Kinetics and mechanism of the reactions of Ru(II)-arene complex with some biologically relevant ligands

Abstract

The reactions of ruthenium(II)-arene complex [RuII(η 6-p-cym)(pydc)Cl] (where p-cym = p-isopropyl toluene, pydc = 2,3-pyridinedicarboxylato) with biologically nitrogen-donor nucleophiles, such as guanosine-5′-monophosphate (5′-GMP), guanosine (Guo) and l-histidine (l-His) were studied by UV-Vis spectrophotometry and 1H NMR spectroscopy. The reactions were studied at pH 2.5 and at 7.2. All reactions were followed under pseudo-first order conditions with large excess of the nucleophiles. The selected nucleophiles have a high affinity for Ru(II)-arene complex. The reactivity of the used ligands follow the same order at both pH values: Guo > 5′-GMP > l-His, while the reactions at pH 7.2 are always faster. The negative entropies of activation (ΔS≠) support an associative mode of activation. However, the rate constants obtained by 1H NMR at 295 K in D2O follow the same order of the ligand reactivity. The hydrolysis of the [RuII(η6-p- cym)(pydc)Cl] complex was very fast and completed by the time the first spectrum was measured. Addition of excess of NaCl to equilibrium solutions reversed the hydrolysis. © 2011 Elsevier Ltd. All rights reserved.