Ethylammonium Nitrate Research Articles

Hydration counteracts the separation of lanthanides by solvent extraction.

The extraction of lanthanides from aqueous nitrate solutions by quaternary ammonium nitrate ionic liquids (e.g., [A336][NO3]) shows a negative sequence (i.e., light lanthanides are more efficiently extracted than heavy lanthanides), which conflicts with the lanthanide contraction. In this study, we explored the origin of the negative sequence by investigating the extraction of lanthanides from ethylammonium nitrate by [A336][NO3]. The extraction shows a positive sequence, which is converted to a negative sequence with the addition of water. The transformation from positive to negative sequences reveals that the negative sequence is caused by the hydration of lanthanide ions: hydration of lanthanide ions counteracts the extraction. Therefore, the use of solvents that have weak solvation with lanthanide ions might enhance the separation of the elements by solvent extraction.

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Probing amyloid formation of intrinsically disordered proteins (IDPs) in aqueous solutions with ionic liquids (ILs) could help identify the IL–IDP interactions causing the process in this media. Takekiyo et al. report that ethylammonium nitrate (EAN) initiates the formation of intermolecular β‐sheet structure – amyloid‐like aggregates – of α‐synuclein. The cations and anions of EAN function as charges to mask side chains, leading to the formation of a polyproline II helix that assists the formation of α‐synuclein aggregates. The present results could help develop promoting agents for amyloid aggregates in biomaterials science. (DOI: 10.1002/bip.23352) image

Self-diffusion in ionic liquids with nitrate anion: Effects of confinement between glass plates and static magnetic field

Alkylammonium nitrate protic ionic liquids (ILs), when placed between flat polar borosilicate glass plates, have demonstrated enhanced diffusivity and the gradual decrease of diffusivity after exposure to an external static magnetic field (Filippov et al., 2018). This phenomenon has been explained by phase transformations taking place in the ILs. In this study, we observed similar processes occurring in systems prepared with ethylammonium nitrate confined between quartz plates. A higher content of silicon oxide in the plates does not significantly alter the phenomenon previously found in the system prepared with borosilicate glass plates. For the first time, we have observed similar effects of confinement and magnetic field on the aprotic IL, 1‑ethyl‑3‑methylimidazolium nitrate. Substitution of the ethylammonium cation with a 1‑ethyl‑3‑methylimidazolium cation slows down the kinetics and increases magnitude of the processes occurring in the IL exposed to a magnetic field. We suggested that the main factor determining these effects is the presence and modification of the hydrogen-bonding network in the studied protic and aprotic ILs. The process of inverse phase transformation for the confined ethylammonium nitrate after removing the sample from the magnetic field was observed and analysed.

Formation of α-synuclein aggregates in aqueous ethylammonium nitrate solutions.

The effect of adding ethylammonium nitrate (EAN), which is an ionic liquid (IL), on the aggregate formation of α-synuclein (α-Syn) in aqueous solution has been investigated. FTIR and Raman spectroscopy were used to investigate changes in the secondary structure of α-Syn and in the states of water molecules and EAN. The results presented here show that the addition of EAN to α-Syn causes the formation of an intermolecular β-sheet structure in the following manner: native disordered state → polyproline II (PPII)-helix → intermolecular β-sheet (α-Syn amyloid-like aggregates: α-SynA). Although cations and anions of EAN play roles in masking the charged side chains and PPII-helix-forming ability involved in the formation of α-SynA, water molecules are not directly related to its formation. We conclude that EAN-induced α-Syn amyloid-like aggregates form at hydrophobic associations in the middle of the molecules after masking the charged side chains at the N- and C-terminals of α-Syn.

Unexpected Strong Acidity Enhancing the Effect in Protic Ionic Liquids Quantified by Equilibrium Acidity Studies: A Crucial Role of Cation Structures on Dictating the Solvation Properties.

