Electrospray Ionization Mass Spectrometry in the structural characterization of a mixed nitrido-Tc heterocomplex of interest for myocardial imaging

The widespread use in diagnostic nuclear medicine of the metastable isotope 99mTc, a pure ƒ×-emitter with ideal physical properties for nuclear imaging (t1/2 = 6.06 h, Eƒ× = 140 keV), and easy availability through the commercial 99Mo/99mTc generator, and the recent advent of the ƒÒ-emitting radionuclides 186Re (t1/2 = 3.8 d, EƒÒmax = 1.07 MeV) and 188Re (t1/2 = 0.7 d, EƒÒmax = 2.11 MeV) as promising candidates for the application of injectable radiopharmaceuticals to the therapy of malignant and degenerative diseases, has made inorganic chemistry studies with the group VII elements technetium and rhenium very attractive. The focus of these investigations is the determination of the molecular structure of 99mTc- and 188/186Re-based agents produced at very low concentrations (micromolar scale or ¡¥non carrier added¡¦ level, nca). This can be conveniently achieved through the comparison of their chemical properties with those of the corresponding compounds prepared at the millimolar level (¡¥carrier added¡¦, ca) using the long-lived ƒÒ-emitting isotope 99Tc and the naturally occurring mixture of non-radioactive Re isotopes; the latter can be fully characterized by standard analytical and spectroscopic methods. Indeed, it is apparent that the possibility to clearly establish the chemical identity of a specific tracer is of utmost importance for the elucidation of its biological behavior.