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Iron: Models of Proteins with Dinuclear Active Sites

  1. Ferman A. Chavez1,
  2. Lawrence Que2

Published Online: 15 MAR 2006

DOI: 10.1002/0470862106.ia109

Encyclopedia of Inorganic Chemistry

Encyclopedia of Inorganic Chemistry

How to Cite

Chavez, F. A. and Que, L. 2006. Iron: Models of Proteins with Dinuclear Active Sites . Encyclopedia of Inorganic Chemistry. .

Author Information

  1. 1

    Oakland University, Rochester, MI, USA

  2. 2

    University of Minnesota, Minneapolis, MN, USA

Publication History

  1. Published Online: 15 MAR 2006

Abstract

The nonheme diiron enzymes are a class of metalloproteins that share a common function in the binding and activation of dioxygen. In recent years, interest in these enzymes has grown at a steady rate. The focus is both of a fundamental and applied nature. Understanding how these enzymes have evolved to perform synthetically challenging organic transformations under moderate conditions will provide insights into evolutionary processes and possibly help to develop techniques for engineering such active sites into proteins. These studies have led to the development of synthetic catalysts for these transformations through the ‘biomimetic’ approach. Through structural studies it has become clear that many of the metal binding sites in nonheme diiron enzymes possess carboxylate-rich ligation, which is believed to be important in facilitating redox processes and structural rearrangements during catalysis. The use of model compounds to study these enzymes has many advantages that are not offered with other approaches. For example, a model for a proposed reactive intermediate may be stabilized at low temperature and studied. Synthetic compounds can also be selectively modified to examine the influence of a certain geometry, ligand set, or chemical environment on the properties and reactivity of the compound. In this article, several approaches are discussed toward the development of diiron model compounds. In one approach, multidentate ligands possessing two metal binding sites are examined. This approach has led to metal complexes with closely spaced iron centers, a key structural feature in these enzymes. In a second approach, mononuclear metal complexes supported by multidentate ligands are bridged by oxygen groups to generate the diiron core structure. A third approach focuses on dicarboxylate ligands that bridge the two iron centers. This approach allows for variation of the remaining terminal ligands. The fourth approach relies on steric interactions. Intramolecular ligand interactions are used to control the geometry of the diiron complex. To date, these four approaches have been very successful in generating many of the intermediates seen in the diiron enzyme catalytic cycles and a few have been shown to reproduce the catalytic activity to some extent. It is anticipated that many more insights will be garnered from model studies and that new chemistries will be discovered.

Keywords:

  • nonhem diiron site;
  • dioxygen activation;
  • oxidation;
  • methane monooxygenase;
  • ribonucleotide reductase;
  • delta 9 desaturase;
  • peroxo intermediate;
  • intermediate Q;
  • intermdiate X;
  • iron oxo species;
  • hydrophobic active site;
  • high-valent iron species