The equilibrium acidities for several series of structural and electronic different organic acids were measured in 3-pyrrolidinium-based aprotic and protic ionic liquid (IL) analogues, that is, [Bmpy][NTf2], [BpyH][NTf2], and [PyH2][NTf2], by the UV-Vis method. The acidities of neutral acids are found to be much stronger in the protic ILs (PILs) than aprotic ILs (AILs), and the acidifying effect in the two PILs roughly increases proportionally to the number of protons in the cation of the PIL. On the other hand, interestingly, the cationic N+-H acids exhibit similar acidities in [Bmpy][NTf2] and [BpyH][NTf2] but much weaker than those in [PyH2][NTf2]. The Hammett ρ values for the acidic dissociation of para-substituted benzoic acids in two PILs are about the same as that in water (1.00) but significantly smaller than that in the AIL [Bmpy][NTf2] (2.66). The correlations between the acidities in the PILs and water show double-linear relationships with different slopes and intercepts for the neutral and cationic acids. These, together with previous observations in the PILs [DBUH][OTf] (DBU = 1,5-diazabicyclo(5.4.0)-5-undecene) and EAN (ethylammonium nitrate), clearly indicate that the structure of the cation plays a subtle but a crucial role on sensing the electronic nature of solutes and strongly affects the solvation behaviors of PILs.

Structural, Thermodiffusive and Thermoelectric Properties of Maghemite Nanoparticles Dispersed in Ethylammonium Nitrate

Ethylammonium nitrate (ionic liquid) based ferrofluids with citrate-coated nanoparticles and Na + counterions were synthesized for a wide range of nanoparticle (NP) volume fractions ( Φ ) of up to 16%. Detailed structural analyses on these fluids were performed using magneto-optical birefringence and small angle X-ray scattering (SAXS) methods. Furthermore, the thermophoretic and thermodiffusive properties (Soret coefficient S T and diffusion coefficient D m ) were explored by forced Rayleigh scattering experiments as a function of T and Φ . They were compared to the thermoelectric potential (Seebeck coefficient, Se) properties induced in these fluids. The results were analyzed using a modified theoretical model on S T and Se adapted from an existing model developed for dispersions in more standard polar media which allows the determination of the Eastman entropy of transfer ( S ^ NP ) and the effective charge ( Z 0 e f f ) of the nanoparticles.

Structural, Thermodiffusive and Thermoelectric Properties of Maghemite Nanoparticles Dispersed in Ethylammonium Nitrate

Structural, Thermodiffusive and Thermoelectric Properties of Maghemite Nanoparticles Dispersed in Ethylammonium Nitrate

Formation of Surface Protic Ionic Liquid Nanodroplets for Nanofabrication

AbstractFemtoliter droplets at solid interfaces attract significant interest as the basic units in many physical and biological processes. One challenge in the application of these tiny droplets is their fast evaporation rate in air due to their large surface‐to‐volume ratio. Ionic liquids with low volatility present an opportunity to overcome this challenge. The advanced properties of ionic liquids (ILs) have enabled them to be widely applied in chemical reactions, biopolymers, molecular self‐assembly and separations. At interfaces, the wettability of ILs is pursued in next‐generation lubricants and battery technology. Previously, IL droplets at solid surfaces have been prepared by nanodispensing, micropipette, and solvent evaporation. Here, the solvent exchange protocol is extended to yield protic ionic liquid droplets at the interface with controlled size, distribution, location, and stability in both liquid and air surroundings. During growth, the droplets demonstrate an interesting dewetting dynamic. This behavior has not been observed for molecular liquids during solvent exchange and suggests interesting interfacial dynamics of the ionic liquid. One proof‐of‐concept application of using surface nanodroplets of the protic ionic liquid ethylammonium nitrate for compartmentalized reactions and templating SiO2 nanostructures is demonstrated. This work broadens and intertwines the opportunities of ILs and nanodroplets.

Conformational dynamics of amyloid-β (16-22) peptide in aqueous ionic liquids.

