Technetium targeted

Meltzer, P. C.,Blundell, P., Jones,A. G. etal. A technetium-99m SPECT imaging agent which targets the dopamine transporter in primate brain. J. Med. Chem. 40 1835-1844, 1997. 

The periodic trends that distinguish the chemical behavior of rhenium and technetium are manifested in differences between the biological behavior between analogous rhenium and technetium compounds. The comparison can shed light on the mechanism of accumulation in target... 

Metal-essential radiopharmaceuticals are those whose targeting properties are inherent in the structure and chemistry of the complex itself rather than a biomolecule whose targeting ability is independent of the attachment of the metal. While this class of tracers includes many well-developed technetium complexes, it includes relatively few rhenium complexes. 

Preparation. It can be made by the irradiation of molybdenum targets with deuterium nuclei. Technetium metal may be easily prepared by reduction of NH4Tc04 (or TcC>2) with hydrogen or by electrodeposition from an NH4Tc04 solution. 

Other elements often separated from pile or cyclotron targets by distillation or volatilisation are tritium (3), germanium as the bromide (23), arsenic as the trichloride (67), technetium (23), (91), rhenium (24), (25) and osmium (25) as oxides. 

A selective separation of fission technetium induced by fission of can be performed by stopping the speed of the Tc nuclides in solid KCl and SrClj catchers. At temperatures of 300 to 750 °C, 30% to 85% of Tc is selectively released. Purified nitrogen is used for the transportation of the nuclides from the target to the detector. The release is accelerated by increasing the temperature and adding ZrCl as a carrier. 

Technetium isotopes formed upon irradiation of a molybdenum target by protons with an energy of 22 MeV have been ascertained by mass spectrometry. After separation of technetium by ion exchange, the isotopes Tc (0.5 %), Tc (56.0%), Tc (17.3%) and Tc (26.7%) are detected. The sensitivity of this method is very high 5 x 10 g of technetium can be detected. Mass spectrometric determination of technetium is also described by Kukavadze et al. . Pertech-netate is reduced to technetium metal and Tc ions are produced at 1600 to 1800 °C. 

It might be noted that the oxidation states for technetium can easily change from one to the other. The oxidation states of Tc(III), Tc(IV), and Tc(V) for various compounds can be adjusted to target different organs when used for medical diagnostics and treatments. 

Fig. 2 The three fundamental building blocks and precursor complexes in organometallic radiopharmaceuticals in red the sites which can be substituted by targeting molecules (second generation) or ligands for technetium essential radiopharmaceuticals (first generation)...

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