This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports research by Professor David L. Tierney at the University of New Mexico to systematically investigate a library of model compounds by a combination of x-ray absorption spectroscopy and paramagnetic resonance (PMR), simultaneously applying mutli-frequency electron paramagnetic resonance (EPR, 9 and 35 GHz), electron-nuclear double resonance (ENDOR, 9 and 35 GHz) and nuclear magnetic resonance (NMR, H = 100, 300 and 500 MHz; NMRD, H . 1 75 MHz), to define the field- and temperature-dependence of electronnuclear hyperfine interactions in a broad array of high-spin Co(II) systems. Electronic relaxation will be examined in detail by field- and temperature-dependent NMR relaxation and by NMR dispersion (NMRD). The behavior of the model systems will guide spectroscopic studies of systems of unknown structure, where x-ray absorption spectroscopy (XAS) will provide additional, critical structural constraints. The systems mimic two key structural elements in the metallobiochemistry of cobalt: Co-Nhistidine and Co-Scysteine. A series of bis- (Bp) and tris- (Tp) pyrazolylborate complexes will be studied to emulate metal-histidine interactions. Homoleptic and heteroleptic complexes allow preparation of neutral hs Co(II) complexes that are 4-, 5- or 6-coordinate, all with the same donor set. Complexes of Mn(II) and V(II), defining the contributions of global symmetry and spin-orbit coupling to the observed electron-nuclear interactions, will be examined. Efforts to model Co-Scys interactions will involve common alkyl- and arylthiolate small-molecule chemistry, and methyl transfer reactions will be examined, affording a unique opportunity to evaluate the Co-for-Zn substitution in a functional model system. To bridge the gap between small-molecule and metalloprotein studies, a set of de novo metal-binding peptides, designed to present cys4, cys3his and cys2his2 binding sites, will be studied. PMR studies are proposed that will greatly advance our knowledge of cobalt-sulfur bonding.
Minority enrollment University-wide represents 49 % of the student body. Of this, 28% of the students are Hispanic and 11% are Native American. At the present time, the overall number of declared chemistry undergraduate majors is 110, with 46% of these coming from traditionally under-represented groups. The ethnic breakdown of both the graduate program and the Tierney labs are similarly diverse. The PI has re-developed the senior-level, undergraduate Synthesis and Characterization laboratory, with experiments developed out of results from previous and current research experience and will incorporate new developments derived from the proposed research into the course material.
