Technetium species

Chemical separation of technetium in soils is not easy, but it is fairly well-known that under aerobic conditions pertechnetate Tc(YII) is readily transferred to plants while under anaerobic conditions insoluble TcCh (or its hydrate) is not transferred to them. Even under aerobic conditions, however, the transfer rate decreases with time [28], indicating that soluble pertechnetate changes to insoluble forms by the action of microorganisms which produce a local anaerobic condition around themselves [29,30]. Insoluble technetium species may be TcOz, sulfide or complexes of organic material such as humic acid. 

Egorov, O. B., O Hara, M. J., and Grate, J. W., Microwave-assisted sample treatment in a fully automated flow-based instrument Oxidation of reduced technetium species in the analysis of total technetium-99 in caustic aged nuclear waste samples, Anal. Chem., 76, 3869-3877, 2004. 

Table VH shows that hydrazine is the only important variable for technetium sorption on each of the geologic solids. Hydrazine causes technetium to be removed from solution either by sorption or by precipitation of the reduced technetium species. Hydrazine is a powerful reducing agent and should reduce TcO/ to technetium(IV) according to standard half-cell potentials. No Tc02 was observed however, since the technetium passed through...

Throughout this paper, reference has beem made to reduced technetium species. Although it has been assumed that Tc(IV) is formed, there is no direct evidence for this. Experiments are now underway to determine the nature of the sorbed species using Fourier Transform Infrared Spectroscopy. 

Technetium(IV) is an oxidation state where high crystal field activation energies may be expected, and indeed substitution at [TcBrg] " and at [TcF ] " is very slow. Under forcing conditions the latter gives di-/i.-oxo-di-technetium species, indicating a complex mechanism. The much-studied and much-used... 

Knowledge of the complex chemistry of technetium is primarily based on laboratory experiments using the isotopic tracers Tc (Ti/2 = 6.02h), Tc (Ti/2 = 2.6 X 10 years), Tc (T1/2 = 90 days), and Tc (Ti/2 = 61 days). In aqueous solution, the physicochemical forms of technetium will depend on pH and redox conditions (Eh). From Eh-pH diagrams it can be deduced that TcOT is the only stable physicochemical form in aerobic natural waters. Under anaerobic conditions, however, Tc04T is reduced to Tc02, TcO(OH)2, or TcCle". Technetium-species in oxidation state IV may associate with organic material such as humic substances in anoxic sediments, and thereby behave as organic colloids. 

Technetium-99m coordination compounds are used very widely as noniavasive imaging tools (35) (see Imaging technology Radioactive tracers). Different coordination species concentrate ia different organs. Several of the [Tc O(chelate)2] types have been used. In fact, the large majority of nuclear medicine scans ia the United States are of technetium-99m complexes. Moreover, chiral transition-metal complexes have been used to probe nucleic acid stmcture (see Nucleic acids). For example, the two chiral isomers of tris(1,10-phenanthroline)mthenium (IT) [24162-09-2] (14) iateract differentiy with DNA. These compounds are enantioselective and provide an addition tool for DNA stmctural iaterpretation (36). 

Technetium-99m (the m signifies a metastable, or moderately stable, species) is generated in nuclear reactors and shipped to hospitals for use in medical imaging. The radioisotope has a half-life of 6.01 h. If a 165-mg sample of technetium-99m is shipped from a nuclear reactor to a hospital 125 kilometers away in a truck that averages 50.0 kmh. what mass of technetium-99m will remain when it arrives at the hospital ... 

Great interest in diphosphino complexes of technetium arose when Deutsch and co-workers found that lipophilic cations are able to be accumulated in heart tissue and can thus be candidates for myocardium perfusion agents [120]. Both the Tc(V) DMPE complex, [Tc02L2]+, and the [TcL2X2] + and [TcL3] + species in oxidation states +3 and +1 have been evaluated. Whereas the [Tc02L2] +... 

Crystals of [Tc(tu)6]Cl3 or [TcCl(tu)5]Cl2 are often employed for the synthesis of technetium(III) complexes. However, since the direct reduction of pertechnetate with excess thiourea in a hydrochloric acid solution yields [Tc(tu)6]3+ in high yield [37], direct use of the aqueous solution of the thiourea complex would be preferable for the synthesis of the technetium(III) complex without isolation of the crystals of the thiourea complex. In fact, technetium could be extracted from the aqueous solution of the Tc-thiourea complex with acetylacetone-benzene solution in two steps [38]. More than 95% extraction of technetium was attained using the following procedure [39] First a pertechnetate solution was added to a 0.5 M thiourea solution in 1 M hydrochloric acid. The solution turned red-orange as the Tc(III)-thiourea complex formed. Next, a benzene solution containing a suitable concentration of acetylacetone was added. After the mixture was shaken for a sufficient time (preliminary extraction), the pH of the aqueous phase was adjusted to 4.3 and the aqueous solution was shaken with a freshly prepared acetylacetonebenzene solution (main extraction). The extraction behavior of the technetium complex is shown in Fig. 6. The chemical species extracted into the organic phase seemed to differ from tris(acetylacetonato)technetium(III). Kinetic analysis of the two step extraction mechanism showed that the formation of 4,6-dimethylpyrimidine-... 

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