Size Distribution of Droplets in a Two Liquid-phase Mixture Compared between Liquid Spraying and Mechanical Stirring.

A new liquid-liquid extraction method, called the "emulsion flow" method, is expected to realize an ideal liquid-liquid extraction by controlling the emulsion generation and separation using liquid spraying, only by solution sending. In order to understand the mechanism of emulsion control in the emulsion flow method, the size distribution of droplets in two liquid-phase mixtures was compared by using originally designed apparatuses 1) for the case of liquid spraying and 2) for the case of mechanical stirring. We demonstrated that the size distribution of droplets generated near a mixing device (a nozzle for liquid spraying or an impeller head for mechanical stirring) determines the phase-separation property.

Continuous Liquid-Liquid Extraction of Uranium from Uranium-containing Wastewater Using an Organic Phase-refining-type Emulsion Flow Extractor.

A previously reported emulsion flow (EF) extraction system does not equip the refining device for any used organic phase. Therefore, the processing of large quantities of wastewater by using the EF extractor alone could lead to the accumulation of extracted components into the organic phase, and a lowering of the extraction performance. In the present study, we developed an organic phase-refining-type EF system, which is equipped with a column for refining a used organic phase to prevent accumulation, and successfully applied it for treating uranium-containing wastewater.

Comprehensive extraction study using N,N-dioctyldiglycolamic acid.

We report on the acid dissociation constants (Ka) of diglycolamic acid-type ligands together with comprehensive data on the extraction performance of N,N-dioctyldiglycolamic acid (DODGAA) for 54 metal ions. The pKa of the diglycolamic acid framework was determined to be 3.54 ± 0.03 in water (0.1 M LiCl, 25°C) by potentiometric titration, indicating that DODGAA is strongly acidic compared with acetic acid. DODGAA can quantitatively transfer various metal ions among the 54 metal ions through a proton-exchange reaction, and provides excellent extraction performance and separation ability for rare-earth metal ions, In(III), Fe(III), Hg(II), and Pb(II) among the 54 metal ions.

Highly efficient extraction separation of lanthanides using a diglycolamic acid extractant.

Liquid-liquid extraction of lanthanide ions (Ln(3+)) using N,N-dioctyldiglycolamic acid (DODGAA) was comprehensively investigated, together with fluorescence spectroscopic characterization of the resulting extracted complexes in the organic phase. DODGAA enables the quantitative partitioning of all Ln(3+) ions from moderately acidic solutions, while showing selectivity for heavier lanthanides, and provides remarkably high extraction separation performance for Ln(3+) compared with typical carboxylic acid extractants. Furthermore, the mutual separation abilities of DODGAA for light lanthanides are higher than those of organophosphorus extractants. Slope analysis, loading tests, and electrospray ionization mass spectrometry measurements demonstrated that the transfer of Ln(3+) with DODGAA proceeded through a proton-exchange reaction, forming a 1:3 complex, Ln(DODGAA)3. The stripping of Ln(3+) from the extracting phase was successfully achieved under acidic conditions. Time-resolved laser-induced fluorescence spectroscopy revealed that the extracted Eu(3+) ions were completely dehydrated by complexation with DODGAA.

Extraction behavior and selective separation of lead(II) using N,N-dioctyldiglycol amic acid.

Selective separation of lead ions (Pb(2+)) from aqueous solutions containing multiple divalent metal ions (Pb(2+), Cu(2+), Cd(2+), Zn(2+), Mn(2+), Co(2+), and Ni(2+)) was investigated using liquid-liquid extraction. N,N-Dioctyldiglycol amic acid (DODGAA) enabled quantitative extraction and efficient separation of Pb(2+) from the metal ion mixture under mildly acidic conditions. Compared with conventional commercial extractants, DODGAA provided better extraction and excellent selectivity for Pb(2+). The extraction of Pb(2+) with DODGAA proceeded through a proton-exchange reaction and formed a 1:2 complex, Pb(DODGAA)(2). The Pb(2+) was readily stripped from the extracting phase under acidic conditions, and the organic solution with DODGAA could be recycled.

