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On the reversible O 2 binding of the Fe–porphyrin complex
Author(s) -
Nakashima Hiroyuki,
Hasegawa JunYa,
Nakatsuji Hiroshi
Publication year - 2006
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.20339
Subject(s) - intersystem crossing , singlet state , chemistry , dissociation (chemistry) , triplet state , porphyrin , density functional theory , photochemistry , ground state , binding energy , potential energy surface , atomic physics , computational chemistry , excited state , molecule , physics , organic chemistry
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