Presence Of Protic Ionic Liquids Research Articles

Hydration behavior of L-proline in the presence of mono, bis, tris-(2-hydroxyethyl) ammonium acetate protic ionic liquids: Thermophysical properties

The hydration behavior of amino acids, essential for biological macromolecules, is influenced by ammonium biomaterials. The protic ionic liquids (PILs) are gaining attention in the food and pharmaceutical industries due to their nontoxicity and adjustable properties. Thus, study of the amino acids, such as L-proline, in the presence of PILs is crucial for understanding their hydration behavior. In this work, the effect of PILs, including mono, bis, tris (2-hydroxyethyl)ammonium acetate protic ionic liquids that might be naturally produced in human body, on L-proline hydration behavior was studied using COSMO calculations and thermophysical measurements. Measurements were the density, speed of sound, viscosity, and refractive index data of the solutions (L-proline + PILs + water) at various PIL concentrations at temperatures (298.15 to 318.15) K and under atmospheric pressure. The study indicates L-proline has weaker interactions with water compared to PILs ([2-HEA][Ac], [bis-2-HEA][Ac], and [tris-2-HEA][Ac]) due to its compact structure and lower negative dielectric energy. PILs interact more strongly with water through hydrogen bonding. Increasing temperature affects L-proline’s hydration layer, releasing more water molecules compared to PIL solutions. This effect is more pronounced with [tris-2-HEA][Ac], likely due to its larger size and complex structure. While L-proline promotes an ordered water structure, PILs can disrupt this by rearranging water molecules and forming their own hydrogen bonds.

Impedance Analysis of Capacitive and Faradaic Processes in the Pt/[Dema][TfO] Interface.

The electrochemical reaction kinetics, especially the oxygen reduction reaction (ORR) at the cathode, is crucial for the performance of a fuel cell. In this study, the electrochemical processes on a polycrystalline Pt electrode in the presence of protic ionic liquid (PIL) electrolyte diethylmethylammonium triflate [Dema][TfO] are investigated by means of cyclic voltammetry and electrochemical impedance spectroscopy. Since water is continually produced during fuel cell operation, the effect of the water content in the PIL has been intensively analyzed. In order to reveal the dependence of the interfacial reaction characteristics on the electrode potential, the impedance spectra were simulated by an equivalent circuit whose parameters can be related to both Faradaic and capacitive processes. Two interfacial resistances were identified, which differ by about 3 orders of magnitude. The larger one is a charge transfer resistance that can be associated with slow Faradaic processes like the ORR and platinum oxidation/oxide reduction. The smaller resistance is probably linked with fast processes that involve water molecules, such as hydrogen deposition and oxidation. The high- and midfrequency capacitive processes are attributed to "classical" double layer and pseudocapacitive behavior, similar to those identified under nitrogen atmosphere.

Double layer capacitance of a platinum electrode in a protic ionic liquid: The influence of cation acidity

Protic ionic liquids (PILs) are promising candidates as electrolytes for future intermediate-temperature polymer electrolyte membrane fuel cells (PEMFCs). A deeper understanding of their double layer properties is essential for the improvement of oxygen reduction reaction (ORR) kinetics in the interface of the platinum catalyst and PIL. In this study, we investigate the double layer differential capacitance of platinum in the presence of PILs with acidic cations of various proton donor strengths as a function of the electrode potential, bulk water content, and temperature. Complex capacitance plots of impedance spectra enable the evaluation of a high-frequency double layer capacitance, C1, and a mid-frequency pseudo-double layer capacitance, C2. The C1-capacitance curves were simulated by two mean field models that account for the presence of water, short range correlations of ions, and, in the case of the second model, also for the non-monotonic charging of the Pt surface that has a strong impact on the double-layer structure and properties. The simulations reveal different double-layer properties of [2-Sema][TfO], a PIL with a highly acidic cation, compared to the less acidic [1-EIm][TfO] and [Dema][TfO]. These variations are associated with differences in interionic forces, degrees of ion pairing, and the compactness of ionic layers. Most likely, these effects correlate with hygroscopicity and ability to form the hydrogen bonds of the cation, rather than with its acidity. The different pseudo-double layer capacitances of [2-Sema][TfO] and of the less acidic PILs at higher potentials are explained by different mechanisms of oxide formation.

