Selective Lanthanide Research Articles

Relationship of interface structure to the dynamics of selective lanthanide extraction

Recent synchrotron X-ray studies have revealed a variety of specific ion effects in the structures formed by lanthanides and surfactants at air-water and solvent-water interfaces. However, the relevance of the interfacial structure to extraction and selective separation processes has been unclear. We have studied solvent extraction from aqueous solutions containing lanthanide ions to organic solvents containing model extractants, and correlated the results to the interfacial structure. The selectivity, extraction rates and extraction efficiencies are consistent with the postulate that when hydrophobic bilayers form at the interface, there is faster and better extraction. Further, selectivity during extraction from mixtures is enhanced when there is less extractant than needed for complete extraction of all the ions present.

Enhanced rare-earth separation with a metal-sensitive lanmodulin dimer

Technologically critical rare-earth elements are notoriously difficult to separate, owing to their subtle differences in ionic radius and coordination number1–3. The natural lanthanide-binding protein lanmodulin (LanM)4,5 is a sustainable alternative to conventional solvent-extraction-based separation6. Here we characterize a new LanM, from Hansschlegelia quercus (Hans-LanM), with an oligomeric state sensitive to rare-earth ionic radius, the lanthanum(III)-induced dimer being >100-fold tighter than the dysprosium(III)-induced dimer. X-ray crystal structures illustrate how picometre-scale differences in radius between lanthanum(III) and dysprosium(III) are propagated to Hans-LanM’s quaternary structure through a carboxylate shift that rearranges a second-sphere hydrogen-bonding network. Comparison to the prototypal LanM from Methylorubrum extorquens reveals distinct metal coordination strategies, rationalizing Hans-LanM’s greater selectivity within the rare-earth elements. Finally, structure-guided mutagenesis of a key residue at the Hans-LanM dimer interface modulates dimerization in solution and enables single-stage, column-based separation of a neodymium(III)/dysprosium(III) mixture to >98% individual element purities. This work showcases the natural diversity of selective lanthanide recognition motifs, and it reveals rare-earth-sensitive dimerization as a biological principle by which to tune the performance of biomolecule-based separation processes.

Efficient and selective lanthanide recovery from highly acidic solutions by using a porous pillar[5]arene-based diglycolamide impregnated resin

The recovery of lanthanides from high level liquid waste (HLLW) is of great significance for both environmental protection and sustainable development of resources. Traditional methods for this purpose are often plagued by poor selectivity, low capacity, and limited acid tolerance. Here we report a new material prepared by impregnating P[5]A-DGA onto porous Amberlite XAD-7 resin for efficient and selective lanthanide adsorption from highly acidic solutions. The as-prepared composite material (PDA resin) shows outstanding sorption efficiency for lanthanides in a wide range of acidities (0.01–3 M HNO3) and exhibits good selectivity towards lanthanides over different kinds of competing metal ions in simulated nuclear wastewater. Adsorption equilibrium can be achieved within 60 min and the pseudo-second-order model shows better correlation with the kinetic data, indicating that chemical adsorption is the rate determining step. Adsorption isotherm data can be well fitted by Langmuir model, giving a Eu(III) sorption capacity of 33.3 mg/g at 1 M HNO3, which is superior to other materials employed for the similar purpose. Importantly, the adsorption capacity can be regenerated by using a mixture of 1 M guanidine carbonate and 0.05 M EDTA-2Na solution as the eluent, and the lanthanide adsorption efficiency from simulated nuclear wastewater remains at the initial level after three desorption-adsorption cycles. Finally, the possible configurations of the ligand-Ln(III) complexes were optimized by DFT calculations, which suggest that each Ln(III) tends to bind to three DGA arms via a nine coordination mode. This research advances the development of pillar[5]arenes for lanthanide recovery by demonstrating a simple and generally applicable method to convert P[5]A-DGA extractant into an efficient adsorbent.

