Ethylammonium nitrate enhances the extraction of transition metal nitrates by tri-n-butyl phosphate (TBP)

Several molecular polar solvents have been used as solvents of the more polar phase in the solvent extraction (SX) of metals. However, the use of hydrophilic ionic liquids (ILs) as solvents has seldomly been explored for this application. Here, the hydrophilic IL ethylammonium nitrate (EAN), has been utilized as a polar solvent in SX of transition metal nitrates by tri-n-butyl phosphate (TBP). It was found that the extraction from EAN is considerably stronger than that from a range of molecular polar solvents. The main species of Co(II) and Fe(III) in EAN are likely [Co(NO₃)₄]²⁻ and [Fe(NO₃)₄]⁻, respectively. The extracted species are likely Fe(TBP)₃(NO₃)₃ and a mixture of Co(TBP)₂(NO₃)₂ and Co(TBP)₃(NO₃)₂. The addition of H₂O or LiCl to EAN reduces the extraction because the metal cations coordinate to water molecules and chloride ions stronger than to nitrate ions. This study highlights the potential of using hydrophilic ILs to enhance SX of metals.     

Optimization of Formulation Variables to Increase Antigen Entrapment in PLGA Particles

Efficient antigen entrapment is a key factor in preparation of poly (lactide-co-glycolide) acid (PLGA) vaccine formulations when the antigen is of short supply. This study presents a systematic approach in the testing of formulation variables with the objective to increase antigen entrapment in particles when the antigen stock concentration was low. Some of the experimental variables tested were poly (vinyl) alcohol (PVA) concentration in the inner (W₁) and outer (W₂) aqueous phase, W₁/oil (O) phase ratio and choice of organic solvent. The double emulsion solvent evaporation technique was applied to prepare PLGA particles with sonication as the emulsifying force. To measure antigen entrapment efficiency, the antigen (bovine serum albumin, BSA) was isotope labeled with ¹²⁵iodine (¹²⁵I). Our results demonstrated that a low PVA concentration in the inner aqueous (W₁) phase was beneficial to achieve a high encapsulation efficiency of antigen. On the contrary, in the outer aqueous (W₂) phase, a high PVA concentration favored antigen entrapment. We also demonstrated that decreasing the W₁ to O/polymer ratio contributed to increased entrapment efficiency. Testing different organic solvents (ethyl acetate, dichloromethane and chloroform), either alone or in combination, revealed that using chloroform as solvent resulted in the highest encapsulation of antigen and the highest production yield. Some of the results presented in this work are in disagreement with well-established formulation variables from previous studies.     

ANION EFFECT ON SELECTIVITY IN SOLVENT EXTRACTION OF ALKALI METAL SALTS BY CROWN ETHERS

ABSTRACT

The influence of the co-extracted anion upon competitive solvent extraction of five alkali metal cations from aqueous solutions into organic diluents by the cis-syn-cis and cis-anti-cis isomers of dicyclohexano-18-crown-6 has been assessed. The anions are bromide, chloride, iodide, nitrate, perchlorate, and thiocyanate and the organic diluents are chloroform and 1-octanol. The extraction efficiency is markedly influenced by the identity of the anion and exhibits some correlation with the inverse of the hydration enthalpy of the anion. Although potassium is the best extracted cation with all anions, the selectivities for potassium over lithium, sodium, rubidium, and cesium are strongly affected by anion variation in chloroform, but not in 1-octanol. The selectivity ordering in chloroform does not correlate with the hydration enthalpy or softness parameter for the anion. Instead it appears to result from variation of the dimensional structure and the availability of specific binding sites in the anion.     