Sustainable Method for the Synthesis of Alternative Bis(2-Ethylhexyl) Terephthalate Plasticizer in the Presence of Protic Ionic Liquids

Inexpensive Brønsted acidic ionic liquids based on trimethylamine and sulfuric acid are proposed as both solvents and catalysts in the synthesis of alternative plasticizer bis(2-ethylhexyl) terephthalate, which has a broad spectrum of applications in plasticization processes. The utilization of 50 mol % of Brønsted ionic liquid led to the full conversion of terephthalic acid after 8 h of reaction at 120 °C. Additionally, a 100% selectivity of bis(2-ethylhexyl) terephthalate was obtained. The advantage of the presented reaction system is based on the formation of a biphasic system during the reaction. The bottom phase consists of an ionic liquid and water, and the upper phase is created by the ester and unreacted alcohol. This phenomenon helps overcome the equilibrium of the reaction and drives it towards a high yield of product. The presented new approach is proposed as a safe, cost-effective, and alternative method to conventional processes with organometallic compounds that, in turn, leads to greener and a more economically viable technology.

Evaluating Protic Ionic Liquid for Woody Biomass One-Pot Pretreatment + Saccharification, Followed by Rhodosporidium toruloides Cultivation

Woody biomass feedstocks pose challenges in their use as sustainable carbon sources due to their recalcitrance. One-pot ionic liquid-based processes are a promising bioproduction strategy to reduce water consumption (removing the washing of biomass), reduce costs, and minimize the presence of inhibitory compounds. We evaluated the one-pot ionic liquid pretreatment + saccharification configuration as a scheme for the deconstruction and conversion of two different woody feedstocks, eucalyptus, and pine. A comparative study of protic ionic liquids 2-hydroxylethylammonium acetate-based ionic liquids, bis-2-hydroxyethylammonium acetate, and cholinium lysinate for pretreatment of eucalyptus and pine was conducted. The impact of ionic liquids at 11% w/w on the saccharification and toxicity of hydrolysates containing the ionic liquid for downstream use for microbial cultivation was evaluated. Protic ionic liquids were more effective in eucalyptus than in pine pretreatment and less toxic than cholinium lysinate at concentrations ≤10% w/w. 2-hydroxylethylammonium acetate yielded the highest digestibility, of up to 75% in eucalyptus. As a proof of concept of an integrated feedstocks-to-biofuels process, we tested the growth of the fungal strain Rhodosporidium toruloides in hydrolysates with low amounts of ionic liquids and phenolic compounds. The proof of concept demonstrated the ability of Rhodosporidium toruloides to grow in the presence of 2-hydroxyethylammonium acetate (5% w/w), the importance to adjust the pH after saccharification, and the ability to consume lignin monomers. This work offers a valid starting point for further studies aimed at increasing cellulose digestibility in a one-pot configuration in the presence of protic ionic liquids.

Polar Diels-Alder Reactions Under Microwave Irradiation Employing Different Heterocyclic Compounds as Electrophiles

During the last twenty years, our research group has been working with aromatic nitrosubstituted compounds acting as electrophiles in Polar Diels-Alder (P-DA) reactions with different dienes of diverse nucleophilicity. In this type of reaction, after the cycloaddition reaction, the nitrated compounds obtained as the [4+2] cycloadducts suffer cis-extrusion with the loss of nitrous acid and a subsequent aromatization. In this form, the reaction results are irreversible. On the other hand, the microwave-assisted controlled heating become a powerful tool in organic synthesis as it makes the reaction mixture undergo heating by a combination of thermal effects, dipolar polarization and ionic conduction. As the Diels-Alder (D-A) reaction is one of the most important process in organic synthesis, the microwave (MW) irradiation was applied instead of conventional heating, and this resulted in better yields and shorter reaction times. Several substituted heterocyclic compounds were used as electrophiles and different dienes as nucleophiles. Two experimental situations are involved: one in the presence of Protic Ionic Liquids (PILs) as solvent and the other under solvent-free conditions. The analysis is based on experimental data and theoretical calculations.

