Uranyl Binding Research Articles

Skeleton design engineering of covalent organic frameworks to enable in situ incorporation of coordination sites for improved extraction of uranyl ions

The development of advanced porous materials for effectively separating uranium from nuclear wastewater or seawater is a highly coveted yet formidable task. However, the importance of the covalent organic frameworks (COFs) skeletons and the specific arrangement of adjacent atoms is often disregarded when configuring coordination settings for chelating molecules. In this study, a novel material for oxygen-enriched COFs was developed. The optimized oxygen-rich COFs showed aligned neighboring bonds and triazine groups along the skeletons, resulting in an increase in uranyl binding sites and a threefold rise in the total number of binding sites. The synergistic interaction of ether bonds and triazine groups in the π-conjugated skeletons significantly reduced the energy band gap, leading to improved uranium affinity and recovery. The adsorption capacity reached an impressive 660 mg/g, surpassing that of most COF-based adsorbents using a chemical coordination mechanism in uranium-containing aqueous solutions. This study provides valuable insights into designing novel adsorbents for uranium separation.

Uptake and coordination behaviour of uranyl on functionalised silica

The safe decommissioning of nuclear reactors is a complex process, requiring a range of technological options for it to be done effectively. It has become more important in recent years, with the substantial number of reactors entering the decommissioning phase. This paper details the use of functionalised silica for the recovery of uranium from aqueous hydrochloric acid solutions, a potential agent for the treatment of steel reactor components during nuclear reactor decommissioning. Silica functionalised with either phosphonic acid, bistriazine, or bistriazinylbipyridine ligands was shown to extract uranium, with the commercially available phosphonic acid functionality being the most effective. Extractions of 100 % were observed at [H+] ≤ 0.24 M, further the phosphonic acid functionality also had the highest loading capacity. Increasing [H+] has a suppressive effect on uranyl recovery, which was more pronounced for the in-house synthesized silica, and was attributed to protonation of the extracting moiety. Extended x-ray absorption fine structure spectroscopy was also used to determine the uranium coordination environments on the functionalised silica, and gain insights into the extraction mechanism. The uranyl cation was bound by two phosphonic acid groups, two bis-triazine groups, and one bistriazinylbipyridine group, respectively on each respective extractant. Uranyl was found to be penta-coordinate in the equatorial plane for all systems, with oxygen and/or chloride always present in the first coordination sphere. Evaluation of the mechanism indicated that uranyl must be loading onto the phosphonic acid functionality via multiple mechanisms, to both the phosphonic acid and silica related surface groups, although preferential binding of uranyl to the phosphonic acid groups was observed.

Cinnamic Acid: A Low-Toxicity Natural Bidentate Ligand for Uranium Decorporation.

Uranium accumulation in the kidneys and bones following internal contamination results in severe damage, emphasizing the pressing need for the discovery of actinide decorporation agents with efficient removal of uranium and low toxicity. In this work, cinnamic acid (3-phenyl-2-propenoic acid, CD), a natural aromatic carboxylic acid, is investigated as a potential uranium decorporation ligand. CD demonstrates markedly lower cytotoxicity than that of diethylenetriaminepentaacetic acid (DTPA), an actinide decorporation agent approved by the FDA, and effectively removes approximately 44.5% of uranyl from NRK-52E cells. More importantly, the results of the prompt administration of the CD solution remove 48.2 and 27.3% of uranyl from the kidneys and femurs of mice, respectively. Assessments of serum renal function reveal the potential of CD to ameliorate uranyl-induced renal injury. Furthermore, the single crystal of CD and uranyl compound (C9H7O2)2·UO2 (denoted as UO2-CD) reveals the formation of uranyl dimers as secondary building units. Thermodynamic analysis of the solution shows that CD coordinates with uranyl to form a 2:1 molar ratio complex at a physiological pH of 7.4. Density functional theory (DFT) calculations further show that CD exhibits a significant 7-fold heightened affinity for uranyl binding in comparison to DTPA.

Layered charge separation in surface boron doped copper with phosphate groups boosts the electrochemical uranium extraction from seawater

Electrochemical uranium extraction from seawater is an attractive project for sustainable nuclear industry, whereas the active sites of electrode materials require further promotion on uranyl binding to increase the efficiency and kinetics of uranium extraction. Herein, we construct a strategy of layered charge separation in surface boron-doped copper with surface phosphate ions (B:Cu-PO4) for charge-enhanced uranyl binding and extraction in seawater. The B atoms were demonstrated to decrease the negative charge in surface Cu atoms and increase the negative charge in outer O atoms of PO43- groups, thus enhancing the uranyl binding. In a real seawater experiment, the B:Cu-PO4 extracted 24.9 μg of uranium from 10 L of seawater. Such performance corresponded to a considerable extraction capacity of 2.1 mg/g per day, which outperformed most of the state-of-the-art materials. The successful construction of charge separation in B:Cu-PO4 broadened the material design for uranium extraction from real seawater.

