Diethylenetriaminepentaacetic Complex Research Articles

Complexation of trivalent lanthanides and actinides with diethylenetriaminepentaacetic acid: Theoretical unraveling of bond covalency

Separation of trivalent actinides (An(III)) and lanthanides (Ln(III)) is a pivotal step with respect to the treatment of nuclear waste based on the partitioning and transmutation (P&T) strategy, which is also extraordinarily challenging due to their similar coordination chemistry. The diethylenetriaminepentaacetate (DTPA) ligand has been demonstrated to possess selective separation ability toward An(III) over Ln(III) in aqueous media. Nevertheless, the extracted complexes of An(III)/Ln(III) with DTPA, and the origin of selectivity for An(III) are still not well deciphered. In this work, from theoretical perspective and at the molecular level, the geometrical structures, bonding nature as well as thermodynamic behaviors of possible complexes of An(III) (An = Am, Cm, Cf) and Ln(III) (Ln = Nd, Eu) with DTPA in the aqueous phase have been systematically studied using scalar relativistic density functional theory (DFT). All bonding analyses indicate that the metal-ligand bonds possess weak but non-negligible covalent interactions, and An(III)-DTPA species demonstrate more covalency compared to Ln(III) analogues. In addition, the covalency of the metal-ligand bonding of An(III)-DTPA increases across the actinide series from Am to Cf, which stems from the increased orbital degeneracy of the 5f orbitals of actinides and the 2p orbitals of the ligands. According to thermodynamic analysis, the anhydrous species [Cf(HDTPA)]− is the most likely species for Cf(III) in acidic solution, whereas [M(HDTPA)(H2O)]− are more favorable for Am(III) and Cm(III), probably due to the different bonding nature of the transplutonium series. This work affords new theoretical insights into the coordination chemistry of An(III)/Ln(III)-DTPA complexes, and paves the way to further design efficient DTPA-based ligands for An(III)/Ln(III) separation. Moreover, the DTPA ligand may also be applied for in-group separation of trivalent actinides, which is quite meaningful for the extraction of Cf(III).

Injectable hyaluronic acid hydrogels with the capacity for magnetic resonance imaging

Monitoring hydrogel degradation in real time using noninvasive imaging techniques is of great interest for designing a scaffold in tissue engineering. We report the preparation of gadolinium (Gd)-labeled and injectable hyaluronic acid (HA) hydrogels that can be visualized using T1- and T2-weighted magnetic resonance imaging (MRI). An HA derivative functionalized with thiol and hydrazide was labeled using a diethylenetriaminepentaacetate complex modified with “clickable” dithiopyridyl functionalities (degree of modification was 3.77% with respect to HA repeat units). The HA derivative modified with cross-linkable groups and Gd complex exhibited relaxivities r1 = 3.78 mM−1s−1 and r2 = 56.3 mM−1s−1. A hydrazone hydrogel network was obtained by mixing Gd-labeled HA-hydrazide and HA-aldehyde derivatives. Enzymatic hydrogel degradation could be followed using MRI because the MR images showed great correlation with the hydrogel mass loss. Ex vivo MRI of injected Gd-labeled hydrogels demonstrated that they show a significant contrast difference (SNRcoronal = 456; SNRaxial = 459) from the surrounding tissues. These results indicate that our Gd-labeled HA hydrogel has great potential as an injectable biocompatible hydrogel that can be used for longitudinal tracking in vivo using MRI.

Oxidation of metal–diethylenetriamine-pentaacetate (DTPA) – complexes during drinking water ozonation

This study investigates the oxidative transformation of diethylenetriaminepentaacetate (DTPA), a synthetic ligand, during drinking water ozonation. The rate coefficients for the reactions of CaDTPA3− and ZnDTPA3− with ozone were determined to be 6200 and 3500±150M−1s−1, respectively. The reactivity of Fe(III)DTPA2− towards ozone was found to be much lower (<10M−1s−1), but near neutral pH the reactivity of the Fe(III)-complexes is dominated by [Fe(III)(OH)]DTPA3−. For the reaction of Fe[(III)(OH)]DTPA3− with ozone a rate coefficient of 2.4±0.2×105M−1s−1 was measured. The rate coefficients of the reactions of the ZnDTPA-and Fe(III)DTPA with OH radicals have been determined by a competitive method as 2.4±0.4×109 and 1.5±0.1×109M−1s−1, respectively at pH=7. The degradation of low concentrations of DTPA complexes during ozonation was investigated in natural waters under drinking water relevant conditions. Based on our findings CaDTPA3− and ZnDTPA3− are judged as easily degradable. Fe(III)DTPA complexes showed a somewhat lower reactivity, but were still typically degraded by one order of magnitude at ozone dosages of ∼20μM(1mgL−1) in the three natural waters tested. Molecular ozone was found to be the major oxidant for the metal–DTPA complexes during ozonation.

