Eric C. Brown
B.S., University of Idaho, 1997
Ph.D., Oregon State University, 2002
NIH Postdoctoral Fellow, University of Minnesota, 2003-2006
Proteins containing transition metal ions carry out a variety of important functions in biological systems. Consequently, understanding how these chemical transformations occur and what factors regulate their reactivity is an important research area. The focus of our research is to provide fundamental insight into the structure and function of metalloenzymes by using the synthetic modeling approach. The synthetic modeling approach involves the synthesis of low molecular weight complexes that model the structural and functional units of the enzymes. Useful information such as spectroscopic and structural data and identification of possible intermediates or pathways in the enzymatic cycle can be obtained through studies of the synthetic model complexes.
Students involved in research in our laboratory will obtain multidisciplinary training in the synthesis of organic and inorganic compounds. They will also be exposed to a variety of characterization methods that are used to characterize inorganic compounds and to examine their reactivity. These include X-ray crystallography and NMR, IR, UV-Vis, and EPR spectroscopies. Finally, students will develop an understanding of mechanism by examining the reactivity and kinetics of their model complexes with either natural or model substrates.
Below are examples of different bioinorganic projects we are currently pursuing in our laboratory.
I. Activation of Sulfur-Containing Heterocumulenes:
Emissions of carbon dioxide (CO2) and carbonyl sulfide (COS) are expected to increase within the next century and could have a significant impact on the earth's climate. Consequently, the development of a practical method for converting CO2 and COS into more useful compounds is recognized to be important for a sound long-term energy policy. Our research focuses on the synthesis and structural definition of new bio-inspired inorganic compounds useful for the activation of sulfur-containing heterocumulenes, such as COS and CS2. The inspiration behind the design features of our inorganic compounds is carbonic anhydrase and CS2 hydrolase. Studies have shown carbonic anhydrase in plants, algae and lichens and CS2 hydrolase in thermophilic archaea react with COS and CS2, respectively, to give hydrogen sulfide (H2S). Studies directed at understanding the mechanism of COS and CS2 activation by carbonic anhydrase and CS2 hydrolase has been very limited and is the impetus for this research.
II. Preparation of Metal Complexes Containing N2S Donor Atom Sets of Relevance to Peptide Deformylase:
The function of the metalloenzyme peptide deformylase (PDF) is to deformylate proteins that contain N-formylated methionine. Since this deformylation sequence is unique to prokaryotes, understanding the detailed mechanism of PDF may be important in the development of future antibiotics. In addition, further motivation for studying the mechanism comes from the unusual finding that the most active form of PDF is not a zinc-containing enzyme but instead an iron-containing enzyme. To gain insight into the unusual metal-dependent reactivity of PDF, our research is focused on the design, synthesis and mechanistic evaluation of FeII and ZnII hydroxide complexes supported with novel N2S ligand systems. These N2S ligand systems model the cysteine and two histidine binding motif present in the active site of PDF.
1. Spiropulos, N.G.; Standley, E.A.; Shaw, I.R.; Ingalls, B.L.; Diebels, B.; Krawczyk, S.V.; Gherman, B.F.; Arif, A.M.; Brown, E.C. “Synthesis of Zinc and Cadmium O-Alkyl Thiocarbonate and Dithiocarbonate Complexes and a Cationic Zinc Hydrosulfide Complex.” Inorg. Chim. Acta 2012, 386, 83-92.
2. Warner, D. L.; Brown, E. C.; Shadle, S. E.; Towns, M. H. “A Rubric for Assessing Student’s Experimental Problem Solving Ability.” J. Chem. Educ. 2012, 89, 319-325.
3. Spiropulos, N. G.; Chingas, G. C.; Sullivan, M.; York, J. T.; Brown, E. C. “Examining the Impact of Steric and Electronic Variation in N2S Scorpionate Ligand on the Properties of Zinc(II) and Cadmium(II) Complexes.” Inorg. Chim. Acta 2011, 376, 562-573.
4. Paviet-Hartmann, P.; Roman, A.; Campbell, K.; Horkley, J.; Brown, E.; Gomez-Aleixandre, A.; Espartero, A. G. “Development of an Extraction Process for the Removal of Technetium 99 from Waste Streams.” International Solvent Extraction Conference Proceedings 2011.
5. Paviet-Hartmann, P.; Horkley, J.; Pak, J.; Brown, E.; Todd, T. “Resorcinarenes and Aza-Crowns as New Extractants for the Separation of Technetium-99.” MRS Proceedings 2009, 1124, 1124-Q10-04.
6. Brown, E. C.; Johnson, B.; Palavicini, S.; Kucera, B. E.; Casella, L.; Tolman, W. B. “Modular Syntheses of Multidentate Ligands with Variable N-Donors: Applications to Tri- and Tetracopper (I) Complexes.” J. Chem. Soc., Dalton Trans. 2007, 28, 3035-3042.
7. Brown, E.C.; Bar-Nahum, I.; York, J.T.; Aboelella, N.W.; Tolman, W.B. “Ligand Structural Effects on Cu2S2 Bonding and Reactivity in Side-On Disulfido-Bridged Dicopper Complexes.” Inorg. Chem. 2007, 46, 486-496.
8. York, J.T.; Brown, E.C.; Tolman, W.B. “Characterization of Complex Comprising a [Cu2(S2)2]2+ Core: Bis(μ-S22-)dicopper(III) or bis(μ-S2•-)dicopper(II)?.” Angew. Chem., Int. Ed. 2005, 44, 7745-7748.
9. Brown, E.C.; York, J.T.; Antholine, W.E.; Ruiz, E.; Alvarez, S.; Tolman, W.B. “[Cu3(μ-S)2]3+ Clusters Supported by N-Donor Ligands: Progress Towards a Synthetic Model of the Catalytic Site of Nitrous Oxide Reductase.” J. Am. Chem. Soc. 2005, 127, 13752-13753.
10. Brown, E.C.; Aboelella, N.W.; Reynolds, A.M.; Aullón, G.; Alvarez, S.; Tolman, W.B. “A New Class of (μ-η2:η2-Disulfido)dicopper Complexes: Synthesis, Characterization, and Disulfide Exchange.” Inorg. Chem. 2004, 43, 3335-3337.
11. Gable, K.P.; Brown, E.C. “Rhenium-Catalyzed Epoxide Deoxygenation.” Synlett 2003, 2243-2245.
12. Gable, K.P.; Brown, E.C. “Kinetics and Mechanism for Rhenium-Catalyzed O-Atom Transfer from Epoxides.” J. Am. Chem. Soc. 2003, 125, 11018-11026.
13. Gable, K.P.; Brown, E.C. “Coordination of a Tethered Epoxide to a Coordinatively Unsaturated Rhenium Oxo Complex.” Organometallics 2003, 22, 3096-3101.
14. Gable, K.P.; Brown, E.C. “Efficient Catalytic Deoxygenation of Epoxides Using [Tris(3,5-dimethylpyrazolyl) hydridoborato]rhenium Oxides.” Organometallics 2000, 19, 944-946.