OXIDATION-STATES OF TECHNETIUM IN DIPHOSPHONATE COMPLEXES

Valence states of technetium in two most prominent bone imaging agents . i.e., their model complexes with Tc-99 (Tc-99-MDP and Tc-99-DPD) wer e determined by redox potentiometric titration. Titrations of Tc-99-pe rtechnetate by Sn(II) solutions were performed in the presence of a li gand (MDP or DPD), as well as without them. Tc(III) was obtained in co mplexes with MDP and DPD in strongly alkaline medium (pH 12 - 13) whil e in the absence of the ligands Tc(IV) was formed. In strongly acidic medium (pH 2 - 3) the redox process resulted Tc(IV) in both complexes, while Tc(III) was formed in the absence of the ligands. At pH values near neutral or exactly neutral (important for radiopharmaceutical com plexes Tc-99m-MDP and Tc-99m-DPD), it was possible to perform titratio ns in the ligand absence only at pH values from 7 to 11.8 (due to in h ydrolysis) while the resulting oxidation state of Tc in the presence o f ligand depended on the used ligand: Tc(IV)-MDP (pH 5.4 - 5.9 and pH 7.0-7.4), and Tc(III)-DPD (pH 8.0).