Determination of the ionization constants of 4-iodo-2,6-dimethylphenylcarbamoylmethyl iminodiacetic acid

In order to develop a radiopharmaceutical for hepatobiliary scintigraphy with better hepatobiliary properties new ligand for complexation of ^99mTc, 4-iodo-2,6-dimethylphenylcarbamoylmethyl iminodiacetic acid (METHYLIODIDA), was synthesized. Acid–base equilibria of METHYLIODIDA were studied potentiometrically, because these data are important for determination of complex formation conditions. It was established that METHYLIODIDA undergoes a complex acid–base equilibrium due to its zwitterionic nature and four proton-binding sites. The stoichiometric ionization constants were determined at 25 °C and constant ionic strength 0.1 M (NaClO₄): pK₁=1.7±0.1; pK₂=2.44±0.07; pK₃=6.29±0.02 and pK₄=10.91±0.06, respectively.