The dramatic effect of N-methylimidazole on trans axial ligand binding to ferric heme: experiment and theory
Résumé
The binding energy of CO, O 2 and NO to isolated ferric heme, [Fe III P] + , was studied in the presence and absence of a s donor (N-methylimidazole and histidine) as the trans axial ligand. This study combines the experimental determination of binding enthalpies by equilibrium measurements in a low temperature ion trap using the van't Hoff equation and high level DFT calculations. It was found that the presence of N-methylimidazole as the axial ligand on the [Fe III P] + porphyrin dramatically weakens the [Fe III P-ligand] + bond with an up to sevenfold decrease in binding energy owing to the s donation by N-methylimidazole to the Fe III (3d) orbitals. This trans s donor effect is characteristic of ligation to iron in hemes in both ferrous and ferric redox forms; however, to date, this has not been observed for ferric heme.
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Origine : Fichiers produits par l'(les) auteur(s)