using a Drude particle polarizable force field. The structure of the ions has been analyzed, with close attention paid to the configurations of the ions. The "charge arm" concept is used to explain certain changes of these configurations that would be difficult to rationalize otherwise, e.g., trans → cis isomerization of the bis(trifluoromethylsulfonyl)imide anion and extension of the alkyl chain of the cation. It has also been shown that the ions orient themselves so that their charge arms align with and stretch out along the field, and these effects occur at lower external electric field strengths than cause a change in the inherent diffusion of the ions. The dynamics of the system parallel and perpendicular to the field were analyzed, and it was found that the applied field affected the diffusion normal to the field. This is explained as a secondary effect of a change in the ion cage formed by the surrounding counterions of a given ion in the ionic liquid. The breakdown of the ion cages was rationalized by correlating changes to the inherent diffusion of the ions with other changes to the diffusion and bulk structure of the liquid, as well as considering the average forces on the ions compared to the force the ions would be expected to experience in an electric field. Parallel to the field, a drift was observed at every electric field studied. In electric fields with no changes to the ion cage structure, the relationship between the drift and electric field was found to be linear, becoming nonlinear as the ion cage structure breaks down.

Large-scale network dysfunction in vascular cognitive disorder supports connectional diaschisis in advanced arteriosclerosis

BACKGROUND AND PURPOSE

The interrelation of cognitive performance, cerebrovascular damage and brain functional connectivity (FC) in advanced arteriosclerosis remains unclear. Our aim was to investigate the associations between FC, white matter damage and cognitive impairment in carotid artery disease.

METHODS

Seventy-one participants with a recent cerebrovascular event and with written informed consent underwent resting-state functional magnetic resonance imaging and the Addenbrooke's Cognitive Examination - Revised (ACE-R). Network and inter-hemispheric FC metrics were compared between cognitively normal and impaired subjects, and interrelated with cognition. In order to explore the nature of FC changes, their associations with microstructural damage of related white matter tracts and cognitive performance were investigated, followed by mediation analysis.

RESULTS

Participants with global cognitive impairment showed reduced FC compared to the cognitively intact subjects within the central executive network (CEN), and between hemispheres. Patients with executive dysfunction had decreased CEN FC whilst patients with memory loss demonstrated low FC in both the CEN and the default mode network (DMN). Global performance correlated with connectivity metrics of the CEN hub with DMN nodes, and between hemispheres. Cingulum mean diffusivity (MD) was negatively correlated with ACE-R and CEN-DMN FC. The cingulum MD-cognition association was partially mediated by CEN-DMN FC.

CONCLUSIONS

Long-range functional disconnection of the CEN with DMN nodes is the main feature of cognitive impairment in elderly subjects with symptomatic carotid artery disease. Our findings provide further support for the connectional diaschisis concept of vascular cognitive disorder, and highlight a mediation role of functional disconnection to explain associations between microstructural white matter tract damage and cognitive impairment.

On the structural origin of free volume in 1-alkyl-3-methylimidazolium ionic liquid mixtures: a SAXS and 129Xe NMR study

Ionic liquid (IL) mixtures enable the design of fluids with finely tuned structural and physicochemical properties for myriad applications. In order to rationally develop and design IL mixtures with the desired properties, a thorough understanding of the structural origins of their physicochemical properties and the thermodynamics of mixing needs to be developed. To elucidate the structural origins of the excess molar volume within IL mixtures containing ions with different alkyl chain lengths, 3 IL mixtures containing 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ILs have been explored in a joint small angle X-ray scattering (SAXS) and 129Xe NMR study. The apolar domains of the IL mixtures were shown to possess similar dimensions to the largest alkyl chain of the mixture with the size evolution determined by whether the shorter alkyl chain was able to interact with the apolar domain. 129Xe NMR results illustrated that the origin of excess molar volume in these mixtures was due to fluctuations within these apolar domains arising from alkyl chain mismatch, with the formation of a greater number of smaller voids within the IL structure. These results indicate that free volume effects for these types of mixtures can be predicted from simple considerations of IL structure and that the structural basis for the formation of excess molar volume in these mixtures is substantially different to IL mixtures formed of different types of ions.

Ionic liquids: a brief history

There is no doubt that ionic liquids have become a major subject of study for modern chemistry. We have become used to ever more publications in the field each year, although there is some evidence that this is beginning to plateau at approximately 3500 papers each year. They have been the subject of several major reviews and books, dealing with different applications and aspects of their behaviours. In this article, I will show a little of how interest in ionic liquids grew and developed.