Specific cooperative effect of a macrocyclic receptor for metal ion transfer into an ionic liquid.

An intramolecular cooperative extraction system for the removal of strontium cations (Sr(2+)) from water by use of a novel macrocyclic receptor (H(2)ßDA18C6) composed of diaza-18-crown-6 and two ß-diketone fragments in ionic liquid (IL) is reported, together with X-ray spectroscopic characterization of the resulting extracted complexes in the IL and chloroform phases. The covalent attachment of two ß-diketone fragments to a diazacrown ether resulted in a cooperative interaction within the receptor for Sr(2+) transfer, which remarkably enhanced the efficiency of Sr(2+) transfer relative to a mixed ß-diketone and diazacrown system. The intramolecular cooperative effect was observed only in the IL extraction system, providing a 500-fold increase in extraction performance for Sr(2+) over chloroform. Slope analysis and potentiometric titration confirmed that identical extraction mechanisms operated in both the IL and chloroform systems. Extended X-ray absorption fine structure spectroscopy revealed that the average distance between Sr(2+) and O atoms in the Sr(2+) complex was shorter in IL than in chloroform. Consequently, Sr(2+) was held by H(2)ßDA18C6 more rigidly in IL than in chloroform, representing an important factor dominating the magnitude of the intramolecular cooperative effect of H(2)ßDA18C6 for Sr(2+). Furthermore, competitive extraction studies with alkaline earth metal ions revealed that the magnitude of the intramolecular cooperative effect depended on the suitability between metal ion size and the cavity size of H(2)ßDA18C6. Sr(2+) was successfully recovered from IL by controlling the pH in the receiving phase, and the extraction performance of H(2)ßDA18C6 in IL was maintained after five repeated uses.

Effects of substituents in ß-diketones and their tris-iron(III) complexes on partitioning between various micellar phases and the bulk aqueous phase.

To determine the factors that affect the partitioning of solutes in micellar systems, we investigated the partitioning of several ß-diketones and their tris-complexes with iron(III) between the bulk aqueous phase and micelles of various polyoxyethylene (POE)-type nonionic surfactants (C(12)POE(8), Brij 35, Brij 58, and Triton X-100). The trends of the partition constants in the micellar systems differed from those in typical liquid-liquid systems; these differences may have been due to the effects of the substituent groups on the extractants, and to the effects of the inner-sphere chemistry of the micelles. The bulkiness and the low wettability of the extractants and the complexes hindered their extraction into the micellar phase. The interaction between the polyoxyethylene moiety of the surfactants and water molecules dissolved in the micellar mantle may have hampered the penetration of such solutes with bulky or low-wettability substituents into the mantle. The locus of the solutes in the micelles seemed to play an important role in the partitioning behavior.

Facile, rapid and efficient biofabrication of gold nanoparticles decorated with functional proteins.

We report a one-pot biological approach to fabricate gold nanoparticle (AuNP)-ZZ domain conjugates using peptide-functionalized proteins that can simultaneously direct both biomineralization and surface modification of AuNPs. In addition, immuno-AuNPs are readily prepared through the specific binding of antibodies to the ZZ domain on the AuNPs.

Counter current "emulsion flow" extractor for continuous liquid-liquid extraction from suspended solutions.

A single current "emulsion flow" liquid-liquid extraction apparatus has a head with a number of holes from which micrometer-sized droplets of an aqueous phase spout into an organic phase to mix the two liquid phases. For practical use, however, a fatal problem can occur when particulate components in the aqueous phase plug the holes. In the present study, we have succeeded in solving the problem by applying a counter current-type emulsion flow extractor where micrometer-sized droplets of the organic phase are generated.

Reversed-micellar extraction of strontium(II) from model solutions of seawater.

