Isolation and characterization of a new polyoxometalate ligand, HSbWO, and its interactions with f-elements.

We report the synthesis and characterization (Raman, FTIR, DLS, single crystal XRD) of CsHSbWO·6HO, which contains a new polyoxometalate building block: HSbWO (SbW). Solution-state fluorescence, DLS, and UV-vis absorbance results with Nd, Eu, Am, and Cm confirm that SbW acts as an efficient complexant and fluorescence sensitizer for f-elements.

Biogeochemistry of Actinides: Recent Progress and Perspective.

Actinides are elements that are often feared because of their radioactive nature and potentially devastating consequences to humans and the environment if not managed properly. As such, their chemical interactions with the biosphere and geochemical environment, i.e.

From +I to +IV, Alkalis to Actinides: Capturing Cations across the Periodic Table with Keggin Polyoxometalate Ligands.

Coordination chemistry trends across the periodic table are often difficult to probe experimentally due to limitations in finding a versatile but consistent chelating platform that can accommodate various elements without changing its coordination mode. Herein, we present new metal/ligand systems covering a wide range of ionic radii, charges, and elements. Five different ligands derived from the Keggin structure (HBWO, PWO, SiWO, GeWO, and GaWO) were successfully crystallized with six different cations (Na, Sr, Ba, La, Ce, and Th) and characterized by single-crystal X-ray diffraction.

Polyoxometalate Ligands Reveal Different Coordination Chemistries Among Lanthanides and Heavy Actinides.

Experimental studies involving actinide compounds are inherently limited in scope due to the radioactive nature of these elements and the scarcity and cost of their research isotopes. Now, ∼80 years after the introduction of the actinide concept by Glenn Seaborg, we still only have a limited understanding of the coordination chemistry of f-block metals when compared to more common elements such as the s-, p-, and d-blocks. This is particularly true for transplutonium actinides (Am, Cm, Bk, etc.

Characterization of the first Peacock-Weakley polyoxometalate containing a transplutonium element: curium bis-pentatungstate [Cm(WO)].

Leveraging microgram-level techniques, we here present the first transplutonium bis-pentatungstate complex: NaCsCm(WO)·14HO (CmW). Single crystal XRD, Raman, and fluorescence characterization show significant differences relative to analogous lanthanide compounds. The study reveals the unsuspected impact of counterions on fluorescence and vibrational modes of the curium complex and its lanthanide counterparts.

Impact of a Biological Chelator, Lanmodulin, on Minor Actinide Aqueous Speciation and Transport in the Environment.

Minor actinides are major contributors to the long-term radiotoxicity of nuclear fuels and other radioactive wastes. In this context, understanding their interactions with natural chelators and minerals is key to evaluating their transport behavior in the environment. The lanmodulin family of metalloproteins is produced by ubiquitous bacteria and lanmodulin (LanM) was recently identified as one of nature's most selective chelators for trivalent f-elements.

Contrasting Trivalent Lanthanide and Actinide Complexation by Polyoxometalates via Solution-State NMR.

Deciphering the solution chemistry and speciation of actinides is inherently difficult due to radioactivity, rarity, and cost constraints, especially for transplutonium elements. In this context, the development of new chelating platforms for actinides and associated spectroscopic techniques is particularly important. In this study, we investigate a relatively overlooked class of chelators for actinide binding, namely, polyoxometalates (POMs).

Polyoxometalates as ligands to synthesize, isolate and characterize compounds of rare isotopes on the microgram scale.

The synthesis and study of radioactive compounds are both inherently limited by their toxicity, cost and isotope scarcity. Traditional methods using small inorganic or organic complexes typically require milligrams of sample-per attempt-which for some isotopes is equivalent to the world's annual supply. Here we demonstrate that polyoxometalates (POMs) enable the facile formation, crystallization, handling and detailed characterization of metal-ligand complexes from microgram quantities owing to their high molecular weight and controllable solubility properties.

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.

In situ beam reduction of Pu(IV) and Bk(IV) as a route to trivalent transuranic coordination complexes with hydroxypyridinone chelators.

