Density-functional computation of (99)Tc NMR chemical shifts

99Tc chemical shifts of TcO4(-), TcH9(2-), TcOF5, TcO2F4(-), TcOCl4(-), Tc2(CO)10, and Tc(CO)3L3(+) (L = CO, MeCN, H2O) are computed using geometries optimized with the gradient-corrected BP86 and hybrid B3P86 density functionals, at the gauge-including atomic orbitals (GIAO), -BPW91 and -B3LYP levels. For this set of compounds, substituent effects on delta(99Tc) are better described with the pure BPW91 functional than with B3LYP, in contrast to most other transition-metal chemical shifts studied so far. A rough, qualitative correlation is found between computed electric-field gradients at the Tc nuclei and the corresponding 99Tc NMR line widths. Thermal and solvation effects on magnetic shielding constants of aqueous TcO4(-), as assessed by averaging these properties over trajectories from Car-Parrinello molecular dynamics simulations, are indicated to be small and comparable to those of MnO4(-). Complexation to aqueous uranyl, UO2(2+), is predicted to affect delta(99Tc) of TcO4(-) only slightly; somewhat larger complexation shifts are obtained for the oxygen nuclei of pertechnetate, suggesting that 17O NMR could be a useful probe for the extent of association between both radionuclides in solution.     

Analysis of99Tc atmospheric samples

The analysis of⁹⁹Tc was carried out in filter, peat and rainwater samples. A solvent extraction technique was used to separate Tc from them, where tributylphosphate was the extracting agent. Radiochemical yield was obtained by using^99mTc as an internal tracer. A typical value of 60% was found for it. However, problems encountered in its determination are discussed in the text. Additionally, rainwater samples were analyzed for¹³⁷Cs. This was adsorbed in ammonium phosphomolibdate. Radiochemical yield was obtained by using¹³⁴Cs as an internal tracer.Work partially supported under Contract CAICYT No. 2849/83.     

99Tc NMR determination of the oxygen isotope content in 18O‐enriched water

⁹⁹Tc NMR has been suggested as an original method of evaluating the content of oxygen isotopes in oxygen‐18‐enriched water, a precursor for the production of radioisotope fluorine‐18 used in positron emission tomography. To this end, solutions of NH₄TcO₄ or NaTcO₄ (up to 0.28 mol/L) with natural abundance of oxygen isotopes in virgin or recycled ¹⁸O‐enriched water have been studied by ⁹⁹Tc NMR. The method is based on ¹⁶O/¹⁷O/¹⁸O intrinsic isotope effects in the ⁹⁹Tc NMR chemical shifts, and the statistical distribution of oxygen isotopes in the coordination sphere of TcO₄⁻ and makes it possible to quantify the composition of enriched water by measuring the relative intensities of the ⁹⁹Tc NMR signals of the Tc¹⁶O_4−n¹⁸O_n⁻ isotopologues. Because the oxygen exchange between TcO₄⁻ and enriched water in neutral and alkaline solutions is characterized by slow kinetics, gaseous HCl was bubbled through a solution for a few seconds to achieve the equilibrium distribution of oxygen isotopes in the Tc coordination sphere without distortion of the oxygen composition of the water. Pertechnetate ion was selected as a probe due to its high stability in solutions and the significant ⁹⁹Tc NMR shift induced by a single ¹⁶O→¹⁸O substitution (−0.43 ± 0.01 ppm) in TcO₄⁻ and spin coupling constant ¹J(⁹⁹Tc–¹⁷O) (131.46 Hz) favourable for the observation of individual signals of Tc¹⁶O_4−n¹⁸O_n⁻ isotopologues.     

Half-life and specific activity of 99Tc

The half-life and specific activity of ⁹⁹Tc were redetermined by measuring the activity of a known weight (determined coulometrically) of ⁹⁹Tc by a liquid scintillation method and found to be 2·14(±0.·05) × 10⁵ years and 3·75(±0·11) × 10⁴ disintegration/min per μg respectively. These results are in excellent agreement with previous values.     

Synthesis and Molecular Structure of 99Tc Corroles

The first ⁹⁹Tc corroles have been synthesized and fully characterized. A single‐crystal X‐ray structure of a ⁹⁹TcO triarylcorrole revealed nearly identical geometry parameters as the corresponding ReO structure. A significant spectral shift between the Soret maxima of TcO (410–413 nm) and ReO (438–441 nm) corroles was observed and, based on two‐component spin–orbit ZORA TDDFT calculations, ascribed to relativistic effects in the Re case. The syntheses reported herein potentially pave the way toward ^99mTc‐porphyrinoid‐based radiopharmaceuticals.     