Towards tailoring hydrophobic interaction with uranyl(VI) oxygen for C-H activation.

Bovine serum albumin (BSA) has a uranyl(VI) binding hotspot where uranium is tightly bound by three carboxylates. Uranyl oxygen is "soaked" into the hydrophobic core of BSA. Isopropyl hydrogen of Val is trapped near UO22+ and upon photoexcitation, C-H bond cleavage is initiated. A unique hydrophobic contact with "yl"-oxygen, as observed here, can be used to induce C-H activation.

Efficient Removal of Uranium from the Kidney by a Picolinate-based Pentadentate Chelator

In conjunction with theoretical calculations, the in vitro and in vivo uranyl binding capabilities of a bidentate picolinate (Pic) and its pentadentate derivative (H2dpa) are investigated here. The planar N3O2-donor...

In Silico Simulations Reveal Molecular Mechanism of Uranyl Ion Toxicity towards DNA-Binding Domain of PARP-1 Protein.

The molecular toxicity of the uranyl ion (UO22+) in living cells is primarily determined by its high affinity to both native and potential metal-binding sites that commonly occur in the structure of biomolecules. Recent advances in computational and experimental research have shed light on the structural properties and functional impacts of uranyl binding to proteins, organic ligands, nucleic acids, and their complexes. In the present work, we report the results of the computational investigation of the uranyl-mediated loss of DNA-binding activity of PARP-1, a eukaryotic enzyme that participates in DNA repair, cell differentiation, and the induction of inflammation. The latest experimental studies have shown that the uranyl ion directly interacts with its DNA-binding subdomains, zinc fingers Zn1 and Zn2, and alters their tertiary structure. Here, we propose an atomistic mechanism underlying this process and compute the free energy change along the suggested pathway. Our Quantum Mechanics/Molecular Mechanics (QM/MM) simulations of the Zn2-UO22+ complex indicate that the uranyl ion replaces zinc in its native binding site. However, the resulting state is destroyed due to the spontaneous internal hydrolysis of the U-Cys162 coordination bond. Despite the enthalpy of hydrolysis being +2.8 kcal/mol, the overall reaction free energy change is -0.6 kcal/mol, which is attributed to the loss of domain's native tertiary structure originally maintained by a zinc ion. The subsequent reorganization of the binding site includes the association of the uranyl ion with the Glu190/Asp191 acidic cluster and significant perturbations in the domain's tertiary structure driven by a further decrease in the free energy by 6.8 kcal/mol. The disruption of the DNA-binding interface revealed in our study is consistent with previous experimental findings and explains the loss of PARP-like zinc fingers' affinity for nucleic acids.

Skeleton engineering of rigid covalent organic frameworks to alter the number of binding sites for improved radionuclide extraction

Crystalline porous covalent frameworks (COFs) have been considered as a platform for uranium extraction from seawater and nuclear waste. However, the role of rigid skeleton and atomically precise structures of COFs is often ignored in the design of defined binding configuration. Here, a COF with an optimized relative position of two bidentate ligands realizes full potential in uranium extraction. Compared with the para-chelating groups, the optimized ortho-chelating groups with oriented adjacent phenolic hydroxyl groups on the rigid skeleton endow an additional uranyl binding site, thereby increasing the total number of binding sites up to 150%. Experimental and theoretical results indicate that the uranyl capture is greatly improved via the energetically favored multi-site configuration and the adsorption capacity reaches up to 640 mg g−1, which exceeds that of most reported COF-based adsorbents with chemical coordination mechanism in uranium aqueous solution. This ligand engineering strategy can efficiently advance the fundamental understanding of designing the sorbent systems for extraction and remediation technology.

Probing the interaction of uranyl(VI) complex with bovine serum albumin via in-depth experimental and computational perspectives

Interaction aspects of uranyl(VI) complexes as well as the coordinated ONNO-donor ligand with bovine serum albumin (BSA) were investigated by the fluorescence spectroscopy and computational insights. Under optimal physiological condition, it was observed that there was significant decrease in fluorescence intensity of BSA upon interaction with uranyl(VI) complexes as well as the ligand. The mechanism of interaction between the uranyl(VI) complex and BSA protein was examined by fluorescence measurement. The Stern-Volmer constant, binding affinity, binding constant, standard free energy, and fluorescence lifetime decay profile of BSA in the absence as well as in the presence of uranyl(VI) complex were determined. Furthermore, the conformational binding of uranyl(VI) complexes with BSA protein was explored via molecular docking studies, and confirmed that there is a strong affinity between the Trp-213 residue in the binding pocket of sub-domain IIA and uranyl(VI) complex.

