Study on binding of dioxygen to heme using scan functional
Density functional theory, a quantum mechanical based electronic structure method with GGA-PBE and MGG-SCAN functionals, are used to investigate the structure and energies of singlet, triplet, and quintet spin states of FeP (iron Porphyrin), FePIm (imidazole iron porphyrin), and FePImO2 (dioxygen imidazole iron porphyrin) systems. The binding and release of dioxygen to and from hemoglobin (Hb) are the most crucial reaction takes place in human body to sustain the existence of life. FePImO2 is used to model this phenomenon. When O2 binds to FePIm, the system undergoes a conformational change. i.e. from domed structure of FePIm in which the Fe atom moves away from the porphyrin plane to a planar structure of singlet FePImO2 in which the Fe atom lies on the porphyrin plane. Quintet FePImO2 resembles FePIm due to the pronounced movement of Fe atom above the porphyrin plane. GGA-PBE functional correctly predict the ground states of FeP (S=1) and FePImO2 (S=0) that agrees with experimental data but failed to predict the ground state of FePIm (S=2). On the other hand, MGGA-SCAN functional correctly predict the ground states of FeP (S=1) and FePIm (S=2) that are agreed with experimental results but failed to predict the ground state of FePImO2 (S=0).
Muhammed, Zegnet Yimer, "Study on binding of dioxygen to heme using scan functional" (2016). ETD Collection for University of Texas, El Paso. AAI10151211.