Affiliate Professor of Chemistry
Ph.D. California Institute of Technology, 1982
(Inorganic, Organometallic, Bioinorganic, and Physical Organic Chemistry)
Research in the Mayer group spans the fields of inorganic, organometallic, bioinorganic, and physical organic chemistry. The work is focused on redox reactions that involve bond formation and bond cleavage, and particularly reactions that involve the transfer of both electrons and protons. Current projects range from fundamental studies of simple, well characterized model systems to the development of new soluble electrocatalysts. Professor Mayer is a member of the Center for Enabling New Technologies in Catalysis (CENTC), funded by the U.S. National Science Foundation, which draws together a group of investigators conducting research aimed toward the development of new catalytic systems. He is also a member of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy
Professor Mayer and his group are building a new fundamental understanding of reactions in which a proton and an electron are transferred together (proton-coupled electron transfer, PCET). One class of these reactions are hydrogen atom transfers, which are key steps in chemical processes from combustion and industrial selective hydrocarbon oxidations to the catalytic cycles of a variety of metalloenzymes. They have shown for the first time that the rates of hydrogen atom transfer processes follow Marcus theory in most cases. This means that the rate constants are determined by the driving force for transfer of H, and the intrinsic barriers to this transfer. The driving force is related to the strength of the bond the oxidant can make to a hydrogen atom (the bond dissociation free energy, BDFE). Since a hydrogen atom is an electron and a proton, the BDFE can be determined from the affinity of a reagent for an electron (a redox potential) and then a proton (a pKa).
Many energy-related and biochemical processes involve PCET reactions in which the electron and proton are or become separated. In the ruthenium model system shown below, the proton-accepting carboxylate is 11.2 Å removed from the ruthenium center that accepts the electron. Despite this separation, there is concerted transfer of e– and H+ from the substrate to the ruthenium complex. Parallel studies with phenol model systems containing pendant bases, as illustrated schematically below, are examining fundamental properties of reactions in which proton and electron move in different directions but are still coupled.
With a growing understanding of such separated PCET reactions, Mayer and his group are developing new catalytic reactions. The iron complex below, for example, is a rapid electrocatalyst for dioxygen reduction to water. The carboxylic acid groups appear to play an important role as ‘proton relays,’ delivering protons to oxygen species bound at the iron center.
PCET reactions also appear to be an important part of the reactivity at semiconducting metal oxide surfaces. Such interfacial redox reactions are important in the production of fuels from electricity (‘solar fuels’), in efficient conversions of chemical to electrical energy (as in a fuel cell), in dye-sensitized solar cells, and in other applications. Mayer and his group are developing metal oxide nanoparticles as models for such PCET processes. For instance, reduced nanoparticles can donate e– + H+ to a substrate such as a phenoxyl radical, as shown below. In this case, the electron comes from the conduction band of the semiconductor and the proton is present at the surface of the nanocrystal.
All of these projects involve synthesis, spectroscopy of various kinds, and mechanistic and kinetic studies. This broad exposure to different systems, approaches and techniques is very stimulating and helps to prepare students for a variety of future endeavors.
"Multiple-Site Concerted Proton-Electron Transfer Reactions of Hydrogen-Bonded Phenols are Non-adiabatic and Well Described by Semi-Classical Marcus Theory." J. N. Schrauben, M. Cattaneo, T. C. Day, A. L. Tenderholt, J. M. Mayer. J. Am. Chem. Soc. 2012, 134, 16635-16645.
"Titanium and Zinc Oxide Nanoparticles Are Proton-Coupled Electron Transfer Agents." J. N. Schrauben, R. Hayoun, C. N. Valdez, M. Braten, L. Fridley, J. M. Mayer. Science 2012, 336, 1298-1301.
"Protonation and Concerted Proton-Electron Transfer Reactivity of a Bis-Benzimidazolate Ligated [2Fe-2S] Model for Rieske Clusters." C. T. Saouma, W. Kaminsky, J. M. Mayer. J. Am. Chem. Soc. 2012, 134, 7293-7296.
"Electrocatalytic Oxygen Reduction by Iron Tetra-arylporphyrins Bearing Pendent Proton Relays." C. T. Carver, B. D. Matson, J. M. Mayer, J. Am. Chem. Soc. 2012, 134, 5444-5447.
"Copper-Based Water Oxidation Electrocatalysts." S. M. Barnett, K. I. Goldberg, J. M. Mayer. Nat. Chem. 2012, 4, 498-502.
"Understanding Hydrogen Atom Transfer: from Bond Strengths to Marcus Theory.” J. M. Mayer. Acc. Chem. Res. 2011, 44, 36-46. DOI: 10.1021/ar100093z
"Electron Transfer Between Colloidal ZnO Nanocrystals.” R. Hayoun, K. M. Whitaker, D. R. Gamelin, J. M. Mayer. J. Am. Chem. Soc. 2011, 133, 4228-4231.
"Proton-Coupled Electron Transfer Reactions at a Heme-Propionate in an Iron-Protoporphyrin-IX Model Compound.” J. J. Warren, J. M. Mayer, J. Am. Chem. Soc. 2011, 133, 8544-8551. DOI: 10.1021/ja201663p
"Directing Protons to the Dioxygen Ligand of a Ruthenium(II) Complex with Pendent Amines in the Second Coordination Sphere." T. A. Tronic, M. Rakowski DuBois, W. Kaminsky, M. K. Coggins, T. Liu, J. M. Mayer, Angew. Chem. Int. Ed. 2011, 50, 10936-10939. DOI: 10.1002/anie.201105266
"Spin-Forbidden Hydrogen Atom Transfer Reactions in a Cobalt Biimidazoline System.” V.W. Manner, A.D. Lindsay, E.A. Mader, J.N. Harvey, J.M. Mayer, Chem. Sci., Advance Article. DOI: 10.1039/C1SC00387A