Molecular dynamics simulations of amyloid-β (16–22) peptide dimer in water as well as at two different experimentally studied concentrations of hydrated ionic liquids (ILs), ethylammonium mesylate (EAM), ethylammonium nitrate (EAN), and triethylammonium mesylate (TEAM), were carried out employing an umbrella sampling method. We used the average Ψ angle of the peptide backbone as the reaction coordinate to observe the conformational changes of a peptide dimer. Secondary structural element values were calculated for the peptide dimer along the reaction coordinate to see the transition of the peptide dimer between β-sheet and α-helix conformations. We observe the β-sheet conformation as the global minimum on the free energy surfaces in both EAM and EAN ILs at both the concentrations and at a low concentration of TEAM. However, we observe α-helix conformation as the global minimum at a high concentration of TEAM. Our results are in good correlation with the experimental findings. We calculated the average number of intramolecular and intermolecular hydrogen bonds of α-helix and β-sheet conformations in all solutions, and they are in correlation with the secondary structure element values. To understand the peptide–IL interactions, atom–atom radial distribution functions of cation, anion, and water around amide oxygen and hydrogen atoms were calculated. The solvent-accessible surface area of the peptide dimer was calculated to understand the exposure of the peptide towards the solvent during conformational changes. Finally, van der Waals (vdW) and Coulomb interaction energies were calculated between peptide–cation, peptide–anion, and peptide–water to understand the stability of conformations in different concentrations. We find that the TEA cation has more vdW interaction energy compared to Coulomb interaction energy with peptide in 70% (w/w) TEAM, which mimics a membrane-like environment to induce α-helix conformation rather than β-sheet conformation.

Solvation properties of protic ionic liquid-molecular solvent mixtures.

Ionic liquids (ILs) are increasingly receiving interest for a wide range of applications. However, for many applications their cost and/or viscosity can be too high. This can be addressed by using protic ionic liquids as cheaper alternatives, and through mixing with molecular solvents. However, mixing ILs with a molecular solvent adds another dimension to the compositional space, as well as increasing the complexity of solvent-solute interactions. In this study, we have investigated the solvation properties of binary mixtures of PILs with molecular solvents. The selected binary solvent systems are the PILs ethylammonium nitrate (EAN) and propylammonium nitrate (PAN) combined with either water, methanol, acetonitrile or DMSO. In addition, water is combined with the other molecular solvents for comparison. The mole fractions of the secondary solvents were 0, 0.25, 0.5, 0.75, 0.9 and 1 for all combinations, which resulted in a total of 66 solvent mixtures. The solvation properties in each of these mixtures were determined from spectroscopic measurements of 4 well-known solvatochromic probe molecules as solutes. The solvation properties were comparatively investigated, and interpreted, in terms of the specific and non-specific interactions between PIL-solvent, PIL-solute and solvent-solute. All 66 solvent mixtures were also analysed using FTIR with no probe molecules present. In addition, through molecular dynamics simulations, the dye-solvent interactions were simulated for two of the dye molecules in water-EAN binary systems, and the radial distribution functions for the key interactions were obtained. The results showed that the solvation parameters of the binary mixtures deviated considerably from the ideal solvation behaviour. In many cases, bulk compositions and the estimated excess compositions in the solvation shells of the probes were different, suggesting preferential solvation, the extent of which is solute dependent. Our results clearly show that using PILs in a mixture with molecular solvents can strongly enhance the solvation capability.

Molecular-level insights into the structures, dynamics, and hydrogen bonds of ethylammonium nitrate protic ionic liquid at the liquid-vacuum interface.

A series of molecular dynamics simulations have been used to systematically explore the structures, dynamics and hydrogen bonds (HBs) of ethylammonium nitrate (EAN) protic ionic liquid (IL) and their mutual relationship at the liquid-vacuum interface. The simulation results clearly demonstrate that there exists a sandwich structure at the interface, with the double-layer of the EA+ cations on both sides and one intercalated layer of the NO3- anions in the middle. Wherein, the outermost cation layer prefers the orientation with the CH3 groups pointing to the vacuum phase due to the hydrophobic interactions, while the CH3 groups in the second layer direct to the bulk liquid phase owing to the HB formation between their NH3+ groups and the intercalated NO3- anions in the middle layer. On the other hand, the continuous HB strength of the cations in the outermost layer (denoted as Cation-1) is found to be almost identical with the counterpart of the cations in the second layer (denoted as Cation-2), whereas the intermittent HB strength of Cation-1 is much larger than that of Cation-2 at all temperatures. Furthermore, the rotational motion of Cation-1 with the normal vector of the C-C-N plane in the cation is faster than that of Cation-2 with the same vector, resulting from more free space in the outermost layer. On the contrary, the rotational motion of Cation-1 with the vector from the mass center of the cation to its N atom is much slower than that of Cation-2 with the same vector, which can be attributed to the combined effects of the stronger intermittent HBs of Cation-1 and the hydrophobic interactions of its CH3 group in the outermost layer.