Engineering lanmodulin's selectivity for actinides over lanthanides by controlling solvent coordination and second-sphere interactions.

Developing chelators that combine high affinity and selectivity for lanthanides and/or actinides is paramount for numerous industries, including rare earths mining, nuclear waste management, and cancer medicine. In particular, achieving selectivity between actinides and lanthanides is notoriously difficult. The protein lanmodulin (LanM) is one of Nature's most selective chelators for trivalent actinides and lanthanides. However, mechanistic understanding of LanM's affinity and selectivity for f-elements remains limited. In order to decipher, and possibly improve, the features of LanM's metal-binding sites that contribute to this actinide/lanthanide selectivity, we characterized five LanM variants, substituting the aspartate residue at the 9th position of each metal-binding site with asparagine, histidine, alanine, methionine, and selenomethionine. Spectroscopic measurements with lanthanides (Nd3+ and Eu3+) and actinides (243Am3+ and 248Cm3+) reveal that, contrary to the behavior of small chelator complexes, metal-coordinated water molecules enhance LanM's affinity for f-elements and pH-stability of its complexes. Furthermore, the results show that the native aspartate does not coordinate the metal directly but rather hydrogen bonds to coordinated solvent. By tuning this first-sphere/second-sphere interaction, the asparagine variant nearly doubles LanM's selectivity for actinides versus lanthanides. This study not only clarifies the essential role of coordinated solvent for LanM's physiological function and separation applications, but it also demonstrates that LanM's preference for actinides over lanthanides can be further improved. More broadly, it demonstrates how biomolecular scaffolds possess an expanded repertoire of tunable interactions compared to most small-molecule ligands – providing an avenue for high-performance LanM-based actinide/lanthanide separation methods and bio-engineered chelators optimized for specific medical isotopes.

Lanthanide-dependent coordination interactions in lanmodulin: a 2D IR and molecular dynamics simulations study

Lanmodulin's selectivity for lanthanides is determined by a highly-tuned balance of mono and bi-dentate carboxylate configurations. A proline mutation impacts the orientation of key coordinating residues and increases binding-site disorder.

Cultivation techniques to study lanthanide metal interactions in the haloalkaliphilic Type I methanotroph "Methylotuvimicrobium buryatense" 5GB1C.

Lanthanide metals are commonly used in technological devices including batteries, computers, catalysts and magnets. Despite their important properties, mining difficulties and pollution concerns limit the number of mines worldwide. Because of these concerns, biometallurgy is an attractive possibility for lanthanide extraction from recycled materials or from contaminated sites. Methylotrophs, bacteria that grow on reduced carbon substrates like methane and methanol, utilize lanthanides for a central reaction in their metabolisms. They must have some mechanism for uptake or trafficking, and are therefore excellent candidates for applying small molecules or proteins for selective lanthanide metal recycling. The haloalkaliphilic methanotroph "Methylotuvimicrobium buryatense" 5GB1C is the fastest growing methanotroph isolated to date, and thus has great industrial potential. The MxaFI enzyme complex uses calcium as a Lewis acid in conjunction with the pyroquinoline quinone cofactor to oxidize methanol, while the alternative enzyme XoxF uses lanthanide metals (e.g. lanthanum and cerium) for the same function. Lanthanide metals, abundant in the earth's crust, strongly repress the transcription of mxaF yet activate the transcription of xoxF, implying that XoxF may be the predominant methanol dehydrogenase in the bacterium's native environment. It may be that lanthanum interaction mechanisms are different from those in other microorganisms. In addition, the facile genetics in this strain and existing background information make it a good study organism for biological lanthanum uptake. The interesting physiology of this organism required empirical work to develop cultivation methods that allow robust assays of gene expression and measurement of lanthanum associated with cell biomass. In this chapter, we show that altering the metal chelator increased the availability of lanthanum to the cell as measured by the specific gene expression response. We also made further alterations to prevent lanthanum precipitation in medium for the growth of haloalkaliphiles.