In order to monitor a radioactive nuclide of strontium-90 in seawater around nuclear facilities, a solvent-extraction method for collecting Sr(II) in seawater was examined. A reversed-micellar extraction system containing an anionic surfactant AOT and a molecular extractant N,N,N',N'-tetra(n-octyl)diglycolamide (TODGA) in n-hexane was chosen for the extraction of Sr(II) from model solutions of seawater containing 0.5 M NaCl (1 M = 1 mol dm(-3)), 0.05 M MgCl(2), and/or 0.01 M CaCl(2). The combination of AOT-forming reversed micelles and TODGA coordinating with Sr(II) as an organic ligand (extractant) was found to be efficient for the extraction of Sr(II) from model solutions. The mechanism of the reversed-micellar extraction system was also considered in the present study.

Thermochromic properties of low-melting ionic uranyl isothiocyanate complexes.

Temperature-dependent yellow-to-red colour changes of uranyl thiocyanate complexes with 1-alkyl-3-methylimidazolium cations have been studied by different spectroscopic methods and this phenomenon is attributed to changes in the local environment of the uranyl ion, including the coordination number, as well as to cation-anion interactions.

New apparatus for liquid-liquid extraction, "emulsion flow" extractor.

A simple and low-cost apparatus for continuous and efficient liquid-liquid extraction, which does not need continual mechanical forces (stirring, shaking, etc.) other than solution sending, has newly been developed. This apparatus, named "emulsion flow" extractor, is composed of a column part where an emulsified state fluid flow (emulsion flow) is generated by spraying micrometer-sized droplets of an aqueous phase into an organic phase and a phase-separating part where the emulsion flow is destabilized by means of a sudden decrease in its vertical liner velocity due to a drastic increase in cross-section area of the emulsion flow passing through. In the present study, the performance of a desktop emulsion flow extractor in the extraction of Yb(III) and U(VI) from aqueous HNO(3) solutions into isooctane containing bis(2-ethylhexyl) phosphoric acid (D2EHPA) was evaluated. The mixing efficiency of the emulsion flow extractor was found to be comparable with that of a popular liquid-liquid extractor, mixer-settler. Moreover, the emulsion flow extractor proved to have an overwhelming advantage in terms of phase-separating ability.

Synergistic effect of 18-crown-6 derivatives on chelate extraction of lanthanoids(III) into an ionic liquid with 2-thenoyltrifluoroacetone.

The synergistic effect of 18-crown-6 derivatives, such as 18-crown-6 (18C6), cis-dicyclohexano-18-crown-6 (DC18C6) and dibenzo-18-crown-6 (DB18C6), on the extraction of trivalent lanthanoids (Ln(3+)) into an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, with 2-thenoyltrifluoroacetone (Htta) was investigated. The extractability of lighter Ln(3+) was enhanced by adding 18C6 or DC18C6, whereas no enhancement of the extractability was observed by adding DB18C6. Moreover, the synergistic effect by the crown ether (CE) was increased along with the decrease in the atomic number of Ln. In the synergistic extraction system, Ln(3+) was extracted as cationic ternary complexes Ln(tta)(2)(CE)(+) and Ln(tta)(CE)(2+), and it was suggested that the formation of the Ln(tta)(CE)(2+) complex as an extracted species results in the large synergistic effect. This synergistic effect originated in a size-fitting effect of CE on complexation to Ln(3+).

Cooperative intramolecular interaction of diazacrown ether bearing beta-diketone fragments on an ionic liquid extraction system.

A novel extractant beta-diketone-substituted diaza-18-crown-6 demonstrated very efficient extraction of Sr(2+) due to an intramolecular synergistic effect on the ionic liquid extraction system and recovery of Sr(2+) from the ionic liquid was successfully achieved under acidic conditions.

Extraction behavior of lanthanides using a diglycolamide derivative TODGA in ionic liquids.

