Recent advances in the use of ionic liquids as solvents for protein-based materials and chemistry

Proteins are a diverse class of molecules that can act as catalysts and structural components. Interest in their interactions with ionic solvents is on the increase due to the tuneable possibilities for non-aqueous biocatalysis, improved thermostability of biomaterials, and possible roles in medicine, such as drug delivery and use as cell-growth scaffolds. We summarise here the recent examples of these exciting new aspects of protein-ionic solvent interactions, highlighting future directions.     

A high-swelling reagent scaffold suitable for use in aqueous and organic solvents

A polymeric scaffold with excellent swelling properties in organic and aqueous environments is highly desirable for the medicinal chemist. Here, we demonstrate that a cross-linked polyacrylamide hydrogel that displays large swelling properties in both organic solvent and water can serve as a scaffold for the photosensitizer hematoporphyrin. Upon exposure to light, the resulting resin efficiently generates singlet oxygen which can then react with appropriate substrates.     

On the use of azo dyes for the spectrophotometric determination of uranium and thorium in mixed solvents

Summary Solochrome Black 6 BN in an acetate buffered medium containing methanol reacts with U(IV) to give a blue complex which permits photometric determination with 5g U/ml to 100g U/ml.In the presence of zinc acetate, uranyl ion also may be spectrophotometrically determined by means of the same dye. From 2g U/ml to 40g U/ml may be determined with a relative error of less than ± 0.05.

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Zusammenfassung Es werden zwei Methoden zur spektrophotometrischen Bestimmung von Uran mittels Solochromschwarz 6 BN beschrieben. Dieser Farbstoff bildet mit U(IV) in acetatgepuffertem, methanolhältigem Medium einen blaugefärbten Komplex, der die Bestimmung von 5 bis 100g U/ml erlaubt.Mit demselben Farbstoff lassen sich auch 2 bis 40g U/ml in Lösungen von Uranylchlorid bestimmen.

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Résumé Le noir solochrome 6 BN en milieu tampon acétique contenant du méthanol réagit avec U-IV en donnant un complexe bleu qui permet le dosage photométrique de 5 g U/ml à 100 g U/ml.En présence d'acétate de zinc, on peut aussi doser l'ion uranyle par spectrophotométrie avec le même colorant. On peut doser de 2 g U/ml à 40 g U/ml avec une erreur relative inférieure à ± 0,05.

     

Crosslinked integrally skinned asymmetric polyaniline membranes for use in organic solvents

Solvent stable integrally skinned asymmetric nanofiltration membranes were prepared from polyaniline. These membranes were made by phase inversion and then crosslinked using two different chemical crosslinkers, α,α′-dichloro-p-xylene and glutaraldehyde. The resultant membranes were found to be stable in various organic solvents including acetone, methanol, ethyl acetate, tetrahydrofuran and N,N-dimethyl formamide. Nanofiltration experiments carried out in acetone and dimethyl formamide showed that the membranes gave stable permeate fluxes and good separation performances in the nanofiltration range. Molecular weight cut-off (MWCO) of the membranes was found to be between 150 and 250 g mol⁻¹. These membranes were also found to be stable for operations at elevated temperatures up to 70 °C and possibly higher. Furthermore, no fillers or preservative agents are required to maintain the membranes in a dry state thereby increasing the ease of handling.     

Hazard analysis of tetrahydrofuran and dimethylsulfoxide mixture solvents for efficient use in reaction processes

Organic solvents are often used in mixture solvent systems to optimize synthetic reactions. However, they may also produce unexpected effects, some of which may be hazardous and cause a runaway reaction and/or lead to an accident. Thus, the proper accident scenarios and thermal risk assessment models are needed to use mixture solvents more safely and efficiently. For chemical process safety, Stoessel suggests the systematic assessment of accident scenarios. However, if scenarios are changed by the properties of mixture solvents, Stoessel’s concept does not cover them. Our previous study evaluated characteristic scenarios of mixture solvents based on Stoessel’s model. In this study, as a characteristic scenario pattern, we focused on the energy release of the solvent and the material derived from degraded solvent and investigated them experimentally using tetrahydrofuran (THF) and dimethylsulfoxide (DMSO) as a representative mixture solvent. From hazard and scenario identification of THF and DMSO, we assumed that THF peroxide and DMSO play roles in energy release. THF containing peroxide and DMSO were mixed, and thermal analysis and chemical composition analysis were performed. Our results indicated that DMSO promotes the decomposition of THF peroxide, and the decomposition temperature of DMSO decreases upon mixing with degraded THF. Therefore, we verified the scenario pattern of energy release of solvent and the material derived from degraded solvent.     

