Sequestering agents for uranyl chelation: new calixarene ligands

Synthesis of sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) calixarene ligands and determination of their binding abilities for the uranyl cation were described. Chelating properties were determined by UV spectrophotometry in aqueous media under various pH conditions and further studied by ¹H NMR analysis of the resonance signals of both aromatics' protons of the chelating groups. Each ligand shows a more or less pronounced affinity for uranium. HOPO calixarenes exhibit significant affinity towards uranyl ion at acidic and neutral pH while CAMS calixarene is more efficient at basic pH.     

Complexation of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid with Cd(II), Hg(II) and Pb(II) ions in aqueous solution

The persistence of widely used chelating agents EDTA and DTPA in nature has been of concern and there is a need for ligands to replace them. In a search for environmentally friendly metal chelating ligands for industrial applications, complex formation equilibria of N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA6) with Cd(II), Hg(II) and Pb(II) in aqueous 0.1 M NaNO₃ solution were studied at 25°C by potentiometric titration. Complexation was modeled and the stability constants of the different complexes were determined for each metal ion using the computer program SUPERQUAD. With all metal ions, stable ML^4? complexes dominated the complex formation. The stabilities of Cd(II), Hg(II) and Pb(II) chelates of BCA6 are remarkably lower than those of EDTA and DTPA. Environmental advantages of the use of BCA6 instead of EDTA and DTPA are better biodegradability and lower nitrogen content with a possibility to save chemicals and process steps in pulp bleaching.     

The influence of linker geometry in bis(3-hydroxy-N-methyl-pyridin-2-one) ligands on solution phase uranyl affinity

Seven water-soluble, tetradentate bis(3-hydroxy-N-methyl-pyridin-2-one) (bis-Me-3,2-HOPO) ligands were synthesized that vary only in linker geometry and rigidity. Solution-phase thermodynamic measurements were conducted between pH 1.6 and pH 9.0 to determine the effects of these variations on proton and uranyl cation affinity. Proton affinity decreases by introduction of the solubilizing triethylene glycol group as compared to unsubstituted reference ligands. Uranyl affinity was found to follow no discernable trends with incremental geometric modification. The butyl-linked 4 li-Me-3,2-HOPO ligand exhibited the highest uranyl affinity, consistent with prior in vivo decorporation results. Of the rigidly-linked ligands, the o-phenylene linker imparted the best uranyl affinity to the bis-Me-3,2-HOPO ligand platform.     

Hexadentate terephthalamide(bis-hydroxypyridinone) ligands for uranyl chelation: structural and thermodynamic consequences of ligand variation

Several linear, hexa- and tetradentate ligands incorporating a combination of 2,3-dihydroxy-terephthalamide (TAM) and hydroxypyridinone-amide (HOPO) moieties have been developed as uranyl chelating agents. Crystallographic analysis of several {UO(2)[TAM(HOPO)(2)]}(2-) complexes revealed a variable and crowded coordination geometry about the uranyl center. The TAM moiety dominates the bonding in hexadenate complexes, with linker rigidity dictating the equality of equatorial U-O bonding. Hexadentate TAM(HOPO)(2) ligands demonstrated slow binding kinetics with uranyl affinities on average 6 orders of magnitude greater than those of similarly linked bis-HOPO ligands. Study of tetradentate TAM(HOPO) ligands revealed that the high uranyl affinity stems primarily from the presence of the TAM moiety and only marginally from increased ligand denticity. Uranyl affinities of TAM(HOPO)(2) ligands were within experimental error, with TAM(o-phen-1,2-HOPO)(2) exhibiting the most consistent uranyl affinity at variable pH.     

Sequestering agent for uranyl chelation: new binaphtyl ligands

The synthesis of phosphonate, sulfocatecholamide (CAMS) and hydroxypyridinone (HOPO) binaphtyl ligands is presented. Their binding abilities for uranyl cation were determined by UV spectrophotometry in aqueous media versus pH. These titrations showed that the efficiency of these chelating agents depends on the nature of the chelating group. Each ligand shows a more or less pronounced affinity towards uranium. While the bisphosphonate compound did not show any affinity towards the uranyl ion, the BINHOPO derivative exhibits significant affinity at acidic and neutral pH while the BINCAMS is more efficient at basic pH.     

