Tetrabutylphosphonium Cation Research Articles

Model study on potential removal of toxic Se(VI) by organically modified montmorillonite

The theoretical DFT-D3 approach was used in the model study of the immobilisation of the toxic selenate oxyanion, with montmorillonite clay modified by poly(2-methyl-2-oxazoline) polymer represented by a pentamer unit, and tetrabutylphosphonium cation. The calculated basal spacing for Se-POx-Mt and Se-TBP-Mt models provided similar results differing by 0.2 Å (18.3 Å for Se-POx-Mt and/or 18.5 Å for Se-TBP-Mt, respectively). The calculated intercalation energy, ΔEint, showed a suitability of both modified Mts for trapping of (SeO4)2– oxyanions favouring the Se-TBP-Mt (–210.7 kJ/mol) system compared to Se-POx-Mt (–124.5 kJ/mol). The main interactions in both models were classified as hydrogen bonds of weak (CH···O) and moderate-to-strong (OH···O) strength. The calculated total and projected vibrational density of states of the Se-POx-Mt and Se‑TBP‑Mt models, obtained from the ab initio molecular dynamics simulations, were used for distinct identification of vibrational modes of the intercalated (SeO4)2– ion in the interlayer space of both models.

Development of Edaravone Ionic Liquids and Their Application for the Treatment of Cerebral Ischemia/Reperfusion Injury.

Preparation of the ionic liquid (IL) form of active pharmaceutical ingredients (APIs), termed API-IL, has attracted attention because it can improve upon certain disadvantages of APIs, such as poor water solubility and low stability. Edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) is a clinically approved cerebroprotective agent against ischemic stroke and amyotrophic lateral sclerosis, while new formulations that enable improvement of its physicochemical properties and biodistribution are desired. Herein, we report a newly developed API-IL of edaravone (edaravone-IL), in which edaravone is used as an anionic molecule. We investigated the physicochemical properties of edaravone-IL and its therapeutic effect against cerebral ischemia/reperfusion (I/R) injury, a secondary injury after an ischemic stroke. Among the cationic molecules used for edaravone-IL preparation, the IL prepared with tetrabutylphosphonium cation existed as a liquid at room temperature, and significantly increased the water solubility of edaravone without decreasing its antioxidative activity. Importantly, edaravone-IL formed negatively charged nanoparticles upon suspension in water. Intravenous administration of edaravone-IL showed significantly higher blood circulation time and lower distribution in the kidney compared with edaravone solution. Moreover, edaravone-IL significantly suppressed brain cell damage and motor functional deficits in model rats of cerebral I/R injury and showed comparable cerebroprotective effect to edaravone. Taken together, these results suggest that edaravone-IL could be a new form of edaravone with superior physicochemical properties and could be useful for the treatment of cerebral I/R injury.

Anion Effect on Forward Osmosis Performance of Tetrabutylphosphonium-Based Draw Solute Having a Lower Critical Solution Temperature

The applicability of ionic liquids (ILs) as the draw solute in a forward osmosis (FO) system was investigated through a study on the effect of the structural change of the anion on the FO performance. This study evaluated ILs composed of tetrabutylphosphonium cation ([P4444]+) and benzenesulfonate anion ([BS]-), para-position alkyl-substituted benzenesulfonate anions (p-methylbenzenesulfonate ([MBS]-) and p-ethylbenzenesulfonate ([EBS-]), and methanesulfonate anion ([MS]-). The analysis of the thermo-responsive properties suggested that the [P4444][MBS] and [P4444][EBS] ILs have lower critical solution temperatures (LCSTs), which play a beneficial role in terms of the reusability of the draw solute from the diluted draw solutions after the water permeation process. At 20 wt% of an aqueous solution, the LCSTs of [P4444][MBS] and [P4444][EBS] were approximately 36 °C and 25 °C, respectively. The water flux and reverse solute flux of the [P4444][MBS] aqueous solution with higher osmolality than [P4444][EBS] were 7.36 LMH and 5.89 gMH in the active-layer facing the draw solution (AL-DS) mode at osmotic pressure of 25 atm (20 wt% solution), respectively. These results indicate that the [P4444]+-based ionic structured materials with LCST are practically advantageous for application as draw solutes.

