Reactivity of technetium(I) thioether carbonyl complexes towards histidine—an EXAFS study in solution

• Published in: Inorganica Chimica Acta 2001-10, Vol.322 (1), p.79-86
• Main Authors: Seifert, Sepp, Künstler, Jens-Uwe, Gupta, Antje, Funke, Harald, Reich, Tobias, Pietzsch, Hans-Jürgen, Alberto, Roger, Johannsen, Bernd
• Format: Article
• Language: English
• Subjects: Histidine; Ligand exchange reaction; Technetium complexes; X-ray absorption spectroscopy
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/S0020-1693(01)00544-8

Technetium(I) thioether carbonyl complexes and their reaction products with histidine were prepared and characterised by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, various chromatographic and electrophoretic methods and electrospray mass spectrometry. Their behaviour in aqueous solutions was studied on the carrier-added ( 99Tc) and the no-carrier-added ( 99mTc) levels. HPLC and electrophoretic studies show the identity of reaction products at both concentration levels. Technetium(I) carbonyl complexes containing a bidentate dithioether ligand [Tc(CO) 3Cl(SS)], as well as a tridentate carboxylato thioether ligand [Tc(CO) 3(SSO)], undergo a ligand exchange reaction with histidine and form the complex [Tc(CO) 3His]. EXAFS measurements were performed to estimate the structural parameters of the dissolved technetium(I) carbonyl complexes and their reaction products after the challenge experiments. The calculated bond lengths and coordination numbers are in agreement with the expected values and confirm the ligand exchange reactions. EXAFS analysis was used successfully to determine the structural parameters of Tc(I) tricarbonyl complexes in solutions. In connection with other methods, it was found that Tc(I) tricarbonyl dithioether complexes undergo ligand exchange reactions with histidine and form the corresponding Tc(I) histidine tricarbonyl complex. Probably, similar reactions lead to the strong protein binding of Tc(I) thioether tricarbonyl complexes observed in vitro as well as in vivo.