A Computational Study of Pb(II) Complexes with Tetraazamacrocyclic Ligands

Viktorie REICHOVÁ^1), Přemysl LUBAL^1)


^1) Department of Chemistry, Faculty of Science, Masaryk University, Kamenice 5, CZ-625 00 BRNO,
Czech Republic, e-mail: reichova.viki@gmail.com


^203/212Pb(II) macrocyclic complexes have potential in cancer theranostics as cytotoxic α emitters
[1,2]. In order to utilize these complexes in vivo and for any other applications, their behavior
in various conditions must be understood. This work first experimentally examines the thermodynamic
and kinetic properties of a series of Pb(II) complexes with tetraazamacrocyclic-based ligands. The
rates of formation and dissociation of these complexes in varying conditions were monitored using
UV-Vis spectroscopy. The most thermodynamically stable complexes with Pb(II) are formed with a
ligand with four acetate-based pendant arms, while the most thermodynamically labile complexes have
a larger or smaller cavity or phospinic-acid based pendant arms. The complexes with the fastest
rates of formation are those with phosphinic-acid based pendant arms or a smaller cavity. The
mechanisms of formation and dissociation of these complexes are also proposed.

This work further examines the investigated complexes using computational chemistry. DFT
calculations using the PBE0 functional with the Def2TZVP basis set were used to optimize the
geometries of the complexes and calculate parameters such as bond length. The AIMAll program was
also used to calculate the delocalization indexes of the optimized complexes. These values were
then correlated with experimental results, such as stability constants and rates of
formation/dissociation, and certain trends were observed. Complexes with longer Pb-N bond lengths
and lower complex energies have faster rates of formation, while complexes with longer Pb-O bond
lengths and a higher delocalization index have enhanced kinetic inertness, a larger stability
constant, and a longer complex half-life. This information can be used for the rational design of
ligands having desired properties for the specific application of interest.

































Acknowledgments:

            This study was supported by the Ministry of Education of the Czech Republic and Masaryk
University (MUNI/A/1359/2018).


References:

[1]        C.S. Cutler, H.M Hennkens, N. Sisay, S. Huclier-Markai, S.S. Jurisson, Chem. Rev., 2013,
113(2), 858-   883.

[2]        C.G. Pipin, T.J. McMurry, M.W. Brechbiel, M. McDonald, R. Lambrecht, D. Milenic, M.
Roselli, D. Colcher, O.A. Gansow, Inorg. Chim. Acta 1995, 239(1-2), 43-51.