BIOLOGICAL VANADIUM--MODELS OF STRUCTURE AND REACTIVITY

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We set froth program to evaluate the chemistry of vanadium in the +3, +4 and +5 oxidation states using ligands that are designed to incorporate biologically relevant heteroatom donors. Our goal is to define the basic coordination properties of vanadium and its reactivity patterns both in redox and non-redox and non-redox roles. The recognition of vanadium as an important element in biology has increased considerably in the last five years due to the isolation of the first vanadium containing enzymes. Prior to this period, vanadium was a curiosity in certain species of sessile tunicates and in the poisonous mushroom A. muscaria. Vanadium was also known to be a phosphate mimic acting as an inhibitor of phosphoryl transfer enzymes, ATPases and as an insulin activator. It is now established that a mononuclear vanadium (V) catalyzes haloperoxidase chemistry previously restricted to heme or non-heme iron enzymes. Furthermore, vanadium appears to substitute for molybdenum in the vanadium containing nitrogenase. It is especially likely that as marine bioinorganic chemistry develops additional enzymes requiring vanadium may be uncovered. The chemistry described herein will develop and examine models for the active site structure and chemical mechanism of the algal bromoperoxidases. Each newly isolated material will be subjected to chemical analysis such as X-ray crystallography, epr, NMR, UV-vis spectroscopies and electrochemistry. The second phase of our work will evaluate the binding properties of vanadium to phytosiderophores and siderophore analogs. This project is aimed at establishing possible mechanism of vanadium uptake and accumulation in plant and bacterial cells. The third area of study is the development of vanadium chemistry in higher nuclearity clusters. Although presently unknown, it is within the realm of possibilities that dinuclear vanadium enzymes will be discovered that may be analogous to dinuclear iron, manganese or copper enzymes. Our final topic is the reactivity of vanadium complexes in redox roles and exploring further the manganese/vanadium reactivity analogy for two electron organic transformations. The information gathered from these studies shall lay the foundation of adequate guiding principles for vanadium, placing us in a better position to define the chemistry of known biological processes with an essential requirement for this element.