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Kinetic studies of the reactions between dichlorido(1,2-diaminoethane)zinc(II) and biologically relevant nucleophiles in the presence of chloride

Posted on 16. April, 2018.

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The mole-ratio method was used for determining metal–ligand stoichiometry for the reaction between [ZnCl2(en)] (where en = 1,2-diaminoethane or ethylenediamine) and chloride ion at pH 7.2. The results have shown step-wise formation of 1:1 and 1:2 complexes and indicate additional coordination of chloride ions in the first coordination sphere. 

The kinetics of ligand substitution reactions of the zinc(II) complex and biologically relevant nucleophiles such as inosine-5'-monophosphate (5'-IMP), guanosine-5'-monophosphate (5'-GMP), L-methionine (L-Met), glutathione (GSH) and DL-aspartic acid (DL-Asp) were investigated at pH 7.2 as a function of nucleophile concentration in the presence of 0.010 M NaCl. The reactions were followed under pseudo first-order conditions by UV-Vis spectrophotometry. The substitution reactions include two steps of consecutive displacement of chlorido ligands and changes in coordination geometry. In the presence of an excess of chloride, the octahedral complex anion [ZnCl4(en)]2– formed. The first step of the substitution reactions could be interpreted as substitution of the axial chlorido ligands in the cis position to bidentate ethylenediamine by the biologically relevant nucleophiles, while the second step could be interpreted as substitution of the equatorial chlorido ligand. The order of reactivity of the investigated nucleophiles for the first reaction step is 5'-IMP > GSH > L-Met > DL-Asp > 5'-GMP, while for the  second reaction step the order of reactivity is GSH > L-Met > 5'-IMP > DL-Asp > 5'-GMP.

Published in Progress in Reaction Kinetics and Mechanism, Volume 43, Number 1, 2018, pp. 53-61.


Authors: Tanja Soldatovic* and Enisa Selimovic
Department of Chemical-Technological Science, State University of Novi Pazar, Vuka, Karadžica bb, 36300 Novi Pazar, Serbia

Keywords: zinc(II) complex, biologically relevant nucleophile, excess chloride

Image: Step-wise formation of 1:1 and 1:2 complexes in the presence of excess chloride.