Ion-pair extractions by the use of planar and non-planar extracting solvents

The effect of extracting solvent was studied on the ion-pair extraction reactions with a special interest in the effect of molecular shape (planar or non-planar) of the solvent. The following two reactions were investigated: (HNN)_o + (Q⁺)_W (Q·NN)_o + (H⁺)_W (Extraction I); (Q-ClO₄)_o + (Pi^–)_w (Q·Pi)_o + (ClO ₄ ^– )_w (Extraction II), where HNN, NN^–, Pi^–, and Q⁺ represent 1-nitro-2-naphthol, its base form (1-nitro-2-naphtholate), picrate, and a cationic species, respectively. Above extraction equilibria were confirmed to hold in cases of various extracting solvents including planar solvents (1-chloronaphthalene, etc.) and non-planar solvents (1,2-dichloroethane, chloroform). An approximately linear relationship was found to exist between the extraction constants of Extraction I (logK _ex ^I ) and the Kosower's Z-value of extracting solvents. It was also found that the compatibility between the molecular shape of the ion-pair complexes and that of the extracting solvents affected the extractability to a considerable extent.     

Investigation of the contact charge transfer absorption of organic solvents with oxygen for use in oxygen determination

The contact charge transfer (CCT) absorption spectra of dimethylsulphoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), ethanol, methanol, water, benzene (Bz), N,N'-diethylaniline (DEA), N,N'-dimethyl-p-toluidine (DMT) and N,N'-diethyl-p-toluidine with molecular oxygen have been investigated. These solvents form strong ultraviolet/visible CCT absorption spectra with intensities that are related to the partial pressure of the applied oxygen. DMSO, DMF, DMA, Bz, DEA and DMT are shown to form 1:1 molecular contact complexes with molecular oxygen. A simple oxygen sensing system is described using CCT absorption spectroscopy of DMT at a wavelength of 400 nm, with a gas flow rate of 60 cm(3) min(-1) through the solvent in a cuvette with a pathlength of 1 cm. Inexpensive plastic fibres are used to relay the light from a xenon lamp source to the cuvette and back to a photo-detector. The response of the sensing system to changes in oxygen concentration is reversible, non-linear and in good agreement with the Beer-Lambert law. The most sensitive response region is from 0 to 20% O(2) with a change in signal level of about 35%. The solvent used shows no deterioration in performance over a long period and can be used to determine gaseous oxygen concentrations from 0 to 100%. It does not respond to carbon dioxide.     

The use of deuterated solvents in high-performance liquid chromatography-Fourier transform infrared spectrometry

Summary Deuterated compounds have been used as mobile phases for microcolumn high-performance liquid chromatography (HPLC) employing flow-cell Fourier transform infrared spectroscopy for detection. Separations were carried out on adsorption, reversed-phase, non-aqueous size-exclusion and aqueous size-exclusion chromatographic columns. Due to the IR transparency of deuterated compounds in a C–H stretching region they represent nearly ideal eluents in terms of universal detection. In addition, due to the shift in the absorption wavenumber following deuteration, deuterated solvents allow FTIR detection of solutes in other regions, where otherwise it would be prohibited, or sensitivity sacrified by interfering solvent absorption.     

Acid decomposition of difficultly soluble potassium ores with the use of organic solvents

The dissolution of polyhalite ore in a hydrochloric acid solution at temperatures 50–100°C and salting out of potassium and magnesium sulfates from the obtained solutions with the use of selective organic solvents was studied. The effect exerted by temperature and solvent type on the extraction process was determined. A principal scheme of the ore processing was suggested.     

Design and synthesis of bistereogenic chiral ionic liquids and their use as solvents for asymmetric Baylis-Hillman reactions

Three novel chiral ionic liquids (CILs) containing two chiral centers in the side chain bonded to the 2-position of the imidazolium cation and different anions have been synthesized, characterized and used as chiral solvents for asymmetric Baylis-Hillman (BH) reactions; good yields and fair enantioselectivities were obtained.     

Determination and correlation of the solubility for diosgenin in alcohol solvents

Using a laser monitoring technique, the solubility of diosgenin in ethanol, 1-propanol, 1-butanol, isobutyl alcohol, tert-butanol, 1-pentanol, and iso-octyl alcohol was measured over the temperature range from (290.15 to 330.15) K at atmospheric pressure. Its corresponding (solid + liquid) equilibrium data will provide essential support for industrial design and further theoretical studies. From the experimental results, the solubility of diosgenin in ethanol, 1-propanol, 1-butanol, isobutyl alcohol, tert-butanol, 1-pentanol, and iso-octyl alcohol was found to increase with increasing temperature and decrease with the increase of the polarity of the alcohols solvents. The Apelblat equation, the ideal model and the λh equation were used to correlate the solubility values. The results showed that the three models mentioned above agreed well with the experimental data.     

Potential use of deep eutectic solvents to facilitate lignocellulosic biomass utilization and conversion

High reliance on crude oil for energy consumption results in the urgent need to explore and develop alternative renewable sources. One of the most promising routes is the transformation of biomass into biofuels and chemicals. The introduction of deep eutectic solvents in 2004 received a considerable amount of attention across different research fields, particularly in biomass processing. The effectiveness of deep eutectic solvents in breaking down the recalcitrant structure in biomass highlights its impact on the transformation of biomass into various value-added products. In addition, deep eutectic solvents are widely regarded as promising “green” solvents due to their low cost, low toxicity, and biodegradable properties. In this paper, some background information on lignocellulosic biomass and deep eutectic solvents is given. Furthermore, the roles of deep eutectic solvents in biomass processing are discussed, focusing on the impacts of deep eutectic solvents on the selectivity of chemical processes and dissolution of biomass. This review also highlights the advantages and limitations of deep eutectic solvents associated with their usage in biomass valorization.     

