Kinetic and mechanistic studies on reactions of diruthenium(II,III) with biologically relevant reducing agents.

Diruthenium(ii,iii)-tetracarboxylates have shown promising anticancer properties as metallotherapeutics. On the basis of the role that bio-reducing agents may play on the mode of action of ruthenium-based anticancer drugs, we performed detailed kinetic studies on the reaction of ascorbic acid and glutathione with the [Ru2(RCOO)4](+) paddlewheel framework by using the non-drug, diaqua complex ion [Ru2(CH3COO)4(H2O)2](+). In the presence of the reducing agents, the diaqua-Ru2 species first undergo a ligand substitution reaction by which the axially-coordinated water is displaced by the reducing agent. In both cases, this reaction is followed by an intra-molecular electron transfer process during which the metal-metal center is reduced from Ru2(5+) to Ru2(4+) and the reducing agent is oxidized. Product analyses were performed with the application of ESI-MS and (1)H-NMR techniques. Rate and activation parameters are reported for the different reaction steps.