Search

Due to physical decay properties commonly associated with therapeutic radionuclides, 188Re (t 1/2 = 16.98 h, E max = 2.12 MeV) is of high interest for endovascular brachytherapy and endoradiotherapy in general. Rhenium precursors in the low oxidation state +I, such as the organometallic fac-[Re(H2O)3(CO)3]+ are promising lead compounds compared to those with oxidation states +III and +V since they can be prepared under mild conditions and do not tend to reoxidize to oxidation state +VII while multidentate ligands can be attached under substitution of coordinated water molecules. This study comprises the application of the Free-Ion Selective Radiotracer Extraction (FISRE) technique in order to determine dissociation rate constants of complexes bearing the [188Re(CO)3]+-core at tracer levels in vitro with regards to their time-dependent kinetic speciation. As ligands, the tridentate l-histidine as well as the dipeptides l-carnosine (β-alanyl-l-histidine) and glycyl-l-histidine were chosen in order to study the effects of different moieties attached to the primary amine of l-histidine.

Free-ion selective radiotracer extraction (FISRE) is a technique combining ion exchange and the use of radiotracers in order to determine labilities of metal complexes. The aminocarboxylate chelates 90Y-EDTA, 90Y-DTPA as well as 90Y-DOTATOC, a radiopharmaceutical for neuroendocrine tumor treatment have been studied by FISRE using Chelex cation exchanger within the pH range 5.0–7.4. Time-dependent speciation and dissociation rate constants have been determined in a time frame of 0.6 s–648 h. As indicated by thermodynamic constants, the lability decreases significantly with higher ligand denticity, cyclic coordination and upon peptide coupling resulting in the lability order Y-EDTA>Y-DTPA>Y-DOTA>Y-DOTATOC. Besides, studies of the effects of the metal/ligand ratio on FISRE suggest that – in contrast to EDTA and DTPA – cyclic ligands DOTA and DOTATOC tend to shield the ion exchanger from free yttrium ions after complex dissociation even at slight excess of metal ions. Copyright © 2008 John Wiley & Sons, Ltd.

Representative banded iron-formations (BIFs) from various locations of the eastern Indian geological belt were investigated by instrumental neutron activation analysis (INAA). After pre-concentration, irradiation was carried out using a neutron flux of 5.1·1016 m−2·s−1, 1.0·1015 m−2·s−1 and 3.7·1015 m−2s−1, with thermal, epi-thermal and fast neutrons, respectively. The activities in these samples were measured by a HPGe detector. Ten rare-earth elements, such as La, Ce, Nd, Sm, Eu, Tb, Ho, Tm, Yb and Lu, have been qualitatively identified and quantitatively estimated in these samples. The present investigation is an example of employing a pre-concentration method for high iron-containing ores prior to neutron activation analysis.

Cryosublimation is one technique, which allows the accumulation of tritium from aqueous solutions using certain chemical compounds. After studying several inorganic compounds such as zeolites and metal salts,1 as well as some humic substances,2 we have now investigated several mono-and polysaccharides, such as glucose, maltose, galactose, starch, agar, and gelatine. Except for starch all of the above mentioned compounds showed a clear enrichment of tritium. The highest value was reached for Agartine, which gave an enrichment factor of 6.2. Since mono-and polysaccharides form weak hydrogen bonds, these results prove again our theory that tritium is preferably accumulated in exchangeable hydrogen bonds.

Within this work the analysis of the kinetic stability of a series of yttrium complexes, i.e., Y-citrate, Y-NTA, Y-CDTA as well as Y-humic acid (Y-HA) has been successfully performed by the free-ion selective radiotracer extraction (FISRE) method. FISRE uses 90Y with a high specific activity to perform CHELEX extractions in a buffered aqueous solution at pH 6 in two different modes by monitoring the dissociation and association reactions of the corresponding complexes. Whereas in the case of Y-citrate the dissociation profile could be successfully described in terms of (pseudo) first order kinetics, the other complexes tend to form two species with different kinetic properties, although only one species is predicted by speciation calculations. In the batch FISRE method, all (except Y-NTA) corresponding association rate constants were determined by monitoring the formation rate of the yttrium complexes.

A bipolar electrolysis system for tritium accumulation and HTO waste volume reduction was designed and built. Experiments were performed to achieve the system specific separation factor for iron and stainless steel cathodes in a 1M sodium hydroxide solution. A separation factor of about 6 for stainless steel and 19 to 26 for iron was measured. The vapor pressure isotope effect under experimental conditions was determined as 1.09±0.03 (T = 279 K).

Tritium exchange and enrichment was studied for several different metal salts, e.g., AlF3 . H2O, FeO(OH), CsI, CsF, NaI, NaF and Al(OH)3 using a cryosublimation apparatus. Experiments were performed below equilibrium vapor pressure to avoid any isotope effects. A comparable tritium enrichment factor of 1.14 to 1.43 was obtained for all systems, except for CsF, which gave an enrichment factor of 1.93. These results confirm the concept, that 3H is accumulated in weak hydrogen bonds as already observed in organic molecules.

