Halogen bonding aza-BODIPYs for anion sensing and anion binding-modulated singlet oxygen generation

Two novel aza-BODIPY based anion sensors, decorated with halogen bonding recognition sites, are capable of detecting halide anions at biologically-relevant near-IR wavelengths. With potential application for improving the selectivity of photodynamic therapy agents, unprecedented supramolecular host-guest anion binding-modulated singlet oxygen generation is demonstrated.

Molecular Hosts for the Sensing and Separation of 99TcO4. Chemistry 2024;30:e202401551. [PMID: 38779975 DOI: 10.1002/chem.202401551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

In recent years, European Union member states have hastened energy policy deliberations to address supply and sustainability concerns, placing a significant emphasis on nuclear energy as a means to achieve decarbonization goals. However, despite its significant role in power generation, nuclear energy faces significant challenges linked to fuel reprocessing and waste disposal, that hinder its broader expansion. In this context, the separation of technetium represents a concerning issue. Indeed, technetium's catalytic activity can impede the extraction of uranium, neptunium, and plutonium, affecting waste reprocessing efficiency. Additionally, the stable form of technetium in aerobic conditions, pertechnetate (TcO4 -), poses risks of groundwater contamination due to its mobility and solubility. Hence, sensing and separation of TcO4 - is imperative for both nuclear fuel processing and minimising radioactive contamination in the environment. However, the binding of TcO4 - and its separation from contaminated solutions present challenges due to the acidic (or basic) waste components and the high ionic strength in real matrices. Supramolecular chemists have addressed these issues by designing receptors inspired by molecular recognition principles. This article explores recent advancements and future directions in TcO4 - sensing and separation (using extraction and sorption) with a focus on molecular hosts. Metal-organic receptors will also be discussed.

Superiority of the Supramolecular Halogen Bond Receptor over Its H-Bond Analogue toward the Efficient Extraction of Perrhenate from Water

A halogen bond-based water-soluble tetrapodal iodoimidazolium receptor, (L-I)(4Br), exhibited a high degree of efficiency (∼96%) in extracting ReO₄^- from 100% aqueous medium within a wide range of concentrations and of pH values along with excellent reusability. The solid-state X-ray diffraction study showed the trapping of ReO₄^- by (L-I)(4Br) via the Re-O····I halogen bonding interaction. XPS studies also suggested the interaction between I and ReO₄^- through polarization of the electron density of I atoms by ReO₄^-. (L-I)(4Br) is found to be capable of retaining its high extraction efficiency in the presence of competing anions such as F^-, Cl^-, I^-, SO₄^2-, H₂PO₄^-, CO₃^2-, NO₃^-, BF₄^-, ClO₄^-, Cr₂O₇^2-, and a mixture of these anions. Interestingly, (L-I)(4Br) was found to be superior in ReO₄^- extraction as compared to its hydrogen-bond donor analogue, (L-H)(4Br), as confirmed by a series of control experiments and theoretical calculations. Our synthesized dipodal and tripodal halogen bond donor receptors and their H-analogues validated the superiority of these classes of supramolecular halogen bond donor receptors over their hydrogen-bond analogues. (L-I)(4Br) also showed superior practical applicability in terms of the removal of ReO₄^- at anion concentrations as low as ∼100 ppm, which was a major shortcoming of (L-H)(4Br).

Halogen microregulation in metal-organic frameworks for enhanced adsorption performance of ReO4-/TcO4. JOURNAL OF HAZARDOUS MATERIALS 2023;446:130744. [PMID: 36630874 DOI: 10.1016/j.jhazmat.2023.130744]