The use of infrared probes in solvation studies: Acetone in mixed protic-aprotic solvents

Infrared spectra ot acetone in the CO stretching region have been studied as a function of the composition of a range of mixed protic-aprotic solvents. For methanolic systems, equilibria between hydrogen-bonded and non hydrogen-bonded acetone dominate the spectral changes, but for aqueous systems at least four distinct components need to be considered.     

Vacuum system for the semi-automatic degassing of solvents

A semi-automatic system capable of quickly degassing large amounts of solvent is described.     

The use of a new carboranylamidophosphite ligand in the asymmetric Pd-catalysed allylic alkylation in organic solvents and supercritical carbon dioxide

A novel P-monodentate ligand based on carboranyl alcohol and (S)-2-(anilinomethyl)pyrrolidine provides high enantioselectivities (ee’s up to 95%) in the Pd-catalyzed allylic alkylation of (E)-1,3-diphenylallyl acetate. The first example of the Pd-catalysed allylic alkylation in supercritical carbon dioxide is also described.     

Improving gas chromatographic determination of residual solvents in pharmaceuticals by the combined use of headspace solid-phase microextraction and isotopic dilution

Cyclohexane and toluene were gas chromatographically determined via headspace solid-phase microextraction both in ketoprofen drug substance and ketoprofen capsules by a procedure relying on isotopic dilution (ID), an analytical tool derived from mass spectrometry (MS). This approach, using an internal standard method, gave mean precision and accuracy (RSD 2.56%, 2.97% and bias 0.21%, -0.99% for cyclohexane and toluene, respectively) not obtainable by the more commonly used external standard ones in the presence of real sample matrices. Optimisation of the operative conditions was also supported by experimental design. More generally, the proposed method, exploiting ID without resort to the costly MS instrumentation, could be recommended whenever opportune deuterated analogues of the target analytes and GC capillary columns able to separate all the peaks involved are ready available on the market.     

The use of two nematic solvents in the determination of molecular structure of systems providing deceptively simple spectra

The use of two liquid crystals as solvents in the determination of molecular structure has been demonstrated for systems which do not provide structural information from studies in a single solvent owing to the fact that the spectra are deceptively simple, with the result that all the spectral parameters cannot be derived with reasonable precision. The specific system studied was 2-(p-bromophenyl)-4,6-dichloropyrimidine, for which relative inter-proton discances have been determined from the proton NMR spectra in two nematic solvents.     

The use of novel ionic liquid-in-water microemulsion without the addition of organic solvents in a capillary electrophoretic system

In this work, a new ionic liquid-in-water (IL/W) microemulsion without requiring toxic organic solvents was investigated as a pseudostationary phase (PSP) in CE. As observed during the IL/W microemulsion system, a fast and an efficient separation of eight phenolic acids was achieved using 1-butyl-3-methylimidazolivmhexa fluorophosphate (bmimPF(6)) as oil drops, Tween 20 as the surfactant, and borate as the BGE. The effects of oil phase, surfactant, buffer and pH on the separation were explored in detail to evaluate the novel PSP. In contrast, the detection efficiency of these same analytes was markedly decreased using oil-in-water (O/W) MEEKC. We have also validated the practicality of the IL/W microemulsion method by quantitative determination of acidic compounds in pharmaceutical injection. The results obtained indicated that an additional association between the IL cations and analytes tested seemed to play a prominent role in the separation mechanism exhibited by this novel PSP compared with the conventional O/W MEEKC.     

Modified enzymes for reactions in organic solvents

Recent studies on biocatalysis in water—organic solvent biphasic systems have shown that many enzymes retain their catalytic activities in the presence of high concentrations of organic solvents. However, not all enzymes are organic solvent tolerant, and most have limited and selective tolerance to particular organic solvents. Protein modification or protein tailoring is an approach to alter the characteristics of enzymes, including solubility in organic solvents. Particular amino acids may play pivotal roles in the catalytic ability of the protein. Attaching soluble modifiers to the protein molecule may alter its conformation and the overall polarity of the molecule. Enzymes, in particular lipases, have been chemically modified by attachment of aldehydes, polyethylene glycols, and imidoesters. These modifications alter the hydrophobicity and conformation of the enzymes, resulting in changes in the microenvironment of the enzymes. By these modifications, newly acquired properties such as enhancement of activity and stability and changes in specificity and solubility in organic solvents are obtained. Modified lipases were found to be more active and stable in organic solvents. The optimum water activity (a _w ) for reaction was also shifted by using modified enzymes. Changes in enantioselective behavior were also observed.