Basic aqueous chemistry of [M(OH₂)₃(CO)₃]⁺(M=Re,Tc) directed towards radiopharmaceutical application

Abstract
A review on the synthesis and properties of the organometallic aqua-ion [M(OH2)3(CO)3]+ (M = Re, 99Tc, 99mTc), as relevant for radiopharmaceutical application, is presented. These important starting compounds can be prepared quantitatively a) on the no carrier added level (99mTc) in water or b) in organic solvents (Re, 99Tc) at atmospheric pressure in a short time and from [MO4]-. The main characteristics of these carbonyl complexes are the high substitution stability of the three CO ligands and the substitution lability of the coordinated water molecules. [M(OH2)3(CO)3]+ can be considered as a "semi aquo-ion". On the macroscopic level, upon titration with OH-, hydroxo-bridged oligomers have been isolated and characterized. The formation of hydroxo-bridged complexes is a consequence of the considerable Broenstedt acidity of [M(OH2)3(CO)3]+, whereas on the no carrier added level (n.c.a.) no such behavior was observed. Conditions and products of the water exchange by imidazole (im) and derivatives thereof (histamine, histidine) will be presented. The different mononuclear complexes with these ligands are of extraordinary inertness, which is the base for a potential application in biology and nuclear medicine. Finally, as a base for bioorganometallic chemistry, the adoption of the results from basic coordination chemistry to the labeling of biomolecules with an organometallic moiety will be exemplified with a selected penta-peptide and a recombinant single chain fragment.
Keywords: Tc-carbonyls, Tc-peptide complexes, scFv, cancer diagnosis, radiopharmacy