The solution-state interactions of plutonium and berkelium with the octadentate chelator 3,4,3-LI(1,2-HOPO) (343-HOPO) were investigated and characterized by X-ray absorption spectroscopy, which revealed in situ reductive decomposition of the tetravalent species of both actinide metals to yield Pu(III) and Bk(III) coordination complexes. X-ray absorption near-edge structure (XANES) measurements were the first indication of in situ synchrotron redox chemistry as the Pu threshold and white-line position energies for Pu-343-HOPO were in good agreement with known diagnostic Pu(III) species, whereas Bk-343-HOPO results were found to mirror the XANES behavior of Bk(III)-DTPA. Extended X-ray absorption fine structure results revealed An-O bond distances of 2.

Bridging Hydrometallurgy and Biochemistry: A Protein-Based Process for Recovery and Separation of Rare Earth Elements.

The extraction and subsequent separation of individual rare earth elements (REEs) from REE-bearing feedstocks represent a challenging yet essential task for the growth and sustainability of renewable energy technologies. As an important step toward overcoming the technical and environmental limitations of current REE processing methods, we demonstrate a biobased, all-aqueous REE extraction and separation scheme using the REE-selective lanmodulin protein. Lanmodulin was conjugated onto porous support materials using thiol-maleimide chemistry to enable tandem REE purification and separation under flow-through conditions.

Capturing an elusive but critical element: Natural protein enables actinium chemistry.

Actinium-based therapies could revolutionize cancer medicine but remain tantalizing due to the difficulties in studying and limited knowledge of Ac chemistry. Current efforts focus on small synthetic chelators, limiting radioisotope complexation and purification efficiencies. Here, we demonstrate a straightforward strategy to purify medically relevant radiometals, actinium(III) and yttrium(III), and probe their chemistry, using the recently discovered protein, lanmodulin.

Characterization of Americium and Curium Complexes with the Protein Lanmodulin: A Potential Macromolecular Mechanism for Actinide Mobility in the Environment.

Anthropogenic radionuclides, including long-lived heavy actinides such as americium and curium, represent the primary long-term challenge for management of nuclear waste. The potential release of these wastes into the environment necessitates understanding their interactions with biogeochemical compounds present in nature. Here, we characterize the interactions between the heavy actinides, Am and Cm, and the natural lanthanide-binding protein, lanmodulin (LanM).

Efficient discrimination of transplutonium actinides by models.

Transplutonium actinides are among the heaviest elements whose macroscale chemical properties can be experimentally tested. Being scarce and hazardous, their chemistry is rather unexplored, and they have traditionally been considered a rather homogeneous group, with most of their characteristics extrapolated from lanthanide surrogates. Newly emerged applications for these elements, combined with their persistent presence in nuclear waste, however, call for a better understanding of their behavior in complex living systems.

Spectrophotometric methods to probe the solution chemistry of lanthanide complexes with macromolecules.

Lanthanide biochemistry has experienced a revival in recent years owing to the discovery of new biomolecular platforms that are amenable to bind, sequester, or transport lanthanide ions. This has inherently created a need for physicochemical methods that report on lanthanide-containing macromolecular systems. In this chapter, the use of spectrophotometric methods to study the stability of lanthanide-macromolecule complexes in solution is discussed.

Combining the Best of Two Chelating Titans: A Hydroxypyridinone-Decorated Macrocyclic Ligand for Efficient and Concomitant Complexation and Sensitized Luminescence of f-Elements.

An ideal chelator for f-elements features rapid kinetics of complexation, high thermodynamic stability, and slow kinetics of dissociation. Here we present the facile synthesis of a macrocyclic ligand bearing four 1-hydroxy-2-pyridinone units linked to a cyclen scaffold that rapidly forms thermodynamically stable complexes with lanthanides (Sm , Eu , Tb , Dy ) and a representative late actinide (Cm ) in aqueous media and concurrently sensitizes them. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed an increase in the Ln/An-O bond lengths following the trend Cm>Eu>Tb and EXAFS data were compatible with time-resolved luminescence studies, which indicated one to two water molecules in the inner metal coordination sphere of Eu(III) and two water molecules for the Cm(III) complex.