Bovine serum albumin (BSA) and lysozyme (LSZ) were radiolabeled with 125I. Three different methods for protein iodination with 125I were optimized. Parameters like incubation time and ratio of oxidizing agent and amount of protein were established. During protein iodination with 125I, structural damages caused by the introduction of iodine into the protein may occur. These damages depend on the oxidizing agent used and may lead to considerable changes in the protein structure and, hence, their biological activity. Changes in secondary structure of LSZ and BSA were examined by circular dichroism (CD). Enzymatic activity tests were performed with lysozyme to check its biological activity. The Iodo Bead was found the best oxidizing agent for protein iodination.

A study of the extraction of polonium from aqueous solutions containing α-hydroxyisobutyric acid (α-HIBA) was performed with four different extractants, di-n-octyl sulphide (DOS), Cyanex 272, Cyanex 301 and Cyanex 302, dissolved in toluene. The extracted complex for DOS at low α-HIBA concentrations is most likely PoO(α-HIB)2·2DOS, while at higher α-HIBA concentrations there seems to be a solvating effect implicating an extracted complex of the type PoO(α-HIB)2(α-HIBA)2·2DOS. For the extraction of polonium with Cyanex 272 the results are inconclusive. The extracted complex is either PoOA2 or PoO(α-HIB)2·2HA. For extraction with Cyanex 301 or Cyanex 302 the major extracted species does not contain any α-HIBA molecules. The neutral species in both cases is PoOA2, extracted at low extractant concentrations, while at higher extractant concentrations a complex of the type PoOA2·xHA is extracted. The extraction of polonium increases in the order Cyanex 272 < DOS < Cyanex 302 < Cyanex 301.

Subsecond 224 Pa (T1/2 = 0.85 s) was produced via the 209 Bi(18 O,3n)224 Pa reaction at the 88 inch cyclotron at the Lawrence Berkeley National Laboratory. After production it was transported via a gas-jet system to the centrifuge system SISAK 3. Following on-line extraction with trioctylamine/scintillation solutions from 1M lactic acid, 224 Pa was detected applying on-line α-liquid scintillation counting. Unambiguous identification was achieved using time-correlated α-α-decay chain analysis. This constitutes the first chemical on-line separation and detection of a subsecond α-decaying nuclide, 0.85-s 224 Pa with the fast extraction system SISAK 3.

Two simple diphosphonates, CH6P2 O6(MDP) and C2 H8 P2 O7 (HEDP),have been irradiated with neutrons to produce the corresponding 32P-labeled compounds. After irradiation for 0.5–5 hours in a thermalneutron flux of 4.2 . 1016 n . m —2 s—1 the irradiated compounds were dissolved and fractionated using a SephadexG10 column. The separated fractions were identified using planar paper chromatographyand autoradiography. The labeling yield was ca 35% for each of the compounds,and the specific activity attainable ranged up to 4.8 GBq . mol —1 . For practical applications, the labeled diphosphonates have to bepurified further.

[32P]-labelled sodium monofluorophosphate (Na2FPO3) was prepared according to a procedure, which is based on melting of a mixture of carrier-added [32P]-phosphoric acid and ammonium bifluoride, both solid. Monofluorophosphate was precipitated as the silver salt from the reaction mixture, then it was converted to the sodium salt by using a cation exchange column in Na+ form. The influence of the molar ratios of the reactants, and the reaction time on the final yield was studied. Powder X-ray diffraction showed a chemical purity of about 98% and absence of NaF in the final product. After a reaction time of 2 hours and a molar ratio of the reactants of 1 : 1, the yield for the reaction was 30% of the initial 32P activity, corresponding to a specific activity of 56 MBq 32P per mmol. An increase in yield is possible by increasing the reaction time, a higher specific activity may be obtained by a decrease of carrier phosphoric acid. The advantages of the procedure developed are the availability of [32P]-phosphoric acid, and the simple preparation of the compound. Copyright © 1999 John Wiley & Sons, Ltd.

Fast solvent extraction is a chemical separation method, which can be applied to study exotic nuclides. Since about 1970 the SISAK technique, which is an on-line method based on multi-stage solvent extraction separations, has been successfully used to investigate the nuclear properties of β-decaying nuclides with half-lives down to about one second. During the last decade it has become possible to produce transactinide elements in high enough yields to investigate their chemical properties on a one-atom-at-a-time scale. For this purpose it was necessary to improve and change the detection part of the SISAK system in order to be capable to detect spontaneously fissioning and α-decaying nuclides in a flowing organic solution. This technique is based on liquid scintillation counting with pulse-shape discrimination and pile-up rejection