BIOORGANOMETALLIC COMPLEXES RELEVANT TO THE 'PUSH EFFECT' IN HEMOPROTEINS

摘要

Bioorganometallic iron-aryl and iron-alkyl adducts of hemoproteins are known to contain an S = 1/2 ferric center sigma-bonded to a carbon atom. Here, DFT geometry optimization results are reported for models of the known phenyl and methyl adducts of heme-thiolate and heme-histidine enzyme active sites. Differences among thiolate and imidazole ligated models are examined, and parallels are drawn between these complexes (where the trans effect of thiolate and imidazole axial ligands shows virtually no pi component) and heme-peroxo or -superoxo complexes of hemoproteins (where a well-defined pi component is expected to exist). A novel, entirely mechanical, component of the "thiolate push" effect in cytochrome P450 monooxygenase is discussed.