顺磁性聚酯金属配合物的合成及其驰豫性能的研究

本文通过二乙三胺五乙酸（ＤＴＰＡ）或乙二胺四乙酸（ＥＤＴＡ）的双酸酐与二元醇或二元酚进行聚合反应，制备了两个系列共１５种新的聚酯型大分子配体及其顺磁性金属配合物，用核磁、红外光谱以及元素分析表征了配体和配合物的结构。初步试验结果表明，与相应的小分子金属配合物相比，聚酯金属配合物具有较高的弛豫性能。     

STUDY ON SYNTHESIS AND RELAXIVITY OF PARAMAGNETIC POLYESTER METAL COMPLEXES FOR MRI

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STUDY ON SYNTHESIS AND RELAXIVITY OF PARAMAGNETIC POLYESTER METAL COMPLEXES FOR MRI

Fifteen new polyester ligands were prepared by copolymerization of EDTA (ethylenediaminetertraacetic acid)dianhydride or DTPA (diethylenetriamine pentaacetic acid) dianhydride and dihydric alcohol or dihydric phenol.Their paramagnetic metal complexes were also synthesized.All polyester ligands and metal complexes were characterized by ^1HNMR,IR spectra and elemental analyses.Preliminary study showed that the polyester metal complexes had higher relaxation effectiveness as compared to corresponding small molecular metal complexes.     

Detection of equimolar EDTA and DTPA in spiked wastewater effluents

Ethylenediaminetetraacetic acid (EDTA) and diethylenetriamine-pentaacetic acid (DTPA) are water ‘softening’ agents that are present in numerous household and industrial detergents. Since these particular chelating agents are not significantly degraded during conventional wastewater treatment processes, wastewater treatment plant (WTP) effluents can contain up to 19 µM of EDTA and 7 µM of DTPA. Little, however, is known about the release of EDTA and DTPA from WTPs to rivers. To gain insight, we here report on the development of a cost-effective analytical method. This method is based on the chromatography of a humic acid-cadmium (HA-Cd) complex on a size-exclusion chromatography column (SEC, Sephadex G-15) while using WTP effluents from Lethbridge, Banff and Canmore which contained 10 mM Tris-buffer as the mobile phase (pH 8.2). The intact HA-Cd complex is detected by means of a flame atomic absorption spectrometer (FAAS). The addition of equimolar EDTA and DTPA up to 10 µM allowed us to observe a concentration-dependent increase of the retention time of the main Cd-peak. This behaviour was qualitatively comparable between the WTP effluents and was rationalised by the EDTA/DTPA-mediated mobilisation of Cd from the HA-Cd complex. The signal intensity that corresponded to the mobilised Cd was used to establish calibration curves with corresponding correlation coefficients in the range of 0.950–0.978. Therefore, the developed method yields robust results for realistic concentrations of equimolar EDTA/DTPA in real WTP effluents. The developed method can now be applied to analyse real WTP effluent for the presence of chelating agents, whose concentrations may be expressed as being equivalent to a particular equimolar EDTA/DTPA concentration.     

Specific capture of uranyl protein targets by metal affinity chromatography

To improve general understanding of biochemical mechanisms in the field of uranium toxicology, the identification of protein targets needs to be intensified. Immobilized metal affinity chromatography (IMAC) has been widely developed as a powerful tool for capturing metal binding proteins from biological extracts. However uranyl cations (UO2(2+)) have particular physico-chemical characteristics which prevent them from being immobilized on classical metal chelating supports. We report here on the first development of an immobilized uranyl affinity chromatography method, based on the cation-exchange properties of aminophosphonate groups for uranyl binding. The cation distribution coefficient and loading capacity on the support were determined. Then the stability of the uranyl-bonded phase under our chromatographic conditions was optimized to promote affinity mechanisms. The successful enrichment of uranyl binding proteins from human serum was then proven using proteomic and mass spectral analysis.     

