Proton-Coupled Electron Transfer in the Oxidation of Guanosine Monophosphate by Ru(bpy)₃³⁺

Oxidation of guanine by the outer-sphere metal complex oxidant Ru­(bpy)₃³⁺ (bpy is 2,2′-bipyridine) has been explored in deoxyguanosine-5′-monophosphate with the added buffers succinic acid/succinate Hsuc/suc^–• (pK_a = 5.6), H₂PO₄^–/HPO₄^2– (pK_a = 7.2), and Tris [(HOCH₂)₃CNH₃⁺/(HOCH₂)₃CNH₂] (pK_a = 8.1) at 23 ± 2 °C. Over an extended range of buffer concentrations and ratios, there is clear evidence for the mechanistic importance of pathways involving concerted electron–proton transfer. In this pathway, proton transfer to the base form of the buffer occurs in concert with electron transfer to the oxidant, Ru­(bpy)₃³⁺.