The governing theme of this research program is to develop systematic and rational strategies for the synthesis of model complexes containing one, two or more iron ions bridged by simple ligands such as oxide hydroxide, water, and/or carboxylates. These complexes are to serve as structural, electronic and functional models of non-heme iron centers in biological systems and of general iron-oxo aggregation processes, in order to better understand the critical role of iron in Nature. Particular attention is to be placed on the interaction of iron(II) complexes with dioxygen. Iron plays a crucial role in dioxygen and electron transfer reactions as well as many enzymatic processes including those involved in the synthesis of DNA. Other iron(II) complexes act as anti-cancer drugs by using their activation of dioxygen to attack DNA, thus an understanding of the formation and function of these iron centers and the storage of iron is essential for health. Disruption of the efficient usage of iron in all its diverse roles leads to a number of diseases. Drugs such as aspirin, for example, interact with iron enzymatic sites and a more complete understanding of the coordination chemistry and reactivity of iron with oxygen will aid in the design of such drugs. The systematic approach to this exploratory area of chemistry involves first the isolation and characterization of a variety of iron(II) mononuclear and multinuclear complexes; their interconversions and interactions with dioxygen to form multinuclear iron(III) oxo aggregates. A second generation of ligand system is to be developed that more closely mimics the actual metalloprotein environment through the utilization of concepts of molecular recognition and the formation of supramolecular complexes. These complexes more closely mimic the subtleties of the protein environment that dictate the varied interaction of iron(II) with dioxygen. This interaction with dioxygen models a number of crucial biological functions - as diverse as reversible dioxygen transport, to substrate oxidation (hydrocarbon hydroxylation) and radical generation (DNA synthesis). The stepwise formation of these aggregates is subsequently determined in as much detail as possible in order to arrive at principles which govern metal aggregate formation. The iron aggregation processes within the iron storage protein ferritin are of particular concern and are being approached from two directions, aggregates where only single oxygen bridges are involved and those in which bidentate carboxylate and phosphate groups play a structural role. Physicochemical techniques relied upon to characterize new materials are X-ray crystallography, 1H NMR, EPR, UV-Vis spectroscopies and Mossbauer and magnetic properties. Specific attention is to be placed on the interpretation of the 13C and 15N NMR spectra of carboxylates and azide bound to these paramagnetic complexes as potential tool for the elucidation of protein structure and function. Understanding the properties of these well defined model compounds greatly accelerates the interpretation of physical properties of metalloproteins.