(Digital Presentation) Physicochemical Characterization of Sulfonate-Based Phosphonium Ionic Liquids

Ionic liquids (ILs) have unique physicochemical properties such as favorable solubility of organic and inorganic compounds, relatively high ionic conductivity, no measurable vapor pressure, high thermal stability, low flammability, etc. ILs are also promising liquid materials available for various applications because their function can be easily controlled by changing the combination of cations and anions and by introducing substituents. Although many kinds of ILs have already been investigated, phosphonium cation based ILs have rarely been proposed. We have previously designed and synthesized the phosphonium ILs together with typical sulfonylamide-based anions such as bis(trifluoromethylsulfonyl)amide and bis(fluorosulfonyl)amide anions.1,2) On the other hand, interests in phosphonium ILs consisting of the other anions is increasing for diverse applications. In this work, we design and prepare the ILs based on tetrabutylphosphonium cation (P4444 +) together with various sulfonate-based anions (Fig. 1), characterizing their physicochemical properties as a new family of ILs. The phosphonium IL was prepared by an aqueous neutralization reaction of tetrabutylphosphonium hydroxide with the stoichiometric amounts of various sulfonic acids. The obtained phosphonium ILs were isolated by water evaporation, and were dried in vacuo for at least 1 day. The physicochemical properties of ILs, e.g. density, viscosity, conductivity (ac impedance method) and thermal decomposition temperature (thermogravimetric analysis), were measured under argon atmosphere.The phosphonium salts based on unsubstituted sulfonate anions such as SO3CH3, SO3CH2CH3 and SO3(CH2)2CH3 were white crystalline solids at room temperature, whereas both amino- and hydroxy- substituted sulfonate salts were viscous liquids at room temperature. All phosphonium salts obtained were hydrophilic. Table 1 summarizes the physicochemical properties of phosphonium ILs based on amino- and hydroxy-substituted sulfonate anions. These phosphonium ILs exhibited considerably high viscosities when compared to the previously published viscosity value of P4444-lactate IL (415 mPa s at 25 °C)3), which suggests that the electrostatic interaction between P4444 cation and the sulfonate anions is much stronger than those in the case of carboxylate-based phosphonium ILs. It should be noted that P4444-SO3(CH2)3NH2 obviously indicated not only the highest density but also the highest viscosity and the lowest conductivity, which might be due to the fact that the IL has the largest anion to give a significant van der Waals interaction. Figure 1

Synthesis of metal sulfides via ionic liquid-mediated assembly strategy and their photocatalytic degradation of dyes in water

Metal sulfide nanomaterials have been extensively studied due to their attractive applications in various fields. Although various synthetic approaches have been developed, it remains a great challenge to establish a universal and green method for fabricating metal sulfide nanomaterials with tailorable structures (e.g., shapes and sizes). Here we report a ionothermal strategy to synthesize metal sulfide particles with diverse components and controllable architectures. Transition metal sulfide (TMS) nanostructures such as hierarchical Cu7S4 microspheres, ZnS and CdS nanoparticles, PdS polyhedrons, and Bi2S3 nanorods have been successfully synthesized with metal salts and amino acid-based ionic liquids, [TBP][Cys] (tetrabutyl-phosphonium cation and L-cysteine anion). We unveiled the structures, optical properties, and formation mechanism of TMSs. As a typical application of the as-prepared TMSs, the hierarchically structured Cu7S4 nanocrystals enable high-performance photocatalysis degradation of dyes (e.g., methylene blue) in water. Our study not only provides new insights into the ionic liquid-mediated assembly strategy but also achieves an efficient catalyst for photocatalytic degradation.