High-efficiency uranium extraction from seawater by low-cost natural protein hydrogel

Utilization of uranium resource in seawater are highly possible to meet the growth demands for the sustainable development of nuclear energy industry. Bio-adsorbents exhibit high performance in terms of adsorption selectivity, equilibrium speed, and environmental friendliness, while the high fabrication cost hinders their practical application. In this study, a low-cost soy protein isolate (SPI) is used to fabricate adsorbent named SPI hydrogel for uranium extraction. This is the first report on applying bio-adsorbents derived from low-cost natural proteins for uranium extraction. The SPI hydrogel showed high uranium adsorption capacity of 53.94 mg g−1 in simulated nuclear wastewater and 5.29 mg g−1 is achieved in natural seawater, which is higher than all currently available adsorbents based on non-modified natural biomolecules. The amino and oxygen-containing groups are identified as the functional groups for uranyl binding by providing four oxygen and two nitrogen atoms to form equatorial coordination with uranyl, which guarantees the high binding selectivity and affinity to uranyl ions. The low cost for accessing the raw material together with the environmental friendliness, high salt tolerance, high uranium adsorption ability, and high selectivity to uranium, make SPI hydrogel a promising adsorbent for uranium extraction from seawater and nuclear wastewater.

Simulation of uranyl-biomolecule interaction using a cationic dummy atom model

We report a multisite cationic dummy atom model of the uranyl cation, suitable for atomistic simulation of the interaction of this ion with water and biomolecules. This reproduces geometry of model complexes with typical ligands, interactions and diffusion coefficient in water, and the structure of an adduct with a uranyl binding protein. A protocol for prediction of binding mode and strength of complexes formed with small peptides is proposed.

Inter-Site Cooperativity of Calmodulin N-Terminal Domain and Phosphorylation Synergistically Improve the Affinity and Selectivity for Uranyl.

Uranyl-protein interactions participate in uranyl trafficking or toxicity to cells. In addition to their qualitative identification, thermodynamic data are needed to predict predominant mechanisms that they mediate in vivo. We previously showed that uranyl can substitute calcium at the canonical EF-hand binding motif of calmodulin (CaM) site I. Here, we investigate thermodynamic properties of uranyl interaction with site II and with the whole CaM N-terminal domain by spectrofluorimetry and ITC. Site II has an affinity for uranyl about 10 times lower than site I. Uranyl binding at site I is exothermic with a large enthalpic contribution, while for site II, the enthalpic contribution to the Gibbs free energy of binding is about 10 times lower than the entropic term. For the N-terminal domain, macroscopic binding constants for uranyl are two to three orders of magnitude higher than for calcium. A positive cooperative process driven by entropy increases the second uranyl-binding event as compared with the first one, with ΔΔG = -2.0 ± 0.4 kJ mol-1, vs. ΔΔG = -6.1 ± 0.1 kJ mol-1 for calcium. Site I phosphorylation largely increases both site I and site II affinity for uranyl and uranyl-binding cooperativity. Combining site I phosphorylation and site II Thr7Trp mutation leads to picomolar dissociation constants Kd1 = 1.7 ± 0.3 pM and Kd2 = 196 ± 21 pM at pH 7. A structural model obtained by MD simulations suggests a structural role of site I phosphorylation in the affinity modulation.

Benignly-fabricated supramolecular poly(amidoxime)-alginate-poly(acrylic acid) beads synergistically enhance uranyl capture from seawater