Lyotropic liquid crystal phase behavior of a cationic amphiphile in aqueous and non-stoichiometric protic ionic liquid mixtures.

Protic ionic liquids (PILs) are the largest and most tailorable known class of non-aqueous solvents which possess the ability to support amphiphile self-assembly. However, little is known about the effect of solvent additives on this ability. In this study, the lyotropic liquid crystal phase (LLCP) behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated in the model PILs of ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), and derived multi-component solvent systems containing them to determine phase formation and diversity with changing solvent composition. The solvent systems were composed of water, nitric acid and ethylamine (or ethanolamine), with 26 unique compositions for each PIL covering the apparent pH and ionicity ranges of 0-13.5 and 0-11 M, respectively. The LLCPs were studied using cross polarized optical microscopy (CPOM) and small and wide-angle X-ray scattering (SAXS/WAXS). Partial phase diagrams were constructed for CTAB concentrations of 50 wt% and 70 wt% in the temperature range of 25 °C to 75 °C to characterise the effect of surfactant concentration and temperature on the LLCPs in each solvent environment. Normal micellar (L1), hexagonal (H1) and bicontinuous cubic (V1) phases were identified at both surfactant concentrations, and from temperatures as low as 35 °C, with large variations dependent on the solvent composition. The thermal stability and diversity of phases were greater and broader in solvent compositions with excess precursor amines present compared to those in the neat PILs. In acid-rich solvent combinations, the same phase diversity was found, though with reduced onset temperatures of phase formation; however, some structural changes were observed which were attributed to oxidation/decomposition of CTAB in a nitric acid environment. This study showed that the ability of PIL solutions to support amphiphile self-assembly can readily be tuned, and that the ability of PILs to promote amphiphile self-assembly is robust, even with other solvent species present.

Ionogels as Precursors To Prepare ZnS Nanoparticles for Colorimetric Sensing of Sulfide Ions

In this study, novel supramolecular ionogels with ultrahigh efficient gelation and robust mechanical properties were prepared by mixing 4′-para-phenylcarboxyl-2,2′:6′,2″-terpyridine (PPCT) and zinc ions (Zn2+) in ethylammonium nitrate (EAN). The microstructure of the ionogels was determined to be three-dimensional networks of fibrous aggregates. X-ray diffraction and Fourier-transform infrared spectroscopy measurements demonstrated that ionogel formation involve the following steps: the terpyridine rings of PPCT form an assembled unit via π–π interaction, the unit further aggregates to form fibers using Zn2+ via hydrogen bonding and Zn2+ coordination, and the fibers stretch and intertwine to form a cross-linked network to immobilize EAN by solvophobic interactions, electrostatic interactions, and van der Waals forces. Rheological results revealed that ionogels exhibited high mechanical strength with an elastic modulus and a yield stress of 50 000 and 900 Pa, respectively. The ionogels of PPCT and Zn2+ mixtures served as the precursors to produce zinc sulfide (ZnS) nanoparticles (NPs). The uniform 10 nm-sized ZnS exhibited higher surface area and higher peroxidase-like activity that can be used for sulfide ion (S2–) colorimetric sensing to detect S2– at a lower limit detection of 5.27 nmol·L–1. Furthermore, an innovative, green, and convenient approach has been developed to produce ZnS NPs, which are an environmentally friendly and sustainable candidate material in bioengineering technology, environmental protection, and food industries.

