COMPLEXES OF TECHNETIUM WITH HYDROXYCARBOXYLIC ACIDS - GLUCONIC, GLUCOHEPTONIC, TARTARIC, AND CITRIC

Abstract

Tc complexes of several hydroxycarboxylic acids are used as radiopharmaceuticals for medical imaging. To determine the oxidation state of Tc in these agents, the reduction of pertechnetate [99Tc] in 0.1 M solutions of 4 hydroxycarboxylic acids was studied using polarography and amperometric titration with Sn2+. In D-gluconate below pH 6, Tc3+ and Tc5+ complexes were positively identified and Tc4+ was questionable; at pH 6-10, Tc4+ and Tc5+ were formed; and above pH 10, Tc3+, Tc4+ and Tc5+ were found. In D-glucoheptonate below pH 6, Tc3+ and Tc5+ were formed and Tc4+ was questionable; at pH 6-10, Tc5+; and above pH 10, Tc3+, Tc5+ and probably Tc4+ were formed. In L-tartrate below pH 6, Tc3+, Tc4+ and Tc5+ were formed; above pH 6, Tc4+ and Tc5+ were formed. In citrate below pH 10, Tc3+, Tc4+ and Tc5+ were formed; above pH 10, Tc4+ and Tc5+ were formed. For all 4 ligands the initial product of reduction by Sn2+ at Ph 3-9 was Tc5+. In freshly prepared Sn-labeled imaging agents of this class the oxidation state was probably Tc5+. Lower stable oxidation states occurred using reducing agents stronger than Sn; these may show altered imaging properties.