Indirect determination of the sum of chelons in drinking- and ground-waters by anodic stripping voltammetry

The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions.     

Complexometric catalytic titrations using the indicator reaction periodate-triethanolamine

The possibility of applying a new indicator reaction, i.e., periodate-triethanolamine, as the indicator in titrations of ethylenediamine-N,N,N′,N′-tetracetic acid (EDTA), 1,2-diaminocyclohexanetetraacetic acid (DCTA), and diethylenetriaminepentaacetic acid (DTPA) with standard manganese(II) sulfate solution (phosphate buffer pH 6.84) has been investigated. The titration course was followed potentiometrically using a perchlorate ion-selective electrode. The optimum conditions for determinations in relation to concentration of the indicator reaction components have been established. Furthermore, the influence of some ions on the possibility of EDTA determination was considered and maximally tolerable concentrations under these conditions were established. The amounts of 0.170–18.00 mg of EDTA, 0.150–16.00 mg of DCTA, and 0.180–19.00 mg of DTPA were determined with a maximal relative standard deviation less than 1.0%. Results are in good agreement with those of comparable methods. Finally, the experimental catalytic titration curves obtained in this way are compared to the simulated ones.     

Analysis of EDTA and DTPA

In this paper, analytical techniques for the determination of ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA) are reviewed. These compounds, especially EDTA, are used as metal chelating agents in several industries. As they are likely to be poorly degraded in waste water treatment plants, significant amounts of EDTA and DTPA are released into natural waters. The overview consists of comparing chromatographic, electrochemical, spectrophotometric, titrimetric and atomic absorption methods and their applicability to the determination of EDTA and DTPA in different matrices.     

Indirect determination of the sum of chelons in drinking- and ground-waters by anodic stripping voltammetry

The complexing ligand EDTA can be determined as its complex with bismuth by indirect anodic stripping voltammetry down to 0.1 μg/L without a concentration step. Interfering copper and excess bismuth have to be removed by cation exchange, although in presence of these metals EDTA can be determined down to 0.5 μg/L only. If NTA, EDTA, and DTPA are present simultaneously, the accumulation curves for the corresponding bismuth-complexes can overlap, preventing a separate determination of the three chelons. Due to the interaction of NTA and DTPA with soil normally only EDTA is present in ground-waters. Similarly, EDTA also dominates in surface-waters. Thus it seems to be sufficient to determine the sum of the three chelons as EDTA (index of bismuth-complexation) using suitable electrochemical conditions. Received: 9 September 1996 / Revised: 2 December 1996 / Accepted: 11 January 1997     

Synthesis of bis(amidoxime)s and evaluation of their properties as uranyl-complexing agents

Uranium pollution involves high toxicity and radioactivity and, therefore, constitutes a grave threat to human health and the environment. Chelation is an effective method for sequestering uranium. It is well known that chelators based on oxime groups are able to complex uranyl cations efficiently. To this end, various bis(amidoxime)s were synthesized by reaction of hydroxylamine with the corresponding dinitriles. In these compounds the amidoximes are separated by chains of various lengths, some including a heterocycle (pyridine or 1,3,5-triazine). The abilities of these bis(amidoxime)s to complex uranyl cation in water were evaluated by determining their affinity constants and thermodynamic parameters by means of Isothermal Titration Calorimetry (ITC). DFT calculations were also performed, to determine the optimum structures of the complexes formed between uranyl cations and the oximate groups. A tetrakis(amidoxime), also synthesized in this work, shows good affinity for uranium, and a single molecule is able chelate several uranyl cations. These results are of importance for the remediation of uranium-polluted wastewaters, and open up several perspectives for the design and synthesis of new amidoxime compounds.     