The role of hydrogen-bond in solubilizing drugs by ionic liquids: A molecular dynamics and density functional theory study

The solvation mechanisms of aspirin and etomidate in four combinations of [Emim]⁺ and [BuGun]⁺ paired with [OAc]⁻ and [NTf₂]⁻ were systematically studied by molecular dynamics simulations and DFT calculations. It was shown that the favorable solvation of aspirin and etomidate correlated well with hydrogen-bond (H-bond) basicity of anions and the H-bond acidity of cations, respectively. Wherein, the H-bond between aspirin and [OAc]⁻ anion with high H-bond basicity possessed covalent feature, so ILs containing [OAc]⁻ anion has the best effective in solubilizing aspirin. However, H-bond interactions between etomidate and cations exhibited an electrostatic dominant, and moderate cation–anion interaction could weaken it. Accordingly, for etomidate, the best ILs solvent comprised a weakly interacting anion and a cation with strong H-bond acidity, that is, [BuGun][NTf₂]. This solvation difference was because aspirin with carboxyl group displayed strongly H-bond donating characteristic, whereas etomidate with no active hydrogen protons mainly formed H-bond with cations. Additionally, we found that π–π stacking interactions were of secondary importance for the solubilization of etomidate, but little for aspirin. These simulations will be helpful for experimental design new ILs to solubilize some drugs with aspirin-like or etomidate-like structures.     

Liposome Microencapsulation for the Surface Modification and Improved Entrapment of Cytochrome c for Targeted Delivery

In this study, we established a procedure based on the microencapsulation vesicle (MCV) method for preparing surface‐modified liposomes, using polyethylene glycol (PEG) and a site‐directed ligand, with high entrapment efficiency of cytochrome c (Cyt c). For preparing a water‐in‐oil (W/O) emulsion, egg phosphatidylcholine and cholesterol were dissolved in organic solvents (O phase) and emulsified by sonication with aqueous solution of Cyt c (W₁). Although the dispersion stability of the W₁/O emulsion was low when n‐hexane was used to dissolve the lipids in the O phase, it was substantially improved by using mixed solvents consisting of n‐hexane and other organic solvents, such as ethanol and dichloromethane (DCM). The W₁/O emulsion was then added to another water phase (W₂) to prepare the W₁/O/W₂ emulsion. PEG‐ and/or ligand‐modified lipids were introduced into the W₂ phase as external emulsifiers not only for stabilizing the W₁/O/W₂ emulsion but also for modifying the surface of liposomes obtained later. After solvent evaporation and extrusion for downsizing the liposomes, approximately 50% of Cyt c was encapsulated in the liposomes when the mixed solvent consisting of n‐hexane and DCM at a volume ratio of 75/25 was used in the O phase. Finally, the fluorescence‐labeled liposomes, with a peptide ligand having affinity to the vasculature in adipose tissue, were prepared by the MCV method and intravenously injected into mice. Confocal microscopy showed the substantial accumulation of these liposomes in the adipose tissue vessels. Taken together, the MCV technique, along with solvent optimization, could be useful for generating surface‐modified liposomes with high drug entrapment efficiency for targeted delivery.     

INTERFACIAL TENSION ESTIMATION IN ORGANIC/AQUEOUS SYSTEM

ABSTRACT

Linear solvation energy relationships are used to estimate the interfacial tension at solvent/water interfaces for systems containing ‘dry’ and ‘wet’ solvents. The correlation analysis works also in the systems containing Primene 81R and metal salts. The models

?^° = a - b, log x_S,W - b₂ log x_W,S and

?^° = a - b log (x_S,W + x_W,S)give good estimation of the interfacial tension. In the systems containing Primene 81R the surface pressure is correlated with solvent parameters according to relation ?°-7 = a + D7r*=c/3     

Synergistic Extraction of Lanthanides (III) with Mixtures of TODGA and Hydrophobic Ionic Liquid into Molecular Diluent

