Geometric and electronic structure contributions to function in bioinorganic chemistry: Active sites in non-heme iron enzymes

Spectroscopy has played a major role in the definition of structure/functio n correlations in bioinoganic chemistry. The importance of spectroscopy com bined with electronic structure calculations is clearly demonstrated by the non-heme iron enzymes. Many members of this large class of enzymes activat e dioxygen using a ferrous active site that has generally been difficult to study with most spectroscopic methods. A new spectroscopic methodology has been developed utilizing variable temperature, variable field magnetic cir culardichroism, which enables one to obtain detailed insight into the geome tric and electronic structure of the non-heme ferrous active site and probe its reaction mechanism on a molecular level. This spectroscopic methodolog y is presented and applied to a number of key mononuclear non-heme iron enz ymes leading to a general mechanistic strategy for O-2 activation. These st udies are then extended to consider the new features present in the binucle ar non-heme iron enzymes and applied to understand (1) the mechanism of the two electron/coupled proton transfer to dioxygen binding to a single iron center in hemerythrin and (2) structure/function correlations over the oxyg en-activating enzymes stearoyl-ACP Delta (9)-desaturase, ribonucleotide red uctase, and methane monooxygenase. Electronic structure/reactivity correlat ions for O-2 activation by non-heme relative to heme iron enzymes will also be developed.