Selective Lanthanide Sensing with Gold Nanoparticles and Hydroxypyridinone Chelators.

The octadentate hydroxypyridinone chelator 3,4,3-LI(1,2-HOPO) is a promising therapeutic agent because of its high affinity for f-block elements and noncytotoxicity at medical dosages. The interaction between 3,4,3-LI(1,2-HOPO) and other biomedically relevant metals such as gold, however, has not been explored. Gold nanoparticles functionalized with chelators have demonstrated great potential in theranostics, yet thus far, no protocol that combines 3,4,3-LI(1,2-HOPO) and colloidal gold has been developed. Here, we characterize the solution thermodynamic properties of the complexes formed between 3,4,3-LI(1,2-HOPO) and Au3+ ions and demonstrate how under specific pH conditions the chelator promotes the growth of gold nanoparticles, acting as both reducing and stabilizing agent. 3,4,3-LI(1,2-HOPO) ligands on the nanoparticle surface remain active and selective toward f-block elements, as evidenced by gold nanoparticle selective aggregation. Finally, a new colorimetric assay capable of reaching the detection levels necessary for the quantification of lanthanides in waste from industrial processes is developed based on the inhibition of particle growth by lanthanides.

The Chemistry of Lanthanides in Biology: Recent Discoveries, Emerging Principles, and Technological Applications.

The essential biological role of rare earth elements lay hidden until the discovery in 2011 that lanthanides are specifically incorporated into a bacterial methanol dehydrogenase. Only recently has this observation gone from a curiosity to a major research area, with the appreciation for the widespread nature of lanthanide-utilizing organisms in the environment and the discovery of other lanthanide-binding proteins and systems for selective uptake. While seemingly exotic at first glance, biological utilization of lanthanides is very logical from a chemical perspective. The early lanthanides (La, Ce, Pr, Nd) primarily used by biology are abundant in the environment, perform similar chemistry to other biologically useful metals and do so more efficiently due to higher Lewis acidity, and possess sufficiently distinct coordination chemistry to allow for selective uptake, trafficking, and incorporation into enzymes. Indeed, recent advances in the field illustrate clear analogies with the biological coordination chemistry of other metals, particularly CaII and FeIII, but with unique twists—including cooperative metal binding to magnify the effects of small ionic radius differences—enabling selectivity. This Outlook summarizes the recent developments in this young but rapidly expanding field and looks forward to potential future discoveries, emphasizing continuity with principles of bioinorganic chemistry established by studies of other metals. We also highlight how a more thorough understanding of the central chemical question—selective lanthanide recognition in biology—may impact the challenging problems of sensing, capture, recycling, and separations of rare earths.

NIR induced modulation of the red emission from erbium ions for selective lanthanide imaging

Upon direct excitation with green light (522 nm), Er3+ ion doped nanoparticles feature a number of radiative and non-radiative decay pathways, leading to distinct and sharp emission lines in the visible and near-infrared (NIR) range. Here we apply, in addition to continuous 522 nm irradiation, a modulated NIR irradiation (1143 nm) to actively control and modulate the red emission intensity (around 650 nm). The modulation of red Er3+ ion emission at a chosen frequency allows us to reconstruct fluorescence images from the Fourier transform amplitude at this particular frequency. Since only the emission from the Er3+ ion is modulated, it allows to selectively recover the lanthanide specific signal, removing any non-modulated auto-fluorescence or background emission resulting from the continuous 522 nm excitation. The modulated emission of specific lanthanides can open up new detection opportunities for selective signal recovery.

Selective Lanthanide Distribution within a Comprehensive Series of Heterometallic [LnPr] Complexes.

