Kinetics and mechanism of the substitution reactions of dinuclear platinum(II) complexes with important bio-molecules

Abstract

© 2018 Elsevier B.V. Substitution reactions of the series of dinuclear platinum(II) complexes with the general formula {[Pt(L)Cl]2(μ-pz)}Cl2 (1–4) (where L is ethylenediamine (en), 1; (±)-1,2-propylenediamine (1,2-pn), 2; isobutylenediamine (ibn) 3; trans-(±)-1,2-diaminocyclohexane (dach), 4) and biologically important ligands such as thiourea (Tu), glutathione (GSH) and L-methionine (L-Met) were studied in a medium consisting of 25 mM Hepes buffer and 40 mM NaCl, at pH 7.2 and 310 K using UV-Vis spectrophotometry. In addition, substitution reactions of complexes 2 and 3 with L-histidine (L-His) and guanosine-5′-monophosphate (5′-GMP) were investigated and the obtained results were compared with those previously published for complexes 1 and 4. The observed order of reactivity of the studied complexes toward selected nucleophiles is: 1 > 2 > 3 > 4, while the reactivity of nucleophiles follows the order: Tu > L-Met > GSH > L-His > 5′-GMP. The reactions with Tu and L-Met were followed by decomposition of the starting dinuclear platinum(II) complexes, whereas the structures of all complexes were preserved during substitution with GSH, L-His and 5′-GMP. To confirm the reaction pathways, 1H NMR spectroscopy and the HPLC method were additionally used. Furthermore, the two pKa values for the aqua complexes, {[Pt(1,2-pn)(H2O)]2(μ-pz)}4+ 2a and {[Pt(ibn)(H2O)]2(μ-pz)}4+ 3a were determined and compared with those previously reported for complexes {[Pt(en)(H2O)]2(μ-pz)}4+ 1a and {[Pt(dach)(H2O)]2(μ-pz)}4+ 4a.