Technetium and rhenium: coordination chemistry and nuclear medical applications

Ulrich Abram, Roger Alberto
2006 Journal of the Brazilian Chemical Society  
Compostos de coordenação do elemento radioativo tecnécio são empregados para diagnóstico em medicina nuclear, sendo vários complexos do nuclídeo emissor de radiação γ 99m Tc usados rotineiramente na obtenção de imagens de órgãos. As tendências modernas da química radiofarmacêutica concentram-se na marcação de moléculas biologicamente ativas tais como peptídeos, esteróides ou outras espécies com receptor específico. Por esta razão é necessário conhecer melhor a química de coordenação deste metal
more » ... denação deste metal de transição artificial, especialmente no que diz respeito às esferas de coordenação estáveis ou inertes que possibilitam o acoplamento a biomoléculas, de acordo com a estratégia de formação de bioconjugados. O papel dominante dos compostos de tecnécio nos procedimentos de diagnóstico sugere o uso dos isótopos do rênio emissores de radiação β, 186 Re e 188 Re, para fins terapêuticos em medicina nuclear. O isótopo 188 Re é facilmente obtido a partir do isótopo 188 W, e as abordagens sintéticas empregadas na química do tecnécio podem ser investigadas para a obtenção dos complexos de rênio. Coordination compounds of the radioactive element technetium are well established in diagnostic nuclear medicine, and various complexes of the γ-emitting nuclide 99m Tc are routinely used for organ imaging. Modern trends in the radiopharmaceutical chemistry of technetium focus on the 'labeling' of biologically active molecules such as peptides, steroids or other receptor-seeking units. This requires more knowledge about the coordination chemistry of the artificial transition metal, particularly with regard to stable or kinetically inert coordination spheres, which allow couplings to biomolecules following a bioconjugate approach. The dominant role of technetium compounds in diagnostic procedures recommends the β --emitting rhenium isotopes 186 Re and 188 Re for applications in nuclear-medical therapy. 188 Re is readily available from an 188 W/ 188 Re radionuclide generator system and general synthetic approaches can be adopted from the established technetium chemistry. of technetium compounds applying conventional chemical and spectroscopic methods including X-ray diffraction. The weak β --emission of 99 Tc (E max = 0.3 MeV) permits the handling of milligram amounts of 99 Tc in normal glassware, since the β --particles are effectively shielded by the glass walls and secondary X-rays (bremsstrahlung) become important only with larger amounts of 99 Tc. Nevertheless, gloves and safety glasses are essential when working with radioactive materials and particular care must be taken to avoid any ingestion or inhalation, since (although being a weak β --emitter) 99 Tc may cause serious damages to biological tissue, when incorporated. Almost all our chemical and structural knowledge about technetium and its compounds derived from studies performed with 99 Tc. The main motivation for most of these studies is related to practical applications of its γ-emitting isomer 99m Tc, which is the workhorse of nuclear medicine. 5 The unstable parent isotope of 99m Tc is 99 Mo, which is a β --emitter and disintegrates with a half-life time of 66 h (Scheme 2) to 99
doi:10.1590/s0103-50532006000800004 fatcat:ncolg3ybjfgr5gxfyszkh5g6bi