The extraction of lanthanides(III) from aqueous nitric acid solutions with N,N,N’,N’-tetra(n-octyl)diglycolamide (TODGA) and with mixtures of TODGA and the hydrophobic ionic liquid (IL) [C₄mim][Tf₂N] into 1,2-dichloroethane (DCE) has been investigated. The extraction efficiency of Ln(III) ions was greatly enhanced by the addition of a small amount of IL to an organic phase containing TODGA. The synergistic effect comes from the higher hydrophobicity of Ln(III) extracted species formed by TODGA and the weakly coordinating Tf₂N^? anions compared with those formed by TODGA and NO₃^? ions as the counter-anions. The partition of Tf₂N^? anions between the organic and aqueous phases is the dominant factor governing the extractability of lanthanides(III) with mixtures of TODGA and [C₄mim][Tf₂N]. The extraction of Ln(III) from aqueous nitric acid solutions by TODGA alone and its mixtures with [C₄mim][Tf₂N] into DCE can be described on the basis of the solvation extraction mechanism. However, in the extraction system with added [C₄mim][Tf₂N], the partition of Tf₂N^? between two immiscible phases and the interaction between HTf₂N and TODGA in the organic phase should be taken into account. Possible reasons of the antagonistic effect in the TODGA–[C₄mim][Tf₂N] extraction system are discussed.     

Solvation models in the reaction between phenacyl bromide and 2-mercaptobenzimidazole

The reaction between phenacyl bromide and 2-mercaptobenzimidazole has been studied in 12 different protic and aprotic solvents. The kinetic study shows that the reaction is second-order with first-order dependence each on (phenacyl bromide) and (2-mercaptobenzimidazole). Analysis of rate data shows that there is no direct correlation between the rate constant and dielectric constant of the solvent. Correlation of rate data with different solvent parameters like hydrogen bond acceptor basicity, polarizability and solvent electrophilicity, using linear multiple regression analysis shows that the reaction is influenced by these properties of the solvent. From the regression coefficients, information on the mode of solvation of the reactants and the transition state is obtained. The reaction has also been studied at different temperatures and the thermodynamic parameters Δ H ^#, Δ S ^# and Δ G ^# are evaluated.     

A Striking Effect of Ionic‐Liquid Anions in the Extraction of Sr2+ and Cs+ by Dicyclohexano‐18‐Crown‐6

Abstract

The nature of the ionic‐liquid (IL) anion has been found to have a remarkable effect on the solvent extraction of Sr²⁺ and Cs⁺ by dicyclohexano‐18‐crown‐6 dissolved in ionic liquids. In particular, the extraction efficiency increases with the hydrophobicity of the IL anion as reflected by the solubility in water of ILs having a common cation. Since a cation‐exchange mechanism is operating in these systems, the influence of the IL anion is in large part attributable to an expected Le Chatelier effect in which a greater aqueous concentration of IL cation, obtained when using an IL anion of lower hydrophobicity, opposes cation exchange. This dependence is opposite to that found for IL cations, indicating a significant advantage of using ILs with hydrophobic anions for cation extraction. Furthermore, the extraction selectivity for Sr²⁺ over Na⁺, K⁺, and Cs⁺ can be significantly improved through the use of hydrophobic anions for the ILs containing 1‐ethyl‐3‐methylimidazolium or 1‐butyl‐3‐methylimidazolium cations.     

Experimental investigation of sheet flexibility of layered double hydroxides: One-pot morphosynthesis of inorganic intercalates

The sheet flexibility of layered double hydroxides (LDHs) has been investigated experimentally using co-precipitation and urea hydrolysis methods in an aqueous solution of long-chain anion surfactant in this work. Using dodecylsulfate (DS) anion as morphology-controlling agent, layer-bended or contorted Mg/Al-LDH is obtained successfully. The morphology of bent layers is retained during either in situ decomposition of interlayer DS to SO₄²⁻ or ion exchange of interlayer DS by CO₃²⁻. The direct synthesis of the layer-distorted LDHs intercalated with small inorganic anions is quite difficult. It has been achieved using layer-bended LDHs pillared with bulky organic anions as precursors in this paper. The morphosynthesis is expanded to Co/Al and Ni/Al-LDHs, indicative of the general flexibility of this kind of anionic clays.     