Statistic-Driven Proton Transfer Affecting Nanoscopic Organization in an Ethylammonium Nitrate Ionic Liquid and 1,4-Diaminobutane Binary Mixture: A Steamy Pizza Model

Herein, we report on the theoretical and experimental investigation of the chemical equilibrium in a Ethylammonium Nitrate (EAN)/1,4-Diaminobutane (DAB) binary mixture displaying a significant excess of the latter component (namely, a 1:9 mole ratio). Both the neutral compounds, i.e., ethylamine (EtNH2) and DAB, present very similar chemical properties, especially concerning their basic strength, resulting in a continuous jump of the proton from the ethylammonium to the diamine (and vice-versa). Due to the significant excess of DAB, the proton is (statistically) expected to be bound to one of its nitrogen atoms, leading to the formation of a new (ternary) mixture containing DAB (ca. 80%), ethylamine (ca. 10%) and 4-amino-1-butylammonium nitrate (ABAN, ca. 10%). This is probed by means of SAXS measurements, showing LqE (low q excess) that increases over time. This feature tends to stabilize after approximately one day. When the measurement is repeated after one year, the LqE feature shows an increased intensity. Based on the results of our simulations, we suggest that this phenomenon is likely due to partial ethylamine evaporation, pushing the equilibrium toward the formation of ABAN.

Aggregation selectivity of amyloid β1‐11 peptide in aqueous ionic liquid solutions

AbstractUnderstanding the aggregation selectivity of peptide fragments of full‐length proteins in aqueous solutions with ionic liquids (ILs) could facilitate the elucidation of the relationship between the IL‐protein interactions and structural behavior of intrinsically disordered proteins (IDPs) such as amyloid β protein following the addition of ILs. In the present study, we investigate structural changes in peptide fragment 1‐11 (Aβ1‐11) of amyloid β protein in aqueous solutions with two ILs including 1‐butyl‐3‐methylimidazolium thiocyanate ([bmim][SCN]) and ethylammonium nitrate (EAN) using optical spectroscopy. The addition of [bmim][SCN], which exhibits strong protein denaturant ability, induced the formation of an intermolecular β‐sheet structure (aggregation), while the addition of EAN, which has a weaker denaturant ability compared with [bmim][SCN], did not cause aggregation. Since the role of cations is related to the ability to mask the charged residues of Aβ1‐11, the aggregation selectivity of Aβ1‐11 depends on the anionic species and anions with high denaturation ability enhanced aggregation. Our results demonstrated that the structural change in peptide fragment in aqueous IL solutions could be used to evaluate the relationship between the IL‐protein interactions and aggregation selectivity in IDPs in aqueous IL solutions.

Proton Thermodynamics in a Protic Ionic Liquid, Ethylammonium Nitrate.

In order to investigate the proton solvation state in protic ionic liquids (PILs), ten acid dissociation enthalpies and entropies of eight compounds were determined in ethylammonium nitrate (EAN). Regardless of the nature of the compound, 24 kJ mol-1 larger enthalpy and 65 J mol-1 K-1 larger entropy than those in water, respectively, were observed. These values were reasonably explained by the differences in the proton solvation structure in EAN and water. Namely, protons in EAN exist as HNO3 , having a higher reaction energy than that of H3 O+ in water, undergo entropic stabilization as a result of the less-structured solvation. As such, the entropic effect of the proton solvation structure on the acid-base property is possibly applicable to all PILs. In addition, based on these proton thermodynamics, enthalpy and entropy windows were proposed as a novel perspective for the characterization of solvents. Use of this concept enabled the visualization of similarities and differences between EAN and water.

Nitrate protic ionic liquids as electrolytes: Towards hydrogen sorption in Pd

The process of hydrogen electrosorption in the Pd thin film electrode was examined in three nitrate ionic liquids (ILs): ethylammonium nitrate (EAN), propylammonium nitrate (PAN) and 1-ethylimidazolium nitrate (C2IMN). The Pd electrode was obtained by electrodeposition on a golden matrix from palladium chloride solution. Cyclic voltammetry, chronoamperometry and chronopotentiometry were used for the electrochemical analysis. The hydrogen capacity (H/Pd) of Pd electrodes subjected to various pretreatment procedures was determined using cyclic voltammetry. The max. H/Pd equals to 0.6–0.7. In case of C2IMN IL, the noticeable phenomenon of a significant Pd dissolution under the open circuit conditions and during electrochemical hydrogen sorption experiment was observed. The physicochemical properties such as density, ionic conductivity, dynamic viscosity and water content before and after electrochemical measurements were designated. The nitrate ionic liquid stability under the electrochemical measurement conditions was confirmed by the means of Raman and 1H NMR spectroscopies. 1H NMR spectroscopy also served as a tool to compare the acidity of nitrate ILs: C2IMN>PAN>EAN.

