Thermodynamic and Kinetic Study of Mono- and Bis-triazamacrocyclic Ligands and their Transition Metal Complexes Mimicking Hydrolytic Enzyme Activity

Polyaza-macrocyclic ligands are recently utilized to bind some radioisotopes for application in medicinal chemistry (60–64,67Cu, 66–68Ga, 86,90Y, 111In) [1,2] and the formed metal complexes of high thermodynamic stability and kinetic inertness are required for their use in vivo for medical purposes. Several copper(II) and zinc(II) complexes of bis-polyaza-macrocyclic ligands catalyse some chemical reactions and therefore they can be used as model systems mimicking enzymes activity. In this work, the protonation constants of novel macrocyclic ligands as well as stability constants of their copper(II) and zinc(II) complexes were determined by glass-electrode potentiometry and molecular absorption spectroscopy. The formation of the copper(II) complexes of both ligands is accelerated with increased pH. The dissociation of both copper(II) complexes does not differ within experimental error indicating no cooperative effect for binucleating ligand. However, both complexes demonstrate significant catalytic activity in hydrolysis of model phosphodiester compounds.