This award in the Inorganic, Bioinorganic and Organometallic Chemistry program supports Professor David L. Tierney at the University of New Mexico to investigate a library of model compounds, encompassing 4-, 5- and 6-coordination, by a combination of x-ray absorption spectroscopy and paramagnetic resonance (PMR). An integrated approach to PMR would be used simultaneously applying mutli-frequency electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR) and nuclear magnetic resonance (NMR). PMR would be used to define the field- and temperature-dependence of electron-nuclear hyperfine interactions in a broad array of hs Co(II) systems. Electronic relaxation will be examined 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 for initial focus mimic two key structural elements in the metallobiochemistry of cobalt - Co-Nhistidine and Co-Scysteine. To emulate metal-histidine interactions, we will study a series of bis- (Bp) and tris- (Tp) pyrazolylborate complexes. Efforts to model Co-Scys interactions will involve common alkyl- and arylthiolate small-molecule chemistry. To bridge the gap between small-molecule and metalloprotein studies, a set of de novo metal-binding peptides, designed to present four cysteine or penicillamine thiolates as potential ligands, will be examined.
The application of ENDOR spectroscopy to hs Co(II) systems will help lay the foundation for the full development of Co(II) as a spectroscopic probe of Zn(II) metalloenzymes. Professor Tierney has re-developed a senior-level, undergraduate "Synthesis and Characterization" laboratory, with experiments developed from his current research. The student body of The University of New Mexico has a large minority enrollment with a high fraction of undergraduate chemistry majors coming from traditionally under-represented groups.