Impact of alkyl chain length of temperature-responsive ionic liquids on the aggregation behavior in ionic liquid microemulsions

As is known to all, the alkyl chain is a perfect tool to regulate the microstructure of ionic liquid(IL) microemulsion directly. However, it is still a great challenge to design a new type of temperature-responsive IL with different alkyl chain length to construct the stimulus microemulsion. In this study, a new class of temperature-responsive IL microemulsions was built for the first time, which is composed by [P444,n]Br (n = 8,10,12,14,16,18), [C12mim]Br and H2O. The phase diagram and dynamic light scattering analysis revealed that the size of IL microemulsion droplets can be effective regulated by the alkyl chain length of temperature-responsive IL, so as to gain a series of organized structures. The molecular dynamic(MD) simulations were performed by a series of [P444,n]Br/[C12mim]Br/H2O mixture systems to illustrate this unique aggregation behavior of droplet. Simulation results are presented and discussed via the data of interaction energies, aggregation numbers, radial distribution functions (RDFs) and coordination numbers. The results indicate that the aggregation sizes of [C12mim]+ become smaller with the increase of alkyl chain length of tetrabutylphosphonium cation, which agrees well with experimental results. This is because that the weakened interaction of temperature-responsive IL and water molecules by the long alkyl chain could reduce the electrostatic repulsion of the polarity groups of the surfactants, which may decrease the size of the aggregate. These finding can help in further understanding the structure variation law of temperature-responsive IL microemulsions and thereby improve microemulsion theory.

Bifunctional ionic liquid and conducting ceramic co-assisted solid polymer electrolyte membrane for quasi-solid-state lithium metal batteries

Development of solid polymer electrolytes (SPEs) with high thermal and mechanical stability and fast ion conductivity is the key for high-performance lithium metal batteries (LMBs) with high safety. In this work, a flexible poly-(ethylene oxide) (PEO)-lithium bis(trifluoromethanesulfonyl)imide) (LiTFSI) SPE assisted with a bifunctional ionic liquid (IL) of tetrabutylphosphonium 2-hydroxypyridine (TBPHP) as well as a garnet-type fast-ion conducting ceramic of Li6.4La3Zr1.4Ta0.6O12 (LLZTO) was fabricated via a solvent-free procedure and applied for the LMBs. It is found that the tetrabutylphosphonium cation (TBP+) and 2-hydroxypyridine anion (HP−) of IL effectively tuned the crystallinity of PEO and enhanced lithium ion (Li+) transference, respectively, and the TBPHP and LLZTO played a synergistic role in improving the performance of SPEs. Meanwhile, the density functional theory (DFT) study was performed to understand the interaction between TBPHP and LiTFSI. As a result, the obtained PEO8-LiTFSI-TBPHP-12.5% LLZTO composite SPE possessed a high ionic conductivity of 9.39 × 10−4 S cm−1 at 50 °C and a wide electrochemical stability window (more than 5 V) with significantly promoted uniform Li plating/stripping properties. The quasi-solid-state-LMBs assembled with LiFePO4 cathode also rendered excellent cycling stability with a high discharge capacity above 150 mA h·g−1 even after 100 cycles at 0.2 C and 50 °C. Besides, the fabricated flexible pouch cell showed excellent performance. It is expected that such a bifunctional ionic liquid and conducting ceramic co-assisted polymer composite could be a promising solid electrolyte for the next-generation of safe LMBs.

Density functional theory study of the stability of the tetrabutylphosphonium and tetrabutylammonium montmorillonites

AbstractThe stability of organoclays prepared from smectites and organic cations depends on the type of used cation, among other factors. This study provides a prediction of the structure, stability and dynamic properties of organoclays based on montmorillonite (Mt) intercalated with two types of organic cations – tetrabutylammonium (TBA) and tetrabutylphosphonium (TBP) – using first-principle density functional theory. The results obtained from simulations were also used in the interpretation of the experimental infrared spectrum of the TBP-Mt organoclay. Analysis of interatomic distances showed that weak C–O···H hydrogen bonds were important in the stabilization of both TBA- and TBP-Mt models, with slightly stronger hydrogen bonds for the TBP cation. Calculated intercalation and adsorption reaction energies (ΔEint//ΔEads*/ΔEads**) confirmed that TBP-Mt structures (–72.4//–32.8/–53.8 kJ/mol) were considerably more stable than TBA-Mt structures (–56.7//–22.6/–37.4 kJ/mol). The stronger interactions of the alkyl chains of the TBP cation with Mt basal surfaces in comparison to those of the TBA cation were also correlated with the positions of the calculated bands of the C–H stretching vibrations.