Effective and selective removal of ⁹⁹TcO₄^-, one of the most nuisance radionuclides in nuclear waste, is highly desirable but remains a significant challenge. Herein, two isostructural MOFs, NCU-3-X (X = Cl, Br) were constructed by ZnX₂ coordinated to nitrogen-containing neutral ligand tri(4-(1H-imidazole-1-l) phenyl) amine for efficient adsorption ReO₄^-/TcO₄^-. Owning to the twofold interpenetrating structure, both of them exhibit strong alkaline resistance. Consequently, NCU-3-Br exhibited superior adsorption performances with a maximum capacity as high as 483 mg/g, which is 2.23 times larger than that of NCU-3-Cl. The primary reasons accounting for the enhanced adsorption performances of NCU-3-Br are that compared to chlorine atoms, the smaller electronegativity of bromine atoms as halogen bonds donor can facilitate the formation of σ-holes, enhance positively charged skeleton, and reduce the adsorption energy associated with ReO₄^-/TcO₄^-. In addition, the one-dimensional hydrophobic channels in the NCU-3-Br framework enable NCU-3-Br to have highly selective toward ReO₄^-, which has a low relative charge density against interfering ions. The SRS simulation removal experiment further confirmed the excellent adsorption capacity of NCU-3-Br to ReO₄^-/TcO₄^-. This work illustrated that the halogenated new strategy incorporated different halogen atoms into MOF skeletons can dramatically modulate the adsorption performances for ReO₄^-/TcO₄^-.

Discovery, nuclear properties, synthesis and applications of technetium-101

Technetium-101 (101Tc) has been poorly studied in comparison with other Tc isotopes, although it was first identified over ~80 years ago shortly after the discovery of the element Tc itself. Its workable half-life and array of production modes, i.e., light/heavy particle reactions, fission, fusion-evaporation, etc., allow it to be produced and isolated using an equally diverse selection of chemical separation pathways. The inherent nuclear properties of 101Tc make it important for research and applications related to radioanalytical tracer studies, as a fission signature, fusion materials, fission reactor fuels, and potentially as a radioisotope for nuclear medicine. In this review, an aggregation of the known literature concerning the chemical, nuclear, and physical properties of 101Tc and some its applications are presented. This work aims at providing an up-to-date and first-of-its-kind overview of 101Tc that could be of importance for further development of the fundamental and applied nuclear and radiochemistry of 101Tc.

Aminomethylpyridine isomers functionalized cellulose microspheres for TcO4-/ReO4- uptake: Structure-properties relationship and their application in different aquatic systems

Technetium-99 (⁹⁹Tc) is a long-lived radioactive nuclide that poses great threat to environment, hence selective removal of ⁹⁹Tc from aquatic system is always an issue. Aminomethylpyridine (AMP) equipped with pyridine and amino, is a promising receptor for TcO₄^- and its surrogate ReO₄^-, thus it is of interest to explore and understand the structure-properties relationship of ReO₄^- adsorption related to n-AMP structure that differ in amino methyl position. In this work, three n-AMP functionalized cellulose microspheres (n-AMPR, n = 2, 3, 4) were synthesized and employed for TcO₄^-/ReO₄^- uptake. The effect of aminomethyl position on adsorption properties of n-AMPR for ReO₄^- were investigated and compared. Adsorption kinetics and adsorption isotherm showed that adsorption speed and adsorption capacity were in order of 3-AMPR > 2-AMPR > 4-AMPR. DFT calculation verified that the adsorption of ReO₄^- by n-AMPR was attributed to electrostatic interaction and hydrogen bonding interaction, the order of adsorption abilities of n-AMPR was due to that steric effect and hydrogen bond collaborated in stabilizing n-AMPR-ReO₄^- complexes. The column experiments demonstrated that 3-AMPR can be selectively remove ReO₄^- from simulated groundwater. More importantly, ⁹⁹Tc column experiments showed that 3-AMPR had a better ability for actual radioactive TcO₄^-.

Chiroptical sensing of perrhenate in aqueous media by a chiral organic cage

A chiral cage is proposed as an effective chiroptical sensor for perrhenate (surrogate for 99TcO4-) in water, fruit juice and artificial urine medium. The key mechanism for the chiroptical sensing...