The preparation of heterometallic, lanthanide-only complexes is an extremely difficult synthetic challenge. By a ligand-based strategy, a complete isostructural series of dinuclear heterometallic [LnPr] complexes has been synthesized and structurally characterized. The two different coordination sites featured in this molecular entity allow study of the preferences of the praseodymium ion for a specific position depending on the ionic radii of the accompanying lanthanide partner. The purity of each heterometallic moiety has been evaluated in the solid state and in solution by means of crystallographic and spectrometric methods, respectively, revealing the limits of this strategy for ions with similar sizes. DFT calculations have been carried out to support the experimental results, confirming the nature of the site-selective lanthanide distribution. The predictable selectivity of this system has been exploited to assess the magnetic properties of the [DyPr] and [LuPr] derivatives, showing that the origin of the slow dynamics observed in the former arises from the dysprosium ion.

Zirconium phosphonate sorbents with tunable structure and function

Porous zirconium phosphonate materials have been produced via template-free hydrothermal synthesis of a zirconium precursor and amino tris(methylenephosphonic acid). To provide insights into the final structure and function of these materials and how the material properties can be influenced by the synthesis parameters, a variety of samples were prepared. Synthesis conditions were varied by changing P/Zr molar ratios, Zr precursors, pH and temperature. The resulting porous, amorphous zirconium phosphonate materials were characterised via x-ray diffraction, elemental analysis, nitrogen porosimetry, electron microscopies, nuclear magnetic resonance, small angle x-ray scattering and extended x-ray absorption fluorescence spectroscopy. The ultimate functional behaviour of the materials was also measured via competitive metal ion sorption experiments. The resultant materials were found to be selective lanthanide sorbents with capacities dependent on the synthesis conditions. Inducing crystallinity through addition of potassium fluoride during synthesis was shown to produce materials with reduced capacity and selectivity. Characterisation of the porosity of these materials demonstrated that in some cases different structures existed when the samples were wet versus dry and that this was dependent on the synthesis conditions used. All of the synthesis parameters investigated impacted the chemical structure, porosity and sorption properties of the resulting zirconium phosphonate materials.

Lanthanide selective adsorption by ion-imprinted polymer with chelidonic acid monoamide groups

ABSTRACTLanthanide selective adsorbent with chelidonic acid monoamide group was synthesized based on the ion-imprint method and its adsorption character was investigated. A polymerizable ligand 3 with chelidonic acid group was obtained by condensation of chelidonic acid and 4-aminostyrene. A Nd-complex monomer 7 was synthesized from the obtained ligand 3 and Nd(NO3)3. Copolymerization of the Nd-complex monomer, styrene and divinylbenzene afforded Nd-containing polymer 8. To obtain Nd-imprinted polymer 9, Nd ion was removed by hydrochloric acid. A non-imprinted polymer 6 composed by 3, styrene and divinylbenzene was also synthesized. Elemental analysis revealed that the content of chelidonic acid monoamide ligand in the 6 and 9 is 1.70 and 1.56 mmol·g−1, respectively. BET method indicated that 6 and 9 has specific surface area of 14.7 and 1.51 m2·g−1, respectively. Nd adsorption experiments revealed 9 exhibits imprinting factor (IF) 4.3 at initial concentration 0.4 mmol-Nd/L, despite 9 has 0.92-fold of ligands and 0.1-fold of specific surface area of 6. Mixed ion solution including Nd, Dy, Cu, Zn, and Co was used as a model solution for an adsorption experiment. 9 exhibits high lanthanide selectivity in a range of pH of 3.0–7.0 and a maximum adsorption amount at pH 3.75, despite 6 shows the maximum at pH 5.0. Density functional theory (DFT) calculation of a model system revealed that the ion-imprint effect and inhibition effect is cause of large adsorption amount of 9.