Stability of Tetrabutylphosphonium Beidellite Organoclay

Organoclays originating by interaction of clays with organic cations/molecules are important in industrial processes for their physicochemical properties. The beidellite (Bd) mineral is an interesting material, e.g., as a potential sorbent of waste and pesticides. For this reason, its behavior at the atomic scale is of great interest. The DFT method is used to investigate the stability of Bd intercalated with a tetrabutylphosphonium cation (TBP). The interlayer distances (d001) of the proposed models agree well with the experimental values. The ab initio molecular dynamics (AIMD) is successfully employed in a detailed explanation of the experimental FTIR spectrum of the TBP-Bd which has a complicated structure with overlapped bands. Detailed analysis of the present hydrogen bonds and calculated intercalation energies shows that the TBP-Bd is a highly stable intercalate. Its stability decreases with growing amount of water, but the high stability is still preserved (−87.5 kJ mol–1).

Ionic Liquid Anion Controlled Nanoscale Gold Morphology Grown at a Liquid Interface

Two different ionic liquids comprising the tetrabutylphosphonium cation ([P4444]) paired with the strongly coordinating anions 6-aminocaproate ([6-AC]) or taurinate ([tau]) were prepared and employed in an aqueous/organic liquid bilayer system to generate nanoscale gold by Au(OH)4- photoreduction. Generally, as the concentration of ionic liquid in the organic phase was increased, the resulting quasi-spherical gold nanoparticles were smaller in size and presented less aggregation, leading to marked increases in the catalytic efficiency for 4-nitrophenol reduction using borohydride. The diffusion of the ionic liquids across the liquid/liquid interface was also investigated, revealing partition coefficients of 6.0 and 7.6 for [P4444][6-AC] and [P4444][tau], respectively. Control studies elucidated that biphasic interfacial reduction was necessary to achieve stable nanoparticles possessing high catalytic activity. When the ionic liquid anion was instead replaced by the weakly coordinating bis(trifluoromethylsulfonyl)imide ([Tf2N]), photoreduction of Au(OH)4- led to holey, wavy gold nanowires instead of spherical nanoparticles, indicating the dramatic morphological control exerted by the coordination strength of the ionic liquid anion. This strategy is straightforward and simple and opens up a number of intriguing avenues for controllably preparing plasmonic colloids for a range of applications from catalysis to optical sensing.

Good's Buffer Ionic Liquids as Relevant Phase-Forming Components of Self-Buffered Aqueous Biphasic Systems.

A series of new self-buffering ionic liquids (ILs) based on Good's buffers (GBs) anions and the tetrabutylphosphonium cation ([P4444]+) was here synthesized and characterized. The self-buffering behaviour of the GB-ILs was confirmed by measuring their protonation constants by potentiometry. Further, their ability to form aqueous biphasic systems with the biodegradable potassium citrate salt was evaluated, and further investigated for the extraction of proteins, using bovine serum albumin (BSA) as a model protein. If these ionic structures display self-buffering characteristics as well as a low toxicity towards the luminescent bacteria Vibrio fischeri, they were additionally found to be highly effective in the formation of ABS and in the extraction of BSA - extraction efficiencies of 100% to the IL-rich phase obtained in a single-step. The BSA secondary structure in the aqueous IL-rich solutions was evaluated through infrared spectroscopic studies revealing the protein-friendly nature of the synthesized ILs. Dynamic light scattering (DLS), "COnductor-like Screening MOdel for Real Solvents" (COSMO-RS), and molecular docking studies were finally carried out to better understand the main driving forces of the extraction process. The results suggest that van der Waals and hydrogen-bonding interactions are important driving forces of the protein migration towards the GB-IL-rich phase, while the molecular docking investigations demonstrated a stabilizing effect of the studied ILs over the protein.