Understanding the Role of Protic Ionic Liquids (PILs) in Reactive Systems: Rational Selection of PILs for the Design of Green Synthesis Strategies for Allylic Amines and β-Amino Esters.

The reactive behaviour of protic ionic liquids (PILs) has been shown to be governed not only by their chemical structures but also by their global compositions, which include the presence of free acids and bases at equilibrium with ionic pairs. Six PILs composed of primary, secondary, or tertiary alkyl ammonium cations with two couterions, nitrate or acetate, were tested in model reactions with unsaturated substrates. The free species that were naturally present in these liquids were identified by cyclic voltammetry. Only tributylammonium nitrate was found to be mostly composed just of the ionic pair; the other five PILs also contain variable amounts of free acid and amine. In reactive systems, these free species determine the products of the reaction. In particular, allylic amines and β-amino esters were obtained in good yields (91 and 75 %, respectively) by reaction of conjugated dienes and acrylates in the presence of PILs. By taking into account the actual composition of each PIL, it was possible to direct the reaction path towards a specific product with good yields, to ensure acid catalysis, to avoid polymerization of the substrate, and to promote phase transfer of products. These results establish some useful guidelines for the rational design of new PIL-based one-step synthetic strategies.

One-Pot Synthesis of Ion-Containing CO2-Based Polycarbonates Using Protic Ionic Liquids as Chain Transfer Agents

An analysis of the construction of ion-containing CO2-based polycarbonates via metal-catalyzed immortal copolymerization of propylene oxide (PO) and carbon dioxide in the presence of protic ionic liquids (ILs) as chain transfer agents is described. The reactions were catalyzed by the binary (salen)CoO2CCF3/onium salt system in the absence of added solvent. On the basis of the results of this study, which includes 1H NMR and MALDI-TOF-MS data, it is clear that the role of the protic IL in this process is dominated by its anion. When the anion of the protic ionic liquid is nucleophilic, such as chloride, the protic ionic liquid acts as a cocatalyst in the reaction system for epoxide ring opening, and the chain transfer reaction initiated by the cation is completely suppressed. However, when the anion of the protic ionic liquid is non-nucleophilic, such as BF4–, the protic ionic liquid acts as an effective chain transfer agent to afford IL-based polycarbonates by rapid and reversible chain transfer processes...

Protic ionic liquid applied to enhance the immobilization of lipase in sol–gel matrices

This work evaluated the capacity of protic ionic liquid (PIL) used as an additive to enhance the immobilization of lipase from Bacillus sp. in a sol–gel matrix. The immobilized derivatives were characterized with respect to the specific surface area, adsorption–desorption isothermic values, pore volume and size by nitrogen adsorption, thermal analysis and full recovery of activity. The lipases were immobilized using different PILs of the same cation (N-methylmonoethanolamine) and different anions (acetate, propionate, butyrate and pentanoate). The results showed that the total recovery of activity for the samples encapsulated in the presence of PIL was always higher than those without the encapsulated additive (total activity yield, Ya = 71%), particularly when using the more hydrophobic nature PILs (Ya = 305%), and at concentrations of 0.5 mass%. The positive effect of using PILs was also observed in the formation of the porous structure of the biocatalysts, as well as the increases in surface area (78 to 278 m2 g−1) and pore volume (0.018 to 0.414 cc g−1). The thermal analysis has revealed the key role of water content on the hydration shell of the enzyme caused by the change in the alkyl chain of ionic liquids, showing that the PILs are an excellent alternative for immobilization processes.

Thermodynamic and ultrasonic properties of ascorbic Acid in aqueous protic ionic liquid solutions.

In this work, we report the thermodynamic and ultrasonic properties of ascorbic acid (vitamin C) in water and in presence of newly synthesized ammonium based protic ionic liquid (diethylethanolammonium propionate) as a function of concentration and temperature. Apparent molar volume and apparent molar isentropic compression, which characterize the solvation state of ascorbic acid (AA) in presence of protic ionic liquid (PIL) has been determined from precise density and speed of sound measurements at temperatures (293.15 to 328.15) K with 5 K interval. The strength of molecular interactions prevailing in ternary solutions has been discussed on the basis of infinite dilution partial molar volume and partial molar isentropic compression, corresponding volume of transfer and interaction coefficients. Result has been discussed in terms of solute-solute and solute-solvent interactions occurring between ascorbic acid and PIL in ternary solutions (AA + water + PIL).