Annulated Mesoporous Silica as Potent Lanthanide Ion Adsorbents and Magnetic Resonance Contrast Enhancing Agents

We report a series of SBA-15 type mesoporous silica (MS) possessing functional annulated rings of different sizes obtained by post-synthesis grafting with diamines containing backbones and different numbers of carbon atoms as efficient magnetic resonance imaging (MRI) contrasting agents. Interestingly, lanthanide ion adsorption assays in aqueous solutions of pH 7 at room temperature showed that adsorption efficiency was higher for materials with rings than those without rings. Furthermore, annulated MS synthesized with 1,5-diaminopetane exhibited selective chelation with smaller Yb(III) ions owing to the “macrocyclic effect” of the cation cavity that offers a “best fit.” Additionally, Gd(III) ions chelated with the material modified by 1, 5-diaminopetane denoted as Gd@annulated-MS exhibited high r2/r1 relaxivities of 12, 12, and 28 while measured with 7.0 T (300 MHz), 9.4 T (400 MHz), and 11.4 T (500 MHz), respectively. Finally, the nanoscale parent materials for annulated modification were successfully synthesized for further in vivo applications. The MS materials thus obtained open auxiliary avenues for selective lanthanide ion absorption via manipulation of the annular ring size to be potentially applied in new generation MRI contrast agents.

Zirconium organophosphonates as high capacity, selective lanthanide sorbents

Novel and versatile zirconium organophosphonate coordination networks have been developed as sorbent platforms via simple, low-temperature hydrothermal reactions of zirconium propoxide with amino tris(methylene phosphonic acid) (ATMP). The resulting materials exhibited hierarchical porosity and possessed exceptional selectively for lanthanide elements over mono- and divalent metal ions during competitive sorption experiments in 0.1MHNO3, as well as modest intra-lanthanide selectivity. As such, the present materials have potential as solid phase extractants for lanthanide separations in applications including mining, radioactive waste treatment and environmental remediation. Lanthanide sorption was shown to occur via uncoordinated PO groups in the ATMP molecule. The structure, porosity and sorption properties of the coordination network platform could be tuned through varying the molar ratio of phosphorus to zirconium. Interestingly, the sample with the lowest surface area (<2m2/g) demonstrated the highest sorption capacity. Optimal compositions demonstrated europium sorption with fast kinetics and very high capacities of up to 0.63g/mgmin and 60mg/g respectively. As such, these highly stable zirconium organophosphonates, prepared from inexpensive precursor chemicals using one-pot methods, perform comparably to costly commercially available polymer resins.

Structural Rearrangement Through Lanthanide Contraction in Dinuclear Complexes

A new series of lanthanide complexes was synthesized, and the geometry and preliminary magnetic measurements of the complexes were explored. The specific ligand used (N'-(2-hydroxy-3-methoxybenzylidene)benzhydrazide) (H2hmb) was synthesized using a Schiff-base approach and was employed due to the presence of a coordination pocket that is able to accommodate magnetically selective lanthanide ions. The series can be divided into two groups that are categorized by a drastic structural rearrangement. The first group, Type I, contains six analogous complexes with the formula [M(III)2(Hhmb)3(NCS)3]·2MeOH·py (M = Y 1, Eu 2, Gd 3, Tb 4, Dy 5, Ho 6), while the second group, Type II, contains two dinuclear complexes with formula [M(III)2(Hhmb)2(NCS)4(MeOH)2] (M = Er 7, and Yb 8). Single-crystal X-ray analysis revealed that all M(III) ions in Type I exhibit monocapped distorted square antiprismatic geometries, while those of Type II exhibit distorted dodecahedron geometry. The direct current and alternating current magnetic measurements were carried out on all complexes, with 5, 7, and 8 exhibiting slow relaxation of the magnetization under an applied optimum dc field. Furthermore, complex 8 is the first example of a dinuclear Yb-based single-molecule magnet showing field-dependent multiple relaxation processes.

Introducing dual excitation and tunable dual emission in ZnO through selective lanthanide (Er3+/Ho3+) doping

Dual emission in Ho3+ doped ZnO showing red and green emission600 dpi in TIF format)??&gt; under UV (DC) and IR (UC) excitation.

