Tricarbonyltechnetium(I) and tricarbonylrhenium(I) complexed with N-methyl-2-pyridinecarboxyamide as potential radiopharmaceuticals: a computational study

The electronic and thermodynamic properties of the ‘2 + 1’ tricarbonyltechnetium(I) and -rhenium(I) mixed ligand complexes with N-methylpyridine-2-carboxyamide (MPCA) as a bidentate ligand and chloride, water, or tert-butyl-3-isocyanopropanoate (BCP), were investigated within the framework of Density Functional Theory. The atomic charges of all complexes, polarization of the CO groups, as well as the effect of transfer of π-electron density between the ligands through the metal were calculated and compared. The free energies of the reaction of formation of the isocyanide complexes in aqueous solution were calculated based on calculated total free energies in aqueous solution of the products and the substrates. The dissociation energies of the complexes were also determined in order to rationalize the experimentally observed higher resistance of the rhenium compared to the technetium complexes in the challenge experiments with the standard sulfur-containing amino acids.