Preliminary study of quality control of99m Tc from99Mo generators

The separation of Tc(VII) from Mo(VI) by thin-layer and paper-chromatography is discussed. Some aspects concerning the formation and identification of lower oxidation states of Tc(VII) are also mentioned. Finally, a spot test is recommended for the determination of Mo(VI) and Al, which can be contaminants in the Tc(VII) solution eluted from the⁹⁹Mo column, filled with Al₂O₃.     

Supported Cobalt Nanoparticles for Hydroformylation Reactions

Hydroformylation of olefins has been studied in the presence of specific heterogeneous cobalt nanoparticles. The catalytic materials were prepared by pyrolysis of preformed cobalt complexes deposited onto different inorganic supports. Atomic absorption spectroscopy (AAS) measurements indicated a correlation of catalyst activity and cobalt leaching as well as a strong influence of the heterogeneous support on the productivity. These new, low-cost, easy-to-handle catalysts can substitute more toxic, unstable and volatile cobalt carbonyl complexes for hydroformylations on a laboratory scale.     

Reconstruction of Supported Metal Nanoparticles in Reaction Conditions

Metal nanoparticles (NPs) dispersed on a high‐surface‐area support are normally used as heterogeneous catalysts. Recent in situ experiments have shown that structure reconstruction of the NP occurs in real catalysis. However, the role played by supports in these processes is still unclear. Supports can be very important in real catalysis because of the new active sites at the perimeter interface between nanoparticles and supports. Herein, using a developed multiscale model coupled with in situ spherical aberration‐corrected (Cs‐corrected) TEM experiments, we show that the interaction between the support and the gas environment greatly changes the contact surface area between the metal and support, which further leads to the critical change in the perimeter interface. The dynamic changes of the interface in reactive environments can thus be predicted and be included in the rational design of supported metal nanocatalysts. In particular, our multiscale model shows quantitative consistency with experimental observations. This work offers possibilities for obtaining atomic‐scale structures and insights beyond the experimental limits.     

A new detection method of99Tc by nuclear excitation

A new nuclear excitation process,⁹⁹Tc (, )^99mTc reaction, was applied for the first time to radioactivation analysis of technetium. Bremsstrahlung irradiation of⁹⁹Tc samples gave the reaction product^99mTc which emits -ray measurable with ease by a semiconductor detector. The production rate of^99mTc per g⁹⁹Tc was linearly correlated with the flux of bremsstrahlung. The detection limit of⁹⁹Tc was estimated to be nanogram order (0.63 Bq⁹⁹Tc) under the optimum irradiation condition. Possible interference by¹⁰⁰Ru(, p)^99mTc reaction was also studied, which could be discriminated from the (, ) reaction by simultaneously occurring⁹⁸Ru (, p)⁹⁷Ru reaction.     

Accumulation, elimination and retention of 99Tc by duckweed

This study deals with the accumulation dynamics of the long-lived fission product technetium (⁹⁹Tc) in duckweed. Duckweed serves as model for aquatic plants, because of its representative foliar uptake for ⁹⁹Tc. This study shows that ⁹⁹Tc is irreversibly accumulated and distributed over cytoplasm, chloroplasts and mitochondria. Autoradiography showed that ⁹⁹Tc was not transported to new biomass. Irreversible storage of ⁹⁹Tc in plant biomass means that steady-state situations cannot be interpreted as a balance between uptake and elimination of ⁹⁹Tc, but that ⁹⁹Tc continuously builds up in each single duckweed plant and overall Tc concentrations are averaged over new biomass.     

Determination of99Tc in fuel leachates using extraction chromatography

A simple technique using a combination of cation exchange and solid phase extraction chromatographic resins has been developed for the separation of⁹⁹Tc from other radionuclides present in nuclear fuel leachates. Quantification of the isolated⁹⁹Tc is accomplished using liquid scintillation counting. The method provides consistently high recoveries (>96%), generates small amounts of waste compared to classical methods, and requires less analysis time.     

Radiochemical measurements of99Tc: Sources and environmental levels

A method of⁹⁹Tc determination has been developed based on sample decomposition followed by purification from interfering elements by hydroxide and oxide precipitations. Technetium is extracted by TBP and electrodeposited onto stainless steel discs from sodium hydroxide solution.⁹⁹Tc^m is used as yield monitor. The method has been applied to study releases from different sources and contents in different samples of atmospheric, terrestrial and marine origin. Results show enhanced⁹⁹Tc/¹³⁷Cs activity ratios for samples collected in recent years which are only expected to be contaminated from fallout from nuclear tests. Integrated fallout measurements did not reflect these enhanced ratios.     

