EXAFS analyses of technetium(I) carbonyl complexes – stability studies in solutions

Mono-, bi-, or tridentate ligands? The labeling of peptides with 99mTc-carbonyls

The labeling of targeting peptides with (99m)Tc is a useful concept for the diagnosis of various diseases such as cancer. Although in research for at least one decade, only a very few radiopharmaceuticals based on peptides are in clinical use. The difficulty of labeling, and the resulting authenticity of the new vector, is largely responsible for this observation. In this overview, we present an alternate strategy based on the organometallic fac-[(99m)Tc(CO)(3)](+) core for introducing (99m)Tc in biomolecules in general and in peptides in particular. The three coordination sites available in [(99m)Tc(OH(2))(3)(CO)(3)](+) can be occupied with many different ligand types, pendant to a biomolecule and serving as the anchor group for labeling. This makes the appropriate choice difficult. We intend to present some useful concepts for the practice. Monodentate chelators are robust but bear the risk of multiple binding of biomolecules. Coordinating a bidentate ligand of choice prior to labeling bypasses this problem and enables a systematic drug discovery by variation of the bidentate ligand. Bidentate ligands attached to the biomolecule are stronger but occasionally require protection of the remaining site by a monodentate ligand. Both approaches refer to a mixed-ligand [2+1] approach. Tridentate chelators are the most efficient but need some protecting group chemistry in order to achieve selectivity for the coupling process. Examples with cysteine and histidine are presented. This article aims to provide versatile and reproducible approaches for the labeling of biomolecules while not focusing on particular systems. It should be left to the readers to derive a strategy for their own peptide.

Identification of the non-pertechnetate species in Hanford waste tanks, Tc(I)--carbonyl complexes

Immobilization of the high-level nuclear waste stored at the Hanford Reservation has been complicated by the presence of soluble, lower-valent technetium species. Previous work by Schroeder and Blanchard has shown that these species cannot be removed by ion-exchange and are difficult to oxidize. The Tc K-edge XANES spectra of the species in Tanks SY-101 and SY-103 were reported by Blanchard, but they could not be assigned to any known technetium complex. We report that the XANES spectra are most likely those of Tc(I)-carbonyl species, especially fac-Tc(CO)3(gluconate)(2-). This is further supported by EXAFS and 99Tc-NMR studies in nonradioactive simulants of these tank wastes.