Preparation of Indium-115-Labeled Diethylenetriaminetetraacetic Acid Monoacetamide Peptides Purified by 8-Hydroxyquinoline

In this communication we describe a novel procedure for the preparation and purification of diethylenetriaminepentaacetic (DTPA)-acylated and 115In3+-labeled oligopeptides using 8-hydroxyquinoline for the removal and quantification of nonbound indium ions. First the Nα- or Nα,Nϵ-DTPA oligopeptides containing C-terminal KDEL signal motif were produced by solid-phase synthesis. For this the free carboxyl group of DTPA dianhydride was activated in situ for a short period of time yielding a major product. Reversed-phase HPLC-purified DTPA oligopeptides were labeled with 115In3+ in aqueous buffer solution at pH 3.8. For the removal as well as for the detection of uncoordinated 115In3+ ions we have utilized the 115In3+ complex-forming ability of 8-hydroxyquinoline in chloroform. Following an optimized extraction procedure the free indium ion content was measured by spectrophotometry in the organic phase. Data obtained by this method and verified by total-reflection X-ray fluorescence spectroscopy and thin-layer chromatography demonstrated that free 115In3+ could be efficiently removed and sensitively detected in the presence of DTPA oligopeptide chelator. No release of 115In3+ from its DTPA complex was observed. This method could be useful for the preparation of indium complexes of peptides and perhaps proteins containing a DTPA moiety and nonradioactive isotope ligand.

NMR identification of protein surfaces using paramagnetic probes

Paramagnetic agents produce line broadening and thus cancellation of anti phase cross-peak components in two-dimensional correlated nuclear magnetic resonance spectra. The specificity of this effect was examined to determine its utility for identifying surface residues of proteins. Ubiquitin and hen egg white lysozyme, for which X-ray crystal structures and proton NMR assignments are available, served as test cases. Two relaxation reagents were employed, 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy and the gadolinium (III) diethylenetriaminepentaacetate complex ion. Correlations were sought between reagent-produced decreases of side-chain cross-peak volumes in double-quantum-filtered proton correlation (DQF-COSY) spectra and the solvent-exposed side-chain surface area of the corresponding residues. The lanthanide complex produced strong effects ascribable to association with carboxylate groups but was not otherwise useful in delineating surface residues. The nitroxyl, on the other hand, produced clear distinctions among the Val, Leu, and Ile residues that generally paralleled side-chain exposure in the crystal, although consistent correlations were not observed with residues of other types. Although an instance of possible specific protein-nitroxyl association was noted, the nitroxyl appears to be a tool for identifying hydrophobic surface residues.

The differential pulse polarographic determination of chromium in gallium arsenide

The method described for the determination of chromium in gallium arsenide is based on the catalytic current produced by nitrate in the electrolytic reduction of the chromium(VI)-diethylenetriaminepentaacetate complex. Matrix effects, primarily caused by gallium, are discussed in detail. The method is suitable for determinations of chromium at levels as low as about 1 μg g −1 with about 50 mg of sample; the r.s.d. is better than 10%.

Aminopolycarboxylates of rare earths—VIII: Kinetic study of exchange reactions between Eu 3+ ions and lanthanide(III) diethylenetriaminepentaacetate complexes

The kinetics of the exchange reactions between Ln(III)-diethylenetriaminepentaacetate complexes (Lndtpa; Ln  La, Nd, Ho and Lu) were studied by a spectrophotometric method. At higher pH values, the exchange takes place mainly via the direct encounter of the complexes Lndtpa and Eu 3+ ions, while at lower pH values the rate-determining step is the proton-catalyzed dissociation of the complexes, at a rate proportional to the square of the H + ion concentration. At higher H + ion concentrations, the rate of the exchange is decreased by increase of the Eu 3+ concentration, presumably because of the formation of the binuclear complexes LndtpaEu +, which undergo further transformation only slowly, The sequence of rate constants as a function of the atomic number is just the opposite to the sequence of complex stability constants; the rate constants exhibit a minimum at Ho.

Radiolysis of Aqueous Solution of Complexes of CO (II) and Co (III) and Diethylenetriamine Pentaacetic Acid

Radiolysis of Co(II) and Co(III) diethylenetriamine pentaacetate complex, both in the presence and the absence of oxygen, was investigated. The radiolytic degradation of the ion chelate was determined. A radiolylic mechanism has been proposed and discussed