On the reversible O2 binding of the Fe–porphyrin complex

✍ Scribed by Hiroyuki Nakashima; Jun-Ya Hasegawa; Hiroshi Nakatsuji

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 250 KB
• Volume: 27
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.20339

✦ Synopsis

Abstract

Electronic mechanism of the reversible O~2~ 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) + O~2~(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 O~2~+ deoxyheme system is triplet in the dissociation limit [Fe(S = 2) + O~2~(S = 1)], the O~2~ 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 O~2~ 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 O~2~ binding. The potential surface is associative/dissociative when the Fe atom locates in‐plane/out‐of‐plane. © 2006 Wiley Periodicals, Inc. J Comput Chem 4: 426–433, 2006