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A major contemporary challenge is development of efficient and sustainable systems for energy utilization. Biology is instructive in this endeavor, providing biochemical solutions to a variety of physiological needs in energy conversion and storage. Metalloproteins play central roles in these solutions and thus provide impetus for understanding the mechanistic bioinorganic chemistry of metalloproteins for application to practical bioinspired catalysis.

Our laboratory is using what we, and others, learn about how metalloproteins function as inspiration for development of unique energy conversion and storage systems. Being at the nexus of bioinorganic and bioinspired chemistry requires us to employ a multi-disciplinary approach spanning chemical synthesis, molecular biology, physical methods, and theory. This approach fosters a rich training environment for students.

More broadly, our fundamental interest in metalloprotein mechanism overlaps problems with significant health, environmental, and technology implications. Metalloproteins are an intrinsically interesting way to study inorganic chemistry as some metalloprotein catalyzed reactions exist for which there is no benchtop equivalent. Click below for details on a few of the questions we are currently investigating.
Cytochrome c oxidase converts oxygen to water using four equivalents of ferrous cytochrome c as the source of electrons. The free energy gained by redox is efficiently used to vectorially translocate (pump) four H+ across the inner mitochondrial membrane, thereby creating charge separation to be used downstream by ATP synthase. The molecular mechanism of proton pumping is a longstanding unresolved problem in bioenergetics despite decades of sustained research emphasis. We are solving this problem by the combination of genetic incorporation of unnatural amino acid vibrational probes that report on changes to the local electric fields within the protein caused by proton translocation, coupled to a novel high-resolution time-resolved Fourier transform UV resonance Raman spectrometer.
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These studies span advanced techniques in molecular biology, biophysics, and computational molecular dynamics with the goal of spatially and temporally resolving the distribution of protons during pumping, molecular level detail required to understand this central biological energy conversion process.
A promising alternative to the use of fossil fuels is the use of fuels derived from solar energy. The key energetic event in natural photosynthesis is the oxidation of water by sunlight to generate the energy carrier NADPH, which is used downstream in a thermoneutral reaction to fix carbon dioxide. Consequently, the critical need in practical artificial systems is an efficient catalyst for performing the water oxidation half reaction.

Considerable progress has been made creating homo- and heterogeneous catalysts, which predominately employ electrophillic attack of high-valent metal-oxo moieties on water. Unfortunately, these catalysts have yet to achieve the targets required for broad adoption.

We have initiated a program exploring an alternative mechanistic strategy involving reversible O—O bond formation via late first row transition metal complexes. The ultimate goal is to create practical electrocatalysts for oxygen evolution. These studies involve advanced spectroscopies (resonance Raman, electron paramagnetic resonance, X-ray absorption), electrochemistry, and density functional theory calculations in addition to significant chemical synthesis.
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Ethylene is a phytohormone influencing virtually all phases of plant growth and development. Thus, there is significant interest in regulation and control of ethylene signaling in crop plants for maximizing energy conversion in foodstuff and biofuel production. The key component of the ethylene signaling pathway is the ethylene receptor (ETR1), a copper dependent protein; however, there are significant gaps in knowledge on the architecture of the active site and how ethylene binding initiates the signaling cascade. This information is critical for understanding factors that drive how plants build and use their energy conversion and storage systems.
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We are elucidating the geometric and electronic structure of the proposed ethylene binding active site and the molecular mechanism of ethylene signal transduction by this receptor family through the combination of bioinorganic spectroscopy (XAS and biomolecular NMR) of the receptor coupled to synthesis and study of small molecule analogs of the active site. These studies significantly expand the scope of the emerging fields of small molecule signaling by metalloproteins and organometallic biochemistry.
