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Nature of the Catecholate—Fe(III) Bond: High Affinity Binding and Substrate Activation in Bioinorganic Chemistry

  1. Edward I. Solomon1,
  2. Monita Y. M. Pau1,
  3. Rosalie K. Hocking2,3

Published Online: 15 SEP 2009

DOI: 10.1002/0470862106.ia653

Encyclopedia of Inorganic Chemistry

Encyclopedia of Inorganic Chemistry

How to Cite

Solomon, E. I., Pau, M. Y. M. and Hocking, R. K. 2009. Nature of the Catecholate—Fe(III) Bond: High Affinity Binding and Substrate Activation in Bioinorganic Chemistry. Encyclopedia of Inorganic Chemistry. .

Author Information

  1. 1

    Stanford University, Stanford, CA, USA

  2. 2

    Stanford University, Stanford, CA

  3. 3

    USA and Monash University, Clayton, Australia

Publication History

  1. Published Online: 15 SEP 2009

Abstract

Catecholate-Fe(III) (high-spin) bonds are important in many areas of bioinorganic chemistry. These exhibit low-energy, intense ligand-to-metal charge transfer (LMCT) transitions reflecting highly covalent bonds. This high covalency can make a major contribution to function. In this review, we develop the method of metal L-edge X-ray absorption spectroscopy (XAS) as a probe of differential orbital covalency (DOC), the amount of ligand character in the different d orbitals of a metal site in a highly covalent environment. We then apply this method to experimentally determine the covalency of the ligand-metal bonds related to the siderophores and computationally evaluate this contribution to their high stability constants. We then use variable-temperature, variable-field, magnetic circular dichroism (VTVH MCD) spectroscopy to assign the LMCT transitions of the catecholate-, substrate-bound FeIII site of the intradiol dioxygenases. A reaction coordinate is presented where this charge transfer can overcome the spin-forbidden nature of the reaction of the bound catecholate (singlet) with dioxygen (triplet).

Keywords:

  • catecholate;
  • ferric;
  • intradiol dioxygenases;
  • siderophores;
  • XAS;
  • MCD