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

Abstract

In order to develop a radiopharmaceutical for hepatobiliary scintigraphy with better hepatobiliary properties new ligand for complexation of Tc-99m, 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 degreesC and constant ionic strength 0.1 M (NaClO4): pK(1) = 1.7 +/- 0.1; pK(2) = 2.44 +/- 0.07; pK(3) = 6.29 +/- 0.02 and pK(4) = 10.91 +/- 0.06, respectively.