Physical and Electrochemical Properties of Ionic Liquids Based on Quaternary Phosphonium Cations and Carboxylate Anions as Electrolytes

A new group of ionic liquids based on tetraethylphosphonium and tetrabutylphosphonium cations together with several carboxylate anions is proposed and presented in this report. In obtained ionic liquids, tetrabutylphosphonium formate and tetrabutyl-phosphonium lactate became room temperature ionic liquids. It was found that the phosphonium ionic liquids showed the typical VTF-type convex curve behaviors. The phosphonium ionic liquids also had a high cathodic stability similar to those of the TFSA- and FSA-anion based phosphonium ionic liquids. On the other hand, relatively low anodic potential window was observed. The thermal stability of the phosphonium ionic liquids showed higher thermal stabilities than those of the corresponding ammonium ionic liquids.

Automated cytochrome c oxidase bioassay developed for ionic liquids’ toxicity assessment

A fully automated cytochrome c oxidase assay resorting to sequential injection analysis (SIA) was developed for the first time and implemented to evaluate potential toxic compounds. The bioassay was validated by evaluation of 15 ionic liquids (ILs) with distinct cationic head groups, alkyl side chains and anions. The assay was based on cytochrome c oxidase activity reduction in presence of tested compounds and quantification of inhibitor concentration required to cause 50% of enzyme activity inhibition (EC50). The obtained results demonstrated that enzyme activity was considerably inhibited by BF4 anion and ILs incorporating non-aromatic pyrrolidinium and tetrabutylphosphonium cation cores. Emim [Ac] and chol [Ac], on contrary, presented the higher EC50 values among the ILs tested.The developed automated SIA methodology is a simple and robust high-throughput screening bioassay and exhibited good repeatability in all the tested conditions (rsd<3.7%, n=10). Therefore, it is expected that due to its simplicity and low cost, the developed approach can be used as alternative to traditional screening assays for evaluation of ILs toxicity and identification of possible toxicophore structures. Additionally, the results presented in this study provide further information about ILs toxicity.

Porous Solids Impregnated with Task-Specific Ionic Liquids as Composite Sorbents

This work examines six task-specific ionic liquids (TSILs), comprised of the taurinate anion paired with five tetraalkylammonium cations (where alkyl = methyl, ethyl, propyl, butyl, and hexyl) and a tetrabutylphosphonium cation, impregnated in ordered mesoporous silica, SBA-15. The composites showed significantly increased CO2 uptakes relative to the parent SBA-15 materials. The surface area of these materials varies from approximately 5 to 1000 m2/g depending on the amount of IL loaded into the silica pores. The presence of n-hexyl side chains on the TSIL significantly reduces water loading, indicating that judicious IL selection may provide a means of controlling water uptake. After exposure to water vapor, three of the six cation-taurinate composites displayed an increase in CO2 capacity. X-ray diffraction data of the composite of tetramethylammonium taurinate and SBA-15 shows that the ionic liquid is crystalline inside the pores of the silica. Isotherms are measured at several different temperatures and the results show that storage at ambient humidity significantly impacts the capacity of these materials. By comparison, the TSILs supported on an amorphous porous support, BPL activated carbon, showed no increase in CO2 adsorption capacity. The results provide physical insight into the synthesis, structure, porosity, and sorption capacity of composites of adsorbents and ionic liquids that need to be considered prior to application.

Water solubility and dynamics of CO2 capture ionic liquids having aprotic heterocyclic anions

A computational study was carried out to investigate the solubility and dynamics of water in five different ionic liquids capable of chemically reacting with CO2. All the ionic liquids have a common tetrabutylphosphonium cation paired with five different aprotic heterocyclic anions. These ionic liquids have properties that make them attractive candidates for use in CO2 capture applications, but the impact of water on their properties is unknown. The simulations show that the ionic liquid having a 2-cyanopyrrolide anion is the most hydrophobic of all the liquids studied, but that upon reaction with CO2 it becomes much more hydrophilic. The other ionic liquids investigated show little change in water solubility upon reaction with CO2. Henry's Law constants, enthalpies and entropies of water absorption, liquid structure, hydrogen bonding and self-diffusivities were computed and found to correlate well with the strength of interaction between water and the anions and the relative hydrophobicity of the liquids.

