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

The reactions of ruthenium(II)-arene complex [Ru-II(eta(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 H-1 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 (Delta S-not equal) support an associative mode of activation. However, the rate constants obtained by H-1 NMR at 295 K in D2O follow the same order of the ligand reactivity. The hydrolysis of the [Ru-II(eta(6)-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. (C) 2011 Elsevier Ltd. All rights reserved.