The effect of alkyl ammonium ionic liquids on thermal denaturation aggregation of β-lactoglobulin

Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), small-angle neutron scattering (SANS) measurements, and scanning and transmission electron microscope (SEM and TEM) of β-lactoglobulin (β-LG) are performed in alkyl (methyl, ethyl, and propyl) ammonium nitrate ionic liquids (RAN-ILs) – water mixtures at 25–100 °C. The addition of these RANs decreased the thermal denaturation temperature of β-LG, and the effect is larger with an increase of the hydrophobic part of the cation of the ILs. In ethyl ammonium nitrate (EAN) and propyl ammonium nitrate (PAN) mixtures, the fractal aggregate structure of β-LG was found after the thermal denaturation occurred. On the other hand, in methyl ammonium nitrate (MAN) mixture, an amorphous aggregate was formed as well as in NaCl and NaNO3 solutions. The difference of the effect between MAN and EAN (and PAN) could arise from the balance of hydrophobic/hydrophilic parts of the cation of RAN. These results are similar to those of alcohol-water mixtures. The nanoheterogeneous structure of the RAN-water mixture which consists of the hydrophobic and hydrophilic parts might affect the aggregation structure of β-LG.

Solubilization and recovery of heat-aggregated cytochrome c using alkylammonium nitrate

We investigated the solubilization and recovery of heat-aggregated cytochrome c using alkylammonium nitrates (RAN-ILs), which are a group of protic ionic liquids (ILs), including methylammonium nitrate (MAN), ethylammonium nitrate (EAN), and propylammonium nitrate (PAN), in a wide range of concentrations (X = 0–40 mol%IL for MAN and 0–100 mol%IL for EAN and PAN) using absorption and circular dichroism spectroscopy to obtain basic information on solubilization/recovery solvents for heat-aggregated proteins using ILs. On the whole, the increase of absorbance at the soret band (~405 nm) of cytochrome c indicated that solubilization ability was observed in aqueous solutions with MAN and EAN (X > 10) and PAN (X > 5). These results indicate that the three RAN-ILs studied have solubilization ability for heat-aggregated cytochrome c, and increasing the alkyl-chain length of the cation causes an enhancement of the solubilization ability for heat-aggregated cytochrome c. The activity, secondary structure and heme coordination state (Fe–His18/Met80) of the solubilized cytochrome c in aqueous PAN solutions, which have the highest solubilization ability among the three RAN-ILs, were recovered up to X = 30 after removing PAN by dialysis. The present findings indicate that aqueous solutions with RAN-ILs have a high potential as recovery agents for heat-aggregated proteins.

Luminescent Vesicles and Lyotropic Liquid Crystals in Ethylammonium Nitrate from a Partially Amphiphilic Eu Complex.

Soft luminescent materials have attracted much attention because of their self-assembled and controllable properties. To explore their facile and effective fabrication ways, we report here the self-assembling of luminescent vesicles and lyotropic liquid crystals (LLCs) in a protic ionic liquid, ethylammonium nitrate, by a partially amphiphilic europium β-diketonate complex (Eu(III)) with a 1-dodecyl-3-methylimidazolium cation as the counter ion. An interesting result came from the complex-induced vesicle formation of corresponding amphiphile, 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br), which has been rarely reported in the past. It was the interaction between the Eu(III) and imidazolium group that changed the critical packing parameter of [C12mim]Br, which finally resulted in the occurrence of vesicles. The obtained vesicle aggregates exhibited enhanced fluorescence intensity and lifetime compared to those of Eu(III) solution. Meanwhile, a hexagonal LLC phase with better fluorescence properties was found at higher [C12mim]Br concentration. The obtained photophysical data confirmed that the order degree of Eu(III)-containing aggregates could effectively increase the energy transition efficiency of ligands. The better luminescent properties of LLC resulted from the stronger stabilizing and binding effects on Eu(III) in LLC than that in vesicles, which might be caused by closer molecular packing in LLC. The results presented here will not only expand the strategy of constructing lanthanide-containing luminescent soft materials in ionic liquids but also provide reference to better understand the effect of organized aggregates on luminescence properties.