| Description |
Triaza-macrocyclic ligands are recently utilized to bind some radioisotopes for application in medicinal chemistry (60–64,67Cu, 66–68Ga, 86,90Y, 111In) [1,2]. Among them, copper radioisotopes are promising for application in diagnosis (positron emission tomography - PET, 64Cu with half-life 12.8 h) or in radio-immunotherapy (67Cu with half-life 62 h) [1,2]. Cu(II) ion should be bound in the form of metal complexes of high thermodynamic stability and kinetic inertness, which are required for the use in vivo for medical purposes. One of the most frequently used triaaza-macrocyclic ligand is H3nota (1,4,7-triazacyclononane-1,4,7-triacetic acid). Despite that, broad range of basic data regarding structural and some thermodynamic properties and kinetic behavior of its complexes has not been reported. Scheme: Formula of 1,4,7-triazacyclononane-1,4,7-triacetic acid (H3nota) Here, we report on protonation constants as well as stability constants of metal complexes (Cu(II), Zn(II), Ni(II), Co(II), Cd(II), Pb(II), Ca(II), Mg(II)) which show that the ligand cavity is too small for large metal ions and, therefore, the stability constants are significantly decreasing. This observation was confirmed for molecular structure of [Pb(nota)]– complex found in the solid state. The kinetic studies show the fast formation and slow dissociation of copper(II) complexes and, therefore, this ligand is suitable for sequestering of copper radioisotopes utilized in nuclear medicine. The results are compared with rate constants obtained for open-chain ligands, e.g. EDTA, or other triazamacrocyclic ligands without pendant arms.
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