Our primary objective is to synthesize and determine the geometric and electronic structures of various cobalt (II)-dioxygen complexes that act as models of the active sites in the naturally-occurring blood pigments hemoglobin and myoglobin. Using X-ray diffraction, and Raman and EPR spectroscopic techniques, we intend to obtain from these compounds quantitative information regarding the geometry of the coordinated dioxygen ligand and core to an understanding of the mode of its binding to the metal atoms in the naturally occurring hemoproteins. The long term objective is, of course, to contribute to the study of the mechanism of dioxygen transport in living organisms. With the aid of a previous MBRS grant, the PI has acquired considerable experience in synthesizing and structurally characterizing cobalt(II)-dioxygen model complexes. Our structural results are the most accurate every obtained for any synthetic iron or cobalt-dioxygen model complex. We want to expand our previous efforts and understand precisely the factors that influence the geometric and electronic structures of the CoO2 moiety, and whether they operate trans or cis to bound dioxygen. Our preliminary results also indicate the importance of hydrogen-bond stabilization of bound dioxygen in small molecules with distal histidine amino acid residues in hemoproteins is currently a 'hot topic', as these and other polar interactions are important in stabilization the Fe(II)-O2 group against the spontaneous auto- oxidation of Fe(II) to its physiologically inactive Fe(III) met form, and in regulating O2 and CO binding. We intend to obtain a clever understanding of the factors that influence the strength of these interactions and determine what effect (if any) they have on the binding properties of dioxygen. Professor Michael Hitchman, Department of Chemistry, University of Tasmania, Australia, has agreed to obtain FT- IR/Raman and EPR spectra for both the unoxygenated and oxygenated compounds, which will nicely compliment our X-ray work. Funds are requested to purchase a Nonius CCD X-ray diffractometer and low- temperature cryostat in order to collect data at the University of Hawaii- Hilo campus. The PI is a trained crystallographer who has had considerable experience in using these instruments and in teaching chemical crystallography to minority undergraduate students. The CCD diffractometer would greatly facilitate the structure of these compounds as many tend to form small crystals that decompose quite quickly.
Showing the most recent 10 out of 23 publications