Fusion-Based Neutron Generator Production of Tc-99m and Tc-101: A Prospective Avenue to Technetium Theranostics

Presented are the results of ^99mTc and ¹⁰¹Tc production via neutron irradiation of natural isotopic molybdenum (Mo) with epithermal/resonance neutrons. Neutrons were produced using a deuterium-deuterium (D-D) neutron generator with an output of 2 × 10¹⁰ n/s. The separation of Tc from an irradiated source of bulk, low-specific activity (LSA) Mo on activated carbon (AC) was demonstrated. The yields of ^99mTc and ¹⁰¹Tc, together with their potential use in medical single-photon emission computed tomography (SPECT) procedures, have been evaluated from the perspective of commercial production, with a patient dose consisting of 740 MBq (20 mCi) of ^99mTc. The number of neutron generators to meet the annual 40,000,000 world-wide procedures is estimated for each imaging modality: ^99mTc versus ¹⁰¹Tc, D-D versus deuterium-tritium (D-T) neutron generator system outputs, and whether or not natural molybdenum or enriched targets are used for production. The financial implications for neutron generator production of these isotopes is also presented. The use of ¹⁰¹Tc as a diagnostic, therapeutic, and/or theranostic isotope for use in medical applications is proposed and compared to known commercial nuclear diagnostic and therapeutic isotopes.

Superiority of a polymeric scavenger over its hexapodal monomer towards efficient ReO4- removal in water

A new imidazolium functionalized hexapodal polymeric receptor, [PHIm-Br], showed selective and efficient removal (>99%) of perrhenate (ReO4-), from 100% aqueous medium via solid-liquid extraction, which was 13% higher as compared to its monomeric analouge [HIm-Br]. Most importantly, [PHIm-Br] overcomes the drawback of [HIm-Br] in terms of removal of ReO4- at lower anion concentration of ∼100 ppm along with excellent radiation resistivity and reusability within a wide pH range, which implies its potential towards practical applications.

Syntheses and evaluation of new hydrophilic azacryptands used as masking agents of technetium in solvent extraction processes

The extraction of technetium, present in nitric acid medium as pertechnetate anion, is an issue in solvent extraction processes used to recover uranium and plutonium. In the present study, a complexing agent is added in the aqueous nitric acid solution to bind selectively the pertechnetate anion and prevent its extraction into the organic phase or to back extract it in the aqueous phase. Several azacryptands with the addition of hydrophilic groups were synthesized to improve the solubility of the previously studied cage molecule in nitric acid medium. Solvent extraction tests reveal that all the synthesized ligands have a similar complexation strength towards pertechnetate and are able to maintain this anion in the aqueous phase (0.5 M HNO3). These ligands are able to overcome the Hofmeister bias and selectively bind technetium in nitric acid solution. The azacryptand concentration can be increased by a factor of three in the liquid-liquid extraction conditions compared to our previous work. Coordination studies using microcalorimetry, Single Crystal X-Ray Diffraction (SC-XRD), infrared and Raman spectroscopies show the formation of an inclusion complex with hydrogen bonds stabilizing the oxo-anion within the cavity. This solubility improvement is promising for the introduction of this kind of macrocyclic azacryptands in a solvent extraction process.

Optimizing Strategy for Enhancing the Stability and 99TcO4 - Sequestration of Poly(ionic liquids)@MOFs Composites

Metal-organic frameworks (MOFs) are a class of promising sorbents for effective sequestration of radioactive ⁹⁹TcO₄ ^- anions. However, their poor stability and slow sorption kinetics in the industrial condition pose a great challenge. Herein, we demonstrate an optimizing strategy via in situ polymerization of ionic liquids (ILs) encapsulated in the pores of MOFs, forming polyILs@MOFs composites with greatly enhanced TcO₄ ^- sequestration compared with the pristine MOFs. Notably, the cross-linked polymerization of ILs facilitates the formation of both the inside ionic filler as the active sites and outside coating as the protective layers of MOFs, which is significantly beneficial to obtain the optimized sorption materials of exceptional stability under extreme conditions (e.g., in 6 M HNO₃). The final optimized composite shows fast sorption kinetics (<30 s), good regeneration (>30 cycles), and superior uptake performance for TcO₄ ^- in highly acidic conditions and simulated recycle stream. This strategy opens up a new opportunity to construct the highly stable MOF-based composites and extend their applicability in different fields.

