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    STUDIA CHEMIA - Issue no. 1 / 2005  
         
  Article:   DISCONTINUUM BETWEEN FERROUS-SUPEROXO AND FERRIC-PEROXO IN HEME [FEO2]9 COMPLEXES?.

Authors:  RADU SILAGHI-DUMITRESCU, IOAN SILAGHI-DUMITRESCU.
 
       
         
  Abstract:  Low-spin [FeO2]9 complexes (where the superscript denotes the sum of iron d electrons and dioxygen * electrons), generally described as ferric-peroxo or ferrous-superoxo, have been implicated in the catalytic cycles of heme and non-heme proteins. Experimental observation of these complexes, mainly by ENDOR spectroscopy, has led to two distinct descriptions of heme [FeO2]9, depending on whether or not hydrogen bonding to the oxygen ligand is available. Hydrogen-bonded [FeO2]9 were described as ferric-peroxo, while non hydrogen-bonded [FeO2]9 were described as ferrous-superoxo. Reported here is a DFT investigation of the effects of hydrogen bonding on the structure of heme [FeO2]9 complexes. Calculated bond lengths, spin densities and hyperfine couplings all argue against a ferrous-superoxo/ferric-peroxo discontinuum. Possible implications of this finding are discussed.  
         
     
         
         
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