Oxidation of Glutathione by Hexachloroiridate(IV), Dicyanobis(bipyridine)iron(III), and Tetracyano(bipyridine)iron(III)

The aqueous oxidations of glutathione (GSH) by [IrCl6]2–, [Fe­(bpy)2(CN)2]+, and [Fe­(bpy)­(CN)4]− are described. All three reactions are highly susceptible to catalysis by traces of copper ions, but this catalysis can be fully suppressed with suitable chelating agents. The direct oxidation by [IrCl6]2– yields [IrCl6]3– and GSO3 –; some GSSG is also obtained in the presence of O2. The two FeIII oxidants are reduced to their corresponding FeII complexes with nearly quantitative formation of GSSG. The kinetics of these reactions have been studied at 25 °C and μ = 0.1 M between pH 1 and 11. All three reactions have rate laws that are first order in [Mox] and [GSH]t and show a general increase in rate with increasing pH. Detailed studies of the pH dependence enable the rate law to be elaborated with terms for reaction of the individual protonation states of GSH. These pH-resolved rate constants are interpreted with a mechanism having rate-limiting outer-sphere electron-transfer from the various thiolate forms of GSH.