Design of task-specific fluorinated ionic liquids: nanosegregation versus hydrogen-bonding ability in aqueous solutions

Fluorinated ionic liquids rich-nanosegregated behaviour reduces the impact of the addition of water upon the ionic liquids's H-bond acceptance ability.

A closer look into deep eutectic solvents: exploring intermolecular interactions using solvatochromic probes

Kamlet Taft solvatochromic parameters, namely the hydrogen-bond acidity, hydrogen-bond basicity and dipolarity/polarizability and E_TN parameters of a wide range of DESs composed of cholinium chloride, dl-menthol and a quaternary ammonium salt ([N₄₄₄₄]Cl), and corresponding ILs are here presented.

Structure and lifetimes in ionic liquids and their mixtures

With the aid of molecular dynamics simulations, we study the structure and dynamics of different ionic liquid systems.

Evidence for the spontaneous formation of N-heterocyclic carbenes in imidazolium based ionic liquids

We present a study of the reactions of aldehydes in ionic liquids which gives evidence for the spontaneous formation of N-heterocyclic carbenes in ionic liquids based on 1,3-dialkyl substituted imidazolium cations from the lack of a deuterium isotope effect on the reaction of these ionic liquids with aldehydes.

Linking the structures, free volumes, and properties of ionic liquid mixtures

The formation of ionic liquid (IL) mixtures has been proposed as an approach to rationally fine-tune the physicochemical properties of ILs for a variety of applications. However, the effects of forming such mixtures on the resultant properties of the liquids are only beginning to be understood. Towards a more complete understanding of both the thermodynamics of mixing ILs and the effect of mixing these liquids on their structures and physicochemical properties, the spatial arrangement and free volume of IL mixtures containing the common [C₄C₁im]⁺ cation and different anions have been systematically explored using small angle X-ray scattering (SAXS), positron annihilation lifetime spectroscopy (PALS) and ¹²⁹Xe NMR techniques. Anion size has the greatest effect on the spatial arrangement of the ILs and their mixtures in terms of the size of the non-polar domains and inter-ion distances. It was found that differences in coulombic attraction between oppositely charged ions arising from the distribution of charge density amongst the atoms of the anion also significantly influences these inter-ion distances. PALS and ¹²⁹Xe NMR results pertaining to the free volume of these mixtures were found to strongly correlate with each other despite the vastly different timescales of these techniques. Furthermore, the excess free volumes calculated from each of these measurements were in excellent agreement with the excess volumes of mixing measured for the IL mixtures investigated. The correspondence of these techniques indicates that the static and dynamic free volume of these liquid mixtures are strongly linked. Consequently, fluxional processes such as hydrogen bonding do not significantly contribute to the free volumes of these liquids compared to the spatial arrangement of ions arising from their size, shape and coulombic attraction. Given the relationship between free volume and transport properties such as viscosity and conductivity, these results provide a link between the structures of IL mixtures, the thermodynamics of mixing and their physicochemical properties.

The impact of ionic liquids on the coordination of anions with solvatochromic copper complexes

Traditionally weakly associating anions demonstrate a stronger than expected level of coordinating ability within ILs.

Ionic liquids for metal extraction from chalcopyrite: solid, liquid and gas phase studies

Non-oxidative leaching in ionic liquids revealed novel dependencies between the evolution of gas species, passivation layers and metal extraction efficiency.

Effect of pretreatment severity on the cellulose and lignin isolated from Salix using ionoSolv pretreatment

The ionoSolv pretreatment is a new technique employing protic low-cost ionic liquids and has previously been applied to successfully fractionate switchgrass and the grass Miscanthus giganteus. This study investigates the effect of using the protic ionic liquid solution [N₂₂₂₀][HSO₄]_80% with two different acid/base ratios (1.02 and 0.98) at 120, 150 and 170 °C on the pretreatment outcome of the hardwood willow. The ionic liquid solution was able to fractionate willow, and a pulp and lignin fraction were recovered after treatment. The pretreatment success was determined via enzymatic hydrolysis of the pulp, which showed that the ionoSolv pretreatment was able to increase enzymatic glucose yields compared to untreated willow biomass. The pretreatment produced a cellulose-rich pulp with high hemicellulose and lignin removal. The pulp composition and glucose yield after saccharification were greatly influenced by the acidity of the ionic liquid solution, temperature and pretreatment time. The extracted lignin was analysed via 2-D HSQC NMR spectroscopy and GPC to investigate the changes in the lignin structure induced by the pretreatment severity. The lignin structure (in terms of inter-unit linkages and S/G ratio) and molecular weight varied significantly depending on the pretreatment conditions used.

