Complexes of technetium with hydroxycarboxylic acids: gluconic, glucoheptonic, tartaric, and citric

Technetium complexes of several hydroxycarboxylic acids are used for medical imaging. To determine the oxidation state of technetium in these agents, we studied the reduction of pertechnetate (Tc-99) in 0.1 M solutions of four hydroxycarboxylic acids, using polarography and amperometric titration with Sn(II). In D-gluconate below pH 6, Tc(III) and Tc(V) complexes were identified with certainty, Tc(IV) questionably; at pH 6 to 10, Tc(IV) and Tc(V) were formed; above pH 10, Tc(III), Tc(IV), and Tc(V). In D-glucoheptonate below pH 6, Tc(III) and Tc(V) were formed, and questionably Tc(IV); at pH 6 to 10, Tc(V); above pH 10, Tc(III), Tc(V), and probably Tc(IV). In L-tartrate below pH 6, Tc(III), Tc(IV), and Tc(V) were formed; above pH 6, Tc(IV) and Tc(V). In citrate below pH 10, Tc(III), Tc(IV), and Tc(V) were formed; above pH 10, Tc(IV) and Tc(V). For all four ligands the initial product of reduction by Sn(II) at pH 3 to 9 was Tc(V). In freshly prepared tin-labeled imaging agents of this class, the oxidation state is probably Tc(V). Lower stable oxidation states exist, attainable by using reducing agents stronger than tin; these may show altered imaging properties.