Volumetric Properties of Disaccharides in Aqueous Solutions of Benzyldimethylammonium Acetate as a Function of Temperature

Densities, ρ, and speeds of sound, u, of two disaccharides (D-(+)-maltose and D-(+)-cellobiose) in water and in the presence of protic ionic liquid (PIL) (i.e., benzyldimethylammonium acetate, BDMAAc) were measured at different temperatures (288.15–318.15) K at atmospheric pressure. These data were used to calculate the apparent molar volume, apparent molar isentropic compressibility, infinite dilution partial molar volume, infinite dilution partial molar isentropic compressibility, and corresponding transfer parameters (ΔtV°2 and ΔtK°s,2) for disaccharides from water to aqueous PIL solutions. The effect of BDMAAc on the basic taste quality of disaccharides was evaluated from apparent specific volume and apparent specific isentropic compressibility, as these parameters are grouped in various taste qualities.

Volumetric properties of amino acids in aqueous solutions of ammonium based protic ionic liquids

Apparent molar volumes, V2,ϕ of amino acids (glycine and dl-α-alanine) in water and in aqueous solutions of ammonium based protic ionic liquids (PILs), namely, propylammonium formate (PAF) and 3-hydroxypropylammonium formate (3-HPAF) determined from precise density measurements, increase with concentration of amino acids and increase in temperature (288.15–318.15) K. Partial molar volume of transfer, ΔtV2° are both positive and negative in case of PAF, whereas only negative ΔtV2° values have been observed in case of 3-HPAF over the studied concentration range. Thermal expansion coefficients, (∂V2°/∂T)P of amino acids in presence of PILs are higher as compared to that observed in water and further, (∂2V2°/∂T2)P values are found to be negative, which suggest that studied amino acids behave as structure breakers in these solutions. Hydration number, nH for studied amino acids in aqueous PILs solutions follows the order: 3-HPAF>PAF, which suggest a strong dehydration effect of PAF.

Screening of immobilization method in aerogel matrix in the presence of protic ionic liquid

Aerogel and xerogel are formed via hydrolysis and polycondensation reactions of silica precursors, such as tetraethylorthosilicate (TEOS), always careful not to cause collapse, reduction in surface area and pore size. Several studies shown the use sol-gel entrapment possesses a number of desirable attributes, as the enzyme is physically entrapped in a rigid glass framework that permitted stabilization of the enzymes, terciary structure owing to the tight gel network. In this study, have focused on the screening of immobilization method in aerogel matrix in the presence of protic ionic liquid (PIL) with evaluation catalytic efficiency and operational stability. The novel mesoporous silica supports (aerogels) obtained by the sol-gel technique was used to immobilize commercial Burkholderia cepacia (BC) lipase by physical adsorption, covalent binding and encapsulation in the absence and presence de protic ionic liquid (N-methylmonoethanolamine pentanoate - C5). Catalytic efficiency was determined in the analyses of hydrolytic activities were carried out on the lipase loading solution and immobilized enzyme to determine the total activity recovery yield, Ya (%). For physical adsorption the recovery of activity with PIL was 82.95% (ADSLI) and in the absence 70.31% (ADS). Operational stability of the enzyme has also been examined and obtained similar values a half-life of 0.73 h to ADSLI and 0.88 h for ADS occurs with 2 batches. And other immobilized technique, covalent binding the results showed that in aerogels supports in the presence of C5 obtained 69.13% (CBLI) of total activity recovery yield and 39.11% (CB). Under such conditions, the operational stability tests indicated that a small enzyme deactivation occurs after 15 batches, revealing a biocatalyst half-life of 7.5 h for CBLI. For encapsulation, the recovery of activity with PIL (ENLI) was 45% and 37% in the absence PIL (EN). ENLI exhibited a half life of more than 23 batches with 70% of its activity remaining, with around 11.5 h. And EN the half-life was 6.5 hours, totaling 13 batches. Therefore, ADSLI presented good efficiency with total activity recovery yield but for operational stability ENLI showed the best between immobilization methods studied. Hence, it is rather appropriate for application in hydrolytic processes.