Correction: Determination of Kamlet-Taft parameters for selected solvate ionic liquids

Correction for 'Determination of Kamlet-Taft parameters for selected solvate ionic liquids' by Daniel J. Eyckens et al., Phys. Chem. Chem. Phys., 2016, 18, 13153-13157.

Building an Inclusive Culture in the Chemistry Department at Imperial College

One of the main aims of any department is to appoint the very best chemists and to support them to reach their full potential. Success in this aim cannot look like a male to female ratio of professors of 20:1. In this Guest Editorial, T. Welton, Dean of the Faculty of Natural Sciences at Imperial College London, describes the processes introduced that led to the Chemistry Department at Imperial achieving a gold Athena SWAN award.

Doubly ionic hydrogen bond interactions within the choline chloride–urea deep eutectic solvent

Computational analysis indicates flexibility and diversity in the hydrogen bonding, but limited charge delocalisation, within the choline chloride–urea eutectic.

Azoniaspiro salts: towards bridging the gap between room-temperature ionic liquids and molten salts

Organic spirocyclic tetraalkylammonium chloride salts exhibit enhanced thermal stabilities relative to traditional dialkylimidazolium ionic liquid analogues.

Determination of Kamlet–Taft parameters for selected solvate ionic liquids

The normalised polarity ENT and Kamlet–Taft parameters of recently described solvate ionic liquids, composed of lithium bis(trifluoromethyl)sulfonimide (LiTFSI) in tri- (G3TFSI) or tetraglyme (G4TFSI) have been determined and compared to the parent glyme (G3 and G4).

Solubility of alkali metal halides in the ionic liquid [C4C1im][OTf]

Experimental solubility data of alkali halides in [C₄C₁im][OTf] is fitted to a variety of models and explored using DFT calculations.

A structural investigation of ionic liquid mixtures

The role of hydrogen bonding, π⁺–π⁺ stacking and anion–π⁺ interactions on the structure of ionic liquid mixtures has been elucidated through a combined theoretical and experimental approach.

Solvents and sustainable chemistry

Solvents are widely recognized to be of great environmental concern. The reduction of their use is one of the most important aims of green chemistry. In addition to this, the appropriate selection of solvent for a process can greatly improve the sustainability of a chemical production process. There has also been extensive research into the application of so-called green solvents, such as ionic liquids and supercritical fluids. However, most examples of solvent technologies that give improved sustainability come from the application of well-established solvents. It is also apparent that the successful implementation of environmentally sustainable processes must be accompanied by improvements in commercial performance.

On the origin of ionicity in ionic liquids. Ion pairing versus charge transfer

In this paper we show by using static DFT calculations and classical molecular dynamics simulations that the charge transfer between ionic liquid ions plays a major role in the observed discrepancies between the overall mobility of the ions and the observed conductivities of the corresponding ionic liquids, while it also directly suppresses the association of oppositely charged ions, thus the ion pairing. Accordingly, in electrochemical applications of these materials it is important to consider this reduction of the total charges on the ions, which can greatly affect the performance of the given process or device in which the ionic liquid is used. By slightly shifting from the salt-like to a molecular liquid-like system via the decreased charges, the charge transfer also fluidizes the ionic liquid. We believe that this vital information on the molecular level structure of ionic liquids offers a better understanding of these materials, and allows us to improve the a priori design of ionic liquids for any given purpose.

Hydrogen bonding and π–π interactions in imidazolium-chloride ionic liquid clusters

The importance of 1° and 2° hydrogen-bonding and anion–π⁺ interactions for ionic liquid structuring.

A physicochemical investigation of ionic liquid mixtures

Ionic liquids have earned the reputation of being 'designer solvents' due to the wide range of accessible properties and the degree of fine-tuning afforded by varying the constituent ions. Mixtures of ionic liquids offer the opportunity for further fine-tuning of properties. A broad selection of common ionic liquid cations and anions are employed to create a sample of binary and reciprocal binary ionic liquid mixtures, which are analysed and described in this paper. Physical properties such as the conductivity, viscosity, density and phase behaviour (glass transition temperatures) are examined. In addition, thermal stabilities of the mixtures are evaluated. The physical properties examined for these formulations are found to generally adhere remarkably closely to ideal mixing laws, with a few consistent exceptions, allowing for the facile prediction and control of properties of ionic liquid mixtures.