Multiple-site proton-coupled electron transfer

Many PCET reactions occur by transfer of e and H+ to or from different locations, and therefore do not resemble hydrogen atom transfers. When the e and H+ transfer in the same kinetic step, these are called multiple site, concerted proton-electron transfer reactions (MS-CPET). Such reactions are increasingly recognized in biological systems, and likely play an important role in many catalytic and electrocatalytic PCET processes. We are interested in PCET reagents in which the e and H+ transfer to or from very separated sites. In the example below with an iron porphyrin (heme), proton transfer to the carboxylate is concerted with quite long range electron transfer (14 Å). Other examples are given in the Biomimetic reactivity of transition metal complexes section.

We are also preparing and examining organic molecules designed to react by MS-CPET, as described in the Probing PCET with organic molecules section. These studies are revealing the effects of distance – the distances over which the electron and proton travel, and the distances between the e and H+ in the initial and final states. We are also probing the role(s) of the interaction or coupling between the electron and proton, including the basic questions of what is meant by this coupling and how can we measure it. The results are being analyzed with Marcus Theory and sometimes more sophisticated theories of PCET.

Relevant Publications

Morris, W. D.; Mayer, J. M.
Separating Proton and Electron Transfer Effects in Three-Component Concerted PCET Reactions
J. Am. Chem. Soc.  2017139, 10312-10319.  
Saouma, C.T.; Pinney, M.M.; Mayer, J.M.
Electron Transfer and Proton-Coupled Electron Transfer Reactivity and Self-Exchange of Synthetic [2Fe-2S] Complexes: Models for Rieske and mitoNEET Clusters
Inorg. Chem.   201453, 3153–3161.  
Warren, J.J.; Menzeleev, A.R.; Kretchmer, J.S.; Miller, III, T.F.; Gray, H.B.; Mayer, J.M.
Long-Range Proton-Coupled Electron-Transfer Reactions of Bis(imidazole) Iron Tetraphenylporphyrins Linked to Benzoates
J. Phys. Chem. Lett.   20134, 519–523.  
Schrauben, J.N.; Cattaneo, M.; Day, T.C.; Tenderholt, A.L.; Mayer, J.M.
Multiple-Site Concerted Proton-Electron Transfer Reactions of Hydrogen-Bonded Phenols are Non-adiabatic and Well Described by Semi-Classical Marcus Theory
J. Am. Chem. Soc.   2012134, 16635-16645.  
Warren, J.J.; Mayer, J.M.
Tuning of the Thermochemical and Kinetic Properties of Ascorbate by Its Local Environment: Solution Chemistry and Biochemical Implications
J. Am. Chem. Soc.   2010132, 7784-7793.  
Markle, T.F.; Rhile, I.J.; DiPasquale, A.G.; Mayer, J.M.
Probing Concerted Proton-Electron Transfer in Phenol-Imidazoles
Proc. Natl. Acad. Sci.   2008105, 8185-8190.  
Markle, T.F.; Mayer, J.M.
Concerted Proton-Electron Transfer in Pyridylphenols: The Importance of the Hydrogen Bond
Angew. Chem., Int. Ed.   200847, 738-740.