Comprehensive extraction study using N,N-dioctylthiodiglycolamic acid: effect of S donor on metal extraction.

Extraction ability of N,N-dioctylthiodiglycolamic acid (T-DODGAA), a soft-base sulfur donor ligand with an amide group and a carboxylic acid connected by a thioether chain, for 56 metal ions have been comprehensively investigated and compared with that of N,N-dioctyldiglycolamic acid (DODGAA) with an etheric oxygen atom, a hard-base donor. The acid dissociation constant (pKa) of the thiodiglycolamic acid framework was determined to be 3.71 ± 0.06 in water (0.1 M LiCl, 25 °C) by potentiometric titration, indicating that T-DODGAA is a slightly weaker acid than DODGAA (pKa = 3.54 ± 0.03). T-DODGAA can quantitatively extract various metal ions from the 56 metal ions into the organic phase (isooctane) through a proton-exchange reaction. T-DODGAA provided higher extraction performance than DODGAA for Hf(IV), Cr(III), Fe(III), Ni(II), Cu(II), Pd(II), Ag(I), Au(III), Hg(II), Al(III), and Ga(III), especially for soft metal ions. Furthermore, to demonstrate the practical feasibility of T-DODGAA for hydrometallurgy and metal recycling, we performed selective separation tests of rare metal ions such as Sc(III), Ni(II), Co(II), Pd(II), Au(III), In(III), and Ga(III) in metal-mixed extraction systems.

Extended X-ray absorption fine structure spectroscopy measurements and ab initio molecular dynamics simulations reveal the hydration structure of the radium(II) ion.

Radium is refocused from the viewpoint of an environmental pollutant and cancer therapy using alpha particles, where it mainly exists as a hydrated ion. We investigated the radium hydration structure and the dynamics of water molecules by extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulation. The EXAFS experiment showed that the coordination number and average distance between radium ion and the oxygen atoms in the first hydration shell are 9.2 ± 1.9 and 2.87 ± 0.06 Å, respectively. They are consistent with those obtained from the AIMD simulations, 8.4 and 2.88 Å. The AIMD simulations also revealed that the water molecules in the first hydration shell of radium are less structured and more mobile than those of barium, which is an analogous element of radium. Our results indicate that radium can be more labile than barium in terms of interactions with water.

Marking actinides for separation: Resonance-enhanced multiphoton charge transfer in actinide complexes.

Precise separation and purification of f-block elements are important and challenging especially for the reduction of nuclear waste and the recycling of rare metals but are practically difficult mainly because of their chemical similarity. A promising way to overcome this difficulty is controlling their oxidation state by nonchemical processes. Here, we show resonance-enhanced multiphoton charge transfer in actinide complexes, which leads to element-specific control of their oxidation states owing to the distinct electronic spectra arising from resonant transitions between f orbitals. We observed oxidation of trivalent americium in nitric acid. In addition, we found that the coordination of nitrates is essential for promoting the oxidation reaction, which is the first finding ever relevant to the primary process of photoexcitation via resonant transitions of f-block elements. The resonance-enhanced photochemical process could be used in the nuclear waste management, as it would facilitate the mutual separation of actinides, such as americium and curium.

Lanthanide extraction using a thiodiglycolamic acid extractant: effect of S-donor on lanthanide separation.

Liquid-liquid extraction of lanthanide (Ln) ions was investigated using N,N-dioctylthiodiglycolamic acid (DOTDGAA), which is a sulfur donor ligand with an amide group and a carboxyl group connected by a thioether chain. The extraction performance and selectivity of DOTDGAA for Ln ions were compared with those of N,N-dioctyldiglycolamic acid (DODGAA), which is also an oxygen donor ligand with a similar chemical structure, to assess the effect of the soft/hard donor atom on Ln separation. DOTDGAA quantitatively extracted all Ln ions while being selective toward the light and middle Ln ions, in contrast to the selectivity of DODGAA for heavier Ln ions. Slope analysis demonstrated that the Ln3+ transfer using DOTDGAA proceeded through a proton-exchange reaction, forming a 1:3 complex, Ln(DOTDGAA)3. The back-extraction of Ln ions from the extracting phase was successfully achieved under acidic conditions.

Study on Phenanthroline Carboxamide for Lanthanide Separation: Influence of Amide Substituents.

