Iron-57 NMR chemical shifts and mössbauer quadrupole splittings in metalloporphyrins, ferrocytochrome c, and myoglobins: A density functional theory investigation

We have evaluated the 57Fe nuclear magnetic resonance chemical shielding and Mossbauer electric field gradient tensors and their orientations for a cytochrome c model compound as well as for isopropyl isocyanide and carbon monoxy−myoglobin model systems and two simple metalloporphyrins containing bis(pyridine) and bis(trimethylphosphine) ligands, using Kohn−Sham density functional theory. For cytochrome c we used a model Fe(II) porphyrin structure together with a 1-methylimidazole base (to represent His-18) and a dimethyl sulfide molecule (to represent Met-80 in the structure of horse heart ferrocytochrome c), both located at the X-ray coordinates for cyt c Fe(II). For the Mb calculations, we used the coordinates of two recently characterized metalloporphyrins:  (i-PrNC)(1-methylimidazole)(5,10,15,20-tetraphenylporphinato)Fe(II) and (CO)(1-methylimidazole)(5,10,15,20-tetraphenylporphinato)Fe(II), while literature structures were used for the bis-ligand adducts. We used a “locally dense” basis to evaluate ...