Liquid-liquid extraction of lanthanides from aqueous solutions into ionic liquids (ILs) has been investigated using N,N,N',N'-tetra(n-octyl)diglycolamide (TODGA) as an extractant, and compared with that in the isooctane system. Application of ILs as the extracting phase provided unprecedented enhancement of the extraction performance of TODGA for lanthanides compared with that of the isooctane system. Slope analysis confirmed that TODGA in ILs formed a 1:3 complex with La3+, Eu3+, or Lu3+. On the other hand, the molar ratios of species extracted into isooctane were 1:3 for La3+ or 1:4 for Eu3+ and Lu3+, depending on the atomic number of the lanthanide. The transfer of lanthanides with TODGA into ILs proceeded via a cation-exchange mechanism, in contrast to ion pair extraction in the isooctane system. Furthermore, we clarified that TODGA provided selectivity for the middle lanthanides in the ILs systems, but heavier lanthanides in the isooctane system.

Extraction behavior and separation of lanthanides with a diglycol amic acid derivative and a nitrogen-donor ligand.

The extraction and separation of lanthanides have been investigated using CHON-type extractants, which are composed of only C, H, O, and N atoms. N,N-Dioctyldiglycol amic acid (DODGAA) showed high extraction and separation performances for heavier lanthanides compared with typical CHON-type extractants. On the other hand, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) provided an unprecedentedly high selectivity for lighter lanthanides. Furthermore, it was found that the combination of DODGAA and TPEN under suitable conditions enabled the mutual separation of light, middle, and heavy lanthanides.

Calixarene-assisted protein refolding via liquid-liquid extraction.

In this paper we report on protein refolding by means of a liquid-liquid transfer technique using a calixarene. We have found that a calix[6]areneacetic acid derivative forms a supramolecular complex with urea-denatured cytochrome c at the oil-water interface, which enables quantitative transfer of the protein from an 8 M urea aqueous solution into an organic phase through a proton-exchange mechanism. Denatured cytochrome c is completely separated from the denaturant and is isolated from other denatured cytochrome c molecules to suppress the generation of aggregates due to protein-protein interactions. The recovery of cytochrome c from the organic phase is successfully achieved under acidic conditions using an appropriate amount of 1-butanol. UV-vis, CD, and fluorescence spectroscopic characterizations demonstrate that cytochrome c transferred into a denaturant-free aqueous solution regains its native structure. The reduction kinetics of refolded cytochrome c using ascorbic acid indicates that the protein provides approximately 72% of native activity as an electron-transfer protein.

Extractive solubilization, structural change, and functional conversion of cytochrome c in ionic liquids via crown ether complexation.

This article reports on the extraction behavior of heme proteins from an aqueous phase into ionic liquids (ILs) with dicyclohexano-18-crown-6 (DCH18C6), and the structure-function relationship of cytochrome c (Cyt-c) dissolved in ILs. We have found that DCH18C6 enables transfer of Lys-rich proteins into ILs via supramolecular complexation. The hydrophobicity and functional groups of ILs have a great influence on protein partitioning, and a hydroxyl group-containing IL with DCH18C6 is capable of the quantitative partitioning of Cyt-c. On the other hand, protein transfer using conventional organic solvents is negligibly small. UV-visible, CD, and resonance Raman spectroscopic characterizations indicate that the sixth ligand Met 80 in the heme group of the Cyt-c-DCH18C6 complex in IL is replaced by other amino acid residues of the peptide chain and that a non-natural, six-coordinate, low-spin ferric heme structure is induced in IL. Solubilization of Cyt-c in IL causes the environmental change of the heme vicinity of Cyt-c, which triggers the functional conversion of Cyt-c from an electron-transfer protein to peroxidase. The Cyt-c-DCH18C6 complex in IL provides remarkably high peroxidase activity compared with native Cyt-c, because of enhancement of the affinity for H2O2.

Selective separation of Am(III) from lanthanides(III) by solvent extraction with hydrophobic field of "superweak" anion.

The weakly coordinating hydrophobic anion TFPB-, whose surface is covered with a hydrophobic field, gives rise to a selective separation of Am(III) from lanthanides(III) in their solvent extraction even with a hard-donor extractant that shows no selectivity for Am(III) in traditional solvent extraction.