Tetraalkylphosphonium Decavanadates: Synthesis, Structures, and Solution Properties

AbstractA novel intercluster compound, [(n‐C4H9)4P]3[H3V10O28] (IL01‐V10), constructed from the tetrabutylphosphonium cation and decavanadate, has been synthesized and unequivocally characterized by elemental analysis, FTIR spectroscopy, mass spectrometry, X‐ray crystallography, and solution 1H, 13C, 31P{1H}, and 51V NMR spectroscopy. Compound IL01‐V10 was formed by ionic interaction between the phosphonium cation and the decavanadate anion. Cryospray high‐resolution mass spectrometry revealed the [H3V10O28]3– cluster remains intact in solution. Three further phosphonium polyoxovanadates were synthesized and characterized by the same techniques as used for IL01‐V10.

Ionic liquids containing fluorinated β-diketonate anions: synthesis, characterization and potential applications

Ionic liquids (ILs) sporting anions comprising the β-diketonate functionality were prepared, fully characterized via ESI-MS, FTIR, and 1H/13C NMR, and tested in multiple scenarios. We present eight new salts based on four different β-diketonate anions, each coupled with the choline or tetrabutylphosphonium cation. The thermal stabilities and transitions of these β-diketonate salts were explored using DSC and TGA. Seven of the compounds displayed melting points at or below 100 °C and hence formally qualify as ILs. The inherent binding capability of the β-diketonate moiety made possible a task-specific IL amenable to lanthanide recognition. For example, coordination with Eu3+ was accompanied by a striking three order-of-magnitude intensification of luminescence (‘turn-on’). Additionally, these ILs display prominent acidochromism. That is, the intense visible color of β-diketonate ILs is modulated in the presence of an acid source, permitting the visual transduction of local pH changes. Utility for carbon capture was also considered, however, these ILs were essentially incapable of binding CO2. Computational studies were better able to elucidate this behavior, revealing that the association of CO2 with the β-diketonate anion is thermodynamically unfavored and sterically hindered. Despite this negative result for CO2 capture, these newly introduced β-diketonate ILs show interesting and useful physicochemical properties applicable to a number of future applications.

Introduction of hydrophilic groups onto the ortho-position of benzoate anions induced phase separation of the corresponding ionic liquids with water

Ionic liquids (ILs) composed of tetrabutylphosphonium cations and benzoate anion derivatives with hydrophilic hydroxyl or carboxyl groups introduced onto the ortho-position were found to be less hydrophilic and showed phase separation with water, whereas unmodified benzoate-type IL was freely miscible with water.

Amino Acid Ionic Liquids

The preparation of ionic liquids derived from amino acids, and their properties, are outlined. Since amino acids have both a carboxylic acid residue and an amino group in a single molecule, they can be used as either anions or cations. These groups are also useful in their ability to introduce functional group(s). Twenty different natural amino acids were used as anions, to couple with the 1-ethyl-3-methylimidazolium cation. The salts obtained were all liquid at room temperature. The properties of the resulting ionic liquids (AAILs) depend on the side groups of the amino acids involved. These AAILs, composed of an amino acid with some functional groups such as a hydrogen bonding group, a charged group, or an aromatic ring, had an increased glass transition (or melting) temperature and/or higher viscosity as a result of additional interactions among the ions. Viscosity is reduced and the decomposition temperature of imidazolium-type salts is improved by using the tetrabutylphosphonium cation. The chirality of AAILs was maintained even upon heating to 150 degrees C after acetylation of the free amino group. The amino group was also modified to introduce a strong acid group so as to form hydrophobic and chiral ionic liquids. Unique phase behavior of the resulting hydrophobic ionic liquids and water mixture is found; the mixture is clearly phase separated at room temperature, but the solubility of water in this IL increases upon cooling, to give a homogeneous solution. This phase change is reversible, and separation occurs again by raising the temperature a few degrees. It is extraordinary for an IL/water mixture to display such behavior with a lower critical solution temperature. Some likely applications are proposed for these amino acid derived ionic liquids.

Liquids intermediate between “molecular” and “ionic” liquids: Liquid Ion Pairs?

Ionic liquids comprised of tetradecyltrihexyl- and tetrabutyl-phosphonium cations paired with chloride or sulfonyl amide anions exhibit properties that reflect strong ion association, including comparatively low viscosity as well as a degree of volatility, and hence exemplify an interesting intermediate state between true ionic and true molecular liquids.