Design of amidoxime-based adsorbents in a cooperative and synergistic manner together with a concept of facile and green fabrication is becoming highly desirable to harvest uranium from seawater. Herein, taking benefit of supramolecular ionic-crosslinking and hydrogen bonding interactions, we have reported a simple and environmentally benign approach to construct novel bifunctional poly(amidoxime)-alginate-poly(acrylic acid) (PAO-A-PAA) composite beads. As a result of synergistic uranyl binding, the PAO-A-PAA composite beads reached a high adsorption capacity of 735.1 mg g−1 for uranium aqueous solution (36 ppm), which is 2.24 and 1.46 times that of monofunctional Alg-PAA (328.1 mg g−1) and Alg-PAO (502.2 mg g−1), respectively. More importantly, the PAO-A-PAA exhibits excellent selectivity towards U(VI) in the presence of natural organic matter and multiple coexisting metal ions in simulated seawater. The XPS analysis reveals the utilization and coordination of both amidoxime and carboxylate ligands of PAO-A-PAA for uranyl binding, which results in energetically more stable synergistic uranyl complexes (Ebinding = −9.45 to −10.34 eV) as proved by the density functional theory study. The adsorption efficiency of PAO-A-PAA is further supported by its ability to extract µg L−1-level uranium in real seawater (94.7–99.5%). The PAO-A-PAA also demonstrates good mechanical and chemical stability over a wide pH range, as well as good reusability. These findings provide insight into the significance of designing efficient sorbent material for enhanced uranyl capture via a supramolecular strategy.

In Situ Synthesis of Uranyl‐Imprinted Nanocage for Selective Uranium Recovery from Seawater

AbstractAn adaptive coordination structure is vital for selective uranium extraction from seawater. By strategy of molecular imprinting, uranyl is introduced into a multivariate metal–organic framework (MOF) during the synthesis process to guide the in situ construction of proper nanocage structure for targeting uranyl binding. Except for the coordination between uranium with four oxygen from the materials, the axial oxygen of uranyl also forms hydrogen bonds with hydrogen from the phenolic hydroxyl group, which enhances the binding affinity of the material to uranyl. Attributing to the high binding affinity, the adsorbent shows high uranium binding selectivity to uranyl against not only the interfering metal ions, but also the carbonate group that coordinates with uranyl to form [UO2(CO)3]4− in seawater. In natural seawater, the adsorbent realizes a high uranium adsorption capacity of 7.35 mg g−1, together with an 18.38 times higher selectivity to vanadium.

In Situ Synthesis of Uranyl‐Imprinted Nanocage for Selective Uranium Recovery from Seawater

Adaptive coordination structure is vital for selective uranium extraction from seawater. By strategy of molecular imprinting, uranyl is introduced into the m ultivariate metal-organic framework (MOF) during the synthesis process to guide the in-situ construction of proper nanocage structure for targeting uranyl binding. Except for the coordination between uranium with four oxygen from the materials, the axial oxygen of uranyl also forms hydrogen bonds with hydrogen from the phenolic hydroxyl group, which enhances the binding affinity of the material to uranyl. Attributing to the high binding affinity, the adsorbent shows high uranium binding selectivity to uranyl against not only the interfering metal ions, but also the carbonate group that coordinates with uranyl to form [UO 2 (CO) 3 ] 4 - in seawater. In natural seawater, the adsorbent realizes a high uranium adsorption capacity of 7.35 mg g -1 ,t ogether with an 18.38 times higher selectivity to vanadium. Integrated into account the high reusability, this adsorbent is a promising alternative for uranium recovery from seawater.

A Membrane‐Supported Bifunctional Poly(amidoxime‐ethyleneimine) Network for Enhanced Uranium Extraction from Seawater and Wastewater

Uranium extraction from natural seawater and wastewater are quintessential requirements to supply uninterrupted carbon-free nuclear energy and to prevent potential radiochemical and toxicological effects, respectively. Owing to the complexity and low-concentration uranium of these water samples, the design and synthesis of sorbent materials for uranium extraction with meaningful efficiencies remains a grand challenge. Herein, we reported a novel three-dimensional bifunctional network of hyperbranched poly(amidoxime-ethyleneimine) (PAO-h-PEI) using PEI as the skeleton material via cyanoethylation, crosslinking and then amidoximation. As a result of the synergistic supramolecular strategy, the PAO-h-PEI membrane achieved a remarkable adsorption capacity of 985.7 mg/g for aqueous uranium solution, which was 2.5 folds that of the monofunctional h-PEI membrane (387.6 mg/g). The PAO-h-PEI membrane also exhibited good selectivity towards uranium in the presence of various metal ions, high-content salt, and natural organic matter as well as common anions. According to the XPS and FTIR results, the utilization of amines as the second ligand enhanced uranyl binding by providing additional coordination sites or by interacting with oxime to force N-OH dissociation. The good reusability (adsorption rate of 93% after six adsorption-desorption cycles) and satisfactory adsorption performance in extracting low-concentration uranium in real seawater demonstrate its practicability.