Extraction of Cs+ and Sr2+ from HNO3 Solution Using Macrocyclic Polyethers

Abstract

A series of crown compounds has been studied in connection with the development of a solvent extraction process for removing Cs⁺ and Srs²⁺ from acidic high activity nuclear waste. Crown compounds were investigated because of their ability to form organic soluble complexes with the alkali metals and the alkaline earth metals. The solvent (tributyl phosphate and kerosene) was chosen because of its compatibility with the Purex process currently used at the Savannah River Plant for plutonium and uranium purification. The crown compounds were found not to be sufficiently strong complexing agents to extract these metals from an aqueous phase with an inorganic anion such as nitrate or chloride. However, the use of large organic soluble anions which also functioned as liquid ion exchangers made it possible to extract Cs⁺ from 3 M HNO₃ while leaving Sr²⁺ and La³⁺ behind. The use of .02 M bis-(4,4′(5′)-[q-hydroxyheptyl]-benzo)-18-crown-6 in 0.076 M (5 vol-%) didodecylnaphthalene sulfonic acid (DNS)-27 vol-% TBP-68 vol-% kerosene gave the most favorable results for cesium extraction. The two phases separated cleanly and rapidly, yielding a distribution coefficient of 2.0 org/aq from 3 M HNQ₃. Strontium and lanthanum did not extract significantly at this acid concentration. The distribution data in the low acid region (10^?4 M) are best explained by steric hindrance effects. The lanthanum did not extract at any acid concentration while the strontium extracted very well by a liquid ion-exchange mechanism but the addition of the crown compound did not improve the distribution. The addition of the crown compound improved the Cs⁺ distribution markedly in the low acid region even though the Cs⁺ diameter is larger than the 18-crown-6-crown cavity while Sr²⁺ should fit very well.     

A novel Wells–Dawson polyoxometalate-based metal–organic framework constructed from the uncommon in-situ transformed bi(triazole) ligand and azo anion

A novel Wells–Dawson polyoxometalate (POM)-based metal–organic framework (MOF) constructed from bi(triazole) ligand and azo anion, namely, [Ag₁₃(L)₆(N₂)(HP₂W₁₈O₆₂)] (1) (HL = 4-(1 H-1,2,4-triazol-3-yl)-2 H-1,2,4-triazolyl) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, IR spectra, PXRD analysis. In compound 1, the rigid bi(triazole) ligands connected Ag^I ions to construct a 2D metal–organic layer, which was further extended by azo anions forming a 3D framework. The Wells–Dawson type [P₂W₁₈O₆₂]^6 − anion as a multidentate inorganic ligand coordinated with the Ag^I ions, consolidating the 3D MOF. The L ligands and azo anions were in-situ transformed from a bi(triazole) derivative, which has never been observed in previous reports. In addition, the electrocatalytic and photocatalytic properties of compound 1 have been investigated.     

Ion-solvent interactions - studies on the solvation of electrolytes in mixed solvents

In order to throw light on ion-solvent interactions, the solvation numbers of electrolytes in different mixed solvents (methanol + water and ethanol + water mixtures) have been determined using ultrasonic interferometer. The anomalies in the solvation number of cations (in aqueous solutions) like K⁺, Na⁺ and H⁺ are presented. The changes in the solvation numbers of electrolytes with increasing quantities of alcohol indicates some interesting features and are explained on the basis of:(i) decrease in the solvent molecules.(ii) structural re-arrangement.(iii) preferential solvation of cations and anions.(iv) Approximations in the determination of solvation numbers. The role of the solvents could hardly be explained in absence of a complete knowledge of the nature of solvation of electrolytes and particularly of ions. The subject has attracted considerable attention and the solvation number has been determined using different well-known techniques[1-4].In order to throw light on the ion-solvent interactions, we tried to determine the solvation numbers of different known electrolytes like HCl, NaCl and KCl in water, methanol + water and ethanol + water mixtures by the compressibility method using ultrasonic interferometer. The results are presented in this communication.     