  1. Kieber-Emmons, M.T.; Ginsbach, J.W.; Wick, P. K.; Lucas, H.; Helton, M. E; Lucchese, B.; Suzuki, M.; Zuberbuhler, A.; Karlin, K.D.; Solomon, E.I. “Observation of a CuII2(μ-1,2- peroxo)/CuIII2(μ-oxo)2 Equilibrium and its Implications for Copper–Dioxygen Reactivity” Angew. Chem. 2014, 126, 5035-5039.
  2. Solomon, E.I.; Heppner, D. E.; Johnston, E. M.; Ginsbach, J.; Cirera, J.; Qayyum, M.F.; Kieber- Emmons, M.T.; Kjaergaard, C.H.; Hadt, R.G.; Tian, L.; “Copper Active Sites in Biology” Chem. Rev. 2014, 114, 3659-3853.
  3. Ginsbach, J.W.; Kieber-Emmons, M.T.; Noguchi, A.; Nomoto R.; Noguchi, A.; Ohnishi, Y.; Solomon, E.I. “Structure/function correlations among coupled binuclear copper proteins through spectroscopic and reactivity studies of NspF” Proc. Nat. Acad. Sci. 2012, 109, 10793-10797.
  4. Kieber-Emmons, M.T.; Halime, Z.; Qayyum, M.F.; Hodgson, K.O.; Hedman, B.; Karlin, K.D; Solomon, E.I. “Spectroscopic Elucidation of a New Structure Type in Heme/Cu Dioxygen Chemistry: Implications for O—O Bond Rupture in Cytochrome c Oxidase” Angew. Chem. 2012, 51, 168-172.
  5. Kieber-Emmons, M.T.; Li, Y.; Halime, Z.; Karlin, K.D.; Solomon , E.I. “Electronic Structure of a Low-spin Heme/Cu Peroxide Complex: Spin-State and Spin-Topology Contributions to Reactivity” Inorg. Chem. 2011, 50, 11777-11786.
  6. Solomon, E.I.; Ginsbach, J.; Heppner, D. E.; Kieber-Emmons, M.T.; Kjaergaard, C.H.; Smeets, P.J.; Tian, L.; Woertnik, J. “Copper dioxygen (bio)inorganic chemistry” Faraday Discuss. 2011, 148, 11-39.
  7. Lee,Y.; Lee, D.H.; Park, G.Y.; Lucas, H.R.; Narducci-Sarjeant, A.A.; Kieber-Emmons, M.T.; Vance, M.A.; Milligan, A.E.; Solomon, E.I.; Karlin, K.D. “Sulfur Donor Atom Effects on Copper(I)/O2 Chemistry with Thioanisole Containing Tetradentate N3S Ligand Leading to μ-1,2- Peroxo-Dicopper(II) species” Inorg. Chem. 2010, 49, 8873-8885.
  8. Halime, Z.; Kieber-Emmons, M.T.; Qayyum, M.F.; Mondal, B.; Puiu, S.C.; Chufán, E.C.; Sarjeant, A.A.N.; Hodgson, K.O.; Hedman, B.; Solomon, E.I.; Karlin, K.D. “Heme- Copper/Dioxygen Complexes: Towards Understanding Ligand Environmental Effects on Coordination Geometry, Electronic Structure and Reactivity” Inorg. Chem. 2010, 49, 3629-3645.
  9. Van Heuleven, K.M.; Kieber-Emmons, M.T.; Riordan, C.G.; Brunold, T.C. “Spectroscopic and Computational Studies on the Trans-μ-1,2-Persulfido-Bridged Dinickel(II) Species [Ni2(tmc)2(S2)](OTf)2: Comparison of End-on Persulfido and Peroxo Bonding in Ni(II) and Cu(II) Species” Inorg. Chem. 2010, 49, 3104-3112.
  10. * Mock, M.T.; Kieber-Emmons, M.T.; Popescu, C.V.; Yap, G.P.A.; Riordan, C.G.; A Series of Cyanide-Bridged Binuclear Complexes” Inorg. Chim. Acta. 2009, 362, 4553-4562. *Invited paper for a special issue honoring Swiatoslav “Jerry” Trofimenko.
