Technetium isomers

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). 

Perrier and Segre suggested the name technetium , since it was the first element to be prepared artificially. 20 isotopes and numerous isomers with half-lives between about one second and several million years have hitherto been known (Table 1). 

Isomer shift data, Fe,S4 clusters, 38 20, 50 Isomorphic substitution, 39 179, 186 p-Isonicotinamide complexes, osmium, 37 307 p-lsonicotinamidepoly(proline) complexes, osmium, 37 307 Isonitrile complexes osmium, 37 245 technetium(I), 41 13-14 technetium(II), 41 31 technetium(IIl), 41 45 Isopolymolybdates, 19 239ff 19 265-280 crystallization from aqueous solution, 19 265-269... 

DPPB)(tricine)] interconvert at elevated temperatures, suggesting that the presence of these isomers might be due to conformational changes in the macro-cyclic technetium chelate. The LC-MS data for these two macrocyclic 99mTc complexes are completely consistent with the proposed composition. These phosphine-containing HYNIC chelators may have the potential to act as bifunctional chelators for 99mTc labeling of small BMs [56]. 

Tc and other isotopes and isomers of technetium are nuclides of medium radio-toxicity [26] licensing limits, annual limits of intake and maximum permitted air concentrations arc compiled in Table 5.4.A. 

The element, with atomic number 43 in the periodic table, was named technetium, a word derived from Greek meaning artificial. Thus, the name reflects the artificial origin of being produced by nuclear reactions, as no stable isotope of the element exists. Twenty-one radioactive isotopes of technetium and seven isomers are known from nuclear chemistry. Of these, only three isotopes have long physical half-lives Tc (T1/2 = 2.6 x 10 years), Tc (Ti/2 = 4.2x 10 years), and Tc (Ti/2 = 2.1 X 10 years). Being a long-lived fission product from neutron-induced fission of and... 

Hexamethylpropyleneamine oxime (HMPAO) stereoisomers and their technetium-99m complexes were resolved on a 40°C Chiralcel OD column [614]. The d- and /-uncomplexed isomers were separated in 20 min using a 97/3 hexane/IPA (0.01% diethylamine) mobile phase. The ""Tc complexes were also resolved but with an 85/15 hexane/IPA mobile phase. Temperature increases from 20°C to 40°C greatly improved peak shape and resolution. A table of resolution for the Tc complexes of meso-, d- and /-HMPAO was generated for 90/10 to 0/100 hexane/IPA mobile phases. Retention times for 65/35 to 85/15 hexane/IPA were also tabulated. For all these mobile phases the retention times were under 15 min. 

Technetium isotopes in the PWR primary coolant show a behavior which is quite different from that of the other fission products treated in this section. Whereas the short-lived Tc is only of minor radiological relevance, its long-lived isomer c (halflife 2.1 HP a) deserves some attention with respect to safety analyses for the final storage of radioactive wastes. Normally, c is not analyzed in the reactor coolant because of its very low activity concentration and of its unfavorable radiation properties (P 0.3 MeV, negligible y transition). For this reason, the Tc mass is frequently determined rather than its radioactivity suitable techniques for this task are neutron activation analysis, inductively-coupled mass spectrometry and laser resonance ionization mass spectrometry (see, for example, the comparative evaluation given by Trautmann, 1993). In each case, very expensive analytical procedures are required therefore, the greatest part of the available information on Tc behavior in reactor primary circuits has been derived from measurements of y-emitting Tc. 

Substitution of a phenyl by the CpRe(CO)3 moiety, bulkier and not easily oxidizable but more lipophilic (log 4-3 for (Z)-30d 3.2 (Z)-OH-tamoxifen) thus produces complexes with an antiestrogenic effect very close to that of OH-tamoxifen itself, an effect that is not influenced by the length of the side chain or by the isomer used. Radioactive forms of these complexes could be envisaged for use either as Re p emitters in radiotherapy, or, since the chemical behavior of technetium is known to be similar to that of rhenium, as technetium y emitters for use in radioimaging. Owing to the very short half-life required in radioisotopes for medical applications, new synthetic routes will have to be found that allow the radioactive entity to be incorporated easily and in good yield at the final step of the synthesis. 

Radioactive elements have no stable isotopes. Among the natural elements, polonium (atomic number 84) and heavier ones are radioactive. Technetium with its atomic number 43 is the lightest of all elements having no stable isotopes. Another light such dementis 61 promethium. Technetium has 26 unstable and 11 metastable (isomer) isotopes, all radioactive [28.9]. Details of the three most long-lived isotopes and two metastable (m) isotopes, important for tracer work, are collected in Table 28.3. 

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