5,5-Di-chloro-6-hy-droxy-dihydro-pyrimidine-2,4(1H,3H)-dione: mol-ecular and crystal structure, Hirshfeld surface analysis and the new route for synthesis with Mg(ReO4)2 as a new catalyst

The mol-ecular and crystal structures of the title compound, C4H4Cl2N2O3, were investigated by single-crystal X-ray diffraction and a Hirshfeld surface analysis. The title compound was synthesized by a new type of reaction using Mg(ReO4)2 as a new catalyst and a possible mechanism for this reaction is proposed. The six-membered ring adopts a half-chair conformation. In the crystal, hydrogen bonds connect the mol-ecules into double layers, which are connected to each other by halogen bonds. The Hirshfeld surface analysis revealed that the most important contributions for the crystal packing are from O⋯H/H⋯O (35.8%), Cl⋯Cl (19.6%), Cl⋯H/H⋯Cl (17.0%), H⋯H (8.3%), C⋯O/O⋯C (4.3%), Cl⋯O/O⋯Cl (4.2%) and O⋯O (4.1%) contacts.

Proton affinities of pertechnetate (TcO4-) and perrhenate (ReO4-)

The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO4 and ReO4-, which according to Cooks' kinetic method indicates that the proton affinity (PA) of TcO4- is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol-1 and PA[ReO4-] = 297.2 kcal mol-1. Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO4- is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena.

Perrhenate and pertechnetate complexation by an azacryptand in nitric acid medium

Azacryptand addition in nitric acid medium for the recognition of the pertechnetate anion for extraction studies.

Selective and efficient removal of perrhenate by an imidazolium based hexapodal receptor in water medium

This work reports a new cationic imidazolium based hexapodal receptor, [L.6Br], for selective and efficient removal of perrhenate (ReO₄⁻) as [L.6ReO4] from 100% aqueous medium via extraction through precipitation.

Cationic Covalent Organic Nanosheets for Rapid and Selective Capture of Perrhenate: An Analogue of Radioactive Pertechnetate from Aqueous Solution

Capture of radioactive TcO₄^- from nuclear wastes is extremely desirable for waste disposal and environmental restoration. Here, we report the synthesis of hydrolytically stable cationic covalent organic nanosheets (iCON) for efficient uptake of ReO₄^-, a nonradioactive surrogate of TcO₄^-. The iCON combines cationic guanidine-based knots with hydroxyl anchored neutral edge units and chloride ions loosely bonded in the pores, rendering extremely fast exchange kinetics toward ReO₄^- with high uptake capacity of 437 mg g^-1 and prominent distribution coefficient of 5.0 × 10⁵. The removal efficiency remains stable over a pH range of 3-12 and allows selective capture of ReO₄^- in the presence of excessive competing anions such as NO₃^-, CO₃^2-, PO₄^3- and SO₄^2- with good removal efficiency for ReO₄^- in a simulated Hanford LAW Melter Recycle Stream. Anion exchange between the ReO₄^- in solution and the chloride ion in iCON plays dominant role in the adsorption of ReO₄^-. The iCON shows promise for effective removal of radioactive ⁹⁹Tc from nuclear waste.

Anion-adaptive crystalline cationic material for 99TcO4- trapping

Efficient anion recognition is of great significance for radioactive 99TcO4- decontamination, but it remains a challenge for traditional sorbents. Herein, we put forward a tactic using soft crystalline cationic material with anion-adaptive dynamics for 99TcO4- sequestration. A cucurbit[8]uril-based supramolecular metal-organic material is produced through a multi-component assembly strategy and used as a sorbent for effective trapping of TcO4-. Excellent separation of TcO4-/ReO4- is demonstrated by fast removal kinetics, good sorption capacity and high distribution coefficient. Remarkably, the most superior selectivity among metal-organic materials reported so far, together with good hydrolytic stability, indicates potential for efficient TcO4- removal. The structure incorporating ReO4- reveals that the supramolecular framework undergoes adaptive reconstruction facilitating the effective accommodation of TcO4-/ReO4-. The results highlight opportunities for development of soft anion-adaptive sorbents for highly selective anion decontamination.