  11. Ariyananda, P.W.G.; Kieber-Emmons, M.T.; Yap, G.P.A.; Riordan, C.G.; “Secondary Coordination Sphere Effects on the Reductive Elimination of Thioester in Acetyl Coenzyme A Synthase” Dalton Trans. 2009, 4359-4369.
  12. Kieber-Emmons, M.T.; Van Heuvelen, K.M.; Brunold, T.C.; Riordan, C.G.; “Identification of a Trans-μ-1,2-Persulfide Bridged Dinickel(II) species” J. Am. Chem. Soc. 2009, 131, 440-441.
  13. Kieber-Emmons, M.T.; Riordan, C.G.; “Dioxygen Activation at Mono-Valent Nickel” Acc. Chem. Res. 2007, 40, 618-625.
  14. Kieber-Emmons, M.T.; Annaraj, J.; Seo, M.S.; Van Heuvelen, K.M.; Tosha, T.; Kitagawa, T.; Brunold, T.C.; Nam,W.; Riordan, C.G. “Identification of an “End-on” Nickel-Superoxo Adduct, [Ni(tmc)(O2)]+” J. Am. Chem. Soc. 2006, 128, 14230-14231.
  15. Schenker, R.; Mock, M.T.; Kieber-Emmons, M.T.; Riordan, C.G; Brunold, T.C. “Spectroscopic and Computational Studies on [Ni(tmc)CH3]OTf: Implications for Ni-Methyl Bonding in the A Cluster of Acetyl-CoA Synthase” Inorg. Chem. 2005, 44, 3605-3617.
  16. Schenker, R.; Kieber-Emmons, M.T.; Riordan, C.G.; Brunold, T.C.; ”Spectroscopic and Computational Studies on the Trans-μ-1,2-Peroxo-Bridged Dinickel(II) Species [{Ni(tmc)}2(O2)](OTf)2: Nature of End-On Peroxo−Nickel(II) Bonding and Comparison with Peroxo−Copper(II) Bonding” Inorg. Chem. 2005, 44, 1752−1762.
  17. * Kieber-Emmons, M.T.; Schenker, R.; Yap, G.P.A.; Brunold, T.C.; Riordan, C.G.; “Spectroscopic Elucidation of a Peroxo Ni2(μ-O2) Intermediate Derived from a Nickel(I) Complex and Dioxygen” Angew. Chem. Int. Ed. 2004, 43, 6716 –6718. *Designated a Very Important Publication by journal.
  18. Hammes, B.S.; Kieber-Emmons, M.T.; Letizia, J.A.; Shirin, Z.; Carrano, C.J.; Zakharov, L.N.; Rheingold, A.L.; “Synthesis and characterization of several zinc(II) complexes containing the bulky heteroscorpionate ligand bis(5-tert-butyl-3methylpyrazol-2-yl)acetate: relevance to the resting states of the zinc(II) enzymes thermolysin and carboxypeptidase A” Inorg. Chim. Acta. 2003, 346, 227-238.
  19. Monzavi-Karbassi, B.; Shamloo, S.; Kieber-Emmons, M.; Jousheghany, F.; Luo, P.; Lin, K.Y.; Cunto-Amesty, G.; Weiner, D.B.; Kieber-Emmons, T.; “Priming characteristics of peptide mimotopes of carbohydrate antigens” Vaccine, 2003, 21, 753–760.
  20. Hammes, B.S.; Kieber-Emmons, M.T.; Sommer, R.; Rheingold, A.L.; “Modulating the Reduction Potential of Mononuclear Cobalt(II) Complexes via Selective Deprotonation of Tris[(2- benzimidazolyl)methyl]amine” Inorg. Chem. 2002, 41, 1351−1353.
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Department of Chemistry | University of Utah |
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