Professor of Chemistry
Ph.D. Harvard University, 1986
(Bioinorganic and Inorganic Chemistry)
Transition-metal-containing enzymes (metalloenzymes) promote a number of critical biological processes ranging from the biosynthesis of neurotransmitters, and hormones, to DNA replication and repair, the conversion of electrochemical to chemical energy, and the photosynthetic production of dioxygen (O2). The molecular-level details of metalloenzyme function emerge from several complementary lines of study, at the interface of chemistry, biology, and physics. By modeling the metal ion’s local environment and making systematic changes to this environment, one can determine, at the molecular-level, how reactivity correlates with structural, magnetic, and spectroscopic properties.
The highly covalent nature of metal-thiolate bonds impart unique properties that serve to promote catalytic reactions. Thiolates favor coordinatively unsaturated geometries, stabilize higher oxidation states, facilitate electron and H-atom transfer reactions, as well as product release, and lower the activation barrier to O2 binding. Thiolate-ligated transition-metal complexes tend to be intensely colored, and low-spin, making it easy to spectroscopically monitor reactivity.
The general approach used by the Kovacs lab involves the design of nitrogen- and sulfur-containing organic molecules with a molecular architecture that enforces a desired stereochemistry around the metal ion. We then examine the reactivity of the resulting synthetic transition-metal complexes, and look for correlations between structure and properties, such as spin-state and electronic structure, by systematically altering the organic framework of our ligands. Reactivity of these models is then compared on the basis of kinetic and thermodynamic parameters. Techniques used by our group include low temperature electronic absorption spectroscopy, EPR, electrochemistry, and X-ray crystallography.
The Kovacs group reported the first and only examples of biomimetic superoxide reductase analogues, the only examples of metastable thiolate-ligated Fe(III)-OOH intermediates, and the first and only crystallographically characterized Mn(III)-OOR. Manganese peroxos are implicated as key intermediates in DNA repair, photosynthetic O2-evolution, and the metabolism of prostaglandins. Iron-peroxos are implicated as key intermediates in the biosynthesis of neurotransmitters, fatty acids, and steroids.
Villar-Acevedo, G.; Lugo-Mas, P.; Blakely, M. N.; Rees, J. A.; Ganas, A. S.; Hanada, E. M.; Kaminsky, W.; Kovacs, J. A. Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate. J. Am. Chem. Soc. 2017, 139, 119–129.
Kovacs, J. A. Tuning the Relative Stability and Reactivity of Manganese Dioxygen and Peroxo Intermediates via Systematic Ligand Modification. Acc. Chem. Res. 2015, 48, 2744–2753.
Rees, J. A.; Martin-Diaconescu, V.; Kovacs, J. A.; DeBeer, S. X-ray Absorption and Emission Study of Dioxygen Activation by a Small-Molecule Manganese Complex. Inorg. Chem. 2015, 54, 6410–6422.
Brines, L. M.; Coggins, M. K.; Poon, P. C. Y.; Toledo, S.; Kaminsky, W.; Kirk, M. L.; Kovacs, J. A. Water-Soluble Fe(II)–H2O Complex with a Weak O–H Bond Transfers a Hydrogen Atom via an Observable Monomeric Fe(III)–OH. J. Am. Chem. Soc. 2015, 137, 2253–2264.
Coggins, M. K.; Brines, L. M.; Kovacs, J. A. Synthesis and Structural Characterization of a Series of Mn(III)–OR Complexes, Including a Water-Soluble Mn(III)–OH that Promotes Aerobic Hydrogen Atom Transfer. Inorg. Chem. 2013, 52, 12383–12393.
Coggins, M. K.; Toledo, S.; Kovacs, J. A. Isolation and Characterization of a Dihydroxo-Bridged Iron(III,III)(μ-OH)2 Diamond Core Derived from Dioxygen. Inorg. Chem. 2013, 52, 13325–13331.
Coggins, M. K.; Sun, X.; Kwak, Y.; Solomon, E. I.; Rybak-Akimova, E.; Kovacs, J. A. Characterization of Metastable Intermediates Formed in the Reaction Between a Mn(II) Complex and Dioxygen, Including a Crystallographic Structure of a Binuclear Mn(III)–Peroxo Species. J. Am. Chem. Soc. 2013, 135, 5631–5640. Highlighted on a JACS/IC virtual issue as “a significant recent publication.”
Coggins, M. K.; Martin-Diaconescu, V.; DeBeer, S.; Kovacs, J. A. Correlation Between Structural, Spectroscopic, and Reactivity Properties Within a Series of Structurally Analogous Metastable Manganese(III)–Alkylperoxo Complexes. J. Am. Chem. Soc. 2013, 135, 4260–4272.