Electronic structure characterization of FeIII-protoporphyrin IX (FeIII-PPIX) and β-hematin using calculated nuclear quadrupole resonance (NQR) and Mössbauer parameters

In this work, we performed the ab initio calculation of quadrupolar parameters of 17O and 14N atoms in FeIII-protoporphyrin IX (FeIII-PPIX) and β-hematin molecules. Furthermore, the quadrupole splitting of iron atoms in these molecules were calculated. The calculations were carried out to explore the differences between the electronic structures of FeIII-PPIX and β-hematin. The results show that the value of quadrupole splitting of iron atom, Δ(57Fe), in FeIII-PPIX is exactly three-fold of its value in β-hematin. The electric field gradient (EFG) at the site of quadrupolar nuclei were calculated to obtain quadupolar parameters (χ, η, and Δ), using B3LYP method and an all-electron representation for iron (62111111/3311111/3111), as well as the 6-31G* basis for all other atoms.Key words: nuclear quadrupole resonance (NQR), hematin, β-hematin, malaria.