Selective lanthanide sorption and mechanism using novel hybrid Lewis base (N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide) ligand modified adsorbent

This study aims to develop a highly selective Lewis base adsorbent to investigate the selective sorption and recovery of Eu(III) and Sm(III) from wastewater. The oxygen and nitrogen donor atoms containing Lewis base N-methyl-N-phenyl-1,10-phenanthroline-2-carboxamide (MePhPTA) ligand was synthesized and subsequently an adsorbent was prepared by direct immobilization onto mesoporous silica. Determined maximum adsorption capacities were 125.63 and 124.38mg/g for Eu(III) and Sm(III), respectively. Experiments with mixed-cations solutions showed that the sequence of preferential adsorption was Eu(III)>Sm(III). The lanthanide sorption by hybrid Lewis base adsorbent (HyLBA) was not adversely affected by the presence of sodium, potassium, calcium, magnesium, chloride, sulfate and nitrate ions due to strong affinity between hard Lewis acid lanthanide and hard Lewis base adsorbent. The crystallography for the Sm-MePhPTA complex suggested that MePhPTA was strongly coordinated to Sm(III) with oxygen and nitrogen by forming a stable complex with two 5-membered rings. The data clarified that bond lengths between Sm(III) and amide oxygen (2.475Å) were shorter than SmN (2.662Å) in phenanthroline moiety indicating strong oxygen driven HyLBA. The results suggested that HyLBA has a good prospect of promising applications for separation/sorption of lanthanide ions from effluents.

ChemInform Abstract: New Lariat Ether Carboxylic and Hydroxamic Acids: Synthesis and Lanthanide Ion Complexation.

Twenty-six new lariat ether carboxylic and hydroxamic acids based upon dibenzo-13-crown-4, dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 ring systems are synthesized and the solid-state structure for a dibenzo-19-crown-6 lariat ether hydroxamic acid is determined. The efficiency and selectivity for lanthanide ion extraction into chloroform by these proton-ionizable lariat ethers is strongly influenced by the crown ether ring size, lipophilic group attachment site and identity of the acidic function. In general, the lariat ether hydroxamic acids were more efficient and selective lanthanide ion extractants than the corresponding lariat ether carboxylic acids. The 1H nmr and ir binding studies indicate that both the macrocyclic polyether unit and the proton-ionizable group are involved in lanthanide ion complexation.

Peptide quantitation using primary amine selective metal chelation labels for mass spectrometry

Primary amine selective lanthanide metal chelating labels are demonstrated for enhancing the number of simultaneous relative peptide quantitation measurements that can be performed in mass spectrometry analyses.

Malonamide-Functionalized Gold Nanoparticles for Selective, Colorimetric Sensing of Trivalent Lanthanide Ions

A selective and sensitive molecular sensor for trivalent lanthanide (Ln(3+)) ions based upon a malonamide-functionalized gold nanoparticle was developed for colorimetric detection in water. A new synthetic approach permits nanoparticle synthesis, stabilization, and incorporation of a selective lanthanide binding site in a single, direct step. The design incorporates a specifically tailored dual function precursor ligand that bears a sodium thiosulfate (Bunte salt) group that links to the gold nanoparticle core and a tetramethylmalonamide (TMMA) group that serves as a selective Ln(3+) binding site. The sensor's colorimetric response to lanthanide ions is immediate, and it is sensitive down to approximately 50 nM for Eu(3+) and Sm(3+). This study demonstrates a general strategy for direct, convenient nanoparticle synthesis that enables the incorporation of analyte binding groups directly to the nanoparticle surface, allowing colorimetric sensors to be developed for widespread use. The one-step synthesis offers uniform surface ligand composition, reduces the volume of waste generated during nanoparticle synthesis and purification, produces functionalized gold nanoparticles that are stable in nonmodified aqueous environments, and offers colorimetric detection at ambient temperature.