Elucidating the radical kinetics involved in the radiolytic destruction of lanthanide-complexed DTPA

The reprocessing of nuclear fuels to extract the remaining actinides is one of the most important strategies for viable nuclear power in the future, as geologic waste disposal of high-level radioactive waste could have considerable negative impacts on the environment. As many of these strategies are based on solvent extraction processes, our aim is to establish the radiolytic stability of the component extraction ligands. The oxidative stability of the lanthanide metal-complexed extraction ligand DTPA (diethylenetriaminepentaacetic acid) has been investigated through its reaction rate constant with the hydroxyl radical under TALSPEAK acidic pH conditions, both for the free ligand and complexed with Eu³⁺, Lu³⁺ and Gd³⁺. Specific rate constants were obtained over a range of pH conditions using thiocyanate competition kinetics. The rate constants for the complexed metals are seen to be greater than the corresponding values determined for only the DTPA protonated ligands at these pHs.     

螯合剂与牛血清白蛋白竞争镍作用的研究

用凝胶色谱法研究了13种螯合剂使牛血清白蛋白镍配合物BSANi(Ⅱ)中的镍活动化的能力,发现DTPA、NTA等氨羧类螯合剂有较好的竞争能力,而巯基类较差。用透析法研究了螯合剂与BSANi(Ⅱ)反应动力学机理,结果表明,在pH7.4和4℃时,L-组氨酸、EDTA为解离机理,而亚氨二乙酸,二乙三氨五乙酸为加合机理。测定了有关的动力学参数,依据竞争能力参数F讨论了可能作为治疗镍中毒的促排螯合剂。     

Insight into Coordination of Uranyl Ions with N,N′‐bis(2‐five‐membered heterocyclidene)‐1,8‐anthradiamines

To find new adsorbents for uranyl ions, the density functional theory (DFT) was adopted to design a series of new ligands containing an anthracene and two five‐membered heterocycles with nitrogen family nonmetal elements (N, P, As) or oxygen family nonmetal elements (O, S, Se, Te), for example, ligands N,N′‐bis(2‐five‐membered heterocyclidene)‐1,8‐anthradiamines (BFHADAs). Then the uranyl ions were coordinated with BFHADAs to generate five new coordination complexes (Uranyl‐BFHADAs) with heteroatoms N, S, As, Se and Te, respectively. The five‐membered heterocyclic rings of Uranyl‐BFHADA with oxygen atoms were broken under the structural optimization and Uranyl‐BFHADA with heterocyclic atoms P was not obtained. Several structures and property parameters of the ligands BFHADAs (containing heteroatoms N, S, As, Se and Te) and their uranyl complexes Uranyl‐BFHADAs were theoretically investigated and analyzed. The results showed that uranyl ions could form stable coordination complexes with these five BFHADAs. The formed bonds between uranyl ions and the heteroatoms in BFHADAs were coordination bonds rather than other types of bonds. These results could provide insightful information and theoretical guidance for the coordination of uranyl with the atoms N, S, Se, As and Te in other ligands.     

A 228Ra-212Pb tandem generator for potential application in biomedical studies

A new tandem generator system (cation-exchange generator column coupled to anion-exchange), based on the ²²⁸Ra as starting radionuclide, for ²¹²Pb/²¹²Bi production in the solutions suitable to direct application in biomedical investigations has been developed. Optimum conditions have been found for retention of Ra, Th and Ac parent radionuclides on the cation-exchange column and repeated elution of Pb with subsequent concentration on anion-exchange column using HBr and mixed HBr/CH₃OH solutions. It was shown that Pb/Bi could be eluted from anion — exchange column with a small volume of EDTA, DTPA, NaCl solutions or heated H₂O. The advantages of the tandem generator system for production of short-lived Pb/Bi radionuclides and their application for biomedical studies are discussed.     

Radiochemische Bestimmung von Plutonium in Urin bei Gegenwart von Komplexen Dekorporationsmitteln

The interfering effect of DTPA or EDTA on the coprecipitation of Pu from urine with Ca(Mg)-phosphate is cancelled nearly by adding an excess of Ni²⁺ (about 1.8 g/l) to the urine samples before precipitating. After subsequent extraction with Alamine-336 (10% in xylene), reextraction with 10N HCl/NH₄I, and electrodeposition on stainless steel, the recoveries of Pu are about 70% in comparison with 85% in absence of DTPA or EDTA.