Liquid-Liquid Phase Distribution Studies of Chromium(VI) between Mineral Acid Solutions and 5-(4-Pyridyl)nonane N-Oxide in Benzene,and Enrichment by Extraction Plant with Pulsation Column

Abstract

A liquid-liquid extraction system consisting of a benzene solution of 5-(4-pyridyl)nonane N-oxide (P_yNO_x) and mineral acid solutions has been studied for the extraction of chromium(VI). The optimal conditions for the extraction have been carefully selected from a critical study of the various factors involved, such as the effects of the concentration of the mineral acids, chromium, and the solvent; and the salting and complexing agents. Common anions have little effect on extraction in concentrations up to 0.5 M. Backextraction of the metal can be accomplished by a number of solutions and by water. Extraction of several metals was investigated under optimal conditions for the extraction of chromium. Common base metal ions like iron, aluminum, magnesium, calcium, etc. are not extracted. The mechanism of extraction has been studied by using slope analyses and saturation experiments. The predominant mode of extraction appears to be ionic association with the probable composition of the extracted species being P_yNO_xH⁺.HCr₂O₇ ^?, with some additional contribution by benzene. Extraction at a high aqueous to organic ratio has been studied by using an extraction plant with a pulsation column.     

Detection of Reduced W n+ Sites on WO3–ZrO2 and Pt/WO3–ZrO2 Catalysts by Infrared Spectroscopy of Adsorbed NO

Adsorption of NO on oxidized WO₃–ZrO₂ catalysts leads to formation of adsorbed N₂O, surface nitrates, NO⁺, and Zr⁴⁺(NO^- ₃)–NO species. When NO is adsorbed on a sample reduced at 523 K, W⁵⁺ –NO (1855 cm^-1) and W⁴⁺(NO)₂ (1785 and 1700 cm^-1) species are formed in low concentration. Reduction at 573 K increases the density of W⁴⁺ sites and this density remains unchanged after reduction up to 673 K. The W⁴⁺(NO)₂ species are stable towards evacuation and in the presence of oxygen; however, they quickly disappear in the simultaneous presence of NO and O₂ as a result of the oxidation of the W⁴⁺ cations to W⁶⁺. The density of the W⁴⁺ sites on a Pt/WO₃–ZrO₂ sample is significant even after reduction at 523 K. This is explained by the promotion effect of platinum on the support reduction. The use of NO as a probe molecule for detection of reduced W ⁿ⁺ sites on tungstated zirconia is discussed.     

How imidazolium-based ionic liquids solubilize the poorly soluble ibuprofen? A theoretical study

Molecular dynamics simulations were performed to study combinations of [AcO]⁻, [TfO]⁻, [BF₄]⁻, and [PF₆]⁻ anions paired with imidazolium cations of increasing alkyl chain length to elucidate the roles of anions and cations in solvating ibuprofen. Our simulation results revealed that ionic liquids (ILs) with strong ibuprofen solvation capacity should possess strong van der Waals force from cations and strong hydrogen bond (HB) from anions. Accordingly, it was found that ILs containing anions with strong HB acceptability, such as [AcO]⁻ anion, were the best effective solvent for ibuprofen solvation, while the longer alkyl chain in the imidazolium cations decrease the polarity, thus increasing the affinity with ibuprofen. Therefore, it was suggested that the heterocyclic structure of imidazolium cation with moderate polarity and longer alkyl chain is a promising cation candidate, whereas the anions which have a strong HB acceptability and substituents without electron withdrawing groups are beneficial. The obtained results can provide useful information for rational design and selection of new ILs to dissolve insoluble drugs.     

SYNERGISTIC EXTRACTION OF EUROPIUM(III) WITH BENZOIC ACID AND THENOYLTRIFLUOROACETONE

ABSTRACT

The solvent extraction of europium(III) into solutions of thenoyltrifluoroacetone and benzoic acid in cyclohexane, carbon tetrachloride, benzene, chloroform, pentachloroethane, and tetrachloroethane has been measured at 25°C. It has been found that the extracted species involve two types of adducts, EuA₃· HB and EuA₃· 2HB where A denotes the TTA anion and HB the benzoic acid monomer. The magnitude of the adduct formation constants in different solvents has been correlated with the dimerization constants of benzoic acid in the solvents.     

