On the reversible O2 binding of the Fe-porphyrin complex

: Electronic mechanism of the reversible O2 binding by heme was studied by using Density Functional Theory calculations. The ground state of oxyheme was calculated to be open singlet state [Fe(S 1/2) O2(S 1/2)]. The potential energy surface for singlet state is associative, while that for triplet state is dissociative. Because the ground state of the O2 deoxyheme system is triplet in the dissociation limit [Fe(S 2) O2(S 1)], the O2 binding process requires relativistic spin-orbit interaction to accomplish the intersystem crossing from triplet to singlet states. Owing to the singlet-triplet crossing, the activation energies for both O2 binding and dissociation become moderate, and hence reversible. We also found that the deviation of the Fe atom from the porphyrin plane is also important reaction coordinate for O2 binding. The potential surface is associative/dissociative when the Fe atom locates in-plane/out-of-plane.

• Type: Journal
• Year: 2006
• Where: JCC
• Authors: Hiroyuki Nakashima, Jun-Ya Hasegawa, Hiroshi Nakatsuji
• Keywords: JCC 2006, Potential Energy Surface, Reversible O2, Singlet State