Prevention of insulin self-aggregation by a protic ionic liquid

The self-aggregation and thermal instability of insulin (In) was considerably controlled in the presence of ammonium-based protic ionic liquids (PILs). The thermal stability of In in PILs was observed using fluorescence and absorption spectroscopy of the Tyr environment of the biomolecule. Additionally, from circular dichroism (CD) measurements, we observed the shift in the wavelength towards lower values in the presence of PILs, which indicates the formation of monomers of In, further evidently supported by dynamic light scattering (DLS) measurements. Surprisingly, it is the monomeric form of the In that exists in the active form. For the first time, ammonium-based PILs have been shown to be novel solvents for In, which prevent it from associating into an inactive form and also stabilizes In against thermal influence.

Protic ionic liquid as additive on lipase immobilization using silica sol–gel

Ionic liquids (ILs) have evolved as a new type of non-aqueous solvents for biocatalysis, mainly due to their unique and tunable physical properties. A number of recent review papers have described a variety of enzymatic reactions conducted in IL solutions, on the other hand, to improve the enzyme's activity and stability in ILs; major methods being explored include the enzyme immobilization (on solid support, sol–gel, etc.), protic ionic liquids used as an additive process. The immobilization of the lipase from Burkholderia cepacia by the sol–gel technique using protic ionic liquids (PIL) as additives to protect against inactivation of the lipase due to release of alcohol and shrinkage of the gel during the sol–gel process was investigated in this study. The influence of various factors such as the length of the alkyl chain of protic ionic liquids (monoethanolamine-based) and a concentration range between 0.5 and 3.0% (w/v) were evaluated. The resulting hydrophobic matrices and immobilized lipases were characterised with regard to specific surface area, adsorption–desorption isotherms, pore volume (Vp) and size (dp) according to nitrogen adsorption and scanning electron microscopy (SEM), physico-chemical properties (thermogravimetric – TG, differential scanning calorimetry – DSC and Fourier transform infrared spectroscopy – FTIR) and the potential for ethyl ester and emulsifier production. The total activity yields (Ya) for matrices of immobilized lipase employing protic ionic liquids as additives always resulted in higher values compared with the sample absent the protic ionic liquids, which represents 35-fold increase in recovery of enzymatic activity using the more hydrophobic protic ionic liquids. Compared with arrays of the immobilized biocatalyst without additive, in general, the immobilized biocatalyst in the presence of protic ionic liquids showed increased values of surface area (143–245m2g−1) and pore size (19–38Å). Immobilization with protic ionic liquids also favoured reduced mass loss according to TG curves (always less than 42.9%) when compared to the immobilized matrix without protic ionic liquids (45.1%), except for the sample containing 3.0% protic ionic liquids (46.5%), verified by thermogravimetric analysis. Ionic liquids containing a more hydrophobic alkyl group in the cationic moiety were beneficial for recovery of the activity of the immobilized lipase. The physico-chemical characterization confirmed the presence of the enzyme and its immobilized derivatives obtained in this study by identifying the presence of amino groups, and profiling enthalpy changes of mass loss.

Diels–Alder reactions of N-tosylpirroles developed in protic ionic liquids. Theoretical studies using DFT methods

N-Tosyl-2-nitropirrole and N-tosyl-3-nitropirrole react with poorly and activated dienes using protic ionic liquids as reaction media. They exhibit a dienophile character producing the corresponding indoles through a Diels–Alder process. In all cases the presence of protic ionic liquids as reaction media improves the yields with respect to use of molecular solvent, while the temperature and the reaction time decrease. Part of this work is specifically concerned with theoretical studies using DFT methods. The global and local electrophilicity and nucleophilicity indices were calculated for the dienophiles and dienes used in this study in order to evaluate reactivity and regioselectivity.