Physicochemical Properties of Nanoparticles: Interaction of Supported Platinum Nanoparticles with Gaseous Reactants

The shapes, sizes, and electronic structures of platinum nanoparticles supported onto highly oriented pyrolytic graphite and oxidized silicon by different methods and their adsorptive properties with respect to hydrogen, oxygen, water, and ammonia were established. The apparent activation energy of the reduction of single oxidized platinum nanoparticles with molecular hydrogen was determined. The possibility of controlling the rate of ammonia decomposition by a nanostructured platinum coating by the application of electric potentials of different values and polarities to it was demonstrated.     

Extractive scintillating resin for 99Tc quantification in aqueous solutions

A method utilizing extractive scintillating resin for ⁹⁹Tcmonitoring in aqueous solutions is presented. These extractive scintillatorscombine analyte selective uptake and scintillating properties to produce dualfunctionality analytical resins. These resins were produced by (1) co-locatedextraction chromatographic resin and plastic scintillating beads, (2) immobilizingfluors in macroporous polystyrene supports to which chains of monomethylatedpolyethylene glycol have been grafted and (3) co-immobilizing organic scintillatingfluors and a quaternary ammonium extractant (Aliquat-336) within macroporousacrylic and polystyrene supports. The first and third resins selectively extractpertechnetate ions from dilute acid whereas the second resin selectively extractspertechnetate ions from high ionic strength solutions. These resins were utilizedin ~0.20 ml pore volume columns while ⁹⁹Tc was continually monitoredwith commercially available scintillation detection systems. Manual and automatedmicrofluidics were used to deliver sample and reagent solution for loadingand elution of the ⁹⁹Tc. The detection efficiencies were determinedto be 45 and 70% for acrylic and polystyrene based resins, respectively, andindependent of extractant. Minimum detectable ⁹⁹Tc concentrationusing the Aliquat-336/acrylic-based resin was 6.2 Bq . l –1 for a 50-mlsample and 30-minute count time. The new methodology was applied towards analysisof contaminated groundwater samples and nuclear waste simulants.     

磁性纳米粒子负载催化剂的应用研究进展

简要评述了近年来磁性纳米粒子负载钯及小分子催化剂在Suzuki,Heck和Sonogashir等偶联反应中的应用研究.参考文献29篇.     

Detection of99Tc by accelerator mass spectrometry: Preliminary investigations

Accelerator mass spectrometry (AMS) is an established technique for the detection of long-lived radionuclides at environmental levels. At LLNL, planned facility upgrades and advances in detection techniques are allowing us to explore the applicability of AMS to isotopes not previously pursued. One such isotope is⁹⁹Tc. We have performed a number of preliminary tests to examine the technical feasibility of AMS for the detection of⁹⁹Tc. The questions addressed were negative ion production in the cesium sputter source, transport efficiency for the ions through the spectrometer, and detection efficiency for⁹⁹Tc ions after the spectrometer. Based on the positive results of these tests, we have begun to develo measurement protocol.     

Determination of99Tc in rain and dry fallout by ICP-MS

Due to the difficulty of⁹⁹Tc analysis, data are insufficient for discussing its behavior in the environment. In this study, we focused on the determination of⁹⁹Tc in rain and dry fallout samples. The samples were collected monthly at Nakaminato, Japan, from June 1993. They were concentrated by heating on a hot plate without any loss of Tc. The solution was filtrated and then a liquid-liquid extraction (LLX) with trioctylamine (TOA), which works as a liquid anion exchanger, was carried out. Technetium was extracted from 5% HNO₃ solution into the organic phase with a high extractability. After being back-extracted from TOA/xylene into 1M K₂CO₃, LLX with cyclohexanone was used to remove ruthenium, which has a stable isotope of mass 99. Technetium was back-extracted into deionized water, and the solution was measured by inductively coupled plasma mass spectrometry (ICP-MS). The average recovery under the experimental conditions was 67% and the instrumental detection limit was 0.04 ppt (0.03 mBq/mL).     

Diffusion of 99Tc in granite under aerobic and anoxic conditions

Summary  Vezetéknév     

Determination and lebels of99Tc in environmental and biological samples

In this paper, the physical and chemical methods used in our laboratory for the measurement of⁹⁹Tc in natural samples are reviewed. Levels of⁹⁹Tc in rainwater, algae, and freshwater samples are given. In addition, and estimation of the radiological impact of⁹⁹Tc to the population, derived from our earliear atmospheric⁹⁹Tc measurements, is presented. For rainwater, levels of¹³⁷Cs are also given for comparison.Work partially supported by the contract PB86-0207 of the Spanish CICYT.