Probing electronic structure in berkelium and californium via an electron microscopy nanosampling approach.

Due to their rarity and radioactive nature, comparatively little is known about the actinides, particularly those with atomic numbers higher than that of plutonium, and their compounds. In this work, we describe how transmission electron microscopy can provide comprehensive, safe, and cost-effective characterization using only single nanogram amounts of highly-radioactive, solid compounds. Chlorides of the rare elements berkelium and californium are dropcast and then converted in situ to oxides using the electron beam.

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution.

The solution-state interactions between octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) chelating ligands and uranium were investigated and characterized by UV-visible spectrophotometry and X-ray absorption spectroscopy (XAS), as well as electrochemically via spectroelectrochemistry (SEC) and cyclic voltammetry (CV) measurements. Depending on the selected chelator, we demonstrate the controlled ability to bind and stabilize U, generating with 3,4,3-LI(1,2-HOPO), a tetravalent uranium complex that is practically inert toward oxidation or hydrolysis in acidic, aqueous solution. At physiological pH values, we are also able to bind and stabilize U to a lesser extent, as evidenced by the mix of U and U complexes observed via XAS.

Open questions on the environmental chemistry of radionuclides.

Understanding the biogeochemistry of radionuclides in the environment is essential for effective isolation of nuclear waste in repositories, management of contaminated sites, ensuring long-term protection of our ecosystems, and limiting impacts on human health. Here the authors discuss the extreme complexity of this multidimensional chemistry problem, highlighting the outstanding open questions for the next generations of environmental radiochemists.

Selective and Efficient Biomacromolecular Extraction of Rare-Earth Elements using Lanmodulin.

Lanmodulin (LanM) is a recently discovered protein that undergoes a large conformational change in response to rare-earth elements (REEs). Here, we use multiple physicochemical methods to demonstrate that LanM is the most selective macromolecule for REEs characterized to date and even outperforms many synthetic chelators. Moreover, LanM exhibits metal-binding properties and structural stability unseen in most other metalloproteins.

Hydroxypyridinone Derivatives: A Low-pH Alternative to Polyaminocarboxylates for TALSPEAK-like Separation of Trivalent Actinides from Lanthanides.

Separation of lanthanides (Ln) from actinides (An) is unanimously challenging in reprocessing used nuclear fuel despite of much dedicated efforts over the past several decades. The TALSPEAK process is the current reference method in the United States for Ln/An separation but suffers from several limitations, such as a narrow working pH window (3.5-4.

Developing scandium and yttrium coordination chemistry to advance theranostic radiopharmaceuticals.

The octadentate siderophore analog 3,4,3-LI(1,2-HOPO), denoted 343-HOPO hereafter, is known to have high affinity for both trivalent and tetravalent lanthanide and actinide cations. Here we extend its coordination chemistry to the rare-earth cations Sc and Y and characterize fundamental metal-chelator binding interactions in solution via UV-Vis spectrophotometry, nuclear magnetic resonance spectroscopy, and spectrofluorimetric metal-competition titrations, as well as in the solid-state via single crystal X-ray diffraction. Sc and Y binding with 343-HOPO is found to be robust, with both high thermodynamic stability and fast room temperature radiolabeling, indicating that 343-HOPO is likely a promising chelator for in vivo applications with both metals.

Structural properties of ultra-small thorium and uranium dioxide nanoparticles embedded in a covalent organic framework.

We report the structural properties of ultra-small ThO and UO nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior.

Combinatorial design of multimeric chelating peptoids for selective metal coordination.

Current methods for metal chelation are generally based on multidentate organic ligands, which are generated through cumbersome multistep synthetic processes that lack flexibility for systematically varying metal-binding motifs. Octadentate ligands incorporating hydroxypyridinone or catecholamide binding moieties onto a spermine scaffold are known to display some of the highest affinities towards f-elements. Enhancing binding affinity for specific lanthanide or actinide ions however, necessitates ligand architectures that allow for modular and high throughput synthesis.