N,N'-BIS(2-MERCAPTOETHYL)ETHYLENEDIAMINE-N,N'-DIACETIC ACID AN EFFECTIVE LIGAND FOR INDIUM(III)

The formation constant of the In(III) complex of the sexadentate ligand N,N'-bis(2-mercaptoethyl)ethylenediamine-N,N'-diacetic acid has been determined by potentiometric measurement of its competition with EDTA. Its stability constant, 10(37.0), is higher than that of Ga(III) (10(35.6)) and is higher than that of any In(III) complex thus far reported. Its pM value of 30.4 under physiological conditions (pH 7.4, 100% excess ligand) indicates that the In-111 complex of this ligand would be a very effective radiopharmaceutical for diagnostic purposes.