Title:Investigation of Substitution Reactions Between Zinc(II) Complexes with Different Geometries and N-Bonding Nucleophiles
Volume: 1
Issue: 5
Author(s): Tanja Soldatović*Enisa Selimović
Affiliation:
- Department of Chemical-Technological Sciences, State University of Novi Pazar, Vuka Karadžića bb, Novi Pazar 36300,Serbia
Keywords:
Zinc(II), nitrogen relevant nucleophiles, structure-reactivity correlation, kinetics, cancer chemotherapy, platinumdrugs.
Abstract:
Aims: The study aimed at investigating interactions between zinc(II) complexes with different
geometrical structures and relevant nitrogen donor nucleophiles at physiological pH.
Background: Lack of clear distinction between the therapeutic and toxic doses of platinum drugs is
a major challenge for the design of novel non-platinum DNA and protein targeting metal-based anticancer
agents. The non-platinum antitumor complexes could be alternatives to platinum-based
drugs due to their better characteristics and different mechanisms of action.
Objective: This study could provide more information regarding the design of future zinc-based anticancer
drugs, providing a better understanding of the mechanism of interactions between Zn(II) complexes
and nitrogen-donor nucleophiles (important from the medical point of view), and clarifying the
changes in geometrical structures of zinc(II) that are referred to structure-reactivity correlations.
Methods: Mole-ratio method and UV-V is spectroscopic kinetic method have been used.
Results: The results indicated additional coordination of chlorides in the first coordination sphere
with changes in coordination geometry and formation of the octahedral complex anion [ZnCl4(en)]2-
while the excess of chloride did not affect the square-pyramidal structure of [ZnCl2(terpy)]. The
substitutions of studied complexes and relevant nucleophiles proceeded in two consecutive reaction
steps that depended on the nucleophile concentration. Octahedral complex anion [ZnCl4(en)]2- forms
rapidly and all substitution processes of this complex species should be considered. We assume that
the first reaction step is accompanied by the dissociation of chloride ligands. Nucleophile 1,2,4-
triazoles have shown the highest affinity toward [ZnCl2(en)], and rates of both steps were almost of
the same value, indicating parallel reactions.
Conclusion: The different order of reactivity of relevant N-donor ligands toward [ZnCl2(en)] and
[ZnCl2(terpy)] complexes for the first reaction step occurred because of the influence of different
geometrical structures of complexes, while low reaction rates for the second reactions of
[ZnCl2(en)] complex with imidazole and pyrazine were a consequence of interconversion between
octahedral and tetrahedral structure during substitution processes.