Phenanthroline carboxamide compounds are promising for lanthanide intra-series separation. This paper presents a study on the effect of structure modification of phenanthroline carboxamides on the extraction of the whole lanthanide series. The study consists of theoretical calculations, extraction experiments of the 14 stable lanthanides, and extended X-ray absorption fine structure (EXAFS) analyses of Nd and Dy complexes. Tridentate monocarboxamides and tetradentate dicarboxamides show different trends in series extraction, although both preferentially extract the light lanthanides. The amide substituents, although not directly coordinating the metal ions, were also found to impact the distribution ratio, most probably due to a modification in the internal polarity of the molecules. This latter effect, if extrapolated to other nitrogen-based ligands such as pyridines or triazines, can be used to further fine-tune extractants for a process improvement.

Solvent Extraction of Technetium(VII) and Rhenium(VII) Using a Hexaoctylnitrilotriacetamide Extractant.

Liquid-liquid extraction for the removal of pertechnetate (99TcO4-) and perrhenate (ReO4-) is reported based on using the tripodal extractant N,N,N',N',N″,N″-hexa-n-octylnitrilotriacetamide (HONTA) composed of three amide groups and a tertiary amine. The extraction behaviors were compared with those using alkyldiamideamines (ADAAM(Oct) and ADAAM(EH)), and the commercial amine-type extractant, trioctylamine (TOA). HONTA quantitatively extracted 99TcO4- and ReO4- in the pH range from 1.0 to 2.5 by the co-extraction of protons. The extraction performance of the extractants was improved in the order of HONTA > ADAAM(Oct) > ADAAM(EH) > TOA. 99TcO4- and ReO4- in the extracting phase were successfully stripped using neutral aqueous solutions as the receiving phase, and the extraction ability of HONTA was maintained after five repeated uses.

Extraction Ability of 4-Benzoyl-3-phenyl-5-isoxazolone towards 4f-Ions into Ionic and Molecular Media.

The distribution constants of 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) and deprotonated one (PBI-) between hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C1C4im][Tf2N]) and aqueous phases were determined, together with the acid-dissociation constant of HPBI. The solvent extraction of three selected lanthanoid ions (La3+, Eu3+, and Lu3+) with HPBI from aqueous nitrate phase into [C1C4im][Tf2N] has been investigated. Application of the ionic liquid as the extracting phase greatly enhanced the extraction performance of HPBI for lanthanoid ions compared with that in the chloroform system. A slope analysis was conducted in order to compare the results of the solution 4f-ion coordination chemistry in ionic and molecular media. The composition of the extracted species was established to be anionic tetrakis entities, Ln(PBI)4-, for light, middle, and heavy lanthanoid ions in an ionic environment (Ln denotes lanthanoid ion). Nevertheless, the typical neutral chelate lanthanoid complexes of the type Ln(PBI)3 have been detected when the conventional molecular diluent chloroform was applied as an organic phase.

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.

Enzymatic fabrication of protein-decorated gold nanoparticles by the aid of artificial peptides with gold-binding affinity.

Here, we report a new approach for the biofabrication of protein-immobilized gold nanoparticles (Au NPs), using oxidoreductase with gold-binding peptide-tagged recombinant proteins. The reduction of Au ions to Au(0) was achieved using a natural electron-donating cofactor, nicotinamide adenine dinucleotide, which was regenerated by the glycerol dehydrogenase (GLD) enzyme. First, we selected the A3 peptide (AYSSGAPPMPPF) as a gold binding moiety. The A3 peptide was introduced to the C-terminus of fusion proteins of immunoglobulin G (IgG)-binding domains of protein G and protein A. In the presence of the recombinant protein, the GLD-catalyzed cofactor reduction resulted in the efficient in situ fabrication of Au NPs immobilized with the fusion protein. Moreover, the protein-immobilized Au NPs were shown to have IgG binding activity. Although the A3 peptide had the ability to stabilize Au NPs, the results suggested that its binding affinity for Au NPs was unexpectedly weaker than that of His-tag. A cysteine residue was thus introduced to a recombinant protein adjacent to the A3 peptide. Finally, an artificial peptide, comprising A3 sequence with the C-terminal single cysteine residue, enabled the stable display of a fusion protein while maintaining its IgG binding activity through the Au-S bond. This enzyme-assisted one-pot methodology for protein-Au NPs conjugation offers one potent route for the facile fabrication of biomolecule-decorated metal NPs.

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.

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.

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.

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+).

Uphill transport of rare-earth metals through a highly stable supported liquid membrane based on an ionic liquid.

We have developed a highly stable supported liquid membrane based on ionic liquids (ILs) for the separation of rare-earth metals, employing N,N-dioctyldiglycol amic acid as a mobile carrier. The quantitative transport of Y and Eu through the membrane was successfully attained, and separation from metal impurities, Zn, was efficiently accomplished. A membrane stable enough for long-term operation was constructible from imidazolium-based ILs having a longer alkyl chain, such as octyl or dodecyl groups in an imidazolium cation.

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.