Thermodynamic and kinetic study of Ln(III) complexes of NOTA


      Filip Smrčka^1*, Jakub Vaněk^1,2, Přemysl Lubal^1,2, Vojtěch Kubíček^3, Petr Hermann^3,

                                                 ^

    ^1 Department of Chemistry, Masaryk University, Kotlářská 2, CZ-611 37 Brno, Czech Republic

       ^2 Central European Institute of Technology (CEITEC), Masaryk University, Kamenice 5,
                                    CZ-625 00 Brno, Czech Republic

              ^3 Department of Inorganic Chemistry, Charles University, Hlavova 2030,
                                        CZ-128 40 Prague, Czech Republic

                                                 ^

                                      *filip.smrcka@gmail.com


Lanthanide(III) complexes of polyaza-macrocyclic ligands (primarily DOTA-like ligands) are utilized
in many areas of medicine (e.g. complexes of metal radioisotopes as ^90Y, ^153Sm, ^166Ho, ^177Lu in
nuclear medicine, Gd(III) complexes as MRI contrast agents, Eu(III) or Tb(III) complexes as
luminescent probes). For any biomedical applications, such metal complexes should exhibit a high
thermodynamic stability as well as kinetic inertness under physiological conditions and, therefore,
knowledge of these properties is important.

One of frequently used triazamacrocycle-based ligands is NOTA
(1,4,7-triazacyclononane-1,4,7-triacetic acid; Fig. 1). Since basic data regarding thermodynamic
properties of its complexes are, surprisingly, very scarce [1], we report here on its protonation
constants as well as on stability constants of its complexes with selected Ln(III) ions. Their
values show that NOTA cavity is too small for large Ln(III) ions in comparison with that of
DOTA-like ligands. In addition, stability constants of Ln(III) complexes are significantly
increasing for smaller Ln(III) ions. Kinetic properties of several Ln(III) complexes of NOTA were
studied by molecular absorption and luminescence spectroscopies in UV/VIS region. Reaction
mechanisms of formation (pH = 4.0–6.0, t = 25 °C, I = 0.1 M KCl) and acid-assisted dissociation (t
= 10–37 °C, I = 3.0 M (Na,H)ClO[4]) of Eu(III) complex were proposed from time-resolved
luminescence spectroscopy. The results were compared with data obtained for Ln(III) complexes of
similar tetraaza-macrocyclic ligands [1, 2].



N

N

N

C

O

O

H

C

O

O

H

H

O

O

C
>

                   Figure 1. 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA)

This work was supported by the Grant Agency of the Czech Republic (No. 13-08336S) and Ministry of
Education of the Czech Republic (CEITEC 2020 – LQ 1601) and it was carried out in frame of COST
Action CM1006 (EUFEN).

References

1.      Anderegg G., Arnaud-Neu F., Delgado R., Felcman J., Popov K., Pure App. Chem. 2005, 77,
1445-1495.

2.      Táborský P., Svobodová I., Lubal P., Hnatejko Z., Lis S., Hermann. P., Polyhedron 2007, 26,
4119-4130.