Uranyl-Binding Proteins on Silica Nanoparticles for Repeatable Capture of Uranyl Ions

Successful protein-based enrichment of uranyl, the predominant form of uranium from seawater, relies not only on selective binding of uranyl with a high affinity but also on the reusability of protein binder and a supporting matrix that is abundantly available at low cost. In this work, we propose a silica-binding peptide-enabled approach that allows the non-covalent immobilization of super uranyl-binding protein (SUP) onto silica nanoparticles for their repeated use. We first thoroughly examined solution conditions that affect the stability of uranyl-binding proteins and identified suitable physical conditions that are beneficial for the non-covalent SUP immobilization and subsequent capture of uranyl. We found that the molecular linker between SUP and silica binding peptide plays an important role in improving interaction strength between the silica nanoparticles and the engineered proteins. Consequently, we have demonstrated repeatable recovery and enrichment of uranyl ions from synthetic seawater using the engineered protein on silica nanoparticles. Our approach does not require chemical modification of silica nanoparticles, yet offers strong attachment of SUP to the silica interface and thus attractive reusability of protein-silica nanomaterials.

Molecular Structure of the Surface-Immobilized Super Uranyl Binding Protein

Recently, a super uranyl binding protein (SUP) was developed, which exhibits excellent sensitivity/selectivity to bind uranyl ions. It can be immobilized onto a surface in sensing devices to detect uranyl ions. Here, sum frequency generation (SFG) vibrational spectroscopy was applied to probe the interfacial structures of surface-immobilized SUP. The collected SFG spectra were compared to the calculated orientation-dependent SUP SFG spectra using a one-excitonic Hamiltonian approach based on the SUP crystal structures to deduce the most likely surface-immobilized SUP orientation(s). Furthermore, discrete molecular dynamics (DMD) simulation was applied to refine the surface-immobilized SUP conformations and orientations. The immobilized SUP structures calculated from DMD simulations confirmed the SUP orientations obtained from SFG data analyzed based on the crystal structures and were then used for a new round of SFG orientation analysis to more accurately determine the interfacial orientations and conformations of immobilized SUP before and after uranyl ion binding, providing an in-depth understanding of molecular interactions between SUP and the surface and the effect of uranyl ion binding on the SUP interfacial structures. We believe that the developed method of combining SFG measurements, DMD simulation, and Hamiltonian data analysis approach is widely applicable to study biomolecules at solid/liquid interfaces.

Reaction: Porous Organic Polymers for Uranium Capture

Cafer T. Yavuz received his PhD from Rice University in 2008 with a Welch scholarship under the supervision of Vicki Colvin. He then worked as a postdoctoral scholar at the University of California, Santa Barbara, with Galen Stucky. He started his independent group in 2010 at KAIST, Korea. He is currently a professor of chemistry at the King Abdullah University of Science and Technology in Saudi Arabia. His research focuses on the design and synthesis of nanoscale and porous materials for applications in energy and the environment. He uses fine chemistry in confined spaces to enable rapid and targeted transformations of CO2, methane, and water.

Synthesis of polyamide 6/nano-hydroxyapatite hybrid (PA6/n-HAp) for the sorption of rare earth elements and uranium

Polyamide (PA6) and hydroxyapatite (n-HAp) have intrinsic sorption properties for metal ions. Their association by melt compounding allows manufacturing a composite material (PA6/n-HAp) efficient for the binding of uranyl and rare earth metal ions (REEs) in acidic solution (in the pH range 2–2.5). The composite shows enhanced sorption capacities (5–7 times) compared with single PA6 material. The structuration of the material slightly improves textural properties but contributes to improve the accessibility and availability of reactive groups (including by size distribution). Metal sorption proceeds mainly through complexation of amide reactive groups as shown by FTIR characterization (modification of the environment of CO and NH groups) rather than ion-exchange/electrostatic attraction. Maximum sorption capacities approach 0.34 mmol U g−1, 0.49 mmol Er g−1 and 0.70 mmol Nd g−1: the preference may be correlated to the covalent rather than ionic character of these metal ions. Uptake kinetics are relatively slow (requiring up to 6−8 h, under selected experimental conditions): the textural properties of the composite (pore size: 2.6 nm) limit the mass transfer properties (though slightly enhanced compared with PA6 precursor). The resistance to intraparticle diffusion constitutes the major controlling step for uptake kinetics. Nitric acid is the most efficient eluent for the desorption of loaded metals (efficiency exceeds 94 %); noticeably U(VI) elution is optimal at 1 M HNO3 concentration, contrary to REEs that require lower concentration (i.e., 0.1 M). Preliminary tests on sulfuric acid leachates of Egyptian ores demonstrate that the sorbent maintains good sorption properties for REEs and U despite the complexity of the solution. The sorbent has a marked preference for REEs, U and Th against base and alkali metals.