Metalloproteins active site, model development

Fig. 1. Steps in the development of models for a metalloprotein active site.

The goal of diiron model chemistry is to develop small molecule systems that accurately reproduce spectroscopic, structural, and more ambitiously, reactivity aspects of diiron metalloproteins. Despite being structurally similar, diiron enzymes carry out a variety of catalytic processes see Iron Proteins with Dinuclear Active Sites). Advancements in the synthesis and characterization of small molecule mimics for nonheme diiron enzymes have been tremendous in the last decade. Biomimetic studies have been carried out in efforts to reproduce the structural and functional aspects of these biocatalysts. Although this has been a challenging endeavor, much information regarding the structural and mechanistic aspects of catalytic intermediates has been obtained. 

The ability to selectively enhance the modes of the resonant chromophore has fueled the steady development of RR spectroscopy and its transient RR and TR variants as exquisite probes of active site structure and dynamics in a wide range of metalloproteins and enzymes. Inasmuch as this remarkable potential has been more fully realized in the study of heme proteins than for any other class of metalloproteins, it is natural that the illustrative applications presented here be focused on these systems. However, excellent summaries of applications to other metalloproteins and their model compounds are available, including copper proteins,iron-sulfur proteins, and non-heme oxo-iron clusters. ... 

Before plunging into a discussion of how such complexes are prepared, it is perhaps worthwhile to consider explicitly the rationale for such activity. The synthesis and characterization of accurate model complexes for a given metal site in a protein or other macromolecule allows one to (l) determine the intrinsic properties of the metal site in the absence of perturbations provided by the protein environment or (il) in favorable cases, deduce the structure of the metal site by comparison of corresponding physical and spectroscopic properties of the model and metalloprotein (3). The first class of model complexes has been termed "corroborative models" by Hill (4), while the second are termed "speculative models" (4). To date, virtually all the major achievements of the synthetic model approach have been in development of corroborative models. 

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