Dehydrating Effect of Concentrated Aqueous Alkaline Solutions in Aliphatic Nucleophilic Substitutions Carried out in Aqueous-Organic Two-Phase Systems. The Different Behavior of Various Phase-Transfer Catalysts: Quaternary Salts,Crown Ethers and Cryptands

Concentrated aqueous NaOH and KOH solutions affect the hydration and hence the reactivity of anions (Cl⁻, Br⁻, I⁻, SCN⁻, N⁻₃) in aliphatic nucleophilic substitutions catalyzed by lipophilic quaternary onium salts, cryptands and crown ethers under phase-transfer (PTC) condtions. In the presence of aqueous 50% NaOH or 53% KOH non-hydrated anions are transferred from the aqueous into the organic phase by quaternary salts. The anionic reactivity thus becomes identical to that found under anhydrous homogeneous conditions in non-polar organic media. Unlike quaternary salts, in the presence of cryptates water is not completely removed even at the highest KOH concentration, i.e. conditions in which aH₂O ∼ 0. Residual hydration depends on the nature of the anion and is the highest for anions with localized and/or less polarizable charge, such as Cl⁻, Br⁻ and N⁻₃. As a consequence, rate constants noticeably increase in comparison with those found under conventional PTC conditions, but don't reach those of anhydrous solutions. Behavior of crown ethers is in between that of quaternary salts and cryptates, since residual hydration in the presence of 53% aqueous KOH is lower than that of cryptates, whereas anionic reactivity become practically identical to that found under anhydrous conditions. A comparison of the catalytic efficiency of lipophilic quaternary salts, cryptands and crown ethers under various reaction conditions is also included.     

Solvation of Substituted Phenoxide Ions in T-Butyl Alcohol-Water Mixtures,from Kinetic Studies of Proton Exchange

Rate constants (k_2W or k_2A) for proton exchange between a phenol, its conjugate base, and a water or t -butyl alcohol molecule have been measured in a t -butyl alcohol-water mixture by nuclear magnetic resonance. Since k_2W and k_2A are both high (k_2W > 10⁸ sec^?1 M^?1), the ratio k_2W/k_2A measures the selective solvation of the O^?-site (of the phenoxide ions) by water and t -butyl alcohol. In 11.47 mole % t -butyl alcohol — 88.53 mole % water, k_2W/k_2A is found to be 14 ± 3 when the ionic reactant is ortho -bromophenoxide ion, and 32 ± 8 when it is meta -nitrophenoxide ion. The results suggest that substituents have a marked effect on the selective solvation of the O^?-site.     

Extraction of Trivalent Lanthanides and Americium by Tri-n-octylphosphine Oxide from Ammonium Thiocyanate Media

Abstract

An investigation of the solvent extraction of trivalent lanthanides and Am³⁺ from ammonium-thiocyanate media by tri(n-octyl)phosphine oxide (TOPO) in toluene has been completed. This system is of interest both for its potential as a means of separating transplutonium actinides from fission-product lanthanides and for inherent interest in thiocyanate-based solvent extraction systems. Partitioning was monitored using radiotracer techniques where appropriate, and ICP-OES or ICP-MS for others. The extraction behavior of all members of the lanthanide series (except for Pm) plus Y have been investigated. Conditional enthalpies (all exothermic) were determined (for selected systems) from the temperature dependence of the extraction reaction. A comparison with nitrate media shows higher extractive power of TOPO in contact with thiocyanate media, arising at least in part from the lower heat of the phase transfer of thiocyanate (relative to nitrate). The moderate tendency of HSCN to partition into the extractant phase has been profiled. Slope analysis indicates that TOPO solvation decreases from four (M(SCN)₃TOPO₄) for the light members of the series to three (or less) for the heavy lanthanide ions; Am³⁺ is extracted with four TOPO molecules. Despite the decrease in Ln:TOPO stoichiometry across the series, extraction is generally flat for the light lanthanides and increases from Gd³⁺ to Lu³⁺. The extraction of Am³⁺ from mildly-acidic ammonium-thiocyanate media was found to be at least 10 times stronger than that of the lanthanides between La³⁺ and Gd³⁺.